Paf-acether synthesis by Helicobacter pylori

Pharmacological insight of rutin as a potential candidate against peptic ulcer

Peptic ulcer is a sore on the stomach lining that results from the erosion of the gastrointestinal tract mucosa due to various influencing factors. Of these, Helicobacter pylori infection and non-steroidal anti-inflammatory drugs (NSAIDs) stand out as the most prominent causes. This condition poses a significant global health concern due to its widespread impact on individuals worldwide. While various treatment strategies have been employed, including proton pump inhibitors and histamine-2 receptor antagonists, these have notable side effects and limitations. Thus, there is a pressing need for new treatments to address this global health issue. Rutin, a natural flavonoid, exhibits a range of biological activities, including anti-inflammatory, anticancer, and antioxidant properties. This review explores the potential anti-ulcer effect of rutin in experimental models and how rutin can be a better alternative for treating peptic ulcers. We used published literature from different online databases such as PubMed, Google Scholar, and Scopus. This work highlights the abundance of rutin in various natural sources and its potential as a promising option for peptic ulcer treatment. Notably, the anti-inflammatory properties of rutin, which involve inhibiting inflammatory mediators and the COX-2 enzyme, are emphasized. While acknowledging the potential of rutin, it is important to underscore the necessity for further research to fully delineate its therapeutic potential and clinical applicability in managing peptic ulcers and ultimately improving patient outcomes. This review on the anti-ulcer potential of rutin opened a new door for further study in the field of alternative medicine in peptic ulcer management.

Of blood and guts: association between Helicobacter pylori and the gastric microcirculation

The relative importance of acid in Helicobacter pylori (H. pylori) ulcer pathogenesis is in doubt, with possibilities existing that other contributing factors may be involved. Vascular insufficiency may lead to the development of ischemic lesions or ulcers within the gastric mucosa. H. pylori produces a striking inflammatory response following infection and one of the major components of gastrointestinal inflammation is alterations in the vascular structure and function. This suggests that the microcirculation may be a key target of H. pylori-released factors. Recent evidence has accumulated to suggest that H. pylori can affect a number of microcirculatory variables including blood flow, leukocyte activity and also induce changes in the endothelial lining of the vessels themselves. The majority of these findings have been described by employing the technique of fluorescent in vivo microscopy, which allows direct, dynamic and real time observations of the microcirculation to be made. A universal feature of these experimental studies has been the formation of circulating or adherent platelet aggregates. It is now recognized that platelets participate in the inflammatory response by acting as a potent source of inflammatory mediators and modulating the activity of other inflammatory cells. Circulation of platelet emboli may be of cause for concern, especially as a number of studies have demonstrated an association between H. pylori infection and coronary heart disease. The present review highlights the major findings from these studies and proposes an important role for the gastric microcirculation in the pathophysiology of H. pylori-induced injury.

Isolation and structural elucidation of biologically active phospholipids from Scytonema julianum (cyanobacteria)

The role of platelet-activating factor (PAF) as a mediator appeared in rather primitive organisms like protozoans and was maintained in more evolved organisms. No reports exist for the presence of PAF or PAF analogues - or even compounds that exhibit PAF-like activity - in cyanobacteria, even though they belong to a a group of organisms at a low evolutionary level where the content of alkylacyl forms of ether lipids is expected to be high. In addition, cyanobacteria serve as a rich source of novel bioactive metabolites. In the present study the total lipids of a strain of Scytonema julianum, a filamentous cyanobacterium isolated from a Greek cave, were separated into neutral lipids and phospholipids, the latter being further fractionated by HPLC. Each phospholipid fraction was tested in vitro for its ability to inhibit PAF-, arachidonic acid- and ADP-induced washed-rabbit-platelet aggregation and/or to cause platelet aggregation. Two types of phospholipids causing platelet aggregation were detected and shown to be an acetylsphingomyelin and an acylacetylglycerol phosphoacetylated glycolipid. The existence of the sphingomyelin analogues is very important, since ceramides, cerebrosides and related lipids are intracellular second messengers. The identification of the phosphoglycoglycerolipid demonstrates a new type of lipid in cyanobacteria, namely one that exhibits a biological activity very similar to that of PAF. Its presence reinforces the concept that PAF is a member of a large family of lipid mediators, apparently having different physiological roles in prokaryotic and eukaryotic organisms. In addition, Scytonema julianum contains a phosphatidylcholine (C(16:0)/(18:2)), even though bacteria in general seldom contain choline-containing phosphoacylglycerols.

Platelet-activating factor regulates chloride transport in colonic epithelial cell monolayers

Platelet-activating factor (PAF) has been implicated in the pathogenesis of gastrointestinal diseases such as necrotizing enterocolitis, Crohn's disease, and ulcerative colitis. However, neither the physiologic role of PAF in the intestine, nor the mechanisms by which PAF participates in the pathogenesis of disease are well understood. The aim of the present study was to determine the direct effect of PAF on intestinal epithelial cell ion transport, and to delineate the mechanisms of regulation. Ion transport was evaluated by measuring short circuit current (I(sc)) in HT29-CL19A cell monolayers using Ussing chambers. PAF receptor polarity was assessed using domain-selective biotinylation followed by immunoprecipitation and streptavidin blotting of intact epithelial monolayers. PAF (1-200 microM) stimulated I(sc) that followed the direction of a Cl(-) gradient and was specifically inhibited by the Cl(-) channel blockers glybenclamide, 2,2' iminodibenzoic acid and 4,4' diisothiocyanostilbene-2, 2' disulfonic acid, but was unaffected by the inhibition of prostaglandin synthesis with indomethacin. Stimulated I(sc) was only detected after apical addition of PAF, correlating with the results of biotinylation experiments indicating an exclusive apical polarity of the PAF receptor. PAF receptor antagonists CV6209 and octylonium bromide abolished PAF-stimulated I(sc). Thus, mucosal acting PAF directly and specifically stimulates ion transport via activation of an apical Cl(-) channel in intestinal epithelial cell monolayers independent of prostaglandin biosynthesis.

