a1 School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK
a2 Genome Instability Group, Department of Cancer & Molecular Medicine, University of Leicester, Leicester LE2 7LX, UK
Ascorbate can act as both a reducing and oxidising agent in vitro depending on its environment. It can modulate the intracellular redox environment of cells and therefore is predicted to modulate thiol-dependent cell signalling and gene expression pathways. Using proteomic analysis of vitamin C-treated T cells in vitro, we have previously reported changes in expression of five functional protein groups associated with signalling, carbohydrate metabolism, apoptosis, transcription and immune function. The increased expression of the signalling molecule phosphatidylinositol transfer protein (PITP) was also confirmed using Western blotting. Herein, we have compared protein changes elicited by ascorbate in vitro, with the effect of ascorbate on plasma potassium levels, on peripheral blood mononuclear cell (PBMC) apoptosis and PITP expression, in patients supplemented with vitamin C (0–2 g/d) for up to 10 weeks to investigate whether in vitro model systems are predictive of in vivo effects. PITP varied in expression widely between subjects at all time-points analysed but was increased by supplementation with 2 g ascorbate/d after 5 and 10 weeks. No effects on plasma potassium levels were observed in supplemented subjects despite a reduction of K+ channel proteins in ascorbate-treated T cells in vitro. Similarly, no effect of vitamin C supplementation on PBMC apoptosis was observed, whilst ascorbate decreased expression of caspase 3 recruitment domain protein in vitro. These data provide one of the first demonstrations that proteomics may be valuable in developing predictive markers of nutrient effects in vivo and may identify novel pathways for studying mechanisms of action in vivo.
(Received January 04 2008)
(Revised June 09 2008)
(Accepted August 06 2008)
(Online publication October 24 2008)
p1 Present address: Birmingham University Dental School, UK.
p2 Present address: School of Health, Cranfield University, UK.
Abbreviations: PITP, phosphoinositol transfer protein; PBMC, peripheral blood mononuclear cell; Tris, 2-amino-2-hydroxymethyl-1,3-propanediol; TTBS, Tween Tris-buffered saline