Cyclosporin A (CsA) causes a number of clinically relevant drug–drug interactions (DDIs) by inhibiting OATP1B1 and OATP1B3. In the present study, long-lasting inhibitory effects of CsA on these transporters were examined in comparison to tacrolimus (TCR). OATP1B1- and OATP1B3-expressing HEK293T cells, OATP1B1-expressing MDCK II cells, and human hepatocytes were preincubated with CsA or TCR, and uptake studies were carried out in their presence or absence. Western blot or immunohistochemical studies were done in OATP1B1-expressing HEK293T cells. The pretreatment of OATP1B1- and OATP1B3-expressing cells with 0.5–10 µM CsA, but not TCR, resulted in a reduction in their activity, even after washing out CsA from the incubation media. Preincubating the cells with CsA significantly enhanced its inhibitory effects on OATP1B1 and OATP1B3 by coincubation at 0.1–1 µM. Preincubation with 1 µM CsA caused a reduction in OATP1B1 activity for at least 18 h after its removal. The expression of OATP1B1 was not affected by incubation with CsA and no obvious change in its intracellular localization was observed. The long-lasting inhibition by CsA was also observed in human hepatocytes. Thus, CsA has a long-lasting inhibitory effect on OATP1B1 and OATP1B3. It may attribute to the clinically relevant DDIs between OATP substrates and CsA.
In the present study, amorphous solid dispersion (ASD) formulations of tranilast (TL) with 8 hydrophilic polymers were prepared by a solvent evaporation method with the aim of improving dissolution behavior in gastric fluid and thereby enhancing oral bioavailability. The physicochemical properties were characterized with a focus on morphology, crystallinity, thermal behavior, dissolution, drug-polymer interaction, and stability. Of all TL formulations, ASD formulation with Eudragit EPO exhibited the highest improvement in dissolution behavior with a 3,000-fold increase in the first-order dissolution rate under acidic conditions (pH 1.2). Spectroscopic studies using infrared and near-infrared analyses revealed the drug-polymer interaction in the Eudragit EPO-based ASD formulation. On the basis of dissolution, crystallinity, and stability data, the maximum allowable drug load in the Eudragit EPO-based ASD formulation was deduced to be ca. 50%. Pharmacokinetic profiling of orally dosed TL formulations in rats was also carried out using UPLC/ESI-MS. After oral administration of the Eudragit EPO-based ASD formulation in rats, enhanced TL exposure was observed with an increase of oral bioavailability by 19-fold, and the variation of AUC was ca. 4 times lower than that with crystalline TL. With these data, the ASD approach could be a viable formulation strategy for enhancing the wettability and oral bioavailability of TL, resulting in improved therapeutic potential of TL for the treatment of inflammatory diseases.
UDP-glucuronosyltransferases (UGTs) are glycoproteins in endoplasmic reticulum membranes. UGT2B7 is an important UGT isoenzyme expressed in human liver and glucuronidates various endogenous and exogenous substances. Although this enzyme has three potential N-glycosylation sites (asparagine at positions 67, 68 and 315), no information is available on the actual glycosylated sites and the effects of N-glycosylation on its enzymatic functions. We thus constructed HEK293 cells expressing wild-type UGT2B7 and five mutants (N67Q, N68Q, N315Q, N68Q/N315Q and N67Q/N68Q/N315Q) in which an asparagine at one or more potential N-glycosylation sites was substituted with a glutamine. An immunoblot analysis of whole cell lysate (S9) fractions with or without treatment with an endoglycosidase revealed that UGT2B7 was N-glycosylated at Asn-68 and Asn-315 but not Asn-67. Kinetic analysis employing the S9 fractions as enzyme sources and zidovudine (AZT) and morphine as typical substrates demonstrated that the abolition of N-glycosylation decreased the affinity for AZT but increased that for morphine without affecting reaction velocities, while it decreased the affinity for UDPGA as a cofactor regardless of the substrate used. These results suggest that N-glycosylation differentially affects the glucuronidation of AZT and morphine by human UGT2B7.
