IkappaB kinases alpha and beta show a random sequential kinetic mechanism and are inhibited by staurosporine and quercetin

The inhibitor of κB kinase β (IKKβ) phosphorylates IκBα twice in a single binding event through a sequential mechanism

Phosphorylation of Inhibitor of κB (IκB) proteins by IκB Kinase β (IKKβ) leads to IκB degradation and subsequent activation of nuclear factor κB transcription factors. Of particular interest is the IKKβ-catalyzed phosphorylation of IκBα residues Ser32 and Ser36 within a conserved destruction box motif. To investigate the catalytic mechanism of IKKβ, we performed pre-steady-state kinetic analysis of the phosphorylation of IκBα protein substrates catalyzed by constitutively active, human IKKβ. Phosphorylation of full-length IκBα catalyzed by IKKβ was characterized by a fast exponential phase followed by a slower linear phase. The maximum observed rate (kp) of IKKβ-catalyzed phosphorylation of IκBα was 0.32 s-1 and the binding affinity of ATP for the IKKβ•IκBα complex (Kd) was 12 μM. Substitution of either Ser32 or Ser36 with Ala, Asp, or Cys reduced the amplitude of the exponential phase by approximately 2-fold. Thus, the exponential phase was attributed to phosphorylation of IκBα at Ser32 and Ser36, whereas the slower linear phase was attributed to phosphorylation of other residues. Interestingly, the exponential rate of phosphorylation of the IκBα(S32D) phosphomimetic amino acid substitution mutant was nearly twice that of WT IκBα and 4-fold faster than any of the other IκBα amino acid substitution mutants, suggesting that phosphorylation of Ser32 increases the phosphorylation rate of Ser36. These conclusions were supported by parallel experiments using GST-IκBα(1-54) fusion protein substrates bearing the first 54 residues of IκBα. Our data suggest a model wherein, IKKβ phosphorylates IκBα at Ser32 followed by Ser36 within a single binding event.

Quercetin, a flavonoid, combats rotavirus infection by deactivating rotavirus-induced pro-survival NF-κB pathway

Rotavirus (RV) is the leading cause of acute gastroenteritis and watery diarrhea in children under 5 years accounting for high morbidity and mortality in countries with poor socioeconomic status. Although vaccination against RV has been implemented in more than 100 countries, the efficacy of vaccine has been challenged in low-income settings. The lack of any FDA-approved drug against RV is an additional concern regarding the treatment associated with rotavirus-induced infantile death. With the purpose for the discovery of anti-RV therapeutics, we assessed anti-rotaviral potential of quercetin, a well-characterized antioxidant flavonoid. In vitro study revealed that quercetin treatment resulted in diminished production of RV-SA11 (simian strain) viral particles in a concentration-dependent manner as estimated by the plaque assay. Consistent with this result, Western blot analysis also revealed reduced synthesis of viral protein in quercetin-treated RV-SA11-infected MA104 cells compared to vehicle (DMSO) treated controls. Not surprisingly, infection of other RV strains A5-13 (bovine strain) and Wa (Human strain) was also found to be abridged in the presence of quercetin compared to DMSO. The IC₅₀ of quercetin against three RV strains ranges between 2.79 and 4.36 Mm, and S.I. index is greater than 45. Concurrent to the in vitro results, in vivo study in mice model also demonstrated reduced expression of viral proteins and viral titer in the small intestine of quercetin-treated infected mice compared to vehicle-treated infected mice. Furthermore, the result suggested anti-rotaviral activity of quercetin to be interferon-independent. Mechanistic study revealed that the antiviral action of quercetin is co-related with the inhibition of RV-induced early activation of NF-κB pathway. Overall, this study delineates the strong anti-RV potential of quercetin and also proposes it as future therapeutics against rotaviral diarrhea.

Anti-Hepatocellular Carcinoma Biomolecules: Molecular Targets Insights

This report explores the available curative molecules directed against hepatocellular carcinoma (HCC). Limited efficiency as well as other drawbacks of existing molecules led to the search for promising potential alternatives. Understanding of the cell signaling mechanisms propelling carcinogenesis and driven by cell proliferation, invasion, and angiogenesis can offer valuable information for the investigation of efficient treatment strategies. The complexity of the mechanisms behind carcinogenesis inspires researchers to explore the ability of various biomolecules to target specific pathways. Natural components occurring mainly in food and medicinal plants, are considered an essential resource for discovering new and promising therapeutic molecules. Novel biomolecules normally have an advantage in terms of biosafety. They are also widely diverse and often possess potent antioxidant, anti-inflammatory, and anti-cancer properties. Based on quantitative structure-activity relationship studies, biomolecules can be used as templates for chemical modifications that improve efficiency, safety, and bioavailability. In this review, we focus on anti-HCC biomolecules that have their molecular targets partially or completely characterized as well as having anti-cancer molecular mechanisms that are fairly described.

Beyond direct Nrf2 activation; reinvestigating 1,2,4-oxadiazole scaffold as a master key unlocking the antioxidant cellular machinery for cancer therapy

Harnessing the antioxidant cellular machinery has sparked considerable interest as an efficient anticancer strategy. Activating Nrf2, the master switch of the cellular redox system, suppresses ROS, alleviates oxidative stress, and halts cancer progression. 1,2,4-oxadiazoles are iconic direct Nrf2 activators that disrupt Nrf2 interaction with its endogenous repressor Keap1. This study introduces rationally designed 1,2,4-oxadiazole derivatives that inhibit other Nrf2 suppressors (TrxR1, IKKα, and NF-kB) thus enhancing Nrf2 activation for preventing oxidative stress and carcinogenesis. Preliminary screening showed that the phenolic oxadiazoles 11, 15, and 19 were comparable to ascorbic acid (ROS scavenging) and EDTA (iron chelation), and superior to doxorubicin against HepG-2, MDA-MB231, and Caco-2 cells. They suppressed ROS by 3 folds and activated Nrf2 by 2 folds in HepG-2 cells. Mechanistically, they inhibited TrxR1 (IC₅₀; 13.19, 17.89, and 9.21 nM) and IKKα (IC₅₀; 11.0, 15.94, and 19.58 nM), and downregulated NF-κB (7.6, 1.4 and 1.9 folds in HepG-2), respectively. They inhibited NADPH oxidase (IC₅₀; 16.4, 21.94, and 10.71 nM, respectively) that potentiates their antioxidant activities. Docking studies predicted their important structural features. Finally, they recorded drug-like in silico physicochemical properties, ADMET, and ligand efficiency metrics.

Compounds from Natural Sources as Protein Kinase Inhibitors

The advantage of natural compounds is their lower number of side-effects when compared to most synthetic substances. Therefore, over the past several decades, the interest in naturally occurring compounds is increasing in the search for new potent drugs. Natural compounds are playing an important role as a starting point when developing new selective compounds against different diseases. Protein kinases play a huge role in several diseases, like cancers, neurodegenerative diseases, microbial infections, or inflammations. In this review, we give a comprehensive view of natural compounds, which are/were the parent compounds in the development of more potent substances using computational analysis and SAR studies.

Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19)

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) represents an emergent global threat which is straining worldwide healthcare capacity. As of May 27th, the disease caused by SARS-CoV-2 (COVID-19) has resulted in more than 340,000 deaths worldwide, with 100,000 deaths in the US alone. It is imperative to study and develop pharmacological treatments suitable for the prevention and treatment of COVID-19. Ascorbic acid is a crucial vitamin necessary for the correct functioning of the immune system. It plays a role in stress response and has shown promising results when administered to the critically ill. Quercetin is a well-known flavonoid whose antiviral properties have been investigated in numerous studies. There is evidence that vitamin C and quercetin co-administration exerts a synergistic antiviral action due to overlapping antiviral and immunomodulatory properties and the capacity of ascorbate to recycle quercetin, increasing its efficacy. Safe, cheap interventions which have a sound biological rationale should be prioritized for experimental use in the current context of a global health pandemic. We present the current evidence for the use of vitamin C and quercetin both for prophylaxis in high-risk populations and for the treatment of COVID-19 patients as an adjunct to promising pharmacological agents such as Remdesivir or convalescent plasma.

The Effects of Quercetin Supplementation on Blood Pressures and Endothelial Function Among Patients with Metabolic Syndrome and Related Disorders: A Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND

This systematic review and meta-analysis of randomized controlled trials (RCTs) were performed to determine the effect of quercetin administration on blood pressures and endothelial function among patients with metabolic syndrome (MetS) and related disorders.

METHODS

We searched systematically online databases including Cochrane Library, EMBASE, MEDLINE, and Web of Science to identify the relevant RCTs until December 2018. Q-test and I2 statistics were applied to assess heterogeneity among the included studies. Data were pooled using a random-effects model and weighted mean difference (WMD) was considered as the overall effect size.

RESULTS

Out of 284 citations, 8 RCTs were included in the meta-analysis. We found a significant reduction in systolic blood pressure (SBP) (WMD: -1.69; 95% CI: -3.22, -0.17) following the intake of quercetin supplements. However, quercetin supplementation did not significantly affect diastolic blood pressure (DBP) (WMD: -3.14; 95% CI: -8.24, 1.95), vascular cell adhesion molecule 1 (VCAM-1) (WMD: -24.49; 95% CI: -53.74, 4.77) and intercellular adhesion molecule 1 (ICAM-1) (WMD: -5.78; 95% CI: -12.93, 1.38).

CONCLUSION

In summary, the current meta-analysis demonstrated that quercetin supplementation significantly reduced SBP, yet did not affect DBP, VCAM-1 and ICAM-1 among patients with MetS and related disorders.

Inhibition and Activation of Kinases by Reaction Products: A Reporter-Free Assay

Kinases are widely distributed in nature and are implicated in many human diseases. Thus, an understanding of their activity and regulation is of fundamental importance. Several kinases are known to be inhibited by ADP. However, thorough investigation of this phenomenon is hampered by the lack of a simple and effective assay for studying this inhibition. We now present a quick, general approach for measuring the effects of reaction products on kinase activity. The method, based on isothermal titration calorimetry, is the first universal, reporter-free, continuous assay for probing kinase inhibition or activation by ADP. In applications to an aminoglycoside phosphotransferase [APH(3')-IIIa] and pantothenate kinases from Escherichia coli (EcPanK) and Pseudomonas aeruginosa (PaPanK), we found ADP to be an efficient inhibitor of all three kinases, with inhibition constant (K_i) values similar to or lower than the Michaelis-Menten constant (K_m) values of ATP. Interestingly, ADP was an activator at low concentrations and an inhibitor at high concentrations for EcPanK. This unusual effect was quantitatively modeled and attributed to cooperative interactions between the two subunits of the dimeric enzyme. Importantly, our results suggest that, at typical bacterial intracellular concentrations of ATP and ADP (approximately 1.5 mM and 180 μM, respectively), all three kinases are partially inhibited by ADP, allowing enzyme activity to rapidly respond to changes in the levels of both metabolites.

Nuclear factor-kappa β as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD) is a typical progressive, chronic neurodegenerative disorder with worldwide prevalence. Its clinical manifestation involves the presence of extracellular plaques and intracellular neurofibrillary tangles (NFTs). NFTs occur in brain tissues as a result of both Aβ agglomeration and Tau phosphorylation. Although there is no known cure for AD, research into possible cures and treatment options continues using cell-cultures and model animals/organisms. The nuclear factor-kappa β (NF-κβ) plays an active role in the progression of AD. Impairment to this signaling module triggers undesirable phenotypic changes such as neuroinflammation, activation of microglia, oxidative stress related complications, and apoptotic cell death. These imbalances further lead to homeostatic abnormalities in the brain or in initial stages of AD essentially pushing normal neurons toward the degeneration process. Interestingly, the role of NF-κβ signaling associated receptor-interacting protein kinase is currently observed in apoptotic and necrotic cell death, and has been reported in brains. Conversely, the NF-κβ signaling pathway has also been reported to be involved in normal brain functioning. This pathway plays a crucial role in maintaining synaptic plasticity and balancing between learning and memory. Since any impairment in the pathways associated with NF-κβ signaling causes altered neuronal dynamics, neurotherapeutics using compounds including, antioxidants, bioflavonoids, and non-steroidal anti-inflammatory drugs against such abnormalities offer possibilities to rectify aberrant excitatory neuronal activity in AD. In this review, we have provided an extensive overview of the crucial role of NF-κβ signaling in normal brain homeostasis. We have also thoroughly outlined several established pathomechanisms associated with NF-κβ pathways in AD, along with their respective therapeutic approaches.

Quercetin attenuates atherosclerotic inflammation and adhesion molecule expression by modulating TLR-NF-κB signaling pathway

Adhesion molecules expressed by activated endothelial cells play key role in regulating leukocyte trafficking to sites of inflammation. The present study attempted to explore whether the polyphenolic flavonoid quercetin influence leukocyte endothelial attraction and the involvement of TLR-NF-κB signaling pathway in the expression of adhesion molecules involved in the early development of atherosclerosis. Quercetin at 25μM concentration significantly reduced the HUVEC expression of VCAM-1 and ICAM-1 evidently enhanced by oxLDL. In addition, quercetin significantly downregulated the mRNA expression of MCP-1 and alleviated the nuclear translocation of NF-κB p65 subunit in oxLDL induced HUVECs. Western blot and PCR analyses revealed that quercetin significantly attenuated the expression of both protein and mRNA expression of TLR2 and TLR4. Quercetin supplementation significantly decreased the inflammatory mediators like COX, 5-LOX, MPO, NOS, CRP and the mRNA expression of the cytokine; IL-6 in hypercholesterolemic diet (HCD) fed atherosclerotic rats. The results demonstrate that quercetin is effective to regulate the atherosclerotic inflammatory process by inhibiting oxLDL induced endothelial leukocyte adhesion by attenuating the TLR-NF-κB signaling pathway in endothelial cells and decrease the inflammatory process induced by HCD in rats. Therefore, quercetin acts as anti-inflammatory and anti-atherogenic agent, which may have implications for strategies attenuating endothelial dysfunction-related atherosclerosis.

