A pivotal role of the human kidney in catabolism of HDL protein components apolipoprotein A-I and A-IV but not of A-II

Characterization of novel truncated apolipoprotein A-I in human high-density lipoprotein generated by sequential treatment with myeloperoxidase and chymase

High-density lipoprotein (HDL) cholesterol is a well-known biomarker, which has been associated with reduction in the risk of cardiovascular diseases (CVD). However, some HDL anti-atherosclerotic functions may be impaired without altered HDL-cholesterol (HDL-C) level via its dysfunctional proteins or other physiological reactions in vivo. We previously showed that activated mast cell-derived chymase could modestly cleave apolipoprotein A-I (apoA-I) in HDL3, and further easily cleave lipid-free apoA-I. In contrast, myeloperoxidase (MPO) secreted by macrophages, the main cell type in atherosclerotic plaques, could oxidize HDL proteins, which might modify their tertiary structures, increasing their susceptibility to other enzymes. Here we focused on the co-modification and impact of chymase and MPO, usually secreted during inflammation from cells with possible co-existence in atheromas, on HDL. Only after sequential treatment with MPO and then chymase, two novel truncated apoA-I fragments were generated from HDL. One fragment was 16.5 kDa, and the cleavage site by chymase after MPO modification was the C-terminal of Tyr100 in apoA-I, cross-validated by three different mass spectrometry methods. This novel apoA-I fragment can be trapped in HDL particles to avoid kidney glomerular filtration and has a specific site for antibody generation for ELISA tests. As such, its quantification can be useful in predicting patients with CVD having normal HDL-C levels.

Association of HDL Subfraction Profile with the Progression of Insulin Resistance

Type 2 diabetes mellitus (T2DM) is a major global public health problem, as it is associated with increased morbidity, mortality, and healthcare costs. Insulin resistance (IR) is a condition characterized by disturbances in carbohydrate and lipid metabolism that precedes T2DM. The aim of the present study was to investigate the association between HDL and its subfraction profile and the progression of IR, as assessed by the Homeostatic Model Assessment for IR (HOMA-IR) index, and to define cut-off values to identify an increased risk of IR. Individuals with a HOMA-IR greater than 3.63 were considered to have IR. The HDL subfractions were separated using the Lipoprint system, which identifies ten subfractions (HDL-1-10) in three subclasses as large (HDL-L), intermediate (HDL-I) and small (HDL-S). Analyses were performed on samples from 240 individuals without IR and 137 with IR from the Hungarian general and Roma populations. The HDL-1 to -6 subfractions and the HDL-L and -I classes showed a significant negative association with the progression and existence of IR. Among them, HDL-2 (B = -40.37, p = 2.08 × 10-11) and HDL-L (B = -14.85, p = 9.52 × 10-10) showed the strongest correlation. The optimal threshold was found to be 0.264 mmol/L for HDL-L and 0.102 mmol/L and above for HDL-2. Individuals with HDL-L levels below the reference value had a 5.1-fold higher risk of IR (p = 2.2 × 10-7), while those with HDL-2 levels had a 4.2-fold higher risk (p = 3.0 × 10-6). This study demonstrates that the HDL subfraction profile (especially the decrease in HDL-2 and -L) may be a useful marker for the early detection and intervention of atherogenic dyslipidemia in subjects with impaired glucose and insulin metabolism.

Biokinetics, radiopharmacokinetics and estimation of the absorbed dose in healthy organs due to Technetium-99m transported in the core and on the surface of reconstituted high-density lipoprotein nanoparticles

The development of rHDL-radionuclide theragnostic systems requires evaluation of the absorbed doses that would be produced in healthy tissues and organs at risk. Technetium-99m is the most widely used radionuclide for diagnostic imaging, therefore, the design of theragnostic reconstituted high density-lipoprotein (rHDL) nanosystems labeled with Technetium-99m offers multiple possibilities.

OBJECTIVE

To determine the biokinetics, radiopharmacokinetics and estimate the absorbed doses induced in healthy organs by Technetium-99m transported in the core and on the surface of rHDL.

METHODS

Biokinetic and radiopharmacokinetic models of rHDL/[99mTc]Tc-HYNIC-DA (Technetium-99m in the core) and [99mTc]Tc-HYNIC-rHDL (Technetium-99m on the surface) were calculated from their ex vivo biodistribution in healthy mice. Absorbed doses were estimated by the MIRD formalism using OLINDA/EXM and LMFIT softwares.

RESULTS

rHDL/[99mTc]Tc-HYNIC-DA and [99mTc]Tc-HYNIC-rHDL show instantaneous absorption in kidney, lung, heart and pancreas, with slower absorption in spleen. rHDL/[99mTc]Tc-HYNIC-DA is absorbed more slowly in the intestine, while [99mTc]Tc-HYNIC-rHDL is absorbed more slowly in the liver. The main target organ for rHDL/[99mTc]Tc-HYNIC-DA, which is hydrophobic in nature, is the liver, whereas the kidney is for the more hydrophilic [99mTc]Tc-HYNIC-rHDL. Assuming that 925 MBq (25 mCi) of Technetium-99m, carried in the core or on the surface of rHDL, are administered, the maximum tolerated doses for the organs of greatest accumulation are not exceeded.

CONCLUSION

Theragnostic systems based on 99mTc-labeled rHDL are safe from the dosimetric point of view. The dose estimates obtained can be used to adjust the 99mTc-activity to be administered in future clinical trials.

Urinary Apolipoprotein A1 and Neutrophil Gelatinase-associated Lipocalin in Children with Idiopathic Nephrotic Syndrome

Urinary biomarkers are a promising diagnostic modality whose role was explored in nephrotic syndrome (NS). We estimated urinary apolipoprotein A1 (Apo A1) and neutrophil gelatinase-associated lipocalin (NGAL) in children with first-episode NS (FENS) and controls with a longitudinal follow-up to see the serial changes during remission. The study groups comprised 35 children with FENS and an equal number of age- and sex-matched controls. Patients were followed up at regular intervals, and 32 patients were classified as having steroid-sensitive NS (SSNS) and 3 as having steroid-resistant NS (SRNS). The mean follow-up period was 8.7 ± 4.2 months. Three patients in the SSNS group were labeled as having frequent relapses or steroid-dependent disease during follow-up. Of the three children with SRNS, two had minimal changes in the disease and one had idiopathic membranous nephropathy. The levels of Apo A1:creatinine, NGAL:creatinine, and spot urinary protein:urinary creatinine ratios were significantly higher in children with FENS compared with controls. The levels of the urine biomarkers decreased significantly at subsequent follow-up with remission. The Apo A1 and NGAL levels in SSNS patients were significantly high compared with both the controls and FENS patients. Urinary Apo A1 levels in SRNS patients were lower at initial presentation. This longitudinal study revealed changes in the urinary Apo A1 and NGAL in NS over the course of the disease.

