Mid-life adiposity factors relate to blood-brain barrier integrity in late life

Metabolic syndrome and the phenotype of multiple sclerosis

BACKGROUND

Comorbidities, particularly vascular comorbidities, have been shown to exacerbate the progression of disability in multiple sclerosis (MS). Metabolic syndrome (MetS) is a cluster of conditions including abdominal obesity, insulin resistance, atherogenic dyslipidemia, and vascular dysfunction, which contribute to vascular morbidity and chronic inflammation.

OBJECTIVE

To describe the characteristics of MetS in a cohort of MS patients and evaluate its relationship with the MS phenotype.

METHODS

A monocentric cohort study was conducted on MS patients, collecting demographic, clinical, radiological, and therapeutic data, as well as metabolic data including waist circumference, blood pressure, serum triglycerides, high-density lipoprotein cholesterol, and fasting blood glucose.

RESULTS

Among the 84 patients included in the study, 27% were diagnosed with MetS. MetS was found to be associated with secondary progressive MS (SPMS). Patients with SPMS had a higher prevalence of MetS compared to those with relapsing-remitting MS (RRMS), even after adjusting for disease duration. While MetS was associated with Expanded Disability Status Scale (EDSS) progression in the 3-year period according to univariate analysis, it did not show a significant association with disease activity.

CONCLUSION

This study provides evidence supporting the connection between MetS and the progression of disability in MS, independent of disease relapse activity.

Association of changes in predicted body composition with subsequent risk of dementia

OBJECTIVE

The effect of body composition change on the risk of dementia is not clear. This study analyzed the associations of changes in predicted lean body mass index (pLBMI), predicted appendicular skeletal muscle mass index (pASMI), and predicted body fat mass index (pBFMI) with the risk of dementia.

METHODS

In this nationwide cohort study, data were obtained from the Korean National Health Insurance Service database. The exposure was defined as changes in pLBMI, pASMI, and pBFMI derived from validated prediction equations. The outcome was dementia, defined based on the dementia diagnosis with prescription of anti-dementia medication. Cox proportional hazards regression analyses were performed to obtain the hazard ratio with a 95% confidence interval for risk of dementia according to changes in predicted body composition.

RESULTS

A total of 13,215,208 individuals with no prior record of dementia who underwent health screenings twice between 2009-2010 and 2011-2012 were included. A 1-kg/m2 increase in pLBMI and pASMI had an association with reduced risk of dementia (aHR: 0.85, 95% CI 0.84-0.87; aHR: 0.70, 95% CI 0.69-0.72, respectively for men, and aHR: 0.69, 95% CI 0.67-0.71; aHR: 0.59, 95% CI 0.57-0.61, respectively for women). A 1-kg/m2 increase in pBFMI had an association with a raised risk of dementia (aHR: 1.19, 95% CI 1.17-1.21 for men and aHR: 1.53, 95% CI 1.48-1.57 for women). These results remained consistent regardless of sex or weight change.

INTERPRETATION

Increase in pLBMI or pASMI, or reduction in pBFMI was linked to lower risk of dementia.

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.

The influence of physiological and pathological perturbations on blood-brain barrier function

The blood-brain barrier (BBB) is located at the interface between the vascular system and the brain parenchyma, and is responsible for communication with systemic circulation and peripheral tissues. During life, the BBB can be subjected to a wide range of perturbations or stresses that may be endogenous or exogenous, pathological or therapeutic, or intended or unintended. The risk factors for many diseases of the brain are multifactorial and involve perturbations that may occur simultaneously (e.g., two-hit model for Alzheimer's disease) and result in different outcomes. Therefore, it is important to understand the influence of individual perturbations on BBB function in isolation. Here we review the effects of eight perturbations: mechanical forces, temperature, electromagnetic radiation, hypoxia, endogenous factors, exogenous factors, chemical factors, and pathogens. While some perturbations may result in acute or chronic BBB disruption, many are also exploited for diagnostic or therapeutic purposes. The resultant outcome on BBB function depends on the dose (or magnitude) and duration of the perturbation. Homeostasis may be restored by self-repair, for example, via processes such as proliferation of affected cells or angiogenesis to create new vasculature. Transient or sustained BBB dysfunction may result in acute or pathological symptoms, for example, microhemorrhages or hypoperfusion. In more extreme cases, perturbations may lead to cytotoxicity and cell death, for example, through exposure to cytotoxic plaques.

Obesity-mediated Lipoinflammation Modulates Food Reward Responses

Accumulation of white adipose tissue (WAT) during obesity is associated with the development of chronic low-grade inflammation, a biological process known as lipoinflammation. Systemic and central lipoinflammation accumulates pro-inflammatory cytokines including IL-6, IL-1β and TNF-α in plasma and also in brain, disrupting neurometabolism and cognitive behavior. Obesity-mediated lipoinflammation has been reported in brain regions of the mesocorticolimbic reward circuit leading to alterations in the perception and consumption of ultra-processed foods. While still under investigation, lipoinflammation targets two major outcomes of the mesocorticolimbic circuit during food reward: perception and motivation ("Wanting") and the pleasurable feeling of feeding ("Liking"). This review will provide experimental and clinical evidence supporting the contribution of obesity- or overnutrition-related lipoinflammation affecting the mesocorticolimbic reward circuit and enhancing food reward responses. We will also address neuroanatomical targets of inflammatory profiles that modulate food reward responses during obesity and describe potential cellular and molecular mechanisms of overnutrition linked to addiction-like behavior favored by brain lipoinflammation.

Palmitic Acid Modulates Microglial Cell Response to Metabolic Endotoxemia in an In Vitro Study

Metabolic endotoxemia (ME) is characterized by a 2-3-fold increase in blood endotoxin levels and low-grade systemic inflammation without apparent infection. ME is usually accompanied by metabolic syndrome, characterized by central obesity and hyperlipidemia. According to numerous studies, ME may lead to functional brain disorders, including cognitive decline, depression, and dementia. In the current in vitro study, we aimed to determine the direct and indirect impact of endotoxin (LPS) and palmitic acid (PA), representing saturated fatty acids, on the inflammatory and oxidative stress response in the human microglial HMC3 cells unstimulated and stimulated with IFNγ. The study's results revealed that direct HMC3 cell exposition to endotoxin and PA increased inflammatory response measured as levels of IL-6 and MCP-1 released into the medium and PGE2 levels in cell lysates. Moreover, direct HMC3 cell treatment with PA and LPS induced oxidative stress, i.e., ROS and COX-2 production and lipid peroxidation. On the contrary, an indirect effect of LPS and PA on microglial cells, assessed as the impact of macrophage metabolites, was much lower regarding the inflammatory response, although still associated with oxidative stress. Interestingly, IFNγ had a protective effect on microglial cells, reducing the production of pro-inflammatory mediators and oxidative stress in HMC3 cells treated directly and indirectly with LPS and PA.

