69
Toxicology Letters, 53 (1990) 69-13 Elsevier
TOXLET 02387
Mechanisms underlying cyclosporin A nephrotoxicity
Paul H. Whiting Department
of Clinical Biochemistry,
University of Aberdeen, Aberdeen (U.K.)
Key words: Cyclosporin A nephrotoxicity; Vasoconstriction;
Tubulopathy; Biochemical mechanisms
INTRODUCTION
Nearly all patients on cyclosporin A (&A) demonstrate some degree of renal impairment which, in the most severe cases, has lead to end-stage renal failure. Clinically, there appear to be 3 main types of renal structural damage associated with CsA administration [l]. None of these is specific, but all are present more commonly following CsA administration than in other situations. First, in patients with prolonged oliguria or anuria following renal transplantation, the kidneys may show diffuse interstitial fibrosis (‘interactive toxicity’). Second, acute toxicity, which is dose-related and less common now that lower initial doses of CsA and drug tapering are employed, may be accompanied by structural abnormalities; if changes are present, they comprise a toxic proximal tubulopathy. The third type of CsA-induced renal lesion is chronic toxicity, associated with either striped (i.e. radial) interstitial fibrosis and/ or an arteriolopathy. There are, to date, few studies which describe the pathological effects of chronic administration of CsA on renal structure and function in animal models. Such information is particularly important as it is this form of CsA-nephrotoxicity, apparently neither dose-related nor responsive to dose reduction, which may restrict the clinical use of CsA. MECHANISMS UNDERLYING
The pathogenesis
CYCLOSPORIN A TOXICITY
of CsA-induced renal dysfunction
has recently been reviewed
correspondence: Dr. P.H. Whiting, Department of Clinical Biochemistry, University of Aberdeen, Medical Buildings, Foresterhill, Aberdeen AB9 2ZD, U.K.
Address for
0378-4274/90/S
3.50 @ 1990 Elsevier Science Publishers B.V. (Biomedical Division)
70
[ 1,2] and only references which supersede this article have been included. Most attention has been directed towards understanding the pathogenesis of CsA-induced acute renal dysfunction and it is only recently, with the development of appropriate animal models, that the study of chronic CsA renal dysfunction has begun. Experimental evidence indicates that the fall in glomerular filtration rate (GFR), due to vasoconstriction, observed following CsA administration may be disproportionate to the fall in renal blood Sow [3]. Selective hypofiltration in the absence of reduced GFR [4] and reduced GFR in the absence of vasoconstriction have also been reported [S]. Although the mechanisms underlying CsA-induced renal dysfunction still remain unclear, and the literature contains many anecdotal and conflicting reports, altered renal haemodynamics mediated via either stimulation of the renin-an~otensin-aldosterone system (RAAS), altered renal prostaglan~n metabolism, a-adrenergic stimulation, tubulo-glomerular feedback mechanisms stimulated by renal tubular damage and/or dysfunction, or altered intrarenal control of GFR, caused perhaps by hy~~lasia of the juxtaglomerular apparatus, have all been suggested from the results of animal studies [l]. It has also been suggested that endothelial cell injury occurring in the presence of reduced production or release of prostacyclin-stimulating factor by endothelial cells (and consequently impaired vasodilatory prostagiandin production) could predispose to platelet agg~gation and thrombosis in the capillary circulation. However, in the rat the acute, haemodynamically-mediated CsA nephrotoxicity may be related to either inhibition of vasodilatory prostaglandins or to a lack of response to vasodilators but not mediated via endotheli~-delved relaxant factor [l]. A role for platelet-activating factor and protein kinase C has also been suggested ]697l. Although the severity of acute CsA nephrotoxicity is related to circulating drug levels, there is stilt a ~ntroversy as to whether native CsA or a metabolite initiates the toxic response, although most information favours the former. There is now extensive evidence that interference with hepatic CsA metabolism in both experimental and clinical studies affects the extent of renal functional and structural impairment. Thus, co-trea~ent with known inducers (e.g., phenobarbitone) or inhibitors (e.g., ketoconazole) of hepatic cytochrome P-450 dependent mono-oxygenase activity results in lower circulating CsA levels and diminished nephrotoxicity or higher circulating drug concentrations and enhanced nephrotoxicity, respectively. A cytochrome P450 isozyme, immun~hemi~lly similar to the phenobarbitone-inducible form in liver, has recently been demonstrated in the kidneys of CsA-treated rats, suggesting that increased renal CsA metabolism may generate a toxic metabolite [l]. However, inhibition of degradation, rather than increased synthesis of the haem molecule, resulting in increased kidney cytochrome P-450 concentrations, has also been suggested
