Histological Analysis of Rabbit Lacrimal Gland in Response to Intraglandular Botulinum Toxin A Therapy

Background: Although surgical intervention is the therapeutic mainstay for epiphora secondary to nasolacrimal obstruction, offlabel injection of onabotulinumtoxinA (BTX-A) into the lacrimal gland has emerged as an effective, minimally invasive alternative. We investigated the structural and molecular changes within the lacrimal gland of the New Zealand White rabbit model, following intraglandular BTX-A injections. Methods: Experimental animal study. In a volume of 0.1 ml, 0.625-, 1.25-, or 2.5-units of BTX-A were injected into separate lacrimal glands under direct visualization. Lacrimal gland samples were obtained via surgical biopsies at 2and 4-week intervals. Negative (untreated) and positive control rabbits (treated with 0.1 ml of 0.9% sodium chloride) were established. Tissue analysis was performed via histopathology, immunohistochemistry, and electron microscopy. Results: At 2 and 4 weeks, mild intraglandular inflammation was noted in both lowand high-dose BTX-A treated lacrimal glands. Increased collagen and mild fibrosis were noted surrounding the acini, suggestive of minor gland destruction and regeneration. Electron microscopy demonstrated no distinct intracellular changes. Immunohistochemistry revealed upregulation of ATPase expression levels in the ducts, as well as upregulation of acinar and ductal AQP4 and AQP5 levels. Conclusions: Our preliminary data shows that BTX-A induces dose-dependent inflammation and structural remodeling within lacrimal gland tissue that may contribute to its clinical efficacy. The immunohistochemistry profile quantifies an increase in ductal ATPase levels and concomitant increase in ductal/acinar AQP4 and AQP5 expression, implying a possible change in glandular energy demands as well as an alteration of the aqueous flow patterns within the gland following injections with BTX-A.