Mechanisms of toxicity of hydroxylated polybrominated diphenyl ethers (HO-PBDEs) determined by toxicogenomic analysis with a live cell array coupled with mutagenesis in Escherichia coli.
Results of previous studies have indicated that 6-HO-BDE-47, the addition of the hydroxyl (HO) group to the backbone of BDE-47, significantly increased the toxicity of the chemical compared to its postulated precursor analogues, BDE-47 and 6-MeO-BDE-47. However, whether such a result is conserved across polybrominated diphenyl ether (PBDE) congeners was unknown. Here, cytotoxicity of 32 PBDE analogues (17 HO-PBDEs and 15 MeO-PBDEs) was further tested and the underlying molecular mechanism was investigated. A total of 14 of the 17 HO-PBDEs inhibited growth of Escherichia coli during 4 or 24 h durations of exposure, but none of the MeO-PBDEs was cytotoxic at the concentrations tested. 6-HO-BDE-47 and 2-HO-BDE-28 were most potent with 4 h median effect concentrations (EC50) of 12.13 and 6.25 mg/L, respectively, which trended to be lesser with a longer exposure time (24 h). Expression of 30 modulated and validated genes by 6-HO-BDE-47 in a previous study was also observed after exposure to other HO-PBDE analogues. For instance, uhpT was upregulated by 13 HO-PBDEs, and three rRNA operons (rrnA, rrnB, and rrnC) were downregulated by 8 HO-PBDEs. These unanimous responses suggested a potential common molecular signaling modulated by HO-PBDEs. To explore new information on mechanisms of action, this work was extended by testing the increased susceptibility of 182 mutations of transcriptional factors (TFs) and 22 mutations as genes modulated by 6-HO-BDE-47 after exposure to 6-HO-BDE-47 at the 4 h IC50 concentration. Although a unanimous upregulation of uhpT was observed after exposure to HO-PBDEs, no significant shift in sensitivity was observed in uhpT-defective mutants. The 54 genes, selected by cut-offs of 0.35 and 0.65, were determined to be responsible for "organic acid/oxoacid/carboxylic acid metabolic process" pathways, which supported a previous finding.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing 210089, People's Republic of China.
Guanyong
G
Su
Hongxia
H
Yu
Michael H W
MH
Lam
John P
JP
Giesy
Xiaowei
X
Zhang
D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D053263:Gene Regulatory Networks; D005798:Genes, Bacterial; D055768:Halogenated Diphenyl Ethers / Q000737:chemistry / Q000633:toxicity*; D006900:Hydroxylation; D050296:Microbial Viability / Q000187:drug effects / Q000235:genetics; D016296:Mutagenesis / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D043922:Toxicogenetics / Q000379:methods*; D014157:Transcription Factors / Q000378:metabolism
D055768:Halogenated Diphenyl Ethers; D014157:Transcription Factors