The role of inflammatory cytokines in diabetic nephropathy

The Role of Transforming Growth Factor-Beta in Diabetic Nephropathy

Several studies have demonstrated that chronic and low-grade inflammation is closely linked to type 2 diabetes mellitus. The associated mechanisms are related to synthesis and release of proinflammatory and anti-inflammatory cytokines, mainly by the adipose tissue. Moreover, there are evidences that cytokines and adhesion molecules are important for development of diabetic nephropathy. Among the cytokines associated with inflammatory responses in type 2 diabetes mellitus, the transforming growth factor-β (TGF-β) has been recognized as a central player in the diabetic nephropathy being involved in the development of glomerulosclerosis and interstitial fibrosis, as observed in the course of end-stage renal disease. Although TGF-β1 is classically an anti-inflammatory immune mediator it has been shown that in the presence of IL-6, which increases before the onset of T2D, TGF-β1 favors the differentiation of T helper 17 (Th17) cells that are activated in many pro-inflammatory conditions. Since TGF-β1 mRNA and consequently serum TGF-β1 levels are under genetic control, this review aims to discuss the relationship of TGF-β1 levels and polymorphisms in the development of nephropathy in type 2 diabetes mellitus.

IVS1 -397T>C estrogen receptor α polymorphism is associated with low-grade systemic inflammatory response in type 1 diabetic girls

PURPOSE

The study aimed to investigate the influence of estrogen receptor α (ER-α) genotypes on inflammatory response and development of microvascular complications in girls with type 1 diabetes.

METHODS

152 young regularly menstruating girls with diagnosed type 1 diabetes and 84 young, healthy menstruating girls were recruited. ER-α genotyping was carried out by PCR. Serum concentrations of 17β-estradiol, as well as IL-6, TNF-α, VEGF, and IL-10, were measured. CD4(+)Foxp3(+) TH17 cells were isolated and analyzed by flow cytometry.

RESULTS

Type 1 diabetic girls carrying TT genotype were characterized by the lowest serum estradiol level and IL-10 and highest IL-6, TNF-α, and VEGF. The association between the level of certain cytokine and the genetic variant of estrogen receptor α polymorphism was analyzed. Frequencies of CD4(+)Foxp3(+) TH17 cells were also enhanced in TT bearing girls with type 1 diabetes and correlated with the level of analyzed cytokines. In addition, the correlation between serum estradiol level and cytokine concentrations was observed.

CONCLUSIONS

We propose that TT variant of estrogen receptor α polymorphism may be associated with enhanced inflammatory response, which in turn may lead to acceleration of diabetic retino- and nephropathy in girls with type 1 diabetes. This finding may help the physicians to predict the onset and progression of diabetic microvascular complications.

TNF-α and microalbuminuria in patients with type 2 diabetes mellitus

AIM

Recent evidence suggests that chronic subclinical inflammation plays a key role in the pathogenesis and progression of diabetic nephropathy. Aim of the present study was to investigate possible correlation between the presence and degree of microalbuminuria and markers of inflammation in patients with type 2 diabetes mellitus (DM).

PATIENTS-METHODS

Eighty patients were enrolled and clinical and laboratory data were recorded. Albumin-creatinine ratio (ACR) was calculated in first-morning urine samples. Serum and urinary tumor necrosis factor-α (TNF-α) levels were determined by ELISA.

RESULTS

Forty-five patients had normoalbuminuria, 33 microalbuminuria, and 2 macroalbuminuria. Patients with microalbuminuria were older, with higher glycosylated hemoglobin levels (HbA1c) and they more frequently had diabetic retinopathy, neuropathy, and cardiovascular disease and were on treatment with angiotensin converting enzyme inhibitors (ACEi) and/or angiotensin receptor blockers (ARBs). ACR was significantly correlated with the presence of cardiovascular disease, hypertension, and HbA1c levels and the administration of clopidogrel and ACEi or ARBs. ACR was not correlated with C-reactive protein, fibrinogen, or serum TNF-α levels but had a strong correlation with urinary TNF-α levels.

CONCLUSIONS

In patients with type 2 DM, urinary, but not serum, TNF-α levels are associated with the presence and severity of microalbuminuria.

Autonomic neuropathy in diabetes mellitus

Diabetic autonomic neuropathy (DAN) is a serious and common complication of diabetes, often overlooked and misdiagnosed. It is a systemic-wide disorder that may be asymptomatic in the early stages. The most studied and clinically important form of DAN is cardiovascular autonomic neuropathy defined as the impairment of autonomic control of the cardiovascular system in patients with diabetes after exclusion of other causes. The reported prevalence of DAN varies widely depending on inconsistent definition, different diagnostic method, different patient cohorts studied. The pathogenesis is still unclear and probably multifactorial. Once DAN becomes clinically evident, no form of therapy has been identified, which can effectively stop or reverse it. Prevention strategies are based on strict glycemic control with intensive insulin treatment, multifactorial intervention, and lifestyle modification including control of hypertension, dyslipidemia, stop smoking, weight loss, and adequate physical exercise. The present review summarizes the latest knowledge regarding clinical presentation, epidemiology, pathogenesis, and management of DAN, with some mention to childhood and adolescent population.

Kolaviron, a Garcinia biflavonoid complex ameliorates hyperglycemia-mediated hepatic injury in rats via suppression of inflammatory responses

BACKGROUND

Chronic inflammation plays a crucial role in hyperglycemia-induced liver injury. Kolaviron (KV), a natural biflavonoid from Garcinia kola seeds have been shown to possess anti- inflammatory properties which has not been explored in diabetes. To our knowledge, this is the first study to investigate the effect of KV on pro-inflammatory proteins in the liver of diabetic rats.

METHODS

Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg) in male Wistar rats. Kolaviron (100 mg/kg) was administered orally five times a week for six weeks. The concentrations of cytokines and chemokine were measured using Bio-plex Pro™ magnetic bead-based assays (Bio-Rad Laboratories, Hercules, USA). Plasma glucose and serum biomarkers of liver dysfunction were analyzed with diagnostic kits in an automated clinical chemistry analyzer. Insulin concentration was estimated by radioimmunoassay (RIA).

RESULT

Kolaviron (100mg/kg) treatment significantly ameliorated hyperglycemia and liver dysfunction. Serum levels of hepatic marker enzymes were significantly reduced in kolaviron treated diabetic rats. Kolaviron prevented diabetes induced increase in the hepatic levels of proinflammatory cytokines; interleukin (IL)-1beta, IL-6, tumour necrosis factor (TNF-α) and monocyte chemotactic protein (MCP-1).

CONCLUSION

The results of this study demonstrate that the hepatoprotective effects of kolaviron in diabetic rats may be partly associated with its modulating effect on inflammatory responses.

Attenuation of hyperlipidemia- and diabetes-induced early-stage apoptosis and late-stage renal dysfunction via administration of fibroblast growth factor-21 is associated with suppression of renal inflammation

Background

Lipotoxicity is a key feature of the pathogenesis of diabetic kidney disease, and is attributed to excessive lipid accumulation (hyperlipidemia). Increasing evidence suggests that fibroblast growth factor (FGF)21 has a crucial role in lipid metabolism under diabetic conditions.

Objective

The present study investigated whether FGF21 can prevent hyperlipidemia- or diabetes-induced renal damage, and if so, the possible mechanism.

Methods

Mice were injected with free fatty acids (FFAs, 10 mg/10 g body weight) or streptozotocin (150 mg/kg) to establish a lipotoxic model or type 1 diabetic model, respectively. Simultaneously the mice were treated with FGF21 (100 µg/kg) for 10 or 80 days. The kidney weight-to-tibia length ratio and renal function were assessed. Systematic and renal lipid levels were detected by ELISA and Oil Red O staining. Renal apoptosis was examined by TUNEL assay. Inflammation, oxidative stress, and fibrosis were assessed by Western blot.

Results

Acute FFA administration and chronic diabetes were associated with lower kidney-to-tibia length ratio, higher lipid levels, severe renal apoptosis and renal dysfunction. Obvious inflammation, oxidative stress and fibrosis also observed in the kidney of both mice models. Deletion of the fgf21 gene further enhanced the above pathological changes, which were significantly prevented by administration of exogenous FGF21.

Conclusion

These results suggest that FFA administration and diabetes induced renal damage, which was further enhanced in FGF21 knock-out mice. Administration of FGF21 significantly prevented both FFA- and diabetes-induced renal damage partially by decreasing renal lipid accumulation and suppressing inflammation, oxidative stress, and fibrosis.

