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Preparation, Crystal Structures, and Oral Bioavailability of Two Cocrystals of Emodin with Berberine Chloride Yanping Deng,†,§ Yanjie Zhang,‡,§ Yali Huang,‡ Mei Zhang,‡ and Benyong Lou*,‡ †

The School of Pharmacy, Fujian Medical University, Fuzhou, Fujian, 350122, China Ocean College, Minjiang University, Fuzhou, Fujian, 350108, China

‡

Crystal Growth & Design Downloaded from pubs.acs.org by UNIV OF WINNIPEG on 11/26/18. For personal use only.

S Supporting Information *

ABSTRACT: Two cocrystals of emodin (EM) with berberine chloride (BER), EM-BER (1) and 2EM-BER-EtOH (2), were prepared and characterized. There exist reliable O-H··· Cl− hydrogen-bonding interactions between the 2-hydroxyl group of emodin and chloride anion. Various π−π interactions dominate the packing structures of 1 and 2. In 1, emodin molecules stack into a supramolecular layer through π−π interactions while π−π interactions between berberine cations also result in a similar layer. In 2, berberine cation simultaneously interacts with two different emodin through π−π interactions to give rise to a 1D chainlike array. Cocrystals 1 and 2 present a low moisture adsorption curve in the range of 0−95% relative humidity values at 25 °C. The sustained release of berberine chloride in pure water could be achieved after forming cocrystals 1 and 2. Emodin in the form of cocrystals 1 and 2 has a higher Cmax and AUC compared with pure emodin.

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INTRODUCTION During the past 15 years, many kinds of pharmaceutical cocrystals with improved physicochemical properties have been obtained by the use of supramolecular synthons between active pharmaceutical ingredients (APIs) and organic formers.1−4 Even more than two kinds of properties of one API could be simultaneously improved by cocrystallization.5 Moreover, a new effective approach for capturing elusive cocrystals has also been developed.6,7 Drug-drug cocrystals based on two kinds of APIs have attracted new attention in recent years.8−13 Drug-drug cocrystals have the advantage over traditional pharmaceutical cocrystals since two APIs could be combined together into a single medicine to cooperatively treat a specific disease while improving the performances of APIs.14 The rational design of drug-drug cocrystals depends mainly on whether reliable supramolecular synthons could occur between two specific APIs with different chemical structures. Emodin (EM) (Scheme 1) is a natural anthraquinone derived from Chinese herbs such as DaHuang (Rheum palmatum L.), which was found to have various therapeutic effects such as antibacterial,15 anticancer,16 antidiabetic,17 vasorelaxant effects,18 and immune-suppressive activities.19 Berberine is a kind of natural alkaloid extracted from HuangLian (Rhizoma coptidis) which has been used as an effective antidiarrheal drug for thousands of years in Traditional Chinese Medicine.20 Berberine could also be a promising drug in the treatment of diabetes,21 hyperlipidemia,22 and cancer.23 Berberine is commonly marketed © XXXX American Chemical Society

Scheme 1. Molecular Structures of Emodin and Berberine Chloride

as berberine chloride (BER), and poor oral bioavailability has limited its applications.24 Until now, pharmaceutical cocrystallization based on berberine chloride has not systematically been exploited. The reason might be that there is no reliable synthon resulting from the parent structure of berberine. In fact, chloride anion as an effective hydrogen-bonded acceptor has been ignored for cocrystal design of berberine chloride. More than 500 hits could be returned by a search of organic crystals with hydrogen-bonding interactions between chloride anions and phenolic hydroxyl groups in the Cambridge Structural Database (May 2018 version). In the crystal structure of emodin (CSD code: ETANIY01),25 4- and 5-hydroxyl groups of emodin are involved in intramolecular hydrogen-bonding interactions with the 10carbonyl group. Two emodin molecules interact through Received: August 20, 2018 Revised: November 10, 2018

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DOI: 10.1021/acs.cgd.8b01257 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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metrically. H atoms bonded to O were located by difference maps and the displacement factors were refined freely. In 2, H atom bonded to O of ethanol was refined with a displacement factor of 1.2 times Ueq (O). Crystal data are listed in Table 1, and hydrogen-bonding parameters are listed in Table 2.

hydrogen-bonding interactions between 2-hydroxyl and 9carbonyl groups (Scheme 2). For emodin monohydrate (CSD Scheme 2. Hydrogen-Bonding Interactions (Dashed Lines) in Emodin (Left) and Emodin Monohydrate (Right).

