Lipotoxic effects of triacylglycerols in J774.2 macrophages

Exposure of cigarette smoke condensate activates NLRP3 inflammasome in THP-1 cells in a stage-specific manner: An underlying role of innate immunity in atherosclerosis

BACKGROUND

Smoking is known to affect all the phases of atherosclerosis, thus is considered as an independent and major risk factor. The underlying mechanism responsible for the atherogenic effects of smoking is still uncertain and a major concern. Recent evidence implicates NLRP3 inflammasome, an innate immunity component in the pathogenesis of atherosclerosis. Therefore, we hypothesized that NLRP3 inflammasome may be an associated pathway between smoking and atherosclerosis.

METHODS AND RESULTS

Differentiation in monocytes, macrophages and foam cells are the key stages in atherosclerotic plaque development, best mimicked by THP-1 cells. Therefore, to determine whether cigarette smoke condensate (CSC) could induce differentiation of THP-1 monocytes into macrophages, morphological changes and the expression levels of the inflammatory surface markers, i.e. CD11b, CD14 and CD36 were analyzed. The results showed that CD14 and CD36 levels were significantly increased in CSC-treated THP-1 monocytes. Further, we investigated the effect of CSC exposure on the status of NLRP3 inflammasome markers, i.e. NLRP3, pro-caspase-1, caspase-1, pro-IL-18, pro-IL-1β, IL-1β and IL-18 in a stage-specific manner. For this, THP-1 monocytes, PMA-differentiated macrophages and oxidized-low density lipoprotein (ox-LDL)-induced macrophage foam cells were exposed to 10 μg/ml of CSC for 6 h. CSC exposure significantly upregulated the expression of NLRP3 inflammasome in CSC-treated cells at both transcriptional and translational levels. Moreover, downstream pro-cytokines, i.e. IL-1β and IL-18 levels were also significantly increased in culture supernatants of CSC-exposed cells.

CONCLUSION

These observations suggest that CSC exposure may activate NLRP3 inflammasome in a stage-specific manner and may promote initiation and progression of atherosclerosis.

Caspase-2 mediates triglyceride (TG)-induced macrophage cell death

Triglyceride (TG) accumulation causes macrophage cell death, which affects the development of atherosclerosis. Here, we examined whether caspase-2 is implicated in TG-induced macrophage cell death. We found that caspase-2 activity is increased in TG-treated THP-1 macrophages, and that inhibition of caspase-2 activity drastically inhibits TG-induced cell death. We previously reported that TG-induced macrophage cell death is triggered by caspase-1, and thus investigated the relationship between caspase-2 and caspase-1 in TG-induced macrophage cell death. Inhibition of caspase-2 activity decreased caspase-1 activity in TG-treated macrophages. However, caspase-1 inhibition did not affect caspase-2 activity, suggesting that caspase-2 is upstream of caspase-1. Furthermore, we found that TG induces activation of caspase-3, -7, -8, and -9, as well as cleavage of PARP. Inhibition of caspase-2 and -1 decreased TG-induced caspase-3, -7, -8, and -9 activation and PARP cleavage. Taken together, these results suggest that TG-induced macrophage cell death is mediated via the caspase-2/caspase-1/apoptotic caspases/PARP pathways.

Supplementation with linoleic acid-rich soybean oil stimulates macrophage foam cell formation via increased oxidative stress and diacylglycerol acyltransferase1-mediated triglyceride biosynthesis

