Predicted mean (lines) and 95% CIs (shaded regions) for CSF F2-isoprostane concentrations vs age in cognitively normal participants across adult ages calculated from model 3 and stratified by sex (A), body mass index (BMI) (calculated as weight in kilograms divided by height in meters squared) (B), and smoking status (C).
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Peskind ER, Li G, Shofer JB, et al. Influence of Lifestyle Modifications on Age-Related Free Radical Injury to Brain. JAMA Neurol. 2014;71(9):1150–1154. doi:10.1001/jamaneurol.2014.1428
The Healthy Brain Initiative 2013-2018 seeks to optimize brain health as we age. Free radical injury is an important effector of molecular and cellular stress in the aging brain that derives from multiple sources.
To identify potentially modifiable risk factors associated with increased markers of brain oxidative stress.
Design, Setting, and Participants
This cross-sectional, academic multicenter study consisted of 320 research volunteers (172 women) aged 21 to 100 years who were medically healthy and cognitively normal.
Main Outcomes and Measures
Free radical injury to the brain was assessed using cerebrospinal fluid (CSF) F2-isoprostane (F2-IsoP) concentrations correlated with age, sex, race, cigarette smoking, body mass index, inheritance of the ε4 allele of the apolipoprotein E gene (APOE), and CSF biomarkers of Alzheimer disease.
The concentration of CSF F2-IsoP increased with age by approximately 3 pg/mL (approximately 10%) from age 45 to 71 years in medically healthy, cognitively normal adults (P < .001). The CSF F2-IsoP concentration increased by approximately more than 10% for every 5-U increase in body mass index (P < .001). Current smoking had an approximately 3-fold greater effect on CSF F2-IsoPs compared with age (P < .001). Women had greater mean CSF F2-IsoP concentrations than men at all ages after adjusting for other factors (P = .02). Neither the concentration of CSF Alzheimer disease biomarkers nor inheritance of the APOE ε4 allele was associated with the CSF F2-IsoP concentration in this group of medically healthy, cognitively normal adults (P > .05). The association between CSF F2-IsoP concentrations and race was not significant after controlling for the effect of current smoking status (P = .45).
Conclusions and Relevance
Our results are consistent with an age-related increase in free radical injury in the human brain and uniquely suggest that this form of injury may be greater in women than in men. Our results also highlighted 2 lifestyle modifications (ie, body mass index and smoking) that would have an even greater effect on suppressing free radical injury to the brain than would suppressing the processes of aging. These results inform efforts to achieve success in the Healthy Brain Initiative 2013-2018.
The Healthy Brain Initiative 2013-20181 formulated by the Centers for Disease Control and Prevention and the Alzheimer’s Association is a challenge to researchers, health care providers, and public health officials to devise and deliver approaches that optimize brain health as we age. Free radical injury, an important effector of molecular and cellular stress in the central nervous system as we age, derives from multiple sources including processes of aging, genetics, environmental factors, and latent Alzheimer disease (AD). Clarification of the sources of age-related free radical injury to the central nervous system is important because sources that are approachable through lifestyle modification or treatment offer an opportunity to optimize brain heath across the human life span. The present study focused on several potential drivers of age-related free radical injury in the central nervous system in 320 research volunteers aged 21 to 100 years, who were considered healthy on the basis of medical examination and extensive cognitive testing, by determining the associations of genetic, environmental, demographic, and cerebrospinal fluid (CSF) AD biomarker data with CSF F2-isoprostanes (IsoPs), which are widely used biomarkers of free radical injury to the brain.2-9
