The role of sulphonylureas in the management of type 2 diabetes mellitus

Glucose toxicity: the leading actor in the pathogenesis and clinical history of type 2 diabetes - mechanisms and potentials for treatment

AIM

Although it is now well established that the deleterious effects of chronic hyperglycaemia (i.e., glucose toxicity) play an important role in the progressive impairment of insulin secretion and sensitivity, the two major actors of the pathogenesis of type 2 diabetes mellitus, the precise biochemical and molecular mechanisms responsible for the defects induced by glucose toxicity still remain to be defined.

DATA SYNTHESIS

here we will briefly report on convincing evidence that glucose toxicity acts through oxidative stress, modifications in the exosamine pathway, protein kinase C and others. After inducing or contributing to the genesis of type 2 diabetes, these same mechanisms are considered responsible for the appearance and worsening of diabetic specific microvascular complications, while its role in increasing the risk of cardiovascular diseases is less clear. Recent intervention studies (ADVANCE, ACCORD, VADT), conducted to evaluate the effects of strict glycaemic control, apparently failed to demonstrate an effect of glucose toxicity on cardiovascular diseases, at least in secondary prevention or when diabetes is present for a prolonged time. The re-examination, 20 years later, of the population studied in the UKPDS study, however, clearly demonstrated that the earliest is the strict glycaemic control reached, the lowest is the incidence of cardiovascular diseases observed, including myocardial infarction.

CONCLUSION

The acquaintance of the role of glucose toxicity should strongly influence the usual therapeutic choices and glycaemic targets where the reduced or absent risk of hypoglycaemia, durability of action, and data on prolonged safety should be the preferred characteristics of the drug of choice in the treatment of type 2 diabetes mellitus.

Islet G protein-coupled receptors as potential targets for treatment of type 2 diabetes

Islet dysfunction - characterized by a combination of defective insulin secretion, inappropriately high glucagon secretion and reduced beta-cell mass - has a central role in the pathophysiology of type 2 diabetes. Several G protein-coupled receptors (GPCRs) expressed in islet beta-cells are known to be involved in the regulation of islet function, and therefore are potential therapeutic targets. This is evident from the recent success of glucagon-like peptide 1 (GLP1) mimetics and dipeptidyl peptidase 4 (DPP4) inhibitors, which promote activation of the GLP1 receptor to stimulate insulin secretion and inhibit glucagon secretion, and also have the potential to increase beta-cell mass. Other islet beta-cell GPCRs that are involved in the regulation of islet function include the glucose-dependent insulinotropic peptide (GIP) receptor, lipid GPCRs, pleiotropic peptide GPCRs and islet biogenic amine GPCRs. This Review summarizes islet GPCR expression, signalling and function, and highlights their potential as targets for the treatment of type 2 diabetes.

Emerging dipeptidyl peptidase-4 inhibitors for the treatment of diabetes

Inhibition of dipeptidyl peptidase-4 (DPP-4) prevents the inactivation of glucagon-like peptide-1 (GLP-1). This increases circulating levels of active GLP-1, stimulates insulin secretion and inhibits glucagon secretion, resulting in lowering of glucose levels and improvement of glycemic control in patients with type 2 diabetes. Several DPP-4 inhibitors are emerging for therapeutic use. Most experience exists for sitagliptin, vildagliptin, saxagliptin and alogliptin. They all improve metabolic control in type 2 diabetes in monotherapy and in combination therapy with metformin, sulfonylurea and thiazolidinediones. Vildagliptin and alogliptin have also been shown to improve glycemic control when added to insulin therapy, and sitagliptin improves glycemic control in triple therapy with metformin plus thiazolidinedione. DPP-4 inhibition also shows a favorable safety profile, high tolerability, only a minimal risk of hypoglycemia, and body-weight neutrality. The main clinical indication for DPP-4 inhibitors will be in the early stage of type 2 diabetes, in combination with metformin or other treatments in subjects with inadequate glycemic control on these treatments alone. The durability and long-term safety of DPP-4 inhibition, as well as clinical positioning in relation to GLP-1 mimetics, remain now to be established.

Treating type 2 diabetes: how safe are current therapeutic agents?

Sulphonylureas (SUs) and biguanides (metformin) are the current mainstays in the treatment of type 2 diabetes (T2DM) and represent the most commonly used oral hypoglycaemic agents (OHAs). In recent years, a variety of new OHAs have become available, including thiazolidinediones, glinides, alpha-glucosidase inhibitors, glucagon-like peptide-1 agonists, amylin analogues and dipeptidyl peptidase-IV inhibitors, providing physicians with a larger therapeutic catalogue than ever before. The traditional drugs metformin and SUs have an established safety profile through long-term use. However, long-term clinical trials and routine use are lacking for many of the new agents, and some potentially serious side effects have been reported with several of these compounds. Until adequate data is obtained, it is difficult to assess the risk-benefit ratio of these agents in relation to the traditional drugs. Until that becomes fully documented, it may be wise to start pharmacologic treatment of patients on an individual basis, weighing the benefits and costs of each medication. Thus, there remains a place for well-established drugs that have a proven safety record and are supported by years of clinical use for the treatment of T2DM.

SNAP-25(1-180) enhances insulin secretion by blocking Kv2.1 channels in rat pancreatic islet beta-cells

Voltage-gated outward K(+) currents from pancreatic islet beta-cells are known to repolarize the action potential during a glucose stimulus, and consequently to modulate Ca(2+) entry and insulin secretion. The voltage gated K(+) (Kv) channel, Kv2.1, which is expressed in rat islet beta-cells, mediates over 60% of the Kv outward K(+) currents. A novel peptidyl inhibitor of Kv2.1/Kv2.2 channels, guangxitoxin (GxTX)-1, has been shown to enhance glucose-stimulated insulin secretion. Here, we show that SNAP-25(1-180) (S180), an N-terminal SNAP-25 domain, but not SNAP-25(1-206) (S206), inhibits Kv current and enhances glucose-dependent insulin secretion from rat pancreatic islet beta-cells, and furthermore, this enhancement was induced by the blockade of the Kv2.1 current. This study indicates that the Kv2.1 channel is a potential target for novel therapeutic agent design for the treatment of type 2 diabetes. This target may possess advantages over currently-used therapies, which modulate insulin secretion in a glucose-independent manner.

Ginsenosides Rb1 and Rg1 suppress triglyceride accumulation in 3T3-L1 adipocytes and enhance beta-cell insulin secretion and viability in Min6 cells via PKA-dependent pathways

Ginseng root is known to induce anti-diabetic activity, but the key components involved are unknown. We investigated which major ginsenosides in ginseng enhanced glucose homeostasis by in vitro studies. Rb1 and Rg1 reduced the triglyceride accumulation in 3T3-L1 adipocytes by activating PKA with increased intracellular cAMP. However, the insulin-stimulated glucose uptake was enhanced by Rb1 and Rg1 via activation of phosphatidylinositol-3 kinase. Rb1 and Rg1 promoted glucose-stimulated insulin secretion and cell viability in Min6 cells through PKA which augmented IRS2 expression to enhance insulin/IGF-1 signaling. These results suggest that Rb1 and Rg1 improved glucose homeostasis through the activation of a PKA like glucagon-like peptide-1 receptor agonist.

