Influence of phenotype at diagnosis and of other potential prognostic factors on the course of inflammatory bowel disease.

OBJECTIVES: Disease course in inflammatory bowel disease (IBD) is variable and difficult to predict. To optimize prognosis, it is of interest to identify phenotypic characteristics at disease onset and other prognostic factors that predict disease course. The aim of this study was to evaluate such factors in a population-based IBD group. METHODS: IBD patients diagnosed between 1 January 1991 and 1 January 2003 were included. A follow-up questionnaire was developed and medical records were reviewed. Patients were classified according to phenotype at diagnosis and risk factors were registered. Disease severity, cumulative medication use, and "surgical" and "nonsurgical" recurrence rates were calculated as outcome parameters. RESULTS: In total, 476 Crohn's disease (CD), 630 ulcerative colitis (UC), and 81 indeterminate colitis (IC) patients were diagnosed. In CD (mean follow-up 7.6 years), 50% had undergone resective surgery. In UC (mean follow-up 7 years), colectomy rate was 8.3%. First year cumulative recurrence rates per 100 patient-years for CD, UC, and IC were 53, 44, and 42%, respectively. In CD, small bowel localization and stricturing disease were negative prognostic factors for surgery, as was young age. Overall recurrence rate was increased by young age and current smoking. In UC, extensive colitis increased surgical risk. In UC, older age at diagnosis initially increased recurrence risk but was subsequently protective. CONCLUSIONS: This population-based IBD study showed high recurrence rates in the first year. In CD, small bowel localization, stricturing disease, and young age were predictive for disease recurrence. In UC, extensive colitis and older age at diagnosis were negative prognostic predictors.

Absence of nodular regenerative hyperplasia after low-dose 6-thioguanine maintenance therapy in inflammatory bowel disease patients.

BACKGROUND: The use of 6-thioguanine has been proposed as a rescue drug for inflammatory bowel disease patients. Initial data on short-term efficacy and toxicity of 6-thioguanine were promising; however, these have been challenged by reports concerning its potential hepatotoxic effect (nodular regenerative hyperplasia). We proposed that these histological liver abnormalities may well be dose- or level-dependent. AIMS: We performed a prospective multi-centre study on the hepatotoxic potential of long-term and (as compared with prior studies) low-dose 6-thioguanine use. PATIENTS: Inflammatory bowel disease patients using 6-thioguanine for at least 30 consecutive months and consenting to undergo a liver biopsy were enrolled. METHODS: Liver biopsy specimens were scored by two pathologists, unaware of clinical data. Laboratory parameters, determined prior to initiation of 6-thioguanine therapy and prior to biopsy, were reviewed. RESULTS: Twenty-eight biopsies were analysed. The majority of patients (89%) were azathioprine and/or 6-mercaptopurine intolerant inflammatory bowel disease patients. In 26 patients (93%) no signs of nodular regenerative hyperplasia were detected; in two additional patients nodular regenerative hyperplasia could not be excluded due to inconclusive pathological findings. The mean 6-thioguanine dosage, 6-thioguaninenucleotides level, duration of use and cumulative dosage were 19.5mg, 564 pmol/8 x 10(8) RBC, 38 months and 22491 mg, respectively. CONCLUSIONS: We have demonstrated that low-dose 6-thioguanine maintenance therapy in inflammatory bowel disease patients is not likely to be associated with induction of nodular regenerative hyperplasia. The induction of nodular regenerative hyperplasia appears to be 6-thioguanine dose or 6-thioguaninenucleotides level dependent.

Pancytopenia due to high 6-methylmercaptopurine levels in a 6-mercaptopurine treated patient with Crohn's disease.

