Nicotinamide supplementation induces detrimental metabolic and epigenetic changes in developing rats. Br J Nutr. 2013;110:2156-2164. [PMID: 23768418 DOI: 10.1017/s0007114513001815]

Exploring nicotinamide adenine dinucleotide precursors across biosynthesis pathways: Unraveling their role in the ovary

Natural Nicotinamide Adenine Dinucleotide (NAD+) precursors have attracted much attention due to their positive effects in promoting ovarian health. However, their target tissue, synthesis efficiency, advantages, and disadvantages are still unclear. This review summarizes the distribution of NAD+ at the tissue, cellular and subcellular levels, discusses its biosynthetic pathways and the latest findings in ovary, include: (1) NAD+ plays distinct roles both intracellularly and extracellularly, adapting its distribution in response to requirements. (2) Different precursors differs in target tissues, synthetic efficiency, biological utilization, and adverse effects. Importantly: tryptophan is primarily utilized in the liver and kidneys, posing metabolic risks in excess; nicotinamide (NAM) is indispensable for maintaining NAD+ levels; nicotinic acid (NA) constructs a crucial bridge between intestinal microbiota and the host with diverse functions; nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) increase NAD+ systemically and can be influenced by delivery route, tissue specificity, and transport efficiency. (3) The biosynthetic pathways of NAD+ are intricately intertwined. They provide multiple sources and techniques for NAD+ synthesis, thereby reducing the dependence on a single molecule to maintain cellular NAD+ levels. However, an excess of a specific precursor potentially influencing other pathways. In addition, Protein expression analysis suggest that ovarian tissues may preferentially utilize NAM and NMN. These findings summarize the specific roles and potential of NAD+ precursors in enhancing ovarian health. Future research should delve into the molecular mechanisms and intervention strategies of different precursors, aiming to achieve personalized prevention or treatment of ovarian diseases, and reveal their clinical application value.

Effect of Nicotinamide Mononucleotide Concentration in Human Milk on Neurodevelopmental Outcome: The Tohoku Medical Megabank Project Birth and Three-Generation Cohort Study

(1) Background: Breast milk is the only source of nutrition for breastfed infants, but few studies have examined the relationship between breast milk micronutrients and infant neurodevelopmental outcome in exclusively breastfed infants. The aim of this study was to characterize the association between nicotinamide adenine dinucleotide (NAD)-related compounds in the breast milk of Japanese subjects and infant neurodevelopmental outcome. (2) Methods: A total of 150 mother-child pairs were randomly selected from the three-generation cohort of the Tohoku Medical Megabank in Japan. Infants were exclusively breastfed for up to 6 months. Breast milk was collected at 1 month postpartum, and the quantity of NAD-related substances in the breast milk was quantified. The mothers also completed developmental questionnaires at 6, 12, and 24 months. The relationship between the concentration of NAD-related substances in breast milk and developmental indicators was evaluated via ordinal logistic regression analysis. (3) Results: Nicotinamide mononucleotide (NMN) was quantified as the major NAD precursor in breast milk. The median amount of NMN in the breast milk was 9.2 μM. The NMN concentration in breast milk was the only NAD-related substance in breast milk that showed a significant positive correlation with neurodevelopmental outcome in infants at 24 months. (4) Conclusions: The results suggest that NMN in human milk may be an important nutrient for early childhood development.

The effects of NAD+ precursor (nicotinic acid and nicotinamide) supplementation on weight loss and related hormones: a systematic review and meta-regression analysis of randomized controlled trials

Background

Despite the fact that obesity and overweight are serious major health problems worldwide, fighting against them is also considered a challenging issue. Several interventional studies have evaluated the potential weight-reduction effect of nicotinamide adenine dinucleotide (NAD+) precursor. In order to obtain a better viewpoint from them, this study aimed to comprehensively investigate the effects of NAD+ precursor supplementation on weight loss, adiponectin, and leptin.

Methods

Scopus, PubMed/Medline, Web of Science, Cochrane, and Embase databases were searched using standard keywords to identify all controlled trials investigating the weight loss and related hormones effects of NAD+ precursor. Pooled weighted mean difference and 95% confidence intervals were achieved by random-effects model analysis for the best estimation of outcomes.

Results

Twenty two treatment arms with 5,144 participants' were included in this systematic review and meta-regression analysis. The pooled findings showed that NAD+ precursor supplementation has an effect on lowering BMI (weighted mean difference (WMD): -0.19 kg/m2, 95% confidence interval (CI): -0.29 to -0.09, p < 0.001) and increasing adiponectin (WMD: 1.59 μg/mL, 95% CI: 0.49 to 2.68, p = 0.004) in humans compared with control groups. However, no significant effect was observed on body weight and leptin. There was a significant relationship between doses of intervention with changes in BMI. In addition, subgroup analysis showed that BMI reduction was greater when receiving nicotinic acid (NA) supplementation than nicotinamide (NE) supplementation.

Conclusion

NAD+ precursor had significant effects on weight management with the reduction of BMI and increasing adiponectin.

Defining NAD(P)(H) Catabolism

Dietary vitamin B3 components, such as nicotinamide and nicotinic acid, are precursors to the ubiquitous redox cofactor nicotinamide adenine dinucleotide (NAD⁺). NAD⁺ levels are thought to decline with age and disease. While the drivers of this decline remain under intense investigation, strategies have emerged seeking to functionally maintain NAD⁺ levels through supplementation with NAD⁺ biosynthetic intermediates. These include marketed products, such as nicotinamide riboside (NR) and its phosphorylated form (NMN). More recent developments have shown that NRH (the reduced form of NR) and its phosphorylated form NMNH also increases NAD⁺ levels upon administration, although they initially generate NADH (the reduced form of NAD⁺). Other means to increase the combined levels of NAD⁺ and NADH, NAD(H), include the inhibition of NAD⁺-consuming enzymes or activation of biosynthetic pathways. Multiple studies have shown that supplementation with an NAD(H) precursor changes the profile of NAD(H) catabolism. Yet, the pharmacological significance of NAD(H) catabolites is rarely considered although the distribution and abundance of these catabolites differ depending on the NAD(H) precursor used, the species in which the study is conducted, and the tissues used for the quantification. Significantly, some of these metabolites have emerged as biomarkers in physiological disorders and might not be innocuous. Herein, we review the known and emerging catabolites of the NAD(H) metabolome and highlight their biochemical and physiological function as well as key chemical and biochemical reactions leading to their formation. Furthermore, we emphasize the need for analytical methods that inform on the full NAD(H) metabolome since the relative abundance of NAD(H) catabolites informs how NAD(H) precursors are used, recycled, and eliminated.

