Action of 3-methylquercetin on poliovirus RNA replication

Unravelling the Immune Modulatory Effect of Indian Spices to Impede the Transmission of COVID-19: A Promising Approach

Months after WHO declared COVID-19 as a Global Public Health Emergency of International Concern, it does not seem to be flattening the curve as we are still devoid of an effective treatment modality and vaccination is in the first phase in many countries. Amid such uncertainty, being immune is the best strategy to defend against corona attacks. As the whole world is referring back to immune-boosting traditional remedies, interest is rekindled in the Indian system of Medicine, which is gifted with an abundance of herbal medicines as well as remedies. Among them, spices (root, rhizome, seed, fruit, leaf, bud, and flower of various plants used to add taste and flavors to food) are bestowed with immense medicinal potential. A plethora of clinical as well as preclinical studies reported the effectiveness of various spices for various ailments. The potential immune-boosting properties together with their excellent safety profiles are making spices the current choice of phytoresearch as well as the immune-boosting home remedies during these sceptical times. The present review critically evaluates the immune impact of various Indian spices and their potential to tackle the novel coronavirus, with comments on the safety and toxicity aspects of spices.

The Role of Micronutrients to Support Immunity for COVID-19 Prevention

The World Health Organization declared the novel coronavirus, named as SARS-CoV-2, as a global pandemic in early 2020 after the disease spread to more than 180 countries leading to tens of thousands of cases and many deaths within a couple of months. Consequently, this paper aims to summarize the evidence for the relationships between nutrition and the boosting of the immune system in the fight against the disease caused by SARS-CoV-2. This review, in particular, assesses the impact of vitamin and mineral supplements on the body's defence mechanisms against SARS-CoV-2. The results revealed that there is a strong relationship between the ingestion of biological ingredients like vitamins C-E, and minerals such as zinc, and a reduction in the effects of coronavirus infection. These can be received from either nutrition rich food sources or from vitamin supplements. Furthermore, these macromolecules might have roles to play in boosting the immune response, in the healing process and the recovery time. Hence, we recommend that eating healthy foods rich in vitamins C-E with zinc and flavonoids could boost the immune system and consequently protect the body from serious infections.

GRAPHICAL ABSTRACT

Repurposing potential of Ayurvedic medicinal plants derived active principles against SARS-CoV-2 associated target proteins revealed by molecular docking, molecular dynamics and MM-PBSA studies

All the plants and their secondary metabolites used in the present study were obtained from Ayurveda, with historical roots in the Indian subcontinent. The selected secondary metabolites have been experimentally validated and reported as potent antiviral agents against genetically-close human viruses. The plants have also been used as a folk medicine to treat cold, cough, asthma, bronchitis, and severe acute respiratory syndrome in India and across the globe since time immemorial. The present study aimed to assess the repurposing possibility of potent antiviral compounds with SARS-CoV-2 target proteins and also with host-specific receptor and activator protease that facilitates the viral entry into the host body. Molecular docking (MDc) was performed to study molecular affinities of antiviral compounds with aforesaid target proteins. The top-scoring conformations identified through docking analysis were further validated by 100 ns molecular dynamic (MD) simulation run. The stability of the conformation was studied in detail by investigating the binding free energy using MM-PBSA method. Finally, the binding affinities of all the compounds were also compared with a reference ligand, remdesivir, against the target protein RdRp. Additionally, pharmacophore features, 3D structure alignment of potent compounds and Bayesian machine learning model were also used to support the MDc and MD simulation. Overall, the study emphasized that curcumin possesses a strong binding ability with host-specific receptors, furin and ACE2. In contrast, gingerol has shown strong interactions with spike protein, and RdRp and quercetin with main protease (M^pro) of SARS-CoV-2. In fact, all these target proteins play an essential role in mediating viral replication, and therefore, compounds targeting aforesaid target proteins are expected to block the viral replication and transcription. Overall, gingerol, curcumin and quercetin own multitarget binding ability that can be used alone or in combination to enhance therapeutic efficacy against COVID-19. The obtained results encourage further in vitro and in vivo investigations and also support the traditional use of antiviral plants preventively.

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.