Enhanced anti-inflammatory effects of DHA and quercetin in lipopolysaccharide-induced RAW264.7 macrophages by inhibiting NF-κB and MAPK activation

The aim of the present study was to investigate the anti-inflammatory effects of docosahexaenoic acid (DHA) + quercetin (QE) used in combination. DHA and QE are natural compounds derived from various foods and have been demonstrated to exert anti‑inflammatory effects The protein mRNA expression involved in the nuclear factor (NF)-κB and mitogen-activated protein kinase (MAPK) signalling pathway was analyzed by western blot analysis and reverse transcription-polymerase chain reaction methods respectively, other cytokines were detected by an enzyme‑linked immunosorbent assay kit. The results of the present study demonstrated that combined treatment of lipopolysaccharide (LPS)‑stimulated RAW264.7 cells with DHA + QE decreased the levels of pro‑inflammatory mediators to a greater extent than QE or DHA alone. Additionally, DHA + QE synergistically suppressed nitric oxide, prostaglandin E2 and cyclooxygenase-2 levels. Molecular‑level studies indicated that the DHA + QE combination can significantly inhibit the mRNA expression of NF‑κB subunits p50 and p65, extracellular signal‑regulated kinase (ERK) 1/2 and c‑JUN N‑terminal kinase (JNK) 1/2, which suggests that the NF‑κB signalling pathway is involved in the synergistic effects observed. Furthermore, western blot analysis demonstrated that DHA + QE synergistically inhibit the phosphorylation of p50, p65, ERK1/2 and JNK1/2. This finding indicates that the enhanced anti‑inflammatory effects of the combined compounds are achieved by suppressing NF‑κB and MAPK signalling in LPS‑stimulated RAW264.7 cells. The results of the present study suggest that DHA and QE in combination may be utilized as potent anti‑inflammatory compounds, with potential preventative or palliative effects on obesity, atherosclerosis and cardiovascular diseases.

Quercetin inhibits multiple pathways involved in interleukin 6 secretion from human lung fibroblasts and activity in bronchial epithelial cell transformation induced by benzo[a]pyrene diol epoxide

The interaction between epithelial and stromal cells through soluble factors such as cytokines plays an important role in carcinogenesis. Breaking this cancer-promoting interaction poses an opportunity for cancer prevention. The tumor-promoting function of interleukin 6 (IL-6) has been documented; however, the underlying mechanisms of this function in lung carcinogenesis are not well elucidated. Here, we show that benzo[a]pyrene diol epoxide (BPDE, the active metabolite of cigarette smoke carcinogen benzo[a]pyrene)-induced human bronchial epithelial cell (HBEC) transformation was enhanced by IL-6 in vitro. The carcinogen/IL-6-transformed cells exhibited higher expression of STAT3 (signal transducer and activator of transcription 3) when compared with cells transformed by BPDE alone. Constitutive STAT3 activation drove cell proliferation and survival through anti-apoptosis gene expression. We further show that quercetin, a dietary compound having preventive properties for lung cancer, decreased BPDE-stimulated IL-6 secretion from human lung fibroblasts through inhibition of the NF-κB and ERK pathways. The inhibition was accomplished at clinically achievable concentrations of the compound. Finally, quercetin blocked IL-6-induced STAT3 activation in HBECs, and IL-6 enhancement of HBEC transformation by BPDE was abolished by quercetin treatment. Altogether, our data reveal novel mechanisms for IL-6 in lung carcinogenesis and for the preventive role of quercetin in the process. © 2015 Wiley Periodicals, Inc.

Mechanistic interpretation of conventional Michaelis-Menten parameters in a transporter system

The aim was to elucidate how steps in drug translocation by a solute carrier transporter impact Michaelis-Menten parameters Km, Ki, and Vmax. The first objective was to derive a model for carrier-mediated substrate translocation and perform sensitivity analysis with regard to the impact of individual microrate constants on Km, Ki, and Vmax. The second objective was to compare underpinning microrate constants between compounds translocated by the same transporter. Equations for Km, Ki, and Vmax were derived from a six-state model involving unidirectional transporter flipping and reconfiguration. This unidirectional model is applicable to co-transporter type solute carriers, like the apical sodium-dependent bile acid transporter (ASBT) and the proton-coupled peptide cotransporter (PEPT1). Sensitivity analysis identified the microrate constants that impacted Km, Ki, and Vmax. Compound comparison using the six-state model employed regression to identify microrate constant values that can explain observed Km and Vmax values. Results yielded some expected findings, as well as some unanticipated effects of microrate constants on Km, Ki, and Vmax. Km and Ki were found to be equal for inhibitors that are also substrates. Additionally, microrate constant values for certain steps in transporter functioning influenced Km and Vmax to be low or high.

Quercetin: a pleiotropic kinase inhibitor against cancer

Increased consumption of fruits and vegetables can represent an easy strategy to significantly reduce the incidence of cancer. From this observation, derived mostly from epidemiological data, the new field of chemoprevention has emerged in the primary and secondary prevention of cancer. Chemoprevention is defined as the use of natural or synthetic compounds able to stop, reverse, or delay the process of tumorigenesis in its early stages. A large number of phytochemicals are potentially capable of simultaneously inhibiting and modulating several key factors regulating cell proliferation in cancer cells. Quercetin is a flavonoid possessing potential chemopreventive properties. It is a functionally pleiotropic molecule, possessing multiple intracellular targets, affecting different cell signaling processes usually altered in cancer cells, with limited toxicity on normal cells. Simultaneously targeting multiple pathways may help to kill malignant cells and slow down the onset of drug resistance. Among the different substrates triggered by quercetin, we have reviewed the ability of the molecule to inhibit protein kinases involved in deregulated cell growth in cancer cells.

Therapeutic targets for rheumatoid arthritis: Progress and promises

Recent therapeutic advancements in understanding of molecular and cellular mechanisms of rheumatoid arthritis (RA) have highlighted the strategies that aim to inhibit the harmful effects of up-regulated cytokines or other inflammatory mediators and to inhibit their associated signaling events. The utility of cytokine as therapeutic targets in RA has been unequivocally demonstrated by the success of tumor necrosis factor (TNF)-α blockade in clinical practice. Partial and non-responses to TNF-α blocking agents, however, together with the increasing clinical drive to remission induction, requires that further therapeutic targets be identified. Numerous proinflammatory mediators with their associated cell signaling events have now been demonstrated in RA, including interleukin (IL)-1 and IL-12 superfamilies. Continued efforts are ongoing to target IL-6, IL-15 and IL-17 in clinical trials with promising data emerging. In the present review, we focus on IL-7, IL-18, IL-32 and IL-10 family of cytokines (IL-19, IL-20 and IL-22) as they are implicated in contributing to the pathogenesis of RA, which could be targeted and offer new therapeutic options for RA therapy. Recent evidences also suggest that multiligand receptor for advanced glycation end products (RAGE), several adipokines and various components of immune system play a critical role in the pathophysiology of RA; therefore we have also highlighted them as therapeutic targets for RA therapy. Components of subcellular pathways, involve in nuclear transcription factor (NF)-κB, mitogen-activated protein kinases (MAPKs) and the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway have also been discussed and offer several novel potential therapeutic opportunities for RA.

