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

Differential therapeutic effects of nateglinide and acarbose on fasting and postprandial lipid profiles: a randomized trial

BACKGROUND

Dyslipidemia is commonly seen in patients with type 2 diabetes mellitus (T2DM). The current study sought to compare the effects of nateglinide and acarbose, two antihyperglycemic agents, on both fasting and postprandial lipid profiles in Chinese subjects with T2DM.

SUBJECTS AND METHODS

For this multicenter, open-label, randomized, active-controlled, parallel-group study, 103 antihyperglycemic agent-naive patients with T2DM were recruited from four hospitals in China. In total, 85 subjects (44 in the nateglinide group, 41 in the acarbose group) with a known complete lipid profile underwent the entire clinical trial and were included in the final analysis. Serum was collected in the fasting state and 30 and 120 min after a standardized meal (postprandial states) to measure the baseline lipid profiles; the same testing was performed upon completion of a 2-week course of nateglinide (120 mg three times a day) or acarbose (50 mg three times a day).

RESULTS

Fasting triglyceride (TG) levels were significantly reduced by both nateglinide and acarbose (P<0.001), with acarbose providing a significantly more robust improvement (vs. nateglinide, P=0.005). Additionally, the TG levels at both postprandial times were significantly reduced by acarbose (P<0.001 at 30 min and P=0.002 at 120 min), whereas nateglinide treatment only significantly reduced the 30-min postprandial TG (P=0.029). Neither nateglinide nor acarbose treatment had significant impact on total cholesterol, high-density lipoprotein, low-density lipoprotein, or non-high-density lipoprotein cholesterol.

CONCLUSIONS

Compared with nateglinide, acarbose has superior therapeutic efficacy for reducing fasting and postprandial TG levels in patients with T2DM.

Hypolipidemic effect of Pleurotus eryngii extract in fat-loaded mice

Pleurotus eryngii water extract (PEE), which showed the most significant inhibitory activity against pancreatic lipase in vitro among eight edible mushrooms, was investigated to determine the mechanism of its anti-lipase activity in vitro and its hypolipidemic effect in fat-loaded mice. The inhibitory effects of mushroom extracts on pancreatic lipase activity were examined using 4-methylumbelliferyl oleate (4-MUO) or trioleoylglycerol emulsified with lecithin, gum arabic or Triton X-100 as a substrate. For in vivo experiments, blood samples were taken after oral administration of corn oil and [(3)H]trioleoylglycerol with or without PEE to food-deprived mice. PEE inhibited hydrolysis of 4-MUO and trioleoylglycerol emulsified with lecithin or Triton X-100, but not that of trioleoylglycerol emulsified with gum arabic. PEE suppressed the elevations of plasma and chylomicron triacylglycerol levels after oral administration of corn oil, but had no effect on lipoprotein lipase activity. [(3)H]Trioleoylglycerol absorption was also decreased by administration of PEE. The results of in vitro studies suggest that PEE may prevent interactions between lipid emulsions and pancreatic lipase. The hypolipidemic effect of PEE in fat-loaded mice may be due to low absorption of fat caused by the inhibition of pancreatic lipase.

Pancreatic islet overproduction of H2S and suppressed insulin release in Zucker diabetic rats

Hydrogen sulfide (H(2)S) has been traditionally known for its toxic effects on living organisms. The role of H(2)S in the homeostatic regulation of pancreatic insulin metabolism has been unclear. The present study is aimed at elucidating the effect of endogenously produced H(2)S on pancreatic insulin release and its role in diabetes development. Diabetes development in Zucker diabetic fatty (ZDF) rats was evaluated in comparison with Zucker fatty (ZF) and Zucker lean (ZL) rats. Pancreatic H(2)S production and insulin release were also assayed. It was found that H(2)S was generated in rat pancreas islets, catalyzed predominantly by cystathionine gamma-lyase (CSE). Pancreatic CSE expression and H(2)S production were greater in ZDF rats than in ZF or ZL rats. ZDF rats exhibited reduced serum insulin level, hyperglycemia, and insulin resistance. Inhibition of pancreatic H(2)S production in ZDF rats by intraperitoneal injection of DL-propargylglycine (PPG) for 4 weeks increased serum insulin level, lowered hyperglycemia, and reduced hemoglobin A1c level (P<0.05). Although in ZF rats it also reduced pancreatic H(2)S production and serum H(2)S level, PPG treatment did not alter serum insulin and glucose level. Finally, H(2)S significantly increased K(ATP) channel activity in freshly isolated rat pancreatic beta-cells. It appears that insulin release is impaired in ZDF because of abnormally high pancreatic production of H(2)S. New therapeutic approach for diabetes management can be devised based on our observation by inhibiting endogenous H(2)S production from pancreas.

