estriol-3-glucuronide and estradiol-17-beta-glucuronide

Human multidrug resistance protein 7 (MRP7, ABCC10) is a recently described member of the C family of ATP binding cassette proteins (Cancer Lett 162:181-191, 2001). However, neither its biochemical activity nor physiological functions have been determined. Here we report the results of investigations of the in vitro transport properties of MRP7 using membrane vesicles prepared from human embryonic kidney 293 cells transfected with MRP7 expression vector. It is shown that expression of MRP7 is specifically associated with the MgATP-dependent transport of 17beta-estradiol-(17-beta-D-glucuronide) (E(2)17betaG). E(2)17betaG transport was saturable, with K(m) and V(max) values of 57.8 +/- 15 microM and 53.1 +/- 20 pmol/mg/min. By contrast, with E(2)17betaG, only modest enhancement of LTC(4) transport was observed and transport of several other established substrates of MRP family transporters was not detectable to any extent. In accord with the notion that MRP7 has a bipartite substrate binding pocket composed of sites for anionic and lipophilic moieties, transport of E(2)17betaG was susceptible to competitive inhibition by both amphiphiles, such as leukotriene C(4) (K(i(app)), 1.5 microM), glycolithocholate 3-sulfate (K(i(app)), 34.2 microM) and MK571 (K(i(app)), 28.5 microM), and lipophilic agents such as cyclosporine A (K(i(app)), 14.4 microM). Of the inhibitors tested, LTC(4) was the most potent, in agreement with the possibility that it is a substrate of the pump. The determination that MRP7 has the facility for mediating the transport of conjugates such as E(2)17betaG indicates that it is a lipophilic anion transporter involved in phase III (cellular extrusion) of detoxification.

Topics: Biological Transport; Cells, Cultured; Cyclosporine; Estradiol; Glycocholic Acid; Humans; Kinetics; Leukotriene Antagonists; Leukotriene C4; Multidrug Resistance-Associated Proteins; Osmotic Pressure; Propionates; Quinolines; Recombinant Proteins; Transfection

The multidrug resistance (MDR) gene family has been shown to be highly expressed in several normal tissues including the canalicular membrane of the hepatocyte. We report that a cholestatic estrogen metabolite, 17 beta-estradiol glucuronide (E217G), is a substrate for the MDR transporter, P-glycoprotein. In cytotoxicity studies, the MDR sarcoma cell line Dx5 was 4.7-fold resistant to E217G, and the K562/R7 leukemia MDR cell line was 5.0-fold resistant to E217G relative to their parental cell lines. There was also a 2- to 3-fold accumulation defect of [3H]E217G in the MDR cells relative to their parental cell lines. E217G (100 microM) modulated resistance ot doxorubicin, taxol, vinblastine, and etoposide in the Dx5 cells, completely reversing the 30- to 60-fold resistance observed with these agents. E217G had no effect on the toxicity of these compounds in the parental cell line (MES-SA). In contrast, MDR cells were not resistant to the noncholestatic estrogen metabolite, estriol 3-glucuronide, and this metabolite did not modulate resistance to MDR substrates. ATP-dependent transport of [3H]E217G in rat canalicular membranes was inhibited by several MDR substrates including vinblastine, etoposide, verapamil, cyclosporine, and PSC-833.

Topics: Cholestasis; Doxorubicin; Drug Resistance; Estradiol; Estriol; Etoposide; Humans; Leukemia, Myeloid; Paclitaxel; Sarcoma; Tumor Cells, Cultured; Vinblastine

In attempt to find a more reliable and earlier predictor of ovulation, radioimmunoassay methods were investigated which could measure the levels of steroid glucuronides (follicular estrogens), varying levels of which would warn of approaching ovulation well before (up to 96 hours) its occurrence so that abstinence can be practiced during the period of sperm viability before the egg is released. To this end, daily urine collections were made on 9 subjects and the steroid glucuronides were totalled. In addition, the excretion of 5 beta-pregnanediol-3 alpha-glucuronide was measured throughout the menstrual cycle. Measurement of this parameter seemed of more practical value since the ratio of estrone-3-glucuronide/pregnanediol-3 alpha-glucuronide rises during the periovulatory period and falls sharply after the formation of the corpus lutuem. This parameter, unlike measurement of total steroid glucuronides, is not dependent on the rate of excretion or on concentration. In all 9 subjects, a significant increase in this ratio (P .05) was detected 48-120 hours before the plasma lutropin maximum. For assay, this ratio value is easier to assess because the assay kit would be applicable to early morning urine samples and would not involve any measurement of urine volume or time. A short discussion follows the experimental presentation.

Topics: Estradiol; Estriol; Estrogens; Estrone; Female; Fertility; Glucuronates; Humans; Menstruation; Ovulation