Hemodialysis reduces plasma apolipoprotein C-I concentration making VLDL a better substrate for lipoprotein lipase

Closing the gaps in patient management of dyslipidemia: stepping into cardiovascular precision diagnostics with apolipoprotein profiling

In persons with dyslipidemia, a high residual risk of cardiovascular disease remains despite lipid lowering therapy. Current cardiovascular risk prediction mainly focuses on low-density lipoprotein cholesterol (LDL-c) levels, neglecting other contributing risk factors. Moreover, the efficacy of LDL-c lowering by statins resulting in reduced cardiovascular risk is only partially effective. Secondly, from a metrological viewpoint LDL-c falls short as a reliable measurand. Both direct and calculated LDL-c tests produce inaccurate test results at the low end under aggressive lipid lowering therapy. As LDL-c tests underperform both clinically and metrologically, there is an urging need for molecularly defined biomarkers. Over the years, apolipoproteins have emerged as promising biomarkers in the context of cardiovascular disease as they are the functional workhorses in lipid metabolism. Among these, apolipoprotein B (ApoB), present on all atherogenic lipoprotein particles, has demonstrated to clinically outperform LDL-c. Other apolipoproteins, such as Apo(a) - the characteristic apolipoprotein of the emerging risk factor lipoprotein(a) -, and ApoC-III - an inhibitor of triglyceride-rich lipoprotein clearance -, have attracted attention as well. To support personalized medicine, we need to move to molecularly defined risk markers, like the apolipoproteins. Molecularly defined diagnosis and molecularly targeted therapy require molecularly measured biomarkers. This review provides a summary of the scientific validity and (patho)physiological role of nine serum apolipoproteins, Apo(a), ApoB, ApoC-I, ApoC-II, ApoC-III, ApoE and its phenotypes, ApoA-I, ApoA-II, and ApoA-IV, in lipid metabolism, their association with cardiovascular disease, and their potential as cardiovascular risk markers when measured in a multiplex apolipoprotein panel.

Role of apolipoprotein C1 in lipoprotein metabolism, atherosclerosis and diabetes: a systematic review

Apolipoprotein C1 (apoC1) is a small size apolipoprotein whose exact role is not totally clarified but which seems to modulate significantly the metabolism of lipoproteins. ApoC1 is involved in the metabolism of triglyceride-rich lipoproteins by inhibiting the binding of very low density lipoproteins (VLDL) to VLDL-receptor (VLDL-R), to low density lipoprotein receptor (LDL-R) and to LDL receptor related protein (LRP), by reducing the activity of lipoprotein lipase (LPL) and by stimulating VLDL production, all these effects leading to increase plasma triglycerides. ApoC1 takes also part in the metabolism of high density lipoproteins (HDL) by inhibiting Cholesterol Ester Transfer Protein (CETP). The functionality of apoC1 on CETP activity is impaired in diabetes that might account, at least in part, for the increased plasma CETP activity observed in patients with diabetes. Its different effects on lipoprotein metabolism with a possible role in the modulation of inflammation makes the net impact of apoC1 on cardiometabolic risk difficult to figure out and apoC1 might be considered as pro-atherogenic or anti-atherogenic depending on the overall metabolic context. Making the link between total plasma apoC1 levels and the risk of cardio-metabolic diseases is difficult due to the high exchangeability of this small protein whose biological effects might depend essentially on its association with VLDL or HDL. The role of apoC1 in humans is not entirely elucidated and further studies are needed to determine its precise role in lipid metabolism and its possible pleiotropic effects on inflammation and vascular wall biology. In this review, we will present data on apoC1 structure and distribution among lipoproteins, on the effects of apoC1 on VLDL metabolism and HDL metabolism and we will discuss the possible links between apoC1, atherosclerosis and diabetes.

