Disruption of thyroid hormone (TH) levels and TH-regulated gene expression by polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and hydroxylated PCBs in e-waste recycling workers

Abstract

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are the primary toxicants released by electronic waste (e-waste) recycling, but their adverse effects on people working in e-waste recycling or living near e-waste sites have not been studied well. In the present study, the serum concentrations of PBDEs, PCBs, and hydroxylated PCBs, the circulating levels of thyroid hormones (THs), and the mRNA levels of seven TH-regulated genes in peripheral blood leukocytes of e-waste recycling workers were analyzed. The associations of the hormone levels and gene expression with the exposure to these contaminants were examined using multiple linear regression models. There were nearly no associations of the TH levels with PCBs and hydroxylated PCBs, whereas elevated hormone (T and T) levels were associated with certain lower-brominated BDEs. While not statistically significant, we did observe a negative association between highly brominated PBDE congeners and thyroid-stimulating hormone (TSH) levels in the e-waste workers. The TH-regulated gene expression was more significantly associated with the organohalogen compounds (OHCs) than the TH levels in these workers. The TH-regulated gene expression was significantly associated with certain PCB and hydroxylated PCB congeners. However, the expression of most target genes was suppressed by PBDEs (mostly highly brominated congeners). This is the first evidence of alterations in TH-regulated gene expression in humans exposed to OHCs. Our findings indicated that OHCs may interfere with TH signaling and/or exert TH-like effects, leading to alterations in related gene expression in humans. Further research is needed to investigate the mechanisms of action and associated biological consequences of the gene expression disruption by OHCs.

Thyroid Disrupting Chemicals

“…In the cohort, there was a negative correlation between free T3 (FT3) and PCB levels, and no correlation was found with the hormone levels in the cord blood [11]. A very recent study conducted on a population of electronic waste recycling workers didn't show any correlation between thyroid hormone and PCB or hydroxylated PCB levels examined in the population [12]. The potential effect of perinatal exposure to PCBs and hydroxylated PCBs (OH-PCBs) from the background on thyroid hormones in serum and cord blood was assessed in a cohort of 100 mothers and infants.…”

“…At the time of delivery, a relationship between the PBDEs level and reduced levels of TT4, FT4 and TSH was noticed [11]. The same study evaluating the effect of PCBs on thyroid function in population of electronic waste recycling workers showed a positive association between thyroid hormones and some low brominated congeners from a mixture of BDEs; a negative association was also seen between TSH and some highly brominated BDEs of the mixture used [12]. Zheng et al studied a cohort of 72 pair mother-foetus in Wenling, China, an area where the exposure to PBDE is due to the electronic waste activity.…”

“…The expression of most target genes was suppressed by PBDEs (mostly highly brominated congeners). [12] Correlation between levels of PBDEs in maternal and foetal serum with thyroid hormones in an Indiana population.…”

Cytochrome P450 1A2 activity and incidence of thyroid disease and cancer after chronic or acute exposure to dioxins

“…Dioxins have been associated with thyroid disruption through various mechanisms such as altering transport across cell membranes and inhibition of sulfation of thyroid hormones . Thyroid disruption has been observed after PCBs or dioxin exposure in the general population, pregnancy and infants . An analysis of the US‐veteran affairs healthcare system showed a higher prevalence thyroid cancer in Vietnam veterans exposed to Agent Orange that was used as defoliant.…”

“…36 Thyroid disruption has been observed after PCBs or dioxin exposure in the general population, pregnancy and infants. [37][38][39][40] An analysis of the US-veteran affairs healthcare system showed a higher prevalence thyroid cancer in Vietnam veterans exposed to Agent Orange 41 that was used as defoliant. In another longitudinal study, it was shown that serum TCDD levels were correlated with serum TSH levels.…”