Objective Cancer cachexia and muscle loss are associated with increased morbidity and mortality. In preclinical animal models, blocking activin receptor (ACVR) ligands has improved survival and prevented muscle wasting in cancer cachexia without an effect on tumour growth. However, the underlying mechanisms are poorly understood. This study aimed to identify cancer cachexia and soluble ACVR (sACVR) administration-evoked changes in muscle proteome. Methods Healthy and C26 tumour-bearing (TB) mice were treated with recombinant sACVR. The sACVR or PBS control were administered either prior to the tumour formation or by continued administration before and after tumour formation. Muscles were analysed by quantitative proteomics with further examination of mitochondria and nicotinamide adenine dinucleotide (NAD + ) metabolism. To complement the first prophylactic experiment, sACVR (or PBS) was injected as a treatment after tumour cell inoculation. Results Muscle proteomics in TB cachectic mice revealed downregulated signatures for mitochondrial oxidative phosphorylation (OXPHOS) and increased acute phase response (APR). These were accompanied by muscle NAD + deficiency, alterations in NAD + biosynthesis including downregulation of nicotinamide riboside kinase 2 ( Nrk2 ), and decreased muscle protein synthesis. The disturbances in NAD + metabolism and protein synthesis were rescued by treatment with sACVR. Across the whole proteome and APR, in particular, Serpina3n represented the most upregulated protein and the strongest predictor of cachexia. However, the increase in Serpina3n expression was associated with increased inflammation rather than decreased muscle mass and/or protein synthesis. Conclusions We present evidence implicating disturbed muscle mitochondrial OXPHOS proteome and NAD + homeostasis in experimental cancer cachexia. Treatment of TB mice with a blocker of activin receptor ligands restores depleted muscle NAD + and Nrk2 , as well as decreased muscle protein synthesis. These results indicate putative new treatment therapies for cachexia and that although acute phase protein Serpina3n may serve as a predictor of cachexia, it more likely reflects a condition of elevated inflammation.

Nicotinamide adenine dinucleotide (NAD + ) precursor nicotinamide riboside (NR) has emerged as a promising compound to improve obesity-associated mitochondrial dysfunction and metabolic syndrome in mice. However, most short-term clinical trials conducted so far have not reported positive outcomes. Therefore, we aimed to determine whether long-term NR supplementation boosts mitochondrial biogenesis and metabolic health in humans. Twenty body mass index (BMI)–discordant monozygotic twin pairs were supplemented with an escalating dose of NR (250 to 1000 mg/day) for 5 months. NR improved systemic NAD + metabolism, muscle mitochondrial number, myoblast differentiation, and gut microbiota composition in both cotwins. NR also showed a capacity to modulate epigenetic control of gene expression in muscle and adipose tissue in both cotwins. However, NR did not ameliorate adiposity or metabolic health. Overall, our results suggest that NR acts as a potent modifier of NAD + metabolism, muscle mitochondrial biogenesis and stem cell function, gut microbiota, and DNA methylation in humans irrespective of BMI.

Cachexia is a debilitating wasting syndrome and highly prevalent comorbidity in cancer patients. It manifests especially with energy and mitochondrial metabolism aberrations that promote tissue wasting. We recently identified nicotinamide adenine dinucleotide (NAD+) loss to associate with muscle mitochondrial dysfunction in cancer hosts. In this study we confirm that depletion of NAD+ and downregulation of Nrk2, an NAD+ biosynthetic enzyme, are common features of severe cachexia in different mouse models. Testing NAD+ repletion therapy in cachectic mice reveals that NAD+ precursor, vitamin B3 niacin, efficiently corrects tissue NAD+ levels, improves mitochondrial metabolism and ameliorates cancer- and chemotherapy-induced cachexia. In a clinical setting, we show that muscle NRK2 is downregulated in cancer patients. The low expression of NRK2 correlates with metabolic abnormalities underscoring the significance of NAD+ in the pathophysiology of human cancer cachexia. Overall, our results propose NAD+ metabolism as a therapy target for cachectic cancer patients.

Cachexia is a debilitating wasting syndrome and highly prevalent comorbidity in cancer patients. It manifests especially with energy and mitochondrial metabolism aberrations that promote tissue wasting. We recently identified nicotinamide adenine dinucleotide (NAD+) loss to associate with muscle mitochondrial dysfunction in cancer hosts. In this study we confirmed that depletion of NAD+ and downregulation of Nrk2, an NAD+ biosynthetic enzyme, are common features of different mouse models and cachectic cancer patients. Testing NAD+ repletion therapy in cachectic mice revealed that NAD+ precursor, vitamin B3 niacin, efficiently corrected tissue NAD+ levels, improved mitochondrial metabolism and ameliorated cancer- and chemotherapy-induced cachexia. To examine NAD+ metabolism in a clinical setting, we showed that the low expression of NRK2 in cancer patients correlated with metabolic abnormalities underscoring the significance of NAD+ in the pathophysiology of human cancer cachexia. Overall, our results propose a novel therapy target, NAD+ metabolism, for cachectic cancer patients.

SummaryNAD+ precursor nicotinamide riboside (NR) has emerged as a promising compound to improve obesity-associated mitochondrial dysfunction and metabolic syndrome in mice. However, most short-term clinical trials conducted so far have failed to report positive outcomes. Therefore, we aimed to determine whether long-term NR supplementation boosts mitochondrial biogenesis and metabolic health in humans. Twins from 22 BMI-discordant monozygotic pairs were supplemented with an escalating dose of NR (250-1000 mg/day) for 5 months (clinicaltrials.gov entry NCT03951285). NR improved blood and tissue NAD+ metabolism, muscle mitochondrial number, myoblast differentiation and gut microbiota composition independent of BMI. NR also showed a capacity to modulate epigenetic control of gene expression in muscle and adipose tissue. However, NR did not ameliorate adiposity or metabolic health. Overall, our results suggest that NR acts as a potent modifier of NAD+ metabolism, muscle mitochondrial biogenesis and stem cell function, gut microbiota, and DNA methylation in humans irrespective of BMI.