The beneficial effects of C-Peptide on diabetic polyneuropathy

Generation of a Beta-Cell Transplant Animal Model of Diabetes Using CRISPR Technology

Since insulin deficiency results from pancreatic beta-cell destruction, all type 1 and most type 2 diabetes patients eventually require life-long insulin injections. Insulin gene synthesis could also be impaired due to insulin gene mutations as observed in diabetic patients with MODY 10. At this point, insulin gene therapy could be very effective to recompense insulin deficiency under these circumstances. For this reason, an HIV-based lentiviral vector carrying the insulin gene under the control of insulin promoter (LentiINS) was generated, and its therapeutic efficacy was tested in a beta-cell transplant model lacking insulin produced by CRISPR/Cas9-mediated genetically engineered pancreatic beta cells. To generate an insulin knockout beta-cell transplant animal model of diabetes, a dual gene knockout plasmid system involving CRISPR/Cas9 was transfected into a mouse pancreatic beta cell line (Min6). Fluorescence microscopy and antibiotic selection were utilized to select the insulin gene knockout clones. Transplantation of the genetically engineered pancreatic beta cells under the kidney capsule of STZ-induced diabetic rats revealed LentiINS- but not LentiLacZ-infected Ins2KO cells transiently reduced hyperglycemia similar to that of MIN6 in diabetic animals. These results suggest LentiINS has the potential to functionally restore insulin production in an insulin knockout beta-cell transplant animal model of diabetes.

Lentivirus Mediated Pancreatic Beta-Cell-Specific Insulin Gene Therapy for STZ-Induced Diabetes

Autoimmune destruction of pancreatic beta cells is the characteristic feature of type 1 diabetes mellitus. Consequently, both short- and intermediate-acting insulin analogs are under development to compensate for the lack of endogenous insulin gene expression. Basal insulin is continuously released at low levels in response to hepatic glucose output, while post-prandial insulin is secreted in response to hyperglycemia following a meal. As an alternative to multiple daily injections of insulin, glucose-regulated insulin gene expression by gene therapy is under development to better endure postprandial glucose excursions. Controlled transcription and translation of proinsulin, presence of glucose-sensing machinery, prohormone convertase expression, and a regulated secretory pathway are the key features unique to pancreatic beta cells. To take advantage of these hallmarks, we generated a new lentiviral vector (LentiINS) with an insulin promoter driving expression of the proinsulin encoding cDNA to sustain pancreatic beta-cell-specific insulin gene expression. Intraperitoneal delivery of HIV-based LentiINS resulted in the lowering of fasting plasma glucose, improved glucose tolerance and prevented weight loss in streptozoticin (STZ)-induced diabetic Wistar rats. However, the combinatorial use of LentiINS and anti-inflammatory lentiviral vector (LentiVIP) gene therapy was required to increase serum insulin to a level sufficient to suppress non-fasting plasma glucose and diabetes-related inflammation.

L-carnitine ameliorates peripheral neuropathy in diabetic mice with a corresponding increase in insulin‑like growth factor‑1 level

Diabetic peripheral neuropathy (DPN) is one of the common complications in diabetes, affecting more than half of patients with diabetes. L‑carnitine (LC) was recently demonstrated to serve a positive role in ameliorating DPN. Therefore, the aim of the present study was to investigate the underlying mechanisms of LC in ameliorating DPN. Male Kunming mice were randomly assigned into five groups, including the control group, diabetes mellitus group, pre‑treatment group, treatment group and post‑treatment group. Type 2 diabetes was induced in mice using a combination of high‑fat diet and streptozotocin injection. Subsequently, peripheral neuropathy was measured and the levels of LC, insulin and insulin‑like growth factor‑1 (IGF‑1) were detected. When diabetic mice were treated with LC, the levels of IGF‑1 in the plasma and pancreas were increased. In addition, hyperalgesia, as determined by the tail‑flick test as well as food intake, body weight and blood glucose levels were decreased. An amelioration of demyelination, axonal atrophy and mitochondria swelling in the nerve fibres of diabetic mice was also observed. The present study demonstrated that LC ameliorated peripheral neuropathy in type 2 diabetic mice and the effect of LC may in part be mediated by an increase in local and circulatory IGF‑1 levels.

