Correspondence/Rebuttal Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Responses to Comments on “Differential Health Effects of Constant and Intermittent Exposure to Formaldehyde in Mice: Implications for Building Ventilation Strategies”
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oxidative stress biomarkers, thereby leading to inflammatory damage of the lung. In line with what we have mentioned above, a number of previous studies have histopathologically demonstrated the inflammatory effect of formaldehyde and its damage to lung tissue. Cheng et al. exposed Kunming male mice randomly to 0, 0.08, and 0.8 mg/m3 formaldehyde 24h per day to investigate the toxicity of low-dose formaldehyde inhalation to mice during a continuous long-term. Pathological changes involving inflammatory cell infiltration, edema in the alveolar spaces and disordered alveolar structures were observed in the mice exposed to 0.08 and 0.8 mg/m3 formaldehyde.13 In Murta’s study, male Fischer rats were exposed to 0, 1%, 5%, and 10% formaldehyde for 5 consecutive days, 60 min/day, and from results, 10% formaldehyde exposure promoted an increase of inflammatory cells in BAL fluid and the exposure to 5% formaldehyde exposure reduced the volume density of the alveolar septa and increased the alveolar lumen area in the lung parenchyma.14 Mohamed et al. paid attention to the pulmonary toxicity induced by formaldehyde (0.5 part per thousand gaseous formaldehyde inhalation) and observed morphological changes such as congestion in most lobes, bronchiolar epithelial, pulmonary fibrosis, lymphocytic aggregations, and focal pneumonic organization in lung tissues.15 Similarly, pathological changes of lung tissue have been revealed in several other studies.16−19 Li et al. exposed both Balb/c and C57BL/6 mice to 0, 0.5, and 3 mg/m3 formaldehyde 6 h/day for 25 days and found that the levels of Th2-type cytokines like IL-4, IL-5, and IL-13 in BAL fluid were all elevated in formaldehyde-treated groups.20 Sul et al. exposed SD rats to ambient air, 5 and 10 ppm formaldehyde for 2 weeks (6 h/day, 5 days/week), 21 genes involved in apoptosis, immunity, metabolism, signal transduction and oncogenesis were found to be up- or down-regulated in lung tissues following formaldehyde treatment.21 Hence, even if gaseous formaldehyde could not actually come into the lungs, pulmonary toxicity resulting from formaldehyde inhalation has been observed in numerous studies. We believe that formaldehyde induced ROS might initiate or mediate an inflammatory response in the lung, thereby causing histological lung tissue damage. 2. The second concern of Drs. Wolkoff and Nielsen is about our method for the generation of formaldehyde. They state “The generation of aerosol-free gaseous formaldehyde can be tricky without a generation system using paraformaldehyde. We have not been able to identify the formaldehyde generator system mentioned as ref. 32 (Procedia Engineering, Vol 121 (p. 1−2240), X. Sun, J. Pei, eds., Tianjin, 12−15 July 2015) in the paper by Zhang et al. Thus, we assume that their generator system is similar to that described in other publications from
e appreciate Drs. Wolkoff and Nielsen’s comments on our paper. We would like to take this opportunity to address their concerns and express our views. 1. Drs. Wolkoff and Nielsen’s primary concern is about the damage to lungs in our study. They are surprised by our findings on significant histopathological and inflammatory responses in the lungs, because they believe that gaseous formaldehyde deposits almost completely in the nasal cavity and does not reach internal organs.1 They do acknowledge our finding that formaldehyde did induce increases in oxidative stress as indicated by measured biomarkers in the bronchioalveolar lavage fluid (BALF), and that this finding is not surprising. We do not think that deposition of formaldehyde in the lung is the absolutely required first step for formaldehyde-induced lung injury. Instead, formaldehyde could cause histological and inflammatory lung damage via mechanisms such as the spillover effect of oxidative stress that was initially produced in the upper airways such as nasal cavity. Reactive oxygen species (ROS), including free radicals such as the hydroxyl radical (OH•) and superoxide (O2•−) as well as hydrogen peroxide (H2O2) and organic peroxides can react with various cellular components to cause cell damage and