Medium-chain triglyceride-specific appetite is regulated by the β-oxidation of medium-chain fatty acids in the liver

Most studies on fat appetite have focused on long-chain triglycerides (LCTs) due to their obesogenic properties. Medium-chain triglycerides (MCTs), conversely, exhibit antiobesogenic effects; however, the regulation of MCT intake remains elusive. Here, we demonstrate that mice can distinguish between MCTs and LCTs, and the specific appetite for MCTs is governed by hepatic β-oxidation. We generated liver-specific medium-chain acyl-CoA dehydrogenase (MCAD)-deficient (MCADL-/-) mice and analyzed their preference for MCT and LCT solutions using glyceryl trioctanoate (C8-TG), glyceryl tridecanoate (C10-TG), corn oil, and lard oil in two-bottle choice tests conducted over 8 days. In addition, we used lick microstructure analyses to evaluate the palatability and appetite for MCT and LCT solutions. Finally, we measured the expression levels of genes associated with fat ingestion (Galanin, Qrfp, and Nmu) in the hypothalamus 2 h after oral gavage of fat. Compared with control mice, MCADL-/- mice exhibited a significantly reduced preference for MCT solutions, with no alteration in the preference for LCTs. Lick analysis revealed that MCADL-/- mice displayed a significantly decreased appetite for MCT solutions only while the palatability of both MCT and LCT solutions remained unaffected. Hypothalamic Galanin expression in control mice was elevated by oral gavage of C8-TG but not by LCTs, and this response was abrogated in MCADL-/- mice. In summary, our data suggest that hepatic β-oxidation is required for MCT-specific appetite but not for LCT-specific appetite. The induction of hypothalamic galanin upon MCT ingestion, dependent on hepatic β-oxidation, could be involved in the regulation of MCT-specific appetite.NEW & NOTEWORTHY Whether and how medium-chain triglyceride (MCT) intake is regulated remains unknown. Here, we showed that mice can discriminate between MCTs and LCTs. Hepatic β-oxidation participates in MCT-specific appetite, and hypothalamic galanin may be one of the factors that regulate MCT intake. Because of the antiobesity effects of MCTs, studying MCT-specific appetite may help combat obesity by promoting the intake of MCTs instead of LCTs.

Binding Interaction Between Lauric Acid and Cluster of Differentiation 36 Underpinned by a Fluorescence- Intensifying Assay

Cluster of differentiation 36 (CD36) is a scavenger receptor expressed in various vertebrate cells that contains diverse ligands, including long-chain fatty acids. This receptor has recently been suggested as a captor of specific volatile odorants (e.g., aliphatic acetates) in the mammalian nasal epithelium. This study used a fluorescence-intensifying assay to produce the first evidence that lauric acid, an odorous fatty acid, directly binds to CD36. This expansion of the repertoire of volatile ligands supports potential applications for nasal CD36. Our present findings could promote future research aimed at understanding the mechanisms of fatty acid interactions with CD36.

A point of view on human fat olfaction - do fatty derivatives serve as cues for awareness of dietary fats?

Fat (triglycerides) consumption is critical for the survival of animals, including humans. Being able to smell fat can be advantageous in judging food value. However, fat has poor volatility; thus, olfaction of fat seems impossible. What about fatty acids that comprise fat? Humans smell and discriminate medium-chain fatty acids. However, no conclusive evidence has been provided for the olfactory sense of long-chain fatty acids, including essential acids such as linoleic acid (LA). Instead, humans likely perceive the presence of essential fatty acids through the olfaction of volatile compounds generated by their oxidative breakdown (e.g., hexanal and γ-decalactone). For some people, such scents are pleasing, especially when they come from fruit. Nonetheless, it remains unclear whether the olfaction of these volatiles leads to the recognition of fat per se. Nowadays, people often smell LA-borne aldehydes such as E,E-2,4-decadienal that occur appreciably, for example, from edible oils during deep frying, and are pronely captivated by their characteristic "fatty" note, which can be considered a "pseudo-perception" of fat. However, our preference for such LA-borne aldehyde odors may be a potential cause behind the modern overdose of n-6 fatty acids. This review aims to provide a view of whether and, if any, how we olfactorily perceive dietary fats and raises future purposes related to human fat olfaction, such as investigating sub-olfactory systems for detecting long-chain fatty acids.

Post COVID-19 condition of the Omicron variant of SARS-CoV-2

Objectives

To investigate the prevalence of post coronavirus disease (COVID-19) condition of the Omicron variant in comparison to other strains.

Study design

A single-center cross-sectional study.

Methods

Patients who recovered from Omicron COVID-19 infection (Omicron group) were interviewed via telephone, and patients infected with other strains (control group) were surveyed via a self-reporting questionnaire. Data on patients’ characteristics, information regarding the acute-phase COVID-19, as well as presence and duration of COVID-19-related symptoms were obtained. Post COVID-19 condition in this study was defined as a symptom that lasted for at least 2 months, within 3 months of COVID-19 onset. We investigated and compared the prevalence of post COVID-19 condition in both groups after performing propensity score matching.

Results

We conducted interviews for 53 out of 128 patients with Omicron and obtained 502 responses in the control group. After matching cases with controls, 18 patients from both groups had improved covariate balance of the factors: older adult, female sex, obesity, and vaccination status. There were no significant differences in the prevalence of each post COVID-19 condition between the two groups. The number of patients with at least one post COVID-19 condition in the Omicron and control groups were 1 (5.6%) and 10 (55.6%) (p = 0.003), respectively.

Conclusions

The prevalence of post Omicron COVID-19 conditions was less than that of the other strains. Further research with a larger sample size is needed to investigate the precise epidemiology of post COVID-19 condition of Omicron, and its impact on health-related quality of life and social productivity.

