Photodynamic inactivation of herpes simplex virus: a status report

Trends and targets in antiviral phototherapy

Photodynamic therapy (PDT) is a well-established treatment option in the treatment of certain cancerous and pre-cancerous lesions. Though best-known for its application in tumor therapy, historically the photodynamic effect was first demonstrated against bacteria at the beginning of the 20^th century. Today, in light of spreading antibiotic resistance and the rise of new infections, this photodynamic inactivation (PDI) of microbes, such as bacteria, fungi, and viruses, is gaining considerable attention. This review focuses on the PDI of viruses as an alternative treatment in antiviral therapy, but also as a means of viral decontamination, covering mainly the literature of the last decade. The PDI of viruses shares the general action mechanism of photodynamic applications: the irradiation of a dye with light and the subsequent generation of reactive oxygen species (ROS) which are the effective phototoxic agents damaging virus targets by reacting with viral nucleic acids, lipids and proteins. Interestingly, a light-independent antiviral activity has also been found for some of these dyes. This review covers the compound classes employed in the PDI of viruses and their various areas of use. In the medical area, currently two fields stand out in which the PDI of viruses has found broader application: the purification of blood products and the treatment of human papilloma virus manifestations. However, the PDI of viruses has also found interest in such diverse areas as water and surface decontamination, and biosafety.

Porphyrin-based cationic amphiphilic photosensitisers as potential anticancer, antimicrobial and immunosuppressive agents

Photodynamic therapy (PDT) combines a photosensitiser, light and molecular oxygen to induce oxidative stress that can be used to kill pathogens, cancer cells and other highly proliferative cells. There is a growing number of clinically approved photosensitisers and applications of PDT, whose main advantages include the possibility of selective targeting, localised action and stimulation of the immune responses. Further improvements and broader use of PDT could be accomplished by designing new photosensitisers with increased selectivity and bioavailability. Porphyrin-based photosensitisers with amphiphilic properties, bearing one or more positive charges, are an effective tool in PDT against cancers, microbial infections and, most recently, autoimmune skin disorders. The aim of the review is to present some of the recent examples of the applications and research that employ this specific group of photosensitisers. Furthermore, we will highlight the link between their structural characteristics and PDT efficiency, which will be helpful as guidelines for rational design and evaluation of new PSs.

Synergism between Electrolysis and Methylene Blue Photodynamic Action inEscherichia Coli

There is interest in the use of photodynamic therapy for the treatment of certain diseases, including cancer. However, weak penetration of visible light in tissues has restricted its use. In this study the possibility of enhancing photodynamic effects by the use of energies that penetrate more deeply in tissues was investigated. Weak electric currents (1.0 mA) applied to Escherichia coli cells for short periods, producing little or no lethal damage, was found to act synergistically with the photodynamic action of methylene blue, significantly enhancing the effects of this treatment. This synergism exists also between electrolysis and X-rays but not between electrolysis and UV-254 nm. It is suggested that this synergism might eventually be used to improve the results obtained in therapeutic practice based on the utilization of photodynamic action.

Effects of methylene blue-treated plasma on red cells and stored platelet concentrates

BACKGROUND

Photochemical methods can effectively inactivate extracellular viruses and bacteria found in blood components. Treatment of plasma with methylene blue (MB), a phenothiazine dye, and visible light inactivates enveloped viruses including HIV-1. The effects of MB-treated plasma on cellular components stored in vitro have not been well characterized.

STUDY DESIGN AND METHODS

MB-treated plasma (83 microg MB/250 mL plasma) was added to single-donor platelets, stored AS-1 red cells (RBCs), irradiated RBCs, and frozen-deglycerolized RBCs. In vitro platelet assays performed after 1 and 5 days of storage in MB-treated plasma included pH, pO2, pCO2, HCO3, platelet number, lactate dehydrogenase, glucose, osmotic recovery, and CD62 expression. RBC components were examined at specific intervals for leakage of potassium, plasma hemoglobin level, and percentage of hemolysis. Direct antiglobulin tests, osmotic fragilities, and RBC antigen stability tests were also performed on RBCs stored in MB-treated plasma. Components stored with autologous plasma or nontreated allogeneic plasma served as controls.

