Is chronic calcineurin inhibitor toxicity responsible for long-term deterioration of renal function in transplant recipients?

Is Chronic Calcineurin Inhibitor Toxicity Responsible for Long-Term Deterioration of Renal Function in Transplant Recipients? Matthew R. Weir Dose reduction or discontinuation of calcineurin inhibitors (CIs) in renal allograft recipients results in a measurable improvement in renal function, as assessed by a decrease in serum creatinine or improvement in glomerular filtration rate. In general, this effect has been presumed to result from a discontinuation of the acute vasoconstrictive action of CIs on the afferent arteriole. Does it reflect the resolution of chronic CI toxicity? Does chronic CI toxicity explain part of the syndrome of chronic allograft nephropathy (CAN)? We have observed evidence of a continued improvement in renal function or a lack of further deterioration after CI dose reduction or discontinuation in patients with CAN. This improvement in renal function remains evident for up to several years after the intervention and is observed even when the period of acute vasoconstriction (6 months after intervention; the period when the greatest rate of change occurs) is taken into account. These findings suggest a detrimental effect of CIs on renal function that may be, at least in part, reversible and independent of vasoconstriction. In this review, we examine the data concerning the relationship between CI and chronic graft dysfunction. © 2003 Elsevier Inc. All rights reserved.

s calcineurin inhibitor (CI) toxicity responsible for the long-term deterioration of renal function in transplant recipients? Historically, the transplant community has considered chronic rejection the cause of much of the deterioration of kidney function in patients who are successful recipients of long-term renal transplants. The causes of chronic allograft nephropathy (CAN) are likely muhifactorial and include both immunologic and nonimmunologic events. An important clinical question is whether CI toxicity contributes to either the initiation or the propagation of the progressive scarring process, which results in loss of renal function. Part of the difficulty in designing clinical trials to evaluate this question is that the histologic diagnosis of CAN does not always indicate a progressive disease process. Many patients with the diagnosis of CAN have stable renal function. Thus most of the experience in trying to diagnose and treat chronic nephropathy is based on clinical trials that are frequently small and have a

I

From the Department of Medicine, Division of Nephrolo~,, Univerritr of Marl,land School of Medicine, Baltimore, MD. Address reprint requests to Matthew R. Weir. MD, Division of NephroL ogl,, Universi9' of Mao,land Medical @stem, 2") .South Greene Street, Baltimore, MD 21201-1595. © 2003 Elsevier .Inc. Aft rights reserved. 0955-470.¥/03/1701-0004530.00/0 doi."l O.1053/trre.2003.5 90

short-duration lbllow-up and in which the diagnosis or the cause of progressive renal function deterioration is not certain. There are no compelling data to show that the slope of loss of renal function over tirne in a renal transplant population on a regimen of CIs is any different fi'om the slope of a population on a regimen of other immunosuppressant drugs. Tbus the purpose of the discussion herein is to probe the question of whether it is appropriate to consider CI dose reduction or discontinuation in patients who have already manifested evidence of dwindling kidney function and biopsy evidence of CAN. This is an important clinical question because CIs are so important in the immunosuppressant regimen as a means of prophylaxis against acute rejection, which is one of the well-described variables that can contribute to progressive loss of graft function over time. Thus approaches to reducing CI dose or discontinuation need to be considered vmT careftdly ~dth regard to therapeutic index because any incremental risk in rejection ~d[l more likely than not reduce possible beneficial effects of CI dose reduction or discontinuation on renal structure and function.

CI Dose Reduction Or Discontinuation and Renal Function CIs, such as cyclosporine, exert acute and reversible vasoconstrictive effects on the afferent arteriole of

Transplantation Reviews, I/ol IZ No I (Januao,), 2003.'pp 20-30

Calcineurin Inhibitors and Renal To,dcit),

the kidney, which result in decreased glomerular filtration rate (GFR) and increased renal vascular resistance, t,2 The net result of these hemodynamic effects explains the increase in serum creatinine associated with ongoing use of CIs, an event most often categorized as nephrotoxicity. 3-5 The loss of renal function over time that is often associated with the use of these drugs suggests that there is progressive structural damage in addition to the hemodynamic effects. Indeed, at almost an t, posttransplantation point, regardless of renal function, cessation of CIs results in at least a temporal T improvement in renal function. It is cleat', however, that multiple factors may contribute to a decline in renal function in kidney transplant recipients, and it is difficult to attribute such an event solely to the use of CIs. Nonetheless, with the advent of newer, nonnephrotoxic immunosuppressive agents, many centers, inch, ding our own, are now investigating regimens that allow reduction or discontinuation of CIs. Pressure on the donor organ p001 has created a need for increased use of marginal kidneys (eg, kidneys fi'om older donors or those with long cold ischemia times or acute tubular necrosis). With increasing use of marginal kidneys for transplantation, it can be anticipated that CAN will continue to be a major factor contributing to graft loss in the next decade. Use of immunosuppressive agents that may in any way adversely affect kidney function in allografts that are already starting off with a limited functional capacity, or nephron mass, would thus seem counterintuitive. Experience has now been gained with regimens aimed at redt, cing CI use in renal transplantation. Two meta-analyses of these trials have suggested no adverse impact of CI discontinuation (particularly cyclosporine) on graft function or patient survival. 6,7 Indeed, discontinuation or dose reduction of CIs with use of azathioprine, ~,'J mycophenolate mofetil (MMF), m-13 or sirolimus (rapamycin)t4 is associated with a marked reduction in serum creatinine and improved GFR. In the absence of long-term follow-up data for many of these studies, it has been generally assumed that this improvement in renal function is a direct consequence of a discontinuation of the previously mentioned vasoconstrictive effects of CIs. This may indeed be the case for patients with stable (as opposed to chronically deteriorating) renal function, 9a3 and, in fact, in clinical practice there is little motivation to discontinue CIs in patients with stable renal function. The case for patients with progressively declining renal function associated

