Quercetin potentiates TNF-induced antiviral activity

Evaluation of Ameliorative Effect of Quercetin and Candesartan in Doxorubicin-Induced Cardiotoxicity

BACKGROUND

Several mechanisms have been explored for the anthracycline myocardial toxicity. These are free-radical generation, myocyte apoptosis, lipid peroxidation, mitochondrial deterioration, and direct repression of muscle-specific gene expression. Adriamycin (Doxorubicin) is a potent anti-cancer agent. Adriamycin in prolonged use is fatal and generates free radicals that lead to dose-dependent cardiac toxicity.

OBJECTIVE

The intent of the study was to explore the protective activity of candesartan and quercetin in cardiomyopathy induced by doxorubicin in rats.

METHODS

To induce cardiac toxicity, rats were intraperitoneally treated with doxorubicin (06 equivalent injections of 2.5 mg/kg, i. p. at 48 hour interval for 02 consecutive weeks to achieve a cumulative dose of 15 mg/kg). Individual and combined oral treatment of candesartan (5 mg/kg/day) and quercetin (10 mg/kg/day) was administered for four weeks.

RESULTS

Following cardiomyopathy, heart/body weight ratio (3.526 × 10^-3), serum creatine kinase (352.4±16.99 IU/L), lactate dehydrogenase (661.7±20.45 IU/L) levels were elevated in addition to altered lipid profile (TC - 118.4±4.25 mg/dL, TG - 263.3±9.99 mg/dL, VLDL - 52.66±1.99 mg/dL, LDL - 52.99±5.80 mg/dL and HDL - 12.78±0.36 mg/dL). The pre-cotreatment of candesartan and quercetin significantly restored the values to normal. The increased level of lipid peroxides (33.12±1.63 µmol/mg protein), serum troponin-T (1.82 ± 0.11 pg/mL) and nitric oxide (13.33±0.73 nmol/mg protein) level along with attenuating antioxidant profile, ie catalase, glutathione and superoxide dismutase (1.43±0.12 nmol/mg protein, 8.48±0.42 nmol/mg protein and 2.09±0.031 U/mg protein) were reversed to normal. Morphometry and histopathologic changes represented a beneficial effect of single and combination pre-cotreatment of drugs which significantly decreases adriamycin cardiac toxicity.

CONCLUSION

The overall result depicts more beneficial and cardioprotective effect of quercetin and candesartan combination as compared to their individual effects in doxorubicin treated animals. Therefore, this combination might be a suitable option to treat the cardiotoxic effect of doxorubicin.

The Protective Effects of Nutraceutical Components in Methotrexate-Induced Toxicity Models—An Overview

There are multiple concerns associated with methotrexate (MTX), widely recognized for anti-neoplastic and anti-inflammatory effects in life-threatening disease conditions, i.e., acute lymphoblastic leukemia, non-Hodgkin’s lymphoma, psoriasis, and rheumatoid arthritis, due to long-term side effects and associated toxicity, which limits its valuable potential. MTX acts as an inhibitor of dihydrofolate reductase, leading to suppression of purine and pyrimidine synthesis in high metabolic and turnover cells, targeting cancer and dysregulated immune cells. Due to low discrimination between neoplastic cells and naturally high turnover cells, MTX is prone to inhibiting the division of all fast-dividing cells, causing toxicity in multiple organs. Nutraceutical compounds are plant-based or food-derived compounds, used for their preventive and therapeutic role, ascertained in multiple organ dysfunctions, including cardiovascular disease, ischemic stroke, cancer, and neurodegenerative diseases. Gut microbiota and microbiota-derived metabolites take part in multiple physiological processes, their dysregulation being involved in disease pathogenesis. Modulation of gut microbiota by using nutraceutical compounds represents a promising therapeutic direction to restore intestinal dysfunction associated with MTX treatment. In this review, we address the main organ dysfunctions induced by MTX treatment, and modulations of them by using nutraceutical compounds. Moreover, we revealed the protective mechanisms of nutraceuticals in MTX-induced intestinal dysfunctions by modulation of gut microbiota.

Therapeutic Potential of Nutraceuticals and Dietary Supplements in the Prevention of Viral Diseases: A Review

Nowadays, despite enormous scientific advances, viral diseases remain the leading cause of morbidity worldwide, and their potential to spread is escalating, eventually turning into pandemics. Nutrition can play a major role in supporting the immune system of the body and for the optimal functioning of the cells of the immune system. A healthy diet encompassing vitamins, multi-nutrient supplements, functional foods, nutraceuticals, and probiotics can play a pivotal role in combating several viral invasions in addition to strengthening the immune system. This review provides comprehensive information on diet-based scientific recommendations, evidence, and worldwide case studies in light of the current pandemic and also with a particular focus on virus-induced respiratory tract infections. After reviewing the immune potential of nutraceuticals based on the lab studies and on human studies, it was concluded that bioactive compounds such as nutraceuticals, vitamins, and functional foods (honey, berries, etc.) with proven antiviral efficacy, in addition to pharmaceutical medication or alone as dietary supplements, can prove instrumental in treating a range of virus-induced infections in addition to strengthening the immune system. Milk proteins and peptides can also act as adjuvants for the design of more potent novel antiviral drugs.