Engineered rHDL Nanoparticles as a Suitable Platform for Theranostic Applications

Reconstituted high-density lipoproteins (rHDLs) can transport and specifically release drugs and imaging agents, mediated by the Scavenger Receptor Type B1 (SR-B1) present in a wide variety of tumor cells, providing convenient platforms for developing theranostic systems. Usually, phospholipids or Apo-A1 lipoproteins on the particle surfaces are the motifs used to conjugate molecules for the multifunctional purposes of the rHDL nanoparticles. Cholesterol has been less addressed as a region to bind molecules or functional groups to the rHDL surface. To maximize the efficacy and improve the radiolabeling of rHDL theranostic systems, we synthesized compounds with bifunctional agents covalently linked to cholesterol. This strategy means that the radionuclide was bound to the surface, while the therapeutic agent was encapsulated in the lipophilic core. In this research, HYNIC-S-(CH2)3-S-Cholesterol and DOTA-benzene-p-SC-NH-(CH2)2-NH-Cholesterol derivatives were synthesized to prepare nanoparticles (NPs) of HYNIC-rHDL and DOTA-rHDL, which can subsequently be linked to radionuclides for SPECT/PET imaging or targeted radiotherapy. HYNIC is used to complexing 99mTc and DOTA for labeling molecules with 111, 113mIn, 67, 68Ga, 177Lu, 161Tb, 225Ac, and 64Cu, among others. In vitro studies showed that the NPs of HYNIC-rHDL and DOTA-rHDL maintain specific recognition by SR-B1 and the ability to internalize and release, in the cytosol of cancer cells, the molecules carried in their core. The biodistribution in mice showed a similar behavior between rHDL (without surface modification) and HYNIC-rHDL, while DOTA-rHDL exhibited a different biodistribution pattern due to the significant reduction in the lipophilicity of the modified cholesterol molecule. Both systems demonstrated characteristics for the development of suitable theranostic platforms for personalized cancer treatment.

High-Density Lipoproteins in Kidney Disease

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

Multifaced Roles of HDL in Sepsis and SARS-CoV-2 Infection: Renal Implications

High-density lipoproteins (HDLs) are a class of blood particles, principally involved in mediating reverse cholesterol transport from peripheral tissue to liver. Omics approaches have identified crucial mediators in the HDL proteomic and lipidomic profile, which are involved in distinct pleiotropic functions. Besides their role as cholesterol transporter, HDLs display anti-inflammatory, anti-apoptotic, anti-thrombotic, and anti-infection properties. Experimental and clinical studies have unveiled significant changes in both HDL serum amount and composition that lead to dysregulated host immune response and endothelial dysfunction in the course of sepsis. Most SARS-Coronavirus-2-infected patients admitted to the intensive care unit showed common features of sepsis disease, such as the overwhelmed systemic inflammatory response and the alterations in serum lipid profile. Despite relevant advances, episodes of mild to moderate acute kidney injury (AKI), occurring during systemic inflammatory diseases, are associated with long-term complications, and high risk of mortality. The multi-faceted relationship of kidney dysfunction with dyslipidemia and inflammation encourages to deepen the clarification of the mechanisms connecting these elements. This review analyzes the multifaced roles of HDL in inflammatory diseases, the renal involvement in lipid metabolism, and the novel potential HDL-based therapies.

High-Density Lipoproteins and Acute Kidney Injury

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

A systematic review of the biodistribution of biomimetic high-density lipoproteins in mice

For the past two decades, biomimetic high-density lipoproteins (b-HDL) have been used for various drug delivery applications. The b-HDL mimic the endogenous HDL, and therefore possess many attractive features for drug delivery, including high biocompatibility, biodegradability, and ability to transport and deliver their cargo (e.g. drugs and/or imaging agents) to specific cells and tissues that are recognized by HDL. The b-HDL designs reported in the literature often differ in size, shape, composition, and type of incorporated cargo. However, there exists only limited insight into how the b-HDL design dictates their biodistribution. To fill this gap, we conducted a comprehensive systematic literature search of biodistribution studies using various designs of apolipoprotein A-I (apoA-I)-based b-HDL (i.e. b-HDL with apoA-I, apoA-I mutants, or apoA-I mimicking peptides). We carefully screened 679 papers (search hits) for b-HDL biodistribution studies in mice, and ended up with 24 relevant biodistribution profiles that we compared according to b-HDL design. We show similarities between b-HDL biodistribution studies irrespectively of the b-HDL design, whereas the biodistribution of the b-HDL components (lipids and scaffold) differ significantly. The b-HDL lipids primarily accumulate in liver, while the b-HDL scaffold primarily accumulates in the kidney. Furthermore, both b-HDL lipids and scaffold accumulate well in the tumor tissue in tumor-bearing mice. Finally, we present essential considerations and strategies for b-HDL labeling, and discuss how the b-HDL biodistribution can be tuned through particle design and administration route. Our meta-analysis and discussions provide a detailed overview of the fate of b-HDL in mice that is highly relevant when applying b-HDL for drug delivery or in vivo imaging applications.

Urinary apolipoprotein AI in children with kidney disease

BACKGROUND

Although high-density lipoprotein (HDL) modulates many cell types in the cardiovascular system, little is known about HDL in the kidney. We assessed urinary excretion of apolipoprotein AI (apoAI), the main protein in HDL.

METHODS

We enrolled 228 children with various kidney disorders and 40 controls. Urinary apoAI, albumin, and other markers of kidney damage were measured using ELISA, apoAI isoforms with Western blot, and renal biopsies stained for apoAI.

