Anti-diabetic activity and stability study of the formulated leaf extract of Zizyphus spina-christi (L.) Willd with the influence of seasonal variation.

AIM OF THE STUDY: The present study aimed to evaluate the anti-diabetic activity of Zizyphus spina-christi leaf extract (200 mg/kg b.w.), plain and formulated in STZ-diabetic rats. Percentage yield of extracts, marker yield (christinin-A) and antihyperglycemic potencies, depending on seasonal variation were investigated. The chemical stability, study of storage conditions, shelf life T90 prediction of both plain extract and formulated soft gelatin capsules by accelerated studies were studied.
MATERIAL AND METHODS: Changes in all studied parameters after oral administration of Z. spina-christi extract for 28 days were reported. Seasonal variation affecting yield and activities was studied. Flavonoid contents were HPLC evaluated. The capsules were stored at 30, 40 and 50°C [75% relative humidity] and their residual christinin-A content was assayed for 24 weeks. Christinin-A chemical degradation was monitored by HPLC stability indicating method previously validated. Possible physical examination was checked by dissolution test of the content of the capsules using dissolution tester USP XXIV. RESULT: Oral administration of Z. spina-christi leaf extract, plain and formulated for 28 days reduced blood glucose level with significant increase in serum insulin and C-peptide levels. Marked elevation in total antioxidant capacity with normalization of percentage of glycated hemoglobin (HbA1C%) was reported. Moreover, they succeeded to reduce the elevated blood lactate level and to elevate the reduced blood pyruvate content of diabetic rats. In line with amelioration of the diabetic state, Zizyphus extract, plain and formulated restored liver and muscle glycogen content together with significant decrease of hepatic glucose-6-phosphatase and increase in glucose-6-phosphate dehydrogenase activities. In vitro experiments showed a dose-dependent inhibitory activity of Zizyphus extract against α-amylase enzyme with (IC(50)) at 0.3 mg/ml. Such finding has been supported by the in vivo suppression of starch digestion and absorption by Zizyphus extract in normal rats. The flavonoids content of the formulated leaves (collected during June 2009) were found to be 11.5 μg/g of the dry plant material (expressed as quercetin) and 58.8 μg/g of the dry plant material (expressed as rutin). The shelf life for the capsules stored at 30, 40 and 50°C [75% relative humidity] for plain and formulated extract were calculated to be 66.90 and 70.74 weeks, respectively.
CONCLUSION: The current work revealed that Z. spina-christi leaf extract, plain and formulated, improved glucose utilization in diabetic rats by increasing insulin secretion which may be due to both saponin and polyphenols content and controlling hyperglycemia through attenuation of meal-derived glucose absorption that might be attributed to the total polyphenols. Studies showed that leaves are preferably collected from June to October. Finally, the release followed the Higuchi kinetic model, indicating diffusion dominated drug release with no drop in the dissolution values throughout the test period.