AT-1 receptor blockade prevents proteinuria, renal failure, hyperlipidemia, and glomerulosclerosis in the Imai rat

Association of apoE gene polymorphisms with lipid metabolism in renal diseases

BACKGROUND AND OBJECTIVES

Apolipoprotein E (apoE) plays a central role in the metabolism and homeostasis of lipids. ApoE gene encodes three major isoforms: ε2, ε3 a nd ε4 forming six phenotypes: E2E2, E2E3, E2E4, E3E3, E3E3 and E4E4. Disorders of the lipid metabolism and the homeostasis are frequently coexist in renal diseases. The association between gene polymorphisms of apoE and lipid metabolism were not consistent. This meta-analysis was performed to assess the association between gene polymorphisms of apoE and lipid metabolism in renal diseases.

METHODS

A pre-defined literatures search and selection of eligible relevant investigations were performed to extract and collect data from electronic databases.

RESULTS

Sixteen articles were enrolled for the analysis of association between apoE gene polymorphisms and lipid metabolism. Subjects with E3E4 had a higher total cholesterol (TC) than those with E3E3, and subjects with E2E3 had a lower TC than those with E3E3. Subjects with ε2, had a lower TC than those with ε3 or ε4, and subjects with ε4 had a higher TC than those with, ε3. Subjects with E2E2, E2E3 or E4E4 had a higher triglyceride (TG) than those with E3E3. Subjects with ε4 had a higher TG than those with ε3. Subjects with ε2, had a higher level of TG than those with non-ε2. Subjects with E3E4 had a slightly lower high-density lipoprotein (HDL) than those with E3E3. E3E4 appeared to be associated with lower levels of HDL. Subjects with E2E2, E2E3 had a notably lower low-density lipoprotein (LDL) than those with E3E3. Subjects with ε2, had a lower LDL than those with ε3 or ε4 ApoE gene polymorphisms were not associated with very low-density lipoprotein, and lipoprotein (a) [Lp(a)]. Subjects with E2E3 or E2E4 had higher apoE levels than those with E3E3, and subjects with E4E4 had lower apoE levels than those with E3E3.

CONCLUSION

ApoE gene polymorphisms are associated with the expression of TC, TG HDL, LDL, Lp(a) or apoE.

Reactive Oxygen Species and Redox Signaling in Chronic Kidney Disease

Chronic kidney disease (CKD) remains a worldwide public health problem associated with serious complications and increased mortality rates. Accumulating evidence indicates that elevated intracellular levels of reactive oxygen species (ROS) play a major role in the pathogenesis of CKD. Increased intracellular levels of ROS can lead to oxidation of lipids, DNA, and proteins, contributing to cellular damage. On the other hand, ROS are also important secondary messengers in cellular signaling. Consequently, normal kidney cell function relies on the "right" amount of ROS. Mitochondria and NADPH oxidases represent major sources of ROS in the kidney, but renal antioxidant systems, such as superoxide dismutase, catalase, or glutathione peroxidase counterbalance ROS-mediated injury. This review discusses the main sources of ROS and antioxidant systems in the kidney, and redox signaling pathways leading to inflammation and fibrosis, which result in abnormal kidney function and CKD progression. We further discuss the important role of the nuclear factor erythroid 2-related factor 2 (Nrf2) in regulating antioxidant responses, and other mechanisms of redox signaling.

The dipeptidyl peptidase-4 inhibitor teneligliptin reduces kidney damage from hypercholesterolemia in apolipoprotein E-deficient mice

Hypercholesterolemia is a well-established risk factor for kidney injury that can lead to chronic kidney disease (CKD).

Low-protein diet supplemented with ketoacids ameliorates proteinuria in 3/4 nephrectomised rats by directly inhibiting the intrarenal renin-angiotensin system

