Drug Metabolism Letters - Volume 6, Issue 2, 2012

Phenotyping of cytochrome P450 2A6 (CYP2A6) was determined by assessing urinary caffeine metabolites in a Japanese population with a high frequency of CYP2A6 whole-gene deletion (CYP2A6*4). The levels of 1,7-dimethyluric acid (17U), 1-methylxanthine (1X), and 1,7-dimethylxanthine (17X) were measured in non-smokers whose CYP2A6 and NAT2 genotypes had been determined. Low 17U/1X ratios were observed in accumulated overnight urine samples of subjects genotyped as CYP2A6*4/*4 after caffeine treatment. The individual 17U/1X ratios in spot urine samples were almost constant before and 2–8 h after caffeine treatment, with or without prior abstention from dietary caffeine. The average 17U/1X ratios obtained from subjects with CYP2A6 *4/ *4 or CYP2A6 *1/ *4 genotypes were significantly lower than those from subjects with wild-type CYP2A6 *1/ *1 under dietary caffeine consumption. The present results suggest that impaired CYP2A6 function associated with CYP2A6 *4/ *4 could be determined using the 17U/1X ratios in spot urine samples under normal dietary caffeine consumption in Japanese non-smokers, without the need for additional caffeine administration or prior abstention from caffeine.

The metabolic fate of green tea catechins [(-)-epicatechin ((-)-EC), (-)-epicatechin-3-gallate (ECG) (-)- epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG)] in cryopreserved human, monkey, dog, rat and mouse hepatocytes was studied. Methylation, glucuronidation, sulfation and isomerization pathways of (-)-EC in all five species were found. Methylation, glucuronidation, sulfation, hydrolysis, isomerization and glucosidation pathways of ECG were found. Species differences in metabolism of (-)-EC or ECG were observed. Surprisingly, no metabolites of EGC or EGCG were detected, but chemical oxidation and polymerization were observed under these experimental conditions. It appeared that enzymatic reactions and chemical reactions were differentiated by an additional hydroxyl group on the B-ring between (-)-EC/ECG and EGC/EGCG. For (-)-EC, thirty-five metabolites including isomerized (M6. M10 and M25), glucuronidated (M3, M5 and M11), sulfated (M7, M15, M16, M18, M20, M23, M26), methylated (M2, M9, M12, M17, M19, M21, M27, M30, M32), glucuronated/methylated (M4, M8, M13, M14), sulfated/methylated (M22, M24, M28, M29, M31, M33, M34, M35) and diglucuronidate (M1), were detected and characterized. M11, M18, M19 and M23 were major metabolites in human hepatocytes; M11, M26 and M31 were major metabolites in monkey hepatocytes; M10, M20, M22, M26 and M31 were major metabolites in dog hepatocytes; M5, M6 and M10 were major metabolites in rat hepatocytes; and M5, M6 and M13 were major metabolites in mouse hepatocytes. For ECG, twelve metabolites including isomerized (M1), hydrolyzed (M3), glucosidated (M2), glucuronidated (M4 and M6), sulfated (M9, M11 and M12), methylated (M7), sulfated/glucuronidated/methylated (M8 and M10) and diglucuronidated (M5), were detected and characterized. M4, M11 and M12 were major metabolites in human hepatocytes; M11 and M12 were major metabolites in monkey hepatocytes; M3 and M11 were major metabolites in dog hepatocytes; M4, M6 and M11 were major metabolites in rat hepatocytes, and M3 was a major metabolite in mouse hepatocytes. The experimental results have demonstrated that fate of catechins in in vitro hepatocytes depends on metabolism and chemical stability. In certain experimental conditions, the chemical reaction may become a dominant pathway.

Objective: Phenotyping cytochrome P450 (CYP) 2C9 activity with S-warfarin requires extensive blood sampling to characterize area under the concentration-time curve (AUC). This retrospective data analysis was conducted to determine if truncated S-warfarin AUCs can be used to measure CYP2C9 activity. Methods: S-warfarin plasma concentrations were obtained from healthy adults (n = 84) genotyped as CYP2C9 extensive metabolizers (EMs) from 6 published studies. Subjects received a single 10 mg oral warfarin dose during baseline and treatment conditions. AUC zero to infinity (AUCINF) and truncated AUCs at 48 h (AUC48), at 72 h (AUC72) and at 96 h (AUC96) were determined by noncompartmental analysis. Equivalence was determined via least squares geometric mean ratios (LS-GMRs) with 90% confidence intervals (CI) within 0.8–1.25. Results: A lack of equivalence was observed for AUC48 and AUC72 compared to AUCINF during baseline conditions in all evaluated studies and during treatment conditions in 5 of 6 studies. Equivalence was observed for AUC96 compared to AUCINF during all baseline and treatment conditions. Results were consistent across all evaluated AUCs between baseline and treatment without a CYP2C9-mediated drug-drug interaction and during induction with an oral contraceptive. During inhibition with fluvastatin, a lack of equivalence was observed with AUCINF (LS-GMR [90%CI] = 1.25 [1.16-1.34]) and AUC96 (1.2 [1.13=1.27]). In contrast, equivalence was observed for AUC48 (1.15 [1.08-1.22]) and AUC72 (1.18 [1.11-1.24]). Conclusions: S-warfarin truncated AUC48 and AUC72 poorly characterize AUCINF and are unable to detect weak CYP2C9 inhibition with fluvastatin. S-warfarin phenotyping parameters need to ensure blood sampling of at least 96 h to characterize AUC and thus CYP2C9 activity.

