Caprylic Acid Improves Lipid Metabolism, Suppresses the Inflammatory Response and Activates the ABCA1/p-JAK2/p-STAT3 Signaling Pathway in C57BL/6J Mice and RAW264.7 Cells.

OBJECTIVE: This study aimed to investigate the effects of caprylic acid (C8:0) on lipid metabolism and inflammation, and examine the mechanisms underlying these effects in mice and cells. METHODS: Fifty-six 6-week-old male C57BL/6J mice were randomly allocated to four groups fed a high-fat diet (HFD) without or with 2% C8:0, palmitic acid (C16:0) or eicosapentaenoic acid (EPA). RAW246.7 cells were randomly divided into five groups: normal, lipopolysaccharide (LPS), LPS+C8:0, LPS+EPA and LPS+cAMP. The serum lipid profiles, inflammatory biomolecules, and ABCA1 and JAK2/STAT3 mRNA and protein expression were measured. RESULTS: C8:0 decreased TC and LDL-C, and increased the HDL-C/LDL-C ratio after injection of LPS. Without LPS, it decreased TC in mice ( P < 0.05). Moreover, C8:0 decreased the inflammatory response after LPS treatment in both mice and cells ( P < 0.05). Mechanistic investigations in C57BL/6J mouse aortas after injection of LPS indicated that C8:0 resulted in higher ABCA1 and JAK2/STAT3 expression than that with HFD, C16:0 and EPA, and resulted in lower TNF-α, NF-κB mRNA expression than that with HFD ( P < 0.05). In RAW 264.7 cells, C8:0 resulted in lower expression of pNF-κBP65 than that in the LPS group, and higher protein expression of ABCA1, p-JAK2 and p-STAT3 than that in the LPS and LPS+cAMP groups ( P < 0.05). CONCLUSION: Our studies demonstrated that C8:0 may play an important role in lipid metabolism and the inflammatory response, and the mechanism may be associated with ABCA1 and the p-JAK2/p-STAT3 signaling pathway.

CD11cHi monocyte-derived macrophages are a major cellular compartment infected by Mycobacterium tuberculosis.

During tuberculosis, lung myeloid cells have two opposing roles: they are an intracellular niche occupied by Mycobacterium tuberculosis, and they restrict bacterial replication. Lung myeloid cells from mice infected with yellow-fluorescent protein expressing M. tuberculosis were analyzed by flow cytometry and transcriptional profiling to identify the cell types infected and their response to infection. CD14, CD38, and Abca1 were expressed more highly by infected alveolar macrophages and CD11cHi monocyte-derived cells compared to uninfected cells. CD14, CD38, and Abca1 "triple positive" (TP) cells had not only the highest infection rates and bacterial loads, but also a strong interferon-γ signature and nitric oxide synthetase-2 production indicating recognition by T cells. Despite evidence of T cell recognition and appropriate activation, these TP macrophages are a cellular compartment occupied by M. tuberculosis long-term. Defining the niche where M. tuberculosis resists elimination promises to provide insight into why inducing sterilizing immunity is a formidable challenge.

Activation of liver X receptors inhibit LPS-induced inflammatory response in primary bovine mammary epithelial cells.

Liver X Receptors (LXRs) belong to the nuclear receptor superfamily, have been reported that activation of LXRs with synthetic ligands has anti-inflammatory effects in various inflammatory diseases. This study aims at investigating the effects of T0901317 (T0), a synthetic LXRs ligand, on lipopolysaccharide (LPS)-stimulated primary bovine mammary epithelial cells (bMECs). BMECs were stimulated by LPS in the presence or absence of T0. The results showed that treatment with T0 significantly inhibited LPS-induced tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), and interleukin-6 (IL-6) expression. LPS-induced NF-κB activation was also suppressed by T0. Furthermore, T0 was found to inhibit the translocation of TLR4 to lipid rafts. T0 could activate ATP-binding cassette transporter A1 (ABCA1) dependent pathway which induced cholesterol efflux from cells and disrupted the formation of lipid rafts. Thus, based on those findings we proposed that LXRs agonist might become a novel therapeutic target for inflammation.

Impact of TLR 2, TLR 4-activation on the Expression of ABCA1 and ABCG1 in Raw Cells.

