SUN-103 A Direct Comparison Of Metabolic Responses To Nad Repletion In C57bl/6j And C57bl/6n Diet-induced Obesity Mouse Models

Background and Aim:Supplementation with precursors of nicotinamide adenine dinucleotide (NAD) such as nicotinamide riboside (NR) was shown to be beneficial in preventing high fat diet- or age-induced metabolic dysfunction in mice. However, initial human studies investigating NR supplementation have shown little metabolic benefit in the mildly obese or elderly. A reason for lack of NR effects could be the use of mouse strains with underlying dysfunction such as being deficient in the mitochondrial NADPH generating nicotinamide nucleotide transhydrogenase (Nnt), as seen in C57BL/6J mice commonly used for NR studies. Here, we evaluated NR effectson whole-body energy metabolism and mitochondrial function in C57BL/6J and C57BL/6N, a strain with functional Nnt. Methods: Mice were fed a high fat diet (HFD, 60% fat) or standard chow ± supplementation of 3g/l NR in the drinking water for 8 weeks. Metabolic phenotype was determined by assessing body and organ weight, glucose tolerance, indirect calorimetry and measuring high resolution mitochondrial O2 flux in liver, skeletal muscle and heart. Results: Both strains developed mild obesity and impaired glucose tolerance. NR supplementation had a positive effect on fasting blood glucose and on energy expenditure of C57BL/6N mice on HFD, with lower overall energy expenditure than C57BL/6J mice. In both chow and HFD-fed C57BL/6J, not C57BL/6N mice, NR influenced substrate usage as determined by respiratory exchange ratio. Mitochondrial non-coupled O2 flux (1.4-fold, p<0.01, n=5) and citrate synthase activity (1.3-fold, p<0.05, n=7) were increased by NR supplementation specifically in heart muscle fibers of C57BL/6N, but not C57BL/6J mice on HFD. No significant effect on mitochondrial function was detected in the other tissues. Heart oxidative stress markers 4-hydroxynonenal and expression of NADPH oxidase 4 were significantly suppressed by NR only in C57BL/6N mice. The suppression of oxidative stress markers in C57BL/6N was associated with 2-fold upregulation of Nnt protein (p<0.01, n=5). Conclusion: NR can support mitochondrial function in diet-induced obesity, but its effect is influenced by mouse strain, possibly related to oxidative stress and Nnt function, in which augmenting NAD availability in the context of oxidative stress could be beneficial for the heart.The authors declare that there is no conflict of interest. AG, DMC, LO, RSF, YME, DN, DJH, DPL, CLD, CL, KK, GGL.This project was funded by the European Union H2020 grant EXNADMINA 705869 (AG and GGL), Wellcome Trust Senior Research Fellowship (GGL), University of Birmingham Research Development Award (AG) and Society for Endocrinology Early Career Grant (AG).