Identification of a Direct-Acting Antiviral Agent Targeting RNA Helicase via a Graphene Oxide Nanobiosensor

Dengue virus (DENV), an arbovirus transmitted by mosquitoes, causes infectious diseases such as dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. Despite the dangers posed by DENV, there are no approved antiviral drugs for treatment of DENV infection. Considering the potential for a global dengue outbreak, rapid development of antiviral agents against DENV infections is crucial as a preemptive measure; thus, the selection of apparent drug targets, such as the viral enzymes involved in the viral life cycle, is recommended. Helicase, a potential drug target in DENV, is a crucial viral enzyme that unwinds double-stranded viral RNA, releasing single-stranded RNA genomes during viral replication. Therefore, an inhibitor of helicase activity could serve as a direct-acting antiviral agent. Here, we introduce an RNA helicase assay based on graphene oxide, which enables fluorescence-based analysis of RNA substrate-specific helicase enzyme activity. This assay demonstrated high reliability and ability for high-throughput screening, identifying a new helicase inhibitor candidate, micafungin (MCFG), from an FDA-approved drug library. As a direct-acting antiviral agent targeting RNA helicase, MCFG inhibits DENV proliferation in cells and an animal model. Notably, in vivo, MCFG treatment reduced viremia, inflammatory cytokine levels, and viral loads in several tissues and improved survival rates by up to 40% in a lethal mouse model. Therefore, we suggest MCFG as a potential direct-acting antiviral drug candidate.

Direct evidence of a low barrier hydrogen bond in the catalytic triad of a Serine protease

Serine proteases are one of the largest groups of enzymes, found in both eukaryotes and prokaryotes, and are responsible for many different functions. The detailed information about the hydrogen-bonds in the catalytic triad (Asp…His…Ser) of these enzymes is of importance in order to fully understand the mechanism of action. The aspartate of the triad is hydrogen bonded to the histidine but the exact nature of this bond has been under discussion for some time. It is either a common short ionic hydrogen bond (SIHB) or a delocalized low barrier hydrogen bond (LBHB) were the hydrogen bond is shorter. So far, the evidence for LBHB in proteins have not been conclusive. Here we show clear NMR evidence that LBHB does exist in NS3, a serine protease from Dengue. The one bond coupling constant between the hydrogen and nitrogen was shown to be only 52 Hz instead of the usual 90 Hz. This together with a 1H chemical shift of 19.93 ppm is evidence that the hydrogen bond distance between His and Asp is shorter than for SIHB. Our result clearly shows the existence of LBHB and will help in understanding the mechanism of the catalytic triad in the important group of serine proteases.

Detection and quantification of dengue virus using a novel biosensor system based on dengue NS3 protease activity

Background

The traditional methods, plaque assays and immuno-focus assays, used to titrate infectious dengue virus (DENV) particles are time consuming and labor intensive. Here, we developed a DENV protease activity detection system (DENPADS) to visualize DENV infection in cells based on dengue protease activity.

Methodology/Principal findings

Dengue NS3 protease cleaves NS4B-NS5. BHK-21 cells stably expressing the sensor module comprising DENV-2 NS4 and the 10 amino-terminal amino acids of NS5 (_N10NS5) fused with the SV40 nuclear localization signal (NLS) and Cre recombinase (Cre), were generated. Cre is constrained outside the nucleus in the absence of NS3 activity but translocates into the nucleus through NS4B-NS5 cleavage when cells are infected with DENV. Nuclear translocation of Cre can trigger the reporter system, which contains a cis-loxP-flanked mCherry with three continuous stop codons following an SV40 polyA tail cDNA upstream of EGFP or mHRP cDNA. Our results show that DENPADS is an efficient and accurate method to titrate 4 DENV serotypes in 24 hours. Compared with current virus titration methods, the entire process is easy to perform, and the data are easily acquired.

Conclusions/Significance

In this study, we demonstrate that DENPADS can be used to detect dengue viral infection through a fluorescence switch or HRP activity in the infected cells. This approach is sensitive with less incubation time and labor input. In addition, DENPADS can simultaneously evaluate the efficacy and cytotoxicity of potential anti-DENV candidates. Overall, DENPADS is a useful tool for dengue research.

