Effect of simulated systemic administration of aspirin, salicylate, and indomethacin on amphibian gastric mucosa

Elemental diet and IV-TPN-induced bacterial translocation is associated with loss of intestinal mucosal barrier function against bacteria

OBJECTIVE

The goal of the current study was to directly assess the role of loss of mucosal barrier function in nutritionally induced bacterial translocation.

BACKGROUND

Parenteral and certain elemental enteral diets have been shown to promote bacterial translocation. The mechanisms underlying this observation, especially the question of whether nutritionally induced bacterial translocation is primarily related to loss of intestinal barrier function, versus an impaired immune system, remain to be fully elucidated.

METHODS

Bacterial translocation was measured in vivo, ileal mucosal membranes were harvested, and their electrophysiologic properties and barrier function were measured ex vivo in the Ussing chamber system 7 days after receiving total parenteral nutrition solution parenterally (IV-TPN) or enterally (elemental diet). Chow-fed rats served as control subjects.

RESULTS

The incidence of bacterial translocation was significantly increased both to the mesenteric lymph nodes in vivo and across the in vitro Ussing chamber-mounted ileal mucosal membranes of the elemental diet-fed and IV-TPN-fed rats. The magnitude of Escherichia coli and phenol red transmucosal passage in the Ussing chamber was significantly higher in the IV-TPN-fed rats than in the elemental diet-fed or chow-fed animals. The potential differences across the ileal membrane were similar between the three groups at all time points. However, the specific resistances of the ileal membranes of the IV-TPN and elemental diet groups were significantly less than the chow-fed animals, indicating increased membrane permeability.

CONCLUSIONS

Loss of intestinal barrier function plays a major role in nutritionally induced bacterial translocation, and the loss of mucosal barrier function to both E. coli and phenol red appeared greater in the IV-TPN than the elemental diet-fed rats.

Effects of misoprostol on delayed ulcer healing induced by aspirin

Clinical studies have suggested that treatment with the prostaglandin E1 analog, misoprostol, leads to significant healing of ulcers in patients taking regular nonsteroidal antiinflammatory therapy. This study aimed to investigate mechanisms involved in this healing using a rat model. Gastric ulcers were induced by application of acetic acid using a standard technique. Rats were treated with 200 mg/kg aspirin, 100 micrograms/kg misoprostol, a combination of both treatments, or methylcellulose vehicle for up to two weeks, starting two days after ulcer induction. Ulcers were assessed by macroscopic measurements of area and by quantitative histological measurements. Aspirin delayed ulcer healing compared with controls, while misoprostol significantly reversed this effect. Quantitative histology revealed that misoprostol cotreatment significantly increased mucosal regeneration compared with aspirin treatment alone. However, misoprostol did not reverse the effects of aspirin on an index of wound contraction. We conclude that treatment with misoprostol significantly reverses the delayed healing effect of aspirin, and this may occur via an effect on epithelial regeneration.

Some of the factors that may mediate or modify the gastrointestinal mucosal damage induced by non-steroidal anti-inflammatory drugs

Numerous factors are involved in the gastrointestinal mucosal damage induced by non-steroidal anti-inflammatory drugs. The physico-chemical-acidic-property of the drugs is responsible partly for the rapid absorption, mucosal accumulation and barrier breaking effect, partly for the topical irritant action. The drugs decrease the defensive mechanisms of the stomach at different level, destroy the mucosal barrier, decrease the surface hydrophobicity, the mucosal blood flow, and inhibit the prostaglandin synthesis. Exogenous sulfhydryls and interleukin-1 inhibit the NSAID-induced mucosal damage, whether they are also involved in the ulcerogenic action has not been clearly determined. On the other hand, injurious factors are also stimulated; enhanced gastric acid secretion, increased pepsin activity, enhanced formation of free radicals and leukotrienes, as well as activation of leukocyte can also contribute to the mucosal lesions induced by NSAIDs. Prior Campylobacter pylori infection may make the mucosa more susceptible to NSAID-associated injury.

