Serum cystatin C and the risk of Alzheimer disease in elderly men

A molecular index for biological age identified from the metabolome and senescence-associated secretome in humans

Unlike chronological age, biological age is a strong indicator of health of an individual. However, the molecular fingerprint associated with biological age is ill-defined. To define a high-resolution signature of biological age, we analyzed metabolome, circulating senescence-associated secretome (SASP)/inflammation markers and the interaction between them, from a cohort of healthy and rapid agers. The balance between two fatty acid oxidation mechanisms, β-oxidation and ω-oxidation, associated with the extent of functional aging. Furthermore, a panel of 25 metabolites, Healthy Aging Metabolic (HAM) index, predicted healthy agers regardless of gender and race. HAM index was also validated in an independent cohort. Causal inference with machine learning implied three metabolites, β-cryptoxanthin, prolylhydroxyproline, and eicosenoylcarnitine as putative drivers of biological aging. Multiple SASP markers were also elevated in rapid agers. Together, our findings reveal that a network of metabolic pathways underlie biological aging, and the HAM index could serve as a predictor of phenotypic aging in humans.

Cystatins: unravelling the biological implications for neuroprotection

Cystatins, a family of proteins known for their inhibitory role against cysteine proteases, have garnered significant attention in the field of neurodegeneration. Numerous genetic, experimental, and clinical studies concerning cystatin C suggest it plays an important role in the course of neurodegenerative diseases. Its beneficial effects are associated with cysteine protease inhibition, impact on β-amyloid aggregation, as well as regulation of cell proliferation, autophagy, and apoptosis. Cystatin isolated from chicken egg white, called ovocystatin, has been widely used in medical and pharmaceutical research due to its structural and biological similarities to human cystatin C. This article focuses on the potential use of cystatins, with special emphasis on easily obtained ovocystatin, in the treatment of neurodegenerative diseases, such as dementia. The current evidence on cystatin use has shed light on its mechanisms of action and therapeutic implications for neuroprotection and maintenance of cognitive functions.

The association between kidney function, cognitive function, and structural brain abnormalities in community-dwelling individuals aged 50+ is mediated by age and biomarkers of cardiovascular disease

AIMS

Cognitive impairment has been associated with kidney function and chronic kidney disease. Whether this association is due to accelerated cardiovascular disease (CVD) or an independent specific kidney function effect related to toxins is unclear. We investigated the impact of an array of clinical factors, inflammatory biomarkers, and cardiovascular biomarkers on the association between kidney function, cognitive function, and structural brain abnormalities.

METHODS AND RESULTS

We used data from the first and third waves of the TILDA Study, a population-representative prospective cohort of Irish adults aged 50 years and over, based on stratified random sampling (n = 3774). The MRI sub-study included participants who consented to MRI brain imaging in addition to the health assessment. Multivariable linear and mixed-effect longitudinal regression models were fitted separately for each kidney marker/estimated glomerular filtration rate (eGFR) equation after adjusting for baseline age and demographics, clinical vascular risk factors, and biomarkers. Unadjusted analyses showed an association between low eGFR, cognitive dysfunction, and cognitive decline (P < 0.001 for all kidney markers). Kidney function markers were also associated with white matter disease [OR = 3.32 (95% CI: 1.11, 9.98)], total grey matter volume (β = -0.17, 95% CI -0.27 to -0.07), and regional grey matter volumes within areas particularly susceptible to hypoxia (P < 0.001 for all). All the associations decreased after adjusting for age and were also diminished after adjusting for CVD biomarkers. Age and CVD-biomarker score were significant mediators of the adjusted associations between eGFR and cognitive status. These results remained consistent for cross-sectional and longitudinal outcomes and specific cognitive domains.

CONCLUSION

Decreased kidney function was associated with cerebrovascular disease. The association appeared to be mediated predominantly by age and the combination of CVD markers [namely N-terminal pro-B-type natriuretic peptide (NT-proBNP) and Growth Differentiation Factor 15 (GDF15)], supporting the idea that shared biological pathways underline both diseases. Further mechanistic studies of the specific molecular mechanisms that lead to both kidney and cognitive decline are warranted.

Identification of potential biomarkers related to mesenchymal stem cell response in patients with Alzheimer's disease

BACKGROUND

Preclinical studies showed that mesenchymal stem cells (MSCs) ameliorate tau phosphorylation, amyloid-beta accumulation, and inflammation in Alzheimer's disease (AD) mouse models via secretion of neurotrophic factors and cytokines. We aimed to identify CSF biomarkers that can be used to predict or monitor the response to MSCs in patients with AD.

METHODS

AD patients were injected with human umbilical cord blood-MSCs (n = 22) or placebo (n = 12). The cerebrospinal fluid (CSF) samples were collected at baseline, one day after the first injection, and one day after the third injection. The patients injected with MSCs were classified into good responder (GR) or poor responder (PR) groups based on the rate of changes in the ratio of total-tau and phosphorylated-tau in the CSF. We selected three typical participants in each group, and their CSF protein levels were analyzed using liquid chromatography/tandem mass spectrometry (LC-MS/MS).

RESULTS

In the LC-MS/MS analysis, 1,667 proteins were identified. Eleven proteins showed significant differences between the typical GR and PR at baseline. Based on their significance level and known functions, two proteins, reticulocalbin-3 (RCN3) and follistatin-related protein 3 (FSTL3), were selected as potential biomarkers to predict MSC response. A total of 173 proteins showed significant change one day after the third injection compared to the baseline in typical GR. We excluded 45 proteins that showed significant change after the third injection compared to the baseline in the typical PR. Based on their significance level and known function, four proteins, scrapie-responsive protein 1 (SCRG1), neural proliferation differentiation and control protein (NPDC1), apolipoprotein E (ApoE), and cystatin C (CysC), were selected as potential biomarker to monitor MSC response. Additionally, functional analysis revealed that the increased CSF proteins after the third injection compared to the baseline in the typical GR were associated with synaptogenesis.

CONCLUSIONS

This study identified two proteins (RCN3 and FSTL3) that may be potential biomarkers for predicting MSC response and four proteins (SCRG1, NPDC1, ApoE, CysC) that may be potential biomarkers for monitoring MSC response in patients with AD. Further studies are needed to validate our results. Trial registration Clinical Trials.gov, NCT02054208. Registered on 4 February 2014. Samsung Medical Center IRB File No.2017-04-025. Registered on 20 June 2017.

Decomposing interaction and mediating effects of race/ethnicity and circulating blood levels of cystatin C on cognitive status in the United States health and retirement study

Background and objectives

Elevated circulating cystatin C is associated with cognitive impairment in non-Hispanic Whites, but its role in racial disparities in dementia is understudied. In a nationally representative sample of older non-Hispanic White, non-Hispanic Black, and Hispanic adults in the United States, we use mediation-interaction analysis to understand how racial disparities in the cystatin C physiological pathway may contribute to racial disparities in prevalent dementia.

Methods

In a pooled cross-sectional sample of the Health and Retirement Study (n = 9,923), we employed Poisson regression to estimate prevalence ratios and to test the relationship between elevated cystatin C (>1.24 vs. ≤1.24 mg/L) and impaired cognition, adjusted for demographics, behavioral risk factors, other biomarkers, and chronic conditions. Self-reported racialized social categories were a proxy measure for exposure to racism. We calculated additive interaction measures and conducted four-way mediation-interaction decomposition analysis to test the moderating effect of race/ethnicity and mediating effect of cystatin C on the racial disparity.

Results

Overall, elevated cystatin C was associated with dementia (prevalence ratio [PR] = 1.2; 95% CI: 1.0, 1.5). Among non-Hispanic Black relative to non-Hispanic White participants, the relative excess risk due to interaction was 0.7 (95% CI: -0.1, 2.4), the attributable proportion was 0.1 (95% CI: -0.2, 0.4), and the synergy index was 1.1 (95% CI: 0.8, 1.8) in a fully adjusted model. Elevated cystatin C was estimated to account for 2% (95% CI: -0, 4%) for the racial disparity in prevalent dementia, and the interaction accounted for 8% (95% CI: -5, 22%). Analyses for Hispanic relative to non-white participants suggested moderation by race/ethnicity, but not mediation.

Discussion

Elevated cystatin C was associated with dementia prevalence. Our mediation-interaction decomposition analysis suggested that the effect of elevated cystatin C on the racial disparity might be moderated by race/ethnicity, which indicates that the racialization process affects not only the distribution of circulating cystatin C across minoritized racial groups, but also the strength of association between the biomarker and dementia prevalence. These results provide evidence that cystatin C is associated with adverse brain health and this effect is larger than expected for individuals racialized as minorities had they been racialized and treated as non-Hispanic White.

