Nicotinuric acid

The biosynthesis and metabolism of nicotinic acid in disease has received little attention metabolic studies deal mainly with normal animals and man (01, R5). After a tryptophan load dose, the main catabolites in the urine are nicotinuric acid, N1-methylnicotinamide, nicotinamide, quinolinic acid, kynurenine, 6-pyridone, anthranilic acid, and 3-hydroxyanthranilic acid. These excretory products were estimated... 

FIGURE I A reconstructed extracted ion chromatogram of nicotinic acid and its six metabolites under HILIC conditions. Column Hypersil silica (4.6 X 50 mm) at a flow rate of 4 mL/min. Mobile phase A is water, mobile phase B is acetonitrile, both containing 1% formic acid. Gradient is 0.01-0.25 min 90% B to 65% B 0.25-0.90 min 65% B to 50% B. NA nicotinic acid NAM nicotinamide NUA nicotinuric acid 2-PY l-methyl-2-pyridone-5-carboxamide l-MNAM I-methyl-nicotinamide NAMO nicotinamide-N-oxide 4-PY l-methyl-4-pyridone-5-carboxamide. (Reprinted with permission from Reference 20.)... 

Figure 8.3. Metabolites of nicotinamide and nicotinic acid. Nicotinamide deamidase (nicotinamidase), EC 3.5.1.19 nicotinamide Af-methyltransferase, EC 2.1.1.1 aldehyde dehydrogenase, EC 1.1.1.1. Relative molecular masses (Mr) nicotinamide, 123.1 nicotinic acid, 122.1 nicotinamide JV-oxide, 139.1 Af -methyl nicotinamide, 139.1 trigonelline, 137.1 nicotinuric acid, 179.2 and methyl pyridone carboxamides, 154.1.

Nicotinic acid can be conjugated with glycine to form nicotinuric acid (nicotinoyl-glycine), or may be methylated to trigonelline (AT -methyl nicotinic... 

Disposition in the Body. It is excreted in the urine as unchanged drug, nicotinic acid, V-methylnicotinamide, and nicotinuric acid. 

Disposition in the Body. Readily absorbed after oral administration. Metabolised to A -methylnicotinamide, A-methyl-6-oxo-pyridine-3-carboxamide, iV-methyl-4-oxopyridine-3-carbox-amide, and by glycine conjugation to nicotinuric acid. It is rapidly excreted in the urine, and after administration of therapeutic doses about 34% is excreted unchanged in 6 hours. Nicotinic acid is a metabolite of nicergoline, nicotinamide, and nicotinyl tartrate. 

Quantification. High Pressure Liquid Chromatography. In plasma or urine nicotinic acid and nicotinuric acid, sensitivity 500 ng/ml, UV detection—N. Hengen et al., Clin. Chem., 1978,... 

The conversion of N-methylnicotinamide to its 6-pyridone has been studied enzymically (429). The isomeric 2-pyridone may well be formed in small amount (542), but most methods for determination do not distinguish between the isomers (e.g., 397). The 6-pyridone is not hydrolyzed to the corresponding acid (398 but see 1012). The enzyme of rat liver converting nicotinic acid to nicotinuric acid occurs in the mitochondria (454). Methylation of nicotinamide is carried out by a soluble enzyme, nicotinamide methylkinase, which has been studied by Cantoni (135, 136). The methyl group is derived from methionine. 

The doses of regular (crystalline) niacin used to treat dyslipidemia are almost completely absorbed, and peak plasma concentrations are achieved within 30-60 minutes. The t is 60 minutes, which accounts for the necessity of twice- or thrice-daily dosing. At lower doses, most niacin is taken up by the liver only the major metabolite, nicotinuric acid, is found in the urine. 

N-(2-hydroxyethyl)-nicotinamide, which undergoes further side-chain degradation to nicotinuric acid and, subsequently, nicotinamide and nicotinamide metabolites (e.g., nicotinic acid and N-methylnicotinamide). The nicotinamide derived from nicorandil merges into the endogenous pool of nicotinamide adenine dinucleoside coenzymes. Its elimination half-life is approximately 1 hour. Approximately 30% of nicorandil is excreted into the urine as metabolites, with less than 1% excreted unchanged. 

