Dysfunctional high-density lipoproteins in children with chronic kidney disease

HDL Function across the Lifespan: From Childhood, to Pregnancy, to Old Age

The function of high-density lipoprotein (HDL) particles has emerged as a promising therapeutic target and the measurement of HDL function is a promising diagnostic across several disease states. The vast majority of research on HDL functional biology has focused on adult participants with underlying chronic diseases, whereas limited research has investigated the role of HDL in childhood, pregnancy, and old age. Yet, it is apparent that functional HDL is essential at all life stages for maintaining health. In this review, we discuss current data regarding the role of HDL during childhood, pregnancy and in the elderly, how disturbances in HDL may lead to adverse health outcomes, and knowledge gaps in the role of HDL across these life stages.

HDL and chronic kidney disease

Low HDL-cholesterol (HDL-C) concentrations are a typical trait of the dyslipidemia associated with chronic kidney disease (CKD). In this condition, plasma HDLs are characterized by alterations in structure and function, and these particles can lose their atheroprotective functions, e.g., the ability to promote cholesterol efflux from peripheral cells, anti-oxidant and anti-inflammatory proprieties and they can even become dysfunctional, i.e., exactly damaging. The reduction in plasma HDL-C levels appears to be the only lipid alteration clearly linked to the progression of renal disease in CKD patients. The association between the HDL system and CKD development and progression is also supported by the presence of genetic kidney alterations linked to HDL metabolism, including mutations in the APOA1, APOE, APOL and LCAT genes. Among these, renal disease associated with LCAT deficiency is well characterized and lipid abnormalities detected in LCAT deficiency carriers mirror the ones observed in CKD patients, being present also in acquired LCAT deficiency. This review summarizes the major alterations in HDL structure and function in CKD and how genetic alterations in HDL metabolism can be linked to kidney dysfunction. Finally, the possibility of targeting the HDL system as possible strategy to slow CKD progression is reviewed.

Protective effect and mechanism of Shenkang injection on adenine-induced chronic renal failure in rats

Purpose:

To investigate the protective effects of Shenkang injection (SKI) on adenine-induced chronic renal failure (CRF) in rat.

Methods:

Sprague Dawley rats were randomly divided into five groups: control, model, and SKI groups (5, 10, 20 mL/kg). Rats in model and SKI groups were treated with adenine i.g. at a dose of 150 mg/kg every day for 12 weeks to induce CRF. Twelve weeks later, SKI was administered to the rat i.p. for four weeks. The effects of SKI on kidney injury and fibrosis were detected.

Results:

SKI inhibited the elevation of the urine level of N-acetyl-b-D-glucosaminidase, kidney injury molecule-1, beta-2-microglobulin, urea protein in CRF rats. The serum levels of uric acid and serum creatinine increased and albumin decreased in the model group, which was prevented by SKI. SKI inhibited the release of inflammatory cytokines and increasing the activities of antioxidant enzymes in serum. SKI inhibited the expression of transforming growth factor-β1, vascular cell adhesion molecule 1, intercellular adhesion molecule 1, collagen I, collagen III, endothelin-1, laminin in kidney of CRF rats.

Conclusions:

SKI protected against adenine-induced kidney injury and fibrosis and exerted anti-inflammatory, and antioxidant effects in CRF rats.

Insights from the 4C-T Study suggest increased cardiovascular burden in girls with end stage kidney disease before and after kidney transplantation

Mortality in children with kidney failure is higher in girls than boys with cardiovascular complications representing the most common causes of death. Pulse wave velocity (PWV), a measure of vascular stiffness, predicts cardiovascular mortality in adults. Here, PWV in children with kidney failure undergoing kidney replacement therapy was investigated to determine sex differences and potential contributing factors. Two-hundred-thirty-five children (80 girls; 34%) undergoing transplantation (150 pre-emptive, 85 with prior dialysis) having at least one PWV measurement pre- and/or post-transplantation from a prospective cohort were analyzed. Longitudinal analyses (median/maximum follow-up time of 6/9 years) were performed for PWV z-scores (PWVz) using linear mixed regression models and further stratified by the categories of time: pre-kidney replacement therapy and post-transplantation. PWVz significantly increased by 0.094 per year and was significantly higher in girls (PWVz +0.295) compared to boys, independent of the underlying kidney disease. During pre-kidney replacement therapy, an average estimated GFR decline of 4ml/min/1.73m² per year was associated with a PWVz increase of 0.16 in girls only. Higher diastolic blood pressure and low density lipoprotein were independently associated with higher PWVz during pre-kidney replacement therapy in both sexes. In girls post-transplantation, an estimated GFR decline of 4ml/min/1.73m² per year pre-kidney replacement therapy and a longer time (over 12 months) to transplantation were significantly associated with higher PWVz of 0.22 and of 0.57, respectively. PWVz increased further after transplantation and was positively associated with time on dialysis and diastolic blood pressure in both sexes. Thus, our findings demonstrate that girls with advanced chronic kidney disease are more susceptible to develop vascular stiffening compared to boys, this difference persist after transplantation and might contribute to higher mortality rates seen in girls with kidney failure.

Supportive Effects of Online Hemodiafiltration Therapy on the Nutritional State and Lipid Profile in Very Elderly Dialysis Patients

INTRODUCTION

Online hemodiafiltration (HDF) therapy has been recognized as one of the potential dialysis modalities. However, the long-term effects of online HDF therapy on very elderly dialysis patients older than 75 years have yet to be fully elucidated.

METHODS

Seventy-four very elderly patients older than 75 years undergoing maintenance dialysis therapy were studied retrospectively. Twenty-four (mean ± SE, 81.5 ± 1.0 years) were treated by predilution online HDF, and fifty (81.2 ± 0.6 years) were treated by conventional hemodialysis (HD) for 3 years. Laboratory data related to the nutritional state and lipid profile were collected. Body composition was measured by a bioelectrical impedance method.

RESULTS

Dry weight and body mass index decreased in HD patients (2.9%, p = 0.003 and 3.1%, p = 0.001, respectively), while no significant changes were found in online HDF patients. Serum albumin levels reduced in both HD and online HDF groups (3.5%, p = 0.003 and 2.9%, p = 0.026, respectively). The geriatric nutritional risk index decreased in HD patients (3.0%, p < 0.001), while no significant change was shown in online HDF patients. Body composition analysis demonstrated a significant decrease in intracellular water and increases in extracellular water and edema ratio in both groups. Fat mass and %fat showed significant decreases in HD patients (8.1%, p = 0.003 and 7.3%, p = 0.003, respectively), but no significant changes in online HDF patients. Among laboratory data, serum high-density lipoprotein cholesterol levels did not change in HD patients. However, the levels elevated significantly (10.6%, p = 0.03) in online HDF patients.

DISCUSSION/CONCLUSION

These results indicated that the time-dependent deterioration of the nutritional state in very elderly dialysis patients was inevitable; however, such deterioration was not prominent in online HDF patients. Moreover, the lipid profile showed unique changes in online HDF patients. In order to treat very elderly dialysis patients, online HDF should preferentially be taken into consideration because the maintenance of general condition seems to be a practical goal against the natural time-dependent deterioration.

Breakfast partly restores the anti-inflammatory function of high-density lipoproteins from patients with type 2 diabetes mellitus

Background and aims

High-density lipoproteins (HDL) of patients with type 2 diabetes mellitus (T2DM) have impaired anti-inflammatory activities. The anti-inflammatory activity of HDL has been determined ex vivo after isolation by different methods from blood mostly obtained after overnight fasting. We first determined the effect of the HDL isolation method, and subsequently the effect of food intake on the anti-inflammatory function of HDL from T2DM patients.

Methods

Blood was collected from healthy controls and T2DM patients after an overnight fast, and from T2DM patients 3 h after breakfast (n = 17 each). HDL was isolated by a two-step density gradient ultracentrifugation in iodixanol (HDL_DGUC2), by sequential salt density flotation (HDL_SEQ) or by PEG precipitation (HDL_PEG). The anti-inflammatory function of HDL was determined by the reduction of the TNFα-induced expression of VCAM-1 in human coronary artery endothelial cells (HCAEC) and retinal endothelial cells (REC).

