Abstract 3756: ALOX12 and ALOX15 tagSNPs, NSAID use, and the risk of colorectal neoplasia

Introduction: Arachidonate lipoxygenase (ALOX) enzymes generate potent inflammatory mediators via the metabolism of arachidonic acid. Genetic polymorphisms in the lipoxygenase gene family have been implicated in cancer and inflammatory diseases such as asthma, bone loss, and atherosclerosis. NSAIDs, which reduce colorectal cancer risk, induce apoptosis in colon cancer cells via upregulation of ALOX15. We hypothesize that polymorphisms in lipoxygenases ALOX12 and ALOX15 may influence colorectal neoplasia risk and protective NSAIDs effects.

Methods: A linkage-disequilibrium (LD)-based tagSNP-selection algorithm (r2=0.90, MAF=4%) identified tagSNPs in ALOX12 and ALOX15 representing common genetic variation in Europeans. We genotyped 17 SNPs in ALOX12 and 21 SNPs in ALOX15 in three independent study populations that capture the range of colorectal carcinogenesis by including adenoma, colon, and rectal cancer cases. We investigated these SNPs in relation to colorectal neoplasia risk and potential interactions with NSAID use in three US population-based case-control studies of colon cancer (n=1424/1780 cases/controls), rectal cancer (n=583/775), and colorectal adenoma (n=485/578). Multiple logistic regression analysis was used, adjusting for age, sex, and study site, and restricted to Caucasians (>90% of all study participants). A p value < 0.05 without multiple comparison adjustment was considered statistically significant.

Results: In ALOX12, rs11571364 was associated with a modestly increased risk of colon cancer among variant allele carriers (OR: 1.23, 95% CI: 1.01-1.51). A risk increase was also seen in rectal cancer, but was not statistically significant (OR: 1.26, 95% CI: 0.92-1.71). The homozygous variant genotype of another SNP in ALOX12 showed a possible reduced risk of rectal cancer (rs2073438, OR: 0.66, 95% CI: 0.42-1.04), but not colon cancer or adenomas. No significant interactions between SNPs in ALOX12 and NSAID use were observed in any of the three studies. In ALOX15, rs2619112 showed a suggested increase in rectal cancer risk. However, the risk was more elevated among those with a heterozygous genotype (OR: 1.37; 95% CI: 1.06-1.77) than among those with a homozygous variant genotype (OR: 1.13, 95% CI: 0.83-1.55). We detected a significant interaction between this SNP and NSAID use. Among NSAID non-users, the homozygous genotype was associated with increased rectal cancer risk (OR: 1.24). Among NSAID users, the homozygous wildtype and homozygous variant genotypes were associated with decreased risk, but there was no association among heterozygous NSAID users (p-interaction=0.04).

Conclusion: Polymorphisms in ALOX12 and ALOX15 are associated with risk of rectal and colon cancer, but not colorectal adenomas. An ALOX15 SNP previously associated with bone mineral density levels and coronary artery disease risk was associated with rectal cancer risk and showed possible interaction with NSAID use.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3756. doi:10.1158/1538-7445.AM2011-3756

Rotating night shift work and risk of ovarian cancer

BACKGROUND

Night shift work has been associated with higher risks of breast and endometrial cancer, but few studies have evaluated associations with other reproductive cancers.

METHODS

We examined the association between rotating night shift work and risk of ovarian cancer during 20 years of follow-up in 181,548 women participating in two large cohort studies, the Nurses' Health Study (NHS) and NHSII. Number of years of rotating night shift work was queried in 1988 for NHS and in 1989, 1991, 1993, 2001, and 2005 for NHSII. We used Cox proportional hazards regression to model HRs and 95% CIs of ovarian cancer for each shift work category (1-2, 3-5, 6-9, 10-14, 15-19, and 20+ years).

RESULTS

We confirmed 718 incident cases of ovarian cancer over 2,974,672 person-years of follow-up. Rotating shift work was not associated with ovarian cancer risk in either cohort individually. Combining both cohorts, compared with women without any night work, the HR for 15 to 19 years of rotating night shift work was 1.28 (95% CI: 0.84-1.94) and for 20+ years 0.80 (95% CI: 0.51-1.23).

CONCLUSIONS

In this large prospective study, there was no association between duration of rotating night shift work and risk of ovarian cancer.