A small compound targeting the interaction between nonstructural proteins 2B and 3 inhibits dengue virus replication

The non-structural protein NS2B/NS3 serine-protease complex of the dengue virus (DENV) is required for the maturation of the viral polyprotein. Dissociation of the NS2B cofactor from NS3 diminishes the enzymatic activity of the complex. In this study, we identified a small molecule inhibitor that interferes with the interaction between NS2B and NS3 using structure-based screening and a cell-based viral replication assay. A library containing 661,417 small compounds derived from the Molecular Operating Environment lead-like database was docked to the NS2B/NS3 structural model. Thirty-nine compounds with high scores were tested in a secondary screening using a cell-based viral replication assay. SK-12 was found to inhibit replication of all DENV serotypes (EC50=0.74-4.92 μM). In silico studies predicted that SK-12 pre-occupies the NS2B-binding site of NS3. Steady-state kinetics using a fluorogenic short peptide substrate demonstrated that SK-12 is a noncompetitive inhibitor against the NS2B/NS3 protease. Inhibition to Japanese encephalitis virus by SK-12 was relatively weak (EC50=29.81 μM), and this lower sensitivity was due to difference in amino acid at position 27 of NS3. SK-12 is the promising small-molecule inhibitor that targets the interaction between NS2B and NS3.

Rational design of a live attenuated dengue vaccine: 2'-o-methyltransferase mutants are highly attenuated and immunogenic in mice and macaques

Dengue virus is transmitted by Aedes mosquitoes and infects at least 100 million people every year. Progressive urbanization in Asia and South-Central America and the geographic expansion of Aedes mosquito habitats have accelerated the global spread of dengue, resulting in a continuously increasing number of cases. A cost-effective, safe vaccine conferring protection with ideally a single injection could stop dengue transmission. Current vaccine candidates require several booster injections or do not provide protection against all four serotypes. Here we demonstrate that dengue virus mutants lacking 2′-O-methyltransferase activity are highly sensitive to type I IFN inhibition. The mutant viruses are attenuated in mice and rhesus monkeys and elicit a strong adaptive immune response. Monkeys immunized with a single dose of 2′-O-methyltransferase mutant virus showed 100% sero-conversion even when a dose as low as 1,000 plaque forming units was administrated. Animals were fully protected against a homologous challenge. Furthermore, mosquitoes feeding on blood containing the mutant virus were not infected, whereas those feeding on blood containing wild-type virus were infected and thus able to transmit it. These results show the potential of 2′-O-methyltransferase mutant virus as a safe, rationally designed dengue vaccine that restrains itself due to the increased susceptibility to the host's innate immune response.

The four serotypes of dengue virus cause severe outbreaks globally in tropical countries with thousands of patients requiring hospitalization. The health care and indirect economic cost of dengue in endemic countries is huge. Despite this, no clinically approved vaccine or antiviral treatment is currently available. Dengue transmission could be stopped with a vaccine that provides full protection to all serotypes. Dengue afflicts many developing countries and a vaccine should therefore be cost-effective and should provide protection with ideally a single injection. Here we present a novel dengue vaccine approach that harbours mutation(s) in the 2′-O-methyltransferase (MTase), a viral enzyme that methylates viral RNA as a strategy to escape the host immune response. Non-methylated RNA is recognized as “foreign” and triggers an interferon response in the cell. The MTase mutant virus is immediately recognized by the host's immune response and hardly has a chance to spread in the organism while an immune response is efficiently triggered by the initially infected cells. Mice and monkeys infected with the mutant virus developed an immune response that fully protected them from a challenge with wild-type virus. Furthermore, we show that MTase mutant dengue virus cannot infect Aedes mosquitoes. Collectively, the results suggest 2′-O-MTase mutant dengue virus as a safe, highly immunogenic vaccine approach.

Inhibition of Dengue virus and West Nile virus proteases by click chemistry-derived benz[d]isothiazol-3(2H)-one derivatives

Two click chemistry-derived focused libraries based on the benz[d]isothiazol-3(2H)-one scaffold were synthesized and screened against Dengue virus and West Nile virus NS2B-NS3 proteases. Several compounds (4l, 7j-n) displayed noteworthy inhibitory activity toward Dengue virus NS2B-NS3 protease in the absence and presence of added detergent. These compounds could potentially serve as a launching pad for a hit-to-lead optimization campaign.

Small molecule inhibitors that selectively block dengue virus methyltransferase

Crystal structure analysis of Flavivirus methyltransferases uncovered a flavivirus-conserved cavity located next to the binding site for its cofactor, S-adenosyl-methionine (SAM). Chemical derivatization of S-adenosyl-homocysteine (SAH), the product inhibitor of the methylation reaction, with substituents that extend into the identified cavity, generated inhibitors that showed improved and selective activity against dengue virus methyltransferase (MTase), but not related human enzymes. Crystal structure of dengue virus MTase with a bound SAH derivative revealed that its N6-substituent bound in this cavity and induced conformation changes in residues lining the pocket. These findings demonstrate that one of the major hurdles for the development of methyltransferase-based therapeutics, namely selectivity for disease-related methyltransferases, can be overcome.

