Synthesis and alpha-D-glucosidase inhibitory activity of N-substituted valiolamine derivatives as potential oral antidiabetic agents

Troglitazone combination therapy in obese type 2 diabetic patients poorly controlled with alpha-glucosidase inhibitors

The efficacy and safety of treatment with troglitazone combined with an alpha-glucosidase inhibitor, in obese type 2 diabetic patients who were previously administered alpha-glucosidase inhibitors alone, in improving glycaemic control and reducing insulin resistance were studied. Obese type 2 diabetic patients, poorly controlled with alpha-glucosidase inhibitors, were randomized to receive either oral troglitazone 200 mg twice daily (22 patients: group A) or a placebo (20 patients: group B) in addition to their usual alpha-glucosidase inhibitor. In group A, significant decreases in the mean levels of haemoglobin A1c and basal plasma insulin levels were observed 6 months after the start of combined therapy. Serum triglyceride levels significantly decreased but serum lactic acid dehydrogenase and body weight significantly increased. New systemic oedema was observed in six patients. Combined therapy with troglitazone and alpha-glucosidase inhibitors may be effective for diabetic metabolic abnormalities, although the potential development of adverse effects such as body-weight gain and systemic oedema demands vigilance.

Effect of an alpha-glucosidase inhibitor (voglibose), in combination with sulphonylureas, on glycaemic control in type 2 diabetes patients

A multicentre study was conducted to evaluate the effect of the alpha-glucosidase inhibitor, voglibose, on glycaemic control in 113 patients with type 2 diabetes whose blood glucose control was poor on treatment with a sulphonylurea drug. The patients were treated for 24 weeks with 0.6 mg voglibose, given orally three times daily, before a meal, together with their usual sulphonylurea drug treatment. In the 86 patients who completed the study, fasting plasma glucose, 2-h post-prandial plasma glucose and haemoglobin showed statistically significant decreases in FPG, 2h-PPG and HbA1c compared with the baseline (P < 0.05) at almost all time-points during treatment. No serious adverse reactions were reported and there were no significant changes in mean body weights. Plasma glucose control was considered to be improved in 65% of patients; there were no adverse events in 92.9% of patients. The results suggest that the combined use of this alpha-glucosidase inhibitor and sulphonylurea drugs may be effective in controlling plasma glucose in patients with type 2 diabetes and that this combination might delay the onset of vascular complications in these patients.

Antihyperglycemic effects of N-containing sugars from Xanthocercis zambesiaca, Morus bombycis, Aglaonema treubii, and Castanospermum australe in streptozotocin-diabetic mice

The aqueous MeOH extract of the leaves and root of Xanthocercis zambesiaca (Leguminosae) and eight structurally related nitrogen-containing sugars, fagomine (1), 4-O-beta-D-glucopyranosylfagomine (2), 3-O-beta-D-glucopyranosylfagomine (3), 3-epifagomine (4), 2,5-dideoxy-2,5-imino-D-mannitol (5), castanospermine (6), alpha-homonojirimycin (7), and 1-deoxynojirimycin (8) were evaluated for antihyperglycemic effects in streptozotocin (STZ)-diabetic mice. The insulin-releasing effects of 1 were also investigated. The blood glucose level fell after i.p. injection of the extract (50 mg/kg). Compounds 1, 2, 5, and 6 reduced the blood glucose level after i.p. injection of 150 mumol/kg. Compound 1 increased plasma insulin level in STZ-diabetic mice and potentiated the 8.3-mM glucose-induced insulin release from the rat isolated-perfused pancreas. The 1-induced potentiation of insulin release may partly contribute to antihyperglycemic action.

Comparison of the effects of acarbose and voglibose in healthy subjects

Acarbose and voglibose are alpha-glucosidase inhibitors. Although the pharmacologic effects and incidence of abdominal adverse events associated with the two drugs have been reported to differ, no study has directly compared acarbose and voglibose. To compare the pharmacologic effects and gastrointestinal adverse events associated with the two drugs, a randomized, placebo-controlled, double-masked, fivefold crossover study was performed in 20 healthy male subjects. To assess the pharmacologic effects, plasma immunoreactive insulin (IRI), plasma glucose, and 24-hour urinary connecting-peptide immunoreactivity (CPR) excretion were measured. Although the postprandial increase in plasma glucose level was reduced significantly with both acarbose and voglibose, the rate of reduction was small. The maximum concentration (Cmax) and area under the plasma concentration-time curve (AUC) of plasma IRI after meals decreased significantly with all treatments except voglibose 0.3 mg compared with placebo. Overall, the Cmax and AUC of plasma IRI decreased more when subjects received acarbose than voglibose. Urinary CPR excretion decreased by 30.6% and 41.7%, respectively, in subjects who received acarbose 50 mg or 100 mg compared with the previous day when no drug was given, whereas the urinary CPR excretion did not decrease significantly with voglibose. There was no significant difference in the frequency of gastrointestinal adverse events between groups, including the placebo group. One-day administration of acarbose and voglibose at currently recommended clinical doses demonstrated that acarbose was more effective in sparing endogenous insulin secretion than was voglibose.

