Study design

One hundred and forty healthy male and female participants were enrolled in a randomized, double-blind, placebo-controlled parallel study to investigate the safety and effect of NR (100 mg/day, 300 mg/day, and 1000 mg/day) on NAD+ metabolite concentrations in urine and blood over 8 weeks. The study consisted of a 2-week run-in and 8-week supplementation period (Fig. 1). To minimize the effect of dietary influences on NAD+ metabolite levels, subjects were instructed to avoid foods that contain high amounts of tryptophan and forms of vitamin B3 during the run-in and NR supplementation periods. After screening, all subjects attended the clinic prior to the run-in period to review their medical history and health status and receive counseling for the dietary restrictions. At the end of the run-in period (Day 0), the subjects visited the clinic for baseline safety assessments, blood and urine collection, randomization to one of four supplementation groups (placebo, 100 mg, 300 mg, 1000 mg NIAGEN per day groups; n = 35/group), and additional dietary restriction counseling. The subjects were then released to consume their study product for the subsequent 56 days, attending the clinic on Day 7, 14, 28, and 56 for safety assessments, and blood and urine collection. The study was conducted at KGK Science Inc. Suite 1440, One London Place, 255 Queens Ave, London, Ontario, following Good Clinical Practice (GCP) guidelines and in accordance with the ethical principles that have their origins in the Declaration of Helsinki and its subsequent amendments. The study was reviewed by the Natural Health Product Directorate (NHPD), Health Canada and a research ethics board. Notice of authorization was granted on December 9th, 2015 by the NHPD, Ottawa, Ontario and unconditional approval was granted on February 5th, 2016 by the Institutional Review Board (IRB Services, Aurora, Ontario). The study was registered on clinicaltrials.org on March 18, 2016 as NCT0271593 and posted to the WHO International Clinical Trial Registry Platform on January 3, 2016. External monitoring of source documents was conducted by ClynProject Consulting, LLC.

Figure 1 Study design. Subjects were screened over a 4-week period. Eligible subjects were enrolled and instructed to avoid foods containing high amounts of tryptophan and forms of niacin for the duration of the study. Following a 2-week run-in period, the subjects visited the clinic on Day 0 for baseline safety assessments, blood and urine collection, and randomization to one of four supplementation groups (placebo, 100 mg, 300 mg, 1000 mg NIAGEN per day). The subjects then consumed either placebo or the NIAGEN treatments for 56 days and visited the clinic on Day 7, 14, 28, and 56 for safety assessments, and blood and urine collection. Dietary counseling and food records were dispensed and collected throughout the run-in and supplementation periods to ensure that the subjects adhered to the dietary restrictions. Full size image

The primary objective was to evaluate the difference in urinary MeNAM levels between placebo and NIAGEN (100 mg, 300 mg, and 1000 mg) after 8 weeks of supplementation. The secondary objectives were to evaluate the rate of increase in urinary MeNAM levels between placebo and NIAGEN (100 mg, 300 mg, and 1000 mg) after 8 weeks of supplementation, the difference and rate of increase in other NR metabolites levels in blood between placebo and NIAGEN (100 mg, 300 mg, and 1000 mg) after 8 weeks of supplementation, the difference and rate of increase in other NR metabolites levels in urine between placebo and NIAGEN (100 mg, 300 mg, and 1000 mg) after 8 weeks of supplementation, and the difference in other NR metabolites levels in muscle between placebo and NIAGEN (100 mg, 300 mg, and 1000 mg) after 8 weeks of supplementation. Exploratory outcomes included exploring the changes in Resting Energy Expenditure (REE) relative to placebo after 8 weeks of supplementation, the changes in blood levels of branched-chain amino acids relative to placebo after 8 weeks of supplementation, the changes in blood levels of high sensitivity C-reactive protein (hsCRP) relative to placebo after 8 weeks of supplementation. The safety objectives included the difference in vital signs, hematology and clinical chemistry parameters including high density lipoprotein cholesterol (HDL-C), LDL-C, triglycerides, and total cholesterol between the placebo- and NIAGEN-treated groups, and the difference in the incidence of adverse events between the placebo- and NIAGEN-treated groups. The effect of NIAGEN on plasma HCY levels was determined as a post hoc analysis. There were no changes to the trial outcomes or method during the trial and interim analyses were not conducted.

