Effects of cyclooxygenase and lipoxygenase inhibition on eicosanoids and healing of acetic acid colitis in rats

Mucosal healing in inflammatory bowel diseases: is there a place for nutritional supplementation?

Advanced mucosal healing (MH) after intestinal mucosal inflammation coincides with sustained clinical remission and reduced rates of hospitalization and surgical resection, explaining why MH is increasingly considered as a full therapeutic goal and as an endpoint for clinical trials. Intestinal MH is a complex phenomenon viewed as a succession of steps necessary to restore tissue structure and function. These steps include epithelial cell migration and proliferation, cell differentiation, restoration of epithelial barrier functions, and modulation of cell apoptosis. Few clinical studies have evaluated the needs for specific macronutrients and micronutrients and their effects on intestinal MH, most data having been obtained from animal and cell studies. These data suggest that supplementation with specific amino acids including arginine, glutamine, glutamate, threonine, methionine, serine, proline, and the amino acid-derived compounds, polyamines can favorably influence MH. Short-chain fatty acids, which are produced by the microbiota from undigested polysaccharides and protein-derived amino acids, also exert beneficial effects on the process of intestinal MH in experimental models. Regarding supplementation with lipids, although the effects of ω-3 and ω-6 fatty acids remain controversial, endogenous prostaglandin synthesis seems to be necessary for MH. Finally, among micronutrients, several vitamin and mineral deficiencies with different frequencies have been observed in patients with inflammatory bowel diseases and supplementation with some of them (vitamin A, vitamin D3, vitamin C, and zinc) are presumed to favor MH. Future work, including clinical studies, should evaluate the efficiency of supplementation with combination of dietary compounds as adjuvant nutritional intervention for MH of the inflamed intestinal mucosa.

The role of arachidonic acid regulatory enzymes in colorectal disease

PURPOSE

Nonsteroidal anti-inflammatory drugs have a wide ranging effect on diseases of the colon and rectum. Interestingly, nonsteroidal anti-inflammatory drugs seem to play a beneficial role in colorectal cancer chemoprevention and adenoma regression, but may have a deleterious effect in inflammatory bowel disease. Prostaglandin inhibition is central to both the beneficial and toxic effects of this class of drugs. Arachidonic acid metabolism is essential to prostaglandin synthesis.

METHODS

A Medline search using "nonsteroidal anti-inflammatory drugs," "colon cancer," "inflammatory bowel disease," "colitis," "COX inhibitors," "arachidonic acid," and "chemoprevention" as key words was performed for English-language articles. Further references were obtained through cross-referencing the bibliography cited in each work.

RESULTS

Based on numerous studies, nonsteroidal anti-inflammatory drugs have a beneficial role in colon cancer and colonic adenomas. However, they have been reported to have a deleterious effect on the colon in inflammatory bowel disease and have been shown to cause colitis. Nonsteroidal anti-inflammatory drugs work via multiple pathways, some well defined, and others unknown.

CONCLUSIONS

In the new millennium, nonsteroidal anti-inflammatory drugs may be used for chemoprevention of colorectal and other cancers. In addition, they may be used in combination with surgery and chemotherapy to primarily treat colorectal carcinoma. Undoubtedly, the use of novel cyclooxygenase inhibitors with less of a toxicity profile will allow more widespread use of nonsteroidal anti-inflammatory drugs for a variety of diseases. The future of this class of drugs is promising.

5-lipoxygenase and cyclooxygenase regulate wound closure in NIH/3T3 fibroblast monolayers

