Glutamine supplements in the critically ill

Structural and biochemical imaging reveals systemic LPS-induced changes in the rat brain

Despite mounting evidence for the role of inflammation in Major Depressive Disorder (MDD), in vivo preclinical investigations of inflammation-induced negative affect using whole brain imaging modalities are scarce, precluding a valid model within which to evaluate pharmacological interventions. Here we used an E. coli lipopolysaccharide (LPS)-based model of inflammation-induced depressive signs in rats to explore brain changes using multimodal neuroimaging methods. During the acute phase of the LPS response (2 h post injection), prior to the emergence of a task-quantifiable depressive phenotype, striatal glutamine levels and splenial, retrosplenial, and peri-callosal hippocampal cortex volumes were greater than at baseline. LPS-induced depressive behaviors observed at 24 h, however, occurred concurrently with lower than control levels of striatal glutamine and a reversibility of volume expansion (i.e., shrinkage of splenial, retrosplenial, and peri-callosal hippocampal cortex to baseline volumes). In both striatum and hippocampus at 24 h, mRNA expression in LPS relative to control animals demonstrated alterations in enzymes and transporters regulating glutamine homeostasis. Collectively, the observed behavioral, in vivo structural and metabolic, and mRNA expression alterations suggest a critical role for astrocytic regulation of inflammation-induced depressive behaviors.

Glutamine-Loaded Liposomes: Preliminary Investigation, Characterization, and Evaluation of Neutrophil Viability

Glutamine has received attention due to its ability to ameliorate the immune system response. Once conventional liposomes are readily recognized and captured by immune system cells, the encapsulation of glutamine into those nanosystems could be an alternative to reduce glutamine dosage and target then to neutrophils. Our goals were to nanoencapsulate glutamine into conventional liposomes (Gln-L), develop an analytical high-performance liquid chromatography (HPLC) method for its quantification, and evaluate the viability of neutrophils treated with Gln-L. Liposomes were prepared using the thin-film hydration technique followed by sonication and characterized according to pH, mean size, zeta potential, and drug encapsulation efficiency (EE%). We also aimed to study the effect of liposomal constituent concentrations on liposomal characteristics. The viability of neutrophils was assessed using flow cytometry after intraperitoneal administration of free glutamine (Gln), Gln-L, unloaded-liposome (UL), and saline solution as control (C) in healthy Wistar rats. The selected liposomal formulation had a mean vesicle size of 114.65 ± 1.82 nm with a polydispersity index of 0.30 ± 0.00, a positive surface charge of 36.30 ± 1.38 mV, and an EE% of 39.49 ± 0.74%. The developed chromatographic method was efficient for the quantification of encapsulated glutamine, with a retention time at 3.8 min. A greater viability was observed in the group treated with glutamine encapsulated compared to the control group (17%), although neutrophils remain viable in all groups. Thus, glutamine encapsulated into liposomes was able to increase the number of viable neutrophils at low doses, thereby representing a promising strategy for the treatment of immunodeficiency conditions.

Tumor necrosis factor-α suppresses the protein fractional synthesis rate of the small intestine stimulated by glutamine in rats

The objective of this study was to examine whether and how TNF-α affects glutamine-enhanced protein synthesis and the expression of the amino acid transporter ASCT2 in the small intestine at the mRNA and protein levels. A total of 30 male Sprague-Dawley rats were randomly assigned into three groups, namely the total parenteral nutrition (TPN; control), glutamine-treated (Gln), and glutamine- and tumor necrosis factor-α (TNF-α)-treated (TNF-α) groups. At 30 min prior to examination, all rats were mainlined with [L-¹⁵N]leucine. The concentration of TNF-α in plasma and of glutamine in plasma and the small intestine was measured. The fractional synthesis rate (FSR) of protein and the mRNA and protein expression levels of ASCT2 in the small intestine were assessed. The level of TNF-α was highest in the TNF-α group and the glutamine concentration was elevated to a greater extent in the TNF-α group than in the other two groups. However, the FSR of protein in the small intestine was significantly higher in the Gln group compared with that in the TNF-α group. The mRNA and protein expression levels of ASCT2 in the experimental groups were significantly higher that those in the control group, but did not differ significantly between the Gln and TNF-α groups. These results indicate that TNF-α may attenuate glutamine-stimulated protein synthesis in the small intestine in the early stage of sepsis in rats. The mechanism may be that TNF-α inhibits the function of the glutamine transporter in the uptake the glutamine into target cells for protein synthesis. This inhibition may occur at or following protein translation.

