Osmium tetroxide (OsO4)

Osmium tetroxide, commonly known as osmic acid, is a highly volatile inorganic compound used primarily as a fixative in electron microscopy and as an oxidizing agent in chemical synthesis (PubChem CID 30318). In medical applications, it has been utilized for chemical synovectomy to treat persistent joint inflammation in conditions like rheumatoid arthritis and hemophilic arthropathy (PubMed: 1183535). It is unique in that it does not possess a defined pharmacologic molecular target, such as a specific receptor or enzyme. Instead, its therapeutic effect is derived from its ability to non-specifically oxidize and cross-link cellular proteins and lipids, leading to the fixation and subsequent necrosis of the synovial membrane (Wikipedia: Osmium tetroxide). This process effectively reduces synovial hypertrophy and joint effusion. However, its clinical utility is significantly hampered by its extreme toxicity, including the risk of severe ocular damage, respiratory irritation, and systemic toxicity upon exposure (StatPearls: Synovectomy).

Other names

Osmic acidOsmium(VIII) oxidePerosmic oxideOsmium tetraoxide

Non-specific chemical synovectomy via oxidation and fixation of synovial tissue