CD36 may determine our desire for dietary fats

Fat malabsorption in short bowel syndrome: A review of pathophysiology and management

Fat malabsorption is central to the pathophysiology of short bowel syndrome (SBS). It occurs in patients with insufficient intestinal surface area and/or function to maintain metabolic and growth demands. Rapid intestinal transit and impaired bile acid recycling further contribute to fat malabsorption. A significant portion of patients require parenteral nutrition (PN) for their survival but may develop sepsis and liver dysfunction as a result. Despite advancements in the treatment of SBS, fat malabsorption remains a chronic issue for this vulnerable patient population. Peer-reviewed literature was assessed on the topic of fat malabsorption in SBS. Current management of patients with SBS involves dietary considerations, PN management, antidiarrheals, glucagon-like peptide 2 agonists, and multidisciplinary teams. Clinical trials have focused on improving intestinal fat absorption by facilitating fat digestion with pancreatic enzymes. Targeting fat malabsorption in SBS is a potential pathway to improving lifestyle and reducing morbidity and mortality in this rare disease.

Fatty acid translocase (FAT/CD36) in silver pomfret (Pampus argenteus): Molecular cloning and functional characterization

Understanding the mechanisms of lipid transport and metabolism in fish is crucial to enhance dietary lipid utilization. Here, fatty acid translocase (CD36) gene was characterized in silver pomfret (Pampus argenteus). The open reading frame of silver pomfret cd36 gene was 1395 bp, encoding 464 amino acids. The silver pomfret CD36 protein contained typical transmembrane regions and N-glycosylation modification sites, and was localized to the cytomembrane. The cd36 gene was ubiquitously expressed in all tested tissues, with the highest expression observed in brain tissue. In vivo, both fasting and short-term high-fat feeding could increase cd36 expression in intestinal tissue. In vitro, cd36 expression was induced by palmitic acid, oleic acid, linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid treatment in intestinal tissue. Furthermore, dual-luciferase reporter assay results indicated that peroxisome proliferator-activated receptor gamma (PPARγ) could enhance cd36 promoter activity, and the co-expression of cd36 and pparγ was observed in EPA-incubated intestine, suggesting that EPA may regulate the expression of cd36 via PPARγ to maintain the homeostasis of intestinal lipid metabolism in silver pomfret. These results highlighted the crucial role of CD36 in silver pomfret, and suggested that the cd36 expression may be regulated by PPARγ. This study could contribute to a greater understanding of lipid metabolism and the development of effective strategies for nutrient requirements in fish.

Genetic Variants in CD36 Involved in Fat Taste Perception: Association with Anthropometric and Clinical Parameters in Overweight and Obese Subjects Affected by Type 2 Diabetes or Dysglycemia-A Pilot Study

Obesity and overweight represent a growing health problem worldwide. Genes regulating the intake and metabolism of different nutrients can positively or negatively influence the efficacy of nutritional interventions against obesity and its complications. The aim of this study was to assess changes in anthropometric and clinical parameters and the adherence to a Mediterranean diet (MedDiet) over time in relation to nutrigenetic variants in overweight or obese subjects affected by Type 2 Diabetes (T2D) or dysglycemia, who were included in a nutritional program. A total of 23 subjects were included in this study. Clinical parameters, physical activity levels, and the adherence to a MedDiet were evaluated at baseline, at 6 (T6), and at 12 months (T12) during and after a diet/lifestyle intervention. In a single blood sample from each subject, rs1984112 (A>G) and rs1761667 (G>A) in CD36; rs7950226 (G>A) in BMAL1; and rs1801260 (A>G), rs4864548 (A>G), and rs3736544 (G>A) in CLOCK were genotyped with Real-Time PCR. Significant associations were observed between CD36 rs1761667 and weight (p = 0.025), hip circumference (p = 0.042), triglycerides (p = 0.047), and HbA1c (p = 0.012) at baseline. Moreover, the genotype AA in CD36 rs1761667 was significantly associated with a lower BMI when compared to G carriers at baseline, at T6, and also at T12. In addition, subjects with the AA genotype at CD36 rs1984112 had significantly lower levels of HbA1c (p = 0.027) than the GG and AG genotypes at baseline. These results show that variants in CD36 can have an impact on anthropometric and clinical parameters in overweight or obese subjects affected by T2D or dysglycemia, and that it might influence the success of the diet/lifestyle intervention.

Understanding across the senses: cross-modal studies of cognition in cetaceans

Cross-modal approaches to the study of sensory perception, social recognition, cognition, and mental representation have proved fruitful in humans as well as in a variety of other species including toothed whales in revealing equivalencies that suggest that different sensory stimuli associated with objects or individuals may effectively evoke mental representations that are, respectively, object based or individual based. Building on established findings of structural equivalence in the form of spontaneous recognition of complex shapes across the modalities of echolocation and vision and behavior favoring identity echoic-visual cross-modal relationships over associative echoic-visual cross-modal relationships, examinations of transitive inference equivalencies from initially learned associations of visual and acoustic stimuli, and recent work examining spontaneous cross-modal social recognition of individual identity across acoustic and gustatory chemical modalities (i.e., the equivalence relationships among an individual's characteristics), we examine the history, utility and implications for cross-modal research in cetacean cognition. Drawing from research findings on bottlenose dolphins and beluga whales as well as other species we suggest future directions for cetacean cross-modal research to further illuminate understanding how structural and individual sensory equivalencies lead to object-centered and individual-centered mental representations, as well as to explore the potential for practical applications related to cetacean conservation.

Amentoflavone-Enriched Selaginella rossii Warb. Suppresses Body Weight and Hyperglycemia by Inhibiting Intestinal Lipid Absorption in Mice Fed a High-Fat Diet

Many Selaginellaceae species are used as traditional medicines in Asia. This study is the first to investigate the anti-obesity and anti-diabetic effects of Selaginella rossii (SR) in high-fat diet (HFD)–fed C57BL/6J mice. Seven-day oral administration of ethanol extract (100 mg/kg/day) or ethyl acetate (EtOAc) extract (50 mg/kg/day) from SR improved oral fat tolerance by inhibiting intestinal lipid absorption; 10-week long-term administration of the EtOAc extract markedly reduced HFD-induced body weight gain and hyperglycemia by reducing adipocyte hypertrophy, glucose levels, HbA1c, and plasma insulin levels. Treatment with SR extracts reduced the expression of intestinal lipid absorption-related genes, including Cd36, fatty acid-binding protein 6, ATP-binding cassette subfamily G member 8, NPC1 like intracellular cholesterol transporter 1, and ATP-binding cassette subfamily A member 1. In addition, the EtOAc extract increased the expression of protein absorption–related solute carrier family genes, including Slc15a1, Slc8a2, and Slc6a9. SR extracts reduced HFD-induced hepatic steatosis by suppressing fatty acid transport to hepatocytes and hepatic lipid accumulation. Furthermore, amentoflavone (AMF), the primary compound in SR extracts, reduced intestinal lipid absorption by inhibiting fatty acid transport in HFD-fed mice. AMF-enriched SR extracts effectively protected against HFD-induced body weight gain and hyperglycemia by inhibiting intestinal lipid absorption.