Serum cystatin C and mild cognitive impairment: The mediating role of glucose homeostasis

Background

This study explored the mediating role of glucose homeostasis indicators in the relationship between serum cystatin C and mild cognitive impairment (MCI).

Methods

The present study used a cross-sectional design and included 514 participants aged ≥50 years in Beijing, China. The Mini-Mental State Examination was used to assess cognitive function. Serum cystatin C and a comprehensive set of glucose homeostasis indicators were detected, including fasting blood glucose (FBG), glycosylated albumin percentage (GAP), glycated hemoglobin (HbAlc), insulin, and homeostatic model assessment of insulin resistance (HOMA-IR), and beta cell function (HOMA-β). Generalized linear models were used to investigate the associations among cystatin C, glucose homeostasis indicators, and cognitive function. Mediation analysis was conducted to explore potential mediator variables.

Results

In this study of 514 participants, 76 (14.8%) had MCI. Those with cystatin C levels ≥1.09 mg/L had a 1.98-fold higher risk of MCI than those with levels &lt;1.09 mg/L (95% CI, 1.05–3.69). FBG, GAP, and HbA1c increased the risk of MCI, while HOMA-β decreased the risk. Notably, the associations between MCI risk and cystatin C or glucose homeostasis were only founded in diabetes patients. Serum cystatin C was found to be positively associated with HOMA-β (beta (95% CI): 0.20 [0.06, 0.34]), HOMA-IR (0.23 [0.09, 0.36]), and insulin (0.22 [0.09, 0.34]) levels. Moreover, HOMA-β was identified as playing a negative mediating role (proportion mediated: −16%) in the relationship between cystatin C and MCI.

Conclusion

Elevated levels of cystatin C are associated with an increased risk of MCI. The glucose homeostasis indicator, HOMA-β, plays a negative mediating role in the relationship between cystatin C and MCI risk.

Contribution of Extracellular Vesicles and Molecular Chaperones in Age-Related Neurodegenerative Disorders of the CNS

Many neurodegenerative disorders are characterized by the abnormal aggregation of misfolded proteins that form amyloid deposits which possess prion-like behavior such as self-replication, intercellular transmission, and consequent induction of native forms of the same protein in surrounding cells. The distribution of the accumulated proteins and their correlated toxicity seem to be involved in the progression of nervous system degeneration. Molecular chaperones are known to maintain proteostasis, contribute to protein refolding to protect their function, and eliminate fatally misfolded proteins, prohibiting harmful effects. However, chaperone network efficiency declines during aging, prompting the onset and the development of neurological disorders. Extracellular vesicles (EVs) are tiny membranous structures produced by a wide range of cells under physiological and pathological conditions, suggesting their significant role in fundamental processes particularly in cellular communication. They modulate the behavior of nearby and distant cells through their biological cargo. In the pathological context, EVs transport disease-causing entities, including prions, α-syn, and tau, helping to spread damage to non-affected areas and accelerating the progression of neurodegeneration. However, EVs are considered effective for delivering therapeutic factors to the nervous system, since they are capable of crossing the blood-brain barrier (BBB) and are involved in the transportation of a variety of cellular entities. Here, we review the neurodegeneration process caused mainly by the inefficiency of chaperone systems as well as EV performance in neuropathies, their potential as diagnostic biomarkers and a promising EV-based therapeutic approach.

Association Between Serum Cystatin C and Cognitive Decline Independently from Creatinine: Evidence from Two Nationally Representative Aging Cohorts

BACKGROUND

Studies on the association between cystatin C based estimated glomerular filtration rate (eGFRcys) and cognitive outcomes yielded inconsistent results.

OBJECTIVE

The present study aimed to examine the potential association of eGFRcys with subsequent cognitive decline rate.

METHODS

A total of 11,503 community-based participants were involved in our analyses, including 5,837 (aged 72.9±6.3; 58.6% women) in the Health and Retirement Study (HRS) from the US and 5,666 (aged 58.1±9.2; 49.0% women) in the China Health and Retirement Longitudinal Study (CHARLS). The association of eGFRcys with subsequent cognitive decline rate was evaluated by linear mixed models.

RESULTS

During 85,266 person-years of follow-up, both baseline elevated serum cystatin C (-0.048 standard deviation [SD]/year per mg/L; 95% confidence interval [CI], -0.060 to -0.036; p < 0.001) and decreased eGFRcys (0.026 SD/year per 30 mL/min/1.73m2; 95% CI, 0.020 to 0.032; p < 0.001) were associated with faster cognitive decline rate after full adjustment. Compared with those had eGFRcys ≥90 mL/min/1.73m2, participants with eGFRcys between 60 to 90 mL/min/1.73m2 (-0.012 SD/year; 95% CI, -0.020 to -0.004; p = 0.004) and those with eGFRcys <60 mL/min/1.73m2 (-0.048 SD/year; 95% CI, -0.058 to -0.039; p < 0.001) experienced statistically significantly faster cognitive decline after adjustment. The associations were independent from serum creatinine/eGFRcre (eGFR that was calculated from serum creatinine).

CONCLUSION

Decreased eGFRcys are significantly associated with faster cognitive decline after full adjustment, independently from serum creatinine/eGFRcre. Serum cystatin C might be a risk factor or a prodromal biomarker of cognitive decline.

Association between serum cystatin C level and cognition in older adults: a cross-sectional analysis

Introduction

Serum Cystatin C level, an indication of kidney function, has been implicated in the pathogenesis of Alzheimer's disease and cognitive impairment. In this cross-sectional study, we looked into the relation between serum Cystatin C levels and cognition in a group of U.S. older adults.

Method

The data of this study were from the National Health and Nutrition Examination Survey (NHANES) 1999-2002. A total of 4,832 older adults aged ≥60 who met the inclusion criteria were included. The Dade Behring N Latex Cystatin C assay, which is a particle-enhanced nephelometric assay (PENIA), was utilized to assess Cystatin C levels in participants' blood samples. Participants' cognition was examined using the digit symbol substitution test (DSST). Z-scores of the DSST were calculated based on sample means and standard deviations (SD). To investigate the relationships between the quartiles of serum Cystatin C level and DSST z scores, multiple linear regression models were developed while controlling for age, sex, race/ethnicity, and education.

Results

The average age of the participants was 71.1 (SD 7.8). The participants were about half female (50.5%), non-Hispanic White (61.2%), and (36.1%) who had completed at least some college. They had an average serum Cystatin C level of 1.0 mg/dl (SD 0.44). After performing multiple linear regression with a reference group consisting of participants in quartile one of plasma Cystatin C levels, we found that serum Cystatin C levels in quartiles three and four were independently associated with lower DSST z scores (β = -0.059, 95% CI -0.200 to -0.074 and β = -0.108, 95% CI -0.319 to -0.184, respectively).

Conclusion

Higher serum Cystatin C level is associated with worse processing speed, sustained attention, and working memory in older adults. Cystatin C level may be a biomarker for cognitive decline in older adults.

Kidney function and risk of dementia: Observational study, meta-analysis, and two-sample mendelian randomization study

Whether impaired kidney function is associated with increased risk of developing dementia is unclear. We investigated the association between estimated glomerular filtration rate (eGFR) and dementia. Using a triangulation approach, we performed (1) a prospective study in 90,369 Danes from the Copenhagen General Population Study (CGPS), (2) a meta-analysis in 468,699 Scandinavians (including CGPS) and (3) a two-sample Mendelian randomization study in 218,792-1,004,040 Europeans using summary data from largest publicly available genome wide association studies (GWASs). During up to 15 years of follow-up (CGPS), 2,468 individuals developed dementia. Age and sex standardized percentile of eGFR below versus above the median conferred a multifactorially adjusted hazard ratio of 1.09 (95% confidence interval: 1.01-1.18). In meta-analysis, random-effects risk of dementia was 1.14 (1.06-1.22) for mildly decreased eGFR (60-90 mL/min/1.73 m²), 1.31 (0.92-1.87) for moderately decreased eGFR (30-59 mL/min/1.73 m²) and 1.91 (1.21-3.01) for severely decreased eGFR (< 30 mL/min/1.73 m²), compared to reference eGFR (> 90 mL/min/1.73 m²). Using directly comparable eGFR measures (log[eGFR] scaled to one standard deviation, as well as eGFR below versus above 60 mL/min/1.73 m²), we found no association with risk of dementia in observational CGPS or in Mendelian randomization analyses. In conclusion, impaired kidney function was associated with modestly increased risk of developing dementia. This was not supported by causal, genetic analyses using a Mendelian randomization approach. However, future stronger genetic instruments for kidney function and larger GWASs with more dementia cases, particularly for the vascular dementia subtype, warrant a re-evaluation of the causal hypothesis.

