Evaluation of Alpha-Amylase Inhibitory Activity of Phenol Rich Fraction of Newbouldia laevis Using Two In-vitro Models

Abstract

The continued patronage and popularity of natural plant products is strongly rooted in the culture of the people, as traditional medicine practitioners may have used a particular plant to treat ailments. Increased interest in self-care, population increase, and economic downturn have led many Nigerians to resort to natural plant products as affordable sources of therapy for their immediate health needs. The present study investigated the alpha-amylase inhibitory activity of the phenol-rich fraction (PRF) from Newbouldia laevis using two in vitro models. Leaves were extracted with methanol and fractionated using n-hexane, ethyl acetate, and butanol. The phytochemical analysis revealed the presence of saponins, flavonoids, tannins, glycosides, steroids, and terpenoids in the extract. The ethyl acetate fraction exhibited the highest total phenolic content (337.9 mg/GAE), followed by the butanol fraction (331.8 mg/GAE). The inhibitory effect of PRF on alpha-amylase activity was evaluated using starch-iodine and 3,5-dinitrosalicylic acid (DNS) methods with acarbose as a reference standard. Both PRF and acarbose showed concentration-dependent inhibition in both assay methods, with starch-iodine demonstrating higher inhibitory effects compared to DNS (IC50:533.79 vs 688.46 µg/ml for PRF; 52.98 vs 64.72 µg/ml for acarbose). Although PRF exhibited a lower potency than acarbose, it demonstrated promising enzyme inhibition. Comparative analysis revealed non-significant differences in the percentage of enzyme inhibition at lower doses, with significant differences occurring at higher concentrations. Correlation analysis showed a positive correlation between the two methods (R2:0.9994 for PRF and 0.9983 for acarbose), indicating their reliability in assessing alpha-amylase inhibitory activity. The inhibitory effect exhibited by the phenol-rich fraction may be connected to its structural features and may provide additional benefits in the management of post-prandial hyperglycemia in diabetic disease conditions. The findings suggest that the phenol-rich fraction of N. laevis may have potential therapeutic applications in managing postprandial hyperglycemia associated with type 2 diabetes. Further research is warranted to identify the specific phenolic compounds responsible for this activity and evaluate their efficacy and safety In vivo.