Rhinovirus RNA Polymerase

Human rhinovirus is responsible for causing 50% of common cold infections in infants and adults. It belongs to the picornavirus family of nonenveloped positive-strand RNA viruses. The RNA synthesis of rhinovirus is carried out by RNA-dependent RNA polymerase, also known as 3D^Pol. It catalyzes the synthesis of negative-strand RNA using a positive-strand template. The structure of the enzyme consists of three domains: palm, fingers, and thumb domains and Mg²⁺ in the active site. These conserved structural features of the enzyme help in catalyzing phosphodiester bond formation between the two consecutive nucleotide units complimentary to the template RNA using a VPg primer. Owing to the presence of over 100 serotypes of the enzyme, designing specific inhibitors targeting the polymerase is a challenging task and until now no clinically approved antirhino viral drug is reported. In this review, we have given detailed information about the structure and function of the enzyme and also discussed some of the inhibitors and their in vivo activity against 3D^Pol.

Orobol: An Inhibitor of Vesicular Stomatitis Virus that Blocks the Synthesis of Viral Nucleic Acids and the Glycosylation of G Protein

The naturally occurring isoflavonoid orobol exhibits antiviral effects against some animal viruses. Addition of the compound after virus entry inhibits the appearance of late viral protein synthesis in Vesicular Stomatitis Virus, influenza, or vaccinia virus-infected cells, but has no effect on poliovirus protein synthesis. Concentrations of the compound above 10–50 Mg ml−1 are sufficient to decrease the synthesis of VSV proteins when added early during infection, but have no effect on viral translation if added later, indicating that orobol does not block VSV translation directly. The synthesis of VSV nucleic acids is one of the targets of this flavonoid. The synthesis of both minus and plus-stranded viral RNA are inhibited by orobol when added during the first 2 h of infection. In addition, this compound interferes potently with the glycosylation of VSV G protein, indicating that orobol has several targets of antiviral action. The possibility that orobol interferes with the function of the cellular vesicular system is discussed.

Flavonoids: Potent Inhibitors of Poliovirus RNA Synthesis

Some naturally occurring flavonoids, such as 3-methyl quercetin and Ro-090179, show potent anti-picornavirus activity. They inhibit poliovirus replication at concentrations 100-fold or 1000-fold lower than hydroxybenzyl-benzimidazole (HBB) and guanidine, respectively. Ro-090179 selectively blocks viral RNA synthesis in poliovirus-infected HeLa cells more strongly than 3-methyl quercetin and is therefore the most potent and selective inhibitor of poliovirus RNA synthesis described until now. In addition, Ro-090179 discriminates in its inhibition between plus- and minus-stranded RNA synthesis. Thus, analysis of the viral RNA made in poliovirus-infected cells when the compound is added late in the infection cycle, indicates that the synthesis of genomic RNA is potently blocked, whereas minus-stranded RNA synthesis is not inhibited. These findings make Ro-090179 a valuable compound for obtaining insight into the molecular mechanisms of poliovirus RNA replication.

The value of central-African traditional medicine for lead finding: Some case studies

Ethnoparmaological relevance: One of the possible methodologies for the discovery of novel drugs is the screening of selected plant extracts for a broad array of pharmacological activities.

MATERIALS AND METHODS

The selection based on enthnomedicinal uses, combined with a follow-up of existing literature on the plants' chemotaxonomic properties, would seem to be the most cost-effective strategy for finding active plant extracts. A bioassay-guided fractionation of the active extracts should subsequently lead to the isolation and identification of the active lead constituent(s).

RESULTS AND DISCUSSION

Taking into account the enormous number and the amazing structural diversity of the currently known plant constituents, one might hope that promising model compounds with new structures and/or novel mechanisms of action might be found. In order, however, to optimize such a natural product drug discovery methodology, dereplication and selectivity of activity should be included in the screening system. Dereplication by which known compounds can rapidly be identified from a partially purified mixture prevents a research group from wasting resources by rediscovering known compounds. The use of single-target specific bioassays such as tests on isolated enzymes or on receptor-binding, or multiple target functional bioassays on isolated organs or intact cells must allow at an early stage to isolate compounds with specific pharmacological properties.

CONCLUSIONS

In this publication, several examples of bioassay-guided isolation and identification of pharmacologically active lead compounds from plants used in Central-African traditional medicine by our research group will be presented and discussed.

