Effect of PpIX photoproducts formation on pO2 measurement by time-resolved delayed fluorescence spectroscopy of PpIX in solution and in vivo

Tailoring the Electrocatalytic Properties of Porphyrin Covalent Organic Frameworks for Highly Selective Oxygen Sensing In Vivo

In vivo selective sensing of oxygen (O2) dynamics in the central nervous system could provide insights into energy metabolism and neural activities. Although the electrocatalytic four-electron oxygen reduction reaction (ORR) paves an effective way to the electrochemical sensing of O2 in vivo, the concurrent hydrogen peroxide reduction reaction (HPRR) within the potential windows for four-electron ORR unfortunately poses a great challenge to the conventional mechanism employed for selective electrochemical O2 sensing. In this work, we find that regulation of the linkers within the skeleton of porphyrin-based covalent organic frameworks (COFs) could improve the selectivity of the O2 sensor against hydrogen peroxide (H2O2). The electrochemical results reveal that the Co porphyrin active sites facilitate the direct four-electron pathway for ORR and that the Co porphyrin-based COF, enriched with pyrene units, shows enhanced four-electron ORR kinetics and better tolerance to HPRR. The theoretical calculation suggests that introducing pyrene units essentially weakens the adsorption of H2O2, leading to suppression of the HPRR. The microsensor fabricated with the Co porphyrin-based COF as the electrocatalyst features a high selectivity for real-time monitoring of O2 in a living rat brain.

Effect of a 5-aminolevulinic acid gel and 660 nm red LED light on human oral osteoblasts: a preliminary in vitro study

This study aimed to evaluate the effects of a new photodynamic protocol (ALAD-PDT) on primary human osteoblasts (hOBs). The ALAD-PDT protocol consists of a heat-sensitive gel with 5% 5-delta aminolevulinic acid commercialized as Aladent (ALAD), combined with 630 nm LED. For this purpose, the hOBs, explanted from human mandible bone fragments, were used and treated with different ALAD concentrations (10%, 50%, 100% v/v) incubated for 45 min and immediately afterwards irradiated with a 630 nm LED device for 7 min. The untreated and unirradiated cells were considered control (CTRL). The cellular accumulation of the photosensitizer protoporphyrin IX (PpIX), the proliferation, the alkaline phosphatase (ALP) activity, and the calcium deposition were assessed. All concentrations (10, 50, 100%) determined a significant increment of PpIX immediately after 45 min of incubation (0 h) with the highest peak by ALAD (100%). The consequent 7 min of light irradiation caused a slight decrease in PpIX. At 48 h and 72 h, any increment of PpIX was observed. The concentration 100% associated with LED significantly increased hOB proliferation at 48 h (+ 46.83%) and 72 h (+ 127.75%). The 50% and 100% concentrations in combination to the red light also stimulated the ALP activity, + 12.910% and + 14.014% respectively. The concentration 100% with and without LED was selected for the assessment of calcium deposition. After LED irradiation, a significant increase in calcium deposition was observed and quantified (+ 72.33%). In conclusion, the ALAD-PDT enhanced proliferation, the ALP activity, and mineralized deposition of human oral osteoblasts, highlighting a promising potential for bone tissue regeneration.

Protoporphyrin IX delayed fluorescence imaging: a modality for hypoxia-based surgical guidance

SIGNIFICANCE

Hypoxia imaging for surgical guidance has never been possible, yet it is well known that most tumors have microregional chronic and/or cycling hypoxia present as well as chaotic blood flow. The ability to image oxygen partial pressure (pO2) is therefore a unique control of tissue metabolism and can be used in a range of disease applications to understand the complex biochemistry of oxygen supply and consumption.

AIM

Delayed fluorescence (DF) from the endogenous molecule protoporphyrin IX (PpIX) has been shown to be a truly unique reporter of the local oxygen partial pressure in tissue. PpIX is endogenously synthesized by mitochondria in most tissues, and the particular property of DF emission is directly related to low microenvironmental oxygen concentration. Here, it is shown that PpIX has a unique emission in hypoxic tumor tissue regions, which is measured as a DF signal in the red to near-infrared spectrum.