Recent advances in our understanding of insulin signalling to the podocyte

It is becoming increasingly clear that the insulin responses of a number of different cell types within the kidney are important in the maintenance of normal renal function. This review summarizes our current understanding of renal insulin signalling, with specific focus on the podocyte, presenting recent evidence that suggests these responses are altered in systemic insulin-resistant states and chronic kidney disease via a number of different mechanisms.

Apelin inhibits the development of diabetic nephropathy by regulating histone acetylation in Akita mouse

Diabetic nephropathy is the primary cause of end-stage renal disease. Increasing numbers of patients are suffering from this disease and therefore novel medications and therapeutic approaches are urgently needed. Here, we investigated whether apelin-13, the most active member of the adipokine apelin group, could effectively suppress the development of nephropathy in Akita mouse, a spontaneous type 1 diabetic model. Apelin-13 treatment decreased diabetes-induced glomerular filtration rate, proteinuria, glomerular hypertrophy, mesangial expansion and renal inflammation. The inflammatory factors, activation of NF-κB, histone acetylation and the enzymes involved in histone acetylation were further examined in diabetic kidneys and high glucose- or sodium butyrate-treated mesangial cells in the presence or absence of apelin-13. Apelin-13 treatment inhibited diabetes-, high glucose- and NaB-induced elevation of inflammatory factors, and histone hyperacetylation by upregulation of histone deacetylase 1. Furthermore, overexpression of apelin in mesangial cells induced histone deacetylation under high glucose condition. Thus, apelin-13 may be a novel therapeutic candidate for treatment of diabetic nephropathy via regulation of histone acetylation.

Toll-like receptors: sensing and reacting to diabetic injury in the kidney

Accumulating evidence indicates that immunologic and inflammatory elements play an important role in initiating and orchestrating the development of diabetic nephropathy (DN), but until recently, the identity of specific innate immune pattern recognition receptors or sensors that recognize diverse diabetic 'danger signals' to trigger the proinflammatory cascade during DN remains unknown. Toll-like receptors (TLRs) are an emerging family of receptors that recognize pathogen-associated molecular patterns as well as damage-associated molecular patterns to promote the activation of leukocytes and intrinsic renal cells in non-immune kidney disease. Recent data from in vitro and in vivo studies have highlighted the critical role of TLRs, mainly TLR2 and TLR4, in the pathogenesis of DN. This review focuses on emerging findings elucidating how TLR signaling could sense and react to the metabolic stress and endogenous ligands activated by the diabetic state, thereby initiating and perpetuating renal inflammation and fibrogenesis in diabetic kidney disease. Novel strategies potentially targeting TLR signaling that could have therapeutic implications in DN are also discussed.

LC-MS/MS analysis of plasma polyunsaturated fatty acids in type 2 diabetic patients after insulin analog initiation therapy

Background

Eicosanoids derived from omega-6 (n6) polyunsaturated fatty acids (PUFAs) have proinflammatory functions whereas eicosanoids derived from omega-3 (n3) PUFAs have anti-inflammatory properties. This study was designed to evaluate the effect of insulin analog initiation therapy on n6 and n3 PUFAs in type 2 diabetic patients during early phase.

Methods

Sixteen type 2 diabetic patients with glycosylated hemoglobin (HbA1c) levels above 10% despite ongoing combination therapy with sulphonylurea and metformin were selected. Former treatment regimen was continued for the first day followed by substitution of sulphonylurea therapy with different insulin analogs (0.4 U/kg/day) plus metformin. Blood samples were obtained from all patients at 24 and 72 hours. Plasma levels of arachidonic acid (AA, C20:4n6), dihomo-gamma-linolenic acid (DGLA, C20:3n6), eicosapentaenoic acid (EPA, C20:5n3) and docosahexaenoic acid (DHA, C22:6n3) were determined by an optimized multiple reaction monitoring (MRM) method using ultra fast-liquid chromatography (UFLC) coupled with tandem mass spectrometry (MS/MS). Prostaglandin E₂ (PGE2) was measured in serum samples by enzyme immunoassay.

Results

All measured PUFAs were significantly increased after treatment with insulin analogs plus metformin compared to before treatment levels. The mean AA/EPA ratio was significantly lower after treatment with insulin analogs plus metformin. A 22% decrease was observed in PGE2 levels after treatment with insulin analogs plus metformin compared to pretreatment levels (p > 0.05).

Conclusion

The significant decrease in AA/EPA ratio indicates that insulin analog initiation therapy has anti-inflammatory properties by favoring the increase of n3 fatty acid EPA.

Association of biomarkers of inflammation and oxidative stress with the risk of chronic kidney disease in Type 2 diabetes mellitus in North Indian population

Chronic kidney disease (CKD) is a major cause of morbidity and mortality worldwide. It results from diverse etiologies, diabetes being a frontrunner amongst them. Type 2 diabetes mellitus (DM) is being increasingly recognized as a proinflammatory state with increased oxidative stress which enormously increases the risk of micro and macro vascular diseases. This study was planned to explore the possible association between tumor necrosis factor-alpha (TNF-α), urinary monocyte chemoattractant protein-1 (uMCP-1), high-sensitivity C-reactive protein (hsCRP) and parameters of oxidative stress in patients with Type 2 diabetes mellitus (DM) and diabetic chronic kidney disease (DM-CKD). Fifty patients each were recruited in DM, DM-CKD and healthy control groups. Plasma TNF-α, hsCRP and uMCP-1 levels as inflammatory mediators were measured by ELISA, reduced glutathione (GSH), ferric reducing ability of plasma (FRAP) as parameters of antioxidant activity and malondialdehyde (MDA) as marker of oxidative stress, were measured spectrophotometrically. Plasma TNF-α, hsCRP and uMCP-1 were significantly higher in DM-CKD compared to DM and healthy controls. Lipid peroxidation, measured as MDA was significantly higher in patients with DM-CKD as compared to patients with DM and healthy controls. Further, antioxidant capacity of blood measured as FRAP and GSH was found to be significantly lower in patients with DM and DM-CKD as compared to healthy controls (p<0.001). Plasma TNF-α and uMCP-1 showed a significant positive correlation with HbA1c (r=0.441, 0.643), hsCRP (r=0.400, 0.584) and MDA (r=0.423, 0.759) and significant negative correlation with GSH (R=-0.370, -0.800) and FRAP (r=-0.344, -0.684) Increased inflammatory markers viz. TNF-α, hsCRP and uMCP-1 and markers of oxidative stress i.e. increased MDA and decreased GSH and FRAP in DM-CKD suggest an important role of inflammation and oxidative stress in the pathogenesis of renal damage in diabetic patients.

Toxicological impact of inhaled electric mosquito-repellent liquid on the rat: a hematological, cytokine indications, oxidative stress and tumor markers

CONTEXT

High malaria burden has led to the increased use of insecticides in the tropics and subtropics. This study thus aimed at assessing the hematological effects alteration of pyrethroid insecticide exposure using the experimental animal model.

OBJECTIVE

A commonly available Electric Mosquito-Repellent Liquid pyrethroid insecticide containing prallethrin 1.6% w/w is widely used for mosquito control in Saudi Arabia. The immunotoxic effects after inhalation exposures to the preparation for a continuous period of 24, 48, and 72 h were investigated in rats.

METHODS AND MATERIALS

Rats were exposed to prallethrin 1.6% w/w by inhalation for 72 consecutive hours. Total blood count, blood indices of creatine kinase (CK), gamma-glutamyltranspeptidase (γ-GT), superoxide dismutase (SOD), nitric oxide (NO), malondialdehyde (MDA), interleukin (IL)-2, tumor necrosis factors (TNF)α, alpha-fetoprotein (AFP), carbohydrate antigen (CA) 19.9 and carcinoembrionic antigen (CEA) were assayed.

RESULTS

The administration of prallethrin 1.6% w/w created significant increased changes in the levels of total WBC, lymphocytes, RBC, hemoglobin, packed cell volume, platelets, mean corpuscular volume, and mean corpuscular hemoglobin in rats after 24, 48, and 72 h of continuous inhalation; however, there was a significant reduction in neutrophils at transient reduction in the monocytes after 24 and 48 h to return to normal after 72 h. Significant increases in the levels of CK, γ-GT, SOD, NO, MDA, AFP, IL-2, and TNFα were recorded. CA and CEA did not exhibit any change.

CONCLUSIONS

Continuous inhalation to prallethrin 1.6% insecticides poses toxicity on hematological variables. It is also concluded that pyrethroid group of insecticide may cause hematological, biochemical, cytokine disturbances and possible mutagenic damage to the tissues.

