Cyclosporine- and FK506-induced sympathetic activation correlates with calcineurin-mediated inhibition of T-cell signaling

Tacrolimus-associated neurotoxicity isolated to the brainstem: two illustrative cases and a systematic review of the literature

INTRODUCTION

Tacrolimus-associated neurotoxicity (TAN) manifests with wide clinical spectrum, ranging from mild tremors to severe encephalopathy. The isolated involvement of the brainstem is a rarely documented presentation of TAN, and its clinical and diagnostic characteristics are unclear.

METHODS

We report two cases of brainstem-isolated TAN (bi-TAN). Moreover, we performed a systematic review of the literature on bi-TAN and extracted data concerning demographics, clinical characteristics, radiological features, and management. The systematic literature search followed PRISMA guidelines and a pre-defined protocol.

RESULTS

Eleven patients, including our two, were identified (mean age: 41.3 years, ± 18.8; five males, 45%). Speech disturbance was the most common clinical presentation (45%). The mean latency from Tacrolimus initiation to bi-TAN onset was 26 days (± 30.8). Tacrolimus serum level tested above the reference range in three patients (mean: 26.83 ± 5.48). Brain MRI showed T2-FLAIR hyperintensities; three showed restricted diffusion on ADC maps. Neurological symptoms resolved completely in seven patients (63%) after Tacrolimus withdrawal or dose reduction.

CONCLUSIONS

Our findings suggest that bi-TAN could represent a brainstem variant of posterior reversible encephalopathy syndrome. Recognition of bi-TAN as a potential cause of isolated brainstem lesions is crucial to disentangle the diagnostic work-up and ensure prompt withdrawal or reduction of the offending agent.

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.

Immunosuppressive calcineurin inhibitor cyclosporine A induces proapoptotic endoplasmic reticulum stress in renal tubular cells

Current immunosuppressive strategies in organ transplantation rely on calcineurin inhibitors cyclosporine A (CsA) or tacrolimus (Tac). Both drugs are nephrotoxic, but CsA has been associated with greater renal damage than Tac. CsA inhibits calcineurin by forming complexes with cyclophilins, whose chaperone function is essential for proteostasis. We hypothesized that stronger toxicity of CsA may be related to suppression of cyclophilins with ensuing endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in kidney epithelia. Effects of CsA and Tac (10 µM for 6 h each) were compared in cultured human embryonic kidney 293 (HEK 293) cells, primary human renal proximal tubule (PT) cells, freshly isolated rat PTs, and knockout HEK 293 cell lines lacking the critical ER stress sensors, protein kinase RNA-like ER kinase or activating transcription factor 6 (ATF6). UPR was evaluated by detection of its key components. Compared with Tac treatment, CsA induced significantly stronger UPR in native cultured cells and isolated PTs. Evaluation of proapoptotic and antiapoptotic markers suggested an enhanced apoptotic rate in CsA-treated cells compared with Tac-treated cells as well. Similar to CsA treatment, knockdown of cyclophilin A or B by siRNA caused proapoptotic UPR, whereas application of the chemical chaperones tauroursodeoxycholic acid or 4-phenylbutyric acid alleviated CsA-induced UPR. Deletion of protein kinase RNA-like ER kinase or ATF6 blunted CsA-induced UPR as well. In summary, inhibition of cyclophilin chaperone function with ensuing ER stress and proapoptotic UPR aggravates CsA toxicity, whereas pharmacological modulation of UPR bears potential to alleviate renal side effects of CsA.

Angiotensin II receptor blockade alleviates calcineurin inhibitor nephrotoxicity by restoring cyclooxygenase 2 expression in kidney cortex

AIM

The use of calcineurin inhibitors such as cyclosporine A (CsA) for immunosuppression after solid organ transplantation is commonly limited by renal side effects. CsA-induced deterioration of glomerular filtration rate and sodium retention may be related to juxtaglomerular dysregulation as a result of suppressed cyclooxygenase 2 (COX-2) and stimulated renin biosynthesis. We tested whether CsA-induced COX-2 suppression is caused by hyperactive renin-angiotensin system (RAS) and whether RAS inhibition may alleviate the related side effects.

METHODS

Rats received CsA, the RAS inhibitor candesartan, or the COX-2 inhibitor celecoxib acutely (3 days) or chronically (3 weeks). Molecular pathways mediating effects of CsA and RAS on COX-2 were studied in cultured macula densa cells.

RESULTS

Pharmacological or siRNA-mediated calcineurin inhibition in cultured cells enhanced COX-2 expression via p38 mitogen-activated protein kinase and NF-kB signalling, whereas angiotensin II abolished these effects. Acute and chronic CsA administration to rats led to RAS activation along with reduced cortical COX-2 expression, creatinine clearance and fractional sodium excretion. Evaluation of major distal salt transporters, NKCC2 and NCC, showed increased levels of their activating phosphorylation upon CsA. Concomitant candesartan treatment blunted these effects acutely and completely normalized the COX-2 expression and renal functional parameters at long term. Celecoxib prevented the candesartan-induced improvements of creatinine clearance and sodium excretion.

CONCLUSION

Suppression of juxtaglomerular COX-2 upon CsA results from RAS activation, which overrides the cell-autonomous, COX-2-stimulatory effects of calcineurin inhibition. Angiotensin II antagonism alleviates CsA nephrotoxicity via the COX-2-dependent normalization of creatinine clearance and sodium excretion.

Tacrolimus-induced epilepsy with primary membranous nephropathy: A case report

RATIONALE

Tacrolimus-associated neurologic disorders can be found in some cases, mainly in organ transplantation patients. However, epilepsy induced by tacrolimus in primary membranous nephropathy (PMN) patient is scare.

PATIENT CONCERNS

A 63-year-old man experienced 1-year history of foamy urine, and edema of lower extremity.

DIAGNOSIS

The patient had proteinuria, hypoalbuminemia, which indicated nephrotic syndrome. Further, we performed renal biopsy for this patient. Combined with the renal biopsy result, the diagnosis of primary membranous nephropathy was established.

INTERVENTION

At first, irbesartan was administrated for 6 months. However, the proteinuria had no obvious improvement. Tacrolimus was administrated afterwards.

