Reduction of oxidative stress blunts the NLRP3 inflammatory cascade in LPS stimulated human gingival fibroblasts and oral mucosal epithelial cells

Pyroptosis: A major trigger of excessive immune response in the gingiva

OBJECTIVES

The gingival mucosal barrier, an important oral cavity barrier, plays a significant role in preventing pathogenic microorganism invasion and maintaining periodontal tissue health. Pathogenic microorganism invasion of the gingival mucosa produces a large number of cytokines. Among them, pyroptosis is an important player in exacerbating immune-inflammatory responses, leading to tissue destruction. However, the mechanism of pyroptosis and the immune response it triggers have not been fully elucidated. We provide an overview of recent advances in understanding gingival physical barrier pyroptosis and inflammation-induced hyperimmunity.

METHODS

PubMed, Web of Science databases were searched for articles, reviews, and clinical studies published until March 2024.

RESULTS

We summarised the importance of the gingival barrier in terms of the functions of different cells, described the progress in research on gingival epithelial cell and gingival fibroblast pyroptosis and the immune-inflammatory response it induces, and discussed the relationship between pyroptosis and systemic diseases, association of multiple cell death systems. Finally, we propose future directions for pyroptosis research.

CONCLUSIONS

Pyroptosis often triggers a range of inflammatory immune responses that lead to associated diseases. Therefore, further study of the molecular mechanisms of pyroptosis and the immune responses is warranted.

Euterpe oleracea Mart. Bioactive Molecules: Promising Agents to Modulate the NLRP3 Inflammasome

Inflammation is a vital mechanism that defends the organism against infections and restores homeostasis. However, when inflammation becomes uncontrolled, it leads to chronic inflammation. The NLRP3 inflammasome is crucial in chronic inflammatory responses and has become a focal point in research for new anti-inflammatory therapies. Flavonoids like catechin, apigenin, and epicatechin are known for their bioactive properties (antioxidant, anti-inflammatory, etc.), but the mechanisms behind their anti-inflammatory actions remain unclear. This study aimed to explore the ability of various flavonoids (isolated and combined) to modulate the NLRP3 inflammasome using in silico and in vitro models. Computer simulations, such as molecular docking, molecular dynamics, and MM/GBSA calculations examined the interactions between bioactive molecules and NLRP3 PYD. THP1 cells were treated with LPS + nigericin to activate NLRP3, followed by flavonoid treatment at different concentrations. THP1-derived macrophages were also treated following NLRP3 activation protocols. The assays included colorimetric, fluorometric, microscopic, and molecular techniques. The results showed that catechin, apigenin, and epicatechin had high binding affinity to NLRP3 PYD, similar to the known NLRP3 inhibitor MCC950. These flavonoids, particularly at 1 µg/mL, 0.1 µg/mL, and 0.01 µg/mL, respectively, significantly reduced LPS + nigericin effects in both cell types and decreased pro-inflammatory cytokine, caspase-1, and NLRP3 gene expression, suggesting their potential as anti-inflammatory agents through NLRP3 modulation.

Inflammasome activity regulation by PUFA metabolites

Oxidative stress and the accompanying chronic inflammation constitute an important metabolic problem that may lead to pathology, especially when the body is exposed to physicochemical and biological factors, including UV radiation, pathogens, drugs, as well as endogenous metabolic disorders. The cellular response is associated, among others, with changes in lipid metabolism, mainly due to the oxidation and the action of lipolytic enzymes. Products of oxidative fragmentation/cyclization of polyunsaturated fatty acids (PUFAs) [4-HNE, MDA, 8-isoprostanes, neuroprostanes] and eicosanoids generated as a result of the enzymatic metabolism of PUFAs significantly modify cellular metabolism, including inflammation and the functioning of the immune system by interfering with intracellular molecular signaling. The key regulators of inflammation, the effectiveness of which can be regulated by interacting with the products of lipid metabolism under oxidative stress, are inflammasome complexes. An example is both negative or positive regulation of NLRP3 inflammasome activity by 4-HNE depending on the severity of oxidative stress. 4-HNE modifies NLRP3 activity by both direct interaction with NLRP3 and alteration of NF-κB signaling. Furthermore, prostaglandin E2 is known to be positively correlated with both NLRP3 and NLRC4 activity, while its potential interference with AIM2 or NLRP1 activity is unproven. Therefore, the influence of PUFA metabolites on the activity of well-characterized inflammasome complexes is reviewed.

