Rat Remnant Kidney Research Articles

NaHCO3 loading causes increased arterial pressure and kidney damage in rats with chronic kidney disease.

Sodium bicarbonate (NaHCO3) is commonly utilized as a therapeutic to treat metabolic acidosis in people with chronic kidney disease (CKD). While increased dietary sodium chloride (NaCl) is known to promote volume retention and increase blood pressure, the effects of NaHCO3 loading on blood pressure and volume retention in CKD remain unclear. In the present study, we compared the effects of NaCl and NaHCO3 loading on volume retention, blood pressure, and kidney injury in both 2/3 and 5/6 nephrectomy remnant kidney rats, a well-established rodent model of CKD. We tested the hypothesis that NaCl loading promotes greater volume retention and increases in blood pressure than equimolar NaHCO3. Blood pressure was measured 24 h daily using radio telemetry. NaCl and NaHCO3 were administered in drinking water ad libitum or infused via indwelling catheters. Rats were housed in metabolic cages to determine volume retention. Our data indicate that both NaHCO3 and NaCl promote hypertension and volume retention in remnant kidney rats, with salt-sensitivity increasing with greater renal mass reduction. Importantly, while NaHCO3 intake was less pro-hypertensive than equimolar NaCl intake, NaHCO3 was not benign. NaHCO3 loading significantly elevated blood pressure and promoted volume retention in rats with CKD when compared with control rats receiving tap water. Our findings provide important insight into the effects of sodium loading with NaHCO3 in CKD and indicate that NaHCO3 loading in patients with CKD is unlikely to be benign.

PS-B04-1: ANTI-HYPERTENSIVE AND ANTI-PROTEIURIC EFFECTS OF MELINJO SEED EXTRACT IN THE RAT REMNANT KIDNEY MODEL

Melinjo (Gnetum gnemon L.) is a fruit native to Indonesia and is considered as a healthy food. Melinjo resveratrol (MjR) is a resveratrol derivative extracted from the melinjo seed. Interestingly, recent literatures have documented that MjR exhibits the angiotensin converting enzyme inhibitory activity. Hence, we hypothesized that MjR exhibits beneficial effects in the chronic kidney disease. In order to test our hypothesis, MjR was administered in the rat remnant kidney (RK) model. Rats were divided into three groups: sham operated rats (SHAM, n = 4), untreated remnant kidney rats (RK, n = 5), RK rats treated with MjR 300 mg/kg/day (RK + MjR, n = 5). The rats were sacrificed at twelve weeks. Blood pressure and urinary protein levels significantly increased whereas creatinine clearance (CCr) significantly descread in the RK group compared to the SHAM group at twelve weeks. MjR significantly reduced systolic blood pressure (108 ± 2 vs. 147 ± 2 mmHg, p < 0.05) as measured by tail-cuff methods. Urine protein excretion was significantly ameliorated by MjR compared with that in RK (79.8 ± 54.8 vs. 269 ± 87.5 mg/day, p < 0.0015). Although Ccr was not altered in RK + MjR compared with RK rats, histological evaluation revealed that the glomerular sclerosis was attenuated in RK + MjR group. Podocytes in the RK rats showed increase in desmin, a marker of podocyte injury, which was alleviated with the administration of MjR. In conclusion, MjR reduced blood pressure, proteinuria and glomerular damage in the RK rats. These data suggest that MjR may mitigate the progression of chronic kidney disease, which needs further confirmation.

Moderate hyperuricaemia ameliorated kidney damage in a low-renin model of experimental renal insufficiency.

