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

Deciphering the mitochondria-inflammation axis: Insights and therapeutic strategies for heart failure

Heart failure (HF) is a clinical syndrome resulting from left ventricular systolic and diastolic dysfunction, leading to significant morbidity and mortality worldwide. Despite improvements in medical treatment, the prognosis of HF patients remains unsatisfactory, with high rehospitalization rates and substantial economic burdens. The heart, a high-energy-consuming organ, relies heavily on ATP production through oxidative phosphorylation in mitochondria. Mitochondrial dysfunction, characterized by impaired energy production, oxidative stress, and disrupted calcium homeostasis, plays a crucial role in HF pathogenesis. Additionally, inflammation contributes significantly to HF progression, with elevated levels of circulating inflammatory cytokines observed in patients. The interplay between mitochondrial dysfunction and inflammation involves shared risk factors, signaling pathways, and potential therapeutic targets. This review comprehensively explores the mechanisms linking mitochondrial dysfunction and inflammation in HF, including the roles of mitochondrial reactive oxygen species (ROS), calcium dysregulation, and mitochondrial DNA (mtDNA) release in triggering inflammatory responses. Understanding these complex interactions offers insights into novel therapeutic approaches for improving mitochondrial function and relieving oxidative stress and inflammation. Targeted interventions that address the mitochondria-inflammation axis hold promise for enhancing cardiac function and outcomes in HF patients.

Renal Denervation in the Treatment of Resistant Hypertension and Difficult-to-Control Hypertension - Consensus Document of the Croatian Hypertension League - Croatian Society of Hypertension, Croatian Cardiac Society, Croatian Endovascular Initiative, Croatian Society for Diabetes and Metabolic Diseases, Croatian Renal Association, and Croatian Society of Family Physicians of the Croatian Medical Association

Renal denervation (RDN) as a method of treating arterial hypertension (AH) was introduced in Croatia in 2012. A multidisciplinary team and a network of hospitals that diagnose and treat patients with severe forms of AH were established, and a very strict diagnostic-treatment algorithm was prepared. At monthly meetings patients with truly resistant hypertension who were candidates for RDN were discussed. According to the 2021 ESH position statement and 2023 ESH guidelines, RDN is considered an alternative and additional, not a competitive method of treating patients with various forms of AH which must be performed by following a structured procedure and the patient's preference should be considered. In view of the changes in the global scientific community, the Croatian Hypertension League brings this consensus document on RDN conducted with radiofrequency-based catheter, the only currently available method in Croatia. In this document, exclusion and inclusion criteria are shown, as well as three groups of patients in whom RDN could be considered. The new diagnostic-treatment algorithm is prepared and follow-up procedure is explained. In Croatia, RDN is reimbursed by the national insurance company, thus pharmacoeconomic analyses is also shown. Criteria required by an individual centre to be approved of RDN are listed, and plans for prospective research on RDN in Croatia, including the Croatian registry for RDN, are discussed.

Cyclosporine A Decreases Dryness-Induced Hyperexcitability of Corneal Cold-Sensitive Nerve Terminals

Cyclosporine A (CsA) is used for the treatment of dry eye (DE) with good clinical results, improving tear secretion and decreasing subjective symptoms. These effects are attributed to the improved tear film dynamics, but there are no data on the effect of CsA on the abnormal sensory nerve activity characteristic in DE. Our purpose was to evaluate the CsA effect on the enhanced activity of corneal cold thermoreceptors in a tear-deficient DE animal model using in vitro extracellular recording of cold thermoreceptors nerve terminal impulses (NTIs) before and in the presence of CsA. NTI shape was also analyzed. Blinking frequency and tearing rate were also measured in awake animals before and after topical CsA. CsA increased the tearing and blinking of treated animals. CsA significantly decreased the peak response to cold of cold thermoreceptors. Neither their spontaneous NTIs discharge rate nor their cooling threshold were modified. CsA also seemed to reverse some of the changes in NTI shape induced by tear deficiency. These data suggest that, at least in part, the beneficial clinical effects of CsA in DE can be attributed to a direct effect on sensory nerve endings, although the precise mechanisms underlying this effect need further studies to be fully clarified.

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.

Effect of Probiotics Supplementation on Heart Rate: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

Background and Aims

Probiotics consumption lowers the risk of cardiovascular disease, but whether it affects heart rate (HR) remains controversial. Therefore, our study aimed to assess the chronotropic effects of probiotics on heartbeat via a meta-analysis of randomized clinical trials.

Methods

Relevant studies were identified by searching PubMed, Cochrane library, and Clinical Trials databases up to October 2021. Either a fixed-effects or a random-effects model was used to calculate the pooled effect sizes and 95% confidence intervals (CIs).

Results

This meta-analysis included 13 studies involving 16 interventional trial arms and 931 participants according to inclusion criteria. The overall pooled estimate showed that probiotics supplementation had a slight, but no significant reduction of 0.28 bpm (95% CI: −1.17, 0.60) on HR. Relatively high heterogeneity was observed among included trials (I² = 80.8%, P heterogeneity < 0.001). Subgroup analysis displayed that probiotics supplementation significantly reduced HR by 2.94 bpm (95% CI: −5.06, −0.82) among participants with baseline HR ≥ 75 bpm, by 1.17 bpm (95% CI: −2.34, −0.00) with probiotics dose ≥1 × 10¹⁰ CFU/day, and by 1.43 bpm (95% CI: −2.69, −0.17) with multiple-strain intervention. Meta-regression analysis showed that baseline HR was a major potential effect modifier of probiotics supplementation on lowering HR.

Conclusion

Hitherto, the overall evidence in the literature was insufficient to support the notion that probiotics supplementation has a class effect on HR reduction. However, in subgroup analysis, probiotics reduced HR significantly in those who had higher baseline HR, received a higher dose or multiple strains of probiotics.

