Common pathophysiological mechanisms of chronic kidney disease: Therapeutic perspectives

Renoprotective effects of novel interleukin-1 receptor-associated kinase 4 inhibitor AS2444697 through anti-inflammatory action in 5/6 nephrectomized rats

Renal inflammation is a final common pathway of chronic kidney disease (CKD), and its progression can be used to effectively gauge the degree of renal dysfunction. Interleukin-1 (IL-1) receptor-associated kinase 4 (IRAK-4) has been reported to be a pivotal molecule for IL-1 receptor- and Toll-like receptor-induced signaling and activation of proinflammatory mediators. In this study, we hypothesized that if inflammation plays a key role in renal failure, then the anti-inflammatory effect of IRAK-4 inhibitor should be effective in improving CKD. To determine its pharmacological potency, we investigated the renoprotective properties of the novel IRAK-4 inhibitor AS2444697 (N-[3-carbamoyl-1-(tetrahydro-2H-pyran-4-yl)-1H-pyrazol-4-yl]-2-(2-methylpyridin-4-yl)-1,3-oxazole-4-carboxamide hydrochloride (1:1)) in 5/6 nephrectomized (Nx) rats, a model of CKD. Six weeks' repeated administration of AS2444697 (0.3-3 mg/kg, twice daily) dose-dependently and significantly reduced urinary protein excretion and prevented the development of glomerulosclerosis and interstitial fibrosis without affecting the blood pressure. In addition, AS2444697 showed beneficial effects on renal function as demonstrated by the decrease in levels of plasma creatinine and blood urea nitrogen and attenuation of decline in creatinine clearance. 5/6 Nx rats exhibited low-grade inflammation as evidenced by increased renal mRNA expression and plasma levels of proinflammatory cytokines (IL-1β, IL-6, TNF-α, and MCP-1) and C-reactive protein as a marker of systemic inflammation. AS2444697 significantly reduced or showed a decreasing trend in expression and levels of these inflammatory parameters. These results suggest that AS2444697 suppresses the progression of chronic renal failure via anti-inflammatory action and may therefore be potentially useful in treating CKD patients.

Relevant role of PKG in the progression of fibrosis induced by TNF-like weak inducer of apoptosis

TNF-like weak inducer of apoptosis (TWEAK) is an inflammatory cytokine that activates the FGF-inducible 14 receptor. Both TWEAK and the FGF-inducible 14 receptor are constitutively expressed in the kidney. TWEAK has been shown to modulate several biological responses, such as inflammation, proliferation, differentiation, and apoptosis, that contribute to kidney injury. However, the role of TWEAK in fibrosis and TWEAK-activated intracellular signaling pathways remain poorly understood. We tested the hypothesis that TWEAK can be a potent inducer of renal fibrosis by increasing transforming growth factor (TGF)-β1 expression (a well-known switch in the fibrosis process) through PKG-I downregulation. We showed that in human mesangial cells, TWEAK increased TGF-β1 expression and activity, leading to higher levels of the extracellular matrix protein fibronectin and decreased PKG-I expression and activity via the Ras pathway. PKG-I activation with 8-bromo-cGMP, Ras inactivation with dominant negative Ras, or Ras pathway inhibition with the ERK1/2 inhibitor PD-98059 resulted in the prevention of TWEAK-induced TGF-β1 upregulation. In vivo, exogenous administration of TWEAK to wild-type mice downregulated kidney PKG-I and increased kidney TGF-β1 expression. These effects were blunted in H-Ras knockout mice. Together, these data demonstrate, for the first time, the key role of PKG-I in TGF-β1 induction by TWEAK in kidney cells.

TREM-1 regulates macrophage polarization in ureteral obstruction

Chronic kidney disease (CKD) is an emerging worldwide public health problem. Inflammatory cell infiltration and activation during the early stages in injured kidneys is a common pathologic feature of CKD. Here, we determined whether an important inflammatory regulator, triggering receptor expressed on myeloid cells (TREM)-1, is upregulated in renal tissues collected from mouse ureteral obstruction-induced nephritis. TREM-1 is crucial for modulating macrophage polarization, and has a pivotal role in mediating tubular injury and interstitial collagen deposition in obstructive nephritis. Lysates from nephritic kidneys triggered a TREM-1-dependent M1 polarization ex vivo, consistent with the observation that granulocyte-macrophage colony-stimulating factor (GM-CSF)-derived M1 macrophages express higher levels of TREM-1 in comparison with M-CSF-derived cells. Moreover, agonistic TREM-1 cross-link significantly strengthens the inductions of iNOS and GM-CSF in M1 cells. These observations are validated by a strong clinical correlation between infiltrating TREM-1-expressing/iNOS-positive macrophages and renal injury in human obstructive nephropathy. Thus, TREM-1 may be a potential diagnostic and therapeutic target in human kidney disease.

