Imaging Liver Development/Remodeling in the See-Through Medaka Fish

Stage Dependent Enantioselective Metabolism of Bifenthrin in Embryos of Zebrafish (Danio rerio) and Japanese Medaka (Oryzias latipes)

Bifenthrin (BF) is a widely used pyrethroid that has been frequently detected in surface waters. Previous studies indicated that BF had antiestrogenic activity in zebrafish embryos but estrogenic activity in posthatch fish. To determine whether age-related differences in metabolism contribute to the endocrine effects in developing fish, embryos from zebrafish and Japanese medaka were exposed to BF before and after liver development. Since the commercial mixture of BF is an isomer-enriched product containing two enantiomers (1R-cis-BF and 1S-cis-BF), enantioselective metabolism was also evaluated. The estrogenic metabolite, 4-hydroxybifenthrin (4-OH-BF) was identified in zebrafish embryos, and formation was higher in animals after liver development (>48 hpf). Treatments with β-glucuronidase indicated that 4-OH-BF underwent conjugation in embryos. Formation was reduced by cotreatment of the cytochrome P450 (CYP450) inhibitor, ketoconazole. Formation of 4-OH-BF was greater when treated with 1R-cis-BF compared to the S-enantiomer. However, metabolites were not observed in medaka embryos. These data indicate enantioselective oxidation of BF to an estrogenic metabolite occurs in zebrafish embryos and, since it is increased after liver development, may partially explain estrogenic activity observed in older animals. The lack of activity in medaka suggests species-specific effects with BF metabolism and may influence risk assessment strategies in wildlife.

Stage susceptibility of Japanese medaka (Oryzias latipes) to selenomethionine and hypersaline developmental toxicity

Anthropogenic disturbance of seleniferous soils can lead to selenium contamination of waterways. Although selenium is an essential micronutrient, bioaccumulation and maternal transfer of proteinaceous selenomethionine (SeMet) can result in embryo toxicity. Furthermore, as the climate changes, the salinity of spawning grounds in water-restrained estuaries is increasing. Although a small increase in salinity may not directly impact adult fish, it may alter the detoxification strategies of developing organisms. Previous research indicates that hypersalinity may potentiate SeMet embryo toxicity at an early developmental stage. However, embryonic development is a complex, spatiotemporal process with a constantly shifting cellular microenvironment. To generate thresholds and an adverse outcome pathway for the interactions between selenium and salinity, we sought to identify windows of susceptibility for lethality and deformities in the Japanese medaka (Oryzias latipes). Embryos were treated in freshwater or saltwater for 24 h with 0.5 µM, 5 µM, and 50 µM SeMet at 6 different developmental stages (9, 17, 25, 29, 34, and 38). Survival, hatch, deformities (total, type, and severity), and days to hatch were quantified. Selenium embryo tissue measurements were performed. Selenomethionine exposures of 5 µM and 50 µM significantly decreased survival and hatch at all stages. However, SeMet uptake was stage-dependent and increased with stage. Stage 17 (early neurulation) was identified as the most susceptible stage for lethality and deformities. Selenomethionine in saltwater caused significantly greater toxicity than freshwater at stage 25 (early organogenesis), suggesting a role for liver and osmoregulatory organogenesis in toxicity.

High hydrostatic pressure influences the in vitro response to xenobiotics in Dicentrarchus labrax liver

