Studies of the genetic regulation involved in drug metabolizing enzymes and drug transporters are of great interest to understand the molecular mechanisms of drug response and toxic events. Recent reports have revealed that hydrophobic ligands and several nuclear receptors are involved in the induction or down-regulation of various enzymes and transporters involved in Phase I, II, and III xenobiotic metabolizing systems. Nuclear receptors (NRs) form a family of ligand-activated transcription factors (TFs). These proteins modulate the regulation of target genes by contacting their promoter or enhancer sequences at specific recognition sites. These target genes include metabolizing enzymes such as cytochrome P450s (CYPs), transporters, and NRs. Thus it was now recognized that these NRs play essential role in sensing processing xenobiotic substances including drugs, environmental chemical pollutants and nutritional ingredients. From literature, we picked up target genes of each NR in xenobiotic response systems. Possible cross-talk, by which xenobiotics may exert undesirable effects, was listed. For example, the role of NRs was comprehensively drawn up in cholesterol and bile acid homeostasis in human hepatocyte. Summarizing current states of related research, especially for in silico response element search, we tried to elucidate nuclear receptor mediated xenobiotic processing loops and direct future research.

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  A bootstrap method is proposed for assessing statistical histograms of pharmacokinetic parameters (AUC, MRT, CL and V_ss) from one-point sampling data in animal experiments. A computer program, MOMENT(BS), written in Visual Basic on Microsoft Excel, was developed for the bootstrap calculation and the construction of histograms. MOMENT(BS) was applied to one-point sampling data of the blood concentration of three physiologically active proteins (¹¹¹In labeled Hsp70, Suc₂₀-BSA and Suc₄₀-BSA) administered in different doses to mice. The histograms of AUC, MRT, CL and V_ss were close to a normal (Gaussian) distribution with the bootstrap resampling number (200), or more, considering the skewness and kurtosis of the histograms. A good agreement of means and SD was obtained between the bootstrap and Bailer's approaches. The hypothesis test based on the normal distribution clearly demonstrated that the disposition of ¹¹¹In-Hsp70 and Suc₂₀-BSA was almost independent of dose, whereas that of ¹¹¹In-Suc₄₀-BSA was definitely dose-dependent. In conclusion, the bootstrap method was found to be an efficient method for assessing the histogram of pharmacokinetic parameters of blood or tissue disposition data by one-point sampling.

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  We investigated and compared the expression of human CYPs mRNA in primary cultures of cryopreserved human hepatocytes and in chimeric mice constructed by transplanting hepatocytes from the same human donors. Analysis was performed by real-time reverse-transcription polymerase chain reaction. Initial expression levels for the 12 human CYPs mRNA in chimeric mouse hepatocytes were higher than those in human hepatocytes, but a low correlation coefficient was observed (r=0.690). After 24 h of culture, the correlation remained low (r=0.699). The medium was replaced with fresh medium without human epidermal growth factor, and after 48 h of culture, expression of the 12 human CYPs mRNA were very similar in human hepatocytes and chimeric mouse hepatocytes, and a higher correlation coefficient was observed (r=0.809). After 72 h of culture, the correlation remained high (r=0.873). The ratio of human CYP1A2 mRNA to β-actin mRNA in chimeric mouse hepatocytes decreased quickly during the first 24 h of culture, and then remained constant. Expression profiles of human CYP1A2 mRNA in chimeric mouse hepatocytes were similar to those in human hepatocytes after exposure of β-naphthoflavone. CYP3A4 mRNA expression was increased significantly by rifampicin (Rif) exposure in human hepatocytes, whereas Rif-induced increases in CYP3A4 mRNA expression in chimeric mouse hepatocytes was seen for two of the three donors. In conclusion, we demonstrated that expression and induction of human CYPs in human hepatocytes can be reproduced in chimeric mouse hepatocytes.

