Oxidation and genotoxicity of fecapentaene-12 are potentiated by prostaglandin H synthase

Plasmalogens, platelet-activating factor and beyond - Ether lipids in signaling and neurodegeneration

Glycerol-based ether lipids including ether phospholipids form a specialized branch of lipids that in mammals require peroxisomes for their biosynthesis. They are major components of biological membranes and one particular subgroup, the plasmalogens, is widely regarded as a cellular antioxidant. Their vast potential to influence signal transduction pathways is less well known. Here, we summarize the literature showing associations with essential signaling cascades for a wide variety of ether lipids, including platelet-activating factor, alkylglycerols, ether-linked lysophosphatidic acid and plasmalogen-derived polyunsaturated fatty acids. The available experimental evidence demonstrates links to several common players like protein kinase C, peroxisome proliferator-activated receptors or mitogen-activated protein kinases. Furthermore, ether lipid levels have repeatedly been connected to some of the most abundant neurological diseases, particularly Alzheimer’s disease and more recently also neurodevelopmental disorders like autism. Thus, we critically discuss the potential role of these compounds in the etiology and pathophysiology of these diseases with an emphasis on signaling processes. Finally, we review the emerging interest in plasmalogens as treatment target in neurological diseases, assessing available data and highlighting future perspectives. Although many aspects of ether lipid involvement in cellular signaling identified in vitro still have to be confirmed in vivo, the compiled data show many intriguing properties and contributions of these lipids to health and disease that will trigger further research.

Oxidative stress in Helicobacter pylori-induced gastric cell injury

Oxygen radicals are supposed to be involved in inflammation and cell proliferation. Helicobacter pylori induces decrease in antioxidant defense factors, such as GSH, mucus and constitutive nitric oxide (NO), gastric mucosal injury and inflammation. Inflammation and injury might be caused by oxidant-mediated expression of inflammatory cytokine interleukin-8 (IL-8) and inflammatory enzymes such as cyclooxtgenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), which were mediated by oxidant-sensitive transcription factors such as nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1), possibly with mitogen activated protein kinase (MAPK) activation. H. pylori-induced alterations in protein expression demonstrate the involvement of oxidative stress in the pathogenesis of H. pylori-induced gastric diseases. The differentially expressed genes and proteins may be useful as prognostic indices for gastric diseases associated with H. pylori infection. In conclusion, oxygen radicals are produced in gastric epithelial cells infected with H. pylori, which may reduce the antioxidant defense mechanism and turn on the expression of inflammatory genes, adhesion molecules and mediators stimulating cell proliferation, as well as defensive molecular chaperones in gastric epithelial cells.

Increased expression of cyclooxygenase-2 in first-degree relatives of gastric cancer patients

AIM: To study the expression of cyclooxygenase-2 (COX-2) in human gastric cancer tissues and their paired adjacent mucosa, as well as mucosa from gastric antrum and corpus of the first-degree relatives of the recruited cancer patients.

METHODS: The expression of COX-2 mRNA in 38 patients with gastric cancer and their 29 first-degree relatives and 18 healthy controls was assessed by the real time RT-PCR. The expression of COX-2 protein was determined by Western blot.

RESULTS: A marked increase in COX-2 mRNA expression was found in 20 of 37 (54%) cancerous tissues compared to their respective paired normal mucosa (P<0.001). Interestingly, increased COX-2 mRNA expression was also found in mucosa of the corpus (6/29) and antrum (13/29) of their first-degree relatives. Increased COX-2 mRNA expression was more frequently observed in the antrum biopsies from cancer patients than in the antrum biopsies from healthy controls (P<0.05). In addition, 3 of 23 (13%) patients with atrophic mucosa and 6 of 35 (17%) patients with intestinal metaplasia showed increased COX-2 mRNA expression. Furthermore, COX-2 expression increased in H pylori-positive tissues, especially in antrum mucosa.

CONCLUSION: Increased COX-2 expression is involved in gastric carcinogenesis, and may be necessary for maintenance of the malignant phenotype and contribute to Helicobacter pylori-associated malignant transformation.

