Pathophysiology of early ischaemia reperfusion injury of the colon in aortic surgery

Introduction

Ischaemia-reperfusion (I-R) injury of the colon has been implicated in the systemic inflammatory response syndrome, which may lead to multiple organ dysfunction syndrome and death. The aim of this study was to investigate the early cellular events in I-R injury using elective aortic surgery as a model.

Methods

Twenty patients undergoing elective abdominal aortic aneurysm surgery were prospectively recruited. Ten underwent conventional open repair and 10 had endovascular aneurysm repair (EVAR). Mucosal biopsies of the sigmoid colon were taken immediately preoperatively and postoperatively. Microscopic examination was performed using H&E and TUNEL staining for apoptosis, and in situ hybrdisation techniques were used to detect IL-6 mRNA expression. Intraoperatively, systemic and splanchnic blood was sampled in the conventional surgery group. In the EVAR group only systemic blood was taken. Plasma was assayed for nitrosothiols (nitric oxide donors) and IL-6.

Results

There were no histological features of acute inflammation in the preoperative or postoperative biopsies in either group. H&E and TUNEL staining showed a 3.5-fold rise in apoptotic bodies following conventional surgery. There was no significant change following EVAR. IL-6 expression occurred in the colonic epithelium localized to the base of the crypts. Splanchnic blood showed a fourfold increase in nitrosothiols and a 22-fold increase in IL-6 within 15 min of reperfusion. Peripheral blood showed a five-fold increase in IL-6 (Student's t test P < 0.05).

Conclusions

There is a significant increase in IL-6 release both from the colon and in the systemic circulation following reperfusion, which is accompanied by an increase in nitrosothiols. The colonic epithelium is a source of IL-6. Apoptosis, rather than necrosis, has been shown to be the principal mode of cell death in early I-R injury.