Molybdenum hydroxylases, which include aldehyde oxidase and xanthine oxidoreductase, are involved in the metabolism of some medicines in humans. They exhibit oxidase activity towards various heterocyclic compounds and aldehydes. The liver cytosol of various mammals also exhibits a significant reductase activity toward nitro, sulfoxide, N-oxide and other moieties, catalyzed by aldehyde oxidase. There is considerable variability of aldehyde oxidase activity in liver cytosol of mammals: humans show the highest activity, rats and mice show low activity, and dogs have no detectable activity. On the other hand, xanthine oxidoreductase activity is present widely among species. Interindividual variation of aldehyde oxidase activity is present in humans. Drug-drug interactions associated with aldehyde oxidase and xanthine oxidoreductase are of potential clinical significance. Drug metabolizing ability of molybdenum hydroxylases and the variation of the activity are described in this review.

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  Cell lines which stably express reporter proteins through CYP3A4 gene activation have been developed for use in predicting CYP3A4 induction. Twelve clones showing distinct profiles on chemical-induced response were isolated. Among them, two clones showing high response for CYP3A4 inducers, namely clone 3-1-10 and 3-1-20, were further evaluated for their sensitivities, reproducibilities and applicabilities to predict CYP3A4 induction in human. Clone 3-1-10 showed higher response to rifampicin than to clotrimazole, whereas clone 3-1-20 had rather higher response to clotrimazole. Optimal plating density and highly reproducible response were observed at the range of 1.65-5.0×10⁴ cell/cm². Clear induction responses of more than ten chemicals were observed in both cell lines. The reporter activity was further dramatically increased after an introduction of human PXR. Induction with rifampicin was, however, not much altered between the absence and presence of hPXR. The luciferase activity remained unaltered and showed little fluctuation during the culture for more than 6 months.
   Due to the strikingly high sensitivity and reproducibility of this system, as compared to previously published systems, these HepG2-derived cell lines showing distinct response profiles as developed in the present study will offer high advantages for chemical screening of CYP3A4 inducibility.

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  The ATP-binding cassette transporter, ABCG2, which is expressed at high levels in the intestine and liver, functions as an efflux transporter for many drugs, including clinically used anticancer agents such as topotecan and the active metabolite of irinotecan (SN-38). In this study, to elucidate the linkage disequilibrium (LD) profiles and haplotype structures of ABCG2, we have comprehensively searched for genetic variations in the putative promoter region, all the exons, and their flanking introns of ABCG2 from 177 Japanese cancer patients treated with irinotecan. Forty-three genetic variations, including 11 novel ones, were found: 5 in the 5′-flanking region, 13 in the coding exons, and 25 in the introns. In addition to 9 previously reported nonsynonymous single nucleotide polymorphisms (SNPs), 2 novel nonsynonymous SNPs, 38C>T (Ser13Leu) and 1060G>A (Gly354Arg), were found with minor allele frequencies of 0.3%. Based on the LD profiles between the SNPs and the estimated past recombination events, the region analyzed was divided into three blocks (Block -1, 1, and 2), each of which spans at least 0.2 kb, 46 kb, and 13 kb and contains 2, 24, and 17 variations, respectively. The two, eight, and five common haplotypes detected in 10 or more patients accounted for most (>90%) of the haplotypes inferred in Block -1, Block 1, and Block 2, respectively. The SNP and haplotype distributions in Japanese were different from those reported previously in Caucasians. This study provides fundamental information for the pharmacogenetic studies investigating the relationship between the genetic variations in ABCG2 and pharmacokinetic/pharmacodynamic parameters.

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  Tacrolimus is a calcineurin inhibitor that has been widely used to prevent allograft rejection after transplantation. We report a case of a living-donor liver transplant recipient experiencing a considerable increase in the trough blood concentration of tacrolimus after concomitant ingestion of grapefruit juice (250 mL) 4 times for 3 days. The trough blood concentrations of tacrolimus were not changed during or immediate after the repeated intake of grapefruit juice. However, almost 1 week after the final ingestion, the blood concentration of tacrolimus markedly increased to as much as 47.4 ng/mL from 4.7 ng/mL before the ingestion, resulting in a profound reduction of calcineurin phosphatase activity in peripheral blood mononuclear cells. Furthermore, headache and nausea, but not nephrotoxicity or hyperglycemia, took place throughout the period of the elevated blood concentrations. Grapefruit juice may have a clinically significant effect on the pharmacokinetics and pharmacodynamics of tacrolimus. It is recommended to avoid the consumption of grapefruit juice in transplant recipients treated with tacrolimus.

