Cognitive dysfunction and cerebral volumetric deficits in individuals with Alzheimer's disease, alcohol use disorder, and dual diagnosis

Hepatic LRP-1 plays an important role in amyloidosis in Alzheimer's disease mice: Potential role in chronic heavy alcohol feeding

BACKGROUND

Hepatic lipoprotein receptor-related protein 1 (LRP-1) plays a central role in peripheral amyloid beta (Aβ) clearance, but its importance in Alzheimer's disease (AD) pathology is understudied. Our previous work showed that intragastric alcohol feeding to C57BL/6 J mice reduced hepatic LRP-1 expression which correlated with significant AD-relevant brain changes. Herein, we examined the role of hepatic LRP-1 in AD pathogenesis in APP/PS1 AD mice using two approaches to modulate hepatic LRP-1, intragastric alcohol feeding to model chronic heavy drinking shown by us to reduce hepatic LRP-1, and hepato-specific LRP-1 silencing.

METHODS

Eight-month-old male APP/PS1 mice were fed ethanol or control diet intragastrically for 5 weeks (n = 7-11/group). Brain and liver Aβ were assessed using immunoassays. Three important mechanisms of brain amyloidosis were investigated: hepatic LRP-1 (major peripheral Aβ regulator), blood-brain barrier (BBB) function (vascular Aβ regulator), and microglia (major brain Aβ regulator) using immunoassays. Spatial LRP-1 gene expression in the periportal versus pericentral hepatic regions was confirmed using NanoString GeoMx Digital Spatial Profiler. Further, hepatic LRP-1 was silenced by injecting LRP-1 microRNA delivered by the adeno-associated virus 8 (AAV8) and the hepato-specific thyroxine-binding globulin (TBG) promoter to 4-month-old male APP/PS1 mice (n = 6). Control male APP/PS1 mice received control AAV8 (n = 6). Spatial memory and locomotion were assessed 12 weeks after LRP-1 silencing using Y-maze and open-field test, respectively, and brain and liver Aβ were measured.

RESULTS

Alcohol feeding reduced plaque-associated microglia in APP/PS1 mice brains and increased aggregated Aβ (p < 0.05) by ELISA and 6E10-positive Aβ load by immunostaining (p < 0.05). Increased brain Aβ corresponded with a significant downregulation of hepatic LRP-1 (p < 0.01) at the protein and transcript level, primarily in pericentral hepatocytes (zone 3) where alcohol-induced injury occurs. Hepato-specific LRP-1 silencing significantly increased brain Aβ and locomotion hyperactivity (p < 0.05) in APP/PS1 mice.

CONCLUSION

Chronic heavy alcohol intake reduced hepatic LRP-1 expression and increased brain Aβ. The hepato-specific LRP-1 silencing similarly increased brain Aβ which was associated with behavioral deficits in APP/PS1 mice. Collectively, our results suggest that hepatic LRP-1 is a key regulator of brain amyloidosis in alcohol-dependent AD.

Alcohol Use Disorder and Dementia: A Review

PURPOSE

By 2040, 21.6% of Americans will be over age 65, and the population of those older than age 85 is estimated to reach 14.4 million. Although not causative, older age is a risk factor for dementia: every 5 years beyond age 65, the risk doubles; approximately one-third of those older than age 85 are diagnosed with dementia. As current alcohol consumption among older adults is significantly higher compared to previous generations, a pressing question is whether drinking alcohol increases the risk for Alzheimer's disease or other forms of dementia.

SEARCH METHODS

Databases explored included PubMed, Web of Science, and ScienceDirect. To accomplish this narrative review on the effects of alcohol consumption on dementia risk, the literature covered included clinical diagnoses, epidemiology, neuropsychology, postmortem pathology, neuroimaging and other biomarkers, and translational studies. Searches conducted between January 12 and August 1, 2023, included the following terms and combinations: "aging," "alcoholism," "alcohol use disorder (AUD)," "brain," "CNS," "dementia," "Wernicke," "Korsakoff," "Alzheimer," "vascular," "frontotemporal," "Lewy body," "clinical," "diagnosis," "epidemiology," "pathology," "autopsy," "postmortem," "histology," "cognitive," "motor," "neuropsychological," "magnetic resonance," "imaging," "PET," "ligand," "degeneration," "atrophy," "translational," "rodent," "rat," "mouse," "model," "amyloid," "neurofibrillary tangles," "α-synuclein," or "presenilin." When relevant, "species" (i.e., "humans" or "other animals") was selected as an additional filter. Review articles were avoided when possible.

