Increased urinary excretion of monocyte chemoattractant protein-1 in proteinuric renal diseases

Independent Prognostic and Predictive Role of Interstitial Macrophages in Kidney Biopsies of IgA Nephropathy Patients

A relevant percentage of IgAN patients experience a progressive decline in kidney function. According to the KDIGO guidelines, proteinuria and eGFR are the only validated prognostic markers. The role of interstitial macrophages in kidney biopsies of IgAN patients and the outcome of patients treated with renin-angiotensin system inhibitors (RASBs) alone or combined with glucocorticoids were evaluated. Clinical and laboratory records (age, gender, hypertension, hematuria, proteinuria, eGFR, serum creatinine, and therapy), MEST-C parameters of the Oxford classification, C4d deposition, peritubular capillaries, and glomerular and interstitial macrophages in 47 IgAN patients undergoing kidney biopsy consecutively between 2003 and 2016 were examined. A high number of interstitial macrophages significantly correlated with peritubular capillary rarefaction and impairment of kidney function. Cox's multivariable regression analysis revealed that a value > 19.5 macrophages/HPF behaved as an independent marker of an unfavorable outcome. Patients exhibiting > 19.5 macrophages/HPF treated at the time of diagnosis with RASBs combined with methylprednisolone had an estimated probability of a favorable outcome higher than patients treated with RASBs alone. Thus, a value > 19.5 macrophages/HPF in IgAN biopsies can predict an unfavorable outcome and endorse a well-timed administration of glucocorticoids. Studies evaluating urine biomarkers associated with peritubular capillary rarefaction in patients with marked macrophage infiltration may help personalized treatment decisions.

Tubular epithelial cell-derived extracellular vesicles induce macrophage glycolysis by stabilizing HIF-1α in diabetic kidney disease

Background

Albuminuria is a hallmark of diabetic kidney disease (DKD) that promotes its progression, leading to renal fibrosis. Renal macrophage function is complex and influenced by macrophage metabolic status. However, the metabolic state of diabetic renal macrophages and the impact of albuminuria on the macrophage metabolic state are poorly understood.

Methods

Extracellular vesicles (EVs) from tubular epithelial cells (HK-2) were evaluated using transmission electron microscopy, nanoparticle tracking analysis and western blotting. Glycolytic enzyme expression in macrophages co-cultured with HSA-treated HK-2 cell-derived EVs was detected using RT-qPCR and western blotting. The potential role of EV-associated HIF-1α in the mediation of glycolysis was explored in HIF-1α siRNA pre-transfected macrophages co-cultured with HSA-treated HK-2 cell-derived EVs, and the extent of HIF-1α hydroxylation was measured using western blotting. Additionally, we injected db/db mice with EVs via the caudal vein twice a week for 4 weeks. Renal macrophages were isolated using CD11b microbeads, and immunohistofluorescence was applied to confirm the levels of glycolytic enzymes and HIF-1α in these macrophages.

Results

Glycolysis was activated in diabetic renal macrophages after co-culture with HSA-treated HK-2 cells. Moreover, HSA-treated HK-2 cell-derived EVs promoted macrophage glycolysis both in vivo and in vitro. Inhibition of glycolysis activation in macrophages using the glycolysis inhibitor 2-DG decreased the expression of both inflammatory and fibrotic genes. Mechanistically, EVs from HSA-stimulated HK-2 cells were found to accelerate macrophage glycolysis by stabilizing HIF-1α. We also found that several miRNAs and lncRNAs, which have been reported to stabilize HIF-1α expression, were increased in HSA-treated HK-2 cell-derived EVs.

Conclusion

Our study suggested that albuminuria induced renal macrophage glycolysis through tubular epithelial cell-derived EVs by stabilizing HIF-1α, indicating that regulation of macrophage glycolysis may offer a new treatment strategy for DKD patients, especially those with macroalbuminuria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00525-1.

