Gene delivery in salivary glands: from the bench to the clinic

Evaluation of Alginate Hydrogel Microstrands for Stromal Cell Encapsulation and Maintenance

Mesenchymal stromal cells (MSCs) have displayed potential in regenerating organ function due to their anti-fibrotic, anti-inflammatory, and regenerative properties. However, there is a need for delivery systems to enhance MSC retention while maintaining their anti-fibrotic characteristics. This study investigates the feasibility of using alginate hydrogel microstrands as a cell delivery vehicle to maintain MSC viability and phenotype. To accommodate cell implantation needs, we invented a Syringe-in-Syringe approach to reproducibly fabricate microstrands in small numbers with a diameter of around 200 µm and a porous structure, which would allow for transporting nutrients to cells by diffusion. Using murine NIH 3T3 fibroblasts and primary embryonic 16 (E16) salivary mesenchyme cells as primary stromal cell models, we assessed cell viability, growth, and expression of mesenchymal and fibrotic markers in microstrands. Cell viability remained higher than 90% for both cell types. To determine cell number within the microstrands prior to in vivo implantation, we have further optimized the alamarBlue assay to measure viable cell growth in microstrands. We have shown the effect of initial cell seeding density and culture period on cell viability and growth to accommodate future stromal cell delivery and implantation. Additionally, we confirmed homeostatic phenotype maintenance for E16 mesenchyme cells in microstrands.

Gene Therapeutic Delivery to the Salivary Glands

The salivary glands, exocrine glands in our body producing saliva, can be easily damaged by various factors. Radiation therapy and Sjogren's syndrome (a systemic autoimmune disease) are the two main causes of salivary gland damage, leading to a severe reduction in patients' quality of life. Gene transfer to the salivary glands has been considered a promising approach to treating the dysfunction. Gene therapy has long been applied to cure multiple diseases, including cancers, and hereditary and infectious diseases, which are proven to be safe and effective for the well-being of patients. The application of this treatment on salivary gland injuries has been studied for decades, yet its clinical progress is delayed. This chapter provides a coup d'oeil into gene transfer methods and various gene/vector types for salivary glands to help the new scientists and update established scientists on the progress that has been made during the past decades for the treatment of salivary gland disorders.

Diagnosis, Prevention, and Treatment of Radiotherapy-Induced Xerostomia: A Review

In patients with head and neck cancer, irradiation (IR)-sensitive salivary gland (SG) tissue is highly prone to damage during radiotherapy (RT). This leads to SG hypofunction and xerostomia. Xerostomia is defined as the subjective complaint of dry mouth, which can cause other symptoms and adversely affect the quality of life. In recent years, diagnostic techniques have constantly improved with the emergence of more reliable and valid questionnaires as well as more accurate equipment for saliva flow rate measurement and imaging methods. Preventive measures such as the antioxidant MitoTEMPO, botulinum toxin (BoNT), and growth factors have been successfully applied in animal experiments, resulting in positive outcomes. Interventions, such as the new delivery methods of pilocarpine, edible saliva substitutes, acupuncture and electrical stimulation, gene transfer, and stem cell transplantation, have shown potential to alleviate or restore xerostomia in patients. The review summarizes the existing and new diagnostic methods for xerostomia, along with current and potential strategies for reducing IR-induced damage to SG function. We also aim to provide guidance on the advantages and disadvantages of the diagnostic methods. Additionally, most prevention and treatment methods remain in the stage of animal experiments, suggesting a need for further clinical research, among which we believe that antioxidants, gene transfer, and stem cell transplantation have broad prospects.

In Vivo Transfection of Rat Salivary Glands With Fluorescently Tagged Aquaporin-5 Channel DNA

Background 

The acinar cells of salivary glands are responsible for most saliva production and are, unfortunately, h­­ighly radiosensitive. As such, dry mouth or xerostomia is an adverse effect experienced by half of head and neck cancer patients treated with radiation. We evaluate a novel method of gene transfection of aquaporin channels to rat salivary glands.

Materials and methods

A green fluorescent protein (GFP)-tagged human Aquaporin-5 (AQP5) cDNA sequence cloned into a pCMV6-AC-GFP vector was complexed with lipofectamine 2000. One submandibular gland of the anesthetized rats was injected with the complexed cDNA and lipid solution under ultrasound guidance, while the opposite gland was injected with the vehicle control. The animals were sacrificed between 24 to 48 hours post-injection. The salivary glands were removed and evaluated via fluorescence imaging. Western blot assays were also performed to determine AQP5 cDNA expression.

Results 

In the experiments, the submandibular glands were identified and injected under ultrasound guidance. Four control glands and eight experimental glands were evaluated. The cDNA was expressed successfully and variably within the experimental glands, noting greater intensity along the cell surface consistent with appropriate trafficking of the AQP5 channel. Western blot analysis demonstrated variable expression in the experimental sample with no expression in the control sample. Several glands across the groups showed mild to moderate interstitial edema or inflammation.

Conclusion 

In this study, we demonstrate an alternative in vivo transfection method via lipofection and demonstrate the successful expression of the AQP5 channel in rat salivary gland tissue.