Unique characteristics of the neonatal intestinal mucosal barrier

The purpose of this study was to compare the newborn and weanling intestinal mucosa to determine differences in: (1) the electrophysiologic characteristics of the mucosal barrier; (2) the effects of glutamine supplementation on these physiological characteristics; and (3) transmucosal bacterial passage. The Ussing chamber was used to study ileal mucosa from newborn (1 to 4 days old) and weanling (21 days old) piglets. After the seromuscularis was stripped off the bowel wall, the mucosa was mounted in the chamber and perfused with Hanks Balanced Salt Solution (HBSS) or HBSS + 20 mmol/L of glutamine. Following initial stabilization, potential difference (PD) and resistance (R) were measured at 30-minute intervals for 2 hours. Transmucosal bacterial passage was measured by quantitative cultures of the mucosal and serosal reservoirs obtained 2 hours after adding 10(8) E coli C-25 to the mucosal reservoir. Six groups of membranes were studied: (1) newborn and HBSS; (2) weanling and HBSS; (3) newborn and HBSS + glutamine; (4) weanling and HBSS + glutamine; (5) newborn - HBSS + glutamine + E coli; and (6) weanling - HBSS + glutamine + E coli. Newborn ileal mucosa had significantly lower PD and R compared with weanling at all time points. Glutamine led to a significant increase in PD in both newborn and weanling. Newborn mucosa had a significantly increased incidence of transmucosal bacterial passage (4/7) compared with weanling (0/10). These findings suggest that: (1) newborn mucosal barrier has uniquely different electrophysiologic characteristics; (2) glutamine improves the metabolic activity as measured by PD in both newborn and weanling; and (3) the newborn mucosal barrier allows increased transmucosal passage of bacteria.

Inability of cytoprotection to occur during a period of gastric ischemia

Prostaglandin E2 (PGE2), colloidal bismuth subcitrate (CBS), and sucralfate (SUC) are known to protect the gastric mucosa from ethanol injury. The proposed central role for the microcirculation in gastric mucosal defense and as a site for the expression of the protective effects of these agents was investigated in the rat stomach. Animals were pretreated with either PGE2, CBS, or SUC. Control rats were given normal saline. After allowing 15 min for expression of the pretreatment, ethanol was administered as a 10%, 25%, 50%, or 100% solution to groups of rats with normally perfused stomach and to other groups of rats in whom the stomach was made ischemic by cross-clamping the supracoeliac aorta immediately prior to the instillation of ethanol. The extent of gastric mucosal damage was measured using quantitative histological techniques and expressed as a percentage of surface area and volume of mucosa damaged. In the presence of ischemia, the extent of damage by ethanol was markedly increased, with total destruction of the mucosa by the 50% and 100% solutions. With 25% ethanol, the volume of mucosal damage was increased from 0.5% in the normally perfused stomach to 53.5% with ischemia. When 10% ethanol was instilled into the ischemic stomach, only 0.8% of the volume of the mucosa was damaged, which was not different from the volume of mucosa damaged after the ischemic stomach was exposed to normal saline alone (1.0%). Pretreatment with PGE2, CBS, or SUC did not significantly change the extent of damage seen with exposure of the ischemic stomach to 25% or 50% ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonsalicylate nonsteroidal antiinflammatory drugs augment prestimulated acid secretion in rabbit parietal cells. Investigation of the mechanisms of action

The effects of nonsalicylate nonsteroidal antiinflammatory drugs on acid secretion were studied in isolated rabbit parietal cells. Indomethacin, naproxen, and carprofen (10(-6)-10(-4) mol/L) potentiated histamine-, forskolin-, 3-isobutyl-1-methylxanthine-, and dibutyryl cyclic adenosine monophosphate-stimulated acid secretion without affecting basal acid secretion. This augmentation of secretagogue-stimulated acid secretion was dependent on extracellular calcium because potentiation was abolished by calcium depletion of the medium or in the presence of the calcium antagonist lanthanum chloride. Potentiation was independent of the H2 and muscarinic receptors and did not appear to involve guanine nucleotide regulatory proteins. Proton pump activity was unaffected by indomethacin. Furthermore, nonsteroidal antiinflammatory drugs increased calcium efflux through the plasma membrane, as measured by calcium 45, and decreased endogenous prostaglandin E2 content. Exogenous dimethyl prostaglandin E2 inhibited the potentiating effect of these drugs on histamine-stimulated but apparently not on dibutyryl cyclic adenosine monophosphate-stimulated acid secretion. The data indicate that nonsalicylate nonsteroidal antiinflammatory drugs interacted at a postreceptor site between adenylate cyclase and the proton pump. The potentiating effects of these drugs were regulated by calcium and possibly modulated by prostanoids.

