Janneche Utne Skåre

Natural mixtures of POPs affected body weight gain and induced transcription of genes involved in weight regulation and insulin signaling

Obesity is reaching epidemic proportions worldwide, and is associated with chronic illnesses such as diabetes, cardiovascular disease, hypertension and dyslipidemias (metabolic syndrome). Commonly held causes of obesity are overeating coupled with a sedentary lifestyle. However, it has also been postulated that exposure to endocrine disrupting chemicals (EDCs) may be related to the significant increase in the prevalence of obesity and associated diseases. In the present study, developmental and reproductive effects of lifelong exposure to environmentally relevant concentrations of two natural mixtures of persistent organic pollutants (POPs) were investigated using classical and molecular methods in a controlled zebrafish model. The mixtures used were extracted from burbot (Lota lota) liver originating from freshwater systems in Norway (Lake Mjøsa and Lake Losna). The concentration of POPs in the zebrafish ranged from levels detected in wild fish (Lake Mjøsa and Lake Losna), to concentrations reported in human and wildlife populations. Phenotypic effects observed in both exposure groups included (1) earlier onset of puberty, (2) elevated male/female sex ratio, and (3) increased body weight at 5 months of age. Interestingly, genome-wide transcription profiling identified functional networks of genes, in which key regulators of weight homeostasis (PPARs, glucocoricoids, CEBPs, estradiol), steroid hormone functions (glucocoricoids, estradiol, NCOA3) and insulin signaling (HNF4A, CEBPs, PPARG) occupied central positions. The increased weight and the regulation of genes associated with weight homeostasis and insulin signaling observed in the present study suggest that environmental pollution may affect the endocrine regulation of the metabolism, possibly leading to increased weight gain and obesity.

Natural Mixtures of Persistent Organic Pollutants (POP) Increase Weight Gain, Advance Puberty, and Induce Changes in Gene Expression Associated with Steroid Hormones and Obesity in Female Zebrafish

In the present study, developmental and reproductive effects of lifelong exposure to environmental relevant concentrations of two natural mixtures of persistent organic pollutants (POP) were investigated using classical and molecular methods in a controlled zebrafish model. The mixtures used were extracted from burbot ( Lota lota ) liver originating from freshwater systems in Norway: one mixture with high levels and one mixture with background levels of polybrominated diphenyl ethers (PBDE), polychlorinated biphenyls (PCB), and dichlorodiphenyltrichloroethane metabolites (DDT). The concentration of POP measured in the zebrafish ranged from levels detected in wild fish from Lake Mjøsa to concentrations reported in human and wildlife populations, indicating that the experimental fish were exposed to concentrations comparable with wild fish. Phenotypic effects observed in both exposure groups included earlier onset of puberty, increased male/female sex ratio, and differences in body weight at 5 mo of age. Interestingly, genome-wide transcription profiling showed changes in regulation of genes involved in endocrine signaling and growth. The transcriptomics changes include key regulator genes for steroid hormone functions ( ncoa3 ), and growth (c/ebp, ncoa3 ). The effects observed in the experimental zebrafish model raise the question whether chemical pollution represents a risk to reproductive health of wild fish inhabitating the freshwater system.

Transcriptional Regulation in Liver and Testis Associated with Developmental and Reproductive Effects in Male Zebrafish Exposed to Natural Mixtures of Persistent Organic Pollutants (POP)

Persistent organic pollutants (POP) occur as mixtures in nature and it is difficult to predict the toxicity of such mixtures based on knowledge about toxicity and mechanisms of action for single compounds. The present knowledge on the combined toxic effects and modes of actions of exposure to mixtures is limited. Thus, the scientifically based hazard and risk assessment of POP requires analytical and toxicological data from studies with environmental mixtures of POP. The application of genome wide transcription profiling in toxicology, in combination with classical endpoints, will improve the current understanding of the mechanisms of toxic processes. Furthermore, gene expression data may be useful in establishing new hypothesis and discovering new biomarkers for known toxicity as well as not yet recognized toxicity endpoints. In the present study, developmental and reproductive effects of lifelong exposure to environmental relevant concentrations of two natural mixtures of POP were investigated using classical and molecular methods in a controlled zebrafish model. The mixtures used were extracted from burbot (Lota lota) liver originating from freshwater systems in Norway: one mixture with high levels and one mixture with background levels of polybrominated diphenyl ethers (PBD), polychlorinated biphenyls (PCB), and DDT. The concentration of POP in the zebrafish ranged from levels detected in wild fish from Lake Mjøsa, to concentrations reported in human and wildlife populations. Phenotypic effects observed in both exposure groups included (1) reduced survival, (2) earlier onset of puberty, (3) increased male/female sex ratio, and (4) differences in body weight at 5 mo of age. Interestingly, genome-wide transcription profiling showed changes in regulation of genes involved in endocrine signaling and growth. The transcriptomics changes included (1) key regulator genes for steroid and thyroid hormone functions (cga, ncoa3), (2) insulin signaling and metabolic homeostasis (pik3r1, pfkfb3, ptb1), and (3) p53 activation (mdm4). The effects observed in the experimental zebrafish model raise the question of whether chemical pollution represents a risk to the reproductive health of wild fish inhabiting the freshwater system.