The institutional review boards of the participating institutions (the University of Washington Alzheimer Disease Research Center and collaborating AD centers including the University of California at San Diego, Oregon Health & Science University, Indiana University, the University of Pennsylvania, and the University of California at Davis) approved all procedures. The participants provided written informed consent before study enrollment and received financial compensation. A total of 320 individuals who were cognitively normal were recruited from AD centers in which they were already serving as control participants in studies from October 26, 2011, to September 24, 2009; were healthy as determined by medical examination; had Mini-Mental State Examination scores of 26 or more and a Clinical Dementia Rating score of 0; and had no evidence or history of cognitive or functional decline. The neuropsychological tests included in the present study examined multiple aspects of cognition.10 The Wechsler Memory Scale–Revised, Logical Memory Immediate and Delayed paragraph recall tasks, measure verbal episodic memory.11,12 The Trail Making A task measures psychomotor speed, visuospatial function, and visual attention; the Trail Making B task adds a set-shifting element and captures executive function.13 Category fluency (animals) is a measure of semantic memory and language.14 Cerebrospinal fluid was collected in the morning after an overnight fast, frozen immediately, and stored at −80°C until F2-IsoPs, β-amyloid 42, total tau, and phosphorylated tau181 were quantified, as described previously.15,16 All CSF protein, glucose, and cell values were within the reference ranges (not shown).3 Apolipoprotein E genotype (APOE) was determined by a restriction digest method.16
Linear regression was used to assess associations between CSF F2-IsoP concentration and age, sex, race (white vs nonwhite), current smoking status (yes vs no), body mass index (BMI) (per 5-U increase; calculated as weight in kilograms divided by height in meters squared), presence or absence of the APOE ε4 allele, and CSF AD biomarker concentrations (β-amyloid 42, total tau, and phosphorylated tau181). Total tau and phosphorylated tau181were strongly correlated (r = 0.77; P < .001); therefore, to avoid colinearity, only total tau was included in the modeling. Age was modeled as a 3-degree restricted cubic spline summarized as the mean difference in CSF F2-IsoP concentrations in participants aged 71 years (75th percentile for age) compared with those aged 45 years (25th percentile). Each study characteristic was modeled first as an independent variable with adjustment for age (model 1). The CSF AD biomarkers were added to age in model 2. All other variables, including sex, race, BMI, current smoking status, and APOE ε4 allele, were then added to model 2 to determine which variable had an independent association with CSF F2-IsoPs in the presence of all others (model 3). Finally, an age by each potential effect modifier (sex, BMI, smoking status, or APOE ε4) interaction term was added to model 3. All models were summarized using adjusted R2. Analyses were carried out with R, version 2.15.2,17 using the rms package.18
Women (n = 172) and men (n = 148) were matched well (Table 1). As expected, there was a positive association between CSF F2-IsoP concentration and age across the adult human life span (Table 2) that was independent of CSF AD biomarkers and other variables (model 3). This association was approximately linear, although with some suggestion of accelerated increase in advanced age after adjustment for covariates in model 3 (nonlinear trend, P = .05). Results from all 3 models estimated that the CSF F2-IsoP concentration increased by approximately 3 pg/mL (approximately 10%), from age 45 to 71 years.
Body mass index and smoking were the strongest independent correlates of CSF F2-IsoP concentration (P < .001), which increased by approximately more than 10% for every 5-U increase in BMI (model 3) (Figure). Current cigarette smokers had a significantly higher CSF F2-IsoP concentration compared with nonsmokers (model 3) (Figure) that was approximately 3-fold greater than the effect of age. Women had a greater mean CSF F2-IsoP concentration than did men after adjusting for other factors (model 3) (Figure), although the estimated difference between men and women was smaller than that observed for advancing age. None of these 3 variables was a significant effect modifier of the association between age and the CSF F2-IsoP concentration (sex, P = .91; BMI, P = .29; and current cigarette smoking, P = .11). The difference in the CSF F2-IsoP concentration by smoking status tended to be greatest in midlife; however, the number of current smokers in our study sample may have been too few for detection of a significant effect modification.
The CSF AD biomarkers were not associated with CSF F2-IsoP concentration after adjustment for age (model 2) or other covariates (model 3). Similarly, there was no significant effect on CSF F2-IsoP concentrations when stratified into participants with vs those without an APOE ε4 allele (P = .29; model 3). The association between the CSF F2-IsoP concentration and age did not differ significantly by APOE ε4 status (age by ε4 allele interaction, P = .64).
