Role of oxygen in phagocyte microbicidal action

Generation and Aerobic Oxidation of Azavinyl Captodative Radicals

We describe a cascade reaction that selectively incorporates oxygen into the carbon-carbon backbone of alkynes using air as the source. The process starts by lithiating readily available, electron-deficient 1,2,3-triazoles, resulting in an amphoteric lithium ketenimine intermediate. This intermediate can react with both electrophiles and nucleophiles. Under the conditions outlined in this study, we generate azavinyl radicals, which are a rare subset of captodative radicals. When exposed to atmospheric oxygen, these radicals efficiently transform into α-oxygenated amidines─a class of compounds that has not been extensively studied. This process uniquely utilizes molecular oxygen without requiring metal or photocatalysts, and it occurs under mild conditions. Our mechanistic studies provide insights into the intricate sequence involved in the formation and selective capture of azavinyl captodative radicals.

Current status and development direction of hyperbaric medicine in Korea

Background: The indications of hyperbaric oxygen therapy (HBOT) covered by the health insurance in Korea increased to 16 in 2019, which includes acute central retinal artery obstruction within 24 hours of vision loss; anemia due to excessive bleeding, since blood transfusion is impractical; chronic refractory osteomyelitis (Wagner grade ≥3); and intracranial abscess.Current Concepts: HBOT affects the treatment in the primary and secondary mechanisms. According to the Boyle’s law, the primary mechanism is important in treating decompression sickness and intravascular air embolism by decreasing the volume of air bubbles when pressure increases, whereas the secondary mechanism involves hyperoxygenation of the primary mechanism and various effects, such as vasoconstriction, angiogenesis, immune function enhancement, reperfusion injury prevention, antimicrobial action, and gas washout effect, occur. In the past 5 years, domestic HBOT has made significant progress. However, there are many non-therapeutic lowpressure HBOT facilities that are limited by insurance coverage issues, quality equipment management, and medical personnel in HBOT facilities.Discussion and Conclusion: To solve the problem, the introduction of the definition of therapeutic hyperbaric pressure and certification system of HBOT facilities must be initiated. Moreover, the system should be improved so that insurance can be applied for a more indication of HBOT.

Translational suppression of SARS-COV-2 ORF8 protein mRNA as a Viable therapeutic target against COVID-19: Computational studies on potential roles of isolated compounds from Clerodendrum volubile leaves

The open reading frame 8 (ORF8) protein of SARS-CoV-2 has been implicated in the onset of cytokine storms, which are responsible for the pathophysiology of COVID-19 infection. The present study investigated the potential of isolated compounds from Clerodendrum volubile leaves to stall oxidative bursts in vitro and interact with ORF8 mRNA segments of the SARS-CoV-2 whole genome using computational tools. Five compounds, namely, harpagide, 1-(3-methyl-2-butenoxy)-4-(1-propenyl)benzene, ajugoside, iridoid glycoside and erucic acid, were isolated from C. volubile leaves, and their structures were elucidated using conventional spectroscopy tools. Iridoid glycoside is being reported for the first time and is thus regarded as a new compound. The ORF8 mRNA sequences of the translation initiation sites (TIS) and translation termination sites (TTSs) encoding ORF8 amino acids were retrieved from the full genome of SARS-CoV-2. Molecular docking studies revealed strong molecular interactions of the isolated compounds with the TIS and TTS of ORF8 mRNA. Harpagide showed the strongest binding affinity for TIS, while erucic acid was the strongest for TTS. The immunomodulatory potentials of the isolated compounds were investigated on neutrophil phagocytic respiratory bursts using luminol-amplified chemiluminescence technique. The compounds significantly inhibited oxidative burst, with 1-(3-methyl-2-butenoxy)-4-(1-propenyl)benzene having the best activity. Ajugoside and erucic acid showed significant inhibitory activity on T-cell proliferation. These results indicate the potential of C. volubile compounds as immunomodulators and can be utilized to curb cytokine storms implicated in COVID-19 infection. These potentials are further corroborated by the strong interactions of the compounds with the TIS and TTS of ORF8 mRNA from the SARS-CoV-2 whole genome.

Targeting the initiation and termination codons of SARS-CoV-2 spike protein as possible therapy against COVID-19: the role of novel harpagide 5-O-β-D-glucopyranoside from Clerodendrum volubile P Beauv. (Labiatae)

The global spread of the coronavirus infections disease − 2019 (COVID-19) and the search for new drugs from natural products particularly from plants are receiving much attention recently. In this study, the therapeutic potential of a new iridoid glycoside isolated from the leaves of Clerodendrum volubile against COVID-19 was investigated. Harpagide 5-O-β-D-glucopyranoside (HG) was isolated, characterised and investigated for its druglikeness, optimized geometry, and pharmacokinetics properties. Its immunomodulatory was determined by chemiluminescence assay using polymorphonuclear neutrophils (PMNs) in addition to T-cell proliferation assay. In silico analysis was used in determining its molecular interaction with severe acute respiratory syndrome coronavirus-2 (SARS-COV-2). HG displayed potent druglikeness properties, with no inhibitory effect on cytochrome P₄₅₀ (1A2, 2C19, 2C9, 2D6 and 3A4) and a predicted LD₅₀ of 2000 mg/kg. Its ¹H-NMR chemical shifts showed a little deviation of 0.01 and 0.11 ppm for H-4 and H-9, respectively. HG significantly suppressed oxidative bursts in PMNs, while concomitantly inhibiting T-cell proliferation. It also displayed a very strong binding affinity with the translation initiation and termination sequence sites of spike (S) protein mRNA of SARS-COV-2, its gene product, and host ACE2 receptor. These results suggest the immunomodulatory properties and anti-SARS-COV-2 potentials of HG which can be explored in the treatment and management of COVID-19.