21

with CAN, however, may be more complicated, and this is a much more common indication for CI withdrawal. In patients receiving marginal kidneys, complete CI avoidance or use of much lower doses may be the best strategy. Our efforts have been tbcused on improving renal function, specifically in patients with chronic and progressive declines in renal function associated with CAN. Our general approach to patients with CAN has been to reduce their dose of CI to approximately 50% of the baseline level (cyclosporine, 12-hour trough, 50-125 ng/mL; tacrolimus, 12-hour trough, 5-7 ng/mL) or, in some cases, discontinue the CI completely. This intervention is combined with the addition (or continuation) of MMF (1 g twice a day) and a standard regimen of low-dose steroids (prednisone, 0.1 mg/kg pet" day)J:' In our clinical experience, in about half of patients with biopsy-proven CAN, renal function continues to improve over an extended period after CI close reduction or withdrawaI? -~j70fnote, when the first 6 months after CI close reduction or withdrawal is censored, the reciprocal of serum creatinine over time continues to show improvement (Fig 1)? 7 This effect is sustained beyond the initial transitional period after intervention, and we propose that additional mechanisms beyond a lessening of vasoconstriction may contribute to the improvement. In a long-term follow-up review of a cohort of 118 patients, we recently confirmed an improvement in renal ft, nction or lack of deterioration in renal function over a mean of 1.78 years after intervention? -~Furthermore, using 2 different methods for modeling renal function, we confirmed that intervention is correlated with the observed improvement in renal functionJ "~ These results suggest that pathologic mechanisms other than vasoconstriction may be contributing to graft deterioration and loss of renal function over time. A definitive relation between the acute nephrotoxic effects of CIs and development of CAN has been difficult to establish, s This is in part because of a marked similarity in the structural lesions observed in patients with CAN and cyclosporine toxicity. 5`m Moreover, pathogenesis of CAN in renal allograft recipients is multifactorial, involving both immunologic (eg, acute rejection, human leukocyte antigen mismatch) and nonimmunologic (eg, donor age, donor brain death, cytomegalovirus infection) parameters, t9 Factors such as donor age have been found to affect the overall incidence of CAN, 9° and this trend can be expected to continue, especially with ongoing use of older kidneys.

22

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Detailed reviews of all the pathogenic mechanisms contributing to CAN may be found elsewhere. 2',22 This review specifically focuses on the direct or indirect adverse effects of CIs that may contribute to progression of CAN in renal allograft recipients, which we think serves to justify our treatment of CI dose reduction or withdrawal in patients with CAN.

Why Reduce or Discontinue CIs? In some studies, the acute nephrotoxic effects of cyclosporine have not been associated with a deterioration of renal function over follow-up periods as long as 8 years. 3,4a3,'4 In fact, a positive relation between cyclosporine dose and graft survival has been observed in a retrospective study, suggesting that control of immunologic variables (ie, acute rejection) is more important in the prevention of CAN. 2~ In a recent study of 2-year protocol biopsies (N = 144 patients), patients experiencing an acute rejection in the first year were more likely to have histopathologic evidence of CAN at 2 years versus those without rejection (77.4% versus 60.4%, P = .045). Patients experiencing nephrotoxicity in the first year were also significantly more likely to have CAN versus those with no nephrotoxic episode (P < .001)20 These findings suggest that nephrotoxicity may be as important as acute rejection in determining overall risk of CAN. Data from the meta-analyses ofKasiske et al 6,7 show that CI withdrawal, although increasing the incidence of acute rejection, does not adversely affect long-term graft function. 6,7 Hunsicker et a126 also recently showed that acute rejec-

2000

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Figure 1. Change in renal function after wclosporine reduction in M~lF-treated patients with CAN.

tion affects only 6-month creatinine clearance but not the rate of functional decline thereafter. These findings suggest that reducing nephrotoxicity and fibrosis fi'om an acute injury may be a more effective means of presetwing function in the allograft rather than increasing immunosuppression to compensate for its occurrence. Indeed, CIs themselves may be an integral component of profibrotic mechanisms, and CI-associated metabolic disturbances (eg, hyperlipidemia, diabetes) may also affect the ability of the allograft to recover fi'om acute injury (see later). Our data suggest an ongoing improvement in renal function because of an apparent reversal of CAN-associated damage. Tl~s benefit is, at least in part, independent of CI's vasoconstrictive action.

CIs and Soluble Mediators of Fibrosis and Apoptosis Structural damage to the kidney caused by ongoing use of CIs has received much attention as a possible contributory mechanism for CAN. The lesions associated with chronic cyclosporine toxicity are well known. 5aa Among the most common histologic findings associated with chronic cyclosporine toxicity is tubulointerstitial fibrosis (TIF). Unfortunately, TIF is also a common feature associated with CAN, 2~,27 and it is difficult to distinguish these 2 entities histologically.5,m Nonetheless, there is evidence that cyclosporine rriay enhance the production of transforming growth factor/3 (TGF-/3),28-3° a profibrotic cytokine that has been implicated in the development of TIF2 9,a',32 In c3,closporine-treated patients diagnosed with chronic allograft fibrosis, TGF-/3 lev-

