History of Biomarkers - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 25

2.3.7 Heat Shock Proteins
Heat shock proteins (Hsps) are ubiquitous proteins, widely conserved throughout the evo-
lution of eukaryotes. They are named according to their apparent molecular weight using
sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) (Schlesinger et al.
1982; Atkinson and Walden 1985; Moromoto et al. 1990), in particular HSP 40, 60, 70, and
90. The Hsp of lower molecular weight (8 kDa) is called ubiquitine. Cellular response to
stress was reported for the first time by Ritossa (1962), who observed Hsp induction in the
case of a very significant temperature rise, hence their name. Hsps are now called stress
proteins because they are overexpressed in response to a certain number of physical and
chemical factors including anoxia (Spector et al. 1986), salinity stress (Ramagopal 1987),
metals (Hammond et al. 1982; Caltabiano et al. 1986), xenobiotics (Sanders 1990), and oxida-
tive stress in general (Freeman et al. 1999).
Some Hsps are constitutive; for example, Hsp 60 and 70 are involved in the homeosta-
sis of proteins under normal conditions while playing a protective and repairing role in
the event of environmental stresses (Rothman 1989; Welch 1990). Stress proteins have a
capacity to repair proteins harmed by stress or to eliminate them when they cannot be
repaired any further. They work as molecular “chaperones,” accompanying, monitoring,
and protecting other proteins (Frydman 2001; Hartl and Hayer-Hartl 2002). They can act in
the posttranslational spatial configuration of proteins and intervene in the transfer of pro-
teins to the mitochondria, and in the induction and control of apoptosis (Craig et al. 1994;
Creagh et al. 2000). Stress proteins and the genes that code for them have been sequenced
in many organisms. Because of their sensitivity to environmental pollutants such as met-
als, several researchers quantified Hsp 60 and 70 in the bivalve sentinel species M. edulis
(Sanders et al. 1991, 1994; Brown et al. 1995; Werner and Hinton 1999). Hsp levels reflect the
physiological state of the animal.
Another group of proteins, that of glucose-regulated proteins (GPRs), has been discov-
ered (Welch 1990; Hightower 1993). GPRs have very strong analogies with Hsps.
2.4 Damage Biomarkers
2.4.1 AChE Activity
The inhibition of cholinesterase activity can be regarded as one of the first biomarkers
proposed in environmental monitoring studies, since its development in human medi-
cine as an index of exposure to neurotoxins, in particular organophosphates from war
gases, goes back several decades. For many authors, the measurement of AChE activity
is the best marker of contamination by organophosphorous pesticides and carbamates
(Holland et al. 1967; Coppage and Braidech 1976; Galgani and Bocquené 1989; Day and
Scott 1990). Cholinesterases are enzymes that catalyze the hydrolysis of esters of choline
more quickly than other esters. In vertebrates, two cholinesterases have been identified:
AChE (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8, BuChE). AChE is inhibited by
excess of substrate but BuChE is not. In spite of the limited number of genes apparently
involved, ChEs present a large variety of molecular forms including globular (monomer,
dimer, tetramer) and asymmetric forms (from 4 to 12 subunits with a collagen tail). At least
eight forms of AChEs are found with a different oligomeric organization, solubility, and