Glycolaldehyde impairs neutrophil biochemical parameters by an oxidative and calcium-dependent mechanism--protective role of antioxidants astaxanthin and vitamin C

Melatonin restores neutrophil functions and prevents apoptosis amid dysfunctional glutathione redox system

Melatonin is a chronobiotic hormone, which can regulate human diseases like cancer, atherosclerosis, respiratory disorders, and microbial infections by regulating redox system. Melatonin exhibits innate immunomodulation by communicating with immune system and influencing neutrophils to fight infections and inflammation. However, sustaining redox homeostasis and reactive oxygen species (ROS) generation in neutrophils are critical during chemotaxis, oxidative burst, phagocytosis, and neutrophil extracellular trap (NET) formation. Therefore, endogenous antioxidant glutathione (GSH) redox cycle is highly vital in regulating neutrophil functions. Reduced intracellular GSH levels and glutathione reductase (GR) activity in the neutrophils during clinical conditions like autoimmune disorders, neurological disorders, diabetes, and microbial infections lead to dysfunctional neutrophils. Therefore, we hypothesized that redox modulators like melatonin can protect neutrophil health and functions under GSH and GR activity-deficient conditions. We demonstrate the dual role of melatonin, wherein it protects neutrophils from oxidative stress-induced apoptosis by reducing ROS generation; in contrast, it restores neutrophil functions like phagocytosis, degranulation, and NETosis in GSH and GR activity-deficient neutrophils by regulating ROS levels both in vitro and in vivo. Melatonin mitigates LPS-induced neutrophil dysfunctions by rejuvenating GSH redox system, specifically GR activity by acting as a parallel redox system. Our results indicate that melatonin could be a potential auxiliary therapy to treat immune dysfunction and microbial infections, including virus, under chronic disease conditions by restoring neutrophil functions. Further, melatonin could be a promising immune system booster to fight unprecedented pandemics like the current COVID-19. However, further studies are indispensable to address the clinical usage of melatonin.

Age-dependent Changes in Plasma Amino Acids Contribute to Alterations in Glycoxidation Products

BACKGROUND

Glycative stress is involved in the pathogenesis of various degenerative disorders. This study sought to determine the effect of age-related changes in amino acids on serum levels of pentosidine and carboxymethyl-lysine (CML) in healthy individuals.

METHODS

The subjects were 78 healthy individuals categorized into three age groups. The ages of the groups were as follows: 26 young adults (20-30 y, 25.2±3.03), 26 middle-aged adults (35-50 y, 39.46±6.97) and 26 older adults (60 y or older, 69.80±10.01). Serum levels of pentosidine and CML were measured by ELISA and levels of plasma amino acids were determined using HPLC.

RESULTS

Serum levels of pentosidine and CML in the youngest group were higher than in the oldest group (p=0.026, 0.029, respectively). There was a positive correlation between the serum levels of pentosidine and CML and the levels of plasmaTyrosine (p=0.032, r=0.211 and p=0.037, r=0.224), Valine (p=0.037, r=0.224 and p=0.021, r=0.247) and Isoleucine (p=0.041, r=0.203 and p=0.021, r=0.247), respectively. Serum levels of pentosidine and CML may be modulated by the plasma levels of selected amino acids.

CONCLUSIONS

Better understanding of the role of these selective amino acids might provide new perception of how glycation pathways may be altered and pave the way for new therapeutic principles.

Development and Application of High-Content Biological Screening for Modulators of NET Production

