Fatty acid sensing in the gut and the hypothalamus: in vivo and in vitro perspectives

Post-operative cognitive dysfunction is exacerbated by high-fat diet via TLR4 and prevented by dietary DHA supplementation

Post-operative cognitive dysfunction (POCD) is an abrupt decline in neurocognitive function arising shortly after surgery and persisting for weeks to months, increasing the risk of dementia diagnosis. Advanced age, obesity, and comorbidities linked to high-fat diet (HFD) consumption such as diabetes and hypertension have been identified as risk factors for POCD, although underlying mechanisms remain unclear. We have previously shown that surgery alone, or 3-days of HFD can each evoke sufficient neuroinflammation to cause memory deficits in aged, but not young rats. The aim of the present study was to determine if HFD consumption before surgery would potentiate and prolong the subsequent neuroinflammatory response and memory deficits, and if so, to determine the extent to which these effects depend on activation of the innate immune receptor TLR4, which both insults are known to stimulate. Young-adult (3mo) & aged (24mo) male F344xBN F1 rats were fed standard chow or HFD for 3-days immediately before sham surgery or laparotomy. In aged rats, the combination of HFD and surgery caused persistent deficits in contextual memory and cued-fear memory, though it was determined that HFD alone was sufficient to cause the long-lasting cued-fear memory deficits. In young adult rats, HFD + surgery caused only cued-fear memory deficits. Elevated proinflammatory gene expression in the hippocampus of both young and aged rats that received HFD + surgery persisted for at least 3-weeks after surgery. In a separate experiment, rats were administered the TLR4-specific antagonist, LPS-RS, immediately before HFD onset, which ameliorated the HFD + surgery-associated neuroinflammation and memory deficits. Similarly, dietary DHA supplementation for 4 weeks prior to HFD onset blunted the neuroinflammatory response to surgery and prevented development of persistent memory deficits. These results suggest that HFD 1) increases risk of persistent POCD-associated memory impairments following surgery in male rats in 2) a TLR4-dependent manner, which 3) can be targeted by DHA supplementation to mitigate development of persistent POCD.

Young adult and aged female rats are vulnerable to amygdala-dependent, but not hippocampus-dependent, memory impairment following short-term high-fat diet

Global populations are increasingly consuming diets high in saturated fats and refined carbohydrates, and such diets have been well-associated with heightened inflammation and neurological dysfunction. Notably, older individuals are particularly vulnerable to the impact of unhealthy diet on cognition, even after a single meal, and pre-clinical rodent studies have demonstrated that short-term consumption of high-fat diet (HFD) induces marked increases in neuroinflammation and cognitive impairment. Unfortunately though, to date, most studies on the topic of nutrition and cognition, especially in aging, have been performed only in male rodents. This is especially concerning given that older females are more vulnerable to develop certain memory deficits and/or severe memory-related pathologies than males. Thus, the aim of the present study was to determine the extent to which short-term HFD consumption impacts memory function and neuroinflammation in female rats. Young adult (3 months) and aged (20-22 months) female rats were fed HFD for 3 days. Using contextual fear conditioning, we found that HFD had no effect on long-term contextual memory (hippocampus-dependent) at either age, but impaired long-term auditory-cued memory (amygdala-dependent) regardless of age. Gene expression of Il-1β was markedly dysregulated in the amygdala, but not hippocampus, of both young and aged rats after 3 days of HFD. Interestingly, modulation of IL-1 signaling via central administration of the IL-1 receptor antagonist (which we have previously demonstrated to be protective in males) had no impact on memory function following the HFD in females. Investigation of the memory-associated gene Pacap and its receptor Pac1r revealed differential effects of HFD on their expression in the hippocampus and amygdala. Specifically, HFD induced increased expression of Pacap and Pac1r in the hippocampus, whereas decreased Pacap was observed in the amygdala. Collectively, these data suggest that both young adult and aged female rats are vulnerable to amygdala-dependent (but not hippocampus-dependent) memory impairments following short-term HFD consumption, and identify potential mechanisms related to IL-1β and PACAP signaling in these differential effects. Notably, these findings are strikingly different than those previously reported in male rats using the same diet regimen and behavioral paradigms, and highlight the importance of examining potential sex differences in the context of neuroimmune-associated cognitive dysfunction.

