Quantitative histological changes in murine tail skin following photodynamic therapy

Mechanisms in photodynamic therapy: part two-cellular signaling, cell metabolism and modes of cell death

Photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as a tumor therapy, some of its most successful applications are for non-malignant disease. In the second of a series of three reviews, we will discuss the mechanisms that operate in PDT on a cellular level. In Part I [Castano AP, Demidova TN, Hamblin MR. Mechanism in photodynamic therapy: part one-photosensitizers, photochemistry and cellular localization. Photodiagn Photodyn Ther 2004;1:279-93] it was shown that one of the most important factors governing the outcome of PDT, is how the photosensitizer (PS) interacts with cells in the target tissue or tumor, and the key aspect of this interaction is the subcellular localization of the PS. PS can localize in mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus and plasma membranes. An explosion of investigation and explorations in the field of cell biology have elucidated many of the pathways that mammalian cells undergo when PS are delivered in tissue culture and subsequently illuminated. There is an acute stress response leading to changes in calcium and lipid metabolism and production of cytokines and stress proteins. Enzymes particularly, protein kinases, are activated and transcription factors are expressed. Many of the cellular responses are centered on mitochondria. These effects frequently lead to induction of apoptosis either by the mitochondrial pathway involving caspases and release of cytochrome c, or by pathways involving ceramide or death receptors. However, under certain circumstances cells subjected to PDT die by necrosis. Although there have been many reports of DNA damage caused by PDT, this is not thought to be an important cell-death pathway. This mechanistic research is expected to lead to optimization of PDT as a tumor treatment, and to rational selection of combination therapies that include PDT as a component.

Intronic parent-of-origin dependent differential methylation at the Actn1 gene is conserved in rodents but is not associated with imprinted expression

Parent-of-origin differential DNA methylation has been associated with regulation of the preferential expression of paternal or maternal alleles of imprinted genes. Based on this association, recent studies have searched for parent-of-origin dependent differentially methylated regions in order to identify new imprinted genes in their vicinity. In a previous genome-wide analysis of mouse brain DNA methylation, we found a novel differentially methylated region in a CpG island located in the last intron of the alpha 1 Actinin (Actn1) gene. In this region, preferential methylation of the maternal allele was observed; however, there were no reports of imprinted expression of Actn1. Therefore, we have tested if differential methylation of this region is common to other tissues and species and affects the expression of Actn1. We have found that Actn1 differential methylation occurs in diverse mouse tissues. Moreover, it is also present in other murine rodents (rat), but not in the orthologous human region. In contrast, we have found no indication of an imprinted effect on gene expression of Actn1 in mice: expression is always biallelic regardless of sex, tissue type, developmental stage or isoform. Therefore, we have identified a novel parent-of-origin dependent differentially methylated region that has no apparent association with imprinted expression of the closest genes. Our findings sound a cautionary note to genome-wide searches on the use of differentially methylated regions for the identification of imprinted genes and suggest that parent-of-origin dependent differential methylation might be conserved for functions other that the control of imprinted expression.

PDT induced bystander effect on human xenografted colorectal tumors as evidenced by sodium MRI

BACKGROUND

Previous in vivo studies on photodynamic therapy (PDT)-treated, high cellular density tumors showed evidences of a bystander effect accompanying the therapy, cellular death continuing beyond the limits of the photochemical reactions in time and space. This process is generated by the initially damaged cells on the light pathway. The aim of this study was to determine if the bystander effect may be induced as well in colorectal xenografted tumors (less compact structure) and if the cellular signaling depends primarily on cellular proximity or not.

METHODS

The photosensitizer was a glycoconjugated, meso substituted porphyrin derivative synthesized at Institut Curie. The longitudinal follow-up of the tumors was carried out by (23)Na/(1)H MRI, ideal imaging modality for mapping the extracellular compartment. Two regimens were followed in order to target either blood vessels alone or blood vessels and cancer cells simultaneously.

RESULTS

The antivascular PDT did not succeed to arrest the tumors growth at the end of the follow-up. For double targeting PDT, we managed to stop the tumoral evolution. Sodium MRI evidenced a bystander effect.

CONCLUSION

The results obtained showed that the bystander effect is more difficult to induce for the type of colorectal tumors used in this work. It needs a double treatment, 4 days apart, in order to be promoted.

Radiographic assessment of photodynamic therapy as an adjunctive treatment on induced periodontitis in immunosuppressed rats

Objective

The aim of this study was to assess radiographically the effect of photodynamic therapy (PDT) as an adjunctive treatment to scaling and root planing (SRP) on induced periodontitis in dexamethasone-induced immunosuppressed rats.

Material and Methods

The animals were divided into 2 groups: ND group (n=60): saline treatment; D group (n=60): dexamethasone treatment. In both ND and D groups, periodontal disease was induced by the placement of a ligature in the left first mandibular molar. After 7 days, ligature was removed and all animals received SRP, being divided according to the following treatments: SRP: saline and PDT: phenothiazinium dye (TBO) plus laser irradiation. Ten animals per treatment were killed at 7, 15 and 30 days. The distance between the cementoenamel junction and the height of the alveolar bone crest in the mesial surface of the mandibular left first molars was determined in millimeters in each radiograph. The radiographic values were analyzed statistically by ANOVA and Tukey's test at a p value <0.05.

