Effects of C-peptide on expression of eNOS and iNOS in human cavernosal smooth muscle cells
Haikun Li1, Liping Xu, Joseph C Dunbar
1Department of Urology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
Objectives:
To investigate the role of C-peptide alone or in conjunction with insulin on the expression of nitric oxide synthase (NOS) in human corpus cavernosum smooth muscle cells (HCSMCs). Erectile dysfunction, among diabetic patients, is a significant health problem. The specific causes of erectile dysfunction are unknown. It has been suggested that impairment of penile relaxation is related to a reduction of penile NOS. Plasma levels of C-peptide and insulin are decreased in individuals with type 1 diabetes and late-stage type 2 diabetes.
Methods:
Primary cultures were initiated from explants of HCSMCs. Confluent cells at passages 2 to 4 were assigned to one of four groups with the following incubation conditions: (a) 27 mM glucose, (b) 27 mM glucose and insulin, (c) 27 mM glucose and human recombinant (hr)C-peptide, and (d) 27 mM glucose, insulin, and hrC-peptide. After 24 hours, total RNA and protein were extracted from cells and subjected to reverse transcriptase-polymerase chain reaction and Western blot analysis, respectively. Intracellular Ca(2+) was examined under the four conditions, using the Fura 2 method.
Results:
The least expression of endothelial NOS (eNOS) and inducible NOS (iNOS) in HCSMCs was observed in cells exposed to 27 mM glucose alone. Increased expression of eNOS and iNOS was found after treatment with insulin or hrC-peptide alone, and the maximal expression of eNOS and iNOS was detected in HCSMCs exposed to both insulin and hrC-peptide. Western blot analyses using eNOS and iNOS antibodies confirmed the RNA data. These effects are likely mediated by the insulin-induced and/or C-peptide-induced increase in intracellular Ca(2+).
Conclusions:
Our results demonstrated that C-peptide, in the presence of insulin, increases the expression of iNOS and eNOS in HCSMCs. These results suggest that C-peptide, especially in conjunction with insulin, may have beneficial effects on cavernosal smooth muscle relaxation.
Insights
C-peptide, particularly with insulin, boosts nitric oxide synthase (NOS) expression in human corpus cavernosum smooth muscle cells (HCSMCs). This finding suggests potential benefits for erectile dysfunction by improving cavernosal smooth muscle relaxation.
Area of Science:
- Endocrinology
- Molecular Biology
- Urology
Background:
- Erectile dysfunction (ED) is a significant health issue in diabetic patients, potentially linked to reduced penile nitric oxide synthase (NOS).
- Plasma levels of C-peptide and insulin are often decreased in diabetes, suggesting a role in ED pathogenesis.
- Understanding the molecular mechanisms of ED in diabetes is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the effect of C-peptide, alone or with insulin, on nitric oxide synthase (NOS) expression in human corpus cavernosum smooth muscle cells (HCSMCs).
- To explore the potential of C-peptide and insulin in modulating pathways relevant to erectile function.
Main Methods:
- Primary cultures of HCSMCs were established and treated with high glucose (27 mM) alone, or with added insulin, C-peptide, or both.
- Gene and protein expression of NOS isoforms (eNOS and iNOS) were analyzed using RT-PCR and Western blotting.
- Intracellular calcium levels were measured using the Fura 2 method.
Main Results:
- High glucose alone reduced eNOS and iNOS expression in HCSMCs.
- Treatment with insulin or C-peptide individually increased eNOS and iNOS expression.
- Combined treatment with insulin and C-peptide resulted in maximal eNOS and iNOS expression.
- Increased intracellular calcium levels were observed, suggesting a mediating role for this ion.
Conclusions:
- C-peptide, especially when combined with insulin, significantly enhances iNOS and eNOS expression in HCSMCs.
- These findings indicate that C-peptide may offer therapeutic benefits for erectile dysfunction by promoting cavernosal smooth muscle relaxation.
- The study highlights the potential role of C-peptide in managing diabetes-related erectile dysfunction.
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