Interplay between Helicobacter pylori and host gene polymorphisms in inducing oxidative DNA damage in the gastric mucosa
Infection by Helicobacter pylori is the most important risk factor for gastric cancer. However, only a small fraction of colonized individuals, representing at least half of the world's population, develop this malignancy. In order to shed light on host-microbial interactions, gastric mucosa biopsies were collected from 119 patients suffering from dyspeptic symptoms. 8-Hydroxy-2'-deoxyguanosine (8-oxo-dG) levels in the gastric mucosa were increased in carriers of H.pylori, detected either by cultural method or by polymerase chain reaction, and were further increased in subjects infected with strains positive for the cagA gene, encoding the cytotoxin-associated protein, cagA. Oxidative DNA damage was more pronounced in males, in older subjects, and in H.pylori-positive subjects suffering from gastric dysplasia. Moreover, 8-oxo-dG levels were significantly higher in a small subset of subjects having a homozygous variant allele of the 8-oxoguanosine-glycosylase 1 (OGG1) gene, encoding the enzyme removing 8-oxo-dG from DNA. Conversely, they were not significantly elevated in glutathione S-transferase M1 (GSTM1)-null subjects. Thus, both bacterial and host gene polymorphisms affect oxidative stress and DNA damage, which is believed to represent a key mechanism in the pathogenesis of gastric cancer. The interplay between bacterial and host gene polymorphisms may explain why gastric cancer only occurs in a small fraction of H.pylori-infected individuals.
Interplay between Helicobacter pylori and host gene polymorphisms in inducing
oxidative DNA damage in the gastric mucosa
, Silvio De Flora
, Cristina Cartiglia
Bianca Maria Are
, Mariagrazia Longobardi
, Ida Mura
, Maria Pina Dore
Antonio Mario Scanu
, Paolo Cossu Rocca
and Andrea Piana
Department of Health Sciences, University of Genoa, Via A. Pastore 1,
I-16132, Genoa, Italy,
Institute of Hygiene and Preventive Medicine,
Institute of General Medical Clinic and Medical Therapy,
Surgical Clinic and
Institute of Anatomy and Histopathology,
University of Sassari, 07100 Sassari, Italy
To whom correspondence should be addressed. Tel: +39 010 3538500;
Fax: +39 010 3538504;
Infection by Helicobacter pylori is the most important risk
factor for gastric cancer. However, only a small fraction
of colonized individuals, representing at least half of
the world’s population, develop this malignancy. In order
to shed light on host-microbial interactions, gastric
mucosa biopsies were collected from 119 patients suffering
from dyspeptic symptoms. 8-Hydroxy-2
(8-oxo-dG) levels in the gastric mucosa were increased in
carriers of H.pylori, detected either by cultural method or
by polymerase chain reaction, and were further increased
in subjects infected with strains positive for the cagA gene,
encoding the cytotoxin-associated protein, cagA. Oxidative
DNA damage was more pronounced in males, in older
subjects, and in H.pylori-positive subjects suffering from
gastric dysplasia. Moreover, 8-oxo-dG levels were sig-
niﬁcantly higher in a small subset of subjects having a
homozygous variant allele of the 8-oxoguanosine-glycosy-
lase 1 (OGG1) gene, encoding the enzyme removing 8-
oxo-dG from DNA. Conversely, they were not signiﬁcantly
elevated in glutathione S-transferase M1 (GSTM1)-null
subjects. Thus, both bacterial and host gene polymor-
phisms affect oxidative stress and DNA damage, which is
believed to represent a key mechanism in the pathogenesis
of gastric cancer. The interplay between bacterial and
host gene polymorphisms may explain why gastric cancer
only occurs in a small fraction of H.pylori-infected
Mortality rates for stomach cancer have steadily declined
during the last decades in most countries (1), due to the
so-called ‘unplanned triumph’ of medicine (2). Nevertheless,
this type of cancer, and chieﬂy gastric adenocarcinoma, still
remains the second commonest cancer in the world (3). After
the ﬁrst report suggesting an association between infection
with the Gram-negative bacterium Helicobacter pylori
(H.pylori) and both chronic gastritis and peptic ulcer (4),
H.pylori has become the ﬁrst bacterium linked to a human
cancer, and has been categorized by IARC as a Group 1
human carcinogen, with an attributable risk for gastric cancer
and mucosa-associated lymphoma tumor (MALT) of 50–60%
(5). This infection is considered to be the most important risk
factor for gastric cancer, also taking into account that
H.pylori colonizes the stomach of at least half of the world’s
population. However, the odds ratios characterizing the
association between H.pylori infection and gastric cancer
are somewhat weak (6,7).
