In vivo and in vitro inhibition of the L-type calcium current in isolated guinea-pig cardiomyocytes by the immunosuppressive agent cyclosporin A

Direct, pleiotropic protective effect of cyclosporin A against simulated ischemia-induced injury in isolated cardiomyocytes

Cyclosporin A is an immunosuppressor that prolongs graft survival but its use is limited by cardiotoxicity. The effects of cyclosporin A on several functional and biological characteristics were thus evaluated in rat cardiomyocytes in normal conditions and in a substrate-free, hypoxia-reoxygenation model of ischemia-reperfusion. Cyclosporin A (100 and 1000 ng/ml) did not induce cardiocytotoxicity in basal conditions. Simulated ischemia gradually decreased and then blocked the spontaneous electromechanical activity. Cyclosporin A at 100 and 1000 ng/ml permitted the maintenance of electromechanical functions that were abolished in control cells. Cyclosporin A also improved the post-"ischemic" functional recovery. Cyclosporin A reduced the "ischemia"-induced lactate dehydrogenase and troponine I releases and the successive rises in heat shock protein mRNA observed after "ischemia" and reoxygenation. Moreover, cyclosporin A improved the resumption of the mitochondrial function. To conclude, cyclosporin A displayed a direct, pleiotropic protection of isolated cardiomyocytes against physiological, metabolic, structural and stress signaling changes induced by ischemia-reperfusion mimicked in vitro.

Calreticulin is an upstream regulator of calcineurin

Ca(2+) is a signalling molecule involved in virtually every aspect of cell function. The endoplasmic reticulum (ER) is an important and dynamic organelle responsible for storage of the majority of intracellular Ca(2+). Within the ER lumen are proteins that function as Ca(2+) buffers and/or molecular chaperones including calreticulin, a multifunctional Ca(2+)-binding protein. Calreticulin-deficiency is lethal in utero due to impaired cardiac development. In the absence of calreticulin Ca(2+) storage capacity in the ER and InsP(3) receptor mediated Ca(2+) release from ER are compromised. Remarkably, over-expression of constitutively active calcineurin in the hearts of calreticulin deficient mice rescues them from embryonic lethality and produces live calreticulin deficient animals. These observations provide first evidence that calreticulin is a key upstream regulator of calcineurin in the Ca(2+)-signalling cascade and they highlight the importance of ER during early stages of cellular commitment and tissue development during organogenesis.

Calcineurin and hypertrophic heart disease: novel insights and remaining questions

In the past 2 years, an emerging body of research has focused on a novel transcriptional pathway involved in the cardiac hypertrophic response. Ever since its introduction, the significance of the calcineurin-NFAT module has been subject of controversy. The aim of this review is to provide both an update on the current status of knowledge and discuss the remaining issues regarding the involvement of calcineurin in hypertrophic heart disease. To this end, the molecular biology of calcineurin and its direct downstream transcriptional effector NFAT are discussed in the context of the genetic studies that established the existence of this signaling paradigm in the heart. The pharmacological mode-of-action and specificity of the calcineurin inhibitors cyclosporine A (CsA) and FK506 is discussed, as well as their inherent limitations to study the biology of calcineurin. A critical interpretation is given on studies aimed at analyzing the role of calcineurin in cardiac hypertrophy using systemic immunosuppression. To eliminate the controversy surrounding CsA/FK506 usage, recent studies employed genetic inhibitory strategies for calcineurin, which confirm the pivotal role for this signal transduction pathway in the ventricular hypertrophy response. Finally, unresolved issues concerning the role of calcineurin in cardiac pathobiology are discussed based upon the information available, including its controversial role in cardiomyocyte viability, the reciprocal relationship between myocyte Ca(2+) homeostasis and calcineurin activity and the relative importance of calcineurin in relation to other hypertrophic signaling cascades.

Cyclosporine A as a potential neuroprotective agent: a study of prolonged hypothermic circulatory arrest in a chronic porcine model

OBJECTIVE

To assess whether Cyclosporine A (CsA) or cycloheximide (CHX) can reduce ischemia-induced neurological damage by blocking apoptotic pathways, we assessed their effects on cerebral recovery in a chronic animal model of hypothermic circulatory arrest (HCA).

