Interaction Of Cyclosporin A Research Articles

Prediction of Cyclosporin-Mediated Drug Interaction Using Physiologically Based Pharmacokinetic Model Characterizing Interplay of Drug Transporters and Enzymes.

Uptake transporter organic anion transporting polypeptides (OATPs), efflux transporters (P-gp, BCRP and MRP2) and cytochrome P450 enzymes (CYP450s) are widely expressed in the liver, intestine or kidney. They coordinately work to control drug disposition, termed as “interplay of transporters and enzymes”. Cyclosporine A (CsA) is an inhibitor of OATPs, P-gp, MRP2, BCRP and CYP3As. Drug–drug interaction (DDI) of CsA with victim drugs occurs via disordering interplay of transporters and enzymes. We aimed to establish a whole-body physiologically-based pharmacokinetic (PBPK) model which predicts disposition of CsA and nine victim drugs including atorvastatin, cerivastatin, pravastatin, rosuvastatin, fluvastatin, simvastatin, lovastatin, repaglinide and bosentan, as well as drug–drug interactions (DDIs) of CsA with nine victim drugs to investigate the integrated effect of enzymes and transporters in liver, intestinal and kidney on drug disposition. Predictions were compared with observations. Most of the predictions were within 0.5–2.0 folds of observations. Atorvastatin was represented to investigate individual contributions of transporters and CYP3As to atorvastatin disposition and their integrated effect. The contributions to atorvastatin disposition were hepatic OATPs >> hepatic CYP3A > intestinal CYP3As ≈ efflux transporters (P-gp/BCRP/MRP2). The results got the conclusion that the developed PBPK model characterizing the interplay of enzymes and transporters was successfully applied to predict the pharmacokinetics of 10 OATP substrates and DDIs of CsA with 9 victim drugs.

Combined multispectroscopic and molecular dynamics simulation investigation on the interaction between cyclosporine A and β-lactoglobulin

β-Lactoglobulin (β-LG), the major whey protein in milks of many mammals, has a high affinity for a wide range of compounds. Cyclosporine A (CsA), is an immunosuppressant drug mainly prescribe in organ transplantation to prevent rejection. In this study, the interaction of CsA with β-LG was investigated using various spectroscopic techniques (UV–visible and fluorescence) in an aqueous medium at two temperatures of 298 and 310K in combination with a molecular dynamics simulation study. The titration results indicated that CsA quenched the fluorescence intensity of β-LG through a static mechanism. The binding constants for the binding of CsA to β-LG at two different temperatures 298 and 310K were obtained 1.12×105 and 0.87×105M−1, respectively. Thermodynamic data indicated that the hydrophobic interactions and hydrogen bonds dominate in the binding site. Results of fluorescence resonance energy transfer (FRET) measurements suggest that resonance energy transfer occurs between β-LG and CsA. Moreover, MD simulation results implied that CsA can interact with β-LG, without affecting the secondary structure of β-LG. Experimental and MD simulations data reciprocally supported each other.

Development of a cyclosporin-A-induced immune tolerant rat model to test marrow allograft cell type effects on bone repair.

Bone repair is an important concept in tissue engineering, and the ability to repair bone in hypotrophic conditions such as that of irradiated bone, represents a challenge for this field. Previous studies have shown that a combination of bone marrow and (BCP) was effective to repair irradiated bone. However, the origin and role played by each cell type in bone healing still remains unclear. In order to track the grafted cells, the development of an animal model that is immunotolerant to an allograft of bone marrow would be useful. Furthermore, because the immune system interacts with bone turnover, it is of critical importance to demonstrate that immunosuppressive drugs do not interfere with bone repair. After a preliminary study of immunotolerance, cyclosporin-A was chosen to be used in immunosuppressive therapy. Ten rats were included to observe qualitative and quantitative bone repair 8 days and 6 weeks after the creation of bone defects. The defects were filled with an allograft of bone marrow alone or in association with BCP under immunosuppressive treatment (cyclosporin-A). The results showed that there was no significant interaction of cyclosporin-A with osseous regeneration. The use of this new immunotolerant rat model of bone marrow allograft in future studies will provide insight on how the cells within the bone marrow graft contribute to bone healing, especially in irradiated conditions.

