Selective activation of liver X receptors by acanthoic acid-related diterpenes

Biological activities of acanthoic acid and its pharmacological potential: a literature review

Plant-derived compounds can influence human physiology and have been harnessed through infusions and teas, which addressed human health since prehistory. Thus, acanthoic acid is a natural pimaradiene diterpene found in species of the Annonaceae family. This botanical family includes fruit-bearing trees such as cherimoyas, custard apples, soursops, and rollinia, popularly using these species for antiparasitic, anti-leishmanial, antimicrobial, cytotoxic, and antioxidant purposes. This review aims to consolidate key findings in the literature regarding acanthoic acid and its biological activities. Original articles published in English between the years 2013 and 2023 were included. The results indicated that only 15 articles were identified during the investigated period, all focused on preclinical or in silico studies. Among the main effects observed, antimicrobial, anti-inflammatory, hepatoprotective, and antitumor activities were highlighted. However, additional studies examining other facets are imperative, including toxicity, pharmacokinetics, and systemic effects, such as those on the central nervous and renal systems.

Calliloboapins A-L, diterpenoids from the branches and leaves of Callicarpa loboapiculata and their biological activities

Eleven new isopimarane diterpenoids and one new ent-pimarane diterpenoid, named calliloboapins A-L (1-12), were isolated from the branches and leaves of Callicarpa loboapiculata F. P. Metcalf. Their structures and absolute configurations were established by HRESIMS, UV, IR, 1D and 2D NMR spectroscopic analyses, single crystals X-ray diffraction and ECD calculations. Structurally, compound 1 possesses an unusual tricyclo [2.2.2.0] octane structure, and compound 2 is characterized by a cyclopentane ring B. Compound 3 contains an unprecedented ten-membered ring with an oxygen bridge connecting C-8 and C-9. The anti-inflammatory activities of all isolated compounds were evaluated by LPS-induced RAW264.7 cells. Compounds 1-12 inhibited the release of NO to varying degrees, and 3, 4, 8, 11 and 12 significantly suppressed the overexpression of inducible NO synthase. Moreover, liver X receptor alpha (LXRα) was predicted to be the probable target of isolates by Swiss Target Prediction tool, and compounds 2-4, 11 and 12 increased the protein expression of ATP-binding cassette transporter (ABCA1), showing potential antiatherogenic properties.

Ergosterol and its metabolites as agonists of Liver X receptor and their anticancer potential in colorectal cancer

Aberrant cholesterol homeostasis is a well-recognized hallmark of cancer and is implicated in metastasis as well as chemotherapeutic resistance, the two major causes of cancer associated mortality. Liver X receptors (LXRs) are the key transcription factors that induce cholesterol efflux via enhancing the expression of ABCA1 and ABCG1. Therefore, a comprehensive analysis of several novel sterols namely ergosta-7,22,24(28)-trien-3β-ol (Erg1), ergosta-5,22,25-trien-3-ol (Erg2), ergosta-5,7,22,24(28)-tetraen-3β-ol (Erg3), and ergosta-7,22-dien-3β-ol (Erg4) as LXR agonists has been performed. Molecular docking studies have shown that these sterols possess higher binding affinities for LXRs as compared to the reference ligands (GW3965 and TO901317) and also formed critical activating interactions. Molecular dynamic (MD) simulations further confirmed that docking complexes made of these sterols possess significant stability. To assess the extent of LXR activation, ABCA1 promoter was cloned into luciferase reporter plasmid and transfected into HCT116 cells. It was observed that treatment with Erg, Erg2 and Erg4 led to a significant LXR activation with an EC50 of 5.64 µM, 4.83 and 3.03 µM respectively. Furthermore, a significant increase in mRNA expression of NR1H2 and LXR target genes i.e. ABCA1, ABCG1 and ApoE was observed upon Erg treatment. Flow cytometric analysis have revealed a significant increase in the accumulation of ABCA1 upon Erg treatment. Cytotoxicity studies conducted on colorectal cancer cell and normal epithelial cell line showed that these sterols are selectively toxic towards cancer cells. Taken together, our findings suggests that ergosterol activates LXRs, have significant anticancer activity and could be a likely candidate to manage aberrant cholesterol homeostasis.

Assessing the Efficacy of Acanthoic Acid Isolated from Acanthopanax koreanum Nakai in Male Infertility: An In Vivo and In Silico Approach

Acanthoic acid, a diterpene isolated from the root bark of Acanthopanax koreanum Nakai, possesses diverse pharmacological activities, including anti-inflammatory, anti-diabetic, gastrointestinal protection, and cardiovascular protection. This study is the first to investigate the egg-hatching rates of Drosophila melanogaster affected by acanthoic acid. Notably, male flies supplemented with 10 μM acanthoic acid exhibited a strong increase in hatching rates compared with controls under adverse temperature conditions, suggesting a potential protective effect against environmental stressors. Molecular docking simulations revealed the binding affinities and specific interactions between acanthoic acid and proteins related to male infertility, including SHBG, ADAM17, and DNase I, with binding affinity values of -10.2, -6.8, and -5.8 kcal/mol, respectively. Following the docking studies, molecular dynamic simulations were conducted for a duration of 100 ns to examine the stability of these interactions. Additionally, a total binding energy analysis and decomposition analysis offered insights into the underlying energetic components and identified key contributing residues.

