Ultrasound-assisted nonviral gene transfer of AQP1 to the irradiated minipig parotid gland restores fluid secretion

The involvement of aquaporin 5 in the inflammatory response of primary Sjogren's syndrome dry eye: potential therapeutic targets exploration

Sjogren's syndrome (SS) is a chronic autoimmune disease. Mainly due to the infiltration of lymphoplasmic cells into the exocrine glands, especially the salivary glands and lacrimal glands, resulting in reduced tear and saliva secretion. Reduced tear flow can trigger Sjogren's syndrome dry eye (SSDE). Although the pathophysiology of SSDE xerosis remains incompletely understood, recent advances have identified aquaporin-5 (AQP5) as a critical factor in dysregulation of the exocrine gland and epithelium, influencing the clinical presentation of SSDE through modulation of inflammatory microenvironment and tear secretion processes. This review aims to explore AQP5 regulatory mechanisms in SSDE and analyze its potential as a therapeutic target, providing new directions for SSDE treatment.

Involvement of aquaporin 5 in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease with the pathological hallmark of lymphoplasmacytic infiltration of exocrine glands - more specifically salivary and lacrimal glands - resulting in a diminished production of tears and saliva (sicca syndrome). The pathophysiology underscoring the mechanisms of the sicca symptoms in SS has still yet to be unraveled but recent advances have identified a cardinal role of aquaporin-5 (AQP5) as a key player in saliva secretion as well as salivary gland epithelial cell dysregulation. AQP5 expression and localization are significantly altered in salivary glands from patients and mice models of the disease, shedding light on a putative mechanism accounting for diminished salivary flow. Furthermore, aberrant expression and localization of AQP5 protein partners, such as prolactin-inducible protein and ezrin, may account for altered AQP5 localization in salivary glands from patients suffering from SS and are considered as new players in SS development. This review provides an overview of the role of AQP5 in SS salivary gland epithelial cell dysregulation, focusing on its trafficking and protein-protein interactions.

Cell-Free Therapies: The Use of Cell Extracts to Mitigate Irradiation-Injured Salivary Glands

Radiotherapy is a standard treatment for head and neck cancer patients worldwide. However, millions of patients who received radiotherapy consequently suffer from xerostomia because of irreversible damage to salivary glands (SGs) caused by irradiation (IR). Current treatments for IR-induced SG hypofunction only provide temporary symptom alleviation but do not repair the damaged SG, thus resulting in limited treatment efficacy. Therefore, there has recently been a growing interest in regenerative treatments, such as cell-free therapies. This review aims to summarize cell-free therapies for IR-induced SG, with a particular emphasis on utilizing diverse cell extract (CE) administrations. Cell extract is a group of heterogeneous mixtures containing multifunctional inter-cellular molecules. This review discusses the current knowledge of CE's components and efficacy. We propose optimal approaches to improve cell extract treatment from multiple perspectives (e.g., delivery routes, preparation methods, and other details regarding CE administration). In addition, the advantages and limitations of CE treatment are systematically discussed by comparing it to other cell-free (such as conditioned media and exosomes) and cell-based therapies. Although a comprehensive identification of the bioactive factors within CEs and their mechanisms of action have yet to be fully understood, we propose cell extract therapy as an effective, practical, user-friendly, and safe option to conventional therapies in IR-induced SG.

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.

Ultrasound-Targeted Microbubble Destruction: Modulation in the Tumor Microenvironment and Application in Tumor Immunotherapy

