Cholesterol levels, bacterial endotoxin, and inflammation

Acute inflammation and infection maintain circulating phospholipid levels and enhance lipopolysaccharide binding to plasma lipoproteins< Richard L. Kitchens1,*, Patricia A. Thompson*, Robert S. Munford*, and Grant E. O'Keefe,** * Departments of Internal Medicine, The University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9113 Microbiology, The University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9113 Surgery, The University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9113 ** Department of Surgery, University of Washington, Harborview Medical Center, Seattle, WA 98104-2499 To whom correspondence should be addressed. e-mail: richard.kitchens@utsouthwestern.edu Circulating lipoproteins are thought to play an important role in the detoxification of lipopolysaccharide (LPS) by binding the bioactive lipid A portion of LPS to the lipoprotein surface. It has been assumed that hypocholesterolemia contributes to inflammation during critical illness by impairing LPS neutralization. We tested whether critical illness impaired LPS binding to lipoproteins and found, to the contrary, that LPS binding was enhanced and that LPS binding to the lipoprotein classes correlated with their phospholipid content. Whereas low serum cholesterol was almost entirely due to the loss of esterified cholesterol (a lipoprotein core component), phospholipids (the major lipoprotein surface lipid) were maintained at near normal levels and were increased in a hypertriglyceridemic subset of septic patients. The levels of phospholipids found in the LDL and VLDL fractions varied inversely with those in the HDL fraction, and LPS bound predominantly to lipoproteins in the LDL and VLDL fractions when HDL levels were low. Lipoproteins isolated from the serum of septic patients neutralized the bioactivity of the LPS that had bound to them. Our results show that the host response to acute inflammation and infection tends to maintain lipoprotein phospholipid levels and that, despite hypocholesterolemia and reduced HDL levels, circulating lipoproteins maintain their ability to bind and neutralize an important bacterial agonist, LPS.