DOSE-RESPONSE ASSESSMENT AND EFFECT OF PARTICLES IN GUINEA PIGS EXPOSED CHRONICALLY TO DIESEL EXHAUST: ANALYSIS OF VARIOUS BIOLOGICAL MARKERS IN PULMONARY ALVEOLAR LAVAGE FLUID AND CIRCULATING BLOOD

Abstract

To elucidate dose-response and other effects of diesel particles in guinea pigs chronically exposed to diesel exhaust, various biomarkers for chronic obstructive lung diseases were studied using bronchoalveolar lavage (BAL) fluid and blood specimens. Guinea pigs were exposed 16 h/day, 6 days/wk, for 6, 12, 18, or 24 mo to filtered air (control group, n = 8-10), a low level of diesel exhaust (L group: NO 2 = 0.22 ± 0.03 ppm; SO 2 = 0.6 ± 0.19 ppm; particles = 0.21 ± 0.07 mg/m 3, n = 8-10), medium level of diesel exhaust (M group; NO 2 = 1.07 ± 0.09 ppm; SO 2 = 2.83 ± 0.73 ppm; particles = 1.14 ± 0.26 mg/m 3, n = 8-10), and high level of diesel exhaust (H group: NO 2 = 2.88 ± 0.29 ppm; SO 2 = 6.49 ± 1.75 ppm; particles = 2.94 ± 0.69 mg/m 3, n = 8-10), or at a medium concentration of diesel exhaust without particulate matters (MG group: NO 2 = 1.01 ± 0.09 ppm; SO 2 = 2.66 ± 0.64 ppm; particles = 0.01 ± 0.01 mg/m 3, n = 8-10). Anesthetized animals were sacrificed and BAL fluid from the lung and blood from right ventricle were collected. Various biomarkers of inflammation, components of mucus and surfactant, bronchoconstrictors were determined. Changes of leukotriene C4 in plasma, eosinophil counts, biomarkers of inflammation and cytotoxicity, and mucus and surfactant components in BAL fluid were statistically different among the C, L, M, and H groups after adjustment for the exposure period and group-by-exposure period with respect to their interactions in two-way analysis of variance (ANOVA). The levels of these biomarkers in the H group were higher than those of the M group, whereas those of the L group showed no significant changes compared with those of the C group during experimental period. Onset of significant changes of these biomarkers for the M group was at 18 mo of exposure, whereas that for the H group was at 12 mo of exposure, which resulted in changes in the levels of biomarkers in BAL fluid. Although numbers of eosinophils in BAL fluid increased significantly in the M and H groups at 12 mo, only leukotrine C4 increased at 18 and 24 mo in blood and at 24 mo in BAL fluid. Animals exposed to the medium level of diesel exhaust without particulate matter showed significantly less increase of these biomarkers as compared with animals exposed to the same level of diesel exhaust with particulate matters. These findings indicate that chronic exposure to diesel exhaust induced continuous inflammation, overproduction of mucus, and phospholipids in the lung. Animals exposed to the high dose of diesel exhaust showed a plateau of biological responses at 12 mo of exposure. Particulate matter in diesel exhaust appears to play an important role in development of lung injury by chronic emission exhaust exposure.