Effects of Pravastatin on the Expression of ATP-Binding Cassette Transporter A1

Statins to Prevent Pacing-Induced Cardiomyopathy: Evidence from the Bench applied to Clinical Studies

BACKGROUND

Pacing-induced cardiomyopathy is an undesired outcome in atrioventricular block (AVB) patients and our animal model showed lipotoxic cardiomyopathy following pacing.

OBJECTIVES

This study aimed to explore the mechanisms and clinical outcomes of statins in AVB patients receiving pacing.

METHODS

Rat ventricular cardiomyocytes were treated with atorvastatin, liver X receptor (LXR) agonist, and LXR antagonist during pacing. Pigs were divided into 3 groups: right ventricular pacing, pacing with concomitant atorvastatin treatment, and sham control. Clinically, we enrolled 1,717 AVB patients received permanent pacemaker from Chang Gung Memorial Hospital Medical database. The primary outcome (cardiovascular death or heart failure (HF) hospitalization) and individual outcome were compared between statin and non-statin groups after inverse probability of treatment weighting.

RESULTS

Lipid accumulation in rat cardiomyocytes by pacing was significantly reduced by treatment with LXR agonist and atorvastatin while LXR antagonist counteracted the atorvastatin effect on lipid expression. Left ventricular ejection fraction (LVEF) was significantly lower in the AVB pig pacing group compared to those concomitantly treated with atorvastatin. Moreover, lipid accumulation and fibronectin expression were significantly ameliorated by concomitant treatment of atorvastatin. In the clinical study, statin group had significantly lower risk of the primary outcome event (HR: 0.69, 95% CI: 0.56-0.84), less HF hospitalization (HR: 0.45, 95% CI: 0.30-0.67) and higher LVEF than non-statin group.

CONCLUSION

In experimental models, atorvastatin ameliorated lipid accumulation in cardiomyocytes and fibrosis in LV myocardium induced by pacing. Clinically, treatment with statins was associated with less HF hospitalization and cardiovascular death in AVB patients receiving pacemaker therapy.

Molecular-level changes induced by hydroxycinnamic acid derivatives in HepG2 cell line: Comparison with pravastatin

Hydroxycinnamic acid derivatives are an important class of polyphenols found in fruits, vegetables, and medicinal plants and widely consumed in human diet. In the present work, alterations of HepG2 cells biochemical profile under the effect of four hydroxycinnamic acid derivatives (caffeic acid, m-coumaric acid, chlorogenic acid and rosmarinic acid) relatively to the effect of pravastatin, a drug often prescribed to inhibit HMG-CoA reductase enzyme, the regulator enzyme in the cholesterol biosynthesis pathway, were reported. The application of FTIR spectroscopy in combination with multivariate analysis by PCA showed a similarity between pravastatin and the four hydroxycinnamic acid derivatives in metabolite profile modification expressed by various changes in proteins region, the phosphate region which mainly corresponds to nucleic acids as well as in lipids regions. FTIR structural analysis in the amide I region, using resolution enhancement methods, such as second derivative and amide I deconvolution method, revealed significant decrease in α-helix/random coil and intermolecular β-sheet decreased while intramolecular β-sheet in treated cells showed an increase. It was also noticed that the intracellular cholesterol as well as esterified ingredients such as cholesterol esters in the cell membrane decreased. Moreover, principal component analysis (PCA) of the spectral data showed that the compounds and pravastatin were well separated from untreated cells showing a different mode of action on HepG2 treated cells for each compound.

Lipid lowering therapy in cardiovascular disease: From myth to molecular reality

Lipid-lowering therapy is one major cornerstone of medical treatment of cardiovascular disease in order to modulate atherosclerosis. Statins, ezetimibe and novel PCSK9-inhibitors are already recommended in current guidelines and were shown to improve lipid profiles and have positive effects on the rate of ischemic events and cardiovascular mortality. Recent studies suggest that the concept of "The lower the better" might be valid at least regarding low density lipoproteins. In addition, lowering lipoprotein (a) still displays a major challenge in lipid therapy. Furthermore, also lowering triglycerides seems to improve cardiovascular outcome. Regarding triglycerides, icosapent ethyl, a polyunsaturated fatty acid recently attracted attention showing cardiovascular risk reduction due to triglyceride lowering. Therefore, new therapeutic strategies and drug classes are eagerly awaited. Targeting LDL, bempedoic acid and the siRNA inclisiran provide promising results. Moreover, regarding TG a monoclonal antibody called evinacumab and an antisense-oligonucleotide against ANGPTL3 showed effective TG-lowering. At least, using antisense-oligonucleotides against ApoC-III and Lp(a) resulted in promising outcomes. In this review, current and future options for lipid management are presented depending on different drug classes.

