Antiproteinuric effect predicts renal protection by angiotensin-converting enzyme inhibition in rats with established adriamycin nephrosis

Diabetic Kidney Disease: An Update

Diabetes is a major public health challenge and diabetic kidney disease (DKD), a broader diagnostic term than diabetic nephropathy, is the leading cause of chronic kidney disease and end-stage kidney disease in the United States and worldwide. A better understanding of the underlying pathophysiological mechanisms of DKD, and recent clinical trials testing new therapeutic interventions, have shown promising results to curb this epidemic. Given the global health burden of DKD, it is extremely important to prioritize prevention, early recognition, referral, and aggressive management of DKD in the primary care setting.

Combined sodium glucose co-transporter-2 inhibitor and angiotensin-converting enzyme inhibition upregulates the renin-angiotensin system in chronic kidney disease with type 2 diabetes: Results of a randomized, double-blind, placebo-controlled exploratory trial

AIM

Sodium glucose co-transporter-2 inhibitors (SGLT-2i) improve cardiorenal outcomes in patients with chronic kidney disease (CKD), with and without type 2 diabetes. The molecular mechanisms underlying these pleiotropic effects remain unclear, yet it is speculated that SGLT-2i elicit a neurohormonal modulation resulting in renin-angiotensin system (RAS) activation. We hypothesized that combined SGLT-2 and angiotensin-converting enzyme inhibition (ACEi) favours RAS regulation towards the beneficial angiotensin-(1-7)-driven axis.

MATERIALS AND METHODS

This randomized controlled prospective study investigated the effect of 12 weeks treatment with the SGLT-2i empagliflozin on top of ACEi on the molecular RAS dynamics in 24 diabetic and 24 non-diabetic patients with CKD. Systemic RAS peptides were quantified by mass spectrometry.

RESULTS

In patients with type 2 diabetes, combined SGLT-2i and ACEi significantly upregulated plasma renin activity [pre-treatment median and interquartile range 298.0 (43.0-672.0) pmol/L versus post-treatment 577.0 (95.0-1543.0) pmol/L; p = .037] and angiotensin I levels [pre-treatment 289.0 (42.0-668.0) pmol/L versus post-treatment 573.0 (93.0-1522.0) pmol/L; p = .037], together with a significant increase of angiotensin-(1-7) levels [pre-treatment 14.0 (2.1-19.0) pmol/L versus post-treatment 32.0 (5.7-99.0) pmol/L; p = .012]. Empagliflozin treatment resulted in a 1.5 to 2-fold increase in main RAS peptides in patients with diabetes compared with placebo. No significant effect of empagliflozin on top of ACEi on RAS peptides was found in patients with CKD without diabetes.

CONCLUSION

A distinct RAS modulation by SGLT-2i occurs in diabetic kidney disease reflected by enhancement of the beneficial angiotensin-(1-7) providing a molecular background for this renoprotective therapeutic approach.

Treatment With Lisinopril Prevents the Early Progression of Glomerular Injury in Obese Dahl Salt-Sensitive Rats Independent of Lowering Arterial Pressure

Recently, we reported that obese Dahl salt-sensitive leptin receptor mutant (SSLepRmutant) rats develop glomerular injury and progressive proteinuria prior to puberty. Moreover, this early progression of proteinuria was associated with elevations in GFR. Therefore, the current study examined whether treatment with lisinopril to reduce GFR slows the early progression of proteinuria in SSLepRmutant rats prior to puberty. Experiments were performed on 4-week-old SS and SSLepRmutant rats that were either treated with vehicle or lisinopril (20 mg/kg/day, drinking water) for 4 weeks. We did not observe any differences in MAP between SS and SSLepRmutant rats treated with vehicle (148 ± 5 vs. 163 ± 6 mmHg, respectively). Interestingly, chronic treatment with lisinopril markedly reduced MAP in SS rats (111 ± 3 mmHg) but had no effect on MAP in SSLepRmutant rats (155 ± 4 mmHg). Treatment with lisinopril significantly reduced proteinuria in SS and SSLepRmutant rats compared to their vehicle counterparts (19 ± 5 and 258 ± 34 vs. 71 ± 12 and 498 ± 66 mg/day, respectively). Additionally, nephrin excretion was significantly elevated in SSLepRmutant rats versus SS rats, and lisinopril reduced nephrin excretion in both strains. GFR was significantly elevated in SSLepRmutant rats compared to SS rats, and lisinopril treatment reduced GFR in SSLepRmutant rats by 30%. The kidneys from SSLepRmutant rats displayed glomerular injury with increased mesangial expansion and renal inflammation versus SS rats. Chronic treatment with lisinopril significantly decreased glomerular injury and renal inflammation in the SSLepRmutant rats. Overall, these data indicate that inhibiting renal hyperfiltration associated with obesity is beneficial in slowing the early development of glomerular injury and renal inflammation.

Zataria multiflora and its main ingredient, carvacrol, affect on the renal function, histopathological, biochemical and antioxidant parameters in adriamycin-induced nephrotic rats

Oxidative stress has a major role in the nephrosis. In the present study, the effects of hydroalcoholic extract of Zataria multiflora (ZM) and carvacrol (CAR) were evaluated on the renal damage induced by adriamycin (ADR). The animals accidentally divided into four groups including: Control, ADR, ZM + ADR and CAR + ADR. The renal tissue, urine, and blood samples subjected to biochemical markers and histopathological evaluation. ADR significantly decreased glomerular filtration rate (GFR) while escalated urine protein excretion as well as protein clearance (p < .01 to p < .001). Also, ADR significantly reduced the antioxidants and boosted the malondialdehyde (MDA) compared to the control (p < .05 to p < .01). In groups treated by ZM and CAR, GFR, and antioxidants significantly increased, whereas urine protein excretion and MDA decreased (p < .05 to p < .001). ZM and CAR induced an improvement in ADR-induced renal damage by improving renal function as well as antioxidant activity.

Proteinuria converts hepatic heparan sulfate to an effective proprotein convertase subtilisin kexin type 9 enzyme binding partner

Hepatic uptake of triglyceride-rich remnant lipoproteins is mediated by the low-density lipoprotein receptor, a low-density lipoprotein receptor related protein and the heparan sulfate proteoglycan, syndecan-1. Heparan sulfate proteoglycan also mediates low-density lipoprotein receptor degradation by a regulator of cholesterol homeostasis, proprotein convertase subtilisin kexin type 9 (PCSK9), thereby hampering triglyceride-rich remnant lipoproteins uptake. In this study, we investigated the effects of proteinuria on PCSK9, hepatic heparan sulfate proteoglycan and plasma triglyceride-rich remnant lipoproteins. Adriamycin-injected rats developed proteinuria, elevated triglycerides and total cholesterol (all significantly increased). Proteinuria associated with triglycerides and total cholesterol and serum PCSK9 (all significant associations) without loss of the low-density lipoprotein receptor as evidenced by immunofluorescence staining and western blotting. In proteinuric rats, PCSK9 accumulated in sinusoids, whereas in control rats PCSK9 was localized in the cytoplasm of hepatocytes. Molecular profiling revealed that the heparan sulfate side chains of heparan sulfate proteoglycan to be hypersulfated in proteinuric rats. Competition assays revealed sulfation to be a major determinant for PCSK9 binding. PCSK9 partly colocalized with hypersulfated heparan sulfate in proteinuric rats, but not in control rats. Hence, proteinuria induces hypersulfated hepatic heparan sulfate proteoglycans, increasing their affinity to PCSK9. This might impair hepatic triglyceride-rich remnant lipoproteins uptake, causing proteinuria-associated dyslipidemia. Thus, our study reveals PCSK9/heparan sulfate may be a novel target to control dyslipidemia.

