Inhibitory Activity Of Flavonoids Research Articles

Effects of flavonoids on SARS–CoV–2 main protease (6W63): A molecular docking study

Public health is still under attack by a worldwide pandemic caused by a coronavirus which is known to cause mainly respiratory and enteric disease in humans. Currently, still limited knowledge exists on the exact action mechanism and biology of SARS‒CoV‒2 although there are several effective vaccines and antiviral treatment. Besides, there is a considerable amount of 3D protein structures for SARS–CoV–2, related to its main protease resolved by X–ray diffraction. Here, we used molecular docking strategy to predict possible inhibitory activities of flavonoids on SARS–CoV–2 Mpro enzyme. For this, 800 flavonoids were retrieved from the ZINC database. Results suggested that avicularin was the lead flavonoid which docked to Mpro with the best binding energy. However, most of flavonoids showed H–bond interactions with Hie–41 and Cys–145 catalytic dyad, which were important residues for the catalytic activity of SARS–CoV–2 Mpro. Strong hydrogen bonding (2.36 Å) with Sγ atom of Cys145 residue was observed. This might suggest an initial formation of covalent bonding. Findings showed that selected flavonoids could be promising inhibitors of this enzyme and have the potential for future therapeutic drugs against COVID–19 after immediate experimental validation and clinical approvals.

Inhibitory activities of flavonoids from Scutellaria baicalensis Georgi on amyloid aggregation related to type 2 diabetes and the possible structural requirements for polyphenol in inhibiting the nucleation phase of hIAPP aggregation

Human islet amyloid polypeptide (hIAPP)-mediated cytotoxicity is identified as a potential target for developing new anti-diabetic molecules. Herein, we investigated the effect of the major bioactive compounds of Scutellaria baicalensis Georgi (S. baicalensis), including baicalein, baicalin, wogonin and oroxylin A, on hIAPP aggregation. We found that all of these compounds inhibited hIAPP fibril formation in a dose-dependent manner. But baicalein and baicalin, especially baicalein are more effective than wogonin and oroxylin A in stabilizing hIAPP monomers and eliminating toxic hIAPP assembly, suggesting that flavonoids with ortho-hydroxyl group on the A-ring exhibited higher anti-hIAPP nucleation potential than those without this structure. This stimulated our interest in further studying the possible structure-activity relationship between polyphenol and hIAPP aggregation inhibition. Our results demonstrated that flavonoids with ortho-hydroxyl group on the B-ring are also more effective against hIAPP nucleation than those without this structure. These results suggest that the ortho-hydroxybenzene structure is a key structural feature required for polyphenols to effectively inhibit hIAPP nucleation. This was further confirmed by the effects of polyphenol and phenols in inhibiting hIAPP nucleation. The conclusion that pyrogallol-type polyphenols are potential lead inhibitors may provide a valuable structural template for the further development of polyphenol-based inhibitor of amyloid peptides.

In Vitro Cytotoxicity and Aromatase Inhibitory Activity of Flavonoids: Synthesis, Molecular Docking and In silico ADME Prediction.

Many natural and synthetic flavonoids have been studied and documented by inhibiting aromatase enzymes for their anti-cancer activity against breast carcinoma. The aromatase enzyme is a possible target for the estrogen's positive breast cancer receptor. Hence, a series of flavonoids have been synthesized and assessed for their in vitro cytotoxicity and aromatase inhibitory activity. 39 Flavonoids were synthesized and characterized by spectroscopic techniques, and their computational study was performed using the maestro version of the Schrodinger. In silico ADME properties were checked by QikProp software. A total of 18 compounds were evaluated based on the docking score using cytotoxicity assay in human breast cancer cell line MCF-7. Of the 18 compounds tested, 07 compounds, namely 2b, 8b, 14b, 15b, 19b, 24b, and 30b flavonoids were found to be more active with their IC50 values of 20.73 μM, 1.636 μM, 16.08 μM, 22.02 μM, 15.75 μM, 0.345 μM and 16.08 μM, respectively, compared with the reference drug letrozole. The in vitro aromatase inhibitory activity of six compounds 2b, 8b, 14b, 19b, 24b, and 30b was conducted using a fluorogenic assay kit. The values of IC50 for compounds 2b and 24b were found to be 0.31 μM and 0.36 μM, respectively. Therefore, it was concluded that compounds 2b and 24b had a potent inhibitory effect of aromatase compared with letrozole with an IC50 value of 0.86 μM. At the same time, the other compounds 8b, 14b, 30b, and 19b were considered to have similar aromatase inhibitory activity. Hence, their essential aromatase inhibitory activities make them good lead candidates for developing potent inhibitors of aromatase.

