Rutger M. van Ree

High urinary excretion of kidney injury molecule-1 is an independent predictor of graft loss in renal transplant recipients

Background. Chronic transplant dysfunction is characterized by renal function decline and proteinuria. Kidney injury molecule (KIM)-1, a transmembrane tubular protein with unknown function, is undetectable in normal kidneys, but markedly induced after injury. Urinary KIM-1 excretion has been quantified as biomarker of renal damage. We prospectively studied whether urinary KIM-1 predicts graft loss, independent of renal function and proteinuria. Methods. Renal transplant recipients (n=145) visiting our outpatient clinic between August 2001 and July 2003 collected 24-hour urine samples for assessment of baseline urinary KIM-1 excretion (microsphere-based Luminex technology), and were followed for graft loss. Results. Recipients participated at a median (interquartile range) of 6.0 (2.5–12.0) years posttransplant in baseline measurements. Follow-up beyond baseline was 4.0 (3.2–4.5) years. Urinary KIM-1 excretion was 0.72 (0.42–1.37) ng per 24 hours. Occurrence of graft loss increased over tertiles of KIM-1 excretion: 3 (6.3%), 11 (22.4%), and 17 cases (35.4%; P=0.001), respectively. High KIM-1 excretion was associated with proteinuria, low creatinine clearance, and high donor age (all P<0.01). In multivariate Cox regression analyses, prediction of graft loss by KIM-1 appeared independent of creatinine clearance, proteinuria, and donor age. Hazard ratios (95% CI) for the second and third tertile of KIM-1 excretion were 3.6 (0.9–13.5) and 5.1 (1.5–17.8) in the final model. Conclusions. Urinary excretion of KIM-1 is an independent predictor of long-term graft loss and therefore a promising new biomarker in early prediction of graft loss.

Urinary creatinine excretion reflecting muscle mass is a predictor of mortality and graft loss in renal transplant recipients

Background. Insulin resistance has been implicated to underlie both excess cardiovascular disease and chronic transplant dysfunction after renal transplantation. Skeletal muscle mainly determines peripheral insulin resistance, and could therefore affect outcome. Methods. All transplant recipients at our outpatient clinic with a functioning graft more than 1 year were invited to participate between 2001 and 2003. Mortality and death censored graft loss were recorded until August 2007. We used 24 hr urine creatinine excretion as measure of muscle mass. Cox regression was used to analyze the prospective data. Results. Six hundred four renal transplant recipients (age 51±12 years, 55% men) were studied. Creatinine excretion was 10.1±2.6 mmol/24 hr in women and 13.6±3.4 mmol/24 hr in men. During follow-up of 5.3 (4.7–5.7) years, 95 recipients died and 42 suffered graft loss. Determinants of creatinine excretion were weight, sex, age, height, cumulative prednisolone doses, and diabetes (r2=0.45). Creatinine excretion was associated with both mortality (3rd vs. 1st tertile Hazard ratio: 0.4 [95% confidence interval 0.2–0.7], P=0.003) and graft loss (3rd vs. 1st tertile Hazard ratio: 0.4 [95% confidence interval 0.1–0.9], P=0.03) independent of age, sex, serum creatinine, proteinuria, insulin resistance related factors, time after transplantation, and duration of dialysis. Conclusions. Creatinine excretion as measure of muscle mass is associated with mortality and graft loss after renal transplantation, independent of insulin resistance and its related factors. We speculate that preservation of muscle mass by stimulating exercise, sufficient diet, and less use of corticosteroids may be relevant for improving prognosis in renal transplant recipients.