Dynamic regulation of the extracellular matrix in reward memory processes: a question of time

Substance use disorders are a global health problem with increasing prevalence resulting in significant socioeconomic burden and increased mortality. Converging lines of evidence point to a critical role of brain extracellular matrix (ECM) molecules in the pathophysiology of substance use disorders. An increasing number of preclinical studies highlight the ECM as a promising target for development of novel cessation pharmacotherapies. The brain ECM is dynamically regulated during learning and memory processes, thus the time course of ECM alterations in substance use disorders is a critical factor that may impact interpretation of the current studies and development of pharmacological therapies. This review highlights the evidence for the involvement of ECM molecules in reward learning, including drug reward and natural reward such as food, as well as evidence regarding the pathophysiological state of the brain's ECM in substance use disorders and metabolic disorders. We focus on the information regarding time-course and substance specific changes in ECM molecules and how this information can be leveraged for the development of therapeutic strategies.

How does neurovascular unit dysfunction contribute to multiple sclerosis?

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system (CNS) and the most common non-traumatic cause of neurological disability in young adults. Multiple sclerosis clinical care has improved considerably due to the development of disease-modifying therapies that effectively modulate the peripheral immune response and reduce relapse frequency. However, current treatments do not prevent neurodegeneration and disease progression, and efforts to prevent multiple sclerosis will be hampered so long as the cause of this disease remains unknown. Risk factors for multiple sclerosis development or severity include vitamin D deficiency, cigarette smoking and youth obesity, which also impact vascular health. People with multiple sclerosis frequently experience blood-brain barrier breakdown, microbleeds, reduced cerebral blood flow and diminished neurovascular reactivity, and it is possible that these vascular pathologies are tied to multiple sclerosis development. The neurovascular unit is a cellular network that controls neuroinflammation, maintains blood-brain barrier integrity, and tightly regulates cerebral blood flow, matching energy supply to neuronal demand. The neurovascular unit is composed of vessel-associated cells such as endothelial cells, pericytes and astrocytes, however neuronal and other glial cell types also comprise the neurovascular niche. Recent single-cell transcriptomics data, indicate that neurovascular cells, particular cells of the microvasculature, are compromised within multiple sclerosis lesions. Large-scale genetic and small-scale cell biology studies also suggest that neurovascular dysfunction could be a primary pathology contributing to multiple sclerosis development. Herein we revisit multiple sclerosis risk factors and multiple sclerosis pathophysiology and highlight the known and potential roles of neurovascular unit dysfunction in multiple sclerosis development and disease progression. We also evaluate the suitability of the neurovascular unit as a potential target for future disease modifying therapies for multiple sclerosis.

Effect of Estimated Blood Volume and Body Mass Index on GFAP and NfL Levels in the Serum and CSF of Patients With Multiple Sclerosis

BACKGROUND AND OBJECTIVES

To increase the validity of biomarker measures in multiple sclerosis (MS), factors affecting their concentration need to be identified. Here, we test whether the volume of distribution approximated by the patients' estimated blood volume (BV) and body mass index (BMI) affect the serum concentrations of glial fibrillary acidic protein (GFAP). As a control, we also determine the relationship between BV/BMI and GFAP concentrations in CSF. To confirm earlier findings, we test the same hypotheses for neurofilament light chain (NfL).

METHODS

NfL and GFAP concentrations were measured in serum and CSF (sNFL/sGFAP and cNFL/cGFAP) in 157 patients (n = 106 with MS phenotype and n = 51 with other neurologic/somatoform diseases). Using multivariate linear regressions, BV was tested in the MS cohort as a predictor for each of the biomarkers while controlling for age, sex, MS phenotype, Expanded Disability Status Scale score, gadolinium-enhancing lesions, and acute relapse. In addition, overweight/obese patients (BMI ≥25 kg/m2) were compared with patients with BMI <25 kg/m2 using the general linear model. The analyses were repeated including the neurologic/somatoform controls.

RESULTS

In the MS cohort, BV predicted sGFAP (ß = -0.301, p = 0.014). Overweight/obese patients with MS had lower sGFAP concentrations compared with patients with MS and BMI <25 kg/m2 (F = 4.732, p = 0.032). Repeating the analysis after adding patients with other neurologic/somatoform diseases did not change these findings (ß = -0.276, p = 0.009; F = 7.631, p = 0.006). Although sNfL was inversely correlated with BV (r = -0.275, p = 0.006) and body weight (r = -0.258, p = 0.010), those results did not remain significant after adjusting for covariates. BV and BMI were not associated with cGFAP or cNfL concentrations.

DISCUSSION

These findings support the notion that the volume of distribution of sGFAP approximated by BV and BMI is a relevant variable and should therefore be controlled for when measuring sGFAP in MS, while this might not be necessary when measuring cGFAP concentrations.

Sex Differences in Cognition Across Aging

Sex and gender differences are seen in cognitive disturbances in a variety of neurological and psychiatry diseases. Men are more likely to have cognitive symptoms in schizophrenia whereas women are more likely to have more severe cognitive symptoms with major depressive disorder and Alzheimer's disease. Thus, it is important to understand sex and gender differences in underlying cognitive abilities with and without disease. Sex differences are noted in performance across various cognitive domains - with males typically outperforming females in spatial tasks and females typically outperforming males in verbal tasks. Furthermore, there are striking sex differences in brain networks that are activated during cognitive tasks and in learning strategies. Although rarely studied, there are also sex differences in the trajectory of cognitive aging. It is important to pay attention to these sex differences as they inform researchers of potential differences in resilience to age-related cognitive decline and underlying mechanisms for both healthy and pathological cognitive aging, depending on sex. We review literature on the progressive neurodegenerative disorder, Alzheimer's disease, as an example of pathological cognitive aging in which human females show greater lifetime risk, neuropathology, and cognitive impairment, compared to human males. Not surprisingly, the relationships between sex and cognition, cognitive aging, and Alzheimer's disease are nuanced and multifaceted. As such, this chapter will end with a discussion of lifestyle factors, like education and diet, as modifiable factors that can alter cognitive aging by sex. Understanding how cognition changes across age and contributing factors, like sex differences, will be essential to improving care for older adults.

Palmitic Acid and Oleic Acid Differently Modulate TLR2-Mediated Inflammatory Responses in Microglia and Macrophages

The relationship between systemic immunity and neuroinflammation is widely recognised. Infiltration of peripheral immune cells to the CNS during certain chronic inflammatory states contributes significantly to neuropathology. Obesity and its co-morbidities are primary risk factors for neuroinflammatory and neurodegenerative conditions, including Alzheimer’s disease (AD). Dietary fats are among the most proinflammatory components of the obesogenic diet and play a prominent role in the low-grade systemic inflammation associated with the obese state. Saturated fatty acid (SFA) is largely implicated in the negative consequences of obesity, while the health benefits of monounsaturated fatty acid (MUFA) are widely acknowledged. The current study sought to explore whether SFA and MUFA differently modulate inflammatory responses in the brain, compared with peripheral immune cells. Moreover, we assessed the neuroinflammatory impact of high-fat-induced obesity and hypothesised that a MUFA-rich diet might mitigate inflammation despite obesogenic conditions. Toll-like receptor (TLR)2 mediates the inflammation associated with both obesity and AD. Using the TLR2 agonist lipoteichoic acid (LTA), we report that pre-exposure to either palmitic acid (PA) or oleic acid (OA) attenuated cytokine secretion from microglia, but heightened sensitivity to nitric oxide (NO) production. The reduction in cytokine secretion was mirrored in LTA-stimulated macrophages following exposure to PA only, while effects on NO were restricted to OA, highlighting important cell-specific differences. An obesogenic diet over 12 weeks did not induce prominent inflammatory changes in either cortex or hippocampus, irrespective of fat composition. However, we reveal a clear disparity in the effects of MUFA under obesogenic and non-obesogenic conditions.