Tumor immunotherapy has shown strong therapeutic potential for stimulating or reconstructing the immune system to control and kill tumor cells. It is a promising and effective anti-cancer treatment besides surgery, radiotherapy and chemotherapy. Presently, some immunotherapy methods have been approved for clinical application, and numerous others have demonstrated promising in vitro results and have entered clinical trial stages. Although immunotherapy has exhibited encouraging results in various cancer types, however, a large proportion of patients are limited from these benefits due to specific characteristics of the tumor microenvironment such as hypoxia, tumor vascular malformation and immune escape, and current limitations of immunotherapy such as off-target toxicity, insufficient drug penetration and accumulation and immune cell dysfunction. Ultrasound-target microbubble destruction (UTMD) treatment can help reduce immunotherapy-related adverse events. Using the ultrasonic cavitation effect of microstreaming, microjets and free radicals, UTMD can cause a series of changes in vascular endothelial cells, such as enhancing endothelial cells' permeability, increasing intracellular calcium levels, regulating gene expression, and stimulating nitric oxide synthase activities. These effects have been shown to promote drug penetration, enhance blood perfusion, increase drug delivery and induce tumor cell death. UTMD, in combination with immunotherapy, has been used to treat melanoma, non-small cell lung cancer, bladder cancer, and ovarian cancer. In this review, we summarized the effects of UTMD on tumor angiogenesis and immune microenvironment, and discussed the application and progress of UTMD in tumor immunotherapy.

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.

Mechanism, Prevention, and Treatment of Radiation-Induced Salivary Gland Injury Related to Oxidative Stress

Radiation therapy is a common treatment for head and neck cancers. However, because of the presence of nerve structures (brain stem, spinal cord, and brachial plexus), salivary glands (SGs), mucous membranes, and swallowing muscles in the head and neck regions, radiotherapy inevitably causes damage to these normal tissues. Among them, SG injury is a serious adverse event, and its clinical manifestations include changes in taste, difficulty chewing and swallowing, oral infections, and dental caries. These clinical symptoms seriously reduce a patient’s quality of life. Therefore, it is important to clarify the mechanism of SG injury caused by radiotherapy. Although the mechanism of radiation-induced SG injury has not yet been determined, recent studies have shown that the mechanisms of calcium signaling, microvascular injury, cellular senescence, and apoptosis are closely related to oxidative stress. In this article, we review the mechanism by which radiotherapy causes oxidative stress and damages the SGs. In addition, we discuss effective methods to prevent and treat radiation-induced SG damage.

Immunosuppressed Miniswine as a Model for Testing Cell Therapy Success: Experience With Implants of Human Salivary Stem/Progenitor Cell Constructs

An urgent need exists to develop large animal models for preclinical testing of new cell therapies designed to replace lost or damaged tissues. Patients receiving irradiation for treatment of head and neck cancers frequently develop xerostomia/dry mouth, a condition that could one day be treated by cell therapy to repopulate functional saliva-producing cells. Using immunosuppression protocols developed for patients receiving whole face transplants, we successfully used immunosuppressed miniswine as a suitable host animal to evaluate the long-term stability, biocompatibility, and fate of matrix-modified hyaluronate (HA) hydrogel/bioscaffold materials containing encapsulated salivary human stem/progenitor cells (hS/PCs). An initial biocompatibility test was conducted in parotids of untreated miniswine. Subsequent experiments using hS/PC-laden hydrogels were performed in animals, beginning an immunosuppression regimen on the day of surgery. Implant sites included the kidney capsule for viability testing and the parotid gland for biointegration time periods up to eight weeks. No transplant rejection was seen in any animal assessed by analysis of the tissues near the site of the implants. First-generation implants containing only cells in hydrogel proved difficult to handle in the surgical suite and were modified to adhere to a porcine small intestinal submucosa (SIS) membrane for improved handling and could be delivered through the da Vinci surgical system. Several different surgical techniques were assessed using the second-generation 3D-salivary tissue (3D-ST) for ease and stability both on the kidney capsule and in the capsule-less parotid gland. For the kidney, sliding the implant under the capsule membrane and quick stitching proved superior to other methods. For the parotid gland, creation of a tissue “pocket” for placement and immediate multilayer tissue closure were well tolerated with minimal tissue damage. Surgical clips were placed as fiduciary markers for tissue harvest. Some implant experiments were conducted with miniswine 90 days post-irradiation when salivation decreased significantly. Sufficient parotid tissue remained to allow implant placement, and animals tolerated immunosuppression. In all experiments, viability of implanted hS/PCs was high with clear signs of both vascular and nervous system integration in the parotid implants. We thus conclude that the immunosuppressed miniswine is a high-value emerging model for testing human implants prior to first-in-human trials.

