Hepatic NAD⁺ levels and NAMPT abundance are unaffected during prolonged high-fat diet consumption in C57BL/6JBomTac mice

Dietary supplementation of nicotinamide adenine dinucleotide (NAD⁺) precursors has been suggested as a treatment for non-alcoholic fatty liver disease and obesity. In the liver, NAD⁺ is primarily generated by nicotinamide phosphoribosyltransferase (NAMPT), and hepatic levels of NAMPT and NAD⁺ have been reported to be dependent on age and body composition. The aim of the present study was to identify time course-dependent changes in hepatic NAD content and NAD⁺ salvage capacity in mice challenged with a high-fat diet (HFD). We fed 7-week-old C57BL/6JBomTac male mice either regular chow or a 60% HFD for 6, 12, 24, and 48 weeks, and we evaluated time course-dependent changes in whole body metabolism, liver steatosis, and abundance of hepatic NAD-associated metabolites and enzymes. Mice fed a 60% HFD rapidly accumulated fat and hepatic triglycerides with associated changes in respiratory exchange ratio (RER) and a disruption of the circadian feeding pattern. The HFD did not alter hepatic NAD⁺ levels, but caused a decrease in NADP⁺ and NADPH levels. Decreased NADP⁺ content was not accompanied by alterations in NAD kinase (NADK) abundance in HFD-fed mice, but NADK levels increased with age regardless of diet. NAMPT protein abundance did not change with age or diet. HFD consumption caused a severe decrease in protein lysine malonylation after six weeks, which persisted throughout the experiment. This decrease was not associated with changes in SIRT5 abundance. In conclusion, hepatic NAD⁺ salvage capacity is resistant to long-term HFD feeding, and hepatic lipid accumulation does not compromise the hepatic NAD⁺ pool in HFD-challenged C57BL/6JBomTac male mice.