Supplementation with a low dose of L-arginine reduces blood pressure and endothelin-1 production in hypertensive uraemic rats

L-arginine and lisinopril supplementation protects against sodium fluoride-induced nephrotoxicity and hypertension by suppressing mineralocorticoid receptor and angiotensin-converting enzyme 3 activity

Sodium fluoride (NaF) is one of the neglected environmental toxicants that has continued to silently cause toxicity to both humans and animals. NaF is universally present in water, soil, and atmosphere. The persistent and alarming rate of increase in cardiovascular and renal diseases caused by chemicals such as NaF in mammalian tissues has led to the use of various drugs for the treatment of these diseases. The present study aimed at evaluating the renoprotective and antihypertensive effects of L-arginine against NaF-induced nephrotoxicity. Thirty male Wistar rats (150-180 g) were used in this study. The rats were randomly divided into five groups of six rats each as follows: Control, NaF (300 ppm), NaF + L-arginine (100 mg/kg), NaF + L-arginine (200 mg/kg), and NaF + lisinopril (10 mg/kg). Histopathological examination and immunohistochemistry of renal angiotensin-converting enzyme (ACE) and mineralocorticoid receptor (MCR) were performed. Markers of renal damage, oxidative stress, antioxidant defense system, and blood pressure parameters were determined. L-arginine and lisinopril significantly (P < 0.05) ameliorated the hypertensive effects of NaF. The systolic, diastolic, and mean arterial blood pressure of the treated groups were significantly (P < 0.05) reduced compared with the hypertensive group. This finding was concurrent with significantly increased serum bioavailability of nitric oxide in the hypertensive rats treated with L-arginine and lisinopril. Also, there was a significant reduction in the level of blood urea nitrogen and creatinine of hypertensive rats treated with L-arginine and lisinopril. There was a significant (P < 0.05) reduction in markers of oxidative stress such as malondialdehyde and protein carbonyl and concurrent increase in the levels of antioxidant enzymes in the kidney of hypertensive rats treated with L-arginine and lisinopril. The results of this study suggest that L-arginine and lisinopril normalized blood pressure, reduced oxidative stress, and the expression of renal ACE and mineralocorticoid receptor, and improved nitric oxide production. Thus, L-arginine holds promise as a potential therapy against hypertension and renal damage.

Effect of l-Arginine Supplementation on Blood Pressure in Adults: A Systematic Review and Dose-Response Meta-analysis of Randomized Clinical Trials

A decade-old meta-analytic work indicated that l-arginine supplementation might have a blood pressure (BP)-lowering effect in different populations. However, several relevant investigations have emerged in the last 10 y, and an up-to-date systematic review and meta-analysis on this topic is currently lacking. Therefore, we aimed to examine the impact of l-arginine supplementation on BP by conducting a systematic review and dose-response meta-analysis of randomized placebo-controlled clinical trials (RCTs). We searched online databases using relevant keywords up to April 2021 to identify RCTs using oral l-arginine on systolic BP (SBP) and diastolic BP (DBP) in adults. Inclusion criteria were adult participants and an intervention duration ≥4 d. Exclusion criteria were the use of l-arginine infusion and acute interventions. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% CI. Twenty-two RCTs with 30 effect sizes were included in this meta-analysis. The pooled analysis demonstrated significant decreases in SBP (WMD = -6.40 mmHg; 95% CI: -8.74, -4.05; P < 0.001) and DBP (WMD = -2.64 mmHg; 95% CI: -3.94, -1.40; P < 0.001) after l-arginine supplementation. Subgroup analysis showed significant reductions in SBP and DBP regardless of baseline BP category (normotensive, hypertensive), study duration (≤24 d, >24 d), sex (female, male), health status (healthy, unhealthy), and BMI (normal, overweight, obese). No significant changes were observed with dosages >9 g/d, trial duration >24 d, or in obese individuals. l-Arginine supplementation also appears to decrease DBP more effectively in females than in males. Moreover, meta-regression analysis for DBP demonstrated a significant relation between the dose of l-arginine intake and changes in DBP (P = 0.020). In the nonlinear dose-response analysis, the effective dosage of l-arginine supplementation was detected to be ≥4 g/d for SBP (P = 0.034), independent of trial duration. Overall, l-arginine supplementation may be effective for decreasing BP. This study was registered at PROSPERO as CRD42021242772.

New drug targets for hypertension: A literature review

Hypertension is one of the most prevalent cardiovascular diseases worldwide. However, in the population of resistant hypertension, blood pressure is difficult to control effectively. Moreover, antihypertensive drugs may have adverse effect currently. Hence, new therapeutic targets and treatments are needed to uncovered and exploited to control hypertension and its comorbidities. In the past, classical drug targets, such as the aldosterone receptor, aldosterone synthase, and ACE2/angiotensin 1-7/Mas receptor axis, have been investigated. Recently, vaccines and drugs targeting the gastrointestinal microbiome, which represent drug classes, have also been investigated for the management of blood pressure. In this review, we summarized current knowledge on classical and new drug targets and discussed the potential utility of new drugs in the treatment of hypertension.

Protective effects of either C-peptide or l-arginine on pancreatic β-cell function, proliferation, and oxidative stress in streptozotocin-induced diabetic rats

Diabetes and cardiometabolic risk factors including hypertension and dyslipidemia are the major threats to human health in the 21st century. Apoptosis in pancreatic tissue is one of the major causes of diabetes type 1 progression. The aim of this study was to investigate the effects of C-peptide or l-arginine on some cardiometabolic risk factors, pancreatic morphology, function and apoptosis, and the mechanisms of their actions. Forty adult male albino rats were divided into four equal groups: 1-control nondiabetic, 2-diabetic (no treatment), 3-diabetic + C-peptide, and 4-diabetic +  l-arginine. Diabetes was induced by a single intraperitoneal injection of high dose streptozotocin. At the end of the experiment, sera glucose, insulin levels, total antioxidant capacity (TAC), malondialdehyde (MDA), nitric oxide (NO), and pancreatic MDA, TAC, and B-cell lymphoma 2 were measured. The morphology and proliferating activity of the pancreas were examined by hematoxylin and eosin histological stain, proliferative cell nuclear antigen (PCNA), and insulin antibodies. Our results showed that induction of diabetes caused hyperglycemia, dyslipidemia, and oxidative stress. However, administration of C-peptide or l-arginine significantly improved the pancreatic histopathology with a significant increase in the area % of insulin immunoreactivity, the number of PCNA immunopositive cells, the number of islets, and the diameter of islets compared with the diabetic group. C-peptide treatment of the diabetic rats completely corrected these errors, while l-arginine partially antagonized the above diabetic complications. So the administration of C-peptide as an adjuvant therapy in type 1 diabetes can significantly decrease apoptosis of pancreas and subsequent progression of diabetes complication.

