Alterations in neutrophil (PMN) free intracellular alpha-keto acid profiles and immune functions induced by L-alanyl-L-glutamine, arginine or taurine

Adenosine A2(A) receptor modulates the oxidative stress response of primed polymorphonuclear leukocytes after parabolic flight

Space flight and gravitational stress can alter innate immune function. Parabolic flights (PFs) as a model for short-term gravitational changes prime the cytotoxic capability of polymorphonuclear leukocytes (PMNs). In view of the emerging role of adenosine in the regulation of innate immune responses, we examined the potency of adenosine to control the release of cytotoxic H(2)O(2) by primed PMNs via the adenosine receptor system. During PFs, microgravity conditions (<10(-2) G) are generated for approximately 22 seconds, followed by a hypergravity (1.8 G) phase resulting in gravitational stress. We studied the ex vivo effects of adenosine on the production of H(2)O(2) by stimulated PMNs and determined adenosine plasma levels and adenosine A2(A) receptor transcripts of leukocytes of PF participants (n = 15). Increasing concentrations of adenosine dose dependently reduced tissue-toxic H(2)O(2) production by PMNs with a half-maximal inhibitory concentration (IC(50)) of 19.5 nM before takeoff and 7.6 nM at 48 hours after PF. This increase in the adenosine-mediated inhibition of PMNs' H(2)O(2) production was completely reversed by addition of the A2(A) receptor antagonist ZM241385. PF induced a nonsignificant elevation in adenosine plasma levels; A2(A) receptor mRNA from leukocytes remained almost unchanged. Adenosine limits the oxidative stress response of PMNs after PFs through an upregulation of the adenosine A2(A) receptor function. This stop signal on inflammation is stronger than that under normal physiologic states and may limit further cytotoxic damage. Pharmacologic manipulation of the adenosine A2(A) receptor pathway could be a potential target for control of unwanted exacerbations of cytotoxic PMN functions.

Pyruvate: immunonutritional effects on neutrophil intracellular amino or alpha-keto acid profiles and reactive oxygen species production

For the first time the immunonutritional role of pyruvate on neutrophils (PMN), free α-keto and amino acid profiles, important reactive oxygen species (ROS) produced [superoxide anion (O(2) (-)), hydrogen peroxide (H(2)O(2))] as well as released myeloperoxidase (MPO) acitivity has been investigated. Exogenous pyruvate significantly increased PMN pyruvate, α-ketoglutarate, asparagine, glutamine, aspartate, glutamate, arginine, citrulline, alanine, glycine and serine in a dose as well as duration of exposure dependent manner. Moreover, increases in O(2) (-) formation, H(2)O(2)-generation and MPO acitivity in parallel with intracellular pyruvate changes have also been detected. Regarding the interesting findings presented here we believe, that pyruvate fulfils considerably the criteria for a potent immunonutritional molecule in the regulation of the PMN dynamic α-keto and amino acid pools. Moreover it also plays an important role in parallel modulation of the granulocyte-dependent innate immune regulation. Although further research is necessary to clarify pyruvate's sole therapeutical role in critically ill patients' immunonutrition, the first scientific successes seem to be very promising.

Postresuscitation N-acetylcysteine treatment reduces cerebral hydrogen peroxide in the hypoxic piglet brain

OBJECTIVE

Reactive oxygen species have been implicated in the pathogenesis of hypoxia-reoxygenation injury. However, little information is known regarding the temporal profile of cerebral hydrogen peroxide (HPO) production and its response to N-acetylcysteine (an antioxidant) administration during neonatal hypoxia-reoxygenation. Using an acute swine model of neonatal hypoxia-reoxygenation, we examined the short-term neuroprotective effects of N-acetylcysteine on cerebral HPO production and oxidative stress in the brain.

DESIGN

Controlled, block-randomized animal study.

SETTING

University animal research laboratory.

SUBJECTS

Newborn piglets (1-3 days, 1.7-2.1 kg).

INTERVENTIONS

At 5 min after reoxygenation, piglets were given either saline or N-acetylcysteine (20 or 100 mg/kg/h) in a blinded, randomized fashion.