GPR84 Is Essential for the Taste of Medium Chain Saturated Fatty Acids

The ability of mammalian taste cells to respond to fatty acids (FAs) has garnered significant attention of late and has been proposed to represent a sixth primary taste. With few exceptions, studies on FA taste have centered exclusively on polyunsaturated FAs, most notably on linoleic acid. In the current study, we have identified an additional FA receptor, GPR84, in the gustatory system that responds to the medium-chain saturated FAs (MCFAs) in male mice. GPR84 ligands activate both Type II and Type III taste cells in calcium imaging and patch-clamp recording assays. MCFAs depolarize and lead to a rise in intracellular free [Ca2+] in mouse taste cells in a concentration-dependent fashion, and the relative ligand specificity in taste cells is consistent with the response profile of GPR84 expressed in a heterologous system. A systemic Gpr84-/- mouse model reveals a specific deficit in both the neural (via chorda tympani recording) and behavioral responses to administration of oral MCFAs compared with WT mice. Together, we show that the peripheral taste system can respond to an additional class of FAs, the saturated FAs, and that the cognate receptor necessary for this ability is GPR84.

Transection of Gustatory Nerves Differentially Affects Dietary Fat Intake in Obesity-Prone and Obesity-Resistant Rats

The current prevalence of obesity has been linked to the consumption of highly palatable foods and may be mediated by a dysregulated or hyposensitive orosensory perception of dietary fat, thereby contributing to the susceptibility to develop obesity. The goal of the current study was to investigate the role of lingual taste input in obesity-prone (OP, Osborne-Mendel) and obesity-resistant (OR, S5B/Pl) rats on the consumption of a high-fat diet (HFD). Density of fungiform papillae was assessed as a marker of general orosensory input. To determine if orosensory afferent input mediates dietary fat intake, surgical transection of the chorda tympani and glossopharyngeal nerves (GLX/CTX) was performed in OP and OR rats and HFD caloric intake and body weight were measured. Fungiform papillae density was lower in OP rats, compared with OR rats. GLX/CTX decreased orosensory input in both OP and OR rats, as measured by an increase in the intake of a bitter, quinine solution. Consumption of low-fat diet was not altered by GLX/CTX in OP and OR rats; however, GLX/CTX decreased HFD intake in OR, without altering HFD intake in OP rats. Overall, these data suggest that inhibition of orosensory input in OP rats do not decrease fat intake, thereby supporting that idea that hyposensitive and/or dysregulated orosensory perception of highly palatable foods contribute to the susceptibility to develop obesity.

Soluble Receptors Affecting Stroke Outcomes: Potential Biomarkers and Therapeutic Tools

Soluble receptors are widely understood to be freestanding moieties formed via cleavage from their membrane-bound counterparts. They have unique structures, are found among various receptor families, and have intriguing mechanisms of generation and release. Soluble receptors’ ability to exhibit pleiotropic action by receptor modulation or by exhibiting a dual role in cytoprotection and neuroinflammation is concentration dependent and has continually mystified researchers. Here, we have compiled findings from preclinical and clinical studies to provide insights into the role of soluble/decoy receptors, focusing on the soluble cluster of differentiation 36, the soluble cluster of differentiation 163, and soluble lipoprotein-related protein 1 (sCD36, sCD163, and sLRP1, respectively) and the functions they could likely serve in the management of stroke, as they would notably regulate the bioavailability of the hemoglobin and heme after red blood cell lysis. The key roles that these soluble receptors play in inflammation, oxidative stress, and the related pharmacotherapeutic potential in improving stroke outcomes are described. The precise pleiotropic physiological functions of soluble receptors remain unclear, and further scientific investigation/validation is required to establish their respective role in diagnosis and therapy.

Studies of human twins reveal genetic variation that affects dietary fat perception

To learn more about the mechanisms of human dietary fat perception, 398 human twins rated fattiness and liking for six types of potato chips that differed in triglyceride content (2.5, 5, 10, and 15% corn oil); reliability estimates were obtained from a subset (n = 50) who did the task twice. Some chips also had a saturated long-chain fatty acid (hexadecanoic acid, 16:0) added (0.2%) to evaluate its effect on fattiness and liking. We computed the heritability of these measures and conducted a genome-wide association study (GWAS) to identify regions of the genome that co-segregate with fattiness and liking. Perceived fattiness and liking for the potato chips were reliable (r = 0.31-0.62, p < 0.05) and heritable (up to h2 = 0.29, p < 0.001, for liking). Adding hexadecanoic acid to the potato chips significantly increased ratings of fattiness but decreased liking. Twins with the G allele of rs263429 near GATA3-AS1 or the G allele of rs8103990 within ZNF729 reported more liking for potato chips than did twins with the other allele (multivariate GWAS, p < 1×10-5), with results reaching genome-wide suggestive but not significance criteria. Person-to-person variation in the perception and liking of dietary fat was (a) negatively affected by the addition of a saturated fatty acid and (b) related to inborn genetic variants. These data suggest liking for dietary fat is not due solely to fatty acid content and highlight new candidate genes and proteins within this sensory pathway.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

Elevated CD36 expression correlates with increased visceral adipose tissue and predicts poor prognosis in ccRCC patients

