Resolution Of Inflammatory Diseases Research Articles

Specialized Proresolving Mediators for Therapeutic Interventions Targeting Metabolic and Inflammatory Disorders

Uncontrolled inflammation is considered the pathophysiological basis of many prevalent metabolic disorders, such as nonalcoholic fatty liver disease, diabetes, obesity, and neurodegenerative diseases. The inflammatory response is a self-limiting process that produces a superfamily of chemical mediators, called specialized proresolving mediators (SPMs). SPMs include the ω-3-derived family of molecules, such as resolvins, protectins, and maresins, as well as arachidonic acid-derived (ω-6) lipoxins that stimulate and promote resolution of inflammation, clearance of microbes, and alleviation of pain and promote tissue regeneration via novel mechanisms. SPMs function by binding and activating G protein-coupled receptors, such as FPR2/ALX, GPR32, and ERV1, and nuclear orphan receptors, such as RORα. Recently, several studies reported that SPMs have the potential to attenuate lipid metabolism disorders. However, the understanding of pharmacological aspects of SPMs, including tissue-specific biosynthesis, and specific SPM receptors and signaling pathways, is currently limited. Here, we summarize recent advances in the role of SPMs in resolution of inflammatory diseases with metabolic disorders, such as nonalcoholic fatty liver disease and obesity, obtained from preclinical animal studies. In addition, the known SPM receptors and their intracellular signaling are reviewed as targets of resolution of inflammation, and the currently available information on the therapeutic effects of major SPMs for metabolic disorders is summarized.

Changes in Plasma Itaconate Elevation in Early Rheumatoid Arthritis Patients Elucidates Disease Activity Associated Macrophage Activation.

Changes in the plasma metabolic profile were characterised in newly diagnosed rheumatoid arthritis (RA) patients upon commencement of conventional disease-modifying anti-rheumatic drug (cDMARD) therapy. Plasma samples collected in an early RA randomised strategy study (NCT00920478) that compared clinical (DAS) disease activity assessment with musculoskeletal ultrasound assessment (MSUS) to drive treatment decisions were subjected to untargeted metabolomic analysis. Metabolic profiles were collected at pre- and three months post-commencement of nonbiologic cDMARD. Metabolites that changed in association with changes in the DAS44 score were identified at the three-month timepoint. A total of nine metabolites exhibited a clear correlation with a reduction in DAS44 score following cDMARD commencement, particularly itaconate, its derived anhydride and a derivative of itaconate CoA. Increasing itaconate correlated with improved DAS44 score and decreasing levels of C-reactive protein (CRP). cDMARD treatment effects invoke consistent changes in plasma detectable metabolites, that in turn implicate clinical disease activity with macrophages. Such changes inform RA pathogenesis and reveal for the first time a link between itaconate production and resolution of inflammatory disease in humans. Quantitative metabolic biomarker-based tests of clinical change in state are feasible and should be developed around the itaconate pathway.

Use of DAMPs and SAMPs as Therapeutic Targets or Therapeutics: A Note of Caution.

This opinion article discusses the increasing attention paid to the role of activating damage-associated molecular patterns (DAMPs) in initiation of inflammatory diseases and suppressing/inhibiting DAMPs (SAMPs) in resolution of inflammatory diseases and, consequently, to the future roles of these novel biomarkers as therapeutic targets and therapeutics. Since controlled production of DAMPs and SAMPs is needed to achieve full homeostatic restoration and repair from tissue injury, only their pathological, not their homeostatic, concentrations should be therapeutically tackled. Therefore, distinct caveats are proposed regarding choosing DAMPs and SAMPs for therapeutic purposes. For example, we discuss the need to a priori identify and define a context-dependent “homeostatic DAMP:SAMP ratio” in each case and a “homeostatic window” of DAMP and SAMP concentrations to guarantee a safe treatment modality to patients. Finally, a few clinical examples of how DAMPs and SAMPs might be used as therapeutic targets or therapeutics in the future are discussed, including inhibition of DAMPs in hyperinflammatory processes (e.g., systemic inflammatory response syndrome, as currently observed in Covid-19), administration of SAMPs in chronic inflammatory diseases, inhibition of SAMPs in hyperresolving processes (e.g., compensatory anti-inflammatory response syndrome), and administration/induction of DAMPs in vaccination procedures and anti-cancer therapy.

