Depressed renal and vascular nitric oxide synthase expression in cyclosporine-induced hypertension

Cardiovascular toxicities by calcineurin inhibitors: Cellular mechanisms behind clinical manifestations

Calcineurin inhibitors (CNI), including cyclosporine A (CsA) and tacrolimus (TAC), are cornerstones of immunosuppressive therapy in solid organ transplant recipients. While extensively recognized for their capacity to induce nephrotoxicity, hypertension, and dyslipidemia, emerging reports suggest potential direct cardiovascular toxicities associated with CNI. Evidence from both in vitro and in vivo studies has demonstrated direct cardiotoxic impact of CNI, manifesting itself as induction of cardiomyocyte apoptosis, enhanced oxidative stress, inflammatory cell infiltration, and cardiac fibrosis. CNI enhances cellular apoptosis through CaSR via activation of the p38 MAPK pathway and deactivation of the ERK pathway, and enhancement of miR-377 axis. Although CNI could attenuate cardiac hypertrophy in certain animal models, CNI concurrently impaired systolic function, enhanced cardiac fibrosis, and increased the risk of heart failure. Evidence from in vivo studies demonstrated that CNI prolong the duration of action potentials through a decrease in potassium current. CNI also exerted direct effects on endothelial cell injury, inducing apoptosis and enhancing oxidative stress. CNI may induce vascular inflammation through TLR4 via MyD88 and TRIF pathways. In addition, CNI affects vascular function by impairing endothelial-dependent vasodilation and promoting vasoconstriction. Clinical studies in transplant patients also revealed an increased incidence of cardiac remodeling. However, the evidence is constrained by the limited number of participants and potential confounding factors. Several studies indicate differing cardiovascular toxicity profiles between CsA and TAC, and these could be potentially due to their different interactions with calcineurin subunits and calcineurin-independent effects. Further studies are needed to clarify these mechanisms to improve cardiovascular outcomes for transplant patients with CNI.

Apelin pathway in cardiovascular, kidney, and metabolic diseases: Therapeutic role of apelin analogs and apelin receptor agonists

The apelin/apelin receptor (ApelinR) signal transduction pathway exerts essential biological roles, particularly in the cardiovascular system. Disturbances in the apelin/ApelinR axis are linked to vascular, heart, kidney, and metabolic disorders. Therefore, the apelinergic system has surfaced as a critical therapeutic strategy for cardiovascular diseases (including pulmonary arterial hypertension), kidney disease, insulin resistance, hyponatremia, preeclampsia, and erectile dysfunction. However, apelin peptides are susceptible to rapid degradation through endogenous peptidases, limiting their use as therapeutic tools and translational potential. These proteases include angiotensin converting enzyme 2, neutral endopeptidase, and kallikrein thereby linking the apelin pathway with other peptide systems. In this context, apelin analogs with enhanced proteolytic stability and synthetic ApelinR agonists emerged as promising pharmacological alternatives. In this review, we focus on discussing the putative roles of the apelin pathway in various physiological systems from function to dysfunction, and emphasizing the therapeutic potential of newly generated metabolically stable apelin analogs and non-peptide ApelinR agonists.

Adverse Effects of Immunosuppression: Nephrotoxicity, Hypertension, and Metabolic Disease

The use of Immunosuppression has led to the tremendous improvement in graft survival. However, immunosuppressants have been found to cause a variety of metabolic derangements including but not limited to: insulin resistance and diabetes, hyperlipidemia, hypertension, and weight gain after transplantation. This combination of metabolic risk factors may be associated with increased cardiovascular disease (Grundy et al., Circulation 112(17):2735, 2005). In addition many transplant recipients may have many of these risk factors pre-transplant that are exacerbated by immunosuppression. These facts emphasize the need for rigorous follow-up and management of these risk factors post-transplant.The most common immune suppressant regimens may include different combinations of these agents: Corticosteroids, Calcineurin inhibitors (CNIs), Mammalian Target of Rapamycin (mTOR) Inhibitors, Antimetabolite.

Unique Considerations When Managing Hypertension in the Transplant Patient

For the select fortunate recipients of organ transplants, transplantation affords the rare opportunity for a new life. Given the scarcity of organs for transplantation, it is imperative that the health of transplant recipients be optimized in order to fully benefit from this gift of life. Unfortunately, hypertension is highly prevalent in the transplant population and it is considered a major cardiovascular risk factor contributing to mortality and morbidity in this population. In this chapter, we expound on the epidemiology, unique pathophysiology, evaluation, and management of hypertension as it pertains to the solid organ transplant recipient. In addition, a brief commentary is made on the subject of hypertension following living kidney donation, and practical aspects of management of hypertension in the solid organ recipient are summarized at the end of the chapter.

Treatment With Dimethyl Fumarate Attenuates Calcineurin Inhibitor-induced Nephrotoxicity

BACKGROUND

Cyclosporine A (CsA) is an immunosuppressive drug which has been widely used to prevent rejection after organ transplantation. However, its therapeutic use is limited by nephrotoxicity, in part mediated by oxidative stress. The present study aims to investigate the protective effects of dimethyl fumarate (DMF) on CsA-induced nephrotoxicity by enhancing the antioxidant defense system.

METHODS

Male Sprague-Dawley rats were treated with CsA (n = 8, 20 mg/kg per day intraperitoneally) or CsA + DMF (n = 7, 50 mg/kg per day orally) for 28 days. Renal function, histopathology, malondialdehyde (MDA), myeloperoxidase levels, and antioxidant enzyme expression were determined.

RESULTS

The DMF cotreatment ameliorated CsA-induced renal dysfunction as evidenced by significant decrease in serum creatinine (CsA 0.79 ± 0.02 mg/dL vs CsA + DMF 0.62 ± 0.04 mg/dL, P = 0.001) and urea (CsA 66.9 ± 0.4 mg/dL vs CsA + DMF 53.3 ± 2.6 mg/dl, P < 0.0001) levels, as well as improvement of creatinine clearance. Dimethyl fumarate also significantly decreased serum MDA and renal tissue MDA and myeloperoxidase contents. The protein expression of NAD(P)H quinone oxidoreductase-1, a major cellular antioxidant and detoxifying enzyme, was significantly enhanced by DMF administration in kidney.

CONCLUSIONS

Administration of DMF has a protective potential against CsA nephrotoxicity. The protection afforded by DMF is mediated in part through inhibiting oxidative stress and inflammation and enhancing the antioxidant capacity.

Cyclosporine A loaded self-nanoemulsifying drug delivery system (SNEDDS): implication of a functional excipient based co-encapsulation strategy on oral bioavailability and nephrotoxicity

The present work focusses on the formulation development and evaluation of a functional excipient, a vitamin E TPGS loaded self-nanoemulsifying drug delivery system, for improving the deliverability and safety profile of cyclosporine A.

Association of kidney function and albuminuria with prevalent and incident hypertension: the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

Decreased kidney function and kidney damage may predate hypertension, but only a few studies have investigated both types of markers simultaneously, and these studies have obtained conflicting results.

STUDY DESIGN

Cross-sectional for prevalent and prospective observational study for incident hypertension.

SETTING & PARTICIPANTS

9,593 participants from the ARIC (Atherosclerosis Risk in Communities) Study, aged 53-75 years in 1996-1998.

PREDICTORS

Several markers of kidney function (estimated glomerular filtration rate using serum creatinine and/or cystatin C and 2 novel markers [β-trace protein and β2-microglobulin]) and 1 marker of kidney damage (urinary albumin-creatinine ratio [ACR]). Every kidney marker was categorized by its quintiles (top quintile as a reference for estimated glomerular filtration rates and bottom quintile for the rest).

OUTCOMES

Prevalent and incident hypertension.

MEASUREMENTS

Prevalence ratios and HRs of hypertension based on modified Poisson regression and Cox proportional hazards models, respectively.

RESULTS

There were 4,378 participants (45.6%) with prevalent hypertension at baseline and 2,175 incident hypertension cases during a median follow-up of 9.8 years. Although all 5 kidney function markers were associated significantly with prevalent hypertension, prevalent hypertension was associated most notably with higher ACR (adjusted prevalence ratio, 1.60 [95% CI, 1.50-1.71] for the highest vs lowest ACR quintile). Similarly, ACR was associated consistently with incident hypertension in all models tested (adjusted HR, 1.28 [95% CI, 1.10-1.49] for top quintile), while kidney function markers demonstrated significant associations in some, but not all, models. Even mildly increased ACR (9.14-14.0mg/g) was associated significantly with incident hypertension.

LIMITATIONS

Self-reported use of antihypertensive medication for defining incident hypertension, single assessment of kidney markers, and relatively narrow age range.

CONCLUSIONS

Although all kidney markers were associated with prevalent hypertension, only elevated albuminuria was associated consistently with incident hypertension, suggesting that kidney damage is related more closely to hypertension than moderate reduction in overall kidney function.

Neither cyclosporine nor tacrolimus deteriorate endothelial function in renal transplant recipients assessed with reactive hyperernia index

BACKGROUND

Cardiovascular mortality in renal transplant recipients is nearer 10-fold higher than in general population. Immunosuppressive therapy is one possible cause, for these drugs can modify cardiovascular risk factors, which can induce endothelial dysfunction, the first step in the process of atherosclerosis. The aim of this study was to compare vasodilatatory function of endothelium in renal transplant recipients in relation to the immunosuppressive drug-cyclosporine or tacrolimus.

