Effects of C-peptide on blood flow, capillary diffusion capacity and glucose utilization in the exercising forearm of type 1 (insulin-dependent) diabetic patients

Effects of C-Peptide on Dexamethasone-Induced In Vitro and In Vivo Models as a Potential Therapeutic Agent for Muscle Atrophy

This study aimed to investigate the effects of C-peptide on C2C12 myotubes and a mouse model. Both in vitro and in vivo experiments were conducted to elucidate the role of C-peptide in muscle atrophy. Various concentrations (0, 0.01, 0.1, 1, 10, and 100 nM) of C-peptide were used on the differentiated C2C12 myotubes with or without dexamethasone (DEX). C57BL/6J mice were administered with C-peptide and DEX for 8 days, followed by C-peptide treatment for 12 days. Compared to the DEX group, C-peptide increased the fusion and differentiation indices and suppressed atrophic factor expression in C2C12 myotubes. However, 100 nM C-peptide decreased the fusion and differentiation indices and increased atrophic factor expression regardless of DEX treatment. In C57BL/6J mice, DEX + C-peptide co-treatment significantly attenuated the body and muscle weight loss and improved the grip strength and cross-sectional area of the gastrocnemius (Gas) and quadriceps (Quad) muscles. C-peptide downregulated the mRNA and protein levels of muscle degradation-related markers, particularly Atrogin-1, in Gas and Quad muscles. This study underscores the potential of C-peptides in mitigating muscle weight reduction and preserving muscle function during muscle atrophy via molecular regulation. In addition, the work presents basic data for future studies on the effect of C-peptide on diabetic muscular dystrophy.

The Potential Role of C-peptide in Sexual and Reproductive Functions in Type 1 Diabetes Mellitus: An Update

BACKGROUND

Although hyperglycaemia is known to be the leading cause of diabetic complications, the beneficial effect of optimal glucose control in preventing diabetic complications is still far from being proven. In fact, such complications may not be related to glycaemic control alone.

OBJECTIVE

This review summarizes several studies that suggest that a C-peptide deficiency could be new and common pathophysiology for complications in type 1 diabetes, including sexual and reproductive dysfunction.

METHODS

We reviewed in vitro, in vivo, and human studies on the association between C-peptide deficiency or C-peptide replacement therapy and complications in type 1 diabetes. It seems that Cpeptide replacement therapy may interrupt the connection between diabetes and sexual/reproductive dysfunction.

RESULTS

The Diabetes Control and Complications Trial suggested that maintaining C-peptide secretion is associated with a reduced incidence of retinopathy, nephropathy, and hypoglycaemia. Risk of vascular, hormonal, and neurologic damage in the structures supplying blood to the penis increases with increasing levels of HbA1. However, several human studies have suggested an association between C-peptide production and hypothalamic/pituitary functions. When exposed to C-peptide, cavernosal smooth muscle cells increase the production of nitric oxide. C-peptide in diabetic rats improves sperm count, sperm motility, testosterone levels, and nerve conduction compared to non-treated diabetic rats.

CONCLUSION

C-peptide deficiency may be involved, at least partially, in the development of several pathological features associated with type 1 diabetes, including sexual/reproductive dysfunction. Preliminary studies have reported that C-peptide administration protects against diabetic microand macrovascular damages as well as sexual/reproductive dysfunction. Therefore, further studies are needed to confirm these promising findings.

Specific Binding of Leptin to Red Blood Cells Delivers a Pancreatic Hormone and Stimulates ATP Release

Since its discovery in 1994, leptin continues to have new potential physiological roles uncovered, including a role in the regulation of blood flow. Leptin's role in regulating blood flow is not completely understood. Red blood cell (RBC)-derived ATP is a recognized stimulus of blood flow, and multiple studies suggest that C-peptide, a hormone secreted in equimolar amounts with insulin from the pancreatic β-cells, can stimulate that release when delivered by albumin and in combination with Zn²⁺. Here, we report leptin delivers C-peptide and Zn²⁺ to RBCs in a saturable and specific manner. We labeled leptin with technetium-99 m (^99mTc) to perform binding studies while using albumin to block the specific binding of ^99mTc-leptin in the presence or absence of C-peptide. Our results suggest that leptin has a saturable and specific binding site on the RBC ((K_d = 1.79 ± 0.46) × 10^-7 M) that is statistically equal to the binding affinity in the presence of 20 nM C-peptide ((K_d = 2.05 ± 0.20) × 10^-7 M). While the binding affinity between leptin and the RBC did not change with C-peptide, the moles of bound leptin did increase with C-peptide, suggesting a separate binding site on the cell for a leptin/C-peptide complex. The RBC-derived ATP increased in the presence of a leptin/C-peptide/Zn²⁺ addition, in a concentration-dependent manner. Control RBCs ATP release increased (71 ± 5.6%) in the presence of C-peptide and Zn²⁺, which increased further to (94 ± 5.6%) in the presence of Zn²⁺, C-peptide, and leptin.

Preserved C-peptide secretion in patients with type 1 diabetes and incipient chronic complications is associated with lower serum resistin and higher uric acid levels

Background and aims

Previous studies suggested that long-term perseverance of beta-cell function in patients with type 1 diabetes (T1DM) is associated with lower incidence of microvascular complications. The objective of this study was to evaluate preserved C-peptide secretion in patients with T1DM without overt chronic complications and to explore associations with resistin and uric acid as biomarkers of microvascular complication pathogenesis.

Materials and methods

We assessed residual beta-cell function in 164 T1DM patients (male/female = 91/73; age/diabetes duration range = 18-70/1-30 years) using an ultrasensitive C-peptide ELISA assay with detection limit of 2.5 pmol/L and total coefficient of variation (CV) 5,8% (Mercodia, Sweden). Serum level of uric acid was measured by enzymatic method (AU680, Beckman Coulter, USA) while resistin concentration was determined by the ELISA assay (Biovendor, Czech Republic).

Results

C-peptide secretors had shorter diabetes duration (5.1 vs. 16 years; p < 0,001), lower resistin (4.53 vs. 4.93 mg/mL p = 0.045), and higher uric acid (259 vs 238 μmol/L, p = 0.048) level than T1DM patients with no detectable C-peptide levels, while no differences in routine anthropometric and laboratory variables, including HbA1c, were observed. Although the proportion of C-peptide secretors significantly decreased across categories of diabetes duration (70%, 38%, 17% and 15% for <5, 5-10, 10-20 and 20-30 years of duration, respectively; p < 0,001), detectable C-peptide was found in 5/23 T1DM patients who were diagnosed with T1DM more than 20 years ago.

Conclusion

The results of our study revealed that patients with detectable C-peptide had lower resistin and higher uric acid level compared to patients with undetectable C-peptide.

