Obesity phenotype and patient-reported outcomes in moderate and severe chronic kidney disease: a cross-sectional study from the CKD-REIN cohort study.

PURPOSE: To evaluate the association between obesity phenotypes and health-related quality of life (HRQoL) in non-dialysis-dependent CKD patients. METHODS: Data from the national CKD-REIN cohort which included 3033 patients with stage 3-4 CKD were used. Patients were divided into three groups: non-obese (NO) patients (BMI < 30 kg/m2), metabolically healthy obese (MHO) (BMI ≥ 30 kg/m2 and ≤ 1 criterion NCEP/ATP III), and metabolically unhealthy obese (MUO) (BMI ≥ 30 kg/m2 and ≥ 2 criteria NCEP/ATP III). HRQoL was measured by the KDQOL-36™ which comprised three disease-specific dimensions: symptoms, effects, and burden and two summaries scores: physical (PCS) and mental (MCS). We used a mixed effect model with adjustment on sociodemographic characteristics and comorbidities. RESULTS: A total of 2693 patients completed the self-administered questionnaires. MHO patients accounted for 3.4% of the cohort and for 12% of obese patients. In the NO group, average HRQoL scores were 77.2 ± 15.9 for symptoms, 83.5 ± 16.5 for effects, 76.8 ± 22.7 for burden, 43.5 ± 9.7 for PCS, and 47.9 ± 7.0 for MCS. In the multivariate analysis, scores were similar in MHO and NO patients, but significantly different with those in MUO patients: symptoms (- 0.7; p = 0.71 vs. - 3.0; p = 0.0025), effects (+ 1.2; p = 0.57 vs. - 4.3; p < 0.0001), burden (+ 2.7; p = 0.31 vs. - 3.6; p = 0.0031), and PCS (- 0.6; p = 0.58 vs. - 4.3; p < 0.0001). MCS was not associated with obesity phenotypes. CONCLUSIONS: This study demonstrated an association between obesity phenotypes and QoL in non-dialysis-dependent CKD patients. MUO patients had worse QoL than NO and MHO patients even after adjustment on comorbidities.

The onset of left ventricular diastolic dysfunction in SHR rats is not related to hypertrophy or hypertension.

Left ventricular (LV) diastolic dysfunction, particularly relaxation abnormalities, are known to be associated with the development of LV hypertrophy (LVH). Preliminary human and animal studies suggested that early LV diastolic dysfunction may be revealed independently of LVH. However, whether LV diastolic dysfunction is compromised before the onset of hypertension and LVH remains unknown. We therefore evaluated LV diastolic function in spontaneously hypertensive rats (SHR) at different ages and tested whether LV diastolic dysfunction is associated with abnormal intracellular calcium homeostasis. LV systolic and diastolic functions were evaluated by invasive and echocardiographic methods in 3-week-old (without hypertension) and 5-week-old (with hypertension) SHR and Wistar-Kyoto control rats. Basal intracytoplasmic calcium and sarcoplasmic reticulum (SR) Ca(2+) contents were measured in cardiomyocytes using fura-2 AM. Sarco(endo)plasmic Ca(2+)-ATPase isoform 2a (SERCA 2a) and phospholamban (PLB) expressions were quantified by Western blot and quantitative RT-PCR techniques. LV relaxation dysfunction was observed in 3-week-old SHR rats before onset of hypertension and LVH. An increase in basal intracytoplasmic Ca(2+) and a decrease in SR Ca(2+) release were demonstrated in SHR. Decreased expression of SERCA 2a and Ser16 PLB (p16-PLB) protein levels was also observed in SHR rats, whereas mRNA expression was not decreased. For the first time, we have shown that LV myocardial dysfunction precedes hypertension in 3-week-old SHR rats. This LV myocardial dysfunction was associated with high diastolic [Ca(2+)](i) possibly due to decreased SERCA 2a and p16-PLB protein levels. Diastolic dysfunction may be a potential predictive marker of arterial hypertension in genetic hypertension syndromes.