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   The genotype frequencies of MDR1 T-129C, C1236T, G2677A,T and C3435T SNPs were compared in 154 healthy Japanese and 100 healthy Caucasians to provide basic information on the inter-ethnic differences of pharmacotherapeutic outcome. The variants were found at allelic frequencies of 5.5%, 65.6%, 16.6%, 40.6% and 40.6%, for T-129C, C1236T, G2677A, G2677T and C3435T, respectively, in Japanese, and at 5.1%, 45.9%, 3.6%, 46.4% and 56.6%, respectively, in Caucasians, with a statistically significant difference for C1236T, G2677A,T and C3435T (p<0.001). G2677A was about 5-fold more frequent in Japanese than Caucasians. These genotype frequencies were also investigated in 95 Japanese patients with colorectal cancer (CRC) and esophageal squamous cell carcinoma (ESCC), but no significant difference was detected, when compared with healthy Japanese subjects. The haplotype frequency reached a total of about 85% in Japanese with the following 4 major haplotypes;
  T^-129-T¹²³⁶-T²⁶⁷⁷-T³⁴³⁵ (36.1%), T^-129-T¹²³⁶-G²⁶⁷⁷-C³⁴³⁵ (22.5%),
  T^-129-C¹²³⁶-G²⁶⁷⁷-C³⁴³⁵ (14.2%) and T^-129-C¹²³⁶-A²⁶⁷⁷-C³⁴³⁵ (13.3%). The second and fourth haplotypes were hardly inferred in Caucasian, whereas T^-129-C¹²³⁶-G²⁶⁷⁷-T³⁴³⁵ (12.8%) was found to be Caucasian-specific. There was a tendency for higher frequencies of the T^-129/C-¹²⁹-C¹²³⁶-A²⁶⁷⁷-C³⁴³⁵ haplotype in Japanese CRC patients and T^-129-T¹²³⁶-T²⁶⁷⁷-T³⁴³⁵ haplotype in Japanese ESCC patients, compared with that in healthy Japanese subjects.

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  This study aimed to assess the steady-state pharmacokinetics of pranlukast, a leukotriene receptor antagonist, in children with allergic rhinitis and bronchial asthma, and to clarify factors affecting apparent clearance (CL/F). A total of 192 plasma samples were obtained from 98 children (rhinitis 64, asthma 13, complications 21), aged 3-14 years in 2 clinical trials. Plasma concentration of pranlukast was determined by liquid chromatography connected with a tandem mass spectrometer and analyzed by a population approach using NONMEM program. The plasma concentration-time course of pranlukast was described by using a one-compartment model with the first-order absorption and lag time. The robustness of the population pharmacokinetic model was evaluated by using 200 bootstrap samples. The results of population pharmacokinetic analysis showed that only age was a factor affecting the CL/F per body weight, with CL/F decreasing with increasing age. No significant variation was seen in the CL/F between rhinitis and asthma. The interindividual variability in the CL/F and the residual variability were 19.7% and 48.4%, respectively. All the parameters fell within 10% of the bootstrapped mean. In conclusion, the results show that age is the most influential factor for explaining interindividual variability in CL/F, and the difference in diseases does not affect CL/F.

