Delayed In Vivo Catabolism of Intermediate-Density Lipoprotein and Low-Density Lipoprotein in Hemodialysis Patients as Potential Cause of Premature Atherosclerosis

Daring to dream: Targeting lipoprotein(a) as a causal and risk-enhancing factor

Lipoprotein(a) [Lp(a)], a distinct lipoprotein class, has become a major focus for cardiovascular research. This review is written in light of the recent guideline and consensus statements on Lp(a) and focuses on 1) the causal association between Lp(a) and cardiovascular outcomes, 2) the potential mechanisms by which elevated Lp(a) contributes to cardiovascular diseases, 3) the metabolic insights on the production and clearance of Lp(a) and 4) the current and future therapeutic approaches to lower Lp(a) concentrations. The concentrations of Lp(a) are under strict genetic control. There exists a continuous relationship between the Lp(a) concentrations and risk for various endpoints of atherosclerotic cardiovascular disease (ASCVD). One in five people in the Caucasian population is considered to have increased Lp(a) concentrations; the prevalence of elevated Lp(a) is even higher in black populations. This makes Lp(a) a cardiovascular risk factor of major public health relevance. Besides the association between Lp(a) and myocardial infarction, the relationship with aortic valve stenosis has become a major focus of research during the last decade. Genetic studies provided strong support for a causal association between Lp(a) and cardiovascular outcomes: carriers of genetic variants associated with lifelong increased Lp(a) concentration are significantly more frequent in patients with ASCVD. This has triggered the development of drugs that can specifically lower Lp(a) concentrations: mRNA-targeting therapies such as anti-sense oligonucleotide (ASO) therapies and short interfering RNA (siRNA) therapies have opened new avenues to lower Lp(a) concentrations more than 95%. Ongoing Phase II and III clinical trials of these compounds are discussed in this review.

The prevalence of dyslipidemia in patients on hemodialysis: a cross-sectional study from Syria

Dyslipidemia is an established risk factor for cardiovascular disease (CVD), which is the main cause of mortality among haemodialysis (HD) patients. We investigate the prevalence and characteristics of dyslipidemia in HD patients. Also, we aimed to study the prediction scores; Framingham risk score (FRS), and the atherosclerotic cardiovascular disease risk score; among this population.

METHODS

One hundred fifty-three HD patients were enroled in this retrospective cross-sectional study from two HD centres in Syria, from March 2021 to March 2022. Dyslipidemia is considered as follows; hyper-total cholesterol (TC) (≥200 mg/dl), hyper-triglycerides (TG), (≥150 mg/dl), hyper-low-density lipoprotein (LDL) (≥100 mg/dl), hypo-high-density lipoprotein (HDL) (<40 mg/dl), hyper-Non-HDL (≥130 mg/dl).

RESULTS

The most prevalent dyslipidemic parameter was low HDL (72.50%) followed by increased TGs (37.30%). TC, LDL, HDL, and Non-HDL showed differences between males and females (P=0.001, 0.015, 0.024, and 0.025; respectively). These parameters were higher in females. History of CVD showed associations with TC, LDL, HDL, and non-HDL (P=0.003, 0.007, 0.004, and 0.004; respectively). Additionally, statins showed effects on TC, LDL, and non-HDL (P=0.003, 0.0002, and 0.002; respectively); however, no relation with TG and HDL (P=0.9 and 0.4). HDL level showed differences in low (7.5%) and intermediate (10%) FRS (P=0.01 and 0.028; respectively); however, it did not show a difference in high (20%) FRS (P=0.68). The lipids profile did not show differences in different thresholds of atherosclerotic cardiovascular disease scores.

CONCLUSION

The prevalence of dyslipidemia was high in HD patients in Syria. All lipid parameters except TG showed differences between males and females. Comparisons of lipid parameters with CVD risk stratifications support the need for further studies to prove the benefits of these scores in CVD prediction among the dialysis population.

Discordance between LDL-C and Apolipoprotein B Levels and Its Association with Renal Dysfunction: Insights from a Population-Based Study

Low-density lipoprotein cholesterol (LDL-C) and apolipoprotein B (ApoB) are established markers of atherosclerotic cardiovascular disease (ASCVD), but when concentrations are discordant ApoB is the superior predictor. Chronic kidney disease (CKD) is associated with ASCVD, yet the independent role of atherogenic lipoproteins is contentious. Four groups were created based upon high and low levels of ApoB and LDL-C. Continuous and categorical variables were compared across groups, as were adjusted markers of CKD. Logistic regression analysis assessed association(s) with CKD based on the groups. Subjects were categorised by LDL-C and ApoB, using cut-off values of >160 mg/dL and >130 mg/dL, respectively. Those with low LDL-C and high ApoB, compared to those with high LDL-C and high ApoB, had significantly higher body mass index (30.7 vs. 30.1 kg/m²) and waist circumference (106.1 vs. 102.7 cm) and the highest fasting blood glucose (117.5 vs. 112.7 mg/dL), insulin (16.6 vs. 13.1 μU/mL) and homeostatic model assessment of insulin resistance (5.3 vs. 3.7) profiles (all p < 0.001). This group, compared to those with high LDL-C and high ApoB, also had the highest levels of urine albumin (2.3 vs. 2.2 mg/L), log albumin-creatinine ratio (2.2 vs. 2.1 mg/g) and serum uric acid (6.1 vs. 5.6 mg/dL) and the lowest estimated glomerular filtration rate (81.3 vs. 88.4 mL/min/1.73 m²) (all p < 0.001). In expanded logistic regression models, using the low LDL-C and low ApoB group as a reference, those with low LDL-C and high ApoB had the strongest association with CKD, odds ratio (95% CI) 1.12 (1.08-1.16). Discordantly high levels of ApoB are independently associated with increased likelihood of CKD. ApoB remains associated with metabolic dysfunction, regardless of LDL-C.

Dyslipidemia in diabetic kidney disease classified by proteinuria and renal dysfunction: A cross-sectional study from a regional diabetes cohort

AIMS/INTRODUCTION

Diabetic kidney disease (DKD) exacerbates dyslipidemia and increases the incidence of atherosclerotic cardiovascular disease. DKD is a concept that includes typical diabetic nephropathy and an atypical phenotype without proteinuria. We investigated dyslipidemia in different DKD phenotypes that have not been fully studied.

