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1 Division of Gastroenterology, Department of Therapeutic Medicine, Nagoya University Graduate School of Medicine and 2 Department of Endoscopy, Nagoya University Hospital, Nagoya, Japan
Requests for reprints: Naoki Ohmiya, Division of Gastroenterology, Department of Therapeutic Medicine, Nagoya University Graduate School of Medicine, 65 Tsuruma-cho, Showa-ku, Nagoya, Aichi, 466-8550 Japan. Phone: 81-52-744-2172; Fax: 81-52-744-2180. E-mail: nohmiya{at}med.nagoya-u.ac.jp
| Abstract |
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| Introduction |
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As one candidate for the host genetic factors, recent reports have revealed that pro- and anti-inflammatory cytokine [interleukin (IL)-1B, IL-1RN, tumor necrosis factor (TNF) A, and IL-10] polymorphisms are associated with a risk for atrophic gastritis and gastric cancer (5-8). Proinflammatory cytokines such as IL-1ß, TNF-
, and IL-8 are up-regulated during chronic H. pylori infection (9, 10), and play a crucial role in inflammation of gastric mucosa. In addition, T helper cell 1 phenotypepredominant immune response, generally observed in H. pylori-positive gastritis (11), is possibly associated with the development of cancer (12).
IL-8, a member of the CXC chemokine family, was originally identified as a potent chemoattractant for neutrophils and lymphocytes (13, 14). Subsequent studies confirmed that IL-8 could also induce cell proliferation (15) and migration (16), as well as angiogenesis (17). Some studies have reported that IL-8 251 T > A polymorphism in the promoter region is associated with respiratory syncytial virus bronchiolitis (18), prostate cancer (19), enteroaggregative Escherichia coli diarrhea (20), and colorectal cancer (21). Furthermore, the IL-8 251 A allele tended to be associated with increased IL-8 production by lipopolysaccharide-stimulated whole blood (18). Concerning the role of IL-8 polymorphisms in gastric carcinogenesis, one recent study has reported that the IL-8 251 A allele increases the risk of non-cardia and intestinal-type gastric cancer (22). From these findings, we hypothesized that the IL-8 251 T > A polymorphism could affect each stage of gastric carcinogenesis, the extent of atrophic gastritis as a precancerous lesion (23-25), and the risk of development and the different growth of gastric cancer.
In this case-control study, we determined IL-8 251 T/A genotype, as well as IL-1B 511 C/T genotype and IL-1RN variable number of tandem repeat region in intron 2, and elucidated the relationship of these genetic variants to the risk of atrophic gastritis and to the risk of gastric cancer, including its subtypes and clinicopathologic features. We also evaluated the effects of IL-8 polymorphism on IL-8 production in the H. pylori-infected gastric mucosa and on histologic degree of gastritis in the noncancerous gastric mucosa adjacent to cancer of surgical specimens.
| Materials and Methods |
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Patients with gastric cancer (mean age, 62 years; range, 30-91 years; male/female, 291/105) had been diagnosed histologically and treated at Nagoya University Hospital (Nagoya, Japan) between January 1999 and January 2002. Gastric cancers were histologically classified according to Lauren's classification (26) and the Japanese Classification of Gastric Carcinoma (27); detailed information about TNM staging, anatomic location, venous and lymphatic invasion, lymph node and distant metastasis, and peritoneal dissemination was available. Furthermore, in noncancerous gastric mucosa adjacent to cancer from 194 surgical specimens, the degree of neutrophil infiltration, mononuclear cell infiltration, atrophy, and intestinal metaplasia were assessed according to the updated Sydney system (28), and were scored as follows: normal, 0; mild, 1; moderate, 2; marked, 3.
All subjects were Japanese and were surveyed about their history of any illness, and smoking habits. Individuals with past history of gastrectomy were excluded from this study. The Ethics Committee of the Nagoya University Graduate School of Medicine approved the protocol, and prior, written informed consent was obtained from all participating subjects.
Detection of Helicobacter pylori Infection
H. pylori status was assessed by serologic analysis. Peripheral blood was collected from each subject and serum samples separated by centrifugation were stored at 20°C until analysis. The anti-H. pylori IgG antibody titer was determined by HM-CAP IgG EIA assay (Kyowa Medex, Tokyo, Japan), and ELISA values >2.2 were regarded as H. pylori-seropositive.