METHODS

Twenty-eight pigs (28-33 kg) underwent 90 min of HCA at 20 degrees C. In this blinded study, animals were randomized to placebo (n=12), 5 mg/kg CsA (n=8), given intravenously before and subcutaneously for 7 days after HCA, or a single dose of 1 mg/kg CHX (n=8), given after weaning from cardiopulmonary bypass. Hemodynamics, intracranial pressure (ICP) and neurophysiological data (EEG, SSEP) were assessed for 3 h after HCA; early behavioral recovery was scored, and neurological/behavioral evaluation (9=normal) was carried out daily until elective sacrifice on postoperative day (POD) 7. Brains were selectively perfused and evaluated histopathologically for apoptosis.

RESULTS

Basic hemodynamic data revealed no differences between CsA or CHX and control groups. ICP was significantly lower throughout rewarming (P=0.009) and reperfusion (P=0.05) in the CsA group. EEG recovery 3 h after HCA was observed in four of eight CsA animals but in only 1 of 12 controls (P=0.11) and one of eight CHX animals; cortical SSEP recovery also seemed faster in CsA animals, but failed to reach significance. Some early recovery scores were significantly better in the CsA group, and daily behavioral scores were consistently and significantly higher in the CsA-treated animals from POD1 through POD4.

CONCLUSIONS

The data indicate that treatment with Cyclosporine A but not cycloheximide has a positive effect on cerebral recovery following HCA. Whether CsA results in inhibition of neuronal apoptosis, and/or inhibits release of cytokines and thereby reduces postischemic cerebral edema remains to be elucidated. The neuroprotective effect of CsA, if confirmed in further studies, would make its clinical application conceivable.

Galpha(i2) but not Galpha(i3) is required for muscarinic inhibition of contractility and calcium currents in adult cardiomyocytes

Parasympathetic stimulation of the heart acts through M(2)-muscarinic acetylcholine receptors to regulate ion channel activity and subsequent inotropic status. Although muscarinic signal transduction is mediated via pertussis toxin-sensitive G proteins Galpha(i/o), the specific signal transduction requirements of Galpha(i2) and Galpha(i3) in mediating muscarinic regulated L-type calcium currents (I(Ca, L)), intracellular calcium, and cell contractility remain to be determined. Adult ventricular myocytes were isolated from Galpha(i2)-null mice, Galpha(i3)-null mice, and their wild-type littermates. Cell shortening, intracellular calcium levels, and I(Ca, L) were all measured in response to isoproterenol, a beta-adrenergic receptor agonist, and carbachol, a cholinergic receptor agonist. With isoproterenol stimulation, myocytes from all groups demonstrated a marked increase in calcium currents, correlating with augmented intracellular calcium transient amplitude and cell shortening. Carbachol significantly attenuated the isoproterenol response in wild-type and Galpha(i3)-null cells but had no effect in Galpha(i2)-null cells. This study demonstrates that Galpha(i2), but not Galpha(i3), is required for muscarinic inhibition of the beta-adrenergic response in adult murine ventricular myocytes.

Protective effects of low and high doses of cyclosporin A against reoxygenation injury in isolated rat cardiomyocytes are associated with differential effects on mitochondrial calcium levels

In this study we aimed to determine the concentration range of cyclosporin A (CsA) which was effective in protecting against reoxygenation injury in isolated cardiomyocytes, and its effects on intramitochondrial free calcium levels ([Ca2+]m). We also determined whether a high [CsA] had any deleterious effect on normal myocyte function. Isolated adult rat ventricular myocytes were placed in a chamber on the stage of a fluorescence microscope for induction of hypoxia. [Ca2+]m was determined from indo-1/am loaded cells where the cytosolic fluorescence signal had been quenched by superfusion with Mn2+. Cell length was measured using an edge-tracking device. Upon induction of hypoxia, control cells underwent rigor-contracture in 37 +/- 1 min (n = 99) (T1); CsA had no effect on T1. The percentage of control cells which recovered upon reoxygenation depended on the time spent in rigor (T2). With a T2 of 21-30 min, only 36% of control cells recovered compared with 90% and 78% of cells treated with 0.2 microM and 1 microM CsA respectively. After 40 min in rigor, [Ca2+]m was 280 +/- 60 nM in control-recovered cells (50% of cells) and 543 +/- 172 nM and 153 +/- 26 nM in cells treated with 0.2 and 1 microM CsA, respectively (all CsA treated cells recovered). In normoxic studies, CsA had no effect on cell contractility or [Ca2+]m upon rapid pacing, even in presence of an elevated external [Ca2+]. In conclusion, both low and high [CsA] protected against reoxygenation injury to cardiomyocytes despite having opposing effects on [Ca2+]m, suggesting more than one mechanism of action. CsA had no effect on either cell contractility or [Ca2+]m in normoxic cells.