Obesity is associated with structural and functional brain abnormalities: where do we go from here?

The Impact of Biological Sex And High-Fat High-Fructose Diet on Brain Dysfunction in an Animal Model of Sepsis

The aim of this study was to evaluate long-term inflammatory, biochemical and behavioral parameters in adult male and female Wistar rats submitted to a model of high-fat and high fructose diet and sepsis. In the study we used 8-month-old male and female rats. High-fat and high fructose diet was provided for 4 months, and sepsis was induced shortly afterwards. Behavioral tests were performed at 10, 30 and 60 days after sepsis induction, at 30- and 60-days metabolic parameters, leptin and cytokines (prefrontal cortex and hippocampus) were determined. High-fat and high-fructose diet was able to induce glucose intolerance. Sepsis favored anxious behavior at 10 days after sepsis, remaining at 30 days and with apparent improvement at 60 days in females and maintenance of behavior in males. Cognitive damage was observed both at 30 and 60 days in animals from both groups. Plasma metabolic parameters were elevated only males exposed to a high-fat high-fructose diet and submitted to CLP only at 30 days. Long-term brain inflammation was not consistently affected both by sex and high-fat and high fructose diet.The relationship between high-fat and high fructose diet, gender and sepsis is still contradictory, as are the mechanisms involved in this paradox. Models and analyses need to be standardized in order to better understand how this event occurs.

Aqueous Extract of Psiloxylon mauritianum, Rich in Gallic Acid, Prevents Obesity and Associated Deleterious Effects in Zebrafish

Obesity has reached epidemic proportions, and its prevalence tripled worldwide between 1975 and 2016, especially in Reunion Island, a French overseas region. Psiloxylon mauritianum, an endemic medicinal plant from Reunion Island registered in the French pharmacopeia, has recently gained interest in combating metabolic disorders because of its traditional lipid-lowering and “anti-diabetic” use. However, scientific data are lacking regarding its toxicity and its real benefits on metabolic diseases. In this study, we aim to determine the toxicity of an aqueous extract of P. mauritianum on zebrafish eleutheroembryos following the OECD toxicity assay (Organization for Economic Cooperation and Development, guidelines 36). After defining a non-toxic dose, we determined by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) that this extract is rich in gallic acid but contains also caffeoylquinic acid, kaempferol and quercetin, as well as their respective derivatives. We also showed that the non-toxic dose exhibits lipid-lowering effects in a high-fat-diet zebrafish larvae model. In a next step, we demonstrated its preventive effects on body weight gain, hyperglycemia and liver steatosis in a diet-induced obesity model (DIO) performed in adults. It also limited the deleterious effects of overfeeding on the central nervous system (i.e., cerebral oxidative stress, blood-brain barrier breakdown, neuro-inflammation and blunted neurogenesis). Interestingly, adult DIO fish treated with P. mauritianum display normal feeding behavior but higher feces production. This indicates that the “anti-weight-gain” effect is probably due to the action of P. mauritianum on the intestinal lipid absorption and/or on the microbiota, leading to the increase in feces production. Therefore, in our experimental conditions, the aqueous extract of P. mauritianum exhibited “anti-weight-gain” properties, which prevented the development of obesity and its deleterious effects at the peripheral and central levels. These effects should be further investigated in preclinical models of obese/diabetic mice, as well as the impact of P. mauritianum on the gut microbiota.

The impact of obesity-related neuroinflammation on postpartum depression: A narrative review

Obesity is currently one of the most serious health problems, affecting 13% of the world's adult population. Obesity is characterized by persistent low-grade chronic inflammation that assumes systemic proportions and triggers several associated metabolic diseases. Furthermore, obesity has been associated with an increased occurrence of central disorders such as impaired cognitive function, reward system dysfunction, and depression. In summary, there is a quantitative reduction in the release of neurotransmitters in depression. Postsynaptic cells capture lower concentrations of neurotransmitters, which leads to a functional reduction in the central nervous system (CNS). Globally, approximately 15-65% of women experience depressive symptoms during pregnancy, depending on their location. Depressive symptoms persist in some women, leading to postpartum depression (PPD). Thus, obesity may be considered a risk factor for PPD development. This study aimed to synthesize studies on the impact of obesity-related neuroinflammation and PPD. We conducted a narrative review of the relevant literature. The search was performed in electronic databases, specifically PubMed, selecting articles in English published from 2014 to 2021 using the narrative review methodology.

