Mechanisms of immunotoxic effects of nanomaterial in fish

• Autor(a) principal: Costa, Leonor Coutinho
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/12616
• topic: Química analítica; Toxicologia ambiental - Ecossistemas aquáticos; Nanomateriais; Mercúrio - Toxicidade

Information and knowledge related to nanotechnology raise new challenges to the scientific community mainly in terms of human health risks and environmental implications associated to nanomaterials. In this perspective, the contamination of aquatic environments cannot be overlooked since it is an ultimate repository of the contaminants where this emerging appears as part of a cocktail of different classes of contaminants. Thus, the major task of this work was to connect gaps in current knowledge with a comprehensive sequence of biological responses toward environmentally relevant concentrations of engineered nanomaterials (IONM - silica coated iron oxide nanomaterial functionalized with dithiocarbamate group) and their interaction with other conventional anthropogenic contaminant (Hg - mercury), outlining the interaction with the innate immune system of fish. The research was divided into following steps: i) phagocytes macrophages were isolated from peritoneum (P-phagocytes), gill (G-phagocytes), head kidney (HK-phagocytes) and spleen (S-phagocytes) of European eel Anguilla anguilla L. in order to evaluate whether, and how can IONM and its co-exposure to Hg modulate phagocytes status and function; ii) determine the changes in phagocytes activation and their association to peroxidative damage (OBA - oxidative burst activity; LPO - lipid peroxidation); iii) to assess the impact of IONM on phagocytes enzymatic (CAT - catalase; GPX - glutathione peroxidase; GR - glutathione reductase; and GST - glutathione S-transferase) and non-enzymatic (NP-SH - non-protein thiols; and TGSH - total glutathione) antioxidants protection overtime. It was hypothesized that IONM can cause measurable changes in fish immune response and oxidative stress modulation. A period of exposure-dependency was exhibited by IONM alone and IONM+Hg joint exposures accrued impacts on A. anguilla phagocytes. IONM exposure alone lead to an acute response in terms of viability increase in P-phagocytes and modulated phagocytic activity in P-, and S-.phagocytes during 2 hours of exposure; whereas, IONM lead to a chronic immunotoxicity during 72 hours exposure only in S-phagocytes. However, IONM+Hg exposure lead to both acute and chronic response in terms of modulated phagocytic activity with no change in viability in P-, HK- and S-phagocytes only. Increase in the period of exposure to Hg disrupted phagocytic activity of P-, HK- and S-phagocytes, an increase in P- and decrease in HK- and S- phagocytes was perceptible at late hours of exposure. The occurrence of synergism between IONM and Hg was evidenced at 72 hours by significantly increasing trends of phagocytosis increase. A differential extent of OBA and LPO induction at the end of different period of exposure to IONM, Hg or IONM+Hg was also perceptible. The OBA induction and its concomitant association to LPO induction were observed only in gill after exposure to Hg (8 and 48 hours) and IONM+Hg (8 hours). At late hours of exposure, an induction was observed in G- phagocytes (OBA) after exposure to IONM+Hg suggesting that the concomitant exposure was unable to mitigate the Hg-accrued negative impacts. A. anguilla also displayed that the damage was accompanied with a differential modulation of enzymatic and non-enzymatic antioxidants in P, G-, HK- and S-phagocytes. Under IONM alone exposure, no LPO induction along the time was observed probably due to efficient induction of, GR and GST providing a better protection to IONM exposed phagocytes. However, antioxidants protection responses displayed hours of exposure dependency in G- and S-phagocytes where, an insufficiency of elevated CAT, GPX, GST, NP-SH and TGSH was clearly depicted for the maintenance of pro- and antioxidant balance optimum for scavenging ROS and protecting membrane lipids against IONM impact. As increased LPO was observed under IONM alone exposure condition, the joint action of IONM+Hg led to elevated damages to membrane-lipids at 4 and 8 hours (G-phagocytes), 2 hours (HK-phagocytes) and 24 hours (S-phagocytes) of exposure. These responses together, point towards the antioxidants defense failure for the protection of membrane lipids during those periods of exposure to IONM+Hg. However, it is important to underline here that during the late hours of exposure (72 hours), the results imply the positive effect of the concomitant exposure (IONM+Hg) which significantly mitigated the said negative impacts of Hg. Overall, the observations of this study open up new insight into the areas of evaluation of immune defense mechanisms in fish exposed to IONM and recommend that the interactions between IONM and other conventional anthropogenic contaminants should be considered while interpreting the fish immunotoxicity responses to IONM exposure in a multi-pollution state.