Functions of the podocyte proteins nephrin and Neph3 and the transcriptional regulation of their genes

Nephrin and Neph-family proteins [Neph1–3 (nephrin-like 1–3)] belong to the immunoglobulin superfamily of cell-adhesion receptors and are expressed in the glomerular podocytes. Both nephrin and Neph-family members function in cell adhesion and signalling, and thus regulate the structure and function of podocytes and maintain normal glomerular ultrafiltration. The expression of nephrin and Neph3 is altered in human proteinuric diseases emphasizing the importance of studying the transcriptional regulation of the nephrin and Neph3 genes NPHS1 (nephrosis 1, congenital, Finnish type) and KIRREL2 (kin of IRRE-like 2) respectively. The nephrin and Neph3 genes form a bidirectional gene pair, and they share transcriptional regulatory mechanisms. In the present review, we summarize the current knowledge of the functions of nephrin and Neph-family proteins and transcription factors and agents that control nephrin and Neph3 gene expression.

G-CSF prevents progression of diabetic nephropathy in rat

Background

The protective effects of granulocyte colony-stimulating factor (G-CSF) have been demonstrated in a variety of renal disease models. However, the influence of G-CSF on diabetic nephropathy (DN) remains to be examined. In this study, we investigated the effect of G-CSF on DN and its possible mechanisms in a rat model.

Methods

Otsuka Long-Evans Tokushima Fatty (OLETF) rats with early DN were administered G-CSF or saline intraperitoneally. Urine albumin creatinine ratio (UACR), creatinine clearance, mesangial matrix expansion, glomerular basement membrane (GBM) thickness, and podocyte foot process width (FPW) were measured. The levels of interleukin (IL)-1β, transforming growth factor (TGF)-β1, and type IV collagen genes expression in kidney tissue were also evaluated. To elucidate the mechanisms underlying G-CSF effects, we also assessed the expression of G-CSF receptor (G-CSFR) in glomeruli as well as mobilization of bone marrow (BM) cells to glomeruli using sex-mismatched BM transplantation.

Results

After four weeks of treatment, UACR was lower in the G-CSF treatment group than in the saline group (p<0.05), as were mesangial matrix expansion, GBM thickness, and FPW (p<0.05). In addition, the expression of TGF-β1 and type IV collagen and IL-1β levels was lower in the G-CSF treatment group (p<0.05). G-CSFR was not present in glomerular cells, and G-CSF treatment increased the number of BM-derived cells in glomeruli (p<0.05).

Conclusions

G-CSF can prevent the progression of DN in OLETF rats and its effects may be due to mobilization of BM cells rather than being a direct effect.

Zerumbone, a tropical ginger sesquiterpene, ameliorates streptozotocin-induced diabetic nephropathy in rats by reducing the hyperglycemia-induced inflammatory response

Background

Zerumbone is one of the pungent constituents of Zingiber zerumbet (L) Smith (Zingiberaceae family). The aim of the present study was to examine the effects of zerumbone in rats with streptozotocin-induced diabetic nephropathy (DN).

Methods

Diabetic rats were treated orally with zerumbone (20 or 40 mg/kg/day) for 8 weeks. Changes in renal function-related parameters in plasma and urine were analyzed at the end of the study. Kidneys were isolated for pathology histology, immunohistochemistry, and Western blot analyses.

Results

Diabetic rats exhibited renal dysfunction, as evidenced by reduced creatinine clearance, increased blood glucose, blood urea nitrogen and proteinuria, along with marked elevation in the ratio of kidney weight to body weight, that were reversed by zerumbone. Zerumbone treatment was found to markedly improve histological architecture in the diabetic kidney. Hyperglycemia induced p38 mitogen-activated protein kinase activation, leading to increased infiltration of macrophages and increased levels of interleukin (IL)-1, IL-6 and tumor necrosis factor-α. All of the above abnormalities were reversed by zerumbone treatment, which also decreased the expression of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, transforming growth factor-β1 and fibronectin in the diabetic kidneys.

Conclusions

The beneficial effect of zerumbone in rats with DN is at least in part through antihyperglycemia which was accompanied by inhibition of macrophage infiltration via reducing p38 mediated inflammatory response.

Identification of compounds from the water soluble extract of Cinnamomum cassia barks and their inhibitory effects against high-glucose-induced mesangial cells

The difficulty of diabetic nephropathy (DN) treatment makes prevention the best choice. Cinnamomum cassia barks, known as Chinese cinnamon or Chinese cassia, is one of the most popular natural spices and flavoring agents in many parts of the World. Since previous reports indicated that Chinese cinnamon extract could be used for the treatment of diabetes, we proposed that this spice may be beneficial for the prevention of DN. However, the responsible compounds need to be further identified. In this study, we isolated three new phenolic glycosides, cinnacassosides A–C (1-3), together with fifteen known compounds from the water soluble extract of Chinese cinnamon. The structures of the new compounds were identified by comprehensive spectroscopic evidence. Eleven compounds (6-9, 11, 13-18) were isolated from this spice for the first time, despite extensive research on this species in the past, which added new facets for the chemical profiling of this spice. These isolates were purposely evaluated for their inhibitory effects on IL-6 and extracellular matrix production in mesangial cells which are definitely implicated in DN. The results showed that compounds 4-8 could inhibit over secretion of IL-6, collagen IV and fibronectin against high-glucose-induced mesangial cells at 10 µM, suggesting that Chinese cinnamon could be used as a functional food against DN.

Clinical value of inflammatory urinary biomarkers in overt diabetic nephropathy: a prospective study

AIMS

The evolution of diabetic nephropathy is incompletely accounted by current clinical tools. New biomarkers may refine patient assessment and help monitor therapy. We compared the added predictive value of 7 candidate inflammatory urinary biomarkers to known risk factors of progression.

METHODS

We prospectively followed 83 patients with overt diabetic nephropathy for a median 2.1 years and obtained repeated measurements of proteinuria, IL-1β, IL-6, IL-8, MCP-1, TNF-α, TGF-β1, and PAI-1.

RESULTS

Patients had an initial estimated glomerular filtration rate of 25 ± 9 mL/min/1.73 m(2), blood pressure of 142/69 mmHg and used a median of 4 anti-hypertensive medications over the course of the study. The observed rate of renal function decline was 2.9 ± 3.0 mL/min/1.73 m(2)/year. All urinary biomarkers levels were collinear and for each one except IL-1β, elevated levels predicted a more rapid progression. MCP-1 was the only biomarker increasing during follow-up, which also correlated with a worst outcome. Using multivariate linear regression adjusting for clinical risk factors of progression, urinary MCP-1 and TGF-β1 predicted progression independently and additively to the degree of proteinuria. We dichotomized these 3 biomarkers and observed a renal function decline with 0, 1, 2 or 3 elevated biomarkers of -0.8 ± 1.4, -2.1 ± 2.1, -4.2 ± 2.8 and -6.0 ± 2.8 mL/min/1.73 m(2)/year, respectively (p<0.001).

CONCLUSIONS

Multiple urinary biomarkers predict outcome in overt diabetic nephropathy. However, urinary MCP-1 and TGF-β1 are also independent and additive to proteinuria in predicting the rate of renal function decline and could serve as useful clinical tools in patient risk stratification.

Targeting inflammation in the treatment of type 2 diabetes

Islets of patients with type 2 diabetes display the typical features of an inflammatory process characterized by the presence of cytokines, chemokines, immune cell infiltration, impaired function and tissue destruction with fibrotic areas. Functional studies have shown that targeting inflammation may improve insulin secretion and sensitivity. In particular clinical proof of concept studies using modulators of the interleukin-1β (IL-1β)-nuclear factor--κB (NF-κB) pathway demonstrated the role of the innate immune system in type 2 diabetes. This programme has now entered the phase 3 of clinical development. Other targets such as tumour necrosis factor α (TNFα) may be equally important but have been neglected based on poorly designed studies. In this article we discuss the mechanisms of islet inflammation in type 2 diabetes and review the opportunity of clinical translation.

