Models in vivo and in vitro for the study of acute and chronic inflammatory activity: A comprehensive review

Inflammatory conditions are among the principal causes of morbidity worldwide, and their treatment continues to be a challenge, given the restricted availability of effective and safe drugs. Thus, the identification of new compounds with biological activity that can be used for the treatment of inflammatory disorders is an essential field in medical and health research, in order to improve the health and quality of life of patients suffering from these diseases. Evaluation of the anti-inflammatory activity of drugs requires the implementation of models that accurately depict the biochemical and/or physiological responses that characterize human inflammation; for this reason, several in vitro and in vivo models have been developed, providing a platform for discovering novel or repurposed compounds. For this reason, in the present review we have selected twelve commonly used models for the evaluation of the anti-inflammatory effect, and extensively describes the difference between in vivo and in vitro models of inflammation, highlighting their advantages and limitations. On the other hand, the inflammatory mechanisms involved in them, the methods employed for their establishment, and the different parameters assessed to determine the anti-inflammatory activity of a given compound are extensively discussed. We expect to provide a comprehensive guide for the improved selection of a suitable model for the preclinical evaluation of plausible anti-inflammatory agents.

Inhibiting PLA2G7 reverses the immunosuppressive function of intratumoral macrophages and augments immunotherapy response in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is an exceptionally immunosuppressive malignancy characterized by limited treatment options and a dismal prognosis. Macrophages constitute the primary and heterogeneous immune cell population within the HCC microenvironment. Our objective is to identify distinct subsets of macrophages implicated in the progression of HCC and their resistance to immunotherapy.

METHODS

Intratumoral macrophage-specific marker genes were identified via single-cell RNA sequencing analyses. The clinical relevance of phospholipase A2 Group VII (PLA2G7), a pivotal enzyme in phospholipid metabolism, was assessed in patients with HCC through immunohistochemistry and immunofluorescence. Flow cytometry and an in vitro co-culture system were used to elucidate the specific role of PLA2G7 in macrophages. Orthotopic and subcutaneous HCC mouse models were employed to evaluate the potential of the PLA2G7 inhibitor in complementing immune checkpoint blockade (ICB) therapy.

RESULTS

Single-cell RNA sequencing analyses disclosed predominant PLA2G7 expression in intratumoral macrophages within the HCC microenvironment. The macrophage-specific PLA2G7 was significantly correlated with poorer prognosis and immunotherapy resistance in patients with HCC. PLA2G7high macrophages represent a highly immunosuppressive subset and impede CD8 T-cell activation. Pharmacological inhibition of PLA2G7 by darapladib improved the therapeutic efficacy of anti-programmed cell death protein 1 antibodies in the HCC mouse models.

CONCLUSIONS

Macrophage-specific PLA2G7 serves as a novel biomarker capable of prognosticating immunotherapy responsiveness and inhibiting PLA2G7 has the potential to enhance the efficacy of ICB therapy for HCC.

Emerging Roles of Lysophosphatidic Acid in Macrophages and Inflammatory Diseases

Lysophosphatidic acid (LPA) is a bioactive phospholipid that regulates physiological and pathological processes in numerous cell biological functions, including cell migration, apoptosis, and proliferation. Macrophages are found in most human tissues and have multiple physiological and pathological functions. There is growing evidence that LPA signaling plays a significant role in the physiological function of macrophages and accelerates the development of diseases caused by macrophage dysfunction and inflammation, such as inflammation-related diseases, cancer, atherosclerosis, and fibrosis. In this review, we summarize the roles of LPA in macrophages, analyze numerous macrophage- and inflammation-associated diseases triggered by LPA, and discuss LPA-targeting therapeutic strategies.

Regulation of TREM2 on BV2 inflammation through PI3K/AKT/mTOR pathway

This work sought to determine how lipopolysaccharide (LPS)-induced pro-inflammatory factor production in BV2 microglia was influenced by myeloid cell 2 (TREM2) expressions. LPS (0.1, 1, and 10 µg/mL) induced inflammation in BV2 cells, MTT and QPCR were used to detect the occurrence of inflammation; TREM2 activation and inhibition vectors were used to activate and inhibit TREM2; Cell Proliferation was detected using CCK-8 and cell cloning experiments. LY294002 was used to inhibit the activity of PI3K/AKT signal pathway; Western blot and ELISA were used to detect cell polarization and signal pathway changes. CCK-8 and cell clone experiments found that the activation of TERM2 can promote the proliferation of BV2 cells; and the activation of TERM2 can promote the expression of IL6, IL1β, TNFα and the expression of M2 cell phenotype molecules Arg-1 and CD206. The effect of adding LY294002 signaling pathway by TERM2 activation was inhibited, indicating that TERM2 can affect the occurrence of inflammation by regulating the activity of PI3K/AKT signaling pathway. Finally, Western blotting and ELISA showed that activation of TERM2 can promote the expression of Arg-1 and CD206 in BV2 cells, and promote the transformation of BV2 cells to M2 polarization. TERM2 can affect the inflammatory response in microglia through the PI3K/AKT signaling pathway, suggesting that TERM2 may be a target for the treatment of inflammatory response in glial cells. This study provides a treatment plan for alleviating the impact of inflammation on central nervous system.

