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Research ArticleArticle

Nimesulide and 4′-Hydroxynimesulide as Bile Acid Transporters Inhibitors Are Contributory Factors for Drug-Induced Cholestasis

Lei Zhou, Xiaoyan Pang, Jingfang Jiang, Dafang Zhong and Xiaoyan Chen
Drug Metabolism and Disposition May 2017, 45 (5) 441-448; DOI: https://doi.org/10.1124/dmd.116.074104

Abstract

Nimesulide (NIM) is a classic nonsteroidal anti-inflammatory drug. However, some patients treated with NIM experienced cholestatic liver injury. For this reason, we investigated the potential mechanism underlying NIM-induced cholestasis by using in vivo and in vitro models. Oral administration of 100 mg/kg/day NIM to Wistar rats for 5 days increased the levels of plasma total bile acids, alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase by 1.49-, 1.31-, 1.60-, and 1.29-fold, respectively. In sandwich-cultured rat hepatocytes, NIM and 4′-hydroxynimesulide (M1) reduced the biliary excretion index of d8-taurocholic acid (d8-TCA) and 5 (and 6)-carboxy-2ʹ,7ʹ-dichlorofluorescein in a concentration-dependent manner, indicating the inhibition of the efflux transporters bile salt export pump and multidrug resistance–associated protein 2, respectively. In suspended rat hepatocytes, NIM and M1 inhibited the uptake transporters of d8-TCA for Na+-taurocholate cotransporting polypeptide at IC50 values of 21.3 and 25.0 μM, respectively, and for organic anion-transporting proteins at IC50 values of 45.6 and 39.4 μM, respectively. By contrast, nitro-reduced NIM and the further acetylated metabolite did not inhibit or only marginally inhibited these transporters at the maximum soluble concentrations. Inhibitory effects of NIM and M1 on human bile acid transporters were also confirmed using sandwich-cultured human hepatocytes. These data suggest that the inhibition of bile acid transporters by NIM and M1 is one of the biologic mechanisms of NIM-induced cholestasis.

Introduction

Nimesulide (NIM) is a classic nonsteroidal anti-inflammatory drug that selectively inhibits cyclooxygenase-2. It has been marketed in more than 50 countries since 1985. However, severe liver injury has been reported in some patients who received NIM treatment. Thus, the use of NIM was restricted, and NIM was even withdrawn from the market in some countries. Clinically, NIM-induced liver injury is mainly characterized by the following two patterns: hepatocellular necrosis and cholestasis (Romero-Gómez et al., 1999; Stadlmann et al., 2002). Metabolic activation may be associated with the hepatotoxicity of NIM (Li et al., 2009). Studies by our group have demonstrated that oxidative and reductive activation of NIM do not cause the toxicity in primary human and rat hepatocytes (Zhou et al., 2015). The mitochondrial toxicity of the parent drug may play a critical role in NIM-induced rat hepatocellular toxicity (Mingatto et al., 2002). Until now, the mechanism of NIM-induced cholestasis remains unclear.

Inhibition of bile acid transporters has been implicated in drug-induced cholestasis (Stieger et al., 2000; Kostrubsky et al., 2003; Dawson et al., 2012; Li et al., 2015; Slizgi et al., 2016). The major transport proteins responsible for the basolateral uptake of bile acids are Na+-taurocholate cotransporting polypeptide (NTCP) and organic anion- transporting proteins (OATPs). After entering the hepatocytes, bile acids are mainly excreted into canaliculus via the bile salt export pump (BSEP) and multidrug resistance–associated protein (MRP) 2 on the canalicular membrane (Alrefai and Gill, 2007; Halilbasic et al., 2013). A previous study (Saab et al., 2013) demonstrated that 450 μM NIM inhibited the efflux of 5 (and 6)-carboxy-2ʹ,7ʹ-dichlorofluorescein (CDF) in HepG2 cells; therefore, it was concluded that NIM inhibited MRP2. However, this conclusion is apparently insufficiently rigorous. CDF is a substrate for both MRP2 and basolateral efflux transporter MRP3 (Chandra et al., 2005), and reduced CDF efflux is possibly caused by the inhibition of MRP2, MRP3, or both. Moreover, the effects of NIM on other bile acid transporters remain unknown.

NIM undergoes extensive metabolism in humans (Gandini et al., 1991; Carini et al., 1998; Macpherson et al., 2013). The principal metabolic pathways include phenoxy ring hydroxylation to generate 4ʹ-hydroxynimesulide (M1), reduction of the nitro group [nitro-reduced nimesulide (M2)], and subsequent acetylation [acetylated metabolite of nitro-reduced nimesulide (M4)] (Fig. 1). M1 is the major circulating metabolite, and its area under the plasma concentration-time curve is about 67% that of the parent drug. NIM is excreted by the renal route, mainly as M1 and its glucuronide (∼18%), M2, M4, and their derivative (∼20%). The effects of these metabolites on bile acid transporters also remain unclear.