Results

Intragroup radiographic assessment (ND and D groups) showed that there was statistically significant less bone loss in the animals treated with PDT in all experimental periods compared to those submitted to SRP. Intergroup radiographic analysis (ND and D groups) demonstrated that there was greater bone loss in the ND group treated with SRP compared to the D group treated with PDT at 7 and 30 days.

Conclusion

PDT was an effective adjunctive treatment to SRP on induced periodontitis in dexamethasone-induced immunosuppressed rats.

Clinical and immunohistochemical evaluation of psoriatic plaques treated with topical 5-aminolaevulinic acid photodynamic therapy

BACKGROUND/PURPOSE

The aims of this study were to investigate the clinical and immunohistochemical events of psoriatic plaques during photodynamic therapy (PDT) using topical application of 5-aminolaevulinic acid (ALA).

METHODS

Twelve psoriatic patients were recruited for this study. Four of them dropped out because of pain during treatment. The effect of PDT was evaluated in the remaining eight. One plaque was selected in each patient and treated once weekly with PDT 10-30 J/cm(2) two to five times. It was evaluated by using the scale, erythema and induration (SEI) index (maximal score per patient=9). Pain during treatment was assessed by a visual analogue scale (VAS), ranging from 0 to 10. Skin biopsies were taken before treatment, after two treatments and after completion of treatment, and were evaluated by immunohistochemistry.

RESULTS

Median SEI scores were significantly reduced from 7 (range 5-9) before to 1.5 (range 0-3) following treatment (P<0.0001). The median pain during PDT was 7. The number of vessels in the subpapillary dermis, identified by antibodies against Factor VIII and endoglin, increased during and/or after treatment in six of eight patients. Before treatment, the epidermal growth factor (EGF) receptor was displayed throughout the epidermis, keratin 16 suprabasally, involucrin from the stratum granulosum to the lower spinous layers and filaggrin in stratum granulosum with focal absence. There was a moderate dermal infiltrate of CD4(+) cells and a sparse one of CD8(+). Following treatment, the EGF receptor was still displayed throughout the epidermis in seven of eight specimens. Cytokeratin 16 expression decreased markedly. Involucrin was not seen as deep in the spinous layers as before PDT. Filaggrin was expressed throughout the stratum granulosum and often weakly in the upper stratum spinosum. The number of CD4(+) and CD8(+) dermal cells decreased.

CONCLUSION

PDT improved psoriasis and induced dermal neovascularization. Although a good clinical response was seen in most of our patients, the high frequency of discomfort during treatment limits the usefulness of ALA-PDT for psoriasis. The mechanism of the neovascularization is unknown. It may be owing to an indirect effect of PDT on the microvasculature and immune system or recovery phenomena.

Assessment of photosensitizer dosimetry and tissue damage assay for photodynamic therapy in advanced-stage tumors

Photodynamic therapy (PDT) efficacy is a complex function of tissue sensitivity, photosensitizer (PS) uptake, tissue oxygen concentration, delivered light dose and some other parameters. To better understand the mechanisms and optimization of PDT treatment, we assessed two techniques for quantifying tissue PS concentration and two methods for quantifying pathological tumor damage. The two methods used to determine tissue PS concentration kinetic were in vivo fluorescence probe and ex vivo chemical extraction. Both methods show that the highest tumor to normal tissue PS uptake ratio appears 4 h after PS administration. Two different histopathologic techniques were used to quantify tumor and normal tissue damage. A planimetry assessment of regional tumor necrosis demonstrated a linear relationship with increasing light dose. However, in large murine tumors this finding was complicated by the presence of significant spontaneous necrosis. A second method (densitometry) assessed cell death by nuclear size and density. With some exceptions the densitometry method generally supported the planimetry results. Although the densitometry method is potentially more accurate, it has greater potential subjectivity. Finally, our research suggests that the tools or methods we are studying for quantifying PS levels and tissue damage are necessary for the understanding of PDT effect and therapeutic ratio in experimental in vivo tumor research.

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.

The effect of combined modality treatment with ionising radiation and TPPS-mediated photodynamic therapy on murine tail skin

The effect on normal skin of combined modality treatment with 300 kV X-rays and photodynamic therapy (PDT) using the photosensitising drug meso-tetra (sulphonatophenyl) porphine (TPPS) was studied using the mouse tail necrosis assay. Prior treatment with a tolerance dose of PDT produced a significant increase in the probability of necrosis following graded doses of ionising radiation. A tolerance dose of X-rays administered prior to graded doses of PDT also produced a significant rise in the necrosis rate. TPPS appeared to have a radiosensitising effect but, as the animals were kept in subdued light, the low dose of PDT they therefore received may provide an alternative explanation. The effect of prolonging the interval between the modalities on the necrosis rate did not appear to be related to the time course of either the changes in blood flow produced by each modality, measured by xenon clearance studies or the development of the skin reaction following X-ray irradiation.