A novel colon-specific steroid prodrug enhances sodium chloride absorption in rat colitis.

A recently synthesized novel colon-specific dexamethasone prodrug, dexamethasone-beta-D-glucuronide, delivers efficacious amounts of dexamethasone to the colon with limited adrenal suppressive effects. During experimentally induced colitis in rats, the dexamethasone prodrug is significantly more potent than free dexamethasone in improving colonic fluid and electrolyte absorptive injury. The present studies examined whether the improvement in colonic absorption seen with the prodrug occurred as a consequence of alterations in sodium and chloride epithelial transport. The efficacy of the dexamethasone prodrug and free dexamethasone were tested in an acetic acid-induced rat model of colitis. Healing of the induced colitis was assessed by measuring net colonic fluid absorption and surface area ulceration. Transmural unidirectional fluxes of 22Na and 36Cl across sheets of colonic mucosa were measured in Ussing chambers. Treatment of colitis with the prodrug delivered a sixfold higher concentration of dexamethasone to the colon than did treatment with the free drug. The prodrug accelerated healing of colitis by returning in vivo colonic fluid absorption to normal and virtually eliminated colonic macroscopic ulceration, whereas the free drug did not. In vitro transmural fluxes demonstrated that, in addition to repair of mucosal integrity, the prodrug enhanced electroneutral sodium chloride absorption over and above that seen in control animals or after treatment with the free drug. Both the prodrug and the free drug limited theophylline-mediated net chloride and sodium secretion, an effect that would be consistent with the antidiarrheal effect induced by these drugs in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Colonic delivery of dexamethasone from a prodrug accelerates healing of colitis in rats without adrenal suppression.

BACKGROUND/AIMS: Dexamethasone-beta-D-glucuronide, a colon-specific prodrug of dexamethasone, may be useful in the treatment of ulcerative colitis and Crohn's colitis. The aim of this study was to evaluate colonic delivery and efficacy of this prodrug in the rat. METHODS: Distribution of dexamethasone in luminal contents and tissues of the gastrointestinal tract and in plasma was measured after oral administration of dexamethasone-beta-D-glucuronide or free dexamethasone. Efficacy of the prodrug and free drug was tested in an acetic acid-induced rat colitis model. Healing of induced colitis was assessed by measuring net intestinal fluid absorption, colonic surface area of ulceration, histology, and myeloperoxidase activity. Glucocorticosteroid toxicity was evaluated with serum corticosterone and plasma adrenocorticotropic hormone levels. RESULTS: The drug delivery index (a measure of relative targeting efficiency) was 6.7 and 8.6 in the cecal and colonic mucosa, respectively. The prodrug was significantly more potent than free drug in improving net colonic fluid absorption while significantly reducing surface area of ulceration and histological grade in colitic rats. Treatment with free dexamethasone significantly reduced serum corticosterone levels to subnormal levels, and treatment with the prodrug maintained serum corticosterone and plasma adrenocorticotropic hormone levels near control levels. CONCLUSIONS: The prodrug dexamethasone-beta-D-glucuronide delivers efficacious amounts of dexamethasone to the large intestine from lower doses than free dexamethasone.

Acetic acid-induced colitis results in bystander ileal injury.

The extent of the small intestinal injury following experimental acetic acid induction of colitis in rats was examined. Following intraluminal colonic administration of radiolabelled acetic acid, high levels of radioactivity were identified in the colon and in the liver, while low background levels were found in jejunum, ileum, caecum, and heart. The increased level of radioactivity in the liver relative to that of the heart suggests that a significant portion of the colonic intraluminal acetic acid was absorbed directly into the portal circulation. The colon, which was the only segment of intestine in direct contact with the acetic acid, had the highest levels of radiolabelled acetic acid, demonstrated a marked macroscopic mucosal ulceration, an enhanced myeloperoxidase activity, and a fall in in vivo fluid absorption. The jejunum, which demonstrated low levels of radiolabelled acetic acid was normal without evidence of injury. In contrast, the ileum, which displayed the same levels of radiolabelled acetic acid as did the jejunum, also demonstrated a significant fall in in vivo fluid absorption but showed no mucosal ulceration or increased myeloperoxidase activity. These studies have shown that acetic acid induction of colitis produces evidence of ileal injury but that this injury is not the result of inadvertent delivery of acetic acid or recruitment of neutrophils to the ileal mucosa.

Indomethacin worsens and a leukotriene biosynthesis inhibitor accelerates mucosal healing in rat colitis.

