Browsing by Subject "Erythrocytes"
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Item A Bacterial Cholesterol Sensor to Assess Cholesterol Accessibility in Red Blood Cells(2016-01-19) Chakrabarti, Rima Shah; Radhakrishnan, Arun; Cohen, Jonathan C.; Hobbs, Helen H.Mammals are able to gain cholesterol from two sources: diet and endogenous synthesis. However, the only means of cholesterol removal is reverse cholesterol transport (RCT), in which cholesterol is transported to the liver and exported into bile. While high density lipoprotein (HDL) is considered to be the major conduit for RCT, studies with HDL-deficient animals reveal no defect in tissue cholesterol balance. We hypothesize that red blood cells (RBCs), which contain 50% of blood cholesterol, also play a role in RCT. To measure accessible cholesterol in RBCs, we developed an assay that utilizes the cholesterol binding properties of the toxin Anthrolysin-O (ALO). We purified and fluorescently labeled domain 4 of ALO (fALOD4). We then incubated fALOD4 with RBCs from 164 subjects and measured fluorescence intensity using flow cytometry. Both intra-assay and intra-individual variability of the assay were less than 10%. In the test population, fALOD4 binding varied 10-fold. fALOD4 binding did not correlate with total RBC cholesterol but did correlate with RBC phosphatidylcholine (PC) (-0.42, p=6e-7) and lyso-phosphatidylcholine (LPC) (0.40, p=6e-6). Increasing the LPC:PC ratio in RBCs with phospholipase A2 (PLA2) increased fALOD4 binding by 3-fold. fALOD4 binding also correlated with plasma HDL (0.30, p=6e-4) and triglycerides (-0.57, p=2e-12). These data suggest that RBC accessible cholesterol varies in a population, is driven by intrinsic RBC phospholipid composition and interacts with known cholesterol transporters in the blood. Future studies will determine if variability in fALOD4 binding is driven by non-lipid RBC membrane components, is genetically determined, or contributes to atherosclerosis.Item Red blood cells: origin and replacement(2011-06-17) Hsia, Connie C. W.Item [UT Southwestern Medical Center News](2010-07-31) McKenzie, AlineItem Variability of Cholesterol Accessibility in Human Red Blood Cells Measured Using a Bacterial Cholesterol Binding Toxin(2017-03-31) Chakrabarti, Rima Shah; Radhakrishnan, Arun; Horton, Jay D.; Hofmann, Sandra L.Cholesterol partitions into accessible and sequestered pools in cell membranes. Here, we describe a new assay using fluorescently-tagged anthrolysin O, a cholesterol-binding bacterial toxin, to measure accessible cholesterol in human red blood cells (RBCs). Accessible cholesterol levels were stable within individuals, but varied >10 fold among individuals. Significant variation was observed among ethnic groups (Blacks>Hispanics>Whites). Variation in accessibility of RBC cholesterol was unrelated to the cholesterol content of RBCs or plasma, but was associated with the phospholipid composition of the RBC membranes and with plasma triglyceride levels. Pronase treatment of RBCs only modestly altered cholesterol accessibility. Plasma from various healthy individuals differentially modulated RBC cholesterol accessibility. Individuals on hemodialysis, who have an unexplained increase in atherosclerotic risk, had significantly higher RBC cholesterol accessibility. Our data indicate that RBC accessible cholesterol is a stable phenotype with significant inter-individual variability. Factors both intrinsic and extrinsic to the RBC contribute to variation in its accessibility. This assay provides a new tool to assess cholesterol homeostasis among tissues in humans.