Circulating Markers of Endothelial Dysfunction Interact With Proteinuria in Predicting Mortality in Renal Transplant Recipients

Background. Proteinuria is associated with endothelial dysfunction (ED) and increased mortality. We investigated whether urinary protein excretion (UPE) is correlated with markers of ED and whether these markers affect the association of proteinuria with mortality in renal transplant recipients (RTR). Methods. Six hundred four RTR with a functioning graft for more than 1 year were included. RTR were divided according to UPE: less than 0.3, 0.3 to 1.0, and more than 1.0 g/24 hr. Soluble intercellular adhesion molecule type 1 (sICAM-1) and soluble vascular cellular adhesion molecule type 1 (sVCAM-1) were measured using ELISA. Results. UPE (0.2 [0.0–0.5] g/24 hr), sICAM-1 (603 (514–721) ng/mL), and sVCAM-1 (952 [769–1196] ng/mL) were measured at 6.0 (2.6–11.4) years posttransplant. During follow-up for 5.3 (4.7–5.7) years, 94 (16%) RTR died. UPE was correlated with sVCAM-1 (standardized &bgr;=0.13, P=0.001) but not with sICAM-1 (standardized &bgr;=0.04, P=0.3). RTR with UPE more than 1.0 g/24 hr and high sICAM-1 (hazard ratio=4.7, 95% confidence interval 2.3–9.7, P<0.0001) or sVCAM-1 (hazard ratio=4.2, 95% confidence interval 2.0–8.6, P=0.0001) concentrations were at increased risk for death, whereas RTR with UPE more than 1.0 g/24 hr and low concentrations of sICAM-1 and sVCAM-1 were not. Conclusions. In RTR, UPE is correlated with sVCAM-1 but not with sICAM-1. Furthermore, RTR with proteinuria and high concentrations of sICAM-1 or sVCAM-1 have an increased risk for death, compared with RTR without proteinuria, whereas this is not the case in RTR with proteinuria but low concentrations of sICAM-1 and sVCAM-1. These results suggest that ED plays a role in the association of proteinuria with mortality after renal transplantation.

N-terminal pro-B-type natriuretic peptide and mortality in renal transplant recipients versus the general population.

Background. Mortality rates are higher in renal transplant recipients (RTR) than in the general population (GP). It is unknown what risk factors account for this difference. Methods. We prospectively followed a cohort of 606 RTR for 3026 person-years, during which 95 died. A GP cohort of 3234 subjects was followed for 24,940 person-years, during which 130 died. Results. All investigated risk factors, except ethnicity, body mass index, and total cholesterol, differed significantly between cohorts, with an adverse risk profile in the RTR. The age-adjusted and gender-adjusted hazard ratio for mortality in RTR was 6.2 (95% confidence interval [CI] 4.6–8.3) compared with GP, which was reduced to 2.4 (95% CI 1.6–3.6), 4.3 (95% CI 3.0–6.1), and 5.0 (95% CI 3.5–7.3) after additional adjustment for differences in N-terminal pro-B-type natriuretic peptide (NT-proBNP), creatinine clearance, and need for antihypertensive medication, respectively (all P<0.001), whereas adjustment for variables more related to atherosclerosis, including history of cardiovascular disease, diabetes, and high-density lipoprotein cholesterol, did not affect the difference in mortality between RTR and GP. Associations of NT-proBNP, creatinine clearance, and the use of antihypertensive medication with mortality were significantly steeper in RTR than in GP. Risk for mortality was similar for RTR and GP with low NT-proBNP (<100 pg/mL). Conclusions. Elevated NT-proBNP, low creatinine clearance, and need for antihypertensive medication are stronger risk factors for mortality in RTR than in GP. The increased mortality seen in the RTR population may well be related to cardiac failure rather than “accelerated atherosclerosis.”

Smoking is a risk factor for graft failure and mortality after renal transplantation

Background: Smoking in renal transplant recipients (RTR) is an acknowledged cardiovascular risk factor. It is, however, unclear whether smoking also increases the risk of graft failure (GF). Method: In this study, we prospectively assessed the association of current smoking versus past and never smoking with GF and mortality in 604 RTR (age 51.5 ± 12.1 years, 55% male). Results: At inclusion, 133 (22%) were current smokers, 255 (42%) were past smokers and 216 (36%) never smoked. During follow-up of 5.3 (4.7–5.7) years, 41 (7%) RTR experienced GF and 95 RTR (16%) died. Current smoking RTR had higher risk for GF compared to never smoking RTR (hazard ratio, HR = 3.3, 95% CI 1.5–7.1, p = 0.002). Past smoking RTR had similar risk of GF as never smoking RTR (HR = 1.1, 95% CI 0.5–2.6, p = 0.7). Current smoking RTR and past smoking RTR were at higher risk for death than never smoking RTR (HR = 2.1, 95% CI 1.1–3.8, p = 0.016, and HR = 2.4, 95% CI 1.4–4.0, p = 0.001, respectively). Conclusion: Smoking after renal transplantation is associated with risk for GF and mortality. Since past smoking is a risk factor for mortality but not for GF, smoking cessation may be beneficial to RTR in delaying GF in long term.

