Flavonoid-induced reduction of ENaC expression in the kidney of Dahl salt-sensitive hypertensive rat

Flavonoid, a plant extract, exhibits various biological actions. Dietary flavonoid intake is reported to reduce an elevated blood pressure, however the mechanism is unknown. The epithelial Na+ channel (ENaC) in the kidney plays a key role in the regulation of blood pressure by contributing to the Na+ reabsorption in renal tubules. Thus, we investigated the effect of quercetin, a flavonoid, on ENaC mRNA expression in the kidney of hypertensive Dahl salt-sensitive rats. Dahl salt-sensitive rats of 8 weeks were acclimated for 1 week in a metabolic cage and were subsequently kept for 4 weeks under four different conditions: (1) normal salt diet (0.3% NaCl), (2) normal salt diet with quercetin (10 mg/kg/day), (3) high-salt diet (8% NaCl), and (4) high-salt diet with quercetin. Quercetin diminished the alphaENaC mRNA expression in the kidney associated with reduction of the systolic blood pressure elevated by high-salt diet, suggesting that one of the mechanisms of the flavonoid's antihypertensive effect on salt-sensitive hypertension would be mediated through downregulation of ENaC expression in the kidney.     

Role of kidney biomarkers of chronic kidney disease: An update

Chronic kidney disease (CKD) is a progressive pathological condition marked by deteriorating renal function over time. Diagnostic of kidney disease depend on serum creatinine level and glomerular filtration rate which is detectable when kidney function become half. The detection of kidney damage in an early stage needs robust biomarkers. Biomarkers allow monitoring the disease progression at initial stages of disease. On the onset of impairment in cellular organization there is perturbation in signaling molecules which are either up-regulated or down-regulated and act as an indicator or biomarker of diseased stage. This review compiled the cell signaling of different kidney biomarkers associated with the onset of chronic kidney diseases. Delay in diagnosis of CKD will cause deterioration of nephron function which leads to End stage renal disease and at that point patients require dialysis or kidney transplant. Detailed information on the complex network in signaling pathway leading to a coordinated pattern of gene expression and regulation in CKD will undoubtedly provide important clues to develop novel prognostic and therapeutic strategies for CKD.     

Nutrition Facts in Multiple Sclerosis

The question whether dietary habits and lifestyle have influence on the course of multiple sclerosis (MS) is still a matter of debate, and at present, MS therapy is not associated with any information on diet and lifestyle. Here we show that dietary factors and lifestyle may exacerbate or ameliorate MS symptoms by modulating the inflammatory status of the disease both in relapsing-remitting MS and in primary-progressive MS. This is achieved by controlling both the metabolic and inflammatory pathways in the human cell and the composition of commensal gut microbiota. What increases inflammation are hypercaloric Western-style diets, characterized by high salt, animal fat, red meat, sugar-sweetened drinks, fried food, low fiber, and lack of physical exercise. The persistence of this type of diet upregulates the metabolism of human cells toward biosynthetic pathways including those of proinflammatory molecules and also leads to a dysbiotic gut microbiota, alteration of intestinal immunity, and low-grade systemic inflammation. Conversely, exercise and low-calorie diets based on the assumption of vegetables, fruit, legumes, fish, prebiotics, and probiotics act on nuclear receptors and enzymes that upregulate oxidative metabolism, downregulate the synthesis of proinflammatory molecules, and restore or maintain a healthy symbiotic gut microbiota. Now that we know the molecular mechanisms by which dietary factors and exercise affect the inflammatory status in MS, we can expect that a nutritional intervention with anti-inflammatory food and dietary supplements can alleviate possible side effects of immune-modulatory drugs and the symptoms of chronic fatigue syndrome and thus favor patient wellness.     

Vascular risk factors and renal failure

Patients with chronic kidney disease (CKD) have a substantially increased risk of cardiovascular disease (CVD) compared with the general population. The high prevalence of established traditional risk factors for atherosclerosis (diabetes, hypertension, dyslipidemia) in these patients undoubtedly contributes to the accelerated rate of vascular disease. In addition, several hypotheses have emerged to explain the high prevalence of CVD in patients with chronic renal failure. Growing evidence has been gathered over the last 15 years regarding the role of uremia-related risk factors such as inflammation and oxidant stress in the pathogenesis of atherosclerosis in subjects with renal failure. This paper will review current knowledge regarding the potential role of these non-traditional or uremia-related risk factors for atherosclerosis with special emphasis on prevalence, cardiac risk, and management in patients with CKD.     