The Influence of Whey Protein Heating Parameters on Their Susceptibility to Digestive Enzymes and the Antidiabetic Activity of Hydrolysates

The inhibition of dipeptidyl peptidase-IV (DPP-IV) and the release of glucagon-like peptide-1 (GLP-1) could normalize blood glucose levels in diabetic patients. This study evaluated the susceptibility of whey proteins to enzyme hydrolysis and the antidiabetic properties of protein hydrolysates from β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) solutions compared with whey protein isolate (WPI) solution treated at different heating temperatures (65, 75, and 85 °C). α-LA hydrolysate provided the lowest degree of hydrolysis (DH). Those heating temperatures did not significantly affect the DH of all protein hydrolysates. α-LA hydrolysate significantly increased GLP-1 levels and DPP-IV inhibitory activity more than β-LG hydrolysate. WPI hydrolysate inhibited DPP-IV activity less than an α-LA hydrolysate, but they were no significant differences for GLP-1 release activity. Heat treatment could affect the antidiabetic properties of all protein hydrolysates. Heating at 75 °C resulted in greater inhibition of the activity of DPP-IV than at 65 and 85 °C. The highest increase in GLP-1 release was also observed by heating at 75 °C. The recently obtained information is useful for the utilization of α-LA, heated at 75 °C for 30 min, in the preparation of antidiabetic food supplements.

Free d-Amino Acids in Salivary Gland in Rat

Free d-amino acids, which are enantiomers of l-amino acids, are found in mammals, including humans, and play an important role in a range of physiological functions in the central nervous system and peripheral tissues. Several d-amino acids have been observed in saliva, but their origin and the enzymes involved in their metabolism and catabolism remain to be clarified. In the present study, large amounts of d-aspartic acid and small amounts of d-serine and d-alanine were detected in all three major salivary glands in rat. No other d-enantiomers were detected. Protein expression of d-amino acid oxidase and d-aspartate oxidase, the enzymes responsible for the oxidative deamination of neutral and dicarboxylic d-amino acids, respectively, were detected in all three types of salivary gland. Furthermore, protein expression of the d-serine metabolic enzyme, serine racemase, in parotid glands amounted to approximately 40% of that observed in the cerebral cortex. The N-methyl-d-aspartic acid subunit proteins NR1 and NR2D were detected in all three major salivary glands. The results of the present study suggest that d-amino acids play a physiological role in a range of endocrine and exocrine function in salivary glands.

Bringing hydrogel-based craniofacial therapies to the clinic

This review explores the evolution of the use of hydrogels for craniofacial soft tissue engineering, ranging in complexity from acellular injectable fillers to fabricated, cell-laden constructs with complex compositions and architectures. Addressing both in situ and ex vivo approaches, tissue restoration secondary to trauma or tumor resection is discussed. Beginning with relatively simple epithelia of oral mucosa and gingiva, then moving to more functional units like vocal cords or soft tissues with multilayer branched structures, such as salivary glands, various approaches are presented toward the design of function-driven architectures, inspired by native tissue organization. Multiple tissue replacement paradigms are presented here, including the application of hydrogels as structural materials and as delivery platforms for cells and/or therapeutics. A practical hierarchy is proposed for hydrogel systems in craniofacial applications, based on their material and cellular complexity, spatial order, and biological cargo(s). This hierarchy reflects the regulatory complexity dictated by the Food and Drug Administration (FDA) in the United States prior to commercialization of these systems for use in humans. The wide array of available biofabrication methods, ranging from simple syringe extrusion of a biomaterial to light-based spatial patterning for complex architectures, is considered within the history of FDA-approved commercial therapies. Lastly, the review assesses the impact of these regulatory pathways on the translational potential of promising pre-clinical technologies for craniofacial applications. STATEMENT OF SIGNIFICANCE: While many commercially available hydrogel-based products are in use for the craniofacial region, most are simple formulations that either are applied topically or injected into tissue for aesthetic purposes. The academic literature previews many exciting applications that harness the versatility of hydrogels for craniofacial soft tissue engineering. One of the most exciting developments in the field is the emergence of advanced biofabrication methods to design complex hydrogel systems that can promote the functional or structural repair of tissues. To date, no clinically available hydrogel-based therapy takes full advantage of current pre-clinical advances. This review surveys the increasing complexity of the current landscape of available clinical therapies and presents a framework for future expanded use of hydrogels with an eye toward translatability and U.S. regulatory approval for craniofacial applications.

Candida Infection Associated with Salivary Gland-A Narrative Review

Candida species are common global opportunistic pathogens that could repeatedly and chronically cause oral mucosa infection and create an inflammatory environment, leading to organ dysfunction. Oral Candida infections may cause temporary or permanent damage to salivary glands, resulting in the destruction of acinar cells and the formation of scar tissue. Restricted function of the salivary glands leads to discomfort and diseases of the oral mucosa, such as dry mouth and associated infection. This narrative review attempts to summarize the anatomy and function of salivary glands, the associations between Candida and saliva, the effects of Candida infection on salivary glands, and the treatment strategies. Overall, clinicians should proactively manage Candida infections by educating patients on oral hygiene management for vulnerable populations, conducting frequent checks for a timely diagnosis, and providing an effective treatment plan.

Dry mouth diagnosis and saliva substitutes-A review from a textural perspective

The aim of this review is to assess the objective and subjective diagnosis, as well as symptomatic topical treatment of dry mouth conditions with a clear focus on textural perspective. We critically examine both the current practices as well as outline emerging possibilities in dry mouth diagnosis and treatment, including a patent scan for saliva substitutes. For diagnosis, salivary flow rates and patient-completed questionnaires have proven to be useful tools in clinical practice. To date, objective measurements of changes in mechanical properties of saliva via rheological, adsorption, and tribological measurements and biochemical properties of saliva such as assessing protein, mucins (MUC5B) are seldom incorporated into clinical diagnostics; these robust diagnostic tools have been largely restricted to application in non-clinical settings. As for symptomatic treatments of dry mouth, four key agents including lubricating, thickening, adhesive, and moisturizing agents have been identified covering the overall landscape of commercial saliva substitutes. Although thickening agents such as modified celluloses, polysaccharide gum, polyethylene glycol, and so forth are most commonly employed saliva substitutes, they offer short-lived relief from dry mouth and generally do not provide boundary lubrication properties of real human saliva. Innovative technologies such as self-assembly, emulsion, liposomes, and microgels are emerging as novel saliva substitutes hold promise for alternative approaches for efficient moistening and lubrication of the oral mucosa. Their adoption into clinical practice will depend on their efficacies, duration of relief, and ease of application by the practitioners and patient compliance.