Aspirin induces morphological transformation to the secretory state in isolated rabbit parietal cells

The morphological response of rabbit parietal cells to aspirin was evaluated by grading several ultra-structural features including the extent of the tubulovesicular system, intracellular secretory canaliculi, and microvilli. After exposure of isolated parietal cells and gastric glands to aspirin or histamine, there was an approximately twofold increase in the ratio of secretory to nonsecretory parietal cells, and depletion of extracellular Ca2+ abolished the aspirin-induced morphological changes. Morphometry in parietal cells showed that aspirin induced a sixfold increase in secretory canalicular membrane elaboration. Aspirin potentiated histamine-induced parietal cell respiration and aminopyrine uptake ratio but did not increase basal respiration or aminopyrine uptake, suggesting an apparent dissociation from aspirin-induced morphological changes.

Aspirin-induced changes in gastric function: role of endogenous prostaglandins and mucosal damage

The relative roles of prostaglandins and mucosal injury in aspirin-induced changes in gastric function were evaluated. Conscious rhesus monkeys received a subcutaneous injection of sodium bicarbonate or aspirin (25, 50, 100, or 150 mg/kg) and sodium bicarbonate or 150 mg/kg aspirin subcutaneously plus oral sucralfate (25 mg/kg twice a day). Gastric emptying and fluid and H+ outputs were determined during a fasting period and after an 80-ml water load using a 99mTc-diethylenetriaminepentaacetic acid dilution technique. At the end of each study, the monkeys were gastroscoped to assess mucosal damage, which was ranked blindly on a scale of 0 to 5. Biopsy samples were taken from antrum and fundus for determination of prostaglandins and histological evaluation. All doses of aspirin significantly suppressed prostaglandins in both the antrum and fundus. In contrast, the aspirin-induced increase in gastric mucosal injury was dose dependent. Aspirin also produced a dose-dependent decrease in gastric emptying that was significantly correlated with erosions scores. When aspirin-induced lesions were prevented by sucralfate, the inhibition of gastric emptying was blocked during the fasting period and was attenuated following the water load. Acid secretion was also decreased significantly by aspirin. This action was not modified by sucralfate protection, suggesting that aspirin has a direct inhibitory effect on parietal cell secretion. These data show that mucosal damage contributes significantly to the aspirin-induced changes in gastric function. Moreover, prostaglandins may play a role in the control of gastric emptying, especially during early phase of the response to a water load.

Mechanisms of gastroprotection

Gastric mucosa is constantly exposed to various irritants, but it usually maintains its integrity owing to several lines of defense, including mucus-alkaline secretion, mucosal hydrophobicity, rich mucosal blood flow, stabilization of tissue lysosomes, maintenance of mucosal sulfhydryls, and rapid proliferation and renewal of mucosal cells. Prostaglandins (PG) inhibit experimental gastric mucosal damage and ulcerations induced by a wide variety of agents, hence PG have been proposed to contribute to the overall protective process by activation of various mucosal defence lines--particularly by prevention of vasocongestion, ischemia, and deep hemorrhagic necrosis. The relation between tissue PG generation and mucosal protection does not appear to be closely related, and probably only minute amounts of PG are required to maintain mucosal integrity. In contrast to PG, other products of arachidonate metabolism, such as TxA2, LTC4 or LTD4, and the related lipid, platelet-activating factor, appear to mediate mucosal damage mainly by the disturbance in mucosal microcirculation and tissue ischemia. Gastroprotection can be achieved by stimulation of mucosal biosynthesis of protective PG or by the inhibition of the release or action of the proulcerogenic arachidonate metabolites. Certain natural substances, such as sulfhydryls, epidermal growth factor, or polyamines, protect the mucosa via a PG-independent mechanism, probably by enhancing the tissue repair processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin prevents aspirin injury in the canine stomach under in vivo but not in vitro conditions