Association of sequence polymorphism in the mitochondrial D-loop with chronic kidney disease

BACKGROUND

The mitochondrial displacement loop (D-loop) is known to accumulate mutations and single nucleotide polymorphisms (SNPs) at a higher frequency than other regions of mitochondrial DNA (mtDNA).

METHODS

This is a case-control study. We sequenced SNPs in the D-loop of mtDNA and investigated their association with the risk of chronic kidney disease (CKD).

RESULTS

A total of 144 SNPs referring to the positions of the Revised Cambridge Reference Sequence (rCRS) for mitochondrial genome were identified in a case-control study. The minor alleles of nucleotides 73G, 146C, 150T, 194T, 195C and 310C were associated with an increased risk for CKD patients.

CONCLUSION

Analysis of genetic polymorphisms in the mitochondrial D-loop can help identify the people who are at a high risk of developing chronic kidney disease. These SNPs can be considered as potential predictors for CKD.

Interferon-γ Reduces the Proliferation of Primed Human Renal Tubular Cells

BACKGROUND/AIMS

Chronic kidney disease (CKD) is a progressive deterioration of the kidney function, which may eventually lead to renal failure and the need for dialysis or kidney transplant. Whether initiated in the glomeruli or the tubuli, CKD is characterized by progressive nephron loss, for which the process of tubular deletion is of key importance. Tubular deletion results from tubular epithelial cell death and defective repair, leading to scarring of the renal parenchyma. Several cytokines and signaling pathways, including transforming growth factor-β (TGF-β) and the Fas pathway, have been shown to participate in vivo in tubular cell death. However, there is some controversy about their mode of action, since a direct effect on normal tubular cells has not been demonstrated. We hypothesized that epithelial cells would require specific priming to become sensitive to TGF-β or Fas stimulation and that this priming would be brought about by specific mediators found in the pathological scenario.

METHODS

Herein we studied whether the combined effect of several stimuli known to take part in CKD progression, namely TGF-β, tumor necrosis factor-α, interferon-γ (IFN-γ), and Fas stimulation, on primed resistant human tubular cells caused cell death or reduced proliferation.

RESULTS

We demonstrate that these cytokines have no synergistic effect on the proliferation or viability of human kidney (HK2) cells. We also demonstrate that IFN-γ, but not the other stimuli, reduces the proliferation of cycloheximide-primed HK2 cells without affecting their viability.

CONCLUSION

Our results point at a potentially important role of IFN-γ in defective repair, leading to nephron loss during CKD.

Medication-prescribing patterns of primary care physicians in chronic kidney disease

BACKGROUND

We investigated the medication-prescribing patterns of primary care physicians in chronic kidney disease (CKD).

SUBJECTS AND METHODS

This cross-sectional study included 3,310 medical doctors who graduated from Jichi Medical University. The study instrument was a self-administered questionnaire to investigate their age group, specialty, workplace, existence of a dialysis center at workplace, and their prescription frequencies (high, moderate, low, very low) of the following agents--calcium (Ca) inhibitors, angiotensin-converting enzyme inhibitors (ACEIs), angiotensin II receptor antagonist (ARBs), statins, anti-platelet agents, erythropoietin (Epo), AST-120, vitamin D, and sodium hydrogen carbonate (NaHCO(3)).

RESULTS

From a total of 933 responses, 547 (61.0 %) medical doctors prescribed medication for CKD. The prescription frequencies of Ca inhibitors, ACEIs, and ARBs were high (>90 %, high + moderate), those of statins, anti-platelet agents, Epo, and AST-120 were moderate (90-50 %, high + moderate), and those of vitamin D and NaHCO(3) were low (<50 %, high + moderate). The primary care physician's specialty was significantly associated with their prescription frequency of Ca inhibitors (p < 0.01). Their workplace was significantly associated with their prescription frequency of ACEIs (p < 0.01), ARBs (p < 0.01), Epo (p < 0.01) and vitamin D (p < 0.01). The existence of a dialysis center at their workplace was significantly associated with their prescription frequency of Epo (p < 0.01), vitamin D (p < 0.01) and NaHCO(3) (p < 0.01). Their age was not associated with their prescription frequency of any agents.