The therapeutic potential and mechanisms of action of quercetin in relation to lipopolysaccharide-induced sepsis in vitro and in vivo

Sepsis caused by Gram-negative bacterial infection is characterized by extensive inflammatory cytokine production, which leads to multiple organ failure and a high lethality rate. Therefore, compounds that are able to alleviate profound inflammatory responses may have therapeutic potential in relation to sepsis. Quercetin, one of the flavonoids found widely in the human diet, has been reported to have many health benefits, but the mechanisms underlying its biological effects remain obscure. In the present study, our aim was to investigate the molecular mechanisms by which quercetin inhibits lipopolysaccharide (LPS)-induced pro-inflammatory cytokine production and to evaluate the capacity of quercetin to attenuate the mortality rate in a mice model of lethal sepsis. Our results show that quercetin significantly attenuates LPS-induced production of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in RAW264.7 macrophages. The LPS-stimulated phosphorylations of the inhibitors of κB kinase (IKKs), Akt, and c-Jun N-terminal kinase (JNK) are also inhibited by quercetin. Quercetin causes a significant reduction in the phosphorylation and degradation of inhibitor of κBα (IκBα) and in the nuclear level of nuclear factor-κB (NF-κB), the latter being associated with decreased NF-κB binding activity. Most importantly, acute administration of quercetin reduces the lethality rate and circulating levels of TNF-α and IL-1β in C57BL/6J mice with endotoxemia induced by LPS, whereas chronic dietary supplementation with quercetin shows no inhibitory effect on serum TNF-α and IL-1β levels. These findings provide clues that quercetin may be a promising agent for the prevention of systemic inflammatory diseases such as sepsis.

Mechanism of endogenous regulation of the type I interferon response by suppressor of IκB kinase epsilon (SIKE), a novel substrate of TANK-binding kinase 1 (TBK1)

TANK-binding kinase 1 (TBK1) serves as a key convergence point in multiple innate immune signaling pathways. In response to receptor-mediated pathogen detection, TBK1 phosphorylation promotes production of pro-inflammatory cytokines and type I interferons. Increasingly, TBK1 dysregulation has been linked to autoimmune disorders and cancers, heightening the need to understand the regulatory controls of TBK1 activity. Here, we describe the mechanism by which suppressor of IKKε (SIKE) inhibits TBK1-mediated phosphorylation of interferon regulatory factor 3 (IRF3), which is essential to type I interferon production. Kinetic analyses showed that SIKE not only inhibits IRF3 phosphorylation but is also a high affinity TBK1 substrate. With respect to IRF3 phosphorylation, SIKE functioned as a mixed-type inhibitor (K(i, app) = 350 nM) rather than, given its status as a TBK1 substrate, as a competitive inhibitor. TBK1 phosphorylation of IRF3 and SIKE displayed negative cooperativity. Both substrates shared a similar Km value at low substrate concentrations (∼50 nM) but deviated >8-fold at higher substrate concentrations (IRF3 = 3.5 μM; SIKE = 0.4 μM). TBK1-SIKE interactions were modulated by SIKE phosphorylation, clustered in the C-terminal portion of SIKE (Ser-133, -185, -187, -188, -190, and -198). These sites exhibited striking homology to the phosphorylation motif of IRF3. Mutagenic probing revealed that phosphorylation of Ser-185 controlled TBK1-SIKE interactions. Taken together, our studies demonstrate for the first time that SIKE functions as a TBK1 substrate and inhibits TBK1-mediated IRF3 phosphorylation by forming a high affinity TBK1-SIKE complex. These findings provide key insights into the endogenous control of a critical catalytic hub that is achieved not by direct repression of activity but by redirection of catalysis through substrate affinity.

Aberrantly activated EGFR contributes to enhanced IL-8 expression in COPD airways epithelial cells via regulation of nuclear FoxO3A

BACKGROUND

Decreased activity of forkhead transcription factor class O (FoxO)3A, a negative regulator of NF-κB-mediated chemokine expression, is implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Previously, we showed that quercetin reduces lung inflammation in a murine model of COPD. Here, we examined the mechanisms underlying decreased FoxO3A activation and its modulation by quercetin in COPD human airway epithelial cells and in a COPD mouse model.

METHODS

Primary COPD and normal human airway epithelial cells were treated with quercetin, LY294002 or erlotinib for 2 weeks. IL-8 was measured by ELISA. FoxO3A, Akt, and epidermal growth factor (EGF) receptor (EGFR) phosphorylation and nuclear FoxO3A levels were determined by Western blot analysis. Effects of quercetin on lung chemokine expression, nuclear FoxO3A levels and phosphorylation of EGFR and Akt were determined in COPD mouse model.

RESULTS

Compared with normal, COPD cells showed significantly increased IL-8, which negatively correlated with nuclear FoxO3A levels. COPD bronchial biopsies also showed reduced nuclear FoxO3A. Decreased FoxO3A in COPD cells was associated with increased phosphorylation of EGFR, Akt and FoxO3A and treatment with quercetin, LY294002 or erlotinib increased nuclear FoxO3A and decreased IL-8 and phosphorylation of Akt, EGFR and FoxO3A, Compared with control, elastase/LPS-exposed mice showed decreased nuclear FoxO3A, increased chemokines and phosphorylation of EGFR and Akt. Treatment with quercetin partially reversed these changes.

CONCLUSIONS

In COPD airways, aberrant EGFR activity increases PI 3-kinase/Akt-mediated phosphorylation of FoxO3A, thereby decreasing nuclear FoxO3A and increasing chemokine expression. Quercetin restores nuclear FoxO3A and reduces chemokine expression partly by modulating EGFR/PI 3-kinase/Akt activity.

Quercetin inhibits rhinovirus replication in vitro and in vivo

Rhinovirus (RV), which is responsible for the majority of common colds, also causes exacerbations in patients with asthma and chronic obstructive pulmonary disease. So far, there are no drugs available for treatment of rhinovirus infection. We examined the effect of quercetin, a plant flavanol on RV infection in vitro and in vivo. Pretreatment of airway epithelial cells with quercetin decreased Akt phosphosphorylation, viral endocytosis and IL-8 responses. Addition of quercetin 6 h after RV infection (after viral endocytosis) reduced viral load, IL-8 and IFN responses in airway epithelial cells. This was associated with decreased levels of negative and positive strand viral RNA, and RV capsid protein, abrogation of RV-induced eIF4GI cleavage and increased phosphorylation of eIF2α. In mice infected with RV, quercetin treatment decreased viral replication as well as expression of chemokines and cytokines. Quercetin treatment also attenuated RV-induced airway cholinergic hyperresponsiveness. Together, our results suggest that quercetin inhibits RV endocytosis and replication in airway epithelial cells at multiple stages of the RV life cycle. Quercetin also decreases expression of pro-inflammatory cytokines and improves lung function in RV-infected mice. Based on these observations, further studies examining the potential benefits of quercetin in the prevention and treatment of RV infection are warranted.

The flavonoid quercetin in disease prevention and therapy: facts and fancies

Biochemical and genetic studies on cellular and animal models on the mechanism(s) of action of phytochemicals provide a functional explanation of how and why a diet rich in fruits and vegetables is considered healthy. It is not unusual to find molecules that protect against diseases, which greatly differ from a physiopathological point of view, such as cancer and cardiovascular disorders. Quercetin falls into this category and possesses a broad range of biological properties. Uptake, metabolism and circulating concentrations of quercetin and its metabolites suggest that a regular diet provides amounts of quercetin (<1 μM) not compatible with its chemopreventive and/or cardioprotective effects. However, it appears relatively easy to increase total quercetin concentrations in plasma (>10 μM) by supplementation with quercetin-enriched foods or supplements. Multiple lines of experimental evidence suggest a positive association between quercetin intake and improved outcomes of inflammatory cardiovascular risk. The ameliorating effect of quercetin administration can be extended to other chronic inflammatory disorders but only if supplementation occurs in patients. Quercetin can be considered the prototype of a naturally-occurring chemopreventive agent because of its key roles in triggering the "hallmarks of cancer". However, several critical points must be taken into account when considering the potential therapeutic use of this molecule: (1) pharmacological versus nutraceutical doses applied, (2) specificity of its mechanism of action compared to other phytochemicals, and (3) identification of "direct" cellular targets. The design of specific clinical trials is extremely warranted to depict possible applications of quercetin in adjuvant cancer therapy.

