In our previous paper, we have reported that niacin-related compounds, particularly picolinic acid, dipicolinic acid, and isonicotinamide, induced apoptosis in HL-60 cells but that niacin did not. Moreover, picolinamide, N¹-methylnicotinamide, 6-aminonicotinamide, quinolinic acid, and cinchomeronic acid also had the function of DNA fragmentation in HL-60 cells analyzed by flow cytometry, the ratio of DNA fragmentation finally being about 40% after treatment with these compounds at 10 mM for 24 h. In this study, we found that these compounds also induced apoptosis in HL-60 cells. The wide-spectrum caspase inhibitors prevented DNA fragmentation induced by these compounds. Interestingly, 6-aminonicotinamide induced apoptosis at a comparatively low concentration, while picolinic acid, dipicolinic acid, and isonicotinamide did not at 1 mM. Our results suggest that both NAD metabolism and NAD biosynthesis may be related to the process of apoptosis induced by niacin-related compounds.

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