Nucleotide-induced restoration of conjunctival chloride and fluid secretion in adenovirus type 5-infected pigmented rabbit eyes

Protocol for a parallel assignment prospective, randomised, comparative trial to evaluate the safety and efficacy of intense pulsed light (IPL) combined with 3% diquafosol (DQS) ophthalmic solution in dry eye syndrome

INTRODUCTION

Evaporative dry eye (EDE) is common and can lead to ocular pain, decreased visual quality and reduced quality of life. Intense pulsed light (IPL) and 3% diquafosol ophthalmic solution have been found to be beneficial in reducing signs and symptoms of dry eye.

METHODS AND ANALYSIS

A randomised clinical trial will be performed at He Eye Specialist Hospital in Shenyang. 360 dry eye disease patients will be equally divided randomly into the IPL group, DQS group (3% diquafosol ophthalmic solution eye-drops) and IPL+group (IPL combined with 3% diquafosol eye-drops). All groups will be followed up for 4 weeks. The primary outcome measures will be the non-invasive tear break-up time and the Ocular Surface Disease Index change from the baseline. The secondary outcome measures willincludeconjunctival and cornea staining with fluorescein and lissamine, meibomian gland function and secretion quality, tear film lipid layer score, tear meniscus height, conjunctival hyperemia (redness score) changes . Adverse events also will be monitored and documented.

DISCUSSION

This study aimed to assess whether the combination of IPL with 3% diquafosol ophthalmic solution (study group), IPL+ (study group), is more effective than IPL (active control group) or DQS (active control group) in participants with EDE.

ETHICS AND DISSEMINATION

Management of dry eye with IPL combined with 3% diquafosol ophthalmic solution, registered on 23 January 2023. Ethics approval number: IRB (2022) K029.01. The study's findings will be shared regardless of the effect's direction.

TRIAL REGISTRATION NUMBER

NCT05694026.

Conjunctival Fluid Secretion Impairment via CaCC-CFTR Dysfunction Is the Key Mechanism in Environmental Dry Eye

Dry eye disease (DED) is a multifactorial disease with an incidence of approximately 50% worldwide. DED seriously affects quality of life and work. The prevalence of environmental DED (eDED) ranges from 35 to 48%. Conjunctival fluid secretion dysfunction may be one of the major causes of DED. Notably, the Cl^- flux corresponds to the conjunctival fluid secretion and could be affected by ATP. Both the cystic fibrosis transmembrane conductance regulator (CFTR) and the Ca²⁺-activated Cl^- channel (CaCC) are Cl^- channels involved in epithelial fluid secretion. Conjunctival fluid secretion could be increased by activating P2Y₂R (an ATP receptor) in DED. However, the role of the CaCC and CFTR channels regulated by P2Y₂R in eDED remains unclear. In this study, we established a rabbit eDED model using a controlled drying system. A Ussing chamber was used to perform a conjunctival short-circuit current induced by ATP to evaluate the reactivity of the ion channels to the ATP. Our results revealed that eDED accompanied by conjunctival fluid secretion impairment was caused by a P2Y₂R dysfunction, which is related to CaCC-CFTR signaling in the conjunctiva epithelium. Notably, the coupling effect of the ATP-induced CaCC-CFTR activation and intracellular Ca²⁺ may represent a promising therapeutic target for treating eDED.

Impact of Diquafosol Ophthalmic Solution on Tear Film and Dry Eye Symptom in Type 2 Diabetic Dry Eye: A Pilot Study

Background: Diquafosol ophthalmic solution (DQS) stimulates P2Y2 receptors on the ocular surface, which enhances mucin secretion from goblet cells. Therefore, tear film stability and hydration of the ocular surface can be achieved independent from lacrimal gland function. Methods: This prospective, open-label pilot study included 60 eyes of 30 diabetic patients diagnosed with dry eye disease (DED) and were randomly assigned to either DQS (n = 30 eyes) or hyaluronate (HA) group (n = 30 eyes). Participants in the DQS group received 3% diquafosol ophthalmic solution, whereas HA group received 0.1% sodium HA preservative-free artificial tears. The dosage for both drugs was 1 drop, 6 times per day for 4 weeks. Tear film lipid layer (TFLL), noninvasive breakup time (NITBUT), corneoconjunctival staining (CS) score, meibomian gland (MG), conjunctival hyperemia [redness score (RS)], ocular surface disease index (OSDI) was assessed and compared at baseline, day 14, and day 28. Results: Comparing baseline and day 28 measurements revealed that both groups found significant improvements in NITBUT, CS, MG quality, MG expressibility, and OSDI scores significantly (P < 0.05), in addition TFLL improvements were only found in the DQS group. At day 28, the magnitude of change in mean NITBUT was 1.74 (DQS) versus 0.31 (HA), 1.16 (DQS) versus 0.37 (HA) point grade reduction in corneoconjunctival staining score and 9.80 (DQS) versus 4.80 (HA) point grade in mean OSDI score. Conclusion: Three percent diquafosol ophthalmic solution treatment demonstrated the ability to improve the tear film dry eye parameters and clinically reduced sign and symptoms of DED in diabetic dry eye patients. Clinical Trials.gov ID: NCT04980144.