During the last decades there has been a staggering rise in human consumption of soybean oil (SO) and its major polyunsaturated fatty acid linoleic acid (LA). The role of SO or LA in cardiovascular diseases is highly controversial, and their impact on macrophage foam cell formation, the hallmark of early atherogenesis, is unclear. To investigate the effects of high SO or LA intake on macrophage lipid metabolism and the related mechanisms of action, C57BL/6 mice were orally supplemented with increasing levels of SO-based emulsion or equivalent levels of purified LA for 1 month, followed by analyses of lipid accumulation and peroxidation in aortas, serum and in peritoneal macrophages (MPM) of the mice. Lipid peroxidation and triglyceride mass in aortas from SO or LA supplemented mice were dose-dependently and significantly increased. In MPM from SO or LA supplemented mice, lipid peroxides were significantly increased and a marked accumulation of cellular triglycerides was found in accordance with enhanced triglyceride biosynthesis rate and overexpression of diacylglycerol acyltransferase1 (DGAT1), the key enzyme in triglyceride biosynthesis. In cultured J774A.1 macrophages treated with SO or LA, triglyceride accumulated via increased oxidative stress and a p38 mitogen-activated protein kinase (MAPK)-mediated overexpression of DGAT1. Accordingly, anti-oxidants (pomegranate polyphenols), inhibition of p38 MAPK (by SB202190) or DGAT1 (by oleanolic acid), all significantly attenuated SO or LA-induced macrophage triglyceride accumulation. These findings reveal novel mechanisms by which supplementation with SO or LA stimulate macrophage foam cell formation, suggesting a pro-atherogenic role for overconsumption of SO or LA. © 2016 BioFactors, 43(1):100-116, 2017.

Pathogenicity of Mycobacterium tuberculosis is expressed by regulating metabolic thresholds of the host macrophage

The success of Mycobacterium tuberculosis as a pathogen derives from its facile adaptation to the intracellular milieu of human macrophages. To explore this process, we asked whether adaptation also required interference with the metabolic machinery of the host cell. Temporal profiling of the metabolic flux, in cells infected with differently virulent mycobacterial strains, confirmed that this was indeed the case. Subsequent analysis identified the core subset of host reactions that were targeted. It also elucidated that the goal of regulation was to integrate pathways facilitating macrophage survival, with those promoting mycobacterial sustenance. Intriguingly, this synthesis then provided an axis where both host- and pathogen-derived factors converged to define determinants of pathogenicity. Consequently, whereas the requirement for macrophage survival sensitized TB susceptibility to the glycemic status of the individual, mediation by pathogen ensured that the virulence properties of the infecting strain also contributed towards the resulting pathology.

Mycobacterium tuberculosis (Mtb) is a highly successful human pathogen, representing the leading bacterial cause of death worldwide. Mtb infects macrophages and it adapts to the hostile intracellular milieu of this cell by exploiting the plasticity of its central carbon metabolism machinery. While several studies have detailed the bacterial adaptations that accompany infection, it is still unclear whether this process also involves engagement with host metabolic pathways. We therefore profiled the kinetic flux of host cell metabolites in macrophages that were infected with differently virulent Mtb strains. Interestingly, we found that Mtb pathogenicity was indeed intimately linked to its capacity to regulate host cell metabolism. A unique subset of host pathways was targeted so as to integrate the glycolytic threshold governing macrophage viability with mechanisms ensuring intracellular bacterial survival. Perturbation of macrophage glycolytic flux was enforced through pathogen-induced enhancement in glucose uptake, which in turn was also influenced by the extracellular glucose concentration. This observation rationalizes the increased susceptibility of diabetic individuals to TB infection Interestingly, Mtb strains also differed in their capacities to stimulate macrophage glucose uptake. Consequently, the resulting pathology is likely dictated both by the individual's glycemic status, and the nature of the infecting strain.

Triglyceride-induced macrophage cell death is triggered by caspase-1

Triglyceride (TG) induces macrophage cell death which contributes to the development of atherosclerosis. We confirmed that exogenous TG accumulates in human THP-1 macrophages and causes cell death. TG treated THP-1 macrophages exhibited no change in tumor necrosis factor (TNF)-α, interleukin (IL)-18, macrophage inflammatory protein (MIP)-1α, and IL-1R1 receptor mRNA expression. However, there was a marked decrease in IL-1β mRNA expression but an increase in IL-1β protein secretion. Decreased expression of IL-1β mRNA and increased secretion of IL-1β protein was not the direct cause of cell death. Until now, TG was assumed to induce necrotic cell death in macrophages. Since caspase-1 is known to be involved in activation and secretion of IL-1β protein and pyroptotic cell death, next we determined whether caspase-1 is associated with TG-induced macrophage cell death. We found an increase in caspase-1 activity in TG-treated THP-1 macrophages and inhibition of caspase-1 activity using a specific inhibitor partially rescued cell death. These results suggest activation of the pyroptotic pathway by TG. This is the first report implicating the activation of caspase-1 and the triggering of the pyroptosis pathway in TG-induced macrophage cell death.