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  The association between the distribution characteristics of CYP2A6 catalytic activities toward nicotine and coumarin, and the frequency distribution of CYP2A6 variant alleles reported was estimated in 120 healthy Thais. The distributions of the subjects as classified by the amounts of 7-hydroxycoumarin (7-OHC) excreted in the urine and by cotinine/nicotine ratio in the plasma were clearly bimodal. However, the numbers of apparently poor metabolizers for coumarin and nicotine were different. The inter-individual variability in the in vivo dispositions of coumarin and nicotine closely related to the CYP2A6 genetic polymorphism. There was a close correlation between the rate of 7-OHC excretion in the urine and cotinine/nicotine ratio in the plasma among subjects (R=0.92, p<0.001). The frequency of CYP2A6 allele found in the present study was: CYP2A6*1A=32% (95% CI, 22.1-39.4%), CYP2A6*1B=27% (95% CI, 19.4-33.5%), CYP2A6*9=20% (95% CI, 17.6-23.3%), CYP2A6*4=14% (95% CI, 9.6-17.8%), CYP2A6*7=5% (95% CI, 3.7-9.4%), CYP2A6*10=2% (95% CI, 0.8-5.1%). Subjects having CYP2A6*1A/*1B were found to have a higher rate of 7-OHC excretion, as well as a higher cotinine/nicotine ratio in the plasma compared with those of the other genotypes. In contrast, subjects with CYP2A6*4/*7 and CYP2A6*7/*7 almost lacked any cotinine formation, whereas urinary 7-OHC was still detectable. CYP2A6*9 allele clearly resulted in reduced enzyme activities. Despite the absence of the homozygote for CYP2A6*10 allele, the presence of CYP2A6*10 allele significantly decreased the enzyme activities. The results of the present study demonstrate that in vivo phenotyping of CYP2A6 using nicotine and coumarin are not metabolically equivalent. Nicotine is a better probe according to its specificity, while coumarin is still valuable to be used for a routine CYP2A6 phenotyping since the test employs a non-invasive method.

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  The in vivo metabolism of methotrexate (MTX) to 7-hydroxymethotrexate (7-OH-MTX) was studied using four strains of rats. When MTX was administered to these rats, 7-OH-MTX was detected as the major in vivo metabolite, mainly in bile and feces, and also slightly in the urine. There were marked strain differences in the amounts of 7-OH-MTX excreted in bile, feces and urine. The highest recovery of 7-OH-MTX in bile, feces and urine was observed in Sea:SD rats (6.2%, 4.2% and 0.8% of dose, respectively), followed by Jcl:SD and Crj:SD rats. The lowest recovery (0.02%, 0.2% and 0.003%, respectively) was observed in WKA/Sea rats. The variations of excreted amount of 7-OH-MTX were closely correlated with the strain differences of cytosolic MTX 7-hydroxylase and benzaldehyde oxidase activities. Our results indicate that variation of formation of 7-OH-MTX from MTX in vivo in rats is due primarily to variation of aldehyde oxidase.

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  Pancreatic islet transplantation is a curable treatment for type 1 diabetes and has been put into practice in various countries. In this study, we analyzed the pharmacokinetic characteristics of sirolimus and tacrolimus in six Japanese patients with pancreatic islet transplants immediately after surgery, and monitored efficacy and toxicity. The patients were treated with immunosuppressive therapy based on the Edmonton protocol, that is, sirolimus and low-dose tacrolimus. Pharmacokinetic analyses were performed using the nonlinear mixed-effects modeling program NONMEM. Large inter- and intra-individual variability was observed in the pharmacokinetics of sirolimus and tacrolimus. A model with increased apparent clearance in the postoperative period explained well the intra-individual variability in the pharmacokinetics of both drugs. The most frequent drug-induced toxicity was a decrease in the white blood cell count, and two of six patients required the administration of granulocyte colony-stimulating factor. Clinical laboratory tests immediately before the transplantation and cytochrome P450 3A5 genotype were not related to the high blood concentrations of sirolimus after the loading dose. From these results, the apparent clearance of sirolimus and tacrolimus might temporally decline immediately after pancreatic islet transplantation. A high trough concentration of sirolimus might increase the risk of hematological toxicy, and adjustment of the dosage for immunosuppressive treatment will be necessary in Japanese patients.