Neutrophil extracellular traps (NETs) are DNA-based antimicrobial web-like structures whose release is predominantly mediated by reactive oxygen species (ROS); their purpose is to combat infections. However, unbalanced NET production and clearance is involved in tissue injury, circulation of auto-antibodies and development of several chronic diseases. Currently, there is lack of agreement regarding the high-throughput methods available for NET investigation. This study, therefore, aimed to develop and optimize a high-content analysis (HCA) approach, which can be applied for the assay of NET production and for the screening of compounds involved in the modulation of NET release. A suitable paraformaldehyde fixation protocol was established to enable HCA of neutrophils and NETs. Bespoke and in-built bioinformatics algorithms were validated by comparison with standard low-throughput approaches for application in HCA of NETs. Subsequently, the optimized protocol was applied to high-content screening (HCS) of a pharmaceutically derived compound library to identify modulators of NETosis. Of 56 compounds assessed, 8 were identified from HCS for further characterization of their effects on NET formation as being either inducers, inhibitors or biphasic modulators. The effects of these compounds on naïve neutrophils were evaluated by using specific assays for the induction of ROS and NET production, while their modulatory activity was validated in phorbol 12-myristate 13-acetate-stimulated neutrophils. Results indicated the involvement of glutathione reductase, Src family kinases, molecular-target-of-Rapamycin, and mitogen-activated-protein-kinase pathways in NET release. The compounds and pathways identified may provide targets for novel therapeutic approaches for treating NET-associated pathologies.

Scavenging of reactive oxygen species by astaxanthin inhibits epithelial-mesenchymal transition in high glucose-stimulated mesothelial cells

BACKGROUND

High glucose concentrations influence the functional and structural development of the peritoneal membrane. We previously reported that the oral administration of astaxanthin (AST) suppressed peritoneal fibrosis (PF) as well as inhibited oxidative stress, inflammation, and epithelial-mesenchymal transition (EMT) of peritoneal mesothelial cells (PMCs) in a chlorhexidine-induced PF rat model. This suggests that oxidative stress induction of EMT is a key event during peritoneal damage. The present study evaluated the therapeutic effect of AST in suppressing EMT, in response to glucose-induced oxidative stress.

METHODS

Temperature-sensitive mesothelial cells (TSMCs) were cultured in the presence or absence of AST and then treated with 140 mM glucose for 3 or 12 hours. Expression levels of TNF-α, TGF-β, and VEGF were determined at the mRNA and protein levels, and nuclear factor kappa B (NF-κB) activity was evaluated. We measured NO2-/NO3- concentrations in cellular supernatants and determined 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels in mitochondrial and nuclear DNA. The expressions of E-cadherin and alpha-smooth muscle actin (α-SMA) were evaluated by double immunofluorescence and protein levels.

RESULTS

High glucose concentrations induced overproduction of reactive oxidative species (ROS), increasing 8-OHdG mitochondrial DNA and cytokine levels. The NF-κB pathway was activated in response to high glucose concentrations, whereas de novo α-SMA expression was observed with decreased E-cadherin expression. AST treatment attenuated ROS production, inflammatory cytokine production, NF-κB activation, and EMT.

CONCLUSION

The findings of the present study indicate that AST may have an anti-EMT effect due to anti-oxidative and anti-inflammatory activities by scavenging glucose-induced ROS from mitochondria in PMCs. AST may be an efficacious treatment for PF.

Green tea catechins alone or in combination alter functional parameters of human neutrophils via suppressing the activation of TLR-4/NFκB p65 signal pathway

The purpose of this study was to evaluate the potential of a mixture containing the four main catechins found in green tea, as well it separately, as modulators of the functional parameters of human neutrophils. The cells were obtained from peripheral blood of healthy individuals isolated and cultured with a mix: 30 μM of EGCG, 3 μM of EGC, 2 μM of ECG and 1.4 μM of EC, as well as each one alone. We evaluated the cytotoxicity of catechins, production of several reactive oxygen species (ROS), antioxidant enzymes (SOD, CAT, GPx and GR), Nrf2, TLR4/IKK/NFκB, CD11b mRNA levels, intracellular calcium release, chemotactic and phagocytic capacity, myeloperoxidase (MPO), and G6PDH activities, hypochlorous acid (HOCl) and pro-inflammatory cytokines release, protein levels of TLR4, p38 MAPK, iNOS and p-65 NFκB. The actions of the catechins were evidenced by the reduction in inflammatory parameters, including the suppression of TLR4, NFκB and iNOS protein expression, decreased release of TNF-α, IL-1β and IL-6, migration capacity, MPO activity and HOCl production and the suppression of ROS, nitric oxide and peroxynitrite production, while inducing antioxidant enzyme activities and Nrf2 mRNA levels, phagocytic capacity and calcium release. Our results demonstrate that catechins present marked immunomodulatory actions, either alone or in combination.