Designing Biological Microsensors with Chiral Nematic Liquid Crystal Droplets

Biosensing using liquid crystals has a tremendous potential by coupling the high degree of sensitivity of their alignment to their surroundings with clear optical feedback. Many existing set-ups use birefringence of nematic liquid crystals, which severely limits straightforward and frugal implementation into a sensing platform due to the sophisticated optical set-ups required. In this work, we instead utilize chiral nematic liquid crystal microdroplets, which show strongly reflected structural color, as sensing platforms for surface active agents. We systematically quantify the optical response of closely related biological amphiphiles and find unique optical signatures for each species. We detect signatures across a wide range of concentrations (from micromolar to millimolar), with fast response times (from seconds to minutes). The striking optical response is a function of the adsorption of surfactants in a nonhomogeneous manner and the topology of the chiral nematic liquid crystal orientation at the interface requiring a scattering, multidomain structure. We show that the surface interactions, in particular, the surface packing density, to be a function of both headgroup and tail and thus unique to each surfactant species. We show lab-on-a-chip capability of our method by drying droplets in high-density two-dimensional arrays and simply hydrating the chip to detect dissolved analytes. Finally, we show proof-of-principle in vivo biosensing in the healthy as well as inflamed intestinal tracts of live zebrafish larvae, demonstrating CLC droplets show a clear optical response specifically when exposed to the gut environment rich in amphiphiles. Our unique approach shows clear potential in developing on-site detection platforms and detecting biological amphiphiles in living organisms.

The Microbiota and the Gut-Brain Axis in Controlling Food Intake and Energy Homeostasis

Obesity currently represents a major societal and health challenge worldwide. Its prevalence has reached epidemic proportions and trends continue to rise, reflecting the need for more effective preventive measures. Hypothalamic circuits that control energy homeostasis in response to food intake are interesting targets for body-weight management, for example, through interventions that reinforce the gut-to-brain nutrient signalling, whose malfunction contributes to obesity. Gut microbiota-diet interactions might interfere in nutrient sensing and signalling from the gut to the brain, where the information is processed to control energy homeostasis. This gut microbiota-brain crosstalk is mediated by metabolites, mainly short chain fatty acids, secondary bile acids or amino acids-derived metabolites and subcellular bacterial components. These activate gut-endocrine and/or neural-mediated pathways or pass to systemic circulation and then reach the brain. Feeding time and dietary composition are the main drivers of the gut microbiota structure and function. Therefore, aberrant feeding patterns or unhealthy diets might alter gut microbiota-diet interactions and modify nutrient availability and/or microbial ligands transmitting information from the gut to the brain in response to food intake, thus impairing energy homeostasis. Herein, we update the scientific evidence supporting that gut microbiota is a source of novel dietary and non-dietary biological products that may beneficially regulate gut-to-brain communication and, thus, improve metabolic health. Additionally, we evaluate how the feeding time and dietary composition modulate the gut microbiota and, thereby, the intraluminal availability of these biological products with potential effects on energy homeostasis. The review also identifies knowledge gaps and the advances required to clinically apply microbiome-based strategies to improve the gut-brain axis function and, thus, combat obesity.

Dietary Polyphenols to Combat Nonalcoholic Fatty Liver Disease via the Gut-Brain-Liver Axis: A Review of Possible Mechanisms

Polyphenols are a group of micronutrients widely existing in plant foods including fruits, vegetables, and teas that can improve nonalcoholic fatty liver disease (NAFLD). In this review, the existing knowledge of dietary polyphenols for the development of NAFLD regulated by intestinal microecology is discussed. Polyphenols can influence the vagal afferent pathway in the central and enteric nervous system to control NAFLD via gut-brain-liver cross-talk. The possible mechanisms involve in the alteration of microbial community structure, effects of gut metabolites (short-chain fatty acids (SCFAs), bile acids (BAs), endogenous ethanol (EnEth)), and stimulation of gut-derived hormones (ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and leptin) based on the targets excavated from the gut-brain-liver axis. Consequently, the communication among the intestine, brain, and liver paves the way for new approaches to understand the underlying roles and mechanisms of dietary polyphenols in NAFLD pathology.

Peripheral ERK modulates acupuncture-induced brain neural activity and its functional connectivity

Acupuncture has been widely used as a therapeutic intervention, and the brain network plays a crucial role in its neural mechanism. This study aimed to investigate the acupuncture mechanism from peripheral to central by identifying how the peripheral molecular signals induced by acupuncture affect the brain neural responses and its functional connectivity. We confirmed that peripheral ERK activation by acupuncture plays a role in initiating acupuncture-induced peripheral proteomic changes in mice. The brain neural activities in the neocortex, hippocampus, thalamus, hypothalamus, periaqueductal grey, and nucleus of the solitary tract (Sol) were significantly changed after acupuncture, and these were altered by peripheral MEK/MAPK inhibition. The arcuate nucleus and lateral hypothalamus were the most affected by acupuncture and peripheral MEK/MAPK inhibition. The hypothalamic area was the most contributing brain region in contrast task PLS analysis. Acupuncture provoked extensive changes in brain functional connectivity, and the posterior hypothalamus showed the highest betweenness centrality after acupuncture. After brain hub identification, the Sol and cingulate cortex were selected as hub regions that reflect both degree and betweenness centrality after acupuncture. These results suggest that acupuncture activates brain functional connectivity and that peripheral ERK induced by acupuncture plays a role in initiating brain neural activation and its functional connectivity.

