Amino acid regulation of mammalian gene expression in the intestine

Amino Acids in Cell Signaling: Regulation and Function

Amino acids are the main building blocks for life. Aside from their roles in composing proteins, functional amino acids and their metabolites play regulatory roles in key metabolic cascades, gene expressions, and cell-to-cell communication via a variety of cell signaling pathways. These metabolic networks are necessary for maintenance, growth, reproduction, and immunity in humans and animals. These amino acids include, but are not limited to, arginine, glutamine, glutamate, glycine, leucine, proline, and tryptophan. We will discuss these functional amino acids in cell signaling pathways in mammals with a particular emphasis on mTORC1, AMPK, and MAPK pathways for protein synthesis, nutrient sensing, and anti-inflammatory responses, as well as cell survival, growth, and development.

Anti-Inflammatory Potential of Cow, Donkey and Goat Milk Extracellular Vesicles as Revealed by Metabolomic Profile

In recent years, extracellular vesicles (EVs), cell-derived micro and nano-sized structures enclosed in a double-layer membrane, have been in the spotlight for their high potential in diagnostic and therapeutic applications. Indeed, they act as signal mediators between cells and/or tissues through different mechanisms involving their complex cargo and exert a number of biological effects depending upon EVs subtype and cell source. Being produced by almost all cell types, they are found in every biological fluid including milk. Milk EVs (MEVs) can enter the intestinal cells by endocytosis and protect their labile cargos against harsh conditions in the intestinal tract. In this study, we performed a metabolomic analysis of MEVs, from three different species (i.e., bovine, goat and donkey) by mass spectroscopy (MS) coupled with Ultrahigh-performance liquid chromatography (UHPLC). Metabolites, both common or specific of a species, were identified and enriched metabolic pathways were investigated, with the final aim to evaluate their anti-inflammatory and immunomodulatory properties in view of prospective applications as a nutraceutical in inflammatory conditions. In particular, metabolites transported by MEVs are involved in common pathways among the three species. These metabolites, such as arginine, asparagine, glutathione and lysine, show immunomodulating effects. Moreover, MEVs in goat milk showed a greater number of enriched metabolic pathways as compared to the other kinds of milk.

Amino Acid Metabolism in Dairy Cows and their Regulation in Milk Synthesis

Background:

Reducing dietary Crude Protein (CP) and supplementing with certain Amino Acids (AAs) has been known as a potential solution to improve Nitrogen (N) efficiency in dairy production. Thus understanding how AAs are utilized in various sites along the gut is critical.

Objective:

AA flow from the intestine to Portal-drained Viscera (PDV) and liver then to the mammary gland was elaborated in this article. Recoveries in individual AA in PDV and liver seem to share similar AA pattern with input: output ratio in mammary gland, which subdivides essential AA (EAA) into two groups, Lysine (Lys) and Branchedchain AA (BCAA) in group 1, input: output ratio > 1; Methionine (Met), Histidine (His), Phenylalanine (Phe) etc. in group 2, input: output ratio close to 1. AAs in the mammary gland are either utilized for milk protein synthesis or retained as body tissue, or catabolized. The fractional removal of AAs and the number and activity of AA transporters together contribute to the ability of AAs going through mammary cells. Mammalian Target of Rapamycin (mTOR) pathway is closely related to milk protein synthesis and provides alternatives for AA regulation of milk protein synthesis, which connects AA with lactose synthesis via α-lactalbumin (gene: LALBA) and links with milk fat synthesis via Sterol Regulatory Element-binding Transcription Protein 1 (SREBP1) and Peroxisome Proliferatoractivated Receptor (PPAR).

Conclusion:

Overall, AA flow across various tissues reveals AA metabolism and utilization in dairy cows on one hand. While the function of AA in the biosynthesis of milk protein, fat and lactose at both transcriptional and posttranscriptional level from another angle provides the possibility for us to regulate them for higher efficiency.

