Non-ionizing 405 nm Light as a Potential Bactericidal Technology for Platelet Safety: Evaluation of in vitro Bacterial Inactivation and in vivo Platelet Recovery in Severe Combined Immunodeficient Mice

Microbial reduction of prebagged human plasma using 405 nm light and its effects on coagulation factors

Bacterial contamination is the most prevalent infectious complication of blood transfusion in the developed world. To mitigate this, several ultraviolet light-based pathogen reduction technologies (PRTs), some of which require photo-chemicals, have been developed to minimize infection transmission. Relative to UV light, visible 405-nm light is safer and has shown potential to be developed as a PRT for the in situ treatment of ex vivo human plasma and platelet concentrates, without the need for photo-chemicals. This study investigates the effect of 405-nm light on human plasma, with focus on the compatibility of antimicrobial light doses with essential plasma clotting factors. To determine an effective antimicrobial dose that is compatible with plasma, prebagged human plasma (up to 300 mL) was seeded with common microbial contaminants and treated with increasing doses of 405-nm light (16 mW cm-2; ≤ 403 J cm-2). Post-exposure plasma protein integrity was investigated using an AOPP assay, in vitro coagulation tests, and ELISA-based measurement of fibrinogen and Protein S. Microbial contamination in 300 mL prebagged human plasma was significantly reduced (P ≤ 0.05) after exposure to ≤ 288 J cm-2, with microbial loads reduced by > 96.2%. This dose did not significantly affect the plasma protein quality parameters tested (P > 0.05). Increased doses (≥ 345 J cm-2) resulted in a 4.3% increase in clot times with no statistically significant change in protein activity or levels. Overall, this study has demonstrated that the effective microbicidal 405 light dose shows little to no negative effect on plasma quality.

Human platelet concentrates treated with microbicidal 405 nm light retain hemostasis activity

Chemical and UV light-based pathogen reduction technologies are currently in use for human platelet concentrates (PCs) to enhance safety from transfusion-transmitted infections. Relative to UV light, 405 nm violet-blue light in the visible spectrum is known to be less harmful. Hence, in this report for the first time, we have assessed the global hemostasis activity of PCs stored in plasma and the activities of six plasma coagulation factors (CFs) as a measure of in vitro hemostatic activity following exposure to the microbicidal 405 nm light. Apheresis PC samples collected from each screened human donor (n = 22) were used for testing of PCs and platelet poor plasma (PPP). Both PCs and PPPs were treated for 5 h with 405 nm light to achieve a previously established microbicidal light dose of 270 J/cm2. Activated partial thromboplastin time and prothrombin time-based potency assays using a coagulation analyzer and hemostatic capacity via Thromboelastography were analyzed. Thromboelastography analysis of the light-treated PCs and plasma present in the PCs showed little difference between the treated and untreated samples. Further, plasma present in the PCs during the light treatment demonstrated a better stability in potency assays for several coagulation factors compared to the plasma alone prepared from PCs first and subjected to the light treatment separately. Overall, PCs stored in plasma treated with 405 nm violet-blue light retain activity for hemostasis.

Exploring the role of impedance spectroscopy in assessing 405 nm laser-induced inactivation of saccharomyces cerevisiae

Impedance spectroscopy was employed to assess the electrical properties of yeast following 405 nm laser irradiation, exploring the effects of visible, non-ionizing laser-induced inactivation as a more selective and safer alternative for photoinactivation applications compared to the use of DNA targeting, ionizing UV light. Capacitance and impedance spectra were obtained for yeast suspensions irradiated for 10, 20, 30, and 40 min using 100 and 200 mW laser powers. Noticeable differences in capacitance spectra were observed at lower frequencies (40 Hz to 1 kHz), with a significant increase at 40 min for both laser powers. β-dispersion was evident in the impedance spectra in the frequency range of 10 kHz to 10 MHz. The characteristic frequency of dielectric relaxation steadily shifted to higher frequencies with increasing irradiation time, with a drastic change observed at 40 min for both laser powers. These changes signify a distinct alteration in the physical state of yeast. A yeast spot assay demonstrated a decrease in cell viability with increasing laser irradiation dose. The results indicate a correlation between changes in electrical properties, cell viability, and the efficacy of 405 nm laser-induced inactivation. Impedance spectroscopy is shown to be an efficient, non-destructive, label-free method for monitoring changes in cell viability in photobiological effect studies. The development of impedance spectroscopy-based real-time studies in photoinactivation holds promise for advancing our understanding of light-cell interactions in medical applications.

