Biotransformation of benzo(a)pyrene by three rainbow trout

workshop concluded that the biotransformation rate constant represents the principal source .... Chemical analysis). These experiments were repeated t...
0 downloads 9 Views 672KB Size
Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

Article

Biotransformation of benzo(a)pyrene by three rainbow trout (Onchorhynchus mykiss) cell lines and extrapolation to derive a fish bioconcentration factor Julita Stadnicka-Michalak, Frederik T Weiss, Melanie Fischer, Katrin Tanneberger, and Kristin Schirmer Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04548 • Publication Date (Web): 05 Feb 2018 Downloaded from http://pubs.acs.org on February 6, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

Environmental Science & Technology

1

Biotransformation of benzo(a)pyrene by three rainbow

2

trout (Onchorhynchus mykiss) cell lines and extrapolation

3

to derive a fish bioconcentration factor

4

5

Julita Stadnicka-Michalak1,2,§, Frederik T. Weiss1,3,§, Melanie Fischer1, Katrin

6

Tanneberger1,4, Kristin Schirmer1,2,3*

7 8 9

1

Eawag, Überlandstrasse 133, 8600 Dübendorf, Switzerland

10

2

EPF Lausanne, School of Architecture, Civil and Environmental Engineering, 1015

11

Lausanne, Switzerland

12

3

ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, 8092 Zürich, Switzerland

13

4

Ecosens AG, 8304 Wallisellen, Switzerland

14 15

§ These authors contributed equally to this work

16 17 18

* Corresponding author: Prof. Dr. Kristin Schirmer

19

Eawag, Swiss Federal Institute of Aquatic Science and Technology

20

Überlandstrasse 133

21

P.O. Box 611

22

8600 Dübendorf

23

Switzerland

24

Phone: +41 (0)58 765 5266

25

Fax: +41 (0)44 823 53 11

26

email: [email protected] 1 ACS Paragon Plus Environment

Environmental Science & Technology

27

1 Abstract

28

Permanent fish cell lines constitute a promising complement or substitute for fish in the

29

environmental risk assessment of chemicals. We demonstrate the potential of a set of cell

30

lines originating from rainbow trout (Oncorhynchus mykiss) to aid in the prediction of

31

chemical bioaccumulation in fish, using benzo(a)pyrene (BaP) as model chemical. We

32

selected three cell lines from different tissues to more fully account for whole body

33

biotransformation in vivo: the RTL-W1 cell line representing the liver as major site of

34

biotransformation; and the RTgill-W1 (gill) and RTgutGC (intestine) cell lines as important

35

environment-organism interfaces, which likely influence chemical uptake. All three cell lines

36

were found to effectively biotransform BaP. However, rates of in vitro clearance differed,

37

with the RTL-W1 cell line being most efficient, followed by RTgutGC. Co-exposures with

38

alpha-naphthoflavone as potent inhibitor of biotransformation, assessment of CYP1A

39

catalytic activity, as well as the progression of cellular toxicity upon prolonged BaP exposure

40

revealed that BaP is handled differently in the RTgill-W1 compared to the other two cell

41

lines. Application of the cell line derived in vitro clearance rates into a physiology-based

42

toxicokinetic model predicted a BaP bioconcentration factor (BCF) of 909-1057 compared to

43

920 reported in vivo in rainbow trout.

44 45

TOC Art

46

2 ACS Paragon Plus Environment

Page 2 of 30

Page 3 of 30

Environmental Science & Technology

47

2 Introduction

48

Fish are the most extensively used vertebrate in environmental risk assessment of chemicals

49

and effluents. Yet, the enormous resources required for tests relying on fish, along with the

50

ethically questionable nature of such tests, have long prompted recognition that alternative

51

methods are urgently needed.1 One alternative strategy is to apply permanent cell lines from

52

fish.2,

53

eliminates the need to sacrifice additional fish; they are usually homogeneous in nature and

54

easy to maintain. Several recent developments attest to their potential to reduce or replace the

55

use of fish, such as in fish acute toxicity testing4 or for the prediction of chemical impact on

56

fish growth.5 We here extend our efforts to develop alternatives based on permanent fish cell

57

lines with the aim to predict the bioaccumulation of chemicals in fish.

58

Bioaccumulation of a chemical in an organism is the net result of toxicokinetic processes, i.e.

59

uptake, internal distribution, biotransformation and elimination. If the rates of uptake and

60

internal distribution outcompete those of biotransformation and elimination, an increase in

61

internal concentration compared to the exposure environment occurs.6 The resulting

62

bioconcentration factor (BCF) is a common metric of interest in environmental risk

63

assessment of chemicals, and is usually determined from laboratory experiments using fish

64

according to the OECD TG 305.7 Inasmuch as it is not feasible to test all chemicals requiring

65

bioaccumulation assessment in this way, various predictive models have been built. These

66

range from empirical regression models,6 to Quantitative Structure Activity Relationship

67

(QSAR) models for estimating biotransformation rates based on chemical structure8 to one

68

compartmente.g.9 or multiple compartment10 mass balance-based models of differing

69

complexity. One- and multiple compartment models can take, respectively, whole body or

70

even tissue-specific biotransformation rate constants into account. Indeed, a recent expert

71

workshop concluded that the biotransformation rate constant represents the principal source

3

Once established, cell lines comprise a valuable source of biological material that

3 ACS Paragon Plus Environment

Environmental Science & Technology

Page 4 of 30

72

of uncertainty in the bioaccumulation assessment of most hydrophobic chemicals and that in

73

vitro-to-in vivo extrapolation methods for obtaining biotransformation rate information is one

74

approach to address this uncertainty.11

75

In vitro methods to obtain biotransformation rate constants have thus far focused on liver

76

derived entities: fish liver cells, i.e. hepatocytes12-14; liver-derived S9 fractions15, 16 or liver

77

microsomes15, as well as hepatocyte spheroid cultures17, 18. The focus on liver results from its

78

recognition as major site of biotransformation; however, it is conceivable that other tissues,

79

such as the gill or the intestine as large environment-organism interfaces play important roles

80

in the mitigation of chemicals as well. Isolated gut segments or microsomes of channel catfish

81

(Ictalurus punctatus), for example, were shown to biotransform benzo(a)pyrene19,

82

primary rainbow trout gill cells to exhibit 7-ethoxyresorufin-O-deethylase (EROD) activity, a

83

catalytic measure of cytochrome P4501A (CYP1A).21

84

On this background, we hypothesized that it is possible to predict the bioconcentration of

85

chemicals in fish by exposing fish cell lines to a given chemical and monitoring chemical

86

depletion over time to obtain biotransformation rate constants in a manner similar to that

87

previously done with primary hepatocytes, S9 fractions or microsomes. The in vitro rate

88

constants are then incorporated into a physiologically-based toxicokinetic (i.e. a multi-

89

compartment PBTK) model which accounts for chemical uptake, internal distribution and

90

elimination from rainbow trout22 as well as for its biotransformation in different fish organs as

91

determined in vitro for the different cell lines. We proposed the use of rainbow trout

92

(Oncorhynchus mykiss) cell lines originating from gills (RTgill-W123) and intestine

93

(RTgutGC24), as important entry routes for chemicals into the fish body, and of liver (RTL-

94

W125), representing the best-known site of biotransformation. We selected the polycyclic

95

aromatic hydrocarbon (PAH) benzo(a)pyrene (BaP) as a model chemical because its

96

biotransformation has previously been quantified in rainbow trout hepatocytes12,

97

because a BCF has been experimentally determined in vivo in rainbow trout.26 4 ACS Paragon Plus Environment

20

13

and

and

Page 5 of 30

Environmental Science & Technology

98

3. Materials and Methods

99

3.1 Benzo(a)pyrene (BaP)

100

Crystalline BaP with a purity ≥ 96% was purchased from Sigma-Aldrich, Switzerland. For the

101

cell viability and EROD activity tests, a 5 mM BaP stock solution was prepared by dissolving

102

BaP into dimethyl sulfoxide (DMSO; Sigma-Aldrich, Switzerland).