An Aqueous-Ethanol Extract of Liriope spicata var. prolifera Ameliorates Diabetic Nephropathy through Suppression of Renal Inflammation

The tuberous root of Liriope spicata var. prolifera (TRLS; Liliaceae family) is valued for the ability to promote glucose homeostasis, and it may therefore be utilized as an adjuvant therapy in the control of diabetic complications. The aim of the present study was to examine the effects of an aqueous ethanol extract from TRLS (TRLS-ext) (100 or 200 mg kg⁻¹ per day for eight weeks) on rats with streptozotocin-induced diabetic nephropathy (DN). Renal dysfunction in diabetic rats was ameliorated by TRLS-ext as evidenced by reduced creatinine clearance, as well as increased blood urea nitrogen and proteinuria. Treatment with TRLS-ext was found to markedly improve histological architecture in the diabetic kidney. Hyperglycemia induced degradation of inhibitory kappa B and reduced nuclear factor kappa B activation, leading to increased infiltration of macrophages and increased levels of proinflammatory cytokines, including interleukin-1 and tumor necrosis factor-α. All of the above abnormalities were reversed by TRLS-ext treatment, which also decreased the expression of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, and fibronectin in the diabetic kidneys. These findings provide a perspective on the renoprotective effects of TRLS-ext in DN.

An unbalanced monocyte polarisation in peripheral blood and bone marrow of patients with type 2 diabetes has an impact on microangiopathy

AIM/HYPOTHESIS

Monocytes/macrophages play important roles in adipose and vascular tissues and can be polarised as inflammatory M1 or anti-inflammatory M2. We sought to analyse monocyte polarisation status in type 2 diabetes, which is characterised by chronic inflammation.

METHODS

We enrolled 60 individuals without diabetes and 53 patients with type 2 diabetes. We quantified standard monocyte subsets defined by cluster of differentiation (CD)14 and CD16. In addition, based on the phenotype of polarised macrophages in vitro, we characterised and quantified more definite M1 (CD68(+)CCR2(+)) and M2 (CX3CR1(+)CD206(+)/CD163(+)) monocytes. We also analysed bone marrow (BM) samples and the effects of granulocyte-colony stimulating factor (G-CSF) stimulation in diabetic and control individuals.

RESULTS

We found no alterations in standard monocyte subsets (classical, intermediate and non-classical) when comparing groups. For validation of M1 and M2 phenotypes, we observed that M2 were enriched in non-classical monocytes and had lower TNF-α content, higher LDL scavenging and lower transendothelial migratory capacity than M1. Diabetic patients displayed an imbalanced M1/M2 ratio compared with the control group, attributable to a reduction in M2. The M1/M2 ratio was directly correlated with waist circumference and HbA1c and, among diabetic patients, M2 reduction and M1/M2 increase were associated with microangiopathy. A decrease in M2 was also found in the BM from diabetic patients, with a relative M2 excess compared with the bloodstream. BM stimulation with G-CSF mobilised M2 macrophages in diabetic but not in healthy individuals.

CONCLUSIONS/INTERPRETATION

We show that type 2 diabetes markedly reduces anti-inflammatory M2 monocytes through a dysregulation in bone-marrow function. This defect may have a negative impact on microangiopathy.

Chronic administration of EP4-selective agonist exacerbates albuminuria and fibrosis of the kidney in streptozotocin-induced diabetic mice through IL-6

Diabetic nephropathy is currently the most common cause of end-stage renal disease in the western world. Exacerbated inflammation of the kidney is known to contribute acceleration of nephropathy. Despite increased COX-2-mediated production of prostanoid metabolite PGE2, knowledge on its involvement in the progression of diabetic kidney disease is not complete. Here, we show the cross talk of the PGE2-EP4 pathways and IL-6 in inducing albuminuria and fibrosis in an animal model of type 1 diabetes. Hyperglycemia causes enhanced COX-2 expression and PGE2 production. Administration of PGE2 receptor EP4-selective agonist ONO-AE1-329 for 12 weeks exacerbated fibrosis and albuminuria. Diabetes-induced expression of inflammatory cytokines TNFα and TGFβ1 was enhanced in EP4 agonist-treated mice kidney. In addition, urinary excretion of cytokines (TNFα and IL-6) and chemokines (MCP-1 and IP-10) were significantly more in EP4-treated mice than vehicle-treated diabetes. Diabetes-induced collagen I and CTGF expression were also significantly higher in EP4-treated mice. However, EP4 agonist did not alter macrophage infiltration but increased cytokine and chemokine production in RAW264.7 cells. Interestingly, EP4-induced IL-6 expression in the kidney was localized in proximal and distal tubular epithelial cells. To confirm further whether EP4 agonist increases fibrosis and albuminuria through an increase in IL-6 expression, IL-6-knockout mice were administered with EP4 agonist. IL-6-knockout mice were resistant to EP4-induced exacerbation of albuminuria and diabetes and EP4-induced fibrosis. Our data suggest that EP4 agonist through IL-6 induces glomerulosclerosis and interstitial fibrosis, and IL-6 represents a new factor in the EP4 pathway.

Urine miRNAs: potential biomarkers for monitoring progression of early stages of diabetic nephropathy

With a steep increase in the incidence of type 1 and 2 diabetes globally, diabetic nephropathy (DN) has now become the leading cause of renal failure in the world. There are no suitable biomarkers for the diagnosis of early stages of DN. In recent years, tremendous efforts are being made worldwide to delineate the role of micro RNAs in the pathogenesis of DN. Circulating miRNAs in serum, plasma, urine and other body fluids, which reflect a response to various pathophysiological stresses, are being investigated in the context of diabetic nephropathy. Delineation of the changes in miRNA levels in patients with DN may lead to a better understanding of the progression of the disease. We present here an exhaustive survey of the miRNA literature, highlighting various studies performed over the last decade. The aim is to assess if changes in various miRNAs could correlate with the progression of diabetic nephropathy. Based on the survey, we found that miRNA-377, miRNA-192, miRNA-216/217 and miRNA-144 are increased in body fluids of patients with DN, while miRNA-21 and miRNA-375 are decreased. Overall, there are a very few miRNAs that are kidney specific, and although significant differences were observed in the urinary excretion of certain miRNAs, they were not correlative to their levels in the blood or plasma. Thus, it is completely plausible that urine-specific miRNAs could serve as novel biomarkers for the diagnosis of early stages of diabetic nephropathy.

Rationale and design of the Cardiovascular Inflammation Reduction Trial: a test of the inflammatory hypothesis of atherothrombosis

BACKGROUND

Inflammation plays a fundamental role in atherothrombosis. Yet, whether direct inhibition of inflammation will reduce the occurrence of adverse cardiovascular outcomes is not known.

DESIGN

The Cardiovascular Inflammation Reduction Trial (CIRT) (ClinicalTrials.govNCT01594333) will randomly allocate 7,000 patients with prior myocardial infarction (MI) and either type 2 diabetes or the metabolic syndrome to low-dose methotrexate (target dose 15-20 mg/wk) or placebo over an average follow-up period of 3 to 5 years. Low-dose methotrexate is a commonly used anti-inflammatory regimen for the treatment of rheumatoid arthritis and lacks significant effects on lipid levels, blood pressure, or platelet function. Both observational and mechanistic studies suggest that low-dose methotrexate has clinically relevant antiatherothrombotic effects. The CIRT primary end point is a composite of nonfatal MI, nonfatal stroke, and cardiovascular death. Secondary end points are all-cause mortality, coronary revascularization plus the primary end point, hospitalization for congestive heart failure plus the primary end point, all-cause mortality plus coronary revascularization plus congestive heart failure plus the primary end point, incident type 2 diabetes, and net clinical benefit or harm. CIRT will use standardized central methodology designed to ensure consistent performance of all dose adjustments and safety interventions at each clinical site in a manner that protects the blinding to treatment but maintains safety for enrolled participants.

SUMMARY

CIRT aims to test the inflammatory hypothesis of atherothrombosis in patients with prior MI and either type 2 diabetes or metabolic syndrome, conditions associated with persistent inflammation. If low-dose methotrexate reduces cardiovascular events, CIRT would provide a novel therapeutic approach for the secondary prevention of heart attack, stroke, and cardiovascular death.

Can C-peptide mediated anti-inflammatory effects retard the development of microvascular complications of type 1 diabetes?

Hyperglycemia is considered to be the major cause of microvascular complications of diabetes. Growing evidence highlights the importance of hyperglycemia-mediated inflammation in the initiation and progression of microvascular complications in type 1 diabetes. We hypothesize that lack of proinsulin C-peptide and lack of its anti-inflammatory properties contribute to the development of microvascular complications. Evidence gathered over the past 20 years shows that C-peptide is a biologically active peptide in its own right. It has been shown to reduce formation of reactive oxygen species and nuclear factor-κB activation induced by hyperglycemia, resulting in inhibition of cytokine, chemokine and cell adhesion molecule formation as well as reduced apoptotic activity. In addition, C-peptide stimulates and induces the expression of both Na⁺, K⁺-ATPase and endothelial nitric oxide synthase. Animal studies and small-scale clinical trials in type 1 diabetes patients suggest that C-peptide replacement combined with regular insulin therapy exerts beneficial effects on kidney and nerve dysfunction. Further clinical trials in patients with microvascular complications including measurements of inflammatory markers are warranted to explore the clinical significance of the aforementioned, previously unrecognized, C-peptide effects.

