Mechanisms of FK 506-induced hypertension in the rat

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.

Hemorrhagic events associated with tacrolimus: a real-world pharmacovigilance study

BACKGROUND

Tacrolimus is a potent macrolide immunosuppressant frequently used to prevent graft rejection in organ transplantation. Despite the known side effect of hemorrhage, there are no extensive descriptive series of patients who experience hemorrhage events associated with tacrolimus. We sought to review and describe tacrolimus-related hemorrhage events reported by healthcare professionals to the United States Food and Drug Association Adverse Event Reporting System (FAERS) database.

METHODS

The FAERS database (2004q1-2022q4) was retrospectively analyzed to characterize reporting of hemorrhage adverse events (AEs) with tacrolimus. Subgroup analysis was completed on the hemorrhage.

RESULTS

A total of 75,310 tacrolimus-associated AEs were identified, of which 1,511 cases met specific inclusion/exclusion criteria with most occurring in the gastrointestinal tract (422 cases, 27.93% of all included cases). Death was reported in 558 patients (36.93% of hemorrhage cases), the most of which occurred in cases of brain hemorrhage (219 cases, 39.25% of death cases). Among definitive organ transplants, renal transplant was the most common indication for tacrolimus (62 cases, 4.10%) followed by bone marrow transplant (44 cases, 2.91%) and liver transplant (30 cases, 1.99%).

CONCLUSIONS

This study presents the largest collective description of tacrolimus-related hemorrhage events. We additionally described a number of previously unreported tacrolimus-related hemorrhage events.

Calcineurin Is a Universal Regulator of Vessel Function-Focus on Vascular Smooth Muscle Cells

Calcineurin, a serine/threonine phosphatase regulating transcription factors like NFaT and CREB, is well known for its immune modulatory effects and role in cardiac hypertrophy. Results from experiments with calcineurin knockout animals and calcineurin inhibitors indicate that calcineurin also plays a crucial role in vascular function, especially in vascular smooth muscle cells (VSMCs). In the aorta, calcineurin stimulates the proliferation and migration of VSMCs in response to vascular injury or angiotensin II administration, leading to pathological vessel wall thickening. In the heart, calcineurin mediates coronary artery formation and VSMC differentiation, which are crucial for proper heart development. In pulmonary VSMCs, calcineurin/NFaT signaling regulates the release of Ca2+, resulting in increased vascular tone followed by pulmonary arterial hypertension. In renal VSMCs, calcineurin regulates extracellular matrix secretion promoting fibrosis development. In the mesenteric and cerebral arteries, calcineurin mediates a phenotypic switch of VSMCs leading to altered cell function. Gaining deeper insights into the underlying mechanisms of calcineurin signaling will help researchers to understand developmental and pathogenetical aspects of the vasculature. In this review, we provide an overview of the physiological function and pathophysiology of calcineurin in the vascular system with a focus on vascular smooth muscle cells in different organs. Overall, there are indications that under certain pathological settings reduced calcineurin activity seems to be beneficial for cardiovascular health.

The Mineralocorticoid Receptor on Smooth Muscle Cells Promotes Tacrolimus-Induced Renal Injury in Mice

Tacrolimus (Tac) is a calcineurin inhibitor commonly used as an immunosuppressor after solid organ transplantation. However, Tac may induce hypertension, nephrotoxicity, and an increase in aldosterone levels. The activation of the mineralocorticoid receptor (MR) is related to the proinflammatory status at the renal level. It modulates the vasoactive response as they are expressed on vascular smooth muscle cells (SMC). In this study, we investigated whether MR is involved in the renal damage generated by Tac and if the MR expressed in SMC is involved. Littermate control mice and mice with targeted deletion of the MR in SMC (SMC-MR-KO) were administered Tac (10 mg/Kg/d) for 10 days. Tac increased the blood pressure, plasma creatinine, expression of the renal induction of the interleukin (IL)-6 mRNA, and expression of neutrophil gelatinase-associated lipocalin (NGAL) protein, a marker of tubular damage (p < 0.05). Our study revealed that co-administration of spironolactone, an MR antagonist, or the absence of MR in SMC-MR-KO mice mitigated most of the unwanted effects of Tac. These results enhance our understanding of the involvement of MR in SMC during the adverse reactions of Tac treatment. Our findings provided an opportunity to design future studies considering the MR antagonism in transplanted subjects.

Calcineurin Controls Hypothalamic NMDA Receptor Activity and Sympathetic Outflow

Rationale:

Hypertension is a common and serious adverse effect of calcineurin inhibitors, including cyclosporine and tacrolimus (FK506). Although increased sympathetic nerve discharges are associated with calcineurin inhibitor–induced hypertension, the sources of excess sympathetic outflow and underlying mechanisms remain elusive. Calcineurin (protein phosphatase-2B) is broadly expressed in the brain, including the paraventricular nuclear (PVN) of the hypothalamus, which is critically involved in regulating sympathetic vasomotor tone.

Objective:

We determined whether prolonged treatment with the calcineurin inhibitor causes elevated sympathetic output and persistent hypertension by potentiating synaptic N-methyl-D-aspartate (NMDA) receptor activity in the PVN.

Methods and Results:

Telemetry recordings showed that systemic administration of FK506 (3 mg/kg per day) for 14 days caused a gradual and profound increase in arterial blood pressure in rats, which lasted at least 7 days after discontinuing FK506 treatment. Correspondingly, systemic treatment with FK506 markedly reduced calcineurin activity in the PVN and circumventricular organs, but not rostral ventrolateral medulla, and increased the phosphorylation level and synaptic trafficking of NMDA receptors in the PVN. Immunocytochemistry labeling showed that calcineurin was expressed in presympathetic neurons in the PVN. Whole-cell patch-clamp recordings in brain slices revealed that treatment with FK506 increased baseline firing activity of PVN presympathetic neurons; this increase was blocked by the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist. Also, treatment with FK506 markedly increased presynaptic and postsynaptic NMDA receptor activity of PVN presympathetic neurons. Furthermore, microinjection of the NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist into the PVN of anesthetized rats preferentially attenuated renal sympathetic nerve discharges and blood pressure elevated by FK506 treatment. In addition, systemic administration of memantine, a clinically used NMDA receptor antagonist, effectively attenuated FK506 treatment–induced hypertension in conscious rats.

Conclusions:

Our findings reveal that normal calcineurin activity in the PVN constitutively restricts sympathetic vasomotor tone via suppressing NMDA receptor activity, which may be targeted for treating calcineurin inhibitor–induced hypertension.

Adult Renal Transplantation in a Patient 28 Years after Heart Transplantation as a Neonate for Hypoplastic Left Heart Syndrome

We present a case of kidney transplantation in a 28-year-old patient who received a heart transplant at 7 weeks of age due to hypoplastic left heart syndrome. The patient's renal insufficiency was the result of chronic immunosuppression and hypertension. The almost 28-year-old graft demonstrated very good function. This patient represents as one of the longest pediatric cardiac graft recipients living without any significant functional limitations.

