Abstract
Ultrastructural studies revealing morphological differences between intact and photodynamically inactivated virions can point to inactivation mechanisms and molecular targets. Using influenza as a model system, we show that photodynamic virus inactivation is possible without total virion destruction. Indeed, irradiation with a relatively low concentration of the photosensitizer (octacationic octakis(cholinyl) zinc phthalocyanine) inactivated viral particles (the virus titer was determined in Madin Darby Canine Kidney (MDCK) cells) but did not destroy them. Transmission electron microscopy (TEM) revealed that virion membranes kept structural integrity but lost their surface glycoproteins. Such structures are known as “bald” virions, which were first described as a result of protease treatment. At a higher photosensitizer concentration, the lipid membranes were also destroyed. Therefore, photodynamic inactivation of influenza virus initially results from surface protein removal, followed by complete virion destruction. This study suggests that photodynamic treatment can be used to manufacture “bald” virions for experimental purposes. Photodynamic inactivation is based on the production of reactive oxygen species which attack and destroy biomolecules. Thus, the results of this study can potentially apply to other enveloped viruses and sources of singlet oxygen.
Highlights
Photodynamic inactivation (PDI) can be used to destroy pathogenic microorganisms including bacteria, viruses, fungi, and protozoa [1,2,3] which has practical applications for virus-associated lesions treatment [4] and the disinfection of water [5] or blood products [6]
Using a non-purified allantoic liquid with 2 μM of photosensitizer proved to be inadequate because it was difficult to observe any structural features. This is likely due to the high concentration of proteins and other biomolecules within allantoic fluid which mask the virions. These molecules react with the singlet oxygen produced by the photosensitizer
We investigated the ultrastructural properties of photodynamic inactivation of H5N8 influenza virus
Summary
Photodynamic inactivation (PDI) can be used to destroy pathogenic microorganisms including bacteria, viruses, fungi, and protozoa [1,2,3] which has practical applications for virus-associated lesions treatment [4] and the disinfection of water [5] or blood products [6]. The PDI technique works by exposing microorganisms to a photosensitizer which, when irradiated with the spectral region corresponding to the photosensitizer absorption bands, converts molecular oxygen into toxic reactive oxygen species (ROS). As summarized by Costa et al [14], the main types of photodynamic damage to mammalian virus envelopes include: altering protein cross-link formation, a complete loss of proteins, changes in protein conformation or the alteration of molecular mass and charge. These forms of virion damage can prevent viral absorption and host penetration, inhibit membrane fusion, and reduce infectivity. The kinetics of viral inactivation depends on the photosensitizer concentration, yield of singlet oxygen, and parameters of irradiation [9,14]
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