Hydrostatic pressure (HP) increases by about 1 atmosphere (0.1MPa) for each ten-meter depth increase in the water column. This thermodynamical parameter could well influence the response to and effects of xenobiotics in the deep-sea biota, but this possibility remains largely overlooked. To grasp the extent of HP adaptation in deep-sea fish, comparative studies with living cells of surface species exposed to chemicals at high HP are required. We initially conducted experiments with precision-cut liver slices of a deep-sea fish (Coryphaenoides rupestris), co-exposed for 15h to the aryl hydrocarbon receptor (AhR) agonist 3-methylcholanthrene at HP levels representative of the surface (0.1MPa) and deep-sea (5-15MPa; i.e., 500-1500m depth) environments. The transcript levels of a suite of stress-responsive genes, such as the AhR battery CYP1A, were subsequently measured (Lemaire et al., 2012; Environ. Sci. Technol. 46, 10310-10316). Strikingly, the AhR agonist-mediated increase of CYP1A mRNA content was pressure-dependently reduced in C. rupestris. Here, the same co-exposure scenario was applied for 6 or 15h to liver slices of a surface fish, Dicentrarchus labrax, a coastal species presumably not adapted to high HP. Precision-cut liver slices of D. labrax were also used in 1h co-exposure studies with the pro-oxidant tert-butylhydroperoxide (tBHP) as to investigate the pressure-dependence of the oxidative stress response (i.e., reactive oxygen production, glutathione and lipid peroxidation status). Liver cells remained viable in all experiments (adenosine triphosphate content). High HP precluded the AhR agonist-mediated increase of CYP1A mRNA expression in D. labrax, as well as that of glutathione peroxidase, and significantly reduced that of heat shock protein 70. High HP (1h) also tended per se to increase the level of oxidative stress in liver cells of the surface fish. Trends to an increased resistance to tBHP were also noted. Whether the latter observation truly reflects a protective response to oxidative stress will be addressed in future co-exposure studies with both surface and deep-sea fish liver cells, using additional pro-oxidant chemicals. Altogether, data on CYP1A inducibility with D. labrax and C. rupestris support the view that high HP represses AhR signaling in marine fishes, and that only species adapted to thrive in the deep-sea have evolved the molecular adaptations necessary to counteract to some extent this inhibition.

Phenotypic characterization of transgenic Japanese medaka (Oryzias latipes) that express a red fluorescent protein in hepatocytes

Transgenic organisms that express fluorescent proteins are used frequently for in vivo visualization of proteins and cells. The phenotype of a transgenic medaka (Oryzias latipes) strain that expresses a red fluorescent protein (RFP) in hepatocytes was characterized using light and fluorescence microscopy, immunohistochemistry, and transmission electron microscopy (TEM). Expression of RFP was first detected by confocal fluorescence microscopy in the location of the liver bud of live medaka embryos at 60 hr postfertilization (developmental stage 27). Subsequently, RFP signal was observed exclusively in hepatocytes throughout life using fluorescence microscopy in live fish and immunohistochemistry in formalin-fixed, paraffin-embedded liver sections. As the fish aged, prominent intracytoplasmic eosinophilic inclusions immunoreactive for RFP were observed by light microscopy and were correlated with membrane-bound electron dense inclusions on TEM. These results define the onset and location of RFP expression in the Tg(zf.L-fabp:DsRed) medaka and characterize a histologic phenotype that results from RFP expression in hepatocytes.

Non-invasive in vivo imaging of the ionic regimes along the gastrointestinal tract of a freshwater vertebrate model organism (Japanese medaka) using responsive photonic crystal beads

Microspherical photonic colloidal crystalline beads that are responsive to media ionic strength of cationic electrolytes have been developed for in vivo imaging of the morphology and concentration gradient of cationic electrolytes along the gastrointestinal (GI) tract of live Japanese medaka (Oryzias latipes). These responsive photonic beads were assembled from core-shell nano-sized particles with polystyrene-co-polyacrylic acid (PS-co-PAA) cores and poly(hydroxyethyl methacrylate-co-p-styrene sulfonate) (PHEMA-co-PSS) hydrogel shells. The three-dimensional orderly packing of these nano-sized core-shell particles gave rise to the photonic properties of the resultant colloidal crystalline array of microspheres. The cationic electrolyte-induced volume phase transition of the sulfonate-laden hydrogel shells of the nano-sized particles altered the lattice spacing among those particles and brought about the photonic responses of the colloidal crystalline beads. Unambiguous changes in the diffraction colour of the colloidal crystalline beads were observable under ordinary ambient light in solution media of increasing concentration of sodium chloride up to 500 mM. These photonic colloidal crystalline beads were found to possess enough structural integrity for in vivo imaging of the GI tract of live Japanese medaka. With the use of a conventional optical microscope, the gradient in the ionic strength of cationic electrolytes along the GI tract of live Japanese medaka larvae was readily revealed, with a lower electrolyte concentration in the mid-intestine (<50 mM) compared to that of the posterior-intestine (≥50 mM). Our results demonstrated the potential of stimuli-responsive photonic materials in bio-imaging applications.

