Identification of ALK in Thinness.

There is considerable inter-individual variability in susceptibility to weight gain despite an equally obesogenic environment in large parts of the world. Whereas many studies have focused on identifying the genetic susceptibility to obesity, we performed a GWAS on metabolically healthy thin individuals (lowest 6th percentile of the population-wide BMI spectrum) in a uniquely phenotyped Estonian cohort. We discovered anaplastic lymphoma kinase (ALK) as a candidate thinness gene. In Drosophila, RNAi mediated knockdown of Alk led to decreased triglyceride levels. In mice, genetic deletion of Alk resulted in thin animals with marked resistance to diet- and leptin-mutation-induced obesity. Mechanistically, we found that ALK expression in hypothalamic neurons controls energy expenditure via sympathetic control of adipose tissue lipolysis. Our genetic and mechanistic experiments identify ALK as a thinness gene, which is involved in the resistance to weight gain.

Wnt/ß-catenin and NFκB signaling synergize to trigger growth factor-free regeneration of adult primary human hepatocytes.

BACKGROUND AND AIMS: The liver has a remarkable capacity to regenerate, which is sustained by the ability of hepatocytes to act as facultative stem cells that, while normally quiescent, re-enter the cell cycle after injury. Growth factor signaling is indispensable in rodents, whereas Wnt/ß-catenin is not required for effective tissue repair. However, the molecular networks that control human liver regeneration remain unclear. METHODS: Organotypic 3D spheroid cultures of primary human or murine hepatocytes were used to identify the signaling network underlying cell cycle re-entry. Furthermore, we performed chemogenomic screening of a library enriched for epigenetic regulators and modulators of immune function to determine the importance of epigenomic control for human hepatocyte regeneration. RESULTS: Our results showed that, unlike in rodents, activation of Wnt/ß-catenin signaling is the major mitogenic cue for adult primary human hepatocytes. Furthermore, we identified TGFß inhibition and inflammatory signaling through NF-κB as essential steps for the quiescent-to-regenerative switch that allows Wnt/ß-catenin-induced proliferation of human cells. In contrast, growth factors, but not Wnt/ß-catenin signaling, triggered hyperplasia in murine hepatocytes. High-throughput screening in a human model confirmed the relevance of NFκB and revealed the critical roles of polycomb repressive complex 2, as well as of the bromodomain families I, II, and IV. CONCLUSIONS: This study revealed a network of NFκB, TGFß, and Wnt/ß-catenin that controls human hepatocyte regeneration in the absence of exogenous growth factors, identified novel regulators of hepatocyte proliferation, and highlighted the potential of organotypic culture systems for chemogenomic interrogation of complex physiological processes.

High-Density Lipoprotein Anti-Inflammatory Capacity and Incident Cardiovascular Events.

BACKGROUND: The role of high-density lipoprotein (HDL) function in cardiovascular disease represents an important emerging concept. The present study investigated whether HDL anti-inflammatory capacity is prospectively associated with first cardiovascular events in the general population. METHODS: HDL anti-inflammatory capacity was determined as its ability to suppress TNFα (tumor necrosis factor α)-induced VCAM-1 (vascular cell adhesion molecule-1) mRNA expression in endothelial cells in vitro (results expressed as achieved percent reduction by individual HDL related to the maximum TNFα effect with no HDL present). In a nested case-control design of the PREVEND (Prevention of Renal and Vascular End Stage Disease) study, 369 cases experiencing a first cardiovascular event (combined end point of death from cardiovascular causes, ischemic heart disease, nonfatal myocardial infarction, and coronary revascularization) during a median of 10.5 years of follow-up were identified and individually matched to 369 controls with respect to age, sex, smoking status, and HDL cholesterol. Baseline samples were available in 340 cases and 340 matched controls. RESULTS: HDL anti-inflammatory capacity was not correlated with HDL cholesterol or hsCRP (high-sensitivity C-reactive protein). HDL anti-inflammatory capacity was significantly lower in cases compared with controls (31.6% [15.7-44.2] versus 27.0% [7.4-36.1]; P<0.001) and was inversely associated with incident CVD in a fully adjusted model (odds ratio [OR] per 1 SD, 0.74 [CI, 0.61-0.90]; P=0.002). Furthermore, this association was approximately similar with all individual components of the cardiovascular disease end point. The HDL anti-inflammatory was not correlated with cholesterol efflux capacity (r=-0.02; P>0.05). When combining these 2 HDL function metrics in 1 model, both were significantly and independently associated with incident cardiovascular disease in a fully adjusted model (efflux: OR per 1 SD, 0.74; P=0.002; anti-inflammatory capacity: OR per 1 SD, 0.66; P<0.001). Adding HDL anti-inflammatory capacity improved risk prediction by the Framingham risk score, with a model likelihood-ratio statistic increase from 10.50 to 20.40 (P=0.002). CONCLUSIONS: The HDL anti-inflammatory capacity, reflecting vascular protection against key steps in atherogenesis, was inversely associated with incident cardiovascular events in a general population cohort, independent of HDL cholesterol and HDL cholesterol efflux capacity. Adding HDL anti-inflammatory capacity to the Framingham risk score improves risk prediction.