Effects of C-Peptide Replacement Therapy on Bone Microarchitecture Parameters in Streptozotocin-Diabetic Rats

C-peptide therapy protects against diabetic micro- and macrovascular damages and neuropatic complications. However, to date, the role of C-peptide in preventing diabetes-related bone loss has not been investigated. Our aim was to evaluate if C-peptide infusion improves bone quality in diabetic rats. Twenty-three male Wistar rats were randomly divided into three groups: normal control group; sham diabetic control group; diabetic plus C-peptide group. Diabetes was induced by streptozotocin injection and C-peptide was delivered subcutaneously for 6 weeks. We performed micro-CT and histological testing to assess several trabecular microarchitectural parameters. At the end, diabetic plus C-peptide rats had a higher serum C-peptide (p = 0.02) and calcium (p = 0.04) levels and tibia weight (p = 0.02) than the diabetic control group. The diabetic plus C-peptide group showed a higher trabecular thickness and cross-sectional thickness than the diabetic control group (p = 0.01 and p = 0.03). Both the normal control and diabetic plus C-peptide groups had more Runx-2 and PLIN1 positive cells in comparison with the diabetic control group (p = 0.045 and p = 0.034). Diabetic rats receiving C-peptide had higher quality of trabecular bone than diabetic rats not receiving this treatment. If confirmed, C-peptide could have a role in improving bone quality in diabetes.

Comparative Effect Of Curcumin Versus Liposomal Curcumin On Systemic Pro-Inflammatory Cytokines Profile, MCP-1 And RANTES In Experimental Diabetes Mellitus

Purpose

Anti-inflammatory proprieties of curcumin were proved to be useful in various diseases, including diabetes mellitus. The aim of this study was to assess the anti-inflammatory comparative effect of curcumin solution with liposomal curcumin formula, regarding the improvement of serum levels of TNF-α (tumor necrosis factor-alpha), IL-6 (interleukin), IL-1α, IL-1β, MCP-1 (monocyte chemoattractant protein-1) and RANTES in experimental diabetes, induced by streptozotocin (STZ), in rats.

Materials and methods

Six groups of 7 rats were investigated regarding the effect of i.p. (intraperitoneal) administration of two concentrations of curcumin solution (CC1 and CC2) and two concentrations of liposomal curcumin (LCC1 and LCC2): group 1 – control group with i.p. administration of 1 mL saline solution, group 2 – i.p. STZ administration (60mg/kg bw, bw=body weight), group 3 – STZ+CC1 administration, group 4 – STZ+CC2 administration, group 5 – STZ+ LCC1 administration and group 6 – STZ+ LCC2 administration. The concentrations of curcumin formulas were 1 mg/0.1 kg bw for CC1 and LCC1 and 2 mg/0.1 kg bw for CC2 and LCC2, respectively. Serum levels of C-peptide (as an indicator of pancreatic function) and TNF-α, IL-6, IL-1α, IL-1β, MCP-1, and RANTES (as biomarkers for systemic inflammation) were assessed for each group.

Results

The plasma level of C-peptide showed significant improvements when LCC was administrated, with better results for LCC2 when compared to LCC1 (P<0.003). LCC2 pretreatment proved to be more efficient in reducing the level of TNF-α (P<0.003) and RANTES (P<0.003) than CC2 pretreatment. Upon comparing LCC2 with LCC1 formulas, the differences were significant for TNF-α (P=0.004), IL-1β (P=0.022), and RANTES (P=0.003) levels.

Conclusion

Liposomal curcumin in a dose of 2 mg/0.1 kg bw proved to have an optimum therapeutic effect as a pretreatment in DM induced by STZ. This result can constitute a base for clinical studies for curcumin efficiency as adjuvant therapy in type 1 DM.

Anti-inflammatory effects of C-peptide on kidney of type 1 diabetes mellitus animal model

Type 1 diabetes mellitus (T1DM) is characterized by C-peptide deficiency and elevated levels of pro-inflammatory cytokines. The aim of this study was to investigate the role of C-peptide in renal and inflammatory complications in streptozotocin (STZ)-diabetic mice model of T1DM with kidney disease. The study was performed in 8-week old male C57BL/6 mice. Two streptozotocin-diabetic groups (a T1DM animal model), after 4 weeks of diabetes, were treated with subcutaneous infusion of either vehicle (n = 12) or C-peptide (n = 11). Two non-diabetic groups (vehicle, n = 10; C-peptide, n = 9) were treated using the same protocol as described for the diabetic mice. The treatment with C-peptide in the diabetic group reduced the urinary levels of IL17 and TNFα, as well as IL4 and IL10 (p < 0.05). Contrary, the diabetic + C-peptide group presented higher IL10 gene expression in kidney. Besides, it displayed a reduction of TNFα gene expression. The data suggest that C-peptide may modulate pro- and anti-inflammatory signalling pathways, resulting in attenuation of kidney inflammation in T1DM animal model.

An update on the potential role of C-peptide in diabetes and osteoporosis

PURPOSE

C-peptide secretion is deficient or absent in type 1 diabetes mellitus. It is well accepted that insulin replacement therapy cannot prevent the development of long-term diabetes-related complications, which can often be disabling or even life-threatening. Several cross-sectional investigations have suggested that residual C-peptide production in patients with type 1 diabetes mellitus would help prevent a number of complications. In animal models of diabetes and in patients with type 1 diabetes mellitus, C-peptide replacement improves renal function, skin and skeletal muscle blood flow, nerve conduction, glucose utilization, and other diabetes-related complications. Recent investigations suggest a new beneficial effect of C-peptide, which to date has never been studied. It is known that osteoporosis is the most prevalent short-term complication in type 1 diabetes mellitus. This review will highlight new insights into the pathophysiology and future therapeutic modalities for osteoporosis in individuals with diabetes.

METHODS

This review provides a concise summary of old and new insights into the role of C-peptide in diabetes-related complications.

RESULTS

The data suggest that C-peptide is a bioactive peptide, acting independently of insulin, which binds to a G-protein-coupled membrane binding site in different cell types. By triggering Ca²⁺-dependent intracellular signaling pathways, both Na⁺, K⁺-ATPase and endothelial nitric oxide synthase are activated. C-peptide may act on osteoblast cells by ERK 1/2 pathway activation, modulate collagen biosynthesis and RANKL expression. Furthermore, C-peptide-deficient postmenopausal women, not affected by diabetes, have a lower bone mineral density than those with normal C-peptide levels.

CONCLUSION

Taken together these studies encourage further investigations to elucidate the role of C-peptide in preventing bone loss in type 1 diabetes mellitus and in those individuals with C-peptide deficiency and osteoporosis.

ω-3 polyunsaturated fatty acids ameliorate type 1 diabetes and autoimmunity

Despite the benefit of insulin, blockade of autoimmune attack and regeneration of pancreatic islets are ultimate goals for the complete cure of type 1 diabetes (T1D). Long-term consumption of ω-3 polyunsaturated fatty acids (PUFAs) is known to suppress inflammatory processes, making these fatty acids candidates for the prevention and amelioration of autoimmune diseases. Here, we explored the preventative and therapeutic effects of ω-3 PUFAs on T1D. In NOD mice, dietary intervention with ω-3 PUFAs sharply reduced the incidence of T1D, modulated the differentiation of Th cells and Tregs, and decreased the levels of IFN-γ, IL-17, IL-6, and TNF-α. ω-3 PUFAs exerted similar effects on the differentiation of CD4+ T cells isolated from human peripheral blood mononuclear cells. The regulation of CD4+ T cell differentiation was mediated at least in part through ω-3 PUFA eicosanoid derivatives and by mTOR complex 1 (mTORC1) inhibition. Importantly, therapeutic intervention in NOD mice through nutritional supplementation or lentivirus-mediated expression of an ω-3 fatty acid desaturase, mfat-1, normalized blood glucose and insulin levels for at least 182 days, blocked the development of autoimmunity, prevented lymphocyte infiltration into regenerated islets, and sharply elevated the expression of the β cell markers pancreatic and duodenal homeobox 1 (Pdx1) and paired box 4 (Pax4). The findings suggest that ω-3 PUFAs could potentially serve as a therapeutic modality for T1D.