Relationship between hyperuricemia and chronic kidney disease

Because approximately 70% of uric acid is excreted from the kidney, hyperuricemia occurs when renal function deteriorates. Until now, it has not been clear if the hyperuricemia seen in such renal diseases plays a role in the progression of renal disease. However, recent clinical studies show that the serum uric acid value is closely associated with hypertension in hyperuricemic patients (cross-sectional study), and also with the onset of hypertension (longitudinal study). Furthermore, one interesting report shows that treatment of hyperuricemia with allopurinol lowers blood pressure in juvenile essential hypertension patients with hyperuricemia. In addition, it is well known that hyperuricemia is closely associated with chronic kidney disease (CKD), is a risk factor for renal insufficiency in general populations, and is a poor prognostic factor of renal function in patients who also have IgA nephropathy. On the other hand, in intervention studies on hyperuricemia, the treatment of hyperuricemia with allopurinol in CKD has resulted in a fall in blood pressure and inhibition of the progression of renal damage. Conversely, the cessation of allopurinol treatment in CKD was followed by a rise in blood pressure and the development of renal damage. Furthermore, the rise of blood pressure and development of renal damage following cessation of allopurinol treatment are only seen in patients not receiving angiotensin converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB). This suggests that the renin angiotensin (RA) system plays an important role in the development of hypertension and renal damage from hyperuricemia.     

Angiotensin type 1 receptor modulates macrophage polarization and renal injury in obesity

The mechanisms for increased risk of chronic kidney disease (CKD) in obesity remain unclear. The renin-angiotensin system is implicated in the pathogenesis of both adiposity and CKD. We investigated whether the angiotensin type 1 (AT(1)) receptor, composed of dominant AT(1a) and less expressed AT(1b) in wild-type (WT) mice, modulates development and progression of kidney injury in a high-fat diet (HFD)-induced obesity model. WT mice had increased body weight, body fat, and insulin levels and decreased adiponectin levels after 24 wk of a high-fat diet. Identically fed AT(1a) knockout (AT1aKO) mice gained weight similarly to WT mice, but had lower body fat and higher plasma cholesterol. Both obese AT1aKO and obese WT mice had increased visceral fat and kidney macrophage infiltration, with more proinflammatory M1 macrophage markers as well as increased mesangial expansion and tubular vacuolization, compared with lean mice. These abnormalities were heightened in the obese AT1aKO mice, with downregulated M2 macrophage markers and increased macrophage AT(1b) receptor. Treatment with an AT(1) receptor blocker, which affects both AT(1a) and AT(1b), abolished renal macrophage infiltration with inhibition of renal M1 and upregulation of M2 macrophage markers in obese WT mice. Our data suggest obesity accelerates kidney injury, linked to augmented inflammation in adipose and kidney tissues and a proinflammatory shift in macrophage and M1/M2 balance.     

5/6th Nephrectomy in Combination with High Salt Diet and Nitric Oxide Synthase Inhibition to Induce Chronic Kidney Disease in the Lewis Rat

Chronic kidney disease (CKD) is a global problem. Slowing CKD progression is a major health priority. Since CKD is characterized by complex derangements of homeostasis, integrative animal models are necessary to study development and progression of CKD. To study development of CKD and novel therapeutic interventions in CKD, we use the 5/6th nephrectomy ablation model, a well known experimental model of progressive renal disease, resembling several aspects of human CKD. The gross reduction in renal mass causes progressive glomerular and tubulo-interstitial injury, loss of remnant nephrons and development of systemic and glomerular hypertension. It is also associated with progressive intrarenal capillary loss, inflammation and glomerulosclerosis. Risk factors for CKD invariably impact on endothelial function. To mimic this, we combine removal of 5/6th of renal mass with nitric oxide (NO) depletion and a high salt diet. After arrival and acclimatization, animals receive a NO synthase inhibitor (NG-nitro-L-Arginine) (L-NNA) supplemented to drinking water (20 mg/L) for a period of 4 weeks, followed by right sided uninephrectomy. One week later, a subtotal nephrectomy (SNX) is performed on the left side. After SNX, animals are allowed to recover for two days followed by LNNA in drinking water (20 mg/L) for a further period of 4 weeks. A high salt diet (6%), supplemented in ground chow (see time line Figure 1), is continued throughout the experiment. Progression of renal failure is followed over time by measuring plasma urea, systolic blood pressure and proteinuria. By six weeks after SNX, renal failure has developed. Renal function is measured using ''gold standard'' inulin and para-amino hippuric acid (PAH) clearance technology. This model of CKD is characterized by a reduction in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), hypertension (systolic blood pressure>150 mmHg), proteinuria (> 50 mg/24 hr) and mild uremia (>10 mM). Histological features include tubulo-interstitial damage reflected by inflammation, tubular atrophy and fibrosis and focal glomerulosclerosis leading to massive reduction of healthy glomeruli within the remnant population (<10%). Follow-up until 12 weeks after SNX shows further progression of CKD.     

