Mechanistic insights into toxicity pathways induced by nanomaterials in Daphnia magna from analysis of the composition of the acquired protein corona

Identifying proteins present on the surface of nanomaterials (NMs) incubated with plasma, serum, and cell lysates can offer insights into the biological interactions of the NMs, including uptake and toxicity. Organisms such as Daphnia magna respond to the presence of toxicants by secreting proteins and other biomolecules; we demonstrate that the eco-corona acquired during exposure to NMs can provide similar important insights regarding the mechanistic pathways induced by the NM exposure as part of an ecotoxicity assessment. Using freshly dispersed (pristine) and ‘medium aged’ NMs (as environmental pollutants), differing in core material, size and surface properties, the influence of NM physicochemical characteristics and exposure environment on the protein corona composition and potential for in vivo uptake by the model test species Daphnia magna are investigated. Surface bound protein corona compositions changed between NM type, NM ‘age’ and the environmental medium in which the NMs were incubated, thus changing the NM biological identity and interactions. Proteins identified on the freshly dispersed NM surfaces were largely associated with metabolic damage, DNA damage, mitochondrial breakdown and energy processes, all of which are associated with cytotoxic damage. Significantly fewer proteins were bound to the aged NMs in all medium conditions, compared to the freshly dispersed NMs. Proteins bound only to the aged NMs were involved in calcium ion binding and cell redox homeostasis, indicative of significantly lower toxic responses to the aged NMs. Thus, NM protein corona composition can facilitate detection of organism responses to NM exposure and potentially identification of the molecular initiating events in adverse outcome pathways.