Protein kinase C is activated in glomeruli from streptozotocin diabetic rats. Possible mediation by glucose

A protein kinase C α and β inhibitor blunts hyperphagia to halt renal function decline and reduces adiposity in a rat model of obesity-driven type 2 diabetes

Type 2 diabetes (T2D) and its complications can have debilitating, sometimes fatal consequences for afflicted individuals. The disease can be difficult to control, and therapeutic strategies to prevent T2D-induced tissue and organ damage are needed. Here we describe the results of administering a potent and selective inhibitor of Protein Kinase C (PKC) family members PKCα and PKCβ, Cmpd 1, in the ZSF1 obese rat model of hyperphagia-induced, obesity-driven T2D. Although our initial intent was to evaluate the effect of PKCα/β inhibition on renal damage in this model setting, Cmpd 1 unexpectedly caused a marked reduction in the hyperphagic response of ZSF1 obese animals. This halted renal function decline but did so indirectly and indistinguishably from a pair feeding comparator group. However, above and beyond this food intake effect, Cmpd 1 lowered overall animal body weights, reduced liver vacuolation, and reduced inguinal adipose tissue (iWAT) mass, inflammation, and adipocyte size. Taken together, Cmpd 1 had strong effects on multiple disease parameters in this obesity-driven rodent model of T2D. Further evaluation for potential translation of PKCα/β inhibition to T2D and obesity in humans is warranted.

Cellular mechanism of action of forsythiaside for the treatment of diabetic kidney disease

Background: Diabetic kidney disease (DKD) becomes the leading cause of death for end-stage renal disease, whereas the potential mechanism is unclear and effective therapy is still rare. Our study was designed to investigate the cellular mechanism of Forsythiaside against DKD. Materials and Methods: The targets of Forsythiaside and the DKD-related targets were obtained from databases. The overlapping targets in these two sets were regarded as potential targets for alleviation of DKD by Forsythiaside. The targets of diabetic podocytopathy and tubulopathy were also detected to clarify the mechanism of Forsythiaside ameliorating DKD from the cellular level. Results: Our results explored that PRKCA and RHOA were regarded as key therapeutic targets of Forsythiaside with excellent binding affinity for treating DKD podocytopathy. Enrichment analysis suggested the underlying mechanism was mainly focused on the oxidative stress and mTOR signaling pathway. The alleviated effects of Forsythiaside on the reactive oxidative species accumulation and PRKCA and RHOA proteins upregulation in podocytes were also confirmed. Conclusion: The present study elucidates that Forsythiaside exerts potential treatment against DKD which may act directly RHOA and PRKCA target by suppressing the oxidative stress pathway in podocytes. And Forsythiaside could be regarded as one of the candidate drugs dealing with DKD in future experimental or clinical researches.

The Role of Diacylglycerol Kinase in the Amelioration of Diabetic Nephropathy

The drastic increase in the number of patients with diabetes and its complications is a global issue. Diabetic nephropathy, the leading cause of chronic kidney disease, significantly affects patients’ quality of life and medical expenses. Furthermore, there are limited drugs for treating diabetic nephropathy patients. Impaired lipid signaling, especially abnormal protein kinase C (PKC) activation by de novo-synthesized diacylglycerol (DG) under high blood glucose, is one of the causes of diabetic nephropathy. DG kinase (DGK) is an enzyme that phosphorylates DG and generates phosphatidic acid, i.e., DGK can inhibit PKC activation under diabetic conditions. Indeed, it has been proven that DGK activation ameliorates diabetic nephropathy. In this review, we summarize the involvement of PKC and DGK in diabetic nephropathy as therapeutic targets, and its mechanisms, by referring to our recent study.

SNPs in PRKCA-HIF1A-GLUT1 are associated with diabetic kidney disease in a Chinese Han population with type 2 diabetes

OBJECTIVE

To explore the relationship between SNPs in PRKCA-HIF1A-GLUT1 and diabetic kidney disease in Chinese Han people.

MATERIALS AND METHODS

A total of 2552 participants from Shanghai Diabetes Institute Inpatient Database of Shanghai Jiao Tong University Affiliated Sixth People's Hospital were involved in the stage 1 cross-sectional population. A total of 6015 subjects from the Hong Kong Diabetes Register were included for validation. Genotyping of participants was conducted by the MassARRAY Compact Analyzer (Agena Bioscience). The data were analysed by plink, SAS, Haploview.

RESULTS

We identified variants associated with diabetic kidney disease in stage 1. Rs1681851 (P = .0105, OR = 1.331) in GLUT1 as well as rs2301108 (P = .0085, OR = 1.289) and rs79865957 (P = .0204, OR = 1.263) in HIF1A were significantly associated with diabetic kidney disease. Regarding DKD-related traits, rs1681851 was associated with plasma creatinine levels (P = .0169, β = 4.822) and eGFR (P = .0457, β = -6.956). Moreover, the results showed the interactions between PRKCA-GLUT1 in the occurrence of DKD. We further sought validation of the 17 SNPs in a prospective cohort and found that rs900836 and rs844501 were associated with the percentage change in eGFR slope. We performed a meta-analysis of case-control analysis data from the Hong Kong samples together with the stage 1 data from Shanghai. Rs9894851 showed significant correlation with the serum creatinine level as well as eGFR and no SNP showed association with DKD after meta-analysis.

CONCLUSIONS

Our results suggest potential association between SNPs in PRKCA-HIF1A-GLUT1 and diabetic kidney disease in Chinese Han people.

Brain signalling systems: A target for treating type I diabetes mellitus

From early to later stages of Type I Diabetes Mellitus (TIDM), signalling molecules including brain indolamines and protein kinases are altered significantly, and that has been implicated in the Metabolic Disorders (MD) as well as impairment of retinal, renal, neuronal and cardiovascular systems. Considerable attention has been focused to the effects of diabetes on these signalling systems. However, the exact pathophysiological mechanisms of these signals are not completely understood in TIDM, but it is likely that hyperglycemia, acidosis, and insulin resistance play significant roles. Insulin maintains normal glycemic levels and it acts by binding to its receptor, so that it activates the receptor's tyrosine kinase activity, resulting in phosphorylation of several substrates. Those substrates provide binding/interaction sites for signalling molecules, including serine/threonine kinases and indolamines. For more than two decades, our research has been focused on the mechanisms of protein kinases, CaM Kinase and Serotonin transporter mediated alterations of indolamines in TIDM. In this review, we have also discussed how discrete areas of brain respond to insulin or some of the pharmacological agents that triggers or restores these signalling molecules, and it may be useful for the treatment of specific region wise changes/disorders of diabetic brain.

Alleviation of oxidative stress-mediated nephropathy by dietary fenugreek (Trigonella foenum-graecum) seeds and onion (Allium cepa) in streptozotocin-induced diabetic rats

Oxidative stress plays a major role in the progression of diabetes and the pathogenesis of diabetic nephropathy. In this study, the beneficial influence of dietary fenugreek (Trigonella foenum-graecum) seeds and onion (Allium cepa) on oxidative stress-mediated renal injury was evaluated in streptozotocin-induced diabetic rats. Diabetes was induced in adult Wistar rats by the administration of streptozotocin (i.p. 45 mg kg^-1). Dietary interventions were made with 10% fenugreek seeds or 3% onion (freeze-dried) or their combination for 6 weeks. These dietary interventions countered nephromegaly in the diabetic animals, the increase in creatinine clearance and oxidative stress in renal tissue. These dietary interventions significantly countered the increased renal cholesterol and triglycerides associated with the diabetic condition. The up-regulation of the receptor for advanced glycation end products, inflammatory cytokines and oxidative stress markers in the renal tissue of the diabetic rats was effectively countered. Renal 8-hydroxy-2-deoxyguanosine, its excretion, DNA fragmentation and mitochondrial DNA deletion were significantly annulled in the diabetic rats by these dietary interventions. Generally, the beneficial effects were greater in the combined intervention, although they were not additive. Thus, the beneficial influence of dietary fenugreek and onion on oxidative stress-mediated renal injury is higher when consumed together and this may be a strategy to ameliorate diabetic nephropathy.

