Comparison of peptidoglycan-polysaccharide and lipopolysaccharide stimulation of Kupffer cells to produce tumor necrosis factor and interleukin-1

Abstract

Endotoxin (lipopolysaccharide) is a cell wall polymer from gram-negative bacteria that stimulates Kupffer cell release of cytokines such as tumor necrosis factor-α and interleukin-1. Another bacterial cell wall polymer in both gram-negative and gram-positive organisms is peptidoglycan-polysaccharide. Lipopolysaccharide and peptidoglycan-polysaccharide exist together in the intestinal lumen and can cross the intestinal mucosa, enter the portal vein and activate Kupffer cells. The purpose of this study was to compare the effects of lipopolysaccharide stimulation and peptidoglycan-polysaccharide stimulation of Kupffer cells on release of tumor necrosis factor-α and interleukin-1. Both bacterial polymers caused maximum tumor necrosis factor-α release from Kupffer cells after incubation for 4 to 8 hr. Maximum tumor necrosis factor-α release induced by 400 ng/ml lipopolysaccharide was 704 ± 258 pg/ml, compared with 329 ± 91 pg/ml tumor necrosis factor-α after 100 μg/ml peptidoglycan-polysaccharide (p < 0.001). Polymyxin B blocked lipopolysaccharide stimulation of tumor necrosis factor-α by 95% ± 5% but blocked peptidoglycan-polysaccharide–stimulated tumor necrosis factor-α by 30% ± 14% (p < 0.001). Repeat incubation of Kupffer cells with lipopolysaccharide after prior lipopolysaccharide incubation induced low tumor necrosis factor-α release (tolerance). Repeat incubation with peptidoglycan-polysaccharide induced no tolerance to tumor necrosis factor-α release. Incubation of lipopolysaccharide plus peptidoglycan-polysaccharide released less tumor necrosis factor-α than did each polymer used alone, but this inhibition was prevented by indomethacin. Dibutyryl cyclic AMP, prostaglandin E1, prostaglandin E2 and the adenosine A2–receptor agonist N-ethylcarboxyamideadenosine inhibited lipopolysaccharide-stimulated tumor necrosis factor-α release by 83%, 97%, 90% and 94%, respectively, but inhibited peptidoglycan-polysaccharide–stimulated tumor necrosis factor-α release by 52%, 60%, 45% and 51%, respectively (p < 0.001 for each). This indicates that intracellular signaling pathways differ for lipopolysaccharide-stimulated and peptidoglycan-polysaccharide–stimulated tumor necrosis factor-α release. After incubation for 8 and 24 hr, 100 μg/ml peptidoglycan-polysaccharide had induced significantly more interleukin-1 release from cultured Kupffer cells than had 400 ng/ml lipopolysaccharide (p < 0.001). Lipopolysaccharide induced tolerance to interleukin-1 release after repeat incubation, but peptidoglycan-polysaccharide caused no tolerance. These studies show that peptidoglycan-polysaccharide, a ubiquitous bacterial cell wall polymer, shares several proinflammatory properties with lipopolysaccharide but that there are differences that may have pathophysiological significance. (HEPATOLOGY 1994;19:1013–1022.)