Still a reasonable goal: Targeting cholesterol in dialysis and advanced chronic kidney disease patients

Current Understanding of the Relationship of HDL Composition, Structure and Function to Their Cardioprotective Properties in Chronic Kidney Disease

In the general population, the ability of high-density lipoproteins (HDLs) to promote cholesterol efflux is a predictor of cardiovascular events, independently of HDL cholesterol levels. Although patients with chronic kidney disease (CKD) have a high burden of cardiovascular morbidity and mortality, neither serum levels of HDL cholesterol, nor cholesterol efflux capacity associate with cardiovascular events. Important for the following discussion on the role of HDL in CKD is the notion that traditional atherosclerotic cardiovascular risk factors only partially account for this increased incidence of cardiovascular disease in CKD. As a potential explanation, across the spectrum of cardiovascular disease, the relative contribution of atherosclerotic cardiovascular disease becomes less important with advanced CKD. Impaired renal function directly affects the metabolism, composition and functionality of HDL particles. HDLs themselves are a heterogeneous population of particles with distinct sizes and protein composition, all of them affecting the functionality of HDL. Therefore, a more specific approach investigating the functional and compositional features of HDL subclasses might be a valuable strategy to decipher the potential link between HDL, cardiovascular disease and CKD. This review summarizes the current understanding of the relationship of HDL composition, metabolism and function to their cardio-protective properties in CKD, with a focus on CKD-induced changes in the HDL proteome and reverse cholesterol transport capacity. We also will highlight the gaps in the current knowledge regarding important aspects of HDL biology.

Lipid-modifying therapy in chronic kidney disease: Pathophysiological and clinical considerations

Chronic kidney disease (CKD), which affects >10% of the population worldwide, is associated with a dramatically increased rate of cardiovascular disease (CVD). More people with CKD will die from CVD than develop end-stage renal disease with dialysis-dependency. However, the contribution of classical atherosclerotic cardiovascular risk factors is less evident than in the general population. Particularly, the relationship between dyslipidemia and CVD morbidity and mortality in CKD patients is not as evident as in the general population. While LDL cholesterol-lowering drugs such as statins significantly reduce the rate of cardiovascular events in the general population, their role in patients with end-stage renal disease has been questioned. This could be caused by a shift from atherosclerotic to non-atherosclerotic CVD in patients with advanced CKD, which cannot be effectively prevented by lipid-lowering drugs. In addition, many lines of evidence suggest that impaired renal function directly affects the metabolism, composition and functionality of lipoproteins, which may affect their responsiveness to pharmacological interventions. In this review, we highlight the challenges for the therapeutic application of lipid-lowering treatment strategies in CKD and discuss why treatment strategies used in the general population cannot be applied uncritically to CKD patients.

Lipid management in patients with chronic kidney disease

An increased risk of cardiovascular disease, independent of conventional risk factors, is present even at minor levels of renal impairment and is highest in patients with end-stage renal disease (ESRD) requiring dialysis. Renal dysfunction changes the level, composition and quality of blood lipids in favour of a more atherogenic profile. Patients with advanced chronic kidney disease (CKD) or ESRD have a characteristic lipid pattern of hypertriglyceridaemia and low HDL cholesterol levels but normal LDL cholesterol levels. In the general population, a clear relationship exists between LDL cholesterol and major atherosclerotic events. However, in patients with ESRD, LDL cholesterol shows a negative association with these outcomes at below average LDL cholesterol levels and a flat or weakly positive association with mortality at higher LDL cholesterol levels. Overall, the available data suggest that lowering of LDL cholesterol is beneficial for prevention of major atherosclerotic events in patients with CKD and in kidney transplant recipients but is not beneficial in patients requiring dialysis. The 2013 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for Lipid Management in CKD provides simple recommendations for the management of dyslipidaemia in patients with CKD and ESRD. However, emerging data and novel lipid-lowering therapies warrant some reappraisal of these recommendations.

