Quantification and regulation of adipsin in human cerebrospinal fluid (CSF)

Obesity-induced blood-brain barrier dysfunction: phenotypes and mechanisms

Obesity, a burgeoning global health issue, is increasingly recognized for its detrimental effects on the central nervous system, particularly concerning the integrity of the blood-brain barrier (BBB). This manuscript delves into the intricate relationship between obesity and BBB dysfunction, elucidating the underlying phenotypes and molecular mechanisms. We commence with an overview of the BBB's critical role in maintaining cerebral homeostasis and the pathological alterations induced by obesity. By employing a comprehensive literature review, we examine the structural and functional modifications of the BBB in the context of obesity, including increased permeability, altered transport mechanisms, and inflammatory responses. The manuscript highlights how obesity-induced systemic inflammation and metabolic dysregulation contribute to BBB disruption, thereby predisposing individuals to various neurological disorders. We further explore the potential pathways, such as oxidative stress and endothelial cell dysfunction, that mediate these changes. Our discussion culminates in the summary of current findings and the identification of knowledge gaps, paving the way for future research directions. This review underscores the significance of understanding BBB dysfunction in obesity, not only for its implications in neurodegenerative diseases but also for developing targeted therapeutic strategies to mitigate these effects.

Diagnostic, Prognostic, and Mechanistic Biomarkers of Diabetes Mellitus-Associated Cognitive Decline

Cognitive dysfunctions such as mild cognitive impairment (MCI), Alzheimer's disease (AD), and other forms of dementia are recognized as common comorbidities of type 2 diabetes mellitus (T2DM). Currently, there are no disease-modifying therapies or definitive clinical diagnostic and prognostic tools for dementia, and the mechanisms underpinning the link between T2DM and cognitive dysfunction remain equivocal. Some of the suggested pathophysiological mechanisms underlying cognitive decline in diabetes patients include hyperglycemia, insulin resistance and altered insulin signaling, neuroinflammation, cerebral microvascular injury, and buildup of cerebral amyloid and tau proteins. Given the skyrocketing global rates of diabetes and neurodegenerative disorders, there is an urgent need to discover novel biomarkers relevant to the co-morbidity of both conditions to guide future diagnostic approaches. This review aims to provide a comprehensive background of the potential risk factors, the identified biomarkers of diabetes-related cognitive decrements, and the underlying processes of diabetes-associated cognitive dysfunction. Aging, poor glycemic control, hypoglycemia and hyperglycemic episodes, depression, and vascular complications are associated with increased risk of dementia. Conclusive research studies that have attempted to find specific biomarkers are limited. However, the most frequent considerations in such investigations are related to C reactive protein, tau protein, brain-derived neurotrophic factor, advanced glycation end products, glycosylated hemoglobin, and adipokines.

Obesity and Multiple Sclerosis-A Multifaceted Association

BACKGROUND

Given the common elements in the pathophysiological theories that try to explain the appearance and evolution of obesity and multiple sclerosis, the association between the two pathologies has become an increasingly researched topic in recent years. On the one hand, there is the chronic demyelinating inflammation caused by the autoimmune cascade of multiple sclerosis, while on the other hand, according to the latest research, it has been shown that obesity shares an inflammatory component with most chronic diseases.

METHODS

The authors performed independent research of the available literature in the most important electronic databases (PubMed, Google Scholar, Embase, and Science Direct) in February 2021. After applying the exclusion criteria, the reviewers focused on the most relevant articles published during the last 10 years with respect to epidemiology and pathophysiology.

RESULTS

The data presented are a step forward in trying to elucidate the intricate relationship between obesity and MS, especially the causal relationship between childhood and adolescent obesity and MS, focusing on the epidemiological associations observed in the most relevant observational studies conducted in recent years. In the second part, the authors comment on the latest findings related to the pathophysiological mechanisms that may explain the correlations between obesity and multiple sclerosis, focusing also on the role of adipokines.