In a 23-year-old female with colonic Crohn's disease 6-mercaptopurine 100 mg daily (1.7 mg/kg) was added to mesalamine and prednisolone therapy because of ongoing disease activity. One month later she had fever and a pancytopenia. 6-methylmercaptopurine ribonucleotides levels were extremely elevated (57,000 pmol/8x10(8) red blood cells) and 6-thioguanine nucleotides levels were subtherapeutically (126 pmol/8x10(8) red blood cells). Genotyping showed a wildtype thiopurine S-methyltransferase TPMT(H/H) (*1/*1) genotype and a wildtype inosine triphosphate pyrophosphatase gene. TPMT and inosine triphosphate pyrophosphatase activity were normal. The pancytopenia recovered spontaneously within a few weeks, parallel with decreasing 6-methylmercaptopurine ribonucleotides levels after interrupting 6-mercaptopurine treatment. Epstein-Barrvirus, Cytomegalovirus and Herpesvirus infections were excluded by serology. This is the first report of pancytopenia due to extremely high 6-methylmercaptopurine ribonucleotides levels. No relation was found with the genotype of TPMT and inosine triphosphate pyrophosphatase enzymes, which play key roles in the thiopurine metabolic pathway. Apparently, 6-methylmercaptopurine ribonucleotides metabolites can cause pancytopenia, as was already known for 6-thioguanine nucleotides.

Toxicity of 6-thioguanine: no hepatotoxicity in a series of IBD patients treated with long-term, low dose 6-thioguanine. Some evidence for dose or metabolite level dependent effects?

BACKGROUND: 6-Thioguanine is used in inflammatory bowel disease since 2001, with promising short-term results. In 2003, liver histology of some 6-thioguanine treated patients showed nodular regenerative hyperplasia. Recently, magnetic resonance imaging revealed nodular regenerative hyperplasia in patients with normal histology. AIMS: Investigating the presence of nodular regenerative hyperplasia in long-term 6-thioguanine treated patients. PATIENTS AND METHODS: Inflammatory bowel disease patients, using 6-thioguanine minimally 24 months, were asked to undergo liver biopsy and magnetic resonance imaging. RESULTS: Fourteen patients used 6-thioguanine minimally 24 months, 13 participated. Mean 6-thioguanine therapy duration, daily dose and 6-thioguanine nucleotide levels were: 36 months, 18.8 mg (0.28 mg/kg) and 705 pmol/8x10(8) erythrocytes, respectively. Liver histology and magnetic resonance imaging showed no nodular regenerative hyperplasia. DISCUSSION: Liver biopsy and magnetic resonance imaging showed no nodular regenerative hyperplasia in these long-term 6-thioguanine treated inflammatory bowel disease patients. 6-thioguanine dose and metabolite levels were lower compared with previous nodular regenerative hyperplasia reports, suggesting dose or metabolite level-dependent effects. Otherwise, nodular regenerative hyperplasia is related with inflammatory bowel disease itself and immunosuppressives, including azathioprine and 6-mercaptopurine. CONCLUSION: 6-Thioguanine is debated due to nodular regenerative hyperplasia. We found no nodular regenerative hyperplasia in inflammatory bowel disease patients with long-term, low dosed 6-thioguanine, suggesting metabolite level-dependent effects. Therefore, 6-thioguanine still seems useful, but in selected patients, intolerant for other immunosuppressives, low dosed and under close surveillance of metabolite levels and hepatotoxity.

Early prediction of thiopurine-induced hepatotoxicity in inflammatory bowel disease.

BACKGROUND: Hepatotoxicity, gastrointestinal complaints and general malaise are common limiting adverse reactions of azathioprine and mercaptopurine in IBD patients, often related to high steady-state 6-methylmercaptopurine ribonucleotide (6-MMPR) metabolite concentrations. AIM: To determine the predictive value of 6-MMPR concentrations 1 week after treatment initiation (T1) for the development of these adverse reactions, especially hepatotoxicity, during the first 20 weeks of treatment. METHODS: The cohort study consisted of the first 270 IBD patients starting thiopurine treatment as part of the Dutch randomised-controlled trial evaluating pre-treatment thiopurine S-methyltransferase genotype testing (ClinicalTrials.gov NCT00521950). Blood samples for metabolite assessment were collected at T1. Hepatotoxicity was defined by alanine aminotransaminase elevations >2 times the upper normal limit or a ratio of alanine aminotransaminase/alkaline phosphatase ≥5. RESULTS: Forty-seven patients (17%) presented hepatotoxicity during the first 20 weeks of thiopurine treatment. A T1 6-MMPR threshold of 3615 pmol/8 × 108 erythrocytes was defined. Analysis of patients on stable thiopurine dose (n = 174) showed that those exceeding the 6-MMPR threshold were at increased risk of hepatotoxicity: OR = 3.8 (95% CI: 1.8-8.0). Age, male gender and BMI were significant determinants. A predictive algorithm was developed based on these determinants and the 6-MMPR threshold to assess hepatotoxicity risk [AUC = 0.83 (95% CI: 0.75-0.91)]. 6-MMPR concentrations above the threshold also correlated with gastrointestinal complaints: OR = 2.4 (95% CI: 1.4-4.3), and general malaise: OR = 2.0 (95% CI: 1.1-3.7). CONCLUSIONS: In more than 80% of patients, thiopurine-induced hepatotoxicity could be explained by elevated T1 6-MMPR concentrations and the independent risk factors age, gender and BMI, allowing personalised thiopurine treatment in IBD to prevent early failure.