Immunity and inflammation in diabetic kidney disease: translating mechanisms to biomarkers and treatment targets

Increasing incidences of obesity and diabetes have made diabetic kidney disease (DKD) the leading cause of chronic kidney disease and end-stage renal disease worldwide. Despite current pharmacological treatments, including strategies for optimizing glycemic control and inhibitors of the renin-angiotensin system, DKD still makes up almost one-half of all cases of end-stage renal disease in the United States. Compelling and mounting evidence has clearly demonstrated that immunity and inflammation play a paramount role in the pathogenesis of DKD. This article reviews the involvement of the immune system in DKD and identifies important roles of key immune and inflammatory mediators. One of the most recently identified biomarkers is serum amyloid A, which appears to be relatively specific for DKD. Novel and evolving treatment approaches target protein kinases, transcription factors, chemokines, adhesion molecules, growth factors, advanced glycation end-products, and other inflammatory molecules. This is the beginning of a new era in the understanding and treatment of DKD, and we may have finally reached a tipping point in our fight against the growing burden of DKD.

Evaluation of Protein Kinase Cβ and PPARγ Activity in Diabetic Rats Supplemented with Momordica charantia

INTRODUCTION

The present study was taken up to compare and evaluate the effect of Momordica charantia supplementation with pioglitazone on PKC-β and PPAR-γ activity in kidneys of diabetic rats. The hypoglycaemic and lipid lowering effect of Momordica charantia were screened in laboratory animal model and its potency was compared with a Thiazolidinedione (TZD) group antidiabetic drug like pioglitazone.

MATERIALS AND METHODS

Adult healthy albino rats of Wistar strain aged 3-4months, weighing between 170-250gm of either sex were divided into 4 groups; Group 1 (normal controls), Group 2 (diabetic controls), Group 3 (diabetic rats treated with pioglitazone) and Group 4 (diabetic rats treated with bitter melon juice). Type 1 Diabetes was induced in rats by intraperitoneal injection of streptozotocin at a dose of 55 mg/kg body weight, following which glucose levels were estimated by Accu chek- active glucometer on day 0, 7, 14, 21 and 28 days to assess the efficacy of Bitter Melon Juice (BMJ) and pioglitazone. After 28 days of treatment, the rats were sacrificed and blood collected from abdominal vena cava was used for estimation of triglycerides by Glycerol 3 phosphate oxidase phenol aminophenazone method and cholesterol by Cholestrol oxidase phenol aminophenazone method. PKC-β and PPAR-γ were estimated in the dissected kidneys by using double sandwich ELISA based kits on an automated plate reader.

RESULTS

BMJ significantly reduced blood glucose levels in group 4 as compared to diabetic controls (p<0.001). Total cholesterol and triglycerides were significantly reduced in both group 3 and 4. In Group 4, there was reduction in PKC-β levels, when compared to Group 3(p=0.004). PPAR-γ levels were increased in both Group 3 and 4, when compared to Group 2.

CONCLUSION

The results suggest that BMJ has hypoglycaemic and lipid lowering effect in diabetic animal models. BMJ increases PPAR-γ activity and decreases PKC-β activity in kidneys of diabetic rats, thereby preventing the complications of diabetes mellitus. Fresh BMJ mimics action of pioglitazone belonging to TZD group thus showing a potential for further research in identifying the active molecules responsible for glucose and lipid lowering action.

Influence of protein kinase C (PKC) on the prognosis of diabetic nephropathy patients

AIMS

To investigate the association between protein kinase C (PKC) and the prognosis of patients with diabetic nephropathy (DN).

METHODS

92 patients with DN who had received treatments with angiotensin converting enzyme inhibitor (ACEI) or angiotensin-receptor blockade (ARB) were collected. The clinicopathologic characteristics were recorded and a 4-year follow-up with the final result of impaired renal functions (eGFR < 40 mL/min) was conducted. The expression of PKC was detected by immunohistochemical assay. Kaplan-Meier and Cox regression analysis were performed to estimate the effects of PKC on DN prognosis.

RESULTS

According to immunohistochemical analysis, there were 54 cases with positive expression of PKC (positive rate 58.7%). Meanwhile, during the follow-up, the urine protein, mean serum creatinine and eGFR in patients with positive PKC were all higher than those in negative expression group (P < 0.05). The expression of PKC was influenced by age (P < 0.001), course of disease (P < 0.001), blood pressure (P = 0.002), blood glucose (P < 0.001), HbA1c (P = 0.002), renal functions of patients before (P = 0.011) and after (P = 0.041) the biopsy. Besides, the Kaplan-Meier curve revealed that patients with positive PKC expression had shorter survival time than those with negative PKC expression (P < 0.001). Cox regression analysis indicated that HbA1c (P = 0.009), renal functions of patients after the biopsy (P = 0.002) and PKC (P = 0.028) were important factors in the prognosis of DN and they might be independent prognostic markers.

CONCLUSION

The expression of PKC is relatively higher in DN patients than in healthy controls. And PKC may be a valuable prognostic marker for patients with DN.

Diabetic peripheral neuropathy: role of reactive oxygen and nitrogen species

The prevalence of diabetes has reached epidemic proportions. There are two forms of diabetes: type 1 diabetes mellitus is due to auto-immune-mediated destruction of pancreatic β-cells resulting in absolute insulin deficiency and type 2 diabetes mellitus is due to reduced insulin secretion and or insulin resistance. Both forms of diabetes are characterized by chronic hyperglycemia, leading to the development of diabetic peripheral neuropathy (DPN) and microvascular pathology. DPN is characterized by enhanced or reduced thermal, chemical, and mechanical pain sensitivities. In the long-term, DPN results in peripheral nerve damage and accounts for a substantial number of non-traumatic lower-limb amputations. This review will address the mechanisms, especially the role of reactive oxygen and nitrogen species in the development and progression of DPN.

Dual inhibition of classical protein kinase C-α and protein kinase C-β isoforms protects against experimental murine diabetic nephropathy

Activation of protein kinase C (PKC) has been implicated in the pathogenesis of diabetic nephropathy with proteinuria and peritubular extracellular matrix production. We have previously shown that the PKC isoforms α and β mediate different cellular effects. PKC-β contributes to hyperglycemia-induced renal matrix production, whereby PKC-α is involved in the development of albuminuria. We further tested this hypothesis by deletion of both isoforms and used a PKC inhibitor. We analyzed the phenotype of nondiabetic and streptozotocin (STZ)-induced diabetic homozygous PKC-α/β double-knockout mice (PKC-α/β(-/-)). After 8 weeks of diabetes mellitus, the high-glucose-induced renal and glomerular hypertrophy as well as transforming growth factor-β1) and extracellular matrix production were diminished in the PKC-α/β(-/-) mice compared with wild-type controls. Urinary albumin/creatinine ratio also was significantly reduced, however, it was not completely abolished in diabetic PKC-α/β(-/-) mice. Treatment with CGP41252, which inhibits PKC-α and PKC-β, is able to prevent the development of albuminuria and to reduce existing albuminuria in type 1 (STZ model) or type 2 (db/db model) diabetic mice. These results support our hypothesis that PKC-α and PKC-β contribute to the pathogenesis of diabetic nephropathy, and that dual inhibition of the classical PKC isoforms is a suitable therapeutic strategy in the prevention and treatment of diabetic nephropathy.

Downregulation of vasopressin V1A receptors and activation of mitogen-activated protein kinase in rat mesangial cells cultured under high-glucose conditions

SUMMARY

In the present study we examined the effects of high extracellular glucose concentrations on vasopressin (AVP) V(1A) receptor kinetics and signal transduction in cultured rat mesangial cells. Scatchard analysis of [(3) H]-AVP binding to mesangial cell plasma membranes showed that although high glucose (30 mmol/L) decreased V(1A) receptor numbers relative to cells cultured in normal glucose (10 mmol/L), receptor affinity was not affected. This V(1A) receptor downregulation was associated with an attenuated increase in AVP-stimulated cytosolic free calcium concentrations ([Ca(2+) ](i) ). In addition, high glucose increased both the basal and AVP-stimulated activity of the classic mitogen-activated protein kinase, namely extracellular signal-regulated kinase (ERK). Furthermore, high glucose induced activation of protein kinase C (PKC) in mesangial cells that could be inhibited by coincubation with the PKC inhibitor staurosporine (10 nmol/L). Staurosporine also markedly attenuated the high glucose-induced downregulation of V(1A) receptors on mesangial cells and blocked the depressed [Ca(2+) ](i) response and increased ERK activity induced by AVP. The results indicate that high extracellular glucose downregulates V(1A) receptors on rat mesangial cells and modulates their signal transduction properties via PKC activation.

