C-peptide: a new potential in the treatment of diabetic nephropathy

The Antidiabetic Effects and Modes of Action of the Balanites aegyptiaca Fruit and Seed Aqueous Extracts in NA/STZ-Induced Diabetic Rats

Diabetes mellitus (DM) is a chronic metabolic disorder that threatens human health. Medicinal plants have been a source of wide varieties of pharmacologically active constituents and used extensively as crude extracts or as pure compounds for treating various disease conditions. Thus, the aim of this study is to assess the anti-hyperglycemic and anti-hyperlipidemic effects and the modes of action of the aqueous extracts of the fruits and seeds of Balanites aegyptiaca (B. aegyptiaca) in nicotinamide (NA)/streptozotocin (STZ)-induced diabetic rats. Gas chromatography-mass spectrometry analysis indicated that 3,4,6-tri-O-methyl-d-glucose and 9,12-octadecadienoic acid (Z,Z)- were the major components of the B. aegyptiaca fruit and seed extracts, respectively. A single intraperitoneal injection of STZ (60 mg/kg body weight (b.w.)) 15 min after intraperitoneal NA injection (60 mg/kg b.w.) was administered to induce type 2 DM. After induction was established, the diabetic rats were treated with the B. aegyptiaca fruit and seed aqueous extracts (200 mg/kg b.w./day) via oral gavage for 4 weeks. As a result of the treatments with the B. aegyptiaca fruit and seed extracts, the treated diabetic-treated rats exhibited a significant improvement in the deleterious effects on oral glucose tolerance; serum insulin, and C-peptide levels; liver glycogen content; liver glucose-6-phosphatase and glycogen phosphorylase activities; serum lipid profile; serum free fatty acid level; liver lipid peroxidation; glutathione content and anti-oxidant enzyme (glutathione peroxidase, glutathione-S-transferase, and superoxide dismutase) activities; and the mRNA expression of the adipose tissue expression of the insulin receptor β-subunit. Moreover, the treatment with fruit and seed extracts also produced a remarkable improvement of the pancreatic islet architecture and integrity and increased the islet size and islet cell number. In conclusion, the B. aegyptiaca fruit and seed aqueous extracts exhibit potential anti-hyperglycemic and anti-hyperlipidemic effects, which may be mediated by increasing the serum insulin levels, decreasing insulin resistance, and enhancing the anti-oxidant defense system in diabetic rats.

Inhibition of Type-2 Diabetes Mellitus Development by Sophocarpine through Targeting PPARy-Regulated Gene Expression

Diabetes mellitus (DM), a metabolic disorder, is the causes of oxidative stress leading to complications in micro- and macro-vascular system. The present study investigated sophocarpine for anti-diabetic potential in vivo in mice model. Sophocarpine administration to diabetic mice significantly (p < 0.05) attenuated glucose content in the plasma. The diabetes mediated lowering of GSH, ceruloplasmin and vitamin E was prevented in mice plasma by sophocarpine administration. Sophocarpine significantly (p < 0.05) reversed diabetes mediated suppression of insulin level and total Hb content in the mice plasma. In sophocarpine administrated diabetic mice C-peptide level was elevated and glycosylated hemoglobin content was suppressed significantly (p < 0.05) relative to diabetic group. Administration of sophocarpine significantly (p < 0.05) repressed diabetes mediated increase in TG and TC levels in dose-based manner. Administration of sophocarpine exhibited preventive role against diabetes mediated pathological damage to pancreas in the mice. Sophocarpine administration to diabetic mice repressed PPARγ recruitment significantly (p < 0.05) in dose-dependent manner. Sophocarpine prevents oxidative stress mediated pancreatic damage through increase in vitamin E, GSH and C-peptide levels, Moreover, the PPARγ activity was down-regulated, LDL-c content lowered and HDL-c level elevated in diabetic mice by sophocarpine. Therefore, sophocarpine may be developed for treatment of diabetes, however, further in vivo studies need to confirm the same.

First-Phase Insulin and Amylin after Bariatric Surgery: A Prospective Randomized Trial on Patients with Insulin Resistance or Diabetes after Gastric Bypass or Sleeve Gastrectomy

BACKGROUND

Most patients with severe obesity show glucose intolerance. Early after sleeve gastrectomy (LSG) or gastric bypass (LRYGB), a marked amelioration in glycemic control occurs. The underlying mechanism is not yet clear.