Effects of dietary niacinamide and CP concentrations on the nitrogen excretion, growth performance, and meat quality of pigs

Reducing the dietary CP concentration in the formulation of low-protein diets without adverse effects on animal growth performance and meat quality remains challenging. In this study, we investigated the effects of nicotinamide (NAM) on the nitrogen excretion, growth performance, and meat quality of growing-finishing pigs fed low-protein diets. To measure the nitrogen balance, we conducted two trials: in nitrogen balance trial 1, four crossbred (Duroc × Landrace × Large White) barrows (40 ± 0.5 kg BW) were used in a 4 × 4 Latin square design with four diets and periods. The diets consisted of a basal diet + 30 mg/kg NAM (a control dose), basal diet + 90 mg/kg NAM, basal diet + 210 mg/kg NAM, and basal diet + 360 mg/kg NAM. In nitrogen balance trial 2, another four barrows (40 ± 0.5 kg BW) were used in a 4 × 4 Latin square design. The diets consisted of a basal diet + including 30 mg/kg NAM (control), basal diet + 360 mg/kg NAM, low-protein diet + 30 mg/kg NAM, and low-protein diet + 360 mg/kg NAM. To measure growth performance, two trials were conducted. In growth performance trial 1, 40 barrows (37.0 ± 1.0 kg) were randomly allocated to one of four dietary treatments (n = 10 per group), whereas in growth performance trial 2, 300 barrows (41.4 ± 2.0 kg) were randomly allocated to one of four dietary treatments, with each dietary treatment conducted in five repetitions with 15 pigs each. The four diets in the two growth performance trials were similar to those in nitrogen balance trial 2. Supplementing the diet with 210 or 360 mg/kg NAM reduced urinary nitrogen excretion and total nitrogen excretion and increased nitrogen retention comparted with the control diet (P < 0.05). Compared with the control diet, the low-protein diet with 360 mg/kg NAM reduced faecal, urinary, and total nitrogen excretion (P < 0.05) without affecting nitrogen retention and average daily gain (P > 0.05). Pigs fed the low-protein diet with 360 mg/kg NAM showed a decreased intramuscular fat content in the longissimus thoracis muscle when compared with pigs fed the control diet (P > 0.05). Our results suggest NAM as a suitable dietary additive to reduce dietary CP concentration, maximise nitrogen retention and growth performance, and decrease fat deposition in pigs.

Nicotinamide riboside supplementation is not associated with altered methylation homeostasis in Parkinson's disease

Replenishing nicotinamide adenine dinucleotide (NAD) via supplementation of nicotinamide riboside (NR) has been shown to confer neuroprotective effects in models of aging and neurodegenerative diseases, including Parkinson's disease (PD). Although generally considered safe, concerns have been raised that NR supplementation could impact methylation dependent reactions, including DNA methylation, because of increased production and methylation dependent breakdown of nicotinamide (NAM). We investigated the effect of NR supplementation on DNA methylation in a double blinded, placebo-controlled trial of 29 human subjects with PD, in blood cells and muscle tissue. Our results show that NR had no impact on DNA methylation homeostasis, including individuals with common pathogenic mutations in the MTHFR gene known to affect one-carbon metabolism. Pathway and methylation variance analyses indicate that there might be minor regulatory responses to NR. We conclude that short-term therapy with high-dose NR for up to 30 days has no deleterious impact on methylation homeostasis.

Placental Mitochondrial Function and Dysfunction in Preeclampsia

The placenta is a vital organ of pregnancy, regulating adaptation to pregnancy, gestational parent/fetal exchange, and ultimately, fetal development and growth. Not surprisingly, in cases of placental dysfunction-where aspects of placental development or function become compromised-adverse pregnancy outcomes can result. One common placenta-mediated disorder of pregnancy is preeclampsia (PE), a hypertensive disorder of pregnancy with a highly heterogeneous clinical presentation. The wide array of clinical characteristics observed in pregnant individuals and neonates of a PE pregnancy are likely the result of distinct forms of placental pathology underlying the PE diagnosis, explaining why no one common intervention has proven effective in the prevention or treatment of PE. The historical paradigm of placental pathology in PE highlights an important role for utero-placental malperfusion, placental hypoxia and oxidative stress, and a critical role for placental mitochondrial dysfunction in the pathogenesis and progression of the disease. In the current review, the evidence of placental mitochondrial dysfunction in the context of PE will be summarized, highlighting how altered mitochondrial function may be a common feature across distinct PE subtypes. Further, advances in this field of study and therapeutic targeting of mitochondria as a promising intervention for PE will be discussed.

Potential Synergistic Supplementation of NAD+ Promoting Compounds as a Strategy for Increasing Healthspan

Disrupted biological function, manifesting through the hallmarks of aging, poses one of the largest threats to healthspan and risk of disease development, such as metabolic disorders, cardiovascular ailments, and neurodegeneration. In recent years, numerous geroprotectors, senolytics, and other nutraceuticals have emerged as potential disruptors of aging and may be viable interventions in the immediate state of human longevity science. In this review, we focus on the decrease in nicotinamide adenine dinucleotide (NAD+) with age and the supplementation of NAD+ precursors, such as nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), in combination with other geroprotective compounds, to restore NAD+ levels present in youth. Furthermore, these geroprotectors may enhance the efficacy of NMN supplementation while concurrently providing their own numerous health benefits. By analyzing the prevention of NAD+ degradation through the inhibition of CD38 or supporting protective downstream agents of SIRT1, we provide a potential framework of the CD38/NAD+/SIRT1 axis through which geroprotectors may enhance the efficacy of NAD+ precursor supplementation and reduce the risk of age-related diseases, thereby potentiating healthspan in humans.

COVID-19 Mimics Pulmonary Dysfunction in Muscular Dystrophy as a Post-Acute Syndrome in Patients

Although progressive wasting and weakness of respiratory muscles are the prominent hallmarks of Duchenne muscular dystrophy (DMD) and long-COVID (also referred as the post-acute sequelae of COVID-19 syndrome); however, the underlying mechanism(s) leading to respiratory failure in both conditions remain unclear. We put together the latest relevant literature to further understand the plausible mechanism(s) behind diaphragm malfunctioning in COVID-19 and DMD conditions. Previously, we have shown the role of matrix metalloproteinase-9 (MMP9) in skeletal muscle fibrosis via a substantial increase in the levels of tumor necrosis factor-α (TNF-α) employing a DMD mouse model that was crossed-bred with MMP9-knockout (MMP9-KO or MMP9^-/-) strain. Interestingly, recent observations from clinical studies show a robust increase in neopterin (NPT) levels during COVID-19 which is often observed in patients having DMD. What seems to be common in both (DMD and COVID-19) is the involvement of neopterin (NPT). We know that NPT is generated by activated white blood cells (WBCs) especially the M1 macrophages in response to inducible nitric oxide synthase (iNOS), tetrahydrobiopterin (BH4), and tetrahydrofolate (FH4) pathways, i.e., folate one-carbon metabolism (FOCM) in conjunction with epigenetics underpinning as an immune surveillance protection. Studies from our laboratory, and others researching DMD and the genetically engineered humanized (hACE2) mice that were administered with the spike protein (SP) of SARS-CoV-2 revealed an increase in the levels of NPT, TNF-α, HDAC, IL-1β, CD147, and MMP9 in the lung tissue of the animals that were subsequently accompanied by fibrosis of the diaphragm depicting a decreased oscillation phenotype. Therefore, it is of interest to understand how regulatory processes such as epigenetics involvement affect DNMT, HDAC, MTHFS, and iNOS that help generate NPT in the long-COVID patients.

Nicotinamide adenine dinucleotide and the sirtuins caution: Pro-cancer functions

This scoping review aims to perform a brief but comprehensive assessment of existing peer-reviewed literature and determine whether raising nicotinamide adenine dinucleotide can prevent or promote tumorigenesis. The examination of extensive peer-reviewed data regarding the synthesis of nicotinamide adenine dinucleotide has been performed with a focus on nuclear dynamics and the deoxyribose nucleic acid repair pathway. Various enzymatic protective functions have been identified from nicotinamide adenine dinucleotide levels, as well as the threat role that is also explored. Nicotinamide adenine dinucleotide precursors and sirtuin-activating compounds are becoming ubiquitous in the commercial market. Further research into whether elevating levels of nicotinamide adenine dinucleotide or overexpression of sirtuins can increase the potential for neoplasm or other age-related pathophysiology is warranted due to the high energy requirements of certain diseases such as cancer.