Distinct effects on long-term function of injured and contralateral kidneys following unilateral renal ischemia-reperfusion

Salt-sensitive hypertension and chronic kidney disease (CKD) following recovery from acute kidney injury (AKI) may occur secondary to incomplete repair, or by activation of circulating factors stimulated by injury. We created two types of renal injury induced by unilateral ischemia-reperfusion (I/R); in a direct/ipsilateral AKI group, rats were subjected to unilateral I/R and the untouched contralateral kidney was removed by unilateral nephrectomy after 5 wk to isolate effects on the injured kidney. In the remote/contralateral AKI group, the injured kidney was removed after 5 wk to isolate effects on the untouched kidney. When these animals were subsequently challenged with elevated dietary sodium for an additional 4 wk (0.4 to 4%), both remote/contralateral and direct/ipsilateral AKI rats manifested a significant increase in blood pressure relative to sham-operated controls. Similarly, in acute studies, both ipsilateral and contralateral kidneys had impaired pressure natriuresis and hemodynamic responses. Reductions in vascular density were observed following direct/ipsilateral injury, but were not observed in the remote/contralateral kidney. However, both remote/contralateral and direct/ipsilateral kidneys contained interstitial cells, some of which were identified as activated (low CD62L/CD4+) T lymphocytes. In contrast, only the direct/ipsilateral AKI group demonstrated significant CKD following exposure to elevated salt. This was characterized by a significant reduction in creatinine clearance, an increase in albuminuria, and a dramatic expansion of interstitial inflammation. Taken together, these data suggest that the salt-sensitive features of AKI on hypertension and CKD are segregable such that effects on hemodynamics and hypertension occur independent of direct renal damage. However, prior direct injury to the kidney is required to elicit the full manifestation of CKD induced by elevated sodium intake.     

Long Term Metabolic Syndrome Induced by a High Fat High Fructose Diet Leads to Minimal Renal Injury in C57BL/6 Mice

Metabolic syndrome can induce chronic kidney disease in humans. Genetically engineered mice on a C57BL/6 background are highly used for mechanistic studies. Although it has been shown that metabolic syndrome induces cardiovascular lesions in C57BL/6 mice, in depth renal phenotyping has never been performed. Therefore in this study we characterized renal function and injury in C57BL/6 mice with long-term metabolic syndrome induced by a high fat and fructose diet (HFFD). C57BL/6 mice received an 8 months HFFD diet enriched with fat (45% energy from fat) and drinking water enriched with fructose (30%). Body weight, food/water consumption, energy intake, fat/lean mass ratio, plasma glucose, HDL, LDL, triglycerides and cholesterol levels were monitored. At 3, 6 and 8 months, renal function was determined by inulin clearance and measure of albuminuria. At sacrifice, kidneys and liver were collected. Metabolic syndrome in C57BL/6 mice fed a HFFD was observed as early 4 weeks with development of type 2 diabetes at 8 weeks after initiation of diet. However, detailed analysis of kidney structure and function showed only minimal renal injury after 8 months of HFFD. HFFD induced moderate glomerular hyperfiltration (436,4 µL/min vs 289,8 µL/min; p-value=0.0418) together with a 2-fold increase in albuminuria only after 8 months of HFFD. This was accompanied by a 2-fold increase in renal inflammation (p-value=0.0217) but without renal fibrosis or mesangial matrix expansion. In addition, electron microscopy did not show alterations in glomeruli such as basal membrane thickening and foot process effacement. Finally, comparison of the urinary peptidome of these mice with the urinary peptidome from humans with diabetic nephropathy also suggested absence of diabetic nephropathy in this model. This study provides evidence that the HFFD C57BL/6 model is not the optimal model to study the effects of metabolic syndrome on the development of diabetic kidney disease.     

