Endometriosis is an estrogen-dependent disease affecting approximately 10% of women of reproductive age worldwide and is a leading cause of pelvic pain. The pathophysiology of endometriosis involves inflammatory and angiogenic mediators; diagnosis is confirmed by the presence of endometrial-like tissue outside the uterine cavity.1 The recurrence of endometriosis when treatment ceases is not uncommon, and therefore new drugs inhibiting its progression represent an unmet need.
A recent study by Kumar et al. sought to investigate mechanisms leading to the establishment and progression of endometriosis.2 Further to this, they recently identified that lipoxins, a form of endogenous eicosanoids that act as lipid mediators, are estrogenic.3 Because LXA4 (lipoxin 4) is the best characterized and exhibits both anti-inflammatory and pro-resolving properties, the team also sought the protective role of LXA4 in the development and progression of endometriosis.
The researchers were able to determine that there are multiple pathways implicated in the pathogenesis of endometriosis in vivo. These included pathways for inflammation, angiogenesis, PGE2 production and transport, matrix remodeling and estrogen signaling.
Three groups of mice were established: sham, vehicle-treated with endometriosis (Veh), and LXA4-treated with endometriosis (LXA4). After implantation of endometriosis in two of the groups, the LXA4 group was given daily injections of LXA4.
The researchers then extracted the total RNA from individual endometriotic lesions and peritoneal fluid cells (PFCs), checking the RNA concentration and purity using a NanoDrop 2000 spectrophotometer (Thermo Scientific). They then used qPCR to analyze the genes involved in the initiation of inflammatory pathways. The researchers observed significantly reduced IL-1b and IL-6 mRNA expression in endometriotic lesions and PFCs from LXA4-treated mice. Overall, they found a significant reduction in lesion volume in LXA4 mice compared to Veh mice.
LXA4 signals via ALX/FPR2, a G protein-coupled receptor, in many cell types. This receptor was significantly attenuated by LXA4 treatment in both the lesions and PFCs. Additionally, LXA4 treatment resulted in a significant reduction in COX-2 expression in endometriotic lesions and PFCs; COX is known for its role in inflammation.
The authors also found consistently elevated transcript levels of pro-inflammatory cytokines (IL-1b, IL-6) as well as ALX/FPR2, HIF-1a, COX-2, VEGF and MRP4 in PFCs of Veh mice as compared to sham mice, confirming the implication of these mediators in the pathogenesis of disease.
Kumar and colleagues measured VEGF and IL-1b cytokines from PFCs at the protein level via ELISA. They found these to be higher in Veh-treated mice, compared to sham mice. PGE2 was also significantly higher in Veh-treated mice and reduced in the PFCs of LXA4 (compared to Veh-treated mice). LXA4 treatment showed a demonstrable attenuation of the expression of COX-2 protein in endometriotic lesions, in comparison to Veh-treated mice.
Additionally, the LXA4 downregulated MMP-2 and MMP-3 but upregulated MMP-9 mRNA expression in endometriotic lesions. The expression of MMP-9 was downregulated in PFCs by LXA4 treatment.
To determine whether these findings could be clinically relevant, the team investigated the effect of once-daily LXA4 treatment on established lesions in the mice. LXA4 successfully reduced endometriotic lesion volume in established disease. Kumar et al. have not only confirmed a number of potential targets involved in the pathogenesis of endometriosis, but they have also shown that LXA4 itself is a potential new therapeutic.
1. Bulun, S.E., et al. (2009) “Endometriosis,” New England Journal of Medicine, 360 (pp. 268–79).
2. Kumar, R., et al. (2014) “Lipoxin A4 Prevents the Progression of De Novo and Established Endometriosis in a Mouse Model by Attenuating Prostaglandin E2 Production and Estrogen Signaling,” PLOS ONE, 9(2) (p. e89742).
3. Russell, R., et al. (2011) “Lipoxin A4 is a novel estrogen receptor modulator,” FASEB Journal, 25(12) (pp. 4326–37).
Post Author: Miriam Pollak. Miriam specialised in neuroscience as an undergraduate but traded in lab work for a post graduate degree in science communication.
She has since had a career that has spanned science communication, science education and communications management.
However, Miriam has found her bliss balancing her love of writing and disseminating medical research with managing a multimillion dollar research budget for a childhood cancer charity in Australia.