IIf% The severity of acute CsA nephrotoxicity is also increased by co-treatment with other nephrotoxic agents, including gentamicin and amphote~cin B, and also by concomitant administration of the diuretic agents fmosemide and mannitol. Partial pro-
71
tection against CsA nephrotoxicity in the rat is observed when either the angiotensinconverting enzyme inhibitor, enalapril, or the distal tubular antagonist of aldosterone, spironolactone, are co-administered [1,2]. However, although a role for the RAAS has not been confirmed in patient studies, many of the patients studied were receiving drugs which themselves affected the intrarenal control of GFR. However, evidence of a pre-renal element in the development of CsA nephrotoxicity, a reduced fractional excretion of lithium, related to the development of circulatory hypovolaemia [9], has been obtained in both patient and animal studies [l]. In addition, the increased excretion of thromboxane B2 (TxB$ caused by CsA and prevented by cotreatment with either thromboxane A2 synthetase inhibitors, p-aminobenzoic acid-l\‘D-mannoside or fish muscle oil as drug vehicle [ 1,2, lo], also supports this view. Conversely, other animal studies have observed increased enzymuria and urinary flow rate, decreased urinary acidification and inhibition of osmoregulatory renal cell transport, suggesting additional renal proximal tubule damage [ 1,111. OTHER METABOLIC/BIOCHEMICAL
STUDIES
Early animal studies demonstrated that CsA caused a disproportionate increase in serum urea concentration, compared to that of creatinine, with hypoalbuminaemia and, ultrastructurally, a reduction in the number of ribosomes within hepatocytes, all of which suggested an adverse effect on protein synthesis. Recent studies have confirmed that CsA also inhibits renal protein synthesis [12] and it has been postulated that it is this inhibitory effect which may be the underlying mechanism responsible for CsA toxicity. CsA has also recently been shown to inhibit the renal cortical synthesis of both DNA and RNA and also to lower the activity of Na+-K+-ATPase, a membrane-bound enzyme. Other studies have demonstrated that CsA increases the mobility of lipids in the inner membrane and also directly inhibits nuclear function in human lymphocytes. CsA also inhibits the Na+/glucose co-transporter in LLCPK 1 cells in culture; altered renal glucose uptake associated with cell membrane damage and increased lipid peroxidation has also been demonstrated and a role for 02 free radicals suggested. Clinical studies of renal transplant recipients have demonstrated that CsA nephrotoxicity was more pronounced in patients receiving kidneys with long warm or cold ischaemic times, suggesting an effect on renal energy metabolism. In experimental studies, CsA nephrotoxicity is also enhanced by surgical stress and renal ischaemia and the presence of giant mitochondria in the proximal renal tubule of both animals and patients treated with CsA also supports this view. Other animal studies have demonstrated that CsA administration is associated with a decreased level of p-subunit antigen of mitochondrial Fi-ATPase, predominantly in the renal medulla, and also that pre-existing hypertension or renal ischaemia may predispose to nephrotoxicity. One possible explanation for the increased susceptibility is that CsA prevents the adaptive increase in mitochondrial respiration and Ca2+ extrusion, particularly
12
