Lipopolysaccharide from Escherichia coli stimulates mucin secretion by cultured dog gallbladder epithelial cells

Biliary infection is associated with mucin hypersecretion by the biliary epithelium. Mucins have been identified as potent pronucleators of cholesterol in bile. The aim of the present study was to determine whether lipopolysaccharides (LPS) from different bacteria are capable of stimulating mucin secretion by cultured dog gallbladder epithelial (DGBE) cells, and to investigate the mechanism by which LPS stimulate mucin secretion. Mucin secretion by confluent monolayers of DGBE cells was quantified by measuring the secretion of [3H]-N-acetyl-D-glucosamine-labeled glycoproteins. Cell viability was evaluated by measuring the leakage of the enzyme, lactate dehydrogenase (LDH), into the culture medium. LPS, derived from Escherichia coli, Klebsiella pneumonic, and Pseudomonas aeruginosa (200 mu g/mL), all caused an increase in mucin secretion by the DGBE cells, without causing concomitant cell lysis. LPS from E. coli was found to be the most potent stimulator of mucin secretion, and increased mucin secretion by the DGBE cells to 252% +/- 14% of control. LPS from E, coli had no effect on intracellular cyclic adenosine monophosphate (cAMP) levels in the DGBE cells. Addition of the nitric oxide (NO)-releasing compound, NOR-4 (0.125-l mmol/L), to the cells did not result in increased mucin secretion, and the NO synthase inhibitor, N-omega-nitro-L-arginine methyl ester (r-NAME) (4 or 10 mmol/L), did not inhibit the LPS-stimulated mucin secretion. Exogenous tumor necrosis factor or (TNF-alpha) (1-10 ng/mL) did cause a minor increase in mucin secretion by the DGBE cells, but the effect of LPS from E, coli on mucin secretion could not be inhibited by preincubation with a TNF-alpha antibody (10 mu g/mL). We conclude that LPS stimulates mucin secretion by the gallbladder epithelium. Whether this stimulation is mediated by TNF-alpha remains to be determined.