Niacin: an old lipid drug in a new NAD + dress

a switch

Abstract

Niacin, the first antidyslipidemic drug, has been at the center stage of lipid research for many decades before the discovery of statins. However, to date, despite its remarkable effects on lipid profiles, the clinical outcomes of niacin treatment on cardiac events is still debated.

In addition to its historically well-defined interactions with central players of lipid metabolism, niacin can be processed by eukaryotic cells to synthesize a crucial cofactor, NAD+. NAD+ acts as a cofactor in key cellular processes, including oxidative phosphorylation, glycolysis, and DNA repair.

More recently, evidence has emerged that NAD+ also is an essential cosubstrate for the sirtuin family of protein deacylases and thereby has an impact on a wide range of cellular processes, most notably mitochondrial homeostasis, energy homeostasis, and lipid metabolism. NAD+ achieves these remarkable effects through sirtuin-mediated deacetylation of key transcriptional regulators, such as peroxisome proliferator-activated receptor gamma coactivator 1-α, LXR, and SREBPs, that control these cellular processes.

Here, we present an alternative point of view to explain niacin’s mechanism of action, with a strong focus on the importance of how this old drug acts as a control switch of NAD+/sirtuin-mediated control of metabolism.

FULL TEXT: Journal of Lipid Research

NAD deficiency + niacin supplementation

Abstract modern vase with leaf

Abstract

Background: Congenital malformations can be manifested as combinations of phenotypes that co-occur more often than expected by chance. In many such cases, it has proved difficult to identify a genetic cause. We sought the genetic cause of cardiac, vertebral, and renal defects, among others, in unrelated patients.

Methods: We used genomic sequencing to identify potentially pathogenic gene variants in families in which a person had multiple congenital malformations. We tested the function of the variant by using assays of in vitro enzyme activity and by quantifying metabolites in patient plasma. We engineered mouse models with similar variants using the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 system.

Results: Variants were identified in two genes that encode enzymes of the kynurenine pathway, 3-hydroxyanthranilic acid 3,4-dioxygenase (HAAO) and kynureninase (KYNU). Three patients carried homozygous variants predicting loss-of-function changes in the HAAO or KYNU proteins (HAAO p.D162*, HAAO p.W186*, or KYNU p.V57Efs*21). Another patient carried heterozygous KYNU variants (p.Y156* and p.F349Kfs*4). The mutant enzymes had greatly reduced activity in vitro. Nicotinamide adenine dinucleotide (NAD) is synthesized de novo from tryptophan through the kynurenine pathway. The patients had reduced levels of circulating NAD. Defects similar to those in the patients developed in the embryos of Haao-null or Kynu-null mice owing to NAD deficiency. In null mice, the prevention of NAD deficiency during gestation averted defects.

Conclusions: Disruption of NAD synthesis caused a deficiency of NAD and congenital malformations in humans and mice. Niacin supplementation during gestation prevented the malformations in mice.

FULL TEXT: NEJM

EDITOR’S NOTE: Apparent restoration of NAD synthesis was achieved here with a readily available supplement, niacin (vitamin B3).

Niacin

Female Scientist in chemistry lab

Abstract

Nicotinic acid and nicotinamide, collectively referred to as niacin, are nutritional precursors of the bioactive molecules nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). NAD and NADP are important cofactors for most cellular redox reactions, and as such are essential to maintain cellular metabolism and respiration.

NAD also serves as a cosubstrate for a large number of ADP-ribosylation enzymes with varied functions. Among the NAD-consuming enzymes identified to date are important genetic and epigenetic regulators, e.g., poly(ADP-ribose)polymerases and sirtuins.

There is rapidly growing knowledge of the close connection between dietary niacin intake, NAD(P) availability, and the activity of NAD(P)-dependent epigenetic regulator enzymes. It points to an exciting role of dietary niacin intake as a central regulator of physiological processes, e.g., maintenance of genetic stability, and of epigenetic control mechanisms modulating metabolism and aging.

Insight into the role of niacin and various NAD-related diseases ranging from cancer, aging, and metabolic diseases to cardiovascular problems has shifted our view of niacin as a vitamin to current views that explore its potential as a therapeutic.

FULL TEXT: Adv Food Nutr Res

An acetylation switch of the NLRP3 inflammasome

an illustration of a woman, shown from behind, with markers of inflammation

Abstract

It is well documented that the rate of aging can be slowed, but it remains unclear to which extent aging-associated conditions can be reversed. How the interface of immunity and metabolism impinges upon the diabetes pandemic is largely unknown.

Here, we show that NLRP3, a pattern recognition receptor, is modified by acetylation in macrophages and is deacetylated by SIRT2, an NAD +-dependent deacetylase and a metabolic sensor.

We have developed a cell-based system that models aging-associated inflammation, a defined co-culture system that simulates the effects of inflammatory milieu on insulin resistance in metabolic tissues during aging, and aging mouse models; and demonstrate that SIRT2 and NLRP3 deacetylation prevent, and can be targeted to reverse, aging-associated inflammation and insulin resistance.

These results establish the dysregulation of the acetylation switch of the NLRP3 inflammasome as an origin of aging-associated chronic inflammation and highlight the reversibility of aging-associated chronic inflammation and insulin resistance.

FULL TEXT: Cell Metabolism

EDITOR’S NOTE: the deacetylation step, performed by SIRT2, is switched ‘on’ in healthy cells. This is one more part of the NAD+ / sirtuin puzzle. The goal is to keep NAD+ and sirtuins functioning normally.

Sirtuin signaling in cellular senescence + aging

dna-replication-vector-diagram

Abstract

Sirtuin is an essential factor that delays cellular senescence and extends the organismal lifespan through the regulation of diverse cellular processes. Suppression of cellular senescence by sirtuin is mainly mediated through delaying the age-related telomere attrition, sustaining genome integrity and promotion of DNA damage repair.

In addition, sirtuin modulates the organismal lifespan by interacting with several lifespan regulating signaling pathways including insulin/IGF-1 signaling pathway, AMP-activated protein kinase, and forkhead box O. Although still controversial, it is suggested that the prolongevity effect of sirtuin is dependent with the level of and with the tissue expression of sirtuin. Since sirtuin is also believed to mediate the prolongevity effect of calorie restriction, activators of sirtuin have attracted the attention of researchers to develop therapeutics for age-related diseases.

Resveratrol, a phytochemical rich in the skin of red grapes and wine, has been actively investigated to activate sirtuin activity with consequent beneficial effects on aging. This article reviews the evidences and controversies regarding the roles of sirtuin on cellular senescence and lifespan extension, and summarizes the activators of sirtuin including sirtuin-activating compounds and compounds that increase the cellular level of nicotinamide dinucleotide (NAD).

FULL TEXT: BMB Reports