Identifying Blood Biomarkers for Dementia Using Machine Learning Methods in the Framingham Heart Study

Blood biomarkers for dementia have the potential to identify preclinical disease and improve participant selection for clinical trials. Machine learning is an efficient analytical strategy to simultaneously identify multiple candidate biomarkers for dementia. We aimed to identify important candidate blood biomarkers for dementia using three machine learning models. We included 1642 (mean 69 ± 6 yr, 53% women) dementia-free Framingham Offspring Cohort participants attending examination, 7 who had available blood biomarker data. We developed three machine learning models, support vector machine (SVM), eXtreme gradient boosting of decision trees (XGB), and artificial neural network (ANN), to identify candidate biomarkers for incident dementia. Over a mean 12 ± 5 yr follow-up, 243 (14.8%) participants developed dementia. In multivariable models including all 38 available biomarkers, the XGB model demonstrated the strongest predictive accuracy for incident dementia (AUC 0.74 ± 0.01), followed by ANN (AUC 0.72 ± 0.01), and SVM (AUC 0.69 ± 0.01). Stepwise feature elimination by random sampling identified a subset of the nine most highly informative biomarkers. Machine learning models confined to these nine biomarkers showed improved model predictive accuracy for dementia (XGB, AUC 0.76 ± 0.01; ANN, AUC 0.75 ± 0.004; SVM, AUC 0.73 ± 0.01). A parsimonious panel of nine candidate biomarkers were identified which showed moderately good predictive accuracy for incident dementia, although our results require external validation.

Association of Serum Levels of Cystatin C and Cognition in a Cohort of Egyptian Elderly Patients with Chronic Kidney Disease

Chronic kidney disease (CKD) and dementia are common morbidities of elders. Serum cystatin C has been suggested to be an ideal marker for kidney function. The current study aimed to detect the serum levels of cystatin C in CKD patients and to correlate these levels to cognitive performance. The study involved 90 subjects aged 65 years and more, divided into two groups: Group 1: 60 patients with CKD, and Group 2: 30 control participants. Exclusion criteria included cardiac failure, hepatic failure, thyroid diseases, dialysis for more than one month, polycystic kidney disease, organ transplantation, and immunosuppressive therapy within the past six months. All participants had routine laboratory workup, serum cystatin C using enzyme-linked immunosorbent assay kits, and cognitive assessment using mini-mental state examination (MMSE). Serum cystatin level was significantly high in CKD patients while MMSE scores were significantly lower in CKD patients. A high significant negative correlation was found between serum cystatin C levels and both degree of cognitive impairment and glomerular filtration rate (GFR). Also, a significant positive correlation was found between the degree of cognitive impairment and GFR levels. Serum cystatin levels are significantly associated with cognitive impairment in CKD patients, and this correlation becomes more evident with the worsening of CKD stages. That may help in better understanding of the pathogenesis of dementia in CKD patients with the emergence of therapeutic options depending on these data.

Changes in Serum Cystatin C Levels and the Associations With Cognitive Function in Alzheimer's Disease Patients

Background and Objective

Cystatin C is indicated to be involved in the pathogenesis of Alzheimer's disease (AD) and cognitive impairment. Our objective is to examine the serum Cystatin C levels, and to clarify the correlations between serum Cystatin C and cognitive performance in Chinese AD patients.

Methods

The serum Cystatin C concentrations in AD patients and age, sex, and body mass index (BMI) matched-healthy controls were measured. The cognitive functions of the AD patients were evaluated by using the Mini-mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). The severity of dementia was determined with clinical dementia rating (CDR).

Results

A total of 463 AD patients and 1,389 matched healthy subjects were included. AD patients had higher serum Cystatin C than healthy controls. Serum cystatin C levels were correlated with MoCA scores in AD patients. In an ordinal logistic regression model, AD patients with higher serum cystatin C levels had increased odds of severe cognitive dysfunction.

Conclusion

Our study suggested that AD patients had higher levels of serum cystatin C than age/sex/BMI-matched normal control subjects. Higher serum cystatin C may be associated with worse cognitive performance, but more studies are required to verify such association.

The impact of uremic toxins on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia, pathologically characterized by accumulation of senile plaques and neurofibrillary tangles. Chronic kidney disease (CKD) is highly prevalent in elderly population closely associated with occurrence of dementia. Recent epidemiological and experimental studies suggest a potential association of CKD with AD. Both diseases share a panel of identical risk factors, such as type 2 diabetes; and hypertension. However, the relationship between CKD and AD is unclear. Lower clearance of a panel of uremic toxin including cystatin-C, guanidine, and adiponectin due to CKD is implied to contribute to AD pathogenesis. In this review we summarize the current evidence from epidemiological, experimental and clinical studies on the potential contribution of uremic toxins to AD pathogenesis. We describe outstanding questions and propose an outlook on the link between uremic toxins and AD.

Precision Medicine in Alzheimer's Disease: Investigating Comorbid Common Biological Substrates in the Rat Model of Amyloid Beta-Induced Toxicity

Alzheimer's disease (AD), one of the most widespread neurodegenerative disorder, is a fatal global burden for the elder population. Although many efforts have been made, the search of a curative therapy is still ongoing. Individuating phenotypic traits that might help in investigating treatment response is of growing interest in AD research. AD is a complex pathology characterized by many comorbidities, such as depression and increased susceptibility to pain perception, leading to postulate that these conditions may rely on common biological substrates yet to be determined. In order to investigate those biological determinants to be associable with phenotypic traits, we used the rat model of amyloid beta-induced toxicity. This established model of early phase of AD is obtained by the intracerebroventricular injection of soluble amyloid beta1-42 (Aβ) peptide 7 days before performing experiments. In this model, we have previously reported increased immobility in the forced swimming test, reduced cortical serotonin levels and subtle alterations in the cognitive domain a depressive-like phenotype associated with subtle alteration in memory processes. In light of evaluating pain perception in this animal model, we performed two different behavioral tests commonly used, such as the paw pressure test and the cold plate test, to analyze mechanical hyperalgesia and thermal allodynia, respectively. Behavioural outcomes confirmed the memory impairment in the social recognition test and, compared to sham, Aβ-injected rats showed an increased selective susceptibility to mechanical but not to thermal stimulus. Behavioural data were then corroborated by neurochemical and biochemical biomarker analyses either at central or peripheral level. Data showed that the peptide injection evoked a significant increase in hypothalamic glutamate, kynurenine and dopamine content, while serotonin levels were reduced. Plasma Cystatin-C, a cysteine protease, was increased while serotonin and melatonin levels were decreased in Aβ-injected rats. Urinary levels paralleled plasma quantifications, indicating that Aβ-induced deficits in pain perception, mood and cognitive domain may also depend on these biomarkers. In conclusion, in the present study, we demonstrated that this animal model can mimic several comorbid conditions typical of the early phase of AD. Therefore, in the perspective of generating novel therapeutic strategies relevant to precision medicine in AD, this animal model and the biomarkers evaluated herein may represent an advantageous approach.

Blood biomarkers in Alzheimer's disease

INTRODUCTION

Early diagnosis of Alzheimer disease (AD) through the use of biomarkers could assist in the implementation and monitoring of early therapeutic interventions, and has the potential to significantly modify the course of the disease.

DEVELOPMENT

The classic cerebrospinal fluid and approved structural and functional neuroimaging biomarkers are of limited clinical application given their invasive nature and/or high cost. The identification of more accessible and less costly biomarkers, such as blood biomarkers, would increase their use in clinical practice. We review the available published evidence on the main blood biochemical biomarkers potentially useful for diagnosing AD.

CONCLUSIONS

Blood biomarkers are more cost- and time-effective than CSF biomarkers. However, immediate applicability in clinical practice is relatively unlikely. The main limitations come from the difficulty of measuring and standardising thresholds between different laboratories and the failure to replicate results. Of all the molecules studied, apoptosis and neurodegeneration biomarkers and the biomarker panels obtained through "omics" approaches, such as isolated or combined metabolomics, offer the most promising results.

Brain Exosomes: Friend or Foe in Alzheimer's Disease?

