Hypoglycaemic and insulinotropic effects of a novel oral antidiabetic agent, (-)-N-(trans-4-isopropylcyclohexanecarbonyl)-D-phenylalanine (A-4166)

ATP-citrate lyase (ACLY) inhibitors as therapeutic agents: a patenting perspective

INTRODUCTION

ATP citrate lyase (ACLY) is a key enzyme in cellular metabolism, being the main source of acetyl-Coenzyme A, an important precursor for fatty acid, cholesterol and isoprenoid biosynthesis, and it is also involved in protein acetylation. Its expression changes are related to hyperlipidemia and cardiovascular diseases. Other studies have shown that ACLY is closely related to the occurrence of cancer: the increase in lipid synthesis provides the necessary building blocks for cell growth and division. Therefore, finding effective ACLY inhibitors has very important application prospects for lipid-related pathologies and cancer.

AREAS COVERED

: This review covers patents concerning ACLY inhibitors and alternative strategies to modulate ACLY activity, with their potential therapeutic applications.

EXPERT OPINION

In recent years ACLY as a drug target has become a hot spot in the research of innovative drugs for disorders of glucose and lipid metabolism. Many types of small-molecule ACLY inhibitors have been discovered, but few ACLY inhibitors proved to be highly effective in vitro and in vivo, since their main limitations were low cell penetration and low affinity to ACLY. The search for new effective ACLY inhibitors is of great significance and has broad application prospects for the treatment of hyperlipidemia and cancer.

Dextromethorphan and Dextrorphan Influence Insulin Secretion by Interacting with KATP and L-type Ca2+ Channels in Pancreatic β-Cells

The NMDA receptor antagonist dextromethorphan (DXM) and its metabolite dextrorphan (DXO) have been recommended for treatment of type 2 diabetes mellitus because of their beneficial effects on insulin secretion. This study investigates how different key points of the stimulus-secretion coupling in mouse islets and β-cells are influenced by DXM or DXO. Both compounds elevated insulin secretion, electrical activity, and [Ca²⁺]_c in islets at a concentration of 100 µM along with a stimulating glucose concentration. DXO and DXM increased insulin secretion approximately 30-fold at a substimulatory glucose concentration (3 mM). Patch-clamp experiments revealed that 100 µM DXM directly inhibited K_ATP channels by about 70%. Of note, DXM decreased the current through L-type Ca²⁺ channels about 25%, leading to a transient reduction in Ca²⁺ action potentials. This interaction might explain why elevating DXM to 500 µM drastically decreased insulin release. DXO inhibited K_ATP channels almost equally. In islets of K_ATP channel-deficient sulfonylurea receptor 1 knockout mice, the elevating effects of 100 µM DXM on [Ca²⁺]_c and insulin release were completely lost. By contrast, 100 µM DXO still increased glucose-stimulated insulin release around 60%. In summary, DXM-induced alterations in stimulus-secretion coupling of wild-type islets result from a direct block of K_ATP channels and are partly counteracted by inhibition of L-type Ca²⁺ channels. The stimulatory effect of DXO seems to be based on a combined antagonism on K_ATP channels and NMDA receptors and already occurs under resting conditions. Consequently, both compounds seem not to be suitable candidates for treatment of type 2 diabetes mellitus. SIGNIFICANCE STATEMENT: This study shows that the use of dextromethorphan as an antidiabetic drug can cause unpredictable alterations in insulin secretion by direct interaction with K_ATP and L-type Ca²⁺ channels besides its actual target, the NMDA receptor.

High-glucose 3D INS-1 cell model combined with a microfluidic circular concentration gradient generator for high throughput screening of drugs against type 2 diabetes

In vitro models for screening of drugs against type 2 diabetes are crucial for the pharmaceutical industry. This paper presents a new approach for integration of a three-dimensionally-cultured insulinoma cell line (INS-1 cell) incubated in a high concentration of glucose as a new model. In this model, INS-1 cells tended to aggregate in the 3D gel (basement membrane extractant, BME), in a similar way to 3D in vivo cell culture models. The proliferation of INS-1 cells in BME was initially promoted and then suppressed by the high concentration of glucose, and the function of insulin secretion also was initially enhanced and then inhibited by the high concentration of glucose. These phenomena were similar to hyperglycemia symptoms, proving the validity of the proposed model. This model can help find the drugs that stimulate insulin secretion. Then, we identified the difference between the new model and the traditional two-dimensional model in terms of cell morphology, inhibition rate of cell proliferation, and insulin secretion. Simultaneously, we developed a circular drug concentration gradient generator based on microfluidic technology. We integrated the high-glucose 3D INS-1 cell model and the circular concentration gradient generator in the same microdevice, tested the utility of this microdevice in the field of drug screening with glipizide as a model drug, and found that the microdevice was more sensitive than the traditional device to screen the anti-diabetic drugs.

Efficacy and safety of nateglinide plus sitagliptin combination therapy in type 2 diabetes patients inadequately controlled by sitagliptin monotherapy: a phase 3, multicenter, open-label, long-term study

BACKGROUND

Combination therapies of drugs with distinct mechanisms of action are emerging as ways to achieve strict glycemic control, thus preventing the onset and progression of diabetic complications in type 2 diabetes patients. A rapid-acting insulin secretagog, nateglinide, and a potent dipeptidyl peptidase-4 inhibitor, sitagliptin, meet such criteria.

METHODS

A total of 121 patients inadequately controlled with sitagliptin monotherapy received 52-week combination therapy (nateglinide + sitagliptin). The primary endpoint was the safety of the therapy, and its efficacy was also evaluated. A meal tolerance test was performed 4 weeks before the start of combination therapy (week -4) and at week 24 and week 52 after the start of combination therapy.

RESULTS

HbA1c levels were lower at week 52 than at week 0 [-0.42% (95% confidence interval -0.53, -0.31)]. Fasting plasma glucose levels tended to decrease from baseline (week 0) to week 52 [-4.8 mg/dl (-9.4, -0.2)]. In the meal tolerance test, postprandial plasma glucose levels and area under the curve of glucose from before to 2 h after the meal load were lower at week 24 and week 52 than at week -4. In addition, the levels of insulin and active glucagon-like peptide-1 were higher at week 52 than at week -4. Furthermore, the incidence of adverse events in combination therapy with sitagliptin was similar to those previously shown in nateglinide monotherapy.

CONCLUSION

Compared with sitagliptin monotherapy, the combination therapy of nateglinide plus sitagliptin was more effective in type 2 diabetes patients at improving glycemic control while showing similar safety.

Comparison of the postprandial glucose and insulin profiles with nateglinide and gliclazide in type 2 diabetic patients

Aim

The aim of this study was to compare glucose, insulin and proinsulin profiles during nateglinide and gliclazide treatment over an extended postprandial period.

Materials and methods

This double-blind crossover trial was conducted in 23 type 2 diabetic patients (mean HbA1C 6.6%; range 6.0—7.4%) who received, for one week each, nateglinide 120 mg t.i.d., gliclazide 80 mg b.i.d. and placebo, with a one week wash out period between treatments.

Results

The 2-hour postprandial glucose concentration was markedly lower with nateglinide than with gliclazide (5.83 vs. 7.21 mmol/L; p<0.05), as was the post-meal peak glucose elevation (8.63 vs. 9.72 mmol/L; p=0.085), which was associated with earlier, higher and shorter-lived insulin and proinsulin secretory responses. However, 0—7-hour AUCs during standardised meal test for glucose and insulin between the two drugs did not statistically differ. No symptomatic hypoglycaemic events occurred during the 7-hour test period.

Conclusion

Nateglinide was more effective than gliclazide in controlling postprandial hyperglycaemia and showed a faster effect on insulin and proinsulin secretion.

Pancreatic regulation of glucose homeostasis

In order to ensure normal body function, the human body is dependent on a tight control of its blood glucose levels. This is accomplished by a highly sophisticated network of various hormones and neuropeptides released mainly from the brain, pancreas, liver, intestine as well as adipose and muscle tissue. Within this network, the pancreas represents a key player by secreting the blood sugar-lowering hormone insulin and its opponent glucagon. However, disturbances in the interplay of the hormones and peptides involved may lead to metabolic disorders such as type 2 diabetes mellitus (T2DM) whose prevalence, comorbidities and medical costs take on a dramatic scale. Therefore, it is of utmost importance to uncover and understand the mechanisms underlying the various interactions to improve existing anti-diabetic therapies and drugs on the one hand and to develop new therapeutic approaches on the other. This review summarizes the interplay of the pancreas with various other organs and tissues that maintain glucose homeostasis. Furthermore, anti-diabetic drugs and their impact on signaling pathways underlying the network will be discussed.

