Plasma proteomics analysis of vitamin C supplementation in people with type 2 diabetes

Background Evidence from randomised controlled trials shows that vitamin C (VC) supplementation may improve cardiometabolic health outcomes in people with type 2 diabetes (T2D). Plasma proteomics may help to further enhance our understanding of VC’s therapeutic effects and biological mechanisms in T2D. Therefore, our aim was to explore the effects of VC supplementation on the plasma proteome in people with T2D. Methods A double-blind, placebo-controlled, cross-over trial was undertaken in people with T2D, who were administered 1000 mg/day VC or placebo for 4 months. Plasma proteins in 26 participants (22 male, 4 female, age 62.6±6.5 years, HbA1c 60±11 mmol/mol [7.6±0.7%]) were quantified by liquid chromatography/mass spectrometry with data independent acquisition. Differential protein expression was assessed for VC post-supplementation vs. control [pooling of all non-active conditions]. Results Twelve proteins were significantly downregulated and three were upregulated following VC supplementation (|log2-fold change [FC]|≥0.5; false discovery rate<0.05). These included proteins with functions in innate immunity, carbohydrate digestion, unfolded protein binding, and muscle contraction. Protein candidates that had the greatest magnitude decrease (|log2-FC|>1) with VC supplementation were alpha-amylase 1 (AMY1), heat shock protein 75kDa (TRAP1), myosin-1 (MYH1), and serum amyloid protein A1 (SAA1). Pathway enrichment revealed underrepresentation of unfolded protein binding, ATP binding, attenuation phase, and the innate immune system following VC supplementation. TRAP1, alpha-actin-1, Heat shock 70kDa protein-1, and CD166 antigen were associated with previously reported improved blood-pressure outcomes following VC supplementation. Conclusions VC supplementation significantly altered abundance of numerous proteins in plasma, with functions relating to the innate immune system, dietary carbohydrate digestion, and protein folding chaperone activity. We identified novel proteins responsive to VC supplementation and protein-clinical improvement correlations in people with T2D that require further exploration to understand their biological significance.