Subjects

Healthy men and non-pregnant, non-breastfeeding women (40–60 years of age) were eligible for the study if their body mass index was between 25–30, they were willing to avoid vitamin B3 supplements and limit ingestion of foods containing moderate amounts of tryptophan and vitamin B3, maintain current levels of physical activity throughout the study, and refrain from caffeine consumption on days when study visits included blood collection for metabolite measurement. Women of childbearing potential were eligible only if willing to use medically approved forms of birth control. Individuals with diabetes, active peptic ulcer disease, alcohol use >2 standard servings/day or history of drug or alcohol abuse in the past year, using medical marijuana, anti-hypertensives, or lipid lowering medications were excluded. Individuals with a history of renal disease, liver disease, or history of niacin deficiency were also excluded. Individuals were determined healthy by laboratory results, medical exam and physical exam. Informed consent was obtained from each participant at the screening prior to any study-related activities being performed.

Randomization

The participants were assigned to the different groups by simple randomization. Participants were identified by their initials and their date of birth and were assigned a participant number at their screening visit. If the potential participant met all the inclusion criteria and did not meet any of the exclusion criteria at baseline, a randomization number was assigned to the participant by a blinded investigator per the order of the randomization list generated by www.randomization.com.

Study product

The study consisted of a 2-week run-in and 8-week interventional period. Participants received either 100 mg, 300 mg, 1000 mg NR per day or placebo during the 8-week intervention. The NR capsule consisted of 100 mg or 250 mg of NR chloride (99% purity) as the active ingredient and microcrystalline cellulose and vegetarian capsule as non-active ingredients. The placebo capsule consisted of microcrystalline cellulose and a vegetarian capsule. No differences in size, color, taste, texture, or packaging were detectable between the two products. The investigational products and the placebo capsules were sealed in identically-appearing blister packets, which were labelled per ICH-GCP and applicable local regulatory guidelines. Unblinded personnel at KGK Science Inc., who were not involved in any study assessments, labelled the investigational product. A randomization schedule was created and provided to the investigator indicating the order of randomization. Investigators, other site personnel, and participants were blinded to the product.

Participants were instructed to take 4 capsules daily after breakfast beginning the day after their randomization visit (Day 1). The 4 capsules amounted to a single dose of either placebo (a total of 4 placebo capsules) or 100 mg NR (1 capsule containing 100 mg NR and three placebo capsules), 300 mg NR (3 capsules containing 100 mg NR and 1 capsule containing placebo) or 1000 mg NR (4 capsules containing 250 mg NR). Participants were instructed to save all unused and open packages and return them at each visit for a determination of compliance. Compliance to the protocol was also assessed by reviewing the 3-day food record and study diaries completed by each participant for adherence to the study’s dietary restrictions, ingestion of the investigational product, and maintenance of physical activity levels.

Laboratory measurements

Subjects fasted for 12 hours prior to study visits.

Anthropometric measures and vitals were assessed at screening, day 0, 7, 14, 28 and 56. Blood was collected for the assessment of laboratory parameters (CBC, electrolytes Na, K, Cl, HbA1c, creatinine, BUN, AST, ALT, GGT, and bilirubin) at screening, day 0, 7, 14, 28 and 56, blood lipids and NAD+ metabolite analyses on day 0, 7, 14, 28, and 56. Urine was also collected for NAD+ metabolites analyses on day 0, 7, 14, 28, and 56. The assessments of laboratory parameters and blood lipids were conducted by LifeLabs (Etobicoke, Ontario, Canada) using standardized procedures. NAD+ metabolites in blood and urine were quantitated by LC-MS-MS at Keystone Bioanalytical, Inc. (North Wales, PA) using analytically validated methods in accordance with Good Laboratory Practices. Only metabolite data from participants who completed the study and had metabolite levels above the limit of quantitation were included in the analysis.