Approach and Management of Hypertension After Kidney Transplantation

Hypertension is one of the most common cardiovascular co-morbidities after successful kidney transplantation. It commonly occurs in patients with other metabolic diseases, such as diabetes mellitus, hyperlipidemia, and obesity. The pathogenesis of post-transplant hypertension is complex and is a result of the interplay between immunological and non-immunological factors. Post-transplant hypertension can be divided into immediate, early, and late post-transplant periods. This classification can help clinicians determine the etiology and provide the appropriate management for these complex patients. Volume overload from intravenous fluid administration is common during the immediate post-transplant period and commonly contributes to hypertension seen early after transplantation. Immunosuppressive medications and donor kidneys are associated with post-transplant hypertension occurring at any time point after transplantation. Transplant renal artery stenosis (TRAS) and obstructive sleep apnea (OSA) are recognized but common and treatable causes of resistant hypertension post-transplantation. During late post-transplant period, chronic renal allograft dysfunction becomes an additional cause of hypertension. As these patients develop more substantial chronic kidney disease affecting their allografts, fibroblast growth factor 23 (FGF23) increases and is associated with increased cardiovascular and all-cause mortality in kidney transplant recipients. The exact relationship between increased FGF23 and post-transplant hypertension remains poorly understood. Blood pressure (BP) targets and management involve both non-pharmacologic and pharmacologic treatment and should be individualized. Until strong evidence in the kidney transplant population exists, a BP of <130/80 mmHg is a reasonable target. Similar to complete renal denervation in non-transplant patients, bilateral native nephrectomy is another treatment option for resistant post-transplant hypertension. Native renal denervation offers promising outcomes for controlling resistant hypertension with no significant procedure-related complications. This review addresses the epidemiology, pathogenesis, and specific etiologies of post-transplant hypertension including TRAS, calcineurin inhibitor effects, OSA, and failed native kidney. The cardiovascular and survival outcomes related to post-transplant hypertension and the utility of 24-h blood pressure monitoring will be briefly discussed. Antihypertensive medications and their mechanism of actions relevant to kidney transplantation will be highlighted. A summary of guidelines from different professional societies for BP targets and antihypertensive medications as well as non-pharmacological interventions, including bilateral native nephrectomy and native renal denervation, will be reviewed.

Identifying New Substrates and Functions for an Old Enzyme: Calcineurin

Biological processes are dynamically regulated by signaling networks composed of protein kinases and phosphatases. Calcineurin, or PP3, is a conserved phosphoserine/phosphothreonine-specific protein phosphatase and member of the PPP family of phosphatases. Calcineurin is unique, however, in its activation by Ca2+ and calmodulin. This ubiquitously expressed phosphatase controls Ca2+-dependent processes in all human tissues, but is best known for driving the adaptive immune response by dephosphorylating the nuclear factor of the activated T-cells (NFAT) family of transcription factors. Therefore, calcineurin inhibitors, FK506 (tacrolimus), and cyclosporin A serve as immunosuppressants. We describe some of the adverse effects associated with calcineurin inhibitors that result from inhibition of calcineurin in nonimmune tissues, illustrating the many functions of this enzyme that have yet to be elucidated. In fact, calcineurin has essential roles beyond the immune system, from yeast to humans, but since its discovery more than 30 years ago, only a small number of direct calcineurin substrates have been shown (∼75 proteins). This is because of limitations in current methods for identification of phosphatase substrates. Here we discuss recent insights into mechanisms of calcineurin activation and substrate recognition that have been critical in the development of novel approaches for identifying its targets systematically. Rather than comprehensively reviewing known functions of calcineurin, we highlight new approaches to substrate identification for this critical regulator that may reveal molecular mechanisms underlying toxicities caused by calcineurin inhibitor-based immunosuppression.

Calcineurin dephosphorylates Kelch-like 3, reversing phosphorylation by angiotensin II and regulating renal electrolyte handling

Calcineurin inhibitors (CNIs) are potent immunosuppressants; hypertension and hyperkalemia are common adverse effects. Activation of the renal Na-Cl cotransporter (NCC) is implicated in this toxicity; however, the mechanism is unknown. CNIs’ renal effects mimic the hypertension and hyperkalemia resulting from mutations in WNK kinases or in KLHL3-CUL3 ubiquitin ligase. WNKs activate NCC and are degraded by ubiquitylation upon their binding to KLHL3. The binding of WNKs to KLHL3 is prevented by KLHL3 mutations or by PKC-mediated KLHL3 phosphorylation at serine 433. This work shows that calcineurin dephosphorylates KLHL3^S433, promoting WNK4 degradation. Conversely, CNIs inhibit KLHL3^S433 dephosphorylation, preventing WNK degradation. These findings implicate calcineurin in the normal regulation of KLHL3’s binding of WNK4 and identify a direct target causing CNI-induced pathology.

Calcineurin is a calcium/calmodulin-regulated phosphatase known for its role in activation of T cells following engagement of the T cell receptor. Calcineurin inhibitors (CNIs) are widely used as immunosuppressive agents; common adverse effects of CNIs are hypertension and hyperkalemia. While previous studies have implicated activation of the Na-Cl cotransporter (NCC) in the renal distal convoluted tubule (DCT) in this toxicity, the molecular mechanism of this effect is unknown. The renal effects of CNIs mimic the hypertension and hyperkalemia that result from germ-line mutations in with-no-lysine (WNK) kinases and the Kelch-like 3 (KLHL3)–CUL3 ubiquitin ligase complex. WNK4 is an activator of NCC and is degraded by binding to KLHL3 followed by WNK4’s ubiquitylation and proteasomal degradation. This binding is prevented by phosphorylation of KLHL3 at serine 433 (KLHL3^S433-P) via protein kinase C, resulting in increased WNK4 levels and increased NCC activity. Mechanisms mediating KLHL3^S433-P dephosphorylation have heretofore been unknown. We now demonstrate that calcineurin expressed in DCT is a potent KLHL3^S433-P phosphatase. In mammalian cells, the calcium ionophore ionomycin, a calcineurin activator, reduces KLHL3^S433-P levels, and this effect is reversed by the calcineurin inhibitor tacrolimus and by siRNA-mediated knockdown of calcineurin. In vivo, tacrolimus increases levels of KLHL3^S433-P, resulting in increased levels of WNK4, phosphorylated SPAK, and NCC. Moreover, tacrolimus attenuates KLHL3-mediated WNK4 ubiquitylation and degradation, while this effect is absent in KLHL3 with S433A substitution. Additionally, increased extracellular K⁺ induced calcineurin-dependent dephosphorylation of KLHL3^S433-P. These findings demonstrate that KLHL3^S433-P is a calcineurin substrate and implicate increased KLHL3 phosphorylation in tacrolimus-induced pathologies.

