Selective lesions of rabbit extraocular muscles injected with the anti-AChR immunotoxin saporin-mAb 73.
OBJECTIVE
To evaluate the effects on extraocular muscles of a skeletal muscle-specific immunotoxin, saporin-mAb 73, as an alternative to botulinum toxin to induce a permanent correction of oculo-facial dystonias or some forms of ocular motility disorders.


METHODS
An immunotoxin was prepared with a monoclonal antibody (mAb 73) against acetylcholine receptors of skeletal muscle, linked to saporin, a type 1 ribosome-inactivating protein (RIP) from Saponaria officinalis. Sixteen New Zealand white rabbits were treated with a single injection of immunotoxin directly into the medial rectus muscle of one eye. Four different dosages of 2, 5, 20, or 50 ng saporin-mAb 73 were used. The rabbits were sacrificed at two, 7 and 14 days post-injection. The medial rectus muscle and the retractor bulbi muscle of both the injected and the fellow eyes were taken and serial sections were examined by light microscopy in a blinded manner.


RESULTS
Saporin-mAb 73, even at the dosage of 2 ng, brought about focal damage in the extraocular muscles of rabbits without histological changes in adjacent muscles. The histological examination revealed necrotic/apoptotic lesions restricted to the sites of inoculation and largely infiltrated by macrophages. No evident inflammatory reaction was detected at any time and neutrophils were substantially absent. At 14 days after injection, necrosis/apoptosis was still evident and the sclerotic reaction was minimal.


CONCLUSIONS
The immunotoxin saporin-mAb 73 injections into the extraocular muscles of rabbits caused focal damage to the muscles. There was no significant inflammatory reaction and muscle fiber loss was present even at the lower doses. Although the lesions were followed for only 14 days, our results suggest that saporin-mAb 73 has potential to cause safe focal muscle damage but longer-term follow-up are needed to investigate the persistence of muscle weakness.
Ophthalmology Unit, University of Bologna, School of Medicine, Bologna, Italy. campos@alma.unibo.it
Emilio C
EC
Campos
Costantino
C
Schiavi
Andrea
A
Bolognesi
Costantino
C
Bellusci
Chiara
C
Lubelli
Alberta
A
Duca
Letizia
L
Polito
Konstantinos
K
Poulas
Socrates J
SJ
Tzartos
Fiorenzo
F
Stirpe
D000818:Animals; D000911:Antibodies, Monoclonal; D017209:Apoptosis; D001706:Biopsy; D005260:Female; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology*; D007267:Injections; D009699:N-Glycosyl Hydrolases; D009336:Necrosis; D009801:Oculomotor Muscles / Q000187:drug effects* / Q000473:pathology; D010940:Plant Proteins / Q000494:pharmacology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D011817:Rabbits; D011950:Receptors, Cholinergic / Q000276:immunology*; D054789:Ribosome Inactivating Proteins, Type 1; D012449:Safety; D000076985:Saporins; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000911:Antibodies, Monoclonal; D000922:Immunotoxins; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors; D011950:Receptors, Cholinergic; D054789:Ribosome Inactivating Proteins, Type 1; D009699:N-Glycosyl Hydrolases; D000076985:Saporins