Rebaudioside A directly stimulates insulin secretion from pancreatic beta cells: a glucose-dependent action via inhibition of ATP-sensitive K-channels

Recently, we showed that rebaudioside A potently stimulates the insulin secretion from isolated mouse islets in a dose-, glucose- and Ca(2+)-dependent manner. Little is known about the mechanisms underlying the insulinotropic action of rebaudioside A. The aim of this study was to define the signalling system by which, rebaudioside A acts. Isolated mouse islets were used in the cAMP[(125)I] scintillation proximity assay to measure total cAMP level, and in a luminometric method to measure intracellular ATP and ADP concentrations. Conventional and permeabilized whole-cell configuration of the patch-clamp technique was used to verify the effect of rebaudioside A on ATP-sensitive K(+)-channels from dispersed single beta cells from isolated mouse islets. Insulin was measured by radioimmunoassay from insulinoma MIN6 cells. In the presence of 16.7 mM glucose, the addition of the maximally effective concentration of rebaudioside A (10(-9) M) increased the ATP/ADP ratio significantly, while it did not change the intracellular cAMP level. Rebaudioside A (10(-9) M) and stevioside (10(-6) M) reduced the ATP-sensitive potassium channel (K(ATP)) conductance in a glucose-dependent manner. Moreover, rebaudioside A stimulated the insulin secretion from MIN6 cells in a dose- and glucose-dependent manner. In conclusion, the insulinotropic effect of rebaudioside A is mediated via inhibition of ATP-sensitive K(+)-channels and requires the presence of high glucose. The inhibition of ATP-sensitive K(+)-channels is probably induced by changes in the ATP/ADP ratio. The results indicate that rebaudioside A may offer a distinct therapeutic advantage over sulphonylureas because of less risk of causing hypoglycaemia.

Probiotic treatment reduces blood glucose levels and increases systemic absorption of gliclazide in diabetic rats

The action of gliclazide, a sulphonylurea with beneficial extrapancreatic effects in diabetes, may be enhanced by administering probiotics. The aim of this study was to investigate the influence of probiotics on gliclazide pharmacokinetics and the effect of both probiotics and gliclazide on blood glucose levels in healthy and diabetic rats. Male Wistar rats (2 to 3 months, weight 350 +/- 50 g) were randomly allocated to 4 groups (n =10), two of which were treated with alloxan i.v. 30 mg/kg to induce diabetes. One group of healthy and one group of diabetic rats were then gavaged with probiotics (75 mg/kg) for three days after which a gliclazide suspension (20 mg/kg) was administered by gavage to all groups. Blood samples were collected from the tail vein at various time points for 10 hours post-administration for the determination of blood glucose and gliclazide serum concentrations. It was found that probiotic treatment had no effect on blood glucose levels in healthy rats, but it reduced them (up to 2-fold; p < 0.01) in diabetic rats. Probiotic treatment reduced gliclazide bioavailability in healthy rats (3-fold) whereas it increased gliclazide bioavailability in diabetic rats (2-fold; p < 0.01). Gliclazide had no effect on blood glucose levels in either healthy or diabetic rats despite the changes in its bioavailability. In conclusion, the probiotic treatment of diabetic rats increases gliclazide bioavailability and lowers blood glucose levels by insulin-independent mechanisms, suggesting that the administration of probiotics may be beneficial as adjunct therapy in the treatment of diabetes.

Selective small-molecule agonists of G protein-coupled receptor 40 promote glucose-dependent insulin secretion and reduce blood glucose in mice

OBJECTIVE

Acute activation of G protein-coupled receptor 40 (GPR40) by free fatty acids (FFAs) or synthetic GPR40 agonists enhances insulin secretion. However, it is still a matter of debate whether activation of GPR40 would be beneficial for the treatment of type 2 diabetes, since chronic exposure to FFAs impairs islet function. We sought to evaluate the specific role of GPR40 in islets and its potential as a therapeutic target using compounds that specifically activate GPR40.

RESEARCH DESIGN AND METHODS

We developed a series of GPR40-selective small-molecule agonists and studied their acute and chronic effects on glucose-dependent insulin secretion (GDIS) in isolated islets, as well as effects on blood glucose levels during intraperitoneal glucose tolerance tests in wild-type and GPR40 knockout mice (GPR40(-/-)).

RESULTS

Small-molecule GPR40 agonists significantly enhanced GDIS in isolated islets and improved glucose tolerance in wild-type mice but not in GPR40(-/-) mice. While a 72-h exposure to FFAs in tissue culture significantly impaired GDIS in islets from both wild-type and GPR40(-/-) mice, similar exposure to the GPR40 agonist did not impair GDIS in islets from wild-type mice. Furthermore, the GPR40 agonist enhanced insulin secretion in perfused pancreata from neonatal streptozotocin-induced diabetic rats and improved glucose levels in mice with high-fat diet-induced obesity acutely and chronically.

CONCLUSIONS

GPR40 does not mediate the chronic toxic effects of FFAs on islet function. Pharmacological activation of GPR40 may potentiate GDIS in humans and be beneficial for overall glucose control in patients with type 2 diabetes.

Sitagliptin, an dipeptidyl peptidase-4 inhibitor, does not alter the pharmacokinetics of the sulphonylurea, glyburide, in healthy subjects

AIMS

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, is an incretin enhancer that is approved for the treatment of Type 2 diabetes. Sitagliptin is mainly renally eliminated and not an inhibitor of CYP450 enzymes in vitro. Glyburide, a sulphonylurea, is an insulin sensitizer and mainly metabolized by CYP2C9. Since both agents may potentially be co-administered, the purpose of this study was to examine the effects of sitagliptin on glyburide pharmacokinetics.

METHODS

In this open-label, randomized, two-period crossover study, eight healthy normoglycaemic subjects, 22-44 years old, received single 1.25-mg doses of glyburide alone in one period and co-administered with sitagliptin on day 5 following a multiple-dose regimen for sitagliptin (200-mg q.d. x 6 days) in the other period.

RESULTS

The geometric mean ratios and 90% confidence intervals [(glyburide + sitagliptin)/glyburide] for AUC(0-infinity) and C(max) were 1.09 (0.96, 1.24) and 1.01 (0.84, 1.23), respectively.

CONCLUSION

Sitagliptin does not alter the pharmacokinetics of glyburide in healthy subjects.

Insulin exocytosis in Goto-Kakizaki rat beta-cells subjected to long-term glinide or sulfonylurea treatment

Sulfonylurea and glinide drugs display different effects on insulin granule motion in single beta-cells in vitro. We therefore investigated the different effects that these drugs manifest towards insulin release in an in vivo long-term treatment model. Diabetic GK (Goto-Kakizaki) rats were treated with nateglinide, glibenclamide or insulin for 6 weeks. Insulin granule motion in single beta-cells and the expression of SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins were then analysed. Perifusion studies showed that decreased first-phase insulin release was partially recovered when GK rats were treated with nateglinide or insulin for 6 weeks, whereas no first-phase release occurred with glibenclamide treatment. In accord with the perifusion results, TIRF (total internal reflection fluorescence) imaging of insulin exocytosis showed restoration of the decreased number of docked insulin granules and the fusion events from them during first-phase release for nateglinide or insulin, but not glibenclamide, treatment; electron microscopy results confirmed the TIRF microscopy data. Relative to vehicle-treated GK beta-cells, an increased number of SNARE clusters were evident in nateglinide- or insulin-treated cells; a lesser increase was observed in glibenclamide-treated cells. Immunostaining for insulin showed that nateglinide treatment better preserved pancreatic islet morphology than did glibenclamide treatment. However, direct exposure of GK beta-cells to these drugs could not restore the decreased first-phase insulin release nor the reduced numbers of docked insulin granules. We conclude that treatment of GK rats with nateglinide and glibenclamide varies in long-term effects on beta-cell functions; nateglinide treatment appears overall to be more beneficial.