Application of a novel fluorescence intensity assay: identification of distinct fatty acetates as volatile compounds that bind specifically to amino acid region 149-168 of a transmembrane receptor CD36

The cluster of differentiation 36 (CD36) is a transmembrane receptor expressed in various cells and has diverse lipid ligands. The expression of CD36 in the murine olfactory epithelium and its ability to recognize certain species of fatty aldehydes, a class of odor-active volatile compounds, have suggested a role for this receptor in the capture of specific odorants in the nasal cavity of mammals. However, the spectrum of CD36-recognizable volatile compounds is poorly understood. In this study, we employed our recently devised assay with fluorescently labeled peptides as probes (fluorescence intensity assay) and identified distinct fatty acetates as volatile compounds that bind specifically to amino acid region 149-168 of CD36 (eg dodecyl and tetradecyl acetates). The present findings demonstrate the utility of our assay for the discovery of novel CD36 ligands and support the notion that the receptor functions as a captor of volatile compounds in the mammalian olfactory system.

Assessment of direct binding interaction between CD36 and its potential lipid ligands using a peptide mimic of the receptor labeled with a fluorophore

Cluster of differentiation 36 (CD36) is a cell-surface receptor that recognizes diverse substances. We have presented indirect evidence that a short segment of the receptor comprising amino acids 149-168 contains a site for binding of its lipid ligands (e.g., distinct fatty acids and aldehydes). However, experimental support for their direct interactions is yet to be achieved. For this, we devised a fluorescence intensity assay, where a synthetic peptide consisting of CD36 amino acids 149-168 labeled with fluorescein isothiocyanate (FITC-CD36_149-168) and its variant peptides were used as positive and negative probes, respectively. First, we obtained results indicating that 1-palmitoyl-2-(5-keto-6-octenedioyl)phosphatidylcholine (an established CD36 ligand) but not 1-palmitoyl-2-arachidonyl-phosphatidylcholine (a non-ligand of the receptor) bound in a saturable and specific manner to FITC-CD36_149-168. Strikingly, the assay allowed us to provide the first evidence supporting direct and specific binding between the CD36 segment and fatty aldehydes (e.g., Z-11-hexadecenal). However, this method failed to illustrate specific interactions of the segment with fatty acids, such as oleic acid. Nonetheless, our findings offer further insight into the biologically relevant ligands and the role of CD36. In addition, we suggest that this fluorescence-based technique provides a convenient means to evaluate protein (peptide)-lipid interactions.

Length of stay, hospitalisation costs and in-hospital mortality of methicillin-susceptible and methicillin-resistant Staphylococcus aureus bacteremia in Japan

OBJECTIVES

To examine the length of stay, hospitalisation costs and case fatality of methicillin-susceptible and -resistant Staphylococcus aureus (MSSA and MRSA) bacteremia in Japan.

STUDY DESIGN

Retrospective cohort study. Patients with a diagnosis of S. aureus bacteremia who were admitted to a tertiary care hospital (the National Centre for Global Health and Medicine [NCGM]) in Tokyo, Japan, between 1st January 2016 and 31st December 2020 were included in the study.

METHODS

We combined Japan Nosocomial Infections Surveillance data and Diagnosis Procedure Combination data at NCGM from 2016 to 2020. The data were stratified into MSSA and MRSA groups. Length of stay (LoS), LoS after submission of a blood culture specimen (LoS-after), hospitalisation cost, hospitalisation costs per day and clinical outcome were compared after propensity score matching.

RESULTS

Median LoS was 46 (interquartile range [IQR] 28.5-64.5) days in the MSSA group and 66 (IQR 40-91) days in the MRSA group (P = 0.020). Median LoS-after was 38 (IQR 25-62.5) days and 45 (IQR 24-63) days (P = 0.691) in the MSSA and MRSA groups, respectively. Median hospitalisation cost was significantly higher in the MRSA group (26,035 [IQR 18,154-47,362] USD) than in the MSSA group (19,823 [IQR 13,764-32,042] USD) (P = 0.036), but cost per day was not (MRSA: 528.9 [IQR 374.9-647.4] USD; MSSA: 455.6 [IQR 359.2-701.7] USD; P = 0.990). Case fatality rate was higher in the MRSA group than in the MSSA group (22/60 vs 9/60, P = 0.012).

CONCLUSIONS

Patients with MRSA bacteremia had longer LoS and higher costs than those with MSSA bacteremia. However, LoS-after and hospitalisation costs per day were not different. The longer LoS of patients in Japan compared with other countries might contribute to the higher disease burden of S. aureus bacteremia in Japan.

AB1064 IMMUNOGLOBULIN G4-RELATED DISEASE (IgG4-RD): CLINICAL AND LABORATORY CHARACTERISTICS, TREATMENT RESPONSES AND PROGNOSIS IN ONE HUNDRED FIVE PATIENTS

Background:

IgG4-RD is a systemic fibro-inflammatory condition with incompletely understood that is capable of affecting multiple organs.

Objectives:

We aimed to investigate clinical and laboratory findings in Japanese patients with IgG4-RD.

Methods:

Dates on clinical characteristics, laboratory features, and treatment response from patients with IgG4-RD in our hospital were reviewed retrospectively from January 2004 to September 2019.