Low-protein diet plus ketoacids (LPD+KA) has been reported to decrease proteinuria in patients with chronic kidney diseases (CKD). However, the mechanisms have not been clarified. As over-activation of intrarenal renin-angiotensin system (RAS) has been shown to play a key role in the progression of CKD, the current study was performed to investigate the direct effects of LPD+KA on intrarenal RAS, independently of renal haemodynamics. In this study, 3/4 subtotal renal ablated rats were fed 18 % normal-protein diet (Nx-NPD), 6 % low-protein diet (Nx-LPD) or 5 % low-protein diet plus 1 % ketoacids (Nx-LPD+KA) for 12 weeks. Sham-operated rats fed NPD served as controls. The level of proteinuria and expression of renin, angiotensin II (AngII) and its type 1 receptors (AT1R) in the renal cortex were markedly higher in Nx-NPD group than in the sham group. LPD+KA significantly decreased the proteinuria and inhibited intrarenal RAS activation. To exclude renal haemodynamic impact on intrarenal RAS, the serum samples derived from the different groups were added to the culture medium of mesangial cells. It showed that the serum from Nx-NPD directly induced higher expression of AngII, AT1R, fibronectin and transforming growth factor-β1 in the mesangial cells than in the control group. Nx-LPD+KA serum significantly inhibited these abnormalities. Then, proteomics and biochemical detection suggested that the mechanisms underlying these beneficial effects of LPD+KA might be amelioration of the nutritional metabolic disorders and oxidative stress. In conclusion, LPD+KA could directly inhibit the intrarenal RAS activation, independently of renal haemodynamics, thus attenuating the proteinuria in CKD rats.

Osteopontin deficiency reduces kidney damage from hypercholesterolemia in Apolipoprotein E-deficient mice

Hypercholesterolemia is a well-established risk factor for kidney injury, which can lead to chronic kidney disease (CKD). Osteopontin (OPN) has been implicated in the pathology of several renal conditions. This study was to evaluate the effects of OPN on hypercholesterolemia induced renal dysfunction. Eight-week-old male mice were divided into 4 groups: apolipoprotein E knockout (ApoE^−/−) and ApoE/OPN knockout (ApoE^−/−/OPN^−/−) mice fed a normal diet (ND) or high cholesterol diet (HD). After 4 weeks, Periodic acid-Schiff (PAS) and oil red O staining revealed excessive lipid deposition in the glomeruli of ApoE^−/−HD mice, however, significantly suppressed in ApoE^−/−/OPN^−/−HD mice. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression was lower in the glomeruli of ApoE^−/−/OPN^−/−HD mice than ApoE^−/−HD mice. In vitro study, primary mesangial cells were incubated with recombinant mouse OPN (rmOPN). RmOPN induced LOX-1 mRNA and protein expression in primary mesangial cells. Pre-treatment with an ERK inhibitor suppressed the LOX-1 gene expression induced by rmOPN. These results indicate that OPN contributes to kidney damage in hypercholesterolemia and suggest that inhibition of OPN may provide a potential therapeutic target for the prevention of hypercholesterolemia.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

Delayed treatment with oleanolic acid attenuates tubulointerstitial fibrosis in chronic cyclosporine nephropathy through Nrf2/HO-1 signaling

Background

Nuclear factor erythroid-2-related factor-2 (Nrf2) is known to protect against tissue injury by orchestrating antioxidant and detoxification responses to oxidative stress. This study investigated whether upregulation of Nrf2-dependent signaling by oleanolic acid (OA), which is known to activate Nrf2, could attenuate renal inflammation and fibrosis in cyclosporine (CsA)-induced kidney injury.

Methods

Male ICR mice were divided into four treatment groups: Vehicle (VH, n = 6), VH + OA (n = 6), CsA (n = 8), and CsA + OA (n = 8). For the OA-treated groups, OA (25 mg/kg/day) was administered by intraperitoneal injection for the final week of the 4-week experimental period. Renal function, morphologies and signaling were evaluated at the end of the study.

Results

Treatment with CsA resulted in decreased kidney function and urine osmolality and increased urine volume and urinary albumin levels. The CsA-induced changes were improved by OA treatment. Specifically, administration of OA decreased tubulointerstitial fibrosis and inflammation scores that were increased in CsA-treated mice. Furthermore, OA treatment decreased urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) and 8-epi-prostaglandin F2α (8-iso-PGF2α) levels. The beneficial effects of OA were attributed to an increased ratio of nuclear/total Nrf2 and subsequently enhanced expression of heme oxygenase (HO)-1, as well as a stable level of Kelch-like ECH-associated protein 1 (Keap1) expression, indicating that OA enhanced nuclear translocation of Nrf2. Increased apoptotic cell death and a high ratio of B cell leukaemia/lymphoma 2 (Bcl-2)-associated X protein (Bax) to Bcl-2 in CsA-treated mice were also significantly ameliorated by OA treatment.

Conclusion

Our results suggest that OA activates Nrf2/HO-1 signaling in chronic CsA nephropathy, which may have beneficial effects on inflammation and oxidative stress.