MATERIALS AND METHODS

Fasting plasma was obtained from 1,073 diabetes patients enrolled in the regional diabetes cohort (ViNA cohort). Non-proteinuric and proteinuric DKD were defined as an estimated glomerular filtration rate <60 mL/min/1.73 m² in the absence or presence of urinary albumin-to-creatinine ratio >300 mg/g. Novel lipid risk factors, low-density lipoprotein (LDL) triglyceride (TG) and small dense LDL cholesterol were measured using our established homologous assay.

RESULTS

The proportion of atherosclerotic cardiovascular disease patients was higher in non-proteinuric DKD and even higher in proteinuric DKD than in non-DKD. Increased estimated glomerular filtration rate grade and albuminuric stage were independently correlated with higher TG, TG-rich lipoprotein cholesterol and apolipoprotein CIII. Therefore, proteinuric DKD had the highest of these levels. Small dense LDL cholesterol and LDL-TG were higher in the proteinuria without renal dysfunction group in the lipid-lowering drug-free subset. Lipoprotein(a) was higher in DKD regardless of proteinuria.

CONCLUSIONS

Proteinuria was associated with an atherogenic subspecies of LDL, whereas renal dysfunction was associated with increased lipoprotein(a). Proteinuria and renal dysfunction independently exacerbated TG-rich lipoprotein-related dyslipidemia. This is in good agreement with the results of large-scale clinical studies in which proteinuria and renal dysfunction synergistically increased the risk of atherosclerotic cardiovascular disease in populations with diabetes.

Association of Kidney Function With NMR-Quantified Lipids, Lipoproteins, and Metabolic Measures in Mexican Adults

CONTEXT

Chronic kidney disease (CKD) and diabetes are associated with dyslipidemia, metabolic abnormalities, and atherosclerotic risk. Nuclear magnetic resonance (NMR) spectroscopy provides much more detail on lipoproteins than traditional assays.

METHODS

In about 38 000 participants from the Mexico City Prospective Study, aged 35 to 84 years and not using lipid-lowering medication, NMR spectroscopy quantified plasma concentrations of lipoprotein particles, their lipidic compositions, and other metabolic measures. Linear regression related low estimated glomerular filtration rate (eGFR; <60 mL/min/1.73 m2) to each NMR measure after adjustment for confounders and for multiplicity. Analyses were done separately for those with and without diabetes.

RESULTS

Among the 38 081 participants (mean age 52 years, 64% women), low eGFR was present for 4.8% (306/6403) of those with diabetes and 1.2% (365/31 678) of those without diabetes. Among both those with and without diabetes, low eGFR was significantly associated with higher levels of 58 NMR measures, including apolipoprotein B (Apo-B), the particle numbers of most Apo-B containing lipoproteins, the cholesterol and triglycerides carried in these lipoproteins, several fatty acids, total cholines and phosphatidylcholine, citrate, glutamine, phenylalanine, β-OH-butyrate, and the inflammatory measure glycoprotein-A, and significantly lower levels of 13 NMR measures, including medium and small high-density lipoprotein particle measures, very low-density lipoprotein particle size, the ratio of saturated:total fatty acids, valine, tyrosine, and aceto-acetate.

CONCLUSIONS

In this Mexican population with high levels of adiposity and diabetes, low kidney function was associated with widespread alterations in lipidic and metabolic profiles, both in those with and without diabetes. These alterations may help explain the higher atherosclerotic risk experienced by people with CKD.

Lipoproteins and fatty acids in chronic kidney disease: molecular and metabolic alterations

Chronic kidney disease (CKD) induces modifications in lipid and lipoprotein metabolism and homeostasis. These modifications can promote, modulate and/or accelerate CKD and secondary cardiovascular disease (CVD). Lipid and lipoprotein abnormalities - involving triglyceride-rich lipoproteins, LDL and/or HDL - not only involve changes in concentration but also changes in molecular structure, including protein composition, incorporation of small molecules and post-translational modifications. These alterations modify the function of lipoproteins and can trigger pro-inflammatory and pro-atherogenic processes, as well as oxidative stress. Serum fatty acid levels are also often altered in patients with CKD and lead to changes in fatty acid metabolism - a key process in intracellular energy production - that induce mitochondrial dysfunction and cellular damage. These fatty acid changes might not only have a negative impact on the heart, but also contribute to the progression of kidney damage. The presence of these lipoprotein alterations within a biological environment characterized by increased inflammation and oxidative stress, as well as the competing risk of non-atherosclerotic cardiovascular death as kidney function declines, has important therapeutic implications. Additional research is needed to clarify the pathophysiological link between lipid and lipoprotein modifications, and kidney dysfunction, as well as the genesis and/or progression of CVD in patients with kidney disease.

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.

Association of Early Renal Dysfunction with Lipid Profile Parameters among Hypertensives in Kazakhstan

Dyslipidemia plays an essential role in chronic kidney disease (CKD). The role of lipids and lipoproteins in the early pre-disease state of CKD in hypertensive patients is still unclear. The study aimed to evaluate the relationship between early renal dysfunction and lipid profile parameters among hypertensive patients in Kazakhstan. From April 2015 to December 2016, 800 Kazakh males and females with primary hypertension who met the inclusion criteria were included in this cross-sectional study. Data were collected on socio-demographics, lifestyle parameters, family history of cardiovascular disease, and hypertension. Additionally, Dietary Quality Score (DQS), anthropometric data, and blood pressure were recorded. Laboratory blood measurements included eGFR (estimated glomerular filtration rate), lipid profile parameters such as Apolipoprotein B, A1, HDL-C, LDL-C, and TG. We found a linear relationship between early renal dysfunction and LDL-C, Apolipoprotein B, and Apolipoprotein B/A1 ratio, which was in all cases negative and small (r = -0.27, -0.23 and -0.16, respectively). Apolipoprotein A1, HDL-C and TG have not revealed a linear relationship with GFR (r = -0.06, r = -0.06, and ρ = -0.045, respectively). The multicollinearity test restricted the linear model to Apolipoprotein B only. Further linear regression analysis confirmed an inverse significant linear association between eGFR and Apolipoprotein B. Age, DQS, and income appear to be positive confounding factors, significantly fitted the final model. ROC analysis had proven the predictive power of Apolipoprotein B in pre-CKD eGFR decline before and after adjustment for age, DQS and income (AUC = 0.62 and AUC = 0.77, respectively). For differentiating non-diabetic subjects with and without pre-CKD eGFR decrease, 1.05 g/L and 0.98 g/L are likely to be optimal cutoff points in males and females, respectively. These findings will help early prediction of renal dysfunction and contribute to a more accurate estimation of CVD risk.