Distinctive response patterns of CYP3A4 and CYP3A7 to cobalt chloride (CoCl2) in human fetal liver (HFL) cells were observed and compared with those under hypoxic conditions. The expression levels of CYP3A4 and CYP3A7 mRNAs were decreased by CoCl2 and hypoxia, although significance could not be determined in HFL cells cultured under 3% O2. The hypoxia-inducible factor-1α (HIF-1α) protein content in HFL cells was significantly increased by CoCl2 and 3% O2. Transcriptional activities of CYP3A4 and CYP3A7 were not altered by 3% O2 when reporter plasmids containing the promoter region ranging up to about 10 kb and 12 kb upstream, respectively, were transfected into HFL cells, although the activity was significantly suppressed by CoCl2. These results suggested that the mechanisms controlling CYP3A gene expression of HIF-1α chemical stabilizer in fetal hepatocytes might be different from those in adult hepatocytes, and that HIF-1α is not directly involved in regulation of CYP3A4 or CYP3A7 expression.
Cytochrome P450 2D6 (CYP2D6), which has a large number of genetic polymorphisms, is involved in the metabolism of a wide range of substrates. Dextromethorphan (DM) is a well-known probe drug for CYP2D6 and metabolic ratio (MR) is often used to measure the enzyme activity in vivo. Using the literature values of DM MR, we estimated the inter-individual variability of CYP2D6 hepatic intrinsic clearance (CLint,h,2D6) in each genotype by Monte Carlo simulation and found that the homozygote of CYP2D6*1 and the heterozygote of CYP2D6*1 and null alleles had a coefficient of variation (CV) of 43% and 56%, respectively. The variability of homozygotes of CYP2D6*2 and CYP2D6*10 was 63% and 66%, while that of the heterozygotes of CYP2D6*2 and null alleles and CYP2D6*10 and null alleles was 125% and 109%, respectively. Based on the variability and reported frequency of the CYP2D6 genotype in Asians and Caucasians, the inter-individual variability of CLint,h,2D6 of extensive metabolizers was estimated at 60–70%, which provided comparable variability of AUC with the literature values of DM, tolterodine, risperidone and atomoxetine. It is suggested that the produced inter-individual variability of CLint,h,2D6 in each genotype is useful for estimating AUC variability of the CYP2D6 substrates in the regional population.
The aim of this study was to evaluate the influence of CYP3A5 and ABCB1 gene polymorphisms on fentanyl pharmacokinetics and clinical responses in cancer patients undergoing conversion to a transdermal system. Sixty Japanese cancer patients being treated with a fentanyl transdermal reservoir system according to the current Japanese guidelines were enrolled. Blood samples were obtained 192 h after conversion to the fentanyl transdermal system. Clinical responses after fentanyl application were evaluated by determining the incidences of adverse effects and rescue medication. The plasma concentration of fentanyl normalized with the measured absorption rate was significantly higher in the CYP3A5*3/*3 group than in the *1/*1 and *1/*3 groups (p = 0.048 and 0.021, respectively). Greater incidences of central adverse effects were observed in CYP3A5*3/*3 patients than in *1/*1+*1/*3 patients (odds ratio [OR], 3.49; 95% confidence interval [95% CI], 1.13–10.75; p = 0.029). Fewer patients with the ABCB1 1236TT allele than the 1236C allele needed rescue medication (OR, 0.17; 95% CI, 0.03–0.89; p = 0.036). CYP3A5*3 affected the pharmacokinetics of fentanyl and increased the incidence of central adverse effects. ABCB1 1236TT was associated with decreased administration of rescue medication after switching to the transdermal fentanyl system. In conclusion, these gene polymorphisms may predict clinical responses to fentanyl in cancer patients being converted to the transdermal system.
