Re-exploring promising α-glucosidase inhibitors for potential development into oral anti-diabetic drugs: Finding needle in the haystack

Treatment of diabetes mellitus by oral α-glucosidase inhibitors is currently confined to acarbose, miglitol and voglibose marred by efficacy problems and unwanted side effects. Since the discovery of the drugs more than three decades ago, no significant progress has been made in the drug development area of anti-diabetic α-glucosidase inhibitors. Despite existence of a wide chemical diversity of α-glucosidase inhibitors identified to date, majority of them are simply piled up in publications and reports thus creating a haystack destined to be forgotten in the scientific literature without given consideration for further development into drugs. This review finds those "needles" in that haystack and lays groundwork for highlighting promising α-glucosidase inhibitors from the literature that may potentially become suitable candidates for pre-clinical or clinical trials while drawing attention of the drug development community to consider and take already-identified promising α-glucosidase inhibitors into the next stage of drug development.

Miglitol: assessment of its role in the treatment of patients with diabetes mellitus

OBJECTIVE

To evaluate miglitol, a new oral alpha-glucosidase inhibitor, and discuss its pharmacology, therapeutics, pharmacokinetics, dosing guidelines, adverse effects, drug interactions, and clinical efficacy.

DATA SOURCES

A MEDLINE English-language only database search using the keywords miglitol, glyset, and Bay m 1099 (1985 to December 1999), was completed to identify relevant articles including reviews, recent studies, and abstracts; American Diabetes Association 1999 Annual Meeting abstracts; Pharmacia & Upjohn data on file and product information.

STUDY SELECTION

The clinical trials that were selected to be reviewed in detail were randomized, double-blind studies with at least 100 patients in the intention-to-treat group.

DATA EXTRACTION

All articles and abstracts were reviewed along with the product labeling from Pharmacia & Upjohn.

DATA SYNTHESIS

Miglitol is an alpha-glucosidase inhibitor that exerts its effect through the delayed absorption of complex carbohydrates in the small intestine, resulting in a decrease in postprandial glucose concentrations that are directly correlated with the dietary carbohydrate content. Both small, short-term trials and large, clinical trials show a decrease in postprandial glucose concentrations and a modest decrease in glycosylated hemoglobin of approximately 0.5-1.0% as a result of miglitol's action. The adverse effects of miglitol are mild and transitory and include flatulence, diarrhea, and abdominal pain. The incidence of gastrointestinal problems may be reduced with a small initial dose, which is slowly titrated as tolerated.

CONCLUSIONS

Miglitol is an effective and safe treatment option in patients with type 2 diabetes mellitus who are inadequately controlled with diet or oral sulfonylurea therapy. Miglitol is a good choice of therapy in Hispanic, African-American, and elderly patients, or any patients in whom hypoglycemia, weight gain, or lactic acidosis are risks. No published studies comparing miglitol with acarbose have been published, but there appears to be no major clinical or financial advantages to using one agent over the other.

Miglitol, a new alpha-glucosidase inhibitor

Miglitol (Bay m 1099, Bayer) is a second generation alpha-glucosidase inhibitor. It is a derivative of 1-desoxynojirimycin, and binds reversibly to the brushborder alpha-glucosidase enzymes. In contrast to its parent drug (acarbose, Bay g 5421, Bayer), miglitol is almost completely absorbed in the small intestine. It has to be taken with each main meal, and through its effect on carbohydrate digestion it blunts the postprandial blood glucose increase. Miglitol has no or a very small effect on fasting blood glucose levels. The blood-glucose lowering effects of miglitol in patients with Type 2 diabetes are lower than those of the frequently-used sulphonylurea compounds. Long-term studies show that a moderate average reduction of HbA1c of 0.3-0.7% point from baseline can be achieved. An advantage over sulphonylurea is the effect on serum insulin levels: miglitol therapy leads to slightly lower postprandial levels of serum insulin, whereas chronic sulphonylurea treatment usually increases serum insulin levels. This insulin-sparing effect may, in theory, lead to a lesser weight gain or even no weight gain and reduced risk of hypoglycaemia during chronic treatment. Long-term experience in Type 1 diabetic patients is limited. Similarly, miglitol may lead to reduced postprandial glucose excursions, slightly reduced insulin requirements and perhaps, as a consequence, a lower risk of hypoglycaemia. More long-term data are needed to fully assess to the clinical use of miglitol in these patients.

[Current status of the treatment of type 2 diabetes mellitus. Alpha-glucosidase inhibitors]

The development of antidiabetic drugs with complementary mechanisms of action appears more and more necessary in order to achieve durable glycaemic control in type 2 diabetes. By inhibiting in a reversible way the hydrolysis of disaccharides and the ultimate steps of the digestion of dietary polysaccharides, alpha-glucosidase inhibitors reduce postprandial blood glucose raise in diabetics. This therapeutic class, limited in Europe until recently to acarbose, has been enlarged with the marketing of miglitol, whose pharmacokinetic properties might lead to better long term tolerance. The improvement of glycaemic control obtained with alpha-glucosidase inhibitors is now better evaluated and appears similar whatever the combinations with other antidiabetic drugs, including insulin. The role of alpha-glucosidase inhibitors in the overall therapeutic strategy of type 2 diabetes and their benefit on the evolution of long term complications remains to be clarified.

Glucose tolerance and insulin resistance in the JCR:LA-corpulent rat: effect of miglitol (Bay m1099)

A standardized meal tolerance test (MTT) using 5 g rat chow provides a sensitive index of insulin and glucose metabolism in the insulin-resistant, hyperinsulinemic, hypertriglyceridemic, and atherosclerosis-prone JCR:LA-corpulent (cp) strain of rats. The MTT revealed differences in insulin/glucose metabolism that were not evident in either an intravenous (IVGTT) or intraperitoneal (IPGTT) glucose tolerance test. The glycemic response of control rats to a 5-g carbohydrate test meal containing miglitol (Bay m1099) was sharply reduced, with a 50% effective dose (ED50) of 36.4 +/- 7.5 mg/100 g food. At a dose of 60 mg/100 g food, the plasma glucose curve was flat and indistinguishable from that found in the nonfed state. The plasma insulin response was similarly reduced, with an ED50 of 42.8 +/- 14.8 mg/100 g food. Obese male rats were treated with miglitol at 60 mg/100 g food from 6 to 12 weeks of age. Treated rats had a significantly reduced food consumption and lower body weight at 12 weeks of age (P < .05). The treatment resulted in no significant changes in serum lipid concentrations. When subjected to the MTT using control (non-miglitol-containing) food, treated rats demonstrated markedly improved insulin sensitivity, with a greatly reduced insulin response, which may reflect an improved hepatic glucose metabolism. The results confirm that miglitol is highly effective in this obese insulin-resistant animal model. It reduced postprandial glycemic and insulin responses, and on long-term treatment, it improved glucose and insulin metabolism. These beneficial metabolic changes suggest that miglitol may have vascular protective effects in insulin-resistant states.