Mechanisms of photodynamic inactivation of herpes simplex viruses: comparison between methylene blue, light plus electricity, and hematoporhyrin plus light

Instantaneous Inactivation of Herpes Simplex Virus by Silicon Nitride Bioceramics

Hydrolytic reactions taking place at the surface of a silicon nitride (Si3N4) bioceramic were found to induce instantaneous inactivation of Human herpesvirus 1 (HHV-1, also known as Herpes simplex virus 1 or HSV-1). Si3N4 is a non-oxide ceramic compound with strong antibacterial and antiviral properties that has been proven safe for human cells. HSV-1 is a double-stranded DNA virus that infects a variety of host tissues through a lytic and latent cycle. Real-time reverse transcription (RT)-polymerase chain reaction (PCR) tests of HSV-1 DNA after instantaneous contact with Si3N4 showed that ammonia and its nitrogen radical byproducts, produced upon Si3N4 hydrolysis, directly reacted with viral proteins and fragmented the virus DNA, irreversibly damaging its structure. A comparison carried out upon testing HSV-1 against ZrO2 particles under identical experimental conditions showed a significantly weaker (but not null) antiviral effect, which was attributed to oxygen radical influence. The results of this study extend the effectiveness of Si3N4's antiviral properties beyond their previously proven efficacy against a large variety of single-stranded enveloped and non-enveloped RNA viruses. Possible applications include the development of antiviral creams or gels and oral rinses to exploit an extremely efficient, localized, and instantaneous viral reduction by means of a safe and more effective alternative to conventional antiviral creams. Upon incorporating a minor fraction of micrometric Si3N4 particles into polymeric matrices, antiherpetic devices could be fabricated, which would effectively impede viral reactivation and enable high local effectiveness for extended periods of time.

Photodynamic Inhibition of Herpes Simplex Virus 1 Infection by Tricationic Amphiphilic Porphyrin with a Long Alkyl Chain

Photodynamic therapy (PDT) is broadly used to treat different tumors, and it is a rapidly developing approach to inactivating or inhibiting the replication of fungi, bacteria, and viruses. Herpes simplex virus 1 (HSV-1) is an important human pathogen and a frequently used model to study the effects of PDT on enveloped viruses. Although many photosensitizers (PSs) have been tested for their antiviral properties, analyses are usually limited to assessing the reduction in viral yield, and thus the molecular mechanisms of photodynamic inactivation (PDI) remain poorly understood. In this study, we investigated the antiviral properties of TMPyP3-C17H35, a tricationic amphiphilic porphyrin-based PS with a long alkyl chain. We show that light-activated TMPyP3-C17H35 can efficiently block virus replication at certain nM concentrations without exerting obvious cytotoxicity. Moreover, we show that the levels of viral proteins (immediate-early, early, and late genes) were greatly reduced in cells treated with subtoxic concentrations of TMPyP3-C17H35, resulting in markedly decreased viral replication. Interestingly, we observed a strong inhibitory effect of TMPyP3-C17H35 on the virus yield only when cells were treated before or shortly after infection. In addition to the antiviral activity of the internalized compound, we show that the compound dramatically reduces the infectivity of free virus in the supernatant. Overall, our results demonstrate that activated TMPyP3-C17H35 effectively inhibits HSV-1 replication and that it can be further developed as a potential novel treatment and used as a model to study photodynamic antimicrobial chemotherapy.

Interventions for treatment of herpes labialis (cold sores on the lips)

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To assess the effects of interventions for treating herpes labialis among immunocompetent people.

New methylene blue derivatives suggest novel anti-orthopoxviral strategies

Decades after the eradication of smallpox and the discontinuation of routine smallpox vaccination, over half of the world's population is immunologically naïve to variola virus and other orthopoxviruses (OPXVs). Even in those previously vaccinated against smallpox, protective immunity wanes over time. As such, there is a concomitant increase in the incidence of human OPXV infections worldwide. To identify novel antiviral compounds with potent anti-OPXV potential, we characterized the inhibitory activity of PAV-866 and other methylene blue derivatives against the prototypic poxvirus, vaccinia virus (VACV). These compounds inactivated virions prior to infection and consequently inhibited viral binding, fusion and entry. The compounds exhibited strong virucidal activity at non-cytotoxic concentrations, and inhibited VACV infection when added before, during or after viral adsorption. The compounds were effective against other OPXVs including monkeypox virus, cowpox virus and the newly identified Akhmeta virus. Altogether, these findings reveal a novel mode of inhibition that has not previously been demonstrated for small molecule compounds against VACV. Additional studies are in progress to determine the in vivo efficacy of these compounds against OPXVs and further characterize the anti-viral effects of these derivatives.