Quercetin prevents progression of disease in elastase/LPS-exposed mice by negatively regulating MMP expression

Background

Chronic obstructive pulmonary disease (COPD) is characterized by chronic bronchitis, emphysema and irreversible airflow limitation. These changes are thought to be due to oxidative stress and an imbalance of proteases and antiproteases. Quercetin, a plant flavonoid, is a potent antioxidant and anti-inflammatory agent. We hypothesized that quercetin reduces lung inflammation and improves lung function in elastase/lipopolysaccharide (LPS)-exposed mice which show typical features of COPD, including airways inflammation, goblet cell metaplasia, and emphysema.

Methods

Mice treated with elastase and LPS once a week for 4 weeks were subsequently administered 0.5 mg of quercetin dihydrate or 50% propylene glycol (vehicle) by gavage for 10 days. Lungs were examined for elastance, oxidative stress, inflammation, and matrix metalloproteinase (MMP) activity. Effects of quercetin on MMP transcription and activity were examined in LPS-exposed murine macrophages.

Results

Quercetin-treated, elastase/LPS-exposed mice showed improved elastic recoil and decreased alveolar chord length compared to vehicle-treated controls. Quercetin-treated mice showed decreased levels of thiobarbituric acid reactive substances, a measure of lipid peroxidation caused by oxidative stress. Quercetin also reduced lung inflammation, goblet cell metaplasia, and mRNA expression of pro-inflammatory cytokines and muc5AC. Quercetin treatment decreased the expression and activity of MMP9 and MMP12 in vivo and in vitro, while increasing expression of the histone deacetylase Sirt-1 and suppressing MMP promoter H4 acetylation. Finally, co-treatment with the Sirt-1 inhibitor sirtinol blocked the effects of quercetin on the lung phenotype.

Conclusions

Quercetin prevents progression of emphysema in elastase/LPS-treated mice by reducing oxidative stress, lung inflammation and expression of MMP9 and MMP12.

The effects of quercetin in cultured human RPE cells under oxidative stress and in Ccl2/Cx3cr1 double deficient mice

Quercetin, a member of the flavonoid family, is one of the most prominent dietary antioxidants. This study investigates the mechanisms for the effects of quercetin on cultured human RPE cells and in Ccl2/Cx3cr1 double knock-out (DKO) mice, which spontaneously develop progressive retinal lesions mimicking age-related macular degeneration (AMD). In the in vitro experiment, cultured ARPE-19 cells were exposed to 1 mM H(2)O(2) with or without 50 muM quercetin for 2 h. Cellular viability, mitochondrial function, and apoptosis were assessed using crystal violet staining, MTT assay, and comet assay, respectively. Apoptotic molecular transcripts of BCL-2, BAX, FADD, CASPASE-3 and CASPASE-9 were measured by RQ-PCR. COX activity and nitric oxide (NO) level were determined in the supernatant of the culture medium. Quercetin treatment protected ARPE-19 cells from H(2)O(2)-induced oxidative injury, enhanced BCL-2 transcript levels, increased the BCL-2/BAX ratio, suppressed the transcription of pro-apoptotic factors such as BAX, FADD, CASPASE-3 and CASPASE-9, inhibited the transcription of inflammatory factors such as TNF-alpha, COX-2 and INOS, and decreased the levels of COX and NO in the culture medium. In the in vivo experiment, DKO and C57/B6 mice were treated with 25 mg/kg/day quercetin by intraperitoneal injection daily for two months. Funduscopy was performed monthly. After two months, serum was collected to measure NADP(+)/NADPH, COX, PGE-2, and NO levels. The eyes were harvested for histology and A2E measurement. Ocular transcripts of Bcl-2, Bax, Cox-2, Inos, Tnf-alpha, Fas, FasL and Caspase-3 were detected by RQ-PCR. Quercetin treatment did not reverse the progression of retinal lesions in DKO mice funduscopically or histologically. Although quercetin treatment could recover systemic anti-oxidative capacity, suppress the systemic expression of NO, COX and PGE-2, and decrease ocular A2E levels, it could not effectively suppress the transcripts of the ocular inflammatory factors Tnf-alpha, Cox-2 and Inos, or the pro-apoptotic factors Fas, FasL and Caspase-3 in DKO mice. Our data demonstrate that quercetin can protect human RPE cells from oxidative stress in vitro via inhibition of pro-inflammatory molecules and direct inhibition of the intrinsic apoptosis pathway. However, quercetin (25 mg/kg/day) does not improve the retinal AMD-like lesions in the Ccl2(-/-)/Cx3cr1(-/-) mice, likely due to its insufficient suppression of the inflammatory and apoptosis pathways in the eye.

Structural insights into IKKbeta inhibition by natural products staurosporine and quercetin

This Letter describes the results of two combined approaches: homology modeling and molecular docking studies, in order to propose the molecular basis of IKKbeta inhibition by staurosporine and quercetin as ATP-competitive inhibitors. The results provides a rationale and structural frameworks for designing potent ATP binding-site inhibitors of IKKbeta, which is an attractive drug target for inflammatory diseases and has been found to be responsible for some of the already observed pharmacological effects for marketed drugs.

The inhibitory effect of quercitrin gallate on iNOS expression induced by lipopolysaccharide in Balb/c mice

Quercetin 3-O-β-(2"-galloyl)-rhamnopyranoside (QGR) is a naturally occurring quercitrin gallate, which is a polyphenolic compound that was originally isolated from Persicaria lapathifolia (Polygonaceae). QGR has been shown to have an inhibitory effect on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated macrophage RAW 264.7 cells. Therefore, this study was conducted to investigate the inhibitory effect of QGR on nitric oxide production and inducible nitric oxide synthases (iNOS) expression in LPS-stimulated Balb/c mice. To accomplish this, 10 mg/kg of QGR was administered via gavage once a day for 3 days. iNOS was then induced by intraperitoneal injection of LPS. Six hours after the LPS treatment the animals were sacrificed under ether anethesia. The serum levels of NO were then measured to determine if QGR exerted an inhibitory effect on NO production in vivo. LPS induced an approximately 6 fold increase in the expression of NO. However, oral administration of QGR reduced the LPS induced increase in NO by half. Furthermore, RT-PCR and western blot analysis revealed that the increased levels of iNOS expression that occurred in response to treatment with LPS were significantly attenuated in response to QGR pretreatment. Histologically, LPS induced the infiltration of polymorphonuclear neutrophils in portal veins and sinusoids and caused the formation of a large number of necrotic cells; however, pretreatment with QGR attenuated these LPS induced effects. Taken together, these results indicate that QGR inhibits iNOS expression in vivo as well as in vitro and has antiinflammatory potentials.

