Development of Alzheimer disease in old major depressive patients based upon their health status: A retrospective study in Taiwan

Accelerated biological brain aging in major depressive disorder

Major depressive disorder (MDD) patients commonly encounter multiple types of functional disabilities, such as social, physical, and role functioning. MDD is related to an accreted risk of brain atrophy, aging-associated brain diseases, and mortality. Based on recently available studies, there are correlations between notable biological brain aging and MDD in adulthood. Despite several clinical and epidemiological studies that associate MDD with aging phenotypes, the underlying mechanisms in the brain remain unknown. The key areas in the study of biological brain aging in MDD are structural brain aging, impairment in functional connectivity, and the impact on cognitive function and age-related disorders. Various measurements have been used to determine the severity of brain aging, such as the brain age gap estimate (BrainAGE) or brain-predicted age difference (BrainPAD). This review summarized the current results of brain imaging data on the similarities between the manifestation of brain structural changes and the age-associated processes in MDD. This review also provided recent evidence of BrainPAD or BrainAGE scores in MDD, brain structural abnormalities, and functional connectivity, which are commonly observed between MDD and age-associated processes. It serves as a basis of current reference for future research on the potential areas of investigation for diagnostic, preventive, and potentially therapeutic purposes for brain aging in MDD.

Converged avenues: depression and Alzheimer's disease- shared pathophysiology and novel therapeutics

Depression, a highly prevalent disorder affecting over 280 million people worldwide, is comorbid with many neurological disorders, particularly Alzheimer's disease (AD). Depression and AD share overlapping pathophysiology, and the search for accountable biological substrates made it an essential and intriguing field of research. The paper outlines the neurobiological pathways coinciding with depression and AD, including neurotrophin signalling, the hypothalamic-pituitary-adrenal axis (HPA), cellular apoptosis, neuroinflammation, and other aetiological factors. Understanding overlapping pathways is crucial in identifying common pathophysiological substrates that can be targeted for effective management of disease state. Antidepressants, particularly monoaminergic drugs (first-line therapy), are shown to have modest or no clinical benefits. Regardless of the ineffectiveness of conventional antidepressants, these drugs remain the mainstay for treating depressive symptoms in AD. To overcome the ineffectiveness of traditional pharmacological agents in treating comorbid conditions, a novel therapeutic class has been discussed in the paper. This includes neurotransmitter modulators, glutamatergic system modulators, mitochondrial modulators, antioxidant agents, HPA axis targeted therapy, inflammatory system targeted therapy, neurogenesis targeted therapy, repurposed anti-diabetic agents, and others. The primary clinical challenge is the development of therapeutic agents and the effective diagnosis of the comorbid condition for which no specific diagnosable scale is present. Hence, introducing Artificial Intelligence (AI) into the healthcare system is revolutionary. AI implemented with interdisciplinary strategies (neuroimaging, EEG, molecular biomarkers) bound to have accurate clinical interpretation of symptoms. Moreover, AI has the potential to forecast neurodegenerative and psychiatric illness much in advance before visible/observable clinical symptoms get precipitated.

Bidirectional association between major depressive disorder and dementia: Two population-based cohort studies in Taiwan

BACKGROUND

Major depressive disorder (MDD) and dementia are both major contributors to the global burden of disease. Despite existing literature on the association between MDD and dementia, there is a lack of a nationwide longitudinal cohort study that considers the competing risk of death. Therefore, this study assessed the bidirectional associations between MDD and dementia over an 11-year period in population-based settings, accounting for death as a competing risk.

METHODS

We conducted two population-based retrospective cohort studies in Taiwan. We identified 80,742 patients diagnosed with MDD in 2009-2010 and matched them with patients without MDD by sex, age, and year of diagnosis to assess the relative risk of dementia. We also identified 80,108 patients diagnosed with dementia in 2009-2010 and matched them with patients without dementia by sex, age, and year of diagnosis to assess the relative risk of MDD. All patients were followed until they received a diagnosis of new onset MDD or new onset dementia, their death, or the end of 2019. Cause-specific hazards models were used to estimate adjusted hazard ratios (aHRs).