MATERIALS AND METHODS

We examined 40 patients at 48.9 ± 36 months post-renal transplantation: 22 taking tacrolimus (group 1) and 18 taking cyclosporine (group 2). The renal transplant recipients were compared with a control group of 18 healthy people. Endothelial function was assessed by peripheral arterial tonometry (PAT) using the EndoPAT 2000 device to measure RHI (reactive hyperemia index) and AI% (augmentation index%).

RESULTS

The overall median values of RHI were higher than the value accepted as a normal (1.67). The RHI median value in group 1 was 2.00 (quartile 1: 1.66; quartile 2: 2.72), not different from that in group 2 [1.90 (quartile 1: 1.56; quartile 2: 2.17)] or the controls [2.11 (quartile 1: 1.77; quartile 2: 2.50)]. Multivariate analysis revealed age to be the independent factor influencing RHI in all examined groups but treatment with calcium channel blockers appeared to be the only independent factor influencing RHI among renal transplant recipients. AI% values were not significantly different between the 2 groups of renal transplant recipients, but it was significantly higher among the controls than among subjects treated with tacrolimus.

CONCLUSIONS

Vasodilatatory function of endothelium assessed by PAT in renal transplant recipients was not worse than in healthy people. It was not different between cyclosporine or tacrolimus. Arterial stiffness measured as AI% depend on age but not the calcineurin inhibitor, which showed little effect.

Metabolic syndrome: is immunosuppression to blame?

1. Metabolic syndrome (MS) is common after liver transplantation and has been associated with increased risks of cardiovascular disease, cardiovascular death, liver-related death, and overall mortality. 2. Immunosuppression may increase the frequency of hyperlipidemia, diabetes, and hypertension and thus increase the risk and prevalence of MS after transplantation. 3. Corticosteroids are associated with increased rates of diabetes, hypertension, and hyperlipidemia in the short term. These agents are now being used perhaps less frequently and certainly for shorter durations; therefore, the long-term effects on metabolic morbidities may be reduced. 4. Calcineurin inhibitors and mammalian target of rapamycin inhibitors affect many MS parameters to various degrees and contribute to long-term morbidity after transplantation.

Biomarkers of immunosuppressant organ toxicity after transplantation: status, concepts and misconceptions

INTRODUCTION

A major challenge in transplantation is improving long-term organ transplant and patient survival. Immunosuppressants protect the transplant organ from alloimmune reactions, but sometimes also exhibit limiting side effects. The key to improving long-term outcome following transplantation is the selection of the correct immunosuppressive regimen for an individual patient for minimizing toxicity while maintaining immunosuppressive efficacy.

AREAS COVERED

Proteomics and metabolomics have the potential to develop sensitive and specific diagnostic tools for monitoring early changes in cell signal transduction, regulation and biochemical pathways. Here, we review the steps required for the development of molecular markers from discovery, mechanistic and clinical qualification to regulatory approval, and present a critical discussion of the current status of molecular marker development as relevant for the management and individualization of immunosuppressive drug regimens.

EXPERT OPINION

Although metabolomics and proteomics-based studies have yielded several candidate molecular markers, most published studies are poorly designed, statistically underpowered and/or often have not gone beyond the discovery stage. Most molecular marker candidates are still at an early stage. Due to the high complexity of and the resources required for diagnostic marker development, initiatives and consortia organized and supported by funding agencies and regulatory agencies will be critical.

Protective effect of docosahexaenoic acid against cyclosporine A-induced nephrotoxicity in rats: a possible mechanism of action

The aim of this experimental study was to investigate whether, and how then, docosahexaenoic acid (DHA) could alleviate the cyclosporine A (CsA)-induced nephrotoxicity. Three main groups of Sprague-Dawley rats were treated orally with CsA (25 mg/kg), DHA (100 mg/kg), and CsA along with DHA. A corresponding control group was also used. DHA administration significantly reduced CsA-induced nephrotoxicity and associated hyperlipidemia and proteinuria as assessed by estimating serum triacylglycerol, serum total cholesterol, serum total protein, serum urea, and creatinine clearance. Furthermore, urinary excretions of protein and N-acetyl-β-D-glucosaminidase were significantly inhibited following DHA administration. DHA supplementation slightly attenuated the oxidative damage in kidney tissues as evaluated by the levels of thiobarbituric acid-reacting substances and protein carbonyl content in the kidney homogenate, although there were no significant differences between CsA-intoxicated and DHA-treated animals. Moreover, DHA treatment significantly restored total nitric oxide (NO) levels in both renal tissues and urine. This study demonstrates the ability of DHA to ameliorate CsA-induced renal dysfunction, which might be beneficial to enhance the therapeutic index of CsA. The data suggest that the protective potential of DHA in the prevention of CsA nephrotoxicity in rats was mainly associated with the increase of total NO bioavailability in renal tissues. Nevertheless, the exact independent mechanism in which DHA exerts its beneficial effect is yet to be fully elucidated.

Toxicodynamic effects of ciclosporin are reflected by metabolite profiles in the urine of healthy individuals after a single dose

WHAT IS ALREADY KNOWN ABOUT THE SUBJECT * Ciclosporin's nephrotoxicity initially targets the proximal tubule and is, at least in part, driven by increased formation of oxygen radicals. * (1)H-nuclear magnetic resonance spectroscopy (NMR)- and mass spectrometry (MS)-based biochemical profiling (metabolomics) allows for the sensitive detection of metabolite pattern changes in urine. * In systematic studies in rats we showed that ciclosporin caused urine metabolite pattern changes typical for proximal tubule damage and that these pattern changes seemed to be more sensitive than established clinical kidney function markers such as serum creatinine concentrations. WHAT THIS PAPER ADDS * This study showed that urine metabolite pattern changes as assessed by (1)H-NMR and HPLC-MS are sensitive enough to detect the effect of ciclosporin as early as 4 h after a single oral dose. * In our previous rat studies, changes in urine metabolite pattern in response to ciclosporin translated into healthy humans, indicating the involvement of the same toxicodynamic mechanisms. * The results provide proof of concept for further development of this combination molecular marker strategy into diagnostic tools for the detection and monitoring of drug nephrotoxicity. AIMS The immunosuppressant ciclosporin is an efficient prophylaxis against transplant organ rejection but its clinical use is limited by its nephrotoxicity. Our previous systematic studies in the rat indicated urine metabolite pattern changes to be sensitive indicators of the negative effects of ciclosporin on the kidney. To translate these results, we conducted an open label, placebo-controlled, crossover study assessing the time-dependent toxicodynamic effects of a single oral ciclosporin dose (5 mg kg(-1)) on the kidney in 13 healthy individuals. METHODS In plasma and urine samples, ciclosporin and 15-F(2t)-isoprostane concentrations were assessed using HPLC-MS and metabolite profiles using (1)H-NMR spectroscopy. RESULTS The maximum ciclosporin concentrations were 1489 +/- 425 ng ml(-1) (blood) and 2629 +/- 1308 ng ml(-1) (urine). The increase in urinary 15-F(2t)-isoprostane observed 4 h after administration of ciclosporin indicated an increase in oxidative stress. 15-F(2t)-isoprostane concentrations were on average 2.9-fold higher after ciclosporin than after placebo (59.8 +/- 31.2 vs. 20.9 +/- 19.9 pg mg(-1) creatinine, P < 0.02). While there were no conclusive changes in plasma 15-F(2t)-isoprostane concentrations or metabolite patterns, non-targeted metabolome analysis using principal components analysis and partial least square fit analysis revealed significant changes in urine metabolites typically associated with negative effects on proximal tubule cells. The major metabolites that differed between the 4 h urine samples after ciclosporin and placebo were citrate, hippurate, lactate, TMAO, creatinine and phenylalanine. CONCLUSION Changes in urine metabolite patterns as a molecular marker are sufficiently sensitive for the detection of the negative effects of ciclosporin on the kidney after a single oral dose.

The use of cyclosporine in dermatology: part II

Cyclosporine is highly effective in the treatment of a multitude of dermatoses. Concern over its side effect profile has limited its use in dermatology. Adverse effects are, for the most part, dose dependent and related to duration of therapy. Using the recommended monitoring protocols results in a significant decrease in the incidence of cyclosporine-related toxicities. This article provides a comprehensive review of the pharmacokinetics of cyclosporine, potential drug interactions, adverse effects, and recommendations for monitoring in patients treated with cyclosporine. The use of cyclosporine in pregnancy and in the pediatric population is also addressed.

LEARNING OBJECTIVES

After completing this learning activity, participants should be familiar with the monitoring guidelines of cyclosporine, its contraindications, its possible drug interactions, its adverse effect profile, and its use in pregnancy and the childhood and adolescent populations.

Macrophage depletion attenuates chronic cyclosporine A nephrotoxicity

BACKGROUND

Cyclosporine A (CsA)-induced chronic nephrotoxicity is characterized by renal dysfunction and interstitial fibrosis. Early and progressive renal macrophage influx, correlating with latter interstitial fibrotic areas, has been associated with CsA treatment. This study investigated the role of macrophages, the nitric oxide (NO) pathway, and the oxidative stress on chronic CsA nephrotoxicity.