A hallmark of infection by H.pylori, which remains in
the gastric lumen without invading the gastric mucosa, is
inﬁltration of neutrophiles and monocytes producing reactive
oxygen species (ROS) and nitrogen species (8). However, the
mechanisms underlying the involvement of H.pylori in the
pathogenesis of chronic type B gastritis and peptic ulcer
disease, followed by atrophic gastritis, intestinal metaplasia,
and carcinoma in a small proportion of infected individuals,
are poorly deﬁned (9). Therefore, there is a need to shed light
on the host-microbial interaction mechanisms. In particular,
the pathogenicity of H.pylori infection is modulated by
a variety of polymorphic genes belonging both to this
bacterium and to the human host.
The circular H.pylori genome contains 1 667 867 base
pairs and 1590 predicted coding sequences (10). The most
important H.pylori polymorphic genes associated with gastric
cancer are cagA and vacA (11). The cagA gene, encoding
the cytotoxin-associated protein, cagA, is commonly used as
a marker for the entire cag pathogenicity island (PAI),
containing several genes (cag E, G, H, I, L, M) required for
the release of proinﬂammatory cytokines such as interleukin
(IL)-8 from gastric epithelial cells (11). CagA increases cell
proliferation in the absence of a corresponding increase in
apoptosis, a ﬁnding that explains the enhanced risk for gastric
carcinoma associated with H.pylori cagA+ infection (12).
Furthermore, H.pylori cagA+ infected subjects have more
frequently p53 mutations than H.pylori cagA infected
subjects (13). The vacA gene, encoding for the active
vacuolating cytotoxin vacA, induces gastric epithelial cell
Human polymorphic genes that have been associated so
far with H.pylori-related gastric cancer include IL-1b,
IL-1 receptor b, tumor necrosis factor (TNF)-a, and IL-10
(11). These genes encode inﬂammatory cytokines and
activities that inhibit acid secretion and activate intracellular
pathways related to inﬂammation and apoptosis. Subjects
bearing adverse polymorphisms for these genes undergo more
severe consequences following H.pylori infection as com-
pared with subjects bearing wild-type polymorphisms (11).
Oxidative stress plays an important role in the patho-
genesis of H.pylori-induced mucosal damage (8,15–20).
Inﬂammation accompanying H.pylori infection represents a
Abbreviations: H.pylori, Helicobacter pylori; 8-oxo-dG, 8-hydroxy-2
deoxyguanosine; GSTM1, glutathione S-transferase M1; OGG1, 8-oxoguano-
sine-glycosylase 1; ROS, reactive oxygen species.
Carcinogenesis vol.28 no.4 pp.892–898, 2007
Advance Access publication November 24, 2006
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main source of oxidative stress. In addition, the chronic
gastritis induced by H.pylori infection is characterized by
overexpression in the gastric epithelium of nuclear genes
encoding for mitochondrial proteins (21). Mitochondrial
damage is important for H.pylori establishment and growth
because secretion of urease by H.pylori appears to be
insufﬁcient to adequately neutralize the local environment
(22). All factors related to H.pylori, human host and
oxidative stress interact with dietary factors. Therefore, the
global risk for the development of gastric cancer results
from the interaction between environmental exposure (e.g.
ingested nitrates) and endogenous risk factors including
polymorphic genes of both bacteria and host.
These pathogenetic considerations bear relevance for the
primary and secondary prevention of gastric cancer. As an
example, subjects infected by cagA+ H.pylori strains are
expected to receive more beneﬁt from H.pylori eradication
than those infected by cagA strains. Taking into account
that the clinical outcome is related to H.pylori genotypes (23),
anti-H.pylori therapy should be targeted to selected patient
groups considering the multifaced role of H.pylori (24).
Insofar, the genetic variables characterizing H.pylori
infection, including human and bacterial polymorphic genes
and DNA damage, have been mainly analyzed separately.
