Do contaminants in polar bear (Ursus maritimus) modulate the expression of selected genes and cause DNA strand breaks?

• Main Author: Gilmore, Erik Howard
• Format: Master Thesis
• Language: Norwegian
• Published: 2015
• Subjects: Arctic; Norway; Svalbard; Ursus maritimus
• Online Access: http://hdl.handle.net/10852/49050; http://urn.nb.no/URN:NBN:no-52833

Long-range transport and deposition of POPs pose a significant threat to Arctic ecosystems, as they have shown to accumulate in Arctic wildlife and biomagnify along Arctic food chains. High trophic level species such as polar bears (Ursus maritimus) are therefore exposed to high levels of POPs, raising concerns about the implications on their health. The aim of this study was to clarify whether there was relationship between the presence of POPs in polar bears and health-related responses linked to oxidative stress, biotransformation, and genotoxicity. Blood and skin samples were collected from 47 free-ranging polar bears, of mixed age and sex, at Svalbard (Norway), during August and September 2013. POPs in plasma were quantified and grouped into six contaminant classes (ΣOH-PCB, ΣPCB, ΣCHL, HCH, β-HCH, and BDE-47) based on inter-correlations and structural similarities. Ten selected gene transcripts (CYP1A1, CYP1B1, TRXR, SOD, CAT, HSP70, E2F1, GR, MT, and GPX) were quantified in skin biopsies using RT-qPCR. DNA strand breaks in lymphocytes were analyzed using the comet assay. In an attempt to optimize the integrity of DNA, the comet assay runs were performed on site, in the field, and potential inter-run variations were normalized using fresh human blood. Polar bear age, sex, and body condition (BCI) were included in all analyzes as confounding variables. No age or sex-related differences in POP concentrations were observed. However, a significant negative relationship between ΣPCB, ΣCHL, and β-HCH plasma concentrations and BCI was observed, suggesting that seasonal fasts influence the tissue-distribution of certain POPs. None of the genes appeared to be related to sex or BCI. Of the ten genes, only CYP1A1 expression was affected by age, for which expression was significantly lower in sub-adults as compared to in adults. CYP1B1 gene expression was positively correlated with ΣPCB concentrations, indicating the transcriptional up-regulation of CYP1B1 by this POP class. No such response was observed for CYP1A1. TRXR gene expression was positively correlated with ΣPCB, HCB, and β-HCH, suggesting a transcriptional up-regulation of TRXR by these POPs, possibly as a response to oxidative stress. No association between POPs and the remaining oxidative stress-related genes was observed. No relationship between DNA damage in lymphocytes and age, sex, and BCI was observed. A significant negative relationship between DNA strand breaks in lymphocytes and ΣOH-PCB and BDE-47 concentrations in plasma was observed, suggesting reduced genotoxicity with increasing POP concentrations. One possible explanation is a response of the immune system which up-regulates DNA damage repair responses following exposure to these POPs. No association between DNA strand breaks and gene expression profiles was observed. The present study showed that it was possible to perform the comet assay under field conditions, and that human blood was useful for normalization of inter-run variations. Long-range transport and deposition of POPs pose a significant threat to Arctic ecosystems, as they have shown to accumulate in Arctic wildlife and biomagnify along Arctic food chains. High trophic level species such as polar bears (Ursus maritimus) are therefore exposed to high levels of POPs, raising concerns about the implications on their health. The aim of this study was to clarify whether there was relationship between the presence of POPs in polar bears and health-related responses linked to oxidative stress, biotransformation, and genotoxicity. Blood and skin samples were collected from 47 free-ranging polar bears, of mixed age and sex, at Svalbard (Norway), during August and September 2013. POPs in plasma were quantified and grouped into six contaminant classes (ΣOH-PCB, ΣPCB, ΣCHL, HCH, β-HCH, and BDE-47) based on inter-correlations and structural similarities. Ten selected gene transcripts (CYP1A1, CYP1B1, TRXR, SOD, CAT, HSP70, E2F1, GR, MT, and GPX) were quantified in skin biopsies using RT-qPCR. DNA strand breaks in lymphocytes were analyzed using the comet assay. In an attempt to optimize the integrity of DNA, the comet assay runs were performed on site, in the field, and potential inter-run variations were normalized using fresh human blood. Polar bear age, sex, and body condition (BCI) were included in all analyzes as confounding variables. No age or sex-related differences in POP concentrations were observed. However, a significant negative relationship between ΣPCB, ΣCHL, and β-HCH plasma concentrations and BCI was observed, suggesting that seasonal fasts influence the tissue-distribution of certain POPs. None of the genes appeared to be related to sex or BCI. Of the ten genes, only CYP1A1 expression was affected by age, for which expression was significantly lower in sub-adults as compared to in adults. CYP1B1 gene expression was positively correlated with ΣPCB concentrations, indicating the transcriptional up-regulation of CYP1B1 by this POP class. No such response was observed for CYP1A1. TRXR gene expression was positively correlated with ΣPCB, HCB, and β-HCH, suggesting a transcriptional up-regulation of TRXR by these POPs, possibly as a response to oxidative stress. No association between POPs and the remaining oxidative stress-related genes was observed. No relationship between DNA damage in lymphocytes and age, sex, and BCI was observed. A significant negative relationship between DNA strand breaks in lymphocytes and ΣOH-PCB and BDE-47 concentrations in plasma was observed, suggesting reduced genotoxicity with increasing POP concentrations. One possible explanation is a response of the immune system which up-regulates DNA damage repair responses following exposure to these POPs. No association between DNA strand breaks and gene expression profiles was observed. The present study showed that it was possible to perform the comet assay under field conditions, and that human blood was useful for normalization of inter-run variations.