Table 1. Crystal Data and Structural Refinement for 1 and 2 formula molecular weight crystal size, mm crystal system space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z Dc, g/cm3 F000 2θmax, deg reflns collected unique reflns Rint parameters final GooF R1 (I > 2σ(I)) wR (all data)

code: TEVVOG),26 the water molecule interferes with the hydrogen-bonding interactions between emodin and forms a new supramolecular synthon. On the basis of the abovementioned information, it is supposed that chloride anion instead of water could form O-H···Cl− hydrogen-bonding interactions with the 2-hydroxyl group of emodin. Since both emodin and berberine chloride are active ingredients of San-Huang Tablet, a widely used herbal preparation with antioxidant activity,27,28 it is a worthy work to investigate drug-drug cocrystals based on emodin and berberine chloride. In this paper, cocrystallization between emodin and berberine chloride was carried out. As a result, two cocrystals, EM-BER (1) and 2EM-BER-EtOH (2), have been successfully prepared. Crystal structure analysis showed that OH···Cl− hydrogen-bonding interactions dominate intermolecular interactions between emodin and berberine chloride. The bulk powder of the two cocrystals was characterized by powder X-ray powder diffractions (PXRD), thermogravimetry (TG), and differential scanning calorimetry (DSC). The hygroscopicity of cocrystals 1 and 2 was investigated. The solubility, dissolution behavior, and oral bioavailability of cocrystals 1 and 2 were also studied.

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1

2

C35H28ClNO9 642.03 0.10 × 0.10 × 0.05 triclinic P1̅ 7.3203(3) 11.1115(4) 18.0845(6) 97.381(3) 93.956(3) 103.926(3) 1408.27(9) 2 1.514 668 73.61 9680 5485 0.0313 428 1.062 0.0393 0.1111

C52H44ClNO15 958.33 0.15 × 0.10 × 0.10 monoclinic P2(1)/c 7.9754(2) 31.2003(7) 17.8186(4) 90 101.741(2) 90 4341.12(18) 4 1.466 2000 73.89 18325 8545 0.0341 649 1.021 0.0568 0.1531

PXRD and Thermal Analysis. PXRD data were collected on a Rigaku MiniFlex 600 diffractometer, equipped with a Scintillation Counter detector, with Cu Kα radiation (40 kV and 15 mA). Each pattern was collected with a step size of 0.02° in the 2θ range of 5− 50°. DSC and TG were determined with a heating rate of 10 °C/min under a N2 gas atmosphere. DVS. DVS was measured via an SMS (Surface Measurement Systems) DVS Intrinsic at 25 °C. The relative humidity at 25 °C was calibrated against the deliquescence point of LiCl, Mg(NO3)2, and KCl. Then nitrogen flow rate was 200 mL/min. The sample equilibrated at each step with the equilibration criteria of either dm/dt ≤ 0.002% or maximum equilibration time of 3 h. Once one of the criteria was met, the relative humidity (RH) was changed to the next target value, following the 0-95-0% sorption and desorption cycle with a step size of 10% RH. In Vitro Dissolution Study. The starting material (emodin, berberine chloride dihydrate, cocrystal 1 and cocrystal 2) was sieved through a 120 μm screen to produce powders with a similar range in particle size. The tests were carried out in a ZRS-8G dissolution apparatus (Tianjin, China) using the paddle apparatus II (USP 35). The rotational speed of the paddle was set at 100 rpm, and the temperature of the dissolution media was maintained at 37 ± 0.5 °C. The samples equivalent to 10 mg of emodin or berberine chloride dihydrate were taken into the dissolution vessel containing 100 mL of water. The withdrawn slurry was filtered using 0.45 μm cellulose filters for the HPLC assay (n = 3). Solubility. Excess amount of each starting material was added to deionized water. The suspensions were stirred at 37 °C for 48 h to reach equilibrium. Aliquots of solutions were withdrawn and centrifuged (13 000 rpm, 10 min), followed by filtration through 0.45 μm cellulose filters. The filtrates were then diluted with deionized water to an appropriate concentration for the HPLC assay (n = 3).

