Generation of orthotopically functional salivary gland from embryonic stem cells

Organoids generated from pluripotent stem cells are used in the development of organ replacement regenerative therapy by recapitulating the process of organogenesis. These processes are strictly regulated by morphogen signalling and transcriptional networks. However, the precise transcription factors involved in the organogenesis of exocrine glands, including salivary glands, remain unknown. Here, we identify a specific combination of two transcription factors (Sox9 and Foxc1) responsible for the differentiation of mouse embryonic stem cell-derived oral ectoderm into the salivary gland rudiment in an organoid culture system. Following orthotopic transplantation into mice whose salivary glands had been removed, the induced salivary gland rudiment not only showed a similar morphology and gene expression profile to those of the embryonic salivary gland rudiment of normal mice but also exhibited characteristics of mature salivary glands, including saliva secretion. This study suggests that exocrine glands can be induced from pluripotent stem cells for organ replacement regenerative therapy.

[Transplantation of autologous labial salivary glands for severe dry eye]

OBJECTIVE

Autologous labial salivary gland transplantation has been a promising alternative for the treatment of severe dry eye. In this article, we describe the results of the ocular surface changes after labial salivary gland transplantation and investigate the feasibility of this treatment.

METHODS

The results of this technique in 8 patients (eyes) who suffered from severe dry eye were prospectively analyzed after surgery (follow-up of 6 months). The best-corrected visual acuity, Schirmer I test, degree of discomfort, usage of pharmaceutical tear substitutes, tear interferometry and slit lamp examination were investigated at different time before and after surgery.

RESULTS

All grafts remained viable and the survival rate is 100%. All patients showed significant increase in the Schirmer's test and they expressed great improvement in their ocular discomfort. The use of artificial tear substitutes was reduced because of the increased ocular surface lubrication.

CONCLUSION

Although the authors' long-term experience still is limited, we believe that the procedure is a promising alternative approach for severe dry eye.

Adnexal Surgery for Severe Ocular Surface Disease

Secondary causes of ocular surface disease are-to a large extent-due to disorders of the ocular adnexae. The main pathomechanisms involved include exposure, abrasion and malnutrition, resulting from a multitude of disorders such as ec- or entropion (e.g. in cicatrizing conjunctivitis), lid retraction and severe aqueous deficiency. In the presence of these problems, surgical attempts of ocular surface reconstruction frequently fail. Here we review established and evolving new techniques in the field of adnexal surgery to specifically address these problems.

[Radiation-induced xerostomia: prevention, treatment, perspectives]

Most of head and neck cancer patients will undergo radiotherapy. Xerostomia is probably its most frequent side effect. Subjective and objective criteria allow evaluating and grading xerostomia. New radiotherapy techniques and use of cytoprotectants can help to preserve salivary gland function. Parasym-pathicomimetics and saliva substitutes reduce symptoms. Strict mouth cleaning and fluoride's use prevent teeth deterioration and infections. Important breakthroughs have been made in the pathophysiology of xerostomia and new treatments are developed.

Management of salivary hypofunction during and after radiotherapy

Salivary hypofunction, the most common complication of high-dose radiation therapy (RT) to the head and neck, has a significant impact on quality of life, and requires careful planning of long-term dental and oral care. This report documents the results and conclusions of an evidence-based literature review on multidisciplinary team management of salivary hypofunction during and after RT. An update is provided on the pathophysiology of salivary hypofunction during and after RT, and recommendations for clinical management. The paper presents aspects managed by dental professionals (use of cholinergic agonists and other saliva stimulants, prevention of hyposalivation-induced rampant caries, and use of saliva substitutes), as well as the role of the radiation oncologist in minimizing salivary gland damage (parotid-sparing RT; cytoprotectants). This summary includes basic science, translational and clinical research topics with respect to radiation-induced salivary hypofunction, and provides an evidence-based management algorithm.

