C-reactive protein and familial risk for dementia: a phenotype for successful cognitive aging

Impact of hs-CRP concentration on brain structure alterations and cognitive trajectory in Alzheimer's disease

Introduction

Present study was to investigate hs-CRP concentration, brain structural alterations, and cognitive function in the context of AD [Subjective cognitive decline (SCD), mild cognitive impairment (MCI), and AD].

Methods

We retrospectively included 313 patients (Mean age = 76.40 years, 59 SCD, 101 MCI, 153 AD) in a cross-sectional analysis and 91 patients (Mean age = 75.83 years, 12 SCD, 43 MCI, 36 AD) in a longitudinal analysis. Multivariable linear regression was conducted to investigate the relationship between hs-CRP concentration and brain structural alterations, and cognitive function, respectively.

Results

Hs-CRP was positively associated with gray matter volume in the left fusiform (β = 0.16, pFDR = 0.023) and the left parahippocampal gyrus (β = 0.16, pFDR = 0.029). Post hoc analysis revealed that these associations were mainly driven by patients with MCI and AD. The interaction of diagnosis and CRP was significantly associated with annual cognitive changes (β = 0.43, p = 0.008). Among these patients with AD, lower baseline CRP was correlated with greater future cognitive decline (r = -0.41, p = 0.013).

Conclusion

Our study suggests that increased hs-CRP level may exert protective effect on brain structure alterations and future cognitive changes among patients already with cognitive impairment.

Associations of circulating C-reactive proteins, APOE ε4, and brain markers for Alzheimer's disease in healthy samples across the lifespan

The apolipoprotein E gene ε4 allele (APOE ε4) and higher circulating level of C-reactive protein (CRP) have been extensively investigated as risk factors for Alzheimer's disease (AD). Paradoxically, APOE ε4 has been associated with lower levels of blood CRP in middle-aged and older populations. However, few studies have investigated this intriguing relation and its impact on neurological markers for AD in younger ages, nor across the whole lifespan. Here, we examine associations of blood CRP levels, APOE ε4, and biomarkers for AD in a cognitively healthy lifespan cohort (N up to 749; 20-81 years of age) and replicate the findings in UK Biobank (N = 304 322; 37-72 years of age), the developmental ABCD study (N = 10 283; 9-11 years of age), and a middle-aged sample (N = 339; 40-65 years of age). Hippocampal volume, brain amyloid-β (Aβ) plaque levels, cerebrospinal fluid (CSF) levels of Aβ and tau species, and neurofilament protein light protein (NFL) were used as AD biomarkers in subsamples. In addition, we examined the genetic contribution to the variation of CRP levels over different CRP ranges using polygenic scores for CRP (PGS-CRP). Our results show APOE ε4 consistently associates with low blood CRP levels across all age groups (p < 0.05). Strikingly, both ε4 and PGS-CRP associated mainly with blood CRP levels within the low range (<5mg/L). We then show both APOE ε4 and high CRP levels associate with smaller hippocampus volumes across the lifespan (p < 0.025). APOE ε4 was associated with high Aβ plaque levels in the brain (FDR-corrected p = 8.69x10^-4), low levels of CSF Aβ42 (FDR-corrected p = 6.9x10^-2), and lower ratios of Aβ42 to Aβ40 (FDR-corrected p = 5.08x10^-5). Blood CRP levels were weakly correlated with higher ratio of CSF Aβ42 to Aβ40 (p = 0.03, FDR-corrected p = 0.4). APOE ε4 did not correlate with blood concentrations of another 9 inflammatory cytokines, and none of these cytokines correlated with AD biomarkers. CONCLUSION: The inverse correlation between APOEε 4 and blood CRP levels existed before any pathological AD biomarker was observed, and only in the low CRP level range. Thus, we suggest to investigate whether APOEε 4 can confer risk by being associated with a lower inflammatory response to daily exposures, possibly leading to greater accumulation of low-grade inflammatory stress throughout life. A lifespan perspective is needed to understand this relationship concerning risk of developing AD.

Roles of C-reactive protein polymorphisms and life event changes on cognitive function in bipolar patients receiving valproate

Introduction

Patients with bipolar disorder (BD) exhibit an inflamed condition that is associated with metabolic disturbance and cognitive impairment. Whether inflammation, represented by C-reactive protein (CRP), is causally associated with BD and influences treatment outcome has not been established.