Matrix metalloproteinase-9 (mmp-9) in children with dengue virus infection

The purpose of this study was to investigate the role of matrix metalloproteinase-9 (MMP-9) in the pathogenesis of vascular leakage in patients with dengue virus infection. Serum samples from 24 children with serologically confirmed dengue virus infection (dengue fever [DF], 16; dengue hemorrhagic fever [DHF], 8; age, 9.5+/-2.4 years; 67% male] were analyzed for MMP-9 during the febrile and toxic stages and at follow-up. Serum samples obtained from 7 healthy children were used as controls. Serum MMP-9 levels in patients with dengue virus infection were found to be lower at the febrile (227.0+/-186.9 ng/ml) and toxic stages (150.9+/-151.7 ng/ml) than at follow-up (424.5+/-227.8 ng/ml) or in the control group (393.3+/-125.9 ng/ml, P<0.001 by one-way ANOVA). There was no significant difference between MMP-9 levels in patients with DHF and those with DF at any stage of the disease. In conclusion, MMP-9 levels are reduced during the febrile and toxic stages of dengue virus infection.

Differential expression of aldolase, alpha tubulin and thioredoxin peroxidase in peripheral blood mononuclear cells from dengue fever and dengue hemorrhagic fever patients

We determined the differential expression levels of proteins in peripheral blood mononuclear cells of patients with dengue fever (DF) and dengue hemorrhagic fever (DHF). Proteins were subjected to two-dimensional electrophoresis, mass spectrometry and Western blot analysis. We identified 8 proteins that were 2-fold or more up-regulated in patients compared to healthy control, three of which, aldolase, thioredoxin peroxidase and alpha tubulin, were related to dengue infection. Both thioredoxin peroxidase and alpha tubulin were over-expressed 4.9 and 3.3 times respectively in DHF compared to DF patients while aldolase was up-regulated 2.2 times in DF compared to DHF patients. Alpha tubulin and thioredoxin peroxidase have the potential to be utilized as biomarkers for DHF.

[Aminotransferases serum levels in patients with Dengue type 3]

BACKGROUND

Dengue infections may affect the liver, causing inflammation and compromising its function.

AIM

To determine serum aminotransferases in patients with Dengue.

MATERIAL AND METHODS

One hundred eighty four patients with Dengue confirmed with anti-Dengue IgG and IgM antibodies measured by ELISA, aged 1 month to 79 years, were studied. As controls, 40 patients with acute hepatitis B virus infection aged 11 to 59 years and 40 healthy individuals, aged 14 to 55 years, were also studied. Alanine and aspartate aminotransferases (ALT and AST) were determined using a colorimetric method.

RESULTS

Sixty one percent of patients with Dengue had elevated aminotransferase levels. In patients with Dengue and hepatitis B, mean ALT levels were 21.3+/-8.4 and 29.7+/-18.8 U/I, respectively. Mean AST values were 37.3+/-19, 19.6+/- 16.4 and 4.3+/-1.7 U/I in patients with Dengue, hepatitis B and controls, respectively. During the year 2001, there was an increase in the number of cases with hemorrhagic fever caused by Dengue and 65% had elevation of aminotransferases.

CONCLUSIONS

An increase in aminotransf erase levels is common in patients with Dengue.

The impact of dengue on liver function as evaluated by aminotransferase levels

The objective of this study was to evaluate the impact of dengue virus infection on liver function by measuring aminotransferase in blood samples from patients serologically diagnosed by according to two MAC-ELISA protocols. Degrees of liver damage were classified according to aminotransferase levels: grade A--normal enzyme levels; grade B--increased levels of at least one of the enzymes; grade C--increased, with at least one of the enzymes being at levels higher than three times the upper reference values; grade D--acute hepatitis, with aminotransferase levels at least ten times their normal values. Of the 169 serologically confirmed cases of dengue at the dengue referral center in Campos dos Goytacazes in the state of Rio de Janeiro, Brazil, 65.1% had abnormal aminotransferase levels: 81 cases being classified as grade B, 25 as grade C and 3 as grade D. A further 34.9% of cases had normal enzyme levels and were classified as grade A. Liver damage is a common complication of dengue infection and aminotransferase levels are a valuable marker for monitoring these cases.