Activation of central GABAB receptors offsets the cyclosporine counteraction of endotoxic cardiovascular outcomes in conscious rats

We have previously shown that cyclosporine (CSA) counteracts cardiovascular manifestations induced by endotoxemia (lipopolysaccharide, LPS) such as hypotension and cardiac autonomic dysfunction in conscious rats. In this study, we investigated whether the facilitation of central γ-amino butyric acid (GABA) neurotransmission blunts these favorable influences of CSA. The LPS-CSA interaction was determined in the absence and presence of drugs that activate GABA_A or GABA_B receptors or elevate synaptic GABA levels in the central nervous system. The consequent i.v. administration of CSA (10 mg/kg) blunted the LPS-evoked hypotension, tachycardia, and reductions in time- and frequency-domain indices of heart rate variability (measures of cardiac autonomic control) evoked by LPS (10 mg/kg i.v.). The ability of CSA to reverse the LPS effects disappeared in rats treated intracisternally (i.c.) with baclofen (selective GABA_B agonist, 2 μg/rat) but not muscimol (selective GABA_A agonist, 1 μg/rat), indicating a preferential compromising action for central GABA_B receptors on the advantageous effects of CSA. Moreover, the improvement by CSA of LPS-evoked cardiovascular derangements was also eliminated after concurrent i.c. administration of vigabatrin (GABA transaminase inhibitor, 200 μg/rat) or tiagabine (GABA reuptake inhibitor, 100 μg/rat). These results demonstrate that the activation of central GABA_B receptors either directly via baclofen or indirectly following interventions that boost GABA levels in central synapses counterbalances the rectifying action of CSA on endotoxemia.

Novel Approach for Simultaneous Recording of Renal Sympathetic Nerve Activity and Blood Pressure with Intravenous Infusion in Conscious, Unrestrained Mice

Renal sympathetic nerves contribute significantly to both physiological and pathophysiological phenomena. Evaluating renal sympathetic nerve activity (RSNA) is of great interest in many areas of research such as chronic kidney disease, hypertension, heart failure, diabetes and obesity. Unequivocal assessment of the role of the sympathetic nervous system is thus imperative for proper interpretation of experimental results and understanding of disease processes. RSNA has been traditionally measured in anesthetized rodents, including mice. However, mice usually exhibit very low systemic blood pressure and hemodynamic instability for several hours during anesthesia and surgery. Meaningful interpretation of RSNA is confounded by this non-physiological state, given the intimate relationship between sympathetic nervous tone and cardiovascular status. To address this limitation of traditional approaches, we developed a new method for measuring RSNA in conscious, freely-moving mice. Mice were chronically instrumented with radio-telemeters for continuous monitoring of blood pressure as well as a jugular venous infusion catheter and custom-designed bipolar electrode for direct recording of RSNA. Following a 48-72 hour recovery period, survival rate was 100% and all mice behaved normally. At this time-point, RSNA was successfully recorded in 80% of mice, with viable signals acquired up to 4 and 5 days post-surgery in 70% and 50% of mice, respectively. Physiological blood pressures were recorded in all mice (116±2 mmHg; n=10). Recorded RSNA increased with eating and grooming, as well-established in the literature. Furthermore, RSNA was validated by ganglionic blockade and modulation of blood pressure with pharmacological agents. Herein, an effective and manageable method for clear recording of RSNA in conscious, freely-moving mice is described.

Pathophysiological mechanisms of calcineurin inhibitor-induced nephrotoxicity and arterial hypertension

Solid organ transplantation is an established treatment modality in patients with end-stage organ damage in cases where other therapeutic options fail. The long-term outcomes of solid organ transplant recipients have improved considerably since the introduction of the first calcineurin inhibitor (CNI) - cyclosporine. In 1984, the potent immunosuppressive properties of another CNI, tacrolimus, were discovered. The immunosuppressive effects of CNIs result from the inhibition of interleukin-2 synthesis and reduced proliferation of T cells due to calcineurin blockade. The considerable side effects that are associated with CNIs therapy include arterial hypertension and nephrotoxicity. The focus of this article was to review the available literature on the pathophysiological mechanisms of CNIs that induce chronic nephrotoxicity and arterial hypertension. CNIs lead to activation of the major vasoconstriction systems, such as the renin-angiotensin and endothelin systems, and increase sympathetic nerve activity. On the other hand, CNIs are known to inhibit NO synthesis and NO-mediated vasodilation and to increase free radical formation. Altogether, these processes cause endothelial dysfunction and contribute to the impairment of organ function. A better insight into the mechanisms underlying CNI nephrotoxicity could assist in developing more targeted therapies of arterial hypertension or preventing CNI nephrotoxicity in organ transplant recipients, including heart transplantation.

Increased synapsin I expression in cerebral malaria

Synapsin I is a neuronal phosphoprotein contained in the synaptic vesicles of mammalian central and peripheral nervous systems. It regulates both neurotransmitter release and synaptic formation. Variations in synapsin I expression in the brain have been reported to cause brain malfunction. In severe malaria, neurological complications, such as convulsion, delirium and coma, suggest abnormalities in the release of neurotransmitters. This study evaluated synapsin I expression in cerebral malaria (CM). An immunohistochemical method was used to study the semi-quantitative and qualitative expression of synapsin I in the brain of CM patients (10 cases) who died with Plasmodium falciparum, compared with non-cerebral malaria (NCM) (4 cases), and control brain tissues (5). Synapsin I was expressed in the gray matter of the cerebral cortex and the molecular layer of the cerebellum, as a diffusely dense precipitate pattern in the neuropil, with no immunoreactivity in the neurons, neuronal dendrites, glial cells, endothelial cells, and Purkinje cells. The findings were similarly demonstrated in CM, NCM, and control brain tissues. However, in the granular layer of the cerebellum, a significant increase in synapsin I expression was observed in the granule cells, and the glomerular synaptic complex, from the CM group, compared with the NCM, and control brain tissues (all P < 0.05). Parasitemia showed a positive correlation with synapsin I expression in the granule cells (on admission: Spearman's ρ = 0.600, P = 0.023) (before death: Spearman's ρ = 0.678, P = 0.008), and glomerular synaptic complex (before death: Spearman's ρ = 0.571, P = 0.033). It was hypothesized that CM causes pre-synaptic excitation and eventually activation of synapsin I, leading to increased neurotransmitter release. Synapsin I inhibitor should be investigated further as a target for a therapeutic intervention to alleviate neurological symptoms in severe malaria.

Pathophysiology of resistant hypertension in chronic kidney disease

Hypertension associated with chronic kidney diseases often is resistant to drug treatment. This review deals with two main aspects of the management of CKD patients with hypertension: the role of sodium/volume and the need for dietary salt restriction, as well as appropriate use of diuretics and what currently is called sequential nephron blockade; the second aspect that is addressed extensively in this review is the role of the sympathetic nervous system and the possible clinical use of renal denervation.

Renal Denervation Prevents Immune Cell Activation and Renal Inflammation in Angiotensin II-Induced Hypertension

RATIONALE

Inflammation and adaptive immunity play a crucial role in the development of hypertension. Angiotensin II and probably other hypertensive stimuli activate the central nervous system and promote T-cell activation and end-organ damage in peripheral tissues.

OBJECTIVE

To determine if renal sympathetic nerves mediate renal inflammation and T-cell activation in hypertension.

