Inflammation and cognition : the association between biomarker levels, their genetic determinants, and age-related cognitive decline.

Chronic in ammation and variations in blood flow have been implicated in the pathogenesis of cardiovascular disease. It is also possible that inflammatory and rheological processes are involved in the development of mild cognitive impairment and dementia, either through their association with vascular disease or via some other, more direct effect on the brain. Evidence is increasing for a causal relationship between Alzheimer's disease and inflammation, possibly related to inflammatory activation of microglia. Inflammatory processes may also be involved in the pathogenesis of cerebral small vessel disease, which in turn has been linked to cognitive impairment and dementia. There is also evidence showing that rheological factors affect cerebral blood flow. However, despite these findings, the associations between inflammatory and rheological markers and cognitive ability have not been extensively studied in large groups of ageing people. The primary aim of this thesis was to test for associations between late-life levels of inflammatory and rheological markers (C-reactive protein (CRP), fibrinogen, tumor necrosis factor (TNF)-α, interleukin (IL)-6, plasma viscosity, and haematocrit) and cognitive ability. A genetic analysis was then performed to model single nucleotide polymorphisms (SNPs) in the genes encoding the markers against cognition in an attempt to determine the weight of evidence for a causal inflammation-cognition association. Four studies were used to test these aims with the majority of the analysis being performed on the Aspirin for Asymptomatic Atherosclerosis (AAA) Trial (n = 3,350), and the Edinburgh Type 2 Diabetes Study (ET2DS) (n = 1,066). The Edinburgh Artery Study (n = 534), and the 1936 Lothian Birth Cohort (n = 1,091), were used as replication cohorts for the genetic analysis. All cohorts comprised community-dwelling, elderly citizens (aged around 70 years) living in central Scotland. With the exception of the ET2DS, all data used were for secondary analyses. Cognitive ability was assessed in all studies using comprehensive batteries of neuropsychological tests that included a measure of crystallised intelligence in the form of a vocabulary test. As performance on such tests varies little across a lifespan, adjusting for these scores in the late-life models enabled the determination of estimated lifetime cognitive change. In the case of the 1936 Lothian Birth Cohort an actual age-11 IQ measure was available in addition to the cognitive follow-up scores recorded at age-70. Linear regression showed small but significant associations between CRP, fibrinogen, and plasma viscosity, and cognition and estimated lifetime cognitive decline in the AAA Trial. Similar results were observed in the ET2DS for CRP, IL-6, and TNF-α. These associations tended to be of a magnitude whereby the markers explained 1% of the variance of the cognitive test scores. The cognitive domains most consistently associated with the markers were processing speed, and a data derived general intelligence factor. A novel genetic analysis was then undertaken to model SNPs against cognitive ability and decline. Most of the results generated were null findings. However, strongly significant associations were found between the rs2227412 fibrinogen beta gene SNP and the cognitive test scores in the ET2DS. Furthermore, the genotype associated with the lowest cognitive scores was also related to higher levels of plasma fibrinogen. Whilst replication of the association between the fibrinogen SNPs and cognition was not found across all cohorts, these results still indicate a potentially causal role for this haemostatic/inflammatory marker. To date, the majority of inflammation-cognition associations have focussed on the acute-phase protein CRP. The main outcomes from this thesis suggest that its close correlate, fibrinogen, is an equally, if not more important factor in the complex process of cognitive ageing

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

The association between late-life cognitive test scores and retrospective informant interview data

Background: Cognitive assessment of older persons, particularly those with impairment, is hampered by measurement error and the ethical issues of testing people with dementia. A potential source of valuable information about end-of-life cognitive status can be gained from those who knew the respondent well-mostly relatives or friends. This study tested the association between last cognitive assessment before death and a retrospective informant assessment of cognition. Methods: Data were analyzed from 248 participants from the Medical Research Council Cognitive Function and Ageing Study who were aged 71 to 102 years at death. Late-life cognition was assessed 0 to 8 years before death using the Mini-mental State Examination (MMSE) and the informant measure was taken 0 to 7 years after death using a Retrospective Informant Interview (RInI). Results: Zero-inflated Poisson regression showed a strong association between MMSE scores and RInI scores-those scoring 29-30 on the MMSE had a RInI score four times lower than those who scored <18 (p < 0.001). The time between MMSE and death was also a significant predictor with each additional year increasing RInI scores by 12.4% (p < 0.001). The time between death and RInI was only a significant predictor when including measures that were taken four years or more after death. Conclusions: Cognitive scores from retrospective informant interviews are strongly associated with late-life MMSE scores taken close to death. This suggests that the RInI can be used as a proxy measure of cognition in the period leading up to death. © 2010 International Psychogeriatric Association

