Kampo medicine is traditional Japanese medicine modified from the Chinese original. Kampo medicine is a mixture of several medicinal herbs and includes many ingredients such as glycosides. Glycosides are hydrolyzed to aglycons by intestinal bacterial flora and absorbed into the body. Aglycons such as baicalein and glycyrrhetinic acid can be conjugated by UDP-glucuronosyltransferase (UGT) in human liver or small intestine. UGT2B7 is one of the major isoforms responsible for drug conjugation including morphine 3- and 3′- azido-3′-deoxythymidine (AZT) glucuronidation. The present study investigates the effects of 51 Kampo medicines, 14 medicinal herbs and 11 ingredients on UGT2B7 activity in human liver microsomes. Morphine 3-glucuronidation was inhibited by more than 50% by 9 of 51 Kampo medicines such as Ryo-kei-jutsu-kan-to. AZT glucuronidation was inhibited by more than 50% by 24 of 51 Kampo medicines such as Jumi-haidoku-to. Medicinal herbs such as Daio (Rhei Rhizoma), Kanzo (Glycyrrhizae Radix) and Keihi (Cinnamomi Cortex) exhibited more than 80% inhibition on both glucuronidations. The major ingredients of these medicinal herbs inhibited UGT2B7 activity with low Ki. Kampo medicines were found to inhibit the UGT2B7 activity and may cause drug interactions via the inhibition of UGT.
A method of assessing the risk of drug-drug interaction (DDI) caused by mechanism-based inhibition (MBI) was developed for early-stage drug development using cytochrome P450 (CYP) 3A4 inhibition screening data. CYP3A4 inhibition was evaluated using a fluorescent substrate with or without preincubation containing an inhibitor. The results showed that five well-known mechanism-based inhibitors, but not the competitive inhibitor ketoconazole, had lower IC50 after preincubation, suggesting the utility of the IC50 shift by preincubation to discern mechanism-based inhibitors. A method to approximately predict the change in the area under the concentration-time curve (AUC) of a co-administered drug by MBI was found using IC50 shift data and the unbound mean plasma concentration of the inhibitor. From our predictions of change in the AUC for 38 drugs using this method, all mechanism-based inhibitors causing change in the AUC of more than 200% were predicted to be high risk. In conclusion, our method provides a simple assessment of the risk of DDI from mechanism-based inhibitors, especially in the early stages of drug development.
Ixabepilone (BMS-247550, Ixempra™ is a semi-synthetic analog of the natural product epothilone B and marketed for its use in the treatment of cancer. A conventional human ADME study using decay counting methods for 14C detection could not be conducted due to the radiolytic instability of [14C]ixabepilone at a typical specific activity (generally 1-10 μCi/mg). However, [14C]ixabepilone was sufficiently stable at low specific activity (1-2 nCi/mg). These low levels required the use of accelerator mass spectrometry (AMS) for radioactivity detection. The metabolic fate of this compound was investigated in eight patients following single intravenous doses of [14C]ixabepilone (70 mg, 80 nCi; specific activity: 1.14 nCi/mg). Metabolite profiles in pooled urine, feces and plasma samples were determined by HPLC-AMS analysis. The major radioactive component in urine and plasma was [14C]ixabepilone. Feces had a small amount of ixabepilone. There were numerous other drug-related components in both urine and fecal extracts (each <6% of the administered dose). LC/MS analysis of plasma, urine and feces samples showed the presence of three degradants of ixabepilone and several oxidative metabolites (M+16, M+14 and M-2 metabolites). This study demonstrates the utility of AMS in investigating the metabolite and excretion profiles of [14C]ixabepilone following administration to humans.
