C-Peptide as a Therapy for Type 1 Diabetes Mellitus

C-Peptide Ameliorates Particulate Matter 2.5-Induced Skin Cell Apoptosis by Inhibiting NADPH Oxidation

Connecting peptide (C-peptide), a byproduct of insulin biosynthesis, has diverse cellular and biological functions. Particulate matter 2.5 (PM2.5) adversely affects human skin, leading to skin thickening, wrinkle formation, skin aging, and inflammation. This study aimed to investigate the protective effects of C-peptide against PM2.5-induced damage to skin cells, focusing on oxidative stress as a key mechanism. C-peptide mitigated NADPH oxidation and intracellular reactive oxygen species (ROS) production induced by PM2.5. It also suppressed PM2.5-induced NADPH oxidase (NOX) activity and alleviated PM2.5-induced NOX1 and NOX4 expression. C-peptide protected against PM2.5-induced DNA damage, lipid peroxidation, and protein carbonylation. Additionally, C-peptide mitigated PM2.5-induced apoptosis by inhibiting intracellular ROS production. In summary, our findings suggest that C-peptide mitigates PM2.5-induced apoptosis in human HaCaT keratinocytes by inhibiting intracellular ROS production and NOX activity.

Beclin1/LC3II/P62 autophagy pathway activation is involved in the protective action of C-peptide against prostate injury in a rat model of type 1 diabetes

One of the undesirable complications of diabetes is sexual dysfunctions in males which may affect their fertility. This research aims to study the effect of C-peptide administration on the prostate of diabetic rats and focusing on exploring the role of the autophagy pathway in diabetic prostate and whether it is involved in C-peptide action. Forty adult male Wistar albino rats were separated into control group, diabetic group, diabetic + C-peptide and diabetic + C-peptide + 3-Methyladenine (autophagy inhibitor). Serum metabolic parameters and prostatic specific antigen (PSA) were measured. Markers of oxidative stress, inflammation, fibrosis, cell proliferation and cell autophagy were evaluated in prostate tissues using biochemical, western blotting and immunohistochemical techniques. C-peptide administration ameliorated the effects of diabetes on the prostate through its hypoglycaemic, antioxidant, anti-inflammatory, and antiproliferative effects which were reversed with autophagy inhibition. Thus, we concluded that C-peptide prevented the effects of diabetes on the prostate through stimulation of the autophagy pathway.

Potent anti-inflammatory and anti-apoptotic activities of electrostatically complexed C-peptide nanospheres ameliorate diabetic nephropathy

In the present era of "Diabetic Pandemic", peptide-based therapies have generated immense interest however, are facing odds due to inevitable limitations like stability, delivery complications and off-target effects. One such promising molecule is C-peptide (CPep, 31 amino acid polypeptide with t1/2 30 min); it is a cleaved subunit of pro-insulin, well known to suppress microvascular complications in kidney but has not been able to undergo translation to the clinic till date. Herein, a polymeric CPep nano-complexes (NPX) was prepared by leveraging electrostatic interaction between in-house synthesized cationic, polyethylene carbonate (PEC) based copolymer (Mol. wt. 44,767 Da) and negatively charged CPep (Mol. wt. 3299 Da) at pH 7.4 and further evaluated in vitro and in vivo. NPX exhibited a spherical morphology with a particle size of 167 nm and zeta potential equivalent to +10.3, with 85.70 % of CPep complexation efficiency. The cellular uptake of FITC-tagged CPep NPX was 95.61 % in normal rat kidney cells, NRK-52E. Additionally, the hemocompatible NPX showed prominent cell-proliferative, anti-oxidative (1.8 folds increased GSH; 2.8 folds reduced nitrite concentration) and anti-inflammatory activity in metabolic stress induced NRK-52E cells as well. The observation was further confirmed by upregulation of anti-apoptotic protein BCl2 by 3.5 folds, and proliferative markers (β1-integrin and EGFR) by 3.5 and 2.3 folds, respectively, compared to the high glucose treated control group. Pharmacokinetic study of NPX in Wistar rats revealed a 6.34 folds greater half-life than free CPep. In in-vivo efficacy study in STZ-induced diabetic nephropathy animal model, NPX reduced blood glucose levels and IL-6 levels significantly by 1.3 and 2.5 folds, respectively, as compared to the disease control group. The above findings suggested that NPX has tremendous potential to impart sustained release of CPep, resulting in enhanced efficacy to treat diabetes-induced nephropathy and significantly improved renal pathology.

