Links between inflammation and immune functioning with cognitive status among older Americans in the Health and Retirement Study

A systematic review and meta-analysis of pteridines in mild cognitive impairment and Alzheimer's disease

BACKGROUND

Alterations in specific pteridine metabolites, particularly neopterin, biopterin, and tetrahydrobiopterin have been reported in mild cognitive impairment, Alzheimer's disease, and other types of dementia. However, the available evidence regarding such alterations has not been comprehensively and critically appraised.

METHODS

We systematically reviewed studies reporting the concentrations of biopterin, tetrahydrobiopterin, and neopterin in different biological fluids in patients with mild cognitive impairment, Alzheimer's disease or other types of dementia, and healthy controls. Electronic databases were searched from inception to 29 February 2024.

RESULTS

Overall, there were no significant differences in plasma/serum concentrations of neopterin between patients with mild cognitive impairment, Alzheimer's disease, or other types of dementia, when grouped together, and healthy controls after adjusting for publication bias (11 studies, standard mean difference, SMD = 0.20, 95% CI -0.02 to 0.41, p = 0.076). In meta-regression and subgroup analysis, the effect size was significantly associated with age, number of participants, study continent, presence of mild cognitive impairment, presence of Alzheimer's disease, analytical method, and assessment of serum vs. plasma. One study reported higher urine neopterin in patients with Alzheimer's disease vs. controls whereas another study reported non-significant between-group differences in cerebrospinal neopterin. The cerebrospinal fluid concentrations of biopterin were significantly lower in patients with Alzheimer's disease vs. controls (two studies, SMD = -0.75, 95% CI -1.23 to -0.27, p = 0.002; I2 = 0.0%, p = 0.46). One study showed non-significant between-group differences in plasma biopterin whereas another study showed higher concentrations of urine biopterin in patients with Alzheimer's disease. Our search did not identify studies investigating tetrahydrobiopterin.

CONCLUSION

Our study showed no significant differences in circulating neopterin between patients with mild cognitive impairment, Alzheimer's disease, or other types of dementia, when grouped together, and healthy controls. The significant associations observed between the effect size and mild cognitive impairment and Alzheimer's disease in subgroup analysis warrant further investigation. (PROSPERO registration number: CRD42024523478).

Plasma proteomics for cognitive decline and dementia-A Southeast Asian cohort study

INTRODUCTION

The prognostic utility of plasma proteomics for cognitive decline and dementia in a Southeast Asian population characterized by high cerebrovascular disease (CeVD) burden is underexplored.

METHODS

We examined this in a Singaporean memory clinic cohort of 528 subjects (n = 300, CeVD; n = 167, incident cognitive decline) followed-up for 4 years.

RESULTS

Of 1441 plasma proteins surveyed, a 12-protein signature significantly predicted cognitive decline (q-value < .05). Sixteen diverse biological processes were implicated in cognitive decline. Ten proteins independently predicted incident dementia (q-value < .05). A unified prediction model combining plasma proteins with clinical risk factors increased the area under the curve for outcome prediction from 0.62 to 0.85. External validation in the cerebrospinal fluid proteome of an independent Caucasian cohort replicated four of the significantly predictive plasma markers for cognitive decline namely: GFAP, NEFL, AREG, and PPY.

DISCUSSION

The prognostic proteins prioritized in our study provide robust signals in two different biological matrices, representing potential mechanistic targets for dementia and cognitive decline.

HIGHLIGHTS

A total of 1441 plasma proteins were profiled in a Singaporean memory clinic cohort. We report prognostic plasma protein signatures for cognitive decline and dementia. External validation was performed in the cerebrospinal fluid proteome of a Caucasian cohort. A concordant proteomic signature was identified across both biofluids and cohorts. Further studies are needed to explore the therapeutic implications of these proteins for dementia.