Ultra-High-Resolution Liquid Chromatography Coupled with Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry Analysis of Tessaria absinthioides (Hook. & Arn.) DC. (Asteraceae) and Antioxidant and Hypocholesterolemic Properties

Recently, we reported the chemical profile and the hypocholesterolemic effects of a decoction of Tessaria absinthioides (Hook. & Arn.) DC. (Asteraceae). In this study, we evaluated a methanolic extract (METa) instead. Metabolite profiling was conducted using ultra-high-resolution liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOF-MS), identifying thirty compounds, including flavonoids, phenolic acids, fatty acids, and phorbolesters. Antioxidant properties were assessed through 2,2-diphenyl-1-picrylhydrazyl (DPPH), Trolox equivalent antioxidant activity (TEAC), ferric-reducing antioxidant power (FRAP), and inhibition of lipid peroxidation in erythrocytes (ILP) assays, exhibiting robust antioxidant activity. The in vivo impact of METa on serum lipid parameters and liver X receptors (LXRs) was evaluated in a hypercholesterolemic animal model. After 14 days on a high-fat diet, male rats received either a vehicle (V) or METa100, METa200 or METa500 (100; 200 and 500 mg METa/kg animal, respectively) for an additional two weeks. METa500 reduced total cholesterol levels (17.62%; p < 0.05) and all doses increased high-density lipoprotein cholesterol levels (METa100: 86.27%; METa200: 48.37%, and METa500: 29.42%; p < 0.0001). However, METa did not alter LXRs expression. The observed antioxidant and hypocholesterolemic properties of METa may be linked to the presence of six di-caffeoylquinic acids. These findings underscore T. absinthioides as a potential candidate for the treatment of metabolic disease.

Liver X Receptor: a potential target in the treatment of atherosclerosis

INTRODUCTION

Liver X receptors (LXRs) are master regulators of atherogenesis. Their anti-atherogenic potential has been attributed to their role in the inhibition of macrophage-mediated inflammation and promotion of reverse cholesterol transport. Owing to the significance of their anti-atherogenic potential, it is essential to develop and test new generation LXR agonists, both synthetic and natural, to identify potential LXR-targeted therapeutics for the future.

AREAS COVERED

This review describes the role of LXRs in atherosclerotic development, provides a summary of LXR agonists and future directions for atherosclerosis research. We searched PubMed, Scopus and Google Scholar for relevant reports, from last 10 years, using atherosclerosis, liver X receptor, and LXR agonist as keywords.

EXPERT OPINION

LXRα has gained widespread recognition as a regulator of cholesterol homeostasis and expression of inflammatory genes. Further research using models of cell type-specific knockout and specific agonist-targeted LXR isoforms is warranted. Enthusiasm for therapeutic value of LXR agonists has been tempered due to LXRα-mediated induction of hepatic lipogenesis. LXRα agonism and LXRβ targeting, gut-specific inverse LXR agonists, investigations combining LXR agonists with other lipogenesis mitigating agents, like IDOL antagonists and synthetic HDL, and targeting ABCA1, M2 macrophages and LXRα phosphorylation, remain as promising possibilities.

Acanthoic acid, unique potential pimaradiene diterpene isolated from Acanthopanax koreanum Nakai (Araliaceae): A review on its pharmacology, molecular mechanism, and structural modification

Acanthoic acid (AA) is a pimaradiene diterpene isolated from the root bark of Acanthopanax koreanum Nakai (Araliaceae) with a wide range of pharmacological activities, including anti-cancer, anti-inflammatory, anti-diabetes, liver protection, gastrointestinal protection, and cardiovascular protection. In addition, AA promotes its pharmacological effects by targeting liver X receptors (LXRs), nuclear factor-kappa B (NF-κB), Toll-Like Receptor 4 (TLR4) and IL-1 receptor-associated kinase (IRAK) signaling pathways, or AMP-activated protein kinase (AMPK) signaling pathway, etc. Also, some studies focus on the structural modification of AA to improve its pharmacological activities. The review summarizes the pharmacological activities, molecular mechanism, and the structural modification of AA, which might supply information for the development of AA in the future.

Natural Products Targeting Liver X Receptors or Farnesoid X Receptor

Nuclear receptors (NRs) are a superfamily of transcription factors induced by ligands and also function as integrators of hormonal and nutritional signals. Among NRs, the liver X receptors (LXRs) and farnesoid X receptor (FXR) have been of significance as targets for the treatment of metabolic syndrome-related diseases. In recent years, natural products targeting LXRs and FXR have received remarkable interests as a valuable source of novel ligands encompassing diverse chemical structures and bioactive properties. This review aims to survey natural products, originating from terrestrial plants and microorganisms, marine organisms, and marine-derived microorganisms, which could influence LXRs and FXR. In the recent two decades (2000-2020), 261 natural products were discovered from natural resources such as LXRs/FXR modulators, 109 agonists and 38 antagonists targeting LXRs, and 72 agonists and 55 antagonists targeting FXR. The docking evaluation of desired natural products targeted LXRs/FXR is finally discussed. This comprehensive overview will provide a reference for future study of novel LXRs and FXR agonists and antagonists to target human diseases, and attract an increasing number of professional scholars majoring in pharmacy and biology with more in-depth discussion.

