Inhibition of arachidonate release from rat peritoneal macrophage by biflavonoids

Antiviral activities of 4H-chromen-4-one scaffold-containing flavonoids against SARS-CoV-2 using computational and in vitro approaches

The widespread outbreak of the novel coronavirus called severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused the main health challenge worldwide. This pandemic has attracted the attention of the research communities in various fields, prompting efforts to discover rapid drug molecules for the treatment of the life-threatening COVID-19 disease. This study is aimed at investigating 4H-chromen-4-one scaffold-containing flavonoids that combat the SARS-CoV-2 virus using computational and in vitro approaches. Virtual screening studies of the molecule's library for 4H-chromen-4-one scaffold were performed with the recently reported coronavirus main protease (M^pro, also called 3CL^pro) because it plays an essential role in the maturation and processing of the viral polyprotein. Based on the virtual screening, the top hit molecules such as isoginkgetin and afzelin molecules were selected for further estimating in vitro antiviral efficacies against SARS-CoV-2 in Vero cells. Additionally, these molecules were also docked with RNA-dependent RNA Polymerase (RdRp) to reveal the ligands-protein molecular interaction. In the in vitro study, isoginkgetin showed remarkable inhibition potency against the SARS-CoV-2 virus, with an IC₅₀ value of 22.81 μM, compared to remdesivir, chloroquine, and lopinavir with IC₅₀ values of 7.18, 11.63, and 11.49 μM, respectively. Furthermore, the complex stability of isoginkgetin with an active binding pocket of the SARS-CoV-2 M^pro and RdRp supports its inhibitory potency against the SARS-CoV-2. Thus, isoginkgetin is a potent leading drug candidate and needs to be used in in vivo trials for the treatment of SARS-CoV-2 infected patients.

Therapeutic and prophylactic effect of flavonoids in post-COVID-19 therapy

The high incidence of post-covid symptoms in humans confirms the need for effective treatment. Due to long-term complications across several disciplines, special treatment programs emerge for affected patients, emphasizing multidisciplinary care. For these reasons, we decided to look at current knowledge about possible long-term complications of COVID-19 disease and then present the effect of flavonoids, which could help alleviate or eliminate complications in humans after overcoming the COVID-19 infection. Based on articles published from 2003 to 2021, we summarize the flavonoids-based molecular mechanisms associated with the post-COVID-19 syndrome and simultaneously provide a complex view regarding their prophylactic and therapeutic potential. Review clearly sorts out the outcome of post-COVID-19 syndrome according particular body systems. The conclusion is that flavonoids play an important role in prevention of many diseases. We suggest that flavonoids as critical nutritional supplements, are suitable for the alleviation and shortening of the period associated with the post-COVID-19 syndrome. The most promising flavonoid with noteworthy therapeutic and prophylactic effect appears to be quercetin.

A Purified Biflavonoid Extract From Selaginella moellendorffii Alleviates Gout Arthritis via NLRP3/ASC/Caspase-1 Axis Suppression