Shift work schedules alter immune cell regulation and accelerate cognitive impairment during aging

BACKGROUND

Disturbances of the sleep-wake cycle and other circadian rhythms typically precede the age-related deficits in learning and memory, suggesting that these alterations in circadian timekeeping may contribute to the progressive cognitive decline during aging. The present study examined the role of immune cell activation and inflammation in the link between circadian rhythm dysregulation and cognitive impairment in aging.

METHODS

C57Bl/6J mice were exposed to shifted light-dark (LD) cycles (12 h advance/5d) during early adulthood (from ≈ 4-6mo) or continuously to a "fixed" LD12:12 schedule. At middle age (13-14mo), the long-term effects of circadian rhythm dysregulation on cognitive performance, immune cell regulation and hippocampal microglia were analyzed using behavioral, flow cytometry and immunohistochemical assays.

RESULTS

Entrainment of the activity rhythm was stable in all mice on a fixed LD 12:12 cycle but was fully compromised during exposure to shifted LD cycles. Even during "post-treatment" exposure to standard LD 12:12 conditions, re-entrainment in shifted LD mice was marked by altered patterns of entrainment and increased day-to-day variability in activity onset times that persisted into middle-age. These alterations in light-dark entrainment were closely associated with dramatic impairment in the Barnes maze test for the entire group of shifted LD mice at middle age, well before cognitive decline was first observed in aged (18-22mo) animals maintained on fixed LD cycles. In conjunction with the effects of circadian dysregulation on cognition, shifted LD mice at middle age were distinguished by significant expansion of splenic B cells and B cell subtypes expressing the activation marker CD69 or inflammatory marker MHC Class II Invariant peptide (CLIP), differential increases in CLIP+, 41BB-Ligand+, and CD74 + B cells in the meningeal lymphatics, alterations in splenic T cell subtypes, and increased number and altered functional state of microglia in the dentate gyrus. In shifted LD mice, the expansion in splenic B cells was negatively correlated with cognitive performance; when B cell numbers were higher, performance was worse in the Barnes maze. These results indicate that disordered circadian timekeeping associated with early exposure to shift work-like schedules alone accelerates cognitive decline during aging in conjunction with altered regulation of immune cells and microglia in the brain.

Herpesvirus Antibodies Are Correlated With Greater Expression of p16 in the T Cells of Humans

Background

There is an increasing awareness that aging of the immune system, or immunosenescence, is a key biological process underlying many of the hallmark diseases of aging and age-related decline broadly. While immunosenescence can be in part due to normal age-related changes in the immune system, emerging evidence posits that viral infections may be biological stressors of the immune system that accelerate the pace of immunosenescence.

Methods

We used a convenience sample of 42 individuals aged 65 years and older to examine correlations between antiviral immunoglobulin G (IgG) levels for 4 human herpesviruses (cytomegalovirus [CMV], herpes simplex virus [types 1 and 2], and Epstein-Barr virus) and multiple indicators of T-cell immunosenescence.

Results

We found that most of the sample (n = 33) was antiviral IgG positive for 2 or more of the 4 herpesvirus infections. We also examined correlations between both the total number of viruses for which an individual had antiviral IgG and each individual virus and multiple indicators of T-cell immunosenescence, particularly p16 expression. The strongest correlations were observed between the total number of viruses for which an individual had detectable antiviral IgG and p16 mean fluorescent intensity (MFI) among CD27-CD28-CD57+ CD4+ cells (r = 0.60; P < .001) and between anti-CMV IgG and p16 MFI of CD27-CD57+ CD4+ cells (r = 0.59; P < .001).

Conclusions

Broadly, our findings offer compelling preliminary evidence for future investigations to incorporate multiple indicators of persistent viral infections and a more comprehensive set of markers of T-cell immunosenescence in population-based studies of aging.

Immune cells and the trajectories of depression, anxiety, and cognitive function among people with amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) represents a complex syndrome characterized by motor, psychiatric, and cognitive symptoms, where associations between cellular immune features and non-motor manifestations remain unknown.