C-peptide is independent associated with diabetic peripheral neuropathy: a community-based study

BACKGROUND

Because the relationship between C-peptide and diabetic peripheral neuropathy (DPN) is controversial, the aim of our study was to evaluate the relationship between C-peptide and DPN in community-based Chinese patients with type 2 diabetes.

METHODS

In total, 220 consecutive type 2 diabetic patients treated by our regional medical consortium were enrolled. DPN was assessed by clinical symptoms, signs, and electromyography.

RESULTS

Fasting C-peptide, 2-h postprandial C-peptide and ΔC-peptide (i.e., 2-h postprandial C-peptide minus the fasting C-peptide) serum concentrations in the non-DPN group were significantly higher than those in the clinical DPN group (all P ≤ 0.040) and the confirmed DPN group (all P < 0.002). The three C-peptide parameters were independently associated with DPN (all P < 0.05) after adjusting for age, sex, diabetes duration, smoking status, systolic pressure, body mass index, angiotensin-converting enzyme inhibitors/angiotensin receptor blocker use, fasting plasma glucose, HbA1c, triglyceride and estimated glomerular filtration rate. Compared with the ΔC-peptide quartile 1 (reference), patients in quartile 3 (odds ratio [OR], 0.110; 95% confidence interval [CI] 0.026-0.466; P = 0.003) and quartile 4 (OR, 0.012; 95% CI 0.026-0.559; P = 0.007) had a lower risk of DPN after adjusting for the confounders.

CONCLUSIONS

C-peptide was negatively associated with DPN in community-based Chinese type 2 diabetic patients in China.

Serum Phosphorylated Neurofilament-Heavy Chain, a Potential Biomarker, is Associated With Peripheral Neuropathy in Patients With Type 2 Diabetes

Neurofilament (NF), one of the major axonal cytoskeletal proteins, plays a critical role in degenerative diseases in both the central and the peripheral nervous systems. The aim of this study is to explore the relationship between serum phosphorylated neurofilament-heavy chain (pNF-H) and diabetic peripheral neuropathy (DPN) in patients with type 2 diabetes.Serum pNF-H concentrations were measured by ELISA in hospitalized patients with and without DPN (n = 118). DPN was assessed by clinical symptoms, signs, and electromyography.Compared with the non-DPN group (311.98 [189.59-634.12] pg/mL), the confirmed group (605.99 [281.17-1332.78] pg/mL) patients had the higher serum pNF-H levels (P = 0.007). DPN was significantly correlated with C-peptide (r = -0.269), total cholesterol (TC) (r = 0.185), and pNF-H (r = 0.258). Serum pNF-H levels were independently associated with DPN (P = 0.004), even after adjusting for age, sex, duration of diabetes, fasting plasma glucose, glycosylated hemoglobin A1c, TC, C-peptide, urinary albuminto/creatinine ratio, and estimated glomerular filtration rate. Compared with pNF-H quartile 1 (referent), patients in quartile 3 (odds ratio [OR], 3.977; 95% confidence interval [CI], 1.243-12.728; P = 0.021) and quartile 4 (OR, 10.488; 95% CI, 3.020-34.429; P = 0.000) had the higher risk of DPN after adjusting for the confounders.Serum pNF-H levels might be associated with the DPN, and the correlationship between serum pNF-H and DPN should be further studied.

C-peptide replacement therapy as an emerging strategy for preventing diabetic vasculopathy

Lack of C-peptide, along with insulin, is the main feature of Type 1 diabetes mellitus (DM) and is also observed in progressive β-cell loss in later stage of Type 2 DM. Therapeutic approaches to hyperglycaemic control have been ineffective in preventing diabetic vasculopathy, and alternative therapeutic strategies are necessary to target both hyperglycaemia and diabetic complications. End-stage organ failure in DM seems to develop primarily due to vascular dysfunction and damage, leading to two types of organ-specific diseases, such as micro- and macrovascular complications. Numerous studies in diabetic patients and animals demonstrate that C-peptide treatment alone or in combination with insulin has physiological functions and might be beneficial in preventing diabetic complications. Current evidence suggests that C-peptide replacement therapy might prevent and ameliorate diabetic vasculopathy and organ-specific complications through conservation of vascular function, as well as prevention of endothelial cell death, microvascular permeability, vascular inflammation, and neointima formation. In this review, we describe recent advances on the beneficial role of C-peptide replacement therapy for preventing diabetic complications, such as retinopathy, nephropathy, neuropathy, impaired wound healing, and inflammation, and further discuss potential beneficial effects of combined C-peptide and insulin supplement therapy to control hyperglycaemia and to prevent organ-specific complications.

