In the aftermath of tissue injury or infection, an efficient resolution mechanism is crucial to allow tissue healing and preserve appropriate organ functioning. Pro-resolving bioactive lipids prevent uncontrolled inflammation and its consequences. Among these mediators, lipoxins were the first described and their pro-resolving actions have been mainly described in immune cells. They exert their actions mostly through formyl-peptide receptor 2 (ALX/FPR2 receptor), a G-protein-coupled receptor whose biological function is tremendously complex, primarily due to its capacity to mediate variable cellular responses. Moreover, lipoxins can also interact with alternative receptors like the cytoplasmic aryl hydrocarbon receptor, the cysteinyl-leukotrienes receptors or GPR32, triggering different intracellular signaling pathways. The available information about this complex response mediated by lipoxins is addressed in this review, going over the different mechanisms used by these molecules to stop the inflammatory reaction and avoid the development of dysregulated and chronic pathologies.

Atherosclerosis is a cardiovascular disease caused mainly by dyslipidemia and is characterized by the formation of an atheroma plaque and chronic inflammation. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a protease that induces the degradation of the LDL receptor (LDLR), which contributes to increased levels of LDL cholesterol and the progress of atherosclerosis. Given that macrophages are relevant components of the lipidic and inflammatory environment of atherosclerosis, we studied the effects of PCSK9 treatment on human macrophages. Our data show that human macrophages do not express PCSK9 but rapidly incorporate the circulating protein through the LDLR and also activate the pro-inflammatory TLR4 pathway. Both LDLR and TLR4 are internalized after incubation of macrophages with exogenous PCSK9. PCSK9 uptake increases the production of reactive oxygen species and reduces the expression of genes involved in lipid metabolism and cholesterol efflux, while enhancing the production of pro-inflammatory cytokines through a TLR4-dependent mechanism. Under these conditions, the viability of macrophages is compromised, leading to increased cell death. These results provide novel insights into the role of PCSK9 in the crosstalk of lipids and cholesterol metabolism through the LDLR and on the pro-inflammatory activation of macrophages through TLR4 signaling. These pathways are relevant in the outcome of atherosclerosis and highlight the relevance of PCSK9 as a therapeutic target for the treatment of cardiovascular diseases.

The role of extracellular nucleotides as modulators of inflammation and cell stress is well established. One of the main actions of these molecules is mediated by the activation of purinergic receptors (P2) of the plasma membrane. P2 receptors can be classified according to two different structural families: P2X ionotropic ion channel receptors, and P2Y metabotropic G protein-coupled receptors. During inflammation, damaged cells release nucleotides and purinergic signaling occurs along the temporal pattern of the synthesis of pro-inflammatory and pro-resolving mediators by myeloid and lymphoid cells. In macrophages under pro-inflammatory conditions, the expression and activity of cyclooxygenase 2 significantly increases and enhances the circulating levels of prostaglandin E₂ (PGE₂), which exerts its effects both through specific plasma membrane receptors (EP1-EP4) and by activation of intracellular targets. Here we review the mechanisms involved in the crosstalk between PGE₂ and P2Y receptors on macrophages, which is dependent on several isoforms of protein kinase C and protein kinase D1. Due to this crosstalk, a P2Y-dependent increase in calcium is blunted by PGE₂ whereas, under these conditions, macrophages exhibit reduced migratory capacity along with enhanced phagocytosis, which contributes to the modulation of the inflammatory response and tissue repair.

SARS-CoV-2, the causative virus for the COVID-19 disease, uses its spike glycoprotein to bind to human ACE2 as a first step for viral entry into the cell. For this reason, great efforts have been made to find mechanisms that disrupt this interaction, avoiding the infection. Nitric oxide (NO) is a soluble endogenous gas with known antiviral and immunomodulatory properties. In this study, we aimed to test whether NO could inhibit the binding of the viral spike to ACE2 in human cells and its effects on ACE2 enzymatic activity. Our results show that ACE2 activity was decreased by the NO donors DETA-NONOate and GSNO and by the NO byproduct peroxynitrite. Furthermore, we found that DETA-NONOate could break the spike–ACE2 interaction using the spike from two different variants (Alpha and Gamma) and in two different human cell types. Moreover, the same result was obtained when using NO-producing murine macrophages, while no significant changes were observed in ACE2 expression or distribution within the cell. These results support that it is worth considering NO as a therapeutic agent for COVID-19, as previous reports have suggested.

