Mecanismos de regulación de la síntesis de la melatonina para el control de la presión intraocular

Tesis de la Universidad Complutense de Madrid, Facultad de Óptica y Optometría, Departamento de Bioquímica y Biología Molecular IV, leída el 10/11/2017Ocular hypertension, although not considered a disease itself, it leads to glaucoma which eventually cause irreversible vision loss. Consequently, glaucoma therapeutic approach is to lower intraocular pressure (IOP). Nonetheless, anti-glaucoma drugs come often with several side effects that can lead to treatment withdrawal in some cases. In this context, melatonin and its analogs emerges as potential complimentary/alternative treatment, offering the advantage of hypotensive and antioxidant properties. The present PhD thesis aim to investigate endogenous melatonin content in the aqueous humor and describes mechanisms involved in detecting increased IOP, along with a focus on the possibility of melatonin receptors to interact with different receptors with the intention to find a more effective combined therapeutical approach. Finally, to study the attribution of the crystalline lens to the aqueous humor melatonin content and to discover the regulation of its synthesis in this ocular structure. Results showed a correlation between melatonin levels in the aqueous humor and IOP. Melatonin levels were found higher in patients with elevated IOP. Using a glaucomatous animal model (DBA/2J) it was possible to corroborate our findings. In vitro assays pointed to the participation of the TRPV4 channel, which is sensitive to pressure, among other stimuli. Activation of the mentioned channel in human immortalised nonpigmented ciliary body epithelial cells resulted in an increment of melatonin secretion through the increase of aralkylamine N-acetyltransferase (AANAT) expression, the first enzyme in melatonin synthesis. In addition, short term assays showed that the TRPV4 activation leaded to AANAT phosphorylation through a cascade of intracellular events that involves the participation of calmodulin and calcium-calmodulin dependent protein kinase II. This phosphorylation activates AANAT and therefore melatonin synthesis is stimulated...La hipertensión ocular, aunque no se considera una enfermedad en sí, es un factor de riesgo para desarrollar glaucoma, que eventualmente causa pérdida irreversible de la visión. En consecuencia, el enfoque terapéutico más habitual en el glaucoma es reducir la presión intraocular (PIO). No obstante, los fármacos anti-glaucomatosos presentan varios efectos secundarios que pueden conducir a la retirada del tratamiento en algunos casos. En este contexto, la melatonina y sus análogos emergen como un tratamiento complementario/ alternativo, ofreciendo la ventaja de poseer propiedades hipotensoras y antioxidantes. La presente tesis doctoral tiene como objetivo investigar el contenido de la melatonina endógena en el humor acuoso y describir los mecanismos implicados en la detección de los cambios en la IOP. Igualmente se estudia la capacidad de los receptores de melatonina para interactuar con otros receptores con la intención de encontrar un enfoque terapéutico combinado más eficaz. Finalmente, esta tesis también estudia la contribución del cristalinoen su aporte de melatonina al humor acuoso. Los resultados han mostrado una correlación entre los niveles de melatonina en el humor acuoso y la PIO. Los niveles de melatonina se encontraron más altos en pacientes con PIO elevada. El uso de modelo animal glaucomatoso (DBA/2J) corroboró nuestros hallazgos de una manera consistente. Por otro lado, los ensayos in vitro señalaron la participación del canal TRPV4, proteína que es sensible a la presión,como principal activador de la sintesis de la melatonina. De este modo, la estimulación de este canal en células epiteliales del cuerpo ciliar no pigmentadas inmortalizadas humanas dio como resultado un incremento de la secreción de melatonina a través de un aumento de la expresion de la Aralquilamina N-acetiltransferasa(AANAT), la primera enzima en la síntesis de melatonina. Además, los ensayos a corto plazo mostraron que la activación de TRPV4 induce a la fosforilación de AANAT, y su activación, a través de una cascada de eventos intracelulares implica la participación de la calmodulina y la calmodulina quinasa II dependiente de calcio-calmodulina...Unidad Docente de Bioquímica y Biología MolecularFac. de Óptica y OptometríaTRUEunpu

Improving Melatonin Delivery Within the Eye

Melatonin is a neurohormone synthesized in the pineal gland as well as in other organs and it plays an important role in many ocular functions, as it is synthesized in numerous eye structures. Melatonin can reduce the intraocular pressure and to serves as an antioxidant preventing against free radicals, hence cataract formation as well as retinal damage due to glaucoma, among other functions. Ocular pharmacology is a challenging field giving the difficulties of drug delivery inside the eye due to its low bioavailability. In this sense, the present brief commentary is summarizing the latest advances in non-invasive ocular drug delivery focused on the effect of melatonin in different ocular diseases

Melatonina y melanopsina en el ojo: ¿amigos o enemigos?