Genetic Regulatory Networks of Apolipoproteins and Associated Medical Risks

Apolipoproteins (APO proteins) are the lipoprotein family proteins that play key roles in transporting lipoproteins all over the body. There are nearly more than twenty members reported in the APO protein family, among which the A, B, C, E, and L play major roles in contributing genetic risks to several disorders. Among these genetic risks, the single nucleotide polymorphisms (SNPs), involving the variation of single nucleotide base pairs, and their contributing polymorphisms play crucial roles in the apolipoprotein family and its concordant disease heterogeneity that have predominantly recurred through the years. In this review, we have contributed a handful of information on such genetic polymorphisms that include APOE, ApoA1/B ratio, and A1/C3/A4/A5 gene cluster-based population genetic studies carried throughout the world, to elaborately discuss the effects of various genetic polymorphisms in imparting various medical conditions, such as obesity, cardiovascular, stroke, Alzheimer's disease, diabetes, vascular complications, and other associated risks.

Visceral adiposity, inflammation, and hippocampal function in obesity

The 'apple-shaped' anatomical pattern that accompanies visceral adiposity increases risk for multiple chronic diseases, including conditions that impact the brain, such as diabetes and hypertension. However, distinguishing between the consequences of visceral obesity, as opposed to visceral adiposity-associated metabolic and cardiovascular pathologies, presents certain challenges. This review summarizes current literature on relationships between adipose tissue distribution and cognition in preclinical models and highlights unanswered questions surrounding the potential role of tissue- and cell type-specific insulin resistance in these effects. While gaps in knowledge persist related to insulin insensitivity and cognitive impairment in obesity, several recent studies suggest that cells of the neurovascular unit contribute to hippocampal synaptic dysfunction, and this review interprets those findings in the context of progressive metabolic dysfunction in the CNS. Signalling between cerebrovascular endothelial cells, astrocytes, microglia, and neurons has been linked with memory deficits in visceral obesity, and this article describes the cellular changes in each of these populations with respect to their role in amplification or diminution of peripheral signals. The picture emerging from these studies, while incomplete, implicates pro-inflammatory cytokines, insulin resistance, and hyperglycemia in various stages of obesity-induced hippocampal dysfunction. As in the parable of the five blind wanderers holding different parts of an elephant, considerable work remains in order to assemble a model for the underlying mechanisms linking visceral adiposity with age-related cognitive decline.

Infection and Immunometabolism in the Central Nervous System: A Possible Mechanistic Link Between Metabolic Imbalance and Dementia

Metabolic syndromes are frequently associated with dementia, suggesting that the dysregulation of energy metabolism can increase the risk of neurodegeneration and cognitive impairment. In addition, growing evidence suggests the link between infections and brain disorders, including Alzheimer's disease. The immune system and energy metabolism are in an intricate relationship. Infection triggers immune responses, which are accompanied by imbalance in cellular and organismal energy metabolism, while metabolic disorders can lead to immune dysregulation and higher infection susceptibility. In the brain, the activities of brain-resident immune cells, including microglia, are associated with their metabolic signatures, which may be affected by central nervous system (CNS) infection. Conversely, metabolic dysregulation can compromise innate immunity in the brain, leading to enhanced CNS infection susceptibility. Thus, infection and metabolic imbalance can be intertwined to each other in the etiology of brain disorders, including dementia. Insulin and leptin play pivotal roles in the regulation of immunometabolism in the CNS and periphery, and dysfunction of these signaling pathways are associated with cognitive impairment. Meanwhile, infectious complications are often comorbid with diabetes and obesity, which are characterized by insulin resistance and leptin signaling deficiency. Examples include human immunodeficiency virus (HIV) infection and periodontal disease caused by an oral pathogen Porphyromonas gingivalis. This review explores potential interactions between infectious agents and insulin and leptin signaling pathways, and discuss possible mechanisms underlying the relationship between infection, metabolic dysregulation, and brain disorders, particularly focusing on the roles of insulin and leptin.

Screening for mild cognitive impairment in people with obesity: a systematic review

OBJECTIVE

Recent evidence demonstrates that obesity is associated with developing cognitive impairment. However, evidence related to the assessment of mild cognitive impairment (MCI) in people with obesity is limited. Therefore, this systematic review aimed to examine evidence concerning the screening of MCI in people with obesity from the general population.

METHOD

We conducted a systematic search of CINHAL, EMBASE, MEDLINE, PsycINFO and PubMed electronic databases for observational studies to assess MCI in people with obesity from the general population. PRISMA guideline was followed. The articles published from January 2011 to July 2021 were included.

RESULTS

Database search found 3104 sources. After the screening process, two articles from China and Egypt were included. The main age groups assessed were middle-aged adulthood and older adulthood. There were no studies undertaken in young adults or across the life span. Obesity was assessed by body mass index. MCI was assessed by cognitive screening tools; Mini-mental State Examination and Addenbrooke's Cognitive Examination. The prevalence of MCI in people with obesity was 18.5 % and 42.9 % in Chinese and Egyptian studies, respectively. Only one study supported a positive association between MCI and obesity.

CONCLUSIONS

Limited studies were found on screening MCI in people with obesity in the general population. The available evidence was not adequate to explain the overall prevalence, possible associations, and the best tool for assessing MCI in people with obesity. Expanding screening studies for MCI in people with obesity in the general population is essential.

Nutrition, Physical Activity, and Other Lifestyle Factors in the Prevention of Cognitive Decline and Dementia

Multiple factors combined are currently recognized as contributors to cognitive decline. The main independent risk factor for cognitive impairment and dementia is advanced age followed by other determinants such as genetic, socioeconomic, and environmental factors, including nutrition and physical activity. In the next decades, a rise in dementia cases is expected due largely to the aging of the world population. There are no hitherto effective pharmaceutical therapies to treat age-associated cognitive impairment and dementia, which underscores the crucial role of prevention. A relationship among diet, physical activity, and other lifestyle factors with cognitive function has been intensively studied with mounting evidence supporting the role of these determinants in the development of cognitive decline and dementia, which is a chief cause of disability globally. Several dietary patterns, foods, and nutrients have been investigated in this regard, with some encouraging and other disappointing results. This review presents the current evidence for the effects of dietary patterns, dietary components, some supplements, physical activity, sleep patterns, and social engagement on the prevention or delay of the onset of age-related cognitive decline and dementia.

The Blood-Brain Barrier: Much More Than a Selective Access to the Brain

The blood-brain barrier is a dynamic structure, collectively referred to as the neurovascular unit. It is responsible for the exchange of blood, oxygen, ions, and other molecules between the peripheral circulation and the brain compartment. It is the main entrance to the central nervous system and as such critical for the maintenance of its homeostasis. Dysfunction of the blood-brain barrier is a characteristic of several neurovascular pathologies. Moreover, physiological changes, environmental factors, nutritional habits, and psychological stress can modulate the tightness of the barrier. In this contribution, we summarize our current understanding of structure and function of this important component of the brain. We also describe the neurological deficits associated with its damage. A special emphasis is placed in the effect of the exposure to xenobiotics and pollutants in the permeability of the barrier. Finally, current protective strategies as well as the culture models to study this fascinating structure are discussed.

