Helicobacter pylori induces apoptosis in gastric epithelial cells through inducible nitric oxide

A comprehensive review of phytochemical profile, bioactives for pharmaceuticals, and pharmacological attributes of Azadirachta indica

Azadirachta indica L. is a multipurpose medicinal tree of family Meliaceae. It occurs in tropical and semitropical regions of the world. Different parts of this miraculous tree are used to treat pyrexia, headache, ulcer, respiratory disorders, cancer, diabetes, leprosy, malaria, dengue, chicken pox, and dermal complications. The tree is popular for its pharmacological attributes such as hypolipidemic, antifertility, microbicidal, antidiabetic, anti-inflammatory, hepatoprotective, antipyretic, hypoglycemic, insecticidal, nematicidal, antiulcer, antioxidant, neuroprotective, cardioprotective, and antileishmaniasis properties. A. indica is also rich in various phytochemicals for pharmaceuticals such as alkaloids, steroids, flavonoids, terpenoids, fatty acids, and carbohydrates. The fungicidal potential of the tree is due to the presence of azadirachtin and nimbin. Herein, we have compiled a comprehensive review of phytochemical profile, pharmacological attributes, and therapeutic prospective of this multipurpose tree.

Review: Impact of Helicobacter pylori on Alzheimer's disease: What do we know so far?

BACKGROUND

Helicobacter pylori has changed radically gastroenterologic world, offering a new concept in patients' management. Over time, more medical data gave rise to diverse distant, extragastric manifestations and interactions of the "new" discovered bacterium. Special interest appeared within the field of neurodegenerative diseases and particularly Alzheimer's disease, as the latter and Helicobacter pylori infection are associated with a large public health burden and Alzheimer's disease ranks as the leading cause of disability. However, the relationship between Helicobacter pylori infection and Alzheimer's disease remains uncertain.

METHODS

We performed a narrative review regarding a possible connection between Helicobacter pylori and Alzheimer's disease. All accessible relevant (pre)clinical studies written in English were included. Both affected pathologies were briefly analyzed, and relevant studies are discussed, trying to focus on the possible pathogenetic role of this bacterium in Alzheimer's disease.

RESULTS

Data stemming from both epidemiologic studies and animal experiments seem to be rather encouraging, tending to confirm the hypothesis that Helicobacter pylori infection might influence the course of Alzheimer's disease pleiotropically. Possible main mechanisms may include the bacterium's access to the brain via the oral-nasal-olfactory pathway or by circulating monocytes (infected with Helicobacter pylori due to defective autophagy) through disrupted blood-brain barrier, thereby possibly triggering neurodegeneration.

CONCLUSIONS

Current data suggest that Helicobacter pylori infection might influence the pathophysiology of Alzheimer's disease. However, further large-scale randomized controlled trials are mandatory to clarify a possible favorable effect of Helicobacter pylori eradication on Alzheimer's disease pathophysiology, before the recommendation of short-term and cost-effective therapeutic regimens against Helicobacter pylori-related Alzheimer's disease.

The Immune Battle against Helicobacter pylori Infection: NO Offense

Helicobacter pylori is a successful pathogen of the human stomach. Despite a vigorous immune response by the gastric mucosa, the bacterium survives in its ecological niche, thus favoring diseases ranging from chronic gastritis to adenocarcinoma. The current literature demonstrates that high-output of nitric oxide (NO) production by the inducible enzyme NO synthase-2 (NOS2) plays major functions in host defense against bacterial infections. However, pathogens have elaborated several strategies to counteract the deleterious effects of NO; this includes inhibition of host NO synthesis and transcriptional regulation in response to reactive nitrogen species, allowing the bacteria to face the nitrosative stress. Moreover, NO is also a critical mediator of inflammation and carcinogenesis. In this context, we review the recent findings on the expression of NOS2 in H. pylori-infected gastric tissues and epithelial cells, the role of NO in H. pylori-related diseases and H. pylori gene expression, and the mechanisms whereby H. pylori regulates NO synthesis by host cells.

The use of neem for controlling gastric hyperacidity and ulcer

H(2)-receptor blockers and proton pump inhibitors are now used extensively to control gastric and duodenal ulcer, inflammation and pain, but these drugs have limitations and are not always affordable. The development of novel nontoxic antiulcer drugs, including from medicinal plants, is therefore desirable, and Azadirachta indica A. Juss, commonly known as Neem, is known to have potent gastroprotective and antiulcer effects. This review deals with the pharmacological and biochemical studies carried out regarding the antiulcer activities of Neem extracts and their mechanism of action, including the inhibition of acid secretion. A comparison with ranitidine and omeprazole in some animal models has been included and clinical studies, where available, have also been incorporated, along with a safety evaluation. Neem bark extract has the potential for the development of novel medicines for the therapeutic control of gastric hyperacidity and ulcer.

