Identification of the ghrelin-GHSR 1 system and its influence in the modulation of induced ocular hypertension in rabbit and rat eyes

Antioxidative effects of ghrelin on human trabecular meshwork cells

Glaucoma is a group of neurodegenerative diseases characterized by loss of retinal ganglion cells and visual field defects and is one of the major causes of irreversible blindness worldwide. Primary open-angle glaucoma (POAG) is one of the classifications of glaucoma. Oxidative stress in trabecular reticulated cells is one of the possible mechanisms of the development of glaucoma. At present, there is still a lack of effective methods to treat glaucoma. Ghrelin is characterized by its wide distribution and high potency and has anti-inflammatory, antioxidant, and anti-apoptotic effects, which may be beneficial in the treatment of glaucoma. In this study, we investigated whether ghrelin can protect human trabecular meshwork cells (HTMCs) from oxidative damage induced by hydrogen peroxide (H2O2), as well as the possible mechanism of action. CCK8 and flow cytometry results revealed that treatment of HTMCs with ghrelin showed a dose-dependent protective effect against H2O2-induced damage. Ghrelin significantly decreased the rate of apoptosis and levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and increased the level of superoxide dismutase (SOD) and catalase (CAT) in HTMCs. The difference was statistically significant compared with the H2O2 group. Ghrelin activated Nrf2/HO-1/NQO-1 signaling pathways and decreased HIF-1α level in H2O2-injured HTMCs as shown on qPCR and Western blot. In conclusion, ghrelin can protect HTMCs from oxidative damage induced by H2O2 and reduce apoptosis in HTMCs, which can be a new approach to treating POAG. The underlying therapeutic mechanism may be related to Nrf2/HO-1/NQO-1 signaling pathways and HIF-1α.

Ghrelin Mitigates High-Glucose-Induced Oxidative Damage and Apoptosis in Lens Epithelial Cells

Oxidative stress induced by high glucose (HG) plays an important role in the mechanism of diabetic cataract. Evidence has shown that effects from oxidative stress induced damage of lens or human lens epithelial (HLE) cells. Antioxidant supplementation is a plausible strategy to avoid oxidative stress and maintain the function of lens. Ghrelin have been used in treatment of many diseases. In this study, we found that ghrelin attenuated HG-induced loss of cell viability, reduced oxidative damage, and cell apoptosis in HLE cells. Ghrelin inhibited apoptosis through the downregulation of Bax and the upregulation of Bcl-2. Our results suggest that ghrelin could be considered as a promising therapeutic intervention for diabetic cataract. We also observed rat lens transparent in cultured media and examined lens histopathological changes. The results showed that ghrelin could inhibit the histopathological injury of lenses and ultrastructural changes induced by HG. In conclusion, ghrelin may play a role in the treatment of ocular diseases involving diabetic cataract.

Potentiality of ghrelin as antioxidant and protective agent

Background

Oxidative stress is the result of cellular troubles related to aerobic metabolism. Furthermore, this stress is always associated with biological responses evoked by physical, chemical, environmental, and psychological factors. Several studies have developed many approaches of antioxidant defense to diminish the severity of many diseases. Ghrelin was originally identified from the rat stomach, and it is a potent growth hormone-releasing peptide that has pleiotropic functions.

Methods

A systematic review was conducted within PubMed, ScienceDirect, MEDLINE, and Scopus databases using keywords such as ghrelin, antioxidant, oxidative stress, and systemic oxidative stress sensor.

Results

In the last decade, many studies show that ghrelin exhibits protection effects against oxidative stress derived probably from its antioxidant effects. Pieces of evidence demonstrate that systemic oxidative stress increase ghrelin levels in the plasma. The expression of ghrelin and its receptor in ghrelin peripheral tissues and extensively in the central nervous system suggests that this endogenous peptide plays an important role as a systemic oxidative stress sensor

Conclusion

The current evidence confirms that ghrelin and its derived peptides (Desacyl-ghrelin, obestatin) act as a protective antioxidant agent. Therefore, stressor modality, duration, and intensity are the parameters of oxidative stress that must be taken into consideration to determine the role of ghrelin, Desacyl-ghrelin, and obestatin in the regulation of cell death pathways.

Comparison of total/active ghrelin levels in primary open angle glaucoma, pseudoexfoliation glaucoma and pseudoexfoliation syndrome

AIM

To investigate the levels of ghrelin (Gh), acylated ghrelin (AGh) and AGh/Gh ratio in the humor aqueous (HA) of cases with pseudoexfoliation syndrome (PXS), pseudoexfoliation glaucoma (PXG), primary open angle glaucoma (POAG) and to compare these with control subjects.

METHODS

A prospective examination was made of the total Gh, and AGh levels in HA of 67 patients undergoing cataract surgery. Patients were divided into 4 groups. HA samples were aspirated at the beginning of the surgery, stored at -70°C. Gh and AGh quantification was performed with ELISA kits and the AGh/total-Gh ratios were calculated. ANOVA, Kruskal-Wallis, Chi-square and post-hoc tests were used for statistical analysis.

