Evaluation of eye protection efficacy of sweet potato leaf ethanolic extracts In Vivo

Many studies have been verified that human retina contains a large amount of carotenoids such as lutein and zeaxanthin, especially the concentrations of lutein and zeaxanthin in the retina and macula are 1,000 times higher than other tissues in human. Therefore, lutein and zeaxanthin play an important role in the health of human vision. The research and development (R&D) of agricultural functional materials or products for eye protection is urgently needed. In this experiment, except for the normal control group, the other groups were irradiated with light-emitting diode (LED) light at the range of 600-1,000 lux for 12 hours / day for 6 weeks. All BALB/c mice were fed with the normal composition for 6 weeks during the experiment. BALB/c mice in the negative control group and three sweet potato leaf ethanolic extracts (SPLEE) groups were fed SPLEE [0.31, 0.62, and 1.23 mg/kg body weight (BW), respectively] for 6 weeks by gavage during the experiment. During the experiment, the eye status of BALB/c mice in each group were observed every week. At the end of the experiment, the BALB/c mice were sacrificed and their eyes in each group were collected for hematoxylin & eosin (H&E) staining, immunohistochemical (IHC) staining, free radical detection, and the detection of cytokine gene expressions (IL-6; interleukin-6 and TNF-α; tumor necrosis factor-α) and caspase-3 gene expression. Based on the results of this experiment, no obvious lesions by ophthalmoscopy were observed in the eyes of BALB/c mice in three SPLEE groups. H&E and IHC staining results showed that the consumption of high dose (1.23 mg/kg BW) of SPLEE significantly improved retinal outer nuclear layer (ONL) thickness, which was compared to the negative control group. Other evaluation indicators included retinal out segments-inner segments (OS/IS) thickness, glial fibrillary acidic protein (GFAP) staining, and middle-wavelength opsin (M-opsin) staining, showed no significant difference among three SPLEE groups and the negative control group. The free radical detection results showed that no statistical difference between all groups (p > 0.05), however, the trend showed that the free radicals in the high and middle doses (1.23 and 0.62 mg/kg BW) of SPLEE groups were lower than those in the negative control group and the low dose (0.31 mg/kg BW) of SPLEE group. The results of IL-6 and TNF-α gene expression showed that the normal control group and three SPLEE groups were significantly lower than the negative control group (p < 0.05), while the gene expression of caspase-3 was not significantly differences between all groups (p > 0.05). Taken these results together, the high dose SPLEE (1.23 mg/kg BW) has the better potential for improving the retinal ONL thickness and anti-inflammatory effects under LED irradiation.