Anti-nociceptive and anti-edematogenic effects of glibenclamide in a model of acute gouty attack in rats

OBJECTIVE AND DESIGN

We investigated the effect of glibenclamide on inflammatory parameters in a model of acute gouty attack in rats.

TREATMENT

Intra-articular injection of 50 μl of monosodium urate (MSU) crystals (1.25 mg/site) was used to induce gout-related inflammation. The effects of glibenclamide (1-10 mg/kg, s.c.) or dexamethasone (8 mg/kg, s.c., positive control) were assessed on several inflammation parameters.

METHODS

Spontaneous nociception assessment, edema measurement, total and differential leucocyte counts, interleukin (IL)-1β release, prostaglandin E2 production and determination of blood glucose levels were analyzed. Peritoneal macrophages were incubated with MSU and levels of IL-1β were measured. Statistical significance was assessed by one- or two-way analysis of variance.

RESULTS

Glibenclamide (3 mg/kg) or dexamethasone (8 mg/kg) prevented nociception and edema induced by MSU injection in rats. Glibenclamide did not affect leukocyte infiltration, IL-1β release and PGE2 production, but only reduced IL-1β production by MSU-stimulated macrophages at very high concentration (200 μM). Dexamethasone significantly reduced leukocyte infiltration, IL-1β release and PGE2 production. Glibenclamide reduced whereas dexamethasone increased blood glucose levels of MSU-injected rats.

CONCLUSIONS

Glibenclamide reduced nociception and edema, but not leukocyte infiltration, IL-1β release and PGE2 production. However, its substantial effect on nociception and edema suggests that glibenclamide can be an interesting option as an adjuvant treatment for pain induced by acute attacks of gout.

Contribution of organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 to hepatic uptake of nateglinide, and the prediction of drug–drug interactions via these transporters

Objectives

We have investigated the contributions of organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 to the hepatic uptake of nateglinide, and the possibility of drug–drug interactions via these transporters.

Methods

Uptake studies using transporter-expressing HEK293 cells and cryopreserved human hepatocytes were performed to examine the contributions of each transporter. Inhibition studies using cryopreserved human hepatocytes were performed to examine the possibility of drug–drug interactions.

Key findings

The rate of saturable hepatic uptake of nateglinide using human hepatocytes was 47.6%. A certain increase in uptake was observed in the examination using transporter-expressing HEK293 cells, indicating contributions of OATP1B1 and OATP1B3 to hepatic nateglinide uptake. The 50% inhibitory concentration (IC50) values of nateglinide using cryopreserved human hepatocytes for uptake of estrone 3-sulfate (substrate of OATP1B1), and cholecystokinin octapeptide (substrate of OATP1B3) were 168 and 17.4 µmol/l, respectively. Moreover, ciclosporin inhibited saturable hepatic uptake of nateglinide with an IC50 value of 6.05 µmol/l. The calculated 1 + Iin,max,u/IC50 values for inhibition of OATP1B1 and OATP1B3 by nateglinide, and the inhibition of saturable uptake of nateglinide by ciclosporin, were all close to 1, indicating a low clinical risk of drug–drug interaction with nateglinide taken up via OATP1B1 and OATP1B3.

Conclusions

OATP1B1 and OATP1B3 may have contributed to the hepatic uptake of nateglinide, but the possibility of drug–drug interactions appeared to be low.

Comparison of the rapidity of onset of the therapeutic effect between nateglinide and mitiglinide by PK/PD analysis in rats

Nateglinide and mitiglinide are immediate short-acting insulinotropic agents. Both are administered preprandially to control postprandial hyperglycemia. Glinide drugs are characterized by immediate onset as well as rapid disappearance of effect as compared with sulfonylurea drugs. We examined the rapidity of onset of the therapeutic effect between nateglinide and mitiglinide by pharmacokinetic/pharmacodynamic analysis using the receptor-binding-dissociation model in rats. Nateglinide or mitiglinide was administered orally or intravenously to rats and blood samples were collected at various time-points post administration. The plasma concentrations of the unbound drug forms and the blood glucose were measured. When the simultaneous fitting of oral administration and intravenous administration was performed using the receptor-binding-dissociation model, the measured values exhibited good correspondence with the fitting curve. Moreover, the time-courses of changes of the receptor-binding rate (sulfonylurea receptor) were examined using the parameters (k (on): second-order binding association constant to the receptor, Φ: receptor-binding occupancy ratio) obtained from the analysis. The results showed that the binding rate, which is important for glinide drugs in the early phase after administration, was obviously higher for nateglinide than that for mitiglinide from 10 min after oral administration and between 0 and 30 min after intravenous administration. These results suggest a more rapid onset of the therapeutic effect of nateglinide than that of mitiglinide after the drug is distributed into the blood.

Effect of glimepiride and nateglinide on serum insulin and glucose concentration in healthy cats

Glimepiride and nateglinide are two common oral hypoglycemic agents currently being used with humans suffering from Type 2 diabetes mellitus. Neither drug has been tested with cats thus far and it is currently unknown whether either of these drugs exert any effect in cats or not. The objective of this study was to determine the effect of glimepiride and nateglinide on glucose and insulin responses in healthy control cats, in order to determine their potential use in diabetic cats. The intravenous glucose tolerance tests was carried out since it is an excellent test for evaluating pancreatic beta-cell function for insulin secretion. Alterations in the insulin secretion pattern can be perceived as the earliest sign of beta-cell dysfunction in many species, including cats. Nateglinide demonstrated a quick action/short duration type effect with serum glucose nadiring and insulin response peaking at 60 and 20 minutes, respectively. Alternatively, glimepiride is medium-to-long acting with serum glucose nadiring and insulin response peaking at 180 minutes and 60 minutes, respectively. Nateglinide's potency was evident allowing it to induce a 1.5-2 higher preliminary insulin peak (3.7 +/- 1.1 pg/ml) than glimepiride's (2.5 +/- 0.1 pg/ml), albeit only for a short period of time. Because glimepiride and nateglinide have a shared mode of action, no significant differences in overall glucose AUC(0-360 min) (24,435 +/- 2,940 versus 24,782 +/- 2,354 mg min/dl) and insulin AUC(0-360 min) (410 +/- 192 versus 460 +/- 159) in healthy control cats were observed. These findings may provide useful information when choosing a hypoglycemic drug suited for the treatment of diabetic cats depending on the degree of diabetes mellitus the cat is suffering from.

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.

Nateglinide prevents fatty liver through up-regulation of lipid oxidation pathway in Goto-Kakizaki rats on a high-fat diet

Dyslipidemia and fatty liver are important components of the metabolic syndrome and are the factors most commonly associated with the development of nonalcoholic fatty liver disease. Delayed and excessive insulin secretion in response to food intake is a key element in the onset of these risk factors. Nateglinide (NAT) is known to restore early-phase insulin secretion. We assessed the effect of NAT on postprandial hypertriglyceridemia and fatty liver in type 2 diabetic Goto-Kakizaki (GK) rats. The GK rats fed a high-fat diet containing 30% beef tallow twice a day were administered either the vehicle alone or NAT (50 mg/kg) before each meal for 12 weeks. Delayed insulin secretion and an increase of total insulin release were caused by feeding 30% beef tallow to the rats. This diet also induced postprandial hypertriglyceridemia and increased the hepatic triglyceride content. Treatment with NAT restored early-phase insulin secretion without any increase of total insulin release and also reduced postprandial hypertriglyceridemia and the hepatic triglyceride content. There was up-regulation of the hepatic expression of peroxisome proliferators-activated receptor alpha and its downstream enzymes after 12 weeks of NAT treatment, as well as normalization of the plasma total ketone body level. Furthermore, NAT also up-regulated hepatic expression of the adiponectin receptor AdipoR2, although there was no effect on the plasma adiponectin level. These findings indicate that long-term treatment with NAT prevented the development of fatty liver through the up-regulation of hepatic lipid oxidation pathways. Restoration of early-phase insulin secretion and suppression of recurrent postprandial hypertriglyceridemia might be involved in these effects of NAT. The present results may support the use of NAT to prevent the onset and progression of the metabolic syndrome and chronic liver disease.