Results:

Among 105 patients were diagnosed and treated in our hospital, 48% were female and 88% were biopsy-proven. The median age of the patients was 66 years, and female were younger at their diagnosed age (p=0.04). Their medina duration of follow-up was 45 months. 48% of the patients had allergic history (including sinusitis, asthma, hay fever), younger patients tended to have allergy history. Mean serum IgE was 303 IU/dL (2-4965 IU/dL). Salivary and lacrimal grand involvement (63%) and dacryoadenitis and ocular and orbital inflammatory disease (56%), autoimmune pancratitis type 1 pancreatitis (18%), retroperitoneal fibrosis (16%), aortitis (15%) predominantly occurred. 84% of the patients had serum IgG4 higher than 135mg/dL, and high IgG and IgG4 concentration was associated with lower complements (CH50, C4) levels. Mean serum IgG was 1860 mg/dL (861-8432 mg/dL), and IgG4 was 449mg/dL (28-3210mg/dL). Male patients show higher serum IgG and IgG4 concentrations at baseline (p<0.01). Younger patients and low serum C4 level were associated with necessity of treatment, 60 of them used steroid, and the mean dose of prednisone they used was 30mg. Most of them responded well and tapering steroid. Steroid sparing agents were used in 23% of them. Although 23% of patients relapse as tapering steroid, 15% of them could stop treat with steroid. Retreatment with glucocorticoids is not associated with any factors. There were 14 malignancies in 13 patients during the follow-up period.

Conclusion:

Our study revealed that IgG4-RD occurred in middle age with allergic disease in Japanese patients. The pattern of head and neck was predominance. For the most part of the patient serum IgG and IgG4 concentrations was high. Serum low complement level could be associated with its diagnosis and necessity of treatment with steroid. Younger patients tend to treat with steroid and they responded well.

References:

[1]Clin Exp Allergy. 2009;39(4):469.

[2]Allergy. 2014 Feb;69(3):399-402. Epub 2013 Dec 31

[3]Rheumatology (Oxford). 2019 May 1;58(5):820-830.

[4]Am J Surg Pathol 2010 Dec;34(12):1812-9

[5]Ann Rheum Dis. 2020 Jan;79(1):77-87.

[6]Arthritis Res Ther 2018 Apr 10;20(1):65.

[7]Intern Med. 2014;53(3):171-6.

Disclosure of Interests:

None declared

Higher Straight-Chain Aliphatic Aldehydes: Importance as Odor-Active Volatiles in Human Foods and Issues for Future Research

Owing to their apparent lack of health significance, higher straight-chain aliphatic aldehydes, i.e., those having alkyl chains with more than six carbon atoms, have been largely neglected in food and nutraceutical research. However, they are an important class of odor-active volatiles in human foods. Indeed, certain aldehydes, such as hexanal, E-2-nonenal, and E, E-2,4-decadienal, serve as key odorants in a range of our foods and drinks. This perspective describes the significance of higher straight-chain aliphatic aldehydes as food odorants, focusing on several representative ones, and raises the issues regarding these aldehydes to be addressed in the future.

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.

A novel role for scavenger receptor B1 as a contributor to the capture of specific volatile odorants in the nasal cavity

Class B scavenger receptors, scavenger receptor B1 (SR-B1) and cluster of differentiation 36 (CD36), are broadly expressed cell-surface proteins and are believed to serve as multifaceted players in lipid and lipoprotein metabolism in mammals. Because of its ability to recognise distinct odour-active volatile compounds and its presence in murine olfactory epithelium, CD36 has recently emerged as a participant in the detection of odorants within the nasal cavity. However, there have been no attempts to assess whether SR-B1 has such a role. In this study, we performed a cell-free in-vitro assay utilising a peptide mimic of the receptor, and demonstrated that SR-B1 could recognise aliphatic aldehydes (e.g., tetradecanal), a distinct class of volatile odorants, as potential ligands. By reverse transcription-polymerase chain reaction and western immunoblot analyses, we detected the expression of SR-B1 mRNA and protein, respectively, in mouse olfactory tissue. Finally, we immunohistochemically mapped the distribution of SR-B1 in the surface layer of olfactory epithelium in vivo, which is the first line of odorant detection. These findings uncover a novel role for SR-B1 as a contributor to the capture of specific odorants in the nasal cavity of mammals.

CD36 involvement in the olfactory perception of oleic aldehyde, an odour-active volatile compound, in mice

Cluster of differentiation 36 (CD36) is a broadly expressed transmembrane receptor that has multiple ligands. It has been found to occur abundantly on the surface of the olfactory epithelium in mice and postulated to play a role in mammalian olfaction. However, there have been no ethological analyses of the mammalian behaviour showing CD36 involvement in the olfactory perception of a distinct odour-active volatile compound. In this study, we aimed to assess whether mammals perceive oleic aldehyde, an odour-active volatile that serves as a potential CD36 ligand, and if so, whether CD36 is involved in the sensing by following measurements using CD36-knockout mice and their wild-type littermates. In a two-bottle choice test, wild-type mice, but not CD36-knockout mice, discriminated a sucrose solution containing oleic aldehyde from the sucrose solution alone. To assess the importance of the olfactory system in the oleic aldehyde perception, we conducted an exploration test where the animals could rely primarily on the odour of test volatiles for recognition. We found that the wild-type, but not CD36-knockout mice, were aware of the compound. Our results provide behavioural evidence that CD36 plays a role in the perception of specific odour-active volatile compounds in the nasal cavity.

Assessment of direct interaction between CD36 and an oxidized glycerophospholipid species

Cluster of differentiation 36 (CD36) is a transmembrane protein that recognizes multiple diverse ligands. It is believed that (i) oxidized glycerophosphatidylcholine species having a terminal γ-hydroxyl(or oxo)-α,β-unsaturated carbonyl on the sn-2 acyl group (oxGPCCD36), which can occur on the surface of lipoprotein particles, serve as high-affinity ligands for CD36, and (ii) the amino acid 150-168 of CD36 (CD36150-168) is responsible for recognizing oxGPCCD36. However, it remains uncertain whether CD36150-168 directly interacts with oxGPCCD36 alone. In this study, we addressed this issue by investigating and comparing the banding pattern by non-denaturing polyacrylamide gel electrophoresis of a glutathione S-transferase (GST) fusion protein containing CD36150-168 (GST-CD36150-168), in the presence and absence of an oxGPCCD36 species, 1-(palmitoyl)-2-(5-keto-6-octenedioyl)phosphatidylcholine (KOdiA-PC). It was shown that GST-CD36150-168 pre-incubated with KOdiA-PC produced bands at upper positions than did the fusion protein alone. Further analyses revealed that the bands produced by the loading of GST-CD36150-168/KOdiA-PC mixture represent complexes consisting of the fusion protein and lipid. To our knowledge, this is the first evidence for direct interaction between CD36150-168 and oxGPCCD36 alone. It is also notable that the electrophoresis-based technique provides a convenient means to evaluate protein-lipid interactions.