Glutamine depletion induces murine neonatal melena with increased apoptosis of the intestinal epithelium

AIM: To investigate the possible biological outcome and effect of glutamine depletion in neonatal mice and rodent intestinal epithelial cells.

METHODS: We developed three kinds of artificial milk with different amounts of glutamine; Complete amino acid milk (CAM), which is based on maternal mouse milk, glutamine-depleted milk (GDM), and glutamine-rich milk (GRM). GRM contains three-fold more glutamine than CAM. Eighty-seven newborn mice were divided into three groups and were fed with either of CAM, GDM, or GRM via a recently improved nipple-bottle system for seven days. After the feeding period, the mice were subjected to macroscopic and microscopic observations by immunohistochemistry for 5-bromo-2’-deoxyuridine (BrdU) and Ki-67 as markers of cell proliferation, and for cleaved-caspase-3 as a marker of apoptosis. Moreover, IEC6 rat intestinal epithelial cells were cultured in different concentrations of glutamine and were subject to a 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate cell proliferation assay, flow cytometry, and western blotting to examine the biological effect of glutamine on cell growth and apoptosis.

RESULTS: During the feeding period, we found colonic hemorrhage in six of 28 GDM-fed mice (21.4%), but not in the GRM-fed mice, with no differences in body weight gain between each group. Microscopic examination showed destruction of microvilli and the disappearance of glycocalyx of the intestinal wall in the colon epithelial tissues taken from GDM-fed mice. Intake of GDM reduced BrdU incorporation (the average percentage of BrdU-positive staining; GRM: 13.8%, CAM: 10.7%, GDM: 1.14%, GRM vs GDM: P < 0.001, CAM vs GDM: P < 0.001) and Ki-67 labeling index (the average percentage of Ki-67-positive staining; GRM: 24.5%, CAM: 22.4% GDM: 19.4%, GRM vs GDM: P = 0.001, CAM vs GDM: P = 0.049), suggesting that glutamine depletion inhibited cell proliferation of intestinal epithelial cells. Glutamine deprivation further caused the deformation of the nuclear membrane and the plasma membrane, accompanied by chromatin degeneration and an absence of fat droplets from the colonic epithelia, indicating that the cells underwent apoptosis. Moreover, immunohistochemical analysis revealed the appearance of cleaved caspase-3 in colonic epithelial cells of GDM-fed mice. Finally, when IEC6 rat intestinal epithelial cells were cultured without glutamine, cell proliferation was significantly suppressed after 24 h (relative cell growth; 4 mmol/L: 100.0% ± 36.1%, 0 mmol/L: 25.3% ± 25.0%, P < 0.05), with severe cellular damage. The cells underwent apoptosis, accompanied by increased cell population in sub-G0 phase (4 mmol/L: 1.68%, 0.4 mmol/L: 1.35%, 0 mmol/L: 5.21%), where dying cells are supposed to accumulate.

CONCLUSION: Glutamine is an important alimentary component for the maintenance of intestinal mucosa. Glutamine deprivation can cause instability of the intestinal epithelial alignment by increased apoptosis.