Harnessing biomolecules for bioinspired dental biomaterials

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Insight into Salivary Gland Aquaporins

The main role of salivary glands (SG) is the production and secretion of saliva, in which aquaporins (AQPs) play a key role by ensuring water flow. The AQPs are transmembrane channel proteins permeable to water to allow water transport across cell membranes according to osmotic gradient. This review gives an insight into SG AQPs. Indeed, it gives a summary of the expression and localization of AQPs in adult human, rat and mouse SG, as well as of their physiological role in SG function. Furthermore, the review provides a comprehensive view of the involvement of AQPs in pathological conditions affecting SG, including Sjögren's syndrome, diabetes, agedness, head and neck cancer radiotherapy and SG cancer. These conditions are characterized by salivary hypofunction resulting in xerostomia. A specific focus is given on current and future therapeutic strategies aiming at AQPs to treat xerostomia. A deeper understanding of the AQPs involvement in molecular mechanisms of saliva secretion and diseases offered new avenues for therapeutic approaches, including drugs, gene therapy and tissue engineering. As such, AQP5 represents a potential therapeutic target in different strategies for the treatment of xerostomia.

The Role of Medicine and Technology in Shaping the Future of Oral Health

This commentary describes the changes taking place in dentistry and speculates on improvements that could happen soon. Advances in health care will have an impact on the integration and delivery of oral care; conversely, there is growing acceptance that oral health impacts systemic health. Technological innovations are changing the face of medical care and are quickly becoming integrated into dentistry. Advances in novel antimicrobials, genomics, robotics and artificial intelligence are transforming our ability to diagnose and manage disease.

Development of a Primary Human Cell Model for the Study of Human Cytomegalovirus Replication and Spread within Salivary Epithelium

Various aspects of human cytomegalovirus (HCMV) pathogenesis, including its ability to replicate in specific cells and tissues and the mechanism(s) of horizontal transmission, are not well understood, predominantly because of the strict species specificity exhibited by HCMV. Murine CMV (MCMV), which contains numerous gene segments highly similar to those of HCMV, has been useful for modeling some aspects of CMV pathogenesis; however, it remains essential to build relevant human cell-based systems to investigate how the HCMV counterparts function. The salivary gland epithelium is a site of persistence for both human and murine cytomegaloviruses, and salivary secretions appear to play an important role in horizontal transmission. Therefore, it is important to understand how HCMV is replicating within the glandular epithelial cells so that it might be possible to therapeutically prevent transmission. In the present study, we describe the development of a salivary epithelial model derived from primary human "salispheres." Initial infection of these primary salivary cells with HCMV occurs in a manner similar to that reported for established epithelial lines, in that gH/gL/UL128/UL130/UL131A (pentamer)-positive strains can infect and replicate, while laboratory-adapted pentamer-null strains do not. However, while HCMV enters the lytic phase and produces virus in salivary epithelial cells, it fails to exhibit robust spread throughout the culture and persists in a low percentage of salivary cells. The present study demonstrates the utility of these primary tissue-derived cells for studying HCMV replication in salivary epithelial cells in vitro IMPORTANCE Human cytomegalovirus (HCMV) infects the majority of the world's population, and although it typically establishes a quiescent infection with little to no disease in most individuals, the virus is responsible for a variety of devastating sequelae in immunocompromised adults and in developing fetuses. Therefore, identifying the viral properties essential for replication, spread, and horizontal transmission is an important area of medical science. Our studies use novel human salivary gland-derived cellular models to investigate the molecular details by which HCMV replicates in salivary epithelial cells and provide insight into the mechanisms by which the virus persists in the salivary epithelium, where it gains access to fluids centrally important for horizontal transmission.

Involvement of Aquaporins in the Pathogenesis, Diagnosis and Treatment of Sjögren's Syndrome

Sjögren’s syndrome (SS) is a chronic autoimmune disease characterized by lymphocytic infiltration of salivary and lacrimal glands resulting in diminished production of saliva and tears. The pathophysiology of SS has not yet been fully deciphered. Classically it has been postulated that sicca symptoms in SS patients are a double step process whereby lymphocytic infiltration of lacrimal and salivary glands (SG) is followed by epithelial cell destruction resulting in keratoconjunctivitis sicca and xerostomia. Recent advances in the field of the pathophysiology of SS have brought in new players, such as aquaporins (AQPs) and anti AQPs autoantibodies that could explain underlying mechanistic processes and unveil new pathophysiological pathways offering a deeper understanding of the disease. In this review, we delineate the link between the AQP and SS, focusing on salivary glands, and discuss the role of AQPs in the treatment of SS-induced xerostomia.

