Monosodium L-glutamate added to a high-energy, high-protein liquid diet promotes gastric emptying

Maternal antibiotic treatment affects offspring gastric sensing for umami taste and ghrelin regulation in the pig

Background

Scarce is knowledge on the process regulating the development of acid secretion, orexigenic signaling, and chemosensing in the stomach of young pigs. Changes of early microbial encounters by suckling pigs can interact with the gut maturation, by the induction of different molecular signaling. Our goal was to assess if the age of offspring and the maternal environment, influenced by sow antibiotic treatment peripartum, could affect gastric morphology and the expression of genes involved in the control of hydrochloric secretion, feed intake, taste, and inflammation in offspring stomach.

Methods

84 pigs from sows fed a diet with amoxicillin (on –d10 to +d21 from farrowing, ANT) or without (CON) were sacrificed at d14, d21, d28 (weaning) or d42. Samples of oxyntic (OXY), pyloric (PY) and cardiac mucosae close to OXY were collected and parietal and enteroendocrine cells (EECs) were counted. Relative gene expression of a set of 11 key genes (ATP4A, SSTR2, GAST, GHRL, MBOAT4, PCSK1, GNAT1, TAS1R1, TAS1R3, IL8 and TNF) was assessed by qRT-PCR. In addition, 40 offspring obtained from the same ANT and CON sows were offered a normal or a fat-enriched diet for 4 weeks between 140 and 169 d of age, and then OXY and PY were sampled.

Results

The number of parietal and EECs increased with age (P < 0.001). ATP4A increased with age (within suckling, P = 0.043, post-weaning vs. suckling, P < 0.001), SSTR2 increased only after weaning (P < 0.001). In OXY, GHRL increased during suckling (P = 0.012), and post-weaning as a trend (P = 0.088). MBOAT4 tended to increase during suckling (P = 0.062). TAS1R1 increased from suckling to post-weaning period (P =0.001) and was lower in ANT offspring (P = 0.013). GNAT1 in PY was higher in ANT offspring (P = 0.041). Antibiotic treatment of sows peripartum increased expression of GHRL and MBOAT4 in OXY of growing-finishing offspring aged 5 months.

Conclusions

Data show that sensing for umami taste and ghrelin regulation can be affected by maternal environment, but the development of acid secretion, orexigenic signaling and taste perception in the stomach are mostly developmentally controlled.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00557-3.

Potential effects of umami ingredients on human health: Pros and cons

Umami taste is the most recent confirmed basic taste in addition to sour, sweet, bitter, and salty. It has been controversial because of its effects on human nutritional benefit. Based on the available literatures, this review categorized 13 positive and negative effects of umami taste on human health. On the positive side, umami taste can improve food flavor and consumption, improve nutrition intake of the elderly and patients, protect against duodenal cancer, reduce ingestion of sodium chloride, decrease consumption of fat, and improve oral functions. On the other hand, umami taste can also induce hepatotoxicity, cause asthma, induce migraine headaches, damage the nervous system, and promote obesity. Due to its novelty, there are many functions and effects of umami taste waiting to be discovered. With further investigation, more information regarding the effects of umami taste on human health will be discerned.

Gastric Emptying of Elemental Liquid Diets Versus Semisolid Diets in Bedridden Gastrostomy-fed Patients

BACKGROUND

Aspiration is a common problem in bedridden gastrostomy-fed patients. We compared gastric emptying of an elemental liquid diet and a commercial semisolid diet in bedridden gastrostomy-fed patients.

METHODS

Study 1: from January 2013 to December 2016, consecutive bedridden patients receiving percutaneous endoscopic gastrostomy (PEG) semisolid feeding hospitalized due to aspiration pneumonia were switched to elemental liquid diet feedings. The frequency of defecation, tube feed contents aspirated from the trachea, and aspiration pneumonia during hospitalization were retrospectively reviewed. Study 2 was a randomized, crossover trial comparing C sodium acetate gastric emptying of a commercial elemental liquid or a commercial semisolid diet in bedridden PEG patients and controls.

RESULTS

Study 1: 18 patients were enrolled. Elemental liquid diet was aspirated from the trachea in 1 (5.6%) (once in 24 observations); neither aspiration pneumonia nor diarrhea developed during elemental liquid diet feeding over 2 weeks observation. Study 2: 8 PEG patients and 8 healthy subjects were separately randomized to assess gastric emptying of the commercial elemental and semisolid diets. The elemental liquid diet was associated with a significant decrease of the 10%, 30%, or 50% emptying (excretion) time (P<0.05) and an increased the area under the curve (% dose/h) compared with the commercial semisolid diet (P<0.05). In healthy subjects there was no significant difference in gastric empting between the 2 diets.

CONCLUSIONS

Elemental liquid diets emptied more rapidly from the stomach than semisolid diets in bedridden PEG patients. They may prevent or reduce aspiration pneumonia compared with semisolid diets.

Reduction in Gastroesophageal Reflux Disease Symptoms Is Associated with Miso Soup Intake in a Population-Based Cross-Sectional Study: The Nagahama Study

Dietary habits and lifestyles are considered to affect the frequency of epigastric symptoms. In our previous study, we found that three amino acids in Japanese broth promoted gastric emptying. We hypothesized that a higher consumption of miso soup which was mainly composed of Japanese broth and miso paste would be associated with a lower frequency of epigastric symptoms. We conducted a cross-sectional study of the association between frequency of miso soup intake and reflux or dyspepsia symptoms in a general Japanese population. Sixteen items of dietary habits were assessed using a self-reported questionnaire, and epigastric symptoms were evaluated using the Frequency Scale for Symptoms of Gastroesophageal Reflux Disease (FSSG). We fitted generalized linear models to analyze the association between miso soup intake and FSSG, reflux, or dyspepsia scores adjusted by age, sex, body mass index (BMI), another 15 dietary habits, smoking, drinking alcohol, and unfavorable dietary behaviors. A total of 9,364 subjects were included in the analysis. Trend analysis revealed that higher frequency of miso soup intake was associated with lower FSSG scores (p<0.001). In a generalized linear model, daily intake of miso soup was associated with lower FSSG, reflux, and dyspepsia scores independent of age, sex, BMI, other 15 dietary habits, smoking, drinking alcohol, and unfavorable dietary behaviors (estimate=-0.46, -0.22, and -0.27, respectively; 95% CI=-0.83, -0.12; -0.38, -0.07; and -0.47, and -0.08, respectively). Dairy intake of miso soup was associated with lower epigastric symptoms.