Identification of gallic acid as a active ingredient of Syzygium aromaticum against tacrolimus-induced damage in renal epithelial LLC-PK1 cells and rat kidney

Tacrolimus (FK506), a calcineurin inhibitor, is an effective immunosuppressive agent mainly used to lower the risk of organ rejection after allogeneic organ transplant. However, FK506-associated adverse effects, such as nephrotoxicity, may limit its therapeutic use. In this study, we confirmed that epigallocatechin-3-gallate (EGCG), sanguiin H-6, and gallic acid increased cell survival following FK506-induced cytotoxicity in renal epithelial LLC-PK1. Among these compounds, gallic acid exerted the strongest protective effect, further confirmed in the FK506-induced nephrotoxicity rat model. Additionally, we identified supporting evidence for the nephroprotective function of gallic acid using molecular docking and bioavailability investigations.

Mycophenolate mediated remodeling of gut microbiota and improvement of gut-brain axis in spontaneously hypertensive rats

Microbiota has a role in the host blood pressure (BP) regulation. The immunosuppressive drug mofetil mycophenolate (MMF) ameliorates hypertension. The present study analyzes whether MMF improves dysbiosis in a genetic model of hypertension. Twenty weeks old male spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were randomly divided into three groups: untreated WKY, untreated SHR, and SHR treated with MMF for 5 weeks. MMF treatment restored gut bacteria from the phyla Firmicutes and Bacteroidetes, and acetate- and lactate-producing bacteria to levels similar to those found in WKY, increasing butyrate-producing bacteria. MMF increased the percentage of anaerobic bacteria in the gut. The improvement of gut dysbiosis was associated with an enhanced colonic integrity and a decreased sympathetic drive in the gut. MMF inhibited neuroinflammation in the paraventricular nuclei in the hypothalamus. MMF increased the lower regulatory T cells proportion in mesenteric lymph nodes and Th17 and Th1 infiltration in aorta, improved aortic endothelial function and reduced systolic BP. This study demonstrates for the first time that MMF reduces gut dysbiosis in SHR. This effect could be related to its capability to improve gut integrity due to reduced sympathetic drive in the gut associated to the reduced brain neuroinflammation.

Pathological Mechanisms and Potential Therapeutic Targets of Pulmonary Arterial Hypertension: A Review

Pulmonary arterial hypertension (PAH) is a progressive cardiovascular disease characterized by pulmonary vasculature reconstruction and right ventricular dysfunction. The mortality rate of PAH remains high, although multiple therapeutic strategies have been implemented in clinical practice. These drugs mainly target the endothelin-1, prostacyclin and nitric oxide pathways. Management for PAH treatment includes improving symptoms, enhancing quality of life, and extending survival rate. Existing drugs developed to treat the disease have resulted in enormous economic and healthcare liabilities. The estimated cost for advanced PAH has exceeded $200,000 per year. The pathogenesis of PAH is associated with numerous molecular processes. It mainly includes germline mutation, inflammation, dysfunction of pulmonary arterial endothelial cells, epigenetic modifications, DNA damage, metabolic dysfunction, sex hormone imbalance, and oxidative stress, among others. Findings based on the pathobiology of PAH may have promising therapeutic outcomes. Hence, faced with the challenges of increasing healthcare demands, in this review, we attempted to explore the pathological mechanisms and alternative therapeutic targets, including other auxiliary devices or interventional therapies, in PAH. The article will discuss the potential therapies of PAH in detail, which may require further investigation before implementation.

Inhibition of big-conductance Ca2+-activated K+ channels in cerebral artery (vascular) smooth muscle cells is a major novel mechanism for tacrolimus-induced hypertension

Tacrolimus (TAC, also called FK506), a common immunosuppressive drug used to prevent allograft rejection in transplant patients, is well known to alter the functions of blood vessels. In this study, we sought to determine whether chronic treatment of TAC could inhibit the activity of big-conductance Ca²⁺-activated K⁺ (BK) channels in vascular smooth muscle cells (SMCs), leading to hypertension. Our data reveal that the activity of BK channels was inhibited in cerebral artery SMCs (CASMCs) from mice after intraperitoneal injection of TAC once a day for 4 weeks. The voltage sensitivity, Ca²⁺ sensitivity, and open time of single BK channels were all decreased. In support, BK channel β1-, but not α-subunit protein expression was significantly decreased in cerebral arteries. In TAC-treated mice, application of norepinephrine induced stronger vasoconstriction in both cerebral and mesenteric arteries as well as a larger [Ca²⁺]_i in CASMCs. Chronic treatment of TAC, similar to BK channel β1-subunit knockout (KO), resulted in hypertension in mice, but did not cause a further increase in blood pressure in BK channel β1-subunit KO mice. Moreover, BK channel activity in CASMCs was negatively correlated with blood pressure. Our findings provide novel evidence that TAC inhibits BK channels by reducing the channel β1-subunit expression and functions in vascular SMCs, leading to enhanced vasoconstriction and hypertension.

Rieske iron-sulfur protein induces FKBP12.6/RyR2 complex remodeling and subsequent pulmonary hypertension through NF-κB/cyclin D1 pathway

Ca2+ signaling in pulmonary arterial smooth muscle cells (PASMCs) plays an important role in pulmonary hypertension (PH). However, the underlying specific ion channel mechanisms remain largely unknown. Here, we report ryanodine receptor (RyR) channel activity and Ca2+ release both are increased, and association of RyR2 by FK506 binding protein 12.6 (FKBP12.6) is decreased in PASMCs from mice with chronic hypoxia (CH)-induced PH. Smooth muscle cell (SMC)-specific RyR2 knockout (KO) or Rieske iron-sulfur protein (RISP) knockdown inhibits the altered Ca2+ signaling, increased nuclear factor (NF)-κB/cyclin D1 activation and cell proliferation, and CH-induced PH in mice. FKBP12.6 KO or FK506 treatment enhances CH-induced PH, while S107 (a specific stabilizer of RyR2/FKBP12.6 complex) produces an opposite effect. In conclusion, CH causes RISP-dependent ROS generation and FKBP12.6/RyR2 dissociation, leading to PH. RISP inhibition, RyR2/FKBP12.6 complex stabilization and Ca2+ release blockade may be potentially beneficial for the treatment of PH.

FK506 regulates Ca2+ release evoked by inositol 1,4,5-trisphosphate independently of FK-binding protein in endothelial cells

Background and Purpose

FK506 and rapamycin are modulators of FK‐binding proteins (FKBP) that are used to suppress immune function after organ and hematopoietic stem cell transplantations. The drugs share the unwanted side‐effect of evoking hypertension that is associated with reduced endothelial function and nitric oxide production. The underlying mechanisms are not understood. FKBP may regulate IP₃ receptors (IP₃R) and ryanodine receptors (RyR) to alter Ca²⁺ signalling in endothelial cells.

Experimental Approach

We investigated the effects of FK506 and rapamycin on Ca²⁺ release via IP₃R and RyR in hundreds of endothelial cells, using the indicator Cal‐520, in intact mesenteric arteries from male Sprague‐Dawley rats. IP₃Rs were activated by acetylcholine or localised photo‐uncaging of IP₃, and RyR by caffeine.

