Abstract
It has been shown that estrogens need to be metabolized to their hydrophobic estrogen ester derivatives to act as antioxidants in lipoproteins. Data suggest that 17β-estradiol (E2) becomes esterified in LCAT-induced reactions and the esters are transported from HDL particles to LDL and VLDL particles by a CETP-dependent mechanism. In the present study we have further investigated the regulation of E2 esterification by LCAT and focused on the importance of HDL structure and composition in the esterification process. Isolated LDL, HDL2, HDL3, and reconstituted discoidal HDL (rHDL) were incubated with labeled E2, with and without purified LCAT, at 37°C for 24 h. After purification of the lipoprotein fractions, there was a significant peak of radioactivity representing esterified estradiol attached to HDL3 and rHDL, but HDL2 and LDL contained only trace amounts of labeled estradiol ester. TLC analysis confirmed that the radioactivity migrated in a position corresponding to that of 17β-E2 17-monoester standard. The amount of radioactivity associated with HDL3 and rHDL representing esterified E2 was significantly increased by addition of purified LCAT. However, only limited increases of radioactivity were observed in HDL2 and LDL. In conclusion, HDL subfractions differ in their potential to regulate estradiol esterification by LCAT. —Höckerstedt, A., M. J. Tikkanen, and M. Jauhiainen. LCAT facilitates transacylation of 17β-estradiol in the presence of HDL3 subfraction.
Highlights
It has been shown that estrogens need to be metabolized to their hydrophobic estrogen ester derivatives to act as antioxidants in lipoproteins
In order to investigate the formation of 17-E2 17-esters in lipoprotein fractions, we incubated isolated HDL and Höckerstedt, Tikkanen, and Jauhiainen LCAT mediates 17-estradiol esterification 393 major HDL subfractions HDL2 and HDL3 with [3H]17-E2 in the presence and absence of purified LCAT (10–73 nmol/h/ml) as well as with and without DTNB at 37ЊC for 24 h
Incubations were carried out using LDL, and reconstituted discoidal HDL (rHDL) apoA-Icholesterol-egg phosphatidyl cholines (PC) in a molar ratio of 1:8:140, v/v/v)
Summary
It has been shown that estrogens need to be metabolized to their hydrophobic estrogen ester derivatives to act as antioxidants in lipoproteins. Data suggest that 17estradiol (E2) becomes esterified in LCAT-induced reactions and the esters are transported from HDL particles to LDL and VLDL particles by a CETP-dependent mechanism. After purification of the lipoprotein fractions, there was a significant peak of radioactivity representing esterified estradiol attached to HDL3 and rHDL, but HDL2 and LDL contained only trace amounts of labeled estradiol ester. When HDL itself becomes oxidized, the efficacy of reverse cholesterol transport is decreased [14] Both an increase in the HDL-LDL ratio and in the antioxidant capacities of both lipoproteins are considered advantageous. Estrogens decrease the plasma level of LDL cholesterol and increase that of HDL in vivo [15, 16], and they inhibit oxidation of both lipoproteins in vitro [17, 18]
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