Commonly used excipients modulate UDP-glucuronosyltransferase 2b7 activity to improve nalbuphine oral bioavailability in humans.

PURPOSE: Nalbuphine (NAL) is a potent opioid analgesic, but can only be administered by injection. The major aim of this study was to develop an oral NAL formulation employing known excipients as UDP-glucuronosyltransferase 2B7 (UGT2B7) inhibitors to improve its oral bioavailability. METHODS: Twenty commonly used pharmaceutical excipients were screened in vitro by using liver microsomes to identify inhibitors of UGT2B7, the major NAL metabolic enzyme. Tween 20 and PEG 400 were potent UGT2B7 inhibitors and both were co-administered (Tween-PEG) with NAL to rats and humans for pharmacokinetic and/or pharmacodynamic analyses. RESULTS: In animal studies, oral Tween-PEG (4 mg/kg of each) significantly increased the area under the plasma NAL concentration-time curve (AUC) and the maximal plasma concentration (Cmax) by 4- and 5-fold, respectively. The results of the pharmacodynamic analysis were in agreement with those of the pharmacokinetic analysis, and showed that Tween-PEG significantly enhanced the analgesic effects of orally administered NAL. In humans, oral Tween-PEG (240 mg of each) also increased NAL Cmax 2.5-fold, and AUC by 1.6-fold. CONCLUSIONS: Tween-PEG successfully improved oral NAL bioavailability and could formulate a useful oral dosage form for patient's convenience.

Dietary flavonoids modulate CYP2C to improve drug oral bioavailability and their qualitative/quantitative structure-activity relationship.

This study aims to improve the drug oral bioavailability by co-administration with flavonoid inhibitors of the CYP2C isozyme and to establish qualitative and quantitative (QSAR) structure-activity relationships (SAR) between flavonoids and CYP2C. A total of 40 naturally occurring flavonoids were screened in vitro for CYP2C inhibition. Enzyme activity was determined by measuring conversion of tolbutamide to 4-hydroxytolbutamide by rat liver microsomes. The percent inhibition and IC50 of each flavonoid were calculated and used to develop SAR and QSAR. The most effective flavonoid was orally co-administered in vivo with a cholesterol-reducing drug, fluvastatin, which is normally metabolized by CYP2C. The most potent CYP2C inhibitor identified in vitro was tamarixetin (IC50 = 1.4 µM). This flavonoid enhanced the oral bioavailability of fluvastatin in vivo, producing a >2-fold increase in the area under the concentration-time curve and in the peak plasma concentration. SAR analysis indicated that the presence of a 2,3-double bond in the C ring, hydroxylation at positions 5, 6, and 7, and glycosylation had important effects on flavonoid-CYP2C interactions. These findings should prove useful for predicting the inhibition of CYP2C activity by other untested flavonoid-like compounds. In the present study, tamarixetin significantly inhibited CYP2C activity in vitro and in vivo. Thus, the use of tamarixetin could improve the therapeutic efficacy of drugs with low bioavailability.

Genetic polymorphisms of metabolic enzymes and the pharmacokinetics of indapamide in Taiwanese subjects.

To understand the genetic makeup and impact on pharmacokinetics (PK) in the Taiwanese population, we analyzed the pharmacogenetic (PG) profile and demonstrated its effects on enzyme metabolism using indapamide as an example. A multiplex mass spectrometry method was used to examine the single nucleotide polymorphism (SNP) profile of eight major phases I and II metabolic enzymes in 1,038 Taiwanese subjects. A PG/PK study was conducted in 24 healthy subjects to investigate the possible effects of 28 SNPs on drug biotransformation. Among the genetic profile analyzed, eight SNPs from CYP2A6, CYP2C19, CYP2D6, CYP2E1, CYP3A5, and UGT2B7 showed higher variant frequencies than those previously reported in Caucasians or Africans. For instance, we observed 14.7% frequency of the SNP rs5031016 (I471T) from CYP2A6 in Taiwanese, whereas 0% variation was reported in Caucasians and Africans. The PG/PK study of indapamide demonstrated that the polymorphic SNPs CYP2C9 rs4918758 and CYP2C19 rs4244285 appeared to confer lowered enzyme activity, as indicated by increased C max (25% ∼ 64%), increased area under the plasma level-time curves (30~76%), increased area under the time infinity (43% ∼ 80%), and lower apparent clearance values than PK for wild-type indapamide. Our results reinforce the biochemical support of CYP2C19 in indapamide metabolism and identify a possible new participating enzyme CYP2C9. The PG/PK approach contributed toward understanding the genetic makeup of different ethnic groups and associations of enzymes in drug metabolism. It could be used to identify two genetic markers that enable to differentiate subjects with varied PK outcomes of indapamide.

Selected pharmaceutical excipient prevent isoniazid and rifampicin induced hepatotoxicity.