Sodium thiosulfate improves renal function and oxygenation in L-NNA-induced hypertension in rats

Sodium thiosulfate, a reversible oxidation product of hydrogen sulfide, has vasodilating and anti-oxidative properties, making it an attractive agent to alleviate damaging effects of hypertension. In experimental settings, inhibition of nitric oxide synthase causes hypertension, renal dysfunction and damage. We hypothesized that thiosulfate would attenuate renal injury and improve renal function, hemodynamics and the efficiency of oxygen utilization for sodium reabsorption in hypertensive renal disease. Additionally, thiosulfate co-administration would further improve these variables when compared to inhibiting the renin-angiotensin system alone. Nitric oxide synthase was inhibited in Sprague Dawley rats by administering N-ω-nitro-L-arginine (L-NNA) in the food for three weeks. After one week, rats were split into two groups; without and with thiosulfate in the drinking water. In a parallel study, rats given N-ω-nitro-L-arginine and the angiotensin converting enzyme inhibitor lisinopril at a relatively low dose in their food were divided into two groups; without and with thiosulfate in the drinking water. Treatment with thiosulfate alleviated hypertension (mean 190 vs. 229 mmHg), lowered plasma urea (mean 11.3 vs. 20.0 mmol/L) and improved the terminal glomerular filtration rate (mean 503 vs. 260 μl/min/100 gbw), effective renal plasma flow (mean 919 vs. 514 μl/min/100 gbw) and oxygen utilization for sodium reabsorption (mean 14.3 vs. 8.6 μmol/μmol). Combining thiosulfate with lisinopril further lowered renal vascular resistance (mean 43 vs. 63 mmHg/ml/min/100 gbw) and prevented glomerulosclerosis. Thus, our results suggest that thiosulfate has therapeutic potential in hypertensive renal disease and might be of value when added to standard antihypertensive therapies.

Salt-deficient diet exacerbates cystogenesis in ARPKD via epithelial sodium channel (ENaC)

Background

Autosomal Recessive Polycystic Kidney Disease (ARPKD) is marked by cyst formation in the renal tubules, primarily in the collecting duct (CD) system, ultimately leading to end-stage renal disease. Patients with PKD are generally advised to restrict their dietary sodium intake. This study was aimed at testing the outcomes of dietary salt manipulation in ARPKD.

Methods

PCK/CrljCrlPkhd1pck/CRL (PCK) rats, a model of ARPKD, were fed a normal (0.4% NaCl; NS), high salt (4% NaCl; HS), and sodium-deficient (0.01% NaCl; SD) diets for 8 weeks. Immunohistochemistry, GFR measurements, balance studies, and molecular biology approaches were applied to evaluate the outcomes of the protocol. Renin-angiotensin-aldosterone system (RAAS) levels were assessed using LC-MS/MS, and renal miRNA profiles were studied.

Findings

Both HS and SD diets resulted in an increase in cystogenesis. However, SD diet caused extensive growth of cysts in the renal cortical area, and hypertrophy of the tissue; RAAS components were enhanced in the SD group. We observed a reduction in epithelial Na⁺ channel (ENaC) expression in the SD group, accompanied with mRNA level increase. miRNA assay revealed that renal miR-9a-5p level was augmented in the SD group; we showed that this miRNA decreases ENaC channel number in CD cells.

Interpretation

Our data demonstrate a mechanism of ARPKD progression during salt restriction that involves activity of ENaC. We further show that miR-9a-5p potentially implicated in this mechanism and that miR-9a-5p downregulates ENaC in cultured CD cells. Our findings open new therapeutic possibilities and highlight the importance of understanding salt reabsorption in ARPKD.

Inappropriate activity of local renin-angiotensin-aldosterone system during high salt intake: impact on the cardio-renal axis

Although there is a general agreement on the recommendation for reduced salt intake as a public health issue, the mechanism by which high salt intake triggers pathological effects on the cardio-renal axis is not completely understood. Emerging evidence indicates that the renin-angiotensin-aldosterone system (RAAS) is the main target of high Na⁺ intake. An inappropriate activation of tissue RAAS may lead to hypertension and organ damage. We reviewed the impact of high salt intake on the RAAS on the cardio-renal axis highlighting the molecular pathways that leads to injury effects. We also provide an assessment of recent observational studies related to the consequences of non-osmotically active Na⁺ accumulation, breaking the paradigm that high salt intake necessarily increases plasma Na⁺ concentration promoting water retention

Effect of losartan and spironolactone on triglyceride-rich lipoproteins in diabetic nephropathy

Angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARBs) can improve dyslipidemia in patients with diabetes and albuminuria. Whether combined ACEi+ARB or ACEi+mineralocorticoid receptor blockade improves dyslipidemia is not known. We hypothesized long-term administration of either losartan 100 mg or spironolactone 25 mg once daily added onto lisinopril 80 mg once daily would improve dyslipidemia in diabetic nephropathy (DN). We measured lipid levels, very-low-density (V), intermediate-density (I), low-density (LDL), high-density (HDL) lipoprotein, LDL particle size with their respective cholesterol (C) and apolipoprotein B levels (ApoB), and urine albumin/creatinine ratio (UACR) at 12-week interval during a 48-week randomized, double-blind placebo-controlled trial in 81 patients with DN. Plasma lipids and lipoprotein C were analyzed enzymatically and Apo B was determined chemically. Data were analyzed by mixed model repeated measures. ΔUACR differed among treatment arms (placebo −24.6%, los −38.2%, spiro −51.6%, p=0.02). No correlation existed between ΔUACR and ΔTG or any of the lipid or lipoprotein measurements. Compared with placebo losartan, but not spironolactone, decreased TG (−20.9% vs +34.3%, p<0.01), V+I C(−18.8% vs +21.3%, p<0.01), and V+I-ApoB (−13.2% vs +21%, p<0.01). There were no significant changes in body weight, HbA1c or other lipoprotein variables. We conclude losartan improves dyslipidemia in patients with DN. We speculate the mechanism improved clearance of VLDL and remnant lipoproteins.

Dietary sodium restriction: a neglected therapeutic opportunity in chronic kidney disease

PURPOSE OF REVIEW

Restriction of dietary sodium is recommended at a population level as well as for groups at high cardiovascular risk, and chronic kidney disease (CKD). This review addresses recent evidence for the protective effect of dietary sodium restriction in CKD patients specifically.

RECENT FINDINGS

Sodium intake in CKD populations is generally high, and often above population average. Recent data demonstrated that moderately lower sodium intake in CKD patients is associated with substantially better long-term outcome of renin-angiotensin-aldosterone system (RAAS)-blockade, in diabetic and nondiabetic CKD, related to better effects of RAAS-blockade on proteinuria, independent of blood pressure. This is in line with better short-term efficacy of RAAS-blockade during moderate sodium restriction in diabetic and nondiabetic CKD. This effect of sodium restriction is likely mediated by its effects on volume status. Sustainable sodium restriction can be achieved by approaches on the basis of behavioral sciences.

SUMMARY

Moderate restriction of dietary sodium can substantially improve the protective effects of RAAS-blockade in CKD, by specific renal effects apparent from proteinuria reduction. The latter precludes straightforward extrapolation of data from nonrenal populations to CKD. Concerns regarding the adverse effects of a very low sodium intake should not distract from the protective effects of moderate sodium restriction. Prospective studies should assess the efficacy and sustainability of different strategies to target high sodium intake in CKD, along with measures at population level.

VIDEO ABSTRACT

http://links.lww.com/CONH/A14.

Salt intake in kidney disease--a missed therapeutic opportunity?

Although significant progress has been made in the treatment of chronic kidney disease (CKD), treatment is not yet satisfactory, particularly when it is started in the late stages of the disease. Novel modes of intervention to mitigate the burden of disease are required. The reduction of dietary salt intake (which is high in the industrialized world) is one such option. Better understanding of the deleterious effects of salt on renal and cardiovascular health is necessary to raise awareness of the importance of reduction of the salt content in food products. Therefore, we (i) review pathways through which high salt intake exerts damaging effects, (ii) provide an assessment of recent observational studies linking dietary salt intake to the progression of renal and cardiovascular disease and (iii) discuss the interaction between salt intake and rennin-angiotensin-aldosterone-system inhibitors, i.e. the first choice antihypertensive agents for the treatment of CKD.