Effectiveness of supplementation with quercetin-type flavonols for treatment of viral lower respiratory tract infections: Systematic review and meta-analysis of preclinical studies

Viral infections of the lower respiratory tract are considered a public health problem. They affect millions of people worldwide, causing thousands of deaths, and are treated with expensive medicines, such as antivirals or palliative measures. In this study, we conducted a systematic review to describe the use of quercetin‐type flavonols against lower respiratory tract viruses and discussed the preclinical impact of this approach on different signs and clinical mechanisms of infection. The systematic review was performed in PubMed/MEDLINE, Scopus, Scielo, and Biblioteca Virtual de Saúde (BVS). After the database search, 11 relevant studies were identified as eligible. The analysis of these studies showed evidence of antiviral activity of quercetin‐type flavonols with significantly reduced mortality rate (M‐H = 0.19, 95% CI: 0.05 to 0.65, p‐value = 0.008) of infected animals and a reduction in the average viral load (IV = −1.93, 95% CI: −3.54 to −0.31, p‐value = 0.02). Additionally, quercetin and its derivatives reduced the amount of proinflammatory cytokines, chemokines, reactive oxygen species, mucus production, and airway resistance in animals infected with a respiratory virus. Overall, supplementation with quercetin‐type flavonols is a promising strategy for treating viral‐induced lower respiratory tract infections.

Perspectives on plant flavonoid quercetin-based drugs for novel SARS-CoV-2

Background

The world pandemic COVID-19 caused by SARS-CoV-2 is currently claiming thousands of lives. Flavonoids abundantly present in the fruits and vegetables, especially quercetin, are shown to have antiviral activities.

Main text

This paper reviews the capability of the plant flavonoid quercetin to fight the novel coronavirus and the possibility for drug development based on this. The mode of action explaining the known pathways through which this molecule succeeds in the antiviral activity, action of quercetin on SARS-CoV-2 main protease 3CL^pro, antiviral activities of its derivatives on human viruses, effect of combination of zinc co-factor along with quercetin in the COVID-19 treatment, and the regulation of miRNA genes involved in the viral pathogenesis are discussed. Proof for this concept is provided following the virtual screening using ten key enzymes of SARS-CoV-2 and assessing their interactions. Active residues in the 3D structures have been predicted using CASTp and were docked against quercetin. Key proteins 3CL^pro, spike glycoprotein/ human ACE2-BOAT1 complex, RNA-dependent RNA polymerase, main peptidase, spike glycoprotein, RNA replicase, RNA binding protein, papain-like protease, SARS papain-like protease/ deubiquitinase, and complex of main peptidase with an additional Ala at the N-terminus of each protomer, have shown the binding energies ranging between − 6.71 and − 3.37 kcal/ Mol, showing that quercetin is a potential drug candidate inhibiting multiple SARS-CoV-2 enzymes.

Conclusion

The antiviral properties of flavonoid and the molecular mechanisms involved are reviewed. Further, proof for this concept is given by docking of key proteins from SARS-CoV-2 with quercetin.

Graphical abstract

Host-Directed Antiviral Therapy

Antiviral drugs have traditionally been developed by directly targeting essential viral components. However, this strategy often fails due to the rapid generation of drug-resistant viruses. Recent genome-wide approaches, such as those employing small interfering RNA (siRNA) or clustered regularly interspaced short palindromic repeats (CRISPR) or those using small molecule chemical inhibitors targeting the cellular "kinome," have been used successfully to identify cellular factors that can support virus replication. Since some of these cellular factors are critical for virus replication, but are dispensable for the host, they can serve as novel targets for antiviral drug development. In addition, potentiation of immune responses, regulation of cytokine storms, and modulation of epigenetic changes upon virus infections are also feasible approaches to control infections. Because it is less likely that viruses will mutate to replace missing cellular functions, the chance of generating drug-resistant mutants with host-targeted inhibitor approaches is minimized. However, drug resistance against some host-directed agents can, in fact, occur under certain circumstances, such as long-term selection pressure of a host-directed antiviral agent that can allow the virus the opportunity to adapt to use an alternate host factor or to alter its affinity toward the target that confers resistance. This review describes novel approaches for antiviral drug development with a focus on host-directed therapies and the potential mechanisms that may account for the acquisition of antiviral drug resistance against host-directed agents.

