The virucidal effects of 405 nm visible light on SARS-CoV-2 and influenza A virus.

The germicidal potential of specific wavelengths within the electromagnetic spectrum is an area of growing interest. While ultra-violet (UV) based technologies have shown satisfactory virucidal potential, the photo-toxicity in humans coupled with UV associated polymer degradation limit their use in occupied spaces. Alternatively, longer wavelengths with less irradiation energy such as visible light (405 nm) have largely been explored in the context of bactericidal and fungicidal applications. Such studies indicated that 405 nm mediated inactivation is caused by the absorbance of porphyrins within the organism creating reactive oxygen species which result in free radical damage to its DNA and disruption of cellular functions. The virucidal potential of visible-light based technologies has been largely unexplored and speculated to be ineffective given the lack of porphyrins in viruses. The current study demonstrated increased susceptibility of lipid-enveloped respiratory pathogens of importance such as SARS-CoV-2 (causative agent of COVID-19) and influenza A virus to 405 nm, visible light in the absence of exogenous photosensitizers thereby indicating a potential alternative porphyrin-independent mechanism of visible light mediated viral inactivation. These results were obtained using less than expected irradiance levels which are considered safe for humans and commercially achievable. Our results support further exploration of the use of visible light technology for the application of continuous decontamination in occupied areas within hospitals and/or infectious disease laboratories, specifically for the inactivation of respiratory pathogens such as SARS-CoV-2 and Influenza A.

High pressure treatment under subfreezing temperature results in drastic inactivation of enveloped and non-enveloped viruses.

Some viruses are sensitive to high pressure. The freeze-pressure generation method (FPGM) applies pressure as high as 250 MPa on a substance, simply by freezing a pressure-resistant reservoir in which the substance is immersed in water. Here we examined whether the FPGM successfully inactivates herpes simplex virus type 1 (HSV-1), an enveloped DNA virus belonging to the human Herpesviridae, and encephalomyocarditis virus (EMCV), an envelope-free RNA virus belonging to the Picornaviridae. After the treatment, HSV-1 drastically reduced the ability to form plaque in Vero cells in vitro as well as to kill mice in vivo. EMCV that had been pressurized failed to proliferate in HeLa cells and induce interferon response. The results suggest that the FPGM provides a feasible procedure to inactivate a broad spectrum of viruses.

Studies of inactivation of encephalomyocarditis virus, M13 bacteriophage, and Salmonella typhimurium by using a visible femtosecond laser: insight into the possible inactivation mechanisms.

We report experimental results on the inactivation of encephalomyocarditis virus, M13 bacteriophage, and Salmonella typhimurium by a visible femtosecond laser. Our results suggest that inactivation of virus and bacterium by a visible femtosecond laser involves completely different mechanisms. Inactivation of viruses by a visible femtosecond laser involves the breaking of hydrogen∕hydrophobic bonds or the separation of the weak protein links in the protein shell of a viral particle. In contrast, inactivation of bacteria is related to the damage of their DNAs due to irradiation of a visible femtosecond laser. Possible mechanisms for the inactivation of viruses and bacteria are discussed.

The band III ligand dipyridamole protects human RBCs during photodynamic treatment while extracellular virus inactivation is not affected.

BACKGROUND: Recently, the potential usefulness of dipyridamole (DIP) in protecting RBCs against the harmful side effects of photodynamic sterilization was demonstrated. In the present study, the use of DIP for selective protection of RBCs was investigated under conditions more relevant for blood bank practice. STUDY DESIGN AND METHODS: WBC-reduced RBC suspensions (30% Hct) were treated with 1,9-dimethylmethylene blue and red light, and the influence of the inclusion of DIP on photohemolysis was assessed as a function of sensitizer concentration, light dose, and storage time. Furthermore, the possible interference of DIP with inactivation of extracellular virus by use of a panel of different viruses (HIV-1, pseudorabies virus [PRV], bovine viral diarrhea virus [BVDV], VSV, encephalomyocarditis, and canine parvovirus) was investigated. RESULTS: In WBC-reduced RBC suspensions (30% Hct), DIP exerted a clear protective effect against photohemolysis. Part of this protection was achieved with concentrations near the dissociation constant for band III binding. Importantly, efficiency of inactivation of extracellular HIV-1, PRV, BVDV, and VSV was not significantly impaired by the inclusion of DIP. Phototreatment conditions, resulting in a 4 to 5 log inactivation of extracellular HIV-1 and PRV, resulted in a high level of hemolysis after 28 days of storage. This long-term hemolysis could be decreased, but not completely prevented, by the inclusion of DIP. CONCLUSION: Photohemolysis in RBC concentrates can be reduced substantially by the application of DIP, while the efficacy of inactivation of HIV-1 and other viruses remains unchanged.