Preparation and biological activity of manno- and galacto-validamines, new 5a-carba-glycosylamines as alpha-glycosidase inhibitors

Manno- and galacto-validamines, which are epimers of validamine, were semi-synthesized by the configurational inversion of validamine, a pseudo-sugar analogue of alpha-D-gluco-pyranose that has inhibitory activity for alpha-glucosidases. The inhibitory activities of these analogues were determined against several mannosidases and galactosidase. Manno-validamine shows potent inhibition for the alpha-mannosidases (competitive. K(i) = 4.6 x 10(-5) M for jack beans, and competitive, Ki = 2.8 x 10(-5) M for almonds), and galacto-validamine shows weak inhibition for the alpha-galactosidases (coffee bean and E. coli). The inhibitory effect of the epimers on the N-linked oligosaccharide-processing mannosidases involved in glycoprotein biosynthesis and lysosomal mannosidase from rat liver were also examined. Mannovalidamine shows potent inhibition on the endoplasmic reticulumal alpha-mannosidase (competitive, K(i) = 1.2 x 10(-6) M), Golgi mannosidases IA, II (competitive, K(i) = 2.8 x 10(-5) M), and lysosomal alpha-mannosidase (competitive, Ki = 1.7 x 10(-5) M).

Sulfoxide-Mediated Asymmetric Synthesis of Glycosidase Inhibitor Precursors

The highly diastereoselective DIBALH and DIBALH/ZnBr(2) reduction of enantiomerically pure (5S,(S)S)-3-ethoxy-5-(p-tolylsulfinyl)cyclopentenone (9) is used as a key step to the synthesis of oxazolidinone 2, a precursor of glycosidase inhibitor mannostatin. Compound 9 was obtained from 3-ethoxycyclopentenone by direct sulfinylation with (S)-N-benzyl-N-(p-tolylsulfinyl)propionamide.

L-arabinose selectively inhibits intestinal sucrase in an uncompetitive manner and suppresses glycemic response after sucrose ingestion in animals

The objective of this study was to investigate the effects of L-arabinose on intestinal alpha-glucosidase activities in vitro and to evaluate its effects on postprandial glycemic responses in vivo. L-Arabinose inhibited the sucrase activity of intestinal mucosa in an uncompetitive manner (Ki, 2 mmol/L). Neither the optical isomer D-arabinose nor the disaccharide L-arabinobiose inhibited sucrase activity, whereas D-xylose was as potent as L-arabinose in inhibiting this activity. L-Arabinose and D-xylose showed no inhibitory effect on the activities of intestinal maltase, isomaltase, trehalase, lactase, and glucoamylase, or pancreatic amylase. In contrast, a known alpha-glucosidase inhibitor, acarbose, competitively inhibited (Ki, 1.1 mumol/L) sucrase activity and also inhibited intestinal maltase, glucoamylase, and pancreatic amylase. L-Arabinose suppressed the increase of blood glucose after sucrose loading dose-dependently in mice (ED50, 35 mg/kg), but showed no effect after starch loading. The suppressive effect of D-xylose on the increase of blood glucose after sucrose loading was 2.4 times less than that of L-arabinose, probably due to intestinal absorption of the former. Acarbose strongly suppressed glycemic responses in both sucrose loading (ED50, 1.1 mg/kg) and starch loading (ED50, 1.7 mg/kg) in mice. L-Arabinose suppressed the increase of plasma glucose and insulin in rats after sucrose loading, the suppression of the former being uninterruptedly observed in mice for 3 weeks. Thus, the results demonstrated that L-arabinose selectively inhibits intestinal sucrase activity in an uncompetitive manner and suppresses the glycemic response after sucrose ingestion by inhibition of sucrase activity.