Dietary composition modulates impact of food-added monosodium glutamate on behaviour, metabolic status and cerebral cortical morphology in mice

Effects of food-added monosodium glutamate (MSG) on neurobehaviour, serum biochemical parameters, malondialdehyde (MDA) levels, and changes in cerebral cortex, liver and kidney morphology were assessed in mice fed standard diet (SD) or high-fat diet (HFD). Animals were assigned to 8 groups [SD control, HFD control, and six groups fed MSG plus SD or HFD at 0.1, 0.2 and 0.4 g/kg of feed]. Animals were fed for 8 weeks, behavioural tests were conducted, and blood was taken for estimation of biochemical parameters and MDA level. Whole brain was homogenised for neurochemical assays, while the cerebrum, liver and kidneys were processed for histology. In groups fed MSG/SD, there was a decrease in weight gain, increase in food-intake, an increase in locomotion, a decrease in rearing/grooming, and a decrease in anxiety-response. Also observed were derangements in biochemical parameters, increased MDA, and alteration of renal morphology. Compared to HFD, MSG/HFD groups had reduction in weight gain, food-intake, grooming and anxiety-response, an increase in locomotion, and improved memory. Protection against biochemical derangements and HFD-induced organ injuries were also observed. In conclusion, the findings suggest that possible interactions that may occur between dietary constituents and MSG are determinants of the effects of food-added MSG in mice.

Nuclear magnetic resonance-based metabolomics approach to evaluate preventive and therapeutic effects of Gastrodia elata Blume on chronic atrophic gastritis

Chronic atrophic gastritis (CAG) is one of the most common digestive system diseases worldwide which defined by WHO as initial step of cancer. Gastrodia elata Blume (GEB) is a traditional herbal with multiple pharmacological activities which was widely used in Asian countries. This study aims to explore the preventive and therapeutical effects of Gastrodia elata Blume on auto-immune induced CAG in rats. Tissues of stomachs were collected and submitted to ¹H NMR-based metabolomics analysis and histopathological inspection. The biochemical indexes of MDA, SOD, GSH, NO and XOD were measured. Gastrodia elata Blume could apparently ameliorate the damaged gastric glands and the biochemical parameters, enhance gastric acid secretion, and significantly relieve the inflammation of the stomach. Orthogonal signal correction-partial least squares-discriminant analysis (OSC-PLS-DA) of NMR profiles and correlation network analysis revealed that Gastrodia elata Blume could effectively treat CAG via regulating energy and purine metabolisms, and by anti-oxidation and anti-inflammation effects.

Nutrient-Sensing Biology in Mammals and Birds

Nutrient-sensing mechanisms have emerged as the fringe articulating nutritional needs with dietary choices. Carbohydrate, amino acid, fatty acid, mineral, and water-sensing receptors are highly conserved across mammals and birds, consisting of a repertoire of 22 genes known to date. In contrast, bitter receptors are highly divergent and have a high incidence of polymorphisms within and between mammals and birds and are involved in the adaptation of species to specific environments. In addition, the expression of nutrient-sensing genes outside the oral cavity seems to mediate the required decision-making dialogue between the gut and the brain by translating exogenous chemical stimuli into neuronal inputs, and vice versa, to translate the endogenous signals relevant to the nutritional status into specific appetites and the control of feed intake. The relevance of these sensors in nondigestive systems has uncovered fascinating potential as pharmacological targets relevant to respiratory and cardiovascular diseases.

Effects of three major amino acids found in Japanese broth on glucose metabolism and gastric emptying

OBJECTIVES

To our knowledge, the effect of the broth of dried kelp and dried bonito, dashi, on glucose metabolism and digestion has rarely been studied. Based on the component analysis of three actual broths served in traditional restaurants, a chemically synthesized broth with three free amino acids (histidine, glutamate, aspartate) and salt was prepared to investigate their effect on glucose metabolism, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide 1 (GLP-1) secretion, and digestion.

METHODS

In study 1, seven healthy individuals were enrolled in a four-period crossover study. Participants drank or ate hot water, synthesized broth, hot water with rice, and synthesized broth with rice. Plasma glucose, serum insulin, plasma glucagon, plasma GIP, and plasma GLP-1 were measured at baseline and after ingestion. In study 2, 6 of the 7 individuals ingested rice steamed with 13C-labeled sodium acetate with hot water or synthesized broth to estimate gastric emptying by the 13C-labeled acetate breath test in a two-period crossover trial.

RESULTS

Ingesting water or synthesized broth alone elicited no change in plasma glucose or serum insulin levels. Ingesting synthesized broth with rice resulted in a rapid rise in plasma glucose and GLP-1 (P = 0.01 and 0.02, respectively) in an early postprandial phase compared with that by ingesting water with rice, but the area under the curve of those showed no significant differences. Ingesting synthesized broth with rice resulted in a significantly higher gastric emptying coefficient than that after rice with water (P = 0.03).

CONCLUSIONS

Three amino acids and sodium chloride corresponding to those found in actual broth promoted gastric emptying and led to a rapid response of plasma glucose. Our findings suggest that ingestion of the broth of dried kelp and dried bonito may improve gastric motility.