Protective effects of Rho kinase inhibitor fasudil on rats with chronic kidney disease

The protective effects of Rho kinase inhibitor fasudil against renal diseases have recently been reported. We compared the therapeutic effects of fasudil on the spontaneously hypercholesterolemic (SHC) rat, a model of chronic kidney disease (CKD) with proteinuria, with those of the angiotensin receptor blocker olmesartan (OL) by paying attention to the proteinuria and the macrophage phenotype. SHC rats were allocated to six treatment groups: a vehicle (Ve) group, a low-dose fasudil (FL) group, a high-dose fasudil (FH) group, an OL group, a combination of low-dose fasudil and OL (CL) group, and a combination of high-dose fasudil and OL (CH) group. Sprague-Dawley rats treated with vehicle served as a control ( n = 7/each). The rats were treated for 24 wk. Compared with the Ve group, proteinuria was significantly decreased in the FH, OL, and CL groups, and it completely disappeared in the CH group. Glomerular stainings of nephrin and F-actin were focally impaired in the Ve group but were restored in the CH group. Western blotting showed that the CH group had significantly increased renal nephrin expression compared with the Ve group. Interstitial infiltration of macrophages was significantly increased in the Ve group, which was significantly attenuated in all treatment groups. The ratio of CD206 (M2 macrophage marker) to CD68 mRNA was significantly greater in the CH group than in the Ve group. These results indicate that fasudil with OL reduces proteinuria by protecting podocyte integrity and alters the interstitial macrophage density/phenotype, thereby exerting renoprotective effects against CKD.

Role of impaired Nrf2 activation in the pathogenesis of oxidative stress and inflammation in chronic tubulo-interstitial nephropathy

BACKGROUND

Tubulo-interstitial nephropathy (TIN) is a common cause of chronic kidney disease (CKD). Consumption of an adenine-containing diet causes the accumulation of 2,8-dihydroxyadenine in the renal tubules triggering intense chronic TIN and progressive CKD in rats. CKD in this model is associated with, and largely driven by, oxidative stress and inflammation. Oxidative stress and inflammation in rats with spontaneous focal segmental glomerulosclerosis and rats with CKD induced by 5/6 nephrectomy are associated with an impaired activation of nuclear factor-erythroid-2-related factor 2 (Nrf2) which is the master regulator of genes encoding many antioxidant and detoxifying enzymes. The effect of TIN on the Nrf2 pathway and its key target genes is unknown and was investigated here.

METHODS

Sprague-Dawley rats were randomized to control and adenine-treated (rat chow-containing 0.7% adenine for 2 weeks) groups and followed up for 4 weeks.

RESULTS

The adenine-treated animals exhibited marked azotemia, impaired urinary concentrating capacity, intense tubular and glomerular damage, interstitial inflammation and fibrosis. This was associated with an increased expression of NAD(P)H oxidase, cyclooxygenase-2 and 12-lipoxygenase, and activation of NF-κB, the master regulator of pro-inflammatory cytokines and chemokines. Oxidative stress and inflammation in the kidneys of adenine-treated animals was accompanied by an impaired activation of Nrf2 and down-regulation of its target gene products including, catalase, heme oxygenase-1 and glutamate-cysteine ligase.

CONCLUSIONS

Chronic TIN is associated with impaired Nrf2 activity which contributes to the pathogenesis of oxidative stress and inflammation and amplifies their damaging effects on the kidney.

Role of intrarenal angiotensin system activation, oxidative stress, inflammation, and impaired nuclear factor-erythroid-2-related factor 2 activity in the progression of focal glomerulosclerosis

