Pyridoxine functions

B6 function, including pyridoxin (= PN, alcohol), pyridoxal (= PL, aldehyde), pyridoxamine (= PM, amine), and their 5 -phosphoiylised forms. 

The water-soluble vitamins comprise the B complex and vitamin C and function as enzyme cofactors. Fofic acid acts as a carrier of one-carbon units. Deficiency of a single vitamin of the B complex is rare, since poor diets are most often associated with multiple deficiency states. Nevertheless, specific syndromes are characteristic of deficiencies of individual vitamins, eg, beriberi (thiamin) cheilosis, glossitis, seborrhea (riboflavin) pellagra (niacin) peripheral neuritis (pyridoxine) megaloblastic anemia, methyhnalonic aciduria, and pernicious anemia (vitamin Bjj) and megaloblastic anemia (folic acid). Vitamin C deficiency leads to scurvy. 

Rice bran is the richest natural source of B-complex vitamins. Considerable amounts of thiamin (Bl), riboflavin (B2), niacin (B3), pantothenic acid (B5) and pyridoxin (B6) are available in rice bran (Table 17.1). Thiamin (Bl) is central to carbohydrate metabolism and kreb s cycle function. Niacin (B3) also plays a key role in carbohydrate metabolism for the synthesis of GTF (Glucose Tolerance Factor). As a pre-cursor to NAD (nicotinamide adenine dinucleotide-oxidized form), it is an important metabolite concerned with intracellular energy production. It prevents the depletion of NAD in the pancreatic beta cells. It also promotes healthy cholesterol levels not only by decreasing LDL-C but also by improving HDL-C. It is the safest nutritional approach to normalizing cholesterol levels. Pyridoxine (B6) helps to regulate blood glucose levels, prevents peripheral neuropathy in diabetics and improves the immune function. 

The water-soluble vitamins generally function as cofactors for metabolism enzymes such as those involved in the production of energy from carbohydrates and fats. Their members consist of vitamin C and vitamin B complex which include thiamine, riboflavin (vitamin B2), nicotinic acid, pyridoxine, pantothenic acid, folic acid, cobalamin (vitamin B12), inositol, and biotin. A number of recent publications have demonstrated that vitamin carriers can transport various types of water-soluble vitamins, but the carrier-mediated systems seem negligible for the membrane transport of fat-soluble vitamins such as vitamin A, D, E, and K. 

Cleavage of cystathionine is accomplished by cystathi-onase, another pyridoxine-dependent enzyme that is coded on human chromosome 16 (Fig. 40-4 reaction 6). The enzyme functions almost entirely to produce cysteine, there being virtually no reversal of the reaction. 

High levels of homocysteine or one of its metabolites may directly affect brain function. The administration of homocysteine to rats induces grand mal convulsions, a phenomenon that is aggravated by either methionine or pyridoxine. Homocysteine-induced blockade of the y-aminobutyric acid (GABA) receptor may be involved. In addition, brain can oxidize homocysteine to homocys-teic acid, which has a glutamatergic activity. 

Phenomenex (see 2006 Catalog, SPE products) Strata-X Polar functionalized styrene-divinylbenzene polymer Reversed phase with weakly acidic, hydrogen bond donor, acceptor, and dipolar interactions Cetirizine (76) pyridoxine (77) omeprazole (78) mycophenolic acid (79) 25-hydroxy-vitamin D3 (80)... 

Vitamin Ba (pyridoxine, pyridoxal, pyridoxamine) like nicotinic acid is a pyridine derivative. Its phosphorylated form is the coenzyme in enzymes that decarboxylate amino acids, e.g., tyrosine, arginine, glycine, glutamic acid, and dihydroxyphenylalanine. Vitamin B participates as coenzyme in various transaminations. It also functions in the conversion of tryptophan to nicotinic acid and amide. It is generally concerned with protein metabolism, e.g., the vitamin B8 requirement is increased in rats during increased protein intake. Vitamin B6 is also involved in the formation of unsaturated fatty acids. 

After decontamination by emesis or lavage, patients should be carefully monitored for alterations in liver and kidney function, and treated symptomatically if necesseray. Seizures can be treated with anti-convulsant drugs. Because the toxin produces a deficiency of y-amino-butyric acid (GABA), specific treatment with pyridoxine (vitamin Bg) has been recommended. 

Vitamin Be is again a small family of related compounds having the same biological activity. These include pyridoxine, pyridoxai, and pyridoxamine. In humans, these molecules are readily interconverted, accounting for their equivalence as vitamins. The stuff in your vitamin pill is likely to be pyridoxine. The actual molecule that functions as a coenzyme in metabolism is pyridoxai phosphate, in which a phosphate group has been added to pyridoxai in an ATP-dependent reaction. 