HDL functionality and cardiovascular outcome among nondialysis chronic kidney disease patients

CVD remains the leading cause of morbidity and mortality in patients with chronic kidney disease (CKD). CKD profoundly affects HDL composition and functionality, but whether abnormal HDL independently contributes to cardiovascular events in CKD patients remains elusive. In the present study, we assessed whether compositional and functional properties of HDL predict cardiovascular outcome among 526 nondialysis CKD patients who participate in the CARE FOR HOMe study. We measured HDL cholesterol, the content of HDL-associated proinflammatory serum amyloid A (SAA), and activities of the HDL enzymes paraoxonase and lipoprotein-associated phospholipase A2 (Lp-PLA₂). In addition, we assessed the antioxidative activity of apoB-depleted serum. During a mean follow-up of 5.1 ± 2.1 years, 153 patients reached the predefined primary endpoint, a composite of atherosclerotic cardiovascular events including cardiovascular mortality and death of any cause. In univariate Cox regression analyses, lower HDL-cholesterol levels, higher HDL-associated SAA content, and lower paraoxonase activity predicted cardiovascular outcome, while Lp-PLA₂ activity and antioxidative capacity did not. HDL-cholesterol and HDL-paraoxonase activity lost their association with cardiovascular outcome after adjustment for traditional cardiovascular and renal risk factors, while SAA lost its association after further adjustment for C-reactive protein. In conclusion, our data suggest that neither HDL quantity nor HDL composition or function independently predict cardiovascular outcome among nondialysis CKD patients.

ESRD-induced dyslipidemia-Should management of lipid disorders differ in dialysis patients?

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Although numerous modifiable risk factors in the pathogenesis of CVD and its associated mortality have been identified, dyslipidemia remains to be a key focus for therapy. In this regard, significant progress has been made in reducing cardiovascular mortality via the use of lipid-lowering agents such as HMG CoA reductase inhibitors (statins). Yet, despite the disproportionate risk of CVD and mortality in patients with advanced chronic and end stage renal disease (ESRD), treatment of dyslipidemia in this patient population has not been associated with a notable improvement in outcomes. Furthermore, observational studies have not consistently found an association between dyslipidemia and poor outcomes in patients with ESRD. However, it is imperative that examination of dyslipidemia and its association with outcomes take place in the context of the many factors that are unique to kidney disease and may contribute to the abnormalities in lipid metabolism in patients with ESRD. Understanding these intricacies and distinct features will be vital not only to the interpretation of the available clinical data in regards to outcomes, but also to the individualization of lipid therapy in ESRD. In this review, we will examine the nature and underlying mechanisms responsible for dyslipidemia, the association of serum lipids and lipoprotein concentrations with outcomes and the results of major trials targeting cholesterol (mainly statins) in patients with ESRD.

Hemodialysis-induced cardiovascular disease

More than half of all deaths among end stage renal disease (ESRD) patients are due to cardiovascular disease (CVD). Cardiovascular changes secondary to renal dysfunction, including fluid overload, uremic cardiomyopathy, secondary hyperparathyroidism, anemia, altered lipid metabolism, and accumulation of gut microbiota-derived uremic toxins like trimethylamine N-oxidase, contribute to the high risk for CVD in the ESRD population. In addition, conventional hemodialysis (HD) itself poses myocardial stress and injury on the already compromised cardiovascular system in uremic patients. This review will provide an overview of cardiovascular changes in chronic kidney disease and ESRD, a description of reported mechanisms for HD-induced myocardial injury, comparison of HD with other treatment modalities in the context of CVD, and possible management strategies.

Total Bilirubin in Prognosis for Mortality in End-Stage Renal Disease Patients on Peritoneal Dialysis Therapy

Background

Evidence regarding bilirubin's antioxidant properties and predictive roles is growing. However, it is unclear whether serum bilirubin would have a prognostic impact on survival of patients with regular peritoneal dialysis.

Methods and Results

We used the Taiwan Renal Registry Data System utilizing its 2005‐2012 data set. Data from patients on regular peritoneal dialysis were retrieved. The primary end point of observation was 3‐year mortality. A total of 3704 patients (mean age 53.5 years, 44% male) were enrolled, and these patients were divided according to baseline serum total bilirubin levels (<0.3, 0.3‐0.4, 0.4‐0.5, 0.5‐0.6, >0.6 mg/dL). Serum total bilirubin level was linearly related to age, incidence of hypertension, and type 2 diabetes mellitus. At the end of the observation period with a mean follow‐up of 2.12±1.07 years, 1095 (30.6%) deaths were detected. Serum total bilirubin level and 3‐year mortality rate presented a U‐shaped relationship. Those with serum total bilirubin 0.5 to 0.6 mg/dL had the lowest 3‐year mortality rate (24%). After adjustment for age, sex, underlying systemic disorders, medications, and laboratory discrepancies, serum total bilirubin still played an independent role for predicting 3‐year mortality.

Conclusions

Baseline serum total bilirubin level is significantly associated with 3‐year mortality among patients receiving regular peritoneal dialysis.