Results

HDL isolated by the three different methods from healthy controls inhibited TNFα-induced VCAM-1 expression in HCAEC. With apoA-I at 0.7 μM, HDL_DGUC2 and HDL_SEQ were similarly effective (16% versus 14% reduction; n = 3; p > 0.05) but less effective than HDL_PEG (28%, p < 0.05). Since ultracentrifugation removes most of the unbound plasma proteins, we used HDL_DGUC2 for further experiments. With apoA-I at 3.2 μM, HDL from fasting healthy controls and T2DM patients reduced TNFα-induced VCAM-1 expression in HCAEC by 58 ± 13% and 51 ± 20%, respectively (p = 0.35), and in REC by 42 ± 13% and 25 ± 18%, respectively (p < 0.05). Compared to preprandial HDL, postprandial HDL from T2DM patients reduced VCAM-1 expression by 56 ± 16% (paired test: p < 0.001) in HCAEC and by 34 ± 13% (paired test: p < 0.05) in REC.

Conclusions

The ex vivo anti-inflammatory activity of HDL is affected by the HDL isolation method. Two-step ultracentrifugation in an iodixanol gradient is a suitable method for HDL isolation when testing HDL anti-inflammatory function. The anti-inflammatory activity of HDL from overnight fasted T2DM patients is significantly impaired in REC but not in HCAEC. The anti-inflammatory function of HDL is partly restored by food intake.

Rice Endosperm Protein Improves the Anti-Inflammatory Effects of High-Density Lipoprotein and Produces Lower Atherosclerotic Lesion Accelerated by the Renal Mass Reduction than Casein in a Mouse Model

Chronic kidney disease (CKD) impairs the anti-inflammatory effects of high-density lipoprotein (HDL) and increases cardiovascular mortality. Though the potential role of dietary interventions to manage HDL is well studied, the clinical trials aimed to increase HDL levels have failed to reduce cardiovascular risk, rendering HDL function to be explored as a more relevant clinical parameter. This study investigates the effects of rice endosperm protein (REP), a plant-based protein, on the anti-inflammatory properties of HDL and renal injury-driven atherosclerosis in comparison with casein, an animal protein.

Ten-week-old apolipoprotein E-deficient hyperlipidemic mice underwent uninephrectomy. The mice (n = 6 each) were pair-fed a normal casein-based diet or a REP-based diet (both with 20.0% protein content) for seven weeks. Atherosclerotic lesions were detected by en face Sudan IV staining of the aorta.

The number and sizes of the atherosclerotic lesions were significantly lower in the REP-based diet-fed group than the casein-based diet-fed group (p = 0.038). However, the REP-based diet neither elicited an ameliorative effect on kidney function or histology nor impacted the cholesterol profiles. Furthermore, HDL from the REP-based diet-fed mice significantly suppressed the inflammatory cytokine response of human umbilical vein endothelial cells than that from the casein-based diet-fed mice (MCP-1, p = 0.010; IL-6, p = 0.011; IL-1β, p = 0.028).

The REP-based diet has a higher potential to lessen the atherosclerotic lesions accelerated by renal mass reduction than a casein-based diet, which could be associated with the anti-inflammatory effects of HDL.

High-Density Lipoproteins in Kidney Disease

Decades of epidemiological studies have established the strong inverse relationship between high-density lipoprotein (HDL)-cholesterol concentration and cardiovascular disease. Recent evidence suggests that HDL particle functions, including anti-inflammatory and antioxidant functions, and cholesterol efflux capacity may be more strongly associated with cardiovascular disease protection than HDL cholesterol concentration. These HDL functions are also relevant in non-cardiovascular diseases, including acute and chronic kidney disease. This review examines our current understanding of the kidneys’ role in HDL metabolism and homeostasis, and the effect of kidney disease on HDL composition and functionality. Additionally, the roles of HDL particles, proteins, and small RNA cargo on kidney cell function and on the development and progression of both acute and chronic kidney disease are examined. The effect of HDL protein modification by reactive dicarbonyls, including malondialdehyde and isolevuglandin, which form adducts with apolipoprotein A-I and impair proper HDL function in kidney disease, is also explored. Finally, the potential to develop targeted therapies that increase HDL concentration or functionality to improve acute or chronic kidney disease outcomes is discussed.

Subpopulations of High-Density Lipoprotein: Friends or Foes in Cardiovascular Disease Risk in Chronic Kidney Disease?

Dyslipidemia is a major traditional risk factor for cardiovascular disease (CVD) in chronic kidney disease (CKD) patients, although the altered lipid profile does not explain the number and severity of CVD events. High-density lipoprotein (HDL) is a heterogeneous (size, composition, and functionality) population of particles with different atherogenic or atheroprotective properties. HDL-cholesterol concentrations per se may not entirely reflect a beneficial or a risk profile for CVD. Large HDL in CKD patients may have a unique proteome and lipid composition, impairing their cholesterol efflux capacity. This lack of HDL functionality may contribute to the paradoxical coexistence of increased large HDL and enhanced risk for CVD events. Moreover, CKD is associated with inflammation, oxidative stress, diabetes, and/or hypertension that are able to interfere with the anti-inflammatory, antioxidative, and antithrombotic properties of HDL subpopulations. How these changes interfere with HDL functions in CKD is still poorly understood. Further studies are warranted to fully clarify if different HDL subpopulations present different functionalities and/or atheroprotective effects. To achieve this goal, the standardization of techniques would be valuable.

Predicting Factors for Rapid Progressive Chronic Kidney Disease in Primary Glomerular Disease Patients with Moderate-to-Severe Stage

Objective

To investigate the predictive factors associated with rapid progressive chronic kidney disease (CKD) in patients with primary glomerular disease (PGD).

Methods

Baseline data, clinical biochemistry, laboratory data, and imaging data were collected from 112 PGD patients in CKD stages 3 and 4 who were hospitalized at the Third Xiangya Hospital. Patients were divided into rapid progression group (Group R) and no rapid progression group (NR) according to the definition of rapid progression of CKD.

Results

The age, systolic blood pressure (SBP), serum β2-microglobulin (sβ2-MG), urinary α1-microglobulin (uα1-MG), and cardiothoracic ratio (CTR) of the R group were significantly higher than the NR group. However, the size of the kidney, high-dense lipoprotein (HDL), hemoglobin (Hb), and hematocrit of the R group were significantly lower than the NR group (P < 0.05). Binary logistic regression analysis showed that baseline CTR, SBP, size of the kidney, and HDL were independent risk factors for rapid progression of PGD. At the end of follow-up, CTR and SBP of group R were higher than the NR group, and the size of the kidney and HDL of group R were lower than the NR group.

Conclusion

Increased baseline CTR and SBP and decreased baseline HDL and renal volume could be the predictors of rapid progression in patients of PGD at the CKD stages 3 and 4.

Association of carbamylated high-density lipoprotein with coronary artery disease in type 2 diabetes mellitus: carbamylated high-density lipoprotein of patients promotes monocyte adhesion

BACKGROUND

Increasing evidence showed that carbamylated lipoprotein accelerated atherosclerosis. However, whether such modification of high-density lipoprotein (HDL) particles alters in type 2 diabetes mellitus (T2DM) patients and facilitates vascular complications remains unclear. We aimed to investigate the alteration of the carbamylation in HDL among T2DM patients and clarify its potential role in atherogenesis.

METHODS

A total of 148 consecutive T2DM patients undergoning angiography and 40 age- and gender-matched control subjects were included. HDL was isolated from plasma samples, and the concentration of HDL carbamyl-lysine (HDL-CBL) was measured. Furthermore, the HDL from subjects and in-vitro carbamylated HDL (C-HDL) was incubated with endothelial cells and monocyte to endothelial cell adhesion. Adhesion molecule expression and signaling pathway were detected.