The potential of stimulating nitric oxide formation in the treatment of hypertension

INTRODUCTION

Hypertension is a leading cause of morbidity and mortality worldwide. A major pathophysiological factor contributing to hypertension is reduced nitric oxide (NO) bioavailability. Strategies to address this pathophysiological mechanism could offer significant advantages. Areas covered: In this review we aimed at examining a variety of drugs (statins, beta-adrenergic receptor blockers, calcium channel blockers, angiotensin converting enzyme inhibitors, angiotensin II type-1 receptor blockers) used to treat hypertension and other cardiovascular diseases, particularly with respect to their potential of increasing NO bioavailability and activity in the cardiovascular system. There is now evidence supporting the notion that many cardiovascular drugs activate NO signaling or enhance NO bioavailability as a contributing mechanism to their beneficial cardiovascular effects. Moreover, other drugs may attenuate NO inactivation by superoxide and other reactive oxygen species by exerting antioxidant effects. More recently, the NO oxidation products nitrite and nitrate have been acknowledged as sources of NO after recycling back to NO. Activation of the nitrate-nitrite-NO pathway is an alternate pathway that may generate NO from both anions and exert antihypertensive effects. Expert opinion: In this review, we provide an overview of the possible mechanisms by which these drugs enhance NO bioavailability and help in the therapy of hypertension.

Role of cellular L-arginine uptake and nitric oxide production on renal blood flow and arterial pressure regulation

PURPOSE OF REVIEW

L-Arginine (L-Arg) is the substrate for nitric oxide (NO) formation. Reduced NO bioavailability, particularly within the renal circulation, has been identified as a key factor in the pathogenesis of hypertension. This review focuses on the pathogenic role of abnormal L-Arg transport, particularly within the kidney, in hypertension.

RECENT FINDINGS

Most recent studies have attempted to restore NO bioavailability in cardiovascular diseases with the use of antioxidants to reduce NO inactivation, but this approach has failed to provide beneficial effects in the clinical setting. We argue that this may be due to reduced NO formation in hypertension, which has largely been overlooked as a means of restoring NO bioavailability in cardiovascular diseases. Recent data indicate that renal L-Arg transport plays an important role in regulating both renal perfusion and function and the long-term set point of arterial pressure in health. Perturbations in the renal L-Arg transport system can give rise to abnormal renal perfusion and function, initiating hypertension and related renal damage.

SUMMARY

Accordingly, we propose that L-Arg transporters are a new treatment target in hypertension and in disease states where renal NO bioavailability is disturbed.

Neutralization of tumor necrosis factor-alpha reduces renal fibrosis and hypertension in rats with renal failure

BACKGROUND

Increased production of tumor necrosis factor-α (TNF-α) in chronic kidney disease may be involved in the progression of renal failure and injury, and cardiovascular disease. We investigated the effect of TNF-α neutralization on renal failure, inflammation and fibrosis, and blood pressure in rats with renal failure.

METHODS AND RESULTS

Renal failure was induced by renal mass reduction and the animals were treated with PEG-sTNFR1, a pegylated form of soluble TNF type 1 receptor that neutralizes TNF-α, for 6 weeks. Systolic, diastolic and mean arterial pressures were higher in renal failure rats that were associated with increased serum creatinine, albuminuria and renal injury comprised of blood vessel media hypertrophy, focal and segmental glomerulosclerosis, tubular atrophy and interstitial inflammation and fibrosis. These changes were associated with greater levels of TNF-α, transforming growth factor (TGF)-β1, nuclear transcription factor NF-ĸB and cytosolic phospho-IĸB-α, and inflammatory markers expression (ICAM-1, VCAM-1 and MCP-1). Moreover, endothelin (ET)-1 production was also increased, whereas nitric oxide (NO) release was decreased. TNF-α neutralization reduced hypertension, albuminuria and renal inflammation and fibrosis, which were coupled to a reduction in renal NF-ĸB activation, inflammatory markers expression, TGF-β1 and ET-1 production, and an increase in NO release.

CONCLUSION

Neutralization of TNF-α in rats with renal failure decreases NF-ĸB activity that is associated with a reduction in renal TGF-β1 and ET-1 production, and an improvement of NO release. These effects likely reduce renal inflammation and fibrosis, and blood pressure indicating a pivotal role for TNF-α, at least, in the progression of renal injury.

eNOS gene delivery prevents hypertension and reduces renal failure and injury in rats with reduced renal mass

BACKGROUND

Impaired nitric oxide (NO) release in chronic renal failure has been implicated in the pathogenesis of hypertension and the progression of renal insufficiency. We investigated whether gene delivery of the endothelial NO synthase (eNOS) improves NO release and reduces blood pressure and renal failure and injury in rats with reduced renal mass.

METHODS

Renal failure was induced by renal artery branches ligation. Two weeks later, rats with renal failure were divided into three groups and received an intravenous injection of the vehicle or the adenovirus that expresses eNOS or β-galactosidase (β-gal). Systolic blood pressure, renal parameters and histopathology were assessed at Week 4 after gene delivery.