The aim of the herein reported study, whose outline is
summarized in Figure 1, was to analyze in vivo the interplay
among H.pylori and host susceptibility factors in inducing
DNA damage in the human gastric mucosa colonized by
H.pylori strains. To this purpose, we evaluated in parallel
oxidative DNA damage, H.pylori gene polymorphisms
(cagA and vacA), and human host polymorphisms involved
in the response to oxidative stress. These included the
glutathione S-transferase M1 (GSTM1) gene, which is
involved in detoxiﬁcation of electrophiles and ROS, and
8-oxoguanine DNA glycosylase 1 (OGG1)/AP lyase, which
catalyzes removal from DNA of 8-oxodeoxyguanosine, the
most abundant lesion generated by oxidative stress. DNA
damage of gastric cells was evaluated in terms of 8-hydroxy-
-deoxyguanosine (8-oxo-dG), a sensitive marker of DNA
oxidation. The results obtained indicate that the interaction
among H.pylori and human adverse polymorphisms is
crucial in inducing remarkable levels of oxidative DNA
Materials and methods
A total of 119 patients suffering from dyspeptic symptoms were enrolled in
the study. Dyspeptic symptoms included epigastric pain, upper abdominal
discomfort, nausea and vomiting, early satiety, heartburn, and regurgita-
tion lasting for at least 3 months. Patients receiving bismuth compounds,
antisecretory drugs, or antibiotics during the 4 weeks before endoscopy were
excluded. Other exclusion criteria included gastrointestinal surgery, preg-
nancy or lactation, regular use of acetylsalicylic acid and other non-steroidal
antiinﬂammatory drugs, malignancy, known allergy to penicillin, severe
liver, heart or kidney disease, or prior treatment for H.pylori infection. Of
the 119 subjects, 50 were males and 69 females. The age was in the 7–
84 years range, with an overall mean (±SD) of 49.7 ± 17.2 years. BMI was
available for all subjects. A questionnaire was administered regarding
smoking habits and diet, with particular reference to the intake of alcohol,
fruit and vegetables, salt, cuts and grilled food.
A written informed consent was obtained from all patients and the
protocol was approved by the Ethics Committee of the Faculty of Medicine,
University of Sassari, Italy.
Collection of gastric mucosa biopsies
For each patient, eight biopsy specimens, consisting of superﬁcial mucosa,
were collected, four of which from the antrum, two from the angulus, and
two from the corpus of the stomach. Biopsy specimens for histology were
immediately ﬁxed in 10% buffered formalin. Two biopsies from the antrum,
two from the angulus and two from the corpus were stained with
hematoxylin and eosin and with Giemsa to grade the density of H.pylori.
The stage of gastritis was evaluated by using the Sidney system (25). During
histological examination, the presence of dysplasia, intestinal metaplasia,
and inﬂammation were assessed and graded.
One antral biopsy was immediately transported in Portagerm pylori
(bioMerieux, S.p.A., Rome, Italy) for culture, streaked on Columbia agar
plates (bioMerieux) and incubated for 3 ± 5 days at 37
C, in an atmosphere
of 12% CO
and 100% relative humidity. Bacterial growth was identiﬁed
as H.pylori on the basis of colony morphology and positive biochemical
reactions for catalase, urease, oxidase, g-glutamyltransferase, alkaline
phosphatase and negative hippurate hydrolysis and nitrate reduction tests.
The minimum inhibitory concentration for amoxicillin, clarithromycin,
tetracycline and metronidazole was determined by the E-test (AB Biodisk,
Uppsala, Sweden). The breakpoints used to deﬁne resistant H.pylori were
as follows: amoxicillin resistance, MIC >8 mg/ml; clarithromycin resistance,
MIC >2 mg/ml; metronidazole resistance, MIC >8 mg/ml; tetracycline
resistance, MIC >2 mg/ml (26).
PCR analyses of H.pylori
Antral biopsy DNA was extracted using the QIAmp tissue Kit (QIAGEN,
Chatsworth, CA). Speciﬁc primers for H.pylori 16S rRNA (27) were used
to amplify DNA fragments of 521 bp. Two sets of oligonucleotide primers
were designed to amplify a conserved region in the vacA gene. The ﬁrst set,
VAGF and VAGR (27), was used to amplify a 570 bp product for m1 and
645 bp product for m2 from the middle region of the vacA gene. The second
set, VA1F and VA1R (28), was used to amplify a 259 bp product for s1 and
286 bp product for s2 from the signal sequence region of the vacA gene.
One set of primers, F1 and B1, was also used for the ampliﬁcation of the
conserved region of the cagA gene (29). Following initial denaturation at
C for 1 min, each reaction consisted of 35 cycles at 94
C for 1 min,
C for VA1F/R, VAGF/R and 55
C for F1/B1) and extension
for 2-3 min and then at 72
C for 10 min.
Each PCR mixture was subjected to gel electrophoresis on 1% agarose
gels. A 100 bp DNA ladder (Sigma-Aldrich, St Louis, MO) was used as a
reference marker. Two previously described PCR assays for vacA signal and
mid-region genotyping were combined in a multiplex format (28). VacA
alleles were ampliﬁed in a 50 ml reaction containing: 5 ml DNA extract from
gastric biopsy; 200 mM (each) dNTP (GibcoBRL Life Technologies, Paisley,
UK); 0.3 mM each of the primers VA1-F and VA1-R and 0.48 mM each
of the primers VAG-F and VAG-R (MWG Biotech, Ebersberg, Germany);
2.0 mM MgCl
;20mM Tris–HCl, pH 8.4; 50 mM KCl; 0.2% v/v glycerol;
and 1 U Taq polymerase (GibcoBRL). Thermal cycling conditions were
Fig. 1. Outline of the study design.