Downregulation of ABCA1 and ABCG1 transporters by simvastatin in cholangiocarcinoma cells

Disturbances in cholesterol homeostasis of the bile duct epithelium, including transport interruption and the hyperaccumulation of intracellular cholesterol can lead to the initiation and progression of cholangiocarcinoma (CCA). Statins, which are lipid-lowering drugs, have been previously documented to exhibit anti-cancer properties. The role of statins in CCA cell cholesterol transport through the expression and function of ATP-binding cassette (ABC) A1 and ABCG1 was investigated in the current study. In four CCA cell lines, ABCA1 and ABCG1 expression was identified. However, neither ABCG5 nor ABCG8 expression was observed. Immunocytochemistry revealed that the expression of ABCA1 was localized in the proximity of the nucleus, while ABCG1 was more dispersed throughout the cytoplasm of KKU-100 cells. A cholesterol efflux assay was performed using bodipy cholesterol, and the translocation of cholesterol via ABCA1 and ABCG1 to Apo-A1 and high density lipoprotein was confirmed, respectively. Simvastatin and atorvastatin demonstrated the inhibitory effects on CCA cell viability. A reduction in intracellular lipid level and a lower expression of ABCA1 and ABCG1 were observed in KKU-100 cells under simvastatin treatment. The pre-exposure of KKU-100 cells to cholesterol diminished the statin effect. Furthermore, when KKU-100 cells were pre-loaded with cholesterol, ABCA1 and ABCG1-mediated exports were unaffected even though they were treated with simvastatin. The results of the current study indicated the limitations of the use of statin in CCA therapy, particularly under hypercholesterolemia conditions.

Repurposing of statins via inhalation to treat lung inflammatory conditions

Despite many therapeutic advancements over the past decade, the continued rise in chronic inflammatory lung diseases incidence has driven the need to identify and develop new therapeutic strategies, with superior efficacy to treat these diseases. Statins are one class of drug that could potentially be repurposed as an alternative treatment for chronic lung diseases. They are currently used to treat hypercholesterolemia by inhibiting the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, that catalyses the rate limiting step in the mevalonate biosynthesis pathway, a key intermediate in cholesterol metabolism. Recent research has identified statins to have other protective pleiotropic properties including anti-inflammatory, anti-oxidant, muco-inhibitory effects that may be beneficial for the treatment of chronic inflammatory lung diseases. However, clinical studies have yielded conflicting results. This review will summarise some of the current evidences for statins pleiotropic effects that could be applied for the treatment of chronic inflammatory lung diseases, their mechanisms of actions, and the potential to repurpose statins as an inhaled therapy, including a detailed discussion on their different physical-chemical properties and how these characteristics could ultimately affect treatment efficacies. The repurposing of statins from conventional anti-cholesterol oral therapy to inhaled anti-inflammatory formulation is promising, as it provides direct delivery to the airways, reduced risk of side effects, increased bioavailability and tailored physical-chemical properties for enhanced efficacy.

Pravastatin activates the expression of farnesoid X receptor and liver X receptor alpha in Hep3B cells

BACKGROUND

Statins are suggested to preserve gallbladder function by suppressing pro-inflammatory cytokines and preventing cholesterol accumulation in gallbladder epithelial cells. They also affect cross-talk among the nuclear hormone receptors that regulate cholesterol-bile acid metabolism in the nuclei of hepatocytes. However, there is controversy over whether or how statins change the expression of peroxisome proliferator-activated receptor (PPAR)alpha, PPARgamma, liver X receptor alpha (LXRalpha), farnesoid X receptor (FXR), ABCG5, ABCG8, and 7alpha-hydroxylase (CYP7A1) which are directly involved in the cholesterol saturation index in bile.

METHODS

Human Hep3B cells were cultured on dishes. MTT assays were performed to determine the appropriate concentrations of reagents to be used. The protein expression of PPARalpha and PPARgamma was measured by Western blotting analysis, and the mRNA expression of LXRalpha, FXR, ABCG5, ABCG8 and CYP7A1 was estimated by RT-PCR.