The antioxidant silybin prevents high glucose-induced oxidative stress and podocyte injury in vitro and in vivo

Podocyte injury, a major contributor to the pathogenesis of diabetic nephropathy, is caused at least in part by the excessive generation of reactive oxygen species (ROS). Overproduction of superoxide by the NADPH oxidase isoform Nox4 plays an important role in podocyte injury. The plant extract silymarin is attributed antioxidant and antiproteinuric effects in humans and in animal models of diabetic nephropathy. We investigated the effect of silybin, the active constituent of silymarin, in cultures of mouse podocytes and in the OVE26 mouse, a model of type 1 diabetes mellitus and diabetic nephropathy. Exposure of podocytes to high glucose (HG) increased 60% the intracellular superoxide production, 90% the NADPH oxidase activity, 100% the Nox4 expression, and 150% the number of apoptotic cells, effects that were completely blocked by 10 μM silybin. These in vitro observations were confirmed by similar in vivo findings. The kidney cortex of vehicle-treated control OVE26 mice displayed greater Nox4 expression and twice as much superoxide production than cortex of silybin-treated mice. The glomeruli of control OVE26 mice displayed 35% podocyte drop out that was not present in the silybin-treated mice. Finally, the OVE26 mice experienced 54% more pronounced albuminuria than the silybin-treated animals. In conclusion, this study demonstrates a protective effect of silybin against HG-induced podocyte injury and extends this finding to an animal model of diabetic nephropathy.

Mesenchymal stem cells transplantation ameliorates glomerular injury in streptozotocin-induced diabetic nephropathy in rats via inhibiting macrophage infiltration

Mesenchymal stem cells (MSCs) treatment has been shown to be effective in diabetic nephropathy (DN). However, the mechanisms involved in the renoprotective effects of MSCs have not been clearly demonstrated. Especially, there was no study on the relationship of MSCs and macrophages in diabetic kidney. To explore the effect of MSCs on macrophages in DN, streptozotocin-induced diabetes animals received no treatment or treatment with MSCs (2×10(6), via tail vein) for two continuous weeks. Eight weeks after treatment, physical, biochemical and morphological parameters were measured. Immunohistochemistry for fibronectin (FN), CollagenI, ED-1, monocyte chemoattractant protein-1 (MCP-1) was performed. Expressions of pro-inflammatory cytokines and hepatocyte growth factor (HGF) at gene level and protein level were determined by real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Blood glucose, urinary albumin excretion, creatinine clearance were significantly reduced after MSCs treatment. The glomerulosclerosis as revealed by periodic acid Schiff stain and expression of FN and CollagenI was also dramatically attenuated. Most importantly, the expression of MCP-1 and the number of infiltrated macrophages in kidney were effectively suppressed by MSCs treatment. The expression of HGF in MSCs group was up-regulated. Meanwhile, the expressions of IL-1β, IL-6 and TNFα were significantly down-regulated by MSCs treatment. Our study suggest that MSCs treatment ameliorates DN via inhibition of MCP-1 expression by secreting HGF, thus reducing macrophages infiltration, down-regulating IL-1β, IL-6, TNFα expression in renal tissue in diabetic rats.

Reduction of aldosterone production improves renal oxidative stress and fibrosis in diabetic rats

Aldosterone is increased in diabetes and contributes to the development of diabetic nephropathy. The authors hypothesized that reduction in aldosterone production in diabetes by amlodipine or aliskiren improves diabetic kidney disease by attenuating renal oxidative stress and fibrosis. Normoglycemic and streptozotocin-induced diabetic Sprague-Dawley rats were given vehicle, amlodipine, or aliskiren alone and combined for 6 weeks. At the end of study, we evaluated blood pressure (BP), 24-hour urinary sodium (UNaV) and aldosterone excretion rates, renal interstitial fluid (RIF) levels of nitric oxide (NO), cyclic guanosine 3',5'-monophosphate (cGMP), and 8-isoprostane, and renal morphology. BP was not significantly different between any of experimental groups. UNaV increased in diabetic animals and was not affected by different treatments. Urinary aldosterone excretion increased in diabetic rats receiving vehicle and decreased with amlodipine and aliskiren alone or combined. RIF NO and cGMP levels were reduced in vehicle-treated diabetic rats and increased with amlodipine or aliskiren given alone and combined. RIF 8-isoprostane levels and renal immunostaining for periodic acid-Schiff and fibronectin were increased in vehicle-treated diabetic rats and decreased with aliskiren alone or combined with amlodipine. The authors conclude that inhibition of aldosterone by amlodipine or aliskiren ameliorates diabetes induced renal injury via improvement of NO-cGMP pathway and reduction in oxidative stress and fibrosis, independent of BP changes.

Inflammation in obesity and diabetes: islet dysfunction and therapeutic opportunity

The role of the immune system is to restore functionality in response to stress. Increasing evidence shows that this function is not limited to insults by infection or injury and plays a role in response to overnutrition. Initially, this metabolic activation of the immune system is a physiological response, but it may become deleterious with time. Therefore, therapeutic interventions should aim at modulating the immune system rather than simply damping it. In this article, we describe the physiology and pathology of the immune system during obesity and diabetes with a focus on islet inflammation, the IL-1β pathway, and clinical translation.

Sodium glucose cotransporter 2 and the diabetic kidney

PURPOSE OF REVIEW

Reabsorption of glucose in the proximal tubule occurs predominantly via the sodium glucose cotransporter 2 (SGLT2). There has been intense interest in this transporter as a number of SGLT2 inhibitors have entered clinical development. SGLT2 inhibitors act to lower plasma glucose by promoting glycosuria and this review aims to outline the effect on the diabetic kidney of this hypoglycaemic agent.

RECENT FINDINGS

This review provides an overview of recent findings in this area: the transcriptional control of SGLT2 expression in human proximal tubular cells implicates a number of cytokines in the alteration of SGLT2 expression; experimental data show that SGLT2 inhibition may correct early detrimental effects of diabetes by reducing proximal tubular sodium and glucose transport, suggesting a possible renoprotective effect independent of the glucose lowering effects of these agents; and the nonglycaemic effects of SGLT2 inhibitors may have an impact on renal outcomes.

SUMMARY

The available clinical evidence shows consistent reduction in glycaemic parameters and some evidence suggests additional effects including weight loss and mild blood pressure reduction. There are some side effects that warrant further investigation and establishing whether SGLT2 inhibition provides a renal benefit relies on future long-term studies with specific renal end-points.

Renal protective effects of toll-like receptor 4 signaling blockade in type 2 diabetic mice

Chronic inflammation caused by high glucose and high free fatty acid (FFA) concentrations is a major contributor to the pathogenesis of type 2 diabetes. Recent evidence suggests that activation of Toll-like receptor (TLR) signaling induces peripheral insulin resistance and mediates central insulin and leptin resistance. In this study, we investigated the renal effects of TLR4 signaling blockade in type 2 diabetic mice. Eight-week-old db/db mice were treated for 12 weeks with (S,R)-3-phenyl-4,5-dihydro-5-isoxasole acetic acid (GIT27), which targets macrophages through the inhibition of TLR4- and TLR2/6-mediated signaling pathways. Although GIT27 treatment improved glycemic control and insulin tolerance, which is associated with a lower lipid profile, it did not impact body weight or food consumption. GIT27 treatment also markedly decreased urinary albumin excretion, decreased proinflammatory cytokine synthesis, improved tissue lipid metabolism, induced oxidative stress, and improved glomerulosclerosis compared with the control db/db group. In cultured podocytes and adipocytes, high glucose levels with FFA stimulation increased TLR4 expression and proinflammatory cytokine synthesis, but the effects were abolished by GIT27 treatment. In addition, knockdown of TLR4 expression by stealth small interfering RNA abolished FFA-induced proinflammatory cytokine synthesis in cultured podocytes. In conclusion, our results suggest that GIT27 treatment improves insulin resistance and protects against the renal injury that occurs in type 2 diabetic nephropathy through both metabolic and antiglomerulosclerotic mechanisms. These results suggest that TLR pathway inhibition might play a direct protective role in diabetic kidney disease.

