Biomedical subjects

Hideki Fujino

Publications and source records attributed to Hideki Fujino.

12 recordsLinked to original sources

PubMed2006

CYP2C76, a novel cytochrome P450 in cynomolgus monkey, is a major CYP2C in liver, metabolizing tolbutamide and testosterone.

Monkeys are widely used as a primate model to study drug metabolism because they generally show a metabolic pattern similar to humans. However, the paucity of information on cytochrome P450 (P450) genes has hampered a deep understanding of drug metabolism in the monkey. In this study, we report identification of the CYP2C76 cDNA newly identified in cynomolgus monkey and characterization of this CYP2C along with cynomolgus CYP2C20, CYP2C43, and CYP2C75. The CYP2C76 cDNA contains the open reading frame encoding a protein of 489 amino acids that are only approximately 80% identical to any human or monkey P450 cDNAs. Gene and protein expression of CYP2C76 was confirmed in the liver of cynomolgus and rhesus monkeys but not in humans or the great apes. Moreover, CYP2C76 is located at the end of the CYP2C gene cluster in the monkey genome, the region of which corresponds to the intergenic region adjacent to the CYP2C cluster in the human genome, strongly indicating that this gene does not have the ortholog in humans. Among the four CYP2C genes expressing predominantly in the liver, the expression level of CYP2C76 was the greatest, suggesting that CYP2C76 is a major CYP2C in the monkey liver. Assays for the capacity of CYP2C76 to metabolize drugs using several substrates typical for human CYP2Cs revealed that CYP2C76 showed unique metabolic activity. These results suggest that CYP2C76 contributes to overall drug-metabolizing activity in the monkey liver and might account for species difference occasionally seen in drug metabolism between monkeys and humans.

Amino Acid Sequence↗

PubMed2006

Effects of acid and lactone forms of eight HMG-CoA reductase inhibitors on CYP-mediated metabolism and MDR1-mediated transport.

PURPOSE: With the growing clinical usage of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), the number of reports concerning serious drug-drug interaction has been increasing. Because recent studies have shown that conversion between acid and lactone forms occurs in the body, drug-drug interaction should be considered on both acid and lactone forms. Thus, we investigated the inhibitory effects of acid and lactone forms of eight statins, including one recently withdrawn, cerivastatin, and two recently developed, pitavastatin and rosuvastatin, on cytochrome P450 (CYP) 2C8, CYP2C9, and CYP3A4/5 metabolic activities and multidrug resistance protein 1 (MDR1) transporting activity. METHODS: The inhibitory effects of statins on CYP metabolic activities and MDR1 transporting activity were investigated using human liver microsomes and MDR1-overexpressing LLC-GA5-COL150 cells, respectively. RESULTS: The acid forms had minimal inhibitory effects on all CYP activities tested, except for fluvastatin on CYP2C9-mediated tolbutamide 4-hydroxylation (IC50 = 1.7 microM) and simvastatin on CYP3A4/5-mediated paclitaxel 3-hydroxylation (12.0 microM). Lactone forms showed no or minimal inhibitory effects on CYP2C8, CYP2C9, and CYP2C19 activities, except for rosuvastatin on the CYP2C9 activity (20.5 microM), whereas they showed stronger inhibitory effects on the CYP3A4/5 activity with the rank order of atorvastatin (5.6 microM), cerivastatin (8.1 microM), fluvastatin (14.9 microM), simvastatin (15.2 microM), rosuvastatin (20.7 microM), and lovastatin (24.1 microM). Pitavastatin and pravastatin had little inhibitory effect, and a similar order was found also for testosterone 6beta-hydroxylation. MDR1-mediated transport of [3H]digoxin was inhibited only by lactone forms, and the rank order correlated with that of inhibitory effects on both CYP3A4/5 activities. Inhibitory effects on MDR1 activity, and on both CYP3A4/5 activities, could be explained by the lipophilicity; however, a significant correlation was found between the lipophilicity and inhibitory effects on CYP2C8-mediated paclitaxel 6alpha-hydroxylation. CONCLUSIONS: We showed the difference between the acid and lactone forms in terms of drug interaction. The lipophilicity could be one of the important factors for inhibitory effects. In the case of statins, it is important to examine the effects of both forms to understand the events found in clinical settings, including the pleiotropic effects.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

Transporter-mediated influx and efflux mechanisms of pitavastatin, a new inhibitor of HMG-CoA reductase.

