Role of lysosomal acid lipase in the intracellular metabolism of LDL-transported dehydroepiandrosterone-fatty acyl esters

Abstract

H]DHEA-FAE entered cells via LDL receptor or LDL receptorrelated receptor-mediated uptake, followed by intracellular hydrolysis and further metabolism into 5␣-adione and 4-adione that were excreted from cells. Although LAL contributed to the deesterification of DHEA-FAE, it was not solely responsible for the hydrolysis. ribonucleic acid interference; chromatography; dehydroepiandrosterone STEROID FATTY ACYL ESTERS (FAE) such as 17␤-estradiol-FAE (E 2 -FAE) and dehydroepiandrosterone-FAE (DHEA-FAE) belong to a unique family of naturally occurring hydrophobic hormone derivatives (15, 16). These steroids are esterified in a reaction catalyzed by plasma lecithin-cholesterol acyltransferase associated with high-density lipoprotein (HDL) particles and transported to other lipoprotein particles (14,18,30,35,42). The physiological role of steroid-FAE remains unclear. E 2 -FAE have been considered as the storage form of active estrogen in lipoproteins and adipose tissues that may be released as an active unconjugated hormone (3). It has also been suggested that E 2 -FAE may act as an antioxidant, protecting lipoproteins against oxidation (17, 41). Our previous studies (4) in a cell culture model demonstrated that lipoprotein-associated E 2 -FAE can be transferred into target cells and hydrolyzed to free E 2 .Compared with E 2 -FAE that is present in picomolar concentration in the circulation, nanomolar concentrations of circulating DHEA-FAE have been reported (7,26). Moreover, its hydrolysis product, DHEA, is one of the relatively abundant adrenal steroids secreted in humans and the precursor of estrogens and androgens (24). In blood, Ͼ90% of DHEA-FAE is associated with lipoproteins (38, 39). We are interested in the intracellular hydrolysis and metabolic fate of lipoproteinbound DHEA-FAE in target tissues.In postmenopausal women, only trace amounts of E 2 are present in serum, the overwhelming majority of estradiol residing in adipose tissue, mostly in the form of FAE (3). This finding opens up the possibility that adipose tissue could constitute a reservoir of many other steroid-FAEs from which active steroid hormones could, in principle, be liberated by hydrolysis of the FAE bond. Therefore, we aimed at exploring possible hydrolytic mechanisms involved in generating free DHEA and identifying potential bioactive metabolites of DHEA generated in cells. Lysosomal acid lipase (LAL) is the enzyme responsible for the intracellular hydrolysis of LDLassociated cholesteryl esters (cholesteryl-FAE) that are taken up by LDL-receptor-mediated endocytosis (12). Because of the similar ring structure of DHEA and cholesterol, we investigated the possibility that DHEA-FAE is also hydrolyzed by LAL. We chose HeLa cells as a model to study the hydrolysis and metabolism of LDL-associated DHEA-FAE because these cells, derived from the reproductive tract, have previously been useful in the study cholesterol metabolism (19,22,37). Moreover, HeLa cells express LAL mRNA (1) and RNA silencing works very reproducibly in these cells. Thus we inv...

Fatty acid esters of steroids: Synthesis and metabolism in lipoproteins and adipose tissue

“…Further experiments in LALdeficient human fibroblasts showed, however, that this hydrolysis was dependent on LAL activity only to limited extent, suggest- ing the possibility of hormone-sensitive lipase being involved (see Section 3.2). Interestingly, after 48-h incubation of the cells with LDL-associated labeled dehydroepiandrosterone fatty acid esters, the fraction containing esterified dehydroepiandrosterone was recovered in the cellular fraction, while biologically active, unesterified dehydroepiandrosterone and its metabolites, androstenediol and androstenedione were secreted into the cell culture medium [62]. Thus, the findings supported the concept that in this cell line, in addition to esterase activity, other enzyme activities needed for the conversion of dehydroepiandrosterone to other metabolites are present.…”

“…The ratio of fatty acid esterified to nonesterified dehydroepiandrosterone in human male plasma is approximately 0.5 [61]. Wang et al studied the metabolism of LDL-associated dehydroepiandrosterone fatty acid esters in human cultured HeLa cells [62]. The study indicated that the cellular uptake of LDL-associated dehydroepiandrosterone esters was mediated by LDL receptors or related receptors, as excess of LDL competitively inhibited the internalization of radiolabeled dehydroepiandrosterone esters.…”

“…5). Since Roy and Bélanger [61] as well as we have previously reported that lipoprotein-associated steroid fatty acid esters can enter cells by lipoprotein receptor-mediated pathways and intracellularly become hydrolyzed into biologically active steroid hormones [58,62], one possibility is that HDL containing esterified dehydroepiandrosterone could enter endothelial cells followed by the hydrolysis of the ester producing biologically active dehydroepiandrosterone with vasodilatory properties [66].…”

Steroid sulfatase activity in subcutaneous and visceral adipose tissue: a comparison between pre- and postmenopausal women

“…We have previously investigated DHEA in a form of inactive fatty acyl ester and shown that it can be bound by lipoprotein particles in the circulation and taken up by lipoprotein receptors into peripheral cells and hydrolyzed to biologically active DHEA to be used as a precursor for other steroids (12,13,14). In the present study, we investigated hydrolysis of DHEA sulfate ester in adipose tissue samples obtained from premenopausal and postmenopausal women.…”

Quantitative determination of dehydroepiandrosterone fatty acyl esters in human female adipose tissue and serum using mass spectrometric methods

“…DHEA-FAE are hormonally inactive and capable of function only after hydrolysis to free DHEA. Lipoprotein-associated DHEA-FAE can be transferred via lipoprotein receptors into peripheral cells and serve as precursors of DHEA and its metabolites, such as androst-5-ene-3␤,17␤-diol [9], 5␣-androstanedione and androstenedione [10].…”