A intrigante bioquímica da niacina - uma revisão crítica

Abstract

Recebido em 25/11/10; aceito em 29/3/11; publicado na web em 10/6/11 THE INTRIGUING BIOCHEMISTRY OF THE NIACIN -A CRITICAL REVIEW. Niacin (nicotinamide, nicotinic acid) interferes on homeostasis, DNA regulation, signaling and longevity. Nicotinic acid reduces synthesis of lipoproteins-apo-B and increases HDL. Its antilipemic action in liver produces: 1) inhibition of DGAT2, with decreased triacylglycerol synthesis, 2) downregulation of the b-chain of adenosine triphosphate synthase, leading to reduced HDL-apo-A-I catabolism. Nicotinic acid could increase redox potential in vascular endothelium. HM74A receptor activation in macrophages would be responsible for the release of prostaglandins, causing flushing in epidermis. HM74A agonists could assist in identifying antilipemic agents. Extended release niacin in combination with statin appears to protect cardiovascular system of patients with low HDL.Keywords: niacin; homeostasis; antilipemic effects. INTRODUÇÃOO termo niacina é um descritor genérico para designar tanto o ácido nicotínico como a nicotinamida. Esses nomes causam grande controvérsia, porque intuitivamente podem ser associados à nicotina do tabaco. De fato, o ácido nicotínico foi identificado pela primeira vez a partir da oxidação da nicotina.1 De modo geral, existe uma grande confusão na nomenclatura das vitaminas. O próprio ácido nicotínico já foi designado anteriormente como vitamina PP (fator de prevenção da pelagra).2 Neste trabalho de revisão, serão usados os termos: ácido niacínico e niacinamida, em substituição ao ácido nicotínico e à nicotinamida, respectivamente. A niacina, antigamente designada como B 3 (terceira vitamina do complexo B a ser identificada), é uma vitamina hidrossolúvel pertencente ao grupo das vitaminas do complexo B.1 Sua síntese em humanos é insuficiente para suprir as necessidades metabólicas e, portanto, sua ingestão diária é fundamental. Além disso, a niacina, dependendo da dosagem, apresenta efeito farmacológico. Desta forma, a niacina tem dupla identidade: a primeira como vitamina e a segunda como fármaco.Esta revisão tem como objetivo abordar aspectos gerais da estrutura química, distribuição, absorção, transporte, excreção, hipo-, hipervitaminose, estado bioquímico e rota metabólica da niacina, bem como suas ações metabólica e farmacológica. ASPECTOS GERAIS Estrutura química e distribuição nos alimentosAs estruturas químicas do ácido niacínico, da niacinamida e de suas formas coenzímicas, bem como de alguns dos seus precursores e metabólitos são mostradas na Figura 1. A niacinamida é mais solúvel em água, álcool e éter do que o ácido niacínico. Ambos os compostos, quando cristalizados, se apresentam como sólidos brancos e estáveis com absorção máxima a 263 nm. Em solução aquosa, a forma ácida é a mais estável. O ponto de fusão da forma ácida é de 237 o C, enquanto o da forma amida varia de 128-131 o C. O ácido niacínico é anfotérico, formando sais com ácidos e bases. É importante enfatizar que para a atividade vitamínica é imprescindível a presença do anel de piridin...

The different roles of Griffonia simplicifolia in the treatment of depression: a narrative review

“…11 In this sense, foods containing L-tryptophan are of fundamental importance in serotonergic neurotransmission. However, the participation of L-tryptophan still goes beyond neurotransmitter genesis, because part of it is converted in the liver to niacin (vitamin B3) 12 with the help of enzymes that contain vitamin B6 and iron and this niacin associated with pyruvate, omega 3, omega 6 and oxygen are essential in the mitochondria to enable the Krebs cycle, oxidative phosphorylation, formation of ATP, firing of neurons 13 and, consequently, it allows the production of Delta brain waves (2-4Hz), Theta (4-7Hz), Alpha (8-12Hz), Beta-Low (12-15Hz), BETA (15-23Hz), Beta-High (23-38Hz) and Gamma ). 14 In this context, one cannot fail to mention the minerals that are essential for the realization of the entire biochemical process, such as: phosphorus, which is important for pH regulation and for the action of vitamin D3 and calcium and, above all, , which is essential for the assimilation of niacin (also called nicotinamide or Vitamin B3); 15 sulphur, which makes up necessary amino acids for the synthesis of essential metabolites and also makes up thiamine and biotin; copper, which is a constituent of enzymes and substances in the blood with an important role in the oxidation of iron before it is transported in plasma; manganese, which is a constituent of essential enzyme systems, abundant in mitochondria, responsible for cellular respiration of liver cells, bone formation, cholesterol synthesis, thiamine activation, glucose metabolism, synthesis and the release of hormones from thyroid and prevention of allergic processes.…”

Melatonin concentration in the milk of cows supplemented with vitamins and milked twice daily

“…Nicotinamide, generally known as niacin, is a vitamin also synthesized in the tryptophan metabolism (RICHARD et al, 2009). In tissues, nicotinamide is converted into nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are essential coenzymes for energy and lipid metabolism, functioning as electron acceptors in catabolic reactions or as electron donors in anabolic reactions (MARIA;MOREIRA, 2011). The synthesis of niacin from tryptophan is controlled through a negative feedback mechanism, where an adequate level of niacin inhibits its synthesis from tryptophan.…”

“…The synthesis of niacin from tryptophan is controlled through a negative feedback mechanism, where an adequate level of niacin inhibits its synthesis from tryptophan. Thus, increased intestinal absorption of niacin decreases the use of tryptophan in its synthesis and makes this amino acid available for the synthesis of melatonin (DAWN et al, 2009;MARIA;MOREIRA, 2011).…”

Protective Effects of Nicotinamide on Mice Offspring Exposed to Cyclophosphamide during Pregnancy

“…They also play a key role in oxidative and nonoxidative mechanisms of great importance for the correct maintenance and implementation of the metabolic processes of the cells and they also act to modulate the activity of sirtuin enzymes, also called silent regulatory information (SIR) that are deacetylases or ADP-ribosyl transferases, transferring ADP-ribose units to many proteins that will act in several metabolic and cellular signaling pathways that are involved in the transitional regulation, genome stability, neuronal protection and metabolic homeostasis [6]. Considering the actions of nicotinamide and its extensive empirical use [7][8][9] we evaluated its potential inducing effects of changes in animals in undergoing treatment with nicotinamide and its possible protective effects on toxic and teratogenic model induced by cyclophosphamide in mice during pregnancy.…”