A Comparison of Porphyrin Photosensitizers in Photodynamic Inactivation of RNA and DNA Bacteriophages

Effective broad-spectrum antiviral treatments are in dire need as disinfectants and therapeutic alternatives. One such method of disinfection is photodynamic inactivation, which involves the production of reactive oxygen species from dissolved oxygen in response to light-stimulated photosensitizers. This study evaluated the efficacy of functionalized porphyrin compounds for photodynamic inactivation of bacteriophages as human virus surrogates. A blue-light light emitting diode (LED) lamp was used to activate porphyrin compounds in aqueous solution (phosphate buffer). The DNA bacteriophages ΦX174 and P22 were more resistant to porphyrin TMPyP photodynamic inactivation than RNA bacteriophage fr, with increasing rates of inactivation in the order: ΦX174 << P22 << fr. Bacteriophage ΦX174 was therefore considered a resistant virus suitable for the evaluation of three additional porphyrins. These porphyrins were synthesized from TMPyP by inclusion of a central palladium ion (PdT4) and/or the addition of a hydrophobic C14 chain (PdC14 or C14). While the inactivation rate of bacteriophage ΦX174 via TMPyP was similar to previous reports of resistant viruses, ΦX174 inactivation increased by a factor of approximately 2.5 using the metalloporphyrins PdT4 and PdC14. The order of porphyrin effectiveness was TMPyP < C14 < PdT4 < PdC14, indicating that both Pd²⁺ ligation and C14 functionalization aided virus inactivation.

Photodynamic therapy and Acyclovir in the treatment of recurrent herpes labialis: A controlled randomized clinical trial

BACKGROUND

Herpes Simplex Virus Type 1 (HSV-1) is one of the most widespread infections that can effect the orofacial region. Recurrent infection is considered a life-long oral health problem, leading to pain, discomfort, and social restriction due to esthetic features when active. Effective therapies are needed. This study aimed to compare photodynamic therapy (PDT), Topical Acyclovir (AC), and the association of both in the healing process and self-reported symptomologies of HSV-1 recurrences.

METHODS

Patients were randomly assigned into 3 groups (n = 25): PDT (low-power laser, 660 nm, 40 mW, 120 J/cm², 4.8 J, 120 s per point) and methylene blue (0.005 %) as photosensitizer; AC (5%); PDT + AC.Data concerning lesion size, healing time, and self-reported healing parameters, such as pain, tingling, and edema were taken every day up to complete healing for all studied groups.

RESULTS

There was no significant difference in healing time and pain between groups. AC group showed a significant minor reduction of the lesion compared to the AC-PDT group on day 1. Regarding edema and tingling, the comparison of treatments showed a statistical difference only on day 1, where PDT showed better results.

CONCLUSION

With all the limitations of this study, it can be concluded that only on day 1 PDT showed positive effects in the treatment of herpes lesions in comparison to AC.

Human alpha and beta herpesviruses and cancer: passengers or foes?

Based on seroepidemiological studies, human herpes simplex virus types 1 and 2 (HSV-1, HSV-2) are put in relation with a number of cancer diseases; however, they do not appear to play a direct role, being only considered cofactors. Their ability to transform the cells in vitro could be demonstrated experimentally by removing their high lytic ability by a certain dose of UV radiation or by photoinactivation in the presence of photosensitizers, such as neutral red or methylene blue, or culturing under conditions suppressing their lytic activity. However, recent studies indicate that UV irradiated or photoinactivated HSV-1 and HSV-2, able to transform non-transformed cells, behave differently in transformed cells suppressing their transformed phenotype. Furthermore, both transforming and transformed phenotype suppressing activities are pertaining only to non-syncytial virus strains. There are some proposed mechanisms explaining their transforming activity. According to the "hit and run" mechanism, viral DNA induces only initiation of transformation by interacting with cellular DNA bringing about mutations and epigenetic changes and is no longer involved in other processes of neoplastic progression. According to the "hijacking" mechanism, virus products in infected cells may activate signalling pathways and thus induce uncontrolled proliferation. Such a product is e.g. a product of HSV-2 gene designated ICP10 that encodes an oncoprotein RR1PK that activates the Ras pathway. In two cases of cancer, in the case of serous ovarian carcinoma and in some prostate tumours, virus-encoded microRNAs (miRNAs) were detected as a possible cofactor in tumorigenesis. And, recently described herpes virus-associated growth factors with transforming and transformation repressing activity might be considered important factors playing a role in tumour formation. And finally, there is a number of evidence that HSV-2 may increase the risk of cervical cancer after infection with human papillomaviruses. A similar situation is with human cytomegalovirus; however, here, a novel mechanism named oncomodulation has been proposed. Oncomodulation means that HCMV infects tumour cells and modulates their malignant properties without having a direct effect on cell transformation.

