Protective Effect of a Water-Soluble Carotenoid-Rich Extract of Cordyceps militaris against Light-Evoked Functional Vision Deterioration in Mice

Abstract

Light-evoked retinal photodamage is considered an important factor contributing to functional vision deterioration and can even lead to light maculopathy or dry age-related macular degeneration. Loss of visual acuity (VA) and visual contrast sensitivity function (VCSF) are the major symptoms of retinal degenerative diseases. Cordyceps militaris is a carotenoid-rich Chinese medicinal fungus with antioxidant, anti-inflammatory, and immunomodulatory functions. C. militaris extract is a natural substance, and its bioactive constituents have been shown to confer health benefits, but their application in retinal tissue and functional vision protection in vivo remain incompletely understood. In the present study, we evaluated the influence of water-soluble, carotenoid-rich C. militaris extracts on the visual performance of light-damaged mouse retinas in vivo, using adult female CD-1^® (ICR) albino mice. We showed that oral administration of this C. militaris extract (10 mg/kg, twice daily) protected the neural retina tissue against light-evoked photoreceptor cell death, reduced Müller cell hypertrophic gliosis, and elevated GSH levels and promoted the recovery of VA- and VCSF-thresholds, especially for high spatial frequency-characterized vision. These results suggest that, probably because of its water-soluble carotenoids, C. militaris extract has the potential to prevent or treat light-induced visual dysfunction.

Keywords: Cordyceps militaris; cordyxanthins; functional vision; photoreceptor; retinal photodamage; visual contrast sensitivity function; water-soluble carotenoids.

Figure 1

High-performance liquid chromatography-electrospray ionization mass spectrometry analysis of cordyxanthin, a water-soluble carotenoid, in C. militaris extract. (a) ESI source of the mass spectrometer; cordyxanthin-III showed good sensitivity in the positive ion mode; (b) MRM chromatographic profiles of the cordyxanthin from C. militaris extract.

Figure 2

Protective effect of C. militaris extract on light-evoked retinal damage. (a) Timeline of experimental design; (b–f) The analysis of apoptotic cell death in retinas; (g) The density of apoptotic cells; (h–l) The expression of GFAP protein. Data are expressed as mean ± SE. Mann–Whitney U test was used to analyze data. ^#: p < 0.05, *: p < 0.05. Scale bar: 35 μm. INL: the inner nuclear layer; ONL: the outer nuclear layer.

Figure 3

Effects on visual acuity (VA) of C. militaris extract treatment. (a) Changes in VA threshold after light-evoked retinal photodamage; (b) restorative efficacy of VA threshold of water-soluble carotenoid-rich, C. militaris extract-treated and lutein-rich, marigold extract-treated mice. Data are expressed as mean ± SE. A Mann–Whitney U test was performed; ^##: p < 0.01, *: p < 0.05.

Figure 4

Effects on visual contrast sensitivity function (VCSF) of C. militaris extract treatment. (a) The inverted U-shaped diagram of the VCSF curve; (b) The VCSF visibility index; (c) The individual threshold with details represented in 0.033 cpd, (d) 0.055 cpd, (e) 0.082 cpd, (f) 0.164 cpd, (g) 0.328 cpd, and (h) 0.437 cpd. Data are expressed as mean ± SE. A Mann-Whitney U test was performed. ^#: p < 0.05, *: p < 0.05.

Figure 5

Antioxidant protective effect of C. militaris extract. (a) Hematoxylin and eosin staining representing the layers of ONL nuclei; (b) change of ONL nuclei within 0.4~1.0 mm superior and inferior to the optic nerve; (c) average ONL nuclei; (d) normalized GSH level. Data are expressed as mean ± SE. A Mann-Whitney U test was performed. ^#: p < 0.05, *: p < 0.05, **: p < 0.01. Scale bar: 35 μm. INL: the inner nuclear layer; ONL: the outer nuclear layer.