Light Pollution and Oxidative Stress: Effects on Retina and Human Health.

Visible light refers to the frequencies within the electromagnetic spectrum that humans can see, encompassing radiation with wavelengths falling between 380 nm to 760 nm. The energy of a single photon increases with its frequency. In the retina, photoreceptor cells contain light-sensitive pigments that absorb light and convert it into electrical stimuli through a process known as phototransduction. However, since the absorption spectrum of photoreceptors closely aligns with blue light (ranging from 400 to 500 nm), exposure to high light intensities or continuous illumination can result in oxidative stress within these cells, leading to a loss of their functionality. Apart from photoreceptor cells, the retina also houses photosensitive ganglion cells, known as intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells relay information to the suprachiasmatic nucleus in the brain, playing a crucial role in modulating melatonin secretion, which in turn helps in synchronizing the body's circadian rhythms and responses to seasonal changes. Both, ipRGCs and skin possess a peak sensitivity to blue wavelengths, rendering them particularly susceptible to the effects of excessive blue light exposure. This study delves into the consequences of excessive illumination and/or prolonged exposure to blue light on retinal function and explores its implications for human health.

The influence of growth medium on the photodynamic susceptibility of Aggregatibacter actinomycetemcomitans to antimicrobial blue light.

The aim of this study was to investigate whether antimicrobial blue light (aBL) can cause the death of Aggregatibacter actinomycetemcomitans (A.a) and to determine the influence of different culture media, specifically brain heart infusion and blood agar, on bacterial survival fraction. An LED emitting at 403 ± 15 nm, with a radiant power of 1W, irradiance of 588.2 mW/cm2, and an irradiation time of 0 min, 1 min, 5 min, 10 min, 30 min, and 60 min, was used. The plates were incubated in microaerophilic conditions at 37 °C for 48 h, and the colony-forming units were counted. The photosensitizers were investigated using spectroscopy and fluorescence microscopy. There was no significant difference between the culture media (p > 0.05). However, a statistical reduction in both media was observed at 30 min (1058 J/cm2) (p < 0.05). The findings of this study suggest that aBL has the potential to kill bacteria regardless of the culture media used. Light therapy could be a promising and cost-effective strategy for preventing periodontal disease when used in combination with mechanical plaque control.

Exploring the association between a standardized extract of pequi peels (Caryocar brasiliense Cambess) and blue light as a photodynamic therapy for treating superficial wounds.

Natural products derived from plants can be used as photosensitizers for antimicrobial photodynamic therapy (aPDT) combining key therapeutic strategies for tissue repair while controlling microorganisms' growth. We investigated a standardized extract of pequi peels (Caryocar brasiliense Cambess) as a brownish natural photosensitizer for aPDT using blue light. Three concentrations of the pequi extract (PE; 10, 30, or 90 µg/mL) were tested solely or associated with blue laser (445 nm, 100 mW, 138 J/cm2 , 6 J, 60 s). In vitro, we quantified reactive oxygen species (ROS), assessed skin keratinocytes (HaCat) viability and migration, and aPDT antimicrobial activity on Streptococcus or Staphylococcus strains. In vivo, we assessed wound closure for the most active concentration disclosed by the in vitro assay (30 µg/mL). Upon aPDT treatments, ROS were significantly increased in cell monolayers regardless of PE concentration. PE at low doses stimulates epithelial cells. Although PE stimulated cellular migration, aPDT was moderately cytotoxic to skin keratinocytes, particularly at the highest concentration. The antimicrobial activity was observed for PE at the lowest concentration (10 µg/mL) and mostly at PE 10 µg/mL and 30 µg/mL when used as aPDT photosensitizers. aPDT with PE 30 µg/mL presents antimicrobial activity without compromising the initial phases of skin repair.

The N-Terminal Region of the BcWCL1 Photoreceptor Is Necessary for Self-Dimerization and Transcriptional Activation upon Light Stimulation in Yeast.

The BcWCL1 protein is a blue-light photoreceptor from the fungus Botrytis cinerea. This protein has a central role in B. cinerea circadian regulation and is an ortholog to WC-1 from Neurospora crassa. The BcWCL1 and WC-1 proteins have similar protein domains, including a LOV (Light Oxygen Voltage) domain for light sensing, two PAS (Per Arnt Sim) domains for protein-protein interaction, and a DNA binding domain from the GATA family. Recently, the blue-light response of BcWCL1 was demonstrated in a version without PAS domains (BcWCL1PAS∆). Here, we demonstrated that BcWCL1PAS∆ is capable of self-dimerization through its N-terminal region upon blue-light stimulation. Interestingly, we observed that BcWCL1PAS∆ enables transcriptional activation as a single component in yeast. By using chimeric transcription factors and the luciferase reporter gene, we assessed the transcriptional activity of different fragments of the N-terminal and C-terminal regions of BcWCL1PAS∆, identifying a functional transcriptional activation domain (AD) in the N-terminal region that belongs to the 9aaTAD family. Finally, we determined that the transcriptional activation levels of BcWCL1PAS∆ AD are comparable to those obtained with commonly used ADs in eukaryotic cells (Gal4 and p65). In conclusion, the BcWCL1PAS∆ protein self-dimerized and activated transcription in a blue-light-dependent fashion, opening future applications of this photoreceptor in yeast optogenetics.