The miaoyao fanggan sachets regulate humoral immunity and cellular immunity in mice

BACKGROUND

Although some studies in the southeast part of Guizhou Province have suggested that Miaoyao Fanggan sachets (MFS) prevent influenza, little is known about its influence on immune systems. Influenza virus mainly infects immune-compromised individuals. The effects of MFS have mainly been recognized in clinical practice. However, there have been relatively few studies on its biological mechanism. Here we investigated whether MFS was able to affect the mucosal immunization and the activation of alveolar macrophages (AM), CD4+and CD8+ T-cells in vivo.

METHODS

Eighty Kunming male mice were treated with MFS continuously or intermittently with Yu-Ping-Feng powder (YPF-P) (positive control group) or with normal saline (NS) (control group) for 4 weeks, respectively. Mice treated with MFS were further divided into the continuous inhalation group (12 h daily/4 weeks) and the discontinuous inhalation group (1 h, three times a day for 4 weeks). Mice in both groups were placed under 0.5 m3 masks which had four ventilation holes (10×15 cm) containing 40 g MFS. Positive control mice were orally treated with YPF-P 0.2 mg/10 g/day once a day for 4 weeks. Control mice were orally treated with equal volumes of NS once a day for 4 weeks. MFS was replaced every 6 days. Administration of YPF-P was used as a positive control since it has been used as an established Traditional Chinese Medicine (TCM) treatment before. After 4 weeks, mice in all experimental groups were sacrificed. IgA and IgG1 in lung and blood serum were detected by Western blot and enzyme-linked immuno sorbent assay (ELISA). The expression of alveolar macrophages (AM) in mice was analyzed by immunochemistry test based on CD68+staining. Blood samples were collected in which CD4+and CD8+T-cells were analyzed by flow cytometry.

RESULTS

Mice continuously and intermittently inhaling MFS showed a moderate increase in IgA and IgG1 protein levels compared with mice in the control groups. There was also a slightly significant increase in the number of AM in the continuous inhalation group compared with mice in the control groups (p<0.05). Furthermore, compared with controls, there was also a slightly significant increase in the number and percentage of CD4+and CD8+T-cells in both the continuous inhalation group and the discontinuous inhalation group (p<0.05).

CONCLUSIONS

MFS was able to up-regulate the protein levels of sIgA and IgG1. Meanwhile, MFS could activate AM, CD4+and CD8+T-cells in mice. Our data have, for the first time, demonstrated that the protection against influenza by MFS is partly through activation of the innate and adaptive cell-mediated immune responses, indicating MFS as a potential new immune-modulatory agent for respiratory tract infectious disease.

Simultaneous determination of esculetin, quercetin-3-O-β-D-glucuronide, quercetin-3-O-β -D-glucuronopyranside methyl ester and quercetin in effective part of Polygonum Perfoliatum L. using high performace liquid chromatography

Objective:

In the present study, a high performance liquid chromatography (HPLC) coupled with photodiode array detection was developed for simultaneous quantitation of esculetin, quercetin-3-O-β-D-glucuronide, quercetin-3-O-β-D- glucuronopyranoside methyl ester and quercetin in Polygonum perfoliatum L.

Materials and Methods:

The chromatographic separations were performed on a reversed-phase C₁₈ column using a mobile phase composed of acetonitrile -0.5% aqueous acetic acid with gradient elution. The calibration curves for the analytes demonstrated good linearities within the investigated ranges. The satisfactory intra- and inter-day precision, repeatability and stability of the developed analytical method were shown in the method validation procedure. The recoveries of the established method ranged from 95.76 to 102.10% for all the analytes.

Results:

This proposed method was successfully applied for simultaneous quantification of the four compounds in effective part of Polygonum perfoliatum L. from different regions. Hierarchical clustering analysis (HCA) and principal components analysis (PCA) were performed to characterize and classify the samples based on the contents of the four compounds in Polygonum perfoliatum L.

Conclusion:

The established HPLC method combined with chemometric approaches was proven to be useful and efficient for quality control of Polygonum perfoliatum L.

Effect of the Miaoyao Fanggan sachet-derived isorhamnetin on TLR2/4 and NKp46 expression in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Miaoyao Fanggan Sachets (MFS) has long been used as a folk medicine for the prevention of influenza in Southeast of Guizhou Province, China. However, the precise immunological mechanisms by which MFS confers protection have not been defined.