Treatment of diabetic nephropathy with Tripterygium wilfordii Hook F extract: a prospective, randomized, controlled clinical trial

Background

Diabetic nephropathy (DN) is the most common cause of end-stage renal failure. Although angiotensin II receptor blockers (ARBs) can be used to attenuate proteinuria in DN patients, their efficacy remains limited. This clinical trial aimed to evaluate the efficacy of Tripterygium wilfordii Hook F (TwHF) extract in the treatment of type 2 diabetes mellitus (DM)-induced nephropathy.

Methods

A total of 65 DN patients with proteinuria levels ≥ 2.5 g/24 h and serum creatinine levels < 3 mg/dl were enrolled in this six-month, prospective, randomized, controlled study. The patients were randomized into treatment groups that received either 120 mg of TwHF extract per day for three months, followed by 60 mg per day for three more months, or 160 mg of valsartan daily for six months. The urinary protein and estimated glomerular filtration (eGFR) level were measured at one, three, and six months after the commencement of treatment. The primary measure of treatment efficacy was a reduction in the 24-h urine protein level between baseline and the end of the study, and the secondary measure of treatment efficacy was a reduction in the eGFR value.

Results

At the end of the treatment period, the mean urine protein level in the TwHF group was dramatically decreased (4.99 ± 2.25 g/24 h vs 2.99 ± 1.81 g/24 h, p < 0.01), with decreases at one, three, and six months of 32.9%, 38.8%, and 34.3%, respectively. In contrast, the proteinuria in the valsartan group was not significantly attenuated, and the decreases in urine protein levels at treatment months one, three, and six were 1.05%, 10.1%, and -11.7%, respectively. The mean decrease in eGFR in the valsartan group was greater than that in the TwHF group (26.4% vs. 13.7%, respectively; p =0.067).

Conclusions

TwHF extract can reduce the urine protein level of DN patients and represents a novel, potentially effective, and safe drug for the treatment of DN patients with proteinuria.

Trial registration

ClinicalTrials.gov: NCT00518362

Kidney-targeted transplantation of mesenchymal stem cells by ultrasound-targeted microbubble destruction promotes kidney repair in diabetic nephropathy rats

We test the hypothesis that ultrasound-targeted microbubble destruction (UTMD) technique increases the renoprotective effect of kidney-targeted transplantation of bone-marrow-derived mesenchymal stem cells (BM-MSCs) in diabetic nephropathy (DN) rats. Diabetes was induced by streptozotocin injection (60 mg/Kg, intraperitoneally) in Sprague-Dawley rats. MSCs were administered alone or in combination with UTMD to DN rats at 4 weeks after diabetes onset. Random blood glucose concentrations were measured at 1, 2, 4, and 8 weeks, and plasma insulin levels, urinary albumin excretion rate (UAER) values, the structures of pancreas and kidney, the expressions of TGF- β 1, synaptopodin, and IL-10 were assessed at 8 weeks after MSCs transplantation. MSCs transplantation decreased blood glucose concentrations and attenuated pancreatic islets/ β cells damage. The permeability of renal interstitial capillaries and VCAM-1 expression increased after UTMD, which enhanced homing and retention of MSCs to kidneys. MSCs transplantation together with UTMD prevented renal damage and decreased UAER values by inhibiting TGF- β 1 expression and upregulating synaptopodin and IL-10 expression. We conclude that MSCs transplantation reverts hyperglycemia; UTMD technique noninvasively increases the homing of MSCs to kidneys and promotes renal repair in DN rats. This noninvasive cell delivery method may be feasible and efficient as a novel approach for personal MSCs therapy to diabetic nephropathy.

Proteomic analysis of kidney and protective effects of grape seed procyanidin B2 in db/db mice indicate MFG-E8 as a key molecule in the development of diabetic nephropathy

Diabetic nephropathy, as a severe microvascular complication of diabetic mellitus, has become the leading cause of end-stage renal diseases. However, no effective therapeutic strategy has been developed to prevent renal damage progression to end stage renal disease. Hence, the present study evaluated the protective effects of grape seed procyanidin B2 (GSPB2) and explored its molecular targets underlying diabetic nephropathy by a comprehensive quantitative proteomic analysis in db/db mice. Here, we found that oral administration of GSPB2 significantly attenuated the renal dysfunction and pathological changes in db/db mice. Proteome analysis by isobaric tags for relative and absolute quantification (iTRAQ) identified 53 down-regulated and 60 up-regulated proteins after treatment with GSPB2 in db/db mice. Western blot analysis confirmed that milk fat globule EGF-8 (MFG-E8) was significantly up-regulated in diabetic kidney. MFG-E8 silencing by transfection of MFG-E8 shRNA improved renal histological lesions by inhibiting phosphorylation of extracellular signal-regulated kinase1/2 (ERK1⁄2), Akt and glycogen synthase kinase-3beta (GSK-3β) in kidneys of db/db mice. In contrast, over-expression of MFG-E8 by injection of recombinant MFG-E8 resulted in the opposite effects. GSPB2 treatment significantly decreased protein levels of MFG-E8, phospho-ERK1/2, phospho-Akt, and phospho-GSK-3β in the kidneys of db/db mice. These findings yield insights into the pathogenesis of diabetic nephropathy, revealing MFG-E8 as a new therapeutic target and indicating GSPB2 as a prospective therapy by down-regulation of MFG-E8, along with ERK1/2, Akt and GSK-3β signaling pathway.

miR-21 is a key therapeutic target for renal injury in a mouse model of type 2 diabetes

AIMS/HYPOTHESIS

As microRNA-21 (miR-21) plays a pathological role in fibrosis, we hypothesised that it may be a therapeutic target for diabetic nephropathy.

METHODS

Abundance of miR-21 was examined in diabetic kidneys from db/db mice. The therapeutic potential of miR-21 in diabetic kidney injury was examined in db/db mice by an ultrasound-microbubble-mediated miR-21 small hairpin RNA transfer. In addition, the role and mechanisms of miR-21 in diabetic renal injury were examined in vitro under diabetic conditions in rat mesangial and tubular epithelial cell lines by overexpressing or downregulating miR-21.

RESULTS

In db/db mice, a mouse model of type 2 diabetes, renal miR-21 at age 20 weeks was increased twofold compared with db/m (+) mice at the same age, and this increase was associated with the development of microalbuminuria and renal fibrosis and inflammation. More importantly, gene transfer of miR-21 knockdown plasmids into the diabetic kidneys of db/db mice at age 10 weeks significantly ameliorated microalbuminuria and renal fibrosis and inflammation at age 20 weeks, revealing a therapeutic potential for diabetic nephropathy by targeting miR-21. Overexpression of miR-21 in kidney cells enhanced, but knockdown of miR-21 suppressed, high-glucose-induced production of fibrotic and inflammatory markers. Targeting Smad7 may be a mechanism by which miR-21 regulates renal injury because knockdown of renal miR-21 restored Smad7 levels and suppressed activation of the TGF-β and NF-κB signalling pathways.

CONCLUSIONS/INTERPRETATION

Inhibition of miR-21 might be an effective therapy for diabetic nephropathy.

Mechanisms of diabetic complications

It is increasingly apparent that not only is a cure for the current worldwide diabetes epidemic required, but also for its major complications, affecting both small and large blood vessels. These complications occur in the majority of individuals with both type 1 and type 2 diabetes. Among the most prevalent microvascular complications are kidney disease, blindness, and amputations, with current therapies only slowing disease progression. Impaired kidney function, exhibited as a reduced glomerular filtration rate, is also a major risk factor for macrovascular complications, such as heart attacks and strokes. There have been a large number of new therapies tested in clinical trials for diabetic complications, with, in general, rather disappointing results. Indeed, it remains to be fully defined as to which pathways in diabetic complications are essentially protective rather than pathological, in terms of their effects on the underlying disease process. Furthermore, seemingly independent pathways are also showing significant interactions with each other to exacerbate pathology. Interestingly, some of these pathways may not only play key roles in complications but also in the development of diabetes per se. This review aims to comprehensively discuss the well validated, as well as putative mechanisms involved in the development of diabetic complications. In addition, new fields of research, which warrant further investigation as potential therapeutic targets of the future, will be highlighted.