Lipoprotein Abnormalities in Chronic Kidney Disease and Renal Transplantation

Chronic kidney disease (CKD) is one of the most important risk factors for cardiovascular disease (CVD). Despite the kidney having no direct implications for lipoproteins metabolism, advanced CKD dyslipidemia is usually present in patients with CKD, and the frequent lipid and lipoprotein alterations occurring in these patients play a role of primary importance in the development of CVD. Although hypertriglyceridemia is the main disorder, a number of lipoprotein abnormalities occur in these patients. Different enzymes pathways and proteins involved in lipoprotein metabolism are impaired in CKD. In addition, treatment of uremia may modify the expression of lipoprotein pattern as well as determine acute changes. In renal transplantation recipients, the main lipid alteration is hypercholesterolemia, while hypertriglyceridemia is less pronounced. In this review we have analyzed lipid and lipoprotein disturbances in CKD and also their relationship with progression of renal disease. Hypolipidemic treatments may also change the natural history of CVD in CKD patients and may represent important strategies in the management of CKD patients.

Relationship between serum lipid concentrations and impaired renal function in patients with chronic kidney disease: the Fukuoka Kidney Disease Registry Study

BACKGROUND

Patients with chronic kidney disease (CKD) have a higher risk of atherosclerotic cardiovascular disease (ASCVD). Dyslipidemia has been established as a risk factor for ASCVD. In the present study, we aimed to determine the prevalence of dyslipidemia at each stage of CKD.

METHODS

We conducted a cross-sectional study among 4476 patients registered in the Fukuoka Kidney Disease Registry Study, a Japanese prospective cohort study in patients with non-dialysis-dependent CKD. Outcomes were the prevalence of hyper-low-density lipoprotein (LDL) cholesterolemia, hyper-non-high-density lipoprotein (non-HDL) cholesterolemia, hypertriglyceridemia, and hypo-high-density lipoprotein (hypo-HDL) cholesterolemia at each stage of CKD. We analyzed the relationships between CKD stage and the prevalence of dyslipidemia using logistic regression models.

RESULTS

Patients in the advanced stages of CKD were more likely to have hypertriglyceridemia [OR 2.16 (95% CI 1.03-4.56), OR 2.24 (95% CI 1.04-4.84), OR 2.62 (95% CI 1.19-5.78), and OR 2.47 (95% CI 1.04-5.88) for CKD stages G3a, G3b, G4, and G5, respectively] and hypo-HDL-cholesterolemia [OR 2.66 (95% CI 1.21-5.82), OR 3.10 (95% CI 1.38-6.95), OR 2.86 (95% CI 1.25-6.53), and OR 3.30 (95% CI 1.35-8.10) for CKD stages G3a, G3b, G4, and G5, respectively] as compared with patients in CKD stage G1. The prevalence of hyper-LDL-cholesterolemia and hyper-non-HDL-cholesterolemia was not related to CKD stage.

CONCLUSION

Patients with advanced CKD stages are more likely to have hypertriglyceridemia and hypo-HDL-cholesterolemia than those in early stages. This type of lipid profile may represent a risk factor for ASCVD in patients with CKD.

Homocysteine level is positively and independently associated with serum creatinine and urea nitrogen levels in old male patients with hypertension

A cross-sectional study to show whether and how serum fasting homocysteine levels are associated with renal function changes in patients with hypertension. Homocysteine levels were associated with serum creatinine and blood urea nitrogen (BUN) levels with coefficients of 2.04 and 0.07, respectively, only in males and independent of confounders. In addition, low density lipoprotein cholesterol (LDL-C) levels were positively and left ventricular ejection fraction (LVEF) was negatively associated with serum creatinine level in males; age was positively associated with serum creatinine levels in females. Age was a common risk factor positively associated with BUN levels in both sexes, while total cholesterol (TC) levels and glycemic control were independent risk factors that were positively associated with BUN levels only in males. LDL-C levels and LVEF were negatively associated with BUN levels in females. Body mass index (BMI) was positively associated and hemoglobin A1c (HbA1c) levels, high density lipoprotein cholesterol (HDL-C) levels and the presence of stroke were negatively associated with serum uric acid levels in male patients. In contrast, only LVEF was positively associated with uric acid levels in females. In conclusion, homocysteine level is an independent risk factor associated with serum creatinine and BUN levels in male patients with hypertension.

Chronic Kidney Disease as Oxidative Stress- and Inflammatory-Mediated Cardiovascular Disease

Generating reactive oxygen species (ROS) is necessary for both physiology and pathology. An imbalance between endogenous oxidants and antioxidants causes oxidative stress, contributing to vascular dysfunction. The ROS-induced activation of transcription factors and proinflammatory genes increases inflammation. This phenomenon is of crucial importance in patients with chronic kidney disease (CKD), because atherosclerosis is one of the critical factors of their cardiovascular disease (CVD) and increased mortality. The effect of ROS disrupts the excretory function of each section of the nephron. It prevents the maintenance of intra-systemic homeostasis and leads to the accumulation of metabolic products. Renal regulatory mechanisms, such as tubular glomerular feedback, myogenic reflex in the supplying arteriole, and the renin-angiotensin-aldosterone system, are also affected. It makes it impossible for the kidney to compensate for water-electrolyte and acid-base disturbances, which progress further in the mechanism of positive feedback, leading to a further intensification of oxidative stress. As a result, the progression of CKD is observed, with a spectrum of complications such as malnutrition, calcium phosphate abnormalities, atherosclerosis, and anemia. This review aimed to show the role of oxidative stress and inflammation in renal impairment, with a particular emphasis on its influence on the most common disturbances that accompany CKD.