CONCLUSIONS

Based on available epidemiological data, obesity in early life appears to be strongly associated with a higher risk of MS development, independent of other risk factors. Although much research has been done on the pathophysiology of obesity, MS, their possible common mechanism, and the role of adipokines, further studies are needed in order to explain what remains unknown. No relevant data were found regarding the association between obesity, disability (high EDSS score), and mortality risk in MS patients. Thus, we consider that this topic should be elucidated in future research.

Systematic Quantification of Neurotrophic Adipokines RBP4, PEDF, and Clusterin in Human Cerebrospinal Fluid and Serum

CONTEXT

Data on the presence/quantification of the neurotrophic adipokines retinol-binding protein-4 (RBP4), clusterin, and pigment epithelium-derived factor (PEDF) in human cerebrospinal fluid (CSF) are scarce and migration of these adipokines across of the blood-brain barrier (BBB) is uncertain.

OBJECTIVE

This work aimed to quantify RBP4, PEDF, and clusterin in paired serum and CSF samples of patients undergoing neurological evaluation.

METHODS

A total of 268 patients (109 male, 159 female) were included. Adipokine serum and CSF concentrations were measured by enzyme-linked immunosorbent assay in duplicate.

RESULTS

RBP4 was abundant in serum (mean, 31.9 ± 24.2 μg/mL). The serum concentrations were approximately 145 times higher than in CSF (CSF to serum RBP4 ratio, 8.2 ± 4.3 × 10-3). PEDF was detectable in serum (mean, 30.2 ± 11.7 μg/mL) and concentrations were approximately 25 times higher than in CSF (CSF to serum PEDF ratio, 42.3 ± 15.6 × 10-3). Clusterin serum concentrations were abundant with mean levels of 346.0 ± 114.6 μg/mL, which were approximately 40 times higher than CSF levels (CSF to serum clusterin ratio, 29.6 ± 23.4 × 10-3). RBP4 and PEDF serum levels correlated positively with CSF levels, which were increased in overweight/obese patients and in type 2 diabetic patients. The CSF concentrations of all 3 adipokines increased with BBB dysfunction. RBP4 in CSF correlated positively with inflammatory parameters. In detail, only RBP4 showed the kinetics and associations that are mandatory for a putative mediator of the fat-brain axis.

CONCLUSION

RBP4, PEDF, and clusterin are permeable to the BBB and increase with the measure of BBB dysfunction. RBP4 represents an inflammatory neurotrophic adipokine and is a promising mediator of the fat-brain axis.

Association between serum adipsin and plaque vulnerability determined by optical coherence tomography in patients with coronary artery disease

Background

Early identification of vulnerable plaques is important for patients with coronary artery disease (CAD) to reduce acute coronary events and improve their prognosis. We sought to examine the relationship between adipsin, an adipokine secreted from adipocytes, and plaque vulnerability in CAD patients.

Methods

A total of 103 plaques from 99 consecutive patients who underwent coronary angiography were assessed by optical coherence tomography. The serum level of adipsin was measured using enzyme-linked immunosorbent assay (ELISA). The accuracy of adipsin for detecting thin-cap fibroatheroma (TCFA) was determined by the area under the receiver operating characteristic curve (AUC).

Results

Of the 99 patients, 49 were classified into the low adipsin group and 50 into the high adipsin group according to the median level of serum adipsin (2.43 µg/mL). The plaques from the high adipsin group exhibited a greater lipid index (2,700.0 vs. 1,975.9° × mm, P=0.015) and an increased proportion of TCFAs (41.2% vs. 21.2%, P=0.028) compared with the low adipsin group. Serum adipsin was found to be negatively correlated with fibrous cap thickness (ρ=−0.322, P=0.002), while it was positively correlated with average lipid arc (ρ=0.253, P=0.015), maximum lipid arc (ρ=0.211, P=0.044), lipid core length (ρ=0.241, P=0.021), lipid index (ρ=0.335, P=0.001), and vulnerability score (ρ=0.254, P=0.014). Furthermore, adipsin had a significant association with TCFAs (OR: 1.290, 95% CI: 1.048–1.589, P=0.016) in the multivariate analysis, while having a moderate diagnostic accuracy for TCFAs (AUC: 0.710, 95% CI: 0.602–0.817, P<0.001).

