Lowering the Intraocular Pressure in Rats and Rabbits by Cordyceps cicadae Extract and Its Active Compounds

Abstract

Cordyceps cicadae (CC), an entomogenous fungus that has been reported to have therapeutic glaucoma, is a major cause of blindness worldwide and is characterized by progressive retinal ganglion cell (RGC) death, mostly due to elevated intraocular pressure (IOP). Here, an ethanolic extract of C. cicadae mycelium (CCME), a traditional medicinal mushroom, was studied for its potential in lowering IOP in rat and rabbit models. Data showed that CCME could significantly (60.5%) reduce the IOP induced by microbead occlusion after 56 days of oral administration. The apoptosis of retinal ganglion cells (RGCs) in rats decreased by 77.2%. CCME was also shown to lower the IOP of normal and dextrose-infusion-induced rabbits within 60 min after oral feeding. There were dose effects, and the effect was repeatable. The active ingredient, N6-(2-hydroxyethyl)-adenosine (HEA), was also shown to alleviate 29.6% IOP at 0.2 mg/kg body weight in this rabbit model. CCME was confirmed with only minor inhibition in the phosphorylated myosin light chain 2 (pMLC2) pathway.

Keywords: Cordyceps cicadae; N6-(2-hydroxyethyl)-adenosine (HEA); ganglion cells; intraocular pressure (IOP).

Figure 1

Effect of C. cicadae mycelia extract on IOP in the glaucoma model. *: p < 0.05, n = 12, mean ± SEM. versus Glaucoma+PBS group.

Figure 2

The apoptosis of retinal ganglion cells (RGCs) of rats at day 56. (a) Representative terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining of day 56. (b) The number of TUNEL-positive cells in the RGC. (mean ± standard error of the mean, SEM; * p < 0.05).

Figure 3

pMLC2 inhibition for CCME and ROCK inhibitor AR-13324 by Western blot.

Figure 4

Effect of C. cicadae mycelia extracts on IOP in a rabbit model: (a) the ΔIOP (IOPtime-IOP0) of time course on the normotensive rabbit eye model. Dark blue is vehicle, light blue is control, red is 2.5 mg/kg CCME, green is 25 mg/kg CCME, and purple is Timolol. * p < 0.05, ** p < 0.01 and *** p < 0.001 versus vehicle control group; (b) the percentage of ΔIOP on the ocular normotensive rabbit model. Dark blue is vehicle, light blue is control, red is 2.5 mg/kg CCME, green is 25 mg/kg CCME, and purple is Timolol.

Figure 5

Anti-hypertensive effect of C. cicadae mycelia extract (CCME) in dextrose-induced acute glaucoma rabbit (A45—25 mg/kg/b.w.; B—40 mg/kg/b.w.) n = 4, mean ± SEM. * p < 0.05, ** p < 0.01 and *** p < 0.001, compared with solvent control group.

Figure 6

(a) HPLC of adenosine and HEA extracted from C. cicadae with retention times labeled at 27.7 min for adenosine and 30.8 min for HEA. Twenty microliters of adenosine or HEA; (b) LC-QTOF/MS spectra of adenosine with parental ion detected at m/z 268.10440; HEA with parental ion detected at m/z 310.11758.

Figure 6

(a) HPLC of adenosine and HEA extracted from C. cicadae with retention times labeled at 27.7 min for adenosine and 30.8 min for HEA. Twenty microliters of adenosine or HEA; (b) LC-QTOF/MS spectra of adenosine with parental ion detected at m/z 268.10440; HEA with parental ion detected at m/z 310.11758.

Figure 7

Anti-hypertensive IOP effect of HEA in dextrose induced acute glaucoma rabbit (A = 0.1 mg/kg/b.w., B = 0.2 mg/kg/b.w., n = 4). * p < 0.05, ** p < 0.01 and *** p < 0.001, compared with solvent control group.