Abstract: Objective  To investigate the in vitro effect of photoactivated hypericin on anti-Schistosoma japonicum adult male worms.  Methods  Kunming mice were infected with 60-80 Schistosoma japonicum single-sex cercariae. At 6 weeks post-infection, the mice were sacrificed and adult male worms of S. japonicum were collected. The worms were incubated in DMEM medium containing different concentrations of hypericin （0.1, 0.2, 0.5, 1.0, 1.5, 2.0, and 2.5 μmol/L） in the presence or absence of light. In photoactivated hypericin groups, after 6 h of dark incubation the worms were exposed to LED light irradiation（590 nm） for 30, 60, 90, and 120 min, respectively, and then cultured overnight in darkness（16 h）. In the next morning, the parasites were washed, resuspended in drug-free medium, and incubated in the dark for 48 h. These worms were observed with stereomicroscopy and scanning electron microscopy（SEM）.  Results  Photoactivated hypericin showed the ability to kill Schistosoma japonicum in vitro. The death rate was 20% in 0.1 μmol/L photoactivated hypericin group under 30 min irradiation, and 100% in 2 μmol/L under 90 min irradiation and 2.5 μmol/L under 60 min irradiation, respectively. In blank control group, DMSO control group, and hypericin groups without light irradiation, worms were alive. After 60 min irradiation, the worms in 1.0, 2.5, 5.0 μmol/L photoactivated hypericin groups showed spastic paralysis characterized by reduced body length, pronounced tight curl, body stiffness, and complete cessation of movement. Surface tegumental damages of adult worms in 2.0 μmol/L photoactivated hypericin group for 60 min irradiation were observed under SEM, such as vacuole formation, erosion and peeling of the tegument, collapse of the sensory papillae, and even the normal structure disappeared completely. Both death rate and morphological damage of the worms treated by photoactivated hypericin were positively correlated with hypericin dose and light irradiation time.  Conclusion  Photoactivated hypericin has anti-Schistosoma japonicum adult male worms effect in vitro.

Key words: Hypericin, Schistosoma japonicum, Antischistosomal activity