Enalapril and low protein reverse chronic puromycin aminonucleoside nephropathy

Low-Protein Diets and Its Synergistic Role in the SGLT2 Inhibitor Era

Low-protein diets (LPDs), usually defined as a daily dietary protein intake of 0.6 to 0.8 g/kg body weight, have been recommended for decades as a safe and effective lifestyle modification to ameliorate inflammatory damage and proteinuria, reduce glomerular hyperfiltration, and improve metabolic acidosis control in patients with chronic kidney disease (CKD). The mechanism for this is largely attributed to altered tubuloglomerular feedback and afferent arteriole contraction leading to decreased glomerular pressure. Additionally, low protein intake reduces urea generation, which can help delay dialysis initiation in advanced CKD. LPDs have different types including plant-dominant LPDs that can exert additional kidney protective effects as a result of dietary protein quality in addition to quantity. In addition, strong clinical evidence shows that a new class of diabetes mellitus medications, the sodium-glucose cotransporter 2 inhibitors, reduces albuminuria and slows the estimated glomerular filtration rate decline in CKD, even in patients without diabetes mellitus, especially if significant proteinuria is present. Given prior studies investigating the effect of LPDs used in conjunction with angiotensin pathway modulators, we argue that LPDs have a synergistic role in disease management and are expected to display additive effects when combined with sodium-glucose cotransporter 2 inhibitor usage or other pharmacologic agents. Even with medical therapy, it is prudent to implement tailored LPDs for different types of CKD.

The Role for Protein Restriction in Addition to Renin-Angiotensin-Aldosterone System Inhibitors in the Management of CKD

In experimental studies a low-protein diet (LPD) and renin-angiotensin-aldosterone system (RAAS) inhibitors are both reported to slow the progression of chronic kidney disease (CKD) and reduce proteinuria. RAAS activity contributes to increased blood pressure, fluid retention, and positive sodium balance, but also to kidney damage by enhancing glomerular capillary filtration pressure and synthesis of profibrotic molecules such as transforming growth factor β. It has been well established that an LPD decreases glomerular hyperfiltration and the generation of uremic toxins, as well as the burden of acid load, phosphorus, and sodium. In different animal CKD models, a significant reduction in proteinuria and glomerulosclerosis has been achieved when an RAAS inhibitor and LPD were combined. To date, high-quality intervention trials investigating this combined strategy are lacking. We summarize the experimental and clinical studies that have examined a potential additive action of these therapies on CKD progression. We outline potential mechanisms of action and additive efficacy of an LPD and RAAS inhibitors in CKD, with a particular emphasis on phosphate levels, uremic toxin production, acid load, and salt intake. Finally, although the evidence is inadequate to recommend combining RAAS inhibitors and an LPD to slow the progression of CKD, we provide a perspective to support a large-scale randomized clinical trial to study this combination.

Inhibiting angiotensin-converting enzyme promotes renal repair by modulating progenitor cell activation

Independently of the initial insult, activation and accumulation of parietal progenitor cells within the Bowman's space is a peculiar feature of proliferative chronic kidney diseases. Clinical and experimental studies demonstrated that, in the presence of extensive renal damage, progenitor cells proliferate excessively in the failed attempt to replace the injured podocytes, contributing to the development of crescentic lesions. Inhibiting angiotensin-converting enzyme (ACE) halts crescent formation and promotes the restoration of normal glomerular architecture by limiting progenitor cell proliferation and migration towards the glomerular tuft. Among the mediators involved in the dysregulated response of renal precursors, the angiotensin II (ang II)/ang II type-1 (AT₁) receptor/CXCR4 pathway have been demonstrated to be crucial in proliferative diseases. Understanding the mechanisms underlying the formation of crescentic lesions could be instrumental to developing new therapies, which can be more effective and more targeted to molecular mediators than the currently used cytotoxic agents.

Mechanisms of disease reversal in focal and segmental glomerulosclerosis

It is well known that progression of chronic kidney disease can be ameliorated or stabilized by different interventions, but more studies indicate that it can even be reversed. Most data suggest that current therapy, especially renin-angiotensin system inhibition alone, is not sufficient to initiate and maintain long-term regression of glomerular structural injury. In this article, we review the potential reversal of glomerulosclerosis and evidence from both human and animal studies. We discuss mechanisms that involve matrix remodeling, capillary reorganization, and podocyte reconstitution. In the future, a multipronged strategy including novel anti-inflammatory and antifibrotic molecules should be considered to potentiate regression of glomerulosclerosis.

Kidney regeneration in mammals

BACKGROUND

Several organs such as the skin and liver have a great capacity for regeneration. However, many approaches only delay the progression of end-stage kidney disease and do not achieve efficient long-term stabilization, let alone regeneration.

SUMMARY

In mammals, the kidney has an innate but limited capacity for regeneration which can only modify the nephron structure and function but not increase the nephron number. Several clinical and animal studies have indicated that functional improvements and/or structural regression can occur in chronic kidney disease. Cell reconstitution, matrix remodeling, and tissue reorganization are major mechanisms for kidney regeneration. Current approaches achieve only partial kidney regeneration, but this does not occur in all animals and is not sustained in the long term. Multipronged and early interventions are future choices for the induction of kidney regeneration.

KEY MESSAGES

Kidney regeneration in mammals is feasible but limited and may be enhanced by multitargeting key mechanisms.

Animal models of regression/progression of kidney disease

Current medical therapies may delay chronic kidney disease progression. However, increasing experimental evidence indicates remission or even regression can be achieved. In order to study mechanisms progression vs. regression by different interventions, appropriate animal models and research design must be implemented. We review key information of selected models, including etiology, pathogenesis, procedure, time course and assessment of potential regression.

