Cognitive Decline and Alzheimer's Disease in Old Age: A Sex-Specific Cytokinome Signature

"Let's talk about sex, inflammaging, and cognition, baby": A meta-analysis and meta-regression of 106 case-control studies on mild cognitive impairment and Alzheimer's disease

Background

Chronic inflammation is recognised as an important component of Alzheimer's disease (AD), yet its relationship with cognitive decline, sex-differences, and age is not well understood. This study investigated the relationship between inflammatory markers, cognition, sex, and age in individuals with mild cognitive impairment (MCI) and AD.

Methods

A systematic review was performed to identify case-control studies which measured cognitive function and inflammatory markers in serum, plasma, and cerebrospinal fluid in individuals with MCI or AD compared with healthy control (HC) participants. Meta-analysis was performed with Hedges' g calculated in a random effects model. Meta-regression was conducted using age, sex, and mini-mental status exam (MMSE) values.

Results

A total of 106 studies without a high risk of bias were included in the meta-analysis including 18,145 individuals: 5625 AD participants, 3907 MCI participants, and 8613 HC participants. Combined serum and plasma meta-analysis found that IL1β, IL6, IL8, IL18, CRP, and hsCRP were significantly raised in individuals with AD compared to HC. In CSF, YKL40, and MCP-1 were raised in AD compared to HC. YKL40 was also raised in MCI compared to HC. Meta-regression analysis highlighted several novel findings: MMSE was negatively correlated with IL6 and positively correlated with IL1α in AD, while in MCI studies, MMSE was negatively correlated with IL8 and TNFα. Meta-regression also revealed sex-specific differences in levels of IL1α, IL4, IL6, IL18, hsCRP, MCP-1, and YKL-40 across AD and MCI studies, and age was found to account for heterogeneity of CRP, MCP-1, and IL4 in MCI and AD.

Conclusion

Elevated levels of IL6 and YKL40 may reflect microglial inflammatory activity in both MCI and AD. Systemic inflammation may interact with the central nervous system, as poor cognitive function in individuals with AD and MCI was associated with higher levels of serum and plasma proinflammatory cytokines IL6 and TNFα. Moreover, variations of systemic inflammation between males and females may be modulated by sex-specific hormonal changes, such as declining oestrogen levels in females throughout the menopause transition. Longitudinal studies sampling a range of biospecimen types are needed to elucidate the nuances of the relationship between inflammation and cognition in individuals with MCI and AD, and understand how systemic and central inflammation differentially impact cognitive function.

The neutrophil-to-lymphocyte ratio is associated with mild cognitive impairment in community-dwelling older women aged over 70 years: a population-based cross-sectional study

Background

The neutrophil-to-lymphocyte ratio (NLR) is a marker of inflammation that can be obtained quickly, conveniently, and cheaply from blood samples. However, there is no research to explore the effects of sex and age on the relationship between the NLR and mild cognitive impairment (MCI) in community-dwelling older adults.

Methods

A total of 3,126 individuals aged over 60 years in Shanghai were recruited for face-to-face interviews, and blood samples were collected. MCI was assessed by the Mini-Mental State Examination (MMSE) and the Instrumental Activities of Daily Living (IADL) scale, and neutrophil count and lymphocyte counts were measured in fasting blood samples. The NLR was calculated by dividing the absolute neutrophil count by the absolute lymphocyte count.

Results

In females, the NLR in the MCI group was significantly higher than that in the cognitively normal group (2.13 ± 0.94 vs. 1.85 ± 0.83, p < 0.001) but not in men. Logistic regression showed that a higher NLR was an independent risk factor for MCI in women [odds ratio (OR) = 1.33; 95% confidence interval (CI) = 1.14-1.55]. In addition, the elevated NLR quartile was associated with an increased risk of MCI, especially in women older than 70 years (p value for trend = 0.012).

Conclusion

Compared with males, female MCI patients had a significantly higher NLR than cognitively normal controls. In addition, elevated NLR was found to be significantly associated with MCI risk in women older than 70 years. Therefore, elderly Chinese women with a higher NLR value may be the target population for effective prevention of MCI.

