Stephen Zewinger

Abnormal High-Density Lipoprotein Induces Endothelial Dysfunction via Activation of Toll-like Receptor-2

Endothelial injury and dysfunction (ED) represent a link between cardiovascular risk factors promoting hypertension and atherosclerosis, the leading cause of death in Western populations. High-density lipoprotein (HDL) is considered antiatherogenic and known to prevent ED. Using HDL from children and adults with chronic kidney dysfunction (HDL(CKD)), a population with high cardiovascular risk, we have demonstrated that HDL(CKD) in contrast to HDL(Healthy) promoted endothelial superoxide production, substantially reduced nitric oxide (NO) bioavailability, and subsequently increased arterial blood pressure (ABP). We have identified symmetric dimethylarginine (SDMA) in HDL(CKD) that causes transformation from physiological HDL into an abnormal lipoprotein inducing ED. Furthermore, we report that HDL(CKD) reduced endothelial NO availability via toll-like receptor-2 (TLR-2), leading to impaired endothelial repair, increased proinflammatory activation, and ABP. These data demonstrate how SDMA can modify the HDL particle to mimic a damage-associated molecular pattern that activates TLR-2 via a TLR-1- or TLR-6-coreceptor-independent pathway, linking abnormal HDL to innate immunity, ED, and hypertension.

Carbamylated low-density lipoprotein induces endothelial dysfunction

AIMS Cardiovascular events remain the leading cause of death in Western world. Atherosclerosis is the most common underlying complication driven by low-density lipoproteins (LDL) disturbing vascular integrity. Carbamylation of lysine residues, occurring primarily in the presence of chronic kidney disease (CKD), may affect functional properties of lipoproteins; however, its effect on endothelial function is unknown. METHODS AND RESULTS Low-density lipoprotein from healthy donors was isolated and carbamylated. Vascular reactivity after treatment with native LDL (nLDL) or carbamylated LDL (cLDL) was examined in organ chambers for isometric tension recording using aortic rings of wild-type or lectin-like-oxidized LDL receptor-1 (LOX-1) transgenic mice. Reactive oxygen species (ROS) and nitric oxide (NO) production were determined using electron spin resonance spectroscopy. The effect of LDL-carbamyl-lysine levels on cardiovascular outcomes was determined in patients with CKD during a median follow-up of 4.7 years. Carbamylated LDL impaired endothelium-dependent relaxation to acetylcholine or calcium-ionophore A23187, but not endothelium-independent relaxation to sodium nitroprusside. In contrast, nLDL had no effect. Carbamylated LDL enhanced aortic ROS production by activating NADPH-oxidase. Carbamylated LDL stimulated endothelial NO synthase (eNOS) uncoupling at least partially by promoting S-glutathionylation of eNOS. Carbamylated LDL-induced endothelial dysfunction was enhanced in LOX-1 transgenic mice. In patients with CKD, LDL-carbamyl-lysine levels were significant predictors for cardiovascular events and all-cause mortality. CONCLUSIONS Carbamylation of LDL induces endothelial dysfunction via LOX-1 activation and increased ROS production leading to eNOS uncoupling. This indicates a novel mechanism in the pathogenesis of atherosclerotic disease which may be pathogenic and prognostic in patients with CKD and high plasma levels of cLDL.

HDL Cholesterol Is Not Associated with Lower Mortality in Patients with Kidney Dysfunction

In the general population, HDL cholesterol (HDL-C) is associated with reduced cardiovascular events. However, recent experimental data suggest that the vascular effects of HDL can be heterogeneous. We examined the association of HDL-C with all-cause and cardiovascular mortality in the Ludwigshafen Risk and Cardiovascular Health study comprising 3307 patients undergoing coronary angiography. Patients were followed for a median of 9.9 years. Estimated GFR (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration eGFR creatinine-cystatin C (eGFRcreat-cys) equation. The effect of increasing HDL-C serum levels was assessed using Cox proportional hazard models. In participants with normal kidney function (eGFR>90 ml/min per 1.73 m(2)), higher HDL-C was associated with reduced risk of all-cause and cardiovascular mortality and coronary artery disease severity (hazard ratio [HR], 0.51, 95% confidence interval [95% CI], 0.26-0.92 [P=0.03]; HR, 0.30, 95% CI, 0.13-0.73 [P=0.01]). Conversely, in patients with mild (eGFR=60-89 ml/min per 1.73 m(2)) and more advanced reduced kidney function (eGFR<60 ml/min per 1.73 m(2)), higher HDL-C did not associate with lower risk for mortality (eGFR=60-89 ml/min per 1.73 m(2): HR, 0.68, 95% CI, 0.45-1.04 [P=0.07]; HR, 0.84, 95% CI, 0.50-1.40 [P=0.50]; eGFR<60 ml/min per 1.73 m(2): HR, 1.18, 95% CI, 0.60-1.81 [P=0.88]; HR, 0.82, 95% CI, 0.40-1.69 [P=0.60]). Moreover, Cox regression analyses revealed interaction between HDL-C and eGFR in predicting all-cause and cardiovascular mortality (P=0.04 and P=0.02, respectively). We confirmed a lack of association between higher HDL-C and lower mortality in an independent cohort of patients with definite CKD (P=0.63). In summary, higher HDL-C levels did not associate with reduced mortality risk and coronary artery disease severity in patients with reduced kidney function. Indeed, abnormal HDL function might confound the outcome of HDL-targeted therapies in these patients.

