Plasma riboflavin

As shown in Table 7.1, the total riboflavin concentration in plasma is very much lower than in most tissues. About 50% of plasma riboflavin is free riboflavin, which is the main transport form, with 44% as FAD and the remainder as riboflavin phosphate. The vitamin is largely protein bound in plasma free riboflavin binds to both albumin and a- and /3-globulins, and both riboflavin and the coenzymes also bind to immunoglobulins. The products of photolysis of riboflavin bind to albumin with considerably higher affinity than riboflavin itself this albumin binding may represent a mechanism to prevent tissue... 

In laying hens, induction of this riboflavin protein results in a 100-fold increase in plasma riboflavin, compared with males or nonlaying females. In mutant chickens lacking the protein, the adult has massive urinary loss of riboflavin. The embryo develops normally for about 10 days, then develops severe hypoglycemia associated with a reduction in medium-chain acyl coenzyme A (CoA) dehydrogenase to 20% of normal activity and the accumulation of intermediates of fatty acid oxidation (White, 1996). 

Fig. 3 Mean plasma riboflavin concentrations following the administration of 100 mg riboflavin-5-phosphate as the CR-GRDF, CR-DF, or as drug solution to the Beagle dogs (n = 6). (From Ref...

Fritz I, Said H, Harris C, et al. A new sensitive assay for plasma riboflavin using high performance liquid chromatography. J Am Coll Nutr 1987 6 454. 

In a small study of children on PHT, their mean urinary excretion of riboflavin was low, i.e. 14% of dietary intake. This may indicate riboflavin deficiency (Lewis et at. 1998). Patients on inducer AEDs (PHT, PB, PRD and CBZ) have low plasma riboflavin (Apeland et at. 2003 Krause et at. 1988). Low plasma riboflavin may indicate increased risk of vitamin B2 deficiency. Furthermore, patients with low plasma riboflavin also have elevated plasma flavin nucleotides (Apeland et at. 2003). 

Chlorophyll studies of adducts with various biological molecules are also known (bovine plasma albumin and (3-carotene [195], quinone riboflavin [196], and NADH [173]. Mitsui et al. [196] have shown that in porphyrin complexes of viologen the counterion (I-, C1-, Br-) affects the electron transfer process by reduction of the electron-accepting properties of viol-... 

Tucker et al. showed that both sudden severe physical exercise and longer sustained work on a treadmill during training decreases urinary riboflavin excretion during the experimental periods (12) The acute reduction in riboflavin excretion observed by these investigators was attributed to a reduction in renal plasma flow. In order to explain the long-term reduced excretion of the vitamin, they proposed that riboflavin was retained for incorporation into "new muscle tissue". The significance of this study is that if the hypotheses... 

FAD and riboflavin phosphate in foods are hydrolyzed in the intestinal lumen by nucleotide diphosphatase and a variety of nonspecific phosphatases to yield free riboflavin, which is absorbed in the upper small intestines by a sodium-dependent saturable mechanism the peak plasma concentration is related to the dose only up to about 15 to 20 mg (40 to 50 /xmol). Thereafter,... 

Riboflavin and riboflavin phosphate that are not bound to plasma proteins are filtered at the glomerulus the phosphate is generally dephosphorylated in the bladder. Renal tubular reabsorption of riboflavin is saturated at normal plasma concentrations, and there is also active tubular secretion of the vitamin, so that urinary clearance of riboflavin can be two- to three-fold greater than the glomerular filtration rate. 

Neonatal hyperbilirubinemia is normally treated by phototherapy. The peak wavelength for photolysis of bilirubin is 450 nm, the same as that for photolysis of riboflavin (Section 7.1). Infants undergoing phototherapy show biochemical evidence of riboflavin depletion, with a significant increase in the EGR activation coefficient. Provision of additional riboflavin to maintain plasma concentrations enhances the photolysis of bilirubin, apparently as a result of reactive oxygen radicals generated by the products of photolysis of riboflavin. 

There is some evidence that riboflavin status affects the stability of the thermolab ile variant of methylene tetrahydrofolate reductase (Section 10.3.2.1), and that supplements of riboflavin may lower plasma homocysteine (Section 10.3.4.2) in people who are homozygous for the variant enzyme (McNulty et al., 2002). 

Kodentsova VM, Vrzhesinskaya OA, and SpirichevVB (1995) Eluorometric riboflavin titration in plasma by riboflavin-binding apoprotein as a method for vitamin B2 status assessment. Amnals of Nutrition and Metabolism 39,355-60. 

NokuboM, OhtaM,KitaniK,andNagyI (1989) Identification ofprotein-bound riboflavin in rat hepatocyte plasma membrane as a source of autofluorescence. Biochimica et Biophysica Acta 981, 303-8. 

Innis WS, McCormick DB, Merrill AH Jr. Variations in riboflavin binding by human plasma identification of immunoglobulins as the major proteins responsible. Biochem. Med. 1985 34(2) 151-165. 

Merrill, A. H., Frochlich, J. A-, and McCormick, D. D. (1979). Purification of riboflavin-binding proteins from bovine plasma and discovery of a pregnancy-specific riboflavin-binding protein,. Bioi. Chem. 254,9362-9.364. 

When comparing the plasma concentrations of riboflavin following its administration as a CR-GRDF, oral solution or a CR formulation it can be clearly observed the significant increase of the duration of plasma levels obtained by the GRDF as shown in Fig. 

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. 

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