Two subsites on the active center of pig kidney trehalase

A kinetic analysis of the active site of pig kidney trehalase was made by examining two types of inhibitors that are monosaccharide analogs and cause a competitive inhibition of the trehalase. Trehalase hydrolyzes trehalose (alpha-D-glycopyranosyl alpha-D-glucopyranoside) to give an equimolar mixture of alpha-D-glucose and, by inversion of configuration, beta-D-glucose. 1,4-Dideoxyl-1,4-imino-D-arabinitol is considered to be a transition state (glucosyl cation) analog, while methyl beta-D-glucoside, 1,5-dideoxy-1,5-imino-D-glucitol (1-deoxynojirimycin), fagomine, and 1-epivalidamine are considered to be analogs of the beta-D-glucose that is derived by hydrolysis of trehalose. These glucosyl cation inhibitor and beta-D-glucose analog inhibitors competed with each other at the same site on the active center of pig kidney trehalase and were therefore put together in one group (group A). Methyl alpha-D-mannoside and 1-deoxymannojirimycin were also competitive inhibitors of trehalase and competed with each other for the same site. However, an inhibitor in group A did not compete with the methyl alpha-D-mannoside or 1,5-dideoxy-1,5-imino-D-mannitol (1-deoxymannojirimycin). Thus these latter two inhibitors were placed in group B. These results support the hypothesis that the active center of trehalase may comprise two subsites, one for catalysis and one for recognition, that act separately on each of the glucose of the trehalose. The catalysis site requires the correct D-glucose configuration at carbons 2, 3, 4, and 5 or a good superimposition onto the glucosyl cation intermediate. The C2 equatorial OH group of a glucopyranosyl residue appears to be important for binding at the catalytic site since 1-deoxynojirimycin is more tightly bound by two orders of magnitude over its 2-deoxy derivative, fagomine. The beta-D-glucose and glucosyl cation analogs best fit this site. The recognition site is compatible with D-glucose and its analogs bearing the alpha configuration at the anomeric position. alpha-D-Mannose analogs are much more tightly bound than the corresponding D-gluco compound at this site. The extremely high affinity (Ki = 0.52 nM) of validoxylamine A, a mimic of the substrate in the transition state, derives from the synergistic interactions of two cyclitol units with two subsites. The value obtained by multiplying the Ki (1.2 microM) for 1-epivalidamine times that for 1-deoxymannojirimycin (Ki = 0.39 mM) is very close to that for validoxylamine A. The results described here may be applicable to other trehalase molecules.

Improvement of insulin sensitivity and dyslipidemia with a new alpha-glucosidase inhibitor, voglibose, in nondiabetic hyperinsulinemic subjects

This study was undertaken to investigate the effect of voglibose, a new alpha-glucosidase inhibitor, on glucose and lipid metabolism in nondiabetic hyperinsulinemic subjects. Sixteen nondiabetic subjects with hyperinsulinemia participated in the study. They were divided into two groups of eight subjects with normal (NGT) and impaired (IGT) glucose tolerance. A meal tolerance test and a 75-g oral glucose tolerance test (OGTT) were performed at the beginning (baseline phase) and end (treatment phase) of the 12-week treatment. Serum lipid levels were measured every 4 weeks throughout the treatment phase and follow-up phase (8 weeks). All patients received 1 0.2-mg tablet of voglibose before each test meal (3 tablets per day). We also measured insulin sensitivity using a steady-state plasma glucose (SSPG) method in eight normotensive hyperinsulinemic subjects and in eight age- and body mass index (BMI)-matched control subjects before and after the drug treatment. Voglibose significantly decreased the responses of plasma glucose and insulin on the meal tolerance test. The area under the curve for 2-hour insulin during the 75-g OGTT decreased after treatment, whereas that for 2-hour glucose did not change before and after treatment. SSPG was reduced after treatment, indicating improvement of insulin sensitivity. Moreover, treatment with voglibose resulted in a significant decline of triglyceride level and an elevation of high-density lipoprotein (HDL) cholesterol and apolipoprotein A-1. These values returned to near-baseline levels after the drug was discontinued. Consequently, we conclude that this agent not only has a direct hypoglycemic effect through decreased absorption of carbohydrate, but also a hypoinsulinemic and hypolipidemic effect via improved insulin sensitivity.