CONCLUSION

Antihypertensives were highly prescribed, and vitamin D and NaHCO(3) were less prescribed by primary care physicians for CKD. There were certain associations between the prescribing patterns of primary care physicians for CKD and their specialty, workplace and the existence of a dialysis center at their workplace.

ALK1-Smad1/5 signaling pathway in fibrosis development: friend or foe?

Fibrosis is a common phenomenon associated with several pathologies, characterized by an excessive extracellular matrix deposition that leads to a progressive organ dysfunction. Thus fibrosis has a relevant role in chronic diseases affecting the kidney, the liver, lung, skin (scleroderma) and joints (arthritis), among others. The pathogenesis of fibrosis in different organs share numerous similarities, being one of them the presence of activated fibroblasts, denominated myofibroblast, which act as the main source of extracellular matrix proteins. Transforming growth factor beta-1 (TGF-β1) is a profibrotic cytokine that plays a pivotal role in fibrosis. The TGF-β1/ALK5/Smad3 signaling pathway has been studied in fibrosis extensively. However, an increasing number of studies involving the ALK1/Smad1 pathway in the fibrotic process exist. In this review we offer a perspective of the function of ALK1/Smad1 pathway in renal fibrosis, liver fibrosis, scleroderma and osteoarthritis, suggesting this pathway as a powerful therapeutical target. We also propose several strategies to modulate the activity of this pathway and its consequences in the fibrotic process.

Co-medication of pravastatin and paroxetine-a categorical study

Electronic Medical Records (EMRs) are wealthy storehouses of patient information, to which data mining techniques can be prudently applied to reveal clinically significant patterns. Detecting patterns in drug-drug interactions, leading to adverse drug reactions is a powerful application of EMR data mining. Adverse effects of drug treatments can be investigated by mining clinical laboratory tests data which are reliable indicators of abnormal physiological functions. We report here the co-medication effects of pravastatin (HMG-CoA reductase inhibitor) and paroxetine (selective serotonin reuptake inhibitor (SSRI) anti-depressant) on significant clinical parameters, identified through a data mining analysis conducted on the Allscripts data warehouse. We found that the concomitant drug treatments of pravastatin and paroxetine increased the mean values of glucose serum from 113.2 to 132.1 mg/dL and international normalized ratio (INR) from 2.18 to 2.52, respectively. It also decreased the mean values of estimated glomerular filtration rate (eGFR) from 43 to 37 mL/min/1.73 m(3) and blood CO2 levels from 24.8 to 23.9 mEq/L respectively. Our findings indicate that co-medication of pravastatin and paroxetine might have significant impact on blood anti-coagulation, kidney function, and glucose homeostasis. Our methodology can be applied to any EMR data set to reveal co-medication effects of any drug pairs.

Optimized metabolomic approach to identify uremic solutes in plasma of stage 3-4 chronic kidney disease patients

Background

Chronic kidney disease (CKD) is characterized by the progressive accumulation of various potential toxic solutes. Furthermore, uremic plasma is a complex mixture hampering accurate determination of uremic toxin levels and the identification of novel uremic solutes.

Methods

In this study, we applied ¹H-nuclear magnetic resonance (NMR) spectroscopy, following three distinct deproteinization strategies, to determine differences in the plasma metabolic status of stage 3–4 CKD patients and healthy controls. Moreover, the human renal proximal tubule cell line (ciPTEC) was used to study the influence of newly indentified uremic solutes on renal phenotype and functionality.