Improving the efficacy of RAAS blockade in patients with chronic kidney disease

Reduction of blood pressure and proteinuria by blockade of the renin-angiotensin-aldosterone system (RAAS) has been the cornerstone of renoprotective intervention for patients with chronic kidney disease (CKD) for many years. Despite the proven efficacy of RAAS blockade, however, the reduction in proteinuria is insufficient in many patients, and does not prevent further deterioration of renal function. Short-term studies have shown that a variety of treatment intensification strategies have a beneficial effect on blood pressure and proteinuria, including RAAS blockade using either dose escalation or multiple drugs, and restriction of dietary sodium. Large clinical trials have shown that RAAS blockade with multiple drugs does not improve patients' long-term renal or cardiovascular outcome. By contrast, two post-hoc analyses of landmark trials in nephrology show beneficial renal and cardiovascular effects from avoiding excessive dietary sodium intake during single-agent RAAS blockade therapy. The effects of dietary sodium restriction on renal or cardiovascular outcome still require prospective confirmation. However, current data support the implementation of lifestyle changes to reduce dietary sodium intake in combination with single-agent RAAS blockade, rather than dual-agent RAAS blockade, as a potent and feasible strategy to mitigate the burden of renal and cardiovascular disease in patients with CKD.

Sodium intake, ACE inhibition, and progression to ESRD

High sodium intake limits the antihypertensive and antiproteinuric effects of angiotensin-converting enzyme (ACE) inhibitors in patients with CKD; however, whether dietary sodium also associates with progression to ESRD is unknown. We conducted a post hoc analysis of the first and second Ramipril Efficacy in Nephropathy trials to evaluate the association of sodium intake with proteinuria and progression to ESRD among 500 CKD patients without diabetes who were treated with ramipril (5 mg/d) and monitored with serial 24-hour urinary sodium and creatinine measurements. Urinary sodium/creatinine excretion defined low (<100 mEq/g), medium (100 to <200 mEq/g), and high (≥200 mEq/g) sodium intake. During a follow-up of >4.25 years, 92 individuals (18.4%) developed ESRD. Among those with low, medium, and high sodium intakes, the incidence of ESRD was 6.1 (95% confidence interval [95% CI], 3.8-9.7), 7.9 (95% CI, 6.1-10.2), and 18.2 (95% CI, 11.3-29.3) per 100 patient-years, respectively (P<0.001). Patients with high dietary sodium exhibited a blunted antiproteinuric effect of ACE inhibition despite similar BP among groups. Each 100-mEq/g increase in urinary sodium/creatinine excretion associated with a 1.61-fold (95% CI, 1.15-2.24) higher risk for ESRD; adjusting for baseline proteinuria attenuated this association to 1.38-fold (95% CI, 0.95-2.00). This association was independent from BP but was lost after adjusting for changes in proteinuria. In summary, among patients with CKD but without diabetes, high dietary salt (>14 g daily) seems to blunt the antiproteinuric effect of ACE inhibitor therapy and increase the risk for ESRD, independent of BP control.

Dual blockade of the renin-angiotensin-aldosterone system in cardiac and renal disease

PURPOSE OF REVIEW

Renin-angiotensin-aldosterone system (RAAS) blockade improves outcome in cardiovascular disease (CVD) and chronic kidney disease (CKD), but the residual risk during monotherapy RAAS blockade remains very high. This review discusses the place of dual RAAS blockade in improving these outcomes.

RECENT FINDINGS

The combination of angiotensin-converting enzyme inhibitor (ACEI) with angiotensin II type 1 receptor blocker (ARB) generally had a better antihypertensive and antiproteinuric effect than monotherapy in many studies, but is also associated with more adverse effects. Unfortunately, the effect on hard renal and cardiovascular endpoints is not unequivocal. The combination of ACEI (or ARB) with aldosterone blockade has long-term benefits in heart failure, and an added effect on proteinuria in CKD, but data on hard renal endpoints are lacking. Dual blockade including renin inhibition has added antiproteinuric effects, but studies to gather long-term data are still under way. Available strategies to optimize the effect of monotherapy RAAS blockade include dose titration and correction of volume excess. Whether dual blockade has better efficacy and/or fewer adverse effects than optimized monotherapy has not been investigated.

SUMMARY

Several options are available to increase the effect of monotherapy RAAS blockade. For proteinuric CKD, these can be combined in a stepwise approach aimed at maximal proteinuria reduction; this includes dual blockade for patients with persistent proteinuria during optimized monotherapy RAAS blockade. Long-term randomized studies, however, are needed to support the benefits of dual blockade for long-term renal and cardiovascular outcome in CKD.

Effects of dietary sodium and hydrochlorothiazide on the antiproteinuric efficacy of losartan

There is large interindividual variability in the antiproteinuric response to blockade of the renin-angiotensin-aldosterone system (RAAS). A low-sodium diet or addition of diuretics enhances the effects of RAAS blockade on proteinuria and BP, but the efficacy of the combination of these interventions is unknown. Therefore, this randomized, double-blind, placebo-controlled trial to determine the separate and combined effects of a low-sodium diet and hydrochlorothiazide (HCT) on proteinuria and BP was performed. In 34 proteinuric patients without diabetes, mean baseline proteinuria was 3.8 g/d, and this was reduced by 22% by a low-sodium diet alone. Losartan monotherapy reduced proteinuria by 30%, and the addition of a low-sodium diet led to a total reduction by 55% and the addition of HCT to 56%. The combined addition of HCT and a low-sodium diet reduced proteinuria by 70% from baseline (all P < 0.05). Reductions in mean arterial pressure showed a similar pattern (all P < 0.05). In addition, individuals who did not demonstrate an antiproteinuric response to losartan monotherapy did respond when a low-sodium diet or a diuretic was added. In conclusion, a low-sodium diet and HCT are equally efficacious in reducing proteinuria and BP when added to a regimen containing losartan and especially seem to benefit individuals who are resistant to RAAS blockade. Combining these interventions in sodium status is an effective method to maximize the antiproteinuric efficacy of RAAS blockade.

Differential regulation of renal angiotensin-converting enzyme (ACE) and ACE2 during ACE inhibition and dietary sodium restriction in healthy rats

Angiotensin-converting enzyme (ACE) 2 is thought to counterbalance ACE by breakdown of angiotensin (Ang) II and formation of Ang(1-7). Both enzymes are highly expressed in the kidney, but reports on their regulation differ. To enhance our understanding of the regulation of renal ACE and ACE2, we investigated renal ACE and ACE2 expression during conditions of physiological (low-sodium diet) and pharmacological changes (ACE inhibition) in activity of the renin-angiotensin-aldosterone system (RAAS). Healthy rats were treated with vehicle or lisinopril with either a control or a low-sodium diet, and renal ACE2, ACE and plasma angiotensins were studied. During vehicle treatment, low sodium reduced renal ACE mRNA and activity without affecting ACE2 mRNA or activity and plasma Ang(1-7) and Ang II balance. Lisinopril significantly reduced renal ACE activity without affecting renal ACE2 activity. During ACE inhibition, low sodium reduced both ACE and ACE2 mRNA without affecting ACE2 activity or further reducing ACE activity. Measurements of renal neprilysin activity revealed no significant differences between any of the treatment groups. Plasma Ang(1-7) and Ang II balance is positively shifted towards the beneficial vasopeptide Ang(1-7) by the ACE inhibitor lisinopril, especially during a low sodium intake. In conclusion, modulation of the RAAS, by low sodium intake or ACE inhibition, does not affect renal ACE2 despite major variations in renal ACE. Thus, ACE and ACE2 are differentially regulated by low sodium and ACE inhibition. Therefore, we propose that the beneficial effects of ACE inhibitors are predominantly mediated by modulation of ACE and not ACE2. Whether this also applies to renal disease conditions should be investigated in future studies.