Tessaria absinthioides (Hook. & Arn.) DC. (Asteraceae) Decoction Improves the Hypercholesterolemia and Alters the Expression of LXRs in Rat Liver and Hypothalamus

Chronic high-fat diet consumption induces hypercholesterolemia. The effect of Tessaria absinthioides (Hook. & Arn.) DC. (Asteraceae) was studied on the levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-c), and triglycerides, and on the expression of liver X receptors (LXRs) in a hypercholesterolemic model. Adult male rats received a normal diet (ND) or a high-fat diet (HFD; normal diet + bovine fat + cholesterol). After 14 days, rats received water (W) or a decoction of the aerial parts of T. absinthioides (Ta; 10% w/v) for 2, 4, or 6 weeks. Four and six weeks of Ta improved the levels of TC and HDL-c in HFD. After 6 weeks of Ta, the expression of LXRs in HFD was the same as that in ND in both tissues. The Ta chemical profile was studied with an ultrahigh resolution liquid chromatography Orbitrap MS analysis (UHPLC-PDA-OT-MS/MS). Fifty-one compounds were identified, of which twelve are reported for the first time. Among these compounds, caffeoylquinic acid and its derivatives could modify the lipid profile and the expression of LXRs. This is the first in vivo report of T. absinthioides, which may be a potential candidate against hypercholesterolemia.

Liver X receptors conserve the therapeutic target potential for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic multi-system autoimmune disease with extremely complex pathogenesis. Significantly altered lipid paradox related to the inflammatory burden is reported in RA patients, inducing 50% higher cardiovascular risks. Recent studies have also demonstrated that lipid metabolism can regulate many functions of immune cells in which metabolic pathways have altered. The nuclear liver X receptors (LXRs), including LXRα and LXRβ, play a central role in regulating lipid homeostasis and inflammatory responses. Undoubtedly, LXRs have been considered as an attractive therapeutic target for the treatment of RA. However, there are some contradictory effects of LXRs agonists observed in previous animal studies where both pro-inflammatory role and anti-inflammatory role were revealed for LXRs activation in RA. Therefore, in addition to updating the knowledge of LXRs as the prominent regulators of lipid homeostasis, the purpose of this review is to summarize the effects of LXRs agonists in RA-associated immune cells, to explore the underlying reasons for the contradictory therapeutic effects of LXRs agonists observed in RA animal models, and to discuss future strategy for the treatment of RA with LXRs modulators.

Liver X receptors and skeleton: Current state-of-knowledge

The liver X receptors (LXR) is a nuclear receptor that acts as a prominent regulator of lipid homeostasis and inflammatory response. Its therapeutic effectiveness against various diseases like Alzheimer's disease and atherosclerosis has been investigated in detail. Emerging pieces of evidence now reveal that LXR is also a crucial modulator of bone remodeling. However, the molecular mechanisms underlying the pharmacological actions of LXR on the skeleton and its role in osteoporosis are poorly understood. Therefore, in the current review, we highlight LXR and its actions through different molecular pathways modulating skeletal homeostasis. The studies described in this review propound that LXR in association with estrogen, PTH, PPARγ, RXR hedgehog, and canonical Wnt signaling regulates osteoclastogenesis and bone resorption. It regulates RANKL-induced expression of c-Fos, NFATc1, and NF-κB involved in osteoclast differentiation. Additionally, several studies suggest suppression of RANKL-induced osteoclast differentiation by synthetic LXR ligands. Given the significance of modulation of LXR in various physiological and pathological settings, our findings indicate that therapeutic targeting of LXR might potentially prevent or treat osteoporosis and improve bone quality.

Role of Liver X Receptor in Mastitis Therapy and Regulation of Milk Fat Synthesis

Mastitis is important disease that causes huge economic losses in the dairy industry. In recent years, antibiotic therapy has become the primary treatment for mastitis, however, due to drug residue in milk and food safety factors, we lack safe and effective drugs for treating mastitis. Therefore, new targets and drugs are urgently needed to control mastitis. LXRα, one of the main members of the nuclear receptor superfamily, is reported to play important roles in metabolism, infection and immunity. Activation of LXRα could inhibit LPS-induced mastitis. Furthermore, LXRα is reported to enhance milk fat production, thus, LXRα may serve as a new target for mastitis therapy and regulation of milk fat synthesis. This review summarizes the effects of LXRα in regulating milk fat synthesis and treatment of mastitis and highlights the potential agonists involved in both issues.

