Photobleaching Kinetics and Effect of Solvent in the Photophysical Properties of Indocyanine Green for Photodynamic Therapy.

Indocyanine green is an attractive molecule for photodynamic therapy due to its near infrared absorption, resulting in a higher tissue penetration. However, its quantum yields of the triplet and singlet state have been reported to be low and then, reactive oxygen species are unlikely to be formed. Aiming to understand the ICG role in photodynamic response, its photobleaching behavior in solution has been studied under distinct conditions of CW laser irradiation at 780 and 808 nm, oxygen saturations and solvents. Sensitizer bleaching and photoproduct formation were measured by absorption spectroscopy and analyzed using the PDT bleaching macroscopic model to extract physical parameters. ICG photobleaching occurs even at lower oxygen concentrations, indicating that the molecule presents more than one way of degradation. Photoproducts were produced even in solution of less than 4 % oxygen saturation for both solvents and excitation wavelengths. Also, the amplitude of absorption related to J-dimers was increased during irradiation, but only in 50 % PBS solution. The formation of photoproducts was enhanced in the presence of J-type dimers under low oxygen concentration, and the quantum yields of triplet and singlet states were one order of magnitude and two times higher, respectively, when compared to ICG in distilled H2 O.

Organ-on-a-Chip for Drug Screening: A Bright Future for Sustainability? A Critical Review.

Globalization has raised concerns about spreading diseases and emphasized the need for quick and efficient methods for drug screening. Established drug efficacy and toxicity approaches have proven obsolete, with a high failure rate in clinical trials. Organ-on-a-chip has emerged as an essential alternative to outdated techniques, precisely simulating important characteristics of organs and predicting drug pharmacokinetics more ethically and efficiently. Although promising, most organ-on-a-chip devices are still manufactured using principles and materials from the micromachining industry. The abusive use of plastic for traditional drug screening methods and device production should be considered when substituting technologies so that the compensation for the generation of plastic waste can be projected. This critical review outlines recent advances for organ-on-a-chip in the industry and estimates the possibility of scaling up its production. Moreover, it analyzes trends in organ-on-a-chip publications and provides suggestions for a more sustainable future for organ-on-a-chip research and production.

Porphyrin nanoemulsion for antimicrobial photodynamic therapy: effective delivery to inactivate biofilm-related infections.

The management of biofilm-related infections is a challenge in healthcare, and antimicrobial photodynamic therapy (aPDT) is a powerful tool that has demonstrated a broad-spectrum activity. Nanotechnology has been used to increase the aPDT effectiveness by improving the photosensitizer's delivery properties. NewPS is a simple, versatile, and safe surfactant-free nanoemulsion with a porphyrin salt shell encapsulating a food-grade oil core with promising photodynamic action. This study evaluated the use of NewPS for aPDT against microorganisms in planktonic, biofilm, and in vivo models of infected wounds. First, the potential of NewPS-mediated aPDT to inactivate Streptococcus pneumoniae and Staphylococcus aureus suspensions was evaluated. Then, a series of protocols were assessed against S. aureus biofilms by means of cell viability and confocal microscopy. Finally, the best biofilm protocol was used for the treatment of S. aureus in a murine-infected wound model. A high NewPS-bacteria cell interaction was achieved since 0.5 nM and 30 J/cm2 was able to kill S. pneumoniae suspension. In the S. aureus biofilm, enhanced efficacy of NewPS-aPDT was achieved when 100 µM of NewPS was applied with longer periods of incubation at the light dose of 60 J/cm2. The best single and double-session protocol reduced 5.56 logs and 6.03 logs, respectively, homogeneous NewPS distribution, resulting in a high number of dead cells after aPDT. The in vivo model showed that one aPDT session enabled a reduction of 6 logs and faster tissue healing than the other groups. In conclusion, NewPS-aPDT may be considered a safe and effective anti-biofilm antimicrobial photosensitizer.

Lung surfactant negatively affects the photodynamic inactivation of bacteria-in vitro and molecular dynamic simulation analyses.