Nateglinide and Mitiglinide, but Not Sulfonylureas, Induce Insulin Secretion through a Mechanism Mediated by Calcium Release from Endoplasmic Reticulum

Nateglinide and mitiglinide (glinides) are characterized as rapid-onset and short-acting insulinotropic agents. Although both compounds do not have a sulfonylurea structure, it has been postulated that insulin secretion is preceded by their binding to Kir6.2/SUR1 complex, and a mechanism of insulin secretion of glinides has been accounted for by this pathway. However, we hypothesized the involvement of additional mechanisms of insulin secretion enhanced by glinides, and we analyzed the pattern of time course of insulin secretion from MIN6 cells with the existence of agents that have specific pharmacologic actions. Dose-dependent effects of tolbutamide, glibenclamide, nateglinide, and mitiglinide were observed. Insulin secretion induced by 3 microM tolbutamide and 1 nM glibenclamide was completely inhibited by 10 microM diazoxide and 3 microM verapamil, although the latter half-component of insulin secretion profile induced by 3 microM nateglinide or 30 nM mitiglinide remained with the existence of those agents. Glinides enhanced insulin secretion even in Ca2+-depleted medium, and its pattern of secretion was same as the pattern with existence of verapamil. The latter half was suppressed by 1 microM dantrolene, and concomitant addition of verapamil and dantrolene completely suppressed the entire pattern of insulin secretion enhanced by nateglinide. Thus, we conclude that glinide action is demonstrated through two pathways, dependently and independently, from the pathway through K(ATP) channels. We also demonstrated that the latter pathway involves the intracellular calcium release from endoplasmic reticulum via ryanodine receptor activation.

Beneficial metabolic effects of nateglinide versus acarbose in patients with newly-diagnosed type 2 diabetes

AIM

To investigate the acute and chronic effects of nateglinide versus acarbose on plasma asymmetric dimethylarginine (ADMA) levels and lipid profiles in patients with newly-diagnosed type 2 diabetes.

METHODS

A crossover trial of nateglinide and acarbose was conducted on 16 drug-naïve patients with newly-diagnosed type 2 diabetes during a total period of 9 weeks. Plasma glucose, serum insulin, free fatty acids (FFA), lipids and lipoproteins, and plasma ADMA were measured.

RESULTS

The efficiencies of a single dose of nateglinide (120 mg) and acarbose (50 mg) for lowering postprandial hyperglycemia were similar. Compared to acarbose, nateglinide significantly increased postprandial insulin release after a standard meal test in patients with type 2 diabetes. Nateglinide acutely decreased postprandial 120 min FFA concentrations and 240 min ADMA levels more significantly than acarbose. The fasting high-density lipoprotein cholesterol level increased and the low-density lipoprotein cholesterol level decreased significantly, but the fasting levels of triglycerides, total cholesterol, and ADMA were unchanged after 4 weeks of treatment with nateglinide. Acarbose did not affect fasting lipid profiles or the ADMA levels after 4 weeks of treatment.

CONCLUSION

These results suggest that the reduction of postprandial FFA and ADMA concentrations induced by nateglinide may be associated with the partial restoration of early-phase insulin secretion and may impart a cardiovascular advantage in comparison with acarbose.

Effects of the Combination of a Dipeptidyl Peptidase IV Inhibitor and an Insulin Secretagogue on Glucose and Insulin Levels in Mice and Rats

Several combination therapies have been tried for treating of type 2 diabetes to control more effectively fasting hyperglycemia and postprandial hyperglycemia. In this study, we have examined the effects of combining a novel, selective, and competitive dipeptidyl peptidase IV (DPP-IV) inhibitor, 3-but-2-ynyl-5-methyl-2-piperazin-1-yl-3,5-dihydro-4H-imidazo[4,5-d]pyridazin-4-one tosylate (E3024), with a representative of one of two types of insulin secretagogues, i.e., either glybenclamide (a sulfonylurea) or nateglinide (a rapid-onset/short-duration insulin secretagogue), on glucose and insulin levels in an oral glucose tolerance test (OGTT) using mice fed a high-fat diet. In addition, we have investigated the effects of these combinations on blood glucose levels in fasting rats. Two-way analysis of variance showed that the combination of E3024 and glybenclamide improved glucose tolerance additively and also caused a synergistic increase in insulin levels in the OGTT in mice fed a high-fat diet. In a similar way, the combination of E3024 and nateglinide ameliorated glucose tolerance additively and raised insulin levels additively. In fasting rats, coadministration of E3024 with glybenclamide or nateglinide treatment did not affect the glucose-lowering effects of the insulin secretagogues. Therefore, a DPP-IV inhibitor in combination with glybenclamide or nateglinide may be a promising option for the treatment of type 2 diabetes, and particularly, for controlling postprandial hyperglycemia in the clinic.

Nateglinide with glibenclamide examination using the respiratory quotient (RQ)

PURPOSE

The respiratory quotient (RQ) is useful for evaluating glucose and lipid metabolism in vivo. We previously reported that the RQ value, even after fasting, was high in diabetics being treated with sulphonylurea (SU), which might explain the accumulation of fat, leading to weight gain in such individuals. In the present study, we measured the RQ in type II diabetic patients who were being treated with a rapid-onset/short-duration insulinotropic agent, nateglinide, and compared it with those being treated with SU.

METHODS

A glucose tolerance test was performed in 20 patients with type II diabetes mellitus treated with nateglinide and in 14 patients treated with SU, and the RQ was simultaneously measured.

RESULTS

The RQ values in the patients treated with nateglinide, were similar to those in healthy adults, but was lower than in those treated with SU. No weight gain was observed in patients treated with nateglinide.

CONCLUSION

A significant weight gain was reported in subjects treated with SU, accompanied by an increase in RQ. However, weight gain was less frequent in diabetics treated with nateglinide.

Purification by p-aminobenzoic acid (PABA)-affinity chromatography and the functional reconstitution of the nateglinide/H+ cotransport system in the rat intestinal brush-border membrane

(-)-N-(trans-4-isopropylcyclohexanecarbonyl)-D-phenylalanine (nateglinide) is a novel oral hypoglycemic agent possessing a peptide-type bond and a carboxyl group in its structure. Recently, we have shown that nateglinide transport occurs via the ceftibuten/H+ cotransport system, which is distinct from PepT1, and that the fluorescein/H+ cotransport system is involved in the uptake of nateglinide. The aim of this study was to characterize the functional properties of the intestinal nateglinide transporter. In the first part of this study, we demonstrated that the ceftibuten/H+ cotransport system is identical to the fluorescein/H+ cotransport system. We succeeded in purification of the nateglinide transporter from brush-border membranes of the rat small intestine using p-aminobenzoic acid (PABA)-affinity chromatography. We then investigated the functional properties of the nateglinide transporter using proteoliposomes prepared from the PABA-affinity chromatography elute. We demonstrated that nateglinide, ceftibuten, and fluorescein are transported by the same transporter in the intestine.

Effect of the administration of a single dose of nateglinide on insulin secretion at two different concentrations of glucose in healthy individuals

BACKGROUND

Nateglinide is a D-phenylalanine derivative that stimulates fast insulin secretion with a short activity span. It has been suggested that the hypoglycemic effect of nateglinide is related to the glucose concentration, an aspect that still has not been completely evaluated in human beings.

OBJECTIVE

The aim of this study is to evaluate the effect of nateglinide on the insulin secretion at two different concentrations of glucose level.

PARTICIPANTS AND METHODS

A randomized, double-blind, cross-over, placebo-controlled clinical trial with two parallel groups was carried out; each group was made up by six healthy volunteers who were submitted to a hyperglycemic-hyperinsulinemic clamp technique on two different occasions, one of them prior to the administration of 120 mg nateglinide and the other one prior to the administration of an homologated placebo. One group was submitted to and maintained at a hyperglycemia of 6.9 mmol/l above the fasting glucose level and the other group at a hyperglycemia of 4.1 mmol/l above the baseline of fasting glucose level.

RESULTS

In volunteers submitted to the clamp at 4.1 mmol/l above the baseline of glucose level, the insulin secretion in the early phase was 212.4+/-55.8 pmol/l in the placebo test versus 338.4+/-124.8 pmol/l in the nateglinide test (P<.05), whereas in the group submitted at 6.9 mmol/l over the baseline, no significant differences were observed.

CONCLUSION

Nateglinide increased the early insulin secretion in healthy individuals submitted to a mild hyperglycemia, but not at high glucose concentrations.