Mechanisms underlying the development of type 1 diabetes in ART-treated people living with HIV: an enigmatic puzzle

The immunopathogenesis of HIV infection remains poorly understood. Despite the widespread use of effective modern antiretroviral therapy (ART), people living with HIV (PLWH) are known to develop several comorbidities, including type 1 diabetes (T1DM). However, the etiology and critical mechanisms accounting for the onset of T1DM in the preceding context remain unknown. This article proposes to address this topic in order to provide further understanding and future research directions.

Slowing of Peripheral Nerve Conduction Velocity in Children and Adolescents With Type 1 Diabetes Is Predicted by Glucose Fluctuations

Nerve conduction velocity (NCV) abnormalities are the forerunners of diabetic peripheral neuropathy (DPN). Therefore, this study aimed to analyze the effect of glucose profile quality on NCV in children and young adults with type 1 diabetes. Fifty-three children age 5 to 23 years with type 1 diabetes were recruited to participate in the study, which was conducted prospectively at the Children's Hospital of Eastern Switzerland from 2016 to 2022. Glycemic targets were recorded, and a cross-sectional nerve conduction study analyzing the peroneal, tibial, median motor, and median sensory nerves was performed. Data were compared with those of a control group of 50 healthy children. In the age- and height-matched diabetes subgroup aged 10-16 years, all four nerves showed significantly slower NCV, most pronounced for the peroneal nerve. Because height has a retarding effect on peroneal NCV, NCV was adjusted for height (dNCV). Peroneal dNCV correlated negatively with long-term glycated hemoglobin and highly significantly with glucose variability. Because high glucose variability clearly increases the risk of neuropathy, together with but also independently of the mean glucose level, this aspect of glycemic control should be given more attention in the care of individuals with diabetes.

ARTICLE HIGHLIGHTS

There is a strong need for the better identification of early subclinical manifestations of microvascular complications, such as diabetic peripheral neuropathy, in young individuals with diabetes. To identify peripheral neuropathy and contributing factors at an asymptomatic disease stage, and to exclude height as a known modifying factor, we performed association studies of height-adjusted nerve conduction velocity. We identified high glucose variability, especially the SD of mean glucose, as an unexpectedly strong predictor of slowed nerve conduction velocity. More attention should be paid to the goal of low glucose variability in the care of individuals with diabetes.

[Value of C-peptide-based insulin resistance index for evaluating correlation between insulin resistance and serum uric acid level in individuals undergoing health examination]

OBJECTIVE

To investigate the value of C-peptide-based insulin resistance index in evaluating the correlation between insulin resistance and serum uric acid (Ua) level in subjects undergoing health examination.

METHODS

The data of 46 017 subjects undergoing health examination were retrospectively collected from the Second Medical Center of PLA General Hospital from January, 2017 to December, 2021. The subjects were divided into Ua≤420 μmol/L group and Ua>420 μmol/L group for comparison of HOMA insulin resistance index (HOMA2-IR) and HOMA insulin resistance-C peptide (HOMA2 IR-CP). The correlations of HOMA2-IR and HOMA2 IR-CP with Ua level were analyzed using Pearson correlation analysis and linear regression analysis. Hierarchical interaction analysis was conducted to assess the differences in the association between insulin resistance index and Ua level in different subgroups. The ROC curve was used to evaluate the predictive ability of insulin resistance index for an increased Ua level.

RESULTS

The levels of HOMA2-IR and HOMA2 IR-CP were significantly lower in Ua≤420 μmol/L group than in Ua>420 μmol/L group. Univariate Pearson correlation analysis showed a weak correlation of HOMA2-IR with Ua (r=0.262, P<0.001) and moderate correlation of HOMA2 IR-CP with Ua (r=0.409, P<0.001). Multivariate linear regression analysis, after adjustment for confounding factors, demonstrated that HOMA2-IR (R2=0.445, P<0.001) and HOMA2 IR-CP (R2=0.461, P<0.001) were both factors affecting Ua level. Hierarchical interaction analysis showed that the association of insulin resistance index with Ua level varied significantly with gender, age, and glucose metabolism (P<0.001). ROC curve showed that the areas under the curve predicted an increased Ua level by HOMA2-IR and HOMA2 IR-CP were 0.662 and 0.722, respectively.