Uric acid has promoted renal fibrosis and inflammation in experimental studies, but some studies have shown nephroprotective effects due to alleviated oxidative stress. We studied the influence of experimental hyperuricaemia in surgically 5/6 nephrectomized rats. Three weeks after subtotal nephrectomy or sham operation, the rats were allocated to control diet or 2.0% oxonic acid (uricase inhibitor) diet for 9 weeks. Then blood, urine and tissue samples were taken, and renal morphology and oxidative stress were examined. Inflammation and fibrosis were evaluated using immunohistochemistry and real-time PCR (RT-PCR). Remnant kidney rats ingesting normal or oxonic acid diet presented with ~60% reduction of creatinine clearance and suppressed plasma renin activity. Oxonic acid diet increased plasma uric acid levels by >80 μmol/L. In remnant kidney rats, moderate hyperuricaemia decreased glomerulosclerosis, tubulointerstitial damage and kidney mast cell count, without influencing the fibrosis marker collagen I messenger RNA (mRNA) content. In both sham-operated and 5/6 nephrectomized rats, the mast cell product 11-epi-prostaglandin-F2α excretion to the urine and kidney tissue cyclooxygenase-2 (COX-2) levels were decreased. To conclude, hyperuricaemic remnant kidney rats displayed improved kidney morphology and reduced markers of oxidative stress and inflammation. Thus, moderately elevated plasma uric acid had beneficial effects on the kidney in this low-renin model of experimental renal insufficiency.

Glomerular Size in Transplanted Kidneys: Does Size Matter?

Glomerular Size in Transplanted Kidneys: Does Size Matter?

NaCl Intake Promotes Greater Fluid Retention and Blood Pressure Increases than NaHCO 3 in Rats with Chronic Kidney Disease

Several small clinical trials have shown that oral sodium bicarbonate (NaHCO3) can slow kidney disease progression, and NaHCO3 use is now common in chronic kidney disease (CKD) patients. One potential adverse effect of NaHCO3 use in CKD patients is the increased dietary sodium, which may worsen fluid retention and hypertension, potentially driving cardiovascular disease. It remains unclear however whether the anion coupled with sodium is important in mediating volume retention and blood pressure (BP) increases in this setting. Additionally, the effects of NaHCO3 loading on fluid retention and blood pressure compared to sodium chloride (NaCl) have not been rigorously investigated in CKD. We hypothesized that NaCl loading promotes greater volume retention and increases blood pressure to a greater degree than equimolar NaHCO3 across a range of renal mass reduction in rats. We utilized 11, 10-week-old male Sprague Dawley rats that underwent either 2/3 (n=6) or 5/6 nephrectomy (n=5). Following 4 weeks of recovery, animals were allocated to treatment groups based on renal mass reduction and placed in metabolic cages. Rats were then placed on either 0.1M NaCl (n=5) or 0.1M NaHCO3 (n=6) drinking water. Urine output, fluid and food ingestion were determined daily. Urine sodium (Na+) content was measured by flame photometry. BP was measured in separate group with telemetry. Following initiation of treatment, there was a significant increase in urinary Na+ in rats given NaCl (0.89 ± 0.06 mmol vs 5.06 ± 0.14 mmol; paired t-test, p<0.0001). Similarly, rats given NaHCO3 also exhibited a significant increase in urinary Na+ excretion (1.10 ± 0.06 mmol vs 3.13 ± 0.15 mmol; paired t-test, p<0.0001). However, there was no significant difference in Na+ retention observed between NaCl (1.8 ± 0.41 mmol) and NaHCO3 (1.2 ± 0.51 mmol) treated groups (unpaired t-test, p=0.38). No relationship between Na+ retention and degree of renal mass reduction was observed. Interestingly, rats given NaCl tended to have greater volume retention compared to NaHCO3, but this did not reach statistical significance (delta -11.1 ± 2.9 mL vs -4.35 ± 8.5 mL; unpaired t-test, p=0.12). Consistent with greater fluid retention in NaCl treated animals, we found that 0.1M NaCl resulted in greater increases in mean arterial pressure over 7 weeks in 2/3 nephrectomy rats compared to 0.1M NaHCO3 (RM Two-Way ANOVA, PRxGroup=0.0021, PTime<0.0001, PInteraction=0.0266, PSubjects=<0.0001; n=6/6). We conclude NaHCO3 promotes volume retention in CKD, however volume retention may be greater with NaCl than NaHCO3. Further, NaCl increases blood pressure to a greater degree than NaHCO3 in remnant kidney rats despite similar Na+ retention. As NaHCO3 loading may not promote volume retention to the same degree as NaCl, NaHCO3 loading may limit the risk of adverse cardiovascular effects associated with Na+ loading when given as NaHCO3 in patients with CKD.

