Avasimibe and atorvastatin synergistically reduce cholesteryl ester content in THP-1 macrophages

Sterol O-Acyltransferase 2 Contributes to the Yolk Cholesterol Trafficking during Zebrafish Embryogenesis

To elucidate whether Sterol O-acyltransferase (Soat) mediates the absorption and transportation of yolk lipids to the developing embryo, zebrafish soat1 and soat2 were cloned and studied. In the adult zebrafish, soat1 was detected ubiquitously while soat2 mRNA was detected specifically in the liver, intestine, brain and testis. Whole mount in situ hybridization demonstrated that both soat1 and soat2 expressed in the yolk syncytial layer, hatching gland and developing cardiovascular as well as digestive systems, suggesting that Soats may play important roles in the lipid trafficking and utilization during embryonic development. The enzymatic activity of zebrafish Soat2 was confirmed by Oil Red O staining in the HEK293 cells overexpressing this gene, and could be quenched by Soat2 inhibitor Pyripyropene A (PPPA). The zebrafish embryos injected with PPPA or morpholino oligo against soat2 in the yolk showed significantly larger yolk when compared with wild-type embryos, especially at 72 hpf, indicating a slower rate of yolk consumption. Our result indicated that zebrafish Soat2 is catalytically active in synthesizing cholesteryl esters and contributes to the yolk cholesterol trafficking during zebrafish embryogenesis.

Inhibitory effects of balsamic vinegar on LDL oxidation and lipid accumulation in THP-1 macrophages

Oxidized low-density lipoprotein (LDL) is believed to contribute to atherosclerosis in part by being taken up into macrophages via scavenger receptors, thus accounting for foam cells. Balsamic vinegar is made from grapes and generally consumed in the Mediterranean region. In this study, we investigated the preventive effects of balsamic vinegar on LDL oxidation and foam cell formation. Balsamic vinegar had stronger 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging abilities and higher polyphenol concentrations than rice vinegar. Balsamic vinegar dramatically inhibited LDL oxidation by azoradicals and endothelial cell-mediated oxidation in vitro. Further, we assessed the anti-oxidative effect against LDL after balsamic vinegar consumption in human subjects. Balsamic vinegar prolonged the LDL oxidation lag time and decreased lipid peroxide (LPO) and lyso-phosphatidylcholine (LPC) in LDL particles. We next examined the effect of balsamic vinegar on foam cell formation. Oil red O staining showed that balsamic vinegar inhibited oxidized LDL-induced foam cell formation in THP-1 macrophages. The concentrations of intracellular triglycerides and total cholesterols were reduced in the presence of balsamic vinegar. In addition, balsamic vinegar decreased the mRNA and protein expression level of scavenger receptors in THP-1 macrophages. These results showed that balsamic vinegar contained abundant polyphenols and inhibited LDL oxidation and oxidized LDL-induced foam cell formation by decreasing the expression of scavenger receptors.

Geraniol and simvastatin show a synergistic effect on a human hepatocarcinoma cell line

Simvastatin is a competitive inhibitor of 3-hydroxymethylglutaryl coenzyme A reductase activity, whereas geraniol is a monoterpene with multiple pharmacologic effects on mevalonate metabolism. Both of them inhibit growth and proliferation of many cell lines. The present study was designed to determine the action of geraniol, in combination with simvastatin, by assessing their effects in vitro on human hepatocarcinoma cell line (Hep G2). The treatment of Hep G2 cells with concentrations of simvastatin or geraniol that did not inhibit cell proliferation (5 µmol·l⁻¹ of simvastatin and 50 µmol·l⁻¹ of geraniol) resulted in a significant inhibition of cell proliferation. We also examined the effect of simvastatin, geraniol and the combination of both on the biosynthesis of lipids from [¹⁴C]-acetate. Our results demonstrate that the combination of simvastatin and geraniol synergistically inhibited cholesterol biosynthesis and proliferation of Hep G2 cell line, contributing to a better understanding of the action of a component of essential oils targeting a complex metabolic pathway, which would improve the use of drugs or their combination in the fight against cancer and/or cardiovascular diseases.

