Cellular, biochemical and molecular effects of cadmium on marine invertebrates: focus on Paracentrotus lividus sea urchin development

Cadmium is a heavy metal that is toxic for living organisms even at low concentrations. The presence in the environment of this metal has grown because of its large employment in some industrial and agricultural activities. Although heavy metals are terrestrially produced, they flow into the sea through effluents and sewage or are directly discharged from industries placed on the seawater front. In addition to its release into costal waters, cadmium fallout, following atmospheric events, contributes to the pollution of marine ecosystems. It should be considered that cadmium concentrations determined in the field vary widely according to different seawater latitudes and depths and can be strongly influenced by freshwater discharges from heavily polluted rivers. Cadmium does not have any biological role and, since it cannot be degraded, it is irreversibly accumulated into cells, interacting with cellular components and molecular targets. Experimental evidence suggests that the metal crosses the plasma membrane as a bivalent ion, exerting an agonistic role against calcium ionic channels. The metal has been associated with blockage of oxidative phosphorylation, glutathione depletion and antioxidant enzymatic activity inhibition, production of ROS, DNA damage, and inhibition of relative repair mechanisms, a general reduction of protein synthesis coupled with an increase in stress proteins. For many years, the effects of various pollutants onaquatic invertebrates have been studied. Most of these studies examined the developmental defects due to the presence, in rearing media, of a specific toxicant such as cadmium. Considering the capacity of sea urchin embryos and larvae to accumulate contaminants during development, this developmental model offers an excellent opportunity to investigate the possible adaptive response of cells exposed to cadmium during differentiation. In this review, we will examine the cellular, biochemical and molecular effects produced by cadmium ions on Paracentrotus lividus sea urchin embryos. Specifically we will consider the following: i) Cd2+ accumulation during embryonic development; ii) stress protein synthesis and accumulation (HSPs) and metallothioneins; and iii) induction of apoptosis and related pathways.