Exogenous glutamine impairs neutrophils migration into infections sites elicited by lipopolysaccharide by a multistep mechanism

Glutamine modulates neutrophil recruitment and effector functions during sterile inflammation

During sterile inflammation, tissue damage induces excessive activation and infiltration of neutrophils into tissues, where they critically contribute to organ dysfunction. Tight regulation of neutrophil migration and their effector functions is crucial to prevent overshooting immune responses. Neutrophils utilize more glutamine, the most abundant free α-amino acid in the human blood, than other leukocytes. However, under inflammatory conditions, the body's requirements exceed its ability to produce sufficient amounts of glutamine. This study investigates the impact of glutamine on neutrophil recruitment and their key effector functions. Glutamine treatment effectively reduced neutrophil activation by modulating β2-integrin activity and chemotaxis in vitro. In a murine in vivo model of sterile inflammation induced by renal ischemia-reperfusion injury, glutamine administration significantly attenuated neutrophil recruitment into injured kidneys. Transcriptomic analysis revealed, glutamine induces transcriptomic reprograming in murine neutrophils, thus improving mitochondrial functionality and glutathione metabolism. Further, glutamine influenced key neutrophil effector functions, leading to decreased production of reactive oxygen species and formation of neutrophil extracellular traps. Mechanistically, we used a transglutaminase 2 inhibitor to identify transglutaminase 2 as a downstream mediator of glutamine effects on neutrophils. In conclusion, our findings suggest that glutamine diminishes activation and recruitment of neutrophils and thus identify glutamine as a potent means to curb overshooting neutrophil responses during sterile inflammation.

Harnessing amino acid pathways to influence myeloid cell function in tumor immunity

Amino acids are pivotal regulators of immune cell metabolism, signaling pathways, and gene expression. In myeloid cells, these processes underlie their functional plasticity, enabling shifts between pro-inflammatory, anti-inflammatory, pro-tumor, and anti-tumor activities. Within the tumor microenvironment, amino acid metabolism plays a crucial role in mediating the immunosuppressive functions of myeloid cells, contributing to tumor progression. This review delves into the mechanisms by which specific amino acids-glutamine, serine, arginine, and tryptophan-regulate myeloid cell function and polarization. Furthermore, we explore the therapeutic potential of targeting amino acid metabolism to enhance anti-tumor immunity, offering insights into novel strategies for cancer treatment.

Bidirectional role of neutrophils in tumor development

Neutrophils, traditionally considered as non-specific components of the innate immune system, have garnered considerable research interest due to their dual roles in both promoting and inhibiting tumor progression. This paper seeks to clarify the specific mechanisms by which neutrophils play a bidirectional role in tumor immunity and the factors that influence these roles. By conducting a comprehensive analysis and synthesis of a vast array of relevant literature, it has become evident that neutrophils can influence tumor development and invasive migration through various mechanisms, thereby exerting their anti-tumor effects. Conversely, they can also facilitate tumorigenesis and proliferation, as well as affect the normal physiological functions of other immune cells, thus exerting pro-tumor effects. Moreover, neutrophils are influenced by tumor cells and their unique microenvironment, which in turn affects their heterogeneity and plasticity. Neutrophils interact with tumor cells to regulate various aspects of their life activities precisely. This paper also identifies unresolved issues in the research concerning the bidirectional role of neutrophils in tumorigenesis and tumor development, offering new opportunities and challenges for advancing our understanding. This, in turn, can aid in the proper application of these insights to clinical treatment strategies.

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.

Immunometabolic Signature during Respiratory Viral Infection: A Potential Target for Host-Directed Therapies

RNA viruses are known to induce a wide variety of respiratory tract illnesses, from simple colds to the latest coronavirus pandemic, causing effects on public health and the economy worldwide. Influenza virus (IV), parainfluenza virus (PIV), metapneumovirus (MPV), respiratory syncytial virus (RSV), rhinovirus (RhV), and coronavirus (CoV) are some of the most notable RNA viruses. Despite efforts, due to the high mutation rate, there are still no effective and scalable treatments that accompany the rapid emergence of new diseases associated with respiratory RNA viruses. Host-directed therapies have been applied to combat RNA virus infections by interfering with host cell factors that enhance the ability of immune cells to respond against those pathogens. The reprogramming of immune cell metabolism has recently emerged as a central mechanism in orchestrated immunity against respiratory viruses. Therefore, understanding the metabolic signature of immune cells during virus infection may be a promising tool for developing host-directed therapies. In this review, we revisit recent findings on the immunometabolic modulation in response to infection and discuss how these metabolic pathways may be used as targets for new therapies to combat illnesses caused by respiratory RNA viruses.