Feasibility of ApoC1 serum levels as tumor biomarker in glioblastoma patients: a pilot study

Apolipoprotein C1 (ApoC1) has been detected immunohistochemically in glioblastoma tissue, probably expressed by activated monocytes and microglia. The present study was conceived to determine whether the amount of intratumoral ApoC1 expression leads to measurable changes of serum levels after glioblastoma resection or during recurrence. 176 blood samples from 70 glioblastoma patients were collected perioperatively and during subsequent therapy. ApoC1 serum levels were determined using an enzyme linked immunosorbent assay (ELISA). High absorption values due to lipemic or hemolytic serum were removed from the final dataset using a stem and leaf plot. Samples were grouped according to the treatment stage to compare mean ApoC1 serum levels. The number of patients with falling or increasing perioperative values was assessed. 167 ApoC1 serum values from 68 glioblastoma patients were amenable to statistical evaluation. Mean ApoC1 serum level was 91.9 µg/ml (n = 167, sd = 36.0). In samples from patients undergoing first glioblastoma resection, the mean preoperative value was significantly higher (94.8 µg/ml, n = 37, sd = 29.5) than after surgery (77.4 µg/ml, n = 41, sd = 23.2, p = 0.009). Individually, falling ApoC1 levels were detected in 25 and rising levels in 9 patients (p = 0.0061). Single absolute serum levels of ApoC1 do not allow an estimation of glioblastoma activity or tumor response. Although pathophysiologically of interest, ApoC1 serum levels did not qualify as a potential biomarker in glioblastoma management. Our results do not seem to encourage larger, multicenter studies.

The Roles of Fatty Acids and Apolipoproteins in the Kidneys

The kidneys are organs that require energy from the metabolism of fatty acids and glucose; several studies have shown that the kidneys are metabolically active tissues with an estimated energy requirement similar to that of the heart. The kidneys may regulate the normal and pathological function of circulating lipids in the body, and their glomerular filtration barrier prevents large molecules or large lipoprotein particles from being filtered into pre-urine. Given the permeable nature of the kidneys, renal lipid metabolism plays an important role in affecting the rest of the body and the kidneys. Lipid metabolism in the kidneys is important because of the exchange of free fatty acids and apolipoproteins from the peripheral circulation. Apolipoproteins have important roles in the transport and metabolism of lipids within the glomeruli and renal tubules. Indeed, evidence indicates that apolipoproteins have multiple functions in regulating lipid import, transport, synthesis, storage, oxidation and export, and they are important for normal physiological function. Apolipoproteins are also risk factors for several renal diseases; for example, apolipoprotein L polymorphisms induce kidney diseases. Furthermore, renal apolipoprotein gene expression is substantially regulated under various physiological and disease conditions. This review is aimed at describing recent clinical and basic studies on the major roles and functions of apolipoproteins in the kidneys.

Irbesartan ameliorates chronic mountain sickness in a rat model via the cholesterol metabolism: An iTRAQ -based proteomics analysis

OBJECTIVE

To study the effects of irbesartan on pulmonary artery lesions in a rat model with chronic mountain sickness (CMS) and identify the biomarkers involved.

METHODS

In this study, we used a rat model of CMS to evaluate the therapeutic effect of irbesartan by measuring pulmonary artery pressure and evaluating the histopathology of the pulmonary artery. We also used proteomics technology to identify differentially expressed proteins (DEPs) in the serum and performed bioinformatics analysis. Results were then verified by enzyme linked immunosorbent assay (ELISA) and immunohistochemistry (IHC).

RESULTS

Irbesartan treatment induced a significant decrease (P < 0.05) in the pulmonary artery pressure of CMS rats. Histopathological and electron microscope further confirmed that high altitude hypoxia induced changes in the structure of the pulmonary artery tissue and caused ultrastructural lesions. Proteomics analysis identified 40 DEPs; bioinformatics analysis further revealed that the cholesterol metabolism pathway plays a crucial role in the occurrence of CMS. ELISA and IHC verified that several DEPs (Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1) represent critical biological markers in pulmonary artery disease caused by CMS.

CONCLUSIONS

Irbesartan significantly improved pulmonary artery damage in a rat model of CMS possibly by impacting on the cholesterol metabolism pathway and by reducing damage to vascular endothelial cells. Irbesartan also inhibited the expression levels of IGF-1, Profilin1 and Col1a1 to relieve pulmonary artery pressure and improve lung function by inhibiting vascular remodeling. Several proteins were identified as potential biomarkers of CMS, including Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1.