Blood and CSF chemokines in Alzheimer's disease and mild cognitive impairment: a systematic review and meta-analysis

OBJECTIVE

Chemokines, which are chemotactic inflammatory mediators involved in controlling the migration and residence of all immune cells, are closely associated with brain inflammation, recognized as one of the potential processes/mechanisms associated with cognitive impairment. We aim to determine the chemokines which are significantly altered in Alzheimer's disease (AD) and mild cognitive impairment (MCI), as well as the respective effect sizes, by performing a meta-analysis of chemokines in cerebrospinal fluid (CSF) and blood (plasma or serum).

METHODS

We searched three databases (Pubmed, EMBASE and Cochrane library) for studies regarding chemokines. The three pairwise comparisons were as follows: AD vs HC, MCI vs healthy controls (HC), and AD vs MCI. The fold-change was calculated using the ratio of mean (RoM) chemokine concentration for every study. Subgroup analyses were performed for exploring the source of heterogeneity.

RESULTS

Of 2338 records identified from the databases, 61 articles comprising a total of 3937 patients with AD, 1459 with MCI, and 4434 healthy controls were included. The following chemokines were strongly associated with AD compared with HC: blood CXCL10 (RoM, 1.92, p = 0.039), blood CXCL9 (RoM, 1.78, p < 0.001), blood CCL27 (RoM, 1.34, p < 0.001), blood CCL15 (RoM, 1.29, p = 0.003), as well as CSF CCL2 (RoM, 1.19, p < 0.001). In the comparison of AD with MCI, there was significance for blood CXCL9 (RoM, 2.29, p < 0.001), blood CX3CL1 (RoM, 0.77, p = 0.017), and blood CCL1 (RoM, 1.37, p < 0.001). Of the chemokines tested, blood CX3CL1 (RoM, 2.02, p < 0.001) and CSF CCL2 (RoM, 1.16, p = 0.004) were significant for the comparison of MCI with healthy controls.

CONCLUSIONS

Chemokines CCL1, CCL2, CCL15, CCL27, CXCL9, CXCL10, and CX3CL1 might be most promising to serve as key molecular markers of cognitive impairment, although more cohort studies with larger populations are needed.

miRNAs and Alzheimer's Disease: Exploring the Role of Inflammation and Vitamin E in an Old-Age Population

Alzheimer's disease (AD) is the most frequent cause of dementia worldwide and represents one of the leading factors for severe disability in older persons. Although its etiology is not fully known yet, AD may develop due to multiple factors, including inflammation and oxidative stress, conditions where microRNAs (miRNAs) seem to play a pivotal role as a molecular switch. All these aspects may be modulated by nutritional factors. Among them, vitamin E has been widely studied in AD, given the plausibility of its various biological functions in influencing neurodegeneration. From a cohort of old-aged people, we measured eight vitamin E forms (tocopherols and tocotrienols), thirty cytokines/chemokines, and thirteen exosome-extracted miRNAs in plasma of subjects suffering from subjects affected by AD and age-matched healthy controls (HC). The sample population included 80 subjects (40 AD and 40 HC) with a mean age of 77.6 ± 3.8 years, mostly women (45; 56.2%). Of the vitamin E forms, only α-tocopherol differed between groups, with significantly lower levels in AD. Regarding the examined inflammatory molecules, G-CSF, GM-CSF, INF-α2, IL-3, and IL-8 were significantly higher and IL-17 lower in AD than HC. Among all miRNAs examined, AD showed downregulation of miR-9, miR-21, miR29-b, miR-122, and miR-132 compared to controls. MiR-122 positively and significantly correlated with some inflammatory molecules (GM-CSF, INF-α2, IL-1α, IL-8, and MIP-1β) as well as with α-tocopherol even after correction for age and gender. A final binary logistic regression analysis showed that α-tocopherol serum levels were associated with a higher AD probability and partially mediated by miR-122. Our results suggest an interplay between α-tocopherol, inflammatory molecules, and microRNAs in AD, where miR-122 may be a good candidate as modulating factor.

