Protective effect of Sarcandra glabra on radiation-induced parotid injury in rats

Objective To study the changes of inflammatory response and apoptosis in parotid gland tissues of rats after X-ray irradiation, and to explore the protective effect and possible mechanism of Sarcandra glabra on radiation-induced parotid injury in rats. Methods A total of 120 male rats were randomly divided into 5 groups(24 for each): control group, single irradiation group, radiation combined with a high(26.8 g·kg-1·d-1), moderate(13.4 g·kg-1·d-1) and low(6.7 g·kg-1·d-1) dosage of Sarcandra glabra group. The parotid gland of rats in the irradiation group received 15 Gy X-ray. Rats in each group were anesthetized with 2% pentobarbital sodium (0.16 ml/100 g) at 10, 40 and 70 d after irradiation and blood was collected from abdominal aorta. ROS levels in blood serum of each group were detected on the 10th, 40th and 70th days after irradiation. After parotid gland tissue was taken, the pathological changes and ultrastructural changes were observed by hematoxylin-eosin (HE) staining and transmission electron microscopy, respectively. The expression level of TNF-α in parotid gland tissue was detected by immunohistochemistry, and apoptosis of parotid cells was detected by TUNEL assay. Results The content of ROS and the expression of TNF-α protein in the single irradiation group were simultaneously increased compared with the control group (t=-24.723, -35.013, -19.515, P<0.05; t=-13.563, 43.519, -15.249, P<0.05), while they were reduced by Sarcandra glabra in a dosage dependent manner, especially in the high dosage group of Sarcandra glabra (t=5.295, 8.138, 6.545, P<0.05; t=10.093, -7.868, 10.539, P<0.05). In the control group, the parotid gland tissue structure was intact, without congestion, exudation, edema, etc. For the single irradiation group, the parotid gland tissue became hyperemia, edema and inflammatory cell infiltration at 10 d after irradiation followed by fibrosis at 40 d after irradiation. These pathological alterations in the parotid gland tissue were significantly recovered when the rats were treated with Sarcandra glabra before irradiation, and the tissue damage was negatively correlated with drug dosage. TUNEL assay showed that the apoptosis rate of parotid gland cells in the single irradiation groups was higher than that in the control group (t=-4.639, -3.979, P<0.05). Conclusions Sarcandra glabra protects parotid gland from radiation damage by scavenging radiation-induced ROS and declining inflammatory response, and thus it may be applied as a potential protective agent for radiation injury. Key words: Apoptosis; Sarcandra glabra; Radiation induced parotid injury; ROS; TNF-α