Interaction of indomethacin and naproxen with gastric surface-active phospholipids: a possible mechanism for the gastric toxicity of nonsteroidal anti-inflammatory drugs (NSAIDs)

Phospholipid actions on PGHS-1 and -2 cyclooxygenase kinetics

Cyclooxygenase (COX) catalysis by prostaglandin H synthase (PGHS) is a key control step for regulation of prostanoid biosynthesis. Both PGHS isoforms are integral membrane proteins and their substrate fatty acids readily partition into membranes, but the impact of phospholipids and lipid membranes on COX catalysis and the actions of COX inhibitors are not well understood. We have characterized the COX kinetics and ibuprofen inhibition of the purified PGHS isoforms in the presence of phosphatidylcholine (PC) with varying acyl chain structure and physical state. PC was found to directly inhibit COX activity, with non-competitive inhibition by PC monomers binding away from the COX active site and competitive inhibition by micellar/bilayer forms of PC due to sequestration of the arachidonate substrate. Competitive inhibition by native membranes was observed in a comparison of COX kinetics in sheep seminal vesicle microsomes before and after solubilization of PGHS-1. PC liposomes significantly increase the inhibitory potency of ibuprofen against both PGHS isoforms without changing the reversible character of ibuprofen action or requiring binding of PGHS to the liposomes. These results suggest a useful conceptual framework for analyzing the complex interactions among the PGHS proteins, substrates, inhibitors and phospholipid.

DP-155, a lecithin derivative of indomethacin, is a novel nonsteroidal antiinflammatory drug for analgesia and Alzheimer's disease therapy

DP-155 is a lipid prodrug of indomethacin that comprises the latter conjugated to lecithin at position sn-2 via a 5-carbon length linker. It is cleaved by phospholipase A2 (PLA)(2) to a greater extent than similar compounds with linkers of 2, 3, and 4 carbons. Indomethacin is the principal metabolite of DP-155 in rat serum and, after DP-155 oral administration, the half-life of the metabolite was 22 and 93 h in serum and brain, respectively, compared to 10 and 24 h following indomethacin administration. The brain to serum ratio was 3.5 times higher for DP-155 than for indomethacin. In vitro studies demonstrated that DP-155 is a selective cyclooxygenase (COX)-2 inhibitor. After it is cleaved, its indomethacin derivative nonselectively inhibits both COX-1 and -2. DP-155 showed a better toxicity profile probably due to the sustained, low serum levels and reduced maximal concentration of its indomethacin metabolite. DP-155 did not produce gastric toxicity at the highest acute dose tested (0.28 mmol/kg), while indomethacin caused gastric ulcers at a dose 33-fold lower. Furthermore, after repeated oral dosing, gastrointestinal and renal toxicity was lower (10- and 5-fold, respectively) and delayed with DP-155 compared to indomethacin. In addition to reduced toxicity, DP-155 had similar ameliorative effects to indomethacin in antipyretic and analgesia models. Moreover, DP-155 and indomethacin were equally efficacious in reducing levels of amyloid ss (Ass)42 in transgenic Alzheimer's disease mouse (Tg2576) brains as well as reducing Ass42 intracellular uptake, neurodegeneration, and inflammation in an in vitro AD model. The relatively high brain levels of indomethacin after DP-155 administration explain the equal efficacy of DP-155 despite its low systemic blood concentrations. Compared to indomethacin, the favored safety profile and equal efficacy of DP-155 establish the compound as a potential candidate for chronic use to treat AD-related pathology and for analgesia.

[Protection of gastric mucosa against steroids-induced damage by teprenone]

OBJECTIVE

To estimate the effects of teprenone on protecting gastric mucosa against steroids-induced damage.

METHODS

Fifty male Sprague-Dawley rats were randomly divided into 5 equal groups: normal control group, undergoing gastric infusion of normal saline for 7 days and fasting since the 4 th day for 4 days; model control group, undergoing gastric infusion of normal saline for 7 days and fasting and hypodermal injection of prednisolone 40 mg/kg since the 4 th day for 4 days; low dose teprenone group, undergoing gastric infusion of teprenone 50 mg/kg for 7 days and fasting and hypodermal injection of prednisolone 40 mg/kg since the 4 th day; middle dose teprenone group, undergoing gastric infusion of teprenone 50 mg/kg for 7 days and fasting and hypodermal injection of prednisolone 40 mg/kg since the 4 th day; and high dose teprenone group, undergoing gastric infusion of teprenone 200 mg/kg for 7 days and fasting and hypodermal injection of prednisolone 40 mg/kg since the 4 th day. Samples of gastric mucosa were taken out 24 hours after the last drug administration to calculate the ulcer index and observe the histological changes. Blood samples were collected from the abdominal cardinal vein. The levels of plasma ET-1 and prostaglandin E2 were examined by radioimmunoassay. Serum level of nitric oxide (NO) was determined by Griess method.

