Absorption of amino acids from the human mouth

Summary Certain amino acids were transported across buccal mucosa in vivo by a carrier-mediated process. Metabolic loss of L-amino acids from the mouth in a 5 min test period was negligible. The buccal mucosal transport process was stereospecific for most L-amino acids tested. The uptake of L-methionine and L-leucine showed a tendency to saturation with increasing substrate concentration. The absorption of L-leucine, L-isoleucine and L-methionine as single amino acids was inhibited in the presence of each other suggesting at least one common transport mechanism. Administration of equimolar amounts of amino acids revealed a specific pattern of absorption that could be classified into fast, intermediate, and slow groups. Absorption of some amino acids was at least partly dependent on the presence of sodium ions in the luminal solution. In conclusion, our studies demonstrate that the human buccal mucosa is permeable to L-amino acids in a selective manner, and may resemble absorption pattern similar to other locations of the gastrointestinal tract.This work was supported by Grant DK39147 from the National Institutes of Diseases and Digestive and Kidney Diseases, National Institutes of Health, United States Public Health Service, and The Lord Dowding Fund for Humane Research, London, U.K.     

Metabolism of select amino acids in bacteria from the pig small intestine

This study investigated the metabolism of select amino acids (AA) in bacterial strains (Streptococcus sp., Escherichia coli and Klebsiella sp.) and mixed bacterial cultures derived from the jejunum and ileum of pigs. Cells were incubated at 37°C for 3 h in anaerobic media containing 0.5–5 mM select AA plus [U-¹⁴C]-labeled tracers to determine their decarboxylation and incorporation into bacterial protein. Results showed that all types of bacteria rapidly utilized glutamine, lysine, arginine and threonine. However, rates of the utilization of AA by pure cultures of E. coli and Klebsiella sp. were greater than those for mixed bacterial cultures or Streptococcus sp. The oxidation of lysine, threonine and arginine accounted for 10% of their utilization in these pure bacterial cultures, but values were either higher or lower in mixed bacterial cultures depending on AA, bacterial species and the gut segment (e.g., 15% for lysine in jejunal and ileal mixed bacteria; 5.5 and 0.3% for threonine in jejunal mixed bacteria and ileal mixed bacteria, respectively; and 20% for arginine in ileal mixed bacteria). Percentages of AA used for bacterial protein synthesis were 50–70% for leucine, 25% for threonine, proline and methionine, 15% for lysine and arginine and 10% for glutamine. These results indicate diverse metabolism of AA in small-intestinal bacteria in a species- and gut compartment-dependent manner. This diversity may contribute to AA homeostasis in the gut. The findings have important implications for both animal and human nutrition, as well as their health and well-beings.     

Utilization of amino acids by bacteria from the pig small intestine

This study determined the utilization of amino acids (AA) by bacteria from the lumen of the pig small intestine. Digesta samples from different segments of the small intestine were inoculated into media containing 10 mmol/L each of select AA (l-lysine, l-threonine, l-arginine, l-glutamate, l-histidine, l-leucine, l-isoleucine, l-valine, l-proline, l-methionine, l-phenylalanine or l-tryptophan) and incubated for 24 h. The previous 24-h culture served as an inoculum for a subsequent 24-h subculture during each of 30 subcultures. Results of the in vitro cultivation experiment indicated that the 24-h disappearance rates for lysine, arginine, threonine, glutamate, leucine, isoleucine, valine or histidine were 50–90% in the duodenum, jejunum or ileum groups. After 30 subcultures, the 24-h disappearance rates for lysine, threonine, arginine or glutamate remained greater than 50%. The denaturing gradient gel electrophoresis analysis showed that Streptococcus sp., Mitsuokella sp., and Megasphaera elsdenii-like bacteria were predominant in subcultures for utilizing lysine, threonine, arginine and glutamate. In contrast, Klebsiella sp. was not a major user of arginine or glutamate. Furthermore, analysis of AA composition and the incorporation of AA into polypeptides indicated that protein synthesis was a major pathway for AA metabolism in all the bacteria studied. The current work identified the possible predominant bacterial species responsible for AA metabolism in the pig small intestine. The findings provide a new framework for future studies to characterize the metabolic fate of AA in intestinal microbes and define their nutritional significance for both animals and humans.     

氨基酸对炎症性肠病的调控作用北大核心CSCD

炎症性肠病是胃肠道的一种慢性复发性炎症,包括克罗恩病和溃疡性结肠炎,患者众多,而且目前很难实现彻底治愈。由于患者消化功能受损,食物不容易吸收,很容易出现营养不良的情况,临床经常使用营养治疗来克服营养不足、改变炎症状态。氨基酸作为辅助营养治疗,可能有助于维持炎症性肠病患者的肠道完整性,减少炎症、氧化应激和肠道细胞死亡,对炎症性肠病的治疗起到积极的作用。最近在动物方面的研究已经证明氨基酸在炎症性肠病治疗中存在着巨大的潜力,氨基酸的供应和代谢可能是一种有前景的辅助治疗方法。本文就谷氨酰胺、精氨酸、甘氨酸等特定氨基酸的免疫调节作用进行综述,以期提供一种新的治疗炎症性肠病的思路。     