CONCLUSIONS

HOMA2 IR-CP is a more accurate indicator for assessing the correlation between insulin resistance and Ua level.

Copper(II) Affects the Biochemical Behavior of Proinsulin C-peptide by Forming Ternary Complexes with Serum Albumin

Peptide hormones are essential signaling molecules with therapeutic importance. Identifying regulatory factors that drive their activity gives important insight into their mode of action and clinical development. In this work, we demonstrate the combined impact of Cu(II) and the serum protein albumin on the activity of C-peptide, a 31-mer peptide derived from the same prohormone as insulin. C-peptide exhibits beneficial effects, particularly in diabetic patients, but its clinical use has been hampered by a lack of mechanistic understanding. We show that Cu(II) mediates the formation of ternary complexes between albumin and C-peptide and that the resulting species depend on the order of addition. These ternary complexes notably alter peptide activity, showing differences from the peptide or Cu(II)/peptide complexes alone in redox protection as well as in cellular internalization of the peptide. In standard clinical immunoassays for measuring C-peptide levels, the complexes inflate the quantitation of the peptide, suggesting that such adducts may affect biomarker quantitation. Altogether, our work points to the potential relevance of Cu(II)-linked C-peptide/albumin complexes in the peptide's mechanism of action and application as a biomarker.

Affordable oral proinsulin bioencapsulated in plant cells regulates blood sugar levels similar to natural insulin

Diabetes Mellitus is a silent epidemic affecting >500 million, which claimed 6.7 million lives in 2021, a projected increase of >670% in <20 years old in the next two decades but insulin is unaffordable for the large majority of the globe. Therefore, we engineered proinsulin in plant cells to facilitate oral delivery. Stability of the proinsulin gene and expression in subsequent generations, after removal of the antibiotic-resistance gene, was confirmed using PCR, Southern and western blots. Proinsulin expression was high (up to 12 mg/g DW or 47.5% of total leaf protein), stable up to one year after storage of freeze-dried plant cells at ambient temperature and met FDA regulatory requirements of uniformity, moisture content and bioburden. GM1 receptor binding, required for uptake via gut epithelial cells was confirmed by pentameric assembly of CTB-Proinsulin. IP insulin injections (without C peptide) in STZ mice rapidly decreased blood glucose level leading to transient hypoglycemia, followed by hepatic glucose compensation. On the other hand, other than the 15-min lag period of oral proinsulin (transit time required to reach the gut), the kinetics of blood sugar regulation of oral CTB-Proinsulin in STZ mice was very similar to naturally secreted insulin in healthy mice (both contain C-peptide), without rapid decrease or hypoglycemia. Elimination of expensive fermentation, purification and cold storage/transportation should reduce cost and increase other health benefits of plant fibers. The recent approval of plant cell delivery of therapeutic proteins by FDA and approval of CTB-ACE2 for phase I/II human clinical studies augur well for advancing oral proinsulin to the clinic.

Molecular Mechanisms for the Vicious Cycle between Insulin Resistance and the Inflammatory Response in Obesity

The comprehensive anabolic effects of insulin throughout the body, in addition to the control of glycemia, include ensuring lipid homeostasis and anti-inflammatory modulation, especially in adipose tissue (AT). The prevalence of obesity, defined as a body mass index (BMI) ≥ 30 kg/m², has been increasing worldwide on a pandemic scale with accompanying syndemic health problems, including glucose intolerance, insulin resistance (IR), and diabetes. Impaired tissue sensitivity to insulin or IR paradoxically leads to diseases with an inflammatory component despite hyperinsulinemia. Therefore, an excess of visceral AT in obesity initiates chronic low-grade inflammatory conditions that interfere with insulin signaling via insulin receptors (INSRs). Moreover, in response to IR, hyperglycemia itself stimulates a primarily defensive inflammatory response associated with the subsequent release of numerous inflammatory cytokines and a real threat of organ function deterioration. In this review, all components of this vicious cycle are characterized with particular emphasis on the interplay between insulin signaling and both the innate and adaptive immune responses related to obesity. Increased visceral AT accumulation in obesity should be considered the main environmental factor responsible for the disruption in the epigenetic regulatory mechanisms in the immune system, resulting in autoimmunity and inflammation.