Change in long-spacing collagen in Descemet's membrane of diabetic Goto-Kakizaki rats and its suppression by antidiabetic agents

We examined changes in the ultrastructure and localization of major extracellular matrix components, including 5 types of collagen (type I, III, IV, VI, and VIII), laminin, fibronectin, and heparan sulfate proteoglycan in Descemet's membrane of the cornea of diabetic GK rats. In the cornea of diabetic GK rats, more long-spacing collagen fibrils were observed in Descemet's membrane than in the membrane of the nondiabetic Wistar rats. Both GK and Wistar rats showed an age-dependent increase in the density of the long-spacing collagen. Immunoelectron microscopy showed that type VIII collagen was localized in the internodal region of the long-spacing collagen, which was not labelled by any of the other antibodies used. The antidiabetic agents nateglinide and glibenclamide significantly suppressed the formation of the long-spacing collagen in the diabetic rats. Long-spacing collagen would thus be a useful indicator for studying diabetic changes in the cornea and the effect of antidiabetic agents.

A review of islet of Langerhans degeneration in rodent models of type 2 diabetes

Type 2 diabetes mellitus (TTDM) is characterized by progressive loss of glucose control through multifactorial mechanisms. The search for an understanding of TTDM has relied on animal models since the realization of the importance of the pancreas in controlling plasma glucose concentration. Rodent models of TTDM are developed to express hyperglycemia and not islet degeneration per se. Degeneration of the islets of Langerhans with beta-cell loss is secondary to insulin resistance and is regarded as the more important lesion. Despite this, differences between models are seen in the development and progression of islet degeneration. Assessing the differences between the models is important to appreciate the various aspects of TTDM and understand their advantages as well as their deficiencies. Relevant animal models of TTDM provide opportunities to investigate important physiological and cell biological processes that may ultimately lead to development of targeted therapies. This article reviews the importance, advantages, and limitations of rodent models of TTDM in relation to the histopathological changes that characterize islet degeneration. Pathophysiological mechanisms that contribute to islet degeneration are also discussed and are placed into the context of changes in islet histological appearances.

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.

Effect of nateglinide on the size of LDL particles in patients with type 2 diabetes

The objective of the present study was to evaluate the efficacy of nateglinide in controlling blood glucose levels and regulating lipid metabolism in patients with type 2 diabetes by focusing attention particularly on low-density lipoprotein (LDL) particle size. The subjects were 23 patients with type 2 diabetes who were given nateglinide, 90 to 270 mg/d. Laboratory studies were conducted at treatment initiation and 3 mo later. Despite a decline that occurred in the level of fasting plasma glucose before and after administration of nateglinide, no significant difference was recognized. Hemoglobin A1c decreased significantly from 6.37+/- 0.75% to 5.91+/-0.64% (P<.001). A significant decline was also seen in the fasting level of immunoreactive insulin, from 9.82+/-5.69 microU/mL to 8.59+/-4.05 microU/mL (P<.05), and in the homeostasis model assessment for insulin resistance, from 3.06+/-1.83 to 2.55+/-1.26 (P<.05). Regarding lipids, triglycerides significantly decreased from 140.7+/-61.8 mg/dL to 117.3+/-34.7 mg/dL )P<.05). The significant reduction in migration index value, which was used as an index to LDL particle size, from 0.374+/-0.034 to 0.357+/-0.035 (P<.05), confirmed that LDL particle size had increased. The results of the present study show that nateglinide is effective in controlling blood glucose and improving insulin resistance, hypertriglyceridemia, and LDL particle size in patients with mild type 2 diabetes. These effects suggest that nateglinide may effectively control coronary artery disease in this population.

Study of nateglinide in Japan: long-term treatment of patients with type 2 diabetes