Effect of combining ACE inhibition with aldosterone blockade on proteinuria and renal damage in experimental nephrosis

Aldosterone has pro-fibrotic properties and is a potential target for additional intervention in patients with chronic renal disease showing resistance to therapy during treatment with angiotensin-converting enzyme inhibitors (ACEi). Combining ACEi and aldosterone receptor blockade (aldoRB) in proteinuric renal disease reduces proteinuria, but effects on proteinuria-induced renal damage are unknown. We studied the effect of ACEi/aldoRB in adriamycin nephrosis (AN). Six weeks after injection of adriamycin in Wistar rats, randomized treatment with vehicle (VEH, n=8), aldoRB (n=12), ACEi (n=10), or a combination of ACEi/aldoRB (n=14) was given for 12 weeks. Healthy rats served as controls (n=6). Renal damage was quantified by markers of tubular injury (osteopontin (OPN) and kidney injury molecule-1 (Kim-1)), pre-fibrotic lesions (alpha-smooth muscle actin (SMA)), interstitial fibrosis (IF), and focal glomerulosclerosis (FGS). In AN animals, proteinuria was increased compared with controls. ACEi and ACEi/aldoRB significantly reduced proteinuria compared with VEH, whereas aldoRB monotherapy was without effect. Blood pressure was reduced in ACEi and ACEi/aldoRB compared with VEH and aldoRB. OPN and Kim-1 were increased in AN animals, but significantly reduced by ACEi/aldoRB. Treatment with ACEi and ACEi/aldoRB prevented an increase of SMA, IF, and FGS. In conclusion, ACEi/aldoRB effectively reduced proteinuria and markers of tubular injury and prevented renal damage in this rat model of chronic proteinuria-induced renal damage.

Dual Blockade of the Renin-Angiotensin System in the Progression of Renal Disease: The Need for More Clinical Trials

There is clear evidence that pharmacologic blockade of the renin-angiotensin system (RAS) with angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blockers (ARB) reduces proteinuria and slows the progression of renal disease in diabetic and nondiabetic nephropathies, a beneficial effect that is not related to BP control. Some patients exhibit a significant beneficial response, whereas others do not. The absence of response may be explained by the incomplete blockade of the RAS obtained with ACEI. In the search of new alternatives that could improve the antiproteinuric and nephroprotective effects of RAS blockers, the association of ACEI and ARB might prove useful. ARB produces a complete blockade of the RAS. Several studies have shown a more marked antiproteinuric effect of the dual blockade of the RAS versus ACEI or ARB alone. A recent study also demonstrated that this more marked antiproteinuric effect is associated with less progression of renal disease in primary nondiabetic nephropathies despite a similar effect on BP. Until now, there has not been any reference to a beneficial effect on progression of the dual blockade in type 2 diabetic nephropathy, which is the most frequent cause of ESRD. A multicenter, prospective, open, active-controlled, and parallel-group trial was designed to compare the effects of an ACE inhibitor versus an ARB or its combination on renal disease progression, proteinuria, and cardiovascular events in type 2 diabetic nephropathy.

Induction of Glomerular Heparanase Expression in Rats with Adriamycin Nephropathy Is Regulated by Reactive Oxygen Species and the Renin-Angiotensin System

Heparan sulfate (HS) in the glomerular basement membrane (GBM) is important for regulation of the charge-dependent permeability. Heparanase has been implicated in HS degradation in several proteinuric diseases. This study analyzed the role of heparanase in HS degradation in Adriamycin nephropathy (AN), a model of chronic proteinuria-induced renal damage. Expression of heparanase, HS, and the core protein of agrin (to which HS is attached) was determined on kidney sections from rats with AN in different experiments. First, expression was examined in a model of unilateral AN in a time-course study at 6-wk intervals until week 30. Second, rats were treated with the hydroxyl radical scavenger dimethylthiourea (DMTU) during bilateral AN induction. Finally, 6 wk after AN induction, rats were treated with angiotensin II receptor type 1 antagonist (AT1A) or vehicle for 2 wk. Heparanase expression was increased in glomeruli of rats with AN, which correlated with HS reduction at all time points and in all experiments. Treatment with DMTU prevented the increased heparanase expression, the loss of GBM HS, and reduced albuminuria. Finally, treatment of established proteinuria with AT1A significantly reduced heparanase expression and restored glomerular HS. In conclusion, an association between heparanase expression and reduction of glomerular HS in AN was observed. The effects of DMTU suggest a role for reactive oxygen species in upregulation of heparanase. Antiproteinuric treatment by AT1A decreased heparanase expression and restored HS expression. These results suggest involvement of radicals and angiotensin II in the modulation of GBM permeability through HS and heparanase expression.

ACE inhibition has adverse renal effects during dietary sodium restriction in proteinuric and healthy rats

Angiotensin-converting enzyme inhibitors (ACEi) provide renoprotection. A low sodium diet enhances their efficacy. However, the added effect of sodium restriction on proteinuria and blood pressure is not invariably associated with better preservation of renal morphology, suggesting that the combination of ACEi with a low sodium diet can elicit renal structural abnormalities. To test this hypothesis, the effects of ACEi in combination with a control (CS) or a low sodium (LS) diet were investigated in healthy rats and in adriamycin nephrotic rats. After 3 weeks of treatment, rats were sacrificed and kidneys examined for renal structural abnormalities. In healthy rats, ACEi reduced blood pressure: the fall in blood pressure was significantly greater in the ACEi/LS group. Renal morphology was normal in the ACEi/CS group but severe interstitial damage was found in the ACEi/LS group. This was associated with increased interstitial macrophage influx and up-regulation of osteopontin, alpha-smooth muscle actin, and collagen III expression. In addition, ACEi/LS induced an increase in the total medial area of afferent arterioles. In nephrotic rats, ACEi/LS reduced both blood pressure and proteinuria, whereas only blood pressure was reduced in the ACEi/CS group. Mild interstitial damage was present in the ACEi/CS group but, strikingly, pronounced tubulo-interstitial abnormalities occurred in the ACEi/LS group, similar to those seen in ACEi/LS healthy rats, with similar changes in afferent arteriolar walls. In conclusion, the combination of ACEi/LS elicits pronounced renal interstitial abnormalities in healthy and nephrotic rats, despite a significant reduction of proteinuria in the latter. Considering their occurrence in healthy rats, these renal adverse effects cannot be due to specific characteristics of adriamycin nephrosis. Further studies should elucidate the mechanisms underlying these observations and their impact on long-term renoprotection.

Does angiotensin (1-7) contribute to the anti-proteinuric effect of ACE-inhibitors

Angiotensin-converting enzyme inhibitors (ACE-I) reduce proteinuria and protect the kidney in proteinuric renal disease. During ACE-I therapy, circulating levels of angiotensin (1-7) [Ang (1-7)] are increased. As cardiac and renal protective effects of Ang (1-7) have been reported, we questioned whether Ang (1-7) contributes to the anti-proteinuric effects of ACE-I treatment. Therefore, we evaluated whether Ang (1-7) infusion reduces proteinuria in a rat model of adriamycin-induced renal disease. In addition, the effect of a selective Ang (1-7) blocker, [D-Ala7]-Ang (1-7) (A779), was investigated in rats treated with the ACE-I, lisinopril (LIS). Six weeks after induction of proteinuria, therapy was started in four different groups: control, Ang (1-7), LIS, and LIS+A779. After two weeks, the rats were sacrificed. Six weeks after injection of adriamycin, the rats had developed proteinuria of 323+/-40 mg/24 hours. The proteinuria remained stable in the control group and in the Ang (1-7) group, but was reduced in both LIS and LIS+A779-treated groups. Similarly, blood pressure (BP) was unchanged in the control and the Ang (1-7) groups, but reduced in both the LIS and the LIS+A779 groups. Plasma levels of Ang (1-7) were increased in the Ang (1-7) and in both LIS-treated groups. We conclude that systemic Ang (1-7) plays no major role in the anti-proteinuric and BPlowering effects of ACE-I in this rat model of adriamycin-induced nephrosis.

