Regulatory Roles of the Caspase-11 Non-Canonical Inflammasome in Inflammatory Diseases

Inflammation is an immune response mediated by innate immune cells of tissues, against invading microbes and cellular stress. The hallmark of inflammatory responses is the activation of inflammasomes — multiprotein oligomers comprising intracellular pattern recognition receptors and inflammatory effectors — such as ASC and pro-cysteine-aspartic protease (pro-caspase)-1. Inflammasomes can be classified as canonical or non-canonical, and their activation in response to various ligands commonly induces caspase-1 activation and gasdermin D (GSDMD) processing, leading to caspase-1-mediated maturation and secretion of the pro-inflammatory cytokines IL-1β and IL-18, and GSDMD-mediated pyroptosis through pore generation in cell membranes. Although inflammation protects the host from harmful stimuli, chronic inflammation is a critical risk factor for inflammatory diseases, and several studies have investigated the role of canonical inflammasomes in inflammatory responses and diseases, with emerging studies focusing on the role of non-canonical inflammasomes. This review discusses recent studies on the regulatory roles of the caspase-11 non-canonical inflammasome in the pathogenesis of inflammatory diseases. Additionally, it provides an insight into the development of novel therapeutics based on targeting caspase-11 non-canonical inflammasome and its downstream effectors to prevent and treat human inflammatory conditions.

Role of inflammasomes in inflammatory autoimmune rheumatic diseases

Inflammasomes are intracellular multiprotein complexes that coordinate anti-pathogenic host defense during inflammatory responses in myeloid cells, especially macrophages. Inflammasome activation leads to activation of caspase-1, resulting in the induction of pyroptosis and the secretion of pro-inflammatory cytokines including interleukin (IL)-1β and IL-18. Although the inflammatory response is an innate host defense mechanism, chronic inflammation is the main cause of rheumatic diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), ankylosing spondylitis (AS), and Sjögren's syndrome (SS). Since rheumatic diseases are inflammatory/autoimmune disorders, it is reasonable to hypothesize that inflammasomes activated during the inflammatory response play a pivotal role in development and progression of these diseases. Indeed, previous studies have provided important observations that inflammasomes are actively involved in the pathogenesis of inflammatory/autoimmune rheumatic diseases. In this review, we summarize the current knowledge on several types of inflammasomes during macrophage-mediated inflammatory responses and discuss recent research regarding the role of inflammasomes in the pathogenesis of inflammatory/autoimmune rheumatic diseases. This avenue of research could provide new insights for the development of promising therapeutics to treat inflammatory/autoimmune rheumatic diseases.

Hydroquinone suppresses IFN-β expression by targeting AKT/IRF3 pathway

Previous studies have demonstrated the role of hydroquinone (HQ), a hydroxylated benzene metabolite, in modulating various immune responses; however, its role in macrophage-mediated inflammatory responses is not fully understood. In this study, the role of HQ in inflammatory responses and the underlying molecular mechanism were explored in macrophages. HQ down-regulated the expression of interferon (IFN)-β mRNA in LPS-stimulated RAW264.7 cells without any cytotoxicity and suppressed interferon regulatory factor (IRF)-3-mediated luciferase activity induced by TIR-domain-containing adapter-inducing interferon-β (TRIF) and TANK-binding kinase 1 (TBK1). A mechanism study revealed that HQ inhibited IRF-3 phosphorylation induced by lipopolysaccharide (LPS), TRIF, and AKT by suppressing phosphorylation of AKT, an upstream kinase of the IRF-3 signaling pathway. IRF-3 phosphorylation is highly induced by wild-type AKT and poorly induced by an AKT mutant, AKT C310A, which is mutated at an inhibitory target site of HQ. We also showed that HQ inhibited IRF-3 phosphorylation by targeting all three AKT isoforms (AKT1, AKT2, and AKT3) in RAW264.7 cells and suppressed IRF-3-mediated luciferase activities induced by AKT in HEK293 cells. Taken together, these results strongly suggest that HQ inhibits the production of a type I IFN, IFN-β, by targeting AKTs in the IRF-3 signaling pathway during macrophage-mediated inflammation.