Molecular markers in Helicobacter pylori-associated gastric carcinogenesis

Helicobacter pylori infection is a known risk factor of gastric carcino-genesis. This article presents early molecular alterations associated with H. pylori chronic gastritis and advances in the molecular characterization of preneoplastic intestinal metaplasia (IM) and premalignant gastric mucosal lesions. H. pylori infection induces changes in gene expression, genomic instability and accumulation of gene mutations in the stomach epithelium. Mutations, including LOH and microsatellite instability, and gene hypermethylation are seen not only in gastric cancer, but are already detectable in IM and gastric dysplasia/adenoma. Recent reports using microarray expression analysis identified several gastric epithelial genes that are regulated by H. pylori. Among the many genes showing altered epithelial expression in response to H. pylori, some might be useful as markers to assess gastric cancer risk. Profiles of mutagenesis and gene expression in IM and dysplasia/adenoma have been characterized and represent potential markers of preneoplastic and premalignant lesions during gastric carcinogenesis.

Increased expression of inducible nitric oxide synthase and cyclooxygenase-2 in pancreatic cancer

Despite recognition of the devastating malignant potential of the pancreatic ductal cancer, the exact pathophysiological events contributing to tumor growth remain to be elucidated. Expression levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 were found to be frequently elevated in several types of human cancer and have also been directly linked to carcinogenesis. The purpose of this study was to determine the expression of COX-1, COX-2 and iNOS in human pancreatic cancer and matched normal adjacent tissue by the Western blot assay. Marked COX-2 expression was observed in cancer tissue compared with the normal surrounding tissue. The iNOS protein was markedly expressed only in pancreatic cancer while the expression of COX-1 was similar in both normal and cancerous tissue. Our findings indicate that COX-2 up-regulation and the expression of iNOS in pancreatic cancer, not seen in normal tissue, may play a role in the pathogenesis of human pancreatic adenocarcinomas. These observations suggest that COX-2 and iNOS may be a target for prevention or treatment of pancreatic carcinomas.

The kinetics of interactions between fecapentaene-12 and DNA

Fecapentaene-12 (Fp-12) is a potent colon cancer mutagen, which interacts with DNA. In this study, the kinetics of its interactions with DNA is investigated. Various pHs are used. Three first-order rates are observed at each pH. This suggests that interaction between Fp-12 and DNA occurs through three different mechanisms.

Angiogenic markers, neovascularization and malignant deformation of Barrett's esophagus

The molecular events underlying progression of Barrett's esophagus to adenocarcinoma remain an area of active investigation. Neovascularization and angiogenesis have been studied in esophageal adenocarcinomas by counting of microvessels after staining with vascular markers, and by immunohistochemistry for vascular endothelial growth factor. Angiogenesis appears to be increased early in the neoplastic process, but has poor prognostic value. We have demonstrated that expression levels of two important genes that regulate cell growth, namely inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, are frequently upregulated in Barrett's esophagus and associated adenocarcinomas. COX-2 expression may be related to reflux of bile salts, which induce COX-2 expression in Barrett's tissues and esophageal adenocarcinoma cells in vitro. COX-2 inhibition induces apoptosis and blocks proliferation in COX-2-expressing esophageal adenocarcinoma cells in vitro, and blocks angiogenesis in both in vivo and in vitro models. Although controversial, recent evidence suggest that iNOS-derived NO can inhibit angiogenesis in some model systems. In conclusion, both iNOS and COX-2 appear to be involved in Barrett's-associated neoplastic progression, but COX-2 inhibition is more promising as a chemopreventive strategy. COX-2 inhibition may exert beneficial effects by decreasing angiogenesis and epithelial proliferation, and by facilitating apoptosis of epithelial cells that have undergone DNA damage.

Rofecoxib inhibits cyclooxygenase 2 expression and activity and reduces cell proliferation in Barrett's esophagus

BACKGROUND & AIMS

Cyclooxygenase 2 (COX-2) is overexpressed in Barrett's esophagus and adenocarcinoma and up-regulated by acid or bile salt exposure. COX-2 inhibition with the selective inhibitor rofecoxib may be important in chemoprevention of esophageal adenocarcinoma by decreasing cell proliferation.