RESULTS

At the end of the study, systolic blood pressures, serum creatinine, proteinuria, urinary endothelin-1 (ET-1) excretion and renal cortex ET-1 levels were increased, whereas plasma and urine NO(2)/NO(3) were reduced in renal failure rats as compared to normal controls. Renal injury comprised blood vessel media hypertrophy, focal and segmental glomerular sclerosis, tubular atrophy and interstitial fibrosis. Gene delivery of eNOS, but not β-gal, prevented an increase in systolic blood pressure and proteinuria, and a reduction in plasma and urine NO(2)/NO(3). eNOS gene delivery also reduced a rise in serum creatinine, urinary ET-1 excretion and renal cortex ET-1 levels, and the renal vascular, glomerular and tubular injury.

CONCLUSION

This study indicates that eNOS gene delivery in rats with renal failure improves NO release, which likely prevents the aggravation of hypertension and slows down the progression of renal failure and injury.

Endothelin type A and B receptors in the control of afferent and efferent arterioles in mice

BACKGROUND

Endothelin 1 contributes to renal blood flow control and pathogenesis of kidney diseases. The differential effects, however, of endothelin 1 (ET-1) on afferent (AA) and efferent arterioles (EA) remain to be established.

METHODS

We investigated endothelin type A and B receptor (ETA-R, ETB-R) functions in the control of AA and EA. Arterioles of ETB-R deficient, rescued mice [ETB(-/-)] and wild types [ETB(+/+)] were microperfused.

RESULTS

ET-1 constricted AA stronger than EA in ETB(-/-) and ETB(+/+) mice. Results in AA: ET-1 induced similar constrictions in ETB(-/-) and ETB(+/+) mice. BQ-123 (ETA-R antagonist) inhibited this response in both groups. ALA-ET-1 and IRL1620 (ETB-R agonists) had no effect on arteriolar diameter. L-NAME did neither affect basal diameters nor ET-1 responses. Results in EA: ET-1 constricted EA stronger in ETB(+/+) compared to ETB(-/-). BQ-123 inhibited the constriction completely only in ETB(-/-). ALA-ET-1 and IRL1620 constricted only arterioles of ETB(+/+) mice. L-NAME decreased basal diameter in ETB(+/+), but not in ETB(-/-) mice and increased the ET-1 response similarly in both groups. The L-NAME actions indicate a contribution of ETB-R in basal nitric oxide (NO) release in EA and suggest dilatory action of ETA-R in EA.

CONCLUSIONS

ETA-R mediates vasoconstriction in AA and contributes to vasoconstriction in EA in this mouse model. ETB-R has no effect in AA but mediates basal NO release and constriction in EA. The stronger effect of ET-1 on AA supports observations of decreased glomerular filtration rate to ET-1 and indicates a potential contribution of ET-1 to the pathogenesis of kidney diseases.

Multiple antioxidants and L-arginine modulate inflammation and dyslipidemia in chronic renal failure rats

The kidney is an important source of L-arginine, the endogenous precursor of nitric oxide (NO). Surgical problems requiring extensive renal mass reduction (RMR) decrease renal NO production, leading to multiple hemodynamic and homeostatic disorders manifested by hypertension, oxidative stress, and increased inflammatory cytokines. Using the RMR model of chronic renal failure (CRF), we assessed the effects of twelve weeks' administration of L-arginine and/or a mixture of antioxidants (L-carnitine, catechin, vitamins E and C) on plasma cytokines, soluble intercellular adhesion molecule-1 (sICAM-1), nitrate and nitrites (NO(2)/NO(3)), lipid profile, blood pressure, and renal function. CRF rats showed increased plasma IL-1 alpha, IL1-beta, IL-6, TNF-alpha, and sICAM-1 levels and decreased anti-inflammatory cytokines IL-4 and 10 levels, hypertension, and dyslipidemia. L-arginine treatment improved kidney functions, decreased systolic blood pressure, and decreased inflammatory cytokines levels. Antioxidants administration decreased inflammatory cytokines and sICAM-1 levels and increased IL-4 levels. Combined use of both L-arginine and the antioxidant mixture were very effective in their tendency to recover normal values of kidney functions, plasma cytokines, sICAM-1, blood pressure, NO(2)/NO(3), cholesterol, and triglycerides concentrations. Indeed, the effects of L-arginine and the antioxidants on the reduction of proinflammatory cytokines may open new perspectives in the treatment of uremia.

Role of oxidative stress in erythropoietin-induced hypertension in uremic rats

BACKGROUND

Erythropoietin (EPO) administration in uremic rats leads to an increase in blood pressure (BP). Because chronic renal failure has been associated with oxidative stress, we hypothesize that EPO treatment could accentuate this condition and contribute to hypertension. The present study was designed to investigate the role of reactive oxygen species in EPO-induced hypertension and the effect of tempol, a superoxide dismutase-mimetic.

METHODS

Renal failure was induced by a two-stage 5/6 nephrectomy followed by a 3-week stabilization period. Uremic rats were divided into four groups and received for 4 weeks: vehicle; EPO (100 U/kg, subcutaneously, three times per week); vehicle + tempol (1 mmol/l in drinking water); and EPO + tempol. Systolic BP and biochemical parameters were assessed before and at the end of the treatment. Renal histology, creatinine clearance rate, endothelin-1 (ET-1) concentrations and superoxide anion production were assessed at the end of the study.

RESULTS

The uremic rats developed anemia and hypertension. ET-1 concentrations and superoxide anion production were increased. EPO administration corrected anemia, but accentuated hypertension and renal injuries such as glomerulosclerosis, interstitial fibrosis, and inflammation. EPO therapy further increased tissue levels of ET-1 and superoxide anion production. Tempol treatment improved hypertension and renal injury, and reduced ET-1 concentrations and superoxide anion production.

CONCLUSION

Oxidative stress contributes to the development of hypertension and to the progression of renal injuries in uremic rats. EPO administration further increases oxidative stress, which might partly account for the accentuation of hypertension and renal injury.