Probiotic Pre-treatment Reduces Gliclazide Permeation (ex vivo) in Healthy Rats but Increases It in Diabetic Rats to the Level Seen in Untreated Healthy Rats

Aim

To investigate the influence of probiotic pre-treatment on the permeation of the antidiabetic drug gliclazide in healthy and diabetic rats.

Methods

Wistar rats (age 2–3 months, weight 350 ± 50 g) were randomly allocated into one of 4 groups (N = 16 each group): healthy control, healthy probiotic, diabetic control, and diabetic probiotic. Probiotics (75 mg/kg, equal quantities of Lactobacillus acidophilus, Bifidobacterium lactis, and Lactobacillus rhamnosus) were administered twice a day for three days to the appropriate groups after diabetes had been induced with alloxan i.v. 30 mg/kg. Rats were sacrificed, ileal tissues mounted in Ussing chambers and gliclazide (200 µg/mL) was administered for the measurement of the mucosal to serosal absorption Jss^(MtoS) and serosal to mucosal secretion Jss^(StoM) of gliclazide.

Results

Treatment of healthy rats with probiotics reduced Jss^(MtoS) of gliclazide from 1.2 ± 0.3 to 0.3 ± 0.1 µg/min/cm² (P < 0.01) and increased Jss^(StoM)from 0.6 ± 0.1 to 1.4 ± 0.3 (P < 0.01) resulting in net secretion while, in diabetic tissues, treatment with probiotics increased both Jss^(MtoS) and Jss^(StoM)fluxes of gliclazide to the comparable levels of healthy tissues resulting in net absorption.

Discussion

In healthy rats, the reduction in Jss^(MtoS) after probiotics administration could be explained by the production of bacterial metabolites that upregulate the mucosal efflux drug transporters Mrp2 that control gliclazide transport. In diabetic rats, the restored fluxes of gliclazide after probiotic treatment, suggests the normalization of the functionality of the drug transporters resulting in a net absorption.

Conclusion

Probiotics may alter gliclazide transport across rat ileal tissue studied ex vivo.

Update on type 2 diabetes mellitus: understanding changes in the diabetes treatment paradigm

Type 2 diabetes mellitus, which is increasingly prevalent in the United States and responsible for the bulk of diabetes-related healthcare costs, has not been adequately managed over the long term with the most commonly prescribed oral hypoglycaemic medications. Although there is evidence that successful management of type 2 diabetes must address both beta-cell deficiency and insulin resistance, most oral agents now prescribed do not prevent the progressive loss of beta-cell function that has traditionally continued during treatment. Increasingly aggressive management guidelines have led to the recommendation that metformin therapy be initiated along with lifestyle modification at the time of diagnosis. It seems unlikely, however, that this strategy will impede the progression of beta-cell dysfunction. Treatment paradigms are emerging that combine routinely used drug categories with newer agents based on the incretin pathway to achieve long-term glycaemic control. The current review discusses the clinical implications of these newer therapeutic alternatives, which enhance insulin secretion through glucose-dependent and physiologic mechanisms.

Clinical presentation and treatment of type 2 diabetes in children

Type 2 diabetes mellitus (T2DM) has dramatically increased throughout the world in many ethnic groups and among people with diverse social and economic backgrounds. This increase has also affected the young such that over the past decade, the increase in the number of children and youth with T2DM has been labeled an 'epidemic'. Before the 1990s, it was rare for most pediatric centers to have significant numbers of patients with T2DM. However, by 1994, T2DM patients represented up to 16% of new cases of diabetes in children in urban areas and by 1999, depending on geographic location, the range of percentage of new cases because of T2DM was 8-45% and disproportionately represented among minority populations. Although the diagnosis was initially regarded with skepticism, T2DM is now a serious diagnostic consideration in all young people who present with signs and symptoms of diabetes in the USA.

Nutrigenomics: concepts and applications to pharmacogenomics and clinical medicine

The maintenance of health and the prevention and treatment of chronic diseases are influenced by naturally occurring chemicals in foods. In addition to supplying the substrates for producing energy, a large number of dietary chemicals are bioactive--that is, they alter the regulation of biological processes and, either directly or indirectly, the expression of genetic information. Nutrients and bioactives may produce different physiological phenotypes among individuals because of genetic variability and not only alter health, but also disease initiation, progression and severity. The study and application of gene-nutrient interactions is called nutritional genomics or nutrigenomics. Nutrigenomic concepts, research strategies and clinical implementation are similar to and overlap those of pharmacogenomics, and both are fundamental to the treatment of disease and maintenance of optimal health.

Polymer-phloridzin conjugates as an anti-diabetic drug that inhibits glucose absorption through the Na+/glucose cotransporter (SGLT1) in the small intestine

Poly(gamma-glutamic acid)s (gamma-PGA) modified with phloridzin, which is an inhibitor of the Na(+)/glucose cotransporter (SGLT1), via a omega-amino triethylene glycol linker were synthesized. The potential of gamma-PGA-phloridzin conjugates (PGA-PRZs) obtained as a novel oral anti-diabetic drug was examined by in vitro and in vivo experiments. A PGA-PRZ with a 15% phloridzin content inhibited glucose transport from mucosal to serosal sides of the everted rat's small intestine, and its inhibitory effect was as strong as that of intact phloridzin. When the PGA-PRZ was given orally to rats before glucose administration, the glucose-induced hyperglycemic effect was significantly suppressed. On the other hand, reduction of an increase in the blood glucose concentration was scarcely observed when the PGA-PRZ was substituted with a double amount of intact phloridzin. This difference in the biological activity between PGA-PRZ and intact phloridzin might have resulted from the improved stability of a glucoside bond of phloridzin through the conjugation with gamma-PGA. These results suggest that the gamma-PGA-phloridzin conjugates have potential as oral anti-diabetic drugs.

