ENDOCRINE-DISRUPTING ACTIVITIES OF PCBs AND OTHER FOOD CONTAMINANTS

Transcription

1 ENDOCRINE-DISRUPTING ACTIVITIES OF PCBs AND OTHER FOOD CONTAMINANTS Miroslav Machala 1, Jan Vondráček 2 1 ; 2 Institute of Biophysics, ASCR, Brno, Czech Republic

2 MECHANISTIC STUDIES REVEALED MULTIPLE MODES OF ACTION OF PCBs AhR activation (TEFs, alternate AhR targets) dioxin-like toxicity vs. non dioxin-like effects disruption of Ca2+ signaling / neurotoxicity (neurotoxic equivalence scheme, Pessah 2006; Simon 2007) additional effects (endocrine disruption, tumor promotion): development of REPs, novel non-ahr modes of action (concentrations of NDL-PCBs > > > concentrations of DL/PCBs

3 PCBs as endocrine disruptors AhR activation; disruption of steroid signaling; disruption of thyroid signaling; CAR/PXR-dependent induction of metabolism of xenobiotics and steroid/thyroid hormones developmental toxicity, including neuronal development; reproductive toxicity; metabolic syndrome, obesity, cardiovascular effects?

4 Toxic equivalency factors (TEFs) / Relative effective potencies (REPs) TEF = 1 TEF = 0.1

5 1. AhR ACTIVATION

6 CURRENT STUDIES ON AhR ACTIVATION established WHO TEFs for DL-PCBs; detailed toxic modes of action (cell adhesion, intercellular communication, intracellular signaling pathways, lipid metabolism...) better knowledge of toxicity mechanisms; new in vitro and in vivo dose-response data may suggest revisions of some TEFs (PCB 126, PCB 118); systemic TEFs (based on actual internal PCB concentrations the EU project SYSTEQ).

7 Search for novel AhR targets - global gene expression in the PCB 126-exposed liver progenitor epithelial cells (Faust et al., Arch. Toxicol., submitted) a) List of candidate AhR target genes b) Validation of AhR target genes Foxq1 - an example of novel AhR target gene sirna AhR Ctr. sirna ARNT Ctr. AhR ERK2 ARNT ERK2 silencing AhR AhR inhibitor TCDD CH TCDD + CH AhR sirna ARNT sirna control sirna

8 Relative effective potencies (REPs) in rat human lung epithelial A459 cell line - comparison of canonical and novel AhR targets % TCDD max A549_2,3,7,8-TCDD CYP1A1 TIPARP AhRR concentration (log M) Krčková ( et al., ms. in preparation)

9 Relative effective potencies (REPs) based on established and novel AhR target genes (Krčková et al., ms. in preparation) RLE-6TN REP (EC 20) compound CYP1A1 CYP1B1 TIPARP AhRR Aldh3a1 FOXQ1 TEF (WHO 2005) 2,3,7,8-TCDD ND 1 1,2,3,7,8-PeCDD ND 1 2,3,4,7,8-PeCDF ND 0.3 PCB ND 0.1 PCB ND PCB153 ND ND ND ND ND ND - PCB ND ND

10 CONCLUSIONS: AhR activation in liver and lung cells The AhR agonists induce numerous toxic events events including: - developmental toxicity and endocrine-disrupting effects related to modulation of steroid catabolism and direct interaction of AhR with steroid hormone receptors; - induction of Fst, Hbegf, Foxq1 and other genes being associated with tumor promotion

11 2. DEVELOPMENT OF NON-AhR REP VALUES USING IN VITRO BIOASSAYS

12 IN VITRO PROFILING OF ULTRAPURE NDL-PCBs (REP values derived in eight in vitro bioassays) AR-CALUX ER-CALUX, E2SULT TTR binding assay; UGT1A1, UGT1A6 and deiodinase-1 expression; Acute inhibition of GJIC (Hamers et al., Toxicol Sci, 2011)