Dietary glutamine, glutamic acid and nucleotide supplementation accelerate carbon turnover (δ13C) on stomach of weaned piglets

The use of stable isotope analysis as a tool for characterization of carbon turnover (δ13C) in piglet's tissues by tracing its feeding system has drawn attention. Thus, this study aimed at evaluating the influence of dietary glutamine, glutamic acid and nucleotides supplementation on carbon turnover in fundic-stomach region of weaned piglets at an average age of 21 days. The diets consisted of additive-free diet - control (C); 1% glutamine (G); 1% glutamic acid (GA) and 1% nucleotides (Nu). At weaning day (day 0: baseline), 3 piglets were slaughtered to quantify the δ13C of stomach. The remaining 120 piglets were blocked by weight and sex, randomly assigned to pens with 3 piglets slaughtered per treatment at days 1, 2, 4, 5, 7, 9, 13, 20, 27 and 49 after weaning in order to verify the fundic-stomach isotopic composition by treatments. Samples were analyzed in terms of 13C/12C ratio by mass spectrometry and converted to relative isotopic enrichment values (δ13C ‰) used to plot the first order exponential curves over time using OriginPro 8.0 software. The inclusion of glutamine, glutamate and nucleotides in piglet's diets has accelerated the carbon turnover in stomach during the post-weaning period, demonstrating also that glutamate has guaranteed fastest 13C incorporation rate on fundic-stomach region and pH-lowering. Besides that, stable isotopes technique (δ13C) has proved to be an important methodology to determine the time-scales at which piglets shift among diets with different isotopic values, characterizing the trophic effects of additives and the phenotypic flexibility of stomach.

Increased Subjective Distaste and Altered Insula Activity to Umami Tastant in Patients with Bulimia Nervosa

The aim of this study was to examine differences in brain neural activation in response to monosodium glutamate (MSG), the representative component of umami, between patients with bulimia nervosa (BN) and healthy women (HW) controls. We analyzed brain activity after ingestion of an MSG solution using functional magnetic resonance imaging (fMRI) in a group of women with BN (n = 18) and a group of HW participants (n = 18). Both groups also provided a subjective assessment of the MSG solution via a numerical rating scale. The BN group subjectively rated the MSG solution lower in pleasantness and liking than the control group, although no difference in subjective intensity was noted. The fMRI results demonstrated greater activation of the right insula in the BN group versus the control group. Compared with the HW controls, the BN patients demonstrated both altered taste perception-related brain activity and more negative hedonic scores in response to MSG stimuli. Different hedonic evaluation, expressed as the relative low pleasing taste of umami tastant and associated with altered insula function, may explain disturbed eating behaviors, including the imbalance in food choices, in BN patients.

Effects of straight alkyl chain, extra hydroxylated alkyl chain and branched chain amino acids on gastric emptying evaluated using a non-invasive breath test in conscious rats

Aim: Some amino acids been known to influence gastric emptying. Thus we have evaluated the effects of straight alkyl chain, extra hydroxylated alkyl chain and branched chain amino acids on gastric emptying. Materials and Methods: Gastric emptying was evaluated in rats after feeding with Racol (nutrient formulae) containing [1-¹³C] acetic acid. Using a breath test, the content of ¹³CO₂ in their expired air was measured by infrared analyzers. Rats were orally administered with test amino acids, while control rats were administered orally with distilled water. Results: The expired ¹³CO₂ content in the expired air increased with time, peaked after about 30 min and decreased thereafter. Among the amino acids having an alkyl chain, l-serine, l-alanine and l-glycine, significantly decreased the ¹³CO₂ content and Cmax, and delayed Tmax, suggesting inhibition and delay of gastric emptying. AUC_120 min values of l-alanine and l-glycine also decreased significantly. l-Threonine significantly decreased ¹³CO₂ content and delayed Tmax, but had no influence on Cmax and AUC_120 min values, suggesting a delay of gastric emptying. l-Isoleucine and l-leucine and l-valine significantly decreased ¹³CO₂ content, suggesting inhibition of the gastric emptying, but Cmax, Tmax and AUC_120 min values were not significantly affected. Conclusion: The results show that the amino acids used in the present study had different effects on gastric emptying. Moreover, it was found that inhibition and delay of gastric emptying were clearly classifiable by analyzing the change in ¹³CO₂ content of the expired air and the Cmax, Tmax and AUC_120 min values.

An Interesting Tour of New Research Results on Umami and Umami Compounds

Knowledge about the fifth basic taste, the umami taste, has been investigated by many scientists in the last years and continues to gain importance. Therefore, a lot of scientific studies were conducted to explore several effects influencing the mechanism of umami, which is elicited and enhanced by defined concentrations of MSG (monosodium glutamate) and umami compounds. This paper covers the most relevant scientific literature regarding umami, its use as a flavor enhancer, and the latest umami compounds, which have been released in the last ten years. The main goal of this overview was to summarize the most important results which were related to umami as one of the five basic tastes, the umami taste receptor, the essential role of umami in a great number of physiological mechanisms, and the MSG symptom complex. Furthermore, the function of umami in the interaction of taste, aftertaste and olfactory pathways has been discussed.

L-Arginine L-Glutamate Enhances Gastric Motor Function in Rats and Dogs and Improves Delayed Gastric Emptying in Dogs

Amino acids are not only constituents of proteins, but also have multiple physiologic functions. Recent findings have revealed that ingested amino acids either activate luminal receptors or are metabolized, causing physiologic reactions in the gastrointestinal (GI) tract. We examined the effect of oral L-arginine L-glutamate (ArgGlu), a pharmaceutical amino acid salt used i.v. for the treatment of hyperammonemia, on gastric motor function in rats and dogs. Gastric emptying was determined using phenol red and ¹³C-breath test methods, whereas gastric relaxation was determined using the barostat method. ArgGlu (10-30 mg/kg, p.o.) dose-dependently promoted gastric emptying in rats. This effect was dependent on vagus nerve activation and comparable to that of the prokinetic mosapride. Intragastric ArgGlu (3-30 mg/kg intragastrically) also dose-dependently enhanced adaptive relaxation of rat stomachs, which was negated not by vagotomy of gastric branches, but by pretreatment with N omega-nitro-L-arginine methyl ester (20 mg/kg i.v.), a nitric oxide synthase inhibitor. Its relaxing effect on the stomach was also confirmed in dogs and was equally as efficacious as treatment with sumatriptan (1-3 mg/kg s.c.). ArgGlu (30 mg/kg p.o.) significantly reduced the half gastric emptying time in clonidine-induced delayed gastric emptying of solids in dogs, and its effect was comparable to that of cisapride (3 mg/kg p.o.). This study demonstrated that the pharmaceutical ingredient ArgGlu, currently used i.v., enhanced gastric motor function when administered orally, suggesting that it could be a new oral medicine indicated for treatment of upper GI hypofunction or dysfunction like functional dyspepsia.