103

and chemical purity ≥ 99%, specific activity: 984.2 Bq/nmol; total amount of

104

Benzo[a]pyrene: 50 µCI = 1.85 106 Bq; molarity: 3.76 mM), obtained from the American

105

Radiolabelled Chemicals Inc., was purchased in toluene. The toluene was evaporated under a

106

gentle stream of nitrogen and replaced by DMSO prior to use. For quantification of BaP by

107

radio-HPLC (see below), a mixture of the 14C-BaP and the unlabelled BaP stock solution was

108

prepared, yielding a 4.14 mM 14C-BaP working solution.

109

3.2 Cell culture and seeding

110

Cells were routinely cultured in 75 cm2 cell culture flasks (Techno Plastic Product AG,

111

Switzerland) with L-15 Leibovitz’s medium (Invitrogen, Switzerland) supplemented with 5%

112

FBSgold (F7524; Sigma-Aldrich, Switzerland) and 1% gentamicin (10 mg/mL; Invitrogen,

113

Switzerland), collectively referred to as culture medium, at 19±1°C in absence of light in

114

ambient atmosphere. Cells of passages 60 to 90 were used for the experiments.

115

For all exposure tests, confluent monolayers of the individual cell lines were used. Cell

116

viability and the EROD activity tests (see below) were carried out in 48-well tissue culture

117

plates (Techno Plastic Products AG, Switzerland). For BaP quantification, 75 cm2 cell culture

118

flasks were used. To obtain confluent cell monolayers in 48-well plates, 17 500 RTgut-GC

119

and RTL-W1 cells, and 75 000 RTgill-W1 cells were plated into 0.5 mL culture medium per

120

cavity. For the 75 cm2 cell culture flasks, 3.375 106 RTgutGC and RTL-W1 cells, and 11.250

121

106 RTgill-W1 cells were plated in 9.5 mL of culture medium. Prior to the exposure, seeded

122

cells were incubated for three days. 5 ACS Paragon Plus Environment

14

C-BaP (radiochemical 14

C-

Environmental Science & Technology

123

All exposures were carried out in the incubator in the dark at 19±1°C in ambient air. Although

124

the fish cells can survive temperatures between 0-28°C at least for short times27, the rationale

125

for choosing 19±1°C was that this is the temperatures to which the cells have physiologically

126

adapted and is thus considered optimal.

127

3.3 Exposure experiments

128

Exposure experiments were designed to measure the impact of BaP on cell viability, the time-

129

dependent activity of 7-ethoxyresorufin-O-deethylase (EROD as indicator of CYP1A), and

130

the distribution of BaP over time. Exposure times and BaP concentrations were adjusted to

131

optimize the recording of each of these measures.

132

Cell viability

133

Cells were exposed to a range of BaP concentrations (0.01, 0.05, 0.1, 0.5, 1, 5 and 10 µM;

134

unlabeled) for 1, 2, 3 and 11 days. For dosing, aliquots of 2.5 µL of BaP in DMSO were

135

added to 0.5 mL culture medium as previously described,28,29 yielding a final DMSO

136

concentration of 0.5% (v/v). An individual 48-well plate was prepared for each exposure time

137

with each concentration being added to 6 wells. Four wells served as DMSO control (no

138

BaP). As well, one additional well was used as negative control (cells with only culture

139

medium) whereas another one was left without cells but received 10 µM BaP (blank) to

140

account for potential background fluorescence by the BaP.28 After the exposure, cell viability

141

was assessed fluorometrically exactly as previously described28,29 using a mixture of

142

alamarBlue (Invitrogen, Switzerland), as a measure of the disturbance of metabolic activity,

143

and 5-carboxyfluorescein diacetate acetoxy methyl ester (CFDA-AM; Invitrogen,

144

Switzerland), as indicator of adverse effects to plasma membrane integrity (SI, Quantification

145

of cell viability).

6 ACS Paragon Plus Environment

Page 6 of 30

Page 7 of 30

Environmental Science & Technology

146

EROD (7-ethoxyresorufin-O-deethylase) activity

147

Cells were exposed to BaP as described above, ranging from 0.0025 to 1 µM of BaP and

148

EROD activity measured after 6, 24, 48 and 72 hours. The plate set-up was essentially as

149

described above with one 48-well plate per time point and each plate containing replicate

150

wells for exposure and appropriate controls. EROD activity was measured in live cells as

151

recommended by Ganassin et al.,30 including addition of CFDA-AM as indicator of cell

152

viability into the EROD assay mixture and using fluorescamine to determine protein content.

153

TCDD (2,3,7,8-tetrachlorodibenzodioxin) was added on each assay plate as positive control.

154

The fluorescent product of the enzyme reaction, resorufin, was quantified at excitation and

155

emission wavelengths of 530 and 590 nm, respectively, using the Infinite M200 multi-well

156

plate reader. CFDA-AM was quantified at the wavelength settings as described above.

157

BaP distribution and depletion

158

A nominal BaP exposure concentration of 1.6 µM was chosen for chemical distribution and

159

depletion analysis. Two criteria were set for deciding on this concentration. The first was that

160

the concentration should be non-toxic to the cells as determined in the cell viability assays

161

(see above) in order to avoid interference in the cell functioning by a cytotoxic action of BaP.

162

The second criterion was to have a sufficient margin for chemical depletion given the limit of

163

quantification of the BaP analysis method, which was 0.02 µM for the cell and plastic

164

compartment and 0.2 µM for the medium (see below). To initiate exposure of the cell

165

monolayers established in 75 cm2 cell culture flasks, 5 mL of the 9.5 mL cell culture medium

166

were removed, transferred into sterile 7 mL amber glass vials (Supelco Sigma, Switzerland)

167

and 3.7 µL of the 4.14 mM

168

transferred back into the respective cell culture flask, yielding a final DMSO content of 0.04%

169

(v/v).

170

To verify the initial amount of BaP in the cell culture medium, i.e. at the beginning of the

171

exposure test, an aliquot of 50 µL was removed from each flask and dissolved in 250 µL 7

14

C-BaP working solution were added. This medium was then

ACS Paragon Plus Environment

Environmental Science & Technology

172

acetonitrile (ACN). A volume of 100 µL of this solution was injected into an HPLC (1100

173

Series, Hewlett-Packard GmbH and Agilent), coupled to a radio detector (radio-HPLC; Flow

174

Scintillation Analyzer; 500 TR Series, A Packard Cranberra company [now PerkinElmer],

175

Switzerland) as described below. After 6, 8, 12, 24, 48 and 72 hours of exposure to BaP, an

176

aliquot of the culture medium, the cells and the plastic wall of the respective cell culture flask

177

were extracted by ACN essentially as previously described31 (see Supporting Information SI:

178

Chemical analysis). These experiments were repeated three independent times starting with

179

cells from different passages. Recovery of BaP from cell-free flasks over the 72 hour period

180

was confirmed to range from 94% to 112% in two independent experiments.

181

In a separate set of experiments, cells were pre-exposed to a potential inhibitor of BaP

182

biotransformation, alpha-naphthoflavone (ANF - Sigma-Aldrich, Switzerland; 1 µM,

183

dissolved in DMSO, according to28) one hour before the addition of BaP. Co-exposures of

184

ANF and BaP were done for 8, 12 and 48 hours with subsequent procedures as described

185

above.

186

Determination of cell number in cell culture flasks

187

To obtain measures of cell size and number for input into the kinetic models (see below), cells

188

plated in 75 cm2 cell culture flasks as described above were exposed to unlabelled BaP. At

189

each time point (0, 6, 8, 12, 48, and 72 hours), cells were dislodged by first washing them

190

with Versene, followed by incubation with trypsin and careful re-suspension in a total volume

191

of 5 mL culture medium. Upon centrifugation, the cell pellet was re-suspended into 2 mL of

192

culture medium. An aliquot of 10 µL of this cell suspension was added to 10 mL CASY

193

solution and cell number and size (set to 7.5-30 µm) recorded using the electric field multi-

194

channel cell counting system CASY1 TCC (Schärfe System, Germany). Measurements were

195

repeated with three independent preparations having three flasks each, yielding relative

196

standard deviations of less than 15% for cell number and less than 6% for cell diameter. The 8 ACS Paragon Plus Environment

Page 8 of 30

Page 9 of 30

Environmental Science & Technology

197

resulting measures and calculations needed for the modelling are presented in SI: PBTK

198

model.

