DNA damage and repair in tumour and non-tumour tissues of mice induced by nicotinamide

The Central Role of the NAD+ Molecule in the Development of Aging and the Prevention of Chronic Age-Related Diseases: Strategies for NAD+ Modulation

The molecule NAD+ is a coenzyme for enzymes catalyzing cellular redox reactions in several metabolic pathways, encompassing glycolysis, TCA cycle, and oxidative phosphorylation, and is a substrate for NAD+-dependent enzymes. In addition to a hydride and electron transfer in redox reactions, NAD+ is a substrate for sirtuins and poly(adenosine diphosphate-ribose) polymerases and even moderate decreases in its cellular concentrations modify signaling of NAD+-consuming enzymes. Age-related reduction in cellular NAD+ concentrations results in metabolic and aging-associated disorders, while the consequences of increased NAD+ production or decreased degradation seem beneficial. This article reviews the NAD+ molecule in the development of aging and the prevention of chronic age-related diseases and discusses the strategies of NAD+ modulation for healthy aging and longevity.

Compartmentalized regulation of NAD+ by Di (2-ethyl-hexyl) phthalate induces DNA damage in placental trophoblast

Di (2-ethyl-hexyl) phthalate (DEHP) is a wildly used plasticizer. Maternal exposure to DEHP during pregnancy blocks the placental cell cycle at the G2/M phase by reducing the efficiency of the DNA repair pathways and affects the health of offsprings. However, the mechanism by which DEHP inhibits the repair of DNA damage remains unclear. In this study, we demonstrated that DEHP inhibits DNA damage repair by reducing the activity of the DNA repair factor recruitment molecule PARP1. NAD+ and ATP are two substrates necessary for PARP1 activity. DEHP abated NAD+ in the nucleus by reducing the level of NAD+ synthase NMNAT1 and elevated NAD+ in the mitochondrial by promoting synthesis. Furthermore, DEHP destroyed the mitochondrial respiratory chain, affected the structure and quantity of mitochondria, and decreased ATP production. Therefore, DEHP inhibits PARP1 activity by reducing the amount of NAD+ and ATP, which hinders the DNA damage repair pathways. The supplement of NAD+ precursor NAM can partially rescue the DNA and mitochondria damage. It provides a new idea for the prevention of health problems of offsprings caused by DEHP injury to the placenta.

Extension of use of nicotinamide riboside chloride as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on the safety of an extension of use of the novel food (NF) nicotinamide riboside chloride (NRC) pursuant to Regulation (EU) 2015/2283. The assessment addresses the use of NRC in 'meal replacement products' and 'nutritional drink mixes' at levels up to 300 mg/day for the general population, and in food for special medical purposes (FSMP) and total diet replacement for weight control (TDRWC) (as per Regulation (EU) No 609/2013) at levels up to 500 mg/day in adults. Benchmark dose modelling was carried out on data from the 90-day oral toxicity studies in rats relevant to the safety assessment. Considering the lack of tolerable upper intake level (UL) for nicotinamide in infants and the narrow margin of exposure between the estimated intake in infants and the lower confidence bound of the benchmark doses (BMDL 05) estimated by the models, the Panel concludes that the safety of the NF has not been established for use in 'meal replacement products' and 'nutritional drink mixes' under the proposed conditions of use. For FSMP and TDRWC, the proposed maximum use level corresponds to an intake of 210 mg nicotinamide per day, which is below the current UL for nicotinamide of 900 mg/day for adults. The Panel considers that the NF is as safe as pure nicotinamide for use in FSMP and TDRWC. The Panel, however, notes experimental data which indicate several pathways by which intakes of nicotinamide (or its precursors), at levels that are substantially higher than the physiological requirement, might cause adverse effects. The Panel considers that further investigations are required and that a re-evaluation of the UL for nicotinamide may be warranted.