E-cadherin promoter hypermethylation induced by interleukin-1beta treatment or H. pylori infection in human gastric cancer cell lines

Interleukin-1beta is up-regulated in the presence of Helicobacter pylori infection. H. pylori infection was associated with E-cadherin methylation. In this study, we examined if IL-1beta could induce promoter methylation of E-cadherin in human gastric cancer cell lines TMK-1, MKN-74 and MKN-7. Cells were treated with IL-1beta (0.025, 0.1, 0.25, 1.0, 2.5 ng/mL) for 6, 12 and 24h. Methylation status was determined by MSP and sequencing. The effects of IL-1beta or H.pylori on the cells, and after blockade with interleukin-1 receptor antagonist (IL-1ra) were tested. Promoter methylation of E-cadherin was induced in all three cells treated with IL-1beta or co-cultured with H. pylori. Treatment of IL-1ra could reverse the phenomena. Our study indicated that IL-1beta is an important step in mediating E-cadherin methylation.

Alzheimer's disease and Helicobacter pylori infection: Defective immune regulation and apoptosis as proposed common links

Although degenerative diseases of the central nervous system, including Alzheimer's disease (AD), have an increasingly high impact on aged population their association with Helicobacter pylori (H. pylori) infection has not as yet been thoroughly researched. Current H. pylori infection appears to induce irregular humoral and cellular immune responses that, owing to the sharing of homologous epitopes (molecular mimicry), cross-react with components of nerves, thereby contributing and possibly perpetuating the apoptotic neural tissue damage observed in neurodegenerative diseases including AD. An association between AD and H. pylori infection has been recently addressed by two studies. A higher seropositivity for anti-H. pylori immunoglobulin G antibodies in 30 patients with AD than in 30 age-matched controls was reported in one study; this serological test, however, has limitations because it does not discriminate between current and old infections. In the other study, by introducing the histological method (the actual gold standard) for diagnosis of H. pylori infection, we reported a higher prevalence of H. pylori infection in 50 AD patients than in 30 anemic controls. This pathogen may influence the pathophysiology of AD by promoting platelet and platelet-leukocyte aggregation; releasing various pro-inflammatory and vasoactive substances; developing cross-mimicry with host antigens; producing reactive oxygen metabolites and circulating lipid peroxides; influencing the apoptotic process; and increasing, through induction of atrophic gastritis, homocysteine, which contributes to vascular disorders implicated in endothelial damage and neurodegeneration.

Infrequent COX-2 expression due to promoter hypermethylation in gastric cancers in Dalian, China

Cyclooxygenase-2 (COX-2) has been shown to play oncogenic roles during stepwise gastrocarcinogenesis, and its expression is correlated with Helicobacter pylori infection, tumor necrosis factor alpha-mediated nuclear factor (NF)-kappaB activation, and Wnt signaling. To examine COX-2 expression and the status of its regulatory factors, we examined 49 gastric cancers (GCs), 21 premalignant tissues, and 10 noncancerous gastric mucosa from residents of Dalian, China. Unexpectedly, it was found that COX-2 expression was infrequent in the gastric samples (18.8%, 15/80) regardless of the type of lesion or morphological phenotype. H pylori infection was detected in 19 of 35 tested GC cases. Tumor necrosis factor alpha expression, NF-kappaB nuclear translocation, or Wnt2 overexpression was observed in 56 (82.3%) of 68, 40 (50.0%) of 80, and 62 (77.5%) of 80 of the gastric tissue samples, respectively. Methylation-sensitive restriction enzyme digestion followed by polymerase chain reaction of COX-2 promoter regions revealed a remarkably high hypermethylation rate (100%, 20/20) among the COX-2-negative GCs, which was associated with the overexpression of DNA methyltransferase (DNMT) 1 (r = 0.587, P < .01). These results indicate that (1) in contrast to previous findings using other GC sources, our results show that COX-2 activity may not be a critical molecular event during GC formation, (2) the tumor-promoting effects of H pylori infection and Wnt and NF-kappaB activities may be mediated by COX-2-independent pathways, and (3) promoter hypermethylation is the major cause of COX-2 silencing in Dalian GCs, apparently because of increased expression of DNMTs (especially DNMT1). Consequently, a COX-2-oriented preventive or therapeutic strategy is not practical for Dalian GCs. The frequent COX-2 hypermethylation observed in Dalian GCs could have insightful epigenetic and epidemiologic implications.

Restoration of heat shock protein70 suppresses gastric mucosal inducible nitric oxide synthase expression induced by Helicobacter pylori

Heat shock proteins (HSPs) are crucial for the maintenance of cell integrity during normal cellular growth as well as during pathophysiological conditions. While functioning mainly as molecular chaperones, HSPs also appear to be involved in diverse biological activities, such as apoptosis, carcinogenesis, and cytoprotection from cytotoxic damage. Infection with Helicobacter pylori causes inflammation in the gastric mucosa, leading to gastritis, gastric ulcers, duodenal ulcer disease, and even gastric cancer, but the role of HSPs in H. pylori-associated gastropathy is not known. Using two-dimensional electrophoretic analysis, we have observed significant shifts in HSP profiles after H. pylori infection in RGM-1 cells. We therefore evaluated the effect of treatments that induce HSPs on H. pylori-induced inducible nitric oxide synthase (iNOS) expression. We found that H. pylori infection significantly attenuated the expression of HSP70, whereas exposure of cells to noncytotoxic heat shock or geranylgeranylacetone restored HSP70 expression, as well as suppressing the expression of iNOS, a major cause of H. pylori-induced gastric tissue damage. Our results suggest that induction of HSP70 confers cytoprotection against H. pylori infection by inhibiting the expression of iNOS. In conclusion, these results provide important insights into the flux in HSPs profiles in response to H. pylori infection and highlight the cytoprotective role of HSP70 in H. pylori infection.

