Thyroid Riboflavin

Standards for dmg chemicals are pubUshed ia USP—NE. Dmg substances are chemicals that have therapeutic or diagnostic uses, whereas pharmaceutical iagredients provide preservative action, fiavoiing, or hilfillment of a function ia the formulation of dosage-form dmgs. Examples of dmg substances are acetaminophen [103-90-2] ampicillin [69-53-4] aspirin [50-78-2] powdered ipecac, riboflavin [83-88-5] staimous fluoride [7783-47-3] and thyroid. Examples of pharmaceutical iagredients are ethylparaben [120-47-8] lactose [63-42-3] magnesium stearate [557-04-0] sodium hydroxide [1310-73-2] starch [9005-25-8] and vanillin [121-33-5],... 

G Levy, MH MacGillivray, JA Procknal. Riboflavin absorption in children with thyroid disorders. Pediatrics 50 896-900, 1972. 

A number of dietary deficiencies may increase the risk of deleterious cyanide effects. Iodine deficiency is involved in the etiology of such thyroid disorders as goiter and cretinism. These disorders may be exacerbated by excess exposure to cyanide (Delange and Ermans 1971 Ermans et al. 1972). Protein deficiencies and vitamin B12, riboflavin and other vitamins and elemental deficiencies may subject people... 

Ascorbic acid, thiamine, riboflavin, and vitamin B12 requirements increase in hyperthyroidism (issue concentrations reduced Vitamin A massive doses of vitamin A inhibit secretion of TSH thyroid hormones required for carotene and retimene conversions Vitamins A, D, E. and K requirements increased in hyperthyroidism tissue concentrations reduced in Vitamin B, . niacin conversion to phosphorylated reactive forms impaired in hyperthyroidism... 

Tissue concentrations of flavin coenzymes in hypothyroid animals may be as low as in those fed a riboflavin-deficient diet, in hypothyroid patients, erythrocyte glutathione reductase (EGR) activity may be as low, and its activation by FAD added in vitro (Section 7.5.2) as high, as in riboflavin-deficient subjects. Tissue concentrations of flavin coenzymes and EGR are normalized by the administration of thyroid hormones, with no increase in riboflavin intake (Cimino et al., 1987). 

The administration of thyroid hormones to hypothyroid animals results in a rapid increase in flavokinase activity as a result of the activation of an inactive precursor protein as flavokinase activity increases, there is a parallel decrease in the tissue content of an apparendy inactive riboflavin binding protein (Lee and McCormick, 1985). 

Riboflavin may also be involved in the metabolism of thyroid hormones. In the presence of oxygen, riboflavin phosphate catalyzes a photolytic deiod-ination of thyroxine. The lower tissue concentration of riboflavin phosphate in hypothyroidism may thus serve to protect such thyroid hormone as is available against catabolism and prolong its action. 

Fig 1. Effect of incubation meditun and excess hormone on L-T and L-T/, uptake by mouse neuroblastoma cells (NBATA3) After 45 min preincubation confluent cells were incubated at 37°C for 2 h with 10 pM labeled thyroid hormone in the absence or presence of lOpM unlabeled hormone. Wells measuring 28.2 cm contained 4 ml of culture medium (RPMI 1640) or Hank s balanced salt solution. After washing with phosphate buffered saline +0.1% serum albumin, the cells were harvested and their radioactivity measured. Mean SEM of 3 experiments performed in duplicate. Experiments were performed under diminished light to avoid spontaneous deiodination especially of T, in RPMI due to riboflavin and folic acid. 

Riboflavin (vitamin B ) plays an essential role in cellular metabolism, being the precursor of the co-enzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) that both act as hydrogen carriers in biological redox reactions involving enzymes such as NADH dehydrogenase. Once riboflavin is absorbed in the human body, the synthesis of these flavin co-enzymes is controlled by thyroid hormones that regulate the activities of the flavin biosynthetic enzymes (Rucker et al. 2001). 

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