Competitive blocking of salivary gland [18F]DCFPyL uptake via localized, retrograde ductal injection of non-radioactive DCFPyL: a preclinical study

Background

PSMA-targeted radionuclide therapy (TRT) is a promising treatment for prostate cancer (PCa), but dose-limiting xerostomia can severely limit its clinical adaptation, especially when using alpha-emitting radionuclides. With [¹⁸F]DCFPyL as a surrogate for PSMA-TRT, we report a novel method to selectively reduce salivary gland (SG) uptake of systemically administered [¹⁸F]DCFPyL by immediate prior infusion of non-radioactive standard of [¹⁸F]DCFPyL (DCFPyL) directly into the SG via retrograde cannulation.

Methods

A dose-finding cohort using athymic nude mice demonstrated proof of principle that SG uptake can be selectively blocked by DCFPyL administered either locally via cannulation (CAN group) or systemically (SYS group). The experiments were repeated in a validation cohort of 22RV1 tumor-bearing mice. Submandibular glands (SMG) of CAN mice were locally blocked with either saline or DCFPyL (dose range: 0.01× to 1000× molar equivalent of the radioactive [18F]DCFPyL dose). The radioactive dose of [18F]DCFPyL was administered systemically 10 min later and the mice euthanized after 1 h for biodistribution studies. Toxicity studies were done at up to 1000× dose.

Results

In the dose-finding cohort, the SYS group showed a dose-dependent 12–40% decrease in both the SMG T/B and the kidney (tumor surrogate). Mild blocking was observed at 0.01× , with maximal blocking reached at 1× with no additional blocking up to 1000× . In the CAN group, blocking at the 0.1× and 1× dose levels resulted in a similar 42–53% decrease, but without the corresponding decrease in kidney uptake as seen in the SYS group. Some evidence of “leakage” of DCFPyL from the salivary gland into the systemic circulation was observed. However, experiments in 22RV1 tumor-bearing mice at the 0.1× and 1× dose levels confirm that, at the appropriate blocking dose, SG uptake of [18F]DCFPyL can be selectively reduced without affecting tumor uptake and with no toxicity.

Conclusion

Our results suggest that direct retrograde instillation of DCFPyL into the SG could predictably and selectively decrease salivary uptake of systemically administered [¹⁸F]DCFPyL without altering tumor uptake, if given at the appropriate dose. This novel approach is easily translatable to clinical practice and has the potential to mitigate xerostomia, without compromising the therapeutic efficacy of the PSMA-TRT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00803-9.

Translating Dental, Oral, and Craniofacial Regenerative Medicine Innovations to the Clinic through Interdisciplinary Commercial Translation Architecture

Few university-based regenerative medicine innovations in the dental, oral, and craniofacial (DOC) space have been commercialized and affected clinical practice in the United States. An analysis of the commercial translation literature and National Institute for Dental and Craniofacial Research's (NIDCR's) portfolio identified barriers to commercial translation of university-based DOC innovations. To overcome these barriers, the NIDCR established the Dental Oral Craniofacial Tissue Regeneration Consortium. We provide generalized strategies to inform readers how to bridge the "valley of death" and more effectively translate DOC technologies from the research laboratory or early stage company environment to clinical trials and bring needed innovations to the clinic. Three valleys of death are covered: 1) from basic science to translational development, 2) from translational technology validation to new company formation (or licensing to an existing company), and 3) from new company formation to scaling toward commercialization. An adapted phase-gate model is presented to inform DOC regenerative medicine teams how to involve regulatory, manufacturability, intellectual property, competitive assessments, business models, and commercially oriented funding mechanisms earlier in the translational development process. An Industrial Partners Program describes how to conduct market assessments, industry maps, business development processes, and industry relationship management methods to sustain commercial translation through the later-stage valley of death. Paramount to successfully implementing these methods is the coordination and collaboration of interdisciplinary teams around specific commercial translation goals and objectives. We also provide several case studies for translational projects with an emphasis on how they addressed DOC biomaterials for tissue regeneration within a rigorous commercial translation development environment. These generalized strategies and methods support innovations within a university-based and early stage company-based translational development process, traversing the many funding gaps in dental, oral, and craniofacial regenerative medicine innovations. Although the focus is on shepherding technologies through the US Food and Drug Administration, the approaches are applicable worldwide.