FGF23 is independently associated with vascular calcification but not bone mineral density in patients at various CKD stages.

SUMMARY: The hormone fibroblast growth factor 23 (FGF23) is involved in mineral homeostasis but may also have a role in vascular calcification and bone mineralization. In a cohort of 142 patients with CKD stages 2-5D, plasma FGF23 was independently associated with aortic calcification but not with pulse wave velocity or bone mineral density. INTRODUCTION: FGF23 is involved in mineral homeostasis but may also have a role in vascular calcification and bone mineralization. Previous studies related to FGF23 and vascular and bone outcomes have been restricted to dialysis patients. The aim of the present study was to establish whether or not plasma FGF23 is associated with aortic and coronary calcification, arterial stiffness, and bone mineral density in patients with early as well as late stages of CKD. METHODS: In a cohort of 142 patients with CKD stages 2-5D, we made routine biochemistry and intact FGF23 determinations, and assessed aortic and coronary calcification, bone mineral density (BMD), and arterial stiffness by multislice spiral computed tomography and automated pulse wave velocity (PWV). RESULTS: Plasma intact FGF23 levels were elevated in CKD patients; the elevation preceded that of serum phosphate in early-stage CKD. Patients with elevated FGF23 levels had higher aortic and coronary calcification scores than patients with lower FGF23 levels. Multivariate linear regression analysis indicated that only age (p < 0.001) and FGF23 (p = 0.008) were independently associated with aortic calcification score. Plasma FGF23 was neither associated with PWV nor with BMD. CONCLUSION: Our data suggest that plasma FGF23 is an independent biomarker of vascular calcification in patients with various CKD stages including early stages. The association between vascular calcification and FGF23 levels appears to be independent of BMD. It remains to be seen whether this association is independent of bone turnover and bone mass.

Is vascular calcification associated with bone mineral density and osteoporotic fractures in ambulatory, elderly women?

UNLABELLED: We analyzed the relationship between aortic calcification and two osteoporotic parameters (bone mineral density (BMD) and incident osteoporotic fractures) in 667 ambulatory, elderly women from the Epidemiology of Osteoporosis (EPIDOS) cohort (mean age, 80 years; range, 72-94 years). We did not find any correlation between the aortic calcification score and BMD or osteoporotic fractures. INTRODUCTION: The aging process is associated with osteoporosis and aortic calcification; conditions which may have similar disease mechanisms. However, the relationship between these two settings remains to be elucidated. We analyzed the relationship between aortic calcification and osteoporotic parameters (BMD and incident osteoporotic fractures) in a cohort of ambulatory, elderly women. METHODS: The study included 667 ambulatory women from the EPIDOS cohort (mean age, 80 years; age range, 72-94 years). The baseline examination included bone investigations, a clinical and functional examination, and a comprehensive questionnaire on health status and lifestyle. Semiquantitative methods were used to determine the abdominal aortic calcification score on baseline radiographs. Incident fractures were recorded via postal questionnaires issued every 4 months for about 4 years. RESULTS: Five hundred three women (75%) had aortic calcification. The mean aortic calcification score was 5.5 (median, 4). During the follow-up period, 186 (28%) women reported one or more incident osteoporotic fractures. We did not find any correlation between the aortic calcification score on one hand and the BMD or the occurrence of incident osteoporotic fractures on the other. Only age and systolic blood pressure were found to be independently associated with the aortic calcification score. Osteoporotic fractures were independently associated with age and BMD. CONCLUSIONS: Osteoporosis and aortic calcification appear to be independent processes in a cohort of ambulatory, elderly women. However, potential confounding factors may be present and prospective studies are needed to investigate this situation further.

Effect of intra-abdominal hypertension on left ventricular relaxation: a preliminary animal study.