EXPERIMENTAL SECTION

Emodin and berberine chloride hydrate were purchased as biological reagent (HPLC ≥ 97%) and used without further purification. Differential scanning calorimetry (DSC) was performed on a NETZSCH DSC 214. Thermogravimetry (TG) was measured on a NETZSCH TG 209 F3 Tarsus. Powder X-ray powder diffractions (PXRD) were performed on a RigakuMiniFlex 600 diffractometer. Dynamic vapor sorption analysis (DVS) was measured via an SMS (Surface Measurement Systems) DVS Intrinsic. Synthesis of EM-BER (1). A mixture of berberine chloride dihydrate (407 mg, 1 mmol) and emodin (270 mg, 1 mmol) was suspended in 10 mL of acetonitrile under stirring for 48 h. The resulting powder was filtered and further washed with cool acetonitrile. The dried products were collected for further analysis. Yellow single crystals could be obtained by recrystallizing the powder in acetonitrile. Synthesis of 2EM-BER-EtOH (2). A mixture of berberine chloride dihydrate (407 mg, 1 mmol) and emodin (540 mg, 2mmol) was suspended in 20 mL of ethanol under stirring for 48 h. The resulting powder was filtered and dried under air conditions. The products were collected for further analysis. Yellow single crystals could be obtained by recrystallizing the powder in ethanol. X-ray Structure Determination. The data were collected on a SuperNova CCD diffractometer at 100 K, using Cu-Kα radiation (λ = 1.54178 Å). The empirical absorption corrections were applied by using the CrysAlisPro program.29 The structures were solved by direct methods and refined on F2 by full-matrix least-squares methods using the SHELX program package.30,31 Non-hydrogen atoms were refined anisotropically, and organic hydrogen atoms were generated geoB

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Table 2. Hydrogen-Bonding Parameters in 1 and 2 D−H···A 1 O5−H5···Cl1 O4−H4···O2 O3−H3A···O2 C19−H19···O1 C24−H24···O7 2 O5−H5A···Cl1 O15−H15···Cl1 O10−H10···O15 O3−H3A···O2 O4−H4···O2 O9−H9···O7 O8−H8A···O7

D−H (Å)

H···A (Å)

D···A (Å)

D−H···A (deg)

symmetry

0.93(3) 0.91(3) 0.93(3) 0.95 0.95

2.07(3) 1.72(3) 1.74(3) 2.28 2.48

2.9790(13) 2.5593(15) 2.5810(15) 3.127(2) 3.3193(18)

166.2 152.2 149.3 147.4 147.6

1 − x, −y, 1 − z

0.89(4) 0.94 0.880(10) 0.880(10) 0.94(3) 0.94(4) 0.85(4)

2.13(4) 2.08 1.730(11) 1.688(12) 1.67(3) 1.74(4) 1.78(4)

3.016(2) 2.988(2) 2.608(3) 2.561(3) 2.559(3) 2.579(3) 2.562(3)

