Drug Metabolism Letters - Volume 6, Issue 3, 2012

Ischemic stroke represents one of the major causes of mortality and disability in the adult population in both developed and developing nations. Considering these epidemiological issues, the improvement of preventive therapeutic strategies has been recently targeted as a pivotal research field for scientific community. On the basis of the results from several large clinical studies and metanalyses, some Task forces of researchers from recognized Scientific Societies have recently produced some consensus Guidelines, recommending the use of statins as a key pharmacologic approach in stroke prevention. In the present narrative review, we will update evidence on safety and efficacy of statins to prevent ischemic cerebral stroke.

Coumadin (R/S-warfarin) is a highly efficacious and widely used anticoagulant; however, its highly variable metabolism remains an important contributor to uncertainties in therapeutic responses. Pharmacogenetic studies report conflicting findings on the clinical relevance of CYP2C19. A resolution to this controversy is impeded by a lack of detail on the potential role of CYP2C19 in warfarin metabolism. Consequently, we assessed the efficiency of CYP2C19 metabolism of R- and S-warfarin and explored possible contributions in the liver using in vitro methods. Recombinant CYP2C19 metabolized R- and S-warfarin mainly to 6-, 7-, and 8-hydroxywarfarin, while 4'-hydroxywarfarin was a minor metabolite. Overall R-warfarin metabolism was slightly more efficient than that for S-warfarin. Metabolic pathways that produce R-6-, 7-, and 8-hydroxywarfarin in human liver microsomal reactions correlated strongly with CYP2C19 Smephenytoin hydroxylase activity. Similarly, CYP1A2 activity toward phenacetin correlated with formation of R-6 and 7- hydroxywarfarin such that R-8-hydroxywarfarin seems unique to CYP2C19 and possibly a biomarker. In following, CYP2C19 likely impacts R-warfarin metabolism and patient response to therapy. Intriguingly, CYP2C19 may contribute to S-warfarin metabolism in patients, especially when CYP2C9 activity is compromised due to drug interactions or genetic polymorphisms.

Hepatic disposition of bromosulfophthalein (BSP), bilirubin and bile salts partially overlap, as these anions share both uptake and excretion mechanisms. Multiple organic anion transporters mediate hepatic BSP uptake, i.e. members of the SLCO and SLC22 gene families and bilitranslocase (TCDB #2.A.65.1.1). This study aimed at evaluating the relative contribution of bilitranslocase in BSP uptake in precision-cut human and rat liver slices. To this purpose, two different anti-sequence bilitranslocase antibodies were used as specific, functional inhibitors of bilitranslocase. The intact liver physiology was accurately reproduced in this BSP uptake assay, since uptake was strongly temperature-dependent and inhibited by hepatotropic organic anions, such as 50 nM bilirubin, 1 μM nicotinic acid, 2 μM digoxin, 5 μM indocyanine green and 100 μM taurocholate. The bilitranslocase antibodies inhibited BSP uptake both in rat and human liver slices. The combined use of bilitranslocase antibodies and taurocholate caused additive-type inhibition, confirming that bilitranslocase is not a bile salt transporter; by contrast, bilirubin caused no additive-type inhibition. In conclusion this data, indicate the role of the bilirubin transporter bilitranslocase as one of the transporters involved in the uptake of anions like BSP in parallel with other organic anion carriers. Moreover this data indicate the value of precision-cut liver slices for phenotypic drug uptake studies.

Tobacco smoking is the most widely known cause of human cancer-related death worldwide. NNK is one of the proved human carcinogens contributing to the development of several types of cancer. The carcinogenic effect of NNK depends on the metabolic pathway. Reduction of NNK by carbonyl reducing enzymes leads to the formation of NNAL. This pathway is generally regarded as detoxification pathway although the conditions and circumstances are quite complicated - the process depends on a formed enantiomer of NNAL. In this study a novel method for the determination of the metabolite NNAL was developed. This makes it possible to find and characterize carbonyl reducing enzymes that are involved in NNK metabolism. This simple HPLC method uses conventional HPLC instrumentation and is designed mainly for biochemical laboratories. A new microsomal carbonyl reducing enzyme participating in the metabolism of NNK in vitro has been described. Its activity was compared with other carbonyl reducing enzymes taking part in the biotransformation of NNK.

m-Hydroxymexiletine (MHM) is a metabolite of mexiletine, a well known class IB anti-arrhythmic drug, which presents almost twice the activity of the parent compound on cardiac voltage-gated sodium channels. Given the different activity of mexiletine enantiomers on sodium currents (being the R-isomer the eutomer), it is conceivable that (R)- and (S)-MHM could differ in pharmacodynamic and pharmacokinetic properties, too. Herein we report the efficient synthesis of MHM enantiomers that could represent useful tools for further investigations on stereospecific requirements of the voltage-gated sodium channel binding site. MHM enantiomers and all the homochiral intermediates were fully characterized. The ee values for (R)- and (S)-MHM were >99%, as assessed by capillary electrophoresis using β-cyclodextrin sulfated sodium salt as a chiral selector.