Transcriptomic responses of hypothalamus to acute exercise in type 2 diabetic Goto-Kakizaki rats

The hypothalamus has an integral role in energy homeostasis regulation, and its dysfunctions lead to the development of type 2 diabetes (T2D). Physical activity positively affects the prevention and treatment of T2D. However, there is not much information on the adaptive mechanisms of the hypothalamus. In this study, RNA sequencing was used to determine how acute exercise affects hypothalamic transcriptome from both type 2 diabetic Goto-Kakizaki (GK) and control Wistar rats with or without a single session of running (15 m/min for 60 min). Through pairwise comparisons, we identified 957 differentially expressed genes (DEGs), of which 726, 197, and 98 genes were found between GK and Wistar, exercised GK and GK, and exercised Wistar and Wistar, respectively. The results of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment revealed that lipid metabolism-related terms and pathways were enriched in GK and exercised GK rats, and nervous system related terms and pathways were enriched in exercised GK and Wistar rats. Furthermore, 45 DEGs were associated with T2D and related phenotypes according to the annotations in the Rat Genome Database. Among these 45 DEGs, several genes (Plin2, Cd36, Lpl, Wfs1, Cck) related to lipid metabolism or the nervous system are associated with the exercise-induced benefits in the hypothalamus of GK rats. Our findings might assist in identifying potential therapeutic targets for T2D prevention and treatment.

Changes in Plasma Free Fatty Acids Associated with Type-2 Diabetes

Type 2 diabetes mellitus (T2DM) is associated with increased total plasma free fatty acid (FFA) concentrations and an elevated risk of cardiovascular disease. The exact mechanisms by which the plasma FFA profile of subjects with T2DM changes is unclear, but it is thought that dietary fats and changes to lipid metabolism are likely to contribute. Therefore, establishing the changes in concentrations of specific FFAs in an individual’s plasma is important. Each type of FFA has different effects on physiological processes, including the regulation of lipolysis and lipogenesis in adipose tissue, inflammation, endocrine signalling and the composition and properties of cellular membranes. Alterations in such processes due to altered plasma FFA concentrations/profiles can potentially result in the development of insulin resistance and coagulatory defects. Finally, fibrates and statins, lipid-regulating drugs prescribed to subjects with T2DM, are also thought to exert part of their beneficial effects by impacting on plasma FFA concentrations. Thus, it is also interesting to consider their effects on the concentration of FFAs in plasma. Collectively, we review how FFAs are altered in T2DM and explore the likely downstream physiological and pathological implications of such changes.

Is the Brain a Key Player in Glucose Regulation and Development of Type 2 Diabetes?

Ever since Claude Bernards discovery in the mid 19th-century that a lesion in the floor of the third ventricle in dogs led to altered systemic glucose levels, a role of the CNS in whole-body glucose regulation has been acknowledged. However, this finding was later overshadowed by the isolation of pancreatic hormones in the 20th century. Since then, the understanding of glucose homeostasis and pathology has primarily evolved around peripheral mechanism. Due to scientific advances over these last few decades, however, increasing attention has been given to the possibility of the brain as a key player in glucose regulation and the pathogenesis of metabolic disorders such as type 2 diabetes. Studies of animals have enabled detailed neuroanatomical mapping of CNS structures involved in glucose regulation and key neuronal circuits and intracellular pathways have been identified. Furthermore, the development of neuroimaging techniques has provided methods to measure changes of activity in specific CNS regions upon diverse metabolic challenges in humans. In this narrative review, we discuss the available evidence on the topic. We conclude that there is much evidence in favor of active CNS involvement in glucose homeostasis but the relative importance of central vs. peripheral mechanisms remains to be elucidated. An increased understanding of this field may lead to new CNS-focusing pharmacologic strategies in the treatment of type 2 diabetes.

Ileal transcriptome analysis in obese rats induced by high-fat diets and an adenoviral infection

BACKGROUND

Obesity has become a worldwide epidemic affecting millions of people. Obesity and associated health consequences tend to be complicated by diverse causes and multi-systemic involvement. Previous studies have investigated obesity induced by a single factor, such as a high-fat diet (HF) of typical energy-dense food and infection by an adipogenic virus, such as a widely studied human adenovirus serotype 36 (Ad-36). In this study, we hypothesized and investigated the synergistic effect of two causal factors, HF and Ad-36, in obesity induction.