New Insights on End-Stage Renal Disease and Healthy Individual Gut Bacterial Translocation: Different Carbon Composition of Lipopolysaccharides and Different Impact on Monocyte Inflammatory Response

Chronic kidney disease induces disruption of the intestinal epithelial barrier, leading to gut bacterial translocation. Here, we appreciated bacterial translocation by analyzing circulating lipopolysaccharides (LPS) using two methods, one measuring only active free LPS, and the other quantifying total LPS as well as LPS lipid A carbon chain length. This was done in end-stage renal disease (ESRD) patients and healthy volunteers (HV). We observed both higher LPS concentration in healthy volunteers and significant differences in composition of translocated LPS based on lipid A carbon chain length. Lower LPS activity to mass ratio and higher concentration of high-density lipoproteins were found in HV, suggesting a better plasma capacity to neutralize LPS activity. Higher serum concentrations of soluble CD14 and pro-inflammatory cytokines in ESRD patients confirmed this hypothesis. To further explore whether chronic inflammation in ESRD patients could be more related to LPS composition rather than its quantity, we tested the effect of HV and patient sera on cytokine secretion in monocyte cultures. Sera with predominance of 14-carbon chain lipid A-LPS induced higher secretion of pro-inflammatory cytokines than those with predominance of 18-carbon chain lipid A-LPS. TLR4 or LPS antagonists decreased LPS-induced cytokine production by monocytes, demonstrating an LPS-specific effect. Thereby, septic inflammation observed in ESRD patients may be not related to higher bacterial translocation, but to reduced LPS neutralization capacity and differences in translocated LPS subtypes.

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.

Human apolipoprotein C1 transgenesis reduces atherogenesis in hypercholesterolemic rabbits

BACKGROUND AND AIMS

Apolipoprotein (apo) C1 is a 6.6 kDa protein associated with HDL and VLDL. ApoC1 alters triglyceride clearance, and it also favors cholesterol accumulation in HDL, especially by inhibiting CETP in human plasma. Apart from studies in mice, which lack CETP, the impact of apoC1 on atherosclerosis in animal models expressing CETP, like in humans, is not known. This study aimed at determining the net effect of human apoC1 on atherosclerosis in rabbits, a species with naturally high CETP activity but with endogenous apoC1 without CETP inhibitory potential.

METHODS

Rabbits expressing a human apoC1 transgene (HuApoC1Tg) were generated and displayed significant amounts of human apoC1 in plasma.

RESULTS

After cholesterol feeding, atherosclerosis lesions were significantly less extensive (-22%, p < 0.05) and HDL displayed a reduced ability to serve as CETP substrates (-25%, p < 0.05) in HuApoC1Tg rabbits than in WT littermates. It was associated with rises in plasma HDL cholesterol level and PON-1 activity, and a decrease in the plasma level of the lipid oxidation markers 12(S)-HODE and 8(S)HETE. In chow-fed animals, the level of HDL-cholesterol was also significantly higher in HuApoC1Tg than in WT animals (0.83 ± 0.11 versus 0.73 ± 0.11 mmol/L, respectively, p < 0.05), and it was associated with significantly lower CETP activity (cholesteryl ester transfer rate, -10%, p < 0.05; specific CETP activity, -14%, p < 0.05).

CONCLUSIONS

Constitutive expression of fully functional human apoC1 in transgenic rabbit attenuates atherosclerosis. It was found to relate, at least in part, to the inhibition of plasma CETP activity and to alterations in plasma HDL.

Apolipoprotein C1: Its Pleiotropic Effects in Lipid Metabolism and Beyond

Apolipoprotein C1 (apoC1), the smallest of all apolipoproteins, participates in lipid transport and metabolism. In humans, APOC1 gene is in linkage disequilibrium with APOE gene on chromosome 19, a proximity that spurred its investigation. Apolipoprotein C1 associates with triglyceride-rich lipoproteins and HDL and exchanges between lipoprotein classes. These interactions occur via amphipathic helix motifs, as demonstrated by biophysical studies on the wild-type polypeptide and representative mutants. Apolipoprotein C1 acts on lipoprotein receptors by inhibiting binding mediated by apolipoprotein E, and modulating the activities of several enzymes. Thus, apoC1 downregulates lipoprotein lipase, hepatic lipase, phospholipase A2, cholesterylester transfer protein, and activates lecithin-cholesterol acyl transferase. By controlling the plasma levels of lipids, apoC1 relates directly to cardiovascular physiology, but its activity extends beyond, to inflammation and immunity, sepsis, diabetes, cancer, viral infectivity, and-not last-to cognition. Such correlations were established based on studies using transgenic mice, associated in the recent years with GWAS, transcriptomic and proteomic analyses. The presence of a duplicate gene, pseudogene APOC1P, stimulated evolutionary studies and more recently, the regulatory properties of the corresponding non-coding RNA are steadily emerging. Nonetheless, this prototypical apolipoprotein is still underexplored and deserves further research for understanding its physiology and exploiting its therapeutic potential.