The Preclinical Validation of 405 nm Light Parasiticidal Efficacy on Leishmania donovani in Ex Vivo Platelets in a Rag2-/- Mouse Model

Violet-blue light of 405 nm in the visible spectrum at a dose of 270 J/cm2 alone has been shown to be an effective microbicidal tool for inactivating several bacteria, HIV-1, and Trypanosoma cruzi in ex vivo plasma and platelets. Unlike chemical- and ultraviolet (UV)-based pathogen inactivation methods for plasma and platelet safety, 405 nm light is shown to be less toxic to host cells at light doses that are microbicidal. In this report, we evaluated the parasiticidal activity of a 405 nm light treatment on platelets spiked with the Leishmania donovani parasite. Following the light treatment, parasite viability was observed to be near zero in both low- and high-titer-spiked platelets relative to controls. Furthermore, to test the residual infectivity after inactivation in vivo, the light-treated low-titer L. donovani-spiked platelets were evaluated in an immunodeficient Rag2-/- mouse model and monitored for 9 weeks. The parasiticidal efficacy of 405 nm light was evident from the lack of a presence of parasites in the mice spleens. Parasiticidal activity was confirmed to be mediated through 405 nm light-induced reactive oxygen species (ROS), as quantitatively measured by a 2',7'-Dichlorodihydrofluorescein diacetate (H2DCFDA)-based assay. Overall, these results confirm the complete inactivation of L. donovani spiked in ex vivo platelets by 405 nm light treatment and exemplify the utility of the Rag2-/- mouse infection model for the preclinical validation of the parasiticidal efficacy of 405 nm light and this light-based technology as a potential PRT for ex vivo platelets.

Metabolomics evaluation of the photochemical impact of violet-blue light (405 nm) on ex vivo platelet concentrates

INTRODUCTION

Microbicidal violet-blue light in the visible spectrum (405 nm) has been under evaluation for pathogen inactivation in ex vivo human plasma and platelets (PLTs) stored in plasma. Results to date have demonstrated that several blood-borne infectious disease-causing pathogens can be successfully reduced to significantly low levels in the light-treated plasma and PLTs.

METHOD

In order to evaluate whether the microbicidal 405 nm light is safe for the treatment of PLT concentrates for pathogen inactivation, LC/MS-based metabolomics analyses were performed to evaluate the overall impact of 405 nm violet-blue light treatment on ex vivo PLT concentrates suspended in plasma and on plasma itself, and to identify metabolome changes in intra-platelet and extra-cellular medium (i.e., plasma).

RESULTS

The metabolomics data identified that platelet activating factors (PAFs), agonists and prostaglandins, which can influence PLT basic functions such as integrity, activation, and aggregation potential were unaltered, suggesting that 405 nm light illumination is safe regarding PLT basic functions. Distinct increases in hydroxyl fatty acids and aldehydes, as well as decreases in antioxidant metabolites indicated that reactive oxygen species (ROS) were generated at high levels after only one hour of exposure to 405 nm light. Distinctly changed endogenous photosensitizer metabolites after 1 h of light exposure provided good evidence that 405 nm light was an effective microbicide acting through ROS mechanism and no external additive photosensitizers were required.

Antimicrobial 405 nm violet-blue light treatment of ex vivo human platelets leads to mitochondrial metabolic reprogramming and potential alteration of Phospho-proteome

