Disrupted homeostasis in coelomocytes of Eisenia fetida and Allolobophora chlorotica exposed dermally to heavy metals

Earthworms exposed dermally to heavy metals can accumulate copper, lead, and cadmium avidly, but zinc is efficiently regulated. Allolobophora chlorotica is more sensitive to Cu, and less sensitive to both Pb and Cd ions than Eisenia fetida. During dermal exposure to heavy metals, the elemental composition of E. fetida immunocompetent cells, coelomocytes, is disrupted, including time-dependent fluctuations in intracellular metal content and Ca/P and S/P balance. In coelomocytes of the both species, all investigated heavy metals induce upregulation of the protective stress proteins (HSP70, HSP72, and metallothionein w-MT2), while an upregulation of caspase-3, a key molecular component of the apoptotic programmed cell death pathway, is induced by Cu, Pb, Cd, but not Zn exposure. In the both species, the number of coelomocytes is significantly reduced in a time dependent manner in Cu, Pb, and Cd exposed animals, but not in those exposed to Zn. In conclusion, coelomocytes homeostasis is significantly disrupted, at least transiently, in coelomocytes from earthworms subjected to metal stressors under laboratory conditions. The overall similarity in the responses of the epigeic E. fetida and endogeic A. chlorotica indicates that E. fetida is a reasonable surrogate for soil-dwelling earthworm species in short-duration laboratory-based ecotoxicological tests.