Methods

We examined whether CRP is a causal factor for the risk of BD in drug-naïve, depressed BD patients and investigated whether polymorphisms in CRP and life event changes influence cognitive function in BD patients receiving valproate (VPA) treatment.

Results

Our results showed that BD patients had significantly higher CRP levels and worse cognitive function than the controls, while the frequencies of CRP single nucleotide polymorphisms in BD patients and in controls were not different. In addition, the life event scale score was higher for BD patients than for controls. Furthermore, the genotypes of CRP polymorphisms and the interactions between polymorphisms of CRP and life event scale score had a significant influence on cognitive performance in BD patients after 12 weeks of VPA treatment.

Conclusion

Our study demonstrated the clinical utility of the application of functional genetics in clarifying the interactions among CRP, life event stress, and BD and suggested the important roles of CRP gene–environment interactions in developing treatment strategies for BD.

Longitudinal associations between C-reactive protein and cognitive performance in normative cognitive ageing and dementia

BACKGROUND

systemic inflammation appears to play an important role in the pathogenesis and expression of Alzheimer's disease and other dementias. Previous research has found that elevated levels of serum C-reactive protein (CRP) is associated with poorer cognitive functioning and increased risk for dementia. However, most studies are limited by single CRP measurements, which fail to capture long-term inflammatory exposures or dynamic changes in inflammation and cognition which may occur across repeated measurements.

METHODS

using data from 3,563 older adults aged 65-101 from the Health and Retirement Study, we examined bivariate changes in CRP and cognition measured repeatedly over a 10-year follow-up. Bivariate multilevel models estimated the effect of time-varying CRP on cognition among cognitively healthy older adults and in a subset of 427 participants who reported incident dementia onset during the follow-up period.

RESULTS

in cognitively healthy participants, CRP was associated with lower level of cognitive functioning, but not rate of change over time. This effect was significant in participants under 80 years of age (b = -0.09, standard error (SE) = 0.05, P = 0.04), but not in older participants. In participants with incident dementia, those with higher CRP experienced smaller rates of cognitive decline, leading up to dementia diagnosis.

CONCLUSIONS

elevated levels of CRP predict poorer cognition and increased dementia risk in cognitively healthy adults under the age of 80. Conversely, increased CRP may confer protective effects on cognition in the prodromal stage of dementia.

C-reactive protein and risk of cognitive decline: The REGARDS study

Markers of systemic inflammation are associated with increased risk of cognitive impairment, but it is unclear if they are associated with a faster rate of cognitive decline and whether this relationship differs by race. Our objective was to examine the association of baseline C-reaction protein (CRP) with cognitive decline among a large racially diverse cohort of older adults. Participants included 21,782 adults aged 45 and older (36% were Black, Mean age at baseline 64) from the REasons for Geographic And Racial Differences in Stroke (REGARDS) study. CRP was measured at baseline and used as a continuous variable or a dichotomous grouping based on race-specific 90th percentile cutoffs. Cognitive measures of memory and verbal fluency were administered every 2 years for up to 12 years. Latent growth curve models evaluated the association of CRP on cognitive trajectories, adjusting for relevant demographic and health factors. We found that higher CRP was associated with worse memory (B = -.039, 95% CI [-.065,-.014]) and verbal fluency at baseline (B = -.195, 95% CI [-.219,-.170]), but not with rate of cognitive decline. After covariate adjustment, the association of CRP on memory was attenuated (B = -.005, 95% CI [-.031,-.021]). The association with verbal fluency at baseline, but not over time, remained (B = -.042, 95% CI [-.067,-.017]). Race did not modify the association between CRP and cognition. Findings suggest that levels of CRP at age 45+, are a marker of cognitive impairment but may not be suitable for risk prediction for cognitive decline.