Continued efforts to reduce the risk of transfusion-transmitted infections (TTIs) through blood and blood components led to the development of ultraviolet (UV) light irradiation technologies known as pathogen reduction technologies (PRT) to enhance blood safety. While these PRTs demonstrate germicidal efficiency, it is generally accepted that these photoinactivation techniques have limitations as they employ treatment conditions shown to compromise the quality of the blood components. During ex vivo storage, platelets having mitochondria for energy production suffer most from the consequences of UV irradiation. Recently, application of visible violet-blue light in the 400-470 nm wavelength range has been identified as a relatively more compatible alternative to UV light. Hence, in this report, we evaluated 405 nm light-treated platelets to assess alterations in energy utilization by measuring different mitochondrial bioenergetic parameters, glycolytic flux, and reactive oxygen species (ROS). Furthermore, we employed untargeted data-independent acquisition mass spectrometry to characterize platelet proteomic differences in protein regulation after the light treatment. Overall, our analyses demonstrate that ex vivo treatment of human platelets with antimicrobial 405 nm violet-blue light leads to mitochondrial metabolic reprogramming to survive the treatment, and alters a fraction of platelet proteome.

A singlet state oxygen generation model based on the Monte Carlo method of visible antibacterial blue light inactivation

Visible antibacterial blue light (VABL) has received much attention recently as a nondestructive inactivation approach. However, due to the sparse distribution of bacteria, the light energy evaluation method used in existing studies is inaccurate. Thus, the sensitivity of microorganisms to VABL in different experiments cannot be compared. In this paper, a Monte Carlo-based photon transport model with the optimized scattering phase function was constructed. The model calculated the spatial light energy distribution and the temporal distribution of cumulative singlet state oxygen (CSO) under various cell and medium parameters. The simulation results show that when the cells are sparsely distributed, <30% of light energy from the light source is absorbed by microbes and participates in photochemical reactions. The CSO produced increases with cell density and cell size. Little light energy is available, and thus, the concentration of CSO produced is insufficient to inactivate microbes at deeper depths. As the light intensity and inactivation time increased, the production of singlet state oxygen tended to level off. The model proposed here can quantify the generation of singlet state oxygen and provide a more accurate light energy guide for the VABL inactivation process.

Visible 405 nm Violet-Blue Light Successfully Inactivates HIV-1 in Human Plasma

Despite significant advances in ensuring the safety of the blood supply, there is continued risk of transfusion transmitted infections (TTIs) from newly emerging or re-emerging infections. Globally, several pathogen reduction technologies (PRTs) for blood safety have been in development as an alternative to traditional treatment methods. Despite broad spectrum antimicrobial efficacy, some of the approved ultraviolet (UV) light-based PRTs, understandably due to UV light-associated toxicities, fall short in preserving the full functional spectrum of the treated blood components. As a safer alternative to the UV-based microbicidal technologies, investigations into the use of violet-blue light in the region of 405 nm have been on the rise as these wavelengths do not impair the treated product at doses that demonstrate microbicidal activity. Recently, we have demonstrated that a 405 nm violet-blue light dose of 270 J/cm² was sufficient for reducing bacteria and the parasite in plasma and platelets suspended in plasma while preserving the quality of the treated blood product stored for transfusion. Drawn from the previous experience, here we evaluated the virucidal potential of 405 nm violet-blue light dose of 270 J/cm² on an important blood-borne enveloped virus, the human immunodeficiency virus 1 (HIV-1), in human plasma. Both test plasma (HIV-1 spiked and treated with various doses of 405 nm light) and control plasma (HIV-1 spiked, but not treated with the light) samples were cultured with HIV-1 permissive H9 cell line for up to 21 days to estimate the viral titers. Quantitative HIV-1 p24 antigen (HIV-1 p24) levels reflective of HIV-1 titers were measured for each light dose to assess virus infectivity. Our results demonstrate that a 405 nm light dose of 270 J/cm² is also capable of 4–5 log HIV-1 reduction in plasma under the conditions tested. Overall, this study provides the first proof-of-concept that 405 nm violet-blue light successfully inactivates HIV-1 present in human plasma, thereby demonstrating its potential towards being an effective PRT for this blood component safety.

Violet-blue Light Induces "Natural" Photodynamic Plasma Disinfection with Endogenous Sensitizers

Naturally, endogenous porphyrins can provide sensitized disinfection power, and to photobiologists' delight, violet-blue light has potential virtues. But progress is needed before violet-blue light treatment can used for microbe treatment of blood samples, and yet safeguard against plasma protein photooxidation. A report by Maclean et al. in this issue of Photochemistry & Photobiology on microbe reduction of blood samples showing negligible competing protein photooxidation may bring that goal a step closer.

