Photodynamic therapy (PDT) and/or photodetection (PDD) based on protoporphyrin IX (PpIX) are used in many medical fields. However, the endogenous production of PpIX in the tissue after administration of its precursor, 5-aminolevulinic acid (ALA), is frequently insufficient and, in particular, inhomogeneous, leading to unsatisfactory treatment outcomes or false negatives. Photobiomodulation (PBM), which is based on the application of a sub-thermal dose of red or near infrared light (typically in the range of 600 – 900 nm), is known to modulate, among others, the cell metabolism, as demonstrated by an increased production of adenosine triphosphate and changes of the mitochondrial potential. Yet, the precise mechanism of PBM and, furthermore, the optimal irradiation conditions are to be determined. In the work reported here, we have studied the dependence of the endogenous PpIX production by U-87 glioma cells on various PBM irradiation protocols (wavelengths, irradiations, light doses). We have shown that PBM can increase, and even homogenize the endogenous production of PpIX in these cells. Therefore, combining PBM with PDT or PDD could lead to more potent and satisfying cancer treatments or detections outcomes, in particular in neurosurgery, dermatology, and urology.
Models mimicking the endogenous production of protoporphyrin IX (PpIX), as well as its fluorescence, are of high interest for applied and fundamental studies in the fields of cancer detection by fluorescence imaging, photodynamic therapy (PDT), and photobiomodulation (PBM). Here, we present and describe optical properties of the yeast-based models able to produce PpIX endogenously after the administration of 5-aminolevulinic acid (ALA) and/or 2,2’-bipyridyl. As their optical properties have an important impact on the spatial distribution of the fluence rate in these liquid models, their absorption and reduced scattering coefficients were determined to be between 400 and 808 nm for two yeast solutions previously described by our group. These coefficients were derived from measurements of the total reflectance and light penetration depth using a dedicated Monte Carlo simulation. We observed that absorption and scattering coefficients were smaller than those of soft tissues at all wavelengths. This work will enable the production of a low-cost optical phantom loaded with appropriate amounts of light-absorbing and -scattering particles to mimic tumors containing PpIX, offering a useful tool to optimize the spectral and radiometric design of certain cancer photodetection setups.
The determination of the oxygen partial pressure (pO2) in real time in living biological tissues is of high interest for numerous therapeutics, including photodynamic therapy (PDT) and radiotherapy. The minimally invasive and real-time measurement of the pO2 also enables to obtain interesting fundamental information regarding the metabolic activities in cells and tissues. The development of time-resolved luminescence measurement (TRLM) methods combined with the availability of new oxygen-sensitive molecular probes is at the origin of the significant progress that have been achieved during these past decades to measure the pO2 in living organisms. These probes include porphyrins, such as aminolevulinic acid-induced protoporphyrin IX (PPIX), which is an approved photosensitizer. Using the photosensitizer to probe the pO2 is of high interest in PDT since the level of oxygen is measured at the precise location where the phototoxic mechanisms take place. However, PPIX has drawbacks to measure the pO2 by TRLM, including its significant photobleaching. Since the PPIX excitation during pO2 measurements leads to the generation of its photoproducts, we studied the impact of their luminescence on the measurement of the PPIX triplet state lifetime in solution and in vivo on the Chick’s Chorioallantoic Membrane (CAM) model. We performed this study under various oxygen conditions. Our results indicate that perturbations induced by these photoproducts can be avoided if the PPIX luminescence is detected between 620 and 640 nm, or if PPIX is excited at 405 nm with light doses < 1 J/cm2.
The main aim of this study was to assess conditions at which simple yeast-based model organism produces maximal levels of protoporphyrin IX (PpIX) after an exogenous administration of its precursor, 5-aminolevulinic acid (ALA), and the ferrous-ion chelator 2,2’-bipyridyl.
We observed that the fluorescing porphyrin, produced after these administrations, was likely to be PpIX since fluorescence spectroscopy of the porphyrins produced endogenously in yeast cells resembles that of PpIX in DMSO and in vivo in the chick’s chorioallantoic membrane model. Also, fluorescence lifetimes of these porphyrins are very similar to that of PpIX in vitro and in vivo. This suggests that PpIX is the main fluorescent compound produced by yeast in our conditions. We found that the conditions at which yeast produces the maximal PpIX were a synchronous administration of 5 μM ALA and 1 mM 2,2’-bipyridyl for yeast incubated in aqueous glucose and 1 mM 2,2’-bipyridyl in the presence of YPD medium.
Such a simple model is of high interest to study basic mechanisms involved in the mitochondrial respiration since PpIX, which is produced in this organelle, can be used as an oxygen sensor, or to perform photodynamic therapy and photodiagnosis. Since the absorption and scattering coefficients of this model are much smaller than those of soft tissues over the visible part of the spectrum, a version of this model loaded with appropriated amounts of light absorbing and scattering particles could be designed as a phantom to mimic tumors containing PpIX, a useful tool to optimize certain cancer photodetection set-ups.
The availability of reproducible, convenient, and inexpensive model organisms able to generate predictable levels of endogenous porphyrins, including protoporphyrin IX (PpIX), is essential in photomedicine research. Saccharomyces cerevisiae produces endogenous PpIX and was used as a model organism for this study with the aim to maximize endogenous PpIX fluorescence intensity. It was found that PpIX fluorescence was significantly enhanced by administration of 5-aminolevulinic acid (ALA) and 2,2′-bipyridyl. Fluorescence intensity and spectroscopy of PpIX produced endogenously were measured in diluted yeast solutions under various conditions. The optimal protocol was: 5 μM ALA and 1 mM 2,2′-bipyridyl administered synchronously at 32°C. After 3 h, PpIX in yeast demonstrated similar steady-state and time-resolved spectroscopy as that of PpIX in DMSO. Moreover, under hypoxic conditions, the reciprocal lifetime of PpIX delayed fluorescence measured in real time was correlated to the partial pressure of oxygen (pO2) measured concomitantly with a commercially available pO2 probe. These data show that yeast can, in optimal conditions, reproducibly generate PpIX. This is of interest in various fields such as photodiagnosis, photodynamic therapy, and photobiomodulation. Use of this model organism focuses on essential mechanisms, without the complexity of a multicellular organism.
We will show in this paper that a new approach combining Photonic crystal (PC) and nano-antennas (NA's) allows for an efficient addressing of NA using a wide Gaussian beam. First, we will present results from a phenomenological approach (coupled mode theory in the time domain) of this mixed device. We derive the key factors that govern the coupling processes and show that high Q PC structures are required for efficient coupling. The design rules for high Q PC structures providing resonant slow Bloch modes above the light line are presented, on the basis of FDTD simulation results. We will end the presentation with FDTD simulations of the mixed structure (PC+NA), confirming the prediction of the coupled mode theory. Preliminary technological realization will be presented, together with a discussion on potential applications for optical trapping.
A new type of porous-silicon based photonic biosensor is presented. The device is a 1D planar photonic crystal
supporting resonant modes that can be excited at normal incidence. The study of theoretical performances demonstrates a
high sensitivity with similar performances in air and in aqueous environment. The experimental realization of the sensor
is discussed and preliminary biosensing experiments show very promising results.
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