Proteolytic dysfunction in bovine digital dermatitis caused by Treponema spp. and the therapeutic use of non-antimicrobial matrix metalloproteinase inhibitors

Digital dermatitis (DD) is a painful hoof disease in cattle, closely linked to Treponema spp., for which the pathogenesis remains poorly understood and effective treatments are lacking. This study identifies a persistent pro-inflammatory proteomic signature in untreated, non-healing active DD lesions in the foot skin of cattle, characterized by increased immune cell infiltration and elevated matrix metalloproteinase (MMP) activity. Treatment of active DD lesions with CMC2.24, a non-antibiotic MMP inhibitor, maintains the lesions in an M2 stage in most cases; however, it reduces histological dermatitis, lowering reactive oxygen species (ROS) levels and downregulating proteomic keratinization pathways. Mechanistically, CMC2.24 dampens inflammatory IL-1β cell responses in bovine macrophages exposed to DD-associated T. phagedenis. Active DD lesions treated with oxytetracycline (OTC) antibiotics remain clinically similar to CMC2.24; however, they progress to chronic M4 stages, becoming keratinized and maintaining inflammatory features, including increased S100A8 expression and reactive oxygen species (ROS) production. These findings integrate clinical and histological observations from treatments with conventional antibiotics and antibiotic-free protease inhibitors, highlighting novel therapies for managing DD and mitigating the exaggerated inflammatory response.