Inactivation of acyclovir-sensitive and -resistant strains of herpes simplex virus type 1 in vitro by photodynamic antimicrobial chemotherapy

PURPOSE

To evaluate the efficacy of photodynamic antimicrobial chemotherapy (PACT) with the new porphyrin derivative TONS 504 and a light-emitting diode (LED) against acyclovir (ACV)-sensitive and -resistant herpes simplex virus type 1 (HSV-1).

METHODS

Human FL cells infected with the viral strains were subjected to PACT with TONS 504 at various concentrations (0.01 to 10 mg/l) and irradiation at various light energies (10 to 30 J/cm(2)) and were then incubated for 24 h before analysis.

RESULTS

Immunocytofluorescence analysis with antibodies to HSV-1 revealed that PACT eliminated HSV-1 and ACV-resistant HSV-1 in a manner dependent on the TONS 504 concentration and light energy. Complete eradication of both viruses was apparent at a TONS 504 concentration of 10 mg/l and light energy of 10 to 30 J/cm(2) as well as at a TONS 504 concentration of 1 mg/l and light energy of 20 or 30 J/cm(2). No antiviral effect was apparent with TONS 504 in the absence of irradiation or with irradiation in the absence of TONS 504. Staining of cell nuclei with 4', 6-diamidino-2-phenylindole revealed no apparent cytotoxicity of the PACT system, a finding that was confirmed by the system's failure to induce the release of lactate dehydrogenase from the host cells.

CONCLUSIONS

We conclude that our PACT system based on TONS 504 and an LED is effective for eliminating HSV-1 and ACV-resistant HSV-1 without a harmful effect on host cells.

Laser treatment of recurrent herpes labialis: a literature review

Recurrent herpes labialis is a worldwide life-long oral health problem that remains unsolved. It affects approximately one third of the world population and causes frequent pain and discomfort episodes, as well as social restriction due to its compromise of esthetic features. In addition, the available antiviral drugs have not been successful in completely eliminating the virus and its recurrence. Currently, different kinds of laser treatment and different protocols have been proposed for the management of recurrent herpes labialis. Therefore, the aim of the present article was to review the literature regarding the effects of laser irradiation on recurrent herpes labialis and to identify the indications and most successful clinical protocols. The literature was searched with the aim of identifying the effects on healing time, pain relief, duration of viral shedding, viral inactivation, and interval of recurrence. According to the literature, none of the laser treatment modalities is able to completely eliminate the virus and its recurrence. However, laser phototherapy appears to strongly decrease pain and the interval of recurrences without causing any side effects. Photodynamic therapy can be helpful in reducing viral titer in the vesicle phase, and high-power lasers may be useful to drain vesicles. The main advantages of the laser treatment appear to be the absence of side effects and drug interactions, which are especially helpful for older and immunocompromised patients. Although these results indicate a potential beneficial use for lasers in the management of recurrent herpes labialis, they are based on limited published clinical trials and case reports. The literature still lacks double-blind controlled clinical trials verifying these effects and such trials should be the focus of future research.

Photodynamic inactivation of mammalian viruses and bacteriophages

Photodynamic inactivation (PDI) has been used to inactivate microorganisms through the use of photosensitizers. The inactivation of mammalian viruses and bacteriophages by photosensitization has been applied with success since the first decades of the last century. Due to the fact that mammalian viruses are known to pose a threat to public health and that bacteriophages are frequently used as models of mammalian viruses, it is important to know and understand the mechanisms and photodynamic procedures involved in their photoinactivation. The aim of this review is to (i) summarize the main approaches developed until now for the photodynamic inactivation of bacteriophages and mammalian viruses and, (ii) discuss and compare the present state of the art of mammalian viruses PDI with phage photoinactivation, with special focus on the most relevant mechanisms, molecular targets and factors affecting the viral inactivation process.