Fine-grained investigation of the relationship between human nutrition and global DNA methylation patterns

PURPOSE

Nutrition is an important, modifiable, environmental factor affecting human health by modulating epigenetic processes, including DNA methylation (5mC). Numerous studies investigated the association of nutrition with global and gene-specific DNA methylation and evidences on animal models highlighted a role in DNA hydroxymethylation (5hmC) regulation. However, a more comprehensive analysis of different layers of nutrition in association with global levels of 5mC and 5hmC is lacking. We investigated the association between global levels of 5mC and 5hmC and human nutrition, through the stratification and analysis of dietary patterns into different nutritional layers: adherence to Mediterranean diet (MD), main food groups, macronutrients and micronutrients intake.

METHODS

ELISA technique was used to measure global 5mC and 5hmC levels in 1080 subjects from the Moli-sani cohort. Food intake during the 12 months before enrolment was assessed using the semi-quantitative EPIC food frequency questionnaire. Complementary approaches involving both classical statistics and supervised machine learning analyses were used to investigate the associations between global 5mC and 5hmC levels and adherence to Mediterranean diet, main food groups, macronutrients and micronutrients intake.

RESULTS

We found that global DNA methylation, but not hydroxymethylation, was associated with daily intake of zinc and vitamin B3. Random Forests algorithms predicting 5mC and 5hmC through intakes of food groups, macronutrients and micronutrients revealed a significant contribution of zinc, while vitamin B3 was reported among the most influential features.

CONCLUSION

We found that nutrition may affect global DNA methylation, suggesting a contribution of micronutrients previously implicated as cofactors in methylation pathways.

The effects of vitamins and dietary pattern on epigenetic modification of non-communicable diseases

Background: Non-communicable diseases (NCDs) have received more attention because of high prevalence and mortality rate. Besides genetic and environmental factors, the epigenetic abnormality is also involved in the pathogenesis of NCDs. Methylation of DNA, chromatin remodeling, modification of histone, and long non-coding RNAs are the main components of epigenetic phenomena. Methodology: In this review paper, the mechanistic role of vitamins and dietary patterns on epigenetic modification was discussed. All papers indexed in scientific databases, including PubMed, Scopus, Embase, Google Scholar, and Elsevier were searched during 2000 - 2021 using, vitamins, diet, epigenetic repression, histones, methylation, acetylation, and NCDs as keywords. Results: The components of healthy dietary patterns like Mediterranean and dietary approaches to stop hypertension diets have a beneficial effect on epigenetic hemostasis. Both quality and quantity of dietary components influence epigenetic phenomena. A diet with calorie deficiency in protein content and methyl-donor agents in a long time, with a high level of fat, disrupts epigenetic hemostasis and finally, causes genome instability. Also, soluble and insoluble vitamins have an obvious role in epigenetic modifications. Most vitamins interact directly with methylation, acetylation, and phosphorylation pathways of histone and DNA. However, numerous indirect functions related to the cell cycle stability and genome integrity have been recognized. Conclusion: Considering the crucial role of a healthy diet in epigenetic homeostasis, adherence to a healthy dietary pattern containing enough levels of vitamin and avoiding the western diet seems to be necessary. Having a healthy diet and consuming the recommended dietary level of vitamins can also contribute to epigenetic stability.

Mechanistic Basis and Clinical Evidence for the Applications of Nicotinamide (Niacinamide) to Control Skin Aging and Pigmentation

Vitamin B3 (nicotinic acid, niacin) deficiency causes the systemic disease pellagra, which leads to dermatitis, diarrhea, dementia, and possibly death depending on its severity and duration. Vitamin B3 is used in the synthesis of the NAD+ family of coenzymes, contributing to cellular energy metabolism and defense systems. Although nicotinamide (niacinamide) is primarily used as a nutritional supplement for vitamin B3, its pharmaceutical and cosmeceutical uses have been extensively explored. In this review, we discuss the biological activities and cosmeceutical properties of nicotinamide in consideration of its metabolic pathways. Supplementation of nicotinamide restores cellular NAD+ pool and mitochondrial energetics, attenuates oxidative stress and inflammatory response, enhances extracellular matrix and skin barrier, and inhibits the pigmentation process in the skin. Topical treatment of nicotinamide, alone or in combination with other active ingredients, reduces the progression of skin aging and hyperpigmentation in clinical trials. Topically applied nicotinamide is well tolerated by the skin. Currently, there is no convincing evidence that nicotinamide has specific molecular targets for controlling skin aging and pigmentation. This substance is presumed to contribute to maintaining skin homeostasis by regulating the redox status of cells along with various metabolites produced from it. Thus, it is suggested that nicotinamide will be useful as a cosmeceutical ingredient to attenuate skin aging and hyperpigmentation, especially in the elderly or patients with reduced NAD+ pool in the skin due to internal or external stressors.

Nicotinamide mononucleotide (NMN) as an anti-aging health product – Promises and safety concerns

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Provides an overview of promises and safety concerns of NMN as an anti-aging product.

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Shows that NMN’s beneficial effects supported by in vivo studies.

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Reveals that there is a lack of NMN’s clinical safety and efficacy studies

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Suggests that proper clinical investigations are urgently needed on the effectiveness and safety of NMN supplementation.

Background

Aim of review

Key scientific concepts of review

Melatonin Alleviates the Toxicity of High Nicotinamide Concentrations in Oocytes: Potential Interaction with Nicotinamide Methylation Signaling

Despite the numerous studies on melatonin and nicotinamide (NAM, the active form of vitamin B3), the linkage between these two biomolecules in the context of signaling pathways regulating preimplantation embryo development has not yet been investigated. In this study, we used bovine oocyte model to elucidate the effect of melatonin on the developmental competence of oocytes under the stress of high NAM concentrations. Results showed that NAM (20 mM) administration during in vitro maturation (IVM) significantly reduced oocyte maturation and actin distribution, while induced reactive oxygen species (ROS) accumulation and mitochondrial dysfunction, the multiple deleterious effects that were alleviated by melatonin (10⁻⁷ M). The RT-qPCR and/or immunofluorescence showed upregulation of the apoptosis (Caspase-3, Caspase-9, and BAX), autophagy (Beclin-1, LC3A, LC3B, ATG7, LAMP1, and LAMP2), cell cycle (P21, P27, and P53), and DNA damage (COX2 and 8-OxoG) specific markers in oocytes matured under NAM treatment, compared to NAM-melatonin dual-treated and the untreated ones. In addition, the total cleavage and blastocyst development rate, as well as the total number of cells and the inner cell mass (ICM) per blastocyst, were reduced, while DNA fragmentation was induced, in the group of NAM sole treatment than NAM-melatonin cotreatment and control. Inspecting the underlying mechanisms behind NAM-associated toxicity revealed an increase in transcription pattern of NAM methylation (NNMT and AHCY) genes in NAM-treated oocytes while the opposite profile was observed upon melatonin supplementation. In conclusion, to our knowledge, this is the first study reporting that melatonin can protect oocytes and embryos from NAM-induced injury through its ROS-scavenging activity together with potential interaction with NAM methylation signaling.

