Angiotensin II antagonists--therapeutic benefits spanning the cardiovascular disease continuum from hypertension to heart failure and diabetic nephropathy

Is Thoracic Aortic Diameter an Independent Predictor of Cardiovascular Disease and Mortality? A Narrative Review

Subclinical alterations in cardiac structure and function include a variety of abnormal phenotypes of recognized adverse prognostic values, such as left ventricular hypertrophy (LVH), concentric remodeling, systolic/diastolic dysfunction, left atrial dilatation, and alterations of LV geometry. The excess cardiovascular risk associated with these markers has been documented in multiple clinical settings, such as the general population, hypertensive cohorts, patients with coronary heart disease, diabetes mellitus, chronic heart failure, and chronic kidney disease. On the contrary, the value of aortic root (AR) and ascending aortic diameter in predicting cardiovascular outcomes and all-cause mortality in populations free from overt aortic pathology is still debated. The present review, aimed at pointing out the prognostic implications of thoracic aortic dimensions in populations free from known connective and aortic diseases, suggests that available evidence supporting an association between aortic diameter and cardiovascular events, and all-cause mortality is based on the limited number of studies, conducted with different imaging techniques and definition of the aortic phenotype.

Radiation-induced cognitive impairment--from bench to bedside

Approximately 100,000 patients per year in the United States with primary and metastatic brain tumor survive long enough (>6 months) to develop radiation-induced brain injury. Before 1970, the human brain was thought to be radioresistant; the acute central nervous system (CNS) syndrome occurs after single doses of ≥ 30 Gy, and white matter necrosis can occur at fractionated doses of ≥ 60 Gy. Although white matter necrosis is uncommon with modern radiation therapy techniques, functional deficits, including progressive impairments in memory, attention, and executive function have become increasingly important, having profound effects on quality of life. Preclinical studies have provided valuable insights into the pathogenic mechanisms involved in radiation-induced cognitive impairment. Although reductions in hippocampal neurogenesis and hippocampal-dependent cognitive function have been observed in rodent models, it is important to recognize that other brain regions are affected; non-hippocampal-dependent reductions in cognitive function occur. Neuroinflammation is viewed as playing a major role in radiation-induced cognitive impairment. During the past 5 years, several preclinical studies have demonstrated that interventional therapies aimed at modulating neuroinflammation can prevent/ameliorate radiation-induced cognitive impairment independent of changes in neurogenesis. Translating these exciting preclinical findings to the clinic offers the promise of improving the quality of life in patients with brain tumors who receive radiation therapy.

Long-term use and tolerability of irbesartan for control of hypertension

In this review, we discuss the pharmacological and clinical properties of irbesartan, a noncompetitive angiotensin II receptor type 1 antagonist, successfully used for more than a decade in the treatment of essential hypertension. Irbesartan exerts its antihypertensive effect through an inhibitory effect on the pressure response to angiotensin II. Irbesartan 150-300 mg once daily confers a lasting effect over 24 hours, and its antihypertensive efficacy is further enhanced by the coadministration of hydrochlorothiazide. Additionally and partially beyond its blood pressure-lowering effect, irbesartan reduces left ventricular hypertrophy, favors right atrial remodeling in atrial fibrillation, and increases the likelihood of maintenance of sinus rhythm after cardioversion in atrial fibrillation. In addition, the renoprotective effects of irbesartan are well documented in the early and later stages of renal disease in type 2 diabetics. Furthermore, both the therapeutic effectiveness and the placebo-like side effect profile contribute to a high adherence rate to the drug. Currently, irbesartan in monotherapy or combination therapy with hydrochlorothiazide represent a rationale pharmacologic approach for arterial hypertension and early-stage and late-stage diabetic nephropathy in hypertensive type II diabetics.