HDL in Children with CKD Promotes Endothelial Dysfunction and an Abnormal Vascular Phenotype

Endothelial dysfunction begins in early CKD and contributes to cardiovascular mortality. HDL is considered antiatherogenic, but may have adverse vascular effects in cardiovascular disease, diabetes, and inflammatory conditions. The effect of renal failure on HDL properties is unknown. We studied the endothelial effects of HDL isolated from 82 children with CKD stages 2-5 (HDL(CKD)), who were free of underlying inflammatory diseases, diabetes, or active infections. Compared with HDL from healthy children, HDL(CKD) strongly inhibited nitric oxide production, promoted superoxide production, and increased vascular cell adhesion molecule-1 expression in human aortic endothelial cells, and reduced cholesterol efflux from macrophages. The effects on endothelial cells correlated with CKD grade, with the most profound changes induced by HDL from patients on dialysis, and partial recovery observed with HDL isolated after kidney transplantation. Furthermore, the in vitro effects on endothelial cells associated with increased aortic pulse wave velocity, carotid intima-media thickness, and circulating markers of endothelial dysfunction in patients. Symmetric dimethylarginine levels were increased in serum and fractions of HDL from children with CKD. In a longitudinal follow-up of eight children undergoing kidney transplantation, HDL-induced production of endothelial nitric oxide, superoxide, and vascular cell adhesion molecule-1 in vitro improved significantly at 3 months after transplantation, but did not reach normal levels. These results suggest that in children with CKD without concomitant disease affecting HDL function, HDL dysfunction begins in early CKD, progressing as renal function declines, and is partially reversed after kidney transplantation.

HDL cholesterol: reappraisal of its clinical relevance

BackgroundWhile several lines of evidence prove that elevated concentrations of low-density lipoproteins (LDL) causally contribute to the development of atherosclerosis and its clinical consequences, high-density lipoproteins are still widely believed to exert atheroprotective effects. Hence, HDL cholesterol (HDL-C) is in general still considered as “good cholesterol”. Recent research, however, suggests that this might not always be the case and that a fundamental reassessment of the clinical significance of HDL-C is warranted.MethodThis review article is based on a selective literature review.ResultsIn individuals without a history of cardiovascular events, low concentrations of HDL-C are inversely associated with the risk of future cardiovascular events. This relationship may, however, not apply to patients with metabolic disorders or manifest cardiovascular disease. The classical function of HDL is to mobilise cholesterol from extrahepatic tissues for delivery to the liver for excretion. These roles in cholesterol metabolism as well as many other biological functions of HDL particles are dependent on the number as well as protein and lipid composition of HDL particles. They are poorly reflected by the HDL-C concentration. HDL can even exert negative vascular effects, if its composition is pathologically altered. High serum HDL-C is therefore no longer regarded protective. In line with this, recent pharmacological approaches to raise HDL-C concentration have not been able to show reductions of cardiovascular outcomes.ConclusionIn contrast to LDL cholesterol (LDL-C), HDL-C correlates with cardiovascular risk only in healthy individuals. The calculation of the ratio of LDL-C to HDL-C is not useful for all patients. Low HDL-C should prompt examination of additional metabolic and inflammatory pathologies. An increase in HDL-C through lifestyle change (smoking cessation, physical exercise) has positive effects and is recommended. However, HDL-C is currently not a valid target for drug therapy.

Potassium: an ion with dangerous airs and graces

Take home figureFactors promoting hypokalaemia and hyperkalaemia. CHF, chronic heart failure; CKD, chronic kidney disease.

