Thymosin β4: a potential novel dry eye therapy

The Pathophysiological Role of Thymosin β4 in the Kidney Glomerulus

Diseases affecting the glomerulus, the filtration unit of the kidney, are a major cause of chronic kidney disease. Glomerular disease is characterised by injury of glomerular cells and is often accompanied by an inflammatory response that drives disease progression. New strategies are needed to slow the progression to end-stage kidney disease, which requires dialysis or transplantation. Thymosin β4 (Tβ4), an endogenous peptide that sequesters G-actin, has shown potent anti-inflammatory function in experimental models of heart, kidney, liver, lung, and eye injury. In this review, we discuss the role of endogenous and exogenous Tβ4 in glomerular disease progression and the current understanding of the underlying mechanisms.

Dry eye syndrome: comprehensive etiologies and recent clinical trials

Dry eye syndrome (DES) is multifactorial and likely to be a cause of concern more so than ever given the rapid pace of modernization, which is directly associated with many of the extrinsic causative factors. Additionally, recent studies have also postulated novel etiologies that may provide the basis for alternative treatment methods clinically. Such insights are especially important given that current approaches to tackle DES remains suboptimal. This review will primarily cover a comprehensive list of causes that lead to DES, summarize all the upcoming and ongoing clinical trials that focuses on treating this disease as well as discuss future potential treatments that can improve inclusivity.

Recombinant Human Thymosin β4 (rhTβ4) Modulates the Anti-Inflammatory Responses to Alleviate Benzalkonium Chloride (BAC)-Induced Dry Eye Disease

Dry eye disease (DED) is a multifactorial ocular disorder that interferes with daily living and reduces quality of life. However, there is no most ideal therapeutic treatment to address all the deleterious defects of DED. The purpose of this study was to investigate the ability of recombinant human thymosin β4 (rhTβ4) to promote healing in a benzalkonium chloride (BAC)-induced mice DED model and the anti-inflammatory effects involved in that process. Eye drops consisting of 0.05% and 0.1% rhTβ4 were used for treatment of DED. Tear volume and corneal staining scores were measured after 7 days. Periodic acid-Schiff staining for gobleT cells in conjunctiva, immunohistochemical staining for CD4⁺ T cells, TUNEL assay for apoptotic positive cells in cornea and conjunctiva, qRT-PCR and ELISA assays for multiple cytokines were performed. All clinical parameters showed improvement in both the 0.05% and 0.1% rhTβ4 groups. Specifically, topical application of rhTβ4 significantly increased conjunctival gobleT cells and reduced apoptotic cells in conjunctiva. Mechanically, the rhTβ4 groups showed significantly reduced inflammatory cytokine levels and CD4⁺ T cells in conjunctiva by blocking NF-κB (nuclear factor kappa B) activation, suggesting that 0.05–0.1% rhTβ4 eye drops may be used as a potential therapeutic treatment for DED.

Current Advances in Mechanisms and Treatment of Dry Eye Disease: Toward Anti-inflammatory and Immunomodulatory Therapy and Traditional Chinese Medicine

Dry eye is currently one of the most common ocular surface disease. It can lead to ocular discomfort and even cause visual impairment, which greatly affects the work and quality of life of patients. With the increasing incidence of dry eye disease (DED) in recent years, the disease is receiving more and more attention, and has become one of the hot research fields in ophthalmology research. Recently, with the in-depth research on the etiology, pathogenesis and treatment of DED, it has been shown that defects in immune regulation is one of the main pathological mechanisms of DED. Since the non-specific and specific immune response of the ocular surface are jointly regulated, a variety of immune cells and inflammatory factors are involved in the development of DED. The conventional treatment of DED is the application of artificial tears for lubricating the ocular surface. However, for moderate-to-severe DED, treatment with anti-inflammatory drugs is necessary. In this review, the immunomodulatory mechanisms of DED and the latest research progress of its related treatments including Chinese medicine will be discussed.