Inflammatory Cascade in Alzheimer's Disease Pathogenesis: A Review of Experimental Findings

Alzheimer’s disease (AD) is the leading cause of dementia worldwide. Most AD patients develop the disease in late life, named late onset AD (LOAD). Currently, the most recognized explanation for AD pathology is the amyloid cascade hypothesis. It is assumed that amyloid beta (Aβ) aggregation and deposition are critical pathogenic processes in AD, leading to the formation of amyloid plaques, as well as neurofibrillary tangles, neuronal cell death, synaptic degeneration, and dementia. In LOAD, the causes of Aβ accumulation and neuronal loss are not completely clear. Importantly, the blood–brain barrier (BBB) disruption seems to present an essential role in the induction of neuroinflammation and consequent AD development. In addition, we propose that the systemic inflammation triggered by conditions like metabolic diseases or infections are causative factors of BBB disruption, coexistent inflammatory cascade and, ultimately, the neurodegeneration observed in AD. In this regard, the use of anti-inflammatory molecules could be an interesting strategy to treat, delay or even halt AD onset and progression. Herein, we review the inflammatory cascade and underlying mechanisms involved in AD pathogenesis and revise the anti-inflammatory effects of compounds as emerging therapeutic drugs against AD.

From Metabolic Syndrome to Neurological Diseases: Role of Autophagy

Metabolic syndrome is not a single pathology, but a constellation of cardiovascular disease risk factors including: central and abdominal obesity, systemic hypertension, insulin resistance (or type 2 diabetes mellitus), and atherogenic dyslipidemia. The global incidence of Metabolic syndrome is estimated to be about one quarter of the world population; for this reason, it would be desirable to better understand the underlying mechanisms involved in order to develop treatments that can reduce or eliminate the damage caused. The effects of Metabolic syndrome are multiple and wide ranging; some of which have an impact on the central nervous system and cause neurological and neurodegenerative diseases. Autophagy is a catabolic intracellular process, essential for the recycling of cytoplasmic materials and for the degradation of damaged cellular organelle. Therefore, autophagy is primarily a cytoprotective mechanism; even if excessive cellular degradation can be detrimental. To date, it is known that systemic autophagic insufficiency is able to cause metabolic balance deterioration and facilitate the onset of metabolic syndrome. This review aims to highlight the current state of knowledge regarding the connection between metabolic syndrome and the onset of several neurological diseases related to it. Furthermore, since autophagy has been found to be of particular importance in metabolic disorders, the probable involvement of this degradative process is assumed to be responsible for the attenuation of neurological disorders resulting from metabolic syndrome.

Sex differences in the blood-brain barrier and neurodegenerative diseases

The number of people diagnosed with neurodegenerative diseases is on the rise. Many of these diseases, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and motor neuron disease, demonstrate clear sexual dimorphisms. While sex as a biological variable must now be included in animal studies, sex is rarely included in in vitro models of human neurodegenerative disease. In this Review, we describe these sex-related differences in neurodegenerative diseases and the blood-brain barrier (BBB), whose dysfunction is linked to neurodegenerative disease development and progression. We explain potential mechanisms by which sex and sex hormones affect BBB integrity. Finally, we summarize current in vitro BBB bioengineered models and highlight their potential to study sex differences in BBB integrity and neurodegenerative disease.

Obesity-induced cognitive impairment in older adults: a microvascular perspective

Over two-thirds of individuals aged 65 and older are obese or overweight in the United States. Epidemiological data show an association between the degree of adiposity and cognitive dysfunction in the elderly. In this review, the pathophysiological roles of microvascular mechanisms, including impaired endothelial function and neurovascular coupling responses, microvascular rarefaction, and blood-brain barrier disruption in the genesis of cognitive impairment in geriatric obesity are considered. The potential contribution of adipose-derived factors and fundamental cellular and molecular mechanisms of senescence to exacerbated obesity-induced cerebromicrovascular impairment and cognitive decline in aging are discussed.

Animal Models of Metabolic Disorders in the Study of Neurodegenerative Diseases: An Overview

The incidence of metabolic disorders, as well as of neurodegenerative diseases—mainly the sporadic forms of Alzheimer’s and Parkinson’s disease—are increasing worldwide. Notably, obesity, diabetes, and hypercholesterolemia have been indicated as early risk factors for sporadic forms of Alzheimer’s and Parkinson’s disease. These conditions share a range of molecular and cellular features, including protein aggregation, oxidative stress, neuroinflammation, and blood-brain barrier dysfunction, all of which contribute to neuronal death and cognitive impairment. Rodent models of obesity, diabetes, and hypercholesterolemia exhibit all the hallmarks of these degenerative diseases, and represent an interesting approach to the study of the phenotypic features and pathogenic mechanisms of neurodegenerative disorders. We review the main pathological aspects of Alzheimer’s and Parkinson’s disease as summarized in rodent models of obesity, diabetes, and hypercholesterolemia.

Blood-Brain Barrier Dynamics to Maintain Brain Homeostasis

The blood-brain barrier (BBB) is a dynamic platform for exchange of substances between the blood and the brain parenchyma, and it is an essential functional gatekeeper for the central nervous system (CNS). While it is widely recognized that BBB disruption is a hallmark of several neurovascular pathologies, an aspect of the BBB that has received somewhat less attention is the dynamic modulation of BBB tightness to maintain brain homeostasis in response to extrinsic environmental factors and physiological changes. In this review, we summarize how BBB integrity adjusts in critical stages along the life span, as well as how BBB permeability can be altered by common stressors derived from nutritional habits, environmental factors and psychological stress.

Increase in blood-brain barrier leakage in healthy, older adults

Blood-brain barrier (BBB) breakdown can disrupt nutrient supply and waste removal, which affects neuronal functioning. Currently, dynamic contrast-enhanced (DCE) MRI is the preferred in-vivo method to quantify BBB leakage. Dedicated DCE MRI studies in normal aging individuals are lacking, which could hamper value estimation and interpretation of leakage rate in pathological conditions. Therefore, we applied DCE MRI to investigate the association between BBB disruption and age in a healthy sample. Fifty-seven cognitively and neurologically healthy, middle-aged to older participants (mean age: 66 years, range: 47-91 years) underwent MRI, including DCE MRI with intravenous injection of a gadolinium-based contrast agent. Pharmacokinetic modeling was applied to contrast concentration time-curves to estimate BBB leakage rate in each voxel. Subsequently, leakage rate was calculated in the white and gray matter, and primary (basic sensory and motor functions), secondary (association areas), and tertiary (higher-order cognition) brain regions. A difference in vulnerability to deterioration was expected between these regions, with especially tertiary regions being affected by age. Higher BBB leakage rate was significantly associated with older age in the white and gray matter, and also in tertiary, but not in primary or secondary brain regions. Even in healthy individuals, BBB disruption was stronger in older persons, which suggests BBB disruption is a normal physiologically aging phenomenon. Age-related increase in BBB disruption occurred especially in brain regions most vulnerable to age-related deterioration, which may indicate that BBB disruption is an underlying mechanism of normal age-related decline.Netherlands Trial Register number: NL6358, date of registration: 2017-03-24.