Arylalkylamine N-acetyltransferase (AANAT): Blue light induction, nuclear translocation, and potential role in the survival of chicken retina neuronal cells.

In vertebrates, arylalkylamine N-acetyltransferase (AANAT; EC 2.3.1.87) is the time-keeping and key regulatory enzyme in melatonin (Mel) biosynthesis. AANAT is present in the pineal gland, retina, and other regions where it is controlled by light, cyclic adenosine monophosphate (cAMP) levels, and the molecular clock. AANAT converts serotonin to N-acetyl serotonin (NAS) and the last enzyme in the pathway, hydroxy-o-methyltransferase (HIOMT), forms Mel by NAS methylation. We have previously shown that AANAT is expressed in chicken retinal ganglion cells (RGCs) during daytime at the level of mRNA and enzyme activity. Here we investigated the presence of AANAT protein and mRNA throughout development in the chicken embryonic retina as well as AANAT expression, phosphorylation, and its sub-cellular localization in primary cultures of retinal neurons from E10 embryonic retinas exposed to blue light (BL) and controls kept in the dark (D). From embryonic days 7-10 (E7-10) AANAT mRNA and protein were visualized mainly concentrated in the forming ganglion cell layer (GCL), while from E17 through postnatal days, expression was detectable all through the different retinal cell layers. At postnatal day 10 (PN10) when animals were subjected to a 12:12 h LD cycle, AANAT was mainly expressed in the GCL and inner nuclear layer cells at noon (Zeitgeber Time (ZT 6)) and in the photoreceptor cell layer at night (ZT 21). Primary cultures of retinal neurons exhibited an induction of AANAT protein when cells were exposed to BL for 1 h as compared with D controls. After BL exposure, AANAT showed a significant change in intracellular localization from the cytoplasm to the nucleus in the BL condition, remaining in the nucleus 1-2 h in the D after BL stimulation. BL induction of nuclear AANAT was substantially inhibited when cultures were treated with the protein synthesis inhibitor cycloheximide (CHD). Furthermore, the phosphorylated form of the enzyme (pAANAT) increased after BL in nuclear fractions obtained from primary cultures as compared with D controls. Finally, the knockdown of AANAT by sh-RNA in primary cultures affected cell viability regardless of the light condition. AANAT knockdown also affected the redox balance, sh-AANAT treated cultures showing higher levels of reactive oxygen species (ROS) than in the sh-control. Our results support the idea that AANAT is a BL-sensing enzyme in the inner retina of diurnal vertebrates, undergoing phosphorylation and nuclear importation in response to BL stimulation. Moreover, it can be inferred that AANAT plays a novel role in nuclear function, cell viability, and, likely, through redox balance regulation.

Photobiomodulation with Blue Light on Wound Healing: A Scoping Review.

BACKGROUND: Photobiomodulation consists of inducing healing by irradiating light. This scoping review investigates the effect of blue light on the healing process. METHODS: The MEDLINE, Web of Science, Scopus, and CINAHL databases were searched. Two reviewers independently examined the search results and extracted data from the included studies. A descriptive analysis was performed. RESULTS: Twenty-two articles were included. Studies were categorized as in vitro/mixed, preclinical, and clinical. The power density used was 10-680 mW/cm2 in most of the in vitro/preclinical studies, the irradiation time ranged from 5 s to 10 min, and different wavelengths and energy densities were used. In clinical studies, the wavelength ranged from 405 to 470 nm, and the energy density varied from 1.5 to 30 J/cm2. CONCLUSIONS: A low energy density (<20 J/cm2) was able to stimulate the different cell types and proteins involved in healing, while a high energy density, 20.6-50 J/cm2, significantly reduced cell proliferation, migration, and metabolism. There is a great variety of device parameters among studies, and this makes it difficult to conclude what the best technical specifications are. Thus, further studies should be performed in order to define the appropriate parameters of light to be used.

Photodynamic therapy with acai (Euterpe oleracea) and blue light in oral cells: A spectroscopic and cytotoxicity analysis.