RESULTS

Similar storage-induced changes in pH, glucose, and platelet numbers, as well as increases in lactate dehydrogenase, CD62 expression, and lactate were seen in single-donor platelets stored with MB-treated and control plasma. Platelet morphology scores and osmotic recoveries were not altered. Plasma hemoglobin and potassium and percentage of hemolysis increased equally in the various RBC components stored with MB-treated or nontreated plasma. Osmotic fragility and RBC antigen stability were not appreciably altered by MB-treated plasma.

CONCLUSION

Plasma treated by MB photoinactivation can be used for in vitro resuspension and storage of platelets or RBCs, because of the lack of influence of MB-treated plasma on a variety of in vitro platelet and RBC assays.

Photoinactivation of viruses in human fresh plasma by phenothiazine dyes in combination with visible light

We developed a photodynamic method to inactivate viruses in human fresh plasma. Single plasma bags were illuminated with visible light in the presence of low doses of phenothiazine dyes like methylene blue or toluidine blue. By this treatment the infectivity of different enveloped viruses including the causative agent of AIDS, HIV-1, was completely removable from the plasma. Non enveloped viruses, however, proved to be more stable. The activities of clotting factors and other plasma proteins were only slightly decreased. There was no indication that the procedure led to important structural modifications of plasma proteins. The dyes are photodynamically active at concentrations much lower than those at which they are therapeutically used as antidots in the treatment of methemoglobinemia.

Photodynamic inactivation of pseudorabies virus with methylene blue dye, light, and electricity

Pseudorabies virus was photoinactivated with a combination of methylene blue dye, light, and electricity. Viral suspensions were mixed with variable amounts of methylene blue dye and then were placed in a current source apparatus. Total inactivation of pseudorabies virus (1.7 X 10(6) 50% tissue culture infective doses per ml) was achieved with constant mixing, a methylene blue dye concentration of 10(-4) M, and an electrical current of 12 microA for 12 min.

Proflavin: an unusual mutagen

In the Salmonella typhimurium mutagenicity assay, proflavin (PF), in the dark, was shown to possess some direct-acting frameshift mutagenic activity for strains TA1537 and TA98. In the presence of microsomal enzymes from mouse, hamster and rat livers, frameshift mutagenic activity for strain TA1538 and enhanced mutagenicity for strain TA1537 was observed. Exposure of bacteria to PF in the presence of visible light resulted in base substitution (strain TA1535) as well as frameshift (TA1537, TA1538, TA98) genetic activities. The findings are taken to indicate that PF possesses direct-acting frameshift activity (TA1537 and TA98) by virtue of its ability to intercalate between DNA base-pairs. The frameshift activity (TA1538, TA98 and enhanced TA1537) seen following metabolic or photo-activation may be due to the formation of chemical adducts between the cellular DNA and oxidation products of PF (a base-displacement effect). The light-induced base-substitution activity probably results from the generation of singlet oxygen which reacts with the guanine moiety of DNA. The mutagenic photoproduct of PF appears to be stable.

The wavelength dependence of 8-methoxypsoralen photosensitization of radiation-enchanced reactivation in a mammalian cell-virus system

The combined effect of 8-methoxypsoralen (8-MOP) and ultraviolet (UV) radiation on the ability of an irradiated mammalian cell (CV-1) to reactivate UV-irradiated mammalian virus (Herpes simplex) was tested. Prior treatment of cells with 8-MOP was found to increase Radiation-Enhanced Reactivation (RER) at one wavelength (297 nm) in the far ultraviolet but not at others (240-289 nm). This same treatment induced RER in the near UV (302-370 nm) and the visible region (380-400 nm). An action spectrum for the photo-sensitized induction of this cellular parameter was obtained. This action spectrum is consistent with the absorption spectrum for 8-MOP and the theory that damage to DNA is, at least in part, responsible for Radiation-Enhanced Reactivation.