173.4 164.4 175.4 172.4 155.3 147.3 152.3

HPLC. The concentrations of emodin and berberine chloride in the collected filtrate were determined by an HPLC system equipped with a Diamonsil C18(2) column (4.6 × 250 mm, 5 μm). The mobile phase consisted of acetonitrile and 0.03 mol/L potassium dihydrogen phosphate (60/40, v/v). The flow rate was set at 1 mL/min, and the inject volume was 10 μL. The absorbance was measured at a wavelength of 245 nm, and the column temperature was set at 30 °C. In Vivo Pharmacokinetic Study. To evaluate the effects of cocrystallization for pharmacokinetics of emodin and berberine chloride, the bulk samples of emodin, berberine chloride, cocrystals 1 and 2 were utilized to conduct the pharmacokinetics experiments. Healthy male Sprague-Dawley (SD) rats (200 ± 10 g) were obtained from the Laboratory Animal Center of Fujian Medical University. Prior to the experiments, the rats were housed in a temperature and humidity controlled room (20−25 °C, 55 ± 5% air humidity) with 12 h light/dark cycles and free access to water and standard rat chow. All animal experiments were carried out in accordance with the local institutional guidelines for animal care of Fujian Medical University. The rats were fasted overnight with free access to water prior to the start of the experiment. Thirty-six rats were randomly divided into six groups (six rats in each group). Emodin or cocrystal 1, cocrystal 2 at a dose of 40 mg/kg emodin was given. Berberine chloride dihydrate or cocrystal 1, cocrystal 2 at a dose of 100 mg/kg berberine chloride dihydrate was given. The samples were dispersed in the appropriate amount of deionized water, and then administered by gavage. The blood samples were collected from the eye socket vein into a heparinized tube at predetermined time points. The plasma samples were separated by centrifugation (4000 rpm, 10 min) and stored at −80 °C until analysis. The determination of emodin and berberine chloride were achieved using an Agilent 1260 LC-6410 MS system, which was composed of an LC system and a triple quadrupole mass spectrometry equipped with an electrospray ionization (ESI) source. Chromatographic separation of berberine chloride was achieved on an Agilent column (XB-C18, 2.1 × 150 mm,3.5 μm) with a guard column (XB-C18, 3 μm, Agilent, USA) through gradient elution at 30 °C. Mobile phase A was water (0.025% formic acid, 1.25 mM ammonium formate), and mobile phase B was methanol. The gradient elution was performed at 0−3 min 30% B, 3.1 min 90% B, 4.8 min 90% B, 4.9 min 30% B. The stop time was 10.0 min.The flow rate was 0.3 mL/min, and the injection volume was 5 μL. MS was operated in the positive ion mode, and quantification was obtained in a multiple reaction monitoring (MRM) mode. The standard solutions of berberine chloride were used to optimize MS operating conditions. The optimized MS parameters were as follows: gas temperature: 350 °C; gas flow: 10 L/min; nebulizer gas pressure: 30 psi; capillary voltage: 3500 V. MRM 336.2→320.2; collision energy: 33 eV; fragmentor voltage: 130 V. Plasma samples were extracted using a protein precipitation (PPT) method. 100 μL of acetonitrile was added into 50 μL of rat plasma. The mixture was vortexed for 3 min and centrifuged at 4 °C (14 000 rpm, 10 min), and the supernatant was

transferred to another centrifuge tube. And the supernatant was again centrifuged at 4 °C (14 000 rpm, 10 min), and the supernatant was analyzed via LC-MS. Chromatographic separation of emodin was achieved on an Ultimate XB-C18 (2.1 × 50 mm,3.5 μm). The mobile phase containing water (A) and methanol (B) ran 0.2 mL/min. The gradient elution was performed at 0−0.5 min 40% B, 0.8 min 95% B, 3.0 min 95% B, 3.1 min 40% B. The stop time was 6.4 min. The injection volume was 3 μL, and the column temperature was maintained at 30 °C. The mass spectrometric analysis was operated in negative ion detection mode. Detection and quantification were carried out in the multiple reaction monitoring (MRM) mode. The ion transitions for emodin and daidzein were 269.1→225.1 and 253.1→222.9, respectively. The fragmentor voltage was 98 V for emodin and 95 V for daidzein, while the collision energy for emodin and daidzein was 35 and 30 eV, respectively. The MS parameters were optimized as follows: the source temperature was 350 °C and gas flow was 10 L/min. The nebulizer pressure and capillary voltage were 30 psi and 3500 V. 100 μL of rat plasma was mixed with 10 μL of daidzein (internal standard, 1 μg/mL in methanol). After vortexing for 2 min, the plasma samples were extracted with 500 μL of ethyl acetate by vortex mixing for 10 min and then centrifuged at 10 000 rpm for 10 min. The supernatant was evaporated to dryness, and the residue was dissolved in a methanol−water (50:50, v/v) solvent mixture. The solution was introduced into the LC-MS system. Pharmacokinetic parameters, such as the elimination half-time (T1/2), maximum plasma concentration (Cmax), time to reach the maximum concentration (Tmax), mean residence time (MRT0‑t), and area under the concentration−time curve (AUC0‑t), were estimated by noncompartmental modeling using DAS 3.0 (Mathematical Pharmacology Professional Committee of China, Shanghai, China). The results were expressed as the mean ± standard deviation (SD). Student t test was used to analyze the differences between two groups, and p < 0.05 and p < 0.01 were considered statistically significant.