A Search for CD36 Ligands from Flavor Volatiles in Foods with an Aldehyde Moiety: Identification of Saturated Aliphatic Aldehydes with 9-16 Carbon Atoms as Potential Ligands of the Receptor

Volatile compounds with an aldehyde moiety such as (Z)-9-octadecenal are potential ligands for cluster of differentiation 36 (CD36), a transmembrane receptor that has recently been shown to play a role in mammalian olfaction. In this study, by performing an assay using a peptide mimic of human CD36, we aimed to discover additional ligands for the receptor from volatiles containing a single aldehyde group commonly found in human foods. Straight-chain, saturated aliphatic aldehydes with 9-16 carbons exhibited CD36 ligand activities, albeit to varying degrees. Notably, the activities of tridecanal and tetradecanal were higher than that of oleic acid, the most potent ligand among the fatty acids tested. Among the aldehydes other than aliphatic aldehydes, only phenylacetaldehyde showed a weak activity. These findings make a contribution to our knowledge of recognition mechanisms for flavor volatiles in foods with an aldehyde group.

Immunohistochemical localization of fatty acid transporters and MCT1 in the sebaceous glands of mouse skin

The sebaceous glands secrete sebum to protect the epidermis and hairs by the oily products. The glands express several transporters and binding proteins for the production of fatty acids and uptake of their sources. The present immunohistochemical study examined the expression and localization of CD36, MCT1, FATP4, and E-FABP in the sebaceous glands, including the meibomian and preputial glands of mice. CD36 and MCT1 in sebaceous glands were largely co-localized along the plasma membrane of secretory cells, while they were separately expressed in the glandular portion of meibomian and preputial glands. Immunoreactivities for FATP4 and E-FABP appeared diffusely in the cytoplasm of secretory cells. Genetic deletion of CD36 did not affect the immunolocalization of the three other molecules. The sebaceous glands were judged to be useful for analyzing the functions and relation of fatty acid transporters and binding proteins.

A single aldehyde group can serve as a structural element for recognition by transmembrane protein CD36

Transmembrane protein CD36 is considered to bind its distinct ligands such as long-chain fatty acids primarily by recognizing their terminal carboxyl moiety. In this study, we provide evidence that long-chain fatty aldehydes, such as oleic aldehyde, can be recognized by CD36. We suggest that a single aldehyde group may also serve as one of the structural elements recognizable by CD36.

Mechanisms Involved in Guiding the Preference for Fat Emulsion Differ Depending on the Concentration

High-fat foods tend to be palatable and can cause addiction in mice via a reinforcing effect. However, mice showed preference for low fat concentrations that do not elicit a reinforcing effect in a two-bottle choice test with water as the alternative. This behavior indicates the possibility that the mechanism underlying fat palatability may differ depending on the dietary fat content. To address this issue, we examined the influences of the opioid system and olfactory and gustatory transductions on the intake and reinforcing effects of various concentrations of a dietary fat emulsion (Intralipid). We found that the intake and reinforcing effects of fat emulsion were reduced by the administration of an opioid receptor antagonist (naltrexone). Furthermore, the action of naltrexone was only observed at higher concentrations of fat emulsion. The intake and the reinforcing effects of fat emulsion were also reduced by olfactory and glossopharyngeal nerve transections (designated ONX and GLX, respectively). In contrast to naltrexone, the effects of ONX and GLX were mainly observed at lower concentrations of fat emulsion. These results imply that the opioid system seems to have a greater role in determining the palatability of high-fat foods unlike the contribution of olfactory and glossopharyngeal nerves.

Dynamics of Optically-Generated Carriers in Si (100) and Si (111) Substrate-Grown GaAs/AlGaAs Core-Shell Nanowires

GaAs/Al0.1Ga0.9As core-shell nanowires (CSNWs), with average lateral size of 125 nm, were grown on gold nanoparticle-activated Si (100) and Si (111) substrates via molecular beam epitaxy. Room temperature-photoluminescence (RT-PL) from the samples showed bulk-like GaAs and Al0.1Ga0.9As bandgap emission peaks at 1.43 and 1.56 eV, respectively. Higher PL emission intensity of the sample on Si (111) compared to that on Si (100) is attributed to uniform Al0.1Ga0.9As shell passivation of surface states on Si (111)-grown CSNWs. Carrier dynamics in two different temporal regimes were studied. In the sub-nanosecond time scale (300-500 ps), time-resolved radiative recombination efficiency of carriers was examined. In the 0-4 ps range, surface field-driven ballistic transport of carriers was probed in terms of the radiated terahertz (THz) waves. Time-resolved PL measurements at 300 K revealed that the carrier recombination lifetime of the GaAs core on Si (100)-grown CSNWs is 333 ps while that on Si (111)-grown sample is 500 ps. Ultrafast photoexcitation of GaAs core on the two samples generated a negligible difference in the intensity and bandwidth of emitted THz radiation. This result is ascribed to the fact that the deposited GaAs material on both substrates produced samples with comparable NW densities and similar GaAs core average diameter of about 75 nm. The samples' difference in GaAs core's carrier recombination lifetime did not influence THz emission since the two processes involve distinct mechanisms. The THz spectrum of CSNWs grown on Si (111) exhibited Fabry-Perot modes that originated from multiple reflections of THz waves within the Si substrate.