Objective: Growing evidence has proved obesity one of the confirmed important etiologic indicators for renal cell carcinoma (RCC). CD36 is underpinned to be involved in adipose absorption, but its role in clear cell renal cell carcinoma (ccRCC) remains unclear. This study aimed to investigate the mRNA expression of CD36 in anthropometric measures of adipose tissue and defining its value in predicting prognosis in ccRCC patients. Methods: Real-Time qPCR gene expression analysis was detected from 367 paired ccRCC and adjacent normal tissues. Distributions of categorical clinical-pathological data together with levels of CD36 expression were compared with χ²-test in a contingency table. Subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) were measured by magnetic resonance imaging (MRI) and identified at the level of the umbilicus. Pearson's correlation coefficient was utilized to quantify relations between body mass index (BMI), VAT%, SAT and CD36 expression respectively. Partial likelihood test from univariate and multivariate Cox regression analysis were developed to address the influence of independent factors on progression-free survival (PFS) and overall survival (OS). The Kaplan-Meier method and log-rank test were performed to assess the survival benefits between discrete levels. Results: In the current study, CD36 mRNA was demonstrated highly expressed in ccRCC compared with normal tissues. In addition, CD36 mRNA expression was significantly increased in patients with advanced TNM stage (p=0.003, p<0.001, p<0.001), and high VAT% (p=0.004). Pearson's correlation coefficient indicated that CD36 amplification positively correlated with BMI (r=0.117, p=0.025), VAT% (r=0.465, p<0.001), while negatively associated with SAT (r=-0.296, p=0.002). Median PFS was 60 months and OS was 99 months. Meanwhile, ccRCC patients with elevated CD36 expression held shorter PFS and OS, with hazard ratios [HR; 95% confidence interval (CI)] of 4.873 (3.300-7.196, p<0.001) and 4.610 (2.956-7.189, p<0.001). In 104 cases with available MRI scans, VAT was significantly correlated with poor PFS and OS, with HR of 2.556 (1.036-6.310, p<0.042) and 3.291 (1.034-10.477, p<0.044). A total of 100 significant genes were obtained from GSEA, and CD36 was found involved in the most significant pathways including fatty acid metabolism, UV response, angiogenesis and transforming growth factor beta (TGF-β) signaling pathways. Conclusion: In conclusion, our study first reveal that elevated CD36 mRNA expression is positively correlated to distribution of abdominal adipose, particularly VAT%, which, in addition, notably predicts poor prognosis in ccRCC patients.

Brain Imaging of Taste Perception in Obesity: a Review

PURPOSE OF REVIEW

We summarize neuroimaging findings related to processing of taste (fat, salt, umami, bitter, and sour) in the brain and how they influence hedonic responses and eating behaviors and their role in obesity.

RECENT FINDINGS

Neuroimaging studies in obese individuals have revealed alterations in reward/motivation, executive control/self-regulation, and limbic/affective circuits that are implicated in food and drug addiction. Psychophysical studies show that sensory properties of food ingredients may be associated with anthropometric and neurocognitive outcomes in obesity. However, few studies have examined the neural correlates of taste and processing of calories and nutrient content in obesity. The literature of neural correlated of bitter, sour, and salty tastes remains sparse in obesity. Most published studies have focused on sweet, followed by fat and umami taste. Studies on calorie processing and its conditioning by preceding taste sensations have started to delineate a dynamic pattern of brain activation associated with appetition. Our expanded understanding of taste processing in the brain from neuroimaging studies is poised to reveal novel prevention and treatment targets to help address overeating and obesity.

Idiopathic Chyluria with Nephrotic-range Proteinuria and Hypothyroidism

The patient was a 75-year-old man who was admitted to our hospital because of fatigue, leg edema and heavy proteinuria. Due to his cloudy urine and elevated triglyceride level in his urine, he was diagnosed with chyluria. Tests for infectious disease were negative, and lymphoscintigraphy showed no blockage in the lymphatic system. He was therefore diagnosed with idiopathic chyluria. Hypothyroidism was also found and his cloudy urine and heavy proteinuria disappeared without dietary modifications after starting levothyroxine treatment for hypothyroidism. The patient is currently being followed up in an outpatient clinic and is doing well, with no recurrence of chyluria.

Fatty acid transport receptor soluble CD36 and dietary fatty acid pattern in type 2 diabetic patients: a comparative study

Recently, it has been remarked that dietary fatty acids and fatty acid receptors might be involved in the aetiology of diabetes. Therefore, this study was conducted to determine the relationship between dietary fatty acid pattern, fatty food preferences and soluble CD36 (sCD36) and insulin resistance in type 2 diabetes mellitus (DM). The study was carried out with thirty-eight newly diagnosed type 2 DM patients and thirty-seven healthy volunteers, aged 30-65 years. In the study, socio-demographic characteristics, dietary fat type and fatty acid pattern of individuals were recorded. After anthropometric measurements were taken, blood CD36, glucose, TAG and insulin levels were analysed. The results showed that although the type of fatty acid intake did not differ between the groups (P>0·05), the consumption of olive oil in the type 2 DM group was lower than the control group (P0·05). Crucially, elevated sCD36 levels increased the type 2 DM risk (OR 1·21, P<0·05). In conclusion, sCD36 level may be a possible biomarker, independent from the dietary fatty acid pattern, for type 2 DM owing to its higher levels in these patients. Therefore, the new insights make CD36 attractive as a therapeutic target for diabetes.

A role for scavenger receptor B1 as a captor of specific fatty acids in taste buds of circumvallate papillae

Class B scavenger receptor family members, scavenger receptor B1 (SR-B1) and cluster of differentiation 36 (CD36), are broadly expressed cell-surface proteins, both of which are believed to serve as multifaceted players in lipid and lipoprotein metabolism in mammals. Because of its presence in the apical part of taste receptor cells within circumvallate taste buds and its ability to recognise long-chain fatty acids, CD36 has been believed to participate in the sensing of the lipid species within the oral cavity. However, there have been no attempts to address whether SR-B1 has such a role to date. In this study, by reverse transcription- polymerase chain reaction analysis, we detected SR-B1 mRNA in a total RNA sample isolated from the circumvallate papillae of mouse tongue. Immunohistochemical analysis of tongue sections from the animals revealed the expression of SR-B1 protein in a population of taste bud cells of circumvallate papillae. In addition, the pattern of staining in the papillae for SR-B1 agreed closely with that for CD36 in double immunostaining analysis. We performed a cell-free in-vitro assay utilising a peptide mimic of SR-B1 and provided evidence that the receptor could recognise certain of the unsaturated long-chain fatty acids such as oleic acid. Our present findings suggest an additional role for SR-B1 as a captor of specific fatty acids in the oral cavity of mammals and contribute to expanding our knowledge of the physiological function of the receptor.