RESULTS

The incidence density (ID) of dementia was higher in patients with MDD than in patients without MDD (7.63 vs. 2.99 per 1000 person-years), with an aHR of 2.71 (95% confidence interval [CI]: 2.55-2.88). The ID of MDD was higher in patients with dementia than in patients without dementia (12.77 vs. 4.69 per 1000 person-years), with an aHR of 2.47 (95% CI: 2.35-2.59).

CONCLUSIONS

This population-based study found a bidirectional association between MDD and dementia. Our findings suggest the need to identify dementia in patients with MDD and vice versa.

Human tau-overexpressing mice recapitulate brainstem involvement and neuropsychiatric features of early Alzheimer's disease

Alzheimer's disease (AD) poses an ever-increasing public health concern as the population ages, affecting more than 6 million Americans. AD patients present with mood and sleep changes in the prodromal stages that may be partly driven by loss of monoaminergic neurons in the brainstem, but a causal relationship has not been firmly established. This is due in part to a dearth of animal models that recapitulate early AD neuropathology and symptoms. The goal of the present study was to evaluate depressive and anxiety-like behaviors in a mouse model of AD that overexpresses human wild-type tau (htau) prior to the onset of cognitive impairments and assess these behavior changes in relationship to tau pathology, neuroinflammation, and monoaminergic dysregulation in the dorsal raphe nucleus (DRN) and locus coeruleus (LC). We observed depressive-like behaviors at 4 months in both sexes and hyperlocomotion in male htau mice. Deficits in social interaction persisted at 6 months and were accompanied by an increase in anxiety-like behavior in males. The behavioral changes at 4 months coincided with a lower density of serotonergic (5-HT) neurons, downregulation of 5-HT markers, reduced excitability of 5-HT neurons, and hyperphosphorylated tau in the DRN. Inflammatory markers were also upregulated in the DRN along with protein kinases and transglutaminase 2, which may promote tau phosphorylation and aggregation. Loss of 5-HT innervation to the entorhinal cortex and dentate gyrus of the hippocampus was also observed and may have contributed to depressive-like behaviors. There was also reduced expression of noradrenergic markers in the LC along with elevated phospho-tau expression, but this did not translate to a functional change in neuronal excitability. In total, these results suggest that tau pathology in brainstem monoaminergic nuclei and the resulting loss of serotonergic and/or noradrenergic drive may underpin depressive- and anxiety-like behaviors in the early stages of AD.

Mechanism of METTL3-mediated m6A modification in depression-induced cognitive deficits

Depressive disorder (DD) is associated with N6-methyladenosine (m6A) hypermethylation. This study sought to explore the molecular mechanism of Methyltransferase-like 3 (METTL3) in cognitive deficits of chronic unpredictable mild stress (CUMS)-treated rats and provide novel targets for DD treatment. A DD rat model was established via CUMS treatment. Cognitive deficits were assessed via body weighing and behavioral tests. METTL3, microRNA (miR)-221-3p, pri-miR-221, GRB2-associated binding protein 1 (Gab1) expressions in hippocampal tissues were detected via RT-qPCR and Western blotting. m6A, DiGeorge syndrome critical region gene 8 (DGCR8)-bound pri-miR-221 and pri-miR-221 m6A levels were measured. The binding relationship between miR-221-3p and Gab1 was testified by dual-luciferase and RNA pull-down assays. Rescue experiments were designed to confirm the role of miR-221-3p and Gab1. METTL3 was highly expressed in CUMS rats, and silencing METTL3 attenuated cognitive deficits of CUMS rats. METTL3-mediated m6A modification facilitated processing and maturation of pri-miR-221 via DGCR8 to upregulate miR-221-3p. miR-221-3p targeted Gab1. miR-221-3p overexpression or Gab1 downregulation reversed the role of silencing METTL3 in CUMS rats. Overall, METTL3-mediated m6A modification facilitated processing and maturation of pri-miR-221 to upregulate miR-221-3p and then inhibit Gab1, thereby aggravating cognitive deficits of CUMS rats.