Advances on mechanism and treatment of salivary gland in radiation injury

Oral squamous cell carcinoma (OSCC) is the most frequent tumour in head and neck malignant. The current treatment is mainly based on surgery therapy, radiation therapy and chemical therapy. Meanwhile, there are many a defect in the treatment. For example, there are many defects in radiotherapy. Radioactive salivatitis is the most common. In addition, there are a series of changes such as dry mouth, oral mucositis, rampant dental caries, and radioactive osteomyelitis of jaw, which cause swallowing, chewing problems, and taste dysfunction. Currently, the research on radioactive salivatitis is progressing rapidly, but its mechanism is more complication. This paper review aims to summarize the research progress in this field.

Building a Functional Salivary Gland for Cell-Based Therapy: More than Secretory Epithelial Acini

A few treatment options exist for patients experiencing xerostomia due to hyposalivation that occurs as a result of disease or injury to the gland. An opportunity for a permanent solution lies in the field of salivary gland replacement through tissue engineering. Recent success emboldens in the vision of producing a tissue-engineered salivary gland composed of differentiated salivary epithelial cells that are able to differentiate to form functional units that produce and deliver saliva to the oral cavity. This vision is augmented by advances in understanding cellular mechanisms that guide branching morphogenesis and salivary epithelial cell polarization in both acinar and ductal structures. Growth factors and other guidance cues introduced into engineered constructs help to develop a more complex glandular structure that seeks to mimic native salivary gland tissue. This review describes the separate epithelial phenotypes that make up the gland, and it describes their relationship with the other cell types such as nerve and vasculature that surround them. The review is organized around the links between the native components that form and contribute to various aspects of salivary gland development, structure, and function and how this information can drive the design of functional tissue-engineered constructs. In addition, we discuss the attributes of various biomaterials commonly used to drive function and form in engineered constructs. The review also contains a current description of the state-of-the-art of the field, including successes and challenges in creating materials for preclinical testing in animal models. The ability to integrate biomolecular cues in combination with a range of materials opens the door to the design of increasingly complex salivary gland structures that, once accomplished, can lead to breakthroughs in other fields of tissue engineering of epithelial-based exocrine glands or oral tissues.

Nerve growth factor protects salivary glands from irradiation-induced damage

AIMS

Radiotherapy has become a basic treatment modality for head and neck cancer. However, radiotherapy results in inevitable side effects, particularly radiation sialadenitis, that significantly impairs quality of life. A previous study indicated that nerve growth factor (NGF) has a radio-protective effect, but the mechanism was not determined in salivary glands. In this study, we explored the functional role and mechanism regarding how NGF protects salivary glands against IR-induced damage.

MAIN METHODS

Human salivary gland (HSG) cells and C57BL/6 mice were selected to establish an IR-induced salivary gland damage model in vitro and in vivo. Recombinant NGF protein and NGF siRNA and over-expression plasmids were applied to manipulate NGF expression in vitro. AAV-NGF was retrogradely perfused into the submandibular gland (SMG) through the SMG duct to manipulate NGF expression in vitro. Small-molecule inhibitors and siRNAs were applied to inhibit AKT and JNK. Western blotting, quantitative PCR, flow cytometry and histology assays were performed to analyse the functional role and mechanism of NGF.

KEY FINDINGS

Our study demonstrated that NGF expression was upregulated following radiotherapy both in human HSG cells and mouse SMG tissues. NGF could reduce IR-induced HSG cell apoptosis, and AAV-mediated gene therapy could restore the salivary flow rate and protect the salivary gland against IR-induced apoptosis in vivo. Mechanistically, NGF protects salivary glands from IR-induced apoptosis by de-phosphorylating JNK kinase rather than promoting AKT phosphorylation.

SIGNIFICANCE

The current study findings indicated that the modulation of the NGF pathway might prevent IR-induced salivary hypo-function.