C-Peptides for diagnostics and therapy: a veterinary medicine point of view

ABSTRACT: Empirical studies proved that C-peptides are performing numerous intrinsic biological roles, and serve as a marker for pancreatic performance analysis. Since the last decade, C-peptide assays for differential diagnosis in veterinary diabetic patients are becoming more available, but still only for a very limited number of species. Studies on C-peptide as a diagnostic tool, therapy for associated complications, or as replacement therapies for C-peptide deficiency still showed not to be a common practice in veterinary medicine. This review was conducted to determine the potential importance of C-peptide in Veterinary Medicine, relevant in the diagnosis of diabetes and for other metabolic processes, as well as its proposed therapeutic benefits. Numerous articles were identified that reported positive results in their experimental studies, whether C-peptide as a biomarker for pancreatic performance in dogs, cats, and horses, as a non-invasive method to monitor nutritional status in primates, or to investigate its potential therapeutic benefits for diabetes-related illnesses.

Efficacy of a long-acting C-peptide analogue against peripheral neuropathy in streptozotocin-diabetic mice

AIMS

To investigate the efficacy of a pegylated C-peptide (Peg-C-peptide) against indices of peripheral neuropathy in a mouse model of type 1 diabetes and to compare efficacy of this C-peptide analogue against that of the native molecule.

METHODS

C57Bl/6 mice were injected with two consecutive doses of streptozotocin (STZ) to induce type 1 diabetes. Mice were treated twice daily with native C-peptide [0.4-1.3 mg/kg subcutaneously (s.c.)] or twice weekly with Peg-C-peptide (0.1-1.3 mg/kg s.c.) for 20 weeks. Motor and sensory nerve conduction velocities, thermal and tactile responses and rate dependent H-wave depression were assessed after 20 weeks of diabetes. Foot skin intraepidermal fibres and corneal nerves were counted, and sciatic nerve substance P and plasma C-peptide levels were also determined.

RESULTS

After 5 months of STZ-induced diabetes, mice exhibited significant motor and sensory nerve conduction slowing, thermal hypoalgesia, tactile allodynia and attenuation of rate-dependent depression of the H reflex. These functional disorders were accompanied by nerve substance P depletion but not loss of small sensory fibres in the hind paw epidermis or the cornea. The efficacy of twice-daily treatment with native C-peptide in preventing these disorders was matched or exceeded by twice-weekly treatment with Peg-C-peptide. Both native and Peg-C-peptide also increased corneal nerve occupancy in the sub-basal nerve plexus of control rats.

CONCLUSIONS

These data identify actions of C-peptide against novel and clinically pertinent aspects of diabetic neuropathy in mice and also establish Peg-C-peptide as a long-acting therapeutic method of potential clinical value.

C-peptide: new findings and therapeutic possibilities

Much new information on C-peptide physiology has appeared during the past 20 years. It has been shown that C-peptide binds specifically to cell membranes, elicits intracellular signaling via G-protein and Ca2+ -dependent pathways, resulting in activation and increased expression of endothelial nitric oxide synthase, Na+, K+ -ATPase and several transcription factors of importance for anti-inflammatory, anti-oxidant and cell protective mechanisms. Studies in animal models of diabetes and early clinical trials in patients with type 1 diabetes demonstrate that C-peptide in replacement doses elicits beneficial effects on early stages of diabetes-induced functional and structural abnormalities of the peripheral nerves, the kidneys and the retina. Much remains to be learned about C-peptide's mechanism of action and long-term clinical trials in type 1 diabetes subjects will be required to determine C-peptide's clinical utility. Nevertheless, even a cautious evaluation of the available evidence presents the picture of a bioactive endogenous peptide with therapeutic potential.

Prognostic value of endothelial dysfunction in type 1 diabetes mellitus

Patients with diabetes mellitus are at high risk of developing atherosclerosis, associated with higher rates of micro and macro vascular involvement such as coronary artery disease and renal disease. The role of hyperglycemia to induce synthesis of reactive oxygen species by the oxidation of glucose, leading to an increased production of advanced glycosylation end products, as well as inflammation and oxidative stress has been proposed as a possible mechanism in the pathogenesis of endothelial dysfunction (ED). The interaction between C-peptide - the connecting segment of pro-insulin-and nitric oxide in vasodilation is also discussed. Therefore, endothelial dysfunction has been identified as an early marker of vascular disorder in type 1 and type 2 diabetes mellitus. In some other diseases, ED has been considered an independent predictor of vascular disease, regardless of the method used. Studies have demonstrated the importance of endothelial dysfunction as an useful tool for identifying the risk of vascular complications in patients with type 1 diabetes mellitus, particularly as regards to renal impairment. The aim of this review is to clarify the prognostic value of endothelial dysfunction as a marker of vascular disease in these subjects.

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.

Prevention of VEGF-mediated microvascular permeability by C-peptide in diabetic mice

AIMS

Human C-peptide has a beneficial effect on the prevention of diabetic neuropathy, nephropathy, and vascular complications; however, its role in protection against increased vascular permeability in diabetes remains unclear. Our purpose was to explore the potential protective role of C-peptide against microvascular permeability mediated by vascular endothelial growth factor (VEGF)-induced reactive oxygen species (ROS) generation in diabetes.

METHODS AND RESULTS

Generation of intracellular ROS, real-time changes in intracellular Ca(2+), ROS-dependent stress fibre formation, and the disassembly of the adherens junctions were studied by a confocal microscopy in human umbilical vein endothelial cells (HUVECs). VEGF-induced vascular leakage was investigated in the skin of diabetic mice using a Miles vascular permeability assay. Microvascular leakage in the retina of streptozotocin diabetic mice was investigated using a confocal microscopy after left ventricle injection of fluorescein isothiocyanate (FITC)-dextran. C-peptide inhibited the VEGF-induced ROS generation, stress fibre formation, disassembly of vascular endothelial cadherin, and endothelial permeability in HUVECs. Intradermal injection of C-peptide prevented VEGF-induced vascular leakage. Consistent with this, intravitreal injection of C-peptide prevented the extravasation of FITC-dextran in the retinas of diabetic mice, which was also prevented by anti-VEGF antibody and ROS scavengers in diabetic mice. Conclusions/interpretation C-peptide prevents VEGF-induced microvascular permeability by inhibiting ROS-mediated intracellular events in diabetic mice, suggesting that C-peptide replacement is a promising therapeutic strategy to prevent diabetic retinopathy.