Normal fasting triglyceride levels and incident type 2 diabetes in the general population.

BACKGROUND: Type 2 diabetes is increasing worldwide. Traditionally, only hypertriglyceridemia is considered a risk factor. We investigated whether also normal triglycerides prospectively associate with incident type 2 diabetes in healthy subjects. METHODS: Incident type 2 diabetes was determined in healthy individuals with normal triglyceride levels from a prospective longitudinal cohort study (PREVEND, n = 2085, 11.4-year median follow-up). RESULTS: Type 2 diabetes incidence was 3.8%. In linear regression analysis baseline insulin, HOMA-IR, total cholesterol, HDL cholesterol, eGFR, systolic blood pressure (all p < 0.001), glucose, age and creatinine (all p < 0.01) independently associated with triglycerides within the normal range, comparable to what would be expected from associations with increased triglycerides. In Kaplan-Meier analysis sex-stratified tertiles of normal triglycerides prospectively associated with de novo type 2 diabetes (p < 0.001). Cox regression confirmed a significant prospective association independent of HOMA-IR [HR (95% CI), 1.39 (1.12, 1.74), p = 0.002] and several other recognized risk factors. CONCLUSIONS: Even in healthy subjects without metabolic syndrome increasing triglyceride levels within the normal range confer a continuous increase in type 2 diabetes incidence. These data indicate that virtually everyone could potentially benefit from triglyceride lowering, further encouraging implementation of lifestyle changes in the general population.

Remnant lipoprotein cholesterol is associated with incident new onset diabetes after transplantation (NODAT) in renal transplant recipients: results of the TransplantLines Biobank and cohort Studies.

BACKGROUND: New onset diabetes after transplantation (NODAT) is a frequent and serious complication of renal transplantation resulting in worse graft and patient outcomes. The pathophysiology of NODAT is incompletely understood, and no prospective biomarkers have been established to predict NODAT risk in renal transplant recipients (RTR). The present work aimed to determine whether remnant lipoprotein (RLP) cholesterol could serve as such a biomarker that would also provide a novel target for therapeutic intervention. METHODS: This longitudinal cohort study included 480 RTR free of diabetes at baseline. 53 patients (11%) were diagnosed with NODAT during a median [interquartile range, IQR] follow-up of 5.2 [4.1-5.8] years. RLP cholesterol was calculated by subtracting HDL and LDL cholesterol from total cholesterol values (all directly measured). RESULTS: Baseline remnant cholesterol values were significantly higher in RTR who subsequently developed NODAT (0.9 [0.5-1.2] mmol/L vs. 0.6 [0.4-0.9] mmol/L, p = 0.001). Kaplan-Meier analysis showed that higher RLP cholesterol values were associated with an increased risk of incident NODAT (log rank test, p < 0.001). Cox regression demonstrated a significant longitudinal association between baseline RLP cholesterol levels and NODAT (HR, 2.27 [1.64-3.14] per 1 SD increase, p < 0.001) that remained after adjusting for plasma glucose and HbA1c (p = 0.002), HDL and LDL cholesterol (p = 0.008) and use of immunosuppressive medication (p < 0.001), among others. Adding baseline remnant cholesterol to the Framingham Diabetes Risk Score significantly improved NODAT prediction (change in C-statistic, p = 0.01). CONCLUSIONS: This study demonstrates that baseline RLP cholesterol levels strongly associate with incident NODAT independent of several other recognized risk factors.

