[The controversy over early diagnosis of Alzheimer's disease: A literature review of the advantages and disadvantages]

BACKGROUND

The continuum of Alzheimer's disease (AD) comprises three stages: the pre-clinical stage (with few to no subjective symptoms), the prodromal stage (measurable mild cognitive impairment) and the final stage of clinically manifest (AD) dementia. Neuropathological correlates in accordance with these stages have been found with varying frequency. The aim of early AD diagnosis is to determine such correlates in these preclinical and prodromal stages and to determine the probability of the manifestation of a later AD dementia. In this regard, the prognostic validity is of vital importance. From the perspective of those affected, the issue of early diagnosis cannot be reduced to AD, although Alzheimer's dementia is by far the most common form of dementia. The aim of this review is to provide a literature-based overview of the advantages and disadvantages of early AD diagnosis in contrast to other types of dementia. Based on this, recommendations will be formulated for the prioritisation of early diagnostic advantages and disadvantages in the patient counselling situation in clinical practice.

METHODS

Three databases were searched for current reviews addressing the advantages, disadvantages and ethical aspects of early AD diagnosis. The search was limited to current German or English reviews published between January 1, 2018 to November 30, 2022. The systematic search strategy was based on the PICO model and included both a Boolean and a focus-expanding keyword search using previously defined search terms. In addition, snowballing was used as a search strategy. Qualitative synoptic content analysis in accordance with Mayring was used to analyse both advantages and disadvantages. Similar arguments were combined into single statements. The resulting statements were categorized into three main groups: social, individual or clinical aspects. To emphasize the aforementioned aims, arguments were additionally distinguished into "only valid for early AD diagnosis" and "valid for early diagnosis of all types of dementia".

RESULTS

Overall, seven reviews with suitable content were included. Social aspects of early AD diagnosis comprise the protection of the affected person and the society as well as potential stigmatisation of the affected and their family members. Individual arguments range from the right to a "rational suicide", including the avoidance of financial and caregiving burdens on family members, to the right not to know the diagnosis. Clinical arguments include, for example, the scientific research context (facilitating the identification of suitable clinical trial participants) and various negative effects of a false positive or false negative early diagnosis.

CONCLUSION

Early diagnosis of AD as well as of other forms of dementia are characterised by numerous advantages and disadvantages of a social, individual and clinical nature. The decision for or against early diagnosis should always be made by weighing the current advantages against the disadvantages in a specific case. In particular, the desires of the person affected, the validity of the diagnostic procedures available and, above all, the availability of effective preventive or therapeutic measures must be taken into account.

Histamine H3 receptor antagonists with peptidomimetic (keto)piperazine structures to inhibit Aβ oligomerisation

Alzheimeŕs disease (AD) is the most prominent neurodegenerative disorder with high medical need. Protein-protein-interactions (PPI) interactions have a critical role in AD where β-amyloid structures (Aβ) build toxic oligomers. Design of disease modifying multi target directed ligand (MTDL) has been performed, which disable PPI on the one hand and on the other hand, act as procognitive antagonists at the histamine H₃ receptor (H₃R). The synthetized compounds are structurally based on peptidomimetic amino acid-like structures mainly as keto, diketo-, or acyl variations of a piperazine moiety connected to an H₃R pharmacophore. Most of them showed low nanomolar affinities at H₃R and some with promising affinity to Aβ-monomers. The structure-activity relationships (SAR) described offer new possibilities for MTDL with an optimized profile combining symptomatic and potential causal therapeutic approaches in AD.

Derivatives of montanine-type alkaloids and their implication for the treatment of Alzheimer's disease: Synthesis, biological activity and in silico study

Alzheimeŕs disease (AD) is the most common neurodegenerative disorder, characterized by neuronal loss and cognitive impairment. Currently, very few drugs are available for AD treatment, and a search for new therapeutics is urgently needed. Thus, in the current study, twenty-eight new derivatives of montanine-type Amaryllidaceae alkaloids were synthesized and evaluated for their ability to inhibit human recombinant acetylcholinesterase (hAChE) and butyrylcholinesterase (hBuChE). Three derivatives (1n, 1o, and 1p) with different substitution patterns demonstrated significant selective inhibitory potency for hAChE (IC₅₀ < 5 µM), and one analog, 1v, showed selective hBuChE inhibition activity (IC₅₀ = 1.73 ± 0.05 µM). The prediction of CNS availability, as disclosed by the BBB score, suggests that the active compounds in this survey should be able pass through the blood-brain barrier (BBB). Cytotoxicity screening and docking studies were carried out for the two most pronounced cholinesterase inhibitors, 1n and 1v.