Methods

In this cohort study, we enrolled 250 incident people with ALS (pwALS) assessed with the Hospital Anxiety and Depression Scale, and 226 pwALS with the Montreal Cognitive Assessment, including 218 overlapping pwALS. All individuals were diagnosed between January 2015 and January 2023 in Stockholm, Sweden. We applied joint latent class models to delineate distinct trajectories of anxiety, depression, and cognition, incorporating survival outcomes. A majority of the pwALS had data on leukocyte counts and flow cytometric analyses using a comprehensive T cell panel. We then used immune cell subtypes measured at diagnosis to predict trajectories of these outcomes following ALS diagnosis.

Results

We identified two distinct trajectories for anxiety, depression, and cognitive function following ALS diagnosis. PwALS with longer survival displayed more stable trajectories, while those with shorter survival showed decreasing anxiety symptom, increasing depressive symptom, and declining cognitive function. Higher count of leukocytes at the time of ALS diagnosis tended to associate with anxiety and depression trajectories related to shorter survival. Among T cell subpopulations, several CD8+ T cell subsets were associated with a stable trajectory of depressive symptom, and, in turn, better survival.

Conclusion

ALS-associated psychiatric and cognitive trajectories vary significantly between pwALS with different prognosis. Certain T cell subsets measured at diagnosis might be indicative of depression trajectories post-diagnosis.

Blood DNA Methylation Signature for Incident Dementia: Evidence from Longitudinal Cohorts

INTRODUCTION

Distinguishing between molecular changes that precede dementia onset and those resulting from the disease is challenging with cross-sectional studies.

METHODS

We studied blood DNA methylation (DNAm) differences and incident dementia in two large longitudinal cohorts: the Offspring cohort of the Framingham Heart Study (FHS) and the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. We analyzed blood DNAm samples from over 1,000 cognitively unimpaired subjects.

RESULTS

Meta-analysis identified 44 CpGs and 44 differentially methylated regions consistently associated with time to dementia in both cohorts. Our integrative analysis identified early processes in dementia, such as immune responses and metabolic dysfunction. Furthermore, we developed a Methylation-based Risk Score, which successfully predicted future cognitive decline in an independent validation set, even after accounting for age, sex, APOE ε4, years of education, baseline diagnosis, and baseline MMSE score.

DISCUSSION

DNA methylation offers a promising source of biomarker for early detection of dementia.

A novel DNA methylation-based surrogate biomarker for chronic systemic inflammation (InfLaMeS): results from the Health and Retirement Study

Chronic low-grade systemic inflammation is a risk factor for chronic diseases and mortality and is an important biomarker in health research. DNA methylation (DNAm) surrogate biomarkers are valuable exposure, risk factor and health outcome predictors in studies where the measures cannot be measured directly and often perform as well or better than direct measure. We generated a DNAm surrogate biomarker for chronic, systemic inflammation from a systemic inflammation latent variable of seven inflammatory markers and evaluated its performance relative to measured inflammatory biomarkers in predicting several age-associated outcomes of interest, including mortality, activities of daily living and multimorbidity in the Health and Retirement Study (HRS). The DNAm surrogate, Inflammation Latent Variable Methylation Surrogate (InfLaMeS), correlated with seven individual inflammation markers (r= -0.2-0.6) and performed as well or better to the systemic inflammation latent variable measure when predicting multimorbidity, disability, and 4-year mortality in HRS. Findings were validated in an external cohort, The Irish Longitudinal Study of Ageing. These results suggest that InfLaMeS provides a robust alternative to measured blood-chemistry measures of inflammation with broad applicability in instances where values of inflammatory markers are not measured but DNAm data is available.

Food insecurity, inflammation, and immune function among older US adults: Findings from the health and Retirement study

BACKGROUND

Food insecurity (FI) is a pressing public health concern among older adults and has been associated with adverse cardiovascular outcomes. Greater systemic inflammation may provide a pathway to explain these associations, but few studies have examined the link between FI and markers of inflammation. Thus, the objective of the present study was to evaluate the associations between FI and multiple inflammatory and immune functioning biomarkers using a nationally representative study of US adults aged > 50 years.