RESULTS

Patients followed in nephrology clinic had elevated urinary apoAI vs. controls (median 0.074 μg/mg; interquartile range (IQR) 0.0160-0.560, vs. 0.019 μg/mg; IQR 0.004-0.118, p < 0.001). Patients with tubulopathies, renal dysplasia/congenital anomalies of the kidney and urogenital tract, glomerulonephritis, and nephrotic syndrome (NS) in relapse had the greatest elevations (p ≤ 0.01). Patients with NS in remission, nephrolithiasis, polycystic kidney disease, transplant, or hypertension were not different from controls. Although all NS in relapse had higher apoAI excretion than in remission (0.159 vs. 0.0355 μg/mg, p = 0.01), this was largely driven by patients with focal segmental glomerulosclerosis (FSGS). Many patients, especially with FSGS, had increased urinary apoAI isoforms. Biopsies from FSGS patients showed increased apoAI staining at proximal tubule brush border, compared to diffuse cytoplasmic distribution in minimal change disease.

CONCLUSIONS

Children with kidney disease have variably increased urinary apoAI depending on underlying disease. Urine apoAI is particularly elevated in diseases affecting proximal tubules. Kidney disease is also associated with high molecular weight (HMW) apoAI isoforms in urine, especially FSGS. Whether abnormal urinary apoAI is a marker or contributor to renal disease awaits further study.

Lipoprotein modulation of proteinuric renal injury

High-density lipoprotein (HDL) and its main protein, apolipoprotein AI (apoAI), have established benefits in various cells, but whether these cytoprotective effects of HDL pertain to renal cells is unclear. We investigated the in vitro consequences of exposing damaged podocytes to normal apoAI, HDL, and apoAI mimetic (L-4F), and the in vivo effects of L-4F on kidney and atherosclerotic injury in a podocyte-specific injury model of proteinuria. In vitro, primary mouse podocytes were injured by puromycin aminonucleoside (PAN). Cellular viability, migration, production of reactive oxygen species (ROS), apoptosis, and the underlying signaling pathway were assessed. In vivo, we used a proteinuric model, Nphs1-hCD25 transgenic (NEP25⁺) mice, which express human CD25 on podocytes. Podocyte injury was induced by using immunotoxin (LMB2) and generated a proteinuric atherosclerosis model, NEP25⁺:apoE^-/- mice, was generated by mating apoE-deficient (apoE^-/-) mice with NEP25⁺ mice. Animals received L-4F or control vehicle. Renal function, podocyte injury, and atherosclerosis were assessed. PAN reduced podocyte viability, migration, and increased ROS production, all significantly lessened by apoAI, HDL, and L-4F. L-4F attenuated podocyte apoptosis and diminished PAN-induced inactivation of Janus family protein kinase-2/signal transducers and activators of transcription 3. In NEP25⁺ mice, L-4F significantly lessened overall proteinuria, and preserved podocyte expression of synaptopodin and cell density. Proteinuric NEP25⁺:apoE^-/- mice had more atherosclerosis than non-proteinuric apoE^-/- mice, and these lesions were significantly decreased by L-4F. Normal human apoAI, HDL, and apoAI mimetic protect against podocyte damage. ApoAI mimetic provides in vivo beneficial effects on podocytes that culminate in reduced albuminuria and atherosclerosis. The results suggest supplemental apoAI/apoAI mimetic may be a novel candidate to lessen podocyte damage and its complications.

High-Density Lipoproteins: Effects on Vascular Function and Role in the Immune Response

The focus in studies of high-density lipoproteins was on their capacity to remove excess cholesterol and deliver it to the liver. Other functions and vascular effects have been described. Clinical trials and translational/genetic studies have led to a refined understanding of the role of high-density lipoprotein; it is likely not a causal cardiovascular risk factor. In healthy subjects, it limits lipid oxidation, protects endothelial cell functions/integrity, and exerts antiinflammatory/antiapoptotic effects. In patients with coronary disease or diabetes, it undergoes modifications/remodeling, resulting in dysfunctional high-density lipoprotein. We summarize recent findings about the regulation of its function and discuss the clinical implications.

Loss of LCAT activity in the golden Syrian hamster elicits pro-atherogenic dyslipidemia and enhanced atherosclerosis

OBJECTIVE

Lecithin cholesterol acyltransferase (LCAT) plays a pivotal role in HDL metabolism but its influence on atherosclerosis remains controversial for decades both in animal and clinical studies. Because lack of cholesteryl ester transfer protein (CETP) is a major difference between murine and humans in lipoprotein metabolism, we aimed to create a novel Syrian Golden hamster model deficient in LCAT activity, which expresses endogenous CETP, to explore its metabolic features and particularly the influence of LCAT on the development of atherosclerosis.

METHODS

CRISPR/CAS9 gene editing system was employed to generate mutant LCAT hamsters. The characteristics of lipid metabolism and the development of atherosclerosis in the mutant hamsters were investigated using various conventional methods in comparison with wild type control animals.

RESULTS

Hamsters lacking LCAT activity exhibited pro-atherogenic dyslipidemia as diminished high density lipoprotein (HDL) and ApoAI, hypertriglyceridemia, Chylomicron/VLDL accumulation and significantly increased ApoB100/48. Mechanistic study for hypertriglyceridemia revealed impaired LPL-mediated lipolysis and increased very low density lipoprotein (VLDL) secretion, with upregulation of hepatic genes involved in lipid synthesis and transport. The pro-atherogenic dyslipidemia in mutant hamsters was exacerbated after high fat diet feeding, ultimately leading to near a 3- and 5-fold increase in atherosclerotic lesions by aortic en face and sinus lesion quantitation, respectively.

CONCLUSIONS

Our findings demonstrate that LCAT deficiency in hamsters develops pro-atherogenic dyslipidemia and promotes atherosclerotic lesion formation.