ApoB and apoM - New aspects of lipoprotein biology in uremia-induced atherosclerosis

Chronic kidney disease affects as much as 13% of the population, and is associated with a markedly increased risk of developing cardiovascular disease. One of the underlying reasons is accelerated development of atherosclerosis. This can be ascribed both to increased occurrence of traditional cardiovascular risk factors, and to risk factors that may be unique to patients with chronic kidney disease. The latter is reflected in the observation that the current treatment modalities, mainly directed against traditional risk factors, are insufficient to prevent cardiovascular disease in the patient with chronic kidney disease. This review discusses mechanisms accelerating uremic atherosclerosis with a specific focus on the putative roles of apolipoprotein(apo)s B and M that may be particularly important in patients with chronic kidney disease.

Dyslipidemia in patients with chronic kidney disease

Chronic kidney disease (CKD) is associated with high risk for cardiovascular disease (CVD). This association is multifactorial, but CKD is often associated with dyslipidemia, which likely contributes. Patients with CKD have dyslipidemia even at early stages of renal dysfunction and dyslipidemia tends to progress with deterioration of kidney function. The dyslipidemia in CKD is largely due to increased triglyceride levels, decreased HDL-C and varying levels of LDL-C. Current management of CKD may also affect lipid levels. Robust clinical trials demonstrate that statins are safe and efficacious in both lipid lowering and prevention of CVD events in pre-end stage CKD and post-transplant. However, there is no evidence of improved CVD outcomes with statin use in dialysis patients. This review will focus on mechanisms underlying dyslipidemia in CKD and clinical trial evidence for lipid lowering therapy in patients with CKD.

Correlation between Serum Lipid Levels and Measured Glomerular Filtration Rate in Chinese Patients with Chronic Kidney Disease

Introduction

Dyslipidemia is often detected in patients with chronic kidney disease (CKD). Previous studies of the relationship between lipid profiles and kidney function have yielded variable results. We aimed to investigate the correlation between serum lipid levels and kidney function evaluated by measured glomerular filtration rate (mGFR) in Chinese patients with CKD.

Methods

A cross-sectional study was conducted on 2036 Chinese CKD patients who had mGFR. Linear regression analysis was performed to evaluate the correlation between different serum lipid levels and mGFR, while logistic regression analysis was used to investigate the association between CKD stages and the risk of different types of dyslipidemia.

Results

The mean age was 55 years and the mean mGFR was 63 mL/min/1.73m². After adjusting for some confounders (age, gender, body mass index, a history of diabetes, fasting glucose, a history of hypertension, systolic blood pressure, diastolic blood pressure, smoking status, hemoglobin, serum potassium, serum albumin, and serum uric acid), serum triglyceride level showed a negative correlation with mGFR (β = -0.006, P = 0.006) in linear regression analysis, and CKD stages were positively related to the risk of hypertriglyceridemia (odds ratios were 1.329, 1.868, 2.514 and P were 0.046, < 0.001, < 0.001 for CKD stage 2, 3, 4/5, respectively) in logistic regression anlysis.

Conclusions

Serum triglyceride level is independently association with mGFR. Patients with reduced kidney function are more likely to have higher serum triglyceride levels. Further longitudinal, multicenter and well-conducted studies are needed to provide more evidence.

New Insight into Atherosclerosis in Hemodialysis Patients: Overexpression of Scavenger Receptor and Macrophage Colony-Stimulating Factor Genes

BACKGROUND

Scavenger receptors (SRs) play a pivotal role in atherogenesis. The mechanism of atherosclerosis, which is specific to hemodialysis (HD) patients, was studied on the basis of SR gene expressions.

METHODS

The gene expressions of SR type A (SR-A) and CD36 were studied in peripheral monocytes by real-time reverse transcription polymerase chain reaction. Data were compared between HD (n = 30) and age-matched control subjects (n = 10). Serum levels of macrophage colony-stimulating factor (M-CSF) were measured with enzyme-linked immunosorbent assay to test its role in SR expression. The statistical differences and associations between two continuous variables were assessed using the Mann-Whitney U test and Pearson's correlation coefficient, respectively.

RESULTS

The relative quantities of SR mRNAs were significantly greater in HD patients than in controls [median (interquartile range): SR-A, 1.67 (0.96-2.76) vs. 0.90 (0.60-1.04), p = 0.0060; CD36, 1.09 (0.88-1.74) vs. 0.74 (0.64-0.99), p = 0.0255]. The serum concentration of M-CSF was significantly higher in HD patients than in controls [1, 121 (999-1,342) vs. 176 (155-202) pg/ml, p < 0.0001]. In addition, the relative quantity of M-CSF mRNA was significantly greater in HD patients than in controls [0.79 (0.42-1.53) vs. 0.42 (0.28-0.66), p = 0.0392]. The serum M-CSF levels were positively correlated with both the relative quantity of SR-A mRNA (r² = 0.1681, p = 0.0086) and that of CD36 mRNA (r² = 0.1202, p = 0.0284) in all subjects (n = 40).

CONCLUSION

HD patients are predisposed to atherosclerosis as a consequence of their enhanced monocyte SR expressions. SRs and M-CSF are potential therapeutic targets for atherosclerosis in this high-risk population.

The serum lipids levels may be underestimated in patients on hemodialysis

OBJECTIVE

Although lipid disorders are a well-known risk factor for cardiovascular disease (CVD) in the general population, the optimal management with lipid-lowering therapy to reduce CVD risks and mortality in hemodialysis (HD) patients remains controversial. In the clinical setting, dyslipidemia can be diagnosed based on the detection of elevated lipid concentrations at the beginning of HD. This study investigated changes in the levels of serum lipids during a single HD session.

METHODS

The serum total cholesterol, triglyceride and high-density lipoprotein (HDL) cholesterol levels were measured in 31 HD patients at zero, two and four hours after the beginning of a single HD session. The data were analyzed using the Wilcoxon signed-rank test, a linear mixed model and Spearman's rank correlation analysis.

RESULTS

The serum total cholesterol, HDL cholesterol and non-HDL cholesterol levels increased significantly during the HD session. Even after the lipid parameters were corrected for changes in the total protein level, the total cholesterol and HDL cholesterol levels increased, whereas the non-HDL cholesterol levels did not change significantly. The percentage change in the serum levels of these lipid fractions correlated strongly with the percentage change in the ultrafiltration volume per body weight. In contrast, the serum triglyceride levels were decreased significantly at two hours compared with the levels noted at the beginning of HD and gradually increased at four hours.

