Jimmy F.P. Berbée

Niacin Increases HDL by Reducing Hepatic Expression and Plasma Levels of Cholesteryl Ester Transfer Protein in APOE*3Leiden.CETP Mice

Objective—Niacin potently decreases plasma triglycerides and LDL-cholesterol. In addition, niacin is the most potent HDL-cholesterol–increasing drug used in the clinic. In the present study, we aimed at elucidation of the mechanism underlying its HDL-raising effect. Methods and Results—In APOE*3Leiden transgenic mice expressing the human CETP transgene, niacin dose-dependently decreased plasma triglycerides (up to −77%, P<0.001) and total cholesterol (up to -66%, P<0.001). Concomitantly, niacin dose-dependently increased HDL-cholesterol (up to +87%, P<0.001), plasma apoAI (up to +72%, P<0.001), as well as the HDL particle size. In contrast, in APOE*3Leiden mice, not expressing CETP, niacin also decreased total cholesterol and triglycerides but did not increase HDL-cholesterol. In fact, in APOE*3Leiden.CETP mice, niacin dose-dependently decreased the hepatic expression of CETP (up to −88%; P<0.01) as well as plasma CETP mass (up to −45%, P<0.001) and CETP activity (up to −52%, P<0.001). Additionally, niacin dose-dependently decreased the clearance of apoAI from plasma and reduced the uptake of apoAI by the kidneys (up to −90%, P<0.01). Conclusion—Niacin markedly increases HDL-cholesterol in APOE*3Leiden.CETP mice by reducing CETP activity, as related to lower hepatic CETP expression and a reduced plasma (V)LDL pool, and increases HDL-apoAI by decreasing the clearance of apoAI from plasma.

Brown fat activation reduces hypercholesterolaemia and protects from atherosclerosis development

Brown adipose tissue (BAT) combusts high amounts of fatty acids, thereby lowering plasma triglyceride levels and reducing obesity. However, the precise role of BAT in plasma cholesterol metabolism and atherosclerosis development remains unclear. Here we show that BAT activation by β3-adrenergic receptor stimulation protects from atherosclerosis in hyperlipidemic APOE*3-Leiden.CETP mice, a well-established model for human-like lipoprotein metabolism that unlike hyperlipidemic Apoe−/− and Ldlr−/− mice expresses functional apoE and LDLR. BAT activation increases energy expenditure and decreases plasma triglyceride and cholesterol levels. Mechanistically, we demonstrate that BAT activation enhances the selective uptake of fatty acids from triglyceride-rich lipoproteins into BAT, subsequently accelerating the hepatic clearance of the cholesterol-enriched remnants. These effects depend on a functional hepatic apoE-LDLR clearance pathway as BAT activation in Apoe−/− and Ldlr−/− mice does not attenuate hypercholesterolaemia and atherosclerosis. We conclude that activation of BAT is a powerful therapeutic avenue to ameliorate hyperlipidaemia and protect from atherosclerosis.

Angptl4 Upregulates Cholesterol Synthesis in Liver via Inhibition of LPL- and HL-Dependent Hepatic Cholesterol Uptake

Background—Dysregulation of plasma lipoprotein levels may increase the risk for atherosclerosis. Recently, angiopoietin-like protein 4, also known as fasting-induced adipose factor Fiaf, was uncovered as a novel modulator of plasma lipoprotein metabolism. Here we take advantage of the fasting-dependent phenotype of Angptl4-transgenic (Angptl4-Tg) mice to better characterize the metabolic function of Angptl4. Methods and Results—In 24-hour fasted mice, Angptl4 overexpression increased plasma triglycerides (TG) by 24-fold, which was attributable to elevated VLDL-, IDL/LDL- and HDL-TG content. Angptl4 overexpression decreased post-heparin LPL activity by stimulating conversion of endothelial-bound LPL dimers to circulating LPL monomers. In fasted but not fed state, Angptl4 overexpression severely impaired LPL-dependent plasma TG and cholesteryl ester clearance and subsequent uptake of fatty acids and cholesterol into tissues. Consequently, hepatic cholesterol content was significantly decreased, leading to universal upregulation of cholesterol and fatty acid synthesis pathways and increased rate of cholesterol synthesis. Conclusions—The hypertriglyceridemic effect of Angptl4 is attributable to inhibition of LPL-dependent VLDL lipolysis by converting LPL dimers to monomers, and Angptl4 upregulates cholesterol synthesis in liver secondary to inhibition of LPL- and HL-dependent hepatic cholesterol uptake.