CERE-120 Prevents Irradiation-Induced Hypofunction and Restores Immune Homeostasis in Porcine Salivary Glands

Salivary gland hypofunction causes significant morbidity and loss of quality of life for head and neck cancer patients treated with radiotherapy. Preventing hypofunction is an unmet therapeutic need. We used an adeno-associated virus serotype 2 (AAV2) vector expressing the human neurotrophic factor neurturin (CERE-120) to treat murine submandibular glands either pre- or post-irradiation (IR). Treatment with CERE-120 pre-IR, not post-IR, prevented hypofunction. RNA sequencing (RNA-seq) analysis showed reduced gene expression associated with fibrosis and the innate and humoral immune responses. We then used a minipig model with CERE-120 treatment pre-IR and also compared outcomes of the contralateral non-IR gland. Analysis of gene expression, morphology, and immunostaining showed reduced IR-related immune responses and improved secretory mechanisms. CERE-120 prevented IR-induced hypofunction and restored immune homeostasis, and there was a coordinated contralateral gland response to either damage or treatment. CERE-120 gene therapy is a potential treatment for head and neck cancer patients to influence communication among neuronal, immune, and epithelial cells to prevent IR-induced salivary hypofunction and restore immune homeostasis.

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.

Tetravalent dengue DNA vaccine is not immunogenic when delivered by retrograde infusion into salivary glands

Introduction and background

A tetravalent DNA vaccine for Dengue virus is under development but has not yet achieved optimal immunogenicity. Salivary glands vaccination has been reported efficacious in rodents and dogs. We report on a pilot study testing the salivary gland as a platform for a Dengue DNA vaccine in a non-human primate model.

Materials and methods

Four cynomolgus macaques were used in this study. Each macaque was pre-medicated with atropine and sedated with ketamine. Stensen’s duct papilla was cannulated with a P10 polyethylene tube, linked to a 500ul syringe. On the first two infusions, all macaques were infused with 300ul of TVDV mixed with 2 mg of zinc. For the 3rd infusion, to increase transfection into salivary tissue, two animals received 100uL TVDV mixed with 400uL polyethylenimine 1μg/ml (PEI) and the other two animals received 500uL TVDV with zinc. Antibody titers were assessed 4 weeks following the second and third infusion.

Results and conclusions

SGRI through Stensen’s duct is a well-tolerated, simple and easy to reproduce procedure. TVDV infused into macaques salivary glands elicited a significantly weaker antibody response than with different delivery methods.

Transcutaneous Ultrasound-Mediated Nonviral Gene Delivery to the Liver in a Porcine Model

Ultrasound (US)-mediated gene delivery (UMGD) of nonviral vectors was demonstrated in this study to be an effective method to transfer genes into the livers of large animals via a minimally invasive approach. We developed a transhepatic venous nonviral gene delivery protocol in combination with transcutaneous, therapeutic US (tUS) to facilitate significant gene transfer in pig livers. A balloon catheter was inserted into the pig hepatic veins of the target liver lobes via jugular vein access under fluoroscopic guidance. tUS exposure was continuously applied to the lobe with simultaneous infusion of pGL4 plasmid (encoding a luciferase reporter gene) and microbubbles. tUS was delivered via an unfocused, two-element disc transducer (H105) or a novel focused, single-element transducer (H114). We found applying transcutaneous US using H114 and H105 with longer pulses and reduced acoustic pressures resulted in an over 100-fold increase in luciferase activity relative to untreated lobes. We also showed effective UMGD by achieving focal regions of >10⁵ relative light units (RLUs)/mg protein with minimal tissue damage, demonstrating the feasibility for clinical translation of this technique to treat patients with genetic diseases.

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.

