Alleviation of cyclosporine nephrotoxicity with verapamil and ATP-MgCl2. Mitochondrial respiratory and calcium studies

Cyclosporin A and cardioprotection: from investigative tool to therapeutic agent

Ischaemic heart disease (IHD) is the leading cause of death and disability worldwide. The pathophysiological effects of IHD on the heart most often result from the detrimental effects of acute ischaemia-reperfusion injury (IRI) on the myocardium. Therefore, novel therapeutic targets for protecting the myocardium against acute IRI are required to reduce injury to the heart, preserve cardiac function and improve clinical outcomes in patients with IHD. In this regard, the mitochondrial permeability transition pore (mPTP) has emerged as a critical target for cardioprotection which is readily amenable to intervention at the time of myocardial reperfusion. The formation and opening of the mPTP at the onset of myocardial reperfusion is a major determinant of mitochondrial dysfunction and cardiomyocyte death in the setting of acute IRI. The seminal discovery in the late 1980s that mPTP opening could be pharmacologically inhibited by the immunosuppressive agent, cyclosporin A (CsA), has been fundamental in the elucidation of the critical role of the mPTP as a mediator of acute IRI and, therefore, a viable target for cardioprotection. Its initial role as an investigative tool was used to identify mitochondrial cyclophilin D to be a regulatory component of the mPTP. The mPTP as a viable target for cardioprotection has recently been translated into the clinical setting with CsA reducing myocardial infarct size in patients. In this article, we review the intriguing role of CsA as a tool for investigating the mPTP as a target for cardioprotection and its potential role as a therapeutic agent for patients with IHD.

The effect of cyclosporin A on Hg(2+)-poisoning mitochondria. In vivo and in vitro studies

The protective effect of cyclosporin A on the damage induced by Hg2+ in kidney mitochondria was studied. Cyclosporin, added in vitro at a concentration of 0.5 microM, reversed the deleterious effects of Hg2+ on transmembrane potential and Ca2+ accumulation. However, when injected in rats, together with Hg2+, cyclosporin failed to protect against Hg2+ poisoning. Due to the low activity of cyclophilin found in kidney mitchondria, it is proposed that the protection of cyclosporin in vitro must be exerted through an independent mechanism different from its binding to cyclophilin.

Effects of cyclosporin A on the blood flow of the native and transplanted rat pancreas and duodenum

The aim of the present study was to evaluate the effects of cyclosporin A (CyA) on the blood perfusion of the transplanted pancreas. For this purpose syngeneic pancreaticoduodenal transplantations were performed in Wistar-Furth rats. After nephrectomy the graft was anastomosed using a nonsuturing cuff technique to the left renal vessels. Beginning 7 days after transplantation and then continuing for 2 weeks, CyA (15 mg/kg body weight) or vehicle was given p.o. once daily, 6 days a week. The serum CyA concentrations were greater than 600 ng/ml at all points in time tested. Intraperitoneal glucose tolerance tests were normal in CyA-treated animals after 12 days, but the pancreatic insulin concentration was decreased to the same extent in the native and transplanted pancreas. A microsphere technique was used to measure the blood perfusion of the pancreaticoduodenal graft, the native pancreas and duodenum, and remaining kidney 14 days after starting the CyA treatment. The renal blood flow was markedly decreased by CyA when compared with the control animals. In rats given vehicle alone, pancreatic, islet, and duodenal blood flows were higher in the graft than in the corresponding native organs. However, in rats given CyA, hyperperfusion of the graft was not observed. We conclude that the administration of CyA prevents the transplantation-induced blood flow increase seen in pancreaticoduodenal grafts of vehicle-treated rats. These observations may reflect graft denervation.

Contrast media nephrotoxicity: comparison of diatrizoate, ioxaglate, and iohexol after intravenous and renal arterial administration

In several studies in humans and animals it has been suggested that high osmolality and ionicity of contrast media are responsible for higher nephrotoxicity. To examine this suggestion, we evaluated the renal effects of three different contrast media--an ionic high osmolar, an ionic low osmolar, and a nonionic--following intravenous and renal arterial administration, in a population of 84 unselected, nondiabetic patients with adequate renal function. The results showed that the nephrotoxicity is minimal and equal for all three contrast media and for both routes of their administration, and it is concluded that in this category of patients the far higher cost of the newer low osmolar ionics and nonionics should be considered seriously in regard to nephrotoxicity.