Clinical studies were conducted to investigate the pharmacokinetics of roxatidine acetate hydrochloride capsules (ALTAT® CAPSULES) in children. In a single-dose pharmacokinetic (PK) study in pediatric patients aged between 6 and 14 years with acid-related diseases, 37.5 mg or 75 mg roxatidine capsules were given orally, and blood samples were collected to determine the plasma roxatidine concentrations. Meanwhile, a single-dose PK study in healthy adult volunteers was newly conducted; subjects were given 37.5 mg, 75 mg or 150 mg roxatidine capsules. Differences were present between the PK parameters in pediatric patients and those in healthy adult volunteers. However, the CL/F and Vd/F adjusted by body surface area (BSA) or body weight (BW) were comparable. A close correlation of the Cmax and AUC0–∞ to the dose per unit BSA (mg/m2) or BW (mg/kg) was also shown. In the multiple-dose study in pediatric patients, no roxatidine accumulation in plasma was observed, as was the case with a previous study in adults. These data show that the PK profile of roxatidine in pediatric patients is similar to the profile in healthy adult volunteers when adjusted by BSA or BW.
Pregnane X receptor (PXR) mRNA was detected in HepG2 cells by RT-PCR, but not in human fetal liver (HFL) cells. CYP3A4 was induced by rifampicin (RIF), mifepristone (RU486), clotrimazole (CTZ), and dexamethasone (DEX) in HepG2 cells, while these PXR ligands with the exception of DEX did not induce CYP3A4 mRNA expression in HFL cells. Ad-PXR infection increased mRNA levels of PXR and CYP3A4 in both cells despite the absence of PXR ligands. Similar results were observed in reporter gene assays. However, in HFL cells, RIF-mediated CYP3A4 induction was insufficient compared with HepG2 cells, despite PXR overexpression. The expression levels of five coactivators (HNF4α, PGC1α, SRC1, CBP, and P300) related to CYP3A4 expression in HepG2, HFL cells, and human adult liver were analyzed by RT-PCR. Expression levels of HNF4α and PGC1α in HFL cells were downregulated to 20% of those in the human adult liver. On the other hand, the expression level of HNF4α in HepG2 cells was higher than that in HFL cells, although PGC1α expression level was almost the same as that in HFL cells. HNF4α mRNA expression level in HepG2 cells was 57% of that in human adult liver, and the level in HFL cells was 30% of that in HepG2 cells. These results suggested that lower expression of HNF4α and PGC1α may impair RIF-mediated CYP3A4 induction under conditions of PXR overexpression in HFL cells.
The purpose of this study was to clarify the transport characteristics of nucleosides in rat placenta and the changes of functional expression of nucleoside transporters in rat placenta with experimental diabetes mellitus. Placental uptake clearances of [3H]adenosine and [3H]zidovudine from maternal blood was much higher than that of [14C]mannitol. Xenopus oocytes injected with rat ENT1 and ENT2 cRNA took up [3H]adenosine with Km values of 6.1 and 26 µM, respectively. [3H]Adenosine transport by rat placental brush-border membrane vesicles (BBMV) was saturable and was inhibited by nitrobenzylthioinosine (NBMPR), a specific ENT inhibitor, in a manner consistent with involvement of both rat ENT1 and ENT2. [3H]Didanosine was modestly taken up by placenta, and the inhibitory effect of 100 µM NBMPR on [3H]ddI uptake by BBMV suggested a role of ENT2-mediated transport. Expression of ENT1, ENT2, ENT3, CNT2, and CNT3 mRNAs was detected in placenta of control and streptozotocin (STZ)-induced diabetic pregnant rats, and CNT2 (SLC28A2) expression was significantly increased in STZ-induced diabetic rats. Consistently, Na+-dependent adenosine uptake by BBMV from STZ-induced diabetic pregnant rats was higher than that from control rats. These results suggest the involvement of placental ENT2 as well as ENT1 in nucleoside uptake from maternal blood, and the induction of CNT2 in experimental diabetes mellitus.
