Main active constituents and mechanism of toxicity of raphides from Arisaema erubescens against Oncomelania hupensis

Abstract

To find a high-efficiency and environment-friendly biogenic molluscicide against Oncomelania hupensis, and prevent aquatic ecosystem from being contaminated by chemical molluscicides and being toxic. We extracted and purified raphides from the tubers of Arisaema erubescent, and determined the active constituents and molluscicidal activity of the raphides, detoxification enzyme activity, and liver damage. The results showed that the raphides had a strong molluscicidal activity. O. hupensis snails were exposed to the lethal concentration (LC50) of 70.95 mg/L and 44.25 mg/L for treatment with raphides for 48 h and 72 h, respectively. The raphides of molluscicidal activity of the main constituents was as follows: intact raphides > calcium oxalate crystals > AEL (Arisaema erubescens Lectin). The activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) in the snail livers increased significantly at the early stage of treatment (24 h), but decreased sharply in the later stage (120 h), compared with that in the control group. The results indicated that after treatment with 1/2 LC50 raphides for 120 h, the activities of POD, SOD, and CAT in the snail livers decreased by 82.5 %, 62.9 %, and 84.7 %, respectively. In addition, electron micrographs have shown that the raphides were needle-shaped crystals and tended to be sharp at both ends (with a groove down both sides) and some were barbed, which caused damage to the snail livers to different extent. Overall, our results indicate that the mechanism of toxicity of raphides against O. hupensis may be that the calcium oxalate crystals pricked the liver surface of snail and produced mechanical damage; and then the harmful protease AEL in the raphides was injected into the liver, which reduced the activities of detoxification enzymes, produced severe toxic reactions and eventually killed the O. hupensis snails.