Comorbidity-associated glutamine deficiency is a predisposition to severe COVID-19

SARS-CoV-2 vaccinations have greatly reduced COVID-19 cases, but we must continue to develop our understanding of the nature of the disease and its effects on human immunity. Previously, we suggested that a dysregulated STAT3 pathway following SARS-Co-2 infection ultimately leads to PAI-1 activation and cascades of pathologies. The major COVID-19-associated metabolic risks (old age, hypertension, cardiovascular diseases, diabetes, and obesity) share high PAI-1 levels and could predispose certain groups to severe COVID-19 complications. In this review article, we describe the common metabolic profile that is shared between all of these high-risk groups and COVID-19. This profile not only involves high levels of PAI-1 and STAT3 as previously described, but also includes low levels of glutamine and NAD+, coupled with overproduction of hyaluronan (HA). SARS-CoV-2 infection exacerbates this metabolic imbalance and predisposes these patients to the severe pathophysiologies of COVID-19, including the involvement of NETs (neutrophil extracellular traps) and HA overproduction in the lung. While hyperinflammation due to proinflammatory cytokine overproduction has been frequently documented, it is recently recognized that the immune response is markedly suppressed in some cases by the expansion and activity of MDSCs (myeloid-derived suppressor cells) and FoxP3+ Tregs (regulatory T cells). The metabolomics profiles of severe COVID-19 patients and patients with advanced cancer are similar, and in high-risk patients, SARS-CoV-2 infection leads to aberrant STAT3 activation, which promotes a cancer-like metabolism. We propose that glutamine deficiency and overproduced HA is the central metabolic characteristic of COVID-19 and its high-risk groups. We suggest the usage of glutamine supplementation and the repurposing of cancer drugs to prevent the development of severe COVID-19 pneumonia.

Effect of systemic photobiomodulation in the course of acute lung injury in rats

Acute lung injury (ALI) is a severe, multifactorial lung pathology characterized by diffuse alveolar injury, inflammatory cell infiltration, alveolar epithelial barrier rupture, alveolar edema, and impaired pulmonary gas exchange, with a high rate of mortality; and sepsis is its most common cause. The mechanisms underlying ALI due to systemic inflammation were investigated experimentally by systemic lipopolysaccharide (LPS) administration. Photobiomodulation (PBM) has been showing good results for several inflammatory diseases, but there are not enough studies to support the real benefits of its use, especially systemically. Considering that ALI is a pathology with high morbidity and mortality, we studied the effect of systemic PBM with red light-emitting diode (LED) (wavelength 660 nm; potency 100 mW; energy density 5 J/cm; total energy 15 J; time 150 s) in the management of inflammatory parameters of this disease. For this, 54 male Wistar rats were submitted to ALI by LPS injection (IP) and treated or not with PBM systemically in the tail 2 and 6 h after LPS injection. Data were analyzed by one-way ANOVA followed by Student's Newman-Keuls. Our results point to the beneficial effects of systemic PBM on the LPS-induced ALI, as it reduced the number of neutrophils recruited into the bronchoalveolar lavage, myeloperoxidase activity, and also reduced interleukins (IL) 1β, IL-6, and IL-17 in the lung. Even considering the promising results, we highlight the importance of further studies to understand the mechanisms involved, and especially the dosimetry, so that in near future, we can apply this knowledge in clinical practice.

Neutrophil Metabolic Shift during their Lifecycle: Impact on their Survival and Activation

Polymorphonuclear neutrophils (PMNs) are innate immune cells, which represent 50% to 70% of the total circulating leukocytes. How PMNs adapt to various microenvironments encountered during their life cycle, from the bone marrow, to the blood plasma fraction, and to inflamed or infected tissues remains largely unexplored. Metabolic shifts have been reported in other immune cells such as macrophages or lymphocytes, in response to local changes in their microenvironment, and in association with a modulation of their pro-inflammatory or anti-inflammatory functions. The potential contribution of metabolic shifts in the modulation of neutrophil activation or survival is anticipated even though it is not yet fully described. If neutrophils are considered to be mainly glycolytic, the relative importance of alternative metabolic pathways, such as the pentose phosphate pathway, glutaminolysis, or the mitochondrial oxidative metabolism, has not been fully considered during activation. This statement may be explained by the lack of knowledge regarding the local availability of key metabolites such as glucose, glutamine, and substrates, such as oxygen from the bone marrow to inflamed tissues. As highlighted in this review, the link between specific metabolic pathways and neutrophil activation has been outlined in many reports. However, the impact of neutrophil activation on metabolic shifts' induction has not yet been explored. Beyond its importance in neutrophil survival capacity in response to available metabolites, metabolic shifts may also contribute to neutrophil population heterogeneity reported in cancer (tumor-associated neutrophil) or auto-immune diseases (Low/High Density Neutrophils). This represents an active field of research. In conclusion, the characterization of neutrophil metabolic shifts is an emerging field that may provide important knowledge on neutrophil physiology and activation modulation. The related question of microenvironmental changes occurring during inflammation, to which neutrophils will respond to, will have to be addressed to fully appreciate the importance of neutrophil metabolic shifts in inflammatory diseases.