Allopurinol-induced Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) is strongly associated with HLA-B*58:01 in various populations including Japanese. We demonstrated that several single nucleotide polymorphisms (SNPs) around the HLA region on chromosome 6 were strongly linked with HLA-B*58:01 in a previous study using Japanese allopurinol-related SJS/TEN patients. Their very strong linkage suggests that these SNPs could be used as surrogate biomarkers to find carriers of HLA-B*58:01 to avoid these serious adverse effects. In the present study, to expedite the application of this pharmacogenomic information to the proper usage of allopurinol in a clinical situation, we developed a polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) assay for the genotyping of rs9263726 in the psoriasis susceptibility 1 candidate 1 (PSORS1C1) gene, which is in absolute linkage disequilibrium (r2 = 1, D′ = 1) with HLA-B*58:01. The developed PCR-RFLP assay using FokI restriction enzyme was able to detect three different genotypes, GG, GA, and AA of rs9263726 robustly, and thus to find HLA-B*58:01 carriers. This robust and inexpensive assay would be useful for pre-screening the subjects with HLA-B*58:01, a genetically high risk factor for allopurinol-induced SJS/TEN.
Estrogen plays important roles in estrogen-responsive tissues, such as mammary glands, ovaries, and the uterus. In the liver, the major drug metabolizing organ, estrogen is known to regulate expression of some drug-metabolizing enzymes. Due to the lack of information on the role of estrogen in hepatic gene expression in primate species, we previously investigated the late response of hepatic gene expression to estradiol in cynomolgus macaques. To understand the early response of hepatic gene expression to estradiol, in this study, microarray analysis was conducted using cynomolgus macaque liver samples collected at 1 h and 5 h after estradiol injection. Comparison of expression profiles in estradiol and solvent (control)-treated ovariectomized cynomolgus macaques revealed 27 differentially expressed genes (>2.0-fold), including 18 at 1 h and 9 at 5 h after estradiol injection. As indicated by Gene Ontology analysis, these genes were related to oxidoreductase activity and transferase activity, partly representing important aspects of drug-metabolizing enzymes. Further analysis by quantitative polymerase chain reaction revealed that estradiol down-regulated CYP2A24, CYP2C76, and CYP2E1 (>2.0-fold) at 1 h and up-regulated GSTM5 (>2.0-fold) at 5 h after estradiol injection. These results suggest that the short-term estradiol treatment influenced expression of hepatic genes, including drug-metabolizing enzyme genes, in cynomolgus macaque liver.
MCT4 (SLC16A3) is the third member of the monocarboxylate transporter (MCT) family and is involved in the transportation of metabolically important monocarboxylates such as lactate, pyruvate, acetate and ketone bodies. This study aimed to identify genetic variations of the SLC16A3 gene that may be present in the ethnic Chinese (n = 95) and Indian (n = 96) groups of the Singaporean population. The genetic variations in the promoter, coding region and exon-intron junctions of the SLC16A3 gene encoding the MCT4 transporter were screened by DNA sequencing. A total of 46 genetic variants were detected in the SLC16A3 gene, of which 33 are novel. Of these variants, 22 are located in the promoter regions, 2 in the 5′ untranslated region (UTR), 10 in the coding exons (5 nonsynonymous and 5 synonymous variations), 6 in 3′UTR and 6 in the intron. Of the 5 nonsynonymous variants, only 44C>T (Ala15Val) was predicted by PolyPhen and SIFT as having a potentially damaging effect on protein function, whereas 55G>A (Gly19Ser), 574G>A (Val192Met) and 916G>A (Gly306Ser) had conflicting results between the SIFT and PolyPhen algorithms. Finally, 641C>T (Ser214Phe) was predicted to be a tolerated variant.