Lipid peroxides in middle ear fluid after acute otitis media in guinea pigs.

Oxygen free radical damage has been demonstrated in the middle ear mucosa of a guinea pig model of acute otitis media (AOM). Potential sources of free radicals include both neutrophils responding to infection and Streptococcus pneumoniae, a common AOM pathogen. This project was conducted to examine the middle ear fluid in a guinea pig model of AOM for evidence of elevated lipid peroxide (LPO) as a marker of free radical damage. Twenty-one guinea pigs were injected transtympanically with bacteria into the left (infected) middle ear cavity and sterile saline into the right (control) middle ear. Middle ear fluid was recovered on postoperative day 5. The fluid was weighed and analyzed for quantity of LPO. Results indicated an increased absolute level of LPO, as well as an increased level of LPO divided by the weight of the fluid recovered. Histologic examination confirmed leukocyte infiltration and mucosal edema that were consistent with mucosal damage. While free radical damage to the middle ear mucosa in a guinea pig model of AOM is well documented, this is the first study to demonstrate evidence of free radical damage in middle ear fluid. These results are relevant because they correlate mucosal damage with lipoperoxidation in fluid. Additionally, this serves as an important precursor to human studies, since middle ear fluid is readily available in patients with otitis media.