Erythrocytes glutathione reductase

The FAD-dependent enzyme glutathione reductase plays a role in the antioxidant system. Glutathione reductase restores reduced glutathione (GSH), the most important antioxidant in erythrocytes, from oxidized glutathione (GSSG) [1, 2]. 

Although riboflavin is fundamentally involved in metabolism, and deficiencies are found in most countries, it is not fatal as there is very efficient conservation of tissue riboflavin. Riboflavin deficiency is characterized by cheilosis, lingual desquamation and a seborrheic dermatitis. Riboflavin nutritional status is assessed by measurement of the activation of erythrocyte glutathione reductase by FAD added in vitro. 

Ribarov S, Benov L. 1985. Glutathione reductase and glucose-6-phosphate dehydrogenase in erythrocytes treated with heavy metals. Acta Physiol Pharmacol Bulg 11 51-54. 

Today, biochemical deficiency of riboflavin is accepted in the absence of clinical signs of deficiency. Biochemical signs of deficiency include change in the amount of the vitamin which is excreted in the urine, or change in the level of activity of a red blood cell (erythrocyte) enzyme, which is known as the erythrocyte glutathione reductase. Requirements for the vitamin are defined as that amount which will prevent both clinical and biochemical signs of deficiency. 

Darby, W. J. (1972) Application of the erythrocyte glutathione reductase assay in evaluating riboflavin nutritional status in a high school student population. Am. J. Clin. Nutr. 

The three enzymes are quite specific for their respective pyridine nucleotide substrates. Under conditions normally used for assay, lipoamide dehydrogenase is less than % as active with NADPH as with NADH IS) and thioredoxin reductase is less than 1% as active with NADH as with NADPH 36, Sff). Lipoamide dehydrogenase can transfer electrons to a number of NAD analogs 37). Yeast glutathione reductase is quite specific for NADPH 60), but the erythrocyte enzyme is 20% as active with NADH as with NADPH under the conditions of the standard assay 30,40,61). 

In pregnant women, there is a progressive increase in the erythrocyte glutathione reductase activation coefficient (an index of functional riboflavin nutritional status Section 7.5.2), which resolves on parturition despite the daily secretion of 200 to 400 /rg (0.5 to 1 /rmol) of riboflavin into milk. This suggests that the estrogen-induced riboflavin binding protein can sequester the vitamin for fetal uptake at the expense of causing functional deficiency in the mother. 

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 impairment of glutathione reductase activity may result in lower availability of glutathione in erythrocytes and hence a more oxidizing environment, which is hostile to the parasites. 

Glutathione reductase is especially sensitive to riboflavin depletion, in deficient animals, the activity of glutathione reductase responds earlier and more markedly than any other index of riboflavin stams apart from liver concentrations of flavin coenzymes and the activity of hepatic flavokinase (Prentice and Bates, 1981a, 1981b). The activity of the enzyme in erythrocytes can therefore be used as an index of riboflavin status. 

Like glutathione reductase, pyridoxine oxidase is sensitive to riboflavin depletion. In normal subjects and in experimental animals, the EGR and pyridoxine oxidase activation coefficients are correlated, and both reflect riboflavin nutritional status. In subjects with glucose 6-phosphate dehydrogenase deficiency, there is an apparent protection of EGR, so that even in riboflavin deficiency it does not lose its cofactor, and the EGR activation coefficient remains within the normal range. The mechanism of this protection is unknown. In such subjects, the erythrocyte pyridoxine oxidase activation coefficient gives a response that mirrors riboflavin nutritional status (Clements and Anderson, 1980). 

Prentice AM and Bates CJ (1981a) A biochemical evaluation of the erythrocyte glutathione reductase (EC 1.6.4.2) test for riboflavin status. 1. Rate and specificity of response in acute deficiency. British Journal of Nutrition 45,37-52. 

Saubcriich, H. E., Judd, J. H., Nichoalds, C. F.., Broquist, H. P, and Darby, W. J, (1972). Application of the erythrocyte glutathione reductase assay in evaluating riboflavin status in a high school student population. Am. /. Cfjri. Nutr, 25, 756-762. 

In 15 patients who had a serious adverse reaction to valproate (including behavioral changes and emesis in six, raised aspartate transaminase in three, raised aspartate transaminase and pancreatitis in one, thombocytopenia in two, and unexpected death in two), erythrocyte glutathione peroxidase activity and plasma selenium and zinc concentrations were significantly reduced, whereas erythrocyte glutathione reductase activity was significantly raised... 

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