Natural and Synthetic Xanthone Derivatives Counteract Oxidative Stress via Nrf2 Modulation in Inflamed Human Macrophages

Nrf2 and its signaling pathways in sepsis and its complications: A comprehensive review of research progress

Sepsis is a life-threatening condition characterized by organ dysfunction resulting from a dysregulated host immune response to infection. It is associated with a high incidence, intricate pathophysiological mechanisms, and rapidly progressive severity, rendering it a leading cause of mortality among patients in intensive care units. The Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) is a transcription factor pivotal for maintaining cellular redox homeostasis by regulating the expression of antioxidant and cytoprotective genes. Emerging evidence suggests that activation of the Nrf2 signaling pathway attenuates sepsis-induced inflammatory responses, oxidative stress, and organ dysfunction, thereby improving clinical outcomes. These findings underscore the potential of Nrf2 as a therapeutic target, offering a promising avenue for the development of novel interventions aimed at mitigating the complications and improving the prognosis of sepsis.

Natural xanthones as modulators of the Nrf2/ARE signaling pathway and potential gastroprotective agents

Oxidative stress is implicated in the initiation, pathogenesis, and progression of various gastric inflammatory diseases (GID). The prevalence of these diseases remains a concern along with the increasing risks of adverse effects in current clinical interventions. Hence, new gastroprotective agents capable of inhibiting oxidative stress by modulating cellular defense systems such as the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway are critically needed to address these issues. A candidate to solve the present issue is xanthone, a natural compound that reportedly exerts gastroprotective effects via antioxidant, anti-inflammatory, and cytoprotective mechanisms. Moreover, xanthone derivatives were shown to modulate the Nrf2/ARE signaling pathway to counter oxidative stress in both in vitro and in vivo models. Thirteen natural xanthones have demonstrated the ability to modulate the Nrf2/ARE signaling pathway and have high potential as lead compounds for GID as indicated by their in vivo gastroprotective action-particularly mangiferin (2), α-mangostin (3), and γ-mangostin (4). Further studies on these compounds are recommended to validate the Nrf2 modulatory ability in relation to their gastroprotective action.

Investigation on Human Carbonic Anhydrase IX and XII Inhibitory Activity and A549 Antiproliferative Activity of a New Class of Coumarinamides

Background-Aggressive solid tumors are commonly characterized by both basic intracellular pH and acidic extracellular pH, which increase cell survival and proliferation. As carbonic anhydrases IX/XII are involved in this pH regulation, their inhibition is an appealing approach in cancer therapy, avoiding cancer cell survival and proliferation. Substituted coumarins are selective non-classical CA IX and CA XII inhibitors. Methods-In this study, new 7-hydroxycoumarinamides were synthesized and assayed for CA inhibition and antiproliferative activity. Results-All of the coumarinamides showed human CA IX and CA XII selective inhibition over the off-target CA I and CA II isoforms. Coumarin acts as a suicide inhibitor because its heterocyclic ring can be hydrolyzed by CA esterase activity to give the corresponding 2-hydroxycinnamic acid derivative which blocks the entrance of the active site. The 2-hydroxycinnamic acid derivatives deriving from the most potent and selective coumarinamides were docked into CA IX and XII to better understand the activity and selectivity against the two CA isoforms. The most active coumarinamides also produced a decrease of A549 cell proliferation and were able to arrest cells at the G1/S checkpoint. Conclusions-These results may open new perspectives for developing coumarin-based CA IX/XII inhibitors.

Anti-Aging Potential of Avocado Oil via Its Antioxidant Effects

Aging is a process characterized by tissue degeneration, increased susceptibility to chronic degenerative diseases, infections, and the appearance of neoplasms, which leads to disability and a reduction in the length and quality of life. This phenomenon is the result of the convergence of multiple processes, including mitochondrial dysfunction, fibrosis, inflammation, dysregulation of cell death processes, and immunosenescence. These processes have as their point of convergence an increase in the production of ROS. Avocado oil (Persea americana Mill.) contains a diverse array of bioactive compounds, including oleic acid, phytosterols, chlorophylls, xanthones, xanthines, and carotenoids. These bioactive compounds have the capacity to modulate the excessive production of ROS, thereby reducing the progression of age-related diseases and extending lifespan in experimental models of aging. In addition, several studies have demonstrated the efficacy of avocado oil in mitigating age-related diseases, including hypertension; insulin resistance; diabetes; non-alcoholic liver disease; and degenerative processes such as hearing loss, cognitive decline, neurodegeneration, and impaired wound healing. In light of these findings, it is hypothesized that avocado oil is a promising agent capable of promoting healthspan in later stages of life owing to its direct antioxidant actions and the activation of pathways that enhance endogenous antioxidant levels.