Association between anticholinergic burden and dementia in UK Biobank

Abstract Background Previous studies on the relationship between anticholinergic drugs and dementia have reported heterogeneous results. This variability could be due to different anticholinergic scales and differential effects of distinct classes of drugs. Methods Using Cox proportional hazards models, we computed the association between annual anticholinergic burden (AChB) and the risk of dementia in UK Biobank with linked general practitioner prescription records between the years 2000 and 2015 (n = 171,775). Results AChB according to most anticholinergic scales (standardized odds ratio range: 1.027–1.125) and the slope of the AChB trajectory (hazard ratio = 1.094; 95% confidence interval: 1.068–1.119) were predictive of dementia. However, the association between AChB and dementia held only for some classes of drugs, especially antidepressants, antiepileptics, and antidiuretics. Discussion The heterogeneity in previous findings may partially be due to different effects for different classes of drugs. Future studies should establish differences in more detail and further examine the practicality of a general measure of AChB relating to the risk of dementia

Attitudes to ageing, biomarkers of ageing and mortality:The Lothian Birth Cohort 1936

Objective: To investigate whether people with more positive attitudes to ageing are biologically younger as defined by leucocyte telomere length, accelerated DNA methylation GrimAge (AgeAccelGrim) and brain-predicted age difference, and whether these biomarkers explain relationships between attitudes to ageing and mortality.Methods: We used linear regression to examine cross-sectionally attitudes to ageing (measured using the Attitudes to Ageing Questionnaire) and the three biomarkers in 758 adults, mean age 72.5 years, from the Lothian Birth Cohort 1936. We used Cox proportional hazards models to examine longitudinally attitudes to ageing and mortality and the role of the biomarkers.Results: More positive attitude to physical change was associated with younger biological age, as measured by AgeAccelGrim and brain-predicted age difference in age-adjusted and sex-adjusted models: for an SD higher score, AgeAccelGrim was lower by -0.73 (95% CI -1.03 to -0.42) of a year, and brain-predicted age difference was lower by -0.87 (1.51 to 0.23) of a year. Both associations were attenuated by adjustment for covariates and not significant after simultaneous adjustment for all covariates and correction for multiple testing. More positive attitudes to physical change were associated with lower mortality: for an SD higher score the age-adjusted and sex-adjusted HR (95% CI) was 0.66 (0.56 to 0.78). Adjustment for AgeAccelGrim or brain-predicted age difference attenuated this association slightly. It remained significant after adjustment for all covariates.Conclusion: We found partial evidence that attitudes to ageing are linked with ageing biomarkers but they accounted for only a little of the association between attitudes and mortality

Examining the influence of gender, education, social class and birth cohort on MMSE tracking over time: a population-based prospective cohort study.

BACKGROUND: Whilst many studies have analysed predictors of longitudinal cognitive decline, few have described their impact on population distributions of cognition by age cohort. The aim of this paper was to examine whether gender, education, social class and birth cohort affect how mean population cognition changes with age. METHODS: The Medical Research Council Cognitive Function and Ageing Study (MRC CFAS) is a multi-centre population based longitudinal study of 13,004 individuals in England and Wales. Using ten years of follow-up data, mean Mini-mental State Examination (MMSE) scores were modelled by age and birth cohort adjusting for non-random drop-out. The model included terms to estimate cohort effects. Results are presented for five year age bands between 65-95 years. RESULTS: At a population level, women show greater change in MMSE scores with age than men. Populations with lower education level and manual work also show similar effects. More recent birth cohorts have slightly higher scores. CONCLUSION: Longitudinal data can allow examination of population patterns by gender, educational level, social class and cohort. Each of these major socio-demographic factors shows some effect on whole population change in MMSE with age.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are