Using pathway-specific comprehensive exposure scores in epidemiology: application to oxidative balance in a pooled case-control study of incident, sporadic colorectal adenomas

No association between mitochondrial DNA copy number and colorectal adenomas

Despite previously reported associations between peripheral blood mtDNA copy number and colorectal cancer, it remains unclear whether altered mtDNA copy number in peripheral blood is a risk factor for colorectal cancer or a biomarker for undiagnosed colorectal cancer. Though colorectal adenomas are well-recognized precursor lesions to colorectal cancer, no study has evaluated an association between mtDNA copy number and colorectal adenoma risk. Hence, we investigated an association between peripheral blood mtDNA copy number and incident, sporadic colorectal adenoma in 412 colorectal adenoma cases and 526 cancer-free controls pooled from three colonoscopy-based case-control studies that used identical methods for case ascertainment, risk factor determination, and biospecimen collection. We also evaluated associations between relative mtDNA copy number and markers of oxidative stress, including circulating F2 -isoprostanes, carotenoids, and fluorescent oxidation products. We measured mtDNA copy number using a quantitative real time polymerase chain reaction (PCR). We used unconditional logistic regression to analyze the association between mtDNA copy number and colorectal adenoma risk after multivariable adjustment. We found no association between logarithmically transformed relative mtDNA copy number, analyzed as a continuous variable, and colorectal adenoma risk (odds ratio = 1.02, 95%CI: 0.82-1.27; P = 0.86). There were no statistically significant associations between relative mtDNA copy number and other markers of oxidative stress. Our findings, taken together with those from previous studies, suggest that relative mtDNA copy number in peripheral blood may more likely be a marker of early colorectal cancer than of risk for the disease or of in vivo oxidative stress. © 2015 Wiley Periodicals, Inc.

Oxidative stress, oxidative balance score, and hypertension among a racially diverse population

Hypertension is a risk factor for several vascular diseases. Evidence suggests that oxidative stress (OS) plays a significant role in its pathophysiology. Human studies have shown inconsistent results, varying based on the OS biomarker and study population. In a racially diverse population, examine the association between: (1) blood pressure or hypertension and four markers of OS and (2) blood pressure or hypertension and oxidative balance score (OBS). Using data (n = 317) from the cross-sectional study on race, stress, and hypertension, an OBS was constructed from various measures of pro-oxidant and antioxidant exposures. OS was assessed by four biomarkers: fluorescence oxidative products, F2-isoprostanes, mitochondrial DNA copy number, and gamma tocopherol. Multivariate linear and logistic regression analyses were used to estimate the associations of interest. None of the adjusted associations between hypertension and OS markers was statistically significant. OBS was inversely associated with hypertension after adjusting for study covariates. Persons with higher OBS have lower odds of having hypertension; however, the evidence on the relationship between OS markers and blood pressure remains unconvincing.

Oxidative balance scores and risk of incident colorectal cancer in a US prospective cohort study

Although oxidative stress is implicated in colorectal carcinogenesis, human studies on associations of individual prooxidants and antioxidants with colorectal cancer (CRC) have been inconclusive. We incorporated individual environmental factors known to affect oxidative stress into 4 oxidative balance scores (OBS) and investigated their associations with CRC in the Cancer Prevention Study II Nutrition Cohort. During 1999-2009, a total of 1,109 incident CRC cases were identified among 80,063 participants in the Nutrition Cohort who had completed detailed questionnaires. Four OBS with different weighting methods (equal weights, literature review-based, a posteriori data-based, and weights based on Bayesian analysis) were created by combining 16 dietary and nondietary lifestyle factors. Higher values for all 4 OBS, representing more antioxidant exposures than prooxidant exposures, were associated with 41%-53% lower risks of CRC; for example, the relative risk for the highest OBS quartile versus the lowest in the Bayesian analysis was 0.50 (95% confidence interval: 0.41, 0.61). The associations were more modest when OBS was restricted to either dietary or nondietary components. These results, obtained using comprehensive summary measures of oxidative balance-especially considering the similarity of the findings derived using the different weighting methods-support the hypothesis that a predominance of antioxidant lifestyle exposures (both dietary and nondietary) over prooxidant lifestyle exposures reduces risk of CRC.

Oxidative balance score as predictor of all-cause, cancer, and noncancer mortality in a biracial US cohort

PURPOSE

We previously proposed an oxidative balance score (OBS) that combines pro- and anti-oxidant exposures to represent the overall oxidative balance status of an individual. In this study, we investigated associations of the OBS with all-cause and cause-specific mortality, and explored alternative OBS weighting methods in the Reasons for Geographic and Racial Differences in Stroke Study cohort.