RESULTS

In cultured Hep3B cells, pravastatin activated PPARalpha and PPARgamma protein expression, induced stronger expression of PPARgamma than that of PPARalpha, increased LXRalpha mRNA expression, activated ABCG5 and ABCG8 mRNA expression mediated by FXR as well as LXRalpha, enhanced FXR mRNA expression, and increased CYP7A1 mRNA expression mediated by the PPARgamma and LXRalpha pathways, together or independently.

CONCLUSION

Our data suggested that pravastatin prevents cholesterol gallstone diseases via the increase of FXR, LXRalpha and CYP7A1 in human hepatocytes.

HNF4α Increases Liver-Specific Human ATP-Binding Cassette Transporter A1 Expression and Cholesterol Efflux to Apolipoprotein A-I in Response to Cholesterol Depletion

Objective—

Hepatic ATP-binding cassette transporter A1 (ABCA1) plays the major role in maintaining plasma high-density lipoprotein levels by producing cholesterol-accepting nascent high-density lipoprotein, whereas peripheral ABCA1 is responsible for releasing cellular cholesterol. We previously reported that in rodents, cholesterol depletion reduces ABCA1 expression in peripheral but not hepatic cells by increasing a liver-specific ABCA1 transcript via the sterol regulatory element-binding protein-2 system. However, the regulatory element is not conserved in humans. Here we investigated the mechanism of sterol-regulated human hepatic ABCA1 gene expression.

Methods and Results—

ABCA1 mRNA variant type L3 is a novel and human-liver-specific transcript accounting for ≈25% of total ABCA1 mRNA in the liver and is induced by cellular cholesterol depletion. Specific knockdown or forced expression revealed that type L3 produces functional ABCA1 protein in cholesterol efflux. We identified a regulatory enhancer element for L3 expression lying within intron 3 of the human ABCA1 gene, to which hepatocyte nuclear factor (HNF) 4α binds in response to cholesterol depletion. HNF4α knockdown abolished induction of liver-specific L3 and L2b transcripts (and consequently the liver-type response of ABCA1 expression to cellular cholesterol status) and diminished cholesterol efflux activity.

Conclusion—

These findings indicate that HNF4α regulates human hepatic ABCA1 expression in response to cholesterol depletion.

Influence of dosing time on the efficacy and safety of finasteride in rats

Finasteride (FIN), a widely used medication for the treatment of androgen-dependent diseases, blocks the conversion of testosterone to a more potent androgen, dihydrotestosterone (DHT). In this study, we investigated a dosing time-dependent effect and safety of FIN in rats. Androgen receptor (AR) mRNA and nuclear protein levels exhibited clear daily rhythms with the peak during the dark period in the prostate and during the light period in the liver. Repeated oral administration of FIN (5 or 100 mg/kg) at 3 h after lights on (HALO) for 2 weeks decreased serum DHT concentration throughout a 24-h period, whereas the dosing of the agent at 15 HALO decreased its level only transiently even in the higher dose group. FIN caused laboratory abnormalities in the 3 HALO group but not in the 15 HALO group. However, the effect of FIN on the prostate weight was not influenced by the dosing time. These results suggest that the safety, but not effect, of FIN depends on its dosing time in rats. The dosing of FIN in the active period might be a rational dosage regimen, which is needed to be confirmed in human subjects.

Effects of lipid-lowering drugs on reverse cholesterol transport gene expressions in peripheral blood mononuclear and HepG2 cells

AIMS

The ATP-binding cassette transporters, ABCA1 and ABCG1, are LXR-target genes that play an important role in reverse cholesterol transport. We examined the effects of inhibitors of the cholesterol absorption (ezetimibe) and synthesis (statins) on expression of these transporters in HepG2 cells and peripheral blood mononuclear cells (PBMCs) of individuals with primary (and nonfamilial) hypercholesterolemia (HC).

MATERIALS & METHODS

A total of 48 HC individuals were treated with atorvastatin (10 mg/day/4 weeks) and 23 were treated with ezetimibe (10 mg/day/4 weeks), followed by simvastatin (10 mg/day/8 weeks) and simvastatin plus ezetimibe (10 mg of each/day/4 weeks). Gene expression was examined in statin- or ezetimibe-treated and control HepG2 cells as well as PBMCs using real-time PCR.