Calcineurin Inhibitors and Renal Toxicity

els are enhanced and this is well correlated with a significant decline in renal function.~ Similarly, TGF-/3 levels have also been associated with chronic cTclosporine toxicity and poorer graft outcomes in patients treated with cyclosporine.:~4 In support of a TGF-/3 involvement in the process of functional decline, Hueso et al ~ showed that in patients with declining renal function a CI dose reduction and the addition of MMF improve renal function and decrease systemic TGF-/3 levels, tt Moreover, our own studies, in which we used a similar overall approach, have demonstrated significant (P < .05) improvements in renal histologic characteristics and reduction of immunohistochemical staining of renal tissue TGF-/3 levels in patients whose renal function improved after CI withdrawal. :~.~In mice, TGF-~ mimics and anti-TGF-/3 inhibits the effect ofcyclosporine on matrix protein accumulation and renal histologic abnormality, 3~Isuggesting that TGF-/3 is at least one mediator of the long-term effects of cyclosporine. Although supported by both clinical and experimental studies, whether TGF-/3 is directly responsible for the cyclosporine-associated decline in renal function remains controversial. It may be argued that many types of acute injury can elicit production of TGF-/3. Nonetheless, reports relating renal tissue and serum TGF-/3 levels to long-term cyclosporine use and nephrotoxicity are suggestive of some degree of cyclosporine-induced renal injury. Enhanced fibrosis caused by TGF-/3 induced by ongoing cyclosporine use and also through other metabolic pathways (see later) may thus be a major contributor to graft damage and long-term functional deterioration. Patients with chronic c3,closporine toxicity but not chronic rejection (ie, CAN) also appear to have elevated levels of proinflammatory cytokines, including endothelin 1 (ET-1), RANTES (regulated upon activation, normal T cell expressed and secreted), and monocyte chemoattractant protein 1 (MCP-I), and associated TIF and tubular atrophy. 37 These mediators appear to be localized to sites of renal cyclosporine-associated damage and TIF, and thus a causal relation between increased cytokine expression and structural damage can be inferred.37 Macrophage influx has been found to precede development of TIF in an animal model of chronic cyclosporine toxicity, suggesting a model whereby local inflammatory cytokine production contributes to development of TIF. 38 Accumulation of these inflammatory mediators may also be associated with a loss of renal functional and reparative capacity. Animal studies have also described an up-regulation of proapoptotic

23

genes in a model of chronic cyclosporine nephrotoxicity.~'j After 4 weeks of cyclosporine treatment, apoptosis inducers (eg, p53, Bax, FasL) were up-regulated, whereas apoptosis inhibitors (eg, Bcl-2) were down-regulated. Changes in gene expression were correlated with an increase in the number ofapoptotic cells, as well as with tubular atrophy and TIFP 9 These findings support a mechanism whereby cyclosporine-induced chronic up-regulation of proapoptotic pathways results in a progressive loss of cellularity and a diminished proliferative capacity of the graft to repair acutely damaged tissues. 39 Such mechanisms may indeed contribute to declining renal function in patients with CAN. In our studies, we have found that cyclosporine withdrawal is associated with significant (P < .05) reductions in apoptosis and p53 expression, as well as improvements in renal pathologic scores for interstitial fibrosis, vascular sclerosis, transplant glomerulopathy, and vascular hyalinosis.4° It is interesting that the improvement in renal function after cyclosporine discontinuation, as assessed by 2-phase regression in some of our patients, appeared to require a lag time between intervention and recovery (Fig 2). It is tempting to speculate that this lag may be caused by a healing process in the allograft, possibly involving reduced either TGF-/3 or apoptosis (or both), after intervention.

Metabolic Effects: Hypertension Adverse effects of CIs on metabolic parameters represent another factor contributing to the incidence of renal dysfunction and CAN. Hypertension, caused in part by acute renal vasoconstrictive effects of CIs, as well as neurotoxic effects,41,42 may be a source of further stress on the allograft. Some studies, 43 but not others, 4 have suggested that tacrolimus (FK506) produces somewhat less hypertension than cyclosporine in renal allograft recipients. However, tacrolimus acts through a similar calcineurin inhibitory pathway and alters vascular hemodynamics,'I-1.'H and both CIs exhibit neurotoxic effects4'-'.45 capable of contributing at some level to hypertension. A number of studies "~48 have shown associations between hypertension and poorer graft outcome. Retrospective analyses have identified increased systolic and diastolic blood pressure as significant predictors of graft failure.4~IIn another study, hypertensive renal allograft recipients were found to have a significantly poorer GFR at 1 year (P = .01), and uncontrolled hypertension was associated with the worst

24

Matthew R. Weir

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graft prognosis over 8 years (P < .03).'/" More recently, statistically significant associations between systolic blood pressure or mean arterial blood pressure and allograft survival have been reported, and there was no blood pressure value below which improved allograft outcomes were not observed? 7 These findings suggest that hypertension clearly has a detrimental effect on graft function. TGF-/3 production also appears to be enhanced in monocytes of hypertensive as opposed to normotensire patients49; as such, this provides at least one possible link between the metabolic effects of CIs and the above-described profibrotic effects. Findings of reduced serum TGF-~ on CI dose reduction II are supportive of this notion. However, the direct involvement of hypertension with declining renal function is difficult to establish, and it may also be argued that hypertension is a consequence, not a cause, of reduced renal function associated, for example, with CAN. "t7,48 In our own studies, we have seen that patients with improved renal function did have a corresponding improvement in blood pressureJ 5 Long-term studies with use of antihypertensive agents to control blood pressure in renal transplant recipients are warranted to determine conclusively whether reductions in blood pressure alone will afford these patients any benefit in graft survival. In the short term, it appears that use of antihypertensire agents does not confer any significant protective effect on graft function. 47 Irrespective of the effect on graft survival, however, it can certainly be anticipated that reductions in blood pressure in patients withdrawn from CIs will likely improve patient sur-

I 3

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Figure 2. Change in renal function with cyclosporine reduction in 67 patients with CAN with use of 2-phase reg,'ession. (Reprinted with permission.17)

vival. Indeed, hypertension has been identified as a risk factor for cardiovascular disease and stroke, ~":'~ leading causes of death in the renal transplant population. ~'-':'~As such, we advocate stringent control of blood pressure (<130 mm H g systolic) in all our transplant recipients, the goal being to minimize stresses on the allograft and prevent accumulation of vasculopathy-associated risk facto,'s. In addition, we a,'e currently evaluating angiotensin-conve,'ting enzyme inhibitors and angiotensin receptor blockers as preferred strategies to p,'event progression of CAN in patients with ,'eduction of CI.