GQ-11: A new PPAR agonist improves obesity-induced metabolic alterations in LDLr-/- mice

BACKGROUND

Obesity and insulin resistance/diabetes are important risk factors for cardiovascular diseases and demand safe and efficacious therapeutics.

OBJECTIVE

To assess the effects of a new thiazolidine compound-GQ-11-on obesity and insulin resistance induced by a diabetogenic diet in LDL receptor-deficient (LDLr-/-) mice.

METHODS

Molecular docking simulations of GQ-11, PPARα and PPARγ structures were performed. Male C57BL/6J LDLr-/- mice fed a diabetogenic diet for 24 weeks were treated with vehicle, GQ-11 or pioglitazone or (20 mg/kg/day) for 28 days by oral gavage. Glucose tolerance test, insulin, HOMA-IR, adipokines (leptin, adiponectin) and the lipid profile were assessed after treatment. Adipose tissue was analysed by X-ray analysis and morphometry; gene and protein expression were evaluated by real-time PCR and western blot, respectively.

RESULTS

GQ-11 showed partial agonism to PPARγ and PPARα. In vivo, treatment with GQ-11 ameliorated insulin sensitivity and did not modify subcutaneous adipose tissue and body weight gain. In addition, GQ-11 restored adipokine imbalance induced by a diabetogenic diet and enhanced Glut-4 expression in the adipose tissue. Improved insulin sensitivity was also associated with lower levels of MCP-1 and higher levels of IL-10. Furthermore, GQ-11 reduced triglycerides and VLDL cholesterol and increased HDL-cholesterol by upregulation of Apoa1 and Abca1 gene expression in the liver.

CONCLUSION

GQ-11 is a partial/dual PPARα/γ agonist that demonstrates anti-diabetic effects. Additionally, it improves the lipid profile and ameliorates chronic inflammation associated with obesity in atherosclerosis-prone mice.

Ligands of Therapeutic Utility for the Liver X Receptors

Liver X receptors (LXRs) have been increasingly recognized as a potential therapeutic target to treat pathological conditions ranging from vascular and metabolic diseases, neurological degeneration, to cancers that are driven by lipid metabolism. Amidst intensifying efforts to discover ligands that act through LXRs to achieve the sought-after pharmacological outcomes, several lead compounds are already being tested in clinical trials for a variety of disease interventions. While more potent and selective LXR ligands continue to emerge from screening of small molecule libraries, rational design, and empirical medicinal chemistry approaches, challenges remain in minimizing undesirable effects of LXR activation on lipid metabolism. This review provides a summary of known endogenous, naturally occurring, and synthetic ligands. The review also offers considerations from a molecular modeling perspective with which to design more specific LXRβ ligands based on the interaction energies of ligands and the important amino acid residues in the LXRβ ligand binding domain.

New PPARγ partial agonist improves obesity-induced metabolic alterations and atherosclerosis in LDLr(-/-) mice

Peroxisome proliferator-activated receptor gamma (PPARγ) regulates multiple pathways involved in the pathogenesis of obesity and atherosclerosis. Here, we evaluated the therapeutic potential of GQ-177, a new thiazolidinedione, on diet-induced obesity and atherosclerosis. The intermolecular interaction between PPARγ and GQ-177 was examined by virtual docking and PPAR activation was determined by reporter gene assay identifying GQ-177 as a partial and selective PPARγ agonist. For the evaluation of biological activity of GQ-177, low-density lipoprotein receptor-deficient (LDLr(-/-)) C57/BL6 mice were fed either a high fat diabetogenic diet (diet-induced obesity), or a high fat atherogenic diet, and treated with vehicle, GQ-177 (20mg/kg/day), pioglitazone (20mg/kg/day, diet-induced obesity model) or rosiglitazone (15mg/kg/day, atherosclerosis model) for 28 days. In diet-induced obesity mice, GQ-177 improved insulin sensitivity and lipid profile, increased plasma adiponectin and GLUT4 mRNA in adipose tissue, without affecting body weight, food consumption, fat accumulation and bone density. Moreover, GQ-177 enhanced hepatic mRNA levels of proteins involved in lipid metabolism. In the atherosclerosis mice, GQ-177 inhibited atherosclerotic lesion progression, increased plasma HDL and mRNA levels of PPARγ and ATP-binding cassette A1 in atherosclerotic lesions. GQ-177 acts as a partial PPARγ agonist that improves obesity-associated insulin resistance and dyslipidemia with atheroprotective effects in LDLr(-/-) mice.