End-Stage Renal Disease-Associated Gut Bacterial Translocation: Evolution and Impact on Chronic Inflammation and Acute Rejection After Renal Transplantation

Chronic inflammation in end-stage renal disease (ESRD) is partly attributed to gut bacterial translocation (GBT) due to loss of intestinal epithelium integrity. Increased levels of circulating lipopolysaccharide (LPS) –a surrogate marker of GBT– contribute to maintain a chronic inflammatory state. However, circulating LPS can be neutralized by lipoproteins and transported to the liver for elimination. While ESRD-associated GBT has been widely described, less is known about its changes and impact on clinical outcome after kidney transplantation (KT). One hundred and forty-six renal transplant recipients with serum samples obtained immediately before and 1 year after transplantation (1-Year post KT) were included. Intestinal epithelium integrity (iFABP), total LPS (by measuring 3-hydroxymyristate), LPS activity (biologically active LPS measured by the LAL assay), inflammatory biomarkers (sCD14 and cytokines), lipoproteins and LPS-binding proteins (LBP and phospholipid transfer protein [PLTP] activity) were simultaneously measured. At 1-Year post KT, iFABP decreased but remained higher than in normal volunteers. Total LPS concentration remained stable while LPS activity decreased. Inflammation biomarkers decreased 1-Year post KT. We concomitantly observed an increase in lipoproteins. Higher sCD14 levels before transplantation was associated with lower incidence of acute rejection. Although GBT remained stable after KT, the contemporary increase in lipoproteins could bind circulating LPS and contribute concomitantly to neutralization of LPS activity, as well as improvement in ESRD-associated chronic inflammation. Chronic exposure to LPS in ESRD could promote endotoxin tolerance and explain why patients with higher pre-transplant sCD14 are less prompt to develop acute rejection after transplantation.

Effect of hemodialysis on extracellular vesicles and circulating submicron particles

BACKGROUND

Although hemodialysis is a highly effective treatment for diffusive clearance of low molecular weight uremic toxins, its effect on circulating extracellular vesicles and submicron particles is less clear. The purpose of this study was to examine the impact of hemodialysis on circulating levels of submicron particles.

METHODS

Plasma samples from patients were collected immediately before and after the mid-week hemodialysis session. Total submicron particles were assessed by nanoparticle tracking analysis and levels of endothelial (CD144+), platelet (CD41+), leukocyte (CD45+), and total (Annexin V+) membrane microparticles (MPs) were assessed by flow cytometry.

RESULTS

Total submicron particle number was significantly lower post-dialysis with reductions in particles < 40 nm, 40-100 nm, and 100-1000 nm in size. Circulating annexin V+ MPs, platelet MPs, leukocyte MPs, and endothelial MPs were all reduced following dialysis. Assessment of protein markers suggested that extracellular vesicles were not present in the dialysate, but rather adsorbed to the dialysis membrane.

CONCLUSIONS

In summary, hemodialysis is associated with reductions in circulating submicron particles including membrane MPs. Accordingly, there may be significant interdialytic variation in circulating submicron particles. Investigators interested in measuring extracellular vesicles in patients undergoing hemodialysis should therefore carefully consider the timing of biosampling.

Investigating apolipoproteins of human high-density lipoprotein by cyclodextrin-micellar electrokinetic chromatography

A cyclodextrin-micellar electrokinetic chromatography (CD-MEKC) method has been developed to determine the apolipoproteins (apos) of human high-density lipoprotein (HDL). The optimal CD-MEKC conditions included a separation buffer mixture of 5 mM sodium phosphate, 40 mM bile salts (50% sodium cholate and 50% sodium deoxycholate), 25 mM carboxymethyl-β-CD (CM-β-CD) and pH 7.0. The separation voltage was 15 kV, and the capillary temperature was 15℃. The CD-MEKC profiles of human HDL apolipoproteins showed good repeatability and sensitivity. Linear analysis has been performed for human apolipoprotein standards including apos AI, AII, CI, CII, CIII and E. Linear regression lines with coefficients of determination (R²) greater than 0.99 were obtained for apos AI, AII, CI, CII and E. The linear ranges for the six apolipoproteins were within 0.18-0.70 mg/mL, and the concentration limits of detection (LOD) were lower than 0.0617 mg/mL. Apos AI, AII, CI and CIII were identified and quantified in human HDL by comparing with apolipoprotein standards. Furthermore, the CD-MEKC profiles of uremic patients differed significantly from healthy subjects. The concentration ratios of apo AI/apo CIII were significantly lower for uremic patients than healthy subjects. This study demonstrated the feasibility of determining human HDL apolipoproteins by CD-MEKC. In the future, it might help monitor the progression of uremia and cardiovascular disease.