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RESULTS AND DISCUSSION Preparation of Cocrystals 1 and 2. Pure cocrystal 1 could be reliably obtained by stirring emodin and berberine chloride dihydrate at a molar ratio of 1:1 in acetonitrile. The PXRD patterns are in accordance with simulated patterns from the single crystal structure (Figure 1). Pure cocrystal 2 could be obtained by stirring emodin and berberine chloride dihydrate at a molar ratio of 2:1 in ethanol. However, cocrystal 1 could be still isolated when cocrystallization was carried out at a molar ratio of 2:1 in acetonitrile. Likewise, cocrystal 2 could result from cocrystallization in ethanol at a molar ratio of 1:1. This indicates that acetonitrile benefits the formation of cocrystal 1 and ethanol could promote the formation of

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DOI: 10.1021/acs.cgd.8b01257 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 4. Supramolecular layer of emodin resulting from π−π interactions in 1.

Figure 1. PXRD patterns of cocrystals 1 and 2.

Figure 5. Supramolecular layer of berberine resulting from π−π and C-H···O interactions in 1.

cocrystal 2. The pure cocrystal 1 could also be obtained by stirring emodin and berberine chloride at a molar ratio of 1:1 in methanol and acetone. Thermal Analysis and Stability. Cocrystals 1 and 2 exhibit quite different thermal properties with berberine chloride dihydrate and emodin (Figure 2). The DSC curve of berberine chloride dihydrate shows endothermic peaks at 89.5, 127.0, and 201.9 °C, which could be attributed to dehydration, crystal phase transition, and the fusion of the crystal, respectively (TG curve in Figure S1). The DSC curve of emodin shows a sharp single melting endotherm with a peak at 263.4 °C. Cocrystal 1 exhibits a single sharp endothermic peak at 235.8 °C, while cocrystal 2 shows a similar endothermic melting peak at 234.4 °C. The endothermic peak at 139.1 °C for cocrystal 2 corresponds to the desolvation process (Figure S1). Thermal stability of cocrystal 1 and cocrystal 2 was investigated. There was no change in PXRD pattern for cocrystal 1 after heating for 30 days at 60 °C (Figure S2). Slight changes could be observed for cocrystal 2 after heating for 30 days at 60 °C (Figure S3), which indicates cocrystal 1 has better thermal stability than cocrystal 2. Crystal Structure of Cocrystal 1. Cocrystal 1 contains one berberine cation, one chloride, and one emodin molecule in the asymmetric unit (Figure 3). 4- and 5-hydroxyl groups of emodin are involved in intramolecular hydrogen-bonding interactions with the 10-carbonyl group [O4···O2 = 2.5593(15) Å, O3···O2 = 2.5810(15) Å]. There exist obvious hydrogen-bonding interactions between the 2-hydroxyl group of emodin and chloride anion [O5···Cl1 = 2.9790(13) Å]. Berberine cation interacts with emodin through weak C-H···O interactions [C19···O1 = 3.127(2) Å]. Emodin contains three coplanar phenyl rings in its molecular structure, and there exist various π−π interactions between emodin molecules. Ring A of emodin is involved in π−π interactions with ring B of an adjacent emodin (1 − x, 1 − y,

Figure 2. DSC curves of emodin, berberine chloride dihydrate, cocrystals 1 and 2.

Figure 3. ORTEP plot of cocrystal 1 with 50% probability level. Dashed lines represent hydrogen-bonding interactions.

