Restoration of renal function does not correct impairment of uremic HDL properties

Associations Between Gut Microbial Features and Sickness Symptoms in Kidney Transplant Recipients

PURPOSE

The study investigated the relationship of gut microbiome features and sickness symptoms in kidney transplant recipients.

METHODS

Employing a prospective, longitudinal design, we collected data from 19 participants who had undergone living-donor kidney transplant at three timepoints (pre-transplant and 1 week and 3 months post-transplant). Sickness symptom data and fecal specimens were collected at each timepoint. Participants were grouped either as high or low sickness symptom severity at baseline. Shotgun metagenomics sequencing characterized gut microbial structure and functional gene content. Fecal microbial features, including alpha (evenness and richness within samples) and beta (dissimilarities between samples) diversity and relative abundances, were analyzed using R statistical packages. Cross-sectional and longitudinal analyses examined relationships between gut microbial features and sickness symptoms.

RESULTS

Although our exploratory findings revealed no significant differences in alpha and beta diversity between groups, the high-severity group showed lower microbial richness and evenness than the low-severity group. The high-severity group had enriched relative abundance of bacteria from the genera Citrobacter and Enterobacter and reduced relative abundance of bacteria from the genus Akkermansia across timepoints. No functional genes differed significantly between groups or timepoints.

CONCLUSIONS

Kidney transplant recipients with high symptom burden displayed increased putative proinflammatory bacteria and decreased beneficial bacteria. This study provides an effect size that future large cohort studies can employ to confirm associations between gut microbial features and sickness symptom experiences in the kidney transplant population. The study findings also have implications for future interventional studies aiming to alleviate the sickness symptom burden in this population.

Changes in serum pigment epithelium-derived factor levels after kidney transplantation in patients with end-stage renal disease

Background

Pigment epithelium-derived factor (PEDF) is a serin protease inhibitor and a potent inhibitor of angiogenesis. Its serum level has significant associations with metabolic parameters. However, little is known about the association between PEDF levels and lipid parameters in renal transplanted (TX) patients. Therefore, our aim was to investigate the relationship between PEDF level and lipid parameters in TX patients.

Methods

Seventy TX patients (47 males, 23 females, mean age 51.7 ± 12.4 years) and 34 healthy controls were enrolled. We examined the serum creatinine, C-reactive protein, fasting glucose and lipid parameters right before, then 1 and 6 months after TX. High-density lipoprotein (HDL)-associated paraoxonase-1 (PON1) activities were measured spectrophotometrically. Lipoprotein subfractions were determined by Lipoprint. PEDF and oxidized low-density liporotein (oxLDL) levels were measured by ELISA.

Results

Before transplantation, patients had had a significantly higher PEDF level compared to control subjects (p < 0.001). One month after transplantation, their PEDF level decreased significantly reaching the healthy controls’ level, and this lower level was maintained during the 6 months follow-up period as well. The initial oxLDL level was significantly higher, while PON1 activities were significantly lower in the patient group compared to the control group. We found a significant positive correlation between PEDF and total cholesterol, low-density lipoprotein (LDL)-cholesterol, triglyceride, oxLDL and small HDL subfraction; while negative correlations were found between PEDF and mean LDL size and large HDL subfraction during the entire follow-up period.

Conclusion

PEDF may play an important role in the increased oxidative stress and enhanced atherogenesis in renal transplant patients.

The HDL Proteome Watch: Compilation of studies leads to new insights on HDL function

PURPOSE OF REVIEW

High density lipoproteins (HDL) are a heterogeneous family of particles that contain distinct complements of proteins that define their function. Thus, it is important to accurately and sensitively identify proteins associated with HDL. Here we highlight the HDL Proteome Watch Database which tracks proteomics studies from different laboratories across the world.

RECENT FINDINGS

In 45 published reports, almost 1000 individual proteins have been detected in preparations of HDL. Of these, 251 have been identified in at least three different laboratories. The known functions of these consensus HDL proteins go well beyond traditionally recognized roles in lipid transport with many proteins pointing to HDL functions in innate immunity, inflammation, cell adhesion, hemostasis and protease regulation, and even vitamin and metal binding.