Modulation of osteopontin in proteinuria-induced renal interstitial fibrosis

Proteinuria is associated with macrophage-dependent interstitial fibrosis (IF). Osteopontin (OPN), a macrophage chemoattractant, may be involved in the transition of proteinuria to IF but protective properties have also been reported. To elucidate whether OPN may be involved in the proteinuria-induced cascade of tubulointerstitial damage, renal expression of OPN was studied during the development of proteinuria-induced renal damage and during anti-proteinuric intervention with ACE inhibition (ACEi). First, the temporal relationships between proteinuria, interstitial OPN induction, and IF in adriamycin nephrosis (AN), a model of chronic proteinuria-induced renal damage, were studied. Second, the effect of anti-proteinuric treatment on OPN expression was investigated. The time course of OPN induction and markers of renal damage was studied in rats with unilateral AN at 6-week intervals until week 30. In a second study, a renal biopsy was taken 6 weeks after induction of bilateral AN; subsequently, rats were treated with ACEi until termination (week 12). In unilateral AN, proteinuria developed gradually and stabilized at week 10. In proteinuric kidneys, OPN expression was induced from week 12 onwards. Simultaneously, a progressive increase in interstitial macrophages, alpha-smooth muscle actin (alpha-SMA), collagen type III, and focal glomerulosclerosis (FGS) was observed. In bilateral AN, ACEi reduced proteinuria and OPN protein and stabilized fibrosis. In untreated animals, OPN mRNA increased, with stable OPN protein and fibrosis and increased FGS. Thus, in AN, development of proteinuria is followed by up-regulation of OPN along with markers of renal damage. The up-regulation of OPN is reversible by anti-proteinuric treatment without a corresponding reduction in fibrosis. Whereas these data are consistent with a role for OPN in the cascade of transition from proteinuria to fibrosis, intervention with ACEi showed that reduction of OPN does not attenuate established fibrosis.

Mycophenolate mofetil slows progression in anti-thy1-induced chronic renal fibrosis but is not additive to a high dose of enalapril

Tubulointerstitial inflammation and fibrosis are hallmarks of chronic progressive renal diseases. To characterize the functional interaction between cell infiltration and matrix expansion, this study compared the immunosuppressant mycophenolate mofetil (MMF), intended as primarily anti-inflammatory intervention, the angiotensin-converting enzyme inhibitor enalapril, intended as primarily an anti-fibrotic drug, and a combination of both as anticipated anti-inflammatory/anti-fibrotic intervention. The model used was anti-thy1-induced chronic-progressive glomerulosclerosis (cGS) in the rat, where a brief anti-thy1-induced glomerular injury progresses spontaneously toward tubulointerstitial fibrosis and renal insufficiency. cGS was induced by injection of anti-thy1 antibody into uninephrectomized Wistar rats. One week after disease induction, animals were randomly assigned to the following groups: cGS, cGS plus MMF (20 mg·kg body wt−1·day−1), cGS plus high-dose enalapril (12 mg·kg body wt−1·day−1), and cGS plus both. At week 16 after disease induction, MMF or enalapril alone reduced signs of chronic renal disease significantly and similarly compared with the untreated cGS group. Variables measured included proteinuria, blood pressure, tubulointerstitial and glomerular matrix accumulation, expression of transforming growth factor-β1, fibronectin, and plasminogen activator inhibitor-1, infiltration of lymphocytes and macrophages, plasma creatinine and urea levels, and glomerular filtration rate. Combined MMF and enalapril treatment was not superior to single therapy. In conclusion, MMF slows the progression of chronic renal fibrosis and renal insufficiency as effectively as high-dose enalapril in the anti-thy1-induced chronic-progressive glomerulosclerosis model. The dual anti-inflammatory/anti-fibrotic intervention does not yield additive renoprotective effects, indicating that MMF and enalapril interfere with similar or very closely related pathways involved in progression of renal disease.

Renal accumulation of pentosidine in non-diabetic proteinuria-induced renal damage in rats

BACKGROUND

Advanced glycation end-products (AGEs) contribute to the pathogenesis of diabetic glomerulopathy. The role of AGEs in non-diabetic renal damage is not well characterized. First, we studied whether renal AGE accumulation occurs in non-diabetic proteinuria-induced renal damage and whether this is ameliorated by renoprotective treatment. Secondly, we investigated whether renal AGE accumulation was due to intrarenal effects of local protein trafficking.

METHODS

Pentosidine was measured (by high-performance liquid chromatography) in rats with chronic bilateral adriamycin nephropathy (AN), untreated and treated with lisinopril. Age-matched healthy rats served as negative controls. Secondly, we compared renal pentosidine in mild proteinuric and non-proteinuric kidneys of unilateral AN and in age-matched controls at 12 and 30 weeks. Intrarenal localization of pentosidine was studied by immunohistochemistry.

RESULTS

Renal pentosidine was elevated in untreated AN (0.14+/-0.04 micromol/mol valine) vs healthy controls (0.04+/-0.01 micromol/mol valine, P<0.01). In lisinopril-treated AN, pentosidine was lower (0.09+/-0.02 micromol/mol valine) than in untreated AN (P<0.05). In unilateral proteinuria, pentosidine was similar in non-proteinuric and proteinuric kidneys. After 30 weeks of unilateral proteinuria, pentosidine was increased in both kidneys (0.26+/-0.10 micromol/mol valine) compared with controls (0.18+/-0.06 micromol/mol valine, P<0.05). Pentosidine (AN, week 30) was also increased compared with AN at week 12 (0.16+/-0.06 micromol/mol valine, P<0.01). In control and diseased kidneys, pentosidine was present in the collecting ducts. In proteinuric kidneys, in addition, pentosidine was present in the brush border and cytoplasm of dilated tubular structures, i.e. at sites of proteinuria-induced tubular damage.

CONCLUSION

Pentosidine accumulates in non-diabetic proteinuric kidneys in damaged tubules, and renoprotective treatment by angiotensin-converting enzyme (ACE) inhibitors inhibits AGE accumulation, supporting a relationship between abnormal renal protein trafficking, proteinuria-induced tubular damage and tubular pentosidine accumulation. Future studies, applying specific AGE inhibitors, should be conducted to provide insight into the pathophysiological significance of renal AGEs in non-diabetic renal disease.

Individual differences in renal ACE activity in healthy rats predict susceptibility to adriamycin-induced renal damage

BACKGROUND

In man, differences in angiotensin-converting enzyme (ACE) levels, related to ACE (I/D) genotype, are associated with renal prognosis. This raises the hypothesis that individual differences in renal ACE activity are involved in renal susceptibility to inflicted damage. Therefore, we studied the predictive effect of renal ACE activity for the severity of renal damage induced by a single injection of adriamycin in rats.

METHODS

Renal ACE activity (Hip-His-Leu cleavage by cortical homogenates) was determined by renal biopsy in 27 adult male Wistar rats. After 1 week of recovery, proteinuria was induced by adriamycin [1.5 mg/kg intravenously (i.v.) n = 18; controls, saline i.v. n = 9]. Proteinuria was measured every 2 weeks. After 12 weeks, rats were sacrificed and their kidneys harvested.

RESULTS

As anticipated, adriamycin elicited nephrotic range proteinuria, renal interstitial damage and mild focal glomerulosclerosis. Baseline renal ACE positively correlated with the relative rise in proteinuria after adriamycin (r = 0.62, P<0.01), renal interstitial alpha-smooth muscle actin (r = 0.49, P<0.05), interstitial macrophage influx (r = 0.56, P<0.05), interstitial collagen III (r = 0.53, P<0.05), glomerular alpha-smooth muscle actin (r = 0.74, P<0.01) and glomerular desmin (r = 0.48, P<0.05). Baseline renal ACE did not correlate with focal glomerulosclerosis (r = 0.22, NS). In controls, no predictive values for renal parameters were observed.