Fluoride exposure altered metabolomic profile in rat serum

It is well known that serum is an ideal and potential choice to reflect the toxicity of fluoride. However, the effects of fluoride on serum metabolome have not been reported until now. In this study, the models of 3-week-old rats exposed fluoride by breast milk and 11-week-old rats exposed fluoride via breast milk and drinking water containing sodium fluoride (100 mg/L) were established. Using Ultra Performance Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (UPLC-MS/MS), as compared with control group, 28 negative (NEG) and 52 positive (POS) metabolites were significantly up-regulated, meanwhile 30 NEG and 21 POS significantly down-regulated metabolites were found in serum of 3-week-old rats exposed to fluoride. For 11-week-old fluorosis rats, there were 119 NEG and 65 POS metabolites significantly increased, and 7 NEG, 5 POS metabolites were obviously decreased. Importantly, nicotinamide, adenosine, 1-Oleoyl-sn-glycero-3-phosphocholine (OGPC), and 1-Stearoyl-sn-glycerol 3-phosphocholine (SGPC) were shared by two models. The metabolites of urea cycle, such as urea and N2-Acetyl-l-ornithine, betaine as a methyl donor, were regarded to reflect the fluorosis degree. These metabolites could be the potential markers of fluorosis, contributing to the prevention and treatment of fluorosis.

Possible Adverse Effects of High-Dose Nicotinamide: Mechanisms and Safety Assessment

Nicotinamide (NAM) at doses far above those recommended for vitamins is suggested to be effective against a wide spectrum of diseases and conditions, including neurological dysfunctions, depression and other psychological disorders, and inflammatory diseases. Recent increases in public awareness on possible pro-longevity effects of nicotinamide adenine dinucleotide (NAD+) precursors have caused further growth of NAM consumption not only for clinical treatments, but also as a dietary supplement, raising concerns on the safety of its long-term use. However, possible adverse effects and their mechanisms are poorly understood. High-level NAM administration can exert negative effects through multiple routes. For example, NAM by itself inhibits poly(ADP-ribose) polymerases (PARPs), which protect genome integrity. Elevation of the NAD+ pool alters cellular energy metabolism. Meanwhile, high-level NAM alters cellular methyl metabolism and affects methylation of DNA and proteins, leading to changes in cellular transcriptome and proteome. Also, methyl metabolites of NAM, namely methylnicotinamide, are predicted to play roles in certain diseases and conditions. In this review, a collective literature search was performed to provide a comprehensive list of possible adverse effects of NAM and to provide understanding of their underlying mechanisms and assessment of the raised safety concerns. Our review assures safety in current usage level of NAM, but also finds potential risks for epigenetic alterations associated with chronic use of NAM at high doses. It also suggests directions of the future studies to ensure safer application of NAM.

Diverse therapeutic efficacies and more diverse mechanisms of nicotinamide

BACKGROUND

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD⁺) may be a major factor in its efficacy. The augmentation of cellular NAD⁺ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD⁺-dependent deacetylases, play important roles in many of NAM's effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM's effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases.

AIM OF REVIEW

This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM.

KEY SCIENTIFIC CONCEPTS OF REVIEW

NAM, by itself or through altering metabolic balance of NAD⁺ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM's metabolites.

Safety of nicotinamide riboside chloride as a novel food pursuant to Regulation (EU) 2015/2283 and bioavailability of nicotinamide from this source, in the context of Directive 2002/46/EC

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Allergens (NDA) was asked to deliver an opinion on nicotinamide riboside chloride as a novel food (NF) pursuant to Regulation (EU) 2015/2283, including an evaluation of the safety of its use in food supplements as a source of niacin, and the bioavailability of nicotinamide from this source, in the context of Directive 2002/46/EC. The NF, a synthetic form of nicotinamide riboside, is proposed to be used in food supplements for the healthy adult population at levels up to 300 mg/day. The production process, composition, specifications, batch-to-batch variability and stability of the NF do not raise safety concerns. Animal and human data indicate that the NF contributes to the nicotinamide body pool. There are no concerns regarding genotoxicity. Human studies do not raise safety concerns. The proposed maximum use level corresponds to an amount of nicotinamide, which is sixfold lower than the tolerable upper intake level (UL) set for adults, excluding pregnant and lactating women. The margin of exposure (MoE) of 70 derived from repeated dose toxicity studies with rats and dogs is considered sufficient for the adult population, excluding pregnant and lactating women. Regarding these two population groups, the MoE of 76 derived from a developmental toxicity study in rats is considered insufficient in the absence of data which could justify accepting a MoE lower than 100. The Panel concludes that the NF is safe under the proposed conditions of use for the healthy adult population, excluding pregnant and lactating women, and that an intake of the NF up to 230 mg/day is safe for pregnant and lactating women. The Panel also concludes that the NF is a source from which nicotinamide, a form of niacin, is bioavailable.

Role of Nicotinamide Adenine Dinucleotide and Related Precursors as Therapeutic Targets for Age-Related Degenerative Diseases: Rationale, Biochemistry, Pharmacokinetics, and Outcomes

Significance: Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that serves as an essential cofactor and substrate for a number of critical cellular processes involved in oxidative phosphorylation and ATP production, DNA repair, epigenetically modulated gene expression, intracellular calcium signaling, and immunological functions. NAD+ depletion may occur in response to either excessive DNA damage due to free radical or ultraviolet attack, resulting in significant poly(ADP-ribose) polymerase (PARP) activation and a high turnover and subsequent depletion of NAD+, and/or chronic immune activation and inflammatory cytokine production resulting in accelerated CD38 activity and decline in NAD+ levels. Recent studies have shown that enhancing NAD+ levels can profoundly reduce oxidative cell damage in catabolic tissue, including the brain. Therefore, promotion of intracellular NAD+ anabolism represents a promising therapeutic strategy for age-associated degenerative diseases in general, and is essential to the effective realization of multiple benefits of healthy sirtuin activity. The kynurenine pathway represents the de novo NAD+ synthesis pathway in mammalian cells. NAD+ can also be produced by the NAD+ salvage pathway. Recent Advances: In this review, we describe and discuss recent insights regarding the efficacy and benefits of the NAD+ precursors, nicotinamide (NAM), nicotinic acid (NA), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN), in attenuating NAD+ decline in degenerative disease states and physiological aging. Critical Issues: Results obtained in recent years have shown that NAD+ precursors can play important protective roles in several diseases. However, in some cases, these precursors may vary in their ability to enhance NAD+ synthesis via their location in the NAD+ anabolic pathway. Increased synthesis of NAD+ promotes protective cell responses, further demonstrating that NAD+ is a regulatory molecule associated with several biochemical pathways. Future Directions: In the next few years, the refinement of personalized therapy for the use of NAD+ precursors and improved detection methodologies allowing the administration of specific NAD+ precursors in the context of patients' NAD+ levels will lead to a better understanding of the therapeutic role of NAD+ precursors in human diseases.