Nateglinide, a non-sulfonylurea rapid insulin secretagogue, increases pancreatic islet blood flow in rats

We studied whether the rapid hypoglycemic action of nateglinide is associated with an increase in islet blood flow. Islet blood flow was measured using the two-colour microsphere method. Orally administered nateglinide with glucose acutely increased islet blood flow to levels greater than those after glucose alone or tolbutamide with glucose in conscious Sprague-Dawley rats (percent increase at 10 min after oral administration; nateglinide+glucose, 125+/-25%; glucose, 33+/-11%, p<0.001; tolbutamide+glucose, 42+/-23%, p<0.01). Nateglinide administered with non-metabolisable 3-O-methylglucose also increased islet blood flow (61+/-17%). The stimulated islet blood flow significantly correlated with serum insulin levels. N(G)-monomethyl-L-arginine, a nitric oxide synthase inhibitor, completely inhibited the increase in islet blood flow induced by nateglinide with glucose. Intravenously administered nateglinide did not significantly affect the already increased islet blood flow in diabetic Otsuka Long-Evans Tokushima Fatty rats. Our results indicated that nateglinide acutely increased islet blood flow at least in part through a nitric oxide-dependent mechanism.

Postmarketing surveillance study of nateglinide in Japan

Nateglinide is an oral antidiabetic medication that acts through rapid, short-term stimulation of insulin production. This study was undertaken to identify the incidence and nature of adverse effects of nateglinide and to assess its efficacy in clinical practice. Patients (n = 3254) were recruited from 606 centers in Japan with a 12-week observation period. Pretreatment and posttreatment values were obtained for fasting blood glucose, postprandial blood glucose, hemoglobin A1c (HbA1c), triglycerides, cholesterol, and body mass index. All adverse events were reported, along with standard laboratory blood variables. The incidence of adverse events was 7.40%; hypoglycemia, including hypoglycemic symptoms, was reported as the most prevalent (1.62%). Adverse events were observed more frequently in patients with hepatic or renal dysfunction; no significant findings were noted in the remaining patient population. The efficacy rating determined by the treating physicians was 76.40%. HbA1c decreased by 0.81% from 7.70+/-1.53% to 6.89+/-1.22%, postprandial glucose decreased by 54.05 mg/dL from 228.91+/-73.69 mg/dL to 174.86+/-62.86 mg/dL, and fasting glucose decreased by 23.73 mg/dL from 164.15+/-51.42 mg/dL to 140.43+/-42.63 mg/dL. These effects were most marked in patients who were previously medication naïve or who had been diagnosed with diabetes for a short period. Mean body mass index decreased, and nateglinide was equally effective in obese patients. Nateglinide showed good therapeutic effect when used as the first choice in patients with a short duration of diabetes, and in those with no history of previous treatment. Moreover, nateglinide seemed to be useful for the treatment of elderly patients and obese patients.

Nateglinide uptake by a ceftibuten transporter in the rat kidney brush-border membrane

Nateglinide, a novel oral hypoglycemic agent, possesses a carbonyl group and a peptide-type bond in its structure. We previously reported that nateglinide transport occurs via a single system that may be identical to the ceftibuten/H(+) cotransport system by the rat small intestine. We speculated that the absorption system present on the intestinal epithelium may be similar to that found on the renal tubular epithelium. The aim of this study was to characterize the transporters on the apical side of the kidney that may contribute to the reabsorption of ceftibuten and nateglinide. The uptake of nateglinide by rat renal brush-border membranes is associated with an H(+)-coupled transport system. Ceftibuten competitively inhibited H(+)-dependent nateglinide uptake. In contrast, Gly-Sar, cephradine and cephalexin had no effect on nateglinide uptake. Nateglinide competitively inhibited H(+)-driven transporter-mediated ceftibuten uptake. We conclude that nateglinide transport occurs via a single system that is H(+)-dependent and may be identical to the ceftibuten/H(+) cotransport system.

No acute effect of nateglinide on postprandial lipid and lipoprotein responses in subjects at risk for type 2 diabetes

BACKGROUND

To study the acute effect of nateglinide, an insulinotropic agent, on the postprandial triglyceride and lipoprotein responses in subjects at risk for type 2 diabetes.

METHODS

Six women and 10 men, with at least one first-degree relative with type 2 diabetes were included (Age: 48 +/- 7 years, BMI: 27.5 +/- 2.8 kg m(-2), P-triglycerides: 1.3 +/- 0.4 mmol L(-1), P-cholesterol: 5.4 +/- 0.6 mmol L(-1), B-glucose: 4.6 +/- 0.3 mmol L(-1)). They each had two 8-h meal tolerance tests with either nateglinide or placebo given 10 min prior to the meals in randomized order. Lipoprotein fractions were separated by density gradient ultracentrifugation. First-phase insulin secretion was assessed by an intravenous glucose tolerance test (300 mg kg(-1) body weight) and insulin sensitivity by a hyperinsulinaemic euglycaemic clamp (40 mU m(-2) min(-1)).

RESULTS

The 1-h insulin levels during the meal tolerance test were significantly higher with nateglinide (577 +/- 81 vs 376 +/- 58 pmol L(-1), p < 0.001), as well as the response during the first two hours (IAUC: 41 243 +/- 5844 vs 29 956 +/- 4662 pmol L(-1) min, p < 0.01). Accordingly, nateglinide lowered the 8-h postprandial glucose response by around 60% compared to placebo (p < 0.001). In contrast, no significant lowering was seen in the excursion of postprandial triglycerides in total plasma or lipoprotein fractions. Consistently, the concentration of exogenous (apoB-48) and endogenous (apoB-100) lipoproteins was not reduced by nateglinide.

CONCLUSIONS

Acute administration of nateglinide reduces, as expected, the postprandial glucose concentration, but no reduction in triglyceride or lipoprotein responses are seen in subjects at risk for type 2 diabetes.

Weight loss-associated changes in acute effects of nateglinide on insulin secretion after glucose loading: results of glucose loading on 2 consecutive days

AIM

The aim of this study was to investigate the influence of changes in insulin resistance and early insulin secretion on the insulin secretagogic effects of nateglinide.

METHODS

Oral glucose tolerance testing (OGTT, 75 g) was performed in obese patients before and after weight loss on 2 consecutive days (first day OGTT without nateglinide, second day OGTT with nateglinide), to compare any weight loss associated changes in the nateglinide-induced insulin response to glucose loading.

RESULTS

Reductions in visceral fat, liver fat, skeletal muscle fat and homeostasis model assessment (HOMA)-R due to weight loss were associated with increased Delta insulin 30 min/Delta glucose 30 min (DeltaI30/DeltaG30), and reduced area under the curve (AUC) for plasma glucose as seen in OGTT results. Results from OGTT showed that nateglinide administration was associated with reductions in plasma glucose AUC, both before and after weight loss. Before weight loss, although there was a significant elevation of DeltaI30/DeltaG30 associated with nateglinide treatment, no major change in the insulin-secreting dynamics after glucose loading was observed. After weight loss, nateglinide administration produced a significant increase in DeltaI30/DeltaG30, with insulin secretion peaking more quickly.

CONCLUSION

Insulin response to nateglinide after glucose loading varied greatly in conjunction with weight loss. This may be accounted for not only by the enhancement of early insulin response to nateglinide associated with the improvement of early insulin response with weight loss but also by the reduced visceral fat, which in turn led to reduced levels of free fatty acids in portal blood and hepatic triglycerides, as well as increased hepatic insulin clearance.

Protein tyrosine phosphatases: their role in insulin action and potential as drug targets

Protein tyrosine phosphatases (PTPases) are the enzymes responsible for the selective dephosphorylation of tyrosine residues. PTPases function to regulate a wide array of biological responses mediated by growth factors and other stimuli by balancing the cellular level of phosphotyrosine in concert with their counterparts, protein tyrosine kinases. The important roles which PTPases play in regulating intracellular signalling and, ultimately, biological function along with the recent availability of information regarding their structural features has highlighted them as potential targets for pharmacological modulation. This is demonstrated by the increased level of activity directed towards the identification of novel small-molecule PTPase inhibitors. The rationale and potential utility of this drug discovery approach is discussed here, with particular emphasis on its application for the treatment of insulin resistance and Type 2 diabetes.