METHODS

The 7-week-old Wistar rats (n = 1214/group) were randomly divided into weight-matched groups and induced for obesity with mock-control, HF, Ad-36, or HF + Ad-36 for 8-30 weeks, and compared for obesity phenotype. A global transcriptomic RNA-Seq analysis was used to profile signature gene response pathways in ileal tissues from 8-week control and obese animals during this early phase of obesity induction.

RESULTS

HF only and particularly co-administration of Ad-36 and HF (HF + Ad-36) induced significant obesity in rats (p < 0.05 or p < 0.005). Compared with either Ad-36 or HF alone, HF + Ad-36 treatment significantly aggravates obesity in rats regarding body weight (n = 12-14/group) and adiposity index (n = 6-7). Genome-wide transcriptomic analyses of intestinal tissues revealed signature genes on an inter-systemic scale, including many genes in the pathways of circadian rhythm and antiviral immunity focusing on IFN signaling.

CONCLUSIONS

Ad-36 exacerbated the induction of obesity in rats compared with those treated with HF alone. Gene-responsive pathways involved in circadian rhythm and antiviral immunity in ileal tissues were significantly (p < 0.05, and FDR < 0.01) regulated during the early phase of obesity induction. This study provided a co-factorial model for obesity induction and profiled molecular targets for further validation and molecular manipulation.

Sex-dependent effect on mitochondrial and oxidative stress parameters in the hypothalamus induced by prepubertal stress and access to high fat diet

OBJECTIVE

Some factors related to lifestyle, including stress and high-fat diet (HFD) consumption, are associated with higher prevalence of obesity. These factors can lead to an imbalance between ROS production and antioxidant defenses and to mitochondrial dysfunctions, which, in turn, could cause metabolic impairments, favoring the development of obesity. However, little is known about the interplay between these factors, particularly at early ages, and whether long-term sex-specific changes may occur. Here, we evaluated whether social isolation during the prepubertal period only, associated or not with chronic HFD, can exert long-term effects on oxidative status parameters and on mitochondrial function in the whole hypothalamus, in a sex-specific manner.

METHODS

Wistar male and female rats were divided into two groups (receiving standard chow or standard chow + HFD), that were subdivided into exposed or not to social isolation during the prepubertal period. Oxidative status parameters, and mitochondrial function were evaluated in the hypothalamus in the adult age.

RESULTS

Regarding antioxidant enzymes activities, HFD decreased GPx activity in the hypothalamus, while increasing SOD activity in females. Females also presented increased total thiols; however, non-protein thiols were lower. Main effects of stress and HFD were observed in TBARS levels in males, with both factors decreasing this parameter. Additionally, HFD increased complex IV activity, and decreased mitochondrial mass in females. Complex I-III activity was higher in males compared to females.

CONCLUSION

Stress during the prepubertal period and chronic consumption of HFD had persistent sex-specific effects on oxidative status, as well as on its consequences for the cell and for mitochondrial function. HFD had more detrimental effects on females, inducing oxidative imbalance, which resulted in damage to the mitochondria. This HFD-induced imbalance may be related to the development of obesity.

Addition of high load of lysophosphatidic acid to standard and high-fat chows causes no significant changes of its circulating and peripheral tissue levels but affects body weight and visceral fat mass of mice

Oral administration of lysophosphatidic acid (LPA), a critical intercellular lipid mediator, exerts wound healing and antiulcer effects on gastrointestinal system. To evaluate effects of food-derived LPA on body homeostasis, we measured LPA levels by liquid chromatography-tandem mass spectrometry in chows, feces, plasma, liver, and visceral fat of mice fed a normal or high-fat chow supplemented with or without LPA-rich soybean phospholipids for 30 days. Reductions in daily body weight gains and visceral fat mass were mainly related to lower chow intake by mice fed the LPA-rich high-fat chow, whereas reduced body weight gains and fat mass were mainly related to decreased intestinal triacylglycerol absorption in mice fed LPA-rich chow. Our results showed no significant increase in plasma, liver, or adipose LPA levels, even if a quite high LPA concentration (2.0%) in chows was ingested daily, suggesting limited effects of food-derived LPA on the lumen side of the digestive tract. © 2018 BioFactors, 44(6):548-557, 2018.

