PTPN1 and type 2 diabetes mellitus: However, PTP1B inhibitors are limited by their high anionic charge that prevents their binding affinities; the bioavailability of apigenin 7-O-β-D-glucuronide, which has a carboxylic acid group, can be improved by using its methyl or ethyl derivative; therefore, it is a potential natural T2DM inhibitor.