Effect of carnosine on erythrocyte deformability in diabetic rats

It is known that oxidative stress plays an important role in the chronic complications of diabetes. Lipid peroxidation is one of the consequences of oxidative stress. Erythrocyte deformability abilities are reduced as a result of lipid peroxidation. Conversely, a decrease nitric oxide (NO) production seems to be responsible in endothelial dysfunction which occurs in diabetic vascular complications. Carnosine is a molecule with anti-oxidant properties. The aim of this study was to investigate erythrocyte deformability indices and the effects of carnosine on erythrocyte deformability in diabetes and to determine a possible relationship between carnosine and nitric oxide. Male Wistar albino rats were used in the study. Injections were administered to seven groups consisting of eight rats each. The groups were: Control, Carnosine, L-NAME (NG-nitro-L-arginine methyl ester), Diabetic, STZ (Streptozotocin) +Carnosine, STZ+L-NAME and STZ+Carnosine+L-NAME. In addition, glucose, insulin, MDA (Malondialdehyde) and NO levels were measured and erythrocyte deformability indices were calculated in all groups. Erythrocyte deformability indices and NO levels were decreased and MDA levels were found to be increased in diabetic group. It was also found that carnosine can significantly reverse erythrocyte deformability, reduce lipid peroxidation and increase NO levels in diabetes. It can be concluded that carnosine can recover from microvascular circulation problems by increasing erythrocyte deformability, can protect cells and tissues against lipid peroxidation and can be used as a multi-functional anti-oxidant in the treatment of diabetes mellitus to prevent the complications of diabetes.

Elucidating mechanisms underlying altered renal autoregulation in diabetes

Previous studies have reported that high-salt intake paradoxically activates tubuloglomerular feedback (TGF) in type 1 diabetes. Using Zucker lean (ZL) and diabetic fatty (ZDF) rats on normal and high-salt diets, renal hemodynamics and the renin-angiotensin system (RAS) were characterized. On normal salt diet, glomerular filtration rate (GFR) was higher in ZDF than ZL rats. Autoregulation of GFR was less efficient and lithium clearance was lower in ZDF rats than ZL rats. Salt load reduced GFR in ZDF rats with restoration of lithium clearance and partial improvement in autoregulatory index (AI). The administration of 8-cyclopentyl-1,3-dipropylxanthine, a selective adenosine-1 receptor antagonist to ZDF rats on a high-salt diet abolished the improvement of AI in GFR. However, this effect was seen by neither (Cx40)GAP27 nor (Cx37,43)GAP27, which inhibits connexin (Cx) 40 or Cx37. Renal ANG II was higher in ZDF than ZL rats on normal salt diet, but the difference was eliminated by a salt load. The present data provide the first demonstration for a salt paradox in type 2 diabetes and implicate that in addition to Cx alterations, an enhanced proximal reabsorption attenuates TGF, underlying glomerular hyperfiltration and RAS activation. These data suggest that a high-salt diet standardizes distal delivery in diabetes, suppressing the RAS, and improving GFR autoregulation and hyperfiltration through adenosine.

The essential role of protein kinase Cδ in diabetes-induced neural tube defects

BACKGROUND

Maternal diabetes causes neural tube defects (NTDs) in the embryos via activating protein kinase Cs (PKCs), which regulate programmed cell death (apoptosis). The aims of this study are to investigate the role of proapoptotic PKCδ in NTD formation and the underlying mechanisms.

METHODS

PKCδ heterozygous (pkcδ(+/-)) female mice were diabetic (DM) induced by intravenous injection of streptozotocin. Occurrence of NTDs was evaluated at embryonic day 11.5 and compared between wild type (WT) and PKCδ homozygous (pkcδ(-/-)) embryos. Changes in oxidative and endoplasmic reticulum (ER) stress-associated factors and stress-response c-Jun N-terminal kinases (JNKs) were assessed using Western blot assay.

RESULTS

Compared to DM/WT, the DM/PKCδ(-/-) embryos had significantly lower NTD rate and lower levels of oxidative and ER stress factors and JNK activation. These values were similar to those in the non-diabetic control group.

CONCLUSION

PKCδ plays a critical role in diabetes-induced NTDs, potentially through increasing oxidative and ER stress and JNK-associated stress-response pathways.

Effects of high glucose on AVP-induced hyperplasia, hypertrophy, and type IV collagen synthesis in cultured rat mesangial cells

INTRODUCTION

Hyperglycemia is a principal characteristic of diabetes and influences many cellular functions. Diabetic nephropathy is characterized by glomerular mesangial expansion which could result from increased mesangial cell extracellular matrix synthesis induced by hyperglycemia.

METHODS

To investigate whether the physiological functions of mesangial cells are altered in a diabetic environment, we evaluated the effect of high extracellular glucose concentration on thymidine/leucine incorporation, hyperplasia/hypertrophy, and type IV collagen synthesis, induced by vasopressin (AVP), in cultured rat mesangial cells.

RESULTS

The exposure of mesangial cells to a high glucose concentration (30 mM) significantly reduced AVP-induced thymidine incorporation and hyperplasia compared with normal glucose (10 mM). By contrast, treatment of mesangial cells with AVP in the presence of high extracellular glucose significantly increased leucine incorporation, hypertrophy, and type IV collagen synthesis compared with those at normal glucose levels. The administration of staurosporine, a protein kinase C inhibitor, reversed these effects of high-glucose conditions. Furthermore, the nonpeptide AVP V(1A) receptor-selective antagonists potently inhibited these AVP-induced physiological responses in mesangial cells cultured in high-glucose conditions.

CONCLUSIONS

These results demonstrate that high glucose suppresses mesangial cell proliferation but enhances hypertrophy and type IV collagen synthesis induced by AVP. This increased mesangial cell hypertrophy and extracellular matrix synthesis may play a crucial role in the glomerular mesangial expansion common to diabetic nephropathy.

C-peptide increases Na,K-ATPase expression via PKC- and MAP kinase-dependent activation of transcription factor ZEB in human renal tubular cells

BACKGROUND

Replacement of proinsulin C-peptide in type 1 diabetes ameliorates nerve and kidney dysfunction, conditions which are associated with a decrease in Na,K-ATPase activity. We determined the molecular mechanism by which long term exposure to C-peptide stimulates Na,K-ATPase expression and activity in primary human renal tubular cells (HRTC) in control and hyperglycemic conditions.

METHODOLOGY/PRINCIPAL FINDINGS

HRTC were cultured from the outer cortex obtained from patients undergoing elective nephrectomy. Ouabain-sensitive rubidium ((86)Rb(+)) uptake and Na,K-ATPase activity were determined. Abundance of Na,K-ATPase was determined by Western blotting in intact cells or isolated basolateral membranes (BLM). DNA binding activity was determined by electrical mobility shift assay (EMSA). Culturing of HRTCs for 5 days with 1 nM, but not 10 nM of human C-peptide leads to increase in Na,K-ATPase α(1)-subunit protein expression, accompanied with increase in (86)Rb(+) uptake, both in normal- and hyperglycemic conditions. Na,K-ATPase α(1)-subunit expression and Na,K-ATPase activity were reduced in BLM isolated from cells cultured in presence of high glucose. Exposure to1 nM, but not 10 nM of C-peptide increased PKCε phosphorylation as well as phosphorylation and abundance of nuclear ERK1/2 regardless of glucose concentration. Exposure to 1 nM of C-peptide increased DNA binding activity of transcription factor ZEB (AREB6), concomitant with Na,K-ATPase α(1)-subunit mRNA expression. Effects of 1 nM C-peptide on Na,K-ATPase α(1)-subunit expression and/or ZEB DNA binding activity in HRTC were abolished by incubation with PKC or MEK1/2 inhibitors and ZEB siRNA silencing.