The Gut-Brain Axis, the Human Gut Microbiota and Their Integration in the Development of Obesity

Obesity is a global epidemic, placing socioeconomic strain on public healthcare systems, especially within the so-called Western countries, such as Australia, United States, United Kingdom, and Canada. Obesity results from an imbalance between energy intake and energy expenditure, where energy intake exceeds expenditure. Current non-invasive treatments lack efficacy in combating obesity, suggesting that obesity is a multi-faceted and more complex disease than previously thought. This has led to an increase in research exploring energy homeostasis and the discovery of a complex bidirectional communication axis referred to as the gut-brain axis. The gut-brain axis is comprised of various neurohumoral components that allow the gut and brain to communicate with each other. Communication occurs within the axis via local, paracrine and/or endocrine mechanisms involving a variety of gut-derived peptides produced from enteroendocrine cells (EECs), including glucagon-like peptide 1 (GLP1), cholecystokinin (CCK), peptide YY3-36 (PYY), pancreatic polypeptide (PP), and oxyntomodulin. Neural networks, such as the enteric nervous system (ENS) and vagus nerve also convey information within the gut-brain axis. Emerging evidence suggests the human gut microbiota, a complex ecosystem residing in the gastrointestinal tract (GIT), may influence weight-gain through several inter-dependent pathways including energy harvesting, short-chain fatty-acids (SCFA) signalling, behaviour modifications, controlling satiety and modulating inflammatory responses within the host. Hence, the gut-brain axis, the microbiota and the link between these elements and the role each plays in either promoting or regulating energy and thereby contributing to obesity will be explored in this review.

Effects of Enzymatically Synthesized Glycogen and Exercise on Abdominal Fat Accumulation in High-Fat Diet-Fed Mice

The combination of diet and exercise is the first choice for the treatment of obesity and metabolic syndrome. We previously reported that enzymatically synthesized glycogen (ESG) suppresses abdominal fat accumulation in obese rats. However, the effect of the combination of ESG and exercise on abdominal fat accumulation has not yet been investigated. Our goal in this study was therefore to evaluate the effects of dietary ESG and its combination with exercise on abdominal fat accumulation in high-fat diet (HFD)-fed mice. Male ICR mice were assigned to four groups: HFD, HFD containing 20% ESG, HFD with exercise, HFD containing 20% ESG with exercise. Treadmill exercise was performed for 3 wk (25 m/min, 30 min/d, 3 d/wk) after 5-d adaption to running at that speed. Both ESG and exercise significantly reduced the weights of abdominal adipose tissues. In addition, the combination of ESG and exercise significantly suppressed abdominal fat accumulation, suggesting that ESG and exercise showed an additive effect. Exercise significantly increased the mRNA levels of lipid metabolism-related genes such as lipoprotein lipase, peroxisome proliferator-activated receptor delta; factor-delta (PPARδ), carnitin palmitoyltransferase b, adipose triglyceride lipase (ATGL), and uncoupling protein-3 in the gastrocnemius muscle. On the other hand, dietary ESG significantly decreased the mRNA levels of PPARδ and ATGL in the gastrocnemius muscle. These results suggest that the combined treatment of ESG and exercise effectively suppresses abdominal fat accumulation in HFD-fed mice by different mechanisms.

Metabolic Effects of Bariatric Surgery

BACKGROUND

Obesity can be defined as a chronic subcortical brain disease, as there is an important neurophysiological component to its etiology based on changes in the functioning of those areas of the brain controlling food intake and reward. Extensive metabolic changes accompany bariatric surgery-based treatment of obesity. Consequently, the term “metabolic” surgery is being increasingly adopted in relation to the beneficial effects these procedures have on chronic diseases like type 2 diabetes.

CONTENT

In the present review, we focus on the key biochemical and physiological changes induced by metabolic surgery and highlight the beneficial effects accrued systemically with the use of an organ-based approach. Understanding the impact on and interactions between the gut, brain, adipose tissue, liver, muscle, pancreas, and kidney is key to understanding the sum of the metabolic effects of these operations.

SUMMARY

Further mechanistic studies are essential to assess the true potential of metabolic surgery to treat metabolic comorbidities of obesity beyond type 2 diabetes. Approaches that may mitigate the metabolic side effects of surgery also require attention. Understanding the positive impact of metabolic surgery on metabolic health may result in a wider acceptance of this intervention as treatment for metabolic, comorbid conditions.

