Endogenous Metabolite
D-Glutamine primarily targets metabolic enzymes and pathways involved in glutamine metabolism, though its specific receptor binding is less defined compared to L-glutamine. It interacts with enzymes such as phosphate-dependent glutaminase (PDG) in renal ammoniagenesis and glutamate dehydrogenase, which are key regulators of glutamine metabolism. D-Glutamine may also influence the activity of glutamine synthetase, which is present in skeletal muscle and plays a role in nitrogen homeostasis. In the context of intestinal barrier function, D-glutamine modulates pathways that protect against acetaldehyde-induced disruption, though the precise molecular targets remain under investigation. Its effects are blocked by acivicin, a selective antagonist of glutamine metabolism, indicating that its activity is mediated through metabolic pathways rather than direct receptor binding.

In the glutamate/GABA-glutamine cycle (GGC), glutamine is a crucial amino acid in the central nervous system (CNS). In order to replenish the pools of excitatory and inhibitory neurotransmitters, glutamine is moved from astrocytes to neurons in the GGC[1]. The function of D-glutamine in providing protection against acetaldehyde-induced disruption of barrier function in Caco-2 cell monolayer has been investigated. The Caco-2 cell monolayer is used to assess the role of glutamine in shielding the intestinal epithelium from acetaldehyde-induced loss of barrier function. In a time- and dose-dependent way, L-glutamine mitigated the acetaldehyde-induced decrease in transepithelilal electrical resistance and increase in permeability to inulin and lipopolysaccharide; no discernible protection was produced by D-glutamine, L-aspargine, L-arginine, L-lysine, or L-alanine. Additionally, acetaldehyde-induced TER drop and inulin flux increase are not affected by D-glutamine. Glutaminase or D-glutamine as an inhibitor did not affect TER or inulin flow in cell monolayers treated with acetaldehyde or left in control. The fact that D-glutamine has no effect on acetaldehyde protection suggests that L-glutamine mediates stereospecific protection[2].

---

D-glutamine at 2 mM failed to prevent acetaldehyde-induced decrease in transepithelial electrical resistance (TER) and increase in inulin flux in Caco-2 cell monolayers, showing no significant protective effect compared to acetaldehyde alone. [2]
D-glutamine at 2 mM, when administered to the apical or basal compartments, did not significantly alter TER or inulin flux in control or acetaldehyde-treated cells. [2]
D-Glutamine has demonstrated protective effects in vitro, particularly in Caco-2 cell monolayers where it confers protection against acetaldehyde-induced disruption of barrier function. Supplementation with D-glutamine yielded similar results to L-glutamine, although with lesser potency. Both L- and D-glutamine equivalently reduced Caco-2 dipeptidyl dipeptidase activity, and these effects were blocked by 1 to 3 mmol/L acivicin, a selective antagonist of glutamine metabolism. D-Glutamine has also been used to study its role in cellular protection and metabolic function in various cell-based assays, contributing to the understanding of glutamine's pharmaconutrient properties in stress and injury responses. Its effects are mediated through multiple mechanisms including direct protection of cells and tissues from injury, attenuation of inflammation, and preservation of metabolic function.

Glutamine shows the greatest benefit when administered at doses greater than 0.35 g/kg/day, with optimal benefit potentially occurring at 0.5 g/kg/day.
In vivo studies on D-glutamine are limited compared to its L-isomer, but it has been investigated in animal models of intestinal injury and metabolic stress. Glutamine, in general, exerts protective effects via multiple mechanisms including direct protection of cells and tissue from injury, attenuation of inflammation, and preservation of metabolic function. D-Glutamine has been studied in the context of renal ammoniagenesis, where glutamine metabolism plays a critical role in acid-base homeostasis. While specific in vivo data for D-glutamine are sparse, its L-isomer is well-established as a key pharmaconutrient in the body's response to stress and injury. D-Glutamine may serve as a research tool to investigate stereospecific effects of glutamine in vivo, though its lower potency compared to L-glutamine suggests limited therapeutic application.

Glutamine is a key amino acid in the CNS, playing an important role in the glutamate/GABA-glutamine cycle (GGC). In the GGC, glutamine is transferred from astrocytes to neurons, where it will replenish the inhibitory and excitatory neurotransmitter pools. Different transporters participate in this neural communication, i.e., the transporters responsible for glutamine efflux from astrocytes and influx into the neurons, such as the members of the SNAT, LAT, y+LAT, and ASC families of transporters. The SNAT family consists of the transporter isoforms SNAT3 and SNAT5 that are related to efflux from the astrocytic compartment, and SNAT1 and SNAT2 that are associated with glutamine uptake into the neuronal compartment. The isoforms SNAT7 and SNAT8 do not have their role completely understood, but they likely also participate in the GGC. The isoforms LAT2 and y+LAT2 facilitate the exchange of neutral amino acids and cationic amino acids (y+LAT2 isoform) and have been associated with glutamine efflux from astrocytes. ASCT2 is a Na+-dependent antiporter, the participation of which in the GGC also remains to be better characterized. All these isoforms are tightly regulated by transcriptional and translational mechanisms, which are induced by several determinants such as amino acid deprivation, hormones, pH, and the activity of different signaling pathways. Dysfunctional glutamine transporter activity has been associated with the pathophysiological mechanisms of certain neurologic diseases, such as Hepatic Encephalopathy and Manganism. However, there might also be other neuropathological conditions associated with an altered GGC, in which glutamine transporters are dysfunctional. Hence, it appears to be of critical importance that the physiological and pathological aspects of glutamine transporters are thoroughly investigated[1].