The genotoxic and mutagenic effects of two commonly used organochlorine pesticides, lindane (LND) and endosulfan (ENS), and two commonly used organophosphate pesticides, chlorpyrifos (CPF) and monocrotophos (MCP) were assessed using in vivo mouse bone marrow micronucleus test and in vitro Ames Salmonella/ microsome mutagenicity test. The results showed that these pesticides alone or in combination, induced significantly high frequency of micronuclei (MN) formation that increased with concentration of pesticides. All these four pesticides produced significant increase in the frequencies of micronucleated-polychromatic erythrocytes (MN-PCE) and decrease in frequencies of PCE in dose-dependent manner. The results indicate the suppression of proliferative activity of the bone marrow and increase in the extent of cell death. ENS and MCP showed mutagenic potential in Salmonella/ microsome assay. ENS induced mutagenic and nontoxic response only in TA98 tester strain of S.typhimurium at the dose of 500 μg /plate and in the absence of metabolic activation. MCP showed weak mutagenic and nontoxic effect only in TA100 tester strain at the dose of 5000 μg/plate in both assays, with or without metabolic activation when compared with negative control. MCP was toxic in TA98 tester strain at the dose of 5000 μg/plate in absence of metabolic activation while reduction in toxicity was seen on addition of S9 mixture. The study clearly showed the genotoxic potential of all these four pesticides and mutagenic response of endosulfan and monocrotophos.

Purpose: Menthol in cigarettes has been suggested to inhibit metabolism of nicotine and 4-(methylnitrosamino)-1- (3-pyridyl)-1-butanone (NNK). The objective of this study was to investigate the glucuronide metabolite ratios (MR) for nicotine (NICGLUC/NIC), cotinine (COTGLUC/COT), trans 3'-hydroxy cotinine (3OHCOTGLUC/3OHCOT). 4- methylnitrosamino-1-(3-pyridyl)-1-butanol (NNAL – NNALGLUC/NNAL); and the ratio of trans 3'-hydroxy cotinine to cotinine (3OHCOT/COT) between adult menthol and non-menthol smokers (AS). Methods: The data was collected from the Total Exposure Study (TES), a stratified, multi-center, cross-sectional study that included 3,585 AS and 1,077 non-smokers. Daily urinary excretion of nicotine and five metabolites, NNAL and NNAL glucuronides, and serum cotinine were measured in the AS. The analysis included 1044 menthol (448 African- Americans, AA) and 2297 non-menthol (161 AA) AS. Results: Smoking mentholated cigarettes did not decrease any of the MR. Race was the most important significant main effect for all the MRs. AAs exhibited statistically significantly lower NICGLUC/NIC, COTGLUC/COT, NNALGLUC/ NNAL and 3OHCOT/COT, but higher 3OHCOTGLUC/3OHCOT compared to Whites. Age, liver function, alcoholic beverages, etc., were some of the other significant effects for some MRs. Menthol was not a statistically significant effect, e.g. the adjusted mean NNALGLUC/NNAL between menthol and non-menthol AS was 2.93 vs. 2.80 (p>0.05, AA) and 3.38 vs. 3.35 (p>0.05, Whites). The models only explained 2.6-12.6% of the MR variability. Number of cigarettes was the most important factor affecting serum cotinine levels. Conclusions: Menthol does not inhibit the metabolism of nicotine or NNK. The daily exposure of related constituents is primarily influenced by number of cigarettes smoked per day.

CYP450 enzymes are basics for the metabolism of several medications such as numerous AEDs. As AEDs polypharmacy could lead to hidden pharmacokinetic interactions due to CYP450, therefore, the aim of this study was to determine a proper guideline for AEDs prescription in Iranian epileptic population. A cross-sectional study of fifty-four patients' (n=23 females; n= 31 males with a mean age of 27 years) located in the Epilepsy Ward of Kashani Hospital of Isfahan University of Medical Sciences was carried out during the year 2011. Variables including sex, age, age of seizure onset, type and number of AEDs were recorded in d-Base. Results showed that the number of prescriptions based on AEDs polypharmacy was 77.8%. The most important drugs in prescriptions were carbamazepine (n=41) that is a potent inducer of CYP450 and valproic acid (n=31) that is a potent inhibitor of CYP450 simultaneously. Administration of AEDs was based on: three (n=17), four (n=7), five (n=4) or six (n=3) AEDs simultaneously. To avoid side effects, in prescribing AEDs that act as CYP450inhibitors or inducers concomitantly, their spectrum of interactions should be predicted.

Carotenoid lutein was investigated for its antimutagenic activity in vitro by Ames test using Salmonella typhimurium strains TA 98, TA 100, TA 102 and TA 1535. Mutagens used were direct acting mutagens such as sodium azide (NaN3) (5μg/ plate), nitro-o- phenylendiamine (NPDA) (20μg/ plate), N-methyl- N'-nitro-N-nitrosoguanidine (MNNG) (1&μg/ plate), tobacco extract (50mg/ plate) and acetamidofluorene (AAF) (20&μg/ plate) which needed microsomal activation. Lutein significantly inhibited the mutagenicity produced by direct acting mutagens as well as mutagens needing activation by cytochrome P450 enzymes at very low concentration (IC50 < 50 &μg/plate). Lutein also inhibited the mutagenicity induced by tobacco extract (IC50 < 50 &μg/plate). Cytochrome P 450 enzymes which are involved in the activation of several biological agents were found to be inhibited by lutein. Results indicated that strong antioxidant activity of lutein as well as inhibition of carcinogen metabolisom enzymes are the major reason for the inhibition of mutagenicity by this oxycarotenoid.