AO-128, alpha-glucosidase inhibitor: antiobesity and antidiabetic actions in genetically obese-diabetic rats, Wistar fatty

Antiobesity and antidiabetic actions of the alpha-glucosidase inhibitor AO-128 were examined using genetically obese-diabetic rats, Wistar fatty. Ten-week-old, male fatty rats were kept on CE-2 diet containing 10 or 25 ppm of AO-128 for 4 weeks. The average drug intake was calculated to be 0.74 or 1.78 mg/kg/day from the average food intake, respectively. The intestinal maltase and sucrase activities were decreased by AO-128 in a dose-related fashion. Food intake of fatty rats treated with AO-128 was decreased throughout the experiment. This decrease in food intake could hardly be explained only by diarrhea which occurred for the first 5 days of the administration of AO-128. AO-128 normalized hyperglycemia and markedly reduced hypertriglyceridemia and hyperinsulinemia in fatty rats. In addition, AO-128 decreased body weight gain, food efficiency, epididymal adipose tissue weight, carcass weight, and body fat deposition. These findings indicate that AO-128 may be useful for treating human obesity and diabetes.

An alpha-glucosidase inhibitor, AO-128, retards carbohydrate absorption in rats and humans

The present study was designed to determine the possible significance of a therapeutic dose (0.2 mg) of AO-128 on carbohydrate absorption by measuring the breath hydrogen concentration, which is an index of the amount of unabsorbed carbohydrate in the large intestine. Post-prandial hyperglycemia is common among diabetic patients. AO-128, a potent alpha-glucosidase inhibitor, suppressed post-prandial hyperglycemia and hyperinsulinemia in healthy volunteers at a dose of 0.2 mg with each meal. These volunteers increased the breath hydrogen concentration in response to ingestion of non-absorbable lactulose, but decreased only slightly its concentration from the basal level after sucrose ingestion, indicating complete absorption. When AO-128 (0.2 mg) was given with sucrose, hydrogen production increased only slightly compared with placebo, suggesting that the inhibitory effect of AO-128 on sucrose absorption was minimal. Only 5 g of the 100 g of sucrose was not absorbed and this 5% reduction is too small to explain the observed inhibitory effect on the post-prandial rise in plasma glucose. Sucrose loading in rats (about 443 mg) sharply increased blood glucose and was accompanied by the rapid disappearance of sucrose from the upper small intestine. AO-128 (0.03 or 0.1 mg/kg) lessened the elevation of blood glucose after sucrose ingestion. The lower dose (0.03 mg/kg) retarded small intestinal absorption, but did not induce an influx of sucrose into the cecum and large intestine, while the higher dose (0.1 mg/kg) caused an increased influx of sucrose into the large bowel. These results indicated that AO-128 retards the absorption of carbohydrate and reduces post-prandial hyperglycemia.

Treatment of non-insulin-dependent diabetes mellitus and its complications. A state of the art review

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem which occurs predominantly in the older population; 16.8% of persons over age 65 years have NIDDM. The total health costs of NIDDM are in excess of $US20 billion annually. The primary objective in the treatment of NIDDM is to achieve normoglycaemia, without aggravating coexisting abnormalities. Common abnormalities include obesity, hypertension, retinopathy, nephropathy and neuropathies. Diet, and consequent bodyweight reduction, is the cornerstone of therapy for NIDDM. Total calorie intake should be limited, while the percentage of calories from carbohydrates should be increased and that from fats and cholesterol should be decreased. Exercise may also help to reduce bodyweight. Sulphonylurea drugs stimulate insulin secretion from beta-cells, and may be a useful adjunct to nonpharmacological therapy. Failure to respond to sulphonylurea drugs may be primary (25 to 30% of initially treated patients) or secondary (5 to 10% per year). It is not clear which is the most effective pharmacological intervention in such cases. Options include switching to or combining therapy with insulin, a biguanide, or other insulin-sparing antihyperglycaemic agents, e.g. alpha-glucosidase inhibitors, thiazolidinediones, chloroquine or hydroxychloroquine, or fibric acid derivatives such as clofibrate. Other experimental agents include the fatty acid oxidation inhibitors and dichloroacetate. Specific agents, such as antihypertensives, lipid lowering agents and sorbitol inhibitors, may be needed to prevent the complications arising from the spectrum of clinical and metabolic abnormalities which arise from insulin resistance.

