Cellular mechanisms by which proinsulin C-peptide prevents insulin-induced neointima formation in human saphenous vein

Abstract

Aims/hypothesisEndothelial cells (ECs) and smooth muscle cells (SMCs) play key roles in the development of intimal hyperplasia in saphenous vein (SV) bypass grafts. In diabetic patients, insulin administration controls hyperglycaemia but cardiovascular complications remain. Insulin is synthesised as a pro-peptide, from which C-peptide is cleaved and released into the circulation with insulin; exogenous insulin lacks C-peptide. Here we investigate modulation of human SV neointima formation and SV-EC and SV-SMC function by insulin and C-peptide.MethodsEffects of insulin and C-peptide on neointima formation (organ cultures), EC and SMC proliferation (cell counting), EC migration (scratch wound), SMC migration (Boyden chamber) and signalling (immunoblotting) were examined. A real-time RT–PCR array identified insulin-responsive genes, and results were confirmed by real-time RT–PCR. Targeted gene silencing (siRNA) was used to assess functional relevance.ResultsInsulin (100 nmol/l) augmented SV neointimal thickening (70% increase, 14 days), SMC proliferation (55% increase, 7 days) and migration (150% increase, 6 h); effects were abrogated by 10 nmol/l C-peptide. C-peptide did not affect insulin-induced Akt or extracellular signal-regulated kinase signalling (15 min), but array data and gene silencing implicated sterol regulatory element binding transcription factor 1 (SREBF1). Insulin (1–100 nmol/l) did not modify EC proliferation or migration, whereas 10 nmol/l C-peptide stimulated EC proliferation by 40% (5 days).Conclusions/interpretationOur data support a causative role for insulin in human SV neointima formation with a novel counter-regulatory effect of proinsulin C-peptide. Thus, C-peptide can limit the detrimental effects of insulin on SMC function. Co-supplementing insulin therapy with C-peptide could improve therapy in insulin-treated patients.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-010-1736-6) contains supplementary material, which is available to authorised users.

C-peptide and the risk for incident complications and mortality in type 2 diabetic patients: a retrospective cohort study after a 14-year follow-up

“…Some studies have demonstrated the beneficial effects of C-peptide on vessels by inhibiting smooth muscle cell proliferation and migration and antiinflammatory activity in endothelial cells (2,27,28). Other studies have revealed C-peptide deposition in the arteriosclerotic lesions of diabetic patients, chemotactic activity towards monocytes and CD4C lymphocytes and the induction of vascular smooth muscle cell proliferation (24,25).…”

“…It has been postulated that C-peptide normally acts as a counter-regulatory peptide towards the effects of insulin on vessels; the insulin/C-peptide relationship is perturbed when exogenous insulin is administered alone (28). In type 2 diabetes, the situation is more complex because of the coexistence of multiple cardiovascular risk factors, associated with increased C-peptide levels, the potential down-regulation of C-peptide receptors and the less clear interaction between insulin and C-peptide.…”

C-peptide reduces high-glucose-induced apoptosis of endothelial cells and decreases NAD(P)H-oxidase reactive oxygen species generation in human aortic endothelial cells

“…Moreover, pancreas or islet transplantation, with restoration of endogenous insulin and C-peptide secretion, is known to be accompanied by improvement of diabetes-induced abnormalities of nerve function, endothelial function and both structural and functional changes of the kidneys [37,38]. C-peptide has been shown to display anti-inflammatory activity on endothelial cells exposed to a variety of damaging insults and to be beneficial in endothelial dysfunction during type 1 diabetes [39]. In this regard, pretreatment with C-peptide to rats injected with the inflammatory agents thrombin or N w -nitro-L-arginine methyl ester (L-NAME), which cause acute endothelial dysfunction, resulted in reduced expression of intercellular cell adhesion molecule (ICAM)-1 and P-selectin on the mesenteric microvascular endothelium [28].…”

Proinsulin C-peptide activates α-enolase: implications for C-peptide–cell membrane interaction

“…For example, C-peptide prevents insulin-induced neointima formation [19] and reduces hyperglucose-induced proliferation of vascular smooth muscle cells [3,20].…”

“…When given to patients or animals with type 1 diabetes mellitus, C-peptide decreases glomerular hyperfiltration [6][7][8][9][10], diminishes urinary excretion of albumin [7][8][9][10], reduces urinary sodium waste [11] and induces body weight gain regardless of hyperglycemia and glycosuria [11,12]. Moreover, C-peptide lowers the leakage of albumin or fluorescein across the blood-retina barrier [13], increases glucose uptake in skeletal muscle [14,15] and improves autonomic nerve and microvascular functions [6,7,13,14,[16][17][18].More recently, anti-inflammatory properties of C-peptide have been demonstrated.For example, C-peptide prevents insulin-induced neointima formation [19] and reduces hyperglucose-induced proliferation of vascular smooth muscle cells [3,20].Additionally, C-peptide replacement reduces diabetes-induced upregulation of RAGE expression, and activation of NF-κB and of pro-inflammatory factors in hippocampi [21]. C-peptide treatment improves the survival rate after acute endotoxemia, with reduction of pro-inflammatory cytokines [22].…”