Background: Activation of nucleotide oligomerization domain-like receptor protein 3 (NLRP3) inflammasome plays a crucial role in gout. Selaginella moellendorffii has been confirmed effective for the treatment of gout in hospital preparations. Flavonoids, such as amentoflavone (AM), are the main active components of this medicine. Purpose: We aimed to investigate the flavonoid extract (TF) and AM's effects on NLRP3 inflammasome in vitro and their preventive effects on gout in vivo. Methods: LC-MS method was employed to investigate the chemical profile of TF. The cellular inflammation model was established by lipopolysaccharide (LPS) or monosodium urate (MSU) stimulation. The cell membrane integrality and morphological characteristics were determined by using Lactate dehydrogenase (LDH) assay kits, propidium iodide (PI) stain, and scanning electron microscopy (SEM). The inflammatory cytokines and NLRP3 inflammasome activation were determined using enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (RT-PCR), immunofluorescence staining, and western blotting. The acute gout mouse model was induced by MSU injection into footpads, and then the paw edema, inflammatory mediators, and histological examination (HE) were analyzed. Results: The main constituents in TF are AM and robustaflavone. In the cellular inflammation model, TF down-regulated the levels of nitric oxide (NO), TNF-α, and LDH, suppressed NLRP3 inflammasome-derived interleukin-1β (IL-1β) secretion, decreased caspase-1 activation, repressed mature IL-1β expression, inhibited ASC speck formation and NLRP3 protein expression. In an acute gout mouse model, oral administration of TF to mice effectively alleviated paw edema, reduced inflammatory features, and decreased the levels of IL-1β in mouse foot tissue. Similarly, the characteristic constituent AM was also able to down-regulated the levels of NO, TNF-α, and LDH, down-regulate the mRNA expression of IL-1β, TNF-α, caspase-1, and NLRP3. Besides, the foot thickness, lymphocyte infiltration, and IL-1β level were also prevented by AM. Conclusion: The results indicated that TF and its main constituent AM alleviate gout arthritis via NLRP3/ASC/Caspase-1 axis suppression.

Biflavonoids Isolated from Selaginella tamariscina and Their Anti-Inflammatory Activities via ERK 1/2 Signaling

Selaginella tamariscina (S. tamariscina) (Beauv.) Spring (Selaginellaceae) has been used in oriental medicine for the treatment of dysmenorrhea, chronic hepatitis, hyperglycemia, amenorrhea, hematuria, prolapse of the anus and metrorrhagia. In the present study, we isolated two strong anti-inflammatory compounds, the biflavonoids hinokiflavone (H) and 7′-O-methyl hinokiflavone (mH), from S. tamariscina and examined their anti-inflammatory activities in lipopolysaccharide (LPS)-mediated murine macrophages (RAW 264.7) and colon epithelial cells (HT-29). H and mH suppressed the production of the inflammatory mediators nitric oxide (NO), interleukin (IL)-6, IL-8, and tumor-necrosis factor (TNF)-α, which are most highly activated in inflammatory bowel disease (IBD). In addition, Western blot analysis revealed that H and mH suppressed the LPS-induced expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, and the activation of nuclear factor-κB (NF-κB) and extracellular regulated kinases (ERK) 1/2. These results suggest that H and mH are compounds having potent anti-inflammatory effects that could be used to treat such diseases as IBD.

Natural Biflavonoids Modulate Macrophage-Oxidized LDL Interaction In Vitro and Promote Atheroprotection In Vivo

The accumulation of oxidized ApoB-100-containing lipoproteins in the vascular intima and its subsequent recognition by macrophages results in foam cell formation and inflammation, key events during atherosclerosis development. Agents targeting this process are considered potentially atheroprotective. Since natural biflavonoids exert antioxidant and anti-inflammatory effects, we evaluated the atheroprotective effect of biflavonoids obtained from the tropical fruit tree Garcinia madruno. To this end, the pure biflavonoid aglycones morelloflavone (Mo) and volkensiflavone (Vo), as well as the morelloflavone's glycoside fukugiside (Fu) were tested in vitro in primary macrophages, whereas a biflavonoid fraction with defined composition (85% Mo, 10% Vo, and 5% Amentoflavone) was tested in vitro and in vivo. All biflavonoid preparations were potent reactive oxygen species (ROS) scavengers in the oxygen radical absorbance capacity assay, and most importantly, protected low-density lipoprotein particle from both lipid and protein oxidation. In biflavonoid-treated macrophages, the surface expression of the oxidized LDL (oxLDL) receptor CD36 was significantly lower than in vehicle-treated macrophages. Uptake of fluorescently labeled oxLDL and cholesterol accumulation were also attenuated in biflavonoid-treated macrophages and followed a pattern that paralleled that of CD36 surface expression. Fu and Vo inhibited oxLDL-induced ROS production and interleukin (IL)-6 secretion, respectively, whereas all aglycones, but not the glucoside Fu, inhibited the secretion of one or more of the cytokines IL-1β, IL-12p70, and monocyte chemotactic protein-1 (MCP-1) in lipopolysaccharide (LPS)-stimulated macrophages. Interestingly, in macrophages primed with low-dose LPS and stimulated with cholesterol crystals, IL-1β secretion was significantly and comparably inhibited by all biflavonoid preparations. Intraperitoneal administration of the defined biflavonoid fraction into ApoE^-/- mice was atheroprotective, as evidenced by the reduction of the atheromatous lesion size and the density of T cells and macrophages infiltrating the aortic root; moreover, this treatment also lowered the circulating levels of cholesterol and the lipid peroxidation product malondialdehyde. These results reveal the potent atheroprotective effects exerted by biflavonoids on key events of the oxLDL-macrophage interphase: (i) atheroligand formation, (ii) atheroreceptor expression, (iii) foam cell transformation, and (iv) prooxidant/proinflammatory macrophage response. Furthermore, our results also evidence the antioxidant, anti-inflammatory, hypolipemiant, and atheroprotective effects of Garcinia madruno's biflavonoids in vivo.