Intestinal uptake of nateglinide by an intestinal fluorescein transporter

Nateglinide, a novel oral hypoglycemic agent, rapidly reaches its maximum serum concentration after oral administration, suggesting that it is rapidly absorbed in the intestine. However, nateglinide itself is not transported by MCT1 or PEPT1. The aim of this study was to characterize the transporters on the apical side of the small intestine that are responsible for the rapid absorption of nateglinide. It has been reported that the uptake of fluorescein by Caco-2 cells occurs via an H+-driven transporter and that the intestinal fluorescein transporter is probably not MCT1. We examined the contribution of the fluorescein transporter to the uptake of nateglinide by Caco-2 cells. Fluorescein competitively inhibited H+-dependent nateglinide uptake. All of fluorescein transporter inhibitors examined reduced the uptake of nateglinide. Furthermore, nateglinide inhibited fluorescein uptake. We conclude that the intestinal nateglinide/H+ cotransport system is identical to the intestinal fluorescein/H+ cotransport system.

Role of early insulin secretion in postglucose-loading hyperglycaemia and postfat-loading hyperlipidaemia: comparing nateglinide and glibenclamide for acute effects on insulin secretion in OLETF rats

AIM

The aim of this study was to clarify the role of an early insulin secretion in postprandial hyperglycaemia and hyperlipidaemia; a study using spontaneously type 2 diabetic Otsuka Long-Evans Tokushima Fatty rats with visceral obesity was performed to investigate the acute effect of nateglinide (NAT) vs. glibenclamide (GB) on increases in glucose after glucose loading and on increases in triglyceride (TG) after fat loading.

METHODS

Fasting rats were given 50 mg/kg of NAT, 1 mg/kg of GB or 5% methyl cellulose (vehicle) as control and then immediately given oral glucose 1 g/kg.

RESULTS

An acute increase in insulin levels in portal blood peaked at 15 min in the NAT group, while insulin levels in the GB group continued to increase significantly after 60 min. Glucose levels in peripheral blood were significantly lower in the NAT group at 30 and 60 min and in the GB group at 120, 180 and 270 min after glucose loading, compared with those in the vehicle group. Subsequently, fasting rats were given NAT, GB or vehicle and then immediately given oral fat emulsion (soy oil 2 g/kg). An acute increase in insulin secretion was seen with NAT, peaking at 30 min, while TG, chylomicron and very low-density lipoprotein levels after fat loading were shown to be significantly lower with NAT than with vehicle. However, the continued insulin secretion observed with GB led to no significant decrease in TG levels after fat loading. In addition, lipoprotein lipase mRNA expression in adipose tissue increased significantly 120 min after NAT administration in comparison with baseline. This increase was not noted with GB administration.

CONCLUSION

Abnormalities in early insulin secretion are closely associated with the pathogenesis of various disease conditions that combine to characterize type 2 diabetes, suggesting that normalizing early insulin response in portal blood represents an important treatment not only for postprandial hyperglycaemia but also for postprandial hyperlipidaemia.

[Pharmacological and clinical profile of mitiglinide calcium hydrate (Glufast), a new insulinotropic agent with rapid onset]

Mitiglinide calcium hydrate (mitiglinide, Glufast) is a new insulinotropic agent of the glinide class with rapid onset. Mitiglinide is thought to stimulate insulin secretion by closing the ATP-sensitive K(+) (K(ATP)) channels in pancreatic beta-cells, and its early insulin release and short duration of action would be effective in improving postprandial hyperglycemia. In studies of various cloned K(ATP) channels, mitiglinide shows a higher selectivity for the beta-cell type of SUR1/Kir6.2 than the cardiac and smooth muscle types of K(ATP) channels in comparison with glibenclamide and glimepiride. In vitro and in vivo studies demonstrated the insulinotropic effect of mitiglinide is more potent than that of nateglinide, and mitiglinide surpassed in controlling postprandial hyperglycemia in normal and diabetic animals. In clinical trials, treatment with mitiglinide provided lasting improvement of postprandial hyperglycemia in Type 2 diabetic patients and decreased the fasting plasma glucose levels and HbA(1C) values. The incidence of adverse events related to mitiglinide were nearly equivalent to placebo; in particular there was no difference with the frequency of hypoglycemia. The results from these studies indicated that mitiglinide could be expected to possess good therapeutic features of being effective in reducing postprandial glucose excursions in the early stage of Type 2 diabetes and less incidence of events suggestive of hypoglycemia.

H+-dependent transport mechanism of nateglinide in the brush-border membrane of the rat intestine

(-)-N-(trans-4-Isopropylcyclohexanecarbonyl)-D-phenylalanine (nateglinide) is a novel oral hypoglycemic agent possessing a carboxyl group and a peptide-type bond in its structure. Although nateglinide quickly reaches the maximal serum concentration after oral administration, nateglinide itself is not transported by PepT1 or MCT1. The aim of this study was to characterize the transporters on the apical side of the small intestine that are responsible for the rapid absorption of nateglinide. The uptake of nateglinide by rat intestinal brush-border membrane vesicles is associated with a proton-coupled transport system. Ceftibuten competitively inhibited H(+)-dependent nateglinide uptake. Glycylsarcosine (Gly-Sar), cephradine, and cephalexin did not significantly inhibit the uptake of nateglinide. The combination of Gly-Sar and nateglinide greatly reduced the uptake of ceftibuten. The effect of the combined treatment was significantly greater than that of Gly-Sar alone. Furthermore, nateglinide competitively inhibited H(+)-driven ceftibuten transporter-mediated ceftibuten uptake. Ceftibuten transport occurs via at least two H(+)-dependent transport systems: one is PepT1, and the other is the ceftibuten/H(+) cotransport system. On the other hand, we demonstrated that nateglinide transport occurs via a single system that is H(+) dependent but is distinct from PepT1 and may be identical to the ceftibuten/H(+) cotransport system.

Comparison of voglibose and nateglinide for their acute effects on insulin secretion and free fatty acid levels in OLETF rat portal blood after sucrose loading

OBJECTIVE

Short-term hypoglycemic effects of single dose voglibose and nateglinide were compared after sucrose loading in spontaneously diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats.

MATERIALS AND METHODS

After a 17-h fasting period, the animals received 0.06 mg/kg of voglibose (VOG group, n = 6), 50 mg/kg of nateglinide (NAT group, n = 6), or 0.5% methyl cellulose (control group, n = 6), immediately followed by 2.5 g/kg of sucrose.

RESULTS

Compared to control group values, glucose levels after sucrose loading were significantly decreased in the portal blood in the VOG group and in the peripheral blood in the NAT and VOG groups. The portal glucose AUC0-120 min was significantly lower in the VOG group than in the control and NAT groups, whereas the peripheral glucose AUC0-120 min was significantly lower in the VOG and NAT groups than in the control group. Portal insulin levels in the VOG group were significantly decreased compared to the control group. However, portal insulin levels in the NAT group were acutely increased, peaking 15 min after sucrose loading. Portal FFA levels were decreased in the NAT group 15, 30, and 60 min after sucrose loading; no FFA reductions were seen in the VOG group.

CONCLUSIONS

Although both drugs produced similar hypoglycemic effects after sucrose loading in the peripheral blood, these drugs generated vastly different results in portal blood. Reduced FFA in the portal blood, observed after single administration of nateglinide, may have a favorable impact not only on glucose metabolism but also on lipid metabolism.

Clinical characteristics of nateglinide response as assessed by insulinogenic indices: preliminary study to determine an optimal indication for nateglinide

Insulin secretion dynamics and response to nateglinide were studied in patients with type 2 diabetes and reduced early-phase insulin secretion. On day 1, 24 patients underwent a 75-g oral glucose tolerance test without taking nateglinide. On day 2, they were given oral nateglinide 90 mg immediately before the oral glucose tolerance test. After glucose loading, insulin levels increased significantly at 30, 60, 90, and 120 minutes after the patients took nateglinide, along with insulinogenic indices, the total area under the insulin curve, the area under the 0- to 90-minute insulin curve, and the area under the 90- to 180-minute insulin curve. Both the plasma glucose level at 60, 90, 120, and 180 minutes and the total area under the glucose curve were significantly reduced following nateglinide administration. Compared with the low responders (n=13), the high responders (n=11) had a significantly shorter duration of disease, significantly higher insulinogenic indices in the absence of nateglinide administration, and a higher homeostasis model assessment-beta cell performance. Nateglinide demonstrated a rapid-onset and rapid-offset insulin secretion-stimulating effect in this study population. A single dose of nateglinide may be indicated for patients with a relatively high homeostasis model assessment-beta cell performance, a short duration of disease, and relatively high insulinogenic indices prior to nateglinide administration.

Effects of nateglinide on the secretion of glycated insulin and glucose tolerance in type 2 diabetes

AIMS

Glycation of insulin has been demonstrated within pancreatic beta-cells and the resulting impaired bioactivity may contribute to insulin resistance in diabetes. We used a novel radioimmunoassay to evaluate the effect of nateglinide on plasma concentrations of glycated insulin and glucose tolerance in type 2 diabetes.

