Immunological alterations mediated by adenosine during host-microbial interactions

Nanomaterials-mediated adenosine pathway inhibition for strengthening cancer immunotherapy

Immunotherapy has developed into an attractive tumor treatment strategy. However, the existence of an immunosuppressive tumor microenvironment (ITME) greatly reduces the efficacy of immunotherapy. Adenosine (ADO) is one of the vital negative feedbacks in ITME, which inhibits antigen presentation and immune cell activation by binding to adenosine receptors (ADORs), thus tremendously suppressing immune response. Currently, the treatment effect of numerous inhibitors targeting the ADO pathway has been demonstrated in early clinical trials of various tumors. Nevertheless, the clinical application of these inhibitors is still plagued by diverse issues, such as short half-life, a single administration route, low bioavailability, etc. With the progress of nanotechnology, the delivery system of ADO inhibitors based on nanomaterials can solve the above problems. This review discusses the utilization of nanomaterials as a prospective method to inhibit ADO pathway and enhance immunotherapy outcomes. Specifically, the immunosuppressive mechanisms of ADO are summarized, and the corresponding intervention strategies are proposed. Then plentiful nanomaterials targeting the ADO pathway are highlighted, including phospholipids and polymers-based nanomaterials, mesoporous nanomaterials, biomimetic nanomaterials and metal-based nanomaterials. Finally, the outlook and challenges about nanomaterials-mediated ADO pathway inhibition were outlined, expecting to promote the clinical application of ADO inhibitor nanomedicines.

Novel immunomodulatory properties of adenosine analogs promote their antiviral activity against SARS-CoV-2

The COVID-19 pandemic reminded us of the urgent need for new antivirals to control emerging infectious diseases and potential future pandemics. Immunotherapy has revolutionized oncology and could complement the use of antivirals, but its application to infectious diseases remains largely unexplored. Nucleoside analogs are a class of agents widely used as antiviral and anti-neoplastic drugs. Their antiviral activity is generally based on interference with viral nucleic acid replication or transcription. Based on our previous work and computer modeling, we hypothesize that antiviral adenosine analogs, like remdesivir, have previously unrecognized immunomodulatory properties which contribute to their therapeutic activity. In the case of remdesivir, we here show that these properties are due to its metabolite, GS-441524, acting as an Adenosine A2A Receptor antagonist. Our findings support a new rationale for the design of next-generation antiviral agents with dual - immunomodulatory and intrinsic - antiviral properties. These compounds could represent game-changing therapies to control emerging viral diseases and future pandemics.

Adenosine: a partially discovered medicinal agent

Background

A plethora of chemicals exists in human body which can alter physiology in one way or other. Scientists have always been astounded by such abilities of chemicals but as the technology advances, even the chemical which was once expected to be well known changes its status to not really well known. Adenosine is one of the chemicals which is in consonance with the aforementioned statements, although previous articles have covered vast information on role of adenosine in cardiovascular physiology, bacterial pathophysiology and inflammatory diseases. In this review we have discussed adenosine and its congeners as potential promising agents in the treatment of Huntington’s disease, post-traumatic stress disorder, erectile dysfunction, viral infections (SARS-CoV) and anxiety.

Main text

Adenosine is a unique metabolite of ATP; which serves in signalling as well. It is made up of adenine (a nitrogenous base) and ribo-furanose (pentose) sugar linked by β-N9-glycosidic bond. Adenosine on two successive phosphorylation forms ATP (Adenosine Triphosphate) which is involved in several active processes of cell. It is also one of the building blocks (nucleotides) involved in DNA (Deoxy-ribonucleic Acid) and RNA (Ribonucleic Acid) synthesis. It is also a component of an enzyme called S-adenosyl-L-methionine (SAM) and cyano-cobalamin (vitamin B-12). Adenosine acts by binding to G protein-coupled receptor (GPCR: A1, A2A, A2B and A3) carries out various responses some of which are anti-platelet function, hyperaemic response, bone remodelling, involvement in penile erection and suppression of inflammation. On the other hand, certain microorganisms belonging to genus Candida, Staphylococcus and Bacillus utilize adenosine in order to escape host immune response (phagocytic clearance). These microbes evade host immune response by synthesizing and releasing adenosine (with the help of an enzyme: adenosine synthase-A), at the site of infection.