Mitochondrial dysfunction in Alzheimer's disease: Therapeutic implications of lithium

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases, characterized by the accumulation of abnormal tau proteins within neurons and amyloid plaques in the brain parenchyma, which leads to progressive loss of neurons in the brain. While the detailed mechanism of the pathogenesis of AD is still unknown, evidence suggests that mitochondrial dysfunction likely plays a fundamental role in the pathogenesis of this disease. Due to the relevance of mitochondrial alterations in AD, recent works have suggested the therapeutic potential of mitochondrial-targeted lithium. Lithium has been shown to possess neuroprotective and neurotrophic properties that could also be related to the upregulation of mitochondrial function. In the current work, we perform a comprehensive investigation of the significance of mitochondrial dysfunction in AD and pharmacological treatment with lithium as imperative in this pathology, through a brief review of the major findings on the effects of lithium as a therapeutic approach targeting mitochondria in the context of AD.

Chronic intermittent hypoxia induces changes on the expression and activity of neprilysin (EC 3.4.24.11) in the brain of rats

Obstructive sleep apnea (OSA) is a frequent sleeping breathing disorder associated with cognitive impairments. Neprilysin (NEP) is responsible for degrading several substrates related to cognition; however, the effect of chronic intermittent hypoxia (CIH) on NEP is still unknown. This study aimed to evaluate the expression and activity of NEP in cognitive-related brain structures of rats submitted to CIH. Western blot, qRT-PCR and enzyme activity assay, demonstrated that a six-week intermittent hypoxia increased NEP expression and activity, selectively in temporal cortex, but not in the hippocampus and frontal cortex. The increase in NEP activity and expression was reverted followed by two weeks recovery in normoxia. These data show that CIH protocol increases the expression and activity of NEP selectively in the temporal cortex. Additional mechanisms must be investigated to elucidate the effects of CIH in cognition.

Apolipoprotein E DNA methylation and late-life disease

Background

This study aims to investigate if DNA methylation of the apolipoprotein E (APOE) locus affects the risks of dementia, Alzheimeŕs disease (AD) or cardiovascular disease (CVD).

Methods

DNA methylation across theAPOE gene has previously been categorized into three distinct regions: a hypermethylated region in the promoter, a hypomethylated region in the first two introns and exons and a hypermethylated region in the 3′exon that also harbours theAPOE ε2 and ε4 alleles. DNA methylation levels in leukocytes were measured using the Illumina 450K array in 447 Swedish twins (mean age 78.1 years). We used logistic regression to investigate whether methylation levels in those regions affect the odds of disease.

Results

We found that methylation levels in the promoter region were associated with dementia and AD after adjusting for sex, age at blood draw, education, smoking and relatedness among twins [odds ratio (OR) 1.32 per standard deviation increase in methylation levels, 95% confidence interval (CI) 1.08–1.62 for dementia; OR 1.38, 95% CI 1.07–1.78 for AD). We did not detect any difference in methylation levels between CVD cases and controls. Results were similar when comparing within discordant twin pairs, and did not differ as a function ofAPOE genotype.

Conclusions

We found that higher DNA methylation levels in the promoter region ofAPOE increase the odds of dementia and AD, but not CVD. The effect was independent ofAPOE genotype, indicating that allelic variation and methylation variation inAPOE may act independently to increase the risk of dementia.

Low serum insulin-like growth factor-I (IGF-I) level is associated with increased risk of vascular dementia

BACKGROUND

Insulin-like growth factor-I (IGF-I) is important for the adult brain, but little is known of the role of IGF-I in Alzheimeŕs disease (AD) or vascular dementia (VaD).

METHODS

A prospective study of 342 patients with subjective or objective mild cognitive impairment recruited at a single memory clinic. We determined whether serum IGF-I concentrations at baseline were associated with the risk of all-cause dementia, AD, or VaD. Patients developing mixed forms of AD and VaD were defined as suffering from VaD. The statistical analyses included Cox proportional hazards regression analysis.