Fig. 1.
Fig. 1.

Simplified metabolic pathways of NIM.

In the present study, the cholestatic effect of NIM in rats was elucidated, and the effects of NIM and its main metabolites on bile acid transporters were studied using sandwich-cultured human and rat hepatocytes and isolated suspended rat hepatocytes. Our results revealed a potential mechanism of NIM-induced cholestasis.

Materials and Methods

Chemicals and Reagents.

All reagents used in cell culture were supplied by Invitrogen (Carlsbad, CA) unless otherwise stated. d5-Taurocholic acid (TCA) and d8-TCA were purchased from Martrex, Inc. (Minnetonka, MN). Cholic acid (CA), deoxycholic acid (DCA), chenodeoxycholic acid (CDCA), ursodeoxycholic acid (UDCA), lithocholic acid (LCA), glycocholic acid (GCA), glycodeoxycholic acid (GDCA), glycochenodeoxycholic acid (GCDCA), glycoursodeoxycholic acid (GUDCA), taurochenodeoxycholic acid (TCDCA), and TCA were purchased from Toronto Research Chemicals, Inc. (North York, ON, Canada). M1, M2, and M4 were synthesized according to reported methods (Küçükgüzel SG et al., 2005; Li et al., 2009); mass spectrometry and 1H NMR analyses were applied to confirm these metabolites, which were >98% pure. The assay kits for total bile acid (TBA), alkaline phosphatase (ALP), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were purchased from Nanjing Jiancheng Bioengineering Institute (Jiangsu, People’s Republic of China). The BCA protein assay kit was purchased from Beyotime (Jiangsu, People’s Republic of China). All other solvents and reagents were obtained from Sigma-Aldrich (St. Louis, MO).

Animal Experiments.

All procedures in animal studies were performed in accordance with the Guide for the Care and Use of Laboratory Animals of Shanghai Institute of Materia Medica, Chinese Academy of Sciences. Male Wistar rats weighing 200–250 g were randomized into two groups (n = 6/group). One group of rats received orally 100 mg/kg/day NIM formulated in 0.5% sodium carboxymethyl cellulose (CMC-Na) for 5 successive days, and the other group of rats received orally the corresponding vehicle control. At 24 hours after the last dose, the animals were anesthetized and sacrificed through exsanguination. Their livers were collected and frozen at −80°C. Plasma samples were obtained by centrifugation of blood samples at 11,000 rpm for 5 minutes and then were frozen at −80°C until further analysis. Plasma ALP, ALT, and AST levels were determined using the corresponding assay kits according to the manufacturer protocol. For the bile flow studies, two groups of rats (n = 4/group) were treated with the same dosage regimen mentioned above. At 24 hours after the last dose, the animals were anesthetized and placed on their backs under a heat lamp to maintain their body temperature at 37°C. The bile duct was subsequently cannulated with a polyethylene tube. After an equilibration period of 30 minutes, bile was collected every 30 minutes for 2.5 hours. After the last sample collection, the rats were sacrificed and their livers were collected. The TBA levels in rat plasma and bile were determined using a TBA assay kit according to the manufacturer protocol. The concentrations of 11 bile acids in rat plasma and liver were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as described by Li et al. (2015).

Hepatocytes Isolation and Culture.

Rat hepatocytes were isolated from male Wistar rats using a collagenase perfusion as previously described (Zhou et al., 2015). Fresh rat hepatocytes were seeded at a density of 6.0 × 105 cells/ml in 48-well plates precoated with rat tail collagen and then cultured in Williams’ E medium supplemented with 0.1 μM dexamathasone, 5% fetal bovine serum, 100 U penicillin, 100 μg/ml streptomycin, 2 mM glutamine, and 1% Insulin-Transferrin-Selenium (ITS). After incubation for 4 hours at 37°C in a humidified incubator containing 95% O2/5%CO2, a serum-free Williams’ E medium containing 0.1 μM dexamathasone, 100 U penicillin, 100 μg/ml streptomycin, 2 mM glutamine, and 1% ITS was used to replace the plating medium, and the hepatocytes were overlaid with 0.25 mg/ml ice-cold Matrigel (BD Biosciences, San Jose, CA) to form a sandwich configuration (McRae et al., 2006; Li et al., 2015). The serum-free Williams’ E medium was replaced every 24 hours until the experiments were conducted. Rat hepatocytes cultured for 4 hours could be directly used for the transporter-mediated uptake assays.