Glutamina: aspectos bioquímicos, metabólicos, moleculares e suplementação

A glutamina é o aminoácido livre mais abundante no plasma e no tecido muscular. Nutricionalmente é classificada como um aminoácido não essencial, uma vez que pode ser sintetizada pelo organismo a partir de outros aminoácidos. A glutamina está envolvida em diferentes funções, tais como a proliferação e desenvolvimento de células, o balanço acidobásico, o transporte da amônia entre os tecidos, a doação de esqueletos de carbono para a gliconeogênese, a participação no sistema antioxidante e outras. Por meio de técnicas de biologia molecular, estudos demonstram que a glutamina pode também influenciar diversas vias de sinalização celular, em especial a expressão de proteínas de choque térmico (HSPs). As HSPs contribuem para a manutenção da homeostasia da célula na presença de agentes estressores, tais como as espécies reativas de oxigênio (ERO). Em situações de elevado catabolismo muscular, como após exercícios físicos intensos e prolongados, a concentração de glutamina pode tornar-se reduzida. A menor disponibilidade desse aminoácido pode diminuir a resistência da célula a lesões, levando a processos de apoptose celular. Por essas razões, a suplementação com L-glutamina, tanto na forma livre, quanto como dipeptídeo, tem sido investigada. Alguns aspectos bioquímicos, metabólicos e mecanismos moleculares da glutamina, bem como os efeitos de sua suplementação, são abordados no presente trabalho.

Changes of plasma glutamine concentration and hepatocyte membrane system N transporters expression in early endotoxemia

BACKGROUND

Glutamine plays important roles in health and critical illness. During endotoxemia, glutamine metabolism, including its plasma level and transport, changes markedly. Previous studies have demonstrated that system N transporters in hepatocytes play a major role in hepatic glutamine transport. However, little is known about the changes of mRNA and protein expression of system N transporters in hepatocyte plasma membrane. Furthermore, the alteration of plasma glutamine concentration during endotoxemia is still controversial. In this study, we investigated the changes in early endotoxemic rats by intraperitoneal injection of lipopolysaccharide (LPS).

MATERIALS AND METHODS

Three, 6, 12 mg/kg body weight doses of LPS were injected intraperitoneally to establish the endotoxemic rat model; equal volume of 0.9% saline was used as the control. Before and 2, 4, 6, 12, 24h after injections, plasma glutamine concentration, mRNA, and protein expression of SNAT3 and SNAT5 transporters in hepatocyte plasma membrane were detected by high performance liquid chromatography, real-time PCR, and Western blot, respectively.

RESULTS

LPS injection resulted in a marked increase of the plasma glutamine concentration from 4 to 12h (3mg/kg) and 2 to 6h (6 mg/kg, 12 mg/kg) after the injection compared with its physiologic level, and a significant decrease in 6, 12 mg/kg groups at 24h. Both the mRNA and protein expression of SNAT3 and SNAT5 were enhanced by LPS in a time- and dose-dependent manner.

CONCLUSIONS

The plasma glutamine concentration in endotoxemic rat increased transiently during early endotoxemia but subsequently decreased over time. The effect of LPS on system N expression occurs not only at the protein level, but also at the mRNA level. It is reasonable to supplement glutamine for patients with sepsis or endotoxemia begin at 6 to 12h after the development of disease.

The effect of glutamine-supplemented total parenteral nutrition on nutrition and intestinal absorptive function in a rat model

The aim of the present study was to evaluate the effect of short-term (7 days) glycyl-glutamine-supplemented total parenteral nutrition (TPN) on nutrition and intestinal absorptive function in a rat model. Thirty Wistar rats, weighting 140-180 g, were divided into three groups (n=10) randomly. The animals received isonitrogenous and isocaloric TPN solutions for 7 days. The nitrogen was supplied by glycyl-glutamine dipeptide-supplemented amino acid solution (group G), and two standard amino acid solutions (group V, group N), respectively. Body weight, plasma glutamine level, nitrogen balance, total tissue water and intestinal absorptive function, assessed by (15-N)-glycine absorption, were investigated. Body weight decreased in three groups at the end of TPN; there was no significant difference in relative body-weight changes. There was a significant improvement of cumulative nitrogen balance and nitrogen retention in group G compared to other groups (P<0.05). There was no significant difference in intestinal glycine absorption (P>0.05) among the three groups. Total tissue water of left thigh muscle was significantly higher in group V and group N than that in group G (P<0.05). The results indicated that short-term (7 days) TPN supplemented with glycyl-glutamine improved plasma glutamine level and nitrogen balance, decreased water content of muscle, but had no beneficial effect on absorptive function in a rat model.