Background Vitamin C is an essential element required for normal metabolic function. We investigated the effect of vitamin C supplementation on circulating miRNA (miR) expression in subjects with poorly controlled type 2 diabetes mellitus (T2DM). Changes in miR expression were also correlated with clinical measures of disease. Methods Pre- and post-vitamin C supplementation samples from five participants who had increased vitamin C levels, improved oxidative status and polymorphonuclear (PMN) function after receiving 1,000 mg of vitamin C daily for six weeks were screened for miRNA expression using the NanoString miRNA assay. Differences in miRNA expression identified from the miRNA screen were validated by qRT-PCR. Results Four miRNAs showed significantly different expression post-vitamin C supplementation relative to baseline, including the down-regulation of miR-451a (−1.72 fold change (FC), p = 0.036) and up-regulation of miR-1253 (0.62 FC, p = 0.027), miR-1290 (0.53 FC, p = 0.036) and miR-644a (0.5 FC, p = 0.042). The validation study showed only miR-451a expression was significantly different from baseline with vitamin C supplementation. MiR-451a expression was negatively correlated with vitamin C levels (r =  − 0.497, p = 0.049) but positively correlated with levels of malondialdehyde (MDA) (r = 0.584, p = 0.017), cholesterol (r = 0.564, p = 0.022) and low-density lipoproteins (LDL) (r = 0.522, p = 0.037). Bioinformatics analysis of the putative target genes of miR-451a indicated gene functions related to signaling pathways involved in cellular processes, such as the mammalian target of rapamycin (mTOR) signaling pathway. Conclusions Vitamin C supplementation altered circulating miR-451a expression. The results from this pilot study suggest that miRNAs could be used as biomarkers to indicate oxidative status in subjects with T2DM and with poor glycemic control and could lead to a novel molecular strategy to reduce oxidative stress in T2DM.

Vitamin C (ascorbic acid, ascorbate) promotes immune cell activities by supporting various cellular functions especially, in neutrophils or polymorphonuclear (PMN) leukocytes, which play an important role in bacterial infection and acute inflammation. Little data have been reported in impact of vitamin C on PMN function during bacterial phagocytosis in healthy individuals. Here, we have elucidated the effect of vitamin C on PMN phagocytosis and oxidative burst to Staphylococcus aureus by whole blood assay and flow cytometry after pre-incubation without and with vitamin C in vary concentrations. The results showed that vitamin C concentration at 20 mM induced a significant increase phagocytosis (p-value=0.03) and had trend to significant increase oxidative burst (p-value=0.06) while vitamin C concentration of 30 mM showed significant increase both phagocytosis and oxidative burst (p-value=0.04 and 0.02, respectively) at only 15 min of exposure to the bacteria. As a minimal concentration that can increase phagocytosis, we selected vitamin C at 20 mM as optimal concentration to investigate more data by enrollment of healthy volunteers (n=17). The results revealed significant difference both phagocytosis and oxidative burst after 20 mM vitamin C pre-incubation (p<0.0001). In conclusion, we showed that vitamin C at 20 mM can boost phagocytosis and oxidative burst of neutrophils in healthy adults within 15 min after bacterial exposure. This rapid activation may be applied to fight bacterial infection. Nevertheless, further research in clinical trial and underlying mechanisms await further studies.