Acid regulates inflammatory response in a rat model of induction of gastric ulcer recurrence by interleukin 1beta

Abstract

Background: In a previous study we showed that interleukin 1beta (IL-1beta) caused recurrence of gastric ulcers in rats, and that adhesion molecules (intercellular adhesion molecule 1 and leucocytic beta2 integrins) play a role in this recurrence. Although gastric acid plays an important role in many types of gastric injuries, including peptic ulcer recurrence, the mechanism(s) remains unclear.

Aims: To examine the involvement of gastric acid in induction of ulcer recurrence by IL-1beta, and to investigate the role of gastric acid in inflammatory responses during ulcer recurrence.

Methods: Rats with healed ulcers were used. Rats were given 1 microg/kg IL-1beta intraperitoneally. Another group of rats was given 20 mg/kg omeprazole for three days to inhibit acid secretion, and received IL-1beta 20 hours after the first administration of omeprazole. They were then given 0.15 N HCl or vehicle at 0, 12, 24, and 36 hours after IL-1beta treatment. Some rats were given acid alone at the same time points. Expression of adhesion molecules was examined immunohistochemically and concentrations of IL-1beta and tumour necrosis factor alpha (TNF-alpha) were measured by ELISA in scar tissue 24 hours after IL-1beta treatment.

Results: IL-1beta increased expression of adhesion molecules and concentrations of IL-1beta and TNF-alpha in scar tissue by 24 hours after IL-1beta treatment, and nine of 11 healed ulcers had recurred by 48 hours. Omeprazole inhibited the effects of IL-1beta. HCl acid abolished the inhibitory effects of omeprazole. Acid alone affected neither expression of adhesion molecules nor cytokine concentrations, and did not cause recurrence.

Conclusions: Gastric acid is required for recurrence of gastric ulcers caused by IL-1beta, and gastric acid stimulates the inflammatory process in scarred mucosa during ulcer recurrence.

Figure 1

Expression of intercellular adhesion molecule 1 (ICAM-1) in scarred mucosa 24 hours after injection of interleukin 1β (IL-1β). A marked increase in expression of ICAM-1 was observed by 24 hours in rats given IL-1β (A) while there was no increase in expression of ICAM-1 in rats administered omeprazole together with IL-1β (B). Original magnification ×40.

Figure 2

Comparison of numbers of infiltrating leucocytes positive for lymphocyte function associated antigen 1 (LFA-1) or Mac-1 in scarred mucosa. The numbers of LFA-1 or Mac-1 positive cells infiltrating scarred mucosa were counted, and the mean numbers of such cells were compared with those in control animals (not given IL-1β). Results are mean (SEM), n=6. OPZ, omeprazole; IL-1β, interleukin 1β; ICAM-1, intercellular adhesion molecule 1. *p<0.05, **p<0.01 compared with control animals.

Figure 3

Comparison of numbers of infiltrating leucocytes positive for lymphocyte function associated antigen 1 (LFA-1) or Mac-1 in normal mucosa. The numbers of LFA-1 or Mac-1 positive cells infiltrating the normal mucosa were counted, and the mean numbers of such cells were compared with those in control animals (not given IL-1β). Results are mean (SEM), n=6. OPZ, omeprazole; IL-1β, interleukin 1β; ICAM-1, intercellular adhesion molecule 1.

Figure 4

Comparison of numbers of lymphocyte function associated antigen 1 (LFA-1) and Mac-1 positive leucocytes in superficial and deep portions of scarred mucosa at 24 hours. LFA-1 and Mac-1 positive cells were counted separately in the deep and superficial portions of scarred mucosa, and the mean numbers of cells were compared with those in control animals (not given IL-1β). Results are mean (SEM), n=6. OPZ, omeprazole; IL-1β, interleukin 1β; ICAM-1, intercellular adhesion molecule 1. **p<0.01 compared with control animals.

Figure 5

Interleukin 1β (IL-1β) and tumour necrosis factor α (TNF-α) concentrations in scar tissue at 24 hours. Concentrations of IL-1β (A) and TNF-α (B) in scar tissue were assayed 24 hours after IL-1β treatment. Results are mean (SEM), n=6. OPZ, omeprazole. *p<0.05, **p<0.01 compared with control animals (not given IL-1β).

Figure 6

Cellular infiltration and immunohistochemical staining for interleukin 1β (IL-1β) and tumour necrosis factor α (TNF-α) in superficial mucosa at 24 hours after IL-1β treatment. (A) IL-1β induced infiltration by leucocytes, including neutrophils, in the superficial portion of scarred mucosa. (B) Monocytes/macrophages were abundant in this region. IL-1β (C) and TNF-α (D) were detected mainly in inflammatory cells in the superficial mucosa. The numbers of cells stained for IL-1β (E) and TNF-α (F) were small in rats given the antibody against intercellular adhesion molecule 1. Original magnification ×200 (A-D) and ×50 (E, F).