Myotoxic Effects of the Skeletal Muscle-Specific Immunotoxin, Ricin-mAb35, on Orbicularis Oculi Muscle After Eyelid Injections in Rabbits

Purpose: The authors recently demonstrated that a single injection of the immu-notoxin ricin-mAb35 has potent and long-lasting myotoxic effects in extraocular muscles. The myotoxicity of injected ricin-mAb35 was tested in the eyelids of rabbits to determine its potential for use in the treatment of benign essential blepharospasm and other dystonias. Methods: The immunotoxin ricin-mAb35 was injected in one eyelid of adult rabbits. After 1 week, 1 month, or 6 months, the rabbits were euthanized, and the eyelids were prepared for histologic examination of inflammatory cell infiltrate with immunohistochemical localization of cd11b and myosin heavy chain isoform expres-sion. Muscle loss was quantified by analysis of muscle fiber cross-sectional area and total myofiber number. Results: Within the first week after a single injection of ricin-mAb35, some edema developed, which resolved by the second week. Otherwise, the eyelids were normal in appearance. A short-lived inflammatory response was seen at 1 week, but this resolved 1 month after treatment. One week after injection, there was a significant decrease i