L-Glutamine in vitro Modulates some Immunomodulatory Properties of Bone Marrow Mesenchymal Stem Cells

Glutamine (GLUT) is a nonessential amino acid that can become conditionally essential under stress conditions, being able to act in the modulation of the immune responses. Mesenchymal stem cells (MSCs) are known to their capability in the modulation of immune responses through cell-cell contact and by the secretion of soluble factors. Considering that GLUT is an immunonutrient and little is known about the influence of GLUT on the capability of MSCs to modulate immune cells, this work aims to investigate how variations in GLUT concentrations in vitro could affect some immunomodulatory properties of MSCs. In order to evaluate the effects of GLUT on MSCs immunomodulatory properties, cell proliferation rates, the expression of NFκB and STAT-3, and the production of IL-1β, IL-6, IL-10, TGF-β and TNF-α by MSCs were assessed. Based on our findings, GLUT at high doses (10 mM) augmented the proliferation of MSCs and modulated immune responses by decreasing levels of pro-inflammatory cytokines, such as IL-1β and IL-6, and by increasing levels of anti-inflammatory cytokines IL-10 and TGF-β. In addition, MSCs cultured in higher GLUT concentrations (10 mM) expressed lower levels of NF-κB and higher levels of STAT-3. Furthermore, conditioned media from MSCs cultured at higher GLUT concentrations (10 mM) reduced lymphocyte and macrophage proliferation, increased IL-10 production by both cells types, and decreased IFN-γ production by lymphocytes. Overall, this study showed that 10 mM of GLUT is able to modify immunomodulatory properties of MSCs.

Glutamine metabolism in advanced age

Glutamine, reviewed extensively in the last century, is a key substrate for the splanchnic bed in the whole body and is a nutrient of particular interest in gastrointestinal research. A marked decrease in the plasma glutamine concentration has recently been observed in neonates and adults during acute illness and stress. Although some studies in newborns have shown parenteral and enteral supplementation with glutamine to be of benefit (by decreasing proteolysis and activating the immune system), clinical trials have not demonstrated prolonged advantages such as reductions in mortality or risk of infections in adults. In addition, glutamine is not able to combat the muscle wasting associated with disease or age-related sarcopenia. Oral glutamine supplementation initiated before advanced age in rats increases gut mass and improves the villus height of mucosa, thereby preventing the gut atrophy encountered in advanced age. Enterocytes from very old rats continuously metabolize glutamine into citrulline, which allowed, for the first time, the use of citrulline as a noninvasive marker of intestinal atrophy induced by advanced age.

Effects of glutamine alone on the acute necrotizing pancreatitis in rats

BACKGROUND

The effects of the glutamine on the acute pancreatitis are controversial in the clinical and experimental studies. The aim of this study was to investigate the influence of glutamine alone on acute necrotizing pancreatitis (ANP) induced by glycodeoxycholic acid in rats.

MATERIAL AND METHODS

Fifty-two male Sprague-Dawley rats weighing 300-350 g were used. Rats were divided into four groups as sham + saline, sham + glutamine, ANP + saline and ANP + glutamine. ANP in rats was induced by glycodeoxycholic acid. The extent of acinar cell injury, mortality, systemic cardiorespiratory variables, functional capillary density, renal/hepatic functions, and changes in some enzyme markers for pancreatic and lung tissue were investigated during ANP in rats.

RESULTS

The induction of ANP resulted in a significant increase in the mortality rate, pancreatic necrosis, and serum activity of amylase, alanine aminotransferase, interleukin-6, lactate dehydrogenase in bronchoalveolar lavage fluid, serum concentration of urea, and tissue activity of myeloperoxidase and malondialdehyde in the pancreas and lung, and a significant decrease in concentrations of calcium, blood pressure, urine output, pO2, and functional capillary density. The use of glutamine alone improved these changes.

CONCLUSIONS

Glutamine demonstrated beneficial effect on the course of ANP in rats. Therefore, it may be used by itself in the treatment of acute pancreatitis.

Targeting arginine-dependent cancers with arginine-degrading enzymes: opportunities and challenges

Arginine deprivation is a novel antimetabolite strategy for the treatment of arginine-dependent cancers that exploits differential expression and regulation of key urea cycle enzymes. Several studies have focused on inactivation of argininosuccinate synthetase 1 (ASS1) in a range of malignancies, including melanoma, hepatocellular carcinoma (HCC), mesothelial and urological cancers, sarcomas, and lymphomas. Epigenetic silencing has been identified as a key mechanism for loss of the tumor suppressor role of ASS1 leading to tumoral dependence on exogenous arginine. More recently, dysregulation of argininosuccinate lyase has been documented in a subset of arginine auxotrophic glioblastoma multiforme, HCC and in fumarate hydratase-mutant renal cancers. Clinical trials of several arginine depletors are ongoing, including pegylated arginine deiminase (ADI-PEG20, Polaris Group) and bioengineered forms of human arginase. ADI-PEG20 is furthest along the path of clinical development from combinatorial phase 1 to phase 3 trials and is described in more detail. The challenge will be to identify tumors sensitive to drugs such as ADI-PEG20 and integrate these agents into multimodality drug regimens using imaging and tissue/fluid-based biomarkers as predictors of response. Lastly, resistance pathways to arginine deprivation require further study to optimize arginine-targeted therapies in the oncology clinic.

