ИСТИНА

Nicotinamide adenine dinucleotide (NAD) is an essential electron carrier in redox reactions. Moreover, NAD also serves as a substrate of several families of regulatory proteins such as protein deacetylases (Sirtuins), ADP-ribosyltransferases and Poly-ADP-ribosyl polymerases and thereby plays a key role in a variety of central signaling pathways. Dysregulation of NAD-dependent signaling pathways is associated with metabolic diseases such as diabetes and metabolic syndrome. Alterations of NAD level are also associated with neurodegeneration,cardiovascular disease and cancer. Generally, human cells regulate their NAD supply through the biosynthesis using various precursors delivered with the diet. In this work we characterized the efficiency of NAD biosynthesis from its major precursors: nicotinamide (Nam), nicotinic acid(NA), nicotinamide riboside (NR) and nicotinic acid riboside (NAR) as well as from nicotinamide mononucleotide (NMN) in cultures of various human cell lines. Cells were grown in standard medium, containing Nam as the sole precursor of NAD. NAD synthesis from Nam was suppressed by addition of FK866, a potent inhibitor of the phosphoribosyltransferase NamPRT, which triggers a rapid decline of the NAD level and cell death. In the presence of the inhibitor, cells were also treated with alternative precursors each of which was the only source for generation of intracellular NAD. Then we assessed the cell viability and intracellular NAD levels. We have found that NA does not maintain intracellular NAD level and viability of HepG2, A549 and IMR-32 cells, while A431, HEK293 and HeLa cells as well as primary human dermal fibroblasts efficiently utilize NA for NAD biosynthesis. NAR and NMN were the most and the least efficient NAD precursors, respectively, in the majority of human cell lines used in this study.