Wound healing involves multiple cell signaling pathways, including those regulating cell-extracellular matrix adhesion. Previous work demonstrated that arachidonate oxidation to leukotriene B(4) (LTB(4)) by 5-lipoxygenase (5-LOX) signals fibroblast spreading on fibronectin, whereas cyclooxygenase-2 (COX-2)-catalyzed prostaglandin E(2) (PGE(2)) formation facilitates subsequent cell migration. We investigated arachidonate metabolite signaling in wound closure of perturbed NIH/3T3 fibroblast monolayers. We found that during initial stages of wound closure (0-120 min), all wound margin cells spread into the wound gap perpendicularly to the wound long axis. At regular intervals, between 120 and 300 min, some cells elongated to project across the wound and meet cells from the opposite margin, forming distinct cell bridges spanning the wound that act as foci for later wound-directed cell migration and resulting closure. 5-LOX inhibition by AA861 demonstrated a required LTB(4) signal for initial marginal cell spreading and bridge formation, both of which must precede wound-directed cell migration. 5-LOX inhibition effects were reversible by exogenous LTB(4). Conversely, COX inhibition by indomethacin reduced directed migration into the wound but enhanced early cell spreading and bridge formation. Exogenous PGE(2) reversed this effect and increased cell migration into the wound. The differential effects of arachidonic acid metabolites produced by LOX and COX were further confirmed with NIH/3T3 fibroblast cell lines constitutively over- and underexpressing the 5-LOX and COX-2 enzymes. These data suggest that two competing oxidative enzymes in arachidonate metabolism, LOX and COX, differentially regulate sequential aspects of fibroblast wound closure in vitro.

Both constitutive and inducible prostaglandin H synthase affect dermal wound healing in mice

In an attempt to define the roles of prostaglandin H synthase 1 (PGHS-1, cyclooxygenase-1, COX-1) and prostaglandin H synthase 2 (PGHS-2, cyclooxygenase-2, COX-2) in wound healing, we investigated the healing of incisional dermal wounds in wild-type, PGHS-1 null, and PGHS-2 null mice. We measured tensile strength of the wounds, levels of PGHS-1 and PGHS-2 mRNA in the wound site, and histologic markers for the inflammatory, proliferative, and remodeling phases of wound healing. Although no gross visible differences were noted among healed wounds of the different mouse types, measurement of tensile strength showed that both PGHS-1 and PGHS-2 null wounds were weaker (75% and 70%, respectively) than wild-type wounds at 12 days after incision. At Day 8 the endothelial staining was 70% greater in the wounds of PGHS-2 null mice compared with their wild-type counterparts. In contrast at Day 12, staining for macrophages and myofibroblasts was less in PGHS-1 null wounds compared with wild-type and PGHS-2 null tissue. Compensatory expression of the alternate PGHS mRNA could be demonstrated by RT-PCR in the wounds of PGHS null mice on Days 1 and 4. We conclude that both PGHS-1 and PGHS-2 genes play distinct roles in the process of dermal wound healing.

Increase in cyclooxygenase-2 and nitric oxide-synthase-2 mRNAs in pouchitis without modification of inducible isoenzyme heme-oxygenase-1

OBJECTIVES

The pathophysiology of pouchitis occurring after ileal pouch-anal anastomosis remains controversial. Prostaglandins and nitric oxide synthesized in excess by cyclooxygenase-2 and nitric oxide synthase-2 are thought to be involved in the inflammatory process. Because heme oxygenase-1, by its antioxidant properties, could modulate inflammatory reaction, we analyzed mRNAs of the three enzymes (cyclooxygenase-2, nitric oxide synthase-2, and heme oxygenase-1) in patients with ileal pouch-anal anastomosis.

METHODS

Endoscopic biopsies were obtained in eight patients with normal ileal pouch-anal anastomosis, in eight patients with pouchitis, and in normal ileum of six healthy subjects. A relative quantitative RT-PCR was performed to determine the levels of cyclooxygenase-2, nitric oxide synthase-2, and heme oxygenase-1 mRNAs.

RESULTS

Cyclooxygenase-2 and nitric oxide synthase-2 mRNAs were increased both in normal ileal pouch-anal anastomosis and in pouchitis, compared with healthy subjects. Pouchitis disease activity index was correlated with mRNA levels of cyclooxygenase-2 (r = 0.71; p < 0.01) and nitric oxide synthase-2 (r = 0.51; p < 0.05). Heme oxygenase-1 mRNA levels were not significantly different in patients versus healthy subjects.

