Modulation of Macrophage Inflammatory Responses by UDP-Glucuronosyltransferase-Mediated PGE₂ Glucuronidation

Background/Objectives: Macrophages polarized into M1 and M2 phenotypes differentially regulate immune and drug responses. Despite their distinct functional roles, differences in UDP-glucuronosyltransferase (UGT) expression and activity between M1 and M2 macrophages remain poorly understood. This study aimed to characterize differential UGT expression in M1 and M2 macrophages and to elucidate how UGT-mediated prostaglandin E2 (PGE2) glucuronidation modulates macrophage inflammatory responses. Methods: THP-1 cells were chemically differentiated into macrophages (M0) and subsequently polarized into M1 and M2 phenotypes. UGT expression profiles were assessed using RT-PCR, quantitative RT-PCR, and Western blotting. UGT enzymatic activity was compared by quantifying glucuronide metabolites derived from UGT-specific substrates using LC-MS/MS, along with measurement of free PGE2 and PGE2-glucuronide by ELISA. Pro-inflammatory cytokine expression and secretion in M1 macrophages were quantified using quantitative RT-PCR and ELISA. Results: UGT1A1, UGT1A4, UGT1A5, UGT1A9, and UGT2B7 were markedly upregulated in M1 compared with M2 macrophages at both the mRNA and protein levels. UGT enzymatic activity was significantly higher in M1 macrophages (p < 0.01) and was attenuated in a concentration-dependent manner by the UGT inhibitor diclofenac. Enhanced UGT activity in M1 macrophages was reflected by increased formation of estradiol-3-glucuronide and naloxone-3-glucuronide (both p < 0.01). Furthermore, PGE2 glucuronidation was more pronounced in M1 macrophages, and inhibition of UGTs with atazanavir reduced PGE2-glucuronide formation and pro-inflammatory cytokine production, including IL-1β, IL-6, and TNF-α. Conclusion: UGT-mediated PGE2 glucuronidation in M1 macrophages plays a critical role in sustaining pro-inflammatory cytokine responses. These findings identify UGTs as important regulators of macrophage phenotype and inflammatory signaling.