METHODS

The macrophages were depleted by clodronate liposomes. Animals were distributed into four groups: vehicle (olive oil for 21 days), CsA 7.5 mg/kg per day (21 days), CsA plus clodronate (5 mg/mL intraperitoneally on days -4, 1, 4, 11, and 18 of CsA treatment), or vehicle plus clodronate. On day 22, glomerular filtration rate, renal blood flow, renal tubulointerstitial fibrosis, CsA blood levels, serum malondialdehyde and renal tissue immunohistochemistry for macrophages, inducible NO synthase, transforming growth factor-beta, nuclear factor-kbeta, alpha-smooth muscle actin, vimentin, and nitrotyrosine were assessed.

RESULTS

CsA-induced increase in the macrophage was prevented by clodronate. Macrophage depletion attenuated the reductions in the glomerular filtration rate and renal blood flow, the development of tubulointerstitial fibrosis, malondialdehyde increase and increases in nuclear factor-kbeta, transforming growth factor-beta, vimentin, inducible NO synthase, and nitrotyrosine expression provoked by CsA. Clodronate did not affect alpha-smooth muscle actin expression and CsA blood levels.

CONCLUSIONS

Renal macrophage influx plays an important role in CsA-induced chronic nephrotoxicity. The NO pathway and oxidative stress are likely mechanisms involved in the genesis of this form of renal injury.

Cyclosporine stimulates the renal epithelial sodium channel by elevating cholesterol

Cyclosporine A (CsA) is an efficient immunosuppressant used for reducing allograft rejection but with a severe side effect of causing hypertension. We hypothesize that the renal epithelial sodium channel (ENaC) may participate in CsA-induced hypertension. In the present study, we used the patch-clamp cell-attached configuration to examine whether and how CsA stimulates ENaC in A6 distal nephron cells. The data showed that CsA significantly increased ENaC open probability. Since CsA is an inhibitor of the ATP-binding cassette A1 (ABCA1) transporter, we employed 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), another ABCA1 inhibitor, and found that DIDS mimicked the effects of CsA on ENaC basal and cholesterol-induced activity but without any additive effect if combined with CsA. CsA and DIDS also had an identical effect on reduced ENaC activity caused by cholesterol extraction. ABCA1 protein was detected in A6 cells by Western blot analysis. Confocal microscopy data showed that both CsA and DIDS facilitated A6 cells to uptake cholesterol. Since enhanced ENaC activity is known to cause hypertension, these data together suggest that CsA may cause hypertension by stimulating ENaC through a pathway associated with inhibition of ABCA1 and consequent elevation of cholesterol in the cells.

Upregulation of endothelial and inducible nitric oxide synthase expression by reactive oxygen species

BACKGROUND

The effect of reactive oxygen species (ROS) on nitric oxide synthase (NOS) expression remains uncertain. This study explored the effect of increased ROS activity on NOS expression in vitro in human coronary artery endothelial cells (HCAECs) grown in culture and in intact animals.

METHODS

Endothelial NOS (eNOS) expression and nuclear factor kappaB (NFkappaB) activation were determined in HCAECs grown in culture and exposed to oxidative stress with xanthine-xanthine oxidase (X-XO) generated superoxide, H(2)O(2), or glutathione depletion with buthionine sulfoximine (BSO) for 24 h. In parallel experiments, cells were treated with a nitric oxide (NO) scavenger (hemoglobin), and with an NO donor S-nitroso-N-acetyl penicillamine (SNAP)]. In addition, eNOS and inducible NOS (iNOS) expressions were determined in rats treated with either BSO or vehicle for 48 h.

RESULTS

Increases in ROS activity, achieved by exogenous superoxide and H(2)O(2) or by glutathione depletion, upregulated the expression of eNOS at both transcriptional and translational levels in HCAECs. Similar effects were seen with the non-radical NO scavenger, hemoglobin. The upregulatory action of hemoglobin on eNOS messenger RNA (mRNA) and protein expressions was overcome by the NO donor, SNAP, thereby suggesting that there is a negative feedback regulation of eNOS by NO. Nuclear translocation of NFkappaB (p65) was noted within 5 min of exposure to H(2)O(2) and at least 15 min after exposure to superoxide or BSO. Induction of oxidative stress by glutathione depletion led to upregulation of renal and aorta eNOS and iNOS in live animals.

CONCLUSIONS

An increase in ROS activity upregulates NOS expression in vitro in HCAECs grown in culture, and also in vivo in animals. This effect appears to be, in part, mediated by limiting the availability of NO, thereby exerting a negative feedback influence on NOS expression through activation of NFkappaB.

Dual effect of nitrate therapy for cyclosporine-induced hypertension on vascular and platelet morphofunctional markers; an animal model

The present study sought to evaluate the prevention and reversion effects of isosorbide-5-mononitrate (Is-5-Mn) on the development of hypertension (HT) and on the underlying vascular and platelet morphofunctional disturbances, using an animal model of cyclosporine (CsA)-induced HT. The following rat groups (n = 8) were tested: (1) a control group (orange juice, for 7 weeks); (2) the CsA group (5 mg/kg/d for 7 weeks); (3) the Is-5-Mn group (150 mg/kg/d, twice a day for 7 weeks); (4) the prevention group (Is-5-Mn + CsA) treated for 2 weeks with Is-5-Mn only and thereafter with both drugs for 7 weeks; (5) the curative group (CsA + Is-5-Mn) beginning 7 weeks after CsA and following thereafter with both drugs for 5 weeks. Blood pressure, lipid profile, vascular lesion, platelet aggregation and morphology, and platelet thromboxane A(2)/vascular prostacyclin equilibrium were evaluated. Is-5-Mn + CsA therapy prevented (systolic blood pressure [SBP]: 114.3 +/- 1.9 mm Hg, P < .001; diastolic blood pressure [DBP]: 97.0 +/- 3.3 mm Hg, P < .001) the CsA-induced HT (SBP: 146.2 +/- 4.5 mm Hg, P < .001; DBP: 124.9 +/- 4.5 mm Hg, P < .001 vs control: SBP: 111.6 +/- 0.7 mm Hg; DBP: 94.6 +/- 1.0 mm Hg), as well as the vascular lesion and the platelet morphofunctional disturbances. The curative group did not show attenuated CsA-induced BP increase; it showed further enhancement of the HT effect (SBP: 159.7 +/- 5.5 mm Hg, P < .05; DBP: 132.8 +/- 2.8 mm Hg), as well as worsened vascular lesions and platelet function, namely a disruption in the TXA(2)/PGI(2) equilibrium. Our data suggested that Is-5-Mn therapy may be a valid choice to prevent the morphofunctional changes associated with CsA-induced HT, when used as a preventive therapy. A careful evaluation of the impact of nitrate therapy should be considered, particularly the negative effect on cardiovascular hemodynamics, when considering its use after previous CsA disturbances have been established.

New insights into the pathophysiology of cyclosporine nephrotoxicity: a role of aldosterone

Cyclosporine A (CsA), a calcineurin inhibitor, has improved allograft survival in solid organ transplantation and has been increasingly applied in the management of autoimmune diseases. While marked progress has been made in patient and allograft survival rates, clinical use of CsA is often limited by its nephrotoxic effect, which can be presented as two distinct and well-characterized forms: acute and chronic nephrotoxicity. The acute form is characterized by renal vasoconstriction, induced by an imbalance of vasoactive substances release, which leads to renal dysfunction. This form is reversible. The chronic toxicity, in contrast, is characterized by the vasoconstriction plus the development of structural damage that includes arteriolopathy and tubulointerstitial fibrosis that are often not reversible. The exact mechanisms of these deleterious effects are not fully understood, but major advances have occurred over the last few years. Here we review the current literature regarding the pathogenesis and strategies that have been used to ameliorate renal injury in chronic CsA nephrotoxicity. Recent observations suggest that aldosterone plays a central role in the pathogenesis of CsA nephrotoxicity and that spironolactone could be a useful agent to prevent it. These studies and the use of mineralocorticoid receptor blockade are discussed.

Protective effect of L-propionylcarnitine in chronic cyclosporine-a induced nephrotoxicity

Cyclosporine (CyA) is an immunosuppressive agent used after solid organ transplantation, but its clinical use is limited by side effects, the most important of which is nephrotoxicity. In a previous work we demonstrated that L-propionylcarnitine (L-PC), a propionyl ester of L-carnitine, is able to prevent CyA-induced acute nephrotoxicity reducing lipid peroxidation in the isolated and perfused rat kidney. CyA administration was associated with a dose dependent increase in renovascular resistance prevented by a pretreatment with L-PC. The aim of the present study was to confirm L-PC protective effect, previously described in vitro, in an in vivo rat model. Chronic nephrotoxicity study was carried out for 28 days. L-PC was administered (i.p. 25 mg/kg b.w.) since the first day, while CyA treatment was performed for the last 21 days (by oral administration 25 mg/kg b.w.). We demonstrate that L-PC was able to significantly lower blood pressure in CyA treated animals and to prevent CyA induced decrease in creatinine clearance. Moreover renal tissue analysis revealed that L-PC was able to reduce lipid hydroperoxide content and morphological abnormalities associated to chronic CyA administration. In conclusion our study demonstrated for the first time in vivo that L-PC protects against functional and tissue damage associated to chronic CyA administration.

