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The physiology and reproductive performance of eelpout (Zoarces viviparus) have been monitored along the Swedish coast for more than three decades. In this study, transcriptomic profiling was applied for the first time as an exploratory tool to search for new potential candidate biomarkers and to investigate possible stress responses in fish collected from a chronically polluted area. An oligonucleotide microarray with more than 15,000 sequences was used to assess differentially expressed hepatic mRNA levels in female eelpout collected from the contaminated area at Göteborg harbor compared to fish from a national reference site, Fjällbacka. Genes involved in apoptosis and DNA damage (e.g., SMAC/diablo homolog and DDIT4/DNA-damage-inducible protein transcript 4) had higher mRNA expression levels in eelpout from the harbor compared to the reference site, whereas mRNA expression of genes involved in the innate immune system (e.g., complement components and hepcidin) and protein transport/folding (e.g., signal recognition particle and protein disulfide-isomerase) were expressed at lower levels. Gene Ontology enrichment analysis revealed that genes involved biological processes associated with protein folding, immune responses and complement activation were differentially expressed in the harbor eelpout compared to the reference site. The differential mRNA expression of selected genes involved in apoptosis/DNA damage and in the innate immune system was verified by quantitative PCR, using the same fish in addition to eelpout captured four years later. Thus, our approach has identified new potential biomarkers of pollutant exposure and has generated hypotheses on disturbed physiological processes in eelpout. Despite a higher mRNA expression of genes related to apoptosis (e.g., diablo homolog) in eelpout captured in the harbor there were no significant differences in the number of TUNEL-positive apoptotic cells between sites. The mRNA level of genes involved in apoptosis/DNA damage and the status of the innate immune system in fish species captured in polluted environments should be studied in more detail to lay the groundwork for future biomonitoring studies.

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Melanocytes contain several substances formed by the nucleophilic addition of cysteine to dopaquinone. 5-S-Cysteinyldopa is the quantitatively dominant catecholic amino acid belonging to this group of compounds. Glutathione is the thiol most abundantly present in all cells studied, and the reactivity of the SHgroup of this tripeptide with dopaquinone is about one-third that of cysteine. However, the amount of glutathionyldopa is at least two orders of magnitude less than that of cysteinyldopa in the melanocyte. A rapid metabolism of glutathionyldopa has therefore been suggested as an explanation for the above-mentioned findings. The enzyme responsible for hydrolysis of the y-glutamyl bond of glutathione, y-glutamyltranspeptidase, is present in the melanocyte, but in small quantities. Furthermore, S-cysteinylglycinyldopa, which is the product of hydrolysis by y-glutamyltranspeptidase, is found in only very small amounts. These facts taken together contradict the hypothesis that S-cysteinyldopas in the melanocyte are formed from S-glutathionyldopas. The present investigation on IGRl melanoma cells was performed by in situ derivatization of thiols with monobromobimane. Quantitation of the stable bimane adducts of cysteine and glutathione was achieved by reverse-phase high-performance liquid chromatography with fluorimetric detection. The concentration of reduced cysteine in the melanocytes was found to be a few percent of that of reduced glutathione. The quantities of 5-S-cysteinyldopa, 5-S-glutathionyldopa, cysteine, and glutathione observed in the cultured melanoma cells could best be explained by a pronounced compartmentalization of cysteine within the melanocyte, with a high cysteine concentration at the site of the dopaquinone formation.

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