C-peptide levels are associated with mortality and cardiovascular mortality in patients undergoing angiography: the LURIC study

OBJECTIVE

C-peptide is a proinsulin cleavage product released from the pancreas in amounts equimolar to insulin, and elevated levels of C-peptide have been found in patients with insulin resistance and early type 2 diabetes mellitus. Recent data suggest that C-peptide could play a causal role in the pathophysiology of vascular disease, but nothing is known about the prognostic value of C-peptide concentrations in the circulation.

RESEARCH DESIGN AND METHODS

We examined whether C-peptide is associated with cardiovascular and total mortality in 2,306 patients from the Ludwigshafen Risk and Cardiovascular Health Study who underwent coronary angiography at baseline (1997-2000).

RESULTS

During a mean follow-up of 7.6 years, 440 deaths (19.1%) occurred, 252 (10.9%) of which were due to cardiovascular causes. Age- and sex-adjusted hazard ratios (HRs) in the third compared with the first tertile of C-peptide were 1.46 (95% CI 1.15-1.85; P = 0.002) for all cause and 1.58 (1.15-2.18; P = 0.005) for cardiovascular mortality. After further adjustment for common risk factors as well as markers of glucose metabolism, these HRs remained significant at 1.46 (1.10-1.93; P = 0.008) and 1.55 (1.07-2.24; P = 0.022), respectively. Moreover, patients in higher tertiles of C-peptide exhibited higher levels of markers of endothelial dysfunction and atherosclerosis as well as a more severe extent of coronary lesions.

CONCLUSIONS

In patients undergoing coronary angiography, C-peptide levels are independently associated with all cause and cardiovascular mortality as well as presence and severity of coronary artery disease. Further studies are needed to examine a potential causal role of C-peptide in atherogenesis in humans.

Early transcriptional regulation by C-peptide in freshly isolated rat proximal tubular cells

BACKGROUND

Clinical studies have shown that proinsulin C-peptide exerts renoprotective effects in type 1 diabetes, although the underlying mechanisms are poorly understood. As C-peptide has been shown to induce several intracellular events and to localize to nuclei, we aimed to determine whether gene transcription is affected in proximal tubular kidney cells, and if so, whether the genes with altered transcription include those related to protective mechanisms.

METHODS

The effect of C-peptide incubation (2 h) on gene expression was investigated in freshly isolated proximal tubular cells from streptozotocin-diabetic Sprague-Dawley rats using global gene expression profiling and real-time quantitative polymerase chain reaction. Protein expression was assayed using western blotting. Different bioinformatic strategies were employed.

RESULTS

Gene transcription profiling demonstrated differential transcription of 492 genes (p < 0.01) after 2 h of C-peptide exposure, with the majority of these genes repressed (83%). Real-time quantitative polymerase chain reaction validation supported a trend of several G protein-coupled receptors being activated, and certain transcription factors being repressed. Also, C-peptide repressed the transcription of genes associated with the pathways of circulatory and inflammatory diseases.

CONCLUSION

This study shows that C-peptide exerts early effects on gene transcription in proximal tubular cells. The findings also bring further knowledge to the renoprotective mechanisms of C-peptide in type 1 diabetes, and support a transcriptional activity for C-peptide. It is suggested that C-peptide may play a regulatory role in the gene expression of proximal tubular cells.

Renal and vascular benefits of C-peptide: Molecular mechanisms of C-peptide action

C-peptide has long been thought to be an inert byproduct of insulin production, but it has become apparent, and accepted, that C-peptide has important biological properties. C-peptide displays beneficial effects in many tissues affected by diabetic complications, such as increased peripheral blood flow and protection from renal damage. However, the mechanisms mediating these effects remain unclear. C-peptide interacts with cellular membranes at unidentified sites distinctive of the insulin family of receptors, and signals to multiple targets known to play a role in diabetes and diabetic complications, such as Na⁺/K⁺-ATPase and NOS. In general, the physiological and molecular effects of C-peptide resemble insulin, but C-peptide also possesses traits separate from those of insulin. These basic studies have been confirmed in human studies, suggesting that C-peptide may lend itself to clinical applications. However, the molecular and physiological properties of C-peptide are not completely elucidated, and large clinical studies have not begun. In order to further these goals, we critically summarize the current state of knowledge regarding C-peptide’s renal and vascular effects and the molecular signaling of C-peptide.

C-peptide stimulates nitrites generation via the calcium-JAK2/STAT1 pathway in murine macrophage Raw264.7 cells

AIMS

C-peptide is a product of pro-insulin cleavage. Numerous studies have demonstrated that C-peptide, although not influencing blood glucose control, may play a role in preventing and potentially reversing some of the chronic complications of type 1 diabetes. The aim of this paper was to present a novel function of C-peptide, focusing on its role in nitric oxide (NO) generation.

MAIN METHODS

Murine macrophage Raw264.7 cells and primary peritoneal macrophages were incubated under control conditions, or with C-peptide. Expression level of iNOS and phosphorylation status of JAK2/STAT1 were analyzed by Western blot. Fluorometric NO assay kit was used to assess the concentration of nitrite in culture medium. Intracellular calcium concentration was measured with calcium indicator dyes, such as Fura-2 and Fluo-3 AM.

KEY FINDINGS

C-peptide increased the level of nitrites in murine macrophage Raw264.7 cells. The nitrites production induced by lipopolysaccharide (LPS) was further enhanced by co-treatment of C-peptide. This up-regulation of nitrites generation also correlated with the induction of inducible nitric oxide synthase (iNOS), a prominent marker of macrophage activation. In addition, C-peptide increased the intracellular concentration of calcium levels. Moreover, C-peptide-induced nitrites generation and increase in calcium was observed in freshly isolated primary peritoneal macrophages. In addition, C-peptide specifically affected the Janus activated kinase (JAK)/signal transducer and activated transcription (STAT) pathway. Finally, C-peptide-mediated nitrites generation and JAK2/STAT1 phosphorylation were not detected in the presence of the intracellular calcium chelator, BAPTA-AM.

SIGNIFICANCE

These results suggest that C-peptide may elicit immune modulatory function via modulation of the calcium/JAK-STAT pathway.

Molecular effects of C-Peptide in microvascular blood flow regulation

C-Peptide is produced in beta-cells in the pancreas, and secreted into the blood stream in equimolar amounts with insulin. For a long time, C-peptide was considered as an important component in the biosynthesis of insulin, but otherwise believed to possess minimal biological activity. In the recent years, numerous studies demonstrated that lacking C-peptide in type 1 diabetic patients might exert an important role in the development of microvascular complications such as nephropathy or neuropathy. There is increasing evidence that the biological effects of C-peptide are, at least in part, mediated through the modulation of endothelial function and microvascular blood flow. In several tissues, an increase in microvascular and nutritional blood flow could be observed during substitution of physiological amounts of C-peptide. Recent studies confirmed that C-peptide stimulates endothelial NO release by the activation of Ca2+ calmodulin-regulated endothelial NO synthase. A restoration of Na+/K+-ATPase activity during C-peptide supplementation could be observed in erythrocytes and renal tubular cells. The improvement of erythrocyte Na+/K+-ATPase is associated with an increase in erythrocyte deformability, and improved rheological properties. In this article, we consider the role of C-peptide in the context of endothelial function and microvascular blood flow as pathophysiologic components in the development of microvascular complications in patients with diabetes mellitus and loss of beta-cell function.