pathogenesis of Helicobacter pylori-induced gastric inflammation

Helicobacter pylori causes persistent inflammation in the human stomach, yet only a minority of persons harbouring this organism develop peptic ulcer disease or gastric malignancy. An important question is why such variation exists among colonized individuals. Recent evidence has demonstrated that H. pylori isolates possess substantial phenotypic and genotypic diversity, which may engender differential host inflammatory responses that influence clinical outcome. For example, H. pylori strains that possess the cag pathogenicity island induce more severe gastritis and augment the risk for developing peptic ulcer disease and distal gastric cancer. An alternative, but not exclusive, hypothesis is that enhanced inflammation and injury is a consequence of an inappropriate host immune response to the chronic presence of H. pylori within the gastric niche. Investigations that precisely delineate the mechanisms responsible for induction of gastritis will ultimately help to define which H. pylori-colonized persons bear the highest risk for subsequent development of clinical disease, and thus, enable physicians to focus eradication therapy.

Effect of platelet-activating factor on gastrin release from cultured rabbit G-cells

Gastric infection with Helicobacter pylori is associated with hypergastrinemia. Platelet activating factor (PAF) is produced in H. pylori-infected mucosa. The effects of PAF on gastrin release from cultured antral rabbit G cells were examined. Rabbit antral G-cells were obtained by collagenase-EDTA digestion and enriched by centrifugal elutriation. After 40 hr in culture, gastrin release in response to PAF was assessed. PAF stimulated gastrin release in a dose-dependent manner. A maximal release of 67% above basal was seen with PAF at 100 nM. PAF also enhanced the gastrin release stimulated by forskolin and bombesin. PAF-stimulated gastrin release was abolished by a PAF-receptor antagonist. Gastrin release stimulated by PAF was abolished by chelation of intra- or extracellular calcium or the L-type calcium channel inhibitor verapamil as well as by the protein kinase C inhibitor chelerythrine. Platelet-activating factor may contribute to the hypergastrinemia of H. pylori infection by stimulating gastrin release from G cells. PAF-stimulated gastrin release involves influx of extracellular calcium via L-type channels and activation of protein kinase C.

Circulating cytokines and gastrin levels in asymptomatic subjects infected by Helicobacter pylori (H. pylori)

The pathophysiology of hypergastrinemia in H. pylori infection has been largely investigated and different reports clearly show that the infected antrum has a marked inflammatory response with a suggestive local production of cytokines. Notwithstanding, a few data are available on the circulating levels of cytokines and gastrin in the asymptomatic people carrying H. pylori infection. Thus, aim of the study was to evaluate circulating proinflammatory cytokines [Interleukin (IL)-8, Interleukin (IL)-10, Interferon (IFN)-gamma, and Tumor Necrosis Factor (TNF)-alpha] and gastrin levels in H. pylori positive asymptomatic subjects vs. H. pylori negative ones. To this end, thirty healthy volunteers with no digestive symptoms or systemic disease were enrolled and H. pylori infection was identified by a 13C-urea breath test. Plasma levels of gastrin were determined using the RIA kit whereas IL-8, TNF-alpha, IL-10, and IFN-gamma levels in serum were measured with a solid-phase ELISA. Fifteen infected people showed significantly higher gastrin and TNF-alpha levels than uninfected subjects. On the contrary, IL-8 levels were significantly higher in the uninfected subjects than in H. pylori positive ones (P < 0.0422). IFN-gamma and IL-10 circulating levels were not affected by H. pylori presence, being not significantly different in the two groups.

Mechanisms of Helicobacter pylori-induced rat gastric mucosal microcirculatory disturbances in vivo

The exact mechanisms by which Helicobacter pylori infection results in gastric mucosal injury are unclear. However, it has been demonstrated that surface protein extracts of the bacterium can induce a number of disturbances within the rat gastric mucosal microcirculation, including platelet aggregation and macromolecular leakage (MML) of labeled albumin. This study aimed to determine the mechanisms involved in inducing these events using the technique of fluorescent in vivo microscopy. Male Wistar rats were pretreated with either ketotifen, a mast cell stabilizer (1 mg/kg), pyrilamine, an H1-receptor antagonist (30 mg/kg), hexanolamine-PAF, a PAF-receptor antagonist (10 microg/kg), L-arginine, the nitric oxide precursor (300 mg/kg) or vehicle, saline. Then 0.5 ml of H. pylori extract was administered to the exteriorized gastric mucosa of the anesthetized rat. Alterations in fluorescein-labeled albumin leak, vessel diameters, and acridine red-labeled leukocyte and platelet activity were determined over a 2-hr period. Saline pretreated animals demonstrated significant MML with a peak at 5 min (11%, P<0.02). This was prevented with ketotifen and pyrilamine, but not with hexanolamine-PAF (17.5%, P<0.05) and L-arginine (13%, P<0.05). Significant numbers of platelet emboli and thrombi were observed within mucosal capillaries and postcapillary venules with vehicle pretreatment; this was prevented with hexanolamine-PAF and L-arginine, but not with ketotifen and pyrilamine. In conclusion, these studies demonstrate that more than one mediator is involved in inducing the rat gastric mucosal microcirculatory disturbances associated with H. pylori administration. Mast cells and histamine are linked to MML, with PAF, probably not derived from mast cells, involved in platelet activation.