Toll-like receptors (TLR) activation is thought to modulate the macrophage cholesterol efflux and contribute to the atherosclerosis progression; however, the precise pathophysiological mechanism remains unclear. We investigated the effects of TLR2- and TLR4-activation on the expression of the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 in a mouse macrophage cell line, Raw 264.7. Both TLR2- and TLR4-activation upregulated the expression of ABCA1 mRNA but downregulated that of ABCG1 mRNA. These alterations may be mainly regulated by the following 3 cascades: (1) the TLR/myeloid differentiation primary-response protein 88/Liver X receptor pathway, which upregulated the ABCA1 mRNA; (2) NF-κB pathway, which downregulated the ABCG1 mRNA, and (3) the p38 pathway, which upregulated and stabilized ABCA1 mRNA. These cascades are involved in a complex crosstalk and result in the upregulation of ABCA1 mRNA without a change in ABCA1 protein and the down-regulation of ABCG1 mRNA leading to the increase in ABCG1 protein. These alterations, especially the induction of ABCG1 protein, may be closely involved with the development of atherosclerosis.

MicroRNA-33 Regulates the Innate Immune Response via ATP Binding Cassette Transporter-mediated Remodeling of Membrane Microdomains.

MicroRNAs (miRNAs) are short non-coding RNAs that regulate gene expression by promoting degradation and/or repressing translation of specific target mRNAs. Several miRNAs have been identified that regulate the amplitude of the innate immune response by directly targeting Toll-like receptor (TLR) pathway members and/or cytokines. miR-33a and miR-33b (the latter present in primates but absent in rodents and lower species) are located in introns of the sterol regulatory element-binding protein (SREBP)-encoding genes and control cholesterol/lipid homeostasis in concert with their host gene products. These miRNAs regulate macrophage cholesterol by targeting the lipid efflux transporters ATP binding cassette (ABC)A1 and ABCG1. We and others have previously reported that Abca1(-/-) and Abcg1(-/-) macrophages have increased TLR proinflammatory responses due to augmented lipid raft cholesterol. Given this, we hypothesized that miR-33 would augment TLR signaling in macrophages via a raft cholesterol-dependent mechanism. Herein, we report that multiple TLR ligands down-regulate miR-33 in murine macrophages. In the case of lipopolysaccharide, this is a delayed, Toll/interleukin-1 receptor (TIR) domain-containing adapter-inducing interferon-ß-dependent response that also down-regulates Srebf-2, the host gene for miR-33. miR-33 augments macrophage lipid rafts and enhances proinflammatory cytokine induction and NF-κB activation by LPS. This occurs through an ABCA1- and ABCG1-dependent mechanism and is reversible by interventions upon raft cholesterol and by ABC transporter-inducing liver X receptor agonists. Taken together, these findings extend the purview of miR-33, identifying it as an indirect regulator of innate immunity that mediates bidirectional cross-talk between lipid homeostasis and inflammation.

The A's Have It: Developing Apolipoprotein A-I Mimetic Peptides Into a Novel Treatment for Asthma.

New treatments are needed for patients with asthma who are refractory to standard therapies, such as individuals with a phenotype of "type 2-low" inflammation. This important clinical problem could potentially be addressed by the development of apolipoprotein A-I (apoA-I) mimetic peptides. ApoA-I interacts with its cellular receptor, the ATP-binding cassette subfamily A, member 1 (ABCA1), to facilitate cholesterol efflux out of cells to form nascent high-density lipoprotein particles. The ability of the apoA-I/ABCA1 pathway to promote cholesterol efflux from cells that mediate adaptive immunity, such as antigen-presenting cells, can attenuate their function. Data from experimental murine models have shown that the apoA-I/ABCA1 pathway can reduce neutrophilic airway inflammation, primarily by suppressing the production of granulocyte-colony stimulating factor. Furthermore, administration of apoA-I mimetic peptides to experimental murine models of allergic asthma has decreased both neutrophilic and eosinophilic airway inflammation, as well as airway hyperresponsiveness and mucous cell metaplasia. Higher serum levels of apoA-I have also been associated with less severe airflow obstruction in patients with asthma. Collectively, these results suggest that the apoA-I/ABCA1 pathway may have a protective effect in asthma, and support the concept of advancing inhaled apoA-I mimetic peptides to clinical trials that can assess their safety and effectiveness. Thus, we propose that the development of inhaled apoA-I mimetic peptides as a new treatment could represent a clinical advance for patients with severe asthma who are unresponsive to other therapies.