RESULTS

In PBMCs, statins and ezetimibe downregulated ABCA1 and ABCG1 mRNA expression but did not modulate NR1H2 (LXR-β) and NR1H3 (LXR-α) levels. Positive correlations of ABCA1 with ABCG1 and of NR1H2 with NR1H3 expressions were found in all phases of the treatments. In HepG2 cells, ABCA1 mRNA levels remained unaltered while ABCG1 expression was increased by statin (1.0-10.0 µM) or ezetimibe (5.0 µM) treatments. Atorvastatin upregulated NR1H2 and NR1H3 only at 10.0 µM, meanwhile ezetimibe (1.0-5.0 µM) downregulated NR1H2 but did not change NR1H3 expression.

CONCLUSION

Our findings reveal that lipid-lowering drugs downregulate ABCA1 and ABCG1 mRNA expression in PBMCs of HC individuals and exhibit differential effects on HepG2 cells. Moreover, they indicate that the ABCA1 and ABCG1 transcript levels were not correlated directly to LXR mRNA expression in both cell models treated with lipid-lowering drugs.

HMG-CoA reductase inhibitors (statins) activate expression of PPARalpha/PPARgamma and ABCA1 in cultured gallbladder epithelial cells

In gallbladder epithelial cells (GBEC), PPARalpha and PPARgamma ligands modulate inflammation by suppression of TNFalpha production and prevent excessive accumulation of cholesterol by ABCA1 activation. Recently, HMG-CoA reductase inhibitors (statins) were shown to activate PPARalpha and PPARgamma in various cells but no studies of their effects in GBEC have been conducted. The objective of this study was, therefore, to determine the effects of statins on PPAR and ABCA1 expression and the anti-inflammatory effect of statins in GBEC. Canine GBEC were cultured on Petri dishes. Expression of the proteins PPARalpha, PPARgamma, and ABCA1 was measured by western blotting analysis after treatment with simvastatin, pravastatin, NO-pravastatin, PPARalpha ligand, or PPARgamma ligand in the culture media. Expression of ABCA1 and LXRalpha mRNAs was estimated by RT-PCR. Expression of TNFalpha mRNA was measured by RT-PCR after 24 h pre-treatment with the statins, preceding 1 h of lipopolysaccharide (LPS) loading. Simvastatin, pravastatin, and NO-pravastatin increased expression of the proteins PPARalpha, PPARgamma, and ABCA1, and expression of the mRNA of ABCA1 and LXRalpha in GBEC. Pre-treatment with simvastatin, pravastatin, and NO-pravastatin suppressed the production of TNFalpha mRNA induced by LPS. In conclusion, statins probably contribute to the preservation of GBEC function by activation of PPARalpha and PPARgamma, which have anti-inflammatory effects by suppression of pro-inflammatory cytokines, and ABCA1 activation mediated by LXRalpha, which prevents the accumulation of cholesterol in GBEC.

ABCA1 expression and statins: inhibitory effect in peripheral blood mononuclear cells

The ATP-binding cassette transporter A1 (ABCA1) has an essential role in the formation of nascent high-density lipoprotein particles and also participates in the cholesterol efflux from macrophages in the artery wall. Several substances, such as statins, or even gene variants are able to modulate ABCA1 expression. There is strong evidence that statin treatment downregulates the ABCA1 expression in nonloaded macrophages. Interestingly, in cholesterol-loaded macrophages, which are more relevant to atherogenesis, this effect is lost. We observed an inhibitory effect of atorvastatin in peripheral blood mononuclear cells of hypercholesterolemic individuals. Moreover, in these individuals, the ABCA1 -14C>T polymorphism was associated with high baseline gene-expression levels. Other studies are needed to evaluate how relevant these findings are to the formation of arterial foam cells in vivo.

Cytochrome P450 and gene activation--from pharmacology to cholesterol elimination and regression of atherosclerosis

BACKGROUND

Lipoproteins are closely associated with the atherosclerotic vascular process. Elevated levels of high-density lipoprotein cholesterol (HDL-C) and apolipoprotein AI (apo AI) in plasma indicate a low probability of coronary heart disease (CHD) together with enhanced longevity, and elevated levels of low-density lipoprotein-cholesterol (LDL-C) and apo B indicate an increased risk of CHD and death. Studies linking gene activation and the induction of cytochrome P450 with elevated plasma levels of apo AI and HDL-C and lowered plasma levels of LDL-C presented a new potential approach to prevent and treat atherosclerotic disease.