OUTCOMES

Twenty-two days after tacrolimus treatment, epilepsy occurred. Sodium valproate and carbamazepine were successively given to control epilepsy. However, the epileptic symptoms were not effectively controlled. During the treatment, the concentration of tacrolimus fluctuated greatly. At last, levetiracetam was given to maintain the curative effect. Fortunately, the patient did not suffer from epilepsy again. The concentration of temporary tacrolimus was stable, whereas proteinuria gradually decreased.

LESSONS

Tacrolimus-induced epilepsy should be considered in patients exhibiting acute neurological symptoms. Early diagnosis and effective treatment play a vital role for favorable prognosis.

Autonomic Cardiovascular Alterations in Chronic Kidney Disease: Effects of Dialysis, Kidney Transplantation, and Renal Denervation

PURPOSE OF REVIEW

To review the results of studies of the effects of dialysis and kidney transplantation on the autonomic nervous system alterations that occur in chronic kidney disease.

RECENT FINDINGS

Vagal control of the heart mediated by arterial baroreceptors is altered early in the course of the renal disease. Sympathetic activation occurs, with increases in resting heart rate, venous plasma norepinephrine levels, muscle sympathetic nerve traffic, and other indirect indices of adrenergic drive. The magnitude of the changes reflects the clinical severity of the kidney disease. Both the sympathetic and parasympathetic alterations have a reflex origin, depending on the impairment in baroreflex and cardiopulmonary reflex control of the cardiovascular system. These alterations are partially reversed during acute hemodialysis, but the responses are variable depending on the specific type of dialytic treatment that is employed. Renal transplantation improves reflex cardiovascular control, resulting in sympathoinhibition following renal transplantation if the native kidneys are removed. Sympathoinhibitory effects have been also reported in renal failure patients after bilateral renal denervation. Assessment of autonomic nervous system responses to dialysis and renal transplantation provides information of clinical interest, given the evidence that autonomic alterations are involved in the development and progression of cardiovascular complications, as well as in the prognosis of chronic kidney disease.

Acute symptomatic seizure due to tacrolimus-related encephalopathy after liver transplantation: two case reports

Liver transplantation is suitable for acute and chronic liver diseases that cannot be cured by other methods. Immunosuppressants such as azathioprine, methylprednisolone, cyclophosphamide, cyclosporine A, and tacrolimus have been applied to prevent rejection after liver transplantation. Among them, tacrolimus is generally effective in resisting rejection, and its main adverse reaction is nephrotoxicity. Tacrolimus-induced seizures are rarely reported. The present report describes trismus, restlessness, and generalized muscle twitching in a 44-year-old man and a 59-year-old man who received tacrolimus after liver transplantation. Tacrolimus-induced epilepsy was diagnosed by clinical symptoms and video-electroencephalography. After the patients developed epileptic symptoms, they received intramuscular injections of diazepam and phenobarbital. When the symptoms were relieved, the patients were treated with oral levetiracetam tablets. The tacrolimus was immediately stopped, and the epilepsy symptoms gradually disappeared after treatment with sedatives and levetiracetam. The patients continued taking the levetiracetam for approximately 2 weeks. No evidence of seizures occurred during the next 8 months. Although tacrolimus is reportedly effective against rejection after liver transplantation, tacrolimus-induced epilepsy should be carefully managed to prevent death. Additionally, epilepsy may rarely occur in patients with a normal blood concentration of tacrolimus. Further study on the mechanism of such neurological complications is needed.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

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.

An Elastomeric Polymer Matrix, PEUU-Tac, Delivers Bioactive Tacrolimus Transdurally to the CNS in Rat

Central nervous system (CNS) neurons fail to regrow injured axons, often resulting in permanently lost neurologic function. Tacrolimus is an FDA-approved immunosuppressive drug with known neuroprotective and neuroregenerative properties in the CNS. However, tacrolimus is typically administered systemically and blood levels required to effectively treat CNS injuries can lead to lethal, off-target organ toxicity. Thus, delivering tacrolimus locally to CNS tissues may provide therapeutic control over tacrolimus levels in CNS tissues while minimizing off-target toxicity. Herein we show an electrospun poly(ester urethane) urea and tacrolimus elastomeric matrix (PEUU-Tac) can deliver tacrolimus trans-durally to CNS tissues. In an acute CNS ischemia model in rat, the optic nerve (ON) was clamped for 10s and then PEUU-Tac was used as an ON wrap and sutured around the injury site. Tacrolimus was detected in PEUU-Tac wrapped ONs at 24 h and 14 days, without significant increases in tacrolimus blood levels. Similar to systemically administered tacrolimus, PEUU-Tac locally decreased glial fibrillary acidic protein (GFAP) at the injury site and increased growth associated protein-43 (GAP-43) expression in ischemic ONs from the globe to the chiasm, consistent with decreased astrogliosis and increased retinal ganglion cell (RGC) axon growth signaling pathways. These initial results suggest PEUU-Tac is a biocompatible elastic matrix that delivers bioactive tacrolimus trans-durally to CNS tissues without significantly increasing tacrolimus blood levels and off-target toxicity.

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PEUU-Tac locally delivers tacrolimus to CNS tissues

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PEUU-Tac positively modulates CNS tissue remodeling

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PEUU-Tac minimizes off-target tacrolimus toxicity

Central nervous system (CNS) injury typically results in permanently lost neurological function. Tacrolimus is an FDA-approved drug used during organ transplantation that also has CNS neuroprotective and neuroregenerative properties. However, tacrolimus is typically delivered systemically in the blood and delivering effective concentrations to CNS tissues requires tacrolimus blood levels that can lead to adverse side effects in multiple organs. Herein we show that PEUU-Tac, a tacrolimus-eluting matrix, can locally deliver tacrolimus to injured CNS tissues without increasing blood levels, suggesting PEUU-Tac can be used to treat CNS injuries locally while minimizing adverse side effects.