BACKGROUND: In the intensive care unit, intra-abdominal hypertension (IAH) is a frequently encountered, life-threatening condition. The aim of this animal study was to evaluate the effect of IAH on left ventricular (LV) relaxation (i.e. the active phase of diastole). METHODS: Seven male rabbits were anaesthetized before mechanical ventilation. A 20 mm Hg increase in intra-abdominal pressure (IAP) was then induced by intraperitoneal infusion of 1.5% glycine solution. Haemodynamic parameters were recorded and the relaxation time constant tau (considered to be the best index of left ventricle relaxation) was calculated. All haemodynamic measurements were recorded at baseline and then after induction of IAH. RESULTS: A 20 mm Hg increase in IAP was not followed by a significant change in arterial pressure, but was associated with increases in central venous pressure (from 2 [-2 to 6] to 7 [-2 to 12] mm Hg, P= 0.03), LV end-diastolic pressure (from 7 [6-8] to 15 [11-19] mm Hg, P= 0.04) and the relaxation time constant tau (from 16 [14-18] to 43 [34-52] ms, P= 0.048). CONCLUSIONS: In this animal study, a 20 mm Hg increase in IAP impaired LV relaxation. Further studies are necessary to identify the causes of this impairment.

Pathophysiological mechanisms and consequences of cardiovascular calcifications: role of uremic toxicity.

SUMMARY: Chronic kidney disease (CKD) represents an accelerated model of the active cardiovascular calcification process. Recent data from our laboratory indicate the presence of a possible vascular remodeling leading to vascular calcification similar to that observed in bone tissue, and emphasize the role of uremic toxicity. Uremic serum not only induces differentiation of smooth muscle cells into an osteoblast-like phenotype but also inhibits the differentiation of monocyte-macrophages cells into osteoclasts. The imbalance between the two processes in vascular walls in favor of osteoblast-like formation could lead to calcification. Cardiovascular calcification may contribute to the high rate of cardiovascular disease in patients with CKD. However, uremic toxicity, which participates in the pathogenesis of cardiovascular calcification, seems to have independent effects on vascular walls, at least in the early stages of CKD. We recently reported that functional (i.e. endothelial dysfunction) rather than structural changes, including vascular calcification, may contribute to the aortic hemodynamic changes observed during early CKD. Uremic toxicity also appears to be associated with calcification of intracranial arteries. Knowledge concerning the pathogenesis and consequences of cardiovascular calcification derived from the uremic model therefore opens up new perspectives for pharmacologic treatments that may also help to prevent and/or treat cardiovascular calcification, and consequently cardiovascular mortality and morbidity, not only in CKD patients but also in the general population.

The pathophysiology of vascular calcification: are osteoclast-like cells the missing link?

There is increasing evidence to suggest that the initiation of vascular calcification is an active process involving vascular smooth muscle cell (VSMC) apoptosis and trans-differentiation into calcifying cells. This active process results in the deposition of an osteogenic extracellular matrix and may be exacerbated by a reduction in the levels of one or more native calcification inhibitors (such as fetuin A and pyrophosphate). Here, we present data which strongly suggest that the regression of vascular calcification might also be an active cellular process involving osteoclast-like cells. However, the presence of osteoclast like cells in the vascular wall is rather limited. To explain this rarity of osteoclast-like cells, we recently observed that the same factors, which promote the trans-differentiation of VSMCs into osteoblast-like cells are also capable of inhibiting the in vitro differentiation of monocytes/macrophages into osteoclast-like cells. An imbalance between osteoblast-like and osteoclast-like cell activities would therefore favour the occurrence of a pathological calcification process in vessel walls. Our new data are strongly evocative of a vascular remodelling process similar to that observed in bone tissue. To confirm this hypothesis, strategies for activating osteoclasts in the vascular wall (with a view to preventing or reversing vascular calcifications) are required.

Mortality due to bleeding, myocardial infarction and stroke in dialysis patients.