Helicobacter pylori and extra-digestive diseases

Helicobacter pylori is a recently rediscovered gram-negative bacteria that causes peptic ulcer disease, gastric lymphoma and gastric carcinoma. Helicobacter pylori achieves its pathogenetic role by triggering an intense leucocyte infiltration of the gastric submucosa which is mediated by proinflammatory cytokines. This pathogenetic mechanism is common to many other diseases and, therefore, Helicobacter pylori seroprevalence has also been investigated in other diseases. It is now known that H. pylori seropositivity is associated with an increasing number of cardiovascular, respiratory, extra-gastroduodenal digestive, neurological, skin, autoimmune, growth and miscellaneous disorders. Although the precise role for H. pylori is unknown in these diseases, it is of tremendous interest to most clinicians and scientists as H. pylori is amenable to eradication therapy using simple and reliable drug regimens. The conditions associated with H. pylori seropositivity are highlighted in this concise article.

Effect of ranitidine bismuth citrate on the phospholipase A2 activity of Naja naja venom and Helicobacter pylori: a biochemical analysis

BACKGROUND

Helicobacter pylori has become recognized as a fundamental pathogen in the development of gastritis and peptic ulcer disease. Bismuth compounds in combination with antibiotics are widely used to treat H. pylori associated peptic ulcer disease.

METHODS

In this study we measured and analysed the inhibitory effect of ranitidine bismuth citrate (RBC, Pylorid, Tritec) on the activity and kinetics of phospholipase A2 (PLA2) (E.C.3.1.1.4) of commercial cobra (Naja naja) venom and H. pylori (French press lysates) using L-alpha-dipalmitoyl-(2[1-14C]palmitoyl)-phosphatidylcholine as substrate.

RESULTS

Our data suggest that RBC might exert a dose-dependent uncompetitive inhibition on PLA2 activity of both H. pylori and Naja naja venom. the inhibitory effect of RBC on the PLA2 activity cannot be abolished by the optimal concentration of calcium (10 mM), indicating its mechanism to be unrelated to the displacement of calcium from the activation site of the enzyme.

CONCLUSION

Our results suggest that one of the mechanisms by which bismuth compounds are therapeutically effective in the treatment of H. pylori associated gastritis is by inhibiting the activity of the degradative PLA2 enzyme secreted by H. pylori. As a consequence of the inhibitory action of RBC on PLA2 of the bacteria, the extracellular and/or intracellular phospholipid components of the gastric mucosal barrier are preserved.

Increased gastric production of platelet-activating factor, leukotriene-B4, and tumor necrosis factor-alpha in children with Helicobacter pylori infection

The concentrations of platelet-activating factor (PAF), leukotriene-B4 (LTB4), and tumour necrosis factor-alpha (TNF-alpha) in homogenate supernatants of gastric mucosal biopsy specimens and in gastric juice from Helicobacter pylori-positive (N = 21) and -negative children (N = 14) were investigated in order to determine whether these lipid mediators and the cytokine are involved in the inflammatory reaction of H. pylori-associated gastritis. PAF and LTB4 concentrations were measured after high-performance liquid chromatography (HPLC) purification by specific radioimmunoassay, and TNF-alpha concentrations were determined by using an enzyme-linked immunosorbent assay. The concentrations of PAF, LTB4, and TNF-alpha measured in gastric juice and biopsy homogenate supernatants of children with H. pylori-positive gastritis were found to be statistically elevated and in positive correlation with each other. This study suggested that increased local mucosal production of potent proinflammatory agents such as PAF, LTB4, and TNF-alpha may be implicated in the pathogenesis of H. pylori-associated gastritis in childhood.

How does Helicobacter pylori cause mucosal damage? Its effect on acid and gastrin physiology

Helicobacter pylori infection increases gastric acid secretion in patients with duodenal ulcers but diminishes acid output in patients with gastric cancer and their relatives. Investigation of the basic mechanisms may show how H. pylori causes different diseases in different persons. Infection of the gastric antrum increases gastrin release. Certain cytokines released in H. pylori gastritis, such as tumor necrosis factor alpha and specific products of H. pylori, such as ammonia, release gastrin from G cells and might be responsible. The infection also diminishes mucosal expression of somatostatin. Exposure of canine D cells to tumor necrosis factor alpha in vitro reproduces this effect. These changes in gastrin and somatostatin increase acid secretion and lead to duodenal ulceration. But the acid response depends on the state of the gastric corpus mucosa. The net effect of corpus gastritis is to decrease acid secretion. Specific products of H. pylori inhibit parietal cells. Also, interleukin 1 beta, which is overexpressed in H. pylori gastritis, inhibits both parietal cells and histamine release from enterochromaffin-like cells. H. pylori also promotes gastric atrophy, leading to loss of parietal cells. Factors such as a high-salt diet and a lack of dietary antioxidants, which also increase corpus gastritis and atrophy, may protect against duodenal ulcers by decreasing acid output. However, the resulting increase of intragastric pH may predispose to gastric cancer by allowing other bacteria to persist and produce carcinogens in the stomach.

Effects of rebamipide, a novel anti-ulcer agent, on gastric mucosal injury induced by platelet-activating factor in rats

We examined the role of gastric mucosal blood flow, lipid peroxidation, and neutrophil accumulation mediated by platelet-activating factor in the protective effect of rebamipide against gastric mucosal injury in rats. The intravenous injection of platelet-activating factor induced hyperemia and hemorrhagic erosions in rat stomachs. Rebamipide did not affect the decrease in the gastric mucosal blood flow induced by platelet-activating factor. The increase in gastric injury score after platelet-activating factor injection and the increase in thiobarbituric acid-reactive substances were significantly inhibited by the administration of rebamipide. The gastric injury score was closely correlated with the accumulation of lipid peroxides. Tissue-associated myeloperoxidase activity in the gastric mucosa significantly increased after platelet activating factor injection; this increase was not influenced by rebamipide treatment. The protective effect of rebamipide against the platelet-activiting factor-induced gastric mucosal injury may be due to direct inhibition of lipid peroxidation or scavenging of oxygen radicals that initiate lipid peroxidation.

