C-Peptide Prevents Hippocampal Apoptosis in Type 1 Diabetes

To explore mechanisms underlying central nervous system (CNS) complications in diabetes, we examined hippocampal neuronal apoptosis and loss, and the effect of C-peptide replacement in type 1 diabetic BB/W rats. Apoptosis was demonstrated after 8 months of diabetes, by DNA fragmentation, increased number of apoptotic cells, and an elevated ratio of Bax/Bcl-x_L, accompanied by reduced neuronal density in the hippocampus. No apoptotic activity was detected and neuronal density was unchanged in 2-month diabetic hippocampus, whereas insulin-like growth factor (IGF) activities were impaired. In type 1 diabetic BB/W rats replaced with C-peptide, no TdT-mediated dUTP nick-end labeling (TUNEL)- positive cells were shown and DNA laddering was not evident in hippocampus at either 2 or 8 months. C-peptide administration prevented the preceding perturbation of IGF expression and reduced the elevated ratio of Bax/Bcl-x_L. Our data suggest that type 1 diabetes causes a duration-dependent programmed cell death of the hippocampus, which is partially prevented by C-peptide.     

The Insulin-Like Growth Factor System and Neurological Complications in Diabetes

The IGF system plays vital roles in neuronal development, metabolism, regeneration and survival. It consists of IGF-I, IGF-II, insulin, IGF-I-receptor, and those of IGF-II and insulin as well as IGF-binding proteins. In the last decades it has become clear that perturbations of the IGF system play important roles in the pathogenesis of diabetic neurological complications. In the peripheral nervous system IGF-I, insulin, and C-peptide particularly in type 1 diabetes participate in the development of axonal degenerative changes and contributes to impaired regenerative capacities. These abnormalities of the IGF system appear to be less pronounced in type 2 diabetes, which may in part account for the relatively milder neurological complications in this type of diabetes. The members of the IGF system also provide anti-apoptotic effects on both peripheral and central nervous system neurons. Furthermore, both insulin and C-peptide and probably IGF-I possess gene regulatory capacities on myelin constituents and axonal cytoskeletal proteins. Therefore, replenishment of various members of the IGF system provides a reasonable rational for prevention and treatment of diabetic neurological complications.     

Type 1 Diabetic Neuropathy and C-peptide

The most common microvascular diabetic complication, diabetic peripheral polyneuropathy (DPN), affects type 1 diabetic patients more often and more severely. In recent decades, it has become increasingly clear that perpetuating pathogenetic mechanisms, molecular, functional, and structural changes and ultimately the clinical expression of DPN differ between the two major types of diabetes. Impaired insulin/C-peptide action has emerged as a crucial factor to account for the disproportionate burden affecting type 1 patients. C-peptide was long believed to be biologically inactive. However, it has now been shown to have a number of insulin-like glucoseindependent effects. Preclinical studies have demonstrated dose-dependent effects on Na⁺,K⁺-ATPase activity, endothelial nitric oxide synthase (eNOS), and endoneurial blood flow. Furthermore, it has regulatory effects on neurotrophic factors and molecules pivotal to the integrity of the nodal and paranodal apparatus and modulatory effects on apoptotic phenomena affecting the diabetic nervous system. In animal studies, C-peptide improves nerve conduction abnormalities, prevents nodal degenerative changes, characteristic of type 1 DPN, promotes nerve fiber regeneration, and prevents apoptosis of central and peripheral nerve cell constituents. Limited clinical trials have confirmed the beneficial effects of C-peptide on autonomic and somatic nerve function in patients with type 1 DPN. Therefore, evidence accumulates that replacement of C-peptide in type 1 diabetes prevents and even improves DPN. Large-scale food and drug administration (FDA)-approved clinical trials are necessary to make this natural substance available to the globally increasing type 1 diabetic population.     

