Carboxyl-glucuronidation of mitiglinide by human UDP-glucuronosyltransferases

Gene-environment interaction identification via penalized robust divergence

In high-throughput cancer studies, gene-environment interactions associated with outcomes have important implications. Some commonly adopted identification methods do not respect the "main effect, interaction" hierarchical structure. In addition, they can be challenged by data contamination and/or long-tailed distributions, which are not uncommon. In this article, robust methods based on γ$\gamma$ -divergence and density power divergence are proposed to accommodate contaminated data/long-tailed distributions. A hierarchical sparse group penalty is adopted for regularized estimation and selection and can identify important gene-environment interactions and respect the "main effect, interaction" hierarchical structure. The proposed methods are implemented using an effective group coordinate descent algorithm. Simulation shows that when contamination occurs, the proposed methods can significantly outperform the existing alternatives with more accurate identification. The proposed approach is applied to the analysis of The Cancer Genome Atlas (TCGA) triple-negative breast cancer data and Gene Environment Association Studies (GENEVA) Type 2 Diabetes data.

Predicting drug-metagenome interactions: Variation in the microbial β-glucuronidase level in the human gut metagenomes

Characterizing the gut microbiota in terms of their capacity to interfere with drug metabolism is necessary to achieve drug efficacy and safety. Although examples of drug-microbiome interactions are well-documented, little has been reported about a computational pipeline for systematically identifying and characterizing bacterial enzymes that process particular classes of drugs. The goal of our study is to develop a computational approach that compiles drugs whose metabolism may be influenced by a particular class of microbial enzymes and that quantifies the variability in the collective level of those enzymes among individuals. The present paper describes this approach, with microbial β-glucuronidases as an example, which break down drug-glucuronide conjugates and reactivate the drugs or their metabolites. We identified 100 medications that may be metabolized by β-glucuronidases from the gut microbiome. These medications included morphine, estrogen, ibuprofen, midazolam, and their structural analogues. The analysis of metagenomic data available through the Sequence Read Archive (SRA) showed that the level of β-glucuronidase in the gut metagenomes was higher in males than in females, which provides a potential explanation for the sex-based differences in efficacy and toxicity for several drugs, reported in previous studies. Our analysis also showed that infant gut metagenomes at birth and 12 months of age have higher levels of β-glucuronidase than the metagenomes of their mothers and the implication of this observed variability was discussed in the context of breastfeeding as well as infant hyperbilirubinemia. Overall, despite important limitations discussed in this paper, our analysis provided useful insights on the role of the human gut metagenome in the variability in drug response among individuals. Importantly, this approach exploits drug and metagenome data available in public databases as well as open-source cheminformatics and bioinformatics tools to predict drug-metagenome interactions.

Hypoglycemia during the Concomitant Use of Repaglinide and Clopidogrel in an Elderly Patient with Type 2 Diabetes and Severe Renal Insufficiency

Hypoglycemia should be avoided when treating patients with diabetes. Repaglinide is an insulin secretagogue with a low hypoglycemic risk because of its rapid- and short-acting effects. However, its blood concentration has been reported to increase in combination with clopidogrel, an antiplatelet drug, and in patients with severe renal insufficiency. We herein report an elderly patient with type 2 diabetes mellitus and severe renal insufficiency who received repaglinide and hypoglycemia three days after starting clopidogrel. The concomitant use of repaglinide and clopidogrel can lead to hypoglycemia, especially in patients with severe renal insufficiency.

Risk of hypoglycemia associated with repaglinide combined with clopidogrel, a retrospective cohort study

Background

Repaglinide is widely prescribed to reduce postprandial hyperglycemia and elevated glycated hemoglobin (HbA1c) levels associated with type 2 diabetes, and clopidogrel is a thienopyridine antiplatelet agent and widely used in cardiovascular and cerebrovascular diseases. It has been suggested that the concomitant use of repaglinide with clopidogrel may inhibit repaglinide metabolism, because repaglinide is a substrate of cytochrome P450 2C8 (CYP2C8) and the main metabolite of clopidogrel acyl-β-D-glucuronide inhibits CYP2C8 activity. In this study, we retrospectively investigated the effect of clopidogrel with repaglinide on plasma glucose and the risk of hypoglycemia associated with the combination of both drugs.