199

Incorporating in vitro intrinsic clearance rates into the PBTK model

200

The PBTK model used in this study, and originally developed for rainbow trout10,32, was

201

improved by including the tissue compositions from Bertelsen et al.33, blood:water and

202

lipid:blood partition coefficients and fecal egestion rate from Arnot et al.34 and Nichols et

203

al.35, the volume of fat compartment as in Stadnicka et al.22, and the biotransformation process

204

as in Jones et al.36 and this study. The PBTK model used here consists of six different

205

compartments: liver, kidney, fat, guts, and richly and poorly perfused tissues. The “guts”

206

compartment is distinguished from the richly perfused compartment in order to account for

207

the biotransformation process in the intestinal cells. The guts compartment includes stomach,

208

pyloric caeca and upper and lower intestine. The model parameters needed for this

209

compartment (like the organs’ volumes or lipid content) were obtained from the PBTK model

210

for dietary uptake.37

211

The in vitro (that is the cell-line based) reaction rate constants (ki) are derived as the slope of

212

the relationship of measured concentrations of the parent chemical (ln y-axis) over time (x-

213

axis) (see SI, PBTK Model: Equations and notes; eq. 22). The cell-line specific reaction rate

214

constants are then divided by the respective average cell concentrations measured in the

215

experiments with each cell line in order to obtain the in vitro intrinsic clearance rate (CLIN

216

VITRO).

217

respective organ (SI: Table S-1, eq. 23). The rate for the RTgill-W1 cell line was applied to

218

represent all richly perfused tissues (aside from liver and intestine) in an attempt to account

219

for biotransformation in the entire organism. These values, together with the so-called binding

220

correction term (fU, SI: eq. 25), allow to include not only the liver but the additional

221

elimination routes of the intestine and other richly perfused tissues (represented by the gills),

This rate is then multiplied by the cell number (Tcell,i) predicted to amount to 1 g of the

9 ACS Paragon Plus Environment

Environmental Science & Technology

222

i.e., in vivo intrinsic clearance rates (CLIN VIVO, SI: eq. 24), in the model according to Jones et

223

al.36 (SI eq. 11, 15-17). The fU is used to account for the free chemical fraction in the in vitro

224

systems. It was calculated based on the equation given in Nichols et al.38 for hepatocytes,

225

given the fact that experiments for both the cell lines and the hepatocytes were carried out in

226

L-15 cell culture medium and assuming comparable cell size (see SI Note to eq. 23).

227

Inasmuch as the correction term is still debated because it has led to BCF overestimation in

228

models that assume chemical biotransformation in fish liver alone,38,39 this term is often

229

artificially set to 1.40 Thus, in addition to the calculated fU, in the results section, the BaP BCF

230

is also given for the fU set to 1.

231

The model was implemented and solved using ModelMaker (version 4.0, Cherwell Scientific

232

Ltd., Oxford, UK), and all the model parameters and equations are presented in the SI: PBTK

233

model.

234

4. Results and Discussion

235

The aim of our study was to test whether bioconcentration of BaP in fish, specifically rainbow

236

trout, can be predicted based on in vitro intrinsic clearance rate constants obtained in three

237

rainbow trout-derived cell lines: RTgill-W1 (gill), RTgutGC (intestine), and RTL-W1 (liver).

238

We hypothesized that gill and intestine are potential sites of biotransformation of BaP in fish

239

in addition to the liver. Thus, by accounting for BaP depletion in different tissues, one may

240

more closely approach the whole body biotransformation rate implicitly accounted for in the

241

in vivo tests.

242

Impact of BaP on cell viability

243

BaP led to a time-dependent impact on cell viability for all three cell lines as indicated by the

244

measures of cell metabolic activity (alamarBlue) and cell membrane integrity (CFDA-AM)

245

(SI: Cell viability, Figure S1). However, the pattern of impact prominently differed for 10 ACS Paragon Plus Environment

Page 10 of 30

Page 11 of 30

Environmental Science & Technology

246

RTgill-W1 cells. In contrast to the other two cell lines, the impact on cell viability in RTgill-

247

W1 cells took longer to establish and was overall much less pronounced.

248

Several lines of evidence suggest that the development of cytotoxicity is a result of BaP

249

biotransformation and that the differences in cytotoxicity between the cell lines result from

250

different biotransformation routes. First, our results are reminiscent of those reported for the

251

two rainbow trout liver cell lines, RTL-W1 and R1, where distinct patterns of cell viability

252

upon BaP exposure were implied to result from dissimilar routes of biotransformation active

253

in the cells.28 The scenario of 11 days of exposure to BaP in that prior study was comparable

254

to the one performed here and indeed resulted in similar results for RTL-W1 (see Fig. 7E in

255

Schirmer et al.28). The results for the R1 cell line, on the other hand, resemble more those

256

obtained here for RTgill-W1 cells with no to very little observable toxicity. According to the

257

previous study, the difference seen between RTL-W1 and R1 cells was attributed to,

258

respectively, the presence or absence of inducible CYP1A, measured as EROD activity,

259

although a role of CYP1B could not be ruled out. Finally, when tested individually, two

260

common biotransformation products of BaP, namely BaP 7,8-dihydrodiol (BDP) and 6,12

261

BaP quinone (BQ), also caused cytotoxicity, though to different degrees. While the BDP was

262

only slightly toxic and only to RTL-W1 cells, the BQ caused a clear impact in cell viability to

263

both cell lines with R1 cells being more responsive.28 While BDP is a product of CYP-

264

dependent biotransformation, BQ can additionally result from alternative enzymatic reactions,

265

such as those catalyzed by peroxidases.41

266 267

CYP1A catalytic activity measured as EROD

268

BaP exposure led to significant EROD induction in RTL-W1 and RTgutGC, but not in

269

RTgill-W1 cells (Figure 1). This result indicates that the former two cell lines express CYP1A

270

at the functional level whereas RTgill-W1 cells do not. EROD induction rose to significant 11 ACS Paragon Plus Environment

Environmental Science & Technology

271

levels between 6 and 24 hours in both RTL-W1 and RTgutGC cells and, while observed

272

maximum EROD levels continued to increase up to about 72 hours, the dose-response curves

273

gradually shifted to the right, yielding higher EC50 values with time. A similar time-

274

dependent shift has previously been described in RTL-W1 cells for two other PAHs,

275

benzo(k)fluoranthene42 and 3-methylcholathrene,43 in contrast to TCDD, for which EC50

276

values remained constant over time.42,44 As discussed in Bols et al.,42 the time-dependency of

277

the EROD induction can be explained by the progressive loss of the PAH as inducing agent

278

while it is being transformed by the enzyme(s) it induces. At the same time, EROD induction

279

can be prolonged if biotransformation products themselves can act as inducers of EROD

280

activity. Little information on this phenomenon exists thus far; however, BaP-7,8-dihydrodiol

281

and 6,12-BaP quinone have been identified, respectively, as strong and weak inducer of

282

EROD activity in RTL-W1.28 Finally, at higher nominal BaP exposure concentrations, a drop

283

in EROD activity can be observed, which was more pronounced in RTL-W1 than in

284

RTgutGC cells (Figure 1). This behavior has been reported extensively both for individual

285

PAH exposures42,

286

absence of any cytotoxicity (SI Figure S1), attributable to competitive inhibition of the

287

CYP1A enzyme by the substrate 7-ethoxyresorufin and BaP.

288

While this and another recent study46 encompass the first demonstration of EROD induction

289

in RTgutGC cells, EC50 values in RTL-W1 cells have been reported in previous studies for

290

24 hours of BaP exposure. The values obtained here are in excellent agreement with

291

previously measured values, which were, despite about two-fold differing cell starting

292

densities, 2.85 ± 0.53 10-2 µM in Schirmer et al., 2000;28, 2.55 ± 0.73 10-2 µM in Bols et al.,42

293

compared to 2.14 10-2 µM here. These results confirm the robustness of the cell line and its

294

response to BaP.

