In-vitro and in-vivo hypoglycemic effect of water extract of Averrhoa carambola L. (Star fruit)

Abstract

Over the past decades there has been a dramatic increase in the prevalence of diabetes and obesity. Hyperglycemia is one of the main factor that affect these health disorders. Recently, literature has emerged indicating star fruit as a tool for managing hyperglycemia. However, its effects on inhibiting carbohydrate digestion have not been properly investigated. The purpose of this research was to investigate the inhibitory effect of water extract (WE) of A.carambola on pancreatic alpha amylase activity in vitro and hypoglycemic effect of WE in vivo. Fruit juice of A.carambola was lyophilized to obtain the WE and it was tested for in- vitro α-amylase inhibition using the chromogenic DNSA (3, 5-dinitrosalicylic acid) method, in-vitro DPPH free radical scavenging activity and hypoglycemic effect in normoglycemic, male Sprague Dawley rats. In the in-vivo long term rodent study, treatment group was orally fed with WE (128 mg/ kg b.w) and the control group was given distilled water. The blood samples were collected from the rats on 0ᵗʰ, 4ᵗʰ and 8ᵗʰ week and analyzed for fasting glucose levels. In addition, preliminary qualitative phytochemical analysis was performed on WE. The yield of WE was 4.00%. A.carambola WE (20.3%) showed moderate in- vitro inhibitory effects on α-amylase compared to acarbose (86.7%). Whereas the IC₅₀ values of WE was 2.204 ± 0.028 mg/mL. WE exhibited strong DPPH radical scavenging activity with EC₅₀ value of 244.2 ± 2.43 μg/mL. Moreover, in vivo study showed that 128 mg/ kg dose of WE reduced fasting blood glucose level in treated rats (105.5 mg/dL) compared to control group (126.97 mg/dL) during 8 weeks of the study. Furthermore, presence of alkaloids, flavonoids, phenols and tannins, diterpenes, terpenoids, fats and oils were identified in the extract. Our in vitro study demonstrated an appreciable α-amylase inhibition, hence this may possibly be one of the mechanisms for the hypoglycemic effect exhibited by WE of A.carambola in this study. Therefore, these results indicate that water extract of A.carambola may be useful in controlling blood glucose level. These findings suggest that the WE of star fruit may be a potential candidate for the search of phytochemicals as potent oral hypoglycemic agents.