Genotyping of Cytokine Gene Polymorphisms
Genomic DNA was isolated from peripheral blood using a standard phenol/chloroform extraction method. The IL-8 polymorphism was genotyped by PCR-RFLP. Primer sequences for PCR were as follows: forward primer, 5'-TTCTAACACCTGCCACTCTAG-3'; reverse primer, 5'-CTGAAGCTCCACAATTTGGTG-3'. PCR was carried out in a volume of 10 µL containing 40 ng of genomic DNA, 1x reaction buffer, 0.125 mmol/L deoxynucleotide triphosphates, 1.5 mmol/L MgCl2, 0.75 µmol/L of each primer and 0.5 units of Platinum Taq DNA polymerase (Gibco BRL, Gaithersburg, MD). The DNA was denatured at 94°C for 4 minutes, followed by 35 cycles at 94°C for 30 seconds, 60°C for 30 seconds, and 72°C for 30 seconds with a final extension at 72°C for 7 minutes. The enzyme digestion using 5 units of MfeI (New England Biolabs, Inc., Bevely, MA) was done to analyze the IL-8 251 T > A polymorphism and yielded a product of 108 bp (251 T) and 76 + 32 bp (251 A). The digestion was incubated overnight at 37°C and then its products were visualized on a 5% agarose gel stained with ethidium bromide.
The IL-1B 511 C > T polymorphism was distinguished by 5' nuclease PCR assay (TaqMan) using TaqI for 511. For the TaqMan assay, sequences of primers and probes were courtesy of Dr. Emad M. El-Omar. Thermal cycling of optical plates was done in GeneAmp PCR System 9700 and end point analysis was done in the ABI PRISM 7700 Sequence Detection System (Applied Biosystems, Foster City, CA). For IL-1RN, genomic DNA was amplified using PCR encompassing an 86-bp variable number of tandem repeats in intron 2. The PCR products were separated by electrophoresis on 2% agarose gels and stained with ethidium bromide. The alleles were coded conventionally as follows: allele 1, four repeats; allele 2, two repeats; allele 3, five repeats; allele 4, three repeats; and allele 5, six repeats. Because alleles 3, 4, and 5 were very rare, these alleles were classified into the short (allele 2: *2) and long alleles (alleles 1, 3, 4, and 5: L) for the purpose of statistical analysis in accordance with the recent study (7).
Detection of p53 Mutational Analysis
In 226 of 396 patients with gastric cancer, DNA was extracted from frozen tumor tissue by the standard phenol/chloroform method. Complete coding sequences and splice junctions for exons 5 to 8 of p53 gene were screened for mutations by PCR-based single-strand conformational polymorphism analysis as previously described by us (29). The sequences of the used primers were: forward, 5'-TCTGTCTCCTTCCTCTTCCTG-3'; reverse, 5'-TCTCTCCAGCCCCAGCTG-3'; forward, 5'-CTGATTCCTCACTGATTGCTC-3'; reverse, 5'-GAGACCCCAGTTGCAAAC-3'; forward, 5'-CTTGGGCCTGTGTTGTCTC-3'; reverse, 5'-AGGGTGGCAAGTGGCTCC-3'; and forward, 5'-GCTTCTCTTTTCCTATCCTGA-3'; reverse, 5'-GCTTCTTGTCCTGCTTGC-3' for exons 5 to 8, respectively. PCR was carried out with Platinum Taq DNA polymerase (Gibco BRL) for 1 cycle at 94°C for 4 minutes followed by 35 cycles at 94°C for 30 seconds, 46°C to 61°C for 30 seconds, and 72°C for 30 seconds with a final 7-minute extension at 72°C in the presence of 0.2 mCi of [32P]dCTP. PCR-single-strand conformational polymorphism was done using MDE (FMC BioProducts, Rockland, ME) gels. The DNA fragments that showed mobility shifts were excised from the gels and reamplified using the same primers. The PCR fragments were purified using the Microcon-100 microconcentrator (Amicon, Stonehouse, United Kingdom) and sequenced using the ABI Prism Big-Dye Terminator Cycle Sequencing Reaction Kit (Applied Biosystems).
No significant differences were found between cases without analysis of p53 mutations and cases with analysis with respect to sex, age, distribution of IL-8 polymorphism, histologic type, tumor location, staging, and other clinical features.
