Serum C-peptide as a key contributor to lipid-related residual cardiovascular risk in the elderly

C-peptide in diabetes: A player in a dual hormone disorder?

C-peptide, a byproduct of insulin synthesis believed to be biologically inert, is emerging as a multifunctional molecule. C-peptide serves an anti-inflammatory and anti-atherogenic role in type 1 diabetes mellitus (T1DM) and early T2DM. C-peptide protects endothelial cells by activating AMP-activated protein kinase α, thus suppressing the activity of NAD(P)H oxidase activity and reducing reactive oxygen species (ROS) generation. It also prevents apoptosis by regulating hyperglycemia-induced p53 upregulation and mitochondrial adaptor p66shc overactivation, as well as reducing caspase-3 activity and promoting expression of B-cell lymphoma-2. Additionally, C-peptide suppresses platelet-derived growth factor (PDGF)-beta receptor and p44/p42 mitogen-activated protein (MAP) kinase phosphorylation to inhibit vascular smooth muscle cells (VSMC) proliferation. It also diminishes leukocyte adhesion by virtue of its capacity to abolish nuclear factor kappa B (NF-kB) signaling, a major pro-inflammatory cascade. Consequently, it is envisaged that supplementation of C-peptide in T1DM might ameliorate or even prevent end-organ damage. In marked contrast, C-peptide increases monocyte recruitment and migration through phosphoinositide 3-kinase (PI-3 kinase)-mediated pathways, induces lipid accumulation via peroxisome proliferator-activated receptor γ upregulation, and stimulates VSMC proliferation and CD4+ lymphocyte migration through Src-kinase and PI-3K dependent pathways. Thus, it promotes atherosclerosis and microvascular damage in late T2DM. Indeed, C-peptide is now contemplated as a potential biomarker for insulin resistance in T2DM and linked to increased coronary artery disease risk. This shift in the understanding of the pathophysiology of diabetes from being a single hormone deficiency to a dual hormone disorder warrants a careful consideration of the role of C-peptide as a unique molecule with promising diagnostic, prognostic, and therapeutic applications.

The impact of insulin induced lipohypertrophy on carotid intima-media thickness in patients with type 2 diabetes mellitus

Lipohypertrophy (LH) is a major localized complication of insulin therapy. We aimed to investigate the association between insulin-induced LH and carotid intima-media thickness (CIMT) in patients with type 2 diabetes mellitus (DM). A total of 75 patients with DM treated with insulin were included in this study. The insulin injection sites of the patients were evaluated by inspection and palpation and then radiologically with ultrasound. The CIMT of the patients was evaluated using ultrasonography. According to the guideline recommendation, the CIMT cutoff value was taken as 0.9 mm, and the patients were categorized into 2 groups according to the CIMT value and evaluated statistically. The presence of LH (CI: 1.379-30.000; OR = 6.432; P < .05), age (CI: 1.036-1.149; OR = 1091; P < .05), BMI (CI: 1.003-1.262; OR = 1.125; P < .05) and duration of DM (CI: 1.001-1.300; OR = 1.141; P < .05) were independent risk factors for high-CIMT in patients with DM. The most interesting result of this study was that the presence of LH was an independent risk factor for increased CIMT. According to this result, we think that LH may increase the risk of cardiovascular disease as well as being a complication that disrupts the blood glucose regulation of patients with DM and increases the cost of treatment.

Blood C-peptide concentration as a proxy marker of cardiovascular disease: An observational cross-sectional study

Background and Aims

Cardiovascular diseases (CVDs) are among the leading causes of disability and early death in sub-Saharan Africa. Most of the current blood tests for CVD diagnosis involve performing about three test profiles; often at additional cost to patients. C-peptide, a cleavage product of proinsulin, is a promising marker that has the potential to serve as a proxy marker for diagnosing CVDs in resource-poor settings.

Methodology

The study was an observational cross-sectional one and involved 127 consenting persons diagnosed with CVD and 127 individuals without CVD. The socio-demographic and clinical characteristics of participants were obtained. Blood levels of C-peptide, fasting plasma glucose (FPG), total creatinine kinase (CK), creatine kinase myocardial bound (CKMB), lactate dehydrogenase (LDH), propeptide of brain natriuretic peptide (PBNP), Troponin T, lipids, and biomarkers of kidney and liver function were analyzed using ELISA and an automated analyzer. Insulin resistance was computed using the modified homeostatic model assessment (HOMA-IR).