Cytochrome P450 2C9 *2 and *3 polymorphisms and the dose and effect of sulfonylurea in type II diabetes mellitus

Sulfonylurea hypoglycemics are mainly metabolized by the cytochrome P450 2C9 (CYP2C9) enzyme. The CYP2C9*2 and *3 polymorphisms encode proteins with less enzymatic activity and are correlated with elevated serum levels of sulfonylurea, as demonstrated in healthy volunteers. In this study, the effect of these variants is described for patients with diabetes mellitus treated with sulfonylurea. Associations between CYP2C9 polymorphisms, prescribed doses of sulfonylurea, and change in glucose levels after the start of sulfonylurea therapy were assessed in all patients with incident diabetes mellitus starting on sulfonylurea therapy in the Rotterdam Study, a population-based cohort study of 7,983 elderly people. In CYP2C9*3 allele carriers using tolbutamide, the prescribed dose was lower compared to patients with the wild-type CYP2C9 genotype. No differences in the prescribed dose were found in tolbutamide users with the CYP2C9*1/*2 or CYP2C9*2/*2 genotype compared to wild-type patients or in patients using other sulfonylurea. In CYP2C9*3 allele carriers, the mean decrease in fasting serum glucose levels after the start of tolbutamide therapy was larger than in patients with the wild-type genotype, although not statistically significant. Patients with diabetes mellitus who are carriers of a CYP2C9*3 allele require lower doses of tolbutamide to regulate their serum glucose levels compared to patients with the wild-type genotype.

Screening candidate longevity therapeutics using gene-expression arrays

BACKGROUND

We review studies showing that CR acts rapidly, even in late adulthood, to extend health- and lifespan in mice. These rapid physiological effects are closely linked to patterns of gene expression in liver and heart. Non-human primate and human studies suggest that the signal transduction pathways responsible for the lifespan and health effects of caloric restriction (CR) may also be involved in human longevity. Thus, pharmaceuticals capable of mimicking the effects of CR (and other methods of lifespan extension) may have application to human health.

OBJECTIVE

We show that lifespan studies are an inefficient and theoretically problematic way of screening for longevity therapeutics. We review studies suggesting that rapid changes in patterns of gene expression can be used to identify pharmaceuticals capable of mimicking some positive effects of caloric restriction.

RESULTS

We present a traditional study of the effects of melatonin, melatonin and pregnenolone, aminoguanidine, aminoguanidine and alpha-lipoic acid, aminoguanidine, alpha-lipoic acid, pregnenolone, and coenzyme-Q(10) on the lifespan of mice. No treatment extended lifespan. However, because the mice die mostly of cancer, only chemopreventives active against specific cancers can be identified by such studies. The studies were also time-consuming and expensive. We discuss high-density microarray studies of the effectiveness of glucoregulatory drugs and putative cancer chemopreventatives at reproducing the hepatic gene-expression profiles of long-term and short-term CR. We describe the identification of one compound, metformin, which reproduces a subset of the gene-expression and physiological effects of CR.

CONCLUSION

Taken together, our results suggest that gene-expression biomarkers may be superior to lifespan studies for initial screening of candidate longevity therapeutics.

A role for beta-cell-expressed G protein-coupled receptor 119 in glycemic control by enhancing glucose-dependent insulin release

Pancreatic beta-cell dysfunction is a hallmark event in the pathogenesis of type 2 diabetes. Injectable peptide agonists of the glucagon-like peptide 1 (GLP-1) receptor have shown significant promise as antidiabetic agents by virtue of their ability to amplify glucose-dependent insulin release and preserve pancreatic beta-cell mass. These effects are mediated via stimulation of cAMP through beta-cell GLP-1 receptors. We report that the Galpha(s)-coupled receptor GPR119 is largely restricted to insulin-producing beta-cells of pancreatic islets. Additionally, we show here that GPR119 functions as a glucose-dependent insulinotropic receptor. Unlike receptors for GLP-1 and other peptides that mediate enhanced glucose-dependent insulin release, GPR119 was suitable for the development of potent, orally active, small-molecule agonists. The GPR119-specific agonist AR231453 significantly increased cAMP accumulation and insulin release in both HIT-T15 cells and rodent islets. In both cases, loss of GPR119 rendered AR231453 inactive. AR231453 also enhanced glucose-dependent insulin release in vivo and improved oral glucose tolerance in wild-type mice but not in GPR119-deficient mice. Diabetic KK/A(y) mice were also highly responsive to AR231453. Orally active GPR119 agonists may offer significant promise as novel antihyperglycemic agents acting in a glucose-dependent fashion.

Drug-drug and food-drug pharmacokinetic interactions with new insulinotropic agents repaglinide and nateglinide

This review describes the current knowledge on drug-drug and food-drug interactions with repaglinide and nateglinide. These two meglitinide derivatives, commonly called glinides, have been developed for improving insulin secretion of patients with type 2 diabetes mellitus. They are increasingly used either in monotherapy or in combination with other oral antihyperglycaemic agents for the treatment of type 2 diabetes. Compared with sulfonylureas, glinides have been shown to (i) provide a better control of postprandial hyperglycaemia, (ii) overcome some adverse effects, such as hypoglycaemia, and (iii) have a more favourable safety profile, especially in patients with renal failure. The meal-related timing of administration of glinides and the potential influence of food and meal composition on their bioavailability may be important. In addition, some food components (e.g. grapefruit juice) may cause pharmacokinetic interactions. Because glinides are metabolised via cytochrome P450 (CYP) 3A4 isoenzyme, they are indeed exposed to pharmacokinetic interactions. In addition to CYP3A4, repaglinide is metabolised via CYP2C8, while nateglinide metabolism also involves CYP2C9. Furthermore, both compounds and their metabolites may undergo specialised transport/uptake in the intestine, another source of pharmacokinetic interactions. Clinically relevant drug-drug interactions are those that occur when glinides are administered together with other glucose-lowering agents or compounds widely coadministered to diabetic patients (e.g. lipid-lowering agents), with drugs that are known to induce (risk of lower glinide plasma levels and thus of deterioration of glucose control) or inhibit (risk of higher glinide plasma levels leading to hypoglycaemia) CYP isoenzymes concerned in their metabolism, or with drugs that have a narrow efficacy : toxicity ratio. Pharmacokinetic interactions reported in the literature appear to be more frequent and more important with repaglinide than with nateglinide. Rifampicin (rifampin) reduced repaglinide area under the plasma concentration-time curve (AUC) by 32-85% while it reduced nateglinide AUC by almost 25%. Reported increases in AUCs with coadministration of drugs inhibiting CYP isoenzymes never exceeded 80% for repaglinide (except with ciclosporin and with gemfibrozil) and 50% for nateglinide. Ciclosporin more than doubled repaglinide AUC (+144%), a finding that should raise caution when using these two drugs in combination. The most impressive pharmacokinetic interaction was reported with combined administration of gemfibrozil (a strong CYP2C8 inhibitor) and repaglinide (8-fold increase in repaglinide AUC). Although no studies have been performed in patients with type 2 diabetes, the latter combination should be avoided in clinical practice.

Antidiabetic agents in subjects with mild dysglycaemia: prevention or early treatment of type 2 diabetes?