OBJECTIVE: To evaluate the potential of photodynamic therapy (PDT) with blue light-emitting diode (LED) 460 nm at 25, 50 and 100 J/cm2 using three concentrations of acai extracts (100, 40, and 10 mg/ml), in the proliferation and viability of head and neck tumor lines (SCC9). METHODS: Three groups of cells were analyzed for 3 days in an in vitro assay with MTT (3- (4,5-dimethylthiazol-2-yl) -2,5, -diphenyltetrazolium bromide) and crystal violet: cells in the absence of acai extract and PDT (control group); cells in the presence of acai extract and no light; and cells in the presence of acai extract and LED blue light (PDT groups). RESULTS: When using acai as a PS combined with blue LED (460 nm, 0.7466 cm2 , 1000 mW/cm2 ) and irradiation at 25, 50, and 100 J/cm2 , after 72 h, cell viability (p < 0.0001 vs. control, p = 0.0027 vs. 100 mg/ml açai group, p = 0.0039 vs. 40 mg/ml açai group, p = 0.0135 vs. 10 mg/ml açai group; One-Way ANOVA/Tukey) and proliferation (p < 0.05, One-Way ANOVA/Tukey) decreased. CONCLUSION: The acai in question is a potential photosensitizer (PS), with blue light absorbance and efficacy against head and neck tumor lines (SCC9).

Expanding the molecular versatility of an optogenetic switch in yeast.

In the budding yeast Saccharomyces cerevisiae, the FUN-LOV (FUNgal Light Oxygen and Voltage) optogenetic switch enables high levels of light-activated gene expression in a reversible and tunable fashion. The FUN-LOV components, under identical promoter and terminator sequences, are encoded in two different plasmids, which limits its future applications in wild and industrial yeast strains. In this work, we aim to expand the molecular versatility of the FUN-LOV switch to increase its biotechnological applications. Initially, we generated new variants of this system by replacing the promoter and terminator sequences and by cloning the system in a single plasmid (FUN-LOVSP). In a second step, we included the nourseothricin (Nat) or hygromycin (Hph) antibiotic resistances genes in the new FUN-LOVSP plasmid, generating two new variants (FUN-LOVSP-Nat and FUN-LOVSP-Hph), to allow selection after genome integration. Then, we compared the levels of light-activated expression for each FUN-LOV variants using the luciferase reporter gene in the BY4741 yeast strain. The results indicate that FUN-LOVSP-Nat and FUN-LOVSP-Hph, either episomally or genome integrated, reached higher levels of luciferase expression upon blue-light stimulation compared the original FUN-LOV system. Finally, we demonstrated the functionality of FUN-LOVSP-Hph in the 59A-EC1118 wine yeast strain, showing similar levels of reporter gene induction under blue-light respect to the laboratory strain, and with lower luciferase expression background in darkness condition. Altogether, the new FUN-LOV variants described here are functional in different yeast strains, expanding the biotechnological applications of this optogenetic tool.

Antimicrobial and Photoantimicrobial Activities of Chitosan/CNPPV Nanocomposites.

Multidrug-resistant bacteria represent a global health and economic burden that urgently calls for new technologies to combat bacterial antimicrobial resistance. Here, we developed novel nanocomposites (NCPs) based on chitosan that display different degrees of acetylation (DAs), and conjugated polymer cyano-substituted poly(p-phenylene vinylene) (CNPPV) as an alternative approach to inactivate Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. Chitosan's structure was confirmed through FT-Raman spectroscopy. Bactericidal and photobactericidal activities of NCPs were tested under dark and blue-light irradiation conditions, respectively. Hydrodynamic size and aqueous stability were determined by DLS, zeta potential (ZP) and time-domain NMR. TEM micrographs of NCPs were obtained, and their capacity of generating reactive oxygen species (ROS) under blue illumination was also characterized. Meaningful variations on ZP and relaxation time T2 confirmed successful physical attachment of chitosan/CNPPV. All NCPs exhibited a similar and shrunken spherical shape according to TEM. A lower DA is responsible for driving higher bactericidal performance alongside the synergistic effect from CNPPV, lower nanosized distribution profile and higher positive charged surface. ROS production was proportionally found in NCPs with and without CNPPV by decreasing the DA, leading to a remarkable photobactericidal effect under blue-light irradiation. Overall, our findings indicate that chitosan/CNPPV NCPs may constitute a valuable asset for the development of innovative strategies for inactivation and/or photoinactivation of bacteria.

Protective role of Caesalpinia sappan extract and its main component brazilin against blue light-induced damage in human fibroblasts.