Hypothalamic Integration of Metabolic, Endocrine, and Circadian Signals in Fish: Involvement in the Control of Food Intake

The regulation of food intake in fish is a complex process carried out through several different mechanisms in the central nervous system (CNS) with hypothalamus being the main regulatory center. As in mammals, a complex hypothalamic circuit including two populations of neurons: one co-expressing neuropeptide Y (NPY) and Agouti-related peptide (AgRP) and the second one population co-expressing pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) is involved in the integration of information relating to food intake control. The production and release of these peptides control food intake, and the production results from the integration of information of different nature such as levels of nutrients and hormones as well as circadian signals. The present review summarizes the knowledge and recent findings about the presence and functioning of these mechanisms in fish and their differences vs. the known mammalian model.

Nutrient Sensing Systems in Fish: Impact on Food Intake Regulation and Energy Homeostasis

Evidence obtained in recent years in a few species, especially rainbow trout, supports the presence in fish of nutrient sensing mechanisms. Glucosensing capacity is present in central (hypothalamus and hindbrain) and peripheral [liver, Brockmann bodies (BB, main accumulation of pancreatic endocrine cells in several fish species), and intestine] locations whereas fatty acid sensors seem to be present in hypothalamus, liver and BB. Glucose and fatty acid sensing capacities relate to food intake regulation and metabolism in fish. Hypothalamus is as a signaling integratory center in a way that detection of increased levels of nutrients result in food intake inhibition through changes in the expression of anorexigenic and orexigenic neuropeptides. Moreover, central nutrient sensing modulates functions in the periphery since they elicit changes in hepatic metabolism as well as in hormone secretion to counter-regulate changes in nutrient levels detected in the CNS. At peripheral level, the direct nutrient detection in liver has a crucial role in homeostatic control of glucose and fatty acid whereas in BB and intestine nutrient sensing is probably involved in regulation of hormone secretion from endocrine cells.

Tanycytes and a differential fatty acid metabolism in the hypothalamus

Although the brain controls all main metabolic pathways in the whole organism, its lipid metabolism is partially separated from the rest of the body. Circulating lipids and other metabolites are taken up into brain areas like the hypothalamus and are locally metabolized and sensed involving several hypothalamic cell types. In this study we show that saturated and unsaturated fatty acids are differentially processed in the murine hypothalamus. The observed differences involve both lipid distribution and metabolism. Key findings were: (i) hypothalamic astrocytes are targeted by unsaturated, but not saturated lipids in lean mice; (ii) in obese mice labeling of these astrocytes by unsaturated oleic acid cannot be detected unless β-oxidation or ketogenesis is inhibited; (iii) the hypothalamus of obese animals increases ketone body and neutral lipid synthesis while tanycytes, hypothalamic cells facing the ventricle, increase their lipid droplet content; and (iv) tanycytes show different labeling for saturated or unsaturated lipids. Our data support a metabolic connection between tanycytes and astrocytes likely to impact hypothalamic lipid sensing. GLIA 2017;65:231-249.

Ceramides are involved in the regulation of food intake in rainbow trout (Oncorhynchus mykiss)

We hypothesize that ceramides are involved in the regulation of food intake in fish. Therefore, we assessed in rainbow trout (Oncorhynchus mykiss) the effects of intracerebroventricular treatment with C6:0 ceramide on food intake. In a second experiment, we assessed the effects in brain areas of ceramide treatment on neuropeptide expression, fatty acid-sensing systems, and cellular signaling pathways. Ceramide treatment induced a decrease in food intake, a response opposed to the orexigenic effect described in mammals, which can be related to enhanced mRNA abundance of cocaine and amphetamine-related transcript and proopiomelanocortin and decreased mRNA abundance of Agouti-related protein and neuropeptide Y. Fatty acid-sensing systems appear to be inactivated by ceramide treatment. The mRNA abundance of integrative sensors AMPK and sirtuin 1, and the phosphorylation status of cellular signaling pathways dependent on protein kinase B, AMPK, mammalian target of rapamycin (mTOR), and forkhead box protein O1 (FoxO1) are generally activated by ceramide treatment. However, there are differences between hypothalamus and hindbrain in the phosphorylation status of AMPK (decreased in hypothalamus and increased in hindbrain), mTOR (decreased in hypothalamus and increased in hindbrain), and FoxO1 (increased in hypothalamus and decreased in hindbrain) to ceramide treatment. The results suggest that ceramides are involved in the regulation of food intake in rainbow trout through mechanisms comparable to those characterized previously in mammals in some cases.