METHODS

Biopsy specimens of esophagus, Barrett's esophagus, and duodenum were obtained at baseline from 12 patients and were compared with biopsy specimens obtained after 10 days of therapy with rofecoxib 25 mg orally daily. All patients were maintained asymptomatic on their proton pump inhibitor therapy throughout the study. COX-2 expression, proliferating cell nuclear antigen (PCNA) expression (proliferation marker), and prostaglandin E2 (PGE2) biopsy content (marker of COX activity) were assessed by immunoblotting and enzyme immunoabsorbence assays.

RESULTS

At baseline, COX-2 expression was 3-fold higher in Barrett's esophagus than esophagus and duodenum (P < 0.05). After rofecoxib therapy, COX-2 expression in Barrett's esophagus decreased by 77% (P < 0.005). Similarly at baseline, PGE2 content was 2-fold higher in Barrett's esophagus than esophagus or duodenum. After rofecoxib therapy, PGE2 content decreased in Barrett's esophagus by 59% (P < 0.005). At baseline, PCNA expression was also 2-fold higher in Barrett's esophagus than squamous esophagus and duodenum (P < 0.005). After rofecoxib therapy, PCNA expression in Barrett's esophagus decreased by 62.5% (P < 0.005).

CONCLUSIONS

Rofecoxib 25 mg orally once daily reduces COX-2 expression, PGE2 release, and cell proliferation in Barrett's esophagus. Together with acid suppressive therapy, rofecoxib may be a promising chemoprevention agent against dysplasia and esophageal adenocarcinoma.

Role of Helicobacter pylori in gastric carcinogenesis

Peptic ulcers and gastric malignancies are the two major complication of the course of Helicobacter pylori-associated chronic gastritis. Both gastric adenocarcinomas and MALT lymphomas occur in association with H. pylori infection, and studies support an etiological association. This article discusses the natural history of H. pylori-related gastric carcinogenesis and criteria to identify people susceptible to H. pylori infection-associated gastric cancer. It then reviews the molecular and genetic mechanisms underlying the malignant transformation of the gastric mucosa associated with H. pylori.

Expression of cyclooxygenase-2 in chronic hepatitis B and the effects of anti-viral therapy

BACKGROUND

Cyclooxygenase-2 may play a role in the development of hepatocellular carcinoma, but the relationship between cyclooxygenase-2 and chronic hepatitis B is unknown.

AIM

To investigate the expression and cellular localization of cyclooxygenase-2 in chronic hepatitis B patients and the effects of anti-viral therapy.

METHODS

Using immunohistochemistry, in situ hybridization, Western blot and reverse transcription polymerase chain reaction, protein and messenger RNA expression and cellular localization of cyclooxygenase-2 in 35 chronic hepatitis B patients were assessed. Fourteen histologically normal and non-viral-infected livers were used as controls. The cyclooxygenase-2 immunoreactivities of paired liver biopsies from 12 patients receiving anti-viral therapy were compared.

RESULTS

Immunohistochemistry and in situ hybridization revealed that cyclooxygenase-2 expression was confined to hepatocytes. Patients with chronic hepatitis B had significantly higher cyclooxygenase-2 expression compared with controls. The cyclooxygenase-2 expression of hepatitis B e antigen-positive and -negative chronic hepatitis B patients was not significantly different, although the necro-inflammatory activity of the latter group was significantly lower. Over-expression of cyclooxygenase-2 in patients with chronic hepatitis B was further confirmed by Western blot and reverse transcription polymerase chain reaction. Twelve hepatitis B e antigen-positive chronic hepatitis B patients received anti-viral therapy: lamivudine in seven and interferon in five. Despite hepatitis B e antigen seroconversion, disappearance of hepatitis B virus DNA in serum, normalization of liver enzymes and a significant reduction in necro-inflammatory activity in all 12 patients, no significant change in cyclooxygenase-2 expression was found.