Mirizzi's syndrome.

A case is described emphasising rare complication of gallstone disease: the Mirizzi syndrome in which an impacted gallstone in the Hartmann's pouch or cystic duct causes common hepatic duct obstruction and by eroding a fistula. Diagnosis is made by endoscopic retrograde cholangiopancreatography and treatment includes cholecystectomy.

The pharmacokinetic effect of discontinuation of mesalazine on mercaptopurine metabolite levels in inflammatory bowel disease patients.

BACKGROUND: In vitro studies suggest interactions between mesalazine (mesalamine) and thiopurines by thiopurine S-methyltransferase (TPMT) inhibition, influencing the balance of hepatotoxic 6-methylmercaptopurine ribonucleotide and immunosuppressive tioguanine (thioguanine) metabolites. AIM: To examine the in vivo pharmacokinetic interaction between mesalazine and mercaptopurine. METHODS: A prospective study was performed in quiescent inflammatory bowel disease patients using the combination of mercaptopurine and mesalazine. Laboratory parameters, 6-methylmercaptopurine ribonucleotide and tioguanine levels and thiopurine S-methyltransferase activity in erythrocytes were measured at stable medication, after mesalazine discontinuation and mesalazine reintroduction, further mercaptopurine was continued. RESULTS: Seventeen patients were participated. Mean mercaptopurine dose was 0.78 mg/kg/day and median of mesalazine dose was 3000 mg/day. After mesalazine discontinuation, mean tioguanine levels changed significantly from 262 to 209 pmol/8 x 10(8) red blood cell, increasing to 270 after reintroduction. Mean 6-methylmercaptopurine ribonucleotide levels were 1422, 2149 and 1503 pmol/8 x 10(8) red blood cell respectively. Mean 6-methylmercaptopurine ribonucleotide/tioguanine ratio increased significantly from 6.3 at baseline to 11.2. Mean baseline thiopurine S-methyltransferase activity was 0.58 pmol/10(6) red blood cell/h and stable. All patients had wild-type thiopurine S-methyltransferase genotypes however, leucocyte counts were stable. DISCUSSION: A significantly higher tioguanine levels and improving 6-methylmercaptopurine ribonucleotide/tioguanine ratio were found during mesalazine/mercaptopurine combination. Theoretically, mesalazine inhibits thiopurine S-methyltransferase activity. In vivo thiopurine S-methyltransferase activity did not change, however. CONCLUSION: Mesalazine has synergistic effects on mercaptopurine therapy, but the mechanism is unclear. Combining these drugs may be further indication for mesalazine in inflammatory bowel disease treatment.

Therapeutic drug monitoring in patients with inflammatory bowel disease and established azathioprine therapy.

