Hanan Awad Alkozi

Recent developments on dry eye disease treatment compounds

Dry eye syndrome is a common tears and ocular surface multifactorial disease, described by changes in the ocular surface epithelia related to reduced tears quantity and ocular surface sensitivity, leading to inflammatory reaction. Managing the eye inflammation proved helpful to patients with dry eye disease and current treatment is based on the use of topically applied artificial tear products/lubricants, tear retention management, stimulation of tear secretion and using anti-inflammatory drugs. In this article we revise the corresponding literature and patents assembling the new treatment approaches of novel and future pharmaceutical compounds destined for the dry eye disease treatment. The most frequent categories of compounds presented are secretagogues and anti-inflammatory drugs. These compounds are the research outcome of novel therapeutic strategies designed to reduce key inflammatory pathways and restore healthy tear film.

Presence of melanopsin in human crystalline lens epithelial cells and its role in melatonin synthesis

ABSTRACT Melanopsin is a non‐image forming photoreceptor known to be present in the retina and it is considered to have light regulated tasks among other functions. In the present work, melanopsin presence in human lens epithelial cells as well as in human lens tissue is described for the first time. Moreover, studying the concentration of melatonin and its synthesising enzyme AANAT proved a clear link between melanopsin activation and the suppression of melatonin synthesis. Melanopsin sensitivity to specific wavelength (465–480 nm, blue) was confirmed after making temporal studies incubating lens epithelial cells under light, red, green, blue and total darkness for 2, 4, 8, 12 h and analysing the concentration of both melatonin and its synthesising enzyme AANAT, discovering that melatonin levels after submitting cells to total darkness are significantly higher to ones submitted to white or specifically blue light (***p < 0.001, n = 6). The involvement of melanopsin in the regulation of melatonin was also determined by using a specific inhibitor AA92593 and by inhibiting melanopsin‐induced phospholipase C activation. Under this situation neither AANAT nor melatonin levels changed under light conditions (n = 4, ***p < 0.001). The discovery of melanopsin in the lens opens the possibility of regulating melatonin synthesis with the corresponding implication as an antioxidant substance. HighlightsHuman lens epithelial cells present melanopsin.Activation of melanopsin with light reduces the synthesis of melatonin.Darkness increases melatonin production and AANAT expression.Melanopsin is activated by blue wavelength and insensitive to red or green light.

Epigenetics in the Eye: An Overview of the Most Relevant Ocular Diseases

Sight for mammals is one of the most appreciated senses. In humans there are several factors that contribute to the increment in all kind of eye diseases. This mini-review will focus on some diseases whose prevalence is steadily increasing year after year for non-genetic reasons, namely cataracts, dry eye, and glaucoma. Aging, diet, inflammation, drugs, oxidative stress, seasonal and circadian style-of-live changes are impacting on disease prevalence by epigenetics factors, defined as stable heritable traits that are not explained by changes in DNA sequence. The mini-review will concisely show the data showing epigenetics marks in these diseases and on how knowledge on the epigenetic alterations may guide therapeutic approaches to have a healthy eye.

Melatonin synthesis in the human ciliary body triggered by TRPV4 activation: Involvement of AANAT phosphorylation

ABSTRACT Melatonin is a substance synthesized in the pineal gland as well as in other organs. This substance is involved in many ocular functions, giving its synthesis in numerous eye structures. Melatonin is synthesized from serotonin through two enzymes, the first limiting step into the synthesis of melatonin being aralkylamine N‐acetyltransferase (AANAT). In this current study, AANAT phosphorylation after the activation of TRPV4 was studied using human non‐pigmented epithelial ciliary body cells. Firstly, it was necessary to determine the adequate time and dose of the TRPV4 agonist GSK1016790A to reach the maximal phosphorylation of AANAT. An increase of 72% was observed after 5 min incubation with 10 nM GSK (**p < 0.05, n = 6) with a concomitant rise in N‐acetyl serotonin and melatonin synthesis. The involvement of a TRPV4 channel in melatonin synthesis was verified by antagonist and siRNA studies as a previous step to studying intracellular signalling. Studies performed on the second messengers involved in GSK induced AANAT phosphorylation were carried out by inhibiting several pathways. In conclusion, the activation of calmodulin and calmodulin‐dependent protein kinase II was confirmed, as shown by the cascade seen in AANAT phosphorylation (***p < 0.001, n = 4). This mechanism was also established by measuring N‐acetyl serotonin and melatonin levels. In conclusion, the activation of a TRPV4 present in human ciliary body epithelial cells produced an increase in AANAT phosphorylation and a further melatonin increase by a mechanism in which Ca‐calmodulin and the calmodulin‐dependent protein kinase II are involved. HIGHLIGHTSTRPV4 activation promotes the synthesis of melatonin.This synthesis is mediated by the enzyme AANAT phosphorylation.AANAT phosphorylation is carried out by Calcium Calmodulin Dependent Kinase II.The increase of melatonin triggered by TRPV4 permits the control of IOP.

Docking studies for melatonin receptors

ABSTRACT Introduction: Melatonin is a neurohormone that controls many relevant physiological processes beyond the control of circadian rhythms. Melatonin’s actions are carried out by two main types of melatonin receptors; MT1 and MT2. These receptors are important, and not just because of the biological actions of its natural agonist; but also, because melatonin analogues can improve or antagonize their biological effect. Area covered: The following article describes the importance of melatonin as a biologically relevant molecule. It also defines the receptors for this substance, as well as the second messengers coupled to these receptors. Lastly, the article describes the amino acid residues involved in the docking process in both MT1 and MT2 melatonin receptors. Expert opinion: The biological actions of melatonin and their interpretations are becoming more relevant and therefore require the development of new pharmacological tools. Understanding the second messenger mechanisms involved in melatonin actions, as well as the characteristics of the docking of this molecule to MT1 and MT2 melatonin receptors, will permit the development of more selective agonists and antagonists which will help us to better understand this molecule as well to develop new therapeutic compounds.

TRPV4 Stimulation Induced Melatonin Secretion by Increasing Arylalkymine N-acetyltransferase (AANAT) Protein Level

Melatonin is a molecule which has gained a great deal of interest in many areas of science; its synthesis was classically known to be in the pineal gland. However, many organs synthesize melatonin, such as several ocular structures. Melatonin is known to participate in many functions apart from its main action regulating the circadian rhythm. It is synthesized from serotonin in two steps, with a rate-limiting step carried out by arylalkymine N-acetyltransferase (AANAT). In this report, the role of TRPV4 channel present in human ciliary body epithelial cells in AANAT production was studied. Several experiments were undertaken to verify the adequate time to reach the maximal effect by using the TRPV4 agonist GSK1016790A, together with a dose–response study. An increase of 2.4 folds in AANAT was seen after 18 h of incubation with 10 nM of GSK1016790A (p < 0.001, n = 6). This increment was verified by antagonist assays. In summary, AANAT levels and therefore melatonin synthesis change after TRPV4 channel stimulation. Using this cell model together with human ciliary body tissue it is possible to suggest that AANAT plays an important role in pathologies related to intraocular pressure.