Association of HIV serostatus and metabolic syndrome with neurobehavioral disturbances

Metabolic syndrome (MetS), a constellation of related metabolic risk factors, is a common comorbidity associated with cognitive difficulty in people living with HIV (PLWH). Neurobehavioral disturbances (e.g., behavioral manifestations of frontal-subcortical dysfunction) are also prevalent in HIV, yet the role MetS might play in HIV-associated neurobehavioral disturbances is unknown. Thus, we examined the link between MetS and neurobehavioral disturbances in PLWH. Participants included 215 adults (117 PLWH, 98 HIV-uninfected), aged 36 to 65 years, from a cohort study at the University of California San Diego. Using the Frontal Systems Behavior Scale, we captured neurobehavioral disturbances (apathy, disinhibition, and executive dysfunction). MetS was defined by the National Cholesterol Education Program's Adult Treatment Panel-III criteria. Covariates examined included demographic, neurocognitive impairment, and psychiatric characteristics. When controlling for relevant covariates, both HIV serostatus and MetS were independently associated with greater apathy and executive dysfunction. HIV, but not MetS, was associated with greater disinhibition. The present findings suggest an additive effect of HIV and MetS on specific neurobehavioral disturbances (apathy and executive dysfunction), underscoring the importance of identifying and treating both HIV and MetS to lessen central nervous system burden among PLWH.

Body mass index associated with childhood and adolescent high-risk B-cell acute lymphoblastic leukemia risk: A Children's Oncology Group report

BACKGROUND

Obesity is a risk factor for many adulthood cancers, but its role in childhood, adolescent, and young adult (AYA) cancer is unknown. Childhood and AYA acute lymphoblastic leukemia (ALL) incidence and obesity prevalence have shown concurrent increases. We sought to identify whether obesity may be a risk factor for childhood and AYA ALL.

METHODS

Characteristics from individuals with ALL, aged 2-30 years, diagnosed 2004-2017 and treated on Children's Oncology Group (COG) protocols with available pre-treatment anthropometric data (N = 4726) were compared to National Health and Nutrition Examination Survey controls (COG AALL17D2). Body mass index (BMI) was defined using standard CDC definitions. Multivariate conditional logistic regression assessed associations between BMI and ALL with additional analyses stratified by sex and race/ethnicity.

RESULTS

Among cases (72% high-risk (HR) B-ALL, 28% T-ALL), 5% had underweight, 58% normal weight, 17% overweight, and 20% obesity. Underweight (OR 2.11, 95% CI 1.56-2.85) and obesity (OR 1.32, 95% CI 1.15-1.53) were associated with B-ALL diagnosis. Specifically, obesity was associated with B-ALL among males (OR 1.57, 95% CI 1.30-1.91) and Hispanic children (OR 1.78, 95% CI 1.39-2.29). Obesity was also associated with central nervous system (CNS) involvement.

CONCLUSION

Pre-treatment obesity is associated with HR B-ALL among males and Hispanics, as well as with CNS involvement, suggesting common physiology between obesity and leukemogenesis. An association between underweight and ALL was confirmed, likely due to cancer-associated wasting. These results have important public health implications for obesity prevention and treatment in children and adolescents to reduce cancer risk.

Dietary Patterns and Cognitive Decline: key features for prevention

The decline in cognitive function is generally the result of the complex interaction of several factors. First of all, age, but also demographic, educational, genetic, socio-economic, and environmental determinants, including nutrition. Cognitive decline and dementia prevalence are increasing, and they are projected to continue increasing in the next decades due to the aging of the world population. Currently, there are no effective pharmacological treatments for these devastating and disabling conditions, which emphasize the key role of preventive strategies. There is compelling evidence of the role of diet and lifestyle on cognitive function. Therefore, dietary/ nutritional approaches that contribute to prevent, or slow cognitive decline may have a remarkable public health impact. Numerous studies have explored the role of dietary components and patterns on age-associated cognitive decline, with accruing evidence that combinations of foods and nutrients can have synergistic effects beyond those attributable to individual foods or nutrients. Dietary patterns show the strongest evidence for slowing the development of cognitive decline, Alzheimer's disease and other dementias including the Mediterranean diet, the Dietary Approaches to Stop Hypertension diet, and their combination (the MedDiet-DASH Intervention for Neurodegenerative Delay - MIND), among others with few positive results. There are also dietary patterns with no evidence of such effects. This review examines the evidence for the effects of some dietary patterns as neuroprotective with a potential to delay cognitive decline and the onset of dementia.

A Preliminary Investigation of the Effects of a Western Diet on Hippocampal Volume in Children

Introduction: Over the course of the 20th century, there has been a sharp increase in the consumption of saturated fat and refined sugars. This so-called "western diet" (WD) has been extensively linked to biological alterations and associated functional deficits in the hippocampus of animals. However, the effects of a WD on the human hippocampus are less well-characterized. This preliminary study aimed to extend prior animal work by investigating the effects of a WD on hippocampal volume in children. Methods: Twenty-one healthy children (ages 5-9) completed a structural T1-weighted magnetic resonance imaging scan. Bilateral hippocampal volumes (as regions-of-interest) and bilateral amygdala volumes (as medial temporal lobe control regions-of-interest) were calculated. WD variables were derived from the parent-completed Youth/Adolescent Food Frequency Questionnaire. Specifically, variables were calculated as percent of daily calories consumed from sugars, fats, or a combination of these (WD). Results: While the relationships between overall WD consumption and bilateral hippocampal volumes were not significant, increased fat consumption was significantly related to decreased left hippocampal volume. Sugar consumption was not related to hippocampal size. Control region volumes were not related to any diet variables. Discussion: This study is the first to directly link diet-specifically fat consumption-to decreased left hippocampal volume in children. This extends previous work showing smaller left hippocampal volume related to obesity in pediatric samples. Though preliminary, findings represent an important step toward understanding the impact of diet on child brain development.

Aging-related changes in fluid intelligence, muscle and adipose mass, and sex-specific immunologic mediation: A longitudinal UK Biobank study

BACKGROUND

Obesity in midlife and early late-life is associated with worse normal cognitive aging. Dual-energy X-ray absorptiometry (DEXA) suggests that visceral adipose mass (VAM) plays a predominant role, whereas non-visceral adipose mass (NVAM) and lean muscle mass (LMM) have shown conflicting relationships. It is unknown how longitudinal, cognitive changes in age-sensitive domains like fluid intelligence (FI) correspond to VAM, NVAM, and LMM in women and men. Furthermore, changes over time in blood leukocyte sub-populations may partially or fully account for sex-specific associations.

METHODS

Data on 4431 late middle-aged, cognitively unimpaired adults (mean = 64.5 y) was obtained from the UK Biobank prospective cohort across 22 centers. FI scores, blood leukocyte counts, and covariates (age, social class, education) were measured at three 2-year intervals over 6 years. DEXA collection overlapped with these intervals. Sex-stratified growth curves, structural equations, and Preacher-Hayes mediation were used to estimate direct and indirect effects. β-weights were standardized.