RESULTS

In the model control group, the ulcer index, grade of histological lesions and ET-1 level increased significantly compared with the normal control group (44.5 vs. 0, 5.5 vs. 0, and 399 pg/ml +/- 74 pg/ml vs. 279 pg/ml +/- 56 pg/ml, all P < 0.01), the PGE(2) level decreased significantly. (154 pg/mg +/- 83 pg/mg vs 337 pg/mg +/- 112 pg/mg, P < 0.01), and the NO level did not changed significantly. In the 3 teprenone groups, the ulcer index decreased (32.5, 23.0, and 23.0 vs. 44.5, all P < 0.01), grade of histological lesions decreased (3.0, 3.0, and 1.5 vs. 5.5, all P < 0.01), ET-1 level decreased (299 pg/ml +/- 99 pg/ml, 284 pg/ml +/- 85 pg/ml, and 189 pg/ml +/- 32 pg/ml vs. 399 pg/ml +/- 74 pg/ml, P < 0.05, P < 0.01, and P < 0.01), the No level increased (56 micromol/L +/- 16 micromol/L, 62 micromol/L +/- 12 micromol/L, and 83 micromol/L +/- 9 micromol/L vs. 27 micromol/L +/- 5 micromol/L, all P < 0.01), and the PGE(2) level increased (190 pg/mg +/- 58 pg/mg, 196 pg/mg +/- 35 pg/mg, 241 pg/mg +/- 65 pg/mg vs. 154 pg/mg +/- 83 pg/mg, P > 0.05, P > 0.05, and P < 0.05) compared with the model control group.

CONCLUSION

Teprenone is a beneficial cytoprotective agent of gastric mucosa. Pretreatment with teprenone has gastroprotective effect against steroids-induced mucosal damage to a certain extent with a mechanism related to ET-1, NO, and PGE(2) concentrations in blood or gastric mucosa.

NSAID injury to the gastrointestinal tract: evidence that NSAIDs interact with phospholipids to weaken the hydrophobic surface barrier and induce the formation of unstable pores in membranes

In this review, we have discussed our current understanding of the barrier properties that are in place to protect the upper gastrointestinal mucosa from luminal acid, and the pathogenic mechanism by which nonsteroidal anti-inflammatory drugs (NSAIDs) induce injury to the gastrointestinal tract. The changes in our view of the importance of NSAID-induced cyclo-oxygenase (COX) inhibition on the pathogenesis and prevention of NSAID-induced gastrointestinal injury is presented. The focus of this paper has been placed on the effects of NSAIDs on the mucosal surface, and specifically the effect of these powerful drugs in inducing changes in the hydrophobicity, fluidity, biomechanical and permeability properties of extracellular and membrane phospholipids. Lastly, recent evidence is presented that salicylic acid and related NSAIDs may alter the stability of membranes, inducing the formation of unstable pores that may lead to back-diffusion of luminal acid and membrane rupture. This understanding of the interaction of NSAIDs with membrane phospholipids may prove valuable in the design of novel NSAID formulations with reduced gastrointestinal side-effects.

Surface phospholipids in gastric injury and protection when a selective cyclooxygenase-2 inhibitor (Coxib) is used in combination with aspirin

BACKGROUND AND PURPOSE

Clinical studies demonstrate that aspirin consumption reverses the gastrointestinal (GI) benefits of coxibs, by an undefined mechanism.