Characterization of the photochromic pigments in red fluorescent proteins purified from the gut juice of the silkworm Bombyx mori L

Multiple forms of red fluorescent proteins (RFPs) were observed in the gut juice of the silkworm, Bombyx mori L. It is to be noted that only one RFP band is reported in the literature so far. However, we report here three electrophoretically separated RFPs (A, B and C) found to be heterogeneous with respect to their components, namely the protein part and the fluorescent tetrapyrrole pigment moiety. Of the three RFPs, band C was found to be a glycoprotein. The absorption extinction coefficients and fluorescence quantum yields of the three RFPs were estimated. Further, this is the first communication demonstrating the presence of three different chlorophyll derivatives associated with the three different RFPs. The pigments were analyzed by thin layer chromatography followed by their elution to characterize the pigments by spectrophotometric and spectrofluorometric methods. Spectral characteristics have led to the identification of monovinyl chlorophyllide a, divinyl protochlorophyllide a and monovinyl pheophytin a as being associated with RFP bands A, B and C, respectively. These three purified RFPs can serve as the source of the three pigments as the standards.

Anti-herpes simplex virus activities of two novel disulphated cyclitols

By screening a library of sulphated compounds of low molecular weight, we have found that several cyclitol derivatives, each modified with two sulphate groups in addition to pyrrole and various aromatic moieties, inhibited infectivity of herpes simplex virus (HSV) at concentrations approximately 100 times lower than those toxic for cultured cells. These disulphated cyclitols interfered with HSV-1 attachment to cells, and efficiently reduced the cell-to-cell spread of the virus. This effect is most likely due to their low molecular weight and associated with the compounds' capability to access the narrow intercellular spaces. Furthermore, these disulphated cyclitols also inactivated infectivity of HSV. However, the virus-inactivating activities of these compounds were to some extent diminished in the presence of human cervical secretions or other protein-rich solutions suggesting that disulphated cyclitols may have some features of surfactant-type virucides. In conclusion, this new class of anti-HSV compounds offers potential for further development.

Novel therapeutic strategy for prevention of malignant tumor recurrence after surgery: Local delivery and prolonged release of adenovirus immobilized in photocured, tissue-adhesive gelatinous matrix

We have been developing a new gene delivery method using a styrenated gelatin-based tissue-adhesive matrix that allows in situ adenovirus-immobilized gel formation on living tissue and sustained virus release to permeate carcinoma tissue. Styrenated gelatin was synthesized by the condensation reaction of gelatin with 4-vinylbenzoic acid. Aqueous styrenated gelatin solution premixed with AdLacZ, adenovirus encoding beta-galactosidase cDNA, and carboxylated camphorquinone (CQ) as a photoinitiator was irradiated with visible light to form a styrenated gelatin gel. The in vitro adenovirus release from the styrenated gelatin gel to a medium strongly depended not on styrenated gelatin concentration but on CQ concentration. Maximal beta-galactosidase expression was observed on day 1, followed by a rapid decrease that continued up to 1 month for a styrenated gelatin gel prepared with a low styrenated gelatin concentration and a low CQ concentration. Dose-dependent reduced expression of beta-galactosidase activity with increasing CQ under photoirradiation was observed. AdLacZ-immobilized styrenated gelatin gel was formed on a hybrid tissue, which is a cell traction-induced collagenous gel entrapped with fibroblasts, and lacZ gene expression of fibroblasts in the hybrid tissue was observed for more than one month. The result of this in vitro model experiment implies that the tissue-adhesive styrenated gelatin may be applicable for the delivery of adenovirus encoding cDNA for tumor dormancy therapy into malignant tissue to prevent tumor recurrence after surgery when cDNA is properly selected.