Biomarkers in Progressive Chronic Kidney Disease. Still a Long Way to Go

The traditional chronic kidney disease (CKD) biomarkers (eGFR based on serum creatinine, sex and age and albuminuria) cannot predict a patient's individual risk for developing progressive CKD. For this reason, it is necessary to identify novel CKD biomarkers that will be able to predict which patients are prone to develop progressive disease and discriminate between disease processes in different parts of the nephron (glomeruli or tubules). A good biomarker should change before or simultaneously with lesion development and its changes should correlate strongly with lesion development. Also, there should be a close relationship between severity of injury and amount of detectable biomarker and its levels should decrease with diminishing injury. Among the large number of molecules under investigation, we have reviewed the most promising ones: NGAL and KIM-1, MCP-1, MMP-9, clusterin, MMP-9, TIMP-1, Procollagen I alpha 1 and suPAR. All these, have been studied as biomarkers for prediction of CKD progression in cohorts of patients with chronic kidney disease of different stages and various aetiologies (proteinuric and non-proteinuric, glomerulonephritides, diabetic, hypertensive and polycystic kidney disease). There is evidence that these molecules could be useful as biomarkers for progressive chronic kidney disease, however, the available data are not enough to draw final conclusions. Further studies with large cohorts and long follow-up are required to identify appropriate biomarkers, that will be able to accurately and reliably define the risk for progressive chronic kidney disease.

Value of urinary levels of interleukin-6, epidermal growth factor, monocyte chemoattractant protein type1 and transforming growth factor β1 in predicting the extent of fibrosis lesions in kidney biopsies of patients with IgA nephropathy

OBJECTIVE

To analyse the associations between urinary levels of IL-6 EGF, MCP-1 and TGFβ1 and clinical, biochemical and histopathological characteristics in patients with primary IgA nephropathy and their ability to predict the extent of lesions of glomerular and/or interstitial sclerosis.

PATIENTS AND METHODS

A total of 58 patients with IgA nephropathy were studied. We determined the urine levels of IL-6, EGF, MCP-1, and TGFβ1 at the time of diagnosis. The extent of glomerular and interstitial fibrosis was analyzed by quantitative morphometry and kidney biopsies were classified according to the Oxford criteria. We analysed the ability of these molecules to predict the extent of glomerular and interstitial fibrosis lesions.

RESULTS

IL-6, TGFβ1 and MCP-1 were associated with focal glomerulosclerosis and interstitial fibrosis extension but not with the presence of mesangial, extracapillary or endocapillary proliferation. EGF showed a negative association with interstitial fibrosis. By categorising patients according to the Oxford classification, patients with T1 and T2 scores had significantly higher levels of IL-6, MCP-1, TGF-β1 and significantly lower levels of EGF than patients with T0 scores. By multiple regression and logistic regression analyses, the levels of MCP-1, IL-6 and EGF were independent predictors of the fibrosis surface, after adjusting for age and eGFR.

CONCLUSION

The urinary concentration of IL-6, EGF and MCP-1 provides additional information that significantly improves the estimation of the surface of interstitial fibrosis in patients with IgA nephropathy.

Inflammatory Mechanisms as New Biomarkers and Therapeutic Targets for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of CKD and end-stage kidney disease (ESKD) worldwide. Approximately 30-40% of people with diabetes develop this microvascular complication, placing them at high risk of losing kidney function as well as of cardiovascular events, infections, and death. Current therapies are ineffective for arresting kidney disease progression and mitigating risks of comorbidities and death among patients with DKD. As the global count of people with diabetes will soon exceed 400 million, the need for effective and safe treatment options for complications such as DKD becomes ever more urgent. Recently, the understanding of DKD pathogenesis has evolved to recognize inflammation as a major underlying mechanism of kidney damage. In turn, inflammatory mediators have emerged as potential biomarkers and therapeutic targets for DKD. Phase 2 clinical trials testing inhibitors of monocyte-chemotactic protein-1 chemokine C-C motif-ligand 2 and the Janus kinase/signal transducer and activator of transcription pathway, in particular, have produced promising results.

Clinical significance of fractional magnesium excretion (FEMg) as a predictor of interstitial nephropathy and its correlation with conventional parameters

BACKGROUND

Elevated urine Mg excretion and its correlation with histological damage in tubulo-interstitial nephropathy (TIN) were reported. Here we investigated the clinical significance of the fractional excretion of Mg (FEMg) for the prediction of TIN.

METHODS

We enrolled and assessed 94 adult patients with various renal diseases diagnosed principally by renal biopsy.

