Arginine is Essential in Reversing Prostaglandin E2 T-Cell Suppression by Hypertonic Saline

Protective effects of pentoxifylline on T-cell viability under inflammatory conditions

Introduction: Pentoxifylline (PTX) reduces the levels of pro-inflammatory cytokines; however, its effects on immune system is not well understood. The aim of this study was to investigate the effect of PTX on T cells under inflammatory conditions in co-culture with THP-1-derived macrophages.

Methods: Toll-like receptor 4 (TLR4) and macrophage migration inhibitory factor (MIF) levels were measured after addition of PTX to lipopolysaccharide (LPS)-stimulated differentiated THP-1 cells. T cell viability and MIF levels were measured after PTX was added to prostaglandin E2 (PGE2)-stimulated Jurkat T-cell leukemia line. Co-culture was conducted to determine the effect of LPS-stimulated differentiated THP-1 cells that are affected by PTX on Jurkat cells. To prevent the direct effects of LPS and PTX on Jurkat cells, LPS and PTX were washed from THP-1 cells before co-culture. T cell viability and interleukin-2 (IL-2) levels were determined in Jurkat cells. Results: Increase in the MIF concentration and TLR4 expression level in differentiated THP-1 cells stimulated with LPS were reversed after PTX addition. However, PTX did not improve T cell viability in PGE2–stimulated Jurkat cells. Co-culturing Jurkat cell and LPS-stimulated differentiated THP-1 cells resulted in a decreased viability of T cells. The addition of PTX restored T cell viability to normal control levels and IL-2 expression level in Jurkat cells. Conclusion: LPS-stimulated THP-1-derived macrophages reduced the T cell viability under inflammation. However, PTX restored T cells viability and IL-2 back to normal levels. Therefore, the immunomodulatory action of PTX may be mediated by macrophage-T cell interactions.

Acquired Amino Acid Deficiencies: A Focus on Arginine and Glutamine

Nonessential amino acids are synthesized de novo and therefore not diet dependent. In contrast, essential amino acids must be obtained through nutrition since they cannot be synthesized internally. Several nonessential amino acids may become essential under conditions of stress and catabolic states when the capacity of endogenous amino acid synthesis is exceeded. Arginine and glutamine are 2 such conditionally essential amino acids and are the focus of this review. Low arginine bioavailability plays a pivotal role in the pathogenesis of a growing number of varied diseases, including sickle cell disease, thalassemia, malaria, acute asthma, cystic fibrosis, pulmonary hypertension, cardiovascular disease, certain cancers, and trauma, among others. Catabolism of arginine by arginase enzymes is the most common cause of an acquired arginine deficiency syndrome, frequently contributing to endothelial dysfunction and/or T-cell dysfunction, depending on the clinical scenario and disease state. Glutamine, an arginine precursor, is one of the most abundant amino acids in the body and, like arginine, becomes deficient in several conditions of stress, including critical illness, trauma, infection, cancer, and gastrointestinal disorders. At-risk populations are discussed together with therapeutic options that target these specific acquired amino acid deficiencies.

Arginine Supplementation Induces Arginase Activity and Inhibits TNF-α Synthesis in Mice Spleen Macrophages After Intestinal Obstruction

BACKGROUND

The purpose of this study was to assess the effect of arginine supplementation on arginase activity, tumor necrosis factor-α (TNF-α) and interleukin-10 (IL-10) synthesis in cultured splenic macrophages from a murine model of intestinal obstruction (IO). The effects of nitric oxide synthase (iNOS) inhibition were also studied using iNOS knockout animals.

MATERIAL AND METHODS

Male C57BL6/J wild-type (WT) and iNOS knockout (iNOS-/-) mice were randomized into 6 groups: Sham and Sham-/- (standard chow), IO and IO-/- (standard chow + IO), and Arg and Arg-/- (standard chow supplemented with arginine + IO). After 7 days of treatment with standard or supplemented chow, IO was induced. Arginase activity as well as TNF-α and IL-10 levels were analyzed in splenic macrophage cultures.