EXPERIMENTAL APPROACH

Rodent models were employed to investigate the effects of combinations of celecoxib and aspirin on gastric ulcerogenesis, bleeding, surface hydrophobicity (by contact angle analysis) and ulcer healing. We also evaluated the effects of phosphatidylcholine (PC)-associated aspirin in these rodent models and confirmed its cyclooxygenase (COX)-inhibitory activity by measuring mucosal prostaglandin E(2) (PGE(2)) concentration. We present evidence that aspirin's ability to induce gastric injury and bleeding in rats, was exacerbated in the presence of a coxib and was dependent on its ability to reduce gastric surface hydrophobicity. In contrast, co-administration of phosphatidylcholine (PC)-associated aspirin and celecoxib induced little or no gastric injury/bleeding and maintained the stomach's hydrophobic properties. Interestingly, aspirin and aspirin/PC equally inhibited gastric mucosal PGE(2) concentration. Aspirin in combination with a coxib retarded the healing of experimentally induced gastric ulcers, whereas healing rates of rats treated with celecoxib in combination with aspirin/PC were comparable to controls.

CONCLUSIONS AND IMPLICATIONS

Aspirin's gastric toxicity in combination with a coxib can be dissociated from its ability to inhibit COX-1 and appears to be dependent, in part, on its ability to attenuate the stomach's surface hydrophobic barrier. This adverse drug interaction between aspirin and coxibs, which impacts the treatment of osteoarthritic and cardiac patients requiring cardiovascular prophylaxis, can be circumvented by the administration of phosphatidylcholine (PC)-associated aspirin, to maintain the stomach's hydrophobic properties.

Drug injury in the upper gastrointestinal tract: nonsteroidal anti-inflammatory drugs

It is well established that nonsteroidal anti-inflammatory drugs (NSAIDs) and aspirin confer significant morbidity and mortality. The widespread use of these drugs has increased the absolute numbers of cases of NSAID- or aspirin-related upper gastrointestinal complications. Emerging data indicate that antidepressants, such as selective serotonin reuptake inhibitors and tricyclic antidepressants, may also increase risk for gastrointestinal bleeding. Multiple factors have been identified that increase risk for NSAID- and aspirin-related upper gastrointestinal complications. The highest risks are related to age (>60 years) and prior complicated peptic ulcer; additional risk factors include use of multiple NSAIDs and high doses of NSAIDS. Recent studies have demonstrated enhanced healing and prevention of NSAID- and aspirin-related gastrointestinal lesions with proton pump inhibitors.

[NSAID-colonopathy]

The pain-relief properties of NSAID/ASA preparations have been known for a long time. In particular, the gastrointestinal tract shows side effects such as: erosion, ulceration, and even perforation. In the upper gastrointestinal tract, our group has shown that a correct histological diagnosis of NSAID/ASA induced lesions can be made in a high percentage of cases on the basis of recognition of ischemic necrosis. NSAID/ASA induced lesions are less commonly found in the lower gastrointestinal tract. We could also demonstrate a correct histological diagnosis of NSAID-colonopathy on the basis of finding ischemic necrosis. Besides the known complications, another typical complication is diaphragm-like stenosis, which must not be mistaken for tumor stenosis. The differential diagnosis of NSAID-colonopathy includes ischemic colitis, which cannot be distinguished histologically if the exact endoscopic description is not available. Sometimes NSAID/ASA induced lesions are misdiagnosed as Crohn's disease due to the focal character of the lesions. Since all of our analyses are retrospective, the criteria developed by our group should be checked prospectively.

Strictures, diaphragms, erosions or ulcerations of ischemic type in the colon should always prompt consideration of nonsteroidal anti-inflammatory drug-induced lesions

AIM: To investigate whether NSAIDs/ASA lesions in the colon can histologically be diagnosed on the basis of ischemic necrosis similar to biopsy-based diagnosis of NSAIDs/ASA-induced erosions and ulcers of the stomach.

METHODS: In the period between 1997 and 2002, we investigated biopsy materials obtained from 611 patients (415 women, 196 men, average age 60.5 years) with endoscopic focal erosions, ulcerations, strictures or diaphr-agms in the colon. In the biopsies obtained from these lesions, we always established the suspected diagnosis of NSAID-induced lesions whenever necroses of the ischemic type were found. Together with the histological report, we enclosed a questionnaire to investigate the use of medication. The data provided by the questionnaire were then correlated with the endoscopic findings, the location, number and nature of the lesions, and the histological findings.

RESULTS: At the time of their colonoscopy, 86.1% of the patients had indeed been taking NSAID/ASA medication for years (43.9%) or months (29.5%). The most common indication for the use of these drugs was pain (64.3%), and the most common indication for colonoscopy was bleeding (55.5%). Endoscopic inspection revealed multiple erosions and/or ulcers in 60.6%, strictures in 15.8%, and diaphragms in 3.0% of the patients. The lesions were located mainly in the right colon including the transverse colon (79.9%). A separate analysis of age and sex distribution, endoscopic and histological findings for NSAIDs alone, ASA alone, combined NSAID/ASA, and for patients denying the use of such drugs, revealed no significant differences among the groups.