IMPACT

Although associated with other cancers, night shift work does not appear to be associated with increased risk of ovarian cancer. However, further exploration of the association between melatonin and risk of ovarian cancer is warranted.

Prediagnostic non-steroidal anti-inflammatory drug use and survival after diagnosis of colorectal cancer

OBJECTIVE

Non-steroidal anti-inflammatory drug (NSAID) use decreases both the incidence of colorectal cancer and recurrence of adenomas among patients with prior colorectal neoplasia. However, few studies have investigated the association between NSAID use and colorectal cancer-specific survival. The role of prediagnostic NSAID use was therefore examined in relation to colorectal cancer-specific survival among cases from the Seattle Colon Cancer Family Registry (Seattle Colon CFR).

METHODS

This was a follow-up study that included incident cases of colorectal cancer from the Seattle Colon CFR. Cases were aged 20-74, diagnosed from 1997 to 2002, and were identified using the population-based Puget Sound SEER registry. Detailed information on history of NSAID use, including type, recency and duration, was collected through an interviewer-administered questionnaire. Follow-up for mortality was completed through linkages to the National Death Index. The main outcome measure was death due to colorectal cancer after diagnosis. Cox proportional hazards regression was used to investigate the relationship between prediagnostic NSAID use and colorectal cancer-specific mortality among cases.

RESULTS

NSAID use prior to colorectal cancer diagnosis was associated with an ~20% lower rate of colorectal cancer mortality after diagnosis compared with never use (HR 0.79; 95% CI 0.65 to 0.97). This relationship appeared to be duration dependent, with longer reported use prior to diagnosis associated with lower rates of colorectal cancer mortality among cases. The most pronounced reductions in mortality were observed among cases diagnosed with proximal disease (HR 0.55; 95% CI 0.37 to 0.82), whereas no association was observed between NSAID use prior to diagnosis and colorectal cancer-specific mortality among cases diagnosed with distal or rectal disease.

CONCLUSIONS

The findings suggest that regular use of NSAIDs prior to diagnosis is associated with improved colorectal cancer survival, particularly among cases diagnosed with proximal disease and in longer term NSAID users.

Abstract B100: Rotating night shift work and risk of ovarian cancer

Introduction: Night shift work has been associated with higher risks of breast, endometrial, colorectal, prostate cancer and non-Hodgkin's lymphoma. These associations may be driven by a diminished ability of the pineal gland to produce melatonin among those exposed to light at night. Melatonin likely has multiple anti-cancer mechanisms, including down-regulation of the reproductive axis and direct actions of melatonin on estrogen receptors — both of note for ovarian cancer. Moreover, melatonin exhibits a growth-inhibitory effect on ovarian cancer cell lines. Few epidemiological studies have evaluated an association between night shift work and ovarian cancer risk. Within the NHS and NHSII cohorts, we prospectively assessed the association of rotating night shift work with ovarian cancer risk.

Methods: Total number of years of rotating night shift work (defined as at least 3 nights per month in addition to days and evenings during that month) was queried in 1988 for NHS and in 1989 for NHSII. Duration was updated in 1991, 1993, 2001, and 2005 for NHSII. We used Cox proportional hazards regression to model the incidence rate ratios (RR) and 95% confidence intervals (CI) of ovarian cancer for each shift work category (1-2 years, 3-5 years, 6-9 years, 10-14 years, 15-19 years, 20-29 years, and 30+ years), compared to those who never worked rotating shifts, adjusting for age in months, cohort, tubal ligation, duration of oral contraceptive use, parity, BMI, smoking status, menopausal status, family history of ovarian cancer, and duration of breastfeeding. In our analysis, we updated the values for these covariates when new data were available and otherwise carried forward the values from the previous cycle or the last cycle when each covariate was assessed.

Results: There were 666 cases of ovarian cancer among 2,856,537 person-years of follow-up time. Overall, rotating shift work was not associated with ovarian cancer risk: 15-19 years vs. none: OR: 1.21; 95% CI: 0.78-1.86; 20-29 years vs. none: OR: 0.65; 95% CI: 0.35-1.19; 30+ years vs. none: OR: 0.79; 95% CI: 0.40-1.54. Estimates were unchanged when adjusted for menstrual irregularity.

Conclusion: In this large prospective study, overall, there was no association between duration of rotating night shift work and risk of ovarian cancer. Additional analyses stratifying by hormonal receptor status. menopausal status and other potential effect modifiers are ongoing and may reveal subgroup associations.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):B100.