Expression patterns of tight junction proteins in porcine major salivary glands: a comparison study with human and murine glands

Tight junction (TJ) proteins play a dynamic role in paracellular fluid transport in salivary gland epithelia. Most TJ studies are carried out in mice and rats. However, the morphology of rodent salivary glands differs from that of human glands. This study aimed to compare the histological features and the expression pattern of TJ proteins in porcine salivary glands with those of human and mouse. The results showed that porcine parotid glands were pure serous glands. Submandibular glands (SMGs) were serous acinar cell-predominated mixed glands, whereas sublingual glands were mucous acinar cell-predominated. Human SMGs were mixed glands containing fewer mucous cells than porcine SMGs, whereas the acinar cells of murine SMGs are seromucous. The histological features of the duct system in the porcine and human SMGs were similar and included intercalated, striated and excretory ducts, but the murine SMG contained a specific structure, the granular convoluted tubule. TJ proteins, including claudin-1 to claudin-12, occludin and zonula occludin-1 (ZO-1), were detected in the porcine major salivary glands and human SMGs by RT-PCR; however, claudin-6, claudin-9 and claudin-11 were not detected in the murine SMG. As shown by immunofluorescence, claudin-1, claudin-3, claudin-4, occludin and ZO-1 were distributed in both acinar and ductal cells in the porcine and human SMGs, whereas claudin-1 and claudin-3 were mainly present in acinar cells, and claudin-4 was mainly distributed in ductal cells in the murine SMG. In addition, 3D images showed that the TJ proteins arranged in a honeycomb-like structure on the luminal surface of the ducts, whereas their arrangements in acini were irregular in porcine SMGs. In summary, the expression pattern of TJ proteins in salivary glands is similar between human and miniature pig, which may be a candidate animal for studies on salivary gland TJ function.

Comparing human and mouse salivary glands: A practice guide for salivary researchers

Mice are a widely utilized in vivo model for translational salivary gland research but must be used with caution. Specifically, mouse salivary glands are similar in many ways to human salivary glands (i.e., in terms of their anatomy, histology, and physiology) and are both readily available and relatively easy and affordable to maintain. However, there are some significant differences between the two organisms, and by extension, the salivary glands derived from them must be taken into account for translational studies. The current review details pertinent similarities and differences between human and mouse salivary glands and offers practical guidelines for using both for research purposes.

CRISPR-Cas9 HDR system enhances AQP1 gene expression

Ionizing radiation (IR) isthe primarytherapeutic tool to treat patients with cancerous lesions located in the head and neck. In many patients, IR results in irreversible and severe salivary gland dysfunction or xerostomia. Currently there are no effective treatment options to reduce the effects of xerostomia. More recently, salivary gland gene therapy utilizing the water-specific protein aquaporin 1 (AQP1) has been of great interest to potentially correct salivary dysfunction. In this study, we used CRISPR-Cas9 gene editing along with the endogenous promoter of AQP1 within theHEK293 and MDCK cell lines. The successful integration of the cytomegalovirus (CMV) promoterresultedin a significant increase of AQP1 gene transcription and translation. Additionalfunctional experiments involvingthe MDCK cell line confirmedthat over-expressed AQP1increasedtransmembrane fluid flux indicative of increased intracellular fluid flux. The off-target effect of designed guided RNA sequence was analyzed and demonstrateda high specificity for the Cas9 cleavage. Considering the development of new methods for robust DNA knock-in, our results suggest that endogenous promoter replacement may be a potential treatment forsalivary gland dysfunction.

Optimal timing and frequency of bone marrow soup therapy for functional restoration of salivary glands injured by single-dose or fractionated irradiation

Injections of bone marrow (BM) cell extract, known as 'BM soup', were previously reported to mitigate ionizing radiation (IR) injury to salivary glands (SGs). However, the optimal starting time and frequency to maintain BM soup therapeutic efficacy remains unknown. This study tested the optimal starting time and frequency of BM soup injections in mice radiated with either a single dose or a fractionated dose. First, BM soup treatment was started at 1, 3 or 7 weeks post-IR; positive (non-IR) and negative (IR) control mice received injections of saline (vehicle control). Second, BM soup-treated mice received injections at different frequencies (1, 2, 3 and 5 weekly injections). Third, a 'fractionated-dose radiation' model to injure mouse SGs was developed (5 Gy × 5 days) and compared with the single high dose radiation model. All mice (n = 65) were followed for 16 weeks post-IR. The results showed that starting injections of BM soup between 1 and 3 weeks mitigated the effect of IR-induced injury to SGs and improved the restoration of salivary function. Although the therapeutic effect of BM soup lessens after 8 weeks, it can be sustained by increasing the frequency of weekly injections. Moreover, both single-dose and fractionated-dose radiation models are efficient and comparable in inducing SG injury and BM soup treatments are effective in restoring salivary function in both radiation models. In conclusion, starting injections of BM soup within 3 weeks post-radiation, with 5 weekly injections, maintains 90-100% of saliva flow in radiated mice.