A network approach for low dimensional signatures from high throughput data

One of the main objectives of high-throughput genomics studies is to obtain a low-dimensional set of observables-a signature-for sample classification purposes (diagnosis, prognosis, stratification). Biological data, such as gene or protein expression, are commonly characterized by an up/down regulation behavior, for which discriminant-based methods could perform with high accuracy and easy interpretability. To obtain the most out of these methods features selection is even more critical, but it is known to be a NP-hard problem, and thus most feature selection approaches focuses on one feature at the time (k-best, Sequential Feature Selection, recursive feature elimination). We propose DNetPRO, Discriminant Analysis with Network PROcessing, a supervised network-based signature identification method. This method implements a network-based heuristic to generate one or more signatures out of the best performing feature pairs. The algorithm is easily scalable, allowing efficient computing for high number of observables ([Formula: see text]-[Formula: see text]). We show applications on real high-throughput genomic datasets in which our method outperforms existing results, or is compatible with them but with a smaller number of selected features. Moreover, the geometrical simplicity of the resulting class-separation surfaces allows a clearer interpretation of the obtained signatures in comparison to nonlinear classification models.

Gender differences contribute to variability of serum lipid biomarkers for Alzheimer's disease

Background: Alzheimer's disease (AD) cannot currently be diagnosed by a blood test. One reason may be gender differences. Another may be the statistical methods used. The authors evaluate these possibilities. Objective: The authors applied serum lipidomics to find AD biomarkers in men and women. They hypothesized that AD biomarkers would differ between genders and that machine-learning algorithms would improve diagnostic performance. Methods: Serum lipids were analyzed by mass spectrometry for a training set of AD cases and controls and in a blinded test set. Statistical analyses considered gender differences. Results: Lipids best classifying AD subjects differed significantly between men and women. Robust statistical algorithms did not improve diagnostic performance. Conclusion: Poor performance of AD biomarkers appears to be due primarily to inherent variability in AD patients.

Decreased levels of cytokines implicate altered immune response in plasma of moderate-stage Alzheimer's disease patients

Alzheimer's Disease (AD) is a neurodegenerative disease characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain. However, increasing evidence suggests that the pathogenesis of the disease is associated with peripheral inflammation. Here, we aimed to determine plasma concentrations of multiple cytokines and chemokines from moderate-stage AD and age-matched controls. Changes in a total of 20 cytokines and chemokines in plasma of moderate-stage AD were evaluated by using quantitative microarray. Six of them, namely MCP-1, MIP-1a, MIP-1b, MMP-9, RANTES, and VEGF, were found to be significantly reduced in moderate-stage AD patients (n = 25) in comparison to age-matched and non-demented controls (n = 25). However, GM-CSF, GRO-α/β/γ, IFN- γ, IL-1α, IL-1β, IL-10, IL-12 p70, IL-13, IL-2, IL- 4, IL-5, IL-6, IL-8, and TNF-α showed no significant differences between the patient and control groups. On the contrary to previous early-stage AD studies that show increased plasma cytokine/chemokine levels, our results indicate that inflammatory plasma molecules are reduced in moderate-stage AD. This finding points out the reduced immune responsiveness, which is known to be directly correlated to the degree of AD.

Women with lower systemic inflammation demonstrate steeper cognitive decline with age: Results from a large prospective, longitudinal sample

Background

Men and women experience large disparities in prevalence, detection, and clinical course of neurodegenerative diseases. Inflammation has been implicated in the pathogenesis of neurodegenerative diseases, yet there is a paucity of literature documenting sex differences in this phenomenon in prospective, longitudinal studies.

Methods

Participants were 4217 non-smoking individuals (62.2% female; aged 46–91 at enrollment) enrolled in the Health and Retirement Study who provided dried blood spots and completed a standardized assessment of cognitive function 3 times across 8 years. Inflammation was indexed using C-reactive protein (CRP).