Cryopreserved primary human hepatocytes (lot #393A; Caucasian female; 29 years of age) were obtained from BD Gentest (Woburn, MA) and were treated in a fashion similar to that of rat hepatocytes except that human hepatocytes were seeded at a density of 7.0 × 105 cells/ml in 24-well plates precoated with rat tail collagen.

Accumulation Studies in Sandwich-Cultured Hepatocytes.

Accumulation studies were conducted on day 4 of culture for rat hepatocytes and on day 5 for human hepatocytes. Hepatocytes were rinsed three times with either standard HBSS or Ca2+-free HBSS and then equilibrated with the same buffer in the presence of test compounds (0–400 μM NIM, M1, or M2; 0–200 μM M4; 10 μM cyclosporine A (CyA); and 20 μM MK-571) for 10 minutes at 37°C. The highest concentrations were set as the limit of solubility for each analyte. Incubation in standard HBSS maintains the integrity of tight junctions, whereas incubation in Ca2+-free HBSS disrupts tight junctions, leading to the release of bile acid from canaliculi. After the initial incubation, the hepatocytes were incubated with standard HBSS containing probe substrates [1 μM d8-TCA and 2 μM 5 (and 6)-CDF diacetate (CDFDA)] and test compounds for another 10 minutes. Subsequently, the transport was quenched by removing the buffer and rinsing the cells three times with ice-cold standard HBSS. CDF accumulation in bile canaliculi was visualized using a fluorescence microscope (Olympus, Tokyo, Japan). The hepatocytes were subsequently lysed with 200 μl of 0.1% Triton X-100 (v/v) in deionized water and then vortexed gently for 30 minutes at room temperature prior to CDF analysis at 488 nm (excitation) and 525 nm (emission) by using a microplate fluorescence reader (Molecular Devices, Sunnyvale, CA). The hepatocytes treated with d8-TCA were lysed with 200 μl of deionized water followed by three freeze-thaw cycles and then stored at −80°C until LC-MS/MS analysis. The amount of substrates accumulated in each well was corrected with protein concentration as measured by a BCA protein assay kit.

Efflux Studies in Sandwich-Cultured Hepatocytes.

According to previously reported methods (Guo et al., 2014), the rat hepatocytes were preincubated with standard HBSS for 10 minutes at 37°C and then incubated with 2 μM CDFDA or 1 μM d8-TCA in standard HBSS for another 10 minutes. At the end of incubation, the hepatocytes were quickly washed with ice-cold standard HBSS three times to terminate the accumulation process. The efflux was initiated by incubating the cells with warm standard HBSS containing inhibitors (0–200 μM NIM or M1 and 20 μM MK-571). After 20 minutes of incubation at 37°C, the efflux medium was collected for analysis.

d8-TCA Uptake Inhibition Assay.

To investigate the effects of NIM and its metabolites on NTCP- and OATP-mediated uptake of d8-TCA by rat hepatocytes, the Na+ in standard HBSS was replaced with choline chloride. The hepatocytes were rinsed three times with standard HBSS or with choline chloride buffer and then pretreated in the same buffer with test compounds (0–400 μM NIM, M1, or M2; 0–200 μM M4; and 10 μM CyA) for 10 minutes. The uptake assay was initiated by adding standard HBSS containing 1 μM d8-TCA and test compounds. After 2 minutes of incubation, the cells were quickly rinsed three times with ice-cold standard HBSS and then lysed by adding 200 μl of deionized water.

Sample Pretreatment.

To measure NIM and related metabolites in rat plasma, 25 μl of sample was mixed with 25 μl of internal standard (10 μg/ml glycyrrhetinic acid for the determination of NIM, M1, and M4; and 20 ng/ml propafenone for determination of M2) and 100 μl of acetonitrile. After vortexing and centrifugation at 11,000g for 5 minutes, the supernatant was injected into the LC-MS/MS system for analysis. The rat livers (200 mg) were homogenized in 1 ml of ethanol/water (1:1, v/v) followed by ultrasonication for 20 minutes. The resulting liver homogenate was treated in a manner similar to that described for plasma.

For the samples obtained from transporter assays, 50 μl of sample was added into a mixture containing 25 μl of internal standard (20.0 ng/ml d5-TCA) and 100 μl of acetonitrile followed by vortexing and centrifugation. The resultant supernatant was analyzed by LC-MS/MS.

LC-MS/MS Analysis.

The LC system consisted of a LC-30AD pump equipped with a SIL-30AC Autosampler (Shimadzu, Kyoto, Japan). An Eclipse Plus C18 (100 × 2.1 mm i.d., 3.5 μm; Agilent Technologies, Santa Clara, CA) column was used to simultaneously determine NIM, M1, and M4. The mobile phase consisted of 5 mM ammonium acetate and acetonitrile (40:60, v/v) at a flow rate of 0.5 ml/min. An Eclipse Plus C18 (100 × 4.6 mm i.d., 3.5 μm; Agilent Technologies) column was used to analyze M2. The mobile phase consisted of a mixture of 5 mM ammonium acetate containing 0.1% formic acid and acetonitrile (40:60, v/v) at a flow rate of 0.6 ml/min. d8-TCA was quantitatively determined according to the method described by Li et al. (2015).