Association between individual response to food taste and gastroesophageal symptoms

OBJECTIVE

Taste is an important element in food preferences. Gastroesophageal reflux disease (GERD) is related to lifestyles including eating habits. We aimed to investigate the relationship between responses to specific tastes and GERD.

METHODS

Altogether 280 patients including 170 men with a mean age of 58.6 years were included in the study to determine the relationship between their liking for specific tastes and GERD using a new self-administered questionnaire (responses to various tastes and participants' sensitivity to taste and hot food and on the frequency of stomatitis). Another self-administrated questionnaire was administrated for a diagnosis of GERD (the frequency scale for the symptoms of GERD cut-off score of 10). Furthermore, 142 of 280 patients who had received esophagogastroduodenoscopy (EGD) were investigated on the association between endoscopic esophagitis and their favorite tastes.

RESULTS

In the association analyses between responses to specific tastes and GERD, the group liking salty food and the group with a high frequency of stomatitis had a significantly higher incidence of GERD (salty food: odds ratio [OR] 2.059, 95% confidence interval [CI] 1.215-3.488, P = 0.0073; stomatitis: OR 2.861, 95% CI 1.558-5.253, P = 0.0007, respectively). In association analyses with endoscopic esophagitis, the groups liking salty and sour food had a significantly higher incidence rate of endoscopic esophagitis (salty: OR 2.718, 95% CI 1.330-5.555, P = 0.0061; sour: OR 3.267, 95% CI 1.491-7.160, P = 0.0031, respectively).

CONCLUSIONS

Sensitivity and response to specific food taste were associated with GERD. The results of a preference to hot or salty food and endoscopic esophagitis suggest that physical stimuli are important for esophageal injuries.

Sudden unexpected fatal encephalopathy in adults with OTC gene mutations-Clues for early diagnosis and timely treatment

Background

X-linked Ornithine Transcarbamylase deficiency (OTCD) is often unrecognized in adults, as clinical manifestations are non-specific, often episodic and unmasked by precipitants, and laboratory findings can be normal outside the acute phase. It may thus be associated with significant mortality if not promptly recognized and treated. The aim of this study was to provide clues for recognition of OTCD in adults and analyze the environmental factors that, interacting with OTC gene mutations, might have triggered acute clinical manifestations.

Methods

We carried out a clinical, biochemical and molecular study on five unrelated adult patients (one female and four males) with late onset OTCD, who presented to the Emergency Department (ED) with initial fatal encephalopathy. The molecular study consisted of OTC gene sequencing in the probands and family members and in silico characterization of the newly detected mutations.

Results

We identified two new, c.119G>T (p.Arg40Leu) and c.314G>A (p.Gly105Glu), and three known OTC mutations. Both new mutations were predicted to cause a structural destabilization, correlating with late onset OTCD. We also identified, among the family members, 8 heterozygous females and 2 hemizygous asymptomatic males. Patients' histories revealed potential environmental triggering factors, including steroid treatment, chemotherapy, diet changes and hormone therapy for in vitro fertilization.

Conclusions

This report raises awareness of the ED medical staff in considering OTCD in the differential diagnosis of sudden neurological and behavioural disorders associated with hyperammonemia at any age and in both genders. It also widens the knowledge about combined effect of genetic and environmental factors in determining the phenotypic expression of OTCD.

Both dietary supplementation with monosodium L-glutamate and fat modify circulating and tissue amino acid pools in growing pigs, but with little interactive effect

BACKGROUND

The Chinese population has undergone rapid transition to a high-fat diet. Furthermore, monosodium L-glutamate (MSG) is widely used as a daily food additive in China. Little information is available on the effects of oral MSG and dietary fat supplementation on the amino acid balance in tissues. The present study aimed to determine the effects of both dietary fat and MSG on amino acid metabolism in growing pigs, and to assess any possible interactions between these two nutrients.

METHODS AND RESULTS

Four iso-nitrogenous and iso-caloric diets (basal diet, high fat diet, basal diet with 3% MSG and high fat diet with 3% MSG) were provided to growing pigs. The dietary supplementation with fat and MSG used alone and in combination were found to modify circulating and tissue amino acid pools in growing pigs. Both dietary fat and MSG modified the expression of gene related to amino acid transport in jejunum.

CONCLUSIONS

Both dietary fat and MSG clearly influenced amino acid content in tissues but in different ways. Both dietary fat and MSG enhance the absorption of amino acids in jejunum. However, there was little interaction between the effects of dietary fat and MSG.

Gastric emptying and duodenal motility upon intake of a liquid meal with monosodium glutamate in healthy subjects

Glutamate is thought to serve as a special signal for gut functions. We investigated the effects of monosodium l‐glutamate (MSG) on gastric emptying and duodenal motility. Ten healthy male volunteers underwent rapid magnetic resonance imaging (MRI) of the abdomen. Coronal images were successively acquired after ingestion of liquid meal (200 kcal in 200 mL: 9 g protein, 28.4 g carbohydrate, 5.6 g fat, 370 mg Na⁺) with and without 0.5% MSG. During the acquisition of MRI, participants breathed freely. In all participants, the gastric residual volume gradually decreased to 80.1 ± 14.2% without MSG and to 75.9 ± 14.3% with MSG after 60 min (P = 0.45 between the groups, n = 10). In two of 10 participants, gastric emptying slowed down significantly, whereas in the remaining eight participants, gastric residual volume decreased to 84.0 ± 13.1% without MSG, and to 73.0 ± 14.6% with MSG after 60 min (P = 0.015, n = 8). There was no difference in the shape of the stomach between groups. In four of the eight participants responding positively to MSG, the duodenum wall was sufficiently identified to quantify the motions. The inclusion of MSG enhanced duodenal motility, judging from changes in (1) the magnitude of the duodenal area, (2) the center of gravity, and (3) the mean velocity of the wall motions. The third parameter most significantly indicated the excitatory effect of l‐glutamate on duodenum motility (~ three‐ to sevenfold increase during 60 min, P < 0.05, n = 4). These results suggest that MSG accelerates gastric emptying by facilitating duodenal motility, at least in subjects with positive responses to MSG.