Persistent organic pollutants and mercury in dead and dying glaucous gulls (Larus hyperboreus) at Bjørnøya (Svalbard).

Dead and dying glaucous gulls (Larus hyperboreus) were collected on Bjørnøya in the Barents Sea in 2003, 2004 and 2005. Autopsies of the seabirds only explained a clear cause of death for three (14%) of the 21 birds. A total of 71% of the birds were emaciated. Liver and brain samples were analysed for organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ether (PBDEs), hexabromocyclododecanes (HBCDs) and mercury (Hg). High levels of SigmaOCPs, SigmaPCBs, SigmaPBDEs and alpha-HBCD were found in liver and brain. Compared to the dead and dying glaucous gulls found 1989, the congeners composition tended to change toward more persistent compounds in the 2003-2005 samples. The brain levels of OCPs and PCBs did not differ between 1989 and 2003-2005, while the liver levels were significantly lower. The brain/liver ratio for PCB and PBDE significantly decreased with halogenations of the molecule, indicating a clear discrimination of highly halogenated PCBs and PBDEs entering the brain. There was further a clear negative correlation between contaminant concentrations and body condition. The brain levels were not as high as earlier published lethal levels of p,p-DDE or PCB. However, more recent studies reported a range of sub-lethal OCP- and PCB-related effects in randomly sampled glaucous gulls. An additional elevation of pollutants due to emaciation may increase the stress of the already affected birds. The high brain levels of OCP, PCB and PBDE of present study might therefore have contributed to the death of weakened individuals of glaucous gull.

Parental exposure to natural mixtures of POPs reduced embryo production and altered gene transcription in zebrafish embryos.

Determination of toxicity of complex mixtures has been proposed to be one of the most important challenges for modern toxicology. In this study we performed genome wide transcriptome profiling to assess potential toxicant induced changes in gene regulation in zebrafish embryos following parental exposure to two natural mixtures of persistent organic pollutants (POPs). The mixtures used were extracted from burbot (Lota lota) liver originating from two lakes (Lake Mjøsa and Lake Losna) belonging to the same freshwater system in Norway. The dominating groups of contaminants were polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane metabolites (DDTs). Because both mixtures used in the present study induced similar effects, it is likely that the same toxicants are involved. The Mjøsa mixture contains high levels of PBDEs while this group of pollutants is low in the Losna mixture. However, both mixtures contain substantial concentrations of PCB and DDT suggesting these contaminants as the predominant contributors to the toxicity observed. The observed effects included phenotypic traits, like embryo production and survival, and gene transcription changes corresponding with disease and biological functions such as cancer, reproductive system disease, cardiovascular disease, lipid and protein metabolism, small molecule biochemistry and cell cycle. The changes in gene transcription included genes regulated by HNF4A, insulin, LH, FSH and NF-κB which are known to be central regulators of endocrine signaling, metabolism, metabolic homeostasis, immune functions, cancer development and reproduction. The results suggest that relative low concentrations of the natural mixtures of POPs used in the present study might pose a threat to wild freshwater fish living in the lakes from which the POPs mixtures originated.

Endocrine effects of real-life mixtures of persistent organic pollutants (POP) in experimental models and wild fish.

ABSTRACT A series of studies have assessed the occurrence, levels, and potential adverse effects of persistent organic pollutants (POP) in fish from Lake Mjøsa. In this lake, high levels of various POP were detected in biota. Fish from the nearby Lake Losna contain background levels of POP and served as reference (controls) in these studies. Significantly higher prevalence of mycobacteriosis and pathological changes were documented in burbot (Lota lota) from Mjøsa compared to burbot from Losna. Further, transcriptional profiling identified changes in gene expression in burbot from Mjøsa compared to burbot from Losna associated with drug metabolism enzymes and oxidative stress. POP extracted from burbot liver oil from the two lakes was used to expose zebrafish (Danio rerio) during two consecutive generations. During both generations, POP mixtures from both lakes increased the rate of mortality, induced earlier onset of puberty, and skewed sex ratio toward males. However, opposite effects on weight gain were found in exposure groups compared to controls during the two generations. Exposure to POP from both lakes was associated with suppression of ovarian follicle development. Analyses of genome-wide transcription profiling identified functional networks of genes associated with weight homeostasis, steroid hormone functions, and insulin signaling. In human cell studies using adrenocortical H295R and primary porcine theca and granulosa cells, exposure to lake extracts from both populations modulated steroid hormone production with significant difference from controls. The results suggest that POP from both lakes may possess the potential to induce endocrine disruption and may adversely affect health in wild fish.