MS detection was performed using an AB Sciex Triple Quad 5500 System (Applied Biosystems, Concord, ON, Canada) equipped with a TurboIonSpray ion source. Multiple reaction monitoring was used to quantify compounds in the positive ion mode (m/z 279.0 → m/z 200.0 for M2; and m/z 341.7 → m/z 115.9 for the internal standard propafenone) or in the negative ion mode (m/z 307.0 → m/z 229.0 for NIM; m/z 323.1 → m/z 245.1 for M1; m/z 319.1 → m/z 239.1 for M4; and m/z 469.2 → m/z 425.3 for the internal standard glycyrrhetinic acid).

Data Analysis.

All mass values were normalized to the protein content (milligrams of protein per well). The accumulation in standard HBSS represents the total mass of uptaken and excreted compound (cell plus bile), whereas the accumulation in Ca2+-free HBSS represents the mass of compound in the hepatocyte (cell only). The biliary excretion index (BEI), in vitro biliary clearance (Clbiliary), and basolateral efflux were calculated according to the following equations (Liu et al., 1999; Guo et al., 2014).

Embedded Image(1)Embedded Image(2)Embedded Image(3)

For rat hepatocyte experiments, all data were compiled from at least three separate rat liver preparations and are presented as the mean ± S.D. Statistical analysis was performed using GraphPad Prism 5.0 software (GraphPad Software, La Jolla, CA). Unpaired, two-tailed Student’s t test was used for between-group comparisons: *P < 0.05, **P < 0.01, and ***P < 0.001 indicated statistical significance.

Results

Cholestatic Effect of NIM in Rats.

To assess the cholestatic effect of NIM, the AST, ALT, ALP, and TBA levels in rat plasma were measured. Relative to those in the control group, the plasma AST, ALT, ALP, and TBA levels in rats that had received NIM increased to 129%, 160%, 131%, and 149%, respectively (Fig. 2, A and B). The individual level of bile acid, including CA, DCA, CDCA, UDCA, LCA, GCA, GDCA, GCDCA, GUDCA, TCA, and TCDCA, in rat plasma and liver was measured by using a LC-MS/MS method. As shown in Table 1, the levels of unconjugated bile acid CA, DCA, CDCA, and UDCA in rat plasma significantly increased in NIM group compared with those in the control group (>2-fold), but the levels of conjugated bile acids did not change. In rat liver, a significant elevation of CA, CDCA, and GCDCA levels was also observed (Table 2).

Fig. 2.
Fig. 2.

Effects of NIM on activities of plasma levels of AST, ALT, and ALP (A), plasma levels of TBA (B), biliary secretion of bile acids (C), and bile flow rate in Wistar rats (D). Data are reported as the mean ± SD (n = 4 or 6). *P < 0.05 and **P < 0.01 versus the control group.

View this table:
TABLE 1

Plasma bile acid levels in rats receiving oral administration of 100 mg/kg/day NIM or 0.5% CMC-Na for 5 days

Blood samples were collected at 24 hours after the last dose. Data are reported as the mean ± S.D. (n = 6).

View this table:
TABLE 2

Liver bile acid levels in rats receiving oral administration of 100 mg/kg/day NIM or 0.5% CMC-Na for 5 days

Liver samples were collected at 24 hours after the last dose. Data are reported as the mean ± S.D. (n = 6).

The biliary secretion of bile acids significantly decreased in the NIM group compared with that in the control group (Fig. 2C). However, no significant change was observed in the bile flow (Fig. 2D).

Metabolism of NIM in Rats.

NIM and its three major metabolites (M1, M2, and M4) were detected in rat plasma and liver tissue at 24 hours after the last dose. The concentrations of NIM, M1, M2, and M4 were quantified by using the LC-MS/MS method, and results are shown in Table 3.

View this table:
TABLE 3

Concentrations of NIM and its metabolites (M1, M2, and M4) in rat plasma and liver tissue at 24 hours after the last dose of NIM

The rats received oral administration of 100 mg/kg/day NIM for 5 days. Data are reported as the mean ± S.D. (n = 6).

Hepatobiliary Disposition of d8-TCA in Sandwich-Cultured Rat Hepatocytes.