The association between CSF F2-IsoP concentrations and race was complex and confounded by a greater prevalence of cigarette smoking among nonwhite compared with white participants (24% vs 4%). Multivariable analysis (model 3) did not detect a significant association between race and CSF F2-IsoP concentrations after controlling for the effect of current smoking status.
Our results from evaluation of a large group of adult research volunteers who were cognitively normal and in good medical health are consistent with an age-related increase in free radical injury in the human brain and suggest that this form of central nervous system injury may be slightly but consistently greater in women than in men. This difference is consistent with other reports20-22 of a sex difference in brain reserve and clinical manifestations of AD pathologic changes, although this association remains a point of discussion. Our results also showed that smoking and increased BMI, already known to be associated with increased free radical injury in peripheral organs,23,24 were associated with increased concentrations of CSF F2-IsoPs. Thus, avoidance of smoking and reducing BMI, in addition to their already established benefits, may be beneficial in reducing molecular and cellular stress to brains. Within the limitations of the present study, our data do not implicate latent AD, inheritance of APOE ε4, or race as major contributors to this form of brain injury in healthy adults. Indeed, other factors likely are involved, as seen in our model 3 results, where most of the F2-IsoP variability is not explained by the defined variables. For example, obesity is associated with a variety of other abnormalities, including diabetes mellitus and dyslipidemia, which could contribute to or modify the observed effect. Finally, although CSF F2-IsoPs are widely used biomarkers of free radical injury,2-9 they also activate the thromboxane A2 receptor and thereby contribute to abnormal vasoconstriction in multiple organs including the cerebrum.25-27
Our results highlight 2 lifestyle modifications (ie, body mass index and smoking) that would have an even greater effect on suppressing free radical injury to the brain than would suppressing the processes of aging. Taken together, they contribute genetic and lifestyle data to the evidence base necessary for achieving the long-term goal of the Healthy Brain Initiative 2013-2018: “to maintain or improve the cognitive performance of all adults.”
Accepted for Publication: May 1, 2014.
Corresponding Author: Thomas J. Montine, MD, PhD, Department of Pathology, University of Washington, PO Box 357470, Seattle, WA 98195 (email@example.com).
Published Online: July 21, 2014. doi:10.1001/jamaneurol.2014.1428.
Author Contributions: Dr Montine had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Peskind, Li, Raskind, Montine.
Acquisition, analysis, or interpretation of data: Peskind, Li, Shofer, Millard, Leverenz, Yu, Quinn, Galasko.
Drafting of the manuscript: Peskind, Li, Shofer, Millard, Galasko, Montine.
Critical revision of the manuscript for important intellectual content: Peskind, Leverenz, Yu, Raskind, Quinn, Galasko.
Statistical analysis: Li, Shofer, Millard.
Obtained funding: Peskind, Raskind, Quinn, Galasko, Montine.
Study supervision: Li, Leverenz.
Conflict of Interest Disclosures: Dr Leverenz serves as a consultant for Boehringer Ingelheim, Citigroup, Navidea Biopharmaceuticals, and Piramal Health Care. Dr Galasko serves as the editor of Alzheimer’s Research & Therapy; serves on data safety monitoring boards for Elan Pharmaceuticals Inc, Janssen, and Balance Pharmaceuticals; and is a consultant for Elan Pharmaceuticals Inc and Genentech Inc. He receives research support from the National Institutes of Health, the Michael J. Fox Foundation, and the Alzheimer’s Drug Discovery Foundation. No other disclosures were reported.
Funding/Support: This work was generously supported by the National Institutes of Health grants P50AG05136, P30AG008017, and P50AG005131 and the Nancy and Buster Alvord Endowment.
Role of the Sponsor: The sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Additional Contributions: We thank Kathleen Montine, PhD (School of Medicine, University of Washington), for editorial assistance. There was no financial compensation.