Short-chain PEG molecules strongly bound to magnetic nanoparticle for MRI long circulating agents

This study developed an approach for the synthesis of magnetic nanoparticles coated with three different polyethylene glycol (PEG)-derived molecules. The influence of the coating on different properties of the nanoparticles was studied. Magnetite nanoparticles (7 and 12 nm in diameter) were obtained via thermal decomposition of a coordination complex as an iron precursor to ensure nanoparticle homogeneity in size and shape. Particles were first coated with meso-2,3-dimercaptosuccinic acid by a ligand exchange process to remove oleic acid, followed by modification with three distinct short-chain PEG polymers, which were covalently bound to the nanoparticle surface via 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride activation of the carboxylic acids. In all cases, colloidal suspensions had hydrodynamic sizes <100 nm and low surface charge, demonstrating the effect of PEG coating on the aggregation properties and steric stabilization of the magnetic nanoparticles. The internalization and biocompatibility of these materials in the HeLa human cervical carcinoma cell line were tested. Cells preincubated with PEG-coated iron nanoparticles were visualized outside the cells, and their biocompatibility at high Fe concentrations was demonstrated using a standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Finally, relaxivity parameters (r1 and r2) were used to evaluate the efficiency of suspensions as magnetic resonance imaging contrast agents; the r2 value was similar to that for Resovist and up to four times higher than that for Sinerem, probably due to the larger nanoparticle size. The time of residence in blood of the nanoparticles measured from the relaxivity values, and the Fe content in blood was doubled for rats and rabbits due to the PEG on the nanoparticle surface. The results suggest that this PEGylation strategy for large magnetic nanoparticles (>10nm) holds promise for biomedical applications.

Increased expression of interleukin-1β in triglyceride-induced macrophage cell death is mediated by p38 MAP kinase

Triglycerides (TG) are implicated in the development of atherosclerosis through formation of foam cells and induction of macrophage cell death. In this study, we report that addition of exogenous TG induced cell death in phorbol 12-myristate 13-acetate-differentiated THP-1 human macrophages. TG treatment induced a dramatic decrease in interleukin-1β (IL-1β) mRNA expression in a dose- and time-dependent manner. The expression of granulocyte macrophage colony-stimulating factor and platelet endothelial cell adhesion molecule remained unchanged. To identify signaling pathways involved in TG-induced downregulation of IL-1β, we added p38 MAPK, protein kinase C (PKC) or c-Raf1 specific inhibitors. We found that inhibition of p38 MAPK alleviated the TG-induced downregulation of IL-1β, whereas inhibition of PKC and c-Raf1 had no effect. This is the first report showing decreased IL-1β expression during TG-induced cell death in a human macrophage line. Our results suggest that downregulation of IL-1β expression by TG-treated macrophages may play a role during atherogenesis.

Nitric oxide, can it be only good? Increasing the antioxidant properties of nitric oxide in hepatocytes by YC-1 compound

The aim of the study was to evaluate the effect of Nitric oxide (NO) on redox changes and fat accumulation in hepatocytes. AML-12 hepatocytes were exposed to the NO donor Diethylenetriamine-NONOate (DETA-NO). DETA-NO led to a dose- and time-dependent increase in lipid accumulation in the cells, measured by Nile red fluorescence. Exposure of the cells to 1mM DETA-NO for 24h increased reactive oxygen species production, mainly peroxides. At the same time, NO induced elevation of reduced glutathione (GSH) and a mild activation of the antioxidant transcription factors Hypoxia-inducible factor 1α (HIF1α) and NF-E2 related factor 2 (Nrf-2). We used 100 μM YC-1 to inhibit HIF1α activity and induce activation of soluble Guanylate Cyclase (sGC). YC-1 alone did not affect fat accumulation, and only moderately increased the expression of Nrf-2-targeted genes Heme oxygenase 1 (Hmox1), NAD(P)H dehydrogenase (quinone 1) (Nqo1) and Glutathione S-transferase α1 (Gstα1). However, YC-1 abolished the negative effect of NO on fat accumulation when administered together. Strikingly, YC-1 potentiated the effect of NO on Nrf-2 activation, thus increasing dramatically the antioxidant properties of NO. Moreover, YC-1 intensified the effect of NO on the expression of peroxisome-proliferator-activated receptor-gamma co-activator 1α (PGC1α) and mitochondrial biogenesis markers. This study suggests that YC-1 may shift the deleterious effects of NO into the beneficial ones, and may improve the antioxidant properties of NO.