The Mannich base NC1153 promotes long-term allograft survival and spares the recipient from multiple toxicities

JAK3 is a cytoplasmic tyrosine kinase with limited tissue expression but is readily found in activated T cells. Patients lacking JAK3 are immune compromised, suggesting that JAK3 represents a therapeutic target for immunosuppression. Herein, we show that a Mannich base, NC1153, blocked IL-2-induced activation of JAK3 and its downstream substrates STAT5a/b more effectively than activation of the closely related prolactin-induced JAK2 or TNF-alpha-driven NF-kappaB. In addition, NC1153 failed to inhibit several other enzymes, including growth factor receptor tyrosine kinases, Src family members, and serine/threonine protein kinases. Although NC1153 inhibited proliferation of normal human T cells challenged with IL-2, IL-4, or IL-7, it did not block T cells void of JAK3. In vivo, a 14-day oral therapy with NC1153 significantly extended survival of MHC/non-MHC mismatched rat kidney allografts, whereas a 90-day therapy induced transplantation tolerance (>200 days). Although NC1153 acted synergistically with cyclosporin A (CsA) to prolong allograft survival, it was not nephrotoxic, myelotoxic, or lipotoxic and did not increase CsA-induced nephrotoxicity. In contrast to CsA, NC1153 was not metabolized by cytochrome P450 3A4. Thus, NC1153 prolongs allograft survival without several toxic effects associated with current immunosuppressive drugs.

Expression of endothelial nitric oxide synthase is suppressed in the renal vasculature of angiotensinogen-gene knockout mice

We have attempted to elucidate the mechanism by which endothelial-type nitric oxide synthase (eNOS) is regulated in the kidney, with special reference to the role of renal hemodynamics and angiotensin II (Ang II). We compared angiotensinogen gene knockout (Atg-/-) mice, which lacked Ang II (resulting in sodium/water depletion and severe hypotension), with wild-type (Atg+/+) mice. Using Western blot analysis and the NADPH diaphorase histochemical reaction, we found that the expression and activity of eNOS were markedly lower in the renal vessels of Atg-/- mice compared with wild-type (Atg+/+) mice. Dietary salt loading significantly enhanced renal eNOS levels and increased blood pressure in Atg-/- mice, but severe hypotension almost abolished the effects of salt loading. In contrast, in Atg+/+ mice, altered salt intake or hydralazine had no effect on renal eNOS levels. These results suggest that perfusion pressure plays an essential role in maintaining renal vascular eNOS activity, whereas Ang II plays a supportive role, especially when renal circulation is impaired.

Methoxyethyl-modified intercellular adhesion molecule-1 antisense phosphorothiateoligonucleotides inhibit allograft rejection, ischemic-reperfusion injury, and cyclosporine-induced nephrotoxicity

BACKGROUND

The addition of phosphorothioate (PS) groups to natural phosphodiester (PD) antisense oligodeoxynucleotides (oligo) prevents their in vivo hydrolysis by nucleases allowing an RNase-dependent elimination of targeted mRNA. To further improve oligo function 2'-methoxyethyl (ME) groups were attached to selected nucleotides at the 3'-end because ME groups block RNase activity.

METHODS/RESULTS

ME modification of PS- or PD/PS-oligo targeting human intracellular adhesion molecule (ICAM)-1 mRNA significantly increased the degree and duration of the in vitro inhibitory effects without compromising selectivity and specificity. A 7-day intravenous or oral therapy with rat ME/PS-modified ICAM-1 antisense oligo extended the survivals of kidney allografts. In addition, ME/PS-modified ICAM-1 antisense oligo reduced ischemic-reperfusion injury in kidneys, as measured by glomerular filtration rate, creatinine levels, and infiltration with leukocytes. Finally, a 14-day treatment with cyclosporine (CsA)-induced nephrotoxicity in syngeneic kidney transplants correlated with both increased ICAM-1 protein expression and infiltration with leukocytes. Graft perfusion and treatment of recipients with ICAM-1 antisense ME/PS-oligo alleviated the nephrotoxic effect and decreased ICAM-1 expression and leukocyte infiltration.

CONCLUSIONS

ME/PS-modified ICAM-1 antisense oligo is very effective in inhibiting the ICAM-1-dependent mechanism of graft infiltration and tissue damage involved in allograft rejection, ischemic-reperfusion injury, and CsA-induced nephrotoxicity.

Effect of molsidomine and l-arginine in cyclosporine nephrotoxicity: role of nitric oxide

Cyclosporine A (CsA) is a potent and effective immunosuppressive agent, but its action is frequently accompanied by severe renal toxicity. To determine if the renal alterations are mediated directly by cyclosporine or by secondary homodynamic alterations induced by cyclosporine, we evaluated if L-arginine and a nitric oxide donor, molsidomine could prevent these alterations. Eight groups of rats were employed in this study, group 1 served as control, group 2 rats were treated with CsA (20 mg/kg, s.c. for 21 days), group 3 received CsA along with L-arginine (125 mg/kg in drinking water concurrently with CsA), groups 4 and 5 received CsA along with molsidomine (5 and 10 mg/kg, p.o. 24 h before and 21 days concurrently with CsA), group 6 received CsA along with L-arginine (125 mg/l in drinking water concurrently with CsA) and L-NAME (10 mg/kg), groups 7 and 8 received L-NAME (10 mg/kg) along with CsA and molsidomine (5 and 10 mg/kg), respectively. Renal function was assessed by measuring serum creatinine, blood urea nitrogen, creatinine and urea clearance. Tissue and urine nitrite and nitrate levels were measured to estimate the total nitric oxide levels. The renal oxidative stress was measured by renal malondialdehyde levels, reduced glutathione levels and by enzymatic activity of catalase and superoxide dismutase. Renal morphological alterations were assessed by histopathological examination. CsA administration for 21 days resulted in a marked renal oxidative stress, significantly deranged the renal functions as well as renal morphology. Treatment with L-arginine as well as with molsidomine significantly improved the renal dysfunction; tissue and urine total nitric oxide levels, renal oxidative stress and prevented the alterations in renal morphology. This protection against CsA nephrotoxicity was attenuated by treatment with L-NAME, clearly indicating that NO plays a pivotal role in renoprotective effect of L-arginine and molsidomine against cyclosporine nephrotoxicity.

A high-fat, refined-carbohydrate diet induces endothelial dysfunction and oxidant/antioxidant imbalance and depresses NOS protein expression

We tested whether consumption of a high-fat, high-sucrose (HFS) diet can affect endothelium-dependent relaxation, whether this precedes the development of diet-induced hypertension previously noted in this model, and whether it is mediated, in part, by changes in nitric oxide synthase (NOS) and/or NOS regulatory proteins. Female Fischer rats were fed either a HFS diet or standard low-fat, complex-carbohydrate chow starting at 2 mo of age for 7 mo. Vasoconstrictive response to KCl and phenylephrine was similar in both groups. Vasorelaxation to acetylcholine was significantly impaired in the HFS animals, and there were no differences in relaxation to sodium nitroprusside, suggesting that the endothelial dysfunction is due, at least in part, to nitric oxide deficiency. HFS consumption decreased protein expression of endothelial NOS in aorta, renal, and heart tissues, neuronal NOS in kidney, heart, aorta, and brain, and inducible NOS in heart and aorta. Caveolin-1 and soluble guanylate cyclase protein expression did not change, but AKT protein expression decreased in heart and aorta and increased in kidney tissue. Consumption of HFS diet raised brain carbonyl content and plasma hydrogen peroxide concentration and diminished plasma total antioxidant capacity. Because blood pressure, which is known to eventually rise in this model, was not as yet significantly elevated, the present data suggest that endothelial dysfunction precedes the onset of diet-induced hypertension. The lack of a quantitative change in caveolin-1 and soluble guanylate cyclase protein content indicates that alteration in these proteins is not responsible for the endothelial dysfunction. Thus nitric oxide deficiency combined with antioxidant/oxidant imbalance, appears to be a primary factor in the development of endothelial dysfunction in this model.

Up-regulation of kidney NAD(P)H oxidase and calcineurin in SHR: Reversal by lifelong antioxidant supplementation

BACKGROUND

Spontaneously hypertensive rats (SHR) are born normotensive and develop hypertension (HTN) later in life (age 4 to 5 weeks). HTN in SHR is associated with and caused in part, by oxidative stress and renal interstitial inflammation. This study tested the hypothesis that lifelong antioxidant supplementation beginning at prenatal period may delay the onset and reduce the severity of HTN in SHR. The study further sought to explore the effect of diet modification on renal tissue NAD(P)H oxidase and calcineurin abundance.

METHODS

Pregnant SHR and their offspring were fed either an antioxidant-fortified diet (a chow containing alpha-tocopherol 5000 IU/kg, ascorbic acid 500 ppm, selenium 2.76 ppm, and zinc 350 ppm) or regular diet (alpha-tocopherol 40 IU/kg, selenium 0.2 ppm, and zinc 70 ppm). Animals were observed for 24 weeks. Wistar-Kyoto rats fed either a regular or antioxidant diet served as control.

