Inhibition of endotoxin effects on cultured human middle ear epithelium by bactericidal permeability-increasing protein.

HYPOTHESIS/BACKGROUND: Endotoxin can induce morphologic changes to middle ear epithelium, which can disturb the mucociliary clearance system (MCS) and lead to otitis media with effusion (OME). The bactericidal/permeability-increasing (BPI) protein is a major component of neutrophil granules and binds with high affinity to endotoxin. In this study, the capacity to inhibit the effects of endotoxin by rBPI21, a recombinant amino-terminal analog derived from BPI, was investigated on cultured human middle ear epithelium using light microscopy and scanning- and transmission electron microscopy. METHODS: Human middle ear epithelium was air-exposed cultured on a collagenous underlayer with different additions of endotoxin and rBPI21 to the culture medium. The tissue specimens were inspected after 4 weeks for the number of ciliated and secretory cells, thickness of the mucosal layer, and cell size. RESULTS: The morphologic changes induced by endotoxin were increased thickness of the mucosal layer and increased number of secretory cells. These changes were significantly diminished or even absent when endotoxin was added with rBPI21 to the culture medium. CONCLUSION: rBPI21 can inhibit morphologic changes in the middle ear epithelium due to endotoxin. Hence, the authors believe that rBPI21 can be a new therapeutic agent in the treatment of OME.

Effect of endotoxin on cultured human middle ear epithelium.

The effect of endotoxin was investigated on air-exposed cultured human middle ear epithelium. Concentrations of 0, 1 and 100 ng/ml endotoxin were used. Complete differentiation of the cells was not reached at 12 days. After 21 days, endotoxin had induced an increased proliferation of the epithelial layer. Furthermore, an increase in the number of secretory cells and in the amount and length of microvilli was observed at this time. There were no significant morphological differences between the high and the low endotoxin concentrations, which supports our hypothesis that endotoxin induces an all-or-nothing reaction. These findings are in agreement with our previous results on serially submerged cultured rat middle ear epithelium. From these results we conclude that endotoxin is an important factor in the disturbance of the morphology of the middle ear epithelium, which may lead to chronic otitis media with effusion. In addition, our tissue culture method proved to be a good model for further studies on human middle ear mucosa.