STUDY AIM

To explore the effects of MFS on innate immune system responses using a cold stress-induced immune impairment model as a means of examining MFS-mediated influenza prevention. We investigated the effects of MFS on toll-like receptor 2 and 4 (TLR2/4) gene and protein expression levels and on the percentage of NKp46(+) cells present in serum. No overt toxicity was observed following continuous administration of MFS at high doses.

METHODS

Kunming male mice (n=40) were randomly divided into 4 groups consisting of the continuous inhalation Sachet group, Yu-Ping-Feng powder (YPF-P) gavage positive control group, discontinuous inhalation MFS group and untreated controls. After 4 weeks, mice were sacrificed and lungs harvested. The expression of toll-like receptors 2 and 4 (TLR2/4) gene and protein levels was assessed using real-time polymerase chain reaction (RT-PCR) and Western blot analyses, respectively. An additional 60 Kunming mice were randomly divided into 6 groups comprised of a blank control group, continuous MFS inhalation group, an immune-compromised continuous MFS inhalation group, an immuno-compromised group, an immune-compromised MFS discontinuous inhalation group and an immune-compromised positive control group. Immune suppression was induced by cold stress (4 °C/4 h daily for 3 days) and mice were treated with MFS or YPF-P before cold stress treatments. Immuno-compromised mice were treated with MFS continuously or intermittently, or treated with YPF-P. Blood samples were collected and examined for natural killer cells based on positive NKp46 staining. The isorhamnetin associated with MFS-induced immune modulation was obtained from 'wo ga le' which is considered to be a major component of MFS, and analyzed by HPLC.

RESULTS

Mice continuously inhaling MFS showed a moderate increase in TLR2/4 mRNA and protein levels compared to mice in the control and discontinuous inhalation groups. MFS significantly increased the TLR2/4 expression in a dose-dependent manner. Furthermore, there was also a slightly significant increase in the number of NKp46(+) cells in the continuous inhalation group compared to controls and discontinuous inhalation group. Pretreatment with MFS partially prevented cold stress-induced inhibition of NKp46(+) cells. HPLC analysis of the 'wo ga le' associated with immune function identified the major component to be isorhamnetin.

CONCLUSIONS

Taken together, these data suggested that MFS significantly enhanced TLR2/4 expression levels and the number of NKp46(+) cells in mice and moderately affected innate immune responses associated with protection against influenza, suggesting that isorhamnetin in the MFS enhanced innate immune potency. The use of MFS for the prevention of various respiratory tract infections can be attributed to its antimicrobial properties. In a pilot study, a large quantity (40 g) was administered over a prolonged period did not produce apparent toxicity.

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.

Selective inhibitors of picornavirus replication

Picornaviruses cover a large family of pathogens that have a major impact on human but also on veterinary health. Although most infections in man subside mildly or asymptomatically, picornaviruses can also be responsible for severe, potentially life-threatening disease. To date, no therapy has been approved for the treatment of picornavirus infections. However, efforts to develop an antiviral that is effective in treating picornavirus-associated diseases are ongoing. In 2007, Schering-Plough, under license of ViroPharma, completed a phase II clinical trial with Pleconaril, a drug that was originally rejected by the FDA after a New Drug Application in 2001. Rupintrivir, a rhinovirus protease inhibitor developed at Pfizer, reached clinical trials but was recently halted from further development. Finally, Biota's HRV drug BTA-798 is scheduled for phase II trials in 2008. Several key steps in the picornaviral replication cycle, involving structural as well as non-structural proteins, have been identified as valuable targets for inhibition. The current review aims to highlight the most important developments during the past decades in the search for antivirals against picornaviruses.