in the renal cortex, following an ischaemic insult. However, effects on renal mitochondrial function are harder to define. It has been demonstrated that CsA inhibits renal mitochondrial electron transfer in vitro and that the drug also decreases State 3 respiration and the uncoupled respiration of succinate and glutamate/malate in vivo without however, adversely effecting renal cortical ATP concentrations. However, following treatment with CsA for 30 days at 30 mg/kg/d p-0. in the rat, augmentation of renal mitochondrial oxidative phosphorylation was observed; the ADP-stimulated respiratory rate was increased by 37% with glutamate plus malate as respiratory substrates but not with succinate [13], indicating enhancement of mitochondrial complex I activity. These findings were interpreted as being an adaptive response to the 33% reduction observed in renal blood flow. Conversely, during severe depression in GFR, only minor alterations in mitochondrial function have been noted in the rat [14]. However, CsA has been shown to be a potent inhibitor of mitochondrial permeability transition, reducing the movement of small molecules and ions through the inner membrane [ 151. COMMENT
Considering the structural and functional abnormalities associated with CsA administration, it seems likely that the underlying overall mechanism will involve a combination of several of those mentioned above. Furthermore, the development of CsA-induced renal toxicity may be temporally unrelated to that developing in other systems. In addition, although, many underlying pathophysiological processes have been suggested, it is not clear whether one CsA-induced abnormality alone or a combination of one or more effects is the primary signal for the development of toxicity. REFERENCES 1 Whiting, P.H. and Thomson, A.W. (1989) Pathological effects of cyclosporin A in experimental models. In: A.W. Thomson (Ed.), Cyclosporin: Mode of Action and Clinical Application. Kluwer Academic Publishers, Boston, pp. 303-323. 2 Burke, M.D., MacIntyre, F., Cameron, D. and Whiting, P.H. (1989) Cyclosporin A metabolism and drug interactions. In: A.W. Thomson (Ed.), Cyclosporin: Mode of Action and Clinical Application. Kluwer Academic Publishers, Boston, pp. 267-302. 3 Myers, B.D., Ross, J., Newton, L., Luetscher, J. and Perloth, M. (1984) Cyclosporine-associated chronic nephropathy. N. Engl. J. Med. 311,699-705. 4 Perico, N., Benigni, A., Zoja, C., Delaini, F. and Remuzzi, G. (1986) Functional significance ofexaggerated renal thromboxane A2 synthesis induced by cyclosporine. Am. J. Physiol. 251, F581-F587. 5 Winston, J.A., Feingold, R. and Safirstein, R. (1989) Glomerular haemodynamics in cyclosporine nephrotoxicity following uninephrectomy. Kidney Int. 35, 1175-l 182. 6 DOS Santos, Q.F., Boim, M.A., Bregman, R., Draibe, S.A., Barros, E.J., Pirotxky, E., Schor, N. and Braquet, P. (1989) Effect of platelet-activating factor antagonist on cyclosporine nephrotoxicity. Glomerular haemodynamics evaluation. Transplantation 47,592-595. 7 Walker, R.J., Lazzaro, V.A., Duggin, G.G., Horvath, J.S. and Tiller, D.J. (1989) Cyclosporin A inhibits protein kinase C activity: a contributing mechanism in the development of nephrotoxicity? B&hem. Biophys. Res. Commun. 14,409-415.
73 8 Mayer, R.D., Berman, S., Cockett, A.T. and Maines, M.D. (1989) Differential effects of cyclosporin on hepatic and renal heme, cytochrome P-450 and drug metabolism. Possible role in nephrotoxicity of the drug. Biochem. Pharmacol. 38,1001-1007. 9 Devarajan, P., Kaskel, F.J., Arbeit, L.A. and Moore, L.C. (1989) Cyclosporine nephrotoxicity: blood volume, sodium conservation, and renal hemodynamics. Am. J. Physiol. 256, F71-F78. 10 Craighead, LB., Heys, SD., Smart, L.M., Thomson, A.W. and Whiting, P.H. (1990) Allevation of experimental cyclosporin A toxicity by substitution of fish muscle oil as drug vehicle. Immunopharmacology (in press). 11 Terreros, D.A. and Coombs, J. (1989) Cyclosporine nephropathy: inhibition of osmoregulatory renal cell transport. Ann. Clin. Lab. Sci. 19,337-344. 12 Buss, WC., Stepanek, J. and Bennett, W.M. (1989) A new proposal for the mechanism of cyclosporine A nephrotoxicity. Inhibition of renal microsomal protein chain elongation following in vivo cyclosporine A. Biochem. Pharmacol. 38,40854093. 13 Lemmi, C.A., Pelikan, P.C., Sikka, S.C., Hirschberg, R., Geesaman, B., Miller, R.L., Park, KS., Liu, S.C., Koyle, M. and Rajfer, J. (1989) Cyclosporine augments renal mitochondrial function in vivo and reduces renal blood flow. Am. J. Physiol. 257, F837-F841. 14 Elzinga, L.W., Mela-Riker, L.M., Widener, L.L. and Bennett, W.M. (1989) Renal cortical mitochondrial integrity in experimental cyclosporine nephrotoxicity. Transplantation 48, 102-106. 15 Brokenness, K.M. and Pfeiffer, D.R. (1989) Cyclosporin A-sensitive and insensitive mechanisms produce permeability transition in mitochondria. Biochem. Biophys. Res. Commun. 163, 561-566.