Confirmation of linkage to and localization of familial colon cancer risk haplotype on chromosome 9q22

Genetic risk factors are important contributors to the development of colorectal cancer. Following the definition of a linkage signal at 9q22-31, we fine mapped this region in an independent collection of colon cancer families. We used a custom array of single-nucleotide polymorphisms (SNP) densely spaced across the candidate region, performing both single-SNP and moving-window association analyses to identify a colon neoplasia risk haplotype. Through this approach, we isolated the association effect to a five-SNP haplotype centered at 98.15 Mb on chromosome 9q. This haplotype is in strong linkage disequilibrium with the haplotype block containing HABP4 and may be a surrogate for the effect of this CD30 Ki-1 antigen. It is also in close proximity to GALNT12, also recently shown to be altered in colon tumors. We used a predictive modeling algorithm to show the contribution of this risk haplotype and surrounding candidate genes in distinguishing between colon cancer cases and healthy controls. The ability to replicate this finding, the strength of the haplotype association (odds ratio, 3.68), and the accuracy of our prediction model (approximately 60%) all strongly support the presence of a locus for familial colon cancer on chromosome 9q.

Polymorphic human prostaglandin H synthase-2 proteins and their interactions with cyclooxygenase substrates and inhibitors

The cyclooxygenase (COX) activity of prostaglandin H synthase-2 (PGHS-2) is implicated in colorectal cancer and is targeted by nonsteroidal anti-inflammatory drugs (NSAIDs) and dietary n-3 fatty acids. We used purified, recombinant proteins to evaluate the functional impacts of the R228H, E488G, V511A and G587R PGHS-2 polymorphisms on COX activity, fatty acid selectivity and NSAID actions. Compared to wild-type PGHS-2, COX activity with arachidonate was ∼20% lower in 488G and ∼20% higher in 511A. All variants showed time-dependent inhibition by the COX-2-specific inhibitor (coxib) nimesulide, but 488G and 511A had 30-60% higher residual COX activity; 511A also showed up to 70% higher residual activity with other time-dependent inhibitors. In addition, 488G and 511A differed significantly from wild type in Vmax values with the two fatty acids: 488G showed ∼20% less and 511A showed ∼20% more discrimination against eicosapentaenoic acid. The Vmax value for eicosapentaenoate was not affected in 228H or 587R, nor were the Km values or the COX activation efficiency (with arachidonate) significantly altered in any variant. Thus, the E488G and V511A PGHS-2 polymorphisms may predict who will most likely benefit from interventions with some NSAIDs or n-3 fatty acids.

Abstract 895: NFκB and IκBKB polymorphisms and colorectal cancer survival in the Seattle Colon Cancer Family Registry

Introduction: IκBKB and NFκB are regulatory enzymes that interact with the prostaglandin synthesis pathway, which plays a key role in inflammation and colorectal carcinogenesis. Transcriptional targets of the nuclear factor NFκB have been linked to cellular proliferation, angiogenesis, and metastasis. IκBKB binds NFκB within the cytoplasm and can prevent its nuclear localization. The role of variability in these genes in relation to colorectal cancer (CRC) survival has not been investigated; we therefore examined polymorphisms in both IκBKB and NFκB in relation to CRC survival.

Methods: CRC cases were ascertained from 1997-2002 from the Seattle Colon Cancer Family Registry and were matched through linkages to the National Death Index records to obtain date and cause of death. A subgroup of CRC cases was genotyped for selected tagSNPs (9 in IκBKB; 44 in NFκB), including non-synonymous candidate polymorphisms (IκBKB: rs17875749, rs2272736; NFκB: rs4648072, rs4648099). Cox proportional hazards regression models were used to estimate hazard ratios investigating the relationship between polymorphisms in IκBKB and NFκB and CRC-specific mortality.

Results: We observed statistically significant inverse associations between four SNPs in IκBKB (rs11986055, rs2272733, rs6474387, and rs9694958) and the risk of CRC mortality after diagnosis. The observed survival benefit ranged from 86% reduced CRC mortality risk for rs11986055 (HR AA vs. AC or CC: 0.14, 95% CI 0.02-1.03) to 59% reduced CRC mortality risk for rs2272733 (HR GG vs. GA or AA: 0.41, 95% CI 0.20-0.82). The functional significance of these SNPs is unknown; none of these SNPs were in high linkage disequilibrium, with all r2 values < 0.7. No SNPs investigated in NFκB were significantly associated with colorectal cancer survival.

