Botulinum toxin A treatment of epiphora secondary to autologous submandibular gland transplantation

Salivary Gland Transplantation as a Promising Approach for Tear Film Restoration in Severe Dry Eye Disease

With increased awareness of dry eye disease (DED), a multitude of therapeutic options have become available. Nevertheless, the treatment of severe DED remains difficult. In a patient whose DED is related to the loss of lacrimal function without severe destruction of the salivary glands, autologous transplantation of the latter as functioning exocrine tissue to rebuild a stable tear film is an attractive idea. All three major and minor salivary glands have been used for such transplantation. Due to the complications associated with and unfavorable prognosis of parotid duct and sublingual gland transplantation, surgeons now prefer to use the submandibular gland (SMG) for such procedures. The transplantation of the SMG not only has a high survival rate, but also improves dry eye symptoms and signs for more than 20 years post-surgery. The regulation of the secretion of the transplanted SMG is critical because the denervated SMG changes its mechanism of secretion. Innovative procedures have been developed to stimulate secretion in order to prevent the obstruction of the Wharton's duct and to decrease secretion when postoperative "epiphora" occurs. Among the minor salivary glands, the transplantation of the labial salivary glands is the most successful in the long-term. The measurement of the flow rates of minor salivary glands and donor-site selection are critical steps before surgery.

Surgical Procedures in the Treatment of Dry Eye Disease

Dry eye disease (DED) is a multifactorial disease affecting 5% to 50% in different populations. The most severe cases of DED are often caused by aqueous deficient dry eye disease (ADDE) due to lacrimal gland (LG) hypofunction. Many patients with severe ADDE do not experience adequate symptom relief from topical treatment, severely reducing their quality of life. The focus of this review is to describe the surgical interventions presently being used or investigated when topical treatment with eye drops is insufficient. The conventional surgical approach is to proceed to punctal occlusion or partial or total tarsorrhaphy. However, novel surgical procedures have been reported to have higher efficacy and patient satisfaction than conventional treatments. These procedures include amniotic membrane transplantation, transposition or transplantation of the salivary glands, and cell-based injections into the LG, each with strengths and weaknesses. Further development of these treatment modalities might prove pivotal in treating dry eye patients in the future.

Lacrimal gland botulinum toxin injection for epiphora management

PURPOSE

Epiphora remains an often difficult to manage ocular complaint for ophthalmologists in all subspecialties. This review seeks to examine the safety and efficacy of botulinum toxin injection for management of chronic epiphora.

METHODS

The authors conducted a Pubmed search for studies on the use of lacrimal and transplanted salivary gland botulinum toxin injections for the management of epiphora within the past 20 years. Studies included had a minimum of four glandular injections.

RESULTS

The authors identified 14 studies and divided them by indication for injection; either functional epiphora, non-functional epiphora, or mixed studies. Seven studies examined injections for cases of functional epiphora, four for non-functional epiphora, and four for mixed cases. The number of glandular injections reported ranged from 4 to 65. Side effects reported were limited to diplopia, eyelid or lacrimal gland hematoma, papillary conjunctivitis, dry eye, ptosis, and bleeding.

CONCLUSIONS

Glandular botulinum toxin injection should be considered as a viable treatment strategy for both functional and nonfunctional epiphora. From the studies reviewed, botulinum toxin injection was shown to be effective in both children and adults. Injection can be performed in the outpatient setting, is minimally invasive, technically easy to administer, has a favorable side effect profile, and good efficacy. Furthermore, repeat injections can be performed with similar efficacy.

[Role and mechanism of muscarinic acetylcholine receptor in the regulation of submandibular gland secretion]

Muscarinic acetylcholine receptors (mAChRs), including M1-M5 subtypes, are classic receptors in regulating water, ion, and solute transport in salivary gland. Our work focuses on the studies on the expression pattern and function of mAChR in the submandibular gland (SMG), and the underlying mechanism involved in the mAChR-regulated secretion, together with the effect of parasympathectomy on the salivary secretion. Microvascular autotransplantation of SMG into the temporal fossa provides a continuous and endogenous source of fluids, and is currently an effective method for treating severe keratoconjunctivitis sicca. By using RT-PCR, Western blotting, and immunofluorescence, our data demonstrated that the expression of M1 and M3 subtypes were decreased in latent period in rabbit SMG autotransplantation model, whereas carbachol stimulation promoted the salivary secretion, as well as M1 and M3 expressions. By contrast, mAChRs were hypersensitive in epiphora SMGs, whereas atropine gel and botulinum toxin A application significantly inhibited the hypersecretion in both animal models and patients. Furthermore, the possible intracellular signal molecules involved in the mAChR-modulated salivary secretion were explored. Activation of mAChR upregulated the expression of aquaporin 5 (AQP5), the main transporter that mediated water secretion through transcellular pathway, and led to AQP5 trafficking from lipid rafts to non-lipid microdomain. Extracellular signal-regulated kinase 1/2 (ERK1/2) was involved in the mAChR-regulated AQP5 content. mAChR activation also modulated the expression, distribution, and function of tight junction proteins, and increased paracellular permeability. ERK1/2/β-arrestin2/clathrin/ubiquitin signaling pathway was responsible for the mAChR-regulated downregulation of tight junction molecule claudin-4. Cytoskeleton filamentous actin (F-actin) was also involved in the distribution and barrier function of epithelial tight junctions. Besides, endothelial tight junctions were opened by mAChR agonist-evoked salivation in the mice. Furthermore, parasympathetic denervation increased resting salivary secretion in the long terminrats and minipigs. Taken together, our work demonstrated that mAChR regulated saliva secretion via transcellular and paracellular pathways in SMG epithelium as well as tight junction opening in SMG endothelium. Modulation of mAChR might be a promising strategy to ameliorate SMG dysfunction.