295

Spatio-temporal distribution of BaP

43

as well as for complex environmental samples45 and maybe, in the

12 ACS Paragon Plus Environment

Page 12 of 30

Page 13 of 30

Environmental Science & Technology

296

Mass balance analysis, i.e. the summation of BaP amounts in the different compartments,

297

over time confirmed a rapid loss of parent BaP from the system but not only in RTL-W1 and

298

RTgutGC cells but as well in RTgill-W1. As can be seen in Figure 2 and SI Table S-2, BaP

299

medium concentrations declined quickly, falling below quantifiable levels after 12 hours in

300

the case of RTL-W1 and RTgutGC and 24 hours in the case of RTgill-W1. Highest BaP

301

concentrations in cells were found for RTL-W1 and RTgutGC cell lines at the earliest point of

302

observation, 6 hours, after which BaP concentrations continuously declined to near or below

303

the level of quantification. A similar pattern was seen for RTgill-W1 cells, though again

304

delayed, with highest BaP concentrations in cells detected after 8 hours of BaP exposure. The

305

plastic surface also contained significant amounts of BaP with highest levels measured at the

306

first time point. Thereafter, the sorption to plastic reflected the kinetics of loss of BaP – it

307

declined as BaP in the medium and the cells also declined. This finding is in agreement with a

308

previous report on the distribution of BaP in a culture system using a mouse cell line model31

309

and indicates that the sorption process was reversible: as the concentration gradient between

310

plastics and medium/cells increased due to biotransformation, more of the BaP was released

311

from the plastic surface. Taken together, while in the absence of cells BaP concentrations

312

remained stable, BaP was transformed in the presence of cells by more than 90% within 24

313

hours in the case of RTL-W1 and RTgutGC and within 48 hours of exposure in the case of

314

RTgill-W1.

315

The distribution of BaP in the culture flasks was also followed after a one hour pre-incubation

316

with alpha-naphthoflavone (ANF) in order to provide further proof of biotransformation in the

317

cell lines (SI Figure S2). ANF is an inhibitor of CYP1A activity and, in fact, other

318

cytochromes41 and enzyme systems, such as prostaglandin-H-synthase, which consists of a

319

cyclooxygenase and a peroxidase activity.47,48 ANF was previously shown to inhibit EROD

320

activity in RTL-W1.28 As depicted in Figure 3, presence of ANF clearly affected the kinetics

321

of BaP in the cells, leading to an initial retardation of biotransformation in RTL-W1 and 13 ACS Paragon Plus Environment

Environmental Science & Technology

322

RTgutGC cells and a severe arrest of biotransformation in RTgill-W1 cells. These results not

323

only confirm that the loss of BaP in the system is due to biotransformation but also that the

324

routes of biotransformation differ between the cell lines expressing inducible EROD activity

325

(RTL-W1, RTgutGC) or not (RTgill-W1), as discussed above. Studying the repertoire of

326

biotransformation reactions in the different fish cell lines and their dependence on culture

327

conditions, such as temperature or medium composition, are important next steps to directly

328

link the kinetic processes with underlying enzymatic reactions. One approach is that described

329

by Thibaut et al.50, who monitored the appearance of a set of phase I and phase II

330

biotransformation products in the PLHC-1 (hepatocellular carcinoma cell line of Poeciliopsis

331

lucida) and the RTL-W1 cell line using radio-labelled substrates. Moreover, similar studies

332

are needed from tissue-based investigations or also freshly isolated cells, especially of gill and

333

intestine, to shed light on the tissue-specific biotransformation capabilities in fish. With

334

regard to the gills, one prior study reported inducible EROD activity in a primary gill cell

335

culture upon exposure to BaP21; as well, an ex vivo rainbow trout gill filament assay51

336

confirmed CYP1A protein expression and EROD induction by BaP. Compared to our results

337

with the RTgill-W1, these prior studies indicate that the cell line model does not fully mimic

338

an in vivo phenotype. Yet, more comparative studies are needed, both with respect to enzyme

339

patterns and clearance rates, to better address this issue.

340

In vitro reaction and intrinsic clearance rate constants

341

The overall loss of BaP in the culture flasks was plotted over time to obtain the in vitro

342

reaction rate constants (Figure 2D). These were in the order from highest to lowest: 0.143 h-1

343

for RTL-W1 > 0.114 h-1 for RTgutGC >> 0.071 h-1 for RTgill-W1 cells. One other previous

344

study has quantified the disappearance of BaP in confluent monolayers of fish cell cultures

345

over time:52 the bluegill fry cell line, BF-2 (from caudal trunk tissue), the rainbow trout gonad

346

cell line, RTG-2 (from embryonic gonad tissue), and the brown bullhead cell line, BB (from

14 ACS Paragon Plus Environment

Page 14 of 30

Page 15 of 30

Environmental Science & Technology

347

posterior trunk tissue), were all capable of biotransforming BaP. Calculable reaction rate

348

constants from these cell lines amount to between 0.036 h-1 (BF-2) and 0.045 h-1 (BB), with

349

the BaP starting concentration being 2 µM. These reaction rate constants are lower than those

350

measured in our study; however, they were also obtained in larger flasks (175 cm2) with a

351

larger volume (50 mL). Cell numbers were not counted but monolayers were used as in our

352

case. If we assume that about the same number of fish cells leads to a confluent monolayer,

353

the culture surface to culture volume ratio can be applied. This ratio amounts to 3.5 in the

354

study by Smolarek et al. (1987)52 compared to 7.9 (75 cm2/9.5 mL) by us, giving a value of

355

about 2-fold higher in our study. Translating this ratio to the in vitro intrinsic clearance rate

356

(CLIN_VITRO), would therefore indicate very similar rates to the one determined for RTgill-W1

357

(see Table 1 for values of CLIN_VITRO). This finding supports our hypothesis that the gill cell

358

line may exemplify in vitro intrinsic clearance in richly perfused tissues which are, however,

359

not major hubs for biotransformation. The higher reaction rates and CLIN_VITRO for the

360

intestinal and the liver cell model, on the other hand, indicate a distinct contribution of these

361

tissues to the biotransformation of BaP. Our results with the intestinal cell line are in

362

agreement with previous studies in channel catfish which have shown that BaP can be

363

biotransformed by intestinal segments or microsomes.19, 20

364

The in vitro intrinsic clearance rate obtained in the RTL-W1 fish liver cell line might be

365

compared to rates reported for primary liver cell models. However, big differences between

366

intrinsic clearance rates were found among the primary cells: 0.054±0.023 mL/h/106cells for

367

freshly isolated hepatocytes13 compared to 0.214±0.067 mL/h/106cells for cryopreserved

368

hepatocytes.12 The CLIN_VITRO obtained for RTL-W1 (0.425±0.0198 mL/h/106cells) was

369

higher than those obtained for primary hepatocytes. It cannot as yet be stated, however, if

370

these differences are of cell intrinsic nature or are due to differences in the incubation

371

conditions. For example, RTL-W1 cells were exposed in the presence of a 5% serum

372

supplement. On the one hand, serum could contribute to BaP binding, thereby reducing 15 ACS Paragon Plus Environment

Environmental Science & Technology

373

bioavailability and potentially intrinsic clearance.13 On the other hand, serum components

374

may in fact facilitate uptake, as pointed out by Kramer and colleagues.53 Moreover, Jones and

375

Houston54 demonstrated a trend towards higher values of intrinsic clearance for different

376

chemicals with decreasing numbers of rat hepatocytes per mL of exposure medium. Indeed,

377

our experiments with the cell line were performed with a much lower cell concentration (0.34

378

Mio cells measured per mL compared to 2 Mio for the fish hepatocytes). In addition, the

379

hepatocytes were incubated in suspension whereas RTL-W1 cells are cultured as monolayers.

380

A study focusing on rat hepatocytes in suspension and in monolayer culture has pointed out

381

that these two systems cannot easily be compared:55 intrinsic clearance rates were comparable

382

for some chemicals but both higher and lower for others.