Alzheimer's disease (AD) is the most common neurodegenerative disease. It is known to be a multifactorial disease and several causes are associated with its occurrence as well as progression. However, the accumulation of amyloid beta (Aβ) is widely considered its major pathogenic hallmark. Additionally, neurofibrillary tangles (NFT), mitochondrial dysfunction, oxidative stress, and aging (cellular senescence) are considered as additional hits affecting the disease pathology. Several studies are now suggesting important role of inflammation in AD, which shifts our thought towards the brain's resident immune cells, microglia, and astrocytes; how they interact with neurons; and how these interactions are affected by intra and extracellular stressful factors. These interactions can be modulated by different mechanisms and pathways, in which exosomes could play an important role. Exosomes are multivesicular bodies secreted by nearly all types of cells. The exosomes secreted by glial cells or neurons affect the interactions and thus the physiology of these cells by transmitting miRNAs, proteins, and lipids. Exosomes can serve as a friend or foe to the neuron function, depending upon the carried signals. Exosomes, from the healthy microenvironment, may assist neuron function and health, whereas, from the stressed microenvironment, they carry oxidative and inflammatory signals to the neurons and thus prove detrimental to the neuronal function. Furthermore, exosomes can cross the blood-brain barrier (BBB), and from the blood plasma they can enter the brain cells and activate microglia and astrocytes. Exosomes can transport Aβ or Tau, cytokines, miRNAs between the cells, and alter the physiology of recipient cells. They can also assist in Aβ clearance and regulation of synaptic activity. The exosomes derived from different cells play different roles, and this field is still in its infancy stage. This review advocates exosomes' role as a friend or foe in neurodegenerative diseases, especially in the case of Alzheimer's disease.

Cerebrospinal Fluid Proteome Changes in Older Non-Cardiac Surgical Patients with Postoperative Cognitive Dysfunction

Background:

Postoperative cognitive dysfunction (POCD), a syndrome of cognitive deficits occurring 1–12 months after surgery primarily in older patients, is associated with poor postoperative outcomes. POCD is hypothesized to result from neuroinflammation; however, the pathways involved remain unclear. Unbiased proteomic analyses have been used to identify neuroinflammatory pathways in multiple neurologic diseases and syndromes but have not yet been applied to POCD.

Objective:

To utilize unbiased mass spectrometry-based proteomics to identify potential neuroinflammatory pathways underlying POCD.

Methods:

Unbiased LC-MS/MS proteomics was performed on immunodepleted cerebrospinal fluid (CSF) samples obtained before, 24 hours after, and 6 weeks after major non-cardiac surgery in older adults who did (n = 8) or did not develop POCD (n = 6). Linear mixed models were used to select peptides and proteins with intensity differences for pathway analysis.

Results:

Mass spectrometry quantified 8,258 peptides from 1,222 proteins in > 50%of patient samples at all three time points. Twelve peptides from 11 proteins showed differences in expression over time between patients with versus without

POCD (q < 0.05), including proteins previously implicated in neurodegenerative disease pathophysiology. Additionally, 283 peptides from 182 proteins were identified with trend-level differences (q < 0.25) in expression over time between these groups. Among these, pathway analysis revealed that 50 were from 17 proteins mapping to complement and coagulation pathways (q = 2.44^*10^–13).

Conclusion:

These data demonstrate the feasibility of performing unbiased mass spectrometry on perioperative CSF samples to identify pathways associated with POCD. Additionally, they provide hypothesis-generating evidence for CSF complement and coagulation pathway changes in patients with POCD.

Kidney Function, Kidney Function Decline, and the Risk of Dementia in Older Adults: A Registry-Based Study

OBJECTIVE

Community-based reports regarding the association between the estimated glomerular filtration rate (eGFR) and dementia risk show conflicting results. The aim of this study is to investigate the links among kidney function, kidney function decline, and dementia incidence.

METHODS

We analyzed the association of eGFR with the risk of dementia (defined as a new dementia diagnosis or initiation of dementia treatments) among 329,822 residents of Stockholm who accessed health care during 2006 to 2011, were ≥65 years of age, had no history of dementia, or underwent kidney replacement therapy. We also estimated the rate of eGFR decline among 205,622 residents with repeated eGFR measurements during the first year of observation and investigated its association with subsequent dementia risk.

RESULTS

We detected 18,983 cases of dementia (5.8% of participants) over a median follow-up of 5 years. Dementia incidence rates were progressively higher with lower eGFR: from 6.56/1,000 person-years in those with eGFR of 90 to 104 mL/min to 30.28/1,000 person-years in those with eGFR <30 mL/min. After multivariable adjustment, lower eGFR was associated with a higher dementia risk (hazard ratio [HR] 1.71, 95% confidence interval [CI] 1.54-1.91 in eGFR 30-59 mL/min; HR 2.62, 95% CI 1.91-3.58 in eGFR <30 mL/min) compared with eGFR of 90 to 104 mL/min. A steeper decline in eGFR (decline >2 mL/min/1.73 m2/y) within 1 year was associated with higher dementia risk. Risk magnitudes were stronger for vascular dementia than for Alzheimer dementia. As many as 10% (95% CI 6%-14%) of dementia cases could be attributed to eGFR <60 mL/min/1.73 m2, a proportion higher than that attributed to other dementia risk factors such as cardiovascular disease and diabetes.

CONCLUSIONS

Both lower kidney function and steeper kidney function decline are associated with the development of dementia.

Alzheimer's Disease Susceptibility Gene Apolipoprotein E (APOE) and Blood Biomarkers in UK Biobank (N = 395,769)

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative condition where the underlying etiology is still unclear. Investigating the potential influence of apolipoprotein E (APOE), a major genetic risk factor, on common blood biomarkers could provide a greater understanding of the mechanisms of AD and dementia risk.

OBJECTIVE

Our objective was to conduct the largest (to date) single-protocol investigation of blood biomarkers in the context of APOE genotype, in UK Biobank.

METHODS

After quality control and exclusions, data on 395,769 participants of White European ancestry were available for analysis. Linear regressions were used to test potential associations between APOE genotypes and biomarkers.

RESULTS

Several biomarkers significantly associated with APOEɛ4 'risk' and ɛ2 'protective' genotypes (versus neutral ɛ3/ɛ3). Most associations supported previous data: for example, ɛ4 genotype was associated with elevated low-density lipoprotein cholesterol (LDL) (standardized beta [b] = 0.150 standard deviations [SDs] per allele, p < 0.001) and ɛ2 with lower LDL (b = -0.456 SDs, p < 0.001). There were however instances of associations found in unexpected directions: e.g., ɛ4 and increased insulin-like growth factor (IGF-1) (b = 0.017, p < 0.001) where lower levels have been previously suggested as an AD risk factor.

CONCLUSION

These findings highlight biomarker differences in non-demented people at genetic risk for dementia. The evidence herein supports previous hypotheses of involvement from cardiometabolic and neuroinflammatory pathways.

Brain Ventricular System and Cerebrospinal Fluid Development and Function: Light at the End of the Tube: A Primer with Latest Insights

The brain ventricular system is a series of connected cavities, filled with cerebrospinal fluid (CSF), that forms within the vertebrate central nervous system (CNS). The hollow neural tube is a hallmark of the chordate CNS, and a closed neural tube is essential for normal development. Development and function of the ventricular system is examined, emphasizing three interdigitating components that form a functional system: ventricle walls, CSF fluid properties, and activity of CSF constituent factors. The cellular lining of the ventricle both can produce and is responsive to CSF. Fluid properties and conserved CSF components contribute to normal CNS development. Anomalies of the CSF/ventricular system serve as diagnostics and may cause CNS disorders, further highlighting their importance. This review focuses on the evolution and development of the brain ventricular system, associated function, and connected pathologies. It is geared as an introduction for scholars with little background in the field.

Effects of Cystatin C on Cognitive Impairment in Older Chinese Adults

OBJECTIVE

To find a suitable dividing value to classify cystatin C and evaluate the association between cognition and levels of cystatin C.

METHODS

Using data from the China Health and Retirement Longitudinal Study, We conducted a longitudinal analysis of a prospective cohort of 6,869 middle-aged and older Chinese without cognitive impairment at baseline. Levels of cystatin C were categorized into 2 groups by method of decision tree. Logistic regression models evaluated whether cystatin C was related to cognitive impairment.

RESULTS

Respondents were categorized as lower levels of cystatin C and higher levels of cystatin C, cut-point was 1.11 mg/L. Higher levels of cystatin C was associated with the odds of cognitive impairment (OR, 1.56; 95% CI, 1.10-2.22) after multivariable adjustment. Respondents with higher levels of cystatin C had worse cognition scores.

