Inflammatory states are associated with the extracellular release of nucleotides, especially ATP.[48] Adenosine originates from intracellular purine metabolism and nucleotide metabolism, and a reduction in its signaling can result in increased production of inflammatory cytokines.[49] Allopurinol in purine metabolism can inhibit xanthine oxidase to improve mixed granulocytic airway inflammation induced by toluene diisocyanate.[50] Notably, purine metabolism and nucleotide metabolism are enriched with common metabolites including guanosine and its downstream product deoxyguanosine. This evidence concerns the gene XDH and inflammation.