Obtain cultures Obtain cultures and determine susceptibility before treatment. Determine blood levels Determine blood levels weekly for patients having reduced renal function, for individuals receiving more than 500 mg/day, and for those with symptoms of toxicity. Adjust dosage to maintain blood level less than 30 mcg/mL. Anticonvulsant drugs or sedatives Anticonvulsant drugs or sedatives may be effective in controlling symptoms of CNS toxicity, such as convulsions, anxiety, and tremor. Closely observe patients receiving more than 500 mg/day for such symptoms. Pyridoxine may prevent CNS toxicity, but its efficacy has not been proven. 

Vitamin Bg is a mixture of six interrelated forms pyridoxine (or pyridoxol) (Figure 19.23), pyri-doxal, pyridoxamine, and their 5 -phosphates derivatives. Interconversion is possible between all forms. The active form of the vitamin is pyridoxal phosphate, which is a coenzyme correlated with the function of more than 60 enzymes involved in transamination, deamination, decarboxylation, or desulfuration reactions. 

Mechanism of Action Acts as a coenzyme for various metabolic functions, including metabolism of proteins, carbohydrates, and fats. Aids in the breakdown of glycogen and in the synthesis of gamma-aminobutyric acid in the CNS. Therapeutic Effect Prevents pyridoxine deficiency. Increases the excretion of certain drugs, such as iso-niazid, that are pyridoxine antagonists. 

The B-group is a heterogeneous collection of water-soluble vitamins, most of which function as co-enzymes or are precursors of co-enzymes. The B-group vitamins are thiamin, riboflavin, niacin, biotin, pantothenic acid, pyridoxine (and related substances, vitamin B6), folate and cobalamin (and its derivatives, vitamin B12). 

Vitamin B6 occurs naturally in three related forms pyridoxine (6.26 the alcohol form), pyridoxal (6.27 aldehyde) and pyridoxamine (6.28 amine). All are structurally related to pyridine. The active co-enzyme form of this vitamin is pyridoxal phosphate (PLP 6.29), which is a co-factor for transaminases which catalyse the transfer of amino groups (6.29). PLP is also important for amino acid decarboxylases and functions in the metabolism of glycogen and the synthesis of sphingolipids in the nervous system. In addition, PLP is involved in the formation of niacin from tryptophan (section 6.3.3) and in the initial synthesis of haem. 

All aminotransferases have the same prosthetic group and the same reaction mechanism. The prosthetic group is pyridoxal phosphate (PLP), the coenzyme form of pyridoxine, or vitamin B6. We encountered pyridoxal phosphate in Chapter 15, as a coenzyme in the glycogen phosphorylase reaction, but its role in that reaction is not representative of its usual coenzyme function. Its primary role in cells is in the metabolism of molecules with amino groups. 

Vitamins are chemically unrelated organic compounds that cannot be synthesized by humans and, therefore, must must be supplied by the diet. Nine vitamins (folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid) are classified as water-soluble, whereas four vitamins (vitamins A, D, K, and E) are termed fat-soluble (Figure 28.1). Vitamins are required to perform specific cellular functions, for example, many of the water-soluble vitamins are precursors of coenzymes for the enzymes of intermediary metabolism. In contrast to the water-soluble vitamins, only one fat soluble vitamin (vitamin K) has a coenzyme function. These vitamins are released, absorbed, and transported with the fat of the diet. They are not readily excreted in the urine, and significant quantities are stored in Die liver and adipose tissue. In fact, consumption of vitamins A and D in exoess of the recommended dietary allowances can lead to accumulation of toxic quantities of these compounds. 

Vitamin B6 is a collective term for pyridoxine, pyridoxal, and pyridox amine, all derivatives of pyridine. They differ only in the nature of the functional group attached to the ring (Figure 28.10). Pyridoxine occurs primarily in plants, whereas pyridoxal and pyridoxamine are found in foods obtained from animals. All three compounds can serve as precur sors of the biologically active coenzyme, pyridoxal phosphate. Pyridoxal phosphate functions as a coenzyme for a large number of enzymes, par ticularly those that catalyze reactions involving amino acids. 

Vitamin B6 (pyridoxine, pyridoxamine, and pyridoxal) has the active form, pyridoxal phosphate. It functions as a cofactor for enzymes, particularly in amino acid metabolism. Deficiency of this vitamin is rare, but causes glossitis and neuropathy. The deficiency can be induced by isoniazid, which causes sensory neuropathy at high doses. 