Health effects of quercetin: from antioxidant to nutraceutical

Quercetin, a member of the flavonoids family, is one of the most prominent dietary antioxidants. It is ubiquitously present in foods including vegetables, fruit, tea and wine as well as countless food supplements and is claimed to exert beneficial health effects. This includes protection against various diseases such as osteoporosis, certain forms of cancer, pulmonary and cardiovascular diseases but also against aging. Especially the ability of quercetin to scavenge highly reactive species such as peroxynitrite and the hydroxyl radical is suggested to be involved in these possible beneficial health effects. Consequently, numerous studies have been performed to gather scientific evidence for these beneficial health claims as well as data regarding the exact mechanism of action and possible toxicological aspects of this flavonoid. The purpose of this review is to evaluate these studies in order to elucidate the possible health-beneficial effects of the antioxidant quercetin. Firstly, the definitions as well as the most important aspects regarding free radicals, antioxidants and oxidative stress will be discussed as background information. Subsequently, the mechanism by which quercetin may operate as an antioxidant (tested in vitro) as well as the potential use of this antioxidant as a nutraceutical (tested both ex vivo and in vivo) will be discussed.

Avenanthramides, polyphenols from oats, inhibit IL-1beta-induced NF-kappaB activation in endothelial cells

The chronic inflammation of arterial walls is associated with the development of atherosclerosis. Earlier we reported that avenanthramide (Avn)s-enriched extract of oats (AvnsO) significantly suppressed interleukin (IL)-1beta-stimulated secretion of proinflammatory cytokines, such as IL-6, IL-8, and MCP-1, by human aortic endothelial cells (HAEC). The main objective of the current study was to determine if the mechanism of inhibitory effect of these polyphenols from oats on the expression of proinflammatory cytokines is mediated through modulation of nuclear factor kappaB (NF-kappaB)-dependent transcription. Confluent HAEC monolayers were treated for 24 h with AvnsO, and synthetically prepared Avn-c suppressed IL-beta-stimulated activation of NF-kappaB in a concentration-dependent manner. CH3-Avn-c, a synthetically prepared methyl ester derivative of Avn-c with a high biological potency, significantly and dose dependently decreased mRNA expression and secretion of IL-6, IL-8, and MCP-1 by HAEC as determined by real-time RT-PCR and ELISA, and it inhibited IL-1beta- and TNFalpha-stimulated NF-kappaB activation as determined by a NF-kappaB DNA binding assay and a NF-kappaB luciferase reporter assay. AvnsO and Avn-c as well as CH3-Avn-c also inhibited the NF-kappaB-dependent reporter gene expression activated by TNFR-associated factor 2 and 6 (TRAF2, TRAF6) and NFkappaB-inducing kinase (NIK). CH3-Avn-c also significantly and dose dependently decreased the phosphorylation level of IkappaB kinase (IKK) and IkappaB, and prevented IkappaB degradation as measured by Western blotting. In addition, CH3-Avn-c markedly increased the overall levels of high mass ubiquitin-conjugated protein levels while it mildly inhibited proteasome activity. These observations suggest that Avns, unique polyphenols from oats, decrease the expression of endothelial proinflammatory cytokines at least in part through inhibition of NF-kappaB activation by inhibiting the phosphorylation of IKK and IkappaB, and by suppressing proteasome activity.

delta-Opioid receptor stimulation enhances the growth of neonatal rat ventricular myocytes via the extracellular signal-regulated kinase pathway

1. The aims of the present study were to determine whether delta-opioid receptor stimulation enhanced proliferation of and to investigate the role of the extracellular signal-regulated kinase (ERK) pathway in ventricular myocytes from neonatal rats. 2. At concentratins ranging from 10 nmol/L to 10 micromol/L, [D-Ala2,D-Leu5]enkephalin (DADLE) concentration-dependently promoted myocardial growth and DNA synthesis and altered the cytoskeleton. 3. At 1 micromol/L, DADLE also increased the expression and phosphorylation of ERK. 4. These effects of 1 micromol/L DADLE were abolished by 10 micromol/L naltrindole, a selective delta-opioid receptor antagonist, 10 nmol/L U0126, a selective ERK antagonist, 1 micromol/L staurosporine, an inhibitor of protein kinase (PK) C, and 100 micromol/L Rp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Rp-cAMPS), an inhibitor of PKA. 5. In conclusion, delta-opioid receptor stimulation enhances the proliferation and development of the ventricular myocytes of neonatal rats. The ERK pathway and related signalling mechanisms, namely PKC and PKA, are involved.

Scavenging of peroxynitrite-derived radicals by flavonoids may support endothelial NO synthase activity, contributing to the vascular protection associated with high fruit and vegetable intakes

Ample intakes of fruit and vegetables have been linked epidemiologically with reduced risk for coronary disease, stroke, hypertension, obesity, many types of cancer, chronic pulmonary disease, osteoporosis, and various ocular disorders. The favorable impact of diets rich in fruit and vegetables on coronary risk has been confirmed in meta-analyses, and is thought to be largely attributable to the folk acid and potassium supplied by these foods. Although high intakes of vitamin C appear to confer some cardiovascular protection, the amounts supplied by typical diets may be too low to be of much benefit in this regard. High flavonoid intakes emerge as protective in some epidemiological studies, albeit the dose-response pattern observed is often L-shaped - seemingly more consistent with low intakes being harmful, than with high intakes being protective. Nonetheless, flavonoids have shown anti-atherogenic activity in rodent models, and both clinical and rodent supplementation studies with foods and food extracts rich in flavonoids demonstrate improvements in endothelium-dependent vasodilation traceable to increased endothelial nitric oxide synthesis. However, flavonoids do not appear to increase the expression of endothelial NO synthase, nor do they modify endothelial superoxide production. A likely explanation is that, even in nanomolar concentrations achievable in vivo, flavonoids can act as efficient scavengers of peroxynitrite-derived radicals, thereby protecting the cofactor tetrahydrobiopterin, crucial for NO synthase activity. Studies with cultured endothelial cells should be useful for evaluating this possibility. It would also be appropriate to assess the effects of flavonoids on prostacylin synthetase activity, on endothelial catabolism of asymmetric dimethylarginine, and on signaling mechanisms that activate NO synthase. Since peroxynitrite can induce mutagenic damage to DNA, it is conceivable that scavenging of peroxynitrite-derived radicals contributes to the reduction in mutagenesis associated with high intakes of fruits and vegetables. Carotenoids also have the potential to prevent peroxynitrite-mediated damage, although, as contrasted with flavonoids, there is comparatively little evidence that these compounds are anti-atherogenic or beneficial for endothelial function; a recent meta-analysis of epidemiological studies suggests that high lutein intakes may modestly reduce coronary risk.