MEASUREMENTS AND RESULTS

Newborn piglets were block-randomized into a sham-operated group (without hypoxia-reoxygenation, n = 5) and three hypoxic-reoxygenated groups (2 h of normocapnic alveolar hypoxia followed by 2h of reoxygenation, n = 7/group). Heart rate, mean arterial pressure, cortical HPO concentration, amino acid levels in cerebral microdialysate, and cerebral tissue glutathione and lipid hydroperoxide levels were examined. Hypoxic piglets were hypotensive and acidotic, and they recovered similarly in all hypoxic-reoxygenated groups. In hypoxic-reoxygenated control piglets, the cortical HPO concentration gradually increased during reoxygenation. Both doses of N-acetylcysteine abolished the increased HPO concentration and oxidized glutathione levels and tended to reduce the glutathione ratio and lipid hydroperoxide levels in the cerebral cortex (p = 0.08 and p = 0.1 vs. controls, respectively). N-acetylcysteine at 100mg/kg/h also increased the cerebral extracellular taurine levels.

CONCLUSION

In newborn piglets with hypoxia-reoxygenation, postresuscitation administration of N-acetylcysteine reduces cerebral HPO production and oxidative stress, probably through a taurine-related mechanism.

Efeitos do estresse agudo de contenção, do estresse crônico de natação e da administração de glutamina sobre a liberação de superóxido por macrófagos alveolares de ratos

OBJETIVO: Avaliar a liberação de ânion superóxido por macrófagos alveolares em ratos submetidos ou não ao estresse agudo, ao exercício físico de natação e à suplementação com glutamina. MÉTODOS: Quarenta e dois ratos machos da linhagem Wistar com idade em torno de 62 (desvio-padrão=3) dias de idade foram divididos em grupos controle, treino, estresse e glutamina. Após a intervenção, macrófagos alveolares foram coletados e estimulados com acetato de formol miristato para a avaliação da liberação de ânion superóxido. RESULTADOS: Em comparação à primeira hora (controle=26,2, desvio-padrão=4,2; treino=28,7, desvio-padrão=5,1; estresse=20,3, desvio-padrão=4,4; glutamina=26,2, desvio-padrão=4,2), houve aumento (p<0,001) da liberação de superóxido em todos os grupos experimentais na segunda hora (controle=38,4, desvio-padrão=4,9; treino=40,7, desvio-padrão=6,1; estresse=30,2, desvio-padrão=5,6; glutamina=39,2, desvio-padrão=5,2) de observação. O treinamento e a suplementação com glutamina não provocaram diferenças na liberação de superóxido em macrófagos alveolares quando comparados ao grupo controle. Apenas nos ratos submetidos a estresse houve redução da liberação de superóxido tanto na primeira (20,3, desvio-padrão=4,4; p<0,05) quanto na segunda hora (30,2, desvio-padrão=5,6; p<0,05) de observação. CONCLUSÃO: Os achados sugerem que o estresse pode ser um dos fatores implicados na imunossupressão, uma vez que a redução da produção de ânion superóxido por macrófagos pode levar à diminuição de sua capacidade microbicida. No entanto, o protocolo de treinamento físico de natação usado e a suplementação com glutamina, na quantidade e na forma administrada, não alteraram a liberação de superóxido por macrófagos alveolares.

Which mechanisms are involved in taurine-dependent granulocytic immune response or amino- and α-keto acid homeostasis?

We examined the effects of beta-alanine (taurine analogue and taurine transport antagonist), taurine (regarding its role in neutrophil (PMN) immunonutrition) and taurine combined either with L-NAME (inhibitor of *NO-synthase), SNAP (*NO donor), DON (glutamine-analogue and inhibitor of glutamine-requiring enzymes), DFMO (inhibitor of ornithine-decarboxylase) and beta-alanine on neutrophil amino- and alpha-keto acid profiles or important PMN immune functions in order to establish whether taurine transport-, nitric oxide-, glutamine- or ornithine-dependent mechanisms are involved in any of the taurine-induced effects. According to the present findings, the taurine-mediated effect appears to be based primarily on a modulation of important transmembraneous transport mechanisms and only secondarily on directly or indirectly induced modifications in intragranulocytic amino- and alpha-keto acid homoeostasis or metabolism. Although a direct relation to the parallel observed immunological modifications can only be presumed, these results show very clearly that compositional modifications in the free intragranulocytic amino- and alpha keto-acid pools coinciding with changes in intragranulocytic taurine levels are relevant metabolic determinants that can significantly influence the magnitude and quality of the granulocytic immune response.

