Uptake and subcellular localization of bacterial lipopolysaccharide in the adrenal gland

For determination of the kinetics of uptake and subcellular localization of lipopolysaccharide (LPS) from LPS-high density lipoprotein (LPS-HDL) complexes in the adrenal gland, LPS-HDL complexes were isolated by immunoaffinity chromatography of 125I-Salmonella minnesota Re595 LPS that had been incubated with 20 mM EDTA-rabbit plasma. After intravenous injection of LPS-HDL complexes in rabbits, preferential uptake of the LPS was observed in the adrenal, so that by 5 hours, adrenal-tissue-bound LPS concentrations (determined by use of 131I-BSA blood marker) exceeded all other tissues examined, including liver and spleen, by at least three-fold. For determination of the subcellular localization of LPS, cholesterol-rich (lipid droplet) fractions and cholesterol-depleted fractions were obtained by ultracentrifugation of homogenates of adrenal tissue from rabbits killed at various times after injection of LPS-HDL complexes. As much as 40% of the adrenal-tissue-bound LPS was recovered in the cholesterol-rich fraction 2.5-24 hours after injection of LPS-HDL complexes. Electron-microscopic autoradiographic and immunocytochemical analysis of adrenal cortex of animals killed 5 hours after injection of LPS-HDL complexes demonstrated specific localization of LPS in lipid droplets. These data thus provide direct evidence for the uptake of LPS into the adrenal cortex of animals with intravascular LPS-HDL complexes and indicate that further study of the effect of LPS on adrenocortical function is warranted.