Modeling approach for multiple transporters-mediated drug–drug interactions in sandwich-cultured human hepatocytes: Effect of cyclosporin A on hepatic disposition of mycophenolic acid phenyl-glucuronide

A lower exposure of mycophenolic acid (MPA) in patients receiving MPA-mofetil in combination with cyclosporin A (CsA) is thought to be due to the inhibition of enterohepatic circulation of phenyl-glucuronide of MPA (MPAG). This study aimed to evaluate the interaction of CsA with hepatic disposition of MPA and MPAG in sandwich-cultured human hepatocytes (SCHH) by a mathematical modeling approach. In addition, the inhibition of CsA for glucuronidation of MPA to MPAG was examined in human liver microsomes. Inhibitory parameters of CsA for hepatic disposition of MPAG were estimated using a non-linear mixed effect model program, NONMEM. As a result, CsA did not influence the conversion of MPA to MPAG in either SCHH or human liver microsomes. In contrast, CsA inhibited the basolateral uptake of MPAG with an estimated maximum inhibitory effect (Imax) of 32.4%. CsA also inhibited basolateral efflux and biliary excretion of MPAG formed in SCHH, and the concentration producing 50% of Imax (IC50) for biliary excretion was lower than that for basolateral efflux. Our modeling approach suggests that CsA inhibits both basolateral uptake and biliary excretion of MPAG and leads to changes in systemic exposure of MPA and MPAG in humans.

The Potent Antimalarial Peptide Cyclosporin A Induces the Aggregation and Permeabilization of Sphingomyelin-Rich Membranes

Cyclosporin A (CsA) is a hydrophobic peptide drug produced by the fungus Tolypocladium inflatum. CsA is commonly used as an immunosuppressive drug, but it also has antimalarial activity. The immunosuppressive activity of CsA is clearly due to its association with specific proteins of immune cells such as cyclophilins. By contrast, the antimalarial properties of this peptide are completely independent of the association with a parasite's cyclophilins. Because of its hydrophobicity, CsA may interact with biological membranes, which may participate in its therapeutic effect. Recently, we have shown a marked preference of CsA for insertion into sphingomyelin (SM) monolayers. In this article, we measure for the first time the ability of CsA to induce permeabilization and aggregation and to change the lipid order, especially in the presence of SM. Calcein-release experiments permitted us to show that CsA causes the leakage of the fluorescent probe from SM-rich liposomes by 40% and PC liposomes by 11%, suggesting a lipid-selective effect. Electron microscopy and dynamic light scattering experiments confirmed the different interaction of CsA with SM and PC vesicles: it formed much larger aggregates with SM than with PC. Our results taken together suggest that CsA could specifically weaken and aggregate SM-rich membranes, which could in turn explain why CsA is efficient in the treatment of malaria. Indeed, CsA could inhibit the development of Plasmodium by permeabilizing and aggregating the SM-rich membrane network formed by the parasite during its intraerythrocytic growth cycle.

Improved dissolution and pharmacokinetic behavior of cyclosporine A using high-energy amorphous solid dispersion approach

The aim of the present investigation is to develop solid dispersion (SD) formulations of cyclosporine A (CsA) for improving the oral bioavailability of CsA. Amorphous SDs of CsA with eight hydrophilic polymers were prepared with wet-mill employing zirconia beads. The physicochemical properties were characterized with a focus on morphology, crystallinity, thermal behavior, dissolution, and interaction of CsA with co-existing polymer. Although CsA molecules were found to be amorphous in all wet-milled formulations, some SD formulations failed to improve the dissolution. Of all CsA formulations, SD using polymer with HPC(SSL) exhibited the largest improvement in dissolution behavior. Pharmacokinetic profiling of orally dosed CsA in rats was carried out using UPLC/ESI-MS. After the oral administration of HPC(SSL)-based SD, enhanced CsA exposure was observed with increases in C max and AUC of ca. 5-fold, and the variation in AUC was ca. 40% less than that of amorphous CsA. Infrared spectroscopic studies suggested an interaction between CsA and HPC(SSL), as evidenced by the conformational transition of CsA. From the improved dissolution and pharmacokinetic data, the amorphous SD approach using wet-milling technology should lead to consistent and enhanced bioavailability, leading to an improved therapeutic potential of CsA.