Results

Protein removal via ultrafiltration and acetonitrile precipitation are complementary techniques and both are required to obtain a clear metabolome profile. This new approach, revealed that a total of 14 metabolites were elevated in uremic plasma. In addition to confirming the retention of several previously identified uremic toxins, including p-cresyl sulphate, two novel uremic retentions solutes were detected, namely dimethyl sulphone (DMSO₂) and 2-hydroxyisobutyric acid (2-HIBA). Our results show that these metabolites accumulate in non-dialysis CKD patients from 9±7 µM (control) to 51±29 µM and from 7 (0–9) µM (control) to 32±15 µM, respectively. Furthermore, exposure of ciPTEC to clinically relevant concentrations of both solutes resulted in an increased protein expression of the mesenchymal marker vimentin with more than 10% (p<0.05). Moreover, the loss of epithelial characteristics significantly correlated with a loss of glucuronidation activity (Pearson r = −0.63; p<0.05). In addition, both solutes did not affect cell viability nor mitochondrial activity.

Conclusions

This study demonstrates the importance of sample preparation techniques in the identification of uremic retention solutes using ¹H-NMR spectroscopy, and provide insight into the negative impact of DMSO₂ and 2-HIBA on ciPTEC, which could aid in understanding the progressive nature of renal disease.

Transurethral resection of the prostate in kidney transplant recipients: urological and renal functional outcomes at long-term follow-up

OBJECTIVES

To assess prospectively the safety and efficacy of transurethral resection of the prostate (TURP) for the treatment of lower urinary tract symptoms attributable to benign prostatic hyperplasia (BPH) in patients who have undergone renal transplantation (RT). To assess the impact of TURP on renal graft function.

PATIENTS AND METHODS

Urological and renal functional outcomes of TURP performed in RT recipients for treatment of lower urinary tract obstruction attributable to BPH were prospectively assessed in a series of 32 consecutive patients with follow-up of ≥48 months. Maximum urinary flow rate (Qmax ) at uroflowmetry, International Prostate Symptom Score (IPSS), post-void residual urine volume (PVR), haemoglobin and serum creatinine (sCr) levels were recorded before TURP and 1, 6, 24 and 48 months after the procedure. The trends in these variables after TURP were evaluated. Early and delayed complications were assessed and graded according to the Clavien classification system.

RESULTS

TURP was performed at a mean of 6 months after RT. No intraoperative complications occurred. Seven postoperative complications were observed (21.9%): two Clavien grade II and five Clavien grade IIIa. Qmax , IPSS and PVR improved significantly after surgery and the improvement was maintained until 48 months. No patient required a repeat TURP during follow-up. SCr levels significantly decreased 1 and 6 months after TURP and did not significantly increase at long-term follow-up.

CONCLUSIONS

TURP for lower urinary tract obstruction attributable to BPH in RT recipients is safe and effective since it improves urinary flow, bladder emptying and related urinary symptoms. TURP allows an early significant improvement of graft function that is maintained at a follow-up of 48 months.

Role of TGF-β in chronic kidney disease: an integration of tubular, glomerular and vascular effects

Transforming growth factor beta (TGF-β) has been recognized as an important mediator in the genesis of chronic kidney diseases (CKD), which are characterized by the accumulation of extracellular matrix (ECM) components in the glomeruli (glomerular fibrosis, glomerulosclerosis) and the tubular interstitium (tubulointerstitial fibrosis). Glomerulosclerosis is a major cause of glomerular filtration rate reduction in CKD and all three major glomerular cell types (podocytes or visceral epithelial cells, mesangial cells and endothelial cells) participate in the fibrotic process. TGF-β induces (1) podocytopenia caused by podocyte apoptosis and detachment from the glomerular basement membrane; (2) mesangial expansion caused by mesangial cell hypertrophy, proliferation (and eventually apoptosis) and ECM synthesis; (3) endothelial to mesenchymal transition giving rise to glomerular myofibroblasts, a major source of ECM. TGF-β has been shown to mediate several key tubular pathological events during CKD progression, namely fibroblast proliferation, epithelial to mesenchymal transition, tubular and fibroblast ECM production and epithelial cell death leading to tubular cell deletion and interstitial fibrosis. In this review, we re-examine the mechanisms involved in glomerulosclerosis and tubulointerstitial fibrosis and the way that TGF-β participates in renal fibrosis, renal parenchyma degeneration and loss of function associated with CKD.

HSP27 and HSP70 serum and urine levels in patients suffering from chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a condition associated with inflammation and high levels of uremic toxins and reactive oxygen species. As a counterregulation to systemic stress heat shock proteins (HSP) are increased expressed to minimize cell death and preserve cell integrity by inhibiting apoptotic pathways. The aim of this study was to determine HSP27 and HSP70 concentrations in sera and urine of patients suffering from CKD.