Low levels of sRAGE are associated with increased risk for mortality in renal transplant recipients

Objective. Infusion of the soluble form of the receptor for advanced glycation end-products (sRAGE) was protective against atherosclerosis and nephropathy in animal models. In this study we investigated determinants of endogenous sRAGE in renal transplant recipients and whether sRAGE was associated with mortality and graft loss. Methods and Results. A total of 591 patients participated at a median time of 6 years after transplantation. Independent determinants of sRAGE were mycophenolate mofetil medication (&bgr;=−0.21, P<0.001), creatinine clearance (&bgr;=−0.15, P<0.001), BMI (&bgr;=−0.12, P=0.003) and fasting insulin concentration (&bgr;=−0.14, P=0.001). Low sRAGE levels were associated with a 2–3 times higher risk for mortality especially after correction for creatinine clearance (P=0.006). Conclusion. A lack of sRAGE is a risk factor for mortality in renal transplant recipients. The putatively protective role of sRAGE and in particular its association with mycophenolate mofetil usage needs further investigation.

Plasma Procalcitonin Is an Independent Predictor of Graft Failure Late After Renal Transplantation

Background. Chronic low-grade inflammation is involved in chronic transplant dysfunction after renal transplantation. Procalcitonin (PCT), known to reflect microbial inflammation, may also reflect ongoing noninfectious chronic low-grade inflammation in organ parenchyma, including transplanted kidneys. We aimed to compare predictive performance of plasma PCT for development of graft failure in renal transplant recipients (RTR) with that of high-sensitivity C-reactive protein (hsCRP), an established marker of systemic chronic low-grade inflammation. Methods. We included 575 RTR with functioning grafts for more than or equal to 1 year at a median (interquartile range) time of 6.1 (2.9–11.7) years posttransplant. PCT was determined using an ultrasensitive immunoluminometric assay and hsCRP using high-sensitivity enzyme-linked immunosorbent assay. Results. Median (interquartile range) plasma PCT and hsCRP concentrations were 0.023 (0.017–0.036) ng/mL and 2.1 (0.8–4.9) mg/L, respectively. After a median (interquartile range) of 5.2 (4.5–5.7) years of follow-up, incidence of graft failure was 0.5%, 2.6%, and 18.5% according to increasing PCT tertiles (P<0.001 by log-rank test). Area under the curve of receiver operating characteristic analysis of PCT for prediction of graft failure was significantly higher than that of hsCRP (0.84 vs. 0.56, P<0.001). After adjustment for potential confounders, PCT remained an independent predictor of graft failure (hazard ratio=2.3 [95% confidence interval 1.4–3.7] per doubling PCT, P=0.0004), whereas this was not the case for hsCRP. Conclusion. We identified plasma PCT as a strong and an independent predictor of graft failure in RTR. These data suggest that PCT in RTR reflects ongoing inflammation in parenchyma of transplanted kidneys. Further studies are required to investigate whether PCT could be of use as an early biomarker for chronic transplant dysfunction.

Skin-autofluorescence is an independent predictor of graft loss in renal transplant recipients.