Communicated by Ramaswamy H. Sarma

Neutrophil Leukocyte: Combustive Microbicidal Action and Chemiluminescence

Neutrophil leukocytes protect against a varied and complex array of microbes by providing microbicidal action that is simple, potent, and focused. Neutrophils provide such action via redox reactions that change the frontier orbitals of oxygen (O₂) facilitating combustion. The spin conservation rules define the symmetry barrier that prevents direct reaction of diradical O₂ with nonradical molecules, explaining why combustion is not spontaneous. In burning, the spin barrier is overcome when energy causes homolytic bond cleavage producing radicals capable of reacting with diradical O₂ to yield oxygenated radical products that further participate in reactive propagation. Neutrophil mediated combustion is by a different pathway. Changing the spin quantum state of O₂ removes the symmetry restriction to reaction. Electronically excited singlet molecular oxygen (¹O₂^*) is a potent electrophilic reactant with a finite lifetime that restricts its radius of reactivity and focuses combustive action on the target microbe. The resulting exergonic dioxygenation reactions produce electronically excited carbonyls that relax by light emission, that is, chemiluminescence. This overview of neutrophil combustive microbicidal action takes the perspectives of spin conservation and bosonic-fermionic frontier orbital considerations. The necessary principles of particle physics and quantum mechanics are developed and integrated into a fundamental explanation of neutrophil microbicidal metabolism.

Linoleic acid hydroperoxide reacts with hypochlorous acid, generating peroxyl radical intermediates and singlet molecular oxygen

The reaction of hypochlorous acid (HOCl) with hydrogen peroxide is known to generate stoichiometric amounts of singlet molecular oxygen [O2 (1Deltag)]. This study shows that HOCl can also react with linoleic acid hydroperoxide (LAOOH), generating O2 (1Deltag) with a yield of 13 +/- 2% at physiological pH. Characteristic light emission at 1,270 nm, corresponding to O2 (1Deltag) monomolecular decay, was observed when HOCl was reacted with LAOOH or with liposomes containing phosphatidylcholine hydroperoxides, but not with cumene hydroperoxide or tert-butyl hydroperoxide. The generation of O2 (1Deltag) was confirmed by the acquisition of the spectrum of the light emitted in the near-infrared region showing a band with maximum intensity at 1,270 nm and by the observation of the enhancing effect of deuterium oxide and the quenching effect of sodium azide. Mechanistic studies using 18O-labeled linoleic acid hydroperoxide (LA18O18OH) showed that its reaction with HOCl yields 18O-labeled O2 (1Deltag) [18O2 (1Deltag)], demonstrating that the oxygen atoms in O2 (1Deltag) are derived from the hydroperoxide group. Direct analysis of radical intermediates in the reaction of LAOOH with HOCl by continuous-flow electron paramagnetic resonance spectroscopy showed a doublet signal with a g-value of 2.014 and a hyperfine coupling constant from the alpha-hydrogen of a(H) = 4.3 G, indicating the formation of peroxyl radicals. Taken together, our results clearly demonstrate that HOCl reacts with biologically relevant lipid hydroperoxides, generating O2 (1Deltag). In addition, the detection of 18O2 (1Deltag) and peroxyl radicals strongly supports the involvement of a Russell mechanism in the generation of O2 (1Deltag).

Macrophage-mediated candidacidal activity is augmented by exposure to eosinophil peroxidase: a paradigm for eosinophil-macrophage interaction

Various disease states are associated with eosinophilia and the release of eosinophil peroxidase (EPO) into the microenvironment. The present study targets the effects of low levels of EPO on macrophage (M phi) phagocytosis and intracellular killing of Candida albicans as well as M phi oxidative activity measured as the luminescence product of luminol dioxygenation. Resident murine peritoneal M phi were exposed to various concentrations of EPO. Chemiluminescence data indicate that nanomolar concentrations of EPO markedly enhanced the dioxygenation activity (respiratory burst) of M phi. In other studies, the exposure of M phi to 0.17 microM EPO for 10 min. enhanced M phi-mediated candidacidal activity 10 fold. The above data indicate that EPO enhances certain M phi functions. Also the results illustrate a previously un-recognized interaction between eosinophils and M phi and implicate yet another possible role for EPO in host defenses against disease.

Beta-adrenergic modulation of FMLP- and zymosan-induced intracellular and extracellular oxidant production by polymorphonuclear leukocytes

Evaluation of catecholamine modulation of PMNL extracellular and intracellular oxidant production may reflect beneficial and harmful effects of beta-adrenergic agonists in various disease states. We investigated the kinetics and potency of adrenaline-mediated inhibition of oxidant generation in FMLP- and zymosan-stimulated PMNLs. In FMLP-stimulated cells, the short-term burst of oxidant generation was inhibited by adrenaline in a dose-dependent fashion. Intra- and extracellular chemiluminescence and extracellular superoxide anion and hydrogen peroxide generation showed similar IC50 values for adrenaline (1.3-3.0 x 10(-8) M) indicating that both extracellular and intracellular events were inhibited with the same potency. In contrast, intracellular oxidant production evoked by the phagocytosis of zymosan was only minimally affected by 3 x 10(-5) -3 x 10(-12) M adrenaline. Extracellular inhibition of oxidant production was also apparent in zymosan-stimulated cells. In conclusion, adrenaline's ability to depress extracellular generation of oxygen metabolites while retaining prolonged intracellular oxidant production for phagocytosis supports its beneficial role as selectively targeted physiological protector.