12 wk of NR supplementation in doses of 2000 mg/d appears safe, but does not improve insulin sensitivity and whole-body glucose metabolism in obese, insulin-resistant men. This trial was registered at clinicaltrials.gov as NCT02303483.

Key points This is the first long‐term human clinical trial to report on effects of nicotinamide riboside (NR) on skeletal muscle mitochondrial function, content and morphology. NR supplementation decreases nicotinamide phosphoribosyltransferase (NAMPT) protein abundance in skeletal muscle. NR supplementation does not affect NAD metabolite concentrations in skeletal muscle. Respiration, distribution and quantity of muscle mitochondria are unaffected by NR. NAMPT in skeletal muscle correlates positively with oxidative phosphorylation Complex I, sirtuin 3 and succinate dehydrogenase. Abstract Preclinical evidence suggests that the nicotinamide adenine dinucleotide (NAD+) precursor nicotinamide riboside (NR) boosts NAD+ levels and improves diseases associated with mitochondrial dysfunction. We aimed to determine if dietary NR supplementation in middle‐aged, obese, insulin‐resistant men affects mitochondrial respiration, content and morphology in skeletal muscle. In a randomized, placebo‐controlled clinical trial, 40 participants received 1000 mg NR or placebo twice daily for 12 weeks. Skeletal muscle biopsies were collected before and after the intervention. Mitochondrial respiratory capacity was determined by high‐resolution respirometry on single muscle fibres. Protein abundance and mRNA expression were measured by Western blot and quantitative PCR analyses, respectively, and in a subset of the participants (placebo n = 8; NR n = 8) we quantified mitochondrial fractional area and mitochondrial morphology by laser scanning confocal microscopy. Protein levels of nicotinamide phosphoribosyltransferase (NAMPT), an essential NAD+ biosynthetic enzyme in skeletal muscle, decreased by 14% with NR. However, steady‐state NAD+ levels as well as gene expression and protein abundance of other NAD+ biosynthetic enzymes remained unchanged. Neither respiratory capacity of skeletal muscle mitochondria nor abundance of mitochondrial associated proteins were affected by NR. Moreover, no changes in mitochondrial fractional area or network morphology were observed. Our data do not support the hypothesis that dietary NR supplementation has significant impact on skeletal muscle mitochondria in obese and insulin‐resistant men. Future studies on the effects of NR on human skeletal muscle may include both sexes and potentially provide comparisons between young and older people.

Objective Augmenting nicotinamide adenine dinucleotide (NAD+) metabolism through dietary provision of NAD+ precursor vitamins translates to improved glucose handling in rodent models of obesity and diabetes. Preclinical evidence suggests that the NAD+/SIRT1 axis may be implicated in modulating important gut-related aspects of glucose regulation. We sought to test whether NAD+ precursor supplementation with nicotinamide riboside (NR) affects β-cell function, α-cell function, and incretin hormone secretion as well as circulating bile acid levels in humans. Design A 12-week randomized, double-blind, placebo-controlled, parallel-group trial in 40 males with obesity and insulin resistance allocated to NR at 1000 mg twice daily (n = 20) or placebo (n = 20). Two-hour 75-g oral glucose tolerance tests were performed before and after the intervention, and plasma concentrations of glucose, insulin, C-peptide, glucagon, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were determined. β-Cell function indices were calculated based on glucose, insulin, and C-peptide measurements. Fasting plasma concentrations of bile acids were determined. Results NR supplementation during 12 weeks did not affect fasting or postglucose challenge concentrations of glucose, insulin, C-peptide, glucagon, GLP-1, or GIP, and β-cell function did not respond to the intervention. Additionally, no changes in circulating adipsin or bile acids were observed following NR supplementation. Conclusion The current study does not provide evidence to support that dietary supplementation with the NAD+ precursor NR serves to impact glucose tolerance, β-cell secretory capacity, α-cell function, and incretin hormone secretion in nondiabetic males with obesity. Moreover, bile acid levels in plasma did not change in response to NR supplementation.

