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Original Article

Proliferation of Peripheral Blood Mononuclear Cells Increases Riboflavin Influx

Department of Pediatrics, University of Arkansas for Medical Sciences and the Arkansas Children's Hospital Research Institute, Little Rock, Arkansas 72202

Previously we demonstrated that proliferation of peripheral blood mononuclear cells (PBMC) causes a five-fold increase in cellular uptake of biotin; this increase is mediated by an increased number of biotin transporters on the PBMC surface. In the present study, we investigated the specificity of this phenomenon by determining whether the cellular uptake of riboflavin also increases in proliferating PBMC and whether the increase is also mediated by an increased number of transporters per cell. We characterized [³H]riboflavin uptake in both quiescent and proliferating PBMC. In quiescent PBMC, [³H]riboflavin uptake exhibited saturation kinetics and was reduced by addition of unlabeled riboflavin (P < 0.05) or lumichrome (P < 0.01). These observations are consistent with transporter-mediated uptake. [³H]Riboflavin uptake was reduced at 4°C compared with 37°C (P < 0.01) and by 2,4-dinitrophenol (P < 0.05) but not by ouabain or incubation in sodium-free medium. These data provide evidence for an energy-dependent but sodium-independent transporter. Proliferating PBMC accumulated approximately four times more [³H]riboflavin than quiescent PBMC (P < 0.05). Because both transporter affinity and transporter number per cell (as judged by maximal transport rate) were similar in quiescent and proliferating PBMC, we hypothesize that the increased riboflavin uptake by proliferating PBMC reflects only increased cellular volume. To test this hypothesis, PBMC volume was reduced using hyperosmolar medium; [³H]riboflavin uptake decreased to about 50% of isotonic controls (P < 0.01). Thus we conclude that proliferating PBMC increase cellular content of riboflavin and biotin by two different mechanisms.

This article has been cited by other articles:

				K. C. Manthey, Y. C. Chew, and J. Zempleni Riboflavin Deficiency Impairs Oxidative Folding and Secretion of Apolipoprotein B-100 in HepG2 Cells, Triggering Stress Response Systems J. Nutr., May 1, 2005; 135(5): 978 - 982. [Abstract] [Full Text] [PDF]

				J. Zempleni, R. M. Helm, and D. M. Mock In Vivo Biotin Supplementation at a Pharmacologic Dose Decreases Proliferation Rates of Human Peripheral Blood Mononuclear Cells and Cytokine Release J. Nutr., May 1, 2001; 131(5): 1479 - 1484. [Abstract] [Full Text]