Inhibitory activity of flavonoids against human sucrase-isomaltase (α-glucosidase) activity in a Caco-2/TC7 cellular model

Type 2 diabetes (T2D) is the most common form of diabetes, and the number of people with this metabolic disease is steadily increasing worldwide. Among the available antidiabetic agents, α-glucosidase inhibitors are the most effective at reducing postprandial hyperglycaemia (PPHG), one of the main characteristics of T2D. However, most of the studies that have been performed have used the more readily available rat intestinal preparations or yeast α-glucosidase as the enzyme source, which despite being useful and cost effective, have a questionable physiological value. The present study evaluates the inhibitory activity of a selected group of flavonoids against human sucrase-isomaltase (SI), the α-glucosidase found in Caco-2/TC7 cells. A microassay using the physiological substrates sucrose and maltose, and a synthetic substrate, p-nitrophenyl-α-D-glucopyranoside (pNPG) was performed. The most active flavonoid was compound 4 (melanoxetin), presenting an IC50 value similar using the two natural substrates. In contrast, the tested flavonoids were not effective at inhibiting SI, when pNPG was used as a substrate. Hydroxylation of flavonoids at C-3 of the C ring, at C-3' and C-4' of the B ring, and at C-7 and C-8 of the A ring were the features that improved the inhibitory activity of flavonoids against human SI. These phenolic compounds deserve further exploration as alternatives to the currently available α-glucosidase inhibitors. The present study also demonstrates that the non-clinical in vitro studies conducted for the evaluation of α-glucosidase activity should use the human source rather than surrogate sources of α-glucosidase.

Inhibitory activity of flavonoids from Ephedrae Herba on hypoxia signaling in PANC-1 cells and the evaluation of their mechanisms.

Pancreatic cancer is a lethal disease with a very poor prognosis. Recent reports indicate that hypoxia signaling mediated by hypoxia-inducible factor (HIF) contributes to the progression of pancreatic cancer. Therefore, elucidating the inhibitor of hypoxia signaling may lead to the development of a candidate for new anticancer agents. During our screening program for HIF inhibitor from crude drug extracts, new acylated kaempferol glycosides, kaempferol 3-O-[4″-(E)-p-coumaroyl-3″-O-dihydroxypalmityl] rhamnoside (1) and kaempferol 3-O-[4″-(E)-p-coumaroyl-2″-O-dihydroxypalmityl] rhamnoside (2), were isolated from an acetone extract of Ephedrae Herba, together with eight known flavonol glycosides (3-10). The structures of novel compounds 1 and 2 were elucidated based on spectroscopic and chemical analyses. Using a cell-based HRE-driven luciferase reporter assay in a PANC-1 pancreatic cancer cell line, we found that these compounds demonstrated potent inhibitory activity on hypoxia signaling with IC50 values of 18.0 ± 0.6 and 13.3 ± 2.2µM, respectively. Mechanistically, 2 reduced the amount of HIF-1α protein in the nuclear at 30µM via the ubiquitin-proteasome pathway with no effect on the nuclear translocation of HIF proteins from cytosol and subsequently decreased Glut1 mRNA. These results indicate that 2 inhibits hypoxia signaling through a mechanism involving the reduction of HIF-1α protein levels and Glut1 mRNA and may have anti-pancreatic cancer effects.

Inhibition of d-glycero-β-d-manno-heptose 1-phosphate adenylyltransferase from Burkholderia pseudomallei by epigallocatechin gallate and myricetin.

Flavonoids play beneficial roles in various human diseases. In this study, a flavonoid library was employed to probe inhibitors of d-glycero-β-d-manno-heptose-1-phosphate adenylyltransferase from Burkholderia pseudomallei (BpHldC) and two flavonoids, epigallocatechin gallate (EGCG) and myricetin, have been discovered. BpHldC is one of the essential enzymes in the ADP-l-glycero-β-d-manno-heptose biosynthesis pathway constructing lipopolysaccharide of B. pseudomallei. Enzyme kinetics study showed that two flavonoids work through different mechanisms to block the catalytic activity of BpHldC. Among them, a docking study of EGCG was performed and the binding mode could explain its competitive inhibitory mode for both ATP and βG1P. Analyses with EGCG homologs could reveal the important functional moieties, too. This study is the first example of uncovering the inhibitory activity of flavonoids against the ADP-l-glycero-β-d-manno-heptose biosynthesis pathway and especially targeting HldC. Since there are no therapeutic agents and vaccines available against melioidosis, EGCG and myricetin can be used as templates to develop antibiotics over B. pseudomallei.