Pathophysiology of Helicobacter pylori-induced gastritis and peptic ulcer disease

Helicobacter pylori causes persistent infection and inflammation in the human stomach, yet only a small fraction of persons harboring this organism develop peptic ulcer disease. An important question is why this variation in infection outcome exists. Recent studies have demonstrated that H pylori isolates possess substantial phenotypic and genotypic diversity that may engender differential host inflammatory responses that influence clinical outcome. Further investigation in this field may help to define which H pylori-infected persons bear the highest risk for subsequent development of peptic ulcer disease, and thus enable physicians to focus eradication therapy.

Effect of BN 50727 on pathological findings and tissue platelet activating factor levels during ileal ischemia in newborn piglets

The role of platelet activating factor (PAF), a potent ulcerogen mediator in the digestive tract, is thought to be important in the genesis of necrotizing enterocolitis. The aim of this study was to evaluate the role of PAF in the perpetuation and aggravation of gastrointestinal damage resulting from limited ischemia in the 2-day-old piglet using a natural PAF antagonist (BN 50727). Animals were separated into six groups: U4, controls; S, sham operated animals undergoing laparotomy; I4 and I9, ligation of the mesenteric vessels in the last ileal loop; IT4 and IT9, same procedure together with treatment with BN 50727 (50 mg/kg) orally before and after surgery and intraperitoneally during surgery. Animals were killed at day 4 in groups U4, S, I4 and IT4 and at day 9 in groups I9 and IT9, with histological studies and mediator measurements taken. Macroscopic and histological lesions of intestinal wall in groups I4, I9, IT4 and IT9 were similar to those of human neonatal necrotizing enterocolitis and did not vary according to the absence or the presence of BN 50727 treatment (P = .7, I4 v IT4 and P = .9, I9 v IT9). Peritoneal bands were significantly reduced in treated groups IT4 and IT9 as compared with untreated ones I4 and I9 (P = .003). Mucosal PAF levels in the terminal ileum were higher in group I4 than in groups U4 or I9. In the upper loop, mucosal PAF levels were comparable in all groups. An increase in stool PAF levels was observed only in group I9 (26.4 ng/g v 4.7 ng/g, I9 v U4 + S, P < .05), whereas values comparable to those observed in controls were detected in other groups (I4, 7.2 ng/g; IT4, 4.5 ng/g; IT9, 6.8 ng/g). Tumor necrosis factor alpha (TNF alpha) measurements did not exhibit any difference between groups. Using a PAF antagonist, the role of PAF in the aggravation of intestinal damage after ischemia was not remarkable because treatment did not induce any modifications of parietal intestinal lesions. PAF antagonists appeared to reduce significantly the local peritoneal consequences of local inflammation.

Helicobacter pylori and peptic disease in the pediatric patient

The data accumulated on Helicobacter pylori infection in children suggests an important causative role of the organism in gastritis and peptic ulcer disease in this age group. The importance of eradication of H pylori in asymptomatic children in relation to its role in peptic disease and cancer in adults is debatable. This article describes the current data on bacteriologic features, pathologic spectrum, clinical significance, epidemiology, methods of diagnosis, and treatment of H pylori infection in children. Further studies will provide the information on the pathogenicity, mode of transfer, and optimal treatment of H pylori infection.

The role of Helicobacter pylori in pathogenesis: the spectrum of clinical outcomes

Helicobacter pylori is probably the commonest bacterial infection worldwide and is now accepted as the cause of chronic active type B gastritis. Most patients continue through life with a chronic superficial gastritis while some develop either duodenal or gastric ulcer. In a very small proportion the lymphoid reaction to H. pylori infection appears to progress to become a mucosal associated lymphoid tissue (MALT) lymphoma, while in others the evidence suggests that chronic superficial gastritis progresses to atrophy, the loss of gastric acid secretory capacity and the development of gastric cancer. The mechanisms involving H. pylori infection in peptic ulceration are increasingly well understood and H. pylori is now accepted as having a critical role in duodenal ulcer, where the prevalence of infection is 90 to 95%. More important is the dramatic reduction in duodenal ulcer recurrence after successful eradication of the organism to about 4% in a year compared to recurrences of up to 80% in those who ulcers have been healed but in whom the infection persists. There is also increasing evidence for the involvement of H. pylori in gastric ulcer, where infection is seen in between 60 and 80%, and there is a similar dramatic reduction in recurrence following cure of H. pylori infection. The progression of H. pylori gastritis from the acute infection to chronic superficial gastritis, predominantly antral gastritis or a pangastritis with increasing atrophy appears to be associated with the differing outcomes seen in this disease. Moreover, there is increasing data on the roles played by bacterial heterogeneity and the virulence of the organism, host factors such as the HLA genotype and immune response, environmental factors and the age of acquisition of infection play in determining these clinical outcomes of the disease.

Enhanced levels of chemiluminescence and platelet activating factor in urease-positive gastric ulcers

Helicobacter pylori are believed to play an important role in the formation of gastric ulcer in a syndrome characterized by a high urease activity. On the other hand, the production of oxygen radicals and platelet activating factor (PAF) is enhanced in gastric ulcers. The present study is designed to investigate the relationship between the different aspects of gastric mucosal injury, urease activity, oxygen radical production, and PAF content in gastric specimens. Biopsy specimens taken from 35 gastric ulcer patients were studied. Urease activity was detected by a rapid urease test (CLO). Oxygen radical production was measured as a value of luminol-dependent chemiluminescence (ChL) and PAF content was determined by radioimmunoassay in the biopsy samples. The CLO-positive rate was significantly higher in the gastric ulcer group in comparison with that in controls. ChL values and PAF content were significantly increased in gastric ulcers, especially in CLO-positive specimens. The CLO-positive rate, ChL values, and PAF content were also found to be increased at a distant site beyond the ulcer lesions. During the course of macroscopic ulcer healing of CLO-positive cases, the CLO positive level and the ChL values were not significantly decreased, although PAF content was significantly lower. Enhanced oxygen radical and PAF production were observed not only in the ulcer region but also at a distant site from the ulcer in the urease-positive gastric mucosa. The persistent enhancement of ChL values during the healing stage of urease-positive gastric ulcers suggests its involvement in the recurrence of gastric ulcers.