The gut and brain share many neurotransmitters and hormones, thereby gut motility frequently reflects mental conditions in humans. So far, procedures to quantify gut motility in vivo have not yet been established. This study of abdominal rapid magnetic resonance imaging (MRI) demonstrates that monosodium L‐glutamate (MSG) accelerates gastric emptying by facilitating duodenal motility, at least in subjects with positive responses to MSG.

Taste receptors of the gut: emerging roles in health and disease

Recent progress in unravelling the nutrient-sensing mechanisms in the taste buds of the tongue has triggered studies on the existence and role of chemosensory cells in the gut. Indeed, the gastrointestinal tract is the key interface between food and the human body and can sense basic tastes in much the same way as the tongue, through the use of similar G-protein-coupled taste receptors. These receptors 'taste' the luminal content and transmit signals that regulate nutrient transporter expression and nutrient uptake, and also the release of gut hormones and neurotransmitters involved in the regulation of energy and glucose homeostasis. Hence, they play a prominent role in the communication between the lumen, epithelium, smooth muscle cells, afferent nerve fibres and the brain to trigger adaptive responses that affect gastrointestinal function, food intake and glucose metabolism. This review summarises how sensing of nutrients by taste receptors along the gut plays a key role in the process of digestion, and how disturbances or adaptations of these chemosensory signalling pathways may contribute to the induction or resolution of a number of pathological conditions related to diabetes, obesity, or diet-induced symptom generation in irritable bowel syndrome. Targeting these receptors may represent a promising novel route for the treatment of a number of these diseases.

Supplementing monosodium glutamate to partial enteral nutrition slows gastric emptying in preterm pigs(1-3)

Emerging evidence suggests that free glutamate may play a functional role in modulating gastroduodenal motor function. We hypothesized that supplementing monosodium glutamate (MSG) to partial enteral nutrition stimulates gastric emptying in preterm pigs. Ten-day-old preterm, parenterally fed pigs received partial enteral nutrition (25%) as milk-based formula supplemented with MSG at 0, 1.7, 3.0, and 4.3 times the basal protein-bound glutamate intake (468 mg·kg(-1)·d(-1)) from d 4 to 8 of life (n = 5-8). Whole-body respiratory calorimetry and (13)C-octanoic acid breath tests were performed on d 4, 6, and 8. Body weight gain, stomach and intestinal weights, and arterial plasma glutamate and glutamine concentrations were not different among the MSG groups. Arterial plasma glutamate concentrations were significantly higher at birth than after 8 d of partial enteral nutrition. Also at d 8, the significant portal-arterial concentration difference in plasma glutamate was substantial (∼500 μmol/L) among all treatment groups, suggesting that there was substantial net intestinal glutamate absorption in preterm pigs. MSG supplementation dose-dependently increased gastric emptying time and decreased breath (13)CO2 enrichments, (13)CO2 production, percentage of (13)CO2 recovery/h, and cumulative percentage recovery of (13)C-octanoic acid. Circulating glucagon-like peptide-2 (GLP-2) concentration was significantly increased by MSG but was not associated with an increase in intestinal mucosal growth. In contrast to our hypothesis, our results suggest that adding MSG to partial enteral nutrition slows the gastric emptying rate, which may be associated with an inhibitory effect of increased circulating GLP-2.

Elemental diets may reduce the risk of aspiration pneumonia in bedridden gastrostomy-fed patients

OBJECTIVES

Our clinical experience suggested that elemental diets were associated with a reduction in aspiration pneumonia among bedridden patients with percutaneous endoscopic gastrostomy (PEG). We compared the effects of elemental and standard liquid diets on the risk of clinical aspiration pneumonia and gastric emptying in bedridden patients receiving PEG feedings.

METHODS

Study 1: consecutive bedridden PEG patients received elemental diets or standard liquid diets in the same fashion. The frequency of defecation, diet aspirated from the trachea, and aspiration pneumonia during hospitalization were prospectively recorded. Study 2: a randomized, crossover trial using elemental or standard liquid diets containing (13)C sodium acetate as a tracer given to bedridden PEG patients who had experienced aspiration pneumonia. (13)C breath tests were performed to estimate gastric emptying.

RESULTS

Study 1: 127 patients were enrolled, 60 with elemental and 67 with standard liquid diets. The diet was aspirated from the trachea in none (0%) with the elemental diet vs. 8 (11.9%) with standard liquid diets (P=0.0057); aspiration pneumonia developed none with the elemental diet vs. 5 (7.5%) with standard liquid diets (P=0.031) (number needed to treat 14, 95% confidence interval 7-85). Study 2: 19 patients were enrolled. The elemental diet was associated with a significant increase in the 10, 30 or 50% emptying (excretion) time (P<0.001) and increased the area under the curve (% dose/h) compared with the standard liquid diet (P<0.05).

CONCLUSIONS

Elemental diets were associated with more rapid gastric empting and fewer episodes of aspiration than standard liquid diets in bedridden PEG patients. They may be preferred for bedridden PEG patients especially who have experienced aspiration pneumonia. Properly performed randomized-controlled trials are needed to prove this potential benefit.

Nutrient sensing in the gut: new roads to therapeutics?