M e t a b o l i c Effects: H y p e r l i p i d e m i a Another possible CAN-contributory mechanism is the effect of CIs on lipids. As with hypertension, some analyses have suggested that h)q~erlipidemia is associated with poorer graft survival in selected populations of renal allograft recipients, s4-.s" A recent study identified hypercholesterolemia as a risk factor for graft loss in male patients with a previous acute rejection episode but not in those free of an acute rejection episodeP ~i It is interesting tlmt these findings suggest a detrimental effect oflipids on recovery fi'om an acute endothelial injury (ie, rejection). In this model, hypercholesterolemia may cause sclerosis and hyperplasia of the graft vessels, similar to well-known models of atherosclerosis. -~ti-.~"Another study found an adverse effect of hypercholesterolemia on graft survival that was limited to younger patients. 54 The significance of this finding on renal function and the possible development of CAN is less

CaMneurin Inhibitors and Renal 7bxqciO,

clear. Nonetheless, there is ample evidence from experimental models that kidney disease is worsened by lipid abnormalities/'-'~,~i~ In addition, irrespective of the effect on renal function and CAN, hyperlipidemia (particularly the serum low-density lipoprotein/ high-density lipoprotein ratio) has been identified as a risk factor for cardiovascular disease and atherosclerosis/~.~;'-' and this ma t, detract from long-term patient survival iq renal transplant patients. Although long-term corticosteroid use is also associated with elevations in serum cholesterol and triglycerides, the disruptive effect of CIs on serum lipids has been shown in renal allografl recipients. ~;:~.f~In a comparative study ofcTclosporine-prednisolone- and azathioprine-prednisolone-treated patients, cyclosporine-treated patients had a more atherogenic lipid profile than azathioprine-treated patients? ~' It has also been shown that tacrolimus was less likely to cause hyperlil~idemia compared with cyelosporine in a study of patients matched for baseline hyperlipidemia risk factors and steroid close?~~ In our own patients, we have observed a statistically significant decrease in serum cholesterol alier CI dose reduction "~ or withdrawal. Ic' These results are further eviclence of a direct adverse effect of CIs on lipid levels. Similar findings of decreased cholesterol and lipids after CI withdrawal have been observed in other CI-sparing studies? ~,~'-' Whether judicious management of hyperlipidemia in patients with ongoing CI use will again afford an t, benefit in terms of graft survival remains to be seen in longterm controlled trials of lipid-lowering agents in renal transplant recipients.

Metabolic Effects: Diabetes Although post-renal transplantation diabetes mellitus is associated with steroid use, a diabetogenic effect with CIs has also been identified. The incidence of diabetes has been associated more with tacrolimus use than with cyclosporine? Strategies to adjust doses of steroids and CIs have helped improve glycemic control. Increases in serum glucose are of prognostic importance because the incidence ofdiabetes in renal transplant recipients negatively affects graft survival. ~16,67Hyperglycemia-induced microvascular complications, including diabetic nephropathy, may invoke further stresses on the allograft, and they have been associated with increased intrarenal TGF-/3 levels. ~i8 Hyperglycemia-induced activation of protein kinase C-/3 may also contribute to higher

25

TGF-/3 levels, again supporting a profibrotic state in the allograft. 69 The diabetic milieu is of concern over time with regard to development of vasculopathy, not only in the graft but also in the patient. Cardiovascular mortality is high in diabetic graft recipients, 7° as is the incidence of infectious complications, 6~,67 which may greatly complicate posttransplantation care. Reductions in the incidence of post-renal transplantation diabetes mellitus associated with steroid or CI reduction or withdrawal may therefore reduce profibrotic mechanisms in the allograft, as well as potentially improve overall patient outcomes. Epidemiologic studies suggest that control of glucose levels reduces the incidence of microvascular and macrovascular complications in patients with type 1 or type 2 diabetes. 7t,72 Thus, regardless of the effect of diabetes on the progression to CAN, stringent glycemic control should be advocated for all renal transplant patients, and, to the extent that patients can be kept within American Diabetes Association guidelines for normoglycemia, this should certainly be a goal.

Other Mechanisms: Fibrinolytic Activity Manifestations of CAN may be viewed as resulting from a generalized vasculopathy in renal transplant patients made worse by ongoing accumulation of metabolic abnormalities. In addition to hypertension, hypercholesterolemia, and hyperglycemia, alterations in fibrinolytic activity m a y also be important. Fibrinogen level is recognized as a strong predictor of cardiovascular disease, and elevated fibrinogen levels ma t, increase risks for potentially fatal cerebrovascular and cardiovascular events. 73 It has been suggested that fibrinogen is a risk factor for cardiovascular disease that is as important as smoking, cholesterol, and hypertension and is also a very strong risk factor for other thrombotic events such as stroke. 7~ It is notable that, in a study of renal transplant recipients, cyclosporine-treated patients, compared with control patients, were found to have elevated plasma fibrinogen levels, hematocrit, and blood viscosity, as well as increases in other cardiovascular risk factors, such as blood pressure and serum triglyceride levels. TM At least 1 study has shown that withdrawal of cyclosporine has a beneficial effect; patients switched from cyclosporine to azathioprine had a substantial improvement in fibrinolytic activity. 75 It is not clear what effect improved fibrinolytic activity may have on graft sur-

26

Matthew R. Weir

vival; however, it may aid in reducing the complication of vasculopathy that is so common in this population.