Method

Patients were taking clopidogrel (75 mg/day) and started taking glinide (1.5 mg/day repaglinide or 30 mg/day mitiglinide) for the first time from April 2012 to March 2017. We targeted subjects who were hospitalized at the start of glinide and whose preprandial plasma glucose was measured by a nurse. The glucose levels were collected for up to 5 days before and after the glinide start date.

Results

Average fasting plasma glucose levels (before breakfast) in the repaglinide and clopidogrel group before and after starting repaglinide were 180.1±35.5 and 136.5 ± 44.1 mg/dL, with a mean decrease of 43.6 ± 33.6 mg/dL. In contrast, there was only a moderate decrease of 11.6 ± 30.0 mg/dL in the mitiglinide and clopidogrel group. Minimum plasma glucose levels in the repaglinide and clopidogrel group before and after starting repaglinide were 145.2 ± 42.9 and 93.3 ± 36.3 mg/dL, respectively. Decrease in minimum levels after starting glinide in the repaglinide and clopidogrel group (51.9 ± 47.5 mg/dL) was more significant than those in the mitiglinide and clopidogrel group (only 2.1 ± 29.1 mg/dL), and the repaglinide group (without clopidogrel, 15.5 ± 20.0 mg/dL). Hypoglycemia was observed in 6 of 15 patients in the repaglinide and clopidogrel group, but only 1 of 15 patients in the mitiglinide and clopidogrel group, and no patients in the repaglinide group.

Conclusion

These findings indicate that minimum plasma glucose levels were significantly decreased in patients taking repaglinide and clopidogrel. Considering the risk of hypoglycemia associated with taking repaglinide and clopidogrel, when a glinide is required in patients taking clopidogrel, mitiglinide may be a better choice.

Diabetes therapies in hemodialysis patients: Dipeptidase-4 inhibitors

Although several previous studies have been published on the effects of dipeptidase-4 (DPP-4) inhibitors in diabetic hemodialysis (HD) patients, the findings have yet to be reviewed comprehensively. Eyesight failure caused by diabetic retinopathy and aging-related dementia make multiple daily insulin injections difficult for HD patients. Therefore, we reviewed the effects of DPP-4 inhibitors with a focus on oral antidiabetic drugs as a new treatment strategy in HD patients with diabetes. The following 7 DPP-4 inhibitors are available worldwide: sitagliptin, vildagliptin, alogliptin, linagliptin, teneligliptin, anagliptin, and saxagliptin. All of these are administered once daily with dose adjustments in HD patients. Four types of oral antidiabetic drugs can be administered for combination oral therapy with DPP-4 inhibitors, including sulfonylureas, meglitinide, thiazolidinediones, and alpha-glucosidase inhibitor. Nine studies examined the antidiabetic effects in HD patients. Treatments decreased hemoglobin A1c and glycated albumin levels by 0.3% to 1.3% and 1.7% to 4.9%, respectively. The efficacy of DPP-4 inhibitor treatment is high among HD patients, and no patients exhibited significant severe adverse effects such as hypoglycemia and liver dysfunction. DPP-4 inhibitors are key drugs in new treatment strategies for HD patients with diabetes and with limited choices for diabetes treatment.

Pharmacokinetic drug interactions with clopidogrel: updated review and risk management in combination therapy

Background

Coprescribing of clopidogrel and other drugs is common. Available reviews have addressed the drug–drug interactions (DDIs) when clopidogrel is as an object drug, or focused on combination use of clopidogrel and a special class of drugs. Clinicians may still be ignorant of those DDIs when clopidogrel is a precipitant drug, the factors determining the degree of DDIs, and corresponding risk management.

Methods

A literature search was performed using PubMed, MEDLINE, Web of Science, and the Cochrane Library to analyze the pharmacokinetic DDIs of clopidogrel and new P2Y₁₂ receptor inhibitors.