OBJECTIVE AND METHODS

This is a review aimed at clarifying the effects of P450-enzymes and gene activation on cholesterol homeostasis, the atherosclerotic vascular process, prevention and regression of atherosclerosis and the manifestation of atherosclerotic disease, particularly CHD, the leading cause of death in the world.

RESULTS

P450-enzymes maintain cellular cholesterol homeostasis. They respond to cholesterol accumulation by enhancing the generation of hydroxycholesterols (oxysterols) and activating cholesterol-eliminating mechanisms. The CYP7A1, CYP27A1, CYP46A1 and CYP3A4 enzymes generate major oxysterols that enter the circulation. The oxysterols activate-via nuclear receptors-ATP-binding cassette (ABC) A1 and other genes, leading to the elimination of excess cholesterol and protecting arteries from atherosclerosis. Several drugs and nonpharmacologic compounds are ligands for the liver X receptor, pregnane X receptor and other receptors, activate P450 and other genes involved in cholesterol elimination, prevent or regress atherosclerosis and reduce cardiovascular events.

CONCLUSIONS

P450-enzymes are essential in the physiological maintenance of cholesterol balance. They activate mechanisms which eliminate excess cholesterol and counteract the atherosclerotic process. Several drugs and nonpharmacologic compounds induce P450 and other genes, prevent or regress atherosclerosis and reduce the occurrence of non-fatal and fatal CHD and other atherosclerotic diseases.

Study of ATP-binding cassette transporter A1 (ABCA1)-mediated cellular cholesterol efflux in diabetic golden hamsters

The effects of cyclic adenosine monophosphate (cAMP) and atorvastatin on macrophage adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux were investigated in a diabetic animal model. Golden hamsters were fed a high-fat diet which resulted in insulin resistance. Diabetes was induced by a single intraperitoneal injection of streptozotocin (30 mg/kg). Normal golden hamsters were used as controls. Peritoneal macrophages were incubated with apolipoprotein A-1 (apoA-1), 8-bromoadenosine-3',5'-cyclic monophosphate (8-br-cAMP), and atorvastatin in vitro. Intracellular cholesterol accumulation was greater in the diabetic animals than in the insulin-resistant animals. Expression of ABCA1 mRNA in macrophages from diabetic animals was upregulated by 8-br-cAMP and atorvastatin. ApoA-1 caused a time-dependent cellular cholesterol efflux. Both atorvastatin and 8-br-cAMP significantly facilitated ABCA1-mediated cellular cholesterol efflux, with the maximal cholesterol efflux rate observed in the macrophages from diabetic animals. Accumulation of cholesterol in the macrophages of diabetic animals can be significantly alleviated by atorvastatin or 8-br-cAMP through improving ABCA1-mediated cellular cholesterol efflux.

The effect of statins on ABCA1 and ABCG1 expression in human macrophages is influenced by cellular cholesterol levels and extent of differentiation

The ATP-binding cassette transporters, ABCA1 and ABCG1, are LXR-target genes that participate in the removal of cholesterol from lipid-laden macrophages, a crucial anti-atherogenic mechanism. Statins are currently the most efficacious therapy for the treatment of hypercholesterolemia and cardiovascular disease. We and others have shown that statins decrease ABCA1 and ABCG1 expression as well as cholesterol efflux from human macrophages. However, other studies have reported that statins produce no change, or even a modest increase in these variables. In an attempt to reconcile these conflicting reports, we investigated how the effect of statins on transcription of ABCA1 and ABCG1 is modulated by cellular cholesterol status and the extent of macrophage differentiation. We showed that supplementing human macrophages with cholesterol reversed the statin-mediated down-regulation of ABC transporter expression whereas depletion of cellular cholesterol tended to accentuate the statin effect. Down-regulation of ABC transporter expression was more pronounced with increased macrophage differentiation status and already evident at statin concentrations equivalent to those present in plasma. Addition of LXR agonists, which are currently on trial as anti-atherogenic agents, reversed the effects on ABC transporter expression while PPAR alpha and PPAR gamma agonists did not. The significance of these results in light of current and future combination therapies is discussed.

