Erythrocyte glutathion reductase activation

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. 

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... 

Urinary thiamine excretion Erythrocyte thiamine concentration Erythrocyte glutathione reductase activity Erythrocyte flavin... 

Sharada, D., and Bamji, M. S., Erythrocyte glutathione reductase activity and riboflavin concentration in experimental deficiency of some water soluble vitamins. Int. J. Vitam. Nutr. Res. 42, 43—49 (1972). 

Long, W. K., and Carson, P. E., 1961, Increased erythrocyte glutathione reductase activity in diabetes mellitus, Biochem. Biophys. Res. Commun. 5 394-399. 

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. 

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. 

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. 

The reference interval for eiythrocyte riboflavin using a fluorometric method is 10 to 50jig/dL (266 to 1330nmol/L). The reference interval for serum or plasma levels of riboflavin is 4 to 24 Lig/dL (106 to 638 nmol/L). Guidance reference intervals for the activation coefficient of erythrocyte glutathione reductase by FAD are 1.20 (adequacy), 1.21 to 1.40 (marginal deficiency), and 1.41 and above (deficiency)... 

Use of oral contraceptives may increase the dietary requirement for riboflavin. Riboflavin status can be evaluated from the activity of erythrocyte glutathione reductase, an FAD-requiring enzyme, before and after addition of exogenous FAD. A low initial activity or a marked stimulation by FAD (or both) is indicative of ariboflavi-nosis. 

A more specific type of chemical assay is based on enzymatic measurement of vitamin co-enzyme activity. This approach is designed to detect a vitamin deficiency in tissues, and is only feasible for those vitamins that serve as co-enzymes. For instance, thiamin depletion in a subject can be diagnosed by measuring the transketolase activity in red blood cells with and without the addition of thiamin pyrophosphate (TPP) in vitro. If TPP increases the activity by more than a given amount, thiamin deficiency is indicated. Similarly, a subnormal level of riboflavin is indicated in tissues if the activity of erythrocyte glutathione reductase is increased after the addition of flavin adenine dinucleotide (FAD). Erythrocyte transaminase activation by pyridoxal-5 -phosphate (PLP) can be measured to establish a deficiency of vitamin B . 

Washburn, M.P., and Wells, W.W. 1999. Identification of the dehydroascorbic acid reductase and thioltransferase (glutaredoxin) activities of bovine erythrocyte glutathione peroxidase. Biochem. Biophys. Res. Commun. 257 567-571. 

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). 

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. 

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