SUMMARY

The HDL proteome derived across multiple studies using various methodologies provides confidence in protein identifications that can offer interesting new insights into HDL function. We also point out significant issues that will require additional study going forward.

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.

Lipoproteins in chronic kidney disease: from bench to bedside

Chronic kidney disease (CKD) is associated with high cardiovascular risk. CKD patients exhibit a specific lipoprotein pattern termed 'uraemic dyslipidaemia', which is characterized by rather normal low-density lipoprotein cholesterol, low high-density lipoprotein cholesterol, and high triglyceride plasma levels. All three lipoprotein classes are involved in the pathogenesis of CKD-associated cardiovascular diseases (CVDs). Uraemia leads to several modifications of the structure of lipoproteins such as changes of the proteome and the lipidome, post-translational protein modifications (e.g. carbamylation) and accumulation of small-molecular substances within the lipoprotein moieties, which affect their functionality. Lipoproteins from CKD patients interfere with lipid transport and promote inflammation, oxidative stress, endothelial dysfunction as well as other features of atherogenesis, thus contributing to the development of CKD-associated CVD. While, lipid-modifying therapies play an important role in the management of CKD patients, their efficacy is modulated by kidney function. Novel therapeutic agents to prevent the adverse remodelling of lipoproteins in CKD and to improve their functional properties are highly desirable and partially under development.

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.

High-Density Lipoproteins and Acute Kidney Injury

High-density lipoprotein (HDL) particles, best known for their anti-atherosclerotic effects, also may play a beneficial role during acute renal stress. HDL from healthy human beings also shows anti-inflammatory and anti-oxidant capacities, promotes endothelial function and repair, and serves as a systemic signaling mechanism facilitating rapid interorgan communication during times of physiologic stress. Higher concentrations of HDL are associated with less acute kidney injury after sepsis, cardiac and vascular surgery, and contrast-exposure during percutaneous coronary interventions. A better understanding of the interplay between HDL and the kidney both under homeostatic conditions and under acute physiologic stress could lead to the identification of novel risk factors and therapeutic targets for acute kidney injury prevention and treatment in the future.

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.

Multiplexed MRM-based protein quantification of putative prognostic biomarkers for chronic kidney disease progression in plasma

Current diagnostic measures for Chronic Kidney Disease (CKD) include detection of reduced estimated glomerular filtration rate (eGFR) and albuminuria, which have suboptimal accuracies in predicting disease progression. The disease complexity and heterogeneity underscore the need for multiplex quantification of different markers. The goal of this study was to determine the association of six previously reported CKD-associated plasma proteins [B2M (Beta-2-microglobulin), SERPINF1 (Pigment epithelium-derived factor), AMBP (Protein AMBP), LYZ (Lysozyme C), HBB (Hemoglobin subunit beta) and IGHA1 (Immunoglobulin heavy constant alpha 1)], as measured in a multiplex format, with kidney function, and outcome. Antibody-free, multiple reaction monitoring mass spectrometry (MRM) assays were developed, characterized for their analytical performance, and used for the analysis of 72 plasma samples from a patient cohort with longitudinal follow-up. The MRM significantly correlated (Rho = 0.5–0.9) with results from respective ELISA. Five proteins [AMBP, B2M, LYZ, HBB and SERPINF1] were significantly associated with eGFR, with the three former also associated with unfavorable outcome. The combination of these markers provided stronger associations with outcome (p < 0.0001) compared to individual markers. Collectively, our study describes a multiplex assay for absolute quantification and verification analysis of previously described putative CKD prognostic markers, laying the groundwork for further use in prospective validation studies.

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.

Novel Associations between Related Proteins and Cellular Effects of High-Density Lipoprotein

BACKGROUND AND OBJECTIVES

Recent studies have examined the structure-function relationship of high-density lipoprotein (HDL). This study aimed to identify and rank HDL-associated proteins involved in several biological function of HDL.

METHODS

HDLs isolated from 48 participants were analyzed. Cholesterol efflux capacity, effect of HDL on nitric oxide production, and vascular cell adhesion molecule-1 expression were assessed. The relative abundance of identified proteins in the highest vs. lowest quartile was expressed using the normalized spectral abundance factor ratio.