Clinical utility of insulin and insulin analogs

Diabetes is a pandemic disease characterized by autoimmune, genetic and metabolic abnormalities. While insulin deficiency manifested as hyperglycemia is a common sequel of both Type-1 and Type-2 diabetes (T1DM and T2DM), it does not result from a single genetic defect--rather insulin deficiency results from the functional loss of pancreatic β cells due to multifactorial mechanisms. Since pancreatic β cells of patients with T1DM are destroyed by autoimmune reaction, these patients require daily insulin injections. Insulin resistance followed by β cell dysfunction and β cell loss is the characteristics of T2DM. Therefore, most patients with T2DM will require insulin treatment due to eventual loss of insulin secretion. Despite the evidence of early insulin treatment lowering macrovascular (coronary artery disease, peripheral arterial disease and stroke) and microvascular (diabetic nephropathy, neuropathy and retinopathy) complications of T2DM, controversy exists among physicians on how to initiate and intensify insulin therapy. The slow acting nature of regular human insulin makes its use ineffective in counteracting postprandial hyperglycemia. Instead, recombinant insulin analogs have been generated with a variable degree of specificity and action. Due to the metabolic variability among individuals, optimum blood glucose management is a formidable task to accomplish despite the presence of novel insulin analogs. In this article, we present a recent update on insulin analog structure and function with an overview of the evidence on the various insulin regimens clinically used to treat diabetes.

Axonal dysfunction prior to neuropathy onset in type 1 diabetes

BACKGROUND

The present study was undertaken to determine whether there were changes evident in axonal membrane function prior to the onset of neuropathy in patients with type 1 and type 2 diabetes.

METHODS

From a cohort of 110 consecutive referrals, nerve excitability was investigated in 40 diabetic patients without clinical evidence of neuropathy (20 type 1 diabetic patients and 20 type 2 diabetic patients). Groups were matched for gender, disease duration and HbA(1c). Studies were also undertaken in two control groups, younger controls and older controls, matched for age and gender with the diabetic cohorts.

RESULTS

Subjects with type 1 diabetes demonstrated significant nerve excitability abnormalities when compared with younger normal controls. Specifically, type 1 subjects showed a significant reduction at multiple time points in both depolarising and hyperpolarising threshold electrotonus. Additionally, the relative refractory period was prolonged (type 1, 3.19 ms; younger normal controls, 3.0 ms; p < 0.05) and superexcitability was reduced (type 1, -23.12%; younger normal controls, -26.37%; p < 0.05), consistent with axonal membrane depolarisation. Correlations were identified in type 1 patients between disease duration and nerve excitability parameters, including the relative refractory period (r = -0.533, p < 0.05). In contrast, only minor non-specific changes were noted in the type 2 group.

DISCUSSION

This study provides clear evidence of altered axonal function in patients with type 1 diabetes in the absence of clinical neuropathy. These findings suggest that altered axonal membrane potential may precede neuropathy onset in type 1 diabetes and as such may indicate a window of opportunity to intervene and potentially reverse axonal membrane dysfunction before the development of irreversible neuropathy.

Correlations between Glucagon Stimulated C-peptide Levels and Microvascular Complications in Type 2 Diabetes Patients

BACKGROUND

This study aimed to investigate whether stimulated C-peptide is associated with microvascular complications in type 2 diabetes mellitus (DM).

METHODS

A cross-sectional study was conducted in 192 type 2 diabetic patients. Plasma basal C-peptide and stimulated C-peptide were measured before and 6 minutes after intravenous injection of 1 mg glucagon. The relationship between C-peptide and microvascular complications was statistically analyzed.