Levosimendan and Dobutamin Attenuate LPS-Induced Inflammation in Microglia by Inhibiting the NF-κB Pathway and NLRP3 Inflammasome Activation via Nrf2/HO-1 Signalling

Hypovolemic shock is a circulatory failure, due to a loss in the effective circulating blood volume, that causes tissue hypoperfusion and hypoxia. This condition stimulates reactive oxygen species (ROS) and pro-inflammatory cytokine production in different organs and also in the central nervous system (CNS). Levosimendan, a cardioprotective inodilator, and dobutamine, a β1-adrenergic agonist, are commonly used for the treatment of hypovolemic shock, thanks to their anti-inflammatory and antioxidant effects. For this reason, we aimed at investigating levosimendan and dobutamine's neuroprotective effects in an "in vitro" model of lipopolysaccharide (LPS)-induced neuroinflammation. Human microglial cells (HMC3) were challenged with LPS (0.1 µg/mL) to induce an inflammatory phenotype and then treated with levosimendan (10 µM) or dobutamine (50 µM) for 24 h. Levosimendan and dobutamine significantly reduced the ROS levels and markedly increased Nrf2 and HO-1 protein expression in LPS-challenged cells. Levosimendan and dobutamine also decreased p-NF-κB expression and turned off the NLRP3 inflammasome together with its downstream signals, caspase-1 and IL-1β. Moreover, a reduction in TNF-α and IL-6 expression and an increase in IL-10 levels in LPS-stimulated HMC3 cells was observed following treatment. In conclusion, levosimendan and dobutamine attenuated LPS-induced neuroinflammation through NF-κB pathway inhibition and NLRP3 inflammasome activation via Nrf2/HO-1 signalling, suggesting that these drugs could represent a promising therapeutic approach for the treatment of neuroinflammation consequent to hypovolemic shock.

Antimicrobial, antioxidant and cytotoxic activities of the leaf and stem extracts of Carissa bispinosa used for dental health care

BACKGROUND

Carissa bispinosa (L.) Desf. ex Brenan is one of the plants used traditionally to treat oral infections. However, there is limited data validating its therapeutic properties and photochemistry. The aim of this study was to investigate the protective efficacy of the leaf and stem extracts of C. bispinosa against oral infections.

METHODS

The phenolic and tannin contents were measured using Folin-Ciocalteau method after extracting with different solvents. The minimum inhibitory concentrations (MIC) of the extracts were assessed using the microdilution method against fungal (Candida albicans and Candida glabrata) and bacterial (Streptococcus pyogenes, Staphylococcus aureus and Enterococcus faecalis) strains. The 2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing power (FRP) models were utilised to assess the antioxidant potential of the extracts. Cytotoxicity of the leaf acetone extract was evaluated using the methylthiazol tetrazolium assay.

RESULTS

The methanol leaf extract had the highest phenolic content (113.20 mg TAE/g), whereas hexane extract displayed the highest tannin composition of 22.98 mg GAE/g. The acetone stem extract had the highest phenolic content (338 mg TAE/g) and the stem extract yielded the highest total tannin content (49.87 mg GAE/g). The methanol leaf extract demonstrated the lowest MIC value (0.31 mg/mL), whereas the stem ethanol extract had the least MIC value of 0.31 mg/mL. The stem methanol extract had the best DPPH free radical scavenging activity (IC50, 72 µg/mL) whereas the stem ethanol extract displayed maximum FRP with absorbance of 1.916. The leaf acetone extract had minimum cytotoxicity with the lethal concentration (LC50) of 0.63 mg/mL.

CONCLUSIONS

The results obtained in this study validated the protective effect of C. bispinosa against oral infections.

