Trihydroxyflavones with antioxidant and anti-inflammatory efficacy

Anti-inflammatory compounds and a new sesquiterpene lactone from Centaurea gabrieljanae Greuter

The traditional use of Centaurea spp. for anti-inflammatory purposes is widespread among the people in Turkiye. For this, the methanol extract of Centaurea gabrieljanae and sub-fractions of the methanol extract were tested for anti-inflammatory activity using 5-LOX, while their antioxidant activities, total phenol, and total flavonoid contents were also examined. The ethyl acetate fraction exhibited potent anti-inflammatory activity (IC50 = 3.864 ± 0.9 µg/ml), from which five known compounds (astragalin, picein, p-hydroxy benzoic acid, 3,4-dimethoxy-cinnamic acid, 4-hydroxybenzoic acid 4-O-β-glucopyranoside) and a new sesquiterpene lactone named Pterochlorin were obtained. Pterochlorin showed potent anti-inflammatory activity with a value of IC50 12.71 ± 0.7 µg/ml compared to standard indomethacin. Similarly, astragalin was found to be strong (IC50 = 18.23 µg/ml). In addition, 4-hydroxybenzoic acid 4-O-β-glucopyranoside was isolated for the first time in Centaurea species, and its anti-inflammatory activity was tested. This study may be a guide for the discovery of a new anti-inflammatory drug derived from natural sources.

Trilobatin, an Active Dihydrochalcone from Lithocarpus polystachyus, Prevents Cisplatin-Induced Nephrotoxicity via Mitogen-Activated Protein Kinase Pathway-Mediated Apoptosis in Mice

Although naturally occurring flavonoids have shown beneficial effects on the side effects caused by cisplatin, there are few reports on the protective effect of dihydrochalcone on the cisplatin-induced toxicity. Trilobatin (TLB), as the major sweetener and active ingredient in Lithocarpus polystachyus Rehd, is a dihydrochalcone-like compound that can be present in concentrations of up to 10% or more in tender leaves. Herein, a cisplatin-induced acute kidney injury (AKI) model was established to investigate the protective effect and mechanism of TLB against the cisplatin-induced nephrotoxicity in mice. The results showed that TLB significantly reversed the inhibition of CRE, BUN, and MDA levels compared with the cisplatin group. Furthermore, TLB treatment (50 and 100 mg/kg) for 10 days significantly alleviated cisplatin-induced renal pathological changes. TUNEL staining showed that TLB administration can effectively improve the occurrence of apoptosis of renal tissue cells caused by cisplatin exposure. Importantly, western blot analysis verified that TLB alleviated cisplatin-induced nephrotoxicity by regulating the AKT/MAPK signaling pathway and apoptosis. In summary, our findings showed clearly that TLB has a significant preventive effect on cisplatin-induced AKI.

Anti-Inflammatory Potential of Phenolic Compounds Isolated From Entada africana Guill. & Perr. Used in the Republic of Benin

In West African medicine, Entada africana Guill. & Perr. from the family of Fabaceae is used to treat inflammatory conditions in the management of fractures, wounds, and sprains in the northern region of the Republic of Benin. The aim of the present study was to isolate and elucidate phenolic compounds from a hydroalcoholic leaf extract from E. africana and to identify compounds with anti-inflammatory activity in vitro. Eleven compounds were purified from three fractions, which have shown strong to medium anti-inflammatory activity. The isolated compounds were characterized by HRESI-MS and NMR methods as gallic acid (1), ethyl gallate (2), 5,7-dihydroxychromen-4-one (3), 3′,4′,7-trihydroxyflavone (4), dihydrokaempferol-7-O-glucoside (5), catechin (6), quercetin-3-O-[β-apiosyl-(1‴→2″)-β-glucoside] (7), quercetin-3-O-glucoside (8), naringenin-7-O-glucoside (9), aromadendrin (10), and myricetin-3-O-glucoside (11). Nine of the major phenolic compounds were tested using TNF-α stimulated human keratinocytes (HaCaT) as skin inflammation model to identify molecules, which may explain the use of the plant leaves as an anti-inflammatory remedy by assessing the release of proinflammatory cytokines IL-8 and IL-6. The hydroacoholic leaf extract of E. africana exerted a medium inhibitory effect on the release of IL-8. 3′,4′,7-trihydroxyflavone, aromadendrin, dihydrokaempferol-7-O-glucoside and ethyl gallate demonstrated a strong to medium effect on the release of IL-6. For the release of IL-8, 3′,4′,7-trihydroxyflavone demonstrated a medium activity. This study provides for the first time a detailed screening of phenolic compounds occurring in the hydroethanolic leaf extract of E. africana. Additionally, it is shown that E. africana contains active compounds which may justify its traditional medicinal use as an anti-inflammatory remedy to treat inflammatory and pain-related skin conditions in the Republic of Benin.