Behavioral palatability of dietary fatty acids correlates with the intracellular calcium ion levels induced by the fatty acids in GPR120-expressing cells

We recently reported that G-protein-coupled receptor 120 (GPR120) is expressed on taste buds, and that rodents showed preference for long-chain fatty acids (LCFA) at a low concentration. We also showed that the LCFA (1% linoleic acid) increased the extracellular dopamine (DA) level in the nucleus accumbens (NAc), which participates in reward behavior. However, the mechanism underlying the involvement of the GPR120-agonistic activity of LCFA in the palatability of dietary fat remains elusive. Therefore, we examined the association between the GPR120-agonistic activity and palatability of LCFA. First, we measured Ca(2+) signaling in HEK293 cells stably expressing GPR120 under stimulation by various LCFAs. We then assessed the palatability of the various LCFAs by testing the licking behavior in mice and measured the changes in the NAc-DA level by in vivo microdialysis. Consequently, 14- to 22-carbon unsaturated LCFAs showed strong GPR120-agonistic activity. Additionally, mice displayed high licking response to unsaturated 16- and 18-carbon LCFAs, and unsaturated 18-carbon LCFA significantly increased the DA level. The licking rate and the LCFA-dependent increase in DA level also correlated well with the GPR120- agonistic activity. These findings demonstrate that chemoreception of LCFA by GPR120 is involved in the recognition and palatability of dietary fat.

Expression of CD36 by Olfactory Receptor Cells and Its Abundance on the Epithelial Surface in Mice

CD36 is a transmembrane protein that is involved in the recognition of certain amphiphilic molecules such as polar lipids in various tissues and body fluids. So far, CD36 homologues in insects have been demonstrated to be present on the surface of olfactory dendrites and to participate in the perception of exogenous compounds. However, little is known about the relationship between CD36 and mammalian olfaction. Indeed, the detection of only CD36 mRNA in the mouse olfactory epithelium has been reported to date. In the present study, to provide potential pieces of evidence for the involvement of CD36 in mammalian olfactory perception, we extensively investigated the localisation of this protein in the mouse olfactory mucosa. In situ hybridisation analysis using antisense oligonucleotides to CD36 mRNA detected aggregated signals within the deeper epithelial layer of olfactory mucosa. The mRNA signals were also detected consistently in the superficial layer of the olfactory epithelium, which is occupied by supporting cells. Immunostaining with an anti-CD36 polyclonal antibody revealed that CD36 localises in the somata and dendrites of distinct olfactory receptor cells and that it occurs abundantly on the olfactory epithelial surface. However, immunoreactive CD36 was rarely detectable in the nerve bundles running in the lamina propria of olfactory mucosa, the axons forming the olfactory nerve layer in the outermost layer of the bulb and axon terminals in the glomeruli. We also obtained electron microscopic evidence for the association of CD36 protein with olfactory cilia. Altogether, we suggest that CD36 plays a role in the mammalian olfaction. In addition, signals for CD36 protein were also detected on or around the microvilli of olfactory supporting cells and the cilia of nasal respiratory epithelium, suggesting a role for this protein other than olfaction in the nasal cavity.

A matter of symmetry: terahertz polarization detection properties of a multi-contact photoconductive antenna evaluated by a response matrix analysis

While terahertz time domain spectroscopy (THz-TDS) is a well-established technique, polarization sensitive measurements are challenging due to the need of broadband polarization devices. Here, we characterize our recently introduced multi-contact photoconductive detector antenna with a response matrix analysis. We show that the lead lines attached to electrodes reduce the antenna symmetry and thereby influence the properties of the response matrices. With a wire grid polarizer, we simulate a sample influencing the polarization angle and the intensity of the incident THz pulse. Evaluating the measurements with the response matrix analysis, our results show a well agreement of the adjusted and measured polarization angles and intensities over a frequency range from 0.25 to 0.8 THz.

The opioid system majorly contributes to preference for fat emulsions but not sucrose solutions in mice

Rodents show a stronger preference for fat than sucrose, even if their diet is isocaloric. This implies that the preference mechanisms for fat and sucrose differ. To compare the contribution of the opioid system to the preference of fat and sucrose, we examined the effects of mu-, delta-, kappa-, and non-selective opioid receptor antagonists on the preference of sucrose and fat, assessed by a two-bottle choice test and a licking test, in mice naïve to sucrose and fat ingestion. Administration of non-selective and mu-selective opioid receptor antagonists more strongly inhibited the preference of fat than sucrose. While the preference of fat was reduced to the same level as water by the antagonist administration that of sucrose was still greater than water. Our results suggest that the preference of fat relies strongly on the opioid system, while that of sucrose is regulated by other mechanisms in addition to the opioid system.

A Role of a Lymphocyte Tryptase, Granzyme A, in Experimental Ulcerative Colitis

In the large-intestinal mucosae of rats orally administered dextran sulfate sodium, which induces an enteritis resembling ulcerative colitis (UC), the activity for granzyme A, a lymphocyte tryptase, increased at an earlier stage than that at which UC markers (growth-regulated gene product/cytokine-induced neutrophil chemoattractant-1 and caspase-3) increased. This suggests involvement of the enzyme in the exacerbation and perpetuation of enteritis.