CONCLUSIONS

The increase in cyclooxygenase-2 and nitric oxide synthase-2 mRNA levels both in pouchitis and normal ileal pouch-anal anastomosis demonstrates that a latent inflammatory process occurs in the ileal pouch mucosa. This inflammatory process was not found to be associated with an induction of heme oxygenase mRNA, a possible regulator of the inflammatory response.

Effect of ecabet sodium enema on mildly to moderately active ulcerative proctosigmoiditis: an open-label study

OBJECTIVES

Ecabet sodium (ES), a nonabsorbable antigastric ulcer agent, has been shown to adhere to the region of an ulcer. It topically enhances gastric mucosal defensive factors such as the endogenous prostaglandins, capsaicin-sensitive sensory nerves, nitric oxide, and mucin. All of these mucosal defensive factors play an important role in maintaining the mucosal integrity of the colon and rectum. Therefore, we investigated the effect of ES in patients with mildly to moderately active ulcerative proctosigmoiditis.

METHODS

In an open-label study, seven patients with mildly to moderately active ulcerative colitis (UC) who had an inflamed mucosa in the rectum and/or sigmoid and were resistant to 4-wk topical and systemic standard treatment were treated with an ES enema b.i.d. for 14 days. The enema consisted of ES (1 g) and tepid water (20 or 50 ml). These patients were assessed by the Clinical Activity Index, colonoscopically, and histologically before and after the ES therapy. The ES therapy was started after obtaining informed consent from the patients.

RESULTS

Six of the seven patients responded to therapy and achieved clinical, endoscopic, and histological remissions. One patient was withdrawn because of increased stool frequency. All six patients who completed the study showed a significant change in the mean Clinical Activity Index score from 5.3+/-1.4 (mean +/- SD) to 0.5+/-0.8 (p < 0.05), in the colonoscopic score from 3.0+/-0.9 to 0.8+/-0.4 (p < 0.05), and in the histological score from 2.7+/-0.5 to 0.5+/-0.6 (p < 0.05), and achieved remission at the end of the study. There were no side effects attributable to the ES therapy. Five of the six patients are still in clinical remission after a median follow-up period of 5 months.

CONCLUSIONS

The ES enemas proved to be a safe and potentially useful adjuvant therapy currently available for treating patients with mildly to moderately active ulcerative proctosigmoiditis. A controlled study is necessary to confirm our results.

Physiological assessment of epithelial function in damaged rat colon

OBJECTIVE

To assess colonic damage quantitatively by electrophysiological parameters such as membrane potential difference, short circuit current and transepithelial resistance, and by colonic membrane permeability (permeation clearance) of FITC-labelled dextran 4000.

MATERIALS AND METHODS

For experimental colitis models of rats, trinitrobenzene sulphonic acid-, acetic acid-, and dextran sulphate sodium-induced models were employed. The Ussing-type chamber was used for determination of the electrophysiological parameters and permeation clearance of FITC-labelled dextran 4000.

RESULTS

Reductions of all the above electrophysiological parameters were observed in trinitrobenzene sulphonic acid- and acetic acid-induced models. No good correlation between the reduction in the parameters and the intestinal damage score was found in any of the models. This shows that damage scores do not necessarily reflect precise changes in physiological epithelial function. In contrast, the electrophysiological parameters were well correlated with membrane permeability. The reduction in transepithelial resistance, i.e. reduction in barrier function, was supported by an increase in permeation clearance of FITC-labelled dextran 4000 and the plasma appearance of endotoxin in the trinitrobenzene sulphonic acid-induced model. Through the recovery of transepithelial resistance and permeation clearance of FITC-labelled dextran 4000 to control values in the acetic acid-induced model, automatic recovery of the model to normal occurred.

CONCLUSION

Examination of the electrophysiological parameters and permeation clearance of FITC-labelled dextran 4000 can provide a useful method of assessment of epithelial damage.

