EFFECT OF GLUTAMINE ON CELLULAR ADHESION MOLECULE EXPRESSION AND LEUKOCYTE TRANSMIGRATION IN ENDOTHELIAL CELLS STIMULATED BY PLASMA OR PERITONEAL DRAIN FLUID FROM A SURGICAL PATIENT

Glutamine Deficiency Promotes Immune and Endothelial Cell Dysfunction in COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has caused the death of almost 7 million people worldwide. While vaccinations and new antiviral drugs have greatly reduced the number of COVID-19 cases, there remains a need for additional therapeutic strategies to combat this deadly disease. Accumulating clinical data have discovered a deficiency of circulating glutamine in patients with COVID-19 that associates with disease severity. Glutamine is a semi-essential amino acid that is metabolized to a plethora of metabolites that serve as central modulators of immune and endothelial cell function. A majority of glutamine is metabolized to glutamate and ammonia by the mitochondrial enzyme glutaminase (GLS). Notably, GLS activity is upregulated in COVID-19, favoring the catabolism of glutamine. This disturbance in glutamine metabolism may provoke immune and endothelial cell dysfunction that contributes to the development of severe infection, inflammation, oxidative stress, vasospasm, and coagulopathy, which leads to vascular occlusion, multi-organ failure, and death. Strategies that restore the plasma concentration of glutamine, its metabolites, and/or its downstream effectors, in conjunction with antiviral drugs, represent a promising therapeutic approach that may restore immune and endothelial cell function and prevent the development of occlusive vascular disease in patients stricken with COVID-19.

The ERK1/2 pathway participates in the upregulation of the expression of mesenteric artery α1 receptors by intravenous tail injections of mmLDL in mice

Minimally modified low density lipoprotein (mmLDL) is a risk factor for cardiovascular diseases. However, no studies examining the effect of mmLDL on vascular smooth muscle receptors have been released. The current study investigated the effect of mmLDL on the mesenteric artery α1 adrenoceptor and the molecular mechanisms. Mice were divided into the normal saline (NS), mmLDL, and mmLDL+U0126 groups. In the mmLDL+U0126 group, the animals were subjected to an intravenous tail injection of mmLDL and an intraperitoneal injection of U0126. Vascular tension caused by noradrenaline (NA) in mesenteric arteries was measured with a sensitive myograph system. The serum levels of oxLDL, TNF-α, and IL-1β were detected using enzyme-linked immunosorbent assays. The expressions of the α1 adrenoceptor, the α2 adrenoceptor, TNF-α, IL-1β, and pERK1/2 were detected using real-time polymerase chain reactions and Western blot analysis. Compared with the NS group, the mmLDL group exhibited a noticeably enhanced NA shrinkage dose-response curve and a significantly increased Emax value (P<0.01). Prazosin (α1 adrenoceptor antagonist) caused a noticeable right shift of the dose-response curve. U0126 inhibited the increases in the serum levels and vessel wall expression of IL-1β and TNF-α and enhanced the NA shrinkage dose-response curve caused by mmLDL, as observed by a significantly decreased Emax value (P<0.01). It inhibited the increased α1 adrenoceptor expression caused by mmLDL. The serum levels of IL-1β and TNF-α demonstrated a positive correlation with the NA-induced maximum shrinkage percentage. U0126 inhibited the mmLDL-induced increase in the pERK1/2 protein level in the vessel wall. In conclusion, mmLDL increased the serum levels of IL-1β and TNF-α in vivo by activating the ERK1/2 pathway, which resulted in α1 receptor-mediated vasoconstriction and an increase in the expression of α1 adrenoceptor. The results of this study may provide new ideas for the prevention and cure of cardiovascular diseases in the future.

Oral glutamine supplement inhibits ascites formation in peritoneal carcinomatosis mouse model

Background. Peritoneal carcinomatosis (PC) accompanied with ascites formation causes several distressing symptoms, resulting in poor quality of life. Methods. Twenty BALB/c nude mice generated by direct orthotopic injection of human pancreatic cancer PANC-1 cells were randomized to receive either a stock laboratory diet or a stock diet supplemented with glutamine. Half of the mice were sacrificed at day 76 to measure the amount of ascitic fluid and pancreatic tumor volume. The remaining mice were subject to survival analysis. Serum albumin levels were estimated every 2 weeks. Results. At day 76, the average amount of ascitic fluid measured in the control group was 1.2 ± 0.3 mL compared to 0.5 ± 0.5 mL from the glutamine-supplemented mice (P = 0.045). The volume of pancreatic tumor was 2.60 ± 0.8 cm³ in the control group and 1.98 ± 1.3 cm³ in glutamine-supplemented mice (P = 0.39). The mean survival time of glutamine-supplemented mice was prolonged from 87 ± 4 to 101 ± 2 days (P = 0.0024). Mean serum albumin levels were higher in the glutamine-supplemented group. Conclusions. This preclinical study showed that oral supplementation of glutamine may provide ascites-reducing activity in pancreatic cancer patients with PC, via a cell-mediated immunity-independent mechanism.