Effect of L-arginine oral supplementation on response to myocardial infarction in hypercholesterolemic and hypertensive rats

The well known metabolic functions of L-arginine have been recently increased with the discovery of its role as the substrate for the synthesis of nitric oxide (NO), which has emerged as an endogenous signaling molecule with potential therapeutic implications for cardiovascular disease. Steady-state levels of NO are derived in part from dietary sources. It has been reported that supplementation of L-arginine reduces atherosclerosis in rabbits and reduces the arterial pressure in hypertensive rats. Therefore, we investigated the effect of L-arginine supplementation using a group of induced hypercholesterolemic rats and a group of spontaneously hypertensive rats; the infarcted area in cardiac tissue of both groups was measured during the response to myocardial infarction in the ischemia-reperfusion model. Hypercholesterolemic rats supplemented with 170 mg kg(-1) of L-arginine showed a significant (P <or= 0.05) reduction in total cholesterol (25.2%) and LDL (27.8%). Spontaneously hypertensive rats supplemented with L-arginine presented a significant reduction (20.3%) in mean blood pressure (P <or= 0.05). The index infarcted area/total heart area, in both: hypercholesterolemic and hypertensive rats supplemented with L-arginine, showed a significant 36% and 29% of cardio protection (P <or= 0.05) effect, respectively. Dietary supplementation with L-arginine may represent a potentially novel nutritional strategy for the treatment of cardiovascular disease.

Effects of TGF-beta1 on endothelial factors

This study investigated the mechanistic effect of transforming growth factor-beta1 (TGFbeta1) on the endothelial mediators: endothelin-1 (ET-1), prostacyclin (PGI(2)) and nitric oxide (NO) in the endothelial cell line 1G11. Endothelial cells were incubated with increasing concentrations of TGFbeta1 in the presence and absence of growth medium (deprived) or various inhibitors. In deprived cells, TGFbeta1 increased the release of PGI(2) (6-keto-PGF1alpha) concomitantly to an increase in COX-2 expression, whereas the production of ET-1 and NO metabolites was not affected. Either the removal of prior serum and heparin deprivation or NO synthase inhibition by L-NAME unmasked an inhibitory effect of TGFbeta1 on ET-1 production. Indomethacin abolished the TGFbeta1 inhibitory action on L-NAME-increased ET-1 production. These results show that TGFbeta1 induces an increase in production of PGI(2) that is consecutive to an induction of COX-2 in endothelial cells. This increase in PGI(2) partly accounts for the inhibitory action of TGFbeta1 on ET-1 secretion.

L-arginine supplementation reduces cardiac noradrenergic neurotransmission in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) are known to have cardiac noradrenergic hyperactivity due to an impaired nitric oxide (NO)-cGMP pathway. We hypothesized that dietary l-arginine supplementation may correct this autonomic phenotype. Male SHR and Wistar Kyoto rats (WKY) aged 16-18 weeks were given l-arginine (10 g/L in drinking water) for 1 week. Separate control groups received no supplementation. The SHR control had a significantly lower plasma l-arginine than WKY control, but this was increased to a comparable level following l-arginine. Atrial cGMP was lower in the SHR control compared with the WKY control (2.4+/-0.4 pmol/mg vs 3.9+/-0.5 pmol/mg, p<0.05), but increased to 4.1+/-0.5 pmol/mg protein (n=8, p<0.05) with l-arginine. Evoked [(3)H]norepinephrine release in isolated spontaneously beating right atria from the SHR control (328+/-19%, n=19) was 28% higher than the WKY control (256+/-20%, n=14, p<0.05), but was reduced to 258+/-11% with l-arginine feeding (n=24, p<0.01). Soluble guanylyl cyclase (sGC) inhibition caused a greater increase of evoked norepinephrine release in the l-arginine fed SHR compared with the non-fed SHR. l-arginine feeding did not reduce evoked norepinephrine release in the WKY. In-vitro heart rate response to exogenous norepinephrine (0.1-5 mumol/L) was similar between l-arginine fed (n=13) and non-fed SHR (n=10), suggesting that l-arginine supplementation worked pre-synaptically. Myocardial tyrosine hydroxylase protein was decreased in SHR following l-arginine supplementation, providing a link to reduced synthesis of norepinephrine. In conclusion, l-arginine supplementation corrects local cardiac noradrenergic hyperactivity in the SHR, probably via increased pre-synaptic substrate availability of NOS-sGC-cGMP pathway and reduced tyrosine hydroxylase levels.

Endothelin-1, big endothelin-1, and nitric oxide in patients with chronic renal disease and hypertension

The complex pathogenesis of chronic renal disease (CRD) depends on endothelin (ET) axis (ETs and ET receptors) and nitric oxide (NO) because of their vasoactive effects and their role in general modulation of vascular homeostasis. Various renal cells synthesize ETs and NO that play a significant role in renal hemodynamics as well as in water and salt excretion via urine. ET-1 is a strong vasoconstrictor. Besides its vasoactive effects, ET-1 modulates mitosis and apoptosis in a cell type-dependent manner, and may play an important role in CRD pathogenesis. The aims of this study were to emphasize the role and interactions of ET-1, Big ET-1, and NO in CRD. Concentrations of these vasoactive molecules were measured in plasma/serum and/or urine of 57 patients with diabetic nephropathy (subgroup 1), arterial hypertension (subgroup 2) or CRD with chronic renal insufficiency (subgroup 3), and in healthy control subjects (n=18). In comparison with control group, urine concentration of Big ET-1 was significantly increased (13.13 pmol/L vs. 11.34 pmol/L; P<0.001) in CRD patients, whereas plasma and urine concentrations of ET-1 did not differ significantly. NO concentrations were also significantly increased in CRD patients (serum, 72.55 micromol/L; P<0.001, and urine 141.74 micromol/L; P<0.05) as compared to control group. Study results indicated that Big ET-1 and NO could be useful diagnostic parameters in CRD for their diagnostic sensitivity and diagnostic specificity (Big ET-1 in urine: 56.1 and 88.9%, and NO in serum: 66.7 and 83.3%, respectively). In addition, Big ET-1 may prove useful in the differential diagnosis of diabetic nephropathy (78.6% diagnostic sensitivity and 88.9% diagnostic specificity).