cascading tissue and systemic damage.2 When male Balb/c mice were exposed to 0, 0.5, 1.0, and 3 mg/m3 of formaldehyde continuously for 7 days, 8 h/day, Ye et al. observed significant dose-dependent increases in ROS and malondialdehyde (MDA) and decreases in glutathione (GSH) in all organs examined, including the lungs.3 Park et al. showed that formaldehyde (>100 μM) decreased cell viability of lung alveolar macrophage cells and induced apoptosis via oxidative stress in Raw 264.7 cells.4 In the study conducted by Aydemir et al., female and male Wistar albino rats were exposed to 6 ppm formaldehyde through inhalation for 6 weeks, the level of ROS in lung tissue was raised and the level of GSH was decreased.5 In another study, after 1% formaldehyde was administrated to male Wistar rats 90 min/day for 3 days, the physiological balance between oxidant and antioxidant enzymes in lung tissue was disrupted.6 It is well documented that the accumulation of ROS, reflecting increased levels of oxidative stress, can initiate a proinflammatory response.7 Rahman et al. pointed out that ROS have been implicated in initiating inflammatory responses in the lungs through the activation of transcription factors, such as nuclear factor NF-κB and activator protein AP-1, and other signal transduction pathways like MAPK and PI-3K, leading to increased gene expression of pro-inflammatory mediators.8−10 ROS can trigger an inflammatory response and contribute to the pathological consequences of chronic inflammation.11 Moreover, ROS appears to mediate TNF-α-induced apoptosis.12 Our study showed that formaldehyde exposure enhanced ROS production, as reflected in BALF concentrations of © XXXX American Chemical Society
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DOI: 10.1021/acs.est.8b00844 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Correspondence/Rebuttal
the same laboratory, where formaldehyde is generated from a 10% formalin solution by impinging.”22 We did not use the Zhang et al. apparatus as Drs. Wolkoff and Nielsen assumed in their comments. In fact, the schematic of our formaldehyde generator presented below (Figure 1) is in
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Xu Zhang Yun Zhao Jing Song Xu Yang Junfeng Zhang Yinping Zhang* Rui Li* AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Yinping Zhang: 0000-0001-9175-7890 Notes
The authors declare no competing financial interest.
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Figure 1. Schematic of the generator system for formaldehyde.
the Supporting Information of the present EST paper. The formaldehyde solution was injected into the heating chambers whose flow rates could be accurately controlled by the squirm pumps. In consideration of systematic errors such as the absorption of walls, we performed a calculation to make the formaldehyde inhaled by mice reach 0.4 ppm for constant exposure and 0.8 ppm for intermittent exposure as Table 1 shows. Table 1. Calculation for the FA Concentrations squirm speed
formaldehyde solution concentration
air flow rate
formaldehyde concentration
0.28 μL/min 0.14 μL/min
14.8 μg/μL
3 L/min
1.38 mg/m3
14.8 μg/μL
3 L/min
0.69 mg/m3
REFERENCES
(1) Nielsen, G. D.; Larsen, S. T. P. Re-evaluation of the WHO (2010) formaldehyde indoor air quality guideline for cancer risk assessment. Arch. Toxicol. 2017, 91 (1), 1−27. (2) Andersen, J. K. Oxidative stress in neurodegeneration: cause or consequence? Nat. Rev. Neurosci. 2004, 10 (Suppl.), S18−S25. (3) Ye, X.; Ji, Z.; Wei, C.; et al. Inhaled formaldehyde induces DNAprotein crosslinks and oxidative stress in bone marrow and other distant organs of exposed mice. Environmental & Molecular Mutagenesis 2013, 54 (9), 705−718. (4) Park, S. H. Involvement of Oxidative Stress in Formaldehydeinduced Apoptosis in Cultured Lung Macrophage Cells. Korean Journal of Environmental Agriculture 2009, 28 (3), 295−300. (5) Aydemir, S.; Akgun, S. G.; Beceren, A.; et al. Original Article Melatonin ameliorates oxidative DNA damage and protects against formaldehyde-induced oxidative stress in rats. International Journal of Clinical & Experimental Medicine 2017, 10 (4), 6250−6261. (6) Lino-Dos-Santos-Franco, A.; Correa-Costa, M.; Oliveira, A. P. L. D.; et al. Formaldehyde induces lung inflammation by an oxidant and antioxidant enzymes mediated mechanism in the lung tissue. Toxicol. Lett. 2011, 207 (3), 278−285. (7) Zhang, K.; Kaufman, R. J. From