Biomarkers of Defense, Tolerance, and Ecological Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 55

Progression of disease

Lysosomal
stability

Cellular death

Protein carbonyls

SOD

MDR

Healthy Stressed Curable

Incurable

Health status

FIGURE 3.1
Theoretical diagram of the conceptual links between biomarkers and health status of individuals in the context
of “effects at the population level” prediction. (Adapted from Allen, J.J., Moore, M.N., Mar. Environ. Res. , 58,
227-232, 2004.)

3.3.3 Phases I and II Enzymes

Phase I enzymes, such as 7-ethoxyresorufin o -deethylase (EROD), and phase II enzymes,
such as GST (glutathione- S -transferase), are usually considered as defense biomarkers
(cf. Chapter 2), involved in the detoxification of organic compounds (Newman and Unger
2003). Yet the activity of phase I cytochrome P450-dependent enzymes can trigger the
activation of the initial compounds, especially of PAHs, whose subsequent metabolites can
cause cellular damage by binding to biological macromolecules such as DNA and various
proteins. The induction of cytochrome P4501A (CYP1A) by nonmetabolized halogenated
aromatic hydrocarbons can induce the production of ROS. Resistance to various organic
contaminants (PCBs, PCDDs, PAHs) in fish populations living in highly contaminated
sites is linked to the absence of CYP1A induction (Romeo and Wirgin in Amiard-Triquet
et al. 2011). Various hypotheses have been proposed to explain this resistance, such as
high GST activity (Armknecht et al. 1998). Indeed, in response to exposure to 1-chloro-2,4
dinitrobenzene, GST expression and activity in resistant fish ( Fundulus heteroclitus ) from
a contaminated estuary were respectively four times and twice as high as in fish from a
reference site. Antioxidant defenses (Meyer et al. 2003; see Section 3.3.2) and MXR (Cooper
1999; see Section 3.3.5) have also been suggested. Paetzold et al. (2009) suggested that in
multixenobiotic-resistant killifish ( F. heteroclitus ) populations liver coordinated up-regu-
lation of phase I and II enzymes associated with ABC transporters (ABCC2 and ABCG2)
may confer contaminant resistance to organisms. Moreover, the resistance and the altered
CYP1 phenotype observed in a population of chronically PAH-exposed killifish may be
explained by blocking AhR2 expression, leading to protection of organisms from the tera-
togenicity of PAH in exposed embryos (Wills et al. 2010).
Nutrient resources or the quality of food resources can have consequences on the total
energetic budget of organisms with possible effects on metabolization capacities. A 3- to
7-week-long fasting period in rainbow trout Oncorhynchus mykiss led to a modification of