Renin-angiotensin system blockers and modulation of radiation-induced brain injury

Radiation-induced brain injury remains a major cause of morbidity in cancer patients with primary or metastatic brain tumors. Approximately 200,000 individuals/year are treated with fractionated partial or whole-brain irradiation, and > half will survive long enough (≤6 months) to develop radiation-induced brain injury, including cognitive impairment. Although short-term treatments have shown efficacy, no long-term treatments or preventive approaches are presently available for modulating radiation-induced brain injury. Based on previous preclinical studies clearly demonstrating that renin-angiotensin system (RAS) blockers can modulate radiation-induced late effects in the kidney and lung, we and others hypothesized that RAS blockade would similarly modulate radiation-induced brain injury. Indeed, studies in the last 5 years have shown that both angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor antagonists (AT(1)RAs) can prevent/ameliorate radiation-induced brain injury, including cognitive impairment, in the rat. The mechanistic basis for this RAS blocker-mediated effect remains the subject of ongoing investigations. Putative mechanisms include, i] blockade of Ang II/NADPH oxidase-mediated oxidative stress and neuroinflammation, and ii] a change in the balance of angiotensin (Ang) peptides from the pro-inflammatory and pro-oxidative Ang II to the anti-inflammatory and anti-oxidative Ang-1-7). However, given that both ACEIs and AT(1)RAs are 1] well-tolerated drugs routinely prescribed for hypertension, 2] exhibit some antitumor properties, and 3] can prevent/ameliorate radiation-induced brain injury, they appear to be ideal drugs for future clinical trials, offering the promise of improving the quality of life of brain tumor patients receiving brain irradiation.

PPARalpha activator fenofibrate modulates angiotensin II-induced inflammatory responses in vascular smooth muscle cells via the TLR4-dependent signaling pathway

Angiotensin II (Ang II) is a crucial contributor to inflammatory processes involved in development and progression of atherosclerotic lesion. Toll-like receptor 4 (TLR4) signaling responsible for the initiation of inflammation also participates in pathogenesis of atherosclerosis. The protective effect of peroxisome proliferator-activated receptor alpha (PPARalpha) activators on atherosclerosis may be due to their impact on vascular inflammation, plaque instability and thrombosis. However, mechanisms underlying the inhibitory effects of PPARalpha activators on Ang II-induced vascular inflammation and the TLR4-dependent signaling pathway involved in vascular smooth muscle cells (VSMCs) remain unclear. The present study demonstrated that PPARalpha activator fenofibrate decreased Ang II-induced generation of pro-inflammatory mediators such as TLR4, MMP-9 and TNF-alpha, but enhanced production of anti-inflammatory molecules like PPARalpha and 6-keto-PGF(1alpha) both in vivo and in vitro. Meanwhile, treatment of VSMCs with the TLR4 inhibitor or TLR4 siRNA showed that the inhibitory effects of fenofibrate on Ang II-induced inflammatory responses in VSMCs were dependent on TLR4. Furthermore, fenofibrate depressed Ang II-induced inflammatory responses in VSMCs by intervening the downstream effector molecules of the TLR4-dependent signaling pathway, including interferon-gamma inducible protein 10 (IP-10), protein kinases C (PKC) and nuclear factor kappaB (NF-kappaB). Thus, these findings provide the evidence for beneficial effects of PPARalpha activator fenofibrate to counter-regulate vascular inflammation induced by Ang II. More importantly, anti-inflammatory action of fenofibrate via interfering with the TLR4-dependent signaling pathway (TLR4/IP-10/PKC/NF-kappaB) works in concert to protect against atherosclerosis.

The AT1 receptor antagonist, L-158,809, prevents or ameliorates fractionated whole-brain irradiation-induced cognitive impairment

PURPOSE

We hypothesized that administration of the angiotensin type 1 (AT1) receptor antagonist, L-158,809, to young adult male rats would prevent or ameliorate fractionated whole-brain irradiation (WBI)-induced cognitive impairment.

MATERIALS AND METHODS

Groups of 80 young adult male Fischer 344 x Brown Norway (F344xBN) rats, 12-14 weeks old, received either: (1) fractionated WBI; 40 Gy of gamma rays in 4 weeks, 2 fractions/week, (2) sham-irradiation; (3) WBI plus L-158,809 (20 mg/L drinking water) starting 3 days prior, during, and for 14, 28, or 54 weeks postirradiation; and (4) sham-irradiation plus L-158,809 for 14, 28, or 54 weeks postirradiation. An additional group of rats (n = 20) received L-158,809 before, during, and for 5 weeks postirradiation, after which they received normal drinking water up to 28 weeks postirradiation.