METHODS

Ten patients (5 M/5 F, age 57.8+/-1.9 years, HbA(1c) 7.6+/-0.5%, fasting plasma glucose 9.4+/-1.2 mmol/l, creatinine 81.6+/-4.5 microM/l) received oral nateglinide 120 mg or placebo, 10 min prior to 75 g oral glucose in a random, single blind, crossover design, 1 week apart. Blood samples were taken for glycated insulin, glucose, insulin and C-peptide over 225 min.

RESULTS

Plasma glucose and glycated insulin responses were reduced by 9% (P=0.005) and 38% (P=0.047), respectively, following nateglinide compared with placebo. Corresponding AUC measures for insulin and C-peptide were enhanced by 36% (P=0.005) and 25% (P=0.007) by nateglinide.

CONCLUSIONS

Glycated insulin in type 2 diabetes is reduced in response to the insulin secretagogue nateglinide, resulting in preferential release of native insulin. Since glycated insulin exhibits impaired biological activity, reduced glycated insulin release may contribute to the antihyperglycaemic action of nateglinide.

The effect of nateglinide taken with food on gastric emptying rates in healthy subjects

OBJECTIVES

The aim of this study was to determine the effect of the timing of food intake on the pharmacokinetics and pharmacodynamics of oral nateglinide 60 mg and the effect of nateglinide on the rate of gastric emptying.

METHODS

A randomized, double-blind, placebo-controlled, single-dose, 6-period, crossover study conducted in healthy male volunteers aged 18 to 50 years. On 5 occasions, subjects received a single 60-mg tablet of nateglinide at -30, -10, -5, -1, or 40 minutes from the start of a standard metal. Treatment blind was maintained by administration of placebo tablets at all other time points. On the sixth occasion, subjects received placebo tablets at all dosing time points. Each subject received acetaminophen 1 g at the beginning of the standard breakfast on each treatment day as an indicator of the rate of gastric emptying. Plasma samples were collected over a 6-hour period to determine nateglinide, glucose, insulin, and acetaminophen concentrations.

RESULTS

Twelve white men with a mean (SD) age of 30 (6.8) years (range, 21-47 years) and mean (SD) weight of 73.3 (11.0) kg completed all 6 periods of the study. Nateglinide absorption was faster when administered at -5 or -10 minutes relative to food, as characterized by higher nateglinide area under the concentration-time curve from 0 to 5 hours (AUC(0-5)) and maximum plasma concentration (C(max)) values, compared with those observed at other dosing time points. Mean time to C(max) (T(max)) was also shorter when nateglinide was given at -10 minutes versus other dosing time points. Mean nateglinide half-life was similar for all 5 treatments (range, 81.3-94.6 minutes). The overall treatment effect was statistically significant for nateglinide AUC(0-5) (P = 0.031), C(max) (P = 0.001), and T(max) (P < 0.001). Insulin T(max) was shorter after nateglinide administration at -30 or -10 minutes, which was associated with lower glucose C(max) values (-30 minutes, P < 0.05) and a tendency for lower glucose AUC(0-5) values (-10 minutes, P = NS). NS). No treatment effects were observed for any of the acetaminophen indices, as demonstrated by the absence of any change in acetaminophen T(max) or C(max) value.

CONCLUSIONS

Nateglinide was well tolerated and no treatment-limiting adverse events were reported in the population studied. Nateglinide administration appeared to have no effect on the rate of gastric emptying as indicated by acetaminophen indices, regardless of the time of nateglinide administration. The findings imply that the time for nateglinide administration to obtain optimal pharmacodynamic effects is prior to food consumption.

Nateglinide, a D-phenylalanine derivative lacking either a sulfonylurea or benzamido moiety, specifically inhibits pancreatic beta-cell-type K(ATP) channels

A novel antidiabetic agent, nateglinide, is a D-phenylalanine derivative lacking either a sulfonylurea or benzamido moiety. We examined with the patch-clamp method the effect of nateglinide on recombinant ATP-sensitive K(+) (K(ATP)) channels expressed in human embryonic kidney 293T cells transfected with a Kir6.2 subunit and either of a sulfonylurea receptor (SUR) 1, SUR2A, and SUR2B. In inside-out patches, nateglinide reversibly inhibited the spontaneous openings of all three types of SUR/Kir6.2 channels. Nateglinide inhibited SUR1/Kir6.2 channels with high and low affinities (K(i) = 75 nM and 114 microM) but SUR2A/Kir6.2 and SUR2B/Kir6.2 channels only with low affinity (K(i) = 105 and 111 microM, respectively). Nateglinide inhibited the K(ATP) current mediated by Kir6.2 lacking C-terminal 26 amino acids only with low affinity (K(i) = 290 microM) in the absence of SUR. Replacement of serine at position 1237 of SUR1 to tyrosine [SUR1(S1237Y)] specifically abolished the high-affinity inhibition of SUR1/Kir6.2 channels by nateglinide. MgADP or MgUDP (100 microM) augmented the inhibitory effect of nateglinide on SUR1/Kir6.2 but not SUR1(S1237Y)/Kir6.2 or SUR2A/Kir6.2 channels. This augmenting effect of MgADP was also observed with the SUR1/Kir6.2(K185Q) channel, which was not inhibited by MgADP, but not with the SUR1(K1384A)/Kir6.2 channel, which was not activated by MgADP. These results indicate that therapeutic concentrations of nateglinide (approximately 10 microM) may selectively inhibit pancreatic type SUR1/Kir6.2 channels through SUR1, especially when the channel is activated by intracellular MgADP, even though the agent does not contain either a sulfonylurea or benzamido moiety.

Pharmacological agents that directly modulate insulin secretion

Blood glucose levels are sensed and controlled by the release of hormones from the islets of Langerhans in the pancreas. The beta-cell, the insulin-secreting cell in the islet, can detect subtle increases in circulating glucose levels and a cascade of molecular events spanning the initial depolarization of the beta-cell membrane culminates in exocytosis and optimal insulin secretion. Here we review these processes in the context of pharmacological agents that have been shown to directly interact with any stage of insulin secretion. Drugs that modulate insulin secretion do so by opening the K(ATP) channels, by interacting with cell-surface receptors, by altering second-messenger responses, by disrupting the beta-cell cytoskeletal framework, by influencing the molecular reactions at the stages of transcription and translation of insulin, and/or by perturbing exocytosis of the insulin secretory vesicles. Drugs acting primarily at the K(ATP) channels are the sulfonylureas, the benzoic acid derivatives, the imidazolines, and the quinolines, which are channel openers, and finally diazoxide, which closes these channels. Methylxanthines also work at the cell membrane level by antagonizing the purinergic receptors and thus increase insulin secretion. Other drugs have effects at multiple levels, such as the calcineurin inhibitors and somatostatin. Some drugs used extensively in research, e.g., colchicine, which is used to study vesicular transport, have no effect at the pharmacological doses used in clinical practice. We also briefly discuss those drugs that have been shown to disrupt beta-cell function in a clinical setting but for which there is scant information on their mechanism of action.

No effect of the novel antidiabetic agent nateglinide on the pharmacokinetics and anticoagulant properties of warfarin in healthy volunteers

The novel hypoglycemic agent nateglinide is pharmacologically distinct from oral hypoglycemic agents such as sulfonylureas and repaglinide. The present study investigated the effects in healthy volunteers of multiple doses of nateglinide on the pharmacokinetics and pharmacodynamics of warfarin. The study comprised a randomized two-group, two-way crossover, open-label design in 12 healthy male subjects. One group of 6 subjects initially received a single oral dose of warfarin 30 mg and then, after a 7- to 14-day washout, received both warfarin and nateglinide (120 mgnateglinide, 10 min before meals for 4 days and a single dose of 30 mg warfarin on the second day). The alternate group of 6 subjects received treatments in the opposite order. Pharmacokinetic profiles were derived from plasma warfarin and nateglinide concentrations. Prothrombin measurements were evaluated in both periods as a measure of warfarin activity. When administered alone or in combination, there were no statistically significant differences in mean warfarin (R- and S-enantiomers) or nateglinide pharmacokinetic parameters. The concurrent administration of nateglinide and warfarin did not affect the maximal change in prothrombin time that follows warfarin administration. In this study, there was no evidence of an effect of coadministration of nateglinide on the pharmacodynamic action of warfarin or any pharmacokinetic interaction between warfarin and nateglinide.