Proteinuria impairs podocyte regeneration by sequestering retinoic acid

In CKD, the risk of kidney failure and death depends on the severity of proteinuria, which correlates with the extent of podocyte loss and glomerular scarring. We investigated whether proteinuria contributes directly to progressive glomerulosclerosis through the suppression of podocyte regeneration and found that individual components of proteinuria exert distinct effects on renal progenitor survival and differentiation toward a podocyte lineage. In particular, albumin prevented podocyte differentiation from human renal progenitors in vitro by sequestering retinoic acid, thus impairing retinoic acid response element (RARE)-mediated transcription of podocyte-specific genes. In mice with Adriamycin nephropathy, a model of human FSGS, blocking endogenous retinoic acid synthesis increased proteinuria and exacerbated glomerulosclerosis. This effect was related to a reduction in podocyte number, as validated through genetic podocyte labeling in NPHS2.Cre;mT/mG transgenic mice. In RARE-lacZ transgenic mice, albuminuria reduced retinoic acid bioavailability and impaired RARE activation in renal progenitors, inhibiting their differentiation into podocytes. Treatment with retinoic acid restored RARE activity and induced the expression of podocyte markers in renal progenitors, decreasing proteinuria and increasing podocyte number, as demonstrated in serial biopsy specimens. These results suggest that albumin loss through the damaged filtration barrier impairs podocyte regeneration by sequestering retinoic acid and promotes the generation of FSGS lesions. Our findings may explain why reducing proteinuria delays CKD progression and provide a biologic rationale for the clinical use of pharmacologic modulators to induce regression of glomerular diseases.

Renal progenitors in non-diabetic and diabetic nephropathies

Chronic kidney disease represents a major health problem worldwide. Although the kidney has the ability to repopulate structures that have sustained some degree of injury, the mechanisms underlying its regenerative capacity have been unclear. Recent evidence now supports the existence of a renal progenitor system able to replace podocytes and tubular cells, localized within the urinary pole of Bowman's capsule and along the tubule. Altered growth or differentiation of renal progenitors has been reported in several renal disorders including diabetic nephropathy. Pharmacological modulation of renal progenitor growth or differentiation can enhance kidney regeneration, suggesting that treatments aimed at reversing kidney injury are possible. Renal progenitors may represent a novel target in diabetic nephropathy and other kidney disorders.

Podocyte biology in segmental sclerosis and progressive glomerular injury

During the past 2 decades, progress has been made in understanding the biology and mechanisms of podocyte injury and the relationship of these processes to glomerulosclerosis. In addition, studies of human biopsies and animal models have provided insights into the mechanisms of glomerular disease progression and repair. These new developments are critical for establishing better therapeutic guidelines that target specific pathways, which otherwise would lead to irreversible injury.

Increased capillary branching contributes to angiotensin type 1 receptor blocker (ARB)-induced regression of sclerosis

Chronic kidney disease is characterized by progressive glomerulosclerosis and tubulointerstitial fibrosis. High-dose angiotensin type 1 receptor blocker (ARB) or angiotensin-converting enzyme inhibitor can induce regression of existing glomerulosclerosis, at least in part by decreasing matrix accumulation. However, the potential mechanisms of remodeling of capillary loops remain obscure. This study aimed to determine whether capillary branching was augmented in glomeruli with ARB-induced regression of sclerosis. Three-dimensional confocal images were assessed by graph theory analysis to explore the topology of the glomerular capillary network. Compared with normal glomeruli, glomeruli of rats with progressive sclerosis were enlarged but had a significantly reduced number of capillary segments and capillary branch points and decreased complexity of the glomerular network. In contrast, in rats with regression of sclerosis induced by ARB, glomerular enlargement was due to a significantly increased number of glomerular capillary segments and capillary branch points and restored complexity of the capillary network. These data support the theory that capillary growth contributes to regression of sclerosis and is mediated at least in part by ARB-induced increased complexity and branching of capillary segments.

The role of renin angiotensin system inhibition in kidney repair

Chronic kidney diseases share common pathogenic mechanisms that, independently from the initial injury, lead to glomerular hyperfiltration, proteinuria, and progressive renal scarring and function loss. Inhibition of the renin angiotensin system (RAS) has been consistently found to reduce or halt the progressive deterioration of renal function through reduction of blood pressure and proteinuria, the two main determinants of renal function decline. In few instances, RAS inhibition may even promote amelioration of the glomerular filtration rate. Animal data suggest that chronic therapy with angiotensin-converting enzyme inhibitors or angiotensin II receptor type I blockers promotes regression of glomerulosclerosis, even in later phases of the disease. In humans, studies investigating the effect of angiotensin II inhibition on renal structural changes have shown inconsistent results, possibly due to small numbers and/or short duration of follow-up. Whether regression of glomerulosclerosis relies on a direct regenerative effect of RAS inhibition or on spontaneous kidney self-repair after the injury has been removed is still unknown. Improved understanding of mechanisms that promote renal regeneration may help in designing specific therapies to prevent the development of end-stage renal disease. This is a desirable goal, considering the economic burden of chronic kidney diseases and their effect on morbidity and mortality.

Kidney regeneration

Neonephrogenesis, the capacity to regenerate renal tissue, is a distinctive feature of fish but not usually of mammals. However, evidence exists for kidney repair in response to insulting agents for animals and human beings. Studies have therefore been designed in the past few years to clarify the cellular and molecular basis of renal repair, with the aim to investigate the potential regenerative capacity of animal and human kidneys. Three main questions are being addressed by this research: whether terminally differentiated cells in adult animal kidneys have regenerative capacity; whether multipotent progenitor cells exist in kidneys; and whether renal repair can be favoured or accelerated by cells of extrarenal origin migrating to the kidney in response to injury. In this Review, we describe evidence of cellular and molecular pathways related to renal repair and regeneration, and review data from animal and human studies that show that the kidney might have regenerative capacity.