RESULTS

Onset of HTN was delayed and severity of HTN was reduced in antioxidant-treated compared with untreated SHR. Markers of oxidative stress (i.e., plasma hydrogen peroxide, renal tissue malondialdehyde, and nitrotyrosine abundance) were elevated in untreated but not in antioxidant-treated SHR. gp91phox and p22phox subunits of NAD(P)H oxidase were markedly elevated in the renal cortex of untreated SHR and partially restored in the treated SHR. Similarly, renal calcineurin Aalpha and B subunits were elevated in untreated SHR and were partially restored in the treated SHR. Antioxidant therapy had no effect on the measured parameters in the WKY control.

CONCLUSION

Lifelong consumption of antioxidant-rich diet ameliorates HTN and oxidative stress in SHR. This is associated with the reduction of superoxide-generating enzyme, NAD(P)H oxidase, and immunoregulatory factor calcineurin. Antioxidant-rich diet appears to attenuate oxidative stress, not only by fortifying antioxidant defense capacity but also by lowering NAD(P)H oxidase, which is a major source of reactive oxygen species.

Downregulation of nitric oxide synthase in nephrotic syndrome: role of proteinuria

Blood pressure is frequently elevated, blood volume is usually normal or increased and plasma renin and aldosterone are usually low in nephrotic syndrome (NS). These observations challenge the conventional view attributing sodium retention in NS to a hypoalbuminemia-induced intravascular volume contraction. Given the pivotal role of nitric oxide (NO) in regulation of renal sodium (Na) handling, vascular resistance and sympathetic activity, we considered that Na retention and hypertension in NS may be associated with impaired NO system. Urinary excretion of Na and NO metabolites (NOx), as well as immunodetectable endothelial (eNOS), inducible (iNOS) and neuronal (nNOS) NO synthases were determined in rats with puromycin aminonucleoside (PAN)-induced NS, rats with protein overload proteinuria, Nagase rats (NAR) with inherited analbuminemia, iNOS inhibitor (aminoguanidine)-treated rats, prenephrotic PAN-treated and placebo-treated control rats. The NS group showed marked proteinuria, hypoalbuminemia, decreased fractional excretion of Na (FENa), reduced urinary NOx excretion, and severe reduction of iNOS and nNOS protein abundance in the kidney. Similar results were found in rats with protein overload proteinuria in which proteinuria was present without hypoalbuminemia. In contrast, despite extreme hypoalbuminemia, NAR showed normal FENa, increased urinary NOx excretion and upregulations of iNOS and nNOS protein abundance in the kidney. Administration of aminoguanidine for 3 weeks lowered FENa in normal rats to levels approximating those found in the NS group. Animals studied 2 days after PAN administration (wherein proteinuria was absent) showed no abnormality. Thus, chronic PAN-induced NS results in downregulation of kidney iNOS and nNOS, which can contribute to the reduction of FENa by augmenting renal tubular Na reabsorption, and preglomerular vasoconstriction. Findings in the NAR, which had profound hypoalbuminemia without proteinuria, and in rats with protein overload proteinuria, which had proteinuria without hypoalbuminemia, point to proteinuria as the primary mediator of kidney iNOS and nNOS deficiency and impaired Na excretion in PAN-induced NS.

Nitric oxide, inducible nitric oxide synthase and inflammation in veterinary medicine

Inflammation is a process consisting of a complex of cytological and chemical reactions which occur in and around affected blood vessels and adjacent tissues in response to an injury caused by a physical, chemical or biological insult. Much work has been performed in the past several years investigating inducible nitric oxide synthase (NOS, EC 1.14.13.39) and nitric oxide in inflammation. This has resulted in a rapid increase in knowledge about iNOS and nitric oxide. Nitric oxide formation from inducible NOS is regulated by numerous inflammatory mediators, often with contradictory effects, depending upon the type and duration of the inflammatory insult. Equine medicine appears to have benefited the most from the increased interest in this small, inflammatory mediator. Most of the information on nitric oxide in traditional veterinary species has been produced using models or naturally occurring inflammatory diseases of this species.

Isosorbide-5-mononitrate treatment prevents cyclosporin A-induced platelet hyperactivation and the underlying nitric oxide-cyclic guanosine-3',5'-monophosphate disturbances

INTRODUCTION

The clinical use of cyclosporin A (CsA) is commonly associated with the development of hypertension and increased risk of thromboembolic events. Decreased endothelium-dependent relaxation and increased platelet activation seems to be involved on those side effects, but the underlying mechanisms are not yet elucidated. The present study aimed to evaluate the CsA effect on the platelet NO-cyclic guanosine-3',5'-monophosphate (cGMP) pathway and the putative benefits of concomitant isosorbide-5-mononitrate (IS-5-MN) administration on CsA-induced hypertension and on platelet hyperactivation.

MATERIALS AND METHODS

Blood pressures, platelet NO synthase activity and cGMP content, intracellular free calcium concentration ([Ca2+]i) and whole blood platelet aggregation were assessed in three rat groups orally treated, during 7 weeks, with the following diets: orange juice (control group), 5 mg/kg/day of CsA (CsA group) and 150 mg/kg/day, b.i.d., of IS-5-MN for 2 weeks and IS-5-MN plus 5 mg/kg/day of CsA for 7 weeks (IS-5-MN+CsA group).

RESULTS

IS-5-MN treatment has prevented hypertension development obtained in the solely CsA-treated rats. CsA treatment has inhibited NOS activity, which was reverted by the concomitant IS-5-MN and CsA administration. On the contrary, platelets from CsA-treated rats had cGMP content increased when compared with the control rats. The variation obtained when ISMN was present was less predominant. Therefore, the organic nitrate treatment has prevented platelet hyperactivation, namely, by decreasing thrombin-evoked [Ca2+]i and collagen-evoked platelet aggregation, when compared with the solely CsA-treated group. The preventive effect of IS-5-MN was reinforced by electron microscopy studies of platelet activation.

CONCLUSIONS

By increasing [Ca2+]i and aggregation, CsA induces platelet hyperactivation and simultaneously increases cGMP content, which might represent a compensatory inhibitory mechanism. The concomitant IS-5-MN treatment prevents the above-mentioned platelet hyperreactivity and tends to normalize the NO-cGMP pathway as well as the development of hypertension.

A high-fat, refined-carbohydrate diet affects renal NO synthase protein expression and salt sensitivity

Chronic consumption of a high-fat, refined-carbohydrate (HFS) diet causes hypertension. In an earlier study, we found increased nitric oxide (NO) inactivation by reactive oxygen species (ROS) and functional NO deficiency in this model. Given the critical role of NO in renal sodium handling, we hypothesized that diet-induced hypertension may be associated with salt sensitivity. Female Fischer rats were fed an HFS or a standard low-fat, complex-carbohydrate (LFCC) rat chow diet starting at 2 mo of age for 2 yr. Arterial blood pressure, renal neuronal NO synthase (nNOS), endothelial NO synthase (eNOS), and inducible NO synthase (iNOS) protein and nitrotyrosine abundance (a marker of NO inactivation by ROS), and urinary NO metabolite excretion were measured. To assess salt sensitivity, the blood pressure response to a high-salt (4%) diet for 1 wk was determined. After 2 yr, renal nNOS and urinary NO metabolite excretion were significantly depressed, whereas arterial pressure, eNOS, iNOS, and nitrotyrosine were elevated in the HFS group but remained virtually unchanged in the LFCC group. Consumption of the high-salt diet resulted in a significant rise in arterial pressure in the HFS, but not in the LFCC, group. Thus chronic consumption of an HFS diet results in hypertension and salt sensitivity, which may be in part due to a combination of ROS-mediated NO inactivation and depressed renal nNOS protein expression.

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.

Impairment of vascular and platelet levels of nitric oxide and cyclic guanosine-3',5'-monophosphate in cyclosporin A-induced hypertensive rats

The therapeutic use of the immunosuppressive agent cyclosporin A (CsA) is associated with arterial hypertension and increased risk of thromboembolism. Impaired endothelium-mediated relaxation is one of the main hypotheses explaining the CsA-induced vascular hyper-reactivity. Since nitric oxide (NO) modulates both vascular and platelet activity, we studied the effects of CsA on the levels of arterial and platelet NO as well as 3',5'-cyclic guanosine monophosphate (cGMP) levels which are influenced by NO. An animal model of CsA-induced hypertension was used. Wistar rats were treated with a clinically relevant, oral dose of 5 mg/kg CsA, daily, for 4 weeks. CsA increased both systolic and diastolic blood pressures compared to non-treated rats (P < 0.01). Nitrite, a NO metabolite, decreased in the entire aorta wall (30%, P < 0.05) and in the aorta wall without the endothelial layer (70 %, P < 0.05) in CsA-treated vs. control groups. cGMP content was also decreased in the CsA-treated group (67%, P < 0.01) vs. control. Taken together, these results suggest a defect on the endothelial NO generation, acceleration of breakdown and/or consumption of NO, as well as marked alterations directly on cGMP metabolism. Conversely, platelet nitrite and cGMP content significantly increased in the CsA-treated rats, which was also observed in in vitro studies of platelet nitrite release following CsA treatment. This suggests a platelet self-regulation mechanism against CsA-induced platelet hyper-reactivity, which, in turn, could compensate vascular impairment.