RESULTS

After adjustment by multiple testing, six proteins, thyroxine-binding globulin, alpha-1B-glycoprotein, plasma serine protease inhibitor, vitronectin, angiotensinogen, and serum amyloid A-4, were more abundant (relative abundance ratio ≥2) in HDLs with the highest cholesterol efflux capacity. In contrast, three proteins, complement C4-A, alpha-2-macroglobulin, and immunoglobulin mu chain C region, were less abundant (relative abundance ratio <0.5). In terms of nitric oxide production and vascular cell adhesion molecule-1 expression, no proteins showed abundance ratios ≥2 or <0.5 after adjustment. Proteins correlated with the functional parameters of HDL belonged to diverse biological categories.

CONCLUSIONS

In summary, this study ranked proteins showing higher or lower abundance in HDLs with high functional capacities and newly identified multiple proteins linked to cholesterol efflux capacity.

Association of Serum Paraoxonase/Arylesterase Activity With All-Cause Mortality in Maintenance Hemodialysis Patients

CONTEXT

In end-stage renal disease (ESRD), serum high-density lipoprotein cholesterol (HDL-C) level is not an accurate predictor of mortality, partly because it does not necessarily correlate with indices of HDL function. Paraoxonase (PON) is a major enzyme constituent of HDL and a key component of HDL antioxidant activity. Apolipoprotein A-I (Apo A-1) is the core HDL structural protein that plays a major role in various aspects of HDL function.

OBJECTIVE

We sought to examine PON activity and Apo A-I levels in patients with ESRD vs healthy controls.

DESIGN AND SETTING

PON/arylesterase activity was measured in 499 patients with maintenance hemodialysis (MHD) and 24 healthy controls with similar distributions of age, sex, and race/ethnicity. Serum acrolein-modified Apo A-I was measured in 30 patients with MHD and 10 healthy controls.

MAIN OUTCOME MEASURES

Multilevel Cox models were used to assess associations among PON activity, Apo A-I, and HDL-C levels with 12-month all-cause mortality.

RESULTS

PON activity was significantly lower in patients with MHD vs controls. Furthermore, acrolein-modified Apo A-I levels were higher in patients with MHD vs controls. In fully adjusted models, high PON activity was associated with lower 12-month mortality, whereas no difference of mortality risk was observed across HDL-C levels. The combination of high PON and low Apo A-I compared with low PON and low Apo A-I was associated with lower mortality risk.

CONCLUSIONS

In patients with MHD, PON activity had a stronger association with 12-month mortality than HDL-C. Future studies are needed to examine the role of these markers as potential diagnostic and therapeutic tools in ESRD.

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.

Deepening our understanding of HDL proteome

Introduction: High-density lipoprotein (HDL) particles are heterogeneous and their proteome is complex and distinct from HDL cholesterol. However, it is largely unknown whether HDL proteins are associated with cardiovascular protection. Areas covered: HDL isolation techniques and proteomic analyses are reviewed. A list of HDL proteins reported in 37 different studies was compiled and the effects of different isolation techniques on proteins attributed to HDL are discussed. Mass spectrometric techniques used for HDL analysis and the need for precise and robust methods for quantification of HDL proteins are discussed. Expert opinion: Proteins associated with HDL have the potential to be used as biomarkers and/or help to understand HDL functionality. To achieve this, large cohorts must be studied using precise quantification methods. Key factors in HDL proteome quantification are the isolation methodology and the mass spectrometry technique employed. Isolation methodology affects what proteins are identified in HDL and the specificity of association with HDL particles needs to be addressed. Shotgun proteomics yields imprecise quantification, but the majority of HDL studies relied on this approach. Few recent studies used targeted tandem mass spectrometry to quantify HDL proteins, and it is imperative that future studies focus on the application of these precise techniques.