Besides lifestyle, various pharmacological treatments have proven their efficacy to reduce the incidence of type 2 diabetes in high-risk individuals, especially in those with impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG). Major placebo-controlled clinical trials demonstrated favourable effects of various glucose-lowering drugs generally used for the treatment of type 2 diabetes, i.e. metformin, acarbose and thiazolidinediones (glitazones). These trials showed a lower rate of progression to overt diabetes and a higher regression rate to a normal glucose status with active treatment as compared to placebo after a follow up of several years. Ongoing trials should confirm such a favourable effect with those drugs and may demonstrate a similar protective effect with other pharmacological approaches such as glinides or even basal insulin regimen. However, the reported favourable effects were generally observed while the subjects were still on treatment, and partially vanished after a rather short period of wash-out of several weeks. Therefore, the distinction between a true preventing effect and simply a masking effect is difficult with glucose-lowering drugs. In addition, as type 2 diabetes is a progressive disease, it is still questionable whether the effect corresponds to a prevention effect or only to a postponing of the development of the disease. Owing to the pathophysiology of the disease, the only way to block the progression of type 2 diabetes is probably to avoid the progressive loss of beta-cell function and/or mass. Whatsoever, these data obtained in large clinical trials bring further argument to support early treatment of diabetes, even at a prediabetic state, in order to stop the vicious circle leading to an inevitable deterioration of glycaemia in predisposed subjects.

Comparative safety of newer oral antidiabetic drugs

Oral antidiabetic agents were introduced into clinical practice during the 1950s. Biguanides and sulfonylureas are still used extensively today and their safety and tolerability profiles are well defined. Developments and refinements within these classes have included the introduction of second- and third-generation sulfonylureas, the introduction of modified-release preparations, and the emergence of fixed-dose preparations with metformin and with novel drugs. The latter include the thiazolidinediones, agents with a putative genomic mechanism of action that have been under intense scrutiny since the emergence of severe hepatotoxicity with troglitazone. Recent concerns about thiazolidinediones have centred on the issue of oedema and the risk of precipitating heart failure in vulnerable patients. Only prolonged exposure will determine the long-term safety of thiazolidinediones. Rapid-acting non-sulfonylurea secretagogues appear to be effective and perhaps safer than sulfonylureas in some groups of patients with certain comorbidities (e.g., those with renal impairment). alpha-Glucosidase inhibitors have an excellent safety record and acarbose has been shown to retard the progression from impaired glucose tolerance to Type 2 diabetes. However, their use is limited by tolerability issues.

Simultaneous determination of metformin and glipizide in human plasma by liquid chromatography–tandem mass spectrometry

A method has been developed for the simultaneous quantification of metformin (I) and glipizide (II) in human plasma. It is based on high-performance liquid chromatography with electrospray ionization tandem mass (LC-ESI-MS/MS) spectrometric detection in positive ionization mode. Phenformin (III) and gliclazide (IV) were used as internal standards for I and II, respectively. The MS/MS detection was performed in multiple reaction monitoring (MRM) mode. The precursor-product ion combinations of m/z 130 --> 71, 446 --> 321, 206 --> 60 and 324 --> 127 were used to quantify I, II, III and IV, respectively. This method was validated in the concentration ranges of 0.02-4 microg/mL for I and 0.004-0.8 microg/mL for II. It was utilized to support a clinical pharmacokinetic study after single dose oral administration of a combination of I and II.

Oral antidiabetic agents as cardiovascular drugs

The increased risk of cardiovascular disease associated with type 2 diabetes is well documented. Lesser degrees of abnormal glucose metabolism including impaired fasting glycaemia and impaired glucose tolerance are also associated with increased cardiovascular risk. Studies showing improved cardiovascular outcomes with oral antidiabetic agents are limited, with the UKPDS demonstrating improved macrovascular outcomes only in a subgroup of obese patients with type 2 diabetes treated with metformin, and the heavily criticized STOP NIDDM trial showing a reduction in the number of cardiovascular events with the alpha glucosidase inhibitor acarbose. In recent years there has been an increase in the number of oral antidiabetic drugs available to treat the hyperglycaemia of diabetes. Some of these drugs have complex metabolic properties, additional to their antihyperglycaemic effect, improving endothelial function and markers of atherogenesis, with the potential to reduce cardiovascular morbidity and mortality, as supported by the recently published results of the PROACTIVE study. The results of further long-term cardiovascular outcome studies with these newer agents are awaited.

Are sulfonylureas passé?

Sulfonylureas and similarly acting rapid insulin secretagogues have long been available to manage type 2 diabetes. These agents have a well understood mechanism of action and are in large part well tolerated. However, sulfonylurea therapy is unlikely to sustain adequate long-term glycemic control and has potential side effects, including hypoglycemia and weight gain. Additional concerns exist regarding detrimental effects of certain sulfonylureas on ischemic preconditioning and cardiac outcomes. Fortunately, newer agents such as glimepiride appear less likely to adversely affect the myocardium. These agents can often be used successfully as one component of combination therapy for diabetes management.

A new benzoxazine compound blocks KATP channels in pancreatic beta cells: molecular basis for tissue selectivity in vitro and hypoglycaemic action in vivo

BACKGROUND AND PURPOSE

The 2-propyl-1,4 benzoxazine (AM10) shows a peculiar behaviour in skeletal muscle, inhibiting or opening the ATP-sensitive K(+) (KATP) channel in the absence and presence of ATP, respectively. We focused on tissue selectivity and mechanism of action of AM10 by testing its effects on pancreatic KATP channels by means of both in vitro and in vivo investigations.

EXPERIMENTAL APPROACH

In vitro, patch-clamp recordings were performed in native pancreatic beta cells and in tsA201 cells expressing the Kir6.2 Delta C36 channel. In vivo, an intraperitoneal glucose tolerance test was performed in normal mice.

KEY RESULTS

In contrast with what observed in the skeletal muscle, AM10, in whole cell perforated mode, did not augment KATP current (I(KATP)) of native beta cells but it inhibited it in a concentration-dependent manner (IC(50): 11.5 nM; maximal block: 60%). Accordingly, in current clamp recordings, a concentration-dependent membrane depolarization was observed. On excised patches, AM10 reduced the open-time probability of KATP channels without altering their single channel conductance; the same effect was observed in the presence of trypsin in the bath solution. Moreover, AM10 inhibited, in an ATP-independent manner, the K(+) current resulting from expressed Kir6.2 Delta C36 (maximal block: 60% at 100 microM; IC(50): 12.7 nM) corroborating an interaction with Kir. In vivo, AM10 attenuated the glycemia increase following a glucose bolus in a dose-dependent manner, without, at the dose tested, inducing fasting hypoglycaemia.

CONCLUSION AND IMPLICATIONS

Altogether, these results help to gain insight into a new class of tissue specific KATP channel modulators.

Targeting postprandial hyperglycemia

In healthy individuals, blood glucose levels in the fasting state are maintained by the continuous basal-level insulin secretion. After a meal, the rise in postprandial glucose (PPG) is controlled by the rapid pancreatic release of insulin, stimulated by both glucose and the intestinal production of the incretins glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1. In diabetic individuals, postprandial insulin secretion is insufficient to suppress an excessive rise in PPG. There is increasing evidence that elevated PPG exerts a more deleterious effect on the vascular system than elevation of fasting plasma glucose. In particular, individuals with normal fasting plasma glucose but impaired glucose tolerance have significantly increased risk of cardiovascular events. With the recognition of the importance of PPG and the availability of new pharmacologic options, management of diabetes will shift to greater attention to PPG levels. The prototype for such an approach is in the treatment of gestational diabetes and diabetic pregnancies where PPG is the primary target of efforts at glycemic control. These efforts have been extremely successful in improving the outlook for diabetic pregnant women. There are many approaches to reduction of PPG; dietary management and promotion of exercise are very effective. Sulfonylureas, meglitinides, metformin, thiazolidinediones, and disaccharidase inhibitors all counteract PPG elevation. The development of glucagon-like peptide 1 agonists such as exendin and dipeptidyl peptidase IV inhibitors such as vildagliptin offers a new approach to suppression of PPG elevation. New semisynthetic insulin analogues permit a more aggressive response to postprandial glucose elevation, with lower risk of hypoglycemia, than with regular insulin. Inhaled insulin also has a rapid onset of action and offers benefits in PPG control. It is proposed that an aggressive treatment approach focusing on PPG, similar to the current standards for diabetic pregancies, be directed at individuals with diabetes and impaired glucose tolerance.

