Vitamin carnitine

Vitamin C is an essential vitamin beheved important for synthesis of cellular components, catecholamines, steroids, and carnitine. Vitamin C is indicated in the prevention and treatment of scurvy. 

Camitine deficiency can occur particularly in the newborn—and especially in preterm infants—owing to inadequate biosynthesis or renal leakage. Losses can also occur in hemodialysis. This suggests a vitamin-fike dietary requirement for carnitine in some individuals. Symptoms of deficiency include hypoglycemia, which is a consequence of impaired fatty acid oxidation and hpid accumulation with muscular weakness. Treatment is by oral supplementation with carnitine. 

A number of iron-containing, ascorbate-requiring hydroxylases share a common reaction mechanism in which hydroxylation of the substrate is linked to decarboxylation of a-ketoglutarate (Figure 28-11). Many of these enzymes are involved in the modification of precursor proteins. Proline and lysine hydroxylases are required for the postsynthetic modification of procollagen to collagen, and prohne hydroxylase is also required in formation of osteocalcin and the Clq component of complement. Aspartate P-hydroxylase is required for the postsynthetic modification of the precursor of protein C, the vitamin K-dependent protease which hydrolyzes activated factor V in the blood clotting cascade. TrimethyUysine and y-butyrobetaine hydroxylases are required for the synthesis of carnitine. 

Carnitine is a vitamin-like quaternary ammonium salt, playing an important role in the human energy metabolism by facilitating the transport of long-chained fatty acids across the mitochondrial membranes. An easy, fast, and convenient procedure for the separation of the enantiomers of carnitine and 0-acylcarnitines has been reported on a lab-made teicoplanin-containing CSP [61]. The enantioresolution of carnitine and acetyl carnitine was enhanced when tested on a TAG CSP, prepared in an identical way [45]. Higher a values were reached also in the case of A-40,926 CSP [41]. 

Pharmacology Vitamin C, a water-soluble vitamin, is an essential vitamin in man however, its exact biological functions are not fully understood. It is essential for the formation and the maintenance of intercellular ground substance and collagen, for catecholamine biosynthesis, for synthesis of carnitine and steroids, for conversion of folic acid to folinic acid and for tyrosine metabolism. 

Historically choline, inositol and carnitine have been considered to be part of the vitamin B complex. However, for the general population there has been no demonstration of a dietary need for these agents and also for none of them has there been a therapeutic role established. Vitamins of the B family are found in many food ingredients like in yeast, in meat, in dairy products and also in eggs and grain cereals and separate vitamin B deficiencies are unlikely to occur. Excessive intake of these vitamins is eliminated in the urine because of the fact that they are water-soluble. 

Ascorbic acid or vitamin C is found in fruits, especially citrus fruits, and in fresh vegetables. Man is one of the few mammals unable to manufacture vitamin C in the liver. It is essential for the formation of collagen as it is a cofactor for the conversion of proline and lysine residues to hydroxyproline and hydroxylysine. It is also a cofactor for carnitine synthesis, for the conversion of folic acid to folinic acid and for the hydroxylation of dopamine to form norepinephrine. Being a lactone with two hydroxyl groups which can be oxidized to two keto groups forming dehydroascorbic acid, ascorbic acid is also an anti-oxidant. By reducing ferric iron to the ferrous state in the stomach, ascorbic acid promotes iron absorption. 

Carter HE, Bhattacharyya PK, Weidman KR, Fraenkel G (1952) Chemical studies on vitamin isolation and characterization as carnitine. Arch Biochem Biophys 38 405-416... 

Bhattacharyya PK, Carter HE, Fraenkel G, Weidman KR (1952) The identity of vitamin with carnitine. Arch Biochem 35 241-242... 

Carnitine is present in nearly all organisms and in all animal tissues. The highest concentration is found in muscle where it accounts for almost 0.1% of the dry matter. Carnitine was first isolated from meat extracts in 1905 but the first clue to its biological action was obtained in 1948 when Fraenkel and associates described a new dietary factor required by the mealworm, Tenebrio molitor. At first designated vitamin Bt, it was identified in 1952 as carnitine. Most organisms synthesize their own carnitine from lysine side chains (Eq. 24-30). 

Lactic acidosis is a severe and potentially fatal form of mitochondrial toxicity. Metabolic stress or vitamin deficiencies (riboflavin, carnitine) might provoke it. There is suggestive evidence of clinical benefit with riboflavin therapy (846). 

A 37-year-old HIV-infected woman receiving stavudine, lamivudine, and indinavir developed epigastric pain, anorexia, and vomiting. She had lactic acidosis (serum lactate 4.9 mmol/1), raised liver enzymes, and an increased prothrombin time. She had hepatomegaly and tachypnea and required mechanical ventilation. Her progress was complicated by pancreatitis and acute respiratory distress syndrome. Antiviral medication was stopped and she was treated with co-enzyme Q, carnitine, and vitamin C. The serum lactic acid and transaminases returned to normal over 4 weeks and she was weaned off the ventilator after 4 months. 