TNF-α-induced Inflammation Stimulates Apolipoprotein-A4 via Activation of TNFR2 and NF-κB Signaling in Kidney Tubular Cells

Apo-A4 expression was increased in tissues from chronic kidney disease (CKD) patients compared to that in normal kidney tissue. We determined the association of apo-A4 and its regulatory signals following acute kidney injury and elucidated the effects of apo-A4 on cell signaling pathways related to kidney injury in vitro and in vivo. Tumor necrosis factor (TNF)-α, which causes inflammatory cell injury, induced significantly increased expression of apo-A4 protein levels, and these levels were related to pro-inflammatory acute kidney injury in human kidney cells. Apo-A4 expression was also increased in experimented rat kidney tissues after ischemic reperfusion injury. The expression of tumor necrosis factor receptor (TNFR) 2 was increased in both kidney cell lines and experimented rat kidney tissues following acute kidney injury. The expression of apo-A4 and TNFR2 was increased upon treatment with TNF-α. Immunohistochemistry revealed positive apo-A4 and TNFR2 staining in ischemic reperfusion injury rat kidneys compared with levels in the sham operation kidneys. After neutralization of TNF-α, NF-κB expression was only observed in the cytoplasm by immunofluorescence. Therefore, the apo-A4 expression is increased by stimulation of injured kidney cells with TNF-α and that these effects occur via a TNFR2-NFκB complex.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Increased expression of ApoA1 after neuronal injury may be beneficial for healing

ApoA1 is a player in reverse cholesterol transport that initiates multiple cellular pathways on binding to its receptor ABCA1. Its relation to neuronal injury is however unclear. We found ApoA1 to be increasingly abundant at a later time point in the secondary phase of traumatic spinal cord injury. In a cellular injury model of neuroblastoma, ApoA1 showed an initial diminished expression after infliction of injury, which sharply increased thereafter. Subsequently, ApoA1 was shown to alter wound healing dynamics in neuroblastoma injury model. It was observed that an initial lag in scratch wound closure was followed by rapid healing in the ApoA1 treatment group. Activation of ERK pathway and Actin polymerisation by ApoA1 corroborated its role in healing after neuronal injury. We propose that ApoA1 is increasingly expressed and secreted as a delayed response to neuronal injury, and this is a self-protecting mechanism of the injured system.

High-Density Lipoprotein, Lecithin: Cholesterol Acyltransferase, and Atherosclerosis

Epidemiological data clearly show the existence of a strong inverse correlation between plasma high-density lipoprotein cholesterol (HDL-C) concentrations and the incidence of coronary heart disease. This relation is explained by a number of atheroprotective properties of HDL, first of all the ability to promote macrophage cholesterol transport. HDL are highly heterogeneous and are continuously remodeled in plasma thanks to the action of a number of proteins and enzymes. Among them, lecithin:cholesterol acyltransferase (LCAT) plays a crucial role, being the only enzyme able to esterify cholesterol within lipoproteins. LCAT is synthetized by the liver and it has been thought to play a major role in reverse cholesterol transport and in atheroprotection. However, data from animal studies, as well as human studies, have shown contradictory results. Increased LCAT concentrations are associated with increased HDL-C levels but not necessarily with atheroprotection. On the other side, decreased LCAT concentration and activity are associated with decreased HDL-C levels but not with increased atherosclerosis. These contradictory results confirm that HDL-C levels per se do not represent the functionality of the HDL system.

Increased HDL Size and Enhanced Apo A-I Catabolic Rates Are Associated With Doxorubicin-Induced Proteinuria in New Zealand White Rabbits

The catabolism and structure of high-density lipoproteins (HDL) may be the determining factor of their atheroprotective properties. To better understand the role of the kidney in HDL catabolism, here we characterized HDL subclasses and the catabolic rates of apo A-I in a rabbit model of proteinuria. Proteinuria was induced by intravenous administration of doxorubicin in New Zealand white rabbits (n = 10). HDL size and HDL subclass lipids were assessed by electrophoresis of the isolated lipoproteins. The catabolic rate of HDL-apo A-I was evaluated by exogenous radiolabelling with iodine-131. Doxorubicin induced significant proteinuria after 4 weeks (4.47 ± 0.55 vs. 0.30 ± 0.02 g/L of protein in urine, P < 0.001) associated with increased uremia, creatininemia, and cardiotoxicity. Large HDL2b augmented significantly during proteinuria, whereas small HDL3b and HDL3c decreased compared to basal conditions. HDL2b, HDL2a, and HDL3a subclasses were enriched with triacylglycerols in proteinuric animals as determined by the triacylglycerol-to-phospholipid ratio; the cholesterol content in HDL subclasses remained unchanged. The fractional catabolic rate (FCR) of [(131)I]-apo A-I in the proteinuric rabbits was faster (FCR = 0.036 h(-1)) compared to control rabbits group (FCR = 0.026 h(-1), P < 0.05). Apo E increased and apo A-I decreased in HDL, whereas PON-1 activity increased in proteinuric rabbits. Proteinuria was associated with an increased number of large HDL2b particles and a decreased number of small HDL3b and 3c. Proteinuria was also connected to an alteration in HDL subclass lipids, apolipoprotein content of HDL, high paraoxonase-1 activity, and a rise in the fractional catabolic rate of the [(131)I]-apo A-I.

Serum amyloid a gene polymorphism and its association with lipid profile in Saudi females with osteoporosis

Background and Objective:

Osteoporosis can be defined as a systemic skeletal disease characterized by low bone mass and micro architectural decline of bone tissue. Serum amyloid A (SAA) is a family of protein that increases up to 1,000-fold in blood during inflammation. In this study, we aimed to study the relationship between SAA1 gene polymorphism (rs12218) and lipid profile and osteoporosis.

Methods:

The study was performed on the female students of Taibah University in Al Medina, KSA during June 2014 to April 2015. According to BMD; osteoporosis group (138 students) and control group (128 students). All groups were subjected to; BMI, BMD, calcium, phosphorus, creatinine, lipid profile and SAA. Polymerase chain reaction and Real Time were done to determine the distribution of allele and genotype frequency of SAA (rs12218) C/T polymorphism.

Results:

This study shows that the TT genotype of rs12218 was more frequent in osteoporosis group than control group (P<0.001). Also, TT genotype and T allel was found to be associated with plasma total cholesterol, TG, LDLc, HDLc, Tscore, Zscore and SAA1 level in osteoporosis group (P=0.000, P=0.05, and P=0.000, P=0.000, P=0.01, P=0.02, P=0.000 respectively). The logistic regression analysis with and without lipid disorders in the osteoporosis group also show that the TT genotype of rs12218 still differed significantly between these two groups (P=0.001, OR=1.814, 95% CI: 0.719-4.577).