Progress on the Function and Application of Thymosin β4

Thymosin β4 (Tβ4) is a multifunctional and widely distributed peptide that plays a pivotal role in several physiological and pathological processes in the body, namely, increasing angiogenesis and proliferation and inhibiting apoptosis and inflammation. Moreover, Tβ4 is effectively utilized for several indications in animal experiments or clinical trials, such as myocardial infarction and myocardial ischemia-reperfusion injury, xerophthalmia, liver and renal fibrosis, ulcerative colitis and colon cancer, and skin trauma. Recent studies have reported the potential application of Tβ4 and its underlying mechanisms. The present study reveals the progress regarding functions and applications of Tβ4.

Efficacy of topical ophthalmic drugs in the treatment of dry eye disease: A systematic literature review

Dry eye disease (DED) is a multifactorial and complex disease of the ocular surface, with a high prevalence in adults. We systematically reviewed efficacy and safety data from published articles reporting results from prospective, controlled trials of topical ophthalmic drugs for DED. PubMed was searched for articles from January 1997 to October 2017. Twenty-six unique trials investigating 13 ophthalmic drugs were identified, including trials of the approved drugs cyclosporine A, cyclosporine A cationic emulsion, diquafosol, rebamipide and lifitegrast. All identified studies provided level 1 evidence. None of the large (N > 100) studies demonstrated statistical significance of primary endpoints for both a sign and a symptom endpoint versus a control treatment in the same published trial. Publications on lifitegrast reported statistical superiority in a symptom or sign endpoint versus the control group in a large (N > 200), multicenter trial, with results repeated in trials of similar design. The most common adverse events associated with the approved drugs related to ocular discomfort upon instillation, especially burning/stinging and ocular irritation. The trial design and endpoints used across the studies varied considerably, highlighting the importance of standardization in clinical trials for DED. Recent advances in drug delivery and improved understanding of DED should contribute to new ophthalmic drug approvals.

Thymosin Beta-4 and Ciprofloxacin Adjunctive Therapy Improves Pseudomonas aeruginosa-Induced Keratitis

With increasing multidrug resistance and contraindication for corticosteroid use, the goal of this study was to develop thymosin beta-4 (Tβ4) as an adjunctive therapy to antibiotics for the treatment of bacterial keratitis that effectively promotes enhanced wound healing, host defense, and inflammation resolution. Disease outcome was assessed by clinical score, slit lamp photography, and histopathology. Cytokine profile, bacterial load, PMN infiltration, and Griess and reactive oxygen species (ROS) levels were determined. Adjunct Tβ4 treatment resulted in a significant improvement compared to PBS, Tβ4, and most remarkably, ciprofloxacin, correlating with changes in mediators of inflammation and wound healing. Collectively, these data provide evidence that wound healing is an essential aspect in the development of new therapies to treat corneal infection. Use of adjunctive Tβ4 provides a more efficacious approach for bacterial keratitis by addressing both the infectious pathogen and deleterious host response.

Loss of endogenous thymosin β4 accelerates glomerular disease

Glomerular disease is characterized by morphologic changes in podocyte cells accompanied by inflammation and fibrosis. Thymosin β₄ regulates cell morphology, inflammation, and fibrosis in several organs and administration of exogenous thymosin β₄ improves animal models of unilateral ureteral obstruction and diabetic nephropathy. However, the role of endogenous thymosin β₄ in the kidney is unknown. We demonstrate that thymosin β₄ is expressed prominently in podocytes of developing and adult mouse glomeruli. Global loss of thymosin β₄ did not affect healthy glomeruli, but accelerated the severity of immune-mediated nephrotoxic nephritis with worse renal function, periglomerular inflammation, and fibrosis. Lack of thymosin β₄ in nephrotoxic nephritis led to the redistribution of podocytes from the glomerular tuft toward the Bowman capsule suggesting a role for thymosin β₄ in the migration of these cells. Thymosin β₄ knockdown in cultured podocytes also increased migration in a wound-healing assay, accompanied by F-actin rearrangement and increased RhoA activity. We propose that endogenous thymosin β₄ is a modifier of glomerular injury, likely having a protective role acting as a brake to slow disease progression.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Peptide therapies for ocular surface disturbances based on fibronectin-integrin interactions

