Effects of benfluorex on fatty acid and glucose metabolism in isolated rat hepatocytes: from metabolic fluxes to gene expression

Assessing Drug-Induced Mitochondrial Toxicity in Cardiomyocytes: Implications for Preclinical Cardiac Safety Evaluation

Drug-induced cardiotoxicity not only leads to the attrition of drugs during development, but also contributes to the high morbidity and mortality rates of cardiovascular diseases. Comprehensive testing for proarrhythmic risks of drugs has been applied in preclinical cardiac safety assessment for over 15 years. However, other mechanisms of cardiac toxicity have not received such attention. Of them, mitochondrial impairment is a common form of cardiotoxicity and is known to account for over half of cardiovascular adverse-event-related black box warnings imposed by the U.S. Food and Drug Administration. Although it has been studied in great depth, mitochondrial toxicity assessment has not yet been incorporated into routine safety tests for cardiotoxicity at the preclinical stage. This review discusses the main characteristics of mitochondria in cardiomyocytes, drug-induced mitochondrial toxicities, and high-throughput screening strategies for cardiomyocytes, as well as their proposed integration into preclinical safety pharmacology. We emphasize the advantages of using adult human primary cardiomyocytes for the evaluation of mitochondrial morphology and function, and the need for a novel cardiac safety testing platform integrating mitochondrial toxicity and proarrhythmic risk assessments in cardiac safety evaluation.

Inhibition of lysosomal phospholipase A2 predicts drug-induced phospholipidosis

Phospholipidosis, the excessive accumulation of phospholipids within lysosomes, is a pathological response observed following exposure to many drugs across multiple therapeutic groups. A clear mechanistic understanding of the causes and implications of this form of drug toxicity has remained elusive. We previously reported the discovery and characterization of a lysosome-specific phospholipase A2 (PLA2G15) and later reported that amiodarone, a known cause of drug-induced phospholipidosis, inhibits this enzyme. Here, we assayed a library of 163 drugs for inhibition of PLA2G15 to determine whether this phospholipase was the cellular target for therapeutics other than amiodarone that cause phospholipidosis. We observed that 144 compounds inhibited PLA2G15 activity. Thirty-six compounds not previously reported to cause phospholipidosis inhibited PLA2G15 with IC₅₀ values less than 1 mM and were confirmed to cause phospholipidosis in an in vitro assay. Within this group, fosinopril was the most potent inhibitor (IC₅₀ 0.18 μM). Additional characterization of the inhibition of PLA2G15 by fosinopril was consistent with interference of PLA2G15 binding to liposomes. PLA2G15 inhibition was more accurate in predicting phospholipidosis compared with in silico models based on pKa and ClogP, measures of protonation, and transport-independent distribution in the lysosome, respectively. In summary, PLA2G15 is a primary target for cationic amphiphilic drugs that cause phospholipidosis, and PLA2G15 inhibition by cationic amphiphilic compounds provides a potentially robust screening platform for potential toxicity during drug development.

Factors affecting insulin-regulated hepatic gene expression

Obesity has become a major concern of public health. A common feature of obesity and related metabolic disorders such as noninsulin-dependent diabetes mellitus is insulin resistance, wherein a given amount of insulin produces less than normal physiological responses. Insulin controls hepatic glucose and fatty acid metabolism, at least in part, via the regulation of gene expression. When the liver is insulin-sensitive, insulin can stimulate the expression of genes for fatty acid synthesis and suppress those for gluconeogenesis. When the liver becomes insulin-resistant, the insulin-mediated suppression of gluconeogenic gene expression is lost, whereas the induction of fatty acid synthetic gene expression remains intact. In the past two decades, the mechanisms of insulin-regulated hepatic gene expression have been studied extensively and many components of insulin signal transduction pathways have been identified. Factors that alter these pathways, and the insulin-regulated hepatic gene expression, have been revealed and the underlying mechanisms have been proposed. This chapter summarizes the recent progresses in our understanding of the effects of dietary factors, drugs, bioactive compounds, hormones, and cytokines on insulin-regulated hepatic gene expression. Given the large amount of information and progresses regarding the roles of insulin, this chapter focuses on findings in the liver and hepatocytes and not those described for other tissues and cells. Typical insulin-regulated hepatic genes, such as insulin-induced glucokinase and sterol regulatory element-binding protein-1c and insulin-suppressed cytosolic phosphoenolpyruvate carboxyl kinase and insulin-like growth factor-binding protein 1, are used as examples to discuss the mechanisms such as insulin regulatory element-mediated transcriptional regulation. We also propose the potential mechanisms by which these factors affect insulin-regulated hepatic gene expression and discuss potential future directions of the area of research.

