Riboflavin blood

Rice bran is the richest natural source of B-complex vitamins. Considerable amounts of thiamin (Bl), riboflavin (B2), niacin (B3), pantothenic acid (B5) and pyridoxin (B6) are available in rice bran (Table 17.1). Thiamin (Bl) is central to carbohydrate metabolism and kreb s cycle function. Niacin (B3) also plays a key role in carbohydrate metabolism for the synthesis of GTF (Glucose Tolerance Factor). As a pre-cursor to NAD (nicotinamide adenine dinucleotide-oxidized form), it is an important metabolite concerned with intracellular energy production. It prevents the depletion of NAD in the pancreatic beta cells. It also promotes healthy cholesterol levels not only by decreasing LDL-C but also by improving HDL-C. It is the safest nutritional approach to normalizing cholesterol levels. Pyridoxine (B6) helps to regulate blood glucose levels, prevents peripheral neuropathy in diabetics and improves the immune function. 

Later in the Second World War, Bradford worked at the Charterhouse Rheumatism Clinic, London, from where she coauthored papers on winter sources of vitamin C and on the determination of riboflavin in blood. After the war, she was employed by J. C. Lyons Co. Ltd., from where she authored four papers for The Analyst two on riboflavin in tea, one on the microbiological assay of vitamins, and one on the use of a single tap source to simultaneously run three different applications. Later in life, Bradford married Mr. Bentley and became a Consultant. She died on 20 August 1981, aged 79 years. 

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. 

Inadequate saturation of enzymes with (vitamin-derived) coenzymes. This can be tested for three vitamins, using red blood cell enzymes thiamin (Section 6.5.3), riboflavin (Section 7.5.2), and vitamin Be (Section 9.5.3). 

Photolysis of riboflavin leads to the formation of lumiflavin in alkaline solution and lumichrome in acidic or neutral solution (see Figure 7.2). Because lumiflavin is chloroform extractable, photolysis in alkaline solution, followed by chloroform extraction and fluorimetric determination, is the basis of commonly used chemical methods of assaying riboflavin. The photolysis proceeds by way of intermediate formation of cytotoxic riboflavin radicals, and the addition of riboflavin and exposure to light has been suggested as a means of inactivating vimses and bacteria in blood products (Goodrich, 2000). 

Goodrich RP (2000) The use of riboflavin for the inactivation of pathogens in blood products. Vbx Sang78(Suppl 2), 211-15. 

Urinary excretions of nicotinic acid metabolites and 2-pyridone, as well as of 4-pyridoxic and xanthurenic acids were determined in 15 South African Bantu pellagrins before and after tryptophan administration (P13). Red blood cell riboflavine levels and serum glutamic-oxalacetic transaminase levels were also measured. The authors discussed the apparent inability of the pellagra patients to convert tryptophan to nicotinic acid as indicated by their low excretion of nicotinic acid metabolites before and after tryptophan load. The possibility that the subjects were also suffering from a riboflavine deficiency was also discussed. 

Flavins are lost from the body as intael riboflavin, rather than as a breakdown product of riboflavin. Hence, vitamin status may be assessed by measuring the level of urinary riboflavin. Generally, the loss of 30 ig of riboflavin/g creatinine or less per day indicates a deficiency. This metht>d of assessment is not preferred because it is influenced by a number of factors unrelated to vitamin status. Another problem with this method is its great sensitivity to a short-term deficiency thus, it does not necessarily reflect the true concentrations of FAD and FMN in tissues. The most reliable way to assess riboflavin status is by a functional test. The test involves the assay of glutathione reductase, using red blood cells as the source of... 

Glutathione is discussed further in the section on selenium and glutathione in Chapter 10. The enzyme assay is conducted using glutathione reductase extracted from red blood cells with and without added FAD. Chmnic consumption of a diet deficient in riboflavin allows the continued synthesis of a variety of flavoproteins, but results in the accumulation of apoenzyme without its conversion to holoen-zyme. Addition of chemically pure FAD to a biological fluid containing apoenzyme results In the stimulation of enzyme activity because of the formation of the holoenzyme. It is this stimulation of enzyme activity that is used to determine vitamin status in humans. 

The existence of apoenzyme and holoenzyme forms of various enzymes is of use to the clinician. The proportion of a specific enzyme occurring in apoenzyme and holoenzyme forms is used to assess vitamin status in the cases of vitamin Bg, thiamin, and riboflavin. Vitamin status is determined by measuring the percentage stimulation of enzyme activity that occurs after adding the appropriate cofactor to a biological sample (blood) containing the enz3me of interest. 

Zempleni, J. Galloway, J.R. McCormick, D.B. The identification and kinetics of 7a-hydroxyriboflavin (7-hydroxymethylriboflavin) in blood plasma from humans following oral administration of riboflavin supplements. Int. J. Vitam. Nutr. Res. 1996, 66, 151-157. 

Knoblock E, Hodr R, Janda J, et al. Spectrofluorimet-ric micromethod for determining riboflavin in the blood of newborn babies and their mothers. Int J Vitam Nutr Res 1979 49 144-51. 

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