Arachidonic acid metabolites in otitis media pathogenesis

Early-response cytokine expression in adult middle ear effusions

Various cytokines are presently known to be associated with the regulation of inflammatory responses. In pediatric otitis media, cytokines that correlate with various degrees of inflammation are present in middle ear effusions as inflammatory mediators. The present study was undertaken to examine the potential role of the early-response cytokines, interleukin-1beta and tumor necrosis factor-alpha, in adult otitis media. Fifty-nine adults with otitis media underwent tympanocentesis, and the effusion specimens were analyzed for the presence of both cytokines by enzyme-linked immunosorbent assay methods. Eighty-eight percent of the effusions were serous in nature. Sixty-seven percent of the patients had a known history of head and neck malignancy and radiation to the temporal bone. Twelve percent of the effusions were positive for interleukin-1beta expression, compared with 85% of effusions in children with otitis media. Eight percent of the effusions contained tumor necrosis factor-alpha, compared with 85% of those collected in pediatric otitis media. All of the specimens that contained tumor necrosis factor-alpha also contained interleukin-1beta. In the present study, there was no correlation with head and neck malignancy/radiation or the clinical degree of inflammation with the presence of either cytokine. We conclude that adult otitis media is associated with lower expression of an acute inflammatory response, as judged by the levels of interleukin-1beta and tumor necrosis factor-alpha in the effusions. Additionally, adult otitis probably represents a less severe and more chronic inflammatory state in comparison with pediatric otitis media. Further analysis of inflammatory mediators in adult otitis media is necessary to evaluate the contribution of cytokines in relation to various etiologic factors.

Expression of acute otitis media after receptor blockade of platelet activating factor, thromboxane, and leukotrienes in the chinchilla

To determine the role of inflammatory products of phospholipid metabolism in acute otitis media (AOM), we infected 128 chinchillas with Streptococcus pneumoniae and randomly assigned them to one of four equal-sized treatment groups receiving intramuscular ampicillin sodium (control) or intramuscular ampicillin plus receptor blockers of platelet activating factor (WEB 2086, 5 mg/d orally), of leukotriene (MK 571, 0.5 mg/d orally), or of thromboxaneA2 (GR 32191B, 5 mg/d orally). All treatments were begun on day 2 postinoculation and continued for 10 days. On days 3, 6, 9, and 12, 8 animals from each group were sacrificed. Effusions were recovered for biochemical assay, and the right middle ears were prepared for histologic study. Differences among groups in the number of ears with effusion or in effusion volume were not statistically significant. In comparison to the control group, mucosal thickness and the number of ears with histopathologic signs of inflammation were significantly less in the GR and WEB treatment groups, but not the MK group. Also, effusion concentrations of free fatty acids, protease, and hydrolytic enzymes were significantly less in those groups. These results show that the addition of a receptor blocker for either platelet activating factor and/or thromboxane to ampicillin in the treatment of AOM reduces mucosal inflammation and decreases the production of other inflammatory chemicals. The failure of a receptor blocker of leukotrienes to moderate disease expression suggests either a less important role for these chemicals in AOM or an insufficient bioavailability of the specific MK 571 inhibitor. These results confirm that platelet activating factor and thromboxane are active mediators of inflammation in AOM.

Epidemiology and pathogenesis of chronic suppurative otitis media: implications for prevention and treatment

Despite advances in public health and medical care, chronic suppurative otitis media is still prevalent around the world. It is most common in developing countries and in certain high risk populations in developed nations, as well as among children who have tympanostomy tubes inserted. Since this chronic infection is caused by persistent acute otorrhea, which in turn is usually secondary to acute otitis media, prevention should be directed toward prompt and appropriate treatment of the acute middle-ear infection. Repair of chronic perforations should prevent recurrence, since reinfection is due either to reflux of pathogenic organisms from the nasopharynx into the middle ear, or water contamination from the external canal. Information from epidemiological studies, which show that populations can be categorized into highest, high, low and lowest prevalence, can be helpful in setting national priorities for prevention and treatment.

