6-shogaol, a bioactive component of ginger, alleviates aging-induced ocular inflammation and ER stress in the 25-month-old mice

Abstract

In the elderly population, age-related macular degeneration (AMD) is a major cause of visual impairment, characterized by a thinner retinal pigment epithelium and loss of photoreceptors. 6-shogaol (6S), a component of dried Zingiber officinale Roscoe, has been studied for its multiple therapeutic effects. The current study aimed to investigate the effect of 6S supplementation on AMD. 25-month-old C57BL/6 mice were orally administered with 10 mg/kg of 6S for 28 consecutive days. The thickness of the retinal layer was measured by histological analysis. mRNA expression related to fibrosis, inflammation and endoplasmic reticulum stress was measured by real-time polymerase chain reaction. As a result, 6S increased the thickness of the retinal layer and promoted postsynaptic density protein-95 expression in the outer plexiform layer of the aged mice. Moreover, 6S suppressed ocular mRNA expression related to the fibrotic process, including transforming growth factor beta, collagen type 1 alpha 1, and alpha smooth muscle actin. Furthermore, 6S reduced pro-inflammatory cytokines including tumor necrosis factor alpha, interleukin 1 beta, cyclooxygenase-2, and inducible nitric oxide synthase in the eyeballs of aged mice. Lastly, 6S inhibited ocular endoplasmic reticulum stress measured by mRNA expression of C/EBP homologous protein and spliced X-box binding protein-1 in the aged mice. Taken together, these findings suggest that 6S and dried ginger could be a potential nutraceutical candidate for AMD or other age-related eye diseases.