Increase In Light Dose Research Articles

Antibacterial photodynamic therapy mediated by 5-aminolevulinic acid on methicillin-resistant Staphylococcus aureus.

The emergence of drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), has brought great difficulties to clinical treatment. Antibacterial photodynamic therapy (aPDT) is a new non-antibiotic treatment strategy for a variety of drug-resistant bacteria. However, there are few studies on the antimicrobial mechanism of a PDT mediated by 5-aminolevulinic acid (ALA-PDT) for MRSA. In this study, we observed the bactericidal effect of ALA-PDT on MRSA. We found that ALA-PDT had the strongest bactericidal effect when ALA was at 0.05 mM, and the bactericidal activity of aPDT increased with the increase of light dose. MRSA was almost completely eliminated at 0.05 mM and 384 Jcm-2. In addition, the bactericidal morphology was also observed under a fluorescence microscope using a LIVE/DEAD® BacLight™ Bacterial Viability Kit and an electron microscope. It was also found that proteins and DNA were damaged by ALA-PDT. Finally, the transcription level of the specific gene of MRSA, nuc, was decreased by 0.74-fold (P < 0.05) after ALA-PDT treatment by qRT-PCR analysis. The findings suggest that ALA-PDT can effectively inhibit MRSA by damaging cell membrane, cytoplasm, proteins and nucleic acid.

Monte Carlo simulation of light fluence calculation during pleural PDT.

A thorough understanding of light distribution in the desired tissue is necessary for accurate light dosimetry in PDT. Solving the problem of light dose depends, in part, on the geometry of the tissue to be treated. When considering PDT in the thoracic cavity for treatment of malignant, localized tumors such as those observed in malignant pleural mesothelioma (MPM), changes in light dose caused by the cavity geometry should be accounted for in order to improve treatment efficacy. Cavity-like geometries demonstrate what is known as the "integrating sphere effect" where multiple light scattering off the cavity walls induces an overall increase in light dose in the cavity. We present a Monte Carlo simulation of light fluence based on a spherical and an elliptical cavity geometry with various dimensions. The tissue optical properties as well as the non-scattering medium (air and water) varies. We have also introduced small absorption inside the cavity to simulate the effect of blood absorption. We expand the MC simulation to track photons both within the cavity and in the surrounding cavity walls. Simulations are run for a variety of cavity optical properties determined using spectroscopic methods. We concluded from the MC simulation that the light fluence inside the cavity is inversely proportional to the surface area.

Photofrin ® photodynamic therapy: 2.0 mg/kg or not 2.0 mg/kg that is the question

Photodynamic therapy (PDT) is an innovative minimally invasive therapy that has great potential for both tumor ablation and normal tissue preservation. However, while in recent years the standards of surgery, radiation and chemotherapy have dramatically improved in terms of outcomes and morbidity, the same cannot be said of PDT in general and Photofrin((R))-based PDT in particular. As currently practiced PDT dosimetry has not really improved tumor ablation and diminished side effects over reports from two decades ago. We critically examine the clinical variables available for PDT dosimetry and conclude that the simple maneuver of diminishing drug dose, with an appropriate increase in light dose, can enhance disease control with a significantly lower risk of morbidity. This conclusion should also be applicable to most systemically introduced photosensitizer.

Dose-related structural effects of photodynamic therapy on choroidal and retinal structures of human eyes.

To determine the effects of photodynamic therapy (PDT) on choroidal and retinal structures of human eyes. One eye from each of three patients with large malignant melanomas of the uvea destined for enucleation received PDT using verteporfin according to the approved treatment recommendations for patients with age-related macular degeneration. Two laser spots and two light doses (50 J/cm(2) and 100 J/cm(2)) were applied in unaffected chorioretinal areas. The effects of PDT were assessed by fluorescein and indocyanine-green angiography. The eyes were enucleated 1 week later, fixed in buffered paraformaldehyde/glutaraldehyde solution, bisected along the laser spots, and processed for light and electron microscopy. In agreement with the clinical angiographic findings of hypofluorescence, a rather selective occlusion of the choriocapillary layer was observed in the 50-J/cm(2) PDT areas, whereas the 100-J/cm(2) PDT areas additionally revealed closure of deeper choroidal vessels and focal alterations of the retinal pigment epithelium. The overlying neurosensory retina, including photoreceptors and retinal capillaries, was well preserved in all PDT areas. Electron microscopy showed that alterations of the choriocapillary endothelium comprised swelling, shrinkage and fragmentation of endothelial cells, detachment from their basement membrane up to complete degeneration of the endothelial lining, leading to platelet aggregation, degranulation, and thrombus formation. Complete occlusion of capillary lumina by fibrin, thrombocytes, and cellular debris was observed. Remaining intact endothelial cells appeared to be reorganized into novel smaller vascular channels within occluded lumina. PDT with verteporfin at a dosage used clinically induces selective occlusion of the physiological choriocapillaris without affecting deeper choroidal, retinal, and optic nerve vessels or the overlying retinal pigment epithelium and neurosensory retina. The main mechanism of action appears to be vascular thrombosis induced by cytotoxic damage of endothelial cells and platelet activation. An increase in light dose enhances the occlusive effect with thrombosis within deeper choroidal layers and damage to the retinal pigment epithelium. However, photoreceptors remained intact at all light doses used.

