Alginic acid cell entrapment: a novel method for measuring in vivo macrophage cholesterol homeostasis

Abstract

This article is available online at http://www.jlr.org the uptake of free and esterifi ed cholesterol by the cells from modifi ed LDL ( 2 ). The excess free cholesterol is converted to cholesteryl ester by the enzymatic activity of ACAT and stored in lipid droplets. As cholesterol loading plays a critical role in atherosclerosis progression, there is great interest in understanding factors that prevent cholesterol accumulation either through decreased cellular cholesterol uptake or increased cholesterol effl ux. Cholesterol loading engenders a complex network of changes in gene and protein expression, mostly furthering infl ammation. Increased cholesterol effl ux is the fi rst step in reverse cholesterol transport (RCT), in which excess cholesteryl ester is hydrolyzed and transported through the plasma membrane by means of ABC transporters to extracellular acceptors, which carry the effl uxed cholesterol through the plasma to the liver for conversion to bile acids for subsequent excretion in the feces ( 3 ). It is by means of this RCT that HDL and its associated apolipoproteins (e.g., apoA-I and apoE) are thought to exhibit some of their antiatherogenic properties and to furnish the basis of the epidemiologic inverse correlation between HDL levels and coronary artery disease ( 4-6 ). There is an extensive body of literature demonstrating the in vitro impact of apoA-I, HDL, and cholesterol transporters on macrophage cholesterol levels ( 7,8 ). Until recently, however, there have been no in vivo methods to examine the impact of RCT on the macrophages themselves, in other words, on the cholesterol balance within the macrophage foam cells. Recent work by Weibel and colleagues ( 9 ) has demonstrated the importance of considering both cholesterol infl ux and effl ux when evaluating the impact of serum components on cholesterol homeostasis and atherosclerosis. Cardiovascular disease including atherosclerosis continues to be one of the leading causes of mortality throughout the world ( 1 ). The accumulation of cholesterol-loaded macrophages is a critical step in the progression of atherosclerotic lesion development.

Do the Apoe −/− and Ldlr −/– Mice Yield the Same Insight on Atherogenesis?

“…On the other hand, peritoneal macrophages from the double knockout mice did not have an increased load of cholesterol compared to Ldlr−/− mice 45 , perhaps because the plasma cholesterol was substantially lower in the double knockouts. With Apoe−/−Apoa1−/− mice fed a Western type diet, no obvious skin lesions were noted and the peritoneal macrophages isolated at 6 weeks of diet had twice the cholesterol load compared to their single Apoe−/− counterparts 46 . The basis for these distinctions is not clear.…”

A Theragnosis Probe Based on BSA/HSA-Conjugated Biocompatible Fluorescent Silicon Nanomaterials for Simultaneous in Vitro Cholesterol Effluxing and Cellular Imaging of Macrophage Cells

“…The selection of these cell lines were made on the basis of the fact that macrophages participate in cholesterol homeostasis. Further, the overdeposition of cholesterol causes atherosclerosis in foam cell macrophages in the arterial walls, and hence, these cells can act as cholesterol donors. − …”

Apoprotein E and Reverse Cholesterol Transport

“…The entrapment of macrophages of various tissue sources in alginate capsules in vivo offers an unexplored opportunity to attempt to resolve these questions, using the same macrophages in culture and in vivo. This complexity is preliminarily illustrated in a recent publication [ 17 ].…”

“…Nor does it inform us about the possible contribution to the cholesterol pool by endogenous synthesis. To address some of these issues, Sontag and colleagues described a procedure in which macrophages loaded with cholesterol, with or without radiolabeled free cholesterol, are sequestered in alginate capsules under the skin [ 17 ]. The capsules are easily formed and recovered 24–48 h after injection.…”