383

Prediction of the BaP bioconcentration factor in fish

384

In order to predict the bioconcentration of BaP in fish, we applied the PBTK model adapted

385

from.22 Without taking the biotransformation process into account, a BCF of 7 045 is

386

predicted for rainbow trout, compared to a measured BCF of 920 specifically for this species

387

of fish26 (Table 1). While the predicted BCF is seven times higher than the measured, it is

388

almost 3 times lower than a previously reported BCF prediction of BaP in rainbow trout (19

389

620).12 This latter BCF was based on a one-compartment model not considering

390

biotransformation but using a fish-water partitioning coefficient that would result in a

391

different blood:water partition coefficient than the one used in our study - adapting the same

392

fish-water partitioning coefficient to our model would yield a predicted BCF of 17 800.

393

In order to take biotransformation into account, we first included the in vitro intrinsic

394

clearance rate constant, CLIN_VITRO, obtained for the RTL-W1 cell line in our PBTK model

395

together with the calculated binding correction term, fU. This reduced the predicted BaP BCF

396

by about 3.5-fold (Table 1). When the CLIN_VITRO for RTgutGC and RTgill-W1 were

397

additionally added, the predicted BCF dropped to between 909 (for 50g fish) and 1057 (for 30 16 ACS Paragon Plus Environment

Page 16 of 30

Page 17 of 30

Environmental Science & Technology

398

g fish). Thus, including clearance rates from all three cell line models yields the predicted

399

BCF closest to the measured in vivo value of 920. In past biotransformation studies using

400

rainbow trout S9 fractions or hepatocytes, it has repeatedly been found that BCF predictions

401

based on calculated fU yielded comparatively high BCFs and a better correlation with in vivo

402

measured values was found when fU was set to 1.38,39 When doing so using the CLIN_VITRO for

403

the fish cell lines, BCF predictions fall well below the measured values, especially when

404

biotransformation in gill and intestine are additionally taken into account (Table 1). Thus, in

405

the case of our study, the use of calculated fU appears to lead to a better BCF prediction. This

406

result supports the hypothesis of Escher et al.39 that accounting for chemical

407

biotransformation in more fish organs than the liver may result in a better agreement between

408

predicted and measured BCFs when applying the calculated fU.

409

Taken together, our results provide a proof-of-principle that cell lines of rainbow trout can be

410

used to obtain in vitro intrinsic clearance rates that aid in the prediction of a chemical’s BCF

411

using PBTK models. Indeed, this is the first presentation of not only using fish cell lines to

412

predict BCFs but is also the first to incorporate in vitro biotransformation rate data for organs

413

of different origin into a fish PBTK model. We demonstrate that all three rainbow trout cell

414

lines are capable of biotransforming BaP although the exact biotransformation pathways and

415

the resemblance of these pathways with those of the respective tissues in vivo are not yet

416

know. Despite of this uncertainty, the finding of biotransformation in all three cell lines

417

confirms the significance of liver-derived cells for biotransformation and as well highlights

418

the gill and the intestine as important biotransformation sites. The relative importance of the

419

gill and the intestine for the biotransformation of a particular chemical likely depends on the

420

physico-chemical properties. For example, biotransformation can be expected to be more

421

important in the intestine than in the gill for hydrophobic chemicals, which adsorb to food and

422

thus enter the fish predominantly via this route. More water soluble and ionizable compounds,

423

on the other hand, would be expected to have greater contact with the gill surface, at least 17 ACS Paragon Plus Environment

Environmental Science & Technology

424

initially.56 Thus, application of fish cell lines holds great potential for further investigating the

425

role of their tissue origin in the biotransformation of chemicals with a wide spectrum of

426

properties. Fish cell lines not only comprise a true alternative to using fish in chemical testing

427

but as well yield highly reproducible results. In addition, they are very flexible with regard to

428

different exposure regimes, e.g. exposure times can be extended to days in case of slowly

429

biotransformed compounds. Yet, comparison of cell line-derived clearance rates to those

430

found in freshly isolated gill, intestinal and also liver tissue, is an important future direction.

431

Among the variables to be explored are the influence of temperature57 and chemical starting

432

concentration58. Moreover, several model uncertainties need to be acknowledged. First, we

433

compare the BCF predicted with our approach to the one available in vivo-derived BCF for

434

rainbow trout, which was obtained before the OECD TG 305 was in place. Second,

435

uncertainty arises from the PBTK model itself, e.g. from the model equations or the fish

436

physiological parameters used. Two respective examples highlighted in our study are the

437

correction binding term, fU, and the chemical blood-water partition coefficient, Pbw. To

438

address such model uncertainties is one aim of an OECD expert group that is currently

439

developing of a guidance document for in vitro-in vivo BCF predictions for fish. Our work

440

focusses on rainbow trout derived cell lines combined with a PBTK model that was explicitly

441

designed to reflect physiological features of this ecologically and economically important

442

species of fish. However, PBTK models have already been developed for other species of

443

fish, e.g. various species of trouts,31,59,60 fathead minnow,22 channel catfish,61 zebrafish62 or

444

European eel.63 Thus, further cell line development and PBTK application could also aid in

445

comparing species for their biotransformation potential and sensitivity toward chemical

446

exposure.

447

18 ACS Paragon Plus Environment

Page 18 of 30

Page 19 of 30

Environmental Science & Technology

448

5. Acknowledgement

449

We would like to thank Nadine Bramaz for her excellent support in the cell culture work,

450

particularly the EROD assay, and Danielle Madureira for her collaboration during the initial

451

establishment of the BaP dosing and extraction protocol.

452

6. Supporting Information

453

Contains details on chemical analysis (BaP extraction and quantification), the PBTK model

454

(abbreviations and symbols; equations and notes), as well as additional results (cell viability

455

and data for time-dependent distribution of BaP in culture flasks).

456

19 ACS Paragon Plus Environment

Environmental Science & Technology

457

7. References

458

1.

459

Guinea, J.; Klüver, N.; Schirmer, K.; Tanneberger, K.; Tobor-Kapłon, M.; Witters, H.;

460

Belanger, S.; Benfenati, E.; Creton, S.; Cronin, M. T. D.; Eggen, R. I. L.; Embry, M.; Ekman,

461

D.; Gourmelon, A.; Halder, M.; Hardy, B.; Hartung, T.; Hubesch, B.; Jungmann, D.; Lampi,

462

M. A.; Lee, L.; Léonard, M.; Küster, E.; Lillicrap, A.; Luckenbach, T.; Murk, A. J.; Navas, J.

463

M.; Peijnenburg, W.; Repetto, G.; Salinas, E.; Schüürmann, G.; Spielmann, H.; Tollefsen, K.

464

E.; Walter-Rohde, S.; Whale, G.; Wheeler, J. R.; Winter, M. J., A European perspective on

465

alternatives to animal testing for environmental hazard identification and risk assessment.

466

Regul. Toxicol. Pharmacol. 2013, 67 (3), 506-530.

467

2.

468

in the toxicology and ecotoxicology of fish. Piscine cell lines in environmental toxicology. In

469

Biochemistry and Molecular Biology of Fishes, Mommsen, T. P.; Moon, T. W., Eds. Elsevier:

470

2005; Vol. Volume 6, pp 43-84.

471

3.

472

substitutes for regulatory testing of chemicals and effluents using fish. Toxicology 2006, 224,

473

163-183.

474

4.

475

Schirmer, K., Predicting fish acute toxicity using a fish gill cell line-based toxicity assay.

476

Environ. Sci. Technol. 2013, 47 (2), 1110-1119.

477

5.

478

population growth in vitro predicts reduced fish growth. Sci. Adv. 2015, 1 (7), e1500302.

479

6.

480

bioaccumulation factor (BAF) assessments for organic chemicals in aquatic organisms.

481

Environ. Rev. 2006, 14 (4), 257-297.

482

7.

483

in Fish: Aqueous and Dietary Exposure. http://www.oecd-ilibrary.org/environment/test-no-

484

305-bioaccumulation-in-fish-aqueous-and-dietary-exposure_9789264185296-en 2012, 305.