Background. Skin-autofluorescence (skin-AF) noninvasively measures the tissue accumulation of advanced glycation end products (AGEs). AGEs are nephrotoxic and potential effectors of cardiovascular mortality. We investigated whether skin-AF predicted graft loss after kidney transplantation. Methods. A total of 302 renal transplant recipients were enrolled at a median time of 6.1 (2.6-12.1) years after transplantation and were subsequently followed up for first occurrence of graft loss (i.e., graft failure or all-cause mortality) for 5.2 (4.6-5.4) years. The association of baseline skin-AF with graft loss was investigated with univariable and multivariable Cox-regression and receiver-operator-characteristic curve analyses. Results. Baseline skin-AF was 2.7±0.8 arbitrary units. Skin-AF predicted graft loss in a univariable Cox regression analysis (Hazard ratios 2.40 [1.75-3.29], P<0.001) and in a multivariable model (Hazard ratios 1.83 [1.22-2.75], P=0.003), adjusted for other identified risk-factors, including patient age, creatinine clearance, protein excretion, high sensitivity C-reactive protein (hsCRP), and human leukocyte antigen-DR mismatching. The area under the receiver-operator-characteristic curve for skin-AF as predictor of graft loss was significantly different from 0.5. Skin-AF was also a significant predictor of graft failure and mortality as separate end points. Conclusions. We conclude that skin-AF is an independent predictor of graft loss in kidney transplant recipients. Although skin-AF is not a direct measurement for AGEs, we believe that our results do support the hypothesis that accumulation of AGEs in renal transplant recipients contributes to the development of graft loss.

Influence of C-reactive protein and urinary protein excretion on prediction of graft failure and mortality by serum albumin in renal transplant recipients.

Background. Hypoalbuminemia is an established predictor of poor outcome in renal transplant recipients (RTR). It is considered to reflect inflammation, poor nutritional status, or proteinuria. We explored the roles of high-sensitivity C-reactive protein (hsCRP) and urinary protein excretion in prediction of graft failure and mortality by serum albumin in RTR. Methods. We included 605 RTR at a median (interquartile range) time of 6.0 years (2.5–11.5 years) after transplantation for baseline measurements. Results. At baseline, urinary protein excretion (&bgr;=−0.242, P<0.0001), hsCRP concentration (&bgr;=−0.207, P<0.0001), recipient age (&bgr;=−0.115, P=0.004), living kidney donor (&bgr;=0.100, P=0.01), and a history of myocardial infarction (&bgr;=−0.084, P=0.03) were independently related to serum albumin. Prospectively, 94 RTR died and 42 had graft failure during 5.3 years (4.7–5.7 years) of follow-up. After adjustment for potential confounders, including hsCRP and urinary protein excretion in Cox-regression analyses, low serum albumin was significantly associated with graft failure (hazard ratio=0.34 [95% confidence interval=0.15–0.76] per g/dL, P=0.008) and mortality (hazard ratio=0.43 [95% confidence interval=0.24–0.78] per g/dL, P=0.005), with significant modification of the effect of serum albumin on graft failure by urinary protein excretion (P=0.003). Conclusion. Low serum albumin concentrations predict graft failure and mortality in RTR independent of hsCRP and urinary protein excretion. The effect of serum albumin on graft failure is strongly modified by urinary protein excretion. These results suggest that chronic low-grade inflammation is not an important mechanism underlying inverse associations of serum albumin with graft failure and mortality. They also suggest that proteinuria is involved in the association of low serum albumin with graft failure.

Latent cytomegalovirus infection is an independent risk factor for late graft failure in renal transplant recipients.

Summary Background Cytomegalovirus (CMV) is a risk factor for rejection and mortality soon after renal transplantation. Little is known about its consequences longer after transplantation. We prospectively investigated whether latent CMV infection is a risk factor for graft failure and mortality long after transplantation. Material/Methods Our study included 606 renal transplant recipients (RTR) with a functioning graft for >1 year. CMV serology was determined using ELISA. RTRs were divided into CMV-seronegative and latent CMV (seropositive + seroconverted). Results We measured CMV IgG at 6.0 [2.6–11.4] years post-transplant. During follow-up (7.0 [6.2–7.5] years), 54 (9%) RTRs experienced graft failure and 137 (23%) RTRs died. Risk for graft failure and mortality was significantly higher in RTRs with latent CMV compared to CMV-seronegative RTRs (HR=3.1, P=0.005 and HR=2.0, P=0.002, respectively). After adjustment for potential confounders, latent CMV infection remained an independent risk factor for graft failure (HR=4.6, P=0.001), but not for mortality (HR=1.4, P=0.2). Conclusions Latent CMV is an independent risk factor for graft failure long after renal transplantation and carries a higher risk for graft failure than for mortality. These findings confirm the notion that latent CMV can be harmful in transplanted kidneys.