CI-Sparing Regimens Within the past 5 years, the opportunity; to develop CI-sparing regimens has come to fruition with the introduction of the following 3 new therapeutic agents: anti-CD25 monoclonal antibodies (daclizumab and basiliximab), ~ I F , and sirolimus. Also on the horizon are other new compounds that hold promise in that they are nonnephrotoxic and minimally affect blood pressure, carbohydrate metabolism, and lipid metabolism. Early trials with anti-CD25 monoclonal antibodies have been very successful in reducing the incidence of" rejection by about 30% to 38%, compared with placebo, when combined with various fornas of immunosuppression. 7~i,77Use of these antibody preparations may provide an opportunity.' lbr withholding CI use until adequate graft ftmction has been established, for example, in patients with delayed graft function. Some preliminar T studies have also assessed whether anti-CD25 therapy can obviate the need for CI use fi'om the outset of transplantation. These latter trials, however, have been associated with an unacceptably high risk for, albeit easily managed, rejection. 7u.7'-'Therefore it is likely, that these agents may provide a greater long-term opportunity for CI-sparing approaches as opposed to their complete avoidance. Use of anti-CD25 receptor antibodies is a simple nontoxic strateg3, to reduce the risk of rejection. Ultimately, these antibodies hold promise as one of the easiest ways to reduce the amount of long-term immunosuppression. MMF has been shown to be superior to azathioprine a°,Ht or placebo a=' for prevention of acute rejection when used as a component of triple therapy with CI and steroids. MMF acts through the inhibition of purine biosynthesis and is free of nephrotoxic el:fects, a3 Therefore we have replaced azathioiporine in our protocols with MA,IF. t-~-j7 A number of other trials of CI sparing in which M2MF was used have met with considerable success in allowing for the discontinuation or dose reduction of CIs and prevention of acute rejection, I°'r-' including 1 large open-label randomized multicenter European trial. ~t In other cases, MMF has been used as monotherapy, allowing for complete replacement of either cyclosporine or tacrolimus in the context of a very low-toxicity, steroid-free immunosuppressive regimen in selected

populations, j3 MMF has also heen used safely in patients with delayed graft function, resuhing in fewer acute reiections and less neod lbr antilymphoc3,te treatmeut compared with patients treated with azathioprine."-' In addition, some registry data are now beginning to indicate a beneficial effect of MMF on graft survival that is independent of its ability, to prevent acute rejection. ~i Overall, it appears that MMF is a useful and effective inlmunosuppressant to allow CI sparing. This has been the case in our experience after the first posttransplantation year. Beyond the first year, there is not a lot of publishod experience. Side effects encountered with M~IF (nausea, diarrhea) appear to be manageable with appropriate dosing. "].~'' Sirolimus is another new agent that inhibits calcineurin via a distinct mechanism that is different from either cyclosporine or tacrolimus. "7 In a recent trial, it was also shown to be superior to azathioprine in the prevention of acute rejection when used as a component of triple therapy. ~ Some preliminary studies have shown that sirolimus may be useful as a replacement for CIs in patients with associated nepbrotoxicity, H and, indeed, renal function appears to improve, as expected with cyclosporine discontinuation. Cyclosporine levels ma t, also need to be lower than those traditionally usod to avoid nephrotoxicity. Although sirolimus itself is not nephrotoxic, it may increase the nephrotoxicity of cyclosporine, through mediators that are not well described, when these drugs are used together. A potential drawback to the use of sirolimus is its effects on lipids; Iwpertriglyceridemia and hyq~ercholesterolenaia are not tmcommon occurrences with sirolimus theralLv. ~.~"

Conclusions Because CIAN is likely, to be a significant issue in the foreseeable future of renal transplantation, especially with the use of an iucreasing ntnnl~er of marginal kidneys, our approach to immunosuppression must change, with an enaphasis on less toxic regimens to promote long-term patient and allograft survival. Altlaough the direct contribution of CIs to declining renal function Ires been difficuh to establish, the fact that renal function continues to improve over long-term follow-up after CI roduction or withdrawal suggests that there is a direct correlation. Possible mechanisms involved in this improvement ma t, include a discontinuation of profibrogenic, proapoptotic mechanisms in the allograli (eg, reduced TGF-/3 and p53) or a discontinuation of other

Caldneurin Inhibitors and Renal Toxicity

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Figure3.

Contribution of CI toxicity to metabolic state and the progression of chronic allograft nephropathy.

metabolic insults, including hypertension, diabetes, a,ad Iwperlilfidemia, some of which (eg, hypertension, diabetes) may also resuh in elevated intrarenal o," serum TGF-/3 levels (Fig 3). A causative role lbr TGF-/3 in the long-term effects of cyclosporine or tacrolimus o,a re,aal fnnction is far fi'om conclusive. However, it is notable that TGF-/3 expression and T I F are observed even with low-dose cyclosporine and without aherations in renal hemodynamics." Tiffs finding, ahhough experimental, suggests that cyclosporine-induced hemodynamic changes and T I F occt, r independently of each other. If so, the additional mechanisms outlined in this review might provide for a CI-related contributory effect on CAN. Indeed, all of these mechanisms may contribute to what can really be seen as a generalized vasculopathy in renal transplant patients who have a chronic and progressive deterioration of graft fu,action. Ou," first-line intervention has been to reduce or discontinue CIs in such patients and to ensure adequate imnaunosuppression with other drugs. Furthermore, we fi'equently evaluate the adequacy of blood pressure, glycemic, and lipid control. We have focused more effort on using drugs that block the renin-angiotensin system for assisting in blood pressure control and routinely use aspirin and statins. These strategies will foster improvements in patient

survival and quality of life. Also important for future clinical research is to identify factors to predict loss of renal function (eg, C-reactive protein) and surrogate measures to assess the impact of various therapeutic interventions.

