MDL 29311. Antioxidant with marked lipid- and glucose-lowering activity in diabetic rats and mice.

MDL 29311, an analogue of probucol, administered to rats as a 1% dietary admixture for 2 wk before and 5 days after intravenous injection of 40 mg/kg of ALX significantly (P < 0.05) reduced plasma glucose (6.9 +/- 0.3 vs. 19.2 +/- 1.3 mM) and serum triglyceride (0.17 +/- 0.01 vs. 1.82 +/- 0.39 mM) levels in overnight-fasted ALX-plus-MDL 29311-administered rats vs. ALX-administered rats. A cross-over study indicated that MDL 29311 did not attenuate the diabetogenic action of ALX, but rather, directly lowered glucose and triglycerides. In rats injected intravenously with 45, 65, or 85 mg/kg of STZ and then administered control or MDL 29311 diet for 7 days, MDL 29311 decreased fasted plasma glucose to nondiabetic levels, decreased fasted and nonfasted plasma triglycerides by 49-79%, but did not affect plasma insulin levels. In STZ-induced (65 mg/kg) diabetic rats, MDL 29311 attenuated the increase in plasma nonesterified fatty acids during an 18-h fast; had little or no effect on glucagon, pyruvate, lactate, beta-hydroxybutyrate, acetoacetate, or cholesterol; and did not induce hypoglycemia in rats fasted up to 64 h. In nonfasted hyperinsulinemic db/db mice treated for 10 wk, MDL 29311 significantly lowered glucose levels by 14-40%, triglyceride levels by 31-63% and GHb from 8.0 to 5.4%, and had no consistent effect on plasma insulin levels. Because of its marked glucose- and lipid-lowering activity in both nonfasted hyperinsulinemic and fasted insulinopenic animals, MDL 29311 merits additional investigation as a potential antidiabetic agent.

New potent alpha-glucohydrolase inhibitor MDL 73945 with long duration of action in rats.

Inhibition of intestinal alpha-glucohydrolase activity is one approach for reducing the glycemic response from dietary carbohydrate and may prove useful for the treatment of diabetes mellitus. In this article, we describe the pharmacological properties of a time-dependent intestinal alpha-glucohydrolase inhibitor, MDL 73945. When preincubated 2 h with a rat intestinal mucosa preparation before substrate addition, MDL 73945 was a potent inhibitor of sucrase, maltase, glucoamylase, and isomaltase activities (MDL 73945 concentrations required to cause a 50% decrease in enzyme activity, 2 x 10(-7), 1 x 10(-6), 5 x 10(-6), and 8 x 10(-6) M, respectively); without preincubation, it was 10- to 500-fold less potent. In rats, a single oral dose of MDL 73945 administered simultaneously with 2 g/kg body wt sucrose resulted in a dose-dependent reduction in the area under the 0- to 3-h glycemic response curve, which was significant at 1 (45% reduction) and 3 (65% reduction) mg/kg. When administered 1 h before sucrose, the compound was more potent, with 0.3 mg/kg MDL 73945 significantly reducing the glycemic response to sucrose by 62%. A reduction in the glycemic response to sucrose was accompanied by reduced insulin secretion. MDL 73945 was slightly less effective against a starch load, with 3 and 10 mg/kg MDL 73945 administered 0.5 h before starch reducing the glycemic response by 39 and 52%, respectively. MDL 73945 was more effective against a sucrose load in streptozocin-administered rats than in control rats and was as effective after 16 daily doses as after a single dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative relationship of lysosomal glycogen accumulation to lysosomal alpha-glucosidase inhibition in castanospermine-treated rats.

To quantitatively examine the relationship between lysosomal acid alpha-glucosidase (LAAG, alpha-D-glucoside glucohydrolase, EC 3.2.1.20) inhibition and glycogen accumulation, rats were treated with castanospermine (CS), and liver lysosomal/mitochondrial fractions were analyzed for glycogen content and LAAG activity. Liver lysosomal glycogen accumulation positively correlated (r = 0.90) with the amount of LAAG inhibition when inhibition was about 50% or greater. Glycogen did not accumulate when LAAG inhibition was less than 50%. The route of CS administration had little effect on the amount of LAAG inhibition observed. In rats killed 17 hr after CS administration, the doses estimated to cause 50% LAAG inhibition were 0.77, 0.11, and 0.22 mg/kg for i.p., i.v., and oral administration respectively. After 89% inhibition of LAAG activity with a single oral dose of 10 mg CS/kg, LAAG activity returned to 50% of normal value in about 2.5 days. Accumulated glycogen disappeared as LAAG activity recovered. Surprisingly, twelve daily CS doses of 1 mg/kg had only a small cumulative effect on LAAG inhibition and did not cause more glycogen accumulation than a single dose.

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.

Castanospermine-glucosides are potent, selective, long-acting sucrase inhibitors.