Hepatic transcript profiling in early-lactation dairy cows fed rumen-protected niacin during the transition from late pregnancy to lactation

In dairy cows, administration of high dosages of niacin (nicotinic acid, NA) was found to cause antilipolytic effects, which are mediated by the NA receptor hydroxyl-carboxylic acid receptor 2 (HCAR2) in white adipose tissue (WAT), and thereby an altered hepatic lipid metabolism. However, almost no attention has been paid to possible direct effects of NA in cattle liver, despite evidence that HCAR2 is also expressed in the liver and is even more abundant than in WAT. Because of this, we hypothesized that feeding a high dosage of rumen-protected NA to dairy cows influences critical metabolic or signaling pathways in the liver by inducing changes in the hepatic transcriptome. To identify these pathways, we applied genome-wide transcript profiling in liver biopsies obtained at d 7 postpartum (p.p.) from dairy cows used in our recent study; cows received either no NA (control group, n = 9) or 79 mg of rumen-protected NA/kg of body weight daily (NA group, n = 9) from 21 d before calving until 3 wk p.p. Hepatic transcript profiling revealed that 487 transcripts were differentially expressed (filter criteria: fold change >1.2 or <-1.2 and P < 0.05) in the liver at d 7 p.p. between cows fed NA and control cows. Substantially more transcripts were downregulated (n = 338), whereas only 149 transcripts were upregulated by NA in the liver of cows. Gene set enrichment analysis for the upregulated transcripts revealed that the most-enriched gene ontology biological process terms were exclusively related to immune processes, such as leukocyte differentiation, immune system process, activation of immune response, and acute inflammatory response. Gene set enrichment analysis of the downregulated transcripts showed that the most-enriched biological process terms were related to metabolic processes, such as cellular metabolic process, small molecule metabolic process, lipid catabolic process, organic cyclic compound metabolic process, small molecule biosynthetic process, and cellular lipid catabolic process. In conclusion, hepatic transcriptome analysis showed that rumen-protected NA induces genes that are involved mainly in immune processes, including acute phase response and stress response, in dairy cows at d 7 p.p. Thus, supplementation of a high dosage of rumen-protected NA to dairy cows in the periparturient period may induce or amplify the systemic inflammation-like condition that is typically observed in the liver of high-yielding dairy cows in the p.p. period.

Mammalian Sulfur Amino Acid Metabolism: A Nexus Between Redox Regulation, Nutrition, Epigenetics, and Detoxification

SIGNIFICANCE

Transsulfuration allows conversion of methionine into cysteine using homocysteine (Hcy) as an intermediate. This pathway produces S-adenosylmethionine (AdoMet), a key metabolite for cell function, and provides 50% of the cysteine needed for hepatic glutathione synthesis. The route requires the intake of essential nutrients (e.g., methionine and vitamins) and is regulated by their availability. Transsulfuration presents multiple interconnections with epigenetics, adenosine triphosphate (ATP), and glutathione synthesis, polyol and pentose phosphate pathways, and detoxification that rely mostly in the exchange of substrates or products. Major hepatic diseases, rare diseases, and sensorineural disorders, among others that concur with oxidative stress, present impaired transsulfuration. Recent Advances: In contrast to the classical view, a nuclear branch of the pathway, potentiated under oxidative stress, is emerging. Several transsulfuration proteins regulate gene expression, suggesting moonlighting activities. In addition, abnormalities in Hcy metabolism link nutrition and hearing loss.

CRITICAL ISSUES

Knowledge about the crossregulation between pathways is mostly limited to the hepatic availability/removal of substrates and inhibitors. However, advances regarding protein-protein interactions involving oncogenes, identification of several post-translational modifications (PTMs), and putative moonlighting activities expand the potential impact of transsulfuration beyond methylations and Hcy.

FUTURE DIRECTIONS

Increasing the knowledge on transsulfuration outside the liver, understanding the protein-protein interaction networks involving these enzymes, the functional role of their PTMs, or the mechanisms controlling their nucleocytoplasmic shuttling may provide further insights into the pathophysiological implications of this pathway, allowing design of new therapeutic interventions. Antioxid. Redox Signal. 29, 408-452.

Hyperhomocysteinemia in polycystic ovary syndrome: decreased betaine-homocysteine methyltransferase and cystathionine β-synthase-mediated homocysteine metabolism

RESEARCH QUESTION

What are the metabolic characteristics of homocysteine in polycystic ovary syndrome (PCOS)?

DESIGN

Homocysteine concentrations were determined in serum samples from non-obese and obese control subjects and PCOS patients. Homocysteine metabolism was studied in a rat model of PCOS established using dehydroepiandrosterone (DHEA) or DHEA in combination with a high-fat diet (HFD).

RESULTS

It was shown that (i) serum homocysteine concentrations were greater in PCOS patients than in control subjects in the obese group (P < 0.05) and serum homocysteine concentrations were significantly higher in the obese group than in the non-obese group, regardless of PCOS status (both P < 0.05); (ii) serum homocysteine concentrations were significantly increased in DHEA + HFD-induced rats compared with controls (P < 0.05); (iii) when compared with the control group, mRNA concentrations of homocysteine metabolic enzymes Bhmt and Cbs were significantly reduced in the liver tissues of DHEA + HFD-induced rats (both P < 0.0001); (iv) when compared with the control group, there was a significant decrease in the methylation concentrations of the Cbs (P < 0.05) and Bhmt (P < 0.05 and P < 0.0001) promoter in the DHEA + HFD group. The methylation patterns, together with previous data, indicate that hypomethylated promoter-mediated transcriptional activation of Bhmt and Cbs might be a defence mechanism against PCOS-related hyperhomocysteinemia.

CONCLUSIONS

These findings indicate that decreased liver Bhmt and Cbs-mediated homocysteine metabolism might have a role in hyperhomocysteinemia in PCOS and provides further evidence for a potential role of decreased liver function in PCOS.

Nicotinamide prevents sweet beverage-induced hepatic steatosis in rats by regulating the G6PD, NADPH/NADP+ and GSH/GSSG ratios and reducing oxidative and inflammatory stress

The disruption of redox state homeostasis, the overexpression of lipogenic transcription factors and enzymes, and the increase in lipogenic precursors induced by sweetened beverages are determinants of the development of nonalcoholic fatty liver disease. This study evaluated the action of nicotinamide (NAM) on the expression of glucose-6-phosphate dehydrogenase (G6PD) and redox, oxidative, and inflammatory states in a model of nonalcoholic hepatic steatosis induced by high and chronic consumption of carbohydrates. Male rats were provided drinking water with 30% glucose or fructose ad libitum for 12 weeks. Additionally, 30 days after the beginning of carbohydrate administration, some rats were simultaneously provided water with 0.06% or 0.12% NAM for 5h daily over the next 8 weeks. Biochemical profiles and expression levels of G6PD, tumor necrosis factor α (TNFα), and NADPH oxidase 4 (NOX4) were evaluated together with glutathione/glutathione disulfide (GSH/GSSG) and reduced nicotinamide adenine dinucleotide (phosphate)/nicotinamide adenine dinucleotide (phosphate) [NAD(P)H/NAD(P)] ratios and thiobarbituric acid reactive substances (TBARS). The results showed that hepatic steatosis induced by the chronic consumption of glucose or fructose was associated with body weight gain and increased levels of serum glucose, insulin, triacylglycerols, free fatty acids, transaminases, and TBARS. In the liver, the expression and activity of G6PD increased along with the GSSG, TBARS, and TG concentrations. These alterations were reduced by NAM treatment through the attenuation of increases in G6PD expression and activity and in the NADPH/NADP⁺ ratio, thereby slowing liver steatosis. NAM prevents redox, oxidative, and inflammatory alterations induced by high carbohydrate consumption.

Effects of nutrient and bioactive food components on Alzheimer's disease and epigenetic

Alzheimer's disease (AD) is the most common form of dementia in the elderly and is a chronic neurodegenerative disease that is becoming widespread. For this reason, in recent years factors affecting the development, progression and cognitive function of the AD have been emphasized. Nutrients and other bioactive nutrients are among the factors that are effective in AD. In particular, vitamins A, C and E, vitamins B₁, B₆ and B₁₂, folate, magnesium, choline, inositol, anthocyanins, isoflavones etc. nutrients and bioactive nutrients are known to be effective in the development of AD. Nutrients and nutrient components may also have an epigenetic effect on AD. At the same time, nutrients and bioactive food components slow down the progression of the disease. For this reason, the effect of nutrients and food components on AD was examined in this review.