Inhibitory activities of flavonoids from Eupatorium adenophorum against acetylcholinesterase

Fifteen flavonoids isolated from the Eupatorium adenophorum showed inhibitory activities against acetylcholinesterase (AChE) isolated from Caenorhabditis elegans and Spodoptera litura. Their IC50 values ranged from 12.54 to 89.06μg/mL and 12.08 to 86.01μg/mL, respectively against the AChE isolated from the nematode and insect species. AChE was inhibited in a dose-dependent manner by all tested flavonoids, The isolated compound quercetagetin-7-O-(6-O-caffeoyl-β-D-glucopyranoside) displayed the highest inhibitory effect against AChE from C. elegans and S. litura, with IC50 values of 12.54 μg/mL and 12.58 μg/mL, respectively. The structure-activity relationship of flavonoids on the inhibitory activities indicated that additional phenolic hydroxyl groups in the glucose were favorable for their inhibitory effects and the degree of increase in inhibitory activity also depended on the number of phenolic hydroxyl groups. The Lineweaver-Burk and Dixon plots indicated that quercetagetin-7-O-(6-O-caffeoyl-β-d-glucopyranoside) is a reversible inhibitor against AChE. Quercetagetin-7-O-(6-O-caffeoyl-β-d-glucopyranoside), 5,4′-Dihydroxytlavone and quercetin-3-O-β-d-glucopyranoside inhibited AChE in a mixed-type competitive manner and these compounds might be the dual binding site AChE inhibitors. Further, nine compounds showed poisonous effects against C. elegans and inhibitory effects on the growth and development of S. litura.

Isolation, characterization, and xanthine oxidase inhibitory activities of flavonoids from the leaves of Perilla frutescens

Phytochemical investigation of the water extract from the leaves of Perilla frutescens (Lamiaceae) led to the isolation of a new flavanone, a new chalcone, and a new aurone, namely, (2S)-5,7-dimethoxy-8,4'-dihydroxyflavanone (1), 2',4'-dimethoxy-4,5',6'-trihydroxychalcone (2), and (Z)-4,6-dimethoxy-7,4'-dihydroxyaurone (3), respectively. The structures were unambiguously elucidated on the basis of spectroscopic data. And the absolute configuration of 1 was determined by analysis of electronic circular dichroism spectrum. The isolated compounds were evaluated for their inhibitory effects on xanthine oxidase in vitro. Among them, 2 showed more potent activity than the positive control allopurinol, a well-known XO inhibitor clinically used for treatment of gout. Lineweaver-Burk transformation of the inhibition kinetics data demonstrated that it was a mixed-type inhibitor.

Construction of explicit models to correlate the structure and the inhibitory activity of aldose reductase: Flavonoids and sulfonyl-pyridazinones as inhibitors.

The correlation between binding energies and bioactivities is the core of structure-based computer-aided drug design. However, many models to address this correlation are still strongly system-dependent at current stage. We constructed two explicit models to correlate the binding energies with the inhibitory activities of flavonoids and sulfonyl-pyridazinones as inhibitors of aldose reductase. The introduction of multiple complex states comprised of protein, coenzyme, substrate, and inhibitor can remarkably improve the correlation coefficients, compared with that using single complex state. Recombination of energy terms from complex structures and molecular descriptors of inhibitors can further improve the correlation. The explicit models provide correlation coefficients of 0.90 and 0.92 for flavonoids and sulfonyl-pyridazinones, respectively. These models also steadily present the contribution from each energy term and the favorite of protein-inhibitor complex states. Meanwhile, we also observed that some inhibitors can accommodate alternative sites out of the conserved binding pocket at the presence/absence of coenzyme and substrate. It is responsible for the remarkable change in the binding energies and thus significantly influences the correlation between the structures and the inhibitory activities. Overall, this work presents a rational way to construct reliable explicit models through the combination of multiple physically accessible complex states, even though each of them only bears marginal information related to their activities.

