Ichthammol and Sodium Bituminosulfonate for Retinal Neuroprotection: Molecular Rationale, Translational Barriers and Ocular Safety of an Untested Hypothesis

Age-related macular degeneration, diabetic retinopathy, retinal vein occlusion, and inherited retinal dystrophies share a final common pathway of chronic low-grade inflammation, oxidative stress, and progressive loss of photoreceptors, retinal pigment epithelium, and inner retinal neurons, and the inflamed microenvironment of the degenerating retina is a major obstacle to cell-based therapies. Sulfonated shale oils—ammonium bituminosulfonate (ichthammol) and sodium bituminosulfonate, marketed since 1882 under the trade name Ichthyol—have been used topically in dermatology for more than a century and inhibit, in leukocytes, macrophages, and cell-free assays, several mediators that also drive retinal degeneration: 5-lipoxygenase and leukotriene B4 synthesis, the phagocyte oxidative burst, matrix metalloproteinase 9, and neutrophil release of elastase and vascular endothelial growth factor. This hypothesis-generating review asks whether this pharmacology could be relevant to the posterior segment and states at the outset what the evidence does not contain: no study of bituminosulfonates has ever been performed in retinal cells, retinal tissue, animal models of retinal disease, patients with retinal disease, or any neural tissue; no ocular pharmacokinetic or toxicological data exist; and product labels and safety data sheets classify these preparations as eye irritants for external use only, not to be used in the eye. Their historical ophthalmic use was confined to eyelid skin. Within these constraints, we map the non-ocular mechanisms of bituminosulfonates onto retinal pathobiology and onto the obstacles of retinal cell therapy, compare them with repurposed anti-inflammatory agents already tested in retinal trials, and examine the biological differences between skin and retina and the pharmacokinetic barriers to retinal exposure. We conclude that retinal toxicity, rather than efficacy, is the first question to be answered, and we propose a stepwise, go/no-go preclinical program—from retinal cell cultures to organoids, explants, and animal models—whose negative outcome at any stage would close the hypothesis. No clinical use of bituminosulfonates in or near the posterior segment is suggested by this article.