Clinical studies on the effect of Neem (Azadirachta indica) bark extract on gastric secretion and gastroduodenal ulcer

We have shown earlier that Neem (Azadirachta indica) bark aqueous extract has potent antisecretory and antiulcer effects in animal models and has no significant adverse effect (Bandyopadhyay et al., Life Sciences, 71, 2845-2865, 2002). The objective of the present study was to investigate whether Neem bark extract had similar antisecretory and antiulcer effects in human subjects. For this purpose, a group of patients suffering from acid-related problems and gastroduodenal ulcers were orally treated with the aqueous extract of Neem bark. The lyophilised powder of the extract when administered for 10 days at the dose of 30 mg twice daily caused a significant (p < 0.002) decrease (77%) in gastric acid secretion. The volume of gastric secretion and its pepsin activity were also inhibited by 63% and 50%, respectively. Some important blood parameters for organ toxicity such as sugar, urea, creatinine, serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase, albumin, globulin, hemoglobin levels and erythrocyte sedimentation rate remained close to the control values. The bark extract when taken at the dose of 30-60 mg twice daily for 10 weeks almost completely healed the duodenal ulcers monitored by barium meal X-ray or by endoscopy. One case of esophageal ulcer (gastroesophageal reflux disease) and one case of gastric ulcer also healed completely when treated at the dose of 30 mg twice daily for 6 weeks. The levels of various blood parameters for organ toxicity after Neem treatment at the doses mentioned above remained more or less close to the normal values suggesting no significant adverse effects. Neem bark extract thus has therapeutic potential for controlling gastric hypersecretion and gastroesophageal and gastroduodenal ulcers.

Smoking and the pathogenesis of gastroduodenal ulcer--recent mechanistic update

Peptic ulcer is a common disorder of gastrointestinal system and its pathogenesis is multifactorial, where smoking and nicotine have significant adverse effects. Smoking and chronic nicotine treatment stimulate basal acid output which is more pronounced in the smokers having duodenal ulcer. This increased gastric acid secretion is mediated through the stimulation of H2-receptor by histamine released after mast cell degranulation and due to the increase of the functional parietal cell volume or secretory capacity in smokers. Smoking and nicotine stimulate pepsinogen secretion also by increasing chief cell number or with an enhancement of their secretory capacity. Long-term nicotine treatment in rats also significantly decreases total mucus neck cell population and neck-cell mucus volume. Smoking also increases bile salt reflux rate and gastric bile salt concentration thereby increasing duodenogastric reflux that raises the risk of gastric ulcer in smokers. Smoking and nicotine not only induce ulceration, but they also potentiate ulceration caused by H. pylori, alcohol, nonsteroidal anti-inflammatory drugs or cold restrain stress. Polymorphonuclear neutrophils (PMN) play an important role in ulcerogenesis through oxidative damage of the mucosa by increasing the generation of reactive oxygen intermediates (ROI), which is potentiated by nicotine and smoking. Nicotine by a cAMP-protein kinase A signaling system elevates the endogenous vasopressin level, which plays an aggressive role in the development of gastroduodenal lesions. Smoking increases production of platelet activating factor (PAF) and endothelin, which are potent gastric ulcerogens. Cigarette smoking and nicotine reduce the level of circulating epidermal growth factor (EGF) and decrease the secretion of EGF from the salivary gland, which are necessary for gastric mucosal cell renewal. Nicotine also decreases prostaglandin generation in the gastric mucosa of smokers, thereby making the mucosa susceptible to ulceration. ROI generation and ROI-mediated gastric mucosal cell apoptosis are also considered to be important mechanism for aggravation of ulcer by cigarette smoke or nicotine. Both smoking and nicotine reduce angiogenesis in the gastric mucosa through inhibition of nitric oxide synthesis thereby arresting cell renewal process. Smoking or smoke extract impairs both spontaneous and drug-induced healing of ulcer. Smoke extract also inhibits gastric mucosal cell proliferation by reducing ornithine decarboxylase activity, which synthesises growth-promoting polyamines. It is concluded that gastric mucosal integrity is maintained by an interplay of some aggressive and defensive factors controlling apoptotic cell death and cell proliferation and smoking potentiates ulcer by disturbing this balance.