Triple combination therapy with telmisartan, amlodipine, and hydrochlorothiazide ameliorates albuminuria in a normotensive rat remnant kidney model

BackgroundSome types of antihypertensive drugs may have pleiotropic effects in patients with chronic kidney disease (CKD). However, whether triple combination therapy with angiotensin II receptor blockers (ARBs), calcium channel blockers (CCBs), and thiazide diuretics (TZD) confer renoprotective effects in normotensive CKD remains unknown. Thus, we explored this issue using a normotensive rat remnant kidney model.MethodsSprague-Dawley rats were randomly allocated into four groups: sham (n = 10), 5/6 nephrectomy (NTx) (n = 9), NTx treated with telmisartan and amlodipine (dual) (n = 8), and NTx treated with telmisartan, amlodipine, and hydrochlorothiazide (triple) (n = 7), and followed for 4 weeks. Blood pressure (BP), blood chemistry including renal function, urinary albumin excretion (UAE), and renal pathology were evaluated in all groups.ResultsThere was no significant change in systolic BP among the four groups during the study period. Serum blood urea nitrogen (BUN) was significantly higher, and 24-h creatinine clearance (Ccr) was lower in all NTx groups (p < 0.001). Dual therapy further increased the glomerular diameter in NTx rats (p < 0.001), which was significantly ameliorated by triple therapy (p < 0.001). Triple therapy, but not dual therapy, significantly reduced NTx-induced UAE levels (p < 0.05), whereas BUN, 24-h Ccr, and tubulointerstitial injury scores were comparable among all the NTx groups.ConclusionsOur results suggest that triple combination therapy with telmisartan, amlodipine, and hydrochlorothiazide could ameliorate glomerular hypertrophy and albuminuria in normotensive CKD rats in a BP-lowering independent manner.

Late intervention in the remnant kidney model attenuates proteinuria but not glomerular filtration rate decline.

The use of animal models to predict the response to new therapies in humans is a vexing issue in nephrology. Unlike patients with chronic kidney disease (CKD), few rodent models develop a progressive decline in glomerular filtration rate (GFR) so that experimental studies frequently report a reduction in proteinuria as the primary efficacy outcome. Moreover, while humans present with established kidney disease that continues to progress, many experimental studies investigate therapies in the prevention rather than in a therapeutic setting. We used the remnant kidney (subtotal nephrectomy [SNX]) rat model that develops a decline in GFR in conjunction with heavy proteinuria and hypertension along with the histological hallmarks of CKD in humans, glomerulosclerosis and tubulointerstitial fibrosis. Using agents that had been shown to improve GFR as well as proteinuria in the prevention setting, angiotensin-converting enzyme (ACE) inhibition with enalapril and SIRT1 activation with SRT3025, treatment was initiated 6 weeks after SNX. While enalapril reduced blood pressure, proteinuria and histological injury, it did not improve GFR, as measured by inulin clearance. SRT3025 improved neither GFR nor structural damage despite a reduction in proteinuria. These findings demonstrate that neither a reduction in proteinuria nor a reversal of structural damage in the kidney will necessarily translate to a restoration of kidney function.

Efficacy of a Si-based agent against developing renal failure in a rat remnant kidney model