The release of gut hormones involved in the control of food intake is dependent on the acute nutritional status of the body, suggesting that chemosensory mechanisms are involved in the control of their release. G protein-coupled taste receptors similar to those in the lingual system, that respond to sweet, bitter, umami, and fatty acids, are expressed in endocrine cells within the gut mucosa, and coordinate, together with other chemosensory signaling elements, the release of hormones that regulate energy and glucose homeostasis. In health, these nutrient sensors are likely to function as inhibitors to excessive nutrient exposure, and their malfunction may be responsible for a variety of metabolic dysfunctions associated with obesity; they may thus be considered as new therapeutic targets.

Monosodium glutamate stimulates secretion of glucagon-like peptide-1 and reduces postprandial glucose after a lipid-containing meal

BACKGROUND

Monosodium l-glutamate (MSG) is known to influence the endocrine system and gastrointestinal (GI) motility. The mechanism of postprandial glycemic control by food in the GI tract is mostly unknown and of great interest.

AIM

To investigate the effect of MSG on glucose homeostasis, incretin secretion and gastric emptying in humans after a lipid-containing meal.

METHODS

Thirteen healthy male volunteers (mean age, 25.5 years) and with no Helicobcter pylori infection were enrolled. A 400 mL (520 kcal) liquid meal with MSG (2 g, 0.5% wt:vol) or NaCl (control) was ingested in a single-blind placebo-controlled cross-over study. Blood glucose, serum insulin, plasma glucagon, plasma glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide were measured. Gastric emptying was monitored by a 13C acetate breath test. Postprandial symptoms were assessed on a visual analogue scale.

RESULTS

The 30-min postprandial glucose concentration was significantly reduced by adding MSG to the test meal. The area under the glucose concentration vs. time curve (0-60 min) was also significantly reduced by adding MSG (40.6 ± 3.51 mg·1 hr/dL with MSG vs. 49.2 ± 3.86 mg·1 hr/dL with NaCl, P = 0.047), whereas, the 30-min postprandial plasma GLP-1 level was significantly increased (58.1 ± 15.8 pmol/L with MSG vs. 13.4 ± 15.8 pmol/L with NaCl, P = 0.035). MSG did not affect the half gastric emptying time or postprandial symptoms.

CONCLUSIONS

Monosodium l-glutamate improved early postprandial glycaemia after a lipid-containing liquid meal. This effect was not associated with a change in gastric emptying, but was possibly related to stimulation of glucagon-like peptide-1 secretion.

Nutritional and physiological significance of luminal glutamate-sensing in the gastrointestinal functions

Recent evidence indicates that free amino acids are nutrients as well as acting as chemical transmitters within the gastrointestinal tract. Gut glutamate research is the most advanced among 20 amino acids. Free glutamate carries the umami taste sensation on the tongue and a visceral sensation in the gut, especially the stomach. In the field of taste physiology, the physiological meaning of the glutamate-derived chemical sense, the umami taste, has been proposed to be a marker of protein intake. Experimental evidence in gut glutamate physiology strongly supports this hypothesis. Free glutamate is sensed by the abdominal vagus and regulates gastrointestinal functions such as secretion and emptying to accelerate protein digestion. Clinical application of glutamate has also just begun to treat gastrointestinal disorders such as dyspepsia, ulcer, dry mouth and functional dyspepsia. In this review, we introduce recent advances in gut glutamate research and consider the possible contribution of glutamate to health.

New therapeutic strategy for amino acid medicine: effects of dietary glutamate on gut and brain function

The gustatory and visceral stimulation from food regulates digestion and nutrient utilization, and free glutamate (Glu) release from food is responsible for the umami taste perception that increases food palatability. The results of recent studies reveal a variety of physiological roles for Glu. For example, luminal applications of Glu into the mouth, stomach, and intestine increase the afferent nerve activities of the glossopharyngeal nerve, the gastric branch of the vagus nerve, and the celiac branch of the vagus nerve, respectively. Additionally, luminal Glu evokes efferent nerve activation of each branch of the abdominal vagus nerve. The intragastric administration of Glu activates several brain areas (e.g., insular cortex, limbic system, and hypothalamus) and has been shown to induce flavor-preference learning in rats. Functional magnetic resonance imaging of rats has shown that the intragastric administration of Glu activates the nucleus tractus solitarius, amygdala, and lateral hypothalamus. In addition, Glu may increase flavor preference as a result of its postingestive effect. Considering these results, we propose that dietary Glu functions as a signal for the regulation of the gastrointestinal tract via the gut-brain axis and contributes to the maintenance of a healthy life.

Dietary free glutamate prevents diarrhoea during intra-gastric tube feeding in a rat model

Recent studies indicate that l-glutamate (l-Glu), abundant in many foods, is a stimulator of gastric vagal afferent nerves. The aim of the present study was to examine the possibility that l-Glu supplementation of a protein-rich liquid diet may prevent the incidence of diarrhoea during repetitive intra-gastric tube feeding. The gastric vagal afferent nerve recording of rats indicated that intra-gastric administration of a protein-rich liquid diet supplemented with 0·5 % monosodium glutamate enhanced the basal afferent activities seen with the protein-rich diet alone. The examination of the faeces showed that the addition of monosodium glutamate to the liquid diet significantly prevented the incidence of diarrhoea induced by repetitive gastric feeding. In conclusion, supplementation of an enteral liquid diet with free l-Glu may ameliorate diarrhoea during intra-gastric tube feeding by sending visceral glutamate information from the stomach to the brain.

