Maternal diesel inhalation increases airway hyperreactivity in ozone-exposed offspring

Abstract

Air pollutant exposure is linked with childhood asthma incidence and exacerbations, and maternal exposure to airborne pollutants during pregnancy increases airway hyperreactivity (AHR) in offspring. To determine if exposure to diesel exhaust (DE) during pregnancy worsened postnatal ozone-induced AHR, timed pregnant C57BL/6 mice were exposed to DE (0.5 or 2.0 mg/m(3)) 4 hours daily from Gestation Day 9-17, or received twice-weekly oropharyngeal aspirations of the collected DE particles (DEPs). Placentas and fetal lungs were harvested on Gestation Day 18 for cytokine analysis. In other litters, pups born to dams exposed to air or DE, or to dams treated with aspirated diesel particles, were exposed to filtered air or 1 ppm ozone beginning the day after birth, for 3 hours per day, 3 days per week for 4 weeks. Additional pups were monitored after a 4-week recovery period. Diesel inhalation or aspiration during pregnancy increased levels of placental and fetal lung cytokines. There were no significant effects on airway leukocytes, but prenatal diesel augmented ozone-induced elevations of bronchoalveolar lavage cytokines at 4 weeks. Mice born to the high-concentration diesel-exposed dams had worse ozone-induced AHR, which persisted in the 4-week recovery animals. Prenatal diesel exposure combined with postnatal ozone exposure also worsened secondary alveolar crest development. We conclude that maternal inhalation of DE in pregnancy provokes a fetal inflammatory response that, combined with postnatal ozone exposure, impairs alveolar development, and causes a more severe and long-lasting AHR to ozone exposure.

Figure 1.

Effects of maternal diesel exhaust (DE) exposure or maternal DE particle (DEP) oropharyngeal aspiration versus air (DE control) or vehicle (Veh; DEP control) on fetal cytokines at Gestation Day 18. Data are means of 10 animals per group (±SEM); *P < 0.001 versus air or vehicle control. KC, keratinocyte-derived chemokine; RANTES, regulated upon activation, normal T cell expressed and secreted.

Figure 2.

Effect of prenatal air or DE (0.5 or 2.0 mg/m³) with or without postnatal air or ozone on body weight at Postnatal Day 28 (n = 25–30 animals/group; mean ± SEM); *P < 0.05 versus preair/postair control.

Figure 3.

(A) Effect of prenatal air or DE (0.5 or 2.0 mg/m³) with or without postnatal air or ozone on bronchoalveolar lavage leukocyte counts at P28. Data are means (±SEM) (n = 10/group). There were no significant differences between treatment groups. (B) Effect of prenatal air or 2.0 mg/m³ DE with or without postnatal air or ozone on cytokine concentrations in bronchoalveolar lavage fluid. Data are means of five animals per group (±SEM). *P < 0.05 versus preair/postair control; ⁺P < 0.05 versus preair/postozone.

Figure 4.

(A–C) Total respiratory system resistance in response to nebulized methacholine in mice born to dams exposed to inhaled DE (A) or aspirated DEP (B) at 4 weeks, after postnatal air or O₃ exposure, and (C) 4 weeks after cessation of air or O₃. Gray lines, prenatal air exposure; black lines, prenatal diesel exposure (ambient DE: closed squares, 0.5 mg/m³; closed diamonds, 2.0 mg/m³; open circles, instilled DEP). Solid lines, postnatal air exposure; dashed lines, postnatal ozone exposure. Data are means of 10–12 animals/group (±SEM). *P < 0.05 versus air/air control; ⁺P < 0.05 versus air/O₃; ^#P < 0.05, prenatal DE versus prenatal air. (D–F) Effects of pre- and postnatal exposures on (D) tissue damping, (E) respiratory system compliance, and (F) tissue elastance, at 4 (shaded bars) and 8 (closed bars) weeks. Data are means of 10–12 animals/group (±SEM); *P < 0.05 versus 4 weeks. C, respiratory system compliance; G, tissue damping; H, tissue elastance.

Figure 5.

Effect of prenatal air or DE (2 mg/m³) exposure plus postnatal air or ozone exposure on (A) alveolar volume density, (B) alveolar surface density, and (C) secondary alveolar crest density at 4 weeks. Data are means of five animals/group (±SEM); *P < 0.05 versus prenatal DE/postnatal air.