EFFECT OF SEPSIS ON LIPID METABOLISM

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Gram-negative sepsis is a major complication for the patient with trauma injuries, extensive surgery, organ transplant, and severe metabolic diseases. These proposed studies will provide a greater understanding of the disturbances in lipid metabolism during sepsis thus enabling clinicians to provide more appropriate nutritional support. Hypertriglyceridemia and fatty infiltration of the liver are two major lipid abnormalities associated with gram-negative sepsis. The plasma lipoproteins are altered with respect to their lipid and apoprotein composition. In particular, the hypertriglyceridemia is associated with a defect in the lipoprotein lipase (LPL) clearing mechanism. Additionally, lipids accumulate in the livers of the septic rats because the synthesis of triglycerides (TG), cholesterol, and total phospholipids are increased. Feeding a structured lipid emulsion (SLE), n-3 fatty acids and medium chain triglycerides (MCT), by continuous intragastric infusion prevents hypertriglyceridemia and lipid accumulation in the liver. The hypotheses to be tested are: (1) changes in tissue LPL during fasted septic state are due to alterations in the genetic expression which are modified by feeding, (2) the changes in plasma apo B can be attributed to an increase in the rates of liver production which is associated with higher levels of apo B mRNA, (3) the hepatic uptake of TG-rich lipoprotein remnant particles is increased which also contributes to the fatty liver of sepsis, and (4) the lipid-lowering effects of n-3 fatty acids will be mediated by decreasing apo B and TG production. The regulation of LPL during sepsis will be investigated in fasted and fed septic rats by comparing changes in LPL activity with measurements of LPL mRNA, synthesis of LPL, and LPL mass. The mechanism for the altered apoprotein composition of the plasma lipoproteins in fasted and fed septic rats will be studied in the intact perfused liver by determining the composition of the nascent lipoproteins, the synthesis and secretion of the apoproteins, and the liver uptake of VLDL remnants and LDL. The regulation of apo B and apo E synthesis will be studied by measuring apo B mRNA and apo E mRNA. The mechanism for the lipid-lowering effects of n-3 fatty acids and MCT will be evaluated by measuring: the lipid and apoprotein composition of the plasma lipoproteins, the clearance rates of VLDL-TG, the uptake of VLDL apo B, and synthesis and secretion of lipids and apoproteins in primary cultured hepatocytes.