Podocyte repopulation contributes to regression of glomerular injury induced by ACE inhibition

Angiotensin-converting enzyme (ACE) inhibition induces glomerular repair in the Munich Wistar Frömter (MWF) rat, a model of spontaneous glomerular injury. In this study, we investigated whether this effect is related to changes in glomerular cell number, particularly of podocytes, which are progressively lost with age. MWF rats with advanced nephropathy were studied at both 40 weeks and after 20 weeks of observation either with or without treatment with the ACE inhibitor lisinopril. Forty-week-old Wistar rats were used as controls. In untreated MWF rats, proteinuria, hypertension, glomerulosclerosis, and renal function worsened, while lisinopril induced regression of both functional and structural changes. Despite glomerular hypercellularity in untreated MWF rats, the number of endothelial cells per glomerulus did not change, and podocyte number even decreased. ACE inhibition halted the progressive increase in glomerular cell number and enhanced endothelial cell volume density. Surprisingly, lisinopril not only halted age-related podocyte loss but also increased the number of glomerular podocytes above baseline, which was associated with an increased number of proliferating Wilms tumor 1-positive cells, loss of cyclin-dependent kinase inhibitor p27 expression, and increased number of parietal podocytes. These data indicate that ACE inhibition restructures glomerular capillary, primarily by restoring the podocyte population in this model of glomerular injury. Increased parietal podocyte number in lisinopril-treated MWF rats suggests that the remodeling of Bowman's capsule epithelial cells contributes to this effect.

Effects of celecoxib and nordihydroguaiaretic acid on puromycin aminonucleoside-induced nephrosis in the rat

The selective cyclooxygenase-2 (COX-2) and 5-lipoxygenase (LOX) inhibitors might inhibit prostaglandin synthesis and reduce proteinuria. The present study was designed to investigate the anti-proteinuric effects of nordihydroguaiaretic acid (NDGA) as compared with celecoxib in puromycin aminonucleoside (PAN) nephrosis rats. Fifty five male Sprague-Dawley rats were divided into 4 groups; A, normal control; B, PAN group; C, PAN+COX-2 inhibitor (celecoxib) group; and D, PAN+5-LOX inhibitor (NDGA) group. After induction of PAN nephrosis through repeated injections of PAN (7.5 and 15 mg/100 g body weight), rats were treated with celecoxib, NDGA, or vehicle for 2 weeks. Twenty four hour urine protein excretions were significantly lower in PAN+celecoxib and PAN+NDGA groups than in PAN group. Serum creatinine (SCr) concentrations and 24 hr urine creatinine clearances (CCr) were not significantly different in the four groups. Electron microscopy showed that podocyte morphology was changed after the induction of PAN nephrosis and was recovered after celecoxib or NDGA administration. Celecoxib significantly recovered the expressions of nephrin, CD2AP, COX-2, and TGF-beta. NDGA also recovered TGF-beta expression, but did not alter the expressions of nephrin, CD2AP and COX-2. The present study suggested that celecoxib and NDGA might effectively reduce proteinuria in nephrotic syndrome without impairing renal function.

Regression of glomerular injury by losartan in experimental diabetic nephropathy

Many features of chronic kidney disease may be reversed, but it is unclear whether advanced lesions, such as adhesions of sclerotic glomerular tufts to Bowman's capsule (synechiae), can resolve during treatment. We previously showed, using a renal ablation model, that the renoprotective effect of the AT-1 receptor blocker, losartan, is dose-dependent. Here we determined if moderate and advanced glomerular lesions, associated with streptozotocin-induced diabetes, regress with conventional or high-dose losartan treatment. Using daily insulin injection for 10 months, we maintained diabetic adult male Munich-Wistar rats in a state of moderate hyperglycemia. Following this period, some rats continued to receive insulin with or without conventional or high-dose losartan for an additional 2 months. Diabetic rats pretreated with insulin for 10 months and age-matched non-diabetic rats served as controls. Mesangial expansion was found in the control diabetic rats and was exacerbated in those rats maintained on only insulin for an additional 2 months. Conventional and high-dose losartan treatments reduced this mesangial expansion and the severity of synechiae lesions below that found prior to treatment; however, the frequency of the latter was unchanged. There was no dose-response effect of losartan. Our results show that regression of mesangial expansion and contraction of sclerotic lesions is feasible in the treatment of diabetes, but complete resolution of advanced glomerulosclerosis may be hard to achieve.

Reversal of proteinuric renal disease and the emerging role of endothelin

Proteinuria is a major long-term clinical consequence of diabetes and hypertension, conditions that lead to progressive loss of functional renal tissue and, ultimately, end-stage renal disease. Proteinuria is also a strong predictor of cardiovascular events. Convincing preclinical and clinical evidence exists that proteinuria and the underlying glomerulosclerosis are reversible processes. This Review outlines the mechanisms involved in the development of glomerulosclerosis--particularly those responsible for podocyte injury--with an emphasis on the potential capacity of endothelin receptor blockade to reverse this process. There is strong evidence that endothelin-1, a peptide with growth-promoting and vasoconstricting properties, has a central role in the pathogenesis of proteinuria and glomerulosclerosis, which is mediated via activation of the ET(A) receptor. Several antiproteinuric drugs, including angiotensin-converting-enzyme inhibitors, angiotensin receptor antagonists, statins and certain calcium channel blockers, inhibit the formation of endothelin-1. Preclinical studies have demonstrated that endothelin receptor antagonists can reverse proteinuric renal disease and glomerulosclerosis, and preliminary studies in humans with renal disease have shown that these drugs have remarkable antiproteinuric effects that are additive to those of standard antiproteinuric therapy. Additional clinical studies are needed.

Improvement in eGFR in patients with chronic kidney disease attending a nephrology clinic. Int Urol Nephrol. 2008;40:841-848. [PMID: 18386153 DOI: 10.1007/s11255-008-9360-9]

BACKGROUND

The adverse effects arising from late referral to a nephrologist of patients with chronic kidney disease (CKD) are well known. Retrospectively we examined the initial characteristics of patients referred in various stages of CKD to our nephrology division and tried to identify potential baseline factors associated with subsequent changes in estimated glomerular filtration rate (eGFR).