Mesenchymal Stem Cells in Primary Sjögren's Syndrome: Prospective and Challenges

Primary Sjögren's syndrome (pSS) is a chronic systemic inflammatory autoimmune disease characterized by lymphocytic infiltrates in exocrine glands. Current approaches do not control harmful autoimmune attacks or prevent irreversible damage and have considerable side effects. Mesenchymal stem cells (MSCs) have been effective in the treatment of several autoimmune diseases. The objective of this review is to illustrate the potential therapeutic role of MSCs in pSS. We summarize the recent advances in what is known about their immunomodulatory function and therapeutic applications in pSS. MSC transfusion can suppress autoimmunity and restore salivary gland secretory function in mouse models and patients with pSS by inducing regulatory T cells, suppressing Th1, Th17, and T follicular helper cell responses. In addition, MSCs can differentiate into salivary epithelial cells, presenting an option as a suitable alternative treatment. We also discuss current bioengineering methods which improve functions of MSCs for pSS. However, there remain many challenges to overcome before their wide clinical application.

Salivary hypofunction: An update on therapeutic strategies

OBJECTIVE

To perform a literature review addressing the therapeutic strategies for salivary hypofunction.

BACKGROUND

Qualitative and quantitative salivary dysfunctions predispose to changes in the oral mucosa and teeth, cause impairment to oral functions and negative impact on quality of life.

MATERIALS AND METHODS

A MEDLINE/PubMed search was conducted using the terms "Xerostomia" AND, "Saliva Artificial" OR, "Citric Acid," "Malic Acid," "Chewing Gum," "Acupuncture" OR, "Pilocarpine" OR, "Bethanechol" OR, "Cevimeline" OR, "Hyperbaric Oxygen Therapy" OR, "Stem Cell Therapy" OR "Genetic Therapy" and their Mesh Terms.

RESULTS

We selected 25 clinical trials investigating the effects of salivary substitutes, chewing gum, malic and citric acids, pilocarpine, cevimeline, bethanechol, acupuncture, hyperbaric oxygen therapy and regenerative therapies on salivary hypofunction. In most studies, the number of participants was low and the follow-up times short. The therapeutic modalities were classified according to the level of evidence on salivary dysfunction.

CONCLUSIONS

Pilocarpine and cevimeline had the strongest evidence of beneficial effect on salivary hypofunction. Citric and malic acids increase salivary flow but also increase the risk of erosion and dental caries. There are no controlled clinical trials supporting the efficacy of acupuncture, stem cell therapy and gene therapy on salivary dysfunction, although clinical observations suggest a promising effect. There is no evidence supporting salivary substitutes, chewing gum, bethanechol or hyperbaric oxygen on the treatment of salivary hypofunction.

In vivo Endocrine Secretion of Prostacyclin Following Expression of a Cyclooxygenase-1/Prostacyclin Fusion Protein in the Salivary Glands of Rats Via Nonviral Gene Therapy

Pulmonary arterial hypertension (PAH) is a progressive disease that culminates in right heart failure and death. Prostacyclin (PGI2) and its derivatives are effective treatments for PAH when administered as continuous parenteral infusions. This treatment paradigm requires medical sophistication, and patients are at risk for complications from an indewelling catheter; drug interruptions may result in rebound pulmonary hypertension and death. We hypothesized that the salivary gland can be repurposed into an endogenous production site for circulating PGI2 through the expression of a fusion protein embodying cyclooxygenase-1 (Cox1) and prostacyclin synthase (PGIS) domains. We utilized ultrasound-assisted gene transfer, a nonviral gene transfer strategy that achieves robust gene transfer to the salivary gland. We initially found that Cox1-PGIS expression in livers of mice using an adenoviral vector dramatically increased circulating PGI2 relative to untreated rats or rats treated with PGIS alone. We then utilized ultrasound-assisted gene transfer to express Cox1-PGIS in the submandibular glands of rats and showed a significant elevation of circulating PGI2 that corresponded to approximately 30% of that seen in humans undergoing intravenous infusion therapy for PAH. These results suggest the feasibility of gene therapy to drive endogenous biosynthesis of PGI2 as a therapeutic strategy for the treatment of PAH.

Retroductal Nanoparticle Injection to the Murine Submandibular Gland

Two common goals of salivary gland therapeutics are prevention and cure of tissue dysfunction following either autoimmune or radiation injury. By locally delivering bioactive compounds to the salivary glands, greater tissue concentrations can be safely achieved versus systemic administration. Furthermore, off target tissue effects from extra-glandular accumulation of material can be dramatically reduced. In this regard, retroductal injection is a widely used method for investigating both salivary gland biology and pathophysiology. Retroductal administration of growth factors, primary cells, adenoviral vectors, and small molecule drugs has been shown to support gland function in the setting of injury. We have previously shown the efficacy of a retroductally injected nanoparticle-siRNA strategy to maintain gland function following irradiation. Here, a highly effective and reproducible method to administer nanomaterials to the murine submandibular gland through Wharton's duct is detailed (Figure 1). We describe accessing the oral cavity and outline the steps necessary to cannulate Wharton's duct, with further observations serving as quality checks throughout the procedure.

Regenerative medicine and cell-based approaches to restore pancreatic function

The pancreas is a complex organ with exocrine and endocrine components. Many pathologies impair exocrine function, including chronic pancreatitis, cystic fibrosis and pancreatic ductal adenocarcinoma. Conversely, when the endocrine pancreas fails to secrete sufficient insulin, patients develop diabetes mellitus. Pathology in either the endocrine or exocrine pancreas results in devastating economic and personal consequences. The current standard therapy for treating patients with type 1 diabetes mellitus is daily exogenous insulin injections, but cell sources of insulin provide superior glycaemic regulation and research is now focused on the goal of regenerating or replacing β cells. Stem-cell-based models might be useful to study exocrine pancreatic disorders, and mesenchymal stem cells or secreted factors might delay disease progression. Although the standards that bioengineered cells must meet before being considered as a viable therapy are not yet established, any potential therapy must be acceptably safe and functionally superior to current therapies. Here, we describe progress and challenges in cell-based methods to restore pancreatic function, with a focus on optimizing the site for cell delivery and decreasing requirements for immunosuppression through encapsulation. We also discuss the tools and strategies being used to generate exocrine pancreas and insulin-producing β-cell surrogates in situ and highlight obstacles to clinical application.