Conclusion:

The results of this study shows a significant association between TT genotype of rs12218 and both lipid level and osteoporosis in Saudi female population.

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

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

HDL cholesterol as a predictor for the incidence of lower extremity amputation and wound-related death in patients with diabetic foot ulcers

OBJECTIVE

We examined whether HDL cholesterol levels are a predictor for an incidence of lower-extremity amputation (LEA) and wound-related death in patients with diabetic foot ulcers (DFUs).

RESEARCH DESIGN AND METHODS

This was a single-center, observational, longitudinal historical cohort study of 163 Japanese ambulatory patients with DFUs, 45 woman and 118 men, with a mean (standard deviation) age of 62 (14) years. The primary composite endpoint was defined as the worst of the following outcomes for each individual; (1) minor amputation, defined as amputation below the ankle, (2) major amputation, defined as amputation above the ankle, and (3) wound-related death.

RESULTS

During the median follow-up period of 5.1 months, 67 patients (41.1%) reached the endpoint (43 minor amputations, 16 major amputations, and 8 wound-related deaths). In the univariate Cox proportional hazard model analysis, lower HDL cholesterol levels (mmol/L) were significantly associated with the incidence of the primary composite endpoint (hazard ratio 0.16 [95% CI 0.08-0.32], p < 0.001). In the multivariate Cox proportional hazard model analysis using a stepwise variable-selecting procedure, HDL cholesterol levels in addition to the presence of ankle brachial index <0.9 or ≥1.4 and serum albumin levels were selected as independent risk factors for the incidence of the endpoint (hazard ratio 0.30 [95% CI 0.14-0.63], p = 0.002). Similar results were obtained when HDL cholesterol levels were treated as a categorical variable (≥1.03 mmol/L or less).

CONCLUSIONS

HDL cholesterol levels might be a novel clinical predictor for the incidence of LEA and wound-related death in patients with DFUs.

Genetic polymorphisms of serum amyloid A1 and coronary artery disease risk

Serum amyloid A (SAA) protein is not only an inflammatory factor but also an apolipoprotein that can replace apolipoprotein A1 (apoA1) as the major apolipoprotein of high-density lipoprotein cholesterol (HDL-C). However, the relationship between genetic polymorphisms of SAA and coronary artery disease (CAD) remains unclear. A total of four single nucleotide polymorphisms (rs12218, rs4638289, rs7131332, and rs11603089) of the SAA gene were genotyped using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method in two independent case-control studies, one of the Han population (1416 CAD patients and 1373 control subjects) and the other of the Uygur population (588 CAD patients and 529 control subjects). We found that the rs12218 CC genotype was more frequent among the CAD patients than among the controls in both the Han (8.3% vs. 4.8%, P < 0.001) and Uygur populations (15.5% vs. 11.3%, P < 0.05). After adjustments for confounding factors, such as sex, age, smoking, drinking, hypertension, diabetes, and serum levels of triglycerides, total cholesterol, HDL, and plasma SAA, the differences remained significant in the Han (CC vs. CT+TT, P < 0.001, OR = 3.863, 95% CI: 1.755-12.477) and Uygur groups (CC vs. CT+TT, P = 0.031, OR = 3.022, 95% CI: 1.033-8.840). Genetic polymorphisms in SAA1 are associated with CAD in the Han and Uygur populations in western China.

HDL biogenesis, remodeling, and catabolism

In this chapter, we review how HDL is generated, remodeled, and catabolized in plasma. We describe key features of the proteins that participate in these processes, emphasizing how mutations in apolipoprotein A-I (apoA-I) and the other proteins affect HDL metabolism. The biogenesis of HDL initially requires functional interaction of apoA-I with the ATP-binding cassette transporter A1 (ABCA1) and subsequently interactions of the lipidated apoA-I forms with lecithin/cholesterol acyltransferase (LCAT). Mutations in these proteins either prevent or impair the formation and possibly the functionality of HDL. Remodeling and catabolism of HDL is the result of interactions of HDL with cell receptors and other membrane and plasma proteins including hepatic lipase (HL), endothelial lipase (EL), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP), apolipoprotein M (apoM), scavenger receptor class B type I (SR-BI), ATP-binding cassette transporter G1 (ABCG1), the F1 subunit of ATPase (Ecto F1-ATPase), and the cubulin/megalin receptor. Similarly to apoA-I, apolipoprotein E and apolipoprotein A-IV were shown to form discrete HDL particles containing these apolipoproteins which may have important but still unexplored functions. Furthermore, several plasma proteins were found associated with HDL and may modulate its biological functions. The effect of these proteins on the functionality of HDL is the topic of ongoing research.

HDL in innate and adaptive immunity

During infections or acute conditions high-density lipoproteins cholesterol (HDL-C) levels decrease very rapidly and HDL particles undergo profound changes in their composition and function. These changes are associated with poor prognosis following endotoxemia or sepsis and data from genetically modified animal models support a protective role for HDL. The same is true for some parasitic infections, where the key player appears to be a specific and minor component of HDL, namely apoL-1. The ability of HDL to influence cholesterol availability in lipid rafts in immune cells results in the modulation of toll-like receptors, MHC-II complex, as well as B- and T-cell receptors, while specific molecules shuttled by HDL such as sphingosine-1-phosphate (S1P) contribute to immune cells trafficking. Animal models with defects associated with HDL metabolism and/or influencing cell cholesterol efflux present features related to immune disorders. All these functions point to HDL as a platform integrating innate and adaptive immunity. The aim of this review is to provide an overview of the connection between HDL and immunity in atherosclerosis and beyond.

High-Density Lipoprotein

High-density lipoprotein (HDL) is a complex mixture of lipoproteins that is associated with many minor proteins and lipids that influence the function of HDL. Although HDL is a promising marker and potential therapeutic target based on its epidemiological data and the effects of healthy HDL in vitro in endothelial cells and macrophages, as well as based on infusion studies of reconstituted HDL in patients with hypercholesterolemia, it remains still uncertain whether or not HDL cholesterol–raising drugs will improve outcomes. Recent studies suggest that HDL becomes modified in patients with coronary artery disease or acute coronary syndrome because of oxidative processes that result in alterations in its proteome composition (proteome remodelling) leading to HDL dysfunction.

