Comparison of plasma and urinary levels of 2-hydroxyestrogen and 16α-hydroxyestrogen metabolites

Abstract

A modified ELISA assay for measurement of the two estrogen metabolites 2-hydroxyestrone (2OHE1) and 16α-hydroxyestrone (16αOHE1) in plasma and serum has been developed. Previously, these have only been measured in urine. It is not known how well the measurements of these metabolites in urine and plasma are correlated.

The goal of this study was to compare urinary and plasma levels of 2OHE1 and 16αOHE1 and their ratios and to explore how they were affected by ethnicity, dietary and genetic factors, and medication use. Blood and urine samples were obtained from 511 nulliparous women, aged 17–35, from four ethnic groups during the same visit at the study center, on a random day of the menstrual cycle. The overall correlation between the 2OHE1/16αOHE1 ratio in plasma and urine was fair (r_s = 0.52; p < 0.0001). In general, the correlation between the 2OHE1/16αOHE1 ratio in urine and plasma was higher among women not using oral contraceptives (OCs) (r_s = 0.58; p < 0.0001) than among women currently using OCs (r_s = 0.34; p < 0.0001). The correlation was highest for samples obtained during the mid-cycle in among non-OC users (r_s = 0.83; p < 0.0001). Among non-OC users, the urinary 2OHE1/16αOHE1 ratio was stable over the menstrual cycle while there was an increase in the plasma 2OHE1/16αOHE1 ratio. The strongest factors predicting discordance between the urinary and plasma 2OHE1/16αOHE1 ratios among non-OC users were a baseline urinary 2OHE1/16αOHE1 ratio in the three upper quartiles (p < 0.001), the menstrual cycle phase (p = 0.001), and the number of cups of coffee consumed per day (p = 0.006). Among current OC users, the strongest predictors of discordance between the urinary and plasma 2OHE1/16αOHE1 ratios were a baseline urinary 2OHE1/16αOHE1 ratio in the three lower quartiles (p < 0.001), being black (p = 0.001), and being Asian (p = 0.014). In conclusion, we found that the correlation between the two methods was fair and varied according to the baseline urinary 2OHE1/16αOHE1 ratio, ethnic group, OC status, coffee consumption, and time of menstrual cycle when the samples were obtained.

Introduction

Metabolism of estrogen occurs primarily via two mutually exclusive pathways, yielding primarily 2-hydroxylated and 16α-hydroxylated metabolites. Studies have shown that the 2-hydroxylated metabolites, mainly 2-hydroxyestrone (2OHE1), act as a weak estrogens or anti-estrogens [1], whereas 16α-hydroxyestrone (16αOHE1) is uniquely procarcinogenic [2]. Tissue levels of the estrogen metabolites are thought to correlate with the risk of cancer in hormone sensitive organs such as the breast, endometrium, and cervix [3], [4], [5], [6], [7], [8], [9], [10]. Tissue levels of these estrogen metabolites have mainly been inferred from measurements of the 2OHE1 and 16αOHE1 in urine, which can be quite impractical in the clinical setting. Enzyme immunoassays for measurement of 2OHE1 and 16αOHE1 in urine [11] have been modified to measure these metabolites in serum and plasma.

It is known that urinary 2OHE1/16αOHE1 ratios are fairly stable over the menstrual cycle [12]. On the other hand, the 2OHE1 to 16αOHE1 ratios in plasma vary over the menstrual cycle in premenopausal women [13]. However, the variation in the 2OHE1/16αOHE1 ratios in plasma demonstrated during the menstrual cycle is negligible compared to the differences in ratios between women using and those not using oral contraceptives [13].

With the development of a modified ELISA assay for these same estrogen metabolites in plasma/serum, two questions have arisen. First, how well do the measurements of these metabolites in urine and plasma correlate? Second, which assay might better reflect the tissue levels of these hormones? We therefore measured the levels of 2OHE1 and 16αOHE1 in nulliparous young women in plasma and in urine samples that were obtained during the same visit at the study center. We also performed repeated measurements of the two metabolites in multiple adjacent slices of breast tissue obtained from mammoplastic surgeries.

The goal of this study was to compare urinary and plasma levels of 2OHE1 and 16αOHE1 and their ratios among young, nulliparous women from four ethnic groups and to explore how they were affected by ethnicity, dietary and life style factors, and medication use.