Immunoregulatory Sertoli Cell Allografts Engineered to Express Human Insulin Survive Humoral-Mediated Rejection

An effective treatment and possible cure for type 1 diabetes is transplantation of pancreatic islets. Unfortunately, transplanted islets are rejected by the immune system with humoral-mediated responses being an important part of rejection. Sertoli cells (SC), an immune regulatory cell shown to survive as allografts long-term without immunosuppressants, have the potential to be used as a cell-based gene therapy vehicle to deliver endogenous insulin-a possible alternative to islets. Previously, we transduced a mouse SC line to produce human insulin. After transplantation into diabetic mice, these cells consistently produced low levels of insulin with graft survival of 75% at 50 days post-transplantation. The object of this study was to assess humoral immune regulation by these engineered SC. Both nontransduced and transduced SC survived exposure to human serum with complement in vitro. Analysis of allografts in vivo at 20 and 50 days post-transplantation revealed that despite IgG antibody detection, complement factor deposition was low and grafts survived through 50 days post-transplantation. Furthermore, the transduced SC secreted elevated levels of the complement inhibitor C1q binding protein. Overall, this suggests SC genetically engineered to express insulin maintain their ability to prevent complement-mediated killing. Since inhibiting complement-mediated rejection is important for graft survival, further studies of how SC modifies the immune response could be utilized to advance the use of genetically engineered SC or to prolong islet allograft survival to improve the treatment of diabetes.

Poly-L-lysine Coated Oral Nanoemulsion for Combined Delivery of Insulin and C-Peptide

An attempt of co-delivery of insulin and C-peptide enclosed in linseed oil globules has been made employing a protective coating of positively charged poly-L-lysine to manage diabetes-associated complications. Oral water in oil in water (w/o/w) nanoemulsion manufactured by double emulsification method showed good entrapment efficiency of 87.6 ± 7.48% for insulin and 73.4 ± 6.44% for C-peptide. The optimized uncoated nanoemulsion showed a mean globule size of 210.6 ± 9.87 nm with a good PDI of 0.145 ± 0.033 and -21.7 ± 4.5 mV ZP. The poly-L-lysine coating of the nanoemulsion resulted in the reversal of surface charge to positive i.e. 18.3 ± 2.7 mV due to the cationic nature of poly-L-lysine. In vitro drug release showed an initial burst of 15-20% release within 4 h followed by controlled release up to 24 h. The poly-L-lysine coated nanoemulsion showed an 8.28-fold higher uptake than fluorescein isothiocyanate (FITC) solution in HCT116 intestinal cell lines. In vivo studies confirmed that orally administered insulin and C-peptide bearing coated nanoemulsion has the potential to improve glycemic control confirmed by blood glucose level under 200 mg/dL for 12 h compared to that of subcutaneous administration of insulin. The formulation was found stable at 25 °C as well as 4°C for up to 3 months. These findings show a promising approach for delivering oral insulin along with C-peptide for effective glycemic control and management of complications associated with diabetes.

Oral delivery of the intracellular domain of the insulinoma-associated protein 2 (IA-2ic) by bacterium-like particles (BLPs) prevents type 1 diabetes mellitus in NOD mice

Antigen-specific immune tolerance, which possesses great potential in preventing or curing type 1 diabetes mellitus (T1DM), can be induced by oral vaccination with T1DM-related autoantigens. However, direct administration of autoantigens via oral route exhibits a low tolerance-inducing effect as a result of the digestion of protein antigens in the gastrointestinal tract (GIT) and therefore, a large dosage of autoantigens may be needed. In this study, bacterium-like particles (BLPs) made from food-grade lactic acid bacteria were used to deliver the intracellular domain of the insulinoma-associated protein 2 (IA-2ic). For this purpose, BLPs-IA-2ic vaccine in which IA-2ic bound to the surface of BLPs was constructed. BLPs enhanced the stability of the delivered IA-2ic based on the stability analysis in vitro. Oral administration of BLPs-IA-2ic significantly reduced T1DM incidence in NOD mice. The mice fed BLPs-IA-2ic exhibited a significant reduction in insulitis and preserved the ability to secrete insulin. Immunologic analysis showed that oral vaccination with BLPs-IA-2ic induced antigen-specific T cell tolerance. The results revealed that the successful induction of immune tolerance was dependent on the immune deviation (in favor of T helper 2 responses) and CD4+CD25+FoxP3+ regulatory T cells. Hence, oral vaccination with BLPs-IA-2ic shows potential for application in preventing T1DM.