Key Results

While FKBPs were present, FKBP modulation with rapamycin did not alter IP₃‐evoked Ca²⁺ release. Conversely, FK506, which modulates FKBP and blocks calcineurin, increased IP₃‐evoked Ca²⁺ release. Inhibition of calcineurin (okadiac acid or cypermethrin) also increased IP₃‐evoked Ca²⁺ release and blocked FK506 effects. When calcineurin was inhibited, FK506 reduced IP₃‐evoked Ca²⁺ release. These findings suggest that IP₃‐evoked Ca²⁺ release is not modulated by FKBP, but by FK506‐mediated calcineurin inhibition. The RyR modulators caffeine and ryanodine failed to alter Ca²⁺ signalling suggesting that RyR is not functional in native endothelium.

Conclusion and Implications

The hypertensive effects of the immunosuppressant drugs FK506 and rapamycin, while mediated by endothelial cells, do not appear to be exerted at the documented cellular targets of Ca²⁺ release and altered FKBP binding to IP₃ and RyR.

Effect of spironolactone for 1 yr on endothelial function and vascular inflammation biomarkers in renal transplant recipients

Kidney transplantation is associated with increased cardiovascular risk. Endothelial dysfunction and vascular inflammation contribute to negative outcome. In experimental models, mineralocorticoid receptor antagonists improved endothelial function and reduced inflammation. The present study tested the hypothesis that the mineralocorticoid receptor antagonist spironolactone improves endothelial function and reduces vascular inflammation in renal transplant patients. Eighty prevalent renal transplant patients from an ongoing, double-blind randomized placebo-controlled trial were included. Paired plasma samples before and after 1 yr of treatment (n = 39 in the spironolactone-treated group and 41 in the placebo-treated group) were used to determine markers of endothelial dysfunction (nitrite, nitrate, cGMP, arginine, citrulline, ornithine, asymmetric dimethylarginine, symmetric dimethylarginine, N^G-monomethyl-l-arginine, von Willebrand factor, tissue-type plasminogen activator antigen, and plasminogen activator inhibitor 1 antigen) and markers of inflammation (intercellular adhesion molecule, vascular adhesion molecule, high-sensitivity C-reactive protein, and serum amyloid protein A). The median time since the transplantation was 4.6 (0.12-22.3) yr in the spironolactone-treated group and 2.1 (0.17-13.9) yr in the placebo-treated group (P > 0.05). Spironolactone increased plasma aldosterone (P < 0.001) and K⁺ (P < 0.001). Blood pressure did not change significantly. No significant differences were detected between groups in any of the measured markers of endothelial dysfunction or inflammation except in the subgroup analysis of patients with diabetes, where spironolactone decreased nitrite compared with placebo. In this study, mineralocorticoid receptor antagonism did not improve biomarkers of endothelial dysfunction or vascular inflammation in prevalent renal transplant patients. Further studies are needed to evaluate the potential beneficial effect of early or late mineralocorticoid receptor antagonism on vascular outcomes in renal transplant patients.

Immunosuppressive protocols with tacrolimus after cryopreserved aortal allotransplantation in rats

Objectives and design

The aim of our study was to simulate in rats all aspects and techniques used in our new clinical program of cryopreserved alloarterial transplantation and investigate the influence of two immunosuppressive protocols with tacrolimus on acute rejection of these allografts.

Materials and methods

Cryopreserved abdominal aortic grafts were transplanted between Brown-Norway and Lewis rats. Tacrolimus (0.2 mg/kg daily) was administered from day 1 to day 30 (TAC1) or from day 7 to day 30 (TAC7), respectively. No immunosuppressed isogeneic (ISO) and allogeneic (ALO) rats combination served as control. Aortal wall infiltration by immunocompetent cells (MHC II+ cells of recipient origin) was studied on day 30 after transplantation. Flow cytometry was used for the analysis of day 30 sera for the presence of donor specific anti-MHC class I and II antibodies.

Results

The aortal allografts in both immunosuppressed groups showed regular morphology of aortal wall with no depositions of immunoglobulin G on day 30. The adventitial infiltration of non-immunosuppressed aortal allografts by MHC class II positive cells of recipient origin was significantly higher (ALO 20.7±6.7 cells, P<0.001) compared to both immunosuppressed groups (TAC1 5.9±5.5 cells, TAC7 6.1±5.1 cells). Day 30 sera from the allogeneic non-immunosuppressed animals decreased significantly the binding of fluorescence-labelled MHC class I (46.9±19.4%) and class II (65.8±11.9%) antibody to donors spleen cells compared with day 30 sera from both immunosuppressed groups (TAC1, anti-MHC class I 102.4±4.2%, p < 0.001, anti-MHC class II 102.6±6.0%), (TAC7, anti-MHC class I 79.9±3.3%, p < 0.001, anti-MHC class II 80.9±2.7%).

Conclusion

Both immunosuppressed protocols with tacrolimus (administration from day 1 or from day 7 following transplantation) were able to suppress acute cell- and antibody-mediated rejection of cryopreserved abdominal aortic allografts processed in accordance with our new standardized clinical protocol.

Lactobacillus fermentum Improves Tacrolimus-Induced Hypertension by Restoring Vascular Redox State and Improving eNOS Coupling

SCOPE

The aim is to analyze whether the probiotic Lactobacillus fermentum CECT5716 (LC40) can prevent endothelial dysfunction and hypertension induced by tacrolimus in mice.

METHODS AND RESULTS

Tacrolimus increases systolic blood pressure (SBP) and impairs endothelium-dependent relaxation to acetylcholine and these effects are partially prevented by LC40. Endothelial dysfunction induced by tacrolimus is related to both increased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX2) and uncoupled endothelial nitric oxide synthase (eNOS)-driven superoxide production and Rho-kinase-mediated eNOS inhibition. LC40 treatment prevents all the aortic changes induced by tacrolimus. LC40 restores the imbalance between T-helper 17 (Th17)/regulatory T (Treg) cells induced by tacrolimus in mesenteric lymph nodes and the spleen. Tacrolimus-induced gut dysbiosis, that is, it decreases microbial diversity, increases the Firmicutes/Bacteroidetes (F/B) ratio and decreases acetate- and butyrate-producing bacteria, and these effects are prevented by LC40. Fecal microbiota transplantation (FMT) from LC40-treated mice to control mice prevents the increase in SBP and the impaired relaxation to acetylcholine induced by tacrolimus.

CONCLUSION

LC40 treatment prevents hypertension and endothelial dysfunction induced by tacrolimus by inhibiting gut dysbiosis. These effects are associated with a reduction in vascular oxidative stress, mainly through NOX2 downregulation and prevention of eNOS uncoupling, and inflammation possibly because of decreased Th17 and increased Treg cells polarization in mesenteric lymph nodes.