Sustained-release versus immediate-release glipizide for treatment of type 2 diabetes mellitus in chinese patients: A randomized, double-blind, double-dummy, parallel-group, 12-week clinical study

BACKGROUND

Few data exist that have compared sulfonylurea formulations in differing ethnic populations. Most studies of sulfonylureas have been performed in white patients with type 2 diabetes mellitus.

OBJECTIVE

The aim of this study was to compare the efficacy and tolerability of a sustained-release glipizide (GSR) formulation with those of immediate-release glipizide (GIR) in Chinese patients with type 2 diabetes mellitus.

METHODS

This randomized, double-blind, double-dummy, placebo-controlled, parallel-group, clinical study enrolled adult patients with type 2 diabetes mellitus who were already being treated with diet and a sulfonylurea. Patients were randomized to receive either GSR 10 mg PO QD or GIR 5 mg PO BID for 12 weeks. Because these 2 formulations differed in appearance, each patient also received placebo resembling the alternate formulation, to be received at the alternate frequency. Drugs dispensed but not used were returned to the investigators and counted to monitor compliance with the protocol. For efficacy assessment, fasting plasma glucose (FPG) and glycosylated hemoglobin (HbA(1c)) were measured before and after treatment. Tolerability was measured by adverse events (AEs), which were evaluated by the attending physician during each clinical visit.

RESULTS

Of the 57 patients (37 men, 20 women) enrolled in the study, 41 completed it. All were Han Chinese of Taiwanese origin, and had the following characteristics: age range, 33 to 69 years; mean (SE) height, 161.99 (9.42) cm; and mean (SE) body mass index, 25.21 (3.43) kg/m2. An intent-to-treat analysis found that the mean (SE) changes from baseline in FPG (-30.00 [10.67] vs -25.96 [11.15] mg/dL) and in HbA(1c) (-0.08% [0.24%] vs +0.14% [0.22%]) during the 12-week period of the study were not significantly different between the 2 formulations. For patients in the per-protocol analysis, mean (SE) changes from baseline in FPG (-30.00 [10.67] vs -16.52 [7.79] mg/dL) and HbA(1c) (-0.08% [0.24%] vs +0.11% [0.25%]) were also not significantly different. The most frequently reported AEs were urinary abnormality (22.2%) and tachycardia (6.7%) for the GSR group and GIR group, respectively. No serious drug-related AEs were observed in either group.

CONCLUSION

In this small study, treatment with oral GSR (10 mg QD) was not significantly different from that of treatment with GIR (5 mg BID) with respect to short-term (12 weeks) FPG and HbA(1c) reductions in these ethnic Chinese adults with type 2 diabetes mellitus receiving treatment with a sulfonylurea.

Rhes expression in pancreatic beta-cells is regulated by efaroxan in a calcium-dependent process

The monomeric G-protein Rhes has been described to be present in pancreatic beta-cells, and a putative role in the control of insulin release has been proposed. Here, we show that treatment of beta-cells with the imidazoline insulin secretagogue efaroxan resulted in a concentration- and time-dependent increase in the expression of Rhes, which peaked after 4h of efaroxan exposure; thereafter, Rhes mRNA levels decreased. Marked stereoselectivity was displayed, with (-)-efaroxan (the selectively insulinotropic enantiomer) being much more effective than (+)-efaroxan at raising Rhes transcript levels. The mechanism by which Rhes gene expression is activated in beta-cells appears to require the influx of extracellular calcium and de novo protein synthesis, and is not directly associated with the release of insulin. The present results confirm our earlier proposal that Rhes is an imidazoline-regulated transcript in pancreatic beta-cells. Studies to understand the role of Rhes as a regulator of beta-cell function are, thus, warranted.

Drug interactions of clinical importance with antihyperglycaemic agents: an update

Because management of type 2 diabetes mellitus usually involves combined pharmacological therapy to obtain adequate glucose control and treatment of concurrent pathologies (especially dyslipidaemia and arterial hypertension), drug-drug interactions must be carefully considered with antihyperglycaemic drugs. Additive glucose-lowering effects have been extensively reported when combining sulphonylureas (or the new insulin secretagogues, meglitinide derivatives, i.e. nateglinide and repaglinide) with metformin, sulphonylureas (or meglitinide derivatives) with thiazolidinediones (also called glitazones) and the biguanide compound metformin with thiazolidinediones. Interest in combining alpha-glucosidase inhibitors with either sulphonylureas (or meglitinide derivatives), metformin or thiazolidinediones has also been demonstrated. These combinations result in lower glycosylated haemoglobin (HbA(1c)), fasting glucose and postprandial glucose levels than with either monotherapy. Even if modest pharmacokinetic interferences have been reported with some combinations, they do not appear to have important clinical consequences. No significant adverse effects, except a higher risk of hypoglycaemic episodes that may be attributed to better glycaemic control, occur with any combination. Challenging the classical dual therapy with sulphonylurea plus metformin, there is a recent trend to use alternative dual combinations (sulphonylurea plus thiazolidinedione or metformin plus thiazolidinedione). In addition, triple therapy with the addition of a thiazolidinedione to the metformin-sulphonylurea combination has been recently evaluated and allows glucose targets to be reached before insulin therapy is considered. This triple therapy appears to be safe, with no deleterious drug-drug interactions being reported so far.Potential interferences may also occur between glucose-lowering agents and other drugs, and such drug-drug interactions may have important clinical implications. Relevant pharmacological agents are those that are widely coadministered in diabetic patients (e.g. lipid-lowering agents, antihypertensive agents); those that have a narrow efficacy/toxicity ratio (e.g. digoxin, warfarin); or those that are known to induce (rifampicin [rifampin]) or inhibit (fluconazole) the cytochrome P450 (CYP) system. Metformin is currently a key compound in the pharmacological management of type 2 diabetes, used either alone or in combination with other antihyperglycaemics. There are no clinically relevant metabolic interactions with metformin, because this compound is not metabolised and does not inhibit the metabolism of other drugs. In contrast, sulphonylureas, meglitinide derivatives and thiazolidinediones are extensively metabolised in the liver via the CYP system and thus, may be subject to drug-drug metabolic interactions. Many HMG-CoA reductase inhibitors (statins) are also metabolised via the CYP system. Even if modest pharmacokinetic interactions may occur, it is not clear whether drug-drug interactions between oral antihyperglycaemic agents and statins may have clinical consequences regarding both efficacy and safety. In contrast, a marked pharmacokinetic interference has been reported between gemfibrozil and repaglinide and, to a lesser extent, between gemfibrozil and rosiglitazone. This leads to a drastic increase in plasma concentrations of each antihyperglycaemic agent when they are coadministered with the fibric acid derivative, and an increased risk of adverse effects. Some antihypertensive agents may favour hypoglycaemic episodes when co-prescribed with sulphonylureas or meglitinide derivatives, especially ACE inhibitors, but this effect seems to result from a pharmacodynamic drug-drug interaction rather than from a pharmacokinetic drug-drug interaction. No, or only modest, interferences have been described with glucose-lowering agents and other pharmacological compounds such as digoxin or warfarin. The effects of inducers or inhibitors of CYP isoenzymes on the metabolism and pharmacokinetics of the glucose-lowering agents of each pharmacological class has been tested. Significantly increased (with CYP inhibitors) or decreased (with CYP inducers) plasma levels of sulphonylureas, meglitinide derivatives and thiazolidinediones have been reported in healthy volunteers, and these pharmacokinetic changes may lead to enhanced or reduced glucose-lowering action, and thus hypoglycaemia or worsening of metabolic control, respectively. In addition, some case reports have evidenced potential drug-drug interactions with various antihyperglycaemic agents that are usually associated with a higher risk of hypoglycaemia.