Effect of nNOS/iNOS expression on cell apoptosis during stress ulcer of gastric mucosa in mice

AIM: To determine the effect of different type of NOS expression on gastric mucosal cell apoptosis during stress ulcer in mice.

METHODS: Apoptotic cells were quantitated in gastric mucosa by terminal deoxynucleatidyl transferase mediated dUTP nick and labelling (TUNEL) techniques. The expression of nNOS/iNOS proteins was detected by immunohistochemical method. The effects of different dose of nitric oxide inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on gastric mucosal apoptosis was investigated in immersion-restraint stress model of mice.

RESULTS: The expression of iNOS was highly correlated with the apoptotic cell quantities of gastric mucosa. In contract to the high dose of L-NAME (20.0 mg/kg) that increased the quantity of apoptosis 25.8% (P <0.05), small dose of L-NAME (2.0 mg/kg) decreased the quantity of apoptosis 34.6% (P <0.01).

CONCLUSION: The expression of NO is a double-edged sword, a low amount of NO produced by neuronal forms of NOS performs many physiological functions. On the contrary, higher concentration of NO produced by inducible form of NOS induces the epithelial cell apoptosis under stress condition.

Effect of Helicobacter pylori infection on expression of Bcl-2 family members in gastric adenocarcinoma

AIM

To investigate the effect of Helicobacter pylori (H pylori) infection on the expressions of Bcl-2 family members in gastric adenocarcinoma.

METHODS

Gastric adenocarcinoma and resection margin tissues of 95 patients were studied. Semi-quantitative RT-PCR was used to measure Bid, Bax and Bcl-2 mRNA expressions.

RESULTS

Expressions of Bid and Bax in gastric adenocarcinoma tissues without H pylori infection, with cagA- H pylori infection and cagA+ H pylori infection increased significantly in turn (Bid, 0.304, 0.422 and 0.855 respectively, P<0.05; Bax, 0.309, 0.650 and 0.979 respectively, P<0.05). Bcl-2 mRNA levels increased significantly in gastric adenocarcinoma tissues with cagA- H pylori infection and cagA+ H pylori infection, compared with those without H pylori infection (0.696 and 0.849 vs 0.411, P<0.05). Expressions of Bid, Bax and Bcl-2 in resection margin tissues without H pylori infection, with cagA- H pylori infection and cagA+ H pylori infection increased significantly in turn (Bid, 0.377, 0.686 and 0.939 respectively, P<0.05; Bax, 0.353, 0.645 and 1.001 respectively, P<0.05; Bcl-2, 0.371, 0.487 and 0.619 respectively, P<0.05). In H pylori negative specimens, expressions of Bid and Bax correlated negatively with that of Bcl-2 respectively in adenocarcinoma tissues (Bid vs Bcl-2, r=-0.409, P<0.05; Bax vs Bcl-2, r=-0.451, P<0.05). In H pylori positive specimens, expressions of Bid and Bax did not correlate with that of Bcl-2 in adenocarcinoma tissues (Bid vs Bcl-2, r=0.187, P>0.05; Bax vs Bcl-2, r=0.201, P>0.05), but correlated positively with that of Bcl-2 respectively in resection margin tissues (Bid vs Bcl-2, r=0.331, P<0.05; Bax vs Bcl-2, r=0.295, P<0.05).

CONCLUSION

H pylori may enhance Bid, Bax and Bcl-2 mRNA levels and cause deregulation of these apoptosis-associated genes expressions, which may play a role during development of gastric adenocarcinoma induced by H pylori.

Interactions between inducible nitric oxide and other inflammatory mediators during Helicobacter pylori infection

BACKGROUND

Recent studies in both humans and animal models strongly suggest the contribution of the host immune response to Helicobacter pylori-related disease. Inducible nitric oxide synthase has been shown to be up-regulated in the gastric epithelium during H. pylori gastritis, suggesting a role in inflammation.

MATERIALS AND METHODS

C57BL/6 wild-type and inducible nitric oxide synthase gene knockout mice were infected with H. pylori strain SS1. Expression of macrophage inflammatory protein-2 (MIP-2), interleukin-1 beta (IL-1 beta), Th1 (IL-2 and gamma interferon) and Th2 (IL-4 and IL-10) cytokines, and inducible cyclooxygenase mRNA in mice was determined in mouse gastric tissues and quantified using either competitive reverse transcription-polymerase chain reaction or competitive polymerase chain reaction following reverse transcription.

RESULTS

The Th1 cytokine gamma interferon was only detected in wild-type and inducible nitric oxide synthase gene knockout infected mice, while a Th2 (IL-4) response was not detected. H. pylori induced MIP-2 and IL-1 beta mRNA in mice.

CONCLUSIONS

Because similar levels of inflammatory mediators were noted in both wild-type and nitric oxide synthase gene knockout infected mice, our data suggest that inducible nitric oxide synthase does not influence expression of these inflammatory mediators in the early stages of H. pylori infection in mice.