Purinergic signalling in autonomic control

Intercellular purinergic signalling, which utilizes ATP as a transmitter, is fundamental for the operation of the autonomic nervous system. ATP is released together with 'classical' transmitters from sympathetic and parasympathetic nerves supplying various peripheral targets, modulates neurotransmission in autonomic ganglia, has an important role in local enteric neural control and coordination of intestinal secretion and motility, and acts as a common mediator for several distinct sensory modalities. Recently, the role of ATP-mediated signalling in the central nervous control of autonomic function has been addressed. Emerging data demonstrate that in the brain ATP is involved in the operation of several key cardiorespiratory reflexes, contributes to central processing of viscerosensory information, mediates central CO(2) chemosensory transduction and triggers adaptive changes in breathing, and modulates the activities of the brainstem vagal preganglionic, presympathetic and respiratory neural networks.

Glutathione and its transporters in ocular surface defense

Glutathione (GSH) is an abundant antioxidant ubiquitous in nearly all cell types. Deficiency of GSH has been linked to ocular disease and viral infection. Other established vital roles of GSH include detoxification and immunoprotection. Endogenous GSH plays a protagonist's role in safeguarding active transport processes compartmentalized at the interface between conjunctival mucosa and the tear film. Optimal electrokinetic transport across the conjunctival epithelium requires the mucosal presence of GSH. Glutathione is the most abundant known endogenous antioxidant molecule in tear fluid, mainly derived from conjunctival secretion. Conjunctival GSH transport, a major kinetic component of GSH turnover, occurs through multiple functionally distinct mechanisms. Cell membrane potential regulates conjunctival GSH efflux, while conjunctival GSH uptake requires extracellular Na(+). Significant modulation of GSH, its constituent amino acids, and functions of associated transporters occurs in the conjunctival epithelium with viral inflammatory disease. Topical conjunctival delivery of GSH, its metabolic precursors, or pharmacologic stimulation of endogenous conjunctival GSH secretion carry potential in alleviating viral-inflammatory conjunctivitis.

Dinucleoside polyphosphates in the eye: from physiology to therapeutics

Diadenosine polyphosphates are a family of dinucleotides with emerging biochemical, physiological, pharmacological and therapeutic properties in the eye and other tissues. These compounds are formed by two adenosine moieties linked by their ribose 5'-ends to a variable number of phosphates. Diadenosine polyphosphates are present as active components of ocular secretions such as tears and aqueous humour and they can activate P2 purinergic receptors present on the ocular surface, anterior segment and retina. Both metabotropic and ionotropic actions mediated by P2Y and P2X receptors, respectively are responsible for the control of processes such as induction of tear secretion, lysozyme production or acceleration of corneal wound healing. Inside the eye the dinucleotide Ap(4)A can reduce intraocular pressure by acting on P2Y(1) receptors present in trabecular meshwork cells and on P2X(2) receptors present on the cholinergic terminals located in the ciliary muscle. In the retina, derivatives of diadenosine polyphosphates can improve the re-absorption of fluids in retinal detachment. Altogether, diadenosine polyphosphates are not only dinucleotides with roles in the physiology of the eye but it is also possible that their properties may serve to help in the treatment of some ocular pathologies.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Pathophysiology and therapeutic potential of purinergic signaling

The concept of a purinergic signaling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of purines and pyrimidines as signaling molecules. These molecules mediate short-term (acute) signaling functions in neurotransmission, mechanosensory transduction, secretion and vasodilatation, and long-term (chronic) signaling functions in cell proliferation, differentiation, and death involved in development and regeneration. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of autonomic cotransmission. Recent advances in therapies using purinergic-related drugs in a wide range of pathological conditions will be addressed with speculation on future developments in the field.