CONCLUSION

The serum lipid levels are influenced significantly by HD treatment and ultrafiltration. Evaluating the degree of dyslipidemia at the beginning of a HD session may therefore underestimate the levels of serum lipids in HD patients with a large amount of weight gain, thus resulting in the use of insufficient lipid-lowering therapy.

Lipoprotein kinetics in male hemodialysis patients treated with atorvastatin

BACKGROUND AND OBJECTIVES

In vivo metabolism of atherogenic apolipoprotein B (apoB)-containing lipoproteins is severely impaired in patients undergoing hemodialysis (HD), resulting in markedly prolonged residence times of these particles. It is unclear whether treatment with statins improves LDL kinetics in HD patients as is known for the general population. Therefore, this kinetic study assessed apoB-containing lipoproteins in these patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Kinetic measures were analyzed with stable-isotope technology in six men undergoing HD before and after 3 months of daily administration of 10 mg of atorvastatin. Patients were 18-65 years of age, had LDL cholesterol levels between 90 and 200 mg/dl, and had been treated with HD for >6 months. They consumed a standardized isocaloric diet for 3 days before analysis. Fractional catabolic rates (FCRs) and production rates of very-low-density lipoprotein (VLDL)-apoB, intermediate-density lipoprotein-apoB, and LDL-apoB were determined using multicompartment modeling after plasma lipoprotein separation, precipitation of apoB, and determination of tracer-to-tracee ratios using mass spectrometry.

RESULTS

Plasma concentrations of VLDL- and LDL-apoB were significantly lower (mean ± SD, 7.77±2.62 versus 11.27±6.15 mg/dl, P<0.05; 56.9±23.9 versus 84.0±21.1 mg/dl, P=0.03) and their FCRs were significantly higher (7.20±3.08 versus 5.20±2.98 days(-1), P<0.05; 0.851±0.772 versus 0.446±0.232 days(-1), P<0.05) after 3 months of atorvastatin treatment. Accordingly, the residence times in plasma of VLDL- and LDL-apoB were significantly lower after treatment (0.14 versus 0.19 day and 1.2 versus 2.2 days, respectively).

CONCLUSION

Lower plasma concentrations and improved kinetics of atherogenic lipoproteins were observed in HD patients after administration of low-dose atorvastatin.

Lipid abnormalities in patients with chronic kidney disease: implications for the pathophysiology of atherosclerosis

Cardiovascular disease is increased in patients with chronic kidney disease (CKD) and is the principle cause of morbidity and mortality in these patients. In patients with stage 5 CKD, structural changes in the myocardium have been implicated as the principle cardiovascular processes leading to this increase in morbidity and mortality, while atherosclerotic events including acute myocardial infarction and strokes are responsible for approximately 10-15% of cardiovascular deaths. Dyslipidemia is common in CKD patients and is usually not characterized by elevated cholesterol levels, except in patients with marked proteinuria. Increased triglyceride levels in conjunction with decreased high-density lipoprotein levels are the commonest qualitative abnormality. Characteristically, abnormalities in the metabolism of apolipoprotein (apo) B-containing lipoproteins have been described, including both gut derived (apoB-48) as well as those produced by hepatic synthesis (apoB-100). A decrease in enzymatic delipidation as well as reduced receptor removal of these lipoproteins both contribute to the increased levels of these apo-B-containing particles and their remnants (which are believed to be highly atherogenic). Abnormalities in the metabolism of apoA-containing lipoproteins are also present and these changes contribute to the lower levels of HDL seen. Qualitative abnormalities of these HDL particles may be associated with cellular oxidative injury and contribute to a pro-inflammatory, pro-thrombotic milieu that is frequently present in CKD patients.

Chronic kidney disease, dyslipidemia, and atherosclerosis

Patients with chronic kidney disease (CKD) are at an increased risk not only for end-stage kidney disease (ESKD) but also for cardiovascular disease (CVD). In this review article, we summarize the current evidence of CKD as a high-risk condition for CVD based on reports from Japan and other countries to draw attention to the close clinical association between CKD and CVD. Several epidemiologic studies have shown that the presence of CKD and reduced renal function are independent predictors of CVD also in Japan. According to a post-hoc analysis of CASE-J, the power of CKD as a predictor of CVD is as strong as diabetes mellitus and a previous history of ischemic heart disease. CKD worsens classical risk factors including hypertension and dyslipidemia, and dyslipidemia is associated with increased thickness and stiffness of large arteries independent of major confounders. A post-hoc analysis of MEGA indicates that lipid-lowering therapy with statins reduces the risk of CVD, and that it appears to be more efficacious in patients with than without CKD. These reports from Japan and other countries suggest that CKD should be regarded as a high-risk condition comparable to diabetes mellitus, and that strict control of dyslipidemia would be beneficial in preventing CVD, at least early stages of CKD.

Evidence-based statin prescription for cardiovascular protection in renal impairment

Dyslipidemia is a well-known risk factor for cardiovascular disease in the general population, and the cardioprotective role of statins is well established. However, although cardiovascular disease is the major cause of morbidity and mortality in chronic kidney disease (CKD), the role of statin therapy is still under investigation. In CKD the atherosclerotic burden is high and pathophysiology of dyslipidemia is complex; however, the majority of large-scale statin trials excluded patients with CKD. Statins could have different effects in the different stages of CKD. Two large trials involving haemodialysis patients showed unfavourable results, whereas in renal transplant subjects as well as in early CKD subjects, statins reduced cardiovascular risk. The studies involving early CKD patients are post-hoc analyses of large trials and they showed that statins are more effective in secondary than in primary prevention. The aim of this study was to evaluate the effectiveness of statins for prevention of cardiovascular events by calculating the number of patients needed to be treated in different interventional trials. We conclude that dyslipidemia is a modifiable cardiovascular risk and statins appear to be an effective treatment especially in the early stages of CKD. Patients on renal replacement therapy could obtain an advantage from this treatment; however, the patient's clinical prognosis should be taken into account when evaluating treatment.

