Enhancing Diagnostic Accuracy of aMCI in the Elderly: Combination of Olfactory Test, Pupillary Response Test, BDNF Plasma Level, and APOE Genotype

The current status and challenges of olfactory dysfunction study in Alzheimer's Disease

Olfactory functioning involves multiple cognitive processes and the coordinated actions of various neural systems. Any disruption at any stage of this process may result in olfactory dysfunction, which is consequently widely used to predict the onset and progression of diseases, such as Alzheimer's Disease (AD). Although the underlying mechanisms have not yet been fully unraveled, apparent changes were observed in olfactory brain areas form patients who suffer from AD by means of medical imaging and electroencephalography (EEG). Olfactory dysfunction holds significant promise in detecting AD during the preclinical stage preceding mild cognitive impairment (MCI). Owing to the strong specificity, olfactory tests are prevalently applied for screening in community cohorts. And combining olfactory tests with other biomarkers may further establish an optimal model for AD prediction in studies of specific olfactory dysfunctions and improve the sensitivity and specificity of early AD diagnosis.

Brain-derived neurotrophic factor interplay with oxidative stress: neuropathology approach in potential biomarker of Alzheimer's disease

The aging population poses a serious challenge concerning an increased prevalence of Alzheimer's disease (AD) and its impact on global burden, morbidity, and mortality. Oxidative stress, as a molecular hallmark that causes susceptibility in AD, interplays to other AD-related neuropathology cascades and decreases the expression of central and circulation brain-derived neurotrophic factor (BDNF), an essential neurotrophin that serves as nerve development and survival, and synaptic plasticity in AD. By its significant correlation with the molecular and clinical progression of AD, BDNF can potentially be used as an objectively accurate biomarker for AD diagnosis and progressivity follow-up in future clinical practice. This comprehensive review highlights the oxidative stress interplay with BDNF in AD neuropathology and its potential use as an AD biomarker.

The impact of Alzheimer's disease risk factors on the pupillary light response

Alzheimer's disease (AD) is the leading cause of dementia, and its prevalence is increasing and is expected to continue to increase over the next few decades. Because of this, there is an urgent requirement to determine a way to diagnose the disease, and to target interventions to delay and ideally stop the onset of symptoms, specifically those impacting cognition and daily livelihood. The pupillary light response (PLR) is controlled by the sympathetic and parasympathetic branches of the autonomic nervous system, and impairments to the pupillary light response (PLR) have been related to AD. However, most of these studies that assess the PLR occur in patients who have already been diagnosed with AD, rather than those who are at a higher risk for the disease but without a diagnosis. Determining whether the PLR is similarly impaired in subjects before an AD diagnosis is made and before cognitive symptoms of the disease begin, is an important step before using the PLR as a diagnostic tool. Specifically, identifying whether the PLR is impaired in specific at-risk groups, considering both genetic and non-genetic risk factors, is imperative. It is possible that the PLR may be impaired in association with some risk factors but not others, potentially indicating different pathways to neurodegeneration that could be distinguished using PLR. In this work, we review the most common genetic and lifestyle-based risk factors for AD and identify established relationships between these risk factors and the PLR. The evidence here shows that many AD risk factors, including traumatic brain injury, ocular and intracranial hypertension, alcohol consumption, depression, and diabetes, are directly related to changes in the PLR. Other risk factors currently lack sufficient literature to make any conclusions relating directly to the PLR but have shown links to impairments in the parasympathetic nervous system; further research should be conducted in these risk factors and their relation to the PLR.

Increasing Effect of Citrus natsudaidai on Brain-Derived Neurotrophic Factor

The increase in brain-derived neurotrophic factor (BDNF) in the brain is beneficial for the treatment of depression, Alzheimer's disease (AD), and Parkinson's disease (PD); BDNF can cross the blood-brain barrier. Therefore, foods that elevate BDNF concentration in peripheral tissues may increase BDNF in the brain and thereby induce preventive and therapeutic effects against depression, AD, and PD. In this study, we aimed to determine whether Citrus natsudaidai extracts can increase BDNF concentration using the human kidney adenocarcinoma cell line ACHN, which has BDNF-producing and -secreting abilities. As test samples, methanol extracts of C. natsudaidai peel and pulp, and their n-hexane, ethyl acetate, n-butanol, and water fractions were prepared. The BDNF concentrations in culture medium of ACHN cells were assayed after 24 h cultivation in the presence of test samples. Compared with that of control (non-treated) cells, the BDNF concentration increased in the culture medium of ACHN cells treated with the methanol extract of C. natsudaidai peel and its hexane, butanol, and water fractions, as well as the butanol and water fractions of the pulp extract. Quantitative reverse transcription-polymerase chain reaction analysis revealed that ACHN cells treated with the butanol fractions of the peel and pulp extracts showed elevated levels of BDNF mRNA compared with those of non-treated cells. C. natsudaidai may increase BDNF concentration by acting on peripheral tissues and could be a medication for the prevention and treatment of depression, AD, and PD.