Molecular mechanism of lipid-induced cardiac insulin resistance and contractile dysfunction

Long-chain fatty acids are the main cardiac substrates from which ATP is generated continually to serve the high energy demand and sustain the normal function of the heart. Under healthy conditions, fatty acid β-oxidation produces 50-70% of the energy demands with the remainder largely accounted for by glucose. Chronically increased dietary lipid supply often leads to excess lipid accumulation in the heart, which is linked to a variety of maladaptive phenomena, such as insulin resistance, cardiac hypertrophy and contractile dysfunction. CD36, the predominant cardiac fatty acid transporter, has a key role in setting the heart on a road to contractile dysfunction upon the onset of chronic lipid oversupply by translocating to the cell surface and opening the cellular 'doors' for fatty acids. The sequence of events after the CD36-mediated myocellular lipid accumulation is less understood, but in general it has been accepted that the excessively imported lipids cause insulin resistance, which in turn leads to contractile dysfunction. There are several gaps of knowledge in this proposed order of events which this review aims to discuss. First, the molecular mechanisms underlying lipid-induced insulin resistance are not yet completely disclosed. Specifically, several mediators have been proposed, such as diacylglycerols, ceramides, peroxisome proliferator-activated receptors (PPAR), inflammatory kinases and reactive oxygen species (ROS), but their relative contributions to the onset of insulin resistance and their putatively synergistic actions are topics of controversy. Second, there are also pieces of evidence that lipids can induce contractile dysfunction independently of insulin resistance. Perhaps, a more integrative view is needed, in which several lipid-induced pathways operate synergistically or in parallel to induce contractile dysfunction. Unraveling of these processes is expected to be important in designing effective therapeutic strategies to protect the lipid-overloaded heart.

Lingual CD36 and nutritional status differentially regulate fat preference in obesity-prone and obesity-resistant rats

Lingual fatty acid receptors (i.e. CD36) mediate the orosensory perception of fat/fatty acids and may contribute to the susceptibility to develop obesity. The current study tested the hypothesis that fat/fatty acid preference in obesity-prone (OP, Osborne-Mendel) and obesity-resistant (OR, S5B/Pl) rats is mediated by nutritional status and lingual CD36. To determine if nutritional status affected linoleic acid (LA) preference in OP and OR rats, rats were either fasted overnight or fed a high fat diet (60% kcal from fat). In OR rats, fasting increased the preference for higher concentrations of LA (1.0%), while consumption of a high fat diet decreased LA preference. In OP rats, fasting increased the preference for lower concentrations of LA (0.25%), however high fat diet consumption did not alter LA preference. To determine if lingual CD36 mediated the effects of an overnight fast on LA preference, the expression of lingual CD36 mRNA was assessed and the effect of lingual application of CD36 siRNA on LA preference was determined. Fasting increased lingual CD36 mRNA expression in OR rats, but failed to alter lingual CD36 mRNA in OP rats. Following an overnight fast, application of lingual CD36 siRNA led to a decrease in LA preference in OR, but not OP rats. Lingual application of CD36 siRNA was also used to determine if lingual CD36 mediated the intake and preference for a high fat diet in OP and OR rats. CD36 siRNA decreased the preference and intake of high fat diet in OR rats, but not OP rats. The results from this study suggest that the dysregulation of lingual CD36 in OP rats is a potential factor leading to increased fat intake and fat preference and an enhanced susceptibility to develop obesity.

CD36 gene polymorphism is associated with Alzheimer's disease

CD36 gene encodes a membrane glycoprotein (type B scavenger receptor) present on the surface of many types of cells and having multiple cellular functions ranging from angiogenesis to gustatory perception of fatty acids. Using a case control genetic association approach we have analyzed selected single nucleotide polymorphisms (SNP's) in a total of 859 patients with Alzheimer's disease (AD) and controls and have identified the allele A in rs3211892 polymorphism of CD36 gene as significantly increasing the risk of AD. Additionally we have investigated, in the same sample of control subjects and patients, SNP's in ApoE gene and confirmed that the previously identified AD-associated SNP's indeed increased the risk and decreased the age of onset of AD as reported by others earlier. Based on the current knowledge of CD36 biochemistry we propose that the AD risk-imparting variants of CD36 alter cholesterol homeostasis, oxidation stress or induce pathological inflammatory cascades. The SNP rs3211892 has previously been associated with heart disease and other conditions but the present study is the first to identify a significant association between variations in CD36 gene and the risk of Alzheimer's disease.

Iso-α-acids, Bitter Components of Beer, Prevent Inflammation and Cognitive Decline Induced in a Mouse Model of Alzheimer's Disease

Alongside the rapid growth in aging populations worldwide, prevention and therapy for age-related memory decline and dementia are in great demand to maintain a long, healthy life. Here we found that iso-α-acids, hop-derived bitter compounds in beer, enhance microglial phagocytosis and suppress inflammation via activation of the peroxisome proliferator-activated receptor γ. In normal mice, oral administration of iso-α-acids led to a significant increase both in CD11b and CD206 double-positive anti-inflammatory type microglia (p < 0.05) and in microglial phagocytosis in the brain. In Alzheimer's model 5xFAD mice, oral administration of iso-α-acids resulted in a 21% reduction in amyloid β in the cerebral cortex as observed by immunohistochemical analysis, a significant reduction in inflammatory cytokines such as IL-1β and chemokines including macrophage inflammatory protein-1α in the cerebral cortex (p < 0.05) and a significant improvement in a novel object recognition test (p < 0.05), as compared with control-fed 5xFAD mice. The differences in iso-α-acid-fed mice were due to the induction of microglia to an anti-inflammatory phenotype. The present study is the first to report that amyloid β deposition and inflammation are suppressed in a mouse model of Alzheimer's disease by a single component, iso-α-acids, via the regulation of microglial activation. The suppression of neuroinflammation and improvement in cognitive function suggests that iso-α-acids contained in beer may be useful for the prevention of dementia.

