Bioaccumulation and speciation of selenium in fish and insects collected from a mountaintop removal coal mining-impacted stream in West Virginia

A major contaminant of concern for mountaintop removal/valley fill (MTR/VF) coal mining is selenium (Se), an essential micronutrient that can be toxic to fish. Creek chubs (Semotilus atromaculatus), green sunfish (Lepomis cyanellus), and composite insect samples were collected in March-July, 2011-2013 at two sites within the Mud River, West Virginia. One site (MR7) receives MTR/VF coal mining effluent, while the reference site (LFMR) does not. MR7 water had significantly higher concentrations of soluble Se (p < 0.01) and conductivity (p < 0.005) compared to LFMR. MR7 whole insects contained significantly higher concentrations of Se compared to LFMR insects (p < 0.001). MR7 creek chubs had significantly higher Se in fillets, liver, and ovary tissues compared to LFMR samples (p < 0.0001, p < 0.0001, and p < 0.02, respectively). MR7 green sunfish fillets contained significantly higher Se (p < 0.0001). Histological examination showed LFMR creek chub gills contained a typical amount of parasitic infestations; however MR7 gills contained minimal to no visible parasites. X-ray absorption spectroscopic analyses revealed that MR7 whole insects and creek chub tissues primarily contained organic Se and selenite. These two species of Mud River fish were shown to specifically accumulate Se differently in tissues compartments. Tissue-specific concentrations of Se may be useful in determining potential reproductive consequences of Se exposure in wild fish populations.

Immunohistochemical characterization of the hepatic progenitor cell compartment in medaka (Oryzias latipes) following hepatic injury

Laboratory fish species are used increasingly in biomedical research and are considered robust models for the study of regenerative processes. Studies investigating the response of the fish liver to injury have demonstrated the presence of a ductular reaction and oval-like cells in injured and regenerating liver. To date, however, it is unclear if this cell population is the piscine equivalent of oval cells (OCs) or intermediate hepatobiliary cells (IHBCs) identified in rodents and man, respectively. The present study defines the process of OC differentiation in fish liver using histopathology, immunohistochemistry and transmission electron microscopy. To generate OC proliferation in Japanese medaka (Oryzias latipes), hepatic injury was induced by exposure of adult fish to either microcystin LR or dimethylnitrosamine. A transgenic strain of medaka expressing a red fluorescent protein (RFP) exclusively in hepatocytes was used. The morphological response to injury was characterized by a ductular reaction comprised of cytokeratin (CK) AE1/AE3(+) OCs progressing to IHBCs variably positive for CK and RFP and finally mature RFP(+) hepatocytes and CK(+) cholangiocytes. These observations support a bipotential differentiation pathway of fish OCs towards hepatocytes and cholangiocytes. Ultrastructural morphology confirmed the presence of OCs and differentiation towards hepatocytes. These results demonstrated clear similarities between patterns of reaction to injury in fish and mammalian livers. They also confirm the presence of, and support the putative bipotential lineage capabilities of, the fish OC.

A simple osmium post-fixation paraffin-embedment technique to identify lipid accumulation in fish liver using medaka (Oryziaslatipes) eggs and eleutheroembryos as lipid rich models

Hepatic lipidosis is a non-specific biomarker of effect from pollution exposure in fish. Fatty liver is often misdiagnosed or overlooked in histological assessments due to the decreasing application of specific fat procedures and stains. For example, ethanol dehydration in standard paraffin processing removes lipids, leaving vacuoles of which the precise nature is unknown. Lipids can be identified using osmium post-fixation in semi-thin resin sections or transmission electron microscopy. However, both are expensive and technically demanding procedures, often not available for routine environmental risk assessment and monitoring programs. The current emphasis to reduce and refine animal toxicity testing, requires refinement of the suite of histopathological techniques currently available to maximize information gained from using fish for toxicity testing and as bio-indicators of environmental quality. This investigation has successfully modified an osmium post-fixation technique to conserve lipids in paraffin-embedded tissues using medaka (Oryzias latipes) eleutheroembryos and eggs (embryos) as lipid rich models.

Nightmares among Cambodian refugees: the breaching of concentric ontological security

This article explores the nightmares of Cambodian refugees in a cultural context, and the role of nightmares in the trauma ontology of this population, including their role in generating post-traumatic stress disorder (PTSD). Among Cambodian refugees attending a psychiatric clinic, we found that having a nightmare was strongly associated with having PTSD (chi(2) = 61.7, P < 0.001, odds ratio = 126); that nightmares caused much distress upon awakening, including panic attacks, fear of bodily dysfunction, flashbacks and difficulty returning to sleep; that nightmare content was frequently related to traumatic events; that nightmares resulted in a decrease in the sense of "concentric ontology security" (i.e., in an increased sense of physical and spiritual vulnerability in a culture that conceives of the self in terms of concentric, protective layers), including fears of being attacked by ghosts; and that nightmares frequently led to the performance of specific practices and rituals aiming to extrude and repel attacking forces and to create "protective layers." Cases are presented to illustrate these findings. The Discussion considers some treatment implications of the study.

Embryo toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the wood duck (Aix sponsa)

We examined the sensitivity of the wood duck (Aix sponsa) embryo to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by injecting the toxicant into their eggs. Six groups of wood duck eggs (n = 35 to 211 per trial) were injected with 0 to 4600 pg TCDD/g egg between 2003 and 2005. Injections were made into yolk prior to incubation, and eggs were subsequently incubated and assessed weekly for mortality. Significant TCDD-induced mortality was not observed through day 25 (90% of incubation). Liver, heart, eye, and brain histology were generally unremarkable. Hepatic ethoxyresorufin-O-deethylase activity, a biomarker of dioxin-like compound exposure, was induced by 12-fold in the 4600 pg/g treatment relative to controls. The median lethal dose for chicken (Gallus domesticus) eggs we dosed identically to wood duck eggs was about 100 pg/g, similar to other assessments of chickens. Among dioxin-like compound embryo lethality data for 15 avian genera, the wood duck 4600 pg/g no-observed-effect level ranks near the middle. Because no higher doses were tested, wood ducks may be like other waterfowl (order Anseriformes), which are comparatively tolerant to embryo mortality from polychlorinated dibenzo-p-dioxins and dibenzofurans when exposed by egg injection.

Biochemical and toxicopathic biomarkers assessed in smallmouth bass recovered from a polychlorinated biphenyl-contaminated river

Smallmouth bass (Micropterus dolomieu) were collected to quantify the nature and prevalence of biomarker responses, including biochemical indices, toxicopathic lesions and general health indices, among fish collected from polychlorinated biphenyl (PCB)-contaminated and nearby uncontaminated reaches of the Kalamazoo River, Michigan, USA. Blood and tissue samples (gill, liver, spleen, head kidney, trunk kidney, thyroid and gonads) were collected and preserved at necropsy for biochemical and histological analyses. The body condition factor and liver somatic index were significantly lower in fish collected from the downstream, contaminated site. Plasma vitellogenin was not detected in male fish collected from either site. Liver ethoxyresorufin-O-deethylase activity and liver and spleen superoxide dismutase activity were significantly depressed in fish collected from the downstream site. Significant toxicopathic lesions such as glycogen depletion, enhanced macrophage aggregates, hepatic foci of cellular alteration (i.e. preneoplastic lesions) and neoplasia were also detected in the liver of fish collected from the downstream site. This study indicates that many of the biochemical and histopathological biomarker responses were associated with liver and body tissue PCB concentrations. Taken together, the biomarkers of exposure and effect strongly suggest that fish within the downstream site are adversely affected by PCBs and other chemical stressors.

Stage-specific toxicity of cypermethrin to medaka (Oryzias latipes) eggs and embryos using a refined methodology for an in vitro fertilization bioassay

Using original artificial fertilization methods with medaka (Oryzias latipes), the effects of exposure to cypermethrin on gametes, fertilization, and embryonic development were investigated. The relative sensitivity was studied with 96-hour duration, 24-hour renewal exposures to six nominal concentrations of cypermethrin ranging from 3.1 100.0 microg cypermethrin/L. Tests were initiated at different developmental stages: unfertilized egg (stage 0), late morula (stage 9), eminence of swim bladder (stage 29), and maximum flexion of the atrioventricular region (stage 34). Cypermethrin did not affect the fertilization process. Predominant sublethal effects in embryos included transient visceral edemas intimately associated to the gall bladder with subsequent pericardial edemas. Other sublethal effects were observed in surviving larvae and included spastic movements with or without ability to respond to stimulus (>/=6.3 microg cypermethrin/L), spinal curvatures, and delayed or absence of swim bladder inflation (>/=12.5 microg cypermethrin/L). The exposure of the gametes (stage 0) or animals during earlier embryonic development (stages 9 or 29) was not a critical window for cypermethrin exposure. Although the incidence of edemas in embryos occurred mainly during exposure of these early developmental stages, embryo and larva lethality and the incidence of transient sublethal effects in hatchlings showed that the later exposure window (stage 34) was the most sensitive. The stage 34 group involved advanced organogenetic stages in which the chorion partially degraded before hatching. Our studies reinforced the idea that a combination of morphologic and functional impairment evaluation is a more sensitive response to developmental toxicants than morphologic defects alone.

