Potential cow milk xanthine oxidase inhibitory and antioxidant activity of selected phenolic acid derivatives

Xanthine oxidase (XO) found in all mammals and excess activity leads to urolithiasis. The cow milk XO was purified to 305-fold with a specific activity of 8.76 EU/mg and overall yield of 87% by using DEAE-Sepharose chromatography. The phenolics showed potent XO inhibitory effect with K-1, P1(0.412), P2(0.632), P3(0.585), P4(0.886), P5(1.633), P6(0.503), P7(2.882), P8(3.761), P9(4.487), and P10(5.841) mu M. The phenolics P9 and P10 exhibited uncompetitive inhibition; the phenolics P1, P2, P3, P4, and P6 showed competitive inhibition, and other phenolic acids showed noncompetitive inhibition. The studied phenolic compounds showed potent antioxidant activity and expressed as EC50, ranged from, DPPH (4.2-25.8 mu g mL(-1)), ABTS (10.2-42.5 mmol TE 100 g(-1)), and FRAP (6.3-36.8 mol Fe (II) 100 g(-1)). The results obtained from this study might be utilized for design of XO inhibitors and as antigout agent.