Characterization of murine autologous salivary gland graft cells: a model for use with an artificial salivary gland

The purpose of this study was to examine the growth and key functional abilities of primary cultures of salivary epithelial cells toward developing an artificial salivary gland. Cultures of epithelial cells originating from submandibular glands of BALB/c mice were established. Parenchymal cells were isolated by a Percoll gradient technique and thereafter seeded on irradiated NIH 3T3 fibroblasts serving as a feeder layer. The isolated cells were termed autologous salivary gland epithelial (ASGE) cells and could be cultivated for at least five passages (time limit of experiments). ASGE cells presented the typical organizational behavior of epithelial cells and electron microscopy, as well as immunostaining for cytokeratins, confirmed their epithelial origin. Furthermore, measurements of transepithelial resistance and water permeability indicated the ability of the ASGE cells to form a functional epithelial barrier. This study suggests that primary salivary epithelial cells can be obtained that exhibit critical characteristics needed for use with an artificial secretory device.

The patient with xerostomia: medical therapy, prosthetic therapy

The condition of xerostomia has significant consequences on both the hard and the soft components of the oral cavity, and can compromise functionality. Furthermore, this clinical complication produces negative changes in eating habits, frequently causing the loss of several kilograms of body weight. This article aims to provide as complete as possible an overview of therapeutic possibilities. Alongside medical therapy, the article will report on an experimental treatment designed for patients who are scheduled for radiation therapy to an area including a major salivary gland (in particular the parotid gland). The treatment consists in autologous transplantation of a portion of glandular tissue to a site outside the irradiated area. Lastly, a particular method for prosthetic rehabilitation, the so-called "reservoir" denture, is presented. A complete denture is produced with conventional techniques but has a small container for artificial saliva. For mandibular dentures the container is sub-divided into 3 inter-communicating chambers and is situated in the lingual flange; for maxillary dentures, a single chamber is situated in the palatine concavity. In our opinion, the mandibular reservoir denture presented here has better characteristics than other devices that have been reported in the international literature.

Absence of tight junction formation in an allogeneic graft cell line used for developing an engineered artificial salivary gland

An essential structural feature of fluid-secreting epithelial tissues is the presence of tight junctions. To develop a tissue-engineered organ capable of fluid secretion, the cellular component must establish these structures. As part of efforts to create an engineered artificial salivary gland, we have examined the ability of a candidate allogeneic graft cell line, HSG, to produce several key tight junction proteins, as well as to exhibit functional activities consistent with effective tight junction strand formation. In contrast to results obtained with a control kidney cell line, MDCK-II, HSG cells were unable to synthesize four important tight junction-associated proteins: ZO-1, occludin, claudin-1, and claudin-2. In addition, unlike MDCK-II cells, HSG cell monolayers could not restrict paracellular permeability. HSG cells were, thus, unable to generate significant transepithelial electrical resistance or serve as an effective barrier to osmotically imposed fluid movement. Furthermore, these two functional activities could not be reconstituted via the stable transfection of HSG cells with cDNAs encoding either claudin-1 or claudin-2. We conclude that because of their inability to form tight junctions, HSG cells are unsuitable for use as an allogeneic graft cell in an artificial salivary fluid secretory device. These studies also emphasize the importance of graft cell selection in artificial organ development, as certain required characteristics may be difficult to reengineer.

Using HSV-thymidine kinase for safety in an allogeneic salivary graft cell line

Extreme salivary hypofunction is a result of tissue damage caused by irradiation therapy for cancer in the head and neck region. Unfortunately, there is no currently satisfactory treatment for this condition that affects up to 40,000 people in the United States every year. As a novel approach to managing this problem, we are attempting to develop an orally implantable, fluid-secreting device (an artificial salivary gland). We are using the well-studied HSG salivary cell line as a potential allogeneic graft cell for this device. One drawback of using a cell line is the potential for malignant transformation. If such an untoward response occurred, the device could be removed. However, in the event that any HSG cells escaped, we wished to provide additional patient protection. Accordingly, we have engineered HSG cells with a hybrid adeno-retroviral vector, AdLTR.CMV-tk, to express the herpes simplex virus thymidine kinase (HSV-tk) suicide gene as a novel safety factor. Cells were grown on plastic plates or on poly-L-lactic acid disks and then transduced with different multiplicities of infection (MOIs) of the hybrid vector. Thereafter, various concentrations of ganciclovir (GCV) were added, and cell viability was tested. Transduced HSG cells expressed HSV-tk and were sensitive to GCV treatment. Maximal effects were seen at a MOI of 10 with 50 microM of GCV, achieving 95% cell killing on the poly-L-lactic acid substrate. These results suggest that engineering the expression of a suicide gene in an allogeneic graft cell may provide additional safety for use in an artificial salivary gland device.