New indole-thiazolidine attenuates atherosclerosis in LDLr(-/-) mice

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor γ (PPARγ) agonists that improve insulin-mediated glucose uptake and possess beneficial vasculoprotective actions. However, because undesirable side effects are associated with these drugs, novel TZDs are under development. In this study, we evaluated the biological activity of LYSO-7, a new indole-thiazolidine, on PPAR activation, inflammation and atherogenesis using a gene reporter assay, lipopolysaccharide (LPS)-activated RAW 264.7 cell culture, and a low-density lipoprotein receptor knockout (LDLr(-/-)) mouse model of atherosclerosis. LYSO-7 shows low cytotoxicity in RAW 264.7 cells and at 2.5μmol/L induces PPARα and PPARγ transactivation as well as inhibits LPS-induced nitrite production and the mRNA gene expression levels of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1). In addition, treatment with LYSO-7 reduces the development of atherosclerosis in LDLr(-/-) mice, improves the lipid profile, blood glucose levels, and downregulates CD40 and CD40L expression without affecting the body weight of the animals. Altogether, our data show that LYSO-7 possesses anti-inflammatory properties and that treatment with this TZD attenuates atherosclerosis progression in LDLr(-/-) mice by modulating lipid metabolism and inflammation. Thus, LYSO-7 shows potential as a new drug candidate for the treatment of atherosclerosis.

Activating PI3-kinase to dampen inflammation

Diterpene derivatives of the natural product acanthoic acid have potent anti-inflammatory effects in vivo. In this issue of Chemistry & Biolgy, Través and colleagues report that the primary molecular mechanism of action of diterpenes structurally related to acanthoic acid is the direct activation of PI3-kinase signaling in macrophages, which in turn inhibits NF-κB activation and suppresses proinflammatory gene expression.

Acanthoic acid ameliorates lipopolysaccharide-induced acute lung injury

Acanthoic acid, a pimaradiene diterpene isolated from Acanthopanax koreanum, has been reported to have anti-inflammatory activities. However, the effects of acanthoic acid on LPS-induced acute lung injury have not been reported. The purpose of this study was to investigate the protective effect of acanthoic acid on LPS-induced ALI and to clarify the possible anti-inflammatory mechanisms. In vivo, an LPS-induced ALI model in mice was used to assess the protective effects of acanthoic acid on ALI. Meanwhile, mouse alveolar macrophages MH-S were stimulated with LPS in the presence or absence of acanthoic acid. The expressions of TNF-α, IL-6 and IL-1β were measured by ELISA. LXRα and NF-κB expression were detected by Western blot analysis. The results showed that acanthoic acid downregulated LPS-induced TNF-α, IL-6 and IL-1β production in BALF. MPO activity and lung wet-to-dry ratio were also inhibited by acanthoic acid. In addition, acanthoic acid attenuated lung histopathologic changes. In vitro, acanthoic acid inhibited inflammatory cytokines TNF-α, IL-6 and IL-1β production and NF-κB activation in LPS-stimulated alveolar macrophages. Acanthoic acid was found to up-regulated the expression of LXRα. The inhibition of acanthoic acid on LPS-induced cytokines and NF-κB activation can be abolished by LXRα siRNA. In conclusion, our results suggested that the protective effect of acanthoic acid on LPS-induced ALI was due to its ability to activate LXRα, thereby inhibiting LPS-induced inflammatory response.

Anti-inflammatory actions of acanthoic acid-related diterpenes involve activation of the PI3K p110γ/δ subunits and inhibition of NF-κB

The effect of acanthoic acid analogs on the response to proinflammatory challenge was investigated. Some pimarane diterpenes are known activators of the LXRαβ nuclear receptors, but we show here that they also exert a rapid, potent, and selective activation of the p110γ and p110δ subunits of PI3K. Combination of these effects results in an important attenuation of the global transcriptional response to LPS in macrophages. PI3K/Akt activation leads to inhibition of the LPS-dependent stimulation of IKK/NF-κB and p38 and ERK MAPKs. Macrophages from LXRαβ-deficient mice exhibited an inhibition of these pathways similar to the corresponding wild-type cells. Silencing or inhibition of p110γ/δ suppressed the effect of these diterpenes (DTPs) on IKK/NF-κB and MAPKs signaling. Taken together, these data show a multitarget anti-inflammatory mechanism by these DTPs including a selective activation of PI3K isoenzymes.

Modulation of voltage-dependent and inward rectifier potassium channels by 15-epi-lipoxin-A4 in activated murine macrophages: implications in innate immunity

Potassium channels modulate macrophage physiology. Blockade of voltage-dependent potassium channels (Kv) by specific antagonists decreases macrophage cytokine production and inhibits proliferation. In the presence of aspirin, acetylated cyclooxygenase-2 loses the activity required to synthesize PGs but maintains the oxygenase activity to produce 15R-HETE from arachidonate. This intermediate product is transformed via 5-LOX into epimeric lipoxins, termed 15-epi-lipoxins (15-epi-lipoxin A4 [e-LXA4]). Kv have been proposed as anti-inflammatory targets. Therefore, we studied the effects of e-LXA4 on signaling and on Kv and inward rectifier potassium channels (Kir) in mice bone marrow-derived macrophages (BMDM). Electrophysiological recordings were performed in these cells by the whole-cell patch-clamp technique. Treatment of BMDM with e-LXA4 inhibited LPS-dependent activation of NF-κB and IκB kinase β activity, protected against LPS activation-dependent apoptosis, and enhanced the accumulation of the Nrf-2 transcription factor. Moreover, treatment of LPS-stimulated BMDM with e-LXA4 resulted in a rapid decrease of Kv currents, compatible with attenuation of the inflammatory response. Long-term treatment of LPS-stimulated BMDM with e-LXA4 significantly reverted LPS effects on Kv and Kir currents. Under these conditions, e-LXA4 decreased the calcium influx versus that observed in LPS-stimulated BMDM. These effects were partially mediated via the lipoxin receptor (ALX), because they were significantly reverted by a selective ALX receptor antagonist. We provide evidence for a new mechanism by which e-LXA4 contributes to inflammation resolution, consisting of the reversion of LPS effects on Kv and Kir currents in macrophages.

