A variety of carbonyl compounds are present in foods, environmental pollutants, and drugs. These xenobiotic carbonyl compounds are metabolized into the corresponding alcohols by many mammalian NAD(P)H-dependent reductases, which belong to the short-chain dehydrogenase/reductase (SDR) and aldo-keto reductase superfamilies. Recent genomic analysis, cDNA isolation and characterization of the recombinant enzymes suggested that, in humans, the six members of each of the two superfamilies, i.e., total of 12 enzymes, are involved in the reductive metabolism of xenobiotic carbonyl compounds. They comprise three types of carbonyl reductase, dehydrogenase/reductase (SDR family) member 4, 11β-hydroxysteroid dehydrogenase type 1, L-xylulose reductase, two types of aflatoxin B1 aldehyde reductase, 20α-hydroxysteroid dehydrogenase, and three types of 3α-hydroxysteroid dehydrogenase. Accumulating data on the human enzymes provide new insights into their roles in cellular and molecular reactions including xenobiotic metabolism. On the other hand, mice and rats lack the gene for a protein corresponding to human 3α-hydroxysteroid dehydrogenase type 3, but instead possess additional five or six genes encoding proteins that are structurally related to human hydroxysteroid dehydrogenases. Characterization of the additional enzymes suggested their involvement in species-specific biological events and species differences in the metabolism of xenobiotic carbonyl compounds.
The mRNA levels of human cytochrome P450 (CYP)2Cs and CYP3As in primary cultures of freshly isolated human hepatocytes were assessed after exposure to NO-1886 and rifampicin, a typical inducer of CYP3As. mRNA levels were analyzed by real-time RT-PCR using an ABI PRISM 7700 Sequence Detector system. Exposure to NO-1886 for 24 hr at a concentration of less than 10 μM showed only a tendency to reduce or increase the expression levels of CYP2C8, CYP2C9, CYP2C19, CYP3A4, or CYP3A5 mRNA. A higher concentration (50 μM) of NO-1886 induced an increase in CYP2C8 mRNA and a decrease in CYP2C19 mRNA, and these changes continued after additional culture for 24 hr in fresh medium without NO-1886. The expression level of CYP3A4 mRNA after exposure to NO-1886 for 24 hr at 50 μM was about twice that in controls. Following additional culture for 24 hr in fresh medium without NO-1886, the expression of CYP3A4 mRNA was comparable to that in controls. On the other hand, the expression levels of CYP2C9 and CYP3A5 mRNA showed small and variable changes in each donor even at a high concentration (50 μM) of NO-1886. Furthermore, the pharmacokinetics of NO-1886 during repeated oral administration for 14 days was studied in female rats. The pharmacokinetic parameters of NO-1886 were nearly the same on days 1, 7, and 14 of repeated administration. The hepatic microsomal content of CYP isoforms was not affected by repeated administration for 7 days at a dose of 1 to 30 mg/kg in female rats, although the total CYP content was increased at a dose of 30 mg/kg. The expression levels of CYP1A2, CYP2B2, CYP2C12, and CYP2E1 mRNA in primary cultures of rat hepatocytes were not affected by exposure to NO-1886 at 2, 10, or 50 μM. The expression levels of CYP3A1 mRNA in primary cultures of rat hepatocytes were not affected by exposure to NO-1886 at 2 or 10 μM, but were increased, with large individual variation, by exposure at 50 μM. The mRNA expression levels in rat hepatocytes exposed to concentrations comparable to free plasma levels did not change significantly, which was consistent with the equivalence in the in vivo plasma concentrations observed on days 1 and 14 of repeated administration. These results suggest that repeated administration of NO-1886 at clinical doses does not significantly affect the expression levels of CYP isoforms in human liver, although the mRNA levels of the CYP isoforms involved in the metabolism of NO-1886 were increased by exposure to higher concentrations of NO-1886 in human hepatocytes in vitro.