Associations of genetic polymorphisms of SAA1 with cerebral infarction

Background

Serum amyloid A protein (SAA) is both an inflammatory factor and an apolipoprotein. However, the relation between genetic polymorphisms of SAA and cerebral infarction (CI) remains unclear.

Methods and results

The previously reported 4 Single Nucleotide Polymorphisms (rs12218, rs4638289, rs7131332, and rs11603089) of SAA1 gene were genotyped by TaqMan method in a case–control study including 287 cerebral infarction patients and 376 control subjects. We found rs12218 CC genotype and rs7131332 AA genotype were more frequent among CI patients than among controls (9.76% versus 3.19%, P = 0.001; 32.75% versus 24.20%; p = 0.017; respectively). After adjustment of confounding factors such as sex, age, smoking, drinking, hypertension, diabetes, and lipids profile, the difference remained significant in rs12218 (P < 0.01, OR = 2.106, 95% CI: 1.811–7.121).

Conclusion

Genetic polymorphism of SAA1 may be a genetic maker of cerebral infarction in Chinese.

Factors controlling nascent high-density lipoprotein particle heterogeneity: ATP-binding cassette transporter A1 activity and cell lipid and apolipoprotein AI availability

Nascent high-density lipoprotein (HDL) particles arise in different sizes. We have sought to uncover factors that control this size heterogeneity. Gel filtration, native PAGE, and protein cross-linking were used to analyze the size heterogeneity of nascent HDL produced by BHK-ABCA1, RAW 264.7, J774, and HepG2 cells under different levels of two factors considered as a ratio, the availability of apolipoprotein AI (apoAI) -accessible cell lipid, and concentration of extracellular lipid-free apoAI. Increases in the available cell lipid:apoAI ratio due to either elevated ATP-binding cassette transporter A1 (ABCA1) expression and activity or raised cell density (i.e., increasing numerator) shifted the production of nascent HDL from smaller particles with fewer apoAI molecules per particle and fewer molecules of choline-phospholipid and cholesterol per apoAI molecule to larger particles that contained more apoAI and more lipid per molecule of apoAI. A further shift to larger particles was observed in BHK-ABCA1 cells when the available cell lipid:apoAI ratio was raised still higher by decreasing the apoAI concentration (i.e., the denominator). These changes in nascent HDL biogenesis were reminiscent of the transition that occurs in the size composition of reconstituted HDL in response to an increasing initial lipid:apoAI molar ratio. Thus, the ratio of available cell lipid:apoAI is a fundamental cause of nascent HDL size heterogeneity, and rHDL formation is a good model of nascent HDL biogenesis.—Lyssenko, N. N., Nickel, M., Tang, C., Phillips, M. C. Factors controlling nascent high-density lipoprotein particle heterogeneity: ATP-binding cassette transporter A1 activity and cell lipid and apolipoprotein AI availability.

Associations of SAA1 gene polymorphism with lipid lelvels and osteoporosis in Chinese women

Background

The development of osteoporosis is associated with several risk factors, such as genetic polymorphisms and enviromental factors. This study assessed the correlation between SAA1 gene rs12218 polymorphism and HDL-C lelvels and osteoporosis in a population of Chinese women.

Methods

A total of 387 postmenopausal female patients who were diagnosed with osteoporosis (case group) based on bone mineral density measurements via dual-energy x-ray absorptiometry and 307 females with no osteoporosis (control group) were included in this study. Correlations between SAA1 gene rs12218 polymorphism and osteoporosis and HDL-C level were investigated through the identification of SAA1 gene rs12218 polymorphism genotypes using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

Results

The TT genotype of rs12218 was more frequently in osteoporosis patients than in control subjects (P <0.001). And the rs12218 was found to be associated with plasma TG, HDL-C, LDL-C, and BMD levels in osteoporosis patients (P<0.05).

Conclusions

The present results indicate that both osteoporosis and lipids levels are associated with the TT genotype of rs12218 in the human SAA1 gene.

A form of apolipoprotein a-I is found specifically in relapses of focal segmental glomerulosclerosis following transplantation

Recurrence of idiopathic focal segmental glomerulosclerosis (FSGS) following kidney transplantation occurs in a large percentage of patients. Accurate prediction of recurrence and elucidation of its pathogenesis are major therapeutic goals. To detect differential proteins related to FSGS recurrence, proteomic analysis was performed on plasma and urine samples from 35 transplanted idiopathic FSGS patients, divided into relapsing and nonrelapsing. Several proteins were detected increased in urine of relapsing FSGS patients, including a high molecular weight form of apolipoprotein A-I, named ApoA-Ib, found exclusively in relapsing patients. This finding was verified by Western blot individually in the 35 patients and validated in an independent group of 40 patients with relapsing or nonrelapsing FSGS, plus two additional groups: FSGS-unrelated patients showing different proteinuria levels (n = 30), and familial FSGS transplanted patients (n = 14). In the total of 119 patients studied, the ApoA-Ib form was detected in 13 of the 14 relapsing FSGS patients, and in one of the 61 nonrelapsing patients. Only one of the 30 patients with FSGS-unrelated proteinuria tested positive for ApoA-Ib, and was not detected in familial patients. Urinary ApoA-Ib is associated with relapses in idiopathic FSGS and warrants additional investigation to determine its usefulness as biomarker of relapse following transplantation.

HDL dysfunction in diabetes: causes and possible treatments

HDL is known to be inversely correlated with cardiovascular disease due to its diverse antiatherogenic functions. These functions include cholesterol efflux and reverse cholesterol transport, antioxidative and anti-inflammatory activities. However, HDL has been shown to undergo a loss of function in several pathophysiological states, as in the acute phase response, obesity and chronic inflammatory diseases. Some of these diseases were also shown to be associated with increased risk for cardiovascular disease. One such disease that is associated with HDL dysfunction and accelerated atherosclerosis is diabetes mellitus, a disease in which the HDL particle undergoes diverse structural modifications that result in significant changes in its function. This review will summarize the changes that occur in HDL in diabetes mellitus and how these changes lead to HDL dysfunction. Possible treatments for HDL dysfunction are also briefly described.