Helicobacter pylori infection interferes with epithelial Stat6-mediated interleukin-4 signal transduction independent of cagA, cagE, or VacA

Helicobacter pylori is a bacterial pathogen evolved to chronically colonize the gastric epithelium, evade immune clearance by the host, and cause gastritis, peptic ulcers, and even gastric malignancies in some infected humans. In view of the known ability of this bacterium to manipulate gastric epithelial cell signal transduction cascades, we determined the effects of H. pylori infection on epithelial IL-4-Stat6 signal transduction. HEp-2 and MKN45 epithelial cells were infected with H. pylori strains LC11 or 8823 (type 1; cagA(+)/cagE(+)/VacA(+)), LC20 (type 2; cagA(-), cagE(-), VacA(-)), and cagA, cagE, and vacA isogenic mutants of strain 8823, with some cells receiving subsequent treatment with the Th2 cytokine IL-4, a known Stat6 activator. Immunofluorescence showed a disruption of Stat6-induced nuclear translocation by IL-4 in LC11-infected HEp-2 cells. IL-4-inducible Stat6 DNA binding in HEp-2 and MKN45 cells was abrogated by infection, but MKN45 cell viability was unaffected. A decrease in IL-4-mediated Stat6 tyrosine phosphorylation in nuclear and whole cell lysates was also observed following infection with strains LC11 and LC20, while neither strain altered IL-4 receptor chain alpha or Janus kinase 1 protein expression. Furthermore, parental strain 8823 and its isogenic cagA, cagE, and vacA mutants also suppressed IL-4-induced Stat6 tyrosine phosphorylation to comparable degrees. Thus, H. pylori did not directly activate Stat6, but blocked the IL-4-induced activation of epithelial Stat6. This may represent an evolutionarily conserved strategy to disrupt a Th2 response and evade the host immune system, allowing for successful chronic infection.

Suppressed apoptosis in the inflamed gastric mucosa of Helicobacter pylori-colonized iNOS-knockout mice

Deregulated cell turnover in Helicobacter pylori (H. pylori)-colonized gastric mucosa has been suggested to be linked to the gastric carcinogenesis pathway. We previously reported attenuation of apoptosis and enhancement of cellular proliferation in the H. pylori-colonized gastric mucosa of Mongolian gerbils as compared to that in mice, which might reflect a specific link between H. pylori colonization and carcinogenesis in the Mongolian gerbils; the difference between the two strains could be attributable to differences in the host genetic background. Inducible-type nitric oxide synthase (iNOS) is thought to participate in not only the inflammatory response, but also in the regulation of gastric mucosal cell turnover in H. pylori-colonized gastric mucosa. Thus, the present study was designed to examine gastric leukocyte activation and epithelial cell apoptosis in the gastric mucosa following H. pylori inoculation in iNOS-knockout mice.

METHODS

iNOS-knockout mice (iNOS(-/-)) and their iNOS(+/+) littermates were orally inoculated with the Sydney strain of H. pylori (SS1, 10(8) colony-forming units [CFU]). H. pylori infection was confirmed by microaerobic bacterial culture. The stomach of each mouse was evaluated 14 weeks and 30 weeks after the inoculation. Gastric mucosal accumulation of polymorphonuclear leukocytes (PMN) was assessed by determining the myeloperoxidase (MPO) activity and histological score based on the updated Sydney system. The level of apoptosis was determined by estimation of the cytoplasmic levels of mono- and oligonucleosomes and by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling method.

RESULTS

The SS1-inoculated mice showed persistent H. pylori colonization for 12 weeks. While gastric mucosal PMN infiltration increased following SS1 inoculation in both iNOS(+/+) and iNOS(-/-)strains, enhanced DNA fragmentation was observed in only SS1-colonized iNOS(+/+) mice, and not in the iNOS(-/-) mice. In conclusion, although the recruitment of PMN in response to H. pylori was evoked even in the gastric mucosa of iNOS(-/-) mice, epithelial cell apoptosis induced by H. pylori was attenuated in this strain. These data suggest that iNOS may play an important role in promoting apoptosis in the H. pylori-infected inflamed gastric mucosa, and that persistent inflammation without apoptosis in iNOS(-/-) mice with H. pylori infection may be linked to preneoplastic transformation.

A novel antioxidant and antiapoptotic role of omeprazole to block gastric ulcer through scavenging of hydroxyl radical