Proteoglycan binding as proatherogenic function metric of apoB-containing lipoproteins and chronic kidney graft failure.

Lipoprotein-proteoglycan binding is an early key event in atherosclerotic lesion formation and thus conceivably could play a major role in vasculopathy-driven chronic graft failure and cardiovascular mortality in renal transplant recipients. The present study investigated whether lipoprotein-proteoglycan binding susceptibility (LPBS) of apoB-containing lipoproteins and levels of the classical atherosclerosis biomarker LDL-C were associated with cardiovascular mortality (n = 130) and graft failure (n = 73) in 589 renal transplant recipients who were followed up from at least 1 year after transplantation for 9.5 years. At baseline, LPBS was significantly higher in patients who subsequently developed graft failure than in those with a surviving graft (1.68 ± 0.93 vs. 1.46 ± 0.49 nmol/mmol, P = 0.001). Cox regression analysis showed an association between LPBS and chronic graft failure in an age- and sex-adjusted model (hazard ratio: 1.45; 95% CI, 1.14-1.85; P = 0.002), but no association was observed with cardiovascular mortality. LDL-C levels were not associated with graft failure or cardiovascular mortality. This study shows that measurement of cholesterol retention outperformed the traditionally used quantitative parameter of LDL-C levels in predicting graft failure, suggesting a higher relevance of proatherogenic function than the quantity of apoB-containing lipoproteins in chronic kidney graft failure.

Statin use and incident cardiovascular events in renal transplant recipients.

BACKGROUND: Statins achieve potent LDL lowering in the general population leading to a significant cardiovascular (CV) risk reduction. In renal transplant recipients (RTR) statins are included in treatment guidelines, however, conclusive evidence of improved cardiovascular outcomes has not been uniformly provided and concerns have been raised about simultaneous use of statins and the immunosuppressant cyclosporine. This study aimed to elucidate the effect of statins on a compound CV endpoint, comprised of ischaemic CV events and CV mortality in RTR, with subgroup analysis focussing on cyclosporine users. METHOD: 622 included RTR (follow-up 5.4 years) were matched based on propensity scores and dichotomized by statin use. Survival analysis was conducted. RESULTS: Cox regression showed that statin use was not significantly associated with the compound CV endpoint in a fully adjusted model (HR = 0.81, 95% CI = 0.53-1.24, P = .33). Subgroup analyses in RTR using cyclosporine revealed a strong positive association of statin use with the CV compound outcome in a fully adjusted model (HR = 6.60, 95% CI 1.75-24.9, P = .005). Furthermore, statin use was positively correlated with cyclosporine trough levels (correlation coefficient 0.11, P = .04). CONCLUSION: In conclusion, statin use does not significantly decrease incident CV events in an overall RTR cohort, but is independently associated with CV-specific mortality and events in cyclosporine using RTR, possibly due to a bilateral pharmacological interaction.

Preconception insulin resistance and neonatal birth weight in women with obesity: role of bile acids.

RESEARCH QUESTION: Does maternal preconception insulin resistance affect neonatal birth weight among women with obesity? Is insulin resistance associated with circulating bile acids? Do bile acids influence the association between maternal preconception insulin resistance and neonatal birth weight? DESIGN: An exploratory post-hoc analysis of the LIFEstyle randomized controlled trial comparing lifestyle intervention with conventional infertility treatment in women with a BMI of ≥29 kg/m2. Fasting blood samples were collected at randomization and after 3 and 6 months in 469 women. Insulin resistance was quantified using the homeostasis model assessment of insulin resistance (HOMA-IR). Bile acid sub-species were determined by liquid chromatography with tandem mass spectrometry. Singletons were included (n = 238). Birth weight Z-scores were adjusted for age, offspring gender and parity. Multilevel analysis and linear regressions were used. RESULTS: A total of 913 pairs of simultaneous preconception HOMA-IR (median [Q25; Q75]: 2.96 [2.07; 4.16]) and total bile acid measurements (1.79 [1.10; 2.94]) µmol/l were taken. Preconception HOMA-IR was positively associated with total bile acids (adjusted B 0.15; 95% CI 0.09 to 0.22; P < 0.001) and all bile acid sub-species. At the last measurement before pregnancy, HOMA-IR (2.71 [1.91; 3.74]) was positively related to birth weight Z-score (mean ± SD 0.4 ± 1.1; adjusted B 0.08; 95% CI 0.01 to 0.14; P = 0.03). None of the preconception bile acids measured were associated with birth weight. CONCLUSION: Maternal preconception insulin resistance is an important determinant of neonatal birth weight in women with obesity, whereas preconception bile acids are not.

