Brevetoxin inhalation alters the pulmonary response to influenza A in the male F344 rat

Abstract

Epidemiological studies demonstrated that the number of emergency-room visits for respiratory indications increases during periods of Florida Red Tides. The purpose of this study was to examine whether or not repeated brevetoxin inhalation, as may occur during a Florida Red Tide, affects pulmonary responses to influenza A. Male F344 rats were divided into four groups: (1) sham aerosol/no influenza; (2) sham aerosol/influenza; (3) brevetoxin/no influenza; and (4) brevetoxin/influenza. Animals were exposed by nose-only inhalation to vehicle or 50 μg brevetoxin-3/m3, 2 h/d for 12 d. On d 6 of aerosol exposure, groups 2 and 4 were administered 10,000 plaque-forming units of influenza A, strain HKX-31 (H3N2), by intratracheal instillation. Subgroups were euthanized at 2, 4, and 7 d post influenza treatment. Lungs were evaluated for viral load, cytokine content, and histopathologic changes. Influenza virus was cleared from the lungs over the 7-d period; however, there was significantly more virus remaining in the group 4 lungs compared to group 2. Influenza virus significantly increased interleukins-1α and -6 and monocyte chemotactic protein-1 in lung; brevetoxin exposure significantly enhanced the influenza-induced response. At 7 d, the severity of perivascular and peribronchiolar inflammatory cell infiltrates was greatest in group 4. Bronchiolitis persisted, with low incidence and severity, only in group 4 at d 7. These results suggest that repeated inhalation exposure to brevetoxin may delay virus particle clearance and recovery from influenza A infection in the rat lung.

FIG. 1

Experimental time line.

FIG. 2

Clearance of influenza A from the lungs of rats in the presence (Group 2) or absence (Group 4) of brevetoxin inhalation. Results are the mean ± SD of 8 values. “a” indicates means are statistically different (2 way ANOVA, p = 0.0032).

FIG. 3

Cytokines increased by influenza infection and the influence of brevetoxin inhalation; a) = IL-1α; b) = MCP-1; c) = IL-6. Results are the mean ± SD of 4 values for Groups 1 (Brevetoxin −/Influenza −) and 3 (Brevetoxin +/Influenza −) or the mean ± SD of 6–8 values for Groups 2 (Brevetoxin −/Influenza +, and 4–8 values for Group 4 (Brevetoxin +/Influenza +). Bars with different letter designations within each time point are significantly different from each other (p < 0.05).

FIG. 4

Cytokine responses induced by brevetoxin inhalation and the impact of influenza infection. a) = IL-1β; b) = IL-5; c) = IL-18. Data presented are the mean ± SD of 3–4 values (Group 1), 2–4 values (Group 3), 6–8 values (Groups 2; except for IL-5 at 7 days where n = 3), and 4–8 (Group 4). Bars with different letter designations within each time point are significantly different from each other (p < 0.05).

FIG. 5

Mean severity scores for lesions in the peripheral lung and in the conducting airways. Results are the mean ± SD of 4 values for Groups 1 and 3 and 8 values for Groups 2 and 4. Note that in the case where the lesion was absent, a zero severity score was included in the calculation of the mean.