H.pylori and host gene polymorphisms in gastric mucosa
at UniversitÃ degli Studi di Sassari on October 29, 2012http://carcin.oxfordjournals.org/Downloaded from
C for 5 min followed by 35 cycles at 94
C (30 s), 53
C (1 min) and
C (1.5 min) and a ﬁnal elongation at 72
C for 5 min. The PCR products
were separated by electrophoresis on 2% agarose gel in TBE buffer (90 mM
Tris–HCl, 90 mM boric acid and 2 mM EDTA), and stained in ethidium
bromide. American Type Collection Center (ATCC) H.pylori strains were
subjected to ampliﬁcation and used as positive controls.
Detection of 8-oxo-dG in gastric mucosa
Antral biopsy DNA was puriﬁed by a phenol–chloroform procedure using an
automatic DNA extractor (Genepure 341, Applied Biosystems, Foster City,
CA) working under oxygen-free helium atmosphere. Due to the small size
of collected biopsies (1–2 mm) the total amount of DNA extracted was
3.05 ± 2.23 mg (mean ± SD) only. Accordingly, 8-oxo-dG was detected by
P-post-labeling, as previously described (30,31). Brieﬂy, DNA (1–2 mg)
was depolymerized to 3
-monophosphate nucleotides by incubation with
micrococcal nuclease and spleen phosphodiesterase at 37
C for 3.5 h.
Unmodiﬁed dGp nucleotides were selectively removed by incubation with
80% v/v triﬂuoracetic acid for 10 min at room temperature. The samples
were dried by vacuum centrifugation and 3
were labeled by incubation with T4 polynucleotide kinase in the presence of
P (64 mCi, speciﬁc activity 750 Ci/mmol) (ICN, Irvine, CA) at 37
for 40 min. The mixture was subjected to nuclease P1 digestion (2.7 U at
C for 60 min).
P labeled 8-oxo-dG was puriﬁed by monodirectional
thin layer chromatography in unbuffered 1.5 M formic acid, identiﬁed by
electronic autoradiography (InstantImager, Packard, Meriden, CT) and
quantiﬁed by calculating the ratio of
P-labeled 8-oxo-dG to
Positive reference standards were obtained by incubating calf thymus
DNA with 1 mM CuSO
and 50 mM H
and using an authentic 8-oxo-dG
reference standard (National Cancer Institute Chemical Carcinogen Refer-
ence Standard Repository, Midwest Research Institute, Kansas City, MO).
DNA-free samples were used as negative controls. Untreated bacterial DNA
extracted from Salmonella typhimurim was used as reference DNA having
low amounts of 8-oxo-dG. Each DNA sample was analyzed for 8-oxo-dG
in two separate experiments.
GSTM1 deletion polymorphism was analyzed by testing an aliquot of gastric
mucosa DNA by quantitative real time PCR (QPCR). The following primers
(TIB MolBiol, Genoa, Italy) were used to amplify a 230 bp DNA sequence
speciﬁc for GSTM1:P1(5
). The PCR reaction was performed
in a total volume of 100 ml containing 0.1 mg DNA, ATP, GTP, TTP and
CTP 200 mM, 10 ml DMSO, 50 mM MgCl
, and 2 U Platinum Taq DNA
polymerase (Life Technologies, Rockville, MD) and 1 ml of diluted Sybr
green as ﬂuorescent tracer to quantify the PCR ampliﬁcation products.
Polymerase was hot-start activated and ampliﬁcation was performed at 94
for 1 min, 53
C for 1 min and 72
C for 1 min for 40 cycles, using a rotating
real-time thermocycler (Corbett Research, Mortlake, Australia). The ﬂuores-
cent signal was detected before each denaturation cycle. The speciﬁcity of
the reaction products was tested by analyzing the melting curves of PCR
products. GAPDH housekeeping gene was used in all genotype analyses as
inner positive control.
The OGG1 gene Ser326Cys polymorphism, resulting from a C!G
transversion in exon 7, was evaluated by QPCR using a couple of gene-
speciﬁc molecular beacons discriminating the occurrence of this genetic
variant either on both alleles (homozygous mutant) or on one allele only
(heterozygous) or on no allele (wild-type). The sequences of PCR probes
containing molecular beacons were: h-OGG1-Cys(G)mut: 5
Ser(C)wt (wild-type): 5
. The PCR primers sequences were: Primer 1
) and Primer 2 (5
). The reaction mixture (50 ml) contained: 5 ml10· PCR
buffer, 0.4 ml 100 mM dNTP mix, 2 ml 50 mM MgCl
,1ml 10 mM Primer 1,
1 ml 10 mM Primer 2, 1 ml Beacon wild-type, 1 ml Beacon mut, 0.5 m l
Platinum Taq polymerase, 1 ml (200 ng) DNA and 37.1 ml sterile water.