---

Non-cellular enzyme/receptor binding assays for D-glutamine typically involve measuring its interaction with glutamine-metabolizing enzymes such as glutaminase and glutamine synthetase. These assays often utilize purified enzyme preparations to determine the kinetic parameters of D-glutamine as a substrate or inhibitor. For example, phosphate-dependent glutaminase (PDG) activity can be assessed in renal tissue homogenates to evaluate D-glutamine metabolism. The effects of D-glutamine on enzyme activity are typically measured using spectrophotometric or fluorometric methods that detect glutamate or ammonia production. Acivicin, a selective antagonist of glutamine metabolism, is commonly used in these assays to confirm the specificity of D-glutamine's effects. Binding affinity studies may also employ radiolabeled D-glutamine to assess its interaction with transporters or enzymes involved in glutamine metabolism.

Role of L-glutamine in the protection of intestinal epithelium from acetaldehyde-induced disruption of barrier function was evaluated in Caco-2 cell monolayer. L-Glutamine reduced the acetaldehyde-induced decrease in transepithelilal electrical resistance and increase in permeability to inulin and lipopolysaccharide in a time- and dose-dependent manner; d-glutamine, L-aspargine, L-arginine, L-lysine, or L-alanine produced no significant protection. The glutaminase inhibitor 6-diazo-5-oxo-L-norleucine failed to affect the L-glutamine-mediated protection of barrier function. L-Glutamine reduced the acetaldehyde-induced redistribution of occludin, zonula occludens-1 (ZO-1), E-cadherin, and beta-catenin from the intercellular junctions. Acetaldehyde dissociates occludin, ZO-1, E-cadherin, and beta-catenin from the actin cytoskeleton, and this effect was reduced by L-glutamine. L-Glutamine induced a rapid increase in the tyrosine phosphorylation of EGF receptor, and the protective effect of L-glutamine was prevented by AG1478, the EGF-receptor tyrosine kinase inhibitor. These results indicate that L-glutamine prevents acetaldehyde-induced disruption of the tight junction and increase in the paracellular permeability in Caco-2 cell monolayer by an EGF receptor-dependent mechanism[2].

---

Caco-2 cell monolayers grown on polycarbonate membranes in Transwells were used. Cells were incubated with acetaldehyde (600 μM) for 4 hours in the presence or absence of D-glutamine (2 mM) administered to both apical and basal compartments. Transepithelial electrical resistance (TER) was measured using an electrical resistance system, and resistance values were calculated as ohms per cm² after subtracting membrane background. Unidirectional flux of FITC-inulin (0.5 mg/ml) was measured by adding it to the basal well and sampling from apical and basal compartments; fluorescence was read in a microplate reader, and flux was calculated as percentage of total fluorescence per hour per cm². D-glutamine showed no effect on acetaldehyde-induced changes in TER and inulin flux. [2]
In separate experiments, Caco-2 cells were preincubated with D-glutamine (2 mM) for varying times, but no protective effect against acetaldehyde was observed. [2]
D-Glutamine is commonly studied in Caco-2 cell monolayers, a well-established in vitro model of intestinal epithelial barrier function. In these experiments, Caco-2 cells are cultured on permeable supports to form confluent monolayers with tight junctions. D-Glutamine is added to the culture medium at various concentrations, and barrier function is assessed by measuring transepithelial electrical resistance (TEER) or paracellular permeability to fluorescent markers. Acetaldehyde is used to disrupt barrier function, and the protective effects of D-glutamine are evaluated. Additionally, Caco-2 cell proliferation, differentiation, and dipeptidyl dipeptidase activity can be measured to assess the effects of D-glutamine on intestinal epithelial function. These experiments typically include L-glutamine as a positive control and acivicin to block glutamine metabolism and confirm specificity.

In vivo animal studies involving D-glutamine are limited, but general protocols for glutamine research can be adapted. Animal models of intestinal injury, such as acetaldehyde-induced barrier disruption or stress-induced mucosal damage, are commonly used. D-Glutamine is typically administered orally or intraperitoneally at varying doses, and its effects on intestinal permeability, inflammation, and tissue integrity are assessed. For renal ammoniagenesis studies, D-glutamine metabolism is evaluated by measuring ammonia and glutamate levels in blood and urine. Tissue samples from liver, kidney, and skeletal muscle are collected to analyze enzyme activities such as glutaminase and glutamine synthetase. Body weight, food intake, and general health parameters are monitored throughout the study to assess tolerability.