Treatment of late sequelae after radiotherapy for head and neck cancer

Radiotherapy (RT) is used to treat approximately 80% of patients with cancer of the head and neck. Despite enormous advances in RT planning and delivery, a significant number of patients will experience radiation-associated toxicities, especially those treated with concurrent systemic agents. Many effective management options are available for acute RT-associated toxicities, but treatment options are much more limited and of variable benefit among patients who develop late sequelae after RT. The adverse impact of developing late tissue damage in irradiated patients may range from bothersome symptoms that negatively affect their quality of life to severe life-threatening complications. In the region of the head and neck, among the most problematic late effects are impaired function of the salivary glands and swallowing apparatus. Other tissues and structures in the region may be at risk, depending mainly on the location of the irradiated tumor relative to the mandible and hearing apparatus. Here, we review the available evidence on the use of different therapeutic strategies to alleviate common late sequelae of RT in head and neck cancer patients, with a focus on the critical assessment of the treatment options for xerostomia, dysphagia, mandibular osteoradionecrosis, trismus, and hearing loss.

Immune reactivity after adenoviral-mediated aquaporin-1 cDNA transfer to human parotid glands

OBJECTIVES

The purpose of this study was to examine the humoral and cellular immune reactivity to adenoviral vector (AdhAQP1) administration in the human parotid gland over the first 42 days of a clinical gene therapy trial.

METHODS

Of eleven treated subjects, five were considered as positive responders (Baum et al, 2012). Herein, we measured serum neutralizing antibody titers, circulating cytotoxic lymphocytes, and lymphocyte proliferation in peripheral blood mononuclear cells. Additionally, after adenoviral vector stimulation of lymphocyte proliferation, we quantified secreted cytokine levels.

RESULTS

Responders showed little to modest immune reactivity during the first 42 days following gene transfer. Additionally, baseline serum neutralizing antibody titers to serotype 5-adenovirus generally were not predictive of a subject's response to parotid gland administration of AdhAQP1. Cytokine profiling from activated peripheral blood mononuclear cells could not distinguish responders and non-responders.

CONCLUSIONS

The data are the first to describe immune responses after adenoviral vector administration in a human parotid gland. Importantly, we found that modest (2-3 fold) changes in systemic cell-mediated immune reactivity did not preclude positive subject responses to gene transfer. However, changes beyond that level likely impeded the efficacy of gene transfer.

Promising Gene Therapeutics for Salivary Gland Radiotoxicity

More than 0.5 million new cases of head and neck cancer are diagnosed worldwide each year, and approximately 75% of them are treated with radiation alone or in combination with other cancer treatments. A majority of patients treated with radiotherapy develop significant oral off-target effects because of the unavoidable irradiation of normal tissues. Salivary glands that lie within treatment fields are often irreparably damaged and a decline in function manifests as dry mouth or xerostomia. Limited ability of the salivary glands to regenerate lost acinar cells makes radiation-induced loss of function a chronic problem that affects the quality of life of the patients well beyond the completion of radiotherapy. The restoration of saliva production after irradiation has been a daunting challenge, and this review provides an overview of promising gene therapeutics that either improve the gland’s ability to survive radiation insult, or alternately, restore fluid flow after radiation. The salient features and shortcomings of each approach are discussed.

Induction and differentiation of adipose-derived stem cells from human buccal fat pads into salivary gland cells

Atrophy or hypofunction of the salivary gland because of aging or disease leads to hyposalivation that affects patient quality of life by causing dry mouth, deterioration of mastication/deglutition, and poor oral hygiene status. Current therapy for atrophy or hypofunction of the salivary gland in clinical practice focuses on symptom relief using drugs and artificial saliva; therefore, there is still a need to develop new therapies. To investigate potential novel therapeutic targets, we induced the differentiation of salivary gland cells by co-culturing human adipose-derived stem cells isolated from buccal fat pads (hBFP-ASCs) with human salivary-gland-derived fibroblasts (hSG-fibros). We examined their potential for transplantation and tissue neogenesis. Following the culture of hBFP-ASCs and hSG-fibros, differentiated cells were transplanted into the submandibular glands of SCID mice, and their degree of differentiation in tissues was determined. We also examined their potential for functional tissue reconstitution using a three-dimensional (3D) culture system. Co-cultured cells expressed salivary-glandrelated markers and generated new tissues following transplantation in vivo. Moreover, cell reconstituted glandular structures in the 3D culture system. In conclusion, coculture of hSG-fibros with hBFP-ASCs led to successful differentiation into salivary gland cells that could be transplanted to generate new tissues.

Advances in salivary gland gene therapy - oral and systemic implications

INTRODUCTION

Much research demonstrates the feasibility and efficacy of gene transfer to salivary glands. Recently, the first clinical trial targeting a salivary gland was completed, yielding positive safety and efficacy results.

AREAS COVERED

There are two major disorders affecting salivary glands: radiation damage following treatment for head and neck cancers and Sjögren's syndrome (SS). Salivary gland gene transfer has also been employed in preclinical studies using transgenic secretory proteins for exocrine (upper gastrointestinal tract) and endocrine (systemic) applications.