Cyclosporine Does Not Reduce Myocardial Infarct Size in a Porcine Ischemia-Reperfusion Model

Cyclosporine A (CsA) has been shown to protect against myocardial ischemia and reperfusion (I/R) injury in small animal models. The aim of the current study was to evaluate the effects of CsA on myocardial I/R injury in a porcine model. Pigs were randomized between CsA (10mg/kg; n = 12) or placebo (n = 15) and anesthetized with either isoflurane (phase I) or pentobarbital (phase II). By catheterization, the left descending coronary artery was occluded for 45 minutes, followed by reperfusion for 2 hours. Hearts were stained to quantify area at risk (AAR) and infarct size (IS). Myocardial biopsies were obtained for terminal dUTP nick end labeling and immunoblot analysis of proapoptotic proteins (apoptosis-inducing factor [AIF], BCL2/adenovirus E1B 19-kd interacting protein 3 [BNIP-3], and active caspase-3). Cyclosporine A did not reduce IS/AAR compared with placebo (49% vs 41%, respectively; P = .21). Pigs anesthetized with isoflurane had lower IS/AAR than pigs anesthetized with pentobarbital (39% vs 51%, respectively; P = .03). This reduction in IS/AAR seemed to be attenuated by CsA. Apoptosis-inducing factor protein expression was higher after CsA administration than after placebo (P = .02). Thus, CsA did not protect against I/R injury in this porcine model. The data suggest a possible deleterious interaction of CsA and isoflurane.

The Potent Antimalarial Drug Cyclosporin A Preferentially Destabilizes Sphingomyelin-Rich Membranes

Cyclosporin A (CsA) is a hydrophobic cyclic peptide produced by a fungus. CsA is widely used as an immunosuppressive agent to inhibit the rejection of transplanted organs. CsA also exhibits an antiparasitic activity against Plasmodium, the microorganism responsible for malaria disease. This antimalarial activity is not completely understood yet. In this study, we have used Langmuir monolayers and atomic force microscopy to investigate the interaction of CsA with different lipids: phosphatidylcholines with different molecular packing, cholesterol, and sphingomyelin. We have shown that CsA inserts in all kinds of lipid monolayers but it has a marked preference for sphingomyelin monolayers. This preferential insertion of CsA within sphingomyelin-enriched membranes could explain the antimalarial activity of CsA. Indeed, the parasites need to produce a membrane network inside the erythrocytes, which allows for their proper development/multiplication by exchanging nutrients with the external medium. This membrane network is particularly enriched in sphingomyelin, so the preferential insertion of CsA in these bilayers may destabilize them, thereby inhibiting the development of the parasite.

Evidence for the Involvement of a Membrane-Associated Cyclosporin-A-Binding Protein in the Ca2+-Activated Inner Membrane Pore of Heart Mitochondria

Heart and liver mitochondria contain a pore in the inner membrane that is activated by Ca2+ and oxidative stress and that has been implicated in cell injury. Pore opening is blocked by cyclosporin A (CSA). Following previous indications that the interaction of CSA with the pore is inhibited by Ca2+ and promoted by ADP, we have investigated how covalent labelling of heart mitochondria by a photoactive CSA derivative is influenced by these agents. In situ photolabelling of an 11-22-kDa (approximately) membrane fraction was selectively increased in the presence of ADP and decreased in the presence of Ca2+. This fraction also accounted for all the high affinity [3H]CSA-binding capacity and contained peptidylprolyl cis-trans isomerase activity (PPIase). The membrane PPIase was extracted using Chaps as detergent, and was purified to a 22-kDa protein (SDS/PAGE). The enzyme was inhibited by CSA (Ki 5 nM). The major component of the 11-22-kDa fraction, photolabelled in an ADP/Ca(2+)-sensitive manner, also migrated at 22 kDa on SDS/PAGE; a minor 11-kDa component was also detected. On the basis of these criteria, it is suggested that the membrane PPIase may be the target for CSA when it blocks the pore. The presence of a similar PPIase in the membrane fraction of liver mitochondria was also demonstrated. The implications of these findings are discussed.