PATIENTS AND METHODS

Between September 1997 and June 2006 1,443 patients (909 male, 534 female) with CKD, with eGFRs ranging from 15 to 89 ml/min, were referred to our nephrology division and categorized using the National Kidney Foundation classification for CKD based on eGFR. The slope of eGFR change (ml/min-1/1.73/m2-1/year-1) was determined by linear regression analysis and the patients were divided into five groups: (1) significantly progressive slope (deterioration) (more negative than -5 ml/min/year); (2) mildly progressive slope (>-5 to <or=-1); (3) stable slope (>-1 to <or=+1); (4) mildly improved slope (>+1 to <or=+5), and (5) significantly improved slope (>or=+5).

RESULTS

At the first nephrology referral, 5.8% of the patients were on CKD stage 2 (eGFR: 90-60 ml/m), 46.7% on CKD stage 3 (eGFR: 59-30 ml/m), and 47.5% on CKD stage 4 (eGFR: 29-15 ml/m) CKD. Significantly improved slope was detected in 48.2% of CKD stage 2 patients, 29.3% of CKD stage 3 patients, and only 14.7% of CKD stage 4 patients (P<0.05). Being in stage 4 or stage 3 versus being in stage 2 significantly reduced the likelihood of an improved slope in logistic regression analysis whereas age, gender, presence of hypertension, and diabetes mellitus did not reach the level of significance.

CONCLUSION

Referral to a nephrology clinic can lead not only to arrest of progression of CKD but also to regression/improvement. Early referral is a positive predictive factor for improvement in eGFR, which emphasizes the importance of such referral. The previously held idea that, once established, CKD progresses invariably is not valid anymore.

Role of remission clinics in the longitudinal treatment of CKD

Heavy proteinuria is a major determinant of progression to ESRD for patients with chronic nephropathies and reducing proteinuria should be a key target for renoprotective therapy. In the Remission Clinic, we applied a multimodal intervention to target urinary proteins in 56 consecutive patients who had >3 g proteinuria/d despite angiotensin-converting enzyme inhibitor therapy. We compared the rate of GFR decline and incidence of ESRD in this cohort with 56 matched historical reference subjects who had received conventional therapy titrated to a target BP. During a median follow-up of 4 yr, the monthly rate of GFR decline was significantly lower in the Remission Clinic cohort (median -0.17 versus -0.56 ml/min per 1.73 m2; P < 0.0001), and ESRD events were significantly reduced (3.6 versus 30.4% reached ESRD). Follow-up BP, cholesterol, and proteinuria were lower in Remission Clinic patients than in reference subjects, such that disease remission or regression was achieved in up to 50% of patients who would have been otherwise expected to progress rapidly to ESRD on conventional therapy. Proteinuria reduction independently predicted a slower rate of GFR decline and ESRD incidence, but response to treatment differed depending on the underlying disease. Regarding safety, no patient was with drawn because of hyperkalemia. In summary, multidrug treatment titrated to urinary protein level can be safely and effectively applied to normalize proteinuria and to slow the loss of renal function significantly,especially among patients without type 2 diabetes and with otherwise rapidly progressing chronic nephropathies.

ACE inhibition reduces glomerulosclerosis and regenerates glomerular tissue in a model of progressive renal disease

Today angiotensin II inhibition is primarily used to slow the rate of progression of kidney diseases. There is evidence that these therapies can induce a partial regression of glomerular lesions. However, we do not know yet the extent of sclerotic lesion regression and whether new glomerular tissue is formed to help support the renal function. We used male Munich Wistar Fromter (MWF) rats, an experimental model for progressive kidney disease, to quantify kidney structural lesions upon angiotensin-converting enzyme (ACE) inhibition therapy. Animals were studied at 50 weeks of age, when renal function and structure are severely altered, and after a 10-week observation period, without or with treatment with lisinopril (80 mg/l in drinking water). A group of untreated Wistar rats was used as controls. With age, proteinuria, and serum creatinine worsen, but lisinopril almost normalized proteinuria and stabilized serum creatinine. Serial section analysis of whole glomerular tufts showed that at baseline, glomerulosclerosis affected the entire glomerular population, and that these changes further increased with age. Lisinopril significantly reduced incidence and extent of glomerulosclerosis, with the presence of glomerular tufts not affected by sclerosis (23% of glomeruli). Glomerular volume was not significantly affected by treatment, and glomerular mass spared from sclerosis increased from 46.9 to 65.5% upon treatment, indicating consistent regeneration of glomerular tissue. Lisinopril normalized baseline glomerular transforming growth factor-beta and alpha-smooth muscle actin overexpression, and prevented worsening of interstitial changes. Hence, ACE inhibition, which is widely used in human kidney disease, may not only halt the progression of renal failure, but also actually induce the regeneration of new renal tissue.

Low molecular weight heparin in the treatment of puromycin-induced nephrosis

Heparin may have a beneficial effect in proteinuric renal diseases, where negative charges of the glomerular capillary membrane are compromised. We evaluated the role of low molecular weight heparin (LMWH - 3000 Da) in puromycin aminonucleoside (PAN)-induced focal and segmental glomerulosclerosis in male Wistar rats: Controls (C) n=7, LMWH-treated group, n=9, subcutaneously (SC), 6 mg/kg every day. The PAN group (n=7) received 7 doses on weeks 0, 1, 2, 4, 6, 8, 10 (SC - 2mg/100g), and a group PAN+LMWH (n=6). After 12 weeks, cholesterol and triglycerides were higher in nephrotic groups, as well as proteinuria and urinary IgG. Kidney weight, glomerular volume, and glomerular sclerosis index were higher in the PAN-treated groups. Glomerular capillary length density (L(Vcap)) and glomerular capillary surface density (S(Vcap)) were lower in the PAN group, and mesangial fractional volume was higher. Fibronectin immunostaining was more intense in the PAN group, and collagens I and III were absent in the studied glomeruli. Thus, LMWH prevented mesangial expansion and capillaries changes, showing antiproliferative properties, despite worsening glomerular permeability changes in the PAN model. In conclusion, LMWH interferes in the complications of PAN model, but not through inhibition of the proteinuria.