BACKGROUND: Ultraviolet (UV) radiation is a well-known factor that causes skin aging. Recently, with the development of technology, the skin has been exposed to not only the UV radiation but also the blue light from electronic devices. Blue light is a high-energy visible light that penetrates deep into the dermal layer, producing reactive oxygen species (ROS) and resulting in skin aging. In this study, we searched for candidate materials that can inhibit blue light-induced skin aging and found Caesalpinia sappan extract (CSE) to be effective. METHODS: Human dermal fibroblasts (HDFs) were treated with various concentrations of CSE and brazilin and exposed to blue light. We measured that antioxidant activity, MMP-1 levels using MMP-1 ELISA, changes in collagen type 1, collagen type 3, MMP-1, and MMP-3 mRNA expressions, and ROS generation. RESULTS: We confirmed that CSE has high absorption of blue light and antioxidant activity. Blue light irradiation at 30 J/cm2 decreased the expression of collagen types 1 and 3, increased the expression of matrix metalloproteinase (MMP)-1 and 3, and decreased the production of ROS in human dermal fibroblasts as compared to those of the nonirradiated group. However, pretreatment with CSE protected against the damage caused by the blue light. Brazilin, a major constituent of C. sappan, had high absorbance in the blue light region and antioxidant activities. Pretreatment with brazilin also inhibited the damage caused by the blue light in the cells. CONCLUSION: CSE and brazilin are potential agents for inhibiting skin aging caused by blue light-induced damage.

Photoinactivation of Yeast and Biofilm Communities of Candida albicans Mediated by ZnTnHex-2-PyP4+ Porphyrin.

Candida albicans is the main cause of superficial candidiasis. While the antifungals available are defied by biofilm formation and resistance emergence, antimicrobial photodynamic inactivation (aPDI) arises as an alternative antifungal therapy. The tetracationic metalloporphyrin Zn(II) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (ZnTnHex-2-PyP4+) has high photoefficiency and improved cellular interactions. We investigated the ZnTnHex-2-PyP4+ as a photosensitizer (PS) to photoinactivate yeasts and biofilms of C. albicans strains (ATCC 10231 and ATCC 90028) using a blue light-emitting diode. The photoinactivation of yeasts was evaluated by quantifying the colony forming units. The aPDI of ATCC 90028 biofilms was assessed by the MTT assay, propidium iodide (PI) labeling, and scanning electron microscopy. Mammalian cytotoxicity was investigated in Vero cells using MTT assay. The aPDI (4.3 J/cm2) promoted eradication of yeasts at 0.8 and 1.5 µM of PS for ATCC 10231 and ATCC 90028, respectively. At 0.8 µM and same light dose, aPDI-treated biofilms showed intense PI labeling, about 89% decrease in the cell viability, and structural alterations with reduced hyphae. No considerable toxicity was observed in mammalian cells. Our results introduce the ZnTnHex-2-PyP4+ as a promising PS to photoinactivate both yeasts and biofilms of C. albicans, stimulating studies with other Candida species and resistant isolates.

The Intrinsic Blue Light Responses of Avian Müller Glial Cells Imply Calcium Release from Internal Stores.

The retina of vertebrates is responsible for capturing light through visual (cones and rods) and non-visual photoreceptors (intrinsically photosensitive retinal ganglion cells and horizontal cells) triggering a number of essential activities associated to image- and non-image forming functions (photic entrainment of daily rhythms, pupillary light reflexes, pineal melatonin inhibition, among others). Although the retina contains diverse types of neuronal based-photoreceptors cells, originally classified as ciliary- or rhabdomeric-like types, in recent years, it has been shown that the major glial cell type of the retina, the Müller glial cells (MC), express blue photopigments as Opn3 (encephalopsin) and Opn5 (neuropsin) and display light responses associated to intracellular Ca2 + mobilization. These findings strongly propose MC as novel retinal photodetectors (Rios et al., 2019). Herein, we further investigated the intrinsic light responses of primary cultures of MC from embryonic chicken retinas specially focused on Ca2 + mobilization by fluorescence imaging and the identity of the internal Ca2 + stores responsible for blue light responses. Results clearly demonstrated that light responses were specific to blue light of long time exposure, and that the main Ca2 + reservoir to trigger downstream responses came from intracellular stores localized in the endoplasmic reticulum These observations bring more complexity to the intrinsic photosensitivity of retinal cells, particularly with regard to the detection of light in the blue range of visible spectra, and add novel functions to glial cells cooperating with other photoreceptors to detect and integrate ambient light in the retinal circuit and participate in cell to cell communication.Summary statement:Non-neuronal cells in the vertebrate retina, Muller glial cells, express non-canonical photopigments and sense blue light causing calcium release from intracellular stores strongly suggesting a novel intrinsic photosensitivity and new regulatory events mediating light-driven processes with yet unknown physiological implications.