Conclusion: These data suggest that certain polymorphisms in IκBKB may be associated with mortality from colorectal cancer after diagnosis.Associations between IκBKB polymorphisms and CRC survival Hazard Ratio95% CIp-valueAliveDeaadrs11986055 A>C     AA1.00Ref. 20279AC or CC0.140.02-1.030.05241rs2272733 G>A     GG1.00Ref. 17571GA or AA0.410.20-0.820.01519rs6474387 C>T     CC1.00Ref. 18875CT or TT0.400.16-1.000.05365rs9694958 A>G     AA1.00Ref. 18874AG or GG0.370.16-0.860.02386All models reported above adjusted for age, sex, and stage of disease at diagnosis     

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 895.

Abstract 933: Glutathione peroxidase (GPX) candidate and tagSNPs and risk of colorectal neoplasia

Introduction: Glutathione peroxidases (GPXs) are selenium-dependent enzymes that scavenge hydroperoxides linked to oxidative stress, prostaglandin synthesis, inflammation and proliferation. Because these processes are important in carcinogenesis, we hypothesized that genetic variability in the GPXs may influence colorectal neoplasia risk. We investigated candidate polymorphisms and tagSNPs in GPX1-4 in relation to colorectal neoplasia in three independent study populations capturing the range of colorectal carcinogenesis.

Methods: A linkage-disequilibrium (LD)-based tagSNP selection algorithm (r2=0.90, MAF=4%) identified 24 tagSNPs, including the candidates (GPX1 P200L and GPX4 2573 C>T), representing common genetic variation in Europeans. We used an identical Illumina platform to investigate GPX SNPs in three US population-based case-control studies of colon cancer (1424 cases/1780 controls), rectal cancer (583 cases/775 controls), and colorectal adenomas (485 cases/578 controls). For gene-level associations, we conducted principal components analysis (PCA). Multiple logistic regression was used for single SNPs, adjusting for age, sex, and study center, restricted to Caucasians (>90% of all study populations).

Results: In PCA, GPX3 was significant for rectal cancer at p=0.03. Without correction for multiple testing, five polymorphisms in GPX2 and GPX3 were associated with significant differences in rectal cancer risk at α=0.05 (see Table). GPX3 rs8177406 also reduced risk in rectal polyps. The candidate GPX1 P200L showed a marginally increased risk for LP/LL vs. PP (1.22, 0.98-1.52, p=0.06). No other SNPs in GPX1-4 showed significant associations for rectal cancer or adenomas. No associations were observed for colon cancer.

Conclusion: These data provide evidence that genetic variability in GPX2 and GPX3 contributes to risk of rectal cancer but not of colon cancer and thus provide additional support for unique etiological mechanisms for colon and rectal cancer.Table.Selected tagSNPs in GPX1, GPX2 and GPX3 and risk of rectal cancer, adjusted for age, sex, and study center*SNPGenotypeCasesControlsOR95%CIp (2df)p-trendGPX1rs105045**CC252367     2834 C>T, P200LCT or TT3013601.220.981.520.06NAGPX2rs2277502**GG4595741.00..  2834 G>AGA or AA1141890.770.600.990.04NA         rs4902347**GG4565741.00..  1756 G>AGA or AA1141880.780.601.000.05NAGPX3rs3828599CC3404091.00..  1580 C->TCT2142980.850.681.07   TT29660.520.330.830.010.01         rs736775CC2372821.00    9133 C->TCT2753540.910.721.15   TT701380.590.420.830.010.01         rs8177447CC4135001.00    7241 C->TCT1552350.790.621.01   TT14350.480.260.910.020.01* r2 < 0.70, except rs2277502 and rs4902347 (r2 > 0.90)** Dominant model is shown because there were 10 or fewer subjects with the homozygous variant model

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 933.

The effects of obesity and obesity-related conditions on colorectal cancer prognosis

BACKGROUND

Colorectal cancer is the second-leading cause of cancer death in the United States among men and women combined. Refinements in screening, staging, and treatment strategies have improved survival from this disease, with over 65% of patients diagnosed with colorectal cancer surviving over 5 years after diagnosis. In the prognosis of colorectal cancer, clinicopathological factors are important. However, modifiable prognostic factors are emerging as significant contributors to cancer outcomes, including obesity and obesity-related inflammation and metabolic conditions.