Effect of an alpha-glucosidase inhibitor on intestinal fermentation and faecal lipids in diabetic patients

Eight non-insulin-dependent diabetes mellitus patients, in whom oral hypoglycaemic agents were not effective, were treated with an alpha-glucosidase inhibitor, AO-128 (0.9 mg/day) for 6 months. After 6 months of treatment there was a statistically significant decrease in the blood glucose level 1 and 2 h postprandially. The 2 h blood glucose level was also significantly reduced after 2 months' treatment. The insulin and HbA1c levels after 2 and 6 months' treatment were lower than those before administration. Faecal weight, the frequency of bowel movements, the ratio of hydroxy fatty acids to total fatty acids, and faecal short-chain carboxylic acid content were all increased significantly during treatment. The initially hard stools became normal or soft, although no actual diarrhoea developed. Both faecal bile-acid excretion and the ratio of primary bile acids to total bile acids were increased significantly after 2 months, but they showed some recovery towards the pretreatment levels after 6 months' treatment. There was no distinct change in neutral sterol and fatty acid excretion. Breath hydrogen excretion showed a slight increase after treatment. These results suggest that intestinal fermentation was promoted and the intestinal transit time was shortened by AO-128 administration.

Differences in glucagon-like peptide-1 and GIP responses following sucrose ingestion

To investigate the mechanism of oral carbohydrate-stimulated secretion of the two most potent incretin candidates, gastric inhibitory polypeptide (GIP) and truncated glucagon-like peptide-1 (tGLP-1), we studied the changes in the plasma levels of these peptides in five healthy men after sucrose ingestion with or without pretreatment with an alpha-D-glucosidase inhibitor (AO-128). After sucrose ingestion, plasma levels of GIP peaked at 15 min and remained high up to 120 min. Plasma levels of GLP-1 NT measured with antiserum R1043 (N-terminal specific) tended to decrease gradually and those of GLP-1 CT measured with antiserum R2337 (C-terminal specific) increased. Therefore, estimated plasma levels of tGLP-1 increased markedly within 30 min, then declined slightly over the next 60 min. After treatment with AO-128 (0.6 mg/day) for 1 week, increases in plasma glucose and insulin levels were attenuated and the increase in plasma GIP levels was diminished, while the increase in tGLP-1 levels was sustained much longer. It is concluded that GIP secretion is stimulated by glucose absorption and tGLP-1 secretion by the presence of sucrose in the gut.

Histidines, histamines and imidazoles as glycosidase inhibitors

This present study reports the ability of a range of derivatives of L-histidine, histamine and imidazole to act as inhibitors of sweet-almond beta-glucosidase, yeast alpha-glucosidase and Escherichia coli beta-galactosidase. The addition of a hydrophobic group to the basic imidazole nucleus greatly enhances binding to both the alpha- and beta-glucosidases. L-Histidine (beta-naphthylamide (Ki 17 microM) is a potent competitive inhibitor of sweet-almond beta-glucosidase as is omega-N-acetylhistamine (K1 35 microM), which inhibits the sweet-almond beta-glucosidase at least 700 times more strongly than either yeast alpha-glucosidase or Escherichia coli beta-galactosidase, and suggests potential for the development of selective reversible beta-glucosidase inhibitors. A range of hydrophobic omega-N-acylhistamines were synthesized and shown to be among the most potent inhibitors of sweet-almond beta-glucosidase reported to date.

Castanospermine-glucosides as selective disaccharidase inhibitors

Castanospermine (CS) is a potent but non-selective inhibitor of many glycohydrolases including the intestinal disaccharidases. Several CS-glucosides were synthesized to investigate the effect of an attached glucopyranosyl residue on the potency and selectivity of CS toward inhibition of intestinal disaccharidases. 8 alpha-glucosyl-CS and 7 alpha-glucosyl-CS were nearly as potent against sucrase activity as CS (IC50 values = 30, 40, and 20 nM respectively) but were 1/50 or less as potent as CS against lactase and trehalase activities. 8 beta-glucosyl-CS was 1/20 to 1/140 as potent as CS and 1 alpha-glucosyl-CS was 1/57 to 1/1500 as potent as CS against disaccharidase activities. 1 alpha-glc-CS was less selective than CS, whereas the other CS-glucosides were more selective. 7 alpha-glc-CS and 8 alpha-glc-CS were the most sucrase selective and were particularly ineffective against trehalase and lactase activities. 8 beta-glc-CS was similar to CS except for relatively weaker trehalase inhibition. In summary, selectivity toward certain disaccharidases was achieved by glucosylation of CS hydroxyls. However, a simple structural comparison of the CS-glucoside to a disaccharide substrate did not reliably predict which disaccharidase would be more inhibited by the CS-glucoside.