To assay the in vitro xanthine oxidase inhibitory activity of the various fractions of the hydromethanolic extract of the leaves of Erythrina stricta and to determine its enzyme inhibition mechanism.
Xanthine oxidase inhibitory activity was assayed spectrophotometrically under aerobic conditions and the degree of enzyme inhibition was determined by measuring the increase in absorbance at 295 nm associated with uric acid formation. Enzyme kinetics was carried out using Lineweaver-Burk plots using xanthine as the substrate.
Among the fractions tested, the chloroform fraction exhibited highest potency (IC(50) 21.2+/-1.6 microg/ml) followed by the pet-ether (IC(50) 30.2+/-2.2 microg/ml), ethyl acetate (IC(50) 44.9+/-1.4 microg/ml) and residual (IC(50) 100+/-3.3 microg/ml) fractions. The IC(50) value of allopurinol used, as the standard was 6.1+/-0.3 microg/ml. Enzyme inhibition mechanism indicated that the mode of inhibition was of a mixed type.
These results suggest that the use of Erythrina stricta for the treatment of gout could be attributed to its xanthine oxidase inhibitory activity.