Citrate Reverses Cyclosporin A-Induced Metabolic Acidosis and Bone Resorption in Rats

Background: Cyclosporine A (CsA) causes distal renal tubular acidosis (RTA) and osteoporosis. We have recently reported that the reduction of nitric oxide (NO) exacerbates this condition. Distal RTA may deplete bone mineral due to the chronic buffering of acid in the blood. The interaction of CsA and NO in causing metabolic acidosis and bone demineralization has not been studied previously. Nor has the salubrious effect of citrate therapy. Purpose: To examine the effect of systemic pH correction by citrate on renal electrolyte (Na, K, Cl, NH₃, HCO₃) excretion following acute water loading in CsA-treated and NO-reduced rats. We further evaluated femoral bone density and bone demineralization activity after the same treatments. Methods: Rats received CsA, L-arginine (L-Arg), or nitro-L-arginine-methyl ester (L-NAME), or a combination of CsA+L-NAME plus or minus citrate. Urine and blood electrolytes were examined, as well as the urine excretion of deoxypyridinoline and the bone density of both femurs. Results: CsA and L-NAME reduced urine pH and the serum HCO₃^– concentration, and increased serum K⁺ and Cl^– concentrations. The combination of CsA with L-NAME caused more severe deficits in the serum HCO₃^– concentration and elevations in serum K⁺ and Cl^– concentrations than either drug alone. Both CsA and L-NAME reduced urinary nitrate excretion, which was reversed by co-administration of L-Arg. Co-administration of citrate or L-Arg improved the CsA- and L-NAME-induced acidosis and hyperkalemia. Bone resorption and density of the femurs were decreased by CsA and L-NAME and were additive for both drugs. Co-administration of citrate or L-Arg restored both bone resorption and density to normal levels. Conclusion: CsA induces a hyperchloremic metabolic acidosis with hyperkalemia and a reduction in NO. The ensuing systemic acidosis causes bone resorption and demineralization. These effects were corrected by co-treatment with citrate. Citrate, at least in part, directly reduces the protonation of bone in animals treated with CsA and is recommended as a potential adjunct drug to prevent bone demineralization in patients chronically receiving CsA.

Cyclosporine A inhibits acetylcholinesterase activity in selected parts of the rat brain

Cyclosporine A (CsA) is the major immunosuppressive drug used for organ and neural transplantation and the therapy of selected autoimmune diseases. We investigated the effect of CsA on the activity of acetylcholinesterase (AChE) in the frontal cortex, hippocampus, septum, and basal ganglia. AChE was determined spectrophotometrically with acetylthiocholine as substrate and 5,5-bis-2-nitrobenzoic acid as chromogen. CsA was administered in single doses of 20 or 45 mg/kg perorally; in the case of the higher dose we also performed a repeated administration of CsA in three consecutive doses separated by 24 h intervals. Both lower and higher doses of CsA decreased AChE activity in the frontal cortex and hippocampus to practically the same extent. On the contrary, AChE activity was more diminished in the case of the higher dose of CsA used in the septum and basal ganglia. Repeated administration of the higher dose of CsA did not lead, with the exception of the hippocampus, to a further decrease in AChE activity in the brain structures observed. These findings contribute to rare evidence concerning the interaction of CsA and the cholinergic system in the brain.

Cyclophilin-mediated pathways in the effect of cyclosporin A on endothelial cells: role of vascular endothelial growth factor.