Interactions between inflammation and lipid metabolism: relevance for efficacy of anti-inflammatory drugs in the treatment of atherosclerosis.

Dyslipidemia and inflammation are well known causal risk factors the development of atherosclerosis. The interplay between lipid metabolism and inflammation at multiple levels in metabolic active tissues may exacerbate the development of atherosclerosis, and will be discussed in this review. Cholesterol, fatty acids and modified lipids can directly activate inflammatory pathways. In addition, circulating (modified) lipoproteins modulate the activity of leukocytes. Vice versa, proinflammatory signaling (i.e. cytokines) in pre-clinical models directly affects lipid metabolism. Whereas the main lipid-lowering drugs all have potent anti-inflammatory actions, the lipid-modulating actions of anti-inflammatory agents appear to be less straightforward. The latter have mainly been evaluated in pre-clinical models and in patients with chronic inflammatory diseases, which will be discussed. The clinical trials that are currently conducted to evaluate the efficacy of anti-inflammatory agents in the treatment of cardiovascular diseases may additionally reveal potential (beneficial) effects of these therapeutics on lipid metabolism in the general population at risk for CVD.

Apolipoproteins modulate the inflammatory response to lipopolysaccharide

An increasing body of evidence demonstrates a close interplay between lipoprotein metabolism and sepsis. Sepsis results in an increase of plasma triglycerides within VLDL as a consequence of an enhanced hepatic VLDL production and/or inhibited peripheral and hepatic VLDL clearance. In contrast, sepsis decreases plasma cholesterol within LDL and mainly HDL. The decrease in HDL is accompanied by a loss of mainly apoAI-containing particles, an almost total loss of apoCI, and an increase in apoE-containing HDL, as related to the effect of LPS on a wide range of apolipoproteins, plasma enzymes, lipid transfer factors, and receptors that are involved in HDL metabolism. Reciprocally, all lipoprotein classes have been shown to bind LPS and to attenuate the biological response to LPS in vitro and in rodents. Moreover, triglyceride-rich lipoproteins protect rodents against death from LPS and bacterial sepsis. Accumulating evidence indicates that apolipoproteins such as apoE and apoAI, and not the lipid moieties of the particles, may be responsible for these protective effects of lipoproteins. Therefore, to increase our understanding of the complex interaction between lipoprotein metabolism and sepsis, further studies that address the specific roles of apolipoproteins in sepsis are warranted.