Nateglinide suppresses postprandial hypertriglyceridemia in Zucker fatty rats and Goto-Kakizaki rats: comparison with voglibose and glibenclamide

Postprandial hypertriglyceridemia, as well as postprandial hyperglycemia, are important factors contributing to the development of cardiovascular disease in patients with type 2 diabetes. Nateglinide is a recently approved antidiabetic that suppresses postprandial hyperglycemia by stimulating the early phase of insulin secretion. In the present study, we investigated the effects of nateglinide on postprandial hypertriglyceridemia in obese Zucker fatty (ZF) rats and non-obese diabetic Goto-Kakizaki (GK) rats. Administration of an oral fat load caused marked hypertriglyceridemia with a peak at 2 h in ZF and GK rats. Nateglinide (50 mg/kg) significantly suppressed the increase of plasma triglycerides after fat loading in both types of rat (delta AUC [0-4 h]: 15+/-69 mg.h/dl for nateglinide vs. 838+/-100 mg.h/dl for vehicle in ZF rats; p<0.01, 81+/-22 mg x h/dl for nateglinide vs. 164+/-17 mg.h/dl for vehicle in GK rats; p<0.01). In contrast, other antidiabetic agents (voglibose and glibenclamide) did not show a significant effect on the increase of triglycerides after fat loading. The triglyceride components suppressed by nateglinide were mainly at the origin and in the pre beta subfraction on agarose gel electrophoresis, suggesting that chylomicrons and very low density lipoproteins were decreased. Plasma insulin levels were significantly increased at 30 min in nateglinide-treated rats, but not in voglibose- or glibenclamide-treated rats. These results suggest that nateglinide not only suppresses postprandial hyperglycemia, but also suppresses postprandial hypertriglyceridemia, by promoting rapid and pulsatile insulin secretion in patients with type 2 diabetes.

Effects of nateglinide and glibenclamide on postprandial lipid and glucose metabolism in type 2 diabetes

BACKGROUND

Postprandial hyperlipemia and small, dense LDL particles are features of dyslipidemia in type 2 diabetes. The purpose of this study was (1) to determine whether the oral insulinotropic drugs, nateglinide and glibenclamide, can overcome the defect of insulin action to suppress the hepatic VLDL release after a meal and decrease the postprandial lipemia and (2) to evaluate the acute effect of postprandial hypertriglyceridemia on LDL particle size in subjects with type 2 diabetes.

METHODS

Forty-three subjects with type 2 diabetes and mean baseline HbA(1c) 7.6% (95% CI 7.3 to 7.9) were treated with nateglinide 120 mg three times daily or glibenclamide 5 mg once or twice daily for 12 weeks in a double-blind randomised trial. Insulin, glucose, and lipoprotein responses to a mixed fat-rich meal were determined for 8 h postprandially at baseline and at 12 weeks on-trial.

RESULTS

Nateglinide and glibenclamide significantly augmented the maximal response in serum insulin at 60 min postprandially compared with the response without the drug [additional increase 25.0 mU/l (95% CI 11.2-38.8) p = 0.001 and 12.5 mU/l (95% CI 4.6-20.3) p = 0.003, respectively] and reduced hyperglycemia. Neither drug affected fasting or postprandial lipid or lipoprotein levels. LDL size did not significantly change in the 8-h postprandial period.

CONCLUSIONS

Although nateglinide and glibenclamide increase postprandial insulin secretion and attenuate hyperglycemia, they do not alleviate postprandial lipemia in subjects with type 2 diabetes and good glycemic control. Although small LDL particle size is associated with chronic hypertriglyceridemia, LDL size does not change during acute postprandial hypertriglyceridemia.

Differential interactions of nateglinide and repaglinide on the human beta-cell sulphonylurea receptor 1

Repaglinide and nateglinide represent a new class of insulin secretagogues, structurally unrelated to sulphonylureas, that were developed for the treatment of type 2 diabetes. The inhibitory effect of these drugs was investigated on recombinant wild-type and mutant Kir6.2/SUR1 channels expressed in HEK293 cells. Nateglinide and repaglinide dose-dependently inhibited whole-cell Kir6.2/SUR1 currents with half-maximal inhibitory concentration (IC(50)) values of 800 and 21 nmol/l, respectively. Mutation of serine 1237 in SUR1 to tyrosine (S1237Y) abolished tolbutamide and nateglinide block, suggesting that these drugs share a common point of interaction on the SUR1 subunit of the ATP-sensitive K(+) channel. In contrast, repaglinide inhibition was unaffected by the S1237Y mutation (IC(50) = 23 nmol/l). Radioligand binding studies revealed a single high-affinity binding site for [(3)H]repaglinide on membranes prepared from HEK293 cells expressing wild-type (equilibrium dissociation constant [K(D)] = 0.40 nmol/l) or mutant (K(D) = 0.31 nmol/l) Kir6.2/SUR1 channels. Nateglinide and tolbutamide displaced [(3)H]repaglinide binding to wild-type channels with IC(50) values of 0.7 and 26 micro mol/l, respectively, but produced <10% displacement of [(3)H]repaglinide bound to mutant channels. This is consistent with the idea that binding of nateglinide and tolbutamide, but not repaglinide, is abolished by the SUR1[S1237Y] mutation and that the binding site for repaglinide is not identical to that of nateglinde/tolbutamide. These results are discussed in terms of a conformational analysis of the drug molecules.

Interaction of nateglinide with K(ATP) channel in beta-cells underlies its unique insulinotropic action

Nateglinide is a novel insulinotropic agent for the treatment of type 2 diabetes. It is a D-phenylalanine derivative, chemically distinct from repaglinide and sulphonylureas (glyburide or glimepiride). Although each agent is known to stimulate insulin release via the signaling cascade initiated by closure of ATP-dependent K+ (K(ATP)) channels in pancreatic beta-cells, the pharmacological effect of nateglinide is reportedly fast-acting, short-lasting, sensitive to ambient glucose and more resistant to metabolic inhibition. The aim of the present study was to elucidate the molecular mechanism(s) underlying the distinct properties of the insulinotropic action of nateglinide. By using the patch-clamp methods, we comparatively characterized the potency and kinetics of the effect of these agents on K(ATP) channels in rat beta-cells at normal vs. elevated glucose and under physiological condition vs. experimentally induced metabolic inhibition. Our results demonstrated that the mode of the action of nateglinide on K(ATP) current was unique in (a) glucose dependency; (b) increased potency and efficacy under ATP depletion and uncoupling of mitochondrial oxidative phosphorylation than physiological condition; (c) substantially more rapid onset and offset kinetics. The data provide mechanistic rationale for the unique in vivo and ex vivo activity profile of nateglinide and may contribute to reduced hypoglycemic potential associated with excessive insulin secretion.

Effect of KAD-1229, a novel hypoglycaemic agent, on plasma glucose levels after meal load in type 2 diabetic rats

1. The effects of KAD-1229 (a novel non-sulphonylurea agent), voglibose (an alpha-glucosidase inhibitor) and nateglinide (a non-sulphonylurea antihyperglycaemic agent) on hyperglycaemia induced by a meal load were assessed in diabetic rats. 2. KAD-1229 suppressed the increase in plasma glucose levels seen after a meal load and the area under the curve for plasma glucose levels (AUCglucose) up to 5 h after the meal load. 3. Voglibose also suppressed the increase in plasma glucose levels; however, a significant decrease in AUCglucose following voglibose was not observed. 4. Nateglinide suppressed the increase in plasma glucose levels at 30 min and 1 h after the meal load; however, plasma glucose levels was above control thereafter and the AUCglucose was not decreased. 5. The results indicate that KAD-1229 has an antihyperglycaemic effect and KAD-1229 is suggested to be a suitable agent for controlling post-prandial hyperglycaemia.

Randomized dose ranging study of the reduction of fasting and postprandial glucose in type 2 diabetes by nateglinide (A-4166)

OBJECTIVE

This randomized crossover double-blind placebo-controlled study aimed to assess the efficacy of nateglinide (A-4166), a novel phenylalanine-derived insulin secretagogue, in type 2 diabetic subjects while fasting and 5 min before a standard meal.

RESEARCH DESIGN AND METHODS

A single dose of nateglinide (60, 120, or 180 mg) or placebo was given to eight diet-treated overnight-fasted type 2 diabetic patients and to seven patients 5 min before a standard breakfast. Plasma glucose, radioimmunoassay insulin, and nateglinide were measured at baseline and for a further 180 min.