Stability of pro- and anti-inflammatory immune biomarkers for human cohort studies

BackgroundAlthough discovery research has identified the importance of dozens of pro- and anti-inflammatory immune mediators in the pathogenesis, maintenance, exacerbation and resolution of inflammatory diseases, most human cohort studies have incorporated few or no immunological intermediate phenotypes in their analyses. Significant hindrances have been (1) the limited panel of biomarkers known to be readily detected in healthy human populations and (2) the stability, hence utility, of such biomarkers to repeated analysis.MethodsThe frequency and stability of 14 plasma biomarkers linked to in vivo immune regulation of allergic and autoimmune inflammatory disorders was determined in 140 healthy pediatric and adult participants. The impact of initial and multiple subsequent freeze/thaw cycles on pro-inflammatory (CCL2, CXCL10, IL-18, TNFα, IL-6), anti-inflammatory (IL-10, sTNF-RII, IL-1Ra), acute phase proteins (CRP, PTX3) and other biomarkers (sST2, IL-1RAcP) was subsequently quantified.ResultsMultiple biomarkers capable of providing an innate immune signature of inflammation were readily detected directly ex vivo in healthy individuals. These biomarker levels were unaffected when comparing paired data sets from freshly obtained, never frozen plasma or serum and matched aliquots despite extensive freeze/thaw cycles. Neither age nor sex affected stability. Similarly, no quantitative differences were found following repetitive analysis of inflammatory biomarkers in culture samples obtained following in vitro stimulation with TLR and RLR ligands.ConclusionsA broad panel of in vivo and ex vivo cytokine, chemokine and acute phase protein biomarkers that have been linked to human chronic inflammatory disorders are readily detected in vivo and remain stable for analysis despite multiple freeze thaw cycles. These data provide the foundation and confidence for large scale analyses of panels of inflammatory biomarkers to provide better understanding of immunological mechanisms underlying health versus disease.

Dynamic Modulation of Innate Immune Response by Varying Dosages of Lipopolysaccharide (LPS) in Human Monocytic Cells

Innate monocytes and macrophages can be dynamically programmed into distinct states depending upon the strength of external stimuli. Innate programming may bear significant relevance to the pathogenesis and resolution of human inflammatory diseases. However, systems analyses with regard to the dynamic programming of innate leukocytes are lacking. In this study, we focused on the dynamic responses of human promonocytic THP-1 cells to lipopolysaccharide (LPS). We observed that varying dosages of LPS differentially modulate the expression of selected pro- and anti- inflammatory mediators such as IL-6 and IL-33. Super-low dosages of LPS preferentially induced the pro-inflammatory mediator IL-6, while higher dosages of LPS induced both IL-6 and IL-33. Mechanistically, we demonstrated that super-low and high doses of LPS cause differential activation of GSK3 and Akt, as well as the transcription factors FoxO1 and CREB. Inhibition of GSK3 enabled THP-1 cells to express IL-33 when challenged with super-low dose LPS. On the other hand, activation of CREB with adenosine suppressed IL-6 expression. Taken together, our study reveals a dynamic modulation of monocytic cells in response to varying dosages of endotoxin, and may shed light on our understanding of the dynamic balance that controls pathogenesis and resolution of inflammatory diseases.

Molecular mechanisms responsible for the dynamic modulation of macrophage responses to varying dosages of LPS (INM9P.453)

Abstract Monocytes and macrophages can be dynamically programmed into distinct states depending upon the strength of external stimulants. Innate programming may bear significant relevance to the pathogenesis and resolution of human inflammatory diseases. However, systems analyses of the molecular mechanisms responsible for the dynamic programming of innate leukocytes are lacking. In this study, we focused on the macrophage responses to lipopolysaccharide (LPS), a ubiquitous bacterial endotoxin recognized by Toll-like receptor 4 (TLR4). We employed both immortalized human monocytic THP-1 cells and primary murine bone-marrow derived macrophages (BMDM). We observed that varying doses of LPS induce distinct expression profiles of selected pro- and anti- inflammatory cytokines. Lower doses of LPS preferentially suppressed anti-inflammatory mediators, and selectively induced pro-inflammatory mediators. Rising LPS dosages caused a shift in expression profiles, giving rise to double-positive cells. Higher LPS dosages shifted the landscape to anti-inflammatory mediators and drove down the expression of pro-inflammatory mediators. By utilizing BMDM from IRAK-M knockout mice, we identified IRAK-M as a key player in this process, as IRAK-M deletion skews the dynamic responses to varying dosages of LPS. Our study provides a systems view of macrophage programming, and may shed light on our understanding of the dynamic balance between pathogenesis and resolution of inflammatory diseases.

Toll‐like receptor 7 stimulates production of specialized pro‐resolving lipid mediators and promotes resolution of airway inflammation

Although specialized pro-resolving mediators (SPMs) biosynthesized from polyunsaturated fatty acids are critical for the resolution of acute inflammation, the molecules and pathways that induce their production remain elusive. Here, we show that TLR7, a receptor recognizing viral ssRNA and damaged self-RNA, mobilizes the docosahexaenoic acid (DHA)-derived biosynthetic pathways that lead to the generation of D-series SPMs. In mouse macrophages and human monocytes, TLR7 activation triggered production of DHA-derived monohydroxy metabolome markers and generation of protectin D1 (PD1) and resolvin D1 (RvD1). In mouse allergic airway inflammation, TLR7 activation enhanced production of DHA-derived SPMs including PD1 and accelerated the catabasis of Th2-mediated inflammation. D-series SPMs were critical for TLR7-mediated resolution of airway inflammation as this effect was lost in Alox15−/− mice, while resolution was enhanced after local administration of PD1 or RvD1. Together, our findings reveal a new previously unsuspected role of TLR7 in the generation of D-series SPMs and the resolution of allergic airway inflammation. They also identify TLR stimulation as a new approach to drive SPMs and resolution of inflammatory diseases.

