1,25-Dihydroxy vitamin D₃ inhibits LPS-mediated inflammatory responses in endometriosis

Endometriosis, a chronic immune-mediated inflammatory disease, remains elusive in its pathogenesis. Given vitamin D (VD)'s pivotal role in modulating innate and adaptive immune responses, we sought to elucidate how VD modulates inflammatory responses in endometriosis.

We isolated primary human ectopic endometrial stromal cells (EESCs) from ectopic endometrium of ovarian endometrioma, alongside Ishikawa cells, and subjected them to treatment with lipopolysaccharide (LPS), a potent inducer of inflammation, alongside varying concentrations of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), the biologically active form of VD, and its analog TEI-9647 (25-dehydro-1α-hydroxyvitamin D₃-26,23-lactone).

Our results revealed that 1,25(OH)₂D₃ significantly reversed LPS-induced cell proliferation, migration, and inflammatory factor production in EESCs and Ishikawa cells, and induced apoptosis. Additionally, 1,25(OH)₂D₃ inhibited the expression and nuclear translocation of phosphorylated p65 in LPS-activated EESCs and Ishikawa cells. Furthermore, 1,25(OH)₂D₃ counteracted LPS-induced suppression of VD receptor (VDR)/IκBα and enhancement of Toll-like receptor 4 (TLR4)/pyrin domain (PYD)-containing protein 3 (NLRP3) activation, while the addition of TEI-9647 reversed VD's regulatory effects on the NF-κB pathway. In vivo experimental results showed that 1,25(OH)₂D₃ significantly inhibited lesion growth, suppressed NF-κB pathway activation, and corresponding inflammatory phenotypes in a rat model of endometriosis.

Collectively, these results underscore the potential of 1,25(OH)₂D₃ as a therapeutic target for endometriosis via VDR-dependent endometrial homeostasis regulation, suppressing LPS-mediated inflammatory responses and NF-κB signaling pathway through VDR activation and IκBα stabilization.