Regioselectivity switches between anthraquinone precursor fissions involved in bioactive xanthone biosynthesis

Xanthone-based polyketides with complex molecular frameworks and potent bioactivities distribute and function in different biological kingdoms, yet their biosynthesis remains under-investigated. In particular, nothing is known regarding how to switch between the C4a-C10 (C4a-selective) and C10a-C10 bond (C10a-selective) cleavages of anthraquinone intermediates involved in biosynthesizing strikingly different frameworks of xanthones and their siblings. Enabled by our characterization of antiosteoporotic brunneoxanthones, a subfamily of polyketides from Aspergillus brunneoviolaceus FB-2, we present herein the brunneoxanthone biosynthetic gene cluster and the C10a-selective cleavage of anthraquinone (chrysophanol) hydroquinone leading ultimately to the bioactive brunneoxanthones under the catalysis of BruN (an undescribed atypical non-heme iron dioxygenase) in collaboration with BruM as a new oxidoreductase that reduces the anthraquinone into its hydroquinone using NADPH as a cofactor. The insights into the driving force that determines whether the C10a- or C4a-selective cleavages of anthraquinone hydroquinones take place were achieved by a combination of multiprotein sequence alignment, directed protein evolution, theoretical simulation, chemical capture of hydroquinone tautomer, 18O chasing, and X-ray crystal structure of the BruNN441M mutant, eventually allowing for the protocol establishment for the on-demand switch between the two ways of anthraquinone openings. Collectively, the work paves the way for the synthetic biology-based regeneration of uniquely structured high-value xanthones present in low abundance in complex mixtures, and helps to deepen the understanding on why and how such xanthones and their congeners are biosynthesized by different (micro)organisms in nature.

Investigation and development of novel synthetic approaches for synthesis of euxanthone and derived dyes

The historical dye Indian yellow, derived from euxanthic acid formed from 1,7-dihydroxyxanthone (euxanthone) and methyl (tri-O-acetyl-α-d-glucopyranosyl bromide) uronate, has significantly influenced the art world due to its vibrant color and unique production process. Studying Indian yellow is important for its historical relevance and impact on various art forms, as well as the challenges in its synthetic production. Herein, this work investigates the synthesis of the two main components, a novel method for obtaining euxanthone, and attempts to produce euxanthic acid and Indian yellow. All key intermediates and desired compounds have successfully been synthesized with good to high isolated yields, and characterized using different analytical and spectroscopic techniques. A proposed mechanism for euxanthone synthesis via 2,6,2',5'-tetramethoxybenzophenone formation is also offered. During this process, 2,7-dihydroxyxanthone has also been synthesized, revealing an equilibration reaction that produced three isomeric tetramethoxybenzophenones, confirmed by both GC/MS and NMR. Following the synthesis of euxanthone and clarification of the equilibration, the production of Indian yellow via euxanthic acid formation has further been explored.

The Induction of G2/M Phase Cell Cycle Arrest and Apoptosis by the Chalcone Derivative 1C in Sensitive and Resistant Ovarian Cancer Cells Is Associated with ROS Generation

Ovarian cancer ranks among the most severe forms of cancer affecting the female reproductive organs, posing a significant clinical challenge primarily due to the development of resistance to conventional therapies. This study investigated the effects of the chalcone derivative 1C on sensitive (A2780) and cisplatin-resistant (A2780cis) ovarian cancer cell lines. Our findings revealed that 1C suppressed cell viability, induced cell cycle arrest at the G2/M phase, and triggered apoptosis in both cell lines. These effects are closely associated with generating reactive oxygen species (ROS). Mechanistically, 1C induced DNA damage, modulated the activity of p21, PCNA, and phosphorylation of Rb and Bad proteins, as well as cleaved PARP. Moreover, it modulated Akt, Erk1/2, and NF-κB signaling pathways. Interestingly, we observed differential effects of 1C on Nrf2 levels between sensitive and resistant cells. While 1C increased Nrf2 levels in sensitive cells after 12 h and decreased them after 48 h, the opposite effect was observed in resistant cells. Notably, most of these effects were suppressed by the potent antioxidant N-acetylcysteine (NAC), underscoring the crucial role of ROS in 1C-induced antiproliferative activity. Moreover, we suggest that modulation of Nrf2 levels can, at least partially, contribute to the antiproliferative effect of chalcone 1C.