RESULTS

In patients with retinopathy, basal C-peptide was 1.9±1.2 ng/mL, and stimulated C-peptide was 2.7±1.6 ng/mL; values were significantly lower compared with patients without retinopathy (P=0.031 and P=0.002, respectively). In patients with nephropathy, basal C-peptide was 1.6±0.9 ng/mL, and stimulated C-peptide was 2.8±1.6 ng/mL; values were significantly lower than those recorded in patients without nephropathy (P=0.020 and P=0.026, respectively). Stimulated C-peptide level was associated with increased prevalence of microvascular complications. Age-, DM duration-, and hemoglobin A1c-adjusted odds ratios for retinopathy in stimulated C-peptide value were 4.18 (95% confidence interval [CI], 1.40 to 12.51) and 3.35 (95% CI, 1.09 to 10.25), respectively. The multiple regression analysis between nephropathy and C-peptide showed that stimulated C-peptide was statistically correlated with nephropathy (P=0.03).

CONCLUSION

In patients with type 2 diabetes, the glucagon stimulation test was a relatively simple method of short duration for stimulating C-peptide response. Stimulated C-peptide values were associated with microvascular complications to a greater extent than basal C-peptides.

Angiotensin-converting enzyme gene single polymorphism as a genetic biomarker of diabetic peripheral neuropathy: longitudinal prospective study

BACKGROUND

Identifying patients at risk of developing diabetic peripheral neuropathy (DPN) is of paramount importance in those with type 2 diabetes mellitus (T2DM) to provide and anticipate secondary prevention measures as well as intensify action on risk factors, particularly so in primary care. Noteworthy, the incidence of DPN remains unknown in our environment.

AIMS

(i) To analyze a single angiotensin-converting enzyme (ACE) gene polymorphism (D/I) as a genetic marker of risk of developing DPN, and (ii) to determine the incidence of DPN in our environment.

RESEARCH DESIGN AND METHODS

Longitudinal study with annual follow-up for 3years involving a group of T2DM (N=283) randomly selected. ACE gene polymorphism distribution (I=insertion; D=deletion) was determined. DPN was diagnosed using clinical and neurophysiology evaluation.

RESULTS

Baseline DPN prevalence was 28.97% (95% CI, 23.65-34.20). ACE polymorphism heterozygous genotype D/I presence was 60.77% (95% CI, 55.05-66.5) and was independently associated with a decreased risk of DPN (RR, 0.51; 95% CI, 0.30-0.86). DPN correlated with age (P<0.001) but not with gender (P=0.466) or time of evolution of T2DM (P=0.555). Regarding end point, DPN prevalence was 36.4% (95% CI, 30.76-42.04), and accumulated incidence was 10.4% 3years thereafter. In the final Poisson regression analysis, the presence of heterozygous genotype remained independently associated with a decreased risk of DPN (RR, 0.71; (95% CI, 0.53-0.96). DPN presence remained correlated with age (P=0.002), but not with gender (P=0.490) or time of evolution (P=0.630).

CONCLUSIONS

In our series, heterozygous ACE polymorphism (D/I) stands as a protective factor for DPN development. Accumulated incidence of DPN was relevant. Further prospective studies are warranted.

Sequential abnormalities in type 1 diabetic encephalopathy and the effects of C-Peptide

Diabetic encephalopathy is a recently recognized complication in type 1 diabetes. In this review, we summarize a series of experimental results obtained longitudinally in the spontaneously type 1 diabetic BB/Wor-rat, and bringing out the beneficial effects of C-peptide replacement. It is increasingly clear that lack of insulin and C-peptide, and perturbations of their signaling cascades in type 1 diabetes are detrimental to the regulation of neurotrophic factors and their receptors. Other consequences of such deficits and perturbations are innate inflammatory responses with effects on synaptogenesis, neurite degeneration, and early behavioral abnormalities. Replacement of C-peptide, which does not effect hyperglycemia, has beneficial effects on a variety of pro-apoptotic stressors, oxidative stressors, and finally on apoptosis. Eventually, this cascade of events leads to neuronal loss and decreased densities of white matter myelinating cells, with more profound deficits in behavioral and cognitive function. Such changes are likely to underlie gray and white matter atrophy in type 1 diabetes, and are significantly prevented by full C-peptide replacement. Present data demonstrate that C-peptide replacement has beneficial effects on numerous sequential and partly interrelated pathogenetic mechanisms, resulting in prevention of neuronal and oligodendroglial cell loss, with significant prevention of neurobehavioral and cognitive functions.