Assessment of Oxidative Stress-Induced Oral Epithelial Toxicity

Reactive oxygen species (ROS) are highly reactive molecules generated in living organisms and an excessive production of ROS culminates in oxidative stress and cellular damage. Notably, oxidative stress plays a critical role in the pathogenesis of a number of oral mucosal diseases, including oral mucositis, which remains one of cancer treatments' most common side effects. We have shown previously that oral keratinocytes are remarkably sensitive to oxidative stress, and this may hinder the development and reproducibility of epithelial cell-based models of oral disease. Here, we examined the oxidative stress signatures that parallel oral toxicity by reproducing the initial events taking place during cancer treatment-induced oral mucositis. We used three oral epithelial cell lines (an immortalized normal human oral keratinocyte cell line, OKF6, and malignant oral keratinocytes, H357 and H400), as well as a mouse model of mucositis. The cells were subjected to increasing oxidative stress by incubation with hydrogen peroxide (H2O2) at concentrations of 100 μM up to 1200 μM, for up to 24 h, and ROS production and real-time kinetics of oxidative stress were investigated using fluorescent dye-based probes. Cell viability was assessed using a trypan blue exclusion assay, a fluorescence-based live-dead assay, and a fluorometric cytotoxicity assay (FCA), while morphological changes were analyzed by means of a phase-contrast inverted microscope. Static and dynamic real-time detection of the redox changes in keratinocytes showed a time-dependent increase of ROS production during oxidative stress-induced epithelial injury. The survival rates of oral epithelial cells were significantly affected after exposure to oxidative stress in a dose- and cell line-dependent manner. Values of TC50 of 800 μM, 800 μM, and 400 μM were reported for H400 cells (54.21 ± 9.04, p < 0.01), H357 cells (53.48 ± 4.01, p < 0.01), and OKF6 cells (48.64 ± 3.09, p < 0.01), respectively. Oxidative stress markers (MPO and MDA) were also significantly increased in oral tissues in our dual mouse model of chemotherapy-induced mucositis. In summary, we characterized and validated an oxidative stress model in human oral keratinocytes and identified optimal experimental conditions for the study of oxidative stress-induced oral epithelial toxicity.

Blunting Neuroinflammation by Targeting the Immunoproteasome with Novel Amide Derivatives

Neuroinflammation is an inflammatory response of the nervous tissue mediated by the production of cytokines, chemokines, and reactive oxygen species. Recent studies have shown that an upregulation of immunoproteasome is highly associated with various diseases and its inhibition attenuates neuroinflammation. In this context, the development of non-covalent immunoproteasome-selective inhibitors could represent a promising strategy for treating inflammatory diseases. Novel amide derivatives, KJ3 and KJ9, inhibit the β5 subunit of immunoproteasome and were used to evaluate their possible anti-inflammatory effects in an in vitro model of TNF-α induced neuroinflammation. Differentiated SH-SY5Y and microglial cells were challenged with 10 ng/mL TNF-α for 24 h and treated with KJ3 (1 µM) and KJ9 (1 µM) for 24 h. The amide derivatives showed a significant reduction of oxidative stress and the inflammatory cascade triggered by TNF-α reducing p-ERK expression in treated cells. Moreover, the key action of these compounds on the immunoproteasome was further confirmed by halting the IkB-α phosphorylation and the consequent inhibition of NF-kB. As downstream targets, IL-1β and IL-6 expression resulted also blunted by either KJ3 and KJ9. These preliminary results suggest that the effects of these two compounds during neuroinflammatory response relies on the reduced expression of pro-inflammatory targets.

Guiqi Baizhu prescription ameliorates cytarabine-induced intestinal mucositis by targeting JAK2 to inhibit M1 macrophage polarization

BACKGROUND

Intestinal mucositis (IM) is characterized by damage to the intestinal mucosa resulting from inhibition of epithelial cell division and loss of renewal capacity following anticancer chemotherapy and radiotherapy. Cytarabine (Ara-C), the main chemotherapy drug for the treatment of leukemia and lymphoma, is a frequent cause of IM. Guiqi Baizhu prescription (GQBZP) is a traditional Chinese medicine with anti-cancer and anti-inflammatory effects.

PURPOSE

To determine if GQBZP can ameliorate Ara-C induced IM and identify and characterize the pharmacologic and pharmacodynamic mechanisms.

