Reduction of uric acid levels by lactic acid bacteria: in vitro mechanisms and antioxidant activities

To explore the in vitro mechanism of action of lactic acid bacteria (LAB) in reducing uric acid, this study focused on 16 LAB strains isolated from traditional fermented milk in Hulunbuir, Inner Mongolia, China. Through comprehensive evaluation of purine metabolite (xanthine, hypoxanthine, adenine, and guanine) degradation and time-dependent xanthine oxidase (XO) inhibition by viable/dead bacterial suspensions (intracellular/extracellular components), six strains with superior XO-inhibitory were screened. Suspensions of both live and dead cells, intracellular components, and extracellular secretions from these six strains all exhibited strong inhibitory effects on XO. Among these strains (whether live or dead), the extracellular secretions of Lactiplantibacillus plantarum HN2-3, Lactobacillus helveticus M1-1, Lactobacillus rhamnosus N1-4, and L. plantarum N2-4 exhibited significantly stronger inhibitory effects on XO compared to their intracellular extracts (P < 0.05). Meanwhile, in Streptococcus thermophilus ST0, there was no significant difference in inhibition activity between intracellular and extracellular components of both live and dead cells (P > 0.05). Finally, the extracellular secretions from live L. helveticus M1-2 cells and their intracellular components exhibited comparable levels of XO inhibition (P > 0.05). These results indicated some variability in the inhibition of XO. Furthermore, regardless of the viability of all the six strains, their suspensions, extracellular secretions, and intracellular components exhibited varying degrees of scavenging activity against hydroxyl radical, superoxide anion radical, and 1,1-diphenyl-2-picrylhydrazyl radical. In particular, the XO inhibition activity of live strains showed a positive correlation with the antioxidant activity of these bacteria. These findings provide important scientific evidence for the development of novel functional foods and medicines based on LAB.