ERK1/2 activation in human taste bud cells regulates fatty acid signaling and gustatory perception of fat in mice and humans

Obesity is a major public health problem. An in-depth knowledge of the molecular mechanisms of oro-sensory detection of dietary lipids may help fight it. Humans and rodents can detect fatty acids via lipido-receptors, such as CD36 and GPR120. We studied the implication of the MAPK pathways, in particular, ERK1/2, in the gustatory detection of fatty acids. Linoleic acid, a dietary fatty acid, induced via CD36 the phosphorylation of MEK1/2-ERK1/2-ETS-like transcription factor-1 cascade, which requires Fyn-Src kinase and lipid rafts in human taste bud cells (TBCs). ERK1/2 cascade was activated by Ca2+ signaling via opening of the calcium-homeostasis modulator-1 (CALHM1) channel. Furthermore, fatty acid-evoked Ca2+ signaling and ERK1/2 phosphorylation were decreased in both human TBCs after small interfering RNA knockdown of CALHM1 channel and in TBCs from Calhm1-/- mice. Targeted knockdown of ERK1/2 by small interfering RNA or PD0325901 (MEK1/2 inhibitor) in the tongue and genetic ablation of Erk1 or Calhm1 genes impaired preference for dietary fat in mice. Lingual inhibition of ERK1/2 in healthy volunteers also decreased orogustatory sensitivity for linoleic acid. Our data demonstrate that ERK1/2-MAPK cascade is regulated by the opening of CALHM1 Ca2+ channel in TBCs to modulate orogustatory detection of dietary lipids in mice and humans.-Subramaniam, S., Ozdener, M. H., Abdoul-Azize, S., Saito, K., Malik, B., Maquart, G., Hashimoto, T., Marambaud, P., Aribi, M., Tordoff, M. G., Besnard, P., Khan, N. A. ERK1/2 activation in human taste bud cells regulates fatty acid signaling and gustatory perception of fat in mice and humans.

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.

Genetic variations of CD36 and low platelet CD36 expression - a risk factor for lipemic plasma donation in Taiwanese apheresis donors

BACKGROUND

New CD36 mutations are constantly being identified, although no study has specifically targeted a Taiwanese population. CD36 deficiency can result in dyslipid state and slow clearance of chylomicron. This could be linked to more frequent lipemic donations.

STUDY DESIGN AND METHODS

We used flow cytometric methods to study the CD36 deficiency in 640 regular volunteer platelet apheresis donors from Taipei blood centre. The coding exons of CD36 gene were sequenced in CD36-deficient individuals, and the allele frequencies of CD36 variants were determined in the larger population by mutation-specific PCR and oligonucleotide hybridization. Visual inspection of lipemic plasma was routinely performed on samples taken before commencement of apheresis. Individuals found to have lipemic plasma are deferred until next donation. We investigated the link between positive lipemic deferral record and low platelet CD36 expression status.

RESULTS

We found four donors (0·6%) with type I CD36 deficiency (both platelets and monocytes CD36(null) ) and six (1·0%) with type II CD36 deficiency (PLT: CD36(null) , monocyte: CD36(low) ). Six CD36 genetic variants were identified, two of them were novel, all but one are found exclusively in CD36(null) and CD36(low) expressors. Subjects with CD36 genetic variants also displayed deficient or reduced CD36 on monocytes. Donors with null or low PLT CD36 expression were more likely to have a lipemic deferral record than control subjects with normal PLT CD36 expression (X(2) = 27·36, odds ratio = 2·6, 95% conference interval: 1·8-3·8, P < 0·0001).

CONCLUSION

Through this study, we established a donor registry to supply CD36-negative platelets for patients in need.

The A allele of cluster of differentiation 36 (CD36) SNP 1761667 associates with decreased lipid taste perception in obese Tunisian women

Recent studies have suggested that excessive intake of dietary fat is associated with obesity. Some obese subjects have been reported to exhibit high thresholds for the gustatory detection of lipids via lipid receptors, such as cluster of differentiation 36 (CD36). We studied lingual detection thresholds for emulsions containing oleic acid in obese Tunisian women (n 203) using a three-alternative forced choice (3-AFC) method. Genotyping of the TNF-α (rs1800629), IL-6 (rs1800795) and CD36 (rs1761667) genes was performed to associate with lipid taste perception thresholds. The CD36 genotype distribution was as follows: GG (n 42), AG (n 102) and AA (n 59). Women with the CD36 GG genotype exhibited oral detection thresholds for oleic acid that were more than three times lower than those with the CD36 AA genotype. The present study confirms a high threshold of gustatory fat detection in obese women with the CD36 AA genotype, but there is no significant association with the IL-6 and TNF-α gene polymorphisms.

Fat sensing and metabolic syndrome

Overconsumption of dietary fat contributes to the development of obesity and metabolic syndrome. Recent evidence suggests that high dietary fat may promote these metabolic states not only by providing calories but also by inducing impaired control of energy balance. In normal metabolic states, fat interacts with various organs or receptors to generate signals for the regulation of energy balance. Many of these interactions are impaired by high-fat diets or in obesity, contributing to the development or maintenance of obesity. These impairments may arise largely from fundamental alterations in the hypothalamus where all peripheral signals are integrated to regulate energy balance. This review focuses on various mechanisms by which fat is sensed at different stages of ingestion, circulation, storage, and utilization to regulate food intake, and how these individual mechanisms are altered by high-fat diets or in obesity.

CD36- and GPR120-mediated Ca²⁺ signaling in human taste bud cells mediates differential responses to fatty acids and is altered in obese mice

BACKGROUND & AIMS

It is important to increase our understanding of gustatory detection of dietary fat and its contribution to fat preference. We studied the roles of the fat taste receptors CD36 and GPR120 and their interactions via Ca(2+) signaling in fungiform taste bud cells (TBC).

METHODS

We measured Ca(2+) signaling in human TBC, transfected with small interfering RNAs against messenger RNAs encoding CD36 and GPR120 (or control small interfering RNAs). We also studied Ca(2+) signaling in TBC from CD36(-/-) mice and from wild-type lean and obese mice. Additional studies were conducted with mouse enteroendocrine cell line STC-1 that express GPR120 and stably transfected with human CD36. We measured release of serotonin and glucagon-like peptide-1 from human and mice TBC in response to CD36 and GPR120 activation.

RESULTS

High concentrations of linoleic acid induced Ca(2+) signaling via CD36 and GPR120 in human and mice TBC, as well as in STC-1 cells, and low concentrations induced Ca(2+) signaling via only CD36. Incubation of human and mice fungiform TBC with lineoleic acid down-regulated CD36 and up-regulated GPR120 in membrane lipid rafts. Obese mice had decreased spontaneous preference for fat. Fungiform TBC from obese mice had reduced Ca(2+) and serotonin responses, but increased release of glucagon-like peptide-1, along with reduced levels of CD36 and increased levels of GPR120 in lipid rafts.