Deficiency of Nucleotide-binding oligomerization domain-containing proteins (NOD) 1 and 2 reduces atherosclerosis.

Atherosclerosis is crucially fueled by inflammatory pathways including pattern recognition receptor (PRR)-related signaling of the innate immune system. Currently, the impact of the cytoplasmic PRRs nucleotide-binding oligomerization domain-containing protein (NOD) 1 and 2 is incompletely characterized. We, therefore, generated Nod1/Nod2 double knockout mice on a low-density lipoprotein receptor (Ldlr)-deficient background (= Ldlr-/-Nod1/2-/-) which were subsequently analyzed regarding experimental atherosclerosis, lipid metabolism, insulin resistance and gut microbiota composition. Compared to Ldlr-/- mice, Ldlr-/-Nod1/2-/- mice showed reduced plasma lipids and increased hepatic expression of the scavenger receptor LDL receptor-related protein 1 after feeding a high-fat diet for 12 weeks. Furthermore, intestinal cholesterol and its bacterial degradation product coprostanol were elevated in Ldlr-/-Nod1/2-/- mice, correlating with the increased abundance of Eubacterium coprostanoligenes as assessed by 3rd generation sequencing of the gut microbiota. Atherosclerotic plaques of Ldlr-/-Nod1/2-/- mice exhibited less lipid deposition and macrophage accumulation. Moreover, macrophages from Ldlr-/-Nod1/2-/- mice showed higher expression of the cholesterol efflux transporters Abca1 and Abcg1 and accordingly reduced foam cell formation. Deficiency of Nod1 and Nod2 led to reduced plaque lipid deposition and inflammatory cell infiltration in atherosclerotic plaques. This might be explained by diminished plasma lipid levels and foam cell formation due to altered expression of key regulators of the hepatic cholesterol pathway as well as differential intestinal cholesterol metabolism and microbiota composition.

The Origin of Follicular Bile Acids in the Human Ovary.

Bile acids (BAs) are present in ovarian follicular fluid (FF) and are linked to embryo development. However, information on the source of ovarian BA is scarce. Therefore, we aimed to explore local ovarian synthesis and BA transport from blood into FF. BA levels were determined in matching FF and serum from women undergoing in vitro fertilization. In vitro BA production by human mural granulosa cells (MGCs) and cumulus granulosa cells (CGCs) was measured by mass spectrometry. Gene and protein expression were quantified in MGC and CGC and in human ovarian tissue by quantitative PCR and Western blot/immunohistochemistry, respectively. BA levels in blood and FF were significantly correlated (rs = 0.186, P = 0.027) but were almost twofold higher in FF (P < 0.001). Primary BA levels were increased in FF, indicating that, in addition to passive diffusion, other sources of ovarian BA might exist. The key BA synthesis enzyme cytochrome P450 A1 was absent in MGC and CGC; BA production in vitro was undetectable. Therefore, local ovarian BA production is unlikely. However, common BA importers (Na+/taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter) and an exporter (ATP-binding cassette subfamily C member 3) were identified in GC, theca cells, and oocyte. In summary, these results suggest that passive and active transport of BAs from blood into FF constitute sources of FF BA.

HDL (High-Density Lipoprotein) Cholesterol Efflux Capacity Is Associated With Incident Cardiovascular Disease in the General Population.

