Effects of colloidal bismuth subcitrate on aspirin-induced gastric microbleeding, DNA loss, and prostaglandin formation in humans

Role of Bismuth in the Eradication of Helicobacter pylori

Bismuth salts exert their activity within the upper gastrointestinal tract through action of luminal bismuth. Bismuth exerts direct bactericidal effect on Helicobacter pylori by different ways: forms complexes in the bacterial wall and periplasmic space, inhibits different enzymes, ATP synthesis, and adherence of the bacteria to the gastric mucosa. Bismuth also helps ulcer healing by acting as a barrier to the aggressive factors and increasing mucosal protective factors such as prostaglandin, epidermal growth factor, and bicarbonate secretion. To date, no resistance to bismuth has been reported. Also synergism between bismuth salts and antibiotics was present. It was shown that metronidazole and clarithromycin resistant H. pylori strains become susceptible if they are administered together with bismuth. Bismuth-containing quadruple therapy was recommended both by the Second Asia-Pacific Consensus Guidelines and by the Maastricht IV/Florence Consensus Report as an alternative first choice regimen to standard triple therapy, in areas with low clarithromycin resistance, and it is recommended as the first-line therapeutic option in areas with a high prevalence of clarithromycin resistance. Greater than 90% eradication success can be obtained by bismuth-containing quadruple therapy. Choosing bismuth as an indispensable part of first-line therapy is logical as both metronidazole and clarithromycin resistances can be overcome by adding bismuth to the regimen.

[Antiplatelet therapy with acetylsalicylic acid: approaches to reducing the frequency of gastrointenstinal adverse reactions]

Acetylsalicylic acid (ASA) is highly effective in preventing cardiovascular events, but associated with increased risk for digestive adverse reactions. The paper provides an update on the epidemiology, mechanisms, and risk factors of esophagogastroduodeno- and enteropathies during long-term low-dose ACA therapy. It outlines the key principles of their prevention.

Addition of bismuth subnitrate to omeprazole plus amoxycillin improves eradication of Helicobacter pylori

OBJECTIVE

To evaluate whether the addition of bismuth subnitrate to a dual oral therapy regimen with omeprazole plus amoxycillin could improve Helicobacter pylori eradication.

METHODS

Fifty consecutive Helicobacter pylori-positive patients were randomly enrolled to receive either (A) bismuth subnitrate (300 mg q.d.s.), omeprazole (20 mg b.d.) and amoxycillin (500 mg q.d.s.), or (B) omeprazole (20 mg b.d.) and amoxycillin (500 mg q.d.s.). Both groups (n=25 each) received the medication for 14 days. H. pylori status was reassessed 30 days after completion of the therapy in order to evaluate eradication rates.

RESULTS

Six patients were lost to follow-up and therefore excluded from the study (three patients from each group). One patient from Group B withdrew from the study because of side-effects. The addition of bismuth subnitrate to omeprazole and amoxycillin significantly improved its efficacy in eradicating H. pylori, with 72% (18/25) eradication in Group A and 52% (13/25) in Group B (P=0.027). The addition of bismuth subnitrate to dual oral therapy was also capable of improving the healing of peptic ulcers when compared with dual oral therapy alone (100%, 8/8 vs. 58%, 4/7; P=0.021).

CONCLUSION

Our results demonstrate that the addition of bismuth subnitrate to dual oral therapy enhances H. pylori eradication, and improves healing of peptic ulcers.

Cytoprotective effect of bismuth subsalicylate in indomethacin-treated rats is associated with enhanced mucus bismuth concentration

BACKGROUND

Bismuth compounds prevent gastric injury from the short-term administration of nonsteroidal anti-inflammatory drugs. We studied the mechanisms underlying the gastroprotective actions of bismuth subsalicylate against indomethacin-induced injury in rats.

METHODS

An in vivo microscopic technique was used in which acid output, surface cell intracellular pH (pHi), gastric mucus gell thickness and mucosal blood flow were measured simultaneously. Concentrations of bismuth in mucus were measured by atomic absorption.

RESULTS

Indomethacin (60 mg/kg) significantly thinned the mucus gel layer and augmented the decrease of pHi during luminal acid superfusion, consistent with a weakened gastric mucosal barrier to acid. Bismuth subsalicylate partially reversed this effect of indomethacin on pHi, consistent with gastroprotection. Neither a prostaglandin-inhibiting but non-injurious dose of indomethacin (5 mg/kg), bismuth subsalicylate, or their combination affected mucus gel thickness or pHi homeostasis. In separate experiments, indomethacin (60 mg/kg) significantly increased gastric mucus bismuth concentration in rats given bismuth subsalicylate.

CONCLUSION

Bismuth accumulation in the gastric mucus during the evolution of mucosal injury may play an important role in the gastroprotective effect of bismuth subsalicylate against indomethacin injury.