Chronic renal failure is exacerbated by oxidative stress, and this condition is difficult to treat in advanced stages. Because of the lack of effective treatments, the disease is a global public health concern. We developed a Si-based agent that continuously generates hydrogen for more than 24 h by reacting with water under conditions similar to those in the gastrointestinal tract. Given the efficacy of hydrogen in the treatment of conditions associated with oxidative stress, we examined whether the Si-based agent had beneficial effects on the development of renal failure. The Si-based agent was orally administered to rats that were developing renal failure. Rats underwent 5/6 nephrectomy to establish a remnant kidney model. Specifically, on day −7, rats underwent right 2/3 nephrectomy, followed by light nephrectomy on day 0. Starting on day −3, the rats were administered a control or Si-based agent-containing diet for 8 weeks. Compared with the findings in control rats, the Si-based agent greatly suppressed the increases of both serum creatinine and urinary protein levels. All analyzed parameters of oxidative stress were significantly suppressed in the Si-based agent groups. Histopathological examination illustrated that glomerular hypertrophy was suppressed by the treatment. Quantitative real-time reverse transcription-polymerase chain reaction revealed that sirtuin 1 and heme oxygenase-1 expression was increased in the Si-based agent groups, suggesting improved antioxidant activity and reduced hypoxia. In addition, caspase-3 and interleukin-6 expression was suppressed in the Si-based agent groups, indicating the alleviation of apoptosis and inflammation. In conclusion, oral administration of a Si-based agent resulted in renoprotective effects, presumably by suppressing oxidative stress via hydrogen generation.

Renoprotective and neuroprotective effects of enteric hydrogen generation from Si-based agent

We have developed Si-based agent which can generate a large amount of hydrogen. Si-based agent continues generating hydrogen for more than 24 h by the reaction with water under conditions similar to those in bowels, i.e., pH8.3 and 36 °C, and generates ~400 mL hydrogen. To investigate beneficial effects for diseases associated with oxidative stress, Si-based agent is administered to remnant kidney rats and Parkinson’s disease mice. Rats are fed with control or Si-based agent-containing diet for 8 weeks. Si-based agent is found to greatly suppress the development of renal failure and the parameters of oxidative stress. Treatment with Si-based agent in a mouse model of hemi-Parkinson’s disease induced by 6-hydroxydopamine attenuated degeneration of dopaminergic neurons and prevented impairment of motor balance and coordination. These findings indicate that the Si-based agent shows renoprotective and neuroprotective effects presumably via suppression of oxidative stress by generation of hydrogen.

Liraglutide promotes autophagy by regulating the AMPK/mTOR pathway in a rat remnant kidney model of chronic renal failure.

We aimed to determine whether the glucagon-like peptide-1 receptor (GLP-1R) agonist liraglutide (LRG) could ameliorate renal function through promoting autophagy via regulating the AMPK/mTOR pathway in a rat remnant kidney model of chronic renal failure. Rats were divided into four groups (n = 10 per group) as follows: (1) sham, (2) nephrectomy (NPX), (3) LRG control (LRG control), and (4) LRG treatment (LRG). Except for rats in the sham group, all rats underwent 5/6 nephrectomy surgery to establish a remnant kidney model of chronic renal failure. In addition, rats in LRG group received LRG as a subcutaneous injection at a dose of 10mg/kg (once daily) for 4 consecutive weeks, whereas rats in the LRG control group received treatment similar to that of rats in the LRG group, except saline was used instead of LRG. After 4weeks of treatment, serum creatinine (Scr), blood urea nitrogen (BUN), and urinary albumin excretion were determined. Immunofluorescence assay, immunoprecipitation assay, and Western blot analysis were performed to evaluate the AMPK/mTOR pathway expression of proteins. Nephrectomized rats (including rats in the NPX, LRG control, and LRG groups) showed higher levels of the Scr, BUN, and urinary albumin excretion, as well as down-regulation of GLP-1R, LC3-II, and AMPK phosphorylation, and up-regulation of mTOR phosphorylation when compared with rats in the sham group. However, those changes were blocked by liraglutide. Liraglutide may promote autophagythrough regulating the AMPK/mTOR pathway to exert renoprotective effects in a rat remnant kidney model of chronic renal failure.