Preservation of red cell properties after virucidal phototreatment with dimethylmethylene blue.

BACKGROUND: All published reports have described methods for virus photoinactivation which significantly alter red cell (RBC) properties during storage. In order to improve virucidal activity and reduce damage to RBCs, a series of phenothiazine derivatives were either synthesized or purified and screened for bacteriophage inactivation and red cell potassium efflux. One compound, 1,9-dimethylmethylene blue (dimethyl-methylene blue), had superior screening results and was chosen for further characterization. STUDY DESIGN AND METHODS: White cell reduced RBC suspensions (30% hematocrit) were deliberately inoculated with extracellular virus or virus-infected VERO cells, incubated with 4 microM dimethyl-methylene blue and illuminated with cool-white fluorescent light. Control and treated samples were titered for virus inactivation. In parallel studies, RBC suspensions were exposed to dimethylmethylene blue and light under identical conditions and assayed for in vitro RBC storage properties. RESULTS: Phototreatment of RBC suspensions inactivated > 4.4 log10 of extracellular vesicular stomatitis virus (VSV), > 3.0 log10 of intracellular VSV, > 5.0 log10 of extracellular pseudorabies virus (PRV), > 4.8 log10 of intracellular PRV, > 4.7 log10 of extra-cellular bovine virus diarrhea virus, 5.8 log10 of bacterio-phage phi 6 and > 7 log10 of bacteriophage R17. Encephalo-myocarditis virus, a nonenveloped picornavirus, was resistant to photoinactivation. Virucidal conditions resulted in no detectable IgG binding in 11 of 13 samples, unchanged RBC morphology, normal banding patterns of RBC membrane proteins on SDS PAGE, and unaltered characteristics of 12 of 13 RBC antigens during storage as measured by antibody titrations. In addition, minimal changes were observed in RBC osmotic fragility, lysis, potassium efflux, ATP and 2,3-DPG levels, and the strength of one RBC antigen during storage of phototreated samples compared with controls. CONCLUSION: Dimethylmethylene blue photo-treatment can inactivate several intracellular and extracellular model viruses under conditions which minimally alter RBC properties during 42 days storage at 1-6 degrees C.

Antibody-nucleic acid interactions. Antibodies to psoralen-modified RNA as probes of RNA structure.

Antisera elicited by immunization of rabbits with 4'-aminomethyl-trioxsalen (AMT)-modified poly(A,U) complexed with methylated bovine serum albumin was characterized in competition radioimmunoassays (RIA) and enzyme-linked immunosorbent assays (ELISA). AMT-poly(A,U) was over 10,000-fold more reactive than unmodified poly(A,U) or AMT alone. The antiserum cross-reacted to varying extents with AMT-modified-RNA's and -DNA's. The presence of AMT-uridine usually assured strong reactivity. The amino group of AMT contributed to antibody binding to a small degree. Binding was not significantly affected by high ionic strength, suggesting that binding does not involve ion pair formation. Murine encephalomyocarditis virus replicative intermediates, as well as cellular RNA and DNA were modified by psoralen in intact cells, suggesting that EMCV RNA and cellular RNA's in intact cells possess detectable stretches of base pairs. The antibodies described here will be useful in studying the secondary and tertiary structure of RNA's in vitro and in intact cells.

Protein-RNA interaction in encephalomyocarditis virus as revealed by UV light-induced covalent linkages.

UV irradiation of encephalomyocarditis virus led to an increase in the buoyant density of the virus in CsCl gradients from 1.34 to 1.46 g/cm3. Heat treatment of the irradiated virus (20 min at 54 degrees C) reduced the density to 1.40 g/cm3 and led to the loss of approximately 55% of the labeled RNA from the virions. The non-irradiated virions were converted by such heating into empty capsids. Irradiation also resulted in an increase in the accessibility of RNA inside the virions to the action of pancreatic RNase. An increase in the UV dose did not enlarge the fraction of RNA molecules covalently linked to protein; this was revealed by the lack of any secondary increase in the apparent RNase resistance of the labeled RNA in the irradiated virions. Destruction of the irradiated virus with sodium dodecyl sulfate and 2-mercaptoethanol allowed the isolation of a 40S structure containing viral RNA and RNA-linked proteins. The latter comprised no more than 2.5% of the whole protein content of the virion. Polyacrylamide gel electrophoretic analysis of the RNase-treated 40S structure revealed at least three viral structural proteins in the same ratio as was present in the intact virions.

Protein synthesis and membrane integrity in interferon-treated HeLa cells infected with encephalomyocarditis virus.

