Inhibitory Effect of Whey Protein-Derived Peptide Leu-Asp-Gln-Trp on Xanthine Oxidase

Hyperuricemia is associated with various diseases, and xanthine oxidase (XO) is the rate-limiting enzyme in uric acid (UA) production. A previous study reported that Leu-Asp-Gln-Trp (LDQW) in whey protein hydrolysate (WPH) suppressed lipid droplet accumulation in differentiated 3T3-L1 adipocyte-like cells. However, our understanding of LDQW remains limited, further, its efficacy against hyperuricemia has not been elucidated. This study evaluated the XO inhibitory activity of LDQW, one of the bioactive peptides in WPH. In this study, UA produced by the reaction between XO and xanthine was determined using two methods: monitoring the absorbance at 290 nm using absorptiometry and detection using liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis. Allopurinol was used as the positive control, whereas tryptophan and Ala-Leu-Pro-Met (ALPM) were used for comparison. Both absorptiometry and LC-MS/MS analyses demonstrated that LDQW significantly inhibited XO activity in a concentration-dependent manner. The LC-MS/MS analysis results indicated that LDQW, tryptophan, and ALPM inhibition ratios at 20 mM were 58.0% ± 2.8%, 4.4% ± 3.7%, and 45.0% ± 1.0%, respectively. Moreover, it was suggested that Asp-Gln-Trp, a potential digestive peptide predicted by the enzymatic digestion of LDQW in silico, also possessed XO inhibitory activity comparable to that of LDQW in LC-MS/MS analysis. These findings suggest that LDQW is a promising bioactive peptide with potential ameliorative effects against hyperuricemia, similar to those of other XO inhibitory peptides.