METHODS

This report reviews the literature on obesity and obesity-related inflammation and metabolic disturbances and colorectal cancer outcomes (recurrence, disease-free survival, and/or mortality). A PubMed search was conducted of all English-language papers published between August 2003 and 2009 and cited in MEDLINE.

RESULTS

Primary research papers were reviewed for colorectal cancer outcomes related to obesity, inflammation, or metabolic conditions. An association between body size and colorectal cancer recurrence and possibly survival was found; however, reports have been inconsistent. These inconsistent findings may be due to the complex interaction between adiposity, physical inactivity, and dietary intake. Circulating prognostic markers such as C-reactive protein, insulin-like growth factor, and insulin, alone or in combination, have been associated with prognosis in observational studies and should be evaluated in randomized trials and considered for incorporation into surveillance.

CONCLUSIONS

The literature suggests that obesity and obesity-related inflammation and metabolic conditions contribute to the prognosis of colorectal cancer; however, comprehensive large scale trials are needed. Interventions to reduce weight and control inflammation and metabolic conditions, such as diabetes, need to be evaluated and rapidly translated to behavior guidelines for patients.

Genetic variation in prostaglandin E2 synthesis and signaling, prostaglandin dehydrogenase, and the risk of colorectal adenoma

BACKGROUND

Prostaglandins are important inflammatory mediators; prostaglandin E2 (PGE2) is the predominant prostaglandin in colorectal neoplasia and affects colorectal carcinogenesis. Prostaglandins are metabolites of omega-6 and omega-3 polyunsaturated fatty acids; their biosynthesis is the primary target of nonsteroidal anti-inflammatory drugs (NSAID), which reduce colorectal neoplasia risk.

METHODS

We investigated candidate and tagSNPs in PGE2 synthase (PGES), PGE2 receptors (EP2 and EP4), and prostaglandin dehydrogenase (PGDH) in a case-control study of adenomas (n = 483) versus polyp-free controls (n = 582) and examined interactions with NSAID use or fish intake, a source of omega-3 fatty acids.

RESULTS

A 30% adenoma risk reduction was observed for EP2 4950G>A (intron 1; OR(GA/AA vs. GG), 0.71; 95% confidence interval, 0.52-0.99). For the candidate polymorphism EP4 Val294Ile, increasing fish intake was associated with increased adenoma risk among those with variant genotypes, but not among those with the Val/Val genotype (P(interaction) = 0.02). An interaction with fish intake was also observed for PGES -664A>T (5' untranslated region; P(interaction) = 0.01). Decreased risk with increasing fish intake was only seen among those with the AT or TT genotypes (OR(>2 t/wk vs. <1 t/wk), 0.56; 95% confidence interval, 0.28-1.13). We also detected interactions between NSAIDs and EP2 9814C>A (intron 1) and PGDH 343C>A (intron 1). However, none of the observed associations was statistically significant after adjustment for multiple testing. We investigated potential gene-gene interactions using the Chatterjee 1 degree of freedom Tukey test and logic regression; neither method detected significant interactions.

CONCLUSIONS

These data provide little support for associations between adenoma risk and genetic variability related to PGE(2), yet suggest gene-environment interactions with anti-inflammatory exposures.

DNA methyltransferase and alcohol dehydrogenase: gene-nutrient interactions in relation to risk of colorectal polyps

Disturbances in DNA methylation are a characteristic of colorectal carcinogenesis. Folate-mediated one-carbon metabolism is essential for providing one-carbon groups for DNA methylation via DNA methyltransferases (DNMTs). Alcohol, a folate antagonist, could adversely affect one-carbon metabolism. In a case-control study of colorectal polyps, we evaluated three single nucleotide polymorphisms (-149C>T, -283T>C, -579G>T) in the promoter region of the DNMT3b gene, and a functional polymorphism in the coding region of the alcohol dehydrogenase ADH1C gene, ADH1C *2. Cases had a first diagnosis of colorectal adenomatous (n = 530) or hyperplastic (n = 202) polyps at the time of colonoscopy, whereas controls were polyp-free (n = 649). Multivariate logistic regression analysis was used to estimate odds ratios (OR) and corresponding 95% confidence intervals (CI). There were no significant main associations between the DNMT3b or ADH1C polymorphisms and polyp risk. However, DNMT3b -149TT was associated with an increase in adenoma risk among individuals with low folate and methionine intake (OR, 2.00; 95% CI, 1.06-3.78, P interaction = 0.10). The ADH1C *2/*2 genotype was associated with a possibly elevated risk for adenomatous polyps among individuals who consumed >26 g of alcohol/d (OR, 1.95; 95% CI, 0.60-6.30), whereas individuals who were wild-type for ADH1C were not at increased risk of adenoma (P interaction = 0.01). These gene-diet interactions suggest that polymorphisms relevant to DNA methylation or alcohol metabolism may play a role in colorectal carcinogenesis in conjunction with a high-risk diet.