Role of leukotriene B4 and interleukin-8 in acute bacterial and viral otitis media

In order to evaluate the role of polymorphonuclear leukocytes (PMNs) in acute otitis media (AOM), levels of leukotriene B4 (LTB4), a potent inflammatory product of PMNs, and interleukin-8 (IL-8), a PMN chemotactic cytokine, were measured in 271 middle ear fluid (MEF) samples from 106 children with AOM. Forty-two percent of the patients had evidence of respiratory viral infection. At the time of diagnosis, levels of both LTB4 and IL-8 were higher in the MEFs from patients with AOM associated with bacterial or bacterial and viral infection than those MEFs containing no pathogen (p < .05). Antibiotic treatment was not associated with a significant change in levels of LTB4 or IL-8 in the MEFs obtained 2 to 5 days into treatment, compared to those obtained at diagnosis. Bacteriologic failure after 2 to 5 days of treatment was associated with high LTB4 levels in the initial MEFs (p = .05). Recurrence of AOM within 1 month was associated with high IL-8 levels in the initial MEF (p = .04). Our findings suggest that LTB4 and IL-8 are produced during acute infection of the middle ear, and these PMN-related inflammatory substances may play an important role in delaying recovery or in recurrence of AOM. Effective treatment of AOM may require eradication of bacteria by antibiotics, as well as pharmacologic agents that modulate PMN functions.

Effect of SC-41930, a potent selective leukotriene B4 receptor antagonist, in the guinea pig model of middle ear inflammation

Arachidonic acid metabolites such as prostaglandins and leukotrienes have been shown to play an important role in the pathogenesis of otitis media (OM). Among these mediators, leukotriene B4 (LTB4) is one of the most potent inducers of inflammatory processes. SC-41930 has been shown to be a specific LTB4 receptor antagonist both in vitro and in vivo. In this study, anti-inflammatory effects of SC-41930 were investigated in a guinea pig model of OM induced by middle ear (ME) inoculation of killed Staphylococcus aureus. Outcome of treatment was determined by measurement of myeloperoxidase activity in the samples of ME mucosa, evaluation of temporal bone histopathology, and presence of ME fluids. Myeloperoxidase activity in the SC-41930-treated group was found to be significantly lower than that in the control group. Histopathology of temporal bones indicated decreased inflammation in the treated group as compared to the controls. In addition, ME fluids were absent in four out of six treated animals. These results demonstrate that SC-41930 can produce significant anti-inflammatory effects in this model of OM.

Treatment of experimental acute otitis media with ibuprofen and ampicillin

The efficacy of concurrent treatment of experimental acute otitis media with ibuprofen and ampicillin was evaluated in chinchillas with respect to clearance of the effusion and resolution of mucosal inflammation. Sixty-four chinchillas were infected with Streptococcus pneumoniae and randomly assigned to treatment with either IM ampicillin (control) or ampicillin plus ibuprofen (experimental) beginning on day 2 post inoculation. On days 3, 6, 9 and 12, 8 animals from each group were killed, effusions recovered for biochemical assay and the right middle ears prepared for histological study. Between group differences in the number of ears with effusion and effusion volume were not statistically significant. Mucosal thickness and the frequencies of ears with histopathological signs of inflammation were significantly less in the experimental group when compared to the control group. Differences in the effusion concentrations of total protease, 3 of 4 hydrolytic enzymes and free fatty acids favoring the experimental group were observed at the 6, 9 and 12 day endpoints. Also, at those times the levels of the 3 measured products of the cyclooxygenase pathway were less in the experimental group. These results suggest that the addition of ibuprofen to ampicillin for the treatment of acute otitis media decreases production of select eicosonoids, reduces mucosal inflammation and alters the course of the disease in this model of bacterial infection.

Biochemical evidence of platelet-activating factor (PAF) in human middle ear effusions

Platelet-activating factor (PAF) is one of the most potent biological lipid mediators. This is especially true in relation to inflammation. In order to characterize the biochemical features of otitis media with effusion, the authors characterized and determined the concentration of the PAF present in human middle ear effusions obtained from 23 patients with otitis media with effusion. Each sample of middle ear effusion was divided into two groups: serous (n = 12) and mucoid effusions (n = 11). The platelet-activating factor activity was found mainly in mucoid middle ear effusions, and the amounts of PAF were higher in mucoid type (3.55 +/- 1.19 ng/g, mean +/- standard deviation [SD]) than in the serous type (0.44 +/- 0.19 ng/g). Phospholipids obtained from the middle ear effusions contained a large amount of lyso-platelet-activating factor, the biologically inactive precursor or breakdown product of platelet-activating factor. Based on these findings, it is suggested that platelet-activating factor may play an important role as a mediator of the inflammatory responses in the pathogenesis of otitis media with effusion.