Quercetin 3-O-β-(2″-galloyl)-glucopyranoside inhibits endotoxin LPS-induced IL-6 expression and NF-κB activation in macrophages

We previously isolated quercetin 3-O-beta-(2''-galloyl)-glucopyranoside (QG-32) from Persicaria lapathifolia (Polygonacease) as an inhibitor of superoxide production. In the present study, QG-32 was found to inhibit interleukin (IL)-6 production in endotoxin lipopolysaccharide (LPS)-stimulated macrophages RAW 264.7. The QG-32 attenuated LPS-induced synthesis of IL-6 transcript but also inhibited IL-6 promoter activity, indicating that the compound could down-regulate LPS-induced IL-6 expression at the transcription level. Since nuclear factor (NF)-kappaB has been evidenced to play a major mechanism in the LPS-induced IL-6 expression, an effect of QG-32 on NF-kappaB activating pathway was further analyzed. QG-32 inhibited nuclear import as well as DNA binding activity of NF-kappaB complex and subsequently suppressed NF-kappaB transcriptional activity in LPS-stimulated macrophages. However, QG-32 affected neither LPS-induced inhibitory kappaB (IkappaB) degradation nor IkappaB kinase (IKK) activation. In another experiment, QG-32 inhibited expression vector encoding NF-kappaB p65 or p50-elicited IL-6 promoter activity. Taken together, QG-32 could inhibit NF-kappaB-dependent IL-6 expression, targeting nuclear translocation of NF-kappaB complex downstream IkappaB degradation. This mechanism of action would be different from that of quercetin, an aglycone of QG-32, targeting IKK upstream IkappaB degradation. Finally, this study could provide a pharmacological potential of QG-32 in the inflammatory disorders.

Differential actin isoform reorganization in the contracting A7r5 cell

In the present study, we investigated the reorganization of alpha- and beta-actin in the contracting A7r5 smooth muscle cell. The remodeling of these actin variants was markedly different in response to increasing concentrations of phorbol 12, 13-dibutyrate (PDBu). At the lowest concentrations (< or =10(-7) mol/L), cells showed an approximately 70% loss in alpha-actin stress fibers with robust transport of this isoform to podosomes. By comparison, beta-actin remained in stress fibers in cells stimulated at low concentrations (< or =10(-7) mol/L) of PDBu. However, at high concentrations (> or =10(-6)mol/L) approximately 50% of cells showed transport of beta-actin to podosomes. Consistent with these findings, staining with phalloidin indicated a significant decrease in the whole-cell content of F-actin with PDBu treatment. However, staining with DNase I indicated no change in the cellular content of G-actin, suggesting reduced access of phalloidin to tightly packed actin in the podosome core. Inhibition of protein kinase C (staurosporine, bisindolymaleimide) blocked PDBu-induced (5 x 10(-8) mol/L) loss in alpha-actin stress fibers or reversed podosome formation with re-establishment of alpha-actin stress fibers. By comparison, these inhibitors caused partial loss of beta-actin stress fibers. The results support our earlier conclusion of independent remodeling of alpha- and beta-actin cytoskeletal structure and suggest that the regulation of these structures is different.

Bridging the gap between in silico and cell-based analysis of the nuclear factor-kappaB signaling pathway by in vitro studies of IKK2

Previously, we have shown by sensitivity analysis, that the oscillatory behavior of nuclear factor (NF-kappaB) is coupled to free IkappaB kinase-2 (IKK2) and IkappaBalpha(IkappaBalpha), and that the phosphorylation of IkappaBalpha by IKK influences the amplitude of NF-kappaB oscillations. We have performed further analyses of the behavior of NF-kappaB and its signal transduction network to understand the dynamics of this system. A time lapse study of NF-kappaB translocation in 10,000 cells showed discernible oscillations in levels of nuclear NF-kappaB amongst cells when stimulated with interleukin (IL-1alpha), which suggests a small degree of synchronization amongst the cell population. When the kinetics for the phosphorylation of IkappaBalpha by IKK were measured, we found that the values for the affinity and catalytic efficiency of IKK2 for IkappaBalpha were dependent on assay conditions. The application of these kinetic parameters in our computational model of the NF-kappaB pathway resulted in significant differences in the oscillatory patterns of NF-kappaB depending on the rate constant value used. Hence, interpretation of in silico models should be made in the context of this uncertainty.

The ESAT6 protein of Mycobacterium tuberculosis induces apoptosis of macrophages by activating caspase expression

The secreted Mycobacterium tuberculosis protein, ESAT6, has been studied extensively in pathogenicity and vaccine experiments. Despite these studies little is known about the function of this protein. In this report, we demonstrate that ESAT6 induces apoptosis in THP-1 human macrophages using fluorescein isothiocyanate-Annexin V and intracellular caspase staining. We show that the induction of apoptosis by ESAT6 is dependent on the dose of the protein and the expression of caspase genes. Using real-time RT-PCR, we found that expression of caspase-1, -3, -5, -7 and -8 genes was upregulated in cells treated with ESAT6 relative to untreated cells. Furthermore, we show that while infection of THP-1 cells with wild-type M. tuberculosis strain H37Rv resulted in significant apoptosis 48 h post infection, a deletion mutant that does not express ESAT6 failed to induce significant apoptosis. Finally, experimental results using a cell impermeable fluorescent stain suggests that the formation of membrane pores may be a primary mechanism by which ESAT6 evokes an apoptotic response.

Quercetin blocks airway epithelial cell chemokine expression

Quercetin (3,3',4',5,7-pentahydroxyflavone), a dietary flavonoid, is an inhibitor of phosphatidylinositol (PI) 3-kinase and potent antioxidant. We hypothesized that quercetin blocks airway epithelial cell chemokine expression via PI 3-kinase-dependent mechanisms. Pretreatment with quercetin and the PI 3-kinase inhibitor LY294002 each reduced TNF-alpha-induced IL-8 and monocyte chemoattractant protein (MCP)-1 (also called CCL2) expression in cultured human airway epithelial cells. Quercetin also inhibited TNF-alpha-induced PI 3-kinase activity, Akt phosphorylation, intracellular H(2)O(2) production, NF-kappaB transactivation, IL-8 promoter activity, and steady-state mRNA levels, consistent with the notion that quercetin inhibits chemokine expression by attenuating NF-kappaB transactivation via a PI 3-kinase/Akt-dependent pathway. Quercetin also reduced TNF-alpha-induced chemokine secretion in the presence of the transcriptional inhibitor actinomycin D, while inducing phosphorylation of eukaryotic translation initiation factor (eIF)-2alpha, suggesting that quercetin attenuates chemokine expression by post-transcriptional as well as transcriptional mechanisms. Finally, we tested the effects of quercetin in cockroach antigen-sensitized and -challenged mice. These mice show MCP-1-dependent airways hyperresponsiveness and inflammation. Quercetin significantly reduced lung MCP-1 and methacholine responsiveness. We conclude that quercetin blocks airway cell chemokine expression via transcriptional and post-transcriptional pathways.

Mechanisms of suppression of nitric oxide production by 3-O-methylquercetin in RAW 264.7 cells

Rhamnus nakaharai Hayata (Rhamnaceae) is used as a folk medicine in Taiwan for treating constipation, inflammation, tumors, and asthma. 3-O-Methylquercetin (3-MQ), a main constituent of the plant, has been reported to have potential for use in the treatment of asthma. The mechanisms of anti-inflammation of 3-MQ are still unclear. Nitric oxide (NO) production induced by lipopolysaccharide (LPS) through iNOS expression in RAW 264.7 cells, a mouse macrophage cell line, may reflect the degree of inflammation and may provide a measure for assessing the effect of drugs on the inflammatory process. Therefore, we were interested in investigating the mechanisms of suppression of NO production by 3-MQ in RAW 264.7 cells. 3-MQ (1-10 microM) concentration-dependently inhibited LPS (100 ng/mL)-induced NO production in RAW 264.7 cells. The IC(50) value was calculated to be 4.23 microM. 3-MQ (1-10 microM) significantly and concentration-dependently inhibited LPS (100 ng/mL)-induced iNOS protein and mRNA expressions in cells. The IC(50) values were calculated to be 4.36 and 6.53 microM, respectively. There was no significant difference among these three IC(50) values of 3-MQ. In conclusion, 3-MQ may exert its anti-inflammatory effect through the inhibition of iNOS DNA transcription.