CONCLUSIONS

CD36 and GPR120 have nonoverlapping roles in TBC signaling during orogustatory perception of dietary lipids; these are differentially regulated by obesity.

Preference for linoleic acid in obesity-prone and obesity-resistant rats is attenuated by the reduction of CD36 on the tongue

Differential sensing of dietary fat and fatty acids by the oral cavity is proposed to regulate the susceptibility to obesity. In the current experiments, animals that differ in their susceptibility to obesity were used to investigate the influence of the oral cavity on the preference for the polyunsaturated fatty acid, linoleic acid. In experiment 1, the preference for differing concentrations of linoleic acid was determined in obesity-prone Osborne-Mendel (OM) and obesity-resistant S5B/Pl (S5B) rats. The preference threshold for linoleic acid was lower in S5B rats, compared with OM rats. To determine whether differences in linoleic acid preference threshold were related to innate strain differences in the fatty acid receptors on the tongue, the expression of GPR120, GPR40, and CD36 on the circumvallate papillae were assessed in OM and S5B rats. Results indicated that the expression of CD36, GPR40, and GPR120 did not differ between these two strains. Numerous studies have examined the role of CD36 on fat intake; therefore, in experiment 3, RNA interference was used to decrease the expression of CD36 on the tongues of OM and S5B rats, and the effect of decreased CD36 expression on linoleic acid preference was determined. CD36 siRNA attenuated linoleic acid preference for the most preferred concentration in both OM and S5B rats. Overall, these data indicate that there are innate differences in the preference threshold for linoleic acid in obesity-prone and obesity-resistant rats. Experimentally reducing the expression of CD36 on the circumvallate papillae attenuated the preference for linoleic acid in both strains.

Oro-gustatory perception of dietary lipids and calcium signaling in taste bud cells are altered in nutritionally obesity-prone Psammomys obesus

Since the increasing prevalence of obesity is one of the major health problems of the modern era, understanding the mechanisms of oro-gustatory detection of dietary fat is critical for the prevention and treatment of obesity. We have conducted the present study on Psammomys obesus, the rodent desert gerbil which is a unique polygenic natural animal model of obesity. Our results show that obese animals exhibit a strong preference for lipid solutions in a two-bottle test. Interestingly, the expression of CD36, a lipido-receptor, in taste buds cells (TBC), isolated from circumvallate papillae, was decreased at mRNA level, but remained unaltered at protein level, in obese animals. We further studied the effects of linoleic acid (LA), a long-chain fatty acid, on the increases in free intracellular calcium (Ca²⁺) concentrations, [Ca²⁺]i, in the TBC of P. obesus. LA induced increases in [Ca²⁺]i, largely via CD36, from intracellular pool, followed by the opening of store-operated Ca²⁺ (SOC) channels in the TBC of these animals. The action of this fatty acid on the increases in [Ca²⁺]i was higher in obese animals than that in controls. However, the release of Ca²⁺ from intracellular stores, studied also by employing thapsigargin, was lower in TBC of obese animals than control rodents. In this study, we show, for the first time, that increased lipid intake and altered Ca²⁺ signaling in TBC are associated with obesity in Psammomys obesus.

Functionality of fatty acid chemoreception: a potential factor in the development of obesity?

Excess dietary fat consumption is recognized as a strong contributing factor in the development of overweight and obesity. Understanding why some individuals are better than others at regulating fat intake will become increasingly important and emerging associative evidence implicates attenuated fatty acid sensing in both the oral cavity and gastrointestinal (GI) tract in the development of obesity. Functional implications of impaired fatty acid chemoreception include diminished activation of the gustatory system, the cephalic response and satiety. This review will focus on knowledge from animal and human studies supporting the existence of oral fatty acid chemoreception including putative oral detection mechanisms, and how sensitivity to fatty acids is associated with fat consumption and fatty food preference.

Fatty acid ethanolamides modulate CD36-mRNA through dietary fatty acid manipulation in Syrian Golden hamsters

Fatty acids convert to fatty acid ethanolamides which associate with lipid signalling, fat oxidation, and energy balance; however, the extent to which dietary fatty acids manipulation can impact such control processes through fatty acid ethanolamides-related mechanisms remains understudied. The objective was to examine the impact of diets containing 6% corn oil, high oleic canola oil, docosahexaenoic acid + high oleic canola oil, and fish oil on plasma and organ levels of fatty acid ethanolamides, peroxisome proliferator-activated receptor-α regulatory targets, and lipid metabolism in Syrian Golden hamsters. After 29 days, in plasma, animals that were fed fish oil showed greater (p < 0.05) oleoylethanolamide and lower (p < 0.05) arachidonoylethanolamide and palmitoylethanolamide levels compared with other groups, while animals fed canola oil showed higher (p < 0.05) oleoylethanolamide levels in proximal intestine and liver than groups that were fed coin oil and fish oil. The canola oil group showed elevated (p < 0.01) fat oxidation (%) and over 3.0-fold higher (p < 0.05) hepatic-CD36 expression compared with the corn oil group. Hepatic-lipogenesis was lower (p < 0.05) in hamsters that were fed DHA-canola oil compared with the corn oil group. To conclude, dietary fatty acids produced shifts in plasma and organ levels of arachidonoylethanolamide, oleoylethanolamide, and palmitoylethanolamid, which were accompanied by changes in gene expression, lipogenesis, and energy expenditure, suggesting mechanisms through which dietary fatty acids influence disease risk.

CD36 mRNA in the gastrointestinal tract is differentially regulated by dietary fat intake in obesity-prone and obesity-resistant rats

BACKGROUND

The gastrointestinal tract (GI) is important for detection and transport of consumed nutrients and has been implicated in susceptibility to diet-induced obesity in various rat strains.

AIMS

The current studies investigated the regulation of CD36, a receptor which facilitates uptake of long-chain fatty acids, in the GI tract of obesity-prone Osborne-Mendel and obesity-resistant S5B rats fed a high-fat diet.

METHODS

Osborne-Mendel and S5B rats consumed a high-fat diet (HFD, 55 % kcal from fat) or a low-fat diet (10 % kcal from fat) for either 3 or 14 days. CD36 messenger RNA (mRNA) levels were measured from circumvallate papillae of the tongue and from duodenal enterocytes.