A Pilot Trial to Examine the Changes in Carotid Arterial Inflammation in Renal Transplant Recipients as Assessed by 18F-Fluorodeoxyglucose (18F-FDG) Positron Emission Tomography Computed Tomography (PET/CT)

BACKGROUND Inflammatory activity of the artery can be assessed by measuring 18F-fluorodeoxyglucose (18F-FDG) uptake with positron emission tomography computed tomography (PET/CT). Improvement in vascular function after renal transplantation has been reported, but no studies have used 18F-FDG PET/CT to examine the changes in vascular inflammation. This study investigated the changes in the inflammatory activity in the carotid artery after renal transplantation in patients with chronic kidney disease (CKD). MATERIAL AND METHODS 18F-FDG PET/CT was performed before and at 4 months after transplantation. We quantified 18F-FDG uptake as the target-to-background ratio (TBR) in the carotid artery in 10 CKD patients. TBR was evaluated in the whole carotid artery (WH) and most-diseased segment (MDS), and the mean and maximum values were analyzed. The concentrations of inflammatory cytokines, including tumor necrosis factor-alpha, interleukin-6, plasminogen activator inhibitor-1, and endothelin-1, were measured. RESULTS Eight patients showed a decrease in mean or maximum TBR. The average mean or maximum TBRs in the WH and MDS of the right and left arteries were all reduced after transplantation. The average mean TBR for the right WH decreased significantly (% reduction [95% CI]) by -5.74% [-15.37, -0.02] (p=0.047). TBRs did not correlate significantly with cytokine concentrations. The changes in cytokine concentrations after transplantation varied. CONCLUSIONS 18F-FDG uptake by the WH and MDS tended to reduce after renal transplantation. Therefore, renal transplantation may confer an anti-inflammatory effect on carotid atherosclerosis in patients with CKD; however, this effect is not large enough to be demonstrated in this study with small sample size.

BMP type II receptor as a therapeutic target in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a chronic disease characterized by a progressive elevation in mean pulmonary arterial pressure. This occurs due to abnormal remodeling of small peripheral lung vasculature resulting in progressive occlusion of the artery lumen that eventually causes right heart failure and death. The most common cause of PAH is inactivating mutations in the gene encoding a bone morphogenetic protein type II receptor (BMPRII). Current therapeutic options for PAH are limited and focused mainly on reversal of pulmonary vasoconstriction and proliferation of vascular cells. Although these treatments can relieve disease symptoms, PAH remains a progressive lethal disease. Emerging data suggest that restoration of BMPRII signaling in PAH is a promising alternative that could prevent and reverse pulmonary vascular remodeling. Here we will focus on recent advances in rescuing BMPRII expression, function or signaling to prevent and reverse pulmonary vascular remodeling in PAH and its feasibility for clinical translation. Furthermore, we summarize the role of described miRNAs that directly target the BMPR2 gene in blood vessels. We discuss the therapeutic potential and the limitations of promising new approaches to restore BMPRII signaling in PAH patients. Different mutations in BMPR2 and environmental/genetic factors make PAH a heterogeneous disease and it is thus likely that the best approach will be patient-tailored therapies.

Beneficial effects of mycophenolate mofetil on cardiotoxicity induced by tacrolimus in wistar rats

The immunosuppressive drug tacrolimus (TAC) is used clinically to reduce the rejection rate in transplant patients. TAC has contributed to an increased prevalence of cardiovascular disease in patients receiving solid organ transplantation. Mycophenolate mofetil (MMF), a potent inhibitor of de novo purine synthesis, is known to prevent ongoing rejection in combination with TAC. In the present study, we investigated the antioxidant and antigenotoxic effect of MMF on TAC-induced cardiotoxicity in rats. Oral administration of TAC at 2.4, 24, and 60 mg/kg b.w. corresponding, respectively, to 1, 10, and 25% of LD50 for 24 h caused cardiac toxicity in a dose-dependant manner. TAC increased significantly DNA damage level in hearts of treated rats. Furthermore, it increased malondialdehyde (MDA) and protein carbonyl (PC) levels and decreased catalase (CAT) and superoxide dismutase (SOD) activities. The oral administration of MMF at 50 mg/kg b.w. simultaneously with TAC at 60 mg/kg b.w. proved a significant cardiac protection by decreasing DNA damage, MDA, and PC levels, and by increasing the antioxidant activities of CAT and SOD. Thus, our study showed, for the first time, the protective effect of MMF against cardiac toxicity induced by TAC. This protective effect was mediated via an antioxidant process.

The Far Side of Vascular Injury

Substances historically thought to cause direct vascular injury in laboratory animals are a heterogeneous group of toxic agents with varied mechanisms of action. Morphologically, the reviewed agents can be broadly categorized into those targeting endothelial cell (ECs) and those targeting smooth muscle cells (SMCs). Anticancer drugs, immunosuppressants, and heavy metals are targeting primarily ECs while allylamine, β-aminopropionitrile, and mitogen-activated protein kinase kinase inhibitors affect mainly SMCs. It is now recognized that the pathogenicity of some of these agents is often mediated through intermediary events, particularly vasoconstriction. There are clear similarities in the clinical and microscopic findings associated with many of these agents in animals and man, allowing the use of animal models to investigate mechanisms and pathogenesis. The molecular pathogenic mechanisms and comparative morphology in animals and humans will be reviewed.

Calcineurin inhibitors and hypertension: a role for pharmacogenetics?

Hypertension is a common side effect of calcineurin inhibitors (CNIs), which are drugs used to prevent rejection after transplantation. Hypertension after kidney transplantation has been associated with earlier graft failure and higher cardiovascular mortality in the recipient. Recent data indicate that enzymes and transporters involved in CNI pharmacokinetics and pharmacodynamics, including CYP3A5, ABCB1, WNK4 and SPAK, are also associated with salt-sensitive hypertension. These insights raise the question whether polymorphisms in the genes encoding these proteins increase the risk of CNI-induced hypertension. Predicting who is at risk for CNI-induced hypertension may be useful for when selecting specific interventions, including dietary salt restriction, thiazide diuretics or a CNI-free immunosuppressive regimen. This review aims to explore the pharmacogenetics of CNI-induced hypertension, highlighting the knowns and unknowns.

FK506 activates BMPR2, rescues endothelial dysfunction, and reverses pulmonary hypertension

Dysfunctional bone morphogenetic protein receptor-2 (BMPR2) signaling is implicated in the pathogenesis of pulmonary arterial hypertension (PAH). We used a transcriptional high-throughput luciferase reporter assay to screen 3,756 FDA-approved drugs and bioactive compounds for induction of BMPR2 signaling. The best response was achieved with FK506 (tacrolimus), via a dual mechanism of action as a calcineurin inhibitor that also binds FK-binding protein-12 (FKBP12), a repressor of BMP signaling. FK506 released FKBP12 from type I receptors activin receptor-like kinase 1 (ALK1), ALK2, and ALK3 and activated downstream SMAD1/5 and MAPK signaling and ID1 gene regulation in a manner superior to the calcineurin inhibitor cyclosporine and the FKBP12 ligand rapamycin. In pulmonary artery endothelial cells (ECs) from patients with idiopathic PAH, low-dose FK506 reversed dysfunctional BMPR2 signaling. In mice with conditional Bmpr2 deletion in ECs, low-dose FK506 prevented exaggerated chronic hypoxic PAH associated with induction of EC targets of BMP signaling, such as apelin. Low-dose FK506 also reversed severe PAH in rats with medial hypertrophy following monocrotaline and in rats with neointima formation following VEGF receptor blockade and chronic hypoxia. Our studies indicate that low-dose FK506 could be useful in the treatment of PAH.

