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fish hepatocytes frequently involve destabilizing changes in the lysosomal membrane and
the induction of autophagy (Moore and Halton 1973, 1977; Moore 1976, 1980, 1985, 1990,
2002, 2004; Moore et al. 1978, 1979, 1984, 1985, 1986, 1987, 1996, 2006a, b, c, 2007; Moore and
Clarke 1982; Axiak et al. 1988; Köhler et al. 1992, 2002; Cajaraville et al. 1995a, b; Da Ros et
al. 2000; Marigómez and Baybay-Villacorta 2003; Marigómez et al. 2005a, b).
Damaged cellular constituents and redundant products are removed by lysosomal
autophagy, but this is also critically involved in the continuous basal turnover of intra-
cellular components (Hawkins and Day 1996; Ryazanov and Nefsky 2002; Tavernarakis
and Driscoll 2002; Cuervo 2004; Levine 2005). Autophagy is up-regulated in times of
stress or physiological change by breaking down longer-lived proteins and organelles,
and recycling the products into protein synthesis and energy-production pathways: the
process allows cells to be temporarily self-sustaining during periods when nutrients are
restricted (Bergamini et al. 2003; Cuervo 2004; Levine 2005). New evidence also indicates
that autophagy may have a protective role in the context of oxidative stress (Bergamini
et al. 2003; Cuervo 2004; Moore et al. 2006b, c, 2007; Moore 2008). Nutrient deprivation-
induced autophagy in mollusks appears to confer some resistance to the toxicity of both
reactive oxygen species (ROS)-generating PAHs and copper (Viarengo et al. 1987; Moore
2004; Moore et al. 2006a, b, c). Normal tidal fluctuations in salinity, food and oxygen, how-
ever, do not induce a stress syndrome (Bayne et al. 1978, 1979; Moore et al. 1979, 1982, 1987;
Moore 1980; Widdows et al. 1981, 1982).
5.4.2 Accumulation of Pollutant Chemicals in Lysosomes and Oxidative Stress
As mentioned previously, lysosomes are noted for their ability to accumulate a very wide
range of noxious substances including many metals and organic xenobiotics (Figure 5.3).
There is also a substantial body of literature documenting the harmful effects of copper and
PAHs on both blue and green mussels, with much of this involving responses of the lyso-
somal-vacuolar system in the cells of the digestive gland (Viarengo 1989; Krishnakumar
et al. 1990, 1994; Moore 1990; Viarengo and Nott 1993). The processes involved in the lyso-
somal sequestration of metal ions have been described by Viarengo and Nott (1993).
Autophagy of cellular components is associated with pollutant-induced lysosomal reac-
tions and includes autophagic sequestration of copper-induced metallothionein (Viarengo
et al. 1985; Viarengo and Nott 1993), microautophagy induced by phenanthrene, and phos-
pholipidosis induced by anthracene and phenanthrene (Lüllmann-Rauch 1979; Nott and
Moore 1987). The internal environment of secondary lysosomes is acidic, and this contrib-
utes to the ionic trapping of PAHs and heterocyclic compounds including neutral red and
acridine orange (Figure 5.3; Allison and Young 1969; Lüllmann-Rauch 1979; Rashid et al.
1991; Lowe et al. 1992).
Intracellular lysosomes are also a site for generation of ROS, including oxyradicals, as
demonstrated by Winston et al. (1991) in isolated digestive cells of mussels (Brunk and
Terman 2002). Within the lysosomes of normal unstressed digestive gland cells, ROS are
probably generated by transition metal ions, such as iron and copper, which accumulate in
lysosomes from exogenous sources, such as algal and microbial food, and also by autoph-
agic degradation of endogenous metalloproteins (Brunk and Terman 2002; Moore et al.
2006a, 2007). There is also increasing evidence that endocytosed nanoparticles may con-
tribute to the generation of ROS (Howard 2004; Klaine et al. 2008; Bottero et al. 2011; Kroll
et al. 2011). Although digestive cell lysosomes spontaneously generate oxyradicals such as
superoxide, they also contain a superoxide dismutase, which may protect the lysosomal
membrane from excessive oxidative damage (Winston et al. 1991; Livingstone et al. 1992).
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