RESULTS

Compared with the control group, the HDL-CBL level was remarkably increased in T2DM patients (6.13 ± 1.94 vs 12.00 ± 4.06 (ng/mg), P < 0.001). Of note, HDL-CBL demonstrated a more significant increase in T2DM patients with coronary artery disease (CAD) (n = 102) than those without CAD (n = 46) (12.75 ± 3.82 vs. 10.35 ± 4.11(ng/mg), P = 0.001). Multivariate logistic regression analysis demonstrated that higher HDL-CBL level was independently associated with a higher prevalence of CAD in diabetic patients after adjusting for established cofounders (adjusted odds ratio 1.174, 95% confidence Interval 1.045-1.319, p = 0.017). HDL from diabetic patients with CAD enhanced greater monocyte adhesion than that from the non-CAD or the control group (P < 0.001). Such pro-atherogenic capacity of diabetic HDL positively correlated with HDL-CBL level. Furthermore, in-vitro incubation of carbamylated HDL (C-HDL) with endothelial promoted monocyte to endothelial cell adhesion, induced upregulation of cell adhesion molecules expression, and activated NF-κB/p65 signaling in endothelial cells. Inhibiting carbamylation of HDL or NF-κB activation attenuated the monocyte to endothelial cell adhesion and cell surface adhesion molecules expression.

CONCLUSIONS

Our study identified elevated carbamylation modification of HDL from T2DM patients, especially in those with concomitant CAD. We also evidenced that C-HDL enhanced monocyte to endothelial cell adhesion, indicating a potential pro-atherogenic role of C-HDL in atherosclerosis among T2DM patients. Trial registration https://register.clinicaltrials.gov , NCT04390711 Registered on 14 May 2020; Retrospectively registered.

Pro-inflammatory HDL in women with obesity and nonalcoholic steatohepatitis

BACKGROUND

Individuals with non-alcoholic fatty liver disease (NAFLD), which includes non-alcoholic steatohepatitis (NASH), are at increased risk for cardiovascular events, independent of traditional risk factors. Limited data on pro-inflammatory high density lipoprotein (HDL) in NASH exists in the literature. We hypothesized that HDL from individuals with NASH would be more pro-inflammatory than HDL from individuals without NASH.

METHODS

Study participants were individuals with obesity who had undergone bariatric surgery with wedge liver biopsy. Using HDL isolated from serum obtained from study participants at the time of surgery, HDL-elicited macrophage cytokine expression (TNF-α, IL-1β, and IL-6) from THP-1 macrophages, HDL-associated receptor expression (ABCA1 and ABCG1) from apolipoprotein E deficient (apo E^-/-) mouse peritoneal macrophages, and isolevuglandin (isoLG) modified HDL were measured.

RESULTS

11 women with NASH and 15 women without NASH were included in the study. Both TNF-α (P = 0.032) and IL-1β (P = 0.029) were significantly more expressed by THP-1 macrophages exposed to HDL from women with NASH compared to women without NASH. ABCA1 and ABCG1 expression by apo E^-/- mouse peritoneal macrophages was not significantly different when exposed to HDL from either women with NASH or women without NASH. IsoLG-modified HDL isolated from the serum of women with NASH trended higher than women without NASH.

CONCLUSION

Our study suggests a more pro-inflammatory HDL in women with obesity and NASH compared to women with obesity and without NASH.

CKD Increases Carbonylation of HDL and Is Associated with Impaired Antiaggregant Properties

BACKGROUND

CKD is associated with increased oxidative stress that correlates with occurrence of cardiovascular events. Modifications induced by increased oxidative stress particularly affect circulating lipoproteins such as HDL that exhibit antiatheromatous and antithrombotic properties in vitro.

METHODS

To explore the specific role of oxidative modifications of HDL in CKD and their effect on the platelet-targeting antiaggregant properties of HDL, we used a CKD (5/6 nephrectomy) rabbit model. For ex vivo assessment of the antiaggregant properties of HDL, we collected blood samples from 15 healthy volunteers, 25 patients on hemodialysis, and 20 on peritoneal dialysis. We analyzed malondialdehyde, 4-hydroxynonenal (HNE), and 4-hydroxy-2-hexenal protein adduct levels. Platelet aggregation and activation were assessed by aggregometry, thromboxane B2 assay, or FACS. We modified HDL from controls by incubating it overnight at 37°C with 100 µM of HNE.

RESULTS

HDL from CKD rabbits and patients on hemodialysis had HNE adducts. The percentage of platelet aggregation or activation induced by collagen was significantly higher when platelets were incubated with HDL from CKD rabbit and hemodialysis groups than with HDL from the control group. In both rabbits and humans, platelet aggregation and activation were significantly higher in the presence of HNE-modified HDL than with HDL from their respective controls. Incubation of platelets with a blocking antibody directed against CD36 or with a pharmacologic inhibitor of SRC kinases restored the antiaggregative phenotype in the presence of HDL from CKD rabbits, patients on hemodialysis and peritoneal dialysis, and HNE-modified HDL.

CONCLUSIONS

HDL from CKD rabbits and patients on hemodialysis exhibited an impaired ability to inhibit platelet aggregation, suggesting that altered HDL properties may contribute to the increased cardiovascular risk in this population.

The Supportive Treatment of IgA Nephropathy and Idiopathic Nephrotic Syndrome: How Useful are Omega-3 Polyunsaturated Fatty Acids?

IgA nephropathy (IgAN) is the most prevalent glomerular disease in young adults worldwide, while idiopathic nephrotic syndrome (INS) represents the most frequent manifestation of glomerular disease in childhood. Over the years, studies have speculated about the potential benefits of omega-3 polyunsaturated fatty acids (PUFAs) in improving morbidity in both forms of chronic kidney disease (CKD). The proposed mechanisms of action include reduction of proteinuria and modulation of dyslipidemia. Although in vitro and in vivo experimental studies report the suppressive effect of omega-3 PUFAs on inflammatory pathways linked with the progression of nephropathy, the evidence supporting their beneficial effect in IgAN and INS is still weak. Also, their ability to regulate levels of total cholesterol, low-density lipoprotein-cholesterol (LDL-C), and triglycerides (TG) suggests that they could delay both dyslipidemia-associated nephrotoxicity and atherosclerosis. Most of the clinical trials that were conducted on their therapeutic benefits in IgAN patients reported positive outcomes with low and high doses of omega-3 PUFAs. However, few of the trials noted inconclusive findings, with low-quality evidence suggesting potential improvements in surrogate renal function outcomes. If the beneficial effect of omega-3 PUFAs is predicated on their hypolipidemic action, much higher doses could be used in well-designed randomized-controlled trials (RCTs) to determine if they could produce better renal function outcomes and provide much stronger evidence of their therapeutic benefits in IgAN and INS. However, the current hypothetical mechanisms of action in these forms of CKD also include the effect of omega-3 PUFAs on renal inflammatory pathways and glomerular proteinuria. Perhaps, the unresolved therapeutic efficacy of these fatty acids in IgAN and INS suggests that their exact mechanisms of action are yet to be fully established. In this narrative review, we aim to appraise the current evidence of their potential therapeutic benefits in these diseases.

The Role and Function of HDL in Patients with Chronic Kidney Disease and the Risk of Cardiovascular Disease

Chronic kidney disease (CKD) is a worldwide health problem with steadily increasing occurrence. Significantly elevated cardiovascular morbidity and mortality have been observed in CKD. Cardiovascular diseases are the most important and frequent cause of death of CKD patients globally. The presence of CKD is related to disturbances in lipoprotein metabolism whose consequences are dyslipidemia and the accumulation of atherogenic particles. CKD not only fuels the reduction of high-density lipoprotein (HDL) cholesterol concentration, but also it modifies the composition of this lipoprotein. The key role of HDL is the participation in reverse cholesterol transport from peripheral tissues to the liver. Moreover, HDL prevents the oxidation of low-density lipoprotein (LDL) cholesterol by reactive oxygen species (ROS) and protects against the adverse effects of oxidized LDL (ox-LDL) on the endothelium. Numerous studies have demonstrated the ability of HDL to promote the production of nitric oxide (NO) by endothelial cells (ECs) and to exert antiapoptotic and anti-inflammatory effects. Increasing evidence suggests that in patients with chronic inflammatory disorders, HDLs may lose important antiatherosclerotic properties and become dysfunctional. So far, no therapeutic strategy to raise HDL, or alter the ratio of HDL subfractions, has been successful in slowing the progression of CKD or reducing cardiovascular disease in patients either with or without CKD.