Determinants of Renal Tissue Oxygenation as Measured with BOLD-MRI in Chronic Kidney Disease and Hypertension in Humans

Experimentally renal tissue hypoxia appears to play an important role in the pathogenesis of chronic kidney disease (CKD) and arterial hypertension (AHT). In this study we measured renal tissue oxygenation and its determinants in humans using blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) under standardized hydration conditions. Four coronal slices were selected, and a multi gradient echo sequence was used to acquire T2* weighted images. The mean cortical and medullary R2* values ( = 1/T2*) were calculated before and after administration of IV furosemide, a low R2* indicating a high tissue oxygenation. We studied 195 subjects (95 CKD, 58 treated AHT, and 42 healthy controls). Mean cortical R2 and medullary R2* were not significantly different between the groups at baseline. In stimulated conditions (furosemide injection), the decrease in R2* was significantly blunted in patients with CKD and AHT. In multivariate linear regression analyses, neither cortical nor medullary R2* were associated with eGFR or blood pressure, but cortical R2* correlated positively with male gender, blood glucose and uric acid levels. In conclusion, our data show that kidney oxygenation is tightly regulated in CKD and hypertensive patients at rest. However, the metabolic response to acute changes in sodium transport is altered in CKD and in AHT, despite preserved renal function in the latter group. This suggests the presence of early renal metabolic alterations in hypertension. The correlations between cortical R2* values, male gender, glycemia and uric acid levels suggest that these factors interfere with the regulation of renal tissue oxygenation.     

Iron-Hepcidin Dysmetabolism,Anemia and Renal Hypoxia,Inflammation and Fibrosis in the Remnant Kidney Rat Model

Anemia is a common complication of chronic kidney disease (CKD) that develops early and its severity increases as renal function declines. It is mainly due to a reduced production of erythropoietin (EPO) by the kidneys; however, there are evidences that iron metabolism disturbances increase as CKD progresses. Our aim was to study the mechanisms underlying the development of anemia of CKD, as well as renal damage, in the remnant kidney rat model of CKD induced by 5/6 nephrectomy. This model of CKD presented a sustained degree of renal dysfunction, with mild and advanced glomerular and tubulointerstitial lesions. Anemia developed 3 weeks after nephrectomy and persisted throughout the protocol. The remnant kidney was still able to produce EPO and the liver showed an increased EPO gene expression. In spite of the increased EPO blood levels, anemia persisted and was linked to low serum iron and transferrin levels, while serum interleukin (IL)-6 and high sensitivity C-reactive protein (hs-CRP) levels showed the absence of systemic inflammation. The increased expression of duodenal ferroportin favours iron absorption; however, serum iron is reduced which might be due to iron leakage through advanced kidney lesions, as showed by tubular iron accumulation. Our data suggest that the persistence of anemia may result from disturbances in iron metabolism and by an altered activity/function of EPO as a result of kidney cell damage and a local inflammatory milieu, as showed by the increased gene expression of different inflammatory proteins in the remnant kidney. In addition, this anemia and the associated kidney hypoxia favour the development of fibrosis, angiogenesis and inflammation that may underlie a resistance to EPO stimuli and reduced iron availability. These findings might contribute to open new windows to identify putative therapeutic targets for this condition, as well as for recombinant human EPO (rHuEPO) resistance, which occurs in a considerable percentage of CKD patients.     

Low fat adiponectin expression is associated with oxidative stress in nondiabetic humans with chronic kidney disease--impact on plasma adiponectin concentration

In spite of association between high plasma adiponectin and high metabolic and cardiovascular (CV) risk, highest adiponectin increments retain CV and metabolic protective effects in advanced chronic kidney disease (CKD). Passive accumulation can favor CKD-associated hyperadiponectinemia but potential additional regulation by adipose tissue remains undefined. Oxidative stress (OS) is associated with metabolic and CV disease and with CKD [increasing from conservative treatment (CT) to maintenance hemodialysis (MHD)], and OS can reduce adiponectin expression in experimental models. OS (in the form of plasma thiobarbituric acid-reactive substances: TBARS), subcutaneous adipose adiponectin mRNA, and plasma adiponectin were studied in CKD patients (stages 4 and 5) on CT (n = 7) or MHD (n = 11). Compared with CT and controls (C: n = 6) MHD had highest TBARS and lowest adiponectin mRNA (P < 0.05) with lower adipose adiponectin protein (P < 0.05 vs. CT). MHD also had lower plasma adiponectin than CT, although both had higher adiponectin than C (P < 0.05). In renal transplant recipients (RT: CKD stage 3; n = 5) normal TBARS were, in turn, associated with normal adiponectin mRNA (P < 0.05 vs. MHD). In all CKD (n = 23), adiponectin mRNA was associated positively with adiponectin plasma concentration (P < 0.01). In all subjects (n = 29), adiponectin mRNA was related (P < 0.05) negatively with TBARS after adjusting for plasma C-reactive protein (CRP) or CRP and creatinine. Thus altered OS, adiponectin expression, and plasma concentration represent a novel cluster of metabolic and CV risk factors in MHD that are normalized in RT. The data suggest novel roles of 1) MHD-associated OS in modulating adiponectin expression and 2) adipose tissue in contributing to circulating adiponectin in advanced CKD.     