Carcinogen induced unscheduled DNA synthesis in mouse hepatocytes

Mouse primary liver cell cultures were examined for evidence of unscheduled DNA synthesis (UDS) following treatment with the carcinogens; dimethylnitrosamine (DMNA), diethylnitrosamine (DENA), 2-acetylaminofluorene (2-AAF), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), benzo(a)pyrene (BP), dimethylbenzanthracene (DMBA), 1,1,-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), safrole, diethylstilbestrol (DES), aflatoxin B1 (AFB1), and dieldrin and the noncarcinogens; dimethylformamide (DMF), fluorene, and pyrene. Mouse hepatocyte cultures were simultaneously treated with three concentrations of each compound and 3H-thymidine. After 24 hrs, cells were fixed and processed for autoradiography. 3H-thymidine incorporation in both experimental and control cell nuclei, as evidenced by autoradiographic grains, was quantitated microscopically. DMNA, DENA, 2-AAF, MNNG, BP, AFB1 and DMBA significantly increased UDS over untreated cells at all concentrations studied. DDT, DMF, fluorene, pyrene, safrole, DES, and dieldrin were negative for UDS in all concentrations examined. DMNA, 2-AAF and MNNG were also studied for UDS induction in 2 hr old, 1 day old and 4 day old cultures. A progressive decrease in UDS with increased time after plating was found in DMNA and 2-AAF treated cultures. After 4 days DMNA and 2-AAF induced UDS only at the highest concentrations examined (10(-3) M and 10(-4) M respectively). MNNG induced UDS at all time periods and concentrations sampled. An attempt to enhance the sensitivity of the UDS assay by inducing the mixed function oxidative enzyme activity in the hepatocytes with phenobarbital administered in vivo resulted in no statistically significant increase in UDS with DMNA, 2-AAF, MNNG, DDT, and dieldrin when compared with cells from non-induced animals.

Increasing uptake and bioactivation with development positively modulate diazinon toxicity in early life stage medaka (Oryzias latipes)

Diazinon, an organophosphate pesticide, becomes biotransformed to a more potent oxon metabolite that inhibits acetylcholinesterase (AChE). Early life stages (els) of medaka, Oryzias latipes, were used to determine how development of this teleost affects sensitivity to diazinon. With developmental progression, from day of fertilization to 7-day-old larvae, we found that the 96-h LC50 and AChE IC50 values decreased, indicating greater host sensitivity to diazinon upon continued development. We then examined changes in AChE activity, its inhibition by the active metabolite diazoxon, and uptake and bioactivation of the compound. AChE activity remained low during much of development but increased rapidly just prior to hatch. In addition, in vitro incubation of tissue homogenates from embryos or larvae showed no differences in the sensitivity of AChE to diazoxon. Uptake studies with 14C-diazinon revealed greater body burdens of 14C as medaka developed. In addition, AChE IC50 values determined by in vivo exposure to diazoxon were greater in larvae than in embryos. Because diazinon is bioactivated by the P450 enzyme system, two P450 inhibitors were used in vivo to explore the role of metabolism in sensitivity. When exposure to diazinon occurred in the presence of increasing amounts of piperonyl butoxide (PBO), AChE inhibition decreased in a dose-response fashion and 2.0 x 10(-5) M PBO alleviated any difference in inhibition between larvae and embryos. However, PBO did not alter total 14C uptake when exposed simultaneously with 14C-diazinon, nor did it affect AChE inhibition using diazoxon. Controls ruled out differential effects of PBO on uptake and inhibition. In addition, a second general P450 inhibitor, 1-aminobenzotriazole, also decreased AChE inhibition. Finally, using exogenous acetylcholinesterase as a trap for the oxon metabolite, larval microsomes displayed greater bioactivation of diazinon than did a microsomal preparation from embryos. Taken together, results suggest that uptake and bioactivation are working to enhance diazinon sensitivity in this developmental model of a teleost fish.

Differential biomarker gene and protein expressions in nonylphenol and estradiol-17beta treated juvenile rainbow trout (Oncorhynchus mykiss)

The time- and dose-dependent transcriptional and translational expression of biomarker genes in nonylphenol (NP) and estradiol-17beta (E(2)) treated juvenile rainbow trout is reported. Fish were exposed to NP (1, 5 and 25 mg/kg) and E(2) (5 mg/kg) and killed at 2, 6, 12, 24, 48 and 72 h after exposure. The estrogen receptor (ER), vitellogenin (Vtg) and eggshell zona radiata protein (Zr-protein) gene expressions were analyzed in total liver RNA using Northern and slot hybridization with specific cDNA probes. Plasma Vtg and Zr-protein levels were evaluated using indirect ELISA. While Zr-protein gene showed an induction only at 24 h post-exposure, the plasma protein levels showed a time-dependent increase in the 25-mg NP treated group. Vtg transcripts showed an apparent time-dependent increase without a concomitant increase in protein levels in the 25-mg NP treated fish. Time-dependent increases in Vtg and Zr-protein gene expressions without the corresponding increases in ER gene transcription was observed in E(2)-treated fish at 2, 6 and 12 h post-exposure. Induction of ER gene transcripts was observed from 24 h and did not change significantly at 48 and 72 h. In the E(2)-treated fish, induction of plasma Vtg levels was observed at 48 and 72 h, while plasma Zr-protein was induced at 24, 48 and 72 h, after exposure. We conclude that the E(2)- and NP-induced Vtg and Zr-protein gene expressions at the early time intervals after exposure are not dependent on increase in the transcriptional activity of the ER gene and that Vtg and Zr-protein gene transcriptions require only basal or minimal ER concentration, in addition to other mechanisms.

Identification, characterization, and ontogeny of a second cytochrome P450 3A gene from the fresh water teleost medaka (Oryzias latipes)

Multiple copies of cytochrome P450 gene family 3 have been identified from numerous mammalian species. Often these genes exhibit differential catalytic activities and gene regulation. To date however, little information is available regarding multiple forms of this gene family in teleost fishes. In this study, a second isozyme of cytochrome P450 3A has been cloned from the teleost fish Oryzias latipes and designated CYP3A40. Screening of a cDNA library to medaka liver resulted in the identification of a full length cDNA clone containing a 2316 base pair (bp) insert with an open reading frame encoding a single peptide of 502 amino acids. Comparisons of the deduced amino acid sequence to other known cytochrome P450 sequences indicate that this gene product is most similar to the CYP3A gene family and shares a 90% identity to CYP3A38 previously identified from medaka liver. Consistent with Northern blot and Western blot analysis, Southern blots of medaka genomic DNA demonstrated the presence of two CYP3A genes. Gene expression studies demonstrated that CYP3A38 and CYP3A40 are differentially regulated according to embryonic development. Northern blot analysis, using a probe to a conserved region of both CYP3A genes, demonstrated the presence of a single CYP3A transcript for early and late embryonic stages and two CYP3A transcripts in larvae and adult liver. Similarly, Western blots show a single faint immunoreactive cytochrome P450 3A protein in microsomes from early and late embryos and two abundant protein bands in microsomes from larval and adult liver. To further examine the transcriptional differences in CYP3A expression, RT-PCR analysis was performed on embryonic stages 11-35, 1- and 14-day-old larvae, and adult liver using primer sets specific for CYP3A38 and CYP3A40. These results demonstrate that CYP3A40 is expressed early in embryonic development and continues throughout adult stages. CYP3A38, however, is tightly regulated during embryonic development and is only expressed post-hatch.

Toxicity of methyl-tert-butyl ether to freshwater organisms

Increased input of the fuel oxygenate methyl-tert-butyl ether (MTBE) into aquatic systems has led to concerns about its effect(s) on aquatic life. As part of a study conducted by University of California scientists for the State of California, the Aquatic Toxicology Laboratory, UC Davis, reviewed existing literature on toxicity of MTBE to freshwater organisms, and new information was generated on chronic, developmental toxicity in fish, and potential toxicity of MTBE to California resident species. Depending on time of exposure and endpoint measured, MTBE is toxic to various aquatic organisms at concentrations of 57-> 1000 mg/l (invertebrates), and 388-2600 mg/l (vertebrates). Developmental effects in medaka (Oryzias latipes) were not observed at concentrations up to 480 mg/l, and all fish hatched and performed feeding and swimming in a normal manner. Bacterial assays proved most sensitive with toxicity to Salmonella typhimurium measured at 7.4 mg/l within 48 h. In microalgae, decreased growth was observed at 2400 and 4800 mg/l within 5 days. MTBE does not appear to bioaccumulate in fish and is rapidly excreted or metabolized. Collectively, the available data suggests that at environmental MTBE exposure levels found in surface waters (< 0.1 mg/l) this compound is likely not acutely toxic to aquatic life. However, more information is needed on chronic and sublethal effects before we can eliminate the possibility of risk to aquatic communities at currently detected concentrations.