Cardiovascular risk factors in children on dialysis: an update

Cardiovascular disease (CVD) is a life-limiting comorbidity in patients with chronic kidney disease (CKD). In childhood, imaging studies have demonstrated early phenotypic characteristics including increases in left ventricular mass, carotid artery intima-media thickness, and pulse wave velocity, which occur even in young children with early stages of CKD. Vascular calcifications are the signature of an advanced phenotype and are mainly found in adolescents and young adults treated with dialysis. Association studies have provided valuable information regarding the significance of a multitude of risk factors in promoting CVD in children with CKD by using intermediate endpoints of measurements of surrogate parameters of CVD. Dialysis aggravates pre-existing risk factors and accelerates the progression of CVD with additional dialysis-related risk factors. Coronary artery calcifications in children and young adults with CKD accumulate in a time-dependent manner on dialysis. Identification of risk factors has led to improved understanding of principal mechanisms of CKD-induced damage to the cardiovascular system. Treatment strategies include assessment and monitoring of individual risk factor load, optimization of treatment of modifiable risk factors, and intensified hemodialysis if early transplantation is not possible.

Impaired Delivery of Cholesterol Effluxed From Macrophages to Hepatocytes by Serum From CKD Patients May Underlie Increased Cardiovascular Disease Risk

Introduction

Although chronic kidney disease (CKD) is associated with increased risk for coronary artery disease (CAD), the underlying mechanisms are not completely defined. In the present study, we tested the hypothesis that flux of cholesterol from macrophage foam cells to liver is impaired in subjects with CKD.

Methods

Consecutive healthy patients, patients with at least 1 CAD risk factor, patients with established CAD, and patients with CKD stages G3 to G5 (n ≥ 15/group) were recruited prospectively. The ability of total patient serum without any modifications to (i) facilitate efflux of cholesterol from human THP1-macrophage foam cells under physiological conditions (cholesterol efflux capacity [CEC]) and (ii) to deliver this effluxed cholesterol to primary hepatocytes with physiological expression of high-density lipoprotein (HDL) receptor SR-BI (capacity to deliver cholesterol to hepatocytes [CDCH]) was evaluated.

Results

Although healthy patients, patients with at least 1 CAD risk factor, and patients with established CAD all showed similar CEC, patients with CKD showed significantly higher CEC. CDCH was significantly lower in all groups compared with the healthy patients; however, when corrected for higher CEC, CDCH in patients with CKD was significantly lower than in patients with CAD. CDCH correlated with age, body mass index, metabolic parameters, inflammatory markers, and kidney function markers (estimated glomerular filtration rate [eGFR], serum creatinine, and serum cystatin C).

Conclusions

These results suggest that aberrations in delivery of cholesterol effluxed from macrophage foam cells to liver for final elimination or the last step of reverse cholesterol transport, may underlie the increased risk of CAD in patients with CKD.

Kidney as modulator and target of "good/bad" HDL

The strong inverse relationship between low levels of high-density lipoproteins (HDLs) and atherosclerotic cardiovascular disease (CVD) led to the designation of HDL as the "good" cholesterol. The atheroprotection is thought to reflect HDL's capacity to efflux cholesterol from macrophages, followed by interaction with other lipoproteins in the plasma, processing by the liver and excretion into bile. However, pharmacologic increases in HDL-C levels have not led to expected clinical benefits, giving rise to the concept of dysfunctional HDL, in which increases in serum HDL-C are not beneficial due to lost or altered HDL functions and transition to "bad" HDL. It is now understood that the cholesterol in HDL, measured by HDL-C, is neither a marker nor the mediator of HDL function, including cholesterol efflux capacity. It is also understood that besides cholesterol efflux, HDL functionality encompasses many other potentially beneficial functions, including antioxidant, anti-inflammatory, antithrombotic, anti-apoptotic, and vascular protective effects that may be critical protective pathways for various cells, including those in the kidney parenchyma. This review highlights advances in our understanding of the role kidneys play in HDL metabolism, including the effects on levels, composition, and functionality of HDL particles, particularly the main HDL protein, apolipoprotein AI (apoAI). We suggest that normal apoAI/HDL in the glomerular filtrate provides beneficial effects, including lymphangiogenesis, that promote resorption of renal interstitial fluid and biological particles. In contrast, dysfunctional apoAI/HDL activates detrimental pathways in tubular epithelial cells and lymphatics that lead to interstitial accumulation of fluid and harmful particles that promote progressive kidney damage.

Modification of HDL by reactive aldehydes alters select cardioprotective functions of HDL in macrophages

While increased levels of high-density lipoprotein (HDL)-cholesterol correlate with protection against cardiovascular disease, recent findings demonstrate that HDL function, rather than HDL-cholesterol levels, may be a better indicator of cardiovascular risk. One mechanism by which HDL function can be compromised is through modification by reactive aldehydes such as acrolein (Acro), 4-hydroxynonenal, and malondialdehyde (MDA). In this study, we tested the hypothesis that modification of HDL with reactive aldehydes would impair HDL's athero-protective functions in macrophages. Compared to native HDL, Acro- and MDA-modified HDL have impaired abilities to promote migration of primary peritoneal macrophages isolated from C57BL6/J mice. Incubation of macrophages with MDA-HDL also led to an increased ability to generate reactive oxygen species. Our studies revealed that the changes in HDL function following aldehyde modification are likely not through activation of canonical nuclear factor-kappa B signaling pathways. Consistent with this finding, treatment of either noncholesterol-loaded macrophages or foam cells with modified forms of HDL does not lead to significant changes in expression levels of inflammatory markers. Importantly, our data also demonstrate that changes in HDL function are dependent on the type of modification present on the HDL particle. Our findings suggest that modification of HDL with reactive aldehydes can impair some, but not all, of HDL's athero-protective functions in macrophages.

Oxidative stress in chronic kidney disease

Oxidative stress (OS), defined as disturbances in the pro-/antioxidant balance, is harmful to cells due to the excessive generation of highly reactive oxygen (ROS) and nitrogen (RNS) species. When the balance is not disturbed, OS has a role in physiological adaptations and signal transduction. However, an excessive amount of ROS and RNS results in the oxidation of biological molecules such as lipids, proteins, and DNA. Oxidative stress has been reported in kidney disease, due to both antioxidant depletions as well as increased ROS production. The kidney is a highly metabolic organ, rich in oxidation reactions in mitochondria, which makes it vulnerable to damage caused by OS, and several studies have shown that OS can accelerate kidney disease progression. Also, in patients at advanced stages of chronic kidney disease (CKD), increased OS is associated with complications such as hypertension, atherosclerosis, inflammation, and anemia. In this review, we aim to describe OS and its influence on CKD progression and its complications. We also discuss the potential role of various antioxidants and pharmacological agents, which may represent potential therapeutic targets to reduce OS in both pediatric and adult CKD patients.

IL-1 Inhibition and Function of the HDL-Containing Fraction of Plasma in Patients with Stages 3 to 5 CKD

BACKGROUND AND OBJECTIVES

Systemic inflammation modulates cardiovascular disease risk and functionality of HDL in the setting of CKD. Whether interventions that modify systemic inflammation can improve HDL function in CKD is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a post hoc analysis of two randomized, clinical trials, IL-1 trap in participants with GFR 15-59 ml/min per 1.73 m² (study A) and IL-1 receptor antagonist in participants on maintenance hemodialysis (study B), to evaluate if IL-1 blockade had improved the anti-inflammatory activity (IL-6, TNF-α, and Nod-like receptor protein 3), antioxidant function (superoxide production), and net cholesterol efflux capacity of HDL. HDL function was measured using LPS-stimulated THP-1 macrophages or peritoneal macrophages of apoE-deficient mice exposed to the apoB-depleted, HDL-containing fraction obtained from the plasma of the study participants, collected before and after the interventions to block IL-1 effects. Analysis of covariance was used for between group comparisons.