Therapeutic role of TGF-beta-neutralizing antibody in mouse cyclosporin A nephropathy: morphologic improvement associated with functional preservation

TGF-beta is believed to play a central role in the development of Cyclosporin A (CsA)-induced nephropathy. This study investigated the effects of 1D11, a murine pan-specific TGF-beta-neutralizing monoclonal antibody, in an ICR mouse model of chronic CsA nephropathy. Mice were administered a low-salt diet (0.01% sodium) for 1 wk followed by CsA treatment (30 mg/kg, subcutaneously, daily) for 4 wk. 1D11 was administered (2.5 mg/kg, intraperitoneally, 3 times/wk) beginning immediately after the termination of CsA dosing and continued through 8 wk. CsA caused extensive renal histopathologic alterations, including tubular damage, interstitial infiltrates and fibrosis, deposition of collagen III, and apoptosis of tubular epithelial cells. 1D11 ameliorated the CsA-induced histopathologic alterations, with significant reduction in collagen III expression and deposition. Additionally, elevated levels of mRNA encoding TGF-beta1 and TGF-beta2 were significantly reduced. 1D11 also protected tubular epithelial cells from apoptosis by 48% (P < 0.05). In contrast, 13C4 (a control antibody) had no significant effect on any of the endpoints described above. Importantly, the effects of 1D11 on the CsA-induced morphologic alterations were followed by a reduction in serum creatinine level when compared with CsA mice treated with 13C4 (13C4, 0.45 +/- 0.09; 1D11, 0.30 +/- 0.08; P < 0.05) after 8 wk of treatment. Endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), nitrotyrosine, and tissue hypoxia were examined by immunostaining using specific antibodies. eNOS was significantly reduced in the endothelium of arterioles in the kidneys of mice treated with CsA, whereas iNOS was induced in the cortical tubules. Tissue hypoxia was found in both the arterioles and tubules, whereas nitrotyrosine was localized in the tubules. Administration of 1D11 improved tissue hypoxia and reduced nitrotyrosine formation. Moreover, the reciprocal changes in iNOS and eNOS expression were normalized by 1D11. This study demonstrates that 1D11 administration ameliorated morphologic alterations and preserved renal function in the context of existing chronic CsA nephropathy.

Effects of simulated microgravity on arterial nitric oxide synthase and nitrate and nitrite content

The aim of the present work was to investigate the alterations in nitric oxide synthase (NOS) expression and nitrate and nitrite (NOx) content of different arteries from simulated microgravity rats. Male Wistar rats were randomly assigned to either a control group or simulated microgravity group. For simulating microgravity, animals were subjected to hindlimb unweighting (HU) for 20 days. Different arterial tissues were removed for determination of NOS expression and NOx. Western blotting was used to measure endothelial NOS (eNOS) and inducible NOS (iNOS) protein content. Total concentrations of NOx, stable metabolites of nitric oxide, were determined by the chemiluminescence method. Compared with controls, isolated vessels from simulated microgravity rats showed a significant increase in both eNOS and iNOS expression in carotid arteries and thoracic aorta and a significant decrease in eNOS and iNOS expression of mesenteric arteries. The eNOS and iNOS content of cerebral arteries, as well as that of femoral arteries, showed no differences between the two groups. Concerning NOx, vessels from HU rats showed an increase in cerebral arteries, a decrease in mesenteric arteries, and no change in carotid artery, femoral artery and thoracic aorta. These data indicated that there were differential alterations in NOS expression and NOx of different arteries after hindlimb unweighting. We suggest that these changes might represent both localized adaptations to differential body fluid redistribution and other factors independent of hemodynamic shifts during simulated microgravity.

Superoxide dismutase, catalase, glutathione peroxidase and NADPH oxidase in lead-induced hypertension

BACKGROUND

Earlier studies from this laboratory have revealed the presence of oxidative stress and its role in the pathogenesis of lead-induced hypertension (HTN). We have further shown evidence of increased hydroxyl radical (.OH) and superoxide production in lead-treated rats and cultured endothelial cells. This study was designed to determine whether oxidative stress in animals with lead-induced HTN is associated with dysregulation of the main antioxidant enzymes namely superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) or increased superoxide producing enzyme nicotinamide adenine dinucleotide (phosphate) oxidase [NAD(P)H].

METHODS

Male Sprague-Dawley rats were randomly assigned to lead-exposed and control groups. Animals in the lead-exposed group were provided with drinking water containing 100 ppm lead acetate for 12 weeks. The control group was provided with regular drinking water. At the conclusion of the experiment, immunodetectable Cu Zn SOD, Mn SOD, CAT, GPX and gp91 phox subunit of NAD(P)H oxidase were determined by Western analysis in the kidney, brain and left ventricle of control and lead-exposed rats. Subgroups of the study animals were treated with IV infusion (180 micromol/kg/h) of the superoxide trapping agent, tempol, and arterial pressure and urinary nitric oxide (NO) metabolite (NOx) excretion were determined.

RESULTS

Lead exposure for 12 weeks resulted in a marked rise in systolic blood pressure, a significant reduction in urinary NOx excretion, a significant increase in kidney and brain Cu, Zn SOD, a significant increase in brain and insignificant increase in kidney and heart gp91 phox. In contrast, Mn SOD, CAT and GPX in the kidney, brain and left ventricle were unchanged. Incubation with lead acetate did not alter SOD activity in vitro. Infusion of tempol significantly lowered arterial pressure and raised urinary NOx excretion in the lead-exposed group (but had no effect in the control group) pointing to increased superoxide production in the lead-exposed animals.

CONCLUSION

Animals with lead-induced hypertension exhibited oxidative stress which was associated with mild up-regulation of superoxide-generating enzyme, NAD(P)H oxidase, with no evidence of quantitative SOD, CAT or GPX deficiencies.

Acute renal failure: is nitric oxide the bad guy?

Nephrotoxicity is a major side effect in clinical practice, frequently leading to acute renal failure (ARF). Many physiological mechanisms have been implicated in drug-induced renal injury. Currently, nitric oxide (NO) is considered to be an important regulator of renal vascular tone and a modulator of glomerular function under both basal and physiopathological conditions. Historically, NO has been implicated in ARF and, after its discovery, several publications have suggested that changes in NO production could play an important role in the hemodynamic alterations observed in ARF. In this review, we evaluate the participation of NO in ARF and summarize many of the findings in this research area in an attempt to elucidate the role of NO in ARF.

Regulation of endothelial-type NO synthase expression in pathophysiology and in response to drugs

In many types of cardiovascular pathophysiology such as hypercholesterolemia and atherosclerosis, diabetes, cigarette smoking, or hypertension (with its sequelae stroke and heart failure) the expression of endothelial NO synthase (eNOS) is altered. Both up- and downregulation of eNOS have been observed, depending on the underlying disease. When eNOS is upregulated, the upregulation is often futile and goes along with a reduction in bioactive NO. This is due to an increased production of superoxide generated by NAD(P)H oxidase and by an uncoupled eNOS. A number of drugs with favorable effects on cardiovascular disease upregulate eNOS expression. The resulting increase in vascular NO production may contribute to their beneficial effects. These compounds include statins, angiotensin-converting enzyme inhibitors, AT1 receptor antagonists, calcium channel blockers, and some antioxidants. Other drugs such as glucocorticoids, whose administration is associated with cardiovascular side effects, downregulate eNOS expression. Stills others such as the immunosuppressants cyclosporine A and FK506/tacrolimus or erythropoietin have inconsistent effects on eNOS. Thus regulation of eNOS expression and activity contributes to the overall action of several classes of drugs, and the development of compounds that specifically upregulate this protective enzyme appears as a desirable target for drug development.

Endothelial dysfunction in cold-induced hypertensive rats

Endothelial dysfunction can be observed in preatherosclerotic conditions. However, its pathogenetic role in hypertension is still controversial. Endothelial-dependent changes of blood pressure (BP) and expression of endothelial nitric oxide synthase (eNOS) were evaluated in cold-induced hypertensive rats. Wistar rats were exposed to cold stress for 8 weeks. Exposure to cold stress significantly increased the systolic BP in rats. The infusion of acetylcholine significantly lowered mean arterial BP in control rats by 48 +/- 2% and by 32 +/- 1% in cold-induced hypertensive rats. The acetylcholine-induced reduction of mean arterial BP was significantly attenuated in cold-induced hypertensive rats (control rats, 45 +/- 2 mm Hg; cold-induced hypertensive rats, 34 +/- 3 mm Hg; P < .05). Administration of N(G)-nitro-L-arginine-methyl ester for 1 week significantly increased BP in control rats, whereas no effect could be observed in cold-induced hypertensive rats. In cold-induced hypertensive rats eNOS in aortic vessels was significantly reduced compared to control rats. In this nongenetic, nonsurgical animal model of cold-induced hypertensive rats an endothelial dysfunction can be observed due to reduced eNOS.