A feasibility study of salivary gland autograft transplantation for xerostomia

BACKGROUND

Radiation-induced xerostomia is a frequent sequela in patients treated for cancer of the head and neck. One strategy to treat xerostomia would be to relocate portions of salivary tissue to adjacent submucosal sites that lie outside the radiation portals such as the anterior oral vestibule. It is not known whether salivary tissue transplanted as an autogenous free graft can survive, function adequately, and not produce mucoceles.

METHODS

Salivary gland tissue from the parotid and submandibular glands of the Syrian hamster were transplanted into the submucosal layer of the cheek pouch. After 3 months of observation, looking at graft size, graft extrusion, ulceration, infection, and mucocele formation, the graft sites were harvested. The specimens then underwent pathologic analysis by hematoxylin and eosin staining, as well as immunohistochemical methods to determine positivity for cytokeratin, smooth muscle actin (SMA), and amylase.

RESULTS

Histologic analysis of tissue harvested from Syrian hamsters grafted into the cheek pouch demonstrated intact, viable, organized salivary gland tissue. Eighty percent of the animals in the submandibular group and 63% of the animals in the parotid group had at least 1 graft with viable salivary tissue without undue complications.

CONCLUSIONS

Salivary gland tissue can be transplanted successfully as free autogenous grafts in the Syrian hamster model. Further studies are needed to determine whether the grafts will subsequently become functional and whether growth can be biologically stimulated. This approach may be a useful strategy to protect salivary gland tissue in patients undergoing radiotherapy for head and neck cancer.

Salivary gland transplantation: a canine model

Impaired salivary function with resultant severe dryness of the mouth, or xerostomia, may occur in association with a variety of systemic disorders or therapies. No adequate treatment exists for this debilitating condition, which impedes normal oral function, in particular alimentation and phonation. This study explores the feasibility of salivary gland autotransplantation, using a canine model. A salivary gland with its duct and surrounding blood vessels still attached was excised and reimplanted in the dog's thigh by anastomosing the graft's blood vessels to the femoral artery and vein. The duct was sutured to an artificial orifice cut in the thigh's skin, from which the saliva was collected. Salivary secretion was induced by a single intravenous bolus of pilocarpine (5 mg). Preoperative (normal) salivation was measured by collecting saliva from the gland in situ. Periodic functional studies showed normal saliva production during the first month after grafting, after which the salivary flow was reduced by 35% over the next 2 months. This reduction was interpreted as a sign of disuse atrophy resulting from the lack of autonomic innervation. To overcome this impediment, oral pilocarpine (5 mg/day) was administered to the recipient dog, after which normal levels of saliva were excreted through the graft during the 3-month follow-up period. The quality of the graft saliva was assessed by its protein and electrolyte levels, which showed close to normal values.

Mouse cytomegalovirus reactivation in severe combined immune deficient mice after implantation of latently infected salivary gland

The hypothesis that replication-competent mouse cytomegalovirus (MCMV) is detectable in severe combined immunodeficient (scid) mice after implantation of latently infected tissue was examined. Sections of latently infected salivary gland from 5 BALB/c mice were implanted into 20 C.B-17 scid mice. Recipient scid mice were sacrificed weekly for 5 weeks, and MCMV infection was detected in target organs using culture and DNA polymerase chain reaction (PCR). All donors were negative by standard culture but positive by DNA PCR. Replicating MCMV was recovered from 9 of 15 recipient scid mouse salivary gland, lung, liver, or spleen samples at postoperative weeks 2-5. No virus was recovered from recipient scid mice at weeks 1 or 12. Transplantation of latently infected tissues into scid mice resulted in rapid reactivation and dissemination of the virus. Further study of this model promises insight into the mechanisms of CMV latency and reactivation.