Phosphate binding by sucroferric oxyhydroxide ameliorates renal injury in the remnant kidney model

Recent clinical studies indicate that the disturbed phosphate metabolism in chronic kidney disease (CKD) may facilitate kidney injury; nonetheless, the causal role of phosphate in CKD progression remains to be elucidated. Here, we show that intestinal phosphate binding by sucroferric oxyhydroxide (SF) ameliorates renal injury in the rat remnant kidney model. Sprague-Dawley rats received 5/6 nephrectomy (RK) and had a normal chow or the same diet containing SF (RK + SF). RK rats showed increased plasma FGF23 and phosphate levels, which were suppressed by SF administration. Of note, albuminuria in RK rats was significantly ameliorated by SF at both 4 and 8 weeks. SF also attenuated glomerulosclerosis and tubulointerstitial injury. Moreover, several different approaches confirmed the protective effects on podocytes, explaining the attenuation of glomerulosclerosis and albuminuria observed in this study. As a possible mechanism, we found that SF attenuated renal inflammation and fibrosis in RK rats. Interestingly, von Kossa staining of the kidney revealed calcium phosphate deposition in neither RK nor RK + SF rats; however, plasma levels of calciprotein particles were significantly reduced by SF. These data indicate that latent positive phosphate balance accelerates CKD progression from early stages, even when overt ectopic calcification is absent.

Triiodothyronine attenuates the progression of renal injury in a rat model of chronic kidney disease.

This study was designed to investigate whether and how triiodothyronine (T3) affects renal function in an experimental model of chronic kidney disease. Twenty-four female rats were divided into the following groups: sham-operated control group (n = 8), 5/6 nephrectomized group (Nx, n = 8), and 5/6 nephrectomized group treated with T3 for 2 weeks (T3-Nx, n = 8). T3 administration significantly decreased serum levels of urea, creatinine, tumour necrosis factorα, and interleukin-6 compared with serum levels in the Nx group. The levels of malondialdehyde, transforming growth factor β, fibronectin, and collagen IV, as well as the expression of inducible nitric oxide synthase, nuclear factor κB, poly(ADP-ribose) polymerase, caspase-3, and Bax were all significantly decreased, though not normalized, in the remnant kidney of rats in the T3-Nx group compared with Nx rats. Glutathione, heme oxygenase-1 levels, as well as endothelial nitric oxide synthase expression were increased in the remnant kidney of the T3-Nx group. Histological studies revealed focal necrosis of renal tubules associated with inflammatory cell infiltration and fibrosis in the Nx group. These changes were alleviated in T3-Nx rats. This study showed that T3 administration attenuated the clinical and histological signs of renal injury in 5/6 nephrectomized rats by mitigating renal oxidative stress, inflammation, apoptosis, and fibrosis.

Renoprotective and Blood Pressure Lowering Impact of Equisetum arvense and Viscum album Therapy in Experimental Model of Chronic Kidney Disease

Background: Chronic kidney disease (CKD) is an irreversible decline in the glomerular filtration due to nephrosclerosis and glomerular loss. Rat remnant kidney model enables to assess the benefits of different treatment possibilities. Aim: The aim of our study was to investigate renal morphology and functioning after 12 weeks of treatment with Equisetum arvense and Viscum album. Methods: Male Wistar rats with 5/6 nephrectomy received herbal drug preparation Equisetum/Viscum in a dosage of 0.007 g/kg/die (herbal group) or losartan (180 mg/l, ARB group) or remained untreated. Systolic blood pressure (SBP) and proteinuria were measured. Renal cortex tissue samples examined for focal-segmental glomerulosclerosis (FSGS) and interstitial fibrosis (IF). mRNA was isolated to estimate CCL2/MCP-1 gene transcription. Results: SBP was significantly lower both in herbal group and ARB group compared with untreated animals (p between ARB group and untreated NPX (p = 0.001). Quantitative RT-PCR analysis revealed statistically significant differences of mRNA transcription for MCP-1 between herbal group and untreated group (p Conclusions: We report about beneficial impact of horsetail Equisetum arvense and mistletoe Viscum album treatment on kidney functioning and morphology.

Loss of renal SNX5 results in impaired IDE activity and insulin resistance in mice.

