Phenobarbital Treatment Inhibits the Formation of Estradiol-Dependent Mammary Tumors in the August-Copenhagen Irish Rat

Abstract

Exposure of female August-Copenhagen Irish (ACI) rats for 28 weeks to 3 mg of estradiol (E 2 ) contained in cholesterol pellets elevated blood E 2 levels and caused palpable mammary tumors in all animals. Coadministration of phenobarbital (PB) in their drinking water reduced the incidence, number, and size of mammary tumors (MTs) but did not reduce blood E 2 levels. Inhibition of MTs by PB was accompanied by significant changes in total hepatic metabolism of E 2 measured in vitro. PB treatment caused approximately a 4-fold increase in hepatic metabolism of E 2 in control and E 2 -treated rats. The major NAD(P)H-dependent metabolites of E 2 were 2-OH-E 2 and estrone (E 1 ). PB, either alone or together with E 2 , increased microsomal 2-hydroxylation of E 2 ; formation of E 1 was either unaffected or decreased slightly. PB also increased microsomal metabolism of E 2 to minor metabolites (4-OH-E 2 , 6␣-OH-E 2 , 6␤-OH-E 2 , 14␣-OH-E 2 , 6-keto E 1 , and 2-OH-E 1 ) and reduced the formation of the E 2 -17␤-oleoyl ester and the E 2 3-and 17-glucuronides. In contrast, when given in combination with E 2 , PB increased the formation of both glucuronides. Cotreatment of animals with PB and E 2 increased activities of NAD(P)H:quinone oxidoreductase and glutathione S-transferase to a greater extent than either compound alone. Collectively, these results show that the multiple actions of PB on hepatic metabolism of E 2 , including induction of E 2 hydroxylation, glucuronidation, and antioxidant defense enzymes along with inhibition of E 2 esterification in livers of female ACI rats, accompany a marked reduction of E 2 -dependent mammary tumors in this model. (Conney et al., 1973). Treatment of rodents with PB induces the synthesis of hepatic microsomal enzymes that hydroxylate progesterone, estradiol (E 2 ), estrone (E 1 ), deoxycorticosterone, testosterone, ⌬ 4 -androstene-3,17-dione, and cortisol (reviewed by Zhu and Conney, 1998). Endogenous estrogens are hydroxylated at multiple positions by several hepatic and nonhepatic microsomal monooxygenase systems (reviewed by Martucci and Fishman, 1993;Zhu and Conney, 1998). The alteration of microsomal hydroxylation of steroids by PB is reflected in vivo by enhanced metabolism and altered actions of steroids. For example, pretreatment of rats with PB decreases the uterotropic action of E 2 and E 1 and enhances their metabolism in vivo (Levin et al., 1967(Levin et al., , 1968. Treatment of rats with PB also inhibits the growth-promoting effect of testosterone on the seminal vesicles (Levin et al., 1974) and decreases the anesthetic action of progesterone and deoxycorticosterone in rodents (Conney et al., 1966). Phenobarbital (PB) is a known inducer of microsomal hydroxylation of drugs and steroids in rodents and in humansOxidative stress arising from redox cycling of catechol estrogens formed during E 2 metabolism has been suggested as an important factor in initiation and progression of many cancers, including mammary carcinogenesis (Cavalieri et al., 1997;Cavalieri and ...

Prevention of Oxidative DNA Damage by Bioactive Berry Components

“…This includes the modulation of hepatic metabolism of estrogen and subsequent effects on mammary tumorigenesis. Kauffman's laboratory (32,33) has demonstrated that alteration of hepatic metabolism of E 2 significantly alters the mammary tumor in- cidence. Wilson and Reed (34) suggested that the species differences in susceptibility to estrogen-induced tumors may arise from distinctive hepatic metabolism of E 2 to 4E 2 in the ACI rat liver.…”

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin administration and high-fat diet on the body weight and hepatic estrogen metabolism in female C3H/HeN mice

“…Recent studies showed that chronic administration of sodium phenobarbital (a prototypic inducer of hepatic drug/steroid-metabolizing enzymes) significantly inhibited the formation of E 2 -induced mammary tumors in female ACI rats [33]. Metabolic analysis showed that this tumor-inhibitory effect of sodium phenobarbital was accompanied by a several-fold increase in hepatic E 2 2-hydroxylation but with little or no change in its 4-and 16α-hydroxylation, while the plasma levels of E 2 were unchanged in these animals [33].…”

Estrogen and androgen receptor status in hepatocellular hypertrophy induced by phenobarbital, clofibrate, and piperonyl butoxide in F344 rats

“…Previous studies, however, have indicated no change in serum estradiol levels by PB (Mesia-Vela et al, 2006) or CF (Eagon et al, 1996). In rat liver, the ER concentration is low before puberty and subsequently increases (Rochman et al, 1985).…”