RESULTS

Arginine supplementation and the absence of iNOS increased arginase activity in splenic macrophages (Arg, IO-/-, and Arg-/- groups vs the Sham group; P < .05). Arginine was also related to a decrease in TNF-α levels (Arg vs IO group, P < .05) and maintenance of IL-10 levels (Arg vs other groups, P > .05). The inhibition of iNOS did not result in effects on the concentration of cytokines (Sham-/-, IO-/-, and Arg-/- vs other, P < .05).

CONCLUSIONS

Arginine supplementation and iNOS inhibition led to increased arginase activity. Arginine availability decreased plasma TNF-α levels, which may be directly related to nitric oxide derived from arginine.

Effect of hypertonic saline on apoptosis of polymorphonuclear cells

BACKGROUND

The function of polymorphonuclear (PMN) cells can be influenced by the choice of resuscitation fluids in hemorrhagic shock. Widespread interest in the use of hypertonic solutions for resuscitation has led to extensive investigation of their immune-modulating properties. Hypertonic saline (HTS) is known to modulate immune reactions, preventing the multiorgan failure mediated by immune reactions in trauma and hemorrhagic shock. PMN cells play a key role in such immune-mediated inflammatory processes, and HTS is believed to affect these PMN cells. However, how these events influence the actual event of apoptosis has not yet been described. Thus, in the present study, we aimed to investigate the differences in the apoptosis of PMN cells when exposed to isotonic and hypertonic environments and the temporal relations between the interval of administration of HTS after the stimulation of PMN cells.

METHODS

Whole blood was sampled from healthy volunteers, and the PMN cells were isolated. The isolated layer of PMN cells was washed twice with phosphate-buffered saline to yield the PMN cells. The number of cells was kept uniform, and an overall survival rate greater than 95% was maintained. After stimulation of the isolated PMN cells with N-formyl-methionyl-leucyl-phenylalanine, the PMN cells were allocated into 3 study groups (i.e., 1 isotonic group and 2 hypertonic groups with an osmolarity of 160 mM and 180 mM each). The extent of apoptosis was investigated in each group after culturing the PMN cells for 0, 1, 3, 6, 12, 15, 18, and 24 h. Depending on whether the PMN cells were stimulated with N-formyl-methionyl-leucyl-phenylalanine, they were also divided into stimulated and nonstimulated groups. In the stimulated group, the hypertonic environment was fostered immediately (HTS 0 h) and 6 h (HTS 6 h) after stimulation, which was accomplished after allocating the cells into an isotonic group (140 mM) and a hypertonic group (180 mM), according to the concentration of the culture medium. The PMN cells were then cultured at 37°C for 15 h with 5% carbon dioxide incubation. Each PMN suspension was labeled with Annexin V-fluorescein isothiocyanate and propidium iodide. Each sample underwent immediate flow cytometric analysis. PMN cells with high propidium iodide uptake were considered nonviable (necrotic). Among the viable PMN cells, those with no Annexin V uptake were considered normal and those with Annexin V uptake were considered apoptotic.

RESULTS

Decreased apoptosis was observed in the PMN cells stimulated with N-formyl-methionyl-leucyl-phenylalanine. Increased apoptosis was observed in the stimulated PMN cells incubated in hypertonic condition compared with the cells incubated in isotonic condition. Early HTS administration demonstrated increased apoptosis compared with late administration.

CONCLUSIONS

HTS treatment resulted in increased PMN apoptosis and an anti-inflammatory effect. Decreased apoptosis (prolonged lifespan) has been implicated in neutrophil-mediated tissue damage. HTS, by increasing the apoptosis of PMN cells, attenuates the postinjury inflammatory response. Also, early treatment with HTS was more efficient than delayed treatment.

Hypertonic saline downregulate the production level of lipopolysaccharide-induced migration inhibitory factor in THP-1 cells

Purpose

Macrophage migration inhibitory factor (MIF) may serve as a general marker for systemic inflammation in septic and nonseptic acute critical illness. Additionally, our previous experiment has demonstrated that immunosuppressant Prostaglandin E₂ (PGE₂) lowered MIF levels and inhibited T-cells proliferation when compared to control levels. The addition of hypertonic saline (HTS) increased MIF production as compared with PGE₂-stimulated T-cells in concordance with restore PGE₂-suppressed T-cells proliferation. Generally, HTS has been well known for its anti-inflammatory effect so far. Therefore, the experiments were conducted to evaluate MIF after stimulating lipopolysaccharide (LPS) either in the presence or absence of HTS in monocyte, in response to early phase injury.