METHODS

The OBS was calculated by combining information from 14 a priori selected pro- and anti-oxidant factors and then divided into quartiles with the lowest quartile (predominance of pro-oxidants) as reference. Cox proportional hazard models were used to estimate adjusted hazard ratios and 95% confidence intervals for each OBS category compared with the reference.

RESULTS

Over a median 5.8 years of follow-up, 2079 of the 21,031 participants died. The multivariable-adjusted hazard ratios (95% confidence interval) for all-cause, cancer, and noncancer mortality for those in the highest versus the lowest equal-weighting OBS quartile were 0.70 (0.61-0.81), 0.50 (0.37-0.67), and 0.77 (0.66-0.89), respectively (P trend < .01 for all). Similar results were observed with all weighting methods.

CONCLUSIONS

These results suggest that individuals with a greater balance of antioxidant to pro-oxidant lifestyle exposures may have lower mortality.

Oxidative balance score and oxidative stress biomarkers in a study of Whites, African Americans, and African immigrants

CONTEXT

Oxidative balance score (OBS) is a composite measure of multiple pro- and antioxidant exposures.

OBJECTIVE

To investigate associations of OBS with F2-isoprostanes (FIP), mitochondrial DNA copy number (mtDNA), and fluorescent oxidative products (FOP), and assess inter-relationships among the biomarkers.

METHODS

In a cross-sectional study, associations of a thirteen-component OBS with biomarker levels were assessed using multivariable regression models.

RESULTS

Association of OBS with FIP, but not with FOP, was in the hypothesized direction. The results for mtDNA were unstable and analysis-dependent. The three biomarkers were not inter-correlated.

CONCLUSIONS

Different biomarkers of oxidative stress may reflect different biological processes.

Oxidative balance score, colorectal adenoma, and markers of oxidative stress and inflammation

BACKGROUND

An oxidative balance score (OBS) that combines pro- and antioxidant exposures was previously reported to be associated with incident sporadic colorectal adenoma. We extend the previous analyses by assessing associations of the OBS and colorectal adenoma with circulating biomarkers of oxidative stress [F2-isoprostanes (FIP) and fluorescent oxidation products (FOP)], and inflammation [C-reactive protein (CRP)].

METHODS

Using pooled data from two previously conducted colonoscopy-based case-control studies of incident, sporadic colorectal adenoma (n = 365), the OBS was constructed and divided into three approximately equal intervals, with the lowest interval used as the reference. Biomarker levels were dichotomized as "high" versus "low" based on the median values among controls. Multivariable logistic regression was used to calculate adjusted odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

For the OBS-adenoma association, the ORs (95% CIs) for the middle and highest (relative to the lowest) score intervals were 0.81 (0.46-1.43) and 0.39 (0.17-0.89), respectively. The corresponding OBS category-specific ORs (95% CIs) were 0.50 (0.25-1.01) and 0.25 (0.10-0.65) for FIP, 2.01 (1.13-3.75) and 3.48 (1.51-8.02) for FOP, and 0.57 (0.31-1.04) and 0.21 (0.09-0.49) for CRP. The ORs (95% CIs) reflecting associations of adenoma with high levels of FIP, FOP, and CRP were 1.89 (1.08-3.30), 1.82 (1.11-2.99), and 1.45 (0.88-2.40), respectively.

CONCLUSIONS

As hypothesized, the OBS was inversely associated with colorectal adenoma and circulating FIP and CRP levels. The reason for the unexpected direct OBS-FOP association is unknown.

IMPACT

These data support the use of combined measures of pro- and antioxidant exposures in studies of colorectal neoplasia.

No evidence that associations of incident, sporadic colorectal adenoma with its major modifiable risk factors differ by chromosome 8q24 region rs6983267 genotype

A single nucleotide polymorphism (SNP), rs6983267, in the chromosome 8q24 region, has been associated with higher risk for colorectal neoplasms, but its relation to carcinogenic mechanisms is unclear. To investigate whether associations of colorectal adenoma with its major modifiable risk factors differ according to rs6983267 genotype, we performed a pooled analysis of the White participants (n = 401 cases, 518 controls) from three colonoscopy-based, case-control studies of incident, sporadic colorectal adenoma conducted between 1991 and 2002. There was a statistically significant direct association of rs6983267 with colorectal adenoma that was consistent with those in previous reports. We found no clear indications that rs6983267 impacts the association of colorectal adenomas with the following risk factors: physical activity, body mass index (BMI), nonsteroidal anti-inflammatory drug (NSAID) use, tobacco or alcohol use, hormone replacement therapy among women, blood 25-OH-vitamin D3 levels, oxidative balance, or total energy, calcium, red meat, vegetable and fruit, and folate intakes. These findings, together with previously reported null results on 8q24-environment interactions for colorectal cancer, suggest that associations of colorectal adenoma with its major modifiable risk factors may not differ according to chromosome 8q24 region rs6983267 genotype.