How can biophotonics help dentistry to avoid or minimize cross infection by SARS-CoV-2?

Biophotonics is defined as the combination of biology and photonics (the physical science of the light). It is a general term for all techniques that deal with the interaction between biological tissues/cells and photons (light). Biophotonics offers a great variety of techniques that can facilitate the early detection of diseases and promote innovative theragnostic approaches. As the COVID-19 infection can be transmitted due to the face-to-face communication, droplets and aerosol inhalation and the exposure to saliva, blood, and other body fluids, as well as the handling of sharp instruments, dental practices are at increased risk of infection. In this paper, a literature review was performed to explore the application of Biophotonics approaches in Dentistry focusing on the COVID-19 pandemic and how they can contribute to avoid or minimize the risks of infection in a dental setting. For this, search-related papers were retrieved from PubMED, Scielo, Google Schoolar, and American Dental Association and Centers for Disease Control and Prevention databases. The body of evidence currently available showed that Biophotonics approaches can reduce microorganism load, decontaminate surfaces, air, tissues, and minimize the generation of aerosol and virus spreading by minimally invasive, time-saving, and alternative techniques in general. However, each clinical situation must be individually evaluated regarding the benefits and drawbacks of these approaches, but always pursuing less-invasive and less aerosol-generating procedures, especially during the COVID-19 pandemic.

Non-visual Opsins and Novel Photo-Detectors in the Vertebrate Inner Retina Mediate Light Responses Within the Blue Spectrum Region.

In recent decades, a number of novel non-visual opsin photopigments belonging to the family of G protein- coupled receptors, likely involved in a number of non-image-forming processes, have been identified and characterized in cells of the inner retina of vertebrates. It is now known that the vertebrate retina is composed of visual photoreceptor cones and rods responsible for diurnal/color and nocturnal/black and white vision, and cells like the intrinsically photosensitive retinal ganglion cells (ipRGCs) and photosensitive horizontal cells in the inner retina, both detecting blue light and expressing the photopigment melanopsin (Opn4). Remarkably, these non-visual photopigments can continue to operate even in the absence of vision under retinal degeneration. Moreover, inner retinal neurons and Müller glial cells have been shown to express other photopigments such as the photoisomerase retinal G protein-coupled receptor (RGR), encephalopsin (Opn3), and neuropsin (Opn5), all able to detect blue/violet light and implicated in chromophore recycling, retinal clock synchronization, neuron-to-glia communication, and other activities. The discovery of these new photopigments in the inner retina of vertebrates is strong evidence of novel light-regulated activities. This review focuses on the features, localization, photocascade, and putative functions of these novel non-visual opsins in an attempt to shed light on their role in the inner retina of vertebrates and in the physiology of the whole organism.

Blue and red light photoemitters as approach to inhibit Staphylococcus aureus and Pseudomonas aeruginosa growth / Fotoemissores de luz azul e vermelha como abordagem para inibir o crescimento de Staphylococcus aureus e Pseudomonas aeruginosa

The ability of pathogenic bacteria acquire resistance to the existing antibiotics has long been considered a dangerous health risk threat. Currently, the use of visible light has been considered a new approach to treat bacterial infections as an alternative to antibiotics. Herein, we investigated the antimicrobial effect of two range of visible light, blue and red, on Staphylococcus aureus and Pseudomonas aeruginosa, two pathogenic bacterial commonly found in healthcare settings-acquired infections and responsible for high rate of morbidity and mortality. Bacterial cultures were exposed to blue or red light (470 nm and 660 nm) provided by light-emitting diodes - LED. The fluencies and irradiance used for blue and red light were 284.90 J/cm², 13.19 mW/cm² and 603.44 J/cm², 27.93 mW/cm² respectively. Different experimental approaches were used to determine the optimal conditions of light application. Only exposure to blue light for 6 hours was able to inhibit about 75% in vitro growth of both bacterial species after 24 hours. The surviving exposed bacteria formed colonies significantly smaller than controls, however, these bacteria were able to resume growth after 48 hours. Blue light was able to inhibit bacterial growth upon inoculation in both saline solution and BHI culture medium. We can conclude that blue light, but not red light, is capable of temporarily retarding the growth of gram negative and gram positive bacteria.(AU)

