Evaluation of Lens Aldose Reductase Inhibitory and Free Radical Scavenging Potential of Fractions of Lonchocarpus cyanescens: Potential for Cataract Remediation

Introduction: Current research effort at discovering effective anticataract agent is focus on evaluating Aldose reductase inhibition (ARI) capacities of medicinal plants and plant extracts. The present study was aimed at investigating the in vitro ARI activity of fractions of Lonchocarpus cyanescens leaves on partially purified AR from goat lens. Methods: Phytochemical constituents of the leaves were screened for using aqueous and methanolic extract while in vitro free radical scavenging and ARI activities of the fractions were evaluated using partially purified aldose reductase. Kinetics of the enzyme in the presence of fractions of the leaves was then compared using Lineweaver-Burk plot. Results: Phenol, flavonoid, tannins and phlobatannins were detected in both extracts. All the fractions inhibited AR significantly but this was strongest with aqueous (IC₅₀, 0.06 ± 0.02 mM^-1 and chloroform fractions (IC50, 0.09 ± 0.01 mM^-1). Ethyl acetate, hexane and methanol fraction showed competitive inhibition whereas the aqueous and chloroform fractions showed mixed inhibition with a different V_max and K_m when compared with DL-glyceraldehyde. All the fractions also showed antioxidant capacities but this was also strongest with aqueous fraction. Conclusion: The study confirms the ARI and antioxidant capacity of Lonchocarpus cyanescens which may be attributed to its phenolic constituents and whose extraction is solvent dependent. The plant may therefore serve as a base for the development of anticataract agent.