Results

Higher CRP was associated with lower concurrent cognitive function, b = −0.13 (SE = 0.06), p < .05, but less decline in cognitive function over time, b = 0.02 (SE = 0.01), p < .05. Sex moderated the association between CRP and decline in total cognitive function, b = 0.02 (SE = 0.01), p < .05, such that the steepest declines in cognitive function were observed among women with the lowest CRP concentrations.

Conclusions

Women with lower systemic inflammation as measured by CRP may be at risk of going undetected for neurodegenerative disease, especially given their overall higher cognitive scores. This may perpetuate sex-related disparities in prevention and clinical course. Attention to the underlying biological mechanisms explaining the link between lower CRP and risk for cognitive decline for women and its potential clinical implications are needed.

•

Sex differences in links between inflammation and cognitive function are under-explored.

•

Higher CRP was associated with lower concurrent cognitive function, only in men.

•

Women with lower CRP showed the steepest declines in cognitive functioning.

Diagnostic Accuracy of Blood-Based Biomarker Panels: A Systematic Review

Background

Because of high prevalence of Alzheimer's disease (AD) in low- and middle-income countries (LMICs), there is an urgent need for inexpensive and minimally invasive diagnostic tests to detect biomarkers in the earliest and asymptomatic stages of the disease. Blood-based biomarkers are predicted to have the most impact for use as a screening tool and predict the onset of AD, especially in LMICs. Furthermore, it has been suggested that panels of markers may perform better than single protein candidates.

Methods

Medline/Pubmed was searched to identify current relevant studies published from January 2016 to December 2020. We included all full-text articles examining blood-based biomarkers as a set of protein markers or panels to aid in AD's early diagnosis, prognosis, and characterization.

Results

Seventy-six articles met the inclusion criteria for systematic review. Majority of the studies reported plasma and serum as the main source for biomarker determination in blood. Protein-based biomarker panels were reported to aid in AD diagnosis and prognosis with better accuracy than individual biomarkers. Conventional (amyloid-beta and tau) and neuroinflammatory biomarkers, such as amyloid beta-42, amyloid beta-40, total tau, phosphorylated tau-181, and other tau isoforms, were the most represented. We found the combination of amyloid beta-42/amyloid beta-40 ratio and APOEε4 status to be most represented with high accuracy for predicting amyloid beta-positron emission tomography status.

Conclusion

Assessment of Alzheimer's disease biomarkers in blood as a non-invasive and cost-effective alternative will potentially contribute to early diagnosis and improvement of therapeutic interventions. Given the heterogeneous nature of AD, combination of markers seems to perform better in the diagnosis and prognosis of the disease than individual biomarkers.

Hyperactivation of monocytes and macrophages in MCI patients contributes to the progression of Alzheimer's disease

Background

Alzheimer’s disease (AD) is the most common neurodegenerative disease ultimately manifesting as clinical dementia. Despite considerable effort and ample experimental data, the role of neuroinflammation related to systemic inflammation is still unsettled. While the implication of microglia is well recognized, the exact contribution of peripheral monocytes/macrophages is still largely unknown, especially concerning their role in the various stages of AD.

Objectives

AD develops over decades and its clinical manifestation is preceded by subjective memory complaints (SMC) and mild cognitive impairment (MCI); thus, the question arises how the peripheral innate immune response changes with the progression of the disease. Therefore, to further investigate the roles of monocytes/macrophages in the progression of AD we assessed their phenotypes and functions in patients at SMC, MCI and AD stages and compared them with cognitively healthy controls. We also conceptualised an idealised mathematical model to explain the functionality of monocytes/macrophages along the progression of the disease.

Results

We show that there are distinct phenotypic and functional changes in monocyte and macrophage populations as the disease progresses. Higher free radical production upon stimulation could already be observed for the monocytes of SMC patients. The most striking results show that activation of peripheral monocytes (hyperactivation) is the strongest in the MCI group, at the prodromal stage of the disease. Monocytes exhibit significantly increased chemotaxis, free radical production, and cytokine production in response to TLR2 and TLR4 stimulation.