OBJECTIVE: Focus is shifting from HDL-C (high-density lipoprotein cholesterol) as predictive biomarker for cardiovascular disease (CVD) towards antiatherogenic HDL functionalities. Still, limited data exist on the prospective association of HDL function metrics with CVD events. The current work aimed to determine, if baseline HDL-C efflux capacity (CEC) is associated with future CVD events in the general population. Approach and Results: We performed a prospective study among participants of the PREVEND (Prevention of Renal and Vascular End-stage Disease) cohort (follow-up, 12 years). From the overall n=8592 subjects 325 with previous CVD events were excluded; of the remaining 8267 eligible participants all subjects with new CVD events during follow-up were selected and individually matched to controls for age, sex, smoking status, and HDL-C levels. CEC at baseline was quantified using human THP-1-derived macrophage foam cells and apolipoprotein B-depleted plasma. Despite identical HDL-C and apoA (apolipoprotein)-I levels between cases (n=351) and controls (n=354) CEC was significantly lower in cases (0.93±0.29 versus 1.01±0.24 arbitrary units; P<0.001). In all subjects combined, CEC correlated positively with HDL-C and apoA-I and negatively with body mass index, hsCRP (high-sensitivity C-reactive protein), and urinary albumin excretion. CEC was inversely associated with incident CVD events, both expressed per quartile and per 1 SD change (odds ratio, 0.73; 95% CI, 0.62-0.86; P<0.001); this association remained significant after adjustments for HDL-C, hsCRP, kidney function, and several other clinical covariates. CONCLUSIONS: Combined these data demonstrate that in the general population baseline CEC is significantly associated with the future development of CVD events independent of HDL-C and apoA-I plasma levels.

Proceedings of the Ninth HDL (High-Density Lipoprotein) Workshop: Focus on Cardiovascular Disease.

The HDL (high-density lipoprotein) Workshop was established in 2009 as a forum for candid discussions among academic basic scientists, clinical investigators, and industry researchers about the role of HDL in cardiovascular disease. This ninth HDL Workshop was held on May 16 to 17, 2019 in Boston, MA, and included outstanding oral presentations from established and emerging investigators. The Workshop featured 5 sessions with topics that tackled the role of HDL in the vasculature, its structural complexity, its role in health and disease states, and its interaction with the intestinal microbiome. The highlight of the program was awarding the Jack Oram Award to the distinguished professor emeritus G.S. Getz from the University of Chicago. The tenth HDL Workshop will be held on May 2020 in Chicago and will continue the focus on intellectually stimulating presentations by established and emerging investigators on novel roles of HDL in cardiovascular and noncardiovascular health and disease states.

Epigenetic programming at the Mogat1 locus may link neonatal overnutrition with long-term hepatic steatosis and insulin resistance.

Postnatal overfeeding increases the risk of chronic diseases later in life, including obesity, insulin resistance, hepatic steatosis, and type 2 diabetes. Epigenetic mechanisms might underlie the long-lasting effects associated with early nutrition. Here we aimed to explore the molecular pathways involved in early development of insulin resistance and hepatic steatosis, and we examined the potential contribution of DNA methylation and histone modifications to long-term programming of metabolic disease. We used a well-characterized mouse model of neonatal overfeeding and early adiposity by litter size reduction. Neonatal overfeeding led to hepatic insulin resistance very early in life that persisted throughout adulthood despite normalizing food intake. Up-regulation of monoacylglycerol O-acyltransferase ( Mogat) 1 conceivably mediates hepatic steatosis and insulin resistance through increasing intracellular diacylglycerol content. Early and sustained deregulation of Mogat1 was associated with a combination of histone modifications that might favor Mogat1 expression. In sum, postnatal overfeeding causes extremely rapid derangements of hepatic insulin sensitivity that remain relatively stable until adulthood. Epigenetic mechanisms, particularly histone modifications, could contribute to such long-lasting effects. Our data suggest that targeting hepatic monoacylglycerol acyltransferase activity during early life might provide a novel strategy to improve hepatic insulin sensitivity and prevent late-onset insulin resistance and fatty liver disease.-Ramon-Krauel, M., Pentinat, T., Bloks, V. W., Cebrià, J., Ribo, S., Pérez-Wienese, R., Vilà, M., Palacios-Marin, I., Fernández-Pérez, A., Vallejo, M., Téllez, N., Rodríguez, M. À., Yanes, O., Lerin, C., Díaz, R., Plosch, T., Tietge, U. J. F., Jimenez-Chillaron, J. C. Epigenetic programming at the Mogat1 locus may link neonatal overnutrition with long-term hepatic steatosis and insulin resistance.