The relative importance of cyclophilin (CyP) versus calcineurin (Cn)-mediated mechanisms in the effect of cyclosporin A (CsA) on endothelial cells (ECs) is largely unknown. In cultured ECs, CsA was cytotoxic/proapoptotic or cytoprotective/antiapoptotic at high or low concentrations, respectively. CsA analogs (MeVal-4-CsA and MeIle-4-CsA), which bind to CyP but do not inhibit Cn, closely reproduced the CsA effects. Based on our previous data, the role of vascular endothelial growth factor (VEGF) as a mediator of CsA-induced cytoprotection was further analyzed. The actions of CsA and CsA analogs were shifted from a protective to a cell-damaging pattern in the presence of a specific anti-VEGF monoclonal antibody (mAb). This positive interaction was further supported by a transient increase in cytosolic free calcium concentration ([Ca(2+)](i)) by VEGF after pretreatment with either CsA or MeVal-4-CsA and an increase in the expression and synthesis of VEGF receptor 2 (VEGFR2). Of functional importance, blockade of the interaction between VEGF and VEGFR2 by a VEGFR2 mAb abolished the cytoprotective effect of CsA. In addition, preconditioning with low concentrations of CsA or CsA analogs increased both cytoprotection and VEGFR2 mRNA expression when EC were exposed to higher concentrations of CsA. In summary, our results reveal that (1) the biphasic responses to CsA in EC are related to the interaction of CsA with CyP rather than with Cn and (2) VEGF is a critical factor in the cytoprotective effect of CsA, by a mechanism that involves VEGFR2.

Interaction of cyclosporine A and the renin-angiotensin system; new perspectives.

Despite extensive research, the exact mechanisms of cyclosporine A (CsA)-induced hypertension and nephrotoxicity remain obscure. Several lines of evidence suggest an involvement of the renin-angiotensin system (RAS) in CsA toxicity, but the issue is still controversial in more ways than one. Some interesting data of the interaction of CsA and RAS have been presented by us and others during the last years. In rats, activation of RAS by CsA is a consistent finding while the results from clinical studies show controversial results. The mechanisms of activation of RAS may be multifactorial. CsA increases renin release directly from juxtaglomerular cells. However, RAS activation may at least partly account for glomerular ischemia by vasoconstriction. A totally different view about the interaction of CsA and RAS has recently been presented. CsA antagonised the harmful effects of RAS over-expression on renal damage in double transgenic rats harbouring human renin and angiotensinogen genes. The protection was due to anti-inflammatory properties of CsA by inhibition of interleukin-6 and inducible nitric oxide synthase (iNOS) expression. Other studies have confirmed the inhibitory effect of CsA on iNOS. Calcium antagonists have been proposed to be the antihypertensive drugs of choice in treatment of CsA-induced hypertension because of their favourable haemodynamic effects on the kidneys. However, because angiotensin II plays a major role in the development of CsA-induced structural renal damage, pharmacological inhibition of RAS in CsA-treatment may have some beneficial effects beyond blood pressure control.

Effects of low and high density lipoproteins on renal cyclosporine A and cyclosporine G disposition in the isolated perfused rat kidney.

This study investigated the effects of low (LDL) and high density lipoproteins (HDL) on renal cyclosporine A (CsA) and cyclosporine G (CsG) disposition in the isolated perfused rat kidney model. Kidneys were perfused with CsA or CsG in perfusion medium containing 6% protein, bovine serum albumin only (BSA) (Control), LDL (200 mg/dl) and BSA, or HDL (200 mg/dl) and BSA. In vitro protein binding studies were conducted with CsA and CsG in the same media. The unbound fractions (fu) of CsA and CsG were significantly reduced with LDL and HDL in the perfusion media. In the presence of LDL, fu for CsA and CsG was 3.9% and 5.9%, respectively. With HDL, fu was 2.1% for CsA and 1.8% for CsG. fu for the controls was 14.7% for CsA and 11.9% for CsG. Renal clearance (CLR) of CsA and CsG was significantly reduced when perfused with perfusion medium containing LDL and HDL. LDL and HDL had similar effects on reducing CsA and CsG CLR, and were approximately four-fold lower when compared to controls (approximately 0.006 Vs. 0.023 ml/min). Renal CsA and CsG tissue (whole organ, cortex and medulla) concentrations were lower than corresponding controls when perfused with LDL or HDL. The interaction of CsA and CsG with LDL and HDL significantly reduced the CLR and extent of renal tissue distribution of both compounds.

Cyclosporin A treatment induces overexpression of P-glycoprotein in the kidney and other tissues.