Green tea polyphenol extract in vivo attenuates inflammatory features of neutrophils from obese rats

PURPOSE

Our study aimed to evaluate whether obesity induced by cafeteria diet changes the neutrophil effector/inflammatory function and whether treatment with green tea extract (GT) can improve neutrophil function.

METHODS

Male Wistar rats were treated with GT by gavage (12 weeks/5 days/week; 500 mg/kg of body weight), and obesity was induced by cafeteria diet (8 weeks). Neutrophils were obtained from the peritoneal cavity (injection of oyster glycogen). The following analyses were performed: phagocytic capacity, chemotaxis, myeloperoxidase activity (MPO), hypochlorous acid (HOCl), superoxide anion (O 2 (·-) ), hydrogen peroxide (H2O2), IL-1β, IL-6 and TNFα, mRNA levels of inflammatory genes, calcium mobilisation, activities of antioxidant enzymes, hexokinase and G6PDH.

RESULTS

Neutrophils from obese rats showed a significant decrease in migration capacity, H2O2 and HOCl production, MPO activity and O 2 (·-) production. Phagocytosis and CD11b mRNA levels were increased, while inflammatory cytokines release remained unmodified. mRNA levels of TLR4 and IκK were enhanced. Treatment of obese rats with GT increased neutrophil migration, MPO activity, H2O2, HOCl and O 2 (·-) production, whereas TNF-α and IL-6 were decreased (versus obese). Similar reductions in TLR4, IκK and CD11b mRNA were observed. Catalase and hexokinase were increased by obesity, while SOD and G6PDH were decreased. Treatment with GT reduced catalase and increased the GSH/GSSG ratio.

CONCLUSION

In response to a cafeteria diet, we found a decreased chemotaxis, H2O2 release, MPO activity and HOCl production. We also showed a significant immunomodulatory effect of GT on the obese condition recovering some of these factors such H2O2 and HOCl production, also reducing the levels of inflammatory cytokines.

Sulforaphane restores cellular glutathione levels and reduces chronic periodontitis neutrophil hyperactivity in vitro

The production of high levels of reactive oxygen species by neutrophils is associated with the local and systemic destructive phenotype found in the chronic inflammatory disease periodontitis. In the present study, we investigated the ability of sulforaphane (SFN) to restore cellular glutathione levels and reduce the hyperactivity of circulating neutrophils associated with chronic periodontitis. Using differentiated HL60 cells as a neutrophil model, here we show that generation of extracellular O2 (. -) by the nicotinamide adenine dinucleotide (NADPH) oxidase complex is increased by intracellular glutathione depletion. This may be attributed to the upregulation of thiol regulated acid sphingomyelinase driven lipid raft formation. Intracellular glutathione was also lower in primary neutrophils from periodontitis patients and, consistent with our previous findings, patients neutrophils were hyper-reactive to stimuli. The activity of nuclear factor erythroid-2-related factor 2 (Nrf2), a master regulator of the antioxidant response, is impaired in circulating neutrophils from chronic periodontitis patients. Although patients' neutrophils exhibit a low reduced glutathione (GSH)/oxidised glutathione (GSSG) ratio and a higher total Nrf2 level, the DNA-binding activity of nuclear Nrf2 remained unchanged relative to healthy controls and had reduced expression of glutamate cysteine ligase catalytic (GCLC), and modifier (GCLM) subunit mRNAs, compared to periodontally healthy subjects neutrophils. Pre-treatment with SFN increased expression of GCLC and GCM, improved intracellular GSH/GSSG ratios and reduced agonist-activated extracellular O2 (. -) production in both dHL60 and primary neutrophils from patients with periodontitis and controls. These findings suggest that a deficiency in Nrf2-dependent pathways may underpin susceptibility to hyper-reactivity in circulating primary neutrophils during chronic periodontitis.