Supplementing chicken broth with monosodium glutamate reduces hunger and desire to snack but does not affect energy intake in women

The effect of monosodium glutamate (MSG) supplementation in soup or broth on satiety is not well understood. In the present study, the relative effects of four chicken broths with or without added MSG on motivational ratings and energy intakes at the next meal were compared using a double-blinded, within-subject design. A total of thirty-five normal-weight women, aged 20-40 years, took part in four study sessions. The four broths were base chicken broth (63 kJ), broth with added MSG (1.19 g) and nucleotides (0.03 g), broth with added MSG (1.22 g), and broth with added fat (BAF; 681 kJ). The preloads were presented twice at 09.00 and 11.15 hours for a maximum cumulative dose of 2.44 g MSG. Motivational ratings were collected before and at 15 min intervals post-ingestion for a total of 210 min. A test lunch meal was served at 12.00 hours, and plate waste was measured. The addition of MSG to chicken broth did not increase energy intakes at lunch or affect motivational ratings over the entire testing session. Both hunger and desire to snack between the second preload exposure and the test meal were significantly reduced in the MSG condition relative to the base broth condition (both, P = 0.03). However, only the BAF significantly suppressed energy intakes at lunch compared with the base broth control condition. Supplementing chicken broth with MSG can increase subjective ratings for satiety but does not alter energy intake at the next meal relative to an equal energy broth without added MSG.

Change of gastric emptying with chewing gum: evaluation using a continuous real-time C breath test (BreathID system)

Background/Aims

There are few reports on the correlation between chewing gum and the gastrointestinal functions. But previous report showed use of chewing gum to be an effective method for controlling gastrointestinal symptoms. The aim of this study was to determine the correlation between chewing gum and gastric emptying using the continuous real time ¹³C breath test (BreathID system).

Methods

Ten healthy male volunteers participated in this randomized, 2-way crossover study. The subjects fasted overnight and were randomly assigned to chewing gum (Xylish, 2-3/1 tablet) for an hour following intake of a test meal (200 kcal/200 mL) or intake of the test meal alone. Gastric emptying was monitored for 4 hours after administration of the test meal by the ¹³C-acetic acid breath test performed continually using the BreathID system.

Results

No significant differences in the calculated parameters, namely, T_1/2 (median, 111.82 vs 109.26 minutes; P = 0.575), T_lag (median, 53.28 vs 56.53 minutes; P = 0.333), gastric emptying coefficient (median, 3.58 vs 3.65; P = 0.285), regression-estimated constant β (median, 1.85 vs 1.80; P = 0.575) and regression-estimated constant κ (median, 0.61 vs 0.62; P = 0.959) were observed between the test meal alone group and the test meal and chewing gum group.

Conclusions

This study showed that chewing gum had no effect on the rate of gastric emptying. Therefore, since chewing gum did not enhance the speed of gastric emptying, it may ameliorate gastrointestinal symptoms through other mechanisms, such as saliva and autonomic nervous system.

Monosodium glutamate raises antral distension and plasma amino acid after a standard meal in humans

The consumption of monosodium glutamate (MSG) is advocated to elicit physiological and metabolic effects, yet these effects have been poorly investigated directly in humans and in particular in the postprandial phase. Thirteen healthy adults were supplemented for 6 days with a nutritional dose of MSG (2 g) or sodium chloride (NaCl) as control, following a crossover design. On the 7th day, they underwent a complete postprandial examination for the 6 h following the ingestion of the same liquid standard meal (700 kcal, 20% of energy as [(15)N]protein, 50% as carbohydrate, and 30% as fat) supplemented with MSG or NaCl. Real-ultrasound measures of antral area indicated a significant increased distension for the 2 h following the meal supplemented with MSG vs. NaCl. This early postprandial phase was also associated with significantly increased levels of circulating leucine, isoleucine, valine, lysine, cysteine, alanine, tyrosine, and tryptophan after MSG compared with NaCl. No changes to the postprandial glucose, insulin, glucagon-like peptide (GLP)-1, and ghrelin were noted between MSG- and NaCl-supplemented meals. Subjective assessments of hunger and fullness were neither affected by MSG supplementation. Finally, the postprandial fate of dietary N was identical between dietary conditions. Our findings indicate that nutritional dose of MSG promoted greater postprandial elevations of several indispensable amino acids in plasma and induced gastric distension. Further work to elucidate the possible sparing effect of MSG on indispensable amino acid first-pass uptake in humans is warranted. This trial was registered at clinicaltrials.gov as NCT00862017.

New frontiers in gut nutrient sensor research: monosodium L-glutamate added to a high-energy, high-protein liquid diet promotes gastric emptying: a possible therapy for patients with functional dyspepsia

Functional dyspepsia is a clinical syndrome that features abdominal symptoms centered in the upper abdomen without an organic basis. Three possible mechanisms of gastric dysfunction could be related to functional dyspepsia: 1) delayed gastric emptying, 2) impaired gastric accommodation to food intake, and 3) hypersensitivity to gastric distention. Delayed gastric emptying has been suggested to lead to prolonged antral distension that causes dyspeptic symptoms. Delayed gastric emptying is therefore a focal point of debate about anorexia caused by dyspepsia, and prokinetic agents are often administered in Japan for its treatment. Recently, we found that addition of monosodium L-glutamate (MSG) to a high-energy liquid diet rich in casein promoted gastric emptying in healthy men. Therefore, another potential method to improve delayed gastric emptying could be enhancement of chemosensors that activate the autonomic nervous system innervating the gastrointestinal tract. In conclusion, enrichment with glutamate promoted gastric emptying after intake of a high-protein meal, suggesting that free glutamate is important for protein digestion and that MSG may be helpful for management of delayed gastric emptying in patients with functional dyspepsia.

Taste, visceral information and exocrine reflexes with glutamate through umami receptors

Chemical substances of foods drive the cognitive recognition of taste with the subsequent regulation of digestion in the gastrointestinal (GI) tract. Tastants like glutamate can bind to taste membrane receptors on the tip of specialized taste cells eliciting umami taste. In chemical-sensing cells diffused through the GI tract, glutamate induces functional changes. Most of the taste-like receptor-expressing cells from the stomach and intestine are neuroendocrine cells. The signaling molecules produced by these neuroendocrine cells either activate afferent nerve endings or release peptide hormones that can regulate neighboring cells in a paracrine fashion or travel through blood to their target receptor. Once afferent sensory fibers transfer the chemical information of the GI content to the central nervous system (CNS) facilitating the gut-brain signaling, the CNS regulates the GI through efferent cholinergic and noradrenergic fibers. Thus, this is a two-way extrinsic communication process. Glutamate within the lumen of the stomach stimulates afferent fibers and increases acid and pepsinogen release; whereas on the duodenum, glutamate increases the production of mucous to protect the mucosa against the incoming gastric acid. The effects of glutamate are believed to be mediated by G protein-coupled receptors expressed at the lumen of GI cells. The specific cell-type and molecular function of each of these receptors are not completely known. Here we will examine some of the glutamate receptors and their already understood role on GI function regulation.

