Niacin related compounds

Water-soluble vitamins in formulations have been determined by use of ion-pair chromatography. The vitamins include several B vitamins as well as niacin, folic acid, and ascorbic acid (565). Vitamins D and Da were rapidly separated on reverse phase columns (247) as are vitamins A, D, and E in multivitamin tablets (564). Addition of silver ions to the mobile phase has been shown to increase the flexibility inherent in RPC by complexing with the unsaturated bonds and thereby decreasing the retention factor. This effect is also observed with other unsaturated drug molecules including steroids (247). Vitamin A and related compounds have... 

Niacin is also known as vitamin PP or vitamin Bj. The term niacin describes two related compounds, nicotinic acid and nicotinamide (Figure 19.18), both with biological activity. Niacin is formed from the metabolism of tryptophan, and therefore it is not strictly a vitamin. It is a precursor of two cofactors nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are essential for the functioning of a wide range of enzymes involved in redox reactions. 

The vitamin niacin (section 11.8) is important for the formation of two closely related compounds, the nicotinamide nucleotide coenzymes — nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). As shown in Figure 2.16, they differ only in that NADP has an additional phosphate group attached to the ribose. The whole of the coenzyme molecule is essential for binding to enzymes, and most enzymes can bind and use only one of these two coenzymes, either NAD or NADP, despite the overall similarity in their structures. 

Niacin is a generic term which refers to two related chemical compounds, nicotinic acid (6.22) and its amide, nicotinamide (6.23) both are derivatives of pyridine. Nicotinic acid is synthesized chemically and can be easily converted to the amide in which form it is found in the body. Niacin is obtained from food or can be synthesized from tryptophan (60 mg of dietary tryptophan has the same metabolic effect as 1 mg niacin). Niacin forms part of two important co-enzymes, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are co-factors for many enzymes that participate in various metabolic pathways and function in electron transport. 

F-9) (1-7) Niacin (=nicotinic acid). Nicotinamide is a related amide compound with similar activity as niacin ... 

The status of niacin in relation to most other vitamins is different as it can be synthesized by humans to some extend from tryptophan. Body status determination has been based on the determination of urinary excretion of niacin metabolites, predominately N-methyl-2-pyridone-5-carboxylamide and N-methyl-nicotinamide. The ratio of these compounds has been used as indicator of niacin status. Recent studies suggest that the determination of the two niacin-derived coenzymes, NAD and NADP, in erythrocytes, and their ratio are more reliable indicators of niacin status. However, a broadly accepted and easy to use determination method does not seem to exist. 

Table 1. Comparison of the effects of niacin analogs on nuclear events relating to the induction of differentiation of FELCs. Compounds were present at 10 mM in all assays, except ADP-ribose transferase activity, where they were 5 mM. All data represent the mean of triplicate assays with standard error, except % ADP-ribose transferase activity, where only the mean was included.

In the organism that Is required In small amounts In food to sustain the normal metabolic functions of life. The key to this definition Is that this chemical compound must be supplied to the organism because the animal cannot synthesize vitamins. Lack of It produces a specific deficiency syndrome and supplying It cures that deficiency. An exception to this definition Is vitamin D, which can be made In the skin upon adequate exposure to sunlight. However, without adequate exposure, the animal Is dependent on a dietary source. Biotin, panthothenlc acid, and vitamin R are made by bacteria In the human Intestine, based on a symbiotic relation-ship and, thus, are not required by the human. Niacin can also be synthesized In humans from the amino acid tryptophane. 

Nicotinic acid is readily converted to nicotinamide, the physiologically active form. The term niacin is sometimes used to include both compounds which are only distantly related to nicotine, the alkaloid in tobacco. 

Interest in hydroxykynuienine in relation to niacin formation was aroused when it was observed that it yielded nicotinic acid in a Neurospora mutant with a genetic block after kynurenine (298). The compound was first isolated from the larvae of several insects (299, 300). Its importance in the kyniuenine pathway in the mammal was established when it was shown that it was converted to nicotinic acid and could replace the latter as a growth factor (301, 302). No similar conversion of anthranilic acid took place (503). Subsequently it was found that hydroxykynurenine was a constituent of the urine and that its excretion was increased in pyridoxine-deficient animals (304). 

Although vitamins have different structures, sources, requirements, and mechanisms of action, they are classified according to their solubility in water or in fats. Vitamins A, D, E, and K are liposoluble, whereas the B-complex (Bi, B2, Bg, B12, niacin, pantothenic acid, biotin, and folic acid) and C vitamins are hydrosoluble. Moreover, there are some organic compounds related to vitamins that are usually classified with the B vitamins and are also hydrosoluble i.e., p-aminobenzoic acid is included among these substances with similarities to vitamins. 

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