Pharmacological intakes of niacin increase bone marrow poly(ADP-ribose) and the latency of ethylnitrosourea-induced carcinogenesis in rats

Cancer chemotherapy agents cause short-term leukopenia during treatment and the development of secondary leukemias after recovery from the original disease. We reported that niacin deficiency in rats increases the severity of nitrosourea-induced leukopenia and the subsequent development of cancers. This study was designed to test the effects of supplementing an already high quality diet with pharmacologic levels of niacin. For a period of 4 wk, nontumor-bearing weanling Long-Evans rats were pair-fed AIN-93M diets that were niacin adequate (30 mg/kg diet) or pharmacologically supplemented (4 g/kg diet) with nicotinic acid (NA) or nicotinamide (Nam). One week after the initiation of niacin feeding protocols, ethylnitrosourea (ENU) treatment began (12 doses, 30 mg/kg by gavage, every other day). ENU treatment caused leukopenia, which was not prevented by niacin supplementation. At the end of ENU treatment, all rats were switched to a niacin-adequate diet and monitored. Within 36 wk after the start of treatment, all of the ENU-treated rats either lost 5% of peak body weight or had palpable tumors > 1 cm in diameter, and were necropsied. Supplementation with NA or Nam at 4.0 g/kg diet (combined analysis) increased the latency of the ENU-induced morbidity curve, relative to niacin-adequate controls. Morbidity could be attributed in almost all cases to some form of neoplasm, with leukemias the predominant form. In short-term studies, supplementation with either NA or Nam caused dramatic increases in bone marrow NAD(+) (1- to 1.5-fold), basal poly(ADP-ribose) (3- to 5-fold) and ENU-induced poly(ADP-ribose) levels (1.5-fold). These data show that supplementation of a niacin-adequate, high quality diet with pharmacologic levels of nicotinic acid or nicotinamide increases NAD(+) and poly(ADP-ribose) levels in bone marrow and may be protective against DNA damage.

Niacin, poly(ADP-ribose) polymerase-1 and genomic stability

Nicotinic acid (NA) and nicotinamide (NAM), commonly called niacin, are the dietary precursors for NAD(+) (nicotinamide adenine dinucleotide), which is required for DNA synthesis, as well as for the activity of the enzyme poly(ADP-ribose) polymerase-1 (PARP-1; EC 2.4.2.30) for which NAD(+) is the sole substrate. The enzyme PARP-1 is highly activated by DNA strand breaks during the cellular genotoxic stress response, is involved in base excision repair, plays a role in p53 expression and activation, and hence, is thought to be important for genomic stability. In this review, first the absorption, metabolism of niacin to NAD(+), as well as the assessment of niacin status are discussed. Since NAD(+) is important for PARP-1 activity, various aspects of PARP-1 in relation to DNA synthesis and repair, and regulation of gene expression are addressed. This is followed by a discussion on interactions between dietary methyl donor deficiency, niacin status, PARP-1 activity and genomic stability. In vitro studies show that PARP-1 function is impaired and genomic stability decreased when cells are either depleted from NAD(+) or incubated with high concentrations of NAM which is a PARP-1 inhibitor. In vitro as well as animal studies indicate that niacin deficiency increases genomic instability especially in combination with genotoxic and oxidative stress. Niacin deficiency may also increase the risk for certain tumors. Preliminary data suggest that niacin supplementation may protect against UV-induced tumors of the skin in mice, but data on similar preventive effects in humans are not available. NAM has been shown in vitro to have an antioxidant activity comparable to that of ascorbic acid. Data on niacin status and genomic stability in vivo in humans are limited and yield ambiguous results. Therefore, no firm conclusions with respect to optimal niacin intake are possible. As a consequence of oral niacin supplementation, however, NAM levels in the body may increase, which may result in inhibition of PARP-1 and increased genomic instability. More studies are needed to define an optimal level of niacin nutriture in relation to genomic stability and tumorigenesis.

Treatment of chemotherapy-induced leukopenia in a rat model with aqueous extract from Uncaria tomentosa

The Uncaria tomentosa water extracts (C-Med-100) depleted of indole alkaloids (< 0.05%, w/w) have been shown to induce apoptosis and inhibit proliferation in tumor cells in vitro and to enhance DNA repair, mitogenic response and white blood cells in vivo. In this study, the effect of C-Med-100 in the treatment of chemically induced leukopenia was evaluated in a rat model. W/Fu rats were treated first with doxorubicin (DXR) 2 mg/kg x 3 (i.p. injection at 24 hour-intervals) to induce leukopenia. Twenty-four hours after the last DXR treatment, the rats were daily gavaged with C-Med-100 for 16 consecutive days. As a positive control, Neupogen, a granulocyte colony stimulator was also administered by subcutaneous injection at a dose of 5 and 10 microg/ml for 10 consecutive days. The results showed that both C-Med-100 and Neupogen treatment groups recovered significantly sooner (p < 0.05 by Duncan test) than DXR group. However, the recovery by C-Med-100 treatment was a more natural process than Neupogen because all fractions of white blood cells were proportionally increased while Neupogen mainly elevated the neutrophil cells. These results were also confirmed by microscopic examination of the blood smears. The mechanism of the C-Med-100 effect on WBC is not known but other data showing enhanced effects on DNA repair and immune cell proliferative response support a general immune enhancement.