Results

Clopidogrel affects the pharmacokinetics of cerivastatin, repaglinide, ferulic acid, sibutramine, efavirenz, and omeprazole. Low efficacy of clopidogrel is anticipated in the presence of omeprazole, esomeprazole, morphine, grapefruit juice, scutellarin, fluoxetine, azole antifungals, calcium channel blockers, sulfonylureas, and ritonavir. Augmented antiplatelet effects are anticipated when clopidogrel is coprescribed with aspirin, curcumin, cyclosporin, St John’s wort, rifampicin, and angiotensin-converting enzyme inhibitors. The factors determining the degree of DDIs with clopidogrel include genetic status (eg, cytochrome P540 [CYP]2B6*6, CYP2C19 polymorphism, CYP3A5*3, CYP3A4*1G, and CYP1A2-163C.A), species differences, and dose strength. The DDI risk does not exhibit a class effect, eg, the effects of clopidogrel on cerivastatin versus other statins, the effects of proton pump inhibitors on clopidogrel (omeprazole, esomeprazole versus pantoprazole, rabeprazole), the effects of rifampicin on clopidogrel versus ticagrelor and prasugrel, and the effects of calcium channel blockers on clopidogrel (amlodipine versus P-glycoprotein-inhibiting calcium channel blockers). The mechanism of the DDIs with clopidogrel involves modulating CYP enzymes (eg, CYP2B6, CYP2C8, CYP2C19, and CYP3A4), paraoxonase-1, hepatic carboxylesterase 1, P-glycoprotein, and organic anion transporter family member 1B1.

Conclusion

Effective and safe clopidogrel combination therapy can be achieved by increasing the awareness of potential changes in efficacy and toxicity, rationally selecting alternatives, tailoring drug therapy based on genotype, checking the appropriateness of physician orders, and performing therapeutic monitoring.

Pharmacogenomics of glinides

Glinides, including repaglinide, nateglinide and mitiglinide, are a type of fasting insulin secretagogue that could help to mimic early-phase insulin release, thus providing improved control of the postprandial glucose levels. Glinides stimulate insulin secretion by inhibiting ATP-sensitive potassium channels in the pancreatic β-cell membrane. Although glinides have been widely used clinically and display excellent safety and efficacy, the response to glinides varies among individuals, which is partially due to genetic factors involved in drug absorption, distribution, metabolism and targeting. Several pharmacogenomic studies have demonstrated that variants of genes involved in the pharmacokinetics or pharmacodynamics of glinides are associated with the drug response. Polymorphisms of genes involved in drug metabolism, such as CYP2C9, CYP2C8 and SLCO1B1, may influence the efficacy of glinides and the incidence of adverse effects. In addition, Type 2 diabetes mellitus susceptibility genes, such as KCNQ1, PAX4 and BETA2, also influence the efficacy of glinides. In this article, we review and discuss current pharmacogenomics researches on glinides, and hopefully provide useful data and proof for clinical application.

Pharmacokinetic and toxicological considerations for the treatment of diabetes in patients with liver disease

INTRODUCTION

Patients with type 2 diabetes have an increased risk of chronic liver disease (CLD) such as non-alcoholic fatty liver disease and steatohepatitis and about one-third of cirrhotic patients have diabetes. However, the use of several antidiabetic agents may be a cause for concern in the case of hepatic impairment (HI).

AREAS COVERED

An extensive literature search was performed to analyze the influence of HI on the pharmacokinetics (PK) of glucose-lowering agents and the potential consequences for clinical practice as far as the efficacy/safety balance of their use in diabetic patients with CLD is concerned.

EXPERT OPINION

Almost no PK studies have been published regarding metformin, sulfonylureas, thiazolidinediones and α-glucosidase inhibitors in patients with HI. Only mild changes in PK of glinides, dipeptidyl peptidase-4 inhibitors and sodium glucose cotransporters type 2 inhibitors were observed in dedicated PK studies in patients with various degrees of HI, presumably without major clinical relevance although large clinical experience is lacking. Glucagon-like peptide-1 receptor agonists have a renal excretion rather than liver metabolism. Rare anecdotal case reports of hepatotoxicity have been described with various glucose-lowering agents contrasting with numerous reassuring data. Nevertheless, caution should be recommended, especially in patients with advanced cirrhosis, including with the use of metformin.