NaCl cotransporter abundance in urinary vesicles is increased by calcineurin inhibitors and predicts thiazide sensitivity

Animal studies have shown that the calcineurin inhibitors (CNIs) cyclosporine and tacrolimus can activate the thiazide-sensitive NaCl cotransporter (NCC). A common side effect of CNIs is hypertension. Renal salt transporters such as NCC are excreted in urinary extracellular vesicles (uEVs) after internalization into multivesicular bodies. Human studies indicate that CNIs also increase NCC abundance in uEVs, but results are conflicting and no relationship with NCC function has been shown. Therefore, we investigated the effects of CsA and Tac on the abundance of both total NCC (tNCC) and phosphorylated NCC at Thr60 phosphorylation site (pNCC) in uEVs, and assessed whether NCC abundance in uEVs predicts the blood pressure response to thiazide diuretics. Our results show that in kidney transplant recipients treated with cyclosporine (n = 9) or tacrolimus (n = 23), the abundance of both tNCC and pNCC in uEVs is 4–5 fold higher than in CNI-free kidney transplant recipients (n = 13) or healthy volunteers (n = 6). In hypertensive kidney transplant recipients, higher abundances of tNCC and pNCC prior to treatment with thiazides predicted the blood pressure response to thiazides. During thiazide treatment, the abundance of pNCC in uEVs increased in responders (n = 10), but markedly decreased in non-responders (n = 8). Thus, our results show that CNIs increase the abundance of both tNCC and pNCC in uEVs, and these increases correlate with the blood pressure response to thiazides. This implies that assessment of NCC in uEVs could represent an alternate method to guide anti-hypertensive therapy in kidney transplant recipients.

Hypertension in Patients with Cardiac Transplantation

Hypertension is a common complication among post cardiac transplant recipients affecting more than 95% of patients. Increased blood pressure poses a significant cardiovascular morbidity and mortality in these patients; it should be identified quickly and needs to be managed appropriately. Understanding the pathophysiology and contributing factors to this disease in these complex and unique patients is the key to appropriate treatment selection.

Reducing Adverse Effects of Immunosuppressive Agents in Kidney Transplant Recipients

Success in solid organ transplantation with minimal complications can now be achieved for most patients, and a remarkable rate of graft and patient survival can also be expected. However, the potential for adverse events and comorbid conditions increases with longer graft survival. Although the immunosuppressive regimen is central to the outcome of the transplant recipient and directly impacts the survival of the graft, chronic use of immunosuppressive agents is associated with metabolic disturbances such as hypertension, hyperlipidemia, loss of bone density, nephrotoxicity, and diabetes, which may contribute to other comorbid conditions. In addition, changes in appearance, gingival hyperplasia, hirsutism, alopecia, and weight gain disrupt quality of life and may lead to noncompliance with the immunosuppressive regimen. New immunosuppressive medications, including mycophenolate mofetil, sirolimus, basiliximab, and daclizumab, have allowed for experimentation with new regimens designed to reduce or allow discontinuation of corticosteroids and calcineurin inhibitors. This review highlights the impact and cost of immunosuppressive side effects and the potential for new immunosuppressive regimens to reduce this substantial clinical burden in transplantation.

Renal Deletion of 12 kDa FK506-Binding Protein Attenuates Tacrolimus-Induced Hypertension

Tacrolimus is a widely used immunosuppressive drug that inhibits the phosphatase calcineurin when bound to the 12 kDa FK506-binding protein (FKBP12). When this binding occurs in T cells, it leads to immunosuppression. Tacrolimus also causes side effects, however, such as hypertension and hyperkalemia. Previously, we reported that tacrolimus stimulates the renal thiazide-sensitive sodium chloride cotransporter (NCC), which is necessary for the development of hypertension. However, it was unclear if tacrolimus-induced hypertension resulted from tacrolimus effects in renal epithelial cells directly or in extrarenal tissues, and whether inhibition of calcineurin was required. To address these questions, we developed a mouse model in which FKBP12 could be deleted along the nephron. FKBP12 disruption alone did not cause phenotypic effects. When treated with tacrolimus, however, BP and the renal abundance of phosphorylated NCC were lower in mice lacking FKBP12 along the nephron than in control mice. Mice lacking FKBP12 along the nephron also maintained a normal relationship between plasma potassium levels and the abundance of phosphorylated NCC with tacrolimus treatment. In cultured cells, tacrolimus inhibited dephosphorylation of NCC. Together, these results suggest that tacrolimus causes hypertension predominantly by inhibiting calcineurin directly in cells expressing NCC, indicating thiazide diuretics may be particularly effective for lowering BP in tacrolimus-treated patients with hypertension.

Neurotoxicity of commonly used hepatic drugs

Neurologic complications are common side-effects of immunosuppressive medications used in the prevention of graft rejection after organ transplantation. The medications most commonly encountered include the calcineurin inhibitors and mycophenolate mofetil. Depression is the most commonly encountered neurotoxicity; however, severe but rare adverse neurological effects related to these therapies have been reported. Interferons, ribavirin, and protease inhibitors are therapeutic options commonly encountered in the treatment of hepatitis. Nucleoside analogs such as adefovir dipivoxil and entecavir carry significant risks for the development of lactic acidosis and hepatic dysfunction; however, most common adverse effects to these therapies in general are mild. While the mechanisms of action are poorly elucidated, they are discussed along with treatment strategies.

Neurologic complications in renal transplantation

Neurologic complications following kidney transplant are more common than in the general population with the reported incidence around 10-21%. Need for multiple drugs, decreased cellular immunity, accelerated atherosclerotic disease, and frequency of metabolic abnormalities are the most common predisposing factors for neurologic abnormalities. Neurologic side-effects of calcineurin inhibitors range from mild tremors to paraplegia or posterior reversible encephalopathy syndrome (PRES) and are generally reversible by lowering the dose or complete discontinuation of the drug when possible. Clinical presentation of central nervous system infection in transplant recipients can be different from the normal population as the anti-inflammatory effects of immunosuppressive therapy may obscure signs of meningeal inflammation and changes in the level of consciousness may be subtle. Bacterial infections remain the most common infections but unusual pathogens figure prominently in the differential diagnosis. The most frequent malignancies of the brain are lymphomas and metastatic tumors which are for the most part, de novo malignancies from immunosuppression. Decreasing immunosuppression is almost always a part of treating malignancy. The prevalence of stroke is reported to be around 8% with age>40 years, diabetic nephropathy as the underlying cause of end-stage kidney disease, and peripheral vascular disease being the strongest predictors.

Parathyroidectomy after kidney transplantation: short-and long-term impact on renal function

INTRODUCTION

Kidney transplantation corrects endocrine imbalances. Nevertheless, these early favorable events are not always followed by rapid normalization of parathyroid hormone secretion. A possible deleterious effect of parathyroidectomy on kidney transplant function has been reported. This study aimed to compare acute and longterm renal changes after total parathyroidectomy with those occurring after general surgery.