Tissue factor pathway inhibitor 2 is induced by thrombin in human macrophages

Tissue factor pathway inhibitor 2 (TFPI2) is a serine protease inhibitor critical for the regulation of extracellular matrix remodeling and atherosclerotic plaque stability. Previously, we demonstrated that TFPI2 expression is increased in monocytes from patients with familial combined hyperlipidemia (FCH). To gain insight into the molecular mechanisms responsible for this upregulation, we examined TFPI2 expression in THP-1 macrophages exposed to lipoproteins and thrombin. Our results showed that TFPI2 expression was not affected by treatment with very low density lipoproteins (VLDL), but was induced by thrombin (10 U/ml) in THP-1 (1.9-fold increase, p<0.001) and human monocyte-derived macrophages (2.3-fold increase, p<0.005). The specificity of the inductive effect was demonstrated by preincubation with the thrombin inhibitors hirudin and PPACK, which ablated thrombin effects. TFPI2 induction was prevented by pre-incubation with MEK1/2 and JNK inhibitors, but not by the EGF receptor antagonist AG1478. In the presence of parthenolide, an inhibitor of NFκB, but not of SR-11302, a selective AP-1 inhibitor, thrombin-mediated TFPI2 induction was blunted. Our results also show that thrombin treatment increased ERK1/2, JNK and IκBα phosphorylation. Finally, we ruled out the possibility that TFPI2 induction by thrombin was mediated by COX-2, as preincubation with a selective COX-2 inhibitor did not prevent the inductive effect. In conclusion, thrombin induces TFPI2 expression by a mechanism involving ERK1/2 and JNK phosphorylation, leading finally to NFkB activation. In the context of atherosclerosis, thrombin-induced macrophage TFPI2 expression could represent a means of avoiding excessive activation of matrix metalloproteases at sites of inflammation.

Different response of senescent female Sprague-Dawley rats to gemfibrozil and rosiglitazone administration

Eighteen-month-old Sprague-Dawley rats present age-related alterations in lipid and glucose metabolism and are resistant to the effect of PPARalpha-activating hypolipidemic drugs, such as gemfibrozil. We tested if these animals were responsive to the administration of rosiglitazone, an insulin-sensitizer acting on PPARgamma. We determined in 18-month-old female Sprague-Dawley rats treated for 21 days with a daily dose of 3mg gemfibrozil/kg or 3mg rosiglitazone/kg: (i) plasma concentrations of total cholesterol (TC), triglycerides (TG), nonesterified fatty acids (NEFA), glucose, insulin and leptin, (ii) hepatic concentrations of TG, NEFA and cholesteryl esters (CE), and (iii) the liver expression and binding activity of peroxisome proliferator-activated receptor alpha (PPARalpha), and several of its target genes, hepatic nuclear factor-4 (HNF-4), and liver X receptor alpha (LXRalpha). Although gemfibrozil induced mild effects on hepatic PPARalpha, HNF-4, and LXRalpha, only rosiglitazone significantly reduced plasma TG (59%), glucose (19%), insulin (61%), and leptin (66%), and liver TG (43%), CE (49%), and NEFA (27%). These changes were associated to an increased body weight gain and a decrease in visceral fat (8.7-fold and 37% vs. control females, respectively). The beneficial effect of rosiglitazone treatment in 18-month-old female rats could be related to a direct effect on white adipose tissue.

Effects of rosiglitazone and atorvastatin on the expression of genes that control cholesterol homeostasis in differentiating monocytes

We studied the effects of 5 microM atorvastatin, 2 microM rosiglitazone and their combination on intracellular cholesterol levels and on the expression of genes controlling cholesterol trafficking in human monocytes during their differentiation into macrophages. Our results show that treatment with rosiglitazone caused an increase in CD36 mRNA and protein levels (2.7- and 2.9-fold, P<0.001), but significantly induced the expression of most genes related to cholesterol efflux: ABCA1 mRNA (23%, P<0.05) and protein (2.4-fold, P<0.05), apo E protein (2.4-fold, P<0.05), caveolin-1 mRNA (2.6-fold, P<0.001) and SR-BI mRNA (1.9-fold, P<0.001) and protein (3-fold, P<0.01). As a consequence, rosiglitazone treatment reduced intracellular free cholesterol levels by 22% (P<0.01). Treatment with 5 microM atorvastatin caused the opposite effect on the expression of cholesterol efflux-related genes, which was generally reduced: ABCA1 mRNA (71%, P<0.05), apo E mRNA (46%, P<0.001) and protein (5.6-fold, P<0.001), and CYP27 mRNA (15%, P<0.05). Despite these reductions, intracellular total and free cholesterol levels were also reduced by 30% (P<0.01), an effect that can be attributed to the inhibition of de novo cholesterol synthesis by the statins. The combination of rosiglitazone with atorvastatin attenuated CD36 induction, and caused reductions similar to those caused by the statin alone on the expression of genes involved in cholesterol efflux and on intracellular cholesterol levels.