Mechanisms of progression and regression of renal lesions of chronic nephropathies and diabetes

The incidence of chronic kidney diseases is increasing worldwide, and these conditions are emerging as a major public health problem. While genetic factors contribute to susceptibility and progression of renal disease, proteinuria has been claimed as an independent predictor of outcome. Reduction of urinary protein levels by various medications and a low-protein diet limits renal function decline in individuals with nondiabetic and diabetic nephropathies to the point that remission of the disease and regression of renal lesions have been observed in experimental animals and even in humans. In animal models, regression of glomerular structural changes is associated with remodeling of the glomerular architecture. Instrumental to this discovery were 3D reconstruction studies of the glomerular capillary tuft, which allowed the quantification of sclerosis volume reduction and capillary regeneration upon treatment. Regeneration of capillary segments might result from the contribution of resident cells, but progenitor cells of renal or extrarenal origin may also have a role. This review describes recent advances in our understanding of the mechanisms and mediators underlying renal tissue repair ultimately responsible for regression of renal injury.

Complement inhibitors targeted to the proximal tubule prevent injury in experimental nephrotic syndrome and demonstrate a key role for C5b-9

In glomerular diseases of diverse etiologies, dysfunction of the glomerular barrier to protein passage results in proteinuria, and proteinuria is considered an independent risk factor that plays a direct role in inflammation, interstitial fibrosis, and renal failure. The mechanism by which proteinuria leads to nephrotoxic injury is unclear, but a role for complement in mediating interstitial damage appears likely. We describe a strategy for Ag-specific targeting of complement inhibitors using a single chain Ab fragment and show that complement inhibitors targeted to the tubular epithelium protect against tubulointerstitial injury and renal dysfunction in a rat model of puromycin-induced nephrosis. The targeting of systemically administered complement inhibitors markedly enhanced their efficacy and obviated the need to systemically inhibit complement, thus reducing the risk of compromising host defense and immune homeostasis. Targeted inhibition of complement activation by Crry, and of membrane attack complex (MAC) formation by CD59 was equally therapeutic, demonstrating that the MAC plays a key role in proteinuria-induced tubulointerstitial injury. CD59 activity was dependent on its being targeted to the site of complement activation, and this is the first report of specific inhibition of the MAC in vivo after systemic administration of inhibitor. The data establish the MAC is a valid target for pharmaceutical intervention in proteinuric disorders and provide an approach to investigate the role of the MAC in complement-dependent disease under clinically relevant conditions.

Regression of glomerulosclerosis with high-dose angiotensin inhibition is linked to decreased plasminogen activator inhibitor-1

The potential and possible mechanisms for regression of existing glomerulosclerosis by angiotensin II type 1 receptor antagonist (AT1RA) and/or angiotensin I converting enzyme inhibitor (ACEI) were investigated. Adult male Sprague Dawley rats underwent 5/6 nephrectomy (Nx). Glomerulosclerosis was assessed by renal biopsy 8 wk later, and rats were divided into groups with equal biopsy sclerosis and treated for the next 4 wk until they were killed at 12 wk as follows: Control with no further treatment (CONT), high-dose AT1RA, high-dose ACEI, and varying AT1RA+ACEI combinations. Hypertension and proteinuria induced by 5/6 Nx were significantly decreased by all treatments, except high-dose ACEI, which showed persistent proteinuria. High-dose AT1RA and ACEI markedly decreased progression of sclerosis, with -2.3% average decrease in sclerosis from biopsy to autopsy in AT1RA versus 194% increase in CONT (P < 0.0001). Glomerulosclerosis regressed, with less severe lesions at the time when the rats were killed than at biopsy in 62% of AT1RA-treated and 57% of ACEI-treated rats. In contrast, only 17 to 33% of rats in combination groups had regression. Alternatively, these data might be viewed as reflecting halting of progression, as some groups had higher BP and proteinuria. However, this potential confounding effect does not negate the effects to achieve regression of sclerosis in these rats. Regression was not explained by changes in mRNA of TGF-beta1 and matrix metalloproteinase-2 and -9 but was linked to decreased tissue inhibitor of metalloproteinase-1 and plasminogen activator inhibitor-1. It is concluded that angiotensin inhibition mediates regression in part by effects on matrix modulation.

Enalapril in children with Alport syndrome

Ten pediatric patients with Alport syndrome received enalapril for 5 years. There were nine boys. Eight patients have the X-linked form of the disease and two the autosomal recessive form. The median age at the start of treatment was 10.25 years. Only one patient was hypertensive. The starting dose of enalapril was 0.05 mg/kg; the target dose was 0.5 mg/kg per day. The median dose given effectively was 0.24, 0.37, 0.45, 0.43, and 0.49 mg/kg per day at years of study 1, 2, 3, 4, and 5, respectively. The median urinary protein/creatinine ratio was 1.58 g/g (range 0.49-4.60) before treatment. This decreased to 0.98, 1.09, 1.35, 1.11, and 1.38 g/g after 1, 2, 3, 4, and 5 years, respectively. The median creatinine clearance at baseline was 100 ml/min per 1.73 m2 (range 82-133) and after 5 years 92 ml/min per 1.73 m2 (range 22-115). Three patients did not reach the target dose of enalapril because of orthostatic hypotension. One of them was the only patient to develop chronic renal failure within 5 years. The present study indicates that enalapril reduces urinary protein excretion and preserves glomerular filtration in Alport patients as a group. However, there was individual variation, as in most studies of patients with proteinuric nephropathies given inhibitors of the angiotensin-converting enzyme.

Animal models of FSGS: lessons for pathogenesis and treatment

Glomerulosclerosis in a heterogeneous pattern, ie, focal and segmental glomerulosclerosis (FSGS), is a common endpoint in a variety of settings, including idiopathic FSGS, and scarring secondary to other renal or systemic diseases. These different causes contribute to the diverse clinical outcomes of histological focal sclerosis, and the varying histologic manifestations of sclerosis. Numerous models have been established in the rat that aim to mirror the various elements of human glomerulosclerosis. With the availability of knockout gene technology, many, but not all of these models have been translated to mouse species. This review will focus on the remnant kidney model, the podocyte injury models of puromycin aminonucleoside or adriamycin injection, and examples of newly developed genetic models, such as knockout of CD2 associated protein (CD2AP).