CONCLUSIONS

Chronic hepatitis B is associated with elevated cyclooxygenase-2 levels in hepatocytes, and the over-expression of this enzyme does not reflect inflammatory activity. Up-regulation of cyclooxygenase-2 persists after successful anti-viral therapy.

Evidence for reductive activation of carcinogenic aristolochic acids by prostaglandin H synthase -- (32)P-postlabeling analysis of DNA adduct formation

Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, is implicated in an unique type of renal fibrosis, designated Chinese herbs nephropathy (CHN), which can develop to urothelial cancer. Understanding which enzymes are involved in AA activation and/or detoxication is important in the assessment of an individual susceptibility to this natural carcinogen. We examined the ability of prostaglandin H synthase (PHS) to activate AA to metabolites forming DNA adducts with the nuclease P1 and 1-butanol extraction enrichment procedure of the (32)P-postlabeling assay. PHS is a prominent enzyme in the kidney and urothelial tissues. Ram seminal vesicle (RSV) microsomes, which contain high levels of PHS, generated AA-DNA adduct patterns reproducing those found in renal tissues in CHN patients. 7-(Deoxyadenosin-N(6)-yl)aristolactam I, 7-(deoxyguanosin-N(2)-yl)aristolactam I and 7-(deoxyadenosin-N(6)-yl)aristolactam II were identified as AA-DNA adducts formed by AAI. Two adducts, 7-(deoxyguanosin-N(2)-yl)aristolactam II and 7-(deoxyadenosin-N(6)-yl)aristolactam II, were generated from AAII. According to the structures of the DNA adducts identified, nitroreduction is the crucial pathway in the metabolic activation of AA. The identity of PHS as the activating enzyme in RSV microsomes was proven with different cofactors and inhibitors. Only indomethacin, a selective inhibitor of PHS, significantly decreased the amount of adducts formed by RSV microsomes. The inhibitor of NADPH:CYP reductase (alpha-lipoic acid) and some selective inhibitors of cytochromes P450 (CYP) were not effective. Likewise, only cofactors of PHS, arachidonic acid and hydrogen peroxide, supported the DNA adduct formation of AAI and AAII, while NADPH and NADH were ineffective. These results demonstrate a key role of PHS in the activation pathway of AAI and AAII in the RSV microsomal system and were corroborated with the purified enzyme, namely ovine PHS-1. The results presented here are the first report demonstrating a reductive activation of nitroaromatic compounds by PHS-1.

Molecular testing of Helicobacter pylori-associated chronic gastritis and premalignant gastric lesions: clinical implications

Helicobacter pylori-associated gastritis may progress or be complicated by peptic ulcer and gastric malignancy, including gastric carcinoma and mucosa-associated lymphoid tissue lymphoma. Predicting who develops malignancy remains a clinical challenge. The molecular understanding of pathways that are associated with progression of the normal gastric epithelium to malignancy together with classic histologic parameters are promising ways of tackling this problem. Ideally, molecular tools used for screening should be available as noninvasive tests, such as examination of markers detectable in blood samples, but these are not currently available. In contrast, molecular markers that correlate with cancer risk can be examined in the epithelium after endoscopic biopsy and can be of importance in identifying individuals at risk, especially if combined with other parameters of gastric cancer risk.