Melatonin is a neurohormone synthesized in several ocular structures apart from its original source, the pineal gland. It is of great importance in several functions such as maintaining a healthy values of intraocular pressure. Moreover, it decreases intraocular pressure in the case of glaucoma. This nuerohormone is controlled by the activation of a photopigment responible for non-image forming tasks in the eye, this photopigment is Melanopsin, present in a subclass of retinal ganglion cells, and very recently, it was discovered in different ocular structures. When Melanopsin is activated by the short wavelength component of light, it supresses Melatonin synthesis. This action is controlled mainly by light could affect several functions including the regulation of intraocular pressure. In this sense, the present work highlights the history and importance of the relationship between both Melatonin and Melanopsin to maintain a healthy ocular homeostasisLa Melatonina es una neurohormona sintetizada en varias estructuras oculares, aparte de su fuente original, la glándula pineal. Es de gran importancia por varias funciones, como el mantenimiento de valores saludables de presión intraocular. Además, disminuye la presión intraocular en el caso de glaucoma. Esta nuerohormona se controla mediante la activación de un fotopigmento responsable de las tareas no relacionada con la formación de imágenes en el ojo, este fotopigmento es la Melanopsina, presente en una subclase de células ganglionares de la retina y, muy recientemente, se descubrió en diferentes estructuras oculares. Cuando la melanopsina se activa por el componente de longitud de onda corta de la luz, suprime la síntesis de melatonina. Esta acción está controlada principalmente por la luz que podría afectar varias funciones, incluida la regulación de la presión intraocular. En este sentido, el presente trabajo destaca la historia y la importancia de la relación entre la melatonina y la melanopsina para mantener una homeostasis ocular saludable

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

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

Yellow Filter Effect on Melatonin Secretion in the Eye: Role in IOP Regulation

Purpose: Melatonin is a neurohormone mainly synthesized in the pineal gland; however, it is also present in the aqueous humor. One of melatonins’ functions in the eye is the regulation of intraocular pressure (IOP). Melatonin is known to be sensitive to light. Recently, the photopigment which controls melatonin synthesis, melanopsin, was found in the crystalline lens. Therefore, light conditions are an interesting possible way of regulating melatonin levels in the aqueous humor. The current study used yellow filters, since melanopsin is activated by short wavelength (blue light). Methods: New Zealand white rabbits were used, divided in two groups, one under controlled 12 h light/dark cycles, while the rest had their cages encased with a yellow filter (λ 465–480). IOP measurements were taken every week at the same time before they were anesthetized for aqueous humor extraction. Results: Keeping the rabbits under the yellow filter resulted in a decrease in IOP up to 43.8 ± 7.8% after 3 weeks. This effect was reversed after the topical application of selective and nonselective melatonin receptors antagonists, 4PPDOT and luzindole. Also, blocking melanopsin by its antagonist AA92593 under white light condition decreased IOP. Finally, melatonin levels were found significantly higher in the aqueous humor of rabbits developed under yellow filter compared to controls (37.4 ± 4.2 and 15.3 ± 3.1 ng/ml, respectively). Conclusion: Yellow filters modulate melatonin levels in the aqueous humor due to deactivating melanopsin activity. This effect leads to a decrease in IOP mediated by melatonin receptors

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 and the control of intraocular pressure

Melatonin is not only synthesized by the pineal gland but by several ocular structures. This natural indoleamine is of great importance for regulating several eye processes, among which pressure homeostasis is included. Glaucoma, the most prevalent eye disease, also known as the silent thief of vision, is a multifactorial pathology that is associated to age and, often, to intraocular hypertension (IOP). Indeed IOP is the only modifiable risk factor and as such medications are available to control it; however, novel medications are sought to minimize undesirable side effects. Melatonin and analogues decrease IOP in both normotensive and hypertensive eyes. Melatonin activates its cognate membrane receptors, MT1 and MT2, which are present in numerous ocular tissues, including the aqueous-humor-producing ciliary processes. Melatonin receptors belong to the superfamily of G-protein-coupled receptors and their activation would lead to different signalling pathways depending on the tissue. This review describes the molecular mechanisms underlying differential functionalities that are attributed to melatonin receptors. Accordingly, the current work highlights the important role of melatonin and its analogues in the healthy and in the glaucomatous eyes, with special attention to the control of intraocular pressure

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