Nateglinide is an oral antidiabetic medication that acts through rapid, short-term stimulation of insulin production. This study undertook to identify the nature of any adverse effects of nateglinide and to assess its clinical efficacy in long-term use in clinical practice. Patients (n=1014) were recruited from centers in Japan and were followed over a 15-month treatment period. Pretreatment and posttreatment values were obtained for fasting blood glucose, postprandial blood glucose, hemoglobin A1c (HbA1c), triglycerides, and total cholesterol. All adverse reactions were noted, along with standard laboratory blood variables. The efficacy value was rated as 78.76% by the treating physicians; this was indicated by a postprandial glucose decrease of 53.2 mg/dL (from 223.8+/-61.1 mg/dL to 170.6+/-40.7 mg/dL), a fasting glucose decrease of 9.3 mg/dL (from 155.1+/- 40.0 mg/dL to 145.4+/-35.1 mg/dL), and an HbA1c decrease of 0.68% (from 7.51+/- 1.36% to 6.83+/-1.09%). In patients previously treated with sulfonylurea, a decrease in HbA1c was not observed. Changes in HbA1c had no association with age, body mass index (BMI), duration of diabetes, or concomitant disease. No change in BMI was noted after 15 months of nateglinide treatment. Adverse reactions occurred at an incidence of 10.07% (100/993 cases), with hypoglycemic symptoms being the most prevalent (1.91%). Adverse reactions were sometimes associated with extant renal dysfunction, a condition about which the physician had to be aware. No problems such as increased incidences of adverse reactions or deterioration in severity were detected in this long-term study. This study showed the efficacy and safety of long-term treatment with nateglinide of patients with diabetes from various backgrounds.

Nateglinide--current and future role in the treatment of patients with type 2 diabetes mellitus

Therapy for type 2 diabetes mellitus should aim to control not only fasting, but also postprandial glucose levels. Nateglinide, a d-phenylalanine derivative, restores postprandial early phase insulin secretion in a transient and glucose-sensitive manner without affecting basal insulin levels. As nateglinide is administered immediately before meals it provides greater lifestyle flexibility than agents that require patients to eat to avoid hypoglycemic events (e.g. long-acting sulfonylureas). In randomised, double-blind trials in patients with type 2 diabetes, nateglinide monotherapy (mealtime treatment of 120 mg three times daily) significantly improved long-term glycaemic control by significantly reducing glyated haemoglobin (HbA 1c) and preventing mealtime glucose spikes. The combination of nateglinide with insulin-sensitising agents, for example, metformin and thiazolidinediones, addresses the dual defects of loss of insulin secretion and insulin resistance to provide optimal management of type 2 diabetes, and more patients achieve HbA 1c goal with nateglinide combination therapy rather than with monotherapy with other oral agents. Nateglinide also restores early insulin secretion and reduces postprandial hyperglycaemia in prediabetic subjects with impaired glucose tolerance (IGT) and appears similarly effective in elderly and non-elderly populations with type 2 diabetes. It has an excellent safety and tolerability profile, with a low propensity to cause hypoglycaemia due to its transient, selective effect on early phase insulin secretion. Nateglinide as monotherapy or combination therapy is an effective option to reduce mealtime glucose in patients with type 2 diabetes. The results of ongoing research into its potential role in delaying progression to overt diabetes, and protecting against cardiovascular events, in prediabetic patients with IGT are awaited.

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.

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.

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.

A placebo-controlled crossover study comparing the effects of nateglinide and glibenclamide on postprandial hyperglycaemia and hyperinsulinaemia in patients with type 2 diabetes

AIM

This was a randomized, double blind, three period crossover study. The objective was to compare glucose, insulin and C-peptide 24 h profiles in patients with type 2 diabetes mellitus after dosing with nateglinide (given preprandially before three test meals), glibenclamide (administered once before breakfast) or placebo (given before three test meals).

METHODS

Fourteen patients underwent screening followed within 3 weeks by three treatment periods of 1 day, each separated by 7 days. Dosing followed a six-sequence balanced, two 3 x 3-replicated Latin square.

RESULTS

Mean peak serum insulin levels were lower after nateglinide (115 mU/l) than after glibenclamide (145 mU/l.h; p = 0.017) but higher than after placebo (79 mU/l; p = 0.001). However, peak insulin levels were reached earlier after nateglinide [mean time to peak (tmax) 1.7 h] compared to glibenclamide (mean tmax 2.1 h, p = 0.06). Total insulin exposure over the day was higher after glibenclamide compared with that following nateglinide (1216 vs. 1067 mU/l.h; p = 0.009). Similar findings were seen with serum C-peptide. Despite this, mean peak plasma glucose concentrations were lower following nateglinide (11.4 mmol/l from a baseline of 8.3 mmol/l) compared with glibenclamide (13.2 mmol/l from a baseline of 8.5 mmol/l; p = 0.001) and placebo (14.0 mmol/l from a baseline of 8.0 mmol/L; p < 0.001).

CONCLUSIONS

Nateglinide improves early prandial measures of insulin and glucose response to a standard meal, more so than glibenclamide, in people with type 2 diabetes.