Results

The CVD Group had significantly higher levels of C-peptide, CK, CKMB, troponin T, PBNP, FPG, HOMA-IR, and several selected kidney, liver, and lipid parameters compared to the non-CVD Group (p < 0.05 for all). Troponin T recorded a positive correlation (r = 0.34, p < 0.001) with C-peptide among the CVD Group. The sensitivity and specificity of C-peptide in identifying CVD were 96.1% and 91.3% respectively (area under the curve = 0.938, p < 0.001).

Conclusion

C-peptide levels were higher in the CVD Group and appeared to be a valuable (high sensitivity and specificity) biomarker in detecting CVD.

The association of serum C-peptide with the risk of cardiovascular events: a meta-analysis and systematic review

BACKGROUND

C-peptide is considered a peptide with active function in the body, which can affect people's health. However, the results of previous studies on the possible association of C-peptide with the risk of cardiometabolic disorders have not been fully understood. This systematic review and meta-analysis aimed to investigate the association between serum C-peptide level and the risk of cardiovascular disease (CVD) events.

METHODS

The various important databases, including PubMed, Scopus, and Web of Science, were searched comprehensively to November 2022 to identify the relevant studies. The HR(95% CI) or OR(95% CI) for observational studies were extracted and converted into log HR or log OR and their standard deviation(SD) was computed. A random-effects model with an inverse variance weighting method was conducted, to calculate the pooled effect size.

RESULTS

Sixteen observational studies, including one case-control study, eight cohort studies, and seven cross-sectional studies were included in the current meta-analysis. The sample size ranged from 90 to 7030, with an age range from 12 to 85 years. During the follow-up time (ranging from 5 to 17 years), 4852 CVD events occurred. Based on cohort and case-control studies, the pooled results showed no significant association between serum C-peptide with CVD events risk (RR = 1.02;95%CI:0.91-1.15, I2 = 34.7%; P-heterogeneity = 0.140). For cross-sectional studies, the pooled results indicated a positive association between serum C-peptide and the odds of CVD outcomes (OR = 1.35;95%CI:1.04-1.76, I2 = 83.6%; P-heterogeneity < 0.001).

CONCLUSIONS

The pooled results of the current study suggested that C-peptide level was not related to the risk of CVD events in cohort studies, however, the meta-analysis of cross-sectional studies showed a significant association between C-peptide and an increased risk of CVD events.

The association between C-peptide and atrial cardiomyopathy in nondiabetic adults: results from NHANES III

Serum C-peptide exhibits various biological activities. The relationship between C-peptide and atrial cardiomyopathy remains unknown. We aimed to investigate the association between C-peptide level and atrial cardiomyopathy in nondiabetic adults. Our study enrolled 4578 participants without diagnosed diabetes from the Third National Health and Nutrition Examination Survey (NHANES III). Atrial cardiomyopathy was defined as a deep terminal negative P wave in V1 below - 100 µV (more negative), according to the electrocardiogram. The participants were categorized into low C-peptide (≤ 1.46 nmol/L) and high C-peptide (> 1.46 nmol/L) groups, according to the receiver operating characteristic analysis. Odds ratio (OR) and 95% confidence interval (CI) for the association between C-peptide level and atrial cardiomyopathy were generated using multivariate logistic regression analysis. The prevalence of atrial cardiomyopathy was higher in the high C-peptide group than in the low C-peptide group (5.62% vs. 2.31%, P < 0.001, respectively). Multivariate logistic regression analysis showed that participants in the high C-peptide group had a 3.60-fold (95% CI 1.81-6.99) higher risk of atrial cardiomyopathy than those in the low C-peptide group. Per standard deviation increase in C-peptide was linked to a 1.20-fold (95% CI 1.00-1.41) higher risk in atrial cardiomyopathy. High C-peptide level might be an independent risk factor for atrial cardiomyopathy in nondiabetic adults.

Association Between C-Peptide Level and Subclinical Myocardial Injury

BACKGROUND

Previous studies have confirmed an association between C-peptide levels with the risk of cardiometabolic diseases. However, whether circulating C-peptide was related to subclinical myocardial injury (SC-MI) remains unknown.

METHODS

A total of 3,752 participants without a history of cardiovascular diseases were included in our study from National Health and Nutrition Examination Survey III (NHANES III). Multivariable linear regression was performed to explore the correlation between C-peptide and cardiac injury score (CIIS). Multivariate logistic regression was used to examine the association between C-peptide quartile and SC-MI.

