Blood D-Amino Acid Oxidase Levels Increased With Cognitive Decline Among People With Mild Cognitive Impairment: A Two-Year Prospective Study

Serum dysregulation of serine and glycine metabolism as predictive biomarker for cognitive decline in frail elderly subjects

Frailty is a common age-related clinical syndrome characterized by a decline in the function of multiple organ systems, increased vulnerability to stressors, and a huge socio-economic burden. Despite recent research efforts, the physiopathological mechanisms underlying frailty remain elusive and biomarkers able to predate its occurrence in the early stages are still lacking. Beyond its physical component, cognitive decline represents a critical domain of frailty associated with higher risk of adverse health outcomes. We measured by High-Performance Liquid Chromatography (HPLC) a pool of serum amino acids including L-glutamate, L-aspartate, glycine, and D-serine, as well as their precursors L-glutamine, L-asparagine, and L-serine in a cohort of elderly subjects encompassing the entire continuum from fitness to frailty. These amino acids are known to orchestrate excitatory and inhibitory neurotransmission, and in turn, to play a key role as intermediates of energy homeostasis and in liver, kidney, muscle, and immune system metabolism. To comprehensively assess frailty, we employed both the Edmonton Frail Scale (EFS), as a practical tool to capture the multidimensionality of frailty, and the frailty phenotype, as a measure of physical function. We found that D-serine and D-/Total serine ratio were independent predictors of EFS but not of physical frailty. Furthermore, higher levels of glycine, glycine/L-serine and D-/Total serine were associated with worse cognition and depressive symptoms in the frail group. These findings suggest that changes in peripheral glycine and serine enantiomers homeostasis may represent a novel biochemical correlate of frailty.

d-Amino acids: new clinical pathways for brain diseases

Free d-amino acids (d-AAs) are emerging as a novel and important class of signaling molecules in many organs, including the brain and endocrine systems. There has been considerable progress in our understanding of the fundamental roles of these atypical messengers, with increasingly recognized implications in a wide range of neuropathologies, including schizophrenia (SCZ), epilepsy, Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), substance abuse, and chronic pain, among others. Research has enabled the discovery that d-serine, d-aspartate and more recently d-cysteine are essential for the healthy development and function of the central nervous system (CNS). We discuss recent progress that has profoundly transformed our vision of numerous physiological processes but has also shown how d-AAs are now offering therapeutic promise in clinical settings for several human diseases.

Adjunctive transcranial direct current stimulation (tDCS) plus sodium benzoate for the treatment of early-phase Alzheimer's disease: A randomized, double-blind, placebo-controlled trial

Previous studies found that an NMDA receptor (NMDAR) enhancer, sodium benzoate, improved cognitive function of patients with early-phase Alzheimer's disease (AD). Transcranial direct current stimulation (tDCS) induces NMDAR-dependent synaptic plasticity and strengthens cognitive function of AD patients. This study aimed to evaluate efficacy and safety of tDCS plus benzoate in early-phase dementia. In this 24-week randomized, double-blind, placebo-controlled trial, 97 patients with early-phase AD received 10-session tDCS during the first 2 weeks. They then took benzoate or placebo for 24 weeks. We assessed the patients using Alzheimer's disease assessment scale - cognitive subscale (ADAS-cog), Clinician's Interview-Based Impression of Change plus Caregiver Input, Mini Mental Status Examination, Alzheimer's disease Cooperative Study scale for ADL in MCI, and a battery of additional cognitive tests. Forty-seven patients received sodium benzoate, and the other 50 placebo. The two treatment groups didn't differ significantly in ADAS-cog or other measures. Addition of benzoate to tDCS didn't get extra benefit or side effect in this study. For more thoroughly studying the potential of combining tDCS with benzoate in the AD treatment, future research should use other study designs, such as longer-term benzoate treatment, adding benzoate in the middle of tDCS trial sessions, or administering benzoate then tDCS.