Pathogenesis of calcineurin inhibitor-induced hypertension

This article reviews the current understanding of the mechanisms of calcineurin inhibitor-induced hypertension. Already early after the introduction of cyclosporine in the 1980s, vasoconstriction, sympathetic excitation and sodium retention by the kidney had been shown to play a role in this form of hypertension. The vasoconstrictive effects of calcineurin inhibitors are related to interference with the balance of vasoactive substances, including endothelin and nitric oxide. Until recently, the renal site of the sodium-retaining effect of calcineurin inhibitors was unknown. We and others have shown that calcineurin inhibitors increase the activity of the thiazide-sensitive sodium chloride cotransporter through an effect on the kinases WNK and SPAK. Here, we review the pertinent literature on the hypertensinogenic effects of calcineurin inhibitors, including neural, vascular and renal effects, and we propose an integrated model of calcineurin inhibitor-induced hypertension.

The effects of immunosuppressants on vascular function, systemic oxidative stress and inflammation in rats

Immunosuppressants have been associated with increased cardiovascular disease risk. We determined the effects of calcineurin and mammalian target of rapamycin (mTOR) inhibitor administration on endothelial dysfunction and associated inflammation and oxidative stress in adult rats. Cyclosporine A (low and high dose), sirolimus, tacrolimus, everolimus and placebo were administered to 8-week-old male Wistar rats for 10 consecutive days. Aortic vascular endothelial and smooth muscle function were assessed ex vivo in organ baths. Maximal aortic contraction to noradrenaline in sirolimus-treated rats was significantly greater than cyclosporine groups, everolimus and placebo, whereas endothelial-dependent relaxation was significantly impaired with cyclosporine and tacrolimus compared with everolimus. Endothelial-independent relaxation was impaired in tacrolimus-treated rats compared with low dose cyclosporine, everolimus and sirolimus. Sirolimus was associated with a reduction in plasma interleukin (IL)-1β and tumour necrosis factor (TNF)-α and higher levels of catalase and total antioxidant status. In nontransplanted rats, vascular dysfunction was evident following administration of cyclosporine A, sirolimus and tacrolimus, whereas everolimus did not compromise aortic endothelial or smooth muscle function. At the doses administered in this model, the immunosuppressants exerted varying effects on vascular function.

The calcineurin inhibitor tacrolimus activates the renal sodium chloride cotransporter to cause hypertension

Calcineurin inhibitors (CNIs) are immunosuppressive drugs, which are used widely to prevent rejection of transplanted organs and treat autoimmune disease. Hypertension and renal tubule dysfunction, including hyperkalemia, hypercalciuria, and acidosis often complicate their use^1,2. These side effects resemble familial hyperkalemic hypertension (FHHt), a genetic disease characterized by overactivity of the renal sodium chloride co-transporter (NCC), and caused by mutations in WNK kinases. We hypothesized that CNIs induce hypertension by stimulating NCC. In wild-type mice, the CNI tacrolimus caused salt-sensitive hypertension and increased the abundance of phosphorylated NCC, and the NCC regulatory kinases WNK3, WNK4, and SPAK. The functional importance of NCC in this response was demonstrated by showing that tacrolimus did not affect blood pressure in NCC knockout mice, whereas the hypertensive response to tacrolimus was exaggerated in mice over-expressing NCC. Moreover, hydrochlorothiazide reversed tacrolimus-induced hypertension. In kidney transplant recipients treated with tacrolimus, fractional chloride excretion in response to bendroflumethiazide was greater than in controls, and renal NCC abundance was also greater, extending these observations to humans. Together, these findings indicate that tacrolimus-induced hypertension is mediated largely by NCC activation, and suggest that inexpensive and well-tolerated thiazide diuretics may be especially effective in preventing the complications of CNI treatment.

Protein kinase CbetaII-mediated phosphorylation of endothelial nitric oxide synthase threonine 495 mediates the endothelial dysfunction induced by FK506 (tacrolimus)

FK506 [tacrolimus; hexadecahydro-5,19-dihydroxy-3-[2-(4-hydroxy-3-methoxycyclohexyl)-1-methylethenyl]-14,16-dimethoxy-4,10,12,18-tetramethyl-8-(2-propenyl)-15,19-epoxy-3H-pyrido[2,1-c][1,4]oxa-azacyclotricosine-1,7,20,21(4H,23H)-tetrone] is used clinically to reduce the incidence of allograft rejection; however, chronic administration leads to endothelial dysfunction and hypertension. We have previously shown that FK506 activates Ca(2+)/diacylglycerol-dependent conventional protein kinase C (cPKC), which phosphorylates endothelial nitric oxide synthase (eNOS) at one of its inhibitory sites, Thr495. However, which cPKC isoform is responsible for phosphorylating eNOS Thr495 is unknown. The aim of the current study was to determine the cPKC isoform that is activated by FK506, leading to decreased endothelial function. FK506 reduced endothelium-dependent relaxation responses, yet had no effect on endothelium-independent relaxation responses in aortas from control mice. Of the various cPKC isoforms, only the administration of a PKCβ(II) isoform-specific peptide inhibitor restored aortic relaxation responses to that of controls. In aortic endothelial cells, FK506 significantly increased PKCβ(II) activation compared with vehicle-treated controls, and this was prevented by a PKCβ(II) isoform-specific peptide inhibitor. In addition, a PKCβ(II) isoform-specific peptide inhibitor prevented the increase in eNOS Thr495 phosphorylation induced by FK506. Taken together, our results indicate that β(II) is the cPKC isoform responsible for phosphorylating eNOS at the inhibitory site Thr495 in response to FK506. PKCβ(II) inhibition could prove beneficial in ameliorating the endothelial dysfunction and hypertension in patients treated with FK506.