Protective effects of either C-peptide or l-arginine on pancreatic β-cell function,proliferation, and oxidative stress in streptozotocin-induced diabetic rats

Diabetes and cardiometabolic risk factors including hypertension and dyslipidemia are the major threats to human health in the 21st century. Apoptosis in pancreatic tissue is one of the major causes of diabetes type 1 progression. The aim of this study was to investigate the effects of C-peptide or l -arginine on some cardiometabolic risk factors, pancreatic morphology, function and apoptosis, and the mechanisms of their actions. Forty adult male albino rats were divided into four equal groups: 1—control nondiabetic, 2—diabetic (no treatment), 3—diabetic + C-peptide, and 4—diabetic + l -arginine. Diabetes was induced by a single intraperitoneal injection of high dose streptozotocin. At the end of the experiment, sera glucose, insulin levels, total antioxidant capacity (TAC), malondialdehyde (MDA), nitric oxide (NO), and pancreatic MDA, TAC, and B-cell lymphoma 2 were measured. The morphology and proliferating activity of the pancreas were examined by hematoxylin and eosin histological stain, proliferative cell nuclear antigen (PCNA), and insulin antibodies. Our results showed that induction of diabetes caused hyperglycemia, dyslipidemia, and oxidative stress. However, administration of C-peptide or l -arginine significantly improved the pancreatic histopathology with a significant increase in the area % of insulin immunoreactivity, the number of PCNA immunopositive cells, the number of islets, and the diameter of islets compared with the diabetic group. C-peptide treatment of the diabetic rats completely corrected these errors, while l -arginine partially antagonized the above diabetic complications. So the administration of C-peptide as an adjuvant therapy in type 1 diabetes can significantly decrease apoptosis of pancreas and subsequent progression of diabetes complication.     

Autoimmunity against INS-IGF2 Protein Expressed in Human Pancreatic Islets

Insulin is a major autoantigen in islet autoimmunity and progression to type 1 diabetes. It has been suggested that the insulin B-chain may be critical to insulin autoimmunity in type 1 diabetes. INS-IGF2 consists of the preproinsulin signal peptide, the insulin B-chain, and eight amino acids of the C-peptide in addition to 138 amino acids from the IGF2 gene. We aimed to determine the expression of INS-IGF2 in human pancreatic islets and autoantibodies in newly diagnosed children with type 1 diabetes and controls. INS-IGF2, expressed primarily in beta cells, showed higher levels of expression in islets from normal compared with donors with either type 2 diabetes (p = 0.006) or high HbA1c levels (p < 0.001). INS-IGF2 autoantibody levels were increased in newly diagnosed patients with type 1 diabetes (n = 304) compared with healthy controls (n = 355; p < 0.001). Displacement with cold insulin and INS-IGF2 revealed that more patients than controls had doubly reactive insulin-INS-IGF2 autoantibodies. These data suggest that INS-IGF2, which contains the preproinsulin signal peptide, the B-chain, and eight amino acids of the C-peptide may be an autoantigen in type 1 diabetes. INS-IGF2 and insulin may share autoantibody-binding sites, thus complicating the notion that insulin is the primary autoantigen in type 1 diabetes.     

Evidence for unimpaired pancreatic secretion and hepatic removal of insulin in healthy offspring of type 2 (noninsulin-dependent) diabetic couples

The aim of the present study was to investigate the secretion and the hepatic removal of insulin in a group of 14 unaffected offspring of 14 type 2 (noninsulin-dependent) diabetic couples compared to 14 healthy subjects without family history of diabetes mellitus. The two groups, each consisting of 5 obese and 9 nonobese subjects, were carefully matched for sex, age, and body weight. We examined glucose, insulin, and C-peptide levels, as well as C-peptide to insulin ratios and relations during the oral glucose tolerance test. Glucose concentrations and incremental areas were similar in the two groups, as well as insulin and C-peptide levels and areas. C-peptide to insulin molar ratios, both in fasting state and after glucose load, as well as relations between C-peptide and insulin incremental areas were not different. Our results suggest that the healthy offspring of type 2 diabetic couples have a normal response of beta-cell to oral glucose as well as a normal removal of insulin by the liver.     