Glycyrrhetinic acid, the active metabolite of glycyrrhizin, is primarily eliminated by glucuronidation reaction in vivo. In spite of the widespread clinical use of glycyrrhizin, UDP-glucuronosyltransferase (UGT) isoforms involved in the glucuronidation of this drug are still unknown. This report identifies and characterizes the UGT isoforms responsible for glycyrrhetinic acid glucuronidation. In the enzymatic kinetic experiment performed with pooled human liver microsomes (HLMs), Km was 39.4 μM and Vmax was 609.2 pmol/min/mg protein. Of the baculosomes expressing 12 recombinant UGTs investigated, UGT1A1, 1A3, 2B4 and 2B7 showed catalytic activity and UGT1A3 exhibited the highest activity. Km values of recombinant UGT1A3 and 2B7 were 3.4 and 4.4 μM, respectively. Both imipramine (typical substrate of UGT1A3 and 1A4) and flurbiprofen (typical substrate of UGT2B7) inhibit the glucuronidation of glycyrrhetinic acid. Estimated IC50 values were 138 μM for flurbiprofen and 207 μM for imipramine in the inhibition of the glucuronidation of glycyrrhetinic acid in HLMs. These results suggest that glycyrrhetinic acid glucuronidation is primarily mediated by UGT1A1, 1A3, 2B4 and 2B7.
Metabolising enzymes and transport proteins are largely expressed in human tissues. They have major impact on drug disposition and effects. We studied mRNA expression of phase I and II metabolising enzymes and transporters in fetal tissues at different development stages. Hepatic, duodenal, renal and neurological fetal tissues were studied at 15, 27 and 42 weeks gestation and mRNA expression of 84 enzymes and transporters was analysed by with the RT2ProfilerTM PCR array system. There was wide variability in gene expression between different samples. Independently from age, the highest expression levels were observed in the liver and the lowest in the brain for the majority of genes tested. There was significant increase in gene expression with age in duodenal and hepatic tissues.
CYP2C19 is a polymorphic enzyme which metabolizes several clinically important drugs including proguanil. Variation in the 5′ regulatory region may influence CYP2C19 activity. This study evaluates the relationship between proguanil metabolic ratio and genetic variations of CYP2C19 in a South Indian population. Fifty unrelated healthy subjects were genotyped for CYP2C19*2 and *3 alleles and the 5′ flanking region of CYP2C19 was sequenced. Plasma concentrations of proguanil and cycloguanil were estimated by reverse phase HPLC after single oral doses (200 mg) of proguanil. In silico docking analysis of transcription factors binding to its sites in CYP2C19 5′ regulatory region was performed. The mean metabolic ratios (proguanil/cycloguanil) were highest in *1/*2 or *1/*3 subjects and in *2/*2 or *2/*3 as compared to *1/*1 subjects. Subjects with promoter region variation -98T>C showed decrease in the metabolic ratios irrespective of other variation, which may explain the deviation from the genotype-phenotype association of CYP2C19. In silico analysis predicted alteration in the interaction of transcription factors to their binding sites in the presence of variant alleles. The results of this study would be useful in predicting interindividual differences in the metabolism of substrates of CYP2C19.
Trimethylaminuria is caused by excessive malodorous trimethylamine excreted via urine and body secretion by decreased hepatic flavin-containing monooxygenase 3 (FMO3) metabolic capacity for transforming non-odorous trimethylamine N-oxide. This study investigates foodstuff first in healthy volunteers for palliative care for self-reported Japanese trimethylaminuria subjects. Urinary excretion of total trimethylamine in volunteers was determined by gas chromatography under daily food intake or after ingestion of selected fish premeasured for total trimethylamine content. Frequency of individuals showing apparently <40% FMO3 metabolic capacity was 3.8% in 365 Japanese volunteers who suffered from self-reported malodor. Bonitos, especially red flesh, had the lowest total trimethylamine content (~1 μmol per g tissue) among salmon, tuna, swordfish, sea bream or cod in this study. Mean excretion ratio of total trimethylamine in 8 h-urines from six healthy volunteers was approximately 90% after loading test by ingesting bonito (200 g) resulting in less than 2 μmol of free trimethylamine/mmol creatinine excreted in volunteers harboring high FMO3 metabolic capacity, in contrast to approximately 40% after ingestion of 200 g cod. These results in healthy volunteers suggest that bonito may be one of the best nutrient sources and palliative care for self-reported Japanese trimethylaminuria subjects.