EXPERT OPINION

Salivary gland gene transfer is safe and can be beneficial in humans. Applications to treat and prevent radiation damage show considerable promise. A first-in-human clinical trial for the former was recently successfully completed. Studies on SS suffer from an inadequate understanding of its etiology. Proof of concept in animal models has been shown for exocrine and endocrine disorders. Currently, the most promising exocrine application is for the management of obesity. Endocrine applications are limited, as it is currently impossible to predict if systemically required transgenic proteins will be efficiently secreted into the bloodstream. This results from not understanding how secretory proteins are sorted. Future studies will likely employ ultrasound-assisted and pseudotyped adeno-associated viral vector-mediated gene transfer.

Adult stem cells and tissue engineering strategies for salivary gland regeneration: a review

Saliva is an important compound produced by the salivary glands and performs numerous functions. Hyposalivation (dry mouth syndrome) is a deleterious condition often resulting from radiotherapy for patients with head and neck cancer, Sjogren's Syndrome, or as a side effect of certain medications. Hyposalivation negatively affects speaking, mastication, and swallowing in afflicted patients, greatly reducing their quality of life. Current treatments for this pathology include modifying lifestyle, synthetic saliva supplementation, and the utilization of salivary gland stimulants and sialagogues. However, many of these treatments do not address the underlying issues and others are pervaded by numerous side effects. In order to address the shortcomings related to current treatment modalities, many groups have diverted their attention to utilizing tissue engineering and regenerative medicine approaches. Tissue engineering is defined as the application of life sciences and materials engineering toward the development of tissue substitutes that are capable of mimicking the structure and function of their natural analogues within the body. The general underlying strategy behind the development of tissue engineered organ substitutes is the utilization of a combination of cells, biomaterials, and biochemical cues intended to recreate the natural organ environment. The purpose of this review is to highlight current bioengineering approaches for salivary gland tissue engineering and the adult stem cell sources used for this purpose. Additionally, future considerations in regard to salivary gland tissue engineering strategies are discussed.

Double-strand adeno-associated virus-mediated exendin-4 expression in salivary glands is efficient in a diabetic rat model

AIM

Exendin-4 (Ex-4) is an agonist of the glucagon-like peptide 1 (GLP-1) receptor, approved for the treatment of type 2 diabetes (T2DM). Several strategies have been tried to develop stable and efficacious Ex-4 expression systems. The purpose of the current study was to determine whether double-stranded adeno-associated virus (dsAAV)-mediated in vivo expression of exendin-4 in salivary glands (SG), improves pathology in the Sprague-Dawley (SD) rat model of diabetes mellitus (DM).

METHODS

The effects of Ex-4 expression by recombinant dsAAV-NT4-Ex-4 were evaluated in vitro compared with a single-strand (ss) AAV. The dsAAV was delivered into SGs and the blood glucose and insulin levels were assessed in a rat model of DM.

RESULTS

DsAAV-NT4-Ex-4 virus induces significant exendin-4 expression in vitro. Furthermore, Ex-4 expressed from dsAAV virus in SGs enhances insulins secretion in vivo and significantly controls the onset of hyperglycemia in rat model of DM.

CONCLUSIONS

Results suggest that sustained secretion of Ex-4 following dsAAV-mediated gene therapy is feasible. SGs appear to be promising targets with potential clinical applicability for the treatment of DM. This represents the example of a successful use of Ex-4 for diabetes therapy, providing support for direct AAV-mediated in vivo as an easy, safe and efficient therapeutic strategy.

Protective MCMV immunity by vaccination of the salivary gland via Wharton's duct: replication-deficient recombinant adenovirus expressing individual MCMV genes elicits protection similar to that of MCMV

Salivary glands, a major component of the mucosal immune system, confer antigen-specific immunity to mucosally acquired pathogens. We investigated whether a physiological route of inoculation and a subunit vaccine approach elicited MCMV-specific and protective immunity. Mice were inoculated by retrograde perfusion of the submandibular salivary glands via Wharton's duct with tcMCMV or MCMV proteins focused to the salivary gland via replication-deficient adenovirus expressing individual MCMV genes (gB, gH, IE1; controls: saline and replication deficient adenovirus without MCMV inserts). Mice were evaluated for MCMV-specific antibodies, T-cell responses, germinal center formation, and protection against a lethal MCMV challenge. Retrograde perfusion with tcMCMV or adenovirus expressed MCMV proteins induced a 2- to 6-fold increase in systemic and mucosal MCMV-specific antibodies, a 3- to 6-fold increase in GC marker expression, and protection against a lethal systemic challenge, as evidenced by up to 80% increased survival, decreased splenic pathology, and decreased viral titers from 10(6) pfu to undetectable levels. Thus, a focused salivary gland immunization via a physiological route with a protein antigen induced systemic and mucosal protective immune responses. Therefore, salivary gland immunization can serve as an alternative mucosal route for administering vaccines, which is directly applicable for use in humans.

Cost-effectiveness landscape analysis of treatments addressing xerostomia in patients receiving head and neck radiation therapy

Head and neck (H&N) radiation therapy (RT) can induce irreversible damage to the salivary glands thereby causing long-term xerostomia or dry mouth in 68%-85% of the patients. Not only does xerostomia significantly impair patients' quality-of-life (QOL) but it also has important medical sequelae, incurring high medical and dental costs. In this article, we review various measures to assess xerostomia and evaluate current and emerging solutions to address this condition in H&N cancer patients. These solutions typically seek to accomplish 1 of the 4 objectives: (1) to protect the salivary glands during RT, (2) to stimulate the remaining gland function, (3) to treat the symptoms of xerostomia, or (4) to regenerate the salivary glands. For each treatment, we assess its mechanisms of action, efficacy, safety, clinical utilization, and cost. We conclude that intensity-modulated radiation therapy is both the most widely used prevention approach and the most cost-effective existing solution and we highlight novel and promising techniques on the cost-effectiveness landscape.