Targeting Mammalian 5-Lipoxygenase by Dietary Phenolics as an Anti-Inflammatory Mechanism: A Systematic Review

5-Lipoxygenase (5-LOX) plays a key role in inflammation through the biosynthesis of leukotrienes and other lipid mediators. Current evidence suggests that dietary (poly)phenols exert a beneficial impact on human health through anti-inflammatory activities. Their mechanisms of action have mostly been associated with the modulation of pro-inflammatory cytokines (TNF-α, IL-1β), prostaglandins (PGE2), and the interaction with NF-κB and cyclooxygenase 2 (COX-2) pathways. Much less is known about the 5-lipoxygenase (5-LOX) pathway as a target of dietary (poly)phenols. This systematic review aimed to summarize how dietary (poly)phenols target the 5-LOX pathway in preclinical and human studies. The number of studies identified is low (5, 24, and 127 human, animal, and cellular studies, respectively) compared to the thousands of studies focusing on the COX-2 pathway. Some (poly)phenolics such as caffeic acid, hydroxytyrosol, resveratrol, curcumin, nordihydroguaiaretic acid (NDGA), and quercetin have been reported to reduce the formation of 5-LOX eicosanoids in vitro. However, the in vivo evidence is inconclusive because of the low number of studies and the difficulty of attributing effects to (poly)phenols. Therefore, increasing the number of studies targeting the 5-LOX pathway would largely expand our knowledge on the anti-inflammatory mechanisms of (poly)phenols.

3',4'-Dihydroxyflavonol Modulates the Cell Cycle in Cancer Cells: Implication as a Potential Combination Drug in Osteosarcoma

New agents are demanded to increase the therapeutic options for osteosarcoma (OS). Although OS is the most common bone cancer in children and adolescents, it is considered a rare disorder. Therefore, finding adjuvant drugs has potential to advance therapy for this disease. In this study, 3′,4′-dihydroxyflavonol (DiOHF) was investigated to assess the effects in OS cellular models in combination with doxorubicin (Dox). MG-63 and U2OS human OS cells were exposed to DiOHF and Dox and tested for cell viability and growth. To elucidate the inhibitory effects of DiOHF, additional studies were conducted to assess apoptosis and cell cycle distribution, gene expression quantification of cell cycle regulators, and cytokinesis-block cytome assay to determine nuclear division rate. DiOHF decreased OS cell growth and viability in a concentration-dependent manner. Its combination with Dox enabled Dox dose reduction in both cell lines, with synergistic interactions in U2OS cells. Although no significant apoptotic effects were detected at low concentrations, cytostatic effects were demonstrated in both cell lines. Incubation with DiOHF altered cell cycle dynamics and resulted in differential cyclin and cyclin-dependent kinase expression. Overall, this study presents an antiproliferative action of DiOHF in OS combination therapy via modulation of the cell cycle and nuclear division.

Safer anti-inflammatory therapy through dual COX-2/5-LOX inhibitors: A structure-based approach

Inflammatory mediators of the arachidonic acid cascade from cyclooxygenase (COX) and lipoxygenase (LOX) pathways are primarily responsible for many diseases in human beings. Chronic inflammation is associated with the pathogenesis and progression of cancer, arthritis, autoimmune, cardiovascular and neurological diseases. Traditional non-steroidal anti-inflammatory agents (tNSAIDs) inhibit cyclooxygenase pathway non-selectively and produce gastric mucosal damage due to COX-1 inhibition and allergic reactions and bronchospasm resulting from increased leukotriene levels. 'Coxibs' which are selective COX-2 inhibitors cause adverse cardiovascular events. Inhibition of any of these biosynthetic pathways could switch the metabolism to the other, which can lead to fatal side effects. Hence, there is undoubtedly an urgent need for new anti-inflammatory agents having dual mechanism that prevent release of both prostaglandins and leukotrienes. Though several molecules have been synthesized with this objective, their unfavourable toxicity profile prevented them from being used in clinics. Here, this integrative review attempts to identify the promising pharmacophore that serves as dual inhibitors of COX-2/5-LOX enzymes with improved safety profile. A better acquaintance of structural features that balance safety and efficacy of dual inhibitors would be a different approach to the process of understanding and interpreting the designing of novel anti-inflammatory agents.