Castanospermine-glucosides (CS-glcs) are new compounds which have been evaluated as glycohydrolase inhibitors in rats. 7-O-alpha-D-Glucopyranosyl-CS (7 alpha-glc-CS) and 8 alpha-glc-CS were potent sucrase inhibitors with IC50s of 40 and 30 nM, respectively. Their sucrase inhibition was poorly reversible. They were much weaker liver lysosomal alpha-glucosidase inhibitors with IC50s of 40,000 nM. 1 alpha-glc-CS and 8 beta-glc-CS were both weaker and less selective sucrase inhibitors. In vivo, 7 alpha-glc-CS and 8 alpha-glc-CS effectively reduced the glycemic response to an oral 2 g/kg sucrose load at doses less than or equal to 1 mg/kg. 8 alpha-glc-CS was effective when administered up to 4 hr before sucrose. The known glucohydrolase inhibitors 1-deoxynojirimycin and N-hydroxyethyl-1-deoxy-nojirimycin were also potent sucrase inhibitors (IC50s = 200 and 400 nM, respectively) but their sucrase inhibition was readily reversible in vitro and their in vivo duration of action was much shorter than for the CS-glcs. Among the glucohydrolase inhibitors tested, the prolonged in vivo duration of action could be predicted by poor reversibility from sucrase. These CS-glcs provide a new generation of sucrase inhibitors which may be useful in the treatment of diabetes mellitus.

Castanospermine blocks the hyperglycemic response to carbohydrates in vivo: a result of intestinal disaccharidase inhibition.

Castanospermine is a potent inhibitor of rat intestinal glycohydrolases in vitro and prevents the hyperglycemic response to an oral sucrose challenge in vivo. Among the glycohydrolases tested, castanospermine was most effective against sucrase with an IC50 of 1.1 x 10(-7) M. In vivo, a significant effect was seen at doses less than 1 mg/kg in both normal and streptozotocin-treated rats. Castanospermine has a prolonged duration of activity in vivo with significant activity when administered 4 hours before sucrose.

Castanospermine: an apparent tight-binding inhibitor of hepatic lysosomal alpha-glucosidase.

Castanospermine is a potent inhibitor of rat hepatic lysosomal alpha-glucosidase in vitro. The alkaloid showed time-dependent inhibition with an IC50 of 5 X 10(-6) M without preincubation and 1 X 10(-7) M with 1 hr of preincubation. Inhibition appeared competitive without preincubation but noncompetitive after preincubation. The time-dependent inactivation of the enzyme followed pseudo-first-order kinetics with an inactivation constant of 1.2 X 10(3) M-1 sec-1. The apparent irreversibility of enzyme inhibition by castanospermine is postulated to be by tight-binding inhibition.

Inhibition of intestinal disaccharidases and suppression of blood glucose by a new alpha-glucohydrolase inhibitor--MDL 25,637.

MDL 25,637 is a novel compound designed as a transition-state inhibitor of alpha-glucohydrolases. This compound inhibits rat intestinal sucrase, maltase, isomaltase, glucoamylase and trehalase activities at micromolar concentrations. It is a much weaker inhibitor of alpha-amylase and lactase. Inhibition of sucrase was competitive with sucrose. In mice, MDL 25,637 inhibited the rise in serum glucose after a sucrose or starch load but not after a glucose load. MDL 25,637 also reduced the glycemic response to sucrose in rats. The drug was most effective when administered 0 to 30 min before the sucrose load and was as effective in streptozotocin-treated rats as in normals. The inhibition by MDL 25,637 of intestinal glucohydrolases is an effective means of reducing the hyperglycemic response to an oral sucrose or starch load and, as such, warrants further investigation as a potential drug for the treatment of diabetes mellitus.

Effect of a new hypoglycemic agent (MDL-310) on glucose metabolism.

N-[3-(dimethylamino)-2-propoxy-2-propenylidene]- N-methylmethanaminium as the iodide or camsylate salt (MDL-310) is a newly reported chemical which has been shown to produce hypoglycemia in vivo. The studies reported here describe in vivo and in vitro effects of MDL-310 on carbohydrate metabolism. In nonfasted mice, MDL-310 decreased liver glycogen and then produced hypoglycemia, concomitant with a near total depletion of liver glycogen stores. In fasted rats, nonhypoglycemic doses of MDL-310 increased glucose production and utilization as determined by tracer studies with [6-3H]glucose. Hypoglycemic doses decreased glucose production and increased blood lactate, which suggests an inhibition of gluconeogenesis. In isolated rat hepatocytes MDL-310, at concentrations of greater than or equal to 5 X 10(-6) M, inhibited gluconeogenesis from lactate (10 mM) plus pyruvate (2 mM). We conclude that the primary action of MDL-310 is to increase glucose utilization and that decreased production due to the inhibition of gluconeogenesis is involved in the hypoglycemic action. A single metabolic action of MDL-310 to increase glycolytic metabolism of glucose is proposed which could explain both the increase in glucose utilization and decrease in glucose production.