Serum C-peptide level as a predictor of atherosclerosis and cardiovascular disease in type 2 diabetes mellitus

CL Nawal; Laxmi Kant Goyal; Vinay Kumar; Akhil Gautam; Abhishek Agrawal; Pradeep Mital

doi:10.4103/0971-9903.178075

ORIGINAL ARTICLE

Year : 2016 | Volume : 21 | Issue : 1 | Page : 25-29

Serum C-peptide level as a predictor of atherosclerosis and cardiovascular disease in type 2 diabetes mellitus

CL Nawal, Laxmi Kant Goyal, Vinay Kumar, Akhil Gautam, Abhishek Agrawal, Pradeep Mital
Department of Medicine, SMS Medical College, Jaipur, Rajasthan, India

Date of Web Publication

4-Mar-2016

Correspondence Address:
C L Nawal
Bungalow No - 3, Gangwal Park, JNL Marg, Jaipur - 302 015, Rajasthan
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/0971-9903.178075

Abstract

Objective: To assess the correlation of serum C-peptide level to carotid intima media thickness (a surrogate marker of atherosclerosis) and risk of developing cardiovascular disease (CVD) in type 2 diabetes patients as determined by United Kingdom Prospective Diabetes Study (UKPDS) risk engine. Materials and Methods: About 101 cases of diabetes mellitus (DM) type 2 (diagnosed according to American Diabetes Association 2007 criteria) were subjected to detail clinical examination and laboratory investigations. The intima media thickness of both carotid arteries (CIMT) was measured for each patient with color Doppler. The risk of CVD was calculated using UKPDS risk engine. Observations: Age of subjects, glycated hemoglobin (HbA1c), body mass index (BMI), levels of systolic blood pressure (SBP), total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), low-DL (LDL), homocysteine, CIMT, and the 10 years CVD risk according to the UKPDS were significantly different across the C-peptide quartiles (P for trend <0.05). Significant positive correlations of C-peptide levels were found with age of subjects, duration of DM, BMI, fasting plasma glucose, HbA1c, SBP, TC, TG, LDL, and homocysteine. Significant negative correlation of C-peptide levels was observed with HDL. C-peptide levels had significant positive correlation with CIMT (atherosclerosis) and 10 years CVD risk (future CVD) by UKPDS risk engine. Conclusions: Serum C-peptide level seems to be significantly related to the development of atherosclerosis and future CVD in type 2 DM. It may be used as a predictor of subclinical atherosclerosis and CVD in these patients.

Keywords: Atherosclerosis, carotid intima media thickness, C-peptide, type 2 diabetes mellitus, United Kingdom Prospective Diabetes Study risk engine

How to cite this article:
Nawal C L, Goyal LK, Kumar V, Gautam A, Agrawal A, Mital P. Serum C-peptide level as a predictor of atherosclerosis and cardiovascular disease in type 2 diabetes mellitus. J Mahatma Gandhi Inst Med Sci 2016;21:25-9

How to cite this URL:
Nawal C L, Goyal LK, Kumar V, Gautam A, Agrawal A, Mital P. Serum C-peptide level as a predictor of atherosclerosis and cardiovascular disease in type 2 diabetes mellitus. J Mahatma Gandhi Inst Med Sci [serial online] 2016 [cited 2023 Mar 30];21:25-9. Available from: https://www.jmgims.co.in/text.asp?2016/21/1/25/178075

Introduction

Type 2 diabetes mellitus (DM) is characterized by a variable degree of insulin resistance, resulting in hyperinsulinemia and hyperglycemia. In Diabetes Control and Complications Trial study, achieving a euglycemic state was shown to be associated with a decrease in the diabetic complications without significantly reducing the risk of atherosclerosis or cardiovascular disease (CVD). ^[1] This suggests that there might be other factors leading to the development of CVD in diabetics. ^[2]

C-peptide, produced during formation of insulin from larger proinsulin molecule, is a small 31 amino acid co-secreted with insulin from the pancreas. Serum C-peptide levels reflect true insulin secretion from the pancreas. ^[3] C-peptide has been shown to be a biologically active molecule with pro-inflammatory properties. ^[4],[5] It favors vascular endothelial dysfunction, inflammatory cell proliferation, immune response, and smooth muscle cell proliferation. ^[4],[5],[6] All these features result in initiation of atherosclerosis and CVD in DM patients. ^[4],[5],[6]

United Kingdom Prospective Diabetes Study (UKPDS) risk engine is a well-accepted marker for assessment of 10 years CVD risk in DM subjects. ^[7]

This study was aimed to assess the correlation of serum C-peptide level to carotid intima media thickness (a surrogate marker of atherosclerosis) and risk of developing CVD in type 2 diabetes patients as determined by UKPDS risk engine.