Omega-3 Fatty Acids Attenuate Brain Alterations in High-Fat Diet-Induced Obesity Model

This study evaluated the effects of omega-3 on inflammation, oxidative stress, and energy metabolism parameters in the brain of mice subjected to high-fat diet-induced obesity model. Body weight and visceral fat weight were evaluated as well. Male Swiss mice were divided into control (purified low-fat diet) and obese (purified high-fat diet). After 6 weeks, the groups were divided into control + saline, control + omega-3, obese + saline, and obese + OMEGA-3. Fish oil (400 mg/kg/day) or saline solution was administrated orally, during 4 weeks. When the experiment completed 10 weeks, the animals were euthanized and the brain and visceral fat were removed. The brain structures (hypothalamus, hippocampus, prefrontal cortex, and striatum) were isolated. Treatment with omega-3 had no effect on body weight, but reduced the visceral fat. Obese animals showed increased inflammation, increased oxidative damage, decreased antioxidant enzymes activity and levels, changes in the Krebs cycle enzyme activities, and inhibition of mitochondrial respiratory chain complexes in the brain structures. Omega-3 treatment partially reversed the changes in the inflammatory and in the oxidative damage parameters and attenuated the alterations in the antioxidant defense and in the energy metabolism (Krebs cycle and mitochondrial respiratory chain). Omega-3 had a beneficial effect on the brain of obese animals, as it partially reversed the changes caused by the consumption of a high-fat diet and consequent obesity. Our results support studies that indicate omega-3 may contribute to obesity treatment.

n-3 PUFA and obesity: from peripheral tissues to the central nervous system

The current paradigms of prevention and treatment are unable to curb obesity rates, which indicates the need to explore alternative therapeutic approaches. Obesity leads to several damages to the body and is an important risk factor for a number of other chronic diseases. Furthermore, despite the first alterations in obesity being observed and reported in peripheral tissues, studies indicate that obesity can also cause brain damage. Obesity leads to a chronic low-grade inflammatory state, and the therapeutic manipulation of inflammation can be explored. In this context, the use of n-3 PUFA (especially in the form of fish oil, rich in EPA and DHA) may be an interesting strategy, as this substance is known by its anti-inflammatory effect and numerous benefits to the body, such as reduction of TAG, cardiac arrhythmias, blood pressure and platelet aggregation, and has shown potential to help treat obesity. Thereby, the aim of this narrative review was to summarise the literature related to n-3 PUFA use in obesity treatment. First, the review provides a brief description of the obesity pathophysiology, including alterations that occur in peripheral tissues and at the central nervous system. In the sequence, we describe what are n-3 PUFA, their sources and their general effects. Finally, we explore the main topic linking obesity and n-3 PUFA. Animal and human studies were included and alterations on the whole organism were described (peripheral tissues and brain).

White matter microstructure and cognitive decline in metabolic syndrome: a review of diffusion tensor imaging

Metabolic syndrome is a cluster of cardiovascular risk factors defined by the presence of abdominal obesity, glucose intolerance, hypertension and/or dyslipidemia. It is a major public health epidemic worldwide, and a known risk factor for the development of cognitive dysfunction and dementia. Several studies have demonstrated a positive association between the presence of metabolic syndrome and worse cognitive outcomes, however, evidence of brain structure pathology is limited. Diffusion tensor imaging has offered new opportunities to detect microstructural white matter changes in metabolic syndrome, and a possibility to detect associations between functional and structural abnormalities. This review analyzes the impact of metabolic syndrome on white matter microstructural integrity, brain structure abnormalities and their relationship to cognitive function. Each of the metabolic syndrome components exerts a specific signature of white matter microstructural abnormalities. Metabolic syndrome and its components exert both additive/synergistic, as well as, independent effects on brain microstructure thus accelerating brain aging and cognitive decline.

Mitochondrial dysfunction in obesity

Obesity leads to various changes in the body. Among them, the existing inflammatory process may lead to an increase in the production of reactive oxygen species (ROS) and cause oxidative stress. Oxidative stress, in turn, can trigger mitochondrial changes, which is called mitochondrial dysfunction. Moreover, excess nutrients supply (as it commonly is the case with obesity) can overwhelm the Krebs cycle and the mitochondrial respiratory chain, causing a mitochondrial dysfunction, and lead to a higher ROS formation. This increase in ROS production by the respiratory chain may also cause oxidative stress, which may exacerbate the inflammatory process in obesity. All these intracellular changes can lead to cellular apoptosis. These processes have been described in obesity as occurring mainly in peripheral tissues. However, some studies have already shown that obesity is also associated with changes in the central nervous system (CNS), with alterations in the blood-brain barrier (BBB) and in cerebral structures such as hypothalamus and hippocampus. In this sense, this review presents a general view about mitochondrial dysfunction in obesity, including related alterations, such as inflammation, oxidative stress, and apoptosis, and focusing on the whole organism, covering alterations in peripheral tissues, BBB, and CNS.