A review of gene-drug interactions for nonsteroidal anti-inflammatory drug use in preventing colorectal neoplasia

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to be effective chemopreventive agents for colorectal neoplasia. Polymorphisms in NSAID targets or metabolizing enzymes may affect NSAID efficacy or toxicity. We conducted a literature review to summarize current evidence of gene-drug interactions between NSAID use and polymorphisms in COX1, COX2, ODC, UGT1A6 and CYP2C9 on risk of colorectal neoplasia by searching OVID and PubMed. Of 134 relevant search results, thirteen investigated an interaction. One study reported a significant interaction between NSAID use and the COX1 Pro17Leu polymorphism (P=0.03) whereby the risk reduction associated with NSAID use among homozygous wild-type genotypes was not observed among NSAID users with variant alleles. Recent pharmacodynamic data support the potential for gene-drug interactions for COX1 Pro17Leu. Statistically significant interactions have also been reported for ODC (315G>A), UGT1A6 (Thr181Ala+Arg184Ser or Arg184Ser alone), and CYP2C9 (*2/*3). No statistically significant interactions have been reported for polymorphisms in COX2; however, an interaction with COX2 -765G>C approached significance (P=0.07) in one study. Among seven remaining studies, reported interactions were not statistically significant for COX1, COX2 and ODC gene polymorphisms. Most studies were of limited sample size. Definitions of NSAID use differed substantially between studies. The literature on NSAID-gene interactions to date is limited. Reliable detection of gene-NSAID interactions will require greater sample sizes, consistent definitions of NSAID use and evaluation of clinical trial subjects of chemoprevention studies.

Polymorphisms predicted to alter function in prostaglandin E2 synthase and prostaglandin E2 receptors

BACKGROUND AND OBJECTIVE

Prostaglandin synthesis is the primary target of aspirin and other nonsteroidal antiinflammatory drugs, and thus is a pathway of major interest to pharmacology, pharmacogenetics, and epidemiology. Several lines of evidence implicate prostaglandin E2 in carcinogenesis; this study aimed to identify genetic variants in genes related to prostaglandin E2 synthesis and signaling.

METHODS

We resequenced the coding regions of human prostaglandin E2 synthase (PGES), and prostaglandin E2 receptors EP1, EP2, and EP4 in 48 African-Americans and 47 Caucasians.

RESULTS AND CONCLUSIONS

We identified 23 variants, 6 of which cause amino acid changes. The non-synonymous polymorphisms in PGES, EP1, and EP2 were present only among African-Americans; both populations carried non-synonymous polymorphisms in EP4. We used two sequence homology-based programs, SIFT and PolyPhen, to predict the impact of these polymorphisms. These programs predicted that the amino-acid changes p.Phe119Val in EP1, p.Ala44Glu in EP2, and possibly p.Val7Glu in PGES, p.Thr176Ile in EP4 and p.Gly420Asp in EP4 are likely to affect protein function. Thus, these variants may be relevant for inflammatory conditions, carcinogenesis, and pharmacogenetics.

Genetic variability in prostaglandin synthesis, fish intake and risk of colorectal polyps