The Imai rat is a model of spontaneous focal glomerulosclerosis, which leads to heavy proteinuria, hyperlipidemia, hypertension, and progressive renal failure. Treatment with AT1 blockers (ARBs) ameliorates proteinuria, hyperlipidemia, and nephropathy in this model. Progression of renal disease in 5/6 nephrectomized rats is associated with activation of the intrarenal angiotensin system, up-regulation of the oxidative, inflammatory, and fibrogenic pathways, and impaired activity of nuclear factor-erythroid-2-related factor 2 (Nrf2), the master regulator of genes encoding antioxidant molecules. We hypothesized that progressive nephropathy in the Imai rat is accompanied by oxidative stress, inflammation, and impaired Nrf2 activation and that amelioration of nephropathy with AT1 receptor blockade in this model may be associated with the reversal of these abnormalities. Ten-week-old Imai rats were randomized to the ARB-treated (olmesartan, 10 mg/kg/day for 24 weeks) or vehicle-treated groups. Sprague-Dawley rats served as controls. At 34 weeks of age Imai rats showed heavy proteinuria, hypoalbuminemia, hypertension, azotemia, glomerulosclerosis, tubulointerstitial inflammation, increased angiotensin II expressing cell population, up-regulations of AT1 receptor, AT2 receptor, NAD(P)H oxidase, and inflammatory mediators, activation of nuclear factor-κB and reduction of Nrf2 activity and expression of its downstream gene products in the renal cortex. ARB therapy prevented nephropathy, suppressed oxidative stress and inflammation, and restored Nrf2 activation and expression of the antioxidant enzymes. Thus progressive focal glomerulosclerosis in the Imai rats is associated with oxidative stress, inflammation, and impaired Nrf2 activation. These abnormalities are accompanied by activation of intrarenal angiotensin system and can be prevented by ARB administration.

Renin-angiotensin system activation in renal adipogenesis

The kidney is one of the major organs involved in whole-body homeostasis while chronic renal impairment usually leads to fat redistribution and hyperlipidemia. The aim of this study was to elucidate the role of tissue renal renin-angiotensin system (RAS) components, lipogenic peroxisome proliferator-activated receptor-γ (PPARγ), and cytokine TNF-α in the development of ectopic adipogenesis and lipid deposition. Adult male Sprague-Dawley rats were randomized into three groups: untreated uninephrectomized (UNX) rats, UNX rats treated with an angiotensin-converting enzyme inhibitor (ACEI), lisinopril, and sham-operated rats. All animals were euthanized at 10 mo postoperation. The untreated UNX rats showed increased protein expression of renin, angiotensinogen, PPARγ, and the angiotensin II type 2 receptor (AT2R) but reduced protein expression of AT1R and TNF-α in their remnant kidneys. Immunofluorescence staining revealed increased reactivity of angiotensinogen and angiotensin I/II in renal tubular cells and adipocytes of the untreated UNX rats. ACEI treatment largely prevented these disorders in association with restored normolipidemia and normalized renal adipogenesis and lipid deposition. These findings support the notion that tissue RAS, PPARγ, and TNF-α collectively play an important role in the renal adipogenesis and lipid metabolism.

Intrarenal RAS activity and urinary angiotensinogen excretion in anti-thymocyte serum nephritis rats

The differential roles of circulating and intrarenal renin-angiotensin system (RAS) in glomerulonephritis have not been elucidated. In this study, we investigated the levels of circulating and intrarenal RAS activity and urinary angiotensinogen (AGT) excretion in anti-thymocyte serum (ATS) nephritis induced by an ATS injection (ATS group). The effect of olmesartan, an angiotensin II (ANG II) type 1 receptor blocker (ARB), on the development of nephritis was also examined (ATS+ARB group). In addition, the rats received a saline injection instead of ATS (control group). Mesangial proliferation with transient proteinuria, which peaked at day 7, was significantly increased in the ATS group compared with the control group. The levels of glomerular AGT mRNA, intrarenal ANG II, and urinary AGT excretion in the ATS group were increased significantly at day 7 compared with the control group. Administration of olmesartan (ATS+ARB group) significantly decreased the levels of renal lesions, proteinuria, and intrarenal RAS activity compared with the ATS group. In addition, the levels of urinary AGT excretion correlated with the levels of glomerular damage, urinary protein excretion, and immunoreactivity for AGT and ANG II in kidney. On the other hand, plasma renin activity was significantly lower in the ATS group compared with the control group and significantly higher in the ATS+ARB group than in the ATS group. These data suggest that an increase in kidney-specific RAS activity, which parallels urinary AGT excretion, plays an important role in the development of ATS nephritis.

