Dose-response relationships for photodynamic injury to murine skin

Effects of Depilatory Cream Formulation and Contact Time on Mouse Skin

Depilatory creams are widely used in research to remove hair in preparation for surgery, imaging, and other procedures. However, few studies have evaluated the effects of these creams on mouse skin. We sought to determine the cutaneous effects of 2 different depilatory formulations of a widely used brand as related to the duration of exposure. We compared a standard body formula [BF] and a facial formula [FF] that is marketed as being more gentle on skin. The cream was applied to one flank for 15, 30, 60, or 120 s; hair on the contralateral flank was clipped and used as a control. Treatment and control skin were scored for gross lesions (erythema, ulceration, and edema), degree of depilation, and histopathologic changes. C57BL/6J (B6) and Crl:CD-1(ICR) (CD-1) mice were used to allow comparison of an inbred/pigmented strain to an outbred/albino strain. BF caused significant cutaneous injury to both strains of mice, whereas FF produced significant cutaneous injury only in CD-1 mice. Both strains showed gross skin erythema, with the most severe erythema seen in CD-1 mice treated with BF. Contact time did not affect histopathologic changes or gross erythema. Both formulations produced depilation comparable to clipping in both strains when left on for a sufficient duration. In CD-1, mice, BF required at least 15 s of exposure, whereas FF required at least 120 s. In B6 mice, BF required at least 30 s of exposure, whereas FF required at least 120 s. The 2 mouse strains did not show statistically significant differences in erythema or histopathologic lesions. Overall, these depilatory creams were comparable to clippers for hair removal from mice but they produce cutaneous injury that may affect research outcomes.

Photoelectrons Mediating Angiogenesis and Immunotherapy through Heterojunction Film for Noninvasive Disinfection

A light-inspired hydroxyapatite (Hap)/nitrogen-doped carbon dots (NCDs) modified graphene oxide (GO) heterojunction film is developed, which shows a promoted separation of interfacial electrons and holes and an inhibited recombination efficiency via hole depletion. The metabolism of bacteria on this film is significantly inhibited under light irradiation, due to the enhanced photocatalytic and photothermal effects. In addition, the electron transfer from the plasmonic membrane to the GO/NCD/Hap film further inhibits the adenosine triphosphate process of bacteria, thus leading to the synergetic antibacterial efficacy. Meanwhile, the electron transfer between film and cell membrane induces the Ca2+ flow after irradiation, which can promote the migration and proliferation of cells and alkaline phosphatase enhancement, thus favoring the tissue reconstruction. An in vivo test discloses that the vascular injury repair is achieved through the Ca2+-activated PLCγ1/ERK pathway, identified by the enhanced CD31 expression. Moreover, the increased CD4+/CD8+ lymphocytes are ameliorative by activating the PI3K/P-AKT pathway. Consequently, the electron transfer boosts the synergic photodynamic and photothermal therapeutic effects for bacterial infection by Ca2+ flow for immunotherapy. This mild phototherapy approach with GO/NCDs/Hap, which can simultaneously repair injured vessels and relieve inflammation reactions, will increase the clinical application of noninvasive phototherapy in the near future.

The biology of photodynamic therapy

The subcellular, cellular and tissue/tumour interactions with non-toxic photosensitizing chemicals plus non-thermal visible light (photodynamic therapy (PDT) are reviewed. The extent to which endothelium/vasculature is the primary target is discussed, and the biochemical opportunities for manipulating outcome highlighted. The nature of tumour destruction by PDT lends itself to imaging outcome by MRI and PET.