The hepatobiliary disposition of d8-TCA is dependent on the uptake transporters NTCP and OATPs and on the efflux transporter BSEP (Lepist et al., 2014; Li et al., 2015; Slizgi et al., 2016). In sandwich-cultured rat hepatocytes, NIM and M1 reduced d8-TCA cellular accumulation and cellular plus biliary accumulation in a concentration-dependent manner (Fig. 3A). The BEI and Clbiliary values of d8-TCA in the control group were 72.5% and 4.99 μl/min/mg protein, respectively (Fig. 3A). NIM (400 μM) reduced the BEI and Clbiliary values to 51.6% and 0.50 μl/min/mg protein, respectively; moreover, M1 (400 μM) reduced the BEI and Clbiliary values to 48.4% and 0.39 μl/min/mg protein, respectively. Similar results were observed for CyA, a potent inhibitor of NTCP, OATPs, and BSEP (Ansede et al., 2010; Li et al., 2015). In addition, a greater extent of reduction was found in Clbiliary than in BEI after NIM and M1 treatments (Fig. 3B). In M2 and M4 treatments, Clbiliary slightly decreased and BEI remained unchanged (Fig. 3B).

Fig. 3.
Fig. 3.

Effects of NIM and its metabolites (M1, M2, and M4) on the accumulation, BEI, and Clbiliary of d8-TCA (1 μM) in sandwich-cultured rat hepatocytes. CyA (10 μM) was used as the positive inhibitor. (A) d8-TCA accumulation was measured in standard buffer (cells plus bile, solid bars) or Ca2+-free buffer (cells only, open bars) for 10 minutes. (B) BEI and Clbiliary of d8-TCA in the presence of potential inhibitors are expressed as percentages of control. Data were compiled from at least three separate rat liver preparations and are reported as the mean ± S.D. *P < 0.05, **P < 0.01, and ***P < 0.001 versus the control group.

Inhibition of Uptake Transporters in Isolated Rat Hepatocytes.

The suspended rat hepatocytes were used to examine the inhibitory effect of compounds on rat NTCP and OATPs. OATP-mediated d8-TCA uptake is independent of Na+, whereas the NTCP-mediated d8-TCA uptake is dependent on Na+ (Marion et al., 2011; Li et al., 2015). Thus, d8-TCA uptake in cells incubated in choline chloride buffer (Na+ free) is considered OATP-mediated uptake; NTCP-mediated uptake is defined as the difference in uptake by cells incubated in standard HBSS (Na+-containing buffer) and choline chloride buffer (Na+-free buffer). As shown in Fig. 4A, d8-TCA uptake in the presence of Na+ was approximately 4.2 times that in the absence of Na+, suggesting that NTCP was the major transporter mediating d8-TCA uptake; this finding was consistent with that of earlier studies (Marion et al., 2011; Li et al., 2015). Similar to CyA, NIM and M1 greatly inhibited d8-TCA uptake both in Na+-containing and Na+-free buffers. However, M2 and M4 did not inhibit d8-TCA uptake in Na+-containing buffer, and they exerted only weak inhibitory effects on d8-TCA uptake in Na+-free buffer. The inhibition potencies of NIM and M1 on rat NTCP and OATPs were characterized in terms of mean IC50 values. NIM inhibited NTCP- and OATP-mediated d8-TCA uptake at IC50 values of 21.3 and 45.6 μM, respectively; by contrast, M1 inhibited NTCP- and OATP-mediated d8-TCA uptake at IC50 values of 25.0 and 39.4 μM, respectively (Fig. 4, B and C).

Fig. 4.
Fig. 4.

(A) Effects of NIM and its metabolites (M1, M2, and M4) on d8-TCA uptake by rat hepatocytes incubated in Na+-containing buffer (open bar) or in Na+-free buffer (solid bar). Inhibitory effects of NIM (B) and M1 (C) on NTCP- and OATP-mediated d8-TCA uptake by rat hepatocytes. Uptake was measured after 2 minutes of incubation with 1 μM d8-TCA. CyA (10 μM) was used as the positive control. Data were compiled from at least three separate rat liver preparations and are presented as the mean ± S.D. **P < 0.01 and ***P < 0.001 versus the control group.

Hepatobiliary Disposition of CDF in Sandwich-Cultured Rat Hepatocytes.

After its passive diffusion into hepatocytes, CDFDA is hydrolyzed into CDF by esterase. Subsequently, CDF, which is a fluorescent bile acid analog, is excreted either into bile by MRP2 or into blood by MRP3 (Zamek-Gliszczynski et al., 2003). On day 4 of culture, CDF accumulated within the canalicular network in sandwich-cultured rat hepatocytes as demonstrated by fluorescent microscopy (Fig. 5A). MK-571, a well-known MRP2 inhibitor, rendered the fluorescence in bile canaliculi undetectable (Fig. 5F). Similarly, 200 μM NIM and M1 significantly reduced the fluorescent signal in the bile canaliculi (Fig. 5, B and C). Nevertheless, 400 μM M2 and 200 μM M4 did not inhibit or only slightly reduced the fluorescent signal in the bile canaliculi (Fig. 5, D and E).