Identification and developmental expression of leucine-rich repeat-containing G protein-coupled receptor 6 (lgr6) in the medaka fish, Oryzias latipes

G protein-coupled receptors are critical regulators of diverse developmental processes such as oocyte maturation, fertilization, gastrulation, and organogenesis. To further study the molecular mechanisms underlying these processes, we cloned and characterized the orphan leucine-rich repeat-containing G protein-coupled receptor 6 (LGR6), a stem cell marker in mammalian hair follicles, in medaka fish, Oryzias latipes. To examine the expression pattern of lgr6, we performed whole-mount in situ hybridization (WISH) during embryogenesis. The expression of lgr6 was first detected as a band in the anterior part of the posterior brain vesicle in 0.5-1 day post fertilization (dpf) embryos. This band disappeared by 2 dpf, but new signals appeared in the otic vesicles bordering the original band and also detected in the nasal placode and posterior lateral line primordia. At later stages (3-5 dpf), lgr6 was widely expressed in the brain, otic vesicle, neuromasts, root of the pectoral fin, cranial cartilage, and gut. Then, we conducted more detailed expression analysis of lgr6 in adult gut using WISH and immunohistochemical staining. Lgr6-positive cells were detected in the crypt-like proliferative zone and in parts of the villus. We also performed RT-PCR of mRNAs from different tissues. The lgr6 mRNA was found highest in the kidney and gill. The transcript was also present in the brain, heart, liver, spleen, intestine, skeletal muscle, testis, and ovary, similar to that of mammalian LGR6. These results suggest that medaka lgr6 plays an important role in organ development during embryogenesis and serves as a good molecular marker for future studies of postembryonic organ-specific development in mammals.

Mutation in the abcb7 gene causes abnormal iron and fatty acid metabolism in developing medaka fish

The medaka fish (Oryzias latipes) is an emerging model organism for which a variety of unique developmental mutants have now been generated. Our recent mutagenesis screening of the medaka isolated a unique mutant that develops a fatty liver at larval stages. Positional cloning identified the responsible gene as medaka abcb7. Abcb7, a mitochondrial ABC (ATP binding cassette) half-transporter, has been implicated in iron metabolism. Recently, human Abcb7 was found to be mutated in X-linked sideroblastic anemia with cerebellar ataxia (XLSA/A). The homozygous medaka mutant exhibits abnormal iron metabolism in erythrocytes and accumulation of lipid in the liver. Microarray and in situ hybridization analyses demonstrated that the expression of genes involved in iron and lipid metabolisms are both affected in the mutant liver, suggesting novel roles of Abcb7 in the development of physiologically functional liver. The medaka abcb7 mutant thus could provide insights into the pathogenesis of XLSA/A as well as the normal function of the gene.

Non invasive in vivo investigation of hepatobiliary structure and function in STII medaka (Oryzias latipes): methodology and applications

Background

A novel transparent stock of medaka (Oryzias latipes; STII), recessive for all pigments found in chromatophores, permits transcutaneous imaging of internal organs and tissues in living individuals. Findings presented describe the development of methodologies for non invasive in vivo investigation in STII medaka, and the successful application of these methodologies to in vivo study of hepatobiliary structure, function, and xenobiotic response, in both 2 and 3 dimensions.

Results

Using brightfield, and widefield and confocal fluorescence microscopy, coupled with the in vivo application of fluorescent probes, structural and functional features of the hepatobiliary system, and xenobiotic induced toxicity, were imaged at the cellular level, with high resolution (< 1 μm), in living individuals. The findings presented demonstrate; (1) phenotypic response to xenobiotic exposure can be investigated/imaged in vivo with high resolution (< 1 μm), (2) hepatobiliary transport of solutes from blood to bile can be qualitatively and quantitatively studied/imaged in vivo, (3) hepatobiliary architecture in this lower vertebrate liver can be studied in 3 dimensions, and (4) non invasive in vivo imaging/description of hepatobiliary development in this model can be investigated.