NRK1 controls nicotinamide mononucleotide and nicotinamide riboside metabolism in mammalian cells

NAD⁺ is a vital redox cofactor and a substrate required for activity of various enzyme families, including sirtuins and poly(ADP-ribose) polymerases. Supplementation with NAD⁺ precursors, such as nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), protects against metabolic disease, neurodegenerative disorders and age-related physiological decline in mammals. Here we show that nicotinamide riboside kinase 1 (NRK1) is necessary and rate-limiting for the use of exogenous NR and NMN for NAD⁺ synthesis. Using genetic gain- and loss-of-function models, we further demonstrate that the role of NRK1 in driving NAD⁺ synthesis from other NAD⁺ precursors, such as nicotinamide or nicotinic acid, is dispensable. Using stable isotope-labelled compounds, we confirm NMN is metabolized extracellularly to NR that is then taken up by the cell and converted into NAD⁺. Our results indicate that mammalian cells require conversion of extracellular NMN to NR for cellular uptake and NAD⁺ synthesis, explaining the overlapping metabolic effects observed with the two compounds.

Raising cellular levels of the metabolic cofactor NAD⁺ reverses key indicators of aging. Here, Ratajczak et al. show that cellular levels of NAD⁺ depend on the extracellular catalytic activity of NRK1, which processes two NAD⁺ precursors, nicotinamide mononucleotide and nicotinamide riboside, in mice.

Higher maternal serum concentrations of nicotinamide and related metabolites in late pregnancy are associated with a lower risk of offspring atopic eczema at age 12 months

BACKGROUND

Evidence that atopic eczema partly originates in utero is increasing, with some studies linking the risk of developing the condition with aspects of maternal diet during pregnancy. Nicotinamide, a naturally occurring nutrient that is maintained through the dietary intakes of vitamin B3 and tryptophan, has been used in the treatment of some skin conditions including atopic eczema.

OBJECTIVE

To examine the relation of maternal serum concentrations of nicotinamide and related tryptophan metabolites to the risk of atopic eczema in the offspring.

METHODS

Within the UK Southampton Women Survey, infantile atopic eczema at ages 6 and 12 months was ascertained (modified UK Working Party Criteria for the Definition of Atopic Dermatitis). Maternal serum levels of kynurenine, kynurenic acid, anthranilic acid, tryptophan, nicotinamide and N1-methylnicotinamide were measured in late pregnancy by mass spectrometry (n = 497) and related to the odds ratio of infantile atopic eczema.

RESULTS

Maternal nicotinamide and related metabolite concentrations were not associated with offspring atopic eczema at age 6 months. Higher concentrations of nicotinamide and anthranilic acid were, however, associated with a lower risk of eczema at age 12 months (odds ratios 0.69, 95% CI 0.53-0.91/SD change, P = 0.007 and 0.63, 0.48-0.83, P = 0.001, respectively). The associations were robust to adjustment for potentially confounding variables.

CONCLUSION AND CLINICAL RELEVANCE

This is the first study linking maternal serum concentrations of nicotinamide and related metabolites to the risk of atopic eczema in the offspring. The findings point to potentially modifiable maternal influences on this complex and highly prevalent condition.

Comparison of the effects of nicotinic acid and nicotinamide degradation on plasma betaine and choline levels

AIM

The present study was to compare the effects of nicotinic acid and nicotinamide on the plasma methyl donors, choline and betaine.

METHODS

Thirty adult subjects were randomly divided into three groups of equal size, and orally received purified water (C group), nicotinic acid (300 mg, NA group) or nicotinamide (300 mg, NM group). Plasma nicotinamide, N¹-methylnicotinamide, homocysteine, betaine and choline levels before and 1.5-h and 3-h post-dosing, plasma normetanephrine and metanephrine concentrations at 3-h post-dosing, and the urinary excretion of N¹-methyl-2-pyridone-5-carboxamide during the test period were examined.

RESULTS

The level of 3-h plasma nicotinamide, N¹-methylnicotinamide, homocysteine, the urinary excretion of N¹-methyl-2-pyridone-5-carboxamide and pulse pressure (PP) in the NM group was 221%, 3972%, 61%, 1728% and 21.2% higher than that of the control group (P < 0.01, except homocysteine and PP P < 0.05), while the 3-h plasma betaine, normetanephrine and metanephrine level in the NM group was 24.4%, 9.4% and 11.7% lower (P < 0.05, except betaine P < 0.01), without significant difference in choline levels. Similar but less pronounced changes were observed in the NA group, with a lower level of 3-h plasma N¹-methylnicotinamide (1.90 ± 0.20 μmol/l vs. 3.62 ± 0.27 μmol/l, P < 0.01) and homocysteine (12.85 ± 1.39 μmol/l vs. 18.08 ± 1.02 μmol/l, P < 0.05) but a higher level of betaine (27.44 ± 0.71 μmol/l vs. 23.52 ± 0.61 μmol/l, P < 0.05) than that of the NM group.

CONCLUSION

The degradation of nicotinamide consumes more betaine than that of nicotinic acid at identical doses. This difference should be taken into consideration in niacin fortification.

Long-term treatment with nicotinamide induces glucose intolerance and skeletal muscle lipotoxicity in normal chow-fed mice: compared to diet-induced obesity

Nicotinamide (NAM), or vitamin B3, is an essential coenzyme for ATP synthesis and an inhibitor of sirtuin 1. Recently, conflicting results were reported regarding the treatment of NAM in type 2 diabetes and obesity. The aim of this study was to determine whether and how long-term treatment with NAM at lower dose would affect insulin sensitivity in mice fed chow diet. We treated mice with NAM (100 mg/kg/day) and normal chow for 8 weeks. Strikingly, NAM induced glucose intolerance and skeletal muscle lipid accumulation in nonobese mice. NAM impaired mitochondrial respiration capacity and energy production in skeletal muscle, in combination with increased expression of the mediators for mitophagy (p62, PINK1, PARK2 and NIX) and autophagy (FOXO3, Bnip3, CTSL, Beclin1 and LC-3b). Next, we treated mice with high-fat diet (HFD) and resveratrol (RSV; 100 mg/kg/day) for 8 weeks. RSV protected against HFD-induced insulin resistance and obesity. HFD increased skeletal muscle lipid content as well as NAM, but this increase was attenuated by RSV. In contrast to NAM, HFD enhanced fatty acid oxidative capacity. Muscle transcript levels of genes for mitophagy and autophagy were largely suppressed by HFD, whereas RSV did not rescue these effects. These differences suggest that skeletal muscle autophagy may represent adaptive response to NAM-induced lipotoxicity, whereas reduced autophagy in skeletal muscle may promote HFD-induced lipotoxicity. Our results demonstrate that chronic NAM supplementation in healthy individuals, although at lower dose than previously reported, is still detrimental to glucose homeostasis and skeletal muscle lipid metabolism.

