Hypothalamic digoxin, hemispheric chemical dominance, and Alzheimer's disease

Revisiting the Role of Vitamins and Minerals in Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia that affects millions of individuals worldwide. It is an irreversible neurodegenerative disorder that is characterized by memory loss, impaired learning and thinking, and difficulty in performing regular daily activities. Despite nearly two decades of collective efforts to develop novel medications that can prevent or halt the disease progression, we remain faced with only a few options with limited effectiveness. There has been a recent growth of interest in the role of nutrition in brain health as we begin to gain a better understanding of what and how nutrients affect hormonal and neural actions that not only can lead to typical cardiovascular or metabolic diseases but also an array of neurological and psychiatric disorders. Vitamins and minerals, also known as micronutrients, are elements that are indispensable for functions including nutrient metabolism, immune surveillance, cell development, neurotransmission, and antioxidant and anti-inflammatory properties. In this review, we provide an overview on some of the most common vitamins and minerals and discuss what current studies have revealed on the link between these essential micronutrients and cognitive performance or AD.

Altered central and blood glutathione in Alzheimer's disease and mild cognitive impairment: a meta-analysis

BACKGROUND

Increasing evidence implicates oxidative stress (OS) in Alzheimer disease (AD) and mild cognitive impairment (MCI). Depletion of the brain antioxidant glutathione (GSH) may be important in OS-mediated neurodegeneration, though studies of post-mortem brain GSH changes in AD have been inconclusive. Recent in vivo measurements of the brain and blood GSH may shed light on GSH changes earlier in the disease.

AIM

To quantitatively review in vivo GSH in AD and MCI compared to healthy controls (HC) using meta-analyses.

METHOD

Studies with in vivo brain or blood GSH levels in MCI or AD with a HC group were identified using MEDLINE, PsychInfo, and Embase (1947-June 2020). Standardized mean differences (SMD) and 95% confidence intervals (CI) were calculated for outcomes using random effects models. Outcome measures included brain GSH (Meshcher-Garwood Point Resolved Spectroscopy (MEGA-PRESS) versus non-MEGA-PRESS) and blood GSH (intracellular versus extracellular) in AD and MCI. The Q statistic and Egger's test were used to assess heterogeneity and risk of publication bias, respectively.

RESULTS

For brain GSH, 4 AD (AD=135, HC=223) and 4 MCI (MCI=213, HC=211) studies were included. For blood GSH, 26 AD (AD=1203, HC=1135) and 7 MCI (MCI=434, HC=408) studies were included. Brain GSH overall did not differ in AD or MCI compared to HC; however, the subgroup of studies using MEGA-PRESS reported lower brain GSH in AD (SMD [95%CI] -1.45 [-1.83, -1.06], p<0.001) and MCI (-1.15 [-1.71, -0.59], z=4.0, p<0.001). AD had lower intracellular and extracellular blood GSH overall (-0.87 [-1. 30, -0.44], z=3.96, p<0.001). In a subgroup analysis, intracellular GSH was lower in MCI (-0.66 [-1.11, -0.21], p=0.025). Heterogeneity was observed throughout (I² >85%) and not fully accounted by subgroup analysis. Egger's test indicated risk of publication bias.

CONCLUSION

Blood intracellular GSH decrease is seen in MCI, while both intra- and extracellular decreases were seen in AD. Brain GSH is decreased in AD and MCI in subgroup analysis. Potential bias and heterogeneity suggest the need for measurement standardization and additional studies to explore sources of heterogeneity.

Association of Circulating Magnesium Levels in Patients With Alzheimer's Disease From 1991 to 2021: A Systematic Review and Meta-Analysis

Alzheimer's disease (AD) remains a medical and social challenge worldwide. Magnesium (Mg) is one of the most frequently evaluated essential minerals with diverse biological functions in human body. However, the association between circulating Mg levels and AD remains controversial. We conducted a meta-analysis of 21 studies published between 1991 and 2021 to determine whether the Mg levels in the blood and cerebrospinal fluid (CSF) are abnormal in AD. Literatures were searched in PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), and Wanfang Data without language limitations. A pooled subject sample including 1,112 AD patients and 1,001 healthy controls (HCs) was available to assess Mg levels in serum and plasma; 284 AD patients and 117 HCs were included for Mg levels in CSF. It was found that serum and plasma levels of Mg were significantly reduced in AD patients compared with HCs (standardized mean difference [SMD] = -0.89; 95% confidence interval [CI] [-1.36, -0.43]; P = 0.000). There was statistically non-significant for Mg level in CSF between AD and HCs, whereas a decreased tendency were detected (SMD = -0.16; 95% CI [-0.50, 0.18]; P = 0.364). .In addition, when we analyzed the Mg levels of serum, plasma and CSF together, the circulating Mg levels in AD patients was significantly lower (SMD = -0.74, 95% CI [-1.13; -0.35]; P = 0.000). These results indicate that Mg deficiency may be a risk factor of AD and Mg supplementation may be a potentially valuable adjunctive treatment for AD. Systematic Review Registration: www.crd.york.ac.uk/PROSPERO/, registration number CRD42021254557.