The implication of leukotrienes as mediators of inflammation and recent evidence that prostaglandin analogues provide a beneficial effect during experimental colitis led to the speculation that (i) leukotrienes may be injurious and (ii) prostaglandins may be protective to colonic mucosa. Using a 2% acetic acid induced rat colitis model, we administered specific cyclooxygenase (indomethacin) and leukotriene biosynthesis inhibitors (MK-886) to examine the effect of endogenous prostaglandins and leukotrienes on colonic macroscopic injury, mucosal inflammation as measured by myeloperoxidase activity, net in vivo intestinal fluid absorption, and colonic PGE2 and LTB4 levels as measured by in vivo rectal dialysis. Indomethacin treatment prior to induction of colitis reduced endogenous mucosal PGE2 levels and exacerbated macroscopic ulceration and net fluid absorption. Addition of the exogenous PGE1 analogue misoprostol to the indomethacin-exacerbated colitis completely healed colonic macroscopic ulceration and inflammation but only partially improved fluid absorptive injury. The specific leukotriene biosynthesis inhibitor MK-886 administered prior to induction of colitis healed macroscopic ulceration and inflammation but not fluid absorptive injury. This mucosal reparative effect of MK-886 occurred at a dose that reduced colonic LTB4 synthesis while concomitantly enhancing PGE2 levels. Combining MK-886 with misoprostol treatment improved not only macroscopic ulceration and inflammation but also provided a synergistic effect that maintained net colonic fluid absorption at noncolitic control levels. These studies suggest that, during the induction of experimental colitis, endogenous prostaglandins play a pivotal role in providing a mucosal healing effect, and that leukotriene biosynthesis inhibitor may manifest part of its beneficial effect by shifting arachidonic acid metabolism towards production of prostaglandins.

Verapamil alters eicosanoid synthesis and accelerates healing during experimental colitis in rats.

In inflammatory bowel disease, prostaglandins are mucosal protective whereas leukotrienes are proinflammatory. Recent evidence suggests that the formation and action of leukotrienes are calcium-dependent, whereas the formation and action of prostaglandins are not. To examine the possibility that, because of differential regulation of arachidonic acid metabolism, calcium channel blockade might alter mucosal eicosanoid synthesis and accelerate healing during inflammatory bowel disease, we treated a 4% acetic acid-induced colitis model with verapamil and/or misoprostol and determined the effects on colonic macroscopic injury, mucosal inflammation as measured by myeloperoxidase activity, in vivo intestinal fluid absorption, and mucosal prostaglandin E2 and leukotriene B4 (LTB4) levels as measured by in vivo rectal dialysis. In colitic animals, verapamil treatment significantly improved colonic fluid absorption and macroscopic ulceration. This mucosal-protective effect of verapamil occurred in the presence of a twofold reduction in mucosal LTB4 synthesis. In noncolitic animals, verapamil alone had no effect on in vivo fluid absorption, macroscopic ulceration, or myeloperoxidase activity but did induce a threefold reduction in LTB4 synthesis in addition to shifting arachidonic acid metabolism towards a sixfold stimulation of prostaglandin E2 synthesis. Our results show that, when administered before the experimental induction of colitis, the calcium channel blocker, verapamil, has a mucosal-protective effect that occurs as a consequence of reduced mucosal leukotriene synthesis and increased prostaglandin synthesis. This differential regulation of arachidonic acid metabolism may play an important role in the development of novel therapeutic agents for inflammatory bowel disease.

Misoprostol therapy following trinitrobenzene sulfonic acid-induced colitis accelerates healing.

Prostaglandins have been demonstrated to have a mucosal protective effect when administered prior to the experimental induction of colitis in animals. We here determined whether prostaglandins would have a beneficial therapeutic effect when administered after colitis had been established. Diffuse, chronic, trinitrobenzene sulfonic acid-induced colitis was established in rats, and misoprostol was administered daily for up to 10 days following the induction of colitis. The effects of misoprostol therapy were compared to those obtained by treatment with 5-aminosalicylic acid and betamethasone. Misoprostol therapy following trinitrobenzene sulfonic acid-induced colitis accelerated colonic healing, as measured in terms of macroscopic ulceration area and fluid absorption, whereas 5-aminosalicylic acid and betamethasone therapy did not. Ileal fluid absorption impairment was repaired by betamethasone but not by misoprostol or 5-aminosalicylic acid therapy.

Mucosal protective effects of vitamin E and misoprostol during acute radiation-induced enteritis in rats.