Profile of rhythmic gene expression in the livers of obese diabetic KK-Ay mice

Although a number of genes expressed in most tissues, including the liver, exhibit circadian regulation, gene expression profiles are usually examined only at one scheduled time each day. In this study, we investigated the effects of obese diabetes on the hepatic mRNA levels of various genes at 6-h intervals over a single 24-h period. Microarray analysis revealed that many genes are expressed rhythmically, not only in control KK mice but also in obese diabetic KK-A(y) mice. Real-time quantitative PCR verified that 19 of 23 putative circadianly expressed genes showed significant 24-h rhythmicity in both strains. However, obese diabetes attenuated these expression rhythms in 10 of 19 genes. More importantly, the effects of obese diabetes were observed throughout the day in only two genes. These results suggest that observation time influences the results of gene expression analyses of genes expressed circadianly.

Acute digoxin loading reduces ABCA8A mRNA expression in the mouse liver

Human ABCA8, a new member of the ATP binding cassette (ABC) transporter family, transports certain lipophilic drugs, such as digoxin. To investigate the roles of this transporter, we cloned a mouse homologue of ABCA8, from a mouse heart cDNA library, named ABCA8a. The deduced mouse ABCA8a protein is 66% identical with that of human ABCA8 and possesses features common to the ABC superfamily. It was found that ABCA8a was mainly expressed in the liver and heart, similar to human ABCA8. We further evaluated the effect of acute digoxin (a substrate for ABCA8) intoxication on the mRNA expression of ABCA8 using northern blotting with a 3' non-coding region as a probe to avoid cross-hybridization with other ABCA genes. Following acute digoxin infusion, the mRNA expression of ABCA8 was significantly reduced in the liver 12-24 h after injection (14.7% of vehicle treatment), but not in the heart and kidney. Real-time quantitative polymerase chain reaction analysis confirmed the reduction in ABCA8a mRNA. Similar reductions in ABCA5, ABCA7, ABCA8b and ABCA9 mRNA were also observed. A comparable amount of digitoxin did not affect ABCA8a mRNA expression in the liver. The results suggest that ABCA8 may play a role in digoxin metabolism in the liver.

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.

Pitavastatin effect on ATP binding cassette A1-mediated lipid efflux from macrophages: evidence for liver X receptor (LXR)-dependent and LXR-independent mechanisms of activation by cAMP

The promotion of lipid efflux from macrophages is an important ATP binding cassette A1 (ABCA1)-mediated antiatherosclerotic mechanism that prevents peripheral tissues from foam cell accumulation. Statins exert beneficial antiatherosclerotic effects on cardiovascular disease correlated to the cholesterol-lowering properties and the pleiotropic activities. In this work, we investigated the ability of statins to modulate ABCA1-mediated lipid efflux from macrophages, where the protein expression was differently induced. Pitavastatin (0.1-10 microM) and compactin (10 microM) reduced both cholesterol and phospholipid efflux up to 60% from macrophages expressing ABCA1 upon treatment with 8-(4-chlorophenylthio)-cyclic AMP (cpt-cAMP), and this was secondary to a reduction of ABCA1 mRNA and protein content. Conversely, statins did not affect ABCA1 activity when the protein was up-regulated by 22-hydroxycholesterol/9-cis-retinoic acid or through cholesterol loading. Statin inhibition of lipid efflux induced by cpt-cAMP was reversed in the presence of mevalonate, 22-hydroxycholesterol, and cholesterol but not geranyl geraniol. In macrophages obtained from liver X receptor (LXR)-deficient mice, cpt-cAMP still promoted cholesterol efflux, but pitavastatin did not exert any effect. The present work shows that statins may inhibit ABCA1-mediated lipid efflux in macrophages only when ABCA1 protein expression is induced by cpt-cAMP and provides evidence that cAMP may activate ABCA1 independently of an increase of intracellular sterol synthesis but through at least two pathways: one independent of LXR and one involving an intracellular sterol(s) acting as LXR ligand(s). In addition, the lack of inhibitory effect on lipid efflux in cholesterol-loaded macrophages is likely to exclude a potential negative pleiotropic effect by statins.