The purpose of this study was to gain a better understanding of the transport mechanism of pitavastatin, a novel synthetic HMG-CoA reductase inhibitor. Experiments were performed using oocytes of Xenopus laevis expressing several solute carrier (SLC) transporters and recombinant membrane vesicles expressing several human ABC transporters. The acid form of pitavastatin was shown to be a substrate for human OATP1, OATP2, OATP8, OAT3 and NTCP, and for rat Oatp1 and Oatp4 with relatively low K(m) values. In contrast, these SLC transporters were not involved in the uptake of the lactone form. A significant stimulatory effect was exhibited by pitavastatin lactone, while the acid form did not exhibit ATPase hydrolysis of P-glycoprotein. In the case of breast cancer resistant protein (BCRP), the acid form of pitavastatin is a substrate, whereas the lactone form is not. Taking these results into consideration, several SLC and ABC transporters were identified as critical to the distribution and excretion of pitavastatin in the body. This study showed, for the first time, that acid and lactone forms of pitavastatin differ in substrate activity towards uptake and efflux transporters. These results will potentially contribute to the differences in the pharmacokinetic profiles of pitavastatin.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2004

Metabolic stability and uptake by human hepatocytes of pitavastatin, a new inhibitor of HMG-CoA reductase.

To gain a better understanding of the metabolic stability and transport of pitavastatin (CAS 147526-32-7), a new and potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, experiments were conducted using human hepatocytes and oocytes of Xenopus laevis expressing human organic anion transporting polypeptide-2 (OATP2), respectively. Almost the entire radioactivity was from the unchanged substance or lactone form in human hepatocytes, and the cytochrome P450 (CYP)-mediated metabolism of pitavastatin was negligible. The results suggested that CYPs are not critically involved in determining the metabolic fate of pitavastatin. The hepatic uptake of pitavastatin reached saturation with a Km of 2.99 +/- 0.79 micromol/L. Also, the uptake of pitavastatin was mediated by OATP2 expressed in oocytes with a Km of 5.53 +/- 1.70 micromol/L. These results indicated that OATP2 plays a major role in the distribution of pitavastatin in liver. Furthermore, to elucidate the increase in the plasma concentration of pitavastatin in a clinical setting, the inhibitory effect of ciclosporin (cyclosporin A, CAS 59865-13-3) on the uptake of pitavastatin was examined. The uptake of pitavastatin was inhibited in the presence of cyclosporin A and the apparent IC50 value was 2.91 +/- 0.78 micromol/L. This result may at least partly explain the drug-drug interaction between pitavastatin and cyclosporin A. In conclusion, the characterization of transporters needs to be taken into account to avoid transporter-mediated drug-drug interaction.

Animals↗

PubMed2004

[Pharmacological and pharmacokinetic features and clinical effects of pitavastatin (Livalo Tablet)].

Today 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) are the most often prescribed drugs among the therapeutics for hypercholesterolemia. Pitavastatin is a novel statin that has been developed entirely in Japan from the biological screening to clinical studies persuing more efficatious statin than hitherto known. Preclinical studies on drug metabolism revealed that pitavastatin is distributed selectively to the liver, excreted into bile without metabolic modification, and efficiently re-circulates to the liver to show a prolonged plasma half-life. In guinea pigs, pitavastatin enhanced hepatic LDL receptor activity and reduced VLDL secretion in a liver perfusion study, and it lowered plasma total cholesterol (TC) levels at 0.3 mg/kg and triglyceride (TG) levels at 1 mg/kg, respectively, and more. From these results, pitavastatin is assumed to lower LDL cholesterol (LDL-C) by promoting LDL receptor expression and further potentiate the cholesterol-lowering effect and exert TG-lowering effect by reducing VLDL secretion. (14)C-Pitavastatin is metabolized with CYP2C9 to 8-hydroxy derivative, but its Vmax /Km was about 2 micro l/min/mg, about 1/8 to 1/100 in comparison to the reported values of other statins, indicating that pitavastatin is hardly metabolized. Also, other human P450 species were not inhibited by pitavastatin. Therefore, pitavastatin is considered to have little interaction with drugs through P450. In the summarized clinical results with 862 patients, pitavastatin lowered TC and LDL-C by 28% and 40%, respectively. There was no difference in the frequency of side effects and no serious adverse effect was observed for pitavastatin. Pitavastatin possesses superior plasma lipid-improving effects, induces little drug interaction, and is expected to make a good contribution to the medication of hypercholesterolemia.