Proinsulin C-peptide - A Consensus Statement

In recent years the physiological role of the proinsulin C-peptide has received increasing attention, focusing on the potential therapeutic value of C-peptide replacement in preventing and ameliorating type 1 diabetic complications. In order to consolidate these new data and to identify the immediate directions of C-peptide research and its clinical usefulness, an International Symposium was held in Detroit, Michigan, on October 20–21, 2000, under the auspices of the Wayne State University/Morris Hood Jr. Comprehensive Diabetes Center. In this communication, we review the cellular, physiological and clinical effects of C-peptide replacement in animal models and in patients with type 1 diabetes. Finally, recommendations are presented as to the most urgent studies that should be pursued to further establish the biological action of C-peptide and its therapeutic value.     

Amelioration of Diabetic Mouse Nephropathy by Catalpol Correlates with Down-Regulation of Grb10 Expression and Activation of Insulin-Like Growth Factor 1 / Insulin-Like Growth Factor 1 Receptor Signaling

Growth factor receptor-bound protein 10 (Grb10) is an adaptor protein that can negatively regulate the insulin-like growth factor 1 receptor (IGF-1R). The IGF1-1R pathway is critical for cell growth and apoptosis and has been implicated in kidney diseases; however, it is still unknown whether Grb10 expression is up-regulated and plays a role in diabetic nephropathy. Catalpol, a major active ingredient of a traditional Chinese medicine, Rehmannia, has been reported to possess anti-inflammatory and anti-aging activities and then used to treat diabetes. Herein, we aimed to assess the therapeutic effect of catalpol on a mouse model diabetic nephropathy and the potential role of Grb10 in the pathogenesis of this diabetes-associated complication. Our results showed that catalpol treatment improved diabetes-associated impaired renal functions and ameliorated pathological changes in kidneys of diabetic mice. We also found that Grb10 expression was significantly elevated in kidneys of diabetic mice as compared with that in non-diabetic mice, while treatment with catalpol significantly abrogated the elevated Grb10 expression in diabetic kidneys. On the contrary, IGF-1 mRNA levels and IGF-1R phosphorylation were significantly higher in kidneys of catalpol-treated diabetic mice than those in non-treated diabetic mice. Our results suggest that elevated Grb10 expression may play an important role in the pathogenesis of diabetic nephropathy through suppressing IGF-1/IGF-1R signaling pathway, which might be a potential molecular target of catalpol for the treatment of this diabetic complication.     

C-peptide,Na+,K+-ATPase,and Diabetes

Na⁺,K⁺-ATPase is an ubiquitous membrane enzyme that allows the extrusion of three sodium ions from the cell and two potassium ions from the extracellular fluid. Its activity is decreased in many tissues of streptozotocin-induced diabetic animals. This impairment could be at least partly responsible for the development of diabetic complications. Na⁺,K⁺-ATPase activity is decreased in the red blood cell membranes of type 1 diabetic individuals, irrespective of the degree of diabetic control. It is less impaired or even normal in those of type 2 diabetic patients. The authors have shown that in the red blood cells of type 2 diabetic patients, Na⁺,K⁺-ATPase activity was strongly related to blood C-peptide levels in non–insulin-treated patients (in whom C-peptide concentration reflects that of insulin) as well as in insulin-treated patients. Furthermore, a gene-environment relationship has been observed. The alpha-1 isoform of the enzyme predominant in red blood cells and nerve tissue is encoded by the ATP1A1 gene.Apolymorphism in the intron 1 of this gene is associated with lower enzyme activity in patients with C-peptide deficiency either with type 1 or type 2 diabetes, but not in normal individuals. There are several lines of evidence for a low C-peptide level being responsible for low Na⁺,K⁺-ATPase activity in the red blood cells. Short-term C-peptide infusion to type 1 diabetic patients restores normal Na⁺,K⁺-ATPase activity. Islet transplantation, which restores endogenous C-peptide secretion, enhances Na⁺,K⁺-ATPase activity proportionally to the rise in C-peptide. This C-peptide effect is not indirect. In fact, incubation of diabetic red blood cells with C-peptide at physiological concentration leads to an increase of Na⁺,K⁺-ATPase activity. In isolated proximal tubules of rats or in the medullary thick ascending limb of the kidney, C-peptide stimulates in a dose-dependent manner Na⁺,K⁺-ATPase activity. This impairment in Na⁺,K⁺-ATPase activity, mainly secondary to the lack of C-peptide, plays probably a role in the development of diabetic complications. Arguments have been developed showing that the diabetesinduced decrease in Na⁺,K⁺-ATPase activity compromises microvascular blood flow by two mechanisms: by affecting microvascular regulation and by decreasing red blood cell deformability, which leads to an increase in blood viscosity. C-peptide infusion restores red blood cell deformability and microvascular blood flow concomitantly with Na⁺,K⁺-ATPase activity. The defect in ATPase is strongly related to diabetic neuropathy. Patients with neuropathy have lower ATPase activity than those without. The diabetes-induced impairment in Na⁺,K⁺-ATPase activity is identical in red blood cells and neural tissue. Red blood cell ATPase activity is related to nerve conduction velocity in the peroneal and the tibial nerve of diabetic patients. C-peptide infusion to diabetic rats increases endoneural ATPase activity in rat. Because the defect in Na⁺,K⁺-ATPase activity is also probably involved in the development of diabetic nephropathy and cardiomyopathy, physiological C-peptide infusion could be beneficial for the prevention of diabetic complications.     