Autoantibodies to Apolipoprotein A-1 as Independent Predictors of Cardiovascular Mortality in Renal Transplant Recipients

Renal transplant recipients (RTRs) are known to have a high cardio-vascular disease (CVD) burden only partly explained by traditional CVD risk factors. The aim of this paper was therefore to determine: i) the prognostic value of autoantibodies against apoA-1 (anti-apoA-1 IgG) for incidence of CVD mortality, all-cause mortality and graft failure in RTR. Four hundred and sixty two (462) prospectively included RTRs were followed for 7.0 years. Baseline anti-apoA-1 IgG were determined and associations with incidence of CVD mortality (n = 48), all-cause mortality (n = 92) and graft failure (n = 39) were tested. Kaplan-Meier analyses demonstrated significant associations between tertiles of anti-apoA-1 IgG and CVD mortality (log rank test: p = 0.048). Adjusted Cox regression analysis showed a 54% increase in risk for CVD mortality for each anti-apoA-1 IgG levels standard deviation increase (hazard ratio [HR]: 1.54, 95% Confidence Interval [95%CI]: 1.14-2.05, p = 0.005), and a 33% increase for all-cause mortality (HR: 1.33; 95%CI: 1.06-1.67, p = 0.01), independent of CVD risk factors, renal function and HDL function. The association with all-cause mortality disappeared after excluding cases of CVD specific mortality. The sensitivity, specificity, positive predictive value, and negative predictive value of anti-apoA-1 positivity for CVD mortality were 18.0%, 89.3%, 17.0%, and 90.0%, respectively. HDL functionality was not associated with anti-apoA-1 IgG levels. This prospective study demonstrates that in RTR, anti-apoA-1 IgG are independent predictors of CVD mortality and are not associated with HDL functionality.

Angiotensin receptor blocker vs ACE inhibitor effects on HDL functionality in patients on maintenance hemodialysis

BACKGROUND AND AIMS

Angiotensin receptor blockers (ARB) and angiotensin converting enzyme inhibitors (ACEI) reduce cardiovascular events in the general population. Maintenance hemodialysis (MHD) patients are at high cardiovascular risk but few studies have directly addressed the comparative efficacy of these drugs. MHD disrupts the normally atheroprotective actions of high density lipoprotein (HDL), therefore, we compared ACEI or ARB treatment on HDL functions in MHD.

METHODS AND RESULTS

HDL was isolated at the starting point (pre) and 3-6 months later (post) in 30 MHD randomly assigned to placebo, ramipril or valsartan. Outcomes included cholesterol efflux, inflammatory cytokine response, effects on Toll-like receptors (TLR), superoxide production, methylarginine and serum amyloid A (SAA) levels. HDL from ARB- or ACEI-treated subjects was more effective in maintaining efflux than HDL of placebo. HDL from ARB- or ACEI-treated subjects but not placebo lessened cellular superoxide production. In contrast, neither ARB nor ACEI improved HDL anti-inflammatory effect. Indeed, HDL of ACEI-treated subjects potentiated the cytokine responses in association with activation of TLR but did not alter the HDL content of methylarginines or SAA.

CONCLUSION

Both ACEI and ARB stabilized HDL cholesterol acceptor function and sustained cellular anti-oxidative effects but not anti-inflammatory effects, and ACEI-treatment instead amplified the HDL inflammatory response. The findings reveal possible utility of antagonizing angiotensin actions in MDH and suggest a possible mechanism for superiority of ARB vs ACEI in the setting of advanced kidney disease.

HDL in CKD-The Devil Is in the Detail

The picture of HDL cholesterol (HDL-C) as the "good" cholesterol has eroded. This is even more surprising because there exists strong evidence that HDL-C is associated with cardiovascular disease (CVD) in the general population as well as in patients with impairment of kidney function and/or progression of CKD. However, drugs that dramatically increase HDL-C have mostly failed to decrease CVD events. Furthermore, genetic studies took the same line, as genetic variants that have a pronounced influence on HDL-C concentrations did not show an association with cardiovascular risk. For many, this was not surprising, given that an HDL particle is highly complex and carries >80 proteins and several hundred lipid species. Simply measuring cholesterol might not reflect the variety of biologic effects of heterogeneous HDL particles. Therefore, functional studies and the involvement of HDL components in the reverse cholesterol transport, including the cholesterol efflux capacity, have become a further focus of study during recent years. As also observed for other aspects, CKD populations behave differently compared with non-CKD populations. Although clear disturbances have been observed for the "functionality" of HDL particles in patients with CKD, this did not necessarily translate into clear-cut associations with outcomes.