Fig. 5.
Fig. 5.

CDF disposition in sandwich-cultured rat hepatocytes as measured by fluorescence microscopy after 10 minutes of incubation in standard buffer. Cells were treated with vehicle only (A), 200 μM NIM (B), 200 μM M1 (C), 400 μM M2 (D), 200 μM M4 (E), and 20 μM MK-571 (as the positive inhibitor) (F). White arrows indicate the representative tubular structures of the bile canalicular network.

Furthermore, CDF accumulation in cells incubated in the standard and Ca2+-free buffers was quantified using a microplate fluorescence reader. NIM and M1 increased CDF cellular accumulation and cellular plus biliary accumulation in a concentration-dependent manner (Fig. 6). The BEI of CDF was 26.2% in the control group, which is consistent with the reported BEI value of CDF in Wistar rat hepatocyte cultures (30%) (Zhang et al., 2005). A concentration-dependent reduction in BEI was observed both under NIM and M1 treatments. NIM and M1 (200 μM each) reduced the BEI of CDF to 13.0% and 5.3%, respectively. Nevertheless, no reduction or weak reduction in BEI was observed under M2 and M4 treatments (data not shown).

Fig. 6.
Fig. 6.

Effects of NIM and M1 on the accumulation and BEI of CDF in sandwich-cultured rat hepatocytes. CDF accumulation in sandwich-cultured rat hepatocytes was measured in standard buffer (cells plus bile, solid bars) or in Ca2+-free buffer (cells only, open bars) for 10 minutes. Data are expressed as percentages of control (accumulation in the standard buffer), the mean ± S.D. of at least three independent experiments. *P < 0.05, **P < 0.01, and ***P < 0.001 versus the control group.

Compared with that in the control group, the basolateral efflux of CDF under NIM and M1 treatments decreased in a concentration-dependent manner (Fig. 7). The basolateral efflux of CDF decreased to 49.9% and 38.9% of control, respectively, after 20 minutes of incubation with 200 μM NIM and M1.

Fig. 7.
Fig. 7.

Effects of NIM and M1 on the basolateral efflux of CDF in sandwich-cultured rat hepatocytes. MK-571 (20 μM) was used as the positive inhibitor. Data were compiled from at least three separate rat liver preparations and are expressed as the mean ± S.D. *P < 0.05, **P < 0.01, and ***P < 0.001 versus the control group.

Hepatobiliary Disposition of d8-TCA and CDF in Sandwich-Cultured Human Hepatocytes.

In sandwich-cultured human hepatocytes, the cellular accumulation and cellular plus biliary accumulation of d8-TCA decreased in a concentration-dependent manner under NIM and M1 treatments (Fig. 8). The BEI and Clbiliary values of d8-TCA in control group were 78.5% and 17.2 μl/min/mg protein, respectively. NIM (400 μM) decreased the BEI and Clbiliary values to 65.0% and 3.73 μl/min/mg protein, respectively; moreover, M1 (400 μM) decreased the BEI and Clbiliary values to 71.8% and 7.12 μl/min/mg protein, respectively. In addition, 200 μM NIM and M1 significantly decreased the fluorescent signal of CDF in the bile canaliculi, similar to the effect of MK-571 (Fig. 9).

Fig. 8.
Fig. 8.

Effects of NIM and M1 on the accumulation, BEI, and Clbiliary of d8-TCA (1 μM) in sandwich-cultured human hepatocytes. CyA (10 μM) was used as the positive inhibitor. d8-TCA accumulation was measured in standard buffer (cells plus bile, solid bars) or Ca2+-free buffer (cells only, open bars) for 10 minutes. Data are reported as the mean ± S.D. of one experiment in triplicate. The experiment was repeated, and the same trend was observed. ***P < 0.001 versus the control group.

Fig. 9.
Fig. 9.

CDF disposition in sandwich-cultured human hepatocytes as measured by fluorescence microscopy after 10 minutes of incubation in standard buffer. Cells were treated with vehicle only (A), 200 μM NIM (B), 200 μM M1 (C), and 20 μM MK-571 (as the positive inhibitor) (D). White arrows indicate the representative tubular structures of the bile canalicular network.

Discussion

Cholestatic liver injury has been reported in some patients who received NIM treatment (Romero-Gomez et al., 1999; Stadlmann et al., 2002). In the present studies, we explored the cholestatic effect of NIM in rats and further evaluated the effects of NIM and its main metabolites on bile acid transporters using sandwich-cultured human and rat hepatocytes to reveal a possible mechanism for NIM-induced cholestasis.