Human immunodeficiency virus type 1 Vpr induces apoptosis in human neuronal cells

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS) causes AIDS dementia complex (ADC) in certain infected individuals. Recent studies have suggested that patients with ADC have an increased incidence of neuronal apoptosis leading to neuronal dropout. Of note, a higher level of the HIV-1 accessory protein Vpr has been detected in the cerebrospinal fluid of AIDS patients with neurological disorders. Moreover, extracellular Vpr has been shown to form ion channels, leading to cell death of cultured rat hippocampal neurons. Based on these previous findings, we first investigated the apoptotic effects of the HIV-1 Vpr protein on the human neuronal precursor NT2 cell line at a range of concentrations. These studies demonstrated that apoptosis induced by both Vpr and the envelope glycoprotein, gp120, occurred in a dose-dependent manner compared to protein treatment with HIV-1 integrase, maltose binding protein (MBP), and MBP-Vpr in the undifferentiated NT2 cells. For mature, differentiated neurons, apoptosis was also induced in a dose-dependent manner by both Vpr and gp120 at concentrations ranging from 1 to 100 ng/ml, as demonstrated by both the terminal deoxynucleotidyltransferase (Tdt)-mediated dUTP-biotin nick end labeling and Annexin V assays for apoptotic cell death. In order to clarify the intracellular pathways and molecular mechanisms involved in Vpr- and gp120-induced apoptosis in the NT2 cell line and differentiated mature human neurons, we then examined the cellular lysates for caspase-8 activity in these studies. Vpr and gp120 treatments exhibited a potent increase in activation of caspase-8 in both mature neurons and undifferentiated NT2 cells. This suggests that Vpr may be exerting selective cytotoxicity in a neuronal precursor cell line and in mature human neurons through the activation of caspase-8. These data represent a characterization of Vpr-induced apoptosis in human neuronal cells, and suggest that extracellular Vpr, along with other lentiviral proteins, may increase neuronal apoptosis in the CNS. Also, identification of the intracellular activation of caspase-8 in Vpr-induced apoptosis of human neuronal cells may lead to therapeutic approaches which can be used to combat HIV-1-induced neuronal apoptosis in AIDS patients with ADC.     