Dietary betaine modifies hepatic metabolism but not renal injury in rat polycystic kidney disease

We undertook a morphometric and proton nuclear magnetic resonance ((1)H-NMR) study to test the hypothesis that 1% dietary betaine supplementation would ameliorate renal disease in the heterozygous Han:SPRD-cy rat, a model of polycystic kidney disease (PKD) and progressive chronic renal failure. After 8 wk of pair feeding, betaine had no effect on renal cystic change, renal interstitial fibrosis, serum creatinine, serum cholesterol, or serum triglycerides. (1)H-NMR spectroscopy of renal tissue revealed no change in renal osmolytes, including betaine, or renal content of other organic anions in response to diet. (1)H-NMR spectroscopy of hepatic tissue performed to explore the metabolic fate of ingested betaine revealed that heterozygous animals fed the control diet had elevated hepatic levels of gluconeogenic amino acids, increased beta-hydroxybutyrate, and increased levels of some citric acid cycle metabolites compared with animals without renal disease. Betaine supplementation eliminated these changes. Chronic renal failure in the Han:SPRD-cy rat is associated with disturbances of hepatic metabolism that can be corrected with betaine therapy, suggesting the presence of a reversible methylation defect in this form of chronic renal failure.     

Renal Effects and Underlying Molecular Mechanisms of Long-Term Salt Content Diets in Spontaneously Hypertensive Rats

Several evidences have shown that salt excess is an important determinant of cardiovascular and renal derangement in hypertension. The present study aimed to investigate the renal effects of chronic high or low salt intake in the context of hypertension and to elucidate the molecular mechanisms underlying such effects. To this end, newly weaned male SHR were fed with diets only differing in NaCl content: normal salt (NS: 0.3%), low salt (LS: 0.03%), and high salt diet (HS: 3%) until 7 months of age. Analysis of renal function, morphology, and evaluation of the expression of the main molecular components involved in the renal handling of albumin, including podocyte slit-diaphragm proteins and proximal tubule endocytic receptors were performed. The relationship between diets and the balance of the renal angiotensin-converting enzyme (ACE) and ACE2 enzymes was also examined. HS produced glomerular hypertrophy and decreased ACE2 and nephrin expressions, loss of morphological integrity of the podocyte processes, and increased proteinuria, characterized by loss of albumin and high molecular weight proteins. Conversely, severe hypertension was attenuated and renal dysfunction was prevented by LS since proteinuria was much lower than in the NS SHRs. This was associated with a decrease in kidney ACE/ACE2 protein and activity ratio and increased cubilin renal expression. Taken together, these results suggest that LS attenuates hypertension progression in SHRs and preserves renal function. The mechanisms partially explaining these findings include modulation of the intrarenal ACE/ACE2 balance and the increased cubilin expression. Importantly, HS worsens hypertensive kidney injury and decreases the expression nephrin, a key component of the slit diaphragm.     

Antithrombin III prevents progression of chronic kidney disease following experimental ischaemic‐reperfusion injury

Acute kidney disease (AKI) leads to increased risk of progression to chronic kidney disease (CKD). Antithrombin III (ATIII) is a potent anticoagulant with anti‐inflammatory properties, and we previously reported that insufficiencies of ATIII exacerbated renal ischaemia‐reperfusion injury (IRI) in rats. In this study, we examined the characteristic of AKI‐CKD transition in rats with two distinct AKI models. Based on our observation, left IRI plus right nephrectomy (NX‐IRI) was used to determine whether ATIII had therapeutic effects in preventing CKD progression after AKI. It was observed that NX‐IRI resulted in significant functional and histological damage at 5 weeks after NX‐IRI compared with sham rats, which was mitigated by ATIII administration. Besides, we noticed that ATIII administration significantly reduced NX‐IRI‐induced interstitial fibrosis. Consistently, renal expression of collagen‐1, α‐smooth muscle actin and fibronectin were substantial diminished in ATIII‐administered rats compared with un‐treated NX‐IRI rats. Furthermore, the beneficial effects of ATIII were accompanied with decreased M1‐like macrophage recruitment and down‐regulation of M1‐like macrophage‐dependent pro‐inflammatory cytokines such as tumour necrosis factor α, inducible nitric oxide synthase and interleukin‐1β, indicating that ATIII prevented AKI‐CKD transition via inhibiting inflammation. Overall, ATIII shows potential as a therapeutic strategy for the prevention of CKD progression after AKI.