Lipid metabolism, riboflavin

The main metabolic effect of riboflavin deficiency is on lipid metabolism. Riboflavin-deficient animals have a lower metabolic rate than controls, and require a 15—20% higher food intake to maintain body weight. Feeding a high-fat diet leads to more marked impairment of growth and a higher requirement for riboflavin to restore growth. 

Duerden JM and Bates CJ (1985) Effect of riboflavin deficiency on lipid metabolism of liver and brown adipose tissue of sucking rat pups. British Journal of Nutrition 53, 107-15. 

Riboflavin in its coenzyme forms (FMN and FAD) plays key metabolic roles in biological oxidation-reduction reactions involving carbohydrates, amino acids and lipids, and in energy production via the respiratory chain. These coenzymes also act in cellular metabolism of other water-soluble vitamins through the production and activation of folate and pyridoxine (vitamin Bg) to their respective coenzyme forms and in the synthesis of niacin (vitamin B3) from tryptophan. In addition, some neurotransmitters and other amines require FAD for their metabolism. Recently, Chocano-Bedoya et al. (2011) suggested a possible benefit of high intakes of riboflavin (about 2.5 mg/ day) from food sources on the reduction of incidence of premenstrual syndrome. 

Gianazza and co-workers have carried a series of elegant proteomic studies aimed at establishing correlations between flavin metabolism and mitochondrial flavoenzyme dysfunction (Gianazza et al. 2006). A detailed investigation was carried out on muscle mitochondria from a patient with profound muscle weakness associated with MADD. The patient received riboflavin supplementation treatment (200 mg/day) in combination with carnitine treatment (2g/day) which resulted in a substantial improvement, as assessed by biochemical parameters. Prior the therapeutic riboflavin supplementation, the activity of different fatty acid (5-oxidation enzymes, respiratory complexes, the ratio between acyl/free carnitine and the levels of intracellular lipids were altered in respect to controls. These data led the authors to evaluate the FAD and FMN concentrations in whole muscle, and the results evidenced a lower amount of available FAD upon riboflavin therapy the flavin levels were restored to, at least, control levels. 

Riboflavin, also called vitamin B2, is stmcturally composed of an isoafloxazine ring with a ribityl side chain at the nitrogen at position 10. This vitamin functions metabol-icafly as the essoitial component of two flavin coenzymes, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), complexed with proteins, which act as intmnediaries in transfers of electrons in biological oxidation-reduction reactions. Both FAD and FMN function as coenzymes for flavoproteins of flavoenzymes. Flavoproteins are essoitial for the metabolism of carbohydrates, amino acids, and lipids and for pyridoxine and folate conversion to their respective coenzyme forms. 

Animals also depend on plants for essential organic molecules that they are unable to make. We call some of these molecules vitamins. Several vitamins, including niacin, riboflavin, pyridoxine, and biotin, are key players in catabolic and anabolic metabolism, and deficiencies in these vitamins have severe effects. Also, animals are incapable of synthesizing polyunsaturated fatty acids (fatty acids with more than one double bond). Polyunsaturated fatty acids are essential components of membrane lipids and must be obtained in the diet. So, the next time you have a salad, pay a tribute to photosynthesis. 

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