The current RDA for vitamin C is 60 mg/day for a healthy non-smoking adult, Vitamin C is a cofactor for several enzymes involved in the biosynthesis of collagen, neurotransmitters, carnitine (45), hydroxylation of cholesterol (to form bile acids). It is also an important water-soluble antioxidant, which scavenges most of the RS and acts as a coantioxidant by regenerating a-tocopheryl radicals (46). 

Common Name Carnitine L-Carnitine Levocarnitine Vitamin BT Structural Formula ... 

The food additive carnitine (25) is worthy of mention because it has a very close structural relationship to some beta blockers. It is also called vitamin BT. There are many potential routes to this compound, including an asymmetric hydrogenation method.234 236 The method is closely related to that used for Lipitor (Section 31.2.1). Reduction of 4-chloro-3-oxobutyrate provides the desired alcohol isomer. Ester hydrolysis and reaction with triethylamine affords 25. There are two other major approaches one relies on an asymmetric microbial oxidation (Scheme 31.22).237... 

Equally, demonstrating that a compound has a physiological function as a coenzyme or hormone does not classify that compound as a vitamin. It is necessary to demonstrate that endogenous synthesis of the compound is inadequate to meet physiological requirements in the absence of a dietary source of the compound. Table 1.3 lists compounds that have clearly defined functions, but are not considered vitamins because they are not dietary essentials endogenous synthesis normally meets requirements. However, there is some evidence that premature infants and patients maintained on long-term total parenteral nutrition may be unable to meet their requirements for carnitine (Section 14.1.2), choline (Section 14.2.2), and taurine (Section 14.5.3) unless they are provided in the diet, and these are sometimes regarded as... 

Subjects who are maintained for prolonged periods by total parenteral nutrition are obviously wholly dependent on what is provided in the nutrient mixture, normally with no contribution from intestinal bacteria. A great deal has been learned from such patients, including the essentiality of the amino acid histidine, and evidence that endogenous synthesis of taurine (Section 14.5.3) and carnitine (Section 14.1.2) may not be adequate to meet requirements without some dietary provision. However, for obvious ethical reasons, such patients have not been subjected to trials of graded intakes of vitamins, but are generally provided with amounts calculated to be adequate and in excess of minimum requirements. 

In animals, the production of CO2 from [ Cjpalmitate or octanoate is not consistendy affected by riboflavin deficiency, possibly as a result of increased activity of carnitine palmitoyl transferase, which is more a response to food deprivation than to riboflavin deficiency. However, the production of C02 from [ C] adipic acid is significandy reduced, and responds rapidly (with some overshoot) to repletion with the vitamin. It has been suggested that the abiUty to metabolize a test dose of [ Cjadipic acid may provide a sensitive means of investigating ribodavin nutritional status in human beings (Bates, 1989, 1990). 

As a result of the reduced activity of the mutase in vitamin B12 deficiency, there is an accumulation of methyhnalonyl CoA, some of which is hydrolyzed to yield methylmalonic acid, which is excreted in the urine. As discussed in Section 10.10.3, this can be exploited as a means of assessing vitamin B12 nutritional status. There may also be some general metabolic acidosis, which has been attributed to depletion of CoA because of the accumulation of methyl-malonyl CoA. However, vitamin B12 deficiency seems to result in increased synthesis of CoA to maintain normal pools of metabolically useable coenzyme. Unlike coenzyme A and acetyl CoA, neither methylmalonyl CoA nor propionyl CoA (which also accumulates in vitamin B12 deficiency) inhibits pantothenate kinase (Section 12.2.1). Thus, as CoA is sequestered in these metabolic intermediates, there is relief of feedback inhibition of its de novo synthesis. At the same time, CoA may be spared by the formation of short-chain fatty acyl carnitine derivatives (Section 14.1.1), which are excreted in increased amounts in vitamin B12 deficiency. In vitamin Bi2-deficient rats, the urinary excretion of acyl carnitine increases from 10 to 11 nmol per day to 120nmolper day (Brass etal., 1990). 

In addition to the established vitamins, a number of organic compounds have clear metabolic functions they can be synthesized in the body, but it is possible that under some circumstances (as in premature infants and patients maintained on long-term total parenteral nutrition) endogenous synthesis may not be adequate to meet requirements. These compounds include biopterin (Section 10.4), carnitine (Section 14.1), choline (Section 14.2), creatine (Section 14.3), inositol (Section 14.4), molybdopterin (Section 10.5), taurine (Section 14.5), and ubiquinone (Section 14.6). 

Both hydroxylation reactions in the synthesis of carnitine from trimethyllysine are ascorbic acid-dependent, 2-oxoglutarate-linked, reactions (Section 13.3.3), and impaired synthesis of carnitine probably accounts for the muscle fatigue associated with vitamin C deficiency. 

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