Materials and Methods

This was a hospital based analytic-observational study conducted in the Department of Medicine of a tertiary care center in North India during the period from November 2011 to October 2012 among 101 established cases of type 2 DM (diagnosed according to American Diabetes Association 2007 criteria) ^[8] after approval of the Institutional Ethics Committee. The sample size was calculated by expecting correlation of 0.277 between C-peptide and HbA1c and accepting an alpha error of 0.05 and 80% power. It came out to be 100 subjects. ^[9]

Informed consent was taken from all the study participants. Patients who had hepatic impairment, serum creatinine ≥1.4 mg/dl, evidence of any ongoing infection, taking statin, history of ischemic heart disease (IHD)/stroke, electrocardiographic changes suggestive of IHD, basal C-peptide <0.5 ng/ml, or who did not given informed consent were excluded from the study.

After detailed history and thorough clinical examination, blood pressure (BP) was measured in right arm in supine position by a mercury sphygmomanometer. Anthropometric parameters viz. height, weight, body mass index (BMI), and waist circumference were taken.

After overnight fasting, blood samples of the patients were drawn and sent for complete blood count, fasting plasma glucose (FPG), urea, creatinine, uric acid, SGOT, SGPT, glycated hemoglobin (HbA1c), total lipid profile, homocysteine, and basal C-peptide estimation. Plasma glucose was measured with glucose oxidase technique on an automated analyzer. HbA1c was measured by chromatography analyzer (turbidimetric high performance liquid chromatography method). Total lipids were estimated by sulfo-phospho-vanillin assay a colorimetry based method. Total cholesterol (TC), high-density lipoprotein (HDL), low-DL (LDL), and triglycerides (TGs) were also measured. Serum C-peptide was measured using radio-immuno assay.

The 10 years coronary heart disease (CHD) risk was calculated for each patient using the UKPDS risk engine (Windows version 2.0, University of Oxford, Oxford, UK). ^[7] The risk predictors used were age, duration of diabetes, gender, atrial fibrillation, ethnicity, smoking status, HbA1c, systolic BP (SBP), TC, and HDL.

The intima media thickness of both carotid arteries (CIMT) in each patient was measured by an expert radiologist (who was blinded to the study). Carotid ultrasound, followed by a duplex color Doppler examination, was performed with a linear probe of 7.5-12 MHz while the patient was in supine position with head tilted backward. A region of 1 cm from the proximal carotid bulb was identified, and multiple measurements of the distal wall thickness from anterior, lateral, and posterior longitudinal projections were recorded. The arithmetical mean of these measurements was taken as CIMT value.

Statistical analysis

Microsoft Excel ^® and SPSS ^® 17.0 for Windows ^® were used for data storage and analysis. Continuous variables were expressed as mean ± standard deviation. Chi-square test and ANNOVA test were used to determine statistical difference between variables. Pearson's coefficient was used to investigate the correlation between the two variables. Statistical significance was set at P ≤ 0.05. The independent role of C-peptide was examined using quartiles of its distribution (<1.44, 1.44-1.77, 1.78-2.1, and >2.1 ng/ml)

Results

In this study of 101 type 2 DM cases (61 men, 40 women), the mean age was 53.57 ± 10.07 years. The mean duration of diabetes was 6.68 ± 4.39 years. Mean fasting C-peptide measured was 1.80 ± 0.65 ng/ml. The average CIMT was 0.56 ± 0.11 mm and the 10 years CHD risk of the study population according to the UKPDS risk engine was 15.60 ± 12.37% [Table 1].

Table 1: Characteristics of diabetes mellitus cases across C-peptide quartiles

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When the patient data was arranged according to quartiles of C-peptide distribution, several clinical parameters were significantly different across the C-peptide quartiles, including age of subjects, HbA1c, BMI, levels of SBP, TC, TG, HDL, LDL, homocysteine, CIMT, and the 10 years CHD risk according to the UKPDS (P for trend <0.05). However, duration of DM, FPG, and uric acid levels were not significantly different across the quartiles (P for trend >0.05) [Table 1].