Identification of alverine and benfluorex as HNF4α activators

The principal finding of this study is that two drugs, alverine and benfluorex, used in vastly different clinical settings, activated the nuclear receptor transcription factor HNF4α. Both were hits in a high-throughput screen for compounds that reversed the inhibitory effect of the fatty acid palmitate on human insulin promoter activity. Alverine is used in the treatment of irritable bowel syndrome, while benfluorex (Mediator) was used to treat hyperlipidemia and type II diabetes. Benfluorex was withdrawn from the market recently because of serious cardiovascular side effects related to fenfluramine-like activity. Strikingly, alverine and benfluorex have a previously unrecognized structural similarity, consistent with a common mechanism of action. Gene expression and biochemical studies revealed that they both activate HNF4α. This novel mechanism of action should lead to a reinterpretation of previous studies with these drugs and suggests a path toward the development of therapies for diseases such as inflammatory bowel and diabetes that may respond to HNF4α activators.

Efficacy of benfluorex in combination with sulfonylurea in type 2 diabetic patients: an 18 to 34-week, open-label, extension period

AIM

The aim of this trial was to obtain further data on the efficacy and safety of benfluorex as an add-on therapy in type 2 diabetic patients insufficiently controlled by sulfonylurea monotherapy who had a limitation for the use of metformin during a 4-month extension period following a 4-month double-blind trial.

METHODS

Patients who completed the 18-week double-blind period entered the 16-week extension period. Patients in the benfluorex group during the double-blind period continued benfluorex 450 mg/day (B-B group), whilst patients in the placebo group switched to benfluorex 450 mg/day (P-B group). The main efficacy criterion was HbA(1c), analyzed as the change from week 18 (W18) to the end of treatment using a two-sided Student paired t-test. Secondary criteria were fasting plasma glucose (FPG), insulin resistance and lipids.

RESULTS

Between W18 and the end of treatment, HbA(1c) decreased in the P-B group from 8.53+/-1.37% to 7.49+/-1.04% (P<0.001) and remained stable in the B-B group from 7.52+/-1.07% to 7.53+/-1.14% (NS). In the P-B group, parameters of glycemic control showed improvements from W18 to week 34 (W34) which were similar to those observed from baseline to W18 in the B-B group. Overall, the target HbA(1c) (<or=7%) was achieved in 36% (103 of 289) of patients and a decrease in HbA(1c) of at least 1% was seen in 44% (128 of 289) of patients. Digestive disorders were the most common adverse events and the incidence of diarrhoea was 4.9% in patients receiving benfluorex for 34 weeks.

CONCLUSION

The beneficial effect of benfluorex as add-on therapy in lowering HbA(1c) at W18 was maintained at W34 without evidence for a loss of efficacy or an increased incidence of side effects over a 34-week follow-up.

Buformin suppresses the expression of glyceraldehyde 3-phosphate dehydrogenase

The biguanides metformin and buformin, which are clinically used for diabetes mellitus, are known to improve resistance to insulin in patients. Biguanides were reported to cause lactic acidosis as a side effect. Since the mechanism of the side effect still remains obscure, we have examined genes whose expression changes by treating HepG2 cells with buformin in order to elucidate the mechanisms of the side effect. A subtraction cDNA library was constructed by the method of suppressive subtractive hybridization and the screening of the library was performed with cDNA probes prepared from HepG2 cells treated with or without buformin for 12 h. The expression of the gene and the protein obtained by the screening was monitored by real-time RT-PCR with specific primers and Western blotting with specific antibody. The amounts of ATP and NAD+ were determined with luciferase and alcohol dehydrogenase, respectively. We found that expression of the glyceraldehyde 3-phosphate dehydrogenase (GAPD) gene was suppressed by treating HepG2 cells with 0.25 mM buformin for 12 h as a result of the library screening. The decrease in the expression depended on the treatment period. The amount of GAPD protein also decreased simultaneously with the suppression of the gene expression by the treatment with buformin. The amount of ATP and NAD+ in the HepG2 cells treated with buformin decreased to 10 and 20% of the control, respectively. These observations imply that the biguanide causes deactivation of the glycolytic pathway and subsequently the accumulation of pyruvate and NADH and a decrease in NAD+. Therefore, the reaction equilibrium catalyzed by lactate dehydrogenase leans towards lactate production and this may result in lactic acidosis.