The beneficial effects of C-Peptide on diabetic polyneuropathy

Diabetic polyneuropathy (DPN) is a common complication in diabetes. At present, there is no adequate treatment, and DPN is often debilitating for patients. It is a heterogeneous disorder and differs in type 1 and type 2 diabetes. An important underlying factor in type 1 DPN is insulin deficiency. Proinsulin C-peptide is a critical element in the cascade of events. In this review, we describe the physiological role of C-peptide and how it provides an insulin-like signaling function. Such effects translate into beneficial outcomes in early metabolic perturbations of neural Na+/K+-ATPase and nitric oxide (NO) with subsequent preventive effects on early nerve dysfunction. Further corrective consequences resulting from this signaling cascade have beneficial effects on gene regulation of early gene responses, neurotrophic factors, their receptors, and the insulin receptor itself. This may lead to preventive and corrective results to nerve fiber degeneration and loss, as well as, promotion of nerve fiber regeneration with respect to sensory somatic fibers and small nociceptive nerve fibers. A characteristic abnormality of type 1 DPN is nodal and paranodal degeneration with severe consequences for myelinated fiber function. This review deals in detail with the underlying insulin-deficiency-related molecular changes and their correction by C-peptide. Based on these observations, it is evident that continuous maintenance of insulin-like actions by C-peptide is needed in peripheral nerve to minimize the sequences of metabolic and molecular abnormalities, thereby ameliorating neuropathic complications. There is now ample evidence demonstrating that C-peptide replacement in type 1 diabetes promotes insulin action and signaling activities in a more enhanced, prolonged, and continuous fashion than does insulin alone. It is therefore necessary to replace C-peptide to physiological levels in diabetic patients. This will have substantial beneficial effects on type 1 DPN.

Proinsulin C-peptide: friend or foe in the development of diabetes-associated complications?

The proinsulin connecting peptide, C-peptide, is a cleavage product of insulin synthesis that is co-secreted with insulin by pancreatic β-cells following glucose stimulation. Recombinant insulin, used in the treatment of diabetes, lacks C-peptide and preclinical and clinical studies suggest that lack of C-peptide may exacerbate diabetes-associated complications. In accordance with this, several studies suggest that C-peptide has beneficial effects in a number of diabetes-associated complications. C-peptide has been shown to prevent diabetic neuropathy by improving endoneural blood flow, preventing neuronal apoptosis and by preventing axonal swelling. In the vascular system, C-peptide has been shown to prevent vascular dysfunction in diabetic rats, and to possess anti-proliferative effects on vascular smooth muscle cells, which may prevent atherosclerosis. However, C-peptide depositions have been found in arteriosclerotic lesions of patients with hyperinsulinemic diabetes and C-peptide has been shown to induce pro-inflammatory mediators, such as nuclear factor kappa B, inducible nitric oxide synthase, and cyclooxygenase-2, indicating that C-peptide treatment could be associated with side-effects that may accelerate the development of diabetes-associated complications. This review provides a brief summary of recent research in the field and discusses potential beneficial and detrimental effects of C-peptide supplementation.

Cellular and physiological effects of C-peptide

In recent years, accumulating evidence indicates a biological function for proinsulin C-peptide. These results challenge the traditional view that C-peptide is essentially inert and only useful as a surrogate marker of insulin release. Accordingly, it is now clear that C-peptide binds with high affinity to cell membranes, probably to a pertussis-toxin-sensitive G-protein-coupled receptor. Subsequently, multiple signalling pathways are potently and dose-dependently activated in multiple cell types by C-peptide with the resulting activation of gene transcription and altered cell phenotype. In diabetic animals and Type 1 diabetic patients, short-term studies indicate that C-peptide also enhances glucose disposal and metabolic control. Furthermore, results derived from animal models and clinical studies in Type 1 diabetic patients suggest a salutary effect of C-peptide in the prevention and amelioration of diabetic nephropathy and neuropathy. Therefore a picture of Type 1 diabetes as a dual-hormone-deficiency disease is developing, suggesting that the replacement of C-peptide alongside insulin should be considered in its management.

Effects of proinsulin C-peptide on oxygen transport, uptake and utilization in insulinopenic diabetic subjects--a review

Exogenous C-peptide administration has beneficial effects in many of the tissues commonly affected by diabetic complications. Diabetes-induced circulatory impairments such as decreased blood flow are prevented by C-peptide, possibly via Ca2+-mediated effects on nitric oxide release. C-peptide also improves diabetes-induced erythrocyte deformability, which likely improves oxygen availability and uptake in affected tissues. Furthermore, C-peptide prevents diabetic neuropathy via improvements of endoneural blood flow and by preventing axonal swelling. In the kidney, C-peptide normalizes the diabetes-induced increase in oxygen consumption via inhibition of the Na+/K+-ATPase. Surprisingly, C-peptide has also been shown to prevent complications in patients with type II diabetes. Taken together, these results may indicate that C-peptide treatment has the potential to reduce the prevalence of diabetic complications. In this paper, the current knowledge regarding these beneficial effects of C-peptide administered to diabetic subjects will be reviewed briefly.

Role of C-Peptide in the regulation of microvascular blood flow

During the recent years, the role of C-peptide, released from the pancreatic beta cell, in regulating microvascular blood flow, has received increasing attention. In type 1 diabetic patients, intravenous application of C-peptide in physiological concentrations was shown to increase microvascular blood flow, and to improve microvascular endothelial function and the endothelial release of NO. C-peptide was shown to impact microvascular blood flow by several interactive pathways, like stimulating Na⁺K⁺ATPase or the endothelial release of NO. There is increasing evidence, that in patients with declining beta cell function, the lack of C-peptide secretion might play a putative role in the development of microvascular blood flow abnormalities, which go beyond the effects of declining insulin secretion or increased blood glucose levels.

C-Peptide effects on renal physiology and diabetes

The C-peptide of proinsulin is important for the biosynthesis of insulin and has for a long time been considered to be biologically inert. Animal studies have shown that some of the renal effects of the C-peptide may in part be explained by its ability to stimulate the Na,K-ATPase activity. Precisely, the C-peptide reduces diabetes-induced glomerular hyperfiltration both in animals and humans, therefore, resulting in regression of fibrosis. The tubular function is also concerned as diabetic animals supplemented with C-peptide exhibit better renal function resulting in reduced urinary sodium waste and protein excretion together with the reduction of the diabetes-induced glomerular hyperfiltration. The tubular effectors of C-peptide were considered to be tubule transporters, but recent studies have shown that biochemical pathways involving cellular kinases and inflammatory pathways may also be important. The matter theory concerning the C-peptide effects is a metabolic one involving the effects of the C-peptide on lipidic metabolic status.This review concentrates on the most convincing data which indicate that the C-peptide is a biologically active hormone for renal physiology.