A previous study (Warrington et al., 1993) reported that NIM 800 mg daily was tolerated in healthy men with only minor renal toxicity. When corrected for interspecies differences with a dose scaling factor of 6.167 (Singh et al., 2012), a dose of 800 mg daily for humans corresponds to 82.2 mg/kg/day for rats. Our pilot studies showed that 200 mg/kg/day NIM was a lethal dose to rats, whereas a 50 mg/kg/day dose did not show significant liver toxicity. Taken together, a 100 mg/kg/day dose was selected to investigate the cholestatic effect of NIM in rats.

The rats pretreated with 100 mg/kg/day NIM for 5 days via oral administration was associated with a significant increase in plasma levels of AST, ALT, ALP, and TBA, which are markers of cholestasis and hepatotoxicity (Fattinger et al., 2001; Funk et al., 2001a; Kostrubsky et al., 2003; Li et al., 2015). Meanwhile, the biliary secretion of bile acids significantly decreased in the NIM-treated rats. Theoretically, the decreased biliary secretion of bile acids could lead to reduced bile flow (Yoshikado et al., 2011; Li et al., 2017). However, in our study, there was no significant difference in the bile flow rate between the NIM-treated and the nontreated rats. We speculated that hepatic glutathione levels, which markedly increased in the NIM-treated rats (data not shown), possibly caused an increase of bile flow and eventually offset the decreased bile flow dependent on bile acids. It has been reported that the secretion of glutathione is a driving force for the generation of canalicular bile flow in addition to bile acids (Ballatori and Truong, 1992; Zsembery et al., 2000).

Inhibition of the hepatobiliary transporters responsible for bile acid uptake and efflux by the parent drug and/or its metabolites is one possible mechanism leading to cholestasis (Funk et al., 2001b; McRae et al., 2006; Li et al., 2015; Slizgi et al., 2016). NIM underwent extensive metabolism in rats, similar to the metabolic fate in humans. M1 was the major metabolite in rat plasma, whereas M1, M2, and M4 were the major metabolites in rat liver. We then evaluated the effects of NIM and its metabolites (M1, M2, and M4) on bile acid transporters.

First, we explored the effects of NIM, M1, M2, and M4 on the transport of d8-TCA, a probe substrate for NTCP, OATPs, and BSEP (Lepist et al., 2014; Li et al., 2015; Slizgi et al., 2016), in sandwich-cultured rat hepatocytes. Both NIM and M1 reduced the Clbiliary and BEI values of d8-TCA in a concentration-dependent manner. A reduction in BEI values suggested that NIM and M1 inhibited the BSEP-mediated excretion of d8-TCA into the canalicular lumen. Clbiliary is an indicator of the overall effects of test compounds on bile acid excretion. Reduction in Clbiliary under NIM and M1 treatments possibly resulted from the inhibition of basolateral uptake transporters and/or canalicular efflux transporters. Clbiliary of d8-TCA was inhibited to a larger extent than BEI under NIM and M1 treatments, demonstrating that NIM and M1 exerted a greater inhibitory effect on the uptake than on the efflux of d8-TCA. Troglitazone and bosentan, which cause cholestasis in clinics, displayed effects on the hepatobiliary disposition of d8-TCA that were similar to those observed for NIM and M1 (Ansede et al., 2010). The inhibitory effects of NIM and M1 on rat NTCP and OATPs were further evaluated using suspended rat hepatocytes. NIM and M1 exerted greater inhibitory effects on NTCP than on OATPs, as indicated by the lower IC50 values of these compounds in NTCP than in OATPs.

BEI values of d8-TCA barely changed under M2 and M4 treatments, suggesting that these compounds did not interfere with BSEP activity. Moreover, Clbiliary of d8-TCA slightly decreased under M2 and M4 treatments, indicating that d8-TCA uptake was weakly inhibited. However, given the extremely low concentrations of M2 and M4 in rat plasma, their inhibitory effects on the uptake transporters were negligible.

In addition to NTCP, OATPs, and BSEP, MRPs are important transporters mediating the transport of bile acids, especially the sulfated bile acids (Akita et al., 2001; Morgan et al., 2013; Rodrigues et al., 2014). We explored the inhibitory effects of NIM and its metabolites on rat MRP2/3 by using CDF as probe substrate. NIM and M1 (200 μM each) significantly reduced the fluorescent signal of CDF in bile canaliculi, which is similar to the effect of MK-571. Additionally, concentration-dependent reduction in BEI values of CDF was observed under NIM and M1 treatments. Both results suggested that NIM and M1 inhibited MRP2-mediated CDF excretion. Furthermore, NIM and M1 decreased the basolateral efflux of CDF (Fig. 7), which is consistent with the increase in cellular plus biliary accumulation of CDF (Fig. 6), indicating that the basolateral efflux transporter MRP3 was also inhibited by NIM and M1. Dual inhibition of two different excretory pathways, namely, MRP2- and MRP3-mediated effluxes, may lead to a marked increase in some bile acids. By contrast, M2 and M4 did not reduce or slightly reduced the fluorescent signal of CDF in bile canaliculi, suggesting that these metabolites did not inhibit or only marginally inhibited MRP2.