Microbial and Natural Metabolites That Inhibit Splicing: A Powerful Alternative for Cancer Treatment

In eukaryotes, genes are frequently interrupted with noncoding sequences named introns. Alternative splicing is a nuclear mechanism by which these introns are removed and flanking coding regions named exons are joined together to generate a message that will be translated in the cytoplasm. This mechanism is catalyzed by a complex machinery known as the spliceosome, which is conformed by more than 300 proteins and ribonucleoproteins that activate and regulate the precision of gene expression when assembled. It has been proposed that several genetic diseases are related to defects in the splicing process, including cancer. For this reason, natural products that show the ability to regulate splicing have attracted enormous attention due to its potential use for cancer treatment. Some microbial metabolites have shown the ability to inhibit gene splicing and the molecular mechanism responsible for this inhibition is being studied for future applications. Here, we summarize the main types of natural products that have been characterized as splicing inhibitors, the recent advances regarding molecular and cellular effects related to these molecules, and the applications reported so far in cancer therapeutics.

Anti-Inflammatory Effects of Hyptis albida Chloroform Extract on Lipopolysaccharide-Stimulated Peritoneal Macrophages

We examined the effects of a chloroform extract of Hyptis albida (CHA) on inflammatory responses in mouse lipopolysaccharide (LPS) induced peritoneal macrophages. Our findings indicate that CHA inhibits LPS-induced production of tumor necrosis factor (TNF- α ) and interleukin-6 (IL-6). During the process, levels of cyclooxygenase-2 (COX-2), nitric oxide synthase (iNOS), and nitric oxide (NO) increased in the mouse peritoneal macrophages; however, the extract suppressed them significantly. These results provide novel insights into the anti-inflammatory actions of CHA and support its potential use in the treatment of inflammatory diseases.

Extracellular signal-regulated kinase is a direct target of the anti-inflammatory compound amentoflavone derived from Torreya nucifera

Amentoflavone is a biflavonoid compound with antioxidant, anticancer, antibacterial, antiviral, anti-inflammatory, and UV-blocking activities that can be isolated from Torreya nucifera, Biophytum sensitivum, and Selaginella tamariscina. In this study, the molecular mechanism underlying amentoflavone's anti-inflammatory activity was investigated. Amentoflavone dose dependently suppressed the production of nitric oxide (NO) and prostaglandin E₂ (PGE₂) in RAW264.7 cells stimulated with the TLR4 ligand lipopolysaccharide (LPS; derived from Gram-negative bacteria). Amentoflavone suppressed the nuclear translocation of c-Fos, a subunit of activator protein (AP)-1, at 60 min after LPS stimulation and inhibited the activity of purified and immunoprecipitated extracellular signal-regulated kinase (ERK), which mediates c-Fos translocation. In agreement with these results, amentoflavone also suppressed the formation of a molecular complex including ERK and c-Fos. Therefore, our data strongly suggest that amentoflavone's immunopharmacological activities are due to its direct effect on ERK.