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  To determine the pharmacokinetic properties of advanced oxidation protein products (AOPP), we prepared oxidized human serum albumin (oxi-HSA) using chloramine-T (a hypochlorite analogue) in vitro. The AOPP and dityrosine content of oxi-HSA (AOPP content, 244.3±12.3 μM; dityrosine content, 0.7±0.11 nmol of dityrosine/mg protein) were similar to those of uremic patients. In structural analysis, the increases in AOPP and dityrosine content of HSA induced slight decreases in its α-helical content. In pharmacokinetic analysis, oxi-HSA left the circulation rapidly, and organ distribution of oxi-HSA 30 min after intravenous injection was 51% for the liver, 23% for the spleen, and 9% for the kidney, suggesting that the liver and spleen were the main routes of plasma clearance of oxi-HSA. The liver and spleen uptake clearance of oxi-HSA were significantly greater than those of normal HSA (CLliver, 5058±341.6 vs 24±4.2 μL/hr [p<0.01]; CLspleen, 2118±322.1 vs 32±2.7 μL/hr [p<0.01]). However, uptake by other organs was not significantly affected by oxidation. These results suggest that the liver and spleen play important roles in elimination of AOPP.

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  Metabolism of nafamostat, a clinically used serine protease inhibitor, was investigated with human blood and liver enzyme sources. All the enzyme sources examined (whole blood, erythrocytes, plasma and liver microsomes) showed nafamostat hydrolytic activity. V_max and K_m values for the nafamostat hydrolysis in erythrocytes were 278 nmol/min/mL blood fraction and 628 μM; those in plasma were 160 nmol/min/mL blood fraction and 8890 μM, respectively. Human liver microsomes exhibited a V_max value of 26.9 nmol/min/mg protein and a K_m value of 1790 μM. Hydrolytic activity of the erythrocytes and plasma was inhibited by 5, 5′-dithiobis(2-nitrobenzoic acid), an arylesterase inhibitor, in a concentration-dependent manner. In contrast, little or no suppression of these activities was seen with phenylmethylsulfonyl fluoride (PMSF), diisopropyl fluorophosphate (DFP), bis(p-nitrophenyl)phosphate (BNPP), BW284C51 and ethopropazine. The liver microsomal activity was markedly inhibited by PMSF, DFP and BNPP, indicating that carboxylesterase was involved in the nafamostat hydrolysis. Human carboxylesterase 2 expressed in COS-1 cells was capable of hydrolyzing nafamostat at 10 and 100 μM, whereas recombinant carboxylesterase 1 showed significant activity only at a higher substrate concentration (100 μM). The nafamostat hydrolysis in 18 human liver microsomes correlated with aspirin hydrolytic activity specific for carboxylesterase 2 (r=0.815, p<0.01) but not with imidapril hydrolysis catalyzed by carboxylesterase 1 (r=0.156, p=0.54). These results suggest that human arylesterases and carboxylesterase 2 may be predominantly responsible for the metabolism of nafamostat in the blood and liver, respectively.

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  The hepatic extraction of metoprolol is reduced in rats with bilateral ureter ligation (BUL)-induced renal failure. The aim of the present study was to evaluate the effect of uremic substances on the hepatic metabolism of metoprolol in rats with BUL. The metabolic rate in the liver microsomes of BUL rats was similar to that in sham rats, and there was no significant difference between sham and BUL rats in the effect of the supernatant of liver homogenates on the metabolism. The rate of metabolism in the liver microsomes in the presence of the plasma of BUL rats was also similar to that in the presence of the plasma of sham rats. These findings indicated that uremic substances which accumulate in BUL rats do not directly inhibit the activity of CYP2D2, which is responsible for the metabolism of metoprolol in the rat liver.

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  OATP8, a member of the organic anion-transporting polypeptide family, is expressed on the sinusoidal membrane of hepatocytes, and transports endogenous organic anions, such as 17β-glucuronosyl estradiol, and xenobiotic substances, such as digoxin. The objective of this study is to search for polymorphisms of the OATP8 gene and to assess the allele frequency of the polymorphisms in the Japanese population.
   Analysis of the OATP8 gene in 79 subjects revealed complete linkage of two deletion polymorphisms in the 5′ regulatory region, deletion from position -28 to -11 and deletion from position -7 to -4, with an allele frequency of 0.196 for the deletion allele. The polymorphisms T334G (Ser112Ala) and G699A (Met233Ile) were also shown to be in complete linkage disequilibrium, with an allele frequency of 0.728 for the variant (112Ala/233Ile) allele. Interestingly, linkage disequilibrium was identified between the ins/del polymorphism and SNPs at 112 and 233. The predicted major haplotype was the insert-variant type with a haplotype frequency of 0.60.

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