Lipofuscin was produced when HT29, a colon carcinoma cell line, was cultured in millimolar concentrations of xanthine and guanine but not in the presence of other bases. Using a simple assay developed to quantify the fluorescent pigment, it was found that maximum levels of lipofuscin were developed in 3 days. Methylxanthines that are not substrates of xanthine dehydrogenase, such as caffeine and theophylline, did not induce formation of lipofuscin. Xanthine-induced lipofuscin formation could be inhibited by oxypurinol, indicating that the pigment may be formed by free radicals generated by xanthine dehydrogenase. It is suggested that the lipofuscin seen in pseudomelanosis coli may result from the accumulation of purines in the colon.

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