Atorvastatin reverses age-related reduction in rat hepatic PPARalpha and HNF-4

Old rats are resistant to fibrate-induced hypolipidemia owing to a reduction in hepatic peroxisome proliferator-activated receptor alpha (PPARalpha). We tested whether the age-related decrease in PPARalpha is prevented by atorvastatin (ATV), a hypolipidemic statin. We determined the activity and expression of Liver X receptor alpha (LXRalpha) and PPARalpha in the liver of 18-month-old rats treated with 10 mg kg(-1) of ATV for 21 days. We measured fatty acid oxidation (FAO), the expression of PPARalpha-target genes, liver triglyceride (TG) and cholesteryl ester (CE) contents and plasma concentrations of TG, cholesterol, glucose, nonesterified fatty acids (NEFA), insulin and leptin. While old female rats were practically unresponsive, ATV-treated old males showed lower liver TG (-41%) and CE (-48%), and plasma TG (-35%), glucose (-18%) and NEFA (-39%). Age-related alterations in LXRalpha expression and binding activity were reverted in ATV-treated old males. These changes were related to an increase in hepatic FAO (1.2-fold), and PPARalpha mRNA (2.2-fold), PPARalpha protein (1.6-fold), and PPARalpha-binding activity. Hepatic nuclear factor-4 (HNF-4) and chicken ovalbumin upstream-transcription factor-II participate in the transcriptional regulation of the PPARalpha gene, while peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) behaves as a PPAR coactivator. Ageing reduced the hepatic content of HNF-4 (74%) and PGC-1 (77%) exclusively in male rats. ATV administration to old males enhanced the hepatic expression and binding activity (two-fold) of HNF-4. ATV-induced changes in hepatic HNF-4 and PPARalpha may be responsible for the improvement of the lipid metabolic phenotype produced by ATV administration to senescent male rats.

Cholesterol regulation of genes involved in sterol trafficking in human THP-1 macrophages

Modulation of the expression of genes involved in the control of cholesterol homeostasis by sterols in macrophages is crucial to foam cell formation. To characterize this regulation in THP-1 macrophages, we examined the effect of sterol loading and unloading on the expression of a number of genes that participate in lipoprotein uptake and cholesterol efflux. Sterol loading by exposure to acetylated LDL for 24 h resulted in an increase in free and esterified cholesterol of 1.4 and 1.8-fold, respectively. Under these conditions, the mRNA levels for SR-A were reduced a 59%, while those of CYP27 were increased by 4.6-fold. However, the expression of other genes involved in cholesterol efflux (ABCA1, ABCG1 and CLA-1) was not modified, despite a high intracellular cholesterol accumulation specially in the form of esterified cholesterol. On the other hand, HDL exposure reduced intracellular cholesterol content to 70%, and caused an increase in the expression of CD36 (78%), SR-A (51%) and CLA-1 (136%). Conversely, the expression of ABCA1, ABCG1 and CYP27 was decreased by 49, 67 and 57%, respectively. These findings indicate that in THP-1 macrophages, the expression of genes for receptors involved in lipoprotein binding and uptake tends to decrease upon cholesterol loading and to increase by cholesterol depletion, while the opposite pattern is found regarding the mRNA levels for proteins involved in cholesterol efflux.

Sexual dimorphism in lipid metabolic phenotype associated with old age in Sprague-Dawley rats

PURPOSE

Aged male rats show a decrease in liver PPARalpha. We aimed to determine if the sexual dimorphism in lipid metabolism observed in the PPARalpha-/- mouse is also present in senescent rats.

RESULTS

Eighteen-month old rats were obese and presented high plasma NEFA concentrations. Old male rats were more hypercholesterolemic and hyperleptinemic than females, presenting a higher content in hepatic triglycerides and cholesteryl esters, while 18-month old females were more hypertriglyceridemic than males. Although PPARalpha expression and binding activity was reduced in liver from old male and female rats, the mRNA for a PPARalpha target gene, such as CPT-I, was reduced in old males (-56%), while increased by 286% in old females. LXRalpha protein was increased, and its binding activity was decreased in livers of old males, while livers of old females showed an increase in DGAT1 (2.6-fold) and DGAT2 (4.9-fold) mRNA, with respect to 3-month old animals. The increases in DGAT1 and DGAT2 mRNAs matched in old females those of plasma (3.1-fold) and liver triglycerides (5.0-fold).

CONCLUSIONS

These features disclose a marked sexual dimorphism in lipid metabolism associated to old age in rats that can be partially attributed not only to an age-related decrease in liver PPARalpha expression, but also to changes in other hepatic transcription factors and enzymes, such as liver X receptor alpha (LXRalpha) and diacylglycerol acyltransferases (DGAT).

