Development of Causative Treatment Strategies for Lacrimal Gland Insufficiency by Tissue Engineering and Cell Therapy. Part 1: Regeneration of Lacrimal Gland Tissue: Can We Stimulate Lacrimal Gland Renewal In Vivo?

The Potential Role of Exosomes in Ocular Surface and Lacrimal Gland Regeneration

PURPOSE

Dry eye disease (DED), a multifactorial disease of the lacrimal system, manifests itself in patients with various symptoms such as itching, inflammation, discomfort and visual impairment. In its most severe forms, it results in the breakdown of the vital tissues of lacrimal functional unit and carries the risk of vision loss. Despite the frequency of occurrence of the disease, there are no effective curative treatment options available to date. Treatment using stem cells and its secreted factors could be a promising approach in the regeneration of damaged tissues of ocular surface. The treatment using secreted factors as well as extracellular vesicles has been demonstrated beneficial effects in various ocular surface diseases. This review provides insights on the usage of stem cell derived exosomes as a promising therapy against LG dysfunction induced ADDE for ocular surface repair.

METHODS

In order to gain an overview of the existing research in this field, literature search was carried out using the PubMed, Medline, Scopus and Web of Science databases. This review is based on 164 publications until June 2024 and the literature search was carried out using the key words "exosomes", "lacrimal gland regeneration", "exosomes in lacrimal dysfunction".

RESULTS

The literature and studies till date suggest that exosomes and other secreted factors from stem cells have demonstrated beneficial effects on damaged ocular tissues in various ocular surface diseases. Exosomal cargo plays a crucial role in regenerating tissues by promoting homeostasis in the lacrimal system, which is often compromised in severe cases of dry eye disease. Exosome therapy shows promise as a regenerative therapy, potentially addressing the lack of effective curative treatments available for patients with dry eye disease.

CONCLUSION

Stem cell-derived exosomes represent a promising, innovative approach as a new treatment option for ADDE. By targeting lacrimal gland dysfunction and enhancing ocular surface repair, exosome therapy offers potential for significant advances in dry eye disease management. Future research is needed to refine the application of this therapy, optimize delivery methods, and fully understand its long-term efficacy in restoring ocular health.

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

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

Current approaches for the regeneration and reconstruction of ocular surface in dry eye

Significant research revealed the preocular tear film composition and regulations that remain vital for maintaining Ocular surface functional integrity. Inflammation triggered by many factors is the hallmark of Ocular surface disorders or dry eyes syndrome (DES). The tear deficiencies may lead to ocular surface desiccation, corneal ulceration and/or perforation, higher rates of infectious disease, and the risk of severe visual impairment and blindness. Clinical management remains largely supportive, palliative, and frequent, lifelong use of different lubricating agents. However, few advancements such as punctal plugs, non-steroidal anti-inflammatory drugs, and salivary gland autografts are of limited use. Cell-based therapies, tissue engineering, and regenerative medicine, have recently evolved as long-term cures for many diseases, including ophthalmic diseases. The present article focuses on the different regenerative medicine and reconstruction/bioengineered lacrimal gland formation strategies reported so far, along with their limiting factors and feasibility as an effective cure in future.

[Beyond esthetics-Regenerative medicine for severe diseases of the adnexa oculi]

BACKGROUND

Restoration of eyelid and lacrimal functions are important steps on the way to an intact ocular surface. Clinically available substitute tissues or therapeutic options for eyelid reconstruction and lacrimal gland regeneration often reach their limits in patients with severe diseases of the adnexa oculi. Several approaches in regenerative medicine have been intensively researched and clinically tested in recent years. These range from reconstructive approaches with novel tissue matrices in the field of eyelid surgery to stem cell therapies to regenerate lacrimal gland function.

MATERIAL AND METHODS

The state of the art in the current literature is presented and an overview of clinically applied or currently researched tissues for eyelid reconstruction is given. Furthermore, approaches in stem cell therapy of the lacrimal gland as well as own results are presented.

RESULTS

Acellular dermis has been successfully used for eyelid reconstruction and represents a viable option in cases of limited availability of autologous tissue. In vitro grown cellular constructs or tissues with genetically modified cells have already been successfully applied in dermatology for the treatment of burns or severe genodermatoses. First studies on stem cell therapy for severe dry eye in Sjögren syndrome showed a safe and effective application of mesenchymal stem cells by injection into the lacrimal gland.