OBJECTIVE

To determine whether the improvement in glycemic control on the level of endocrine pancreatic function is due to an increased first-phase insulin secretion comparing LRYGB to LSG.

SETTING

University of Basel Hospital and St. Clara Research Ltd., Basel, Switzerland.

METHODS

Sixteen morbidly obese patients with severe obesity and different degrees of insulin resistance were randomized to LSG or LRYGB, and islet cell functions were tested by intravenous glucose and intravenous arginine administration before and 4 weeks after surgery.

RESULTS

Fasting insulin and glucose levels and homeostasis model assessment insulin resistance were significantly lower in both groups after surgery compared to baseline, while no change was seen in fasting C-peptide, amylin, and glucagon. After intravenous glucose stimulation, no statistically significant pre- to postoperative change in area under the curve (AUC 0-60 min) was seen for insulin, glucagon, amylin, and C-peptide. No statistically significant pre- to postoperative change in incremental AUC for first-phase insulin release (AUC 0-10 min), second-phase insulin secretion (AUC 10-60 min), and insulin/glucose ratio could be shown in either group. Arginine-stimulated insulin and glucagon release showed no pre- to postoperative change.

CONCLUSION

Intravenous glucose and arginine administrations show no pre- to postoperative changes of insulin release, amylin, glucagon, or C-peptide concentrations, and no differences between LRYGB and LSG were found. The postoperative improvement in glycemic control is not caused by changes in endocrine pancreatic hormone secretion.

Antidiabetic and Hypolipidemic Effects of 5,7-Dimethoxyflavone in Streptozotocin-Induced Diabetic Rats

BACKGROUND The flavones are considered as competent antidiabetic molecules due to their strong antioxidant activities and higher in vivo stability. The present study evaluated the antidiabetic and hypolipidemic effects of 5,7-dimethoxyflavone in streptozotocin (STZ)-induced diabetic rat models. MATERIAL AND METHODS The antidiabetic potential of 5,7-dimethoxyflavone was evaluated in streptozotocin-induced diabetic rats. The serum levels of triglyceride, total cholesterol, and high-density lipoprotein cholesterol were measured using the Randox assay kit. Histopathological examination was carried out by hematoxylin and eosin (HE) staining. RESULTS Oral administration of 5,7-dimethoxyflavone significantly reduced STZ-induced enhancement in blood sugar and glycosylated hemoglobin, as well as significant increases in C-peptide, insulin, hemoglobin, and total protein content (p<0.05). Additionally, treatment with 5,7-dimethoxyflavone resulted in a remarkable increase in non-enzymic antioxidants. Administration of 5,7-dimethoxyflavone had a hypolipidemic effect by significantly reducing levels of serum triglycerides, total cholesterol, and low-density lipoproteins. The histopathological examination of rat pancreases revealed the beneficial effect of 5,7-dimethoxyflavone and protection of ß cell integrity in STZ-induced diabetic rats. CONCLUSIONS These findings reflect the antidiabetic and hypolipidemic effects of 5,7-dimethoxyflavone, suggesting that 5,7-dimethoxyflavone may be a promising compound for use in development of new antidiabetic drugs.

Patient satisfaction and cost-effectiveness following total pancreatectomy with islet cell transplantation for chronic pancreatitis

OBJECTIVES

Chronic pancreatitis (CP) results in an extremely poor quality of life and substantially increases health care utilization. Few data exist regarding the cost-effectiveness of surgical treatment for CP.

METHODS

This article examined the cost-effectiveness of total pancreatectomy (TP) with islet cell autotransplantation (IAT) for CP.

RESULTS

Sixty patients undergoing TP + IAT and 37 patients undergoing TP were identified. Surgery resulted in significant reduction in opiate use, frequency of hospital admissions, and length of stay as well as visual analog scale scores for pain. Total pancreatectomy + IAT resulted in longer survival than TP alone (16.6 vs 12.9 years); 21.6% of patients with TP + IAT were insulin-independent, and those requiring insulin have reduced daily requirements compared with those having TP alone (22 vs 35 IU). The cost of TP + IAT with attendant admission and analgesia costs over the 16-year survival period was £110,445 compared with £101,608 estimated 16-year costs if no TP + IAT was undertaken.

CONCLUSIONS

Total pancreatectomy + IAT is effective in improving pain and reducing analgesia. Islet cell transplantation offers the chance of insulin independence and results in lower insulin requirements, as well as conferring a survival advantage when compared with TP alone. Total pancreatectomy + IAT is cost-neutral when compared with nonsurgical or segmental surgical therapy.