Newly discovered anti-inflammatory properties of the benzamides and nicotinamides

Our laboratory has concentrated on the possible regulation the benzamides and nicotinamides may have on the processes of DNA repair and apoptosis. Recent reports have suggested that both apoptosis and inflammation are regulated by the transcription factor NF-kappaB. We have initiated studies regarding the hypothesis that the benzamides and nicotinamides could inhibit the production of tumor necrosis factor alpha (TNFalpha) and the inflammatory response as well as induce apoptosis via inhibition of NF-kappaB. Our data have shown that nicotinamide and two N-substituted benzamides, metoclopramide (MCA) and 3-chloroprocainamide (3-CPA), gave dose dependent inhibition of lipopolysacharide induced TNFalpha in the mouse within the dose range of 10-500 mg/kg. Moreover, lung edema was prevented in the rat by 3 x 50 mg/kg doses of 3-CPA or MCA, and 100-200 microM doses of MCA could also inhibit NF-kappaB in Hela cells. Taken together these data strongly support the notion that benzamides and nicotinamides have potent anti-inflammatory and antitumor properties, because their primary mechanism of action is regulated by inhibition at the gene transcription level of NF-kappaB, which in turn inhibits TNFalpha and induces apoptosis.

DNA repair enhancement by a combined supplement of carotenoids, nicotinamide, and zinc

Four volunteers were involved for 5 weeks of a baseline period, followed by 7 weeks of a combined supplementation of nicotinamide, zinc, and carotenoids (Nicoplex). Blood sampling and bioassays were carried out every week during the evaluation period. The supplementation of Nicoplex resulted in statistically significant increased resistance to DNA single-strand breaks induced by H2O2 (DNA retained on filter % from 46.7 +/- 1.9 to 59.4 +/- 4.3; p < 0.01), increased DNA repair 60 min after induction of damage (DNA retained on filter % from 74.6 +/- 4.8 to 88.3 +/- 4.2; p < 0.01), elevated poly (ADP-ribose) polymerase (PARP) activity (p < 0.05), and an increased proliferative response to phytohemagglutinin (PHA) (p < 0.05) when compared with the levels before supplementation. However, when the same subjects were supplemented with nicotinamide, zinc, and carotenoids together with another 17 nutrients or minerals, there were no changes in DNA damage, DNA repair, or proliferative response to PHA. Through the use of a rat model, DNA repair of splenocytes 3 h after 12 Gy whole-body irradiation was significantly enhanced in rats supplemented with Nicoplex for 6 weeks (p < 0.05) and 8 weeks (p < 0.01). Comparison of Nicoplex and its components administered separately revealed that there was an additive effect on DNA repair for both single- and double-strand breaks (both p < 0.05). On the basis of the results, it is hypothesized that the enhanced effect of combined supplement of nicotinamide, zinc, and carotenoids on DNA repair depends on their diversified mechanisms of action while multinutrient supplementation may compromise the effects by inhibitory interactions including uptake and absorption.

Multiple mechanisms of action of the benzamides and nicotinamides as sensitizers of radiotherapy: opportunities for drug design

The benzamides and nicotinamides are a well-known class of drugs that contain many analogs having radio- and chemosensitizing properties. This study reports on a structural analysis in order to explain the chemical features important to their mechanisms of action. In general, N-substituted analogs are distinguished from the non-N-substituted analogs because they (i) are susceptible to radiolysis, (ii) induce cytotoxicity by apoptosis but not necrosis, (iii) inhibit cell proliferation, (iv) activate poly adenosine diphosphate ribosyl transferase (poly ADPRT), and (v) have a much-reduced effect on microregional tumor blood perfusion. It was concluded that the mechanism of action of N-substituted analogs is shifted from primary effects on tumor vascularization as is seen with the non-N-substituted analogs to one where radiosensitization can be explained by selective induction of apoptosis via radiolysis and accumulation of DNA damage. This knowledge may be useful in the design of drugs possessing multiple mechanisms of radiosensitizing action.