Effects of Tempeh Probiotics on Elderly With Cognitive Impairment

Introduction

Oral consumption of probiotics can alter Gut Microbiota by causing changes in the production of probiotic derivatives. Therefore, by utilizing Gut-Brain-Axis (GBA), probiotics could provide an opportunity for central nervous system (CNS) modulation, including cognitive function. Tempeh is a traditional Indonesian food rich in probiotics and beneficial for cognitive function. However, the type of probiotics that play a role in cognitive improvement and the number of probiotics needed for the benefits of increasing cognitive function was unknown.

Method

This experimental study involved a total of 93 subjects, divided into 3 groups: A, B and C/control (n: 33, 32, and 28), who were provided with probiotic supplementation isolated from tempeh for 12 weeks intervention. Inclusion criteria were age > 60 years, and memory impairment with the third repetition value of Word List Memory Immediate Recall (WLMIR) < 7. Subjects with diabetes were excluded. Cognitive function examinations were carried out before and after treatment. The tempeh-derived probiotics were prepared trough several processes. Genomic isolation, detection of GABA-encoding genes, and species identification using the 16S-rRNA gene encoding were performed.

Results

The probiotics isolate used in the intervention was identified as Limosilactobacillus fermentum. We assigned this isolate as L. fermentum A2.8. The presence of the gene encoding GABA was found on this isolate. There was an increase in the cognitive domains of memory, learning process, and verbal fluency (p < 0.05) in group A (probiotics at concentration of 10⁸ CFU/mL). Memory function, visuospatial, and verbal fluency improved (p < 0.05) in group B (probiotics at concentration of 10⁷ CFU/mL). Only an increase in the memory domain was observed in the control group. Improvement of the learning process occurred only in group A (p = 0.006).

Conclusion

Administration of probiotics derived from L. fermentum A2.8 increased the cognitive domains of memory, language and visuospatial function. However, probiotic supplementation at a concentration of 10⁸ CFU/mL was better in improving the learning process. This study succeeded in detecting Lactic Acid Bacterial isolates L. fermentum A2.8 that enclosed gene encoding glutamate decarboxylase (gad) which is involved in the synthesis of -aminobutyric acid (GABA), a neurotransmitter vital for cognitive function.

A narrative review of brain-derived neurotrophic factor (BDNF) on cognitive performance in Alzheimer's disease

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that is highly expressed in the brain. It influences neuronal survival, growth and acts as a control centre for neurotransmitters. It also plays a crucial role in learning and memory. Current evidence indicates that BDNF may be a possible neurotrophic factor that controls cognitive functions under normal and neuropathological conditions. Recent findings indicate a reduction in cognitive performance in individuals with Alzheimer's disease (AD). This relationship between cognitive performance and AD is important for investigating both the time they overlap and the pathophysiological mechanism in each case. Therefore, this study reviewed the existing knowledge about BDNF and cognitive performance in the AD population. The findings support the idea that this tropic factor may be a potential biomarker for evaluating the changes in cognitive performance in AD.

Factors associated with odour identification in older Indonesian and white Australian adults

BACKGROUND AND AIMS

Among older adults, olfactory dysfunction is associated with cognitive impairment, lower quality of life, and increased mortality. While age is a risk factor for olfactory dysfunction, other risk factors are less well understood, and may vary between ethno-regional groups. This study investigated how associations between odour identification (OI) and various risk factors, as well as cognition and language ability, differed or were similar in two distinct ethno-regional groups of older adults.

METHODS

This cross-sectional study used data from two cohorts: 470 Indonesians (aged 67.4 ± 7.4 years) and 819 white Australians (aged 78.7 ± 4.8 years). Univariate and multivariate analyses explored whether OI test scores were associated with age, sex, education, cholesterol levels, apolipoprotein E ε4 status, smoking, diabetes, hypertension and depression scale scores, or with Mini-Mental State Examination (MMSE) and language test performance.