RESULTS

Circulating C-peptide was significantly associated with CIIS (β:0.09, 95% confidence interval [CI]: 0.00-0.17; p = 0.041). Compared with the lowest quartile, the highest quartile of circulating C-peptide increased a 1.48-fold risk of SC-MI (Odds ratio = 1.66, 95% CI: 1.18-1.87; p = 0.001).

CONCLUSIONS

The level of C-peptide was independently associated with CIIS and SC-MI, which could serve as a new risk factor of SC-MI.

The effect of C-peptide on diabetic nephropathy: A review of molecular mechanisms

C-peptide is a small peptide connecting two chains of proinsulin molecule and is dissociated before the release of insulin. It is secreted in an equimolar amount to insulin from the pancreatic beta-cells into the circulation. Recent evidence demonstrates that it has other physiologic activities beyond its structural function. C-peptide modulates intracellular signaling pathways in various pathophysiologic states and, could potentially be a new therapeutic target for different disorders including diabetic complications. There is growing evidence that c-peptide has modulatory effects on the molecular mechanisms involved in the development of diabetic nephropathy. Although we have little direct evidence, pharmacological properties of c-peptide suggest that it can provide potent renoprotective effects especially, in a c-peptide deficient milieu as in type 1 diabetes mellitus. In this review, we describe possible molecular mechanisms by which c-peptide may improve renal efficiency in a diabetic milieu.

Association of C-peptide with diabetic vascular complications in type 2 diabetes

AIM

Fasting serum C-peptide is a biomarker of insulin production and insulin resistance, but its association with vascular complications in type 2 diabetes mellitus (T2DM) has never been fully elucidated. This study aimed to investigate whether C-peptide is associated with cardiovascular disease (CVD) and diabetic retinopathy (DR).

METHODS

A total of 4793 diabetes patients were enrolled from seven communities in Shanghai, China, in 2018. CVD was defined as a self-reported combination of previous diagnoses, including coronary heart disease, myocardial infarction and stroke. DR was examined using fundus photographs. Logistic regression analyses were performed, and multiple imputed data were used to obtain stabilized estimates.

RESULTS

Prevalence of CVD increased with increasing C-peptide levels (Q1, Q2, Q3 and Q4: 33%, 34%, 37% and 44%, respectively; P_{for trend} < 0.001), whereas DR prevalence decreased with increasing C-peptide quartiles (Q1, Q2, Q3 and Q4: 21%, 19%, 15% and 12%, respectively; P_{for trend} < 0.001). On logistic regression analysis, C-peptide levels were significantly associated with CVD prevalence (1.27, 95% CI: 1.13-1.42; P < 0.001) and C-peptide quartiles (Q1: reference; Q2: 1.31, 95% CI: 1.00-1.70; Q3: 1.53, 95% CI: 1.16-2.01; Q4: 1.76, 95% CI: 1.32-2.34; P_{for trend} < 0.001). Given the interaction between C-peptide and BMI and the association between C-peptide and CVD (P_{for interaction} = 0.015), study participants were divided into two subgroups based on BMI which revealed that the association persisted despite different BMI statuses. However, DR prevalence decreased with increasing C-peptide levels (0.73, 95% CI: 0.62-0.86; P < 0.001) and quartiles (Q1: reference; Q2: 1.00, 95% CI: 0.76-1.33; Q3: 0.69, 95% CI: 0.50-0.94; Q4: 0.51, 95% CI: 0.36-0.72; P_{for trend} < 0.001).

CONCLUSION

C-peptide was positively associated with CVD, but inversely associated with DR progression. The association between C-peptide and CVD could be due to associated metabolic risk factors.

Influence of blood glucose fluctuation, C-peptide level and conventional risk factors on carotid artery intima-media thickness in Chinese Han patients with type 2 diabetes mellitus

BACKGROUND

Some studies have suggested that blood glucose fluctuation and C-peptide level were considered as predictive factors for carotid artery intima-media thickness (CIMT). However, the relationships of these variables are unclear. This research was aimed to identify the potential effects of blood glucose fluctuation, C-peptide level and conventional risk factors on CIMT.

METHODS

A total of 280 type 2 diabetes mellitus (T2DM) patients were enrolled into this study. Population characteristics were obtained through medical history and clinical parameters. The patients were divided into two groups according to the critical value of CIMT (0.9). Research data were analyzed to identify risk factors of CIMT between the two groups.