Conclusion

The non-invasive in vivo methodologies described are a unique means by which to investigate biological structure, function and xenobiotic response with high resolution in STII medaka. In vivo methodologies also provide the future opportunity to integrate molecular mechanisms (e.g., genomic, proteomic) of disease and toxicity with phenotypic changes at the cellular and system levels of biological organization. While our focus has been the hepatobiliary system, other organ systems are equally amenable to in vivo study, and we consider the potential for discovery, within the context of in vivo investigation in STII medaka, as significant.

Differential developmental toxicity of naphthoic acid isomers in medaka (Oryzias latipes) embryos

Polycyclic aromatic hydrocarbons (PAHs) are widespread persistent pollutants that readily undergo biotic and abiotic conversion to numerous transformation products in rivers, lakes and estuarine sediments. Here we characterize the developmental toxicity of four PAH transformation products each structural isomers of hydroxynaphthoic acid: 1H2NA, 2H1NA, 2H3NA, and 6H2NA. Medaka fish (Oryzias latipes) embryos and eleutheroembryos were used to determine toxicity. A 96-well micro-plate format was used to establish a robust, statistically significant platform for assessment of early life stages. Individual naphthoic acid isomers demonstrated a rank order of toxicity with 1H2NA>2H1NA>2H3NA>6H2NA being more toxic. Abnormalities of circulatory system were most pronounced including pericardial edema and tube heart. To determine if HNA isomers were AhR ligands, spatial-temporal expression and activity of CYP1A was measured via in vivo EROD assessments. qPCR measurement of CYP1A induction proved different between isomers dosed at respective concentrations affecting 50% of exposed individuals (EC50s). In vitro, all ANH isomers transactivated mouse AhR using a medaka CYP1A promoter specific reporter assay. Circulatory abnormalities followed P450 induction and response was consistent with PAH toxicity. A 96-well micro-plates proved suitable as exposure chambers and provided statistically sound evaluations as well as efficient toxicity screens. Our results demonstrate the use of medaka embryos for toxicity analysis thereby achieving REACH objectives for the reduction of adult animal testing in toxicity evaluations.

Non invasive high resolution in vivo imaging of alpha-naphthylisothiocyanate (ANIT) induced hepatobiliary toxicity in STII medaka

A novel transparent stock of medaka (Oryzias latipes; STII), homozygous recessive for all four pigments (iridophores, xanthophores, leucophores, melanophores), permits transcutaneous, high resolution (<1 microm) imaging of internal organs and tissues in living individuals. We applied this model to in vivo investigation of alpha -naphthylisothiocyanate (ANIT) induced hepatobiliary toxicity. Distinct phenotypic responses to ANIT involving all aspects of intrahepatic biliary passageways (IHBPs), particularly bile preductular epithelial cells (BPDECs), associated with transitional passageways between canaliculi and bile ductules, were observed. Alterations included: attenuation/dilation of bile canaliculi, bile preductular lesions, hydropic vacuolation of hepatocytes and BPDECs, mild BPDEC hypertrophy, and biliary epithelial cell (BEC) hyperplasia. Ex vivo histological, immunohistochemical, and ultrastructural studies were employed to aid in interpretation of, and verify, in vivo findings. 3D reconstructions from in vivo investigations provided quantitative morphometric and volumetric evaluation of ANIT exposed and untreated livers. The findings presented show for the first time in vivo evaluation of toxicity in the STII medaka hepatobiliary system, and, in conjunction with prior in vivo work characterizing normalcy, advance our comparative understanding of this lower vertebrate hepatobiliary system and its response to toxic insult.