The hot-start reaction was performed at 94
C for 2 min, followed by
45 cycles at 94
C for 30 s, 65
C for 20 s, 55
C for 30 s and 72
C for 30 s.
The HEX signal was acquired at the end of the 65
C step and the FAM
signal at the end of the 55
Comparisons of quantitative variables among different groups were evaluated
by ANOVA and Student’s t-test for unpaired data after checking the
normality of the distribution by skew kurtosis analysis. Correlations between
continuous variables were tested by linear regression analysis. Differences of
frequency distributions among nominal variables were tested by Chi-squared
test. All statistical analyses were performed using the Statview software
(Abacus Concept, Berkeley, CA).
Prevalence of H.pylori infection as related to gender, age
and histopathol ogy
Of the 119 subjects under study, 69 (58.0%) had H.pylori
detectable by culturing antral biopsies, and 77 (64.7%) were
positive for H.pylori, as detected by PCR. There was
agreement between H.pylori culture and PCR in 69 positive
cases and in 42 negative cases. The PCR was positive in the
absence of H.pylori growth in culture in eight cases, while
no positive H.pylori culture was obtained in PCR-negative
Table I (ﬁrst two columns) shows the prevalence of
H.pylori positivity by PCR as related to gender, age and
histopathological alterations of the gastric biopsies examined.
The H.pylori infection prevalence was similar in males (33
out of 50, i.e. 66.0%) and females (44 out of 69, i.e. 63.8%).
The age distribution was almost identical in H.pylori-
negative and H.pylori-positive subjects. The prevalence of
positivity for H.pylori culture was affected by the gastritis
stage, being 0% in Stage 1, 55% in Stage 2, 65% in Stage 3,
and 100% in Stage 4 (P < 0.001). Likewise, the prevalence
of PCR positivity was 0% in Stage 1, 82% in Stage 2, 95%
in Stage 3, and 100% in Stage 4 (P < 0.001).
As shown in Table I, the mean stage of gastritis and the
prevalence of severe gastritis (Stages 3–4) were signiﬁcantly
more elevated in H.pylori-positive subjects than in H.pylori-
negative subjects. In contrast, occurrence of either dysplasia
or enteroid metaplasia of the gastric mucosa was not
signiﬁcantly affected by H.pylori infection. The stage of
gastritis (mean ± SD) was slightly but signiﬁcantly more
advanced in males than in females (2.6 ± 0.7 versus 2.3 ±
0.7, P < 0.05). The subjects affected by dysplasia were older
than those unaffected (63.6 ± 6.3 versus 48.9 ± 1.6 years
among all subjects, P < 0.05), a difference that was not
signiﬁcant in H.pylori-positive subjects (59.7 ± 3.8 versus
48.9 ± 2.9 years) but borderline to statistical signiﬁcance in
H.pylori-negative subjects (66.5 ± 11.1 versus 48.8 ± 2.9 years,
P ¼ 0.07).
Table I. Characteristics of the examined subjects as related to detection
of H.pylori by PCR in gastric biopsies and positivity for cagA
Characteristics of subjects H.pylori-
Total number (males/females) 42 (17/25) 77 (33/44) 60 (25/35)
Age (years) (mean ± SD) 50.5 ± 18.7 49.3 ± 16.6 52.2 ± 16.0
Stage of gastritis (mean ± SD) 2.1 ± 0.7 2.5 ± 0.6
2.6 ± 0.6
Subjects affected by severe
gastritis (Stages 3–4) [n (%)]
12 (28.6) 34 (44.2)
Subjects affected by dysplasia
4 (9.5%) 3 (3.9%) 3 (5.0%)
Subjects affected by
enteroid metaplasia [n (%)]
8 (19.1%) 17 (22.1%) 13 (21.7%)
P < 0.01, compared with H.pylori-negative.
P < 0.05, compared with H.pylori-negative.
A.Izzotti et al.
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Sensitivity of H.pylori isolates to antibiotics and prevalence of
VacA and CagA genotypes
Of the 59 H.pylori isolates tested for sensitivity to 4
antibiotics, none was resistant to either tetracyclin or
amoxicillin, while 2 of them (3.4%) were resistant to either
clarythromycin or metronidazol. No signiﬁcant relationship
was detected between antibiotic resistance and other tested
variables, including H.pylori genotypes and host age, gender,
gene polymorphisms, stage of gastritis and oxidative DNA
damage in the gastric mucosa.