Rhythmic messenger ribonucleic acid expression of clock genes and adipocytokines in mouse visceral adipose tissue

Various peripheral tissues show circadian rhythmicity, which is generated at the cellular level by their own core oscillators that are composed of transcriptional/translational feedback loops involving a set of clock genes. Although the circulating levels of some adipocytokines, i.e. bioactive substances secreted by adipocytes, are on a 24-h rhythmic cycle, it remains to be elucidated whether the clock gene system works in adipose tissue. To address this issue, we investigated the daily mRNA expression profiles of the clock genes and adipocytokines in mouse perigonadal adipose tissues. In C57BL/6J mice, all transcript levels of the clock genes (Bmal1, Per1, Per2, Cry1, Cry2, and Dbp) and adipocytokines (adiponectin, resistin, and visfatin) clearly showed 24-h rhythms. On the other hand, the rhythmic expression of these genes was mildly attenuated in obese KK mice and greatly attenuated in more obese, diabetic KK-A(y) mice. Obese diabetes also diminished the rhythmic expression of the clock genes in the liver. Interestingly, a 2-wk treatment of KK and KK-A(y) mice with pioglitazone impaired the 24-h rhythmicity of the mRNA expression of the clock genes and adipocytokines despite the antidiabetic effect of the drug. In contrast, pioglitazone improved the attenuated rhythmicity in the liver. These findings suggest that the intracellular clock gene system acts in visceral adipose tissues as well as liver and is influenced by the conditions of obesity/type 2 diabetes and pioglitazone treatment.

Pharmacogenomics and cardiovascular drugs: need for integrated biological system with phenotypes and proteomic markers

Personalized medicine is based on a better knowledge of biological variability, considering the important part due to genetics. When trying to identify involved genes and their products in differential cardiovascular drug responses, a five-step strategy is to be followed: 1) Pharmacokinetic-related genes and phenotypes (2) Pharmacodynamic targets, genes and products (3) Cardiovascular diseases and risks depending on specific or large metabolic cycles (4) Physiological variations of previously identified genes and proteins (5) Environment influences on them. After summarizing the most well-known genes involved in drug metabolism, we will take as example of drugs, the statins, considered as very important drugs from a Public-Health standpoint, but also for economical reasons. These drugs respond differently in human depending on multiple polymorphisms. We will give examples with common ApoE polymorphisms influencing the hypolipemic effects of statins. These drugs also have pleiotropic effects and decrease inflammatory markers. This illustrates the need to separate clinical diseases phenotypes in specific metabolic pathways, which could propose other classifications, of diseases and related genes. Hypertension is also a good example of clinical phenotype which should be followed after various therapeutic approaches by genes polymorphisms and proteins markers. Gene products are under clear environmental expression variations such as age, body mass index and obesity, alcohol, tobacco and dietary interventions which are the first therapeutical actions taken in cardiovascular diseases. But at each of the five steps, within a pharmacoproteomic strategy, we also need to use available information from peptides, proteins and metabolites, which usually are the gene products. A profiling approach, i.e., dealing with genomics, but now also with proteomics, is to be used. In conclusion, the profiling, as well as the large amount of data, will more than before render necessary an organized interpretation of DNA, RNA as well as proteins variations, both at individual and population level.

Daily rhythms of P-glycoprotein expression in mice

Recent studies have shown the gene expression of several transporters to be circadian rhythmic. However, it remains to be elucidated whether the expression of P-glycoprotein, which is involved in the transport of many medications, undergoes 24 h rhythmicity. To address this issue, we investigated daily profiles of P-glycoprotein mRNA and protein levels in peripheral mouse tissues. In the liver and intestine, but not in the kidney, Abcb1a mRNA expression showed clear 24 h rhythmicity. On the other hand, Abcb1b and Abcb4, the other P-glycoprotein genes, did not exhibit significant rhythmic expression in the studied tissues. In the intestine, levels of whole P-glycoprotein also exhibited a daily rhythm, with a peak occurring in the latter half of the light phase and a trough at the onset of the light phase. Consistent with the day-night change of P-glycoprotein level, the ex vivo accumulation of digoxin, an Abcb1a P-glycoprotein substrate, into the intestinal segments at the onset of dark phase was significantly lower than it was at the onset of the light phase. Thus, Abcb1a P-glycoprotein expression, and apparently its function, are 24 h rhythmic at least in mouse intestine tissue. This circadian variation might be involved in various chronopharmacological phenomena.