Unsaturated fatty acids induce mesenchymal stem cells to increase secretion of angiogenic mediators

Mesenchymal stem cells (MSC) represent emerging cell-based therapies for diabetes and associated complications. Ongoing clinical trials are using exogenous MSC to treat type 1 and 2 diabetes, cardiovascular disease and non-healing wounds due to diabetes. The majority of these trials are aimed at exploiting the ability of these multipotent mesenchymal stromal cells to release soluble mediators that reduce inflammation and promote both angiogenesis and cell survival at sites of tissue damage. Growing evidence suggests that MSC secretion of soluble factors is dependent on tissue microenvironment. Despite the contribution of fatty acids to the metabolic environment of type 2 diabetes, almost nothing is known about their effects on MSC secretion of growth factors and cytokines. In this study, human bone marrow-derived MSC were exposed to linoleic acid, an omega-6 polyunsaturated fatty acid, or oleic acid, a monounsaturated fatty acid, for seven days in the presence of 5.38 mM glucose. Outcomes measured included MSC proliferation, gene expression, protein secretion and chemotaxis. Linoleic and oleic acids inhibited MSC proliferation and altered MSC expression and secretion of known mediators of angiogenesis. Both unsaturated fatty acids induced MSC to increase secretion of interleukin-6, VEGF and nitric oxide. In addition, linoleic acid but not oleic acid induced MSC to increase production of interleukin-8. Collectively these data suggest that exposure to fatty acids may have functional consequences for MSC therapy. Fatty acids may affect MSC engraftment to injured tissue and MSC secretion of cytokines and growth factors that regulate local cellular responses to injury.

Fatty acids-stress attenuates gluconeogenesis induction and glucose production in primary hepatocytes

BACKGROUND

Hepatic gluconeogenesis tightly controls blood glucose levels in healthy individuals, yet disorders of fatty acids (FAs) oxidation are characterized by hypoglycemia. We studied the ability of free-FAs to directly inhibit gluconeogenesis, as a novel mechanism that elucidates the hypoglycemic effect of FAs oxidation defects.

METHODS

Primary rat hepatocytes were pre-treated with FAs prior to gluconeogenic stimuli with glucagon or dexamethasone and cAMP.

RESULTS

Pre-treatment with 1 mM FAs (mixture of 2:1 oleate:palmitate) for 1 hour prior to gluconeogenic induction, significantly decreases the induced expression of the gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6pase) as well as the induced glucose production by the cells. The inhibitory effect of FAs upon gluconeogenesis is abolished when pre-treatment is elongated to 18 hours, allowing clearance of FAs into triglycerides by the cells. Replacement of palmitate with the non-metabolic fatty acid 2-bromopalmitate inhibits esterification of FAs into triglycerides. Accordingly, the increased exposure to unesterified-FAs allows their inhibitory effect to be extended even when pre-treatment is elongated to 18 hours. Similar changes were caused by FAs to the induction of peroxisome-proliferator-activated receptor-γ coactivator 1α (PGC1α) expression, indicating this transcriptional coactivator as the mediating link of the effect. This inhibitory effect of FAs upon gluconeogenic induction is shown to involve reduced activation of cAMP response element-binding (CREB) transcription factor.

CONCLUSIONS

The present results demonstrate that free-FAs directly inhibit the induced gluconeogenic response in hepatocytes. Hence, high levels of free-FAs may attenuate hepatic gluconeogenesis, and liver glucose output.