Targeting lysophosphatidic acid receptor with Ki16425 impedes T cell lymphoma progression through apoptosis induction, glycolysis inhibition, and activation of antitumor immune response

Lysophosphatidic acid (LPA) is a small phospholipid that acts as an extracellular lipid mediator. It promotes cancer progression by altering a wide array of cellular processes, including apoptosis, survival, angiogenesis, invasion, and migration through binding with its cognate receptors. Intriguingly, our previous study showed that in vitro treatment of LPA induced survival of T lymphoma cells. Hence, the present investigation was designed to investigate the antitumor potential of Ki16425, an antagonist of LPA receptors, against T cell lymphoma. Our in vitro results showed inhibition of LPA-mediated survival and metabolic activity of T lymphoma cells by Ki16425. Further, in vivo experimental findings indicated the tumor retarding potential of Ki16425 against T cell lymphoma through apoptosis induction, glycolysis inhibition, and immunoactivation. The administration of Ki16425 triggered apoptosis by down-regulating the expression of Bcl2 and up-regulating p53, Bax, cleaved caspase-3, and Cyt c expression. Further, Ki16425 suppressed glycolytic activity with concomitantly decreased expression of GLUT3 and MCT1. Moreover, we also noticed an elevated level of NO and iNOS in tumor cells after Ki16425 administration which might also be responsible for apoptosis induction and suppressed glycolysis. Additionally, we observed an increased population of total leukocytes, lymphocytes, and monocytes along with increased thymocytes count and IL-2 and IFN-γ levels. Besides, we observed amelioration of tumor-induced kidney and liver damages by Ki16425. Taken together, this is the first study that demonstrates that LPA receptors could be potential future therapeutic targets for designing promising therapeutic strategies against T cell lymphoma.

Inhibition of Autotaxin and Lysophosphatidic Acid Receptor 5 Attenuates Neuroinflammation in LPS-Activated BV-2 Microglia and a Mouse Endotoxemia Model

Increasing evidence suggests that systemic inflammation triggers a neuroinflammatory response that involves sustained microglia activation. This response has deleterious consequences on memory and learning capability in experimental animal models and in patients. However, the mechanisms connecting systemic inflammation and microglia activation remain poorly understood. Here, we identify the autotaxin (ATX)/lysophosphatidic acid (LPA)/LPA-receptor axis as a potential pharmacological target to modulate the LPS-mediated neuroinflammatory response in vitro (the murine BV-2 microglia cell line) and in vivo (C57BL/6J mice receiving a single i.p. LPS injection). In LPS-stimulated (20 ng/mL) BV-2 cells, we observed increased phosphorylation of transcription factors (STAT1, p65, and c-Jun) that are known to induce a proinflammatory microglia phenotype. LPS upregulated ATX, TLR4, and COX2 expression, amplified NO production, increased neurotoxicity of microglia conditioned medium, and augmented cyto-/chemokine concentrations in the cellular supernatants. PF8380 (a type I ATX inhibitor, used at 10 and 1 µM) and AS2717638 (an LPA5 antagonist, used at 1 and 0.1 µM) attenuated these proinflammatory responses, at non-toxic concentrations, in BV-2 cells. In vivo, we demonstrate accumulation of PF8380 in the mouse brain and an accompanying decrease in LPA concentrations. In vivo, co-injection of LPS (5 mg/kg body weight) and PF8380 (30 mg/kg body weight), or LPS/AS2717638 (10 mg/kg body weight), significantly attenuated LPS-induced iNOS, TNFα, IL-1β, IL-6, and CXCL2 mRNA expression in the mouse brain. On the protein level, PF8380 and AS2717638 significantly reduced TLR4, Iba1, GFAP and COX2 expression, as compared to LPS-only injected animals. In terms of the communication between systemic inflammation and neuroinflammation, both inhibitors significantly attenuated LPS-mediated systemic TNFα and IL-6 synthesis, while IL-1β was only reduced by PF8380. Inhibition of ATX and LPA5 may thus provide an opportunity to protect the brain from the toxic effects that are provoked by systemic endotoxemia.