Correlación entre los niveles de glutatión peroxidasa, un marcador de estrés oxidativo, y la presentación clínica del dengue

BACKGROUND

Glutathione peroxidase (GP) can be used as a marker of oxidative stress in infectious diseases.

AIM

To evaluate the association between the levels of glutathione peroxidase (GP) and the manifestations and complications of dengue.

PATIENTS AND METHODS

Between April 2003 and December 2004, 161 patients with dengue were prospectively evaluated. In the first evaluation, within 48 and 96 hours of disease onset, a plasma sample was obtained to measure the GP levels. The association between GP levels, clinical manifestations and complications was evaluated during the follow up.

RESULTS

Mean GP values were 1198 U/L (95% confidence interval 1089-1306). Values greater than 1200 U/L were associated with headache, arthralgias and increased heart rate. There was a negative association between GP levels and serum triglycerides. During follow up, patients with GP >1200 U/L had a higher frequency of spontaneous hemorrhages. In a logistic regression analysis arthralgias, fever and increased heart rate, were independently associated with levels >1200 U/L.

CONCLUSIONS

GP levels was associated to some of the manifestations of dengue. This finding suggests that the intensity of oxidative stress can influence the clinical presentation of dengue.

Pathogenesis of liver involvement during dengue viral infections

The dengue virus can infect many cell types and cause diverse clinical and pathological effects. We describe clinical and experimental observations that suggest that liver involvement occurs during dengue infections, and we outline the possible role played by host immune responses in this process.

Inducible nitric oxide synthase (iNOS) expression in monocytes during acute Dengue Fever in patients and during in vitro infection

Mononuclear phagocytes are considered to be main targets for Dengue Virus (DENV) replication. These cells are activated after infection, producing proinflammatory mediators, including tumour-necrosis factor-alpha, which has also been detected in vivo. Nitric oxide (NO), usually produced by activated mononuclear phagocytes, has antimicrobial and antiviral activities.

METHODS

The expression of DENV antigens and inducible nitric oxide synthase (iNOS) in human blood isolated monocytes were analysed by flow cytometry using cells either from patients with acute Dengue Fever or after DENV-1 in vitro infection. DENV-1 susceptibility to iNOS inhibition and NO production was investigated using NG-methyl L-Arginine (NGMLA) as an iNOS inhibitor, which was added to DENV-1 infected human monocytes, and sodium nitroprussiate (SNP), a NO donor, added to infected C6/36 mosquito cell clone. Viral antigens after treatments were detected by flow cytometry analysis.

RESULTS

INOS expression in activated monocytes was observed in 10 out of 21 patients with Dengue Fever and was absent in cells from ten healthy individuals. DENV antigens detected in 25 out of 35 patients, were observed early during in vitro infection (3 days), significantly diminished with time, indicating that virus replicated, however monocytes controlled the infection. On the other hand, the iNOS expression was detected at increasing frequency in in vitro infected monocytes from three to six days, exhibiting an inverse relationship to DENV antigen expression. We demonstrated that the detection of the DENV-1 antigen was enhanced during monocyte treatment with NGMLA. In the mosquito cell line C6/36, virus detection was significantly reduced in the presence of SNP, when compared to that of untreated cells.

CONCLUSION

This study is the first to reveal the activation of DENV infected monocytes based on induction of iNOS both in vivo and in vitro, as well as the susceptibility of DENV-1 to a NO production.

Use of simple laboratory features to distinguish the early stage of severe acute respiratory syndrome from dengue fever

BACKGROUND

The diagnosis of severe acute respiratory syndrome (SARS) is difficult early in the illness, because its presentation resembles that of other nonspecific viral fevers, such as dengue. Dengue fever is endemic in many of the countries in which the large SARS outbreaks occurred in early 2003. Misdiagnosis may have serious public health consequences. We aimed to determine simple laboratory features to differentiate SARS from dengue.

METHODS

We compared the laboratory features of 55 adult patients with SARS at presentation (who were all admitted before radiological changes had occurred) and 147 patients with dengue. Features independently predictive of dengue were modeled by multivariate logistic regression to create a diagnostic tool with 100% specificity for dengue.

RESULTS

Multivariate analysis identified 3 laboratory features that together are highly predictive of a diagnosis of dengue and able to rule out the possibility of SARS: platelet count of <140 x 10(9) platelets/L, white blood cell count of <5x10(9) cells/L, and aspartate aminotransferase level of >34 IU/L. A combination of these parameters has a sensitivity of 75% and a specificity of 100%.