Alternatively activated macrophage-derived RELM-α is a negative regulator of type 2 inflammation in the lung

Differentiation and recruitment of alternatively activated macrophages (AAMacs) are hallmarks of several inflammatory conditions associated with infection, allergy, diabetes, and cancer. AAMacs are defined by the expression of Arginase 1, chitinase-like molecules, and resistin-like molecule (RELM) α/FIZZ1; however, the influence of these molecules on the development, progression, or resolution of inflammatory diseases is unknown. We describe the generation of RELM-α–deficient (Retnla−/−) mice and use a model of T helper type 2 (Th2) cytokine-dependent lung inflammation to identify an immunoregulatory role for RELM-α. After challenge with Schistosoma mansoni (Sm) eggs, Retnla−/− mice developed exacerbated lung inflammation compared with their wild-type counterparts, characterized by excessive pulmonary vascularization, increased size of egg-induced granulomas, and elevated fibrosis. Associated with increased disease severity, Sm egg–challenged Retnla−/− mice exhibited elevated expression of pathogen-specific CD4+ T cell–derived Th2 cytokines. Consistent with immunoregulatory properties, recombinant RELM-α could bind to macrophages and effector CD4+ Th2 cells and inhibited Th2 cytokine production in a Bruton's tyrosine kinase–dependent manner. Additionally, Retnla−/− AAMacs promoted exaggerated antigen-specific Th2 cell differentiation. Collectively, these data identify a previously unrecognized role for AAMac-derived RELM-α in limiting the pathogenesis of Th2 cytokine-mediated pulmonary inflammation, in part through the regulation of CD4+ T cell responses.

IFN-γ–producing effector CD8 + T cells and IL-10–producing regulatory CD4 + T cells in fixed drug eruption

Background Although effector and regulatory T cells play roles in the progression and resolution of inflammatory diseases, respectively, little in vivo data exist regarding the T-cell dynamics in the pathogenesis of inflammatory skin diseases in humans. Objective Our aim is to phenotypically and functionally characterize the T cells responsible for initiation and regulation of inflammatory events in fixed drug eruption (FDE) as a disease model to study the role of cytokines produced within the epidermis in the pathogenesis of inflammatory skin disease. Methods By use of flow cytometry, we phenotypically and functionally characterized the intraepidermal T cells that persist as a stable population in resting (pigmented) FDE lesions and that are present in active FDE lesions. Results In resting FDE lesions, most of the intraepidermal T cells were of the CD8 phenotype, most of which expressed cutaneous lymphocyte-associated antigen, α4β1, CD11a, αEβ7, and CD45RA but not CD27, CD62L, CCR4, or CCR7. This population selectively expressed CD122 but not CD25. Intracellular staining demonstrated that most intraepidermal CD8 + T cells were capable of producing IFN-γ and TNF-α but produced little IL-2 and IL-4. On the other hand, in the FDE lesions that arose after challenge, a significant number of CD4 + T cells capable of producing IL-10 migrated into the lesional epidermis. Moreover, nearly 70% of the CD4 + T cells migrating into the lesional epidermis expressed CD25. Conclusions Effector IFN-γ–producing CD8 + T cells and regulatory IL-10–producing CD4 + T cells might be responsible for the progression and resolution of FDE, respectively.

Quantitation of Arachidonic Acid Metabolites in Small Tissue Biopsies by Reversed-Phase High-Performance Liquid Chromatography

Arachidonic acid metabolites exert a variety of distinct biological effects on the initiation and resolution of inflammatory diseases and their measurements in tissue can be critical to evaluate their regulatory function during the course of inflammation and to supplement in vitro experiments. The aim of this study was the detection and quantitative analysis of four arachidonic acid metabolites in small-sized biopsies of human periodontal tissues. The biopsies were homogenized and injected directly into a single analytical column of a RP-HPLC system. Detection was performed by a photodiode array detector. Calibration was established by dilutions of authentic standards of prostaglandin E2 (PGE2), leukotriene B4 (LTB4), 12(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), and 15(S)-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE). A total of 38 specimens weighing between 19 and 191 mg (wet tissue) were analyzed (mean = 59.9 ± 30.2 mg). The detection limits were 1 pg for LTB4 and 12-HETE, 0.5 pg for 15-HETE, and 10 ng for PGE2. The concentrations of PGE2 and LTB4 were significantly higher in inflamed than in healthy periodontal tissues (P = 0.0079; P = 0.0114). 12-HETE was detected in one biopsy (30 pg/g); 15-HETE was not detected. This method of homogenization, extraction, and analysis of arachidonic acid metabolites by RP-HPLC appears to be well suited for studies of human oral biopsies. Only small tissue samples and minimal laboratory equipment were required for a sensitive analysis.