Suppression of fibroblast growth by Bacteroides gingivalis endotoxin is not reduced by serum lipoproteins.

Previous studies indicated that Bacteroides and E. coli endotoxins caused a dose-dependent inhibition of human fibroblast growth. However, these endotoxins were relatively weak inhibitors of growth. Since cells were grown with serum, we questioned whether serum lipoproteins, which lessen endotoxin cytotoxicity in vivo, reduced the growth inhibitory effects of endotoxins in vitro. To determine whether serum lipoproteins reduced the growth inhibitory effects of endotoxins, logarithmically growing human periodontal cells were incubated with endotoxin and high density (HDL) or low density lipoprotein (LDL). Neither HDL nor LDL significantly reduced the initial growth inhibitory effects of B. gingivalis or E. coli endotoxins, as judged by 3H-thymidine incorporation. Even with prolonged exposure of up to 10 days in culture, HDL did not ameliorate growth inhibition by endotoxin, as determined by direct cell counts. We conclude that serum lipoproteins do not provide any significant protective effects against fibroblast growth inhibition by endotoxins in vitro.