Relationship between Antioxidant and Anticancer Activity of Trihydroxyflavones

Plant polyphenols have been highlighted not only as chemopreventive, but also as potential anticancer substances. Flavones are a subclass of natural flavonoids reported to have an antioxidant and anticancer activity. The aim of our study was to evaluate antioxidant and anticancer activity of seventeen trihydroxyflavone derivatives, including apigenin (API) and baicalein (BCL). Also, we wanted to find out if there is a correlation between those two effects. Cell growth inhibition testing was carried out using MTT assay in three different human cancer cell lines: lung (A549), breast (MCF-7) and brain epithelial (U87). Antioxidant activity was determined by the DPPH radical scavenging method. Thirteen trihydroxyflavones possessed anticancer activity against at least one tested cancer cell line. They were more active against the MCF-7 cell line, and the lowest activity was determined against the U87 cell line. The majority of compounds inhibited cancer cell growth at EC₅₀ values between 10-50 µM. The most active compound was 3',4',5-trihydroxyflavone 7, especially against A549 and MCF-7 cell lines. The correlation between anti-proliferative and antioxidant activity was only moderate, and it was determined for A549 and U87 cancer cell lines. The most important fragment for those two effects is the ortho-dihydroxy group in ring B.

CONCLUSIONS

Trihydroxyflavones demonstrated anticancer activity. Further and more detailed studies should to be carried out to estimate the structure-activity relationship of these compounds.

A Review of the Antiviral Properties of Black Elder (Sambucus nigra L.) Products

Black elder (Sambucus nigra L.) has a long ethnobotanical history across many disparate cultures as a treatment for viral infection and is currently one of the most-used medicinal plants worldwide. Until recently, however, substantial scientific research concerning its antiviral properties has been lacking. Here, we evaluate the state of current scientific research concerning the use of elderberry extract and related products as antivirals, particularly in the treatment of influenza, as well as their safety and health impacts as dietary supplements. While the extent of black elder's antiviral effects are not well known, antiviral and antimicrobial properties have been demonstrated in these extracts, and the safety of black elder is reflected by the United States Food and Drug Administration approval as generally recognized as safe. A deficit of studies comparing these S. nigra products and standard antiviral medications makes informed and detailed recommendations for use of S. nigra extracts in medical applications currently impractical. Copyright © 2017 John Wiley & Sons, Ltd.

Delonix regia Leaf Extract (DRLE): A Potential Therapeutic Agent for Cardioprotection

Delonix regia (Boj. Ex. Hook) is a flowering plant in the pea family found in tropical areas and its leaves are used informally to treat diseases in folk medicine. However, the cardioprotective effects in this plant are still unclear. In this study, we found that the Delonix regia leaf extract (DRLE) (400 mg/kg/d) can reduce the mortality rate in an isoproterenol (ISO)-induced heart injury and hypertrophy mouse model. Decreased serum levels of creatine phosphokinase, LDH, GOT, TNF-alpha and increased nitric oxide levels were found in DRLE-treated ISO-injured mice. In the in vitro study, the porcine coronary artery exhibited vasodilation effect induced by DRLE in a dose-dependent manner. In the DRLE toxic test, overdose of DRLE showed the high safety in normal mice and may have the ability to remove the metabolic wastes in blood. In conclusion, we demonstrated for the first time that DRLE has the cardioprotective effects by activating the vasodilation through NO pathway and preventing the myocyte injury via inhibition of TNF-alpha pathway. We suggest that DRLE may act as a promising novel herbal medicine for cardioprotection.