IL-8 Protein Measurement
In 50 patients with gastric cancer, two biopsy specimens were obtained from the greater curvature of the upper gastric body mucosa during gastroscopy and were immediately placed in 3 mL of RPMI 1640 (Gibco BRL) at 4°C. After 6 hours, samples were mechanically homogenized and aliquots of homogenate supernatants, obtained by centrifugation (1,000 x g for 10 minutes), were stored at 80°C until use. Total protein in the biopsy method was assayed using the Bradford method. IL-8 protein was measured by chemiluminescent immunoassay using commercially available assay kits (Research and Diagnostic Systems, Minneapolis, MN) according to the manufacturer's instructions. The mucosal IL-8 levels were expressed as picograms of cytokine per milligram of biopsy protein (pg/mg protein). All donors were serologically H. pylori-positive and anatomic location of the tumor was distant enough from the upper gastric body to avoid the influence of inflammation induced by the tumor.
Statistical Analysis
Statistical analyses were done with Fisher's exact probability test or
2 test for the comparison of IL-8, IL-1B, and IL-1RN genotype frequencies between cases and controls. The odds ratios (OR) with 95% confidence intervals (CI) were computed using unconditional logistic models, adjusting for sex, age, and H. pylori seropositivity. Differences among groups in the gastric mucosa levels of IL-8 protein and in the histologic score of gastritis were determined using the Mann-Whitney U test or Kruskal-Wallis rank test. P < 0.05 were considered statistically significant.
| Results |
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In the group of individuals with atrophic gastritis, we found that the IL-8 251 A/A genotype, considered as the high IL-8producing genotype (18), was significantly associated with elevated risk of atrophic gastritis (OR, 2.35; 95% CI, 1.12-4.94). IL-1B 511 and IL-1RN polymorphisms were not associated with the risk of atrophic gastritis (Table 2).
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We further investigated whether the IL-8 251 polymorphism might affect the clinicopathologic features of gastric cancer. Tumor location, staging, histologic classification, lymphatic and venous invasion, lymph node metastasis, peritoneal dissemination, liver metastasis, other distant metastasis, and p53 mutations were included in this stratification analysis. Among these clinicopathologic features, we found that IL-8 251 A/A genotype increased the risk of upper-third location (OR, 3.66; 95% CI, 1.46-9.17), diffuse type (OR, 2.79; 95% CI, 1.21-6.39), poorly differentiated type (OR, 2.70; 95% CI, 1.14-6.38), lymph node metastasis (OR, 2.50; 95% CI, 1.01-6.20), liver metastasis (OR, 5.63; 95% CI, 1.06-30.04), and p53-mutated type (OR, 2.95; 95% CI, 1.18-7.39). IL-8 251 A carriers also had an association with diffuse type (OR, 1.88; 95% CI, 1.16-3.04), poorly differentiated type (OR, 1.84; 95% CI, 1.11-3.05), and p53-mutated type (OR, 1.91; 95% CI, 1.13-3.26; Table 3).
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| Discussion |
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IL-8 stimulated by H. pylori infection induces the recruitment of neutrophils, which secrete proinflammatory cytokines such as TNF-
, IFN-
, and IL-1ß. The cytokine response in gastric mucosa is thought to be T helper cell (Th) 1predominant, characterized by the accumulation of IFN-
, not of IL-4expressing T lymphocytes (11, 34). Chronic inflammation with a Th 1predominant immune response in the gastric mucosa of mice has been reported to cause gastric atrophy, whereas Th2 cytokines are protective against gastric inflammation (35, 36). In addition, proinflammatory cytokines play an important role in cellular proliferation and gastric mucosal damage (37). Our study shows that the 251 A/A genotype is associated with increased risk of both atrophic gastritis and gastric cancer, suggesting that a high producer of IL-8 may induce a Th 1predominant immune response, lead to more severe gastric atrophy, and be more susceptible to gastric cancer than a low producer of IL-8.
On the other hand, the IL-1B and IL-1RN polymorphisms were not associated with the risk of atrophic gastritis or gastric cancer in the present study. It was reported that the IL-1B 511 T and IL-1RN *2 alleles were associated with increased IL-1ß production in H.pylori-infected gastric mucosa (38), and increased the risk of atrophic gastritis (6) and gastric cancer (5). However, some opposite studies have recently been reported. The IL-1B 31 T allele, being in almost complete linkage disequilibrium with the IL-1B 511 C allele, was associated with increased mucosal IL-1ß levels, and increased risk of intestinal-type gastric cancer in Korea (39). In addition, two studies in Japan reported that the IL-1B 511 T allele decreased the risk of gastric atrophy (40) and intestinal metaplasia (41), and was not associated with increased risk of gastric cancer (41). As above, because the functional roles of IL-1B polymorphisms in the risk of atrophic gastritis and gastric cancer vary among the different studies, further investigations are necessary to resolve this controversy.