New insights into lipid metabolism in chronic kidney disease

Disorders in lipid levels in kidney disease consist of alterations both in the levels of the differing lipoprotein classes as well as alteration in their structures. Triglycerides (TGs) are increased, and both high density lipoprotein (HDL) and low density lipoprotein (LDL) levels are reduced. HDL fails to mature normally primarily as a consequence of decreased activity of lecithin cholesterol ester transfer protein (LCAT), and HDL levels are reduced because of increase clearance. The HDL that is present consist of small pre-β discoid HDL that fails to function as an antioxidant. All of the apo B containing lipoproteins exhibit decreased clearance in part because of increased levels of the lipoprotein lipase inhibitory apolipoproteins apo C I and apo C III. The concentration of oxidized LD, an athorgenic risk factor, is increased, in part because of the inability of the HDL that is present to reduce oxidized LDL and in part because of the increased LDL residence time effected by decreased clearance.

Network of vascular diseases, death and biochemical characteristics in a set of 4,197 patients with type 1 diabetes (the FinnDiane Study)

Background

Cardiovascular disease is the main cause of premature death in patients with type 1 diabetes. Patients with diabetic kidney disease have an increased risk of heart attack or stroke. Accurate knowledge of the complex inter-dependencies between the risk factors is critical for pinpointing the best targets for research and treatment. Therefore, the aim of this study was to describe the association patterns between clinical and biochemical features of diabetic complications.

Methods

Medical records and serum and urine samples of 4,197 patients with type 1 diabetes were collected from health care centers in Finland. At baseline, the mean diabetes duration was 22 years, 52% were male, 23% had kidney disease (urine albumin excretion over 300 mg/24 h or end-stage renal disease) and 8% had a history of macrovascular events. All-cause mortality was evaluated after an average of 6.5 years of follow-up (25,714 patient years). The dataset comprised 28 clinical and 25 biochemical variables that were regarded as the nodes of a network to assess their mutual relationships.

Results

The networks contained cliques that were densely inter-connected (r > 0.6), including cliques for high-density lipoprotein (HDL) markers, for triglycerides and cholesterol, for urinary excretion and for indices of body mass. The links between the cliques showed biologically relevant interactions: an inverse relationship between HDL cholesterol and the triglyceride clique (r < -0.3, P < 10^-16), a connection between triglycerides and body mass via C-reactive protein (r > 0.3, P < 10^-16) and intermediate-density cholesterol as the connector between lipoprotein metabolism and albuminuria (r > 0.3, P < 10^-16). Aging and macrovascular disease were linked to death via working ability and retinopathy. Diabetic kidney disease, serum creatinine and potassium, retinopathy and blood pressure were inter-connected. Blood pressure correlations indicated accelerated vascular aging in individuals with kidney disease (P < 0.001).

Conclusion

The complex pattern of links between diverse characteristics and the lack of a single dominant factor suggests a need for multifactorial and multidisciplinary paradigms for the research, treatment and prevention of diabetic complications.

Dyslipidemia of kidney disease

PURPOSE OF REVIEW

Chronic kidney disease is associated with specific alterations of lipoprotein metabolism that may be linked to accelerated atherosclerosis and cardiovascular disease. This review summarizes current knowledge of the pathophysiology of renal dyslipidemia and the therapeutic options.

RECENT FINDINGS

The renal dyslipidemia is characterized by accumulation of intact and partially metabolized triglyceride-rich apoB-containing and apoC-containing lipoproteins. Increased concentrations of atherogenic apoC-III rich lipoproteins, the hallmark of renal dyslipidemia, may result from disturbances of insulin metabolism and action in chronic kidney disease. Novel findings strongly suggest that apoC-III triggers a cascade of pro-inflammatory events, which ultimately can result in endothelial dysfunction and vascular damage. Disappointingly, recently reported intervention trials with statins have failed to show any benefit on cardiovascular disease in patients with advanced renal failure.

SUMMARY

During recent years, our understanding of the character and biological significance of the dyslipidemia of chronic kidney disease, and its link to cardiovascular disease, has increased. However, our knowledge about its proper management is still very limited.

Relationship between adiposity and cardiovascular risk factors in prevalent hemodialysis patients

OBJECTIVE

Increased body mass index (BMI) is associated with reduced all-cause and cardiovascular (CV) mortality in hemodialysis (HD) patients, whereas CV risk increases with BMI in the general population. In the general population, obesity is associated with inflammation, decreased high-density lipoprotein (HDL) cholesterol, increased low-density lipoprotein (LDL) cholesterol, and triglycerides (TGs), all risk factors for CV disease. Low-density lipoprotein cholesterol does not predict CV risk in HD, whereas increased C-reactive protein and interleukin-6 (IL-6), low HDL and apolipoprotein (apo) AI, and increased fasting TGs do predict risk. Renal failure is associated with dyslipidemia and inflammation in normal-weight patients. We hypothesized that the effects of obesity may be obscured by renal failure in HD.

METHODS

We explored the relationship between adipose tissue pools and distribution, i.e., subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) (measured by magnetic resonance imaging) and measures of inflammation (C-reactive protein, IL-6, ceruloplasmin, and alpha1 acid glycoprotein), HDL and LDL cholesterol, total TGs, apo AI, apo B, apo CII (an activator of lipoprotein lipase), apo CIII (an inhibitor of lipoprotein lipase), and the adipokines, leptin and adiponectin, in 48 patients with prevalent HD.

RESULTS AND CONCLUSIONS

Total TG concentrations were positively correlated with VAT controlled for age, sex, and weight. Both apo CII and apo CIII were correlated only with VAT. Adiponectin was inversely correlated with VAT, and leptin was positively associated with SAT. C-reactive protein and alpha1 acid glycoprotein were weakly associated with SAT, whereas ceruloplasmin was strongly associated with VAT according to multiple regression analysis. In contrast, apo B, LDL, apo AI, HDL, and IL-6 were not correlated with any measure of body composition, potentially mitigating the effects of obesity in HD.

Apolipoprotein E genotype predicts cardiovascular endpoints in dialysis patients with type 2 diabetes mellitus

OBJECTIVE

Cardiovascular disease (CVD) is the leading cause of death in patients with type 2 diabetes (T2DM) and end-stage renal disease (ESRD). Lipid metabolism is influenced by environmental and genetic factors. Among the latter, the apolipoprotein E (apoE) genotype is known to be associated with CVD risk and thus may affect cardiovascular outcome.