Effects of four different meal types on the population pharmacokinetics of single-dose rifapentine in healthy male volunteers

Rifapentine and its primary metabolite, 25-desacetyl rifapentine, are active against mycobacterium tuberculosis. The objectives of this study were to describe the population pharmacokinetics of rifapentine and 25-desacetyl rifapentine in fasting and fed states. Thirty-five male healthy volunteers were enrolled in an open-label, randomized, sequential, five-way crossover study. Participants received a single 900-mg dose of rifapentine after meals with high fat (meal A), bulk and low fat (meal B), bulk and high fat (meal C), high fluid and low fat (meal D), or 200 ml of water (meal E). Venous blood samples were collected over 72 h after each rifapentine dose, and plasma was analyzed for rifapentine and 25-desacetyl rifapentine using high-performance liquid chromatography. Pharmacokinetic data were analyzed by nonlinear mixed-effect modeling using NONMEM. Compared with the fasting state, meal A had the greatest effect on rifapentine oral bioavailability, increasing it by 86%. Meals B, C, and D resulted in 33%, 46%, and 49% increases in rifapentine oral bioavailability, respectively. Similar trends were observed for 25-desacetyl rifapentine. As meal behavior has a substantial impact on rifapentine exposure, it should be considered in the evaluation of optimal dosing approaches.

Glutamate. Its applications in food and contribution to health

This article reviews application of glutamate in food and its benefits and role as one of the common food ingredients used. Monosodium glutamate is one of the most abundant naturally occurring amino acids which frequently added as a flavor enhancer. It produced a unique taste that cannot be provided by other basic taste (saltiness, sourness, sweetness and bitterness), referred to as a fifth taste (umami). Glutamate serves some functions in the body as well, serving as an energy source for certain tissues and as a substrate for glutathione synthesis. Glutamate has the potential to enhance food intake in older individuals and dietary free glutamate evoked a visceral sensation from the stomach, intestine and portal vein. Small quantities of glutamate used in combination with a reduced amount of table salt during food preparation allow for far less salt to be used during and after cooking. Because glutamate is one of the most intensely studied food ingredients in the food supply and has been found safe, the Joint Expert Committee on Food Additives of the United Nations Food and Agriculture Organization and World Health Organization placed it in the safest category for food additives. Despite a widespread belief that glutamate can elicit asthma, migraine headache and Chinese Restaurant Syndrome (CRS), there are no consistent clinical data to support this claim. In addition, findings from the literature indicate that there is no consistent evidence to suggest that individuals may be uniquely sensitive to glutamate.

Intragastric monosodium l-glutamate stimulates motility of upper gut via vagus nerve in conscious dogs

Monosodium l-glutamate (MSG) is a substance known to produce the umami taste. Recent studies indicate that MSG also stimulates a variety of activities in the gastrointestinal tract through its receptor in the gut, but no study has reported the activity in conscious large experimental animals. The aim of our study was to investigate whether direct intragastric MSG stimulates gut motility and to identify the mechanism in conscious dogs. Contractile response to intraluminal injection of MSG was studied in the fed and fasted states by means of chronically implanted force transducers. MSG (5, 15, 45, and 90 mM/kg) dissolved in water was injected into the stomach and duodenum in normal and vagotomized dogs. MSG solution was administered into the stomach before feeding, and gastric emptying was evaluated. Several inhibitors of gastrointestinal motility (atropine, hexamethonium, and granisetron) were injected intravenously before MSG administration to the stomach. The effect of MSG was investigated in Pavlov (vagally innervated corpus pouch), Heidenhain (vagally denervated corpus pouch), and antral pouch (vagally innervated) dogs. Upper gut motility was significantly increased by intragastric MSG but not significantly stimulated by intraduodenal MSG. Intragastric MSG (45 mM/kg) stimulated postprandial motility and accelerated gastric emptying. MSG-induced contractions were inhibited by truncal vagotomy, atropine, hexamethonium, and granisetron. Gut motility was increased by intrapouch injection of MSG in the Pavlov pouch, but it was not affected in the Heidenhain or antral pouch dogs. We conclude that intragastric MSG stimulates upper gut motility and accelerates gastric emptying. The sensory structure of MSG is present in the gastric corpus, and the signal is mediated by the vagus nerve.

Can dietary supplementation of monosodium glutamate improve the health of the elderly?

Dietary free l-glutamate has been known for a century to improve taste and palatability. Recent evidence suggests that this effect is mediated through specific l-glutamate receptors located on the taste buds. However, l-glutamate receptors are also present elsewhere in the gastrointestinal tract, such as the stomach. Here, l-glutamate exerts physiologic actions beneficial to gut function by stimulating l-glutamate receptors linked to the gastric vagus nerve. In addition, dietary l-glutamate also appears to be an important energy substrate for gut tissue. Can such l-glutamate effects on taste and gut function be clinically useful? Elderly people often develop health problems related to their nutritional status that can be linked to insufficient energy and nutrient intake. A number of studies have examined the potential usefulness of l-glutamate, added to food in the form of monosodium glutamate (MSG), in promoting better nutrition in the elderly and in patients with poor nutrition. Some positive effects have been observed. This article reviews the physiologic roles of dietary l-glutamate in relation to alimentation and examines the evidence linking the utility of MSG supplementation to the improvement of nutrition in elderly and hospitalized patients.