Evaluation of fish models of soluble epoxide hydrolase inhibition

Substituted ureas and carbamates are mechanistic inhibitors of the soluble epoxide hydrolase (sEH). We screened a set of chemicals containing these functionalities in larval fathead minnow (Pimphales promelas) and embryo/larval golden medaka (Oryzias latipes) models to evaluate the utility of these systems for investigating sEH inhibition in vivo. Both fathead minnow and medaka sEHs were functionally similar to the tested mammalian orthologs (murine and human) with respect to substrate hydrolysis and inhibitor susceptibility. Low lethality was observed in either larval or embryonic fish exposed to diuron [N-(3,4-dichlorophenyl), N'-dimethyl urea], desmethyl diuron [N-(3,4-dichlorophenyl), N'-methyl urea], or siduron [N-(1-methylcyclohexyl), N'-phenyl urea]. Dose-dependent inhibition of sEH was a sublethal effect of substituted urea exposure with the potency of siduron < desmethyl diuron = diuron, differing from the observed in vitro sEH inhibition potency of siduron > desmethyl diuron > diuron. Further, siduron exposure synergized the toxicity of trans-stilbene oxide in fathead minnows. Medaka embryos exposed to diuron, desmethyl diuron, or siduron displayed dose-dependent delays in hatch, and elevated concentrations of diuron and desmethyl diuron produced developmental toxicity. The dose-dependent toxicity and in vivo sEH inhibition correlated, suggesting a potential, albeit undefined, relationship between these factors. Additionally, the observed inversion of in vitro to in vivo potency suggests that these fish models may provide tools for investigating the in vivo stability of in vitro inhibitors while screening for untoward effects.

Identification and characterization of a cDNA encoding cytochrome P450 3A from the fresh water teleost medaka (Oryzias latipes)

A new member of the CYP3A gene family has been cloned from the teleost fish medaka (Oryzias latipes) by reverse-transcriptase polymerase chain reaction (RT-PCR). Degenerate primers homologous to highly conserved regions of known CYP3A sequences were used for initial RT-PCRs. Individual PCR products were cloned, sequenced, and identified as those belonging to the cytochrome P450 superfamily based on amino acid sequence similarity and the presence of the highly conserved heme-binding region. PCR products were subsequently used as probes to screen a complementary DNA library. A full-length cDNA clone was identified containing a 1758-base-pair (bp) insert with an open reading frame encoding a single peptide of 500 amino acids. Comparisons of the deduced amino acid sequence to other known cytochrome P450 sequences indicate that this gene product is most similar to the CYP3A gene family and has been designated as CYP3A38 by the cytochrome P450 nomenclature committee. Northern blot analysis identified two abundant CYP3A related transcripts in liver of both male and female adults and demonstrated quantitative differences in abundance according to gender. Similarly, Western blot analysis demonstrated the presence of two abundant cytochrome P450 related proteins in liver of both male and female adults. These results suggests that O. latipes contains multiple forms of CYP3A. Heterologous expression of CYP3A38 cDNA in HEK 293 cells produced a single protein that was reactive with anti-scup P450A (CYP3A) polyclonal antibody. Microsomes of HEK 293 cells expressing recombinant CYP3A38 protein actively catalyzed the hydroxylation of testosterone.

Sublethal effects of chromium-VI in the Asian clam (Potamocorbula amurensis)

Previously, we have shown that Asian clams (Potamocorbula amurensis) with highest metallic body burdens have highest prevalence of disease and lowest reproduction. The present study was designed to assess and validate potential sublethal toxicity of hexavalent chromium (Cr-VI) in clams under controlled laboratory exposure. For 7 days, three replicates of clam (n = 10 per replicate) were exposed to aqueous solution containing 0.00, 0.92, 8.40, or 25.6 mg l-1 of Cr-VI at 15 degrees C and 15 g l-1 salinity. Mortality reached 100% in the 25.6 mg l-1 group within 7 days. There was no significant difference in mortality among the control, 0.92, and 8.40 mg l-1 groups. Western blot analyses revealed significantly elevated stress protein hsp70 levels in the 8.40 mg l-1 treatment group. Histopathologic analyses revealed mild digestive gland (DG) atrophy in the control group. Clams exposed to 0.92 mg l-1 Cr-VI showed moderate DG atrophy, moderate granulomatous inflammation and necrosis in DG, ovary and testis. Lesions observed in the 8.40 mg l-1 treatment group included severe DG atrophy, severe granulomatous inflammation and necrosis in byssal gland, DG, gill, kidney, ovary and testis. In gills and testes of treated groups, apoptotic cells outnumbered mitotic cells. In addition, gills from clams in the 8.40 mg l-1 group showed enhanced hsp70 staining. Our studies support a cause-effect relationship between contaminants and reduced health in Asian clams and indicate the DGs, gills, and reproductive organs are principal targets of Cr-VI toxicity at sublethal concentrations. Results from this study suggest that Cr-VI may have played a role in the increased incidence of diseased clams seen in previous studies and these adverse effects may be working to decrease clam populations at sites with highest metallic contamination in the San Francisco Bay Estuary.

Tissue and cellular alterations in Asian clam (Potamocorbula amurensis) from San Francisco Bay: toxicological indicators of exposure and effect?

The US Geological Survey has reported the presence of a metal contamination gradient in clam tissues, decreased condition indices, and irregular reproductive patterns have been reported in the Asian clam, Potamocorbula amurensis, from San Francisco Bay. If metals are driving the observed patterns in the field, then biomarkers of exposure, and possibly deleterious effect, should show a corresponding gradient. In this study, biomarkers from sub-cellular to tissue levels of biological organization were assessed in P. amurensis collected from the Bay or exposed to cadmium in the laboratory. Cellular and tissue alterations were assessed using histopathology and enzyme histochemistry (EH). Alterations in the ovary, testis, kidney, and gill tissues were most common at the most contaminated station when data were averaged over a 12-month sampling period. EH analysis indicated decreased active transport, energy status, and glucose oxidation in kidney and digestive gland at the most contaminated site which may indicate a decreased potential for growth. Ovarian lesions observed in feral Asian clams were experimentally induced in healthy clams by cadmium exposure in laboratory exposures. Our results suggest a contaminant etiology for tissue alterations.

Spatial profiles of hsp70 proteins in Asian clam (Potamocorbula amurensis) in northern San Francisco Bay may be linked to natural rather than anthropogenic stressors

Multi-year investigations in northern San Francisco Bay by United States Geological Survey have linked reduced condition indices in populations of Asian clam (Potamocorbula amurensis) with elevated cadmium tissue concentrations. Our study seeks to determine whether levels of hsp70 proteins in P. amurensis can be correlated with these findings, and/or are related to histopathologic alterations and concentrations of metallothionein-like proteins. Here we present our results on stress proteins in clams collected monthly from four field stations between July 1996 and January 1998. In addition, animals were exposed in the laboratory to a range of salinities. Stress proteins were analyzed by Western blotting using monoclonal antibodies. Hsp70 protein levels in field-collected clams were significantly higher at the seaward (high salinity/low cadmium) stations (12.5, 8.1) than at the landward (low salinity/high cadmium) stations (6.1, 4.1). Laboratory studies showed that clams exposed to 0.1 ppt salinity had markedly lower hsp70 levels than clams exposed to higher salinities. In view of our previous laboratory studies showing that cadmium induces hsp70 in P. amurensis, our present results indicate that reduced hsp70 protein levels in field-collected clams may be linked to salinity effects rather than cadmium tissue concentrations.

Determining the sensitive developmental stages of intersex induction in medaka (Oryzias latipes) exposed to 17 beta-estradiol or testosterone

Certain environmentally persistent compounds can adversely affect reproduction by acting as steroid hormone agonists or antagonists. The goal of the present study was to determine the developmental stage most susceptible to exogenous hormone (estradiol and testosterone) exposure using a small teleost model. In the first (pilot study) of two experiments, medaka (Oryzias latipes), at varying developmental stages, were bath-exposed to 5 micrograms/l 17 beta-estradiol for 24 h. At 5 months of age, fecundity, fertility and embryo and larval viability (reproductive success) were investigated in control and exposed groups. Fish at 1, 1.5, 2 and 5.5 months of age were also sampled, processed and examined histologically for gonadal alteration. No significant differences in mortality, gonadal morphology, body weight, sex-ratio or time to maturity were seen between control and exposed fish. At 5 months, however, when exposure groups were compared to controls, significant differences were seen in reproductive success and viability of offspring. A second experiment exposed embryo stage 10, and 1-, 7- and 21-day-old larvae for 6 days to 15 micrograms/l 17 beta-estradiol or 100 micrograms/l testosterone. No significant differences were seen at 5 months in mortality, body weight, or time to sexual maturity. However, sex-ratios were significantly biased toward female in the stage 10, 1- and 7-day post-hatch estradiol exposure groups. No significant changes in sex-ratio were associated with testosterone exposure at any developmental stage. Further, intersex gonads were observed in fish from all groups exposed to 15 micrograms/l estradiol. Only those fish exposed as newly hatched fry or at 1 week post-hatch displayed intersex gonads following 100 micrograms/l testosterone exposure. Data from these experiments show that newly hatched fry are that life stage most sensitive to hormone exposure and the most appropriate to use in determining effects of known endocrine-disrupting compounds.

The role of development and duration of exposure to the embryotoxicity of diazinon

Medaka, Oryzias latipes, were used as a laboratory surrogate for species of concern to define the effects of diazinon exposure on teleost embryogenesis. Medaka embryos were placed in a static, non-renewal system and exposures initiated on days 1, 3, or 5 of development. Following initiation of exposure, replicates (n=5) remained in diazinon for a total of 4 days or from the day of initiation to day 9 of development. This exposure scenario was designed to elucidate sensitive periods in development for diazinon-induced toxicity but also shows the effect of added exposure duration on the degree of toxicity. Embryos were observed daily and endpoints recorded included: edema formation, total hatch, mean day of hatch, percentage of larvae with swim bladder inflation, and total length of larvae on day 14, when observations were terminated. Diazinon exposure resulted in decreases in hatch success, swim bladder inflation and the total length of larvae. In addition, dose-response increases in the incidence of edemas of the pericardial sac and vitelline veins were recorded. As expected, severity of embryotoxicity was positively correlated with duration of exposure. While no developmental period was the most sensitive for all toxic effects, for certain endpoints the severity of effects was dependent on exposure timing. Total hatch was greatly affected in embryos exposed from day 1 until day 5 whereas edema was more prevalent in embryos exposed later in development. Finally, among endpoints recorded, total length of larvae was the most sensitive indicator of exposure with all exposure groups showing significant (P<0.05) decreases in length at 5 ppm.

