TLR2 activation induces antioxidant defence in human monocyte-macrophage cell line models

Oxidative stress stimulation leads to cell-specific oxidant and antioxidant responses in airway resident and inflammatory cells

AIMS

The imbalance between reactive oxygen species (ROS) and the antioxidant response has been linked to various airway diseases, including asthma. However, knowledge on cell-specific responses of the airway resident and inflammatory cells against increased oxidant stress is very limited. We aim to better understand the cell-specific antioxidant response that contributes to the pathophysiology of lung disease in response to oxidative stress.

MATERIALS AND METHODS

The human cell lines of epithelial, fibroblast, endothelial, monocyte, eosinophil and neutrophil were incubated with tert-butyl hydroperoxide (tBHP) or cigarette smoke condensate (CSC). Following stimulation, cell viability, total oxidant and antioxidant activity were assessed in both residential and inflammatory cells. Human Oxidative Stress Plus RT² Profiler PCR array was used to determine 84 gene expression differences in oxidant and antioxidant pathways following oxidant stimulus in all cells.

KEY FINDINGS

We showed that various cell types respond differently to oxidative stress inducers, with distinct gene expression and oxidant-antioxidant generation. Most importantly, eosinophils increased the activity of all main antioxidant enzymes in response to both oxidants. Monocytes, on the other hand, showed no change in response to each stimulation, whereas neutrophils only increased their CAT activity in response to both stimuli. The increase in NRF2-regulated genes HSPA1A, HMOX1 and DUSP1 after both tBHP and CSC in epithelial cells and fibroblasts indicates Nfr2 pathway activation.

SIGNIFICANCE

This study advances our knowledge of the molecular and cellular mechanisms of cell-specific antioxidant response upon exposure to oxidative stress. Additionally, our observations imply that the eosinophils' distinct biological response may be utilized for endotype-based cell-targeted antioxidant therapy.

Cerrado and Pantanal fruit flours affect gut microbiota composition in healthy and post-COVID-19 individuals: an in vitro pilot fermentation study

Cerrado and Pantanal plants can provide fruits with high nutritional value and antioxidants. This study aims to evaluate four fruit flours (from jatobá pulp, cumbaru almond, bocaiuva pulp and bocaiuva almond) and their effects on the gut microbiota in healthy (HD) and post-COVID-19 individuals (PC). An in vitro batch system was carried out, the microbiota was analysed by 16S rRNA amplicon sequencing and the short-chain fatty acids ratio was determined. Furthermore, the effect of jatobá pulp flour oil (JAO) on cell viability, oxidative stress and DNA damage was investigated in a myelo-monocytic cell line. Beyond confirming a microbiota imbalance in PC, we identified flour-specific effects: (i) reduction of Veillonellaceae with jatobá extract in PC samples; (ii) decrease in Akkermansia with jatoba and cumbaru flours; (iii) decreasing trend of Faecalibacterium and Ruminococcus with all flours tested, with the exception of the bocaiuva almond in HD samples for Ruminococcus and (iv) increase in Lactobacillus and Bifidobacterium in PC samples with bocaiuva almond flour. JAO displayed antioxidant properties protecting cells from daunorubicin-induced cytotoxicity, oxidative stress and DNA damage. The promising microbiota-modulating abilities of some flours and the chemopreventive effects of JAO deserve to be further explored in human intervention studies.

Ascorbic acid along with ciprofloxacin regulates S. aureus induced microglial inflammatory responses and oxidative stress through TLR-2 and glucocorticoid receptor modulation