Perturbation of mitiglinide metabolism by chronic unpredicted mild stress in rats

Many diabetic patients complicated with wild to severe depression. It is unclear in diabetic medication whether depression perturbs the drug metabolic process of the hypoglycemic agents or not. The present study was designed to investigate the impact of chronic unpredicted mild stress (CUMS) -induced depression on mitiglinide (MGN) pharmacokinetics in rats. Adult female Sprague-Dawley rats in CUMS group were subjected to different types of stressors and the stress procedures lasted for 8 weeks. Control group without receiving stress had free access to food and water. Open-field test and 5-HT levels were assayed to evaluate the depression. After CUMS all rats were given 2.5 mg/kg of mitiglinide per os. The blood samples were collected at different time and mitiglinide plasma concentration was measured by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Non-compartmental statistical moment analysis was processed with DAS software. In CMUS-induced depression group, peak concentration (Cmax), peak time (Tmax), area under curve (AUC0 → ∞), mean residence time (MRT0 → ∞), and half-life (T1/2z) were reduced while total plasma clearance (CLz/F) was increased compared to control group. These preliminary results indicated that CUMS-induced depression alter the drug metabolic process of mitiglinide in rats. This finding will be significant in clinic.

Relevance of UDP-glucuronosyltransferase polymorphisms for drug dosing: A quantitative systematic review

UDP-glucuronosyltransferases (UGT) catalyze the biotransformation of many endobiotics and xenobiotics, and are coded by polymorphic genes. However, knowledge about the effects of these polymorphisms is rarely used for the individualization of drug therapy. Here, we present a quantitative systematic review of clinical studies on the impact of UGT variants on drug metabolism to clarify the potential for genotype-adjusted therapy recommendations. Data on UGT polymorphisms and dose-related pharmacokinetic parameters in man were retrieved by a systematic search in public databases. Mean estimates of pharmacokinetic parameters were extracted for each group of carriers of UGT variants to assess their effect size. Pooled estimates and relative confidence bounds were computed with a random-effects meta-analytic approach whenever multiple studies on the same variant, ethnic group, and substrate were available. Information was retrieved on 30 polymorphic metabolic pathways involving 10 UGT enzymes. For irinotecan and mycophenolic acid a wealth of data was available for assessing the impact of genetic polymorphisms on pharmacokinetics under different dosages, between ethnicities, under comedication, and under toxicity. Evidence for effects of potential clinical relevance exists for 19 drugs, but the data are not sufficient to assess effect size with the precision required to issue dose recommendations. In conclusion, compared to other drug metabolizing enzymes much less systematic research has been conducted on the polymorphisms of UGT enzymes. However, there is evidence of the existence of large monogenetic functional polymorphisms affecting pharmacokinetics and suggesting a potential use of UGT polymorphisms for the individualization of drug therapy.

Metabolism of BYZX in human liver microsomes and cytosol: identification of the metabolites and metabolic pathways of BYZX

BYZX, [(E)-2-(4-((diethylamino)methyl)benzylidene)-5,6-dimethoxy-2,3-dihydroinden-one], belongs to a series of novel acetylcholinesterase inhibitors and has been synthesized as a new chemical entity for the treatment of Alzheimer’s disease symptoms. When incubated with human liver microsomes (HLMs), BYZX was rapidly transformed into its metabolites M1, M2, and M3. The chemical structures of these metabolites were identified using liquid chromatography tandem mass spectrometry and nuclear magnetic resonance, which indicated that M1 was an N-desethylated and C = C hydrogenation metabolite of BYZX. M2 and M3 were 2 precursor metabolites, which resulted from the hydrogenation and desethylation of BYZX, respectively. Further studies with chemical inhibitors and human recombinant cytochrome P450s (CYPs), and correlation studies were performed. The results indicated that the N-desethylation of BYZX and M2 was mediated by CYP3A4 and CYP2C8. The reduced form of β-nicotinamide adenine dinucleotide 2′-phosphate was involved in the hydrogenation of BYZX and M3, and this reaction occurred in the HLMs and in the human liver cytosol. The hydrogenation reaction was not inhibited by any chemical inhibitors of CYPs, but it was significantly inhibited by some substrates of α,β-ketoalkene C = C reductases and their inhibitors such as benzylideneacetone, dicoumarol, and indomethacin. Our results suggest that α,β-ketoalkene C = C reductases may play a role in the hydrogenation reaction, but this issue requires further clarification.

The dipeptidyl peptidase-4 inhibitor alogliptin improves glycemic control in type 2 diabetic patients undergoing hemodialysis

OBJECTIVES

The potent and selective dipeptidyl peptidase-4 (DPP-4) inhibitor alogliptin improves glycemic control in patients with type 2 diabetes through incretin hormone-mediated increases in both α- and β-cell responsiveness to glucose. In this study, the efficacy and safety of alogliptin in type 2 diabetic patients undergoing hemodialysis (HD) were evaluated.