RESULTS

Administration of L-158,809 before, during, and for 28 or 54 weeks after fractionated WBI prevented or ameliorated the radiation-induced cognitive impairment observed 26 and 52 weeks postirradiation. Moreover, giving L-158,809 before, during, and for only 5 weeks postirradiation ameliorated the significant cognitive impairment observed 26 weeks postirradiation. These radiation-induced cognitive impairments occurred without any changes in brain metabolites or gross histologic changes assessed at 28 and 54 weeks postirradiation, respectively.

CONCLUSIONS

Administering L-158,809 before, during, and after fractionated WBI can prevent or ameliorate the chronic, progressive, cognitive impairment observed in rats at 26 and 52 weeks postirradiation. These findings offer the promise of improving the quality of life for brain tumor patients.

Angiotensin II stimulates elution of Na-K-ATPase from a digoxin-affinity column by increasing the kinetic response to ligands that trigger the decay of E2-P

We earlier observed that treating rat proximal tubules with concentrations of angiotensin II (ANG II) that directly stimulate Na-K-ATPase activity changed how Na-K-ATPase subsequently eluted from an ouabain-affinity column. In this study we tested whether ANG II increases the rate of elution in response to ligands that trigger the decay of E(2)-P, which implies a change in functional properties of Na-K-ATPase, or by decreasing the amount subsequently eluted with SDS, which suggests a change in how Na-K-ATPase interacts with other proteins. We utilized a new digoxin-affinity column and novel lines of opossum kidney (OK) cells that coexpress the rat AT(1a) receptor and either the wild-type rat alpha(1)-isoform of Na-K-ATPase or a truncation mutant missing the first 32 amino acids of its NH(2) terminus. We characterized how rat kidney microsomes bind to and elute from the digoxin-affinity column and demonstrated that they are heterogeneous in the rate at which they release digoxin in response to ligands that trigger the decay of E(2)-P. Incubating OK cells with ANG II stimulated the ensuing elution of wild-type rat alpha(1)-subunit by increasing the kinetic response to ligands that cause a decay of E(2)-P without affecting the amount later eluted with SDS. In contrast, ANG II had no effect on the kinetic response of the truncation mutant but decreased the amount eluted with SDS. These data suggest that ANG II regulates both the kinetic properties of Na-K-ATPase and its interaction with other proteins by a mechanism(s) involving its NH(2) terminus.

Metabolic syndrome: treatment of hypertensive patients

Metabolic syndrome (MetSyndr), a constellation of abnormalities [obesity, glucose intolerance, insulin resistance (IR), dyslipidemia (low HDL-cholesterol, high LDL-cholesterol and triglycerides (TG)], and elevated blood pressure (BP)], increases the risk of cardiovascular (CV) disease and premature death. From 10% to 30% of the adult population in industrialized countries has MetSyndr, which effectively predicts the development of type 2 diabetes mellitus (T2D) and CV disease. Because of the complex etiology of MetSyndr, a multi-targeted, integrated therapeutic approach is required to simultaneously treat high BP, obesity, lipid disorders and T2D (if present), to fully protect CV, cerebrovascular and renal systems. If lifestyle modification (weight control, diet, exercise, smoking cessation, moderation of alcohol intake) is ineffective, pharmaco-theraphy should be added to treat simultaneously the lipid- and non-lipid CV risk factors. Patients with HTN and MetSyndr should be started on angiotensin-converting enzyme (ACE) inhibitors, unless contraindicated. The ACE inhibitors and angiotensin receptor blockers (ARBs) reduce the odds of developing new onset T2D and also decrease albuminuria. The ACE inhibitors provide cardioprotective and renoprotective benefits beyond their effect on BP; they also improve IR. The ARBs are renoprotective in addition to being cardioprotective. Long-acting calcium channel blockers are also recommended in hypertensive patients with MetSyndr; these drugs also improve IR. Thiazides (at low doses) and selected ss-blockers can be given to patients with HTN and MetSyndr. Celiprolol in combination with diuretics has a favorable effect on glucose tolerance and IR in patients with HTN and MetSyndr, and spironolactone added to ACE inhibitor or ARB therapy provides additional reno- and CV protective benefits in patients with diabetic nephropathy. Carvedilol, a ss-blocker with vasodilating properties, added to ACE inhibitor or ARB therapy, is effective in preventing worsening of microalbuminuria in patients with HTN and MetSyndr; it also improves IR and glycemic control. Most patients eventually require two or more antihypertensive drugs to reach BP goal. It is recommended that therapy in patients whose BP is more than 20/10 mm Hg above target at diagnosis be initiated with a combination of antihypertensive drugs, administered either as individual drugs or as fixed-dose formulations. Treatment with fixed-dose combinations, such as irbesartan + hydrochlorothiazide provides good BP control in more than two-thirds of hypertensive patients with MetSyndr. Lipid and BP targets are reached in a high percent of patients with HTN and CV disease treated with a combination of amlodipine + atorvastatin. In conclusion, hypertensive patients with the MetSyndr be treated aggressively for each component of the syndrome to provide CV, cerebrovascular and renal protection.