Cl- secretory effects of EBIO in the rabbit conjunctival epithelium

Experiments were conducted to determine whether the Cl- secretagogue, 1-ethyl-2-benzimidazolinone (EBIO), stimulates Cl- transport in the rabbit conjunctival epithelium. For this study, epithelia were isolated in an Ussing-type chamber under short-circuit conditions. The effects of EBIO on the short-circuit current (I(sc)) and transepithelial resistance (R(t)) were measured under physiological conditions, as well as in experiments with altered electrolyte concentrations. Addition of 0.5 mM EBIO to the apical bath stimulated the control I(sc) by 64% and reduced R(t) by 21% (P < 0.05; paired data). Under Cl(-)-free conditions, I(sc) stimulation using EBIO was markedly attenuated. In the presence of an apical-to-basolateral K+ gradient and permeabilization of the apical membrane, the majority of the I(sc) reflected the transcellular movement of K+ via basolateral K+ channels. Under these conditions, EBIO in combination with A23187 elicited nearly instantaneous 60-90% increases in I(sc) that were sensitive to the calmodulin antagonist calmidazolium and the K+ channel blocker tetraethyl ammonium. In the presence of an apical-to-basolateral Cl- gradient and nystatin permeabilization of the basolateral aspect, EBIO increased the Cl(-)-dependent I(sc), an effect prevented by the channel blocker glibenclamide (0.3 mM). The latter compound also was used to determine the proportion of EBIO-evoked unidirectional 36Cl- fluxes in the presence of the Cl- gradient that traversed the epithelium transcellularly. Overall, EBIO activated apical Cl- channels and basolateral K+ channels (presumably those that are Ca2+ dependent), thereby suggesting that this compound, or related derivatives, may be suitable as topical agents to stimulate fluid transport across the tissue in individuals with lacrimal gland deficiencies.

Impairment of conjunctival glutathione secretion and ion transport by oxidative stress in an adenovirus type 5 ocular infection model of pigmented rabbits

Conjunctival epithelial cells of pigmented rabbits secrete reduced glutathione (GSH) into the apical (mucosal) fluid. The aim of the current study was to determine the effect of oxidative stress resulting from viral infection and that of GSH supplementation on redox status, GSH, and ion transport in freshly excised conjunctival tissues and epithelial cell layers in primary culture (RCEC) of adenovirus type 5 (Ad5)-infected rabbits. Lipid peroxidation (LPO) products, nitric oxide (NO), and expression of nitric oxide synthase (NOS2) were quantitated as a function of time after viral inoculation. Unidirectional fluxes of [3H]GSH and changes in short-circuit current (Isc) from mucosal supplementation of Ad5-inoculated conjunctival tissues with GSH and glutathione monoethyl ester (GSH-MEE) were also measured. Ad5 inoculation significantly decreased conjunctival GSH level by 19, 45, 48, and 50% at 8, 24, 48, and 72 h postinfection, respectively. LPO product and NO levels increased significantly (2- and 100-fold, respectively) above that of uninfected controls on Day 3 post-Ad5 inoculation, and co-treatment with GSH-MEE and tocopherol succinate abolished this effect. NO levels showed a progressive increase post-Ad5 inoculation, reaching 0.22 +/- 0.06, 8.12 +/- 0.91, and 2.05 +/- 0.65 microM on Days 1, 3, and 5, respectively, and the highest level was observed on the day of maximal viral replication (Day 3). A very significant induction of the expression of NOS2 on Days 1, 3, and 5 post-Ad5 inoculation was observed. Uninfected control conjunctival tissues displayed a net serosal-to-mucosal GSH flux (Jsm), where the mucosal-to-serosal flux (Jms) was approximately 14 pmol h(-1) cm(-2) and the Jsm was approximately 22 pmol h(-1) cm(-2). In Ad5-inoculated rabbits similar GSH flux was observed in both the sm and ms directions, and the net GSH flux was negligible. Isc and potential difference (PD) across conjunctival tissues of Ad5-inoculated rabbits decreased by > or = 50% compared with control, while the transepithelial electrical resistance (TEER) remained unchanged. Mucosal, but not serosal, superfusion of GSH or GSH-MEE in Ad5-inoculated conjunctival tissues increased the Isc by up to 40% in approximately 100 min. Our results show that net secretion of GSH across rabbit conjunctiva is totally blocked after Ad5 inoculation and active ion transport rate decreased by approximately 50%. Decreased net GSH secretion into mucosal fluid after Ad5 infection may have resulted from a decreased intracellular GSH pool due to oxyradical-induced changes in redox status and lower active ion transport. Mucosal treatment of Ad5-infected conjunctival tissues with pharmacological levels of GSH appears to transstimulate mucosal GSH secretion and restore active ion transport activity, suggesting a potentially useful therapeutic regimen for ocular infections.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.