We hypothesised that renal sorting nexin 5 (SNX5) regulates the insulin-degrading enzyme (IDE) and, thus, circulating insulin levels. We therefore studied the dynamic interaction between SNX5 and IDE in human renal proximal tubule cells (hRPTCs), as well as in rat and mouse kidneys. The regulation of IDE by SNX5 expressed in the kidney was studied in vitro and in vivo. Snx5 or mock siRNA was added to immortalised hRPTCs (passage <20) in culture or selectively infused, via osmotic mini-pump, into the remnant kidney of uninephrectomised mice and rats. SNX5 co-localised with IDE at the plasma membrane and perinuclear area of hRPTCs and in the brush border membrane of proximal tubules of human, rat, and mouse kidneys. Insulin increased the co-localisation and co-immunoprecipitation of SNX5 and IDE in hRPTCs. Silencing SNX5 in hRPTCs decreased IDE expression and activity. Renal-selective silencing of Snx5 (SNX5 protein: 100±25 vs 29±10, p<0.05 [% of control]) in C57Bl/6J mice decreased IDE protein (100±13 vs 57±6, p<0.05 [% of control]) and urinary insulin excretion, impaired the responses to insulin and glucose, and increased blood insulin and glucose levels. Spontaneously hypertensive rats (SHRs) had increased blood insulin and glucose levels and decreased renal SNX5 (100±27 vs 29±6, p<0.05 [% of control]) and IDE (100±5 vs 75±4, p<0.05 [% of control]) proteins, compared with normotensive Wistar-Kyoto (WKY) rats. Kidney Snx5-depleted WKY rats also had increased blood insulin and glucose levels. The expression of SNX5 and IDE was decreased in RPTCs from SHRs and hypertensive humans compared with cells from normotensive volunteers, indicating a common cause for hyperinsulinaemia and hypertension. Renal SNX5 positively regulates IDE expression and function. This study is the first to demonstrate the novel and crucial role of renal SNX5 in insulin and glucose metabolism.

Role of mitochondrial dysfunction in renal fibrosis promoted by hypochlorite-modified albumin in a remnant kidney model and protective effects of antioxidant peptide SS-31

Oxidative stress aggravates renal fibrosis, a pathway involved in almost all forms of chronic kidney disease (CKD). However, the underlying mechanism involved in the pathogenesis of renal oxidative stress has not been completely elucidated. In this study, we explored the role and mechanism of hypochlorite-modified albumin (HOCl-alb) in mediating oxidative stress and fibrotic response in a remnant-kidney rat model. Five-sixths nephrectomy (5/6 NX) was performed on the rats and then the animals were randomly assigned to intravenous treatment with either vehicle alone, or HOCl-rat serum albumin (RSA) in the presence or absence of SS-31 (administered intraperitoneally). A sham-operation control group was set up concurrently. Compared with the control group, 5/6 NX animals displayed marked mitochondrial (mt) dysfunction, as evidenced by decrease of mitochondrial membrane potential (MMP), ATP production, mtDNA copy number alterations and manganese superoxide dismutase (MnSOD) activity, release of cytochrome C (Cyto C) from mitochondria to the cytoplasm, and increase of mitochondrial reactive oxygen species in renal tissues. They also displayed increased levels of HOCl-alb in both plasma and renal tissues. These changes were accompanied by accumulation of extracellular matrix, worsened proteinuria, deteriorated renal function, and a marked increase of macrophage infiltration along with up-regulation of monocyte chemoattractant protein (MCP)−1 and transforming growth factor (TGF)-β1 expression. HOCl-alb challenge further exacerbated the above biological effects in 5/6 NX animals, but these adverse effects were prevented by administration of SS-31, a mitochondrial targeted antioxidant peptide. These data suggest that accumulation of HOCl-alb may promote renal inflammation and fibrosis, probably related to mitochondrial oxidative stress and dysfunction and that the mitochondrial targeted peptide SS-31 might be a novel therapy for renal fibrosis and chronic renal failure (CRF).

Endothelin type A receptor blockade reduces vascular calcification and inflammation in rats with chronic kidney disease.