SEARCH RESULTS

The two terms "alcoholism" and "aging" retrieved about 1,350 papers; adding phrases-for example, "postmortem" or "magnetic resonance"-limited the number to fewer than 100 papers. Using the traditional term, "alcoholism" with "dementia" resulted in 876 citations, but using the currently accepted term "alcohol use disorder (AUD)" with "dementia" produced only 87 papers. Similarly, whereas the terms "Alzheimer's" and "alcoholism" yielded 318 results, "Alzheimer's" and "alcohol use disorder (AUD)" returned only 40 citations. As pertinent postmortem pathology papers were published in the 1950s and recent animal models of Alzheimer's disease were created in the early 2000s, articles referenced span the years 1957 to 2024. In total, more than 5,000 articles were considered; about 400 are herein referenced.

DISCUSSION AND CONCLUSIONS

Chronic alcohol misuse accelerates brain aging and contributes to cognitive impairments, including those in the mnemonic domain. The consensus among studies from multiple disciplines, however, is that alcohol misuse can increase the risk for dementia, but not necessarily Alzheimer's disease. Key issues to consider include the reversibility of brain damage following abstinence from chronic alcohol misuse compared to the degenerative and progressive course of Alzheimer's disease, and the characteristic presence of protein inclusions in the brains of people with Alzheimer's disease, which are absent in the brains of those with AUD.

Alcohol Use Disorder as a Risk Factor for Cognitive Impairment

BACKGROUND

Alcohol use disorder (AUD) is a worldwide problem. The AUD can take the form of hazardous drinking, binge drinking, or alcohol dependence. The effects of alcohol on cognition can be diverse and complex.

OBJECTIVE

Our study aimed to assess AUD as a risk factor for cognitive impairment.

METHODS

A literature search was conducted using major electronic databases of PubMed, EMBASE, and Web of Science. Abstracts were screened independently to include data from original research reports. The following keywords were used: alcohol abuse, cognitive impairment, Alzheimer's disease, and dementia. In total, 767 abstracts were retrieved. After removing the duplicates, 76 articles met the criteria for full-text review, of which 41 were included in this report.

RESULTS

People with AUD are seen from different geographical areas and cultures. AUD is associated with an increased risk of cognitive impairments, Alzheimer's disease, and dementia, especially vascular dementia. In addition, AUD interacts with comorbidities increasing the risk of cognitive impairment.

CONCLUSION

AUD is associated with an increased risk of cognitive impairments, which may have more than one underlying mechanism.

Ethanol exposure alters Alzheimer's-related pathology, behavior, and metabolism in APP/PS1 mice

Epidemiological studies identified alcohol use disorder (AUD) as a risk factor for Alzheimer's disease (AD), yet there is conflicting evidence on how alcohol use promotes AD pathology. In this study, a 10-week moderate two-bottle choice drinking paradigm was used to identify how chronic ethanol exposure alters amyloid-β (Aβ)-related pathology, metabolism, and behavior. Ethanol-exposed APPswe/PSEN1dE9 (APP/PS1) mice showed increased brain atrophy and an increased number of amyloid plaques. Further analysis revealed that ethanol exposure led to a shift in the distribution of plaque size in the cortex and hippocampus. Ethanol-exposed mice developed a greater number of smaller plaques, potentially setting the stage for increased plaque proliferation in later life. Ethanol drinking APP/PS1 mice also exhibited deficits in nest building, a metric of self-care, as well as increased locomotor activity and central zone exploration in an open field test. Ethanol exposure also led to a diurnal shift in feeding behavior which was associated with changes in glucose homeostasis and glucose intolerance. Complementary in vivo microdialysis experiments were used to measure how acute ethanol directly modulates Aβ in the hippocampal interstitial fluid (ISF). Acute ethanol transiently increased hippocampal ISF glucose levels, suggesting that ethanol directly affects cerebral metabolism. Acute ethanol also selectively increased ISF Aβ40, but not ISF Aβ42, levels during withdrawal. Lastly, chronic ethanol drinking increased N-methyl-d-aspartate receptor (NMDAR) and decreased γ-aminobutyric acid type-A receptor (GABA_AR) mRNA levels, indicating a potential hyperexcitable shift in the brain's excitatory/inhibitory (E/I) balance. Collectively, these experiments suggest that ethanol may increase Aβ deposition by disrupting metabolism and the brain's E/I balance. Furthermore, this study provides evidence that a moderate drinking paradigm culminates in an interaction between alcohol use and AD-related phenotypes with a potentiation of AD-related pathology, behavioral dysfunction, and metabolic impairment.

