High irisin and low BDNF levels in aqueous humor of high myopia

The pathogenesis of myopia remains unclear. Both genetic and environmental factors play a role in the disease progression. Reasons including reduced physical activity (PA) and low-grade intraocular inflammation may be involved in the development of myopia.To analyze the levels of irisin, brain-derived neurotrophic factor (BDNF) and other intraocular cytokines in aqueous humor of high myopia patients, and to evaluate the roles of PA and inflammation in developing myopia.We collected aqueous humor samples from patients with axial length (AL) over 26 mm (n = 35) or shorter than 25 mm (n = 38) during cataract extraction surgery. Samples were assayed using the enzyme-linked immunosorbent assay (ELISA) kit for irisin and a multiplex immunoassay kit for BDNF, interleukin (IL)-6, IL-8 and IL-10, and tumor necrosis factor alpha (TNF-α).Irisin levels in the aqueous samples of the highly myopic eyes were significantly higher than in the control group (p = 0.027). The BDNF levels of the highly myopic group were significantly lower than in the control group (p = 0.043). Median level of leukemia inhibitory factor (LIF) for highly myopic group (2.035 pg/mL) was statistically significantly higher than in the control group (0.750 pg/mL) (U = 210.5, Z = -4.495, p < 0.001). Interleukin 1 receptor antagonist (IL-1ra) level in the aqueous samples of the highly myopic group was significantly lower than in the shorter AL group (p = 0.049). Interleukin 6, IL-8 and IL-10 levels were not significantly different between the 2 groups (p = 0.501, p = 0.059 and p = 0.192, respectively). Tumor necrosis factor α levels could only be detected in 30 samples and median levels in the 2 groups were not statistically significantly different (U = 99, Z = -0.482, p = 0.650). No correlation was found between IL-6, IL-8, IL-10 and TNF-α, and the AL (p > 0.05). Irisin was positively correlated with AL (p = 0.028, r = 0.287). The BDNF was negatively correlated with AL (p = 0.040, r = -0.246). Interleukin 1ra was negatively correlated with AL (p = 0.038, r = -0.276). There was also a correlation between LIF and AL (p < 0.001, r = 0.486).Higher irisin level in high myopia group opens a new direction to discover the relationship between PA and myopia. The decreased BDNF in high myopia group probably demonstrates the connection between myopia and neurodegenerative disease.