Cytotoxic effects of ionizing radiation on gastrointestinal epithelium may be mediated by oxygen free radicals. Therapeutic intervention directed toward oxidant scavenging and increasing tissue oxygen tension may provide a novel approach to management. We investigated the effects of a nonenzymatic oxygen radical scavenger (vitamin E) and an exogenous PGE1 analog known to increase mucosal blood flow (misoprostol) on acute radiation enteritis. Rats were pretreated with: (1) vitamin E, (2) misoprostol, or (3) a combination of both agents prior to 10 Gy abdominal radiation. Three days following irradiation, net fluid absorption using in vivo isolated loops, mucosal histology, and mucosal morphometry using a computerized videoplan were determined in jejunum, ileum, and colon. Nonirradiated control intestine demonstrated net fluid absorption in all segments, which was not altered by vitamin E and/or misoprostol treatment. Irradiation significantly reduced net fluid absorption in jejunum, ileum, and colon. Vitamin E administered prior to irradiation maintained jejunal, ileal, and colonic fluid absorption near control levels. In contrast misoprostol or a combination of vitamin E and misoprostol did not provide protection against the injury caused by abdominal irradiation. Alterations in intestinal fluid absorption occurred without significant changes in histologic or morphometric appearance. In conclusion, ionizing radiation reduces in vivo intestinal fluid absorption without significant changes in histologic or morphometric appearance. Treatment with vitamin E, but not misoprostol, protects gastrointestinal mucosa against radiation-induced absorptive injury.

Fish oil-enriched diet is mucosal protective against acetic acid-induced colitis in rats.

Products of arachidonic acid metabolism are elevated in patients with inflammatory bowel disease and this elevation is correlated with disease activity. Eicosapentaenoic acid competes with arachidonic acid and alters eicosanoid biosynthesis. In this experiment, the possibility that eicosapentaenoic acid could be used in the treatment of inflammatory bowel disease was investigated by determining the effect of 6 weeks of a fish oil-supplemented diet, enriched in eicosapentaenoic acid, on colonic and ileal morphology, histology, and in vivo fluid absorption in rats with 4% acetic acid-induced colitis. The results of an eicosapentaenoic acid-enriched diet were compared with results of saturated and polyunsaturated fatty acid-enriched diets. In rats with misoprostol pretreated acetic acid-induced colitis, an eicosapentaenoic acid-enriched diet reversed net colonic fluid secretion to absorption and prevented macroscopic and histologic injury, compared with saturated and poly-unsaturated fatty acid-enriched diets, which did not. The fish oil mucosal protective effect occurred in the presence of a 30-fold enhancement of PGE2 synthesis. In rats with non-misoprostol pretreated acetic acid-induced colitis, an eicosapentaenoic acid-enriched diet returned ileal fluid absorption to control levels, as compared with saturated and polyunsaturated fatty acid-enriched diets, which did not. In conclusion, a fish oil (eicosapentaenoic acid)-enriched diet, but not a saturated- or a polyunsaturated-enriched diet, protected colonic and ileal net fluid absorption in an experimental model of inflammatory bowel disease.

Misoprostol provides a colonic mucosal protective effect during acetic acid-induced colitis in rats.

This study determined if intracolonically applied prostaglandin E1 analogue (misoprostol) had a mucosal protective effect in rats with 4% acetic acid-induced colitis. The effects of misoprostol were compared with those of 5-aminosalicylic acid and betamethasone. A single application of 4% acetic acid induced an experimental colitis which was maximal at 2 days and showed spontaneous macroscopic and histologic healing by 12 days. Misoprostol (100 micrograms/kg), but not 5-aminosalicylic acid or betamethasone, administered 30 min before induction of colitis, provided macroscopic and histologic colonic mucosal protection but not protection of in vivo fluid absorption. The mucosal protective effect of misoprostol was time, dose, and diluent volume dependent. In the presence of misoprostol-induced colonic morphologic but not functional absorptive mucosal protection, in vitro unidirectional sodium and chloride flux measurements showed protection of theophylline-stimulated chloride secretion but not sodium absorption. Protection of in vivo colonic fluid absorption, in addition to morphologic protection, could be achieved when misoprostol was administered between 2 and 16 min before induction of colitis or when the highest dose (1000 micrograms/kg) of misoprostol was examined. We conclude that intracolonic misoprostol administration provides unique mucosal protective effects in experimental colitis.

Effect of misoprostol in preventing stress-induced intestinal fluid secretion in rats.

Psychological stress may alter gastrointestinal function by central nervous system controlled alteration of local intestinal mediators. Prostaglandins have been shown to prevent epithelial damage to various noxious stimuli. The purpose of this study was to determine (a) if wrap restraint stress altered in vivo intestinal fluid absorption in rats, and (b) if the prostaglandin E1 analogue, misoprostol, could correct observed fluid malabsorption. In vivo loop studies demonstrated net fluid secretion in the ileum and colon of cold wrap restraint stressed rats. In cold wrap restraint stressed rats, misoprostol reversed net secretion to absorption, but it had no effect on fluid absorption in controls. Mild wrap restraint stress did not alter in vivo fluid absorption. We conclude that cold wrap restraint stress is accompanied by net intestinal fluid secretion that can be effectively reversed with misoprostol.