CONCLUSIONS/SIGNIFICANCE

Despite activation of ERK1/2 and PKC by hyperglycemia, a distinct pool of PKCs and ERK1/2 is involved in regulation of Na,K-ATPase expression and activity by C-peptide. Most likely C-peptide stimulates sodium pump expression via activation of ZEB, a transcription factor that has not been previously implicated in C-peptide-mediated signaling. Importantly, only physiological concentrations of C-peptide elicit this effect.

Altered gap junctional communication and renal haemodynamics in Zucker fatty rat model of type 2 diabetes

AIMS/HYPOTHESIS

We examined the link between altered gap junctional communication and renal haemodynamic abnormalities in diabetes in studies performed on Zucker lean (ZL) and the Zucker diabetic fatty (ZDF) rat model of type 2 diabetes.

METHODS

The abundance of connexin (Cx) 37, 40 and 43 was assessed by western blot and immunohistochemistry. Renal haemodynamics was characterised with GAP peptides, which are Cx mimetics, to inhibit gap junctions as a probe in both strains.

RESULTS

ZDF rats exhibited higher plasma glucose, 8-epi-prostaglandin F2α excretion, renal plasma flow and GFR than ZL rats. In ZDF rat kidney phosphorylation of Cx43 was enhanced compared with that in ZL rats. Immunohistochemical study revealed that the density of abundance of Cx37 in renin-secreting cells was significantly reduced in ZDF rats. Although renal autoregulation was markedly impaired in ZDF rats, it was preserved in ZL rats. GAP27 for Cx37,43 and for Cx40 impaired renal autoregulation in ZL rats, but failed to induce further alterations in renal autoregulation in ZDF rats.

CONCLUSIONS/INTERPRETATION

Our findings indicate that ZDF rats have glomerular hyperfiltration with impaired autoregulation. They also demonstrate enhanced phosphorylation of Cxs and reduced production of Cxs in ZDF rat kidney, especially of Cx37 in renin-secreting cells. Finally, our data suggest that an impairment of gap junctional communication in juxtaglomerular apparatus plays a role in altered renal autoregulation in diabetes.

Kidney: its impact on glucose homeostasis and hormonal regulation

According to current textbook wisdom the liver is the exclusive site of glucose production in humans in the postabsorptive state. Although animal and in vitro studies have documented that the kidney is capable of gluconeogenesis, glucose production by the human kidney has been regarded as negligible. This knowledge is based on net balance measurements across the kidney. Recent studies combining isotopic and balance techniques have demonstrated that the human kidney is involved in the regulation of glucose homeostasis by making glucose via gluconeogenesis, taking up glucose from the circulation, and by reabsorbing glucose from the glomerular filtrate. The human liver and kidneys release approximately equal amounts of glucose via gluconeogenesis in the postabsorptive state. In the postprandial state, although overall endogenous glucose release decreases substantially, renal gluconeogenesis actually increases by approximately 2-fold. Following meal ingestion, glucose utilization by the kidney increases. Increased glucose uptake into the kidney may be implicated in diabetic nephropathy. Normally each day, ∼ 180 g of glucose is filtered by the kidneys; almost all of this is reabsorbed by means of sodium glucose cotransporter 2 (SGLT2), expressed in the proximal tubules. However, the capacity of SGLT2 to reabsorb glucose from the renal tubules is finite and when plasma glucose concentrations exceed a threshold, glucose begins to appear in the urine. Renal glucose release is stimulated by epinephrine and is inhibited by insulin. Handling of glucose by the kidney is altered in type 2 diabetes mellitus (T2DM): renal gluconeogenesis and renal glucose uptake are increased in both the postabsorptive and postprandial states, and renal glucose reabsorption is also increased Since renal glucose release is almost exclusively due to gluconeogenesis, it seems that the kidney is as important gluconeogenic organ as the liver. The most important renal gluconeogenic precursors appear to be lactae glutamine and glycerol.

Protein kinase Cβ2 inhibition reduces hyperglycemia-induced neural tube defects through suppression of a caspase 8-triggered apoptotic pathway

OBJECTIVE

Neural tube defects in diabetic embryopathy are associated with increased protein kinase C (PKC)β2 activity and programmed cell death (apoptosis). The apoptosis is triggered by caspase 8, which activates members of the Bcl-2 and caspase families, such as Bid and caspase 3. Whether PKCβ2 regulates caspase 8-induced apoptosis remains to be addressed.

STUDY DESIGN

Mouse embryos at embryonic day 8.5 were cultured in a high concentration of glucose (22 mmol/L) and treated with PKCβ2 inhibitor (50 nmol/L) for 48 hours. The levels of apoptosis and activation of apoptotic factors were quantified using the terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling and Western blot assays, respectively.

RESULTS

Reduction in the rate of neural tube defect by PKCβ2 inhibition is associated with significant decreases in the levels of apoptosis, and caspase 8, caspase 3, and Bid activation, and cytochrome C release from mitochondria, to the similar levels as in euglycemic controls (8.3 mmol/L; P < .05).

CONCLUSION

PKCβ2 influences a caspase 8-regulated apoptotic pathway in diabetic embryopathy.

Endothelin-1 enhances superoxide and prostaglandin E2 production of isolated diabetic glomeruli

Endothelin-1 (ET-1) plays an important role in the pathogenic mechanism of diabetic nephropathy. However, the regulatory effects of ET-1 on superoxide and prostaglandin E2 (PGE2) in diabetic glomeruli are unclear. The aim of this study was to determine whether ET-1 exerts a differential effect on the production of superoxide and PGE2 in diabetic glomeruli. The regulatory effects of indomethacin, insulin, dexamethasone, and heparin were also investigated. Freshly isolated glomeruli were obtained from normal and streptozotocin-induced diabetic rats for 1 week (DM1W), 1 month (DM1M), and 3 months (DM3M), respectively. Our results showed that the basal superoxide production of isolated glomeruli was significantly higher in DM1M and DM3M than in the normal rats (p < 0.01). ET-1 stimulated superoxide production in normal, DM1W and DM1M glomeruli (p < 0.01) but not in DM3M rats. The basal production of PGE2 in isolated glomeruli did not differ between diabetic and normal rats. ET-1 also stimulated PGE2 production in diabetic rats (p < 0.05). Pretreatment with indomethacin further enhanced ET-1-stimulated superoxide production in all groups of diabetic rats (p < 0.05), while the ET-1-stimulated PGE2 production was attenuated by indomethacin. Insulin, dexamethasone and heparin had no additional effects on ET-1-mediated superoxide and PGE2 production. In conclusion, basal glomerular production of superoxide but not PGE2 was increased in the diabetic glomeruli. ET-1 further stimulated production of both superoxide and PGE2. Indomethacin could enhance ET-1-stimulated superoxide production while attenuating PGE2 production.

Aldose reductase inhibitor ameliorates renal vascular endothelial growth factor expression in streptozotocin-induced diabetic rats

PURPOSE

The vascular endothelial growth factor (VEGF) expression of podocyte is one of the well-known major factors in development of diabetic nephropathy. In this study, we investigated the effects of aldose reductase inhibitor, fidarestat on diabetic nephropathy, and renal VEGF expression in a type 1 diabetic rat model.

MATERIALS AND METHODS

Twenty four Sprague-Dawley male rats which were performed intraperitoneal injection of streptozotocin and normal six rats were divided into four groups including a normal control group, untreated diabetic control group, aldose reductase (AR) inhibitor (fidarestat, 16 mg kg(-1) day(-1)) treated diabetic group, and angiotensin receptor blocker (losartan, 20 mg kg(-1) day(-1)) treated diabetic group. We checked body weights and blood glucose levels monthly and measured urine albumin-creatinine ratio (ACR) at 8 and 32 weeks. We extracted the kidney to examine the renal morphology and VEGF expressions.

RESULTS

The ACR decreased in fidarestat and losartan treated diabetic rat groups than in untreated diabetic group (24.79 +/- 11.12, 16.11 +/- 9.95, and 84.85 +/- 91.19, p < 0.05). The renal VEGF messenger RNA (mRNA) and protein expression were significantly decreased in the fidarestat and losartan treated diabetic rat groups than in the diabetic control group.

