Charles Martucci

P450 enzymes of estrogen metabolism

Endogenous and exogenous estrogens undergo extensive oxidative metabolism by specific cytochrome P450 enzymes. Certain drugs and xenobiotics have been found to be potent inducers of estrogen hydroxylating enzymes with C-2 hydroxylase induction being greater than that of C-16 hydroxylase. Oxygenated estrogen metabolites have different biological activities, with C-2 metabolites having limited or no activity and C-4 and C-16 metabolites having similar potency to estradiol. Pathophysiological roles for some of the oxygenated estrogen metabolites have been proposed, e.g. 16 alpha-hydroxyestrone and 4-hydroxyestrone. These reactive estrogens are capable of damaging cellular proteins and DNA and may be carcinogenic in specific cells.

Aspirin prevents tumors in a murine model of familial adenomatous polyposis

BACKGROUND Both human and murine studies suggest that anti-inflammatory drugs prevent intestinal neoplasia. The purpose of this study was to investigate the role of aspirin as a chemopreventive agent for colorectal cancer. METHODS We administered aspirin to the Min/+ mouse, an animal with a germline mutation in Apc, a gene that is essential for normal epithelial cell growth and differentiation. Apc mutation increases cytoplasmic beta-catenin, a regulatory protein associated with the cytoskeleton. Min/+ mice develop multiple intestinal adenomas and exhibit altered cell growth in the preneoplastic intestinal epithelium. RESULTS Aspirin decreased the rate of tumor formation in Min/+ mice by 44%. Aspirin also normalized enterocyte growth by increasing apoptosis and proliferation in the preneoplastic intestinal mucosa. Finally, aspirin produced a decrease in intracellular beta-catenin levels, suggesting that modulation of this protein is associated with tumor prevention. CONCLUSIONS These data confirm a role for aspirin in suppression of Apc-associated intestinal carcinogenesis.

Distinct forms of hepatic androgen 6β-hydroxylase induced in the rat by indole-3-carbinol and pregnenolone carbonitrile

The ability of indole-3-carbinol (IC), an anticarcinogen present in cruciferous vegetables, to induce CYP1A1, CYP1A2, CYP2B1/2, CYP2E1 and CYP3A1/2 in female rat liver was determined by Western analysis using monoclonal antibodies and compared to effects produced by pregnenolone carbonitrile in animals of both sexes. The ontogeny of induction of these cytochrome P450 isozymes in response to oral administration of IC was also investigated. An inverse correlation was observed between the 6 beta-hydroxylation of androsterone (A) and the induction by IC of CYP3A1/2, the P450 isozyme responsible for the bulk of hepatic 6 beta-hydroxylation of 4-androstenedione (AD). The effect of inhibitors on the formation of 6 beta-OHA from A or AD was also determined and shown to differ from their action on the P450 isozymes involved in the formation of the 6 beta-hydroxylated derivatives of AD or lithocholic acid. The results indicate that the enzyme induced by IC is distinct from the CYP3A1/2 which catalyzes hydroxylations at position 6 beta, allylic in AD but not in the fully saturated ring system of A. The increased hepatic conversion of A to its biologically less active 6 beta-OHA metabolite after treatment of female rats with IC could possibly contribute to the anticarcinogenic action of indole carbinols. It is also proposed that the action of multiple inducers present in cruciferous and other vegetables might produce androgen metabolic profiles very different from those produced by individual components isolated from them.

Changes in Serum Bile Acids in Normal Human Subjects following the Adoption of a Low-Fat Diet