485

8.

486

in fish from laboratory data. Environ. Toxicol. Chem. 2008, 27 (2), 341-351.

487

9.

488

factor to screen chemicals for bioaccumulation potential. Environ. Toxicol. Chem. 2012, 31

489

(10), 2261-2268.

Scholz, S.; Sela, E.; Blaha, L.; Braunbeck, T.; Galay-Burgos, M.; García-Franco, M.;

Bols, N. C.; Dayeh, V. R.; Lee, L. E. J.; Schirmer, K., Chapter 2 Use of fish cell lines

Schirmer, K., Proposal to improve vertebrate cell cultures to establish them as

Tanneberger, K.; Knöbel, M.; Busser, F. J. M.; Sinnige, T. L.; Hermens, J. L. M.;

Stadnicka-Michalak, J.; Schirmer, K.; Ashauer, R., Toxicology across scales: Cell

Arnot, J. A.; Gobas, F. A. P. C., A review of bioconcentration factor (BCF) and

OECD, OECD Guidelines for the testing of chemicals. Test No. 305: Bioaccumulation

Arnot, J. A.; Mackay, D.; Bonnell, M., Estimating metabolic biotransformation rates

Costanza, J.; Lynch, D. G.; Boethling, R. S.; Arnot, J. A., Use of the bioaccumulation

20 ACS Paragon Plus Environment

Page 20 of 30

Page 21 of 30

Environmental Science & Technology

490

10.

Nichols, J. W.; McKim, J. M.; Andersen, M. E.; Gargas, M. L.; Ckewell, H. J.;

491

Erickson, R. J., A physiologically based toxicokinetic model for the uptake and disposition of

492

waterborne organic chemicals in fish. Toxicol. Appl. Pharmacol. 1990, 106, 433-447.

493

11.

494

Summary

495

bioaccumulation

496

https://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=307565.

497

12.

498

Peterson, H. M.; Nichols, J. W.; Segner, H.; Han, X., Intra- and interlaboratory reliability of a

499

cryopreserved trout hepatocyte assay for the prediction of chemical bioaccumulation

500

potential. Environ. Sci. Technol. 2014, 48 (14), 8170-8178.

501

13.

502

Xenobiotic intrinsic clearance in freshly isolated hepatocytes from rainbow trout

503

(Oncorhynchus mykiss): Determination of trout hepatocellularity, optimization of cell

504

concentrations and comparison of serum and serum-free incubations. Aquat. Toxicol. 2008, 89

505

(1), 11-17.

506

14.

507

of xenobiotic metabolism in trout for use in environmental bioaccumulation studies.

508

Xenobiotica 2013, 43 (5), 421-431.

509

15.

510

and S9 from rainbow trout (Oncorhynchus mykiss): Comparison of basal-level enzyme

511

activities with rat and determination of xenobiotic intrinsic clearance in support of

512

bioaccumulation assessment. Environ. Toxicol. Chem. 2009, 28 (3), 481-488.

513

16.

514

bioconcentration of fragrance ingredients by rainbow trout using measured rates of in vitro

515

intrinsic clearance. Environ. Sci. Technol. 2014, 48 (16), 9486-9495.

516

17.

517

transporters in trout hepatocyte spheroid cultures. Toxicol. Res. 2015, 4 (2), 494-507.

518

18.

519

W. M.; Jackson, S. K.; Jha, A. N., Pharmaceutical metabolism in fish: Using a 3-D hepatic in

520

vitro

521

https://doi.org/10.1371/journal.pone.0168837.

Nichols, J.; Gobas, F. A. P. C.; MacLeod, M.; Borgå, K.; Leonards, P.; Papa, E.,

of

Cefic-LRI

sponsored

research.

workshop:

Recent

Prepared

scientific

for

developments

Cefic-LRI

in

2015,

Fay, K. A.; Mingoia, R. T.; Goeritz, I.; Nabb, D. L.; Hoffman, A. D.; Ferrell, B. D.;

Han, X.; Mingoia, R. T.; Nabb, D. L.; Yang, C. H.; Snajdr, S. I.; Hoke, R. A.,

Uchea, C.; Sarda, S.; Schulz-Utermoehl, T.; Owen, S.; Chipman, K. J., In vitro models

Han, X.; Nabb, D. L.; Yang, C.-H.; Snajdr, S. I.; Mingoia, R. T., Liver microsomes

Laue, H.; Gfeller, H.; Jenner, K. J.; Nichols, J. W.; Kern, S.; Natsch, A., Predicting the

Uchea, C.; Owen, S. F.; Chipman, J. K., Functional xenobiotic metabolism and efflux

Baron, M. G.; Mintram, K. S.; Owen, S. F.; Hetheridge, M. J.; Moody, A. J.; Purcell,

model

to

assess

clearance.

PLoS

21 ACS Paragon Plus Environment

One

2017,

12

(1),

Environmental Science & Technology

522

19.

Kleinow, K. M.; James, M. O.; Tong, Z.; Venugopalan, C. S., Bioavailability and

523

biotransformation of benzo(a)pyrene in an isolated perfused in situ catfish intestinal

524

preparation. Environ. Health Perspect. 1998, 106 (3), 155-166.

525

20.

526

modulation of phase 1 and phase 2 activities with benzo(a)pyrene and related compounds in

527

the intestine but not the liver of the channel catfish, Ictalurus punctatus. Drug Metab. Dispos.

528

1997, 25 (3), 346-354.

529

21.

530

cultured gill epithelial cells from rainbow trout. Aquat. Toxicol. 1999, 47 (2), 117-128.

531

22.

532

chemicals in fish by using toxicokinetic models. Environ. Sci. Technol. 2012, 46 (6), 3273-

533

3280.

534

23

535

Development of a cell line from primary cultures of rainbow trout, Oncorhynchus mykiss

536

(Walbaum), gills. J. Fish Dis. 1994, 17 (6), 601-611.

537

24.

538

C., Development of a rainbow trout intestinal epithelial cell line and its response to

539

lipopolysaccharide. Aquacult. Nutr. 2011, 17 (2), e241-e252.

540

25.

541

Arts, M.; Mosser, D. D.; Bols, N. C., Development and characterization of a rainbow trout

542

liver cell line expressing cytochrome P450-dependent monooxygenase activity. Cell Biol.

543

Toxicol. 1993, 9 (3), 279-294.

544

26.

545

trout exposed to several polycyclic aromatic compounds. Environ. Res. 1978, 17 (2), 284-295.

546

27.

547

invitroomics: introduction of three new terms for in vitro biology and illustration of their use

548

with the cell lines from rainbow trout. In Vitro Cell. Dev. Biol.: Anim. 2017, 53 (5), 383-405.

549

28.

550

cytotoxicity elicited by benzo[a]pyrene in two cell lines from rainbow trout liver. J. Biochem.

551

Mol. Toxicol. 2000, 14 (5), 262-276.

552

29.

553

for demonstrating and measuring the photocytotoxicity of fluoranthene to fish cells in culture.

554

Toxicol. In Vitro 1997, 11, 107-119.

James, M. O.; Altman, A. H.; Morris, K.; Kleinow, K. M.; Tong, Z., Dietary

Carlsson, C.; Part, P.; Brunstrom, B., 7-Ethoxyresorufin O-deethylase induction in

Stadnicka, J.; Schirmer, K.; Ashauer, R., Predicting concentrations of organic

Bols, N. C.; Barlian, A.; Chirino-Trejo, M.; Caldwell, S. J.; Goegan, P.; Lee, L. E. J.,

Kawano, A.; Haiduk, C.; Schirmer, K.; Hanner, R.; Lee, L. E. J.; Dixon, B.; Bols, N.