ApoE plasma levels and risk of cardiovascular mortality in old age

Background The ɛ2, ɛ3, and ɛ4 alleles of the apolipoprotein E gene (APOE) encode three isoforms, apoE2, E3, and E4, respectively. The apoE isoforms circulate in different plasma concentrations, but plasma concentrations of the same isoform also differ between individuals. Whereas the isoforms have been associated with cardiovascular disease, the relation between plasma apoE levels and cardiovascular disease is unknown. Methods and Findings We assessed APOE genotypes, plasma levels of apoE, cardiovascular risk factors, and mortality in a population-based sample of 546 individuals aged 85 y who participated in the Leiden 85-plus Study and were prospectively followed for specific causes of death for 5 y. Participants in the highest tertile of apoE levels suffered a twofold-increased risk of cardiovascular mortality (hazard ratio compared to lowest tertile, 2.08; 95% confidence interval [CI], 1.30 to 3.33). Among the 324 participants with the ɛ3ɛ3 genotype, the hazard from cardiovascular disease was threefold increased (highest versus lowest tertile 3.01; 95% CI 1.60 to 5.66), with similar estimates for men and women. Other causes of death were not increased significantly. Plasma levels of apoE in ɛ3ɛ3 participants were positively correlated with total cholesterol ( p < 0.001), low-density lipoprotein cholesterol ( p < 0.001) and triglycerides ( p < 0.001) and negatively with high-density lipoprotein cholesterol levels ( p = 0.010). Adjustment for plasma lipids did not change the hazard ratios, whereas interaction was absent. The risk associated with high levels of apoE, however, was strongest in participants from the lowest tertile of C-reactive protein (CRP) levels and absent in those from the highest tertile ( p interaction < 0.001). Among participants from the lowest tertile of CRP levels, those with a high apoE levels had a significantly steeper increase in CRP than those with low apoE levels ( p = 0.020). Similar cardiovascular mortality risks as in ɛ3ɛ3 participants were found in ɛ2 and ɛ4 carriers. Conclusions In old age, high plasma apoE levels precede an increase of circulating CRP and strongly associates with cardiovascular mortality, independent of APOE genotype and plasma lipids.

Apolipoprotein C-I Is Crucially Involved in Lipopolysaccharide-Induced Atherosclerosis Development in Apolipoprotein E–Knockout Mice

Background— Lipopolysaccharide (LPS), which is released from Gram-negative bacteria on multiplication or lysis, aggravates atherosclerosis in humans and rodents by inducing inflammation via toll-like receptors. Because apolipoprotein C-I (apoCI) enhances the LPS-induced inflammatory response in macrophages in vitro and in mice, we investigated the effect of endogenous apoCI expression on LPS-induced atherosclerosis in mice. Methods and Results— Twelve-week-old apoe−/−apoc1−/− and apoe−/−apoc1+/+ mice received weekly intraperitoneal injections of LPS (50 &mgr;g) or vehicle for a period of 10 weeks, and atherosclerosis development was assessed in the aortic root. LPS administration did not affect atherosclerotic lesion area in apoe−/−apoc1−/− mice but increased it in apoe−/−apoc1+/+ mice. In fact, apoCI expression increased the LPS-induced atherosclerotic lesion area by 60% (P<0.05), concomitant with an increase in LPS-induced plasma levels of fibrinogen and E-selectin. This indicated that apoCI increased the LPS-induced inflammatory state, both systemically (ie, fibrinogen) and at the level of the vessel wall (ie, E-selectin). In addition, both macrophage-derived apoCI and HDL-associated apoCI increased the LPS-induced tumor necrosis factor-&agr; response by macrophages in vitro. Conclusions— We conclude that apoCI is crucially involved in LPS-induced atherosclerosis in apoe−/− mice, which mainly relates to an increased inflammatory response toward LPS. We anticipate that apoCI plasma levels contribute to accelerated atherosclerosis development in individuals who have chronic infection.

Chronic helminth infection and helminth-derived egg antigens promote adipose tissue M2 macrophages and improve insulin sensitivity in obese mice.