RESULTS

More LMM predicted gains in FI scores among women (β = 0.130, p < .001) and men (β = 0.089, p < .001). Conversely, more VAM and NVAM independently predicted FI decline equally among sexes (e.g., NVAM: women: β = -0.082, p < .001; men: β = -0.076, p < .001). Among women, FI associations were fully mediated by higher eosinophil counts via VAM (λ = 30.8%, p = .028) and lower lymphocyte counts via LMM (λ = 69.2%, p = .021). Among men, FI associations were partially mediated by lower basophils counts via LMM (λ = 4.5%, p = .042) and higher counts via VAM (λ = 50%, p = .037).

CONCLUSION

The proportion of LMM and VAM equally influenced male FI changes over 6 years, whereas higher LMM among women appeared to more strongly influence. FI changes. Leukocyte counts strongly mediated VAM- and LMM-related FI changes in a sex-specific manner, but not for NVAM. For clinical translation, exercise studies in older adults may benefit from assessing sex-specific values of DEXA-based tissue mass, FI, and leukocyte sub-populations to gauge potential cognitive benefits of less VAM and more LMM.

Metabolic Disturbances of a High-Fat Diet Are Dependent on APOE Genotype and Sex

Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for Alzheimer's disease (AD). APOE4 is also associated with an increased risk of metabolic syndrome. Obesity is a major environmental risk factor for AD. While APOE genotype and obesity independently affect metabolism and cognition, they may also have synergistic effects. Here, we examined the metabolic and behavioral alterations associated with a high-fat diet (HFD) in male and female APOE knock-in mice. Male and female mice were fed a 45% kcal HFD or a 10% kcal low-fat diet (LFD) for 12 weeks and adipose tissue accumulation, glucose levels, anxiety-like behavior, and spatial memory were examined. We found that with HFD, male APOE4 mice were more susceptible to metabolic disturbances, including visceral adipose tissue (VAT) accumulation and glucose intolerance when compared to APOE3 mice, while female APOE3 and APOE4 mice had similar metabolic responses. Behaviorally, there were no effects of HFD in mice of either genotype. Our results suggest that metabolic responses to HFD are dependent on both sex and APOE genotype.

Pathogenetic pathways of cognitive dysfunction and dementia in metabolic syndrome

The prevalence of dementia worldwide is growing at an alarming rate. A number of studies and meta-analyses have provided evidence for increased risk of dementia in patients with metabolic syndrome (MS) as compared to persons without MS. However, there are some reports demonstrating a lack of association between MS and increased dementia risk. In this review, taking into account the potential role of individual MS components in the pathogenesis of MS-related cognitive dysfunction, we considered the underlying mechanisms in arterial hypertension, diabetes mellitus, dyslipidemia, and obesity. The pathogenesis of dementia in MS is multifactorial, involving both vascular injury and non-ischemic neuronal death due to neurodegeneration. Neurodegenerative and ischemic lesions do not simply coexist in the brain due to independent evolution, but rather exacerbate each other, leading to more severe consequences for cognition than would either pathology alone. In addition to universal mechanisms of cognitive dysfunction shared by all MS components, other pathogenetic pathways leading to cognitive deficits and dementia, which are specific for each component, also play a role. Examples of such component-specific pathogenetic pathways include central insulin resistance and hypoglycemia in diabetes, neuroinflammation and adipokine imbalance in obesity, as well as arteriolosclerosis and lipohyalinosis in arterial hypertension. A more detailed understanding of cognitive disorders based on the recognition of underlying molecular mechanisms will aid in the development of new methods for prevention and treatment of devastating cognitive problems in MS.

Pre- and Post-natal High Fat Feeding Differentially Affects the Structure and Integrity of the Neurovascular Unit of 16-Month Old Male and Female Mice

Compelling experimental and clinical evidence supports a role for maternal obesity in offspring health. Adult children of obese mothers are at greater risk of obesity, diabetes, coronary heart disease and stroke. These offspring may also be at greater risk of age-related neurodegenerative diseases for which mid-life obesity is a risk factor. Rodent diet-induced obesity models have shown that high fat (HF) diet consumption damages the integrity of the blood–brain barrier (BBB) in the adult brain. However, there is currently little information about the effect of chronic HF feeding on the BBB of aged animals. Moreover, the long-term consequences of maternal obesity on the cerebrovasculature of aged offspring are not known. This study determined the impact of pre- and post-natal HF diet on the structure and integrity of cerebral blood vessels in aged male and female mice. Female C57Bl/6 mice were fed either a 10% fat control (C) or 45% HF diet before mating and during gestation and lactation. At weaning, male and female offspring were fed the C or HF diet until sacrifice at 16-months of age. Both dams and offspring fed the HF diet weighed significantly more than mice fed the C diet. Post-natal HF diet exposure increased hippocampal BBB leakiness in female offspring, in association with loss of astrocyte endfoot coverage of arteries. Markers of tight junctions, pericytes or smooth muscle cells were not altered by pre- or post-natal HF diet. Male offspring born to HF-fed mothers showed decreased parenchymal GFAP expression compared to offspring of mothers fed C diet, while microglial and macrophage markers were higher in the same female diet group. In addition, female offspring exposed to the HF diet for their entire lifespan showed more significant changes in vessel structure, BBB permeability and inflammation compared to male animals. These results suggest that the long-term impact of prenatal HF diet on the integrity of cerebral blood vessels differs between male and female offspring depending on the post-natal diet. This may have implications for the prevention and management of age- and obesity-related cerebrovascular diseases that differentially affect men and women.

Diet and Alzheimer's dementia - Nutritional approach to modulate inflammation

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease causing dementia in the elderly population. Due to the fact that there is still no cure for Alzheimer's dementia and available treatment strategies bring only symptomatic benefits, there is a pressing demand for other effective strategies such as diet. Since the inflammation hypothesis gained considerable significance in the AD pathogenesis, elucidating the modulatory role of dietary factors on inflammation may help to prevent, delay the onset and slow the progression of AD. Current evidence clearly shows that synergistic action of combined supplementation and complex dietary patterns provides stronger benefits than any single component considered separately. Recent studies reveal the growing importance of novel factors such as dietary advanced glycation end products (d-AGE), gut microbiota, butyrate and vitamin D₃ on inflammatory processes in AD.

CONCLUSION

This paper summarizes the available evidence of pro- and anti-inflammatory activity of some dietary components including fatty acids, vitamins, flavonoids, polyphenols, probiotics and d-AGE, and their potential for AD prevention and treatment.

The Complex Interactions Between Obesity, Metabolism and the Brain

Obesity is increasing at unprecedented levels globally, and the overall impact of obesity on the various organ systems of the body is only beginning to be fully appreciated. Because of the myriad of direct and indirect effects of obesity causing dysfunction of multiple tissues and organs, it is likely that there will be heterogeneity in the presentation of obesity effects in any given population. Taken together, these realities make it increasingly difficult to understand the complex interplay between obesity effects on different organs, including the brain. The focus of this review is to provide a comprehensive view of metabolic disturbances present in obesity, their direct and indirect effects on the different organ systems of the body, and to discuss the interaction of these effects in the context of brain aging and the development of neurodegenerative diseases.

