Evaluation of the glycemic effect ofCeratonia siliquapods (Carob) on a streptozotocin-nicotinamide induced diabetic rat model

Abstract

BackgroundCeratonia siliquapods (carob) have been nominated to control the high blood glucose of diabetics. In Yemen, however, its antihyperglycemic activity has not been yet assessed. Thus, this study evaluated thein vitroinhibitory effect of the methanolic extract of carob pods against α-amylase and α-glucosidase and thein vivoglycemic effect of such extract in streptozotocin-nicotinamide induced diabetic rats.Methods2,2-diphenyl-1-picrylhydrazyl (DPPH) and Ferric reducing antioxidant power assay (FRAP) were applied to evaluate the antioxidant activity of carob.In vitrocytotoxicity of carob was conducted on human hepatocytes (WRL68) and rat pancreatic β-cells (RIN-5F). Acute oral toxicity of carob was conducted on a total of 18 male and 18 femaleSprague-Dawley(SD) rats, which were subdivided into three groups (n = 6), namely: high and low dose carob-treated (CS5000 and CS2000, respectively) as well as the normal control (NC) receiving a single oral dose of 5,000 mg kg−1carob, 2,000 mg kg−1carob and 5 mL kg−1distilled water for 14 days, respectively. Alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, total bilirubin, creatinine and urea were assessed. Livers and kidneys were harvested for histopathology.In vitroinhibitory effect against α-amylase and α-glucosidase was evaluated.In vivoglycemic activity was conducted on 24 male SD rats which were previously intraperitoneally injected with 55 mg kg−1streptozotocin (STZ) followed by 210 mg kg−1nicotinamide to induce type 2 diabetes mellitus. An extra non-injected group (n = 6) was added as a normal control (NC). The injected-rats were divided into four groups (n = 6), namely: diabetic control (D0), 5 mg kg−1glibenclamide-treated diabetic (GD), 500 mg kg−1carob-treated diabetic (CS500) and 1,000 mg kg−1carob-treated diabetic (CS1000). All groups received a single oral daily dose of their treatment for 4 weeks. Body weight, fasting blood glucose (FBG), oral glucose tolerance test, biochemistry, insulin and hemostatic model assessment were assessed. Pancreases was harvested for histopathology.ResultsCarob demonstrated a FRAP value of 3191.67 ± 54.34 µmoL Fe++and IC50of DPPH of 11.23 ± 0.47 µg mL−1.In vitro,carob was non-toxic on hepatocytes and pancreatic β-cells. In acute oral toxicity, liver and kidney functions and their histological sections showed no abnormalities. Carob exerted anin vitroinhibitory effect against α-amylase and α-glucosidase with IC50of 92.99 ± 0.22 and 97.13 ± 4.11 µg mL−1, respectively. In diabetic induced rats, FBG of CS1000 was significantly less than diabetic control. Histological pancreatic sections of CS1000 showed less destruction of β-cells than CS500 and diabetic control.ConclusionCarob pod did not cause acute systemic toxicity and showedin vitroantioxidant effects. On the other hand, inhibiting α-amylase and α-glucosidase was evident. Interestingly, a high dose of carob exhibits anin vivoantihyperglycemic activity and warrants further in-depth study to identify the potential carob extract composition.