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  Amiodarone has pharmacokinetic interactions with a number of therapeutic drugs, including warfarin, phenytoin, flecainide, and cyclosporine. Metoprolol is mainly metabolized by CYP2D6, and desethylamiodarone, a metabolite of amiodarone, has a markedly greater inhibitory effect on CYP2D6 than amiodarone. Therefore, the goal of this study was to evaluate the effect of amiodarone and desethylamiodarone on the serum concentration/dose ratio (C/D) of metoprolol in 120 inpatients with cardiac arrhythmias that received either metoprolol and amiodarone (MET+AMD group, n=30) or metoprolol alone (MET group, n=90). The ratio of administered metoprolol was compared between the MET and the MET+AMD groups. The dose of metoprolol and patient age were significantly higher in the MET group when compared with the MET+AMD group (1.00±0.480 versus 0.767±0.418 mg/kg/day, p<0.050; 68.6±10.6 versus 57.6±14.1 years, p<0.001, respectively), but the C/D ratio was significantly lower in the MET group than in the MET+AMD group (90.8±64.0 versus 136±97.8, p<0.01). Furthermore, a significant correlation was found between the C/D ratio and desethylamiodarone concentration (n=30, r=0.371, p<0.01). The results suggest that there is a significant interaction between amiodarone and metoprolol via desethylamiodarone-induced inhibition of CYP2D6. Therefore, careful monitoring of metoprolol concentrations/bioactivity of CYP2D6 is required in the context of co-administration of amiodarone and metoprolol.

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  The allele and genotype frequencies of MDR1 C3435T polymorphism were determined in 185 unrelated healthy Tamilians. The genomic DNA was extracted from peripheral leucocytes using phenol chloroform method and genotyped by PCR-RFLP method. The frequencies of MDR1 C3435 and T3435 alleles in Tamilian population were 0.46 and 0.54 respectively. The distribution of T3435 in this population was found to be greater than Africans and almost similar to Caucasians and Orientals. The distribution of CC, CT and TT genotypes was 0.18, 0.56 and 0.26 respectively. The frequency distribution of the CC genotype was lower in them when compared with Chinese and Africans whereas CT genotype was higher in comparison with all the major ethnic groups.

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  Forty genetic variations including 14 novel ones were found in the human TYMS gene, which encodes thymidylate synthase, in 263 Japanese cancer patients who received 5-fluorouracil (FU)-based chemotherapy. Three novel variations were located within the 28-bp tandem repeat sequence in the 5′-untranslated region (UTR) and were designated 5Rc, 3Rc-ins and 4Rc. Allele frequencies were 0.021 for 5Rc, 0.006 for 3Rc-ins and 0.002 for 4Rc. Other novel variations included -133G>C and -125G>C in the 5′-UTR; IVS1-278G>A, IVS2-68C>T, IVS2-23T>C, IVS4+122_+123insATTG, IVS4-141G>A, IVS5-100A>T and IVS6-111G>A in the introns; and 1244(*302)A>G and 1264(*322)G>A in the 3′-UTR. The allele frequencies were 0.34 for IVS4+122_+123insATTG, 0.042 for -133G>C, 0.011 for IVS4-141G>A, 0.006 for -125G>C, 0.004 for IVS1-278G>A, IVS2-68C>T, 1244(*302)A>G and 1264(*322)G>A, and 0.002 for IVS2-23T>C, IVS5-100A>T and IVS6-111G>A. Using the detected polymorphisms, linkage disequilibrium (LD) analysis was performed, which divided the TYMS gene into three LD blocks. The 28-bp tandem repeat sequence in the 5′-UTR was assigned as Block 2 with a total of 7 alleles. In Blocks 1 and 3, 7 and 19 haplotypes were determined/inferred, respectively. Our findings provide fundamental and useful information for genotyping TYMS in the Japanese and probably other Asian populations.

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