Aiko P. J. de Vries

Metabolic syndrome is associated with impaired long-term renal allograft function; not all component criteria contribute equally.

Chronic renal transplant dysfunction (CRTD) remains a leading cause of renal allograft loss. Evidence suggests that immunological and ischemic insults are mainly associated with CRTD occurring within the first year after transplantation, whereas nonimmunological insults are predominantly associated with CRTD beyond the first year. Several cardiovascular risk factors, such as obesity, dyslipidemia, hypertension, and diabetes mellitus have been identified as important nonimmunological risk factors for CRTD. These risk factors constitute the metabolic syndrome (MS). As renal allograft function is a surrogate marker of renal allograft loss, we investigated the association of MS with impairment of renal allograft function beyond the first year after transplantation in a cross‐sectional study of 606 renal transplant outpatients. Metabolic syndrome was defined using the definition of the National Cholesterol Education Program. Renal allograft function was assessed as the 24‐h urinary creatinine clearance. A total of 383 out of 606 patients (63%) suffered from MS at a median time of 6 years (2.6–11.4) post‐transplant. Presence of MS was associated with impaired renal allograft function beyond 1 year post‐transplant [−4.1 mL/min, 95%CI (−7.1, −1.1)]. The impact of MS did not change appreciably after adjustment for established risk factors for CRTD [−3.1 mL/min, 95%CI (−6.0, −0.2)]. However, not all component criteria of MS contributed equally. Only systolic blood pressure and hypertriglyceridemia were independently associated with impaired renal allograft function beyond 1 year post‐transplant in multivariate analyses.

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.

Fatty kidney: emerging role of ectopic lipid in obesity-related renal disease.

The global increase in chronic kidney disease (CKD) parallels the obesity epidemic. Obesity conveys a gradual but independent risk of progression of CKD that seems irrespective of the underlying nephropathy. Obesity has been associated with a secondary focal segmental glomerulosclerosis coined obesity-related glomerulopathy (ORG). Pathways through which obesity might cause renal disease are not well understood, and early clinical biomarkers for incipient ORG or renal relevant obesity are currently lacking. Recent human and experimental studies have associated ectopic lipid accumulation in the kidney (fatty kidney) with obesity-related renal disease. There is enough growing insight that ectopic lipid--the accumulation of lipid in non-adipose tissue--is associated with structural and functional changes of mesangial cells, podocytes, and proximal tubular cells to propose the development of ORG as a maladaptive response to hyperfiltration and albuminuria. Recent advances in metabolic imaging might validate ectopic lipid as a biomarker and research aid, to help translate novel therapeutics from experimental models to patients.

Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis

The prevalence of obesity-related glomerulopathy is increasing in parallel with the worldwide obesity epidemic. Glomerular hypertrophy and adaptive focal segmental glomerulosclerosis define the condition pathologically. The glomerulus enlarges in response to obesity-induced increases in glomerular filtration rate, renal plasma flow, filtration fraction and tubular sodium reabsorption. Normal insulin/phosphatidylinositol 3-kinase/Akt and mTOR signalling are critical for podocyte hypertrophy and adaptation. Adipokines and ectopic lipid accumulation in the kidney promote insulin resistance of podocytes and maladaptive responses to cope with the mechanical forces of renal hyperfiltration. Although most patients have stable or slowly progressive proteinuria, up to one-third develop progressive renal failure and end-stage renal disease. Renin–angiotensin–aldosterone blockade is effective in the short-term but weight loss by hypocaloric diet or bariatric surgery has induced more consistent and dramatic antiproteinuric effects and reversal of hyperfiltration. Altered fatty acid and cholesterol metabolism are increasingly recognized as key mediators of renal lipid accumulation, inflammation, oxidative stress and fibrosis. Newer therapies directed to lipid metabolism, including SREBP antagonists, PPARα agonists, FXR and TGR5 agonists, and LXR agonists, hold therapeutic promise.

Accumulation of Advanced Glycation End Products, Measured as Skin Autofluorescence, in Renal Disease

Abstract: Advanced glycation end products (AGEs) accumulate during renal failure and dialysis. Kidney transplantation is thought to reverse this accumulation by restoring renal function. Using a noninvasive and validated autofluorescence reader, we evaluated AGE levels in 285 transplant recipients (mean age, 52 years; range, 41 to 60 years), 32 dialysis patients (mean age, 56 years; range, 43 to 65 years), and 231 normal control subjects (mean age, 51 years; range, 40 to 65 years). Measurements in transplant recipients were performed for a mean of 73 months (range, 32 to 143 months) after transplantation. Dialysis patients were on dialysis therapy for a mean of 42 months (range, 17 to 107 months). Fluorescence was significantly increased in dialysis patients compared with normal control subjects (2.8 vs. 2.0 arbitrary units [a.u.], P < .0001). Although fluorescence levels were significantly decreased in transplant recipients compared with dialysis patients (2.5 vs. 2.8 a.u., P < .0001), fluorescence in transplant recipients was higher than in controls (2.5 vs. 2.0 a.u., P < .0001). In transplant recipients, fluorescence correlated positively with the duration of dialysis prior to transplantation (R= 0.21, P < .0001), and negatively with creatinine clearance (R=−0.34, P < .0001). No correlation was found between time after transplantation and fluorescence in transplant recipients (R=−0.10, P= .10). Fluorescence in dialysis patients was positively correlated with duration of dialysis (R= 0.36, P= .042). Our results, like those of others, suggest that kidney transplantation does not fully correct increased AGE levels found in dialysis patients. The increased AGE levels in kidney transplant recipients cannot be explained by the differences in renal function alone. The availability of a simple, noninvasive method (AGE‐Reader) to measure AGE accumulation may be used to monitor AGE accumulation in a clinical setting as well as in a study setting.