METHOD

Participants (n = 3,924) were drawn from the longitudinal Health and Retirement Study (HRS). Household FI was assessed using the six-item Short Form Food Security Survey Module from the 2013 HRS Health Care and Nutrition Study. Markers of inflammation (neutrophil-lymphocyte ratio, albumin, hs-CRP, IL6, IL10, IL-1Ra, sTNFR-1, and TGFβ-1) and immune functioning (CMV) were collected during the 2016 HRS Venous Blood Study. Multivariate logistic and linear regression models were used to evaluate associations between household FI and inflammatory and immune functioning biomarkers, adjusting for individual and household sociodemographic characteristics.

RESULTS

The weighted prevalence of FI was 18.8 %. Age and sex-adjusted mean showed that FI was associated with higher levels of inflammation and impaired immune functioning (Ps-value < 0.05). Older adults with FI had higher mean levels of albumin, hs-CRP, IL6, IL10, IL-1Ra, TGFß-1, and CMV seronegative and borderline (Ps-value < 0.05). Multivariate-adjusted regression model showed that FI was associated with high-risk categories of hs-CRP (OR 1.34, 95 % CI 1.06, 1.68), IL-6 (OR 1.66, 95 % CI 1.28, 2.14), IL-1Ra (OR 0.67, 95 % CI 0.48, 0.93), TGFß-1 (OR 1.87, 95 % CI 1.45, 2.42), seronegativity for CMV (OR 0.48, 95 % CI 0.35, 0.64).

CONCLUSION

In this nationally representative sample of older adults, FI was positively associated with multiple markers of systemic inflammation and impaired immune functioning. Public health efforts that directly work to reduce FI among older adults are warranted and may result in further improvements in their health and well-being.

Peripheral immune function and Alzheimer's disease: a living systematic review and critical appraisal

BACKGROUND

A growing body of literature examines the relationship between peripheral immune function and Alzheimer's Disease (AD) in human populations. Our living systematic review summarizes the characteristics and findings of these studies, appraises their quality, and formulates recommendations for future research.

METHODS

We searched the electronic databases PubMed, PsycINFO, and Web of Science, and reviewed references of previous reviews and meta-analyses to identify human studies examining the relationship between any peripheral immune biomarkers and AD up to September 7th, 2023. We examined patterns of reported statistical associations (positive, negative, and null) between each biomarker and AD across studies. Evidence for each biomarker was categorized into four groups based on the proportion of studies reporting different associations: corroborating a positive association with AD, a negative association, a null association, and presenting contradictory findings. A modified Newcastle-Ottawa scale (NOS) was employed to assess the quality of the included studies.

FINDINGS

In total, 286 studies were included in this review. The majority were cross-sectional (n = 245, 85.7%) and hospital-based (n = 248, 86.7%), examining relationships between 187 different peripheral immune biomarkers and AD. Cytokines were the most frequently studied group of peripheral immune biomarkers. Evidence supported a positive association with AD for six biomarkers, including IL-6, IL-1β, IFN-γ, ACT, IL-18, and IL-12, and a negative association for two biomarkers, including lymphocytes and IL-6R. Only a small proportion of included studies (n = 22, 7.7%) were deemed to be of high quality based on quality assessment.

INTERPRETATION

Existing research on peripheral immune function and AD exhibits substantial methodological variations and limitations, with a notable lack of longitudinal, population-based studies investigating a broad range of biomarkers with prospective AD outcomes. The extent and manner in which peripheral immune function can contribute to AD pathophysiology remain open questions. Given the biomarkers that we identified to be associated with AD, we posit that targeting peripheral immune dysregulation may present a promising intervention point to reduce the burden of AD.

