Niacin binds to Nicotinate D-ribonucleotide phyrophsopate phosphoribosyltransferase, Nicotinic acid phosphoribosyltransferase, Nicotinate N-methyltransferase and the Niacin receptor. Niacin is the precursor to nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are vital cofactors for dozens of enzymes. The mechanism by which niacin exerts its lipid lowering effects is not entirely understood, but may involve several actions, including a decrease in esterification of hepatic triglycerides. Niacin treatment also decreases the serum levels of apolipoprotein B-100 (apo B), the major protein component of the VLDL (very low-density lipoprotein) and LDL fractions.
Niacin and niacinamide are indicated for prevention and treatment of vitamin B3 deficiency states. Vitamin B3 (Niacin) also acts to reduce LDL cholesterol, triglycerides, and HDL cholesterol. The magnitude of individual lipid and lipoprotein responses may be influenced by the severity and type of underlying lipid abnormality. The increase in total HDL is associated with a shift in the distribution of HDL subfractions (as defined by ultra-centrifugation) with an increase in the HDL2:HDL3 ratio and an increase in apolipoprotein A-I content. Vitamin B3 (Niacin) treatment also decreases the serum levels of apolipoprotein B-100 (apo B), the major protein component of the VLDL (very low-density lipoprotein) and LDL fractions, and of lipoprotein-a, a variant form of LDL independently associated with coronary risk.
Nicotinic acid can cause vasodilation of cutaneous blood vessels resulting in increased blood flow, principally in the face, neck and chest. This produces the niacin- or nicotinic acid-flush. The niacin-flush is thought to be mediated via the prostaglandin prostacyclin. Histamine may also play a role in the niacin-flush. Flushing is the adverse reaction first observed after intake of a large dose of nicotinic acid, and the most bothersome one. LD50 7000 mg/kg (Rat)