RESULTS

Our stratified analysis based on the value of the conventional TIN parameter N-acetylglucosaminidase (NAG) excretion showed that the high-NAG index group (more than median value of NAG-to-Cr ratio, n = 47) demonstrated significantly high FEMg values (p = 0.017). A univariate analysis revealed a significant correlation between the FEMg and the NAG index (R = 0.60) but not for other parameters. A multivariate regression analysis confirmed the significance of the FEMg as an effective predictor of the NAG index. The FEMg showed a significant correlation with the estimated glomerular filtration rate (eGFR) in the patients with eGFR ≤ 30 mL/min. The correlation of FEMg with the NAG index was not observed in the primary glomerulonephritis patients but was apparent in the patients with hypertensive nephrosclerosis or interstitial nephritis.

CONCLUSION

Our findings may indicate that the combination of the FEMg and the NAG index can provide a specific, sensitive assessment for TIN in patients without renal insufficiency.

Adenosine kinase inhibition protects the kidney against streptozotocin-induced diabetes through anti-inflammatory and anti-oxidant mechanisms

Adenosine provides anti-inflammatory effects in cardiovascular disease via the activation of adenosine A2A receptors; however, the physiological effect of adenosine could be limited due to its phosphorylation by adenosine kinase. We hypothesized that inhibition of adenosine kinase exacerbates extracellular adenosine levels to reduce renal inflammation and injury in streptozotocin-induced diabetes. Diabetes was induced in male C57BL/6 mice by daily injection of streptozotocin (50mg/kg/day, i.p. for 5 days). Control and diabetic mice were then treated with the adenosine kinase inhibitor ABT702 (1.5mg/kg, i.p. two times a week for 8 weeks, n=7-8/group) or the vehicle (5% DMSO). ABT702 treatment reduced blood glucose level in diabetic mice (∼20%; P<0.05). ABT702 also reduced albuminuria and markers of glomerular injury, nephrinuria and podocalyxin excretion levels, in diabetic mice. Renal NADPH oxidase activity and urinary thiobarbituric acid reactive substances (TBARS) excretion, indices of oxidative stress, were also elevated in diabetic mice and ABT702 significantly reduced these changes. ABT702 increased renal endothelial nitric oxide synthase expression (eNOS) and nitrate/nitrite excretion levels in diabetic mice. In addition, the diabetic mice displayed an increase in renal macrophage infiltration, in association with increased renal NFκB activation. Importantly, treatment with ABT702 significantly reduced all these inflammatory parameters (P<0.05). Furthermore, ABT702 decreased glomerular permeability and inflammation and restored the decrease in glomerular occludin expression in vitro in high glucose treated human glomerular endothelial cells. Collectively, the results suggest that the reno-protective effects of ABT702 could be attributed to the reduction in renal inflammation and oxidative stress in diabetic mice.

Diabetic nephropathy: traditional to proteomic markers

Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes and it is defined as a rise in the urinary albumin excretion (UAE) rate and abnormal renal function. Currently, changes in albuminuria are considered a hallmark of onset or progression of DN. However, some patients with diabetes have advanced renal pathological changes and progressive kidney function decline even if urinary albumin levels are in the normal range, indicating that albuminuria is not the perfect marker for the early detection of DN. The present article provides an overview of the literature reporting some relevant biomarkers that have been found to be associated with DN and that potentially may be used to predict the onset and/or monitor the progression of nephropathy. In particular, biomarkers of renal damage, inflammation, and oxidative stress may be useful tools for detection at an early stage or prediction of DN. Proteomic-based biomarker discovery represents a novel strategy to improve diagnosis, prognosis and treatment of DN; however, proteomics-based approaches are not yet available in most of the clinical chemistry laboratories. The use of a panel with a combination of biomarkers instead of urinary albumin alone seems to be an interesting approach for early detection of DN, including markers of glomerular damage (e.g., albumin), tubular damage (e.g., NAG and KIM-1), inflammation (e.g., TNF-α) and oxidative stress (e.g., 8-OHdG) because these mechanisms contribute to the development and outcomes of this disease.