MATERIALS AND METHODS

This was a retrospective case-controlled study. Nineteen patients with persistent hyperparathyroidism underwent parathyroidectomy due to hypercalcemia. The control group included 19 patients undergoing various general and urological operations.

RESULTS

In the parathyroidectomy group, a significant increase in serum creatinine from 1.58 to 2.29 mg/dl (P < 0.05) was noted within the first 5 days after parathyroidectomy. In the control group, a statistically insignificant increase in serum creatinine from 1.49 to 1.65 mg/dl occurred over the same time period. The long-term mean serum creatinine level was not statistically different from baseline either in the parathyroidectomy group (final follow-up creatinine = 1.91 mg/dL) or in the non-parathyroidectomy group (final follow-up creatinine = 1.72 mg/dL).

CONCLUSION

Although renal function deteriorates in the acute period following parathyroidectomy, long-term stabilization occurs, with renal function similar to both preoperative function and to a control group of kidney-transplanted patients who underwent other general surgical operations by the final follow up.

Differential effects of acute and sustained cyclosporine and tacrolimus on sympathetic nerve activity

BACKGROUND

We studied the effect of acute and sustained cyclosporine and tacrolimus on muscle sympathetic nerve activity (MSNA) in groups of healthy male volunteers.

METHODS AND RESULTS

Acute cyclosporine in normal dose (2.5 mg/kg) increased MSNA from 11 +/- 6 to 19 +/- 8 bursts/min (P < 0.05). Acute cyclosporine in high dose (10 mg/kg) increased MSNA from 13 +/- 6 to 25 +/- 4 bursts/min (P < 0.05) and increased heart rate and mean arterial pressure (heart rate from 64 +/- 8 to 74 +/- 6 b.p.m., MAP from 92 +/- 10 to 105 +/- 8 mmHg; both P < 0.05). Sustained cyclosporine (2.5 mg/kg b.i.d. for 2 weeks) suppressed MSNA from 14 +/- 6 to 8 +/- 7 bursts/min (P < 0.05). Blood pressure increased from 89 +/- 6 to 98 +/- 6 mmHg (P < 0.05). Body weight increased and plasma renin activity was suppressed. Acute tacrolimus in regular dose (0.05 mg/kg) and high dose (0.20 mg/kg) had no effect on MSNA and blood pressure. Sustained tacrolimus (0.05 mg/kg b.i.d. for 2 weeks) had no effect on blood pressure, body weight and plasma renin activity, but decreased MSNA from 14 +/- 6 to 8 +/- 5 bursts/min (P < 0.05).

CONCLUSION

Sympathetic overactivity plays a role in the acute hypertensive action of cyclosporine. Cyclosporine given during 2 weeks increases blood pressure and suppresses MSNA, possibly by volume retention. Tacrolimus, in the presently applied dosages, does not cause hypertension or sympathetic overactivity. However, sustained tacrolimus also suppresses sympathetic activity, the reason of which is unclear.

Reduction of ciclosporin and tacrolimus nephrotoxicity by plant polyphenols

The immunosuppressants ciclosporin (cyclosporin A, CsA) and tacrolimus can cause severe nephrotoxicity. Since CsA increases free radical formation, this study investigated whether an extract from Camellia sinensis, which contains several polyphenolic free radical scavengers, could prevent nephrotoxicity caused by CsA and tacrolimus. Rats were fed powdered diet containing polyphenolic extract (0-0.1%) starting 3 days before CsA or tacrolimus. Free radicals were trapped with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and measured using an electron spin resonance spectrometer. Both CsA and tacrolimus decreased glomerular filtration rates (GFR) and caused tubular atrophy, vacuolization and calcification and arteriolar hyalinosis, effects that were blunted by treatment with dietary polyphenols. Moreover, CsA and tacrolimus increased POBN/radical adducts in urine nearly 3.5 fold. Hydroxyl radicals attack dimethyl sulfoxide (DMSO) to produce a methyl radical fragment. Administration of CsA or tacrolimus with 12C-DMSO produced a 6-line spectrum, while CsA or tacrolimus given with 13C-DMSO produced a 12-line ESR spectrum, confirming formation of hydroxyl radicals. 4-Hydroxynonenal (4-HNE), a product of lipid peroxidation, accumulated in proximal and distal tubules after CsA or tacrolimus treatment. ESR changes and 4-HNE formation were largely blocked by polyphenols. Taken together, these results demonstrate that both CsA and tacrolimus stimulate free radical production in the kidney, most likely in tubular cells, and that polyphenols minimize nephrotoxicity by scavenging free radicals.

Use of a real-time fluorescence monitoring system for high-throughput screening for prolyl isomerase inhibitors

Cyclophilin is a ubiquitous peptidyl prolyl cis/trans isomerase that plays critical roles in many biological processes. A number of cyclophilin inhibitors have been designed based on the structure of the immunosuppressant cyclosporin A. To discover inhibitors that have other structures, the authors established the high-throughput screening (HTS) method using FDSS6000 real-time fluorescence detector. The inhibitors identified with this HTS showed significant correlation with direct interaction as measured by surface plasmon resonance. This high-throughput assay system is a powerful tool for the discovery of peptidylprolyl isomerase inhibitors.

Neurological complications after orthotopic liver transplantation

BACKGROUND

The number of orthotopic liver transplantation performed each year is increasing due to increased safety and logistic facilities. Therefore, the importance of reducing adverse events is progressively growing.

AIM

To review present knowledge on the neurological complications of orthotopic liver transplantation.

METHODS

The epidemiology, the clinical features and the pathophysiology of the neurological complications of orthotopic liver transplants, resulting from a systematic review of the literature in the last 25 years, are summarized.

RESULTS AND CONCLUSIONS

The review highlights that a relevant variety of neurological adverse events can occur in patients undergoing orthotopic liver transplantation. The knowledge of neurological complications of orthotopic liver transplantation is important for transplantation teams to reduce their prevalence and improve their management. In addition, the likelihood of neurological adverse effects provides evidence for the need of a careful cognitive and neurological work up of patients in the orthotopic liver transplantation waiting list, in order to recognize and interpret neurological dysfunction occurring after orthotopic liver transplantation.