Essentials Mortality due to bleeding vs. arterial thrombosis in dialysis patients is unknown. We compared death causes of 201 918 dialysis patients with the general population. Dialysis was associated with increased mortality risks of bleeding and arterial thrombosis. Clinicians should be aware of the increased bleeding and thrombosis risks. SUMMARY: Background Dialysis has been associated with both bleeding and thrombotic events. However, there is limited information on bleeding as a cause of death versus arterial thrombosis as a cause of death. Objectives To investigate the occurrence of bleeding, myocardial infarction and stroke as causes of death in the dialysis population as compared with the general population. Methods We included 201 918 patients from 11 countries providing data to the ERA-EDTA Registry who started dialysis treatment between 1994 and 2011, and followed them for 3 years. Age-standardized and sex-standardized mortality rate ratios for bleeding, myocardial infarction and stroke as causes of death were calculated in dialysis patients as compared with the European general population. Associations between potential risk factors and these causes of death in dialysis patients were investigated by calculating hazard ratios (HRs) with 95% confidence intervals (CIs) by the use of Cox proportional-hazards regression. Results As compared with the general population, the age-standardized and sex-standardized mortality rate ratios in dialysis patients were 12.8 (95% CI 11.9-13.7) for bleeding as a cause of death (6.2 per 1000 person-years among dialysis patients versus 0.3 per 1000 person-years in the general population), 13.4 (95% CI 13.0-13.9) for myocardial infarction (22.5 versus 0.9 per 1000 person-years), and 12.4 (95% CI 11.9-12.9) for stroke (14.3 versus 0.7 per 1000 person-years). Conclusion Dialysis patients have highly increased risks of death caused by bleeding and arterial thrombosis as compared with the general population. Clinicians should be aware of the increased mortality risks caused by these conditions.

Pleiotropic effects of the non-calcium phosphate binder sevelamer.

The number of chronic kidney disease (CKD) patients and related adverse outcomes has dramatically increased worldwide in the past decade. Therefore, numerous experimental and clinical studies have recently addressed the underlying mechanisms, in particular the marked increase in cardiovascular mortality. Hyperphosphatemia is a major problem in these patients with advanced stage of CKD. Its control by calcium-containing phosphate binders is effective, but at the price of potentially noxious calcium overload. Sevelamer hydrochloride is a phosphate binder that offers an effective control of hyperphosphatemia as calcium-rich binders but without increase of calcium load. Beyond the control of phosphate, sevelamer seems to exert pleiotropic effects which include the correction of lipid abnormalities and the clearance of some uremic toxins.

TWEAK favors phosphate-induced calcification of vascular smooth muscle cells through canonical and non-canonical activation of NFκB.

Vascular calcification (VC) is associated with increased cardiovascular mortality in aging, chronic kidney disease (CKD), type 2 diabetes mellitus (T2DM) and atherosclerosis. TNF-like weak inducer of apoptosis (TWEAK) recently emerged as a new biomarker for the diagnosis and prognosis of cardiovascular diseases. TWEAK binding to its functional receptor Fn14 was reported to promote several steps of atherosclerotic plaque progression. However, no information is currently available on the role of TWEAK/Fn14 on the development of medial calcification, which is highly prevalent in aging, CKD and T2DM. This study explored the involvement of TWEAK in human vascular smooth muscle cells (h-VSMCs) calcification in vitro. We report that TWEAK binding to Fn14 promotes inorganic phosphate-induced h-VSMCs calcification, favors h-VSMCs osteogenic transition, decreasing acta2 and myh11 and increasing bmp2 mRNA and tissue non-specific alkaline phosphatase (TNAP), and increases MMP9 activity. Blockade of the canonical NFκB pathway reduced by 80% TWEAK pro-calcific properties and decreased osteogenic transition, TNAP and MMP9 activity. Blockade of non-canonical NFκB signaling by a siRNA targeting RelB reduced by 20% TWEAK pro-calcific effects and decreased TWEAK-induced loss of h-VSMCs contractile phenotype and MMP9 activity, without modulating bmp2 mRNA or TNAP activity. Inhibition of ERK1/2 activation by a MAPK kinase inhibitor did not influence TWEAK pro-calcific properties. Our results suggest that TWEAK/Fn14 directly favors inorganic phosphate-induced h-VSMCs calcification by activation of both canonical and non-canonical NFκB pathways. Given the availability of neutralizing anti-TWEAK strategies, our study sheds light on the TWEAK/Fn14 axis as a novel therapeutic target in the prevention of VC.