Thiobencarb-induced embryotoxicity in medaka (Oryzias latipes): stage-specific toxicity and the protective role of chorion

Thiobencarb (S-(4-chlorobenzyl)-N,N-diethyl thiol carbamate) has been one of the herbicides previously associated with fish kills in agricultural drains near the Sacramento/San Joaquin rivers and their Delta. This area is an important spawning ground for fish, and thus there are concerns over possible toxic effects on early life stages of fishes. To define targets of thiobencarb embryotoxicity and to determine the degree of protection afforded by the chorion, medaka (Oryzias latipes) embryos were exposed under static nonrenewal conditions. Responses to exposures initiated at blastula or at initiation of heart beat (stages 10 and 23, respectively) were assessed. In addition, enzymatically dechorionated embryos (stage 13, gastrula) were exposed and compared to responses in embryos with intact chorions. Embryos were observed daily for development and for gross abnormalities including: bradycardia, pericardial edema, hemostasis, poor yolk resorption, cephalic and spinal deformities, and abnormal hatching. A subset was also evaluated for histologic alterations. Based on gross abnormalities, the concentration of thiobencarb affecting 50% (EC(50)) of embryos exposed at blastula was 3.6 mg/l, while the putative no observable effect concentration (NOEC) was 1.0 mg/l. For embryos exposed at onset of heart beat (stage 23), these values were 4.1 and 2.5 mg/l, respectively. Dechorionated embryos tended to be more sensitive than their chorionated cohorts (LC(50)=2.5 vs. 1.0 mg/l). Liver histologic alterations were seen in chorionated embryos at EC(50) levels and higher. Stage-specific toxicity was evident; nevertheless, the EC(50) and NOEC values for embryos treated at stage 10 and stage 23 were similar.

Partial hepatectomy and bile duct ligation in rainbow trout (Oncorhynchus mykiss): histologic, immunohistochemical and enzyme histochemical characterization of hepatic regeneration and biliary hyperplasia

Hepatic regeneration following partial hepatectomy (PH) and biliary hyperplasia subsequent to bile duct ligation (BDL) were characterized in rainbow trout (Oncorhynchus mykiss) by light microscopy using routine and special (immunohistochemical and enzyme histochemical) stains. Both PH and BDL involved initial hypertrophy and hyperplasia of bile preductular epithelial cells (BPDECs). BPDECs are small oval cells that form junctional complexes with hepatocytes and bile ductular cells and are commonly found in hepatic tubules of teleost liver. Proliferating BPDECs transitioned through intermediate cell types before final differentiation into large basophilic hepatocytes (following PH) or biliary epithelial cells (after BDL). Normal BPDECs and hepatocytes were both negative for cytokeratin intermediate filaments in control fish when screened with the monoclonal antibody AE1/AE3. In contrast, hyperplastic BPDECs and their progeny (intermediate cells, immature hepatocytes, ductal epithelial cells) were all strongly cytokeratin positive. Cytokeratin expression was transient in newly differentiated hepatocytes (expression decreased as hepatocytes acquired characteristics consistent with full differentiation) but was permanent in biliary epithelial cells (expression was very strong in large mature ducts). BPDECs, intermediate cells, and immature ductal cells were also strongly positive for alkaline phosphatase following BDL. Chronology of histologic events and cytokeratin and enzyme expression all support the hypothesis that BPDECs possess the capacity to differentiate into either hepatocytes or biliary epithelial cells. Thus, BPDECs may be the teleost equivalent of a bipolar hepatic stem cell in mammals.

Variations of light and temperature regimes and resulting effects on reproductive parameters in medaka (Oryzias latipes)

In seasonally breeding fish species, altered fecundity, fertility, and spawning interval are associated with changes in environmental cues such as temperature and photoperiod. To determine quantitative impact of these cues on a suite of reproductive endpoints, groups of medaka (Oryzias latipes; two breeding pairs per group) were subjected to varying photoperiod and temperature regimes. Embryo production ceased after photoperiod reduction from 16L:8D to 8L:16D (at 25 degrees C). A severe decline in production was observed after a temperature decrease of 10 degrees C (25 degrees C to 15 degrees C [16L:8D]). Under reduced photoperiod, histologic analysis showed no mature ova and moderate oocyte atresia in all individuals. However, reduced temperature (15 degrees C) produced only mild oocyte atresia and fewer mature ova. Under both reduced photoperiod and reduced temperature regimes, mature spermatozoa were observed. Offspring viability, along with spawning interval, were not affected by photoperiod reduction. Temperature change had no effect on offspring viability but caused an increase in spawning interval. A shortened photoperiod profoundly affected medaka reproduction, whereas decreased temperature reduced, but did not arrest, fertility; reduced photoperiod decreased fecundity. These findings have important implications for culture of medaka as well as use of this teleost model for reproductive toxicology studies.

Progression of hepatic neoplasia in medaka (Oryzias latipes) exposed to diethylnitrosamine

Progression of hepatic neoplasia was assessed in medaka (Oryzias latipes) following aqueous exposure to diethylnitrosamine (DEN). Larvae (2 weeks old) were exposed to 350 or 500 p.p.m. DEN for 48 h, while adults (3-6 months old) were exposed to 50 p.p.m. DEN for 5 weeks. Fish were maintained as long as possible to determine malignant potential of resultant neoplasms. A total of 423 medaka with 106 hepatic neoplasms were examined. There were marked differences in tumor prevalence between exposure groups including: (i) higher prevalence of hepatocellular carcinomas in medaka exposed as adults (100% of hepatocellular tumors in adult-exposed medaka were malignant, while only 51.5% of larval hepatocellular tumors were malignant); (ii) higher prevalence of biliary tumors in medaka exposed as larvae (46.4% of all tumors in larval-exposed medaka were biliary versus 8.1% in adult-exposed fish); (iii) higher prevalence of mixed hepato-biliary carcinomas in adult-exposed medaka (24.3%) compared with those exposed as larvae (3%). In addition, a unique hepatocellular lesion termed 'nodular proliferation' was only observed in adult-exposed medaka. The lesion was characterized by small size (50-300 microm), complete loss of normal tubular architecture and variable megalocytosis. Nodular proliferation was distinct from preneoplastic foci of cellular alteration and may represent microcarcinomas. There was a step-wise increase in mean diameter with age (days post-exposure) from nodular proliferation (174 microm, 17 days) to hepatocellular carcinoma (1856 microm, 62 days) and mixed carcinomas (3209 microm, 93 days) in adult-exposed medaka. Metastasis was observed with 19 neoplasms and tumors with the highest metastatic potential were hepatocellular and mixed carcinomas. The most common form of metastasis was trans-coelomic, followed by direct invasion and distant metastasis, presumably via the vascular route. Differences in tumor prevalence between exposure groups were believed to be the result of length of DEN exposure rather than age of fish at the time of exposure. In larval medaka with brief (48 h) DEN exposure, neoplasms are thought to be the result of dedifferentiation of hepatic cells, with slow progression of foci of cellular alteration to benign and then malignant tumors. In contrast, with adult medaka and prolonged (5 week) DEN exposure, neoplasms are believed to result from initiation of committed stem cells and formation of microcarcinomas ('nodular proliferation'), before progressing to larger hepatocellular and then mixed carcinomas.

Multiple stressors in the Sacramento River watershed

Aquatic biota in the Sacramento River watershed are stressed by diversion of river flows, by historical mining resulting in cadmium, copper, zinc, and mercury, and, more recently, contamination by agricultural and urban chemical runoff. In addition, the proposed redirection of drainage of saline waters--containing selenium--from the western slope of the San Joaquin River into the Delta formed by the confluence of the Sacramento and San Joaquin Rivers could add to the stress on resident organisms. These combined stressors have led to deterioration in surface water quality and the aquatic habitat. The potential interaction of these stressors, coupled with invasions of foreign species and the export of juvenile fish into aqueducts, has driven several species of fish to near extinction in the system. Effects of historical contamination by heavy metals are potentially exacerbated by presence of organophosphate pesticides, at concentrations exceeding National Academy of Sciences recommendations, throughout the lower watershed and the San Francisco Bay. The Asian clam, Potamocorbula amurensis, an introduced non-indigenous species has apparently become a preferred food item of the sturgeon, Accipenser transmontanus, an important sport and aquaculture species. Since this introduction, sturgeon body burdens for selenium have increased dramatically and analytical chemistry of P. amurensis indicates that these organisms are effective bioaccumulators of selenium. This review examines potential ecotoxicity associated with multiple stressors in the watershed. Data from field monitoring, laboratory toxicity assays with ambient water, and ecotoxicologic investigations are reviewed. Potential designs for multiple stressor investigations are discussed. The information presented on this watershed illustrates the challenge to investigators seeking to evaluate multiple stressor effects on riverine and estuarine organisms.