Sympathetic nerve activity in renal transplant patients before and after withdrawal of cyclosporine

BACKGROUND

It has been suggested that the increase in blood pressure observed in transplant patients treated with cyclosporine is mediated by cyclosporine-induced sympathoexcitation. However, the chronic effects of cyclosporine on sympathetic outflow in renal transplant patients have not been investigated. Therefore we studied sympathetic nerve activity and blood pressure before and 6 months after the withdrawal of cyclosporine in renal transplant patients.

METHODS

Twenty-four renal transplant patients with histologically confirmed chronic allograft nephropathy (age 48 +/- 3 years, 60 +/- 10 months after transplantation) were included in the prospective study and randomly assigned to either withdrawal (n = 12) or continuation (n = 12) of cyclosporine. Both groups received mycophenolate mofetil and prednisolone as additional immunosuppressants. At entry and 6 months later blood pressure, muscle sympathetic nerve activity (MSNA), and plasma norepinephrine were measured. To assess the potential influence of the diseased native kidneys, three renal transplant patients who had their native kidneys removed were studied before and after cyclosporine withdrawal.

RESULTS

Mean arterial pressure decreased significantly in the cyclosporine-withdrawal group (95 +/- 4 versus 105 +/- 4 mmHg 6 versus 0 months, P < 0.05) but not in the cyclosporine-continuation group (103 +/- 3 versus 105 +/- 4 mmHg, NS). However, plasma norepinephrine and MSNA did not change significantly in either group (MSNA 43 +/- 4 versus 44 +/- 3 and 38 +/- 5 versus 39 +/- 4 bursts/min in the cyclosporine-withdrawal and cyclosporine-continuation groups, NS). Graft function remained stable in both groups and in transplant patients who had their native kidneys removed MSNA did not decrease after cyclosporine withdrawal.

CONCLUSION

The withdrawal of cyclosporine in renal transplant patients, receiving relatively low doses of cyclosporine, resulted in a substantial decrease in blood pressure. However, MSNA and norepinephrine did not change. This suggests that cyclosporine treatment does not cause chronic sympathetic activation that could explain the cyclosporine-induced blood pressure elevation in renal transplant patients.

A fluorescence polarization-based assay for peptidyl prolyl cis/trans isomerase cyclophilin A

Peptidyl prolyl cis/trans isomerase cyclophilin A (CypA) serves as a cellular receptor for the important immunosuppressant drug, cyclosporin A. In addition, CypA and its enzyme family have been found to play critical roles in a variety of biological processes, including protein trafficking, HIV and HCV infection/replication, and Ca(2+)-mediated intracellular signaling. For these reasons, cyclophilins have emerged as potential drug targets for several diseases. Therefore, it is extremely important to screen for novel small molecule cyclophilin inhibitors. Unfortunately, the biochemical assays reported so far are not adaptable to a high-throughput screening format. Here, we report a fluorescence polarization-based assay for human CypA that can be adapted to high-throughput screening for drug discovery. The technique is based on competition and uses a fluorescein-labeled cyclosporin A analog and purified human CypA to quantitatively measure the binding capacity of unlabeled inhibitors. Detection by fluorescence polarization allows real-time measurement of binding ratios without separation steps. The results obtained demonstrated significant correlation among assay procedures, suggesting that the application of fluorescence polarization in combination with CypA is highly advantageous for the accurate assessment of inhibitor binding.

Prednisolone suppresses cyclosporin A-induced apoptosis but not cell cycle arrest in MDCK cells

Cyclosporin A (CsA) is a potent immunosuppressive agent, and can cause severe adverse effects including nephrotoxicity partly due to generation of reactive oxygen species (ROS). Glucocorticoids, which are widely used in combination with CsA, have been shown to reduce oxidative injuries in various cells, but its mechanism is not understood well. To investigate the effects of prednisolone (Pd) on CsA-induced cellular damage and ROS generation in Madin-Darby canine kidney (MDCK) tubular epithelial cells, cells were treated with CsA, CsA plus Pd, or CsA plus vitamin E. Pretreatment with Pd protected cells from CsA-induced apoptosis but not from G(0)/G(1) cell cycle arrest even at its maximal protective concentration (30 microM), whereas vitamin E almost completely inhibited both CsA-induced apoptosis and cell cycle arrest at 1 microM concentration. In addition, Pd reduced the amount of CsA-induced ROS and showed partly restored catalase which was down-regulated by 10 microM CsA at both the mRNA and protein levels. Vitamin E completely abolished CsA-induced ROS generation and catalase attenuation at 10 microM concentration. Finally, the effects of 1 microM vitamin E on CsA-induced ROS and apoptosis as well as cell cycle arrest were similar to those of 30 microM Pd. We conclude that, in MDCK cells, Pd protects against CsA-induced cytotoxicity by suppressing ROS generation, although its protective effect is weaker than that of vitamin E.

Neuropathy and Fabry's disease

Fabry's disease is a multisystem disorder that is commonly associated with a painful, debilitating neuropathy. The common coexistence of arthralgias and an elevated erythrocyte sedimentation rate may lead to the misdiagnosis of a rheumatic condition. We report a 38-year-old man who was evaluated for progressive neuropathy and limb pain in the setting of longstanding arthralgias, presumed juvenile rheumatoid arthritis, and past renal transplantation. Histopathologic assessment of nerve and muscle biopsy specimens led to the diagnosis of Fabry's disease, thus allowing the patient to receive enzyme replacement therapy that may slow progression and preserve the transplanted kidney.

Immunosuppression and transplant vascular disease: benefits and adverse effects

Cardiac allograft vasculopathy (CAV) occurs within 5 years of transplantation surgery and represents the main cause of death in long-term heart transplant survivors. The detailed pathogenesis of CAV is unknown, but there are strong indications that immunologic mechanisms, which are regulated by nonimmunologic factors, are the major cause of this phenomenon. Cyclosporine A (CsA) is a frequently used immunosuppressive agent in transplant medicine to prevent rejection. The mechanism of action of CsA involves initial binding to cyclophilin to form a complex that then inhibits calcineurin (CN), leading to reduced interleukin (IL)-2 production as part of the signal transduction pathway for the activation of B-lymphocytes and T-lymphocytes. Based on this proposed mechanism, it was expected that CsA should be an effective strategy in attenuating the host immune response against transplanted allograft tissue; however, CsA has not changed the outcome of CAV. Several mechanisms have been suggested for the ineffectiveness of CsA in long-term prevention of CAV. For example, routine therapeutic doses of CsA may block CN incompletely (50%), whereas complete blockade requires doses that are not clinically tolerable. Another explanation is the possible activation of T-cell receptors directly (CN independent) by the immune response, which induces protein kinase C theta (PKCtheta) and leads to IL-2 production and immune rejection. Moreover, there may be a role for nonimmunologic mechanisms, such as complement, which cannot be controlled by CsA, or CsA may cause hypercholesterolemia or induce overexpression of transforming growth factor-beta (TGF-beta). This review also compares the effect of CsA with other immunosuppressants in allograft artery preservation and their clinical efficacy.