Autotaxin stimulates LPA2 receptor in macrophages and exacerbates dextran sulfate sodium-induced acute colitis

Autotaxin (ATX) is a secreted enzyme that hydrolyzes lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA) and choline. ATX has been implicated in multiple chronic inflammatory diseases, but little is known about its role in the development of inflammatory bowel disease (IBD). Here, we investigated how ATX contributed to intestinal inflammation during colitis. We found that ATX expression levels were upregulated in the intestines of ulcerative colitis (UC) patients in acute state as well as in the intestines of dextran sulfate sodium (DSS)-induced colitis mice, which is likely due to increased infiltration of inflammatory cells including macrophages. Intriguingly, the inhibition of ATX activity led to reduced production of inflammatory cytokines, as well as attenuated colitis. These findings suggest that ATX may display strong pro-inflammatory properties. Supporting this, treatment with recombinant mouse ATX (rmATX) increased the production of inflammatory cytokines and enzymes in mouse macrophage cell line RAW264.7 and bone marrow-derived macrophages (BMDM), whereas silencing ATX by siRNA reduced LPS-stimulated production of pro-inflammatory factors. Notably, we found that the levels of LPA2 (an LPA receptor) were dramatically upregulated in rmATX-treated RAW264.7 cells and DSS-treated mice. Gene silencing of lpa2 in RAW264.7 cells by siRNA led to reduced production of inflammatory cytokines. Moreover, adenovirus-mediated delivery of lpa2 short hairpin RNA into DSS-treated mice ameliorated colitis. Collectively, our research suggests that ATX may exacerbate DSS-induced colitis by activating LPA2 receptor in macrophages and represent a promising target for the treatment of IBD. KEY MESSAGES: Increased ATX expression and secretion in colitic colons are likely due to increased infiltration of inflammatory cells including macrophages. Recombinant ATX promotes, but ATX silencing inhibits, the production of inflammatory cytokines in LPS-stimulated RAW264.7 cells and BMDM. •LPA2 mediates the pro-inflammatory effects of ATX on macrophages. Inhibition of ATX and downregulation of LPA2 ameliorate DSS-induced colitis.

CTRP9 induces iNOS expression through JAK2/STAT3 pathway in Raw 264.7 and peritoneal macrophages

The C1q tumor necrosis factor (TNF)-related proteins 9 (CTRP9), an adipocyte-derived cytokine, affects a number of physiological processes, including immune function and inflammation. We investigated whether CTRP9 affects the expression of inflammation-related genes in Raw 264.7 and peritoneal macrophages. The CTRP9-induced expression of iNOS increased in a time- and dose-dependent manner. LPS and CTRP9 promote the expression of iNOS jointly in Raw 264.7 and peritoneal macrophages. CTRP9 induced the phosphorylation of JAK2 and STAT3 in Raw 264.7 and peritoneal macrophages. VX509 (JAK2 inhibitor) reduced the CTRP9-induced iNOS protein production. In addition, the CTRP9-induced phosphorylation of JAK2 and STAT3 was dramatically reduced by VX509. Collectively, these results suggest that JAK2/STAT3 signaling is involved in the CTRP9-induced expression of iNOS.

Lysophosphatidic acid up-regulates IL-10 production to inhibit TNF-α synthesis in Mϕs stimulated with LPS

Bacterial LPS strongly induces pro-inflammatory responses of Mϕs after binding to CD14 protein and the TLR4/MD-2 receptor complex. The LPS-triggered signaling can be modulated by extracellular lysophosphatidic acid (LPA), which is of substantial importance for Mϕ functioning under specific pathophysiological conditions, such as atherosclerosis. The molecular mechanisms of the crosstalk between the LPS- and LPA-induced signaling, and the LPA receptors involved, are poorly known. In this report, we show that LPA strongly inhibits the LPS-induced TNF-α production at the mRNA and protein levels in primary Mϕs and Mϕ-like J774 cells. The decreased TNF-α production in LPA/LPS-stimulated cells is to high extent independent of NF-κB but is preceded by enhanced expression and secretion of the anti-inflammatory cytokine IL-10. The IL-10 elevation and TNF-α reduction are both abrogated upon depletion of the LPA₅ and LPA₆ receptors in J774 cells and can be linked with LPA-mediated activation of p38. We propose that the binding of LPA to LPA₅ and LPA₆ fine-tunes the LPS-induced inflammatory response by activating p38, and up-regulating IL-10 and down-regulating TNF-α production.