CONCLUSION

We suggested that aldose reductase inhibitor may have preventive effect on diabetic nephropathy by reducing renal VEGF overexpression.

Glycaemic control with insulin prevents the reduced renal dopamine D1 receptor expression and function in streptozotocin-induced diabetes

BACKGROUND

It was demonstrated in streptozotocin (STZ)-induced diabetic rats that the D(1) receptor agonist failed to promote sodium excretion as a result of reduced renal D(1) receptor expression and decreased receptor G protein coupling. The present study examined the influence of glycaemic control with insulin on the renal D(1) receptor dysfunction in STZ-induced type 1 diabetes.

METHODS

Renal function, blood pressure, the natriuretic response to 5% volume expansion (VE) and the effects of the D(1) receptor agonist fenoldopam on natriuresis and on Na(+)/K(+)-ATPase activity in renal tubules were evaluated in uninephrectomized and sham-operated Wistar rats treated with STZ and compared with controls and STZ-treated rats made euglycaemic with insulin. D(1) receptor immunohistochemistry and protein abundance by western blot were also determined in all groups.

RESULTS

Treatment of sham and uninephrectomized rats with STZ caused a 4-fold increase in glucose plasma levels compared to controls and euglycaemic diabetic rats. A blunted natriuretic response to VE was observed in both sham and uninephrectomized hyperglycaemic diabetic rats, and this was accompanied by failure of fenoldopam to increase natriuresis and to inhibit renal Na(+)/K(+)-ATPase activity. In contrast, in both sham and uninephrectomized euglycaemic diabetic rats, the natriuretic response to VE, the fenoldopam-induced natriuresis and the accompanied inhibition of Na(+)/K(+)-ATPase activity were similar to those of the corresponding controls. D(1) receptor immunodetection and protein abundance were reduced in hyperglycaemic diabetic rats, but not in euglycaemic diabetic animals.

CONCLUSIONS

We conclude that the renal expression and natriuretic response to D(1) receptor activation is compromised in both sham and uninephrectomized rats with STZ-induced diabetes. These abnormalities were prevented by lowering glucose blood levels with insulin, thus providing evidence for the involvement of hyperglycaemia in the disturbances that underlie the compromised dopamine-sensitive natriuresis and increase of blood pressure in type 1 diabetes.

Fluvastatin attenuates diabetes-induced cardiac sympathetic neuropathy in association with a decrease in oxidative stress

BACKGROUND

Increased oxidative stress might contribute to diabetic (DM) neuropathy, so the effects of long-term treatment with fluvastatin (FL) on myocardial oxidative stress and cardiac sympathetic neural function were investigated in diabetic rats.

METHODS AND RESULTS

FL (10 mg . kg(-1) . day(-1), DM-FL) or vehicle (DM-VE) was orally administered for 2 weeks to streptozotocin-induced DM rats. Cardiac oxidative stress was determined by myocardial 8-iso-prostaglandin F(2alpha) (PGF(2alpha)) and NADPH oxidase subunit p22(phox) mRNA expression. Sympathetic neural function was quantified by autoradiography using (131)I- and (125)I-metaiodobenzylguanidine (MIBG). FL did not affect plasma glucose levels but remarkably decreased PGF(2alpha) levels compared with DM-VE rats (13.8+/-9.2 vs 175.0+/-93.9 ng/g tissue), although PGF(2alpha) levels were below the detection limit in non-DM rats. FL significantly reduced myocardial p22(phox) mRNA expression. Cardiac (131)I-MIBG uptake was lower in DM-VE rats than in non-DM rats, but the decrease was attenuated in DM-FL rats (1.31+/-0.08, 1.88+/-0.22, and 1.58+/-0.18 %kg dose/g, respectively, P<0.01). Cardiac MIBG clearance was not affected by the induction of DM or by FL, indicating that the reduced MIBG uptake in DM rats might result from impaired neural function.

CONCLUSIONS

FL ameliorates cardiac sympathetic neural dysfunction in DM rats in association with attenuation of increased myocardial oxidative stress.

Role of protein kinase C in diabetic complications

Hyperglycemia is an important factor in the development of macrovascular and microvascular complications in all diabetic patients. Several hypotheses have been postulated to explain the adverse effect of hyperglycemia on the vasculature; and one of these hypotheses is the activation of specific isoforms of protein kinase C (PKC) by diabetes. In this review, we summarize the molecular mechanisms of PKC activation and its relationship to diabetic complications. PKC activity regulates vascular permeability, contractility, extracellular matrix synthesis, hormone receptor turnover and proliferation, cell growth, angiogenesis, cytokine activation and leukocyte adhesion. All of these properties are abnormal in diabetes and are correlated with increased diacylglycerol-PKC pathway and PKCα, β1/2 and δ isoforms activation in the retina, aorta, heart and renal glomeruli.

Protein kinase C-dependent NAD(P)H oxidase activation induced by type 1 diabetes in renal medullary thick ascending limb

Type 1 diabetes provokes a protein kinase C (PKC)-dependent accumulation of superoxide anion in the renal medullary thick ascending limb (mTAL). We hypothesized that this phenomenon involves PKC-dependent NAD(P)H oxidase activation. The validity of this hypothesis was explored using mTAL suspensions prepared from rats with streptozotocin-induced diabetes and from sham (vehicle-treated) rats. Superoxide production was 5-fold higher in mTAL suspensions from diabetic rats compared with suspensions from sham rats. The NAD(P)H oxidase inhibitor apocynin caused an 80% decrease in superoxide production by mTAL from diabetic rats (P<0.05 vs untreated) without altering superoxide production by sham mTAL. NAD(P)H oxidase activity was >2-fold higher in mTAL from diabetic rats than in sham mTAL (P<0.05). Pretreatment with calphostin C (broad-spectrum PKC inhibitor) or rottlerin (PKCdelta inhibitor) reduced NAD(P)H oxidase activity by approximately 80% in both groups; however, PKCalpha/beta or PKCbeta inhibition did not alter NAD(P)H oxidase activity in either group. Protein levels of Nox2, Nox4, and p47phox were significantly higher in diabetic mTAL than in mTAL from sham rats. In summary, elevated superoxide production by mTAL from diabetic rats was normalized by NAD(P)H oxidase inhibition. PKC-dependent, PKCdelta-dependent, and total NAD(P)H oxidase activity was greater in mTAL from diabetic rats compared with sham. Protein levels of Nox2, Nox4, and p47phox were increased in mTAL from diabetic rats. We conclude that increased superoxide production by the mTAL during diabetes involves a PKCdelta-dependent increase in NAD(P)H oxidase activity in concert with increased protein levels of catalytic and regulatory subunits of the enzyme.

EGFR-PLCgamma1 signaling mediates high glucose-induced PKCbeta1-Akt activation and collagen I upregulation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. We have recently shown that epidermal growth factor receptor (EGFR) transactivation mediates high glucose (HG)-induced collagen I upregulation through PI3K-PKCbeta1-Akt signaling in mesangial cells (MC). Phospholipase Cgamma1 (PLCgamma1) interacts with activated growth factor receptors and activates classic PKC isoforms. We thus studied its role in HG-induced collagen I upregulation in MC. Primary rat MC were treated with HG (30 mM) or mannitol as osmotic control. Protein kinase activation was assessed by Western blotting and collagen I upregulation by Northern blotting. Diabetes was induced in rats by streptozotocin. HG treatment for 1 h led to PLCgamma1 membrane translocation and Y783 phosphorylation, both indicative of its activation. Mannitol was without effect. PLCgamma1 Y783 phosphorylation was also seen in cortex and glomeruli of diabetic rats. HG induced a physical association between EGFR and PLCgamma1 as identified by coimmunoprecipitation. PLCgamma1 activation required EGFR kinase activity since it was prevented by the EGFR inhibitor AG1478 or overexpression of kinase-inactive EGFR (K721A). Phosphoinositide-3-OH kinase inhibition also prevented PLCgamma1 activation. HG-induced Akt S473 phosphorylation, effected by PKCbeta1, was inhibited by the PLCgamma inhibitor U73122. PLCgamma1 inhibition or downregulation by small interference RNA also prevented HG-induced collagen I upregulation. Our results indicate that EGFR-PLCgamma1 signaling mediates HG-induced PKCbeta1-Akt activation and subsequent collagen I upregulation in MC. Inhibition of EGFR or PLCgamma1 may provide attractive therapeutic targets for the treatment of diabetic nephropathy.