The prospective association between obesity and major depression in the general population: does single or recurrent episode matter?

BACKGROUND

Obesity and major depressive disorder (MDD) are important public health problems. MDD is a heterogeneous disorder and the direction of its association with obesity remains unclear. Evidence grows that recurrent MDD (MDD-R) differs in etiology and prognosis from single episode MDD (MDD-S), which could affect associations with obesity. However, evidence on this differential effect is lacking. The aim of this study was to examine the direction of the association between obesity and MDD, single or recurrent episode.

METHODS

A longitudinal study was performed in a cohort of 1094 participants of the PREVEND study, on whom data were collected at baseline and at an average 2-year follow-up. MDD-S and MDD-R were assessed by the Composite International Diagnostic Interview (CIDI 2.1). Obesity was defined as Body Mass Index ≥ 30 kg/m(2). Binary logistic regression analyses were conducted to examine whether obesity predicts MDD-S/MDD-R or vice versa, adjusted for potential confounders.

RESULTS

Prospective analyses showed that BMI at baseline was associated with the onset of MDD-R (Odds ratio, OR = 1.32; 95% confidence interval, 95%CI: 1.11; 1.57) during 2-year follow-up, but not with the onset of MDD-S (OR = 0.98; 95%CI: 0.89; 1.07). Obesity at baseline was not associated with the onset of MDD-S during follow-up (OR = 0.75; 95%CI: 0.25; 2.30), but associated with the onset of MDD-R during follow-up (OR = 11.63; 95%CI: 1.05; 128.60). Neither MDD-S nor MDD-R were associated with the development of obesity during 2-year follow-up (OR = 1.67, 95%CI: 0.64; 4.29 and OR = 2.32, 95%CI: 0.82; 6.58, respectively).

CONCLUSIONS

Our findings add to the available evidence that obesity might specifically be associated with the onset of multiple episodes of major depression (MDD-R). Although the reverse association was not found, MDD-R tends to be also associated with subsequent development of obesity, but larger studies are needed to fully assess this issue. The heterogeneity of MDD should be considered when examining the effect of obesity on MDD.

Is Alzheimer's disease related to metabolic syndrome? A Wnt signaling conundrum

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 36 million people worldwide. AD is characterized by a progressive loss of cognitive functions. For years, it has been thought that age is the main risk factor for AD. Recent studies suggest that life style factors, including nutritional behaviors, play a critical role in the onset of dementia. Evidence about the relationship between nutritional behavior and AD includes the role of conditions such as obesity, hypertension, dyslipidemia and elevated glucose levels. The coexistence of some of these cardio-metabolic risk factors is generally known as metabolic syndrome (MS). Some clinical studies support the role of MS in the onset of AD. However, the cross-talk between the molecular signaling implicated in these disorders is unknown. In the present review, we focus on the molecular correlates that support the relationship between MS and the onset of AD. We also discuss relevant issues such as the role of leptin, insulin and renin-angiotensin signaling in the brain and the possible role of Wnt signaling in both MS and AD. We discuss the evidence supporting the use of ob/ob mice, high-fructose diets, aortic coarctation-induced hypertension and Octodon degus, which spontaneously develops β-amyloid deposits and metabolic derangements, as suitable animal models to address the relationships between MS and AD. Finally, we examine emergent data supporting the role of Wnt signaling in the modulation of AD and MS, implicating this pathway as a therapeutic target in both conditions.

Is obesity associated with a decline in intelligence quotient during the first half of the life course?

Cross-sectional studies have found that obesity is associated with low intellectual ability and neuroimaging abnormalities in adolescence and adulthood. Some have interpreted these associations to suggest that obesity causes intellectual decline in the first half of the life course. We analyzed data from a prospective longitudinal study to test whether becoming obese was associated with intellectual decline from childhood to midlife. We used data from the ongoing Dunedin Multidisciplinary Health and Development Study, a population-representative birth cohort study of 1,037 children in New Zealand who were followed prospectively from birth (1972-1973) through their fourth decade of life with a 95% retention rate. Intelligence quotient (IQ) was measured in childhood and adulthood. Anthropometric measurements were taken at birth and at 12 subsequent in-person assessments. As expected, cohort members who became obese had lower adulthood IQ scores. However, obese cohort members exhibited no excess decline in IQ. Instead, these cohort members had lower IQ scores since childhood. This pattern remained consistent when we accounted for children's birth weights and growth during the first years of life, as well as for childhood-onset obesity. Lower IQ scores among children who later developed obesity were present as early as 3 years of age. We observed no evidence that obesity contributed to a decline in IQ, even among obese individuals who displayed evidence of the metabolic syndrome and/or elevated systemic inflammation.