METHODS

A prospective, open-label study of 30 patients (male/female: 24/6; mean age: 69.7 ± 1.7 years) with type 2 diabetes who were undergoing HD without insulin injection therapy was conducted. Patients were administered 6.25 mg/day alogliptin and efficacy and safety were determined by monitoring clinical and laboratory parameters during the 48-week study period.

RESULTS

After 48 weeks, alogliptin had decreased postprandial plasma glucose levels from 212 ± 8 mg/dL baseline to 156 ± 7 mg/dL, hemoglobin A1c levels from 7.1 ± 0.2% baseline to 6.3 ± 0.2% and glycated albumin (GA) levels from 25.6 ± 0.6% baseline to 20.7 ± 0.4% (all p < 0.0001). Alogliptin efficacy did not differ according to median age or body mass index, but the GA reduction was significantly greater in the antidiabetic agents-naïve group. The magnitude of GA reduction was baseline GA-dependent, being greater at higher baseline GA levels. No serious adverse effects, such as hypoglycemia or liver impairment, were observed in any patient.

CONCLUSION

Alogliptin as monotherapy or in combination with other oral antidiabetic agents improved glycemic control and was generally well tolerated in patients with HD over a 48-week period.

Intestinal transport of scutellarein and scutellarin and first-pass metabolism by UDP-glucuronosyltransferase-mediated glucuronidation of scutellarein and hydrolysis of scutellarin

Scutellarin (SG) is a bioactive flavonoid used to treat cardiovascular disease. Scutellarein (S) is the aglycone form of SG. This study aimed to characterize their intestinal transport and first-pass metabolism by UDP-glucuronosyltransferase-mediated glucuronidation and β-glucuronidase-mediated hydrolysis. Results showed that S is more readily passed through Caco-2 cell monolayers by passive diffusion than SG. SG was the predominant metabolite of S, which was formed during the transportation of S across Caco-2 cell monolayers or following incubation of S with human microsomes. SG was extensively generated in human liver microsomes (HLMs), which was demonstrated by its higher catalyzing efficiency (C(lint)) in liver microsomes than in human intestinal microsomes (HIMs). Enzymatic kinetic analysis indicated that the catalyzing efficiency of UGT1A9 was the highest among the tested UGTs under the present experimental conditions, followed by UGT1A1 and UGT1A3. No significant P450-mediated hydroxylation of S was found. SG may be hydrolyzed into S in both HLMs and HIMs.

Repaglinide-gemfibrozil drug interaction: inhibition of repaglinide glucuronidation as a potential additional contributing mechanism

AIM

To further explore the mechanism underlying the interaction between repaglinide and gemfibrozil, alone or in combination with itraconazole.

METHODS

Repaglinide metabolism was assessed in vitro (human liver subcellular fractions, fresh human hepatocytes, and recombinant enzymes) and the resulting incubates were analyzed, by liquid chromatography-mass spectrometry (LC-MS) and radioactivity counting, to identify and quantify the different metabolites therein. Chemical inhibitors, in addition to a trapping agent, were also employed to elucidate the importance of each metabolic pathway. Finally, a panel of human liver microsomes (genotyped for UGT1A1*28 allele status) was used to determine the importance of UGT1A1 in the direct glucuronidation of repaglinide.

RESULTS

The results of the present study demonstrate that repaglinide can undergo direct glucuronidation, a pathway that can possibly contribute to the interaction with gemfibrozil. For example, [³H]-repaglinide formed glucuronide and oxidative metabolites (M2 and M4) when incubated with primary human hepatocytes. Gemfibrozil effectively inhibited (∼78%) both glucuronide and M4 formation, but had a minor effect on M2 formation. Concomitantly, the overall turnover of repaglinide was also inhibited (∼80%), and was completely abolished when gemfibrozil was co-incubated with itraconazole. These observations are in qualitative agreement with the in vivo findings. UGT1A1 plays a significant role in the glucuronidation of repaglinide. In addition, gemfibrozil and its glucuronide inhibit repaglinide glucuronidation and the inhibition by gemfibrozil glucuronide is time-dependent.

CONCLUSIONS

Inhibition of UGT enzymes, especially UGT1A1, by gemfibrozil and its glucuronide is an additional mechanism to consider when rationalizing the interaction between repaglinide and gemfibrozil.