Architectural pattern, tissue and cellular morphology in livers of fishes: relationship to experimentally-induced neoplastic responses

The teleost liver is one of the most sensitive organs to show alteration in biochemistry, physiology and structure following exposure to various types of environmental pollutants. Despite the importance of this organ to environmental toxicology and to ecotoxicology where biomarkers of exposure and of deleterious effect are found, the architectural pattern is not well known. This chapter reviews an architectural plan for teleost liver and compares that to the often cited mammalian pattern. Hepatic tubules composed principally of hepatocytes and biliary epithelial cells are in close proximity to lacunae which are of mesodermal origin. As is described, the tubule and lacunae concepts provide a means to better interpret morphologic alterations following exposure. These concepts are used to illustrate features of the chronic toxicity following exposure to proven carcinogens.

Organophosphate-induced acetylcholinesterase inhibition and embryonic retinal cell necrosis in vivo in the teleost (Oryzias latipes)

Recent monitoring of the Sacramento-San Joaquin River system (CA) indicates that levels of the organophosphate pesticide, diazinon, exceed National Academy of Science guidelines and these levels result in toxicity in USEPA acute toxicity tests with Ceriodaphnia dubia. Since organophosphates (OPs) inhibit acetylcholinesterase (AChE), the present study examined the effects of diazinon on the embryonic nervous system of a model teleost, medaka, Oryzias latipes. Preliminary histological screens revealed limited retinal cell necrosis in control embryos with apparent increased necrosis in diazinon-exposed embryos. Subsequently, embryos were exposed to 1.8 x 10(-5), 4.4 x 10(-5), or to 8.8 x 10(-5) M diazinon and replicates were frozen for biochemical analysis or were fixed for histopathological analysis at days 3, 5, and 7 of development. Diazinon exposure significantly inhibited AChE activity within whole embryos and in homogenates of retinas from treated animals. Histological examination of embryos indicated that as the retina underwent differentiation into distinct cell layers, between days 5 and 7, small foci of necrotic cells became apparent within the inner nuclear layer and isolated individual pyknotic cells were observed in the ganglion layer. Quantification of foci of necrotic cells revealed that 8.8 x 10(-5) M diazinon increased number and area of these lesions. Enzyme histochemistry localized AChE activity to regions equivalent to sites of necrosis. Separate exposures of embryos to the OP, diisopropylphosphorofluoridate, produced large foci of necrotic cells at sites equivalent to those seen following diazinon exposure.

Viral hemorrhagic septicemia virus, Ichthyophonus hoferi, and other causes of morbidity in Pacific herring Clupea pallasi spawning in Prince William Sound, Alaska, USA

Pacific herring Clupea pallasi populations in Prince William Sound, Alaska, USA, declined from an estimated 9.8 x 10(7) kg in 1992 to 1.5 x 10(7) kg in 1994. To determine the role of disease in population decline, 233 Pacific herring from Prince William Sound were subjected to complete necropsy during April 1994. The North American strain of viral hemorrhagic septicemia virus (VHSV) was isolated from 11 of 233 fish (4.7%). VHSV was significantly related to myocardial mineralization, hepatocellular necrosis, submucosal gastritis, and meningoencephalitis. Ichthyophonus hoferi infected 62 of 212 (29%) fish. I. hoferi infections were associated with severe, disseminated, granulomatous inflammation and with increased levels of plasma creatine phosphokinase (CPK) and aspartate aminotransferase (AST). I. hoferi prevalence in 1994 was more than double that of most previous years (1989 to 1993). Plasma chemistry values significantly greater (p < 0.01) in males than females included albumin, total protein, cholesterol, chloride, glucose, and potassium; only alkaline phosphatase was significantly greater in females. Hypoalbuminemia was relatively common in postspawning females; other risk factors included VHSV and moderate or severe focal skin reddening. Pacific herring had more than 10 species of parasites, but they were not associated with significant lesions. Two of the parasites have not previously been described: a renal intraductal myxosporean (11% prevalence) and an intestinal coccidian (91% prevalence). Transmission electron microscopy of a solitary mesenteric lesion revealed viral particles consistent with lymphocystis virus. No fish had viral erythrocytic necrosis (VEN). Prevalence of external gross lesions and major parasites was not related to fish age, and fish that were year-lings at the time of the 1989 'Exxon Valdez' oil spill (1988 year class) had no evidence of increased disease prevalence.

Brevetoxin-6 (PbTx-6), a nonaromatic marine neurotoxin, is a ligand of the aryl hydrocarbon receptor

Brevetoxins (PbTx) are a family of marine polyether toxins that exert their toxic action by activating voltage-sensitive sodium channels. Two forms of brevetoxin, PbTx-2 and -3, induce hepatic cytochrome P4501A1, measured as ethoxyresorufin O-deethylase (EROD) activity, in redfish and striped bass. P4501A1 induction is transcriptionally regulated through the binding of a ligand, typically a planar aromatic compound, to the aryl hydrocarbon receptor (AhR) and subsequent complex formation with the dioxin response element (DRE), an upstream regulatory region of the CYP1A1 gene. To determine if PbTx, a nonaromatic compound, induced EROD by this mechanism, two sets of experiments were performed. Initially, saturation binding assays with PbTx-2, -3, and -6 were carried out to determine if PbTx-2, -3, or -6 was an AhR ligand. Results showed that PbTx-6 inhibited specific binding of dioxin to the AhR, whereas PbTx-2 and -3 had no effect. Subsequently, gel retardation assays showed that PbTx-6 caused a concentration-dependent increase in AhR-DRE complex formation. The most abundant and neurotoxic forms of brevetoxin, PbTx-2 and -3, did not appear to be involved in this process. However, PbTx-6, the epoxide which is a likely biotransformation product, is at least one of the forms of PbTx involved in EROD induction.

Diagnostic criteria for degenerative, inflammatory, proliferative nonneoplastic and neoplastic liver lesions in medaka (Oryzias latipes): consensus of a National Toxicology Program Pathology Working Group

Diagnostic criteria are presented for degenerative, inflammatory, nonneoplastic proliferative, and neoplastic lesions in the liver of medaka (Oryzias latipes), a small fish species frequently used in carcinogenesis studies. The criteria are the consensus of a Pathology Working Group (PWG) convened by the National Toxicology Program. The material examined by the PWG was from Medaka exposed to N-nitrosodiethylamine for 28 days, removed to clean water, and sacrificed 4, 6, or 9 mo after initiation of exposure. Degenerative lesions included hepatocellular intracytoplasmic vacuolation, hepatocellular necrosis, spongiosis hepatis, hepatic cysts, and hepatocellular hyalinization. Inflammatory lesions consisted of granulomas, chronic inflammation, macrophage aggregates, and focal lymphocytic infiltration. Nonneoplastic proliferative lesions comprised foci of cellular alteration (basophilic focus, eosinophilic focus, vacuolated focus, and clear cell focus) and bile duct hyperplasia. Neoplastic lesions included hepatocellular adenoma, hepatocellular carcinoma, cholangioma, and cholangiocarcinoma. Two lesions composed mainly of spindle cells were noted, hemangiopericytoma and spindle cell proliferation. Rather than being an exhaustive treatment of medaka liver lesions, this report draws from the published literature on carcinogen-induced liver lesions in medaka and other fish species and attempts to consolidate lesion criteria into a simplified scheme that might be useful to pathologists and other researchers using medaka lesions for risk assessment or regulatory purposes.

Dioxinlike properties of a trichloroethylene combustion-generated aerosol

Conventional chemical analyses of incineration by-products identify compounds of known toxicity but often fail to indicate the presence of other chemicals that may pose health risks. In a previous report, extracts from soot aerosols formed during incomplete combustion of trichloroethylene (TCE) and pyrolysis of plastics exhibited a dioxinlike response when subjected to a keratinocyte assay. To verify this dioxinlike effect, the complete extract, its polar and nonpolar fractions, some containing primarily halogenated aromatic hydrocarbons, were evaluated for toxicity using an embryo assay, for antiestrogenicity using primary liver cell cultures, and for the ability to transform the aryl hydrocarbon receptor into its DNA binding form using liver cytosol in a gel retardation assay. Each of these assays detect dioxinlike effects. Medaka (Oryzias latipes) embryos and primary liver cell cultures of rainbow trout (Oncorhynchus mykiss) were exposed to concentrations of extract ranging from 0.05 to 45 micrograms/l. Cardiotoxicity with pericardial, yolk sac, and adjacent peritoneal edema occurred after exposure of embryos to concentrations of 7 micrograms/l or greater. These same exposure levels were associated with abnormal embryo development and, at the higher concentrations, death. Some of the fractions were toxic but none was as toxic as the whole extract. In liver cells, total cellular protein and cellular lactate dehydrogenase activity were not altered by in vitro exposure to whole extract (0.05-25 micrograms/l). However, induction of cytochrome P4501A1 protein and ethoxyresorufin O-deethylase activity occurred. In the presence of whole extract, estradiol-dependent vitellogenin synthesis was reduced. Of the fractions, only fraction 1 (nonpolar) showed a similar trend, although vitellogenin synthesis inhibition was not significant. The soot extract and fractions bound to the Ah receptor and showed a significantly positive result in the gel retardation/DNA binding test. Chemical analyses using GC-MS with detection limits for 2,3,7,8-tetrachlorodibenzo-p-dioxin and dibenzofuran in the picomole range did not show presence of these compounds. Our results indicate that other chemicals associated with TCE combustion and not originally targeted for analysis may also pose health risks through dioxinlike mechanisms.