Blockers of the delayed-rectifier potassium current in pancreatic beta-cells enhance glucose-dependent insulin secretion

Delayed-rectifier K+ currents (I(DR)) in pancreatic beta-cells are thought to contribute to action potential repolarization and thereby modulate insulin secretion. The voltage-gated K+ channel, K(V)2.1, is expressed in beta-cells, and the biophysical characteristics of heterologously expressed channels are similar to those of I(DR) in rodent beta-cells. A novel peptidyl inhibitor of K(V)2.1/K(V)2.2 channels, guangxitoxin (GxTX)-1 (half-maximal concentration approximately 1 nmol/l), has been purified, characterized, and used to probe the contribution of these channels to beta-cell physiology. In mouse beta-cells, GxTX-1 inhibits 90% of I(DR) and, as for K(V)2.1, shifts the voltage dependence of channel activation to more depolarized potentials, a characteristic of gating-modifier peptides. GxTX-1 broadens the beta-cell action potential, enhances glucose-stimulated intracellular calcium oscillations, and enhances insulin secretion from mouse pancreatic islets in a glucose-dependent manner. These data point to a mechanism for specific enhancement of glucose-dependent insulin secretion by applying blockers of the beta-cell I(DR), which may provide advantages over currently used therapies for the treatment of type 2 diabetes.

Vildagliptin: an inhibitor of dipeptidyl peptidase-4 with antidiabetic properties

Vildagliptin is a competitive and reversible inhibitor of dipeptidyl peptidase-4. Dipeptidyl peptidase-4 inhibitors act mainly by preventing the rapid degradation of glucagon-like peptide-1. In clinical trials, vildagliptin improves glycaemic control both as monotherapy and in combination with metformin for periods of < or = 52 weeks in subjects with Type 2 diabetes. This is evident by reduced fasting and prandial glucose levels, and reduced glycosylated haemoglobin levels. Vildagliptin acts by increasing active glucagon-like peptide-1, improving beta-cell function and inhibiting glucagon secretion. Furthermore, vildagliptin has proven to be safe and tolerable, with a low occurrence of hypoglycaemia. Further studies are now required to evaluate its long-term durability, effects, safety and tolerability in comparison with other antidiabetic agents and in different patient subgroups.

Use of microarray biomarkers to identify longevity therapeutics

A number of lines of evidence, including nonhuman primate and human studies, suggest that regulatory pathways similar to those invoked by caloric restriction (CR) may be involved in determining human longevity. Thus, pharmaceuticals capable of mimicking the molecular mechanisms of life- and health-span extension by CR (CR mimetics) may have application to human health. CR acts rapidly, even in late adulthood, to begin to extend life- and health-span in mice. We have linked these effects with rapid changes in the levels of specific gene transcripts in the liver and the heart. Our results are consistent with the rapid effects of caloric intake on the lifespan and/or biochemistry and physiology of Drosophila, rodents, rhesus macaques and humans. To test the hypothesis that existing pharmaceuticals can mimic the physiologic effects of CR, we evaluated the effectiveness of glucoregulatory drugs and putative cancer chemo-preventatives in reproducing the hepatic gene-expression profiles produced by long-term CR (LTCR). We found that 8 weeks of metformin treatment was superior to 8 weeks of CR at reproducing the specific changes in transcript levels produced by LTCR. Consistent with these results, metformin reduces cancer incidence in diabetic humans and ameliorates the onset and severity of metabolic syndrome. Metformin extends the mean and maximum lifespans of female transgenic HER-2/neu mice by 8% and 13.1% in comparison with control mice. Phenformin, a close chemical relative of metformin, extends lifespan and reduces tumor incidence in C3H mice. These results indicate that gene-expression biomarkers can be used to identify promising candidate CR mimetics.

Gliquidone Contributes to Improvement of Type 2 Diabetes Mellitus Management

Diabetes mellitus is a global health problem of steadily increasing proportions, with approximately 95% of patients being affected by the type 2 form of the disease. The growing challenge to healthcare systems presented by this disorder has prompted ongoing research into novel therapies with which to improve management. The sulfonylureas constitute a long-established group of drugs with a proven track record in the treatment of type 2 diabetes, but efforts to improve the overall metabolic profile and safety of these agents have led over time to the addition of newer agents such as the second-generation benzenesulfonylurea gliquidone. Gliquidone has extrapancreatic effects that result in increased numbers of insulin receptors in peripheral tissues. The drug is rapidly and almost completely absorbed after oral administration, and has a short elimination half-life (around 1.5 hours). Metabolism is maintained in patients with hepatic insufficiency, and accumulation does not take place in patients with impaired renal function. Plasma glucose levels are controlled for several hours as a result of glucose-induced insulin secretion, and beneficial effects on plasma lipids have been described. In clinical studies, gliquidone has been associated with less hypoglycaemia than glibenclamide (glyburide), and with metabolic control at least as good as that seen with a number of other sulfonylureas. Beneficial effects on platelet aggregation have been documented, and the drug is described by WHO as the preferred sulfonylurea for patients with mild to moderate renal insufficiency. Importantly, in the light of the well documented consequences of increased bodyweight and the large growth in obesity worldwide, gliquidone is not associated with significant bodyweight gain. Thus, gliquidone is a sulfonylurea with proven efficacy and good safety and metabolic profiles that is only rarely associated with hypoglycaemia. In particular, the metabolism and route of excretion of the drug allow its use in patients who have or may be at risk of diabetic nephropathy.

Antidiabetic sulphonylureas activate mitochondrial permeability transition in rat skeletal muscle

Antidiabetic sulphonylureas can bind to various intracellular organelles including mitochondria. The aim of this study was to monitor the influence of antidiabetic sulphonylureas on membrane permeability in mitochondria isolated from rat skeletal muscle. The effects of glibenclamide (and other sulphonylurea derivatives) on mitochondrial function were studied by measuring mitochondrial swelling, mitochondrial membrane potential, respiration rate and Ca2+ transport into mitochondria. We observed that glibenclamide induced mitochondrial swelling (EC50 = 8.2 +/- 2.5 microM), decreased the mitochondrial membrane potential and evoked Ca2+ efflux from the mitochondrial matrix. These effects were blocked by 2 microM cyclosporin A, an inhibitor of the mitochondrial permeability transition. Moreover, 30 microM glibenclamide accelerated the respiratory rate in the presence of glutamate/malate, substrates of complex I of the mitochondrial respiratory chain. In conclusion, we postulate that the antidiabetic sulphonylureas activate the mitochondrial permeability transition in skeletal muscle by increasing its sensitivity to Ca2+.