Cytidine deaminase, encoded by the CDA gene, catalyzes anti-cancer drugs gemcitabine and ara-C into their respective inactive metabolites. In CDA, two functionally significant non-synonymous polymorphisms, 79A>C (Lys27Gln) and 208G>A (Ala70Thr), have been found and their minor allele frequencies (MAFs) were reported in Japanese and Chinese patients and a relatively small numbers of healthy volunteers in Caucasians and Africans. In this study, we determined the MAFs of both polymorphisms in 200 healthy volunteers of Koreans, along with 206 Japanese, 200 Chinese-Americans, 150 Caucasian-Americans and 150 African-Americans to reveal ethnic differences. MAFs of 79A>C (Lys27Gln) were 0.153 in Koreans and 0.327 in Caucasian-Americans, 0.204 in Japanese, 0.155 in Chinese-Americans and 0.087 in African-Americans. MAFs of 208G>A (Ala70Thr) were 0.005 in Koreans and 0.022 in Japanese and the minor allele was not detected in Chinese-Americans, Caucasian-Americans or African-Americans. Thus possibly, MAF of 208G>A in Japanese is likely to be somewhat higher than in Koreans and Chinese-Americans. These data would provide fundamental and useful information for pharmacogenetic studies on cytidine deaminase-catalyzing drugs.
Thiopurines (such as azathioprine and 6-mercaptopurine) are widely used for the treatment of patients suffering from malignancies, rheumatic disease, inflammatory bowel disease and solid organ transplant rejection. These drugs are activated and eliminated by a number of enzymes in the human body. This analyzes all the exons and exon-intron junctions of 5 enzyme genes (hypoxanthine-guanine phosphoribosyltransferase, HGPRT; inosine triphosphate pyrophosphatase, ITPA; inosine monophosphate dehydrogenases 1 and 2, IMPDH1 and IMPDH2 and guanosine monophosphate synthetase, GMPS) involved in the metabolism of thiopurine drugs. Twelve novel single nucleotide polymorphisms (SNPs) (HGPRT: IVS6-12C>A (frequency:0.003); ITPA: 569T>C (Phe189Phe, 0.003); IMPDH1: IVS8-15C>A (0.003), IVS9+227A>G (0.003), IVS17+115C>T (0.003), and 930C>T (Thr310Thr, 0.005); IMPDH2: IVS1+50G>T (0.003), IVS2+15G>A (0.010), IVS3-20G>A (0.003), 609C>T (Arg203Arg, 0.003), and 1534C>T (Arg512Trp, 0.003); and GMPS: 1563T>C (Gly521Gly, 0.003)) and 7 known SNPs (ITPA: 94C>A (Pro32Thr, 0.005), 138G>A (Gln46Gln, 0.586), and 563G>A (Glu187Glu, 0.433); IMPDH1: 987G>C (Leu329Leu, 0.113) and 1575A>G (Ala525Ala, 0.620) and GMPS: IVS5-7T>C (0.153), 993A>G (Thr331Thr, 0.153)) were identified in 200 Japanese subjects. These data should provide useful information for thiopurine therapy in the Japanese and as well as other Asian populations.
ATP7A and ATP7B are involved in cellular resistance to platinum compounds such as cisplatin. By sequencing ATP7A, 38 genetic variations, including 30 novel ones were detected from 203 Japanese cancer patients. Of these, seven nonsynonymous variations were found: novel 1030A>G (R344G), 2111A>G (Q704R), 2200C>A (Q734K), 2948C>T (T983M) and 3112G>A (V1038I) at 0.004 frequencies and known 2299G>C (V767L) and 4390A>G (I1464V) at 0.351 and 0.075 frequencies, respectively. Regarding ATP7B, 28 novel and 33 known genetic variations were detected including 13 nonsynonymous ones: novel 1258A>G (M420V), 1426G>A (A476T), and 2401A>C (T801P) were found at 0.002, 0.005, and 0.002, respectively and known 1216G>T (A406S), 1366G>C (V456L), 2495A>G (K832R), 2785A>G (I929V), 2855G>A (R952K), 2871delC (P957PfsX9), 3419T>C (V1140A), 3836A>G (D1279G), 3886G>A (D1296N) and 3889G>A (V1297I) at 0.483, 0.463, 0.387, 0.005, 0.384, 0.005, 0.387, 0.002, 0.012, and 0.015 frequencies, respectively. Linkage disequilibrium between detected variations was also analyzed. Our results would provide fundamental and useful information for genotyping ATP7A and ATP7B in the Japanese and probably other Asian populations.