D-Glutamine, like L-glutamine, is absorbed from the gastrointestinal tract and metabolized by various tissues. It is primarily metabolized by glutaminase in the liver and glutamine synthetase in skeletal muscle. In renal ammoniagenesis, D-glutamine undergoes intracellular metabolism by phosphate-dependent glutaminase (PDG) and glutamate dehydrogenase, as well as extracellular metabolism by phosphate-independent glutaminase. The pharmacokinetic profile of D-glutamine is expected to differ from L-glutamine due to stereospecific differences in transport and metabolism. However, specific PK data for D-glutamine are limited. Glutamine generally has a short half-life in plasma and is rapidly taken up by tissues. Its solubility in water is ≥32 mg/mL, facilitating administration in research settings.

D-Glutamine is generally considered to have low toxicity, consistent with its status as a naturally occurring amino acid. However, specific toxicological data for D-glutamine are limited. In cell-based studies, D-glutamine has been used at concentrations that do not cause overt cytotoxicity, as evidenced by its use in Caco-2 cell monolayer experiments. The protective effects of glutamine against injury suggest a favorable safety profile. In vivo, glutamine is well-tolerated at physiological doses, though high doses may lead to metabolic disturbances. As with other amino acids, excessive D-glutamine could potentially interfere with nitrogen balance or ammonia detoxification pathways. Research-grade D-glutamine is typically ≥95% pure and intended for laboratory use only.

[1]. The Glutamine Transporters and Their Role in the Glutamate/GABA-Glutamine Cycle. Adv Neurobiol. 2016;13:223-257.

[2]. L-Glutamine ameliorates acetaldehyde-induced increase in paracellular permeability in Caco-2 cellmonolayer. Am J Physiol Gastrointest Liver Physiol. 2004 Sep;287(3):G510-7.

D-Glutamine is the D-enantiomer of glutamine. It plays a metabolic role in mice. It is a D-α-amino acid and also a type of glutamine. It is the conjugate base of D-glutamine. It is the conjugate acid of D-glutamate. It is the enantiomer of L-glutamine. It is the zwitterion tautomer of D-glutamine. It is a non-essential amino acid, widely distributed in the body, and participates in various metabolic processes. It is synthesized from glutamate and ammonia. It is the main nitrogen carrier in the body and an important energy source for many cells. D-Glutamine is a metabolite found in or produced by Escherichia coli (K12 strain, MG1655 strain). D-Glutamine has been reported to exist in water fleas and humans, and relevant data exist. Glutamine is a non-essential amino acid, widely distributed in the body, and participates in various metabolic processes. It is synthesized from glutamate and ammonia. It is the main nitrogen carrier in the body and an important energy source for many cells. See also: glutamine (note moved to).

---

D-glutamine was used as a stereospecific control to demonstrate that the protective effect of L-glutamine on intestinal barrier function is stereospecific and not due to non-specific amino acid effects. D-glutamine did not prevent acetaldehyde-induced redistribution of tight junction proteins (occludin, ZO-1) and adherens junction proteins (E-cadherin, β-catenin) or their dissociation from the actin cytoskeleton. [2]
D-Glutamine is the D-isomer of the amino acid glutamine, a key pharmaconutrient in the body's response to stress and injury. It is primarily used as a research tool to study stereospecific effects of glutamine on cellular metabolism and barrier function. D-Glutamine has been investigated for its protective effects against acetaldehyde-induced disruption of intestinal epithelial barrier function in Caco-2 cell monolayers. Unlike L-glutamine, which is abundant in plasma and widely studied, D-glutamine is less common in biological systems and exhibits lesser potency in some assays. Its metabolism involves enzymes such as glutaminase in the liver and glutamine synthetase in skeletal muscle. D-Glutamine is not approved for clinical use and is strictly a research compound. It is available as a high-purity reagent for laboratory applications.

C5H10N2O3

146.14

146.069

C, 41.09; H, 6.90; N, 19.17; O, 32.84

5959-95-5

DL-Glutamine;6899-04-3;L-Glutamine;56-85-9

145815

Typically exists as white to off-white solids at room temperature

1.5±0.1 g/cm3

353.5±52.0 °C at 760 mmHg

185ºC

167.6±30.7 °C

0.0±1.8 mmHg at 25°C

1.564

-1.28

3

4

4

10

146

1

O([H])C([C@@]([H])(C([H])([H])C([H])([H])C(N([H])[H])=O)N([H])[H])=O

ZDXPYRJPNDTMRX-GSVOUGTGSA-N

InChI=1S/C5H10N2O3/c6-3(5(9)10)1-2-4(7)8/h3H,1-2,6H2,(H2,7,8)(H,9,10)/t3-/m1/s1

(2R)-2,5-diamino-5-oxopentanoic acid

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 12.5 mg/mL (85.53 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication (<60°C).

---

 (Please use freshly prepared in vivo formulations for optimal results.)