In vivo modulation of 17 beta-estradiol-induced vitellogenin synthesis and estrogen receptor in rainbow trout (Oncorhynchus mykiss) liver cells by beta-naphthoflavone

Vitellogenesis or egg yolk production represents a key estrogen initiated process in oviparous vertebrates which is crucial for oocyte maturation. Previous in vitro studies have shown that cytochrome P4501A1 (CYP1A1)-inducing compounds such as beta-naphthoflavone (betaNF) modulate 17 beta-estradiol-induced vitellogenin (Vg) synthesis in primary cultures of juvenile rainbow trout liver cells. In this study, treatment of juvenile trout with 0.5 mg/kg 17 beta-estradiol plus either 25 or 50 mg/kg betaNF confirmed in vivo that betaNF may depress Vg synthesis by the liver. Alternatively, trout treated with 0.5 mg/kg 17 beta-estradiol plus 12.5 mg/kg betaNF or 5 mg/kg 17 beta-estradiol plus 12.5, 25, or 50 mg/kg betaNF showed a potentiation of Vg synthesis relative to estradiol-only injected fish. These results are significant as they suggest that changing plasma estrogen levels in sexually maturing trout will determine whether or not CYP1A1-inducing compounds may suppress, have no effect, or potentiate estrogen-induced liver Vg synthesis. Depressed Vg synthesis by trout injected with 0.5 mg/kg 17 beta-estradiol plus 50 mg/kg of betaNF correlated with depressed estrogen-binding capacity of liver, as assessed by [3H]17 beta-estradiol binding to liver nuclear protein extracts. Using gel mobility shift assay, the decrease in estrogen responsiveness of liver was not attributed to depressed estrogen response element-estrogen receptor binding. The fish liver vitellogenesis process offers a comparative model with which to further study the mechanism(s) of aryl hydrocarbon receptor-mediated antiestrogenicity and endocrine disruption.

Trout liver slices for metabolism and toxicity studies

Aquatic species are increasingly used in metabolism and toxicity studies, both from the perspective of potential for chemical exposure and usefulness as nonmammalian model systems. In the present study, trout liver slices were compared with freshly isolated trout hepatocytes with regard to metabolic capabilities and biochemical indices of cell health. Liver slices were also used to discern toxicant-induced changes in liver cell histology. Levels of ATP and glutathione were similar between liver slice and isolated hepatocyte preparations. The cytochrome P450-dependent rate of formation of biphenyl metabolites was 0.48 +/- 0.04 nmol/min/mg protein in slices and 0.43 +/- 0.06 nmol/min/mg protein in isolated cells. 7-Ethoxycoumarin metabolism was also comparable between preparations (1.36 vs. 1.22 nmol/min/mg protein). For conjugative metabolism, glucuronidation of 7-hydroxycoumarin or 1-naphthol did not differ in the two in vitro systems. However, neither slices nor isolated hepatocytes sulfated 7-hydroxycoumarin, whereas 1-naphthylsulfate represented as much as 20% of total 1-naphthol metabolites in both preparations. Histological evaluation of control liver slices after a 24-hr incubation indicated only minor changes. Response to the hepatotoxicants allyl formate and allyl alcohol was evaluated in slices only. Both compounds, after a 4-hr treatment and at concentrations between 0.1 and 1.0 mM, caused extensive depletion of glutathione, but ATP levels were unchanged. Histopathological damage was seen in slices incubated for 24 hr with either toxicant, but was most pronounced with allyl alcohol. These data indicate that liver slices are an excellent in vitro model for metabolism and toxicity studies in aquatic species.

Isolation and characterization of biliary epithelial cells from rainbow trout liver

Lectin binding and density gradient centrifugation were explored for isolating epithelial cells from trout liver. Hepatocytes exhibited preferential attachment of coverslips coated with Phaseolus vulgaris erythroagglutinin. Biliary epithelial cells attached with glycine max agglutinin; however, significant attachment of cellular debris limited the use of glycine max agglutinin. Percoll-density gradient centrifugation separated liver cells into two distinct populations with biliary cells and hepatocytes banding at densities of 1.04 and 1.09, respectively. A discontinuous gradient composed of 13% Ficoll (wt/wt) separated biliary cells from hepatocytes. The recovery of highly enriched biliary epithelial cells from trout liver using Ficoll gradients yielded approximately 8 million cells (0.1 ml packed cells) from 10 g liver. Western blot analysis demonstrated that the cytokeratin profile for extracts from biliary epithelial cell-enriched populations differ significantly from those seen with whole liver extracts or with extracts with hepatocyte-enriched populations. Ficoll-gradient purified biliary cells and hepatocytes attached to culture plates coated with trout skin extract and carried out linear incorporation of leucine into protein and thymidine into DNA for 24 h. A mixture of growth hormones (insulin, epidermal growth factor, and dexamethasone) stimulated thymidine incorporation into DNA; however, long-term culture of dividing biliary epithelial cells was not achieved. Chemical analysis of neutral and acidic glycolipids indicated that hepatocytes and biliary cells have similar glycolipid profiles with an exception in the region of GM3 mobility, which is attributed to differences in the ceramide moiety. These studies provide a starting point for further characterization of unique cell types of the trout liver that may be important in their responses to toxic and carcinogenic agents.

Histological and histochemical changes in the digestive tract of white sturgeon larvae during ontogeny

Ontogenetic changes in digestive tract histology and digestive enzyme histochemistry were investigated 11 to 36 days post-hatch in white sturgeon Acipenser transmontanus larvae. From initiation of exogenous feeding (12 days post-hatch), larvae were fed a commercial salmonid diet for the ensuing 24 days. The digestive system of white sturgeon displayed a high degree of morphologic organization and functionality at the onset of exogenous feeding. An enhancement of digestive capacities occurred with transition to active feeding. On day 2 of feeding, there was a clear increase of alkaline phosphatase, aminopeptidase M, dipeptidyl peptidase IV, and γ-glutamyl transpeptidase activity in the brush border of the spiral intestine. This strong activity is an apparent confirmation of the importance of this segment of the intestine for protein digestion and nutrient absorption. The functional development of the pyloric intestine occurred on day 4 and was concomitant with an increase in the activity of brush border and cytoplasmic enzymes such as acetylcholinesterase, dipeptidyl peptidase II, α- and β-galactosidases. The absence of acetylcholinesterase, lactase, nonspecific esterase, and weak activity of exopeptidases and alkaline phosphatase in the anterior intestine suggests that this segment of the intestine may be less important in nutrient absorption than the pyloric and spiral intestines. The observed quantitative and qualitative differences in enzyme activity along the intestine indicate a high degree of specialization of each segment for specific digestive and absorptive processes.

Long-term primary culture of epithelial cells from rainbow trout Oncorhynchus mykiss) liver

Long-term primary cultures of epithelial cells from rainbow trout (Oncorhynchus mykiss) liver have been established. Nearly homogenous (> 97%) populations of hepatocytes were placed into primary culture and remained viable and proliferative for at least 70 d. In addition to hepatocytes, proliferative biliary cells persisted in the cultures for at least 30 d. Finally, a third type of epithelial cell, which we have termed a "spindle cell," consistently appeared and proliferated to confluence in these cultures. The confluent cultures of spindle cells were successfully subcultured and passaged. The initial behavior, growth, and optimization of serum and media requirements for these cells is described. All three cell types proliferated as measured by thymidine incorporation, autoradiography, proliferating cellular nuclear antigen analysis, and propidium iodine staining. Further efforts to characterize the cells included western blotting and immunohistochemical staining with antibodies to cytokeratins previously reported in fish liver. From these data, it appears that all three cell populations are epithelial in nature. Furthermore, significant changes in actin organization, often indicative of transformation or pluripotent cells, were observed with increased time in primary culture.

The effect of agricultural discharge on striped bass (Morone saxatilis) in California's Sacramento-San Joaquin drainage

The striped bass (Morone saxatilis) population of the Sacramento-San Joaquin Delta has declined approximately 80% since the mid-1970s. This decline has been attributed to factors such as water diversions, pollution and reduced abundance of food organisms. One source of potential pollutants is agricultural return water. The Colusa Basin Drain discharges water from over 150 000 acres and can account for over 20% of the flow of the Sacramento River. Because discharge occurs at the same time striped bass are spawning, early developmental stages could be adversely affected. Toxicity studies conducted over a 3 year period consistently demonstrated acute toxicity to striped bass larvae and to opossum shrimp (Neomysis mercedis), an important food organism for juvenile striped bass. Acute toxicity was also demonstrated with striped bass embryos. In addition, a model based on pesticide use more effectively predicted striped bass recruitment during the period of decline than did a model based on historically important river flows and delta diversions. These studies indicate that agricultural return water should not be disregarded when considering potential causes of the decline of striped bass.

