Biomarkers of oxidative stress: possible prospective and application in ecotoxicology and health monitoring in avian species

Abstract

All living organisms are constantly exposed to action of oxidative factors, among these the reactive oxygen metabolites (ROMs) are the main reactive compounds that interest aerobic organisms. Part of these compounds are of an environmental nature and partly originate directly from the organism metabolism. The action of the pro-oxidant compounds causes an attack on biological molecules, damaging them and altering their functionality, resulting in damage to cellular structures and, in cascade, to tissues and organs. For this reason, organisms have evolved a series of antioxidant defences, in opposition to the action of free radicals. In particular, birds have evolved extremely efficient antioxidant systems, compensating for the high oxidative pressure resulting from the intense metabolic activity linked to the fly ability. When the oxidative pressure exceeds the antioxidant compensating capacity an organism incurs in a state of Oxidative Stress (OS). The organism OS degree can be investigated through the study of OS biomarkers. There are many factors that can influence the oxidative state of an organism. Speaking of exposure to exogenous compounds, much of the toxic action of heavy metals, such as Hg, Pb, Ni and Cd, derives from their ability to induce the production of ROMs, or from interference action with antioxidant scavenging complexes. Considering biological phenomena intrinsic to organisms, immune activation involves an important release of pro-oxidant factors, partly synthesized as defence factors against non-self antigens and partly dispersed following the increase in the metabolic response associated with immune activation. On the basis of the results generated from this research project, no correlation was found between OS biomarkers and Hg, Pb, Cd and Ni levels measured in the feathers of sentinel bird species, strengthening the hypothesis that the assessment of sentinel species OS degree is not a reliable method for indirect monitoring of heavy metals environmental contamination. On the contrary, the research carried out considering the relation with health and immunity state, showed that OS levels observed in hens bred in an intensive indoor farm environment were significantly higher compared with outdoor free-range conditions. Possibly the higher OS levels could be related to the higher stocking density and dust levels found in the indoor facility. Additionally, the positive correlation between OS indicators levels and total withe blood cell (WBC) count in magpies (Pica pica) suggests that OS level is influenced by immune response. Again, we have observed in hens that following an antigenic stimulus, subjects with higher initial plasmatic levels of ROMs tend to develop greater cellular mobilization, with greater increases of WBC and lymphocythemia, but a minor antibody response. It was also observed that subjects with high levels of plasmatic antioxidant following the antigenic stimulus tend to develop major entity of antibody responses. In conclusion, the study of OS in relation to the immune response could have interesting applications from the clinical diagnostic point of view in avian species.