Effect of Amorphophallus Konjac oligosaccharides on STZ-induced diabetes model of isolated islets.

Three oligosaccharide fractions from the root of Amorphophallus Konjac, which was reported with hypoglycemic effects on diabetes subjects, were isolated and studied using the STZ-treated diabetes model. Among them, one fraction named as KOS-A, was found with nitric oxide (NO(*)) free radical regulation effect, while the other two were not. At concentrations less than 1.5 mM, KOS-A positively decreased STZ-induced NO(*) level of islets, but normal NO(*) release for non-STZ-treated islets was not affected within the range. At 15 mM, KOS-A played a contrary role and increased NO(*) level for islets both with and without STZ-treatment. Islets insulin secretion changed corresponding to NO(*) level in the assay. Increased insulin secretion appeared parallel to the decrease of NO(*), and normal insulin release was not affected by KOS-A less than 1.5 mM. Structure determination of KOS-A shows that it is a tetrasaccharide with Mw of 666 Da and reductive end of alpha-D-mannose. These results indicate that low dosage of KOS-A, with its function on attenuating STZ-induced NO(*) level, doesn't alter normal NO(*) and insulin secretion pathways of isolated islets. The NO(*) attenuation function of KOS-A on the diabetes model is mainly resulted from environmental free radical scavenging by the oligosaccharide. Present results also imply the mechanism of clinical Amorphophallus Konjac hypoglycemic function maybe related with free radical attenuation and lower risks of islets damage from NO(*) radical.