RESULTS

During the follow-up (mean 3.6 years), 95 (28%) of the patients developed all-cause dementia [AD, n=37 (11%) and VaD, n=42 (12%)]. Low as well as high serum IGF-I (quartile 1 or 4 vs. quartiles 2-3) did not associate with all-cause dementia [crude hazard ratio (HR) 1.30, 95% confidence interval (CI): 0.81-2.08 and crude HR 1.05, 95% CI: 0.63-1.75, respectively] or AD (crude HR 0.79, 95% CI: 0.35-1.79 and crude HR 0.94, 95% CI: 0.43-2.06, respectively]. In contrast, low serum IGF-I concentrations were associated with increased risk of VaD (quartile 1 vs. quartiles 2-3, crude HR 2.22, 95% CI: 1.13-4.36). The latter association remained significant also after adjustment for multiple covariates.

CONCLUSIONS

In a memory clinic population, low serum IGF-I was a risk marker for subsequent VaD whereas low IGF-I did not associate with the risk of AD. High serum IGF-I was not related to the risk of conversion to dementia.

Amyloid binding properties of curcumin analogues in Alzheimer's disease postmortem brain tissue

The presence of β-amyloid (Aβ) containing plaques in the brain is a hallmark of Alzheimer's disease (AD) and serves as a biomarker for confirmation of diagnosis postmortem. Early diagnosis is of great importance for optimal treatment and for monitoring disease progression in the brain. Highly specific and sensitive biomarkers are thus greatly needed to assess therapeutic efficacy, not only clinically, but also in terms of clearance of histopathological lesions and decelerated neurodegeneration. The objective of the present study was to give more insight into the binding of curcumin analogues, curcuminoids, to Aβ containing plaques in postmortem tissue from AD patients. In vitro autoradiography was utilized to explore affinity and displacement of the curcuminoids; curcumin, demethoxycurcumin (DMC), bisdemethoxycurcumin (BDMC) and dimethoxycurcumin (DIMC). We found that BDMC had the highest affinity for Aβ containing plaques in cortical AD brain tissue in comparison to other curcuminoids. Subsequently, [(3)H]BDMC showed significantly higher specific binding in cortical AD brain tissue compared to control subjects. These findings suggest that curcumin analogues, especially BDMC, may serve as a potential radioligands for Aβ plaque neuroimaging.

Amyloid-β(25-35) induces a permanent phosphorylation of HSF-1, but a transitory and inflammation-independent overexpression of Hsp-70 in C6 astrocytoma cells

Two hallmarks of Alzheimer diseases are the continuous inflammatory process, and the brain deposit of Amyloid b (Aβ), a cytotoxic protein. The intracellular accumulation of Aβ(25-35) fractions, in the absence of Heat Shock proteins (Hsṕs), could be responsible for its cytotoxic activity. As, pro-inflammatory mediators and nitric oxide control the expression of Hsṕs, our aim was to investigate the effect of Aβ(25-35) on the concentration of IL-1β, TNF-α and nitrite levels, and their relation to pHSF-1, Hsp-60, -70 and -90 expressions, in the rat C6 astrocyte cells. Interleukin-specific ELISA kits, immunohistochemistry with monoclonal anti-Hsp and anti pHSF-1 antibodies, and histochemistry techniques, were used. Our results showed that Aβ25-35 treatment of C6 cells increased, significantly and consistently the concentration of IL-1β, TNF-α and nitrite 3 days after initiating treatment. The immunoreactivity of C6 cells to Hsp-70 reached its peak after 3 days of treatment followed by an abrupt decrease, as opposed to Hsp-60 and -90 expressions that showed an initial and progressive increase after 3 days of Aβ(25-35) treatment. pHSF-1 was identified throughout the experimental period. Nevertheless, progressive and sustained cell death was observed during all the treatment times and it was not caspase-3 dependent. Our results suggest that Hsp-70 temporary expression serves as a trigger to inhibit casapase-3 pathway and allow the expression of Hsp-60 and -90 in C6 astrocytoma cells stimulated with Aβ(25-35).