Microglial inflammatory responses play a central role in the pathogenesis of S. aureus induced brain infections. Upon activation, microglia produces free radicals (ROS/RNS) and disrupts the cellular antioxidant defense to combat invading microorganisms. Despite conventional antibiotic or steroid therapy, microglial over-activation could not be controlled. So, an attempt had been taken by using a natural antioxidant ascorbic acid along with ciprofloxacin to regulate microglial over-activation by involving TLR-2 and glucocorticoid receptor (GR) in an in-vitro cell culture-based study. Combinatorial treatment during TLR-2 neutralization effectively reduced the bacterial burden at 60 min compared to the GR blocking condition (p < 0.05). Moreover, the infection-induced H₂O₂, O₂^.-, and NO release in microglial cell culture was diminished possibly by enhancing SOD and catalase activities in the same condition (p < 0.05). The arginase activity was markedly increased after TLR-2 blocking in the combinatorial group compared to single treatments (p < 0.05). Experimental results indicated that combinatorial treatment may act through up-regulating GR expression by augmenting endogenous corticosterone levels. However, better bacterial clearance could further suppress the TLR-2 mediated pro-inflammatory NF-κB signaling. From Western blot analysis, it was concluded that ciprofloxacin-ascorbic acid combination in presence of anti-TLR-2 antibody exhibited 81.25% inhibition of TLR-2 expression while the inhibition for GR was 3.57% with respect to the infected group. Therefore, during TLR-2 blockade ascorbic acid combination might be responsible for the restoration of redox balance in microglia via modulating TLR-2/GR interaction. The combination treatment could play a major role in the neuroendocrine-immune regulation of S. aureus induced microglial activation.

Intracellular inflammatory signalling cascades in human monocytic cells on challenge with phytohemagglutinin and 2,4,6-trinitrophenol

Phytohemagglutinin (PHA) is a plant mitogen that can agglutinate human leukocytes and erythrocytes. PHA is mainly derived from red kidney beans and can act as an exogenous pyrogen. When entering into the blood circulation, exogenous pyrogens principally interact with monocytes and macrophages and induce the release of pro-inflammatory cytokines. Monocytes and macrophages are the cells that fight against foreign invaders and acts as a primary line of immune defence. Similar to PHA, the chemical 2,4,6-trinitrophenol (TNP) also acts as an exogenous pyrogen. The study focused on the in vitro interaction of PHA and TNP with the human monocyte/macrophage cell model THP-1. The exposure and associated change in cellular morphology, organelle function, mechanism of cell death, inflammatory signalling and expression of inflammation-related genes were analyzed in different time periods. It was observed that PHA and TNP induce dose and time-dependent toxicity to monocytes/macrophages where the mechanism of cell death was different for PHA and TNP. Both PHA and TNP can evoke immune signalling with increased expression of inflammatory genes and associated activation of intracellular signalling cascades.

The Trace Element Selenium Is Important for Redox Signaling in Phorbol Ester-Differentiated THP-1 Macrophages

Physiological selenium (Se) levels counteract excessive inflammation, with selenoproteins shaping the immunoregulatory cytokine and lipid mediator profile. How exactly differentiation of monocytes into macrophages influences the expression of the selenoproteome in concert with the Se supply remains obscure. THP-1 monocytes were differentiated with phorbol 12-myristate 13-acetate (PMA) into macrophages and (i) the expression of selenoproteins, (ii) differentiation markers, (iii) the activity of NF-κB and NRF2, as well as (iv) lipid mediator profiles were analyzed. Se and differentiation affected the expression of selenoproteins in a heterogeneous manner. GPX4 expression was substantially decreased during differentiation, whereas GPX1 was not affected. Moreover, Se increased the expression of selenoproteins H and F, which was further enhanced by differentiation for selenoprotein F and diminished for selenoprotein H. Notably, LPS-induced expression of NF-κB target genes was facilitated by Se, as was the release of COX- and LOX-derived lipid mediators and substrates required for lipid mediator biosynthesis. This included TXB2, TXB3, 15-HETE, and 12-HEPE, as well as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Our results indicate that Se enables macrophages to accurately adjust redox-dependent signaling and thereby modulate downstream lipid mediator profiles.

