Serum Adiponectin in Alzheimer's Disease (AD): Association with AD Biomarkers and Cognitive Outcome

The role of adiponectin in Alzheimer's disease: A translational review

Adiponectin is an adipokine playing a central role in the regulation of energy homeostasis, carbohydrate and lipid metabolism, as well as immunomodulation. The relationship between Alzheimer's disease (AD) and body composition has highlighted the bidirectional crosstalk between AD's pathophysiology and metabolic disorders. This review aimed to report the current state of knowledge about cellular and molecular mechanisms linking adiponectin and AD, in preclinical studies. Then, we reviewed human studies to assess the relationship between adiponectin levels and AD diagnosis. We also examined the risk of incident AD regarding the participants' baseline adiponectin level, as well as the relationship of adiponectin and cognitive decline in patients with AD. We conducted a systematic review, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guideline, of studies published over the last decade on MEDLINE and Cochrane databases. Overall, we reviewed 34 original works about adiponectin in AD, including 11 preclinical studies, two both preclinical and human studies and 21 human studies. Preclinical studies brought convincing evidence for the neuroprotective role of adiponectin on several key mechanisms of AD. Human studies showed conflicting results regarding the relationship between AD and adiponectin levels, as well as regarding the cross-sectional association between cognitive function and adiponectin levels. Adiponectin did not appear as a predictor of incident AD, nor as a predictor of cognitive decline in patients with AD. Despite solid preclinical evidence suggesting the protective role of adiponectin in AD, inconsistent results in humans supports the need for further research.

Sex-specific blood biomarkers linked to memory changes in middle-aged adults: The Framingham Heart Study

The relationship between sex-specific blood biomarkers and memory changes in middle-aged adults remains unclear. We aimed to investigate this relationship using the data from the Framingham Heart Study (FHS). We conducted association analysis, partial correlation analysis, and causal dose-response curves using blood biomarkers and other data from 793 middle-aged participants (≤ 60 years) from the FHS Offspring Cohort. The results revealed associations of adiponectin and fasting blood glucose with midlife memory change, along with a U-shaped relationship of high-density lipoprotein cholesterol with memory change. No significant associations were found for the other blood biomarkers (e.g., amyloid beta protein 42) with memory change. To our knowledge, this is the first sex-specific network analysis of blood biomarkers related to midlife memory change in a prospective cohort study. Our findings highlight the importance of targeting cardiometabolic risks and the need to validate midlife-specific biomarkers that can accelerate the development of primary preventive strategies.

Adiponectin, the adiponectin paradox, and Alzheimer's Disease: Is this association biologically plausible?

Dementia, especially Alzheimer's Disease (AD) and vascular dementia, is a major public health problem that continues to expand in both economically emerging and hegemonic countries. In 2017, the World Alzheimer Report estimated that over 50 million people were living with dementia globally. Metabolic dysfunctions of brain structures such as the hippocampus and cerebral cortex have been implicated as risk factors for dementia. Several well-defined metabolic risk factors for AD include visceral obesity, chronic inflammation, peripheral and brain insulin resistance, type 2 diabetes mellitus (T2DM), hypercholesterolemia, and others. In this review, we describe the relationship between the dysmetabolic mechanisms, although still unknown, and dementia, particularly AD. Adiponectin (ADPN), the most abundant circulating adipocytokine, acts as a protagonist in the metabolic dysfunction associated with AD, with unexpected and intriguing dual biological functions. This contradictory role of ADPN has been termed the adiponectin paradox. Some evidence suggests that the adiponectin paradox is important in amyloidogenic evolvability in AD. We present cumulative evidence showing that AD and T2DM share many common features. We also review the mechanistic pathways involving brain insulin resistance. We discuss the importance of the evolvability of amyloidogenic proteins (APs), defined as the capacity of a system for adaptive evolution. Finally, we describe potential therapeutic strategies in AD, based on the adiponectin paradox.

Plasma adiponectin levels predict cognitive decline and cortical thinning in mild cognitive impairment with beta-amyloid pathology

Background

Blood adiponectin and leptin are adipokines that emerged as potential biomarkers for predicting Alzheimer’s disease (AD) owing to their strong connection with obesity. Although obesity affects the relation between beta-amyloid (Aβ) aggregation and cognitive decline, the longitudinal interactive effect of adipokines and Aβ on cognition and brain structures in humans remains unexplored. Hence, we investigated whether plasma levels of adiponectin and leptin are associated with future cognitive decline and cortical thinning across Aβ conditions (Aβ [+] and Aβ [−]) in individuals with mild cognitive impairment (MCI).

Methods

Of 156 participants with MCI from the longitudinal cohort study of Alzheimer’s Disease Neuroimaging Initiative (ADNI), 31 were Aβ (−) and 125 were Aβ (+) as determined by CSF analysis. The Alzheimer’s Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) scores and the thickness of the parahippocampal and entorhinal cortices were used to evaluate cognition and brain structure, respectively. After stratifying groups by Aβ conditions, the association of cognitive and brain structural changes with baseline plasma levels of adiponectin and leptin was examined.

Results

Of the total 156 participants, 51 were women (32.7%). The mean age of participants was 74.5 (standard deviation 7.57), and the mean follow-up period was 54.3 months, without a difference between the Aβ (+) and (−) groups. After adjustment for confounders, higher plasma adiponectin levels were associated with a faster increase in ADAS-Cog scores, indicating faster cognitive decline under the Aβ (+) condition (beta = 0.224, p = 0.018). Likewise, participants with higher plasma adiponectin presented faster cortical thinning in the bilateral parahippocampal cortices under the Aβ (+) condition (beta = − 0.004, p = 0.012 for the right side; beta = − 0.004, p = 0.025 for the left side). Interestingly, plasma adiponectin levels were not associated with longitudinal ADAS-Cog scores or cortical thickness in the Aβ (−) condition. Plasma leptin levels were not predictive of cognition or cortical thickness regardless of Aβ status.

Conclusion

Plasma adiponectin can be a potential biomarker for predicting the speed of AD progression in individuals with Aβ (+) MCI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01107-3.