The constitutive expression of CYP2D9 is sexually dimorphic, namely, strong in males, but diminutive in females. Repetition of mimic growth hormone (GH) secretion pattern impressively returned the mRNA expression level to that in intact mice: the GH secretion pattern's regulation of CYP2D9 mRNA expression has been predominantly disrupted by exogenous GH-administration. The extensive decline of CYP2D9 mRNA expression becoming a sexually non-specific P450 in 9-week-old male mice exposed as neonates to monosodium L-glutamate (MSG) suggested that the male GH secretion pattern is a key to the regulation of male-specific CYP2D9 mRNA expression in adult mice. Dexamethasone (Dex) showed possibility to induce CYP2D9 mRNA expression in adult MSG-neonatally treated mice of either sex. However, the antagonism was observed by co-administration of Dex and GH in the males. Dex-administration in adrenalectomized mice significantly elevated CYP2D9 mRNA expression levels. These findings suggest that an adrenal hormone participates in the regulatory mechanism of CYP2D9 mRNA expression in association with GH.
In order to evaluate the efficacy of liposomes as a drug carrier for atherosclerotic therapy, a pharmacokinetic analysis of the uptake of liposomes by macrophages and foam cells in vitro and their distribution to atherosclerotic lesions in mice was carried out. In brief, liposomes of three particle sizes (500, 200 and 70 nm) were prepared, and the uptake of liposomes by these cells in vitro and the aortic distribution following intravenous administration to atherogenic mice were examined. The internalization rate constant calculated by measuring uptake and binding was size-dependent in both types of cells in vitro. The aortic clearance (CLa) was size-independent in atherogenic mice and the CLa of 200 nm particles was the highest. Surprisingly, the aortic distribution in vivo did not correspond with the internalization to macrophages and foam cells in vitro. These results suggest that there is an optimal size for the distribution of liposomes to atherosclerotic lesions.
We used ibuprofen as a poorly water soluble model drug, to examine the influence of bile salts and mucin layers on the permeability of that entrapped in an O/W microemulsion, in a rat isolated intestinal membrane by the Ussing chamber method. Under the presence of 3 kinds of the primary bile salts such a sodium taurocholate, etc., or a secondary bile salt such a sodium taurochenodeoxycholate at 0.01 mmol/L concentration, a significant difference was not demonstrated in the permeation clearance of the ibuprofen entrapped O/W microemulsion, as compared with the case without the bile salts. Thus, the bile salts did not have a remarkable influence on the permeability of the drug entrapped in the O/W microemulsion, and it was verified that this O/W microemulsion was hardly influenced by the flow of the bile secretion. On the other hand, when N-acetyl-L-cysteine (NAC) with the removal ability of a mucin layer was combined with the ibuprofen entrapped O/W microemulsion at the concentration of 3 and 10 mmol/L, it was shown that the permeation clearance of free ibuprofen did not decrease, but that of ibuprofen entrapped in the O/W microemulsion decreased with the increase of the NAC concentration. Therefore, it is confirmed that the mucin layer participates in the permeability of the drug entrapped in the O/W microemulsion. From these results, the mechanism in which the drug entrapped in the O/W microemulsion is released in a mucin layer, without passing through the route of the mixed micelle formation by bile, thereafter the drug permeates an intestinal membrane, is supposed.
The clinical efficacy of Maeda's nomogram for vancomycin dosage adjustment was evaluated by comparison with a standard dosage regimen (package insert information: vancomycin dose reduced in elderly patients and patients with renal dysfunction, with Moellering's nomogram used for renal-dysfunction patients) in adult Japanese MRSA pneumonia patients. Using Maeda's nomogram, the vancomycin dose is fixed at 1,000 mg while the dosing interval is varied in accordance with individual creatinine clearance. Using a standard dosage regimen, 5 patients out of 27 (18.5%) achieved target plasma levels of vancomycin (25-40 μg/mL for peak and 5-15 μg/mL for trough) within 2-6 days. Using Maeda's nomogram, 38 patients out of 53 (71.7%) achieved target levels in that time. A higher clinical response (complete resolution of all signs and symptoms of MRSA infection) to vancomycin therapy was also obtained with Maeda's nomogram when evaluated approximately 2-weeks after discontinuation of vancomycin therapy (43.4% versus 18.5% for the standard regimen). In conclusion, the Maeda's nomogram regimen with a 1,000 mg vancomycin dose was shown to achieve target plasma levels of vancomycin at a higher rate and provide higher clinical efficacy in vancomycin therapy of MRSA pneumonia patients, as compared with the currently available standard dosage regimen.