Structural features of guinea pig aldehyde oxidase inhibitory activities of flavonoids explored using QSAR and molecular modeling studies

In this study, guinea pig aldehyde oxidase inhibitory activities of flavonoids were investigated using in silico, quantitative structure–activity relationships, molecular modeling, and experimental techniques, in order to understand more about their mode of interactions. The aldehyde oxidase inhibitory activity values determined experimentally in this work or collected from our previous report were used to derive mathematical models for the prediction purposes employing combined genetic algorithm and partial least square method, as well as multiple linear regression analysis. The statistical parameters for the developed models and the results of leave-one-out internal cross-validation were indicative of the validity of the models. To further investigate the mechanism of interaction between flavonoid inhibitors and guinea pig aldehyde oxidase enzyme, the structural model of the enzyme was built and the inhibitors were docked manually into the binding site. The model for quercetin-aldehyde oxidase complex was validated based on its appropriate stability during 10 ns molecular dynamics simulation, and hence the positioning procedure for the rest of flavonoids was guided based on the manually docked position of quercetin. The identified interactions were compared with those of flavonoids previously reported for rat aldehyde oxidase and the results showed a substantial commonality between the modes of interactions predicted for flavonoids positioned into the binding site of aldehyde oxidase from guinea pig and rat. This commonality is also reflected by the quantitative structure–activity relationships models. The results presented in this work may provide useful information where the structural requirements for aldehyde oxidase inhibition are sought, such as designing novel aldehyde oxidase inhibitors or investigating drug interaction involving aldehyde oxidase mediated biotransformation.

Computational drug design of potential α-amylase inhibitors using some commercially available flavonoids

The primary objective of this study was to investigate the α-amylase inhibitory activity of flavonoids using in silico docking studies. In this perspective, flavonoids like biochanin, chrysin, hesperitin, morin, tricin and vitexycarpin were selected. Acarbose, a known α-amylase inhibitor was used as the stan-dard. In silico docking studies were carried out using AutoDock 4.2, based on the Lamarckian genetic algorithm principle. The results showed that all the selected flavonoids showed binding energy ranging between -7.20 kcal/mol to -6.21 kcal/mol when compared with that of the standard (-2.94 kcal/mol). Inhibition constant (5.31 µM to 27.89 µM) and intermolecular energy (-8.99 kcal/mol to -7.41 kcal/mol) of the flavonoids also coincide with the binding energy. The α-amylase inhibitory activity of the selected flavonoids was in order of tricin > hesperitin > vitexycarpin > chrysin > morin > biochanin. These molecular docking analyses could lead to the further development of potent α-amylase inhibitors for the treatment of diabetes. DOI: http://dx.doi.org/10.3329/bjp.v9i1.17502 Bangladesh J Pharmacol 2014; 9: 72-76

Computational drug discovery of potential TAU protein kinase I inhibitors using in silico docking studies

The objective of the current study is to evaluate the tau protein kinase I inhibitory activity of flavonoids using in silico docking studies. In silico docking studies were carried out using AutoDock 4.2, based on the Lamarckian genetic algorithm principle. Memantine, a known neuro-receptor antagonist is currently used in the treatment of Alzheimer's disease. The results showed that all the selected flavonoids showed binding energy ranging between -7.07 kcal/mol to -4.85 kcal/mol when compared with that of the standard (-5.89 kcal/mol). Inhibition constant (6.62 µM to 280.05 µM) and intermolecular energy (-9.45 kcal/mol to -6.64 kcal/mol) of the ligands also coincide with the binding energy. These molecular docking analyses could lead to the further development of potent tau protein kinase I inhibitors for the treatment of Alzheimer’s disease. Further investigations on the above compounds and in vivo studies are necessary to develop potential chemical entities for the prevention and treatment of Alzheimer's disease.

Comparative study of alpha amylase inhibitory activity of flavonoids of Vitex negundo Linn. and Andrographis paniculata Nees