Biological and Clinical Implications of Sex-Specific Differences in Alzheimer's Disease

Mounting evidence indicates that the female sex is a risk factor for Alzheimer's disease (AD), the most common cause of dementia worldwide. Decades of research suggest that sex-specific differences in genetics, environmental factors, hormones, comorbidities, and brain structure and function may contribute to AD development. However, although significant progress has been made in uncovering specific genetic factors and biological pathways, the precise mechanisms underlying sex-biased differences are not fully characterized. Here, we review several lines of evidence, including epidemiological, clinical, and molecular studies addressing sex differences in AD. In addition, we discuss the challenges and future directions in advancing personalized treatments for AD.

Gut microbiome, cognitive function and brain structure: a multi-omics integration analysis

BACKGROUND

Microbiome-gut-brain axis may be involved in the progression of age-related cognitive impairment and relevant brain structure changes, but evidence from large human cohorts is lacking. This study was aimed to investigate the associations of gut microbiome with cognitive impairment and brain structure based on multi-omics from three independent populations.

METHODS

We included 1430 participants from the Guangzhou Nutrition and Health Study (GNHS) with both gut microbiome and cognitive assessment data available as a discovery cohort, of whom 272 individuals provided fecal samples twice before cognitive assessment. We selected 208 individuals with baseline microbiome data for brain magnetic resonance imaging during the follow-up visit. Fecal 16S rRNA and shotgun metagenomic sequencing, targeted serum metabolomics, and cytokine measurements were performed in the GNHS. The validation analyses were conducted in an Alzheimer's disease case-control study (replication study 1, n = 90) and another community-based cohort (replication study 2, n = 1300) with cross-sectional dataset.

RESULTS

We found protective associations of specific gut microbial genera (Odoribacter, Butyricimonas, and Bacteroides) with cognitive impairment in both the discovery cohort and the replication study 1. Result of Bacteroides was further validated in the replication study 2. Odoribacter was positively associated with hippocampal volume (β, 0.16; 95% CI 0.06-0.26, P = 0.002), which might be mediated by acetic acids. Increased intra-individual alterations in gut microbial composition were found in participants with cognitive impairment. We also identified several serum metabolites and inflammation-associated metagenomic species and pathways linked to impaired cognition.

CONCLUSIONS

Our findings reveal that specific gut microbial features are closely associated with cognitive impairment and decreased hippocampal volume, which may play an important role in dementia development.

Sex-specific transcriptional rewiring in the brain of Alzheimer’s disease patients

Sex-specific differences may contribute to Alzheimer’s disease (AD) development. AD is more prevalent in women worldwide, and female sex has been suggested as a disease risk factor. Nevertheless, the molecular mechanisms underlying sex-biased differences in AD remain poorly characterized. To this end, we analyzed the transcriptional changes in the entorhinal cortex of symptomatic and asymptomatic AD patients stratified by sex. Co-expression network analysis implemented by SWItchMiner software identified sex-specific signatures of switch genes responsible for drastic transcriptional changes in the brain of AD and asymptomatic AD individuals. Pathway analysis of the switch genes revealed that morphine addiction, retrograde endocannabinoid signaling, and autophagy are associated with both females with AD (F-AD) and males with (M-AD). In contrast, nicotine addiction, cell adhesion molecules, oxytocin signaling, adipocytokine signaling, prolactin signaling, and alcoholism are uniquely associated with M-AD. Similarly, some of the unique pathways associated with F-AD switch genes are viral myocarditis, Hippo signaling pathway, endometrial cancer, insulin signaling, and PI3K-AKT signaling. Together these results reveal that there are many sex-specific pathways that may lead to AD. Approximately 20–30% of the elderly have an accumulation of amyloid beta in the brain, but show no cognitive deficit. Asymptomatic females (F-asymAD) and males (M-asymAD) both shared dysregulation of endocytosis. In contrast, pathways uniquely associated with F-asymAD switch genes are insulin secretion, progesterone-mediated oocyte maturation, axon guidance, renal cell carcinoma, and ErbB signaling pathway. Similarly, pathways uniquely associated with M-asymAD switch genes are fluid shear stress and atherosclerosis, FcγR mediated phagocytosis, and proteoglycans in cancer. These results reveal for the first time unique pathways associated with either disease progression or cognitive resilience in asymptomatic individuals. Additionally, we identified numerous sex-specific transcription factors and potential neurotoxic chemicals that may be involved in the pathogenesis of AD. Together these results reveal likely molecular drivers of sex differences in the brain of AD patients. Future molecular studies dissecting the functional role of these switch genes in driving sex differences in AD are warranted.