Low serum leptin predicts mortality in patients with chronic kidney disease stage 5

Methods and potential biomarkers for the evaluation of endothelial dysfunction in chronic kidney disease: a critical approach

The impressive cardiovascular morbidity and mortality of chronic kidney disease (CKD) patients is attributable in a significant proportion to endothelial dysfunction (ED), arterial stiffness, and vascular calcifications. Abnormal vascular reactivity in these patients is more pronounced compared with other high-risk populations, but remains undiagnosed in the usual clinical setting. We briefly review the most important causes and risk factors of ED, oxidative stress, and inflammation related to arterial stiffness. We describe the main methods of ED investigation and the importance of using potential biomarkers together with classic techniques for a more comprehensive assessment of this condition. These methods include evaluation of: forearm blood flow by plethysmography, skin microcirculation by laser Doppler, and flow-mediated vasodilation by Doppler ultrasound imaging. Applanation tonometry is an easy-to-handle tool that allows a clinically reliable assessment of arterial stiffness and is also useful in quantifying endothelium-dependent and -independent vascular reactivity. We also discuss the diagnostic and therapeutic impact of new markers of ED in the CKD population. Improvement of endothelial function is an important challenge for clinical practice, and there are relatively few therapeutical strategies available. Therefore, a combined biomarker and bedside investigational approach could be a starting point for developing optimal therapeutic tools.

Hemodialysis versus peritoneal dialysis: a case control study of survival in patients with chronic kidney disease stage 5

It is still controversial whether the mode of dialysis or preexisting comorbidities may influence the prognosis of patients with chronic kidney disease stage 5. Therefore, we performed a prospective case control study to evaluate whether the mode of dialysis may influence outcome. We found 25 cases on peritoneal dialysis (PD) treatment and 75 age and sex-matched controls on hemodialysis (HD) treatment for more than 3 months. Analysis was by intention-to-treat. During the follow up of 58 months, 6 out of 25 patients (24%) died in the PD group, whereas in the HD group 26 out of 75 patients (35%) died (relative risk 0.69 [95% CI 0.32 to 1.49]; P = 0.46). Survival was not significantly different between the groups as indicated by Mantel-Cox log-rank test (hazard ratio 0.52 [95% CI 0.25 to 1.10]; P = 0.11). Multiple variable regression showed that age and diabetes mellitus, but not mode of dialysis, predicted death in patients with chronic kidney disease. It is concluded that age and comorbidities but not mode of dialysis are important to predict survival in patients with chronic kidney disease stage 5.

Review article: Biomarkers of clinical outcomes in advanced chronic kidney disease

Chronic kidney disease (CKD) is a complex condition, where the decrease in kidney function is accompanied by numerous metabolic changes affecting virtually all the organ systems of the human body. Many of the biomarkers characteristic of the individually affected organ systems have been associated with adverse outcomes including higher mortality in advanced CKD, whereas in persons without CKD these biomarkers may have no bearing on survival. It is believed that the high mortality seen in CKD is a result of several abnormalities conspiring to induce or aggravate a heightened degree of cardiovascular morbidity and predisposition to wasting syndrome. Not all the biomarkers may, however, be causally responsible for the adverse outcomes associated with them. We review various biomarkers of protein-energy wasting, inflammation, oxidative stress, potassium disarrays, acid-base disorders, bone and mineral disorders, glycemic status, and anemia. Although all of these biomarkers have shown associations with worsened outcomes in CKD, markers of protein-energy wasting, especially serum albumin, remain the strongest predictor of survival in CKD patients, especially those undergoing maintenance dialysis treatment. We also review the putative pathophysiologic mechanisms behind these associations, and present potential therapeutic interventions that could result in remedies to improve poor clinical outcomes in CKD, pending the results of current and future controlled trials.

Influence of CD4+/CD25+ regulatory T cells on atherogenesis in patients with end-stage kidney disease

Atherosclerosis, which is influenced by both traditional and nontraditional cardiovascular risk factors and has been characterized as an inflammatory process, is considered to be the main cause of the elevated cardiovascular risk associated with chronic kidney disease. The inflammatory component of atherosclerosis can be separated into an innate immune response involving monocytes and macrophages that respond to the excessive uptake of lipoproteins and an adaptive immune response that involves antigen-specific T cells. Concurrent with the influx of immune cells to the site of atherosclerotic lesion, the role of the adaptive immune response gradually increases. One of those cells are represented by the CD4+/CD25+ Tregs, which play indispensable roles in the maintenance of natural self-tolerance and negative control of pathological, as well as physiological, immune responses. Altered self-antigens such as oxidized LDLs may induce the development of CD4+/CD25+ Tregs with atheroprotective properties. However, atherosclerosis may be promoted by an imbalance between regulatory and pathogenic immunity that may be represented by the low expression of the forkhead box transcription factor (Foxp3) in CD4+/CD25+ Tregs. Such a defect may break immunologic tolerance and alter both specific and bystander immune suppression, leading to exacerbation of plaque development. Patients with end-stage kidney disease (ESKD) display a cellular immune dysfunction and accelerated atherosclerosis. Uremic solutes that accumulate during ESKD may be involved in these processes. In patients with ESKD and especially in those that are chronically hemodialyzed, oxidative stress induced by oxidized LDLs may increase CD4+/CD25+ Treg sensitivity to Fas-mediated apoptosis as a consequence of specific dysregulation of IL-2 expression. This review will focus on the current state of knowledge regarding the influence of CD4+/CD25+ Tregs on atherogenesis in patients with ESKD, and the potential effect of statins on the circulating number and the functional properties of these cells.

Emerging biomarkers for evaluating cardiovascular risk in the chronic kidney disease patient: how do new pieces fit into the uremic puzzle?