A capacidade das bactérias patogênicas adquirirem resistência aos antibióticos existentes há muito tempo é considerada uma ameaça perigosa à saúde. Atualmente, o uso da luz visível tem sido considerado uma nova abordagem no tratamento de infecções bacterianas como alternativa aos antibióticos. Neste trabalho, investigamos o efeito antimicrobiano de duas faixas de luz visível, azul e vermelha, em Staphylococcus aureus e Pseudomonas aeruginosa, duas bactérias patogênicas comumente encontradas em infecções adquiridas em instituições de saúde e responsáveis por alta taxa de morbimortalidade. As culturas bacterianas foram expostas à luz azul ou vermelha(470 nm e 660 nm) fornecida por diodos emissores de luz - LED. As fluências e irradiâncias utilizadas para luz azule vermelha foram 284,90 J/cm², 13,19 mW/cm² e 603,44 J/cm², 27,93 mW/cm², respectivamente. Várias abordagens experimentais foram utilizadas para determinar as condições ótimas de aplicação da luz. Apenas a exposição à luz azul por 6 horas foi capaz de inibir cerca de 75% o crescimento in vitro de ambas as espécies bacterianas após24 horas. As bactérias expostas sobreviventes formaram colônias com um tamanho significativamente menor do que os controles, contudo, essas bactérias conseguiram retomar o crescimento normal após 48 horas. A luz azul foi capaz de inibir o crescimento das bactérias após sua inoculação em solução salina ou no meio de cultura rico em nutrientes BHI. Podemos concluir que a luz azul mas não a luz vermelha é capaz de retardar temporariamente o crescimento de bactérias Gram-negativas e Gram-positivas.(AU)

Blue and red light photoemitters as approach to inhibit Staphylococcus aureus and Pseudomonas aeruginosa growth / Fotoemissores de luz azul e vermelha como abordagem para inibir o crescimento de Staphylococcus aureus e Pseudomonas aeruginosa

The ability of pathogenic bacteria acquire resistance to the existing antibiotics has long been considered a dangerous health risk threat. Currently, the use of visible light has been considered a new approach to treat bacterial infections as an alternative to antibiotics. Herein, we investigated the antimicrobial effect of two range of visible light, blue and red, on Staphylococcus aureus and Pseudomonas aeruginosa, two pathogenic bacterial commonly found in healthcare settings-acquired infections and responsible for high rate of morbidity and mortality. Bacterial cultures were exposed to blue or red light (470 nm and 660 nm) provided by light-emitting diodes - LED. The fluencies and irradiance used for blue and red light were 284.90 J/cm2, 13.19 mW/cm2 and 603.44 J/cm2, 27.93 mW/cm2 respectively. Different experimental approaches were used to determine the optimal conditions of light application. Only exposure to blue light for 6 hours was able to inhibit about 75% in vitro growth of both bacterial species after 24 hours. The surviving exposed bacteria formed colonies significantly smaller than controls, however, these bacteria were able to resume growth after 48 hours. Blue light was able to inhibit bacterial growth upon inoculation in both saline solution and BHI culture medium. We can conclude that blue light, but not red light, is capable of temporarily retarding the growth of gram negative and gram positive bacteria.

A capacidade das bactérias patogênicas adquirirem resistência aos antibióticos existentes há muito tempo é considerada uma ameaça perigosa à saúde. Atualmente, o uso da luz visível tem sido considerado uma nova abordagem no tratamento de infecções bacterianas como alternativa aos antibióticos. Neste trabalho, investigamos o efeito antimicrobiano de duas faixas de luz visível, azul e vermelha, em Staphylococcus aureus e Pseudomonas aeruginosa, duas bactérias patogênicas comumente encontradas em infecções adquiridas em instituições de saúde e responsáveis por alta taxa de morbimortalidade. As culturas bacterianas foram expostas à luz azul ou vermelha (470 nm e 660 nm) fornecida por diodos emissores de luz - LED. As fluências e irradiâncias utilizadas para luz azul e vermelha foram 284,90 J/cm2, 13,19 mW/cm2 e 603,44 J/cm2, 27,93 mW/cm2, respectivamente. Várias abordagens experimentais foram utilizadas para determinar as condições ótimas de aplicação da luz. Apenas a exposição à luz azul por 6 horas foi capaz de inibir cerca de 75% o crescimento in vitro de ambas as espécies bacterianas após 24 horas. As bactérias expostas sobreviventes formaram colônias com um tamanho significativamente menor do que os controles, contudo, essas bactérias conseguiram retomar o crescimento normal após 48 horas. A luz azul foi capaz de inibir o crescimento das bactérias após sua inoculação em solução salina ou no meio de cultura rico em nutrientes BHI. Podemos concluir que a luz azul mas não a luz vermelha é capaz de retardar temporariamente o crescimento de bactérias Gram-negativas e Gram-positivas.

