Effects of methanolic extract and commercial oil of Nigella sativa L. on blood glucose and antioxidant capacity in alloxan-induced diabetic rats

Abstract

Nigella sativa is a medicinal plant widely used in the Arabic and Islamic world against a number of human pathologies. In this present study the methanol extraction (85 % then 50 %) of plant seeds gave an important yield of 27 % of dry substance. The anti-hyperglycaemia effect of the crude methanolic extract and the commercial oil of these seeds were tested in alloxan-induced, intra peritoneal, diabetic rats (150 mg/kg). Effects of these two substances on other diabetes-linked factors such as the reducing power of the plasma and the osmotic fragility of erythrocytes. The daily orally administration of the crude methanolic extract (810 mg/kg/day) and the oil (2.5 ml/kg/day) for 25 days leads to a significant decrease of glycaemia, especially during the first 10 days of treatment (decreases of 58.09 and 73.27 % respectively). However, the dose of 270 mg/kg of crude methanolic extract had no effect, which is probably due to the low dose. In addition the antioxidant capacity, measured by the ferric reducing ability of plasma (FRAP) technique, increased in all diabetic rats and the introduction of either the crude methanolic extract or the oil fraction showed any improvement on this factor. However, a slight resistance, not reaching significance, against the osmotic fragility of erythrocytes was induced in diabetic rats. The antihyperglycaemic effect of both substances is not related to inhibition of intestinal glucose absorption or stimulation of insulin secretion. We suggest that the action is a result of the inhibition of enzymes involved in the neoglucogenesis pathway in the liver. As shown the stress associated with the metabolic perturbation observed in diabetes induces a physiological anti-oxidant response, which probably masks the antioxidant effect of our two substances of this medicinal plant.