Outcome of relapse in lupus nephritis: roles of reversal of renal fibrosis and response of inflammation to therapy

BACKGROUND

Renal relapse in lupus nephritis has been shown to have ominous prognostic significance with the majority of patients progressing to doubling of serum creatinine (CRX2). However, not all patients do so. This report explores the roles of response of inflammation to therapy and of glomerular scarring and interstitial fibrosis and their potential reversal to outcome of renal relapse.

METHODS

Renal biopsies from 71 patients with lupus nephritis with an initial biopsy (Bx1) and systematic control biopsy (Bx2) after six months of therapy, as well as subsequent biopsies for clinical indications, were studied. The relationships of morphologic factors to renal relapse and its outcome as well as to CRX2 and end-stage renal disease (ESRD) were analyzed. Cox proportional hazards modeling was used to assess association of morphologic variables with outcomes.

RESULTS

Renal interstitial fibrosis and glomerular segmental scarring were partially reversible in 17 and 11 patients, respectively. This decline was associated with an excellent prognosis, with only one patient in each group (5.9% and 9.1% respectively) progressing to CRX2. All 18 patients who progressed to CRX2 either failed to respond to therapy (7 patients) as defined by normalization of serum creatinine (SCr) and reduction of proteinuria to < or =1 g/day, or relapsed after initial response (11 patients), as defined by recent rise of SCr > 50% and/or proteinuria > 3.5 g/day. However, relapse also occurred in 11 of 47 other patients without progression to CRX2. These patients showed a greater initial response of inflammation and deposits to therapy and fibrous lesions partially reversed in the period prior to relapse, so that active lesions were superimposed on a lower level of chronic lesions. By contrast, chronic lesions mounted steadily in those who progressed to CRX2. Cox proportional hazards modeling indicated a strong association of inflammatory variables with renal relapse, CRX2 and ESRD. However, the extent of immunoglobulin deposits was not significantly associated with any outcome. Finally, we found that failure of disease to remit also is associated with a high rate of CRX2 (64.8% vs. 13.0%, P = 0.00034).

CONCLUSIONS

Interstitial fibrosis and glomerular scarring in systemic lupus erythematosus are partially reversible, and this reversal is attended by an excellent outcome. The outcome of renal relapse is determined by the initial response of inflammatory and chronicity elements to therapy, those with prior partial reversal of interstitial and glomerular scarring having a good outcome, and those in whom fibrotic lesions have continued to increase and have a poor outcome. Inflammatory variables appear to be more important in determining outcome than immunoglobulin deposits.

Does captopril change oxidative stress in puromycin aminonucleoside nephropathy?

Puromycin aminonucleoside (PAN) nephropathy in rats has been induced by the intraperitoneal injections of PAN. One group of animals which received PAN has been treated simultaneously with captopril (angiotensine converting enzyme-ACE-inhibitor) with the aim to test whether continuing treatment with captopril along with PAN injections would be able to modulate the toxic effects of PAN. The third group of rats was given only captopril. Morphological changes in the kidney were evaluated by scanning electron microscopy that showed the loss of podocyte foot processes in the kidney of PAN treated animals but also in the kidney of captopril treated ones as well as in the animals treated with both drugs simultaneously. Reduced glutathione content, catalase, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), xanthine oxidase activities as well as lipid peroxides were investigated in rat blood and kidney. Captopril given alone produced a significant decrease of plasma lipid peroxides, but it did not show any significant effect on investigated antioxidative factor levels neither in blood nor in the kidney. PAN given alone produced a significant depletion of plasma lipid peroxides, kidney catalase and erythrocyte GSH-Px activity as well as a significant increase of plasma catalase and erythrocyte SOD activity. Treatment of animals with both drugs simultaneously resulted in a significant increase of erythrocyte SOD activity and a significant decrease of plasma lipid peroxides, erythrocyte GSH-Px and kidney SOD activities. Kidney xanthine oxidase activity showed a significant increase in both PAN and PAN plus captopril treated animals in comparison with the values of captopril treated rats. These data suggest that PAN changes the antioxidative factor pattern in rat blood and kidney. Contrary to our expectations that captopril may protect the toxic effects of PAN it only to a certain extent modifies these effects showing protective effect only on tissue catalase activity.

Peritubular capillary flow determines tubulointerstitial disease in idiopathic nephrotic syndrome

The spatial relationship between renal perfusion and nephronal structure was determined in 51 nephrotic patients consisting of 11 patients with steroid sensitive, minimal change (MC) nephrosis, 12 patients with steroid resistant, mesangial proliferative (MesP) nephrosis and without tubulointerstitial fibrosis (TIF), 11 patients with steroid resistant, MesP nephrosis and with low grade TIF and 17 patients with focal segmental glomerulosclerosis (FSGS). The intrarenal hemodynamic study revealed a unique correlation between renal perfusion and nephronal structure. A normal or slight reduction in peritubular capillary flow observed in MC or mild MesP nephrosis correlates with an intact tubulointerstitial structure. A moderate reduction in peritubular capillary flow observed in steroid resistant, MesP nephrosis induces a low incidence of TIF. A severe reduction in peritubular capillary flow denotes a higher incidence of TIF as that observed in nephrosis with FSGS. Thus, it is of notion that the reduction in renal perfusion precedes the development of tubulo-interstitial fibrosis and thereby supports the concept of renal perfusion as a crucial determinant of nephronal structure.