Understanding the Physiological Links Between Physical Frailty and Cognitive Decline

Declines in both physical and cognitive function are associated with increasing age. Understanding the physiological link between physical frailty and cognitive decline may allow us to develop interventions that prevent and treat both conditions. Although there is significant epidemiological evidence linking physical frailty to cognitive decline, a complete understanding of the underpinning biological basis of the two disorders remains fragmented. This narrative review discusses insights into the potential roles of chronic inflammation, impaired hypothalamic-pituitary axis stress response, imbalanced energy metabolism, mitochondrial dysfunction, oxidative stress, and neuroendocrine dysfunction linking physical frailty with cognitive decline. We highlight the importance of easier identification of strategic approaches delaying the progression and onset of physical frailty and cognitive decline as well as preventing disability in the older population.

Outcome age-based prediction of successful cognitive aging by total cholesterol

INTRODUCTION

Some associations of high total cholesterol with dementia risk diminish as the outcome age-age at cognitive assessment-increases.

METHODS

The Framingham Heart Study provided 1897 participants with intact cognition at entry. Cox regression analysis for incident marked cognitive decline included "time-dependent" coefficients, with associations between total cholesterol and covariates changing by outcome age. Decline within age categories of 75-84 and 85-94 years was also examined.

RESULTS

Significant associations of rising total cholesterol linear slope, low entry age, low education, and statin nonuse with risk diminished significantly by outcome age. At 85-94 years, falling linear slope was significant.

DISCUSSION

The protected survival model posits a minority subpopulation with protection against mortality and cognitive decline associated with total cholesterol risk factors. It predicts the observed diminished or reversed cholesterol associations with increasing age. Protection is particularly likely for successful cognitive aging-intact cognition at very old age-despite increased risk from cholesterol.

The association of high sensitivity C-reactive protein and incident Alzheimer disease in patients 60 years and older: The HUNT study, Norway

Background

With ageing, long-standing inflammation can be destructive, contributing to development of several disorders, among these Alzheimer’s disease (AD). C-reactive protein (CRP) is a relatively stable peripheral inflammatory marker, but in previous studies the association between highly sensitive CRP (hsCRP) and AD have shown inconsistent results. This study examines the association between AD and hsCRP in blood samples taken up to 15 years prior to the diagnoses of 52 persons with AD amongst a total of 2150 persons ≥60 years of age.

Results

Data from Norway’s Nord-Trøndelag Health Study (HUNT 2) and the Health and Memory Study (HMS) were linked. The participants had an average age of 73 years, and diagnosed with AD up to 15 years [mean 8.0 (±3.9)] following hsCRP measurement. Logistic regression models showed an adverse association between hsCRP and AD in participants aged 60-70.5 (odds ratio: 2.37, 95% CI: 1.01-5.58). Conversely, in participants aged 70.6-94, there was an inverse association between hsCRP and AD (odds ratio: 0.39, 95% CI: 0.19-0.84). When applying multivariate models the findings were significant in individuals diagnosed 0.4-7 years after the hsCRP was measured; and attenuated when AD was diagnosed more than seven years following hsCRP measurement.

Conclusions

Our study is in line with previous studies indicating a shift in the association between hsCRP and AD by age: in adults (60-70.5 years) there is an adverse association, while in seniors (>70.6 years) there is an inverse association. If our findings can be replicated, a focus on why a more active peripheral immune response may have a protective role in individuals ≥70 years should be further examined.

The protected survivor model: Using resistant successful cognitive aging to identify protection in the very old

For some cardiovascular risk factors, association with risk for cognitive impairment observed in early old age is reduced, or paradoxically even reversed, as age of outcome increases. Successful cognitive aging is intact cognition in the oldest-old; we define resistant successful cognitive aging as successful cognitive aging despite high risk. The protected survivor model posits that a minority of the general population has a protective factor that mitigates the negative effect of a risk factor on successful cognitive aging for the unprotected majority. As age increases, differential failure rates increase the proportion of survivors with protection. Among the unprotected, the proportion with low risk increases, but among those with protection, high risk and low risk do not differ. Due to differential mortality, half the survivors are eventually protected - a majority among those with high risk, and a minority among those with low risk. According to the protective survivor model, an example of Simpson's paradox, the association of the risk factor with survival does not change within an individual, but the association in the surviving population changes as its age increases. We created quantitative illustrations of a simplified protected survivor model applied to successful cognitive aging to explain how the usual association of a risk factor with cognitive decline is reversed in the very old. In the illustrations, probability of subsequent survival was higher for survivors with high risk (mostly protected) than low risk (mostly not protected), an example of Simpson's paradox. Resistance to disease despite the presence of risk factors is consistent with the presence of countervailing protection. Based on the protected survivor model, we hypothesize that studies seeking protective factors against cognitive decline will be more effective by limiting a successful cognitive aging sample to resistant successful cognitive aging - to contrast with a sample without successful cognitive aging.