Impaired pulmonary artery contractile responses in a rat model of microgravity: role of nitric oxide

Vascular contractile hyporesponsiveness is an important mechanism underlying orthostatic intolerance after microgravity. Baroreceptor reflexes can modulate both pulmonary resistance and capacitance function and thus cardiac output. We hypothesized, therefore, that pulmonary vasoreactivity is impaired in the hindlimb-unweighted (HLU) rat model of microgravity. Pulmonary artery (PA) contractile responses to phenylephrine (PE) and U-46619 (U4) were significantly decreased in the PAs from HLU vs. control (C) animals. N(G)-nitro-L-arginine methyl ester (10(-5) M) enhanced the contractile responses in the PA rings from both C and HLU animals and completely abolished the differential responses to PE and U4 in HLU vs. C animals. Vasorelaxant responses to ACh were significantly enhanced in PA rings from HLU rats compared with C. Moreover, vasorelaxant responses to sodium nitroprusside were also significantly enhanced. Endothelial nitric oxide synthase (eNOS) and soluble guanlyl cyclase expression were significantly enhanced in PA and lung tissue from HLU rats. In marked contrast, the expression of inducible nitric oxide synthase was unchanged in lung tissue. These data support the hypothesis that vascular contractile responsiveness is attenuated in PAs from HLU rats and that this hyporesponsiveness is due at least in part to increased nitric oxide synthase activity resulting from enhanced eNOS expression. These findings may have important implications for blood volume distribution and attenuated stroke volume responses to orthostatic stress after microgravity exposure.

Reciprocal regulation of cyclic GMP content by cyclic GMP-phosphodiesterase and guanylate cyclase in SHR with CsA-induced nephrotoxicity

1. The effect of the immunosuppressant drug, cyclosporin A (CsA), on the nitric oxide (NO)-cyclic GMP pathway was examined in spontaneous hypertensive rats (SHR). 2. CsA (50 mg kg(-1)) treatment for 14 days induced typical CsA nephrotoxicity, which was characterized by morphological changes in the glomerulus and proximal tubule as well as an abnormality of creatinine clearance, FENa and BUN. 3. CsA significantly decreased both NOS activity in the kidney and NOx contents in urine, but significantly increased cyclic GMP content in the kidney. 4. A marked change in two kinds of enzyme, which contribute towards the increase in cyclic GMP in tissue, namely, a decrease in cyclic GMP-phosphodiesterase activity and increase in guanylate cyclase activity, was observed in the kidney treated with CsA. 5. In the isolated perfused kidney, a decreased in perfusion pressure induced by SNP in the kidney isolated from CsA group was significantly greater than that of control. 6. There seem to exist a reciprocal mechanism to maintain cyclic GMP content via both a decrease in cyclic GMP degradation and an increase in synthesis of cyclic GMP in the kidney treated with CsA. This mechanism is likely to be playing an important role to regulate the homeostasis in the kidney with CsA nephrotoxicity.

Subclinical renal injury induced by transient cyclosporine exposure is associated with salt-sensitive hypertension

Cyclosporine use is highly associated with the development of salt-sensitive hypertension. We hypothesized that subtle renal injury induced by cyclosporine could lead to salt sensitivity. Cyclosporine nephropathy was induced by treatment for 4 weeks with cyclosporine (15 mg/kg/day) on a low sodium (0.05%) diet, followed by stopping cyclosporine and placement on a high sodium (4%) diet for 4 additional weeks. Control groups included a group treated with cyclosporine (15 mg/kg/day) on a normal salt diet in which nephropathy does not develop, and a vehicle-treated group. A fourth group received half-dose of cyclosporine (8 mg/kg/day) on a low sodium diet, which results in mild nephropathy. Biopsies were obtained at the end of the cyclosporine administration (4 week) and at sacrifice (8 week), and blood pressure and renal function were measured. Rats treated with cyclosporine for 4 weeks on a low sodium diet developed classic features of tubulointerstitial disease and arteriolopathy; these changes were absent in the cyclosporine/normal salt group and in the vehicle group. At 4 weeks, all groups were switched to a high salt diet; only the rats with nephropathy developed hypertension. The degree of hypertension correlated closely with the degree of tubulointerstitial injury (r=0.85) and with the severity of the arteriolopathy (r=0.9) (p<0.0.1). Importantly, renal function (creatinine clearance) was normal in all groups at 8 weeks, documenting that the hypertension could not be attributed to cyclosporine-mediated alterations in glomerular filtration rate (GFR). One mechanism by which cyclosporine induces hypertension is the induction of subtle renal microvascular and tubulointerstitial disease. This mechanism is not dependent on GFR and may persist even after the cyclosporine is discontinued.

Increased tyrosine nitration of the brain in chronic renal insufficiency: reversal by antioxidant therapy and angiotensin-converting enzyme inhibition

Interaction of reactive oxygen species with nitric oxide promotes nitric oxide inactivation and generation of cytotoxic reactive nitrogen species that attack DNA, lipids, and proteins. Nitration of free tyrosine and tyrosine residues of proteins results in production of nitrotyrosine, which can lead to excitotoxicity and frequently is found in the brain of patients and animals with various degenerative, ischemic, toxic, and other neurologic disorders. According to earlier studies, reactive oxygen species activity is increased and neuronal NO synthase expression in the brain is elevated in animals with chronic renal failure (CRF). It was hypothesized, therefore, that tyrosine nitration must be increased in the uremic brain. This hypothesis was tested, through determination of nitrotyrosine abundance (by Western blot analysis), as well as distribution (by immunohistology), in the cerebrum of rats with CRF 6 wk after 5/6 nephrectomy. The results were compared with those of sham-operated controls and antioxidant (lazaroid)-treated and captopril-treated rats with CRF. Western blot analysis revealed a significant increase in nitrotyrosine abundance in the cerebral cortex of rats with CRF. This was accompanied by an intense nitrotyrosine staining of the neuronal processes, including proximal segments of dendrites, axons, and axon terminals of the cortical neurons. Both antioxidant therapy and captopril administration alleviated oxidative stress (as evidenced by normalization of plasma lipid peroxidation product malondialdehyde) and significantly reduced nitrotyrosine abundance in the cerebral cortex of the treated CRF group. In conclusion, CRF resulted in oxidative stress and increased tyrosine nitration in the cerebral cortex. Antioxidant therapy and angiotensin-converting enzyme inhibition alleviated the CRF-induced oxidative stress and mitigated tyrosine nitration in the rats with CRF.

Hyperuricemia exacerbates chronic cyclosporine nephropathy

BACKGROUND

Hyperuricemia frequently complicates cyclosporine (CSA) therapy. The observation that longstanding hyperuricemia is associated with chronic tubulointerstitial disease and intrarenal vasoconstriction raised the hypothesis that hyperuricemia might contribute to chronic CSA nephropathy.

METHODS

CSA nephropathy was induced by the administration of CSA (15 mg/kg/day) for 5 and 7 weeks to rats on a low salt diet (CSA group). The effect of hyperuricemia on CSA nephropathy was determined by blocking the hepatic enzyme uricase with oxonic acid (CSA-OA). Control groups included rats treated with vehicle (VEH) and oxonic acid alone (OA). Histological and functional studies were determined at sacrifice.

RESULTS

CSA treated rats developed mild hyperuricemia with arteriolar hyalinosis, tubular injury and striped interstitial fibrosis. CSA-OA treated rats had higher uric acid levels in association with more severe arteriolar hyalinosis and tubulointerstitial damage. Intrarenal urate crystal deposition was absent in all groups. Both CSA and CSA-OA treated rats had increased renin and decreased NOS1 and NOS3 in their kidneys, and these changes are more evident in CSA-OA treated rats.

CONCLUSION

An increase in uric acid exacerbates CSA nephropathy in the rat. The mechanism does not involve intrarenal uric acid crystal deposition and appears to involve activation of the renin angiotensin system and inhibition of intrarenal nitric oxide production.

Pharmacokinetic interactions augment toxicities of sirolimus/cyclosporine combinations

This study correlated the dynamic effects of sirolimus (rapamycin; RAPA) and cyclosporine (CsA) alone versus in combination to produce renal dysfunction, myelosuppression, or hyperlipidemia, with their corresponding blood and tissue concentrations. After salt-depleted rats were treated with RAPA (0.4 to 6.4 mg/kg per d) and/or CsA (2.5 to 20.0 mg/kg per d) for 14 d, the GFR, lipid levels, bone marrow cellularity, and CsA/RAPA concentrations in whole blood versus liver or renal tissues were measured, and the median effect model was used to discern the type of drug interactions. Compared with vehicle controls (1.98 +/- 0.34 ml/min), GFR values were reduced only by large doses of drug monotherapy, namely RAPA (3.2 mg/kg per d = 1.2 +/- 0.02 ml/min or 6.4 mg/kg per d = 1.3 +/- 0.2 ml/min; both P < 0.01) or CsA (10.0 mg/kg per d = 1.2 +/- 0.1 ml/min or 20.0 mg/kg per d = 0.8 +/- 0.4 ml/min; both P < 0.01). In contrast, hosts that were treated with smaller doses of CsA/RAPA combinations showed more pronounced effects in reduction of GFR values: 2.5/0.4 mg/kg per d, modestly (1.5 +/- 0.5 ml/min; P < 0.01); 5.0/0.8 mg/kg per d, moderately (0.23 +/- 0.01 ml/min; P < 0.001); and higher-dose groups, markedly. The exacerbation of renal dysfunction seemed to be due to a pharmacokinetic interaction of RAPA to greatly increase CsA concentrations in whole blood and, particularly, in kidney tissue. In contrast, the pharmacodynamic effects of CsA to potentiate two RAPA-mediated toxicities-myelosuppression and increased serum cholesterol/low-density lipoprotein cholesterol-occurred independently of pharmacokinetic interactions. RAPA aggravates CsA-induced renal dysfunction owing to a pharmacokinetic interaction, whereas CsA produces a pharmacodynamic effect that augments RAPA-induced myelosuppression and hyperlipidemia.