The role of angiotensin II and plasminogen activator inhibitor-1 in progressive glomerulosclerosis

Regardless of the primary cause, progressive renal deterioration with sclerosis is a hallmark of many renal diseases. Several studies have shown the superiority of angiotensin-converting enzyme inhibitors compared with other antihypertensive agents in providing protection from progressive renal deterioration. Furthermore, animal studies have shown that angiotensin II antagonists in excess of antihypertensive doses can also ameliorate or reverse glomerulosclerosis, leading to the hypothesis that angiotensin II has nonhemodynamic effects that mediate the renoprotective effects shown in these investigations. Although historically angiotensin II has been associated with salt and fluid homeostasis, recent data show that angiotensin II induces cell growth and matrix accumulation in glomerular cells. Plasminogen activator inhibitor-1 has been shown to be the major inhibitor of tissue plasminogen activator and urokinase-like plasminogen activator, with potentially important effects not only on thrombosis/fibrinolysis, but also on matrix degradation because of the proteolytic actions of these substances. Angiotensin II has been shown to influence the actions of plasminogen activator inhibitor-1 and, consequently, its thrombotic and sclerotic effects. Various studies, both in vitro and in vivo, have shown that direct hemodynamic actions, modulation of endothelial injury, and growth factor actions also may be important in the development of sclerosis. These factors can be directly modulated by angiotensin II inhibition. Sclerosis may even be reversed when therapies augment matrix degradation processes, both by directly increasing proteolytic activity and by downregulating inhibitors of matrix degradation. These observations indicate that angiotensin II is important in fibrotic as well as thrombotic renal injuries that lead to progressive renal disease and also in the development of therapies such as specific angiotensin receptor antagonists to prevent or reverse these conditions.

Biphasic glomerular hypertrophy in rats administered puromycin aminonucleoside

Recent evidence suggests that glomerular hypertrophy is a key event in the development of focal and segmental glomerulosclerosis and hyalinosis (FSGS) in humans and in many experimental models of FSGS. The initial aim of the present study was to determine if glomerular hypertrophy occurs in a puromycin aminonucleoside (PAN) model of FSGS, previously considered not to involve glomerular hypertrophy. Upon identifying significant glomerular hypertrophy, our second aim was to determine the contribution of glomerular capillary growth to this hypertrophy. Female Sprague-Dawley rats (approximately 200 g) were administered either PAN (2 mg/100 g body wt) subcutaneously, or an equivalent volume of 0.9% saline at weeks 0, 1, 2, 4, 6, 8 and 10. Tissue was analyzed at weeks 7 and 13. Unbiased stereological methods were used to estimate a range of glomerular parameters. Mean glomerular tuft volume in PAN-treated rats was 48% greater than in saline-treated rats at seven weeks, and 63% greater at 13 weeks. Similar results were found for mean renal corpuscle volume. FSGS was absent at seven weeks and minor at 13 weeks. Two-way analysis of variance indicated: significant effects (P < 0.05 at least) of PAN on capillary length per glomerulus, capillary surface area per glomerulus, capillary diameter and length of capillaries per unit volume of glomerulus; and significant effects of time on capillary diameter, capillary length per unit volume of glomerulus and capillary surface area per unit volume of glomerulus. The mean length of capillaries per glomerulus was 45% greater in PAN-treated rats at week 7 and 22% greater in PAN-treated rats at week 13. Taken together, these results indicate a biphasic pattern of glomerular hypertrophy in this model. In the first phase (to 7 weeks), an increase in capillary length contributes to glomerular hypertrophy. In the second phase (7 to 13 weeks), the continued glomerular enlargement appears more likely to be due to an increase in capillary diameter and/or mesangial matrix expansion.

Abnormal permeability to proteins and glomerular lesions: a meta-analysis of experimental and human studies

Whether abnormal protein traffic through the glomerular capillary is one of the possible causes of glomerular injury has been a matter of considerable controversy. Experimental and clinical evidence indicate an association between the two, and several explanations of potential pathophysiologic pathways are available that may explain protein-dependent forms of renal injury. However, none of the mechanisms suggested thus far have been definitely proven. A meta-analytic review was used to further explore the relationship between urinary protein excretion and glomerular injury in experimental and human proteinuric nephropathies. In experimental models a definite positive association (P < 0.0001) was found between urinary protein excretion and glomerulosclerosis. The overall effect size d for this relationship was 2.36 (95% confidence interval, 2.13 to 2.60), corresponding to a correlation coefficient of r = 0.76. Similarly, the correlation between albuminuria and glomerular sclerotic lesions was highly significant (overall d = 2.88; 95% confidence interval, 2.33 to 3.42; P < 0.0001; correlation coefficient, r = 0.82). In humans the meta-analytic correlation yielded analogous, although less striking, results (overall d = 0.58; 95% confidence interval, 0.43 to 0.73; P < 0.0001; correlation coefficient, r = 0.28). In conclusion, meta-analysis of data from studies examining urinary protein excretion revealed a significant positive correlation with glomerular sclerosis in both experimental models and human diseases. This study supports the role of abnormal protein traffic through the glomerular capillary as one of the possible causes of renal injury. However, the strong relationship found does not necessary establish a cause-and-effect relationship.

ACE inhibition reduces proteinuria, glomerular lesions and extracellular matrix production in a normotensive rat model of immune complex nephritis

We studied the effect of the angiotensin converting enzyme (ACE) inhibitor, quinapril, on the clinical and morphological lesions of a normotensive model of immune complex nephritis. Untreated rats developed massive nephrotic syndrome, intense cell proliferation and glomerular and tubulointerstitial lesions. In the renal cortex of nephritic rats there was a significant increase in gene expression of TGF-beta 1, fibronectin and collagens, and ACE activity. Systolic blood pressure remained normal with progression of the disease. Administration of quinapril for three weeks to animals with glomerular lesions (proteinuria 20 to 50 mg/day) avoided the development of intense proteinuria (79 +/- 28 vs. 589 +/- 73 mg/day, P < 0.001) and decreased cell proliferation, glomerulosclerosis, tubulointerstitial lesions, and inflammatory infiltrates. Cortical gene expression of TGF-beta 1 and matrix proteins was also diminished. ACE activity was inhibited by 68% in renal cortex. These results show that quinapril administration to normotensive rats with immune complex nephritis decreases proteinuria and glomerular and tubulointerstitial lesions, probably modulating the local angiotensin II generation and its effects on cell growth, TGF beta and matrix protein synthesis.