Dyslipidemia and risk of renal replacement therapy or death in incident pre-dialysis patients

Globally the number of patients on renal replacement therapy (RRT) is rising. Dyslipidemia is a potential modifiable cardiovascular risk factor, but its effect on risk of RRT or death in pre-dialysis patients is unclear. The aim of this study was to assess the association between dyslipidemia and risk of RRT or death among patients with CKD stage 4–5 receiving specialized pre-dialysis care, an often under represented group in clinical trials. Of the 502 incident pre-dialysis patients (>18 y) in the Dutch PREPARE-2 study, lipid levels were available in 284 patients and imputed for the other patients. During follow up 376 (75%) patients started RRT and 47 (9%) patients died. Dyslipidemia was defined as total cholesterol ≥5.00 mmol/L, LDL cholesterol ≥2.50 mmol/L, HDL cholesterol <1.00 mmol/L, HDL/LDL ratio <0.4, or triglycerides (TG) ≥2.25 mmol/L, and was present in 181 patients and absent in 93 patients. After multivariable adjustment Cox regression analyses showed a HR (95% CI) for the combined endpoint for dyslipidemia of 1.12 (0.85–1.47), and for high LDL of 1.20 (0.89–1.61). All other HRs were smaller. In conclusion, we did not find an association between dyslipidemia or the separate lipid levels and RRT or death in CKD patients on specialized pre-dialysis care.

Increments in serum high-density lipoprotein cholesterol over time are not associated with improved outcomes in incident hemodialysis patients

BACKGROUND

Elevated serum high-density lipoprotein cholesterol (HDL-C) has not been associated with better cardiovascular (CV) and all-cause mortality in hemodialysis patients. However, the association between change in HDL over time and mortality has not been fully examined.

OBJECTIVE

In a nationally representative cohort of incident hemodialysis patients who had available HDL data at baseline and 6 months after dialysis initiation, we studied the association of change in HDL-C during the first 6 months of dialysis with all-cause and CV mortality.

METHODS

Associations between HDL-C change and mortality were determined in Cox proportional hazard regression models with adjustment for multiple variables.

RESULTS

In case-mix models, there was a J-shaped association between change in HDL-C and mortality, such that quartiles 1 (<-5 mg/dL) and 4 (≥7 mg/dL) were each associated with higher all-cause (hazard ratio, 1.32 [95% confidence interval, 1.21-1.45] and 1.09 [1.01-1.18]) and CV (1.28 [1.06-1.55] and 1.23 [1.04-1.45]) death risk, respectively. In fully adjusted models that included indices of malnutrition and inflammation, the higher death risk observed in the lowest quartile was attenuated, whereas the highest quartile continued to demonstrate significantly higher all-cause (1.11 [1.02-1.20]) and CV mortality (1.15 [1.00-1.32]). These associations persisted across various subgroups.

CONCLUSIONS

Although malnutrition and inflammation may explain the increased risk for mortality in patients with decreasing serum HDL-C concentrations over time, these indices do not mitigate the elevated risk in patients with rising serum HDL-C. We found that increasing serum HDL-C over time is paradoxically associated with worse outcomes in incident hemodialysis 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.

Chronic Kidney Disease and Disproportionally Increased Cardiovascular Damage: Does Oxidative Stress Explain the Burden?

Chronic kidney disease (CKD) patients are among the groups at the highest risk for cardiovascular disease and significantly shortened remaining lifespan. CKD enhances oxidative stress in the organism with ensuing cardiovascular damage. Oxidative stress in uremia is the consequence of higher reactive oxygen species (ROS) production, whereas attenuated clearance of pro-oxidant substances and impaired antioxidant defenses play a complementary role. The pathophysiological mechanism underlying the increased ROS production in CKD is at least partly mediated by upregulation of the intrarenal angiotensin system. Enhanced oxidative stress in the setting of the uremic milieu promotes enzymatic modification of circulating lipids and lipoproteins, protein carbamylation, endothelial dysfunction via disruption of nitric oxide (NO) pathways, and activation of inflammation, thus accelerating atherosclerosis. Left ventricular hypertrophy (LVH) and heart failure are hallmarks of CKD. NADPH oxidase activation, xanthine oxidase, mitochondrial dysfunction, and NO-ROS are the main oxidative pathways leading to LVH and the cardiorenal syndrome. Finally, a subset of antioxidant enzymes, the paraoxonases (PON), deserves special attention due to abundant clinical evidence accumulated regarding reduced serum PON1 activity in CKD as a contributor to the increased burden of cardiovascular disease. Future, meticulously designed studies are needed to assess the effects of antioxidant therapy on patients with CKD.