Catecholamines in Alzheimer's Disease: A Systematic Review and Meta-Analysis

Background and Purpose: Previous studies found inconsistent results regarding the relationship between Alzheimer's disease (AD) and catecholamines, such as dopamine (DA), norepinephrine (NE), and epinephrine (EPI). Therefore, the purpose of this study was to perform a systematic review and meta-analysis to evaluate the results of previous studies on this relationship.

Method: Literature retrieval of eligible studies was performed in four databases (Web of Science, PubMed, Embase, and PsycARTICLES). Standardized mean differences (SMDs) were calculated to assess differences in catecholamine concentrations between the AD groups and controls.

Results: Thirteen studies met the eligibility criteria. Compared with the controls, significant lower concentrations of NE (SMD = −1.10, 95% CI: −2.01 to −0.18, p = 0.019) and DA (SMD = −1.12, 95% CI: −1.88 to −0.37, p = 0.003) were observed in patients with AD. No difference was found in the concentrations of EPI between the two groups (SMD = −0.74, 95% CI: −1.85 to 0.37, p = 0.189).

Conclusion: Overall, these findings are in line with the hypothesis that reduced NE and DA may be an important indicator for AD (Registration number CRD42018112816).

Dopamine and Dopamine Receptors in Alzheimer's Disease: A Systematic Review and Network Meta-Analysis

Background: The dopaminergic system has been associated with the progression of Alzheimer's disease. But previous studies found inconsistent results regarding the relationship between Alzheimer's disease and dopamine when looking at dopamine receptor concentrations. Objective: The aim of this review was to synthesize, using a random-effects model of meta-analysis, the link between the dopaminergic system and Alzheimer's disease. Methods: A detailed analysis protocol was registered at the PROSPERO database prior to data extraction (CRD42018110798). Electronic databases of PubMed, Embase, Web of Science, and Psyc-ARTICLES were searched up to December 2018 for studies that examined dopamine and dopamine receptors in relation to Alzheimer's disease. Standardized mean differences (SMD) were calculated to assess group differences in the levels of dopaminergic neurometabolites. Results: Seventeen studies met the eligibility criteria. Collectively, they included 512 patients and 500 healthy controls. There were significantly lower levels of dopamine in patients with Alzheimer's disease compared with controls (SMD = -1.56, 95% CI: -2.64 to -0.49). In addition, dopamine 1 receptor (SMD = -5.05, 95% CI: -6.14 to -3.97) and dopamine 2 receptor (SMD = -1.13, 95% CI: -1.52 to -0.74) levels were decreased in patients with Alzheimer's disease compared with controls. The results of network meta-analysis indicated that the rank of correlation with Alzheimer's disease from highest to lowest was dopamine (0.74), dopamine 2 receptor (0.49), dopamine 3 receptor (0.46), dopamine 4 receptor (0.33), dopamine 5 receptor (0.31), and dopamine 1 receptor (0.64). Conclusions: Overall, decreased levels of dopaminergic neurotransmitters were linked with the pathophysiology of Alzheimer's disease. Nonetheless, there is a clear need for more prospective studies to validate these hypotheses.

Plasma nutrient status of patients with Alzheimer's disease: Systematic review and meta-analysis

BACKGROUND

Alzheimer disease (AD) patients are at risk of nutritional insufficiencies because of physiological and psychological factors. Nutritional compounds are postulated to play a role in the pathophysiological processes that are affected in AD. We here provide the first systematic review and meta-analysis that compares plasma levels of micronutrients and fatty acids in AD patients to those in cognitively intact elderly controls. A secondary objective was to explore the presence of different plasma nutrient levels between AD and control populations that did not differ in measures of protein/energy nourishment.