Predictive dosimetry for threshold phototoxicity in photodynamic therapy on normal skin: red wavelengths produce more extensive damage than blue at equal threshold doses

The goal of this investigation was to establish methodology to determine and prevent phototoxic responses of normal skin to photodynamic therapy (PDT). The drug used was a second-generation photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA). The dependence of skin phototoxicity on drug dose (0.5-2.0 mg/kg), fluence (1.2-390 J/cm2), and wavelength (690 nm and 458 nm) was studied in the New Zealand albino rabbit in the first 5 h after injection. Skin responses were recorded for 2 wk after irradiation. Noninvasive measurements of drug fluorescence were made on unexposed skin sites during the first 5 h after drug injection. Immediate responses to PDT included erythema induced by 458 nm light and blanching induced by 690 nm light. Delayed reactions included edema on the day of exposure, purpura at 24 h, eschar by day 2 or 3, and scar by the end of follow-up. The threshold fluence for immediate responses correlated strongly with the threshold fluence for delayed reactions. The induction of threshold purpura on day 1 was a reliable index for skin phototoxicity that led to necrosis. The minimum purpura dose on day 1 after irradiation increased exponentially with the interval between drug injection and irradiation, independent of irradiation wavelength, for all drug doses. The action spectrum for threshold purpura mimics closely the absorption spectrum of BPD-MA. The in vivo drug fluorescence correlated with skin phototoxicity, thus allowing predictive dosimetry. This model system defines the safety limits for skin phototoxicity of PDT with BPD-MA.

Vascular function and tissue injury in murine skin following hyperthermia and photodynamic therapy, alone and in combination

The murine tail has been used as a model for injury to skin when hyperthermia (HT) and photodynamic therapy (PDT) using haematoporphyrin derivative, are used in combination. Skin injury by either agent alone was quantitated by the probability of tail necrosis as a function of dose of agent. 'Tolerance' doses of each modality were given and changes in skin vascular function were measured by the rate of clearance of 133Xenon. This was promptly inhibited but restored to normal by 7 days. The absolute numbers of hypodermal vessels of different sizes were measured in tail cross-sections and capillary numbers were found to be greatly reduced between 1 and 7 days, and restored to normal by 21-28 days. When a tolerance dose of PDT was followed at 1, 7, 21 and 28 days by test doses of HT, or vice versa, marked enhancements in probability of necrosis were observed when the interval was 1 or 7 days (Enhancement ratio (ER)PDT-HT = 1.5 and ERHT-PDT = 1.8). Prolonging the interval between modalities to 21-28 days spared the tissue (ERHT-PDT/21 DAYS = 1.1; ERPDT-HT/28 DAYS = 1.0). Close temporal apposition of PDT and HT, such as has been advocated to improve tumour control, may also increase injury to normal tissue through vascular effects common to both.

Mouse skin photosensitization with benzoporphyrin derivatives and Photofrin: macroscopic and microscopic evaluation

A comparative study, at both the macroscopic and microscopic level, of skin photosensitivity caused by four isomeric forms of benzoporphyrin derivative (BPD) has been carried out, and compared to effects of Photofrin. Animals injected intravenously with BPD analogues and exposed to light 3 h later showed extensive photosensitivity. Animals receiving the monoacid derivatives of BPD (BPD-MA and BPD-MB) showed markedly more photosensitivity than those receiving the diacid derivatives (BPD-DA and BPD-DB). Animals receiving BPD analogues which were exposed to light 24 h or more later showed only minimal reactivity. Histological examination of biopsies taken after photosensitizer injection and light exposure showed extensive changes in epidermis and dermis, including epidermal erosion, degranulation of the stratum granulosum, spongiosis, depletion in cellularity and mast cell degranulation. These changes were noted to be similar to changes caused by Photofrin.

In vivo magnetic resonance imaging of the effects of photodynamic therapy

Nuclear magnetic resonance (NMR) proton imaging and measurements of the parameters T1 and T2, have been carried out in vivo on the murine mammary tumour T50/80. Tumours had been treated 24 h previously by photodynamic therapy (PDT, using haematoporphyrin derivative and 630 nm laser light). Proton images clearly demarcated a high signal-intensity region on the side of the tumour closest to the incident light beam, while the parts of the tumour more remote from the beam resembled the images from untreated controls. Both T1 and T2 values were raised in the high-intensity region. This high-intensity region was shown to correspond to PDT-induced histological necrosis, the low-intensity region to histologically intact tumour. Linear regression analysis of the relationship of depth of necrosis measured histologically and 'depth of necrosis' measured from the NMR images, yielded a slope of 0.93 (r2 = 0.95).