BACKGROUND AND OBJECTIVE: Azathioprine is widely used in the treatment of corticosteroid-dependent and refractory inflammatory bowel disease (IBD). The efficacy of this treatment is based on the production of 6-thioguanine nucleotides, but extremely elevated levels may cause bone marrow suppression. Other azathioprine metabolites, 6-methylmercaptopurine ribonucleotides, are associated with hepatotoxicity. Therapeutic drug monitoring (TDM) may be of help in optimising azathioprine treatment, but data on TDM in established azathioprine therapy are lacking. We therefore measured metabolite levels in a small cohort of patients established on azathioprine therapy. PATIENTS AND METHODS: 6-Thioguanine (6-TGN) and 6-methylmercaptopurine (6-MMP) levels in erythrocytes were measured in 15 IBD outpatients established on azathioprine therapy for at least 3 months at baseline and 1, 4 and 8 weeks after inclusion (mean duration of treatment 28 months; range 7-67 months). Disease activity was evaluated by the Crohn's Disease Activity Index (Crohn's disease) or Truelove-Witts (ulcerative colitis) scores. Metabolite levels were measured by modified high-performance liquid chromatography assay (HPLC). Primary outcome measures were 6-TGN and 6-MMP metabolite levels and 95% confidence intervals (CIs). SECONDARY OUTCOMES were correlations between metabolite levels, drug dose, disease activity and laboratory parameters and compliance. RESULTS: One patient had active disease during the study period. Eleven of 15 patients (73%) completed the 8-week study period. Dropout reasons were noncompliance in three patients (20%) and intolerance in one patient (7%). PRIMARY OUTCOMES: At baseline mean 6-TGN levels were 158 (95% CI 113, 203) pmol/8.10(8) RBC (red blood cells), steadily increasing over the 8-week study period, but not significantly. Two patients had zero levels. Another two had significantly increasing levels also suggesting noncompliance. Mean 6-MMP levels showed almost a similar pattern. At baseline, levels were 2213 (95% CI 722, 3704) pmol/8.10(8) RBC. SECONDARY OUTCOMES: A correlation was found between all RBC 6-MMP levels and azathioprine dose (mg/kg bodyweight) [r = 0.43, p = 0.001] and also between the 6-MMP/6-TGN ratio and azathioprine dose (mg/kg) [r = 0.36, p = 0.010). There was no correlation between RBC 6-TGN or 6-MMP levels and haematological parameters or disease activity scores. No hepatic, pancreatic or myelotoxicity occurred.Thirteen of 15 patients (87%) had baseline steady-state 6-TGN levels below the therapeutic threshold of 235 pmol/8.10(8) RBC. Forty percent (6/15) of our patients were noncompliant; TDM revealed this noncompliance in four of the six patients (27% of all patients). CONCLUSION: Our small study demonstrates that TDM may provide insight into individual pharmacokinetics. However, TDM does not seem to be useful in patients with IBD established on azathioprine therapy and without disease activity, although it may be helpful in cases of worsening IBD activity to elucidate noncompliance or inefficient treatment.

The pharmacokinetic effect of adalimumab on thiopurine metabolism in Crohn's disease patients.

BACKGROUND AND AIMS: A drug interaction between infliximab and azathioprine has previously been reported in Crohn's disease patients: the concentration of the main active thiopurine metabolites, the 6-thioguanine nucleotides (6-TGN), increased 1-3 weeks after the first infliximab infusion by 50% compared to baseline. The aim of this prospective study was to determine the effect of adalimumab on thiopurine metabolism in Crohn's disease patients, evaluated by 6-TGN and 6-methylmercaptopurine ribonucleotides (6-MMPR) concentration measurement. METHODS: Crohn's disease patients on azathioprine or mercaptopurine maintenance therapy starting with concomitant adalimumab treatment were included. 6-TGN and 6-MMPR concentrations were determined before initiation of adalimumab and after 2, 4, 6 and 12 weeks of combination therapy. The activity of three essential enzymes involving thiopurine metabolism, thiopurine S-methyltransferase (TPMT), hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and inosine-triphosphate pyrophosphatase (ITPase), was evaluated at baseline and week 4. Clinical outcome was evaluated by the Crohn's disease activity index and C-reactive protein concentrations at baseline, week 4 and week 12. RESULTS: Twelve Crohn's disease patients were analyzed. During the follow-up period of 12 weeks the median 6-TGN and 6-MMPR concentrations did not significantly change compared to baseline. TPMT, ITPase and HGPRT enzyme activity did not change either after 4 weeks. In two patients (17%) myelotoxicity was observed within 2-4 weeks, in whom both low therapeutic 6-TGN and 6-MMPR concentrations were found. CONCLUSIONS: In this study in Crohn's disease patients no pharmacokinetic interaction was shown between adalimumab and the conventional thiopurines, azathioprine and mercaptopurine.

The long-term effect of ursodeoxycholic acid on laboratory liver parameters in biochemically non-advanced primary biliary cirrhosis.