The mechanism of the antiulcer effect of omeprazole was studied placing emphasis on its role to block oxidative damage and apoptosis during ulceration. Dose-response studies on gastroprotection in stress and indomethacin-induced ulcer and inhibition of pylorus ligation-induced acid secretion indicate that omeprazole significantly blocks gastric lesions at lower dose (2.5 mg/kg) without inhibiting acid secretion, suggesting an independent mechanism for its antiulcer effect. Time course studies on gastroprotection and acid reduction also indicate that omeprazole almost completely blocks lesions at 1 h when acid inhibition is partial. The severity of lesions correlates well with the increased level of endogenous hydroxyl radical (*OH), which when scavenged by dimethyl sulfoxide causes around 90% reduction of the lesions, indicating that *OH plays a major role in gastric damage. Omeprazole blocks stress-induced increased generation of *OH and associated lipid peroxidation and protein oxidation, indicating that its antioxidant role plays a major part in preventing oxidative damage. Omeprazole also prevents stress-induced DNA fragmentation, suggesting its antiapoptotic role to block cell death during ulceration. The oxidative damage of DNA by *OH generated in vitro is also protected by omeprazole or its analogue, lansoprazole. Lansoprazole when incubated in a *OH-generating system scavenges *OH to produce four oxidation products of which the major one in mass spectroscopy shows a molecular ion peak at m/z 385, which is 16 mass units higher than that of lansoprazole (m/z 369). The product shows no additional aromatic proton signal for aromatic hydroxylation in (1)H NMR. The product absorbing at 278 nm shows no alkaline shift for phenols, thereby excluding the formation of hydroxylansoprazole. The product is assigned to lansoprazole sulfone formed by the addition of one oxygen atom at the sulfur center following attack by the *OH. Thus, omeprazole plays a significant role in gastroprotection by acting as a potent antioxidant and antiapoptotic molecule.

Effect of Helicobacter pylori on apoptosis and apoptosis related genes in gastric cancer cells

BACKGROUND/AIMS

Helicobacter pylori induces the apoptosis of gastric epithelial cells in vivo and in vitro. However, the molecular mechanism has not been clarified. The aim of this study was to investigate the effect of H pylori on the apoptosis of gastric epithelial cells and the expression of apoptosis related genes in vitro.

METHODS

Human gastric adenocarcinoma SGC-7901 cells were co-cultured with a cytotoxic H pylori strain, NCTC 11637, at various densities ranging from 3.2 x 10(4) to 1.0 x 10(8) colony forming units (CFU)/ml for 48 hours. Apoptosis in gastric cells was determined by transmission electron microscopy, Hoechst 33258 fluorochrome staining, and flow cytometry. The expression of apoptosis related proteins, Bcl-2, Bax, and c-Myc, was measured by an immunohistochemical method, and c-Myc mRNA expression was determined by the reverse transcription-polymerase chain reaction.

RESULTS

Helicobacter pylori induces morphological changes typical of apoptosis. Both fluorochrome staining and flow cytometry showed that the apoptotic index began to increase when H pylori were at a density of > 1.6 x 10(4) CFU/ml, and in a density dependent manner (p < 0.01; one way ANOVA). The expression of the Bax and c-Myc proteins and of c-Myc mRNA was increased, whereas Bcl-2 expression was decreased after co-culture for 48 hours.

CONCLUSIONS

Helicobacter pylori induced apoptosis in gastric epithelial cells is mediated by altered expression of the products of the Bcl-2, Bax, and c-Myc genes.

Inducible nitric oxide synthase expression in chronic viral hepatitis and its relation with histological severity of disease

The role of nitric oxide in the pathogenesis of chronic viral hepatitis is not known. Elevated nitric oxide production is assumed to be responsible for the pathological changes in many inflammatory conditions, mainly via peroxynitrite, a potential oxidant that is produced by the reduction of superoxide anion with nitric oxide. The intensity and the distribution of the immunohistochemical staining of intrahepatic inducible nitric oxide synthase were studied in the biopsy specimens obtained from 63 patients with viral hepatitis and 13 patients with elevated transaminase levels of various aetiologies. Hepatic inducible nitric oxide synthase staining was significantly more intense in the viral hepatitis group (P = 0.000). Inducible nitric oxide synthase staining levels correlated well with the severity of the viral hepatitis using the Knodell's liver histological activity index (r = 0.393, P = 0.002) Among the viral hepatitis group, the pathological distribution of the inducible nitric oxide synthase staining favoured the periportal hepatocytes (zone 1) whereas less staining was observed in parenchymal hepatocytes zone of 2 and 3 and bile duct epithelium. As nitric oxide mediated nitration of hepatocellular proteins is elevated in inflamed hepatic tissues and is correlated with the severity of the disease, we suggest that inducible nitric oxide synthase can possibly have a critical role in the pathogenesis of chronic viral hepatitis.

Gastroprotective effect of Neem (Azadirachta indica) bark extract: possible involvement of H(+)-K(+)-ATPase inhibition and scavenging of hydroxyl radical