Quercetin Is a Flavonoid Breast Cancer Resistance Protein Inhibitor with an Impact on the Oral Pharmacokinetics of Sulfasalazine in Rats

The potential inhibitory effect of quercetin, a major plant flavonol, on breast cancer resistance protein (BCRP) activity was investigated in this study. The presence of quercetin significantly increased the cellular accumulation and associated cytotoxicity of the BCRP substrate mitoxantrone in human cervical cancer cells (HeLa cells) in a concentration-dependent manner. The transcellular efflux of prazosin, a stereotypical BCRP substrate, was also significantly reduced in the presence of quercetin in a bidirectional transport assay using human BCRP-overexpressing cells; further kinetic analysis revealed IC₅₀ and Ki values of 4.22 and 3.91 μM, respectively. Moreover, pretreatment with 10 mg/kg quercetin in rats led to a 1.8-fold and 1.5-fold increase in the AUC_8h (i.e., 44.5 ± 11.8 min∙μg/mL vs. 25.7 ± 9.98 min∙μg/mL, p < 0.05) and C_max (i.e., 179 ± 23.0 ng/mL vs. 122 ± 23.2 ng/mL, p < 0.05) of orally administered sulfasalazine, respectively. Collectively, these results provide evidence that quercetin acts as an in vivo as well as in vitro inhibitor of BCRP. Considering the high dietary intake of quercetin as well as its consumption as a dietary supplement, issuing a caution regarding its food-drug interactions should be considered.

Flavonoids as detoxifying and pro-survival agents: What's new?

The role of flavonoids in the survival machinery of cells has come in the spotlight due to the recent evidence of their effect on the relationship mitochondria-ER stress-proteasome, including the intracellular mechanisms of autophagy and apoptosis. Numerous experimental animal investigations and even human clinical studies have highlighted the major role of these natural compounds in the economy of life and their deep relationship with autotrophic organisms in the evolutionary space. Their role as anti-oxidant and oxidative stress preventive molecules has to date been investigated extensively in the literature. Despite this great amount of promising evidence, many concerns, however, remain, most of which dealing with biochemistry, bioavailability, pharmacokinetics, and interaction of flavonoids with gut microbiome, issues that make difficult any good attempt to introduce these molecules in the human healthcare systems as possible, encouraging therapeutic substances. This review tries to address and elucidate these items.

Bioactive effects of quercetin in the central nervous system: Focusing on the mechanisms of actions

Quercetin, a ubiquitous flavonoid that is widely distributed in plants is classified as a cognitive enhancer in traditional and oriental medicine. The protective effects of quercetin for the treatment of neurodegenerative disorders and cerebrovascular diseases have been demonstrated in both in vitro and in vivo studies. The free radical scavenging activity of quercetin has been well-documented, wherein quercetin has been observed to exhibit protective effects against oxidative stress mediated neuronal damage by modulating the expression of NRF-2 dependent antioxidant responsive elements, and attenuation of neuroinflammation by suppressing NF-κB signal transducer and activator of transcription-1 (STAT-1). Several in vitro and in vivo studies have also shown that quercetin destabilizes and enhances the clearance of abnormal protein such as beta- amyloid peptide and hyperphosphorlyated tau, the key pathological hallmarks of Alzheimer's disease. Quercetin enhances neurogenesis and neuronal longevity by modulating a broad number of kinase signaling cascades such as phophoinositide 3- kinase (P13-kinase), AKT/PKB tyrosine kinase and Protein kinase C (PKC). Quercetin has also been well reported for its ability to reverse cognitive impairment and memory enhancement during aging. The current review focuses on summarizing the recent findings on the neuroprotective effect of quercetin, its mechanism of action and its possible roles in the prevention of neurological disorders.

Development of photoactivable glycerol-based coatings containing quercetin for antibacterial applications

Synthesis of antibacterial coatings derived from glycerol and quercetin for the inhibition of bacteria proliferation.

Quercetin-POM (pivaloxymethyl) conjugates: Modulatory activity for P-glycoprotein-based multidrug resistance

BACKGROUND

We previously demonstrated that the bioactivity of quercetin could be improved through conjugation with a hydrolysable pivaloxymethyl (POM) group.

PURPOSE

Present study aimed to evaluate MDR (multidrug resistance)-modulatory activity of the quercetin-POM conjugates.

STUDY DESIGN/METHODS

MDR-modulatory activity was determined by measuring cytotoxicity of various anticancer agents to MDR MES-SA/Dx5 cell lines upon combination with the quercetin-POM conjugates.

RESULTS

The quercetin-7-O-POM conjugate (7-O-POM-Q) was significantly more potent than quercetin in reversing MDR, which recovered the cytotoxicity of various anticancer agents with EC50 values of 1.1-1.3 µM. A series of mechanistic studies revealed that 7-O-POM-Q competes with verapamil in binding to the same drug-binding site of the major MDR target, Pgp (P-glycoprotein), and inhibits Pgp-mediated drug efflux with a similar potency as verapamil. The physicochemical properties of 7-O-POM-Q were then evaluated, which confirmed that 7-O-POM-Q has remarkably enhanced cellular uptake and intracellular localization compared with quercetin. Additionally, it is noteworthy that 7-O-POM-Q undergoes slow hydrolysis to quercetin over a prolonged period of time.