METHODS AND RESULTS

Based on the German Diabetes and Dialysis Study evaluating 1255 T2DM patients on haemodialysis (HD) (median follow-up 4 years), the impact of the apoE genotype (available for 1177 patients) on pre-specified, centrally adjudicated endpoints was investigated: all-cause mortality (n=558), combined cardiovascular events (CVE: cardiac death, MI, stroke; n=442), and cardiac death (n=218). Patients with at least one epsilon4 allele (epsilon4+) showed a 30% increased risk for CVE (HR 1.299, 95%CI 1.045-1.615, p=0.018) and a 36% increased risk for cardiac death (HR 1.362, 95%CI 1.002-1.852, p=0.048) compared to patients with no epsilon4 allele. Consistently, addition of epsilon4+ to a multivariate ROC model for risk prediction of CVE including atorvastatin treatment, history of cardiovascular disease, dialysis and lipoprotein parameters, hsCRP, and NT-pro-BNP increased the area under the curve from 0.666 (95%CI 0.634-0.698) to 0.671 (95%CI 0.639-0.702), p=0.013.

CONCLUSIONS

The presence of the epsilon4 allele increases the risk for CVE and cardiac death in patients with T2DM and ESRD. Whether treatment strategies guided by apoE genotype will improve outcome needs to be evaluated in the future.

Chronic kidney disease delays VLDL-apoB-100 particle catabolism: potential role of apolipoprotein C-III

To determine the relative contribution of obesity and/or insulin resistance (IR) in the development of dyslipidemia in chronic kidney disease (CKD), we investigated the transport of apolipoprotein (apo) B-100 in nonobese, nondiabetic, nonnephrotic CKD subjects and healthy controls (HC). We determined total VLDL, VLDL(1), VLDL(2), intermediate density lipoprotein (IDL), and LDL-apoB-100 using intravenous D3-leucine, GC-MS, and multicompartmental modeling. Plasma apoC-III and apoB-48 were immunoassayed. In this case control study, we report higher plasma triglyceride, IDL-, VLDL-, VLDL(1)-, and VLDL(2)-apoB-100 concentrations in CKD compared with HC (P < 0.05). This was associated with decreased fractional catabolic rates [FCRs (pools/day)] [IDL:CKD 3.4 (1.6) vs. HC 5.0 (3.2), P < 0.0001; VLDL:CKD 4.8 (5.2) vs. HC 7.8 (4.8), P = 0.038; VLDL(1):CKD 10.1 (8.5) vs. HC 29.5 (45.1), P = 0.007; VLDL(2):CKD 5.4 (4.6) vs. HC 10.4 (3.4), P = 0.001] with no difference in production rates. Plasma apoC-III and apoB-48 were significantly higher in CKD (P < 0.001) and both correlated with impaired FCRs of VLDL, VLDL(1), and VLDL(2) apoB-100 (P < 0.05). In CKD, apoC-III concentration was the only independent predictor of clearance defects in VLDL and its subfractions. Moderate CKD in the absence of central adiposity and IR is associated with mild hypertriglyceridemia due to delayed catabolism of triglyceride rich lipoproteins, IDL, and VLDL, without changes in production rate. Altered apoC-III metabolism may contribute to dyslipidemia in CKD, and this requires further investigation.

Lipid and lipoprotein metabolism in chronic kidney disease

The risk of cardiovascular events and mortality increases as renal function declines although the relative risk of mortality contributed by the standard Framingham risk factors are altered or replaced. Low-density lipoprotein (LDL) cholesterol does not predict mortality but low high-density lipoprotein (HDL) cholesterol and triglycerides remain risk factors. The lipoproteins within each class are shifted to smaller, more dense isoforms. The accumulation of apolipoprotein B-containing lipoproteins, including lipoprotein(a) results primarily from decreased clearance rather than from increased synthesis. Lipoprotein(a) levels are also associated with cardiovascular outcome among dialysis patients. Decreased clearance of very low-density lipoprotein and intermediate-density lipoprotein is a result of decreased lipoprotein lipase, structural alterations in the lipoproteins rendering them poorer substrates, and a decrease in receptor number for these proteins. HDL levels are decreased as a result of an increased fractional catabolic rate both among obese patients with normal renal function and among dialysis patients, but the mechanisms responsible for increased HDL fractional catabolic rate may differ. In patients with advanced kidney disease, HDL fails to mature normally as a result of decreased lecithin cholesterol ester transfer protein, leaving cholesterol ester-poor, triglyceride-rich HDL(3) and pre-beta HDL. HDL in patients with chronic kidney disease is a less effective antioxidative agent than is HDL from normal subjects because of a decrease in paroxonase activity, allowing the accumulation of oxidized LDL.

Reducing lipids for CV protection in CKD patients-current evidence

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

HMG CoA reductase inhibitors and renoprotection: the weight of the evidence

Dyslipidemia and the contributions of oxidized low-density lipoproteins (ox-LDL) are independent cardiovascular risk factors. There is growing evidence that dyslipidemia contributes not only to cardiovascular disease but also to the progressive decline of renal function in diabetic and non-diabetic kidney disease. Ox-LDL, by generating inflammation and oxidative stress, contributes to a pro-atherogenic mileu and leads to endothelial dysfunction, subsequent glomerular filtration barrier damage, and progressive renal injury. Chronic kidney disease (CKD), in turn, induces deleterious effects on lipid metabolism. Therefore, by inhibiting cholesterol synthesis and reducing ox-LDL, HMG CoA reductase inhibitors (statins) are attractive therapeutic options to preserve renal function. Current evidence demonstrates a reduction in cardiovascular risk and improved renal outcomes especially in patients with mild to moderate impairment of renal function. Evidence supports a beneficial role of statins thought to extend beyond their lipid-lowering effect, referred to as pleiotropic actions. These actions include modulatory effects on inflammation, oxidative stress and thrombosis, derived from their ability to prevent the formation of isoprenoid intermediates involved in cellular signaling, posttranslational modification of proteins and cellular function. This translates to potential reductions in the rate of decline in GFR in CKD and adverse effects of type 2 diabetes mellitus in the kidney. This review examines the role of statins for reno-protection as well as cardiovascular benefit in patients with CKD.