Cilostazol inhibits accumulation of triglyceride in aorta and platelet aggregation in cholesterol-fed rabbits

Cilostazol is clinically used for the treatment of ischemic symptoms in patients with chronic peripheral arterial obstruction and for the secondary prevention of brain infarction. Recently, it has been reported that cilostazol has preventive effects on atherogenesis and decreased serum triglyceride in rodent models. There are, however, few reports on the evaluation of cilostazol using atherosclerotic rabbits, which have similar lipid metabolism to humans, and are used for investigating the lipid content in aorta and platelet aggregation under conditions of hyperlipidemia. Therefore, we evaluated the effect of cilostazol on the atherosclerosis and platelet aggregation in rabbits fed a normal diet or a cholesterol-containing diet supplemented with or without cilostazol. We evaluated the effects of cilostazol on the atherogenesis by measuring serum and aortic lipid content, and the lesion area after a 10-week treatment and the effect on platelet aggregation after 1- and 10-week treatment. From the lipid analyses, cilostazol significantly reduced the total cholesterol, triglyceride and phospholipids in serum, and moreover, the triglyceride content in the atherosclerotic aorta. Cilostazol significantly reduced the intimal atherosclerotic area. Platelet aggregation was enhanced in cholesterol-fed rabbits. Cilostazol significantly inhibited the platelet aggregation in rabbits fed both a normal diet and a high cholesterol diet. Cilostazol showed anti-atherosclerotic and anti-platelet effects in cholesterol-fed rabbits possibly due to the improvement of lipid metabolism and the attenuation of platelet activation. The results suggest that cilostazol is useful for prevention and treatment of atherothrombotic diseases with the lipid abnormalities.

Nanoclusters of iron oxide: effect of core composition on structure, biocompatibility, and cell labeling efficacy

Inorganic nanocrystals have a variety of applications in medicine. They may serve as contrast agents, therapeutics, and for in vitro diagnostics. Frequently, the synthesis route yields hydrophobically capped nanocrystals, which necessitates their subsequent coating to render a water-soluble and biocompatible probe. Biocompatibility is crucial for cellular imaging applications, which require large quantities of diagnostically active nanoparticles to be loaded into cells. We have previously reported the design and synthesis of a fluorescent and magnetic resonance imaging-detectable core-shell nanoparticle that encapsulates hydrophobically coated iron oxide nanocrystals. The core of soybean oil and iron oxide is covered by a shell mixture of phospholipids, some of which contained polyethylene glycol. Despite the biocompatibility of these components, we hypothesize that we can improve this formulation with respect to in vitro toxicity. To this aim, we measured the effect of six different core compositions on nanoparticle structure, cell labeling efficacy, and cell viability, as well as cell tracking potential. We methodically investigated the causes of toxicity and conclude that, even when combining biocompatible materials, the resulting formulation is not guaranteed to be biocompatible.

Effects of diabetes and/or hypercholesterolemia on skin development of rat fetuses

OBJECTIVE

To investigate the effects of diabetes and/or hypercholesterolemia on skin development during in utero life at 15, 17 & 19 days old.

METHODS

Sixty pregnant female albino Wistar rats were arranged into three groups: control, diabetic (single i.p. 60 mg streptozotocin/kg B.wt) and hypercholesterolemic (diet supplement 3% cholesterol 6 week prior to conception and throughout gestation). Pregnant rats were sacrificed at 15, 17 & 19 days prenatal). Vibrissae skin biopsies were removed and allowed for scanning (SEM), light, and transmission electron microscopic (TEM) investigation. Also, DNA fragmentation and sodium dodecyl polyacrylamides gel electrophoresis (SDS-PAGE) were carried out.