This study compared the ability of topical 16,16-dimethyl prostaglandin E2 in a dose range of 0.3-3.0 micrograms/ml to prevent aspirin-induced injury in the canine stomach under both in vivo and in vitro conditions. For in vitro studies, isolated strips of oxyntic mucosa were exposed to 10 or 20 mM aspirin (ASA) at pH 1-4, with and without treatment with 16,16-dimethyl prostaglandin E2. For in vivo experiments, a portion of the oxyntic stomach was mounted between the rings of a Lucite chamber, with splenic vessels intact, such that the mucosa was divided into halves. Both sides were exposed to 20 mM ASA at pH 1 or 2, and one side also received concomitant treatment with 16,16-dimethyl prostaglandin E2. After ASA exposure, tissue samples were prepared for quantitative microscopic analysis of the degree of injury. Under both experimental conditions, the magnitude of gastric injury by ASA was pH-related, being most pronounced at pH 1; this damage was worse under in vitro conditions, and both concentrations of ASA were equally damaging in this setting. 16,16-Dimethyl prostaglandin E2 failed to prevent ASA injury in vitro at any pH and ASA concentration tested, but markedly reduced the magnitude of injury in vivo. The most effective protective dose of 16,16-dimethyl prostaglandin E2 under in vivo conditions was 1.0 micrograms/ml. The diminished tolerance to ASA damage in vitro when compared with in vivo, and the inability of 16,16-dimethyl prostaglandin E2 to prevent these damaging effects in vitro, underscores the probable crucial role for blood flow, and possibly neural innervation, in mediating the protective effects of prostaglandins.

Sulfation in vitro of mucus glycoprotein by submandibular salivary gland: effects of prostaglandin and acetylsalicylic acid

Enzymatic sulfation of mucus glycoprotein by rat submandibular salivary gland and the effect of prostaglandin and acetylsalicylic acid on this process were investigated in vitro. The sulfotransferase enzyme which catalyzes the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to submandibular gland mucus glycoprotein has been located in the detergent extracts of Golgi-rich membrane fraction of the gland. Optimum enzyme activity was obtained at pH 6.8 with 0.5% Triton X-100, 25 mM NaF and 4 mM MgCl2, using the desulfated glycoprotein. The enzyme was also capable of sulfation of the intact mucus glycoprotein, but the acceptor capacity of such glycoprotein was 68% lower. The apparent Km of the submandibular gland sulfotransferase for salivary mucus glycoprotein was 11.1 microM. The 35S-labeled glycoprotein product of the enzyme reaction gave in CsCl density gradient a 35S-labeled peak which coincided with that of the glycoprotein. This glycoprotein upon reductive beta-elimination yielded several acidic 35S-labeled oligosaccharide alditols which accounted for 75% of the 35S-labeled glycoprotein label. Based on the analytical data, the two most abundant oligosaccharides were identified as sulfated tri- and pentasaccharides. The submandibular gland sulfotransferase activity was stimulated by 16,16-dimethyl prostaglandin E2 and inhibited by acetylsalicylic acid. The rate of enhancement of the glycoprotein sulfation was proportional to the concentration of prostaglandin up to 2.10(-5) M, at which point a 31% increase in sulfation was attained. The inhibition of the glycoprotein sulfation by acetylsalicylic acid was proportional to the drug concentration up to 2.5.10(-4) M at which concentration a 48% reduction in the sulfotransferase activity occurred. The apparent Ki value for sulfation of salivary mucus glycoprotein in presence of acetylsalicylic acid was 58.9 microM. The results suggest that prostaglandins may play a role in salivary mucin sulfation and that this process is sensitive to such nonsteroidal anti-inflammatory agents as acetylsalicylic acid.

