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The arachidonic acid cascade is a key player in inflammation, and numerous well-established drugs interfere with this pathway. Previous studies have suggested that simultaneous inhibition of 5-lipoxygenase (5-LO) and soluble epoxide hydrolase (sEH) results in synergistic anti-inflammatory effects. In this study, a novel prototype of a dual 5-LO/sEH inhibitor KM55 was rationally designed and synthesized. KM55 was evaluated in enzyme activity assays with recombinant enzymes. Furthermore, activity of KM55 in human whole blood and endothelial cells was investigated. KM55 potently inhibited both enzymes in vitro and attenuated the formation of leukotrienes in human whole blood. KM55 was also tested in a cell function-based assay. The compound significantly inhibited the LPS-induced adhesion of leukocytes to endothelial cells by blocking leukocyte activation.
Over the last years, many microRNAs (miRNAs) have been identified that regulate the formation of bioactive lipid mediators such as prostanoids and leukotrienes. Many of these miRNAs are involved in complex regulatory circuits necessary for the fine-tuning of biological functions including inflammatory processes or cell growth. A better understanding of these networks will contribute to the development of novel therapeutic strategies for the treatment of inflammatory diseases and cancer. In this review, we provide an overview of the current knowledge of miRNA regulation in eicosanoid pathways with special focus on novel miRNA functions and regulatory circuits of leukotriene and prostaglandin biosynthesis.
The miRNA biogenesis is tightly regulated to avoid dysfunction and consequent disease development. Here, we describe modulation of miRNA processing as a novel noncanonical function of the 5-lipoxygenase (5-LO) enzyme in monocytic cells. In differentiated Mono Mac 6 (MM6) cells, we found an in situ interaction of 5-LO with Dicer, a key enzyme in miRNA biogenesis. RNA sequencing of small noncoding RNAs revealed a functional impact, knockout of 5-LO altered the expression profile of several miRNAs. Effects of 5-LO could be observed at two levels. qPCR analyses thus indicated that (a) 5-LO promotes the transcription of the evolutionarily conserved miR-99b/let-7e/miR-125a cluster and (b) the 5-LO-Dicer interaction downregulates the processing of pre-let-7e, resulting in an increase in miR-125a and miR-99b levels by 5-LO without concomitant changes in let-7e levels in differentiated MM6 cells. Our observations suggest that 5-LO regulates the miRNA profile by modulating the Dicer-mediated processing of distinct pre-miRNAs. 5-LO inhibits the formation of let-7e which is a well-known inducer of cell differentiation, but promotes the generation of miR-99b and miR-125a known to induce cell proliferation and the maintenance of leukemic stem cell functions.
5-Lipoxygenase (5LO) is a key enzyme in biosynthesis of leukotrienes (LTs), lipid mediators of inflammation. To study the roles of the 5LO accessory proteins coactosin-like protein (CLP) and 5LO-activating protein (FLAP), we knocked down these proteins in human monocytic cells. Our results show that expression of CLP was required for full cellular 5LO activity when cells were activated with Ca2+ ionophore, as well as with a physiological stimulus (lipopolysaccharide followed by N-formylmethionyl-leucyl-phenylalanine). During LT biosynthesis in stimulated cells, 5LO typically translocates to the nuclear membrane. This redistribution, from cytosolic to perinuclear, was clearly compromised in both CLP- and FLAP-deficient cells. Our results suggest that the CLP–5LO interaction may be a target for reduced LT production.
5-Lipoxygenase (5-LO) is the key enzyme in the formation of pro-inflammatory leukotrienes (LT) which play an important role in a number of inflammatory diseases. Accordingly, 5-LO inhibitors are frequently used to study the role of 5-LO and LT in models of inflammation and cancer. Interestingly, the therapeutic efficacy of these inhibitors is highly variable. Here we show that the frequently used 5-LO inhibitors AA-861, BWA4C, C06, CJ-13,610 and the FDA approved compound zileuton as well as the pan-LO inhibitor nordihydroguaiaretic acid interfere with prostaglandin E2 (PGE2) release into the supernatants of cytokine-stimulated (TNFα/IL-1β) HeLa cervix carcinoma, A549 lung cancer as well as HCA-7 colon carcinoma cells with similar potencies compared to their LT inhibitory activities (IC50 values ranging from 0.1–9.1 µM). In addition, AA-861, BWA4C, CJ-13,610 and zileuton concentration-dependently inhibited bacterial lipopolysaccharide triggered prostaglandin (PG) release into human whole blood. Western Blot analysis revealed that inhibition of expression of enzymes involved in PG synthesis was not part of the underlying mechanism. Also, liberation of arachidonic acid which is the substrate for PG synthesis as well as PGH2 and PGE2 formation were not impaired by the compounds. However, accumulation of intracellular PGE2 was found in the inhibitor treated HeLa cells suggesting inhibition of PG export as major mechanism. Further, experiments showed that the PG exporter ATP-binding cassette transporter multidrug resistance protein 4 (MRP-4) is targeted by the inhibitors and may be involved in the 5-LO inhibitor-mediated PGE2 inhibition. In conclusion, the pharmacological effects of a number of 5-LO inhibitors are compound-specific and involve the potent inhibition of PGE2 export. Results from experimental models on the role of 5-LO in inflammation and pain using 5-LO inhibitors may be misleading and their use as pharmacological tools in experimental models has to be revisited. In addition, 5-LO inhibitors may serve as new scaffolds for the development of potent prostaglandin export inhibitors.