The TLR4 antagonist CRX-526 protects against advanced diabetic nephropathy

We recently showed that Toll-like receptor (TLR) TLR4 was overexpressed in the human diabetic kidney, which could promote tubular inflammation. Here we explored whether the TLR4 antagonist, CRX-526, has therapeutic potential to attenuate renal injuries and slow the progression of advanced diabetic nephropathy in wild-type and endothelial nitric oxide synthase (eNOS) knockout mice. In the latter, the endogenous TLR4 ligand, high-mobility group box 1, was upregulated more than in wild-type animals. Four weeks after streptozotocin induction of diabetes, mice were injected with either CRX-526 or vehicle for 8 weeks. CRX-526 significantly reduced albuminuria and blood urea nitrogen without altering blood glucose and systolic blood pressure in diabetic mice. Glomerular hypertrophy, glomerulosclerosis, and tubulointerstitial injury were attenuated by CRX-526, which was associated with decreased chemokine (C-C motif) ligand (CCL)-2, osteopontin, CCL-5 overexpression, subsequent macrophage infiltration, and collagen deposition. These effects were associated with inhibition of TGF-β overexpression and NF-κB activation. In vitro, CRX-526 inhibited high glucose-induced osteopontin upregulation and NF-κB nuclear translocation in cultured human proximal tubular epithelial cells. Thus, we provided evidence that inhibition of TLR4 with the synthetic antagonist CRX-526 conferred renoprotective effects in eNOS knockout diabetic mice with advanced diabetic nephropathy.

Astragaloside IV ameliorates renal injury in streptozotocin-induced diabetic rats through inhibiting NF-κB-mediated inflammatory genes expression

Accumulating evidence suggests that inflammatory processes are involved in the development of diabetic nephropathy (DN). However, there are no effective interventions for inflammation in the diabetic kidneys. Here, we tested the hypothesis that Astragaloside IV(AS-IV), a novel saponin purified from Astragalus membranaceus (Fisch) Bge, ameliorates DN in streptozotocin (STZ)-induced diabetic rats through anti-inflammatory mechanisms. Diabetes was induced with STZ (65 mg/kg) by intraperitoneal injection in rats. Two weeks after STZ injection, rats were divided into three groups (n=8/each group), namely, diabetic rats, diabetic rats treated with AS-IV at 5 and 10 mgkg(-1)d(-1), p.o., for 8 weeks. The normal rats were chosen as nondiabetic control group (n=8). The rats were sacrificed 10 weeks after induction of diabetes. AS-IV ameliorated albuminuria, renal histopathology and podocyte foot process effacement in diabetic rats. Renal NF-κB activity, as wells as protein and mRNA expression were increased in diabetic kidneys, accompanied by an increase in mRNA expression and protein content of TNF-α, MCP-1 and ICAM-1 in kidney tissues. The α1-chain type IV collagen mRNA was elevated in the kidneys of diabetic rats. All of these abnormalities were partially restored by AS-IV. AS-IV also decreased the serum levels of TNF-α, MCP-1 and ICAM-1 in diabetic rats. These findings suggest that AS-IV, a novel anti-inflammatory agent, attenuated DN in rats through inhibiting NF-κB mediated inflammatory genes expression.

ATP-P2X4 signaling mediates NLRP3 inflammasome activation: a novel pathway of diabetic nephropathy

Tubulointerstitial inflammation plays a key role in the development of diabetic nephropathy (DN). Cytokines in the IL-1 family are the key pro-inflammatory cytokines of tubulointerstitial inflammation. Extracellular ATP can cause P2X receptors to activate the NOD-like receptor 3 (NLRP3) inflammasome and cause IL-1β and IL-18 maturation and release. We investigated the role of ATP-P2X4 signaling in NLRP3 inflammasome activation and renal interstitial inflammation characteristic of DN. Ex vivo studies, P2X4 showed increased expression in renal tubule epithelial cells in patients with nephropathy due to type 2 diabetes compared to those in the control group. Linear correlation analysis shows that P2X4 expression was positively related with urine IL-1β and IL-18 levels. Moreover, P2X4 expression was co-localized with NLRP3, IL-1β, and IL-18 expression. In vitro culture experiments showed NLRP3 protein expression, cleavage of caspase-1 and IL-1β, and release of IL-1β, IL-18 and ATP in HK-2 cells significantly increased after high glucose stimulation. However, apyrase, which consumes extracellular ATP, completely blocked the changes caused by high glucose. The P2 receptor antagonist suramin, P2X receptor antagonist TNP-ATP, P2X4 selective antagonist 5-BDBD, and P2X4 gene silencing attenuated NLRP3 expression, cleavage of caspase-1 and IL-1β, and release of IL-1β and IL-18 induced by high glucose. Taken together, these results suggest that ATP-P2X4 signaling mediates high glucose-induced activation of the NLRP3 inflammasome, regulates IL-1 family cytokine secretion, and causes the development of tubulointerstitial inflammation in DN.

D-saccharic acid 1,4-lactone protects diabetic rat kidney by ameliorating hyperglycemia-mediated oxidative stress and renal inflammatory cytokines via NF-κB and PKC signaling

Increasing evidence suggests that oxidative stress is involved in the pathogenesis of diabetic nephropathy (DN) and this can be attenuated by antioxidants. D-Saccharic acid 1,4-lactone (DSL) is known for its detoxifying and antioxidant properties. Our early investigation showed that DSL can ameliorate alloxan (ALX) induced diabetes mellitus and oxidative stress in rats by inhibiting pancreatic β-cell apoptosis. In the present study we, therefore, investigated the protective role of DSL against renal injury in ALX induced diabetic rats. ALX exposure (at a dose of 120 mg/kg body weight, i. p., once) elevated the blood glucose level, serum markers related to renal injury, the production of reactive oxygen species (ROS), and disturbed the intra-cellular antioxidant machineries. Oral administration of DSL (80 mg/kg body weight) restored all these alterations close to normal. In addition, DSL could also normalize the aldose reductase activity which was found to increase in the diabetic rats. Investigating the mechanism of its protective activity, we observed the activation of different isoforms of PKC along with the accumulation of matrix proteins like collagen and fibronectin. The diabetic rats also showed nuclear translocation of NF-κB and increase in the concentration of inflammatory cytokines in the renal tissue. The activation of mitochondria dependent apoptotic pathway was observed in the diabetic rat kidneys. However, treatment of diabetic rats with DSL counteracted all these changes. These findings, for the first time, demonstrated that DSL could ameliorate renal dysfunction in diabetic rats by suppressing the oxidative stress related signalling pathways.

Proximal tubule-specific overexpression of netrin-1 suppresses acute kidney injury-induced interstitial fibrosis and glomerulosclerosis through suppression of IL-6/STAT3 signaling

Acute kidney injury-induced organ fibrosis is recognized as a major risk factor for the development of chronic kidney disease, which remains one of the leading causes of death in the developed world. However, knowledge on molecules that may suppress the fibrogenic response after injury is lacking. In ischemic models of acute kidney injury, we demonstrate a new function of netrin-1 in regulating interstitial fibrosis. Acute injury was promptly followed by a rise in serum creatinine in both wild-type and netrin-1 transgenic animals. However, the wild-type showed a slow recovery of kidney function compared with netrin-1 transgenic animals and reached baseline by 3 wk. Histological examination showed increased infiltration of interstitial macrophages, extensive fibrosis, reduction of capillary density, and glomerulosclerosis. Collagen IV and α-smooth muscle actin expression was absent in sham-operated kidneys; however, their expression was significantly increased at 2 wk and peaked at 3 wk after reperfusion. These changes were reduced in the transgenic mouse kidney, which overexpresses netrin-1 in proximal tubular epithelial cells. Fibrosis was associated with increased expression of IL-6 and extensive and chronic activation of STAT3. Administration of IL-6 exacerbated fibrosis in vivo in wild-type, but not in netrin-1 transgenic mice kidney and increased collagen I expression and STAT3 activation in vitro in renal epithelial cells subjected to hypoxia-reoxygenation, which was suppressed by netrin-1. Our data suggest that proximal tubular epithelial cells may play a prominent role in interstitial fibrosis and that netrin-1 could be a useful therapeutic agent for treating kidney fibrosis.