Toxicology Letters, 53 (1990) 69-13 Elsevier
TOXLET 02387
Mechanisms underlying cyclosporin A nephrotoxicity
Paul H. Whiting Department
of Clinical Biochemistry,
University of Aberdeen, Aberdeen (U.K.)
Key words: Cyclosporin A nephrotoxicity; Vasoconstriction;
Tubulopathy; Biochemical mechanisms
INTRODUCTION
Nearly all patients on cyclosporin A (&A) demonstrate some degree of renal impairment which, in the most severe cases, has lead to end-stage renal failure. Clinically, there appear to be 3 main types of renal structural damage associated with CsA administration [l]. None of these is specific, but all are present more commonly following CsA administration than in other situations. First, in patients with prolonged oliguria or anuria following renal transplantation, the kidneys may show diffuse interstitial fibrosis (‘interactive toxicity’). Second, acute toxicity, which is dose-related and less common now that lower initial doses of CsA and drug tapering are employed, may be accompanied by structural abnormalities; if changes are present, they comprise a toxic proximal tubulopathy. The third type of CsA-induced renal lesion is chronic toxicity, associated with either striped (i.e. radial) interstitial fibrosis and/ or an arteriolopathy. There are, to date, few studies which describe the pathological effects of chronic administration of CsA on renal structure and function in animal models. Such information is particularly important as it is this form of CsA-nephrotoxicity, apparently neither dose-related nor responsive to dose reduction, which may restrict the clinical use of CsA. MECHANISMS UNDERLYING
The pathogenesis
CYCLOSPORIN A TOXICITY
of CsA-induced renal dysfunction
has recently been reviewed
correspondence: Dr. P.H. Whiting, Department of Clinical Biochemistry, University of Aberdeen, Medical Buildings, Foresterhill, Aberdeen AB9 2ZD, U.K.
Address for
0378-4274/90/S
3.50 @ 1990 Elsevier Science Publishers B.V. (Biomedical Division)
70
[ 1,2] and only references which supersede this article have been included. Most attention has been directed towards understanding the pathogenesis of CsA-induced acute renal dysfunction and it is only recently, with the development of appropriate animal models, that the study of chronic CsA renal dysfunction has begun. Experimental evidence indicates that the fall in glomerular filtration rate (GFR), due to vasoconstriction, observed following CsA administration may be disproportionate to the fall in renal blood Sow [3]. Selective hypofiltration in the absence of reduced GFR [4] and reduced GFR in the absence of vasoconstriction have also been reported [S]. Although the mechanisms underlying CsA-induced renal dysfunction still remain unclear, and the literature contains many anecdotal and conflicting reports, altered renal haemodynamics mediated via either stimulation of the renin-an~otensin-aldosterone system (RAAS), altered renal prostaglan~n metabolism, a-adrenergic stimulation, tubulo-glomerular feedback mechanisms stimulated by renal tubular damage and/or dysfunction, or altered intrarenal control of GFR, caused perhaps by hy~~lasia of the juxtaglomerular apparatus, have all been suggested from the results of animal studies [l]. It has also been suggested that endothelial cell injury occurring in the presence of reduced production or release of prostacyclin-stimulating factor by endothelial cells (and consequently impaired vasodilatory prostagiandin production) could predispose to platelet agg~gation and thrombosis in the capillary circulation. However, in the rat the acute, haemodynamically-mediated CsA nephrotoxicity may be related to either inhibition of vasodilatory prostaglandins or to a lack of response to vasodilators but not mediated via endotheli~-delved relaxant factor [l]. A role for platelet-activating factor and protein kinase C has also been suggested ]697l. Although the severity of acute CsA nephrotoxicity is related to circulating drug levels, there is stilt a ~ntroversy as to whether native CsA or a metabolite initiates the toxic response, although most information favours the former. There is now extensive evidence that interference with hepatic CsA metabolism in both experimental and clinical studies affects the extent of renal functional and structural impairment. Thus, co-trea~ent with known inducers (e.g., phenobarbitone) or inhibitors (e.g., ketoconazole) of hepatic cytochrome P-450 dependent mono-oxygenase activity results in lower circulating CsA levels and diminished nephrotoxicity or higher circulating drug concentrations and enhanced nephrotoxicity, respectively. A cytochrome P450 isozyme, immun~hemi~lly similar to the phenobarbitone-inducible form in liver, has recently been demonstrated in the kidneys of CsA-treated rats, suggesting that increased renal CsA metabolism may generate a toxic metabolite [l]. However, inhibition of degradation, rather than increased synthesis of the haem molecule, resulting in increased kidney cytochrome P-450 concentrations, has also been suggested