2-Substituted-4,7-dihydro-4-ethylpyrazolo[1,5-a]pyrimidin-7-ones alleviate LPS-induced inflammation by modulating cell metabolism via CD73 upon macrophage polarization

Macrophage polarization towards the M1 phenotype under bacterial product-related exposure (LPS) requires a rapid change in gene expression patterns and cytokine production along with a metabolic rewiring. Metabolic pathways and redox reactions are such tightly connected, giving rise to an area of research referred to as immunometabolism. A role in this context has been paid to the master redox-sensitive regulator Nuclear factor erythroid 2-related factor 2 (Nrf2) and to the 5'-ectonucleotidase CD73, a marker related to macrophage metabolism rearrangement under pro-inflammatory conditions. In this light, a cell model of LPS-stimulated macrophages has been established and nine 4,7-dihydro-4-ethylpyrazolo[l,5-a]pyrimidin-7-ones with a potential anti-inflammatory effect have been administered. Our data highlight that two selected compounds (namely, 5 and 8) inhibit the LPS-induced Nrf2 nuclear translocation and ameliorate the activity rate of the antioxidant enzyme catalase. Additionally, the pyridine-containing compound (8) promotes the shift from the pro-inflammatory immunophenotype M1 to the pro-resolving M2 one, by downregulating CD80 and iNOS and by enhancing CD163 and TGFβ1 expression. Most importantly, CD73 is modulated by these compounds as well as the lactate production. Our data demonstrate that pyrazolo[l,5-a]pyrimidine derivatives are effective as anti-inflammatory compounds. Furthermore, these pyrazolo[l,5-a]pyrimidines exert their action via CD73-related signaling and modulation of cell metabolism of activated macrophages.

Immunophenotyping of hemocytes from infected Galleria mellonella larvae as an innovative tool for immune profiling, infection studies and drug screening

In recent years, there has been a considerable increasing interest in the use of the greater wax moth Galleria mellonella as an animal model. In vivo pharmacological tests, concerning the efficacy and the toxicity of novel compounds are typically performed in mammalian models. However, the use of the latter is costly, laborious and requires ethical approval. In this context, G. mellonella larvae can be considered a valid option due to their greater ease of use and the absence of ethical rules. Furthermore, it has been demonstrated that the immune system of these invertebrates has similarity with the one of mammals, thus guaranteeing the reliability of this in vivo model, mainly in the microbiological field. To better develop the full potential of this model, we present a novel approach to characterize the hemocyte population from G. mellonella larvae and to highlight the immuno modulation upon infection and treatments. Our approach is based on the detection in isolated hemocytes from G. mellonella hemolymph of cell membrane markers typically expressed by human immune cells upon inflammation and infection, for instance CD14, CD44, CD80, CD163 and CD200. This method highlights the analogies between G. mellonella larvae and humans. Furthermore, we provide an innovative tool to perform pre-clinical evaluations of the efficacy of antimicrobial compounds in vivo to further proceed with clinical trials and support drug discovery campaigns.

Demethylcalabaxanthone from Garcinia mangostana Exerts Antioxidant Effects through the Activation of the Nrf2 Pathway as Assessed via Molecular Docking and Biological Evaluation

Nuclear factor erythroid 2-related factor 2 (Nrf2) pathway activation promotes the expression of antioxidant enzymes in response to rising oxidative stress, resulting in reactive oxygen species (ROS) detoxification and playing a central role in the maintenance of intracellular redox homeostasis and regulation of inflammation. Moreover, the biological effects of Nrf2 pathway activation contribute to reducing apoptosis and enhancing cell survival. The activity of Nrf2 is negatively regulated by Kelch-like ECH-associated protein 1 (Keap1). Prompted by the recent results reporting the impact of xanthone metabolites on oxidative stress, cancer, and inflammation, the antioxidant properties of xanthones isolated from Garcinia mangostana (γ-mangostin, α-mangostin, 8-deoxygartanin, demethylcalabaxanthone, garcinone D) were assessed. In particular, the capability of these natural products to disrupt the interaction between Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2), triggering the activation of the Nrf2-mediated pathway, was evaluated using molecular docking experiments and in vitro tests. The modulation of some key Nrf2-related mediators like glutathione (GSH) and lactate dehydrogenase (LDH) to highlight a possible direct antioxidant effect was investigated. Among the tested compounds, demethylcalabaxanthone showed an indirect antioxidant effect, as corroborated by a Western blot assay, displaying a significant increase in the translocated protein upon its administration.