Vitamins are required for satisfactory development or function of most yeasts. Wickerham (177) devised a complete yeast medium which included eight vitamins biotin, pantothenic acid, inositol, niacin, p-aminobenzoic acid, pyridoxine, thiamine, and riboflavin. The concentrations of these growth factors varied widely with inositol in the greatest concentration and biotin in trace amounts. Many of these vitamins are considered major growth factors for yeast multiplication and development, as noted in several studies and reviews (178, 179, 180, 181, 182). Generally, the benefit of adding vitamins to musts and wines has not been established as a normal winery practice. This lack of response is because vitamins occur naturally in sufficient quantities in grapes and are produced by yeasts themselves (3). 

Some enzymes require additional chemical species, called cofactors or coenzymes, to be fully active. Cofactors include metal ions such as Fe+2, Zn+2, and Cu+2. Coenzymes are organic molecules that allow transfer of functional groups or reduction/oxidation reactions. Examples include thiamine pyrophosphate (4.6) and pyridoxine 5 -phosphate (4.7) (Figure 4.8). 

A week later he went home on full anti-tuberculosis drugs with stable liver function tests and carbamazepine and the addition of pyridoxine. The white count does not suggest resistance has emerged during this treatment gap but should be monitored over the full treatment course. Any acute liver insult on top of this treatment would be very difficult to resolve. Compliance with the pyridoxine is very important to prevent any toxicity. 

In 1983, sensory neuropathy was reported in seven patients who had been taking between 2,000 to 7,000 mg of pyridoxine/day for several months (Schaumburg et al., 1983). On withdrawal of the vitamin supplements, there was considerable recovery of neuronal function, although there was residual nerve damage in some patients. 

Schaeppi U and Krinke G (1982) Pyridoxine neuropathy correlation of functional tests and neuropathology in beagle dogs treated with large doses ofvitamin Be. Agents and Actions 12, 575-82. 

Vitamin Bf, (pyridoxine, pyridoxal, and pyridox-amine) is a coenzyme that prefers the world of amino acid metabolism, it is the prosthetic group for all transaminases. Amino acid transamination is a particularly important function. For instance ... 

For the authors (PIO) the simplest explanation of the data on tryptophan metabolism in these 3 patients would be as follows in scleroderma (acrosclerosis) there was an abnormal urinary excretion of kynurenine and its metabolites after oral ingestion of tryptophan. The administration of pyridoxine or pyridoxine plus nicotinamide partially corrected the metabolic abnormality. The efficacy of pyridoxine plus Na2EDTA could be explained on the basis of a decrease in tissue calcium and zinc (and possibly other cations), enabling the metal ions, normally functioning with pyridoxal phosphate, as magnesium ions, to be utilized more advantageously. 

Piridoxilate, an equimolar mixture of glyoxylic acid and pyridoxine, is marketed in a few countries (for example France) for peripheral arterial occlusive disease and functional venous disorders. 

Treatment should include correction of metabolic acidosis, inhibition of ethylene glycol metabolism and if necessary, extracorporeal elimination of the parent alcohol and metabolites. Acidemia likely increases tissue penetration of toxic metabolites and hinders renal clearance. Although evidence is lacking, bicarbonate administration should be given to correct acidemia. Although more expensive, fomepizole is preferred to ethanol for ADH inhibition due to proven efficacy, predictable pharmacokinetics, and lack of adverse effects [105]. Inhibition of ADH with fomepizole prevents formation of toxic metabolites and renal injury, and improves add-base status [106]. Elimination half-life of ethylene glycol with fomepizole in patients with preserved renal function is approximately 20 hours [107]. Pyridoxine and thiamine should be administered to promote glyoxyhc add conversion less toxic metabolites than oxalate [108]. 

Hydrazine has strong caustic action on the skin and mucus membranes. Hydrazine produces a functional pyridoxine deficiency that can lead to seizure activity. Hydrazine causes hepatic necrosis. The gastrointestinal... 

In the patient who presents with seizures, airway protection and seizure control are primary goals. Disturbances in cardiac rhythm or function also require immediate attention. Ipecac-induced emesis is contraindicated due to the risk of seizures and the resulting potential for aspiration. Gastrointestinal decontamination via administration of activated charcoal should be considered for substantial recent ingestions. Pyridoxine is administered intravenously to all symptomatic and potentially serious asymptomatic overdoses as it provides rapid relief or prevention of severe toxicity, including seizures. The pyridoxine dosage is... 

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