Page 201 - The Toxicology of Fishes

Biotransformation in Fishes 181

TABLE 4.6
Microsomal Epoxide Hydrolase Activity with Styrene Oxide in Representative Fish Species
Species Organ Activity a Refs.

Channel catfish (Ictalurus punctatus) Liver 2.62 ± 1.0 James et al. (1997); Willett et al.
Intestine 3.78 ± 1.95 (2000)
Liver 1.03 ± 0.06
Brown bullhead (Ameiurus nebulosus) Liver 0.85 ± 0.07 Willett et al. (2000)
Trout (Oncorhynchus mykiss) Liver 1.2 Perdudurand and Cravedi (1989)
Sturgeon (Acipenser baeri) Liver 2.77 Perdudurand and Cravedi (1989)
Kidney 1.37
Gill 1.37
Sheepshead (Archosargus probatocephalus) Liver 5.6 ± 2.4 James et al. (1974)
Kidney 0.05
Intestine 0.74 ± 0.33
Gill 0.16
Ovary 0.08
Testis 0.52
Southern flounder (Paralichthyes lethostigma) Liver 2.0 ± 0.7 James et al. (1974)
Kidney 1.33 ± 0.11
Winter flounder (Pseudopleuronectes americanus) Liver 27.9 ± 15.9 James et al. (1974)
Kidney 8.25 ± 6.11
Northern pike (Esox lucius) Liver 4 Balk et al. (1980)
English sole (Parophrys vetulus) Liver 2.8 ± 0.2 Collier et al. (1986)
Scup (Stenotomus chrysops) Liver 2.6–9 Stegeman and James (1985)
Dogfish shark (Squalus acanthias) Liver 6.3 ± 2.1 James et al. (1974)
Kidney 12.6 ± 3.9
Atlantic stingray (Dasyatis sabina) Liver 6.2 ± 1.8 James et al. (1974)
Kidney 3.1 ± 1.8
Large skate (Raja ocellata) Liver 1.8 ± 0.2 James et al. (1974)
Kidney 0.55
Small skate (Raja erinacea) Liver 0.46 ± 0.4 James et al. (1974)
Kidney 0.16
–1
–1
a In units of nmol · min · mg protein .
In mammalian species, antibodies have been used to quantitate microsomal epoxide hydrolase enzyme
in liver subcellular fractions (Bend et al., 1978). Such studies have not been conducted in fish. The cross-
reactivity of fish epoxide hydrolases with mammalian microsomal or cytosolic epoxide hydrolases is
not known, and no fish epoxide hydrolase protein or gene has yet been reported.
Enzyme Specificity, Regulation, and Inhibition
The first studies of epoxide hydrolase activity in fish were carried out with hepatic, branchial, gonadal,
and intestinal microsomes from marine fish common to coastal Maine or Florida (Bend et al., 1978;
Gill et al., 1982; James et al., 1974, 1976; Westkaemper and Hanzlik, 1981). These studies showed that,
although epoxides were readily hydrolyzed in liver of most fish species, considerable variability exists
between individuals as well as between species in the measured epoxide hydrolase activity. Gill, kidney,
intestine, and gonads generally had lower epoxide hydrolase activity than liver. Freshwater fish also had
readily measured epoxide hydrolase activity in liver and other organs (Parker et al., 1993; Perdudurand
and Cravedi, 1989; Stott and Sinnhuber, 1978; Walker et al., 1978; Willett et al., 2000). Table 4.6 shows
activities found in some representative marine and freshwater species in liver and other organs.
The importance of epoxide hydrolase activity in the biotransformation of polycyclic aromatic hydrocar-
bons was highlighted in a study of the in vitro metabolism of benzo(a)pyrene in scup hepatic microsomes
(Stegeman and James, 1985). The ratio of BaP-9,10-dihydrodiol to 9-hydroxy-BaP was found to correlate
well with the epoxide hydrolase activity of hepatic microsomes. Individual fish with low epoxide hydrolase