Lee, L. E. J.; Clemons, J. H.; Bechtel, D. G.; Caldwell, S. J.; Han, K. B.; Pasitschniak-

Gerhart, E. H.; Carlson, R. M., Hepatic mixed-function oxidase activity in rainbow

Bols, N. C.; Pham, P. H.; Dayeh, V. R.; Lee, L. E. J., Invitromatics, invitrome, and

Schirmer, K.; Chan, A. G. J.; Bols, N. C., Transitory metabolic disruption and

Schirmer, K.; Chan, G. J.; Greenberg, B. M.; Dixon, D. G.; Bols, N. C., Methodology

22 ACS Paragon Plus Environment

Page 22 of 30

Page 23 of 30

Environmental Science & Technology

555

30.

Ganassin R.C.; Schirmer, K.; Bols, N. C., Experimental Models: Cell/Tissue Cultures

556

- Methods for the use of fish cell and tissue culture as model systems in basic and toxicology

557

research. In The Handbook of Experimental Animals, Bullock, G.; Bunton, T. E., Eds.

558

Academic Press: San Diego, CA, 2000; Vol. Laboratory Fish.

559

31.

560

Schirmer, K., Systems toxicology approach to understand the kinetics of benzo(a)pyrene

561

uptake, biotransformation, and DNA adduct formation in a liver cell model. Chem. Res.

562

Toxicol. 2014, 27 (3), 443-453.

563

32.

564

Physiologically based toxicokinetic modeling of three waterborne chloroethanes in rainbow

565

trout (Oncorhynchus mykiss). Toxicol. Appl. Pharmacol. 1991, 110, 374-389.

566

33.

567

Evaluation of logKow and tissue lipid content as predictors of chemical partitioning to fish

568

tissues. Environ. Toxicol. Chem. 1998, 17 (8), 1447–1455.

569

34.

570

aquatic ecosystems. Environ. Toxicol. Chem. 2004, 23 (10), 2343-2355.

571

35.

572

quantitative hepatic biotransformation data for fish. II. Modeled effects on chemical

573

bioaccumulation. Environ. Toxicol. Chem. 2007, 26 (6), 1304-1319.

574

36.

575

discovery. AAPS J. 2009, 11 (1), 155-166.

576

37.

577

Physiologically based toxicokinetic model for dietary uptake of hydrophobic organic

578

compounds by fish. I. Feeding studies with 2,2',5,5'-Tetrachlorobiphenyl. Toxicol. Sci. 2004,

579

77, 206-218.

580

38.

581

E., Toward improved models for predicting bioconcentration of well-metabolized compounds

582

by rainbow trout using measured rates of in vitro intrinsic clearance. Environ. Toxicol. Chem.

583

2013, 32 (7), 1611-1622.

Madureira, D. J.; Weiss, F. T.; Van Midwoud, P.; Helbling, D. E.; Sturla, S. J.;

Nichols, J. W.; McKim, J. M.; Lien, G. J.; Hoffman, A. D.; Bertelsen, S. L.,

Bertelsen, S. L.; Hoffman, A. D.; Gallinat, C. A.; Elonen, C. M.; Nichols, J. W.,

Arnot, J. A.; Gobas, F., A food web bioaccumulation model for organic chemicals in

Nichols, J. W.; Fitzsimmons, P. N.; Burkhard, L. P., In vitro–in vivo extrapolation of

Jones, H. M.; Gardner, I. B.; Watson, K. J., Modelling and PBPK simulation in drug

Nichols, J. W.; Fitzsimmons; Whiteman; Dawson; Babeu; Juenemann, A

Nichols, J. W.; Huggett, D. B.; Arnot, J. A.; Fitzsimmons, P. N.; Cowan-Ellsberry, C.

23 ACS Paragon Plus Environment

Environmental Science & Technology

Page 24 of 30

584

39.

Escher, B. I.; Cowan-Ellsberry, C. E.; Dyer, S.; Embry, M. R.; Erhardt, S.; Halder, M.;

585

Kwon, J. H.; Johanning, K.; Oosterwijk, M. T. T.; Rutishauser, S.; Segner, H.; Nichols, J.,

586

Protein and lipid binding parameters in rainbow trout (Oncorhynchus mykiss) blood and liver

587

fractions to extrapolate from an in vitro metabolic degradation assay to in vivo

588

bioaccumulation potential of hydrophobic organic chemicals. Chem. Res. Toxicol. 2011, 24

589

(7), 1134-1143.

590

40.

591

M. E.; Weisbrod, A. V., Approach for extrapolating in vitro metabolism data to refine

592

bioconcentration factor estimates. Chemosphere 2008, 70 (10), 1804-1817.

593

41.

594

peroxidase

595

benzo[a]pyrene to deoxyribonucleic-acid. Biochem. Pharmacol. 1988, 37 (11), 2183-2187.

596

42.

597

Ability of polycyclic aromatic hydrocarbons to induce 7-Ethoxyresorufin-o-deethylase

598

activity in a trout liver cell line. Ecotox. Environ. Safe. 1999, 44 (1), 118-128.

599

43.

600

as inducers of cytochrome P4501A enzyme activity in the rainbow trout liver cell line, RTL-

601

W1, and in primary cultures of rainbow trout hepatocytes. Environ. Toxicol. Chem. 2001, 20

602

(3), 632-643.

603

44.

604

equivalence factors (TEFs) for selected dioxins, furans and PCBs with rainbow trout and rat

605

liver cell lines and the influence of exposure time. Chemosphere 1997, 34 (5), 1105-1119.

606

45.

607

heterocycles as major polycyclic aromatic cytochrome P4501A-inducers in a contaminated

608

sediment. Environ. Sci. Technol. 2003, 37 (14), 3062-3070.

609

46.

610

benzo[a]pyrene with the in vitro fish gut model: An integrated approach for eco-

611

genotoxicological

612

doi.org/10.1016/j.mrgentox.2017.12.009.

613

47.

614

of trout cytochrome P450s. Toxicol. Appl. Pharmacol. 1998, 148 (2), 237-244.

615

48.

616

diethylstilbestrol by alpha-naphthoflavone and beta-naphthoflavone. J. Biochem. Toxicol.

617

1988, 3, 1-10.

Cowan-Ellsberry, C. E.; Dyer, S. D.; Erhardt, S.; Bernhard, M. J.; Roe, A. L.; Dowty,

Cavalieri, E. L.; Devanesan, P. D.; Rogan, E. G., Radical cations in the horseradishand

prostaglandin-H

synthase

mediated

metabolism

and

binding

of

Bols, N. C.; Schirmer, K.; Joyce, E. M.; Dixon, D. G.; Greenberg, B. M.; Whyte, J. J.,

Behrens, A.; Schirmer, K.; Bols, N. C.; Segner, H., Polycyclic aromatic hydrocarbons

Clemons, J. H.; Dixon, D. G.; Bols, N. C., Derivation of 2,3,7,8-TCDD toxic

Brack, W.; Schirmer, K., Effect-directed identification of oxygen and sulfur

Langan, L.M.; Arossa, S.; Owen, S.F.; Jha, A.N., Assessing the impact of

studies.

Mutat.

Res.

Gen.

Tox.

En.

2018,

Miranda, C. L.; Henderson, M. C.; Buhler, D. R., Evaluation of chemicals as inhibitors

Degen, G. H., Inhibition of prostaglandin H synthase-catalyzed cooxidation of

24 ACS Paragon Plus Environment

Page 25 of 30

Environmental Science & Technology

618

49.

Levine, S. L.; Oris, J. T., Induction of CYP1A mRNA and catalytic activity in gizzard

619

shad (Dorosoma cepedianum) after waterborne exposure to benzo[a]pyrene. Comp. Biochem.

620

Phys. C 1997, 118 (3), 397-404.

621

50.

622

and RTL-W1 fish liver cell lines. Cell Biol. Toxicol. 2009, 25 (6), 611-622.

623

51.

624

induction in rainbow trout gills and liver following exposure to waterborne indigo, benzo(a)

625

pyrene and 3,3 ',4,4 ',5-pentachlorobiphenyl. Aquat. Toxicol. 2006, 79 (3), 226-232.

626

52.

627

M.,

628

dimethylbenz[a]anthracene in fish cell lines in culture. Carcinogenesis 1987, 8 (10), 1501-

629

1509.

630

53.