In the context of the rapid increase of antibiotic-resistant infections, in particular of pneumonia, antimicrobial photodynamic therapy (aPDT), the microbiological application of photodynamic therapy (PDT), comes in as a promising treatment alternative since the induced damage and resultant death are not dependent on a specific biomolecule or cellular pathway. The applicability of aPDT using the photosensitizer indocyanine green with infrared light has been successfully demonstrated for different bacterial agents in vitro, and the combination of pulmonary delivery using nebulization and external light activation has been shown to be feasible. However, there has been little progress in obtaining sufficient in vivo efficacy results. This study reports the lung surfactant as a significant suppressor of aPDT in the lungs. In vitro, the clinical surfactant Survanta® reduced the aPDT effect of indocyanine green, Photodithazine®, bacteriochlorin-trizma, and protoporphyrin IX against Streptococcus pneumoniae. The absorbance and fluorescence spectra, as well as the photobleaching profile, suggested that the decrease in efficacy is not a result of singlet oxygen quenching, while a molecular dynamics simulation showed an affinity for the polar head groups of the surfactant phospholipids that likely impacts uptake of the photosensitizers by the bacteria. Methylene blue is the exception, likely because its high water solubility confers a higher mobility when interacting with the surfactant layer. We propose that the interaction between lung surfactant and photosensitizer must be taken into account when developing pulmonary aPDT protocols.

Photodynamic inactivation of Streptococcus pneumoniae with external illumination at 808 nm through the ex vivo porcine thoracic cage.

Pneumonia is responsible for high mortality rates around the world, and its major treatment is based on antibiotic treatment. Antimicrobial resistance has been increasing in the last years, resulting in relevant public health concern. A promising alternative for pneumonia is antimicrobial photodynamic therapy. The purpose of this study was to investigate whether 808 nm wavelength is able to be transmitted through the biological tissues of the thoracic wall and be delivered in enough energy inside the cage to activate indocyanine green and promote photodynamic response. A light source panel was developed composed of 200 lasers centered at 808 nm with an irradiance of 77.8 ± 10.0 mW/cm2 and tested in an ex vivo thoracic cage model. Monte Carlo simulations were used to understand the photon migration through all the tissues at the thoracic wall. It was observed that tissues responsible for the major absorption of photons are the skin and subcutaneous fat. Experimental measurement of the irradiance was obtained after the light pass-through ex vivo pig thoracic cage, obtaining 3% to 5% of the emitted irradiance. Finally, it was observed that even with 3% of the initial irradiance, a 99.9% reduction of the Streptococcus pneumoniae was successfully achieved after 42.6 minutes of irradiation.

Safety and delivery efficiency of a photodynamic treatment of the lungs using indocyanine green and extracorporeal near infrared illumination.

Photodynamic inactivation (PDI) is a promising alternative for combating infections caused by antimicrobial resistant bacteria. Pneumonias are among the most worrisome infections because of their high-mortality rate. Previous studies have demonstrated the feasibility of using PDI with extracorporeal light to treat pneumonia. In this study, we analyzed key parameters for the viability of this treatment, including the selectivity of the photodynamic response for pathogens over host cells. Our results showed that PDI can induce killing of Staphylococcus aureus (of up to 4.18 log for the strain Xen29 and 3.62 log for Xen36) under conditions where little or no toxicity for host cells is observed. We validated pulmonary delivery of the photosensitizer and light in mice, using photobleaching as an indicator, and demonstrated preservation of healthy tissues as evidence of the safety of the protocol. Overall, PDI displays low toxicity on host tissues, making it a promising tool for treatment of pneumonias caused by S. aureus and other important pathogens.

Nebulization as a tool for photosensitizer delivery to the respiratory tract.

To this day, any photosensitizers for the photodynamic treatment of pulmonary illnesses have been administered intravenously. There is, however, an intrinsic difficulty in reaching the target cells or bacteria in the respiratory system. Nebulization could overcome distribution problems and alleviate side effects by delivering the photosensitizers directly to the lungs. In this study, we evaluated the viability of three photosensitizers (indocyanine green, the chlorine Photodithazine, and the porphyrin Photogem) was evaluated comparatively in a jet nebulizer. Quantitative analysis was performed by looking at the droplet size, extent of nebulization, output over time and stability of the solutions. All of the tested photosensitizers were found to be adequately nebulized. We also demonstrated the delivery of indocyanine green to the pulmonary tract and its activation with infrared light in a murine model using extracorporeal detection of fluorescence. This was an important step toward clinical implementation of the extracorporeally illuminated photodynamic inactivation of pneumonia, recently demonstrated in vivo by this research group.