Selective liver X receptor modulators (SLiMs): what use in human health?

Liver X receptors (LXR) are members of the nuclear receptor family. As activated transcription factors, their putative association with human diseases makes them promising pharmacological targets because of the large potential to develop ligands. LXR are mainly considered as intracellular cholesterol "sensors" whose activation leads to decreased plasma cholesterol. They also modulate numerous physiological functions: fatty acid synthesis and metabolism, glucose homeostasis, steroidogenesis, immunity, and neurological homeostasis. LXR-deficiency in mouse results in several phenotypes mimicking pathological conditions in humans. This review will be focused on the various natural and synthetic LXR agonists and antagonists. Putative clinical targets including atherosclerosis, diabetes, Alzheimer's disease, skin disorders, and cancer will be covered.

Relevance of the MEK/ERK signaling pathway in the metabolism of activated macrophages: a metabolomic approach

The activation of immune cells in response to a pathogen involves a succession of signaling events leading to gene and protein expression, which requires metabolic changes to match the energy demands. The metabolic profile associated with the MAPK cascade (ERK1/2, p38, and JNK) in macrophages was studied, and the effect of its inhibition on the specific metabolic pattern of LPS stimulation was characterized. A [1,2-[(13)C](2)]glucose tracer-based metabolomic approach was used to examine the metabolic flux distribution in these cells after MEK/ERK inhibition. Bioinformatic tools were used to analyze changes in mass isotopomer distribution and changes in glucose and glutamine consumption and lactate production in basal and LPS-stimulated conditions in the presence and absence of the selective inhibitor of the MEK/ERK cascade, PD325901. Results showed that PD325901-mediated ERK1/2 inhibition significantly decreased glucose consumption and lactate production but did not affect glutamine consumption. These changes were accompanied by a decrease in the glycolytic flux, consistent with the observed decrease in fructose-2,6-bisphosphate concentration. The oxidative and nonoxidative pentose phosphate pathways and the ratio between them also decreased. However, tricarboxylic acid cycle flux did not change significantly. LPS activation led to the opposite responses, although all of these were suppressed by PD325901. However, LPS also induced a small decrease in pentose phosphate pathway fluxes and an increase in glutamine consumption that were not affected by PD325901. We concluded that inhibition of the MEK/ERK cascade interferes with central metabolism, and this cross-talk between signal transduction and metabolism also occurs in the presence of LPS.

Anti-inflammatory mechanism of 15,16-epoxy-3α-hydroxylabda-8,13(16),14-trien-7-one via inhibition of LPS-induced multicellular signaling pathways

Phytochemical investigation of Leonurus japonicus has led to the isolation of a labdane diterpene derivative, 15,16-epoxy-3α-hydroxylabda-8,13(16),14-trien-7-one (1), which was tested for its in vitro anti-inflammatory effects. The results demonstrated that 1 exhibits an inhibitory effect on LPS-stimulated RAW 264.7 macrophages. The anti-inflammatory action shown by 1 suppressed LPS-induced NF-κB activation, resulting in the down-regulation of iNOS and COX-2 protein expression, attributable to the inhibitory action of LPS-induced NO and PGE(2) production. Compound 1 inhibited LPS-induced phosphorylation and the degradation of inhibitory kappa B (IκBα) and decreased the nuclear translocation of p50 and p65. In addition, 1 exhibited an inhibitory effect on LPS-induced NF-κB-DNA and AP-1-DNA binding activity, using an electrophoretic mobility shift assay with NF-κB- and AP-1-specific (32)P-labeled probes. The LPS-induced mitogen-activated protein kinases (p-JNK, p-p38, and p-ERK) and p-Akt were inhibited after 30 and 10 min of LPS stimulation, respectively. In addition, TNF-α production was suppressed by 1.