Further validation of unsaturated long-chain fatty acids as inhibitors for oxidized low-density lipoprotein binding to CD36 via assays with synthetic CD36 peptide-cross-linked plates

We recently obtained evidence that unsaturated long-chain fatty acids (LCFAs) (e.g. oleic acid) inhibit binding of oxidized low-density lipoproteins (oxLDLs) to CD36. In the present study, we validated this prediction by examining inhibition by unsaturated LCFAs of Alexa-fluor-labeled oxLDL binding to multiwell plates onto which a synthetic CD36 peptide is covalently immobilized via thiol–maleimide coupling.

Unsaturated long-chain fatty acids inhibit the binding of oxidized low-density lipoproteins to a model CD36

Transmembrane protein CD36 binds multiple ligands, including oxidized low-density lipoproteins (oxLDLs) and long-chain fatty acids (LCFAs). Our aim was to determine whether LCFAs compete with oxLDLs for binding to CD36. We addressed this issue by examining the inhibitory effect of LCFAs against the binding of Alexa-fluor-labeled oxLDLs (AFL-oxLDL) to a synthetic peptide representing the oxLDL-binding site on CD36 (3S-CD36₁₅₀₋₁₆₈). All of the unsaturated LCFAs tested, inhibited the binding of AFL-oxLDL to 3S-CD36₁₅₀₋₁₆₈, albeit to varying degrees. For instance, the concentrations required for 50% inhibition of binding for oleic, linoleic, and α-linolenic acids were 0.25, 0.97, and 1.2 mM, respectively. None of the saturated LCFAs tested (e.g. stearic acid) exhibited inhibitory effects. These results suggest that at least unsaturated LCFAs can compete with oxLDLs for binding to CD36. The study also provides information on the structural requirements of LCFAs for inhibition of oxLDLs-CD36 binding.

A study of an aroma extraction method and evaluation of the aroma extract contribution to the palatability and reinforcement effect of dried bonito using mice

Japanese cuisine has provided satisfying meals by fully utilizing the characteristic aroma and taste of katsuodashi (dried bonito broth), though it is not rich in sugars or fats. Katsuodashi is a very basic and indispensable element in Japanese cuisine, and is a hot water extract of katsuobushi (dried bonito). It has been reported that a dextrin solution containing natural dried bonito broth has a significant reinforcement effect, and has been suggested that the olfactory stimulation is important for the reinforcement effect. We examined various source materials for broth and identified an optimal method of aroma extraction by two-bottle choice and conditioned place preference tests in mice. By two-bottle choice tests, a solution containing arabushi (a type of katsuobushi) aroma extract obtained by a supercritical CO2 extraction method showed a significantly high preference. The conditioned place preference test showed the dashi-taste solution with arabushi supercritical CO2 extract had a reinforcement effect. Our results suggest that the arabushi extract obtained by supercritical CO2 extraction contains components responsible for preference and reinforcement effects in mice; it could become conducive to making Japanese cuisine more satisfying and palatable.

Roles of CUB and LDL receptor class A domain repeats of a transmembrane serine protease matriptase in its zymogen activation

Matriptase is a type II transmembrane serine protease containing two complement proteases C1r/C1s-urchin embryonic growth factor-bone morphogenetic protein domains (CUB repeat) and four low-density lipoprotein receptor class A domains (LDLRA repeat). The single-chain zymogen of matriptase has been found to exhibit substantial protease activity, possibly causing its own activation (i.e. conversion to a disulfide-linked two-chain fully active form), although the activation seems to be mediated predominantly by two-chain molecules. Our aim was to assess the roles of CUB and LDLRA repeats in zymogen activation. Transient expression studies of soluble truncated constructs of recombinant matriptase in COS-1 cells showed that the CUB repeat had an inhibitory effect on zymogen activation, possibly because it facilitated the interaction of two-chain molecules with a matriptase inhibitor, hepatocyte growth factor activator inhibitor type-1. By contrast, the LDLRA repeat had a promoting effect on zymogen activation. The effect of the LDLRA repeat seems to reflect its ability to increase zymogen activity. The proteolytic activities were higher in pseudozymogen forms of recombinant matriptase containing the LDLRA repeat than in a pseudozymogen without the repeat. Our findings provide new insights into the roles of these non-catalytic domains in the generation of active matriptase.

Dietary fat ingestion activates β-endorphin neurons in the hypothalamus

The opioid system regulates food choice, consumption, and reinforcement processes, especially for palatable meals such as fatty food. β-Endorphin is known as an endogenous opioid peptide produced in neurons of the hypothalamus. In this study, we found that Intralipid (fat emulsion) ingestion increased c-fos expression in β-endorphin neurons. However, intragastric infusion of Intralipid only slightly increased c-fos expression 2h after infusion. Further, dissection of glossopharyngeal nerve, innervating posterior tongue taste buds, partially but significantly decreased the Intralipid-induced c-fos expression. These results indicate that mainly the orosensory stimulation from fat may activate β-endorphin neurons, thereby promoting β-endorphin release.

A recombinant catalytic domain of matriptase induces detachment and apoptosis of small-intestinal epithelial IEC-6 cells cultured on laminin-coated surface

Matriptase is a type-II transmembrane serine protease that is expressed strongly in the epithelial elements of various organs. In the small intestine, it is expressed prominently at the villus tip where aged epithelial cells undergo shedding and/or apoptosis. This observation, together with the ability of matriptase to cleave laminin (a basement membrane component critical for epithelial cell attachment), prompted us to hypothesize that it plays an important part in the removal of aged epithelial cells in the small intestine. We tested this hypothesis by determining whether a recombinant catalytic domain of rat matriptase (His(6)t-S-CD) causes detachment and/or apoptosis of small-intestinal epithelial IEC-6 cells. His(6)t-S-CD caused detachment of cells attached to laminin-coated plates but did not detach cells attached to fibronectin- or type-IV collagen-coated plates. Pre-treatment of laminin-coated plates with His(6)t-S-CD decreased the attachment of cells, suggesting that the recombinant matriptase caused detachment through a mechanism involving a direct effect on laminin. His(6)t-S-CD was also found to induce apoptosis in the cells cultured on laminin-coated plates, as assessed by annexin-V staining, DNA fragmentation and caspase-3 activity assays. These findings support our hypothesis regarding the role of matriptase in the small intestine.

