1-Methylxanthine is an active metabolite of caffeine .1,2 It enhances ionizing radiation-induced DNA double-strand break formation in RKO colorectal cancer cells when used at a concentration of 3 mM.1 1-Methylxanthine (100 ?M) inhibits the uptake of 6-carboxyfluorescein in CHO cells overexpressing human organic anion transporter 1 (OAT1).2 It has also been used as a biomarker of caffeine consumption.3
1.Youn, H., Kook, Y.H., Oh, E.-T., et al.1-Methylxanthine enhances the radiosensitivity of tumor cellsInt. J. Radiat. Biol.85(2)167-174(2009) 2.Rengelshausen, J., Lindenmaier, H., Cihlar, T., et al.Inhibition of the human organic anion transporter 1 by the caffeine metabolite 1-methylxanthineBiochem. Biophys. Res. Commun.320(1)90-94(2004) 3.González-Domínguez, R., Castellano-Escuder, P., Carmona, F., et al.Food and microbiota metabolites associate with cognitive decline in older subjects: A 12-year prospective studyMol. Nutr. Food Res.65(23)e2100606(2021)