Proteomics investigation of the changes in serum proteins after high- and low-flux hemodialysis

PURPOSE

This study aimed to use proteomics methods to investigate the changes in serum protein levels after high- and low-flux hemodialysis (HD).

METHODS

Before and after HD, serum samples were obtained from two selected patients who were treated with a Polyflux 140 H high-flux dialyzer and a Polyflux 14 L low-flux dialyzer during two continuous therapy sessions. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to identify the proteins.

RESULTS

A total of 212 and 203 serum proteins were identified after high-flux and low-flux HD, respectively. After high-flux HD, 21 proteins increased, and 132 proteins decreased. After low-flux HD, 87 proteins increased, and 45 proteins decreased. High-flux HD led to a significantly greater reduction in protein levels than low-flux HD (0.73 ± 0.13 vs. 0.84 ± 0.18, p = .00). Among the increased and decreased proteins, the isoelectric point (pI) values mainly ranged from 5 to 7, and the molecular weights (Mws) were mostly smaller than 30 kDa. The serum proteins showed no difference in pI or Mw for high- and low-flux HD. Gene ontology (GO) analysis showed that the detected proteins were related to immune system processes and complement activation.

CONCLUSIONS

Serum protein levels differentially changed after high- and low-flux HD. Long-term effects should be observed in future studies.

Proteomic Characterization of a New asymmetric Cellulose Triacetate Membrane for Hemodialysis

PURPOSE

The artificial membrane inside the haemodialyzer is the main determinant of the quality and success of haemodialysis therapy. The performances of haemodialysis membranes are highly influenced by the interactions with plasma proteins, which in turn are related to the physical and chemical characteristics of the membrane material. The present cross-over study is aimed to analyse the haemodialysis performance of a newly developed asymmetric cellulose triacetate membrane (ATA) in comparison to the conventional parent symmetric polymer (CTA).

EXPERIMENTAL DESIGN

In four chronic non diabetic haemodialysis patients, the protein constituents of the adsorbed material from the filters after the haemodialysis session, and the proteins recovered in the ultrafiltrate during the session, are identified using a bottom-up shotgun proteomics approach.

RESULTS

The ATA membrane shows a lower protein adsorption rate and a lower mass distribution pattern of the proteinaceous material.

CONCLUSIONS AND CLINICAL RELEVANCE

By highlighting the differences between the two haemodialysis filters in terms of adsorbed proteins and flow through, it is demonstrated the higher biocompatibility of the novel ATA membrane, that fulfils the indications for the development of more performant membranes and may represent a step forward for the treatment of patients on chronic haemodialysis.

Treatment of Hyperlipidemia Changes With Level of Kidney Function-Rationale

Lipoprotein abnormalities such as low levels of high-density lipoprotein (HDL) and high triglycerides (TGs), associated with the metabolic syndrome, are also associated with subsequent decline in kidney function. Patients with end-stage kidney disease also exhibit low HDL and high TGs and a modest reduction in low-density lipoprotein (LDL), although the mechanisms responsible for these changes differ when patients with end-stage kidney disease are compared with those having metabolic syndrome with normal kidney function, as do lipoprotein structures. Among dialysis patients, oxidized LDL, levels of TG-rich intermediate-density lipoprotein, and low HDL are associated with aortic pulsewave velocity and other markers of atherosclerosis. Statins are effective in reducing LDL and do decrease risk of cardiovascular events in patients with CKD not requiring dialysis but have no significant effect on outcomes, including all-cause mortality among dialysis patients. Similarly gemfibrozil and other fibrates lower TGs, increase HDL, and reduce cardiovascular events, but not mortality, among patients with CKD not requiring dialysis but have no significant effect on cardiovascular outcomes in dialysis patients. There is potential clinical benefit in treating elevated LDL, TGs, and low HDL in patients with CKD using statins or fibrates in those not yet requiring dialysis.