Nicotinic acid is a B-complex vitamin that is converted to nicotinamide, NAD, and NADP. The latter two compounds are coenzymes and are required tor oxidation/reduction reactions in a variety of biochemical pathways. Additionally, nicotinic acid is metabolized to a number of inactive compounds, including nicotinuric acid and N-methylated derivatives. Normal biochemical regulation and feedback prevent large doses of nicotinic acid from producing excess quantities of NAD and NADP. Thus, small doses of nicotinic acid, such as those used tor dietary supplementation, will be primarily excreted as metabolites, whereas large doses, such as those used tor the treatment of hyperlipoproteinemia, will be primarily excreted unchanged by the kidney (15). 

Nicotinic acid and its derivatives are stable to oxidation by heat, light, acid or alkali and this means that extraction into solvent systems compatible with HPLC is relatively easy by comparison with other vitamins. Biological extracts are readily prepared by deproteini-sation with acetone followed by extraction with dilute hydrochloric acid alternatively, ethyl acetate in combination with hydrochloric acid may be used to extract samples. The most popular HPLC mode for the separation of nicotinic acid is reversed phase ion-pair chromatography. For example, using a fiBondapak Cjg column with a mobile phase of water-methanol (9 1) plus 0.05 M tetrabutylam-monium phosphate as the ion-pair reagent, nicotinamide-A-oxide, 2-hydroxypyridine-5-carboxylic acid, nicotinamide, nicotinic acid and nicotinuric acid were consecutively eluted (Hengen et al., 1978). 

The analysis for niacinamide for all County subjects was done by the microbiological method described by Strohecker and Henning (1966) with use of a strain of Lactobacillus arabinosus (ATCC 8014) responding to niacin, niacinamide, and nicotinuric acid. The procedure was very time-consuming, and was discarded after the development of the chromatographic method described below. The measured amounts were converted by an empirical factor to correspond to the results of the chromatographic method. 

Among 24 compounds containing the tetrazole function prepared by Holland and Pereira [70], 5-(3-pyridyl)-tetrazole (XIII) was found to depress plasma-free fatty acid levels in the fasted dog most effectively. The hypoHpidemic activity of XIII was comparable to that of nicptinic and 3-pyridyl-acetic acids. In fact, the duration of activity was approximately 5 hours which is three times longer than that of nicotinic acid. Moreover, no rebound effect was observed after the hypoHpidemic activity of XIII, while the short inhibitory action of nicotinic acid was followed by a rise of plasma-free fatty acid concentration above the control level in the fasted dog. In contrast, compound XIII was found to be about 3,000 times less potent than nicotinic acid in the in vitro test in which the inhibition of norepinephrine-induced free fatty acid release from isolated adipose tissue was measured. In this assay, 3-pyridyl-acetic acid (IV) was approximately 600 times less active than nicotinic acid. PicoHnic acid and isonicotinic acid were even less active. The metaboHtes of nicotinic acid in man, namely, nicotinic acid amide, iV -methylnicotinamide and nicotinuric acid, were found to be about 10,000 times less active as Hpolysis inhibitors than nicotinic acid. Based on these findings, 5-(3-pyridyl)-tetrazole... 

In addition to niacin, niacine adenine dinucleotide and nicotinuric acid can also be metabolized by L. arabinosus, producing corresponding amounts of lactic acid. 

Nicotinuric acid has a molecular weight of 180.15, melts at 240-242° and crystallizes from dilute hydrochloric acid in white crystals which are very soluble in water and ethanol. 

Nicotinuric acid 3-Acetyl-pyridine Pyridine-3-sulfonic acid... 

This is based on the reaction of derivatives of pyridine with cyanogen bromide in the presence of an aromatic amine giving specific colors. Amines commonly used are 2-naphthylamine-i-sulfonic acid, />-aminoacetophenone, iV-methyl-aminophenol sulphate, aniline and />-naphthylamine. The reaction gives a yellowish-green color which is measured photometrically. The color is soluble in amyl alcohol which can be used to extract it from water solutions, but is not stable unless a phosphate buffer of pH 6.i is used. This method is not specific for nicotinic acid since other pyridine derivatives and derivatives of nicotinic acid such as trigonelline, nicotinuric acid and nicotine give a similar color. 

Py (III) NAD nicotinamide — nicotinamide A(-oxide (IV) NAD —> nicotinamide nicotinic acid — nicotinuric acid (V) NAD —> nicotinamide nicotinic acid V -methylnicotinic acid (trigonelline). In rats, pathway II mainly functions, and in humans pathway I. Pathway V functions in mushrooms, shellfish, and plants, but not in mammals. 

---