CONCLUSION: This uncontrolled retrospective study based on the histological finding of an ischemic necrosis shows that the histologically suspected diagnosis of NSAID-induced lesions in the colon is often correct. The true diagnostic validity of this finding and the differentiation from ischemic colitis should, however, be investigated in a prospective controlled study.

Effect of salicylate on the elasticity, bending stiffness, and strength of SOPC membranes

Salicylate is a small amphiphilic molecule which has diverse effects on membranes and membrane-mediated processes. We have utilized micropipette aspiration of giant unilamellar vesicles to determine salicylate's effects on lecithin membrane elasticity, bending rigidity, and strength. Salicylate effectively reduces the apparent area compressibility modulus and bending modulus of membranes in a dose-dependent manner at concentrations above 1 mM, but does not greatly alter the actual elastic compressibility modulus at the maximal tested concentration of 10 mM. The effect of salicylate on membrane strength was investigated using dynamic tension spectroscopy, which revealed that salicylate increases the frequency of spontaneous defect formation and lowers the energy barrier for unstable hole formation. The mechanical and dynamic tension experiments are consistent and support a picture in which salicylate disrupts membrane stability by decreasing membrane stiffness and membrane thickness. The tension-dependent partitioning of salicylate was utilized to calculate the molecular volume of salicylate in the membrane. The free energy of transfer for salicylate insertion into the membrane and the corresponding partition coefficient were also estimated, and indicated favorable salicylate-membrane interactions. The mechanical changes induced by salicylate may affect several biological processes, especially those associated with membrane curvature and permeability.

Membrane permeabilization by non-steroidal anti-inflammatory drugs

The cytotoxicity of non-steroidal anti-inflammatory drugs (NSAIDs) is involved in the formation of NSAID-induced gastric lesions. The mechanism(s) behind these cytotoxic effects, however, is not well understood. We found here that several NSAIDs tested caused hemolysis when employed at concentrations similar to those that result in cytotoxicity. Moreover, these same NSAIDs were found to directly permeabilize the membranes of calcein-loaded liposomes. Given the similarity in NSAID concentrations for cytotoxic and membrane permeabilization effects, the cytotoxic action of these NSAIDs may be mediated through the permeabilization of biological membranes. Increase in the intracellular Ca(2+) level can lead to cell death. We here found that all of NSAIDs tested increased the intracellular Ca(2+) level at concentrations similar to those that result in cytotoxicity. Based on these results, we consider a possibility that membrane permeabilization by NSAIDs induces cell death through increase in the intracellular Ca(2+) level.

Interaction of antiinflammatory drugs with EPC liposomes: calorimetric study in a broad concentration range

Isothermal titration calorimetry was used to characterize and quantify the partition of indomethacin and acemetacin between the bulk aqueous phase and the membrane of egg phosphatidylcholine vesicles. Significant electrostatic effects were observed due to binding of the charged drugs to the membrane, which implied the use of the Gouy-Chapman theory to calculate the interfacial concentrations. The binding/partition phenomenon was quantified in terms of the partition coefficient (K(p)), and/or the equilibrium constant (K(b)). Mathematical expressions were developed, either to encompass the electrostatic effects in the partition model, or to numerically relate partition coefficients and binding constants. Calorimetric titrations conducted under a lipid/drug ratio >100:1 lead to a constant heat release and were used to directly calculate the enthalpy of the process, DeltaH, and indirectly, DeltaG and DeltaS. As the lipid/drug ratio decreased, the constancy of reaction enthalpy was tested in the fitting process. Under low lipid/drug ratio conditions simple partition was no longer valid and the interaction phenomenon was interpreted in terms of binding isotherms. A mathematical expression was deduced for quantification of the binding constants and the number of lipid molecules associated with one drug molecule. The broad range of concentrations used stressed the biphasic nature of the interaction under study. As the lipid/drug ratio was varied, the results showed that the interaction of both drugs does not present a unique behavior in all studied regimes: the extent of the interaction, as well as the binding stoichiometry, is affected by the lipid/drug ratio. The change in these parameters reflects the biphasic behavior of the interaction-possibly the consequence of a modification of the membrane's physical properties as it becomes saturated with the drug.