Histological responses to Helicobacter pylori infection: gastritis, atrophy and preneoplasia

It is interesting that the principal histological features of acute H. pylori gastritis, surface epithelial degeneration and neutrophil polymorph infiltration, remain as the most sensitive indicators of the 'activity' of infection in the chronic phase. It is not surprising therefore that these are the first features to resolve after successful H. pylori eradication therapy. In one of the earliest studies of histological response to eradication, McNulty et al (1986) endoscoped patients immediately after a three-week treatment regime and found a highly significant decline in polymorph scores. The response was even more striking four weeks after the end of treatment, as at that time biopsies from responders were virtually devoid of polymorphs (Valle et al, 1991). Indeed the disappearance of polymorphs from a post-treatment biopsy is a useful indicator of successful eradication. Less attention has been paid to the recovery of the surface epithelium yet this is an impressive feature when comparing pre- and post-treatment biopsies. Using subjective grading of surface epithelial lesions, Solcia et al (1994) found a dramatic and highly significant improvement in mean grade immediately after anti-H. pylori treatment. Recently a morphometric approach was used to demonstrate a significant increase in surface epithelial cell height corresponding to the recovery that accompanies successful H. pylori eradication (Hassan et al, 1993). Chronic inflammatory cell infiltrate resolution is much slower. There is only a gradual reduction in cell density so that even 6 months after eradication treatment the mean score had only fallen by 50% of pre-treatment values (Solcia et al, 1994). In the author's experience, a minor increase in such cells persists for many months and may never completely resolve, in that more lymphocytes and plasma cells are seen than in a truly normal (pre-infection) stomach. Valle et al (1991) found resolution of chronic inflammation in only 15% of subjects at 6 months and in 51% at one year after eradication. The long delay in disappearance of lymphocytes and plasma cells poses a question over continuing antigenic stimulation in the absence of infection. Possible answers could involve persistence of antigenic moieties in dendritic cells of the lamina propria, or sensitization to host antigens brought about by infection so that an element of autoimmunity persists after eradication. Unravelling these mechanisms will add important new elements to our understanding of the long-term consequences of this fascinating infection.

Pathogenic mechanisms

Research is asking how H. pylori causes diseases, and also why the same bacteria produces different conditions in different persons. The process involves bacterial factors and the host's response. Some bacterial factors such as urease are produced by all strains of H. pylori. This enzyme may damage the gastric epithelium by practically releasing ammonia. Other bacterial factors such as vacuolating toxin are only produced by some strains, and these strains are more likely to cause ulcers or cancer. The host's response has been studied by physiologists, immunologists, and histologists, but the separation of systems is artificial. For example, physiologists find that H. pylori stops gastric D-cells from expressing somatostatin normally, which impairs reflex inhibition of acid secretion, but the D-cell malfunction is probably due to inflammatory factors. In H. pylori gastritis, the gastric epithelial cells behave like immunocytes and express class II molecules and cytokines such as interleukin-8. The patient's histological response to H. pylori is quite closely related to the disease outcome. Patients who respond by developing gastric atrophy are more likely to get gastric ulcers or stomach cancer, but patients whose gastric corpus remains healthy tend to secrete more acid and develop duodenal ulcers, particularly if they have gastric metaplasia in their duodenum. Studies of disease mechanisms provide a valuable insight into the development of these common diseases, and may enable us to identify at-risk groups who particularly merit eradication therapy.

Helicobacter pylori

Helicobacter pylori is an important cause of chronic active gastritis and is strongly associated with peptic ulcer disease and gastric cancer. H. pylori colonizes the surface of the gastric epithelium with production of a number of factors, resulting in inflammation and an altered mucosa. H. pylori infection occurs world-wide and the mode of transmission most likely is from human to human via the fecal-oral and/or the oral-oral route. Treatment and, in the future, prevention of this infection may result in a marked diminution of upper gastrointestinal tract disease.

Low incidence of clinically significant gastroduodenal pathology despite a high incidence of Helicobacter pylori infection

Gastric Helicobacter pylori infection is common throughout the tropics yet does not always correlate with the incidence of serious upper gastrointestinal pathology. In a consecutive series of 213 patients examined by gastroscopy for dyspepsia in northern Nigeria, 176 (92%) of 193 with acceptable biopsies had gastritis. Only 16 (8%) had a histologically normal gastric mucosa. H. pylori was present in 161 of 192 patients (84%); 31/41 (75%) with chronic gastritis and 130/135 (96%) with active gastritis. Serious pathology, ulcer and gastric cancer were present in only 29 (14%).

Mucosal tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-8 production in patients with Helicobacter pylori infection

We investigated whether tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and interleukin-8 (IL-8) are involved in the inflammatory reaction of Helicobacter pylori infection. In 23 patients with H. pylori infection and 16 patients with negative cultures for H. pylori and normal antral mucosa, the mucosal production of TNF-alpha, IL-1 beta, and IL-8 was measured in antral biopsy specimens after 23 h of in vitro culture. The levels of TNF-alpha and IL-1 beta appeared to be significantly higher in H. pylori-positive patients (p = 0.0002 for both TNF-alpha and IL-1 beta). IL-8 production was also higher in H. pylori-infected subjects, but this difference did not reach statistical significance (p = 0.057). No significant differences were found between the level of the cytokines in H. pylori-infected patients with or without duodenal ulcer disease. A strong correlation was found between the production of IL-1 beta and IL-8. The biologic effects of these cytokines may explain the conspicuous recruitment, influx, and activation of neutrophils in the gastric mucosa during H. pylori infection.