All the H.pylori strains detected displayed a s2-m2
polymorphism for the vacA gene, while the s1-m1 adverse
polymorphism was not detected in any strain.
The cagA genotype was present in 60 of the 76 tested
H.pylori strains positive at PCR (79.0%). As shown in
Table I (third column), positivity of H.pylori for cagA was
independent of age and did not affect the stage of gastritis
and occurrence of either dysplasia or enteroid metaplasia of
the gastric mucosa.
Oxidative DNA damage in gastric biopsies
The mean (±SE) levels of 8-oxo-dG in the gastric biopsies of
all 119 examined subjects were 4.0 ± 0.4 8-oxo-dG/10
nucleotides. A variety of factors, including gender, age,
histopathological alterations, H.pylori infection and host,
and H.pylori gene polymorphisms, affected the intensity of
oxidative DNA damage. Table II summarizes the host and
H.pylori factors that signiﬁcantly affected this end-point
either in all subjects or in H.pylori-infected subjects.
8-Oxo-dG levels were signiﬁcantly higher in the 69
females than in the 50 males recruited for the study. By
assuming a cut-off value of 50 years, which was approxi-
mately the overall mean age of all subjects, 8-oxo-dG levels
were higher in subjects aged 50 years than in subjects aged
<50 years. This difference did not reach the statistical
signiﬁcance threshold among all subjects (4.3 ± 0.6 versus
3.1 ± 0.4, means ± SE) but was signiﬁcant in H.pylori-
infected subjects (Table II). As shown in Figure 2, there was
no correlation between age and 8-oxo-dG in H.pylori-negative
subjects (r ¼0.211, not signiﬁcant), but a signiﬁcant corre-
lation was recorded in H.pylori-positive subjects (r ¼ 0.285,
P < 0.05). As to histopathological alterations, oxidative DNA
damage was signiﬁcantly increased in H.pylori-positive
subjects bearing gastric dysplasia (Table II), while the
difference was not signiﬁcant in H.pylori-negative subjects
(2.5 ± 0.6 versus 1.5 ± 0.5). Smoking habits and dietary
factors were not signiﬁcantly associated with either 8-oxo-dG
levels in the gastric mucosa or histopathological alterations.
Alcohol consumption was moderate in all subjects. There
was an inverse correlation between 8-oxo-dG levels and
BMI (BMI, r ¼0.378, P < 0.05). BMI was higher in
males (26.0 ± 0.7, mean ± SE) than in females (23.2 ± 1.0,
P < 0.05), and in ex-smokers (27.0 ± 0.7) than in either
current smokers (23.9 ± 1.4, P < 0.01) or never smokers
(22.8 ± 1.0, P < 0.01). Moreover, BMI signiﬁcantly correlated
with age (r ¼ 0.466, P < 0.01).
H.pylori infection and the H.pylori genotype had a pro-
found effect on oxidative DNA damage in gastric mucosa. In
fact, as shown in Table II, 8-oxo-dG levels were almost
twice as high in H.pylori-infected subjects, irrespective of the
H.pylori detection method (culture or PCR), as compared
with H.pylori-negative subjects. Within H.pylori-positive
Table II. Host and H.pylori (HP)-related factors affecting 8-oxo-dG levels in the gastric mucosa
Variability factor Number of subjects 8-oxo-dG/10
nucleotides (mean ± SE) Fold increase
All subjects 119
Males versus females 50 versus 69 3.0 ± 0.4 versus 4.6 ± 0.6
HP-negative versus HP-positive (culture) 50 versus 68 2.6 ± 0.4 versus 4.7 ± 0.5
HP-negative versus HP-positive (PCR) 42 versus 76 2.4 ± 0.4 versus 4.6 ± 0.5
OGG1 polymorphism: wild-type versus mutant 82 versus 6 3.7 ± 0.5 versus 9.9 ± 2.9
OGG1 polymorphism: heterozygous versus mutant 31 versus 6 3.5 ± 0.6 versus 9.9 ± 2.9
GSTM1 polymorphism: positive versus null 63 versus 56 2.3 ± 0.4 versus 3.5 ± 0.5 1.5
50 versus 69
HP-infected subjects 76
Age (<50 versus 50 years) 35 versus 41 3.2 ± 0.4 versus 5.3 ± 0.7
Gastric dysplasia: unaffected versus affected 71 versus 5 4.4 ± 0.4 versus 9.3 ± 3.4
HP cagA-negative versus cagA-positive 16 versus 60 1.7 ± 0.3 versus 5.1 ± 0.5
OGG1 polymorphism: wild-type versus mutant 52 versus 5 4.2 ± 0.5 versus 12.6 ± 1.8
OGG1 polymorphism: heterozygous versus mutant 19 versus 5 3.7 ± 0.6 versus 12.6 ± 1.8
GSTM1 polymorphism: positive versus null 32 versus 44 2.7 ± 0.4 versus 4.0 ± 0.7 1.5
P < 0.05.