BACKGROUND AND AIMS: Ursodeoxycholic acid (UDCA) has an established effect on liver bio-chemistries in primary biliary cirrhosis (PBC). Few studies have evaluated long-term laboratory treatment effects and data beyond 6 years are not available. The aim of this study was to assess the long-term evolution of liver bio-chemistries during prolonged treatment with UDCA in biochemically non-advanced PBC. PATIENTS AND METHODS: Prospective multicenter cohort study of patients with PBC with pretreatment normal bilirubin and albumin, treated with UDCA 13-15 mg/kg/day. At yearly intervals, follow-up data including serum bilirubin, alkaline phosphatase (ALP), transaminases, albumin and IgM were collected. Data were analyzed with a repeated measurement model. RESULTS: Two hundred and twenty-five patients were included and followed during a median period of 10.3 years. Following 1-year treatment with UDCA 36-100% of the total biochemical improvement was achieved, the maximum response was observed after 3 years. After initial improvements, bilirubin and AST levels increased and albumin levels significantly decreased after 6-10 years. However, these changes were of limited magnitude. The beneficial effects on ALT and ALP were maintained while IgM continued to decrease. CONCLUSION: In non-advanced PBC the biochemical response to UDCA is maintained up to 15 years. The long-term evolution of bilirubin, albumin and ALT differs from that of ALP and AST. The mean IgM level normalised and levels continued to decrease during the period of follow-up.

Proton pump inhibitor use is associated with an increased risk for microscopic colitis: a case-control study.

BACKGROUND: Microscopic colitis causes chronic watery diarrhoea. Recent studies have suggested an aetiological role for various medications, including proton pump inhibitors, in the pathogenesis of microscopic colitis. AIM: To determine whether an association exists between microscopic colitis and proton pump inhibitor use in patients with documented microscopic colitis vs. age- and gender-matched controls. METHODS: In this retrospective case-control study, cases of microscopic colitis from a secondary and tertiary referral medical centre diagnosed in the last 5 years were reviewed. Demographic characteristics, clinical, histological and endoscopic records, as well as exposure to PPIs and NSAIDs were assessed. Controls from the population were matched to cases by gender and by age. RESULTS: During the investigated period, 136 cases were identified in both hospitals. Of these, 95 cases of microscopic colitis were retrieved for detailed analysis. Exposure to proton pump inhibitors at the time of the histological diagnosis was significantly higher in patients with collagenous colitis than in controls [38% vs. 13%, P < 0.001; adjusted OR of 4.5 (95% CI 2.0-9.5)]. CONCLUSIONS: This observation confirms the presumed association between microscopic colitis and PPI use, and it supports the possible aetiological role of PPI exposure in the development of microscopic colitis.

Fatigue and health-related quality of life in inflammatory bowel disease: results from a population-based study in the Netherlands: the IBD-South Limburg cohort.

BACKGROUND: The importance of fatigue in chronic disease has been increasingly recognized; however, little is known about fatigue in inflammatory bowel disease (IBD). The aim of the present study was to investigate the prevalence and severity of fatigue and the impact on health-related quality of life (HRQoL) in patients included in a population-based IBD cohort in the Netherlands. METHODS: IBD patients, diagnosed between January 1st, 1991, and January 1st, 2003, were followed up for a median of 7.1 years. They completed a questionnaire, which included a disease activity score, the Multidimensional Fatigue Inventory (MFI-20), the Inflammatory Bowel Disease Questionnaire (IBDQ), and the Short Form health survey (SF-36). Hemoglobin levels were recorded. RESULTS: Data were available in 304 Crohn's disease (CD), 368 ulcerative colitis (UC), and 35 indeterminate colitis (IC) patients. During quiescent disease, the prevalence of fatigue was nearly 40%. MFI-20 and HRQoL scores were significantly worse in IBD patients having active disease. In a multivariate analysis, disease activity was positively related with the level of fatigue in both CD and UC. In UC, anemia influenced the general fatigue score independently of disease activity. Disease activity as well as fatigue were independently associated with an impaired IBDQ. CONCLUSIONS: In IBD, even in remission, fatigue is an important feature. Both in CD and in UC, fatigue determined HRQoL independently of disease activity or anemia. This implies that in IBD patients physicians need to be aware of fatigue in order to better understand its impact and to improve the HRQoL.

Safe 6-thioguanine therapy of a TPMT deficient Crohn's disease patient by using therapeutic drug monitoring.

The immunosuppressive thiopurines, azathioprine (AZA) and 6-mercaptopurine (6-MP), have proven efficacy in steroid-dependant or refractory inflammatory bowel disease (IBD). In case of TPMT deficiency serious myelosuppression may occur. 6-thioguanine (6-TG), has been suggested in case of AZA and 6-MP resistant or intolerant patients. Our case demonstrates that very low dose 6-TG under close clinical surveillance and frequent therapeutic drug monitoring, may be a rescue drug for IBD-patients with low or without functional TPMT activity.