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.

Kidney function is associated with an altered protein composition of high-density lipoprotein

Patients with chronic kidney disease (CKD) exhibit a myriad of metabolic derangements, including dyslipidemia characterized by low plasma concentrations of high-density lipoprotein (HDL)-associated cholesterol. However, the effects of kidney disease on HDL composition have not been comprehensively determined. Here we used a targeted mass spectrometric approach to quantify 38 proteins contained in the HDL particles within a CKD cohort of 509 participants with a broad range of estimated glomerular filtration rates (eGFRs) (CKD stages I-V, and a mean eGFR of 45.5 mL/min/1.73m²). After adjusting for multiple testing, demographics, comorbidities, medications, and other characteristics, eGFR was significantly associated with differences in four HDL proteins. Compared to participants with an eGFR of 60 mL/min/1.73m² or more, those with an eGFR under 15 mL/min/1.73m² exhibited 1.89-fold higher retinol-binding protein 4 (95% confidence interval 1.34-2.67), 1.52-fold higher apolipoprotein C-III (1.25-1.84), 0.70-fold lower apolipoprotein L1 (0.55-0.92), and 0.64-fold lower vitronectin (0.48-0.85). Although the HDL apolipoprotein L1 was slightly lower among African Americans than among Caucasian individuals, the relationship to eGFR did not differ by race. After adjustment, no HDL-associated proteins associated with albuminuria. Thus, modest changes in the HDL proteome provide preliminary evidence for an association between HDL proteins and declining kidney function, but this needs to be replicated. Future analyses will determine if HDL proteomics is indeed a clinical predictor of declining kidney function or cardiovascular outcomes.

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.

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.

Sports and HDL-Quality Reflected By Serum Amyloid A and Surfactant Protein B

Background: The aim of this prospective study was to investigate the influence of long-term physical activity on HDL quality, reflected by serum amyloid A (SAA) and surfactant protein B (SPB). Methods and results: 109 healthy subjects were recruited, 98 completed the study. Participants perform within the calculated training pulse for 8 months. The performance gain was measured/quantified by bicycle stress tests at the beginning and end of the observation period. SAA and SPB were measured at baseline and after 4 and 8 months by ELISA. In contrary to HDL-quantity, there was no sports-induced change in SAA or SPB observable. However, significant predictors for SPB-levels were smoking status, BMI and weekly alcohol consumption and for SAA weekly alcohol consumption together with sex and hsCRP-levels. Conclusions: Long-term physical activity increases HDL-quantity but has no impact on HDL-quality reflected by SAA and SPB. Smoking is associated with higher SPB-levels and the weekly alcohol intake is associated with both higher SAA and SPB-levels suggesting a damaging effect of smoking and drinking alcohol on the HDL-quality. We assume that HDL-quality is at least as important as HDL-quantity when investigating the role of HDL in (cardiovascular) disease and should receive attention in further studies dealing with HDL.

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.

Proteomic Investigations into Hemodialysis Therapy

The retention of a number of solutes that may cause adverse biochemical/biological effects, called uremic toxins, characterizes uremic syndrome. Uremia therapy is based on renal replacement therapy, hemodialysis being the most commonly used modality. The membrane contained in the hemodialyzer represents the ultimate determinant of the success and quality of hemodialysis therapy. Membrane's performance can be evaluated in terms of removal efficiency for unwanted solutes and excess fluid, and minimization of negative interactions between the membrane material and blood components that define the membrane's bio(in)compatibility. Given the high concentration of plasma proteins and the complexity of structural functional relationships of this class of molecules, the performance of a membrane is highly influenced by its interaction with the plasma protein repertoire. Proteomic investigations have been increasingly applied to describe the protein uremic milieu, to compare the blood purification efficiency of different dialyzer membranes or different extracorporeal techniques, and to evaluate the adsorption of plasma proteins onto hemodialysis membranes. In this article, we aim to highlight investigations in the hemodialysis setting making use of recent developments in proteomic technologies. Examples are presented of why proteomics may be helpful to nephrology and may possibly affect future directions in renal research.