References I. Curtis J], Dubovsky E, Whclchel JD, ct al: Cyclosporine in therapeutic closesincrcases allografi vascular resistance. Lancet 1986, 2:477 2. Weir MR, Kl,~sscnDK, Shell SY, el al: Acute effects of intravenous c3'closporineon blotxl pressure, renal hemodynamics, and urine prostaglandin prtxluction in heahhy humans. Transplantation 1990, 49:4I 3. Kahan BD, Flcchncr SM, Lorber Ml, et al: Complications of c3,closporinc-prednisoneimmunosuppression in 402 renal allograft recipients exclusivelyIbllowedat a single center from one to five years. Transplantation 1987, 43:197 4. Pirsch JD, Miller.L Deierhoi MH, ct al: A comparison of tacrolimus (FKS06) and cyclosporineIbr immunosuppression after cadaveric renal transplantation. Transplantation 1997, 63:977 5. AJldoh TF, Bennett WM: Chronic cyclospo,'inenephrotoxieit),. Cu,T Opiq Nephrol Hypertens 1998, 7:265 6. Kasiske BL, Heim-Duthoy K, Ma JZ: Elective cyclosporine withdrawal after ren~d transplantation.Jka\,lA 1993, 269:395 7. Kasiske BL, Chakkera l-l.A,LouisTA, et al: A meta-analysisof immunosuppression withdrawal trials i,a renal transplantation.J Am Soc Neph,'ol 2000, 11:1910

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8. Mourad G, Vela C, RibsteinJ, et ah Long-term improvement in renal function after cyclosporine reduction in renal transplant recipients with histologically proven chronic c3,closporine nephropathy. Transplantation 1998, 65:661 9. MacPhee IA, BradleyJA, Briggs D, et al: Long-term outcome of a prospective randomized trial of conversion from cyclosporine to azathioprine treatment one ),ear after renal transplantation. Transplantation 1998, 68:1186 10. Schrama YC,JolesJA, ",,an Tol A, et al. Conversion to mycophenolate mofetil in conjunction with stepwise withdrawal of cyclosporine in stable renal transplant recipients. Transplantation 2000, 69:376 I I. Hueso M, Borer J, Ser6n D, et at: Low-dose cyclosporine and mycophenolate mofetil in renal allograft recipients ~dth suboptimal renal function. Transplantation 1998, 66:1727 12. Houde I, Isenring P, Boucher D, et al: Mycopheno!ate mofetil, an alternative to cyclosporine A for a long-term immunosuppression in kidney transplantation? Transplantation 2000, 70: 1251 13. Land W: Mycophenolate mofetil-based immunosuppressive therapy: induction, maintenance, and com,ersion protocols in renal transplantation. Transplant Proc 1999, 31:27S (Suppl) 14. Dominguez J, Mahalati K, Kiberd B, et al: Conversion to rapamycin immunosuppression in renal transplant recipients: report of an initial experience. Transplantation 2000, 70:1244 15. Weir MR, Ward MT, Blahut SA, et al: Long-term impact of discontinued or reduced calcineurin inhibitor in patients with chronic allograft nephropathy. Kidney Int 2001, 59:1567 16. Weir MR, Anderson L, FinkJC, et al: A novel approach to the treatment of chronic allograft nepbropathy. Transplantation 1997, 64:1706 17. Weir MR, Fink JC, Hanes DS, et al: Chronic allograft nephropathy: effect of cyclosporine reduction and addition of mycophenolate mofetil on progression of renal disease. Transplant Proc 1999, 31:1286 18. Mihatseh MJ, Ryffel B, Gudat F: The differential diagnosis between rejection and cTclosporine toxicity. Kidney Inl 1995, 48:S-63 19. Tullius SG, Tilney N: Both alloantigen-dependent and independent factors influence chronic allografi rejection. Transplantation 1995, 59:313 20. Solez K, Vincenti F, Filo RS: Histopathologic findings fi'om 2-year protocol biopsies from a U.S. multicenter kidney transplant trial comparing tacrolimus versus cyclosporine. A report of the FK506 Kidney Transplant Study Group. Transplantation 1998, 66:1736 21. Halloran PF, Melk A: Rethinking chronic allograft nephropathy: the concept of accelerated senescence.J Am Soc Nephrol 1999, 10:167 22. Womer K.L, VellaJP, Sayegh MH: Chronic allograft dysfunction: mechanisms and new approaches to therapy. Semin Nephrol 2000, 20:126 23. Lipkowitz GS, Madden RL, MulhernJ, et al: Long-term maintenance of therapeutic cyclosporine levels leads to optimal graft survival without evidence of chronic nephrotoxicity. Transpl Int 1999, 12:202 24. Burke J F J r , Pirsch JD, Ramos EL, et al: Long-term efficacy. and safety of cyclosporine in renal transplant recipients. N EnglJ Med 1994, 331:358 25. Almond PS, Matas A, Gillingham K, et al: Risk factors for chronic rejection in renal allograft recipients. Transplantation 1993, 55:752