Plasma apolipoprotein C1 concentration is associated with plasma triglyceride concentration, but not visceral fat, in patients with type 2 diabetes

INTRODUCTION

Apolipoprotein C1 (apoC1) is likely to play an important role in triglyceride (TG) metabolism. Mice overexpressing human apoC1 present decreased adipose tissue stores. This study aimed to determine whether apoC1 concentration influences fat mass and distribution and liver fat content (LFC) in patients with type 2 diabetes (T2D).

METHODS

ApoC1 concentrations were measured by ELISA in 113 T2D patients and 56 normolipidaemic-normoglycaemic subjects. Visceral and subcutaneous fat areas were determined by single-slice axial T1-weighted magnetic resonance imaging (MRI), while LFC was measured by hydrogen-1 ((1)H) MR spectroscopy.

RESULTS

ApoC1 concentrations were higher in T2D patients than in normolipidaemic-normoglycaemic subjects (P<0.0001), and did not correlate with visceral or subcutaneous fat areas, but significantly correlated with TG (P<0.0001) and LFC (P=0.02) in T2D patients. However, the correlation between apoC1 and LFC was lost after adjusting for TG. ApoC1 concentration was also significantly higher in T2D patients with TG<1.5mmol/L than in control subjects (P<0.0001), although both groups had similar TG levels. On multivariate analysis performed in T2D patients with TG<1.5mmol/L and control subjects, apoC1 concentration was independently and positively associated with type 2 diabetes (P<0.0001) and TG levels (P=0.03).

CONCLUSION

This study reports, for the first time, that apoC1 is increased in T2D patients and is significantly correlated with TG, whereas no association was found between apoC1 and adipose tissue. This indicates that, in T2D, apoC1 may play a role in TG metabolism, but is unlikely to modulate fat mass and distribution. This increased apoC1 concentration in T2D patients is not only explained by the increased TG level in T2D patients.

The potential of cholesteryl ester transfer protein as a therapeutic target

INTRODUCTION

Over recent decades, attempts to ascertain the pro-atherogenic nature of plasma cholesteryl ester transfer protein (CETP) and to establish the relevance of its pharmacological blockade as a promising high density lipoproteins-raising and anti-atherogenic therapy have been disappointing.

AREAS COVERED

The current review focuses on CETP as a multifaceted protein, on genetic variations at the CETP gene and on their possible consequences for cardiovascular risk in human populations. Specific attention is given to physiological modulation of endogenous CETP activity by the apoC1 inhibitor. Finally, the rationale behind the need for selection of patients to treat is discussed in the light of recent studies.

EXPERT OPINION

At this stage one can only speculate on the clinical outcome of pharmacological CETP inhibitors in high-risk populations, but recent advances give cause to adjust the expectations from now on. The CETP effect is probably largely influenced by the overall metabolic state, and whether CETP blockade may be relevant or not in promoting cholesterol disposal is still questioned. The possible need for a careful stratification of patients to treat with CETP inhibitors is outlined. Finally, manipulation of CETP activity should be considered with caution in the context of sepsis and infectious diseases.

Glycation of apolipoprotein C1 impairs its CETP inhibitory property: pathophysiological relevance in patients with type 1 and type 2 diabetes

OBJECTIVE Apolipoprotein (apo)C1 is a potent physiological inhibitor of cholesteryl ester transfer protein (CETP). ApoC1 operates through its ability to modify the electrostatic charge at the lipoprotein surface. We aimed to determine whether the inhibitory ability of apoC1 is still effective in vivo in patients with diabetes and whether in vitro glycation of apoC1 influences its electrostatic charge and its CETP inhibitory effect. RESEARCH DESIGN AND METHODS ApoC1 concentrations and CETP activity were measured in 70 type 1 diabetic (T1D) patients, 113 patients with type 2 diabetes, and 83 control subjects. The consequences of in vitro glycation by methylglyoxal on the electrostatic properties of apoC1 and on its inhibitory effect on CETP activity were studied. An isoelectric analysis of apoC1 was performed in patients with T1D and in normolipidemic-normoglycemic subjects. RESULTS An independent negative correlation was found between CETP activity and apoC1 in control subjects but not in patients with diabetes. HbA1c was independently associated with CETP activity in T1D patients. In vitro glycation of apoC1 modified its electrostatic charge and abrogated its ability to inhibit CETP activity in a concentration-dependent manner. The isoelectric point of apoC1 in T1D patients was significantly lower than that in control subjects. CONCLUSIONS The ability of apoC1 to inhibit CETP activity is impaired in patients with diabetes. Glycation of apoC1 leads to a change in its electrostatic properties that might account, at least in part, for a loss of constitutive CETP inhibition and an increase in plasma CETP activity in patients with diabetes.

