Hypoxanthine Secretion from Human Adipose Tissue and its Increase in Hypoxia

ObjectiveThe production of uric acid in murine white adipose tissue (mWAT), and that such production was augmented in obese mice, was recently reported. However, little is known about the secretion of metabolites associated with purine catabolism in human WAT (hWAT). The present study analyzed this in hWAT. MethodsFreshly isolated hWAT and mWAT were cultured. The secretion of metabolites associated with purine catabolism was measured. Tissue distribution profiles of genes associated with purine metabolism and metabolite profiling of adipocytes in hypoxia were analyzed. ResultsSecretion of hypoxanthine from hWAT was higher than those of xanthine and uric acid. On the other hand, secretion of uric acid was relatively higher than xanthine and hypoxanthine in mWAT. Xanthine oxidoreductase (XOR) mRNA expression levels in hWAT were markedly lower than that in the human liver. In murine tissues, XOR mRNA expression levels in mWAT were comparable with those in the liver. Cultured human adipocytes secreted hypoxanthine, and its secretion was increased under hypoxia. The metabolic analysis of human adipocytes showed that hypoxia increased metabolites associated with de novo biosynthesis of purine nucleotides. ConclusionsThe present study revealed that hypoxanthine was secreted from human adipose tissue, and the secretion might be increased in local hypoxia.