Targeting the protein kinase C family in the diabetic kidney: lessons from analysis of mutant mice

The protein kinase C (PKC) superfamily comprises proteins that are activated in response to various pathogenic stimuli in the diabetic state. Hyperglycaemia is the predominant stimulus that induces the activation of distinct PKC isoforms within a cell, each mediating specific functions, probably through differential subcellular localisation. The contribution of individual PKC isoforms can be directly addressed in vivo using innovative PKC-isoform-specific knockout (KO) mouse models, which are providing key insights into the physiological function of PKC isoform diversity in the development of diabetic nephropathy. Such studies can be a valuable complementary approach to more commonly used pharmacological analyses using agents such as ruboxistaurin mesylate (Arxxant, LY333531), which is claimed to specifically inhibit the PKC-beta-isoform. As expected given the multiple and specific properties of the isoforms in vitro, deletion of different PKC isoform signalling pathways leads to distinct phenotypes in mice. Notably, KOs of the individual PKCs assigned specific non-redundant biological functions to each isoform, which were not compensated for by the others. Thus, PKC isoform specificity and cellular diversity seem to be responsible for the divergent outcomes leading to albuminuria and/or renal fibrosis according to studies on the streptozotocin-induced mouse model of diabetes. This review discusses the role of individual PKC isoforms in diabetic nephropathy and their potential therapeutic implications. Defining and targeting mediators of increased intracellular activation in the diabetic microvasculature will have important clinical and therapeutic benefits and help in the design of novel effective therapies in the near future.

Protein kinase C-beta inhibition for diabetic kidney disease

Amid the rapidly rising number of people with diabetes worldwide, the prevalence of diabetic kidney disease (DKD) is expected to increase considerably despite available treatments. Consequently, novel therapeutic agents are urgently needed. Ruboxistaurin mesylate is a bisindolylmaleimide that specifically inhibits the beta isoform of protein kinase C (PKC). In experimental models of DKD, ruboxistaurin normalized glomerular hyperfiltration, decreased urinary albumin excretion, preserved kidney function, and reduced mesangial expansion, glomerulosclerosis, and tubulointerstitial fibrosis. These beneficial effects of ruboxistaurin, both alone and combined with renin-angiotensin system inhibition, have been observed in a variety of experimental models of DKD. A phase 2 study of PKC-beta inhibition in persons with type 2 diabetes and DKD already treated with angiotensin converting enzyme inhibition and/or angiotensin receptor blockade has been conducted. Addition of ruboxistaurin for 1 year reduced urinary albumin, prevented an increase in urinary transforming growth factor-beta, and stabilized estimated glomerular filtration rate. Based on secondary analyses of clinical trials in patients with diabetic retinopathy or neuropathy, ruboxistaurin appears safe and may also prevent onset of DKD. PKC-beta inhibition holds promise as a new strategy to improve kidney disease outcomes in diabetes. Large-scale clinical trials will be required to confirm safety and to validate prospective benefits of ruboxistaurin on relevant clinical endpoints in DKD.

Diabetic nephropathy: important pathophysiologic mechanisms

With the global epidemic of type 2 diabetes mellitus, diabetes has become the leading cause of end stage renal failure (ESRF) in most Western countries. Approximately 20-30% of all diabetic subjects will develop evidence of diabetic nephropathy, which represents a continuum from microalbuminuria, to overt nephropathy or macroalbuminuria, and finally ESRF. While there have been significant breakthroughs in the last decade with regards to the prevention and treatment of diabetic kidney disease, in particular blockade of the renin angiotensin system, there is a vital need to identify and target novel pathophysiologic pathways such as advanced glycation which appear to be centrally involved in diabetic renal disease in order to reduce the rising burden of this disease.

Visfatin: a new player in mesangial cell physiology and diabetic nephropathy

Visfatin is an adipocytokine that improves insulin resistance and has an antidiabetic effect. However, the role of visfatin in the kidney has not yet been reported. In this experiment, the synthesis and physiological action of visfatin in cultured mesangial cells (MCs) were studied to investigate the role of visfatin in diabetic nephropathy. Visfatin was found synthesized in MCs as well as adipocytes. Visfatin synthesis was markedly increased, not by angiotensin II, but by high glucose stimuli. In addition, visfatin treatment induced a rapid uptake of glucose, peaking at 20 min after visfatin treatment in a dose-dependent manner. A small inhibiting RNA against insulin receptor significantly blocked visfatin-mediated glucose uptake. Visfatin stimuli also enhanced intracellular NAD levels, and treatment with FK866, which is a specific inhibitor of nicotinamide phosphoribosyltransferase (Nampt), significantly inhibited visfatin-induced NAD synthesis and glucose uptake. Visfatin treatment increased glucose transporter-1 (GLUT-1) protein expression in isolated cellular membranes, and pretreatment with cytochalasin B completely inhibited visfatin-induced glucose uptake. Moreover, immunofluorescent microscopy showed the migration of cytosolic GLUT-1 into cellular membranes after visfatin treatment. In accordance with these results, the activation of protein kinase B was detected after visfatin treatment. Furthermore, visfatin treatment dramatically increased the synthesis of profibrotic molecules including transforming growth factor-beta1, plasminogen activator inhibitor-1, and type I collagen, and pretreatment with cytochalasin B completely inhibited visfatin-induced upregulation of profibrotic molecules. These results suggest that visfatin is produced in MCs, which are a novel target for visfatin, and play an important role in the pathogenesis of diabetic nephropathy.

FR167653 inhibits fibronectin expression and apoptosis in diabetic glomeruli and in high-glucose-stimulated mesangial cells

Previous in vitro studies suggest that the p38 MAPK pathway may be involved in the pathogenesis of diabetic nephropathy, but the consequences of the inhibition of the p38 MAPK pathway have not been well elucidated in diabetic (DM) glomeruli. This study was undertaken to investigate the effect of p38 MAPK inhibitor, FR167653, on fibronectin expression and apoptosis in DM glomeruli and in high-glucose-stimulated mesangial cells (MC). In vivo, 32 Sprague-Dawley rats were injected with diluent (control, N = 16) or streptozotocin intraperitoneally (DM, N = 16). Eight rats from each group were treated with FR167653 for 3 mo. In vitro, rat MC were exposed to medium containing 5.6 mM glucose or 30 mM glucose [high glucose (HG)] with or without 10−6 M FR167653 for 24 h. Fibronectin mRNA and protein expression were determined by real-time PCR and Western blot, respectively. Western blot for apoptosis-related molecules, terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling assay, and Hoechst 33342 staining were performed to determine apoptosis. FR167653 ameliorated the increases in fibronectin-to-GAPDH mRNA ratio and protein expression in DM glomeruli by 89 and 79% and in HG-stimulated MC by 70 and 91%, respectively ( P < 0.05). Under diabetic conditions, Bcl-2 protein expression was decreased, whereas cleaved caspase-3 protein expression was increased ( P < 0.05), and these changes were inhibited by FR167653 treatment. Apoptotic cells were also significantly increased in DM glomeruli and in HG-stimulated MC ( P < 0.05), and FR167653 ameliorated these increases in apoptotic cells, both in vivo and in vitro. In conclusion, these findings suggest that the inhibition of the p38 MAPK pathway has a beneficial effect on the development of diabetic nephropathy by inhibiting the increase in fibronectin expression and apoptosis.

Protein kinase C β inhibition: the promise for treatment of diabetic nephropathy

PURPOSE OF REVIEW

The prevalence of diabetes mellitus is increasing rapidly worldwide. The number of patients with diabetic nephropathy is also expected to increase considerably in the future despite currently available treatments that may prevent or slow kidney disease progression. Additional therapeutic agents are therefore urgently needed.