Differential Diagnosis Findings Between Alzheimer's Disease and Major Depressive Disorder: A Review

Background

Differentiating diagnosis between Alzheimer's disease and major depressive disorder in the elderly is a great clinical challenge. This study aimed to identify the establishment of differential diagnosis protocols between Alzheimer's disease and major depressive disorder.

Methods

We searched studies in the Ovid MEDLINE, EMBASE, PsycINFO, and Web of Science databases between 2009 and 2019. A total of 155 references were found for searching relevant articles using Boolean search. After exclusion of redundancies and assessing of title, abstract, and full text for eligibility, 11 articles were selected. The total sample size was 1077 distributed in 8 different countries.

Results

Significant results were found for differential diagnosis between Alzheimer's disease and major depressive disorder, such as overall mental status, episodic memory, visuospatial construction, delayed recognition task, semantic verbal fluency, visual task in short-term memory, atrophy of the hippocampus, cortical activation in specific tasks, and cerebrospinal fluid biomarkers.

Conclusion

These findings are good pathways for discriminating Alzheimer's disease from major depression in the elderly.

Sex Differences in Cardiovascular Disease and Cognitive Dysfunction in Rural West Elderly Texans

BACKGROUND

The prevalence of cognitive dysfunction increases in elderly due to cardiovascular disease related risk factors in rural communities like West Texas.

OBJECTIVE

The purpose of this study was to find risk factors of cardiovascular disease (CVD) related to cognitive dysfunction and their impact on elderly adults in rural West Texans.

METHODS

Statistical methods such as Pearson's chi-squared and a multinomial logistic regression were utilized to analyze data. We used SPSS software to detect and understand the nature of the risk factors.

RESULTS

A summary of statistics was obtained by using Pearson's chi-squared test for categorical variables. CVD, diabetes mellitus, and depression were significantly associated with cognitive dysfunction for both males and females (p = 0.0001), whereas anxiety was found to be significantly associated with cognitive dysfunction for females (p = 0.0001). Age group and race/ethnicity were significantly associated with cognitive dysfunction for both males and females (p = 0.0001). By performing a multinomial logistic regression method and controlling for confounders, the significant risk factors (p <  0.05)- age (65- 84 years), diabetes, and memory loss for age-associated cognitive impairment; diabetes for cognitive impairment no dementia; age (65- 84, ≥85 years), CVD, diabetes, depression, memory loss, non-Hispanic Whites, and Black/African-Americans for mild cognitive impairment; and age, memory loss, non-Hispanic Whites, Black/African-Americans, and male gender were found for dementia.

CONCLUSION

CVD related risk factors in developing cognitive dysfunction exist and integrating such risk variables may guide relevant policy interventions to reduce Alzheimer's incidence or dementia in rural communities in West Texans.

The Contribution of Rat Studies to Current Knowledge of Major Depressive Disorder: Results From Citation Analysis

Major depressive disorder (MDD) is the most severe depression type and one of the leading causes of morbidity worldwide. Animal models are widely used to understand MDD etiology, pathogenesis, and treatment, but the efficacy of this research for patients has barely been systematically evaluated. Such evaluation is important given the resource consumption and ethical concerns incurred by animal use. We used the citation tracking facilities within Web of Science and Scopus to locate citations of original research papers on rats related to MDD published prior to 2013—to allow adequate time for citations—identified in PubMed and Scopus by relevant search terms. Resulting citations were thematically coded in eight categories, and descriptive statistics were calculated. 178 publications describing relevant rat studies were identified. They were cited 8,712 times. More than half (4,633) of their citations were by other animal studies. 794 (less than 10%) were by human medical papers. Citation analysis indicates that rat model research has contributed very little to the contemporary clinical understanding of MDD. This suggests a misuse of limited funding hence supporting a change in allocation of research and development funds targeting this disorder to maximise benefits for patients.