The antisecretory and antiulcer effects of aqueous extract of Neem (Azadirachta indica) bark have been studied along with its mechanism of action, standardisation and safety evaluation. The extract can dose dependently inhibit pylorus-ligation and drug (mercaptomethylimidazole)-induced acid secretion with ED(50) value of 2.7 and 2 mg Kg(-1) b.w. respectively. It is highly potent in dose-dependently blocking gastric ulcer induced by restraint-cold stress and indomethacin with ED(50) value of 1.5 and 1.25 mg Kg(-1) b.w. respectively. When compared, bark extract is equipotent to ranitidine but more potent than omeprazole in inhibiting pylorus-ligation induced acid secretion. In a stress ulcer model, it is more effective than ranitidine but almost equipotent to omeprazole. Bark extract inhibits H(+)-K(+)-ATPase activity in vitro in a concentration dependent manner similar to omeprazole. It offers gastroprotection against stress ulcer by significantly preventing adhered mucus and endogenous glutathione depletion. It prevents oxidative damage of the gastric mucosa by significantly blocking lipid peroxidation and by scavenging the endogenous hydroxyl radical ((z.rad;)OH)-the major causative factor for ulcer. The (z.rad;)OH-mediated oxidative damage of human gastric mucosal DNA is also protected by the extract in vitro. Bark extract is more effective than melatonin, vitamin E, desferrioxamine and alpha-phenyl N-tert butylnitrone, the known antioxidants having antiulcer effect. Standardisation of the bioactive extract by high pressure liquid chromatography indicates that peak 1 of the chromatogram coincides with the major bioactive compound, a phenolic glycoside, isolated from the extract. The pharmacological effects of the bark extract are attributed to a phenolic glycoside which is apparently homogeneous by HPLC and which represents 10% of the raw bark extract. A single dose of 1g of raw extract per kg b.w. (mice) given in one day and application of 0.6g raw extract per kg b.w. per day by oral route over 15 days to a cumulative dose of 9g per kg was well tolerated and was below the LD(50). It is also well tolerated by rats with no significant adverse effect. It is concluded that Neem bark extract has therapeutic potential for the control of gastric hyperacidity and ulcer.

Protein SV-IV promotes nitric oxide production not associated with apoptosis in murine macrophages

SV-IV (seminal vesicle protein no. 4) is a potent immunomodulatory and anti-inflammatory secretory protein (Mr 9758) produced in large amounts by the rat seminal vesicle epithelium. Here we show that this protein possesses the ability to upregulate in J774 macrophages the expression of the gene coding for the inducible nitric oxide synthase (iNOS). The increase in NO production consequent on the marked enhancement of iNOS activity was not associated with apoptotic damage of the SV-IV-treated cells. In the same experimental model, however, LPS induced upregulation of iNOS coupled with an increase in NO production and marked apoptotic death. Differences in the ability of SV-IV and LPS to control the life/ death signal balance in target cells via trans-membrane activation of apoptotic (mediated by TNF-alpha and NO/iNOS system) and anti-apoptotic (mediated by bcl-2, c-myc, etc.) pathways are suggested to be the basis of the apoptotic fate of the experimentally treated cells. In addition, considering the important role played by NO in the process of mammalian reproduction, SV-IV may be involved in the fine tuning of NO concentration in the female genital tract mucosa via an SV-IV-mediated control of iNOS gene expression in local macrophages.

Analysis of Helicobacter pylori and nonsteroidal anti-inflammatory drug-induced gastric epithelial injury

BACKGROUND

Helicobacter pylori and nonsteroidal anti-inflammatory drugs (NSAIDs) are important factors in gastric mucosal injury. However, the relationship between H. pylori and NSAID-related gastroduodenal mucosal injury has not been clarified.

AIM

To determine the role of H. pylori in NSAID-induced gastric mucosal injury and to examine the effects of H. pylori, indomethacin and sofalcone on gastric epithelial cells in culture, as a useful model to study gastric mucosal injury. In addition, we studied the effect of sofalcone, a gastric mucosal protection agent, on H. pylori and NSAID-induced gastric mucosal injury.

METHODS

Cytotoxic and noncytotoxic strains of H. pylori were used, each with an inoculum of 10(7) cfu/mL. The effect on the growth of RGM-1 cells (a rat gastric epithelial cell line) was studied by MTT assay, and levels of prostaglandin E2 in culture supernatants were measured by EIA.

RESULTS

Both cytotoxic and noncytotoxic strains of H. pylori tended to induce cell injury in RGM-1 cells at 48 h after inoculation. Indomethacin alone induced gastric epithelial injury in a dose-dependent manner, but did not augment cell injury induced by H. pylori. In addition, sofalcone (10(-5) mol/L) showed a suppressive effect on indomethacin-induced gastric epithelial injury.

CONCLUSION

These findings indicate that indomethacin induces gastric mucosal injury regardless of H. pylori infection, and suggests that sofalcone may be a useful drug in the treatment of NSAID-induced mucosal injury.

The regulatory role of nitric oxide in apoptosis

Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death-caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.