CONCLUSION

The quercetin-POM conjugate showed significantly improved MDR-reversing activity compared with quercetin, which could be attributed to its capacity to maintain high intracellular concentrations.

LC-ESI-MS/MS analysis of quercetin in rat plasma after oral administration of biodegradable nanoparticles

A simple, rapid and sensitive LC-MS/MS method was developed and validated for the determination of free quercetin in rat plasma, using fisetin as internal standard. The detection was performed by negative ion electrospray ionization under selected reaction monitoring. Chromatographic separation (isocratic elution) was carried out using acetonitrile-10 m m ammonium formate (80:20, v/v) with 0.1% v/v formic acid. The lower limit of quantification (4.928 ng/mL) provided high sensitivity for the detection of quercetin in rat plasma. The linearity range was from 5 to 2000 ng/mL. Intra- and inter-day variability (RSD) of quercetin extraction from rat plasma was <4.19 and 1.37% with accuracies of 98.77 and 99.67%. The method developed was successfully applied for estimating free quercetin in rat plasma, after oral administration of quercetin-loaded biodegradable nanoparticles (QLN) and quercetin suspension. QLN (C(max), 1277.34 ± 216.67 ng/mL; AUC, 17,458.25 ± 3152.95 ng hr/mL) showed a 5.38-fold increase in relative bioavailability as compared with quercetin suspension (C(max), 369.2 ± 108.07 ng/mL; AUC, 3276.92 ± 396.67 ng hr/mL).

Anti-infective and cytotoxic properties of Bupleurum marginatum

Background

Bupleurum marginatum Wall. ex DC (Apiaceae) is a perennial herb widely used in traditional Chinese and Kampo medicine for the treatment of various infectious diseases. The biological activities of B. marginatum have not been fully investigated. This study aims to investigate the antitrypanosomal, antimicrobial and antiviral activities of methanol (ME) and dichloromethane (DCM) extracts of B. marginatum aerial parts and the ability of both extracts to inhibit the growth of different cancer cell lines.

Methods

Phytochemical characterization of the extracts was performed by LC-MS profiling. The antitrypanosomal activity was evaluated using the resazurin method. The antimicrobial activity was assessed using agar diffusion and microdilution methods, and the minimum inhibitory concentration (MIC) values were determined. The antiviral activity was determined for 6.25, 12.5, and 50 μg/mL doses using a plaque reduction assay. Cytotoxicity was investigated in eight cancer cell lines (Caco-2, CCL-81, CCRF-CEM, COS-7, HL-60, MIA PaCa-2, MCF-7, and PANC-1) using the MTT assay and the caspase 3/7 activity was determined over the range of 62.5–1000 μg/mL.

Results

Phytochemical analyses resulted in the characterization of 15 components, mainly flavonoids and lignans. The DCM extract showed significant antitrypanosomal activity (IC₅₀: 36.21 μg/mL) and moderate activity against Streptococcus pyogenes (MIC value: 0.25 mg/mL). At a dose of 12.5 μg/mL, the DCM extract inhibited 73.6% of the plaque production by hepatitis A virus. CCRF-CEM cells were the most sensitive to both extracts (IC₅₀: 12.5–22.7 μg/mL). The cytotoxicity was mediated by induction of apoptosis (19-fold increase in the cellular caspase 3/7 level after treatment with the DCM extract at 1 mg/mL).

Conclusions

ME and DCM extract of B. marginatum showed anti-infective and antiproliferative effects.

Novel self-emulsifying formulation of quercetin for improved in vivo antioxidant potential: implications for drug-induced cardiotoxicity and nephrotoxicity

Quercetin (QT) was formulated into a novel self-emulsifying drug delivery system (SEDDS) to improve its oral bioavailability and antioxidant potential compared to free drug. Capmul MCM was selected as the oily phase on the basis of optimum solubility of QT in oil. Tween 20 and ethanol were selected as surfactant and cosurfactant from a large pool of excipients, depending upon their spontaneous self-emulsifying ability with the selected oily phase. Pseudoternary-phase diagrams were constructed to identify the efficient self-emulsification regions in various dilution media, viz., water, pH 1.2, and pH 6.8. The ratio of 40:40:20 w/w, Capmul MCM:QT (19:1)/Tween 20/ethanol was optimized based on its ability to form a spontaneous submicrometer emulsion in simulated gastrointestinal fluids. DPPH scavenging assay showed comparable antioxidant activity of QT-SEDDS to free QT. QT-SEDDS was robust in terms of stability against short-term excursion of freeze/thaw cycles and accelerated stability for 6 months as per International Conference on Harmonisation guidelines. A fluorescent dye-loaded SEDDS formulation showed rapid internalization within 1h of incubation with Caco-2 cells as evident by confocal laser scanning microscopy. QT-SEDDS showed a significant increase in cellular uptake by 23.75-fold in comparison with free QT cultured with Caco-2 cells. The SEDDS demonstrated ~5-fold enhancement in oral bioavailability compared to free QT suspension. The in vitro-in vivo relation between in vitro Caco-2 cell uptake and in vivo pharmacokinetics of QT-SEDDS showed a correlation coefficient of ~0.9961, as evident from a Levy plot. Finally, QT-SEDDS showed a significantly higher in vivo antioxidant potential compared to free QT when evaluated as a function of ability to combat doxorubicin- and cyclosporin A-induced cardiotoxicity and nephrotoxicity, respectively.