Role of nitric oxide deficiency in the development of hypertension in hydronephrotic animals

Hydronephrotic animals develop renal injury and hypertension, which is associated with an abnormal tubuloglomerular feedback (TGF). The TGF sensitivity is coupled to nitric oxide (NO) in the macula densa. The involvement of reduced NO availability in the development of hypertension in hydronephrosis was investigated. Hydronephrosis was induced by ureteral obstruction in young rats. Blood pressure and renal excretion were measured in adulthood, under different sodium conditions, and before and after chronic administration of either NG-nitro-l-arginine methyl ester (l-NAME) or l-arginine. Blood samples for ADMA, SDMA, and l-arginine analysis were taken and the renal tissue was used for histology and determination of NO synthase (NOS) proteins. TGF characteristics were determined by stop-flow pressure technique before and after administration of 7-nitroindazole (7-NI) or l-arginine. Hydronephrotic animals developed salt-sensitive hypertension, which was associated with pressure natriuresis and diuresis. The blood pressure response to l-NAME was attenuated and l-arginine supplementation decreased blood pressure in hydronephrotic animals, but not in the controls. Under control conditions, reactivity and sensitivity of the TGF response were greater in the hydronephrotic group. 7-NI administration increased TGF reactivity and sensitivity in control animals, whereas, in hydronephrotic animals, neuronal NOS (nNOS) inhibition had no effect. l-Arginine attenuated TGF response more in hydronephrotic kidneys than in controls. The hydronephrotic animals displayed various degrees of histopathological changes. ADMA and SDMA levels were higher and the renal expressions of nNOS and endothelial NOS proteins were lower in animals with hydronephrosis. Reduced NO availability in the diseased kidney in hydronephrosis, and subsequent resetting of the TGF mechanism, plays an important role in the development of hypertension.

Neutralization of transforming growth factor-beta attenuates hypertension and prevents renal injury in uremic rats

OBJECTIVE

We investigate the role of transforming growth factor-beta (TGF-beta) in hypertension and renal failure progression in uremic rats, and whether it modulates the endothelin (ET) system.

DESIGN

Following renal mass reduction, uremic rats (Nx) received the pan-specific TGF-beta neutralizing antibody 1D11 (0.5 mg/kg, three times/week), the isotype control antibody 13C4 or the AT1 antagonist losartan (10 mg/kg per day) for 6 weeks.

RESULTS

Before treatment, the blood pressure was higher in Nx rats and increased further over time in Nx+13C4 rats. At the end of the study, Nx+13C4 rats exhibited increased serum creatinine, proteinuria and renal expression and excretion of TGF-beta1 and ET-1. ET-1 concentrations were greater in vascular and renal tissues, whereas the ETB receptor expression was reduced. Renal injuries were comprised of blood vessel hypertrophy, glomerular sclerosis, tubular atrophy and interstitial fibrosis, which was associated with increased alpha-smooth muscle actin expression. Treatment of uremic rats with the 1D11 antibody attenuated the increase in blood pressure and the decline in renal function. Losartan normalized the blood pressure and significantly attenuated the increase in serum creatinine and proteinuria. However, both treatments prevented renal TGF-beta1 and ET-1 overexpression, and prevented all renal histological injuries. The 1D11 antibody only improved ETB receptor expression.

CONCLUSIONS

Neutralization of TGF-beta attenuates hypertension and renal failure progression in uremic animals, in part, by preventing renal injury processes. These effects may be related to the modulation of the ET system, preventing renal ET-1 overproduction and the reduction of ETB receptor expression. Our data also suggest that TGF-beta1 is involved, at least in part, in the pathological effects related to angiotensin II in chronic renal failure.

Effect of chronic tetrahydrobiopterin supplementation on blood pressure and proteinuria in 5/6 nephrectomized rats

BACKGROUND

Tetrahydrobiopterin (BH4) is a key cofactor of nitric oxide (NO) synthase. Reduced BH4 levels may mediate endothelial NO synthase uncoupling, resulting in reduced NO synthesis and enhanced oxidative stress. In rats after 5/6 nephrectomy (Nx), administration of BH4 prevents the onset of hypertension, typically observed 10 days after Nx. This effect is associated with an increased synthesis of NO. The aim of the present study was to evaluate the effect of chronic BH4 therapy on blood pressure and renal morphology.

METHODS

During an 8 week period, five groups of rats were studied: untreated 5/6 Nx rats, BH4-treated Nx rats (BH4, 10 mg/kg body weight/day administered intraperitoneally), l-arginine treated Nx rats (LA, 130 mg/kg/day), diltiazem-treated Nx rats (DILT, 30 mg/kg/day) and sham-operated rats. Treatments were commenced 24 h after surgery. Systolic blood pressure values (SBP), 24 h proteinuria (UP) and creatinine clearance rate (CCR) were assessed before and at weeks 4 and 8 of the study period. Histological changes in the kidney were evaluated at the end of the study (week 8).

RESULTS

Compared with baseline, in Nx rats both SBP and UP increased significantly (112+/-1 to 136+/- 1.4 mmHg, P<0.01 and 23+/-2 to 127 +/- 26 mg/day, P<0.01, respectively). Treatment with BH4 normalized SBP values as did treatment with LA and DILT (109+/-3, 115+/-2 and 114+/-2 mmHg, respectively). UP was markedly reduced by BH4, the reduction being similar to that obtained by LA and significantly more marked than that of DILT rats (20+/-2, 28+/-3 and 62+/- 14 mg/day, respectively). CCR was equally decreased in all Nx groups. Histological evaluation showed the development of mesangial expansion in Nx rats, an effect that was significantly blunted by all treatments.

CONCLUSIONS

In rats after 5/6 nephrectomy, BH4 supplementation initiated 24 h after surgery and maintained for 8 weeks preserved SBP, reduced UP and prevented the development of glomerular mesangial expansion.