RESULTS

Univariate analyses identified some factors associated with OI scores in both Indonesians and white Australians, including older age and smoking with lower scores, and MMSE and language test performance with higher scores. Multivariate analyses yielded different and mutually exclusive patterns of associations in the two ethno-regional groups, with language test scores significantly associated with higher OI scores in Indonesians, and age, being male, smoking, having diabetes and higher depression scale scores significantly associated with lower OI scores in white Australians.

CONCLUSION

Ethno-regional differences may need consideration in the attempt to fully understand associations between OI and negative outcomes like dementia and mortality, and interventions for olfactory dysfunction might need to be tailored to specific ethno-regional groups. However, the difference in mean age between cohorts is a limitation of this study, and future studies should aim to compare populations with similar age distributions.

Amyloid beta soluble forms and plasminogen activation system in Alzheimer's disease: Consequences on extracellular maturation of brain-derived neurotrophic factor and therapeutic implications

Soluble oligomeric forms of amyloid beta (Aβ) play an important role in causing the cognitive deficits in Alzheimer’s disease (AD) by targeting and disrupting synaptic pathways. Thus, the present research is directed toward identifying the neuronal pathways targeted by soluble forms and, accordingly, develops alternative therapeutic strategies. The neurotrophin brain‐derived neurotrophic factor (BDNF) is synthesized as a precursor (pro‐BDNF) which is cleaved extracellularly by plasmin to release the mature form. The conversion from pro‐BDNF to BDNF is an important process that regulates neuronal activity and memory processes. Plasmin‐dependent maturation of BDNF in the brain is regulated by plasminogen activator inhibitor‐1 (PAI‐1), the natural inhibitor of tissue‐type plasminogen activator (tPA). Therefore, tPA/PAI‐1 system represents an important regulator of extracellular BDNF/pro‐BDNF ratio. In this review, we summarize the data on the components of the plasminogen activation system and on BDNF in AD. Moreover, we will hypothesize a possible pathogenic mechanism caused by soluble Aβ forms based on the effects on tPA/PAI‐1 system and on the consequence of an altered conversion from pro‐BDNF to the mature BDNF in the brain of AD patients. Translation into clinic may include a better characterization of the disease stage and future direction on therapeutic targets.

Identification of Neuroprotective Factors Associated with Successful Ageing and Risk of Cognitive Impairment among Malaysia Older Adults

The increase of ageing population has raised public attention on the concept of successful ageing. Studies have shown that vitamin D, telomere length, and brain-derived neurotrophic factor (BDNF) have been associated with cognitive function. Therefore, this study aimed to identify neuroprotective factors for cognitive decline in different ageing groups. A total of 300 older adults aged 60 years and above were recruited in this population based cross-sectional study. Participants were categorized into three groups: mild cognitive impairment (MCI) (n = 100), usual ageing (UA) (n = 100), and successful ageing (SA) (n = 100). Dietary vitamin D intake was assessed through Diet History Questionnaire (DHQ). Out of the 300 participants, only 150 were subjected to fasting blood sample collection. These samples were used for serum vitamin D and plasma BDNF measurements. Whole blood telomere length was measured using RT-PCR method. The results show that the reduction of the risk of MCI was achieved by higher serum vitamin D level (OR: 0.96, 95% CI: 0.92–0.99, p < 0.05), higher plasma BDNF level (OR: 0.51, 95% CI: 0.30–0.88,  p < 0.05), and longer telomere (OR: 0.97, 95% CI: 0.95–0.99,  p < 0.001). In conclusion, participants with higher vitamin D level, higher BDNF level, and longer telomere length were more likely to age successfully.

Decreased peripheral brain-derived neurotrophic factor levels in Alzheimer's disease: a meta-analysis study (N=7277)

Studies suggest that dysfunction of brain-derived neurotrophic factor (BDNF) is a possible contributor to the pathology and symptoms of Alzheimer's disease (AD). Several studies report reduced peripheral blood levels of BDNF in AD, but findings are inconsistent. This study sought to quantitatively summarize the clinical BDNF data in patients with AD and mild cognitive impairment (MCI, a prodromal stage of AD) with a meta-analytical technique. A systematic search of Pubmed, PsycINFO and the Cochrane Library identified 29 articles for inclusion in the meta-analysis. Random-effects meta-analysis showed that patients with AD had significantly decreased baseline peripheral blood levels of BDNF compared with healthy control (HC) subjects (24 studies, Hedges' g=-0.339, 95% confidence interval (CI)=-0.572 to -0.106, P=0.004). MCI subjects showed a trend for decreased BDNF levels compared with HC subjects (14 studies, Hedges' g=-0.201, 95% CI=-0.413 to 0.010, P=0.062). No differences were found between AD and MCI subjects in BDNF levels (11 studies, Hedges' g=0.058, 95% CI=-0.120 to 0.236, P=0.522). Interestingly, the effective sizes and statistical significance improved after excluding studies with reported medication in patients (between AD and HC: 18 studies, Hedges' g=-0.492, P<0.001; between MCI and HC: 11 studies, Hedges' g=-0.339, P=0.003). These results strengthen the clinical evidence that AD or MCI is accompanied by reduced peripheral blood BDNF levels, supporting an association between the decreasing levels of BDNF and the progression of AD.