Copious urinary excretion of a male Syrian hamster (Mesocricetus auratus) salivary gland protein after its endocrine-like release upon β-adrenergic stimulation

Salivary glands, although widely considered as typically exocrine, may also release specific proteins in an endocrine manner. However, endocrine release of salivary gland proteins is not generally acknowledged since the evidences are not easily demonstrable. Submandibular salivary glands (SMG) of male Syrian hamsters express male-specific secretory proteins (MSP; which are lipocalins) visible in SDS-PAGE of SMG extracts, as major bands and also detectable in immunoblots of whole-saliva and urine as low MSP crossreactions. We report here that MSP is localized in acinar cells of SMG and acute treatment with isoproterenol (IPR; non-specific β1/β2-adrenergic agonist) results in considerable release of MSP in SMG-saliva. Moreover, acute IPR treatment markedly depletes SMG-MSP in a dose- and time-dependent manner. However, MSP depleted from SMG, far exceeds that recovered in SMG-saliva. Blood, submandibular lymph nodes and kidney of IPR-treated males showed MSP crossreactions and SDS-PAGE of their urine revealed profuse MSP excretion; this was undetectable in IPR-treated-SMG-ablated males, confirming that a substantial amount of MSP depleted from SMG after IPR treatment enters circulation and is excreted in urine. Treatments with specific β1- or β2-adrenergic agonists also reduced SMG-MSP levels and resulted in copious urinary excretion of MSP. Co-treatments with specific β1/β2-blockers indicated that above effects of IPR, β1- and even β2-agonists are very likely mediated by β1-adrenoceptors. MSP's detection by SDS-PAGE in urine after β-agonist treatment is a compelling and easily demonstrable evidence of release into circulation of a salivary gland protein. The possible means (endocrine-like or otherwise) of MSP's release into circulation and significance of its presence in saliva, blood and urine of male hamsters are discussed.

Nanoparticle-mediated gene silencing confers radioprotection to salivary glands in vivo

Radiation treatment of head and neck cancers causes irreversible damage of the salivary glands (SG). Here, we introduce a preclinical mouse model for small-interfering RNA (siRNA)-based gene silencing to provide protection of SG from radiation-induced apoptosis. Novel, pH-responsive nanoparticles complexed with siRNAs were introduced into mouse submandibular glands (SMG) by retroductal injection to modulate gene expression in vivo. To validate this approach, we first targeted Nkcc1, an ion transporter that is essential for saliva secretion. Nkcc1 siRNA delivery resulted in efficient knockdown, as quantified at the mRNA and the protein levels, and the functional result of Nkcc1 knockdown phenocopied the severe decrease in saliva secretion, characteristic of the systemic Nkcc1 gene knockout. To establish a strategy to prevent apoptotic cell loss due to radiation damage, siRNAs targeting the proapoptotic Pkcδ gene were administered into SMG before ionizing radiation. Knockdown of Pkcδ not only reduced the number of apoptotic cells during the acute phase of radiation damage, but also markedly improved saliva secretion at 3 months in irradiated animals, indicating that this treatment confers protection from hyposalivation. These results demonstrate that nanoparticle delivery of siRNAs targeting a proapoptotic gene is a localized, nonviral, and effective means of conferring radioprotection to the SGs.

Early responses to adenoviral-mediated transfer of the aquaporin-1 cDNA for radiation-induced salivary hypofunction

No conventional therapy exists for salivary hypofunction in surviving head and neck cancer patients with Radiation Therapy Oncology Group late grade 2-3 toxicity. We conducted a phase I clinical trial to test the safety and biologic efficacy of serotype 5, adenoviral-mediated aquaporin-1 cDNA transfer to a single previously irradiated parotid gland in 11 subjects using an open label, single-dose, dose-escalation design (AdhAQP1 vector; four dose tiers from 4.8 × 10(7) to 5.8 × 10(9) vector particles per gland). Treated subjects were followed at scheduled intervals. Multiple safety parameters were measured and biologic efficacy was evaluated with measurements of parotid salivary flow rate. Symptoms were assessed with a visual analog scale. All subjects tolerated vector delivery and study procedures well over the 42-d study period reported. No deaths, serious adverse events, or dose-limiting toxicities occurred. Generally, few adverse events occurred, and all were considered mild or moderate. No consistent changes were found in any clinical chemistry and hematology parameters measured. Objective responses were seen in six subjects, all at doses <5.8 × 10(9) vector particles per gland. Five of these six subjects also experienced subjective improvement in xerostomia. AdhAQP1 vector delivery to a single parotid gland was safe and transfer of the hAQP1 cDNA increased parotid flow and relieved symptoms in a subset of subjects.