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.

Artificial Induction of Native Aquaporin-1 Expression in Human Salivary Cells

Gene therapy for dry mouth disorders has transitioned in recent years from theoretical to clinical proof of principle with the publication of a first-in-man phase I/II dose escalation clinical trial in patients with radiation-induced xerostomia. This trial used a prototype adenoviral vector to express aquaporin-1 (AQP1), presumably in the ductal cell layer and/or in surviving acinar cells, to drive transcellular flux of interstitial fluid into the labyrinth of the salivary duct. As the development of this promising gene therapy continues, safety considerations are a high priority, particularly those that remove nonhuman agents (i.e., viral vectors and genetic sequences of bacterial origin). In this study, we applied 2 emerging technologies, artificial transcriptional complexes and epigenetic editing, to explore whether AQP1 expression could be achieved by activating the native gene locus in a human salivary ductal cell line and primary salivary human stem/progenitor cells (hS/PCs), as opposed to the conventional approach of cytomegalovirus promoter-driven expression from an episomal vector. In our first study, we used a cotransfection strategy to express the components of the dCas9-SAM system to create an artificial transcriptional complex at the AQP1 locus in A253 and hS/PCs. We found that AQP1 expression was induced at a magnitude comparable to adenoviral infection, suggesting that AQP1 is primarily silenced through pretranscriptional mechanisms. Because earlier literature suggested that pretranscriptional silencing of AQP1 in salivary glands is mediated by methylation of the promoter, in our second study, we performed global, chemical demethylation of A253 cells and found that demethylation alone induced robust AQP1 expression. These results suggest the potential for success by inducing AQP1 expression in human salivary ductal cells through epigenetic editing of the native promoter.

Late responses to adenoviral-mediated transfer of the aquaporin-1 gene for radiation-induced salivary hypofunction

We evaluated late effects of AdhAQP1 administration in five subjects in a clinical trial for radiation-induced salivary hypofunction (http://www.clinicaltrials.gov/ct/show/NCT00372320?order=). All were identified as initially responding to human aquaporin-1 (hAQP1) gene transfer (Baum et al, 2012). They were followed for 3-4 years after AdhAQP1 delivery to one parotid gland. At intervals we examined salivary flow, xerostomic symptoms, saliva composition, vector presence and efficacy in the targeted gland, clinical laboratory data, and adverse events. All displayed marked increases (71-500% above baseline) in parotid flow 3-4.7 years after treatment, with improved symptoms for ~ 2-3 years. There were some changes in [Na⁺] and [Cl⁻] consistent with elevated salivary flow, but no uniform changes in secretion of key parotid proteins. There were no clinically significant adverse events, nor consistent negative changes in laboratory parameters. One subject underwent a core needle biopsy of the targeted parotid gland 3.1 years post treatment and displayed evidence of hAQP1 protein in acinar, but not duct, cell membranes. All subjects responding to hAQP1 gene transfer initially had benefits for much longer times. First generation adenoviral vectors typically yield transit effects, but these data show beneficial effects can continue years after parotid gland delivery.

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.

Gene Therapy: A Paradigm Shift in Dentistry

Gene therapy holds a promising future for bridging the gap between the disciplines of medicine and clinical dentistry. The dynamic treatment approaches of gene therapy have been advancing by leaps and bounds. They are transforming the conventional approaches into more precise and preventive ones that may limit the need of using drugs and surgery. The oral cavity is one of the most accessible areas for the clinical applications of gene therapy for various oral tissues. The idea of genetic engineering has become more exciting due to its advantages over other treatment modalities. For instance, the body is neither subjected to an invasive surgery nor deep wounds, nor is it susceptible to systemic effects of drugs. The aim of this article is to review the gene therapy applications in the field of dentistry. In addition, therapeutic benefits in terms of treatment of diseases, minimal invasion and maximum outcomes have been discussed.

