History of Biomarkers - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 20

B[ a ]P oxidation), proved to be a biomarker of exposure to PAHs (Akcha et al. 2000). In
some cases, the biotransformation can induce processes of carcinogenesis, mutagenesis,
and toxicity. For example, B[ a ]P is metabolized (7,8-epoxidation, then 9,10-epoxidation) into
a mutagenic compound, the (+)-anti-B[ a ] P, 7 R ,8 S -diol-9S, 10 R -epoxide, which is able to bind
in a covalent manner to DNA and leads to the formation of adducts (Vermeulen 1996;
Akcha et al. 1999).
2.3.2 Fluorescent Aromatic Compounds in Fish Bile
The exposure of fish to crude oils containing PAHs causes an increase in FACs in the bile
(Aas et al. 2000; Gagnon and Holdway 2000). When the exposure takes place through the
food chain, PAHs are absorbed, transported to the liver where they are converted into
more water-soluble metabolites, and are excreted in the bile (Varanasi et al. 1995; Lee 2002).
Laboratory studies show that the depuration period after exposure lasts several weeks,
suggesting that an increased concentration in FACs in bile reflects a relatively recent expo-
sure to PAHs (Huggett et al. 2003). Crude oils with PAHs with two to three rings are
very different in their FACs in bile compared to pyrogenic hydrocarbons with four to six
nonsubstituted rings. This is why it is difficult to link the induction of CYP1A and the
increased concentrations of FACs in the bile to a specific source of PAHs. However, the
concentration of FACs in the bile constitutes a fast and practical tool that clearly shows
the extent of exposure to PAHs in the framework of biomonitoring: they thus constitute a
“relevant” biomarker (Lehtonen et al. 2006).
2.3.3 Phase II Enzymes
Conjugation intervenes in the metabolism of xenobiotics, either following the reactions
of oxidation (phase I), or directly on molecules bearing hydroxylated, thiol, or carbox-
ylic groups. These reactions, also called phase II reactions, are catalyzed by membrane or
cytosolic enzymes functioning with various cofactors (glutathione, sulfates, glucuronic
acid). The enzymes responsible for these conjugations are glutathione S -transferases
(GSTs), UDP-glucuronosyl-transferases (UDPGTs), and sulfotransferases. The activities of
phase II enzymes are lower in fish (Gregus et al. 1983) than in higher vertebrates. In the
fish Platycephalus bassensis , exposed to a mixture of PCBs, UDPGT activities significantly
increase as do cytochrome P450 enzymes (Brumley et al. 1995), whereas the exposure of
trout Salmo gairdneri to various polychlorinated phenols causes a reduction in UDPGT
activities (Castren and Oikari 1987). GSTs are enzymes whose activity is used as a bio-
marker of organic substance exposure, especially in mollusks, where EROD activity is not
routinely measured (Cajaraville et al. 2000). GSTs represent an important enzyme family
whose function is to combine reduced glutathione (GSH) with electrophilic compounds
by formation of a thioether bridge (Foureman 1989). The products are then metabolized in
mercapturates that are excreted in the bile or the urine. GST activity increases in exposed
organisms according to the xenobiotic concentration in the medium.
In fish, contradictory results have been reported (Van Veld and Lee 1988). However, sev-
eral authors have shown that glutathione transferases are involved in the detoxification of
many chemical pollutants: hydrocarbons, organochlorine insecticides, and PCBs (Monod
et al. 1988; George 1994). In mollusks, GST activity is used with more success than in fish as
a biomarker of exposure to these substances (in the marine environment: Fitzpatrick et al.
1997; Hoarau et al. 2001; and for freshwater bodies: Boryslawskyj et al. 1988; Robillard et al.
2003). GSTs play an additional role in the detoxification process, being used as transporting