Controlled comparison of L-5-methyltetrahydrofolate versus folic acid for the treatment of hyperhomocysteinemia in hemodialysis patients.

BACKGROUND: The hyperhomocysteinemia regularly found in hemodialysis patients is largely refractory to combined oral B-vitamin supplementation featuring supraphysiological doses of folic acid. We evaluated whether a high-dose L-5-methyltetrahydrofolate-based regimen provided improved total homocysteine (tHcy)-lowering efficacy in chronic hemodialysis patients. METHODS AND RESULTS: We block-randomized 50 chronic, stable hemodialysis patients on the basis of their screening predialysis tHcy levels, sex, and dialysis center into 2 groups of 25 subjects treated for 12 weeks with oral folic acid at 15 mg/d (FA group) or an equimolar amount (17 mg/d) of oral L-5-methyltetrahydrofolate (MTHF group). All 50 subjects also received 50 mg/d of oral vitamin B(6) and 1.0 mg/d of oral vitamin B(12). The mean percent reductions (+/-95% CIs) in predialysis tHcy were not significantly different: MTHF, 17.0% (12.0% to 22.0%); FA, 14.8% (9.6% to 20.1%); P=0.444 by matched ANCOVA adjusted for pretreatment tHcy. Final on-treatment values (mean with 95% CI) were MTHF, 20.0 micromol/L (18.8 to 21.2 micromol/L); FA, 19.5 micromol/L (18.3 to 20.7 micromol/L). Moreover, neither treatment resulted in "normalization" of tHcy levels (ie, final on-treatment values <12 micromol/L) among a significantly different or clinically meaningful number of patients: MTHF, 2 of 25 (8%); FA, 0 of 25 (0%); Fisher's exact test of between-groups difference, P=0.490. CONCLUSIONS: Relative to high-dose folic acid, high-dose oral L-5-methyltetrahydrofolate-based supplementation does not afford improved tHcy-lowering efficacy in hemodialysis patients. The preponderance of hemodialysis patients (ie, >90%) exhibit mild hyperhomocysteinemia refractory to treatment with either regimen. This treatment refractoriness is not related to defects in folate absorption or circulating plasma and tissue distribution.

Hyperlipidemia and cardiovascular disease after organ transplantation.

Hyperlipidemia, a frequent and persistent complication after solid organ transplantation, contributes to cardiovascular morbidity and mortality and may influence the development of allograft vasculopathy. The pathogenesis of posttransplantation hyperlipidemia is not fully understood, although several epidemiological factors are strongly implicated including age, weight, pretransplantation lipid levels, and immunosuppressive therapy. Management strategies to reduce hyperlipidemia and modify cardiovascular risk include dietary restrictions and the use of lipid-lowering agents. The selective use of immunosuppressants, such as tacrolimus, that have neutral or fewer adverse effects on lipid metabolism may also provide a useful option. A combination of lipid-lowering therapies and optimization of immunosuppressive regimens compatible with prolonged allograft survival is probably necessary to significantly reduce posttransplantation hyperlipidemia and its potentially harmful consequences.

Lovastatin reduces glomerular macrophage influx and expression of monocyte chemoattractant protein-1 mRNA in nephrotic rats.