Dementia Risk and Protective Factors Differ in the Context of Memory Trajectory Groups

BACKGROUND

Previous research has identified multiple risk and protective factors for late onset Alzheimer's disease (LOAD). However, it is not known whether these risk and protective factors differ for individuals who are cognitively stable versus those already experiencing declines.

OBJECTIVE

This study examined how dementia risk factors differ across subgroups of older adults defined by memory trajectory. This line of research may lead to more individualized risk profiles.

METHODS

Risk factors for incident LOAD were compared across previously-validated groups of older adults exhibiting different memory trajectories ("Stable-High," "Stable-Low," "Decliner," "Rapid Decliner") using stratified Cox regressions. Participants included 2,593 racially/ethnically diverse older adults (mean age of 76 at study entry) in the Washington Heights-Inwood Columbia Aging Project.

RESULTS

Predictors of incident dementia differed across trajectory groups: older age only incurred independent risk in stable groups, education did not incur independent protection in the rapidly declining group, depression only incurred independent risk in the stable-low group, stroke incurred independent risk in the two extreme groups, and APOE-ɛ4 only incurred independent risk in the rapidly declining group.

CONCLUSION

The finding that different risk factors for LOAD were associated with specific memory trajectories may reflect the existence of resilience or vulnerability factors that modify the individual influences of risk/protective factors. This study highlights the utility of considering interactions between dementia risk factors and a patient's unique cognitive history.

Peripheral Inflammatory Biomarkers and Cognitive Decline in Older Adults With and Without Alzheimer's Disease: A Systematic Review

Peripheral inflammatory biomarkers may play an important role in the cognitive decline of aging and incidence of Alzheimer's disease (AD); however, data from epidemiological studies present conflicting findings. The purpose of the current review was to systematically determine the current state of the science on the association between peripheral inflammatory biomarkers and cognitive decline. Articles published from January 1, 2006 to October 28, 2016 were searched using the Medline and Embase databases. Nine studies met inclusion criteria (two examined participants with AD dementia and seven examined participants without dementia). Although a wide range of peripheral inflammatory biomarkers was examined, C-reactive protein and interleukin 6 were the most studied. Findings show conflicting results for the association between peripheral inflammatory biomarkers and cognitive decline. Peripheral inflammation may harm and help the brain, and therefore, the challenge of modulating immunity will be to find ways of fine tuning inflammation to delay, prevent, or treat AD. [Journal of Gerontological Nursing, 43(12), 53-60.].

Cognitive Ageing in Great Britain in the New Century: Cohort Differences in Episodic Memory

BACKGROUND

Dementias in high income countries are set to be the third major burden of disease even as older people are increasingly required to think for themselves how to provide for their lives in retirement. Meanwhile the period of older age continues to extend with increase in life expectancy. This challenge demands an understanding of how cognition changes over an extended period in later life. But studying cognitive ageing in the population faces a difficulty from the fact that older respondents are liable to leave (attrite) before study completion. This study tested three hypotheses: trajectories of cognitive ageing in Britain show an improvement beyond the age of 50; and they are lifted by secular improvement in cognition across cohorts; lastly they are susceptible to distortion due to attrition.

METHODS AND FINDINGS

Using the English Longitudinal Study of Ageing, this paper studied trajectories of episodic memory of Britons aged 50-89 from 2002 to 2013 (N = 5931). Using joint models the analysis found that levels of episodic memory follow a curvilinear shape, not a steady decline, in later life. The findings also revealed secular improvement in cognitive ageing such that as a cohort is being replaced episodic memory levels in the population improve. The analysis lastly demonstrated that failure to simultaneously model attrition can produce distorted pictures of cognitive ageing.

CONCLUSION

Old age in this century is not necessarily a period dominated by cognitive decline. In identifying behavioural factors associated with better cognitive ageing, such as social connections of traditional and online kinds, the paper raises possibilities of mustering an adequate response to the cognition challenge.