Infiltrating T lymphocytes in the kidney increase oxidative stress and participate in the development of hypertension and renal disease

The present studies examined the role and mechanism of action of infiltrating T lymphocytes in the kidney during salt-sensitive hypertension. Infiltrating T lymphocytes in the Dahl salt-sensitive (SS) kidney significantly increased from 7.2 ± 1.8 × 10(5) cells/2 kidneys to 18.2 ± 3.9 × 10(5) cells/2 kidneys (n = 6/group) when dietary NaCl was increased from 0.4 to 4.0%. Furthermore, the expression of immunoreactive p67(phox), gp91(phox), and p47(phox) subunits of NADPH oxidase was increased in T cells isolated from the kidneys of rats fed 4.0% NaCl. The urinary excretion of thiobarbituric acid-reactive substances (TBARS; an index of oxidative stress) also increased from 367 ± 49 to 688 ± 92 nmol/day (n = 8/group) when NaCl intake was increased in Dahl SS rats. Studies were then performed on rats treated with a daily injection of vehicle (5% dextrose) or tacrolimus (0.25 mg·kg(-1)·day(-1) ip), a calcineurin inhibitor that suppresses immune function, during the period of high-NaCl intake (n = 5/group). In contrast to the immune cell infiltration, increased NADPH oxidase expression, and elevated urine TBARS excretion in vehicle-treated Dahl SS fed high salt, these parameters were unaltered as NaCl intake was increased in Dahl SS rats administered tacrolimus. Moreover, tacrolimus treatment blunted high-salt mean arterial blood pressure and albumin excretion rate (152 ± 3 mmHg and 20 ± 9 mg/day, respectively) compared with values in dextrose-treated Dahl SS rats (171 ± 8 mmHg and 74 ± 28 mg/day). These experiments indicate that blockade of infiltrating immune cells is associated with decreased oxidative stress, an attenuation of hypertension, and a reduction of renal damage in Dahl SS rats fed high salt.

Cardiac and haemodynamic effects of tacrolimus in the halothane-anaesthetized dog

Tacrolimus (FK506) is a potent immunosuppressant widely used for the treatment of patients with solid organ transplantation and autoimmune diseases. The present study investigated the cardiac, haemodynamic and electrophysiological effects of tacrolimus. Tacrolimus in doses of 0.01 and 0.1 mg/kg was infused over 10 min. with a pause of 20 min. in halothane-anaesthetized dogs under monitoring of plasma drug concentrations (n = 5). Sub-therapeutic dose of 0.01 mg/kg hardly affected any of the cardiovascular variables except that it slightly delayed the repolarization. The clinically relevant dose of 0.1 mg/kg had negative chronotropic, inotropic and dromotropic effects, and lowered blood pressure by 70 +/- 12 mmHg, effects previously ascribed to Ca(2+) channel blocking action. Tacrolimus also delayed the repolarization process in a dose-dependent and reverse use-dependent manner with an increase in electrical vulnerability. The cardiovascular effects of tacrolimus were enhanced after the cessation of drug infusion, despite a decline in the plasma concentrations. In human embryonic kidney 293 cells, however, only supratherapeutic tacrolimus concentrations (>0.1 mumol/l) inhibited hERG K(+) current with a maximum inhibition of 28% at 10 mumol/l, indicating that other mechanisms might have also operated besides direct block of ionic channel function. The present study suggests that tacrolimus has negative chronotropic, inotropic and dromotropic effects in the heart, delays repolarization and lowers blood pressure. Moreover, the monitoring of the actual drug concentration may not necessarily reflect its effects on the cardiovascular system; thus, frequent monitoring of cardiovascular variables may be essential for tacrolimus-treated patients.

Tacrolimus reduces nitric oxide synthase function by binding to FKBP rather than by its calcineurin effect

Hypertension develops in many patients receiving the immunosuppressive drug tacrolimus (FK506). One possible mechanism for hypertension is a reduction in vasodilatory nitric oxide. We found that tacrolimus and a calcineurin autoinhibitory peptide significantly decreased vascular calcineurin activity; however, only tacrolimus altered intracellular calcium release in mouse aortic endothelial cells. In mouse aortas, incubation with tacrolimus increased protein kinase C activity and basal endothelial nitric oxide synthase phosphorylation at threonine 495 but reduced basal and agonist-induced endothelial nitric oxide synthase phosphorylation at serine 1177, a mechanism known to inhibit synthase activity. While this decreased nitric oxide production and endothelial function, the calcineurin autoinhibitory peptide had no such effects. Inhibition of ryanodine receptor opening or protein kinase C blocked the effects of tacrolimus. Since it is known that the FK506 binding protein (FKBP12/12.6) interacts with the ryanodine receptor to regulate calcium release, we propose this as the mechanism by which tacrolimus alters intracellular calcium and endothelial nitric oxide synthase rather than by its effect on calcineurin. Our study shows that prevention of the tacrolimus-induced intracellular calcium leak may attenuate endothelial dysfunction and the consequent hypertension.

The arginine-creatine pathway is disturbed in children and adolescents with renal transplants

Cardiovascular disease is an important cause of morbidity in recipients of renal transplants. The aim of the present study was to analyze the status of the arginine-creatine pathway in such patients, given the relationship between the arginine metabolism and both renal function and the methionine-homocysteine cycle. Twenty-nine children and adolescents (median age 13, range 6-18 years), who had received a renal allograft 14.5-82.0 months before, were recruited for the study. On immunosuppressive therapy, all patients evidenced an adequate level of renal function. Plasma concentrations of homocysteine and glycine were significantly higher, whereas urinary excretions of guanidinoacetate and creatine were significantly lower than controls. Urinary excretions of guanidinoacetate and creatine correlated positively with creatinine clearance. Urinary excretion of creatine was negatively correlated with plasma concentration of homocysteine. The demonstration of disturbances in the arginine-creatine pathway in patients with well-functioning renal transplants and in absence of chronic renal failure represents a novel finding. We speculate that the low urinary excretion of guanidinoacetate and creatine is probably related to the nephrotoxic effect of immunosuppressive therapy and to defective methylation associated with the presence of hyperhomocysteinemia.

ADP-ribosyl cyclase and ryanodine receptor activity contribute to basal renal vasomotor tone and agonist-induced renal vasoconstriction in vivo

An important role for the enzyme ADP-ribosyl cyclase (ADPR cyclase) and its downstream targets, the ryanodine receptors (RyR), is emerging for a variety of vascular systems. We hypothesized that the ADPR cyclase/RyR pathway contributes to regulation of renal vasomotor tone in vivo. To test this, we continuously measured renal blood flow (RBF) in anesthetized Sprague-Dawley rats. Infusion of the ADPR cyclase inhibitor nicotinamide intrarenally at low doses inhibits angiotensin II (ANG II)- and norepinephrine (NE)-induced vasoconstriction by 72 and 67%, respectively ( P < 0.001). RBF studies in rats were extended to mice lacking the predominant form of ADPR cyclase (CD38). Acute renal vasoconstrictor responses to ANG II and NE are impaired by 59 and 52%, respectively, in anesthetized CD38−/− mice compared with wild-type controls ( P < 0.05). Intrarenal injection of the RyR activator FK506 decreases RBF by 22% ( P > 0.03). Furthermore, RyR inhibition with ruthenium red attenuates ANG II and NE responses by 50 and 59%, respectively ( P ≤ 0.01). Given at higher doses, nicotinamide increases basal RBF by 22% ( P > 0.001). Non-receptor-mediated renal vasoconstriction by L-type voltage-gated Ca2+channels is also dependent on ADPR cyclase and RyRs. Nicotinamide and ruthenium red inhibit constriction by the L-type channel agonist BAY K 8644 by 59% ( P > 0.02) and 63% ( P > 0.001). We conclude that 1) ADPR cyclase activity contributes to regulation of renal vasomotor tone under resting conditions, 2) renal vasoconstriction induced by G protein-coupled receptor agonists ANG II and NE is mediated in part by ADPR cyclase and RyRs, and 3) ADPR cyclase and RyRs participate in L-type channel-mediated renal vasoconstriction in vivo.