Prognostic and therapeutic impact of argininosuccinate synthetase 1 control in bladder cancer as monitored longitudinally by PET imaging

Targeted therapies have yet to have significant impact on the survival of patients with bladder cancer. In this study, we focused on the urea cycle enzyme argininosuccinate synthetase 1 (ASS1) as a therapeutic target in bladder cancer, based on our discovery of the prognostic and functional import of ASS1 in this setting. ASS1 expression status in bladder tumors from 183 Caucasian and 295 Asian patients was analyzed, along with its hypothesized prognostic impact and association with clinicopathologic features, including tumor size and invasion. Furthermore, the genetics, biology, and therapeutic implications of ASS1 loss were investigated in urothelial cancer cells. We detected ASS1 negativity in 40% of bladder cancers, in which multivariate analysis indicated worse disease-specific and metastasis-free survival. ASS1 loss secondary to epigenetic silencing was accompanied by increased tumor cell proliferation and invasion, consistent with a tumor-suppressor role for ASS1. In developing a treatment approach, we identified a novel targeted antimetabolite strategy to exploit arginine deprivation with pegylated arginine deiminase (ADI-PEG20) as a therapeutic. ADI-PEG20 was synthetically lethal in ASS1-methylated bladder cells and its exposure was associated with a marked reduction in intracellular levels of thymidine, due to suppression of both uptake and de novo synthesis. We found that thymidine uptake correlated with thymidine kinase-1 protein levels and that thymidine levels were imageable with [(18)F]-fluoro-L-thymidine (FLT)-positron emission tomography (PET). In contrast, inhibition of de novo synthesis was linked to decreased expression of thymidylate synthase and dihydrofolate reductase. Notably, inhibition of de novo synthesis was associated with potentiation of ADI-PEG20 activity by the antifolate drug pemetrexed. Taken together, our findings argue that arginine deprivation combined with antifolates warrants clinical investigation in ASS1-negative urothelial and related cancers, using FLT-PET as an early surrogate marker of response.

Glutamine as an immunonutrient

Dietary supplementation with nutrients enhancing immune function is beneficial in patients with surgical and critical illness. Malnutrition and immune dysfunction are common features in hospitalized patients. Specific nutrients with immunological and pharmacological effects, when consumed in amounts above the daily requirement, are referred to as immune-enhancing nutrients or immunonutrients. Supplementation of immunonutrients is important especially for patients with immunodeficiency, virus or overwhelming infections accompanied by a state of malnutrition. Representative immunonutrients are arginine, omega-3 fatty acids, glutamine, nucleotides, beta-carotene, and/or branched-chain amino acids. Glutamine is the most abundant amino acid and performs multiple roles in human body. However, glutamine is depleted from muscle stores during severe metabolic stress including sepsis and major surgery. Therefore it is considered conditionally essential under these conditions. This review discusses the physiological role of glutamine, mode and dose for glutamine administration, as well as improvement of certain disease state after glutamine supplementation. Even though immunonutrition has not been widely assimilated by clinicians other than nutritionists, immunonutrients including glutamine may exert beneficial influence on diverse patient populations.

Role of the mTOR complex 1 pathway in the in vivo maintenance of the intestinal mucosa by oral intake of amino acids

AIM

Oral intake of nutrients is often compromised in elderly, multimorbid patients, but parenteral nutrition causes intestinal atrophy and impairs intestinal function. To uncover the molecular mechanisms by which amino acids are involved in intestinal atrophy and recovery, we studied whether the rapamycin-sensitive mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) pathway is involved in this process.

METHODS

C57BL/6N mice were fed a glucose solution alone, glucose solution with amino acids or normal chow diet for various lengths of time. Intestinal sections were prepared from these mice and the villus height and villus density were quantified. As a readout for the mTORC1 pathway, the phosphorylation of the ribosomal S6 protein (S6) was analyzed by immunostaining and immunoblotting. To confirm the role of the mTORC1 pathway, the inhibitory effect of a specific mTOR inhibitor, rapamycin, was examined.