Premature cardiovascular disease (CVD), including stroke, peripheral vascular disease, sudden death, coronary artery disease, and congestive heart failure, is a notorious problem in patients with chronic kidney disease (CKD). Because the presence of CVD is independently associated with kidney function decline, it appears that the relationship between CKD and CVD is reciprocal or bidirectional, and that it is this association that leads to the vicious circle contributing to premature death. As randomized, placebo-controlled trials have so far been disappointing and unable to show a survival benefit of various treatment strategies, such a lipid-lowering, increased dialysis dose and normalization of hemoglobin, the risk factor profile seems to be different in CKD compared with the general population. Indeed, seemingly paradoxical associations between traditional risk factors and cardiovascular outcome in patients with advanced CKD have complicated our efforts to identify the real cardiovascular culprits. This review focuses on the many new pieces that need to be fit into the complicated puzzle of uremic vascular disease, including persistent inflammation, endothelial dysfunction, oxidative stress, and vascular ossification. Each of these is not only highly prevalent in CKD but also more strongly linked to CVD in these patients than in the general population. However, a causal relationship between these new markers and CVD in CKD patients remains to be established. Finally, two novel disciplines, proteomics and epigenetics, will be discussed, because these tools may be helpful in the understanding of the discussed vascular risk factors.

Role of fat mass and adipokines in chronic kidney disease

PURPOSE OF REVIEW

As traditional risk factors cannot alone explain the high prevalence and incidence of cardiovascular disease in chronic kidney disease, the complex of insulin resistance, oxidative stress, and endothelial dysfunction has increasingly been studied as an important non-traditional risk factor. Recent studies show that the adipose tissue is a complex organ with pleiotropic functions far beyond the mere storage of energy. Fat tissue secretes a number of adipokines including leptin and adiponectin, as well as cytokines, such as resistin, visfatin, tumor-necrosis factor-alpha and interleukin-6.

RECENT FINDINGS

Adipokine serum levels are markedly elevated in chronic kidney disease, likely due to a decreased renal excretion. Evidence suggests that these pluripotent signaling molecules may have multiple effects modulating insulin signaling, endothelial health and vascular outcome.

SUMMARY

Fat tissue is a storage depot for energy and a source of circulating signaling molecules. It plays an important role in the catabolic uremic milieu, and has been linked to systemic inflammation and uremic anorexia. Further research is needed to investigate the complex interactions between adipokine signaling networks and its effects on vascular health and outcome in chronic kidney disease.

Role of leptin in reverse epidemiology in chronic kidney disease

Leptin is mainly produced by adipocytes and metabolized in the kidney. Leptin is taken up into the central nervous system by a saturable transport system, and controls appetite in rodents and in healthy subjects. Leptin acts on peripheral tissue and increases the inflammatory response by stimulating the production of tumor necrosis factor alpha, interleukin-6 and interleukin-12. In healthy humans, serum leptin concentration is related to the size of adipose tissue mass in the body. The majority of obese subjects have inappropriately high levels of circulating plasma leptin concentrations, indicating leptin resistance. In healthy subjects increased leptin concentration constitutes a biomarker for increased cardiovascular risk. On the other hand, a recent prospective long-term study in patients with chronic kidney disease stage 5 on hemodialysis therapy showed that reduced serum leptin concentration is an independent risk factor for mortality in these patients.

How to reconcile conventional and altered risk factor patterns in dialysis patients

Epidemiological relationships between risk factors and outcome in patients with chronic kidney failure (CKF), including individuals with end-stage kidney failure, can be categorized into three types: risk factor relationships that are similar to those observed in the general population; risk factor relationships that differ from those observed in the general population; and risk factor patterns that are difficult or not possible to compare to the general population, possibly because such risk factors have not been studied or are not capable of being studied in normal individuals. These latter risk factor patterns may or may not be different from what might commonly be anticipated. It is recommended that risk factor relationships in CKF patients which differ from those observed in the general population should be referred to as altered risk factor patterns (ARFPs). The causes for ARFPs include protein-energy wasting and inflammatory disorders, which occur commonly in patients with CKF. Epidemiological and other evidence is presented suggesting that the ARFPs may also have other causes. Since ARFPs are common in CKF, it is important to understand the causes and appropriate therapeutic goals concerning these risk factors. Studies, including interventional clinical trials, are indicated to ascertain the causes of ARFPs and the therapeutic targets for these risk factors for individuals with chronic kidney disease and CKF.

Racial and survival paradoxes in chronic kidney disease

Most of the 20 million people in the US with chronic kidney disease (CKD) die before commencing dialysis. One of every five dialysis patients dies each year in the US. Although cardiovascular disease is the most common cause of death among patients with CKD, conventional cardiovascular risk factors such as hypercholesterolemia, hypertension and obesity are paradoxically associated with better survival in hemodialysis populations. Emerging data indicate the existence of this 'reverse epidemiology' in earlier stages of CKD. There are also paradoxical relationships between outcomes and race and ethnicity. For example, the survival rate of African American dialysis patients seems to be superior to that of whites on dialysis. Paradoxes-within-paradoxes have been detected among Hispanic and Asian American CKD patients. These survival paradoxes might evolve and change over the natural course of CKD progression as a result of the time differentials of competing risk factors and the overwhelming impact of malnutrition, inflammation and wasting. Reversal of the reverse epidemiology as a result of successful kidney transplantation underscores the role of nutritional status and kidney function in engendering these paradoxes. The observation of paradoxes and their reversal might lead to the formulation of new paradigms and management strategies to improve the survival of patients with CKD. Such movement away from the use of targets set on the basis of data gathered in general populations (e.g. the Framingham cohort) would be a major paradigm shift in clinical medicine and public health.