METHODS AND RESULTS

Bilateral renal denervation using phenol application to the renal arteries reduced renal norepinephrine levels and blunted angiotensin II-induced hypertension. Bilateral renal denervation also reduced inflammation, as reflected by decreased accumulation of total leukocytes, T cells, and both CD4+ and CD8+ T cells in the kidney. This was associated with a marked reduction in renal fibrosis, albuminuria, and nephrinuria. Unilateral renal denervation, which partly attenuated blood pressure, only reduced inflammation in the denervated kidney, suggesting that this effect is pressure independent. Angiotensin II also increased immunogenic isoketal-protein adducts in renal dendritic cells (DCs) and increased surface expression of costimulation markers and production of interleukin (IL)-1α, IL-1β, and IL-6 from splenic DCs. Norepinephrine also dose dependently stimulated isoketal formation in cultured DCs. Adoptive transfer of splenic DCs from angiotensin II-treated mice primed T-cell activation and hypertension in recipient mice. Renal denervation prevented these effects of hypertension on DCs. In contrast to these beneficial effects of ablating all renal nerves, renal afferent disruption with capsaicin had no effect on blood pressure or renal inflammation.

CONCLUSIONS

Renal sympathetic nerves contribute to DC activation, subsequent T-cell infiltration and end-organ damage in the kidney in the development of hypertension.

AKAP150 contributes to enhanced vascular tone by facilitating large-conductance Ca2+-activated K+ channel remodeling in hyperglycemia and diabetes mellitus

RATIONALE

Increased contractility of arterial myocytes and enhanced vascular tone during hyperglycemia and diabetes mellitus may arise from impaired large-conductance Ca(2+)-activated K(+) (BKCa) channel function. The scaffolding protein A-kinase anchoring protein 150 (AKAP150) is a key regulator of calcineurin (CaN), a phosphatase known to modulate the expression of the regulatory BKCa β1 subunit. Whether AKAP150 mediates BKCa channel suppression during hyperglycemia and diabetes mellitus is unknown.

OBJECTIVE

To test the hypothesis that AKAP150-dependent CaN signaling mediates BKCa β1 downregulation and impaired vascular BKCa channel function during hyperglycemia and diabetes mellitus.

METHODS AND RESULTS

We found that AKAP150 is an important determinant of BKCa channel remodeling, CaN/nuclear factor of activated T-cells c3 (NFATc3) activation, and resistance artery constriction in hyperglycemic animals on high-fat diet. Genetic ablation of AKAP150 protected against these alterations, including augmented vasoconstriction. d-glucose-dependent suppression of BKCa channel β1 subunits required Ca(2+) influx via voltage-gated L-type Ca(2+) channels and mobilization of a CaN/NFATc3 signaling pathway. Remarkably, high-fat diet mice expressing a mutant AKAP150 unable to anchor CaN resisted activation of NFATc3 and downregulation of BKCa β1 subunits and attenuated high-fat diet-induced elevation in arterial blood pressure.

CONCLUSIONS

Our results support a model whereby subcellular anchoring of CaN by AKAP150 is a key molecular determinant of vascular BKCa channel remodeling, which contributes to vasoconstriction during diabetes mellitus.

Hemodynamic response to propranolol in patients with recurrent hepatitis C virus-related cirrhosis after liver transplantation: a case-control study

Cirrhosis recurrence is frequent after orthotopic liver transplantation for hepatitis C virus (HCV). Because transplantation causes liver denervation, we hypothesized that the response to propranolol might differ in transplant patients versus nontransplant patients with cirrhosis and portal hypertension. Twenty-one patients with cirrhosis recurrence after orthotopic liver transplantation with portal hypertension were compared to 20 nontransplant patients with cirrhosis, HCV, and portal hypertension, and they were matched by sex, age, presence of varices, and Child-Pugh score. The patients underwent systemic and hepatic hemodynamic measurements at the baseline and 20 minutes after intravenous propranolol (0.15 mg/kg). At the baseline, the transplant patients with cirrhosis had a lower hepatic venous pressure gradient (HVPG) than the nontransplant patients with cirrhosis (14.8 ± 2.9 versus 17.3 ± 4.4 mm Hg, P = 0.03) but a higher mean arterial pressure (MAP; 100.3 ± 12.3 versus 91.8 ± 11.6 mm Hg, P = 0.04) and higher systemic vascular resistance (2253 ± 573 versus 1883 ± 525 dyn/second/cm(-5) , P = 0.03). There were no differences in the cardiac index (CI). Propranolol significantly decreased HVPG to similar extents in transplant patients and nontransplant patients with cirrhosis (-14.1% ± 8.0% versus -16.9% ± 9.5%, P > 0.99). MAP tended to increase in transplant patients with cirrhosis, whereas it slightly decreased in nontransplant patients (5.1% ± 14.2% versus -4.8% ± 6.4%, P = 0.007); however, the reduction in CI was less marked in transplant patients with cirrhosis (-18.6% ± 7.6% versus -26.9% ± 9.0%, P = 0.005). In conclusion, patients with HCV-related cirrhosis and portal hypertension after orthotopic liver transplantation have lower baseline HVPG values but similar HVPG responses to propranolol infusions in comparison with nontransplant patients with cirrhosis. In contrast to nontransplant patients, propranolol increases the systemic vascular resistance and arterial pressure in transplant patients with cirrhosis and attenuates the fall in CI.

Neurobehavioural activation during peripheral immunosuppression

Like other physiological responses, immune functions are the subject of behavioural conditioning. Conditioned immunosuppression can be induced by contingently pairing a novel taste with an injection of the immunosuppressant cyclosporine A (CsA) in an associative learning paradigm. This learned immunosuppression is centrally mediated by the insular cortex and the amygdala. However, the afferent mechanisms by which the brain detects CsA are not understood. In this study we analysed whether CsA is sensed via the chemosensitive vagus nerve or whether CsA directly acts on the brain. Our experiments revealed that a single peripheral administration of CsA increases neuronal activity in the insular cortex and the amygdala as evident from increased electric activity, c-Fos expression and amygdaloid noradrenaline release. However, this increased neuronal activity was not affected by prior vagal deafferentation but rather seems to partially be induced by direct action of CsA on cortico-amygdaloid structures and the chemosensitive brainstem regions area postrema and nucleus of the solitary tract. Together, these data indicate that CsA as an unconditioned stimulus may directly act on the brain by a still unknown transduction mechanism.