Repeated periodization of carbohydrate (CHO) intake using a diet‐exercise strategy called the sleep‐low model can potentially induce mitochondrial biogenesis and improve endurance performance in endurance‐trained individuals. However, more studies are needed to confirm the performance‐related effects and to investigate the sustained effects on maximal fat oxidation (MFO) rate and proteins involved in intramuscular lipid metabolism. Thirteen endurance‐trained males (age 23‐44 years; trueV˙O2‐max, 63.9 ± 4.6 mL·kg−1·min−1) were randomized into two groups: sleep‐low (LOW‐CHO) or high CHO availability (HIGH‐CHO) in three weekly training blocks over 4 weeks. The acute metabolic response was investigated during 60 minutes of exercise within the last 3 weeks of the intervention. Pre‐ and post‐intervention, 30‐minute time‐trial performance was investigated after a 90‐minute pre‐load, which as a novel approach included nine intense intervals (and estimation of MFO). Additionally, muscle biopsies (v. lateralis) were obtained to investigate expression of proteins involved in intramuscular lipid metabolism using Western blotting. During acute exercise, average fat oxidation rate was ~36% higher in LOW‐CHO compared to HIGH‐CHO (P = .03). This did not translate into sustained effects on MFO. Time‐trial performance increased equally in both groups (overall time effect: P = .005). We observed no effect on intramuscular proteins involved in lipolysis (ATGL, G0S2, CGI‐58, HSL) or fatty acid transport and β‐oxidation (CD‐36 and HAD, respectively). In conclusion, the sleep‐low model did not induce sustained effects on MFO, endurance performance, or proteins involved in intramuscular lipid metabolism when compared to HIGH‐CHO. Our study therefore questions the transferability of acute effects of the sleep‐low model to superior sustained adaptations.

Background: Deliberately training with reduced carbohydrate availability, a paradigm coined training low, has shown to promote adaptations associated with improved aerobic capacity. In this context researchers have proposed that protein may be ingested prior to training as a means to enhance the protein balance during exercise without spoiling the effect of the low carbohydrate availability. Accordingly, this is being practiced by world class athletes. However, the effect of protein intake on muscle protein metabolism during training low has not been studied. This study aimed to examine if protein intake prior to exercise with reduced carbohydrate stores benefits muscle protein metabolism in exercising and non-exercising muscles. Methods: Nine well-trained subjects completed two trials in random order both of which included a high-intensity interval ergometer bike ride (day 1), a morning (day 2) steady state ride (90 min at 65% VO 2 peak, 90ss), and a 4-h recovery period. An experimental beverage was consumed before 90ss and contained either 0.5 g whey protein hydrolysate [WPH]/ kg lean body mass or flavored water [PLA]. A stable isotope infusion (L-[ring-13 C 6 ]phenylalanine) combined with arterial-venous blood sampling, and plasma flow rate measurements were used to determine forearm protein turnover. Myofibrillar protein synthesis was determined from stable isotope incorporation into the vastus lateralis. Results: Forearm protein net balance was not different from zero during 90ss exercise (nmol/100 ml/min, PLA: 0.5 ± 2.6; WPH: 1.8, ± 3.3) but negative during the 4 h recovery (nmol/100 ml/min, PLA: − 9.7 ± 4.6; WPH: − 8.7 ± 6.5); no interaction (P = 0.5) or main effect of beverage (P = 0.11) was observed. Vastus lateralis myofibrillar protein synthesis rates were increased during 90ss exercise (+ 0.02 ± 0.02%/h) and recovery (+ 0.02 ± 0.02%/h); no interaction (P = 0.3) or main effect of beverage (P = 0.3) was observed. Conclusion: We conclude that protein ingestion prior to endurance exercise in the energy-and carbohydraterestricted state does not increase myofibrillar protein synthesis or improve net protein balance in the exercising and non-exercising muscles, respectively, during and in the hours after exercise compared to ingestion of a non-caloric control.