Monocyte Chemoattractant Protein 1 (MCP-1) in obesity and diabetes

Monocyte Chemoattractant Protein-1 (MCP-1) is the first discovered and most extensively studied CC chemokine, and the amount of studies on its role in the etiologies of obesity- and diabetes-related diseases have increased exponentially during the past two decades. This review attempted to provide a panoramic perspective of the history, regulatory mechanisms, functions, and therapeutic strategies of this chemokine. The highlights of this review include the roles of MCP-1 in the development of obesity, diabetes, cardiovascular diseases, insulitis, diabetic nephropathy, and diabetic retinopathy. Therapies that specifically or non-specifically inhibit MCP-1 overproduction have been summarized.

Aberrant recruitment and activation of T cells in diabetic nephropathy

BACKGROUND/AIMS

Recent evidence has shown that an inflammatory process is involved in the development and progression of diabetic nephropathy. This study examined the impact of activated intrarenal lymphocytes in this inflammatory process.

METHODS

We studied T cell recruitment in mice with streptozotocin (STZ)-induced diabetes by flow cytometry and immunohistochemistry. The kidney biopsy specimens from patients with type 2 diabetes mellitus and diabetic nephropathy were evaluated by immunohistochemistry.

RESULTS

In flow cytometry, intrarenal CD3+ T cells were significantly increased in proteinuric mice at 20 weeks after STZ injection. However, the population of T cells and B cells in diabetic spleen was not different from that of control mice. Immunohistochemistry also showed a marked infiltration of interstitial CD4+, CD8+ T cells in diabetic kidney. Interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) mRNA expression was significantly increased in diabetic mouse kidney compared with controls. Interestingly, flow cytometry analysis of kidney-derived mononuclear cells from diabetic mice showed significantly increased production of IFN-γ and TNF-α by CD3+ T cells. Type 2 diabetic patients also showed a marked increase in CD4+, CD8+ and CD20+ cells in interstitium, and the number of CD4+ and CD20+ cells correlated with the amount of proteinuria.

CONCLUSION

Our results clearly showed that aberrant intrarenal infiltration and the activation of T cells in interstitium are the underlying immunopathological mechanisms of diabetic kidney injury.

The NLRP3 inflammasome promotes renal inflammation and contributes to CKD

Inflammation significantly contributes to the progression of chronic kidney disease (CKD). Inflammasome-dependent cytokines, such as IL-1β and IL-18, play a role in CKD, but their regulation during renal injury is unknown. Here, we analyzed the processing of caspase-1, IL-1β, and IL-18 after unilateral ureteral obstruction (UUO) in mice, which suggested activation of the Nlrp3 inflammasome during renal injury. Compared with wild-type mice, Nlrp3(-/-) mice had less tubular injury, inflammation, and fibrosis after UUO, associated with a reduction in caspase-1 activation and maturation of IL-1β and IL-18; these data confirm that the Nlrp3 inflammasome upregulates these cytokines in the kidney during injury. Bone marrow chimeras revealed that Nlrp3 mediates the injurious/inflammatory processes in both hematopoietic and nonhematopoietic cellular compartments. In tissue from human renal biopsies, a wide variety of nondiabetic kidney diseases exhibited increased expression of NLRP3 mRNA, which correlated with renal function. Taken together, these results strongly support a role for NLRP3 in renal injury and identify the inflammasome as a possible therapeutic target in the treatment of patients with progressive CKD.

Urinary biomarkers involved in type 2 diabetes: a review

Diabetes mellitus is one of the most challenging health concerns of the 21st century. With at least 30% of the diabetic population remaining undiagnosed, effective and early diagnosis is of critical concern. Development of a diagnostic test, more convenient and reliable than those currently used, would therefore be highly beneficial. Urine as a diagnostic medium allows for non-invasive detection of biomarkers, including some associated with type 2 diabetes and its complications. This review provides a synopsis of those urinary biomarkers that potentially may provide a basis for the development of improved diagnostic tests. Three main pathways for the sourcing of potential makers are identified: kidney damage, oxidative stress and low-grade inflammation including atherosclerosis/vascular damage. This review briefly presents each pathway and some of the most relevant urinary biomarkers that may be used to monitor the development or progression of diabetes and its complications. In particular, biomarkers of renal dysfunction such as transferrin, type IV collagen and N-acetyl-beta-D-glucosaminidase might prove to be more sensitive than urinary albumin, the current gold standard, in the detection of incipient nephropathy and risk assessment of cardiovascular disease. Inflammatory markers including orosomucoid, tumour necrosis factor-alpha, transforming growth factor-beta, vascular endothelial growth factor and monocyte chemoattractant protein-1, as well as oxidative stress markers such as 8-hydroxy-2'deoxyguanosine may also be useful biomarkers for diagnosis or monitoring of diabetic complications, particularly kidney disease. However, the sensitivity of these markers compared with albumin requires further investigation.