Identification of the matriptase second CUB domain as the secondary site for interaction with hepatocyte growth factor activator inhibitor type-1

Matriptase is a type II transmembrane serine protease comprising 855 amino acid residues. The extracellular region of matriptase comprises a noncatalytic stem domain (containing two tandem repeats of complement proteases C1r/C1s-urchin embryonic growth factor-bone morphogenetic protein (CUB) domain) and a catalytic serine protease domain. The stem domain of matriptase contains site(s) for facilitating the interaction of this protease with the endogenous inhibitor, hepatocyte growth factor activator inhibitor type-1 (HAI-1). The present study aimed to identify these site(s). Analyses using a secreted variant of recombinant matriptase comprising the entire extracellular domain (MAT), its truncated variants, and a recombinant HAI-1 variant with an entire extracellular domain (HAI-1-58K) revealed that the second CUB domain (CUB domain II, Cys(340)-Pro(452)) likely contains the site(s) of interest. We also found that MAT undergoes cleavage between Lys(379) and Val(380) within CUB domain II and that the C-terminal residues after Val(380) are responsible for facilitating the interaction with HAI-1-58K. A synthetic peptide corresponding to Val(380)-Asp(390) markedly increased the matriptase-inhibiting activity of HAI-1-58K, whereas the peptides corresponding to Val(380)-Val(389) and Phe(382)-Asp(390) had no effect. HAI-1-58K precipitated with immobilized streptavidin resins to which a synthetic peptide Val(380)-Pro(392) with a biotinylated lysine residue at its C terminus was bound, suggesting direct interaction between CUB domain II and HAI-1. These results led to the identification of the matriptase CUB domain II, which facilitates the primary inhibitory interaction between this protease and HAI-1.

Granzyme A and thrombin differentially promote the release of interleukin-8 from alveolar epithelial A549 cells

Some of extracellular serine proteases with trypsin-like specificity of cleavage have been known to increase the release of inflammatory mediators from various cell types. For instance, two well-known trypsin-like serine proteases circulating in blood, granzyme A (GrA) and thrombin, have been found to promote interleukin (IL)-8 release from an alveolar epithelial A549 cell line. However, the mechanisms by which the proteases promote IL-8 release from the cells are not fully understood. In the present study, using A549 cells we found that (1) thrombin promoted IL-8 release from the cells via a mechanism partially involving activation of protease-activated receptor-1, a G-protein coupled receptor, whereas a recombinant form of GrA (rGrA) did it via a mechanism that does not involve the receptor activation; that (2) unlike rGrA, thrombin did not cause detachment and microtubule disruption of the cells; and that (3) the release of IL-8 induced by rGrA was inhibited in the presence of taxol, a microtubule-stabilizing reagent, whereas that induced by thrombin was not. These findings suggest that rGrA and thrombin promote the release of IL-8 from A549 cells through distinct mechanisms.

Intragastric infusion of glucose enhances the rewarding effect of sorbitol fatty acid ester ingestion as measured by conditioned place preference in mice

We investigated substances that induce a rewarding effect during the postingestive process using the conditioned place preference (CPP) test. Although mice showed high affinity for a low-energy fat substitute--sorbitol fatty acid esters and low-concentration linoleic acid solution--they did not exhibit a place preference toward a voluntary intake of fat substitute in the CPP test. However, during a conditioning session of CPP that involved intragastric administration of corn oil immediately before the intake of the fat substitute, the test mice displayed a place preference. Similarly, intragastric administration of glucose, galactose, and dextrin also induced CPP; however, fructose, mannose, and a nonmetabolized carbohydrate did not. These results suggest that administration of corn oil and glucose has the same postingestive effect with regard to inducing CPP and that the structural specificity of carbohydrates influences the postingestive effect.

The optimal activity of a pseudozymogen form of recombinant matriptase under the mildly acidic pH and low ionic strength conditions

Matriptase is a transmembrane serine protease that is strongly expressed in epithelial cells. The single-chain zymogen of matriptase is considered to have inherent activity, leading to its own activation (i.e. conversion to the disulphide-linked-two-chain form by cleavage after Thr-Lys-Gln-Ala-Arg614). Also, there is growing evidence that the activation of zymogen occurs at the cell surface and in relation to the acidification and lowering of ionic strength within cell-surface microenvironments. The present study aimed to provide evidence for the involvement of zymogen activity in its activation in physiologically relevant cellular contexts. For this purpose, the activity of a pseudozymogen form of recombinant matriptase (HL-matriptase zymogen) was examined using acetyl-l-Lys-l-Thr-l-Lys-l-Gln-l-Leu-l-Arg-4-methyl-coumaryl-7-amide as a substrate. HL-matriptase zymogen exhibited optimal activity toward the substrate pH approximately 6.0. The substrate hydrolysis at the pH value was hardly detected when NaCl was present at a concentration of 145 mM. In a buffer of pH 6.0 containing 5 mM NaCl, the activity of HL-matriptase zymogen was only approximately 30-times lower than that of the respective two-chain form. These findings suggest that the in vivo activation of matriptase zymogen occurs via a mechanism involving the zymogen activity.

