Objective To study the protective effects of Engelhardia roxburghiana Wall. leaf extract on mice hematopoietic system injury caused by disposable systemic 4 Gy ¹³⁷Cs γ-rays irradiation.

Methods (1) In vitro experiment. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and 2, 2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) free radical scavenging tests were used to detect the antioxidant activity of Engelhardia roxburghiana Wall. leaf extract in vitro. (2) In vivo experiment. ①Survival experiment. Forty specific pathogen-free male C57BL/6 mice were divided into four groups following a randomized block design: irradiation group, irradiation+low dose, irradiation+middle dose, and irradiation+high dose groups of Engelhardia roxburghiana Wall. leaf extract (20, 40, and 80 mg/kg, respectively). All four groups were irradiated with whole-body 7.2 Gy (lethal dose) ¹³⁷Cs γ-rays at one time. The survival condition of mice 30 days after irradiation was recorded. ② Radiation protection experiment of the hematopoietic system. Sixty specific pathogen-free male C57BL/6 mice were divided into six groups following a randomized block design: control group, irradiation group, Engelhardia roxburghiana Wall. leaf extract high dose group (80 mg/kg), irradiation+low dose, irradiation+middle dose, and irradiation+high dose groups of Engelhardia roxburghiana Wall. leaf extract (20, 40, and 80 mg/kg, respectively). The control group and the Engelhardia roxburghiana Wall. leaf extract high dose group (80 mg/kg) were not irradiated, while the four other groups were irradiated with whole-body 4 Gy ¹³⁷Cs γ-rays at one time. On the 7th day after irradiation, the mice were killed, the peripheral blood was obtained for blood routine detection, and unilateral femoral bone marrow cells were obtained for bone marrow nucleated cells count. The bone marrow cells of the other femur were used for bone marrow DNA content detection, the thymus and spleen were taken to calculate organ index, and liver was sampled to detect the content of reduced glutathione (GSH). In the in vitro experiment, the mice in each group underwent continuous intragastric administration 7 days before and 6 days after irradiation, in which the control group and irradiation group were given 0.5% carboxymethylcellulose sodium, and the other groups were given corresponding doses of Engelhardia roxburghiana Wall. leaf extract. Student's t test was applied to compare differences between two groups, and Kaplan-Meier survival analysis was used to determine the survival rate.

Results (1) In the in vitro experiment, compared with Trolox, the scavenging rate of DPPH free radical by the Engelhardia roxburghiana Wall. leaf extract were higher (89.83% vs. 69.37%, 90.94% vs. 68.53%) when the concentration was 100 μg/ml and 200 μg/ml; and the scavenging rate of ABTS free radical was also higher (94.81% vs. 71.35%, 94.46% vs. 71.93%), and the differences were statistically significant (t=19.58–33.26, all P<0.001). (2) In the in vivo experiment, compared with the irradiation group, the 30-day survival rates of mice in the low, middle, and high dose groups of irradiation+Engelhardia roxburghiana Wall. leaf extract significantly increased after receiving lethal dose irradiation, and the differences were statistically significant (Kaplan-Meier survival analysis, all P<0.05); while the survival days also significantly improved ((19.40±7.70) d vs. (12.50±3.59) d, (20.20±8.48) d vs. (12.50±3.59) d, (20.90±7.96) d vs. (12.50±3.59) d), and the differences were statistically significant (t=2.57, 2.79, 3.04; all P<0.05). The spleen and thymus organ index increased significantly in the irradiation+high dose group of Engelhardia roxburghiana Wall. leaf extract ((2.13±0.43) mg/g vs. (1.67±0.20) mg/g, (1.87±0.39) mg/g vs. (1.39±0.31) mg/g), and the differences were statistically significant (t=3.00, 3.03; both P<0.05). The number of red blood cells increased most significantly in the irradiation+middle dose group of Engelhardia roxburghiana Wall. leaf ((10.12±1.71)×10¹²/L vs. (8.26±0.87)×10¹²/L), and the difference was statistically significant (t=2.89, P<0.05). The number of white blood cells and red blood cells and the hemoglobin content increased significantly in the irradiation+high dose group of Engelhardia roxburghiana Wall. leaf extract ((1.76±0.45)×10⁹/L vs. (1.17±0.23)×10⁹/L, (9.59±0.85)×10¹²/L vs. (8.26±0.87)×10¹²/L, (144.40±14.61) g/L vs. (126.20±13.16) g/L), and the differences were statistically significant (t=3.62, 3.23, 2.93; all P<0.05). In addition, the number of bone marrow nucleated cells, the DNA content in the bone marrow, and GSH content in the liver were significantly increased in the irradiation+high dose group of Engelhardia roxburghiana Wall. leaf extract, and the differences were statistically significant (t=3.28, 3.93, 3.07; all P<0.05).

Conclusion The Engelhardia roxburghiana Wall. leaf extract has a certain protective effect on radiation injury of the hematopoietic system in mice.