RESULTS

Inducing fasting in mice fed only glucose caused time-dependent intestinal mucosal atrophy, whereas supplementation with amino acids protected the intestinal mucosa from atrophy. Phosphorylation of S6 decreased in the intestinal mucosa of mice fed only glucose, whereas supplementation with amino acids increased S6 phosphorylation. Importantly, intraperitoneal injection of rapamycin attenuated the protective effect of amino acids on the intestinal mucosa in a pattern consistent with the decrease of S6 phosphorylation.

CONCLUSIONS

These results indicate that the mTORC1 pathway plays a crucial role in the in vivo maintenance of the intestinal mucosa by the oral intake of amino acids.

Intestinal growth and morphology is associated with the increase in heat shock protein 70 expression in weaning piglets through supplementation with glutamine

The objectives of this study were to determine the effects of oral Gln supplementation on growth performance, intestinal morphology, and expression of heat shock protein (Hsp) 70 in weaning piglets. A total of 65 piglets after weaning at 21 d of age (d 0) were used in this experiment. Five piglets were randomly selected and euthanized initially at d 0 to determine baseline values for the expression of Hsp70 in the small intestine. The remaining piglets were randomly assigned to 1 of 2 treatments and received 0 or 1 g of oral Gln/kg of BW every 12 h. After piglets were humanely killed at d 3, 7, and 14 postweaning, the duodenum, jejunum, and ileum of piglets were sampled to evaluate intestinal morphology and the expression and localization of Hsp70. The results indicated that oral Gln supplementation increased plasma concentrations of Gln compared with those in control piglets (P < 0.05). Average daily gain and ADFI were greater in piglets orally supplemented with Gln than in control piglets during the whole period (P < 0.05). The incidence of diarrhea in piglets orally supplemented with Gln was 24% less than (P = 0.064) that in control piglets at 8 to 14 d after weaning. The weights of the jejunum and ileum were greater in piglets orally supplemented with Gln compared with those of control piglets relative to BW on d 14 postweaning (P < 0.05). The villus height and the villus height:crypt depth ratio in the jejunum and the ileum were greater in piglets receiving oral Gln on d 14 postweaning (P < 0.05) than in control piglets. These results indicate that Gln supplementation can influence the intestinal morphology of weaned piglets. The expression of hsp70 mRNA and Hsp70 proteins in the duodenum and jejunum was greater in piglets supplemented with Gln than in control piglets (P < 0.05). However, Gln supplementation had no effect on the expression of hsp70 mRNA and Hsp70 proteins in the ileum. Moreover, the localization of Hsp70 in the cytoplasm indicated that Hsp70 has a cytoprotective role in epithelial cell function and structure. These results indicate that Gln supplementation may be beneficial for intestinal health and development and may thus mitigate diarrhea and improve growth performance. The protective mechanisms of Gln in the intestine may be associated with the increase in Hsp70 expression.

Glutamine protects against apoptosis via downregulation of Sp3 in intestinal epithelial cells

Glutamine plays a key role in intestinal growth and maintenance of gut function, and as we have shown protects the postischemic gut (Kozar RA, Scultz SG, Bick RJ, Poindexter BJ, Desoigne R, Weisbrodt NW, Haber MM, Moore FA. Shock 21: 433-437, 2004). However, the precise mechanisms of the gut protective effects of glutamine have not been well elucidated. In the present study, RNA microarray was performed to obtain differentially expressed genes in intestinal epithelial IEC-6 cells following either 2 mM or 10 mM glutamine. The result demonstrated that specificity protein 3 (Sp3) mRNA expression was downregulated 3.1-fold. PCR and Western blot confirmed that Sp3 expression was decreased by glutamine in a time- and dose-dependent fashion. To investigate the role of Sp3, Sp3 gene siRNA silencing was performed and apoptosis was assessed. Silencing of Sp3 demonstrated a significant increase in Bcl-2 and decrease in Bax protein expression, as well as a decrease in caspase-3, -8, and -9 protein expression and activity. The protein expression of apoptosis-related proteins after hypoxia/reoxygenation was similar to that of normoxia and correlated with a decrease in DNA fragmentation. Importantly, the addition of glutamine to Sp3-silenced cells did not further lessen apoptosis, suggesting that Sp3 plays a major role in the inhibitory effect of glutamine on apoptosis. This novel finding may explain in part the gut-protective effects of glutamine.