LSD1 Facilitates Pro-Inflammatory Polarization of Macrophages by Repressing Catalase

The increased level of hydrogen peroxide accompanies some modes of macrophage specification and is linked to ROS-based antimicrobial activity of these phagocytes. In this study, we show that activation of toll-like receptors with bacterial components such as LPS is accompanied by the decline in transcription of hydrogen peroxide decomposing enzyme-catalase, suppression of which facilitates the polarization of human macrophages towards the pro-inflammatory phenotype. The chromatin remodeling at the CAT promoter involves LSD1 and HDAC1, but activity of the first enzyme defines abundance of the two proteins on chromatin, histone acetylation status and the CAT transcription. LSD1 inhibition prior to macrophage activation with LPS prevents CAT repression by enhancing the LSD1 and interfering with the HDAC1 recruitment to the gene promoter. The maintenance of catalase level with LSD1 inhibitors during M1 polarization considerably limits LPS-triggered expression of some pro-inflammatory cytokines and markers such as IL1β, TNFα, COX2, CD14, TLR2, and IFNAR, but the effect of LSD1 inhibitors is lost upon catalase deficiency. Summarizing, activity of LSD1 allows for the CAT repression in LPS stimulated macrophages, which negatively controls expression of some key pro-inflammatory markers. LSD1 inhibitors can be considered as possible immunosuppressive drugs capable of limiting macrophage M1 specialization.

Herbal melanin induces interleukin-1β secretion and production by human THP-1 monocytes via Toll-like receptor 2 and p38 MAPK activation

Herbal melanin (HM), extracted from Nigella sativa, is known for its immunogenic properties through the modulation of cytokine production via Toll-like receptor (TLR)4. TLRs play a crucial role in the host defense through the regulation of innate and adaptive immune responses. However, the potential effect of HM on the production of interleukin-1β (IL-1β), the main immunoregulatory cytokine secreted by activated monocytes, has not been reported. The present study aimed to investigate the effects of HM on IL-1β secretion and production, detected by enzyme-linked immunosorbent assay, western blotting and mRNA expression monitored by reverse transcription-PCR, in human monocytes and a monocytic cell line, THP-1. Signaling pathways involved in the HM-induced IL-1β production was investigated in the THP-1 cells. It was shown that HM upregulated the IL-1β mRNA in the THP-1 cells and induced the secretion of IL-1β in the monocytes and THP-1 cells, in a dose-dependent manner, compared to the untreated cells. HM increased the protein expression of IL-1β, TLR2, the main receptor for IL-1β production, and activated p38 mitogen-activated protein kinase (MAPK), a key mediator for stress-induced IL-1β gene expression. The blockade of the p38 MAPK pathway, with the pharmacological inhibitor SB202190, and TLR2 receptor with a neutralization antibody, resulted in the decrease of HM-induced IL-1β production in THP-1 cells. The TLR4 receptor blockade also decreased HM-induced IL-1β production, but to a lesser extent than TLR2 blockade. In conclusion, the present study demonstrated that HM stimulates IL-1β production in monocytes and THP-1 cells, in a TLR2/p38 MAPK pathway-dependent manner, suggesting promising immunoregulatory potentials of HM against inflammatory-associated diseases.

Nucleocapsid and Spike Proteins of the Coronavirus SARS-CoV-2 Induce IL6 in Monocytes and Macrophages-Potential Implications for Cytokine Storm Syndrome

The pandemic of the new coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) has led to the deaths of more than 1.5 million people worldwide. SARS-CoV-2 causes COVID-19, which exhibits wide variation in the course of disease in different people, ranging from asymptomatic and mild courses to very severe courses that can result in respiratory failure and death. Despite the rapid progression of knowledge, we still do not know how individual cells of the immune system interact with the virus or its components, or how immune homeostasis becomes disrupted, leading to the rapid deterioration of a patient's condition. In the present work, we show that SARS-CoV-2 proteins induce the expression and secretion of IL-6 by human monocytes and macrophages, the first line cells of antiviral immune responses. IL-6 may play a negative role in the course of COVID-19 by inhibiting Th1-dependent immunity and stimulating Th17 lymphocytes, thus leading to an increased probability of a cytokine storm.

Antileishmanial macrolides from ant-associated Streptomyces sp. ISID311

Three antifungal macrolides cyphomycin (1), caniferolide C (2) and GT-35 (3) were isolated from Streptomyces sp. ISID311, a bacterial symbiont associated with Cyphomyrmex fungus-growing ants. The planar structures of these compounds were established by 1 and 2D NMR data and MS analysis. The relative configurations of 1-3 were established using Kishi's universal NMR database method, NOE/ROE analysis and coupling constants analysis assisted by comparisons with NMR data of related compounds. Detailed bioinformatic analysis of cyphomycin biosynthetic gene cluster confirmed the stereochemical assignments. Compounds 1-3 displayed high antagonism against different strains of Escovopsis sp., pathogen fungi specialized to the fungus-growing ant system. Compounds 1-3 also exhibited potent antiprotozoal activity against intracellular amastigotes of the human parasite Leishmania donovani with IC₅₀ values of 2.32, 0.091 and 0.073 µM, respectively, with high selectivity indexes.

