History of Biomarkers - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 17

organism or its products (urine, feces, hair, feathers, etc.), indicating a change compared
to the normal state and which cannot be detected in a healthy organism. The term bio-
indicator should be restricted to an organism providing information on the environmental
conditions of its habitat by its presence or its absence or its behavior. The concept of specific
biomarkers (responding to metal pollutants, or to organics or to any defined pollutant)
led to the definition of damage and defense biomarkers put forward by De Lafontaine et
al. (2000). From the 1970s, great developments in biochemistry and molecular toxicology
made it possible to progress quickly in our knowledge of the mechanisms of the toxicity of
xenobiotics, mainly with mammalian models. Thereafter, significant specific biochemical
effects were highlighted in species exposed to some contaminants, particularly in birds,
fish, and mollusks considered as being of ecological interest. The majority of the examples
in this chapter concern the aquatic environment, particularly the marine environment,
which is the final receptacle of chemical pollutants.
Well-known biomarkers, which have been recognized in laboratory and environmental
studies, have been called “core biomarkers” (Pampanin et al. 2006). Such core biomarkers
include the stability of the lysosomal membrane (measured by the neutral red retention
time), inhibition of acetylcholinesterase (AChE) activity, metallothionein (MT) concentra-
tion, ethoxyresorufin O -deethylase (EROD), and the fluorescent metabolites of the bile
[fluorescent aromatic compound (FACs)].
2.3 Defense Biomarkers
2.3.1 Ethoxyresorufin O -Deethylase
Payne and Penrose (1975) were among the first to report elevated cytochrome P450-depen-
dent monoxygenase activity in fish from petroleum-contaminated areas. The first bio-
marker that gained international recognition was consequently the enzymatic activity of
EROD, an isoenzyme cytochrome P4501A termed as CYP1A. EROD belongs to the group of
CYP enzymes that are the main enzymes responsible for the metabolism of certain endog-
enous compounds (hormonal and membrane steroids, biliary acids, vitamin D, fatty acids,
prostaglandins, and pheromones) and nonpolar xenobiotics, including the metabolism of
many environmental toxic chemicals and carcinogens (Nebert 1994). CYPs are enzymes
referred to as mixed function oxidases (MFOs) (Di Giulio et al. 1995). Klingenberg (1958)
and Garfinkel (1958) described successively a pigment present in the microsomal fraction
from mammalian liver, which, in its reduced form, fixes carbon monoxide and absorbs at
450 nm. The denomination “P450 cytochrome” was proposed by Omura and Sato (1964),
who showed that this pigment is a hemoprotein with molecular mass ranging from 43
to 60 kDa. For the first time, Estabrook et al. (1963) demonstrated the involvement of this
hemoprotein in a reaction of monoxidation: the hydroxylation of 17α-hydroxyprogesterone.
CYPs are found to be associated with membranes in the endoplasmic reticulum or mito-
chondria of different tissues: liver, lung, kidney, intestine, etc. (Stegeman and Hahn 1994).
They catalyze the oxidation of a substrate RH (an organic compound that becomes hydrox-
ylated) by inserting one atom of molecular oxygen, whereas the second atom is reduced to
water following the equation:
RH + O 2 + NADPH + H + → ROH + NADP + + H 2 O