Helicobacter pylori stimulates antral mucosal reactive oxygen metabolite production in vivo

To determine if reactive oxygen metabolites have a pathogenic role in Helicobacter pylori (H pylori) related gastroduodenal disease, this study measured their production in antral mucosal biopsy specimens. Two related chemiluminescence techniques were used comparing H pylori positive (n = 105) and negative patients (n = 64) with a similar spectrum of macroscopic disease. After chemiluminescence assays, biopsy specimens were graded histologically. Increased luminol dependent chemiluminescence (detecting reactive oxygen metabolites through peroxidase catalysed reactions) was found in H pylori positive patients (median photon emission = 6.4 x 10(3)/min/mg wet weight (95% confidence intervals 3.6 to 9.9)) but not H pylori negative cases (-0.9 (-1.3 to -0.6)) (p = 0.0001). Similar results were found using lucigenin (which reacts directly with oxygen metabolites, particularly superoxide): (H pylori positive 0.9 (0.1 to 3.2); H pylori negative -1.2 (-3.4 to -0.6)) (p = 0.0003). Chemiluminescence was greater in H pylori positive compared with negative tissue when samples were grouped by equivalent macroscopic or microscopic damage. This difference was in part accounted for by a greater neutrophil infiltration in the H pylori positive mucosa, but when biopsy specimens with equivalent neutrophil infiltration could be compared directly, positive specimens gave greater chemiluminescence than negative. Smoking, drugs, and alcohol consumption had no independent effect. It is concluded that excess mucosal reactive oxygen metabolite production is associated with H pylori gastric antral infection and may be an important pathogenic mechanism. There is no evidence for reactive oxygen metabolite participation in the pathogenesis of gastric mucosal injury in cases unrelated to H pylori infection.

Pathophysiology of Helicobacter pylori infection

Helicobacter pylori is now accepted as the major cause of chronic gastritis. The initial response to infection is acute neutrophilic gastritis, which progresses to active chronic gastritis in most people. To confirm the pathogenic role of H. pylori, both the individual histological features of chronic gastritis and its topographical patterns must be shown to be caused by the infection. Surface epithelial degeneration is a probable result of direct tissue injury by bacterial products. Candidates are ammonia or ammonium products, cytotoxins, phospholipases and pro-inflammatory products such as lipopolysaccharide and platelet-activating factor. Neutrophil polymorph and chronic inflammatory cell infiltration are consequences of the mucosal immune response to bacterial antigens. Complement products and interleukin (IL)-8 are polymorph chemotaxins, and monocyte processing of antigens, followed by T helper cell and B lymphocyte responses, explain the presence of these cells in the mucosa. Atrophy may be a consequence of autodestructive products of neutrophil and monocyte activation, such as reactive oxygen metabolites and proteases. Intestinal metaplasia is most probably an adaptive response, possibly to H. pylori infection, exacerbated by other injurious agents such as bile reflux and dietary irritants. Pangastritis is the usual outcome after H. pylori infection. This is followed by multifocal atrophy and intestinal metaplasia. The latter changes weaken mucosal defences further and peptic ulceration may ensue. Patients with an increased parietal cell mass who become infected with H. pylori will exhibit antral restriction of the gastritis because the high acid output protects the corpus mucosa from bacterial adhesion and the inflammatory consequences. Such patients also have acid-induced gastric metaplasia in the proximal duodenum.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-8 expression in Helicobacter pylori infected, normal, and neoplastic gastroduodenal mucosa

AIMS

To investigate the expression of interleukin-8 (IL-8) in Helicobacter pylori infected normal and neoplastic gastroduodenal mucosa, and in established gastric cancer cell lines.

METHODS

Immunofluorescence techniques were used to localise IL-8 in cryosections of gastric (n = 25) and duodenal (n = 17) endoscopic biopsy specimens an in resected gastric tumour tissue samples from 16 patients. Two gastric cancer cell lines (Kato 3 and MKN 45) were examined for IL-8 protein expression by immunofluorescence and for the presence of IL-8 mRNA by reverse transcription followed by the polymerase chain reaction (RT-PCR).

RESULTS

IL-8 was localised to the epithelium in histologically normal gastric mucosa, with particularly strong expression in the surface cells. IL-8 expression was also a feature of surface epithelium in the duodenal bulb, but was much reduced in the second part of the duodenum. In chronic H pylori-associated gastritis gastritis gastric epithelial IL-8 expression was increased and expression of IL-8 within the lamina propria was evident. By contrast, large areas of IL-8 negative epithelium were observed in the body mucosa of a subject with Ménétrier's disease. In gastric carcinoma the tumour cells were positive for IL-8. IL-8 was also detected by immunofluorescence in unstimulated Kato 3 and MKN 45 cells, and constitutive IL-8 gene expression in these cell lines was confirmed by detection of IL-8 mRNA by RT-PCR.

CONCLUSIONS

Immunoreactive IL-8, a potent neutrophil chemotactic and activating factor, is present in the epithelium of both normal and inflamed gastric mucosa with increased expression in the latter. There is site dependent variation in epithelial IL-8 expression within the gastroduodenal mucosa. The expression of the pro-inflammatory cytokine IL-8 in gastric carcinoma cells may influence peritumoural cellular infiltrates.

