Cadmium‐induced Macrophage LDL and Oxidized LDL Internalization

Abstract

Environmental cadmium exposure has been established as a promotor of vascular inflammation and risk factor for atherosclerosis. Inflammation causes histone release, which was shown to increase macrophage low‐density lipoprotein (LDL) phagocytosis, which initiates foam cell formation, a crucial step in atherosclerosis. The link between histones and macrophages suggests cadmium may increase atherogenesis by upregulating scavenger receptors, which function to bind LDL and Oxidized LDL (OxLDL).RAW 264.7 (murine) macrophages were incubated in a solution of DMEM (Dulbecco's Modified Eagle Medium) and treated with 2 μg LDL, 2 μg histones, and 10 nM, 50 nM, and 200 nM CdCl2 concentrations with varying incubation times (24 hr, 48 hr, and 72 hr). Cells were stained using Oil Red O (lipid sensitive dye) and imaged using a microplate reader at 500 nm. LDL was oxidized by incubation in 10 μM CuSO4 and centrifugal filtration in a PD‐10 spin column. OxLDL was diluted to 2 μg/ml and applied to macrophage cells with the aforementioned conditions, excluding histones. Oil Red O staining and absorbance measurement were performed with similar time constraintsIn vivo studies for measurement of serum LOX‐1, CD‐36 and SR‐A I/II were also performed. LOX‐1, CD‐36, and SR‐A I/II are the main macrophage and endothelial receptors for oxidized LDL. ICR male Mice were exposed to cadmium through drinking water for 8 weeks. Mice were sacrificed, and serum was extracted for assessment of scavenger receptor expression by ELISA assay.Oil Red O staining of RAW 264.7 cells incubated with 2 μg LDL, 2 μg histones and 10 nM, 50 nM, and 200 nM CdCl2 concentrations showed significant dose‐dependent and time‐dependent (24, 48, and 72 hr.) increases in lipid absorbance. Those at the highest CdCl2 concentrations showed the largest increase in LDL uptake, further augmented by histones. Similar results were found in macrophage cells incubated with 2 μg OxLDL. The serum ELISA provided inconclusive results to LOX‐1 serum concentrations.Our data indicates cadmium modulates macrophage function to promote the uptake of LDL, histone‐LDL and OxLDL. We are currently studying the in vitro expression of major scavenger receptors, including LOX‐1, CD‐36 and SR‐A I/II that may provide insight into the mechanism of action for cadmium adverse effects on macrophages.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Association between Heavy Metals, Metalloids and Metabolic Syndrome: New Insights and Approaches

“…In addition to increased lipid biosynthesis and its oxidation due to Cd-induced ROS overproduction [ 89 ], Cd has been shown to induce internalization of LDLs and oxLDLs into macrophages, thus promoting foam cell formation [ 95 ]. Cd exposure increased 35S-sulfate incorporation and LDL binding affinity of carotid artery proteoglycans, resulting in subendothelial retention of atherogenic lipoproteins [ 96 ].…”