Inclusion complexes of quercetin with three β-cyclodextrins derivatives at physiological pH: spectroscopic study and antioxidant activity

Properties of the inclusion complexes of quercetin (QUE) with sulfobutyl ether-β-cyclodextrin (SBE-β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and methylated-β-cyclodextrin (M-β-CD) in tris-HCl buffer solutions of pH 7.40 were investigated. The stoichiometry and thermodynamic parameters for the complexation process (stability constants K, Gibbs free energy change ΔG, enthalpy change ΔH and entropy change ΔS) were determined using phase-solubility and fluorescence spectra analysis. The thermodynamic studies indicated that the inclusion reactions between QUE and the three β-CDs are enthalpy-driven processes. Proton nuclear magnetic resonance spectroscopy indicated that B-ring, C-ring, and part of A-ring of QUE interact with the cavity of β-CDs. The antioxidant activity of QUE and its inclusion complexes were determined by the scavenging of stable radical DPPH(*). The results showed that the complexed QUE/CDs were more effective than free QUE, with the QUE/SBE-β-CD complex as the best form.

Flavonoid-metal ion complexes: a novel class of therapeutic agents

Flavonoids are among the most investigated phytochemicals due to their pharmacological and therapeutic activities. Their ability to chelate with metal ions has resulted in the emergence of a new category of molecules with a broader spectrum of pharmacological activities. However, the biological significance of these flavonoid-metal ion complexes is yet to be completely explored. Moreover, no concerted efforts have been made to elucidate their molecular targets and mechanisms of action. This review attempts to provide a snapshot of the various biological activities reported for flavonoid-metal ion complexes and their potential as therapeutic agents. Understanding the mechanism of action and the influence of structure will provide a strong basis to design novel flavonoid-metal ion complexes of therapeutic significance.

Separation of quercetin's biological activity from its oxidative property through bioisosteric replacement of the catecholic hydroxyl groups with fluorine atoms

An oxidative property has endowed quercetin with numerous biological benefits, and some of quercetin's biological activities may be related, at least partly, to its antioxidant activity. On the other hand, the oxidative property and associated susceptibility to oxidative decomposition has hampered in-depth investigation of the biological targets as well as underlying mechanisms for quercetin's biological activity. This study was undertaken to separate quercetin's biological activities from its antioxidant properties through bioisosteric replacement of the phenolic hydroxyl groups. The novel quercetin derivative 3',4'-difluoroquercetin (2), thus prepared, showed nonoxidizable property with no attenuation of biological activity. Rather, 2 showed a subtle but significant increase in biological activity compared with quercetin, which might be attributed to its lack of oxidative property. The nonoxidizable nature along with the potent biological activity of the quercetin mimic 2 suggests possible oxidation-independent mechanisms for the biological activities of the quercetin that do not require oxidative formation of the highly electrophilic metabolites.

Treating acute cystitis with biodegradable micelle-encapsulated quercetin

Intravesical application of an anti-inflammatory drug is an efficient strategy for acute cystitis therapy. Quercetin (QU) is a potent anti-inflammatory agent; however, its poor water solubility restricts its clinical application. In an attempt to improve water solubility of QU, biodegradable monomethoxy poly(ethylene glycol)-poly(ɛ-caprolactone) (MPEG-PCL) micelles were used to encapsulate QU by self-assembly methods, creating QU/MPEG-PCL micelles. These QU/MPEG-PCL micelles with DL of 7% had a mean particle size of <34 nm, and could release QU for an extended period in vitro. The in vivo study indicated that intravesical application of MPEG-PCL micelles did not induce any toxicity to the bladder, and could efficiently deliver cargo to the bladder. Moreover, the therapeutic efficiency of intravesical administration of QU/MPEG-PCL micelles on acute cystitis was evaluated in vivo. Results indicated that QU/MPEG-PCL micelle treatment efficiently reduced the edema and inflammatory cell infiltration of the bladder in an Escherichia coli-induced acute cystitis model. These data suggested that MPEG-PCL micelle was a candidate intravesical drug carrier, and QU/MPEG-PCL micelles may have potential application in acute cystitis therapy.