CONCLUSION

Individual differences in renal ACE activity predict the severity of adriamycin-induced renal damage in this outbred rat strain. This supports the assumption that differences in renal ACE activity predispose to a less favourable course of renal damage.

Low Sodium Modifies the Vascular Effects of Angiotensin-Converting Enzyme Inhibitor Therapy in Healthy Rats

Low dietary sodium (LS) increases the effect of angiotensin-converting enzyme (ACE) inhibitor therapy in patients and experimental models, but mechanisms underlying this enhanced efficacy are largely unknown. Because the benefits of ACE inhibition are mediated to a considerable extent by their effect on the vasculature, we studied whether low sodium alters the vascular effects of ACE inhibition. Baseline functional and morphological characteristics, and endothelium-dependent and -independent dilatory responses were studied in isolated perfused small intrarenal and mesenteric arteries obtained from control rats (CON), rats on LS, lisinopril-treated rats (CON-LIS), or rats treated with lisinopril during LS (LS-LIS). We found, first, that LS-LIS compared with CON-LIS enhances blood pressure reduction. Second, interlobar renal arteries had increased lumen diameter and reduced adrenergic contractility in CON-LIS compared with CON, without additional effects of LS. In contrast, mesenteric arteries were not altered in CON-LIS compared with CON, but became triggered for increased myogenic and adrenergic constriction in LS-LIS. Third, LS-LIS decreased acetylcholine (ACh)-induced vasodilation in both mesenteric and renal arteries compared with CON-LIS. During the latter condition, opposite prostaglandins are involved in the endothelial function of the two different vascular beds, i.e., increased involvement of contractile prostaglandins in ACh-induced vasodilatation in renal arteries, versus dilatory prostaglandins in mesenteric arteries. Whether cause or consequence of the enhanced blood pressure response, our data demonstrate a modifying effect of dietary sodium on vascular effects of ACE inhibition. These findings provide a rationale for further studies addressing the mechanism-of-actions of our therapies to find additional strategies to improve therapy response.

High Dietary Sodium Blunts Effects of Angiotensin-converting Enzyme Inhibition on Vascular Angiotensin I–to–Angiotensin II Conversion in Rats

High sodium intake blunts the efficacy of angiotensin (Ang)-converting enzyme (ACE) inhibition (ACEi), but the underlying mechanism is incompletely characterized. High sodium has been reported to increase vascular expression and vascular activity of ACE. To investigate whether high-dietary sodium-induced effects on vascular conversion of Ang I might be involved in the sodium-induced blunting of the response to ACEi, the authors studied the vasoconstrictor responses to Ang I and Ang II of isolated aortic rings from healthy rats on low dietary sodium (LS: 0.05% NaCl) and high dietary sodium (HS: 2.0% NaCl) after 3 weeks of ACEi (lisinopril 75 mg/L) or vehicle (CON). Blood pressure was similar in LS and HS in CON, but HS blunted the blood pressure response to ACEi. Functional conversion of Ang I was assessed as the difference in dose-response curves to Ang I and Ang II in parallel aortic rings. Sodium intake did not affect the dose-response curves to Ang I and Ang II in CON. In the ACEi groups, a significant difference was present between the curves for Ang I and Ang II on LS (deltaEC50, 6.7 nM; range, 2.2-13 nM; P < 0.01) but not on HS (deltaEC50: 1.3 nM; range, 0.0-4.1 nM, median [interquartile range], NS). Thus, HS blunts the ACEi-induced reduction of functional vascular Ang I conversion compared with LS. Whether the blunted functional vascular conversion is causally related to the blunted blood pressure response remains to be elucidated.

Inter-individual differences in anti-proteinuric response to ACEi in established adriamycin nephrotic rats are predicted by pretreatment renal damage

ACE inhibition (ACEi) reduces proteinuria and provides reno-protection, but not all subjects benefit from ACEi. Individual differences in the reduction in proteinuria at the onset of treatment and in residual proteinuria during therapy predict differences in renal outcome. The present study investigated whether individual differences in the anti-proteinuric efficacy of ACEi are explained by differences in the severity of pretreatment renal structural damage and whether differences in the level of residual proteinuria during therapy are explained by the severity of renal structural damage at that time, in adriamycin nephrosis in the rat. Pretreatment renal structural damage was assessed in biopsies 6 weeks after exposure to adriamycin (2 mg/kg iv). Then ACEi (75 mg/l lisinopril, n = 23) or vehicle (n = 10) was administered; renal biopsies were repeated after stabilization of the anti-proteinuric response (week 8). Early renal damage (interstitial alpha-smooth muscle actin expression and macrophage accumulation) and established lesions [focal glomerulosclerosis (FGS) and interstitial fibrosis] were scored. During ACEi, proteinuria fell from 834 (487-851) mg/24 h pretreatment to 153 (66-265) mg/24 h at week 8 (p < 0.05); FGS stabilized from 27 (4-70) arbitrar units (AU) pretreatment to 26 (4-84) at week 12, whereas the vehicle did not affect proteinuria, resulting in progressive FGS: 18 (10-26) AU pretreatment versus 88 (46-130) at week 12 (p < 0.05). All parameters of pretreatment damage significantly predicted the anti-proteinuric response. Residual proteinuria during ACEi correlated significantly with renal structural damage parameters at that time. Pretreatment renal damage also predicted renal outcome during extended treatment. Thus, in this experimental setting, in rats with the same renal disorder and the same duration of disease, individual differences in pretreatment renal damage, albeit relatively modest, explain individual differences in renal responsiveness to ACEi. This implies that the limits of the efficacy of ACEi are set by prevalent renal damage. Further studies into the mechanisms of individual resistance to the anti-proteinuric action of ACEi are needed to develop additive intervention strategies.

Involvement of renal ACE activity in proteinuria-associated renal damage in untreated and treated adriamycin nephrotic rats

Proteinuria is assumed to play a pathogenetic role in progressive renal damage. Angiotensin-converting enzyme (ACE) inhibition reduces proteinuria and provides renoprotection. This suggests that ACE activity might play a pathogenetic role in the development of proteinuria-induced renal structural damage. We investigated this hypothesis in untreated and treated established adriamycin nephrosis, a model of proteinuria-induced renal damage. In a time-course experiment, the development of renal structural damage in untreated adriamycin nephrotic rats was paralleled by a significant rise in renal ACE activity. Moreover, on cross-sectional analysis, a consistent positive correlation between renal, but not plasma, ACE activity and proteinuria, focal glomerulosclerosis and interstitial injury was present. Notably, these associations were present, not only in the untreated condition, but also during intervention with either ACE inhibition or AT(1)-receptor antagonism. Interestingly, we found that higher renal ACE activity is associated with more severe renal damage for a given amount of proteinuria, suggesting that renal ACE activity may be either a permissive or a promoting factor in the processes by which proteinuria eventually leads to renal structural damage. This relationship was abolished by renin-angiotensin system (RAS)-blockade, suggesting that RAS-mediated effects are involved in the relationship between renal ACE activity and proteinuria-induced renal damage. In conclusion, in untreated as well as treated adriamycin nephrotic rats, renal ACE activity is closely associated with renal outcome. This association appears to be independent of the specific mode of blockade of the RAS. Renal ACE activity is a consistent marker of individual differences in proteinuria-associated renal damage: further studies are needed to investigate a possible pathogenetic role in renal damage.