IIf% The severity of acute CsA nephrotoxicity is also increased by co-treatment with other nephrotoxic agents, including gentamicin and amphote~cin B, and also by concomitant administration of the diuretic agents fmosemide and mannitol. Partial pro-
71
tection against CsA nephrotoxicity in the rat is observed when either the angiotensinconverting enzyme inhibitor, enalapril, or the distal tubular antagonist of aldosterone, spironolactone, are co-administered [1,2]. However, although a role for the RAAS has not been confirmed in patient studies, many of the patients studied were receiving drugs which themselves affected the intrarenal control of GFR. However, evidence of a pre-renal element in the development of CsA nephrotoxicity, a reduced fractional excretion of lithium, related to the development of circulatory hypovolaemia [9], has been obtained in both patient and animal studies [l]. In addition, the increased excretion of thromboxane B2 (TxB$ caused by CsA and prevented by cotreatment with either thromboxane A2 synthetase inhibitors, p-aminobenzoic acid-l\‘D-mannoside or fish muscle oil as drug vehicle [ 1,2, lo], also supports this view. Conversely, other animal studies have observed increased enzymuria and urinary flow rate, decreased urinary acidification and inhibition of osmoregulatory renal cell transport, suggesting additional renal proximal tubule damage [ 1,111. OTHER METABOLIC/BIOCHEMICAL
STUDIES
Early animal studies demonstrated that CsA caused a disproportionate increase in serum urea concentration, compared to that of creatinine, with hypoalbuminaemia and, ultrastructurally, a reduction in the number of ribosomes within hepatocytes, all of which suggested an adverse effect on protein synthesis. Recent studies have confirmed that CsA also inhibits renal protein synthesis [12] and it has been postulated that it is this inhibitory effect which may be the underlying mechanism responsible for CsA toxicity. CsA has also recently been shown to inhibit the renal cortical synthesis of both DNA and RNA and also to lower the activity of Na+-K+-ATPase, a membrane-bound enzyme. Other studies have demonstrated that CsA increases the mobility of lipids in the inner membrane and also directly inhibits nuclear function in human lymphocytes. CsA also inhibits the Na+/glucose co-transporter in LLCPK 1 cells in culture; altered renal glucose uptake associated with cell membrane damage and increased lipid peroxidation has also been demonstrated and a role for 02 free radicals suggested. Clinical studies of renal transplant recipients have demonstrated that CsA nephrotoxicity was more pronounced in patients receiving kidneys with long warm or cold ischaemic times, suggesting an effect on renal energy metabolism. In experimental studies, CsA nephrotoxicity is also enhanced by surgical stress and renal ischaemia and the presence of giant mitochondria in the proximal renal tubule of both animals and patients treated with CsA also supports this view. Other animal studies have demonstrated that CsA administration is associated with a decreased level of p-subunit antigen of mitochondrial Fi-ATPase, predominantly in the renal medulla, and also that pre-existing hypertension or renal ischaemia may predispose to nephrotoxicity. One possible explanation for the increased susceptibility is that CsA prevents the adaptive increase in mitochondrial respiration and Ca2+ extrusion, particularly
12