Is Histamine and Not Acetylcholine the Missing Link between ADHD and Allergies? Speer Allergic Tension Fatigue Syndrome Re-Visited

Speer allergic tension-fatigue syndrome (SATFS) is a classic allergy syndrome characterized by allergy-like symptoms, muscle tension, headaches, chronic fatigue, and other particular behaviors that were initially described in the fifties. The particular behaviors displayed include symptoms such as hyperkinesis, hyperesthesia (i.e., insomnia), restlessness, and distractibility, among others. Interestingly, these symptoms are very similar to descriptions of attention deficit hyperactivity disorder (ADHD), the most prevalent neurodevelopmental disorder worldwide, which is characterized by inattention, hyperactivity, and impulsivity. The clinical description of SATFS precedes the nomination of ADHD in 1960 by Stella Chess. In this conceptual paper, we stress that there is a gap in the research on the relationship between ADHD and allergic pathologies. The hypotheses of this conceptual paper are (1) SATFS is probably one of the first and best historical descriptions of ADHD alongside a common comorbidity (allergy) displayed by these patients; (2) SATFS (ADHD) is a systemic disease that includes both somatic and behavioral manifestations that may influence each other in a bidirectional manner; (3) The role of neuroinflammation and histamine is key for understanding the pathophysiology of ADHD and its frequent somatic comorbidities; (4) The deficiency of the diamine oxidase (DAO) enzyme, which metabolizes histamine extracellularly, may play a role in the pathophysiology of ADHD. Decreased DAO activity may lead to an accumulation of histamine, which could contribute to core ADHD symptoms and comorbid disorders. Further empirical studies are needed to confirm our hypotheses.

Inverse Association between Cheese Consumption and Lower Cognitive Function in Japanese Community-Dwelling Older Adults Based on a Cross-Sectional Study

Diet modification may contribute to the prevention of age-related cognitive decline. The association between dairy product consumption and cognitive function in older people remains unknown. We investigated whether cheese intake is associated with lower cognitive function (LCF) in community-dwelling older adults. This cross-sectional study included 1503 adults aged over 65 years. The analyzed data were obtained through face-to-face interviews and functional ability measurement. Cognitive function was assessed using the mini-mental state examination (MMSE), and a score ≤23 was defined as LCF. The prevalence of LCF was 4.6%, and this group had smaller calf circumference, slower usual walking speed, and a more frequent history of anemia than subjects with MMSE scores >23. After adjusting for confounding factors, logistic regression analysis revealed cheese intake (odds ratio (OR) = 0.404, 95% confidence interval (CI) = 0.198-0.824), age (OR = 1.170, 95% CI = 1.089-1.256), usual walking speed (OR = 0.171, 95% CI = 0.062-0.472) and calf circumference (OR = 0.823, 95% CI = 0.747-0.908) to be significant factors associated with LCF. Although the present study was an analysis of cross-sectional data of Japanese community-dwelling older adults, the results suggest that cheese intake is inversely associated with LCF.

Differential relationships of NMDAR hypofunction and oxidative stress with cognitive decline

NMDAR hypofunction and oxidative stress are implicated in the pathogenesis of Alzheimer's disease. D-amino acid oxidase (DAO) regulates NMDAR function. Glutathione, superoxide dismutase, and catalase are three first-line endogenous antioxidants. This study explored the associations of these potential biomarkers with mild cognitive impairment. Cognitive function and blood levels of DAO, glutathione, superoxide dismutase, and catalase were measured in 63 mild cognitive impairment patients and 24 healthy individuals every 6 months for 2 years. Among the patients, DAO and glutathione levels at baseline contributed to the cognitive decline 2 years later. Among the healthy individuals, only glutathione levels were associated with cognitive change. The four biomarkers differed in change directions (upward vs. downward) in the patients and in the healthy individuals. Among patients, glutathione levels were negatively correlated with superoxide dismutase and positively correlated with catalase, and DAO levels were negatively correlated with superoxide dismutase. To our knowledge, this is the first study to demonstrate the differential associations of NMDAR hypofunction and oxidative stress with cognitive change between the mild cognitive impairment patients and healthy people. Glutathione may be regarded as an aging marker for both mild cognitive impairment and normal aging; and DAO, a biomarker exclusively for mild cognitive impairment.

Endogenous antioxidants predicted outcome and increased after treatment: A benzoate dose-finding, randomized, double-blind, placebo-controlled trial for Alzheimer's disease

AIM

Previous pilot studies suggest that sodium benzoate may be a potential cognitive enhancer for patients with Alzheimer's disease (AD), schizophrenia, or late-life depression. Especially for AD treatment, a confirmatory trial with predictive biomarkers is urgently needed. This study aimed to confirm benzoate as a novel treatment for AD and to discover its optimal dose and biomarkers.

METHODS

A 24-week, dose-finding, randomized, double-blind, placebo-controlled trial, with clinical measurements at weeks 0, 8, 16, and 24, was conducted in three major medical centers in Taiwan. Among 154 patients screened for AD, 149 were eligible and randomized to one of the four treatments: (i) benzoate 500 group (fixed 500 mg/day); (ii) benzoate 750 (500 mg/day for the first 4 weeks, 750 mg/day from the 5th week); (iii) benzoate 1000 (500 mg/day for the first 4 weeks, 1000 mg/day from the 5th week); and (iv) placebo. The primary outcome measure was AD assessment scale-cognitive subscale (ADAS-cog).

