Genomic profiling reveals an alternate mechanism for hepatic tumor promotion by perfluorooctanoic acid in rainbow trout.
BACKGROUND
Perfluorooctanoic acid (PFOA) is a potent hepatocarcinogen and peroxisome proliferator (PP) in rodents. Humans are not susceptible to peroxisome proliferation and are considered refractory to carcinogenesis by PPs. Previous studies with rainbow trout indicate they are also insensitive to peroxisome proliferation by the PP dehydroepiandrosterone (DHEA), but are still susceptible to enhanced hepatocarcinogenesis after chronic exposure.


OBJECTIVE
In this study, we used trout as a unique in vivo tumor model to study the potential for PFOA carcinogenesis in the absence of peroxisome proliferation compared with the structurally diverse PPs clofibrate (CLOF) and DHEA. Mechanisms of carcinogenesis were identified from hepatic gene expression profiles phenotypically anchored to tumor outcome.


METHODS
We fed aflatoxin B(1) or sham-initiated animals 200-1,800 ppm PFOA in the diet for 30 weeks for tumor analysis. We subsequently examined gene expression by cDNA array in animals fed PFOA, DHEA, CLOF, or 5 ppm 17beta-estradiol (E(2), a known tumor promoter) in the diet for 14 days.


RESULTS
PFOA (1,800 ppm or 50 mg/kg/day) and DHEA treatments resulted in enhanced liver tumor incidence and multiplicity (p < 0.0001), whereas CLOF showed no effect. Carcinogenesis was independent of peroxisome proliferation, measured by lack of peroxisomal beta-oxidation and catalase activity. Alternately, both tumor promoters, PFOA and DHEA, resulted in estrogenic gene signatures with strong correlation to E(2) by Pearson correlation (R = 0.81 and 0.78, respectively), whereas CLOF regulated no genes in common with E(2).


CONCLUSIONS
These data suggest that the tumor-promoting activities of PFOA in trout are due to novel mechanisms involving estrogenic signaling and are independent of peroxisome proliferation.
Tilton
Susan C
SC
Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon, USA. stilton@fhcrc.org
Orner
Gayle A
GA
Benninghoff
Abby D
AD
Carpenter
Hillary M
HM
Hendricks
Jerry D
JD
Pereira
Cliff B
CB
Williams
David E
DE
D016604:Aflatoxin B1 / Q000633:toxicity; D000818:Animals; D002210:Caprylates / Q000633:toxicity*; D015197:Carcinogenicity Tests; D002994:Clofibrate / Q000633:toxicity; D016000:Cluster Analysis; D003687:Dehydroepiandrosterone / Q000633:toxicity; D004195:Disease Models, Animal; D004958:Estradiol / Q000494:pharmacology; D005466:Fluorocarbons / Q000633:toxicity*; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D023281:Genomics; D008113:Liver Neoplasms / Q000139:chemically induced* / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D017686:Oncorhynchus mykiss / Q000235:genetics* / Q000378:metabolism; D020675:Peroxisomes / Q000187:drug effects*; D015398:Signal Transduction
D002210:Caprylates; D005466:Fluorocarbons; D003687:Dehydroepiandrosterone; D004958:Estradiol; C023036:perfluorooctanoic acid; D016604:Aflatoxin B1; D002994:Clofibrate