The dipeptidyl peptidase-4 (DPP-4) inhibitor vildagliptin improves glycemic control in type 2 diabetic patients undergoing hemodialysis

The potent and selective dipeptidyl peptidase-4 inhibitor vildagliptin improves glycemic control in patients with type 2 diabetes through incretin hormone-mediated increases in both α- and β-cell responsiveness to glucose. We conducted a prospective, open-label, parallel group, controlled study of 51 patients with type 2 diabetic patients undergoing hemodialysis (HD) during the 24-week study period. Patients were assigned to two groups: the vildagliptin group (n = 30) and the control group (n = 21). Vildagliptin was administered at 50 mg/day for the first 8 weeks. Then doses were titrated by dose-doubling to a maximum of 100 mg/day if hemoglobin A1c (HbA1c) or glycated albumin (GA) target levels had not been reached. No vildagliptin was administered to the controls. The average final dose of vildagliptin was 80 ± 5 mg daily. After 24 weeks, vildagliptin had decreased average HbA1c levels from 6.7 % baseline to 6.1 %, average GA levels from 24.5 % baseline to 20.5 % and average postprandial plasma glucose levels from 186 mg/dL baseline to 140 mg/dL (all p < 0.0001). In the control group, we observed no such changes. Vildagliptin efficacy did not differ according to age or body mass index, but the GA reduction was significantly greater in the anti-diabetic agents-naïve group. Furthermore, in patients with higher baseline GA levels, a higher vildagliptin dosage was required to produce a noticeable effect. No serious adverse effects such as hypoglycemia or liver impairment were observed in any patient. Vildagliptin was effective as a treatment for diabetic patients undergoing HD.

Mitiglinide: a novel agent for the treatment of type 2 diabetes mellitus

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of mitiglinide, a rapid-acting insulin secretion-stimulating agent to determine its potential role in therapy for the treatment of type 2 diabetes mellitus.

DATA SOURCES

A MEDLINE search (1966-May 2010) was conducted for English-language, human studies using the terms mitiglinide, KAD 1229, S 21403, and meglitinide analogs. Abstracts presented at the American Association and European Association for the Study of Diabetes annual meetings from 2005 to 2009 were also evaluated for relevant data.

STUDY SELECTION AND DATA EXTRACTION

Articles pertinent to the pharmacology, pharmacokinetics, efficacy, and safety of mitiglinide were reviewed.

DATA SYNTHESIS

Mitiglinide has been shown through small clinical studies (N <400) to modestly decrease hemoglobin A(1c), postprandial hyperglycemia, and oxidative stress and inflammatory markers associated with postprandial hyperglycemia. Mitiglinide exerts its hypoglycemic activity by closing adenosine triphosphate (ATP)-sensitive potassium channels in the β-islet cells of the pancreas. This agent has a rapid onset and short duration of action, mimicking a physiologic pattern of insulin release in nondiabetic people. Studies suggest a starting dose of 5 mg 3 times daily with meals and a maximum dose of 20 mg 3 times daily. Overall, mitiglinide is well tolerated, with the most common adverse effect being hypoglycemia.

CONCLUSIONS

Mitiglinide is the third agent in the class of meglitinides that targets postprandial hyperglycemia. Because of a more intensive dosing regimen, potential cost, and lack of studies assessing the clinical impact of mitiglinide therapy on oxidative stress and inflammatory markers secondary to postprandial hyperglycemia, we cannot recommend this therapy over currently approved therapies.

Metabolism of ebracteolata compound B studied in vitro with human liver microsomes, HepG2 cells, and recombinant human enzymes