APPROACH

A time-gated imaging system was used for PpIX DF for wide field direct mapping of pO2 changes. Acquiring both prompt and DF in a rapid sequential cycle allowed for imaging oxygenation in a way that was insensitive to the PpIX concentration. By choosing adequate parameters, the video rate acquisition of pO2 images could be achieved, providing real-time tissue metabolic information.

RESULTS

In this report, we show the first demonstration of imaging hypoxia signals from PpIX in a pancreatic cancer model, exhibiting >5X contrast relative to surrounding normal oxygenated tissues. Additionally, tissue palpation amplifies the signal and provides intuitive temporal contrast based upon neoangiogenic blood flow differences.

CONCLUSIONS

PpIX DF provides a mechanism for tumor contrast that could easily be translated to human use as an intrinsic contrast mechanism for oncologic surgical guidance.

Identification of excimer delayed fluorescence by Protoporphyrin IX: A novel access to local chromophore concentration?

Protoporphyrin IX (PpIX) is a molecule produced in the mitochondria following the administration of its approved precursor, aminolevulinic acid (ALA). Strong light absorber at different wavelengths in the visible range, PpIX is extensively used as a photosensitizer (PS) for Photodynamic Therapy (PDT). PpIX is also an ideal molecular probe for the quantification of the tissue oxygen partial pressure (pO₂), as its delayed fluorescence (DF) is quenched by oxygen, creating a direct relationship between the DF lifetime and the pO₂. A limitation of both techniques is the ignorance of the PpIX concentration in tissues when the pO₂ is measured or during PDT. In this study, the prompt (PF) and delayed fluorescence of PpIX dissolved in DiMethylFormamide (DMF) were acquired, in absence of oxygen, at different PpIX concentrations. Measurements of the PpIX emission for different excitation energies and temperatures, as well as spectral considerations led to the conclusion that E-type (thermal) DF was the dominant DF mechanism at low PpIX excited states concentrations (density of absorbed energy Hε[PpIX] < 1 μJ. cm^-3, H:excitation radiant exposure per pulse, ε: molar extinction coefficient at excitation wavelength) while P-type (Triplet Triplet Annihilation) DF took place at higher excited states concentrations (Hε[PpIX] > 10 μJ. cm^-3). The gradual development of a strong, red-shifted structureless DF peak at 670 nm, invisible in the PF and absorption spectra, strongly points towards the first observation of PpIX excimer DF (EDF). It appears that, similarly to other aromatic molecules, PpIX excimers can be formed either by the encounter of two molecules in the first excited triplet state T₁, or by the reaction of an excited singlet S₁ with a triplet T₁. Excimer DF could be beneficially used to determine the local concentration of PpIX, as the initial DF intensity ratio I₀⁶⁷⁰/I₀⁶³⁰ is linearly correlated with the local PpIX concentration, and thus rises up to the challenge of PpIX based pO₂ measurement and PDT. This work could also pave the way for a fine comprehension of the production, diffusion and catabolization of PpIX in biological tissues.

Influence of Oxidative Stress on Time-Resolved Oxygen Detection by [Ru(Phen)3]2+ In Vivo and In Vitro

Detection of tissue and cell oxygenation is of high importance in fundamental biological and in many medical applications, particularly for monitoring dysfunction in the early stages of cancer. Measurements of the luminescence lifetimes of molecular probes offer a very promising and non-invasive approach to estimate tissue and cell oxygenation in vivo and in vitro. We optimized the evaluation of oxygen detection in vivo by [Ru(Phen)₃]²⁺ in the chicken embryo chorioallantoic membrane model. Its luminescence lifetimes measured in the CAM were analyzed through hierarchical clustering. The detection of the tissue oxygenation at the oxidative stress conditions is still challenging. We applied simultaneous time-resolved recording of the mitochondrial probe MitoTracker^TM OrangeCMTMRos fluorescence and [Ru(Phen)₃]²⁺ phosphorescence imaging in the intact cell without affecting the sensitivities of these molecular probes. [Ru(Phen)₃]²⁺ was demonstrated to be suitable for in vitro detection of oxygen under various stress factors that mimic oxidative stress: other molecular sensors, H₂O₂, and curcumin-mediated photodynamic therapy in glioma cancer cells. Low phototoxicities of the molecular probes were finally observed. Our study offers a high potential for the application and generalization of tissue oxygenation as an innovative approach based on the similarities between interdependent biological influences. It is particularly suitable for therapeutic approaches targeting metabolic alterations as well as oxygen, glucose, or lipid deprivation.