Calcineurin activity in children with Mental handicap

Calcineurin, a Ca(2+)-Calmodulin dependent protein phosphatase, is important for Ca(2+) mediated signal transduction. The main objective of this study was to examine the potential role of calcineurin in idiopathic mental handicap. Calcineurin levels were estimated in 20 children in the age group of 5-16 years with idiopathic mental handicap attending the Special. Education Centre for the Mentally Handicapped in Hyderabad. The results of the present study showed decreased activity of serum calcineurin in children with idiopathic mental handicap compared to those of normal subjects in the same age group. The observations thus suggest impaired calcineurin activity in children with mental handicap. Calcineurin that is involved in biosynthesis and release of neurotransmitters at the synaptic terminal brain is affected thereby causing brain damage and leading to mental handicap. Impaired calcineurin activity was already indicated in many human diseases such as Down's syndrome, Alzheimers, Brain ischemia, cardiac hypertrophy etc. It is therefore necessary to check the calcineurin levels in children with mental handicap to understand the role of calcineurin in the causation of Mental handicap.

Proteomic response to acupuncture treatment in spontaneously hypertensive rats

Previous animal and clinical studies have shown that acupuncture is an effective alternative treatment in the management of hypertension, but the mechanism is unclear. This study investigated the proteomic response in the nervous system to treatment at the Taichong (LR3) acupoint in spontaneously hypertensive rats (SHRs). Unanesthetized rats were subject to 5-min daily acupuncture treatment for 7 days. Blood pressure was monitored over 7 days. After euthanasia on the 7^th day, rat medullas were dissected, homogenized, and subject to 2D gel electrophoresis and MALDI-TOF analysis. The results indicate that blood pressure stabilized after the 5th day of acupuncture, and compared with non-acupoint treatment, Taichong-acupunctured rat’s systolic pressure was reduced significantly (P<0.01), though not enough to bring blood pressure down to normal levels. The different treatment groups also showed differential protein expression: the 2D images revealed 571±15 proteins in normal SD rats’ medulla, 576±31 proteins in SHR’s medulla, 597±44 proteins in medulla of SHR after acupuncturing Taichong, and 616±18 proteins in medulla of SHR after acupuncturing non-acupoint. In the medulla of Taichong group, compared with non-acupoint group, seven proteins were down-regulated: heat shock protein-90, synapsin-1, pyruvate kinase isozyme, NAD-dependent deacetylase sirtuin-2, protein kinase C inhibitor protein 1, ubiquitin hydrolase isozyme L1, and myelin basic protein. Six proteins were up-regulated: glutamate dehydrogenase 1, aldehyde dehydrogenase 2, glutathione S-transferase M5, Rho GDP dissociation inhibitor 1, DJ-1 protein and superoxide dismutase. The altered expression of several proteins by acupuncture has been confirmed by ELISA, Western blot and qRT-PCR assays. The results indicate an increase in antioxidant enzymes in the medulla of the SHRs subject to acupuncture, which may provide partial explanation for the antihypertensive effect of acupuncture. Further studies are warranted to investigate the role of oxidative stress modulation by acupuncture in the treatment of hypertension.

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.

Direct recording of renal sympathetic nerve activity in unrestrained, conscious mice

Renal sympathetic nerve activity (RSNA) has been measured in anesthetized mice. However, anesthesia and acute surgical preparation cause poor cardiovascular stability and unphysiological blood pressures. This compromised physiological state confounds proper interpretation of experimental results considering the inseparable link between cardiovascular status and autonomic nervous tone. We, therefore, developed a surgical and experimental protocol for measuring RSNA in conscious, unrestrained mice. Male C57Bl/6J mice were chronically instrumented with blood pressure radiotelemeters, an indwelling jugular venous catheter and a bipolar electrode for recording RSNA. Mice were placed in a home cage and left to recover for 48 to 72 hours. Survival rate was 100%; all of the mice exhibited normal behavior with no sign of distress 24 hours after surgery. RSNA was successfully recorded in 80% of the mice at 48 and 72 hours postsurgery; viable RSNA was reduced to 70% and 50% at 4 and 5 days postsurgery, respectively. Mean arterial pressure (116±2 mm Hg; n=10) was consistent with values reported previously for conscious mice. RSNA increased with the normal physical activities of eating and grooming and was validated by ganglionic blockade and pharmacological manipulation of blood pressure; reduction in blood pressure to 62±3 mm Hg with nitroprusside increased RSNA by 77±9% above baseline (n=5; P<0.05), whereas an increase in blood pressure to 137±6 mm Hg with phenylephrine reduced RSNA by 79±2% compared with baseline (n=5; P<0.05). Thus, we demonstrate an accessible and effective method for direct assessment of RSNA in conscious, unrestrained mice.

Vascular inflammatory cells in hypertension

Hypertension is a common disorder with uncertain etiology. In the last several years, it has become evident that components of both the innate and adaptive immune system play an essential role in hypertension. Macrophages and T cells accumulate in the perivascular fat, the heart and the kidney of hypertensive patients, and in animals with experimental hypertension. Various immunosuppressive agents lower blood pressure and prevent end-organ damage. Mice lacking lymphocytes are protected against hypertension, and adoptive transfer of T cells, but not B cells in the animals restores their blood pressure response to stimuli such as angiotensin II or high salt. Recent studies have shown that mice lacking macrophages have blunted hypertension in response to angiotensin II and that genetic deletion of macrophages markedly reduces experimental hypertension. Dendritic cells have also been implicated in this disease. Many hypertensive stimuli have triggering effects on the central nervous system and signals arising from the circumventricular organ seem to promote inflammation. Studies have suggested that central signals activate macrophages and T cells, which home to the kidney and vasculature and release cytokines, including IL-6 and IL-17, which in turn cause renal and vascular dysfunction and lead to blood pressure elevation. These recent discoveries provide a new understanding of hypertension and provide novel therapeutic opportunities for treatment of this serious disease.

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.

Calcineurin inhibitor nephrotoxicity

The use of the calcineurin inhibitors cyclosporine and tacrolimus led to major advances in the field of transplantation, with excellent short-term outcome. However, the chronic nephrotoxicity of these drugs is the Achilles' heel of current immunosuppressive regimens. In this review, the authors summarize the clinical features and histologic appearance of both acute and chronic calcineurin inhibitor nephrotoxicity in renal and nonrenal transplantation, together with the pitfalls in its diagnosis. The authors also review the available literature on the physiologic and molecular mechanisms underlying acute and chronic calcineurin inhibitor nephrotoxicity, and demonstrate that its development is related to both reversible alterations and irreversible damage to all compartments of the kidneys, including glomeruli, arterioles, and tubulo-interstitium. The main question--whether nephrotoxicity is secondary to the actions of cyclosporine and tacrolimus on the calcineurin-NFAT pathway--remains largely unanswered. The authors critically review the current evidence relating systemic blood levels of cyclosporine and tacrolimus to calcineurin inhibitor nephrotoxicity, and summarize the data suggesting that local exposure to cyclosporine or tacrolimus could be more important than systemic exposure. Finally, other local susceptibility factors for calcineurin inhibitor nephrotoxicity are reviewed, including variability in P-glycoprotein and CYP3A4/5 expression or activity, older kidney age, salt depletion, the use of nonsteroidal anti-inflammatory drugs, and genetic polymorphisms in genes like TGF-beta and ACE. Better insight into the mechanisms underlying calcineurin inhibitor nephrotoxicity might pave the way toward more targeted therapy or prevention of calcineurin inhibitor nephrotoxicity.