STUDY DESIGN AND METHODS

IM was induced in mice with Ara-C and concurrently treated with orally administered GQBZP. Body weight and food intake was monitored, with HE staining to calculate ileal histomorphometric scoring and villus length/crypt depth. Immunoblotting was used to detect intestinal tissue inflammatory factors. M1 macrophages (M1) were labeled with CD86 by flow cytometry and iNOS + F4/80 by immunofluorescence. Virtual screening was used to find potentially active compounds in GQBZP that targeted JAK2. In vitro, RAW264.7 cells were skewed to M1 macrophage polarization by lipopolysaccharide (LPS) and interferon-γ (INF-γ) and treated orally with GQBZP or potential active compounds. M1 was labeled with CD86 by flow cytometry and iNOS by immunofluorescence. ELISA was used to detect inflammatory factor expression. Active compounds against JAK2, p-JAK2, STAT1 and p-STAT1 were identified by western blotting and HCS fluorescence. Molecular dynamics simulations and pharmacokinetic predictions were carried out on representative active compounds.

RESULTS

Experimental results with mice in vivo suggest that GQBZP significantly attenuated Ara-C-induced ileal damage and release of pro-inflammatory factors by inhibiting macrophage polarization to M1. Molecular docking was used to identify potentially active compounds in GQBZP that targeted JAK2, a key factor in macrophage polarization to M1. By examining the main components of each herb and applying Lipinski's rules, ten potentially active compounds were identified. In vitro experimental results suggested that all 10 compounds of GQBZP targeted JAK2 and could inhibit M1 polarization in RAW264.7 cells treated with LPS and INF-γ. Among them, acridine and senkyunolide A down-regulated the expression of JAK2 and STAT1. MD simulations revealed that acridine and senkyunolide A were stable in the active site of JAK2 and exhibited good interactions with the surrounding amino acids.

CONCLUSIONS

GQBZP can ameliorate Ara-C-induced IM by reducing macrophage polarization to M1, and acridine and senkyunolide A are representative active compounds in GQBZP that target JAK2 to inhibit M1 polarization. Targeting JAK2 to regulate M1 polarization may be a valuable therapeutic strategy for IM.

Transcription Factors as Targets of Natural Compounds in Age-Related Diseases and Cancer: Potential Therapeutic Applications

Inflammation exacerbates systemic pathophysiological conditions and chronic inflammation is a sustained and systemic phenomenon that aggravates aging that can lead to chronic age-related diseases. These inflammatory phenomena have recently been redefined and delineated at the molecular, cellular, and systemic levels. Many transcription factors that are activated in response to tumor metabolic state have been reported to be regulated by a class of histone deacetylase called sirtuins (SIRTs). Sirtuins play a pivotal role in the regulation of tumor cell metabolism, proliferation, and angiogenesis, including oxidative stress and inflammation. The SIRT1-mediated signaling pathway in diabetes and cancer is the SIRT1/forkhead-box class O (FoxO)/nuclear factor-kappa B (NF-κB) pathway. In this review, we describe the accumulation of SIRT1-, NF-κB-, and FoxO-mediated inflammatory processes and cellular proinflammatory signaling pathways. We also describe the proinflammatory mechanisms underlying metabolic molecular pathways in various diseases such as liver cancer and diabetes. Finally, the regulation of cancer and diabetes through the anti-inflammatory effects of natural compounds is highlighted. Evidence from inflammation studies strongly suggests that cells may be a major source of cytokines secreted during various diseases. A better understanding of the mechanisms that underpin the inflammatory response and palliative role of natural compounds will provide insights into the molecular mechanisms of inflammation and various diseases for potential intervention.

An injectable multifunctional thermo-sensitive chitosan-based hydrogel for periodontitis therapy