631

sorption kinetics in solid-phase microextraction:  consequences for chemical analyses and

632

uptake processes. Anal. Chem. 2007, 79 (18), 6941-6948.

633

54.

634

metabolic clearance: Time dependencies in hepatocyte and microsomal incubations. Drug

635

Metab. Dispos. 2004, 32 (9), 973-982.

636

55.

637

hepatocytes: Comparison of suspensions and monolayer cultures. Drug Metab. Dispos. 2005,

638

33 (1), 115-120.

639

56.

640

A.; Schirmer, K.; Nichols, J. W., Assessing the bioaccumulation potential of ionizable organic

641

compounds: Current knowledge and research priorities. Environ. Toxicol. Chem. 2017, 36 (4),

642

882-897.

643

57.

644

metabolism of benzo[a]pyrene in rainbow trout (Oncorhynchus mykiss): a comparison

645

between the liver and immune organs. Drug Metab. Dispos. 2014, 42 (1), 111-118.

646

58.

647

dependence of biotransformation in fish liver S9: optimizing substrate concentrations to

648

estimate hepatic clearance for bioaccumulation assessment. Environ. Toxicol. Chem. 2015, 34

649

(12), 2782-2790.

Thibaut, R.; Schnell, S.; Porte, C., Assessment of metabolic capabilities of PLHC-1

Jonsson, E. M.; Abrahamson, A.; Brunstrom, B.; Brandt, I., Cytochrome P4501A

Smolarek, T. A.; Morgan, S. L.; Moynihan, C. G.; Lee, H.; Harvey, R. G.; Baird, W. Metabolism

and

DNA

adduct

formation

of

benzo[a]pyrene

and

7,12-

Kramer, N. I.; van Eijkeren, J. C. H.; Hermens, J. L. M., Influence of albumin on

Jones, H. M.; Houston, J. B., Substrate depletion approach for determining in vitro

Griffin, S. J.; Houston, J. B., Prediction of in vitro intrinsic clearance from

Armitage, J. M.; Erickson, R. J.; Luckenbach, T.; Ng, C. A.; Prosser, R. S.; Arnot, J.

Moller, A. M.; Hermsen, C.; Floehr, T.; Lamoree, M. H.; Segner, H., Tissue-specific

Lo, J.C.; Allard, G.N.; Otton, S.V.; Campbell, D.A.; Gobas, F.A.P.C., Concentration

25 ACS Paragon Plus Environment

Environmental Science & Technology

650

59.

Lien, G. J.; McKim, J. M.; Hoffman, A. D.; Jenson, C. T., A physiologically based

651

toxicokinetic model for lake trout (Salvelinus namaycush). Aquat. Toxicol. 2001, 51 (3), 335-

652

350.

653

60.

654

toxicokinetic model for maternal transfer of 2,3,7,8-tetrachlorodibenzo-p-dioxin in brook

655

trout (Salvelinus fontinalis). Environ. Toxicol. Chem. 1998, 17, 2422-2434.

656

61.

657

C. A., Physiologically-based toxicokinetic modeling of three waterborne chloroethanes in

658

channel catfish, Ictalurus punctatus. Aquat. Toxicol. 1993, 27, 83-112.

659

62.

660

F.; Beaudouin, R., A physiologically based toxicokinetic model for the zebrafish Danio rerio.

661

Environ. Sci. Technol. 2014, 48 (1), 781-790.

662

63.

663

S.; Reifferscheid, G.; Beiermeister, A.; Hanel, R.; Hollert, H., A physiologically based

664

toxicokinetic (PBTK) model for moderately hydrophobic organic chemicals in the European

665

eel (Anguilla anguilla). Sci. Total Environ. 2015, 536, 279-287.

Nichols, J. W.; Jensen, K. M.; Tietge, J. E.; Johnson, R. D., Physiologically based

Nichols, J. W.; McKim, J. M.; Lien, G. J.; Hoffman, A. D.; Bertelsen, S. L.; Gallinat,

Péry, A. R. R.; Devillers, J.; Brochot, C.; Mombelli, E.; Palluel, O.; Piccini, B.; Brion,

Brinkmann, M.; Freese, M.; Pohlmann, J. D.; Kammann, U.; Preuss, T. G.; Buchinger,

666 667

26 ACS Paragon Plus Environment

Page 26 of 30

Page 27 of 30

668

Environmental Science & Technology

Tables

669 670

Table 1. In vitro intrinsic clearance (CLIN_VITRO), binding correction term (fU) and BaP

671

bioconcentration factors (BCFs) measured and predicted with the PBTK model. Tested cell line CLIN_VITRO [mL/h/106 cells] fU, [ ̶ ]

RTL-W1 0.425 0.090

BCF predicted for rainbow trout no biotransformation biotransformation in RTL-W1$ biotransformation in all cell lines$

fU calculated 7 045 1 842-2 100 909-1 057&

BCF measured in rainbow trout23,£ 672

$

673

values are based on this range.

674

&

675

with fu calculated of 1 126.

676

£

RTgutGC 0.268 0.070

RTgill-W1 0.074 0.032 fU set to 1 7 045 1 212-1 386 567-655

920

According to the source for BCF (ref. 26), fish weight was between 30-50 g and the predicted

For comparison, a fish weight of 10 g, as is most frequently used, would result in a BCF

This study was performed prior to the availability of the OECD305 test guideline.

677 678

27 ACS Paragon Plus Environment

Environmental Science & Technology

679

Page 28 of 30

Figures

680 681 RTgill-W1

EROD activity (pmoles mgProt-1 min-1)

6 hours

24 hours

RTgutGC

RTL-W1

40

40

40

30

30

30

20

20

20

10

10

10

0

0 0.01

0.1

1

0 0.01

10

0.1

1

10

40

40

30

30

20

20

20

10

10

10

0

0 0.01

0.1

1

0.01

10

0.1

30

1

10

0

40

40

30

30

30

20

20

20

10

10

10

0

0

72 hours

0.01

0.1

1

10

0.01

0.1

1

10

0

40 30

20

20

20

10

10

10

0

0

1

10

10

1

10

1

10

1

10

EC50: 0.02 µM

0.01

0.1

EC50: 0.03 µM

30

0.1

1

40

40

0.01

0.1

40 EC50: 0.05 µM

EC50: 0.05 µM

48 hours

0.01

0.01

0.1

40 EC50: 0.09 µM

EC50: 0.07 µM

0.01

0.1

30

1

10

0

0.01

0.1

benzo(a)pyrene concentration (µ µ M)

682 683 684

Figure 1. CYP1A activity, measured as ethoxyresorufin-O-deethylase (EROD) induction,

685

after exposure to BaP concentrations ranging from 0.0025 to 1 µM after 6, 24, 48 and 72

686

hours (from top to bottom) of exposure. The results of two independent experiments are

687

shown (filled black vs. empty white squares). Each symbol represents the average and

688

standard deviation of six culture wells. Data is fitted based on a Gaussian approximation;

689

EC50 values were estimated by considering the ascending part of the curve using the Bell-

690

shaped dose response model (GraphPad Prism 5).

691

28 ACS Paragon Plus Environment

Page 29 of 30

Environmental Science & Technology

692 693

Figure 2. Time-dependent distribution of BaP in culture flasks containing either RTgill-W1

694

(A), RTgutGC (B) or RTL-W1 (C) cells. At each indicated exposure time, the cells, the

695

culture medium and the plastic of the flasks were extracted and analyzed for BaP to obtain a

696

parent compound mass balance. The starting concentration of BaP was 1.6 µM. The

697

difference between total amount recovered and initial amount added was assigned to the %

698

BaP biotransformed (D). Values given are averages of flasks of three independent

699

experiments. For absolute numbers, please refer to SI Table 2.

29 ACS Paragon Plus Environment

Environmental Science & Technology

RTgill-W1

BaP % biotransformed

125

RTgutGC

8h

RTL-W1

125

125

100

100

100

75

75

75

50

50

25

25

25

0

0

0

125

125

100

100

100

75

75

75

50

50

25

25

25

125

12h





50

0

0 125

100

100

75

75

75

50

50

50

25

25

25

48h