CONCLUSION

Due to the limitations of currently available replacement tissues, there is a clinical need for the development of new materials for adnexa oculi reconstruction. Constructs grown in vitro with allogeneic and/or genetically engineered cells are slowly making their way into clinical practice. The efficacy and mode of action of stem cells in severe dry eye are subject matters of current clinical trials.

Lacrimal gland regeneration: The unmet challenges and promise for dry eye therapy

DED (Dry eye disease) is a common multifactorial disease of the ocular surface and the tear film. DED has gained attention globally, with millions of people affected.. Although treatment strategies for DED have shifted towards Tear Film Oriented Therapy (TFOT), all the existing strategies fall under standard palliative care when addressed as a long-term goal. Therefore, different approaches have been explored by various groups to uncover alternative treatment strategies that can contribute to a full regeneration of the damaged lacrimal gland. For this, multiple groups have investigated the role of lacrimal gland (LG) cells in DED based on their regenerating, homing, and differentiating capabilities. In this review, we discuss in detail therapeutic mechanisms and regenerative strategies that can potentially be applied for lacrimal gland regeneration as well as their therapeutic applications. This review mainly focuses on Aqueous Deficiency Dry Eye Disease (ADDE) caused by lacrimal gland dysfunction and possible future treatment strategies. The current key findings from cell and tissue-based regenerative therapy modalities that could be utilised to achieve lacrimal gland tissue regeneration are summarized. In addition, this review summarises the available literature from in vitro to in vivo animal studies, their limitations in relation to lacrimal gland regeneration and the possible clinical applications. Finally, current issues and unmet needs of cell-based therapies in providing complete lacrimal gland tissue regeneration are discussed.

Oculoplastic aspects of ocular surface disease and their management

The normal structure and function of the eyelids, eyelashes, conjunctival fornices, and lacrimal system are essential for the health of the ocular surface, and abnormalities of these structures accompany many cases of ocular surface disease. We describe the role of oculoplastic intervention in the context of ocular surface disease, focusing on blink disorders, lagophthalmos, entropion, lid scarring and keratinization, trichiasis, and punctal and lacrimal sac disease.

MSC Transplantation Improves Lacrimal Gland Regeneration after Surgically Induced Dry Eye Disease in Mice

Dry eye disease (DED) is a multifactorial disease characterized by a disrupted tear film homeostasis and inflammation leading to visual impairments and pain in patients. Aqueous-deficient dry eye (ADDE) causes the most severe progressions and depends mainly on the loss of functional lacrimal gland (LG) tissue. Despite a high prevalence, therapies remain palliative. Therefore, it is of great interest to develop new approaches to curatively treat ADDE. Mesenchymal stem/stromal cells (MSC) have been shown to induce tissue regeneration and cease inflammation. Moreover, an increasing amount of MSC was found in the regenerating LG of mice. Therefore, this study investigated the therapeutic effect of MSC transplantation on damaged LGs using duct ligation induced ADDE in mice. Due to the transplantation of sex-mismatched and eGFP-expressing MSC, MSC could be identified and detected until day 21. MSC transplantation significantly improved LG regeneration, as the amount of vital acinar structures was significantly increased above the intrinsic regeneration capacity of control. Additionally, MSC transplantation modulated the immune reaction as macrophage infiltration was delayed and TNFα expression decreased, accompanied by an increased IL-6 expression. Thus, the application of MSC appears to be a promising therapeutic approach to induce LG regeneration in patients suffering from severe DED/ADDE.

