Botulinum toxin A inhibits salivary secretion of rabbit submandibular gland

Abstract

Botulinum toxin A (BTXA) has been used in several clinical trials to treat excessive glandular secretion; however, the precise mechanism of its action on the secretory function of salivary gland has not been fully elucidated. In this study, we aimed to investigate the effect of BTXA on secretion of submandibular gland in rabbits and to identify its mechanism of action on the secretory function of salivary gland. At 12 weeks after injection with 5 units of BTXA, we found a significant decrease in the saliva flow from submandibular glands, while the salivary amylase concentration increased. Morphological analysis revealed reduction in the size of acinar cells with intracellular accumulation of secretory granules that coalesced to form a large ovoid structure. Expression of M3-muscarinic acetylcholine receptor (M3 receptor) and aquaporin-5 (AQP5) mRNA decreased after BTXA treatment, and distribution of AQP5 in the apical membrane was reduced at 1, 2 and 4 weeks after BTXA injection. Furthermore, BTXA injection was found to induce apoptosis of acini. These results indicate that BTXA decreases the fluid secretion of submandibular glands and increases the concentration of amylase in saliva. Decreased expression of M3 receptor and AQP5, inhibition of AQP5 translocation, and cell apoptosis might involve in BTXA-reduced fluid secretion of submandibular glands.

Histological and immunohistochemical findings of the action of botulinum toxin in salivary gland: systematic review

“…In salivary glands of rats was identified aquaporin 5 (Cheidde and Schor, 1999;Melvin et al, 2005;Catalan et al, 2009). Xu et al (2015) also verified clinically the salivary flow of animals and concluded that salivary flow is reduced depending on the dose applied, agreeing with Shan et al (2013). Regarding the immunohistochemistry for SNAP-25, Xu et al (2015) observed reduced immunoreactivity and proteolysis of SNAP-25 protein in the treated groups and that it is recovered over time.…”

“…The ultra-structural findings of Teymoortash et al (2007), Shan et al (2013) and Younis et al (2013), were similar regarding the changes in secretory granules. Teymoortash et al (2007) and Younis et al (2013), also agree with the changes of the rough endoplasmic reticulum.…”

“…Teymoortash et al (2007) and Younis et al (2013), also agree with the changes of the rough endoplasmic reticulum. The increase in interstitial tissue described by Teymoortash et al (2007), the interlobular space observed by and Younis et al (2013), and stromal fibrosis reported by Shan et al (2013), can be explained by the decrease of acini, and the resulting reduction in this space volume occupied by the parenchymal stromal tissue, or by the tissue reaction that occurs by application of the toxin in the gland. However, no author suggests this mechanism and further studies should occur to clarify such events.…”

“…Wen et al (2009), using botulinum toxin type A in parotid glands of rats, reached the same conclusions, claiming to exist a temporary cell atrophy, disagreeing with the findings of Ellies et al (2000), who also used the parotid gland and observed an increase in acinar volume. Shan et al (2013), injected 10 U and 5 U of botulinum toxin type A in submandibular glands of rabbits and showed a reduction in size of acinar cells, fibrosis, ultrastructural changes in the treated group with coalescence of secretory granules, decreased salivary flow, apoptosis in acinar and ductal cells in the groups treated with the toxin. The morphology of the gland returned to normality as the botulinum toxin was losing its effect.…”

“…Moreover, Shan et al (2013), applying botulinum toxin type A in submandibular glands of rabbits and performing immunofluorescence to aquaporin 5 (AQP5) and PCR for M3, suggested that the molecular mechanism of action of botulinum toxin type A is achieved by inhibiting the muscarinic receptor (M3), blocking the expression of AQP5 protein (an aquoporine) involved in secretion of water. Xu et al (2015), performed immunofluorescence for AQP5 in the submandibular glands of mice and showed decreased AQP5 immunofluorescence in the apical portion of the acinar cells of the groups treated with the toxin, but being reversed over time.…”