Ghrelin in ocular pathophysiology: From the anterior to the posterior segment

• Published in: Peptides (New York, N.Y. : 1980) N.Y. : 1980), 2013-09, Vol.47, p.12-19
• Main Authors: Azevedo-Pinto, Sara, Pereira-Silva, Paulo, Rocha-Sousa, Amândio
• Format: Article
• Language: English
• Subjects: amino acids; animal models; Animals; Ciliary Body - metabolism; Ciliary Body - physiopathology; Databases, Bibliographic; eyes; Gene Expression; Ghrelin; Ghrelin - genetics; Ghrelin - metabolism; GHSR-1a; Glaucoma; Glaucoma - metabolism; Glaucoma - physiopathology; Humans; hypertension; Hypertensive Retinopathy - metabolism; Hypertensive Retinopathy - physiopathology; immune system; Intraocular Pressure; Iris; Iris - metabolism; Iris - physiopathology; Iris muscles; Oculomotor Muscles - metabolism; Oculomotor Muscles - physiopathology; pathophysiology; peptides; prostaglandins; Prostaglandins - metabolism; Receptors, Ghrelin - genetics; Receptors, Ghrelin - metabolism; retinal diseases; Retinopathy; somatotropin; sphincters
• ISSN: 0196-9781; 1873-5169
• DOI: 10.1016/j.peptides.2013.06.011

•Ghrelin is locally produced by the eye and GHSR-1a is also present in the ocular tissue.•Ghrelin induces the relaxation of the iris sphincter and dilator muscles.•The ghrelin-GHSR-1a system induces a significant decrease of ocular hypertension.•Ghrelin and GHSR-1a modulate angiogenesis in both phases of oxygen-induced retinopathy.•Current evidence outlines a role for ghrelin-GHSR-1a as a local regulation system in the eye. Ghrelin is a 28 amino acid acylated peptide produced in several organs that binds the growth hormone secretagogues receptor type 1a (GHSR-1a). It acts over a wide range of systems, e.g. the endocrine, cardiovascular, musculoskeletal and immune systems and the eye. The aim of this work is to review the physiologic and pathologic implications of the ghrelin-GHSR-1a in the eye. A systematic revision of studies published between 2000 and 2013 in English, Spanish or Portuguese in MEDLINE, EMBASE and Scopus was performed. Search words used included: ghrelin, GHSR-1a, ocular production, iris muscular kinetics, ciliary body, glaucoma, retinopathy and uvea. The production of ghrelin by the ocular tissue has been detected both in the anterior and posterior segments, as well as the presence of GHSR-1a. This peptide promotes the relaxation of the iris sphincter and dilator muscles, being this effect independent from GHSR-1a and dependent on prostaglandins release in the first case and dependent on GHSR-1a in the second. Regarding ocular pathology, ghrelin levels in the aqueous humor appear to be decreased in individuals with glaucoma. Moreover, ghrelin has been shown to decrease the intraocular pressure in animal models of ocular hypertension through GHSR-1a. In the posterior segment, the ghrelin-GHSR-1a system interferes with the development of oxygen-induced retinopathy, being protective in the vaso-obliterative phase and deleterious in the vaso-proliferative stage of the disease. Thus, the ghrelin-GHSR-1a system presents as a possible local regulatory mechanism in the eye, with pathophysiological implications, constituting a target for future clinical and therapeutic research and interventions.