METHODS

Concentrations of HSP27 and HSP70 in urine and serum were determined in 119 patients with CKD stages 1 to 5 and 23 healthy volunteers by using ELISA technique.

RESULTS

HSP27 serum levels were significantly elevated in patients suffering from CKD stages 3 to 5 as well as fractional HSP27 excretion in stages 2-5 versus healthy controls. Absolute HSP70 urinary values were significantly elevated in stages 4 and 5 and fractional HSP70 excretion was increased in stage 5 compared to controls. Moreover, ROC curve analysis showed the potential of urine and especially serum HSP levels to identify various stages of CKD.

CONCLUSION

We provide evidence for elevated HSP27 concentrations in serum and urine and increased HSP70 excretion levels in patients suffering from CKD. Moreover, our results show that HSP levels might offer potential to examine the stages of CKD as well as the disease course which could further promote individually adjusted treatment planning.

Uremic toxins inhibit transport by breast cancer resistance protein and multidrug resistance protein 4 at clinically relevant concentrations

During chronic kidney disease (CKD), there is a progressive accumulation of toxic solutes due to inadequate renal clearance. Here, the interaction between uremic toxins and two important efflux pumps, viz. multidrug resistance protein 4 (MRP4) and breast cancer resistance protein (BCRP) was investigated. Membrane vesicles isolated from MRP4- or BCRP-overexpressing human embryonic kidney cells were used to study the impact of uremic toxins on substrate specific uptake. Furthermore, the concentrations of various uremic toxins were determined in plasma of CKD patients using high performance liquid chromatography and liquid chromatography/tandem mass spectrometry. Our results show that hippuric acid, indoxyl sulfate and kynurenic acid inhibit MRP4-mediated [³H]-methotrexate ([³H]-MTX) uptake (calculated Ki values: 2.5 mM, 1 mM, 25 µM, respectively) and BCRP-mediated [³H]-estrone sulfate ([³H]-E1S) uptake (Ki values: 4 mM, 500 µM and 50 µM, respectively), whereas indole-3-acetic acid and phenylacetic acid reduce [³H]-MTX uptake by MRP4 only (Ki value: 2 mM and IC₅₀ value: 7 mM, respectively). In contrast, p-cresol, p-toluenesulfonic acid, putrescine, oxalate and quinolinic acid did not alter transport mediated by MRP4 or BCRP. In addition, our results show that hippuric acid, indole-3-acetic acid, indoxyl sulfate, kynurenic acid and phenylacetic acid accumulate in plasma of end-stage CKD patients with mean concentrations of 160 µM, 4 µM, 129 µM, 1 µM and 18 µM, respectively. Moreover, calculated Ki values are below the maximal plasma concentrations of the tested toxins. In conclusion, this study shows that several uremic toxins inhibit active transport by MRP4 and BCRP at clinically relevant concentrations.

Etiopathology of chronic tubular, glomerular and renovascular nephropathies: clinical implications

Chronic kidney disease (CKD) comprises a group of pathologies in which the renal excretory function is chronically compromised. Most, but not all, forms of CKD are progressive and irreversible, pathological syndromes that start silently (i.e. no functional alterations are evident), continue through renal dysfunction and ends up in renal failure. At this point, kidney transplant or dialysis (renal replacement therapy, RRT) becomes necessary to prevent death derived from the inability of the kidneys to cleanse the blood and achieve hydroelectrolytic balance. Worldwide, nearly 1.5 million people need RRT, and the incidence of CKD has increased significantly over the last decades. Diabetes and hypertension are among the leading causes of end stage renal disease, although autoimmunity, renal atherosclerosis, certain infections, drugs and toxins, obstruction of the urinary tract, genetic alterations, and other insults may initiate the disease by damaging the glomerular, tubular, vascular or interstitial compartments of the kidneys. In all cases, CKD eventually compromises all these structures and gives rise to a similar phenotype regardless of etiology. This review describes with an integrative approach the pathophysiological process of tubulointerstitial, glomerular and renovascular diseases, and makes emphasis on the key cellular and molecular events involved. It further analyses the key mechanisms leading to a merging phenotype and pathophysiological scenario as etiologically distinct diseases progress. Finally clinical implications and future experimental and therapeutic perspectives are discussed.