26. Hunsicker LG, Bennett LE: Acute rejection reduces creatinine clearance (Ccr) at 6 months following renal transplantation but does not affect subsequent slope of Ccr. Transplantatioh 1999, 67:$83 (abstr) 27. Kasiske BL, Kalil RSN, Lee HS, et at: Histopathologie findings associated with a chronic, progressive decline in renal allograft function. Kidney Int 1991, 40:514 28. Shin G-T, Khanna A, Ding R, et al: In vivo expression of transforming growtb factor431 in humans. Transplantation 1998, 65:313 29. Hutchinson IV: Tile role of transforming growth factor-13 in transplant rejection. Transplant Proc 1991, 31:9S (Suppl) 30. El Gamel A, Awad M, Yonan N, et al: Does cyclosporine promote the secretion of TGD-~01 following pulmonary transplantation? Transplant Proc 1998, 30:1525 31. Sharma VK, Bologa RM, Xu G-P, et al: Intragraft TGF-131 mRNA: A correlate of interstitial fibrosis and chronic allograft nephropathy. Kidney hat 1996, 49:1297 32. Yamamoto T, Noble NA, Miller DE, et at: Sustained expression of TGF-/31 underlies development of progressive kidney fibrosis. Kidney Int 1994, 45:916 33. Cuhaci B, Kunmr MSA, Bloom RD, el at: Transforming growth factor /3 levels in human allograft chronic fibrosis correlate with rate of decline in renal function. Transplantation 1999, 68:785 34. Pankewycz OG, Niao L, Isaacs R, et at: Increased renal tubular expression of transforming growth factor beta in human allografts correlates with cyclosporine toxicity. Kidney Int 1996, 50:1634 35. Song H, Seta K, Kinjo M, et at: Decreasing expression of transforming grox~¢h factor beta in human renal biopsies with improvement in renal pathological score following chronic cyclosporine reduction. Transplantation 1999, 67:$236 36. Khanna AK, Cairns VR, Becker CG, el al: Transforming growth factor (TGF)-,B mimics and anti-TGF-/3 antibody at> rogates the in vivo effects of cyclosporine. Transplantation 1999, 67:882 37. Benigni A, Bruzzi 1, Mister M, et al: Nature and mediators of renal lesions in kidney transplant patients given cyclosporine for more than one year. Kidney Int 1999, 55:674 38. Young BA, Burdmann EA, Johnson RJ, et al: Cellular proliferation and macrophage influx precede interstitial fibrosis in ~,closporine nephrotoxicity. Kidney Int 1995, 48:439 39. Shihab IS, Aaldoh TF, Tanner AM, et al: Expression of apoptosis regulator 7 genes in chronic nephroloxicity favors apoptosis. Kidney Int 1999, 56:2147 40. Wei C, Song H, Seta M, et al: Chronic cTclosporine reduction decreases apoptosis and p53 expression in human renal biopsies with improvement of renal pathological score and renal functian.J Am Soc Nephrol 1999, 10:92 41. Sander M, Lyson T, Tbomas GD, et at: Sympathetic neuronal mechanisms of cyclosporine-induced hypertension. Am J Hypertens 1996, 9:12 IS 42. Lyson T, Ermel LD, Belshaw PJ, et al: Cyclosporine- and FK506-induced sympathetic activation correlates with calcineurin mediated inhibition of T-cell signaling. Circ Res 1993, 73:596 . 43. Radermacher J, Meiners M, Bramlage C, et al: Pronounced renal vasoconstriction and systemic hypertension in renal transplant patients treated with cyclosporine A versus FK 506. Transplant Int 1998, 11:3

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4,1-. DeLima IJG, Xue H, Coburn L, et al: Effects of FK506 in rat and human resistance arteries. Kidney Int 1999, 55:1518 45. Bechstein WO: Neurotoxicity ofcalcineurin inhibitors: impact and clinical management. Transpl Int 2000, 13:313 46. Opelz G, Wujciak T, Ritz E, Collaborative Transplant Stud),: Association of chronic kidney graft failure with recipient blood pressure. Kidney lnt 1998, 53:217 47. Mange KC, Cizman B, Joffe M, et al: Arterial hypertension and renal allograft survival.JA.MA 2000, 283:633 48. Vianello A, Mastrosimone S, Calconi G, et al: The role of hypertension as a damaging factor for kidqey grafts under cyclosporine the,'apy. A m J Kidney Dis 1993, 21:79 (Suppl) 49. Porreca E, Di Febbo C, Mincione G, et al: Increased transforming growth facto,'-/3 production and gene expression by peripheral blood monocytcs of hypertensive patients. Hypertension 1997, 30:13'150. Kannel WB, Wolf PA, Verter J, et al: Epidemiologic assessment of the role of blood pressure in stroke: the Framingham Study. JAMA 1970, 214:301 51. MaclVlahon S, Peto R, CutlerJ, et al: Blood pressure, stroke, and corona D, heart disease. Part I, prolonged differences in blood pressure: Prospective observational studies corrected for the regression dilution bias. Lancet 1990, 335:765 52. Kasiskc BL, Guijarro C, Massy 7~, et al: Cardiovascular disease after renal transplantation. J Am Soc Nephrol 1996, 7:158 53. United States Renal Data System: USRDS 1994: Annual data report. Bethesda, MD, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 1994 54. Roodnat Jl, Mulder PGH, Zietse R, et al: Cholesterol as an independent predictor ofoutcome after renal transplantation. Transplantation 2000, 69:1704 55. Peschke B, Scheuermann EH, Geiger H, et al: Hypertension is associated with hypcrlipklc,nia, coronary heart disease and chronic graft failure in kidney transplant recipients. Clin Nephrol 1999, 51:290 56. Wissing KM, Abramowicz D, Broeders N, et al: Hypercholesterolemia is associated with increased kidney graft loss caused by chronic ,'ejection in male patients with previous acute rejection. Transplantation 2000, 70:464 57. Ross R: The pathogenesis ofatherosclerosis: A perspective for the 1990s. Nature 1993, 362:801 58. Ross R: Mechanisms of diseasc:'atherosclerosis~An inflammatory disease. N EnglJ Med 1999, 340:115 59. Kasiske BL, O'Donnell MP, Schmitz PG, et al: The role of lipid abnormalities in the pathogenesis ofchronic, progressive renal disease. Adv Nephrol Necker Hosp 1991, 20:109 60. Keane W'F. The role of lipids in renal disease: future challenges. Kidney Int 2000, 57:$27 (Suppl) 61. Kannel WB: 1Lange of serum cholesterol values in the population developing coronau, artery disease. A m J Cardiol 1995, 76:69C 62. Wong ND, Wilson PWF, Kannel WB: Serum cbolesterol as a prognostic factor after myocardial infarction: the Framingham Study./hm Intern Med 1991, 115:687 63. Kasiske BL, Tortorice KL, Heim-Duthoy KL, et al: The adverse impact of cyclosporine on serum lipids in renal transplant recipients. A m J Kidney Dis 1991, 17:700 64. Satterthwaite R, Aswad S, Sunga V, et al: Incidence of newonset hypercholesterolemia in renal transplant patients