High-density lipoprotein (HDL) and infections: a versatile culprit

For several years, HDL has been referred to as ‘good cholesterol’, exerting a plethora of beneficial effects mainly on cells of the vascular tree. HDL prevents endothelial dysfunction, reduces proinflammatory cell activation, and promotes reverse cholesterol transport. However, many studies questioned this principle of HDL’s protective functions and could intriguingly document that a variety of diseases render HDL dysfunctional. In patients with coronary artery disease, diabetes, or autoimmunological diseases, HDL loses its vasoprotective properties and, in chronic kidney disease, even turns into noxious lipoprotein inducing endothelial dysfunction and increasing arterial blood pressure. Therefore, it is not surprising that neither increased HDL-cholesterol (HDL-C) levels nor single nucleotide polymorphisms (SNPs) associated with elevated HDL-C levels were linked to improved outcomes in patients with prevalent cardiovascular diseases, which is in marked contrast to studies of the general population. In line with these epidemiological findings, studies of HDL-raising therapies by inhibition of the cholesterol ester transfer protein (CETP) yielded neutral (for torcetrapib, dalcetrapib, and evacetrapib) or weakly positive (for anacetrapib) effects. Based on the presence of dysfunctional HDL, particularly in patients with coronary artery disease or myocardial infarction, it makes sense that increasing such ‘dysfunctional HDL’ might not be related to improved outcomes in those patients. Therefore, HDL remains an enigmatic lipoprotein, which cannot be adequately therapeutically targeted. Besides increasing HDL-C, preventing changes of the composition of HDL (such as changes of the proteome or post-translational protein modifications), which are directly linked to the functionality of HDL, has at least the potential to put HDL back in the focus as a therapeutically targetable lipoprotein. However, these drawbacks and recent advances in LDLlowering therapies have pushed HDL somewhat out of the spotlight of cardiovascular medicine. In the current issue of the journal, Madsen and colleagues have opened up a new field of interest in HDL. In two well-characterized and large-scale cohorts of the general population, the authors assessed the association between HDL-C levels and infection-related hospitalization. According to experimental studies demonstrating antiinflammatory effects of HDL, low HDL-C was associated with increased infection risk. Surprisingly, very high HDL-C levels (>93 mg/ dL) were also related to an increased risk for infectious disease events, resulting in a U-shaped association between HDL-C and (bacterial) infections. To strengthen their findings, the authors were able to demonstrate that SNPs in genes encoding hepatic lipoprotein lipase, LIPC, and cholesterol ester transfer protein, CETP, both HDL-C-increasing alleles, were consistently associated with a reduced risk for infections. Because of the low number of viral infection events, the study did primarily identify an association between HDL-C and bacterial infections. It is not unreasonable to explain the association between low HDL-C and increased number of infectious events. HDL may directly reduce the pathogenicity of Gram-positive and Gram-negative bacteria. For 20 years, it has been known that HDL serves as a ‘sponge’, binding bacterial lipopolysaccharide (LPS) from Gramnegative and lipoteichoic acid (LTA) from Gram-positive bacteria. Thereby, HDL has the potential to promote their clearance from the circulation and to prevent an excess of endotoxin. In addition, HDL may also exert an immunomodulatory function by limiting pathogen-mediated activation of the innate immune system. HDL increases the expression of the transcription factor ATF3 in macrophages, which attenuates the production of proinflammatory cytokines after challenge of Toll-like receptors (TLRs) with their ligands such as LPS. Moreover, in endothelial cells, HDL stimulates endothelial nitric oxide (NO) production, which prevents the expression of cell adhesion molecules and, thereby, the interaction between monocytes and endothelial cells, a crucial step in the pathogenesis of an inflammatory response. Furthermore, sphingosine-1 phosphate (S1P), a component of HDL, modulates adaptive immunity by, for instance, increasing the population of regulatory T lymphocytes.

Mycobacterium fortuitum peritonitis in peritoneal dialysis and its effects on the peritoneum.

Mycobacterium fortuitum peritonitis is a rare complication in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). A 47-year-old patient was admitted to our tertiary hospital because of culture-negative peritonitis with persisting signs of infection despite adequate empirical antibiotic treatment. Although M. fortuitum was detected and the antibiotic regime subsequently amended, catheter removal was inevitable and the dialysis modality converted to hemodialysis (HD). After long-term antibiotic treatment and an additional latency of 4 months without signs of residual infection, reinitiation of CAPD was planned. Explorative laparoscopy prior to catheter reinsertion revealed multiple adhesions within the peritoneal cavity, preventing adequate catheter function. The clinical course of M. fortuitum peritonitis, the need for catheter removal and the description of peritoneal changes are discussed regarding to recent literature.