Effects of C-peptide on Microvascular Blood Flow and Blood Hemorheology

Beside functional and structural changes in vascular biology, alterations in the rheologic properties of blood cells mainly determines to an impaired microvascular blood flow in patients suffering from diabetes mellitus. Recent investigations provide increasing evidence that impaired C-peptide secretion in type 1 diabetic patients might contribute to the development of microvascular complications. C-peptide has been shown to stimulate endothelial NO secretion by activation of the Ca²⁺ calmodolin regulated enzyme eNOS. NO himself has the potency to increase cGMP levels in smooth muscle cells and to activate Na⁺ K⁺ ATPase activity and therefore evolves numerous effects in microvascular regulation. In type 1 diabetic patients, supplementation of C-peptide was shown to improve endothelium dependent vasodilatation in an NO-dependent pathway in different vascular compartments. In addition, it could be shown that C-peptide administration in type 1 diabetic patients, results in a redistribution of skin blood flow by increasing nutritive capillary blood flow in favour to subpapillary blood flow. Impaired Na⁺ K⁺ ATPase in another feature of diabetes mellitus in many cell types and is believed to be a pivotal regulator of various cell functions. C-peptide supplementation has been shown to restore Na⁺ K⁺ATPase activity in different cell types during in vitro and in vivo investigations. In type 1 diabetic patients, C-peptide supplementation was shown to increase erythrocyte Na⁺ K⁺ATPase activity by about 100%. There was found a linear relationship between plasma C-peptide levels and erythrocyte Na⁺ K⁺ATPase activity. In small capillaries, microvascular blood flow is increasingly determined by the rheologic properties of erythrocytes. Using laser-diffractoscopie a huge improvement in erythrocyte deformability could be observed after C-peptide administration in erythrocytes of type 1 diabetic patients. Inhibition of the Na⁺ K⁺ATPase by Obain completely abolished the effect of C-peptide on erythrocyte deformability. In conclusion, C-peptide improves microvascular function and blood flow in type 1 diabetic patients by interfering with vascular and rheological components of microvascular blood flow.     

GALNT2 Expression Is Reduced in Patients with Type 2 Diabetes: Possible Role of Hyperglycemia

Impaired insulin action plays a major role in the pathogenesis of type 2 diabetes, a chronic metabolic disorder which imposes a tremendous burden to morbidity and mortality worldwide. Unraveling the molecular mechanisms underlying insulin resistance would improve setting up preventive and treatment strategies of type 2 diabetes. Down-regulation of GALNT2, an UDPN-acetyl-alpha-D-galactosamine polypeptideN-acetylgalactosaminyltransferase-2 (ppGalNAc-T2), causes impaired insulin signaling and action in cultured human liver cells. In addition, GALNT2 mRNA levels are down-regulated in liver of spontaneously insulin resistant, diabetic Goto-Kakizaki rats. To investigate the role of GALNT2 in human hyperglycemia, we measured GALNT2 mRNA expression levels in peripheral whole blood cells of 84 non-obese and 46 obese non-diabetic individuals as well as of 98 obese patients with type 2 diabetes. We also measured GALNT2 mRNA expression in human U937 cells cultured under different glucose concentrations. In vivo studies indicated that GALNT2 mRNA levels were significantly reduced from non obese control to obese non diabetic and to obese diabetic individuals (p<0.001). In vitro studies showed that GALNT2 mRNA levels was reduced in U937 cells exposed to high glucose concentrations (i.e. 25 mmol/l glucose) as compared to cells exposed to low glucose concentration (i.e. 5.5 mmol/l glucose +19.5 mmol/l mannitol). In conclusion, our data indicate that GALNT2 is down-regulated in patients with type 2 diabetes and suggest that this association is, at least partly, secondary to hyperglycemia. Further studies are needed to understand whether GALNT2 down-regulation plays a pathogenic role in maintaining and/or aggravating the metabolic abnormalities of diabetic milieu.     

Sera from patients with type 2 Diabetes and Neuropathy Induce Autophagy and Colocalization with Mitochondria in SY5Y cells

The etiology of diabetic neuropathy is multifactorial and not fully elucidated, although oxidative stress and mitochondrial dysfunction are major factors. We reported previously that complement-inactivated sera from type 2 diabetic patients with neuropathy induce apoptosis in cultured neuronal cells, possibly through an autoimmune immunoglobulin-mediated pathway. Recent evidence supports an emerging role for autophagy in a variety of diseases. Here we report that exposure of human neuroblastoma SH-SY5Y cells to sera from type 2 diabetic patients with neuropathy is associated with increased levels of autophagosomes that is likely mediated by increased titers of IgM or IgG autoimmune immunoglobulins. The increased presence of macroautophagic vesicles was monitored using a specific immunohistochemical marker for autophagosomes, anti-LC3-II immunoreactivity, as well as the immunohistochemical signal for beclin-1, and was associated with increased co-localization with mitochondria in the cells exposed to diabetic neuropathic sera. We also report that dorsal root ganglia removed from streptozotocin-induced diabetic rats exhibit increased levels of autophagosomes and co-localization with mitochondria in neuronal soma, concurrent with enhanced binding of IgG and IgM autoimmune immunoglobulins. To our knowledge, this is the first evidence that the presence of autophagosomes is increased by a serum factor, likely autoantibody(ies) in a pathological condition. Stimulation of autophagy by an autoantibody-mediated pathway can provide a critical link between the immune system and the loss of function and eventual demise of neuronal tissue in type 2 diabetes.     