Photodynamic treatment of adenoviral vectors with visible light: an easy and convenient method for viral inactivation

Recombinant adenovirus vectors are popular tools for gene transfer and gene therapy. However biosafety constraints require that all handling of the vectors and vector-containing samples is restricted to dedicated containment laboratories, unless they had undergone a validated virus-inactivation procedure, which decontaminates the samples from any active virus. In this study we evaluated the feasibility of photodynamic treatment (PDT) with visible light to inactivate recombinant adenovirus vectors in biological samples, with minimum associated effects on other biological activities. Several photosensitizers were tested for their capacity to inactivate a model human adenovirus vector, AdCMVLuc, upon illumination. Four photosensitizers (methylene blue (MB), rose bengal (RB), uroporphyrin (UP) and aluminum phthalocynine tetrasulphonate (AIPcS4)) could inactivate the adenovirus, as measured by expression of the luciferase reporter gene and by plaque assay. Of these, MB demonstrated to be the most effective sensitizer in phosphate-buffered saline (PBS), giving > 7 log10 inactivation of the adenovirus. DNA isolated from MB- and light-treated virions was inefficient as a template for transcription. Furthermore, Southern blot analysis revealed fragmentation of the viral DNA. Based on its preference for DNA, MB is suited for adenovirus inactivation in blood plasma. Spiking experiments in which AdCMVLuc was added to plasma samples demonstrated a reduction (> 4 log10-fold) of reporter gene expression to almost background levels. In contrast to MB, photodynamic treatment with RB, UP or AIPcS4 did not lead to DNA damage. Although alterations of the viral capsid could not be detected, the binding pattern of the particles to target cells was significantly changed. Taken together, our data demonstrate that PDT is an efficient, convenient and useful method for the inactivation of adenovirus vectors in biological samples.

Hepatitis C and human immunodeficiency virus RNA degradation by methylene blue/light treatment of human plasma

Treatment of human plasma with methylene blue in combination with visible light (MB/light) inactivates several bloodborne viruses such as retro viruses and herpes viruses. The viral nucleic acid is thought to be a critical target for the inactivation procedure. We investigated the effects of photodynamic treatment on the RNA of hepatitis C virus (HCV) and human immunodeficiency virus type 1 (HIV-1) using Amplicor reverse transcriptase polymerase chain reaction (RT-PCR), which detects and quantifies a small fragment of the viral RNA. The detectable HCV RNA load (5-nontranslated region) in infected human plasma declined by 94-97 % within 10 min of illumination in small-scale experiments (1-2 ml vol.). Since the same effect was observed in both anti-HCV positive and negative ("window") samples, it can be concluded that HCV antibodies do not influence virus inactivation by photodynamic treatment. The effect of treatment on RT-PCR signals of HIV-1, which is known to be inactivated rapidly by MB/light treatment, was examined. Plasma was infected with HIV-1 and subjected to RT-PCR, which detected a part of the gag gene. The extent and kinetics of PCR signal reduction induced by MB/light treatment were similar to those observed for HCV. Experiments at production scale where single plasma units (300 ml) were infected with HCV showed reduction rates of PCR signals consistent with those measured in the small-scale experiments. The data support the view that MB/light treatment affects the viral nucleic acids and suggest that HCV is susceptible to the procedure.

Inactivation of viruses by chemically and photochemically generated singlet molecular oxygen

Inactivation of viruses in blood plasma can be achieved by photodynamic procedures using methylene blue (MB) or other photoactive dyes. Singlet molecular oxygen (1O2) probably contributes to the virucidal effects of photosensitization. We report the inactivation of herpes simplex virus type 1 (HSV-1) and suid herpes virus type 1 (SHV-1) by chemically generated singlet oxygen, produced by thermal decomposition of the endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate (NDPO2). We demonstrate that viruses can be inactivated by 1O2 generated by chemiexcitation in a reaction in the dark, even in the presence of human plasma. Virus inactivation in phosphate-buffered saline (PBS) was enhanced when water was replaced by deuterium oxide (D2O) and diminished when human plasma or quenchers (imidazole or histidine) were added. The singlet oxygen quenching activities of plasma, imidazole and histidine correlated with their inhibitory effects on virus inactivation. The production of 1O2 was assessed by an indicator reaction: the bleaching of p-nitrosodimethylaniline (RNO) with imidazole as 1O2 acceptor. Virus inactivation and singlet oxygen generation of NDPO2 were compared with those of MB/light-mediated photosensitization. Based on similar amounts of 1O2 generated by either procedure, virus inactivation by MB/light was more effective. Virus inactivation by MB/light was not affected by type I quenchers (e.g. mannitol), but was inhibited by human plasma or singlet oxygen quenchers. Furthermore, in D2O-based PBS, virus inactivation was more effective than that in H2O. These observations confirm that singlet oxygen is involved in virus inactivation by MB/light. Taken together, the results demonstrate that singlet oxygen produced by either procedure is virucidal. The enhanced effect of the photochemical procedure suggests that, in addition to type II, type I reactions and/or the binding affinity of the dye for the virus contribute to virus killing by MB/light.