Anti-inflammatory evaluation and characterization of leaf extract of Ananas comosus

Ananas comosus (L.) Merr (Pineapple) is a tropical plant with an edible fruit. In the present study, the potential anti-inflammatory activity of A. comosus leaf extract (ALE) was studied. ALE prepared using soxhlet apparatus was subjected to preliminary qualitative phytochemical analysis and quantitative estimations of flavonoids and tannins. The components present in ALE were identified using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Inhibitory effects of ALE on protein denaturation, and proteinase activity were assessed. Its effect on secretion of pro-inflammatory cytokines and inflammatory mediators by lipopolysaccharide-stimulated macrophages was also analyzed. Further, its anti-inflammatory activity in carrageenan-induced inflammatory rat model was examined. The preliminary qualitative phytochemical analysis revealed presence of flavonoids, phenols, tannins, carbohydrates, glycosides, and proteins in the extract. Total flavonoids and total tannins were 0.17 ± 0.006 mg equivalent of quercetin/g of ALE and 4.04 ± 0.56 mg equivalent of gallic acid/g of ALE. LC-MS analysis identified the presence of 4-hydroxy pelargonic acid, 3,4,5-trimethoxycinnamic and 4-methoxycinnamic acid, whereas GC-MS analysis identified the presence of campesterol and ethyl isoallocholate that have been previously reported for anti-inflammatory activity. ALE showed significant inhibition of protein denaturation and proteinase activity and also controlled secretion of tumour necrosis factor-α, interleukin-1β and prostaglandins, as well as the generation of reactive oxygen species by activated macrophages. ALE also significantly decreased carrageenan-induced acute paw edema. The study, therefore, identified the components present in ALE that may be responsible for its anti-inflammatory activity and thus demonstrated its potential use against acute inflammatory diseases.

Lysophosphatidic acid directly induces macrophage-derived foam cell formation by blocking the expression of SRBI

The leading cause of morbidity and mortality is the result of cardiovascular disease, mainly atherosclerosis. The formation of macrophage foam cells by ingesting ox-LDL and focal retention in the subendothelial space are the hallmarks of the early atherosclerotic lesion. Lysophosphatidic acid (LPA), which is a low-molecular weight lysophospholipid enriched in oxidized LDL, exerts a range of effects on the cardiovascular system. Previous reports show that LPA increases the uptake of ox-LDL to promote the formation of foam cells. However, as the most active component of ox-LDL, there is no report showing whether LPA directly affects foam cell formation. The aim of this study was to investigate the effects of LPA on foam cell formation, as well as to elucidate the underlying mechanism. Oil red O staining and a Cholesterol/cholesteryl ester quantitation assay were used to evaluate foam cell formation in Raw264.7 macrophage cells. We utilized a Western blot and RT-PCR to investigate the relationship between LPA receptors and lipid transport related proteins. We found that LPA promoted foam cell formation, using 200 μM for 24 h. Meanwhile, the expression of the Scavenger receptor BI (SRBI), which promotes the efflux of free cholesterol, was decreased. Furthermore, the LPA_1/3 receptor antagonist Ki16425 significantly abolished the LPA effects, indicating that LPA_1/3 was involved in the foam cell formation and SRBI expression induced by LPA. Additionally, the LPA-induced foam cell formation was blocked with an AKT inhibitor. Our results suggest that LPA-enhanced foam cell formation is mediated by LPA_1/3 -AKT activation and subsequent SRBI expression.

CD14 is a key mediator of both lysophosphatidic acid and lipopolysaccharide induction of foam cell formation

Macrophage uptake of oxidized low-density lipoprotein (oxLDL) plays an important role in foam cell formation and the pathogenesis of atherosclerosis. We report here that lysophosphatidic acid (LPA) enhances lipopolysaccharide (LPS)-induced oxLDL uptake in macrophages. Our data revealed that both LPA and LPS highly induce the CD14 expression at messenger RNA and protein levels in macrophages. The role of CD14, one component of the LPS receptor cluster, in LPA-induced biological functions has been unknown. We took several steps to examine the role of CD14 in LPA signaling pathways. Knockdown of CD14 expression nearly completely blocked LPA/LPS-induced oxLDL uptake in macrophages, demonstrating for the first time that CD14 is a key mediator responsible for both LPA- and LPS-induced oxLDL uptake/foam cell formation. To determine the molecular mechanism mediating CD14 function, we demonstrated that both LPA and LPS significantly induce the expression of scavenger receptor class A type I (SR-AI), which has been implicated in lipid uptake process, and depletion of CD14 levels blocked LPA/LPS-induced SR-AI expression. We further showed that the SR-AI-specific antibody, which quenches SR-AI function, blocked LPA- and LPS-induced foam cell formation. Thus, SR-AI is the downstream mediator of CD14 in regulating LPA-, LPS-, and LPA/LPS-induced foam cell formation. Taken together, our results provide the first experimental evidence that CD14 is a novel connecting molecule linking both LPA and LPS pathways and is a key mediator responsible for LPA/LPS-induced foam cell formation. The LPA/LPS-CD14-SR-AI nexus might be the new convergent pathway, contributing to the worsening of atherosclerosis.