Inhibition of acid secretion by the nonsteroidal anti-inflammatory drugs diclofenac and piroxicam in isolated gastric glands: analysis of a multifocal mechanism

In nonstimulated rabbit gastric glands, acetylsalicylic acid (10-500 microM) and indomethacin (3-300 microM) did not significantly modify the basal rate of acid secretion, whereas diclofenac and piroxicam (10-1,000 microM each) caused a marked and dose-dependent inhibitory effect (EC(50) = 138 and 280 microM, respectively). In gastric glands stimulated by histamine (100 microM), diclofenac also reduced the rate of acid formation in a dose-dependent manner. In contrast, acetylsalicylic acid, indomethacin, and piroxicam exerted a biphasic effect; thus low concentrations (3-100 microM) of these three agents significantly increased the rate of histamine-stimulated acid secretion (10-20% over the corresponding control value) by a cAMP-independent mechanism, whereas higher concentrations reduced the rate of acid formation. With respect to underlying biochemical mechanisms that could mediate inhibitory effects of NSAIDs on gastric acid formation, it was observed that both diclofenac and piroxicam, but not acetylsalicylic acid or indomethacin, decreased the glandular content of ATP, inhibited hydrolytic activity of gastric gland microsomal H(+)-K(+)-ATPase, and reduced the rate of H(+)-K(+)-ATPase-dependent proton transport across microsomal membranes in a dose-dependent manner. Furthermore, diclofenac and piroxicam also significantly increased passive permeability of microsomal membranes to protons. In conclusion, our work shows that diclofenac and piroxicam cause a significant reduction in the rate of basal and histamine-stimulated acid formation in isolated rabbit gastric glands at concentrations that can be attained in the gastric lumen of patients treated with these drugs. Mechanisms involved in these inhibitory effects appear to be multifocal and include different steps of stimulus-secretion coupling.

Non-steroidal anti-inflammatory drugs affect the methotrexate transport in IEC-6 cells

Methotrexate (MTX) is used not only for the cancer chemotherapy but also for the treatment of rheumatic disease, often together with non-steroidal anti-inflammatory drugs (NSAIDs). MTX is actively cotransported with H(+) in the small intestine, mediated by a reduced folate carrier (RFC). The coadministration of some NSAIDs with MTX to rats caused a decrease of MTX absorption through the small intestine. This may be due to the uncoupling effect of oxidative phosphorylation of the NSAIDs. The present study investigated whether flufenamic acid, diclofenac and indomethacin, NSAIDs, decreased ATP content of rat-derived intestinal epithelial cell line IEC-6 cells and affected the MTX transport in IEC-6 cells. The MTX uptake in IEC-6 cells was dependent on medium pH and maximum around pH 4.5-5.5. The MTX uptake was composed of a transport inhibited by 4, 4'-diisothiocyanostilbene-2, 2'-disulfonic acid (DIDS) and a non-saturable one. The DIDS-sensitive component in the MTX uptake showed a saturation kinetics (Michaelis-Menten constant (Km): 3.91 +/- 0.52 microM, Maximum velocity (Vmax): 94.66 +/- 6.56 pmol/mg protein/5 min). The cellular ATP content in IEC-6 cells decreased significantly at 30 min after the cells were started to incubate with the NSAIDs (250 microM flufenamic acid, 500 microM diclofenac and 500 microM indomethacin). The MTX uptake in IEC-6 cells in the presence of the NSAIDs decreased with the reduction of cellular ATP content and showed a good correlation with the ATP content (correlation coefficient: 0.982). Thus it seems likely that the ATP content in IEC-6 cells with the NSAIDs decreased due to the uncoupling effect of oxidative phosphorylation of the NSAIDs, resulting in the inhibition of the secondary active transport of MTX in IEC-6 cells. The present results also suggest that IEC-6 cells are useful to evaluate the drug interaction relating to this carrier system.