endoplasmic-reticulum stress to the inflammatory response. Nature 2008, 454 (7203), 455−62. (8) Rahman, I.; Adcock, I. M. Oxidative stress and redox regulation of lung inflammation in COPD. Eur. Respir. J. 2006, 28 (1), 219. (9) Rahman, I.; MacNee, W. Oxidative stress and regulation of glutathione in lung inflammation. Eur. Respir. J. 2000, 16 (3), 534− 554. (10) Rahman, I.; Macnee, W. Role of transcription factors in inflammatory lung diseases. Thorax 1998, 53 (7), 601−612. (11) Cerutti, P. A. Prooxidant states and tumor promotion. Science 1985, 227 (4685), 375. (12) Pham, C. G.; Bubici, C.; Zazzeroni, F.; et al. Ferritin heavy chain upregulation by NF-κB inhibits TNFα-induced apoptosis by suppressing reactive oxygen species. Cell 2004, 119 (4), 529−542. (13) Cheng, J.; Long, Z.; Tang, Y.; et al. The toxicity of continuous long-term low-dose formaldehyde inhalation in mice. Immunopharmacol. Immunotoxicol. 2016, 38 (6), 495−501. (14) Murta, G. L.; Campos, K. K.; Bandeira, A. C.; et al. Oxidative effects on lung inflammatory response in rats exposed to different concentrations of formaldehyde. Environ. Pollut. 2016, 211, 206−213. (15) Yaseen, O. Anatomical and Histological Effects of Formaldehyde Inhalation on the Lung of Albino Rat. Journal of American Science 2012, 8 (9), 395−403. (16) Odinko, C. D.; Oladele, A. A.; Aneasato, A. P.; et al. The histological effects of formaldehyde vapour on the lungs. International Journal of Basic Applied & Innovative Research 2012, 1 (4), 176−182. (17) Njoya, H. K.; Ofusori, D. A.; Nwangwu, S. C.; et al. Histopathological effect of exposure of Formaldehyde vapour on the
3. Concerning Drs. Wolkoff and Nielsen’ statement that “we wonder profoundly why Zhang et al. have not compared and discussed their results with effects reported in other exposure studies”, the primary objective of our study is clearly stated in our manuscript. The current study is to compare the toxic effects induced by constant versus intermittent formaldehyde exposures, as opposed to conducting another study of formaldehyde toxicity as done in numerous studies discussed above. Hence our discussion focuses on explaining the differential effects by two different modes of exposure. As Drs. Wolkoff and Nielsen state in their letter, the toxicity of formaldehyde has been extensively studied and described in several reviews. We do not feel it necessary to repeat discussions concerning consistencies and discrepancies of previous studies in the current manuscript. 4. Finally, Drs. Wolkoff and Nielsen consider that our findings and other previous study findings on biomarker responses to formaldehyde exposure are not relevant for human risk assessment. We agree on this point. However, our study is not intended to verify the formaldehyde toxicity relevant to human risk assessment. Instead, the primary goal of our study is to investigate the difference in effects caused by two different modes of formaldehyde exposure. These modes are relevant to practical building ventilation strategies in the real life, as clearly stated in our manuscript. B
DOI: 10.1021/acs.est.8b00844 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Correspondence/Rebuttal
trachea and lung of adult wistar rats. International Journal of Integrative Biology 2009, 7 (3), 160−165. (18) Lino, d S F A; Damazo A S, Hr B D S; et al. Pulmonary neutrophil recruitment and bronchial reactivity in formaldehydeexposed rats are modulated by mast cells and differentially by neuropeptides and nitric oxide. Toxicol. Appl. Pharmacol. 2006, 214 (1), 35−42. (19) Qiao, Y.; Li, B.; Yang, G.; et al. Irritant and adjuvant effects of gaseous formaldehyde on the ovalbumin-induced hyperresponsiveness and inflammation in a rat model. Inhalation Toxicol. 2009, 21 (14), 1200−1207. (20) Li, L.; Hua, L.; He, Y.; et al. Differential effects of formaldehyde exposure on airway inflammation and bronchial hyperresponsiveness in BALB/c and C57BL/6 mice. PLoS One 2017, 12 (6), e0179231. (21) Sul, D.; Kim, H.; Oh, E.; et al. Gene expression profiling in lung tissues from rats exposed to formaldehyde. Arch. Toxicol. 2007, 81 (8), 589−597. (22) Zhang, Y.; Liu, X.; Mchale, C.; et al. Bone Marrow Injury Induced via Oxidative Stress in Mice by Inhalation Exposure to Formaldehyde. PLoS One 2013, 8 (9), e74974.
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DOI: 10.1021/acs.est.8b00844 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