Imaging of hypoxia, oxygen consumption and recovery in vivo during ALA-photodynamic therapy using delayed fluorescence of Protoporphyrin IX

BACKGROUND

Hypoxic lesions often respond poorly to cancer therapies. Particularly, photodynamic therapy (PDT) consumes oxygen in treated tissues, which in turn lowers its efficacy. Tools for online monitoring of intracellular pO2 are desirable.

METHODS

The pO2 changes were tracked during photodynamic therapy (PDT) with δ-aminolevulinic acid (ALA) in mouse skin, xenograft tumors, and human skin. ALA was applied either topically as Ameluz cream or systemically by injection. Mitochondrial pO2 was quantified by time-gated lifetime-based imaging of delayed fluorescence (DF) of protoporphyrin IX (PpIX).

RESULTS

pO2-weighted images were obtained with capture-times of several seconds, radiant exposures near 10 mJ/cm2, spatial resolution of 0.3 mm, and a broad dynamic range 1-50 mmHg, corresponding to DF lifetimes ≈20-2000 μs. The dose-rate effect on oxygen consumption was investigated in mouse skin. A fluence rate of 1.2 mW/cm2 did not cause any appreciable oxygen depletion, whereas 6 mW/cm2 and 12 mW/cm2 caused severe oxygen depletion after radiant exposures of only 0.4-0.8 J/cm2 and <0.2 J/cm2, respectively. Reoxygenation after PDT was studied too. With a 5 J/cm2 radiant exposure, the recovery times were 10-60 min, whereas with 2 J/cm2 they were only 1-6 min. pO2 distribution was spatially non-uniform at (sub)-millimeter scale, which underlines the necessity of tracking pO2 changes by imaging rather than point-detection.

CONCLUSIONS

Time-gated imaging of PpIX DF seems to be a unique tool for direct online monitoring of pO2 changes during PDT with a promising potential for research purposes as well as for comparatively easy clinical translation to improve efficacy in PDT treatment.

Microscopic time-resolved imaging of singlet oxygen by delayed fluorescence in living cells

Singlet oxygen is a highly reactive species which is involved in a number of processes, including photodynamic therapy of cancer. Its very weak near-infrared emission makes imaging of singlet oxygen in biological systems a long-term challenge. We address this challenge by introducing Singlet Oxygen Feedback Delayed Fluorescence (SOFDF) as a novel modality for semi-direct microscopic time-resolved wide-field imaging of singlet oxygen in biological systems. SOFDF has been investigated in individual fibroblast cells incubated with a well-known photosensitizer aluminium phthalocyanine tetrasulfonate. The SOFDF emission from the cells is several orders of magnitude stronger and much more readily detectable than the very weak near-infrared phosphorescence of singlet oxygen. Moreover, the analysis of SOFDF kinetics enables us to estimate the lifetimes of the involved excited states. Real-time SOFDF images with micrometer spatial resolution and submicrosecond temporal-resolution have been recorded. Interestingly, a steep decrease in the SOFDF intensity after the photodynamically induced release of a photosensitizer from lysosomes has been demonstrated. This effect could be potentially employed as a valuable diagnostic tool for monitoring and dosimetry in photodynamic therapy.

Singlet oxygen feedback delayed fluorescence of protoporphyrin IX in organic solutions

The PpIX DF show the significant role of SOFDF mechanism at high concentrations and at atmospheric partial pressure of oxygen and should be considered when developing diagnostic tools for clinical applications.