Antimicrobial blue light: A 'Magic Bullet' for the 21st century and beyond?

Over the past decade, antimicrobial blue light (aBL) at 400 - 470 nm wavelength has demonstrated immense promise as an alternative approach for the treatment of multidrug-resistant infections. Since our last review was published in 2017, there have been numerous studies that have investigated aBL in terms of its, efficacy, safety, mechanism, and propensity for resistance development. In addition, researchers have looked at combinatorial approaches that exploit aBL and other traditional and non-traditional therapeutics. To that end, this review aims to update the findings from numerous studies that capitalize on the antimicrobial effects of aBL, with a focus on: efficacy of aBL against different microbes, identifying endogenous chromophores and targets of aBL, Resistance development to aBL, Safety of aBL against host cells, and Synergism of aBL with other agents. We will also discuss our perspective on the future of aBL.

Violet-blue 405-nm Light-based Photoinactivation for Pathogen Reduction of Human Plasma Provides Broad Antibacterial Efficacy Without Visible Degradation of Plasma Proteins

In transfusion medicine, bacterial contamination can occur in ex vivo stored blood plasma, and there are continued efforts to improve blood safety and reduce the risk of transfusion-transmitted infections. Visible 405-nm violet-blue light has demonstrated potential for in situ pathogen reduction in ex vivo stored plasma and platelet concentrates. This study investigates the broad-spectrum antibacterial efficacy and compatibility potential of 405-nm light for treatment of blood plasma. Human plasma seeded with bacteria at a range of densities (10¹ -10³ , 10⁴ -10⁶ , 10⁷ -10⁸  CFU mL^-1 ) was exposed to 360 J cm^-2 405-nm light (1 h at 0.1 W cm^-2 ), with this fixed dose selected based on the initial analysis of inactivation kinetics. One-dimensional protein mobility analysis and measurement of advanced oxidation protein products (AOPP) was conducted to evaluate compatibility of the antimicrobial dose with plasma proteins and, identify upper levels at which protein degradation can be detected. Broad-spectrum antibacterial efficacy was observed with a fixed treatment of 360 J cm^-2 , with 98.9-100% inactivation achieved across all seeding densities for all organisms, except E. coli, which achieved 95.1-100% inactivation. At this dose (360 J cm^-2 ), no signs of protein degradation occurred. Overall, 405-nm light shows promise for broad-spectrum bacterial inactivation in blood plasma, while preserving plasma protein integrity.

Complete Inactivation of Blood Borne Pathogen Trypanosoma cruzi in Stored Human Platelet Concentrates and Plasma Treated With 405 nm Violet-Blue Light

The introduction of pathogen reduction technologies (PRTs) to inactivate bacteria, viruses and parasites in donated blood components stored for transfusion adds to the existing arsenal toward reducing the risk of transfusion-transmitted infectious diseases (TTIDs). We have previously demonstrated that 405 nm violet-blue light effectively reduces blood-borne bacteria in stored human plasma and platelet concentrates. In this report, we investigated the microbicidal effect of 405 nm light on one important bloodborne parasite Trypanosoma cruzi that causes Chagas disease in humans. Our results demonstrated that a light irradiance at 15 mWcm⁻² for 5 h, equivalent to 270 Jcm⁻², effectively inactivated T. cruzi by over 9.0 Log₁₀, in plasma and platelets that were evaluated by a MK2 cell infectivity assay. Giemsa stained T. cruzi infected MK2 cells showed that the light-treated parasites in plasma and platelets were deficient in infecting MK2 cells and did not differentiate further into intracellular amastigotes unlike the untreated parasites. The light-treated and untreated parasite samples were then evaluated for any residual infectivity by injecting the treated parasites into Swiss Webster mice, which did not develop infection even after the animals were immunosuppressed, further demonstrating that the light treatment was completely effective for inactivation of the parasite; the light-treated platelets had similar in vitro metabolic and biochemical indices to that of untreated platelets. Overall, these results provide a proof of concept toward developing 405 nm light treatment as a pathogen reduction technology (PRT) to enhance the safety of stored human plasma and platelet concentrates from bloodborne T. cruzi, which causes Chagas disease.