Inhibiting Cholesterol Absorption During Lactation Programs Future Intestinal Absorption of Cholesterol in Adult Mice.

In nematodes, the intestine senses and integrates early life dietary cues that lead to lifelong epigenetic adaptations to a perceived nutritional environment-it is not clear whether this process occurs in mammals. We aimed to establish a mouse model of reduced dietary cholesterol availability from maternal milk and investigate the consequences of decreased milk cholesterol availability, early in life, on the metabolism of cholesterol in adult mice. We blocked intestinal absorption of cholesterol in milk fed to newborn mice by supplementing the food of dams (for 3 weeks between birth and weaning) with ezetimibe, which is secreted into milk. Ezetimibe interacts with the intestinal cholesterol absorption transporter NPC1l1 to block cholesterol uptake into enterocytes. Characterization of these offspring at 24 weeks of age showed a 27% decrease in cholesterol absorption (P < .001) and reduced levels of Npc1l1 messenger RNA and protein, but not other cholesterol transporters, in the proximal small intestine. We observed increased histone H3K9me3 methylation at positions -423 to -607 of the proximal Npc1l1 promoter in small intestine tissues from 24-week-old offspring fed ezetimibe during lactation, compared with controls. These findings show that the early postnatal mammalian intestine functions as an environmental sensor of nutritional conditions, responding to conditions such as low cholesterol levels by epigenetic modifications of genes. Further studies are needed to determine how decreased sterol absorption for a defined period might activate epigenetic regulators; the findings of our study might have implications for human infant nutrition and understanding and preventing cardiometabolic disease.

Reverse Cholesterol Transport Is Increased in Germ-Free Mice-Brief Report.

OBJECTIVE: The intestinal microbiota is emerging as a clinically relevant modulator of atherosclerotic risk. Reverse cholesterol transport (RCT) is an atheroprotective metabolic pathway. How the microbiota impacts RCT has not been investigated. Therefore, the aim of this study was to characterize (cholesterol) metabolism and RCT in germ-free mice compared with conventional mice. APPROACH AND RESULTS: In chow-fed germ-free mice, plasma cholesterol was unchanged, whereas liver cholesterol content was higher (1.5-fold; P<0.05) than in conventional controls. Biliary secretion of cholesterol (2-fold; P<0.001) and bile acids (3-fold; P<0.001) was substantially increased in the germ-free model, whereas fecal neutral sterol excretion was unaltered, and fecal bile acid excretion was decreased (P<0.01). However, fecal bile acid profiles of germ-free mice were dominated by the presence of ß-muricholic acid (P<0.001), pointing toward a higher contribution of the alternative acidic pathway to total bile acid synthesis in these mice. As expected, secondary bile acids were absent in the germ-free model. In vivo macrophage-to-feces RCT was increased >2-fold (P<0.01) in the absence of intestinal bacteria. CONCLUSIONS: These data demonstrate that the absence of the intestinal microbiota stimulates RCT >2-fold. Thereby, our results support the importance of intestinal bacteria for metabolic regulation and indicate that specific targeting of the microbiota bears therapeutic potential to prevent and treat cardiovascular disease.

Transintestinal and Biliary Cholesterol Secretion Both Contribute to Macrophage Reverse Cholesterol Transport in Rats-Brief Report.