Gastric metaplasia and Helicobacter pylori infection

Duodenal and antral mucosal biopsy specimens were obtained from 139 patients with dyspeptic complaints to study the prevalence and extent of gastric metaplasia in the duodenal bulb in relation to Helicobacter pylori (H pylori) infection and duodenal ulcer disease. On logistic regression, the presence and extent of gastric metaplasia was not significantly associated with H pylori infection. The prevalence of gastric metaplasia, however, was found to be higher in patients with current or past evidence of duodenal ulcer disease in comparison with subjects with functional dyspepsia (p = 0.01). A follow up study on 22 patients before and at least one year after eradication of H pylori showed that the mean extent of gastric metaplasia did not change significantly after eradication and did not differ when compared with 21 patients with persisting infection. It is concluded that the unchanged gastric acid output after eradication of H pylori is a more important factor in the development of gastric metaplasia than the H pylori related inflammatory process.

Mechanisms involved in Helicobacter pylori-induced inflammation

BACKGROUND

Helicobacter pylori infection is associated with mucosal inflammation. The aims of the present study were to assess whether a water extract of H. pylori promotes neutrophil (polymorphonuclear leukocyte [PMN]) adherence to endothelial cells and define the molecular basis of this adhesive interaction.

METHODS

Intravital microscopy was used to study leukocyte adhesive interactions in rat mesenteric venules in situ. PMN-endothelial cell adhesive interactions were studied in vitro using human PMNs and monolayers of human umbilical vein endothelial cells (HUVEC).

RESULTS

In vivo, superfusion of rat mesentery with the H. pylori extract increased leukocyte adhesion and emigration in venules. In vitro, adhesion of human PMNs to HUVEC was increased by the H. pylori extract in a concentration-dependent manner. Pretreatment of HUVEC alone with H. pylori extract had no effect on PMN adherence, whereas pretreatment of PMN alone significantly increased their adherence to HUVEC. The extract-induced adhesion was significantly diminished by monoclonal antibodies (MAb) directed against either CD11a, CD11b, or CD18 on neutrophils, and by MAbs against intercellular adhesion molecule-1 (ICAM-1), but not E- or P-selectin, on endothelial cells.

CONCLUSIONS

These studies suggest that products of H. pylori elicit gastrointestinal inflammation by promoting PMN adhesion to endothelial cells via CD11a/CD18- and CD11b/CD18-dependent interactions with ICAM-1.

Gastric secretion of platelet activating factor and precursors in healthy humans: effect of pentagastrin

The release of platelet activating factor (PAF-ACETHER or PAF) and its precursors in the gastric lumen was assessed in 13 normal subjects in basal condition and after stimulation by gastrin. Acid, pepsin, and sialic acid outputs were determined under the same conditions. Gastric juice was collected using a nasogastric tube after overnight fast in basal condition for 60 minutes, then under pentagastrin infusion (6 micrograms/kg/hr for 60 minutes). Platelet activating factor was detected at low concentration in 4/13 subjects under basal condition (mean (SEM) 1.2 (0.6) pg/hr) while high concentrations of lyso platelet activating factor (6.1 (1.8) microgram/hr) and of alkyl-acyl-glycerophosphocholine (AAGPC) (11.5 (3) micrograms/hr) were found in 13 and 11 subjects, respectively. Platelet activating factor was not detected during pentagastrin infusion, while lyso platelet activating factor and alkyl-acyl-glycerophosphocholine were detected in 13 and in 12 subjects, respectively. Compared with the basal condition these platelet activating factor precursors increased significantly (p < 0.001) going up to fivefold baseline (31.8 (6.8) micrograms/hr and 53 (9.3) micrograms/hr respectively) in response to pentagastrin. There was a positive correlation between platelet activating factor precursors and acid or pepsin output but not between platelet activating factor precursors and sialic acid. As sialic acid may be considered an index of mucus glycoprotein degradation, it seems that gastrin stimulation of gastric epithelial cells results in a concomittant secretion of platelet activating factor precursors, acid, and pepsin irrespective of mucus glycoprotein degradation.

Gastric interleukin-8 and IgA IL-8 autoantibodies in Helicobacter pylori infection

Gastric infection with Helicobacter pylori is frequently characterized by neutrophil infiltration. The production of the neutrophil-activating peptide (NAP-1/IL-8) and mucosal IgA autoantibodies to IL-8 by human antral biopsies have been examined during short-term in vitro culture. Detectable IL-8 was secreted by 84% of H. pylori-negative patients with normal antral mucosa (range < 0.07-61.5 ng/mg biopsy protein, n = 19). Concentrations in 4 patients with reactive gastritis and 10 with inactive gastritis were not significantly different from subjects with normal mucosa. In H. pylori-positive patients with active gastritis and neutrophil infiltration into the epithelium (n = 17) IL-8 secretion was significantly increased relative to subjects with normal mucosa (P < 0.0001), inactive gastritis (P < 0.001) and reactive gastritis (P < 0.01). IL-8 concentrations in active gastritis were significantly correlated with the extent of epithelial surface degeneration (r = 0.64). IgA autoantibodies were present in 19 patients (13 active, 4 inactive gastritis) and concentrations were significantly correlated with IL-8 production (P < 0.001). Gastric synthesis of IL-8 is likely to be an important factor in regulating mucosal neutrophil infiltration and activation in patients with H. pylori infection. The local production of IgA antibodies to IL-8 may represent a down-regulatory response of the host to limit mucosal damage associated with a chronic bacterial infection.