Thromboxane blockade reduces blood pressure and progression of renal failure independent of endothelin-1 in uremic rats

This study was designed to investigate the role of eicosanoids, thromboxane A2 (TXA2) and prostacyclin (PGI2) as well as their relationship with endothelin-1 (ET-1) in the pathogenesis of renal parenchymal hypertension. Uremic rats were prepared by renal mass ablation and compared with sham-operated controls. The stable metabolites of TXA2 (TXB2) and PGI2 (6-keto-PGF1alpha) and immunoreactive ET-1 concentrations were measured by specific RIAs in biological fluids and in vascular and renal tissues. To investigate the functional role of TXA2 in the progression of hypertension and renal failure, a group of uremic rats were treated with ridogrel (25 mg/kg/day), a TXA2 synthase inhibitor and receptor antagonist. Renal preproET-1 expression was assessed by Northern blot analysis. Systolic blood pressure (SBP), serum creatinine and proteinuria were found to be higher in uremic rats as compared to sham-operated controls (P < 0.01). TXB2 and ET-1 concentrations were increased in blood vessels, the renal cortex and in urine (P < 0.05). 6-keto-PGF1alpha concentrations were also increased in blood vessels and the renal cortex but decreased in urine (P < 0.05). Ridogrel significantly lowered SBP and proteinuria (P < 0.05) and blunted the increase of serum creatinine. Treatment with ridogrel resulted in a marked fall in vascular, renal and urine TXA2 concentrations, while ET-1 and 6-keto-PGF1alpha concentrations remained unchanged. The preproET-1 expression was higher in uremic rats than in the controls and was unaffected by ridogrel. These results suggest that TXA2 is involved in the pathogenesis of hypertension and renal failure progression in rats with subtotal 5/6 nephrectomy and that this effect is independent of the ET-1 system.

Renal neuronal nitric oxide synthase protein expression as a marker of renal injury

BACKGROUND

Animal studies suggest that nitric oxide deficiency occurs in the remnant after 5/6 removal of renal mass. The present studies investigated the time course in relation to progression of renal disease, as well as the impact on individual renal nitric oxide synthase (NOS) isoforms.

METHODS

Rats were studied from 2 to 11 weeks after 5/6 ablation/infarction (A/I) of renal mass, with acceleration of progression by high protein and salt intake, in some groups. Measurements were made before sacrifice of 24-hour protein and creatinine excretion, blood was taken for creatinine and blood urea nitrogen (BUN) determination and the kidneys were investigated histologically for structural damage, abundance of endothelial NOS (eNOS) and neuronal NOS (nNOS), and in some groups for in vitro NOS activity.

RESULTS

A time-dependent fall in glomerular filtration rate (GFR) and rise in proteinuria and glomerular sclerosis developed after 5/6 A/I. The nNOS abundance in cortex and medulla was decreased relative to shams, in all but the mildest injury and there was a strong, steep correlation between level of glomerular sclerosis and the degree of reduction in renal nNOS. Where measured, cortical NOS activity correlated with the nNOS abundance. In contrast, the eNOS abundance was either increased or unchanged in rats post A/I.

CONCLUSION

Renal nNOS abundance was reduced in the 5/6 A/I model of renal disease when plasma creatinine> approximately 1 mg/dL and when> approximately 20% of remaining glomeruli were sclerosed.

Combining lisinopril and l-arginine slows disease progression and reduces endothelin-1 in passive Heymann nephritis

BACKGROUND

Despite angiotensin-converting enzyme (ACE) inhibition is a very powerful therapy, it may not be uniformly renoprotective in patients with proteinuric nephropathies who might refer late in the course of the disease. In accelerated passive Heymann nephritis (PHN), a severe rat model of human membranous nephropathy, with proteinuria and increased urinary excretion of endothelin-1 (ET-1), early treatment with an ACE inhibition limited proteinuria as well as the exuberant formation of renal ET-1, while late treatment reduced urinary proteins not to a significant extent. Since biologic effects and production of ET-1 within the kidney are counteracted by nitric oxide, we studied the effect of combining lisinopril and l-arginine, the natural precursor of nitric oxide, starting late in the disease.

METHODS

Uninephrectomized PHN rats were divided in four groups (N = 10) and daily given orally: vehicle; 1.25 g/L l-arginine; 40 mg/L lisinopril; and l-arginine + lisinopril. Treatments started at 2 months, when rats had massive proteinuria, until 9 months. Six normal rats served as control.

RESULTS

Increase in systolic blood pressure was significantly limited by l-arginine. Lisinopril alone and the combination were more effective. Renal function impairment was not affected by l-arginine, partially ameliorated by ACE inhibitor and normalized by the combined therapy. In rats given l-arginine, proteinuria levels were similar to vehicle. ACE inhibitor kept proteinuria at values comparable to pretreatment and numerically lower than vehicle. Addition of l-arginine to lisinopril was more effective, with values significantly lower than vehicle. Glomerular and tubular changes were limited by the ACE inhibitor and further ameliorated by the combined therapy. Exaggerated urinary ET-1 of PHN was reduced by 23% and 40% after l-arginine and lisinopril, respectively, and by 62% with the combination. Defective urinary excretion of cyclic guanosine monophosphate (cGMP) was partially restored by lisinopril, while normalized by the combined therapy.

CONCLUSION

Combining l-arginine with ACE inhibitors would represent a novel strategy for patients with severe nephropathy not completely responsive to ACE inhibition. Restoring the nitric oxide/ET-1 balance could be of benefit in halting renal disease progression.

Increased plasma phenylacetic acid in patients with end-stage renal failure inhibits iNOS expression

NO prevents atherogenesis and inflammation in vessel walls by inhibition of cell proliferation and cytokine-induced endothelial expression of adhesion molecules and proinflammatory cytokines. Reduced NO production due to inhibition of either eNOS or iNOS may therefore reinforce atherosclerosis. Patients with end-stage renal failure show markedly increased mortality due to atherosclerosis. In the present study we tested the hypothesis that uremic toxins are responsible for reduced iNOS expression. LPS-induced iNOS expression in mononuclear leukocytes was studied using real-time PCR. The iNOS expression was blocked by addition of plasma from patients with end-stage renal failure, whereas plasma from healthy controls had no effect. Hemofiltrate obtained from patients with end-stage renal failure was fractionated by chromatographic methods. The chromatographic procedures revealed a homogenous fraction that inhibits iNOS expression. Using gas chromatography/mass spectrometry, this inhibitor was identified as phenylacetic acid. Authentic phenylacetic acid inhibited iNOS expression in a dose-dependent manner. In healthy control subjects, plasma concentrations were below the detection level, whereas patients with end-stage renal failure had a phenylacetic acid concentration of 3.49 +/- 0.33 mmol/l (n = 41). It is concluded that accumulation of phenylacetic acid in patients with end-stage renal failure inhibits iNOS expression. That mechanism may contribute to increased atherosclerosis and cardiovascular morbidity in patients with end-stage renal failure.