Towards Lacrimal Gland Regeneration: Current Concepts and Experimental Approaches

Dry eye disease (DED) is a complex and multifactorial disease resulting in a continual cycle of tear hyperosmolarity and inflammation. Patients suffering from DED experience severe pain and visual impairments leading to a reduced quality of life. Aqueous-deficient dry eye (ADDE), mainly caused through a loss of functional lacrimal gland tissue, results in the most severe forms of DED. Despite a high prevalence, the current treatments remain palliative and may be insufficient to alleviate the symptoms. Consequently, investigations on experimental approaches for in situ lacrimal gland regeneration are of great clinical interest. This article reviews the current knowledge about processes involved in lacrimal gland regeneration, about lacrimal gland resident stem cells, and offers deductions about possible concepts for in situ lacrimal gland regeneration. Promising starting points might be the utilization of therapeutic proteins, such as bone morphogenetic protein 7, mesenchymal stem cells (MSC) or MSC-based treatments such as conditioned medium, lyophilized cell extracts or adult acinar cells. This review further summarizes current experimental approaches for the treatment of ADDE in animal models and patients. Approaches investigating side population stem cells, epithelial progenitor cells and MSC showed that the transplantation of these cells had therapeutic effects on ADDE. However, the most promising and best-studied experimental approach is the use of MSC for induction/enhancement of in situ lacrimal gland regeneration. Their immunomodulatory effects, low immunogenicity, promotion of tissue regeneration and involvement during spontaneous lacrimal regeneration are favorable traits for clinical applications. In addition, the efficacy and safety of allogeneic MSC transplantation have already been demonstrated in a small patient cohort.

Analysis of lacrimal gland derived mesenchymal stem cell secretome and its impact on epithelial cell survival

In situ regeneration of lacrimal gland (LG) tissue would be a promising approach to curatively treat dry eye disease (DED). Mesenchymal stem cells (MSC) exhibit therapeutic effects in a variety of pathological conditions and our group recently reported that their number increases in regenerating mouse LG. Since the therapeutic effects are suggested to arise from secreted trophic factors, the application of MSC-secreted proteins seems to be a promising approach to induce/enhance LG regeneration. Therefore, this study aims to optimize the isolation of murine LG-MSC and analyze their secretome to investigate its potential for LG epithelial cell survival in vitro. For optimization, LG-MSC were isolated by an explant technique or cell sorting and their secretome was investigated under normal and inflammatory conditions. Results showed that the secretome of MSC had beneficial effects on the viability of ethanol-damaged LG epithelial cells. Additional, Lipocalin-2, prosaposin, ras GTPase-activating protein-binding protein 1 (Rac1) and signal transducer and activator of transcription 1 (STAT1), proteins that were up-regulated under inflammatory conditions, further improved the cell survival of ethanol-damaged LG epithelial cells. Interestingly, recovery of cell viability was highest, when the cells were incubated with STAT1. Summarizing, this study identified promising proteins for further studies on LG regeneration.

Lacrimal gland development: From signaling interactions to regenerative medicine

The lacrimal gland plays a pivotal role in keeping the ocular surface lubricated, and protecting it from environmental exposure and insult. Dysfunction of the lacrimal gland results in deficiency of the aqueous component of the tear film, which can cause dryness of the ocular surface, also known as the aqueous-deficient dry eye disease. Left untreated, this disease can lead to significant morbidity, including frequent eye infections, corneal ulcerations, and vision loss. Current therapies do not treat the underlying deficiency of the lacrimal gland, but merely provide symptomatic relief. To develop more sustainable and physiological therapies, such as in vivo lacrimal gland regeneration or bioengineered lacrimal gland implants, a thorough understanding of lacrimal gland development at the molecular level is of paramount importance. Based on the structural and functional similarities between rodent and human eye development, extensive studies have been undertaken to investigate the signaling and transcriptional mechanisms of lacrimal gland development using mouse as a model system. In this review, we describe the current understanding of the extrinsic signaling interactions and the intrinsic transcriptional network governing lacrimal gland morphogenesis, as well as recent advances in the field of regenerative medicine aimed at treating dry eye disease. Developmental Dynamics 246:970-980, 2017. © 2017 Wiley Periodicals, Inc.

Ocular Emergencies: Red Eye

"Red eye" is used as a general term to describe irritated or bloodshot eyes. It is a recognizable sign of an acute/chronic, localized/systemic underlying inflammatory condition. Conjunctival injection is most commonly caused by dryness, allergy, visual fatigue, contact lens overwear, and local infections. In some instances, red eye can represent a true ocular emergency that should be treated by an ophthalmologist. A comprehensive assessment of red eye conditions is required to preserve the patients visual function. Severe ocular pain, significant photophobia, decreased vision, and history of ocular trauma are warning signs demanding immediate ophthalmological consultation.