C-peptide and its C-terminal fragments improve erythrocyte deformability in type 1 diabetes patients

Aims/hypothesis. Data now indicate that proinsulin C-peptide exerts important physiological effects and shows the characteristics of an endogenous peptide hormone. This study aimed to investigate the influence of C-peptide and fragments thereof on erythrocyte deformability and to elucidate the relevant signal transduction pathway. Methods. Blood samples from 23 patients with type 1 diabetes and 15 matched healthy controls were incubated with 6.6 nM of either human C-peptide, C-terminal hexapeptide, C-terminal pentapeptide, a middle fragment comprising residues 11–19 of C-peptide, or randomly scrambled C-peptide. Furthermore, red blood cells from 7 patients were incubated with C-peptide, penta- and hexapeptides with/without addition of ouabain, EDTA, or pertussis toxin. Erythrocyte deformability was measured using a laser diffractoscope in the shear stress range 0.3–60 Pa. Results. Erythrocyte deformability was impaired by 18–25% in type 1 diabetic patients compared to matched controls in the physiological shear stress range 0.6–12 Pa (P < .01–.001). C-peptide, penta- and hexapeptide all significantly improved the impaired erythrocyte deformability of type 1 diabetic patients, while the middle fragment and scrambled C-peptide had no detectable effect. Treatment of erythrocytes with ouabain or EDTA completely abolished the C-peptide, penta- and hexapeptide effects. Pertussis toxin in itself significantly increased erythrocyte deformability. Conclusion/interpretation. C-peptide and its C-terminal fragments are equally effective in improving erythrocyte deformability in type 1 diabetes. The C-terminal residues of C-peptide are causally involved in this effect. The signal transduction pathway is Ca²⁺-dependent and involves activation of red blood cell Na⁺, K⁺-ATPase.

Influence of C-peptide on glucose utilisation

During the recent years, multiple studies demonstrated that C-peptide is not an inert peptide, but exerts important physiological effects. C-peptide binds to cell membranes, stimulates the Na,K-ATPase and the endothelial nitric oxide (NO) synthase. Moreover, there is evidence that C-peptide decreases glomerular hyperfiltration and increases glucose utilisation. Nevertheless, there is still limited knowledge concerning mechanisms leading to an increased glucose utilisation either in rats or in humans. The aim of this paper is to give an overview over the published studies regarding C-peptide and glucose metabolism from in vitro studies to longer lasting studies in humans.

Effect of C-peptide on diabetic neuropathy in patients with type 1 diabetes

Recent results indicate that proinsulin C-peptide, contrary to previous views, exerts important physiological effects and shows the characteristics of a bioactive peptide. Studies in type 1 diabetes, involving animal models as well as patients, demonstrate that C-peptide in replacement doses has the ability to improve peripheral nerve function and prevent or reverse the development of nerve structural abnormalities. Peripheral nerve function, as evaluated by determination of sensory nerve conduction velocity and quantitative sensory testing, is improved by C-peptide replacement in diabetes type 1 patients with early stage neuropathy. Similarly, autonomic nerve dysfunction is ameliorated following administration of C peptide for up to 3 months. As evaluated in animal models of type 1 diabetes, the improved nerve function is accompanied by reversal or prevention of nerve structural changes, and the mechanisms of action are related to the ability of C-peptide to correct diabetes-induced reductions in endoneurial blood flow and in Na⁺ K⁺-ATPase activity and modulation of neurotrophic factors. Combining the results demonstrates that C-peptide may be a possible new treatment of neuropathy in type 1 diabetes.

Intracellular signalling by C-peptide

C-peptide, a cleavage product of the proinsulin molecule, has long been regarded as biologically inert, serving merely as a surrogate marker for insulin release. Recent findings demonstrate both a physiological and protective role of C-peptide when administered to individuals with type I diabetes. Data indicate that C-peptide appears to bind in nanomolar concentrations to a cell surface receptor which is most likely to be G-protein coupled. Binding of C-peptide initiates multiple cellular effects, evoking a rise in intracellular calcium, increased PI-3-kinase activity, stimulation of the Na(+)/K(+) ATPase, increased eNOS transcription, and activation of the MAPK signalling pathway. These cell signalling effects have been studied in multiple cell types from multiple tissues. Overall these observations raise the possibility that C-peptide may serve as a potential therapeutic agent for the treatment or prevention of long-term complications associated with diabetes.

Metal-activated C-peptide facilitates glucose clearance and the release of a nitric oxide stimulus via the GLUT1 transporter

AIMS/HYPOTHESIS

Proinsulin C-peptide has been implicated in reducing complications associated with diabetes and also in improving blood flow. We hypothesised that incubation of erythrocytes with C-peptide would improve the ability of these cells to release ATP, a stimulus for nitric oxide production.

METHODS

Erythrocytes obtained from rabbits (n = 11) and both healthy and type 2 diabetic humans (n = 7) were incubated with C-peptide in the absence and presence of Fe2+ and Cr3+, and the resulting ATP release was measured via chemiluminescence. This release was also measured in the presence and absence of phloretin, an inhibitor of GLUT1, and also of mannose, a glycolysis inhibitor. To determine glucose transport, 14C-labelled glucose was added to erythrocytes in the presence and absence of the C-peptide-metal complex and the aforementioned inhibitors.

RESULTS

The release of ATP from the erythrocytes of patients with diabetes increased from 64 +/- 13 to 260 +/- 39 nmol/l upon incubation of the cells in C-peptide. The C-peptide activity was dependent upon binding to Fe2+, which was extended upon binding to Cr3+. The increase in ATP release from the erythrocytes is due to metal-activated C-peptide stimulation of glucose transfer into the erythrocytes via the GLUT1 transporter. In the presence of C-peptide complexed to Cr3+, the amount of glucose transferred into the erythrocyte increased by 31%.

CONCLUSIONS/INTERPRETATION

When complexed to Fe2+ or Cr3+, C-peptide has the ability to promote ATP release from erythrocytes. This release is due to an increase in glucose transport through GLUT1.

The effects of C-peptide on type 1 diabetic polyneuropathies and encephalopathy in the BB/Wor-rat

Diabetic polyneuropathy (DPN) occurs more frequently in type 1 diabetes resulting in a more severe DPN. The differences in DPN between the two types of diabetes are due to differences in the availability of insulin and C-peptide. Insulin and C-peptide provide gene regulatory effects on neurotrophic factors with effects on axonal cytoskeletal proteins and nerve fiber integrity. A significant abnormality in type 1 DPN is nodal degeneration. In the type 1 BB/Wor-rat, C-peptide replacement corrects metabolic abnormalities ameliorating the acute nerve conduction defect. It corrects abnormalities of neurotrophic factors and the expression of neuroskeletal proteins with improvements of axonal size and function. C-peptide corrects the expression of nodal adhesive molecules with prevention and repair of the functionally significant nodal degeneration. Cognitive dysfunction is a recognized complication of type 1 diabetes, and is associated with impaired neurotrophic support and apoptotic neuronal loss. C-peptide prevents hippocampal apoptosis and cognitive deficits. It is therefore clear that substitution of C-peptide in type 1 diabetes has a multitude of effects on DPN and cognitive dysfunction. Here the effects of C-peptide replenishment will be extensively described as they pertain to DPN and diabetic encephalopathy, underpinning its beneficial effects on neurological complications in type 1 diabetes.