Conclusion

Our data suggest that the peripheral innate immune system is activated during the progression from SMC through MCI to AD, with the highest levels of activation being in MCI subjects and the lowest in AD patients. Some of these parameters may be used as biomarkers, but more holistic immune studies are needed to find the best period of the disease for clinical intervention.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-021-00236-x.

The improvement of cognitive deficits after whole-body cryotherapy - A randomised controlled trial

BACKGROUND

Whole-body cryotherapy (WBC) - a repetitive, short-term exposure to extremely low temperatures - may become an effective early intervention for mild cognitive impairment (MCI). It is a heterogeneous group of symptoms associated with cognitive dysfunction which is estimated to transform into dementia in 50% cases.

STUDY DESIGN

The prospective randomised double-blind sham-controlled study aimed to determine the efficacy of WBC on cognitive functioning and biological mechanisms. The study was registered with Australian New Zealand Clinical Trials Registry (ACTRN12619001627145).

METHODS

Participants with MCI (n = 62; (20<MoCA>26) were randomly allocated to cryogenic temperatures (-110 °C till -160 °C) (EG, n = 33) or placebo-controlled group (CG, n = 29). Cognitive functions were measured at baseline (T1), after the 10th WBC session (T2) and after 2 week-break (T3) with DemTect, SLUMS and Test Your Memory (TYM). Secondary outcome measures included quality of life (WHOQoL-BREF), self-reported well-being (VAS) and depressive symptoms (GDS). Whole blood samples (10 ml) were collected at T1 and T2 to evaluate levels of cytokines, neurotrophins, NO and biochemical parameters CRP total cholesterol, prolactin).

RESULTS

There were significant differences between groups measured at T2 in immediate recall (DemTect) and in orientation (TYM) in favour of WBC group. Improvement in mood was detected in self-reported depressive symptoms level (WHOQoL-26; T2 p = 0.04; VAS mood T2 p = 0.02; T3 p = 0.07). The significant reduction of BDNF level was observed (p < 0.05).

CONCLUSIONS

WBC may increase the performance of cognitive functions. It seems promising to combine WBC with existing behavioural and cognitive trainings in the future studies investigating early interventions methods in MCI.

Sex-specific associations of inflammation markers with cognitive decline

BACKGROUND/OBJECTIVE

Inflammation is implicated in cognitive decline; however, there is a paucity of data for African American populations and for sex-specific associations.

DESIGN

Prospective cohort study.

SETTING

Genetic Epidemiology Network of Arteriopathy/Genetics of Microangiopathic Brain Injury studies.

PARTICIPANTS

African-American sibships (N = 1010).

MEASUREMENTS

Neurocognitive tests assessed global cognition and four cognitive domains: processing speed, memory, language, and executive function at two time points over seven years. Circulating levels of C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor receptor (TNFR)-1 and TNFR2 were measured at study baseline. Linear mixed models were used to investigate the association between inflammation markers and cognitive decline.

RESULTS

Among men, a one SD increase in CRP was associated with an increased rate of decline over 7 years in global cognitive Z-score (adjusted difference in slopes = -0.31, p = 0.006) and in processing speed Z-score (adjusted difference in slopes = -0.10, p = 0.02), but not declines in memory, language, or executive function Z-scores. Also among men, a one SD increase in IL-6 was associated with an increased decline rate in global cognitive Z-score (adjusted difference in slopes = -0.33, p = 0.002) and in processing speed Z-score (adjusted difference in slopes = -0.12, p = 0.007). There was no difference in decline rates by CRP or IL-6 level in adjusted analyses among women for any cognitive scores. Among men and women combined, a one SD increase in baseline sTNFR1 was associated with a faster rate of decline in memory Z-score (adjusted difference in slopes = -0.09, p = 0.02). Baseline sTNFR2 levels did not significantly predict rate of cognitive decline in any cognitive domains.

CONCLUSIONS

Circulating markers of CRP and IL-6 may be differential risk factors for men and women in relation to cognitive decline. A novel inflammation marker, sTNFR1, may be a useful predictor of memory decline in older adults.