RESULTS

Scanning electron microscopic observations revealed retarded hair follicle growth and deformations of their pattern structure. At light microscopic level, skin exhibited decreased epidermal cornification, as well as degeneration of hair follicles in fetuses of both diabetic and hypercholesterolemic groups. Transmission electron microscopy revealed abundant vacuolar spaces in the epidermis. Degenerative phases become more abundant in keratinocytes as well as in stratum germinativum cells. Fetal skin possessed altered protein expression and missing bands as well as separation of genomic DNA to several degraded bands in skin of 15-, 17-, and 19-day-old, maternally diabetic and/or hypercholesterolemic fetuses.

CONCLUSION

These findings showed that maternal diabetes and/or hypercholesterolemia increased average deformation of hair follicles, vacuolation, and degeneration of epidermal cell layers. The observed findings resulted from altered protein expression and increased DNA fragmentation, which, in turn, disrupt epidermal cell differentiation.

Phospholipase A2 mediates apolipoprotein-independent uptake of chylomicron remnant-like particles by human macrophages

Apolipoprotein E-receptor-mediated pathways are the main routes by which macrophages take up chylomicron remnants, but uptake may also be mediated by receptor-independent routes. To investigate these mechanisms, triacylglycerol (TG) accumulation induced by apolipoprotein-free chylomicron remnant-like particles (CRLPw/o) in human monocyte-derived macrophages was evaluated. Macrophage TG content increased about 5-fold after incubation with CRLPw/o, and this effect was not reduced by the inhibition of phagocytosis, macropinocytosis, apolipoprotein E function, or proteoglycan bridging. The role of lipases, including lipoprotein lipase, cholesteryl ester hydrolase, and secretory (sPLA2) and cytosolic phospholipase A2, was studied using [³H]TG-labelled CRLPw/o. Total cell radioactivity after incubation with [³H]TG CRLPw/o was reduced by 15–30% by inhibitors of lipoprotein lipase and cholesteryl ester hydrolase and by about 45% by inhibitors of sPLA2 and cytosolic PLA₂ . These results suggest that macrophage lipolytic enzymes mediate the internalization of postprandial TG-rich lipoproteins and that sPLA₂ and cytosolic PLA2, play a more important role than extracellular lipoprotein lipase-mediated TG hydrolysis.

Paraoxonase 1 protects macrophages from atherogenicity of a specific triglyceride isolated from human carotid lesion

Human atherosclerotic lesions contain oxidized lipids that facilitate further oxidation of macrophages, LDLs, and oxidative stress (OS)-sensitive markers and inhibit the antiatherogenic enzyme paraoxonase 1 (PON1). Our aim was to isolate and identify the oxidizing agent in a human atherosclerotic lesion lipid extract (LLE) and to explore the mechanisms of oxidation and of PON1's effect on the oxidizing agent. Of the five main fractions separated from the LLE, only fraction 2 (F2) promoted macrophage reactive oxygen species (ROS) production via a mechanism requiring mitochondrial involvement, whereas the NADPH oxidase system was not involved. Incubation of F2 with PON1 abridged the former's peroxide value and reduced its capacity to oxidize OS markers. The active agent was a triglyceride composed of palmitic, oleic, and linoleic acids, with 0.3% of its linoleic moiety in oxidized form. Incubation of either F2 or an identical synthetic triglyceride with PON1 reduced their ability to oxidize macrophages, without affecting cellular accumulation of triglycerides. We conclude that macrophage ROS production by LLE occurs in the presence of a specific triglyceride and requires mitochondrial involvement. Lipid peroxide in the triglyceride can also facilitate lipid autoxidation. Both atherogenic pathways are suppressed by PON1, which acts as an antiatherogenic element.

Insulin increases macrophage triglyceride accumulation under diabetic conditions through the down regulation of hormone sensitive lipase and adipose triglyceride lipase