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treated with FKS06 or cyclosporine. Transplantation 1998, 65:446 65. Schorn TF, Kliem V, Bojanovski M, et al: Impact of long-term immunosuppression with cyclosporin A on serum lipids in stable renal transplant recipients. Transpl Int 1991, 4:92 66. Miles AM, Sumrani N, Horowitz R, et al: Diabetes mellitus after renal transplantation. Transplantation 1998, 65:380 67. Sumrani NB, Delaney V, Ding Z, et al: Diabetes mellitus after renal transplantation in the cyclosporine era An analysis of risk factors. Transplantation 1991, 51:343 68. lwano M, Kubo A, Nishino T, et al: Quantification ofglomerular TGF-/31 mRNA in patients with diabetes mellitus. Kidney Int 1996, 49:1120 69. Koya D, Jirousek MR, Lin YW, et al: Characterization of protein kinase C beta isoform activation on the gene expression of transforming growth factor-beta, extracellular matrLx components, and prostanoids in the glomeruli ofdiabetlc rats. J Clin Invest 1997, 100:115 70. Lemmers IvIJ, Bar D, .]M: Major role for arterial disease in morbidity and mortality after kidney transplantation in diabetic recipients. Diabetes Care 1991, 14:295 71. UK Prospective Diabetes Study (UKPDS) Group: Intensive blood-glncose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type-2 diabetes (UKPDS 33). Lancet 1998, 352:837 72. Diabetes Control and Complication Trial (DCCT) Research Group: The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin dependent diabetes mellitus. N Engl J Med 1993, 329:977 73. Kannel WB, Wolf PA, Castelli WP, et at: Fibrinogen and risk of cardiovascular disease: the Framingham Study. JAMA 1987, 258:1183 74. Linde T, Sandhagen B, Backman U, et al: Altered flow properties of blood and increased plasma fibrinogen in cyclosporine-treated renal allograft recipients. Nephrol Dial Transplant 1999, 14:1525 75. van den Dorpel MA, Man in't Veld AJ', Levi M, et al: Beneficial effects of conversion from cyclosporine to azathioprine on fibrinolysis in renal transplant recipients. Arterioscler Thromb Vase Biol 1999, 19:1555 76. Vincenti F, Kirkman R, Light S, et at: Interleukin-2-receptor blockade with daclizumab to prevent acute rejection in renal transplantation. Daclizumab Triple Therapy Study Group. N EnglJ Med 1998, 338:161 77. Nashan B, Moore R, Amlot P, et at: Randomised trial of basiliximab versus placebo for control of acute cellular rejection in renal allograft recipients. Lancet 1997, 350:1193 78. Vincenti F, GrinyoJ, Ramos E, et al: Can antibody prophylaxis allow sparing of other immunosuppressives? Transplant Proc 1999, 31:1246 79. Tran HTB, Acharya MK, McKay DB, et al: Avoidance of c3rclosporine in renal transplantation: effects of dacfizumab, mycophenolate mofetil and steroids.J Am Soc Nephrol 2000, 11:1903

80. Sollinger HW, US Renal Transplant Study Group: Mycophenolate mofetil for the prevention of acute rejection in primary cadaveric renal allograft recipients. Transplantation 1995, 60: 225 81. Tricontinental IVlycophenolate IVlofetil RenalTransplantation Study Group: A blinded, randomized clinical trial of mycophe-

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nolate mofetil for the prevention of acute rejection in cadaveric renal transplantation. Transplantation 1996, 61:1029 82. European Mycophenolate Mofetil Study Group: Placebo-controlled study of mycophenolate mofetil combined with t3,closporine and corticosteroids for the prevention of acute rejection. Lancet 1995, 345:1321 83. Lui SL, Halloran PF: IVlycophenolate mofetil in kidney transplantation. Curr Opin Nephrol Hypertens 1996, 5:508 84. Dudley CRK, MMF "Creeping Creatinine" Study Group: MMF substitution for CSA is an effective and safe treatment of chronic allograft dysfunction; results of a multi-center randomized controlled study. Transplantation 2002, 2(Suppl 3): 148 (abstr) 85. Arnold AN, Wombolt DG, Whelan "IV, et al: Mycophenolate mofetil, with cyclosporine and prednisone, reduces early rejection while allowing the use of less antilymphocytic agent induction and tTclosporine in renal recipients With delayed graft function. Clin Transplant 2000, 14:42I 86. Ojo AO, Meicr-Kriesche HU, HansonJA, et al: Mycophenolate mofetil reduces late renal allograft loss independent of acute rejection. Transplantation 2000, 69:2405

87. Sehga] SN. Rapamune (sirolimus, rapamycin): An overview and mechanism of action. Ther Drug Monit 1995, 17:660 88. Kahan BD, for the Rapamune US Study Group: Efficacy of sirolimus compared with azathioprine for reduction of acute renal allograft rejection: A randomised multicentre study. Lancet 2000, 356:194 89. Groth CG, Backman L, Morales.lM, et al: Sirolimus Enropean Renal Transplant Study Group: Sirolimus (rapamycin)based therapy in human renal transplantation: similar efficacy and different toxicity compared with cyclosporine. Transplantation 1999, 67:1036 90. Macdonald AS, Tile Rapamune Global Study Group: A world~4de, phase III, randomized, controlled, safety and efficacT stud)' of a sirolimus/cyclosporine regimen for prevention of acute rejection in recipients of primary mismatched renal allogn'afts. Transplantation 2001, 71:27 I 91. Vieira.JMJr, Noronba IL, Malheiros DM, et al: Cyclosporineinduced interstitial fibrosis and arteriolar TGF-/3 expression with preserved renal blo~l flow. Transl)lantation 1999, 68: 1746