Repinotan is a selective full serotonin receptor agonist at the 5-HT1A subtype which has been studied in phase I and II studies involving over 500 healthy subjects and patients. Repinotan is primarily metabolized by CYP2D6 which is known to be subject to polymorphism and ethnic differences in its quantitative and qualitative expression pattern. In order to investigate the effect of ethnicity on repinotan pharmacokinetics (PK) between a Caucasian and Japanese population and to explain PK variability, this population PK evaluation was conducted. A population PK model was established based on the data of 1314 blood samples from 241 patients from 3 Phase II studies. This analysis has characterized the repinotan PK, with particular attention to ethnicity. Using the MIXTURE subroutine of NONMEM, evidence was provided for different CL groups. Repinotan plasma levels in the ‘High CL’ subgroup, which comprised the majority of patients, did not show relevant differences between a Japanese and Caucasian population. In the ‘Low CL’ subgroup, Japanese and Caucasian populations were different. These findings are consistent with the published literature, which reports ethnic differences in the distribution of CYP2D6 activity. The finding of a greater percentage of patients with intermediate CL in the Japanese population falling between poor and extensive metabolizers is consistent with the distribution pattern of CYP2D6 in the Japanese population. The results of this evaluation can be used to assist in designing future trials.
Expression of UDP-glucuronosyltransferases (UGT) in mammals is thought to be regulated in both a tissue- and developmental-specific manner. Furthermore, induction of genes encoding UGT occurs after exposure to xenobiotics including drugs, environmental pollutants and dietary compounds. In human, isoforms of UGT 1A subfamily catalyze the glucuronidation of a greater proportion of drugs, suggesting that the expression of UGT1A isoforms is responsible for the clearance of a diverse range of drugs. To analyze the expression of human UGT1A isoforms, we have developed polyclonal antibodies against specific peptide regions within the isoforms (UGT1A1, 1A3, 1A4, 1A6 and 1A9). The prepared antipeptide antibodies were found to be highly monospecific for each UGT1A isoform and no cross-reactivity with UGT2B isoforms was detected. Analysis of UGT1A protein levels in hepatic microsomes using these antibodies demonstrated interindividual differential expression of each isoform. These highly specific antipeptide antibodies provide an important tool to analyze tissue distribution and interindividual expression levels of human UGT1As.
We sequenced exon 1 of the UDP-glucuronosyltransferase (UGT) 1A7 gene from 52 Japanese cancer patients. Four single nucleotide polymorphisms (SNPs) were found. Three of them caused UGT1A7*2 and UGT1A7*3. A novel SNP (98973G>C) causing amino acid substitution (Ser141Cys) was found. The sequence is as follows: SNP, 050824FujitaK002; GENE NAME, UGT1A7; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5′-TAAAGGAGAGTTG/CTTTTGATGCAGT-3′. One out of 52 cancer patients was heterozygous for the variant allele, resulting in the allele frequency of 0.96%. The patient did not possess UGT1A7*2 or UGT1A7*3.
We sequenced from 5′-franking region to intron 1 (to 337 bp downstream from exon 1) of the UDP-glucuronosyltransferase (UGT) 1A9 gene prepared from 55 Japanese cancer patients. Seven single nucleotide polymorphisms (SNPs) were found. Two of them were UGT1A9 -118(T)n (n=10) and UGT1A9*5, and four were reported SNPs in intron 1 of UGT1A9 gene (89540C>T, 89549G>A, 89616T>A and 89710A>C). A novel SNP (89587T>C) was found. The sequence is as follows: SNP, 050824FujitaK001; GENE NAME, UGT1A9; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5′-CCTTCTTGAAGAT/CATGTATTTATAA-3′. Two patients were heterozygous for the mutant allele, resulting in the allele frequency of 1.82%.