FK506 reduces the severity of cutaneous hypersensitivity in rats with a spinal cord contusion

Spinal cord injury (SCI) leads to persistent pain as well as motor dysfunction, both of which lack effective therapeutics. The immunosuppressant FK506 (tacrolimus) has been shown to improve behavioral outcome following SCI in rats. Just prior to a mid-thoracic spinal cord contusion injury, rats were injected with either vehicle or FK506 and treatment was continued through the duration of the experiment. Vehicle-treated rats developed significant and long-lasting hind paw hypersensitivity to innocuous mechanical stimulation, noxious heat and cooling stimuli. In contrast, FK506 treatment reduced the duration of both mechanical and cold hypersensitivity. Neither treated groups demonstrated an improvement in locomotor function. Thus, some SCI-induced pain is mediated by an FK506-sensitive mechanism. The data also suggest that motor and sensory dysfunctions resulting from SCI are mediated by distinct mechanisms, requiring the use of multiple therapeutic interventions.

Short-term and long-term FK506 treatment alters the vascular reactivity of renal and mesenteric vascular beds

The aims of this study were to investigate the role of endothelin-1 in FK506-induced hypertension and vascular dysfunction of rats treated with the drug for 8 (short-term) or 30 (long-term) days and to measure malondialdehyde levels in the kidneys. Kidney and mesentery of rats were perfused. In the short-term treated groups, there was no significant change in systolic blood pressure. The response to noradrenaline only in renal vascular beds was significantly increased by FK506 and this increase was prevented by Bosentan. FK506 had no significant effect on sodium nitroprusside-induced vasodilation in comparison with solvent in both vascular beds. Bosentan failed to prevent these responses. In the long-term treated groups, at the end of the treatment with FK506, there was a significant increase in blood pressure, but no change in the response to noradrenaline in either kidneys or mesentery. The increase in blood pressure was prevented by bosentan treatment. FK506 increased malondialdehyde levels in the kidneys of the rats from only the long-term treated groups. Bosentan did not change this increase. Our results indicated that endothelin-1 plays a key role in the FK506-induced change in vascular reactivity to noradrenaline in renal vascular beds and drug-induced hypertension in the rats. There was no relationship between oxidative stress and FK506-induced hypertension.

Cardiac function in children post-orthotopic liver transplantation: echocardiographic parameters and biochemical markers of subclinical cardiovascular damage

Tacrolimus and cyclosporin A (CsA), the mainstay of preventive therapy for solid organ rejection, may cause various side-effects, such as hypertension and nephrotoxicity. Furthermore, tacrolimus is associated with cardiac hypertrophy. In the immediate post-transplant period, both drugs raise the levels of Endothelin-1 (ET), a potent vasoconstrictor; and of B-type Natriuretic Peptide (BNP), a sensitive marker of left ventricular volume overload, which may precede echocardiographic changes of cardiac dysfunction. The aim of the study was to investigate the presence of cardiac damage, by echocardiography and by the biochemical markers BNP and ET, in post-orthotopic liver transplantation (OLT) children, receiving long-term immunosuppressive therapy. ET (ELISA) and BNP (RIA) were measured in plasma of 18 children, post-OLT and 18 healthy controls. Children post-OLT were echocardiographically assessed for left ventricular mass (interventricular septum and posterior wall dimensions), systolic function (ejection fraction, fractional shortening) and diastolic parameters (mitral valve E and A waves, deceleration time, isovolumic relaxation time). None of the post-transplant recipients had a history or physical examination consistent with cardiac disease and all recipients were normotensive. Echocardiography revealed no systolic or diastolic dysfunction in any of the recipients. The mean ET and BNP levels tended to be higher among children post-liver transplant, compared with healthy controls (ET: 4.22 +/- 5.35 pg/mL vs. 2.1 +/- 2.0 pg/mL; BNP: 7.05 +/- 4.4 pg/mL vs. 5.87 +/- 2.0 pg/mL, respectively, mean +/- s.d.) although differences did not reach statistical significance. Three children (17%) had elevated BNP and/or ET levels. A strong correlation was observed between ET and BNP levels in post-OLT children (r = 0.79, p < or = 0.05). No correlation was found between ET or BNP levels and echocardiographic findings. In children receiving long-term immunosuppressive therapy post-OLT, although cardiac function is grossly preserved, ET and BNP levels tend to be higher than in healthy, age-matched children. Thus, elevated levels of BNP and/or ET may identify patients with early cardiac damage.

The impact of immunosuppression on endothelial function

Endothelial dysfunction is an early marker for transplant atherosclerosis. Potential mechanisms for allograft endothelial dysfunction include stimulation of alloimmune-dependent pathways, ischemia/reperfusion injury, metabolic alterations, chronic infections, as well as direct endothelial cell activation by immunosuppressive drugs. Thus far, no study has directly compared different immunosuppressive drugs with respect to their potential to modulate endothelial function under normoxic and hypoxic conditions. We examined human microvascular endothelial cells (HMEC-1) in vitro after stimulation with therapeutic concentrations of methylprednisolone (MP), mycophenolic acid (MMF), cyclosporine A (CS), rapamycin (Rapa), and tacrolimus (Tac) to designate the corresponding induction of oxidative stress, apoptosis, metabolic activity, proliferation, endothelin (ET-1) release, and nitric oxide (NO) production. HMEC-1 stimulation with CS, MMF, and Rapa resulted in a stronger induction of oxidative stress compared with MP and Tac. Induction of oxidative stress by immunosuppressives correlated with metabolic activity and apoptosis. Low- and high-dose MMF significantly inhibited cell proliferation under hypoxic conditions, whereas low-dose CS and MP increased endothelial cell proliferation. ET-1 release was significantly elevated by Rapa, Tac, and MP. NO production was significantly enhanced by all immunosuppressive drugs except Tac. Quality and quantity of immunosuppression modify endothelial function and lead to a dose-dependent and oxygenation-state-related endothelial activation. MP and MMF induced minor changes in endothelial function compared with CS, Rapa, and Tac.