RESULTS

Total Gh levels in HA were 189.2±45.6 pg/mL in the control group, 199.2±32.9 pg/mL in PXS, 180.6±20.9 pg/mL in PXG and 176.8±21.4 pg/mL in POAG groups (P>0.05). AGh levels in HA were 23.09±5.01 pg/mL in the control group, 24.13±5.22 pg/mL in PXS, 22.29±1.55 pg/mL in PXG and 19.69±2.93 pg/mL in POAG groups (P>0.05). The ratio of AGh/Gh was 10.3%±2.34% in the control group, 13.03%±2.58% in PXS, 12.3%±1.54% in PXG and 11.79%±1.41% in POAG groups (P=0.044). The difference between the PXS and control groups was significant (P=0.03).

CONCLUSION

In spite of statistically insignificant results, the HA total Gh levels were lower than those of the control subjects but not parallel with the AGh levels in glaucoma patients. The relative increase in the AGh/Gh ratio in glaucoma cases supports the view that proportional increases of AGh might play a role in the pathogenesis of glaucoma.

Characterization of a Monoclonal Antibody Specific for the Growth Hormone Secretagogue Receptor

Ghrelin is an orexigenic peptide hormone that primarily regulates growth hormone secretion, food intake, and energy homeostasis. It has been shown to also play a role in numerous higher brain functions, such as the regulation of inflammation and cell proliferation. Ghrelin is the endogenous ligand of the growth hormone secretagogue receptor (GHSR), a G-protein-coupled receptor highly expressed in brain and detectable in some peripheral tissues. The wide distribution of ghrelin receptor and the number of tissues and cell types known to respond to ghrelin suggest that a number of systems may be affected by treatment with this hormone or its analogues. In this study, we characterized a new GHSR specific monoclonal antibody recognizing specifically the ghrelin receptor. This could be a useful tool for immunoassays aimed at obtaining insights into the physiological and pathological significance of the GHSR/ghrelin system.

Discovery of Molecular Therapeutics for Glaucoma: Challenges, Successes, and Promising Directions

Glaucoma, a heterogeneous ocular disorder affecting ∼60 million people worldwide, is characterized by painless neurodegeneration of retinal ganglion cells (RGCs), resulting in irreversible vision loss. Available therapies, which decrease the common causal risk factor of elevated intraocular pressure, delay, but cannot prevent, RGC death and blindness. Notably, it is changes in the anterior segment of the eye, particularly in the drainage of aqueous humor fluid, which are believed to bring about changes in pressure. Thus, it is primarily this region whose properties are manipulated in current and emerging therapies for glaucoma. Here, we focus on the challenges associated with developing treatments, review the available experimental methods to evaluate the therapeutic potential of new drugs, describe the development and evaluation of emerging Rho-kinase inhibitors and adenosine receptor ligands that offer the potential to improve aqueous humor outflow and protect RGCs simultaneously, and present new targets and approaches on the horizon.

Plasma Levels of Acylated Ghrelin in Children with Pulmonary Hypertension Associated with Congenital Heart Disease

This study aims to estimate plasma levels of acylated ghrelin in children with pulmonary hypertension (PH) associated with congenital heart disease (CHD) and to correlate the levels of acylated ghrelin with endothelin-1 (ET-1), nitric oxide (NO), and clinical hemodynamic parameters. We investigated the plasma concentration of acylated ghrelin, ET-1, NO, and the hemodynamic parameters in 20 children with CHD, 20 children with PH-CHD, and 20 normal children. Plasma-acylated ghrelin and NO levels were significantly higher in CHD group than in control subjects (P < 0.001). Moreover, plasma-acylated ghrelin, ET-1, and NO levels were significantly elevated in PH-CHD group compared with the CHD group (P < 0.05). In PH-CHD children, plasma-acylated ghrelin levels correlated positively with pulmonary artery systolic pressure (PASP; r = 0.740, P < 0.001), pulmonary artery diastolic pressure (PADP; r = 0.613, P = 0.004), right ventricular systolic pressure (RVSP; r = 0.642, P = 0.002), mean pulmonary arterial hypertension (mPAP; r = 0.685, P = 0.001), right ventricle diameter (RVD; r = 0.473, P = 0.035), pulmonary artery trunk diameter (PAD; r = 0.613, P = 0.004), NO (r = 0.463, P = 0.04), and ET-1 (r = 0.524, P = 0.018). Plasma-acylated ghrelin levels were elevated both in CHD and in PH-CHD. Increased acylated ghrelin levels correlated positively with ET-1, NO, PASP, PADP, RVSP, mPAP, RVD, and PAD. Acylated ghrelin may be a new biomarker of PH-CHD.

Present and New Treatment Strategies in the Management of Glaucoma

Glaucoma is a neurodegenerative disease characterized by retinal ganglion cell (RGC) death and axonal loss. It remains a major cause of blindness worldwide. All current modalities of treatment are focused on lowering intraocular pressure (IOP), and it is evident that increased IOP is an important risk factor for progression of the disease. However, it is clear that a significant number of glaucoma patients show disease progression despite of pressure lowering treatments. Much attention has been given to the development of neuroprotective treatment strategies, but the identification of such has been hampered by lack of understanding of the etiology of glaucoma. Hence, in spite of many attempts no neuroprotective drug has yet been clinically approved. Even though neuroprotection is without doubt an important treatment strategy, many glaucoma subjects are diagnosed after substantial loss of RGCs. In this matter, recent approaches aim to rescue RGCs and regenerate axons in order to restore visual function in glaucoma. The present review seeks to provide an overview of the present and new treatment strategies in the management of glaucoma. The treatment strategies are divided into current available glaucoma medications, new pressure lowering targets, prospective neuroprotective interventions, and finally possible neuroregenrative strategies.