Inhibitory effect of antihypertensive drugs on calcineurin in cardiomyocytes

In recent years, a handful of research investigations have shown that some antihypertensive drugs, i.e., angiotensin-converting enzyme inhibitor (ACEI), angiotensin receptor blocker (ARB), and calcium channel blocker (CCB), can inhibit myocardial expression and/or activity of calcineurin. Calcineurin is a Ca(2+)-calmodulin-dependent serine/threonine phosphatase and is a target for some immunosuppressive drugs. It is well known that traditional immunosuppressants, such as cyclosporine A (CsA) and tacrolimus (FK506), are anticalcineurin, and their prohypertensive effects are such that antihypertensive therapy is often required in organ transplant recipients who receive these drugs. Therefore, the idea that ACEI, ARB, and CCBs are both antihypertensive and anticalcineurin seems paradoxical. This invited review tries to summarize these new findings and analyze the scientific and clinical significance of these claims. The review also emphasizes some of the shortcomings in these studies and some questions that need to be addressed in future investigations.

Calcineurin inhibition in splenocytes induced by pavlovian conditioning

Pavlovian conditioning is one of the major neurobiological mechanisms of placebo effects, potentially influencing the course of specific diseases and the response to a pharmacological therapy, such as immunosuppression. In our study with behaviorally conditioned rats, a relevant taste (0.2% saccharin) preceded the application of the immunosuppressive drug cyclosporin A (CsA), a specific calcineurin (CaN) inhibitor. Our results demonstrate that through pavlovian conditioning the particular pharmacological properties of CsA can be transferred to a neutral taste, i.e., CaN activity was inhibited in splenocytes from conditioned rats after reexposure to the gustatory stimulus. Concomitant immune consequences were observed on ex vivo mitogenic challenge (anti-CD3). Particularly, Th1-cytokine, but not Th2-cytokine, production and cell proliferation were impeded. Appropriate pharmacological and behavioral controls certify that all these changes in T-lymphocyte reactivity are attributable to mere taste reexposure. Furthermore, the underlying sympathetic-lymphocyte interaction was revealed modeling the conditioned response in vitro. CaN activity in CD4(+) T lymphocytes is reduced by beta-adrenergic stimulation (terbutaline), with these effects antagonized by the beta-adrenoreceptor antagonist nadolol. In summary, CaN was identified as the intracellular target for inducing conditioned immunosuppression by CsA, contributing to our understanding of the intracellular mechanisms behind "learned placebo effects."

Chronic renal dysfunction following liver transplantation

With most of the immunosuppressive protocols consisting of calcineurin inhibitors (CI), nephrotoxicity has become a major long-term complication often compromising outcome. In a single-center retrospective study, we reviewed 1173 liver transplantations to identify variables indicative for the occurrence of chronic renal dysfunction (CRD) (defined as > or = 1 episode of serum creatinine increase > or = 1.8 mg/dL > or = 2 wk). Chronic renal dysfunction was found in 137 (11.7%) of all transplants [82 (7%) early (after 3-12 months), 55 (4.7%) late-onset (> 12 months)]. Compared to 5-/10-yr survival rates in non-CRD transplants (84/74%) survival was significantly decreased in early (66/46%), but unchanged in late-onset CRD (98/86%). Rates of alcoholic cirrhosis and prior renal dysfunction were significantly increased in patients with CRD. In a multivariate logistic regression analysis, only cyclosporine A (CyA) as immunosuppression remained an independent risk factor. No correlations to age, gender, rejection/retransplantation or diabetes were found. Surprisingly, renal function (creatinine) showed no difference between patients on CI monotherapy (FK/CyA) compared to those who had mycophenolate mofetil (MMF) added. In liver transplantation, early onset CRD significantly compromises survival. CyA-based immunosuppression appears to have a stronger impact than FK. The fact that patients with long-term severe chronic renal dysfunction failed to improve under MMF rescue therapy emphasizes the importance of new diagnostic strategies to earlier identify at-risk patients.

Developmental regulation of calcineurin isoforms in the rodent kidney: association with COX-2

Calcineurin (Cn)-Aα-deficient mice develop abnormalities of postnatal kidney development, similar to that of cyclooxygenase (COX)-2-deficient mice. The present study was undertaken to examine expression and regulation of Cn isoforms in the developing kidney during the postnatal period and further characterize the relationship between Cn and COX-2. The protein expressions of all three Cn isoforms, including Cn-Aα, -Aβ, and -B, as determined by immunoblotting, increased in parallel in the first postnatal week and declined gradually with age. Renal Cn-Aα and -Aβ mRNA expressions were both developmentally regulated in the same fashion as their protein expressions, whereas renal Cn-B1 mRNA was not obviously induced in the first postnatal week. Immunohistochemistry demonstrated colocalization of Cn-Aα, Cn-Aβ, and COX-2 in the same cells of thick ascending limb and macula densa. Administration with cyclosporine A (2.5 mg·kg−1·day−1) during the postnatal period remarkably suppressed renal COX-2 expression as assessed by both immunoblotting and immunohistochemistry. Deletion of Cn-Aα but not Cn-Aβ in mice significantly reduced renal COX-2 expression at the postnatal period. Together, these data suggest that renal Cn isoforms are subject to normal developmental regulation and they may play a role in postnatal kidney development via interaction with COX-2.

Increased vascular resistance and not salt retention characterizes cyclosporine A-induced hypertension: report in an anuric patient

Cyclosporine A (CsA) use is associated with hypertension in most solid-organ transplant recipients. The mechanisms of CsA-induced hypertension have not been fully elucidated and are still controversial. We present a case of CsA-induced hypertension who was anuric and receiving hemodialysis, and in whom noninvasive cardiothoracic bioimpedence revealed elevated systemic vascular resistance without evidence of fluid-volume overload. We briefly discuss the possible mechanisms of CsA-induced hypertension in light of this information.