Reaction pattern of xenografted human salivary glands in nude mice. An immunohistological and autoradiographical study

35 specimens of human parotid gland and 37 of submandibular gland were transplanted into athymic nude mice. At distinct time intervals, from 1 day to 8 months the transplants were collected and examined. The transplanted glands were studied by light microscopy, immunohistology and autoradiography. The following changes were detectable: acute injury to the xenograft and inflammatory reaction (day 1-7), regeneration of the transplant and the beginning of adaptation to the "mouse milieu" (day 8-30), completion of adaptation (day 30 and later). The presence of the following substances was analysed: amylase, lactoferrin, secretory component, tissue polypeptide antigen (TPA). Amylase was only detected in the early transplants. Lactoferrin was seen only in the small duct system. TPA was present during all transplantation periods and was quantitatively correlated with the 3H thymidine labeling index. From our observations we can say that the salivary glands show two different reacting compartments: a large and a small duct system. The histogenesis of the xenografts, and the relationships of the changes observed to human salivary gland diseases were discussed.

Regeneration of submandibular salivary gland autografted in the rat tongue

Autologous SMG fragments were implanted in tongues of male rats which were sacrificed 15-20 min, 24 hr, 72 hr, 1 week, or 8 weeks after implantation. The tongues were excised, fixed, and processed for light and electron microscopy. In addition, some rats were injected with [3H]-thymidine 1 hr before sacrifice and the labeling indices (L.I.) of the salivary epithelial and interstitial cells were calculated. Twenty-four hours after implantation, SMG autografts showed massive central necrosis with some acini and ducts surviving at the periphery of the lobules. There was marked infiltration of the autografts with neutrophils and macrophages. Also the basal laminae surrounding the necrotic acini and ducts remained intact. The morphology of the autografts after 72 hr was similar to that after 24 hr except that there was additional necrosis and acini and ducts could no longer be identified in the autografts. By 1 week after implantation, the autografts showed lobular morphogenesis, ductal branching, and revascularization. At this time, the regenerating salivary epithelium appeared undifferentiated with no evidence of secretory granules. The L.I. of interstitial and ductlike structures showed significant increases over control values at 1 week after implantation, and then declined toward control levels by 3 weeks after implantation. By 8 weeks after implantation, there was evidence of acinar and striated ductal cytodifferentiation in two autografts. The results emphasize the potential of SMG autografts to regenerate subsequent to severe tissue necrosis.

Accelerated mammary cancer development by fetal salivary mesenchyma isografted to adult mouse mammary epithelium

Transplantation of fetal salivary mesenchyma into adult mammary glands resulted in atypical outgrowths from the mammary duct system. These duct-alveolus nodules (DAN) were distinguishable from hyperplastic alveolar nodules (HAN) that arose from normal mammary duct systems in mice infected with murine mammary tumor virus (MuMTV). DAN displayed a type of ductal branching characteristic of salivary gland rather than of mammary gland, reflecting a tissue-specific perturbation of epithelium-mesenchyma in DAN in milk-transmitted MuMTV-infected C3H/HeN mice and in MuMTV-negative BALB/c mice given 7,12-dimethylbenz[a]anthracene (DMBA) subsequent to transplantation of fetal salivary mesenchyma. Mammary cancers were not increased in milk-transmitted MuMTV-free C3H/HeN and GRS/A mice that received salivary mesenchyma transplants. Salivary mesenchyma accelerated mammary carcinogenesis by increasing the mammary epithelial cell population responsive to MuMTV and DMBA.

Studies of the cellular cure for osteopetrosis by transplanted cells: specificity of the cell type in ia rats

Spleen cells from normal rats are known to cure osteopetrosis in ia littermates within 3 weeks. In this study cell suspensions from liver, thymus, bone marrow, salivary gland, skeletal muscle and brain from normal rats were tested for their ability to cure osteopetrosis in ia littermates whose ability to reject these cells had been suppressed by whole-body irradiation. Cells from liver, thymus and bone marrow cured the disease as effectively as spleen cells from normal littermates. Mutants that received cells from salivary gland, muscle and brain remained osteopetrotic. These data suggest that some cell found in spleen, liver, thymus and bone marrow of 10-day-old normal rats, such as a lymphoid cell or stem cell, can restore hemopoiesis and bone resorption in osteopetrotic (ia) rats.