The aim of this study was to investigate the effects of grub extract on the expression of cysteine aspartic protease 8 (Caspase 8), B-cell lymphoma-2 associated X protein (Bax), B-cell lymphoma-2 homology 3 interacting domain death agonist (Bid), and caspase aspartic protease 3 (Caspase 3) in rabbits with photorefractive retinal degeneration.

Thirty experimental rabbits were randomly divided into 5 groups: blank group, model group, low-dose group, medium-dose group and high-dose group. Each group contained 6 rabbits (12 eyes). Except for the blank group, the other four groups established a model of photodamage retinal degeneration. One 40 W white fluorescent tube was placed on each of the six sides of the light frame to adjust light intensity, and the rabbit activity level was measured by ZDS-10 digital illuminometer. Multi-point illumination, with an average of (2000±200) Lx, was adapted to cyclic light for 7 days in 12 h bright and 12 h dark environment, and the rabbits were free for food and water. After 7 days, the light was darkly adapted for 24 h, then illuminated for 12 h, and then dark-adapted for 12 h for 3 consecutive cycles. The total illumination time was 36 h. After the model was established, the blank group and the model group were intragastrically administered with 5 ml/kg of normal saline, and the low-dose group was intragastrically administered with 5 ml of grub extract suspension by 0.45 g/kg grub extract (the medium-dose group by 0.9 g/kg and the high-dose group by 1.8 g/kg). After 14 days all the rabbits were sacrificed, HE staining was performed to observe the structure of retinal cells and immunohistochemistry to detect the expression of Caspase 8, Bax, Bid, and Caspase 3. The integrated optical density values of Caspase 8, Bax, Bid, and Caspase 3 expression were expressed as mean ± standard deviation. One-way ANOVA was used to compare the expression levels of Caspase 8, Bax, Bid, and Caspase 3 in different groups. When the difference was statistically significant, SNK method was used for further comparisons.

The micromorphological observation of the retina showed that the retinal structure of the blank group was well-defined, cells in each layer were arranged neatly, uniformly stained, and the morphology was regular. The retina of the model group was fuzzy, boundary was unclear, and irregular staining occurred. The arrangement was disordered and the number of cells decreased. In the low-dose group, the nucleus of the outer nuclear layer of the retina was looser. In the middle-dose group, the outer nuclear layer of the retina became thick, and the nucleus of the outer nuclear layer of the retina was arranged neatly. The nucleus of the outer nuclear layer of the retina was arranged neatly and showed increased thickness. The distribution of Caspase 8, Bax, Bid, and Caspase 3 positive substances in the cytoplasm of the outer nuclear layer of the blank group was sparse and less, while they were diffusely distributed and contained more in the model group. The expressions of Caspase 8, Bax, Bid, and Caspase 3 in the blank group and the model group were significantly different from those in the other three groups (P<0.05). There were statistically significant differences between the medium-dose group and the low-dose group for the expressions of Caspase 8, and Caspase 3 (F=7.30, 5.43; P<0.05), while no difference for the expression of Bid and Bax (F=2.47, 5.79; P>0.05). There were no significant differences between the high-dose group and the low-dose group for the expression of Caspase 8, Bax, Bid, and Caspase 3 (F=0.11, 0.11, 0.95, 0.01; P>0.05). There was statistically significant difference between the medium-dose group and the high-dose group for the expression of Caspase 8 (F=6.14, P<0.05), while no differences for the expressions of Bax, Bid, and Caspase 3 (F=0.11, 0.79, 1.71; P>0.05).

The grub extract could inhibit the expressions of Caspase 8, Bax, Bid, and Caspase 3. Different dose leads to different effect. For all dosages, medium dose shows better.