Salivary gland transplantation: a canine model

Current status of the development of an artificial salivary gland

Salivary glands (SGs) secrete more than half a liter of saliva daily. Saliva has many functions in maintaining the normal homeostasis of the oral cavity. Several causes underlie salivary impairment, where irradiation therapy to head and neck cancer patients is one of the most debilitating causes leading to considerable decrease in the patients' quality of life. In the last decade, others and we have focused on implementing tissue engineering principles combined with gene transfer and stem cell methodologies to develop an artificial SG device. This manuscript provides an overview of the current status of engineering an artificial SG.

Transplantation of vascularized submandibular gland in dogs

PURPOSE

Presently, treatments for xerostomia only target symptoms, as an active therapy method has not been established. Herein, we discuss the possibility of using a submandibular gland allograft technique for the disease.

MATERIALS AND METHODS

Using a vascularized submandibular gland transplantation method, we extracted portions of the submandibular gland, including the duct and chorda tympani branches, from beagle dogs and placed them into the submental region of age- and weight-matched dogs. We then measured the amount of saliva secretion and examined the grafted glands histologically.

RESULTS

Sufficient quantities of saliva were secreted from the grafted glands with pilocarpine treatment. Histologic findings showed that the acinar cells in the grafted and untreated contralateral glands had some atrophy, as compared with the normal glands; however, periodic acid Schiff staining showed that they produced saliva.

CONCLUSIONS

Transplantation of vascularized submandibular glands into dogs was successful and may become a novel treatment strategy for patients with xerostomia.

Experimental microsurgery of salivary ducts in dogs

The results achieved by experimental microsurgical suturing of salivary ducts in dogs are presented. Nine partial lesions and one complete transection of the ducts were made on parotid and submandibular ducts. Four to seven interrupted microsutures were used for each lesion. The operations were successful in seven out of 10 cases, as observed by sialography. Histologically, granulation tissue compressing the ducts was observed after suturing the lesions. Four venous graft transplantations were performed and none were successful. After venous graft transplantation, the transplant was not apparent histologically, raising doubt as to the potential success of this technique. The use of stenting is discussed based on a summary of the published literature. Those reports indicate that long-term stenting can benefit the outcome of salivary duct repair. The use of dogs as a model for experimental salivary duct operations has been shown to be valuable in assessing various surgical techniques.

The growth and morphological behavior of salivary epithelial cells on matrix protein-coated biodegradable substrata

The purpose of this study was to examine the growth and morphology of a salivary epithelial cell line (HSG) in vitro on several biodegradable substrata as an important step toward developing an artificial salivary gland. The substrates examined were poly-L-lactic acid (PLLA), polyglycolic acid (PGA), and two co-polymers, 85% and 50% PLGA, respectively. The substrates were formed into 20- to 25-mm disks, and the cells were seeded directly onto the polymers or onto polymers coated with specific extracellular matrix proteins. The two copolymer substrates became friable over time in aqueous media and proved not useful for these experiments. The purified matrix proteins examined included fibronectin (FN), laminin (LN), collagen I, collagen IV, and gelatin. In the absence of preadsorbed proteins, HSG cells did not attach to the polymer disks. The cells, in general, behaved similarly on both PLLA and PGA, although optimal results were obtained consistently in PLLA. On FN-coated PLLA disks, HSG cells were able to form a uniform monolayer, which was dependent on time and FN concentration. Coating of disks with LN, collagen I, and gelatin also promoted monolayer growth. This study defines the conditions necessary for establishing a monolayer organization of salivary epithelial cells with rapid proliferation on a biodegradable substrate useful for tissue engineering.

Re-engineering the functions of a terminally differentiated epithelial cell in vivo

Because of their easy access, and important role in oral homeostasis, mammalian salivary glands provide a unique site for addressing key issues and problems in tissue engineering. This manuscript reviews studies by us in three major directions involving re-engineering functions of salivary epithelial cells. Using adenoviral-mediated gene transfer in vivo, we show approaches to i) repair damaged, hypofunctional glands and ii) redesign secretory functions to include endocrine as well as exocrine pathways. The third series of studies show our general approach to develop an artificial salivary gland for clinical situations in which all glandular tissue has been lost.