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Figure 6. Packing structure of 1.

Figure 7. ORTEP plot of cocrystal 2 with 50% probability level.

−z) in the self-complementary way with a distance of 3.532 Å (centroid···centroid). The distance between rings A and C is 3.627 Å, and two ring C stack with a distance of 3.527 Å (centroid···centroid). The 7-methyl group of emodin is also involved in C-H···π interactions with ring B (1 − x, −y, −z) in the self-complementary way with a distance of 3.544 Å (C··· centroid). Emodin stacks into a layer-like supramolecular structure through the various π−π interactions (Figure 4). There also exist various π−π interactions between rings A and B of berberine cations. Berberine cation simultaneously interacts with two adjacent berberine through self-complementary π−π interactions between rings A and B. The distance of centroid···centroid is 3.758 Å and 3.856 Å, respectively. A supramolecular layer of berberine cations results from the π−π interactions as well as C-H···O interactions [C24···O7 = 3.3193(18) Å] (Figure 5). As a result, various weak intermolecular interactions give rise to a packing structure consisting of alternate emodin and berberine layers (Figure 6). Crystal Structure of Cocrystal 2. Cocrystal 2 contains one berberine cation, one chloride anion, two emodin molecules, and one ethanol molecule in the asymmetric unit (Figure 7). 4- and 5-hydroxyl groups of both emodin are involved in intramolecular hydrogen-bonding interactions with 10-carbonyl groups. The 2-hydroxyl group of one emodin is hydrogen-bonded to chloride anion [O5···Cl1 = 3.016(2) Å]. The 2-hydroxyl group of the other emodin is involved in

hydrogen-bonding interactions with an ethanol molecule [O10···O15 = 2.608(3) Å]. There also exist hydrogen-bonding interactions between ethanol and chloride anion [O15···Cl1 = 2.988(2) Å]. Two emodin molecules are parallel to each other through π−π interactions. The distance between ring A of two emodin (centroid···centroid) is 3.684 Å. The distances between ring B and between ring C are 3.692 Å and 3.624 Å, respectively.The ring B of berberine cation is also involved in π−π interactions with ring A from a different emodin with a distance of 3.772 Å and 3.565 Å (centroid···centroid), respectively (Figure 8). The various π−π interactions dominate the packing structure of cocrystal 2 (Figure 9). The intermolecular interactions in cocrystals 1 and 2 are very similar. The expected O-H···Cl− interactions are reliable, and various π−π interactions dominate the packing structures of 1 and 2. In 1, emodin molecules stack into a supramolecular layer through π−π interactions while π−π interactions between berberine cations also result in a similar layer. In 2, the extra emodin molecule resulted in distinct π−π interactions with emodin and berberine cation to give rise to a 1D chainlike array. Hygroscopicity. It has been reported that berberine chloride is hygroscopic and readily transforms between anhydrate, dihydrate, and tetrahydrate with changing relative humidity.32 Emodin, cocrystals 1 and 2 present a low moisture E

DOI: 10.1021/acs.cgd.8b01257 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 11. Dissolution profiles of berberine chloride in cocrystals 1 and 2.

Figure 8. π−π interactions in 2.

Figure 12. Mean plasma concentrations of emodin versus time profiles of emodin, cocrystals 1 and 2.