Insulin secretagogues: who, what, when, and how?

Sulfonylurea compounds were the first available oral antidiabetic agents and they remain an important tool in our quest for optimal glycemic control. The more recent introduction of meglitinides offers an approach to short-term insulin release with minimal hypoglycemic risk during fasting periods. Published trials suggest that individuals with a hemoglobin A(1c) above 8.5% are unlikely to reach currently recommended targets (6.5% to 7%) without the use of one of these insulin secretagogues. Starting and probable maximally effective doses for glimepiride are 1 to 2 mg initially and 4 mg thereafter. For glyburide and glipizide, these are 2.5 to 5 mg initially, and 10 mg effective at a maximum. The large majority of the effect can be seen within a week, making them very attractive when rapid lowering of glucose is needed. An understanding of the principles will facilitate more effective use of initial and combination therapy.

Investigational agents that protect pancreatic islet β-cells from failure

Type 2 diabetes is associated with insulin resistance and reduced insulin secretion, which results in hyperglycaemia. This can then lead to diabetic complications such as retinopathy, neuropathy, nephropathy and cardiovascular disease. Although insulin resistance may be present earlier in the progression of the disease, it is now generally accepted that it is the deterioration in insulin-secretory function that leads to hyperglycaemia. This reduction in insulin secretion in Type 2 diabetes is due to both islet beta-cell dysfunction and death. Therefore, interventions that maintain the normal function and protect the pancreatic islet beta-cells from death are crucial in the treatment of Type 2 diabetes so that plasma glucose levels may be maintained within the normal range. Recently, a number of compounds have been shown to protect beta-cells from failure. This review examines the evidence that the existing therapies for Type 2 diabetes that were developed to lower plasma glucose (metformin) or improve insulin sensitivity (thiazolidinediones) may also have islet-protective function. Newer emerging therapeutic agents that are designed to increase the levels of glucagon-like peptide-1 not only stimulate insulin secretion but also appear to increase islet beta-cell mass. Evidence will also be presented that the future of drug therapy designed to prevent beta-cell failure should target the formation of advanced glycation end products and alleviate oxidative and endoplasmic reticulum stress.

Oral antidiabetic agents: current role in type 2 diabetes mellitus

Type 2 diabetes mellitus is a progressive and complex disorder that is difficult to treat effectively in the long term. The majority of patients are overweight or obese at diagnosis and will be unable to achieve or sustain near normoglycaemia without oral antidiabetic agents; a sizeable proportion of patients will eventually require insulin therapy to maintain long-term glycaemic control, either as monotherapy or in conjunction with oral antidiabetic therapy. The frequent need for escalating therapy is held to reflect progressive loss of islet beta-cell function, usually in the presence of obesity-related insulin resistance. Today's clinicians are presented with an extensive range of oral antidiabetic drugs for type 2 diabetes. The main classes are heterogeneous in their modes of action, safety profiles and tolerability. These main classes include agents that stimulate insulin secretion (sulphonylureas and rapid-acting secretagogues), reduce hepatic glucose production (biguanides), delay digestion and absorption of intestinal carbohydrate (alpha-glucosidase inhibitors) or improve insulin action (thiazolidinediones). The UKPDS (United Kingdom Prospective Diabetes Study) demonstrated the benefits of intensified glycaemic control on microvascular complications in newly diagnosed patients with type 2 diabetes. However, the picture was less clearcut with regard to macrovascular disease, with neither sulphonylureas nor insulin significantly reducing cardiovascular events. The impact of oral antidiabetic agents on atherosclerosis--beyond expected effects on glycaemic control--is an increasingly important consideration. In the UKPDS, overweight and obese patients randomised to initial monotherapy with metformin experienced significant reductions in myocardial infarction and diabetes-related deaths. Metformin does not promote weight gain and has beneficial effects on several cardiovascular risk factors. Accordingly, metformin is widely regarded as the drug of choice for most patients with type 2 diabetes. Concern about cardiovascular safety of sulphonylureas has largely dissipated with generally reassuring results from clinical trials, including the UKPDS. Encouragingly, the recent Steno-2 Study showed that intensive target-driven, multifactorial approach to management, based around a sulphonylurea, reduced the risk of both micro- and macrovascular complications in high-risk patients. Theoretical advantages of selectively targeting postprandial hyperglycaemia require confirmation in clinical trials of drugs with preferential effects on this facet of hyperglycaemia are currently in progress. The insulin-sensitising thiazolidinedione class of antidiabetic agents has potentially advantageous effects on multiple components of the metabolic syndrome; the results of clinical trials with cardiovascular endpoints are awaited. The selection of initial monotherapy is based on a clinical and biochemical assessment of the patient, safety considerations being paramount. In some circumstances, for example pregnancy or severe hepatic or renal impairment, insulin may be the treatment of choice when nonpharmacological measures prove inadequate. Insulin is also required for metabolic decompensation, that is, incipient or actual diabetic ketoacidosis, or non-ketotic hyperosmolar hyperglycaemia. Certain comorbidities, for example presentation with myocardial infarction during other acute intercurrent illness, may make insulin the best option. Oral antidiabetic agents should be initiated at a low dose and titrated up according to glycaemic response, as judged by measurement of glycosylated haemoglobin (HbA1c) concentration, supplemented in some patients by self monitoring of capillary blood glucose. The average glucose-lowering effect of the major classes of oral antidiabetic agents is broadly similar (averaging a 1-2% reduction in HbA1c), alpha-glucosidase inhibitors being rather less effective. Tailoring the treatment to the individual patient is an important principle. Doses are gradually titrated up according to response. However, the maximal glucose-lowering action for sulphonylureas is usually attained at appreciably lower doses (approximately 50%) than the manufacturers' recommended daily maximum. Combinations of certain agents, for example a secretagogue plus a biguanide or a thiazolidinedione, are logical and widely used, and combination preparations are now available in some countries. While the benefits of metformin added to a sulphonylurea were initially less favourable in the UKPDS, longer-term data have allayed concern. When considering long-term therapy, issues such as tolerability and convenience are important additional considerations. Neither sulphonylureas nor biguanides are able to appreciably alter the rate of progression of hyperglycaemia in patients with type 2 diabetes. Preliminary data suggesting that thiazolidinediones may provide better long-term glycaemic stability are currently being tested in clinical trials; current evidence, while encouraging, is not conclusive. Delayed progression from glucose intolerance to type 2 diabetes in high-risk individuals with glucose intolerance has been demonstrated with troglitazone, metformin and acarbose. However, intensive lifestyle intervention can be more effective than drug therapy, at least in the setting of interventional clinical trials. No antidiabetic drugs are presently licensed for use in prediabetic individuals.