Cytotoxicity, antiviral and antimicrobial activities of alkaloids, flavonoids, and phenolic acids

OBJECTIVE

Some natural products consisting of the alkaloids yohimbine and vincamine (indole-type), scopolamine and atropine (tropane-type), colchicine (tropolone-type), allantoin (imidazolidine-type), trigonelline (pyridine-type) as well as octopamine, synephrine, and capsaicin (exocyclic amine-type); the flavonoid derivatives quercetin, apigenin, genistein, naringin, silymarin, and silibinin; and the phenolic acids namely gallic acid, caffeic acid, chlorogenic acid, and quinic acid, were tested for their in vitro antiviral, antibacterial, and antifungal activities and cytotoxicity.

MATERIALS AND METHODS

Antiviral activity of the compounds was tested against DNA virus herpes simplex type 1 and RNA virus parainfluenza (type-3). Cytotoxicity of the compounds was determined using Madin-Darby bovine kidney and Vero cell lines, and their cytopathogenic effects were expressed as maximum non-toxic concentration. Antibacterial activity was assayed against following bacteria and their isolated strains: Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Acinetobacter baumannii, Staphylococcus aureus, Enterococcus faecalis, and Bacillus subtilis, although they were screened by microdilution method against two fungi: Candida albicans and Candida parapsilosis.

RESULTS

Atropine and gallic acid showed potent antiviral effect at the therapeutic range of 0.8-0.05 µg ml(-1), whilst all of the compounds exerted robust antibacterial effect.

CONCLUSION

Antiviral and antimicrobial effects of the compounds tested herein may constitute a preliminary step for further relevant studies to identify the mechanism of action.

Enhanced stability and intracellular accumulation of quercetin by protection of the chemically or metabolically susceptible hydroxyl groups with a pivaloxymethyl (POM) promoiety

In order to increase stability of quercetin, its metabolically and chemically susceptible hydroxyl groups 7-OH and 3-OH respectively were transiently blocked with a pivaloxymethyl (POM) promoiety to provide two novel quercetin conjugates [7-O-POM-Q, 3-O-POM-Q]. In the absence of stabilizer (ascorbic acid), the synthesized conjugates showed significantly increased stability in cell culture media [t(½) = 4 h, 52 h] compared with quercetin (t(½) < 30 min) and quercetin prodrug 1 (t(½) = 0.8 h). In addition, the quercetin conjugate 2 underwent efficient cellular uptake and intracellular levels of its hydrolysis product, quercetin, were maintained up to 12 h. Stability and intracellular accumulation of were demonstrated by its stabilizer-independent cytostatic effect and induction of apoptotic cell death. Even though was more stable than, it failed to penetrate cell membranes. However, the remarkable stability of warrants further investigation of quercetin conjugates with various promoieties at the 3-OH position.

Effect of quercetin on nicotine-induced biochemical changes and DNA damage in rat peripheral blood lymphocytes

We elucidated the protective effect of quercetin, a polyphenolic flavonoid, on lipid peroxidation, endogenous antioxidant status and DNA damage during nicotine-induced toxicity in cultured rat peripheral blood lymphocytes as compared to N-acetylcysteine (NAC), a well-known antioxidant. Lymphocytes were exposed to nicotine (3 mM) with and without quercetin and NAC (1 mM) in RPMI-1640 medium for 1 h. In preliminary experiments to fix the effective dose of quercetin, different doses of quercetin (25, 50, 75, 100 and 200 microM) were administered to lymphocytes with nicotine, and lipid peroxidation markers (thiobarbituric acid reactive substances and hydroperoxides) were analysed. A 75 microM dose of quercetin was found to be effective as evidenced by decreased lipid peroxidation. To evaluate the protective potential of quercetin against genotoxic effects of nicotine we used comet and micronucleus assays, which are valid parameters to assess genetic damage. In addition, biochemical changes including lipid peroxidation and antioxidant status were assessed. There were significant increases in the levels of lipid peroxidation, comet parameters and micronuclei frequencies, followed by decrease in the endogenous antioxidant status, in nicotine-treated lymphocytes, which were brought back to near normal by quercetin or NAC treatment. The protective effect of quercetin against nicotine toxicity was comparable to that of NAC. These findings suggest that quercetin can be as effective as NAC in protecting rat peripheral lymphocytes against nicotine-induced cellular and DNA damage.

Antiviral and Antimicrobial Evaluation of Some Heterocyclic Compounds from Turkish Plants

Antibiotic resistance has become a problem since the discovery of antibiotics. Not long after the introduction of penicillin, Staphylococcus aureus, which can be also transmitted to humans via milk and milk products, began developing penicillin-resistant strains. Therefore, one approach that has been used for the discovery of new antimicrobial agents from natural sources is based on the evaluation of traditional plant extracts. Natural products have played a pivotal role in antibiotic drug innovation and include aminoglycosides, cephalosporins, macrolides, cycloserine, novobiocin, and lipoproteins. However, only a few antiviral agents are available on the market. To this purpose, we have screened a great number of herbal extracts along with some pure natural substances and obtained interesting findings. This chapter covers the results of our rigorous search for new antiviral and antimicrobial alternative compounds from a number of Turkish plants.