BACKGROUND & AIMS: The incidence of isoniazid (INH)- and rifampicin (RIF)-induced abnormal liver enzyme activity is 27% but only 19% with INH alone. Cytochrome P450 2E1 (CYP2E1) is thought to contribute to the synergistic effects of RIF and INH. Pharmaceutical excipients are inactive ingredients that are added to a pharmaceutical compound. The purpose of this study was to screen excipients for CYP2E1 inhibition and identify whether the screened excipients prevented INH/RIF-induced hepatotoxicity. METHODS: Fifty-five known pharmaceutical excipients were screened for CYP2E1 inhibition. The hepatotoxic doses of INH and RIF were 50 and 100 mg/kg/day, respectively. Hepatotoxicity was assessed by the galactose single point (GSP) method (a US Food and Drug Administration (FDA) recommended quantitative liver function test), liver histopathology, malondialdehyde (MDA) assay, and measurement of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity. We chose the CYP2E1-specific substrate chlorzoxazone to assess CYP2E1 activity in animal and human. RESULTS: Mannitol inhibited CYP2E1 activity by 54% in mice with INH/RIF-induced hepatotoxicity (p < 0.005). Serum AST, ALT and GSP levels were significantly increased 3.8- to 7.8-fold in these mice (p < 0.005), and these levels could be lowered by mannitol. Mannitol significantly alleviated the depletion of hepatic glutathione (GSH) and partially reversed the increase in MDA formation in mice treated with INH/RIF (p < 0.005). Mannitol also decreased CYP2E1 activity by 58% in humans (p < 0.005). Furthermore, an antituberculosis (TB) efficacy assay revealed that mannitol did not affect the anti-TB effects of INH/RIF. CONCLUSIONS: Mannitol, an FDA-approved excipient, was found to be a CYP2E1 inhibitor. Mannitol may be a useful adjuvant for drugs that induce hepatotoxicity through CYP2E1, such as INH and RIF.

Protective effects of kaempferol on isoniazid- and rifampicin-induced hepatotoxicity.

Isoniazid (INH) and rifampicin (RIF) are the first-line drugs for antituberculosis (anti-TB) chemotherapy. The levels of serum transaminases [aspartate aminotransferase (AST) and alanine aminotransferase (ALT)] are abnormal in 27% of patients undergoing INH and RIF treatments and in 19% of patients undergoing treatment with INH alone. Cytochrome P450 2E1 (CYP2E1) metabolizes many toxic substrates, including ethanol, carbon tetrachloride, and INH, which ultimately results in liver injury. The objective of this study was to screen for CYP2E1 inhibitors in vitro and investigate whether the selected compound could prevent INH/RIF-induced hepatotoxicity in vivo. We screened 83 known compounds from food and herbal medicines as inhibitors of CYP2E1. The hepatotoxic dose of INH/RIF was 50/100 mg kg(-1) day(-1). Hepatotoxicity was assessed using galactose single-point (GSP) method (a quantitative measurement of liver function), histopathological examination of the liver, malondialdehyde (MDA) assay, and measurement of AST and ALT activities. Kaempferol inhibited CYP2E1 activity in mice by 0.31- to 0.48-fold (p < 0.005). Mice with INH/RIF-induced hepatotoxicity showed significantly abnormal serum levels of AST and ALT, and GSP value, and these values could be decreased by the administration of kaempferol (p < 0.005). Kaempferol significantly reduced the depletion of hepatic glutathione and prevented the increase in MDA formation in mice. Furthermore, kaempferol did not affect the anti-TB effects of INH/RIF. To our knowledge, this is the first report of kaempferol's utility as an adjuvant for preventing CYP2E1-mediated hepatotoxicity induced by drugs such as INH and RIF.

Validated liquid chromatography-tandem mass spectrometry method for determination of totally nine probe metabolites of cytochrome P450 enzymes and UDP-glucuronosyltransferases.