Transcriptional regulatory networks in lipid metabolism control ABCA1 expression

The ATP-binding cassette transporters, ABCA1 and ABCG1, are major players in mediating cellular efflux of phospholipids and cholesterol to apoA-I containing lipoproteins including prebeta-HDL and alphaHDL and thereby exert important antiatherogenic properties. Although the exact mechanisms how ABC transporters mediate lipid transport are not completely resolved, recent evidence from several laboratories including ours suggests that vesicular transport processes involving different interactive proteins like beta2-syntrophin, alpha1-syntrophin, Lin7, and cdc42 are critically involved in cellular lipid homeostasis controlled by ABCA1 and ABCG1. Besides sterols and fatty acids as known physiological modulators of the LXR/RXR and SREBP pathways, a growing list of natural and synthetic substances and metabolic regulators such as retinoids, PPAR-ligands, hormones, cytokines, and drugs are particularly effective in modulating ABCA1 and ABCG1 gene expression. Although ABCA1 protein amounts are regulated at the level of stability, the majority of potent activating and repressing mechanisms on ABCA1 function directly act on the ABCA1 gene promoter. Among the inducing factors, liver-X-receptors (LXR), retinoic acid receptors (RAR) and peroxisome proliferator-activated receptors (PPARs) along with their coactivators provide an amplification loop for ABCA1 and ABCG1 expression. The ABCA1 promoter is further stimulated by the ubiquitous factor Sp1 and the hypoxia-induced factor 1 (HIF1), which bind to GC-boxes and the E-box, respectively. Shutdown of ABCA1 expression in the absence of sterols or in certain tissues is mediated by corepressor complexes involving unliganded LXR, sterol-regulatory element binding protein 2 (SREBP2), Sp3, and the SCAN-domain protein ZNF202, which also impacts nuclear receptor signaling. Thus, a highly sophisticated transcriptional network controls the balanced expression of ABCA1.

ABCA1 and atherosclerosis

ATP binding cassette transporter A1 (ABCA1) mediates the cellular efflux of phospholipids and cholesterol to lipid-poor apolipoprotein A1 (apoA1) and plays a significant role in high density lipoprotein (HDL) metabolism. ABCA1's role in the causation of Tangier disease, characterized by absent HDL and premature atherosclerosis, has implicated this transporter and its regulators liver-X-receptoralpha (LXRalpha) and peroxisome proliferator activated receptorgamma (PPARgamma) as new candidates potentially influencing the progression of atherosclerosis. In addition to lipid regulation, these genes are involved in apoptosis and inflammation, processes thought to be central to atherosclerotic plaque progression. A Medline-based review of the literature was carried out. Tangier disease and human heterozygotes with ABCA1 mutations provide good evidence that ABCA1 is a major candidate influencing atherosclerosis. Animal and in vitro experiments suggest that ABCA1 not only mediates cholesterol and phospholipid efflux, but is also involved in the regulation of apoptosis and inflammation. The complex and beneficial interactions between apoA1 and ABCA1 seem to be pivotal for cholesterol efflux. The expression of the ABCA1 is tightly regulated. Furthermore the plaque microenvironment could potentially promote ABCA1 protein degradation thus compromising cholesterol efflux. PPAR-LXR-ABCA1 interactions are integral to cholesterol homeostasis and these nuclear receptors have proven anti-inflammatory and anti-matrix metalloproteinase activity. Therapeutic manipulation of the ABCA1 transporter is feasible using PPAR and LXR agonists. PPAR agonists like glitazones and ABCA1 protein stabilization could potentially modify the clinical progression of atherosclerotic lesions.

Regulation of cholesterol 7alpha-hydroxylase mRNA expression in C57BL/6 mice fed an atherogenic diet

The nuclear receptors liver X receptor (LXR) alpha and farnesoid X receptor (FXR) are positive and negative regulators of cholesterol 7alpha-hydroxylase (CYP7A1) transcription, respectively. To clarify their roles in the regulation of CYP7A1 in mice, we investigated mRNA expression of their target genes in the livers of C57BL/6 mice fed the following five diets for 2 weeks: a standard diet, cholic acid, cholesterol, cholesterol+high fat, or an atherogenic diet (cholic acid+cholesterol+high fat). The mRNA level of ATP-binding cassette transporter (ABC) A1 gene, one of LXRalpha target genes, significantly increased on the diets containing cholic acid and/or cholesterol+high fat, but not on the diet containing cholesterol alone. On the other hand, the mRNA levels of the FXR target genes ABCB11, ABCC2, and short heterodimer partner increased only on the diet containing cholic acid with or without cholesterol+high fat. Surprisingly, cholesterol alone or cholesterol+high fat did not affect CYP7A1 mRNA level, whereas cholic acid with or without cholesterol+high fat greatly reduced the level. Thus, in the atherogenic diet-fed mice, cholic acid component is needed for the FXR activation, and FXR dominantly regulates CYP7A1 transcription.