Bioactive dietary peptides and amino acids in inflammatory bowel disease

Inflammatory bowel disease (IBD), most commonly ulcerative colitis (UC) and Crohn’s disease (CD), is a chronic inflammation of the gastrointestinal tract. Patients affected with IBD experience symptoms including abdominal pain, persistent diarrhea, rectal bleeding, and weight loss. There is no cure for IBD; thus treatments typically focus on preventing complications, inducing and maintaining remission, and improving quality of life. During IBD, dysregulation of the intestinal immune system leads to increased production of pro-inflammatory cytokines, such as TNF-α and IL-6, and recruitment of activated immune cells to the intestine, causing tissue damage and perpetuating the inflammatory response. Recent biological therapies targeting specific inflammatory cytokines or pathways, in particular TNF-α, have shown promise, but not all patients respond to treatment, and some individuals become intolerant to treatment over time. Dietary peptides and amino acids (AAs) have been shown to modulate intestinal immune functions and influence inflammatory responses, and may be useful as alternative or ancillary treatments in IBD. This review focuses on dietary interventions for IBD treatment, in particular the role of dietary peptides and AAs in reducing inflammation, oxidative stress, and apoptosis in the gut, as well as recent advances in the cellular mechanisms responsible for their anti-inflammatory activity.     

Absorption of neutral amino acids by the gut ofArenicola marina

Summary The absorption of neutral amino acids byArenicola marina was studied using anin vitro preparation of the alimentary canal. Regional variation in absorption was observed, with the intestine being the region of greatest uptake. The L enantiomorphs of the neutral amino acids alanine and leucine were shown to be actively absorbed by the intestine as was the D enantiomorph of alanine. A saturable component was demonstrated in the absorption of L-alanine and this was shared by L-methionine, which was found to competitively inhibit alanine uptake. Inhibition of L-alanine uptake also occurred in the presence of other neutral, basic and acidic amino acids. The greatest inhibition was found with the L stereoisomers of methionine, leucine, valine, histidine and phenylalanine, whilst proline, lysine and aspartic acid decreased uptake to a smaller extent.     

Peptidase-mediated storage of amino acids in small peptides

Adult Calliphora contain a large and heterogenous pool of small peptides, which it is supposed come from protein catabolism. Their composition and rapid turn-over appears to be determined in part by a group of peptidases. The activity of the peptidases is inhibited non-competitively by free amino acids and most effectively by the essential amino acids which are also those which stimulate feeding on protein. Thus it seems that as flies feed on protein containing the essential amino acids peptide emerging from catabolized protein tends to remain as peptide until the internal concentrations of the essential amino acids fall. This provides the fly with a physiologically tolerable reservoir of amino acids.     

Responses of the pancreatic digestive enzyme secretion to amino acids, glucose and cholecystokinin in chicks

1. Pancreatic secretion of digestive enzymes, amylase, trypsinogen and chymotrypsinogen, was studied in response to the wing vein injection of digestive end products, various single amino acids and glucose, with or without cholecystokinin (CCK) in chicks. 2. Among amino acids administered, only phenylalanine significantly (P less than 0.05) increased trypsinogen and chymotrypsinogen secretions, while other amino acids did not. 3. Simultaneous injection of single amino acids with CCK increased digestive enzyme secretion to various extents depending on the kind of amino acids whereas the injection of glucose with CCK did not affect when compared with that of CCK alone. 4. By varying doses, a synergetic action of CCK plus amino acid on the secretion of pancreatic digestive enzymes was observed at 0.5 mM for valine and 5 mM for arginine.     

An efficient one-pot synthesis of polyphenolic amino acids and evaluation of their radical-scavenging activity

A simple and efficient procedure for the synthesis of N-acyl 4-hydroxy, 4-hydroxy-3-methoxy and 3,4-dihydroxy phenylglycine amides by a strategy based on the multicomponent Ugi reaction is proposed. Hydroxybenzaldehyde derivatives were reacted with 4-methoxybenzylamine, cyclohexyl isocyanide and benzoic acid or 2-naphthylacetic acid to give Ugi adducts that were treated with trifluoroacetic acid yielding N-acyl hydroxyphenylglycine amides in good yields. The same procedure using as acid component protocatechuic acid or hydrocaffeic acid gave N-catechoyl 3,4-dihydroxyphenylglycine amides. The use of N-benzyloxycarbonylglycine as acid component allowed the preparation of a 3,4-dihydroxyphenylglycyl dipeptide derivative. Radical-scavenging activity studies of the polyphenolic amino acid derivatives showed a sharp increase in activity with the increase in number of hydroxyl or catechol groups present. Cyclic voltammetry experiments established a correlation between oxidation peak potentials and the radical-scavenging activity.     

Anticonvulsant activity of cyclopentano amino acids

The hypothesis that certain amino acid analogues possessing a five-membered ring structure or amino acid analogues that can be viewed as fragments derived from such a ring would have anticonvulsant activity was proposed and tested. The compounds 1-aminocyclopentane carboxylic acid, 1-amino-3-methylcyclopentane carboxylic acid, 3-aminotetrahydrothiophene carboxylic acid, and -aminoisobutyric acid were found to protect rats against seizures in the maximal electroshock test but offered no protection against metrazol-(pentylenetetrazol) induced seizures in mice. The structural feature of this class of anticonvulsants that allows for hydrophobic interactions at the receptor site is considered to be a major physical factor necessary in promoting the activity of this class of anticonvulsants.