RESULTS

The mean age of the participants was 60±13 years, 72% (n=33) were men, and 39% (n=18) were black. There were 32 CKD (16 IL-1 trap and 16 placebo) and 14 maintenance hemodialysis (7 IL-1 receptor antagonist and 7 placebo) participants. Compared with placebo, IL-1 inhibition, in study A and B reduced cellular expression of TNF-α by 15% (P=0.05) and 64% (P=0.02), IL-6 by 38% (P=0.004) and 56% (P=0.08), and Nod-like receptor protein 3 by 16% (P=0.01) and 25% (P=0.02), respectively. The intervention blunted superoxide production in the treated arm compared with placebo, with the values being higher by 17% in the placebo arm in study A (P<0.001) and 12% in the placebo arm in study B (P=0.004). Net cholesterol efflux capacity was not affected by either intervention.

CONCLUSIONS

IL-1 blockade improves the anti-inflammatory and antioxidative properties of the HDL-containing fraction of plasma in patients with stages 3-5 CKD, including those on maintenance hemodialysis.

High-density lipoproteins (HDL) composition and function in preeclampsia

PURPOSE

To evaluate (a) the properties of high-density lipoproteins (HDL)/cholesterol, which include apolipoprotein A-1 (ApoA1) and paraoxonase1 (PON1), both are negative predictors of cardiovascular risk and (b) HDL function, among women with preeclampsia (PE). PE is a multi-system disorder, characterized by onset of hypertension and proteinuria or other end-organ dysfunction in the second half of pregnancy. Preeclampsia is associated with increased risk for later cardiovascular disease. The inverse association between HDL, cholesterol levels and the risk of developing atherosclerotic cardiovascular disease is well-established.

METHODS

Twenty-five pregnant women [19 with PE and 6 with normal pregnancy (NP)] were recruited during admission for delivery. HDL was isolated from blood samples. PON1 activity and HDL were analyzed. An in vitro model of endothelial cells was used to evaluate the effect of HDL on the transcription response of vascular cell adhesion molecule-1 (VCAM-1) and endothelial nitric oxide synthase (eNOS) mRNA expression.

RESULTS

PON1 activity (units/ml serum) was lower in the PE group compared to normal pregnancy (NP) (6.51 ± 0.73 vs. 9.98 ± 0.54; P = 0.015). Increased ApoA1 was released from PE-HDL as compared to NP-HDL (3.54 ± 0.72 vs. 0.89 ± 0.35; P = 0.01). PE-HDL exhibited increased VCAM-1 mRNA expression and decreased eNOS mRNA expression on TNF-α stimulated endothelial cells as compared to NP-HDL.

CONCLUSIONS

HDL from women with PE reduced PON1 activity and increased ApoA1 release from HDL particles. This process was associated with increased HDL diameter, suggesting impaired HDL anti-oxidant activity. These changes might contribute to higher long-term cardiovascular risks among women with PE.

Molecular mechanisms underlying uremic toxin-related systemic disorders in chronic kidney disease: focused on β2-microglobulin-related amyloidosis and indoxyl sulfate-induced atherosclerosis-Oshima Award Address 2016

Uremic toxins are linked to chronic kidney disease (CKD)-related systemic diseases. β₂-Microglobulin (β₂-m), a water-soluble, middle-sized molecule, is associated with mortality and dialysis-related amyloidosis (DRA). DRA occurs in long-term dialysis patients, with β₂-m amyloid deposited mainly in osteoarticular tissues. We investigated a model of β₂-m amyloid fibril extension at neutral pH in the presence of trifluoroethanol or sodium dodecyl sulfate. Using this model, some biological molecules, including glycosaminoglycans and lysophospholipids, were found to be chaperones for β₂-m amyloid fibril extension. Several protein-bound solutes, such as indoxyl sulfate (IS) and p-cresyl sulfate, are independent risk factors for cardiovascular disease in CKD patients, especially those undergoing dialysis. We investigated kidney injury-induced acceleration of atherosclerosis in association with macrophage phenotypic change to a proinflammatory state as well as increased IS deposition in lesions in an animal model. IS directly induced macrophage inflammation and impaired cholesterol efflux to high-density lipoprotein (HDL) in vitro. In addition, a clinical study showed that HDL isolated from CKD patients induced proinflammatory reactions and impaired cholesterol efflux to macrophages. These findings suggest that protein-bound solutes, including IS, will induce dysfunction of both macrophages and HDL in atherosclerotic lesions. To remove uremic toxins efficiently, we demonstrated the potential efficacy of oral charcoal adsorbent and hexadecyl-immobilized cellulose beads in hemodialysis patients. These findings suggest that uremic toxins induce various CKD-related systemic disorders, and further therapeutic strategies will be needed to reduce uremic toxins enough and improve life expectancy in CKD patients.

Chronic kidney disease alters lipid trafficking and inflammatory responses in macrophages: effects of liver X receptor agonism

BACKGROUND

Our aim was to evaluate lipid trafficking and inflammatory response of macrophages exposed to lipoproteins from subjects with moderate to severe chronic kidney disease (CKD), and to investigate the potential benefits of activating cellular cholesterol transporters via liver X receptor (LXR) agonism.

METHODS

LDL and HDL were isolated by sequential density gradient ultracentrifugation of plasma from patients with stage 3-4 CKD and individuals without kidney disease (HDLCKD and HDLCont, respectively). Uptake of LDL, cholesterol efflux to HDL, and cellular inflammatory responses were assessed in human THP-1 cells. HDL effects on inflammatory markers (MCP-1, TNF-α, IL-1β), Toll-like receptors-2 (TLR-2) and - 4 (TLR-4), ATP-binding cassette class A transporter (ABCA1), NF-κB, extracellular signal regulated protein kinases 1/2 (ERK1/2) were assessed by RT-PCR and western blot before and after in vitro treatment with an LXR agonist.

RESULTS

There was no difference in macrophage uptake of LDL isolated from CKD versus controls. By contrast, HDCKD was significantly less effective than HDLCont in accepting cholesterol from cholesterol-enriched macrophages (median 20.8% [IQR 16.1-23.7] vs control (26.5% [IQR 19.6-28.5]; p = 0.008). LXR agonist upregulated ABCA1 expression and increased cholesterol efflux to HDL of both normal and CKD subjects, although the latter continued to show lower efflux capacity. HDLCKD increased macrophage cytokine response (TNF-α, MCP-1, IL-1β, and NF-κB) versus HDLCont. The heightened cytokine response to HDLCKD was further amplified in cells treated with LXR agonist. The LXR-augmentation of inflammation was associated with increased TLR-2 and TLR-4 and ERK1/2.

CONCLUSIONS

Moderate to severe impairment in kidney function promotes foam cell formation that reflects impairment in cholesterol acceptor function of HDLCKD. Activation of cellular cholesterol transporters by LXR agonism improves but does not normalize efflux to HDLCKD. However, LXR agonism actually increases the pro-inflammatory effects of HDLCKD through activation of TLRs and ERK1/2 pathways.

Serum amyloid A enrichment impairs the anti-inflammatory ability of HDL from diabetic nephropathy patients

AIMS

Impaired anti-inflammatory ability of high-density lipoprotein (HDL) has been demonstrated in patients with type-2 diabetes mellitus (T2DM). However, whether HDL from patients with diabetic nephropathy (DN) suffers additional damage remains unknown. This study compared the anti-inflammatory capacities of HDL from healthy controls, T2DM patients with normal renal function, and T2DM patients with DN.

MATERIALS AND METHODS

HDL was isolated from healthy controls (n=33) and T2DM patients with normal renal function (n=21), chronic kidney disease (CKD) (n=27), and end-stage renal disease (ESRD) (n=27). Human peripheral blood mononuclear cells (PBMCs) from healthy volunteers were pretreated with HDL (100μg/mL) for 1h, then incubated with lipopolysaccharide (LPS) (50ng/mL) for 24h. The anti-inflammatory ability of HDL was measured as the secretion of TNF-α in LPS-activated monocytes.

RESULTS

The anti-inflammatory ability of HDL was gradually impaired as kidney function declined. Serum amyloid A (SAA) concentration in HDL^DN significantly increased and was positively correlated with the impaired anti-inflammatory ability of HDL (Pearson r=0.315, P=0.006). Furthermore, HDL supplemented with SAA significantly increased TNF-α release from PBMCs compared with that from control HDL.

CONCLUSIONS

These findings identified an impaired anti-inflammatory capacity of HDL from DN patients, which might be attributable to SAA enrichment.