and 0.9% of water at 95% RH, respectively. This indicated that both of the two cocrystals are nonhygroscopic. In addition, the desorption curve is close to the absorption curve for both cocrystals, indicating the absorption and desorption processes of the two cocrystals are reversible.33 The low moisture uptake may only correspond to surface absorption. Solubility and Dissolution. The solubility and dissolution rate of emodin and berberine chloride in pure water were evaluated. After forming cocrystals 1 and 2, the solubility of emodin could be slightly improved (Figure S4). However, the solubility of berberine chloride decreases slightly after forming cocrystals 1 and 2. Interestingly, sustained release of berberine chloride in pure water could be achieved after forming cocrystals 1 and 2. The release of berberine chloride could maintain for 6 h (Figure 11). Cocrystal 1 exhibits better sustained release effects than cocrystal 2. In Vivo Pharmacokinetic Study. To investigate the effect of cocrystallization on the absorption of emodin and berberine chloride, in vivo bioavailability studies were performed on pure emodin/berberine chloride and emodin/berberine chloride in the form of cocrystals 1 and 2. The mean plasma concentrations of emodin versus time profiles are shown in Figure 12. The pharmacokinetic parameters are listed in Table 3. It shows that emodin in the form of cocrystals 1 and 2 has a higher Cmax and AUC compared with pure emodin. The AUC0‑36h results show that the relative bioavailability of cocrystal 1 (calculated as AUCtot of the cocrystal divided by AUCtot of emodin) is about 1.7 times that of pure emodin. The relative bioavailability of cocrystal 2 is about 1.2 times that of pure emodin. It can be found that cocrystal 1 has a modest

Figure 9. Packing structure of 2.

Figure 10. DVS isotherm plots for emodin, cocrystals 1 and 2 at 25 °C.

adsorption curve in the range of 0−95% relative humidity values at 25 °C (Figure 10). Cocrystals 1 and 2 uptake 1.3% F

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Table 3. Pharmacokinetics Parameters of Emodin, Cocrystals 1 and 2 after the Oral Administration to Rats at the Dose of 40 mg/kg Emodinb parameters

emodin

cocrystal 1

cocrystal 2

Cmax (μg/L) MRT0‑36h (h) AUC0‑36h (h·μg/L) Tmax (h) T1/2 (h) Frel (%)

139.29 ± 2.31 8.72 ± 1.91 1036.42 ± 10.19 0.17 ± 0.09 5.82 ± 1.57

163.21 ± 3.21 9.32 ± 2.12 1761.51 ± 4.94a 6 ± 1.12a 5.42 ± 2.11 169.96

170.45 ± 2.32 11.86 ± 1.97 1291.43 ± 9.44 0.49 ± 0.13 5.28 ± 1.67 124.60

p < 0.05 vs emodin. bData are expressed as the mean ± SD (n = 6).

a

Notes

improvement of Cmax and AUC compared with pure emodin. In contrast, there is no obvious improvement of bioavailability of berberine chloride after forming cocrystals 1 and 2 (Figure S6, Table S1). This could be related with the decreased solubility of berberine chloride after forming cocrystals 1 and 2.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to the support from the National Natural Science Foundation of China (21503105), the Natural Science Foundation of Fujian Province (2017J05025 and 2018J01434), and the Project for Outstanding Young Talents of Fujian Provincial Universities (2016).

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CONCLUSIONS Two cocrystals of emodin (EM) with berberine chloride (BER), EM-BER (1) and 2EM-BER-EtOH (2), were prepared and characterized. Crystal structure analysis shows there exist reliable O-H···Cl− hydrogen-bonding interactions between the 2-hydroxyl group of emodin and chloride anion, and various π−π interactions dominate the packing structures of 1 and 2. Cocrystals 1 and 2 present a low moisture adsorption curve in the range of 0−95% relative humidity values at 25 °C. The sustained release of berberine chloride in pure water could be achieved after forming cocrystals 1 and 2. Emodin in the form of cocrystals 1 and 2 has a higher Cmax and AUC compared with pure emodin. Cocrystals 1 and 2 represent a class of novel drug-drug cocrystals based on natural polyphenols and alkaloids. Since many alkaloids are used as the form of hydrochloride, this work could provide a new strategy for designing drug-drug cocrystals based on alkaloids and polyphenols through O-H···Cl− hydrogen-bonding interactions.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.8b01257. The experimental details about TG, PXRD, solubility, and pharmacokinetics parameters (PDF) Accession Codes

CCDC 1862498 and 1862517 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86-591-83761630. E-mail: [email protected]. ORCID

Benyong Lou: 0000-0001-6300-5843 Author Contributions §

Y.D. and Y.Z. contributed equally to this work. G

DOI: 10.1021/acs.cgd.8b01257 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

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DOI: 10.1021/acs.cgd.8b01257 Cryst. Growth Des. XXXX, XXX, XXX−XXX