Origin of Energy Metabolism Impairments - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 291

exposure. The effect continued after the chromium had been withdrawn from perfusion
(Bogé et al. 1988).
In addition to direct action on the hydrolytic properties of enzymes, pollutants may
also exert indirect action on enzyme activity with toxic effects on their synthesis and/
or secretion mechanisms. This intracellular toxicity may be especially observed in the
digestive system of animals in which morphological changes (e.g., atrophy and necrosis
of the digestive tissue) have been recorded during exposure to organic or metal pol-
lutants (Auffret 1988; Lowe and Clarke 1989; Cajaraville et al. 1990). In addition to their
implication in digestive processes, certain digestive tissues of vertebrates and inverte-
brates are also involved in the detoxification of pollutants accumulated at the level of
the digestive system or the tegumentary and respiratory systems (and then transferred
by the systemic route) (Najle et al. 2000). The digestive gland of bivalves is particularly
implicated in the detoxification and sequestration of metals accumulated and stored in
the lysosomes of the digestive cells (Janssen and Ertelt-Janssen 1983; Ballan-Dufrançais
et al. 1985). However, this sequestration of metal is not always effective, so that some
of the ions absorbed may remain biologically active within the cells and disturb the
synthesis mechanisms and the secretion of enzymes, or their intracellular activity. For
example, Zambare and Mahajan (2001) observed in the freshwater clam Corbicula stria-
tella a decrease in the quantity of enzymes secreted by the digestive gland cells in clams
exposed to copper or mercury. Likewise, Le Bihan et al. (2004), working on isolated diges-
tive cells of cuttlefish, Sepia officinalis, , recorded inhibition of protease secretions after
exposure to silver. Furthermore, these researchers recorded induction of the intracellular
and extracellular activities of cathepsin during exposure of these cells to a low concen-
tration of cadmium and a repression of these same activities during exposure to a Cd
concentration 1000 times higher.
In addition to exposures carried out at infra-individual levels of biological organization
(i.e., on cells, tissues, organs, or isolated digestive fluids), exposures carried out on whole
organisms have also shown modulation of digestive enzyme activities. For instance, Teo et
al. (1990), Sabapathy and Teo (1992), and Yan et al. (1996) observed in green mussels, Perna
viridis , a repression of amylolytic activity (digestive gland) in the presence of cadmium,
copper, mercury, nickel, lead, or zinc. In addition to invertebrates, inhibition of enzymatic
activities (amylase, proteases, lipases) has also been recorded in various species of fish
exposed in their environment to mercury (Sastry and Gupta 1980; Gupta and Sastry 1981;
Rana and Sharma 1982), cadmium (Golovanova et al. 1994), or lead (Teo et al. 1990; Yan
et al. 1996). Finally, exposure of carp ( C. carpio ) to two doses (0.025 and 0.05 ppm) of arse-
nic, mercury, nickel, and chromium, individually or as a mixture, showed a decrease in
all digestive enzymatic activities (proteases, amylase, lipases) regardless of the treatment
used (Sarita and Jain 2009). Li et al. (2007) observed modulations of different digestive
enzyme activity in Oreochromis sp. (Red Tilapia) during in vitro or in vivo exposure to cop-
per, iron, and zinc. These differences may be due to (1) a dilution of ingested metal ele-
ments, by gastric liquid during intestinal transit leading to concentrations of metal too low
to induce effects on digestive enzymes as opposed to exposure in vitro or (2) a secretion
of digestive enzymes in close relationship with the alimentary intake of metal elements.
Exposure to raised levels of metals may improve the nutritional condition of the organism
and change the physicochemical characteristics of the intestinal membrane and thus affect
digestive enzyme activities.
Examples of the inhibition of digestive enzyme activities have also been highlighted
during exposures of organisms to organic contaminants (Table 11.1). In Daphnia magna ,
inhibitions of β-galactosidase and esterase activities have been observed upon exposure