Marked decrease of cyclosporin bioavailability caused by coadministration of ginkgo and onion in rats

Quercetin was reported to modulate CYP isoenzymes and P-glycoprotein (Pgp), a drug efflux transporter. Our previous study reported that quercetin significantly decreased the bioavailability of cyclosporin, a substrate for CYP3A4 and Pgp, in rats and pigs. Ginkgo and onion contain quercetin and its glycosides as St. John's Wort. The coadministration of cyclosporin with ginkgo or onion may be subject to clinically relevant interactions as St. John's Wort. Therefore, this study aimed to investigate the influences of ginkgo and onion on the absorption and disposition of cyclosporin in rats. Cyclosporin was administered orally and intravenously to rats with and without an oral dose of ginkgo or onion in crossover designs. Blood samples were collected via cardiopuncture and blood cyclosporin concentration was assayed by a specific monoclonal fluorescence polarization immunoassay. Everted gut sac was used to investigate the effects of ginkgo and onion on the function of intestinal Pgp. Oral coadministration of ginkgo and onion significantly decreased the Cmax of cyclosporin by 62% and 60%, and reduced the AUC0-t by 51% and 68%, respectively, whereas no influence was observed when cyclosporin was given intravenously. This indicates that the interactions between cyclosporin and ginkgo or onion occurred mainly at the absorption site. In conclusion, ginkgo and onion markedly decreased the oral bioavailability of cyclosporin. We suggest that concurrent intake of quercetin-rich herbs or foods with cyclosporin are better avoided in order to ensure the efficacy of cyclosporin.

Antispasmodic saponins from bulbs of red onion, Allium cepa L. var. Tropea

A phytochemical analysis of the polar extract from the red bulbs of Allium cepa L. var. Tropea, typical of Calabria, a southern region of Italy, was performed extensively for the first time, leading to the isolation of four new furostanol saponins, named tropeoside A1/A2 (1a/1b) and tropeoside B1/B2 (3a/3b), along with the respective 22-O-methyl derivatives (2a/2b and 4a/4b), almost certainly extraction artifacts. High concentrations of ascalonicoside A1/A2 (5a/5b) and ascalonicoside B (6), previously isolated from Allium ascalonicum Hort., were also found. This is the first report of furostanol saponins in this A. cepa variety. The chemical structures of the new compounds were established through a combination of extensive nuclear magnetic resonance, mass spectrometry and chemical analyses. High concentrations of quercetin, quercetin 4(I)-glucoside, taxifolin, taxifolin 7-glucoside, and phenylalanine were also isolated. The new saponins were found to possess antispasmodic activity in the guinea pig isolated ileum; such an effect might contribute to explaining the traditional use of onion in the treatment of disturbances of the gastrointestinal tract.

Profound difference in pharmacokinetics between morin and its isomer quercetin in rats

Morin and quercetin are isomeric antioxidant flavonols widely distributed in plant foods and herbs. The pharmacokinetics of both flavonols at two doses were investigated and compared in rats. Parent forms and their glucuronides and sulfates in serum were determined by HPLC before and after enzymatic hydrolysis, respectively. After oral dosing of morin, both the parent form, morin, and its glucuronides and sulfates were present in the bloodstream. The conjugated metabolites predominated at the dose of 25 mg kg(-1), whereas the parent form was predominant at the dose of 50 mg kg(-1). Moreover, the AUC of morin parent form increased by a factor of 37 when the dose doubled, indicating that morin showed nonlinear pharmacokinetics. On the other hand, quercetin presented only as glucuronides and sulfates in the blood, indicating negligible bioavailability of quercetin, and the metabolites showed linear pharmacokinetics at the two doses studied. When considering the total AUC of parent form with conjugated metabolites, the extent of absorption of morin was 3 fold that of quercetin at the dose of 50 mg kg(-1). The results indicated that the difference in hydroxylation pattern on B-ring of flavonol markedly affected their fates in rats.

The flavonoid, quercetin, differentially regulates Th-1 (IFNgamma) and Th-2 (IL4) cytokine gene expression by normal peripheral blood mononuclear cells

Flavonoids are plant metabolites that are dietary antioxidants and exert significant anti-tumor, anti-allergic, anti-inflammatory and anti-viral effects. It is generally accepted that Th-1 derived cytokines such as IL-2, IFNgamma and IL-12 promote cellular immunity while Th-2 derived cytokines such as IL-4, IL-5, IL-6 exert negative immunoregulatory effects on cellular immunity while upregulating humoral immunity. The molecular mechanisms underlying the biological activities of flavonoids have not been elucidated. We hypothesize that the flavonoid, quercetin, exert significant anti-viral and anti-tumor effects possibly by modulating the production of Th-1 and Th-2 derived cytokines. Peripheral blood mononuclear cells (PBMC, 1 x 10(6) cells/ml) from normal subjects were cultured with different concentrations of quercetin (0.5-50 microM) for 24-72 h and supernates were quantitated for IFN-gamma and IL-4 by ELISA and antiviral activity of IFNgamma by bioassay. FACS analysis was done to determine the number of IFN-gamma and IL-4 positive cells and RT-PCR was done to quantitate gene expression. Quercetin significantly induces the gene expression as well as the production of Th-1 derived IFNgamma and the downregulates Th-2 derived IL-4 by normal PBMC. Further, quercetin treatment increased the phenotypic expression of IFNgamma cells and decreased IL-4 positive cells by FACS analysis, which corroborate with protein secretion and gene expression studies. These results suggest that the beneficial immuno-stimulatory effects of quercetin may be mediated through the induction of Th-1 derived cytokine, IFNgamma, and inhibition of Th-2 derived cytokine, IL-4.