Flavonoids with anti-Helicobacter pylori activity from Cistus laurifolius leaves

Cistus laurifolius flower buds are used traditionally in folk medicine against gastric ailments. In a prior study we showed that the chloroform extract of Cistus laurifolius had a potent anti-ulcer activity. It has been known that there is a causal relationship between peptic ulcer and Helicobacter pylori infection. Then in a previous study, we demonstrated that chloroform extract of Cistus laurifolius possessed a significant anti-Helicobacter pylori activity. We designed this study to isolate and define the active component(s) involved in the anti-Helicobacter pylori activity of the extract through activity-guided fractionation procedures. The chloroform extract was fractionated by using various chromatography techniques, i.e., Sephadex LH-20 column chromatography and preparative thin layer chromatography and six compounds were isolated (1-6). Each of these six compounds' anti-Helicobacter pylori activity was tested in vitro and was measured as minimum inhibition concentration (MIC) values by using agar dilution method. The compound 2 had the highest activity against Helicobacter pylori (MIC 3.9 microg/mL). Its chemical structure was elucidated as quercetin 3-methyl ether (isorhamnetin) by various spectroscopic techniques. We believe that the therapeutic effect of Cistus laurifolius in ulcer is at least partially related to its effect on Helicobacter pylori. We hope that the isolated flavonoid having anti-Helicobacter pylori activity ultimately can be utilized as an alternative or additive agent to the current therapy.

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.

Partial purification, kinetic analysis, and amino acid sequence information of a flavonol 3-O-methyltransferase from Serratula tinctoria

Serratula tinctoria (Asteraceae) accumulates mainly 3,3'-dimethylquercetin and small amounts of 3-methylquercetin as an intermediate. The fact that 3-methylquercetin rarely accumulates in plants in significant amounts, and given its important role as an antiviral and antiinflammatory agent that accumulates in response to stress conditions, prompted us to purify and characterize the enzyme involved in its methylation. The flavonol 3-O-methyltransferase (3-OMT) was partially purified by ammonium sulfate precipitation and successive chromatography on Superose-12, Mono-Q, and adenosine-agarose affinity columns, resulting in a 194-fold increase of its specific activity. The enzyme protein exhibited an expressed specificity for the methylation of position 3 of the flavonol, quercetin, although it also utilized kaempferol, myricetin, and some monomethyl flavonols as substrates. It exhibited a pH optimum of 7.6, a pI of 6.0, and an apparent molecular mass of 31 kD. Its K(m) values for quercetin as the substrate and S-adenosyl-l-Met (AdoMet) as the cosubstrate were 12 and 45 microm, respectively. The 3-OMT had no requirement for Mg(2+), but was severely inhibited by p-chloromercuribenzoate, suggesting the requirement for SH groups for catalytic activity. Quercetin methylation was competitively inhibited by S-adenosyl-l-homo-Cys with respect to the cosubstrate AdoMet, and followed a sequential bi-bi reaction mechanism, where AdoMet was the first to bind and S-adenosyl-l-homo-Cys was released last. In-gel trypsin digestion of the purified protein yielded several peptides, two of which exhibited strong amino acid sequence homology, upon protein identification, to a number of previously identified Group II plant OMTs. The availability of peptide sequences will allow the design of specific nucleotide probes for future cloning of the gene encoding this novel enzyme for its use in metabolic engineering.

Quantitative RT-PCR ELISA to determine the amount and ratio of positive- and negative strand viral RNA synthesis and the effect of guanidine in poliovirus infected cells

Quantitative reverse transcription-polymerase chain reaction enzyme linked immunosorbent assay (RT-PCR ELISA) is the method of choice to study positive- and negative strand viral RNA synthesis during poliovirus replication. In comparison with other methods used for this purpose, it fulfils all necessary requirements to accurately determine RNA of different polarity. It combines high specificity, high sensitivity, safety, speed, and the ability to perform quantitative analysis. The enterovirus specific RT-PCR ELISA method described in this work, was used to determine quantitatively the amount of de novo poliovirus positive- and negative strand RNA synthesis at different time-points in the viral replication cycle, both in presence and absence of the viral RNA synthesis inhibitor guanidine hydrochloride.

Antipoliovirus flavonoids from Psiadia dentata

The search for antiviral agents against vesicular stomatitis virus, herpes simplex virus type 1 and poliovirus type 2 in plants extracts, led to the isolation of two antipoliovirus flavonoids from the medicinal plant Psiadia dentata (Cass.) DC, Asteraceae: 3-methylkaempferol and 3,4'-dimethylkaempferol. The antipoliovirus activity of both compounds was estimated by comparison with 3-methylquercetin, guanidine and Ro-090179. The most potent inhibitor of poliovirus replication was 3-methylkaempferol, and therefore we investigated its mechanism of action. We showed, using the inhibition of [3H]uridine incorporation in viral RNA and performing a dot-blot with one RNA probe specific for the poliovirus genomic strand RNA, that 3-methylkaempferol inhibits the genomic RNA synthesis of poliovirus.