Proinsulin C-peptide constricts glomerular afferent arterioles in diabetic mice. A potential renoprotective mechanism

OBJECTIVE

an increased glomerular filtration rate (GFR) has been postulated as a potential mechanism involved in the progression of diabetic nephropathy. Studies suggest that C-peptide exerts a renoprotective effect on diabetes. The peptide decreases hyperfiltration in patients with type 1 diabetes, as well as in diabetic animal models. In this study, we investigated whether C-peptide causes a change in arteriolar diameter.

RESEARCH DESIGN AND METHODS

C57-Bl mice were made diabetic by means of a single intravenous injection of alloxan 2 wk prior to the experiment. Age-matched normoglycemic mice served as controls. Afferent arterioles, intact with the glomeruli, were dissected and microperfused. The effect of luminal application of C-peptide, compared with scrambled C-peptide or vehicle, was investigated. The effect of the Rho-kinase inhibitor Y-27632 was also investigated.

RESULTS

C-peptide constricted afferent arterioles in diabetic mice by -27% compared with the control value. Normoglycemic arterioles administered C-peptide displayed a delayed and minute response (-4%). Scrambled C-peptide or vehicle administration, whether administered to hyperglycemic or normoglycemic mice, did not induce any effect. Addition of Y-27632 abolished the effect of C-peptide.

CONCLUSION

C-peptide induces constriction of afferent arterioles in diabetic mice. This can reduce enhanced GFR and may be one of the mechanisms in the renoprotective action of C-peptide in diabetes.

Genome-wide search for susceptibility genes to type 2 diabetes in West Africans: potential role of C-peptide

C-peptide is a substance that the pancreas releases into the circulation in equimolar amounts to insulin and has demonstrated important physiological effects which relate to the vascular field, in particular the microcirculation. For this analysis, we included 321 full and 36 half sibling pairs affected with type 2 diabetes (T2D) from West Africa. A genome-wide panel of 390 tri-nucleotide and tetra-nucleotide repeats with an average distance of 8.9 cM was performed on a total of 691 persons. Variance components based on multipoint linkage approach as implemented in SOLAR were performed for log C-peptide. Significant linkage evidences were observed on 10q23 at D10S2327 with a LOD score of 4.04 (nominal p-value=0.000008, empirical p-value=0.0004); and on 4p15 at D4S2632 with a LOD score of 3.48 (nominal p-value=0.000031, empirical p-value=0.0013). Other suggestive evidence of linkage were observed on 15q14 at D15S659 with a LOD score 2.41 (nominal p-value=0.000435, empirical p-value=0.0068), and on 18p11 near D18S976 with a LOD score 2.18 (nominal p-value=0.000771 and empirical p-value=0.0094). Interestingly, five positional candidate genes for diabetes and related complications are located in our linkage region (the pituitary adenylate cyclase activating polypeptide (PACAP in 18p11); the peroxisome proliferator-activated receptor gamma coactivator 1 (PPARGC1 in 4p15); PTEN, PPP1R5, and IDE located in 10q23. In conclusion, we identified four major genetic loci (10q23, 4p15, 15q14, and 18p11) influencing C-peptide concentration in West Africans with T2D.

Suppression of growth and cancer-induced angiogenesis of aggressive human breast cancer cells (MDA-MB-231) on the chorioallantoic membrane of developing chicken embryos by E-peptide of pro-IGF-I

E-peptide of the pro-Insulin-like growth factor-I (pro-IGF-I) is produced from pre-pro-IGF-I by proteolytic cleavage in the post-translational processing. Previous in vitro studies conducted in our laboratory showed that Ea4-peptide of rainbow trout (rt) pro-IGF-I or Eb-peptide of human (h) pro-IGF-I exhibited activities including induction of morphological differentiation, inhibition of anchorage-independent cell growth and suppression of invasion of several well established human cancer cell lines such as MDA-MB-231, HT-29, SK-N-F1, and HepG-2 (Chen et al. [2002] Gen Comp Endocrinol 126:342-351; Kuo and Chen [2002] Exp Cell Res 280:75-89). Seeding of aggressive human breast cancer cells, MDA-MB-231, on the chorioallantoic membrane (CAM) of 5 days old chicken embryos resulted in rapid growth and invasion of the cells and induction of blood vessel formation around the MDA-MB-231 cell mass in the chicken embryos. The invasion of MDA-MB-231 cells in the chicken embryos was further confirmed by immunocytochemistry. The rapid growth and invasion of MDA-MB-231 cells and the induction of blood vessel formation by MDA-MB-231 cells on chicken CAM are inhibited by treatment with a single or multiple doses of rtEa4- or hEb-peptide. Furthermore, a dose-dependent inhibition of angiogenesis by rtEa4- or hEb-peptide was also demonstrated by the chicken CAM assay. Results of microarray analysis of human gene chips (containing 9,500 unique cDNA clones) and confirmation by comparative real-time RT-PCR analysis showed that a group of genes related to cancer cell activities are up- or down-regulated in MDA-MB-231 cells transfected with a rtEa4-peptide gene. Together these results confirm the anti-tumor activity of rtEa4- and hEb-peptides, and further suggest that these peptides could be developed as therapeutics for treating human cancers.

Inhibition of human breast cancer cell (MBA-MD-231) invasion by the Ea4-peptide of rainbow trout pro-IGF-I

It was shown previously that Ea4-peptide of trout pro-IGF-I exerted mitogenic activity in non-transformed cells and inhibited colony formation in a soft agar medium of established human cancer cells. Here we report that the same peptide inhibits the invasion of human breast cancer cells (MDA-MB-231) through a matrigel membrane in a dose-dependent manner. The expression of urokinase-type plasminogen activator (uPA), tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor 1 (PAI1) genes in MDA-MB-231 cells were downregulated by treatment with rtEa4-peptide. The inhibition of expression of these genes in response to rtEa4-peptide treatment was reduced to the control level when inhibitors for c-Jun N-terminal kinase 1/2 (JNK1/2), mitogen activated protein kinase kinase 1/2 (Mek1/2), p38 mitogen activated protein kinase (p38 MAPK), phosphatidylinositol 3-kinase (PI3K), and phosphokinase C (PKC) were used. These results suggest that inhibition of invasion of MDA-MB-231 cells by rtEa4-peptide may be mediated via the suppression of uPA, tPA, and PAI1 gene activities through signal transduction pathways.