Blue and red light photoemitters as approach to inhibit Staphylococcus aureus and Pseudomonas aeruginosa growth / Fotoemissores de luz azul e vermelha como abordagem para inibir o crescimento de Staphylococcus aureus e Pseudomonas aeruginosa

The ability of pathogenic bacteria acquire resistance to the existing antibiotics has long been considered a dangerous health risk threat. Currently, the use of visible light has been considered a new approach to treat bacterial infections as an alternative to antibiotics. Herein, we investigated the antimicrobial effect of two range of visible light, blue and red, on Staphylococcus aureus and Pseudomonas aeruginosa, two pathogenic bacterial commonly found in healthcare settings-acquired infections and responsible for high rate of morbidity and mortality. Bacterial cultures were exposed to blue or red light (470 nm and 660 nm) provided by light-emitting diodes - LED. The fluencies and irradiance used for blue and red light were 284.90 J/cm², 13.19 mW/cm² and 603.44 J/cm², 27.93 mW/cm² respectively. Different experimental approaches were used to determine the optimal conditions of light application. Only exposure to blue light for 6 hours was able to inhibit about 75% in vitro growth of both bacterial species after 24 hours. The surviving exposed bacteria formed colonies significantly smaller than controls, however, these bacteria were able to resume growth after 48 hours. Blue light was able to inhibit bacterial growth upon inoculation in both saline solution and BHI culture medium. We can conclude that blue light, but not red light, is capable of temporarily retarding the growth of gram negative and gram positive bacteria.

A capacidade das bactérias patogênicas adquirirem resistência aos antibióticos existentes há muito tempo é considerada uma ameaça perigosa à saúde. Atualmente, o uso da luz visível tem sido considerado uma nova abordagem no tratamento de infecções bacterianas como alternativa aos antibióticos. Neste trabalho, investigamos o efeito antimicrobiano de duas faixas de luz visível, azul e vermelha, em Staphylococcus aureus e Pseudomonas aeruginosa, duas bactérias patogênicas comumente encontradas em infecções adquiridas em instituições de saúde e responsáveis por alta taxa de morbimortalidade. As culturas bacterianas foram expostas à luz azul ou vermelha(470 nm e 660 nm) fornecida por diodos emissores de luz - LED. As fluências e irradiâncias utilizadas para luz azule vermelha foram 284,90 J/cm², 13,19 mW/cm² e 603,44 J/cm², 27,93 mW/cm², respectivamente. Várias abordagens experimentais foram utilizadas para determinar as condições ótimas de aplicação da luz. Apenas a exposição à luz azul por 6 horas foi capaz de inibir cerca de 75% o crescimento in vitro de ambas as espécies bacterianas após24 horas. As bactérias expostas sobreviventes formaram colônias com um tamanho significativamente menor do que os controles, contudo, essas bactérias conseguiram retomar o crescimento normal após 48 horas. A luz azul foi capaz de inibir o crescimento das bactérias após sua inoculação em solução salina ou no meio de cultura rico em nutrientes BHI. Podemos concluir que a luz azul mas não a luz vermelha é capaz de retardar temporariamente o crescimento de bactérias Gram-negativas e Gram-positivas.

Blue and red light photoemitters as approach to inhibit Staphylococcus aureus and Pseudomonas aeruginosa growth

Abstract The ability of pathogenic bacteria acquire resistance to the existing antibiotics has long been considered a dangerous health risk threat. Currently, the use of visible light has been considered a new approach to treat bacterial infections as an alternative to antibiotics. Herein, we investigated the antimicrobial effect of two range of visible light, blue and red, on Staphylococcus aureus and Pseudomonas aeruginosa, two pathogenic bacterial commonly found in healthcare settings-acquired infections and responsible for high rate of morbidity and mortality. Bacterial cultures were exposed to blue or red light (470 nm and 660 nm) provided by light-emitting diodes - LED. The fluencies and irradiance used for blue and red light were 284.90 J/cm2, 13.19 mW/cm2 and 603.44 J/cm2, 27.93 mW/cm2 respectively. Different experimental approaches were used to determine the optimal conditions of light application. Only exposure to blue light for 6 hours was able to inhibit about 75% in vitro growth of both bacterial species after 24 hours. The surviving exposed bacteria formed colonies significantly smaller than controls, however, these bacteria were able to resume growth after 48 hours. Blue light was able to inhibit bacterial growth upon inoculation in both saline solution and BHI culture medium. We can conclude that blue light, but not red light, is capable of temporarily retarding the growth of gram negative and gram positive bacteria.