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.

Sirolimus: its discovery, biological properties, and mechanism of action

Sirolimus is the USAN-assigned generic name for the natural product rapamycin. Sirolimus is produced by a strain of Streptomyces hygroscopicus, isolated from a soil sample collected from Rapa Nui commonly known as Easter Island. Although sirolimus was isolated as an antifungal agent with potent anticandida activity, subsequent studies revealed impressive antitumor and immunosuppressive activities. Sirolimus demonstrates activity against several murine tumors, such as B16 43 melanocarcinoma, Colon 26 tumor, EM ependymoblastoma, and mammary and colon 38 solid tumors. Sirolimus is a potent inhibitor of antigen-induced proliferation of T cells, B cells, and antibody production. Demonstration of the potent immunosuppressive activity of sirolimus in animal models of organ transplantation led to clinical trials and subsequent approval by regulatory authorities for prophylaxis of renal graft rejection. Interest in sirolimus as an immunosuppressive therapy in organ transplantation derives from its unique mechanism of action, its unique side-effect profile, and its ability to synergize with other immunosuppressive agents. The molecular mechanism underlying the antifungal, antiproliferative, and immunosuppressive activities of sirolimus is the same. Sirolimus forms an immunosuppressive complex with intracellular protein, FKBP12. This complex blocks the activation of the cell-cycle-specific kinase, TOR. The downstream events that follow the inactivation of TOR result in the blockage of cell-cycle progression at the juncture of G1 and S phase.

Synthesis and biological evaluation of novel cyclosporin a analogues: potential soft drugs for the treatment of autoimmune diseases

Cyclosporin A is effective in the treatment of asthma patients, but its chronic use is limited by toxicity. Novel cyclosporin A analogues were synthesized utilizing the olefin metathesis reaction and evaluated in a calcineurin A inhibition assay. The novel analogues demonstrated activity comparable to activity of the parent molecule and are potential soft drugs.

Cardiovascular toxicities of immunosuppressive agents

Cardiovascular disease is one of the major causes of morbidity and mortality following solid organ transplantation. Many of the current immunosuppressive drugs are associated with an increase of one or more risk factors for the development of atherosclerosis. This review compares the mechanism by which individual immunosuppressive agents may impact on these risk factors and the differential contribution of cyclosporine, tacrolimus, mycophenolate, azathioprine, and Rapamycin to these individual risk factors. Attention to the potential cardiovascular toxicities of individual immunosuppressive agents may help design strategies for maintenance of immunosuppression tailored to individual patients.

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.

Reducing adverse effects of immunosuppressive agents in kidney transplant recipients

Success in solid organ transplantation with minimal complications can now be achieved for most patients, and a remarkable rate of graft and patient survival can also be expected. However, the potential for adverse events and comorbid conditions increases with longer graft survival. Although the immunosuppressive regimen is central to the outcome of the transplant recipient and directly impacts the survival of the graft, chronic use of immunosuppressive agents is associated with metabolic disturbances such as hypertension, hyperlipidemia, loss of bone density, nephrotoxicity, and diabetes, which may contribute to other comorbid conditions. In addition, changes in appearance, gingival hyperplasia, hirsutism, alopecia, and weight gain disrupt quality of life and may lead to noncompliance with the immunosuppressive regimen. New immunosuppressive medications, including mycophenolate mofetil, sirolimus, basiliximab, and daclizumab, have allowed for experimentation with new regimens designed to reduce or allow discontinuation of corticosteroids and calcineurin inhibitors. This review highlights the impact and cost of immunosuppressive side effects and the potential for new immunosuppressive regimens to reduce this substantial clinical burden in transplantation.

Contractile effects of tacrolimus in human and rat isolated renal arteries

1. We tested the vasoactive properties of the immunosuppressive drug FK 506 (tacrolimus) in preconstricted rat and human isolated renal arteries in vitro. 2. In rat renal arteries, tacrolimus (3, 10 microM) showed a direct and dose-dependent contractile effect by maximally 23 microm (10% of the noradrenaline effect), which was only observed in the presence of intact endothelium. Moreover, a lower concentration of tacrolimus (1 microM) potentiated pressor responses to the sympathetic neurotransmitter noradrenaline but not to ATP in this species. ATP- (0.01-10 microM) induced vasodilation was not affected by tacrolimus (1 microM). 3. In contrast, in human interlobar arteries, tacrolimus failed to induce direct vasoconstriction and did not significantly potentiate constrictor responses to noradrenaline. Acetylcholine-(1 microM) induced vasodilation was much smaller in human than in rat renal arteries suggesting the lack of functional endothelium in the human preparation. 4. The findings suggest that tacrolimus releases an endothelium-derived constricting factor in rat renal arteries to increase vascular tone and to potentiate pressor responses to noradrenaline. In human interlobar arteries, this effect of tacrolimus is not observed probably because of the absence of functional endothelium or the necessary mediator mechanism.

Cardiovascular risk factors in renal transplant patients: cyclosporin A versus tacrolimus

The hypertensive and hyperlipidemic effects of cyclosporin A (CsA) may contribute to the high cardiovascular morbidity in renal transplant patients and to the development of chronic transplant nephropathy. Tacrolimus is reported to have less effect on BP and lipids, but steroids, other drugs, and renal function may confound this. This study assessed 24-h BP and lipid profile in stable renal transplant recipients (n = 17) while they were receiving CsA, after 4 wk of receiving tacrolimus, and again after 4 wk of receiving CsA. Antihypertensives were stopped at least 3 wk before. A few patients used low-dose steroids and lipid-lowering drugs, which were not changed during the study. Mean daytime BP decreased from 149 +/- 12 and 95 +/- 8 mmHg to 138 +/- 13 and 87 +/- 9 mmHg (P: < 0.001) after patients were switched to tacrolimus. Mean nighttime BP also decreased, from 140 +/- 12/86 +/- 7 mmHg to 132 +/- 17/79 +/- 10 mmHg (P: < 0.05). Total and low-density lipoprotein cholesterol decreased from 6.1 +/- 0.7 and 3.84 +/- 0.79 mmol/L to 5.1 +/- 0.8 and 2.98 +/- 0.75 mmol/L (P: < 0.001). Return to CsA caused an increase in BP and cholesterol to values similar as during the first CsA period. The conclusion is that tacrolimus has fewer unfavorable effects on BP and lipids than does CsA. Elective conversion from CsA to tacrolimus in stable renal transplant recipients may lead to attenuation of cardiovascular morbidity and chronic transplant nephropathy in the long term.