RESULTS

The comparison results of basic information showed that differences in age and illness years between the two groups were statistically significant (p = 0.0002 and p = 0.0063). Logistic regression analysis results indicated that smoking, uric acid (UA) levels, 2 h C-peptide and standard deviation of blood glucose (SDBG) were the influence factors for CIMT thickening (p = 0.032, p = 0.047, p = 0.049 and p = 0.042, respectively). Blood glucose fluctuation could affect the risk of some complications. In largest amplitude of glycemic excursions (LAGE) > 4.4 group, the CIMT abnormal rate was 27.10%, which was significantly higher than 12.12% in the LAGE ≤ 4.4 group (p = 0.012). The CIMT abnormal rate of SDBG > 2.0 group was 27.81%, which was significantly higher than that of the SDBG ≤ 2.0 group (p = 0.018).

CONCLUSIONS

Blood glucose fluctuation is an independent risk factor associated with CIMT in T2DM patients, in addition to conventional risk factors, such as smoking, high UA level and 2 h C-peptide. Therefore, more attention should be given to the change of CIMT and the complications.

Novel Formulations of C-Peptide with Long-Acting Therapeutic Potential for Treatment of Diabetic Complications

The development and application of novel nanospheres based on cationic and anionic random amphiphilic polypeptides with prolonged stability were proposed. The random copolymers, e.g., poly(l-lysine-co-d-phenylalanine) (P(Lys-co-dPhe)) and poly(l-glutamic acid-co-d-phenylalanine) (P(Glu-co-dPhe)), with different amount of hydrophilic and hydrophobic monomers were synthesized. The polypeptides obtained were able to self-assemble into nanospheres. Such characteristics as size, PDI and ζ-potential of the nanospheres were determined, as well as their dependence on pH was also studied. Additionally, the investigation of their biodegradability and cytotoxicity was performed. The prolonged stability of nanospheres was achieved via introduction of d-amino acids into the polypeptide structure. The cytotoxicity of nanospheres obtained was tested using HEK-293 cells. It was proved that no cytotoxicity up to the concentration of 500 µg/mL was observed. C-peptide delivery systems were realized in two ways: (1) peptide immobilization on the surface of P(Glu-co-dPhe) nanospheres; and (2) peptide encapsulation into P(Lys-co-dPhe) systems. The immobilization capacity and the dependence of C-peptide encapsulation efficiency, as well as maximal loading capacity, on initial drug concentration was studied. The kinetic of drug release was studied at model physiological conditions. Novel formulations of a long-acting C-peptide exhibited their effect ex vivo by increasing activity of erythrocyte Na⁺/K⁺-adenosine triphosphatase.

The Association of Fasting Glucose, Insulin, and C-Peptide, with 19-Year Incidence of Coronary Heart Disease in Older Japanese-American Men; the Honolulu Heart Program

The role of fasting glucose, insulin levels, and C-peptide in coronary heart disease (CHD) in non-diabetic individuals remains uncertain. We examined the association between fasting glucose, insulin and C-peptide with the long-term incidence of CHD in Japanese-American men. In 1980–1982, from a random sample of the Honolulu Heart Program men (n = 1378), aged 61–81 years, data on several CHD and metabolic risk factors were obtained to examine the relation of fasting glucose, insulin and C-peptide to 19-year CHD incidence. Age-adjusted incidence of CHD increased with increasing quintiles of glucose, insulin and C-peptide. Age-adjusted CHD rates in the glucose quintiles were 11.9, 11.6, 14.4, 18.1 and 24.1 per 1000 person-years (trend p < 0.001). In individual Cox models (lowest quintiles of glucose, insulin and C-peptide as reference) the relative risks (95% confidence interval) of CHD incidence for the glucose quintiles adjusting for age, smoking, hypertension, cholesterol, physical activity, and body mass index, were 0.9 (0.6–1.4), 1.2 (0.8–1.8), 1.4 (0.9–2.2), and 1.7 (1.1–2.6), respectively (trend p = 0.004). Insulin and C-peptide were not significantly associated with CHD on multivariate analysis. Fasting glucose remained the only significant predictor of increased CHD risk (p = 0.003) in a model combining all 3 metabolic variables. In this cohort, only fasting glucose independently predicts long-term incidence of CHD. Age-adjusted insulin and C-peptide levels were associated with CHD incidence, but after adjustment for other risk factors, do not independently predict CHD.