Dietary sodium restriction prevents kidney damage in high fructose-fed rats

Sodium depletion has a protective effect on target-organ damage in hypertension independent of blood pressure. Here we tested whether chronic dietary sodium restriction may prevent the development of renal alterations associated with insulin resistance by reducing the inflammatory and oxidant state. Rats were fed normal-salt-60% fructose, low-salt-60% fructose, or control normal-salt diet for 12 weeks. Insulin resistance induced by high-fructose diet was associated with an increase in albuminuria, tubular and glomerular hypertrophy, and inflammation of kidney and adipose tissue. The low-salt diet improved insulin sensitivity and prevented kidney damage. These beneficial effects of sodium depletion were associated with a decrease in renal inflammation (macrophage infiltration, IL-6, TNF-α) and oxidative stress (NADPH oxidase activity), and a prevention of histologic changes in retroperitoneal fat induced by high fructose. Thus, dietary salt depletion has beneficial effects on renal and metabolic alterations associated with a high-fructose diet in rats.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

TNF-α mediates increased susceptibility to ischemic AKI in diabetes

Diabetes is a risk factor for the development of acute kidney injury (AKI) in humans and rodents. However, the mechanistic basis for this observation is unknown. The present studies evaluated the role of inflammation and TNF-α in ischemic AKI in a model of type 2 diabetes mellitus (DM). Diabetic (db/db) and nondiabetic (db/+) littermates were subjected to 20 min of bilateral renal ischemia. The nondiabetic mice developed only mild and transient renal dysfunction. In contrast, the equivalent ischemic insult provoked severe and sustained renal dysfunction in the db/db mice. The expression of TNF-α and Toll-like receptor 4 (TLR4) mRNA was measured in the kidneys of diabetic mice before and after renal ischemia; db/db mice exhibited greater increases in TNF-α and TLR4 mRNA expression following ischemia than did db/+. In addition, urinary excretion of TNF-α after ischemia was higher in db/db mice than in db/+ mice. To determine the possible role of TNF-α in mediating the enhanced susceptibility of diabetic mice to ischemic injury, db/db mice were injected with either a neutralizing anti-mouse TNF-α antibody or nonimmune globulin and then subjected to 20 min of bilateral renal ischemia. Treatment of the db/db mice with the TNF-α antibody provided significant protection against the ischemic injury. These data support the view that diabetes increases the susceptibility to ischemia-induced renal dysfunction. This increased susceptibility derives from a heightened inflammatory response involving TNF-α and perhaps TLR4 signaling.

Fisetin inhibits hyperglycemia-induced proinflammatory cytokine production by epigenetic mechanisms

Diabetes is characterized by a proinflammatory state, and several inflammatory processes have been associated with both type 1 and type 2 diabetes and the resulting complications. High glucose levels induce the release of proinflammatory cytokines. Fisetin, a flavonoid dietary ingredient found in the smoke tree (Cotinus coggygria), and is also widely distributed in fruits and vegetables. Fisetin is known to exert anti-inflammatory effects via inhibition of the NF-κB signaling pathway. In this study, we analyzed the effects of fisetin on proinflammatory cytokine secretion and epigenetic regulation, in human monocytes cultured under hyperglycemic conditions. Human monocytic (THP-1) cells were cultured under control (14.5 mmol/L mannitol), normoglycemic (NG, 5.5 mmol/L glucose), or hyperglycemic (HG, 20 mmol/L glucose) conditions, in the absence or presence of fisetin. Fisetin was added (3–10 μM) for 48 h. While the HG condition significantly induced histone acetylation, NF-κB activation, and proinflammatory cytokine (IL-6 and TNF-α) release from THP-1 cells, fisetin suppressed NF-κB activity and cytokine release. Fisetin treatment also significantly reduced CBP/p300 gene expression, as well as the levels of acetylation and HAT activity of the CBP/p300 protein, which is a known NF-κB coactivator. These results suggest that fisetin inhibits HG-induced cytokine production in monocytes, through epigenetic changes involving NF-κB. We therefore propose that fisetin supplementation be considered for diabetes prevention.

Chronic Administration of Oil Palm (Elaeis guineensis) Leaves Extract Attenuates Hyperglycaemic-Induced Oxidative Stress and Improves Renal Histopathology and Function in Experimental Diabetes

Oil palm (Elaeis guineensis) leaves extract (OPLE) has antioxidant properties and because oxidative stress contributes to the pathogenesis of diabetic nephropathy (DN), we tested the hypothesis that OPLE prevents diabetes renal oxidative stress, attenuating injury. Sprague-Dawley rats received OPLE (200 and 500 mg kg(-1)) for 4 and 12 weeks after diabetes induction (streptozotocin 60 mg kg(-1)). Blood glucose level, body and kidney weights, urine flow rate (UFR), glomerular filtration rate (GFR), and proteinuria were assessed. Oxidative stress variables such as 8-hydroxy-2'-deoxyguanosine (8-OHdG), glutathione (GSH), and lipid peroxides (LPO) were quantified. Renal morphology was analysed, and plasma transforming growth factor-beta1 (TGF-β1) was measured. Diabetic rats demonstrated increase in blood glucose and decreased body and increased kidney weights. Renal dysfunction (proteinuria, elevations in UFR and GFR) was observed in association with increases in LPO, 8-OHdG, and TGF-β1 and a decrease in GSH. Histological evaluation of diabetic kidney demonstrated glomerulosclerosis and tubulointerstitial fibrosis. OPLE attenuated renal dysfunction, improved oxidative stress markers, and reduced renal pathology in diabetic animals. These results suggest OPLE improves renal dysfunction and pathology in diabetes by reducing oxidative stress; furthermore, the protective effect of OPLE against renal damage in diabetes depends on the dose of OPLE as well as progression of DN.

Combination therapy with an angiotensin-converting-enzyme inhibitor and an angiotensin II receptor antagonist ameliorates microinflammation and oxidative stress in patients with diabetic nephropathy

Aims/Introduction

Recent studies have pointed to the effectiveness of combination therapy with an angiotensin‐converting‐enzyme inhibitor (ACEI) and an angiotensin receptor blocker (ARB) for diabetic nephropathy. However, some controversy over this combination treatment remains and the mechanisms underlying its renoprotective effects have not been fully clarified. Therefore, we compared the renoprotective effects of imidapril (ACEI) and losartan (ARB) combination therapy with losartan monotherapy in patients with diabetic nephropathy. We also compared the anti‐inflammatory and anti‐oxidative stress effects of these two treatments.

Materials and Methods

A total of 32 Japanese patients with type 2 diabetes and nephropathy were enrolled. Patients were randomized to either 100 mg/day losartan (n = 16) or 50 mg/day losartan plus 5 mg/day imidapril (n = 16). We evaluated clinical parameters, serum concentrations of high‐sensitivity C‐reactive protein (hs‐CRP), soluble intercellular adhesion molecule‐1 (sICAM‐1), interleukin‐18 (IL‐18) and monocyte chemotactic protein‐1 (MCP‐1), and the urinary concentrations of IL‐18, MCP‐1 and 8‐hydroxy‐2′‐deoxyguanosine (8‐OHdG) at 24 and 48 weeks after starting treatment.

Results

Blood pressure was not significantly different between the two groups. The serum levels of hs‐CRP, sICAM‐1 and IL‐18, as well as urinary excretion of albumin, IL‐18 and 8‐OHdG decreased significantly in the combination therapy group at 48 weeks. The percent decreases in serum IL‐18 concentrations and urinary IL‐18 and 8‐OHdG were significantly greater in the combination therapy group than in the monotherapy group.

Conclusions

Combination therapy with an ACEI and an ARB could be beneficial for treating diabetic nephropathy through its anti‐inflammatory and anti‐oxidative stress effects.

Gamma linolenic acid exerts anti-inflammatory and anti-fibrotic effects in diabetic nephropathy

PURPOSE

This study was undertaken to investigate the effects of gamma linolenic acid (GLA) on inflammation and extracellular matrix (ECM) synthesis in mesangial and tubular epithelial cells under diabetic conditions.

MATERIALS AND METHODS

Sprague-Dawley rats were intraperitoneally injected with either a diluent [n=16, control (C)] or streptozotocin [n=16, diabetes (DM)], and eight rats each from the control and diabetic groups were treated with evening primrose oil by gavage for three months. Rat mesangial cells and NRK-52E cells were exposed to medium containing 5.6 mM glucose and 30 mM glucose (HG), with or without GLA (10 or 100 μM). Intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1 (MCP-1), and fibronectin (FN) mRNA and protein expression levels were evaluated.

RESULTS

Twenty-four-hour urinary albumin excretion was significantly increased in DM compared to C rats, and GLA treatment significantly reduced albuminuria in DM rats. ICAM-1, MCP-1, FN mRNA and protein expression levels were significantly higher in DM than in C kidneys, and these increases were significantly abrogated by GLA treatment. In vitro, GLA significantly inhibited increases in MCP-1 mRNA expression and protein levels under high glucose conditions in HG-stimulated mesangial and tubular epithelial cells (p<0.05, respectively). ICAM-1 and FN expression showed a similar pattern to the expression of MCP-1.

CONCLUSION

GLA attenuates not only inflammation by inhibiting enhanced MCP-1 and ICAM-1 expression, but also ECM accumulation in diabetic nephropathy.