Calcineurin inhibitors cause renal afferent activation in rats: a novel mechanism of cyclosporine-induced hypertension

Inhibition of calcineurin-mediated signaling in T lymphocytes is a major mechanism of cyclosporine A (CsA)-induced immunosuppression, and previous rat studies have suggested that inhibition of calcineurin-mediated signaling in central neuronal pools involved in blood pressure regulation plays an important role in causing acute CsA-induced hypertension. However, a central neural mechanism is difficult to reconcile with other data suggesting that CsA-induced hypertension is due to activation of renal and other subdiaphragmtic visceral afferents that reflexively increase efferent sympathetic nerve activity. Accordingly, we now have revised our hypothesis to suggest that CsA stimulates renal afferents by a calcineurin-dependent process. To test this new hypothesis, in anesthetized rats we recorded arterial pressure and multifiber afferent renal nerve activity from the cut distal end of the renal nerve before, during, and after intravenous infusion of either CsA (5 mg/kg over 20 min, n = 8), FK506 (0.15 mg/kg, n = 7), another potent calcineurin inhibitor that is structurally unrelated to CsA, or rapamycin (0.15 mg/kg, n = 4), a structural analog of FK506 that has no effect on calcineurin. We found that renal afferent discharge was increased markedly by intravenous FK506, as well as CsA, but unaffected by rapamycin (or vehicle), indicating calcineurin mediation. After infusion of either calcineurin inhibitor, afferent renal nerve activity remained elevated for up to 2 h, paralleling the prolonged increase in blood pressure. Thus, the major new conclusion of this study is that, in contrast to what has been assumed previously, calcineurin inhibitors enhance sympathetic neurotransmission by a novel action localized to visceral sensory nerve endings rather than to nerve cell bodies or central synapses. In the rat, calcineurin-dependent activation of renal afferents appears to be the primary mechanism producing the large blood-pressure-raising effect of CsA. Because the data suggest that the major side-effect of CsA and FK506--hypertension--is inexorably linked to calcineurin inhibition in extralymphoid tissue, development of agents that selectively inhibit calcineurin only in T lymphocytes could eliminate this important secondary form of hypertension.

Cyclosporine A-induced hypertension involves synapsin in renal sensory nerve endings

The calcineurin inhibitor cyclosporine A (CsA) has emerged as a major cause of secondary hypertension in humans, but the underlying pathogenetic mechanisms have remained enigmatic. Synapsins are a family of synaptic vesicle phosphoproteins that are essential for normal regulation of neurotransmitter release at synapses. In addition to synaptic vesicles, synapsins and other vesicle proteins are found on microvesicles in sensory nerve endings in peripheral tissues. However, the functions of the sensory microvesicles in general, and of synapsins in particular, are unknown. We now demonstrate in a mouse model that CsA raises blood pressure by stimulating renal sensory nerve endings that contain synapsin-positive microvesicles. In knockout mice lacking synapsin I and II, sensory nerve endings are normally developed but not stimulated by CsA whereas a control stimulus, capsaicin, is fully active. The reflex activation of efferent sympathetic nerve activity and the increase in blood pressure by CsA seen in control are greatly attenuated in synapsin-deficient mice. These results provide a mechanistic explanation for CsA-induced acute hypertension and suggest that synapsins could serve as a drug target in this refractory condition. Furthermore, these data establish evidence that synapsin-containing sensory microvesicles perform an essential role in sensory transduction and suggest a role for synapsin phosphorylation in this process.

A role for leukotrienes in cyclosporine nephrotoxicity

BACKGROUND

Nephrotoxicity associated with cyclosporine A (CsA) administration is characterized by marked renal vasoconstriction, interstitial fibrosis, and arteriolar hypertrophy. While the molecular mechanisms of CsA toxicity are not well characterized, previous studies have demonstrated that altered arachidonic acid (AA) metabolism plays a role its pathogenesis. Using a rat renal transplant model, the purpose of this study was to examine the effects of CsA on the 5-lipoxygenase (5-LO) pathway of AA metabolism.

METHODS

The PVG (RT1c) strain of rats underwent kidney transplantation, and recipients of nonrejecting kidney transplants were treated with either 50 mg/kg/day CsA or vehicle (N = 24). To determine the physiologic significance of increased leukotriene (LT) production, the peptidoleukotriene receptor antagonist SKF 106203 was administered to CsA-treated animals for six days.

RESULTS

CsA caused a substantial reduction in glomerular filtration rate (GFR) in the transplanted rats compared with the vehicle-treated controls (1.5 +/- 0.6 vs. 4.1 +/- 0.8 mL/min/kg, P < 0.05). The reduction in renal function was associated with enhanced urinary excretion of the peptidoleukotriene metabolites LTE4 (1431 +/- 207 vs. 953 +/- 125 pg/24 h, P < 0.05) and N-acetyl-LTE4 (4411 +/- 848 vs. 463 +/- 70 pg/24 h, P < 0.001). LT receptor blockade had a significant protective effect on renal transplant function in CsA-treated animals (GFR, 4.8 +/- 1.1 vs. 1.7 +/- 0.9 mL/min/kg, P < 0.05), such that CsA-treated animals that received SKF106203 maintained GFR at levels similar to controls that never received CsA (4.1 +/- 0.8 mL/min/kg). Peptidoleukotriene receptor blockade also prevented the histomorphological abnormalities caused by CsA, including tubular vacuolization.

CONCLUSIONS

These studies identify a critical role for LTs in the pathophysiology of CsA nephrotoxicity and suggest that LT antagonists may be useful in preventing CsA-associated kidney toxicity.