Effect of dehydroleucodine in experimental colitis in rats and mice

Dehydroleucodine (DhL), a sesquiterpene lactone (SQL) of the guaianolide type isolated from Artemisia douglasiana Besser, shows a pharmacological cytoprotective effect and significantly prevents the formation of gastric and duodenal lesions induced by various necrotising agents in rodents. The effects of DhL, on two models of experimental colitis were examined. Colitis was produced in male Wistar rats by rectal instillation of 5 and 10% acetic acid, following the methods of Eliakim et al. and Le Duc et al., respectively. In mice colitis was produced by rectal instillation of 0.1 ml of 2,4,6-trinitrobenzene sulphonic acid (5 mg in 50% ethanol) (TNB) as previously described by Chin et al. In this study, the administration of DhL 40 mg kg(-1)(1 h before the induction of colitis) significantly decreased mucosal damage. This effect was consistent in both models. The protection provided by DhL was accompanied by significant decreases in diarrhoea and colon weight; and histologically normal mucosa without ulceration and mucus production were observed. This study shows that both TNB and acetic acid colitis can be pharmacologically controlled by DhL. Our results suggest that the protective activity of DhL in experimental colitis is mediated, at least in part, through the increase of glycoprotein synthesis, anti-inflammatory effect and inhibition of COX-2 induction, and by inhibiting the degranulation of cells containing monoamines.

Intracolonic administration of zileuton, a selective 5-lipoxygenase inhibitor, accelerates healing in a rat model of chronic colitis

BACKGROUND

5-Lipoxygenase products play a part in inflammatory response.

AIMS

The effect of intracolonic administration of zileuton (a 5-lipoxygenase inhibitor) on colonic damage and eicosanoid local release was assessed in a rat model of colitis.

METHODS

Ninety rats with trinitrobenzenesulphonic acid induced colitis were randomised to receive placebo, 5-aminosalicylic acid (50 mg/kg), or zileuton (50 mg/kg) intracolonically for four weeks. Local eicosanoid release was monitored by intracolonic dialysis throughout the study. The colon was removed for macroscopic and histological assessment at weeks 1, 2, and 4 after colitis induction in 10 rats of each group.

RESULTS

Zileuton significantly reduced macroscopic damage score after four weeks of treatment in comparison with the other two groups (p = 0.034). In addition, zileuton administration significantly increased the intracolonic release of both thromboxane B2 at week 1 (p = 0.05) and prostaglandin E2 at weeks 2 and 4 (p < 0.05). Zileuton and 5-aminosalicylic acid decreased leukotriene B4 release by 90% at day 3.

CONCLUSIONS

Intracolonic zileuton, compared with 5-aminosalicylic acid and placebo, seems to improve the course of the disease in a model of chronic colitis. This effect may be related to an increased and maintained production of prostaglandin E2 together with inhibition of leukotriene B4 synthesis.

Increased prostaglandin E2 and leukotriene B4 synthesis in isolated colonic mucosal cells in inflammatory bowel disease. a preliminary report

The synthesis of prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) in colonic mucosal cells was investigated in 7 patients and 10 controls. Biopsies obtained from the descending colon were isolated biochemically by a special technique and the suspension of isolated colonic cells was incubated during 45 min. Compared with healthy subjects, patients with an inflammatory bowel disease showed a significantly increased PGE2 production. The LTB4 synthesis was enhanced as well, but this change was not statistical. We conclude that PGE2 is the dominant eicosanoid during less severe inflammatory bowel disease. Age and gender did not influence PGE2 or LTB4 synthesis.

Eicosanoids and the gastrointestinal tract

Determining the role of eicosanoids in gastrointestinal physiology and pathophysiology has been an active area of investigation over the past 20 years. The landmark discovery of prostaglandin endoperoxide synthase and other enzymes involved in the production of arachidonic acid products (lipoxygenases and epoxygenases) ushered in a new era of research. The goal of this review is to distill a large body of work pertaining to studies of eicosanoids in the gastrointestinal tract. This review has been organized according both to functional (secretion and motility) and disease-related (inflammation, mucosal injury, and neoplasia) effects. The aim of this article is to present a clear summary of this area of gastroenterology so that future research can be directed in a logical and productive manner.