Volume 87, Issue 2, February (2002), pp. 97-100 © The Author 2002
doi:10.1079/BJN2001492

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Short communication

Decreased expression of the vitamin C transporter SVCT1 by ascorbic acid in a human intestinal epithelial cell line

Lauren MacDonald, Alfred E.Thumser and Paul Sharp*
Centre for Nutrition and Food Safety, School of Biomedical and Life Sciences, University of Surrey, Guildford GU2 7XH, UK

 (Received 30 April 2001–Revised 24 July 2001–Accepted 4 October 2001) Vitamin C (ascorbic acid) is an essential nutrient that is involved in a number of cellular processes. However, unlike most mammals, man is unable to synthesize vitamin C and it must therefore be acquired from the diet. Absorption of vitamin C is achieved by two transporters, SVCT1 and SVCT2, recently cloned from rat and human kidney. SVCT1 is thought to be the predominant transporter in the intestine. Vitamin C supplements are increasingly common, thus contributing to an increased dietary load, and therefore the aim of the present study was to investigate the effect of high doses of ascorbic acid on SVCT1 expression. Using the Caco-2 TC7 cell model of small intestinal enterocytes, we measured the effects of ascorbic acid (4·5 mg/ml culture medium) on L-[¹⁴C]ascorbic acid uptake and SVCT1 expression (determined by reverse transcription-polymerase chain reaction). Ascorbic acid uptake was decreased significantly in Caco-2 TC7 cells exposed to ascorbate for 24 h (-50 %, P<0·0005). Expression of SVCT1 was also significantly reduced by exposure to elevated levels of ascorbate for 24 h (-77 %, P<0·005). Taken together these results suggest that high-dose supplements might not be the most efficient way of increasing the body pool of vitamin C.

Keywords:
Ascorbic acid: Absorption: Transporters: supplements