Methods

Human acute monocytic leukemic cell line (THP-1) cells were cultured in RPMI media, to a final concentration of 1 × 10⁶ cells/mL. The effect of HTS on LPS-induced MIF was evaluated in monocyte with 1 µg/mL LPS. HTS at 10, 20 or 40 mmol/L above isotonicity was added. MIF concentrations of the supernatant were determined by enzyme-linked immunosorbent assay, and cell lysates were used for Western blots analysis to determine the MIF expression.

Results

MIF concentrations in the cell supernatant increased in LPS-induced cells compared to control cells. Also, levels of MIF protein expression were higher in LPS stimulating cells. However, the addition of HTS to LPS stimulated cell restored MIF concentrations and MIF expression.

Conclusion

The role of HTS in maintaining physiological balance in human beings, at least in part, should be mediated through the MIF pathway.

Effect of hypertonic saline and macrophage migration inhibitory factor in restoration of T cell dysfunction

Purpose

Trauma-induced suppression of cellular immune function likely contributes to sepsis, multiple organ dysfunction syndrome and death. T cell proliferation decreases after traumatic stress. The addition of prostaglandin E₂ (PGE₂), which depresses immune function after hemorrhage and trauma, to T-cells decreases T-cell proliferation; and hypertonic saline restores PGE₂-induced T-cell suppression. Recently, it has become apparent that macrophage migration inhibitory factor (MIF) plays a central role in several immune responses, including T-cell proliferation. However, the role of MIF in mediating hypertonic saline (HTS) restoration of T cell dysfunction is unknown. Therefore, we hypothesize that T cell immune restoration by HTS occurs, at least in part, by a MIF-mediated mechanism.

Methods

Jurkat cells were cultured in Roswell Park Memorial Institute media, at a final concentration of 2.5 × 10⁶ cell/mL. The effects of HTS on T-cell proliferation following PGE₂-induced suppression were evaluated in Jurkat cells: HTS at 20 or 40 mmol/L above isotonicity was added. MIF levels were determined by enzyme-linked immunosorbent assay and western blot analysis.

Results

PGE₂ caused a 15.0% inhibition of Jurkat cell proliferation, as compared to the control. MIF levels decreased in PGE₂-suppressed cells, as compared to the control. MIF levels were higher in cells treated with HTS than PGE₂-stimulated cells.

Conclusion

The role of HTS in restoring Jurkat cells proliferation suppressed by PGE₂, at least in part, should be mediated through a MIF pathway.

Concentration of arginine and optimal time of hypertonic saline in restoration of T-cell dysfunction

BACKGROUND

Hypertonic saline (HS) restores prostaglandin E(2) (PGE(2))-induced T-cell suppression in the presence of 1100 microM arginine. However, under arginine-free culture conditions, HS dose not restore T-cell proliferation. Therefore, we wanted to determine if HS can restore PGE(2)-induced T-cell suppression in the presence of 80 microM of arginine, the physiologically relevant arginine concentration. We also wanted to determine the concentration of arginine that induces HS restoration of PGE(2)-suppressed T-cell proliferation and whether HS restoration of T-cell dysfunction is dependent on the injection time of HS.

MATERIALS AND METHODS

Jurkat cells were cultured in media containing 0, 40, 80, 400, 800, or 1100 microM arginine. In both the PGE(2)-stimulated and HS-treated group, we measured cell proliferation using MTT assay and arginase activity. We also measured cell proliferation relative to HS injection time.

RESULTS

In 80 microM arginine, HS did not restore Jurkat cell proliferation that had been suppressed by PGE(2). Increased concentrations of arginine in the media increased MTT cell proliferation. In 800 microM arginine media, HS restored PGE(2)-suppressed Jurkat cell proliferation to normal. HS restored PGE(2)-suppressed Jurkat cell proliferation when it was added at 2 h, similar to at same time and 1 h after PGE(2) stimulation.

CONCLUSIONS

In order to restore PGE(2)-suppressed Jurkat cell proliferation, HS requires at least 800 microM arginine. HS restored PGE(2)-suppressed Jurkat cell proliferation even though HS was added at 2 h after PGE(2) stimulation.