Racial/Ethnic differences in inflammation levels among older adults 56+: an examination of sociodemographic differences across inflammation measure

OBJECTIVE

Chronic inflammation is a key biological risk factor for many widespread adult health conditions. This study examines racial/ethnic differences in inflammation across several inflammatory markers, including selected cytokines that are identified as important for aging and age-related health outcomes.

METHODS

Data came from the 2016 Venous Blood Collection Subsample of the Health and Retirement Study. Using logistic regression models, we compared high-risk categories of C-reactive protein and cytokine markers (IL-6, IL-10, IL-1RA, TNFR1, and TGF-Beta), across race/ethnicity and whether these differences persisted among men and women.

RESULTS

The findings provided evidence of significant race/ethnic differences in inflammatory measures, but the patterns differed across marker types.

CONCLUSIONS

These findings emphasize that race/ethnic differences are not consistently captured across markers of inflammation and that researchers should proceed with caution when using individual markers of inflammation in an effort to not overlook potential racial/ethnic differences in biological risk.

Stress-related cellular pathophysiology as a crosstalk risk factor for neurocognitive and psychiatric disorders

In this narrative review, we examine biological processes linking psychological stress and cognition, with a focus on how psychological stress can activate multiple neurobiological mechanisms that drive cognitive decline and behavioral change. First, we describe the general neurobiology of the stress response to define neurocognitive stress reactivity. Second, we review aspects of epigenetic regulation, synaptic transmission, sex hormones, photoperiodic plasticity, and psychoneuroimmunological processes that can contribute to cognitive decline and neuropsychiatric conditions. Third, we explain mechanistic processes linking the stress response and neuropathology. Fourth, we discuss molecular nuances such as an interplay between kinases and proteins, as well as differential role of sex hormones, that can increase vulnerability to cognitive and emotional dysregulation following stress. Finally, we explicate several testable hypotheses for stress, neurocognitive, and neuropsychiatric research. Together, this work highlights how stress processes alter neurophysiology on multiple levels to increase individuals' risk for neurocognitive and psychiatric disorders, and points toward novel therapeutic targets for mitigating these effects. The resulting models can thus advance dementia and mental health research, and translational neuroscience, with an eye toward clinical application in cognitive and behavioral neurology, and psychiatry.

The Association Between Neutrophil-Lymphocyte Ratio and Variability with New-Onset Dementia: A Population-Based Cohort Study

BACKGROUND

Previous studies identified that neutrophil-to-lymphocyte ratio (NLR) may be a predictor of dementia. However, the associations between NLR and dementia at the population level were less explored.

OBJECTIVE

This retrospective population-based cohort study was designed to identify the associations between NLR and dementia among patients visiting for family medicine consultation in Hong Kong.

METHODS

The patients were recruited from January 1, 2000, to December 31, 2003, and followed up until December 31, 2019. The demographics, prior comorbidities, medications, and laboratory results were collected. The primary outcomes were Alzheimer's disease and related dementia and non-Alzheimer's dementia. Cox regression and restricted cubic spline were applied to identify associations between NLR and dementia.

RESULTS

A cohort of 9,760 patients (male: 41.08% ; baseline age median: 70.2; median follow-up duration: 4756.5 days) with complete NLR were included. Multivariable Cox regression identified that patients with NLR >5.44 had higher risks of developing Alzheimer's disease and related dementia (hazard ratio [HR]: 1.50, 95% Confidence interval [CI]: 1.17-1.93) but not non-Alzheimer's dementia (HR: 1.33; 95% CI: 0.60-2.95). The restricted cubic splines demonstrated that higher NLR was associated with Alzheimer's disease and related dementia. The relationship between the NLR variability and dementia was also explored; of all the NLR variability measures, only the coefficient of variation was predictive of non-Alzheimer's dementia (HR: 4.93; 95% CI: 1.03-23.61).

CONCLUSION

In this population-based cohort, the baseline NLR predicts the risks of developing dementia. Utilizing the baseline NLR during family medicine consultation may help predict the risks of dementia.