Wavelet methods for spike detection in mouse renal sympathetic nerve activity

Abnormal autonomic nerve traffic has been associated with a number of peripheral neuropathies and cardiovascular disorders prompting the development of genetically altered mice to study the genetic and molecular components of these diseases. Autonomic function in mice can be assessed by directly recording sympathetic nerve activity. However, murine sympathetic spikes are typically detected using a manually adjusted voltage threshold and no unsupervised detection methods have been developed for the mouse. Therefore, we tested the performance of several unsupervised spike detection algorithms on simulated murine renal sympathetic nerve recordings, including an automated amplitude discriminator and wavelet-based detection methods which used both the discrete wavelet transform (DWT) and the stationary wavelet transform (SWT) and several wavelet threshold rules. The parameters of the wavelet methods were optimized by comparing basal sympathetic activity to postmortem recordings and recordings made during pharmacological suppression and enhancement of sympathetic activity. In general, SWT methods were found to outperform amplitude discriminators and DWT methods with similar wavelet coefficient thresholding algorithms when presented with simulations with varied mean spike rates and signal-to-noise ratios. A SWT method which estimates the noise level using a "noise-only" wavelet scale and then selectively thresholds scales containing the physiologically important signal information was found to have the most robust spike detection. The proposed noise-level estimation method was also successfully validated during pharmacological interventions.

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.

Nitric oxide/cytochrome P450 interactions in cyclosporin A-induced effects in the rat

INTRODUCTION

The present study evaluated the contribution of 20-hydroxyeicosatetraenoic acid (20-HETE) and its interaction with nitric oxide (NO) in cyclosporin A-induced nephrotoxicity and hypertension.

METHODS AND RESULTS

The treatment of rats with cyclosporin A (25 mg/kg) for 7 days increased the renal microsomal conversion of arachidonic acid (AA) to 20-HETE (93 +/- 6%, P < 0.05), increased systolic blood pressure (SBP), reduced the urinary excretion of nitrite (53 +/- 8%, P < 0.05), induced renal damage as indicated by a marked increase in protein excretion (163 +/- 14%, P < 0.05), increased renal vasoconstrictor responses to AA (82 +/- 5%, P < 0.05) but not endothelin-1 or phenylephrine, and decreased vasodilator responses to bradykinin (42 +/- 10%, P < 0.05) and sodium nitroprusside (SNP; 56 +/- 13%, P < 0.05) in the renal preglomerular vessel treated with indomethacin and NO synthase inhibitor. The pretreatment of rats with HET0016 (10 mg/kg) or 1-aminobenzotriazole (50 mg/kg), inhibitors of cytochrome P450 (CYP450) activity, attenuated or prevented cyclosporin A-induced increases in 20-HETE production, SBP, and protein excretion, as did L-arginine (4 g/l), a substrate for NO synthase. L-Arginine but not HET0016 or 1-aminobenzotriazole blunted the cyclosporin A-induced decrease in nitrite excretion. Similarly, L-arginine blunted the enhanced vasoconstriction by AA as did HET0016 or 1-aminobenzotriazole. However, cyclosporin A-blunted dilator responses to bradykinin and SNP were not affected by L-arginine, HET0016, or 1-aminobenzotriazole.

CONCLUSIONS

These data suggest that cyclosporin A-induced nephrotoxicity can be accounted for by reduced NO production and a consequent increase in 20-HETE. The cyclosporin A-induced nephrotoxicity is thus an ideal model for evaluating NO/CYP450 interactions.

Hypertension in renal parenchymal disease: why is it so resistant to treatment?

The association between hypertension and chronic renal disease is well known. The pathogenesis of hypertension in patients with chronic kidney disease (CKD) is complex and multifactorial, which may explain why it is resistant to treatment. The traditional paradigm is that hypertension in CKD is due either to an excess of intravascular volume (volume dependent) or to excessive activation of the renin-angiotensin system in relation to the state of sodium/volume balance (renin-dependent hypertension). This review focuses on the importance of less established mechanisms, such as increased activity of the sympathetic nervous system, increased endothelin production, decreased availability of endothelium-derived vasodilators and structural changes of the arteries, renal ischemia, and sleep apnea.

Cyclosporine A induced changes to plasma and erythrocyte antioxidant defences

Organ transplant recipients develop pronounced cardiovascular disease, and decreased antioxidant capacity in plasma and erythrocytes is associated with the pathogenesis of this disease. These experiments tested the hypothesis that the immunosuppressant cyclosporine A (CsA) alters erythrocyte redox balance and reduces plasma antioxidant capacity. Female Sprague-Dawley rats were randomly assigned to a control or CsA treated group. Treatment animals received 25 mg/kg/day of CsA via intraperitoneal injection for 18 days. Control rats were injected with the same volume of the vehicle. Three hours after the final CsA injection, rats were exsanguinated and plasma analysed for total antioxidant status (TAS), alpha-tocopherol, malondialdehyde (MDA), and creatinine. Erythrocytes were analysed for superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glucose-6-phosphate dehydrogenase (G6PD) activities, alpha-tocopherol, and MDA. CsA administration resulted in a significant (P < 0.05) decrease in plasma TAS and significant increases (P < 0.05) in plasma creatinine and MDA. Erythrocyte CAT was significantly (P < 0.05) increased in CsA treated rats compared to controls. There were no significant differences (P > 0.05) in erythrocyte SOD, GPX, G6PD, alpha-tocopherol or MDA between groups. In summary, CsA alters erythrocyte antioxidant defence and decreases plasma total antioxidant capacity.

Time-Domain Evaluation of Cyclosporine Interaction with Hemodynamic Variability in Rats

This study investigated the effects of chronic exposure of Wistar rats to the immunosuppressant drug cyclosporine on blood pressure, heart rate, and their variability and the role of sympathovagal balance in this interaction. The blood pressure variability was determined as the standard deviation of the mean arterial pressure (SDMAP). Two time-domain heart rate variability indices were employed, the standard deviation of beat-to-beat intervals (SDRR) and the root mean square of successive beat-to-beat differences in R-R interval durations (rMSSD). Subcutaneous cyclosporine administration (20 mg/kg/day) for 12 days had no effect on blood pressure or its variability index (SDMAP). In contrast, the average level of heart rate and its variability indices (SDRR and rMSSD) showed significant increases and decreases, respectively, in cyclosporine- compared with vehicle-treated rats. Vagal (atropine) or beta -adrenergic (propranolol) blockade had no effect on blood pressure but elicited increases and decreases, respectively, in heart rate. Compared with control rats, cyclosporine-treated rats exhibited lesser tachycardic responses to atropine and greater bradycardic responses to propranolol, suggesting alterations of cardiac vagal (attenuation) and sympathetic (enhancement) activity by cyclosporine. Further, atropine reduced indices of heart rate variability (rMSSD and SDRR) in control rats, effects that were blunted by cyclosporine treatment. On the other hand, propranolol had no effect on heart rate variability in either cyclosporine-treated or control rats. These findings implicate vagally-mediated alterations in the cardiac sympathovagal balance in the cyclosporine-induced impairment of heart rate oscillations.

