Dehydroepiandrosterone fatty acyl esters in high density lipoprotein: interaction with human vascular endothelial cells and vascular responses ex vivo

Scavenger Receptor Class B type 1 (SR-B1) and the modifiable risk factors of stroke

Stroke is a devastating disease that occurs when a blood vessel in the brain is either blocked or ruptured, consequently leading to deficits in neurological function. Stroke consistently ranked as one of the top causes of mortality, and with the mean age of incidence decreasing, there is renewed interest to seek novel therapeutic treatments. The Scavenger Receptor Class B type 1 (SR-B1) is a multifunctional protein found on the surface of a variety of cells. Research has found that that SR-B1 primarily functions in an anti-inflammatory and anti-atherosclerotic capacity. In this review, we discuss the characteristics of SR-B1 and focus on its potential correlation with the modifiable risk factors of stroke. SR-B1 likely has an impact on stroke through its interaction with smoking, diabetes mellitus, diet, physical inactivity, obesity, hypercholesterolemia, atherosclerosis, coronary heart disease, hypertension, and sickle cell disease, all of which are critical risk factors in the pathogenesis of stroke.

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

OBJECTIVE

Adipose tissue is an important extragonadal site for steroid hormone biosynthesis. After menopause, estrogens are synthesized exclusively in peripheral tissues from circulating steroid precursors, of which the most abundant is dehydroepiandrosterone sulfate (DHEAS). Our aim was to study activity of steroid sulfatase, an enzyme hydrolyzing DHEAS, and expression of steroid-converting enzyme genes in subcutaneous and visceral adipose tissue derived from pre- and postmenopausal women.

DESIGN

Serum and paired abdominal subcutaneous and visceral adipose tissue samples were obtained from 18 premenopausal and seven postmenopausal women undergoing elective surgery for non-malignant reasons in Helsinki University Central Hospital.

METHODS

To assess steroid sulfatase activity, radiolabeled DHEAS was incubated in the presence of adipose tissue homogenate and the liberated dehydroepiandrosterone (DHEA) was measured. Gene mRNA expressions were analyzed by quantitative RT-PCR. Serum DHEAS, DHEA, and estrogen concentrations were determined by liquid chromatography-tandem mass spectrometry.

RESULTS

Steroid sulfatase activity was higher in postmenopausal compared to premenopausal women in subcutaneous (median 379 vs 257 pmol/kg tissue per hour; P=0.006) and visceral (545 vs 360 pmol/kg per hour; P=0.004) adipose tissue. Visceral fat showed higher sulfatase activity than subcutaneous fat in premenopausal (P=0.035) and all (P=0.010) women. The mRNA expression levels of two estradiol-producing enzymes, aromatase and 17β-hydroxysteroid dehydrogenase type 12, were higher in postmenopausal than in premenopausal subcutaneous adipose tissue.

CONCLUSIONS

Steroid sulfatase activity in adipose tissue was higher in postmenopausal than in premenopausal women suggesting that DHEAS, derived from the circulation, could be more efficiently utilized in postmenopausal adipose tissue for the formation of biologically active sex hormones.

Signal transduction by HDL: agonists, receptors, and signaling cascades

Numerous epidemiologic studies revealed that high-density lipoprotein (HDL) is an important risk factor for coronary heart disease. There are several well-documented HDL functions such as reversed cholesterol transport, inhibition of inflammation, or inhibition of platelet activation that may account for the atheroprotective effects of this lipoprotein. Mechanistically, these functions are carried out by a direct interaction of HDL particle or its components with receptors localized on the cell surface followed by generation of intracellular signals. Several HDL-associated receptor ligands such as apolipoprotein A-I (apoA-I) or sphingosine-1-phosphate (S1P) have been identified in addition to HDL holoparticles, which interact with surface receptors such as ATP-binding cassette transporter A1 (ABCA1); S1P receptor types 1, 2, and 3 (S1P1, S1P2, and S1P3); or scavenger receptor type I (SR-BI) and activate intracellular signaling cascades encompassing kinases, phospholipases, trimeric and small G-proteins, and cytoskeletal proteins such as actin or junctional protein such as connexin43. In addition, depletion of plasma cell cholesterol mediated by ABCA1, ATP-binding cassette transporter G1 (ABCG1), or SR-BI was demonstrated to indirectly inhibit signaling over proinflammatory or proliferation-stimulating receptors such as Toll-like or growth factor receptors. The present review summarizes the current knowledge regarding the HDL-induced signal transduction and its relevance to athero- and cardioprotective effects as well as other physiological effects exerted by HDL.