Background: One important therapeutic approach for the treatment of Type 2 Diabetes Mellitus is by decreasing the postprandial increase of glucose. This is possible by inhibiting certain carbohydrate hydrolyzing enzymes like alpha‑amylase. Aim: The objective of the present study was to evaluate the alpha amylase inhibitory activity of flavonoids extracts of different parts of Vitex negundo Linn and Andrographis paniculata Nees. Materials and Methods: In the present study, the percentage inhibitory effect of flavonoids isolated from different parts of Vitex negundo and Andrographis paniculata were studied with salivary alpha amylase and starch as substrate using chromogenic DNSA method and starch iodine method for qualitative estimation. Statistical Analysis: All experiments were performed in 3 different sets with each set in triplicates. The data are expressed as mean ± SEM (standard error of the mean). Statistical difference and linear regression analysis were performed using Graph pad prism 5 statistical software. Statistical analysis was performed for ANOVA (analysis of variance) using Statistical Package for Social Sciences (SPSS) version 11.5. Values of P which were ≤0.05 were considered as significant. Results and Conclusion: The results clearly indicated that highest inhibition (62.22%) was obtained at the concentration of 1.5 mg/ml of flavonoids extracted from the leaves of A. paniculata, with an IC50 value of 0.004 mg/ml. Except Vitex leaf flavonoids extract, all other tested flavonoids of different parts of both the plants have shown more than 50% inhibition of alpha amylase activity. Thus the results are clearly indicating that the flavonoids of V. negundo and A. paniculata might be effective in lowering post prandial hyperglycemia. Key words: Alpha amylase inhibition, Andrographis paniculata, flavonoids, post‑prandial hyperglycemia, Vitex negundo

Docking studies: <i>In silico</i> phosphodiesterase inhibitory activity of commercially available flavonoids

The objective of the current study is to evaluate the phosphodiesterase inhibitory activity of flavonoids using in silico docking studies. In silico docking studies were carried out using AutoDock 4.2, based on the Lamarckian genetic algorithm principle. The results showed that all the selected flavonoids showed binding energy ranging between -7.50 kcal/mol to -6.61 kcal/mol when compared with that of the standard (-4.77 kcal/mol). Inhibition constant (3.17 µM to 14.36 µM) and intermolecular energy (-9.29 kcal/mol to -8.70 kcal/mol) of the ligands also coincide with the binding energy. All the selected flavonoids contributed better phosphodiesterase inhibitory activity because of its structural parameters. Benzopyran ring in the flavonoids are majorly contributed its activity. These molecular docking analyses could lead to the further development of potent phosphodiesterase inhibitors for the treatment of inflammatory diseases.

Inhibitory Activity of Flavonoids against Class I Phosphatidylinositol 3-Kinase Isoforms

Class I PI3 Kinase (PI3K) phosphorylates phosphatidylinositol 4,5-bisphophate (PIP2) to generate the second messenger phosphatidylinositol 3,4,5-trisphosphate (PIP3) and therefore plays an important role in fundamental cellular responses such as proliferation. There are four isoforms of class I PI3K which are known to have different functions and relate to various diseases such as cancer and inflammation. Flavonoids are abundant in fruits, vegetables and plant-derived beverages such as tea. So far, various pharmacological effects of flavonoids have been reported. We previously reported that the flavonoid baicalein exhibits potent PI3K-inhibitory activity. Recently we examined the inhibitory activity of eighteen flavonoids against PI3Kα by using an in vitro homogenous time resolved fluorescence (HTRF) kinase assay, and deduced their structure-activity relationships by comparing the activities of the analogues. Our result suggests that the number of hydroxyl groups in the A and B rings might promote the activity, while loss of C2-C3 double bond might reduce the activity. Furthermore, the activity against 4 class I PI3K isoforms of some selected flavonoids was investigated, and the results indicate that the flavonoids seem to exhibit more potent activity on PI3Kα and δ isoforms compared with that on PI3Kβ and γ isoforms.

Neuroprotective effects of various flavonoids alone and in combination on lipopolysaccharide‐induced neurotoxicity in PC‐12 cells

Pro‐inflammatory cytokines have been detected in Alzheimer's disease (AD) brain suggesting that neuroinflammation also plays a role in the pathogenesis of AD. PC‐12 cells in culture respond to LPS stimuli by upregulating the levels of cytokines TNF‐alpha, IL‐1beta, nitric oxide (NO), and caspase activation thereby causing neuronal cell death. The present study investigated the neuroprotective effects of flavonoids such as fisetin, diosmetin and robinetin when administered alone and in combination, on the proinflammatory responses and apoptosis induced in LPS‐stimulated PC‐12 cells. Our studies showed that all the flavonoids alone and in combination markedly suppressed the production of TNF‐alpha, interleukin (IL)‐1beta, and nitric oxide (NO) in a dose –dependent manner, respectively. In parallel, cell apoptosis triggered by LPS and characterized with caspase‐3 activity, pro‐apoptotic gene Bad and anti‐apoptotic gene Bcl‐2 expressions were also significantly inhibited by these flavonoids. The results indicate that the inhibitory activity of flavonoids was greater when taken in combinations compared to those when taken alone. The present study suggests that flavonoids alone and in combination, might offer therapeutic opportunities to delay the progression of neuroinflammatory diseases such as AD.