Size-dependent resistance of human tumour spheroids to photodynamic treatment

Spheroids derived from the human colon adenocarcinoma cell line, WiDr, were exposed to 10 micrograms ml-1 Photofrin II and irradiated with light (700 nm, 50 mW cm-2). Compared with exponentially growing monolayer cultures, cells in spheroids of 100, 250 and 500 microns diameter were respectively 1.8, 2.5 and 22-fold less sensitive. The small resistance of plateau-phase cultures (1.3-fold) was insufficient to account for this marked spheroid size-dependent resistance. For monolayer cultures and for spheroids of 100 and 250 microns diameter, the results were the same whether irradiations were carried out pre- or post-trypsinisation. However, there was a difference for the largest spheroid size: when irradiations were carried out pre-trypsinisation, spheroids were more resistant than when irradiations were given post-trypsinisation. Drug extraction studies showed that there was no difference in the average drug uptake between cultures of exponentially growing or plateau-phase cells, and 100 microns diameter spheroids while 250 and 500 microns diameter spheroids took up proportionally 0.5 and 0.4 as much drug. Cell contact effects, drug heterogeneity between cells, hypoxia and problems in drug penetration are suggested as possible reasons for the resistance of large spheroids to photodynamic treatment.

Quantitative histological changes in murine tail skin following photodynamic therapy

Mice were treated by an intravenous injection of 2 mg of the photosensitising drug meso-tetra (sulphonatophenyl) porphine (TPPS) and 24 h later a 2.5 cm length of their tails was exposed to visible light (photodynamic therapy, PDT). Using cross-sections from the centre of the treatment field, the absolute areas occupied by epidermis, dermis, hypodermis, tendon and bone, and also the total number and area of the blood vessels in the dermis and hypodermis, were compared between control and PDT-treated animals. There was a significant increase in the mean cross-sectional area of the epidermis, dermis and hypodermis following both 90J cm-2 (a dose expected to produce a low incidence of tail necrosis) and 180J cm-2 (expected to produce a 100% tail necrosis rate), on day 1 and day 5 following light exposure. The cross-sectional area of the vascular compartment was also significantly increased by day 5 at both dose levels. Differences were observed between the two doses when the total number of blood vessels were compared. There was a significant increase in the number of blood vessels by day 5 following 90 J cm-2 in both the dermis and hypodermis, but not following 180J cm-2. This appeared to be due to a significant increase in blood vessels with a cross-sectional area of less than 100 microns2 by day 5 at the lower dose. It is concluded that angiogenesis plays an important role in vascular recovery following PDT.

Mouse skin photosensitivity with dihaematoporphyrin ether (DHE) and aluminium sulphonated phthalocyanine (AlSPc): a comparative study

Skin photosensitivity of sun exposed sites is the major side effect of dihaematoporphyrin ether (DHE) photodynamic therapy (PDT). Reports of severe oedema and erythema have generally been anecdotal. We have studied aluminium sulphonated phthalocyanine (AlSPc) as a potential photosensitiser for PDT. In this paper we report our work comparing the skin photosensitivity reactions of DHE and AlSPc. We have studied: (i) the time course of the skin reactions, (ii) the effect of increasing time from administration of photosensitiser to irradiation, (iii) drug-skin reaction dose response. Groups of Skh I female hairless albino mice were given an intravenous bolus dose of either 0.9% saline solution, AlSPc or DHE (Photofrin II). Drug doses ranged from 0.5 to 50 mg/kg. At times ranging from 1 h to 1 month animals were irradiated with a range of doses of solar simulated radiation (SSR). The skin reaction was observed over a 2 week period. DHE reactions were always more severe than those with AlSPc. Peak skin reaction was seen at 3 h for DHE and 6 h for AlSPc. DHE reactions were still visible 2 weeks after irradiation whereas the AlSPc reaction disappeared by 48 h. Irradiation evoked a reaction up to 2 months after administration of DHE but only up to 2 weeks with AlSPc. The mean SSR dose at which a skin reaction was seen decreased with increasing dose of both agents. The rate of decrease was slower with AlSPc than DHE. This study suggests that in PDT, AlSPc will cause much less skin photosensitivity than DHE.

