Conditioned medium from endotoxin-treated mouse peritoneal exudate cells suppressed lipoprotein lipase activity in differentiating 3T3-L1 mouse preadipocytes by greater than 90%.
Endotoxin promotes the release of a mediator from exudate cells that suppresses lipoprotein lipase activity in preadipocytes, providing a potential mechanism for lipid metabolism alterations during infection.
Conditioned medium from cultures of mouse peritoneal exudate cells incubated wih endotoxin contains a mediator that markedly suppresses (greater than 90%) lipoprotein lipase (triacylglycero-protein acylhydrolase, EC 3.1.1.34) activity in differentiating 3T3-L1 mouse preadipocytes. The effect is dependent upon the amount of mediator and is evident as early as 30 min after the addition of the mediator-containing medium to 3T3-L1 cell cultures. Neither endotoxin nor conditioned medium from cultures of exudate cells not exposed to endotoxin shows the presence of the mediator. Lysates of the exudate cells are also unable to suppress the lipase activity. Increasing the amount of insulin does not reverse this suppression, even at 1000 times the concentration used for standard experiments. The lipoprotein lipase suppression mediator present in the conditioned medium of endotoxin-treated exudate cells is heat labile and has an apparent molecular weight of at least 12,000. The mediator does not inhibit lipoprotein lipase activity directly nor does it affect the half-life of enzyme activity released in the medium. The present study demonstrates that endotoxin promotes the release of a mediator from exudate cells that suppresses the activity of lipoprotein lipase in 3T3-L1 preadipocytes.
Kawakami et al. (1982) studied Hypertriglyceridemia/infection/shock (in vitro model). Conditioned medium from endotoxin-treated exudate cells vs. Conditioned medium from untreated exudate cells or fresh medium was evaluated on Lipoprotein lipase activity. Conditioned medium from endotoxin-treated mouse peritoneal exudate cells suppressed lipoprotein lipase activity in differentiating 3T3-L1 mouse preadipocytes by greater than 90%.