In addition to CDF, d8-TCA can be used as a probe substrate to evaluate the function of MRP3 (Guo et al., 2014). We attempted to use d8-TCA to characterize the function of MRP3. Unexpectedly, the content of d8-TCA in the efflux medium was not reduced but rather slightly increased in the presence of NIM or M1 (data not shown), possibly because that the NTCP-mediated reuptake of TCA was inhibited. Compared with d8-TCA, CDF was a substrate for OATPs rather than for NTCP (Zamek-Gliszczynski et al., 2003). NIM and M1 exerted considerably weaker inhibitory effects on OATPs than on NTCP; thus, CDF content in the efflux medium was mainly dependent on the effects of NIM and M1 on MRP3.

The effects of NIM and M1 on human bile acid transporters were also investigated using sandwich-cultured human hepatocytes. Similar to the results from rat hepatocyte studies, the Clbiliary of d8-TCA was inhibited to a larger extent than BEI values under NIM and M1 treatments, indicating that NIM and M1 exerted a greater inhibitory effect on the uptake transporters than on the efflux transporter of d8-TCA. Besides, the inhibitory effects of NIM and M1 on MRP2 were confirmed by the reduced fluorescent signal of CDF in bile canaliculi.

Overall, both NIM and M1 demonstrated inhibitory effects on the uptake transporters NTCP and OATPs and on the efflux transporters BSEP and MRP2. However, the reduced metabolites of NIM (M2 and M4) did not inhibit or only marginally inhibited these bile acid transporters. The current results suggest that the inhibition of bile acid transporters by NIM and M1 may negatively impact bile acid homeostasis, which may explain, at least in part, the mechanism of NIM-induced cholestasis.

Acknowledgments

We thank Dr. Xiuli Li for helpful discussions. We also thank Hua Cao and Ziqing Zuo for their help in synthesizing the metabolites of NIM.

Authorship Contributions

Participated in research design: Zhou, Pang, and Chen.

Conducted experiments: Zhou, Pang, and Jiang.

Contributed new reagents or analytic tools: Zhou, Pang, and Chen.

Performed data analysis: Zhou, Pang, and Chen.

Wrote or contributed to the writing of the manuscript: Zhou, Zhong, and Chen.

Footnotes

    • Received October 26, 2016.
    • Accepted February 8, 2017.

  • This work was supported by the National Natural Science Foundation of China [Grants 81573500 and 81503153]. The authors declare no conflicts of interest.

  • https://doi.org/10.1124/dmd.116.074104.

Abbreviations

ALP
alkaline phosphatase
ALT
alanine aminotransferase
AST
aspartate aminotransferase
BEI
biliary excretion index
BSEP
bile salt export pump
CA
cholic acid
CDCA
chenodeoxycholic acid
CDF
5 (and 6)-carboxy-2’,7’-dichlorofluorescein
CDFDA
5 (and 6)-carboxy-2’,7’-dichlorofluorescein diacetate
Clbiliary
biliary clearance
CMC-Na
sodium carboxymethyl cellulose
CyA
cyclosporine A
DCA
deoxycholic acid
GCA
glycocholic acid
GCDCA
glycochenodeoxycholic acid
GDCA
glycodeoxy cholic acid
GUDCA
glycoursodeoxycholic acid
HBSS
Hanks’ balanced salt solution
LCA
lithocholic acid
LC-MS/MS
liquid chromatography-tandem mass spectrometry
M1
4′-hydroxynimesulide
M2
nitro-reduced nimesulide
M4
acetylated metabolite of nitro-reduced nimesulide
MRM
multiple reaction monitoring
MRP
multidrug resistance–associated protein
m/z
mass-to-charge ratio
NIM
nimesulide
NTCP
Na+-taurocholate cotransporting polypeptide
OATP
organic anion transporting protein
TBA
total bile acid
TCA
taurocholic acid
TCDCA
taurochenodeoxycholic acid
UDCA
ursodeoxycholic acid

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Nimesulide and Its Metabolite Inhibit Bile Acid Transporters

Lei Zhou, Xiaoyan Pang, Jingfang Jiang, Dafang Zhong and Xiaoyan Chen
Drug Metabolism and Disposition May 1, 2017, 45 (5) 441-448; DOI: https://doi.org/10.1124/dmd.116.074104
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