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.

Constitutive inhibition of plasma CETP by apolipoprotein C1 is blunted in dyslipidemic patients with coronary artery disease

Plasma cholesteryl ester transfer protein (CETP) promotes the cholesterol enrichment of apoB-containing lipoproteins (VLDL and LDL) at the expense of HDL. Recent studies demonstrated that apoC1 is a potent CETP inhibitor in plasma of healthy, normolipidemic subjects. Our goal was to establish whether the modulation of CETP activity by apoC1 is influenced by dyslipidemia in patients with documented coronary artery disease (CAD). In the total CAD population studied (n = 240), apoC1 levels correlated negatively with CETP activity, independently of apoE-epsilon, CETP-Taq1B, and apoC1-Hpa1 genotypes. In multivariate analysis, the negative relationship was observed only in normolipidemic patients, not in those with hypercholesterolemia, hypertriglyceridemia, or combined hyperlipidemia. In the normolipidemic subjects, apoC1 levels were positively associated with higher HDL- to LDL-cholesterol ratio (r = 0.359, P < 0.001). It is concluded that apoC1 as a CETP inhibitor no longer operates on cholesterol redistribution in high-risk patients with dyslipidemia, probably due to increasing amounts of VLDL-bound apoC1, which is inactive as a CETP inhibitor. Patients with dyslipidemia could experience major benefits from treatment with pharmacological CETP inhibitors, which might compensate for blunted endogenous inhibition.

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.

Apolipoprotein C-I genotype and serum levels of triglycerides, C-reactive protein and coronary heart disease

Apolipoprotein C-I (apoCI) is implicated in lipid metabolism and inflammatory response, both important risk factors for human heart disease. However, most findings come from in vitro or animal studies, whereas data on human apoCI are sparse. To elucidate the role of apoCI in human disease, we analyzed a functional polymorphism in the promoter region of the apoCI gene in relation to blood lipids, C-reactive protein (CRP), coronary artery disease (CAD), and myocardial infarction (MI). Rs11568822 is a 4-base pair insertion/deletion (Ins/Del) polymorphism, and the Ins allele leads to a higher transcription in vitro compared with the Del allele. This polymorphism was analyzed in the Intergene study, a case-control study for CAD (N = 1236), and the Stockholm Heart Epidemiology Program, a case-control study for MI (N = 2774). Subjects homozygous for the Ins genotype had significantly higher serum levels of triglycerides (P = .01 and P = .006) and lower serum levels of CRP (P = .02 and P < .0001) compared with all other subjects in both studies. Similar results were obtained when analyzing only the controls of both studies (P = .002 and P = .0002, triglycerides; P = .002 and P < .0001, CRP). However, apoCI was not associated with CAD or MI. In conclusion, our data show that apoCI genotype is associated with serum levels of triglycerides and CRP, confirming the role of apoCI in lipid metabolism and suggesting that it also influences inflammation.

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.

Apolipoprotein CI is a physiological regulator of cholesteryl ester transfer protein activity in human plasma but not in rabbit plasma

Plasma cholesteryl ester transfer protein (CETP) activity is high in rabbits, intermediate in humans, and nondetectable in rodents. Human apolipoprotein CI (apoCI) was found to be a potent inhibitor of CETP. The aim of this study was to compare the ability of rabbit and human apoCI to modulate the interaction of CETP with HDLs and to evaluate to which extent apoCI contributes to plasma cholesteryl ester transfer rate in normolipidemic humans and rabbits. Rabbit apoCI gene was cloned and sequenced, rabbit and human apoCI were purified to homogeneity, and their ability to modify the surface charge properties and the CETP inhibitory potential of HDL were compared. It is demonstrated that unlike human apoCI, rabbit apoCI does not modulate cholesteryl ester transfer rate in total plasma. Whereas both human and rabbit apoCI readily associate with HDL, only human apoCI was found to modify the electrostatic charge of HDL. In humans, both CETP and apoCI at normal, physiological levels contribute significantly to the plasma cholesteryl ester transfer rate. In contrast, CETP is the sole major determinant of cholesteryl ester transfer in normolipidemic rabbit plasma as a result of the inability of rabbit apoCI to change HDL electronegativity.

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).