Mechanisms of hypertension after renal transplantation

Hypertension is extremely prevalent after renal transplantation, affecting up to 70% of all patients. An elevation in blood pressure is associated with an increased cardiovascular risk and may also contribute to chronic allograft failure. Renal transplantation provides interesting insights into the pathogenesis of hypertension. Experimental and human data show that the kidney is an essential organ for blood pressure regulation. In clinical practice a differential diagnosis that is based on excretory allograft function has proved useful.

Mechanism of FK 506/520 action on rat renal proximal tubular Na+, K+-ATPase activity

BACKGROUND

The neurotransmitter in renal sympathetic nerves, norepinephrine (NE), regulates the activity of proximal tubule (PT) Na+,K+-ATPase in a bidirectional manner via stimulation of alpha- and beta-adrenoceptors. The stimulatory alpha-adrenergic pathway is mediated by calcineurin, the target molecule for FK 506 and related compounds. We examined whether the FK 506 analogue FK 520, by interrupting the calcineurin-mediated alpha-adrenergic signaling pathway, enhance the inhibitory beta-adrenergic effect of NE on PT Na+,K+-ATPase activity.

METHODS

The effects of three days of treatment with FK 520 were examined on rat renal PT Na+,K+-ATPase activity, measured as ouabain-sensitive ATP hydrolysis in single, microdissected PT segments. Renal function studies, including glomerular filtration rate (GFR) and urinary excretion of N-acetyl-3-D-glucoseaminidase (NAG), were examined using conventional clearance techniques after three days of treatment with FK 506.

RESULTS

FK 520 treatment induced a pronounced and dose-dependent decrease in PT Na+,K+-ATPase activity. This effect was completely reversed by the competitive FK 520 antagonist, L 685 818, indicating that the effect was dependent on inhibition of calcineurin. To test whether the FK 520-induced decrease in Na+, K+-ATPase activity was mediated by enhanced beta-adrenoceptor signaling, the FK 520 effect was examined in rats pretreated with a beta-adrenoceptor antagonist (propranolol) or rats subjected to renal denervation. Both of these procedures prevented the FK 520-induced decrease in Na+,K+-ATPase activity. Thus, during FK 520 treatment, renal sympathetic nerves mediate an inhibitory effect on PT Na+,K+-ATPase activity via beta-adrenoceptors. Propranolol pretreatment also prevented FK 506-induced decreases in GFR and urinary excretion of NAG, an index of PT dysfunction.

CONCLUSIONS

The results support the hypothesis that the net effect of the neurotransmitter NE on Na+,K+-ATPase activity is dependent on the balance between the alpha- and beta-adrenergic signaling pathways and suggest that agents that interfere with these pathways may, by altering the activity of tubular Na+,K+-ATPase, also alter the function of the renal tubular epithelial cell.

Potent immunosuppressive C32-O-arylethyl ether derivatives of ascomycin with reduced toxicity

The synthesis of C32-O-arylethyl ether derivatives of ascomycin that possess equivalent immunosuppressant activity but reduced toxicity, compared to FK-506, is described.

Effects of FK506 in rat and human resistance arteries

BACKGROUND

FK506 is widely used in organ transplantation and causes hypertension. However, little is known about the impact of the drug on the cardiovascular system.

METHODS

We therefore investigated the effect of FK506 on resistance artery and blood pressure responsiveness to vasoconstrictors and vasodilators. Studies were conducted in vitro using human and murine resistance artery, ex vivo in resistance artery isolated from rats treated with FK506 (6 mg/kg/day), and in vivo in conscious, treated animals.

RESULTS

In vitro exposure (24 hr) of human and rat resistance artery to FK506 (1000 ng/ml) increased the sensitivity to norepinephrine (NE) and impaired the response to acetylcholine (Ach) and sodium nitroprusside (SNp). In contrast, arteries isolated from rats given FK506 for eight days showed a reduced sensitivity to NE (P < 0.05) and a normal endothelium-dependent relaxation. Their incubation with L-arginine caused a significant reduction in Ach sensitivity in the FK506 group (P < 0.05) but not in controls, suggesting enhancement of nitric oxide production by the drug. The sensitivity to SNp was reduced, as in the in vitro experiments (P < 0.05). Rats given FK506 for eight days presented blood pressure similar to that in controls but also presented signs of a compensatory response to excess vasodilation: tachycardia (P < 0.01), reduced blood pressure sensitivity to NE and Ach, blunted heart rate response to both agonists, and exaggerated hypotension at high doses of Ach. After 21 days of treatment, blood pressure remained similar to that in controls, but resistance artery showed further functional deterioration, with significant impairment of the maximum responses to Ach and to SNp.

CONCLUSION

FK506 presents significant vascular toxicity affecting mainly smooth muscle relaxation and alters vascular hemodynamics. The data suggest that similar cardiovascular changes may occur in transplant patients and represent the forerunner of hypertension often seen with more prolonged use of the drug.

Blood pressure control in kidney transplant recipients: influence of immunosuppression

1. Disturbances of the blood pressure regulation, probably due to dysfunction of the autonomic nervous system, are well known complications in chronic renal failure. Haemodialysis and transplantation have been reported to ameliorate nerve dysfunction. 2. In this study, the function of the blood pressure control was investigated in kidney transplant recipients after longtime haemodialysis treated with ciclosporine A and tacrolimus and compared to healthy individuals. To investigate the influence of immunosuppression, the measurements were performed twice, at low and high whole blood concentrations of ciclosporine and tacrolimus. Besides ciclosporine, tacrolimus, azathioprine and prednisolone no other drugs were used in the group of kidney transplant recipients. 3. Kidney transplant recipients (KTR) treated with ciclosporine showed reduced blood pressure and heart rate responses to the cardiovascular stress tests (head-up tilt and cold pressure test) under basal conditions. Two hours after ciclosporine application, the differences in the responses to cardiovascular stress tests between KTR and controls were significantly more pronounced. 4. Patients with tacrolimus immunosuppression showed a similar blood pressure and heart rate response under basal conditions. Two hours after drug application, the blood pressure response following orthostatism and heart rate response to the cold pressure test were significantly higher in tacrolimus treated patients. 5. Our results indicate, that kidney transplant recipients still express an altered function of the blood pressure control. Furthermore, ciclosporine A and tacrolimus seem to contribute to dysfunction of the blood pressure regulation by their own. Tacrolimus immunosuppression does not seem to offer advantages concerning the function of the blood pressure control as compared to ciclosporine A.