HDL Cholesterol Efflux Predicts Graft Failure in Renal Transplant Recipients

High-density lipoprotein (HDL) particles are involved in the protection against cardiovascular disease by promoting cholesterol efflux, in which accumulated cholesterol is removed from macrophage foam cells. We investigated whether HDL cholesterol efflux capacity is associated with cardiovascular mortality, all-cause mortality, and graft failure in a cohort of renal transplant recipients (n=495, median follow-up 7.0 years). Cholesterol efflux capacity at baseline was quantified using incubation of human macrophage foam cells with apolipoprotein B-depleted plasma. Baseline efflux capacity was not different in deceased patients and survivors (P=0.60 or P=0.50 for cardiovascular or all-cause mortality, respectively), whereas recipients developing graft failure had lower efflux capacity than those with functioning grafts (P<0.001). Kaplan-Meier analysis demonstrated a lower risk for graft failure (P=0.004) but not cardiovascular (P=0.30) or all-cause mortality (P=0.31) with increasing gender-stratified tertiles of efflux capacity. Cox regression analyses adjusted for age and gender showed that efflux capacity was not associated with cardiovascular mortality (hazard ratio [HR], 0.89; 95% confidence interval [95% CI], 0.67 to 1.19; P=0.43). Furthermore, the association between efflux capacity and all-cause mortality (HR, .79; 95% CI, 0.63 to 0.98; P=0.031) disappeared after further adjustment for potential confounders. However, efflux capacity at baseline significantly predicted graft failure (HR, 0.43; 95% CI, 0.29 to 0.64; P<0.001) independent of apolipoprotein A-I, HDL cholesterol, or creatinine clearance. In conclusion, this prospective study shows that cholesterol efflux capacity from macrophage foam cells is not associated with cardiovascular or all-cause mortality but is a strong predictor of graft failure independent of plasma HDL cholesterol levels in renal transplant recipients.

Serum amyloid A: high-density lipoproteins interaction and cardiovascular risk

AIMS

High-density lipoproteins (HDLs) are considered as anti-atherogenic. Recent experimental findings suggest that their biological properties can be modified in certain clinical conditions by accumulation of serum amyloid A (SAA). The effect of SAA on the association between HDL-cholesterol (HDL-C) and cardiovascular outcome remains unknown.

METHODS AND RESULTS

We examined the association of SAA and HDL-C with mortality in the Ludwigshafen Risk and Cardiovascular Health (LURIC) study, which included 3310 patients undergoing coronary angiography. To validate our findings, we analysed 1255 participants of the German Diabetes and Dialysis study (4D) and 4027 participants of the Cooperative Health Research in the Region of Augsburg (KORA) S4 study. In LURIC, SAA concentrations predicted all-cause and cardiovascular mortality. In patients with low SAA, higher HDL-C was associated with lower all-cause and cardiovascular mortality. In contrast, in patients with high SAA, higher HDL-C was associated with increased all-cause and cardiovascular mortality, indicating that SAA indeed modifies the beneficial properties of HDL. We complemented these clinical observations by in vitro experiments, in which SAA impaired vascular functions of HDL. We further derived a formula for the simple calculation of the amount of biologically 'effective' HDL-C based on measured HDL-C and SAA from the LURIC study. In 4D and KORA S4 studies, we found that measured HDL-C was not associated with clinical outcomes, whereas calculated 'effective' HDL-C significantly predicted better outcome.

CONCLUSION

The acute-phase protein SAA modifies the biological effects of HDL-C in several clinical conditions. The concomitant measurement of SAA is a simple, useful, and clinically applicable surrogate for the vascular functionality of HDL.

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.