Arterial stiffness and calcification are nontraditional cardiovascular risk factors in chronic kidney disease (CKD). Using a rat model of CKD with mineral imbalance, medial vascular calcification has been associated with inflammation and increased endothelin-1 (ET-1) production. We therefore hypothesized that ET-1, through the endothelin type A (ETA) receptor, induces vascular inflammation, calcification and stiffness in CKD. CKD was induced in Wistar rats by renal mass ablation. To induce medial vascular calcification, mineral imbalance was established with a identified as calcium-rich/phosphate-rich diet and vitamin D supplementation (Ca/P/VitD). One group of CKD + Ca/P/VitD rats was given the ETA receptor antagonist atrasentan (10 mg/kg/day) for 6 weeks. Hemodynamic parameters including SBP, pulse pressure (PP) and pulse wave velocity (PWV) were determined. Vascular calcification, smooth muscle cells osteoblastic differentiation and expression of inflammatory markers such as inflammatory cytokines and calgranulins S100A8 and S100A9 were assessed in the thoracic aorta. As compared with CKD control rats, CKD + Ca/P/VitD rats developed medal vascular calcification that was associated with increased SBP, PP and PWV. These changes were also associated with increased macrophage infiltration and expression of IL-6, calgranulins and osteoblastic markers. Treatment of CKD + Ca/P/VitD rats with atrasentan reduced vascular calcification, SBP, PP and PWV, macrophage infiltration and expression of IL-1β, IL-6, tumor necrosis factor, calgranulins and osteoblastic markers. This study shows that ETA receptor blockade reduced vascular inflammation, smooth muscle cells differentiation, calcification and stiffness indicating a pivotal role for ET-1 in medial vascular calcification in this rat remnant kidney model of CKD with mineral imbalance. Therefore, the endothelin system may be a potential therapeutic target for improving cardiovascular morbidity in patients with CKD.

Cross-talk between AMP-activated protein kinase and renin-angiotensin system in uninephrectomised rats.

Introduction:The renal renin–angiotensin system (RAS) and the ultrasensitive energy sensor AMP-activated protein kinase (AMPK) have been implicated in normal and aberrant states of the kidney, but interaction between the RAS and AMPK remains unknown.Methods:Ninety-six rats were stratified into four groups: sham, uninephrectomised, uninephrectomised rats treated with the angiotensin-converting enzyme inhibitor lisinopril or the angiotensin receptor blocker losartan. Histopathological examination at 9 months post-operation and biochemical measurements at 3, 6 and 9 months were performed for changes in renal structure and function. The expression of AMPK and angiotensin II at 9 months was detected by immunofluorescence microscopy and western blot.Results:Compared with sham rats, uninephrectomised rats demonstrated progressive glomerulosclerosis, tubular atrophy with cast formation and chronic inflammatory infiltration, in parallel to elevated serum urea, creatinine, urine total protein to creatinine ratio and reduced serum albumin. Overexpression of angiotensin II coexisted with a 85.6% reduction of phosphorylated to total AMPK ratio in the remnant kidney of uninephrectomised rats. RAS blockade by the angiotensin-converting enzyme inhibitor or angiotensin receptor blocker substantially normalised AMPK expression, morphological and functional changes of the remnant kidney.Conclusions:Uninephrectomy-induced RAS activation and AMPK inhibition in the remnant kidney could be substantially corrected by RAS blockade, suggesting a cross-talk between AMPK and RAS components in uninephrectomised rats.

A serine protease inhibitor attenuates aldosterone-induced kidney injuries via the suppression of plasmin activity

Emerging evidence has suggested that aldosterone has direct deleterious effects on the kidney independently of its hemodynamic effects. However, the detailed mechanisms of these direct effects remain to be elucidated. We have previously reported that camostat mesilate (CM), a synthetic serine protease inhibitor, attenuated kidney injuries in Dahl salt-sensitive rats, remnant kidney rats, and unilateral ureteral obstruction rats, suggesting that some serine proteases would be involved in the pathogenesis of kidney injuries. The current study was conducted to investigate the roles of serine proteases and the beneficial effects of CM in aldosterone-related kidney injuries. We observed a serine protease that was activated by aldosterone/salt in rat kidney lysate, and identified it as plasmin with liquid chromatography-tandem mass spectrometry. Plasmin increased pro-fibrotic and inflammatory gene expressions in rat renal fibroblast cells. CM inhibited the protease activity of plasmin and suppressed cell injury markers induced by plasmin in the fibroblast cells. Furthermore, CM ameliorated glomerulosclerosis and interstitial fibrosis in the kidney of aldosterone/salt-treated rats. Our findings indicate that plasmin has important roles in kidney injuries that are induced by aldosterone/salt, and that serine protease inhibitor could provide a new strategy for the treatment of aldosterone-associated kidney diseases in humans.