Vascular response to cyclosporine and verapamil in the rat pancreas

Marked elevation of vascular resistance in the rat pancreas is shown after systemic infusion of cyclosporine. Verapamil administration after cyclosporine reversed this effect and allowed maintenance of baseline vascular resistance and blood flow to the pancreas despite additional infusions of cyclosporine. Cyclosporine toxicity in rat pancreas may be directly related to increased vascular resistance. Verapamil might offer protection from this effect.

Kinetics of cyclosporine A-induced inhibition of succinate-coenzyme Q dehydrogenase in rat renal cortical mitochondria

The kinetic mechanism of succinate-coenzyme Q dehydrogenase (Complex II) inhibition by cyclosporine A (CS) on rat renal cortical mitochondria was investigated. CS showed two modes of inhibition of Complex II of the mitochondrial electron transport system: (a) a mixed linear noncompetitive inhibition of resting succinate-limited and ADP-stimulated respirations suggesting that CS binds to Complex II at a different site than the substrate, affecting the dissociation constant for the enzyme-substrate complex and (b) a competitive inhibition of the DNP-stimulated electron transport system suggesting competition with the oxidized form of a component of Complex II. CS action to renal mitochondrial Complex II limits its function, an effect which may be related to CS nephrotoxicity.

Isolated rat cardiomyocytes as an experimental model for studying acute cardiotoxicity of cyclosporin A

The acute cardiotoxicity of cyclosporin A was studied in isolated cardiac myocytes from adult rats. In an initial series of 7 animals, myocytes were incubated with concentrations of cyclosporin A ranging from 1 microgram/ml to 50 micrograms/ml. Shape changes of untreated cells, cells treated with cyclosporin A and cells treated with the solvent of cyclosporin A, Tween 80/ethanol, were evaluated. After 8 hours and 16 hours, respectively, of incubation 92 +/- 4.3% and 72 +/- 8.7% of the non-treated control cells were still rod-shaped. Cyclosporin A, however, in a concentration of 5 micrograms/ml decreased the number of rod-shaped cells (79 +/- 3.2% at 8 hours and 51 +/- 3.5% at 16 hours) in comparison to the solvent (94 +/- 3.5% at 8 hours and 76 +/- 5.8% at 16 hours, P less than 0.02). This effect became more pronounced with higher concentrations of cyclosporin A. On the other hand, Tween 80/ethanol alone in higher concentrations also led to a reduced number of rod-shaped cells. In a second series of 7 animals using Tween 80/ethanol and methanol as drug vehicles, myocytes were incubated for 16 hours with 15 micrograms/ml of cyclosporin A in a calcium containing medium (1 mM) or a calcium free medium (10(-4) M ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid). The number of remaining rod-shaped cells was higher in the calcium free medium as opposed to the medium containing calcium when the cells were exposed to cyclosporin A. It is concluded that in the applied model cyclosporin A at high concentrations has an acute cardiotoxic effect which in part appears to be calcium related.

Effect of verapamil on cephaloridine nephrotoxicity in the rabbit

Cephaloridine produces proximal tubular necrosis in the rabbit kidney. Calcium channel blockers have ameliorated tissue injury due to toxic and ischemic insults. To determine whether renal damage caused by cephaloridine could be modified by pretreatment with verapamil, groups of rabbits were given cephaloridine, 100 mg/kg sc, 90 min after administration of verapamil, 200 micrograms/kg iv. Histologic scoring of the extent of proximal tubular necrosis 48 h later demonstrated increased necrosis in the group receiving verapamil plus cephaloridine. Verapamil pretreatment increased the concentration of cephaloridine in the renal cortex at 0.5 hr, but did not alter the peak concentration (2 hr after the dose) or cortical concentrations at 1 or 3 hr. Assay of total calcium content in cortical mitochondria 2 hr after cephaloridine showed that verapamil pretreatment abolished the increased accumulation following cephaloridine administration. We conclude that verapamil does not protect renal proximal tubular cells from the toxic effect of cephaloridine, and that verapamil prevents the cephaloridine-induced uptake of calcium by cortical mitochondria.