Association between the plasma proteome and serum ascorbic acid concentrations in humans.

Vitamin C has been associated with a reduced risk of chronic diseases, but the biological pathways regulated by vitamin C are not all known. The objective was to use a proteomics approach to identify plasma proteins associated with circulating levels of ascorbic acid. Men and women (n=1022) 20-29 years of age from the Toronto Nutrigenomics and Health Study completed a general health and lifestyle questionnaire and a 196-item food frequency questionnaire and provided a fasting blood sample. Circulating ascorbic acid was analyzed by high-performance liquid chromatography, and a mass-spectrometry-based multiple reaction monitoring method was used to measure 54 proteins abundant in plasma that are involved in numerous physiologic pathways. Mean protein concentrations were compared across tertiles of serum ascorbic acid using analysis of covariance adjusted for sex, ethnocultural group, season of blood draw, hormonal contraceptive use among women, waist circumference and tertiles of plasma α-tocopherol. A Bonferroni significance level of P<.0009 was applied, and analyses were adjusted for multiple comparisons using the Tukey-Kramer procedure. Levels of complement C9, ceruloplasmin, alpha-1-anti-trypsin, angiotensinogen, complement C3, vitamin D binding protein and plasminogen were inversely associated with levels of ascorbic acid. The inverse association between ascorbic acid and vitamin D binding protein was highest in those with higher levels of serum 25-hydroxyvitamin D. In conclusion, several plasma proteins from various physiologic pathways are significantly associated with circulating levels of ascorbic acid. These findings suggest that vitamin C may have novel physiological effects.