Beneficial Effects of the Combination of Nifedipine and Losartan in Hypertensive Dahl Salt-Sensitive Rats

BACKGROUND

The antihypertensive and organ-protective effects of the combination of the angiotensin II type 1 receptor blocker losartan and the calcium channel blocker nifedipine were examined in Dahl salt-sensitive rats.

METHODS

The rats fed with a high-salt diet developed hypertension accompanied by aorta and heart hypertrophy, and impaired renal function. The animals were treated with losartan (30 mg/kg/day), nifedipine (7.8 mg/kg/day) or with a combination of both drugs for 8 weeks. At the end of the study systolic blood pressure, kidney function, organ weight, and mRNA expression were investigated.

RESULTS

Losartan reduced significantly the systolic blood pressure as well as the aorta and left ventricular hypertrophy. Nifedipine and its combination with losartan had similar effects on the systolic blood pressure, aorta and left ventricular hypertrophy but only the combination treatment reduced the expression of transforming growth factor-beta1 in aorta and brain natriuretic peptide in left ventricle significantly. Nifedipine and the combination therapy reduced proteinuria and improved urine creatinine excretion. The expression of collagen III and IV in the kidney was significantly reduced by the combination therapy.

CONCLUSION

These results indicate that although losartan and nifedipine were effective in lowering blood pressure and showed moderate organ protection, additional benefits can be expected by combination therapy with both compounds.

Activation of ERK, JNK, Akt, and G-protein coupled signaling by hybrid angiotensin II AT1/bradykinin B2 receptors expressed in HEK-293 cells

Bradykinin (BK) and angiotensin II (AngII) often have opposite roles in cardiovascular diseases. Our aim here was to construct hybrid receptors which bind AngII but signal as BK. Various sequences of the intracellular face of the AngII type I receptor, AT1R, were replaced with corresponding sequences from the bradykinin B2 receptor (BKB2R). The hybrids demonstrated a number of signaling characteristics of the BKB2R. For example, the hybrids demonstrated BK as opposed to AngII like phosphorylation of Akt and JNK. The hybrids containing the BKB2R intracellular loop 2 (IC2) displayed minimal G-protein, Galphai/Galphaq, linked signaling. Computer based molecular models suggested that Ser-Met-Gly from the IC2 of the BKB2R is detrimental for the Galphai/Galphaq coupled functions of this hybrid. The return of Lys-Ser-Arg of the AT1R to this hybrid led to almost full recovery of Galphai and Galphaq activation. The design and production of AT1/BKB2 hybrid receptors is a potential approach in the treatment of hypertension related diseases where the presence of AngII, its AT1 receptor and the consequent signal transduction has proven detrimental.

Effect of sex hormones on renal estrogen and angiotensin type 1 receptors in female and male rats

