Non-specific abdominal pain and air pollution: a novel association

Abstract

Background: We studied whether short-term exposure to air pollution was associated with non-specific abdominal pain in epidemiologic and animal studies.

Methods: Patients visiting the emergency department with non-specific abdominal pain were identified in Edmonton (1992 to 2002, n = 95,173) and Montreal (1997 to 2002, n = 25,852). We calculated the daily concentrations for ozone (O(3)), nitrogen dioxide (NO(2)), sulfur dioxide (SO(2)), carbon monoxide (CO), and particles <10 (PM(10)) or <2.5 (PM(2.5)) µm. A case crossover study design was used to estimate the odds ratio (OR) and 95% confidence interval (CI) associated with an increase in the interquartile range of the air pollutants. We investigated differential effects by age and sex. Mice were gavaged with urban particle extracts. In animal models, colonic motility was tested, and visceral abdominal pain was measured using a writhing test, and behavioral response to oil of mustard and neostigmine. Motility and pain was measured acutely (1.5 hours after gavage) and chronically (7-days and 21-days after gavage).

Results: Emergency department visits for non-specific abdominal pain were primarily by women between the ages of 15-24 years. Individuals aged 15 to 24 years were at increased risk of non-specific abdominal pain in Edmonton (same day CO: OR = 1.04, 95% CI = 1.02-1.06; and NO(2): OR = 1.06, 95% CI = 1.03-1.09). The risk of air pollution among 15-24 year olds in Montreal was significantly positive (same day CO: OR = 1.11, 95% CI = 1.05-1.17; NO(2): OR = 1.09, 95% CI = 1.01-1.16; SO(2): OR = 1.17, 95% CI = 1.10-1.25; PM(2.5): OR = 1.09, 95% CI = 1.04-1.15). Abdominal pain was increased by an acute gavage of pollution extract but not to chronic exposure to pollutants. Colonic transit was delayed following chronic but not acute exposure with the pollutants.

Conclusions: Epidemiological and animal data suggest that short-term exposure to air pollution may trigger non-specific abdominal pain in young individuals.

Figure 1. Age-specific frequency of admissions to emergency departments (ED) for non-specific abdominal pain stratified by sex.

Figure 2. The effect of EHC-6802 on mouse GI motility.

A) The effect of EHC-6802 (initial concentration 360 µg/200 µl regarded as 1∶1 dilution) on EFS (8 Hz)-stimulated smooth muscle contractions in mouse ileum and colon. Note that EHC-6802 significantly, in a concentration-dependent manner inhibited twitch contractions in mouse colon. Data represent mean ± SEM for n = 8. *P<0.05, as compared with control. B) In vivo effects of EHC-6802 (360 µg/200 µl/animal, QD, p.o.) on colonic bead expulsion time in mice. The results are shown as mean ± SEM of n = 5–10 mice for each experimental group. *P<0.05, as compared with control (animals receiving tap water).

Figure 3. The effect of EHC-6802 (360 µg/200 µl/animal, p.o.) on behavioural pain responses in mice.

A) The effect of EHC-6802 in the writhing test in mice. The number of writhes was determined 5 min after acetic acid injection (0.5%, 10 ml/kg, i.p.) over a period of 15 min. Note that a single 1.5 h- treatment with EHC-6802 significantly increased the total number of writhes. Data represent mean ± SEM of 5–10 mice per group. ***P<0.001, as compared to control (animals receiving tap water). B) The effect of EHC-6802 on the number of pain-related behaviours (licking of abdomen, stretching, squashing, abdominal contractions) evoked by i.c. administration of oil of mustard (1% in 70% EtOH - 30% saline), determined over a period of 20 min. Note that a single 1.5 h- treatment with EHC-6802 significantly increased the number of pain-related behaviours. Data represent mean ± SEM of 5–10 mice per group. **P<0.01, as compared to control (animals receiving tap water). C) The effect of EHC-6802 on the number of pain-related behaviours (licking of abdomen, stretching, squashing, abdominal contractions) evoked by the i.p. administration of neostigmine (2.5 µg/kg), determined over a period of 10 min. Note that a single 1.5 h- treatment with EHC-6802 significantly increased the number of pain-related behaviours. Data represent mean ± SEM of 5–10 mice per group. **P<0.01, as compared to control (animals receiving tap water).