Inhibition of Candida rugosa lipase by saponins, flavonoids and alkaloids

Lipase inhibitors have generated a great interest because they could help in the prevention or the therapy of lipase-related diseases. Therefore, the aim of the work was to evaluate by HPLC, and using Candida rugosa lipase as model, the inhibitory effect of several saponins: β-aescin, digitonin, glycyrrhizic acid (GA) and Quillaja saponin (QS); flavonoids: 3-hydroxyflavone, 5-hydroxyflavone, (±)-catechin and kaempferol; and alkaloids: aspidospermine, papaverine, physostigmine, pilocarpine, raubasine, rescinnamine, reserpine and trigonelline. The inhibition produced by most of these compounds is described here for the first time. Saponins appeared very active, being β-aescin and digitonin the most active compounds (IC 50 = 0.8–2.4 × 10 −5 M). The inhibitory activity of flavonoids was lower than that of saponins (except GA), and (±)-catechin and kaempferol were the most active. Alkaloids was the most heterogeneous group assayed, varying from rescinnamine, with an IC 16 similar to that of digitonin, to papaverine and others which showed almost no inhibition. In conclusion, β-aescin, digitonin, kaempferol or (±)-catechin, strong lipase inhibitors with a low toxicity and present herbal drugs used for lipase-related diseases such as acne or ulcer, are promising candidates for the prevention or the treatment of these diseases.

Inhibitory activity of flavonoids and tannins against HIV-1 protease.

Twenty-nine flavonoids and six hydrolyzable tannins were studied for their inhibitory activity against human immunodeficiency virus (HIV)-1 protease using fluorescence and HPLC assays. Among the flavonoids, flavones, flavanones, flavonols, catechols and chalcones, the flavonols were the most active category while flavanones and catechols displayed low activity. Quercetin was the most potent inhibitor of the target enzyme with an IC50 value of 58.8 microM, while butein and luteolin showed moderate activity. Of the hydrolyzable tannins tested, three ellagitannins which contain a hexahydroxvdiphenoyl (HHDP) unit linked to the O-3 and 0-6 positions of the sugar, were found to strongly inhibit HIV-1 protease. The IC50 values of corilagin and repandusinic acid on HIV-1 protease were 20.7 and 12.5 microM, respectively.

Effects of naturally occurring flavonoids on nitric oxide production in the macrophage cell line RAW 264.7 and their structure–activity relationships

Flavonoids affect the inflammatory process of the mammalian system and possess anti-inflammatory as well as immunomodulatory activities in vitro and in vivo. Since nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) is one of the inflammatory mediators, the effects of various naturally occurring flavonoids on NO production in LPS-activated RAW 264.7 cells were evaluated in vitro. Flavonoids such as apigenin, wogonin, luteolin, tectorigenin, and quercetin inhibited NO production, as measured by nitrite formation at 10–100 μM. The most active among 26 flavonoid derivatives tested were apigenin, wogonin, and luteolin, having ic 50 values of 23, 17, and 27 μM, respectively, while AMT, a synthetic selective iNOS inhibitor, had an ic 50 value of 0.09 μM. In contrast, flavanones, such as naringenin, and flavonoid glycosides, such as apiin, did not demonstrate significant inhibition up to 100 μM. These results clearly indicated that a C-2,3 double bond might be important, and that the potency of inhibition depended upon the substitution patterns of the flavonoid molecules. The inhibitory activity of flavonoids was not due to direct inhibition of iNOS enzyme activity because they did not reasonably inhibit iNOS activity, as measured by [ 3H]citrulline formation from [ 3H]arginine, up to 100 μM. In contrast, wogonin and luteolin concentration-dependently reduced iNOS enzyme expression, when measured by western blotting, at 10–100 μM. All these results clearly demonstrated that certain flavonoids inhibit NO production in lipopolysaccharide-activated RAW 264.7 cells, and their inhibitory activity might be due to reduction of iNOS enzyme expression.

ChemInform Abstract: Relationship Between the Chemical Structure and the Cyclic AMP Phosphodiesterase Inhibitory Activity of Flavonoids as Studied by 13C NMR.

ChemInform Abstract: Relationship Between the Chemical Structure and the Cyclic AMP Phosphodiesterase Inhibitory Activity of Flavonoids as Studied by 13C NMR.