Effects of long-term pravastatin treatment on serum and urinary monocyte chemoattractant protein-1 levels and renal function in type 2 diabetic patients with normoalbuminuria

To explore the renoprotective and anti-inflammatory effects of pravastatin, we analyzed the changes in renal function and urinary monocyte chemoattractant protein-1 (MCP-1) level as a renal tubulointerstitial inflammatory biomarker and serum MCP-1 level as a systemic inflammatory biomarker following the introduction of treatment with 10 mg/day of pravastatin in 10 hyperlipidemic type 2 diabetic patients with normoalbuminuria. Twelve months of the pravastatin treatment did not affect urinary levels of albumin, transferrin, N-acetylglucosaminidase, or MCP-1 in the hyperlipidemic diabetic patients, whereas the treatment significantly reduced serum levels of MCP-1 in the patients. The pravastatin treatment effectively lowered low-density lipoprotein cholesterol (LDL-C) levels in the hyperlipidemic diabetic patients to levels nearly to those in 11 non-hyperlipidemic type 2 diabetic patients with normoalbuminuria. Interestingly, serum MCP-1 levels were significantly lower in the hyperlipidemic patients treated with pravastatin than in the non-hyperlipidemic patients. No significant correlation was observed between serum LDL-C and MCP-1 levels in all the data in the hyperlipidemic patients before and after the pravastatin treatment and in the non-hyperlipidemic patients. These results collectively indicate that pravastatin may ameliorate systemic vascular inflammation rather than local renal inflammation in hyperlipidemic type 2 diabetic patients with normoalbuminuria, independent of its cholesterol-lowering effects.

Association of polymorphisms in monocyte chemoattractant protein-1 promoter with diabetic kidney failure in Korean patients with type 2 diabetes mellitus

Monocyte chemoattractant protein-1 (MCP-1) is suggested to be involved in the progression of diabetic nephropathy. We investigated the association of the -2518 A/G polymorphism in the MCP-1 gene with progressive kidney failure in Korean patients with type 2 diabetes mellitus (DM). We investigated -2518 A/G polymorphism of the MCP-1 gene in type 2 DM patients with progressive kidney failure (n=112) compared with matched type 2 DM patients without nephropathy (diabetic control, n=112) and healthy controls (n=230). The overall genotypic distribution of -2518 A/G in the MCP-1 gene was not different in patients with type 2 DM compared to healthy controls. Although the genotype was not significantly different between the patients with kidney failure and the diabetic control (p=0.07), the A allele was more frequent in patients with kidney failure than in DM controls (42.0 vs. 32.1%, p=0.03). The carriage of A allele was significantly associated with kidney failure (68.8 vs. 54.5%, OR 1.84, 95% CI 1.07-3.18). In logistic regression analysis, carriage of A allele retained a significant association with diabetic kidney failure. Our result shows that the -2518 A allele of the MCP-1 gene is associated with kidney failure in Korean patients with type 2 DM.

Urinary excretion of monocyte chemoattractant protein-1: a biomarker of active tubulointerstitial damage in patients with glomerulopathies

BACKGROUND/AIMS

The urinary concentration of the monocyte chemoattractant protein-1 (uMCP-1) chemokine is increased in several proteinuric and/or inflammatory renal diseases. In the present study, we evaluated the association between uMCP-1 and renal function, proteinuria, glomerular and interstitial macrophage infiltration, and renal fibrosis in patients with primary and secondary glomerulopathies diagnosed by renal biopsy.

METHODS

Thirty-seven patients aged 32.6 +/- 7.7 years were studied. uMCP-1 was determined by ELISA. Renal macrophage expression (CD68 positive cells) is reported as number of macrophages/10(4) microm2 of the cortical tubulointerstitial (TI) area or of glomerular capillary tuft area. Cortical interstitial fibrosis was quantitated by PicroSirius red staining under polarized light by a computerized manner.