CONCLUSIONS

We found a suitable dividing value of cystatin C in middle-aged and older Chinese.

Moderately increased albuminuria, chronic kidney disease and incident dementia: the HUNT study

Background

Epidemiologic studies has shown an association of albuminuria and low estimated glomerular filtration rate (eGFR) with dementia, but the findings are inconsistent. This study examines the association between eGFR, MA with dementia and its subtypes: AD, VaD, a mixture of AD/VaD, and other dementias.

Methods

Data from the second wave of the HUNT 2 Study (1995–1997) were linked with a dementia register known as the Health and Memory Study (HMS) collected during 1995–2011 in Nord-Trøndelag County, Norway. Dementia was ascertained using World Health Organization’s ICD-10 criteria into subtypes: AD,VaD, mixed AD/VaD, and other dementia. eGFR and its association with dementia was examined in 48,508 participants of the HUNT Study, of which 668 were diagnosed with all-cause dementia. Association between MA and dementia were studied in a subset of 7024 participants, and 214 were diagnosed with all-cause dementia. Cox regression models were conducted analyzing the association between dementia and MA using albumin creatine ratio (ACR). Cox regression models and Fine-Gray models were used to examine the association between dementia and eGFR.

Results

A positive association was found between increasing ACR and dementia. ACR in the fourth quartile (> 1.78 mg/mmol) with increased hazard ratio of VaD, 3.97 (1.12 to 14.07), compared with ACR in the first quartile (<.53 mg/mmol). There was no association between eGFR and dementia or its subgroups.

Conclusions

Our results strengthens the hypothesis that vascular mechanisms may affect both kidney and brain as an association between MA and dementia was found. However, eGFR was not significantly associated with dementia independent of diabetes mellitus or hypertension.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1425-8) contains supplementary material, which is available to authorized users.

The regulatory role of cystatin C in autophagy and neurodegeneration

Autophagy is a dynamic cellular process involved in the turnover of proteins, protein complexes, and organelles through lysosomal degradation. It is particularly important in neurons, which do not have a proliferative option for cellular repair. Autophagy has been shown to be suppressed in the striatum of a transgenic mouse model of Parkinson’s disease. Cystatin C is one of the potent regulators of autophagy. Changes in the expression and secretion of cystatin C in the brain have been shown in amyotrophic lateral sclerosis, Alzheimer’s and Parkinson’s diseases, and in some animal models of neurodegeneration, thus proving a protective function of cystatin C. It has been suggested that cystatin C plays the primary role in amyloidogenesis and shows promise as a therapeutic agent for neurodegenerative diseases (Alzheimer’s and Parkinson’s diseases). Cystatin C colocalizes with the amyloid β-protein in the brain during Alzheimer’s disease. Controlled expression of a cystatin C peptide has been proposed as a new approach to therapy for Alzheimer’s disease. In Parkinson’s disease, serum cystatin C levels can predict disease severity and cognitive dysfunction, although the exact involvement of cystatin C remains unclear. The aim: to study the role of cystatin C in neurodegeneration and evaluate the results in relation to the mechanism of autophagy. In our study on humans, a higher concentration of cystatin C was noted in cerebrospinal fluid than in serum; much lower concentrations were observed in other biological fluids (intraocular fluid, bile, and sweat). In elderly persons (61–80 years old compared to practically healthy people at 40–60 years of age), we revealed increased cystatin C levels both in serum and intraocular fluid. In an experiment on C57Bl/6J mice, cystatin C concentration was significantly higher in brain tissue than in the liver and spleen: an indication of an important function of this cysteine protease inhibitor in the brain. Using a transgenic mouse model of Parkinson’s disease (5 months old), we demonstrated a significant increase in osmotic susceptibility of brain lysosomes, depending on autophagy, while in a murine model of Alzheimer’s disease, this parameter did not differ from that in the appropriate control.

Exosomes in Pathogenesis, Diagnosis, and Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the accumulation of β-amyloid peptide 1-42 and phosphorylation of tau protein in the brain. Thus far, the transfer mechanism of these cytotoxic proteins between nerve cells remains unclear. Recent studies have shown that nanoscale extracellular vesicles (exosomes) originating from cells may play important roles in this transfer process. In addition, several genetic materials and proteins are also involved in intercellular communication by the secretion of the exosomes. That proposes novel avenues for early diagnosis and biological treatment in AD, based on exosome detection and intervention. In this review, exosome-related pathways of cytotoxic protein intercellular transfer in AD, and the effect of membrane proteins on exosomes targeting cells are first introduced. The advances in exosome-related biomarker detection in AD are summarized. Finally, the advantages and challenges of reducing cytotoxic protein accumulation via exosomal intervention for AD treatment are discussed. It is envisaged that future research in exosomes may well provide new insights into the pathogenesis, diagnosis, and treatment of AD.

Correlations of serum cystatin C level and gene polymorphism with vascular cognitive impairment after acute cerebral infarction

BACKGROUND

The aim of this study was to explore the possible correlations of serum cystatin C level and cystatin C gene (CST3) polymorphism with vascular cognitive impairment in patients who had acute cerebral infarction.

METHODS

A total of 152 patients with acute cerebral infarction were recruited in this case-control study. Patients were divided into vascular cognitive impairment (VCI) group (n = 71) and cognitive impairment no dementia (CIND) group (n = 81). The serum concentrations of cystatin C were measured with immunoturbidimetric assay while the gene polymorphisms of CST3 were determined by technique polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

In the VCI group, serum cystatin C level was significantly higher than that in the control group. The frequency of the B allele was found to be higher in the VCI group as compared with that of the CIND group (18.5% vs 7.7%, p = 0.006). In logistic regression analysis, significant associations of VCI with high serum cystatin C level (OR 3.837 (1.176-12.520), p = 0.026) and CST3 B allele (OR 2.038 (1.048-3.963), p = 0.036) were also found.

CONCLUSIONS

A high cystatin C level and CST3 B allele confer risks for VCI after acute cerebral infarction. It is probable that measurement of the serum cystatin C level and detection of CST3 gene polymorphism would aid in the early diagnosis of VCI, but further studies are warranted.

Beneficial effect of ovocystatin on the cognitive decline in APP/PS1 transgenic mice

PURPOSE

Cystatin C plays an important role in the course of neurodegenerative diseases and has a beneficial effect through inhibiting cysteine proteases and amyloid-β aggregation. It also induces proliferation and autophagy. Cystatin isolated from chicken egg white, called ovocystatin, has been widely used in the medical and pharmaceutical research due to its structural and biological similarities to human cystatin C. The aim of this study was to assess the effect of administering ovocystatin on the development of dementia-specific cognitive deficits in APP/PS1 transgenic mice.

MATERIALS/METHODS

The study was conducted on transgenic B6C3-Tg(APPswe,PSEN1dE9)85Dbo/Mmjax mice. Ovocystatin was administered to four-month-old transgenic (AD) and wild type (NCAR) mice in drinking water for 24 weeks (at a dose of 40 and 4 μg/ mouse). The locomotor activity and cognitive functions were determined using an actimeter and the Morris water maze test, respectively.

RESULTS

The results of the study indicate that ovocystatin has a beneficial effect on the cognitive functions in APP/PS1 transgenic mice. The strongest effects of ovocystatin were found in the group of AD mice, where ovocystatin was administered in drinking water at a dose of 40 μg/mouse (p < 0.05). Mice from the AD group swam statistically significantly further in the target zone during the trial in the Morris water maze compared to the AD (vehiculum) group (p < 0.05).

CONCLUSIONS

The obtained results encourage further research into the protective effect, which may be used as an adjuvant in the treatment of deteriorating cognitive functions.

Blood biomarkers in Alzheimer's disease

INTRODUCTION

The early diagnosis of Alzheimer's disease (AD) via the use of biomarkers could facilitate the implementation and monitoring of early therapeutic interventions with the potential capacity to significantly modify the course of the disease.

DEVELOPMENT

Classic cerebrospinal fluid biomarkers and approved structural and functional neuroimaging have a limited clinical application given their invasive nature and/or high cost. The identification of more accessible and less costly biomarkers, such as blood biomarkers, would facilitate application in clinical practice. We present a literature review of the main blood biochemical biomarkers with potential use for diagnosing Alzheimer's disease.