RESULTS

The benzoate 1000 group performed best in improving ADAS-cog (P = 0.026 at week 24), with female advantage. Higher plasma catalase at baseline predicted better outcome. Benzoate receivers tended to have higher catalase and glutathione than placebo recipients after treatment. The four intervention groups showed similar safety profiles.

CONCLUSIONS

By enhancing two vital endogenous antioxidants, catalase and glutathione, sodium benzoate therapy improved cognition of patients with AD, with higher baseline catalase predicting better response. Supporting the oxidative stress theory, the results show promise for benzoate as a novel treatment for AD.

Chiral Amino Acid Profiling in Serum Reveals Potential Biomarkers for Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a complex neurodegenerative disease, and increasing evidence has linked dysregulation of amino acids to AD pathogenesis. However, the existing studies often ignore the chirality of amino acids, and some results are inconsistent and controversial. The changes of amino acid profiles in AD from the perspective of enantiomers remain elusive.

OBJECTIVE

The purpose of this study is to investigate whether the levels of amino acids, especially D-amino acids, are deregulated in the peripheral serum of AD patients, with the ultimate goal of discovering novel biomarkers for AD.

METHODS

The chiral amino acid profiles were determined by HPLC-MS/MS with a pre-column derivatization method. Experimental data obtained from 37 AD patients and 34 healthy controls (HC) were statistically analyzed.

RESULTS

Among the 35 amino acids detected, D-proline, D/total-proline ratio, D-aspartate, and D/total-aspartate ratio were decreased, while D-phenylalanine was elevated in AD compared to HC. Significant age-dependent increases in D-proline, D/total-proline ratio, and D-phenylalanine were observed in HC, but not in AD. Receiver operator characteristic analyses of the combination of D-proline, D-aspartate, D-phenylalanine, and age for discriminating AD from HC provided satisfactory area under the curve (0.87), specificity (97.0%), and sensitivity (83.8%). Furthermore, the D-aspartate level was significantly decreased with the progression of AD, as assessed by the Clinical Dementia Rating Scale and Mini-Mental State Examination.

CONCLUSION

The panels of D-proline, D-phenylalanine, and D-aspartate in peripheral serum may serve as novel biomarker candidates for AD. The latter parameter is further associated with the severity of AD.

Catalpol Exerts Antidepressant-Like Effects by Enhancing Anti-oxidation and Neurotrophy and Inhibiting Neuroinflammation via Activation of HO-1

Catalpol is an iridoid glycoside with rich content, rich nutrition, and numerous biological activities in Rehmanniae Radix contained in classic antidepressant prescriptions in Chinese clinical medicine. Catalpol has been confirmed previously its exact antidepressant-like effect involved heme oxygenase (HO)-1, but its antidepressant molecular targets and mechanism are still unclear. Here, catalpol's antidepressant-like molecular target was diagnosed and confirmed by ZnPP intervention [the antagonist of HO-1, (10 μg/rat), intracerebroventricular] for the first time, and its molecule mechanism network was determined through HO-1 related pathway and molecules in the hippocampus. Results showed that ZnPP significantly abolished catalpol's (10 mg/kg) reversal on depressive-like behaviors of chronic unpredictable mild stress rats, abolished catalpol's up-regulation on the phosphorylation level of extracellular regulated protein kinases (ERK)1/2 and brain-derived neurotrophic factor (BDNF)'s receptor tropomyosin-related kinase B (TrkB), the nuclear expression level of nuclear factor E 2-related factor 2 (Nrf2), the levels of anti-oxidant factors (such as HO-1, SOD, GPX, GST, GSH) and BDNF, and abolished catalpol's down-regulation on the levels of peroxide and neuroinflammation factors [cyclooxygenase-2 (COX-2), induced nitrogen monoxide synthase (iNOS), nitric oxide (NO)]. Thus, HO-1 could serve as an important potential molecular target for catalpol's antidepressant-like process, and the antidepressant-like mechanism of catalpol could at least involve the activation of HO-1 triggering the up-regulation of the ERK1/2/Nrf2/HO-1 pathway-related factors to enhance the anti-oxidant defense, triggering the down-regulation of the COX-2/iNOS/NO pathway-related factors to inhibit neuroinflammation, and triggering the up-regulation of the BDNF/TrkB pathway to enhance neurotrophy.