Requirement of the activity of hepatocyte growth factor activator inhibitor type 1 for the extracellular appearance of a transmembrane serine protease matriptase in monkey kidney COS-1 cells

Hepatocyte growth factor activator inhibitor type I (HAI-1) is a membrane-bound, serine protease inhibitor with two protease-inhibitory domains (Kunitz domain I and II). HAI-1 is known as a physiological inhibitor of a membrane-bound serine protease, matriptase. Paradoxically, however, HAI-1 has been found to be required for the extracellular appearance of the protease in an expression system using a monkey kidney COS-1 cell line. In the present study, we show using COS-1 cells that co-expression of recombinant variants of HAI-1 with the inhibition activity toward matriptase, including a variant consisting only of Kunitz domain I (the domain responsible for inhibition of matriptase), allowed for the appearance of this protease in the conditioned medium, whereas that of the variants without the activity did not. These findings suggest that the inhibition activity toward matriptase is critical for the extracellular appearance of protease in COS-1 cells.

Involvement of the cytoplasmic juxtamembrane region of matriptase in its exclusive localization to the basolateral membrane domain of Madin-Darby canine kidney epithelial cells

Matriptase is a type II transmembrane serine protease. This protease is strongly expressed in simple epithelial cells such as enterocytes and kidney tubular cells in which the plasma membranes are separated into apical and basolateral domains. Although matriptase was found previously to occur exclusively on the basolateral membrane of enterocytes, the underlying mechanism of localization is unclear. In the present study, a full-length rat matriptase and a chimera consisting of the cytoplasmic and transmembrane regions of the protease and green fluorescent protein (designated as 1-86GFP) were found to localize exclusively to the basolateral membrane domain when expressed in Madin-Darby canine kidney epithelial cells. Mutagenesis analysis of 1-86GFP revealed that the matriptase cytoplasmic juxtamembrane amino acid residues (Lys45, Val47, and Arg50) play a role in mediating the localization in the cells. This study provides the first evidence that matriptase carries information for its localization in simple epithelia.

Activation of a membrane-bound serine protease matriptase on the cell surface

Matriptase is a type II transmembrane serine protease. The activation (i.e. conversion of the single-chain pro-form to the disulphide-linked-two-chain active form) of this enzyme is known to occur via a mechanism requiring its catalytic triad. We reported previously that the activated enzyme was produced in the conditioned medium when full-length rat matriptase was expressed in monkey kidney COS-1 cells. The present study aimed to address when and where the matriptase activation occurs. COS-1 cells expressing matriptase were labelled with a membrane-impermeable biotin derivative and then solubilized with Triton. Both activated and non-activated matriptase molecules were detected in the avidin precipitants of Triton extracts, whereas only the non-activated molecules were detected in the flow-through fraction of avidin-precipitation procedure. Single-chain matriptase has been thought to have an inherent activity. Indeed, a secreted single-chain variant of recombinant matriptase bearing mutation at the activation-cleavage site was found to exhibit the activity in hydrolyzing a synthetic peptide substrate at pH 7.5. However, the variant had little activity at pH 5.5, as found in the lumen of post-Golgi secretory vesicles. Altogether, it is concluded that the activation of matriptase may occur when the enzyme reaches the cell surface.

Carrageenan inhibits granzyme A-induced detachment of and interleukin-8 release from alveolar epithelial A549 cells

Granzyme A (GrA) is a lymphocyte serine protease that is believed to enter virus-infected cells and growing tumors and induce apoptosis. We found recently that recombinant rat GrA (rGrA) promotes detachment of and interleukin (IL)-8 release from alveolar epithelial A549 cells and suggested that this protease is involved in the pathogenesis of certain inflammatory lung diseases. In the present study, we found that lambda-carrageenan (a sulfated oligosaccharide constituting the cell walls of seaweeds) potently inhibits rGrA-induced detachment and IL-8 release of A549 cells. This sulfated oligosaccharide might be useful for suppressing the development of inflammatory lung diseases in which GrA is thought to be involved.

Mercaptoacetate inhibition of fatty acid β-oxidation attenuates the oral acceptance of fat in BALB/c mice

We investigated the effect of β-oxidation inhibition on the fat ingestive behavior of BALB/c mice. Intraperitoneal administration to mice of mercaptoacetate, an inhibitor of fatty acid oxidation, significantly suppressed intake of corn oil but not intake of sucrose solution or laboratory chow. To further examine the effect of mercaptoacetate on the acceptability of corn oil in the oral cavity, we examined short-term licking behavior. Mercaptoacetate significantly and specifically decreased the number of licks of corn oil within a 60-s period but did not affect those of a sucrose solution, a monosodium glutamate solution, or mineral oil. In contrast, the administration of 2-deoxyglucose, an inhibitor of glucose metabolism, did not affect the intake or short-term licking counts of any of the tasted solutions. These findings suggest that fat metabolism is involved in the mechanism underlying the oral acceptance of fat as an energy source.

Development of an in vitro system for screening the ligands of a membrane glycoprotein CD36

It has well been known that human and rodents exhibit a preference for fats. This suggests the existence of an orosensory system responsible for the detection of dietary fats. A plasma membrane glycoprotein CD36, besides the role in the uptake of long-chain fatty acids (LCFAs) as well as oxidized low-density lipoprotein (OxLDL) in a variety of cells, has been postulated to be a candidate fat taste receptor on the tongue. Therefore, molecules that bind with CD36 to cause intracellular signaling but have fewer calories could be substitutes for dietary fats. In the present study, we developed an in vitro system for the screening of CD36 ligands using Chinese hamster ovary-K1 cells (CHO-K1) stably transfected with human or mouse CD36. When incubated with OxLDL labeled with fluorescence dye, the fluorescence was much higher in the transfected CHO-K1 cells than in non-transfected CHO-K1 cells. Incubation of the transfected cells with OxLDL caused a rapid phosphorylation of extracellular signal regulated kinase, and the degree was significantly higher compared with that in non-transfected CHO-K1 cells. The expression system using CHO-K1 cells could be a convenient tool to screen the novel ligands of CD36.