CONCLUSIONS

Blood biomarkers are cost and time effective with regard to cerebrospinal fluid biomarkers. However, the immediate applicability of blood biochemical biomarkers in clinical practice is not very likely. The main limitations come from the difficulties in measuring and standardising thresholds between different laboratories and in failures to replicate results. Among all the molecules studied, apoptosis and neurodegeneration biomarkers and the biomarker panels obtained through omics approaches, such as isolated or combined metabolomics, offer the most promising results.

Loss of Neuroprotective Factors in Neurodegenerative Dementias: The End or the Starting Point?

Recent clinical, genetic and biochemical experimental evidences highlight the existence of common molecular pathways underlying neurodegenerative diseases. In this review, we will explore a key common pathological mechanism, i.e., the loss of neuroprotective factors, across the three major neurodegenerative diseases leading to dementia: Alzheimer's disease (AD), Frontotemporal dementia (FTD) and Lewy body dementia (LBD). We will report evidences that the Brain Derived Neurotrophic Factor (BDNF), the most investigated and characterized brain neurotrophin, progranulin, a multi-functional adipokine with trophic and growth factor properties, and cystatin C, a neuroprotective growth factor, are reduced in AD, FTD, and LBD. Moreover, we will review the molecular mechanism underlying the loss of neuroprotective factors in neurodegenerative diseases leading to dementia, with a special focus on endo-lysosomal pathway and intercellular communication mediated by extracellular vesicles. Exploring the shared commonality of disease mechanisms is of pivotal importance to identify novel potential therapeutic targets and to develop treatments to delay, slow or block disease progression.

A Parallel Reaction Monitoring Mass Spectrometric Method for Analysis of Potential CSF Biomarkers for Alzheimer's Disease

SCOPE

The aim of this study was to develop and evaluate a parallel reaction monitoring mass spectrometry (PRM-MS) assay consisting of a panel of potential protein biomarkers in cerebrospinal fluid (CSF).

EXPERIMENTAL DESIGN

Thirteen proteins were selected based on their association with neurodegenerative diseases and involvement in synaptic function, secretory vesicle function, or innate immune system. CSF samples were digested and two to three peptides per protein were quantified using stable isotope-labeled peptide standards.

RESULTS

Coefficients of variation were generally below 15%. Clinical evaluation was performed on a cohort of 10 patients with Alzheimer's disease (AD) and 15 healthy subjects. Investigated proteins of the granin family exhibited the largest difference between the patient groups. Secretogranin-2 (p<0.005) and neurosecretory protein VGF (p<0.001) concentrations were lowered in AD. For chromogranin A, two of three peptides had significantly lowered AD concentrations (p<0.01). The concentrations of the synaptic proteins neurexin-1 and neuronal pentraxin-1, as well as neurofascin were also significantly lowered in AD (p<0.05). The other investigated proteins, β2-microglobulin, cystatin C, amyloid precursor protein, lysozyme C, neurexin-2, neurexin-3, and neurocan core protein, were not significantly altered.

CONCLUSION AND CLINICAL RELEVANCE

PRM-MS of protein panels is a valuable tool to evaluate biomarker candidates for neurodegenerative disorders.

Extracellular Vesicles in Brain Tumors and Neurodegenerative Diseases

Extracellular vesicles (EVs) can be classified into apoptotic bodies, microvesicles (MVs), and exosomes, based on their origin or size. Exosomes are the smallest and best characterized vesicles which derived from the endosomal system. These vesicles are released from many different cell types including neuronal cells and their functions in the nervous system are investigated. They have been proposed as novel means for intercellular communication, which takes part not only to the normal neuronal physiology but also to the transmission of pathogenic proteins. Indeed, exosomes are fundamental to assemble and transport proteins during development, but they can also transfer neurotoxic misfolded proteins in pathogenesis. The present review will focus on their roles in neurological diseases, specifically brain tumors, such as glioblastoma (GBM), neuroblastoma (NB), medulloblastoma (MB), and metastatic brain tumors and chronic neurodegenerative diseases, such as Alzheimer, Parkinson, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington, and Prion diseseases highlighting their involvement in spreading neurotoxicity, in therapeutics, and in pathogenesis.

Physical activity predicts reduced plasma β amyloid in the Cardiovascular Health Study

Objective

Higher levels of physical activity (PA) reduce the risk of cognitive impairment, but the underlying mechanisms are unclear. Using longitudinal data from the Cardiovascular Health Study, we examined whether PA predicted plasma Aβ levels and risk for cognitive decline 9–13 years later.

Methods

Linear and logistic regressions (controlling for APOE status, age, gender, body mass index, cardiovascular disease, brain white matter lesions, and cystatin C levels) tested associations between PA, Aβ, and cognitive impairment in a sample of 149 cognitively normal older adults (mean age 83 years).

Results

More PA at baseline predicted lower levels of Aβ 9–13 years later. Higher Aβ levels at year 9 predicted greater risk for cognitive impairment at year 13. Levels of Aβ at year 9 mediated the relationship between PA and cognitive impairment.

Interpretation

Greater PA may reduce plasma levels of a neurotoxic peptide at an age when the risk for cognitive impairment is especially high.

Plasma Cystatin C and High-Density Lipoprotein Are Important Biomarkers of Alzheimer's Disease and Vascular Dementia: A Cross-Sectional Study

Objectives: Cystatin C (Cys C) and high-density lipoprotein (HDL) play critical roles in neurodegenerative diseases, such as dementia, Alzheimer’s disease (AD) and vascular dementia (VaD). However, whether they can be used as reliable biomarkers to distinguish patients with dementia from healthy subjects and to determine disease severity remain largely unknown.

Methods: We conducted a cross-sectional study to determine plasma Cys C and HDL levels of 88 patients with dementia (43 AD patients, 45 VaD patients) and 45 healthy age-matched controls. The severity of dementia was determined based on the Schwab and England Activities of Daily Living (ADL) Scale, the Mini-mental State Examination (MMSE), the Global Deterioration Scale (GDS), the Lawton Instrumental ADL (IADL) Scale, and the Hachinski Ischemia Scale (Hachinski). Receiver operating characteristic (ROC) curves were calculated to determine the diagnostic accuracy of Cys C and HDL levels in distinguishing patients with dementia from healthy subjects.

Results: We found that plasma Cys C levels were higher, but HDL levels were lower in AD and VaD patients respectively, compared to healthy control subjects. Yet, Cys C levels were highest among patients with VaD. Interestingly, plasma Cys C levels were significantly correlated with IADL Scale scores. In addition, the ROC curves for Cys C (area under the curve, AUC 0.816 for AD, AUC 0.841 for VaD) and HDL (AUC 0.800 for AD, AUC 0.731 for VaD) exhibited potential diagnostic value in distinguishing AD/VaD patients from healthy subjects. While the ROC curve for the combination of Cys C and HDL (AUC 0.873 for AD, AUC 0.897 for VaD) showed higher diagnostic accuracy in distinguishing AD/VaD patients from healthy subjects than the separate curves for each parameter.

Conclusions: Our findings suggest that the inflammatory mediators Cys C and HDL may play important roles in the pathogenesis of dementia, and plasma Cys C and HDL levels may be useful screening tools for differentiating AD/VaD patients from healthy subjects.

Dementia risk in renal dysfunction: A systematic review and meta-analysis of prospective studies

OBJECTIVE

Renal dysfunction has been linked with increased risk for cognitive impairment and dementia, but studies are conflicting. For that reason, the aim of the present systematic review and meta-analysis is to summarize the best available evidence on the prospective association between potential markers of renal dysfunction and development of cognitive impairment or dementia.

METHODS

Medline, Embase, and Cochrane Database of Systematic Reviews were searched for potential publications until August 1, 2016. Studies were eligible if they fulfilled the following criteria: population-based study, prospective design, ≥100 participants, aged ≥45 years, ≥1 year follow-up, and cognition/dementia outcomes. Where appropriate, random effects meta-analyses were conducted yielding pooled odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

Twenty-two out of 8,494 abstracts fulfilled the eligibility criteria. Sufficient evidence was found for albuminuria, mixed results for estimated glomerular filtration rate (eGFR), insufficient support for cystatin C, and tentative evidence for serum creatinine and creatinine clearance. Meta-analyses of 5 studies representing 27,805 persons showed a 35% increased risk of cognitive impairment or dementia in those with albuminuria (OR 1.35, 95% CI 1.06-1.73, p = 0.015), whereas eGFR <60 mL/min/1.73 m² showed no significant association (OR 1.28, 95% CI 0.99-1.65, p = 0.063). No meta-analyses could be done for serum creatinine, creatinine clearance, or cystatin C.