Biological activity of rainbow trout Ea4-peptide of the pro-insulin-like growth factor (pro-IGF)-I on promoting attachment of breast cancer cells (MDA-MB-231) via alpha2- and beta1-integrin

E-peptide of pro-IGF-I was considered as biologically inactive. We have demonstrated that rainbow trout (rt) Ea4-peptide exerted biological activities in several established tumor cell lines [Chen et al., 2002; Kuo and Chen, 2002]. Here we report the activity of rtEa4-peptide in promoting attachment of human breast cancer cells (MDA-MB-231). While rtEa2-, rtEa3-, and rtEa4-peptides enhanced the attachment of MDA-MB-231 cells in a dose dependent manner, rtEa4-peptide possessed the highest activity. Antibodies specific to alpha2 and beta1 integrins significantly inhibited the attachment of cells to rtEa4-peptide coated-plates by 40%. In addition, rtEa4-peptide induced the expression of fibronectin 1 and laminin receptor genes in MDA-MB-231 cells. Blocking new protein synthesis by cycloheximide significantly reduced the attachment of MDA-MB-231 cells to rtEa4-peptide coated wells by 50%. These results suggest that rtEa4-peptide may promote cell attachment by interacting with alpha2/beta1 integrin receptors at the cell surface and by inducing the expression of fibronectin 1 and laminin receptor genes. Expression of fibronectin 1 gene induced by rtEa4-peptide in MDA-MB-231 cells was abolished by inhibitors of PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signaling transduction molecules. These results suggested that induction of fibronectin 1 gene expression in MDA-MB-231 cells by rtEa4-peptide may be mediated via PI3K, PKC, Mek1/2, JNK1/2, and p38 MAPK signal transduction molecules.

C-peptide replacement improves weight gain and renal function in diabetic rats

AIM

Recent experimental and clinical data suggest that C-peptide replacement during type 1 diabetes exerts beneficial effects on diabetic nephropathy. The aim of this study was to determine if physiological C-peptide administration in replacement dose during 28 days had beneficial effects on metabolic status and renal functions in type-1 diabetic rats.

METHODS

Four groups of rats were investigated: a non diabetic group treated with buffer (C group, n=6), three streptozotocin diabetic-induced groups treated with either buffer (D group, n=6), insulin (D-I group, n=6) or rat homologous C-peptide (D-C group, n=6). Weight gain was measured every week. All animals were housed in metabolic cages on day 28 for assessment of metabolic data. Blood and urine samples were collected to allow measurement of plasmatic osmolality, C-peptide concentration, sodium, and glucose losses and proteinuria. Glomerular filtration rate (GFR) was determined by creatinine clearance.

RESULTS

All streptozotocin-treated animals were diabetic. Glycaemic control (mg/dl), was markedly improved in D-I (133+/-65) when compared with either D (547+/-49, P<0.05) or D-C (520+/-48, P<0.05) groups. Conversely, weight gain during the study, was improved in D-I and D-C as compared with D animals (135+/-13 and 41+/-18 vs 18+/-21 respectively), despite different glycaemic control. Diabetes-induced glomerular hyperfiltration (ml/min/kg), urinary protein leakage (g/kg/day), and Na urinary losses (mmol/100 g/day) respectively, were significantly (P<0.05) reduced in D-C (3.95+/-0.6; 0.08+/-0.06; 1.5+/-0.9) in comparison with D (4.95+/-0.8; 0.18+/-0.16; 3.7+/-2.1) and D-I (5+/-0.9; 0.19+/-0.11; 2.7+/-0.8) animals. Plasmatic osmolality was significantly increased in D group whereas there were no differences between C group and D-C group. Food and water intakes, urinary volume as well as urinary glucose losses were not significantly different between D-C and D groups.

CONCLUSIONS

C-peptide administration in replacement dose to streptozotocin diabetic rats induces weight gain regardless hyperglycaemia or glycosuria. Diabetic animals supplemented with C-peptide exhibit better renal function resulting in reduced urinary sodium waste and protein excretion together with reduction of the diabetes-induced glomerular hyperfiltration.

Mechanisms of endothelial dysfunction with development of type 1 diabetes mellitus: role of insulin and C-peptide

Complications associated with insulin-dependent diabetes mellitus (type-1diabetes) primarily represent vascular dysfunction that has its origin in the endothelium. While many of the vascular changes are more accountable in the late stages of type-1diabetes, changes that occur in the early or initial functional stages of this disease may precipitate these later complications. The early stages of type-1diabetes are characterized by a diminished production of both insulin and C-peptide with a significant hyperglycemia. During the last decade numerous speculations and theories have been developed to try to explain the mechanisms responsible for the selective changes in vascular reactivity and/or tone and the vascular permeability changes that characterize the development of type-1diabetes. Much of this research has suggested that hyperglycemia and/or the lack of insulin may mediate the observed functional changes in both endothelial cells and vascular smooth muscle. Recent studies suggest several possible mechanisms that might be involved in the observed decreases in vascular nitric oxide (NO) availability with the development of type-1 diabetes. In addition more recent studies have indicated a direct role for both endogenous insulin and C-peptide in the amelioration of the observed endothelial dysfunction. These results suggest a synergistic action between insulin and C-peptide that facilitates increase NO availability and may suggest new clinical treatment modalities for type-1 diabetes mellitus.

[Physiological effects of the connecting peptide]

Insulin-dependent diabetic (IDDM) patients present significantly altered Na,K-ATPase activity in several organs, including kidney. Particularly in kidney tubule, Na,K-ATPase alteration occurs together with changes in glomerular filtration rate, the first step of IDDM-induced renal failure. The latter is a major cause of morbidity and mortality in IDDM patients. The C-peptide of proinsulin is important for the biosynthesis of insulin but has for a long time been considered to be biologically inert. Recent studies have demonstrated that replacement of C-peptide to normal physiological concentrations in IDDM patients either on a short-term basis (1-3 hours) or on a prolonged administration (1-3 months) was accompanied by improvements in renal glomerular and tubular function. Animal studies have shown that most of the renal tubular effects of C-peptide may in part be explained by its ability to stimulate Na,K-ATPase activity. In conclusion, these combined findings indicate that C-peptide is a biologically active hormone. The possibility that C-peptide therapy in IDDM patients may be beneficial should be considered. The present review focuses on: 1) Making a point about C-peptide-induced tubular effects on the basis of clinical and experimental experiments, and 2) precising the molecular mechanisms involved in C-peptide-induced tubular Na,K-ATPase effects.

Trout Ea4- or human Eb-peptide of pro-IGF-I disrupts heart, red blood cell, and vasculature development in zebrafish embryos

E-peptide of the pro-insulin-like growth factor (pro-IGF)-I is produced by proteolytic cleavage of the pro-hormone in post-translational processing. Introduction of a transgene encoding a secreted form of rtEa4- or hEb-peptide into newly fertilized zebrafish (Danio rerio) eggs by electroporation or microinjection resulted in embryos with abnormal cardiovascular features and reduced red blood cells and vasculature. Two different phenocopies of heart developmental defects were observed: (i) Group I embryos exhibited heart development arrested at the heart muscle stage and (ii) group II embryos exhibited heart development arrested at the heart tube stage. Both groups of embryos also exhibited reduction of red blood cells and vasculature. The mRNA levels of genes essential for heart development (GATA 5 and NKX2.5), hematopoiesis (GATA 1 and GATA 2), and vasculogenesis (VEGF) in normal and defective embryos were determined by quantitative real-time RT-PCR at 36 hr post-fertilization (hpf). Significant reduction of GATA 5, NKX2.5, GATA 1, GATA 2, and VEGF mRNA levels was observed in both groups of defective embryos. These results suggest that overexpression of rtEa4 or hEb transgene in zebrafish embryos disrupts heart development, hematopoiesis, and vasculogenesis by reducing the levels of GATA 5, NKX2.5, GATA 1, GATA 2, and VEGF mRNA.