RESULTS

The time-averaged 180-min postdose mean decrease in fasting plasma glucose concentration was greater after nateglinide (1.8 mmol/l; 95% CI 1.5-2.0) than after placebo (0.7 mmol/l; 95% CI 0.3-1.2) (P < 0.001). Hypoglycemia did not develop in any of the subjects. Insulin concentrations increased 1.5-, 1.8-, and 1.9-fold with the 60-, 120-, and 180-mg doses, respectively (P < 0.001), peaking approximately 30 min after the dose. Nateglinide concentrations peaked after approximately 30 min, decreasing to 21% of peak by 180 min. In the meal test, the mean increase (2.9 mmol/l, 2.3-3.6) in plasma glucose over 180 min after placebo was reduced by 1.8 mmol/l (P < 0.001) with the two higher doses of nateglinide.

CONCLUSIONS

A single dose of nateglinide administered to diet-treated type 2 diabetic patients with fasting hyperglycemia increased insulin secretion and reduced fasting glucose without hypoglycemia. Administered 5 min before a meal, nateglinide reduced the postprandial glucose excursion by 64%. With its rapid onset and short duration of action, nateglinide is a promising oral prandial therapy in type 2 diabetes.

Nateglinide: a new rapid-acting insulinotropic agent

The United Kingdom Prospective Diabetes Study has shown that tight glycaemic control significantly reduces microvascular complications in Type 2 diabetes, but the effects on macrovascular complications were less impressive and did not reach statistical significance. Epidemiological studies have shown that post-prandial hyperglycaemia, rather than fasting hyperglycaemia, is more closely related to cardiovascular complications. It is, therefore, possible that previous studies may have overlooked the possible benefits of tight control of post-prandial hyperglycaemia as an important factor in reducing the cardiovascular mortality. Nateglinide is a novel D-phenylalanine derivative that inhibits ATP-sensitive K+ channels in pancreatic beta-cells in the presence of glucose and thereby restores first phase insulin response in patients with Type 2 diabetes. This helps in reducing post-prandial glucose excursion. Combination studies with metformin have shown it to be effective in controlling hyperglycaemia. While metformin reduces the basal plasma glucose, nateglinide helps in controlling post-prandial peaks. Nateglinide provides a new therapeutic option for treating Type 2 diabetes by specifically targeting post-prandial hyperglycaemia.

Early insulin release effectively improves glucose tolerance: studies in two rodent models of type 2 diabetes mellitus

AIM

Islet dysfunction, characterized by the loss of an acute insulin secretory response (AIR) to glucose is a well-established pathology of type 2 diabetes mellitus. Using oral insulin secreting agents with very different pharmacodynamic profiles, the present study was undertaken to test the hypothesis that, within the setting of an underlying insulin resistance, changes in the insulin response profile can differentially affect glycaemic control.

METHOD

The mildly insulin resistant high-fat fed Sprague Dawley (HF) rat and the very insulin resistant Zucker fatty (fa/fa) rat, chronically fitted with indwelling jugular cannula were subjected to an oral glucose load. Compounds were administered 5 min before the oral glucose load. Nateglinide (Nateg) was administered to elicit only an early insulin secretory response and glipizide (Glip) to elicit a later but greater insulin secretory response. Acetaminophen was used as a marker to assess for potential effects of these compounds on gastric emptying rates.

RESULTS

Nateg rapidly increased early insulin release (from -5 to 0) while the effects on total insulin release were similar to those in the controls and glucose excursions were eliminated in both diabetic models with no evidence of sustained hypoglycaemia. Conversely, Glip did not affect early insulin release but increased total insulin release (- 15 to 120 min), but only after the oral glucose load. Glip partially curbed glucose excursions in the mildly insulin resistant HF rodent and was totally ineffective in the very insulin resistant Zucker rat. The differential effects could not be attributed to effects on gastric emptying rates.

CONCLUSION

These data support the importance of early insulin release in type 2 diabetes mellitus and indicate that, independent of the level of insulin resistance, stimulating insulin release early and briefly provides for more effective and tighter glycaemic control than increasing insulin exposure to a greater magnitude later.

Differential effects of short and long duration insulinotropic agents on meal-related glucose excursions

AIM

Abnormal beta-cell function, characterized as the inability of the beta-cell to mount a rapid secretory response to glucose, is a well-established pathology of type 2 diabetes mellitus. These studies were designed to demonstrate the importance of early insulin release on the control of meal-induced glucose excursions by capitalizing on the significant pharmacodynamic differences between several oral insulin secreting agents.

METHODS

Male Sprague Dawley fitted with indwelling jugular cannulas were used to compare the pharmacodynamic profiles of nateglinide (Nateg), glipizide (Glip) and repaglinide (Repag) through frequent blood samples following the administration of these compounds via oral gavage. In similar animals which were pretrained to consume their daily food intake in two discrete 45-min meals, the effects of compound induced changes in pre-meal, meal and post-meal insulin profiles on glycaemic control were assessed through frequent blood sampling following the administration of these compounds 10 min prior to a 30-min meal.

RESULTS

There were significant pharmacodynamics differences between the three oral agents tested and the time to elicit peak insulin secretory responses increased from Nateg (4 min) to Repag (10 min) to Glip (45 min). During the meal tolerance test, glibenclamide did not increase pre-meal insulin levels and glucose excursions paralleled those in the control. Conversely, the other three agents, at doses that produced hypoglycaemic responses of similar magnitude, all increased early insulin release (Delta AUC(-15 to 3 min) = 0.5 +/- 0.01, 1.6 +/- 0.4, 3.6 +/- 0.0, 1.2 +/- 0.1 and 1.73 +/- 0.4 nmol/min, for control, Nateg at 60 and 120 mg/kg, Glip and Repag, respectively) and curbed glucose excursions during the meal at varying rates and degrees (Delta AUC(0--30 min) = 39 +/- 6, 8 +/- 7, 5 +/- 7, - 1 +/- 8 and - 3 +/- 8 mmol/min for control, Nateg at 60 and 120 mg/kg, Glip and Repag, respectively). However, unlike Nateg, the longer duration of action of Repag and Glip elicited sustained post-meal relative hypoglycaemia.

CONCLUSION

These data support the impact of early and rapid insulin release in the control of prandial and post-meal glycaemia and demonstrate that a short anticipatory burst of insulin, restricted to the beginning of a meal, provides a clear metabolic advantage and prevents post-meal hypoglycaemic episodes when compared to a greater but reactive insulin exposure that follows a meal-induced increase in glucose excursion.

Mealtime glucose regulation with nateglinide in healthy volunteers: comparison with repaglinide and placebo

OBJECTIVE

This study was designed to compare the pharmacodynamic effects of single doses of nateglinide (A-4166), repaglinide, and placebo on mealtime insulin secretion and glycemic control in healthy subjects.

RESEARCH DESIGN AND METHODS

Fifteen healthy volunteers participated in this open-label five-period crossover study. They received single 10-min preprandial doses of 120 mg nateglinide, 0.5 or 2 mg repaglinide, or placebo or 1 min preprandially of 2 mg repaglinide. Subjects received each dose only once, 48 h apart. Pharmacodynamic and pharmacokinetic assessments were performed from 0 to 12 h postdose.

RESULTS

Nateglinide induced insulin secretion more rapidly than 2 and 0.5 mg repaglinide and placebo (10 min preprandial), with mean rates of insulin rise of 2.3, 1.3, 1.15, and 0.8 microU x ml(-1) x min(-1), respectively, over the 0- to 30-min postmeal interval. After peaking, insulin concentrations decreased rapidly in the nateglinide-treated group and were similar to placebo within 2 h postdose. After 2 mg repaglinide, peak insulin concentrations were delayed and returned to baseline more slowly than with nateglinide treatment. Nateglinide treatment produced lower average plasma glucose concentrations in the 0- to 2-h postdose interval than either dose of repaglinide and placebo (P < 0.05 vs. 0.5 mg repaglinide and placebo). Plasma glucose concentrations returned more rapidly to predose levels with nateglinide treatment than with either dose of repaglinide. Treatment with repaglinide produced a sustained hypoglycemic effect up to 6 h postdose.

CONCLUSIONS

In this single-dose study in nondiabetic volunteers, nateglinide provided a more rapid and shorter-lived stimulation of insulin secretion than repaglinide, resulting in lower meal-related glucose excursions. If similar results are observed in diabetes, nateglinide may produce a more physiological insulin secretory response with the potential for a reduced risk of postabsorptive hypoglycemia.