Resumo A capacidade das bactérias patogênicas adquirirem resistência aos antibióticos existentes há muito tempo é considerada uma ameaça perigosa à saúde. Atualmente, o uso da luz visível tem sido considerado uma nova abordagem no tratamento de infecções bacterianas como alternativa aos antibióticos. Neste trabalho, investigamos o efeito antimicrobiano de duas faixas de luz visível, azul e vermelha, em Staphylococcus aureus e Pseudomonas aeruginosa, duas bactérias patogênicas comumente encontradas em infecções adquiridas em instituições de saúde e responsáveis por alta taxa de morbimortalidade. As culturas bacterianas foram expostas à luz azul ou vermelha (470 nm e 660 nm) fornecida por diodos emissores de luz - LED. As fluências e irradiâncias utilizadas para luz azul e vermelha foram 284,90 J/cm2, 13,19 mW/cm2 e 603,44 J/cm2, 27,93 mW/cm2, respectivamente. Várias abordagens experimentais foram utilizadas para determinar as condições ótimas de aplicação da luz. Apenas a exposição à luz azul por 6 horas foi capaz de inibir cerca de 75% o crescimento in vitro de ambas as espécies bacterianas após 24 horas. As bactérias expostas sobreviventes formaram colônias com um tamanho significativamente menor do que os controles, contudo, essas bactérias conseguiram retomar o crescimento normal após 48 horas. A luz azul foi capaz de inibir o crescimento das bactérias após sua inoculação em solução salina ou no meio de cultura rico em nutrientes BHI. Podemos concluir que a luz azul mas não a luz vermelha é capaz de retardar temporariamente o crescimento de bactérias Gram-negativas e Gram-positivas.

New Insights Into Blue Light Phototherapy in Experimental Trypanosoma cruzi Infection.

The search for an effective etiologic treatment to eliminate Trypanosoma cruzi, the causative agent of Chagas disease, has continued for decades and yielded controversial results. In the 1970s, nifurtimox and benznidazole were introduced for clinical assessment, but factors such as parasite resistance, high cellular toxicity, and efficacy in acute and chronic phases of the infection have been debated even today. This study proposes an innovative strategy to support the controlling of the T. cruzi using blue light phototherapy or blue light-emitting diode (LED) intervention. In in vitro assays, axenic cultures of Y and CL strains of T. cruzi were exposed to 460 nm and 40 µW/cm2 of blue light for 5 days (6 h/day), and parasite replication was evaluated daily. For in vivo experiments, C57BL6 mice were infected with the Y strain of T. cruzi and exposed to 460 nm and 7 µW/cm2 of blue light for 9 days (12 h/day). Parasite count in the blood and cardiac tissue was determined, and plasma interleukin (IL-6), tumoral necrosis factor (TNF), chemokine ligand 2 (CCL2), and IL-10 levels and the morphometry of the cardiac tissue were evaluated. Blue light induced a 50% reduction in T. cruzi (epimastigote forms) replication in vitro after 5 days of exposure. This blue light-mediated parasite control was also observed by the T. cruzi reduction in the blood (trypomastigote forms) and in the cardiac tissue (parasite DNA and amastigote nests) of infected mice. Phototherapy reduced plasma IL-6, TNF and IL-10, but not CCL2, levels in infected animals. This non-chemical therapy reduced the volume density of the heart stroma in the cardiac connective tissue but did not ameliorate the mouse myocarditis, maintaining a predominance of pericellular and perivascular mononuclear inflammatory infiltration with an increase in polymorphonuclear cells. Together, these data highlight, for the first time, the use of blue light therapy to control circulating and tissue forms of T. cruzi. Further investigation would demonstrate the application of this promising and potential complementary strategy for the treatment of Chagas disease.

Effect of Blue Light on Acne Vulgaris: A Systematic Review.

Acne is a dermatosis that affects almost 90% of the adolescent population worldwide and its treatment is performed with retinoids, antimicrobials, acids, and topical or systemic antibiotics. Side effects such as skin irritation in addition to microbial resistance to antibiotics are the main side effects found. Phototherapy with blue light is being used as an alternative treatment. Our objective was to analyze the use of blue light to treat inflammatory acne. We conducted a systematic literature review, following the recommendation PRISMA (Preferred Reporting Items for Systematic Reviews and MetaAnalyses), including in the sample randomized clinical trial studies that compared blue light with another intervention as control. The research was carried out in the PUBMED and WEB of SCIENCE databases and the methodological quality of the studies evaluated were made by the Cochrane Collaboration Bias Risk Scale. After the exclusion of duplicates, the titles and abstracts of 81 articles were evaluated, and 50 articles were selected for full reading, including in the review at the end 8 articles. Studies have shown significant improvements in the overall picture of acne. It is concluded that despite the great potential in its use in the treatment of acne, there is a need for more detailed trials on the effect of blue light on the treatment of inflammatory acne.