RESULTS

The uMCP-1 ratio (pg/ml/urinary creatinine mg/ml) was positively correlated (Spearman coefficient) with proteinuria (r = 0.4629; p < 0.005) and number of macrophages in the cortical TI area (r = 0.64; p = 0.0005), and negatively correlated with creatinine clearance (r = -0.4877; p < 0.001). The uMCP-1 ratio was not significantly correlated with number of macrophages/glomerular capillary tuft area (r = 0.27; p = 0.19) or with percent cortical interstitial fibrosis (r = 0.08; p = 0.62).

CONCLUSIONS

The uMCP-1 excretion is a biomarker of the inflammatory activity of the TI area, and does not reflect chronic interstitial damage.

Renal upregulation of HO-1 reduces albumin-driven MCP-1 production: implications for chronic kidney disease

Proteinuria contributes to chronic kidney disease by stimulating renal tubular epithelial cells to produce cytokines such as monocyte chemoattractant protein-1 (MCP-1). The present study determined whether cellular overexpression of heme oxygenase-1 (HO-1) can influence albumin-stimulated MCP-1 production. In response to bovine serum albumin, NRK-52E cells constitutively overexpressing HO-1 (HO-1 OE cells) exhibit less induction of MCP-1 mRNA and less production of MCP-1 protein compared with similarly treated, control NRK-52E cells (CON cells). In wild-type NRK-52E cells, and under these conditions, we demonstrate that the induction of MCP-1 is critically dependent on intact NF-κB binding sites in the MCP-1 promoter. In response to albumin, CON cells exhibit activation of NF-κB, and this is reduced in HO-1 OE cells. Albumin also activates ERK1/2 and increases ERK activity, both of which are exaggerated in HO-1 OE cells. Studies with an inhibitor of MAPK/ERK kinase (U0126) demonstrate that the inhibitory effects of U0126 on MCP-1 production are attenuated in HO-1 OE cells. We conclude that HO-1 overexpression in the proximal tubule reduces MCP-1 production in response to albumin, and this occurs, at least in part, by inhibiting an ERK-dependent, NF-κB-dependent pathway at a site that is distal to the activation of ERK. These findings suggest that the induction of HO-1 in the proximal tubule, as occurs in chronic kidney disease, may be a countervailing response that reduces albumin-stimulated production of cytokines such as MCP-1.

Pentoxifylline ameliorates proteinuria through suppression of renal monocyte chemoattractant protein-1 in patients with proteinuric primary glomerular diseases

Proteinuria (albuminuria) reflects dysfunction of the glomerular permeability barrier in which inflammatory cytokines play a key role. Pentoxifylline (PTX) is a phosphodiesterase inhibitor that possesses potent anti-inflammatory and immunomudulatory effects. This study evaluated the effectiveness of PTX to reduce proteinuria and inflammatory mediators in patients with proteinuric primary glomerular diseases. Seventeen patients with primary glomerular diseases, a persistent spot proteinuria exceeding 1.5 g/g creatinine (Cr) and a glomerular filtration rate between 24 and 115 ml/min/1.73 m(2) were treated with PTX 400 mg twice daily for 6 months. Before and after the treatment, serum Cr, plasma renin activity and aldosterone concentrations, plasma and urinary tumor necrosis factor (TNF)-alpha, interleukin-1beta and monocyte chemoattractant protein (MCP)-1, as well as urinary protein and Cr were measured. PTX significantly reduced urinary protein excretion, along with an increase of serum albumin. A significant correlation existed between the basal urinary protein/Cr and the basal urinary MCP-1/Cr ratios. PTX lowered the urinary MCP-1/Cr ratio, and the percent reduction of urinary protein/Cr ratio correlated directly with the precent decrease of urinary MCP-1/Cr ratio after PTX treatment. There was no significant change in blood pressure, renal function, biochemical parameters, plasma renin activity and aldosterone concentrations, or plasma TNF-alpha and MCP-1 levels during the study. In conclusion, administration of PTX 800 mg per day is safe and effective for reducing proteinuria in patients with proteinuric primary glomerular diseases. This beneficial effect occurs in close association with a reduction of urinary MCP-1 excretion.