Antiatherosclerotic Effects of 1-Methylnicotinamide in Apolipoprotein E/Low-Density Lipoprotein Receptor-Deficient Mice: A Comparison with Nicotinic Acid

1-Methylnicotinamide (MNA), the major endogenous metabolite of nicotinic acid (NicA), may partially contribute to the vasoprotective properties of NicA. Here we compared the antiatherosclerotic effects of MNA and NicA in apolipoprotein E (ApoE)/low-density lipoprotein receptor (LDLR)-deficient mice. ApoE/LDLR(-/-) mice were treated with MNA or NicA (100 mg/kg). Plaque size, macrophages, and cholesterol content in the brachiocephalic artery, endothelial function in the aorta, systemic inflammation, platelet activation, as well as the concentration of MNA and its metabolites in plasma and urine were measured. MNA and NicA reduced atherosclerotic plaque area, plaque inflammation, and cholesterol content in the brachiocephalic artery. The antiatherosclerotic actions of MNA and NicA were associated with improved endothelial function, as evidenced by a higher concentration of 6-keto-prostaglandin F1 α and nitrite/nitrate in the aortic ring effluent, inhibition of platelets (blunted thromboxane B2 generation), and inhibition of systemic inflammation (lower plasma concentration of serum amyloid P, haptoglobin). NicA treatment resulted in an approximately 2-fold higher concentration of MNA and its metabolites in urine and a 4-fold higher nicotinamide/MNA ratio in plasma, compared with MNA treatment. In summary; MNA displays pronounced antiatherosclerotic action in ApoE/LDLR(-/-) mice, an effect associated with an improvement in prostacyclin- and nitric oxide-dependent endothelial function, inhibition of platelet activation, inhibition of inflammatory burden in plaques, and diminished systemic inflammation. Despite substantially higher MNA availability after NicA treatment, compared with an equivalent dose of MNA, the antiatherosclerotic effect of NicA was not stronger. We suggest that detrimental effects of NicA or its metabolites other than MNA may limit beneficial effects of NicA-derived MNA.

Vitamin paradox in obesity: Deficiency or excess?

Since synthetic vitamins were used to fortify food and as supplements in the late 1930s, vitamin intake has significantly increased. This has been accompanied by an increased prevalence of obesity, a condition associated with diabetes, hypertension, cardiovascular disease, asthma and cancer. Paradoxically, obesity is often associated with low levels of fasting serum vitamins, such as folate and vitamin D. Recent studies on folic acid fortification have revealed another paradoxical phenomenon: obesity exhibits low fasting serum but high erythrocyte folate concentrations, with high levels of serum folate oxidation products. High erythrocyte folate status is known to reflect long-term excess folic acid intake, while increased folate oxidation products suggest an increased folate degradation because obesity shows an increased activity of cytochrome P450 2E1, a monooxygenase enzyme that can use folic acid as a substrate. There is also evidence that obesity increases niacin degradation, manifested by increased activity/expression of niacin-degrading enzymes and high levels of niacin metabolites. Moreover, obesity most commonly occurs in those with a low excretory reserve capacity (e.g., due to low birth weight/preterm birth) and/or a low sweat gland activity (black race and physical inactivity). These lines of evidence raise the possibility that low fasting serum vitamin status in obesity may be a compensatory response to chronic excess vitamin intake, rather than vitamin deficiency, and that obesity could be one of the manifestations of chronic vitamin poisoning. In this article, we discuss vitamin paradox in obesity from the perspective of vitamin homeostasis.

Nicotinic acid supplementation in the context of alcoholic liver injury: friend or foe?

Li and colleagues (2014) in this issue report that dietary nicotinic acid (NA) supplementation ameliorates ethanol-induced hepatic steatosis, but a deficiency does not worsen injury induced by alcohol alone. The authors further present some mechanistic insights into the protective role of NA supplementation. Results of this and other previous studies in the context of alcoholic liver injury raise one important question as to what should be an adequate dose of NA that will provide the maximum benefit to hepatic and extrahepatic tissues and with minimum adverse effects.

Association of nicotinamide-N-methyltransferase mRNA expression in human adipose tissue and the plasma concentration of its product, 1-methylnicotinamide, with insulin resistance

AIMS/HYPOTHESIS

Nicotinamide-N-methyltransferase (NNMT) was recently shown to be upregulated in mouse models of insulin resistance and obesity. So far, it is unknown whether NNMT is regulated in human disease. We have explored the hypothesis that white adipose tissue (WAT) NNMT expression and plasma 1-methylnicotinamide (MNA) concentration are increased in human insulin resistance and type 2 diabetes.

METHODS

NNMT expression and plasma MNA were analysed in three groups of individuals: (1) 199 patients undergoing abdominal surgery; (2) 60 individuals on a 12-week exercise programme and (3) 55 patients on a two-step bariatric surgery programme.

RESULTS

Patients with manifest type 2 diabetes have a significantly (approximately twofold) higher NNMT expression both in omental and subcutaneous WAT compared with controls. Notably, plasma MNA correlated significantly with WAT NNMT expression in patients with type 2 diabetes (women, r = 0.59, p < 0.001; men, r = 0.61, p < 0.001) but not in healthy control individuals. In insulin-resistant individuals, there was an inverse correlation between insulin sensitivity and plasma MNA (r = 0.44, p = 0.01) or adipose tissue NNMT mRNA (r = 0.64, p < 0.001). The latter association was confirmed in a second cohort (n = 60, r = 0.78, p < 0.001). Interventions improving insulin sensitivity--exercise and bariatric surgery--were associated with a significant (p < 0.001) reduction in WAT NNMT expression. Bariatric surgery was also associated with a significant decrease in plasma MNA.

CONCLUSIONS/INTERPRETATION

We demonstrate that WAT NNMT expression is regulated in human insulin resistance and type 2 diabetes and that plasma MNA correlates with increased tissue NNMT expression and the degree of insulin resistance, making it a potential biomarker for loss of insulin sensitivity.

Pharmacological doses of niacin stimulate the expression of genes involved in carnitine uptake and biosynthesis and improve the carnitine status of obese Zucker rats

Background

Activation of peroxisome proliferator-activated receptor (PPAR)α and PPARδ causes an elevation of tissue carnitine concentrations through induction of genes involved in carnitine uptake [novel organic cation transporter 2, (OCTN2)], and carnitine biosynthesis [γ-butyrobetaine dioxygenase (BBD), 4-N-trimethyl-aminobutyraldehyde dehydrogenase (TMABA-DH)]. Recent studies showed that administration of the plasma lipid-lowering drug niacin causes activation of PPARα and/or PPARδ in tissues of obese Zucker rats, which have a compromised carnitine status and an impaired fatty acid oxidation capacity. Thus, we hypothesized that niacin administration to obese Zucker rats is also able to improve the diminished carnitine status of obese Zucker rats through PPAR-mediated stimulation of genes involved in carnitine uptake and biosynthesis.

Methods

To test this hypothesis, we used plasma, muscle and liver samples from a recent experiment with obese Zucker rats, which were fed either a niacin-adequate diet (30 mg niacin/kg diet) or a diet with a pharmacological niacin dose (780 mg niacin/kg diet), and determined concentrations of carnitine in tissues and mRNA and protein levels of genes critical for carnitine homeostasis (OCTN2, BBD, TMABA-DH). Statistical data analysis of all data was done by one-way ANOVA, and Fisher’s multiple range test.

Results

Rats of the obese niacin group had higher concentrations of total carnitine in plasma, skeletal muscle and liver, higher mRNA and protein levels of OCTN2, BBD, and TMABA-DH in the liver and higher mRNA and protein levels of OCTN2 in skeletal muscle than those of the obese control group (P < 0.05), whereas rats of the obese control group had lower concentrations of total carnitine in plasma and skeletal muscle than lean rats (P < 0.05).

Conclusion

The results show for the first time that niacin administration stimulates the expression of genes involved in carnitine uptake and biosynthesis and improves the diminished carnitine status of obese Zucker rats. We assume that the induction of genes involved in carnitine uptake and biosynthesis by niacin administration is mediated by PPAR-activation.

