Page 395 - The Toxicology of Fishes

Liver Toxicity 375

which have demonstrated early cytological changes in fish liver and damage from exposure to a wide
range of pollutants, including PCBs (Klaunig et al., 1979; Köhler, 1989), 3-methylcholanthrene (Schoor
and Couch, 1979) diethylnitrosamine (Couch, 1993, Hinton et al., 1988), 4-nitrophenol and 4-chloro-
aniline (Braunbeck et al., 1989, 1990a), BaP (Lemaire et al., 1992), and linuron (Oulmi et al., 1995).
With the recent advent of digitized imaging for electron microscopy and computer software for stereo-
logical analysis, quantification of cytological changes on two-dimensional ultrathin sections is no longer
a time-consuming process. Results of morphometry provide more useful quantitative data on cytological
changes in response to contaminants.
Certain persistent environmental pollutants (e.g., PAHs, aromatic amines, nitroso-compounds, azo
compounds) were shown to be potent hepatocarcinogens in fish (Moore and Myers, 1994). Hepatic
carcinogenesis is particularly useful to indicate chronic toxicity in fish. Other hepatic lesions, such as
FCA, MH, and hepatocellular nuclear pleomorphism (NP), were considered as early pathological stages
in the formation of liver neoplasms (Hinton and Lauren, 1990; Hinton et al., 1992, 2001; Myers et al.,
1987; Simpson and Hutchinson 1992); however, the etiology of preneoplastic liver lesions in relation to
pollutant exposure remains largely unknown. The synergistic and antagonistic interactions of chemicals
in water and sediment make it difficult to study cause-and-effect relationships. Moreover, it should be
noted that liver tumors and histopathology are manifestations of chronic toxicity associated with pro-
longed latency periods. These lesions have great overall significance, especially when prevalences are
used to suggest an epizootic at a localized site; however, their presence does not tell us about recent
alterations in environmental quality. For many fish, migration is an annual event that makes it difficult
to assess temporal and spatial aspects of exposure. As we shall see below, the use of biochemical and
cytological endpoints may have more to offer especially when applied to younger fish for which habitats
are known.
The correlation of biochemical and morphological (ultrastructural) changes is important. Not only do
organelles and inclusion bodies show changes in hepatocytes of organisms residing at contaminated sites
or exposed to usually single pollutants in controlled laboratory studies, but also a correlation exists
between these alterations and certain biochemical measures (Grinwis et al., 2000).
Although most of the earlier biomarker studies concentrated on linking individual biochemical and
morphological responses to exposure and effects of pollutants, only a few studies related biochemical
endpoints (e.g., hepatic EROD/MFO activities) to quantitative ultrastructural changes in livers of fish
upon exposure to toxicants (Chui et al., 1985; Hugla and Thome, 1999; Klaunig et al., 1979; Kontir et
al., 1984; Schoor and Couch, 1979). If hepatic EROD activity can be related to quantitative hepatocy-
tological damages, then the measurement of EROD activity would then indicate not only exposure but
also adverse biological effects. Furthermore, the use of hepatic EROD as a biomarker would be more
useful if linked to important biological processes. Some of the associated hepatocytological changes in
fish may also serve as potential effect biomarkers for the early detection of exposure to environmental
pollutants.
Recent studies sought to establish the relationship between quantitative hepatocytological changes
and EROD activities in Solea ovata and Epinephelus areolatus exposed to PAHs and to provide
important information regarding the use of such a relationship. Immature individuals of the demersal
fish S. ovata were exposed intraperitoneally to benzo(a)pyrene, and quantitative cytological alterations
were quantified (Au et al., 1999). A dose–response relationship was shown between exposure to BaP
and changes in hepatic EROD activities. A Spearman rank correlation analysis revealed correlation
between EROD activities and number or absolute volume of peroxisomes as well as lipofuscin granules
in hepatocytes.
In a subsequent field study, chemical analysis of sediment from a dump site showed high levels of
PAHs and PCBs (Au and Wu, 2001). Sexually immature fish from this site exhibited significantly higher
EROD activity compared with counterparts from a reference site. In this case, a significant correlation
was found only between EROD activity and volume density (Vv) of hepatic lipopigments. When this
correlation was tested in juveniles of another species, the areolated grouper (Epinephelus areolatus), it
was shown to exist (Au et al., 2004). These findings seem reasonable given the fact that lipopigment is
a product of lipid peroxidation and could signify oxidative stress in cells. Excessive intracellular lipo-
pigment accumulation could interfere with vital cellular functions and decrease survival of affected cells