Dietary polyunsaturated fatty acids (PUFAs) can be converted to prostaglandins and leukotrienes. Metabolism of omega-6 (n-6) PUFAs results in the production of pro-inflammatory mediators whereas downstream products of omega-3 (n-3) PUFAs have lower inflammatory activity. Elevated n-3 PUFA intake from dietary fish may be associated with lower risk of colorectal neoplasia among those with genetic variants resulting in higher levels of pro-inflammatory mediators. We investigated interactions between dietary fish intake and polymorphisms in cyclooxygenase (COX)-1, COX-2, ALOX5 and PGIS in a case-control study of adenomas (N = 522), hyperplastic polyps (N = 194) and polyp-free controls (N = 626). Polyp risk did not differ by fish intake. A suggested interaction with fish intake was observed for COX-1 P17L. Among those who were homozygous wild type, increasing fish intake was associated with a modestly reduced risk of adenoma, whereas among those with at least one variant allele, the reverse trend was observed (p-interaction = 0.08). The interaction was statistically significant when non-steroidal anti-inflammatory drug (NSAID) use was also taken into account: among those with COX-1 17PP genotypes, high fish intake and regular NSAID use was associated with a decreased risk compared with low fish intake and low NSAID use (odds ratio = 0.60, 95% confidence interval 0.33-1.09). The opposite association was observed among those with COX-1 17PL or LL genotypes (p-interaction = 0.04). Our results suggest that the effects of dietary n-3 PUFA intake and NSAID use may differ by genetic variation in COX-1.

Prostacyclin Synthase and Arachidonate 5-Lipoxygenase Polymorphisms and Risk of Colorectal Polyps

Prostacyclin synthase (PGIS) and arachidonate 5-lipoxygenase (ALOX5) are enzymes relevant to prostaglandin and leukotriene synthesis, both important pathways for colon cancer risk. We hypothesized that genetic variation altering the function of these enzymes would modify risk of colorectal polyps. In a Minnesota-based case-control study of adenomatous (n = 517) or hyperplastic (n = 192) polyps versus polyp-free controls (n = 618), we investigated the role of promoter repeat polymorphisms in PGIS and ALOX5 as well as ALOX5 -1700 G>A. Having fewer than six repeats on both PGIS alleles (<6R/<6R) was associated with an increased risk of adenomas compared with the 6R/6R (wild-type) genotype (OR, 1.90; 95% CI, 1.09-3.30). Having more repeats (>6R/> or =6R) reduced risk (OR, 0.73; 95% CI, 0.40-1.35; P(trend) = 0.03). In allele-based analyses, fewer repeats were associated with a modestly increased risk of adenomas and perhaps hyperplastic polyps. There were no risk differences for either the ALOX5 VNTR or -1700 G>A polymorphisms. Associations with regular use of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) differed by PGIS genotype. Among individuals with at least one wild-type allele, NSAID use was associated with a decreased risk; however, those with fewer PGIS repeats (<6R/<6R) did not benefit (P(interaction) = 0.06). There was also evidence of an interaction between the COX-2 -765 G>C and ALOX5 -1700 G>A genotypes (P(interaction) = 0.07). The PGIS promoter polymorphism may affect risk of colorectal polyps and modify the effects of NSAID use on polyp risk. A more comprehensive investigation of genetic variability in prostaglandin synthesis in relation to risk of colorectal neoplasia and NSAID pharmacogenetics is warranted.

Thromboxane synthase (TBXAS1) polymorphisms in African-American and Caucasian populations: evidence for selective pressure

Thromboxane synthase (TBXAS1), a cytochrome P450 enzyme, converts prostaglandin H2 into thromboxane A2, a potent vasoconstrictor and inducer of platelet aggregation. Thromboxane A2 has been implicated in modulating cell cytotoxicity and in tumor growth and metastasis. Twelve coding-region variants were identified in the human TBXAS1 gene in 48 African-American and 46 Caucasian individuals, of which eight were amino-acid substitutions. The latter were confirmed in an independent Caucasian population (n=94 unrelated individuals). We performed an evolutionary analysis of patterns of nucleotide diversity and identified patterns of amino acid replacement in human-mouse comparisons consistent with purifying selection on an inter-species time scale using the McDonald-Kreitman test. We also observed patterns of nucleotide diversity within humans consistent with purifying selection acting on existing polymorphism using Tajima's D within coding regions. These evolutionary tests suggest that some of the rare coding variations observed in the human population are deleterious. We used two sequence-homology-based software programs and molecular modeling to predict the potential impact of these polymorphisms on TBXAS1 function. The c.772C>T (p.Lys258Glu), c.1249C>G (p.Gln417Glu), and c.1348G>A (p.Glu450Lys) substitutions are predicted as most likely to alter protein function; another, c.1352C>A (p.Thr451Asn), may also affect function. Given the evolutionary evidence, these variants may be functional and therefore of relevance for disease endpoints related to inflammation and angiogenesis, as well as for the pharmacogenetics of non-steroidal anti-inflammatory drugs.