Characterization of 3-methoxyflavones using fast-atom bombardment and collision-induced dissociation tandem mass spectrometry

A mass spectrometric method based on the combined use of fast-atom bombardment (FAB), collision-induced dissociation (CID) and linked scanning at constant B/E has been used for the analysis of the fragmentation behavior of protonated 3-methoxyflavones (3-MFs). It is shown that several diagnostic ions such as (1,3)A (+) and (0,2)B (+) ions allow for an unambiguous localization of functions in the A- and B-rings and that the position of an additional methoxy group in the B-ring could be determined by a detailed analysis of the spectral patterns. Isomeric 3-MFs can be differentiated using this methodology. General fragmentation patterns of 3-MFs are discussed and plausible formation mechanisms of relatively abundant fragment ions are proposed.

Proteolysis of human eukaryotic translation initiation factor eIF4GII, but not eIF4GI, coincides with the shutoff of host protein synthesis after poliovirus infection

Eukaryotic initiation factor (eIF) 4GI is a component of the cap-binding protein complex eIF4F, which is required for cap-dependent translation. Infection of cells by poliovirus results in a precipitous decline of host cell protein synthesis, which is preceded by the cleavage of eIF4GI. Cleavage of eIF4GI results in the inhibition of cap-dependent translation. Poliovirus translation is not affected by eIF4GI cleavage, however, because poliovirus mRNA is translated by a cap-independent mechanism. Cleavage of eIF4GI alone cannot explain the shutoff of host protein synthesis, because after infection in the presence of inhibitors of virus replication, eIF4GI is cleaved, yet host protein synthesis is only partially inhibited. Here we show that eIF4GII, a recently discovered functional homolog of eIF4GI, is more resistant to poliovirus-mediated cleavage than eIF4GI, and that its proteolysis is concomitant with the shutoff of host cell protein synthesis. Moreover, infection with poliovirus in the presence of inhibitors of virus replication resulted in efficient cleavage of eIF4GI, but only partial proteolysis of eIF4GII. Thus, cleavage of both eIF4GI and eIF4GII appears to be required for the shutoff of host protein synthesis after poliovirus infection. These results explain several earlier reports documenting the lack of correlation between eIF4GI cleavage and inhibition of cellular mRNA translation after poliovirus infection.

Poliovirus infection and expression of the poliovirus protein 2B provoke the disassembly of the Golgi complex, the organelle target for the antipoliovirus drug Ro-090179

Infection of Vero cells with poliovirus results in complete disassembly of the Golgi complex. Milestones of the process of disassembly are the release to the cytosol of the beta-COP bound to Golgi membranes, the disruption of the cis-Golgi network into fragments scattered throughout the cytoplasm, and the disassembly of the stacked cisternae by a process mediated by long tubular structures. Transient expression of the viral protein 2B in COS-7 cells also causes the disassembly of the Golgi complex by a process preceded by the accumulation of the protein in the Golgi area. Vero cells infected for 3 h show no recognizable Golgi complexes at the ultrastructural level and display an enormously swollen endoplasmic reticulum (ER) with extensive areas of its surface heavily coated. Ro-090179 (Ro), a flavonoid isolated from the herb Agastache rugosa, provokes the specific swelling and disruption of the Golgi complex and strongly inhibits poliovirus infection. Ro provokes the swelling and the disruption of the stacked cisternae and trans-Golgi elements without affecting the cis-most Golgi cisternae much. Moreover, Ro inhibits the fusion of the Golgi complex with the ER in cells treated with brefeldin A and provokes the accumulation of the intermediate compartment membrane protein p58 into ERD2-positive Golgi elements but has no effect on the anterograde transport involved in protein secretion. Our results indicate that the secretory pathway and specifically the Golgi complex are preferential targets of poliovirus.

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.

Picornavirus inhibitors

Picornaviruses are among the best understood animal viruses in molecular terms. A number of important human and animal pathogens are members of the Picornaviridae family. The genome organization, the different steps of picornavirus growth and numerous compounds that have been reported as inhibitors of picornavirus functions are reviewed. The picornavirus particles and several agents that interact with them have been solved at atomic resolution, leading to computer-assisted drug design. Picornavirus inhibitors are useful in aiding a better understanding of picornavirus biology. In addition, some of them are promising therapeutic agents. Clinical efficacy of agents that bind to picornavirus particles has already been demonstrated.