JS-III-49, a hydroquinone derivative, exerts anti-inflammatory activity by targeting Akt and p38

Since previous studies have reported that hydroquinone (HQ) exerted immunosuppressive and anti-inflammatory activity, various HQ derivatives have been synthesized and their biological activities investigated. In this study, we explored the anti-inflammatory activity of JS-III-49, a novel HQ derivative, in macrophage-mediated inflammatory responses. JS-III-49 suppressed the production of the inflammatory mediators nitric oxide (NO) and prostaglandin E2 (PGE2) and down-regulated the mRNA expression of the inflammatory enzymes cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) as well as the expression of the pro-inflammatory cytokines interleukin-6 (IL-6) and IL-1b without cytotoxicity in LPS-stimulated RAW264.7 cells. JS-III-49 inhibited nuclear translocation of the NF-kB transcription factors p65 and p50 by directly targeting Akt, an upstream kinase of the NF-kB pathway, in LPS-stimulated RAW264.7 cells. However, JS-III-49 did not directly inhibit the kinase activities of Src and Syk, which are upstream kinases of Akt, in LPS-stimulated RAW264.7 cells. Moreover, JS-III-49 suppressed the nuclear translocation of c-Fos, one of the components of AP-1, by specifically targeting p38, an upstream mitogen-activated protein kinase (MAPK) in the AP-1 pathway in LPS-stimulated RAW264.7 cells. These results suggest that JS-III-49 plays an anti-inflammatory role in LPS-stimulated macrophages by targeting Akt and p38 in the NF-kB and AP-1 pathways, respectively.

Folate Receptor-Targeted Diagnostics and Therapeutics for Inflammatory Diseases

Inflammation, an innate immune response mediated by macrophages, forms the first line of defence to protect our body from the invasion of various pathogens. Although inflammation is a defensive response, chronic inflammation has been regarded as the major cause of many types of human diseases such as inflammatory/autoimmune diseases, cancers, neurological diseases, and cardiovascular diseases. Folate receptor (FR) is a cell surface glycosylphosphatidylinositol (GPI)-anchored glycoprotein, and its three isoforms, FR-α, FR-β, and FR-γ, are found in humans. Interestingly, FRs are highly expressed on a variety of cells, including cancer cells and activated macrophages, whereas their expression on normal cells is undetectable, indicating that FR-targeting could be a good selective strategy for the diagnosis and therapeutic treatment of cancers and activated macrophage-mediated inflammatory diseases. Previous studies successfully showed FR-targeted imaging of many types of cancers in animal models as well as human patients. Recently, a number of emerging studies have found that activated macrophages, which are critical players for a variety of inflammatory diseases, highly express FRs, and selective targeting of these FR-positive activated macrophages is a good approach to diagnose and treat inflammatory diseases. In this review, we describe the characteristics and structure of FRs, and further discuss FR-targeted diagnostics and therapeutics of human diseases, in particular, activated macrophage-mediated inflammatory diseases.

Alcohol-induced Hyperlipidemia Is Ameliorated by Orally Administered DWP208, a Sodium Succinate Form of ZYM201

DWP208 is a sodium succinate form of ZYM-201 which is a triterpenoid glycoside isolated from Sanguisorba officinalis, a medicinal plant prescribed for various diseases, such as duodenal ulcers and bleeding in East Asian counties. We demonstrated that this compound is able to normalize the altered lipid metabolism induced by hyperglycemia and a high fat diet. In this study, we determined whether hyperlipidemic conditions induced with chronically treated alcohol can also be restored by DWP208. Similar to our previous results, orally administered DWP208 (1 to 10 mg/kg) also ameliorated the hyperlipidemia that was induced by alcohol. This compound reversed the alcohol-induced hyperlipidemia including (i) up-regulated hyperlipidemic parameters such as low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), atherosclerotic index (AI), triglyceride, and total cholesterol, and (ii) down-regulated hyperlipidemic parameters such as absolute body weight, superoxide dismutase (SOD) activity, and high-density lipoprotein (HDL) in serum and liver. According to our data, the ameliorative activity of DWP208 is due to its indirect anti-oxidative activity as a result of which lipid peroxide and hydroxyl radical levels were reduced and the activity of SOD was enhanced. Therefore, our data strongly suggest that DWP208 can be used as a remedy against alcohol-induced hyperlipidemia.