Effects of apolipoprotein M in uremic atherosclerosis

BACKGROUND AND AIMS

Chronic kidney disease is characterized by uremia and causes premature death, partly due to accelerated atherosclerosis. Apolipoprotein (apo) M is a plasma carrier protein for the lipid sphingosine-1-phosphate (S1P). The Apom-S1P complex associates with HDL, and may contribute to its anti-atherosclerotic effects. The role of Apom/S1P in atherosclerosis is presently controversial and has not been explored in a uremic setting. We aimed to explore whether plasma concentrations of Apom/S1P are altered by uremia and whether Apom overexpression or deficiency affects classical and uremic atherosclerosis.

METHODS

Mild to moderate uremia was induced by subtotal nephrectomy (NX) in 86-92 Apoe-deficient mice that were either Apom-wild type, Apom-deficient, or overexpressed Apom (∼10 fold). The effects of uremia on plasma Apom/S1P and atherosclerosis were evaluated and compared to non-nephrectomized controls.

RESULTS

Uremia increased plasma Apom by ∼25%, but not S1P. Plasma S1P was elevated by ∼300% in mice overexpressing Apom, and decreased by ∼25% in Apom-deficient mice. Apom overexpression augmented aortic root atherosclerosis and plasma cholesterol. In contrast, aortic arch atherosclerosis was unaffected by the Apom genotype. There was no effect of Apom-deficiency or Apom overexpression on uremic atherosclerosis.

CONCLUSIONS

This study highlights the complexity of Apom/S1P in atherosclerosis and challenges the notion that the Apom/S1P complex is anti-atherogenic, at least in Apoe-deficient mice.

The pleiotropic vasoprotective functions of high density lipoproteins (HDL)

The pleiotropic functions of circulating high density lipoprotein (HDL) on peripheral vascular health are well established. HDL plays a pivotal role in reverse cholesterol transport and is also known to suppress inflammation, endothelial activation and apoptosis in peripheral vessels. Although not expressed in the central nervous system, HDL has nevertheless emerged as a potential resilience factor for dementia in multiple epidemiological studies. Animal model data specifically support a role for HDL in attenuating the accumulation of β-amyloid within cerebral vessels concomitant with reduced neuroinflammation and improved cognitive performance. As the vascular contributions to dementia are increasingly appreciated, this review seeks to summarize recent literature focused on the vasoprotective properties of HDL that may extend to cerebral vessels, discuss potential roles of HDL in dementia relative to brain-derived lipoproteins, identify gaps in current knowledge, and highlight new opportunities for research and discovery.

Could high-density lipoprotein cholesterol predict increased cardiovascular risk?

PURPOSE OF REVIEW

Serum high-density lipoprotein (HDL) is considered to be protective against cardiovascular disease. However, there is emerging evidence that under certain conditions the HDL molecule can become dysfunctional and proinflammatory, paradoxically leading to increased risk of cardiovascular disease. This review will provide a brief outline of the potential mechanisms by which HDL can become atherogenic and summarize some of the clinical evidence on this topic.

RECENT FINDINGS

HDL metabolism, structure, and function in addition to its level can be profoundly altered under conditions of marked oxidative stress and chronic inflammation. These abnormalities, in turn, lead to impaired reverse cholesterol transport, increased systemic oxidative stress/inflammation, and endothelial dysfunction that subsequently may contribute to atherogenesis and progression of cardiovascular disease.

SUMMARY

Association of serum HDL cholesterol level with outcomes is not only dependent on its serum concentration but also on the qualities/properties of this lipoprotein at a given point in time. Hence, it is essential that future studies examining association of HDL with risk of cardiovascular disease take into account the complexities of HDL metabolism and function and address the impact of the HDL particle as a whole (quantity as well as various properties) on atherosclerosis and cardiovascular outcomes.

Targeting Immunity in End-Stage Renal Disease

BACKGROUND

Despite the stable incidence of end-stage renal disease (ESRD), it continues to be associated with an unacceptably high cardiovascular risk.

SUMMARY

ESRD is characterized by enhanced oxidative stress and severe inflammation, which boost cardiovascular risk, thus increasing cardiovascular-associated mortality rate. While substantial effort has been made in the technological innovation of dialytic techniques, few significant advances have been made to reduce inflammation in patients with ESRD. Indeed, this contrasts with the extensive scientific breakthroughs made in the basic field of science in targeting inflammation. There is thus a pressing need for clinical trials to test the effect of reducing inflammation in patients with ESRD. Here, we will revisit the negative effect of ESRD on inflammation and explore the impact of enhanced inflammation on cardiovascular outcomes and survival in patients with ESRD. Finally, we will discuss the need for clinical trials that target inflammation in ESRD, as well as weigh potential disadvantages and offer novel innovative approaches. Key Message: We will try to understand why the issue of inflammation has not been successfully addressed thus far in patients with ESRD, while at the same time weighing the potential disadvantages and offering novel innovative approaches for targeting inflammation in patients with ESRD.

Kidneys: key modulators of high-density lipoprotein levels and function

PURPOSE OF REVIEW

The review will examine advances in our understanding of the role kidneys play in high-density lipoprotein (HDL) metabolism and the effect on levels, composition, and function of HDL particles.

RECENT FINDINGS

Components of the HDL particles can cross the glomerular filtration barrier. Some of these components, including apolipoproteins and enzymes involved in lipid metabolism, are taken up by the proximal tubule and degraded, modified, salvaged/returned to the circulation, or lost in the urine. Injury of the glomerular capillaries or tubules can affect these intrarenal processes and modify HDL. Changes in the plasma and urine levels of HDL may be novel markers of kidney damage or mechanism(s) of kidney disease.

SUMMARY

The kidneys have a significant role in the metabolism of individual HDL components, which in turn modulate HDL levels, composition, and functionality of HDL particles. These intrarenal effects may be useful markers of kidney damage and have consequences on kidney-related perturbations in HDL.

High density lipoprotein (HDL) particles from end-stage renal disease patients are defective in promoting reverse cholesterol transport

Atherosclerotic cardiovascular disease (CVD) represents the largest cause of mortality in end-stage renal disease (ESRD). CVD in ESRD is not explained by classical CVD risk factors such as HDL cholesterol mass levels making functional alterations of lipoproteins conceivable. HDL functions in atheroprotection by promoting reverse cholesterol transport (RCT), comprising cholesterol efflux from macrophage foam cells, uptake into hepatocytes and final excretion into the feces. ESRD-HDL (n = 15) were compared to healthy control HDL (n = 15) for their capacity to promote in vitro (i) cholesterol efflux from THP-1 macrophage foam cells and (ii) SR-BI-mediated selective uptake into ldla[SR-BI] cells as well as (iii) in vivo RCT. Compared with HDL from controls, ESRD-HDL displayed a significant reduction in mediating cholesterol efflux (p < 0.001) and SR-BI-mediated selective uptake (p < 0.01), two key steps in RCT. Consistently, also the in vivo capacity of ESRD-HDL to promote RCT when infused into wild-type mice was significantly impaired (p < 0.01). In vitro oxidation of HDL from healthy controls with hypochloric acid was able to fully mimic the impaired biological activities of ESRD-HDL. In conclusion, we demonstrate that HDL from ESRD patients is dysfunctional in key steps as well as overall RCT, likely due to oxidative modification.

Total HDL cholesterol efflux capacity in healthy children - Associations with adiposity and dietary intakes of mother and child

BACKGROUND AND AIMS

High-density lipoprotein (HDL) cholesterol efflux capacity in adults may be a measure of the atheroprotective property of HDL. Little however, is known about HDL cholesterol efflux capacity in childhood. We aimed to investigate the relationship between HDL cholesterol efflux capacity and childhood anthropometrics in a longitudinal study.

