Abstract
High density lipoprotein (HDL) can protect low density lipoprotein (LDL) against oxidation. Oxidized cholesterol esters from LDL can be transferred to HDL and efficiently and selectively removed from the blood circulation by the liver and adrenal in vivo. In the present study, we investigated whether scavenger receptor BI (SR-BI) is responsible for this process. At 30 min after injection, the selective uptake of oxidized cholesterol esters from HDL for liver and adrenal was 2.3- and 2.6-fold higher, respectively, than for native cholesterol esters, whereas other tissues showed no significant difference. The selective uptake of oxidized cholesterol esters from HDL by isolated liver parenchymal cells could be blocked for 75% by oxidized LDL and for 50% by phosphatidylserine liposomes, both of which are known substrates of SR-BI. In vivo uptake of oxidized cholesterol esters from HDL by parenchymal cells decreased by 64 and 81% when rats were treated with estradiol and a high cholesterol diet, respectively, whereas Kupffer cells showed 660 and 475% increases, respectively. These contrasting changes in oxidized cholesterol ester uptake were accompanied by similar contrasting changes in SR-BI expression of parenchymal and Kupffer cells. The rates of SR-BI-mediated selective uptake of oxidized and native cholesterol esters were analyzed in SR-BI-transfected Chinese hamster ovary cells. SR-BI-mediated selective uptake was 3.4-fold higher for oxidized than for native cholesterol esters (30 min of incubation). It is concluded that in addition to the selective uptake of native cholesterol esters, SR-BI is responsible for the highly efficient selective uptake of oxidized cholesterol esters from HDL and thus forms an essential mediator in the HDL-associated protection system for atherogenic oxidized cholesterol esters.
Highlights
In vivo uptake of oxidized cholesterol esters from High density lipoprotein (HDL) by parenchymal cells decreased by 64 and 81% when rats were treated with estradiol and a high cholesterol diet, respectively, whereas Kupffer cells showed 660 and 475% increases, respectively
As for native cholesterol esters, the increased selective uptake of HDL-CEOH by the liver is mediated by the parenchymal cells in vivo [2]
To answer the question of whether scavenger receptor class BI (SR-BI) is mediating this increased selective uptake of HDL-CEOH, the inhibitory effects of known SR-BI substrates on HDL-CEOH uptake by isolated parenchymal cells were compared with the inhibitory effects on the selective uptake of HDL cholesteryl ester (HDL-CE) and HDL particle association as measured by iodinated HDL
Summary
Materials—[Cholesteryl-1,2,6,7-3H(N)]-linoleate was purchased from NEN Life Science Products. [1␣,2␣(n)-3H]Cholesteryl linoleate ([3H]CH18:2) and 125I (carrier free) in NaOH were obtained from Amersham Pharmacia Biotech. 2,2Ј-Azobis-(2,4-dimethyl-valeronitrile) was purchased from Polyscience (Warrington, Florida). 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)(NBD)-23,24-bisnor-5-cholen-3-yl linoleate and carboxyfluorescein diacetate was obtained from Molecular Probes (Eugene, OR). The effect of the labeling procedure on HDL was analyzed by measurement of phospholipid, cholesterol, cholesteryl ester, and triglyceride content (with the phospholipid, cholesterol oxidase-peroxidase aminophenazone, and glycerolphosphate oxidase-peroxidase aminophenazone kits, respectively). HDL lipids were extracted into methanol/hexane (1:5), and the hexane phase, containing the neutral lipids, was dried and analyzed by HPLC as described [2]. For in vitro competition studies, the liver cells were incubated with the indicated amount of radiolabeled HDL and competitors for 180 min in 1 ml of DMEM containing 2% BSA at 37 °C. Bated on glass coverslips in 6-well plates (Costar, Cambridge MA) for 2 h at 4 °C in DMEM supplemented with 2% BSA and the indicated amount of oxidized NBD cholesteryl linoleate-labeled HDL or carboxyfluorescein diacetate. Protein Determination—Protein was determined according to Lowry et al [34] with BSA as standard
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