HDL-C: does it matter? An update on novel HDL-directed pharmaco-therapeutic strategies

It has long been recognized that elevated levels of low-density lipoprotein cholesterol (LDL-C) increase the risk of cardiovascular disease (CHD) and that pharmacologic therapy to decrease LDL-C significantly reduces cardiovascular events. Despite the effectiveness of statins for CHD risk reduction, even optimal LDL-lowering therapy alone fails to avert 60% to 70% of CHD cases. A low plasma concentration of high-density lipoprotein cholesterol (HDL-C) is also associated with increased risk of CHD. However, the convincing epidemiologic data linking HDL cholesterol (HDL-C) to CHD risk in an inverse correlation has not yet translated into clinical trial evidence supporting linearity between HDL-C increases and CHD risk reduction. It is becoming clear that a functional HDL is a more desirable target than simply increasing HDL-C levels. Discoveries in the past decade have shed light on the complex metabolic and antiatherosclerotic pathways of HDL. These insights, in turn, have fueled the development of new HDL-targeted drugs, which can be classified according to four different therapeutic approaches: directly augmenting the concentration of apolipoprotein A-I (apo A-I), the major protein constituent of HDL; indirectly augmenting the concentration of apo A-I and HDL cholesterol; mimicking the functionality of apo A-I and enhancing reverse cholesterol transport. This review discusses the latest in novel HDL directed therapeutic strategies.

Short term dietary sodium restriction decreases HDL cholesterol, apolipoprotein A-I and high molecular weight adiponectin in healthy young men: relationships with renal hemodynamics and RAAS activation

BACKGROUND AND AIMS

We aimed to determine the effect of short-term dietary sodium restriction on plasma total cholesterol, LDL-C, HDL-C, triglycerides, apolipoprotein (apo) A-I, apo B and high molecular weight (HMW) adiponectin in non-obese, normotensive young men. Glomerular filtration rate (GFR), effective renal plasma flow (ERPF), plasma renin activity (PRA) and aldosterone were also measured.

METHODS AND RESULTS

Sixty-five men, aged 23 ± 7 years, were randomly studied on a high sodium intake (HS, 228 ± 77 mmol Na+/24 h) and a low sodium intake (LS, 36 ± 27 mmol Na+/24 h), each period lasting 1 week. LS decreased GFR and ERPF and increased PRA and aldosterone (p < 0.0001 for all). LS also induced a decrease in HDL-C (3.8 ± 10.8%), apo A-I (3.7 ± 6.5%) and HMW-adiponectin (13.6 ± 40.5%) (p < 0.05 for all), but plasma total cholesterol, LDL-C, triglycerides and apo B did not significantly change. The changes in HDL-C and apo A-I were correlated negatively to the changes in effective renal plasma flow (p < 0.05), whereas the changes in HMW adiponectin were correlated negatively to the changes in PRA and aldosterone (p < 0.05 for both).

CONCLUSION

Short term sodium restriction modestly decreases HDL-C, apo A-I and HMW-adiponectin in healthy men. Changes in GFR and ERPF and in the renin-angiotensin-aldosterone system as induced by LS may be involved in these responses.

Emerging role of high density lipoproteins as a player in the immune system

High density lipoproteins (HDL) possess a number of physiological activities. The most studied and, perhaps, better understood is the ability of HDL to promote excess cholesterol efflux from peripheral tissues and transport to the liver for excretion, a mechanism believed to confer protection against atherosclerotic cardiovascular disease. The ability of HDL to modulate cholesterol bioavailability in the lipid rafts, membrane microdomains enriched in glycosphingolipids and cholesterol, is evolutionary conserved and affects the properties of cells involved in the innate and adaptive immune response, tuning inflammatory response and antigen presentation functions in macrophages as well as B and T cell activation. Also sphingosine-1 phosphate (S1P), a major active sphingolipid carried by HDL, is of relevance in the pathogenesis of several immuno-inflammatory disorders through the modulation of macrophage and lymphocyte functions. Furthermore, HDL influence the humoral innate immunity by modulating the activation of the complement system and the expression of pentraxin 3 (PTX3). Finally, in humans, HDL levels and functions are altered in several immune-mediated disorders, such as rheumatoid arthritis, systemic lupus eritematosus, Crohn's disease and multiple sclerosis as well as during inflammatory responses. Altogether these observations suggest that the effects of HDL in immunity could be related, to either the ability of HDL to modulate cholesterol content in immune cell lipid rafts and to their role as reservoir for several biologically active substances that may impact the immune system.

Polymorphisms in the SAA1 gene are associated with ankle-to-brachial index in Han Chinese healthy subjects

OBJECTIVE. Recent study suggested that the genetic polymorphisms of serum amyloid A protein (SAA) were linked to cardiovascular disease (CVD). However, the relationship between genetic polymorphisms of SAA and ankle-to-brachial index (ABI) in healthy subjects has not been studied. We investigated the role of the SAA1 gene polymorphisms with ABI. METHODS AND RESULTS. All participants were selected from a cohort of healthy subjects participating in the Cardiovascular Risk Survey (CRS) study. Four single-nucleotide polymorphisms (SNPs; rs12218, rs4638289, rs7131332 and rs11603089) were genotyped by use of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. There was significant difference between CC genotype and CT genotype [(1.066 ± 0.113) vs (1.119 ± 0.096), p = 0.008], CC genotype and TT genotype [(1.066 ± 0.113) vs (1.127 ± 0.095), p = 0.002] of rs12218 in ABI, and these differences remained significant after adjustment for the sex, age, blood pressure, BMI, alcohol intake, smoking and high-density lipoprotein (HDL) [(1.073 ± 0.018) vs (1.122 ± 0.007), p = 0.012; (1.073 ± 0.018) vs (1.124 ± 0.006), p = 0.009), respectively]. These relationships were not found in rs874957, rs7950019 and rs11603089 before and after multivariate adjustment. CONCLUSIONS. CC genotype of rs12218 in the SAA1 gene was associated with decreased ABI in Chinese Han subjects, which indicated that the carriers of CC genotype of rs12218 have high risk of peripheral arterial disease.