Role of plant polyphenols in genomic stability

Polyphenols are a large and diverse class of compounds, many of which occur naturally in a range of food plants. The flavonoids are the largest and best-studied group of these. A range of plant polyphenols are either being actively developed or currently sold as dietary supplements and/or herbal remedies. Although, these compounds play no known role in nutrition (non-nutrients), many of them have properties including antioxidant, anti-mutagenic, anti-oestrogenic, anti-carcinogenic and anti-inflammatory effects that might potentially be beneficial in preventing disease and protecting the stability of the genome. However not all polyphenols and not all actions of individual polyphenols are necessarily beneficial. Some have mutagenic and/or pro-oxidant effects, as well as interfering with essential biochemical pathways including topoisomerase enzyme activities, prostanoid biosynthesis and signal transduction. There is a very large amount of in vitro data available, but far fewer animal studies, and these are not necessarily predictive of human effects because of differences in bacterial and hepatic metabolism of polyphenols between species. Epidemiological studies suggest that high green tea consumption in the Japanese population and moderate red wine consumption in the French population may be beneficial for heart disease and cancer, and these effects may relate to specific polyphenols. A small number of adequately controlled human intervention studies suggest that some, but not all polyphenol extracts or high polyphenol diets may lead to transitory changes in the antioxidative capacity of plasma in humans. However, none of these studies have adequately considered long-term effects on DNA or the chromosome and unequivocally associated these with polyphenol uptake. Furthermore, clinical trials have required intravenously administered polyphenols at concentrations around 1400mg/m(2) before effects are seen. These plasma concentrations are unlikely to be achieved using the dietary supplements currently available. More focused human studies are necessary before recommending specific polyphenolic supplements at specific doses in the human population.

Nuclear factor-kappaB regulates cyclooxygenase-2 expression and cell proliferation in human gastric cancer cells

Nuclear factor-kappaB (NF-kappaB) is a transcriptional regulator of inducible expression of genes including cyclooxygenase-2 (COX-2), regulating cell proliferation. NF-kappaB is kept silent in the cytoplasm via interaction with the inhibitory protein IkappaBalpha and transmigrated into the nucleus upon activation. However, constitutive NF-kappaB has been found in the nucleus of some cancer cells. We investigated the role of NF-kappaB in COX-2 expression and cell proliferation in human gastric cancer AGS cells. AGS cells were treated with antisense oligodeoxynucleotide (AS ODN) or sense oligodeoxynucleotide (S ODN) for the NF-kappaB subunit p50, or they were transfected with a mutated IkappaBalpha gene (MAD-3 mutant) or a control vector, pcDNA-3. AGS cells were treated with COX-2 inhibitors such as indomethacine and NS-398 or prostaglandin E2. mRNA expression for COX-2, and protein levels for p50, IkappaBalpha, and COX-2 were determined by reverse transcription polymerase chain reaction and Western blot analysis. The NF-kappaB levels were examined by electrophoretic mobility shift assay. Thromboxane B2 (TXB2) and 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) levels were determined by enzyme-linked immunosorbent assay. Cell proliferation was assessed by viable cell counting, [3H] thymidine incorporation, and colony formation. The nuclear level of p50 decreased in AGS cells treated with AS ODN. The IkappaBa mutant was observed in cells transfected with the mutated IkappaBa gene. NF-kappaB was inhibited in cells treated with AS ODN or transfected with the mutated IkappaBalpha gene, compared with the cells treated with S ODN or transfected with control vector. Cell proliferation, mRNA expression and protein level of COX-2, and production of TXB2 and 6-keto-PGF1alpha were inhibited in cells treated with AS ODN or transfected with the mutated IkappaBalpha gene, which had lower NF-kappaB levels than cells treated with S ODN or transfected with control vector. COX-2 inhibitors suppressed cell proliferation and production of TXB2 and 6-keto-PGF1alpha, in a dose-dependant manner. Prostaglandin E2 prevented the inhibition of proliferation in cells treated with AS ODN or transfected with the mutated IkappaBalpha gene. In conclusion, NF-kappaB mediates COX-2 expression, which may be related to cell proliferation, in human gastric cancer cells.

The "aspirin" of the new millennium: cyclooxygenase-2 inhibitors

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin synthesis via the cyclooxygenase (COX) enzyme, the key to both therapeutic benefits and toxicity. COX enzyme exists in 2 isoforms, COX-1 and COX-2. COX-1 enzyme is thought to mediate "housekeeping" or homeostatic functions, and COX-2 is considered an inducible enzyme in response to injury or inflammation. COX-2 inhibitors are the "next-generation" NSAIDs that may selectively block the COX-2 isoenzyme without affecting COX-1 function. This may result in control of pain and inflammation with a lower rate of adverse effects compared with older nonselective NSAIDs. Rapidly evolving evidence suggests that COX-2 enzyme has a diverse physiologic and pathologic role. This article addresses the role of COX-2 enzyme in health and disease as well as the potential therapeutic value and safety issues related to COX-2 inhibition.