The role of DNA damage in PM2 viral inactivation by methylene blue photosensitization

This study investigates the importance of DNA damage in viral inactivation by phenothiazines and light. Phenothiazines, including methylene blue (MB), toluidine blue and azure B are of particular interest because of their ability to bind to nucleic acids in vitro. Initial studies employing phages T7, MS2 and PM2 indicated that both DNA and RNA phages as well as enveloped and nonenveloped phages can be inactivated by phenothiazine photosensitization. PM2, which contains a lipid-protein bilayer and supercoiled DNA, was used for the mechanistic studies to model blood-borne viruses. Viral DNA damage was assessed following treatment of phage to known levels of viral inactivation by extracting the DNA and analyzing for both direct and piperidine-catalyzed strand cleavage by gel electrophoresis. DNA strand cleavage was found to be both sensitizer concentration and light dose dependent. Both viral inactivation and DNA damage were found to be oxygen-dependent events. In parallel experiments, strand cleavage of isolated PM2 DNA treated with MB and light was also found to be oxygen dependent, in contrast to some previous reports. Transfection studies, which measure the infectivity of the extracted viral DNA, indicated that DNA from MB-treated phage was just as capable of generating progeny virus as the untreated controls. It was therefore concluded that the observed DNA damage is not correlated with loss of phage infectivity.

Studies on inactivation of pathogenic microorganisms in culture media and in bovine semen by photosensitive agents

The application of three photosensitive agents for disinfection of bovine semen was investigated. Bovine microbial pathogens suspended in tissue culture medium and/or PBS and also added to bovine semen were exposed to the photosensitive agents followed by irradiation. Hematoporphyrin, hematoporphyrin derivative and thiopyronine were effective against bovine herpes virus-1, bovine viral diarrhoea virus, Mycoplasma bovigenitalium, Mycoplasma canadense, and Ureaplasma diversum in culture media. In addition, thiopyronine was effective against Leptospira pomona. Similar treatments were not effective against Leptospira hardjo, Mycoplasma bovis, or Campylobacter fetus subsp. venerealis. When microorganisms were added to bovine semen, only bovine herpes virus-1 was controlled by the photosensitive agents used at concentrations which did not appear harmful to sperm cells.

Effect of selected neuroleptic agents and stereo-isomeric analogues on virus and eukaryotic cells

Chlorpromazine, cis(Z)-chlorprothixene (Truxal), and the non-neuroleptic trans(E)-chlorprothixene and trans(E)-flupenthixol were studied in vitro for possible antiviral effect on Herpes simplex virus 2 and for toxic effect on human diploid fibroblasts. Based on an enzyme-linked immunosorbent assay (ELISA) antiviral activity was demonstrated for all the compounds in the concentration range 0.39 micrograms/ml-25 micrograms/ml. A cell-toxic effect was shown in the higher concentration range for all the compounds except cis(Z)-chlorprothixene. A cell-stimulatory effect was also detected at the lower concentration range (about 3.13 micrograms/ml) for all compounds. Thus both cell stimulation and antiviral effect can be found for the same agent within the same concentration range. The results point to the possibility of creating different antiviral drugs--which would also include a cell-stimulatory activity--among psychopharmacological drugs and their stereoisomeric analogues.

Photosensitization is required for inactivation of equine infectious anemia virus by hypericin

Hypericin, a photoreactive polycyclic quinone, was found to dramatically reduce infectivity of cell-free stocks of equine infectious anemia virus. However, the antiviral activity of hypericin was completely dependent on the presence of light. Short periods of photosensitization resulted in a partial loss of reverse transcriptase activity and complete inhibition of viral infectivity. These results suggest that the photodynamic effect of hypericin interferes with more than one stage in the virus replication cycle.