Lipid abnormalities and cardiovascular risk in renal disease

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

Hyperlipidemia in chronic kidney disease

The risk of cardiovascular events and mortality increases as renal function declines. The standard Framingham risk factors contributing to the relative risk of mortality (RRM) are altered or replaced. While obesity predicts loss of renal function, among dialysis patients obesity predicts survival rather than mortality. Among dialysis patients, Low Density Lipoprotein cholesterol (LDL) does not predict mortality; however other risk factors, such as low High Density Lipoprotein cholesterol (HDL) and increased intermediate density lipoproteins (IDL), remain cardiovascular risk factors. While HDL levels are decreased as a result of an increased fractional catabolic rate (FCR) both among obese patients with normal renal function and among dialysis patients, the mechanisms responsible for increased HDL FCR may differ. In patients with advanced kidney disease, HDL fails to mature normally as a result of decreased lecithin cholesterol ester transfer protein (LCAT), leaving cholesterol ester-poor, triglyceride (TG)-rich HDL3 and pre-beta-HDL. Chronic kidney disease (CKD) is associated with insulin resistance, providing another potential mechanistic link to low HDL levels. Increased TG levels are found in an expanded Intermediate Density Lipoprotein (IDL) pool and are associated with mortality risk. Lipoprotein (a) (LP(a)) levels are increased. In patients without renal disease, the concentration of Lp(a) is inversely associated with the size of the apo (a) isoform inherited; Lp (a) levels are increased in patients with kidney disease as consequence of increased concentrations, primarily of the high molecular weight isoform resulting from decreased clearance. Lp (a) levels are also associated with cardiovascular outcome among dialysis patients.

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

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

Decreased peroxisome proliferator-activated receptor alpha gene expression is associated with dyslipidemia in a rat model of chronic renal failure

The transcription factor peroxisome proliferator-activated receptor (PPAR) alpha plays an important role in lipid homeostasis. In this study, we examined whether the down-regulation of PPAR-alpha gene expression is associated with dyslipidemia in a rat model of chronic renal failure (CRF). Rats with laboratory-induced uremia by 5/6 nephrectomy were bled at 2 weeks and 10 weeks after the nephrectomy to produce conditions. For the sake of convenience, the rats observed at postoperative week 2 were defined as acute renal failure (ARF) and those observed at week 10 were defined as CRF. Lipids in lipoprotein fractions were measured by high-performance liquid chromatography. The abundance of PPAR-alpha messenger RNA (mRNA) in the liver was measured by reverse transcriptase-polymerase chain reaction. Serum creatinine and blood urea nitrogen levels rose with the progression of renal failure, but the total protein levels remained constant. Serum triglyceride in ARF rats remained unchanged from the level in sham-operated control rats, whereas that in CRF rats was 66% higher than the control level. Serum cholesterol was elevated 1.5-fold in ARF rats and 2-fold in CRF rats compared with the sham-operated counterparts. As with triglyceride, very low-density lipoprotein remained unchanged in ARF rats but rose substantially in CRF rats. All of the major lipoprotein fractions were elevated in CRF rats. These lipid and lipoprotein changes were significantly associated with creatinine and blood urea nitrogen levels. The PPAR-alpha mRNA expression in the liver was unchanged in ARF rats but was 44% lower in CRF rats. The PPAR-alpha mRNA expression was inversely correlated with serum creatinine and lipids in the overall rats. Our results indicate that PPAR-alpha mRNA expression is down-regulated in the liver of CRF rats and that this down-regulation may play a crucial role in the development of dyslipidemia.

Dialysis removes apolipoprotein C-I, improving very low-density lipoprotein clearance

Chronic kidney disease (CKD) is associated with dyslipidemia, characterized by increased levels of triglyceride-rich lipoproteins (TRLPs), including very low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL), with no change or a reduction in low-density lipoprotein (LDL) and low high-density lipoprotein (HDL) levels. Serum triglycerides and IDL are risk factors for vascular disease in dialysis patients, whereas LDL is not. The principal cause of the increase in TRLPs is decreased removal, not increased synthesis. The clearance defect arises from a reduction in specific lipoprotein receptors, decreases in the activity of lipases, and increased levels of low-molecular weight apolipoproteins that inhibit the interaction between TRLPs and both the receptors and the lipases that catabolize them. VLDL from dialysis patients is structurally abnormal and is not metabolized at a normal rate by lipoprotein lipase (LPL).

In vivo turnover study demonstrates diminished clearance of lipoprotein(a) in hemodialysis patients

Lipoprotein(a) (Lp(a)) consists of a low-density lipoprotein-like particle and a covalently linked highly glycosylated protein, called apolipoprotein(a) (apo(a)). Lp(a) derives from the liver but its catabolism is still poorly understood. Plasma concentrations of this highly atherogenic lipoprotein are elevated in hemodialysis (HD) patients, suggesting the kidney to be involved in Lp(a) catabolism. We therefore compared the in vivo turnover rates of both protein components from Lp(a) (i.e. apo(a) and apoB) determined by stable-isotope technology in seven HD patients with those of nine healthy controls. The fractional catabolic rate (FCR) of Lp(a)-apo(a) was significantly lower in HD patients compared with controls (0.164+/-0.114 vs 0.246+/-0.067 days(-1), P=0.042). The same was true for the FCR of Lp(a)-apoB (0.129+/-0.097 vs 0.299+/-0.142 days(-1), P=0.005). This resulted in a much longer residence time of 8.9 days for Lp(a)-apo(a) and 12.9 days for Lp(a)-apoB in HD patients compared with controls (4.4 and 3.9 days, respectively). The production rates of apo(a) and apoB from Lp(a) did not differ significantly between patients and controls and were even lower for patients when compared with controls with similar Lp(a) plasma concentrations. This in vivo turnover study is a further crucial step in understanding the mechanism of Lp(a) catabolism: the loss of renal function in HD patients causes elevated Lp(a) plasma levels because of decreased clearance but not increased production of Lp(a). The prolonged retention time of Lp(a) in HD patients might importantly contribute to the high risk of atherosclerosis in these patients.