Insulin resistance as putative cause of chronic renal transplant dysfunction

Transplantation is the preferred organ replacement therapy for most patients with end-stage renal disease. Despite impressive improvements over recent years in the treatment of acute rejection, approximately half of all grafts will loose function within 10 years after transplantation. Chronic renal transplant dysfunction, also known as transplant atherosclerosis, is a leading cause of late allograft loss. To date, no specific treatment for chronic renal transplant dysfunction is available. Although its precise pathophysiology remains unknown, it is believed that it involves a multifactorial process of alloantigen-dependent and alloantigen-independent risk factors. Obesity, posttransplant diabetes mellitus, dyslipidemia, hypertension, and proteinuria have all been identified as alloantigen-independent risk factors. Notably, these recipient-related risk factors are well-known risk factors for cardiovascular disease, which cluster within the insulin resistance syndrome in the general population. Insulin resistance is considered the central pathophysiologic feature of this syndrome. It is therefore tempting to speculate that it is insulin resistance that underlies the recipient-related risk factors for chronic renal transplant dysfunction. Recognition of insulin resistance as a central feature underlying many, if not all, recipient-related risk factors would not only improve our understanding of the pathophysiology of chronic renal transplant dysfunction, but also stimulate development of new treatment and prevention strategies.

Non-proteinuric pathways in loss of renal function in patients with type 2 diabetes

Largely on the basis of data from patients with type 1 diabetes, the natural history of diabetic renal disease has been classified as a sequence of three stages: normoalbuminuria, microalbuminuria, and macroalbuminuria. Progressive decline of glomerular filtration rate (GFR) was thought to parallel the onset of macroalbuminuria (overt nephropathy), whereas glomerular hyperfiltration was deemed a hallmark of early disease. However, researchers have since shown that albuminuria is a continuum and that GFR can start to decline before progression to overt nephropathy. In addition to proteinuria, other risk factors might contribute to GFR deterioration including female sex, obesity, dyslipidaemia (in particular hypertriglyceridaemia), hypertension, and glomerular hyperfiltration, at least in a subgroup of patients. This phenomenon could explain why patients with type 2 diabetes can have renal insufficiency even before the onset of overt nephropathy, and might also suggest why the heterogeneous phenotype of type 2 diabetic renal disease does not necessarily associate with typical histological lesions of diabetic renal disease, unlike in type 1 diabetic renal disease. Patients with renal insufficiency but without albuminuria are usually excluded from randomised clinical trials in overt nephropathy, thus optimum treatment for this group of patients is unknown. The wide inter-patient variability of the disease probably needs individually tailored intervention.

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.

Determinants of Insulin Resistance in Renal Transplant Recipients

Background. Insulin resistance is considered to play an important role in the development of cardiovascular disease, which limits long-term renal transplant survival. Renal transplant recipients are more insulin-resistant compared with healthy controls. It is not known to date which factors relate to this excess insulin resistance. Therefore, we investigated which factors are related to insulin resistance long-term after renal transplantation. Methods. All renal transplant recipients at our outpatient clinic with a functioning graft for more than one year were invited to participate. We excluded diabetic recipients. Recipient, donor, and transplant characteristics were collected as putative determinants. We used fasting insulin, homeostasis model assessment index, and McAuley’s index as valid estimates of insulin resistance. Linear regression models were created to investigate independent determinants of all indexes. Results. A total of 483 recipients (57% male, 50±12 years) were analyzed at a median (interquartile range) time of 6.0 (2.6–11.6) years posttransplant. The most consistent determinants across all three indices were body mass index (P<0.001), waist-to-hip ratio (P<0.001), and prednisolone dose (P<0.05). Independent associations were present for total cholesterol (P<0.001), high-density lipoprotein cholesterol (P<0.001), creatinine clearance (P<0.05), recipient age (P<0.001), and gender (P≤0.002). No independent associations were present for transplant-related factors such as acute rejection treatment or cytomegalovirus seropositivity. Conclusions. Our results indicate that obesity, distribution of obesity, and prednisolone treatment are the predominant determinants of insulin resistance long term after transplantation. Insulin resistance after renal transplantation could be managed favorably by weight and prednisolone dose reduction, which may reduce cardiovascular disease.