Effects of Spirulina platensis on insulin secretion, DPP-IV activity and both carbohydrate digestion and absorption indicate potential as an adjunctive therapy for diabetes.

Spirulina platensis (S. platensis) has previously been shown in both animals and humans to be useful in the treatment of type 2 diabetes. The present study aims to elucidate the effects of ethanol extract and butanol fraction of S. platensis on insulin release and glucose homeostasis in type 2 diabetic rats, together with their mechanism of actions. Both in vitro and in vivo methods were used including cellular studies to determine potential role of ion channels and cAMP in the insulinotropic actions of the extracts. The ethanol extract and butanol fraction stimulated insulin release from mouse islets and pancreatic β-cells in a concentration-dependent manner. The butanol fraction also similarly stimulated insulin release from perfused rat pancreas. The insulin releasing action was augmented by glucose, isobutyl methylxanthine, tolbutamide and a depolarizing concentration of KCl. The insulin secretory effect was attenuated with diazoxide and verapamil and by omission of extracellular Ca2+. Butanol fraction was found to significantly inhibit DPP-IV enzyme activity. Moreover, butanol fraction improved glucose tolerance following oral glucose administration (2.5 g/kg b.w.). The butanol fraction was tested on 24 h starved rats given an oral sucrose load (2.5 g/kg b.w.) to examine possible effects on carbohydrate digestion and absorption. S. platensis substantially decreased post-prandial hyperglycemia after oral sucrose load and increased unabsorbed sucrose content throughout the gut. During in situ intestinal perfusion with glucose, the butanol fraction reduced glucose absorption and promoted gut motility. Finally, chronic oral administration of butanol fraction for 28 days significantly decreased blood glucose, increased plasma insulin, pancreatic insulin stores, liver glycogen and improved lipid profile. The characterization of active compounds from butanol fraction revealed the presence of p-coumaric acid, β-carotene, catechine and other antioxidant polyphenols. These findings indicate that S. platensis could be a novel adjunctive therapy for the management of type 2 diabetes.