Blood pressure management in the kidney transplant recipient

Hypertension is extremely common after kidney transplantation. It has been observed in up to 80% to 90% of patients. The etiologies are multifactorial but, in large part, rest with the native kidneys, concomitant immunosuppressant drugs, and behavioral factors that promote the development of higher levels of blood pressure, including obesity, salt intake, smoking, and alcohol consumption. There is a direct relationship between kidney allograft failure and level of systolic blood pressure during follow-up. Patients with a systolic blood pressure greater than 180 mmHg have 2-fold greater risk of loss of graft function compared with patients with systolics of less than 140 mmHg. A similar pattern exists for diastolic blood pressure. Some investigators have also demonstrated that higher levels of blood pressure also correlate with an increased risk of acute graft rejection, particularly in African Americans. What is not known is whether more effective control of arterial pressure in the transplant patient will reduce the likelihood of graft loss and improve survival. No prospective outcome trials have ever been performed. However, it is likely, given the marked success of better control of blood pressure in nontransplant patients in reducing cardiovascular death and the rate of progression of kidney disease, that similar benefits will be appreciated in the transplant patient. Given the greater cardiovascular burden in the kidney transplant recipient because of the presence, in many cases, of diabetes and hypertension, perhaps even more risk reduction may be realized with incremental reductions in blood pressure. Preferred treatment strategies for lowering blood pressure depends on the mechanism of action and medical comorbidity. Drugs that block the renin-angiotensin system should be preferentially considered because they may have similar advantages in delaying progressive loss of allograft function, much in the same way they have proven benefits in protecting native kidney function. Treating blood pressure in the kidney transplant recipient is a complicated process because patients are already on multiple medications and many will need 3 to 5 antihypertensive drugs to achieve optimal control of blood pressure, which should preferably be below 130/80 mmHg.

Neurocardiovascular regulation in mice: Experimental approaches and novel findings

1. Neural mechanisms are of major importance in the regulation of arterial blood pressure, blood volume and other aspects of cardiovascular function. The recent explosion in gene discovery and advances in molecular technologies now provide the opportunity to define the molecular and cellular mechanisms essential to integrative neurocardiovascular regulation. The unique susceptibility of mice to genetic manipulation makes this species an attractive model for such investigation. 2. We provide here a brief overview of: (i) experimental approaches used to assess autonomic and reflex control of the circulation in mice; (ii) novel mechanisms of neurocardiovascular regulation revealed using these approaches; and (iii) findings from recent studies involving mouse models of cardiovascular disease.

Cyclosporin effect on noradrenaline release from the sympathetic nervous endings of rat aorta

Arterial hypertension is one of the main side effects of cyclosporin treatment and seems to be due to activation of the sympathetic nervous system. Some authors hypothesized that cyclosporin may act on the sympathetic nervous endings increasing catecholamine release, in agreement with our previous works which demonstrated an increase in rat plasma catecholamine levels after 30 mg/kg per day cyclosporin treatment for 7 weeks. Therefore, the aim of this work was to study the cyclosporin mechanism responsible for that increase in plasma catecholamines. Male Wistar rats were used. Noradrenaline release was performed in vitro experiments after loading rat aorta abdominal segments with 3H-noradrenaline (3H-NA). The release of 3H-NA was measured after electrical stimulation in the presence of 10(-6)M cyclosporin. In another set of experiments electrical stimulation was replaced by a pulse addition of cyclosporin (10(-6)M). Another group of rats was treated with 30 mg/kg per day cyclosporin for 7 weeks and catecholamine contents in aorta abdominal segments and adrenals were measured by high performance liquid chromatography system with electrochemical detection (HPLC-ECD). An increase in the 3H-NA release was observed in both types of in vitro experiments. Since cocaine abolished these cyclosporin effects, the obtained results suggest that cyclosporin may act on the catecholamine transporter across the membrane. In addition, after the 7 weeks of cyclosporin treatment, a significant decrease in catecholamine aorta contents was verified but in adrenals there was no difference regarding to controls. However, the dopamine synthesis/degradation ratio measured by the DA/DOPAC ratio suggests an increase in dopamine synthesis. These facts are in agreement with the enhanced plasma catecholamine levels and with the hypothesis of tissue catecholamine depletion. However, they do not explain the increase in plasma adrenaline levels, since adrenaline is a reflex of adrenal activity. The synthesized dopamine in adrenals seems to be unable to reach vesicles and to be metabolized in adrenaline. The observed decrease in HVA adrenal levels may be a consequence of extraneuronal uptake inhibition or inhibition by cyclosporin of the direct o-methylation of DOPAC. In conclusion, our results suggest that cyclosporin increases catecholamine release from the sympathetic nervous endings by a tyramine-like effect, i.e. by acting directly on the catecholamine transporter of the membrane.

Cyclosporine nephrotoxicity

After more than 20 years of cyclosporine use its nephrotoxicity remains a significant clinical problem. Cyclosporine-induced renal injury has been described in solid organs recipients and in patients treated for autoimmune diseases. It is manifested in 2 distinct and well characterized forms, acute nephrotoxicity and chronic nephrotoxicity. This communication reviews the current literature analyzing the available data about the pathogenesis and mechanisms of acute and chronic cyclosporine-induced nephrotoxicity. A working hypothesis for the possible mechanisms of chronic cyclosporine nephrotoxicity will be provided.

The role of serine/threonine protein phosphatases in exocytosis

Modulation of exocytosis is integral to the regulation of cellular signalling, and a variety of disorders (such as epilepsy, hypertension, diabetes and asthma) are closely associated with pathological modulation of exocytosis. Emerging evidence points to protein phosphatases as key regulators of exocytosis in many cells and, therefore, as potential targets for the design of novel therapies to treat these diseases. Diverse yet exquisite regulatory mechanisms have evolved to direct the specificity of these enzymes in controlling particular cell processes, and functionally driven studies have demonstrated differential regulation of exocytosis by individual protein phosphatases. This Review discusses the evidence for the regulation of exocytosis by protein phosphatases in three major secretory systems, (1) mast cells, in which the regulation of exocytosis of inflammatory mediators plays a major role in the respiratory response to antigens, (2) insulin-secreting cells in which regulation of exocytosis is essential for metabolic control, and (3) neurons, in which regulation of exocytosis is perhaps the most complex and is essential for effective neurotransmission.