Endothelin-1 in chronic renal failure and hypertension

Investigation into the role of endothelin-1 (ET-1) in renal function has revealed two major direct actions leading to the control of extracellular volume and blood pressure. These are the regulation of renal hemodynamics and glomerular filtration rate and the modulation of sodium and water excretion. In the rat remnant kidney model of chronic renal failure, ET-1 production is increased in blood vessels and renal tissues. These changes are related to an increase in preproET-1 expression and correlate with the rise in blood pressure, the development of cardiovascular hypertrophy, and the degree of renal insufficiency and injury. Selective ETA receptor blockade prevents the progression of hypertension and the vascular and renal damage, supporting a role for ET-1 in chronic renal failure progression. The increase in ET-1 production can be associated with other local mediators, including angiotensin II, transforming growth factor-beta1 and nitric oxide, the local production of which is also altered in chronic renal failure. In human patients with essential hypertension, atherosclerosis, and nephrosclerosis, plasma ET-1 levels are increased compared with patients with uncomplicated essential hypertension. Similarly, plasma ET-1 concentrations are markedly increased in patients with end-stage renal disease undergoing dialysis, and this correlates with blood pressure, suggesting that ET-1 may contribute to hypertension in these patients. The treatment of anemia in patients with renal failure with human recombinant erythropoietin increases blood pressure by accentuating the underlying endothelial dysfunction and the elevated vascular ET-1 production. Overall, these results support a role for ET-1 in hypertension and the end-organ damage associated with chronic renal failure. ETA receptor blockade may then represent a potential target for the management of hypertension and cardiovascular and renal protection.

Arginase inhibition slows the progression of renal failure in rats with renal ablation

Exogenous arginine slows the progression of chronic renal failure (CRF) in remnant rats through a nitric oxide (NO)-dependent mechanism. We tested whether the inhibition of arginase could induce similar results through the increased availability of endogenous arginine. Three groups of remnant rats were studied for 8 wk: 1) untreated rats (REM); 2) remnant rats treated with 1% l-arginine (ARG); and 3) remnant rats administered a Mn(2+)-free diet to inhibit arginase (MNF). Normal rats (NOR) were used as controls. Liver arginase activity was depressed in MNF rats (-35% vs. REM, P < 0.01). No difference in metabolic data was detected among the groups throughout the study; blood pressure was significantly lower in MNF vs. ARG and REM rats after 6 wk (P < 0.001). The glomerular filtration rate (GFR) was greatly depressed in REM rats (-47% vs. NOR, P < 0.03) but was higher in ARG and MNF rats (+40 and +43% vs. REM, respectively, P < 0.05), with comparable changes in renal hemodynamics. Despite the better GFR, proteinuria was decreased in both ARG and MNF rats (-42%, P < 0.05, and -57%, P < 0.01, respectively, vs. REM rats). Arginine plasma levels, significantly reduced in REM rats (-41% vs. NOR, P < 0.01), were partially restored in MNF rats (+38% vs. REM), and urinary nitrite excretion, greatly depressed in REM rats (-76% vs. NOR, P < 0.01), was significantly increased in MNF rats (+209% vs. REM, P < 0.05). At the renal level, arginase activity was only slightly depressed in MNF rats (-18% vs. REM), but intrarenal concentrations of arginine were lower in this latter group (P < 0.05 vs. other groups). Beyond the hemodynamic modifications, MNF rats showed a lower glomerular sclerosis index (P < 0.05 vs. REM and ARG). Inhibition of arginase slows the progression of CRF in remnant rats similarly to arginine-treated rats; the better histological protection in MNF rats, however, suggests that additional factors are involved in these modifications.

Relationship between eicosanoids and endothelin-1 in the pathogenesis of erythropoietin-induced hypertension in uremic rats

Recent studies suggest a possible link between recombinant human erythropoietin (rhEPO)-induced hypertension and endothelium-derived vasoconstrictor autocoids. The current study was designed to evaluate the role of eicosanoids such as thromboxane (TX) A and prostacyclin (PGI ) and of endothelin-1 (ET-1) and the relationship between these vasoactive substances in rhEPO-induced hypertension in uremic rats. Renal failure was induced by a two-stage 5/6 nephrectomy followed by a 6-week stabilization period. In protocol A, rats were divided into four groups: vehicle, rhEPO (100 u/kg, subcutaneously, three times per week), a selective ET receptor antagonist (ABT-627, 10 mg/kg/d), and rhEPO + ABT-627 for 5 weeks. In protocol B, uremic animals were divided into two groups: rhEPO and rhEPO + a TX receptor antagonist and synthesis inhibitor, ridogrel (25 mg/kg/d), for 5 weeks. At the end of the study, immunoreactive eicosanoid metabolites (TXB and 6-keto-PGF, stable metabolites of TXA and PGI ), and ET-1 were measured in either the thoracic aorta or in the mesenteric arterial bed. After 5/6 nephrectomy, the animals developed uremia, anemia, and hypertension. rhEPO corrected the anemia but aggravated the hypertension. Both drugs were effective in preventing the progression of hypertension in rhEPO-treated rats although ABT-627 was more potent than ridogrel. rhEPO increased the concentration of ET-1 and TXB in blood vessels and ABT-627 decreased tissue levels of both vasopressors. The concentration of 6-keto-PGF was not significantly changed. Ridogrel significantly decreased tissue TXB concentrations but had no effect on ET-1 levels. These results suggest that endothelium-derived vasoconstrictor autacoids (TXA and ET-1) are involved in the pathogenesis of rhEPO-induced hypertension in uremic rats. TXA probably serves as a mediator of the vascular effect of ET-1.