CONCLUSIONS

Simple laboratory data may be helpful for the diagnosis of disease in adults admitted because of fever in areas in which dengue is endemic when the diagnosis of SARS needs to be excluded. Application of this information may help to optimize the use of isolation rooms for patients presenting with nonspecific fever.

Infection of five human liver cell lines by dengue-2 virus

Elevated serum transaminase levels of dengue patients indicate the possible impact of dengue virus infection on liver function. To elucidate the action of dengue virus infection in liver cells, an in vitro cell line system was established that mimicked the liver status of diverse clinical patients. Briefly, four hepatoma cell lines (HA22T, Huh7, Hep3B, and PLC) and one nonmalignant hepatocyte cell line (Chang liver) were included, representing various levels of tumorigenicity and differentiation. Our data showed that in these five cell lines, dengue-2 virus attached to each cell type equally well; however, this virus had higher replication rates and levels of virion production in differentiated Huh7, PLC, Hep3B, and Chang liver cells. Likewise, a lower replication rate was observed in the de-differentiated HA22T cells. Differentiation-related factors seem to play an important role in dengue virus replication. Further study showed that sodium butyrate (NaB, a differentiation inducer) treatment enhanced dengue virus replication in HA22T cells. Moreover, we found that the severity of morphologic aberration and the increase in aspartate aminotransferase (AST) levels correlated with the virus replication rate in the four infected hepatoma cells. In conclusion, we showed that dengue virus can infect diverse liver cells with differing replication efficiency, which causes cytopathic effects (CPEs) of diverse severity. Among the CPEs, the increased AST levels correlated with the clinical results from 24 dengue fever patients, who showed increased AST levels at the onset of fever. In summary, we find that dengue-2 virus replicates actively and causes severe CPEs in differentiated hepatoma cells. Factors related to differentiation as well as tumorigenicity seem to play critical roles, though the mechanisms of action remain unclear.

Serum phospholipase A2 in dengue

Group II phospholipase A2 is an enzyme involved in the pathologies of various inflammatory diseases, including infections. We measured the concentration of group II phospholipase A2 in sera of 49 patients suffering from dengue, virus serotype 3, during a recent epidemic in The Cook Islands. Group II phospholipase A2 concentrations were elevated above the normal level in 90% of the patients. There was a significant negative correlation between group II phospholipase A2 levels and platelet counts. It was concluded that dengue virus infection causes a generalized inflammatory reaction and acute phase response. Determination of serum group II phospholipase A2 level gives useful information for assessing the severity of viral infections, including dengue.

The impact of dengue haemorrhagic fever on liver function

The impact of dengue haemorrhagic fever (DHF) on liver function was studied by measuring serum transaminase levels on 45 patients with DHF confirmed by virus isolation and serodiagnosis in 1995. Abnormal levels of AST and ALT were observed in 97.7 and 37.3% of the patients, respectively. The fact that the level of AST was higher than that of ALT and that the elevation of transaminases was mild to moderate in most cases (< 5-fold greater than the normal upper limit for AST and ALT) showed that liver involvement was also mild to moderate in most cases of DHF. The results of transaminases did not differ significantly between cases with and without hepatitis B or hepatitis C virus infection, nor between primary and secondary cases of infection, but a significantly higher elevation of AST and ALT was observed in DHF patients with gastrointestinal haemorrhage. Two patients with dengue encephalopathy (in 1992) and one patient with dengue encephalopathy who died of massive gastrointestinal haemorrhage (in 1995) had unusually high transaminase levels as a sign of acute liver failure. It is concluded that DHF may cause mild to moderate liver dysfunction in most cases; only some patients may suffer from acute liver failure leading to encephalopathy and death.

Studies of platelet monoamine oxidase activity in Epstein-Barr and dengue virus infections

As part of a prospective, psychosocial, and biochemical study of infectious mononucleosis, platelet monoamine oxidase (MAO) activity has been evaluated as a host factor. It was found that platelet MAO activity may be a possible predisposing host factor but not a precipitating factor. The results on infectious mononucleosis, a viral disease which involves the host's cell-mediated immune system, are compared with an evaluation of platelet MAO activity in dengue, a viral disorder involving the host's humoral immune system. The platelet MAO activity in these disorders has been compared to that in schizophrenia, a disease for which low platelet MAO activity has been postulated, from retrospective and twin studies, to be a risk factor. One hypothesis suggests that low platelet MAO activity predisposes to development of schizophrenia, but also increases cell-mediated immune system responses.