Neuroprotection following Fluid Percussion Brain Trauma: A Pilot Study Using Quercetin

Previously, we were able to demonstrate the neuroprotective effect of quercetin in an animal model of acute traumatic spinal cord injury. The objective of the present study was to determine whether any neuroprotective effect is seen when quercetin is administered in an animal model of traumatic brain injury. Twenty-six adult male Sprague-Dawley rats were submitted to moderate fluid percussion injury in the anterior midline position. Animals were divided into two experimental groups: one group received 25 mumol/kg quercetin starting 1 h after injury, while animals in the second group received saline vehicle (n = 13 per group). Eight animals were used as uninjured healthy controls. Eight animals in each experimental group were sacrificed at 24 h, while five animals per group were allowed to recover for 72 h following injury. Compound action potential amplitudes (CAPAs) were recorded on 400-microm vibrotome sections of the corpus callosum superfused with oxygenated artificial CSF (n = 3 per animal) in 20 experimental animals and five healthy controls. Three brains from animals in each experimental group and healthy controls were used for histological, immunocytochemical and biochemical analysis after sacrifice at 24 h. CAPAs in uninjured animals had a mean of 1.12 mV. This decreased to 0.55 mV in saline vehicle-treated injured animals by 24 h and changed little over the next 3 days. CAPAs were significantly better at 0.82 mV at 24 h and 0.76 mV at 3 days in quercetin-treated injured animals when compared to injured saline vehicle controls. Quercetin significantly prevented decrease of glutathione levels and decreased myeloperoxidase activity. We conclude that this dietary flavonoid has therapeutic potential following brain trauma.

Quercetin decreases oxidative stress, NF-kappaB activation, and iNOS overexpression in liver of streptozotocin-induced diabetic rats

Increasing evidence in both experimental and clinical studies suggests that oxidative stress is involved in the pathogenesis and progression of diabetic tissue damage. This study investigated the protective effects of quercetin treatment on oxidative stress, nuclear factor (NF)-kappaB activation and expression of inducible nitric oxide synthase (iNOS) in streptozotocin-induced diabetic rats. Male Wistar rats were divided into 4 groups: control rats, control rats treated daily with quercetin (150 micromol/kg, i.p.), untreated diabetic rats, and diabetic rats treated with quercetin. Diabetes was induced by a single i.p. injection of streptozotocin (70 mg/kg). Eight weeks later we measured TBARS and hydroperoxide-initiated chemiluminescence (QL) in liver as markers of oxidative stress, and activities of the antioxidant enzymes catalase, superoxide dismutase (SOD), and glutathione peroxidase, NF-kappaB activation by an electrophoretic mobility shift assay and expression of IkappaB kinases (IKKalpha and IKKbeta), the inhibitor IkappaB (IkappaBalpha and IkappaBbeta), and iNOS by Western blot. The plasma glucose concentration was significantly increased in diabetic rats and was not changed by quercetin. Streptozotocin administration induced significant increases in hepatic TBARS concentration, QL, and SOD and catalase activities that were prevented by quercetin. Activation of NF-kappaB, induction of IKKalpha and iNOS protein levels, and increased degradation of IkappaBalpha were also observed in streptozotocin-treated rats. All of those effects were abolished by quercetin. These findings suggest that quercetin treatment, by abolishing the IKK/NF-kappaB signal transduction pathway, may block the production of noxious mediators involved in the development of early diabetes tissue injury and in the evolution of late complications.

Quercetin attenuates nuclear factor-kappaB activation and nitric oxide production in interleukin-1beta-activated rat hepatocytes

We investigated whether different concentrations of the flavonoid quercetin ameliorate nitric oxide production and nuclear factor (NF)-kappaB activation in interleukin (IL)-1beta-activated rat hepatocytes. Primary cultures of rat hepatocytes were treated with IL-1beta alone or with quercetin in concentrations ranging from 5 to 100 micromol/L. The generation of reactive oxygen species, assessed by flow cytometry using dichlorodihydrofluorescein diacetate, was significantly reduced, and the oxidized:reduced glutathione ratio decreased in cultures treated with 50 and 100 micromol/L of quercetin. Quercetin at 100 micromol/L significantly prevented the IL-1beta-induced release of nitrite into the culture medium. Western blot and reverse transcription-PCR analyses demonstrated that increased levels of inducible nitric oxide synthase (iNOS) protein and mRNA in hepatocytes stimulated by IL-1beta were prevented by 50 micromol/L and 100 micromol/L of quercetin. Electrophoretic mobility shift assay experiments and Western blots indicated that quercetin blocked the activation of NF-kappaB and decreased the inhibitor kappaB protein levels induced by IL-1beta. In summary, quercetin, a natural flavonol widely distributed in the human diet, inhibits NO production in IL-1beta-stimulated hepatocytes through the inhibition of iNOS expression. Although the mode of action remains to be clarified, our findings support the view that the mechanism of action is via inhibition of IL-1beta-induced NF-kappaB activation.

Down-regulatory effect of quercitrin gallate on nuclear factor-kappa B-dependent inducible nitric oxide synthase expression in lipopolysaccharide-stimulated macrophages RAW 264.7

Quercetin 3-O-beta-(2''-galloyl)-rhamnopyranoside (QGR) is a naturally occurring quercitrin gallate, a polyphenolic compound isolated from Persicaria lapathifolia (Polygonaceae). In the present study, QGR compound was discovered to have inhibitory effect on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated macrophages RAW 264.7. QGR compound attenuated LPS-induced synthesis of both mRNA and protein of inducible nitric oxide synthase (iNOS), in parallel, and inhibited LPS-induced luciferase expression as a reporter of iNOS promoter activity in the macrophages. As a mechanism of the anti-inflammatory action shown by QGR compound, suppression of nuclear factor (NF)-kappaB activation has been documented. QGR compound exhibited inhibitory effect on LPS-mediated NF-kappaB transcriptional activity in macrophages RAW 264.7. Furthermore, the compound inhibited LPS-mediated nuclear translocation of NF-kappaB p65 and DNA binding activity of NF-kappaB complex, in parallel, but did not influence LPS-mediated IkappaBalpha degradation. Taken together, QGR compound suppressed LPS-mediated NF-kappaB activation, specifically to nuclear localization step of NF-kappaB p65, which was attributable to its down-regulatory action on LPS-induced NO production and iNOS expression.

Synthesis and structure-activity relationships of novel IKK-beta inhibitors. Part 2: Improvement of in vitro activity

A series of 2-amino-3-cyano-4-alkyl-6-(2-hydroxyphenyl)pyridine derivatives was synthesized and evaluated as IkappaB kinase beta (IKK-beta) inhibitors. Substitution of an aminoalkyl group for the aromatic group at the 4-position on the core pyridine ring resulted in a marked increase in both kinase enzyme and cellular potencies, and provided potent IKK-beta inhibitors with IC(50) values of below 100 nM.