METHODS

We screened literature published after 1990 in the Cochrane Central Register of Controlled Trials, Medline, and Embase electronic databases using Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines for AD patients, controls, micronutrient, vitamins, and fatty acids, resulting in 3397 publications, of which 80 met all inclusion criteria. Status of protein/energy malnutrition was assessed by body mass index, mini nutritional assessment score, or plasma albumin. Meta-analysis, with correction for differences in mean age between AD patients and controls, was performed when more than five publications were retrieved for a specific nutrient.

RESULTS

We identified five or more studies for folate, vitamin A, vitamin B12, vitamin C, vitamin D, vitamin E, copper, iron, and zinc but fewer than five studies for vitamins B1 and B6, long-chain omega-3 fatty acids, calcium, magnesium, manganese, and selenium (the results of the individual publications are discussed). Meta-analysis showed significantly lower plasma levels of folate and vitamin A, vitamin B12, vitamin C, and vitamin E (P < .001), whereas nonsignificantly lower levels of zinc (P = .050) and vitamin D (P = .075) were found in AD patients. No significant differences were observed for plasma levels of copper and iron. A meta-analysis that was limited to studies reporting no differences in protein/energy malnourishment between AD and control populations yielded similar significantly lower plasma levels of folate and vitamin B12, vitamin C, and vitamin E in AD.

CONCLUSIONS

The lower plasma nutrient levels indicate that patients with AD have impaired systemic availability of several nutrients. This difference appears to be unrelated to the classic malnourishment that is well known to be common in AD, suggesting that compromised micronutrient status may precede protein and energy malnutrition. Contributing factors might be AD-related alterations in feeding behavior and intake, nutrient absorption, alterations in metabolism, and increased utilization of nutrients for AD pathology-related processes. Given the potential role of nutrients in the pathophysiological processes of AD, the utility of nutrition may currently be underappreciated and offer potential in AD management.

Fluorescent liposomes for differential interactions with glycosaminoglycans

We have successfully synthesized a lipid containing the pyranine dye as the hydrophilic headgroup. This lipid was incorporated into liposomes with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine as the major component. The resultant liposomes displayed differential modulations in fluorescence emission intensity in the presence of nanomolar concentrations of different glycosaminoglycans. Linear discriminant analysis of the fluorescence response data demonstrate that the liposomes are able to distinguish between different GAGs. In addition, we also demonstrate that the liposomes incorporating the pyranine lipid are able to distinguish between dilute serum from healthy individuals and serum containing elevated chondroitin sulfate (simulated serum from an Alzheimer's disease patient).

Effects of taurine on plasma and liver lipids, erythrocyte ouabain sensitive Na efflux and platelet aggregation in Sprague Dawley rats

The effects of taurine on plasma and liver cholesterol, erythrocyte ouabain sensitive Na efflux and platelet aggregation were examined in Sprague Dawley rats fed control or 0.5% cholesterol with 0.2% cholate diet. Plasma and liver levels of total cholesterol were increased significantly (p<0.05) in rats fed cholesterol diet compared to the control, and taurine significantly decreased the elevated plasma level of cholesterol in rats fed cholesterol diet (p<0.05). HDL-cholesterol was decreased in groups fed the cholesterol diet regardless of taurine supplementation and the difference between groups with and without cholesterol was significant (p<0.01). Plasma triglyceride was decreased and liver triglyceride was increased both significantly (p<0.05) in rats fed cholesterol compared to the control. Plasma and liver triglyceride in rats fed taurine was decreased significantly compared to the control (p<0.05). Intracellular Na tended to be lower in rats fed cholesterol or taurine and higher in rats fed cholesterol plus taurine compared to the control. Na efflux through Na-K ATPase and the passive leak of Na was somewhat reduced in rats fed cholesterol or taurine and was augmented in rats fed cholesterol plus taurine compared to the control, which showed a similar trend to the intracellular Na. Taurine supplementation caused a suppression of Na efflux in groups fed control diet and restored the suppressed Na efflux in groups fed cholesterol. Platelet aggregation was significantly decreased in the group fed taurine compared to the control (p<0.05) and the group fed cholesterol plus taurine was also a little lower in aggregation than the group fed cholesterol. Microscopic examination showed that taurine prevented fatty liver in rats fed cholesterol diet. Taurine known for stimulating Na-K ATPase in some cell types rather decreased erythrocyte ouabain sensitive Na-K ATPase in the present study. Taurine had hypolipidemic and hypocholesterolemic effects and inhibited platelet aggregation which may be favorable for prevention of cardiovascular diseases.