Nitric oxide and superoxide interactions in the kidney and their implication in the development of salt-sensitive hypertension

1. Enhanced superoxide (O2(-)) activity as a result of the inhibition of the superoxide dismutase (SOD) enzyme results in vasoconstrictor and antinatriuretic responses in the canine kidney; these responses were shown to be greatly enhanced during inhibition of nitric oxide synthase (NOS). Glomerular filtration rate remained mostly unchanged during SOD inhibition in the intact nitric oxide (NO) condition, but was markedly reduced during NOS inhibition. These findings indicate that endogenous NO has a major renoprotective effect against O2(-) by acting as an anti-oxidant. Nitric oxide synthase inhibition was also shown to enhance endogenous O2(-) activity. 2. Experiments in our laboratory using dogs, rats and gene knockout mice have shown that renal vasoconstrictor and antinatriuretic responses to acute or chronic angiotensin (Ang) II administration are mediated, in part, by O2(-) generation. In the absence of NO, enhanced O2(-) activity largely contributes to AngII-induced renal tubular sodium reabsorption. Acute or chronic treatment with the O2(-) scavenger tempol in experimental models of hypertension (induced by chronic low-dose treatment with AngII and NO inhibitors) causes an improvement in renal haemodynamics and in excretory function, abolishes salt sensitivity and reduces blood pressure. 3. The present mini review also discusses related studies from many other laboratories implicating a role for O2(-) and its interaction with NO in the development of salt-sensitive hypertension. 4. Overall, the collective data support the hypothesis that an imbalance between the production of NO and O2(-) in the kidney primarily determines the condition of oxidative stress that alters renal haemodynamics and excretory function leading to sodium retention and, thus, contributes to the development of salt-sensitive hypertension.

Effects of pioglitazone and candesartan on renal fibrosis and the intrarenal plasmin cascade in spontaneously hypercholesterolemic rats

The profibrotic effect of plasminogen activator inhibitor-1 (PAI-1) in renal fibrosis is widely recognized, but its mechanism remains controversial especially in chronic progressive kidney disease. In the present study, pioglitazone (Pio) and candesartan (CD), which are reported to inhibit PAI-1, were administered to spontaneously hypercholesterolemic (SHC) rats, a model of chronic progressive kidney disease. Therapeutic effects and effects on the intrarenal plasmin cascade were examined. Eight-wk-old SHC rats were used as controls. Oral administration of vehicle alone, Pio, or CD was performed starting at 8 wk of age and was continued for 24 wk. The degree of renal fibrosis was evaluated by sirius red staining of kidney sections and by total collagen assay of renal homogenates. The renal PAI-1 protein level was assessed by Western blotting, and plasmin activity was analyzed by chromogenic assay and casein gel zymography. Urinary protein and blood urea nitrogen were significantly increased in the vehicle-treated group, but the increase was attenuated in the Pio- and CD-treated groups. This correlated well with the degree of fibrosis as assessed by sirius red staining and total collagen assay. The PAI-1 protein level was also increased significantly in the vehicle-treated group, and the increase was attenuated in the Pio- and CD-treated groups. Despite the presumed plasmin-inhibitory function of PAI-1, plasmin activity changed in parallel with PAI-1. These results suggest that Pio and CD inhibit PAI-1 and exert renoprotective effects against chronic progressive renal disease, but its action is independent of the regulatory function on plasmin activity.

Intra-renal angiotensin II/AT1 receptor, oxidative stress, inflammation, and progressive injury in renal mass reduction

Significant reduction of renal mass triggers a chain of events that result in glomerular hypertension/hyperfiltration, proteinuria, glomerulosclerosis, tubulointerstitial injury, and end-stage renal disease. These events are mediated by a constellation of hemodynamic, oxidative, and inflammatory reactions that are, in part, driven by local AT1 receptor (AT1r) activation by angiotensin II (Ang II). Here we explored the effects of 5/6 nephrectomy with and without AT1r blockade (losartan for 8 weeks) on AT1r and AT2r and Ang II-positive cell count, pathways involved in oxidative stress and inflammation [NAD(P)H oxidase, nuclear factor kappaB (NFkappaB), 12-lipooxygenase, cyclooxygenase (COX)-1, COX-2, monocyte chemoattractant protein (MCP)-1, plasminogen activator inhibitor (PAI)-1, renal T cell, and macrophage infiltration] as well as renal function and structure. The untreated group exhibited hypertension, deterioration of renal function and structure, reduced or unchanged plasma renin activity, aldosterone concentration, marked up-regulations of AT1r (250%), Ang II-expressing cell count (>20-fold), NAD(P)H oxidase subunits (gp91(phox,) p22(phox), and P47(phox); 20-40%), COX-2 (250%), 12-lipooxygenase (100%), MCP-1 (400%), and PAI-1 (>20-fold), activation of NFkappaB, and interstitial infiltrations of T cells and macrophages in the remnant kidneys. AT1r blockade attenuated the biochemical and histological abnormalities, prevented hypertension, and decelerated deterioration of renal function and structure. Thus, the study demonstrated a link between up-regulation of Ang II/AT1r system and oxidative stress, inflammation, hypertension, and progression of renal disease in rats with renal mass reduction.