Peripheral Brain-Derived Neurotrophic Factor Levels in Alzheimer's Disease and Mild Cognitive Impairment: a Comprehensive Systematic Review and Meta-analysis

Alzheimer's disease (AD) is becoming a growing global problem, and there is an urgent need to identify reliable blood biomarkers of the risk and progression of this condition. A potential candidate is the brain-derived neurotrophic factor (BDNF), which modulates major trophic effects in the brain. However, findings are apparently inconsistent regarding peripheral blood BDNF levels in AD patients vs. healthy people. We thus performed a systematic review and meta-analysis of the studies that have examined peripheral BDNF levels in patients with AD or mild cognitive impairment (MCI) and healthy controls. We searched articles through PubMed, EMBASE, and hand searching. Over a total pool of 2061 potential articles, 26 met all inclusion criteria (including a total of 1584 AD patients, 556 MCI patients, and 1294 controls). A meta-analysis of BDNF levels between early AD and controls showed statistically significantly higher levels (SMD [95 % CI]: 0.72 [0.31, 1.13]) with no heterogeneity. AD patients with a low (<20) mini-mental state examination (MMSE) score had lower peripheral BDNF levels compared with controls (SMD [95 % CI]: -0.33 [-0.60, -0.05]). However, we found no statistically significant difference in blood (serum/plasma) BDNF levels between all AD patients and controls (standard mean difference, SMD [95 % CI]: -0.16 [-0.4, 0.07]), and there was heterogeneity among studies (P < 0.0001, I ² = 85.8 %). There were no differences in blood BDNF levels among AD or MCI patients vs. controls by subgroup analyses according to age, sex, and drug use. In conclusion, this meta-analysis shows that peripheral blood BDNF levels seem to be increased in early AD and decreased in AD patients with low MMSE scores respectively compared with their age- and sex-matched healthy referents. At present, however, this could not be concluded from individual studies.

Association between APOE ε4 Genotype and Memory Impairment in Elderly with Normal Global Cognitive Assessment

Aim: Early prediction using cognitive evaluation tools that are less influenced by education level is beneficial for dementia screening. This study investigated the relationship between Word List Memory Immediate Recall (WLM IR) and the Saving Score (SS) with having the APOE ε4 risk allele in the elderly with normal global cognitive assessment. Methods: A cross-sectional study on 105 subjects ≥60 years with normal MMSE scores who met inclusion criteria. Memory impairment (MI) if: WLM IR score on the third trial <8 or an SS score <80%. Results: The majority of the subjects were female (68.6%), 65 ± 7.1 years, had undertaken formal education for <6 years (56.2%), had MI (81%), and the APOE ε4 genotype was detected in 24.8% of subjects. There was a significant relationship between APOE ε4 and lower WLMIR (p = 0.02, OR 7.92, CI 95% (1.00–62.38)). Conclusions: WLM IR score is lower in elderly people with the APOE ε4 despite their normal global cognitive assessment results, and these scores were not influenced by education level. Further research needs to confirm that the WLM IR can be used to screen for early dementia.

Brain-Derived Neurotrophic Factor in Alzheimer's Disease: Risk, Mechanisms, and Therapy

Brain-derived neurotrophic factor (BDNF) has a neurotrophic support on neuron of central nervous system (CNS) and is a key molecule in the maintenance of synaptic plasticity and memory storage in hippocampus. However, changes of BDNF level and expression have been reported in the CNS as well as blood of Alzheimer's disease (AD) patients in the last decade, which indicates a potential role of BDNF in the pathogenesis of AD. Therefore, this review aims to summarize the latest progress in the field of BDNF and its biological roles in AD pathogenesis. We will discuss the interaction between BDNF and amyloid beta (Aβ) peptide, the effect of BDNF on synaptic repair in AD, and the association between BDNF polymorphism and AD risk. The most important is, enlightening the detailed biological ability and complicated mechanisms of action of BDNF in the context of AD would provide a future BDNF-related remedy for AD, such as increment in the production or release of endogenous BDNF by some drugs or BDNF mimics.