Effect of ibuprofen treatment during experimental acute otitis media

In this study, the efficacy of concurrent treatment of experimental acute otitis media with ibuprofen and ampicillin was evaluated in chinchillas with respect to clearance of the effusion, presence of mucosal inflammation, and modulation of biochemical markers. Forty chinchillas were infected with non-typable Haemophilus influenzae and randomly assigned to treatment with either IM ampicillin (control) or ampicillin plus ibuprofen beginning on day 2 post inoculation. On days 5 and 10, animals from each group were killed, effusions recovered for biochemical assay, and the middle ears prepared for histological study. Differences in outcome measures favoring the control group were observed at the 5 day endpoint. However, at the 10 day endpoint, mucosal thickness was significantly less, the number of effusion free ears greater, and the concentrations of free fatty acids and thromboxane less in the animals treated with the combined therapy when compared to the control group. These results suggest that the addition of ibuprofen to ampicillin for the treatment of acute otitis media alters disease pathogenesis in this infectious model.

Experimental otitis media with effusion induced by platelet activating factor

This study tested the hypothesis that platelet activating factor (PAF) in the middle ear can induce otitis media with effusion (OME) and that PAF antagonists can prevent PAF-induced OME. An initial trial of 16 micrograms of PAF was injected into chinchilla bullae, and all ears developed middle ear effusion (MEE) within 48 hours. Subsequent trials were performed to test dose dependency. Interestingly, 1 or 16 micrograms of PAF caused more MEE and inflammation than did 4 or 8 micrograms. A dose of 0.5 micrograms PAF did not cause MEE. Middle ear effusion from injected bullae contained the full spectrum of lipoxygenase and cyclooxygenase products; additionally, more PAF was detected than was injected. Finally, a PAF antagonist (WEB 2170) injected intraperitoneally prevented PAF-induced OME. This study demonstrates that PAF injected into the middle ear can induce OME and that PAF antagonists effectively prevent PAF-induced OME. These findings suggest that PAF plays an important role in the pathogenesis of OME.

Effect of modulation of polymorphonuclear leukocyte migration with anti-CD18 antibody on pathogenesis of experimental otitis media in guinea pigs

Guinea pigs were treated with anti-CD18 antibody (M8), and subsequently middle ears (ME) were infected with nontypeable Haemophilus influenzae. Forty-eight hours after infection, the ME washes of these animals had significantly lower polymorphonuclear leukocyte numbers but higher bacterial counts compared with washes of animals treated with control antibody (M11) or saline. The edema and epithelial damage of ME tissues correlated directly with polymorphonuclear leukocyte numbers and not bacterial counts.

Arachidonic acid metabolites in middle ear effusions of children

Middle ear effusions (MEEs) from 78 children (98 ears) with otitis media were examined for products of arachidonic acid (AA) metabolism, including leukotrienes B4, C4, D4, and E4 and prostaglandins D2 and E2, by high-performance liquid chromatography. Leukotrienes B4 and D4 were recovered most frequently: 59% and 54%, respectively. Leukotriene B4 was found in highest concentration, 1.29 +/- 3.46 ng/0.1 mL. The concentrations of leukotrienes B4 (p less than .03), (4 (p less than .01), and E4 (p less than .02) were significantly higher in culture-positive than in culture-negative MEEs. Neither the concentration nor the type of AA metabolite correlated with bacterial species isolated, chronicity of effusion, age of subject, or consistency of MEE. These data suggest that the AA metabolites are synthesized relatively frequently during otitis media of childhood. Leukotriene B4 is the most frequently detected AA metabolite in MEEs and is highly associated with the presence of viable bacteria.

Outer hair cells as potential targets of inflammatory mediators

Inner ear sequelae with temporary or permanent sensorineural hearing loss can result from inflammatory processes in the middle ear. Loss of outer hair cells in the base of the cochlea has been noted in otitis media, but it is not known how this damage occurs. Evidence supports the permeability of the round window membrane to substances mediating inflammation in the middle ear, and the presence of white blood cells has been reported in the perilymph. In the present study, the potential cytotoxic effects of two representative inflammatory mediators, endotoxin and free radicals, have been evaluated by use of short-term culture of isolated outer hair cells from the guinea pig cochlea model. Incubation with endotoxins from two gram-negative pathogens increased the rate of hair cell death fourfold to sixfold. Free radicals (generated by exposure of cells to UV light or by excitation of intracellular fluorescent dyes) produced morphologic damage to hair cells within 60 seconds. These latter effects were delayed by addition of free-radical scavengers. It is concluded that inflammatory mediators are cytotoxic to hair cells and therefore are potentially ototoxic if permeating the round window membrane.