Significance and regulation of gastric secretion of platelet-activating factor (PAF-acether) in man

Platelet-activating factor (PAF) has been implicated in the pathogenesis of acute inflammatory and ulcerative diseases of the upper gastrointestinal tract. In the present study, we compared the gastric output of PAF and its precursors with gastric acid output, in patients with various upper gastrointestinal tract diseases and healthy controls. PAF and precursors were also extracted from gastric biopsies from subjects with chronic gastritis and/or gastric colonization by Helicobacter pylori. Under basal conditions, hourly gastric PAF output increased in esophagitis and erosive gastritis, but not in duodenal ulcer or Zollinger-Ellison syndrome. In the gastric juice of duodenal ulcer patients, PAF output rose after secretin, but in patients with Zollinger-Ellison syndrome, PAF was only detected when gastric acid secretion had been reduced by antisecretory drugs and no concurrent changes were observed in serum gastrin levels. After pentagastrin, patients and controls exhibited a significant decrease in PAF output and a negative correlation was found between PAF and acid outputs (r = -0.57, p < 0.01). When PAF was incubated with gastric juice in vitro, it underwent degradation irrespective of the medium pH. We found no relation between the outputs of PAF and precursors and the severity of gastritis or gastric colonization by H. pylori. Overall, these results suggest that PAF might be released in the stomach by gastric epithelial cells and could be responsible for mucosal injury of the upper gastrointestinal tract.

PAF-acether and acetylhydrolase in stool of patients with Crohn's disease

PAF-acether (PAF) is a phospholipid mediator with potent biological effects on the digestive tract. We report the presence of PAF in stool of patients with active Crohn's disease (39.1 +/- 13.5 ng/g of stool, mean +/- SEM, N = 19) and its absence in patients with irritable bowel syndrome with diarrhea and diarrhea with malabsorption. Fecal PAF acetylhydrolase activity was higher (P less than 0.04) in patients with Crohn's disease as compared to patients with irritable bowel syndrome with diarrhea and diarrhea with malabsorption. We also report a solid-phase extraction of fecal PAF using silica minicolumns, which yielded results highly correlated with those obtained with a high-performance liquid chromatography method (r = 0.86, P less than 0.001, N = 16). These findings may allow us to implicate PAF in the onset and perpetuation of digestive tract inflammatory symptoms observed during Crohn's disease. They would warrant to investigate the influence of various therapeutic agents, including PAF antagonists, on fecal PAF levels during inflammatory digestive ailments.

Hypotheses on the pathogenesis and natural history of Helicobacter pylori-induced inflammation

Although Helicobacter pylori is now recognized as playing an etiologic role in chronic gastritis and peptic ulcer disease, information on the pathogenesis and natural history of infection is limited. A model is proposed in which luminal H. pylori secrete substances that mediate inflammation that is beneficial to the organism but ultimately deleterious for the host; in addition to tissue damage, inflammation also affects gastric secretory function. In this model, the host may attempt to suppress the inflammatory response, and the adequacy of this postulated down-regulation determines pathological and clinical outcome. The effects of the inflammatory process on gastrin-hydrochloric acid homeostasis may be of critical importance in the pathogenesis of peptic ulcer disease. Because the long-term consequences of H. pylori colonization reflect the continued presence of the organism in the host over years or decades, it may be useful to consider this as a "slow" bacterial infection.

Presence of PAF-acether in stool of patients with pouch ileoanal anastomosis and pouchitis

Platelet-activating factor is an endogenous phospholipid produced by a wide variety of inflammatory cells. Platelet-activating factor induces severe pathological changes in various organs and, among numerous potent effects, causes bowel necrosis. Pouchitis is a poorly understood complication of ileoanal pouch anastomosis which occurs in patients who undergo surgery for ulcerative colitis. The aim of this study was to measure ileal or fecal platelet-activating factor and lyso platelet-activating factor contents in normal volunteers (n = 12), in patients with terminal ileostomy (n = 7), and in patients with ileoanal anastomosis (n = 15) (8 patients have pouchitis defined by the presence of ulcerations on the reservoir). Fecal samples were processed and assessed for platelet-activating factor by platelet aggregation assay. The aggregating material was further characterized as platelet-activating factor by the following: inhibition of the platelet aggregation it induced by specific platelet-activating factor receptor antagonist (BN 52021; IHB, Le Plessis Robinson, France); abolition of platelet aggregation after incubation with phospholipase A2 but not with lipase A1; and retention time on high-performance liquid chromatography. Stool platelet-activating factor content (in nanograms per gram of stool, mean +/- 1SD) was significantly increased in patients with pouchitis (22.2 +/- 16 ng/g) compared with patients with normal reservoir (1.59 +/- 0.63 ng/g, P less than 0.01), terminal ileostomy (0.59 +/- 0.43 ng/g, P less than 0.01), and healthy controls (0 +/- 0 ng/g of stool, P less than 0.001). Lyso platelet-activating factor (nanograms per gram of stool) was increased in patients with pouchitis (10,704 +/- 5499 ng/g) compared with patients with normal reservoir (4721 +/- 4549 ng/g of stool, P less than 0.05), terminal ileostomy (3042 +/- 4019 ng/g, P less than 0.02), and healthy volunteers (128 +/- 107 ng/g, P less than 0.001). In patients with ileoanal anastomosis and pouchitis, increased platelet-activating factor production could be implicated in the inflammation and ulcerations observed in the reservoir.

Helicobacter pylori

Helicobacter pylori is a unique pathogen and the leading cause of chronic gastric inflammation. For many individuals the organism is of low virulence, causing only mild inflammation and generating few, if any, dyspeptic symptoms. For those with more severe inflammation, H. pylori infection may be causal in the generation of dyspeptic symptoms. H. pylori infection appears to be the dominant factor in peptic ulcer disease. Events considered to be of importance are a disturbed gastrin homeostasis and the development of gastric metaplasia in the bulb. The most important argument in support of the dominant role of H. pylori in duodenal ulcer disease is the markedly reduced ulcer relapse after successful eradication. Eradication proves to be difficult, presumably because of the peculiar habitat of the organism. Currently the best pharmacologic approach is triple therapy, combining a bismuth salt, metronidazole, and amoxycillin or tetracycline.