Resveratrol protects diabetic kidney by attenuating hyperglycemia-mediated oxidative stress and renal inflammatory cytokines via Nrf2-Keap1 signaling

Hyperglycemia-mediated oxidative stress plays a crucial role in the progression of diabetic nephropathy. Hence, the present study was hypothesized to explore the renoprotective nature of resveratrol by assessing markers of oxidative stress, proinflammatory cytokines and antioxidant competence in streptozotocin-nicotinamide-induced diabetic rats. Oral administration of resveratrol to diabetic rats showed a significant normalization on the levels of creatinine clearance, plasma adiponectin, C-peptide and renal superoxide anion, hydroxyl radical, nitric oxide, TNF-α, IL-1β, IL-6 and NF-κB p65 subunit and activities of renal aspartate transaminase, alanine transaminase and alkaline phosphatase in comparison with diabetic rats. The altered activities of renal aldose reductase, sorbitol dehydrogenase and glyoxalase-I and elevated level of serum advanced glycation end products in diabetic rats were also reverted back to near normalcy. Further, resveratrol treatment revealed a significant improvement in superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase activities and vitamins C and E, and reduced glutathione levels, with a significant decline in lipid peroxides, hydroperoxides and protein carbonyls levels in diabetic kidneys. Similarly, mRNA and protein analyses substantiated that resveratrol treatment notably normalizes the renal expression of Nrf2/Keap1and its downstream regulatory proteins in the diabetic group of rats. Histological and ultrastructural observations also evidenced that resveratrol effectively protects the kidneys from hyperglycemia-mediated oxidative damage. These findings demonstrated the renoprotective nature of resveratrol by attenuating markers of oxidative stress in renal tissues of diabetic rats.

C-peptide normalizes glomerular filtration rate in hyperfiltrating conscious diabetic rats

Tubular electrolyte transport accounts for a major part of the oxygen consumed by the normal kidney. We have previously reported a close association between diabetes and increased oxygen usage, partly due to increased tubular electrolyte transport secondary to glomerular hyperfiltration during the early onset of diabetes. Several studies have shown that acute administration of C-peptide to diabetic rats with glomerular hyperfiltration results in normalized glomerular filtration rate (GFR). In this study, we validated a novel method for precise and repetitive GFR measurements in conscious rats and used C-peptide injection in diabetic rats for evaluation. First, GFR was determined in normoglycemic control rats before and after C-peptide administration. Thereafter, all rats were made diabetic by an i.v. streptozotocin injection. Fourteen days later, GFR was again determined before and after C-peptide administration. GFR was estimated from plasma clearance curves using a single bolus injection of FITC-inulin, followed by serial blood sampling over 155 min. FITC-inulin clearance was calculated using non-compartmental pharmacokinetic data analysis. Baseline GFR in normoglycemic controls was 2.10 +/- 0.18 ml/min, and was unaffected by C-peptide (2.23 +/- 0.14 ml/min). Diabetic rats had elevated GFR (3.06 +/- .034 ml/min), which was normalized by C-peptide (2.35 +/- 0.30 ml/min). In conclusion, the used method for estimation of GFR in conscious animals result in values that are in good agreement with those obtained from traditional GFR measurements on anaesthetized rats. However, multiple measurements from the same conscious subject can be obtained using this method. Furthermore, as previously shown on anaesthetized rats, C-peptide also normalizes GFR in hyperfiltrating conscious diabetic rats.

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.

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.

C-peptide does not affect ocular blood flow in patients with type 1 diabetes

OBJECTIVE

The aim of the present study was to investigate the effect of intravenous C-peptide infusion on ocular blood flow in patients with type 1 diabetes under euglycemic conditions.

RESEARCH DESIGN AND METHODS

The study was performed in a randomized, placebo-controlled, double-masked, two-way, crossover design in 10 type 1 diabetic patients. C-peptide was intravenously administered at two different dosages (dosage 1: 25 pmol . kg(-1) . min(-1) bolus followed by 5 pmol . kg(-1) . min(-1) continuous infusion; dosage 2: six times higher than dosage 1), each for 60 min. Physiologic saline solution was used as a control for C-peptide on a different study day. On both study days, euglycemic clamps were performed. To assess retinal blood flow, laser Doppler velocimetry (blood flow velocities) and retinal vessel analyzer (vessels diameters) measurements were performed. Laser interferometric measurements of fundus pulsation were used to assess pulsatile choroidal blood flow. Blood velocities in the ophthalmic artery were measured using color Doppler imaging.