Ebracteolata compound B (ECB) is one major active component of both Euphorbia ebracteolata and Euphorbia fischeriana, which have been extensively used as a tuberculocide in the Asian countries. The aim of our present study was to characterize ECB metabolism in human liver microsomes, HepG2 cells, and recombinant human enzymes. One monohydroxylation metabolite, determined by mass spectrometry to be 1-(2,4-dihydroxy-6-methoxy-3-methylphenyl)-2-hydroxyethanone, and one monoglucuronide, isolated and determined by hydrolysis with β-glucuronidase, mass spectrometry, and (1)H NMR to be 2-hydroxy-6-methoxy-3-methyl-acetophenone-4-O-β-glucuronide, were observed in human liver microsomal incubates in the presence of NADPH or UDP-glucuronic acid (UDPGA), respectively. However, the mixed incubation of ECB with human liver microsomes in the presence of both NADPH and UDPGA showed the monoglucuronide to be the most major metabolite, indicating that glucuronidation was probably the major clearance pathway of ECB in humans. No glucuronide and only trace monohydroxylation metabolite were observed in HepG2 cells. The cytochrome P450 and UDP-glucuronosyltransferase (UGT) isoenzymes were identified by using selective chemical inhibition and recombinant human enzymes. The results indicated that CYP3A4 was probably involved in ECB oxidative metabolism and UGT1A6 and UGT1A9 were important catalytic enzymes in ECB glucuronidation. The results from enzymatic kinetic analysis showed the oxidative metabolism in human liver microsomes; the glucuronidation in human liver microsomes and recombinant UGT1A6 exhibited a typical Michaelis-Menten pattern, but the glucuronidation in UGT1A9 exhibited a substrate inhibition pattern. UGT1A6 had the highest affinity compared with human liver microsomes and UGT1A9, indicating its important role in ECB glucuronidation.

Oxidative demethylenation and subsequent glucuronidation are the major metabolic pathways of berberine in rats

Present study was designed to explore roles of metabolic clearance in the disposition of berberine (BBR) in rats, with a focus on oxidative metabolism and subsequent glucuronidation. Plasma from rats after intravenous administration of BBR was collected to identify and quantify BBR and its major metabolites. The major circulating metabolites of BBR were oxidative metabolites M1 (via demethylation) and M2 (via demethylenation) and their corresponding glucuronides, with M2-glucuronide approximately 24-fold higher than M1-glucuronide. Incubations with rat liver microsomes were conducted to examine formation kinetics of two oxidative metabolites-M1 and M2, and depletion kinetics of M1 and M2, leading to the formation of glucuronide conjugates. Efforts were also made to examine roles of key CYPs and UGTs isoforms responsible for BBR metabolism using known chemical inhibitors and/or substrates. In vitro, the formation of M1 and M2 were comparable and multiple CYP enzymes were involved. In contrast, the glucuronidation of M2 was much faster than that of M1. Inhibition studies using well-characterized UGT substrates suggested both M1 and M2 could be glucuronidated by UGT1A1 and UGT2B1 while M2 glucuronidation was favored by UGT1A1. In summary, oxidative demethylenation and the subsequent glucuronidation were the major metabolic pathways of BBR in rats.

Efficacy and safety of mitiglinide in diabetic patients on maintenance hemodialysis

Mitiglinide is a rapid- and short-acting insulinotropic sulfonylurea receptor ligand and features rapid hypoglycemic action. To date, no prospective study has evaluated the use of mitiglinide in diabetic patients receiving hemodialysis (HD). In this study we evaluated the efficacy and safety of mitiglinide in diabetic patients on HD. Following an 8-week baseline period, we enrolled a study population of poorly controlled diabetic HD patients who had mean hemoglobin (Hb)A(1c) levels greater than 6.5% at baseline and who were not receiving insulin injection therapy. Patients were administered mitiglinide, 15 mg for those who were younger than 70 years and 7.5 mg for those who were 70 years and older, daily with each meal for the first 8 weeks. Subsequently, the doses were titrated by dose-doubling to a maximum of 30 mg/day if no adverse effects appeared. The efficacy was determined by monitoring glycemic control (plasma glucose, HbA(1c), and glycated albumin levels). Safety and tolerance were determined by monitoring clinical and laboratory parameters during the 24-week study period. The average final dose of mitiglinide was 20.0 +/- 8.6 mg daily. Mitiglinide was effective in reducing not only HbA(1c) and glycated albumin but also fasting plasma glucose levels from baseline from week 4 after the start of treatment. The agent was also effective in reducing triglyceride levels. No serious adverse effects such as hypoglycemia or liver impairment were observed in any patient. However, we could not completely rule out the possibility of a hypoglycemic episode, including silent hypoglycemia due to autonomic neuropathy, and therefore further clinical studies are required. It is necessary to adjust the dose of mitiglinide according to the status of glycemic control or hypoglycemic symptoms of individual patients. Although mitiglinide was effective as a treatment for diabetic patients on HD therapy, it should be initiated at a lower dose in the HD population, compared with the general population of diabetic patients. Mitiglinide can be safely used for diabetic patients on HD, if careful attention is paid to hypoglycemia.