Photodynamic therapy of experimental intraocular retinoblastomas--dose-response relationships to light energy and photofrin II

The destructive effect on tumour tissue and on normal eye tissue of photodynamic therapy has been investigated in rat eyes containing fast growing retinoblastoma-like tumours. Tumour response was described in terms of local control 90 days after treatment. The curability increased up to a maximum when large Photofrin II doses or light energy doses were administered. Early damage of conjunctiva or cornea also increased with large treatment doses and was an important limitation factor for improvement of the curability in the current model. The level of normal tissue damage decreased rapidly with increasing intervals between administration of Photofrin II and light, suggesting that conjunctival or corneal damage may not be a limitation factor 3-5 days after Photofrin II administration. A reciprocal relationship between light energy doses and Photofrin II doses was demonstrated both for curability and for the normal tissue damage. The results suggested that 2.5 mg/kg Photofrin II in combination with an extended light irradiation provoked less normal tissue damage than 10 mg/kg Photofrin II in combination with an equivalent shorter light exposure in order to obtain 15% curability of the animals.

Cell survival characteristics of a human colon adenocarcinoma cell line after photodynamic treatment: a comparison of Photofrin II and TPPS

A comparison has been made of the in vitro light-activated drug cytotoxicities of two different porphyrin compounds, Photofrin II and TPPS4. An early passage human colon adenocarcinoma cell line, WiDr, has been exposed to either drug for 24 h, the excess drug washed from the cells and the cells irradiated with light using quartz-tungsten-halogen lamps. Neither light nor drug alone under the experimental conditions employed was toxic to WiDr cells. Together, considerable cytotoxicity could be seen and the shapes of the cell survival curves following exposure to either drug then irradiation with light, were similar. For equal amounts of drug in the medium, Photofrin II was a more efficient photosensitizer of WiDr cells than TPPS4, and differences in cellular uptake could only partly explain this. When the experimental procedure was changed by reducing the temperature of irradiation, a reduction in photosensitizing efficiency could be demonstrated. This was more pronounced for Photofrin II, and was seen as a change in the slope of the final portion of the survival curve; and as a change in the shoulder for TPPS4. Two different batches of the two drugs were compared and shown to give slightly different results for Photofrin II (change in shoulder) but not to differ for TPPS4.

The effect of fractionation of light treatment on necrosis and vascular function of normal skin following photodynamic therapy

Sparing of normal tissue, mouse tail skin, by fractionation of light treatment in photodynamic therapy has been demonstrated in BDF1 mice injected with 2 mg tetrasodium-meso-tetra(4-sulphophenyl)porphine dodecahydrate i.v. When the time between 2 fractions of 67.5 J cm-2 and 90 J cm-2 was increased to 2 and 4 days respectively the incidence of necrosis fell to that expected after a single fraction. Blood flow in the tail skin 5 days after the second light fraction, as measured by the clearance of an intradermally injected solution of 133xenon in 0.9% saline, returned to control values when the time between 2 fractions was 2 days with 67.5 J cm-2 fractions, and 3 days with 90 J cm-2 fractions. The time course of recovery of normal mouse tail skin from photodynamic therapy, as shown by these split dose experiments, was found to be similar to the time course for the recovery of blood flow following a single light treatment.

Vascular function and the probability of skin necrosis after photodynamic therapy: an experimental study

The clearance of an intradermally-injected solution of 133Xenon in 0.9% saline has been used to study the impairment and recovery of blood flow in mouse tail for 5 days following photodynamic therapy (PDT) with 2mg TPPS i.v. per mouse and a range of doses of white light. Impairment of blood flow was observed within 10 min of light exposure. Blood flow increased between day 1 and day 5 at light doses less than 151J cm-2 and had returned to control levels by day 5 at light doses less than 129J cm-2. In mice treated with a light dose that caused a 50% incidence of necrosis, there was no significant difference in the initial xenon clearance half-time (measured at 10 min and 1 day after PDT) between those mice which developed tail necrosis and those which healed. However, the latter showed significantly greater improvement in vascular function on days 2, 3 and 4. This suggests that the timing and extent of recovery of blood flow determined the risk of necrosis in individual mice.