Identification of 4-hydroxyheptachlorostyrene in polar bear plasma and its binding affinity to transthyretin: A metabolite of octachlorostyrene?

A new compound, 4-hydroxyheptachlorostyrene (4-OH-HpCS), was identified as a major component in the chlorinated phenolic compound fraction of polar bear plasma. The structure was hypothesized to be 4-OH-HpCS based on mass spectral interpretation, the assumption that it was a metabolite of octachlorostyrene, and the similarity of the structure to hydroxylated polychlorinated biphenyls (OH-PCBs) identified in plasma. High-resolution, electron impact (EI) ionization mass spectrometry of the methylated compound indicated a molecular formula of C9H3OCl7 and major fragment ions of [M - 15](+), [M - 35](+), and [M - 43](+), which was a mass spectral pattern identical to a synthesized and methylated 4-OH-HpCS standard. The identity was further confirmed by matching gas chromatography (GC) retention times on three different GC columns of differing polarity. Levels of 4-OH-HpCS ranged from 2.89 to 22.9 ng/g wet weight in polar bear plasma (N=30) and constituted between 3.8 and 24.8% of the total quantified level of chlorinated phenolic compounds. The mean ratio of 4-OH-HpCS to CB153 concentrations in polar bear plasma samples was 0.712 (+/- 0.580 SD), which suggests selective retention of the 4-OH-HpCS in plasma. The presumed mechanism of retention involves 4-OH-HpCS binding to transthyretin (TTR). The presence of TTR was confirmed for the first time in polar bear plasma by binding of I-125-thyroxine (T-4), the natural ligand of TTR, to separated plasma proteins. The binding affinity of 4-OH-HpCS to human TTR was tested and found to be 1.1 relative to T-4. This suggests that 4-OH-HpCS has the potential to disrupt T-4 and retinol transport, by analogy to OH-PCBs with similar structure. Metabolism of octachlorostyrene (OCS) is the most likely source of 4-OH-HpCS. DCS was shown to be present at low concentrations in polar bear tissues as well as in plasma of ringed seal, the principal prey species of polar hears. The ratio of 4-OH-HpCS to OCS and 4-OH-HpCS to CB153 concentrations were 150- and 44-fold higher in polar bear plasma than in ringed seal plasma. This study indicates that the phenolic metabolites of relatively minor contaminants possess the capacity to bind to circulating proteins, and their significance as potential endocrine-disrupting agents may be underestimated.