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

The progress of prophylactic treatment in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a retinal vascular disorder frequently found in premature infants. Different therapeutic strategies have been developed to treat ROP. However, there are still many children with ROP suffering by severe limitations in vision or even blindness. Recently, ROP has been suggested to be caused by abnormal development of the retinal vasculature, but not simply resulted by retinal neovascularization which takes about 4 to 6wk after birth in premature infants. Thus, instead of focusing on how to reduce retinal neovascularization, understanding the pathological changes and mechanisms that occur prior to retinal neovascularization is meaningful, which may lead to identify novel target(s) for the development of novel strategy to promote the healthy growth of retinal blood vessels rather than passively waiting for the appearance of retinal neovascularization and removing it by force. In this review, we discussed recent studies about, 1) the pathogenesis prior to retinal neovascularization in oxygen-induced retinopathy (OIR; a ROP in animal model) and in premature infants with ROP; 2) the preclinical and clinical research on preventive treatment of early OIR and ROP. We will not only highlight the importance of the mechanisms and signalling pathways in regulating early stage of ROP but also will provide guidance for actively exploring novel mechanisms and discovering novel treatments for early phase OIR and ROP prior to retinal neovascularization in the future.

Gene transfer to the outflow tract

Elevated intraocular pressure is the primary cause of open angle glaucoma. Outflow resistance exists within the trabecular meshwork but also at the level of Schlemm's canal and further downstream within the outflow system. Viral vectors allow to take advantage of naturally evolved, highly efficient mechanisms of gene transfer, a process that is termed transduction. They can be produced at biosafety level 2 in the lab using protocols that have evolved considerably over the last 15-20 years. Applied by an intracameral bolus, vectors follow conventional as well as uveoscleral outflow pathways. They may affect other structures in the anterior chamber depending on their transduction kinetics which can vary among species when using the same vector. Not all vectors can express long-term, a desirable feature to address the chronicity of glaucoma. Vectors that integrate into the genome of the target cell can achieve transgene function for the life of the transduced cell but are mutagenic by definition. The most prominent long-term expressing vector systems are based on lentiviruses that are derived from HIV, FIV, or EIAV. Safety considerations make non-primate lentiviral vector systems easier to work with as they are not derived from human pathogens. Non-integrating vectors are subject to degradation and attritional dilution during cell division. Lentiviral vectors have to integrate in order to express while adeno-associated viral vectors (AAV) often persist as intracellular concatemers but may also integrate. Adeno- and herpes viral vectors do not integrate and earlier generation systems might be relatively immunogenic. Nonviral methods of gene transfer are termed transfection with few restrictions of transgene size and type but often a much less efficient gene transfer that is also short-lived. Traditional gene transfer delivers exons while some vectors (lentiviral, herpes and adenoviral) allow transfer of entire genes that include introns. Recent insights have highlighted the role of non-coding RNA, most prominently, siRNA, miRNA and lncRNA. SiRNA is highly specific, miRNA is less specific, while lncRNA uses highly complex mechanisms that involve secondary structures and intergenic, intronic, overlapping, antisense, and bidirectional location. Several promising preclinical studies have targeted the RhoA or the prostaglandin pathway or modified the extracellular matrix. TGF-β and glaucoma myocilin mutants have been transduced to elevate the intraocular pressure in glaucoma models. Cell based therapies have started to show first promise. Past approaches have focused on the trabecular meshwork and the inner wall of Schlemm's canal while new strategies are concerned with modification of outflow tract elements that are downstream of the trabecular meshwork.

Aqueous humour levels of ghrelin in exfoliation syndrome and exfoliation glaucoma patients

PURPOSE

To investigate levels of ghrelin in the aqueous humour (AqH) of patients with exfoliation syndrome and exfoliation glaucoma and compare them to levels of ghrelin in control subjects.

METHODS

This cross-sectional study involved 15 patients with exfoliation syndrome, 8 with exfoliation glaucoma and 12 control subjects for whom cataract surgery was indicated. The AqH was aspirated from the anterior chamber with a 27-G needle under sterile conditions prior to tissue manipulation. Ghrelin levels were quantified using radioimmunassay kits.

RESULTS

Levels of ghrelin in the AqH were 187.87 ± 80.1 pg/mL in the eyes exhibiting exfoliation syndrome, 98.53 ± 50.9 pg/mL in the eyes exhibiting exfoliation glaucoma and 111.40 ± 77.5 pg/mL in the controls. Ghrelin level of patients with exfoliation syndrome were significantly higher than those of patients with exfoliation glaucoma and the controls (P < 0.05). Ghrelin levels of patients with exfoliation glaucoma were lower than those of the controls but were not reach statistically significant (P > 0.05). Age, gender and IOP did not have a significant effect on ghrelin levels in patients with exfoliation syndrome and exfoliation glaucoma.

CONCLUSION

This study is the first to report elevated levels of ghrelin in the AqH in eyes exhibiting exfoliation syndrome. Findings suggest ghrelin might play role in the etiopathogenesis of exfoliation syndrome to exfoliation glaucoma.

Novel evidence of ghrelin and growth hormone segretagogue receptor expression by human ocular tissues

AIM OF THE STUDY

The gastrointestinal peptide hormone ghrelin (Ghr) was discovered in 1999 as the endogenous ligand for the growth hormone secretagogue receptor (GHSR-1a). It is a pleiotropic peptide that modulates a wide spectrum of biological activities, such as growth hormone (GH) release, feeding stimulation, adiposity and cardiovascular actions. The presence of Ghr mRNA in the iris and ciliary body (CB) epithelium was recently demonstrated in animal models, where a possible myorelaxing effect on the iris muscles has been suggested. Based on these observations, the aim of our study was to investigate the Ghr and GHSR-1a expression and localization in the normal human eye.

MATERIAL

Five different ciliary body/iris samples from normal eyes were subjected to Western blot analysis. Immunohistochemical detection was performed on three enucleated eyes. Twenty aqueous humor (AqH) samples obtained from patients submitted to cataract surgery were analyzed with an ELISA for the presence of Ghr.

RESULTS

Ghr and GHSR-1a were co-expressed by the pigmented epithelium (PE) of the CB, by the retinal pigmented epithelium (RPE) and by the anterior limiting layer (ALL) of the iris. No reaction was detected at the subepithelial level in the ciliary or pupillae smooth muscle cells. The AqH samples were positive for the presence of Ghr.

CONCLUSION

This study provides the first evidence that Ghr and GHSR-1a are expressed in the human eye by specific cells. The understanding of the functional role of Ghr at the human eye level needs more efforts and investigation, but a hypothetical action on the GH retinal synthesis and/or on the circadian clock system could be suggested.

Ghrelin gene products in acute and chronic inflammation

Ghrelin gene products--the peptides ghrelin, unacylated ghrelin, and obestatin--have several actions on the immune system, opening new perspectives within neuroendocrinology, metabolism and inflammation. The aim of this review is to summarize the available evidence regarding the less known role of these peptides in the machinery of inflammation and autoimmunity, outlining some of their most promising therapeutic applications.