Flavonoids inhibit COX-1 and COX-2 enzymes and cytokine/chemokine production in human whole blood

Cyclooxygenase 2 (COX-2) and the production of cytokines/chemokines are important targets for the modulation of the inflammatory response. Although a large variety of inhibitors of these pathways have been commercialized, some of those inhibitors present severe side effects, governing the search for new molecules, as alternative anti-inflammatory agents. This study was undertaken to study an hitherto not evaluated group of flavonoids, concerning its capacity to inhibit COX-1 and COX-2 enzymes, as well as to inhibit the production of the cytokines and a chemokine, in a complex matrix involved in the systemic inflammatory process, the blood, aiming the establishment of a structure-activity relationship. The results obtained reveal promising flavonoids for the modulation of the inflammatory process, namely the ones presenting a catechol group in B ring, as some flavonoids were able to simultaneously inhibit the production of inflammatory prostaglandin E2 and pro-inflammatory cytokines.

Proinflammatory Pathways: The Modulation by Flavonoids

Inflammation is a natural, carefully orchestrated response of the organism to tissue damage, involving various signaling systems and the recruitment of inflammatory cells. These cells are stimulated to release a myriad of mediators that amplify the inflammatory response and recruit additional cells. These mediators present numerous redundancies of functions, allowing a broad and effective inflammatory response, but simultaneously make the understanding of inflammation pathways much difficult. The extent of the inflammatory response is usually self-limited, although it depends on the balance between the pro- and anti-inflammatory signals. When that equilibrium is dislocated, a more widespread inflammatory response may take place. Flavonoids have been shown to be possible alternatives to the traditionally molecules used as anti-inflammatory agents. In fact, the biological activities of flavonoids include the modulation of the diverse phases of inflammatory processes, from the gene transcription and expression to the inhibition of the enzymatic activities and the scavenging of the reactive species. In the present review, the inflammatory network is widely revised and the flavonoids' broad spectrum of action in many of the analyzed inflammatory pathways is revised. This kind of integrated revision is original in the field, providing the reader the simultaneous comprehension of the inflammatory process and the potential beneficial activities of flavonoids.

Inhibition of LOX by flavonoids: a structure-activity relationship study

The lipoxygenase (LOX) products have been identified as mediators of a series of inflammatory diseases, namely rheumatoid arthritis, inflammatory bowel disease, psoriasis, allergic rhinitis, atherosclerosis and certain types of cancer. Hence, LOX inhibitors are of interest for the modulation of these phenomena and resolution of the inflammatory processes. During LOX activity, peroxyl radical complexes are part of the reaction and may function as sources of free radicals. Thus antioxidants, such as flavonoids, capable of inhibiting lipid peroxidation and scavenging free radicals, may act as LOX inhibitors. The aim of this work was to assess the structure-activity relationship among a series of flavonoids concerning 5-LOX inhibition, through a systematic study of the inhibition of the formation of LTB4 in human neutrophils. The type of inhibition of the flavonoids was further studied using soybean LOX, type I, and Saturation Transfer Difference (1)H NMR (STD-(1)H NMR) was used to characterize the binding epitopes of the compounds to LOX-1. The obtained results reinforce flavonoids as effective inhibitors of LTB4 production in human neutrophils. It was also possible to establish a structure/activity relationship for the inhibitory activity and the type of inhibition.

Modulation of human neutrophils' oxidative burst by flavonoids

Inflammation is a normal response towards tissue injury, but may become deleterious to the organism if uncontrolled. The overproduction of reactive species during the inflammatory process may cause or magnify the damage at inflammatory sites. Flavonoids have been suggested as therapeutic agents to avoid such damage, as these compounds exhibit anti-inflammatory activity, through the modulation of oxidative stress and signalling pathways. Both effects may attenuate neutrophils' activities at inflammatory sites. In this study, we investigated the structure/activity relationship of a series of flavonoids on the oxidative burst of human neutrophils in vitro, as a measure of its anti-inflammatory potential. Neutrophils were stimulated with phorbol-12-myristate-13-acetate, and fluorescence and chemiluminescence techniques were used to evaluate the generation of reactive oxygen species. All the tested flavonoids revealed the ability to modulate the neutrophil's oxidative burst. From the obtained results, the pivotal role of the catechol group in the B-ring was evidenced as well as the minor importance of the hydroxylations in the A-ring, which did not appear to be determinant for the activity, although clearly influencing the lipophilicity of the tested flavonoids. It is also clarified the importance of the methylation in the OH group at the B-ring catechol moiety. In conclusion, the obtained results uncover new possible strategies for the resolution of inflammatory processes, using flavonoids to modulate neutrophil's oxidative burst.