Pathological and molecular mechanisms underlying resistance to recombinant human erythropoietin therapy in the remnant kidney rat model of chronic kidney disease associated anemia.

Anemia of chronic kidney disease (CKD) can be corrected by treatment with recombinant human erythropoietin (rHuEPO); however, some patients become hyporesponsive. The molecular mechanisms underlying this resistance remain to be elucidated. Our aim was to study hyporesponsiveness to rHuEPO therapy using the remnant kidney rat model of anemia associated with CKD induced by 5/6 nephrectomy. At starting, male Wistar rats were divided in 3 groups, for a 3-week protocol: Sham, CRF (vehicle) and two rHuEPO (200k/kg body weight [BW]/week) treated groups; at the end of protocol, the rHuEPO treated rats were subdivided in responders (CRF200) and non-responders (CRF200NR), according to their hematologic response; blood, cellular and tissue studies were performed. The CRF200 group achieved correction of anemia, while the CRF200NR group developed anemia, after an initial response (1st week) to rHuEPO therapy. CRF and CRF200NR groups presented a trend to higher serum CRP levels; CRF200NR showed also high levels of renal inflammatory markers, such as interleukin (IL)-6, IL-1β, nuclear factor kappa B, connective tissue growth factor (CTGF) and transforming growth factor beta 1 (TGF-β1); no changes were found in iron metabolism. Our data suggest that the development of anemia/rHuEPO hyporesponsiveness is associated with a higher systemic and renal inflammatory condition, favoring hypoxia and triggering an increase in renal expression of HIF-1α, TGF-β1 and CTGF that will further aggravate renal fibrosis, which will enhance the inflammatory response, creating a cycle that promotes disease progression. New therapeutic strategies to reduce inflammation in CKD patients could improve the response to rHuEPO therapy and reduce hyporesponsiveness.

Liver iron is a major regulator of hepcidin gene expression via BMP/SMAD pathway in a rat model of chronic renal failure under treatment with high rHuEPO doses.

Hepcidin is the major central regulator of iron metabolism, controlling iron absorption and mobilization. Considering its interaction with several factors that are altered in chronic kidney disease (CKD), particularly in hyporesponsive CKD patients under therapy with high recombinant human erythropoietin (rHuEPO) doses, it was aimed to study the impact of increasing rHuEPO doses on the regulation of iron-hepcidin metabolism. The blood, cellular, and tissue studies, using the remnant kidney rat model of CKD induced by 5/6 nephrectomy, under rHuEPO (100, 200, 400, and 600 IU/Kg body weight [BW]/week) treatment during 3 weeks were performed. It was found that the rHuEPO stimulus triggered a first wave to achieve correction of anemia, by inhibiting hepcidin synthesis, favoring erythropoiesis and iron absorption; this continuous stimulus enhanced iron absorption leading to iron overload, as showed by the hepatic iron deposits found in rats treated with higher rHuEPO dose that seems to trigger the upregulation of hepcidin synthesis through the activation of the BMP6/SMAD pathway. The data suggested that liver iron overload was an important stimuli for hepcidin synthesis, stronger than the inhibitory effect of high rHuEPO doses; moreover, the findings raised the hypothesis that when high inflammation (triggering hepcidin expression) was associated with increased iron stores in hemodialysis patients, hepcidin expression was also upregulated via BMP6, enhancing hepcidin synthesis, leading, therefore, to worsening of anemia and, eventually, to a hyporesponse/resistance to rHuEPO therapy. © 2016 BioFactors, 42(3):296-306, 2016.