Next, we investigated the effect of the IL-8 251 T > A polymorphism on the progression of different gastric cancer subtypes by stratification analysis. It was revealed that the 251 A/A genotype holds a higher risk of upper third location, diffuse type of Lauren's classification, poorly differentiated adenocarcinoma of Japanese classification, lymph node metastasis, liver metastasis, and p53-mutated gastric cancers. According to Correa's cascade (23), beginning with chronic gastritis, followed by atrophy, metaplasia, and intestinal type of gastric cancer, we expected that the 251 A/A genotype would be associated with a higher risk of intestinal type gastric cancer in agreement with the recent study (22). However, interestingly, the 251 A/A genotype is related to a higher risk of diffuse type and poorly differentiated adenocarcinomas. A recent study reported that IL-8 was more strongly expressed in diffuse than in intestinal type gastric cancers (42). We did not investigate the effect of IL-8 polymorphisms on the expression of IL-8 protein in gastric cancer tissue, but it is possible that the 251 A allele might affect the production of IL-8 protein even in gastric cancer tissue. IL-8 is shown to decrease expression of the epithelial cell adhesion molecule E-cadherin by autocrine or paracrine mechanisms (43). In gastric cancer, low or absent E-cadherin expression is associated with disintegration of tissue architecture and leads to the progression of the diffuse-type gastric cancer (44). Thus, a high IL-8 producer genotype may be associated with elevated risk of diffuse-type and poorly differentiated adenocarcinoma, frequently developing in the upper third location.
The IL-8 251 A/A genotype also correlated with a higher risk of lymph node and liver metastasis. These results may be due to tumorigenic and angiogenic functions of IL-8, modulating the growth and invasive behavior of malignant tumors (45). It has been reported that the IL-8 mRNA level in gastric cancer directly correlated with the vascularity of the tumors (46), and transfection of gastric carcinoma cells with the IL-8 gene enhanced their tumorigenesis and angiogenesis in the gastric wall of the nude mouse (47). Although these findings suggest that IL-8 induces metastasis by autocrine mechanisms, exogenous IL-8, derived from macrophages or neutrophils, also mediated cell migration and angiogenesis (16, 17). We also revealed that the 251 A/A genotype were associated with more severe neutrophil infiltration in noncancerous gastric mucosa adjacent to cancer, therefore, our results suggest that IL-8 increases the metastatic potential of gastric cancer cells by both autocrine and paracrine mechanisms, and suggests that genetic variants of IL-8 may have some potential to affect the prognosis of gastric cancer.
With regard to the association between the IL-8 251 T > A polymorphism and p53 mutations, the 251 A/A genotype was associated with increased risk of p53-mutated gastric cancer. It is speculated that neutrophils induced by IL-8 synthesize active radicals such as nitric oxide (48). These radicals have a mutagenic potential, which could cause mutations in gastric epithelial cells (49). Specifically, nitric oxide deaminates intact DNA, methylated cytosine in particular, at physiologic pH and leads to cytosine-to-thymine transition (50, 51), which is known as the most common base substitution of p53 (52). Moreover, some studies have reported that aberrant p53 expression is strongly associated with IL-8 mRNA expression in nonsmall cell lung cancer (53) and mutated p53 may up-regulate IL-8 expression by up-regulation of nuclear factor
B transcription activity (54). These findings suggest that p53 mutation induced by high IL-8 expression may enhance IL-8 expression in itself, leading to more altered p53 accumulation. Because p53 alterations are found even in precancerous gastric mucosa, and is considered as an early event in gastric carcinogenesis (55, 56), and these oxidative stresses in the gastric mucosa are attenuated by H.pylori eradication (57), it is expected that H.pylori eradication can suppress p53-mediated gastric carcinogenesis in subjects with the IL-8 251 A/A genotype.
In conclusion, we showed that the IL-8 251 A allele is associated with higher expression of the IL-8 protein, more severe neutrophil infiltration in gastric mucosa, and increased the risk of atrophic gastritis and gastric cancer, especially diffuse type, poorly differentiated adenocarcinoma, lymph node and liver metastasis, and p53 mutations. We investigated the IL-8 251 T > A polymorphism in only a limited area in central Japan. It has been shown that the allelic frequency of the IL-8 251 T > A polymorphism is different between Japanese and Western people (19, 21, 30). Thus, further studies are needed in a larger and ethnically different population to confirm these genetic influences on gastric carcinogenesis.
| Acknowledgments |
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| Footnotes |
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Received 5/ 6/05; revised 8/21/05; accepted 9/ 9/05.
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