Dietary fat and bile acids have been implicated in the etiology of colon cancer.’S2 The mechanism by which these factors are involved in the etiology of this disease is unclear. In an effort to examine the effect of dietary fat on bile acid metabolism, we measured serum bile acids in fasting normal subjects (n = 12) before and three months following the adoption of a low-fat diet. Seven men and five women changed their diet from an average of 33% calories from fat to an average of 22% calories from fat, for a period of three months. Dietary fat was assessed from food records taken before the dietary change and at the end of the study period. The reduction in fat was achieved primarily by increasing carbohydrate. Blood samples were taken for bile acid measurements using a gas-chromatographic te~hnique.~ The following bile acids were identified and measured: lithocholic (LCA), deoxycholic (DCA), cholic (CA), chenodeoxycholic (CDCA), ursodeoxycholic (UDCA), and 7-ketolithocholic acid (7-KLCA). No significant differences were found in the total amounts of serum bile acids. A compositional change in the bile acids was observed. A comparison of the percentage of individual bile acids at baseline versus three months on a low-fat diet indicated a statistically significant increase in CDCA (14.9 f 5.0% to 24.4 2 18.6%, p < 0.001) and a reduction in UDCA (17.9 f 7.6% to 13.2 2 6.6%, p < 0.01); see FIGURE 1. In two subjects, 7-KLCA was present at low levels before the reduced fat diet, but became unmeasurable after three months on the diet. In the other subjects, 7-KLCA was not measurable before or after the diet period. In all subjects, an increase in the ratio of CDCAKJDCA was consistently observed. The observed changes in serum bile acids can be interpreted as resulting from a reduction in the 7a-hydroxysteroid dehydrogenase activity of intestinal bacteria. As shown in FIGURE^, intestinal bacteria are involved in the conversion of CDCA to UDCA. In this conversion, 7-KLCA is an obligatory intermediate (7-KLCA is formed by 7a-hydroxysteroid dehydrogenase from CDCA). An inhibition of 7a-hydroxysteroid dehydrogenase activity is expected to reduce the formation of 7-KLCA and consequently

Effect of a Low-Fat Diet on Estrogen and Bile Acid Metabolism in Normal Human Subjects

The urinary estrogen metabolites, 2-hydroxyestrone (2-OHE1) and 16α-hydroxyestrone (l6α-OHE1), as well as serum testosterone (T), estradiol (E2), and bile acids were measured in fasting normal subjects (n = 12) before and three months after the adoption of a low-fat diet (initial fat content ca. 40% reduced to ca. 20%). The serum bile acids measured were lithocholic (LCA), deoxycholic (DCA), cholic (CA), chenodeoxycholic (CDCA), and ursodeoxycholic acids (UDCA). No significant differences were found in the absolute or relative ratios for 2-OHE1, 16α-OHE1 E2, or T. The composition of the serum bile acids was changed; comparison of the percentage of each plasma bile acid at baseline with that after three months on the diet indicated an increase in CDCA (14.9% to 24.4%; p < 0.001) and a reduction in UDCA (17.9% to 13.2%; p < 0.01). A marked change in the ratio of CDCA/UDCA was also observed; the ratios of the three-month values compared with baseline were consistently increased by the diet (mean 2.72; SEM ±0.71). Only modest or no differences were observed with the ratios for the other bile acids. Because of the product-precursor relationship between CDCA and UDCA, these data can be interpreted as an indication of a dietary change in bile acid metabolism which resulted in inhibition of the oxidation at the 7-hydroxy group of CDCA and epimerization to UDCA.

Biological Properties of 16α-Hydroxyestrone: Implications in Estrogen Physiology and Pathophysiology

Metabolism of estradiol in men with cirrhosis and subjects with systemic lupus erythematosus results in an excessive formation of 16 alpha-hydroxyestrone. Examination of the biological activity of this metabolite showed that it is a potent uterotropic agent and that it exhibits minimal affinity for the human sex hormone-binding globulin. These biological characteristics are consistent with a hyperestrongenic response to the substance, which may be reflected in the pathology and etiology of these diseases.

DIRECTION OF ESTRADIOL METABOLISM AS A CONTROL OF ITS HORMONAL ACTION—UTEROTROPHIC ACTIVITY OF ESTRADIOL METABOLITES

The uterotrophic activities of the catechol metabolites of estradiol 2-hydroxyestrone, 2-methoxyestrone and 2-hydroxyestradiol were measured under conditions of continuous administration of sc implanted paraffin pellets. The activity of these estrogens was compared to that of estradiol-17beta and its other principal metabolites estrone, estriol and 15alpha-hydroxyestriol (estetrol). The major catechol estrogens, 2-hydroxyestrone and 2-methoxyestrone, and the pregnancy metabolite, 15alpha-hydroxyestriol, exhibited no uterotrophic activity. The minor catecholestrogen, 2-hydroxyestradiol, showed some activity whose character was different from that exhibited by implants of estradiol, estrone and estriol all of which were equipotent uterotrophic agents. Implants of 2-hydroxyestrone in the presence of estradiol or estriol pellets did not diminish the response to the latter indicating that the 2-hydroxyestrone is not antiestrogenic under these conditions. It is concluded that the direction of estradiol metabolism can have a profound influence on the expression of peripheral hormonal activity with hydroxylation at C-2 terminating and hydroxylation at C-16 extending it.