Quercetin significantly decreased cyclosporin oral bioavailability in pigs and rats

Cyclosporin, an immunosuppressant with a narrow therapeutic window, is a substrate for both CYP3A4 and P-glycoprotein (Pgp). Quercetin is an inhibitor of CYP3A4 and a modulator of Pgp. This study aimed to measure the effect of quercetin on the absorption and disposition of cyclosporin in pigs and rats. Cyclosporin (Sandimmune, 10 mg/kg) was orally administered with and without a concomitant dose of quercetin (50 mg/kg) to pigs and rats. Cyclosporin concentrations in blood samples were determined by a specific monoclonal fluorescence polarization immunoassay. The pharmacokinetic parameters were calculated by noncompartmental analysis using WINNONLIN. A paired Student's t-test was conducted for statistical comparison. A study using the everted intestinal sac was carried out to evaluate the effect of quercetin on the function of intestinal Pgp. The coadministration of quercetin significantly decreased cyclosporin AUC(0-3) (area under the concentration-time curve from time zero to 3 h) by 56% and AUC(0-t) (area under the concentration-time curve from time zero to the last point) by 43% in pigs and rats, respectively, indicating that the coadministration of quercetin significantly decreased cyclosporin oral bioavailability. However, the inverted sac study showed that quercetin significantly inhibited the function of intestinal Pgp. It is suggested that concurrent use of quercetin or quercetin-containing dietary supplement or herbs with cyclosporin or other medications whose absorption and metabolism are mediated by Pgp and/or CYP3A4 should require close monitoring.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Inactivation of HSV-1 and HSV-2 and prevention of cell-to-cell virus spread by Santolina insularis essential oil

The essential oil obtained in toto from Santolina insularis was investigated for its antiviral activity on herpes simplex type 1 (HSV-1) and type 2 (HSV-2) in vitro. The IC(50) values, determined by plaque reduction assays, were 0.88 and 0.7 microg/ml for HSV-1 and HSV-2, respectively, while the CC(50) determined by the MTT test on Vero cells was 112 microg/ml, indicating a CC(50)/IC(50) ratio of 127 for HSV-1 and 160 for HSV-2. Results obtained by plaque reduction assays also indicated that the antiviral activity of S. insularis was principally due to direct virucidal effects. Antiviral activity against HSV-1 and HSV-2 was not observed in a post-attachment assay, and attachment assays indicated that virus adsorption was not inhibited. Up to 80% inhibition of HSV-1 was achieved at the concentration of 40 microg/ml by yield reduction assay. Furthermore, reduction of plaque formation assays also showed that S. insularis essential oil inhibits cell-to-cell transmission of both HSV-1 and HSV-2.

Review of the biology of Quercetin and related bioflavonoids

The French paradox is a dietary anomaly which has focused attention on the Mediterranean diet. Epidemiological studies revealed that this diet, replete in flavonoid-rich foods (Allium and Brassica vegetables, and red wine), correlated with the increased longevity and decreased incidence of cardiovascular disease seen in these populations. The most frequently studied flavonoid, quercetin, has been shown to have biological properties consistent with its sparing effect on the cardiovascular system. Quercetin and other flavonoids have been shown to modify eicosanoid biosynthesis (antiprostanoid and anti-inflammatory responses), protect low-density lipoprotein from oxidation (prevent atherosclerotic plaque formation), prevent platelet aggregation (antithrombic effects), and promote relaxation of cardiovascular smooth muscle (antihypertensive, antiarrhythmic effects). In addition, flavonoids have been shown to have antiviral and carcinostatic properties. However, flavonoids are poorly absorbed from the gut and are subject to degradation by intestinal micro-organisms. The amount of quercetin that remains biologically available may not be of sufficient concentration, theoretically, to explain the beneficial effects seen with the Mediterranean diet. The role of flavonoids may transcend their presence in food. The activity of flavonoids as inhibitors of reverse transcriptase suggests a place for these compounds in the control of retrovirus infections, such as acquired immunodeficiency syndrome (AIDS). In addition to specific effects, the broad-modulating effects of flavonoids as antioxidants, inhibitors of ubiquitous enzymes (ornithine carboxylase, protein kinase, calmodulin), and promoters of vasodilatation and platelet disaggregation can serve as starting material for drug development programmes.