A simplified, rapid, and selective liquid chromatography-tandem mass spectrometry method for the determination of the activities of cytochrome P450 (CYP) enzymes and UDP-glucuronosyltransferases (UGTs) in two separate settings was developed and successfully applied to 8 CYP isoenzymes and UGT2B7 enzyme activities in rat liver microsomes. The triple-quadrupole mass spectrometric detection was operated in positive mode for the probe metabolites: CYP1A2 (resorufin), CYP2B6 (hydroxybupropion), CYP2C19 (5-hydroxyomeprazole), CYP2D6 (dextrophan), CYP3A4 (6ß-hydroxytestosterone), and UGT2B7 (morphine-3-glucuronide); also in negative mode for CYP2C9 (4-hydroxytolbutamide), CYP2E1 (6-hydroxychloroxazone), and CYP4A (hydroxylauric acid). The metabolic reactions were terminated with acetonitrile, containing metoprolol and acetaminophen as the internal standard for positive and negative ion electrospray ionization, respectively. The method was validated over the concentration range of 25-2500 ng/mL for 5-hydroxyomeprazole, dextrophan, hydroxylauric acid, and morphine-3-glucuronide; 5-500 ng/mL for resorufin; 3-300 ng/mL for hydroxybupropion; 10-1000 ng/mL for 4-hydroxytolbutamide; 40-4000 ng/mL for 6-hydroxychloroxazone; and 63-6300 ng/mL for 6ß-hydroxytestosterone. All of the extraction recoveries of these analytes were greater than 85%, except for hydroxylauric acid at mid-concentration with a recovery of 83.2% ± 3.2%. The matrix effects were between 85.8% and 119.9%; the respective within- and between-run precisions were 0.9-12.0% and 2.0-13.9%; and the within- and between-run accuracy levels were 0.6-17.2% and 0.1-15.1%, respectively, for all these analytes. All of the analytes were stable during the assay and storage in the liver microsomes of Sprague-Dawley rats. The measurement activity of multiple enzymes was feasible using a cocktail approach. This method proved to be a robust, fast, accurate, specific and sensitive assay, and was successfully used to investigate in vivo enzyme activities of 8 major CYP isoenzymes and UGT2B7 in Sprague-Dawley rats with fatty livers. By the end of the eighth week, the CD-fed induced fatty liver rats showed a significant decrease in the activities of CYP1A2 and UGT2B7 as compared to the standard diet group.

A novel mechanism underlies the hepatotoxicity of pyrazinamide.

Relatively little is known about the hepatotoxicity of pyrazinamide (PZA). PZA requires activation by amidase to form pyrazinoic acid (PA). Xanthine oxidase then hydroxylates PA to form 5-hydroxypyrazinoic acid (5-OH-PA). PZA can also be directly oxidized to form 5-OH-PZA. Before this study, it was unclear which metabolic pathway or PZA metabolites led to hepatotoxicity. This study determines whether PZA metabolites are responsible for PZA-induced hepatotoxicity. PZA metabolites were identified and cytotoxicity in HepG2 cells was assessed. Potential PZA and PA hepatotoxicity was then tested in rats. Urine specimens were collected from 153 tuberculosis (TB) patients, and the results were evaluated to confirm whether a correlation existed between PZA metabolite concentrations and hepatotoxicity. This led to the hypothesis that coadministration of amidase inhibitor (bis-p-nitrophenyl phosphate [BNPP]) decreases or prevents PZA- and PZA metabolite-induced hepatotoxicity in rats. PA and 5-OH-PA are more toxic than PZA. Electron microscopy showed that PZA and PA treatment of rats significantly increases aspartate transaminase (AST) and alanine aminotransferase (ALT) activity and galactose single-point (GSP) levels (P < 0.005). PA and 5-OH-PA levels are also significantly correlated with hepatotoxicity in the urine of TB patients (P < 0.005). Amidase inhibitor, BNPP, decreases PZA-induced, but not PA-induced, hepatotoxicity. This is the first report of a cell line, animal, and clinical trial confirming that the metabolite 5-OH-PA is responsible for PZA-induced hepatotoxicity.

A new approach to facilitate diagnosis of nonalcoholic fatty liver disease through a galactose single point method in rats with fatty liver.

BACKGROUND: Liver biopsy reliably diagnoses nonalcoholic fatty liver disease, but its invasiveness and inter- and intra-observer errors limit its usefulness in monitoring. AIMS: Use a galactose single point method or combined biochemical parameters to improve assessments of nonalcoholic fatty liver disease in a rat model. METHODS: Three nonalcoholic fatty liver disease severities were generated in 50 rats: a control group (n=18) on a standard diet, and 2 study groups on a choline-deficient diet (n=18), with and without treatment with silymarin (n=14). At weeks 4, 8, and 18, a galactose solution (0.5 g/kg/body weight) was rapidly injected intravenously. Sixty minutes later, internal artery blood was taken for biochemical analyses, including galactose. The livers were then removed for haematoxylin-eosin staining and to measure the hepatic lipid content. RESULTS: Alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, albumin, and total protein were each significantly correlated with nonalcoholic fatty liver disease severity. Regarding logistic regression, galactose single point method and total protein were significantly predictive. The optimal alanine aminotransferase cutoff point for nonalcoholic fatty liver disease prediction from the receiver-operating characteristic curve had 72.4% sensitivity and 52.4% specificity; galactose single point method alone had 82.8% and 72.4%, whereas galactose single point method+total protein showed 82.8% and 81.0%. CONCLUSIONS: Both galactose single point method and galactose single point method+total protein had greater diagnostic sensitivity and specificity for nonalcoholic fatty liver disease than traditional biochemical tests.