Modulation of macrophage function and metabolism

Several drugs or pharmacologically active molecules such as statins, calcium antagonists, and PPAR agonists have been shown to affect macrophage functions that contribute to atherosclerosis and modulate plaque stability. For example, the modulation of matrix metalloproteinase secretion and cholesterol metabolism in macrophages may help to prevent cardiovascular disease independently of the correction of risk factors.

Statins inhibit HIV-1 infection by down-regulating Rho activity

Human immunodeficiency virus (HIV)-1 infectivity requires actin-dependent clustering of host lipid raft–associated receptors, a process that might be linked to Rho guanosine triphosphatase (GTPase) activation. Rho GTPase activity can be negatively regulated by statins, a family of drugs used to treat hypercholesterolemia in man. Statins mediate inhibition of Rho GTPases by impeding prenylation of small G proteins through blockade of 3-hydroxy-3-methylglutaryl coenzyme A reductase. We show that statins decreased viral load and increased CD4⁺ cell counts in acute infection models and in chronically HIV-1–infected patients. Viral entry and exit was reduced in statin-treated cells, and inhibition was blocked by the addition of l-mevalonate or of geranylgeranylpyrophosphate, but not by cholesterol. Cell treatment with a geranylgeranyl transferase inhibitor, but not a farnesyl transferase inhibitor, specifically inhibited entry of HIV-1–pseudotyped viruses. Statins blocked Rho-A activation induced by HIV-1 binding to target cells, and expression of the dominant negative mutant RhoN19 inhibited HIV-1 envelope fusion with target cell membranes, reducing cell infection rates. We suggest that statins have direct anti–HIV-1 effects by targeting Rho.

Reduction of intracellular cholesterol accumulation in THP-1 macrophages by a combination of rosiglitazone and atorvastatin

Rosiglitazone and atorvastatin combination therapy has beneficial effects on both glycemic control and plasma lipid levels in type 2 diabetic patients. In the present study, we sought to determine whether this combination can also exert direct antiatherosclerotic effects in macrophages. Our results show that 2 microM rosiglitazone, alone or combined with 5 microM atorvastatin, significantly upregulated the expression of the ATP-binding cassette transporter ABCA1 and of the class B scavenger receptor CLA-1 (CD36 and LIMPII analog), both involved in cholesterol efflux from macrophages. On the other hand, the combination with atorvastatin attenuated the inductive response elicited by rosiglitazone alone on CD36 mRNA (34%, P < 0.05) and protein (16%, P < 0.05), while the uptake of oxidized low density lipoprotein (LDL) remained unaffected. When we examined the effects of the drugs on acetyl-LDL-induced cholesterol accumulation, we found that only the combination of atorvastatin with rosiglitazone caused a net depletion in the cholesteryl ester content of macrophages (35%, P < 0.05). Our data suggest that this reduction was not mediated by effects on proteins that regulate cholesterol flux, but it may be related to the inhibition of cholesteryl ester formation elicited by the statin.

New drugs for the treatment of hypercholesterolaemia

Endogenous and exogenous pathways determine plasma levels of cholesterol and lipoproteins. Plasma cholesterol levels and coronary heart disease risk can be reduced pharmacologically by decreasing cholesterol synthesis, increasing its elimination and/or reducing its absorption from the intestine. The more profound knowledge about cholesterol homeostasis has allowed the development of several lipid-lowering drugs with different mechanisms of action, with the purpose of reducing both morbidity and mortality associated with coronary heart disease. Two new and more potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), also called superstatins (rosuvastatin and pitavastatin), are being studied for their ability to improve lipid profiles. Rosuvastatin is a potent, hepato-selective and relatively hydrophilic statin with a low propensity for muscle toxicity and drug interactions. Pitavastatin is another statin with a high oral bioavailability and minimal propensity for cytochrome p450-mediated drug interactions. Rosuvastatin seems to be more potent than other available statins while pitavastatin presents with a similar potency to that of atorvastatin. Another promising approach for lowering total and low-density lipoprotein cholesterol levels is inhibition of cholesterol absorption. A wide variety of new agents with the capacity for inhibiting the intestinal cholesterol absorption is currently being investigated. Ezetimibe is a selective cholesterol absorption inhibitor whose clinical efficacy has been recently demonstrated both in monotherapy and in combination with other lipid-lowering drugs. Colesevelam, a new bile acid sequestrant, has shown a clinical efficacy similar to that of other resins, with minimal gastrointestinal side effects, improving tolerability and patient compliance. Other lipid-lowering drugs with the ability to act at the enterocyte level, such as avasimibe and implitapide, are currently being investigated in humans.