For whole blood NAD+ analysis, NAD+-13C 5 was the internal standard. The lower limit of quantification (LLOQ) was 0.3 µg/ml, the upper limit of the quantification (ULOQ) was 50 µg/ml, and the inter-assay precision (% CV) was 1.10 to 11.83%. Plasma NAM was quantified against a NAM-d4 standard with a LLOQ = 5 ng/ml, ULOQ = 3000 ng/ml, and a % CV of 0.71 to 5.38%. Plasma MeNAM was quantified against an MeNAM-d3 standard with a LLOQ = 4 ng/ml, ULOQ = 2000 ng/ml, and a %CV of 0.34 to 13.31%. Urinary MeNAM and N1-methyl-2-pyridone-5-carboximide (Me2PY) were quantified against internal d3 standards with an LLOQ = 1 µg/ml and ULOQ = 256 µg/ml for both analytes. The %CV for urinary MeNAM and Me2PY were 1.25 to 4.60% and 1.10 to 3.22%, respectively.

Plasma HCY levels were quantified by LC-MS-MS at Keystone Bioanalytical. Sodium citrate-treated plasma was pretreated with 50 µL of 0.5 M DTT (1,4-dithiothreitol) and HCY and the internal standard (HCY-d4) were precipitated using 0.5% formic acid and 0.05% TFA in acetonitrile. After vortexing and centrifuging, 20 µL of the supernatant was diluted in 200 µL of nano-pure water in a clean HPLC vial, and 5–10 µL was injected into the liquid chromatography mass spectrometer. The standard curve range was 0.2–40 µg/mL with the LLOQ of 0.2 µg/mL.

Adverse events (AEs)

Subjects were instructed to record any AEs in a diary and were asked at each visit if they have experienced any difficulties or problems since the last visit.

Statistical analyses

Statistical analyses were completed using the R Statistical Software Package Version 3.2.1 (R Core Team, 2015) for Microsoft Windows. All statistical analyses were performed at a significance level of 5%. Although the primary outcome variable was the difference in urinary MeNAM levels between placebo and NR (100 mg, 300 mg, 1000 mg) treated subjects after 8 weeks of supplementation, the study was powered for a secondary outcome of elevation of blood NAD+. Statistical power was based on the estimated standard deviation of 10.1 µM for blood NAD+ levels46 and 80% power to detect an effect size of at least an 8.7 µM increase. With attrition estimated at 20% throughout the course of the study, a total of 140 subjects were enrolled. For reference, if the study had been powered to detect a significant increase in MeNAM levels, then a total of 128 subjects would have been required.

Statistical analyses were performed on a modified intent-to-treat population (ITT), which consisted of all subjects who received either product, and on whom any post-randomization efficacy information is available. Variables were tested for normality and log-normality where log-normality distributed variables were analyzed in the logarithmic domain. Appropriate non-parametric tests were used to analyze non-normal variables. All missing values were imputed with last observation carried forward (LCOF) imputation. No imputation was performed for missing values of safety variables.

Numerical endpoints were formally tested for significance between groups by analysis of covariance (ANCOVA). The dependent variable was the value at each visit, the factor was the treatment group, and the value at baseline (Day 0) was the covariate. When the effect of supplementation was significant (p-value ≤ 0.05), the pairwise Tukey-Kramer post hoc test was applied. Significant efficacy of the product, relative to placebo, was inferred if the coefficient of the treatment group in the ANCOVA model was significantly different from zero (p ≤ 0.05). Numerical endpoints that are intractably non-normal were assessed by the Mann-Whitney U test. A within group analysis on efficacy endpoints was done using the Student’s paired t-test or, in the case of intractable non-normality, the Wilcoxon sign rank test was performed.