Ochnaflavone and Ochnaflavone 7-O-Methyl Ether two Antibacterial Biflavonoids from Ochna pretoriensis (Ochnaceae)

The acetone extract of Ochna pretoriensis was evaluated for antibacterial activity using bioautography and serial microplate dilution methods against four nosocomial bacterial pathogens namely: Escherichia coli, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa. A bioassay-guided fractionation of the crude extract led to the isolation of two antibacter ial biflavonoids, ochnaflavone and ochnaflavone 7- O-methyl ether. Gram-negative bacteria were more sensitive to the isolated compounds than the Gram-positive bacteria (MIC values: 31.3 μg/mL for P. aeruginosa and 62.5 μg/mL for S. aureus). In addition, the isolated com pounds were assessed for their pot ential toxic effects in the MTT toxicity assay using monkey kidney vero cells and Ames genotoxicity test using Salmonella typhimurium strain TA98. LC50 values were 125.9 μg/mL for ochnaflavone and 162.0 μg/mL for ochnaflavone 7-O- methyl ether. The isolated compounds have selectivity index values r anging from 1.29 to 4.03. Selectivity index values higher than one indicate that test samples are less toxic to the host cells than to the pathogens. The biflavonoids did not have any mutagenic effects in the Salmonella/microsome assay without metabolic activation.

Ginkgetin, a Biflavone from Ginko biloba Leaves, Inhibits Cyclooxygenases-2 and 5-Lipoxygenase in Mouse Bone Marrow-Derived Mast Cells

Ginkgetin, a biflavone from Ginkgo biloba leaves, was previously reported to be a phospholipase A(2) inhibitor and this compound showed the potent antiarthritic activity in rat adjuvant-induced arthritis as well as analgesic activity. This investigation was carried out to find effects on cyclooxygenase-2 (COX-2) in vitro effect. Ginkgetin inhibits COX-2 dependent phases of prostaglandin D(2) (PGD(2)) generation in bone marrow-derived mast cells (BMMC) in a concentration-dependent manner with IC(50) values of 0.75 microM. Western blotting probed with specific anti-COX-2 antibodies showed that the decrease in quantity of the PGD(2) product was accompanied by a decrease in the COX-2 protein level. In addition, this compound consistently inhibited the production of leukotriene C(4) (LTC(4)) in a dose dependent manner, with an IC(50) value of 0.33 microM. These results demonstrate that ginkgetin has a dual cyclooxygenase-2/5-lipoxygenase inhibitory activity. Furthermore, this compound also inhibited degranulation reaction in a dose dependent manner, with an IC(50) value of 6.52 microM. Therefore, this compound might provide a basis for novel anti-inflammatory agents.

Anti-inflammatory plant flavonoids and cellular action mechanisms

Plant flavonoids show anti-inflammatory activity in vitro and in vivo. Although not fully understood, several action mechanisms are proposed to explain in vivo anti-inflammatory action. One of the important mechanisms is an inhibition of eicosanoid generating enzymes including phospholipase A2, cyclooxygenases, and lipoxygenases, thereby reducing the concentrations of prostanoids and leukotrienes. Recent studies have also shown that certain flavonoids, especially flavone derivatives, express their anti-inflammatory activity at least in part by modulation of proinflammatory gene expression such as cyclooxygenase-2, inducible nitric oxide synthase, and several pivotal cytokines. Due to these unique action mechanisms and significant in vivo activity, flavonoids are considered to be reasonable candidates for new anti-inflammatory drugs. To clearly establish the therapeutic value in inflammatory disorders, in vivo anti-inflammatory activity, and action mechanism of varieties of flavonoids need to be further elucidated. This review summarizes the effect of flavonoids on eicosanoid and nitric oxide generating enzymes and the effect on expression of proinflammatory genes. In vivo anti-inflammatory activity is also discussed. As natural modulators of proinflammatory gene expression, certain flavonoids have a potential for new anti-inflammatory agents.