Conclusion

With the recent advancement in attribution of adenosine in physiology and pathological states, adenosine and its congeners are being looked forward to bringing a revolution in treatment of inflammation, viral infections, psychiatric and neurodegenerative disorders.

The Adenosine Pathway and Human Immunodeficiency Virus-Associated Inflammation

Human immunodeficiency virus (HIV) is associated with an increased risk of age-associated comorbidities and mortality compared to people without HIV. This has been attributed to HIV-associated chronic inflammation and immune activation despite viral suppression. The adenosine pathway is an established mechanism by which the body regulates persistent inflammation to limit tissue damage associated with inflammatory conditions. However, HIV infection is associated with derangements in the adenosine pathway that limits its ability to control HIV-associated inflammation. This article reviews the function of purinergic signaling and the role of the adenosine signaling pathway in HIV-associated chronic inflammation. This review also discusses the beneficial and potential detrimental effects of pharmacotherapeutic strategies targeting this pathway among people with HIV.

Impact of Toll-Like Receptor 4 Signaling in Necrotizing Enterocolitis: The State of the Science

Necrotizing enterocolitis (NEC) remains a leading cause of preterm infant mortality. NEC is multifactorial and believed a consequence of intestinal immaturity, microbial dysbiosis, and an exuberant inflammatory response. Over the past decade, exaggerated Toll-like receptor 4 (TLR4) activity in the immature intestine of preterm neonates emerged as an inciting event preceding NEC. Increased TLR4 signaling in epithelial cells results in the initiation of an uncontrolled immune response and destruction of the mucosal barrier. This article discusses the state of the science of the molecular mechanisms involved in TLR4-mediated inflammation during NEC and the development of new therapeutic strategies to prevent NEC.

Adenosine signaling and adenosine deaminase regulation of immune responses: impact on the immunopathogenesis of HIV infection

Infection by human immunodeficiency virus (HIV) causes the acquired immune deficiency syndrome (AIDS), which has devastating effects on the host immune system. HIV entry into host cells and subsequent viral replication induce a proinflammatory response, hyperactivating immune cells and leading them to death, disfunction, and exhaustion. Adenosine is an immunomodulatory molecule that suppresses immune cell function to protect tissue integrity. The anti-inflammatory properties of adenosine modulate the chronic inflammation and immune activation caused by HIV. Lack of adenosine contributes to pathogenic events in HIV infection. However, immunosuppression by adenosine has its shortcomings, such as impairing the immune response, hindering the elimination of the virus and control of viral replication. By attempting to control inflammation, adenosine feeds a pathogenic cycle affecting immune cells. Deamination of adenosine by ADA (adenosine deaminase) counteracts the negative effects of adenosine in immune cells, boosting the immune response. This review comprises the connection between adenosinergic system and HIV immunopathogenesis, exploring defects in immune cell function and the role of ADA in protecting these cells against damage.

Unfolding Role of a Danger Molecule Adenosine Signaling in Modulation of Microbial Infection and Host Cell Response

Ectonucleotidases CD39 and CD73, specific nucleotide metabolizing enzymes located on the surface of the host, can convert a pro-inflammatory environment driven by a danger molecule extracellular-ATP to an adenosine-mediated anti-inflammatory milieu. Accordingly, CD39/CD73 signaling have has strongly implicated in modulating the intensity, duration, and composition of purinergic danger signals delivered to host. Recent studies have eluted potential roles for CD39 and CD73 in selective triggering of a variety of host immune cells and molecules in the presence of pathogenic microorganisms or microbial virulence molecules. Growing evidence also suggests that CD39 and CD73 present complimentary, but likely differential, actions against pathogens to shape the course and severity of microbial infection as well as the associated immune response. Similarly, adenosine receptors A2A and A2B have been proposed to be major immunomodulators of adenosine signaling during chronic inflammatory conditions induced by opportunistic pathogens, such as oral colonizer Porphyromonas gingivalis. Therefore, we here review the recent studies that demonstrate how complex network of molecules in the extracellular adenosine signaling machinery and their interactions can reshape immune responses and may also be targeted by opportunistic pathogens to establish successful colonization in human mucosal tissues and modulate the host immune response.