The bidirectional association of C-peptide with cardiovascular risk in nondiabetic adults and patients with newly diagnosed type 2 diabetes mellitus: a retrospective cohort study

Background

Recent literature reported the biological role of C-peptide, but this role is still controversial and unclear. The primary aim of this study was to investigate associations between C-peptide and cardiovascular biomarkers as well as events.

Methods

A total of 55636 participants who had a health examination from 2017 to 2021 were included. Of them, 6727 participants visited the hospital at least twice. Cardiovascular biomarkers like high-sensitivity C-reactive protein (hs-CRP) and high-sensitivity cardiac troponin T (hs-cTnT) were measured and their relationships with fasting C-peptide were evaluated for all participants. Cardiovascular events were obtained during the last visit and their associations with C-peptide were evaluated for those participants who visited the hospital at least twice.

Results

Among the included participants, 11.1% had a previous type 2 diabetes mellitus (T2DM). In the participants without previous T2DM, the relationships between fasting C-peptide and hs-CRP and hs-cTnT were negative if the value of fasting C-peptide was < 1.4 ng/mL and positive if the value was ≥ 1.4 ng/mL. These relationships remained significant after adjusting for hemoglobin A1c, insulin resistance index, and its interaction with C-peptide, even if the participants were stratified by glucose metabolism status or levels of insulin resistance index. Hazard ratios of cardiovascular events were first decreased and then increased with the increasing of baseline C-peptide levels, though these associations became unsignificant using the multivariate Cox regression model. Unlike the participants without previous T2DM, the associations of C-peptide with cardiovascular biomarkers and events were not significant in the patients with previous T2DM.

Conclusions

The associations of C-peptide with cardiovascular biomarkers and events were different between the participants without previous T2DM and those with previous T2DM. The effect of C-peptide on cardiovascular risk may be bidirectional, play a benefit role at a low level, and play a harmful role at a high level in the nondiabetic adults and the patients with newly diagnosed T2DM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01636-z.

Sertoli Cell Immune Regulation: A Double-Edged Sword

The testis must create and maintain an immune privileged environment to protect maturing germ cells from autoimmune destruction. The establishment of this protective environment is due, at least in part, to Sertoli cells. Sertoli cells line the seminiferous tubules and form the blood-testis barrier (BTB), a barrier between advanced germ cells and the immune system. The BTB compartmentalizes the germ cells and facilitates the appropriate microenvironment necessary for spermatogenesis. Further, Sertoli cells modulate innate and adaptive immune processes through production of immunoregulatory compounds. Sertoli cells, when transplanted ectopically (outside the testis), can also protect transplanted tissue from the recipient’s immune system and reduce immune complications in autoimmune diseases primarily by immune regulation. These properties make Sertoli cells an attractive candidate for inflammatory disease treatments and cell-based therapies. Conversely, the same properties that protect the germ cells also allow the testis to act as a reservoir site for infections. Interestingly, Sertoli cells also have the ability to mount an antimicrobial response, if necessary, as in the case of infections. This review aims to explore how Sertoli cells act as a double-edged sword to both protect germ cells from an autoimmune response and activate innate and adaptive immune responses to fight off infections.