Meliponamycins: Antimicrobials from Stingless Bee-Associated Streptomyces sp

Social insects establish complex interactions with microorganisms, some of which play defensive roles in colony protection. The important role of pollinators such as the stingless bee Melipona scutellaris in nature encouraged us to pursue efforts to study its associated microbiota. Here we describe the discovery of two novel cyclic hexadepsipeptides, meliponamycin A (1) and meliponamycin B (2), from Streptomyces sp. ICBG1318 isolated from M. scutellaris nurse bees. Their structures were established by interpretation of NMR and MS data, and the absolute configuration of the constituent amino acids was determined by the advanced Marfey's method. Compounds 1 and 2 showed strong activity against the entomopathogen Paenibacillus larvae and human pathogens Staphylococcus aureus and Leishmania infantum.

Antifungal compounds from Streptomyces associated with attine ants also inhibit Leishmania donovani

Bacterial strains isolated from attine ants showed activity against the insect specialized fungal pathogen Escovopsis and also against the human protozoan parasite Leishmania donovani. The bioassay guided fractionation of extracts from cultures of Streptomyces sp. ICBG292, isolated from the exoskeleton of Cyphomyrmex workers, led to the isolation of Mer-A2026B (1), piericidin-A₁ (2) and nigericin (3). Nigericin (3) presented high activity against intracellular amastigotes of L. donovani (IC₅₀ 0.129 ± 0.008 μM). Streptomyces puniceus ICBG378, isolated from workers of Acromyrmex rugosus rugosus, produced dinactin (4) with potent anti-L. donovani activity against intracellular amastigotes (IC₅₀ 0.018 ± 0.003 μM). Compounds 3 and 4 showed good selectivity indexes, 88.91 and 656.11 respectively, and were more active than positive control, miltefosine. Compounds 1–4 were also active against some Escovopsis strains. Compounds 1 and 2 were also produced by Streptomyces sp. ICBG233, isolated from workers of Atta sexdens, and detected in ants’ extracts by mass spectrometry, suggesting they are produced in the natural environment as defensive compounds involved in the symbiotic interaction.

Visceral leishmaniasis, caused by Leishmania infantum and L. donovani, is characterized by high rate mortality worldwide. Current treatments for this disease suffer from toxicity, variable efficacy, requirements for parenteral administration and length of treatment regimens. New chemical entities and development of new drugs are important to overcome the impact of this protozoan disease. Actinobacterial strains, such as Streptomyces, have been a source of most naturally derived antibiotics, as well as anticancer, anthelmintic, and antifungal drugs. These microorganisms also produce small molecules important in symbiotic interactions with insects, such as fungus-growing ants, fungus-growing termites, beetles and wasps against pathogens. Several novel compounds have been reported from these microorganisms with promising biological activities. In this work we show an interesting ecologic approach for drug discovery that also shows promise for the identification of antileishmanial natural products from fungus-growing ant ecosystem. Two compounds isolated from Streptomyces strains showed potent activity against L. donovani, higher than the positive control (miltefosine) with high selectivity indexes.

Limited differential expression of miRNAs and other small RNAs in LPS-stimulated human monocytes