Background. During ageing there is a functional decline in the pool of muscle stem cells (MuSCs) which influences the functional and regenerative capacity of skeletal muscle. Preclinical evidence have suggested that Nicotinamide Riboside (NR) and Pterostilbene (PT) can improve muscle regeneration e.g. by increasing MuSC function. The objective of the present study was to investigate if NRPTsupplementation promotes skeletal muscle regeneration after muscle injury in elderly humans by improved recruitment of MuSCs. Methods. 32 elderly men and women (55-80 yr) were randomized to daily supplementation with either NRPT (1000 mg NR + 200 mg PT) or matched placebo. Two weeks after initiation of supplementation, a skeletal muscle injury was induced by electrically-induced eccentric muscle work. Skeletal muscle biopsies were obtained pre, 2h, 2, 8, and 30 days post injury. Results. A substantial skeletal muscle injury was induced by the protocol and associated with release of myoglobin and creatine kinase, muscle soreness, tissue edema, and a decrease in muscle strength. MuSC content, proliferation and cell size revealed a large demand for recruitment post injury but was not affected by NRPT. Furthermore, histological analyses of muscle fiber area, central nuclei and embryonic Myosin Heavy Chain showed no effect of NRPT supplementation. Conclusion. Daily supplementation with 1000 mg NR+200 mg PT is safe but does not improve recruitment of the MuSC pool or other measures of muscle recovery in response to injury or subsequent regeneration in elderly subjects. Trial registration. NCT03754842. 4

Gonadoblastoma and malignant transformations thereof can occur in females with Turner syndrome (TS) and Y chromosomal material. However, in females with TS and no Y chromosomal material, this is rarely seen. We report a female with an apparent 45,X karyotype (in blood and tumor) who was diagnosed with a metastatic embryonal carcinoma. Exome sequencing of blood and the tumor was done, and no Y chromosomal material was detected, while predicted deleterious mutations in KIT (likely driver), AKT1, and ZNF358 were identified in the tumor. The patient was treated with chemotherapy (first-line: cisplatin, etoposide, and bleomycin; second-line: paclitaxel and gemcitabine), and after that surgical debulking was performed. She is currently well and without signs of relapse. We conclude that embryonal carcinoma can apparently occur in 45,X TS without signs of Y chromosomal material.

The gut microbiota impacts systemic levels of multiple metabolites including NAD+ precursors through diverse pathways. Nicotinamide riboside (NR) is an NAD+ precursor capable of regulating mammalian cellular metabolism. Some bacterial families express the NR-specific transporter, PnuC. We hypothesized that dietary NR supplementation would modify the gut microbiota across intestinal sections. We determined the effects of 12 weeks of NR supplementation on the microbiota composition of intestinal segments of high-fat diet-fed (HFD) rats. We also explored the effects of 12 weeks of NR supplementation on the gut microbiota in humans and mice. In rats, NR reduced fat mass and tended to decrease body weight. Interestingly, NR increased fat and energy absorption but only in HFD-fed rats. Moreover, 16S rRNA gene sequencing analysis of intestinal and fecal samples revealed an increased abundance of species within Erysipelotrichaceae and Ruminococcaceae families in response to NR. PnuC-positive bacterial strains within these families showed an increased growth rate when supplemented with NR. The abundance of species within the Lachnospiraceae family decreased in response to HFD irrespective of NR. Alpha and beta diversity and bacterial composition of the human fecal microbiota were unaltered by NR, but in mice, the fecal abundance of species within Lachnospiraceae increased while abundances of Parasutterella and Bacteroides dorei species decreased in response to NR. In conclusion, oral NR altered the gut microbiota in rats and mice, but not in humans. In addition, NR attenuated body fat mass gain in rats, and increased fat and energy absorption in the HFD context.