In vitro photodynamic inactivation of herpes simplex virus with sapphyrins: 22 pi-electron porphyrin-like macrocycles

The photodynamic inactivation of HSV-1, a virus having a membranous envelope, with both a decaalkyl sapphyrin and its dicarboxy-substituted analog was studied. The decaalkyl sapphyrin was as efficient in the inactivation of HSV-1 on a per macrocycle basis as DHE, whereas the efficiency of the dicarboxy-substituted sapphyrin was approximately two orders of magnitude less. Fluorescence studies of sapphyrin's binding to liposomes and VSV suggested that the decaalkylsapphyrin bound monomerically to cholesterol-rich regions of the viral envelope, whereas its charged analog localized in a more polar environment.

Therapeutic potential of plant photosensitizers

Many bioactive phytochemicals have been shown in recent years to be photosensitizers, i.e. their toxic activities against viruses, micro-organisms, insects or cells are dependent on or are augmented by light of certain wavelengths. These activities are often selective, and this has led to the concept of therapeutic prospects in the control of infectious diseases, pests and cancer. Reaction mechanisms commonly involve singlet oxygen and radicals, which are thought to cause photodamage to membranes or macromolecules. The main classes of plant photosensitizers reviewed here are polyyines (acetylenes, thiophenes and related compounds); furanyl compounds; beta-carbolines and other alkaloids; and complex quinones. We propose that within each group of phytochemicals there are several representatives that merit further study for therapeutic abilities in appropriate animal models.

Comparative kinetics of hematoporphyrin derivative uptake and susceptibility of Bacillus subtilis and Streptococcus faecalis to photodynamic action

Hematoporphyrin derivative (HpD) is widely used in photoradiation therapy of tumors and other diseases, and has been shown to affect the viability of gram positive bacteria. This investigation assessed the efficiency of binding of HpD to Bacillus subtilis and Streptococcus faecalis when HpD-treated organisms were exposed to red light. Kinetic studies indicated that the amount of HpD bound increased with increasing external concentration of HpD until saturation of binding sites was reached. S. faecalis had a higher affinity for HpD and was more susceptible to photoinactivation than B. subtilis. The data from this study suggest that differences in susceptibility of microorganisms to photoinactivation are directly related to the affinity of each strain for HpD.

A study on the sequence of phototoxic effects of rose bengal using retinal pigment epithelial cells in vitro

This paper describes a study on the sequence of the phototoxic effects of rose bengal (RB), a fluorescein derivative used as a vital stain in the diagnosis of certain external ocular diseases. Bovine melanotic RPE cells were grown in culture. These cells were labeled with [51Cr] and exposed to visible light in the presence of various concentrations of RB; the leakage of [51Cr] from the cells was used as a measure of cell lysis. Exposure to light of the cells with 0.3-10 microM RB induced approximately 13 to 43% cell lysis. The lysis progressively increased when the exposure time was varied from 10 to 30 min. A relatively short period of irradiation in the presence of RB was sufficient to produce sublytic cellular injury which could subsequently lead to complete cell lysis even in the absence of the photochemical treatment. The dark reaction was time-dependent, and reached a maximum for a given irradiation period. Our results thus show that there are two different processes that could eventually lead to the cell lysis: (a) a phototoxic effect which caused a sublytic damage and (b) a dark reaction that followed.

DNA injection proteins are targets of acridine-sensitized photoinactivation of bacteriophage P22

Viruses and other nucleoprotein complexes are inactivated on exposure to white light in the presence of acridine and related dyes. The mechanism is thought to involve generation of singlet oxygen or related species, but the actual molecular targets of the inactivating event have not been well defined. We have re-examined the mechanism of dye-sensitized photoinactivation taking advantage of the well characterized bacteriophage P22. Though the inactivated phage absorb to their host cells, the cells are not killed and genetic markers cannot be rescued from the inactivated phage. These observations indicate that the chromosome is not injected into the host cell. However, the DNA of the damaged particles shows no evidence of double-stranded breaks or crosslinking. The DNA injection process of P22 requires three particle-associated proteins, the products of genes 7, 16 and 20. Gp16, which can act in trans during injection, is inactivated in the killed particles. Sodium dodecyl sulfate/polyacrylamide gel analysis reveals that gp16, gp7 and gp20 are progressively covalently damaged during photoinactivation. However, this damage does not occur in particles lacking DNA, indicating that it is DNA-mediated. Similar findings were obtained with acridine orange, acridine yellow, proflavin and acriflavin. These results indicate that the actual targets for inactivation are the DNA injection proteins, and that the lethal events represent absorption of photons by acridine molecules stacked in a region of DNA closely associated with the injection proteins.