NF-kappaB, inducible nitric oxide synthase and apoptosis by Helicobacter pylori infection

Oxygen radicals are considered as an important regulator in the pathogenesis of Helicobacter pylori (H. pylori)-induced gastric ulceration and carcinogenesis. Inflammatory genes including inducible nitric oxide synthase (iNOS) may be regulated by oxidant-sensitive transcription factor, nuclear factor-kappaB (NF-kappaB). iNOS induction has been related to gastric apoptosis. We studied the role of NF-kappaB on iNOS expression and apoptosis in H. pylori-stimulated gastric epithelial AGS cells. AGS cells were treated with antisense oligonucleotide (AS ODN) for NF-kappaB subunit p50, an antioxidant enzyme catalase, an inhibitor of NF-kappaB activation pyrrolidine dithiocarbamate (PDTC), iNOS inhibitors N(G)-nitro-L-arginine-methyl ester (L-NAME) and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a peroxynitrite donor SIN-1, and a nitric oxide donor NOC-18 in the presence or absence of H. pylori. H. pylori induced cytotocixity time- and dose-dependently, which occurred with induction in iNOS expression and nitrite production. SIN-1 and NOC-18 induced dose-dependent cytotoxicity in AGS cells. Catalase, PDTC, L-NAME, and AMT prevented H. pylori-induced cytotoxicity and apoptosis. It was related to their inhibition on iNOS expression and nitrite production. The cells treated with AS ODN had low levels of p50 and NF-kappaB and inhibited H. pylori-induced cytotoxicity, apoptosis, iNOS expression, and nitrite production. In conclusion, NF-kappaB plays a novel role in iNOS expression and apoptosis in H. pylori-infected gastric epithelial cells.

Role of virulence factors, cell components and adhesion in Helicobacter pylori-mediated iNOS induction in murine macrophages

To investigate the mechanisms involved in Helicobacter pylori-mediated inducible nitric oxide synthase (iNOS) upregulation in mononuclear cells we cocultivated human THP-1 acute monocytic leukemia cells and murine J774A.1 professional macrophages with different H. pylori wild-type strains and mutants. We have shown that H. pylori-mediated iNOS induction in J774A.1 is independent of established virulence factors but dependent on direct interaction between bacteria and cells. In J774A.1, iNOS was equally upregulated by the wild-type strains J99, 26695, P12, and P1 as well as by mutants lacking the cag pathogenicity island, vacA, katA, alpAB genes and the hp0043 gene taking part in lipopolysaccharide biosynthesis when direct cell contact was allowed but not when bacteria and cells were separated by protein-permeable filter membranes. In contrast, iNOS was not induced in THP-1. This indicates that H. pylori-mediated iNOS induction in J774A.1 is independent of important virulence factors whereas cell contact is crucial which suggests a role of adhesion or phagocytosis.

Apoptosis in gastric epithelium induced by Helicobacter pylori infection: implications in gastric carcinogenesis

OBJECTIVES

Helicobacter pylori is an identified carcinogen for gastric cancer, however, the underlying mechanisms remain to be defined. In this review, we sought to elucidate the role of apoptosis in gastric carcinogenesis, to determine the influence of H. pylori infection on apoptosis, and finally to provide insights into the mechanisms by which H. pylori may lead to gastric carcinogenesis.

METHODS

A broad-based MEDLINE and Current Contents literature search was performed to identify relevant publications between 1966 and March 2000 addressing H. pylori infection, apoptosis, cell proliferation, gastric carcinoma, oncogenes, and tumor suppressor genes, as well as the products of these genes. Abstracts from recent major conferences that provided adequate additional data were also included.

RESULTS

Apoptotic cells are rare in the glandular neck region (the generative cell zone) of normal gastric mucosa. With progression of atrophic gastritis, the generative cell zone shifts downward and a relatively large number of apoptotic cells occur. In intestinalized glands, both apoptotic cells and proliferative cells are present in deeper portions of the glands, corresponding to the generative zone. A higher frequency of apoptosis has been observed in gastric dysplasia than in coexisting gastric carcinomas, whereas the number of proliferative cells is significantly higher in gastric carcinoma than in dysplasia. Upregulation of oncogene bcl-2 in premalignant lesions and "downregulation" of the gene after malignant change is probably a common event. Accumulation of p53 protein is first detected in dysplasia, although mutation of the pS3 gene may occur in intestinal metaplasia. H. pylori infection induces apoptosis in gastric epithelial cells, which returns to normal after eradication of the infection. Numerous molecules produced by H. pylori including cytotoxin (VacA), lipopolysaccharide, monochloramine, and nitric oxide may directly induce apoptosis. Moreover, H. pylori-stimulated host inflammatory/immune responses lead to release of a large amount of cytokines. Cytokines produced by type 1 T helper cells, such as TNF-alpha and IFN-gamma, markedly potentiate apoptosis. Gastric cell proliferation is significantly higher in patients with H. pylori infection than in normal controls, and eradication of the infection leads to a reduction in cell proliferation. Apoptosis and cell proliferation are also increased in precancerous lesions such as gastric atrophy, intestinal metaplasia, and dysplasia in the presence of H. pylori infection. However, H. pylori-induced apoptosis may no longer be cell cycle-dependent in these lesions because of the occurrence of alterations and mutations of apoptosis-regulating genes, resulting in a loss of balance between apoptosis and cell proliferation.

CONCLUSIONS

It is hypothesized that H. pylori-induced apoptosis may play a key role in gastric carcinogenesis by increasing cell proliferation and/or resulting in gastric atrophy.