Ranitidine bismuth citrate and aspirin-induced gastric mucosal injury

The aim of this study was to investigate the protective action of a new compound, ranitidine bismuth citrate, in the prevention of aspirin-induced acute mucosal injury to the upper gastrointestinal tract of healthy human volunteers. In a double-blind randomized three-way cross-over study 24 male volunteers received placebo, 900 mg aspirin or 900 mg aspirin and 800 mg ranitidine bismuth citrate at 12-h intervals for nine doses with a 2-week wash-out period between each treatment. The median (interquartile range) number of erosions seen at endoscopy when ranitidine bismuth citrate was given with aspirin (1 [0-4]) was significantly lower than aspirin alone (24 [16-32]) (P < 0.001) and not significantly different from either baseline or placebo (0 [0-2]). These findings were similarly reflected in the effects on microbleeding following the ninth dose: 12.1 (7.1-21.0) microL/10 min following aspirin alone compared to levels with placebo of 1.2 (0.4-2.9), and with aspirin and ranitidine bismuth citrate of 1.6 (0.8-2.6) (P < 0.005). Ranitidine bismuth citrate conferred substantial protection from aspirin-induced injury to the gastric and duodenal mucosa as determined by both endoscopic assessment and microbleeding rates, reducing injury to placebo levels.

Pathogenesis of gastroduodenal injury due to nonsteroidal antiinflammatory drugs: implications for prevention and therapy

Nonsteroidal antiinflammatory drugs (NSAIDs) initiate gastroduodenal ulceration and promote complications such as bleeding and perforation by interfering with the ability of the proximal gastrointestinal tract to maintain its defensive capabilities. Mucosal defense is composed of three critical components: preepithelial, epithelial, and postepithelial. Preepithelial defense is composed of the mucous gel containing mucin, bicarbonate, and surface-active phospholipids. The epithelial component includes the surface cells, their apical tight junctions, and membrane transporters. Postepithelial defense is maintained by mucosal blood flow, which is essential for both defense and repair. NSAIDs interfere with each component of mucosal defense via direct toxic effects along with cyclooxygenase inhibition and depletion of endogenous prostaglandins. Although NSAID injury is dependent on luminal acid, attempts to prevent NSAID injury by acid suppression using H2-receptor antagonists in humans have had limited success, whereas complete inhibition of acid secretion with proton pump inhibition may have promise. Prostaglandins appear most effective for prevention of NSAID injury, sucralfate appears ineffective, and bismuth compounds have not been studied extensively. Recent evidence suggests that NSAID ulcers heal quickly with proton pump inhibitors compared with H2-receptor antagonists in patients who continue NSAID therapy.

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)

Colloidal bismuth subcitrate causes sustained release of gastric mucosal prostaglandin E2

Gastric application of high doses of colloidal bismuth subcitrate (CBS) stimulates mucosal prostaglandin E2 (PGE2) production, which is considered part of the mechanism by which the drug accelerates peptic ulcer healing. Whether therapeutic, orally administered, doses of CBS cause a sustained stimulation of prostaglandin production is not known. We have, therefore, determined gastric luminal release of PGE2 during 'steady-state' perfusion of the stomach with CBS (10 mg/ml; isotonic mannitol 5 ml/min) and 4 h after the last oral dose of the drug (240 mg b.d.) for 2 weeks (isotonic mannitol 5 ml/min) in 8 healthy volunteers. A significant increase in PGE2 concentrations (712 (409-1076) vs. control 334 (252-655) pg/ml; medians with Q50 ranges; P less than 0.02) and PGE2 output (12.5 (7.3-14.3) vs. control 4.8 (4.1-7.3) ng/15 min; P less than 0.02) occurred during gastric perfusion with CBS. A similar increase in PGE2 concentrations (630 (297-1429) pg/ml; P less than 0.02) and PGE2 output (12.6 (6.4-22.2) ng/15 min; P less than 0.02) was observed following treatment with CBS for 2 weeks. These results suggest that therapeutic doses of CBS cause a sustained stimulation of gastric mucosal PGE2 formation.

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)

Review of the modes of action of colloidal bismuth subcitrate

In recent years considerable progress has been made to elucidate the modes of action of colloidal bismuth subcitrate (CBS). CBS accelerates the healing of experimental chronic ulcers in rats by the formation of occlusive complexes and/or the accumulation of epidermal growth factor (EGF) in the ulcer crater. CBS exhibits gastric protection (cytoprotection) against, for example, ethanol lesions. Microscopic analysis of these lesions reveals that CBS protects against deep mucosal necrosis but not superficial injury, a property also found with prostaglandins. Dose-dependent increases in gastric prostaglandin E2 (PGE2) and bicarbonate secretion were found after CBS, in both animals and human volunteers. CBS in normal clinical doses increases PGE2 output from the gastric mucosa of human volunteers. Gastric injury in human volunteers produced by unbuffered aspirin is also reduced by concomitant administration of CBS, whereby PGE2 production is inhibited. This indicates that CBS exerts its gastric protection by both prostaglandin- and non-prostaglandin-mediated mechanisms. Campylobacter pylori is considered to be a causative factor of chronic antral gastritis and is a potential prerequisite for peptic ulcer disease. CBS, in contrast to other anti-ulcer drugs, prevents the growth of C. pylori in vitro. CBS eradicates C. pylori in patients and resolves chronic antral gastritis. The favourable relapse rates with CBS might be explained by the permanent eradication of C. pylori.