Polymeric Nanostructures Containing Proteins and Peptides for Pharmaceutical Applications

Over the last three decades, proteins and peptides have attracted great interest as drugs of choice for combating a broad spectrum of diseases, including diabetes mellitus, cancer, and infectious and neurological diseases. However, the delivery of therapeutic proteins to target sites should take into account the obstacles and limitations related to their intrinsic sensitivity to different environmental conditions, fragile tertiary structures, and short half-life. Polymeric nanostructures have emerged as competent vehicles for protein delivery, as they are multifunctional and can be tailored according to their peculiarities. Thus, the enhanced bioavailability and biocompatibility, the adjustable control of physicochemical features, and the colloidal stability of polymer-based nanostructures further enable either the embedding or conjugation of hydrophobic or hydrophilic bioactive molecules, which are some of the features of paramount importance that they possess and which contribute to their selection as vehicles. The present review aims to discuss the prevalent nanostructures composed of block copolymers from the viewpoint of efficient protein hospitality and administration, as well as the up-to-date scientific publications and anticipated applications of polymeric nanovehicles containing proteins and peptides.

Insulin Requirement and Complications Associated With Serum C-Peptide Decline in Patients With Type 1 Diabetes Mellitus During 15 Years After Diagnosis

OBJECTIVE

C-peptide is conventionally used in assessing pancreatic function in patients with diabetes mellitus. The clinical significance of this molecule during the course of type 1 diabetes mellitus (T1DM) has been recently revisited. This study aimed to investigate the natural course of C-peptide in T1DM patients over the period of 15 years and analyze the association between the residual C-peptide and diabetes complications.

METHODS

This retrospective study included a total of 234 children and adolescents with T1DM. Patient data including sex, age at diagnosis, anthropometric measures, daily insulin dose, serum HbA1c, post-prandial serum C-peptide levels, lipid profiles, and diabetic complications at the time of diagnosis and 1, 3, 5, 10, and 15 years after diagnosis were retrospectively collected.

RESULTS

Among the 234 patients, 101 were men and 133 were women, and the mean patient age at initial diagnosis was 8.3 years. Serum C-peptide decreased constantly since the initial diagnosis, and showed a significant decline at 3 years after diagnosis. At 15 years after diagnosis, only 26.2% of patients had detectable serum C-peptide levels. The subgroup with older patients and patients with higher BMI standard deviation score showed higher mean serum C-peptide, but the group-by-time results were not significant, respectively. Patients with higher serum C-peptide required lower doses of insulin and had fewer events of diabetic ketoacidosis.

CONCLUSION

Serum C-peptide decreased consistently since diagnosis of T1DM, showing a significant decline after 3 years. Patients with residual C-peptide required a lower dose of insulin and had a lower risk for diabetic ketoacidosis.

Analysis of immune cell components and immune-related gene expression profiles in peripheral blood of patients with type 1 diabetes mellitus

BACKGROUND

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease caused by severe loss of pancreatic β cells. Immune cells are key mediators of β cell destruction. This study attempted to investigate the role of immune cells and immune-related genes in the occurrence and development of T1DM.

METHODS

The raw gene expression profile of the samples from 12 T1DM patients and 10 normal controls was obtained from Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified by Limma package in R. The least absolute shrinkage and selection operator (LASSO)-support vector machines (SVM) were used to screen the hub genes. CIBERSORT algorithm was used to identify the different immune cells in distribution between T1DM and normal samples. Correlation of the hub genes and immune cells was analyzed by Spearman, and gene-GO-BP and gene-pathway interaction networks were constructed by Cytoscape plug-in ClueGO. Receiver operating characteristic (ROC) curves were used to assess diagnostic value of genes in T1DM.

RESULTS

The 50 immune-related DEGs were obtained between the T1DM and normal samples. Then, the 50 immune-related DEGs were further screened to obtain the 5 hub genes. CIBERSORT analysis revealed that the distribution of plasma cells, resting mast cells, resting NK cells and neutrophils had significant difference between T1DM and normal samples. Natural cytotoxicity triggering receptor 3 (NCR3) was significantly related to the activated NK cells, M0 macrophages, monocytes, resting NK cells, and resting memory CD4⁺ T cells. Moreover, tumor necrosis factor (TNF) was significantly associated with naive B cell and naive CD4⁺ T cell. NCR3 [Area under curve (AUC) = 0.918] possessed a higher accuracy than TNF (AUC = 0.763) in diagnosis of T1DM.

CONCLUSIONS

The immune-related genes (NCR3 and TNF) and immune cells (NK cells) may play a vital regulatory role in the occurrence and development of T1DM, which possibly provide new ideas and potential targets for the immunotherapy of diabetes mellitus (DM).