Hepatic cellular distribution of cytochrome P-450 IA1 in rainbow trout (Oncorhynchus mykiss): an immunohisto- and cytochemical study

Monoclonal antibody 1-12-3 reactive against scup (Stenotomus chrysops) cytochrome P450 E (a teleost CYP IA1) has been used to immunohistochemically localize CYP IA1 within hepatocytes and presumably sinusoidal endothelial and biliary epithelial cells of scup and trout. The goal of the present study was to extend immunohistochemical studies to the ultrastructural level determining intracellular locations of CYP IA1 in fish liver. Juvenile trout (5-10 g) were given i.p. injections once (50 micrograms/g b beta-naphthoflavone in cod liver oil; 0.5-ml injectate volume). After 5 days, livers were fixed (0.25% glutaraldehyde) via vascular in situ perfusion, removed, cut in 100-microns slices, infiltrated, and embedded in LR White monomer. Ultrathin sections of exposed livers were incubated in monoclonal antibody 1-12-3, rabbit anti-mouse IgG, and protein G colloidal gold. Membranes of granular endoplasmic reticulum in perinuclear regions of hepatocytes were consistently labeled. In addition, hepatocyte plasma membrane, particularly microvilli at bile canaliculi, was labeled. Biliary epithelial cells were labeled on luminal plasma membrane surrounding biliary passageway. Plasma membrane facing sinusoid and immediately subjacent cytoplasm was labeled in endothelial cells. Presence of CYP IA1 in sinusoidal endothelium could contribute to detoxication and/or bioactivation of blood borne chemicals. Granular endoplasmic reticulum was not uniformly labeled in hepatocytes. Rather, distribution seemed sequestered within highly specific regions and not dispersed along all membrane surfaces. Localization within biliary epithelial cells could signify potential of this cell type to bioactivate polycyclic aromatic hydrocarbons and may explain the common finding of biliary as well as hepatocytic tumors of trout liver.

Chromatophoromas and chromatophore hyperplasia in Pacific rockfish (Sebastes spp.)

Pacific rockfish from Cordell Bank, off central California (United States), were collected and histologically examined from 1985 to 1990. Hyperplastic and neoplastic cutaneous lesions, involving dermal chromatophores, were observed in five species; yellowtail rockfish (Sebastes flavidus), bocaccio (S. paucispinis), olive rockfish (S. serranoides), widow rockfish (S. entomelas), and chilipepper rockfish (S. goodei). Yearly prevalences were highest in S. paucispinis (29-38%). Prevalence was initially low in S. flavidus, but increased more than 3-fold from 1985 (7.5%) to 1990 (25%). The majority of lesions were black, but white, yellow, orange, red, and mixed-color variants were also seen. Lesions were found in skin, fins, lips, gingiva, tongue, urogenital papilla, conjunctiva, and cornea of the eye. Flat lesions were consistent with melanophore (black), xanthophore (yellow or orange), and erythrophore (red) hyperplasia. Neoplastic lesions included melanophoromas, amelanotic melanophoromas, xanthophoromas, erythrophoromas, and mixed chromatophoromas. Although etiology has not been determined, interest is currently focused on potential exposure to chemical and radioactive carcinogens from the Farallon Island Radioactive Waste Dump, 30 km to the south.

Acetaminophen toxicity in cultured trout liver cells. I. Morphological alterations and effects on cytochrome P450 1A1

To better characterize the hepatotoxicity of acetaminophen, the effects of this drug were investigated on isolated liver cells from a species relatively resistant to acetaminophen toxicity, rainbow trout. At high concentrations of acetaminophen (2-10 mM), pathologic effects were detected, including loss of lactate dehydrogenase from cells, disruption of cell-cell aggregation, cell death, and distinctive alterations in cell morphology, as demonstrated by light and electron microscopic examination. Most striking was the acetaminophen-induced rearrangement of mitochondria, which were clustered adjacent to the nucleus and rarely seen at cell periphery. The endoplasmic reticulum was also altered by acetaminophen treatment. In the middle portion of the cytoplasm, parallel arrays of endoplasmic reticulum cisternae were abundant; however, the peripheral cytoplasm was restricted to vesicular profiles of endoplasmic reticulum. Although nuclei in acetaminophen-treated cells displayed peripheral heterochromatin aggregation, acetaminophen did not produce detectable DNA fragmentation, in contrast to effects reported for mouse liver cells. Thus DNA fragmentation does not appear to be required for acetaminophen to manifest cytotoxic effects. In addition, immunohistochemical studies indicated that toxic concentrations of acetaminophen which altered the endoplasmic reticulum helped maintain cytochrome P450 1A1 in liver cells from beta-naphthoflavone-induced trout.

Acetaminophen toxicity in cultured trout liver cells. II. Maintenance of cytochrome P450 1A1

Acetaminophen was demonstrated to maintain cytochrome P450 1A1 (P450 1A1) in isolated rainbow trout liver cells cultured in serum-free medium. This novel finding was characterized in detail. Cultured trout liver cells retained their ability to respond to typical 1A1 inducers in vitro; induction of ethoxyresorufin O-deethylase (EROD) activity was readily demonstrated by exposing liver cells from control trout to beta-naphthoflavone (BNF), Aroclor 1254, or 7,12-dimethylbenz[a]anthracene. BNF was the most potent inducer studied and was used in further experiments. High levels of EROD activity, immunoreactive 1A1, and 1A1 mRNA were expressed in liver cells prepared from trout pretreated with BNF. However, all of these 1A1-specific indicators rapidly declined when cells from BNF-treated trout were placed in culture, and BNF in culture medium was not effective in maintaining EROD activity. Immunohistochemical studies suggested that addition of acetaminophen to liver cells prepared from BNF-induced trout helped maintain elevated levels of P450 1A1. Total cytochrome P450, EROD activity and immunoreactive P450 1A1 were retained in liver cells from BNF-induced trout by the addition of acetaminophen, in a dose-dependent manner. The concentrations of acetaminophen most effective in maintaining P450 1A1 produced cytotoxic effects, including vesiculation of endoplasmic reticulum. Furthermore, the acetaminophen maintenance of P450 1A1 was primarily attributed to elevated levels of P450 1A1 mRNA. In contrast to BNF, acetaminophen was not capable of inducing 1A1 in liver cells prepared from control trout. This is the first report to demonstrate that acetaminophen can help maintain P450 1A1 and that this effect is exerted at the level of P450 1A1 mRNA.

Biochemical and histochemical properties of hepatic tumors of rainbow trout, Oncorhynchus mykiss

Biochemical and histochemical studies were conducted in aflatoxin B1-induced liver tumors in adult rainbow trout. Specific activities of the phase I enzymes, ethoxyresorufin-O-deethylase (EROD), microsomal and cytosolic epoxide hydrolase (mEH and cEH), aldehyde dehydrogenase (ALDH) and DT-diaphorase, and the phase II enzymes, gamma-glutamyltransferase (gamma-GT), glutathione transferase (GST) and uridine diphosphoglucuronyl transferase (UDPGT) were measured. Cryostat sections of tumor and surrounding liver from the same cohorts were analyzed immunohistochemically for cytochrome P450IA1 and histochemically for ALDH (benzaldehyde and hexanal), DT-diaphorase, gamma-GT and uridine diphosphoglucuronyl dehydrogenase (UDPGdH). In tumor tissues, the largest biochemical changes were found with benzaldehyde dehydrogenase, where activity increased from undetectable levels to 7.4 nmol/min/mg protein, and gamma-GT, where activity increased 12-fold over controls. Increases in other enzymes ranged from 1.26 to 2.84 times that of control liver, except EROD, which decreased, and cEH and mEH, which were unchanged. Histochemical analyses showed the induction of ALDH, gamma-GT, DT-diaphorase and UDPGdH, and the depression of cytochrome P450IA1 in hepatic neoplasms. In addition, marker enzyme histochemistry of neoplasms revealed heterogeneous populations of hepatocytes and absence of necrotic areas.

A purified diet for medaka (Oryzias latipes): refining a fish model for toxicological research

The overall nutritional adequacy of a purified casein-based diet (PC-diet) for the medaka (Oryzias latipes) was evaluated and compared with three diets: commercially available flaked fish food (FL-diet), live newly hatched Artemia (A-diet), and a combination of FL-diet plus A-diet (F/A-diet). Survival, growth, reproductive success, general and liver histopathology, and selected hepatic enzyme activities were compared in medaka from first feeding through reproductive maturity. The PC-diet proved adequate in all of the above criteria. When compared with fish fed F/A-diet, an initial lag in early growth rates (i.e., 0 to 30 days) occurred with the fish fed PC-diet. The FL-diet alone was not nutritionally adequate for medaka, resulting in poor growth, reduced reproductive success, lower survival, and emaciation. A significant number of spinal deformities (5.4%) were noted in medaka fed the F/A diet. Ethoxycoumarin 0-deethylase and glutathione S-transferase activities were monitored and a trend toward increasing activity with age was noted. This suggests that PC- and F/A-diets provide adequate nutrition for development of the xenobiotic metabolizing enzymes necessary for detoxification and activation of endogenous and foreign compounds. The PC-diet supported good survival, growth, reproduction, and normal histology. This diet provides a standardized, nutritionally adequate, and consistent alternative to undefined conventional diets and is less likely to contain the range of xenobiotics possible in whole, live food.

