We and others demonstrated that insulin C-peptide has biological activities and may prevent tissue damages by diabetes. Our research using STZ diabetic rats and other models suggested that diabetic vascular dysfunctions, e.g., increased vascular permeability and blood flows are caused by oxidative and nitrosative stress initiated from increased NADH redox (reductive stress). However, C-peptide prevented dysfunctions without normalizing redox state and worked in nondiabetic rats. In this study, we further examined modes of actions and investigated its mechanisms. Male Wistar rats were used in animal study. Human de-differentiated adipocytes (DFAT cells) were used for cell culture study. Lentivirus vector expressing LC3-GFP was created to assess autophagy. Regional blood flow was assessed using microsphere. Acute hyperglycemia induced by glucose infusion for 5 hours resulted in increased regional blood flows in retina, sciatic nerve and kidney. Simultaneous infusion of C-peptide up to 16 mg/kg did not prevent the increases, while twice daily subcutaneous injection of 400 µg/kg for 2-days prior to infusion prevented completely. One-day injection was only slightly effective. Bolus i.v. injection of L-lactate 1 mol/kg but not NaCl caused reductive stress and blood flow increase, and this was also prevented by twice daily 2-days injection of C-peptide. Thus, C-peptide appeared to induce some factors counteracting oxidative stress during 2 days. In DFAT cells, LC3-GFP puncta was increased 3-fold by one time 100 nM C-peptide treatment in 1 hour. This was followed by nuclear localization of Nrf2 transcription factor at 2 hours. At 4 hour, 4-fold increase in Nrf2 target genes, IDH and SRXN1, expression were observed (p<0.05). Similar 35-62% increase in Nrf2 target genes (Idh, Srxn1, Pgd and Hmox) were observed in rat aorta after twice daily 2-days injection of C-peptide. These results suggest that injections of pharmacological dose of C-peptide increase Nrf2 antioxidants expression through activating autophagy.


F. Lan: None. Y. Lin: None. Z. Gao: None. P. Zhao: None. X. Zhang: None. Y. Shiraishi: None. Y. Ido: None.


Japan Society for the Promotion of Science

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