The combination of lovastatin and enalapril in a model of progressive renal disease

Puromycin-induced nephrotic syndrome is an animal model of progressive renal disease. Both angiotensin converting enzyme inhibitors and lipid-lowering agents have been used to preserve renal structure and function in this model, although neither completely prevents progression. We tested the hypothesis that the combination of the two agents would be more protective than either alone. Rats were divided into five groups; all were uninephrectomized. Four groups were given puromycin at a dose of 10 mg/100 g body weight (BW) with additional doses of 4 mg/100 g BW given intraperitoneally at 4, 5, and 6 weeks thereafter. One group was given enalapril (EN) 50 mg/l dissolved in the drinking water; the second received lovastatin (L) 15 mg/kg given daily by gavage; the third received both agents; the fourth was left untreated, and the final group received no puromycin and served as the control group. Eight weeks after the initial dose of puromycin, glomerular filtration rate (GFR), as inulin clearance, and protein excretion were determined and blood was collected for cholesterol and triglycerides. Blood pressure was not different between any of the groups. At the end of the study period, serum cholesterol [mean +/- SD, 252 +/- 185 mg/dl (L), 135 +/- 101 mg/dl (L + EN)] and triglycerides (239 +/- 200, 148 +/- 158 mg/dl) were significantly lower (P < 0.001) in the lovastatin-treated groups than in the untreated puromycin group (535 +/- 255 mg/dl and 579 +/- 561 mg/dl, cholesterol and triglyceride, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Lysosomal iron accumulation and tubular damage in rat puromycin nephrosis and ageing

1. Energy dispersive X-ray spectrometry was used to examine the relationship between proteinuria and increased urinary iron excretion, and structural and functional damage in puromycin nephrosis. 2. After 11-12 days rats treated with puromycin (10 mg/100 g, i.v.i.) had greater proteinuria (211.6 +/- 35.7 mg/day, mean +/- s.e.m.) and urinary iron excretion (15.4 +/- 2.2 micrograms/day) than saline-treated controls (14.5 +/- 1.4 mg/day and 1.1 +/- 0.2 micrograms/day, respectively, both P < 0.001). 3. On day 13, mean lysosomal iron concentration of proximal tubular cells (306.6 +/- 64.5 vs 11.9 +/- 8.6 mg%, P < 0.001), and proximal tubular cell damage assessed semi-quantitatively (1.17 +/- 0.10 vs 0.62 +/- 0.10, P < 0.001) were higher and creatinine clearance (0.15 +/- 0.01 vs 0.29 +/- 0.02 mL/min per g kidney weight, P < 0.001) lower than in control rats. 4. At days 35, 60 and 360 there were no differences in any of the measured parameters between rats treated with puromycin or saline, and in both groups proteinuria, tissue damage and lysosomal iron concentration increased with time. 5. Lysosomal iron accumulation was the only independent predictor of both functional and structural damage. 6. In conclusion, the apparent association between proteinuria and tubulo-interstitial damage in puromycin nephrosis, and with ageing, is best explained by factors associated with accumulation of iron within lysosomes of proximal tubule cells.

Effect of enalapril on proteinuria after kidney transplantation

We studied the effect of enalapril, an inhibitor of angiotensin-converting enzyme (iACE), on proteinuria and renal function in recipients of renal allografts. Twenty-two patients with post-transplant nephrotic syndrome were treated with incremental doses of enalapril for 1 year. Urinary protein excretion decreased after 2 months of treatment from a mean of 8.9 g/day (range 4.0-18.9 g/day) to 4.5 g/day (range 0.4-10.0 g/day; P < 0.01) and remained significantly low for the rest of the study. However, in the same period, creatinine clearance did not change significantly; it went from 47.8 ml/min (range 17.1-110.3 ml/min) before treatment to 44.2 ml/min (range 16.5-88.5 ml/min) after 2 months of iACE therapy. Analysis of individual data showed that there was a significant reduction in proteinuria in 14 of the 22 patients and that the rate of deterioration of renal function did not increase in 17 of the 22 patients. We did not observe any serious side effects of enalapril administration. The results of our study prove that iACE can be used safely and effectively to reduce post-transplant proteinuria.

Cause of variable therapeutic efficiency of angiotensin converting enzyme inhibitor on glomerular lesions

We tested the effect of angiotensin I converting enzyme inhibitor (ACEI) on established glomerular sclerosis. Starting eight weeks after subtotal nephrectomy (sNPX), rats were given enalapril for four weeks in a dose of 50 (Group II, N = 5) or 200 mg/liter drinking water (Group III, N = 5). A third group of sNPX rats not given ACEI served as control (Group I, N = 10). Glomerular sclerosis index (S1, 0 to 4 scale) was assessed three-dimensionally on serial thin sections for individual glomeruli at biopsy (Bx, 8 weeks), and divided into four different ranks of severity and compared to autopsy (Ax, 12 weeks). In Group I control rats, 48% of the glomeruli at Bx had SI between 0 and 1 (rank 1, average: 0.49 +/- 0.06), 36% between 1 and 2 (rank 2, average: 1.53 +/- 0.06), 9% between 2 and 3 (rank 3, average: 2.45 +/- 0.12) and 7% between 3 and 4 (rank 4, average: 3.54 +/- 0.10). Glomeruli of the same rats at Ax were ranked according to severity of sclerosis, and then divided into percentile groups, corresponding to the percent of distribution at Bx. The 48% least sclerotic glomeruli at Ax had average SI of 0.69 +/- 0.08, the next 36% 2.58 +/- 0.11, and next 9% 3.97 +/- 0.02 and the most sclerotic 7% 4.00 +/- 0.00. Thus, sclerosis advanced during the last four weeks after biopsy in all glomeruli, with more accelerated progression occurring toward later stages of sclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)