CONCLUSIONS

The overall evidence for an association between renal dysfunction and cognitive impairment or dementia is modest. Evidence suggests that albuminuria is associated with higher odds of developing cognitive impairment or dementia.

Cystatin C in aging and in Alzheimer's disease

Under normal conditions, the function of catalytically active proteases is regulated, in part, by their endogenous inhibitors, and any change in the synthesis and/or function of a protease or its endogenous inhibitors may result in inappropriate protease activity. Altered proteolysis as a result of an imbalance between active proteases and their endogenous inhibitors can occur during normal aging, and such changes have also been associated with multiple neuronal diseases, including Amyotrophic Lateral Sclerosis (ALS), rare heritable neurodegenerative disorders, ischemia, some forms of epilepsy, and Alzheimer's disease (AD). One of the most extensively studied endogenous inhibitor is the cysteine-protease inhibitor cystatin C (CysC). Changes in the expression and secretion of CysC in the brain have been described in various neurological disorders and in animal models of neurodegeneration, underscoring a role for CysC in these conditions. In the brain, multiple in vitro and in vivo findings have demonstrated that CysC plays protective roles via pathways that depend upon the inhibition of endosomal-lysosomal pathway cysteine proteases, such as cathepsin B (Cat B), via the induction of cellular autophagy, via the induction of cell proliferation, or via the inhibition of amyloid-β (Aβ) aggregation. We review the data demonstrating the protective roles of CysC under conditions of neuronal challenge and the protective pathways induced by CysC under various conditions. Beyond highlighting the essential role that balanced proteolytic activity plays in supporting normal brain aging, these findings suggest that CysC is a therapeutic candidate that can potentially prevent brain damage and neurodegeneration.

Identifying biomarkers of dementia prevalent among amnestic mild cognitively impaired ethnic female patients

Background

There is a need to investigate biomarkers that are indicative of the progression of dementia in ethnic patient populations. The disparity of information in these populations has been the focus of many clinical and academic centers, including ours, to contribute to a higher success rate in clinical trials. In this study, we have investigated plasma biomarkers in amnestic mild cognitively impaired (aMCI) female patient cohorts in the context of ethnicity and cognitive status.

Method

A panel of 12 biomarkers involved in the progression of brain pathology, inflammation, and cardiovascular disorders were investigated in female cohorts of African American, Hispanic, and White aMCI patients. Both biochemical and algorithmic analyses were applied to correlate biomarker levels measured during the early stages of the disease for each ethnicity.

Results

We report elevated plasma Aβ₄₀, Aβ₄₂, YKL-40, and cystatin C levels in the Hispanic cohort at early aMCI status. In addition, elevated plasma Aβ₄₀ levels were associated with the aMCI status in both White and African American patient cohorts by the decision tree algorithm. Eotaxin-1 levels, as determined by the decision tree algorithm and biochemically measured total tau levels, were associated with the aMCI status in the African American cohort.

Conclusions

Overall, our data displayed novel differences in the plasma biomarkers of the aMCI female cohorts where the plasma levels of several biomarkers distinguished between each ethnicity at an early aMCI stage. Identification of these plasma biomarkers encourages new areas of investigation among aMCI ethnic populations, including larger patient cohorts and longitudinal study designs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-016-0211-0) contains supplementary material, which is available to authorized users.

Update on the core and developing cerebrospinal fluid biomarkers for Alzheimer disease

Alzheimer disease (AD) is a complex neurodegenerative disorder, whose prevalence will dramatically rise by 2050. Despite numerous clinical trials investigating this disease, there is still no effective treatment. Many trials showed negative or inconclusive results, possibly because they recruited only patients with severe disease, who had not undergone disease-modifying therapies in preclinical stages of AD before severe degeneration occurred. Detection of AD in asymptomatic at risk individuals (and a few presymptomatic individuals who carry an autosomal dominant monogenic AD mutation) remains impractical in many of clinical situations and is possible only with reliable biomarkers. In addition to early diagnosis of AD, biomarkers should serve for monitoring disease progression and response to therapy. To date, the most promising biomarkers are cerebrospinal fluid (CSF) and neuroimaging biomarkers. Core CSF biomarkers (amyloid β_1-42, total tau, and phosphorylated tau) showed a high diagnostic accuracy but were still unreliable for preclinical detection of AD. Hence, there is an urgent need for detection and validation of novel CSF biomarkers that would enable early diagnosis of AD in asymptomatic individuals. This article reviews recent research advances on biomarkers for AD, focusing mainly on the CSF biomarkers. In addition to core CSF biomarkers, the potential usefulness of novel CSF biomarkers is discussed.

Risk Profiles of Alzheimer Disease

Alzheimer disease (AD) is a dementing, neurodegenerative disorder that affects approximately 500,000 Canadians and its prevalence is expected to double over the next 30 years. Although several medications may temporarily augment cognitive abilities in AD, there presently exists no proven method to avoid the inevitable clinical deterioration in this devastating condition. The delineation of risk factors for the development of AD offers hope for the advent of effective prevention or interventions that might retard the onset of symptoms. In this article, we provide a comprehensive review of midlife risk factors implicated in the etiopathogenesis of sporadic AD. Although some risk factors are heritable and largely beyond our control, others are determined by lifestyle or environment and are potentially modifiable. In a companion paper, we introduce the concept of an Alzheimer Risk Assessment Clinic for ascertainment and mitigation of these and other putative dementia risk factors in middle-aged adults.

Cystatin C and cognitive impairment 10 years later in older women

BACKGROUND

Results of prospective studies examining the association between cystatin C and incident cognitive impairment have been inconsistent. We tested the hypothesis that there is a U-shaped association in older women between cystatin C and risk of incident cognitive impairment 10 years later.

METHODS

We conducted a longitudinal analysis of a prospective cohort of 1,332 community-dwelling elderly women without dementia at baseline who had baseline cystatin C and serum creatinine measurements and completed an extended cognitive battery of neuropsychological tests with determination of cognitive status 10 years later. Incident cognitive impairment was defined as either new onset of adjudicated diagnosis of mild cognitive impairment or dementia.

RESULTS

Incident mild cognitive impairment or dementia was identified among 140 (26.0%) women in quartile 1 (Q1), 122 (22.6%) in Q2, 121 (22.5%) in Q3, and 156 (28.9%) in Q4 of cystatin C. In the fully adjusted model, compared to women in Q2-Q3 of cystatin C, adjusted odds ratios (95% CI) for incident cognitive impairment were 1.31 (0.98-1.75) for Q1, and 1.25 (0.94-1.66) for Q4 Compared to women in Q2-Q3 of estimated glomerular filtration rate (eGFRCysC), adjusted odds ratios (95% CI) for incident cognitive impairment after 10 years of follow-up were 1.18 (0.88-1.58) for Q4 (eGFRCysC 76.1-109.4mL/min/1.73 m(2)) and 1.26 (0.94-1.67) for Q1 (eGFRCysC 21.8-55.5mL/min/1.73 m(2)).

CONCLUSIONS

These results support a U-shaped association between cystatin C concentration and risk of cognitive impairment or dementia 10 years later, but the association is not independent of potential confounding factors.

Higher levels of cystatin C are associated with worse cognitive function in older adults with chronic kidney disease: the chronic renal insufficiency cohort cognitive study

OBJECTIVES

To determine the association between cognition and levels of cystatin C in persons with chronic kidney disease (CKD).

DESIGN

Prospective observational study.

SETTING

Chronic Renal Insufficiency Cohort Cognitive Study.

PARTICIPANTS

Individuals with a baseline cognitive assessment completed at the same visit as serum cystatin C measurement (N = 821; mean age 64.9, 50.6% male, 48.6% white).

MEASUREMENTS

Levels of serum cystatin C were categorized into tertiles; cognitive function was assessed using six neuropsychological tests. Scores on these tests were compared across tertiles of cystatin C using linear regression and logistic regression to examine the association between cystatin C level and cognitive performance (1 standard deviation difference from the mean).

RESULTS

After multivariable adjustment for age, race, education, and medical comorbidities in linear models, higher levels of cystatin C were associated with worse cognition on the modified Mini-Mental State Examination, Buschke Delayed Recall, Trail-Making Test Part (Trails) A and Part B, and Boston Naming (P < .05 for all). This association remained statistically significant for Buschke Delayed Recall (P = .01) and Trails A (P = .03) after additional adjustment for estimated glomerular filtration rate (eGFR). The highest tertile of cystatin C was associated with greater likelihood of poor performance on Trails A (odds ratio (OR) = 2.17, 95% confidence interval (CI) = 1.16-4.06), Trails B (OR = 1.89, 95% CI = 1.09-3.27), and Boston Naming (OR = 1.85, 95% CI = 1.07-3.19) than the lowest tertile after multivariate adjustment in logistic models.