Role of proteinuria in the regulation of renal renin-angiotensin system components in unilateral proteinuric rats

Renin-angiotensin system (RAS) overactivity has been implied in progressive renal function loss. We investigated whether changes in the renal expression of RAS components are specifically associated with the proteinuric kidney. Unilateral adriamycin-induced proteinuria was obtained by clamping the left renal artery before injection of adriamycin. In control animals, both left and right renal arteries were clamped. Twelve weeks later, mRNA expression of RAS components was determined in both kidneys. In the affected and non-affected kidney of the unilateral proteinuric rat, we demonstrate up-regulation of angiotensin- converting enzyme (ACE) mRNA (213%+22 and 188%+24 of controls, respectively), up-regulation of transforming growth factor beta (TGF-beta) mRNA (956%+229 and 418%+56) and down-regulation of angiotensin type 2 receptor (AT2-R) mRNA (24%+5 and 20%+5). The expression of angiotensin type 1 receptor (AT1-R) mRNA and inositol 1,4,5- trisphosphate receptor type I (IP3R-I) mRNA were unchanged. In conclusion, renal expression of ACE, AT2-R, and AT1-R mRNA is not mediated by protein leakage. Local intrarenal protein leakage did influence renal TGF-beta mRNA expression.

Renoprotective effects of VPI versus ACEI in normotensive nephrotic rats on different sodium intakes

BACKGROUND

Control of blood pressure (BP) and optimal reduction of proteinuria (Uprot) are necessary for long-term renoprotection. Unfortunately, angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II (Ang II) antagonists are not effective during sodium repletion. Vasopeptidase inhibitors (VPI) cause dual inhibition of ACE and neutral endopeptidase, the latter resulting in decreased atrial natriuretic peptide (ANP) breakdown and thus enhanced natriuresis. Therefore, in contrast with ACEI, VPI may be effective during high sodium intake.

METHODS

To test this hypothesis, the renoprotective actions of the new VPI gemopatrilat (GEM) were studied during low (0.05% NaCl) and high (3.0% NaCl) sodium diets in normotensive Wistar rats with established adriamycin nephrosis. The ACEI lisinopril (LIS) was used as control. Rats received either GEM (0.3 mg/g chow), an equihypotensive dose of LIS (75 mg/L drinking water), or vehicle (VEH) from week 6 (that is, established Uprot) until sacrifice. The effect of therapy was monitored by measuring systolic BP and Uprot (weekly) and structural renal damage at the end of study (week 16).

RESULTS

During low sodium, GEM effectively reduced Uprot (-48 +/- 4%), but LIS was more effective (-80 +/- 2%), while Uprot slightly increased in VEH (+23 +/- 2%). The focal glomerulosclerosis (FGS) score after GEM (38 +/- 14) was lower than in the VEH group (79 +/- 27), although this was not significant. LIS (18 +/- 6) reduced FGS significantly. Remarkably, on high sodium, GEM was completely ineffective in reducing BP, Uprot and structural renal injury, just like LIS.

CONCLUSIONS

The renoprotective actions of VPI depend on dietary sodium intake in normotensive nephrotic rats: therapeutic efficacy is fully blunted by a high sodium diet. During a low sodium diet, gemopatrilat was renoprotective, but less effective than lisinopril. Whether higher doses of the VPI could improve its renoprotective efficacy remains to be elucidated.

Addition of AT1 blocker fails to overcome resistance to ACE inhibition in adriamycin nephrosis

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors provide renoprotection, but there is considerable interindividual variability in therapeutic efficacy, with residual proteinuria and progressive renal function loss in many individuals. This requires additional strategies to optimize therapy response, particularly for individuals with a poor response to ACE inhibition. We studied whether co-treatment with an angiotensin II subtype 1 (AT1) receptor antagonist (AII-A) improves the individual antiproteinuric response of maximal ACE inhibition in established adriamycin nephrosis.

METHODS

Rats were instituted on lisinopril (75 mg/L) six weeks after disease induction. After two weeks rats were re-stratified for residual proteinuria to continue this regimen, to a higher dose of lisinopril (150 mg/L) or to co-treatment with the AII-A L 158,809 for another four weeks. Groups on monotherapy AII-A and vehicle served as controls (all groups N=15).

RESULTS

Lisinopril lowered proteinuria by 63% from 741 to 246 g/day (range of percentage change -90 to +2%). Neither increasing the dose of the ACE inhibitor nor addition of AII-A to ACE inhibition improved the antiproteinuric efficacy on a group or individual level: non-responders remained non-responders. All drug categories reduced hard end-points of focal glomerulosclerosis to a similar degree.

CONCLUSIONS

ACE inhibition has variable renal protective efficacy in the adriamycin model. Neither increasing the dose of the ACE inhibitor beyond the optimal level nor co-treatment with AII-A overcome the individual therapy resistance. Thus, in established adriamycin nephrosis, blockade of the renin-angiotensin system at two different levels offers no additional benefit over ACE inhibition alone, either on the group or individual level.

Inability of propranolol to prevent alcohol-induced reductions in cardiac protein synthesis in vivo

Rats were acutely injected with alcohol (75 mmol/kg body weight) and at the end of 2.5 h changes in cardiac synthesis rates were assessed with a 'flooding dose' of L-[4-(3)H]phenylalanine. The results showed that acute alcohol dosage reduced the fractional rates of cardiac protein synthesis (k(S), %/day). This effect was also seen when data were expressed relative to either RNA (i.e. k(RNA), mg protein/day/mg RNA) or DNA (i.e. k(DNA), mg protein/day/mg DNA). Both left and right ventricles responded similarly to ethanol. However, propranolol pre-treatment (at doses of 17 and 170 micromol/kg body weight; i.p.) did not prevent these effect of ethanol in either the left or right ventricle. Indeed, there was evidence that propranolol per se perturbed cardiac protein synthesis in vivo in control (i.e. without ethanol) rats particularly in the right ventricle. In conclusion, the results suggest that alcohol is cardiotoxic to the myocardium, which may cause its effects on protein synthesis independently of beta-receptors and/or xanthine oxidase inhibition.

Chronic angiotensin II infusion but not bradykinin blockade abolishes the antiproteinuric response to angiotensin-converting enzyme inhibition in established adriamycin nephrosis

Angiotensin-converting enzyme (ACE) inhibition reduces proteinuria in established adriamycin nephrosis. To investigate whether the reduction in proteinuria is due to decreased generation of angiotensin II (AngII) or to decreased degradation of bradykinin, four series of experiments in established adriamycin nephrosis were performed. In the first series, 2 mg/kg lisinopril reduced BP from 117 +/- 4 to 67 +/- 2 mmHg and proteinuria from 335 +/- 66 to 57 +/- 10 mg/24 h after 2 wk of treatment. Subsequent continuous intraperitoneal infusion of AngII (250 ng/kg per min) for 2 wk partially restored proteinuria to 180 +/- 42 mg/24 h, whereas BP increased to 97 +/- 3 mmHg. Subsequent withdrawal of AngII restored the antiproteinuric effects of lisinopril, whereas subsequent withdrawal of lisinopril restored proteinuria to pretreatment values. In the second series, AT1 receptor blockade induced a fall in BP and proteinuria similar to that by lisinopril. In the third series, lisinopril reduced BP from 121 +/- 5 to 68 +/- 2 mmHg and proteinuria from 355 +/- 90 to 101 +/- 10 mg/24 h. Subsequent intraperitoneal infusion of bradykinin antagonist (HOE 140; 1 mg/kg per 24 h) for 2 wk did not affect BP (72 +/- 2 mmHg) or proteinuria (92 +/- 15 mg/24 h). In the fourth series, bradykinin (3 mg/kg per 24 h) was infused for 2 wk to mimic decreased bradykinin breakdown. This did not affect proteinuria, but induced a fall in BP from 114 +/- 3 to 93 +/- 4 mmHg. The BP-lowering effect of exogenous bradykinin was completely reversed by 1 wk infusion of HOE 140 (93 +/- 4 to 113 +/- 4 mmHg), while proteinuria remained unchanged. In conclusion, the antiproteinuric effect of ACE inhibition appears to be independent of bradykinin in this model, supporting a main role for reduction of AngII in the antiproteinuric action of ACE inhibition.