METHODS AND RESULTS

Seventy-five children (mean age = 9.4 ± 0.4 years) were followed from birth until the age of 9 years. HDL cholesterol efflux capacity was determined at age 9 by incubating serum-derived HDL-supernatants with ³H-cholesterol labeled J774 macrophages and percentage efflux determined. Mothers provided dietary information by completing food frequency questionnaires in early pregnancy and then 5 years later on behalf of themselves and their children. Pearson's correlations and multiple regression analyses were conducted to confirm independent associations with HDL efflux. There was a negative correlation between HDL cholesterol efflux capacity and waist circumference at age 5 (r = -0.3, p = 0.01) and age 9 (r = -0.24, p = 0.04) and BMI at age 5 (r = -0.45, p = 0.01) and age 9 (r = -0.19, p = 0.1). Multiple regression analysis showed that BMI at age 5 remained significantly associated with reduced HDL cholesterol efflux capacity (r = -0.45, p < 0.001). HDL-C was negatively correlated with energy-adjusted fat intake (r = -0.24, p = 0.04) and positively correlated with energy-adjusted protein (r = 0.24, p = 0.04) and starch (r = 0.29, p = 0.01) intakes during pregnancy. HDL-C was not significantly correlated with children dietary intake at age 5. There were no significant correlations between maternal or children dietary intake and HDL cholesterol efflux capacity.

CONCLUSIONS

This novel analysis shows that efflux capacity is negatively associated with adiposity in early childhood independent of HDL-C.

Modified Lipids and Lipoproteins in Chronic Kidney Disease: A New Class of Uremic Toxins

Chronic kidney disease (CKD) is associated with an enhanced oxidative stress and deep modifications in lipid and lipoprotein metabolism. First, many oxidized lipids accumulate in CKD and were shown to exert toxic effects on cells and tissues. These lipids are known to interfere with many cell functions and to be pro-apoptotic and pro-inflammatory, especially in the cardiovascular system. Some, like F2-isoprostanes, are directly correlated with CKD progression. Their accumulation, added to their noxious effects, rendered their nomination as uremic toxins credible. Similarly, lipoproteins are deeply altered by CKD modifications, either in their metabolism or composition. These impairments lead to impaired effects of HDL on their normal effectors and may strongly participate in accelerated atherosclerosis and failure of statins in end-stage renal disease patients. This review describes the impact of oxidized lipids and other modifications in the natural history of CKD and its complications. Moreover, this review focuses on the modifications of lipoproteins and their impact on the emergence of cardiovascular diseases in CKD as well as the appropriateness of considering them as actual mediators of uremic toxicity.

Do HDL and LDL subfractions play a role in atherosclerosis in end-stage renal disease (ESRD) patients?

BACKGROUND

Significantly increased cardiovascular mortality in patients with chronic kidney (CKD) disease cannot be explained by traditional risk factors. Recent studies revealed that the quality of HDL and LDL cholesterol may be more important than their serum levels. The aim of this study was to assess which LDL and HDL subfractions were more abundant in end-stage renal disease (ESRD) patients and to analyse whether subfraction distribution could be associated with accelerated atherosclerotic processes.

METHODS

This study included 50 ESRD patients undergoing dialysis and 20 healthy volunteers. LDL and HDL subfractions were analysed in serum with the use of Lipoprint system. All patients had intima-media thickness (IMT) measured.

RESULTS

Statistically significant differences in subfractions between control and study group were observed in case of: HDL1 (p < 0.0001), HDL2 (p = 0.009), HDL3 (p < 0.0001), HDL4 (p = 0.003), HDL5 (p = 0.01), HDL7 (p < 0.0001), HDL8 (p < 0.0001), HDL9 (p < 0.0001), HDL10 (p < 0.0001), large HDL (p < 0.0001), HDL Small (p < 0.0001) as well as IDL-B (p = 0.014), IDLA (p = 0.011), LDL2 (p = 0.007). Significant differences were also observed in HDL and LDL subfraction distribution between haemodialysis patients with normal and increased IMT: HDL6 (p = 0.020), HDL Large (HDL1-3) (p = 0.017), HDL Intermediate (HDL4-7) (p = 0.017).

CONCLUSIONS

This study revealed that ESRD influenced HDL subfractions. In HD patients, large HDL subfractions are more abundant while small HDL fraction is more frequent in healthy persons. It failed to show the influence of end-stage disease on LDL subfraction levels. Shift in HDL subfractions might be responsible for the increased risk of atherosclerosis in CKD patients.

The macrophage and its related cholesterol efflux as a HDL function index in atherosclerosis

The macrophage and its related cholesterol efflux are considered to be a key player in atherosclerotic formation in relation to the function of high-density lipoprotein (HDL). The HDL function can be evaluated by the reaction between lipid-loaded macrophages and lipid-acceptors in the HDL fraction from the plasma, apolipoprotein B-depleted serum, and/or whole serum/plasma. Recent studies have reported that an impaired cholesterol efflux of HDL is observed in patients with cardiometabolic diseases, such as dyslipidemia, diabetes mellitus, and chronic kidney disease. A population-based cohort study has reported an inverse association between the cholesterol efflux capacity of HDL and the incidence of atherosclerotic disease, regardless of the serum HDL-cholesterol level. Moreover, in this paper, when we summarized several clinical interventional studies of statin treatment that examined cholesterol efflux, a potential increase in the efflux in patients treated with statins was implied. However, the effect was not fully defined in the current situation because of the small sample sizes, lack of a unified protocol for measuring the efflux, and short-term intervention periods without cardiovascular outcomes in available studies. Further investigation is necessary to determine the effect of drugs on cholesterol efflux. With additional advanced studies, cholesterol efflux is a promising laboratory index to understand the HDL function.

Lipoprotein carriers of microRNAs

Lipoproteins, namely high-density lipoproteins (HDL), transport a wide-variety of cargo in addition to cholesterol and lipids. In 2011, HDL and low-density lipoproteins (LDL) were reported to transport microRNAs (miRNA). Since the original discovery, there has been great excitement for this topic and a handful of follow-up publications. Here, we review the current landscape of lipoprotein transport of miRNAs. HDL-miRNAs have been demonstrated to be altered in cardiovascular disease (CVD), including hypercholesterolemia and atherosclerosis. As such, HDL- and LDL-miRNAs may represent a novel class of disease biomarkers. Below, we review HDL-miR-92a and miR-486 levels in myocardial infarction and unstable angina, and HDL-miR-223 and miR-24 levels in coronary artery disease (CAD). Moreover, we address HDL's contribution to the total pool of extracellular miRNAs in plasma and differential distribution of miRNAs across HDL subspecies. Finally, we address current and future challenges for this new field and the barriers to such work. This article is part of a Special Issue entitled: MicroRNAs and lipid/energy metabolism and related diseases edited by Carlos Fernández-Hernando and Yajaira Suárez.

Increased carbamylation level of HDL in end-stage renal disease: carbamylated-HDL attenuated endothelial cell function

It is thought that carbamylated modification plays a crucial role in the development and progression of cardiovascular disease (CVD) in patients with end-stage renal disease (ESRD). However, information on the biological effects of carbamylated high-density lipoprotein (C-HDL) in ESRD is poor. The present study investigated the carbamylation level of HDL in ESRD and the effects of C-HDL on endothelial repair properties. HDL was isolated from healthy control subjects (n = 22) and patients with ESRD (n = 30). The carbamylation level of HDL was detected using ELISA. Isolated C-HDL for use in tissue culture experiments was carbamylated in vitro to a similar extent to that observed in ESRD. Human arterial endothelial cells were treated with C-HDL or native HDL to assess their migration, proliferation, and angiogenesis properties. HDL-associated paraoxonase 1 activity was also determined by spectrophotometry assay. Compared with healthy control subjects, the carbamylation level of HDL in ESRD patients was increased and positively correlated with blood urea concentration. In vitro, C-HDL significantly inhibited migration, angiogenesis, and proliferation in endothelial cells. Mechanistic studies revealed that HDL-associated paraoxonase 1 activity was decreased and negatively correlated with the carbamylation level of HDL in ESRD patients. In addition, C-HDL suppressed the expression of VEGF receptor 2 and scavenger receptor class B type I signaling pathways in endothelial cells. In conclusion, the present study identified a significantly increased carbamylation level of HDL in ESRD. Furthermore, C-HDL inhibited endothelial cell repair functions.