Recent advances in the modification of taste and food preferences following bariatric surgery

There is a large body of evidence indicating that bariatric surgery provides durable weight loss and health benefits to patients who are obese and have comorbidities such as type 2 diabetes (T2D). However, there are still many questions related to mechanisms of metabolic improvement, predictors of success/failure, and long term consequences, which need to be answered. More recently, there has been a particular interest in the modulation of taste and food preferences that occurs after bariatric surgery and how this affects weight loss in different individuals. Animal models as well as human studies have shed some light on the role of taste in changing food preferences and how these changes may affect weight loss after surgery. The goal of this review is to discuss the physiological and behavioral consequences of bariatric surgery as a treatment for obesity and T2D, with particular emphasis on recent studies describing bariatric surgery-induced modifications in taste perception and food preferences.

Upper gastrointestinal sensitivity to meal-related signals in adult humans - relevance to appetite regulation and gut symptoms in health, obesity and functional dyspepsia

Both the stomach and small intestine play important roles in sensing the arrival of a meal, and its physico-chemical characteristics, in the gastrointestinal lumen. The presence of a meal in the stomach provides a distension stimulus, and, as the meal empties into the small intestine, nutrients interact with small intestinal receptors, initiating the release of gut hormones, associated with feedback regulation of gastrointestinal functions, including gut motility, and signaling to the central nervous system, modulating eating behaviours, including energy intake. Lipid appears to have particularly potent effects, also in close interaction with, and modulating the effects of, gastric distension, and involving the action of gut hormones, particularly cholecystokinin (CCK). These findings have not only provided important, and novel, insights into how gastrointestinal signals interact to modulate subjective appetite perceptions, including fullness, but also laid the foundation for an increasing appreciation of the role of altered gastrointestinal sensitivities, e.g. as a consequence of excess dietary intake in obesity, or underlying the induction of gastrointestinal symptoms in functional dyspepsia (a condition characterized by symptoms, including bloating, nausea and early fullness, amongst others, after meals, particularly those high in fat, in the absence of any structural or functional abnormalities in the gastrointestinal tract). This paper will review the effects of dietary nutrients, particularly lipid, on gastrointestinal function, and associated effects on appetite perceptions and energy intake, effects of interactions of gastrointestinal stimuli, as well as the role of altered gastrointestinal sensitivities (exaggerated, or reduced) in eating-related disorders, particularly obesity and functional dyspepsia.

Regulation of energy balance by a gut-brain axis and involvement of the gut microbiota

Despite significant progress in understanding the homeostatic regulation of energy balance, successful therapeutic options for curbing obesity remain elusive. One potential target for the treatment of obesity is via manipulation of the gut-brain axis, a complex bidirectional communication system that is crucial in maintaining energy homeostasis. Indeed, ingested nutrients induce secretion of gut peptides that act either via paracrine signaling through vagal and non-vagal neuronal relays, or in an endocrine fashion via entry into circulation, to ultimately signal to the central nervous system where appropriate responses are generated. We review here the current hypotheses of nutrient sensing mechanisms of enteroendocrine cells, including the release of gut peptides, mainly cholecystokinin, glucagon-like peptide-1, and peptide YY, and subsequent gut-to-brain signaling pathways promoting a reduction of food intake and an increase in energy expenditure. Furthermore, this review highlights recent research suggesting this energy regulating gut-brain axis can be influenced by gut microbiota, potentially contributing to the development of obesity.

Hypothalamic fatty acid sensing in Senegalese sole (Solea senegalensis): response to long-chain saturated, monounsaturated, and polyunsaturated (n-3) fatty acids

We assessed the presence of fatty acid (FA)-sensing mechanisms in hypothalamus of Senegalese sole (Solea senegalensis) and investigated their sensitivity to FA chain length and/or level of unsaturation. Stearate (SA, saturated FA), oleate (OA, monounsaturated FA of the same chain length), α-linolenate [ALA, a n-3 polyunsaturated fatty acid (PUFA) of the same chain length], and eicosapentanoate (EPA, a n-3 PUFA of a larger chain length) were injected intraperitoneally. Parameters related to FA sensing and neuropeptide expression in the hypothalamus were assessed after 3 h and changes in accumulated food intake after 4, 24, and 48 h. Three FA sensing systems characterized in rainbow trout were also found in Senegalese sole and were activated by OA in a way similar to that previously characterized in rainbow trout and mammals. These hypothalamic FA sensing systems were also activated by ALA, differing from mammals, where n-3 PUFAs do not seem to activate FA sensors. This might suggest additional roles and highlights the importance of n-3 PUFA in fish diets, especially in marine species. The activation of FA sensing seems to be partially dependent on acyl chain length and degree of saturation, as no major changes were observed after treating fish with SA or EPA. The activation of FA sensing systems by OA and ALA, but not SA or EPA, is further reflected in the expression of hypothalamic neuropeptides involved in the control of food intake. Both OA and ALA enhanced anorexigenic capacity compatible with the activation of FA sensing systems.