Diabetes mellitus (DM) is a major risk factor for the development of atherosclerosis, and high-serum levels of insulin are strongly associated with type 2 DM. Atherosclerosis is characterized by lipid-laden macrophage foam cell formations, which contain substantial amount of cholesterol and triglycerides (TG). This study analyzed for the first time, the effects of insulin on TG metabolism in macrophages under normal and diabetic conditions. Mouse peritoneal macrophages from C57BL6 mice were cultured under normal (5 mM) or high (diabetic condition, 25 mM) glucose concentration, with or without insulin, followed by the assessment of TGs metabolism in these cells. Under diabetic condition, insulin increased TG accumulation in macrophages by 100%, decreased cellular TG degradation by 21%, and increased C-reactive protein levels in macrophages by 83%. Insulin decreased hormone-sensitive lipase mRNA and protein expression by 28 and 60%, respectively, and adipose TG lipase (ATGL) protein expression by 36%, with no significant reduction in ATGL mRNA levels. The inhibition of insulin-mediated phosphorylation, and the addition of cyclic adenosine 3'5'-monoposphate, abolished the insulin-mediated inhibition of TGs degradation in cells. Insulin increases macrophage TGs accumulation only under diabetic conditions, suggesting that impaired glycemic control in diabetic patients treated with insulin may contribute to foam cell formations and enhanced inflammation in macrophages.

Metabolic and neurologic consequences of chronic lopinavir/ritonavir administration to C57BL/6 mice

It is well established that HIV antiretroviral drugs, particularly protease inhibitors, frequently elicit a metabolic syndrome that may include hyperlipidemia, lipodystrophy, and insulin resistance. Metabolic dysfunction in non-HIV-infected subjects has been repeatedly associated with cognitive impairment in epidemiological and experimental studies, but it is not yet understood if antiretroviral therapy-induced metabolic syndrome might contribute to HIV-associated neurologic decline. To determine if protease inhibitor-induced metabolic dysfunction in mice is accompanied by adverse neurologic effects, C57BL/6 mice were given combined lopinavir/ritonavir (50/12.5-200/50 mg/kg) daily for 3 weeks. Data show that lopinavir/ritonavir administration caused significant metabolic derangement, including alterations in body weight and fat mass, as well as dose-dependent patterns of hyperlipidemia, hypoadiponectinemia, hypoleptinemia, and hyperinsulinemia. Evaluation of neurologic function revealed that even the lowest dose of lopinavir/ritonavir caused significant cognitive impairment assessed in multi-unit T-maze, but did not affect motor functions assessed as rotarod performance. Collectively, our results indicate that repeated lopinavir/ritonavir administration produces cognitive as well as metabolic impairments, and suggest that the development of selective aspects of metabolic syndrome in HIV patients could contribute to HIV-associated neurocognitive disorders.

Inhibitory effect of LXR activation on cell proliferation and cell cycle progression through lipogenic activity

Liver X receptor (LXR), a sterol-activated nuclear hormone receptor, has been implicated in cholesterol and fatty acid homeostasis via regulation of reverse cholesterol transport and de novo fatty acid synthesis. LXR is also involved in immune responses, including anti-inflammatory action and T cell proliferation. In this study, we demonstrated that activated LXR suppresses cell cycle progression and proliferation in certain cell types. Stimulation of LXR with synthetic ligand T0901317 or GW3965 inhibited cell growth rate and arrested the cell cycle at the G1/S boundary in several cells, such as RWPE1, THP1, SNU16, LNCaP, and HepG2. However, LXR ligands did not exhibit antiproliferative activity in PC3, HEK293, or HeLa cells. Interestingly, activated LXR-mediated cell cycle arrest is closely correlated with the lipogenic gene expression and triacylglyceride accumulation. In accordance with these findings, suppression of FAS via small-interference RNA (siRNA) partially alleviated the antiproliferative effect of LXR activation in RWPE1 cells. Together, these data suggest that LXR activation with its ligands inhibits cell proliferation and induces G1/S arrest through elevated lipogenic activity, thus proposing a novel effect of activated LXR on cell cycle regulation.

Cognitive impairment following high fat diet consumption is associated with brain inflammation

C57Bl/6 mice were administered a high fat, Western diet (WD, 41% fat) or a very high fat lard diet (HFL, 60% fat), and evaluated for cognitive ability using the Stone T-maze and for biochemical markers of brain inflammation. WD consumption resulted in significantly increased body weight and astrocyte reactivity, but not impaired cognition, microglial reactivity, or heightened cytokine levels. HFL increased body weight, and impaired cognition, increased brain inflammation, and decreased BDNF. Collectively, these data suggest that while different diet formulations can increase body weight, the ability of high fat diets to disrupt cognition is linked to brain inflammation.