Long-term dietary L-arginine supplementation attenuates proteinuria and focal glomerulosclerosis in experimental chronic renal transplant failure

Glomerular endothelial nitric oxide synthase expression is decreased in humans during acute rejection and chronic renal transplant failure (CRTF). This may contribute to vascular damage through changes in the renal hemodynamics and enhanced endothelial adhesion of leukocytes and platelets. Dietary supplementation of L-arginine may increase endothelial NO production, thereby protecting the vascular wall and improving renal hemodynamics. We tested the hypothesis that long-term L-arginine supplementation attenuates the development of CRTF in an experimental model for renal transplantation. In the Fisher 344 to Lewis rat model for renal transplantation, renal function and histology of untreated rats was compared with rats receiving L-arginine in the drinking water (10g/L), starting 2 days before transplantation. Every 4 weeks systolic blood pressure was measured and serum and urine were collected for measurement of nitrite and nitrate (NO(x)), creatinine, and proteinuria. At 34 weeks the histological renal damage was assessed by scoring focal glomerulosclerosis and measurement of alpha-smooth muscle actin (alpha-SMA) expression. Urinary NO(x) was significantly increased in treated animals. Proteinuria was significantly lower in L-arginine-treated animals from week 24 onward (p<0.05). Plasma creatinine and creatinine clearance did not differ between the groups. The focal and segmental glomerulosclerosis (FGS) score (max 400) at week 34 was also significantly lower in treated rats arbitrary U (20+/-21 vs 61+/-67 arbitrary U; p<0.05). The expression of alpha-SMA was lower in L-arginine-treated rats than in untreated rats (1.93+/-0.8% area surface vs 3.64+/-2.5% area surface). In conclusion, in this experimental model for CRTF, L-arginine administration significantly reduced FGS and proteinuria, without affecting renal function. Our data suggest that dietary L-arginine supplementation attenuates progression of CRTF and may therefore be an additional therapeutic option in human renal allograft recipients.

L-arginine in cardiovascular disease: dream or reality?

L-arginine is the substrate for endothelial nitric oxide synthase (eNOS), and the precursor for the synthesis of nitric oxide (NO). This amino acid exerts a number of actions in the cardiovascular system, mainly through the production of NO. However, it also has a number of NO-independent properties, such as the ability to regulate blood and intracellular pH and the effect on the depolarization of endothelial cell membranes. It also has antihypertensive and antioxidant properties, it influences blood viscosity and the coagulation/fibrinolysis system, and it affects the metabolism of glucose, lipids and proteins. L-arginine influences a number of atherosclerosis risk factors such as hypercholesterolemia, hypertension and smoking, improving endothelial function in these patients. However, it does not affect endothelial function in patients with diabetes mellitus. The role of L-arginine in coronary artery disease is still controversial, but it seems that oral or parenteral administration of this amino acid restores endothelial function in the brachial artery and improves coronary microcirculation. The role of L-arginine in heart failure is currently under investigation, and the first results are rather hopeful. In conclusion, L-arginine seems to provide a hopeful prospect for the treatment of cardiovascular diseases. However, more data derived from large-scale prospective studies evaluating the effects of long-term treatment with L-arginine are needed.

Blood pressure-independent effect of angiotensin AT1 receptor blockade on renal endothelin-1 production in hypertensive uremic rats

OBJECTIVE

We recently reported that treatment of uremic rats with reduced renal mass with the angiotensin II (Ang II) subtype 1 receptor (AT1) antagonist losartan reduces endothelin-1 (ET-1) levels in blood vessels and in glomeruli. Although this suggests an important role for Ang II in the modulation of ET-1 production, the concomitant decrease in blood pressure may also be involved. The present study was designed to investigate whether the modulation of ET-1 production in uremic rats is related to tissue-specific effects of AT1 receptor blockade or to the antihypertensive effect of losartan.

DESIGN

One week after renal mass reduction, uremic rats were treated with the conventional triple therapy (TRx) [reserpine (5 mg/l), hydralazine (80 mg/l) and hydrochlorothiazide (25 mg/l)] or losartan (20 mg/kg per day) for 6 weeks. Immunoreactive-ET-1 (ir-ET-1) levels in plasma and urine, as well as in vascular and renal tissues were measured by a specific radioimmunoassay after sample extraction and purification.

RESULTS

Before treatment, systolic blood pressure was significantly higher in uremic animals compared to sham-operated controls (165+/-4 versus 123+/-2 mmHg, respectively; P < 0.01). Treatment with the TRx or with losartan normalized systolic blood pressure in uremic rats, whereas it was further increased in untreated uremic animals. At week 6, serum creatinine, proteinuria and urinary ET-1 and transforming growth factor-beta1 (TGF-beta1) excretion, as well as vascular and glomerular ET-1 content were increased in uremic rats compared to the controls (P < 0.01). Treatment of uremic rats with the TRx or with losartan reduced ET-1 content in the thoracic aorta and the mesenteric arterial bed (P < 0.01). However, losartan, but not the TRx, significantly attenuated the rise of serum creatinine, proteinuria and urinary ET-1 and TGF-beta1 excretion, as well as ET-1 content in glomeruli of uremic rats. Compared with the controls, renal preproET-1 mRNA expression was also significantly higher in uremic rats. Treatment of uremic rats with losartan prevented renal preproET-1 mRNA overexpression, indicating that changes in glomerular ET-1 content and urinary ET-1 excretion were related to modulation of renal ET-1 production.

CONCLUSIONS

These findings indicate that the effect of losartan on ET-1 production in peripheral blood vessels may be mediated, in part, by the reduction of blood pressure. In contrast, the reduction of renal ET-1 production is mediated by tissue-specific effects of AT1 receptor blockade, and may contribute to the renal protective effects of losartan.