L-Arginine supplementation in sepsis: beneficial or harmful?

PURPOSE OF REVIEW

Recent results are reviewed on the effects of L-arginine supplements in excess of standard nutritional practices during severe sepsis and septic shock.

RECENT FINDINGS

Septic shock has been alternatively viewed as an L-arginine-deficient state or as a syndrome caused by excess nitric oxide, a vasoactive product of L-arginine metabolism. L-Arginine has many physiologic and pharmacologic effects that indicate its potential to affect survival in septic patients. Animal studies have documented immunologic effects of L-arginine and of commercial 'immune-enhancing' diets. However, survival studies in small animals have not consistently favored L-arginine. L-Arginine monotherapy in a canine model of septic shock found significant harm at infusion rates of less than twice that administered in standard formulations of total parenteral nutrition. Meanwhile, clinical studies have suffered from lack of statistical power, patient heterogeneity, randomization failures, and use of complex nutritional formulas. Meta-analyses have noted heterogeneity between the effects of immune-enhancing diets in surgical versus medical patients and mixed critically ill populations that include subjects with sepsis, indicating that these results may not be reliably pooled.

SUMMARY

To date, published evidence has not established the safety and efficacy of L-arginine at doses above standard dietary practices in severe sepsis or septic shock.

Pathways involved in alanyl-glutamine-induced changes in neutrophil amino- and α-keto acid homeostasis or immunocompetence

We examined the effects of DON [glutamine-analogue and inhibitor of glutamine-requiring enzymes], alanyl-glutamine (regarding its role in neutrophil immunonutrition) and alanyl-glutamine combined with L-NAME, SNAP, DON, beta-alanine and DFMO on neutrophil amino and alpha-keto acid concentrations or important neutrophil immune functions in order to establish whether an inhibitor of *NO-synthase [L-NAME], an *NO donor [SNAP], an analogue of taurine and a taurine transport antagonist [beta-alanine], an inhibitor of ornithine-decarboxylase [DFMO] as well as DON could influence any of the alanyl-glutamine-induced effects. In summary, irrespective of which pharmacological, metabolism-inhibiting or receptor-mediated mechanisms were involved, our results showed that impairment of granulocytic glutamine uptake, modulation of intracellular glutamine metabolisation and/or de novo synthesis as well as a blockade of important glutamine-dependent metabolic processes may led to significant modifications of physiological and immunological functions of the affected cells.

[What is your diagnosis? (Cutaneous leishmaniasis)]

Neutrophils are the most abundant, short lived, and terminally differentiated leukocytes with distinct tiers of arsenals to counter pathogens. Neutrophils were traditionally considered transcriptionally inactive cells, but recent researches in the field led to a paradigm shift in neutrophil biology and revealed subpopulation heterogeneity, and functions pivotal to immunity and inflammation. Furthermore, recent unfolding of metabolic plasticity in neutrophils has challenged the long-standing concept of their sole dependence on glycolytic pathway. Metabolic adaptations and distinct regulations have been identified which are critical for neutrophil differentiation and functions. The metabolic reprogramming of neutrophils by inflammatory mediators or during pathologies such as sepsis, diabetes, glucose-6-phosphate dehydrogenase deficiency, glycogen storage diseases (GSDs), systemic lupus erythematosus (SLE), rheumatoid arthritis, and cancer are now being explored. In this review, we discuss recent developments in understanding of the metabolic regulation, that may provide clues for better management and newer therapeutic opportunities for neutrophil centric immuno-deficiencies and inflammatory disorders.