OBJECTIVE: Reverse cholesterol transport comprises efflux of cholesterol from macrophages and its subsequent removal from the body with the feces and thereby protects against formation of atherosclerotic plaques. Because of lack of suitable animal models that allow for evaluation of the respective contributions of biliary cholesterol secretion and transintestinal cholesterol excretion (TICE) to macrophage reverse cholesterol transport under physiological conditions, the relative importance of both pathways in this process has remained controversial. APPROACH AND RESULTS: To separate cholesterol traffic via the biliary route from TICE, bile flow was mutually diverted between rats, continuously, for 3 days. Groups of 2 weight-matched rats were designated as a pair, and both rats were equipped with cannulas in the bile duct and duodenum. Bile from rat 1 was diverted to the duodenum of rat 2, whereas bile from rat 2 was rerouted to the duodenum of rat 1. Next, rat 1 was injected with [3H]cholesterol-loaded macrophages. [3H]Cholesterol secreted via the biliary route was consequently diverted to rat 2 and could thus be quantified from the feces of that rat. On the other hand, [3H]cholesterol tracer in the feces of rat 1 reflected macrophage-derived cholesterol excreted via TICE. Using this setup, we found that 63% of the label secreted with the fecal neutral sterols had travelled via the biliary route, whereas 37% was excreted via TICE. CONCLUSIONS: TICE and biliary cholesterol secretion contribute to macrophage reverse cholesterol transport in rats. The majority of macrophage-derived cholesterol is however excreted via the hepatobiliary route.

ABCA8 Regulates Cholesterol Efflux and High-Density Lipoprotein Cholesterol Levels.

OBJECTIVE: High-density lipoproteins (HDL) are considered to protect against atherosclerosis in part by facilitating the removal of cholesterol from peripheral tissues. However, factors regulating lipid efflux are incompletely understood. We previously identified a variant in adenosine triphosphate-binding cassette transporter A8 (ABCA8) in an individual with low HDL cholesterol (HDLc). Here, we investigate the role of ABCA8 in cholesterol efflux and in regulating HDLc levels. APPROACH AND RESULTS: We sequenced ABCA8 in individuals with low and high HDLc and identified, exclusively in low HDLc probands, 3 predicted deleterious heterozygous ABCA8 mutations (p.Pro609Arg [P609R], IVS17-2 A>G and p.Thr741Stop [T741X]). HDLc levels were lower in heterozygous mutation carriers compared with first-degree family controls (0.86±0.34 versus 1.17±0.26 mmol/L; P=0.005). HDLc levels were significantly decreased by 29% (P=0.01) in Abca8b-/- mice on a high-cholesterol diet compared with wild-type mice, whereas hepatic overexpression of human ABCA8 in mice resulted in significant increases in plasma HDLc and the first steps of macrophage-to-feces reverse cholesterol transport. Overexpression of wild-type but not mutant ABCA8 resulted in a significant increase (1.8-fold; P=0.01) of cholesterol efflux to apolipoprotein AI in vitro. ABCA8 colocalizes and interacts with adenosine triphosphate-binding cassette transporter A1 and further potentiates adenosine triphosphate-binding cassette transporter A1-mediated cholesterol efflux. CONCLUSIONS: ABCA8 facilitates cholesterol efflux and modulates HDLc levels in humans and mice.

HDL Cholesterol Efflux Does Not Predict Cardiovascular Risk in Hemodialysis Patients.

The cardioprotective effect of HDL is thought to be largely determined by its cholesterol efflux capacity, which was shown to inversely correlate with atherosclerotic cardiovascular disease in populations with normal kidney function. Patients with ESRD suffer an exceptionally high cardiovascular risk not fully explained by traditional risk factors. Here, in a post hoc analysis in 1147 patients with type 2 diabetes mellitus on hemodialysis who participated in the German Diabetes Dialysis Study (4D Study), we investigated whether the HDL cholesterol efflux capacity is predictive for cardiovascular risk. Efflux capacity was quantified by incubating human macrophage foam cells with apoB-depleted serum. During a median follow-up of 4.1 years, 423 patients reached the combined primary end point (composite of cardiac death, nonfatal myocardial infarction, and stroke), 410 patients experienced cardiac events, and 561 patients died. Notably, in Cox regression analyses, we found no association of efflux capacity with the combined primary end point (hazard ratio [HR], 0.96; 95% confidence interval [95% CI], 0.88 to 1.06; P=0.42), cardiac events (HR, 0.92; 95% CI, 0.83 to 1.02; P=0.11), or all-cause mortality (HR, 0.96; 95% CI, 0.88 to 1.05; P=0.39). In conclusion, HDL cholesterol efflux capacity is not a prognostic cardiovascular risk marker in this cohort of patients with diabetes on hemodialysis.