Serum irisin levels in chronic open-angle glaucoma

Glaucoma is a progressive and neurodegenerative disease characterized by the loss of the axons of retinal ganglion cells (RGCs) at the level of the optic nerve head (ONH) and visual field (VF) loss.1,2 Although elevated intraocular pressure (IOP) is considered as most important factor in the pathogenesis of glaucoma, clinical reports demonstrate that treatment strategies on lowering IOP is not alone enough to prevent glaucoma progression in all patients. Thus, neuroprotection may be crucial in the treatment of glaucoma.3−6 Neuroprotection is defined as the use of therapeutic agents to prevent, reduce, and even to reverse neuronal cell death because of a neurodegenerative disease or a traumatic or a neurotoxic injury. Recent studies demonstrated that several neuroprotective treatments have been established in some neurodegenerative diseases of the central nervous system (CNS) disease like Alzheimer’s disease (AD).7−11 Irisin is an exercise-induced, 112-amino acid glycosylated protein that is formed by the proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5) in muscle tissue. It has been demonstrated that irisin works in the regulation in glucose homeostasis and the convertion of white adipose tissue to brown. Elevated irisin level increase in energy metabolism, weight loss and improves glucose tolerance causes.12−14 Irisin was firstly discovered from mouse skeletal muscle, and it was shown to be present in a variety of a lot of other tissues including rectum, pericardium, intracranial artery, heart, tongue, optic nerve (ON), uvula, brain, ovary, oviduct, pituitary, seminal vesicles, adrenal gland, esophagus, vena cava, kidney, penis, retina, testis, urethra, urinary bladder, spinal cord, liver, small intestine, tonsil, thyroid, and vagina.15 It has been reported that irisin immunoreactivity is present in the neural retina and muscle fibers in the eye of porcupine.16 In another study, it has been demonstrated that irisin immunoreactivity was found in all layers of the retina excluding the outer nuclear layer and also in the cornea in hamsters.17