Photodynamic therapy of human Barrett's cancer using 5-aminolaevulinic acid-induced protoporphyrin IX: an in-vivo dosimetry study in athymic nude mice.

There has been a dramatic increase in recent years in the incidence of Barrett's oesophagus and the oesophageal adenocarcinoma associated with it. Alongside surgical treatment for early Barrett's carcinomas, endoscopic treatment procedures such as photodynamic therapy (PDT), which have much lower complication and mortality rates, will play an increasing role in the future. In this study, the effects of light energy dose, light fractionation and oxygenation on the efficacy of PDT were investigated for the first time in an in-vivo nude mice tumour model bearing a human Barrett's carcinoma. A total of 387 NMRI strain (nu/nu) nude mice with thymic aplasia (total 53 controls) were transplanted with human Barrett's carcinoma and treated with laser light at 635 nm (light dose 0-200 J/cm2, fluence rate 400 mW/cm2). 5-Aminolaevulinic acid-induced protoporphyrin IX (5-ALA-PpIX) (100 mg 5-ALA/kg body weight administered orally) was used as the photosensitizer. Fractionation studies were performed at 0, 50, 100 and 150 J/cm2. The light dose was administered in four equal fractions divided by three irradiation-free intervals of 120 s. Oxygenation studies were carried out at 150 J/cm2 with simultaneous oxygen supply of 2, 6 and 8 l oxygen/min. Dosimetry studies demonstrated a positive correlation between increase in light dose and tumour destruction up to 150 J/cm2 when using either continuous or fractionated light delivery. The optimal light energy dose was 150 J/cm2. Neither fractionation of light nor simultaneous oxygenation enhanced the efficacy of the PDT. This is the first study in the literature that proves the efficiency of PDT with 5-ALA-PpIX in human Barrett's adenocarcinoma and that demonstrates an exact dosimetry of the optimal light energy dose (150 J/cm2). No general recommendation can be made for the use of fractionation or oxygenation in clinical PDT.

Effects of photosensitizer (hematoporphyrin derivative-HPD) and light dose on vascular targets in the albino mouse ear.

Photodynamic damage to normal tissues, including skin, appears to occur by photooxidative damage to the normal microvasculature as the primary target sensitized by HPD bound to the vascular wall or endothelial cell. Initial damage to the microvasculature was measured by the increase in vascular permeability (VP) as measured by Evans Blue dye (EB) extravasation as a function of HPD and laser light (632 nm) dose. Albino, Swiss-Webster mice (female 122-25 g, 5 mice per group) were injected intraperitoneally (IP) with incremental doses of HPD (Photofrin II, Photofrin Medical, Inc.) (1, 10, 20, 30, 40 and 50 mg/kg). After 48 hours the left ear of each mouse was masked as a control and the right ear was irradiated at 632 nm using the Aurora-Lexel Argon-dye laser (Cooper Laser Sonics, Inc.) with an intensity of 50 mW/cm2 and light doses of 0, 25, 50, 75, and 100 J/cm2 directed to a 3-mm spot on the mouse ear. No EB leakage occurred in the absence of HPD at any light dose or in the absence of light at any HPC dose. Vascular permeability increased as a function of HPD dose up to 30 mg/kg. AT 50 mg/kg HPD, there was a decrease in VP. At each HPD dose above 10 mg/kg, the VP increased as a function of light dose up to 75 J/cm2. Further increase in light dose was without effect. The amount of HPD porphyrin recovered from irradiated ears decreased as a function of light dose. There appeared to be an irreversible photo destruction of the porphyrin exposed to light.