The outcome of esophagogastroduodenoscopy (EGD) in asymptomatic outpatients with iron deficiency anemia after a negative colonoscopy.

Background: Both iron deficiency and iron deficiency anemia require extensive investigation because of their possible association with gastrointestinal malignancy. If no other sources of blood loss are apparent, the gastrointestinal tract is examined to detect sources of occult blood loss. In the absence of gastrointestinal symptoms, the colon is first examined, especially in the elderly. The aim of this study was to determine the outcome of esophagogastroduodenoscopy (EGD) after a prior negative colonoscopy in outpatients without gastrointestinal complaints, referred due to iron deficiency anemia. Methods: Thirty-five patients (22 female and 13 male) with a median age of 71 years were studied over a 2-year period. Anemia was defined as a hemoglobin (Hb) level below 7.4 mmol/l in women or below 8.0 mmol/l in men and iron deficiency if one of the following was present: ferritin level equal to or below 20 µg/l for men and equal to or below 10 µg/l for women, a serum iron concentration equal to or below 45 µg/dl (8.1 µmol/l) with a transferrin saturation of 10% or less, or the absence of iron stores in bone marrow biopsy specimens. Patients with prior gastrointestinal disease or surgery, gastrointestinal symptoms, or other obvious causes of blood loss were excluded. Lesions that were considered to be potential sources of blood loss were clearly defined. Results: The mean Hb level of the 35 patients studied was 5.5 mmol/l (range 1.8-7.8 mmol/l). Abnormalities were found in 10 patients (28.6%), all of which were benign. Erosive and ulcerative lesions in the stomach, in a hiatal hernia, or in the esophagus were diagnosed in eight patients, benign villous adenoma was seen in one patient, and celiac disease in another, although duodenal biopsies were taken in only 15 patients. Erosions and/or ulcerations were found in four of 11 patients (36%) using NSAIDs and/or salicylates (ASA). Seventy percent of the lesions were found in elderly patients (>65 years), 56% of whom were using NSAIDs and/or ASA. Conclusions: EGD should always be performed in patients with iron deficiency anemia after a negative colonoscopy, although upper gastrointestinal malignancy will probably be an infrequent finding. The presence of a significant, treatable lesion is most likely in the elderly and in those with a history of NSAID or ASA use. Routine duodenal biopsies should be performed to further increase the outcome of EGD.

Helicobacter pylori does not mediate the formation of carcinogenic N-nitrosamines.

BACKGROUND: Both N-nitroso compounds and colonization with Helicobacter pylori represent known risk-factors for the development of gastric cancer. Endogenous formation of N-nitroso compounds is thought to occur predominantly in acidic environments such as the stomach. At neutral pH, bacteria can catalyze the formation of N-nitroso compounds. Based on experiments with a noncarcinogenic N-nitroso compound as end product, and using only a single H. pylori strain, it was recently reported that H. pylori only displays a low nitrosation capacity. As H. pylori is a highly diverse bacterial species, it is reasonable to question the generality of this finding. In this study, several genetically distinct H. pylori strains are tested for their capacity to form carcinogenic N-nitrosamines. MATERIALS AND METHODS: Bacteria were grown in the presence of 0-1000 microM morpholine and nitrite (in a 1 : 1 molar ratio), at pH 7, 5 and 3. RESULTS: Incubation of Neisseria cinerea (positive control) with 500 microM morpholine and 500 microM nitrite, resulted in a significant increase in formation of N-nitrosomorpholine, but there was no significant induction of N-nitrosomorpholine formation by any of the H. pylori strains, at any of the three pH conditions. CONCLUSION: H. pylori does not induce formation of the carcinogenic N-nitrosomorpholine in vitro. The previously reported weak nitrosation capacity of H. pylori is not sufficient to nitrosate the more difficulty nitrosatable morpholine. This probably also holds true for other secondary amines. These results imply that the increased incidence of gastric cancer formation that is associated with gastric colonization by H. pylori is unlikely to result from the direct induced formation of carcinogenic nitrosamines by H. pylori. However, this has to be further confirmed in in vivo studies.