Efficacy of benfluorex in combination with sulfonylurea in type 2 diabetic patients: an 18-week, randomized, double-blind study

OBJECTIVE

The aim of this study was to demonstrate the superiority of benfluorex over placebo as an add-on therapy in type 2 diabetic patients in whom diabetes is insufficiently controlled by sulfonylurea monotherapy and who have a limitation for the use of metformin.

RESEARCH DESIGN AND METHODS

Type 2 diabetic patients with HbA(1c) (A1C) (7-10%) who were receiving the maximum tolerated sulfonylurea dose and had a contraindication to or poor tolerance of metformin were randomly assigned (double blind) to receive benfluorex 450 mg/day (n = 165) or placebo (n = 160) for 18 weeks. The main efficacy criterion was A1C, analyzed as the change from baseline to the end of treatment using ANCOVA with baseline and country as covariates. Secondary criteria were fasting plasma glucose (FPG), insulin resistance, and plasma lipid level.

RESULTS

Both groups were similar at baseline in the intention-to-treat population. A1C significantly decreased with benfluorex from 8.34 +/- 0.83 to 7.52 +/- 1.04% (P < 0.001) and tended to increase with placebo from 8.33 +/- 0.87 to 8.52 +/- 1.36% (NS), resulting in a mean adjusted difference between groups of -1.01% (95% CI -1.26 to -0.76; P < 0.001). The target A1C (< or =7%) was achieved in 34% of patients receiving benfluorex versus 12% of patients receiving placebo. Significant between-group differences in favor of benfluorex were observed for mean FPG (-1.65 mmol/l) (P < 0.001) and for homeostasis model assessment of insulin resistance. Overall tolerance was similar in both groups. Serious adverse events were more frequent in the benfluorex group, without evidence of causality relationship.

CONCLUSIONS

Benfluorex as an add-on therapy was superior to placebo in lowering A1C with a between-group difference of 1% in type 2 diabetic patients whose disease was insufficiently controlled with sulfonylurea alone and in whom metformin was contraindicated or not tolerated.

S-15261, a new anti-hyperglycemic agent, reduces hepatic glucose production through direct and insulin-sensitizing effects

S-15261 is a new oral anti-hyperglycemic agent that increases insulin sensitivity in various insulin-resistant animal models. The aim of this study was to determine the short- and long-term effects of S-15261 and its metabolites (S-15511 and Y-415) on fatty acid and glucose metabolism in hepatocytes isolated from 24-h starved rats. During short-term exposure (1h) neither S-15261 nor its metabolites affected fatty acid oxidation whatever the concentration used. By contrast, S-15261 and its two metabolites reduced the rates of glucose production from lactate/pyruvate and dihydroxyacetone. Using crossover plot analysis, it was shown that Y-415 reduced hepatic gluconeogenesis upstream the formation of dihydroxyacetone phosphate. After 48 h in culture, S-15261 and its two metabolites reduced the rates of glucose production from lactate/pyruvate secondarily to a decrease in PEPCK and Glc-6-Pase mRNA levels. A part of these effects on gene expression could be due to a drug-induced reduction in PGC-1 gene expression. When hepatocytes were cultured in the presence of a submaximal concentration of insulin (10(-9)M), S-15261, through its metabolite S-15511, enhanced insulin sensitivity both on gene expression (PEPCK, Glc-6-Pase, PGC-1) and on gluconeogenesis. Furthermore, S-15261 and S-15511 induced the expression of GK and FAS genes as the result of an increased in SREBP-1c mRNA levels. Finally, S-15511 enhanced the stimulatory effect of insulin on GK mRNA level through an additional increase in SREBP-1c gene expression. In conclusion, this work reveals that S-15261 via its metabolites reduces hepatic glucose production through direct and insulin-sensitizing effects on genes encoding regulatory proteins of hepatic glucose metabolism.