Although the mechanisms are not understood, evidence suggests that 17β-estradiol (E2) confers protection from cardiovascular and renal complications in many diseases. We have reported that E2 decreases angiotensin type 1 receptors (AT1Rs) in different tissues and hypothesize that E2 exerts tonic inhibition on AT1Rs, reducing effects of ANG II. This study determined the effects of E2 and dihydrotestosterone (DHT) on cortical estrogen receptors (ERs) and glomerular AT1R binding in rats. Animals underwent sham operation, ovariectomy (Ovx) or orchidectomy (Cas) and were treated (Ovx ± E2; Cas ± DHT) for 3 wk. Cortical ERα protein was 2.5 times greater, and ERβ was 80% less in females vs. males ( P < 0.01). Glomerular AT1R binding was lower in females than males [4,657 ± 838 vs. 7,457 ± 467 counts per minute (cpm), P < 0.01]. Ovx reduced ERα protein by 50%, whereas E2 increased ERα expression after Ovx. The decrease in cortical ERα in Ovx rats was associated with a significant increase in AT1R binding (6,908 ± 609 cpm), and E2 prevented this increase. There was no change in ERα or AT1R binding following Cas ± DHT (25 mg) treatment, although Cas did elevate cortical ERβ (P < 0.01). Interestingly, the high dose DHT (200 mg) elevated ERα 150% above intact levels and profoundly decreased AT1R binding (1,824 ± 705 cpm, P < 0.001 vs. intact male). This indicates that under normal conditions, glomerular AT1R binding is significantly greater in male than female animals, which may be important in development of cardiovascular and renal disease in males. Furthermore, E2 regulates ERα and is inversely associated with glomerular AT1R binding, supporting our hypothesis that E2 tonically suppresses AT1Rs and suggesting a potential mechanism for the protective effects of estrogen.

Kinase inhibitors for cardiovascular disease

Over the last decade, there has been substantial progress toward understanding the pathophysiology and treatment of cardiovascular diseases (CVDs). Elucidating cellular responses to the extracellular environment and signal transduction mechanisms have provided the opportunity to explore novel molecular therapeutic approaches for the treatment of CVDs. Neurohormonal stimulation has been implicated in these diseases; blockade of the renin-angiotensin and beta-adrenergic systems are examples of therapeutic effectiveness. There are multiple cell signaling cascades, some of which are beneficial or compensatory and others deleterious. The balance between these pathways, which in large part is dictated by the cellular environment, determines the outcome as a diseased or non-diseased state. Selective targeting of signaling pathways using protein kinase inhibitors, would have a potential advantage over receptor blockers. We review potential protein kinase targets and recent evidence supporting therapeutic interventional value in CVDs.

A multicenter, randomized, double-blind, parallel-group trial of the antihypertensive efficacy and tolerability of a combination of once-daily losartan 100 mg/hydrochlorothiazide 12.5 mg compared with losartan 100-mg monotherapy in the treatment of mild to severe essential hypertension

BACKGROUND

Because patients with hypertension may require >1 antihypertensive agent to control blood pressure (BP), physicians often prescribe a fixed combination of antihypertensive medications.

OBJECTIVE

This study evaluated the effect of adding low-dose hydrochlorothiazide 12.5 mg (HCTZ12.5) to high-dose losartan 100 mg (L100) in patients with hypertension whose BP was inadequately controlled with L100 monotherapy.

METHODS

Enrolled in this multicenter, randomized, double-blind, parallel-group, filter study were patients aged > or =18 years with a mean trough sitting diastolic BP (SiDBP) of 95 to 120 mm Hg. Patients were treated with L100 QD for 4 weeks. Patients who did not achieve adequate BP control were randomly assigned to receive L100/HCTZ12.5 or L100 QD for 6 weeks. The primary efficacy measure was the mean change in trough SiDBP from baseline in the 2 groups. Responders were defined as patients with a mean trough SiDBP of <90 mm Hg or patients who had a > or =10-mm Hg decrease in mean trough SiDBP.

RESULTS

Demographic characteristics were similar between treatment groups. The patients randomized to the double-blind treatment period were mostly white (65.1%) and male (57.5%), with a mean age of 53.8 years. The mean (SD) duration of hypertension at baseline was 9.7 (8.5) years. The proportion of patients previously treated with antihypertensive therapy was 76.7%. Of the 367 patients enrolled in the L100 filter period, 292 patients had BP inadequately controlled with L100 monotherapy and were randomized to receive L100 (n = 145) or L100/HCTZ12.5 (n = 147). At week 6 after randomization, mean trough SiDBP was significantly lower in the L100/HCTZ12.5 group than in the L100 group (-8.3 vs -5.2, respectively; P < 0.001). The between-group difference was -3.0 mm Hg (95 % CI, -4.6 to -1.40; P < 0.001), and the proportion of responders was significantly greater in the L100/HCTZ12.5 group than in the L100 group (63.0% vs 44.4%; P < 0.001). The incidence of adverse events (AEs) occurring in >2% of patients during the double-blind period was similar for both groups. AEs occurring in the L100 group and the L100/HCTZ12.5 group included respiratory tract infection (6.2% vs 3.4%, respectively), dizziness (2.1% vs 0.7%), and headache (0.7% vs 3.4%).