Ultrastructural alterations in liver of medaka (Oryzias latipes) exposed to diethylnitrosamine

Liver cytotoxic alterations of adult medaka (Oryzias latipes) following short-term bath exposure (48 hr) to 500 mg/L diethylnitrosamine (DEN) were studied (days 3-21) by electron microscopy and cytochemistry. Control medaka displayed hepatic sexual dimorphism as described for other sexually active fish. Following DEN exposure, decreased glycogen stores with loss of cellular compartmentation obscured sexual dimorphism. A spectrum of organelle alterations, previously not reported in livers of fish, was seen. Early changes in hepatocytes included: nuclear lipid inclusions, nucleolar changes, decreased amounts of granular endoplasmic reticulum (GER), increased fractionation and steatosis of GER, proliferation of smooth ER and lysosomes, reduction in number and content of particulate lipoproteins and vitellogenin in Golgi vesicles, and reduction in number and staining intensity of peroxisomes. At day 14 and/or 21, partial to complete reversal of the above alterations indicated hepatic recovery, and fewer necrotic cells were seen at day 21 versus day 14. Lesions that did not resolve during this study were altered mitochondria and areas of spongiosis hepatis that developed at day 8 and continued to increase throughout the study. Infiltration of lymphocytes, granulocytes, and large numbers of macrophages were late changes. The description, timing, and duration of lesions are of value for consideration as biomarkers of exposure and effect in aquatic toxicology.

Induction of differentiation in human myeloblastic leukemia ML-1 cells by heptachlor, a chlorinated hydrocarbon insecticide

Effects of heptachlor, an organochlorine pesticide, on human myeloblastic leukemia ML-1 cells were determined. Similar to 12-O-tetradecanoylphorbol-13-acetate (TPA), a known tumor promoter, heptachlor induced cell adherence and formation of extended cytoplasmic pseudopodia in ML-1 cells. The growth of ML-1 was slightly stimulated by low concentrations (less than 30 nM) of heptachlor. A dose-responsive cell death was also observed when ML-1 cells were treated with heptachlor at concentrations greater than 80 microM. Examination by light microscopy of the cells treated with 80 microM heptachlor revealed a gradual appearance of differentiation characteristics in the culture. On Day 3 of the treatment, 41% of the cells remained unchanged as ML-1, 39% of the cells showed changes and apparent cell differentiation, and 20% of the cells were induced to differentiate to monocyte- or macrophage-like cell type. Electron microscopy also revealed cellular differentiation and the presence of monocyte- and macrophage-like cell types (22%) was confirmed by positive esterase staining.

Cytotoxicity phase of diethylnitrosamine-induced hepatic neoplasia in medaka

Adult Oryzias latipes were exposed to 50 mg of diethylnitrosamine per liter of water for 5 wk and then transferred to clean water for an additional 15 wk. Response of the liver during the first 6 wk were analyzed by enzyme histochemistry and by high-resolution light and transmission electron microscopy. After 1 wk, cytotoxicity was apparent at the light microscopic level by piecemeal necrosis and phagocytosis apoptosis by adjacent hepatocytes and resident macrophages. Spongiosis hepatis and inflammation, found as early as wk 3, were not widespread until wk 6. Glycogen depletion and multifocal increases in gamma-glutamyl transpeptidase were found as early as 3 wk. At 5 wk, macrophage infiltration and aggregation and hepatocyte lysosome proliferation were revealed by an increase in cells staining for acid phosphatase. In addition, a subpopulation of macrophages stained positively for glucose-6-phosphate dehydrogenase during wk 6. Other histochemical biomarkers (Mg2(+)-ATPase, DT-diaphorase, uridine diphosphoglucuronyl dehydrogenase) were not altered. Mitotic figures were rare for the entire 6-wk period. At the ultrastructural level, necrotic alterations of some hepatocytes were seen within 24 h. Within 48 h, an apparent reduction of hepatocyte glycogen and cell volume characterized the majority of hepatocytes; this was accompanied by an increase in interhepatocytic space and the length and complexity of the hepatocyte microvillous projections found in the space of Disse. Lipid vacuolar inclusions inhabited space previously occupied by glycogen. Margins of hepatocyte nuclei were irregular, and mitochondria were condensed and their shape altered so that crescentric and elongated profiles were abundant. Lysosomes and residual bodies were increased after 1 wk. The cytoplasmic processes delineating spongiotic lesions were identified as originating from Ito cells. After 4 wk, apparent proliferation of smooth endoplasmic reticulum and retention of transport lipid within its cisternae were seen. The toxic depletion of hepatocytes and the attendant altered cellular environment are discussed in relation to cell-to-cell interactions and the possible contribution of stromal and extracellular matrix changes to liver regeneration and neoplasia.

Isolated trout liver cells: establishing short-term primary cultures exhibiting cell-to-cell interactions

Composition and interactions of cell types in rainbow trout (Oncorhynchus mykiss) liver digested with collagenase and cultured in serum-free media were investigated. Suspensions obtained after digesting trout liver with collagenase contained all the cell types present in the liver, including liver parenchymal cells (hepatocytes), biliary epithelial cells, sinusoidal endothelium, fat-storing cells of Ito, and macrophages. A major cell pellet, mainly hepatocytes but containing significant numbers of biliary epithelial cells, was obtained by centrifuging the cell suspension at 120 X g for 1 min. Cells present in this pellet quantitatively attached to culture plates coated with a trout skin extract and remain attached for 4 to 6 d with good retention of intracellular enzymes and DNA. When in culture, significant changes in and among the cells were observed. Initial preparations were rounded, single cells. Within several hours, however, cellular interactions leading to aggregation became evident and aggregates increased in size for 2 to 3 d. Scanning electron microscopy (EM) showed frequent shaftlike projections from margins of the aggregates. Transmission EM indicated that these projections represent biliary ductules forming in vitro. Adjacent hepatocytes also showed plasma membrane specializations forming junctional complexes and canaliculi characteristics of normal trout liver. After 5 to 6 d in culture, significant numbers of the cell aggregates dislodged from the plate. Analysis showed the dislodged cells were viable but vacuolated. The reestablishment in vitro of morphologic relationships resembling in situ tissue components suggest these culture preparations may have significant utility in cooperative metabolic studies of cell interactions in trout liver.

Cytochrome P450IA1 induction and localization in endothelium of vertebrate (teleost) heart

Previous studies have shown that high levels of cytochrome P450 can occur in cardiac microsomes of vertebrates [Mol. Pharmacol. 21:517-526, (1982)]. Here we identify the dominant cardiac P450 in the marine fish scup as P450E, a teleost representative of P450IA1, and we describe its restricted cellular localization in the heart. Treatment of scup with beta-naphthoflavone produced an unusually strong (10-fold) induction of spectrally measured P450 in cardiac microsomes, with specific content reaching levels (0.5 nmol/mg) similar to those induced in scup liver. Microsomal ethoxyresorufin O-deethylase and aryl hydrocarbon hydroxylase activities, catalytic functions of scup P450E, were induced in parallel with P450 content. Similar induction was seen in both atrium and ventricle. Immunoblot analysis with monoclonal antibody 1-12-3, specific to scup P450E and other vertebrate P450IA1 proteins, showed that this hydrocarbon-inducible P450 is the dominant and possibly sole P450 form in heart microsomes of experimentally induced animals. Immunohistochemical analysis of scup heart sections (2-4-microns) with monoclonal antibody 1-12-3 revealed that P450E was detectable only in endothelial cells of the endocardium and of the coronary vasculature. A similar endothelial cell localization of the monoclonal antibody 1-12-3 epitope was observed in heart of rainbow trout, induced with beta-naphthoflavone, indicating a general nature for the endothelial localization of induced cardiac P450. Morphometric analysis showed that endothelium could constitute 8-9% of the volume of teleost heart, from which we calculate that P450IA1 could account for as much as 25% of the endothelial cell microsomal protein. Heart microsomes of untreated animals from contaminated environments also contained high levels of P450E, indicating that induction like that caused by beta-naphthoflavone could occur with chemicals in the environment. Strongly induced P450E (P450IA1) in endothelium could play a critical role in chemical-biological interactions involving xenobiotics affecting the vasculature of the heart or other organs.

DNA repair synthesis in isolated rainbow trout liver cells

Isolated trout liver cells were treated with lysolecithin to produce an in situ system for characterizing DNA repair in teleosts. In this preparation, the integrity of the plasma membrane is altered, nuclei remain intact, and the concentrations of dNTPs and nucleotide analogs, which normally do not penetrate intact plasma membranes, can be controlled. Following lysolecithin treatment, 50% of the total cellular protein and nearly 75% of total lactate dehydrogenase activity was released from the liver cells. Microscopic examination indicated that the integrity of the plasma membrane of trout hepatocytes was disrupted by lysolecithin; however, smaller nonhepatocytic liver cells were resistant to the disrupting effects of this detergent. Bleomycin induced DNA repair synthesis in lysolecithin-treated cells, as demonstrated by CsCl gradient analysis of 5-bromo, 2'-deoxyuridine, 5'-triphosphate-labeled DNA. Optimal conditions for bleomycin-induced DNA repair synthesis in lysolecithin-treated trout liver cells were considerably different from that in lysolecithin-treated mammalian cells. Bleomycin-induced DNA repair synthesis was lower in lysolecithin-treated trout liver cells than in lysolecithin-treated mammalian cells at identical concentrations of 2'-deoxyribonucleoside, 5'-triphosphates (dNTPs), suggesting the decreased sensitivity of trout cells in unscheduled DNA synthesis assays can be attributed to factors other than differences in dNTP pools. Bleomycin-induced DNA repair synthesis in trout hepatocytes was shown to be very sensitive to inhibition by 2', 3'-dideoxythymidine, 5'-triphosphate and was resistant to inhibition by cytosine arabinoside, 5'-triphosphate, butylphenyldeoxyguanosine, 5'-triphosphate and aphidicolin. These observations indicate repair of bleomycin-induced DNA damage in trout cells occurs through a mechanism similar to that in mammalian cells, utilizing DNA polymerase beta.