Dietary analysis and nutritional behaviour in people with and without age-related macular disease

Background and Aims: Consumption of antioxidant nutrients can reduce the risk of progression of age-related macular degeneration (AMD) - the leading cause of visual impairment in adults over the age of 50 years in the UK. Lutein and zeaxanthin (L&Z) are of particular interest because they are selectively absorbed by the central retina. The objectives of this study were to analyse the dietary intake of a group of AMD patients, assess their ability to prepare and cook healthy food, and to make comparisons with people not affected by AMD. Methods: 158 participants with AMD were recruited via the UK charity The Macular Society, and fifty participants without AMD were recruited from optometric practice. A telephone interview was conducted by trained workers where participants completed a 24 hour food diary, and answered questions about cooking and shopping capabilities. Results: In the AMD group, the average L&Z intake was low in for both males and females. Those able to cook a hot meal consumed significantly more L&Z than those who were not able. Most participants were not consuming the recommended dietary allowance of fibre, calcium, vitamin D and E, and calorific intake was also lower than recommendations for their age-group. The non-AMD group consumed more kilocalories and more nutrients than the AMD group, but the L&Z intake was similar to those with AMD. The main factor that influenced participant’s food choices was personal preference. Conclusion: For an ‘informed’ population, many AMD participants were under-consuming nutrients considered to be useful for their condition. Participants without AMD were more likely to reach recommended daily allowance values for energy and a range of nutrients. It is therefore essential to design more effective dietary education and dissemination methods for people with, and at risk of, AMD.

In vivo vitamin C supplementation increases phosphoinositol transfer protein expression in peripheral blood mononuclear cells from healthy individuals

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.

Novel repair action of vitamin C upon in vivo oxidative DNA damage

There appears to be a paucity of data examining the effect of dietary antioxidants on levels of oxidative DNA damage in vivo, limiting evidence-based assessment of antioxidant efficacy, mechanisms and recommendation for optimal intake. We have examined levels of 8-oxo-2'-deoxyguanosine (8-oxodG) in mononuclear cell DNA, serum and urine from subjects undergoing supplementation with 500 mg/day vitamin C. Significant decreases in DNA levels of 8-oxodG were seen, correlating strongly with increases in plasma vitamin C concentration. Furthermore we established a timecourse for sequential, significant increases in serum and urinary 8-oxodG levels. These results illustrate, for the first time in humans, the kinetics of 8-oxodG removal and processing in vivo, suggesting a role for vitamin C in the regulation of DNA repair enzymes and thereby demonstrating a non-scavenging antioxidant effect.

Vitamin C exhibits pro-oxidant properties

Vitamin C is marketed as a dietary supplement, partly because of its 'antioxidant' properties. However, we report here that vitamin C administered as a dietary supplement to healthy humans exhibits a pro-oxidant, as well as an antioxidant, effect in vivo.

Dietary supplementation with vitamin C but not vitamin E reduces constitutive expression of ICAM-1 in peripheral blood monocytes of normal subjects with low plasma vitamin C levels

Monocytes play a central role in inflammatory responses through systemic antigen presentation and cytokine secretion. Regulation of monocyte adhesion molecule and inflammatory gene expression is via redox sensitive transcription factors. Therefore we have investigated the hypothesis that dietary antioxidant supplementation with vitamins C (250mg/d) or E (400iU/d) for six weeks can modulate monocyte ICAM-1 expression in healthy male subjects with low plasma vitamin C at baseline. In a randomised, double-blind, crossover study, ICAM-1 mRNA and protein was analysed using quantitative RTPCR with ELISA measurement of PCR products and by flow cytometry and ELISA respectively. Monocyte numbers were unaltered by supplementation. Subjects with low plasma vitamin C (<50uM) prior to supplementation expressed higher levels of monocyte ICAM-1 mRNA, and showed a significant (50%) reduction in ICAM-1 mRNA expression after 6 weeks of 250mg/d vitamin C supplementation compared to subjects with normal plasma vitamin C. This was paralleled by a reduction in plasma sICAM-1. Vitamin E supplementation had no effect on ICAM-1 expression. For the first time, these results show that dietary vitamin C can modulate monocyte ICAM-1 gene expression in vivo, where regulation of gene expression represents a novel mechanism for benefit from dietary antioxidants.

Deoxycytidine glyoxal:Lesion induction and evidence of repair following vitamin C supplementation in vivo

Oxidative DNA damage is postulated to be involved in carcinogenesis, and as a consequence, dietary antioxidants have received much interest. A recent report indicates that vitamin C facilitates the decomposition of hydroperoxides in vitro, generating reactive aldehydes. We present evidence for the in vivo generation of glyoxal, an established product of lipid peroxidation, glucose/ascorbate autoxidation, or free radical attack of deoxyribose, following supplementation of volunteers with 400 mg/d vitamin C. Utilizing a monoclonal antibody to a deoxycytidine-glyoxal adduct (gdC), we measured DNA lesion levels in peripheral blood mononuclear cells. Supplementation resulted in significant (p = .001) increases in gdC levels at weeks 11, 16, and 21, with corresponding increases in plasma malondialdehyde levels and, coupled with previous findings, is strongly suggestive of a pro-oxidative effect. However, continued supplementation revealed a highly significant (p = .0001) reduction in gdC levels. Simultaneous analysis of cyclobutane thymine dimers revealed no increase upon supplementation but, as with gdC, levels decreased. Although no single mechanism is identified, our data demonstrate a pro-oxidant event in the generation of reactive aldehydes following vitamin C supplementation in vivo. These results are also consistent with our hypothesis for a role of vitamin C in an adaptive/repair response and indicate that nucleotide excision repair specifically may be affected. © 2003 Elsevier Science Inc.