Xerostomia: current streams of investigation

Xerostomia is the subjective feeling of dry mouth, and it is often related to salivary hypofunction. Besides medication-related salivary hypofunction, Sjögren syndrome and head-and-neck radiation are two common etiologies that have garnered considerable attention. Approaches to treating and/or preventing salivary hypofunction in patients with these conditions will likely incorporate gene therapy, stem cell therapy, and tissue engineering. Advances in these disciplines are central to current research in the cure for xerostomia and will be key to eventual treatment.

Aquaporins in Salivary Glands: From Basic Research to Clinical Applications

Salivary glands are involved in saliva secretion that ensures proper oral health. Aquaporins are expressed in salivary glands and play a major role in saliva secretion. This review will provide an overview of the salivary gland morphology and physiology of saliva secretion, and focus on the expression, subcellular localization and role of aquaporins under physiological and pathophysiological conditions, as well as clinical applications involving aquaporins. This review is highlighting expression and localization of aquaporins in human, rat and mouse, the most studied species and is pointing out possible difference between major salivary glands, i.e., parotid, submandibular and sublingual glands.

Challenges and achievements in the therapeutic modulation of aquaporin functionality

Aquaporin (AQP) water and solute channels have basic physiological functions throughout the human body. AQP-facilitated water permeability across cell membranes is required for rapid reabsorption of water from pre-urine in the kidneys and for sustained near isosmolar water fluxes e.g. in the brain, eyes, inner ear, and lungs. Cellular water permeability is further connected to cell motility. AQPs of the aquaglyceroporin subfamily are necessary for lipid degradation in adipocytes and glycerol uptake into the liver, as well as for skin moistening. Modulation of AQP function is desirable in several pathophysiological situations, such as nephrogenic diabetes insipidus, Sjögren's syndrome, Menière's disease, heart failure, or tumors to name a few. Attempts to design or to find effective small molecule AQP inhibitors have yielded only a few hits. Challenges reside in the high copy number of AQP proteins in the cell membranes, and spatial restrictions in the protein structure. This review gives an overview on selected physiological and pathophysiological conditions in which modulation of AQP functions appears beneficial and discusses first achievements in the search of drug-like AQP inhibitors.

IL-17 sequestration via salivary gland gene therapy in a mouse model of Sjogren's syndrome suppresses disease-associated expression of the putative autoantigen Klk1b22

INTRODUCTION

IL-17 has a putative role in the pathophysiology of Sjogren's syndrome (SS) and has been shown to be upregulated in the salivary glands of affected individuals. Sequestration of IL-17 with Adenoviral-mediated gene therapy has previously shown a benefit upon the SS-like phenotype in the Aec1/Aec2 mouse model. We sought to understand the proteomic consequences of IL-17 sequestration in the salivary gland of this mouse model as a means of illuminating the role of IL-17 in SS-like disease.

METHODS

Ultrasound-assisted gene transfer (UAGT) was utilized to express a fusion protein composed of the extracellular portion of the IL-17 receptor fused to fragment of crystallization (Fc) in the submandibular glands of Aec1/Aec2 mice at 8 weeks of age. After confirming expression of the fusion protein and local and systemic sequestration of IL-17, proteomic profiling was performed on submandibular glands of a treated cohort of Aec1/Aec2 animals relative to the background strain and sham-treated animals.

RESULTS

The most notable proteomic signatures of IL-17 sequestration on SS-like disease-related proteins were Kallikrein-related peptidases, including the putative autoantigen Klk1b22. IL-17 sequestration also notably led to an isoelectric shift, but not a molecular weight shift, of Kallikrein-1, attributed to phosphorylation.

CONCLUSION

Non-viral IL-17 sequestration gene therapy in the salivary gland is feasible and downregulates expression of a putative SS autoantigen in the Aec1/Aec2 mouse.

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.