Lipoprotein Metabolism and Lipid Management in Chronic Kidney Disease

Reducing lipids for CV protection in CKD patients-current evidence

Lipid parameters are altered in the earliest stages of primary kidney disease, some even when measured glomerular filtration rate (GFR) is still normal. The main problem is that routinely measured lipid parameters are deceivingly normal except low high-density lipoprotein (HDL) and moderately elevated triglycerides (TGs) (>150 mg per 100 ml). Behind this unimpressive spectrum, serious anomalies are hidden: increased very low-density lipoprotein (VLDL) and chylomicron remnants, accumulation of delipidated small dense low-density lipoprotein (LDL), post translational modification of lipoproteins, abnormal concentrations of Lp(a) and nonprotective HDL. A routine parameter with some predictive value is the concentration of non-HDL cholesterol. Several of these abnormal lipoprotein particles stimulate cellular free oxygen radical formation which in turn induce inflammation and impact on endothelial function.A bone of contention is the indication for treatment with statins in endstage renal disease. Poor survival is paradoxically predicted by low cholesterol. This appears to be the result of confounding by microinflammation. One controlled interventional study in hemodialysed type 2 diabetics, the 4-D study, failed to show a significant benefit on the primary cardiovascular endpoint. We discuss potential explanations for this 'negative' outcome and the implications for statin treatment.

Lipid management in chronic kidney disease, hemodialysis, and transplantation

Recent studies have shown the spectrum of dyslipidemia in patients who have chronic kidney disease (CKD) or end-stage renal disease to be different from that of the general population. This article discusses the pathophysiology of dyslipidemia in CKD, dialysis, and renal transplant patients, the therapeutic options, and their association with clinical outcomes. Whenever possible, comparisons are made to outcomes in the general population.

Genetic-epidemiological evidence on genes associated with HDL cholesterol levels: a systematic in-depth review

High-density lipoprotein (HDL) particles exhibit multiple antiatherogenic effects. They are key players in the reverse cholesterol transport which shuttles cholesterol from peripheral cells (e.g. macrophages) to the liver or other tissues. This complex process is thought to represent the basis for the antiatherogenic properties of HDL particles. The amount of cholesterol transported in HDL particles is measured as HDL cholesterol (HDLC) and is inversely correlated with the risk for coronary artery disease: an increase of 1mg/dL of HDLC levels is associated with a 2% and 3% decrease of the risk for coronary artery disease in men and women, respectively. Genetically determined conditions with high HDLC levels (e.g. familial hyperalphalipoproteinemia) often coexist with longevity, and higher HDLC levels were found among healthy elderly individuals. HDLC levels are under considerable genetic control with heritability estimates of up to 80%. The identification and characterization of genetic variants associated with HDLC concentrations can provide new insights into the background of longevity. This review provides an extended overview on the current genetic-epidemiological evidence from association studies on genes involved in HDLC metabolism. It provides a path through the jungle of association studies which are sometimes confusing due to the varying and sometimes erroneous names of genetic variants, positions and directions of associations. Furthermore, it reviews the recent findings from genome-wide association studies which have identified new genes influencing HDLC levels. The yet identified genes together explain only a small amount of less than 10% of the HDLC variance, which leaves an enormous room for further yet to be identified genetic variants. This might be accomplished by large population-based genome-wide meta-analyses and by deep-sequencing approaches on the identified genes. The resulting findings will probably result in a re-drawing and extension of the involved metabolic pathways of HDLC metabolism.

Lipid abnormalities and cardiovascular risk in renal disease

The recent 4D study failed to provide definitive evidence for benefit of statin use in type 2 diabetics on dialysis. This finding stands in stark contrast to a number of other observations in patients with early stages of chronic kidney disease where substantial benefit of statins had been documented. Here we discuss some potential explanations for the unexpected finding of the 4D study and for the negative association between below average total cholesterol and vascular mortality among dialysis patients. Admittedly, in the absence of definite evidence in dialysis patients, we still conclude that the administration of statins is appropriate in patients with manifest coronary disease.

Kinetic studies of atherogenic lipoproteins in hemodialysis patients: do they tell us more about their pathology?

Patients with chronic kidney disease have one of the highest risks for atherosclerotic complications. Several large epidemiological studies described an opposite association of total and low density lipoprotein (LDL) cholesterol with cardiovascular complications and total mortality compared to the general population, a circumstance often called "reverse epidemiology." Many factors might contribute to this reversal such as interaction with malnutrition/inflammation, pronounced fluctuations of atherogenic lipoproteins during the course of renal disease, heterogeneity of lipoprotein particles with preponderance of remnant particles, and chemical modification of lipoproteins caused by the uremic environment. A vicious cycle has been suggested in uremia in which the decreased catabolism of atherogenic lipoproteins such as LDL, IDL and Lp(a) leads to their increased plasma residence time and further modification of these lipoproteins by oxidation, carbamylation, and glycation. Using stable isotope techniques, it has been shown recently that the plasma residence time of these particles is more than twice as long in hemodialysis patients as in nonuremic subjects. This reduced catabolism, however, is masked by the decreased production of LDL, resulting in near-normal plasma levels of LDL. The production rate of Lp(a) in hemodialysis patients is similar to that in controls which together with the doubled residence time results in elevated Lp(a) levels. An increased clearance of these altered lipoproteins via the scavenger receptors of macrophages leads to the transformation of macrophages into foam cells in the vascular wall and might contribute to the pronounced risk for cardiovascular complications of these patients. These observations suggest that the real danger of these particles is not reflected by the measured concentrations but by their metabolic qualities.

Statin therapy is associated with improved outcomes in vascular surgery patients with renal impairment

BACKGROUND

Little is known about the association between baseline kidney function, statin therapy, and outcome after vascular surgery in patients with and without chronic kidney disease.

METHODS

A total of 2126 patients underwent elective major vascular surgery and were divided into 2 categories based on baseline creatinine clearance (CrCl), calculated using the Cockcroft-Gault equation: CrCl > or = 60 mL/min (n = 1358, reference) and CrCl < 60 mL/min (n = 768). Outcome measures were 30-day and long-term all-cause, cardiac, and cerebrocardiovascular mortality. Mean follow-up was 6.0 +/- 3.7 years. Multivariate Cox regression analysis, including potential confounders and propensity score for statin use, was applied. Data are presented as hazard ratios (HRs) with 95% CI.

RESULTS

Thirty-day all-cause, cardiac, and cerebrocardiovascular mortality rates were 3.8% versus 10.2%, 1.3% versus 4.2%, and 2.7% versus 7.8%, respectively, according to the 2 categories of kidney function. In addition, long-term all-cause, cardiac, and cerebrocardiovascular mortality rates were 46.6% versus 72.5%, 14.6% versus 26.4%, and 23.0% versus 40.6%, respectively. Statin therapy was associated with an overall significant improved 30-day and long-term all-cause mortality, independent of other important confounders. However, in patients with a CrCl > or = 60 mL/min, the long-term cardiac and cerebrocardiovascular beneficial effects did not reach statistical significance (HR 0.93, 95% CI 0.61-1.41 and HR 0.89, 95% CI 0.63-1.24, respectively) when compared with patients with a CrCl of < 60 mL/min (HR 0.63, 95% CI 0.41-0.96 and HR 0.67, 95% CI 0.48-0.94, respectively).

CONCLUSIONS

The level of kidney function is an independent predictor of short- and long-term outcome after major noncardiac surgery. In addition, perioperative statin use in patients with kidney disease is associated with a reduction in the short- and long-term all-cause, cardiac, and cerebrocardiovascular mortality.