Chronic low‐grade inflammation associated with obesity contributes to insulin resistance and type 2 diabetes. Helminth parasites are the strongest natural inducers of type 2 immune responses, and short‐lived infection with rodent nematodes was reported to improve glucose tolerance in obese mice. Here, we investigated the effects of chronic infection (12 weeks) with Schistosoma mansoni, a helminth that infects millions of humans worldwide, on whole‐body metabolic homeostasis and white adipose tissue (WAT) immune cell composition in high‐fat diet‐induced obese C57BL/6 male mice. Our data indicate that chronic helminth infection reduced body weight gain (‐62%), fat mass gain (‐89%), and adipocyte size; lowered whole‐body insulin resistance (‐23%) and glucose intolerance (‐16%); and improved peripheral glucose uptake (+25%) and WAT insulin sensitivity. Analysis of immune cell composition by flow cytometry and quantitative PCR (qPCR) revealed that S. mansoni promoted strong increases in WAT eosinophils and alternatively activated (M2) macrophages. Importantly, injections with S. mansonir‐soluble egg antigens (SEA) recapitulated the beneficial effect of parasite infection on whole‐body metabolic homeostasis and induced type 2 immune responses in WAT and liver. Taken together, we provide novel data suggesting that chronic helminth infection and helminth‐derived molecules protect against metabolic disorders by promoting a T helper 2 (Th2) response, eosinophilia, and WAT M2 polarization.—Hussaarts, L., García‐Tardón, N., van Beek, L., Heemskerk, M. M., Haeberlein, S., van der Zon, G. C., Ozir‐Fazalalikhan, A., Berbée, J. F. P., Willems van Dijk, K., van Harmelen, V., Yazdanbakhsh, M., Guigas, B. Chronic helminth infection and helminth‐derived egg antigens promote adipose tissue M2 macrophages and improve insulin sensitivity in obese mice. FASEB J. 29, 3027‐3039 (2015). www.fasebj.org

Brown adipose tissue takes up plasma triglycerides mostly after lipolysis

Brown adipose tissue (BAT) produces heat by burning TGs that are stored within intracellular lipid droplets and need to be replenished by the uptake of TG-derived FA from plasma. It is currently unclear whether BAT takes up FA via uptake of TG-rich lipoproteins (TRLs), after lipolysis-mediated liberation of FA, or via a combination of both. Therefore, we generated glycerol tri[3H]oleate and [14C]cholesteryl oleate double-labeled TRL-mimicking particles with an average diameter of 45, 80, and 150 nm (representing small VLDL to chylomicrons) and injected these intravenously into male C57Bl/6J mice. At room temperature (21°C), the uptake of 3H-activity by BAT, expressed per gram of tissue, was much higher than the uptake of 14C-activity, irrespective of particle size, indicating lipolysis-mediated uptake of TG-derived FA rather than whole particle uptake. Cold exposure (7°C) increased the uptake of FA derived from the differently sized particles by BAT, while retaining the selectivity for uptake of FA over cholesteryl ester (CE). At thermoneutrality (28°C), total FA uptake by BAT was attenuated, but the specificity of uptake of FA over CE was again largely retained. Altogether, we conclude that, in our model, BAT takes up plasma TG preferentially by means of lipolysis-mediated uptake of FA.

Apolipoprotein CI stimulates the response to lipopolysaccharide and reduces mortality in Gram-negative sepsis

Gram‐negative sepsis is a major death cause in intensive care units. Accumulating evidence indicates the protective role of plasma lipoproteins such as high‐density lipoprotein (HDL) in sepsis. It has recently been shown that septic HDL is almost depleted from apolipoprotein CI (apoCI), suggesting that apoCI may be a protective factor in sepsis. Sequence analysis revealed that apoCI possesses a highly conserved consensus KVKEKLK binding motif for lipopolysaccharide (LPS), an outer‐membrane component of Gram‐negative bacteria. Through avid binding to LPS involving this motif, apoCI improved the presentation of LPS to macrophages in vitro and in mice, thereby stimulating the inflammatory response to LPS. Moreover, apoCI dose‐dependently increased the early inflammatory response to Klebsiella pneumoniae‐induced pneumonia, reduced the number of circulating bacteria, and protected mice against fatal sepsis. Our data support the hypothesis that apoCI is a physiological protector against infection by enhancing the early inflammatory response to LPS and suggest that timely increase of apoCI levels could be used to efficiently prevent and treat early sepsis.—Berbée, J. F. P., van der Hoogt, C. C., Kleemann, R., Schippers, E. F., Kitchens, R. L., van Dissel, J. T., Bakker‐Woudenberg, I. A. J. M., Havekes, L. M., Rensen, P. C. N. Apolipoprotein CI stimulates the response to lipopolysaccharide and reduces mortality in Gram‐negative sepsis. FASEB J. 20, E1560 –E1569 (2006)