Increased intestinal luminal carbon monoxide gas in patients with ulcerative colitis

New light on the anti-colitic actions of therapeutic aminosalicylates: the role of heme oxygenase

Although a variety of pharmaceutical preparations of aminosalicylate are commonly used in the clinic for the control of inflammatory bowel disease, the mechanisms underlying their therapeutic actions remain unclear. Recent in vivo and in vitro studies have demonstrated that 5-aminosalicylic acid (5-ASA), regarded as the active moiety in aminosalicylate preparations such as sulfasalazine, can induce the heat shock protein, heme oxygenase-1 (HO-1) and up-regulate HO enzyme activity in the colon. As HO-1 can produce endogenous anti-oxidant and anti-inflammatory moieties such as bilirubin and carbon monoxide (CO), these findings suggest a novel mechanism of action for aminosalicylates, acting as anti-colitic agents through the up-regulation of HO-1 enzyme expression and activity.

Increased intestinal expression of heme oxygenase-1 and its localization in patients with ulcerative colitis

BACKGROUND

Heme oxygenase-1 (HO-1) is regarded as a sensitive and reliable indicator of cellular oxidative stress. Two end products of heme degradation, carbon monoxide (CO) and bilirubin, are involved in the protective role of HO-1 against oxidative injury. We have demonstrated enhanced expression of this enzyme and increased concentration of CO in experimental models of colitis, but the role of HO-1 in patients with ulcerative colitis (UC) has not been extensively investigated. The aim of the present study was to determine the intestinal levels and localization of ho-1 mRNA and HO-1 protein in patients with UC.

METHODS

Eighteen patients with UC and 13 patients with colon cancer were prospectively selected from subjects who underwent colonoscopy. Biopsy specimens were obtained from the inflamed mucosa of UC patients and from the normal mucosa at least 5 cm from the margin of carcinoma. The expression of ho-1 mRNA was assayed by real-time polymerase chain reaction (PCR). The colonic expression of HO-1 was determined by immunohistochemistry and western blotting using a monoclonal antibody against HO-1.

RESULTS

The expression of ho-1 mRNA and HO-1 protein was significantly increased in the colonic mucosa of patients with active UC compared with normal mucosa. In the patients with active UC, mononuclear cells in the submucosa of the colon were positive for HO-1, and there was negligible staining in the epithelial cells.

CONCLUSION

The present findings are evidence of the induction of HO-1 in the colon of UC patients.

Use of carbon monoxide as a therapeutic agent: promises and challenges

As a by-product of heme catabolism by the heme oxygenase system, carbon monoxide (CO) has been neglected for many years, and only recently has its role as an essential signaling molecule been appreciated. In the past decade, the use of CO gas in pre-clinical experimental models of disease has produced some remarkable data indicating that its therapeutic delivery to mammals could alleviate inflammatory processes and cardiovascular disorders. However, the inherent toxic nature of CO cannot be ignored, knowing that inhalation of uncontrolled amounts of this gas can ultimately lead to serious systemic complications and neuronal derangements. From a clinical perspective, a key question is whether a safe and therapeutically effective threshold of CO can be reached locally in organs and tissues without delivering potentially toxic amounts through the lung. The advent of CO-releasing molecules (CO-RMs), a group of compounds capable of carrying and liberating controlled quantities of CO in cellular systems, appears a plausible alternative in the attempt to overcome the limitations of CO gas. Although in its infancy and far from being used for clinical applications, the CO-RMs technology is supported by very encouraging biological results and reflected by the chemical versatility of these compounds and their endless potential to be transformed into CO-based pharmaceuticals.

The involvement of heme oxygenase-1 activity in the therapeutic actions of 5-aminosalicylic acid in rat colitis

The mechanism of action of 5-aminosalicylic acid (5-ASA), the active therapeutic moiety of a number of clinically used anti-colitic agents, is unclear. The present study investigates whether the beneficial effects in vivo could involve induction of the heat shock protein, heme oxygenase-1 (HO-1), known to provide endogenous anti-oxidant and anti-inflammatory moieties which can modulate colonic inflammation. The effects of 5-ASA on the colonic expression and activity of HO-1 along with its effect on the inflammatory damage have been evaluated in the colitis provoked by instillation of trinitrobenzene sulphonic acid (TNBS) over 48 h in the rat. Intracolonic administration of 5-ASA (8, 25 and 75 mg/kg/day) dose-dependently reduced the TNBS-provoked macroscopic colonic inflammatory injury, myeloperoxidase (MPO) activity and TNF-alpha levels, while also dose-dependently increasing colonic heme oxygenase enzyme activity. Colonic HO-1 protein expression, determined by Western blot analysis in this colitis model, was likewise further induced by 5-ASA. Intracolonic administration of 5-ASA alone under unchallenged conditions also induced colonic HO-1 protein expression and stimulated heme oxygenase enzyme activity. Administration of zinc protoporphyrin (50 micromol/kg/day, s.c.), which prevented the increase in colonic heme oxygenase activity, abolished the anti-colitic effect of 5-ASA. These results suggest that 5-ASA may exert its colonic anti-oxidant and anti-inflammatory effects in vivo in part through the up-regulation of HO-1 enzyme expression and activity.