Correlations between various cardiovascular risk factors and C-peptide level were assessed, significant positive correlations of C-peptide levels were found with the age of the subjects, the duration of DM, BMI, FPG, HbA1c, SBP, TC, TG, LDL, homocysteine, CIMT, and 10 years CVD risk by UKPDS risk engine. Significant negative correlation of C-peptide levels was observed with HDL [Table 2] and [Figure 1]. However, diastolic BP did not correlate significantly with serum C-peptide levels.

Figure 1: Correlation of C-peptide levels with carotid arteries intima thickness (a) and 10 year coronary heart disease risk (b)

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Table 2: Correlation of C-peptide level with various cardio-vascular risk factors

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Discussion

Diabetes is a well-known cause of premature atherosclerosis which is a proven major risk factor of CVD associated with DM. ^[2]

C-peptide binds to cell membrane and activates G protein coupled receptors leading to increased intracellular calcium concentration and activation of calcium dependent intracellular pathways. ^[4] C-peptide also stimulates the transcription of inflammatory genes, such as cyclooxygenase-2, via the activation of a protein kinase C/nuclear factor-kB signaling pathway. ^[5] C-peptide is associated with the influx of macrophages and monocytes in atherosclerotic artery intima from diabetic subjects, and it also acts as chemoattractant for CD4-positive lymphocyte and monocytes in early atherosclerotic lesions. ^[6],[10] In previous reports, C-peptide was found in deposits in the carotid artery of diabetic subjects and was supposed to have chemotactic effects on inflammatory cells and a pathognomonic role in atherosclerosis. ^[6] In a recent study, C-peptide levels in type 2 DM were found to positively correlate with intima media thickness of CIMT and the risk of subclinical atherosclerosis. ^[9]

In the current study, several risk factors of CVD were different significantly across C-peptide quartiles, including the age of subjects, the duration of diabetes, HbA1c, BMI, levels of SBP, TC, TG, HDL, LDL, homocysteine, CIMT, and the 10 years CVD risk according to the UKPDS (P for trend <0.05).

Kim et al. ^[9] showed a significant difference in the age of DM cases, BMI, DM duration, HbA1c, TG, and HDL for C-peptide levels but the levels of SBP, TC, and LDL were not significantly different across different C-peptide levels. A Korean study reported significant differences in fasting serum C-peptide levels for obesity and correlation of C-peptide with TG and HDL. ^[11] Significantly higher C-peptide levels were also found among dyslipidemic and coronary artery disease cases in Sari et al. ^[12] study. Serum C-peptide also had a significant association with coronary artery disease in their study.

The current study also reports significant positive correlations of C-peptide levels with the age of subjects, duration of DM, BMI, FPG, HbA1c, SBP, TC, TG, LDL, homocysteine, CIMT, and 10 years CHD risk by UKPDS risk engine. Significant negative correlation of C-peptide levels was observed with HDL. Similarly, Kim et al. ^[9] showed a significant correlation between C-peptide and TG, HDL, and homocysteine, but they found no significant correlation with LDL. Kim et al. ^[9] also did not find correlation of basal C-peptide with the UKPDS risk engine-related factors.

Several studies demonstrated deposition of C-peptide in vascular smooth muscle cells (SMC) in early atherosclerotic lesions of diabetic subjects and dose-dependent proliferation SMC with C-peptide via insulin resistance and compensatory hyperinsulinemia. ^{[6],[13],[14]} These observations favor a possible role for C-peptide to act as a mitogen for SMC and a potential risk factor for atherosclerosis.

CIMT is a well-accepted marker of early atherosclerosis. In the Atherosclerosis Risk in the Communities study, a significant association was found between increased CIMT and endogenous insulin levels. ^[15] Similarly, in the current study, CIMT differed significantly across C-peptide quartiles and also had a significant positive correlation with C-peptide levels. As C-peptide indicates true endogenous insulin secretion, thus it can be used as a marker of early atherosclerosis.

In a large population-based cohort study, C-peptide levels were also associated with increased risk of ischemic vascular disease mortality with the hazard ratio of 1.19 (1.02-1.39). ^[16] Several studies also supported the relation of cardiovascular risk and insulin resistance/C-peptide levels. ^[17],[18]

The present study has some limitations. This was a cross-sectional study with a limited sample size thus, the nature of the investigation and the results cannot be generalised and longitudinal studies with larger sample size are needed.

Conclusion

Serum C-peptide level seems to be significantly related to the development of atherosclerosis and future cardiovascular risk in type 2 DM. It may be used as a predictor of subclinical atherosclerosis and cardiovascular risk in type 2 DM patients. Further research is needed in this area.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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