Polymorphisms in the SAA1/2 gene are associated with carotid intima media thickness in healthy Han Chinese subjects: the Cardiovascular Risk Survey

Background

Serum amyloid A protein (SAA) is not only an inflammatory factor, but also an apolipoprotein that can replace apolipoprotein A1 (apoA1) as the major apolipoprotein of high-density lipoprotein (HDL), which has been linked to atherosclerosis. However, the relationship between genetic polymorphisms of SAA and the intima-media thickness (IMT) of the common carotid artery in healthy subjects remains unclear. We investigated the role of SAA1 and SAA2 gene polymorphisms with IMT in a cohort of healthy subjects participating in the Cardiovascular Risk Survey (CRS) study.

Methodology/Principal Findings

Anthropometric and B-mode ultrasound of the carotid IMT were measured in 1914 subjects (849 men; 1065 women) recruited from seven cities in Xinjiang province, (western China). Four SNPs (rs12218, rs2229338, rs1059559, and rs2468844) were genotyped by use of the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The SNP rs12218 was associated with carotid IMT by analyses of a dominate model (P<0.001) and additive model (P = 0.003), and the difference remained significant after multivariate adjustment (P = 0.008, P<0.001, respectively). This relationship was also observed in rs2468844 after multivariate adjustment by recessive model analysis (P = 0.011) but this was not observed in rs2229338 and rs1059559 before and after multivariate adjustment. These associations were not modified by serum HDL concentration. Furthermore, there were significant interactions between rs2468844 and rs12218 (interaction P<0.001) and rs2229338 (interaction P = 0.001) on carotid IMT.

Conclusion/Significance

Both rs12218 of the SAA1 gene and rs2468844 of SAA2 gene are associated with carotid IMT in healthy Han Chinese subjects.

High-density lipoprotein therapeutics and cardiovascular prevention

The field of cardiovascular prevention has long anticipated the evolution of high-density lipoprotein (HDL) therapy from unproven metabolic tweaking to pillar of risk reduction on par with low-density lipoprotein control. However, the convincing epidemiologic data linking HDL cholesterol (HDL-C) and cardiovascular disease risk in an inverse correlation has not yet translated into clinical trial evidence supporting linearity between HDL-C increases and risk reduction, or identifying obvious goals of therapy. Although HDL-C-increasing lifestyle maneuvers and established HDL drugs such as niacin and fibrates are likely to protect the vasculature, the negative results obtained in trials of a cholesteryl ester transfer protein inhibitor remind us that HDL-C increases are not always beneficial. It is becoming clear that a functional HDL is a more desirable target than simply increasing HDL-C levels. The larger objective of improving HDL functionality (with or without HDL-C level changes) is bound to become the guiding principle for pharmaceutical research in this area. Several new compounds currently being tested bridge the classical aim of increasing HDL-C levels with the novel target of improving HDL function.

Lower HDL-C and apolipoprotein A-I are related to higher glomerular filtration rate in subjects without kidney disease

Animal experiments show that the kidney contributes to apolipoprotein (apo)A-I catabolism. We tested relationships of HDL cholesterol (HDL-C) and apo-I with kidney function in subjects without severe chronic kidney disease. Included was a random sample of the general population (part of the PREVEND cohort). Kidney function [estimated glomerular filtration rate (e-GFR) by two well-established equations and creatinine clearance], HDL-C, triglycerides, apoA-I and insulin resistance (HOMAir) were measured in 2,484 fasting subjects (e-GFR>or=45 ml/min/1.73 m2) without macroalbuminuria, cardiovascular disease, diabetes, or the use of anti-hypertensives and/or lipid-lowering agents. HDL-C (r=-0.056 to -0.102, P<0.01 to <0.001) and apo A-I (r=-0.096 to -0.126, P<0.001) were correlated inversely with both GFR estimates and creatinine clearance in univariate analyses. Multiple linear regression analyses also demonstrated inverse relationships of HDL-C and apoA-I with all measures of kidney function even after adjustment for age, sex, waist circumference, HOMAir, triglycerides, and urinary albumin excretion (P=0.053 to 0.004). In conclusion, HDL-C and apoA-I are inversely related to e-GFR and creatinine clearance in subjects without severely compromised kidney function, which fits the concept that the kidney contributes to apoA-I regulation in humans. High glomerular filtration rate may be an independent determinant of a pro-atherogenic lipoprotein profile.

Acute-phase-HDL remodeling by heparan sulfate generates a novel lipoprotein with exceptional cholesterol efflux activity from macrophages

During episodes of acute-inflammation high-density lipoproteins (HDL), the carrier of so-called good cholesterol, experiences a major change in apolipoprotein composition and becomes acute-phase HDL (AP-HDL). This altered, but physiologically important, HDL has an increased binding affinity for macrophages that is dependent on cell surface heparan sulfate (HS). While exploring the properties of AP-HDLratioHS interactions we discovered that HS caused significant remodeling of AP-HDL. The physical nature of this change in structure and its potential importance for cholesterol efflux from cholesterol-loaded macrophages was therefore investigated. In the presence of heparin, or HS, AP-HDL solutions at pH 5.2 became turbid within minutes. Analysis by centrifugation and gel electrophoresis indicated that AP-HDL was remodeled generating novel lipid poor particles composed only of apolipoprotein AI, which we designate beta2. This remodeling is dependent on pH, glycosaminoglycan type, is promoted by Ca(2+) and is independent of protease or lipase activity. Compared to HDL and AP-HDL, remodeled AP-HDL (S-HDL-SAA), containing beta2 particles, demonstrated a 3-fold greater cholesterol efflux activity from cholesterol-loaded macrophage. Because the identified conditions causing this change in AP-HDL structure and function can exist physiologically at the surface of the macrophage, or in its endosomes, we postulate that AP-HDL contains latent functionalities that become apparent and active when it associates with macrophage cell surface/endosomal HS. In this way initial steps in the reverse cholesterol transport pathway are focused at sites of injury to mobilize cholesterol from macrophages that are actively participating in the phagocytosis of damaged membranes rich in cholesterol. The mechanism may also be of relevance to aspects of atherogenesis.