Animals↗

PubMed2004

Effect of gemfibrozil on the metabolism of pitavastatin--determining the best animal model for human CYP and UGT activities.

A series of studies was conducted to determine the best animal model for human CYP and UGT activities. The investigation focused primarily on the interactions occurring in the CYP- or UGT-mediated metabolism of pitavastatin, and involved in vitro and in vivo experiments. We found that the best animal models for human CYP-mediated hydroxylation and UGT-mediated lactonization of pitavastatin were rats and dogs, respectively. In addition, a large difference in the metabolic properties of pitavastatin was found between monkeys and humans. In the presence of gemfibrozil, the CYP- or UGT-mediated metabolism of pitavastatin was inhibited in vitro. However, gemfibrozil treatment had no inhibitory effect on the AUC of pitavastatin and its lactone form in rats and dogs. We conclude that the plasma level of pitavastatin would not be increased by co-administration of gemfibrozil in humans.

Animals↗

PubMed2003

Interaction between several medicines and statins.

To gain a better understanding of drug-drug interaction between various medicinal substances and statins, in vitro experiments using human hepatic microsomes were performed. The metabolic clearance of atorvastatin (CAS 134523-00-5) was about 32 microliters/min/mg protein, some 15-fold greater than that of pitavastatin (CAS 147526-32-7). On co-incubation with several medicinal substances, metabolic inhibition of pitavastatin was negligible in human hepatic microsomes. However, a remarkable metabolic inhibition of atorvastatin was noted in the presence of various medicinal substances. The intrinsic clearance of atorvastatin lactone was 20-fold greater than that of its acid form, whereas no marked difference was noted between pitavastatin and its lactone form. Pitavastatin lactone showed no inhibitory effect on CYP3A4-mediated metabolism of testosterone in contrast to atorvastatin lactone. These results suggest that pitavastatin and its lactone form will be highly unlikely to interact with other drugs in clinical practice.

Acids↗

PubMed2003

Studies on the interaction between fibrates and statins using human hepatic microsomes.

To gain a better understanding of the mechanism of drug-drug interaction between fibrates and statins, several in vitro experiments were performed. On coincubation with several fibrates, pitavastatin (CAS 147526-32-7) did not displace fibrates from their protein binding in human plasma. The presence of gemfibrozil (CAS 25812-30-0) inhibited the metabolism of statins (cerivastatin (CAS 145599-86-6) and atorvastatin (CAS 134523-00-5)) remarkably. However, the increase of the unchanged form was fairly small for pitavastatin. The metabolic profile of gemfibrozil was also investigated. The cytochrome P (CYP) enzyme CYP2C9 plays a major role in the metabolism of gemfibrozil. Gemfibrozil showed a high affinity for CYP enzymes and a relatively high metabolism velocity. Moreover, several inhibitory effects of gemfibrozil on CYP-mediated metabolism were detected--in contrast to other fibrates. Although the mechanism of the drug-drug interaction was not completely clarified, it is suggested that the increase of plasma concentration caused by the co-administration of gemfibrozil and statins is at least partially due to the inhibition of the CYP-mediated metabolism.

Antibodies, Blocking↗

PubMed2003

Interaction between fibrates and statins--metabolic interactions with gemfibrozil.

An in vitro study was carried out in order to examine the metabolic basis of the interaction between fibrates and statins. Metabolic inhibition of statins was noted in the presence of gemfibrozil. However, increase in the unchanged form was fairly small for pitavastatin, compared with other statins. Several CYP enzymes were shown to be principally responsible for the metabolism of gemfibrozil in contrast to other fibrates. In the presence of gemfibrozil, a focal point was obtained in Dixon plots, demonstrating that there was inhibition of CYP2C8-, CYP2C9- and CYP3A4-mediated metabolism. We propose that the increase of plasma concentration caused by co-administration of gemfibrozil and statins is at least partially due to CYP-mediated inhibition.

