A Stereocontrolled Total Synthesis of Lipoxin B4 and its Biological Activity as a Pro-Resolving Lipid Mediator of Neuroinflammation

Lipoxins A4 and B4 inhibit glial cell activation via CXCR3 signaling in acute retinal neuroinflammation

Lipoxins are small lipids that are potent endogenous mediators of systemic inflammation resolution in a variety of diseases. We previously reported that Lipoxins A4 and B4 (LXA4 and LXB4) have protective activities against neurodegenerative injury. Yet, lipoxin activities and downstream signaling in neuroinflammatory processes are not well understood. Here, we utilized a model of posterior uveitis induced by lipopolysaccharide endotoxin (LPS), which results in rapid retinal neuroinflammation primarily characterized by activation of resident macroglia (astrocytes and Müller glia), and microglia. Using this model, we observed that each lipoxin reduces acute inner retinal inflammation by affecting endogenous glial responses in a cascading sequence beginning with astrocytes and then microglia, depending on the timing of exposure; prophylactic or therapeutic. Subsequent analyses of retinal cytokines and chemokines revealed inhibition of both CXCL9 (MIG) and CXCL10 (IP10) by each lipoxin, compared to controls, following LPS injection. CXCL9 and CXCL10 are common ligands for the CXCR3 chemokine receptor, which is prominently expressed in inner retinal astrocytes and ganglion cells. We found that CXCR3 inhibition reduces LPS-induced neuroinflammation, while CXCR3 agonism alone induces astrocyte reactivity. Together, these data uncover a novel lipoxin-CXCR3 pathway to promote distinct anti-inflammatory and proresolution cascades in endogenous retinal glia.

Promising Anti-Inflammatory Tools: Biomedical Efficacy of Lipoxins and Their Synthetic Pathways

Lipoxins (LXs) have attracted widespread attention as a class of anti-inflammatory lipid mediators that are produced endogenously by the organism. LXs are arachidonic acid (ARA) derivatives that include four different structures: lipoxin A4 (LXA4), lipoxin B4 (LXB4), and the aspirin-induced differential isomers 15-epi-LXA4 and 15-epi-LXB4. Because of their unique biological activity of reducing inflammation in the body, LXs have great potential for neuroprotection, anti-inflammatory treatment of COVID-19, and other related diseases. The synthesis of LXs in vivo is achieved through the action of lipoxygenase (LO). As a kind of important enzyme, LO plays a major role in the physiological processes of living organisms in mammals and functions in some bacteria and fungi. This suggests new options for the synthesis of LXs in vitro. Meanwhile, there are other chemical and biochemical methods to synthesize LXs. In this review, the recent progress on physiological activity and synthetic pathways of LXs is summarized, and new insights into the synthesis of LXs in vitro are provided.