The Protective Effect of Oral Application of Corni Fructus on the Disorders of the Cornea, Conjunctiva, Lacrimal Gland and Retina by Topical Particulate Matter 2.5

Abstract

Particulate matter 2.5 (PM_2.5) may aggravate dry eye disease (DED). Corni Fructus (CF), which is fruit of Cornus officinalis Sieb. et Zucc., has been reported to have various beneficial pharmacological effects, whereas the effect of CF on the eye is still unknown. Therefore, in this study, we investigated the effect of oral administration of water extract of CF (CFW) on the eye, hematology, and biochemistry in a DED model induced by topical exposure to PM_2.5. Furthermore, the efficacy of CFW compared with cyclosporine (CsA), an anti-inflammatory agent, and lutein, the posterior eye-protective agent. Sprague-Dawley rats were topically administered 5 mg/mL PM_2.5 in both eyes four times daily for 14 days. During the same period, CFW (200 mg/kg and 400 mg/kg) and lutein (4.1 mg/kg) were orally administered once a day. All eyes of rats in the 0.05% cyclosporine A (CsA)-treated group were topically exposed to 20 μL of CsA, twice daily for 14 days. Oral administration of CFW attenuated the PM_2.5-induced reduction of tear secretion and corneal epithelial damage. In addition, CFW protected against goblet cell loss in conjunctiva and overexpression of inflammatory factors in the lacrimal gland following topical exposure to PM_2.5. Furthermore, CFW markedly prevented PM_2.5-induced ganglion cell loss and recovered the thickness of inner plexiform layer. Meanwhile, CFW treatment decreased the levels of total cholesterol and low-density lipoprotein cholesterol in serum induced by PM_2.5. Importantly, the efficacy of CFW was superior or similar to that of CsA and lutein. Taken together, oral administration of CFW may have protective effects against PM_2.5-induced DED symptoms via stabilization of the tear film and suppression of inflammation. Furthermore, CFW may in part contribute to improving retinal function and lipid metabolism disorder.

Keywords: Corni Fructus; cyclosporine A; dry eye disease; goblet cells; lutein; particulate matter 2.5; retinal ganglion cells; tear production.

Figure 1

Effect of oral supplements of CFW on tear secretion after topical exposure to PM_2.5 in SD rats. On days 0, 7, and 14, tear volume was determined using phenol red tear threads and the length of color-changed thread was measured. The data are expressed as the means ± standard deviation (n = 5). * p < 0.05, ** p < 0.01, and *** p < 0.001 compared to the control group. # p < 0.05, ## p < 0.01, and ### p < 0.001 compared to the PM_2.5-induced DED group.

Figure 2

Effect of oral supplements of CFW on the detachment of corneal epithelium in PM_2.5-induced DED rats. (A) Representative images of H&E-stained images of corneal sections (n = 4). Black arrows indicate the detached and swollen epithelium. Scale bar, 50 μm. (B) The numbers of the detached corneal epithelium of 100 μm² in five different sections were counted. The data are expressed as the means ± standard deviation (n = 10). * p < 0.05 and *** p < 0.001 compared to the control group. # p < 0.05 and ### p < 0.001 compared to the PM_2.5-induced DED group.

Figure 3

Effect of oral supplements of CFW on conjunctival goblet cell population in PM_2.5-induced DED rats. (A) Representative images of PAS-stained images of conjunctival sections (n = 4). Black arrows indicate the PAS-stained goblet cells, which appeared a strong violet color. Scale bar, 25 μm. (B) The numbers of goblet cells of 100 μm² in five different sections were counted. The data are expressed as the means ± standard deviation (n = 10). *** p < 0.001 compared to control group. # p < 0.05 and ### p < 0.001 compared to the PM_2.5-induced DED group.

Figure 4

Effect of oral administration of CFW on inflammation of the lacrimal gland in PM_2.5-induced DED rats. (A) Representative images of H&E staining in the lacrimal gland (n = 6). Yellow arrows indicate neo-vessels. Scale bar, 50 μm. (B) Representative images of immunohistochemical staining for CD4, IL-17, and TNF-α in lacrimal gland sections (n = 5). Scale bar, 50 μm. The brown-stained precipitates indicate the presence of the target antigen. (C) The stained area of the photograph was quantitative analyzed using ImageJ^® and calculated in terms of the fold of the control. ** p < 0.01 and *** p < 0.001 compared to the control group. The data are expressed as the means ± standard deviation (n = 3). # p < 0.05, ## p < 0.01 and ### p < 0.001 compared to the PM_2.5-induced DED group.

Figure 5

Effect of oral administration of CFW on retinal ganglion cell loss after topical exposure to PM_2.5 in SD rats. (A) Representative images of cross-sectioned retina with H&E staining (n = 5). Nerve fiber layer (NFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), and outer nuclear layer (ONL) are indicated. Scale bar, 50 μm. (B) Thickness of NFL/GCL + IPL layers. (C) The numbers of cells in GCL of 100 μm² in five different sections were counted. (B,C) The data are expressed as the means ± standard deviation (n = 10). * p < 0.05 and *** p < 0.001 compared to the normal group. ## p < 0.01 and ### p < 0.001 compared to the control group.