Bacteria are recognized as the driving factors of periodontitis. However, excessive reactive oxygen species (ROS) can harm periodontal tissue while also causing an uncontrolled inflammatory response. Hence, eliminating excessive ROS and blocking ROS-induced abnormal inflammatory response by antioxidants are achieving remarkable results in periodontitis therapy. Moreover, influenced by the deep and irregular periodontal pockets, injectable thermo-sensitive chitosan-based hydrogels have attracted a lot of attention. This study aimed to formulate an antibacterial and antioxidant therapeutic regimen by incorporating antimicrobial peptides (Nal-P-113) and/or antioxidants (polydopamine nanoparticles, PDNPs) into chitosan-based hydrogels. The hydrogel was characterized in vitro and finally examined in rats using the experimental periodontitis model. The release kinetics showed that the hydrogel could stably release Nal-P-113 and PDNPs for up to 13 days. The scavenging activity of the hydrogel against DPPH was about 80 % and the antibacterial ratio against Streptococcus gordonii (S. gordonii), Fusobacterium nucleatum (F. nucleatum) and Porphyromonas gingivalis (P. gingivalis) was about 99 %. Importantly, it was examined that the hydrogel had the ability to prevent periodontal tissue damage. Thus, chitosan-based hydrogels may provide a basis for designing multifunctional local drug delivery biomaterials for the treatment of periodontitis.

Baicalin inhibits necroptosis by decreasing oligomerization of phosphorylated MLKL and mitigates caerulein-induced acute pancreatitis in mice

Necroptosis is a form of regulated necrosis mainly controlled by receptor-interacting protein kinases 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). Necroptosis has important roles in defensing against pathogenic infections, but it is also implicated in various inflammatory diseases including pancreatitis. Baicalin, a flavonoid from Scutellaria baicalensis Georgi, has been shown to possess anti-inflammatory and anti-pyroptosis properties, yet it is unclear whether baicalin can inhibit necroptosis and confer protection against necroptosis-related diseases. Here we reported that baicalin significantly inhibited necroptosis in macrophages induced by lipopolysaccharide plus pan-caspase inhibitor (IDN-6556), or by tumor-necrosis factor-α in combination with LCL-161 (Smac mimetic) and IDN-6556 (TSI). Mechanistically, baicalin did not inhibit the phosphorylation of RIPK1, RIPK3 and MLKL, nor membrane translocation of p-MLKL, during necroptotic induction, but instead inhibited p-MLKL oligomerization that is required for executing necroptosis. As intracellular reactive oxygen species (ROS) has been reported to be involved in p-MLKL oligomerization, we assessed the effects of N-acetyl-L-cysteine (NAC), an ROS scavenger, on necroptosis and found that NAC significantly attenuated TSI-induced necroptosis and intracellular ROS production concomitantly with reduced levels of oligomerized p-MLKL, mirroring the effect of baicalin. Indeed, inhibitory effect of baicalin was associated with reduced TSI-induced superoxide (indicating mitochondrial ROS) production and increased mitochondrial membrane potential within cells during necroptosis. Besides, oral administration of baicalin significantly reduced the severity of caerulein-induced acute pancreatitis in mice, an animal model of necroptosis-related disease. Collectively, baicalin can inhibit necroptosis through attenuating p-MLKL oligomerization and confers protection against caerulein-induced pancreatitis in mice.

Baicalin Targets HSP70/90 to Regulate PKR/PI3K/AKT/eNOS Signaling Pathways

Baicalin is a major active ingredient of traditional Chinese medicine Scutellaria baicalensis, and has been shown to have antiviral, anti-inflammatory, and antitumor activities. However, the protein targets of baicalin have remained unclear. Herein, a chemical proteomics strategy was developed by combining baicalin-functionalized magnetic nanoparticles (BCL-N3@MNPs) and quantitative mass spectrometry to identify the target proteins of baicalin. Bioinformatics analysis with the use of Gene Ontology, STRING and Ingenuity Pathway Analysis, was performed to annotate the biological functions and the associated signaling pathways of the baicalin targeting proteins. Fourteen proteins in human embryonic kidney cells were identified to interact with baicalin with various binding affinities. Bioinformatics analysis revealed these proteins are mainly ATP-binding and/or ATPase activity proteins, such as CKB, HSP86, HSP70-1, HSP90, ATPSF1β and ACTG1, and highly associated with the regulation of the role of PKR in interferon induction and the antiviral response signaling pathway (P = 10-6), PI3K/AKT signaling pathway (P = 10-5) and eNOS signaling pathway (P = 10-4). The results show that baicalin exerts multiply pharmacological functions, such as antiviral, anti-inflammatory, antitumor, and antioxidant functions, through regulating the PKR and PI3K/AKT/eNOS signaling pathways by targeting ATP-binding and ATPase activity proteins. These findings provide a fundamental insight into further studies on the mechanism of action of baicalin.