Arginine stimulates cdx2-transformed intestinal epithelial cell migration via a mechanism requiring both nitric oxide and phosphorylation of p70 S6 kinase

In intestinal cells, arginine (Arg) is 1 of the 2 most potent amino acid activators of p70(s6k), a key regulator of 5'- terminal oligopyrimidine mRNA translation, a necessary condition for increased cell migration. To investigate the mechanism of response to Arg, we used the rat crypt cell line cdx2-transformed IEC-6 cells (cdx2-IEC) and measured cell migration, immunocytochemical analysis of p70(s6k) activation in response to Arg, and production of nitric oxide (NO). When treated with Arg, cdx2-IEC increased in phosphorylation on Thr-389 of p70(s6k) (pp70(s6k)) compared with control (P < 0.01). Phospho-Thr-421/Ser-424-p70(s6k) was located in the nucleus shortly after Arg treatment. Arg enhanced pp70(s6k), cell migration (55% wound coverage), and NO production. In comparison, the branched-chain amino acid leucine (Leu) activated pp70(s6k), was a weaker stimulator of migration (23% coverage), and did not increase NO. A total of 25 micromol/L DETA-NONOate (DETA/NO) did not significantly enhance phosphorylation of p70(s6k) but enhanced the rate of cell migration by approximately 25%. Wound coverage with Leu plus DETA/NO (25 micromol/L) was greater than coverage with DETA/NO alone (P < 0.01). These and our previous studies lead to a model in which Arg must stimulate both pp70(s6k) (in the nucleus) and NO release to enhance intestinal epithelial cell migration, which may be relevant to diseases that involve intestinal villous injury.

Alanyl-glutamine consumption modifies the suppressive effect of L-asparaginase on lymphocyte populations in mice

Asparaginase (Elspar) is used in the treatment of acute lymphoblastic leukemia. It depletes plasma asparagine and glutamine, killing leukemic lymphoblasts but also causing immunosuppression. The objective of this work was to assess whether supplementing the diet with glutamine modifies the effect of asparaginase on normal lymphocyte populations in the spleen, thymus, and bone marrow. Mice consuming water ad libitum with or without alanyl-glutamine dipeptide (AlaGln; 0.05 mol/L) were injected once daily with 0 or 3 international units/g body weight Escherichia coli L-asparaginase for 7 d. Tissue expression of specific immune cell surface markers was analyzed by flow cytometry. Asparaginase reduced B220+ and sIgM+ cells in the bone marrow (P < 0.05) and diminished total cell numbers in thymus (-42%) and spleen (-53%) (P < 0.05). In thymus, asparaginase depleted double positive (CD4+ CD8+) and single positive (CD4+ CD8-, CD4-CD8+) thymocytes by over 40% (P < 0.05). In spleen, asparaginase reduced CD19+ B cells to 33% of controls and substantially depleted the CD4+ and CD8+ T cell populations. CD11b-expressing leukocytes were reduced by 50% (P < 0.05). Consumption of AlaGln did not lessen the effects of asparaginase in bone marrow or thymus but mitigated cellular losses in the CD4+, CD8+, and CD11b+ populations in spleen. AlaGln also blunted the increase in eukaryotic initiation factor 2 (eIF2) phosphorylation by asparaginase in spleen, whereas eIF2 phosphorylation did not change in thymus in response to asparaginase or AlaGln. In conclusion, asparaginase reduces maturing populations of normal B and T cells in thymus, bone marrow, and spleen. Oral consumption of AlaGln mitigates metabolic stress in spleen, supporting the peripheral immune system and cell-mediated immunity during asparaginase chemotherapy.

EFFECT OF ARGININE ON CELLULAR ADHESION MOLECULE EXPRESSION AND LEUKOCYTE TRANSMIGRATION IN ENDOTHELIAL CELLS STIMULATED BY BIOLOGICAL FLUID FROM SURGICAL PATIENTS

This study investigated the effect of different arginine (Arg) concentrations on adhesion molecule expression on endothelial cells (ECs) and leukocytes and the transendothelial migration of polymorphonuclear neutrophils (PMNs) through ECs stimulated by plasma or peritoneal drain fluid (PDF) from surgical patients. Human umbilical vein ECs (HUVECs) and PMNs from healthy subjects were treated with different concentrations (0, 50, 100, and 1000 micromol/L) of Arg for 24 h. After that, HUVECs were stimulated for 3 h with plasma or PDF from patients who underwent abdominal surgery, and PMNs were allowed to transmigrate through ECs for 2 h. The HUVEC expression of cellular adhesion molecules (CAMs) and integrin (CD11b) and the interleukin (IL) 8 receptor expression on PMNs were measured by flow cytometry. The PMNs transmigrating through ECs were also analyzed. The results showed that CAM and integrin expressions in PDF groups were higher than those in control groups. Among the PDF groups, IL-8 secretions from ECs and PMNs were lower with 100 and 1000 micromol/L Arg than with 0 and 50 micromol/L Arg, and this was consistent with the expression of the IL-8 receptor on PMNs. In addition, CAM expressions on ECs and CD11b expression on PMNs, as well as PMN transmigration, were lower with 100 and 1000 micromol/L Arg than with 0 and 50 micromol/L Arg. The HUVECs stimulated by plasma from surgical patients had similar effects on surface molecule expression as PDF; however, as shown in PDF stimulation, the effects were not so obvious. Inhibition of nitric oxide production results in high CAM and IL-8 expressions comparable with groups with low Arg administration. The results of this in vitro study suggest that ECs and PMNs were activated after patients' plasma or PDF stimulation. A low Arg concentration comparable with catabolic conditions resulted in higher adhesion molecule expression and greater transendothelial migration of neutrophils. Arginine administration at levels similar to or higher than physiological concentrations reduced IL-8 and CAM expression, and PMN transmigration was also decreased after stimulation with plasma or PDF from surgical patients. Inactivation of NO results in high CAM and IL-8 expression. This finding indicated that NO may be an important endogenous inhibitor for EC-PMN interaction and neutrophil transmigration.