Where is the evidence that cyclooxygenase inhibition is the primary cause of nonsteroidal anti-inflammatory drug (NSAID)-induced gastrointestinal injury? Topical injury revisited

In this commentary, we take a critical look at the concept that the gastrointestinal (GI) side-effects of nonsteroidal anti-inflammatory drugs (NSAIDs) are due to the ability of these drugs to inhibit cyclooxygenase-1 (COX-1) that is constitutively expressed in the GI mucosa. Indeed, development of the new "super aspirins," such as Celebrex and Vioxx, that selectively inhibit the inducible COX-2, expressed in areas of inflammation, is a direct outgrowth of this concept. We discuss evidence from both the laboratory and the clinic that appears to be inconsistent with the above concept, and cite a number of examples where the depletion of mucosal prostaglandin levels and the development of GI injury can be dissociated. Instead, we revisit the possibility that NSAID-induced GI side-effects are mostly due to the ability of these drugs to topically injure the GI mucosa. We devote the remainder of the commentary to presenting evidence from our and other laboratories that NSAIDs can directly attenuate the surface hydrophobic barrier of the GI mucosa due to their ability to bind to zwitterionic phospholipids, and that even systemically administered NSAIDs that are secreted into the bile may induce GI ulceration and/or bleeding due to phospholipid interactions and the development of topical mucosal injury.

[Helicobacter pylori and non-steroidal anti-inflammatory agents]

Observations on the interactions between the two main causes of gastroduodenal lesions--treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) and Helicobacter pylori(H.p.)-infection--remain controversial. However, H.p.-infection does not need to be harmful additively or synergistically, but could also be protective against the toxic effects of NSAIDs on the mucosa. Therefore, specific therapeutic strategies are needed for different clinical situations.

Role of biliary phosphatidylcholine in bile acid protection and NSAID injury of the ileal mucosa in rats

BACKGROUND & AIMS

We explored the role of biliary phosphatidylcholine (PC) in protection of the intestinal mucosa against bile salt (BS)-induced intestinal injury and how this property may be blocked by indomethacin (Indo), a nonsteroidal anti-inflammatory drug (NSAID) that is secreted into the bile.

METHODS

We performed in vivo studies in which bile was collected over a 2-hour period after rats were intragastrically administered Indo (25 mg/kg) or an equivalent volume of saline (controls). The bile samples (some of which were supplemented with PC) were then instilled into a loop of distal ileum of anesthetized rats. After a 30-minute exposure period, we measured the hemoglobin concentration of the ileal loop fluid, as an index of bleeding, and mucosal contact angles, as an index of surface hydrophobicity. A similar in vivo experiment was performed in which model bile containing 5 mmol/L each of the BS, sodium deoxycholate, PC, or Indo, alone and in combination, was instilled into ileal loops. In our in vitro test system, human erythrocytes were exposed to the above biliary constituents, and hemolysis was measured spectrophotometrically.

RESULTS

Bile from Indo-pretreated rats decreased the surface hydrophobicity and induced bleeding of ileal loops in comparison with control bile, and both NSAID-induced changes were reversed if PC was added to the bile. Similarly, synthetic BS caused gastrointestinal bleeding, decreased ileal contact angles, and induced erythrocyte hemolysis, all of which were reversed by addition of equimolar PC. This protective role of PC in both the in vivo and in vitro systems was partially blocked by Indo, although the NSAID had no effect on these properties on its own.

CONCLUSIONS

These findings support the hypothesis that PC protects the intestinal mucosa against injurious actions of BS, possibly by forming less toxic mixed micelles. Indo and perhaps other NSAIDs that enter the bile may damage the mucosa, not by a direct action, but by competing for the available protective PC molecules.

Gastroduodenal mucosal defense

Research performed in the laboratory and the clinic over the past several years has added to our understanding of the mechanisms that are operative in protecting the epithelial lining of the stomach and duodenum from injury and ulceration, most frequently caused by necrotic agents in the lumen. The defensive mechanism of the gastroduodenal mucosa comprises a series of physical, chemical, biologic, and immunologic barriers or mechanisms that act in concert to either prevent or limit cellular injury or transformation. The field of gastroduodenal defense can be subdivided into the following four areas: extracellular mucus barrier properties; membrane and ion transport properties; cellular factors promoting growth and restitution; and vascular, neural, and inflammatory factors ensuring optimal tissue perfusion and immune responsiveness, respectively. In addition, a great deal can be learned about gastroduodenal defense by studying the effects of ulcerogenic factors and conditions on the defensive mechanisms described here and specifically how they may be compromised by nonsteroidal anti-inflammatory drugs and Helicobacter pylori infection. This review presents interesting and noteworthy findings impacting on these properties contributing to gastroduodenal defense since the prior review article on this subject appearing in this journal.