Deconstructing the traditional Japanese medicine "Kampo": compounds, metabolites and pharmacological profile of maoto, a remedy for flu-like symptoms

Pharmacological activities of the traditional Japanese herbal medicine (Kampo) are putatively mediated by complex interactions between multiple herbal compounds and host factors, which are difficult to characterize via the reductive approach of purifying major bioactive compounds and elucidating their mechanisms by conventional pharmacology. Here, we performed comprehensive compound, pharmacological and metabolomic analyses of maoto, a pharmaceutical-grade Kampo prescribed for flu-like symptoms, in normal and polyI:C-injected rats, the latter suffering from acute inflammation via Toll-like receptor 3 activation. In total, 352 chemical composition-determined compounds (CCDs) were detected in maoto extract by mass spectrometric analysis. After maoto treatment, 113 CCDs were newly detected in rat plasma. Of these CCDs, 19 were present in maoto extract, while 94 were presumed to be metabolites generated from maoto compounds or endogenous substances such as phospholipids. At the phenotypic level, maoto ameliorated the polyI:C-induced decrease in locomotor activity and body weight; however, body weight was not affected by individual maoto components in isolation. In accordance with symptom relief, maoto suppressed TNF-α and IL-1β, increased IL-10, and altered endogenous metabolites related to sympathetic activation and energy expenditure. Furthermore, maoto decreased inflammatory prostaglandins and leukotrienes, and increased anti-inflammatory eicosapentaenoic acid and hydroxyl-eicosapentaenoic acids, suggesting that it has differential effects on eicosanoid metabolic pathways involving cyclooxygenases, lipoxygenases and cytochrome P450s. Collectively, these data indicate that extensive profiling of compounds, metabolites and pharmacological phenotypes is essential for elucidating the mechanisms of herbal medicines, whose vast array of constituents induce a wide range of changes in xenobiotic and endogenous metabolism.

Pharmacological activities of Kampo, or traditional Japanese herbal medicine, are putatively mediated by complex interactions between the plant-derived compounds and endogenous molecules. To elucidate these properties, we performed comprehensive phytochemical profiling, and pharmacological and metabolomic analyses of maoto, an herbal remedy for flu-like symptoms. In the plasma of maoto-treated rats, we detected maoto-derived compounds, metabolites produced from the chemical transformation of maoto compounds by host metabolism and gut microbes, and endogenous metabolites that were appeared following maoto administration. In an acute inflammatory rat model, maoto ameliorated symptoms of sickness behavior, suppressed inflammatory cytokines, and extensively affected common metabolites and lipid mediators. These data suggest that the diverse chemical composition of Kampo broadly affects the host’s endogenous metabolism and exerts specific pharmacological effects.

Release of Periplasmic Nucleotidase Induced by Human Antimicrobial Peptide in E. coli Causes Accumulation of the Immunomodulator Adenosine

Previous work by our group described that human β-defensin-2 induces accumulation of extracellular adenosine (Ado) in E. coli cultures through a non-lytic mechanism causing severe plasmolysis. Here, we investigate the presence of AMP as a direct precursor and the involvement of a bacterial enzyme in the generation of extracellular Ado by treated bacteria. Following hBD-2 treatment, metabolites were quantified in the supernatants using targeted HPLC-MS/MS analysis. Microbial growth was monitored by optical density and cell viability was determined by colony forming units counts. Phosphatase activity was measured using chromogenic substrate pNPP. The results demonstrate that defensin-treated E. coli strain W releases AMP in the extracellular space, where it is converted to Ado by a bacterial soluble factor. An increase in phosphatase activity in the supernatant was observed after peptide treatment, similar to the effect of sucrose-induced osmotic stress, suggesting that the periplasmic 5'nucleotidase (5'-NT) is released following the plasmolysis event triggered by the peptide. Ado accumulation was enhanced in the presence of Co²⁺ ion and inhibited by EDTA, further supporting the involvement of a metallo-phosphatase such as 5’-NT in extracellular AMP conversion into Ado. The comparative analysis of hBD-induced Ado accumulation in different E. coli strains and in Pseudomonas aeruginosa revealed that the response is not correlated to the peptide's effect on cell viability, but indicates it might be dependent on the subcellular distribution of the nucleotidase. Taken together, these data shed light on a yet undescribed mechanism of host-microbial interaction: a human antimicrobial peptide inducing selective release of a bacterial enzyme (E. coli 5'-NT), leading to the formation of a potent immunomodulator metabolite (Ado).