CONCLUSIONS

After 6 weeks of therapy, L100/HCTZ12.5 was associated with greater antihypertensive efficacy than L100, as measured by the change in mean trough SiDBP The percentage of responders was significantly greater in the L100/HCTZ12.5 group than in the L100 group.

Neuronal angiotensin II type 1 receptor upregulation in heart failure: activation of activator protein 1 and Jun N-terminal kinase

Chronic heart failure (CHF) is a leading cause of mortality in developed countries. Angiotensin II (Ang II) plays an important role in the development and progression of CHF. Many of the important functions of Ang II are mediated by the Ang II type 1 receptor (AT(1)R), including the increase in sympathetic nerve activity in CHF. However, the central regulation of the AT(1)R in the setting of CHF is not well understood. This study investigated the AT(1)R in the rostral ventrolateral medulla (RVLM) of rabbits with CHF, its downstream pathway, and its gene regulation by the transcription factor activator protein 1 (AP-1). Studies were performed in 5 groups of rabbits: sham (n=5), pacing-induced (3 to 4 weeks) CHF (n=5), CHF with intracerebroventricular (ICV) losartan treatment (n=5), normal with ICV Ang II treatment (n=5), and normal with ICV Ang II plus losartan treatment (n=5). AT(1)R mRNA and protein expressions, plasma Ang II, and AP-1-DNA binding activity were significantly higher in RVLM of CHF compared with Sham rabbits (240.4+/-30.2%, P<0.01; 206.6+/-25.8%, P<0.01; 280+/-36.5%, P<0.05; 207+/-16.4%, P<0.01, respectively). Analysis of the stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK) pathway showed that phosphorylated c-Jun proteins, phosphorylated JNK proteins, and JNK activity increased significantly in RVLM of CHF compared with sham (262.9+/-48.1%, 213.8+/-27.7%, 148.2+/-10.1% of control, respectively). Importantly, ICV losartan in CHF rabbits attenuated these increases. ICV Ang II in normal rabbits simulated the molecular changes seen in CHF. This effect was blocked by concomitant ICV losartan. In addition, Ang II-induced AT(1)R expression was blocked by losartan and a JNK inhibitor, but not by extracellular signal-regulated kinase or p38 MAP kinase inhibitors in a neuronal cell culture. These data suggest that central Ang II activates the AT(1)R, SAPK/JNK pathway. AP-1 may further regulate gene expression in RVLM in the CHF state.

Post-Transplant Diabetes Mellitus

New-onset diabetes mellitus in a previously non-diabetic transplant recipient is a serious adverse event that confers significant morbidity and mortality. The most significant consequences of post-transplant diabetes mellitus (PTDM) in solid organ transplant recipients include decreased patient and graft survival, an increased risk of infectious complications, and morbid cardiovascular events. The development of PTDM in the elderly is of particular concern because this group is already at increased risk of progression of cardiovascular disease. Because the elderly, especially those aged >65 years, are the fastest-growing segment of the renal transplant population, attention needs to be given to PTDM risk reduction and post-transplant management. PTDM develops as a consequence of both impaired insulin production and enhanced peripheral insulin resistance. A number of non-modifiable factors such as age, race, family history, hepatitis C, polycystic kidney disease and emerging genetic causes have been identified as risk factors for PTDM. However, a number of modifiable factors can be targets for intervention in high-risk patients, including bodyweight (through dietary restriction and exercise), hypertension, hyperlipidaemia and the effects of certain immunosuppressive agents. The two agents most responsible for PTDM are tacrolimus and corticosteroids, especially when used in combination. Attempts to modify doses and regimens designed to eliminate or avoid these drugs should be considered. Use of HMG-CoA reductase inhibitors ('statins') and ACE inhibitors is particularly helpful in controlling hypertension and hyperlipidaemia in the elderly because these agents confer protection against future adverse cardiovascular events. Bisphosphonates are also advantageous in controlling the progression of osteoporosis and possible increased risk of bone fractures. Future trials in the elderly should focus on such endpoints as PTDM, post-transplant neoplasia, cardiovascular events and bone fracture events in order to identify the safest regimens that provide the optimal control of rejection while limiting the morbidity from these secondary events.