The condition of the corneal epithelium is a critical determinant of corneal transparency and clear vision. The corneal epithelium serves as a barrier to protect the eye from external insults, with its smooth surface being essential for its optical properties. Disorders of the corneal epithelium include superficial punctate keratopathy, corneal erosion, and persistent epithelial defects (PEDs). The prompt resolution of these disorders is important for minimization of further damage to the cornea. Currently available treatment modalities for corneal epithelial disorders are based on protection of the ocular surface in order to allow natural healing to proceed. PEDs remain among the most difficult corneal conditions to treat, however. On the basis of characterization of the pathobiology of PEDs at the cell and molecular biological levels, we have strived to develop new modes of treatment for these defects. These treatments rely on two key concepts: provision of a substrate, such as the adhesive glycoprotein fibronectin, for the attachment and migration of corneal epithelial cells, and activation of these cells by biological agents such as the combination of substance P and insulin-like growth factor-1 (IGF-1). Central to both approaches is the role of the fibronectin-integrin system in corneal epithelial wound healing. Determination of the minimum amino acid sequences required for the promotion of corneal epithelial wound closure by fibronectin (PHSRN) and by substance P (FGLM-amide) plus IGF-1 (SSSR) has led to the development of peptide eyedrops for the treatment of PEDs that are free of adverse effects of the parent molecules.

Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury

Thymosin beta 4 (Tβ4) was previously shown to reduce infarct size and improve contractile performance in chronic myocardial ischemic injury via two phases of action: an acute phase, just after injury, when Tβ4 preserves ischemic myocardium via antiapoptotic or anti-inflammatory mechanisms; and a chronic phase, when Tβ4 activates the growth of vascular or cardiac progenitor cells. In order to differentiate between the effects of Tβ4 during the acute and during the chronic phases, and also in order to obtain detailed hemodynamic and biomarker data on the effects of Tβ4 treatment suitable for use in clinical studies, we tested Tβ4 in a rat model of chronic myocardial ischemia using two dosing regimens: short term dosing (Tβ4 administered only during the first 3 days following injury), and long term dosing (Tβ4 administered during the first 3 days following injury and also every third day until the end of the study). Tβ4 administered throughout the study reduced infarct size and resulted in significant improvements in hemodynamic performance; however, chamber volumes and ejection fractions were not significantly improved. Tβ4 administered only during the first 3 days following injury tended to reduce infarct size, chamber volumes and improve hemodynamic performance. Plasma biomarkers of myocyte injury were significantly reduced by Tβ4 treatment during the acute injury period, and plasma ANP levels were significantly reduced in both dosing groups. Surprisingly, neither acute nor chronic Tβ4 treatment significantly increased blood vessel density in peri-infarct regions. These results suggest the following: repeated dosing may be required to achieve clinically measureable improvements in cardiac function post-myocardial infarction (MI); improvement in cardiac function may be observed in the absence of a high degree of angiogenesis; and that plasma biomarkers of cardiac function and myocardial injury are sensitive pharmacodynamic biomarkers of the effects of Tβ4.

Emerging drugs for the treatment of dry eye disease

INTRODUCTION

Dry eye disease (DED) is a common, age-related ocular condition that in its mildest forms causes bothersome symptoms of ocular discomfort, fatigue, and visual disturbance that interfere with quality of life and in its more severe forms causes chronic pain and fluctuating vision. Though it is highly prevalent and costs billions of dollars to manage, current treatments have largely been inadequate, making it a frustrating condition, both for physicians and patients alike.

AREAS COVERED

This article will cover the recently discovered pathophysiology of DED that has prompted investigators to explore new molecules that target the core mechanisms that drive DED. These include anti-inflammatory/immune-modulatory drugs, secretagogues, lubricant, hormones, and autologous serum. Their potential mechanism of action and data from recent trials on efficacy/safety will be reviewed.

EXPERT OPINION

The emerging drugs have a vast range of putative mechanisms of action that may not only provide symptomatic relief but may potentially break the vicious cycle of DED and provide long-lasting cure. Current and future research may change our perspective on DED and redefine its treatment algorithms.