Age-dependent in situ hepatic and gill CYP1A activity in the see-through medaka (Oryzias latipes)

We used a recently introduced strain of medaka, the see-through medaka, whose internal organs can be seen through the skin, to develop an in situ toxicity assay of ethoxyresorufin-O-deethylase (EROD) activity that detected fluorescence from resorufin, a metabolite of ethoxyresorufin and thus an indicator of CYP1A activity. EROD activity in the liver and gills of 2-week post-hatch see-through medaka exposed simultaneously to various concentrations of 3-methylcholanthrene and 200 microg/L ethoxyresorufin for 24 h was proportional to the 3-methylcholanthrene dose. Activities in the liver and gills peaked at 40 microg/L of 3-methylcholanthrene and then decreased at higher doses, possibly because of 3-methylcholanthrene toxicity. At 1-week post-hatch stage, however, constant high EROD activity was observed in controls and at all 3-methylcholanthrene doses. Four-week post-hatch see-through medaka exhibited less EROD activity than 2-week post-hatch see-through medaka, and activity in the liver peaked at 100 microg/L of 3-methylcholanthrene. Adult see-through medaka were not suitable for fluorescence detection owing to their thick skin, muscle and/or tissue. In tests of oxidative activity response to ethoxyresorufin, 1-day and 1-week post-hatch see-through medaka exhibited high intrinsic EROD activity in the liver, gills, and other organs in the absence of 3-methylcholanthrene. This intrinsic activity declined with growth and explained the high constant EROD activity at 1-week post-hatch stage.

Distribution of nanoparticles in the see-through medaka (Oryzias latipes)

OBJECTIVE

Because the environmental fate of manufactured nanoparticles is considered an emerging environmental concern, I used water-suspended fluorescent nanoparticles (solid latex solution) to investigate the distribution of nanoparticles in the eggs and bodies of see-through medaka (Oryzias latipes).

RESULTS

Particles 39.4-42,000 nm in diameter were adsorbed to the chorion of medaka eggs and accumulated in the oil droplets; 474-nm particles had the highest bioavailability to eggs. Particles 39.4 nm in diameter shifted into the yolk and gallbladder during embryonic development. Adult medaka accumulated 39.4-nm nanoparticles mainly in the gills and intestine when exposed to a 10-mg/L nanoparticle solution. Nanoparticles were also detected in the brain, testis, liver, and blood. Concentrations of nanoparticles in the blood of male and female medaka were 16.5 and 10.5 ng/mg blood protein, respectively. These results suggest that nanoparticles are capable of penetrating the blood-brain barrier and that they eventually reach the brain. Salinity-dependent acute toxicity was observed in medaka eggs exposed for 24 hr to nanoparticles.

CONCLUSION

The bioavailability and toxicity of nanoparticles depend on environmental factors and multiple physicochemical properties. Further studies on the toxic effects of nanoparticles used in commercial products and their environmental relevance, are necessary to define the risks and benefit of nanomaterial applications.

The contributions of hepatitis B virus and hepatitis C virus infections to cirrhosis and primary liver cancer worldwide

BACKGROUND/AIMS

End-stage liver disease accounts for one in forty deaths worldwide. Chronic infections with hepatitis B virus (HBV) and hepatitis C virus (HCV) are well-recognized risk factors for cirrhosis and liver cancer, but estimates of their contributions to worldwide disease burden have been lacking.

METHODS

The prevalence of serologic markers of HBV and HCV infections among patients diagnosed with cirrhosis or hepatocellular carcinoma (HCC) was obtained from representative samples of published reports. Attributable fractions of cirrhosis and HCC due to these infections were estimated for 11 WHO-based regions.

RESULTS

Globally, 57% of cirrhosis was attributable to either HBV (30%) or HCV (27%) and 78% of HCC was attributable to HBV (53%) or HCV (25%). Regionally, these infections usually accounted for >50% of HCC and cirrhosis. Applied to 2002 worldwide mortality estimates, these fractions represent 929,000 deaths due to chronic HBV and HCV infections, including 446,000 cirrhosis deaths (HBV: n=235,000; HCV: n=211,000) and 483,000 liver cancer deaths (HBV: n=328,000; HCV: n=155,000).

CONCLUSIONS

HBV and HCV infections account for the majority of cirrhosis and primary liver cancer throughout most of the world, highlighting the need for programs to prevent new infections and provide medical management and treatment for those already infected.