Antidiabetic effects of some medicinal plant extracts in rats with chemically induced diabetes mellitus

Abstract

Medicinal plants have been recommended for the treatment of diabetes mellitus in Sri Lanka since antiquity. The study investigated the antidiabetic effects of selected medicinal plant extracts in alloxan induced and streptozotocin induced diabetic rats. Medicinal plants selected for the investigation were Spondias pinnata (Ambarella, Anacardiaceae), Kokoona zeylanica (FCokun, Celastraceae), Coccinia grandis (Kowakka, Cucurbitaceae), Momordica charantia (Wal-kariwila, Cucurbitaceae), Sida alnifolia (Kotikan-babila, Malvaceae), Syzygium caryophyllatum (Heen-dan, Myrtaceae), Nyctanthes arbor-tristis (Sepalika, Oleaceae), Scoparia dulcis (Wal-kottamalli, Scrophulariaceae), Gmelina arborea (Et-demata, Verbenaceae) and Languas galanga (Heen-aratta, Zingiberaceae). Aqueous extracts were used for all in vivo experiments. The efficacy of acute hypolgycaemic and antihyperglycaemic activities of ten aqueous plant extracts for a range of doses (0.25-2.00 g/kg b.wt.) were evaluated by the improvement on glucose tolerance in healthy, alloxan induced and streptozotocin induced diabetic rats. The results revealed that the extracts of S. pinnata, C. grandis, M. charantia, S. dulcis and G. arborea possess significant hypoglycaemic effects in healthy rats (p< 0.05). In addition, all the ten plant extracts showed h i g h l y s i g n i f i c a n t d o s e d e p e n d e n t antihyperglycaemic effects in diabetic rats (p< 0.05). On the basis of results of the above investigations, the bark extract of S. pinnata, leaf extract of C. grandis and bark extract of G.arborea were selected at their optimum effective doses for the investigation of antidiabetic mechanisms in diabetic rats. An attempt was also made to study the toxicological effects of the three selected plant extracts at their optimum effective doses in healthy Wistar rats. The effect of administration of the selected plant extracts of S. pinnata, C.grandis1, G. arborea on the concentration of serum/blood glycaemic parameters, concentration of serum lipid parameters, concentration/activities of hepatic oxidative stress markers and regenerative potency of islet cells in the pancreas were investigated in alloxan and streptozotocin induced diabetic rats. Glibenclamide was used as the standard antidiabetic drug. The long term antihyperglycaemic effect was in the decreasing order of C. grandis, G. arborea and A pinnata in diabetic rats. The leaf extract of C. grandis demonstrated a decrease in the percentage of glycated hemoglobin (35%, 33%), fructosamine (30%, 32%), an increase in insulin (72%, 78%), Cpeptide (51%, 60%) in alloxan induced and streptozotocin induced diabetic rats respectively (p< 0.05). The increase in the concentrations of serum insulin and C-peptide and histopathology on H & E stained sections in plant extracts treated rats indicated the formation of functional islet cells, biosynthesis of insulin which was further confirmed through immunohistochemical assessments. The results of this study confirm that the aqueous bark extract of S. pinnata, leaf extract of C. grandis and bark extract of G. arborea possess in vivo antioxidant activities. None of the extracts at their optimum effective dose produced toxic effects in vivo. Increased biosynthesis of insulin along with increased production of C-peptide coupled to |3-cell regeneration in the pancreas of plant extracts treated diabetic rats suggest pronounced pancreatic mechanisms, although extra pancreatic effects cannot be ruled out. The secondary metabolites mainly as polyphenol compounds, flavonoids present in these plant extracts may be responsible for the antidiabetic effects in diabetic rats.The study was performed at Dept, o f Biochemistry and Dept, o f Pathology), Faculty o f Medicine, University o f Ruhuna, Sri Lanka. The results were published in ten original research papers in peer reviewed indexed journals. In addition, 18 abstracts were presented in national and international forums. The study received four outstanding research awards including the Vice chancellor’s Gold Medal fo r the excellent performance during the post graduate study in generating Knowledge that has accepted internationally.