Inducible tertiary lymphoid structures, autoimmunity, and exocrine dysfunction in a novel model of salivary gland inflammation in C57BL/6 mice

Salivary glands in patients with Sjögren's syndrome (SS) develop ectopic lymphoid structures (ELS) characterized by B/T cell compartmentalization, the formation of high endothelial venules, follicular dendritic cell networks, functional B cell activation with expression of activation-induced cytidine deaminase, as well as local differentiation of autoreactive plasma cells. The mechanisms that trigger ELS formation, autoimmunity, and exocrine dysfunction in SS are largely unknown. In this article, we present a novel model of inducible ectopic lymphoid tissue formation, breach of humoral self-tolerance, and salivary hypofunction after delivery of a replication-deficient adenovirus-5 in submandibular glands of C57BL/6 mice through retrograde excretory duct cannulation. In this model, inflammation rapidly and consistently evolves from diffuse infiltration toward the development of SS-like periductal lymphoid aggregates within 2 wk from AdV delivery. These infiltrates progressively acquire ELS features and support functional GL7(+)/activation-induced cytidine deaminase(+) germinal centers. Formation of ELS is preceded by ectopic expression of lymphoid chemokines CXCL13, CCL19, and lymphotoxin-β, and is associated with development of anti-nuclear Abs in up to 75% of mice. Finally, reduction in salivary flow was observed over 3 wk post-AdV infection, consistent with exocrine gland dysfunction as a consequence of the inflammatory response. This novel model has the potential to unravel the cellular and molecular mechanisms that regulate ELS formation and their role in exocrine dysfunction and autoimmunity in SS.

Sustained exendin-4 secretion through gene therapy targeting salivary glands in two different rodent models of obesity/type 2 diabetes

Exendin-4 (Ex-4) is a Glucagon-like peptide 1 (GLP-1) receptor agonist approved for the treatment of Type 2 Diabetes (T2DM), which requires daily subcutaneous administration. In T2DM patients, GLP-1 administration is reported to reduce glycaemia and HbA1c in association with a modest, but significant weight loss. The aim of present study was to characterize the site-specific profile and metabolic effects of Ex-4 levels expressed from salivary glands (SG) in vivo, following adeno-associated virus-mediated (AAV) gene therapy in two different animal models of obesity prone to impaired glucose tolerance and T2DM, specifically, Zucker fa/fa rats and high fed diet (HFD) mice. Following percutaneous injection of AAV5 into the salivary glands, biologically active Ex-4 was detected in the blood of both animal models and expression persisted in salivary gland ductal cell until the end of the study. In treated mice, Ex-4 levels averaged 138.9±42.3 pmol/L on week 6 and in treated rats, mean circulating Ex-4 levels were 238.2±72 pmol/L on week 4 and continued to increase through week 8. Expression of Ex-4 resulted in a significant decreased weight gain in both mice and rats, significant improvement in glycemic control and/or insulin sensitivity as well as visceral adipose tissue adipokine profile. In conclusion, these results suggest that sustained site-specific expression of Ex-4 following AAV5-mediated gene therapy is feasible and may be useful in the treatment of obesity as well as trigger improved metabolic profile.

Local delivery of AAV2-CTLA4IgG decreases sialadenitis and improves gland function in the C57BL/6.NOD-Aec1Aec2 mouse model of Sjögren's syndrome

INTRODUCTION

Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is a key negative costimulatory molecule that displays a wide range of anti-inflammatory properties and is currently approved to treat rheumatoid arthritis as a recombinant fusion protein (CTLA4IgG). To better understand the role of CTLA4IgG in primary Sjögren's syndrome (pSS), we generated a recombinant adeno-associated virus vector serotype 2 (AAV2) expressing a chimera of mouse CTLA-4 fused with a human immunoglobulin (AAV2-CTLA4IgG) and observed the effect of this molecule in C57BL/6.NOD-Aec1Aec2 mice, an animal model of pSS.

METHODS

A recombinant adeno-associated virus-2 (AAV-2) vector was constructed encoding a CTLA4IgG fusion protein. The AAV2-CTLA4IgG vector and an AAV2 control vector encoding beta galactosidase (LacZ) were administered by retrograde cannulation of the submandibular glands of C57BL/6.NOD-Aec1Aec2 mice. Protein expression was measured by ELISA and salivary glands were assessed for inflammation and activity.

RESULTS

Recombinant CTLA4IgG blocked B7 expression on macrophages in vitro. In vivo, localized expression of CTLA4IgG in the salivary glands of C57BL/6.NOD-Aec1Aec2 mice inhibited the loss of salivary gland activity and decreased T and B cell infiltration as well as dendritic cells and macrophages in the glands compared with control mice. In addition a decrease in several proinflammatory cytokines and an increase in transforming growth factor beta-1 (TGF-β1) expression were also observed.

CONCLUSIONS

These data suggest expression of CTLA4IgG in the salivary gland can decrease the inflammation and improve the xerostomia reported in these mice.

Hydrophobic oxime ethers: a versatile class of pDNA and siRNA transfection lipids

The manipulation of the cationic lipid structures to increase polynucleotide binding and delivery properties, while also minimizing associated cytotoxicity, has been a principal strategy for developing next-generation transfection agents. The polar (DNA binding) and hydrophobic domains of transfection lipids have been extensively studied; however, the linking domain comprising the substructure used to tether the polar and hydrophobic domains has attracted considerably less attention as an optimization variable. Here, we examine the use of an oxime ether as the linking domain. Hydrophobic oxime ethers were readily assembled via click chemistry by oximation of hydrophobic aldehydes using an aminooxy salt. A facile ligation reaction delivered the desired compounds with hydrophobic domain asymmetry. Using the MCF-7 breast cancer, H1792 lung cancer and PAR C10 salivary epithelial cell lines, our findings show that lipoplexes derived from oxime ether lipids transfect in the presence of serum at higher levels than commonly used liposome formulations, based on both luciferase and green fluorescent protein (GFP) assays. Given the biological compatibility of oxime ethers and their ease of formation, this functional group should find significant application as a linking domain in future designs of transfection vectors.