Atorvastatin↗

PubMed2003

Uptake mechanism of pitavastatin, a new inhibitor of HMG-CoA reductase, in rat hepatocytes.

To understand the mechanism underlying the highly liver-selective distribution of pitavastatin, uptake experiments were performed using rat hepatocytes. The uptake of pitavastatin into rat hepatocytes is carrier-mediated and involved nonspecific diffusion in the presence of Na(+). The michaelis constant (K(m)) was 26.0 micromol/L, maximal uptake velocity (V(max)) was 3124 pmol/min/mg protein, and non-specific uptake (P(dif)) was 1.16 microL/min/mg protein. There were no remarkable differences in these kinetic parameters between the presence and absence of Na(+). Experiments using metabolic inhibitors revealed that energy-dependent systems contribute to the uptake of pitavastatin in the liver. Some organic anions reduced the uptake into rat hepatocytes in a concentration-dependent manner. The observed rates of inhibition of pitavastatin uptake by BSP, TCA and pravastatin were compared with the predicted rates. The predicted values were calculated, assuming that BSP, TCA and pravastatin inhibit the uptake of pitavastatin in a competitive manner. The observed inhibition by BSP and TCA was similar to that predicted, but the observed inhibition by pravastatin was considerably less than that predicted. In conclusion, most of the pitavastatin taken up into the liver is transported by multiple carrier-mediated transporters such as Na(+)-independent multispecific anion transporters and energy-dependent transporters. In addition, these systems for pitavastatin may have features in common with the BSP and TCA transport system, and may partially involve the pravastatin transport system.

Journal Article↗

PubMed2002

Metabolic fate of pitavastatin (NK-104), a new inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase. Effects on drug-metabolizing systems in rats and humans.

Pitavastatin (CAS 147526-32-7, NK-104) is a new and very potent competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and has been approved for treatment of hyperlipoproteinaemia. Pitavastatin has been studied for its effects on hepatic microsomal drug metabolism in rats, and the activities of several drug-metabolizing enzymes have been measured. No induction of the drug metabolizing enzymes (aniline hydroxylase, aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase and UDP-glucuronic acid transferase) was found in the pitavastatin group compared to the control after the multiple administrations of pitavastatin at the dosage of 1-10 mg/kg per day for 7 days. Based on several different in vitro approaches, it is concluded that CYP2C9 is the enzyme responsible for the metabolism of pitavastatin and no metabolite is present in renal and intestinal microsomes. The CYP2C9 polymorphism was not involved in the pitavastatin metabolism. No inhibitory effect in CYP-mediated metabolism was detected on the tolbutamide 4-hydroxylation (CYP2C9) and testosterone 6 beta-hydroxylation (CYP3A4) in the presence of pitavastatin. The results suggested that pitavastatin did not affect the drug-metabolizing systems.

Animals↗

PubMed2002

Metabolic fate of pitavastatin, a new inhibitor of HMG-CoA reductase--effect of cMOAT deficiency on hepatobiliary excretion in rats and of mdr1a/b gene disruption on tissue distribution in mice.

Pitavastatin is a potent competitive inhibitor of HMG-CoA reductase. In the current study, to elucidate the hepatobiliary excretion of pitavastatin, we investigated the plasma concentration and biliary excretion of (14)C-pitavastatin in EHBR. We also evaluated the distribution of pitavastatin in mdr1a/b knockout mice by whole body autoradiography and quantitative radioassay. In view of the widespread clinical use of pitavastatin and the importance of drug-drug interaction, the inhibitory effect on Pgp-mediated activation of ATPase was also investigated. No marked difference was observed in the plasma concentration and biliary excretion of radioactivity between SDR and EHBR after dosing of (14)C-pitavastatin. Little radioactive transfer into the brain was detected in mdr1a/b knockout mice and the ATPase activity of human Pgp was negligible in the presence of pitavastatin. Moreover, no inhibitory effect on the Pgp-mediated activation of ATPase by verapamil was found in the presence of pitavastatin over a wide concentration range. These results indicated that a cMOAT and Pgp-mediated transport mechanism did not play a major role in the distribution of pitavastatin.

Journal Article↗