P < 0.01.
P < 0.001.
Fig. 2. Correlation between age and oxidative DNA damage in the
gastric mucosa of 119 gastritis patients, either positive or negative for
H.pylori (HP). The equations of the regression lines are y ¼ 3.76 0.026x;
r ¼0.211; not signiﬁcant (HP negative) and y ¼ 1.18 + 0.063x;
r ¼ 0.285; P < 0.05 (HP positive).
H.pylori and host gene polymorphisms in gastric mucosa
subjects, 8-oxo-dG levels were as much as 3-fold higher in
subjects infected by cagA-positive strains.
Prevalence of GSTM1 and OGG1 polymorphisms and their
influence on oxidative DNA damage
Almost half of the examined subjects (46.8%) had a GSTM1-
null genotype. The OGG1 polymorphism was detected as
wildtype in the 68.8% of the examined subjects, as
heterozygous in the 26.0%, and as homozygous mutant in
When comparing GSTM1-null subjects with GSTM1-
positive subjects, a trend for an increased oxidative DNA
damage in GSTM1-null subjects was observed in all and HP
positive subjects, without reaching the statistical signiﬁcance
threshold (Table II). Conversely, homozygous mutation for
the OGG1 Ser326Cys polymorphism exerted a signiﬁcant
and strong effect on oxidative DNA damage as compared with
either wild-type or heterozygous subjects. This effect was
observed both in all subjects and in H.pylori-positive subjects
(Table II), whereas no signiﬁcant difference was noted in
H.pylori–free subjects (wild-type 1.7 ± 0.6, heterozygous
3.0 ± 1.5, and homozygous 1.7 ± 0.1 8-oxo-dG/10
nucleotides). Heterozygosity for OGG1 did not affect oxida-
tive DNA damage, no signiﬁcant difference between wild-
type and heterozygous subjects being detected in either
H.pylori-negative, H.pylori-positive, or all subjects.
Oxidative damage is a crucial step of H.pylori pathogenicity,
being mechanistically related to the link between H.pylori
infection and gastric carcinoma (8). Occurrence of H.pylori-
related oxidative DNA damage has been so far demonstrated
under different experimental conditions and by using various
methodological approaches (8,15–21). In addition, the role
of oxidative stress in the pathogenesis of stomach cancer is
supported by epidemiological data showing that this cancer
is prevented by dietary antioxidants (32). The results of the
present study, evaluating the levels of 8-oxo-dG in gastric
biopsies from 119 subjects, conﬁrm that this indicator of
oxidative DNA damage is increased in gastric samples
colonized with H.pylori, as detected both by cultural method
and, with a higher sensitivity, by PCR. In addition, our
results shed light on the interplay between H.pylori and host
susceptibility factors in the induction of oxidative DNA
8-Oxo-dG is a modiﬁed nucleoside resulting from oxida-
tive DNA damage, which may affect the initiation step of
H.pylori-related gastric carcinogenesis. However, it is most
likely that this molecular marker of exposure may also reﬂect
oxidative stress and inﬂammatory mechanisms involved in
the H.pylor i-host interaction. These mechanisms play a major
role by inducing epigenetic effects and signal transduction
alterations that contribute to the promotion of the multistage
and multimechanistic carcinogenesis process (33,34).
Of the investigated H.pylori gene polymorphisms, we
could not evaluate the role of vacA because all detected
H.pylori strains were vacAs2 . The ﬁnding that H.pylori
strains circulating in Sardinia are devoid of vacA-related
adverse activity contributes to explain the low incidence of
gastric cancer in this region (35), which contrasts with the
high prevalence of H.pylori infection in the population
(36,37). In fact, vacs2/m2 H.pylori strains are the least
virulent (38,39). A similar discrepancy between H.pylori
infection prevalence and gastric cancer prevalence has been
reported in other geographic areas, for instance in certain
African, Indian and Latin American populations. This
phenomenon has been referred to as the ‘African enigma’ (3).