Glomerular expression of monocyte chemoattractant protein-1 (MCP-1) and subsequent glomerular macrophage infiltration may play an important role in the development of glomerulosclerosis. Previous studies have shown that lovastatin ameliorates experimental renal disease and reduces MCP-1 expression in serum-stimulated, cultured mesangial cells. We investigated the effects of lovastatin on glomerular MCP-1 expression and macrophage infiltration in rats with puromycin aminonucleoside (PA) nephrosis, an experimental model of renal disease characterized by early macrophage infiltration. Male Sprague-Dawley rats were pretreated for 5 days with either lovastatin (4 mg/kg) or vehicle. At the end of pretreatment, the lovastatin-pretreated rats received a single i.v. injection of PA (50 mg/kg) and continued to receive daily lovastatin thereafter. The vehicle-pretreated rats received i.v. injections of either PA or saline, and continued to receive daily vehicle treatment thereafter. Ten days after PA injection, the vehicle-treated PA rats showed increased (P < 0.05) serum cholesterol (359 +/- 25 mg/100 mL) and urine albumin excretion (343 +/- 95 mg/24 hr), compared with the vehicle-treated control rats (61 +/- 3 mg/100 mL and 2.5 +/- 0.6 mg/24 hr, respectively). Serum cholesterol (193 +/- 22 mg/dL) and urine albumin excretion (255 +/- 68 mg/24 hr) were less in the lovastatin-treated PA rats than in the vehicle-treated PA rats. The number of glomerular macrophages, assessed as ED-1-positive cells, per glomerular profile was increased 77% in the vehicle-treated PA rats (3.3 +/- 0.2) compared with the vehicle-treated control rats (1.8 +/- 0.2) (P < 0.05). By contrast, the number of glomerular macrophages was not elevated in the lovastatin-treated PA rats (2.3 +/- 0.2). Thus, lovastatin in vivo can attenuate glomerular macrophage infiltration. This may represent one mechanism by which lovastatin ameliorates experimental glomerular disease.

Pathogenesis of atherosclerosis.

Atherosclerosis, a common and complex disease, results from multiple interactions among injurious stimuli and the healing or reparative responses of the arterial wall. After endothelial injury, direct cell-cell interaction, and secretion of chemotactic and growth factors resulting from endothelial cell dysfunction, induce recruitment of monocytes to subintimal regions, smooth muscle cell proliferation, and increased synthesis of matrix proteins. The recruited monocytes become macrophages, accumulate lipid, and ultimately become foam cells. Together with accompanying T lymphocytes, these changes represent the fatty streak, an early histopathological change indicating atherosclerosis. Progression of this atherosclerotic lesion is marked by the accumulation of alternating layers of smooth muscle cells and lipid-laden macrophages. The advanced lesions of atherosclerosis compromise the lumen diameter and, thus, reduce the blood flow in arteries and ultimately participate in the mechanisms that lead to occlusion of the involved arteries.

Clinical correlation between renal allograft failure and hyperlipidemia.

Chronic rejection is the leading cause of late allograft failure, but its pathogenesis is poorly understood. The prominence of the vascular lesions and certain similarities with the pathological features of atherosclerosis suggest that lipids may be involved in the pathogenesis of chronic rejection. Studies have reported an association between different lipid abnormalities and several indicators of chronic renal allograft damage. However, other potential risk factors for the development of chronic rejection were present in most cases, and an independent association between lipids and chronic rejection has not been convincingly demonstrated. In our series of 706 consecutive renal transplants with long-term follow-up, increased post-transplant serum triglycerides, but not total cholesterol, were strong predictors of graft loss to chronic rejection. This effect was independent of other risk factors for chronic rejection such as age, acute rejections, proteinuria and hypoalbuminemia. These results add to existing evidence suggesting that lipid abnormalities may be involved in the pathogenesis of chronic renal allograft rejection.

Clinical predictors of chronic renal allograft rejection.

