18β-glycyrrhetic acid inhibits immune activation triggered by HMGB1, a pro-inflammatory protein found in the tear fluid during conjunctivitis and blepharitis

Abstract

Purpose: High-mobility group proteins are chromatin-binding factors with key roles in nuclear homeostasis. Evidence indicates that extracellularly released high-mobility group box 1 protein (HMGB1) behaves as a cytokine, promoting inflammation and disease pathogenesis. HMGB1 release occurs during endophtalmitis or uveoretinitis.

Methods: The authors investigated the presence of HMGB1 in tear fluid of patients with different inflammatory disorders of the external eye.

Results: Data demonstrate that HMGB1 content is close to detection limit in tears of control subjects but highly increased (about 15-fold) in patients with conjunctivitis or blepharitis. The authors also report that 18β-glycyrrhetic acid impairs antibody recognition of HMGB1, suggesting direct binding to the protein. Accordingly, 18β-glycyrrhetic acid prevented HMGB1-dependent COX2 expression and cluster formation in primary cultures of human macrophages.

Conclusion: Together, these findings suggest that HMGB1 contributes to inflammatory disorders of the external eye, and 18β-glycyrrhetic acid may scavenge the protein and inhibit its detrimental effects.