Repeated systemic inflammation was associated with cognitive deficits in older Britons

Introduction

The relationship of C-reactive protein (CRP) to cognition in the older old group (≥75 years) has recently been found positive on both sides of the Atlantic. We hypothesized that higher levels of CRP and fibrinogen are related to worse episodic memory throughout later life (≥50 years).

Methods

Data are drawn from older Britons free of dementias in the English Longitudinal Study of Aging 2004–2013. We applied growth trajectory models to repeated observations of episodic memory, CRP, and fibrinogen levels (and sociodemographic confounders). We accounted for practice effects in repeated tests of cognition.

Results

Higher levels of both inflammatory markers were associated with worse episodic memory, where a fibrinogen effect is evident throughout later life (coefficient −0.154; 95% confidence interval [CI] −0.254 to −0.054). Most importantly, the CRP effect is strongly negative among the older old group (coefficient −0.179; CI −0.320 to −0.038).

Discussion

Higher levels of fibrinogen are detrimental to older people's cognition, and among the older old, raised CRP levels are comparably deleterious. Repeated measures of inflammation can be considered in clinical practice as part of a response to the challenge of dementias.

Association of apolipoprotein E-e4 and dementia declines with age

OBJECTIVE

To study the association of dementia with apolipoprotein E-e4 (APOE-e4) and its interaction with age in a nonagenarian Costa Rican group (N-sample) and a general elderly contrast group (GE-sample).

METHODS

In both case-control studies, participants were cognitively intact or diagnosed with dementia. The N-sample (N = 112) was at least age 90 years; the GE-sample (N = 98) was at least age 65 years.

RESULTS

Dementia and APOE-e4 were not significantly associated in the N-sample, but were in the GE-sample. There was a significant interaction of age with APOE-e4 in the N-sample, but not in the GE-sample. Descriptively dividing the N-sample at the median (age 93 years) showed a group interaction: APOE-e4 was more associated with dementia in the younger N-sample than in the older N-sample, where six of seven APOE-e4 carriers were cognitively intact.

CONCLUSIONS

The results support the reduction in association of APOE-e4 with dementia in extreme old age, consistent with a survivor effect model for successful cognitive aging.

Long-term systemic inflammation and cognitive impairment in a population-based cohort

OBJECTIVES

Evidence suggests inflammation is associated with cognitive impairment, but previous epidemiological studies have reported conflicting results.

DESIGN

Prospective population-based cohort.

SETTING

Epidemiology of Hearing Loss Study participants.

PARTICIPANTS

Individuals without cognitive impairment in 1998-2000 (N = 2,422; 1,947 with necessary data).

MEASUREMENTS

Cognitive impairment (Mini-Mental State Examination score <24 or diagnosis of dementia) was ascertained in 1998-2000, 2003-2005, and 2009-2010. Serum C-reactive protein (CRP) and interleukin-6 (IL-6) were measured in 1988-1990, 1998-2000, and 2009-2010; tumor necrosis factor-alpha was measured from 1998-2000.

RESULTS

Participants with high CRP in 1988-1990 and 1998-2000 had lower risk of cognitive impairment than those with low CRP at both time points (hazard ratio (HR) = 0.46, 95% confidence interval (CI) = 0.26-0.80). Risk did not differ according to 10-year IL-6 profile or baseline inflammation category in the whole cohort. In sensitivity analyses restricted to statin nonusers, those with high IL-6 at both times had greater risk of cognitive impairment than those with low IL-6 at both times (HR = 3.35, 95% CI = 1.09-10.30). In secondary analyses, each doubling of IL-6 change over 20 years was associated with greater odds of cognitive impairment in 2009-2010 in the whole cohort (odds ratio (OR) = 1.40, 95% CI = 1.04-1.89), whereas a doubling of CRP change over 20 years was associated with cognitive impairment only in statin nonusers (OR = 1.32, 95% CI = 1.06-1.65).

CONCLUSION

With data collected over 20 years, this study demonstrated greater likelihood of cognitive impairment in individuals with repeated high or increasing IL-6. The inconsistent CRP findings may reflect effects of statin medications, survival effects, or adverse effects associated with chronically low CRP. Further studies of long-term inflammation and cognitive impairment are needed.