Our ﬁnding that 8-oxo-dG levels were higher in the antral
mucosa specimens colonized with cagA+ H.pylori strains
than in those colonized with cagA H.pylori strains conﬁrms
the crucial role of this gene as a pathogenetic determinant
triggering biological effects amenable to the carcinogenesis
process. Cag A has been demonstrated to be associated with
severe gastritis (40) and peptic ulcer (41) due to the fact that
this gene encodes proteins that increase gastric mucosa
inﬂammation and stimulate the secretion of higher levels
of proinﬂammatory cytokines (42). CagA+ H.pylori induced
the production of various cytokines by the gastric mucosa,
such as IL-1beta and IL-8, while cagA strains were weak
inducers of these molecules (43). A correlation exists
between infection with cagA+ strains and increase of protein
alterations, expression of IL-8 and inducible nitric oxide
synthase (iNOS) and gastric pathology (44). Occurrence of
higher levels of oxidized and nitrated proteins in H.pylori
cagA+ than in H.pylori cagA infected subjects is associated
with a signiﬁcant oxidative and nitrative stress in the stomach
These mechanisms explain why, in the population of
dyspeptic subjects investigated in the present study, H.pylori
infection was strictly related to the appearance of gastritis,
as demonstrated by the increasing frequency of H.pylori
positivity from Stage 1 to Stage 4 gastritis. This is consistent
with the conclusion that induction of inﬂammation is a
primary pathogenetic mechanism of H.pylori, as further
supported by the ﬁnding that oxidative damage was signiﬁ-
cantly increased in dysplastic mucosa, but only in H.pylori-
infected subjects. While severe gastritis was signiﬁcantly
more frequent in H.pylori carriers, no correlation of H.pylori
infection with either dysplasia or enteroid metaplasia was
found. This ﬁnding may be related to the different
mechanisms involved in these long-term histopathological
alterations. In fact, gastric dysplasia was related to age in
H.pylori-negative subjects, while the inﬂuence of bacterial
infection was prevailing on age-related factors in H.pylori-
A host-related factor affecting oxidative DNA damage was
represented by age. In fact, 8-oxo-dG levels in gastric
mucosa were higher in subjects aged >50 years than in
younger subjects, but the difference was statistically signiﬁ-
cant only in H.pylori-infected subjects. A similar relationship
between age and DNA damage, detected by comet assay, has
been recently reported in a group of Brazilian patients (45).
These ﬁndings suggest that H.pylori infection represents a
risk factor triggering the chronic accumulation of DNA
damage, leading to degenerative processes of the gastric
mucosa and cancer.
As to the investigated host gene polymorphisms, irrespec-
tive of H.pylori infection, 8-oxo-dG levels were not
signiﬁcantly higher in GSTM1-null subjects, compared with
GSTM1 carriers. Previous studies indicated that the GSTM1
homozygous deletion, either alone or in association with the
GSTP1-null polymorphism, did not confer an increased risk
for gastric cancer in Japanese (46) or Chinese (47) subjects.
In an Italian population, GSTM1 was associated with an
A.Izzotti et al.
increased gastric cancer risk but only in combination with
GSTT1 for the double null genotype (48).
Conversely, in spite of the low frequency of the OGG 1
homozygous Ser326Cys polymorphism, our study provided
evidence that this variant allele is associated with a
remarkable and signiﬁcant increase in the occurrence of
oxidative DNA damage in case of H.pylori infection. Note
that the necessity of collecting gastric biopsies limited the
size of the study population but allowed us to evaluate in
parallel 8-oxo-dG in the target tissue and the gene encoding
the enzyme removing this modiﬁed nucleoside from DNA.
Previous studies reported that this polymorphism is associ-
ated with an increased risk of various cancers (49,50). In
a Chinese population, a borderline inﬂuence of OGG1
polymorphism on stomach cancer was related to dietary risk
factors (51). The possible role of OGG1 in gastric carcino-
genesis is supported by the selective upregulation of its
expression in malgun cells, the morphologically modiﬁed
epithelial cells characterizing H.pylori gastritis. Malgun cells
represent a typical morphological change involved in an
early stage of carcinogenesis (52). In this view, our results
indicate a role of OGG1 homozygous mutant polymorphism
in increasing DNA damage but only as related to H.pylori
In conclusion, our study provides evidence that induction
of oxidative DNA damage in gastric mucosa is a pathogen-
etic mechanism that mainly depends on the highly pathogenic
H.pylori cagA+ strains. However, genetic polymorphisms of
the host related to the repair of oxidative DNA damage do
also play an important role. The interplay between H.pylori
and host genetic polymorphisms contributes to explain why
gastric cancer only occurs in a small fraction of H.pylori-
This study was supported by Associazione Italiana per la Ricerca sul Cancro
Conﬂict of Interest Statement: None declared.
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Received September 20, 2006; revised October 18, 2006;
accepted October 20, 2006
A.Izzotti et al.