The survival of interferon (IFN)-treated cells after encephalomyocarditis (EMC) virus infection depends on both the concentration of interferon and the multiplicity of infection (m.o.i.) used. The cell survived EMC infection if a high IFN/m.o.i. ratio was used in the experiment, whereas cell death took place at low IFN/m.o.i. ratios, even if IFN is also present during infection. Analysis by polyacrylamide gel electrophoresis of the proteins synthesized in IFN-treated cells subsequently infected with EMC indicated that no virus proteins were detected at either low or high multiplicities of infection. However, at low m.o.i. the cell survived and continued synthesizing cellular proteins exclusively, whereas at high m.o.i. a drastic shut-off of host protein synthesis took place. Virus which had been inactivated by u.v. irradiation was unable to cause the shut-off of host protein synthesis, either in control or in IFN-treated cells. This result suggests that some virus gene expression occurs in cells treated with IFN, although no virus protein synthesis was detected. The synthesis of virus RNA was also strongly inhibited after treated of cells with IFN. The integrity of the cell membrane in control and in IFN-treated cells was studied by analysing the 86Rb+ ion leakage, the thymidine pool, the chronic uptake and the entry of the translation inhibitor hygromycin B, to which cells are impermeable, at different times after EMC infection. The results obtained indicate that the early membrane leakiness observed after virus infection is not prevented by IFN treatment. However, the development of late leakiness to 86Rb+ ions, thymidine and hygromycin B was not observed in IFN-treated cells.

Photoinactivation of the encephalomyocarditis virus.

Encephalomyocarditis virus was photoinactivated by a dilution of 1:30,000 neutral red and 70 minutes exposure to light. A dye inactivation of the EMC virus is possible without destruction of its antigenicity. The EMC virus vaccine induced a good immunity response in mice; we did not find any infectious virus.

Immunization of mice against encephalomyocarditis virus. II. Intraperitoneal and respiratory immunization with ultraviolet-inactivated vaccine: effect of Bordetella pertussis extract on the immune response.

Mice were immunized by intraperitoneal (ip) or respiratory administration of ultraviolet-inactivated virus alone or with Bordetella pertussis extract (BPE) as an adjuvant. The effect of immunization was tested by determination of antibody titers and by survival of a lethal challenge with 200 LD(50) of a virulent (large-plaque variant) strain of EMC virus. For plain vaccine the ip 50% effective dose (ED(50)) was 37 hemagglutination units (HAU; ca. 4 x 10(6) plaque-forming unit equivalents); with adjuvant the ip ED(50) was reduced to 20 HAU. After respiratory immunization by intratracheal injection, an ED(50) value of 100 HAU was found, which was not affected by BPE. After ip vaccination the primary immune response was enhanced by BPE, but the challenge response, measured 3 weeks after challenge, was unaffected. Respiratory immunization induced a primary response which was not influenced by BPE, but here the challenge response was enhanced by the adjuvant. After secondary treatment (challenge or booster vaccination) serum antibodies and protection against challenge persisted for at least 1 year.

Interferon-inducing characteristics of MM virus.

Interferon induction by MM virus in mice and in L cells was studied. In mice the virus readily induced interferon. The time of appearance was dose-dependent. A large virus dose induced interferon by 4 hr, whereas a small dose resulted in interferon production which paralleled virus replication 24 hr after infection. In L cells the interferon-inducing capacity of the virus was rapidly destroyed by ultraviolet light irradiation. Heating (56 C) of the virus, on the other hand, greatly increased its ability to induce interferon. Interferon production could also be increased by prior treatment of the cells with homologous interferon (priming). The increase in interferon production after priming was dependent on the concentration of interferon used for priming, the length of interferon treatment, and the multiplicity of infection. It is suggested that MM virus might be useful for the further study of the mechanisms involved in the production and action of interferon.

Interaction of encephalomyocarditis virus with ultraviolet-irradiated host cells.

Ultraviolet light (UV) impaired the capacity of L cells to support growth of encephalomyocarditis virus. The loss of capacity was partially restored by high multiplicity of infection (MOI). This phenomenon was not due to an increased probability of an infectious virus particle reaching a site of replication undamaged by UV, since UV-inactivated virus at high MOI induced restoration of the capacity to support multiplication of nonirradiated virus adsorbed at low MOI. Multiplicity reactivation of UV-irradiated virus did not play a role in this phenomenon since restoration of capacity took place without multiplication of the UV-irradiated restoring virus. The evidence indicates that restoration of capacity was not due to viral interactions involving genetic exchange. The ability to restore capacity was a property more radioresistant than infectivity, suggesting that the former is a function only of part of the viral genome.