Triacylglycerol-induced impairment in mitochondrial biogenesis and function in J774.2 and mouse peritoneal macrophage foam cells

The aim of this study was to detect mitochondrial alterations in J774.2 macrophages and mouse peritoneal macrophages (MPM) foam cells. J774.2 and MPM cells were exposed to triacylglycerol (TG) emulsion (1 mg/ml) for induction of fat accumulation. Impairment of mitochondrial function was reflected by reduced cellular ATP production and decreased expression of subunits of mitochondrial complexes I and III. The expression of subunit IV of complex IV remained unchanged, however, the content of its precursor in cells increased. Inhibitors of mitochondrial complexes, rotenone (0.1 microM) and myxothiazol (25 nM), protected the viability in TG-loaded macrophages. The exposure to TG caused downregulation of PPARgamma coactivator (PGC)-1alpha and nuclear respiratory factor (NRF)-1. Activation of peroxisome proliferator-activated receptors attenuated reactive oxygen species production in the foam cells. Treatment with antioxidant N-acetylcysteine (NAC) prevented lipid-mediated mitochondrial and cellular damage. In conclusion, this study demonstrates the important role of mitochondrial biogenesis dysfunction in TG-induced lipotoxicity in macrophages.

25-Hydroxycholesterol-3-sulfate regulates macrophage lipid metabolism via the LXR/SREBP-1 signaling pathway

The oxysterol receptor LXR is a key transcriptional regulator of lipid metabolism. LXR increases expression of SREBP-1, which in turn regulates at least 32 genes involved in lipid synthesis and transport. We recently identified 25-hydroxycholesterol-3-sulfate (25HC3S) as an important regulatory molecule in the liver. We have now studied the effects of 25HC3S and its precursor, 25-hydroxycholesterol (25HC), on lipid metabolism as mediated by the LXR/SREBP-1 signaling in macrophages. Addition of 25HC3S to human THP-1-derived macrophages markedly decreased nuclear LXR protein levels. 25HC3S administration was followed by dose- and time-dependent decreases in SREBP-1 mature protein and mRNA levels. 25HC3S decreased the expression of SREBP-1-responsive genes, acetyl-CoA carboxylase-1, and fatty acid synthase (FAS) as well as HMGR and LDLR, which are key proteins involved in lipid metabolism. Subsequently, 25HC3S decreased intracellular lipids and increased cell proliferation. In contrast to 25HC3S, 25HC acted as an LXR ligand, increasing ABCA1, ABCG1, SREBP-1, and FAS mRNA levels. In the presence of 25HC3S, 25HC, and LXR agonist T0901317, stimulation of LXR targeting gene expression was repressed. We conclude that 25HC3S acts in macrophages as a cholesterol satiety signal, downregulating cholesterol and fatty acid synthetic pathways via inhibition of LXR/SREBP signaling. A possible role of oxysterol sulfation is proposed.

Obesity and vulnerability of the CNS

The incidence of obesity is increasing worldwide, and is especially pronounced in developed western countries. While the consequences of obesity on metabolic and cardiovascular physiology are well established, epidemiological and experimental data are beginning to establish that the central nervous system (CNS) may also be detrimentally affected by obesity and obesity-induced metabolic dysfunction. In particular, data show that obesity in human populations is associated with cognitive decline and enhanced vulnerability to brain injury, while experimental studies in animal models confirm a profile of heightened vulnerability and decreased cognitive function. This review will describe findings from human and animal studies to summarize current understanding of how obesity affects the brain. Furthermore, studies aimed at identifying key elements of body-brain dialog will be discussed to assess how various metabolic and adipose-related signals could adversely affect the CNS. Overall, data suggest that obesity-induced alterations in metabolism may significantly synergize with age to impair brain function and accelerate age-related diseases of the nervous system. Thus, enhanced understanding of the effects of obesity and obesity-related metabolic dysfunction on the brain are especially critical as increasing numbers of obese individuals approach advanced age.