A304 FOOD ANTIGEN-STRESS INTERACTION INCREASES PERIPHERAL PAIN SIGNALING IN A MOUSE MODEL OF IBS

Abstract Background Food and stress are common triggers of symptoms in irritable bowel syndrome (IBS). However, it is unknown whether a specific food antigen alone can induce symptoms such as abdominal pain or if a second trigger, such as stress, is required for a food antigen to increase pain signaling. Aims To determine if a food antigen (ovalbumin) can induce hyperexcitabiity in nociceptive neurons alone and/or in combination with stress. Methods Mice were exposed to water avoidance stress (WAS; 1 hr for 6 days). On day 2, mice were gavaged ovalbumin (20mg) daily after completing WAS (WAS/OVA). These were compared to 3 groups: no WAS and no ovalbumin (control); WAS but no ovalbumin (WAS); and ovalbumin (OVA) alone. On day 8, WAS, OVA and WAS/OVA mice were given ovalbumin (50 μg) subcutaneously; 3 hours later euthanized. Colons were removed and incubated with ovalbumin (100 μg/ml) for 4 hrs. Supernatants were collected and DRG neurons from control mice were incubated overnight with supernatants from each of the four groups. Changes in neuronal excitability were examined by measuring the rheobase (minimal current to evoke an action potential) using perforated patch clamp recording techniques. Stress effects on intestinal permeability in the ileum and colon were assessed in Ussing chambers. One way ANOVA and Bonferroni post hoc test or unpaired t test were used to analyze the data. Results Incubation with supernatants obtained from WAS/OVA mice evoked hyperexcitability in DRG neurons compared to incubation with control supernatant (rheobase: control = 82 ± 10 pA vs WAS/OVA = 56 ± 4 pA, p < 0.05). Similarly, WAS/OVA supernatant decreased the rheobase compared to both OVA mice (OVA = 80 ± 8 pA, p<0.05) and WAS mice (WAS = 81 ± 9 pA, p<0.05). The effect of supernatants from OVA mice and WAS mice did not differ from controls. In a separate series of experiments, the PAR2 antagonist GB83 inhibited the effect of WAS/OVA supernatant (p < 0.01). There was no effect of GB83 on WAS or OVA supernatants. Stress decreased tissue resistance in ileum (p<0.05) but not in colon. Conclusions The food antigen ovalbumin induced hyperexcitability in DRG nociceptive neurons only when combined with stress. This action was PAR2 dependent suggesting a role of tissue proteases. Stress may cause a loss of oral tolerance to ovalbumin by increasing mucosal permeability in the small intestine. The interaction of food antigens and stress may be a mechanism of meal induced increase in abdominal pain in IBS. Funding Agencies CIHR

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