Dilated cardiomyopathy is a major cause of heart failure and is one of the most common forms of cardiomyopathy worldwide. Although there has been significant progress in its clinical management, early diagnosis and precise prognosis remain challenging due to the lack of specificity in current biomarkers. As inflammation plays a key role in DCM, we determined the levels of systemic inflammatory markers and specific pro-resolving lipid mediators (SPMs) in a cohort of DCM patients. Our data show that the levels of lipoxin A4 significantly increased in DCM patients (343 + 75.1 pg/mL in controls vs. 482.2 ± 159.1 pg/mL in DCM patients), whereas the opposite was observed for resolving D1 (57.18 ± 32.68 pg/mL in controls vs. 38.55 ± 25.13 pg/mL in DCM patients). These results may indicate that SPMs could be considered new biomarkers related to the progression of this pathology. Moreover, since microRNAs (miRNAs) are also considered potential biomarkers at the molecular level, we conducted comprehensive miRNA expression profiling using a high-throughput array platform in our cohort. Of the differentially expressed miRNAs identified, we chose to focus on two that were significantly upregulated (miR378-3p and miR486-5p; more than two-folds) or downregulated (miR142-3p and miR328-3p < 20% and 40% vs. the control, respectively) in DCM patients, all of them strongly associated with inflammatory pathways. The selected miRNAs showed considerable potential as biomarkers, exhibiting statistical significance after ROC analysis. In fact, improved performance was observed when combining both miR142-3p and miR328-3p, using a LASSO regression model. However, we found no correlation between miRNAs and traditional inflammatory markers or SPMs ruling out the possibility to proposing them as combined biomarkers in this case. The heterogeneity of DCM leads to the need to identify new biomarkers that, either individually or in combination, may improve the prognosis of affected individuals. In our study, we have identified that some of the main SPMs can provide valuable information about disease progression, in addition to the combination of certain circulating miRNAs, which show promising prognostic values in our cohort. Thus, we have identified novel biomarkers that integrate inflammatory profiles with specific circulating miRNA expression patterns is an important step towards more targeted patient stratification in DCM. This approach can improve DCM diagnosis and prognosis, supporting the development of personalized treatments through a multi-parameter panel of biomarkers that can be measured in peripheral blood and used in routine clinical practice. Such a strategy can enable earlier treatment, resulting in better patient outcomes and quality of life.

The cytokine storm associated with SARS‐CoV‐2 infection is one of the most distinctive pathological signatures in COVID‐19 patients. Macrophages respond to this pro‐inflammatory challenge by reprogramming their functional and metabolic phenotypes. Interestingly, human macrophages fail to express the inducible form of the NO synthase (NOS2) in response to pro‐inflammatory activation and, therefore, NO is not synthesized by these cells. The contribution of exogenously added NO, via a chemical NO‐donor, on the immunometabolic changes associated with the cytokine storm is investigated. By using metabolic, transcriptomic, and functional assays the effect of NO in human macrophages is evaluated and found specific responses. Moreover, through integrative fluxomic analysis, pathways modified by NO that contribute to the expression of a particular phenotype in human macrophages are identified, which includes a decrease in mitochondrial respiration and TCA with a slight increase in the glycolytic flux. A significant ROS increase and preserved cell viability are observed in the presence of NO, which may ease the inflammatory response and host defense. Also, NO reverses the cytokine storm‐induced itaconate accumulation. These changes offer additional clues to understanding the potential crosstalk between NO and the COVID‐19 cytokine storm‐dependent signaling pathways.