ACE inhibition delays development of terminal renal failure in the presence of severe albuminuria

The hypertensive fawn-hooded (FHH) rat develops progressive albuminuria (UalbV) and focal glomerulosclerosis (FGS). Early-onset angiotensin-converting enzyme inhibition (ACE-i) completely prevented the development of hypertension, UalbV, and FGS. ACE-i was still effective when the start of treatment was delayed, albeit less than early-onset treatment. In this study, we examined whether more advanced renal damage reduces the efficacy of ACE-i, and, if so, which factors dampen the efficacy. ACE-i was started in 36-week-old FHH rats, and follow-up consisted of regular assessment of systolic blood pressure (SBP) and UalbV. Untreated rats, matched for age, SBP, and UalbV, served as controls. In separate groups, untreated or treated with ACE-i from either week 7 or week 36, glomerular hemodynamics and FGS were determined at week 40. ACE-i normalized SBP and markedly reduced UalbV. The Initial UalbV response to ACE-i was inversely correlated with pretreatment UalbV, but despite control of SBP, UalbV rose again. Eventually, rats died of terminal renal failure. Life expectancy was significantly increased in treated rats. In both untreated and treated rats, there was a significant inverse correlation between baseline UalbV and survival time. However, the gain in survival time decreased when pretreatment UalbV was higher. Late-onset ACE-i reduced glomerular capillary pressure to the same extent as early-onset ACE-i. There was a significant linear correlation between FGS and UalbV. We conclude that in FHH rats with advanced renal damage, ACE-i slows down the progression to terminal renal failure. The outcome is an increased survival time that is inversely correlated with baseline UalbV.

Systemic factors are involved in the pathogenesis of proteinuria-induced glomerulosclerosis in adriamycin nephrotic rats

This study aims to dissociate the respective roles of systemic nephrosis and of the intrarenal effects of proteinuria in the pathogenesis of focal segmental glomerulosclerosis (FGS) in adriamycin nephrosis. To this purpose, this study examined proteinuria and FGS in bilateral (BAP) and unilateral proteinuria (UAP) in two different rat strains. UAP was obtained by protecting one kidney from exposure to adriamycin by temporary clipping of one renal artery during adriamycin injection. At sacrifice (week 12), FGS was present in BAP and in exposed kidneys in UAP, but not in unexposed kidneys. FGS correlated significantly with proteinuria per kidney in BAP and UAP. Remarkably, for a given proteinuria per kidney, the sclerosis score was higher in BAP than in UAP, reflected by a higher ratio of FGS score per mg proteinuria per kidney (Wistar: 0.09 +/- 0.01 in BAP versus 0.05 +/- 0.01%/mg protein per d in UAP, P < 0.05; Lewis: 0.12 +/- 0.01 in BAP versus 0.07 +/- 0.01%/mg protein per d in UAP, P < 0.05), indicating that the local damaging effects of proteinuria are modified by other factors. Cholesterol correlated with total proteinuria in BAP and UAP. FGS score was positively correlated with cholesterol. The latter correlation was similar in BAP and UAP, indicating that cholesterol was a more uniform predictor for FGS than proteinuria per kidney. This was independent of strain-specific factors. On multilinear regression analysis, cholesterol turned out to be the most consistent predictor of FGS in proteinuric kidneys, with a stronger predictive value than proteinuria per kidney. It is concluded that although systemic sequelae of nephrosis do not induce renal damage in nonproteinuric kidneys, they modify the severity of proteinuria-induced FGS in proteinuric kidneys.

Dose of doxorubicin determines severity of renal damage and responsiveness to ACE-inhibition in experimental nephrosis

Nephrosis induced by doxorubicin (adriamycin) is an experimental model of glomerulosclerosis with relative stable proteinuria which is commonly used for pharmacological intervention studies. It is induced by a single or a double dose of doxorubicin, with doses that vary considerably among investigators from 2 to 7.5 mg/kg. Intervention studies with ACE-inhibitors in this model have provided conflicting results. We hypothesized that these discrepancies might be due to different properties of the doxorubicin model, related to the dose of doxorubicin used to induce proteinuria. We tested this hypothesis by inducing doxorubicin nephrosis with 1, 2 and 3 mg/kg, and evaluating the response to intervention with lisinopril. The 1-mg/kg doxorubicin dose did not induce significant proteinuria. The 2- and the 3-mg/ kg dose resulted in a proteinuria of 684+/-215 mg/24 h and 736+/-277 mg/24 h 6 weeks after induction, respectively (Mean+/-SD). Treatment with lisinopril 2 mg/kg/day reduced proteinuria to 160+/-170 mg/24 h(p<0.01) in the 2-mg/kg doxorubicin group, whereas in the 3-mg/kg doxorubicin group, proteinuria did not respond to lisinopril (529+/-264 mg/24 h). In time control rats, proteinuria remained stable. Renal damage developed in both time control groups, with a glomerulosclerosis score of 29+/-22 in the 2-mg/kg group and 84+/-41 in the 3-mg/kg doxorubicin group. Lisinopril resulted in a significantly lower glomerulosclerosis score in the 2-mg/kg doxorubicin group only (16+/-15, p<0.05), whereas the 3-mg/kg group showed no significant reduction (56+/-29, NS). In conclusion, the dose of doxorubicin used to induce nephrosis is an important determinant not only of the severity of the ensuring renal damage, but also of the response to intervention by ACE-inhibition. These findings have an impact on the interpretation of intervention studies in this model.

Involvement of angiotensin II in development of spontaneous nephrosis in Dahl salt-sensitive rats

We investigated the effect of angiotensin-converting enzyme inhibition on spontaneous nephrosis in Dahl salt-sensitive (Dahl/S) rats. Dahl/S rats fed on a normal sodium diet spontaneously developed nephrosis and mild hypertension from a young age. In young Dahl/S rats, an angiotensin-converting enzyme inhibitor, imidapril, attenuated the development of proteinuria accompanied by a decrease in blood pressure. Methylprednisolone, a potent therapeutic agent for proteinuria, did not affect the development of nephrosis. An angiotensin AT1 receptor antagonist, losartan, but not a Ca2+ channel blocker, verapamil, inhibited the development of nephrosis while both agents decreased blood pressure to a similar extent as imidapril. In mature Dahl/S rats, imidapril suppressed not only the development of proteinuria but also the glomerular lesions. It is concluded that the development of spontaneous nephrosis in Dahl/S rats is mediated by angiotensin II.

A method for accurate measurement of GFR in conscious, spontaneously voiding rats

Renal function measurement by clearance methods relies on accurately timed urine collection. In small experimental animals, renal function measurement is usually performed under anesthesia and/or with the application of bladder catheters to ensure accurate urine collection. To avoid both anesthesia and the need for bladder catheters we developed a method to measure glomerular filtration rate (GFR) in spontaneously voiding conscious rats. GFR was measured as the urinary clearance of constantly infused 125I-iothalamate. To correct for incomplete bladder emptying urinary clearance of 125I-iothalamate was multiplied by the ratio of plasma and urinary clearance of simultaneously infused 131I-hippuran, a correction method that has been previously validated in humans. Reproducibility of the technique was evaluated by analysis of the results of four consecutive clearance periods during the day (intra-assay variation) in a group of 17 rats and of two consecutive clearance periods on two or three separate days in a group of 20 rats (inter-assay variation), all with normal renal function. Application of the correction method reduced the intra-assay coefficient of variation (mean +/- SD) from 37.4 +/- 14.3 to 5.4 +/- 2.3% (P < 0.05). The mean inter-assay coefficient of variation fell slightly from 23.4 +/- 10.3 to 11.0 +/- 7.2% (P < 0.10). In rats with moderately impaired renal function (N = 8) the intra-assay variation fell from 27.9 +/- 20.7 to 2.7 +/- 1.6% (P < 0.05). Our data show that this correction method is a useful technique to assess renal function in conscious, spontaneously voiding rats.