Sera from patients with type 2 diabetes and neuropathy induce autophagy and colocalization with mitochondria in SY5Y cells

The etiology of diabetic neuropathy is multifactorial and not fully elucidated, although oxidative stress and mitochondrial dysfunction are major factors. We reported previously that complement-inactivated sera from type 2 diabetic patients with neuropathy induce apoptosis in cultured neuronal cells, possibly through an autoimmune immunoglobulin-mediated pathway. Recent evidence supports an emerging role for autophagy in a variety of diseases. Here we report that exposure of human neuroblastoma SH-SY5Y cells to sera from type 2 diabetic patients with neuropathy is associated with increased levels of autophagosomes that is likely mediated by increased titers of IgM or IgG autoimmune immunoglobulins. The increased presence of macroautophagic vesicles was monitored using a specific immunohistochemical marker for autophagosomes, anti-LC3-II immunoreactivity, as well as the immunohistochemical signal for beclin-1, and was associated with increased co-localization with mitochondria in the cells exposed to diabetic neuropathic sera. We also report that dorsal root ganglia removed from streptozotocin-induced diabetic rats exhibit increased levels of autophagosomes and co-localization with mitochondria in neuronal soma, concurrent with enhanced binding of IgG and IgM autoimmune immunoglobulins. To our knowledge, this is the first evidence that the presence of autophagosomes is increased by a serum factor, likely autoantibody(ies) in a pathological condition. Stimulation of autophagy by an autoantibody-mediated pathway can provide a critical link between the immune system and the loss of function and eventual demise of neuronal tissue in type 2 diabetes.     

Heat Shock Protein Beta-1 Modifies Anterior to Posterior Purkinje Cell Vulnerability in a Mouse Model of Niemann-Pick Type C Disease

Selective neuronal vulnerability is characteristic of most degenerative disorders of the CNS, yet mechanisms underlying this phenomenon remain poorly characterized. Many forms of cerebellar degeneration exhibit an anterior-to-posterior gradient of Purkinje cell loss including Niemann-Pick type C1 (NPC) disease, a lysosomal storage disorder characterized by progressive neurological deficits that often begin in childhood. Here, we sought to identify candidate genes underlying vulnerability of Purkinje cells in anterior cerebellar lobules using data freely available in the Allen Brain Atlas. This approach led to the identification of 16 candidate neuroprotective or susceptibility genes. We demonstrate that one candidate gene, heat shock protein beta-1 (HSPB1), promoted neuronal survival in cellular models of NPC disease through a mechanism that involved inhibition of apoptosis. Additionally, we show that over-expression of wild type HSPB1 or a phosphomimetic mutant in NPC mice slowed the progression of motor impairment and diminished cerebellar Purkinje cell loss. We confirmed the modulatory effect of Hspb1 on Purkinje cell degeneration in vivo, as knockdown by Hspb1 shRNA significantly enhanced neuron loss. These results suggest that strategies to promote HSPB1 activity may slow the rate of cerebellar degeneration in NPC disease and highlight the use of bioinformatics tools to uncover pathways leading to neuronal protection in neurodegenerative disorders.     