RECENT FINDINGS

Ruboxistaurin mesylate is a bisindolylmaleimide that specifically inhibits the beta-isoform of protein kinase C. In animal models of diabetic nephropathy, ruboxistaurin normalized glomerular hyperfiltration, decreased urinary albumin excretion, preserved renal function and reduced mesangial expansion, glomerulosclerosis, and tubulointerstitial fibrosis. In humans with type 2 diabetes and nephropathy already treated with an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker, treatment with ruboxistaurin for 1 year reduced albuminuria and urinary transforming growth factor-beta, and maintained estimated glomerular filtration rate. Ruboxistaurin has so far been shown to be well tolerated at the doses tested.

SUMMARY

Inhibition of protein kinase C beta may represent a novel strategy to improve kidney outcomes in patients with diabetes mellitus. Large-scale, prospective trials are needed to confirm the safety and potential benefits of ruboxistaurin in patients with diabetic nephropathy.

Role of protein kinase C inhibition in the development of diabetic microvascular complications

Diabetes mellitus affects millions of people in the USA and throughout the world. The global epidemic may be attributed to both the increasing age of the population and the increasing rates of obesity. Diabetes is associated with chronic microvascular (diabetic neuropathy, retinopathy and nephropathy) and macrovascular complications (heart disease, stroke and peripheral vascular disease). Patients with diabetes benefit from a comprehensive approach to prevent complications, including weight loss, smoking cessation, antiplatelet agents, and glycemic and blood pressure control. However, all of these are difficult for patients to achieve and maintain on a daily basis and there is still a risk of developing vascular complications. Specific therapies for diabetic complications targeting molecules that are activated by hyperglycemia are emerging. The aim of this review is to highlight the role of protein kinase Cβ in the development of diabetic microvascular complications while briefly describing clinical experience with the protein kinase Cβ inhibitor ruboxistaurin.

High glucose activates rat pancreatic stellate cells through protein kinase C and p38 mitogen-activated protein kinase pathway

OBJECTIVE

Hyperglycemia is implicated in fibrosis in many organs. Exocrine and endocrine pancreas are closely linked both anatomically and physiologically, and pathological conditions in the exocrine gland can cause impairment of endocrine function and vice versa. Chronic pancreatitis causes pancreatic fibrosis and sometimes results in diabetes mellitus. Pancreatic stellate cells (PSCs) play a pivotal role in pancreatic fibrogenesis. However, the effects of high glucose concentrations on PSC activation have not been fully elucidated.

METHODS

Cultured PSCs were incubated in the presence of various concentrations of glucose. Pancreatic stellate cell proliferation, alpha-smooth muscle actin (alpha-SMA) expression, and collagen production were determined by colorimetric conversion assay, Western blot analysis, and Sirius red dye binding assay, respectively.

RESULTS

High glucose concentrations significantly increased PSC proliferation, alpha-SMA expression, and collagen type I production in PSCs. High glucose concentrations activated protein kinase C (PKC) in PSCs, and PKC inhibitor GF109203X inhibited glucose-stimulated PSC proliferation, alpha-SMA expression, and collagen secretion. High glucose also activated p38 mitogen-activated protein kinase (MAPK) in PSCs, and p38 MAPK inhibitor SB203580 inhibited glucose-stimulated collagen secretion.

CONCLUSIONS

Our results indicate that high glucose concentrations stimulate PSC activation via PKC-p38 MAP kinase pathway and suggest that high glucose may aggravate pancreatic fibrosis.

Activation of the renin-angiotensin system within podocytes in diabetes

The autocrine and paracrine activation of the renin-angiotensin system (RAS) within cells of the kidney plays a role in the overall pathophysiology of the renal disease due to diabetes. In this study, we focus on components of the RAS in the podocyte as these cells are important in the pathogenesis of glomerulosclerosis and proteinuria. Immortalized mouse podocytes were exposed to media containing normal glucose (NG) or high glucose (HG) for in vitro studies. In vivo studies utilized kidney tissue obtained from rats treated for 3 months with streptozotocin to induce diabetes. Angiotensinogen (AGT) and the angiotensin II (AII) type 1 receptor mRNA and protein were significantly increased in the podocytes cultured under the high glucose conditions. Both angiotensins I and II levels were significantly higher in cell lysates and the conditioned media of cells grown in high glucose. There were no differences in renin activity, angiotensin-converting enzyme level, or AII type 2 receptor level. Glomerular AGT and AII type 1 receptor assessed by means of immunohistochemistry were increased in diabetic rats compared with the control rats. Other measured components of the RAS within the glomeruli were not different. We suggest that increased AGT, an attendant increase in AII and increased AII type 1 receptor in podocytes experiencing diabetic conditions play an important role in the pathogenesis of diabetic nephropathy.

Disposition of [14C]Ruboxistaurin in Humans

Ruboxistaurin is a potent and specific inhibitor of the beta isoforms of protein kinase C (PKC) that is being developed for the treatment of diabetic microvascular complications. The disposition of [(14)C]ruboxistaurin was determined in six healthy male subjects who received a single oral dose of 64 mg of [(14)C]ruboxistaurin in solution. There were no clinically significant adverse events during the study. Whole blood, urine, and feces were collected at frequent intervals after dosing. Metabolites were profiled by high performance liquid chromatography with radiometric detection. The total mean recovery of the radioactive dose was approximately 87%, with the majority of the radioactivity (82.6 +/- 1.1%) recovered in the feces. Urine was a minor pathway of elimination (4.1 +/- 0.3%). The major route of ruboxistaurin metabolism was to the N-desmethyl ruboxistaurin metabolite (LY338522), which has been shown to be active and equipotent to ruboxistaurin in the inhibition of PKC(beta). In addition, multiple hydroxylated metabolites were identified by liquid chromatography-mass spectrometry in all matrices. Pharmacokinetics were conducted for both ruboxistaurin and LY338522 (N-desmethyl ruboxistaurin, 1). These moieties together accounted for approximately 52% of the radiocarbon measured in the plasma. The excreted radioactivity was profiled using radiochromatography, and approximately 31% was structurally characterized as ruboxistaurin or N-desmethyl ruboxistaurin. These data demonstrate that ruboxistaurin is metabolized primarily to N-desmethyl ruboxistaurin (1) and multiple other oxidation products, and is excreted primarily in the feces.

Astragaloside IV improved barrier dysfunction induced by acute high glucose in human umbilical vein endothelial cells

The purpose of the present study was to examine the effects of astragaloside IV, a saponin isolated from Astragalus membranaceus (Fisch) Bge, on the impairment of barrier function induced by acute high glucose in cultured human vein endothelial cells. High glucose (27.8 mM) induced a decrease in transendothelial electrical impedance and an increase in cell monolayer permeability in human umbilical vein endothelial cells. Endothelial barrier dysfunction stimulated by high glucose was accompanied by translocation and activation of protein kinase C (PKC), the redistribution of F-actin and formation of intercellular gaps, suggesting that increases in PKC activity and rearrangement of F-actin could be associated with endothelial barrier dysfunction induced by acute high glucose. Application of astragaloside IV inhibited high glucose-induced endothelial barrier dysfunction in a dose-dependent manner, which is compatible with inhibition of PKC translocation and improvement of F-actin rearrangements. Western blot analysis revealed that high glucose-induced PKC alpha and beta2 overexpression in the membrane fraction were significantly reduced by astragaloside IV. These findings indicate that astragaloside IV protected endothelial cells from high glucose-induced barrier impairment by inhibiting PKC activation, as well as improving cytoskeleton remodeling.