13 IN VITRO PROFILING OF ULTRAPURE NDL-PCBs IC50 = um IC50 = um IC50 = > 15 um IC50 = 5-22 um

14 CONTRIBUTION OF INDIVIDUAL CONGENERS TO CALCULATED TOXIC POTENCIES PCB 153 > 138 > 180 PCB 138 > 118 = 180 > 170 PCB 104 > 47 PCB 153 > 138 > 180 PCB 153 > 138 > 180 (168 > 153) PCB 153 > 138 (153 >136) PCB 153 > 138 > 180

15 IN VITRO PROFILING OF ULTRAPURE NDL-PCBs

16 MULTIVARIATE TOXICITY PROFILE based on in vitro REP values (Stenberg et al., Chemosphere, 2011)

17 CONTRIBUTION OF PCB CLUSTERS TO CALCULATED PCB MIXTURE TOXICITY Cluster I: PCB 138, 153, 170, 180, 190 Cluster IV: PCB 95, 101, 136 (when also in vitro data on neurotoxic effects were included into calculations and multivariate toxicity profile used, the smaller ortho-substituted congeners clustered, with PCBs 95, 101 and 136 as generally most active Stenberg et al., Chemosphere, 2011)

18 CLUSTERING OF ASSAYS / ENDPOINTS Anti-AR PCB conc. NEQ GJIC inhibition Anti-ER TTR antagonism ER activity etc. Hamers et al., Toxicol. Sci. 2011; Stenberg et al., Chemosphere, 2011

19 MULTIPLE MECHANISMS CONTRIBUTE TO AhR NRs CROSS-TALK

20 WHAT ARE THE CRITICAL HEALTH EFFECTS OF NDL-PCBs? Anti-AR and other ED effects (hypothyroxinemia) versus neurotoxic equivalency factors (RyR, dopamine, serotonin, glutamate and GABA uptake,...) Developmental toxicity? Mariussen, Fonnum, Toxicology, 2001; Miller et al., J. Dev. Neurosci., 2010; Pessah et al., Pharmacol. Ther., 2010; Hamers et al., Toxicol. Sci. 2011; Stenberg et al., Chemosphere, 2011 Is it presently possible to establish equivalency factors for NDL-PCBs? Are microm concentrations effective in the in vitro assays realistic in view of exposure data?

21 3. ENDOCRINE-DISRUPTING ACTIVITIES OF EMERGING ORGANIC POLLUTANTS

22 REP APPROACH COULD BE USED ALSO FOR RISK ASSESSMENT OF OTHER FOOD CONTAMINANTS?

23 Polybrominated diphenyl ethers (PBDEs) Critical health effect: activation of CAR/PXR metabolic disruption of thyroid hormone homeostasis (systemic concentrations of T3, T4 neurodevelopmental and behaviour effects direct modulation of thyroid hormone receptor (TR) activity neurodevelopmental and behaviour effects ref.: EFSA Journal, 2011

24 CONCLUSIONS - Persistent organic pollutants such as PCBs exert numerous adverse effects on endocrine regulation. - Their ED effects may seriously affect development and reproductive health. - Emerging evidence suggests that in vitro evaluation of their toxic effects may contribute both to risk assessment of individual POP compounds and to identify novel hazards associated with POP exposure such as obesogenic effects.

25 Acknowledgement Katerina Pencikova, Petra Hulinkova, Simona Krckova, Lenka Umannova, Jirina Prochazkova, Marketa Kabatkova, Jan Vondracek, Vitezslav Bryja, Pavel Krcmar Veterinary Research Institute, Brno and Institute of Biophysics AS CR, Brno, Czech Republic 2) Other principal collaborators: Institute of Experimental Medicine AS CR, Prague (development of global gene expression data); Johannes Gutenberg University, Mainz, Germany (disruption of contact inhibition, validation of modulated AhR target genes); University of Utrecht and Free University Amsterdam, The Netherlands (endocrine disruption, toxic equivalency factors etc.). Supported by the EU 6th and 7th FP ATHON and SYSTEQ projects.

26 THANK YOU FOR YOUR ATTENTION