Cot/tpl2 activity is required for TLR-induced activation of the Akt p70 S6k pathway in macrophages: Implications for NO synthase 2 expression

LPS stimulation activates IKK and different MAP kinase pathways, as well as the PI3K-Akt-mTOR-p70 S6k pathway, a negative regulator of these MyD88-dependent intracellular signals. Here, we show that Cot/tpl2, a MAP3K responsible for the activation of the MKK1-Erk1/2, controls P-Ser473 Akt and P-Thr389 p70 S6k phosphorylation in LPS-stimulated macrophages. Analysis of the intracellular signalling in Cot/tpl2 KO macrophages versus WT macrophages reveals lower IκBα recovery and higher phosphorylation of JNK and p38α after 1 h of LPS stimulation. Moreover, Cot/tpl2 deficiency increases LPS-induced NO synthase 2 (NOS2) expression in macrophages. Inhibition of the PI3K pathway abolishes the differences in IκBα and NOS2 expression between Cot/tpl2 KO and WT macrophages following LPS administration. Furthermore, in zymosan- and polyI:C-stimulated macrophages, Cot/tpl2 mediates P-Ser473 Akt phosphorylation, increases IκBα levels and decreases NOS2 expression. In conclusion, these data reveal a novel role for the Cot/tpl2 pathway in mediating TLR activation of the Akt-mTOR-p70 S6k pathway, allowing Cot/tpl2 to fine-control the activation state of other signalling pathways.

Cot/tpl2 (MAP3K8) mediates myeloperoxidase activity and hypernociception following peripheral inflammation

Cot/tpl2 (also known as MAP3K8) has emerged as a new and potentially interesting therapeutic anti-inflammatory target. Here, we report the first study of Cot/tpl2 involvement in acute peripheral inflammation in vivo. Six hours after an intraplantar injection of zymosan, Cot/tpl2(-/-) mice showed a 47% reduction in myeloperoxidase activity, concomitant with a 46% lower neutrophil recruitment and a 40% decreased luminol-mediated bioluminescence imaging in vivo. Accordingly, Cot/tpl2 deficiency provoked a 25-30% reduction in luminol-mediated bioluminescence and neutrophil recruitment together with a 65% lower macrophage recruitment 4 h following zymosan-induced peritonitis. Significantly impaired levels of G-CSF and GM-CSF and of other cytokines such as TNFα, IL-1β, and IL-6, as well as some chemokines such as MCP-1, MIP-1β, and keratinocyte-derived chemokine, were detected during the acute zymosan-induced intraplantar inflammatory response in Cot/tpl2(-/-) mice. Moreover, Cot/tpl2 deficiency dramatically decreased the production of the hypernociceptive ligand NGF at the inflammatory site during the course of inflammation. Most importantly, Cot/tpl2 deficiency significantly reduced zymosan-induced inflammatory hypernociception in mice, with a most pronounced effect of a 50% decrease compared with wild type (WT) at 24 h following intraplantar injection of zymosan. At this time, Cot/tpl2(-/-) mice showed significantly reduced NGF, TNFα, and prostaglandin E(2) levels compared with WT littermates. In conclusion, our study demonstrates an important role of Cot/tpl2 in the NGF, G-CSF, and GM-CSF production and myeloperoxidase activity in the acute inflammatory response process and its implication in inflammatory hypernociception.

Macrophage fatty-acid synthase deficiency decreases diet-induced atherosclerosis

Fatty acid metabolism is perturbed in atherosclerotic lesions, but whether it affects lesion formation is unknown. To determine whether fatty acid synthesis affects atherosclerosis, we inactivated fatty-acid synthase (FAS) in macrophages of apoE-deficient mice. Serum lipids, body weight, and glucose metabolism were the same in FAS knock-out in macrophages (FASKOM) and control mice, but blood pressure was lower in FASKOM animals. Atherosclerotic extent was decreased 20-40% in different aortic regions of FASKOM as compared with control mice on Western diets. Foam cell formation was diminished in FASKOM as compared with wild type macrophages due to increased apoAI-specific cholesterol efflux and decreased uptake of oxidized low density lipoprotein. Expression of the anti-atherogenic nuclear receptor liver X receptor alpha (LXRalpha; Nr1h3) and its downstream targets, including Abca1, were increased in FASKOM macrophages, whereas expression of the potentially pro-atherogenic type B scavenger receptor CD36 was decreased. Peroxisome proliferator-activated receptor alpha (PPARalpha) target gene expression was decreased in FASKOM macrophages. PPARalpha agonist treatment of FASKOM and wild type macrophages normalized PPARalpha target gene expression as well as Nr1h3 (LXRalpha). Atherosclerotic lesions were more extensive when apoE null mice were transplanted with LXRalpha-deficient/FAS-deficient bone marrow as compared with LXRalpha-replete/FAS-deficient marrow, consistent with anti-atherogenic effects of LXRalpha in the context of FAS deficiency. These results show that macrophage FAS deficiency decreases atherosclerosis through induction of LXRalpha and suggest that FAS, which is induced by LXRalpha, may generate regulatory lipids that cause feedback inhibition of LXRalpha in macrophages.

