The pseudotetrasaccharide acarbose inhibits pancreatic islet glucan-1,4-alpha-glucosidase activity in parallel with a suppressive action on glucose-induced insulin release.

The pseudotetrasaccharide acarbose, previously known as a potent inhibitor of intestinal alpha-glucoside hydrolases, was investigated with regard to its influence on islet lysosomal enzyme activities and the insulin secretory processes. We observed that acarbose was a potent inhibitor of mouse islet lysosomal acid glucan-1,4-alpha-glucosidase activity, EC50 approximately 5 mumol/l, as well as of acid alpha-glucosidase activity. In contrast, acarbose did not influence other lysosomal enzyme activities such as acid phosphatase and N-acetyl-beta-D-glucosaminidase. Neutral alpha-glucosidase (endoplasmic reticulum) was only moderately inhibited in homogenate and was unaffected in intact islets. Incubation of isolated mouse islets with acarbose revealed that the pseudotetrasaccharide was a strong inhibitor of glucose-induced insulin secretion, EC50 approximately 500 nmol/l, and a significant inhibition was already observed at a concentration of acarbose as low as 100 nmol/l. The acarbose analogue maltotetrose did not influence either glucose-induced insulin release or islet lysosomal enzyme activities. Further, acarbose as well as two other alpha-glucoside hydrolase inhibitors, the deoxynojirimycin derivatives miglitol and emiglitate, did not affect islet glucose oxidation at low or high glucose levels. Acarbose also inhibited insulin release induced by the sulfonylurea glibenclamide, whereas insulin secretion stimulated by the cholinergic muscarinic agonist carbachol or the phosphodiesterase inhibitor isobutylmethylxanthine was unaffected by the drug. Moreover, complementary in vivo experiments showed that pretreatment of mice with acarbose to allow for endocytosis of the compound markedly suppressed the insulin secretory response to an intravenous glucose load.(ABSTRACT TRUNCATED AT 250 WORDS)