Background: Cannabinoids exert neuroprotective and symptomatic effects in amyotrophic lateral sclerosis (ALS). We assessed the pharmacokinetics (PK) and tolerability of delta-9-tetrahydrocannabinol (THC) in ALS patients. Methods: Nine patients received THC single oral doses of 5mg and 10mg, separated by a wash-out period of two weeks. Blood samples for the determination of THC, 11-nor-9-carboxy-THC (THC-COOH) and hydroxy-THC (THC-OH) were taken up to 8 hours after intake. Adverse events were assessed by visual analogue scales (VAS). Plasma concentrations of the active metabolite THC-OH were submitted to sequential pharmacokinetic-pharmacodynamic population modeling on individual heart rate as a proxy for THC's cardiovasculatory effects. Results: Drowsiness, euphoria, orthostasis, sleepiness, vertigo and weakness were significantly more frequent in patients receiving 10mg compared to 5mg THC. A marked interindividual variability was found for the absorption of oral THC (84%) and elimination of THC-COOH (45%). PK data did not support any clinically relevant deviation from linear PK in the investigated range of concentrations. Plasma concentrations of THC-OH were positively correlated with the individual heart rate. An Emax-model was successfully fitted to individual heart rate, with a THC-OH plasma concentration of 3.2·10-4 μmol/L for EC50 and an Emax of 93 bpm for heart rate. Conclusions: The higher 10mg dose of THC was dose-limiting in patients with ALS. High interindividual PK variability requires individuell titration of THC for potential therapeutic use in patients with ALS.

Buprenorphine, pentazocine, and naloxone are opioid drugs used for the treatment of pain and opioid dependence or overdose. Sulfation as catalyzed by the cytosolic sulfotransferases (SULTs) is involved in the metabolism of a variety of xenobiotics including drug compounds. Sulfation of opioid drugs has not been well investigated. The current study was designed to examine the sulfation of three opioid drugs, buprenorphine, pentazocine, and naloxone, in HepG2 human hepatoma cells and to identify the human SULT(s) responsible for their sulfation. Analysis of the spent media of HepG2 cells, metabolically labeled with [35S]sulfate in the presence of each of the three opioid drugs, showed the generation and release of their [35S]sulfated derivatives. A systematic analysis using eleven known human SULTs revealed SULT1A3 and SULT2A1 as the major responsible SULTs for the sulfation of, respectively, pentazocine and buprenorphine; whereas three other SULTs, SULT1A1, SULT1A2, and SULT1C4, were capable of sulfating naloxone. Enzymatic assays using combinations of these opioid drugs as substrates showed significant inhibitory effects in the sulfation of buprenorphine and pentazocine by naloxone. Differential sulfating activities toward the three opioid drugs were detected in cytosol or S9 fractions of human lung, liver, kidney, and small intestine. Collectively, these results imply that sulfation may play a role in the metabolism of buprenorphine, pentazocine, and naloxone in vivo.

Caffeine is the active constituent in coffee. Continual consumption of caffeine can lead to an attenuated response also known as tolerance. Results from rat studies have shown that caffeine is an inducer of CYP1A2, the enzyme responsible for caffeine's metabolism. This suggests that CYP1A2 induction by caffeine may be in part responsible for caffeine tolerance. However, whether caffeine induces CYP1A2 expression in humans remains unknown. Our results from luciferase assays performed in HepG2 cells showed that caffeine is not an activator of the aromatic hydrocarbon receptor (AhR), a major transcription factor involved in upregulation of CYP1A2. Furthermore, caffeine did not induce CYP1A2 expression in primary human hepatocytes at a concentration attained by ordinary coffee drinking. On the other hand, caffeine enhanced CYP1A2 expression by 9-fold in rat hepatocytes. Our results suggest that caffeine from ordinary coffee drinking does not induce CYP1A2 expression in humans and that factors other than CYP1A2 induction by caffeine likely contribute to development of caffeine tolerance in humans.