Cyclooxygenase 2 expression in Barrett's esophagus and adenocarcinoma: Ex vivo induction by bile salts and acid exposure

BACKGROUND & AIMS

Barrett's esophagus (BE) results from chronic, severe gastroesophageal reflux and predisposes to esophageal adenocarcinoma. Cyclooxygenase (COX)-2 is involved in chronic inflammation and epithelial cell growth. We investigated COX-2 expression in BE and esophageal adenocarcinoma to explore a potential relation between COX-2 expression and metaplasia or carcinogenesis.

METHODS

Endoscopic mucosal biopsy specimens of Barrett's intestinal metaplasia (n = 30), Barrett's dysplasia (n = 11), and esophageal adenocarcinoma (n = 5) were compared with normal esophagus (n = 46) and duodenum (n = 46) and analyzed by Western blotting and immunohistochemistry.

RESULTS

Immunoblots revealed constitutive expression of COX-2 in normal esophagus and duodenum. COX-2 protein expression was significantly higher in patients with Barrett's metaplasia, dysplasia, and adenocarcinoma compared with normal squamous esophageal or columnar duodenal epithelia and was heterogenous in different regions of the BE surface. Immunohistochemistry revealed prominent staining in the glands of BE, dysplasia, and adenocarcinoma and faint staining in the basal layers of squamous esophagus and the surface of the duodenum. In response to pulses of acid or bile salts in an ex vivo organ culture system, COX-2 expression increased significantly in BE tissues, and this effect was attenuated by the selective COX-2 inhibitor NS-398.

CONCLUSIONS

The results show COX-2 expression in normal esophagus, which increases significantly in BE and esophageal adenocarcinoma. COX-2 is regulated ex vivo by exposure to acid or bile salts.

Suppression of tumour development by substances derived from the diet--mechanisms and clinical implications

The concept that cancer can be prevented, or its onset postponed, by certain diet-derived substances is currently eliciting considerable interest. Agents which interfere with tumour development at the stage of promotion and progression in particular are of potential clinical value. As chemopreventive agents have to be administered over a long period of time in order to establish whether they possess efficacy in humans, it is of paramount importance to establish their lack of toxicity. The desire to select the best chemopreventive drug candidates for clinical trial, and the necessity to monitor efficacy in the short and intermediate term, render the identification of specific mechanism-based in vivo markers of biological activity a high priority. Antioxidation, inhibition of arachidonic acid metabolism, modulation of cellular signal transduction pathways, inhibition of hormone and growth factor activity and inhibition of oncogene activity are discussed as mechanisms by which the soya constituent genistein, the curry ingredient curcumin and the vitamin A analogue 13-cis retinoic acid exert tumour suppression. A better understanding of these mechanisms will help the establishment of screens for the discovery of new and better chemopreventive agents and the identification of surrogate markers to assess the outcome of clinical chemoprevention trials.

Cyclo-oxygenase and colon cancer: clues to the aspirin effect?

Epidemiological and experimental studies indicate an inverse relationship between the risk of colon cancer development and intake of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs). All NSAIDs are known inhibitors of cyclo-oxygenase, the enzyme responsible for converting arachidonic acid to prostaglandins. Prostaglandins have been implicated in the pathogenesis of colon cancer and it has been suggested that the preventive effect of NSAIDs is due to inhibition of cyclo-oxygenase activity. Cyclo-oxygenase exists in two different isoforms, cyclo-oxygenase-1 and cyclo-oxygenase-2, and data obtained during the last few years have suggested that cyclo-oxygenase-2 might be involved in both human and experimental colon carcinogenesis. The purpose of this review is to provide an update on recent studies regarding cyclo-oxygenase, in particular cyclo-oxygenase-2, in relation to colon cancer in humans and in experimental models.