CONCLUSION

In individuals with CKD, higher serum cystatin C levels were associated with worse cognition and greater likelihood of poor cognitive performance on attention, executive function, and naming. Cystatin C is a marker of cognitive impairment and may be associated with cognition independent of eGFR.

Direct analytical sample quality assessment for biomarker investigation: qualifying cerebrospinal fluid samples

Measurement of biochemical markers represents an important aid to clinicians in the early diagnosis and prognosis of neurological diseases. Many factors can contribute to increase the chances that a biomarker study becomes successful. In a cerebrospinal fluid analysis (CSF), more than 84% of laboratory errors can be attributed to several preanalytical variables that include CSF collection, storage, and freeze thawing cycles. In this concept paper, we focus on some critical issues arising from basic proteomics investigation in order to highlight some key elements of CSF quality control. Furthermore, we propose a direct assessment of sample quality (DASQ) by applying a fast MALDI-TOF-MS methodology to evaluate molecular features of sample degradation and oxidation. We propose DASQ as a fast and simple initial step to be included in large-scale projects for neurological biomarker studies. In fact, such a procedure will improved the development of standardized protocols in order to have well-characterized CSF biobanks.

Plasma β-amyloid 40 levels are positively associated with mortality risks in the elderly

BACKGROUND

We evaluated if plasma β-amyloid (Aβ) levels were associated with mortality risks in a subsample of the French Three-City (3C) prospective cohort study.

METHODS

Analyses were based on 1254 participants randomly selected from the initial 3C cohort stratified by center, sex, and age in the context of a nested case-cohort study to investigate biological variables. Associations between plasma Aβ and mortality were assessed with the Cox regression model with delayed entry including various potential confounding factors and testing possible mediators.

RESULTS

A relationship between high plasma Aβ1-40 concentrations and risk of mortality (hazards ratio, 1.15; 95% confidence interval, 1.01-1.31, P = .03) was unveiled independently of age, educational level, vascular risk factors, diet, physical activity, cognitive impairment, or frailty status. It was only modified when we included cystatin C levels.

CONCLUSIONS

Further investigations are needed to determine precisely the pathophysiological roles of plasma Aβ1-40 and cystatin C and before envisioning any future clinical applications.

Cerebro-renal interactions: impact of uremic toxins on cognitive function

Cognitive impairment (CI) associated with chronic kidney disease (CKD) has received attention as an important problem in recent years. Causes of CI with CKD are multifactorial, and include cerebrovascular disease, renal anemia, secondary hyperparathyroidism, dialysis disequilibrium, and uremic toxins (UTs). Among these causes, little is known about the role of UTs. We therefore selected 21 uremic compounds, and summarized reports of cerebro-renal interactions associated with UTs. Among the compounds, uric acid, indoxyl sulfate, p-cresyl sulfate, interleukin 1-β, interleukin 6, TNF-α, and PTH were most likely to affect the cerebro-renal interaction dysfunction; however, sufficient data have not been obtained for other UTs. Notably, most of the data were not obtained under uremic conditions; therefore, the impact and mechanism of each UT on cognition and central nervous system in uremic state remains unknown. At present, impacts and mechanisms of UT effects on cognition are poorly understood. Clarifying the mechanisms and establishing novel therapeutic strategies for cerebro-renal interaction dysfunction is expected to be subject of future research.

Kidney function and cognitive health in older adults: the Cardiovascular Health Study

Recent evidence has demonstrated the importance of kidney function in healthy aging. We examined the association between kidney function and change in cognitive function in 3,907 participants in the Cardiovascular Health Study who were recruited from 4 US communities and studied from 1992 to 1999. Kidney function was measured by cystatin C-based estimated glomerular filtration rate (eGFRcys). Cognitive function was assessed using the Modified Mini-Mental State Examination and the Digit Symbol Substitution Test, which were administered up to 7 times during annual visits. There was an association between eGFRcys and change in cognitive function after adjustment for confounders; persons with an eGFRcys of less than 60 mL/minute/1.73 m(2) had a 0.64 (95% confidence interval: 0.51, 0.77) points/year faster decline in Modified Mini-Mental State Examination score and a 0.42 (95% confidence interval: 0.28, 0.56) points/year faster decline in Digit Symbol Substitution Test score compared with persons with an eGFRcys of 90 or more mL/minute/1.73 m(2). Additional adjustment for intermediate cardiovascular events modestly affected these associations. Participants with an eGFRcys of less than 60 mL/minute/1.73 m(2) had fewer cognitive impairment-free life-years on average compared with those with eGFRcys of 90 or more mL/minute/1.73 m(2), independent of confounders and mediating cardiovascular events (mean difference = -0.44, 95% confidence interval: -0.62, -0.26). Older adults with lower kidney function are at higher risk of worsening cognitive function.

Differential effects of indoxyl sulfate and inorganic phosphate in a murine cerebral endothelial cell line (bEnd.3)

Endothelial dysfunction plays a key role in stroke in chronic kidney disease patients. To explore the underlying mechanisms, we evaluated the effects of two uremic toxins on cerebral endothelium function. bEnd.3 cells were exposed to indoxyl sulfate (IS) and inorganic phosphate (Pi). Nitric oxide (NO), reactive oxygen species (ROS) and O2•⁻ were measured using specific fluorophores. Peroxynitrite and eNOS uncoupling were evaluated using ebselen, a peroxide scavenger, and tetrahydrobiopterin (BH₄), respectively. Cell viability decreased after IS or Pi treatment (p < 0.01). Both toxins reduced NO production (IS, p < 0.05; Pi, p < 0.001) and induced ROS production (p < 0.001). IS and 2 mM Pi reduced O2•⁻ production (p < 0.001). Antioxidant pretreatment reduced ROS levels in both IS- and Pi-treated cells, but a more marked reduction of O2•⁻ production was observed in Pi-treated cells (p < 0.001). Ebselen reduced the ROS production induced by the two toxins (p < 0.001); suggesting a role of peroxynitrite in this process. BH₄ addition significantly reduced O2•⁻ and increased NO production in Pi-treated cells (p < 0.001), suggesting eNOS uncoupling, but had no effect in IS-treated cells. This study shows, for the first time, that IS and Pi induce cerebral endothelial dysfunction by decreasing NO levels due to enhanced oxidative stress. However, Pi appears to be more deleterious, as it also induces eNOS uncoupling.

Extracellular vesicle protein levels are related to brain atrophy and cerebral white matter lesions in patients with manifest vascular disease: the SMART-MR study

OBJECTIVES

Extracellular vesicles (EVs) and their protein levels have been identified as a potential risk marker for the development of vascular disease. In the present study, we assessed whether levels of four previously identified EV proteins (cystatin C, serpin G1, serpin F2 and CD14) are associated with cerebral white matter lesions (WMLs) and brain atrophy.

DESIGN

Cohort study; cross-sectional and prospective.

SETTING

Single centre, secondary and tertiary setting.

PARTICIPANTS

1309 patients with manifest vascular disease from the Second Manifestations of ARTerial disease-MR (SMART-MR) study, of which 994 had successful brain MRI and EV protein level measurements.

OUTCOMES

WML and brain parenchymal fraction (BPF), as parameter for brain atrophy, at baseline and follow-up.

STATISTICAL METHODS

The relationship between EV protein levels and WML volume (expressed as log transformed percentage of intracranial volume) and BPF (expressed percentage of intracranial volume) on 1.5 T brain MRI was assessed with multivariable linear regression modelling. Subsequently, the relationship between baseline EV protein levels and progression of atrophy and WML was analysed in 534 patients, in whom a follow-up MRI was obtained after 4 years.

RESULTS

Higher EV-cystatin C and EV-CD14 were significantly associated with larger WML volume (linear regression coefficient (95% CI) 0.10 log %/SD (0.04 to 0.17) and 0.14 log %/SD (0.07 to 0.20), respectively. Higher EV-CD14 was associated with more brain atrophy (-0.14%/SD; -0.27 to -0.01). Baseline EV-CD14 was significantly associated with increase of WMLs (0.11 log %/SD (0.04 to 0.18)). No relationship with EV-serpins was observed at baseline or at follow-up.

CONCLUSIONS

EV proteins cystatin C and CD14 are related to cerebral WMLs and the progression of brain atrophy in patients with manifest vascular disease, potentially identifying EVs in the aetiology of structural brain changes.