The Distinct Alterations Produced in Cardiovascular Functions by Prednisolone and Nitro-prednisolone (NCX-1015) in the Rat Highlight a Causal Role for Endothelin-1

Daily administration of prednisolone, but not the derivative NCX-1015 (or prednisolone 21-[4'-nitrooxymethyl]benzoate), to rats resulted in a time- and dose-dependent increase in mean arterial blood pressure (MABP), significant after 1 week for the dose of 6.9 micromol/kg i.p. (n = 10; P < 0.05), and 3 weeks for the lower dose of 1.38 micromol/kg. A similar dichotomy of behavior was observed with respect to myocardial contractility and renal vascular resistance, in either case augmented by 3-week treatment with prednisolone but not NCX-1015. In contrast, both NCX-1015 and prednisolone reduced plasma levels of corticosterone in a dose- (dose range of 0.69-6.9 micromol/kg i.p.) and time-dependent (1-3 weeks) manner. Similar profiles were obtained for plasma nitrate values, although they were increased selectively after NCX-1015 administration. In contrast, prednisolone, but not NCX-1015, augmented plasma endothelin 1 (ET-1) with a profile that mirrored the changes observed in MABP and renal blood flow. Supply in the drinking water of the ET-1 receptor type A (ETA) antagonist FR139317 [(R-2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]-carbonyl]amino-4-methylpentanoyl]-amino-3-(2-pyridil)propionic] or mixed ETA/B, but not of selective ETB, antagonists prevented the changes produced by a 21-day treatment with prednisolone. In conclusion, this study indicates 1) a lack of occurrence of cardiovascular alterations by nitro-releasing derivative of prednisolone (NCX-1015), and 2) a functional link between prednisolone effects and the endogenous endothelin-1 system.

Regional haemodynamic effects of cyclosporine A, tacrolimus and sirolimus in conscious rats

1. The observation that the immunosuppressants, cyclosporine A (CsA) and tacrolimus, have pressor effects, but sirolimus does not, has led to an hypothesis that generalised sympathoexcitation, resulting from inhibition of calcineurin by CsA and tacrolimus underlies their pressor effects, because sirolimus does not inhibit calcineurin. It is unknown if sirolimus has haemodynamic actions not accompanied by a pressor effect, and whether or not the pressor effects of CsA and tacrolimus are accompanied by similar haemodynamic changes. Therefore, the first aim of our studies was to investigate these possibilities in conscious, chronically-instrumented, male, Sprague-Dawley rats. 2. CsA (5.9 mg kg(-1) bolus i.v.) caused rapid-onset, prolonged hypertension, tachycardia and mesenteric vasoconstriction. There was a slower onset renal vasoconstriction, but no significant change in hindquarters vascular conductance; all the effects of CsA were significantly greater than those of vehicle. CsA given by infusion (over 30 min or 2 h) caused changes qualitatively similar to those above. Repeated administration of CsA over 4 days did not enhance its cardiovascular effects. 3. Pretreatment with the angiotensin (AT(1)) receptor antagonist, losartan, and the endothelin (ET(A) and ET(B)) receptor antagonist, SB 209670, reduced the pressor and mesenteric vasoconstrictor effects of CsA. Additional administration of the alpha-adrenoceptor antagonist, phentolamine, completely inhibited the cardiovascular effects of CsA. 4. Tacrolimus (450 microg kg(-1) bolus i.v.) caused similar peak pressor and tachycardic effects to CsA, but these were much slower in onset, and were maximal when there were no significant regional vasoconstrictions, indicating that the pressor effect was probably due to a rise in cardiac output. However, although propranolol reversed the tachycardic effect of tacrolimus, it did not influence the pressor response. 5. Sirolimus (450 microg kg(-1) bolus i.v.) had no tachycardic action, and only a modest, transient pressor effect, accompanied by equally brief reductions in renal, mesenteric, and hindquarters vascular conductances. 6. The differences between the regional haemodynamic profiles of equipressor doses of CsA and tacrolimus, and the finding that sirolimus has significant cardiovascular actions, indicate that generalised sympathoexcitation, resulting from calcineurin inhibition (with CsA and tacrolimus), is unlikely to be the sole explanation of their pressor effects.

Differential effect of cyclosporine A and SDZ RAD on neointima formation of carotid allografts in apolipoprotein E-deficient mice

BACKGROUND

Apolipoprotein E-deficient (apoE-/-) mice spontaneously develop hypercholesterolemia and atherosclerotic lesions. This may be an appropriate background for the development of graft vessel disease. The authors therefore investigated the effects of cyclosporine A (CsA) and SDZ RAD (RAD, everolimus, Certican) on neointima formation of carotid allografts in apoE-/- mice. To ascertain that equipotent immunosuppressive doses were used, the authors also investigated their effects on cardiac allografts using the same wild-type strain combination.

METHODS

Heterotopic heart allotransplantation was performed in the BALB/c to C57BL/6 strain combination. Graft survival was monitored daily. Orthotopic carotid artery allotransplantation was performed from BALB/c to apoE-/- (C57BL/6) mice. Groups of mice were treated for 8 weeks with placebo; CsA 10, 20, and 30 mg/kg/d; or RAD 0.3, 1.0, and 3.0 mg/kg/d using ALZET minipumps. Body weight, CsA blood levels, serum lipids, and histology were examined 8 weeks after transplantation or on the day of rejection.

RESULTS

Compared with the placebo group, CsA or RAD did not affect body weight. Both CsA and RAD prolonged the survival of cardiac grafts in a dose-dependent manner. CsA blood levels were not different between wild-type and apoE-/- recipients. CsA increased total cholesterol and low-density lipoprotein, but not high-density lipoprotein dose-dependently and significantly, but RAD did not affect the lipids. RAD but not CsA significantly attenuated neointima formation.

CONCLUSIONS

These results suggest that RAD at a dose preventing organ rejection may also prevent transplant vasculopathy even in the presence of hyperlipidemia.

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.

Different effects of tacrolimus and cyclosporine on renal hemodynamics and blood pressure in healthy subjects

BACKGROUND

The side effects of cyclosporine, nephrotoxicity and hypertension, contribute to long-term renal graft failure and cardiovascular morbidity in graft recipients. It is not clear whether tacrolimus is as nephrotoxic and hypertensive as cyclosporine. Data on this subject are not consistent because of differences in dosage and duration of treatment and the presence of comorbidity in the studied patients. A comparison of both drugs with respect to renal hemodynamics and blood pressure has not been performed yet in healthy subjects.

METHODS

We studied blood pressure, glomerular filtration rate, and effective renal plasma flow in eight healthy subjects at baseline and after 2 weeks administration of cyclosporine and tacrolimus, in randomized order. Trough levels of either drug were within the currently recommended therapeutical range of 100-200 ng/ml for cyclosporine and 5-15 ng/ml for tacrolimus.

RESULTS

Tacrolimus did not influence renal hemodynamic parameters, in contrast to cyclosporine. During cyclosporine, glomerular filtration rate decreased from 98+/-9 ml/min/1.732 to 85+/-10 ml/min/1.732 (P<0.05), and ERPF decreased from 597+/-108 ml/min/1.732 to 438+/-84 ml/min/1.732 (P<0.01). Mean arterial blood pressure increased from 93+/-8 mmHg to 108+/-10 mmHg (P<0.05) during cyclosporine and remained unchanged during tacrolimus.

CONCLUSIONS

We conclude that tacrolimus given during 2 weeks in the currently advised dosage has no unfavorable effects on renal hemodynamics and blood pressure in healthy individuals. The use of tacrolimus in organ transplant recipients may in the long-term lead to better renal function and less cardiovascular morbidity than the use of cyclosporine.