We investigated the damage caused by oxidative stress using the yeast Saccharomyces cerevisiae as a model biological system. After inducing oxidative stress with menadione, we were able to evaluate the extent of cellular oxidative stress by utilizing 2´,7´-dichlorofluorescein diacetate (DCFH-DA) as a marker of the presence of reactive oxygen species. Cells were grown on different carbon sources in order to compare fermentative and oxidative metabolism. Under these conditions we evaluated the effectiveness of idebenone (2,3-dimethoxy-5-methyl-6-(10- hydroxydecyl)-1,4-benzoquinone) as a molecule that could relieve menadione-induced growth inhibition in Saccharomyces cerevisiae.

m-Hydroxymexiletine (MHM), a minor metabolite of the class IB anti-arrhythmic drug mexiletine, is about two fold more potent than the parent compound on human cardiac voltage-gated sodium channels (hNav1.5), and equipotent to mexiletine on human skeletal-muscle voltage-gated sodium channels (hNav1.4). Herein, an alternative and simplified synthesis of this promising compound has been accomplished. This route, as well as being more efficient, has the advantage, over the first, to avoid the use of oxidizing agents, such as the meta-chloroperoxybenzoic acid.

Sulfonamide antimicrobials (sulfamethoxazole) contain an arylamine group, oxidized by CYP2C9 to the hydroxylamine with subsequent auto-oxidation to a highly reactive [-nitroso-] intermediate is a necessary (if not sufficient) cause of drug hypersensitivity. Accordingly, xenobiotics that do not contain an arylamine cannot generate this reactive intermediate and do not cross react with sulfonamide antimicrobials. Despite this well-attested observation, product labeling and direct-to-consumer advertising for non-arylamine therapeutic classes of drugs containing the sulfonamido- functional group persist with a warning of the potential for cross-reactivity. It is hoped that by offering an explicit rationale for the lack of cross-reactivity will provide medical practitioners with a level comfort to proceed with prescribing medications such as thiazide diuretics and celecoxib for patients with a history of hypersensitivity to sulfonamide antimicrobials.

In the present study we have developed a simple, time, and cost effective in vivo rodent protocol to screen the susceptibility of a test compound for P-glycoprotein (P-gp) mediated efflux at the blood brain barrier (BBB) during early drug discovery. We used known P-gp substrates as test compounds (quinidine, digoxin, and talinolol) and elacridar (GF120918) as a chemical inhibitor to establish the model. The studies were carried out in both mice and rats. Elacridar was dosed intravenously at 5 mg/kg, 0.5 h prior to probe substrate administration. Plasma and brain samples were collected and analyzed using UPLC-MS/MS. In the presence of elacridar, the ratio of brain to plasma area under the curve (B/P) in mouse increased 2, 4, and 38-fold, respectively, for talinolol, digoxin, and quinidine; whereas in rat, a 70-fold increase was observed for quinidine. Atenolol, a non P-gp substrate, exhibited poor brain penetration in the presence or absence of elacridar in both species (B/P ratio ~ 0.1). Elacridar had no significant effect on the systemic clearance of digoxin or quinidine; however, a trend towards increasing volume of distribution and half life was observed. Our results support the utility of elacridar in evaluation of the influence of P-gp mediated efflux on drug distribution to the brain. Our protocol employing a single intravenous dose of elacridar and test compound provides a cost effective alternative to expensive P-gp knockout mice models during early drug discovery.

Object: To Study the pharmacokinetics and metabolism of Sodium 7,4' -oxo-acetic acid daidzein in rat. Method: Sodium 7,4' -oxo-acetic acid daidzein was determined by reversed-phase HPLC (column: German CenturySIL BDS C18 5μm silica, 200mm×4.6mm i.d; fluid: methanol-water-85% phosphoric acid(57:43:0.05, v/v/v)), with sodium benzoic acid as an internal standard. Biological samples were extracted with acetonitrile. Results: The calibration curve was linear over the range of 1.0-1000μg/ml in rat plasma, urine and feces. The average extraction recoveries were 73.3% (plasma), 73.9% (urine) and 83.7% (feces) respectively and the intra-day and inter-day precisions were less than 8.34%. The assay was applied to the analysis of samples from a pharmacokinetic study. The absolute bioavailability of oral administration was 3.07%. DZ I original compound determined in 6h urine was 32.32%, in 24h urine was 32.71%, in 24h feces was 22.96%.