PPARgamma1 and LXRalpha face a new regulator of macrophage cholesterol homeostasis and inflammatory responsiveness, AEBP1

Peroxisome proliferator-activated receptor γ1 (PPARγ1) and liver X receptor α (LXRα) are nuclear receptors that play pivotal roles in macrophage cholesterol homeostasis and inflammation; key biological processes in atherogenesis. The activation of PPARγ1 and LXRα by natural or synthetic ligands results in the transactivation of ABCA1, ABCG1, and ApoE; integral players in cholesterol efflux and reverse cholesterol transport. In this review, we describe the structure, isoforms, expression pattern, and functional specificity of PPARs and LXRs. Control of PPARs and LXRs transcriptional activity by coactivators and corepressors is also highlighted. The specific roles that PPARγ1 and LXRα play in inducing macrophage cholesterol efflux mediators and antagonizing macrophage inflammatory responsiveness are summarized. Finally, this review focuses on the recently reported regulatory functions that adipocyte enhancer-binding protein 1 (AEBP1) exerts on PPARγ1 and LXRα transcriptional activity in the context of macrophage cholesterol homeostasis and inflammation.

Synthesis and induction of apoptosis signaling pathway of ent-kaurane derivatives

Thirty one ent-kaurane derivatives were prepared from kaurenoic acid (1), grandiflorenic acid (16), 15alpha-acetoxy-kaurenoic acid (26) and 16alpha-hydroxy-kaurenoic acid (31). They were tested for their ability to inhibit cell viability in the mouse leukemic macrophagic RAW 264.7 cell line. The most effective compounds were 12, 20, 21, and 23. These were selected for further evaluation in other human cancer cell lines such as Hela, HepG2, and HT-29. Similar effects were obtained although RAW 264.7 cells were more sensitive. In addition, these compounds were significantly less cytotoxic in non-transformed cells. The apoptotic potential of the most active compounds was investigated and they were able to induce apoptosis with compound 12 being the best inducer. The caspase-3, -8 and -9 activities were measured. The results obtained showed that compounds 12, 21, and 23 induce apoptosis via the activation of caspase-8, whereas compound 20 induces apoptosis via caspase-9. Immunoblot analysis of the expression of p53, Bax, Bcl-2, Bcl-xl, and IAPs in RAW 264.7 cells was also carried out. When cells were exposed to 5 microM of the different compounds, expression levels of p53 and Bax increased whereas levels of antiapoptotic proteins such as Bc1-2, Bc1-x1, and IAPs decreased. In conclusion, kaurane derivatives (12, 20, 21, and 23) induce apoptosis via both the mitochondrial and membrane death receptor pathways, involving the Bcl-2 family proteins. Taken together these results provide a role of kaurane derivatives as apoptotic inducers in tumor cells.

Current concepts in immunology

The annual Congress of the Spanish Immunology Society is the forum at which clinical immunologists and scientists communicate novel findings in the field. This year's meeting was held in Palma de Mallorca, Spain, from 21 to 24 May 2008. It was opened and organized by Nuria Matamoros, head of the Immunology Department of Hospital Son Dureta, Mallorca, Spain. The meeting comprised an opening lecture, four highly successful plenary sessions, 11 oral and poster sessions where recent results of different groups were shown, four workshops in which interlaboratory studies of quality control on different immune tests were discussed and a closing lecture. Some of the most interesting plenary presentations given at this meeting are summarized.

Selective partial agonism of liver X receptor alpha is related to differential corepressor recruitment

Classically, activated transcription by nuclear receptors (NRs) is due to a ligand-induced switch from corepressor- to coactivator-bound states. However, coactivators and corepressors recognize overlapping surfaces of liganded and unliganded NRs, respectively. Here we show that, at sufficiently high concentration, the NR corepressor (NCoR) influences the activity of the liver X receptor (LXR) even in the presence of a potent full agonist that destabilizes NCoR binding. Partial agonist ligands that less effectively dissociate NCoR from LXR are even more sensitive to NCoR levels, in a target gene-selective manner. Thus, differential recruitment of NCoR is a major determinant of partial agonism and selective LXR modulation of target genes.

Suppression of inflammatory responses by labdane-type diterpenoids

A series of 11 labdane-type diterpenoids (1-11) with various patterns of substitution were tested for potential anti-inflammatory activity. Of these compounds, 4 and 11 were selected to evaluate their influence on targets relevant to the regulation of the inflammatory response. These diterpenoids reduced the production of nitric oxide (NO), prostaglandin E2, and tumor necrosis factor-alpha in LPS-activated RAW 264.7 macrophages, with IC50 in the range 1-10 microM. Inhibition of these inflammatory mediators was related to inhibition of the expression of nitric oxide synthase-2 (NOS-2) and cyclooxygenase-2 (COX-2) at the transcriptional level, as determined by western-blot and RT-PCR. Examination of the effects of these diterpenoids on nuclear factor kappaB signaling showed that both compounds inhibit the phosphorylation of IkappaBalpha and IkappaBbeta, preventing their degradation and the nuclear translocation of the NF-kappaB p65 subunit. Inhibition of IKK activity was also observed. These derivatives displayed significant anti-inflammatory activity in vivo, suppressing mouse ear edema induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) and inhibiting myeloperoxidase activity, an index of neutrophil infiltration. The anti-inflammatory effects of these labdane diterpenoids, together with their low cell toxicity, suggest potential therapeutic applications in the regulation of the inflammatory response.