Niacin in pharmacological doses alters microRNA expression in skeletal muscle of obese Zucker rats

Administration of pharmacological niacin doses was recently reported to have pronounced effects on skeletal muscle gene expression and phenotype in obese Zucker rats, with the molecular mechanisms underlying the alteration of gene expression being completely unknown. Since miRNAs have been shown to play a critical role for gene expression through inducing miRNA-mRNA interactions which results in the degradation of specific mRNAs or the repression of protein translation, we herein aimed to investigate the influence of niacin at pharmacological doses on the miRNA expression profile in skeletal muscle of obese Zucker rats fed either a control diet with 30 mg supplemented niacin/kg diet or a high-niacin diet with 780 mg supplemented niacin/kg diet for 4 wk. miRNA microarray analysis revealed that 42 out of a total of 259 miRNAs were differentially expressed (adjusted P-value <0.05), 20 being down-regulated and 22 being up-regulated, between the niacin group and the control group. Using a biostatistics approach, we could demonstrate that the most strongly up-regulated (log2 ratio ≥0.5) and down-regulated (log2 ratio ≤-0.5) miRNAs target approximately 1,800 mRNAs. Gene-term enrichment analysis showed that many of the predicted target mRNAs from the most strongly regulated miRNAs were involved in molecular processes dealing with gene transcription such as DNA binding, transcription regulator activity, transcription factor binding and in important regulatory pathways such as Wnt signaling and MAPK signaling. In conclusion, the present study shows for the first time that pharmacological niacin doses alter the expression of miRNAs in skeletal muscle of obese Zucker rats and that the niacin-regulated miRNAs target a large set of genes and pathways which are involved in gene regulatory activity indicating that at least some of the recently reported effects of niacin on skeletal muscle gene expression and phenotype in obese Zucker rats are mediated through miRNA-mRNA interactions.

Excess vitamin intake: An unrecognized risk factor for obesity

Over the past few decades, food fortification and infant formula supplementation with high levels of vitamins have led to a sharp increase in vitamin intake among infants, children and adults. This is followed by a sharp increase in the prevalence of obesity and related diseases, with significant disparities among countries and different groups within a country. It has long been known that B vitamins at doses below their toxicity threshold strongly promote body fat gain. Studies have demonstrated that formulas, which have very high levels of vitamins, significantly promote infant weight gain, especially fat mass gain, a known risk factor for children developing obesity. Furthermore, ecological studies have shown that increased B vitamin consumption is strongly correlated with the prevalence of obesity and diabetes. We therefore hypothesize that excess vitamins may play a causal role in the increased prevalence of obesity. This review will discuss: (1) the causes of increased vitamin intake; (2) the non-monotonic effect of excess vitamin intake on weight and fat gain; and (3) the role of vitamin fortification in obesity disparities among countries and different groups within a country.

Maternal nicotinamide supplementation causes global DNA hypomethylation, uracil hypo-incorporation and gene expression changes in fetal rats

Recent evidence shows that excess nicotinamide can cause epigenetic changes in developing rats. The aim of the present study was to investigate the effects of maternal nicotinamide supplementation on the fetus. Female rats were randomised into four groups fed a standard chow diet (control group) or diets supplemented with 1 g/kg of nicotinamide (low-dose group), 4 g/kg of nicotinamide (high-dose group) or 4 g/kg of nicotinamide plus 2 g/kg of betaine (betaine group) for 14-16 d before mating and throughout the study. Fetal tissue samples were collected on the 20th day of pregnancy. Compared with the control group, the high-dose group had a higher fetal death rate, and the average fetal body weight was higher in the low-dose group but lower in the high-dose group. Nicotinamide supplementation led to a decrease in placental and fetal hepatic genomic DNA methylation and genomic uracil contents (a factor modifying DNA for diversity) in the placenta and fetal liver and brain, which could be completely or partially prevented by betaine. Moreover, nicotinamide supplementation induced tissue-specific alterations in the mRNA expression of the genes encoding nicotinamide N-methyltransferase, DNA methyltransferase 1, catalase and tumour protein p53 in the placenta and fetal liver. High-dose nicotinamide supplementation increased fetal hepatic α-fetoprotein mRNA level, which was prevented by betaine supplementation. It is concluded that maternal nicotinamide supplementation can induce changes in fetal epigenetic modification and DNA base composition. The present study raises the concern that maternal nicotinamide supplementation may play a role in the development of epigenetic-related diseases in the offspring.

Regulation of DNA methyltransferase 1 transcription in BRCA1-mutated breast cancer: a novel crosstalk between E2F1 motif hypermethylation and loss of histone H3 lysine 9 acetylation

Background

DNA methyltransferase 1 (DNMT1) plays a critical role in breast cancer progression. However, the epigenetic mechanism regulating DNMT1 expression remains largely unknown.

Methods

Epigenetic regulation of DNMT1 was assessed in 85 invasive ductal carcinomas from BRCA1 mutation carriers. Association between clinicopathological features and DNMT1 promoter methylation was determined using Fisher’s exact test. Univariate analysis of survival was performed using the Kaplan-Meier method. Multivariate Cox regression analysis was performed to identify the independent prognostic factors for overall survival.

Results

Hypermethylated E2F transcription factor 1 (E2F1) motif is a key regulatory element for the DNMT1 gene in BRCA1-mutated breast cancer. Mechanistically, the abnormal E2F1 motif methylation-mediated loss of active histone H3 lysine 9 acetylation (H3K9ac) and transcription factor E2F1 enrichment synergistically inhibited the transcription of DNMT1. Clinicopathological data indicated that the hypermethylated E2F1 motif was associated with histological grade, lymph node, Ki67 and E-cadherin status; univariate survival and multivariate analyses demonstrated that lymph node metastasis was an independent and reliable prognostic factor for BRCA1-mutated breast cancer patients.

Conclusions

Our findings imply that genetic (such as BRCA1 mutation) and epigenetic mechanisms (such as DNA methylation, histone modification, transcription factor binding) are jointly involved in the malignant progression of DNMT1-related breast cancer.

Supplementing healthy rats with a high-niacin dose has no effect on muscle fiber distribution and muscle metabolic phenotype

PURPOSE

It was recently shown that niacin prevents the obesity-induced type I to type II fiber switching in skeletal muscle of obese rats and favors the development of a more oxidative metabolic phenotype and thereby increases whole body utilization of fatty acids. Whether niacin also causes type II to type I fiber switching in skeletal muscle of healthy rats has not been investigated yet. Thus, the present study aimed to investigate whether niacin supplementation influences fiber distribution and metabolic phenotype of different skeletal muscles with a distinct type I-to-type II fiber ratio in healthy rats.

METHODS

Twenty-four male, 10-week-old Sprague-Dawley rats were randomly assigned into two groups of 12 rats each and fed either a control diet with 30 mg supplemented niacin/kg diet (control group) or a high-niacin diet with 780 mg supplemented niacin/kg diet (high-niacin group).

RESULTS

After 27 days of treatment, the percentage number of type I fibers in rectus femoris, gastrocnemius, and tibialis anterior muscles was 5-10% greater in the niacin group than in the control group, but did not differ between groups in soleus and vastus intermedius muscles. Transcript levels of genes encoding transcription factors regulating fiber switching, fiber-specific myosin heavy chain isoforms, and proteins involved in fatty acid utilization, oxidative phosphorylation, and angiogenesis did not differ between groups.

CONCLUSIONS

The results show that niacin has only negligible effects on fiber distribution and its regulation as well as the metabolic phenotype of skeletal muscle in healthy rats.