RESULTS

In Osborne-Mendel rats, consumption of HFD for 3 and 14 days led to an increase in CD36 mRNA on circumvallate papillae and in duodenal enterocytes. CD36 mRNA levels were positively correlated with body weight gain and kilocalories consumed at 3 days. In S5B rats, consumption of HFD for 3 days did not alter CD36 mRNA levels on circumvallate papillae or in the duodenum. Duodenal CD36 levels were elevated in S5B rats following 14 days of HFD consumption. CD36 mRNA levels in the duodenum were positively correlated with body weight gain and kilocalories consumed at 14 days.

CONCLUSIONS

These data support the differential sensing of nutrients by two regions of the GI tract of obesity-prone and obesity-resistant rats consuming HFD and suggest a role for CD36 in the strain-specific susceptibility to obesity.

Fatty acid-binding protein expression in the gastrointestinal tract of calves and cows

Fatty acid-binding protein (FABP) has high affinity for long-chain fatty acids and appears to participate in the metabolism and intracellular transport of lipids. Liver- and intestinal-type FABP (L-FABP and I-FABP, respectively) are expressed in the small intestine. However, in the gastrointestinal tract of ruminants, expression and localization of FABPs are unknown. In this study, we investigated the expression of I-FABP and L-FABP in the gastrointestinal tract of cattle. I- and L-FABP had higher messenger RNA (mRNA) and protein expression levels in the duodenum and jejunum relatively to other gastrointestinal regions in both calves and cows. Furthermore, L-FABP mRNA and protein expression were high in the colon. Both these protein types were confirmed to be in the cytosol of jejunal epithelial cells, where they were found in the villi rather than in the crypts. We concluded that duodenal and jejunal FABPs might be involved in the metabolism of fatty acids mainly in epithelial cells in cattle.

Activation of oral trigeminal neurons by fatty acids is dependent upon intracellular calcium

The chemoreception of dietary fat in the oral cavity has largely been attributed to activation of the somatosensory system that conveys the textural properties of fat. However, the ability of fatty acids, which are believed to represent the proximate stimulus for fat taste, to stimulate rat trigeminal neurons has remained unexplored. Here, we found that several free fatty acids are capable of activating trigeminal neurons with different kinetics. Further, a polyunsaturated fatty acid, linoleic acid (LA), activates trigeminal neurons by increasing intracellular calcium concentration and generating depolarizing receptor potentials. Ion substitution and pharmacological approaches reveal that intracellular calcium store depletion is crucial for LA-induced signaling in a subset of trigeminal neurons. Using pseudorabies virus (PrV) as a live cell tracer, we identified a subset of lingual nerve-innervated trigeminal neurons that respond to different subsets of fatty acids. Quantitative real-time PCR of several transient receptor potential channel markers in individual neurons validated that PrV labeled a subset but not the entire population of lingual-innervated trigeminal neurons. We further confirmed that the LA-induced intracellular calcium rise is exclusively coming from the release of calcium stores from the endoplasmic reticulum in this subset of lingual nerve-innervated trigeminal neurons.

Role of gut nutrient sensing in stimulating appetite and conditioning food preferences

The discovery of taste and nutrient receptors (chemosensors) in the gut has led to intensive research on their functions. Whereas oral sugar, fat, and umami taste receptors stimulate nutrient appetite, these and other chemosensors in the gut have been linked to digestive, metabolic, and satiating effects that influence nutrient utilization and inhibit appetite. Gut chemosensors may have an additional function as well: to provide positive feedback signals that condition food preferences and stimulate appetite. The postoral stimulatory actions of nutrients are documented by flavor preference conditioning and appetite stimulation produced by gastric and intestinal infusions of carbohydrate, fat, and protein. Recent findings suggest an upper intestinal site of action, although postabsorptive nutrient actions may contribute to flavor preference learning. The gut chemosensors that generate nutrient conditioning signals remain to be identified; some have been excluded, including sweet (T1R3) and fatty acid (CD36) sensors. The gut-brain signaling pathways (neural, hormonal) are incompletely understood, although vagal afferents are implicated in glutamate conditioning but not carbohydrate or fat conditioning. Brain dopamine reward systems are involved in postoral carbohydrate and fat conditioning but less is known about the reward systems mediating protein/glutamate conditioning. Continued research on the postoral stimulatory actions of nutrients may enhance our understanding of human food preference learning.

Orosensory and Homeostatic Functions of the Insular Taste Cortex

The gustatory aspect of the insular cortex is part of the brain circuit that controls ingestive behaviors based on chemosensory inputs. However, the sensory properties of foods are not restricted to taste and should also include salient features such as odor, texture, temperature, and appearance. Therefore, it is reasonable to hypothesize that specialized circuits within the central taste pathways must be involved in representing several other oral sensory modalities in addition to taste. In this review, we evaluate current evidence indicating that the insular gustatory cortex functions as an integrative circuit, with taste-responsive regions also showing heightened sensitivity to olfactory, somatosensory, and even visual stimulation. We also review evidence for modulation of taste-responsive insular areas by changes in physiological state, with taste-elicited neuronal responses varying according to the nutritional state of the organism. We then examine experimental support for a functional map within the insular cortex that might reflect the various sensory and homeostatic roles associated with this region. Finally, we evaluate the potential role of the taste insular cortex in weight-gain susceptibility. Taken together, the current experimental evidence favors the view that the insular gustatory cortex functions as an orosensory integrative system that not only enables the formation of complex flavor representations but also mediates their modulation by the internal state of the body, playing therefore a central role in food intake regulation.

Decreased expression of CD36 in circumvallate taste buds of high-fat diet induced obese rats

Mammals spontaneously prefer lipid rich foods. Overconsumption of high-fat diet leads to obesity and related diseases. Recent findings indicate that taste may participate in the orosensory perception of dietary lipids and the fatty taste may contribute to a preference for and excessive consumption of dietary fat. CD36, a trans-membrane glycoprotein, which is located in the taste buds of circumvallate papillae of rodents, appears to be a plausible receptor for this fatty taste. Obese subjects present a stronger preference for fatty foods, though the mechanisms involved are complex and are not fully investigated. Our data from immunofluorescence and real-time RT-PCR showed that the expression levels of CD36 in circumvallate taste buds were significantly lower in high-fat diet induced obese rats as compared with that of control rats fed a normal diet. These results suggest that decreased expression of CD36 in circumvallate taste buds of high-fat diet induced obese rats may be associated with diminished fatty taste sensitivity and in order to compensate the preference for dietary fat, rats consume more fatty foods. Therapeutic strategies designed to alter or manipulate CD36 expression or function in taste buds may have important implications in treating obesity and related diseases.