Post-cyclosporine-mediated hypertension and nephropathy: amelioration by vascular endothelial growth factor

Recent studies have demonstrated a role for microvascular and tubulointerstitial injury in some models of salt-sensitive hypertension. We utilized a model of post-cyclosporin A (CsA) nephropathy and hypertension to test the hypothesis that treatment with an angiogenic factor aimed at ameliorating the microvascular and renal injury would prevent the development of hypertension. CsA was administered with a low-salt diet for 45 days, resulting in a renal lesion characterized by afferent arteriolopathy, focal peritubular capillary loss, and tubulointerstitial fibrosis. Rats were then placed on a high-salt diet and randomized to receive either vascular endothelial growth factor (VEGF(121)) or vehicle for 14 days. Placement of rats with established CsA nephropathy on a high-salt diet results in the rapid development of salt-sensitive hypertension. VEGF(121) treatment resulted in lower blood pressure, and this persisted on discontinuing the VEGF. VEGF(121) treatment was also associated with a decrease in osteopontin expression, macrophage infiltration, and collagen III deposition and markedly stimulated resolution of the arteriolopathy (20.9 +/- 7.8 vs. 36.9 +/- 6.1%, VEGF vs. vehicle, P < 0.05). In conclusion, CsA-associated renal microvascular and tubulointerstitial injury results in the development of salt-sensitive hypertension. Treatment of animals with established CsA nephropathy with VEGF reduces the hypertensive response and accelerates histological recovery. The vascular protective effect of VEGF may be due to the improvement of arteriolopathy. Angiogenic growth factors may represent a novel strategy for treating CsA-associated hypertension and renal disease.

Effect of 6 weeks of vitamin E administration on renal haemodynamic alterations following a single dose of neoral in healthy volunteers

BACKGROUND

A single oral dose of cyclosporin-A (CsA) transiently reduces renal plasma flow (RPF) and glomerular filtration rate (GFR) in transplant patients and, in some patients, chronic administration of CsA leads to renal impairment and fibrosis. Based on experimental studies, several mediators including free radicals have been proposed to account for CsA-nephrotoxicity. We have previously reported that administration of the antioxidant vitamin E in a rat model of chronic CsA-nephrotoxicity reduces renal fibrosis and maintains renal function.

METHODS

In the present study, the effect on renal haemodynamics of a single dose of the new oral formulation of CsA (neoral) was assessed before and after 6 weeks of vitamin E (800 IU/day, 2-fold increase in serum vitamin E). GFR (inulin clearance) and RPF (para-amino hippuric acid clearance) were measured before and after a single dose of 5 mg/kg of neoral in 12 healthy subjects under standardised conditions.

RESULTS

Although the mean area under the curve of the CsA levels was 21% lower after the vitamin E period, the peak CsA level at 120 min after neoral was similar both before and after vitamin E administration. At 120 min after neoral, a transient reduction in RPF and GFR was noted both before and after vitamin E administration. The nadir of the reductions in RPF (-81 +/-27 ml/min) and GFR (-14 +/- 6 ml/min) at 120 min compared with baseline tended to be lower before than after the treatment with vitamin E (-51 +/- 33 ml/min of RPF and -12 +/- 8, ml/min of GFR, respectively). Plasma and urine levels of F2-isoprostanes (free radical-catalysed vasoconstrictive prostanoids (F2-iso) at 120 min after the administration of neoral were not different from the pre-neoral levels.

CONCLUSION

The findings demonstrate that a single oral dose of neoral causes transient, yet significant, reductions in RPF and GFR, and suggest that F2-iso might not be involved in the CsA-induced acute renal vasoconstriction. The tendency for a lower reduction in RPF and GFR following CsA during the vitamin E period in healthy humans warrants additional studies in transplant patients.

Effect of severe aortic banding above the renal arteries on nitric oxide synthase isotype expression

BACKGROUND

Severe aortic stenosis above the renal arteries leads to a reduction in renal perfusion, increased renin secretion, and elevation of arterial blood pressure above the stenotic site. Nitric oxide (NO) plays an important role in regulation of renal and systemic vascular resistance, renal blood flow, and Na(+) handling. Abdominal aortic banding provides an excellent model for simultaneous testing of the effects of increased and decreased pressure, flow, and shear stress in the same animal.

METHODS

We studied protein expressions of endothelial NO synthase (eNOS), inducible NOS (iNOS), and neuroneal NOS (nNOS) isotypes in the renal cortex, renal medulla, heart, brain, and aorta segments above and below the stenosis site three weeks after abdominal aortic banding above the renal arteries. The results were compared with those obtained in the sham-operated controls. NOS isotype proteins were measured by Western blot.

RESULTS

Compared with the control group, the banded group showed significant up-regulations of eNOS, iNOS, and nNOS in renal cortex and medulla. Likewise, heart eNOS, brain nNOS, and thoracic aorta eNOS proteins were significantly increased in the banded group. However, eNOS and iNOS expressions were unchanged in the aorta segment below the stenotic site. Likewise, iNOS expression in the heart and thoracic aorta remained unchanged in the banded animals. No significant difference was found in creatinine clearance or urinary protein excretion between the two groups.

CONCLUSIONS

These findings clearly demonstrate the up-regulatory action of increased pressure on eNOS expression in the thoracic aorta and heart and of nNOS expression in the brain. These data further show up-regulation of all NOS isotypes in the kidney, which must have helped to mitigate the associated hypoperfusion.

Effect of antioxidant therapy on blood pressure and NO synthase expression in hypertensive rats

Earlier studies have demonstrated evidence for increased reactive oxygen species, enhanced NO synthase (NOS) expression, and elevated NO production in spontaneously hypertensive rats (SHR). Given the negative-feedback regulation of NOS by NO, we hypothesized that enhanced NO inactivation by ROS may contribute to compensatory upregulation of NOS in SHR. The present study was designed to test this hypothesis. Eight-week-old male SHR and Wistar-Kyoto rats were treated for 3 weeks with either a placebo or the potent antioxidant, lazaroid (desmethyltirilazad, 10 mg. kg(-1). d(-1), by gastric gavage). Tail arterial blood pressure, urinary excretion of NO metabolites (ie, nitrate and nitrite), and immunodetectable NOS isotype proteins in the vascular, renal, cardiac, and cerebral tissues were measured. The placebo-treated SHR group showed a marked elevation of blood pressure and a significant upregulation of aorta, kidney, and cardiac tissue endothelial and inducible NOS (eNOS and iNOS, respectively) proteins and of brain and renal tissue neuronal NOS. Lazaroid therapy ameliorated hypertension and mitigated the upregulation of eNOS and iNOS in vascular, renal, and cardiac tissues but had limited effect on the expression of renal and brain neuronal NOS. In contrast, lazaroid therapy had no effect on blood pressure, urinary nitrate and nitrite excretion, or tissue NOS isotype expressions in the Wistar-Kyoto group. These findings support the role of oxidative stress in the genesis and/or maintenance of hypertension and compensatory upregulation of the expression of eNOS and iNOS in SHR.

Imbalance in endothelial vasoactive factors as a possible cause of cyclosporin toxicity: a role for endothelin-converting enzyme

Cyclosporin A (CsA) is a powerful, widely used immunosuppressant, but it is not devoid of serious clinical side effects such as hypertension and nephrotoxicity. To clarify the mechanisms involved in the genesis of these side effects, we studied the effects of chronic CsA administration on the expression of some endothelial vasoactive factors in the aorta and kidney. For this purpose rats were treated for 30 days with 50 mg/kg/day CsA, and hypertension and renal insufficiency developed. In rats receiving CsA, the mRNA expression of pre-pro-endothelin-1 increased, whereas that of endothelial nitric oxide (NO) synthase decreased, both in the aorta and in the renal cortex (increases in pre-pro-endothelin-1 mRNA in aorta and renal cortex, respectively: 275%+/-18%, 300%+/-27%; decreases in endothelial NO synthase mRNA in aorta and renal cortex respectively: 40%+/-8%, 42%+/-6%). Moreover, long-term CsA treatment also induced an up-regulation of the endothelin-converting enzyme 1 mRNA expression (156% vs. control rats) in the renal cortex, with a significantly increased protein content and enzyme activity. In contrast, no changes were detected in endothelin-converting enzyme 1 mRNA expression in aortas from rats receiving the drug. This imbalance between endothelin-1 and NO systems could explain the hypertension and the deranged kidney function observed after long-term CsA treatment in rats.