C-reactive protein, APOE genotype and longitudinal cognitive change in an older population

Background: circulating measures of inflammatory markers, such as C-reactive protein (CRP) have been associated with an increased risk of future cognitive decline. However, the nature of the relationship among the very old (>75 years) is unclear. Cross-sectional evidence suggests that elevated CRP may even be protective in this age group. This study examines these associations longitudinally.

Methods: logistic regression was used to investigate the association between CRP and drop in cognitive performance (≥3 point change on the Mini-Mental State Examination) over a 4-year period in a population of 266 people, mean age 77 years.

Results: increased levels of CRP were associated with a decreased risk of a drop in cognitive performance; however, this association was only seen in those without an APOE e4 allele [odds ratio of decline per unit increase in ln(CRP) 0.57, P = 0.04]. The magnitude of the finding remained consistent after adjustment for cardiovascular confounders (smoking, drinking, MI, stroke, diabetes, education, medication and blood pressure). For those with an e4 allele, the relationship with longitudinal cognitive decline was neither statistically significant nor in a consistent direction after controlling for acute inflammation.

Conclusions: this study strengthens previous cross-sectional findings and shows elevated levels of CRP to be linked to a decreased risk of longitudinal cognitive decline in the very old. However, as with prior analyses, this was only observed in those not carrying an APOE e4 allele. Future work on larger APOE e4 allele carrying samples is required to determine the nature of the association in this population.

Epigenetic determinants of healthy and diseased brain aging and cognition

A better understanding of normal and diseased brain aging and cognition will have a significant public health impact, given that the oldest-old persons older than 85 years of age represent the fastest-growing segment in the population in developed countries, with more than 30 million new cases of dementia predicted to occur worldwide each year by 2040. Dysregulation of gene expression and, more generally, genome organization and function are thought to contribute to age-related declines in cognition. Remarkably, nearly all neuronal nuclei that reside in an aged brain had permanently exited from the cell cycle during prenatal development, and DNA methylation and histone modifications and other molecular constituents of the epigenome are likely to play a critical role in the maintenance of neuronal health and function throughout the entire lifespan. Here, we provide an overview of age-related changes in the brain's chromatin structures, highlight potential epigenetic drug targets for cognitive decline and age-related neurodegenerative disease, and discuss opportunities and challenges when studying epigenetic biomarkers in aging research.

Dementia in the oldest old: a multi-factorial and growing public health issue

The population of oldest old, or people aged 85 and older, is growing rapidly. A better understanding of dementia in this population is thus of increasing national and global importance. In this review, we describe the major epidemiological studies, prevalence, clinical presentation, neuropathological and imaging features, risk factors, and treatment of dementia in the oldest old. Prevalence estimates for dementia among those aged 85+ ranges from 18 to 38%. The most common clinical syndromes are Alzheimer's dementia, vascular dementia, and mixed dementia from multiple etiologies. The rate of progression appears to be slower than in the younger old. Single neuropathological entities such as Alzheimer's dementia and Lewy body pathology appear to have declining relevance to cognitive decline, while mixed pathology with Alzheimer's disease, vascular disease (especially cortical microinfarcts), and hippocampal sclerosis appear to have increasing relevance. Neuroimaging data are sparse. Risk factors for dementia in the oldest old include a low level of education, poor mid-life general health, low level of physical activity, depression, and delirium, whereas apolipoprotein E genotype, late-life hypertension, hyperlipidemia, and elevated peripheral inflammatory markers appear to have less relevance. Treatment approaches require further study, but the oldest old may be more prone to negative side effects compared with younger patients and targeted therapies may be less efficacious since single pathologies are less frequent. We also highlight the limitations and challenges of research in this area, including the difficulty of defining functional decline, a necessary component for a dementia diagnosis, the lack of normative neuropsychological data, and other shortcomings inherent in existing diagnostic criteria. In summary, our understanding of dementia in the oldest old has advanced dramatically in recent years, but more research is needed, particularly among varied racial, ethnic, and socioeconomic groups, and with respect to biomarkers such as neuroimaging, modifiable risk factors, and therapy.