A selective peroxisome proliferator-activated receptor δ agonist PYPEP suppresses atherosclerosis in association with improvement of the serum lipoprotein profiles in human apolipoprotein B100 and cholesteryl ester transfer protein double transgenic mice

OBJECTIVE

Although peroxisome proliferator-activated receptor (PPAR) δ agonists have been shown to improve the serum lipoprotein profiles in humans, the impact of the changes in these lipoprotein profiles on atherosclerosis remains to be elucidated. The aim of this study was to investigate the relationship between the selective PPARδ agonist-induced alterations of serum lipoprotein profiles and the development of atherosclerosis in human apolipoprotein B100 and cholesterol ester transfer protein double transgenic (hApoB100/hCETP-dTg) mice with human-like hypercholesterolemic dyslipidemia.

METHODS

hApoB100/hCETP-dTg mice fed an atherogenic diet received a novel PPARδ agonist (PYPEP) or vehicle for 18 weeks, followed by evaluation of atherosclerosis. Serum samples were collected during the treatment period at least at 3-week intervals to determine the lipoprotein levels and the levels of an inflammatory marker, macrophage chemotactic protein-1 (MCP-1), and to analyze the lipoprotein profile by fast protein liquid chromatography. The cholesterol efflux capacity of high-density lipoprotein (HDL) was examined using [(3)H]-cholesterol labeled macrophages.

RESULTS

Compared with vehicle treatment, PYPEP treatment caused increases in the serum levels of HDL cholesterol and apolipoprotein A-I (ApoA-I), as well as reductions in the serum non-HDL cholesterol and MCP-1 levels. The HDL fraction from the PYPEP-treated group maintained its cholesterol efflux capacity and showed an increased population of smaller HDL particles. PYPEP substantially suppressed atherosclerotic lesion progression, and the lesion areas had significant correlations with non-HDL cholesterol, HDL cholesterol, ApoA-I and MCP-1 by Pearson's correlation analysis. A multiple regression analysis revealed that non-HDL cholesterol and ApoA-I were significantly associated with the atherosclerotic lesion area.

CONCLUSION

A novel PPARδ agonist, PYPEP, suppressed atherosclerotic lesion progression by improving the serum lipoprotein profiles, including increased levels of ApoA-I and functional HDL particles, as well as a reduced non-HDL cholesterol level, in hApoB100/hCETP-dTg mice with human-like hypercholesterolemic dyslipidemia.

Metabolic Syndrome and Smoking Are Associated with Future Development of Advanced Chronic Kidney Disease in Older Adults

INTRODUCTION

Metabolic syndrome (MetS) and smoking have been identified as risk factors for chronic kidney disease (CKD) in cross-sectional studies in various age groups, but longitudinal data on progression of CKD in older adults are limited. Our objectives were to examine whether MetS and its components and smoking predict the onset of CKD stage 3b (CKD-3b) in older adults.

METHODS

A subset of participants of the Einstein Aging Study who were free of diabetes, dementia, and CKD-3b at enrollment were included in this analysis. CKD-3b was defined as an estimated glomerular filtration rate <45 ml/min/1.73 m(2). Cox proportional hazards models were used in these analyses.

RESULTS

In total, 413 ≥70-year-old individuals were eligible for this study. 65.4% were female and 26.6% were black. 22.3% of the participants had MetS at baseline, 4.4% were active smokers, and 6.1% developed CKD-3b over a mean of 4 years of follow-up. MetS and smoking independently predicted incident CKD in our fully adjusted model (hazard ratio 3.65, 95% CI 1.20-10.60, p = 0.022; hazard ratio 29.69, 95% CI 4.47-197.23, p = 0.000).

CONCLUSION

MetS and smoking are associated with an increased incidence of CKD-3b. These risk factors are modifiable, easily identified and prevented through better health care practice and early diagnosis.

Plasma Nitration of High-Density and Low-Density Lipoproteins in Chronic Kidney Disease Patients Receiving Kidney Transplants

BACKGROUND

Functional abnormalities of high-density lipoprotein (HDL) could contribute to cardiovascular disease in chronic kidney disease patients. We measured a validated marker of HDL dysfunction, nitrated apolipoprotein A-I, in kidney transplant recipients to test the hypothesis that a functioning kidney transplant reduces serum nitrated apoA-I concentrations.

METHODS

Concentrations of nitrated apoA-I and apoB were measured using indirect sandwich ELISA assays on sera collected from each transplant subject before transplantation and at 1, 3, and 12 months after transplantation. Patients were excluded if they have history of diabetes, treatment with lipid-lowering medications or HIV protease inhibitors, prednisone dose > 15 mg/day, nephrotic range proteinuria, serum creatinine > 1.5 mg/dL, or active inflammatory disease. Sera from 18 transplanted patients were analyzed. Four subjects were excluded due to insufficient data. Twelve and eight patients had creatinine < 1.5 mg/dL at 3 and 12 months after transplantation, respectively. RESULTS. Nitrated apoA-I was significantly reduced at 12 months after transplantation (p = 0.039). The decrease in apoA-I nitration was associated with significant reduction in myeloperoxidase (MPO) activity (p = 0.047). In contrast to apoA-I, nitrated apoB was not affected after kidney transplantation.

CONCLUSIONS

Patients with well-functioning grafts had significant reduction in nitrated apoA-I 12 months after kidney transplantation. Further studies are needed in a large cohort to determine if nitrated apoA-I can be used as a valuable marker for cardiovascular risk stratification in chronic kidney disease.

High-Density Lipoprotein Function Measurement in Human Studies: Focus on Cholesterol Efflux Capacity

A low plasma level of high-density lipoprotein (HDL) cholesterol (HDL-C) is a major risk factor for the development of atherosclerotic cardiovascular disease (ASCVD). However, several observations have highlighted the shortcomings of using cholesterol content as the sole reflection of HDL metabolism. In particular, several large randomized controlled trials of extended release niacin and cholesteryl-ester transfer protein (CETP) inhibitors on background statin therapy have failed to show improvement in ASCVD outcomes despite significant increases in HDL-C. Reverse cholesterol transport (RCT) is the principal HDL function that impacts macrophage foam cell formation and other functions such as endothelial activation of endothelial nitric oxide synthase, monocyte adhesion, and platelet aggregation. Cholesterol efflux from macrophages to plasma/serum reflects the first critical step of RCT and is considered a key anti-atherosclerotic function of HDL. Whether this function is operative in humans remains to be seen, but recent studies assessing cholesterol efflux in humans suggest that the cholesterol efflux capacity (CEC) of human plasma or serum is a potent marker of ASCVD risk. This review describes the methodology of measuring CEC ex vivo from human samples and the findings to date linking CEC to human disease. Studies to date confirm that CEC can be reliably measured using stored human blood samples as cholesterol acceptors and suggest that CEC may be a promising new biomarker for atherosclerotic and metabolic diseases. Further studies are needed to standardize measurements and clarify the role CEC may play in predicting risk of developing disease and response to therapies.

Residual Cardiovascular Risk in Chronic Kidney Disease: Role of High-density Lipoprotein

Although reducing low-density lipoprotein-cholesterol (LDL-C) levels with lipid-lowering agents (statins) decreases cardiovascular disease (CVD) risk, a substantial residual risk (up to 70% of baseline) remains after treatment in most patient populations. High-density lipoprotein (HDL) is a potential contributor to residual risk, and low HDL-cholesterol (HDL-C) is an established risk factor for CVD. However, in contrast to conventional lipid-lowering therapies, recent studies show that pharmacologic increases in HDL-C levels do not bring about clinical benefits. These observations have given rise to the concept of dysfunctional HDL where increases in serum HDL-C may not be beneficial because HDL loss of function is not corrected by or even intensified by the therapy. Chronic kidney disease (CKD) increases CVD risk, and patients whose CKD progresses to end-stage renal disease (ESRD) requiring dialysis are at the highest CVD risk of any patient type studied. The ESRD population is also unique in its lack of significant benefit from standard lipid-lowering interventions. Recent studies indicate that HDL-C levels do not predict CVD in the CKD population. Moreover, CKD profoundly alters metabolism and composition of HDL particles and impairs their protective effects on functions such as cellular cholesterol efflux, endothelial protection, and control of inflammation and oxidation. Thus, CKD-induced perturbations in HDL may contribute to the excess CVD in CKD patients. Understanding the mechanisms of vascular protection in renal disease can present new therapeutic targets for intervention in this population.