Purinergic signalling and immune cells

This review article provides a historical perspective on the role of purinergic signalling in the regulation of various subsets of immune cells from early discoveries to current understanding. It is now recognised that adenosine 5'-triphosphate (ATP) and other nucleotides are released from cells following stress or injury. They can act on virtually all subsets of immune cells through a spectrum of P2X ligand-gated ion channels and G protein-coupled P2Y receptors. Furthermore, ATP is rapidly degraded into adenosine by ectonucleotidases such as CD39 and CD73, and adenosine exerts additional regulatory effects through its own receptors. The resulting effect ranges from stimulation to tolerance depending on the amount and time courses of nucleotides released, and the balance between ATP and adenosine. This review identifies the various receptors involved in the different subsets of immune cells and their effects on the function of these cells.

Ecto-5'-nucleotidase (CD73) regulates host inflammatory responses and exacerbates murine salmonellosis

Food-borne Salmonella spp., are a major cause of hospitalization and death. Adenosine, an important immune regulator of inflammation, limits tissue damage during infection. CD39 (nucleoside triphosphate dephosphorylase) combined with ecto-5′-nucleotidase (CD73) metabolizes ATP to adenosine. We studied the expressions of CD39 and CD73 in tissues, and T helper cells in mice after Salmonella infection and evaluated the role of CD73 in regulating immune responses and bacterial clearance in wild-type and CD73-deficient (CD73^−/−) mice. Both CD39 and CD73 transcript levels declined in the infected wild-type mice. Compared to wild-type mice, tissues from infected CD73^−/− mice had significantly higher expression of pro-inflammatory cytokines and reduced anti-inflammatory responses. CD73^−/− mice were more resistant to infection and had a greater inflammatory responses and a significantly lower bacterial load in the liver compared to wild-type mice. Thus, CD73 expression attenuates inflammation during murine Salmonellosis and impairs immunity, leading to increased bacterial colonization and prolonged infection.

Innate immune function by Toll-like receptors: distinct responses in newborns and the elderly

Given the "inborn" nature of the innate immune system, it is surprising to find that innate immune function does in fact change with age. Similar patterns of distinct Toll-like-receptor-mediated immune responses come to light when one contrasts innate immune development at the beginning of life with that toward the end of life. Importantly, these developmental patterns of innate cytokine responses correlate with clinical patterns of susceptibility to disease: A heightened risk of suffering from excessive inflammation is often detected in prematurely born infants, disappears over the first few months of life, and reappears toward the end of life. In addition, risk periods for particular infections in early life reemerge in older adults. The near-mirror-image patterns that emerge in contrasts of early versus late innate immune ontogeny emphasize changes in host-environment interactions as the underlying molecular and teleologic drivers.

Immune heterogeneity in neuroinflammation: dendritic cells in the brain

Dendritic cells (DC) are critical to an integrated immune response and serve as the key link between the innate and adaptive arms of the immune system. Under steady state conditions, brain DC’s act as sentinels, continually sampling their local environment. They share this function with macrophages derived from the same basic hemopoietic (bone marrow-derived) precursor and with parenchymal microglia that arise from a unique non-hemopoietic origin. While multiple cells may serve as antigen presenting cells (APCs), dendritic cells present both foreign and self-proteins to naïve T cells that, in turn, carry out effector functions that serve to protect or destroy. The resulting activation of the adaptive response is a critical step to resolution of injury or infection and is key to survival. In this review we will explore the critical roles that DCs play in the brain’s response to neuroinflammatory disease with emphasis on how the brain’s microenvironment impacts these actions.

Infectious diseases are analogous with cancer. Hypothesis and implications

We propose to disclose first degree analogous features between cancer and infectious diseases and to find out whether these similarities are superficial and negligible, due to the use of the same bodily pathways by the two categories of disease or if they represent significantly parallel characteristics. We have found several primary analogous features, predominantly regarding pathways of spread, but to some extent also concerning the interaction with the immune system. Some of the implications to our hypothesis are probably available in the recent literature, at the experimental or clinical levels. For example endostatin, an angiogenic inhibitor has been used to prevent promotion of metastasis in cancer and to reduce granulomas formation in schistosomiasis. An ECFR antagonist employed to restrain bronchial vessels proliferation in pseudomonas infection, has also been used for the treatment of lung cancer.