Sex differences in Alzheimer's disease: Understanding the molecular impact

Alzheimer's disease (AD) is a common neurodegenerative disorder that presents with cognitive impairment and behavioral disturbance. Approximately 5.5 million people in the United States live with AD, most of whom are over the age of 65 with two-thirds being woman. There have been major advancements over the last decade or so in the understanding of AD neuropathological changes and genetic involvement. However, studies of sex impact in AD have not been adequately integrated into the investigation of disease development and progression. It becomes indispensable to acknowledge in both basic science and clinical research studies the importance of understanding sex-specific differences in AD pathophysiology and pathogenesis, which could guide future effort in the discovery of novel targets for AD. Here, we review the latest and most relevant literature on this topic, highlighting the importance of understanding sex dimorphism from a molecular perspective and its association to clinical trial design and development in AD research field.

Metabolic Syndrome and Neurocognitive Deficits in HIV Infection

BACKGROUND

The adverse consequences of HIV and related comorbidities on the central nervous system remain prevalent in the era of combination antiretroviral therapy. Metabolic syndrome (MetS) is a common comorbidity in HIV and has been linked to increased neurocognitive impairment in the general population. We investigated the association between MetS and neurocognition among persons living with HIV (PLHIV).

METHODS

Participants included 109 PLHIV and 92 HIV-uninfected adults (HIV-) from the Multi-dimensional Successful Aging cohort study at the University of California San Diego (age: M = 50.8, SD = 8.0). Participants completed neuromedical, psychiatric, and neurocognitive assessments. Based on a comprehensive neurocognitive battery, we examined global neurocognitive deficits (based on the entire battery) and neurocognitive deficits in 7 domains (verbal fluency, learning, recall, executive function, working memory, speed of information processing, and fine motor skills). MetS was determined via the standard criteria by the National Cholesterol Education Program's Adult Treatment Panel-III. Covariates examined included demographics and psychiatric comorbidities (and HIV disease characteristics among PLHIV).

RESULTS

MetS had an independent significant effect on global neurocognitive deficits among PLHIV (P = 0.03) but not among their HIV- counterparts (P = 0.93). Among PLHIV, MetS was most strongly associated with the neurocognitive domains of learning, fine motor skills, and executive function. Diabetes and elevated triglycerides were the MetS components most strongly linked with increased global neurocognitive deficits in PLHIV.

CONCLUSIONS

The present findings underscore the need for early identification of PLHIV at risk for MetS and the implementation of preventive and treatment approaches to lessen the development of MetS and neurocognitive impairment among PLHIV.

Endothelial Adora2a Activation Promotes Blood-Brain Barrier Breakdown and Cognitive Impairment in Mice with Diet-Induced Insulin Resistance

Obesity and insulin resistance elicit blood-brain barrier (BBB) breakdown in humans and animal models, but the relative contributions of the two pathologies remain poorly understood. These studies initially addressed the temporal progression of cerebrovascular dysfunction relative to dietary obesity or diet-induced insulin resistance in male mice. Obesity increased BBB permeability to the low molecular weight fluorophore sodium fluorescein (NaFl), whereas diet-induced insulin resistance increased permeability to both NaFl and Evans blue, which forms a high molecular weight complex with serum albumin. Serial section transmission electron microscopy analysis of hippocampal capillaries revealed that diabetes promotes involution of tight junctions, fenestration of endothelial cells, and pericyte regression. Chronic activation of adenosine receptor 2a (Adora2a) erodes tight junctions between endothelial cells of the cerebral vasculature in other models of chronic neuropathology, and we observed that acute Adora2a antagonism normalized BBB permeability in wild-type mice with diet-induced insulin resistance. Experiments in mice with inducible deletion of Adora2a in endothelial cells revealed protection against BBB breakdown with diet-induced insulin resistance, despite comparable metabolic dysfunction relative to nontransgenic littermates. Protection against BBB breakdown was associated with decreased vascular inflammation, recovery of hippocampal synaptic plasticity, and restoration of hippocampus-dependent memory. These findings indicate that Adora2a-mediated signaling in vascular endothelial cells disrupts the BBB in dietary obesity, and implicate cerebrovascular dysfunction as the underlying mechanism for deficits in synaptic plasticity and cognition with obesity and insulin resistance.SIGNIFICANCE STATEMENT The blood-brain barrier (BBB) restricts the entry of circulating factors into the brain, but obesity promotes BBB breakdown in humans and animal models. We used transgenic mice with resistance to BBB breakdown to investigate the role of neurovascular dysfunction in high-fat diet (HFD)-induced cognitive impairment. Transgenic mice with inducible ablation of Adora2a in endothelial cells were protected against BBB breakdown on HFD, despite comparable metabolic impairments relative to normal mice. Transgenic mice were also resistant to HFD-induced cognitive dysfunction and were protected against deficits in hippocampal synaptic plasticity. These findings indicate that Adora2a-mediated signaling in endothelial cells mediates obesity-induced BBB breakdown, and implicate cerebrovascular dysfunction as the mechanism for deficits in synaptic plasticity and cognition with obesity and diabetes.

Central and Peripheral Inflammation Link Metabolic Syndrome and Major Depressive Disorder

Metabolic syndrome and major depression are two of the most common and debilitating disorders worldwide, occurring with significant rates of comorbidity. Recent studies have uncovered that each of these conditions is associated with chronic, low-grade inflammation. This is characterized by increased circulating pro-inflammatory cytokines, altered leukocyte population frequencies in blood, accumulation of immune cells in tissues including the brain, and activation of these immune cells. Cytokines that become elevated during obesity can contribute to the progression of metabolic syndrome by directly causing insulin resistance. During chronic stress, there is evidence that these cytokines promote depression-like behavior by disrupting neurotransmitter synthesis and signal transduction. Animal models of obesity and depression have revealed a bi-directional relationship whereby high-fat feeding and chronic stress synergize and exacerbate metabolic dysregulation and behavioral abnormalities. Although far from conclusive, emerging evidence suggests that inflammation in the central and peripheral immune system may link metabolic syndrome to major depressive disorder. In this review, we will synthesize available data supporting this view and identify critical areas for future investigation.

Associations between atherosclerosis and neurological diseases, beyond ischemia-induced cerebral damage

Neurodegeneration is traditionally viewed as a consequence of peptide accumulation in the brain, stroke and/or cerebral ischemia. Nonetheless, a number of scattered observations suggest that neurological disease and atherosclerosis may be linked by more complex mechanisms. Understanding the intricate link between atherosclerosis and neurological conditions may have a significant impact on the quality of life of the growing ageing population and of high cardiovascular risk groups in general. Epidemiological data support the notion that neurological dysfunction and atherosclerosis coexist long before any evident clinical complications of cardiovascular disease appear and may be causally linked. Baffling, often overlooked, molecular data suggest that nervous tissue-specific gene expression is relaxed specifically in the atheromatous vascular wall, and/or that a systemic dysregulation of genes involved in nervous system biology dictates a concomitant progression of neurological disease and atherosclerosis. Further epidemiological and experimental work is needed to clarify the details and clinical relevance of those complex links.