Evaluation of metabolic,antioxidant and anti-inflammatory effects of Garcinia kola on diabetic rats

Garcinia kola (G. kola), is a plant characterized by its hypoglycemic properties. We recently reported our findings on the extracts of G. kola, in which we found that it prevented the loss of inflammation-sensible neuronal populations in streptozotocin (STZ)-induced rat models of type 1 diabetes mellitus (T1DM).In the present study we assessed the effect of G. kola bioactive compounds extracted successively with water, hexane, methylene chloride, ethyl acetate, and butanol. through analyzing biochemical markers of oxidative stress, inflammation, and metabolic function in STZ-induced diabetic animals.Animals made diabetic by a single injection with STZ (60 mg/kg, i.p.), were treated daily with either vehicle solution, insulin, or G. kola extracts and its fractions from the first to the 6th-week post-injection. Biochemical markers; glucose, insulin, C-peptide, neuron-specific enolase (NSE), creatinine kinase, glutathione peroxidase, malondialdehyde (MDA), resistin, soluble E-selectin (SE-Selectin), and C-reactive proteins (CRP) levels in the sera were determined in the study groups. A marked increase in blood glucose (209.26% of baseline value), and a decrease in body weight (−12.37%) were observed in diabetic control animals but not in animals treated with either insulin or G. kola extracts and its fractions. The sub-fraction F5, G. kola ethyl acetate had the highest bioactive activities, with a maintenance of blood sugar, malondialdehyde, C-peptide, E-selectin, C-reactive protein (CRP) and neuron-specific enolase (NSE) to levels and responses comparable to healthy non-diabetic vehicle group and the positive control diabetic insulin-treated group.Our findings suggest that G. kola may have a strong therapeutic potential against T1DM and its microvascular complications.     

Systemic Perturbations of Key Metabolites in Diabetic Rats During the Evolution of Diabetes Studied by Urine Metabonomics

Background

Elucidation of metabolic profiles during diabetes progression helps understand the pathogenesis of diabetes mellitus. In this study, urine metabonomics was used to identify time-related metabolic changes that occur during the development of diabetes mellitus and characterize the biochemical process of diabetes on a systemic, metabolic level.

Methodology/Principal Findings

Urine samples were collected from diabetic rats and age-matched controls at different time points: 1, 5, 10, and 15 weeks after diabetes modeling. ¹H nuclear magnetic resonance (¹H NMR) spectra of the urine samples were obtained and analyzed by multivariate data analysis and quantitative statistical analysis. The metabolic patterns of diabetic groups are separated from the controls at each time point, suggesting that the metabolic profiles of diabetic rats were markedly different from the controls. Moreover, the samples from the diabetic 1-wk group are closely associated, whereas those of the diabetic 15-wk group are scattered, suggesting that the presence of various of complications contributes significantly to the pathogenesis of diabetes. Quantitative analysis indicated that urinary metabolites related to energy metabolism, tricarboxylic acid (TCA) cycle, and methylamine metabolism are involved in the evolution of diabetes.

Conclusions/Significance

The results highlighted that the numbers of metabolic changes were related to diabetes progression, and the perturbed metabolites represent potential metabolic biomarkers and provide clues that can elucidate the mechanisms underlying the generation and development of diabetes as well as its complication.     

CYP24A1 Exacerbated Activity during Diabetes Contributes to Kidney Tubular Apoptosis via Caspase-3 Increased Expression and Activation

Decreases in circulating 25,hydroxyl-vitamin D3 (25 OH D3) and 1,25,dihydroxyl-vitamin D3 (1,25 (OH)2 D3) have been extensively documented in patients with type 2 diabetes. Nevertheless, the molecular reasons behind this drop, and whether it is a cause or an effect of disease progression is still poorly understood. With the skin and the liver, the kidney is one of the most important sites for vitamin D metabolism. Previous studies have also shown that CYP24A1 (an enzyme implicated in vitamin D metabolism), might play an important role in furthering the progression of kidney lesions during diabetic nephropathy. In this study we show a link between CYP24A1 increase and senescence followed by apoptosis induction in the renal proximal tubules of diabetic kidneys. We show that CYP24A1 expression was increased during diabetic nephropathy progression. This increase derived from protein kinase C activation and increased H₂O₂ cellular production. CYP24A1 increase had a major impact on cellular phenotype, by pushing cells into senescence, and later into apoptosis. Our data suggest that control of CYP24A1 increase during diabetes has a beneficial effect on senescence induction and caspase-3 increased expression. We concluded that diabetes induces an increase in CYP24A1 expression, destabilizing vitamin D metabolism in the renal proximal tubules, leading to cellular instability and apoptosis, and thereby accelerating tubular injury progression during diabetic nephropathy.