To see whether P-glycoprotein (PGP) expressed in renal brush-border membranes (BBM) could interact with compounds known as modulators of multidrug resistance (MDR), photoaffinity-labeling experiments were performed. A 145k-Da protein was photolabeled with [125I] iodoarylazidoprazosin, and this labeling was reduced in the presence of cyclosporin A (CsA) and PSC-833 (PSC). Interaction of CsA with PGP was further investigated by treating rats with daily subcutaneous injections of CsA (10 mg.kg-1.day-1). After this treatment, PGP expression levels were dramatically increased in renal BBM, intestine, liver, and many other tissues except the brain. This induction was a reversible process, since after cessation of CsA administration PGP levels declined to reach values similar to those of the control groups. The increase in PGP expression in the kidney was also detected in photolabeling experiments, suggesting the induction of a functional PGP. A higher dose of CsA (50 mg/kg) given as a bolus injection did not modify PGP expression] in renal BBM. These results demonstrate that CsA induces reversible overexpression of PGP in the rat. This may present significant relevance in the design of clinical trials using CsA as a chemosensitizing agent.

Evidence for the involvement of a membrane-associated cyclosporin-A-binding protein in the Ca(2+)-activated inner membrane pore of heart mitochondria.

Heart and liver mitochondria contain a pore in the inner membrane that is activated by Ca2+ and oxidative stress and that has been implicated in cell injury. Pore opening is blocked by cyclosporin A (CSA). Following previous indications that the interaction of CSA with the pore is inhibited by Ca2+ and promoted by ADP, we have investigated how covalent labelling of heart mitochondria by a photoactive CSA derivative is influenced by these agents. In situ photolabelling of an 11-22-kDa (approximately) membrane fraction was selectively increased in the presence of ADP and decreased in the presence of Ca2+. This fraction also accounted for all the high affinity [3H]CSA-binding capacity and contained peptidylprolyl cis-trans isomerase activity (PPIase). The membrane PPIase was extracted using Chaps as detergent, and was purified to a 22-kDa protein (SDS/PAGE). The enzyme was inhibited by CSA (Ki 5 nM). The major component of the 11-22-kDa fraction, photolabelled in an ADP/Ca(2+)-sensitive manner, also migrated at 22 kDa on SDS/PAGE; a minor 11-kDa component was also detected. On the basis of these criteria, it is suggested that the membrane PPIase may be the target for CSA when it blocks the pore. The presence of a similar PPIase in the membrane fraction of liver mitochondria was also demonstrated. The implications of these findings are discussed.

The role of plasma lipoproteins as carriers for the aromatic hydrocarbons in rats. Biodistribution studies

Cyclosporine A (CsA) and purified CsA metabolites were tested alone and in combination in cell culture to determine their effects on phytohemagglutinin (PHA)-induced lymphocyte proliferation. CsA was significantly more inhibitory than its metabolites at all concentrations tested (0–1000 ng/mL). CsA exerted maximum inhibition (70% decrease in [methyl-3H]thymidine incorporation) at concentrations of 300 ng/mL or greater; metabolites M1, M17, and M21 depressed the response 46, 39, and 23%, respectively, at 300 ng/mL. Metabolites M8, M18, M26, M25, M13, and M203–218 were non-inhibitory. When combinations of M17 and CsA were tested for the effects on PHA-induced lymphocyte transformation, a synergistic effect occurred at combinations of low concentrations of M17 and CsA and an antagonistic effect at the higher concentrations. Of the 49 combinations of CsA and M17 tested, 30 were antagonistic, 16 synergistic and 3 undecided (approaching additivism). When 49 combinations of CsA and the non-immunosuppressive metabolite M8 were tested, 29 of the 49 combinations were synergistic, 17 antagonistic, 1 additive and 2 undecided (approaching additivism). Of the 29 synergistic combinations, 14 were strongly synergistic. The importance of the interaction of CsA and metabolites to the immunopharmacology of CsA therapy is discussed.