Among both immune and nonimmune factors implicated in the pathogenesis of chronic renal allograft rejection, acute rejection episodes represent a strong and consistent predictor. However, all acute rejection episodes are not equally predictive of chronic renal allograft rejection. Early and mild acute rejection episodes do not usually cause chronic renal allograft rejection. On the other hand, late and severe acute rejection episodes occurring more than one year after transplantation are particularly strong predictors of chronic renal allograft rejection. The number of HLA mismatches is a risk factor, but its influence may not be independent of acute rejection and other risk factors. Proteinuria and recently hypoalbuminemia are also independent risk factors for chronic renal allograft rejection. However, whether these nonimmune factors are merely the result of chronic renal allograft rejection, or whether they contribute to the pathogenesis of renal injury in chronic renal allograft rejection is yet unclear. Better HLA matching, new strategies to decrease the severity of acute rejection, and measures to prevent late acute rejection, as well as prospective evaluation of the therapies to reduce proteinuria and other nonimmune risk factors for chronic renal allograft rejection are needed.

Chronic renal allograft rejection and clinical trial design.

Both the choice of endpoints and the selection of patients will be critical study design features in randomized controlled trials needed to test the effectiveness of treatments for chronic renal allograft rejection. We examined the feasibility of carrying out clinical trials with different endpoints and patient inclusion criteria by analyzing data from a population of 627 cadaveric kidney transplant recipients who survived with a functioning allograft for at least six months. Among those who lost grafts to chronic rejection, decreases in renal function of 30% and 60% preceded graft loss by a median of only 1.1 and 0.7 years, respectively, suggesting that little would be gained in a clinical trial that used a predetermined reduction in renal function as a surrogate endpoint. Less clear is whether histologic changes could be used as a surrogate endpoint. At present, graft loss to chronic rejection and graft failure from any cause are the most reliable endpoints. Unfortunately, large numbers of patients are needed to demonstrate clinically relevant therapeutic effects on these endpoints. Limiting enrollment to patients who are at high risk for developing chronic rejection, by selecting patients who already have a decline in renal function, for example, may reduce the number of patients needed in a clinical trial. On the other hand, selecting patients with disease that is too advanced may diminish the effectiveness of therapy. In any case, it is impossible to accurately determine the number of patients needed for a definitive clinical trial without preliminary data demonstrating the expected magnitude of the treatment effect. Thus, well-designed pilot studies are needed to measure possible treatment effects before conducting large-scale clinical trials for chronic renal allograft rejection.

Isoprenoids and Ras: potential role in chronic rejection.

Protein prenylation, the post-translational attachment of isoprenoids to certain cellular proteins, increases protein hydrophobicity and promotes protein-membrane interactions. Of the many cellular proteins that undergo protein prenylation, particular attention has been paid to the protooncogene product Ras. Prenylated Ras protein localizes to the inner cell membrane and appears to function as a "molecular switch" through which peptide growth factors such as PDGF, IGF-1, and FGF, and cytokines such as IL-2, IL-6, and GM-CSF stimulate intracellular events. Binding of these substances to their respective receptors on target cells can activate Ras, triggering intracellular signaling cascades which culminate in processes such as cell proliferation, differentiation, and T-cell activation. Protein prenylation inhibitors block Ras prenylation, prevent membrane localization of Ras, and inhibit growth and proliferation of a variety of cell types. Recent studies in our laboratory have begun to examine the possible role of Ras in chronic allograft rejection. Abdominal aorta segments from donor Lewis rats were transplanted into Buffalo recipient rats. Recipients treated with the HMG-CoA reductase inhibitor lovastatin, which inhibits isoprenoid production, showed significantly decreased allograft intimal area after 12 weeks, when compared with untreated recipients. In a separate study, recipients treated with the agent leflunomide, which inhibits growth factor receptor tyrosine kinases that can activate Ras, had significantly decreased allograft intimal area after 12 weeks. These results suggest that Ras may be important in chronic allograft rejection, and that agents that interfere with Ras protein prenylation or activation by growth factor receptors may ameliorate chronic rejection.