The effect of i.v. indomethacin on the gastric mucosal electrical potential difference and blood flow in anaesthetized dogs

Indomethacin inhibits prostaglandin synthesis and causes gastric mucosal damage. The correlation between the gastric mucosal function and gastric blood flow was investigated. The intragastric liquid junction corrected potential difference (PD) across the stomach wall was used to characterize the gastric mucosal function. Mucosal blood flow was determined by the radiolabelled microsphere technique. Seven dogs were anaesthetized, intragastric PD was measured continuously and blood flow determined at basal condition during sympathetic activation, and after IV indomethacin (7.5 mg/kg). PD was unchanged during the basal period and during mild sympathetic activation. After indomethacin PD was reduced significantly (-40 +/- 6 mV to -20 +/- 5 mV, measured with gastric lumen negative, mean and SD, P less than 0.05). Mucosal blood flow decreased during sympathetic activation and a further significant reduction was seen after indomethacin. PD and flow reductions correlated (R = 0.92). As indomethacin given IV caused a parallel impairment of gastric mucosal function and blood flow, part of the indomethacin-related mucosal damaging effects might be due to the flow reduction.

Parenteral aspirin and sodium salicylate are equally injurious to the rat gastric mucosa

The effects of parenteral aspirin (ASA) or sodium salicylate (SA) on the gastric mucosa were investigated in anesthetized pylorus-ligated rats 3 h after a bolus intravenous injection of ASA or SA, 150 mg/kg, or NaCl (control). Aspirin or SA produced similar extensive gross mucosal hemorrhagic lesions and similar microscopic damage in the presence of luminal acid (luminal pH 1.3 +/- 0.05). Neither ASA nor SA produced gastric mucosal injury with intragastric instillation of saline (luminal pH 3.7 +/- 0.5). Pretreatment for 1 h with luminal or subcutaneous 16,16-dimethyl prostaglandin E2 completely prevented the formation of red streaks in ASA-treated rats but not in SA-treated rats, although prostaglandin E2 pretreatment significantly reduced the gross lesion area in SA-treated rats (p less than 0.05). We conclude the following: (a) Intravenous SA is as damaging as intravenous ASA as long as luminal acid is present. (b) 16,16-Dimethyl prostaglandin E2 completely protected the gastric mucosa from injury by intravenous ASA, and to a lesser extent by intravenous SA. (c) In view of the damaging effects of SA on the gastric mucosa and the rapid conversion of ASA to SA, the mechanism of the gastric mucosal injury by intravenous ASA is much more complex than simple inhibition of endogenous prostaglandin synthesis.

Gastroduodenal mucosal defence mechanisms and the action of non-steroidal anti-inflammatory agents

This review summarises gastroduodenal protective mechanisms, the actions of non-steroidal anti-inflammatory (NSAI) agents on mucus and HCO3 secretions, and the basis of gastric mucosal injury induced by acetylsalicylic and salicylic acids (ASA and SA). Resistance to autodigestion by acid and pepsin present in gastric juice is multifactorial involving pre-epithelial (mucus-bicarbonate barrier) and post-epithelial (blood flow, acid-base balance) factors in addition to properties of the surface cell layer per se. The latter includes mucosal re-epithelialisation, a property which appears particularly important with respect to recovery from acute injury. A range of NSAI agents (ASA, fenclofenac, ibuprofen and indomethacin) inhibit gastric HCO3 transport in isolated mucosal preparations. Inhibition of duodenal HCO3 transport has been demonstrated in response to indomethacin in vitro and in vivo. These effects on secretion can be antagonised by exogenous prostaglandins of the E series. The layer of secreted mucus gel overlying the epithelial surface is not affected by NSAI drugs in the short term. However a number of these agents have been shown to inhibit glycoprotein biosynthesis by the epithelial cells. Thus loss of this protective coat could be anticipated during chronic drug exposure since erosion of adherent mucus by luminal shear and proteolysis would not be compensated by continued secretion. Detailed analysis of the gastric mucosal injury induced by salicylates both in vitro and in vivo reveals that much of the damage previously attributed to ASA is in fact due to the metabolic product SA. In this respect it is concluded that mucosal injury caused by ASA is due to a combination of two factors.(ABSTRACT TRUNCATED AT 250 WORDS)