The Synergistic Effects of APOE Genotype and Obesity on Alzheimer's Disease Risk

The APOE gene has three common alleles—E2, E3, and E4, with APOE4 being the strongest genetic risk factor for developing Alzheimer’s Disease (AD). Obesity is a global epidemic and contributes to multiple metabolic problems. Obesity is also a risk factor for cognitive decline. Here, we review the effects of APOE4 and obesity on cognition and AD development, independently and together. We describe studies that have associated APOE4 with cognitive deficits and AD, as well as studies that have associated obesity to cognitive deficits and AD. We then describe studies that have examined the effects of obesity and APOE genotypes together, with a focus on APOE4 and high fat diets. Both human studies and rodent models have contributed to understanding the effects of obesity on the different APOE genotypes, and we outline possible underlying mechanisms associated with these effects. Data across approaches support a model in which APOE4 and obesity combine for greater detrimental effects on metabolism and cognition, in ways that are influenced by both age and sex.

Impact of Metabolic Syndrome on Neuroinflammation and the Blood-Brain Barrier

Metabolic syndrome, which includes diabetes and obesity, is one of the most widespread medical conditions. It induces systemic inflammation, causing far reaching effects on the body that are still being uncovered. Neuropathologies triggered by metabolic syndrome often result from increased permeability of the blood-brain-barrier (BBB). The BBB, a system designed to restrict entry of toxins, immune cells, and pathogens to the brain, is vital for proper neuronal function. Local and systemic inflammation induced by obesity or type 2 diabetes mellitus can cause BBB breakdown, decreased removal of waste, and increased infiltration of immune cells. This leads to disruption of glial and neuronal cells, causing hormonal dysregulation, increased immune sensitivity, or cognitive impairment depending on the affected brain region. Inflammatory effects of metabolic syndrome have been linked to neurodegenerative diseases. In this review, we discuss the effects of obesity and diabetes-induced inflammation on the BBB, the roles played by leptin and insulin resistance, as well as BBB changes occurring at the molecular level. We explore signaling pathways including VEGF, HIFs, PKC, Rho/ROCK, eNOS, and miRNAs. Finally, we discuss the broader implications of neural inflammation, including its connection to Alzheimer's disease, multiple sclerosis, and the gut microbiome.

Unfavourable gender effect of high body mass index on brain metabolism and connectivity

The influence of Body Mass Index (BMI) on neurodegeneration in dementia has yet to be elucidated. We aimed at exploring the effects of BMI levels on cerebral resting-state metabolism and brain connectivity, as crucial measures of synaptic function and activity, in a large group of patients with Alzheimer's Dementia (AD) (n = 206), considering gender. We tested the correlation between BMI levels and brain metabolism, as assessed by 18F-FDG-PET, and the modulation of the resting-state functional networks by BMI. At comparable dementia severity, females with high BMI can withstand a lower degree of brain metabolism dysfunction, as shown by a significant BMI-brain metabolism correlation in the temporal-parietal regions, which are typically vulnerable to AD pathology (R = 0.269, p = 0.009). Of note, high BMI was also associated with reduced connectivity in frontal and limbic brain networks, again only in AD females (p < 0.05 FDR-corrected, k = 100 voxels). This suggests a major vulnerability of neural systems known to be selectively involved in brain compensatory mechanisms in AD females. These findings indicate a strong gender effect of high BMI and obesity in AD, namely reducing the available reserve mechanisms in female patients. This brings to considerations for medical practice and health policy.

Nrf2 Deficiency Exacerbates Obesity-Induced Oxidative Stress, Neurovascular Dysfunction, Blood-Brain Barrier Disruption, Neuroinflammation, Amyloidogenic Gene Expression, and Cognitive Decline in Mice, Mimicking the Aging Phenotype

Obesity has deleterious effects on cognitive function in the elderly adults. In mice, aging exacerbates obesity-induced oxidative stress, microvascular dysfunction, blood-brain barrier (BBB) disruption, and neuroinflammation, which compromise cognitive health. However, the specific mechanisms through which aging and obesity interact to remain elusive. Previously, we have shown that Nrf2 signaling plays a critical role in microvascular resilience to obesity and that aging is associated with progressive Nrf2 dysfunction, promoting microvascular impairment. To test the hypothesis that Nrf2 deficiency exacerbates cerebromicrovascular dysfunction induced by obesity Nrf2+/+ and Nrf2-/-, mice were fed an adipogenic high-fat diet (HFD). Nrf2 deficiency significantly exacerbated HFD-induced oxidative stress and cellular senescence, impairment of neurovascular coupling responses, BBB disruption, and microglia activation, mimicking the aging phenotype. Obesity in Nrf2-/- mice elicited complex alterations in the amyloidogenic gene expression profile, including upregulation of amyloid precursor protein. Nrf2 deficiency and obesity additively reduced long-term potentiation in the CA1 area of the hippocampus. Collectively, Nrf2 dysfunction exacerbates the deleterious effects of obesity, compromising cerebromicrovascular and brain health by impairing neurovascular coupling mechanisms, BBB integrity and synaptic function and promoting neuroinflammation. These results support a possible role for age-related Nrf2 dysfunction in the pathogenesis of vascular cognitive impairment and Alzheimer's disease.

Nutritional prevention of cognitive decline and dementia

Cognitive impairment results from a complex interplay of many factors. The most important independent predictor of cognitive decline is age but other contributing factors include demographic, genetic, socio-economic, and environmental parameters, including nutrition. The number of persons with cognitive decline and dementia will increase in the next decades in parallel with aging of the world population. Effective pharmaceutical treatments for age-related cognitive decline are lacking, emphasizing the importance of prevention strategies. There is extensive evidence supporting a relationship between diet and cognitive functions. Thus, nutritional approaches to prevent or slow cognitive decline could have a remarkable public health impact. Several dietary components and supplements have been examined in relation to their association with the development of cognitive decline. A number of studies have examined the role of dietary patterns on late-life cognition, with accumulating evidence that combinations of foods and nutrients may act synergistically to provide stronger benefit than those conferred by individual dietary components. Higher adherence to the Mediterranean dietary pattern has been associated with decreased cognitive decline and incident AD. Another dietary pattern with neuroprotective actions is the Dietary Approach to Stop Hypertension (DASH). The combination of these two dietary patterns has been associated with slower rates of cognitive decline and significant reduction in incident AD. This review evaluates the evidence for the effects of some dietary components, supplements, and dietary patterns as neuroprotective, with potential to delay cognitive decline and the onset of dementia.

Shared pathological pathways of Alzheimer's disease with specific comorbidities: current perspectives and interventions

Alzheimer's disease (AD) belongs to one of the most multifactorial, complex and heterogeneous morbidity-leading disorders. Despite the extensive research in the field, AD pathogenesis is still at some extend obscure. Mechanisms linking AD with certain comorbidities, namely diabetes mellitus, obesity and dyslipidemia, are increasingly gaining importance, mainly because of their potential role in promoting AD development and exacerbation. Their exact cognitive impairment trajectories, however, remain to be fully elucidated. The current review aims to offer a clear and comprehensive description of the state-of-the-art approaches focused on generating in-depth knowledge regarding the overlapping pathology of AD and its concomitant ailments. Thorough understanding of associated alterations on a number of molecular, metabolic and hormonal pathways, will contribute to the further development of novel and integrated theranostics, as well as targeted interventions that may be beneficial for individuals with age-related cognitive decline.