Conclusions

Our findings suggest that serum adipsin is significantly and positively correlated with the incidence of TCFAs. The application of adipsin as a biomarker may offer improvement in the diagnosis of vulnerable plaques and clinical benefits for CAD patients.

Plasma levels of adipokines in patients with Alzheimer's disease - where is the "breaking point" in Alzheimer's disease pathogenesis?

Peripheral insulin resistance is associated with decreasing adiponectin and increasing leptin plasma levels, and also with cognitive decline. The effects of adipokines on brain function have been published from both animal and human studies. In particular, the influence of leptin and adiponectin on the development of Alzheimer's disease (AD) has been extensively investigated. However, the association between adipsin and AD is as yet unknown. In 37 patients with AD and 65 controls that followed the same study protocol, we tested whether adiponectin, leptin, and adipsin could be used as biomarkers in the early stages of AD. In contrast with conclusions of cognition studies in insulin resistant states, our study found a correlation of impaired neuropsychological performance with increasing adiponectin and decreasing leptin in AD patients. Nevertheless, no significant differences between patients and controls were found. AD women had significantly increased adipsin compared to controls, and there was a positive correlation of adipsin with age and disease duration. Although adipokines do not appear to be suitable biomarkers for early AD diagnosis, they certainly play a role in the pathogenesis of AD. Further studies will be needed to explain the cause of the adipokine "breaking point" that leads to the pathogenesis of overt AD.

An MRM-Based Multiplexed Quantification Assay for Human Adipokines and Apolipoproteins

Adipokines and apolipoproteins are key regulators and potential biomarkers in obesity and associated diseases and their quantitative assessment is crucial for functional analyses to understand disease mechanisms. Compared to routinely used ELISAs, multiple reaction monitoring (MRM)-based mass spectrometry allows multiplexing and detection of proteins for which antibodies are not available. Thus, we established an MRM method to quantify 9 adipokines and 10 apolipoproteins in human serum. We optimized sample preparation by depleting the two most abundant serum proteins for improved detectability of low abundant proteins. Intra-day and inter-day imprecision were below 16.5%, demonstrating a high accuracy. In 50 serum samples from participants with either normal weight or obesity, we quantified 8 adipokines and 10 apolipoproteins. Significantly different abundances were observed for five adipokines (adipsin, adiponectin, chemerin, leptin, vaspin) and four apolipoproteins (apo-B100/-C2/-C4/-D) between the body mass index (BMI) groups. Additionally, we applied our MRM assay to serum samples from normal weight children and human adipocyte cell culture supernatants to proof the feasibility for large cohort studies and distinct biological matrices. In summary, this multiplexed assay facilitated the investigation of relationships between adipokines or apolipoproteins and phenotypes or clinical parameters in large cohorts, which may contribute to disease prediction approaches in the future.

Association between plasma adipsin level and mild cognitive impairment in Chinese patients with type 2 diabetes: a cross-sectional study

BACKGROUND

The adipokine adipsin contributes to insulin resistance (IR), inflammation, and obesity, which are all regarded as high-risk factors for mild cognitive impairment (MCI) in patients with type 2 diabetes mellitus. This research aimed to uncover the role of adipsin in Chinese type 2 diabetes mellitus (T2DM) population with early cognitive dysfunction and determine whether adipsin contributes to diabetic MCI caused by IR.

METHODS

In our study, 126 patients with T2DM were enrolled. The Montreal Cognitive Assessment (MoCA) was used to assess cognitive impairment. Demographic data and neuropsychological test results were evaluated. Plasma adipsin level was measured by enzyme-linked immunosorbent assay.