Effects of insulin treatment on the response to oleate and octanoate of food intake and fatty acid-sensing systems in rainbow trout

We hypothesized that food intake and the response of fatty acid (FA)-sensing systems in hypothalamus, liver, and Brockmann bodies of rainbow trout to raised levels of oleate (OL) or octanoate (OCT) is modified by insulin treatment. To assess this hypothesis, 15 fish per group received intraperitoneally 10-mL/kg injection of saline solution alone (control), or containing insulin (2-mg bovine insulin/kg body mass), OL (300 μg/kg), OCT (300 μg/kg), insulin + OL, or insulin + OCT to be sampled 6 h later to assess parameters related to FA sensing. Our results suggest that the modulatory role of insulin on the responses of hypothalamic FA-sensing systems to changes in circulating levels of OL or OCT was of minor importance in contrast to the mammalian model. However, this is in contrast with the effects observed in another experiment assessing changes in food intake after similar treatments because insulin treatment enhanced the anorectic effects of FA alone, and the effect was especially relevant (P < 0.001) for OCT, in contrast with the mammalian model where this FA is not inducing an anorectic response. In liver and Brockmann bodies, insulin treatment enhanced the responses to OL or OCT treatment in parameters related to FA sensing. Therefore, we provide for the first time in fish, and in a non-mammalian vertebrate, evidence for the modulation of FA-sensing systems by insulin.

The role of fatty acids in insulin resistance

Insulin resistance is a multi-faceted disruption of the communication between insulin and the interior of a target cell. The underlying cause of insulin resistance appears to be inflammation that can either be increased or decreased by the fatty acid composition of the diet. However, the molecular basis for insulin resistance can be quite different in various organs. This review deals with various types of inflammatory inputs mediated by fatty acids, which affect the extent of insulin resistance in various organs.

Glucoregulatory Relevance of Small Intestinal Nutrient Sensing in Physiology, Bariatric Surgery, and Pharmacology

Emerging evidence suggests the gastrointestinal tract plays an important glucoregulatory role. In this perspective, we first review how the intestine senses ingested nutrients, initiating crucial negative feedback mechanisms through a gut-brain neuronal axis to regulate glycemia, mainly via reduction in hepatic glucose production. We then highlight how intestinal energy sensory mechanisms are responsible for the glucose-lowering effects of bariatric surgery, specifically duodenal-jejunal bypass, and the antidiabetic agents metformin and resveratrol. A better understanding of these pathways lays the groundwork for intestinally targeted drug therapy for the treatment of diabetes.

Does nutrient sensing determine how we "see" food?

The ability to "see" both incoming and circulating nutrients plays an essential role in the maintenance of energy homeostasis. As such, nutrient-sensing mechanisms in both the gastrointestinal tract and the brain have been implicated in the regulation of energy intake and glucose homeostasis. The intestinal wall is able to differentiate individual nutrients through sensory machinery expressed in the mucosa and provide feedback signals, via local gut peptide action, to maintain energy balance. Furthermore, both the hypothalamus and hindbrain detect circulating nutrients and respond by controlling energy intake and glucose levels. Conversely, nutrient sensing in the intestine plays a role in stimulating food intake and preferences. In this review, we highlight the emerging evidence for the regulation of energy balance through nutrient-sensing mechanisms in the intestine and the brain, and how disruption of these pathways could result in the development of obesity and type 2 diabetes.

Nutrigenetics and nutrigenomics insights into diabetes etiopathogenesis

Diabetes mellitus (DM) is considered a global pandemic, and the incidence of DM continues to grow worldwide. Nutrients and dietary patterns are central issues in the prevention, development and treatment of this disease. The pathogenesis of DM is not completely understood, but nutrient-gene interactions at different levels, genetic predisposition and dietary factors appear to be involved. Nutritional genomics studies generally focus on dietary patterns according to genetic variations, the role of gene-nutrient interactions, gene-diet-phenotype interactions and epigenetic modifications caused by nutrients; these studies will facilitate an understanding of the early molecular events that occur in DM and will contribute to the identification of better biomarkers and diagnostics tools. In particular, this approach will help to develop tailored diets that maximize the use of nutrients and other functional ingredients present in food, which will aid in the prevention and delay of DM and its complications. This review discusses the current state of nutrigenetics, nutrigenomics and epigenomics research on DM. Here, we provide an overview of the role of gene variants and nutrient interactions, the importance of nutrients and dietary patterns on gene expression, how epigenetic changes and micro RNAs (miRNAs) can alter cellular signaling in response to nutrients and the dietary interventions that may help to prevent the onset of DM.