ROLE OF HEPATIC MONOOXYGENASES IN GENERATING ESTROGENIC METABOLITES FROM METHOXYCHLOR AND FROM ITS IDENTIFIED CONTAMINANTS

  • 1 January 1985
    • journal article
    • research article
    • Vol. 27  (1) , 115-124
Abstract
Methoxychlor [a pesticide] [1,1,1-trichloro-2,2-bis(4-methoxyphenyl)ethane] contains estrogenic contaminants and is not per se an estrogen but is a proestrogen being metabolized in vivo into estrogenic products. Structurally identified methoxychlor contaminants were examined as to their estrogenic or proestrogenic properties. The estrogenic activity of demethylated metabolites of methoxychlor and of 1 contaminant was determined. To examine these properties, an assay was developed that monitors whether a given compound, incubated with isolated rat uteri, can diminish the uterine cytosolic estrogen receptor and elevate the nuclear estrogen receptor and whether metabolic intervention by hepatic microsomal monooxygenase(s) is required by the respective compound for this cellular redistribution of the receptor. Of the 15 compounds examined which constitute with methoxychlor 99.5% of total technical grade methoxychlor, 2 compounds, 1,1-dichloro-2-(4-hydroxyphenyl)-2-(4-methoxyphenyl)ethene (mono-OH-MDDE) and 1,1,1-trichloro-2-(4-hydroxyphenyl)-2-(4-methoxyphenyl)ethane (mono-OH-methoxychlor), were active per se and 2 compounds, 1,1-dichloro-2,2-bis(4-methoxyphenyl)ethene (MDDE) and methoxychlor, required metabolic transformation for estrogenic activity to be manifested. The mono- and bis-OH metabolites of MDDE and of methoxychlor were active estrogens and the order of activity, either by the above procedure or in terms of relative binding affinity to rat uterine cytosolic receptor, was as follows: bis-OH-MDDE .mchgt. bis-OH-methoxychlor > mono-OH-MDDE > mono-OH-methoxychlor. Following the in vitro observations, the activity of MDDE and bis-OH-MDDE was determined in vivo in immature rats. Apparently both compounds are estrogenic, yielding marked elevation in ornithine decarboxylase (EC 4.1.1.17) levels and moderate increase in uterine weight. A comparison with methoxychlor and bis-OH-methoxychlor [1,1,1-trichloro-2,2-bis(p-hydroxyphenyl)ethane] demonstrates that the order of potencies is similar to that observed in the in vitro determinations. These studies demonstrate the usefulness of the in vitro assay for determining the estrogenic and proestrogenic properties of compounds of which limited quantities are available, often insufficient for in vivo determination. Whereas the in vitro assay is simple and rapid, a lengthy investigation might be required to determine in vivo whether a given compound is an estrogen or a proestrogen. Lastly, this investigation underlines the necessity for using ultrapure materials when examining highly sensitive biological endpoints, such as estrogenic action. Of additional importance is the availability of structurally characterized compounds, particularly when the compound in question is further metabolized into a biologically active substance.