Manifestations of cutaneous diabetic microangiopathy

The etiologies of a variety of skin conditions associated with diabetes have not been fully explained. One possible etiological factor is diabetic microangiopathy, which is known to affect the eyes and kidneys in patients with diabetes. There are many mechanisms by which diabetes may cause microangiopathy. These include excess sorbitol formation, increased glycation end products, oxidative damage, and protein kinase C overactivity. All of these processes occur in the skin, and the existence of a cutaneous diabetic microangiopathy has been well demonstrated. These microangiopathic changes are associated with abnormalities of skin perfusion. Because the skin plays a thermoregulatory role, there is significant capillary redundancy in normal skin. In diabetic patients, loss of capillaries is associated with a decrease in perfusion reserve. This lost reserve is demonstrable under stressed conditions, such as thermal stimulation. The associated failure of microvascular perfusion to meet the requirements of skin metabolism may result in diverse skin lesions in patients with diabetes. Many skin conditions peculiar to diabetes are fairly rare. Necrobiosis lipoidica diabeticorum (NLD) and diabetic bullae occur very infrequently as compared with diabetic retinopathy and nephropathy. Conversely, there is a correlation between diabetic microvascular disease and NLD. This correlation also exists with more common skin conditions, such as diabetic dermopathy. This relationship suggests that diabetic microangiopathy may contribute to these conditions even if it is not primarily causal. Clinically, the major significance of diabetic cutaneous microangiopathy is seen in skin ulceration which is very common and has a major impact on diabetic patients. Many factors contribute to the development of diabetic foot ulcers. Neuropathy, decreased large vessel perfusion, increased susceptibility to infection, and altered biomechanics all play a role, but there is no doubt that inadequate small blood vessel perfusion is a major cause of the inability to heal small wounds that eventually results in ulcer formation. The accessibility of skin capillaries makes cutaneous diabetic microangiopathy an attractive model for research on the evolution of microvascular disease in diabetic patients.

Effects of Blocking the Renin-Angiotensin System on Expression and Translocation of Protein Kinase C Isoforms in the Kidney of Diabetic Rats

BACKGROUND

High glucose and angiotensin II (Ang II) can activate protein kinase C (PKC) in diabetes mellitus. However, it is not clear which isoform of PKC is activated by glucose or Ang II. Our study focused on the effects of angiotensin blockade, using the angiotensin-converting enzyme inhibitor fosinopril, the Ang II receptor blocker irbesartan and their combination, on the expression and translocation of PKC isoforms alpha and betaII in the renal cortex and medulla in diabetes.

METHODS

Hyperglycemia was induced with streptozotocin and diabetic rats were randomized to 4 groups: diabetic control, irbesartan group (40 mg/kg daily), fosinopril group (40 mg/kg daily) and combination group (irbesartan plus fosinopril, 20 mg/kg daily, respectively); age-matched normal rats served as normal control. After 4 weeks, expression and translocation of PKC-alpha and -betaII in the renal cortex and medulla were assessed by immunohistochemistry and Western immunoblotting.

RESULTS

The expression of PKC-alpha in the membrane and cytosol fractions from the renal cortex was significantly higher in diabetic rats (276.83 +/- 32.44% in membrane, 149.04 +/- 23.42% in cytosol) than that in normal ones. The expression of PKC-betaII in the renal cortex of diabetic rats decreased significantly in the membrane (50.00 +/- 11.68%, p < 0.05) and remained unchanged in the cytosol (94.51 +/- 11.69%, p > 0.05) compared with normal controls. Treatment with irbesartan, fosinopril and their combination partially corrected the abnormalities mentioned above. For the expression of PKC-alpha and -betaII in the medulla, no difference was detected among the 5 groups.

CONCLUSION

The renin-angiotensin system was implicated in the pathogenesis of diabetic nephropathy by regulating the activation of PKC isoforms.

Protein Kinase C β Inhibitor LY333531 Attenuates Intercellular Adhesion Molecule-1 and Monocyte Chemotactic Protein-1 Expression in the Kidney in Diabetic Rats

In vitro studies have shown that activation of protein kinase C (PKC) is a key mediator of intercellular adhesion molecule-1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1) in a range of cell types and in response to high glucose, however, its role in the in vivo setting has not been clearly delineated. Streptozotocin-induced diabetic rats were treated with the PKC-beta isoform inhibitor LY333531 for 8 weeks. LY333531 treatment significantly attenuated increased urinary albumin excretion rate and glomerular volume and tubulointerstitial injury index as well as elevated PKC activity and PKC-beta protein expression in the kidney. Level of malondialdehyde was markedly higher and antioxidant enzyme activity such as superoxide diamutase and catalase as well as glutathione peroxidase were significantly lower in the kidney from diabetic rats than that of the control group. LY333531 administration could remit these changes. Increased macrophages recruitment as well as ICAM-1 and MCP-1 protein expression in the kidney were significantly inhibited by LY333531 in diabetic rats. It is concluded that mechanism of renoprotection of LY333531 may be correlated, at least partly, with suppression of increased macrophages recruitment and overexpression of ICAM-1 and MCP-1 in diabetic rats.

Fatty Acids Cause Alterations of Human Arterial Smooth Muscle Cell Proteoglycans That Increase the Affinity for Low-Density Lipoprotein

Objective— The dyslipidemia of insulin resistance, with high levels of albumin-bound fatty acids, is a strong cardiovascular disease risk. Human arterial smooth muscle cell (hASMC) matrix proteoglycans (PGs) contribute to the retention of apoB lipoproteins in the intima, a possible key step in atherogenesis. We investigated the effects of high NEFA levels on the PGs secreted by hASMCs and whether these effects might alter the PG affinity for low-density lipoprotein.

Methods and Results— hASMC exposed for 72 hours to high concentrations (800 μmol/L) of linoleate (LO) or palmitate upregulated the core protein mRNAs of the major PGs, as measured by quantitative PCR. Insulin (1 nmol/L) and the PPARγ agonist rosiglitazone (10 μmol/L) blocked these effects. In addition, high LO increased the mRNA levels of enzymes required for glycosaminoglycan (GAG) synthesis. Exposure to NEFA increased the chondroitin sulfate:heparan sulfate ratio and the negative charge of the PGs. Because of these changes, the GAGs secreted by LO-treated cells had a higher affinity for human low-density lipoprotein than GAGs from control cells. Insulin and rosiglitazone inhibited this increase in affinity.

Conclusions— The response of hASMC to NEFA could induce extracellular matrix alterations favoring apoB lipoprotein deposition and atherogenesis.

New Potential Agents in Treating Diabetic Kidney Disease

Despite the worldwide epidemic of chronic kidney disease complicating diabetes mellitus, current therapies directed against nephroprogression are limited to angiotensin conversion or receptor blockade. Nonetheless, additional therapeutic possibilities are slowly emerging. The diversity of therapies currently in development reflects the pathogenic complexity of diabetic nephropathy. The three most important candidate drugs currently in development include a glycosaminoglycan, a protein kinase C (PKC) inhibitor and an inhibitor of advanced glycation. In targeting primary mechanisms by which hyperglycaemia contributes to diabetic complications, these drugs could provide risk reduction complementary to the partial reduction proven for ACE inhibitors and angiotensin II receptor antagonists (angiotensin receptor blockers). Glycosaminoglycans act to restore glycoproteins present in reduced amounts in the glomerular basement membrane and mesangium of diabetic animal models. Components of the drug sulodexide prevent pathological changes and proteinuria in diabetic rats. Reductions in albuminuria, a hallmark of early diabetic kidney disease, have been reported in initial human trials. In the US, a multicentre phase II study has been completed, with an interim analysis indicating reduction in urinary albumin losses. Pivotal phase II trials have begun in patients with type 2 diabetes. A second metabolic pathway of diabetic complications is overexpression of PKC. Several activators of this family of intracellular kinases have been identified and PKC activation may result in tissue damage through a variety of mechanisms. In animal models, the inhibitor ruboxistaurin reduces albuminuria, diabetic histological changes and kidney injury. Like sulodexide, drug development of ruboxistaurin has reached completion of a phase II evaluation with mixed results. The third metabolic target is the nonenzymatic formulation of advanced glycation end-products (AGEs) through well described biochemical pathways. Multiple pathways lead to AGE accumulation in tissues in diabetes and diverse AGE products are formed. AGE deposition has been implicated in animal models of diabetic nephropathy. The leading AGE inhibitor currently in development is pyridoxamine, which has multiple actions that inhibit glycation. Pyridoxamine is an efficient AGE inhibitor in experimental diabetes. A phase II study in diabetic patients with nephropathy reported mixed efficacy results and a favourable safety profile. Phase III evaluation of pyridoxamine has not begun. These three classes of potential therapies, if successfully developed, will confirm that diabetic kidney disease has entered the era of biochemical treatments.