Lack of direct correlation between p220 cleavage and the shut-off of host translation after poliovirus infection

Poliovirus induces a drastic inhibition of host protein synthesis soon after infection of susceptible cells. The correlation between this inhibition and the cleavage of p220, a polypeptide that forms part of protein synthesis initiation factor elF-4F, has been examined in detail. Measurements of protein synthesis at half-hourly intervals after infection with poliovirus show the lack of direct correlation between p220 cleavage and the blockade of cellular translation. Moreover, the use of inhibitors of poliovirus RNA synthesis helped to dissociate those two events more clearly. Thus, in the presence of guanidine or Ro 09-0179 when little shut-off was induced by poliovirus extensive proteolytic degradation of p220 took place. When HeLa cells infected with poliovirus are placed at 28 degrees the inhibition of host protein synthesis is prevented and cellular translation continues for at least 8 hr, albeit at a reduced level compared to cells incubated at 37 degrees. At 28 degrees, cleavage of p220 is observed and about 80% of p220 is degraded after 6 hr of incubation at that temperature. Strikingly, when cells in which more than 50% of p220 is cleaved are shifted to 37 degrees, cellular translation recuperates to 100%, in spite of the fact that no detectable p220 is present. Furthermore, if poliovirus-infected cells are incubated for 2 hr at 37 degrees to permit the cleavage of p220 and then are shifted to 28 degrees in the presence of guanidine, cellular proteins are synthesized at the same level as uninfected HeLa cells incubated at 28 degrees. These results show that translation of cellular mRNAs takes place in cells containing a cleaved p220 and indicate that this cleavage is not directly responsible for the shut-off of host translation induced by poliovirus.

Gliotoxin: inhibitor of poliovirus RNA synthesis that blocks the viral RNA polymerase 3Dpol

The mode of action of gliotoxin against poliovirus has been analyzed in detail. This fungal metabolite inhibits the appearance of poliovirus proteins when present from the beginning of infection but has no effect on viral translation when added at late times. In agreement with previous findings, this toxin potently inhibited the incorporation of [3H]uridine into poliovirus RNA soon after its addition to the culture medium. Analysis of the synthesis of poliovirus plus- or minus-stranded RNA in the presence of gliotoxin suggests that this compound effectively hampered both processes. This result contrasts with the mode of action of other inhibitors of poliovirus RNA synthesis, such as guanidine or flavones, that selectively block plus-stranded RNA synthesis and suggests that the target of gliotoxin differs from the target of guanidine, i.e., poliovirus protein 2C. Indeed, gliotoxin was found to be a potent inhibitor of poliovirus RNA synthesis in cell-free systems, using membranous crude replication complexes, a reaction that is not blocked by guanidine or Ro 09-0179. Moreover, in vitro activity of the purified poliovirus polymerase 3Dpol was efficiently inhibited by gliotoxin. These results indicate that this toxin acts on the poliovirus polymerase 3Dpol, providing the first description of an inhibitor of this viral enzyme.

Lack of evidence for strand-specific inhibition of poliovirus RNA synthesis by 3-methylquercetin

Buffalo Green Monkey cells were infected with poliovirus-1 in the presence of 3-methylquercetin or guanidine, and the formation of positive- and negative-strand viral RNA was monitored using single-stranded RNA probes. Both 3-methylquercetin and guanidine prevented the formation of plus-strand as well as minus-strand viral RNA, although, due to the high multiplicity of infection used, a high number of genomic viral RNA was always present in the cells.

Comparative sequence analysis of the 5' noncoding region of the enteroviruses and rhinoviruses

A comparative sequence analysis of the 5' noncoding region of a subgroup of the picornaviruses, including the polioviruses, coxsackie B3, and the human rhinoviruses, reveals the conservation of certain features despite the divergence of sequence. In this subgroup, for which nine complete sequences are available, two long stretches of sequence, two pyrimidine-rich regions, and 22 hairpins are conserved. Based on these results, similar secondary structures encompassing the entire 5' noncoding regions of these viruses are predicted. The fact that sequence divergence occurred only in a manner that allowed conservation of these structures implicates a biologically functional role for this region. The possible roles it may have in the picornavirus life cycle are discussed.