The putative diabetic plasma marker, soluble CD36, is non-cleaved, non-soluble and entirely associated with microparticles

BACKGROUND

CD36 is a widely expressed cell surface receptor that binds lipoproteins, and its function has been implicated in many complications of the metabolic syndrome. A cell-free form of CD36, soluble CD36 (sCD36), has been reported in human plasma, found to be elevated in obesity and diabetes, and claimed as a marker of insulin resistance.

OBJECTIVE

To determine the nature of sCD36; in particular, whether sCD36 is truly soluble or, as hypothesized, is found as a component of circulating microparticles (MPs).

METHODS

Lipoproteins were fractionated by density gradient centrifugation, and plasma MPs were isolated by ultracentrifugation, size exclusion, and immunoprecipitation with CD36 detected by immunoblotting. MPs from plasma and activated platelets were analyzed by multicolor flow cytometry, with a DyLight-488 anti-CD36 conjugate in combination with antibodies against different cellular markers.

RESULTS

Cell-free plasma CD36 was not observed associated with lipoproteins and was not a proteolytic fragment; rather, it was associated with the plasma MP fraction, suggesting that sCD36 in the plasma of normal subjects is a product of circulating MPs. Cytometric and immunoblotting analyses of plasma from normal donors showed that these MPs were derived mainly from platelets. Analysis of in vitro activated platelets also showed that CD36 to be secreted in the form of MPs.

CONCLUSIONS

sCD36 is not a proteolytic product, but rather is associated with a specific subset of circulating MPs that can readily be analysed. This finding will enable more specific investigations into the cellular source of the increased levels of plasma CD36 found in subjects with diabetes.

Fatty acid detection during food consumption and digestion: Associations with ingestive behavior and obesity

The inability of humans to adequately regulate fat consumption is a salient contributor to the development of obesity. The macronutrients, fat, protein and carbohydrate, within foods are detected at various stages of consumption, during which their digestive products, fatty acids, amino acids and sugars, interact with chemosensory cells within the oral epithelium (taste receptor cells) and gastrointestinal (GI) tract (enteroendocrine cells). This chemoreception initiates functional responses, including taste perception, peptide secretion and alterations in GI motility, that play an important role in liking of food, appetite regulation and satiety. This review will summarize the available evidence relating to the oral and GI regulation of fat intake and how chemoreception at both locations is associated with digestive behavior, satiety and weight regulation.

Oral fatty acid signaling and intestinal lipid processing: support and supposition

There is increasing recognition that specialized processes once thought to be relatively isolated to the oral cavity (e.g., taste) and intestine (e.g., nutrient absorption) are better characterized as common and continuous. This is exemplified by accumulating evidence linking oral detection of dietary fats to their intestinal processing. This review first summarizes this literature focusing on purported gustatory signaling by free fatty acid stimulation and enterocyte lipid storage and mobilization in humans. It then willfully speculates on the possible functions of this integrated system. It is proposed that it may aid absorption of fat soluble nutrients, enhance acute energy intake, sustain intestinal function during long inter-meal intervals, modulate appetite and/or detoxify ingested compounds including free fatty acids.

Oral and gastrointestinal sensing of dietary fat and appetite regulation in humans: modification by diet and obesity

Dietary fat interacts with receptors in both the oral cavity and the gastrointestinal (GI) tract to regulate fat and energy intake. This review discusses recent developments in our understanding of the mechanisms underlying the effects of fat, through its digestive products, fatty acids (FAs), on GI function and energy intake, the role of oral and intestinal FA receptors, and the implications that changes in oral and small intestinal sensitivity in response to ingested fat may have for the development of obesity.

The gustatory cortex and multisensory integration

The central gustatory pathways are part of the brain circuits upon which rest the decision to ingest or reject a food. The quality of food stimuli, however, relies not only on their taste but also on properties such as odor, texture and temperature. We will review anatomical and functional evidence showing that the central gustatory system, in particular its cortical aspect, functions as an integrative circuit in which taste-responsive neurons also show sensitivity to somatosensory and olfactory stimulation. In addition, gustatory pathways are modulated by the internal state of the body, with neuronal responses to tastes changing according to variations in physiological parameters such as gastrointestinal hormones or blood glucose levels. Therefore, rather than working as the receptive field of peripheral taste receptor cells, the central gustatory pathways seem to operate as a multisensory system dedicated to evaluating the biological significance of intra-oral stimuli.

Fluorescent n-3 and n-6 very long chain polyunsaturated fatty acids: three-photon imaging in living cells expressing liver fatty acid-binding protein

Despite the considerable beneficial effects of n-3 and n-6 very long chain polyunsaturated fatty acids (VLC-PUFAs), very little is known about the factors that regulate their uptake and intracellular distribution in living cells. This issue was addressed in cells expressing liver-type fatty acid-binding protein (L-FABP) by real time multiphoton laser scanning microscopy of novel fluorescent VLC-PUFAs containing a conjugated tetraene fluorophore near the carboxyl group and natural methylene-interrupted n-3 or n-6 grouping. The fluorescent VLC-PUFAs mimicked many properties of their native nonfluorescent counterparts, including uptake, distribution, and metabolism in living cells. The unesterified fluorescent VLC-PUFAs distributed either equally in nuclei versus cytoplasm (22-carbon n-3 VLC-PUFA) or preferentially to cytoplasm (20-carbon n-3 and n-6 VLC-PUFAs). L-FABP bound fluorescent VLC-PUFA with affinity and specificity similar to their nonfluorescent natural counterparts. Regarding n-3 and n-6 VLC-PUFA, L-FABP expression enhanced uptake into the cell and cytoplasm, selectively altered the pattern of fluorescent n-6 and n-3 VLC-PUFA distribution in cytoplasm versus nuclei, and preferentially distributed fluorescent VLC-PUFA into nucleoplasm versus nuclear envelope, especially for the 22-carbon n-3 VLC-PUFA, correlating with its high binding by L-FABP. Multiphoton laser scanning microscopy data showed for the first time VLC-PUFA in nuclei of living cells and suggested a model, whereby L-FABP facilitated VLC-PUFA targeting to nuclei by enhancing VLC-PUFA uptake and distribution into the cytoplasm and nucleoplasm.