RESULTS

The MCI group (n = 57) presented higher plasma adipsin levels compared with the healthy controls (p = 0.018). After adjustment for educational attainment, and age, begative correlations were found between plasma adipsin levels and MoCA, Mini Mental State Exam, and Verbal Fluency Test scores(r = - 0.640, p < 0.001; r = - 0.612, p < 0.001; r = - 0.288, p = 0.035; respectively). Correlation analysis demonstrated that adipsin levels were significantly positively correlated with fasting C-peptide; homeostasis model of assessment for insulin resistance (HOMA-IR) (r = 0.368, p < 0.001; r = 0.494, p < 0.001; respectively). Multivariable regression analysis further indicated that high plasma adipsin level was a significant independent determinant of MCI in the Chinese population withT2DM (p = 0.017).

CONCLUSIONS

Elevated plasma adipsin level was associated with MCI in Chinese T2DM patients. Further large-scale studies should be designed to determine whether adipsin is linked to IR-associated susceptibility to early cognitive decline in T2DM patients.

CSF concentrations of adipsin and adiponectin in patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is described as a neurodegenerative disorder. However, neuroinflammation and chemokine expression are prominent pathological finding at sites of injury. Adipsin and adiponectin are molecules that are implicated in the pathogenesis of neurodegenerative and neuroimmune disorders. Adipsin and adiponectin concentrations were determined in the CSF of ALS patients and controls and the relationship of these chemokines with clinical severity and disease duration in ALS was determined. Seventy-seven ALS patients (mean age 49.5 ± 10.4 years) (mean body mass index 23.5 ± 4.5) were included. Twenty patients had bulbar, 53 spinal, and four bulbospinal onset ALS. Median adipsin CSF level was 12,650.94 pg/ml in ALS patients and 3290.98 pg/ml in controls (p < 0.001). Median adiponectin CSF level was 4608 pg/ml in ALS patients and 3453 pg/ml in controls (p = 0.1). No differences were observed in disease duration, progression rate or disease severity. There was a significant positive correlation between adipsin and adiponectin concentrations (r = 0.379, p = 0.01). No correlation with age, body mass index or ALFRS-R score was found. Adipsin was significantly elevated in CSF, suggesting that this chemokine might have a role in ALS pathogenesis. Adiponectin showed a trend towards higher concentrations, but failed to reach statistical significance. Due to the clinical heterogeneity in our cohort, these chemokines do not appear to be associated with disease duration or severity.

Multiple Sclerosis: Implications of Obesity in Neuroinflammation

Since the discovery of the remarkable properties of adipose tissue as a metabolically active organ, several evidences on the possible link between obesity and the pathogenesis of multiple sclerosis (MS) have been gathered. Obesity in early life, mainly during adolescence, has been proposed as a relevant risk factor for late MS development. Moreover, once MS is initiated, obesity can contribute to increase disease severity by negatively influencing disease progress. Despite the fact that clinical data are not yet conclusive, many biochemical links have been recently disclosed. The "low-grade inflammation" that characterizes obesity can lead to neuroinflammation through different mechanisms, including choroid plexus and blood-brain barrier disruption. Furthermore, it is well known that resident immune cells of central nervous system and peripheral immune cells are involved in the pathogenesis of MS, and adipokines and neuropeptides such as neuropeptide Y may mediate the cross talk between them.

Multiple Sclerosis and Obesity: Possible Roles of Adipokines

Multiple Sclerosis (MS) is an autoimmune disorder of the Central Nervous System that has been associated with several environmental factors, such as diet and obesity. The possible link between MS and obesity has become more interesting in recent years since the discovery of the remarkable properties of adipose tissue. Once MS is initiated, obesity can contribute to increased disease severity by negatively influencing disease progress and treatment response, but, also, obesity in early life is highly relevant as a susceptibility factor and causally related risk for late MS development. The aim of this review was to discuss recent evidence about the link between obesity, as a chronic inflammatory state, and the pathogenesis of MS as a chronic autoimmune and inflammatory disease. First, we describe the main cells involved in MS pathogenesis, both from neural tissue and from the immune system, and including a new participant, the adipocyte, focusing on their roles in MS. Second, we concentrate on the role of several adipokines that are able to participate in the mediation of the immune response in MS and on the possible cross talk between the latter. Finally, we explore recent therapy that involves the transplantation of adipocyte precursor cells for the treatment of MS.