Monocytes are a distinct subset of myeloid cells with diverse functions in early inflammatory immune modulation. While previous studies have surveyed the role of miRNA regulation on different myeloid cell lines and primary cultures, the time-dependent kinetics of inflammatory stimulation on miRNA expression and the relationship between miRNA-to-target RNA expression have not been comprehensively profiled in monocytes. In this study, we use next-generation sequencing and RT-PCR assays to analyze the non-coding small RNA transcriptome of unstimulated and lipopolysaccharide (LPS)-stimulated monocytes at 6 and 24 hours. We identified a miRNA signature consisting of five mature miRNAs (hsa-mir-146a, hsa-mir-155, hsa-mir-9, hsa-mir-147b, and hsa-mir-193a) upregulated by LPS-stimulated monocytes after 6 hours and found that most miRNAs were also upregulated after 24 hours of stimulation. Only one miRNA gene was down-regulated and no other small RNAs were found dysregulated in monocytes after LPS treatment. In addition, novel tRNA-derived fragments were also discovered in monocytes although none showed significant changes upon LPS stimulation. Interrogation of validated miRNA targets by transcriptomic analysis revealed that absolute expression of most miRNA targets implicating in innate immune response decreased over time in LPS-stimulated monocytes although their expression patterns along the treatment were heterogeneous. Our findings reveal a potential role by which selective miRNA upregulation and stable expression of other small RNAs enable monocytes to develop finely tuned cellular responses during acute inflammation.

PARP1-LSD1 functional interplay controls transcription of SOD2 that protects human pro-inflammatory macrophages from death under an oxidative condition

The function of macrophages makes them vulnerable to several sources of stress and damage, and thus there is a considerable requirement for some form of resilient molecular defence. Differentiation of human macrophages and their further pro-inflammatory (M1) polarization with bacterial endotoxin is associated with increased transcription of PARP1 and SOD2. The latter gene responded immediately to LPS with high NFκB-dependent expression rate, and the resulting enzyme made M1 macrophages resistant to hydrogen peroxide-induced oxidative stress and associated cell death. LPS-induced recruitment of RELA to SOD2 promoter was accompanied by release of PARP1 and LSD1 from chromatin and increased H3K4 di- and tri-methylation. PARP1 dissociation from SOD2 promoter occurred at an early stage of SOD2 transcriptional activation. This event contributed to the termination of mRNA synthesis at a later stage of macrophage polarization by allowing LSD1 to rebind to the SOD2 promoter. LSD1 removed transcription-promoting methylation of H3K4 and led to displacement of RELA. Analysis of temporal changes at the SOD2 promoter indicated a direct mutual interdependence between PARP1, LSD1, H3K4 methylation and the ongoing SOD2 transcription, which correlated positively with both PARP1 abundance on the chromatin and dimethylation of H3K4, but negatively with LSD1 and chromatin compaction in LPS-treated macrophages. Deficiency of LSD1 activity and maintenance of PARP1 at the SOD2 promoter substantially upregulated SOD2 level, thereby further increasing resistance of M1 macrophages to hydrogen peroxide. Inhibitors of LSD1 and PARP1 poisons that capture the latter enzyme on the chromatin seem to be prosurvival molecular tools protecting polarized macrophages from certain pro-oxidative conditions.

Increased ROS production and DNA damage in monocytes are biomarkers of aging and atherosclerosis

Background

New evidence demonstrates that aging and dyslipidemia are closely associated with oxidative stress, DNA damage and apoptosis in some cells and extravascular tissues. However, in monocytes, which are naturally involved in progression and/or resolution of plaque in atherosclerosis, this concurrence has not yet been fully investigated. In this study, we evaluated the influence of aging and hypercholesterolemia on serum pro-inflammatory cytokines, oxidative stress, DNA damage and apoptosis in monocytes from apolipoprotein E-deficient (apoE^−/−) mice compared with age-matched wild-type C57BL/6 (WT) mice. Experiments were performed in young (2-months) and in old (18-months) male wild-type (WT) and apoE^−/− mice.

Results

Besides the expected differences in serum lipid profile and plaque formation, we observed that atherosclerotic mice exhibited a significant increase in monocytosis and in serum levels of pro-inflammatory cytokines compared to WT mice. Moreover, it was observed that the overproduction of ROS, led to an increased DNA fragmentation and, consequently, apoptosis in monocytes from normocholesterolemic old mice, which was aggravated in age-matched atherosclerotic mice.

Conclusions

In this study, we demonstrate that a pro-inflammatory systemic status is associated with an impairment of functionality of monocytes during aging and that these parameters are fundamental extra-arterial contributors to the aggravation of atherosclerosis. The present data open new avenues for the development of future strategies with the purpose of treating atherosclerosis.