The relationship between albuminuria, MCP-1/CCL2, and interstitial macrophages in chronic kidney disease

Glomerular-derived proteins may activate tubular cells to express the macrophage-directed chemokine monocyte chemoattractant protein-1 (MCP-1/CCL2). Macrophages at interstitial sites have a central role in directing renal scarring. We have prospectively assessed the relationship between albuminuria, urinary MCP-1/CCL2, interstitial macrophage infiltration, in situ damage, and clinical outcomes in a large group of patients with chronic kidney disease. We studied 215 patients and quantified albumin-creatinine ratio (ACR), urinary MCP-1/CCL2, interstitial macrophage numbers, and in situ damage. ACR correlated with urinary MCP-1/CCL2 (correlation 0.499; P<0.001), interstitial macrophage numbers (correlation 0.481; P<0.001), and index of chronic damage (correlation 0.363; P<0.001). Macrophage numbers closely correlated with in situ damage (correlation 0.755; P<0.001). By multivariate analysis ACR, urinary MCP-1/CCL2, and interstitial macrophage numbers were interdependent. By Kaplan-Meier survival analysis albuminuria, urinary MCP-1/CCL2, interstitial macrophages, and chronic damage predict the outcome. ACR, macrophage numbers, chronic damage, and creatinine independently predicted renal survival. The association of ACR with other variables was strongest in patients with less advanced disease states. There is a close association between albuminuria, urinary MCP-1/CCL2, and interstitial macrophage infiltration with in situ damage and clinical outcomes. These findings support the hypothesis that albuminuria triggers tubular MCP-1/CCL2 expression with subsequent macrophage infiltration. These processes may represent the dominant pathway for the progression of renal injury before the establishment of advanced renal scarring.

Long-term blockade of angiotensin AT1 receptors increases survival of obese Zucker rats

Despite the well-documented effect of irbesartan, an angiotensin AT1 receptor antagonist, on diabetic nephropathy, its effect on mortality related to multiple metabolic risk factors is unknown. To address this question, obese fa/fa Zucker rats were submitted to a 13-month treatment by irbesartan (30 mg/kg/day p.o.). Vehicle-treated obese fa/fa Zucker rats exhibited an important mortality (72%), which was markedly reduced by irbesartan (22%, P<0.05). Mortality in control lean fa/+ rats attained 12%. Irbesartan diminished the elevation in urinary protein excretion, plasma creatinine and urea nitrogen levels, and reduced the extent of glomerular and tubulo-interstitial lesions together with a reduction of urinary monocyte chemoattractant protein-1 excretion in fa/fa Zucker rats. Irbesartan treatment prevented the rise in plasma total cholesterol, triglycerides and glucose levels, and partially corrected low-density lipoprotein/high-density lipoprotein (LDL/HDL) cholesterol ratio in fa/fa Zucker rats. Therefore, prolonged irbesartan treatment preserves renal function and metabolic profile, and substantially increases survival in obese fa/fa Zucker rats.

Genetics of diabetic nephropathy in type 2 DM: candidate gene analysis for the pathogenic role of inflammation

Hypertension, poor glycemic control and albuminuria are well known risk factors for diabetic nephropathy, but these factors do not explain all of the inter-individual variabilities in the rate of progression to kidney failure. Recent evidence showed that genetic predisposition affected the hyperglycemia-induced nephrotoxicity in patients with type 2 diabetes mellitus (DM). We reviewed the present state of knowledge concerning the relationship between genetics and diabetic nephropathy in type 2 DM. However, the results are inconclusive and the genetic determinants of diabetic nephropathy are not fully understood. In addition, genetic background of nephropathy in type 2 DM was thought to be more complex than in type 1 DM. Recent studies suggested that the inflammation would be an essential component of type 2 DM and its complications. We postulated that increased systemic and/or intrarenal inflammation in high glucose milieu is important in the pathogenesis of nephropathy in patients with type 2 DM. To investigate the impact of inflammation on diabetic nephropathy, we studied several polymorphisms in genes encoding inflammatory cytokine and chemokine in patients with type 2 DM. Among them, -511 C/T in interleukin-1beta (IL-1beta), tandem repeat in IL-1 receptor antagonist (IL-1Ra), -308 G/A in tumour necrosis factor-alpha (TNF-alpha) were significantly associated with an increased risk of kidney failure. In addition, some of them were remarkably different from those previously reported in the NCBI or literature based on the western population. Our results suggest that inflammation could play a pathogenic role in diabetic nephropathy in type 2 DM. A better understanding of genetic factors predisposing to diabetic nephropathy would not only help to identify diabetic patients at risk, but also be helpful to unveil the pathogenesis of DN.