Statins in nephrotic syndrome: a new weapon against tissue injury

The nephrotic syndrome is characterized by metabolic disorders leading to an increase in circulating lipoproteins levels. Hypertriglyceridemia and hypercholesterolemia in this case may depend on a reduction in triglyceride-rich lipoproteins catabolism and on an increase in hepatic synthesis of Apo B-containing lipoproteins. These alterations are the starting point of a self-maintaining mechanism, which can accelerate the progression of chronic renal failure. Indeed, hyperlipidemia can affect renal function, increase proteinuria and speed glomerulosclerosis, thus determining a higher risk of progression to dialysis. 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is the rate-limiting enzyme in cholesterol synthesis from mevalonate and its inhibitors, or statins, can therefore interfere with the above-mentioned consequences of hyperlipidemia. Statins are already well known for their effectiveness on primary cardiovascular prevention, which cannot be explained only through their hypolipemic effect. As far as kidney diseases are concerned, statin therapy has been shown to prevent creatinine clearance decline and to slow renal function loss, particularly in case of proteinuria, and its favorable effect may depend only partially on the attenuation of hyperlipidemia. Statins may therefore confer tissue protection through lipid-independent mechanisms, which can be triggered by other mediators, such as angiotensin receptor blockers. Possible pathways for the protective action of statins, other than any hypocholesterolemic effect, are: cellular apoptosis/proliferation balance, inflammatory cytokines production, and signal transduction regulation. Statins also play a role in the regulation of the inflammatory and immune response, coagulation process, bone turnover, neovascularization, vascular tone, and arterial pressure. In this study, we would like to provide scientific evidences for the pleiotropic effects of statins, which could be the starting point for the development of new therapeutical strategies in different clinical areas.

Tubulointerstitial damage and progression of renal failure

The present work reviews the mechanisms and close association between glomerular and tubular damage and its relationship to renal functional impairment. In addition, we present an overview of the pathways involved in the progression of tubulointerstitial fibrosis and a brief summary of the treatments used to retard the progression to end-stage renal failure.

Mycophenolate mofetil ameliorates nephropathy in the obese Zucker rat

BACKGROUND

The obese Zucker rat has metabolic condition resembling type II diabetes, including hyperlipidemia, obesity, insulin resistance, and hyperglycemia. With advancing age, the obese Zucker rat develops glomerulosclerosis, proteinuria, and renal failure. Since immune cells play a central role in the development of chronic renal injury, we evaluated the potential benefit of mycophenolate mofetil (MMF), alone and in combination with angiotensin receptor type 1 blockade (ARB) in the obese Zucker rat.

METHODS

Thirteen-week-old male obese Zucker rats (fa/fa) were randomly assigned to four experimental groups (five rats each) that received the following treatments for 3 months: (1) losartan (100 mg/L in the drinking water), (2) MMF (20 mg/kg/day), (3) MMF and losartan, and (4) placebo. Lean Zucker rats (N = 5) were included as normal controls. Renal function, biochemical parameters, renal histology, and immunohistology were evaluated.

RESULTS

The placebo-treated obese Zucker rats exhibited proteinuria and significant glomerular and tubulointerstitial injury in association with renal immune cell infiltration. Proteinuria, histologic damage, and renal immune cell infiltration were all reduced by MMF treatment alone or in combination with ARB. The improvement of proteinuria and structural damage was more pronounced in the group that received the combination of MMF and losartan.

CONCLUSION

MMF treatment alone, and especially in combination with ARB, improves nephropathy in the obese Zucker rat.

Physiologic evidence of renoprotection by antihypertensive therapy

PURPOSE OF REVIEW

Hypertension is vastly prevalent worldwide and constitutes the second leading cause of end-stage renal disease. Therefore, treating hypertension and protecting the kidney from deterioration are exceedingly important. Although previous studies have explored the renal effects of various antihypertensive drugs in animal models and humans, recent clinical trials are all the more convincing. This review summarizes the latest data demonstrating the physiologic evidence of renoprotection by antihypertensive therapy.