Demonstration of ternary immunophilin-calcineurin complexes with the immunosuppressants cyclosporin and macrolide FK506

The specificity of cyclosporin A (CsA) binding to the major intracellular receptor proteins, cyclophilin A and B, as well as the interaction of CsA with the phosphatase calcineurin were investigated. Binding of photoaffinity-labeled CsA (PL-CS), a photoaffinity probe of CsA, to recombinant human cyclophilin A and B is saturable and specific. Non-specific PL-CS binding to calcineurin is observed in the absence of cyclophilin and calmodulin. In the presence of cyclophilin, cyclosporin-calcineurin binding becomes specific. Ternary complexes containing an equimolar ratio of cyclophilin A or B, PL-CS and calcineurin are resolved using the chemical-crosslinking technique. The formation of these complexes is specific, calcium- but not calmodulin-dependent, and is only inhibitable by cyclosporins, which bind cyclophilin. The drug-immunophilin complex binds to the calcineurin A subunit. The proteolytic 43 kDa product of calcineurin A retains binding properties, suggesting that the C-terminal domains are not necessary for complex formation. A trimeric complex of FKBP-calcineurin is also formed with FK506, but not with rapamycin. As expected, these complexes are only competed with by homologous derivatives. Chemical crosslinking of photolabeled Jurkat T-cells strongly suggests that drug-calcineurin complexes are of biological relevance.

Cyclosporin A blocks 6-hydroxydopamine-induced efflux of Ca2+ from mitochondria without inactivating the mitochondrial inner-membrane pore.

Oxidative stress causes Ca(2+)-loaded mitochondria to release Ca2+. The mechanism of this efflux is unclear, but it appears to be associated with the opening of a pore in the mitochondrial inner membrane. Pore opening depolarizes the mitochondria, letting solutes enter the mitochondrial matrix, causing swelling. Cyclosporin A (CsA) prevents opening of this pore. The neurotoxin 6-hydroxydopamine (6HD) autoxidizes, producing free radicals, which cause oxidative stress. In this paper it is shown that 6HD-induced efflux from Ca(2+)-loaded mitochondria was prevented by CsA. The 6HD-induced Ca2+ efflux was not accompanied by mitochondrial swelling, depolarization of the mitochondrial inner membrane or movement of radiolabelled sucrose into the mitochondrial matrix. In agreement with others [Schlegel, Schweizer and Richter (1992) Biochem. J. 285, 65-69], these findings suggest that the mitochondrial pore remained closed during pro-oxidant-induced Ca2+ efflux. However, the implication that CsA blocks pro-oxidant-induced Ca2+ efflux by some mechanism other than inactivating the mitochondrial pore, suggests that the interaction of CsA with mitochondria may be more complex than is currently supposed.

Synergistic and antagonistic effects of combinations of cyclosporine A and its metabolites on inhibition of phytohemagglutinin-induced lymphocyte transformation in vitro

Cyclosporine A (CsA) and purified CsA metabolites were tested alone and in combination in cell culture to determine their effects on phytohemagglutinin (PHA)-induced lymphocyte proliferation. CsA was significantly more inhibitory than its metabolites at all concentrations tested (0–1000 ng/mL). CsA exerted maximum inhibition (70% decrease in [ methyl- 3H]thymidine incorporation) at concentrations of 300 ng/mL or greater; metabolites M1, M17, and M21 depressed the response 46, 39, and 23%, respectively, at 300 ng/mL. Metabolites M8, M18, M26, M25, M13, and M203–218 were non-inhibitory. When combinations of M17 and CsA were tested for the effects on PHA-induced lymphocyte transformation, a synergistic effect occurred at combinations of low concentrations of M17 and CsA and an antagonistic effect at the higher concentrations. Of the 49 combinations of CsA and M17 tested, 30 were antagonistic, 16 synergistic and 3 undecided (approaching additivism). When 49 combinations of CsA and the non-immunosuppressive metabolite M8 were tested, 29 of the 49 combinations were synergistic, 17 antagonistic, 1 additive and 2 undecided (approaching additivism). Of the 29 synergistic combinations, 14 were strongly synergistic. The importance of the interaction of CsA and metabolites to the immunopharmacology of CsA therapy is discussed.