Upregulation of angiotensin II type 1 receptor, inflammatory mediators, and enzymes of arachidonate metabolism in obese Zucker rat kidney: reversal by angiotensin II type 1 receptor blockade

BACKGROUND

Severe obesity can result in proteinuria and progressive glomerulosclerosis in humans and experimental animals. The associated renal disease is ameliorated by weight reduction and/or blockade of the renin-angiotensin system. Various growth factors, cytokines, and lipid mediators are implicated in the pathogenesis of renal disease. To explore the possible involvement of these mediators in obesity-induced renal disease, we examined the expression of key enzymes of arachidonate metabolism and inflammatory genes in untreated and losartan-treated obese Zucker rats, a model of obesity, insulin resistance, and renal injury.

METHODS AND RESULTS

Seven-week-old male obese Zucker rats were randomized to losartan-treated (100 mg/L drinking H2O) and untreated groups, with lean Zucker rats as controls. After 4 months, RNA and protein were obtained from renal cortical tissue for relative reverse transcription-polymerase chain reaction, Western blots, and immunohistochemistry. Compared with the lean controls, obese Zucker rats showed significant glomerular matrix expansion and increased mRNA expression of the extracellular matrix protein fibronectin, inflammatory mediators interleukin-6 and monocyte chemoattractant protein-1, and 2 major enzymes of arachidonate metabolism, namely, 12/15-lipoxygenase and cyclooxygenase-2. This was associated with significant increases in p38 and extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase activities and marked upregulation of angiotensin II type 1 receptor (AT1R) mRNA and protein expression. These abnormalities and the associated glomerulopathy and proteinuria were prevented by administration of the AT1R blocker losartan.

CONCLUSIONS

These findings indicate that obesity-induced glomerulopathy is associated with upregulation of key inflammatory mediators. These events are associated with and perhaps in part due to upregulation of AT1R, as evidenced by their reversal with AT1R blocker treatment.

Soluble fibronectin induces chemokine gene expression in renal tubular epithelial cells

BACKGROUND

Increasing proteinuria in kidney disease is associated with an increased risk of renal failure. Urinary proteins such as albumin induce inflammatory signaling and gene expression in tubular epithelial cells (TECs). Fibronectin is an extracellular matrix protein that can exist in soluble form and is excreted in the urine of patients with glomerular disease.

METHODS

To explore the impact of soluble fibronectin on tubular epithelium, murine TECs were stimulated with soluble fibronectin and chemokine mRNA was determined by RNase protection assay.

RESULTS

Fibronectin induced the expression of inflammatory chemokine genes, including monocyte chemoattractant protein-1 (MCP-1) (CCL2) and macrophage inflammatory protein-2 (MIP-2) within 2 hours in a dose-dependent manner. Phosphorylation of Src family tyrosine kinases was also increased in TECs following exposure to fibronectin. Src tyrosine kinases were involved in the fibronectin activation of MCP-1 since the Src inhibitors SU6656 and PP2 effectively reduced the induction of this chemokine. Fibronectin also induced the phosphorylation of extracellular signal-regulated protein kinase (ERK1/2) within minutes in TECs. The ERK kinase (MEK1/2) inhibitor U0126 inhibited the fibronectin induction of MCP-1 mRNA suggesting that ERK1/2 was also involved in this inflammatory pathway. Furthermore, fibronectin also induced phosphorylation of IkappaBalpha within 20 minutes in TECs. The nuclear factor-kappaB (NF-kappaB) inhibitors N-acetyl-L-cysteine (NAC) and pyrrolidinecarbodithioic acid (PDTC) effectively blocked fibronectin induction of MCP-1 mRNA.

CONCLUSION

Soluble fibronectin activates MCP-1 gene expression in TECs via Src tyrosine kinases, ERK1/2 and NF-kappaB. These data provide further support to the concept that proteinuria per se contributes to the tubulointerstitial injury observed in glomerular disease.