RECENT FINDINGS

Experimental studies in various models of hypertension with renal injury have demonstrated clearly that angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, or aldosterone antagonists promote beneficial renal actions, through hemodynamic and nonhemodynamic mechanisms. Of particular significance, recent clinical trials have demonstrated renoprotection by angiotensin II inhibition in patients with hypertension and chronic kidney disease. Angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade have provided equivalent renal benefits, and their dual action seems to confer greater renoprotection. The available data on the renal outcomes of other antihypertensive drugs such as calcium antagonists have been inconsistent.

SUMMARY

The results of the numerous experimental and clinical studies have established the renoprotective properties of renin-angiotensin-aldosterone inhibitors, which confer greater benefit by virtue of their effects over and beyond blood pressure reduction. These findings provide the convincing basis for the recommendation of angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, or both as first-line therapy in hypertension with chronic kidney disease.

Add-on and withdrawal effect of pravastatin on proteinuria in hypertensive patients treated with AT1 receptor blockers

BACKGROUND

Although angiotensin receptor antagonists and 3-hydroxy-3-methylgultaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have been shown to attenuate proteinuria individually, it remains unclear whether proteinuria may be additionally improved by statin therapy in well-controlled hypertensive patients treated with angiotensin receptor antagonists-based regimen and whether withdrawal of chronic statin treatment may abrogate this beneficial effect in normolipidemic patients.

METHODS

A total of consecutive 82 proteinuric patients treated with antihypertensive agents, including losartan, were randomized 10 mg of pravastatin or placebo with a 6-month treatment. After completing 6 months of drug treatment, the pravastatin-treated patients were randomly assigned to continue (N= 19) or withdraw (N= 17) pravastatin for a further 6 months.

RESULTS

Subjects treated with pravastatin had significant further improvement of proteinuria at 6 months compared with placebo group (559 +/- 251 mg/24 hours vs. 1262 +/- 557 mg/24 hours) (P < 0.0001). Of 17 patients assigned to withdraw pravastatin, proteinuria returned to the pretreatment levels and was significantly higher than those who continued treatment. Multivariate analysis revealed that proteinuric improvement was significantly correlated with the continuous statin use. Urinary excretion of endothelin-1 (ET-1) is decreased in pravastatin-treated patients, but withdrawal of statin resulted in 27% up-regulation. The linear regression models in the initial statin-treated group showed that changes in urinary ET-1 correlated with urinary protein excretion (r= 0.83, P < 0.0001).

CONCLUSION

We conclude that pravastatin administration is associated with improved proteinuria probably by inhibiting urine ET-1 levels in patients with losartan-based treatment. However, statin withdrawal abrogates this beneficial effect in patients initially responsive to this therapy.

Dyslipidemia and nephrotic syndrome: Recent advances

Patients with nephrotic syndrome (NS) have one of the most pronounced secondary changes in lipoprotein metabolism known, and the magnitude of the changes correlates with the severity of the disease. These changes are of a quantitative as well as a qualitative nature. All apolipoprotein B (apo B)-containing lipoproteins, such as very-low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and lipoprotein(a) [Lp(a)], are elevated in nephrotic syndrome. High-density lipoproteins (HDL) are reported to be unchanged or reduced. In addition to these quantitative changes, the lipoprotein composition is markedly changed, with a higher ratio of cholesterol to triglycerides in the apo B-containing lipoproteins and an increase in the proportion of cholesterol, cholesterol ester, and phospholipids compared with proteins. Also apolipoproteins show major changes, with an increase in apolipoprotein A-I, A-IV, B, C, and E. Particularly the changes in apo C-II, which is an activator of the enzyme lipoprotein lipase (LPL), and apo C-III, an inhibitor of LPL, with an increase of the C-III to C-II ratio, might contribute to the impaired lipoprotein catabolism in NS. The mechanisms for these changes in lipoprotein metabolism are discussed in this review as far as they are known. Furthermore, the tremendous elevations of Lp(a) in nephrotic syndrome and its primary and secondary causes are reviewed. Primary causes became recently apparent by a significantly higher frequency of low-molecular-weight apo(a) phenotypes in patients compared with controls. The secondary causes were shown by an increase of Lp(a) in all apo(a) isoform groups. Because Lp(a) is an LDL-like particle that is usually included in the measured or calculated LDL cholesterol fraction, the influence of the extremely high Lp(a) levels in NS on the measurement of LDL cholesterol is discussed.