RESULTS

Eight patients (two female and six male) completed the study according to the protocol and without adverse events. One patient developed an anaphylactic reaction to C-peptide, which resolved without sequelae. The following results originate from the remaining eight subjects. Systemic hemodynamic parameters remained stable during both study days. Infusion of C-peptide did not affect any ocular hemodynamic parameter.

CONCLUSIONS

The data of the present study indicate that exogenous C-peptide exerts no effect on ocular hemodynamic parameters in type 1 diabetic patients under euglycemic conditions. The maximum detectable change in these parameters was <25%.

The beneficial effects of pancreas transplant alone on diabetic nephropathy

OBJECTIVE

Pancreas transplant alone can be effective in significantly improving the quality of life of type 1 diabetic patients, and it can also eliminate acute diabetes complications, such as hypoglycemic and/or hyperglycemic episodes. The effects of pancreas transplant alone on long-term complications of diabetes, including nephropathy, are still not settled. We evaluated whether restoration of long-lasting normoglycemia by pancreas transplant alone might have beneficial action on diabetic nephropathy.

RESEARCH DESIGN AND METHODS

A total of 32 type 1 diabetic patients were evaluated before and 1 year after successful pancreas transplant alone, together with 30 matched nontransplanted type 1 diabetic subjects. Several metabolic and kidney function parameters were measured, including plasma glucose, glycohemoglobin (A1C), C-peptide, plasma lipids, blood pressure, creatinine, creatinine clearance, and urinary protein excretion.

RESULTS

Pancreas transplant alone restored sustained normoglycemia, without exogenous insulin administration, and improved plasma lipid levels. Blood pressure decreased significantly. Creatinine concentrations and clearances did not differ before and after transplantation. Urinary protein excretion decreased significantly after pancreas transplant alone, with four microalbuminuric and three macroalbuminuric patients who became normoalbuminuric. None of these changes occurred in the nontransplanted group.

CONCLUSIONS

Successful pancreas transplant alone, through restoration of sustained normoglycemia, improves diabetic nephropathy in type 1 diabetic patients.

Rosiglitazone combined with insulin preserves islet beta cell function in adult-onset latent autoimmune diabetes (LADA)

BACKGROUND

LADA is thought to result from the chronic autoimmune destruction of the insulin-producing pancreatic beta cells. In addition to antidiabetic effects, the newly developed insulin sensitizer-thiazolidinediones have the potential to increase the insulin content of islet cells by downregulating local inflammation and autoimmune response. Therefore, we hypothesized that LADA patients might benefit from thiazolidinediones treatment.

METHODS

LADA patients, with a fasting C-peptide (FCP) of 0.3 nmol/L or more, were enrolled and randomly assigned to receive subcutaneous insulin alone (insulin group, n = 12) or rosiglitazone plus insulin (insulin + RSG group, n = 11) to compare the impacts on islet beta cell function. Plasma glucose, HbA 1c, fasting C-peptide (FCP) and C-peptide after 2 h 75-g glucose load (PCP) were determined every 6 months. GAD-Ab and C-peptide were measured with radioimmune assays. Islet beta cell function was evaluated by PCP and DeltaCP(DeltaCP = PCP-FCP).

RESULTS

All of the 23 patients have been followed up for 6 months, 17 cases for 12 months and 14 for 18 months. (1) During 6 months' follow-up, there were no significant changes for DeltaCP and PCP levels in both groups. (2) PCP and DeltaCP levels in insulin + RSG group patients stayed steady during the 12 months' observation (P = 0.161 for both PCP and DeltaCP), while in the insulin alone group, both FCP (P = 0.021) and PCP (P = 0.028) levels decreased significantly. Furthermore, PCP (P = 0.004) and DeltaCP(P = 0.015) differences between 12th month and baseline were higher in insulin + RSG group than those in the insulin group. (3) When observed up to 18 months, PCP and DeltaCP levels in insulin + RSG group patients still stayed steady, while PCP and DeltaCP levels decreased more in the insulin alone group.

CONCLUSIONS

This pilot study suggests that rosiglitazone combined with insulin may preserve islet beta cell function in LADA patients.