in the renal cortex, following an ischaemic insult. However, effects on renal mitochondrial function are harder to define. It has been demonstrated that CsA inhibits renal mitochondrial electron transfer in vitro and that the drug also decreases State 3 respiration and the uncoupled respiration of succinate and glutamate/malate in vivo without however, adversely effecting renal cortical ATP concentrations. However, following treatment with CsA for 30 days at 30 mg/kg/d p-0. in the rat, augmentation of renal mitochondrial oxidative phosphorylation was observed; the ADP-stimulated respiratory rate was increased by 37% with glutamate plus malate as respiratory substrates but not with succinate [13], indicating enhancement of mitochondrial complex I activity. These findings were interpreted as being an adaptive response to the 33% reduction observed in renal blood flow. Conversely, during severe depression in GFR, only minor alterations in mitochondrial function have been noted in the rat [14]. However, CsA has been shown to be a potent inhibitor of mitochondrial permeability transition, reducing the movement of small molecules and ions through the inner membrane [ 151. COMMENT
Considering the structural and functional abnormalities associated with CsA administration, it seems likely that the underlying overall mechanism will involve a combination of several of those mentioned above. Furthermore, the development of CsA-induced renal toxicity may be temporally unrelated to that developing in other systems. In addition, although, many underlying pathophysiological processes have been suggested, it is not clear whether one CsA-induced abnormality alone or a combination of one or more effects is the primary signal for the development of toxicity. REFERENCES 1 Whiting, P.H. and Thomson, A.W. (1989) Pathological effects of cyclosporin A in experimental models. In: A.W. Thomson (Ed.), Cyclosporin: Mode of Action and Clinical Application. Kluwer Academic Publishers, Boston, pp. 303-323. 2 Burke, M.D., MacIntyre, F., Cameron, D. and Whiting, P.H. (1989) Cyclosporin A metabolism and drug interactions. In: A.W. Thomson (Ed.), Cyclosporin: Mode of Action and Clinical Application. Kluwer Academic Publishers, Boston, pp. 267-302. 3 Myers, B.D., Ross, J., Newton, L., Luetscher, J. and Perloth, M. (1984) Cyclosporine-associated chronic nephropathy. N. Engl. J. Med. 311,699-705. 4 Perico, N., Benigni, A., Zoja, C., Delaini, F. and Remuzzi, G. (1986) Functional significance ofexaggerated renal thromboxane A2 synthesis induced by cyclosporine. Am. J. Physiol. 251, F581-F587. 5 Winston, J.A., Feingold, R. and Safirstein, R. (1989) Glomerular haemodynamics in cyclosporine nephrotoxicity following uninephrectomy. Kidney Int. 35, 1175-l 182. 6 DOS Santos, Q.F., Boim, M.A., Bregman, R., Draibe, S.A., Barros, E.J., Pirotxky, E., Schor, N. and Braquet, P. (1989) Effect of platelet-activating factor antagonist on cyclosporine nephrotoxicity. Glomerular haemodynamics evaluation. Transplantation 47,592-595. 7 Walker, R.J., Lazzaro, V.A., Duggin, G.G., Horvath, J.S. and Tiller, D.J. (1989) Cyclosporin A inhibits protein kinase C activity: a contributing mechanism in the development of nephrotoxicity? B&hem. Biophys. Res. Commun. 14,409-415.
73 8 Mayer, R.D., Berman, S., Cockett, A.T. and Maines, M.D. (1989) Differential effects of cyclosporin on hepatic and renal heme, cytochrome P-450 and drug metabolism. Possible role in nephrotoxicity of the drug. Biochem. Pharmacol. 38,1001-1007. 9 Devarajan, P., Kaskel, F.J., Arbeit, L.A. and Moore, L.C. (1989) Cyclosporine nephrotoxicity: blood volume, sodium conservation, and renal hemodynamics. Am. J. Physiol. 256, F71-F78. 10 Craighead, LB., Heys, SD., Smart, L.M., Thomson, A.W. and Whiting, P.H. (1990) Allevation of experimental cyclosporin A toxicity by substitution of fish muscle oil as drug vehicle. Immunopharmacology (in press). 11 Terreros, D.A. and Coombs, J. (1989) Cyclosporine nephropathy: inhibition of osmoregulatory renal cell transport. Ann. Clin. Lab. Sci. 19,337-344. 12 Buss, WC., Stepanek, J. and Bennett, W.M. (1989) A new proposal for the mechanism of cyclosporine A nephrotoxicity. Inhibition of renal microsomal protein chain elongation following in vivo cyclosporine A. Biochem. Pharmacol. 38,40854093. 13 Lemmi, C.A., Pelikan, P.C., Sikka, S.C., Hirschberg, R., Geesaman, B., Miller, R.L., Park, KS., Liu, S.C., Koyle, M. and Rajfer, J. (1989) Cyclosporine augments renal mitochondrial function in vivo and reduces renal blood flow. Am. J. Physiol. 257, F837-F841. 14 Elzinga, L.W., Mela-Riker, L.M., Widener, L.L. and Bennett, W.M. (1989) Renal cortical mitochondrial integrity in experimental cyclosporine nephrotoxicity. Transplantation 48, 102-106. 15 Brokenness, K.M. and Pfeiffer, D.R. (1989) Cyclosporin A-sensitive and insensitive mechanisms produce permeability transition in mitochondria. Biochem. Biophys. Res. Commun. 163, 561-566.
