Cadmium exposure induced oxidative stress and histopathological disruption in the body wall of the freshwater leech Limnatis nilotica (Savigny, 1822)

Abstract

Cadmium (Cd) is considered as one of the most highly toxic heavy metal that is released into the environment on a large scale, and its concentrations in water have significantly increased as a result of human activities. In particular, contamination of rivers and drinking water may easily occur, especially in locations close to industry or mines. In this study, we examined the impact of Cd exposure on the body wall of the freshwater leech Limnatis nilotica at concentrations of 100, 200, and 300 µg/l. The findings showed that the exposure caused histopathological changes as well as oxidative stress (increased malondialdehyde concentrations (MDA)) and changes in antioxidant activity (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (Gpx)). In fact, numerous histological changes were observed, such as cuticle deterioration, a marked increase in the number of secretory cells, increased mucus production, vacuolization of the epithelium, altered epithelial cell borders, and mucus cell hyperplasia. The histological results are consistent with the biochemical findings because we found that MDA levels significantly increased in a dose-dependent manner. Additionally, the Cd exposure disrupted the levels of the antioxidant levels. Indeed, SOD, CAT, and Gpx activities were increased in the group treated with the lower dose (100 g/l), whereas their levels dramatically decreased at higher Cd doses (200 and 300 g/l). Therefore, the presence of this heavy metal in freshwater habitats may have severe ecological risks that may lead to leech aquatic habitat destruction and fragmentation.