Strengthening collaborations at the Biology-Physics interface: trends in antimicrobial photodynamic therapy.

The unbridled use of antimicrobial drugs over the last decades contributed to the global dissemination of drug-resistant pathogens and increasing rates of life-threatening infections for which limited therapeutic options are available. Currently, the search for safe, fast, and effective therapeutic strategies to combat infectious diseases is a worldwide demand. Antimicrobial photodynamic therapy (APDT) rises as a promising therapeutic approach against a wide range of pathogenic microorganisms. APDT combines light, a photosensitizing drug (PS), and oxygen to kill microorganisms by oxidative stress. Since the APDT field involves branches of biology and physics, the strengthening of interdisciplinary collaborations under the aegis of biophysics is welcome. Given this scenario, Brazil is one of the global leaders in the production of APDT science. In this review, we provide detailed reports of APDT studies published by the Laboratory of Optical Therapy (IPEN-CNEN), Group of Biomedical Nanotechnology (UFPE), and collaborators over the last 10 years. We present an integrated perspective of APDT from basic research to clinical practice and highlight its promising use, encouraging its adoption as an effective and safe technology to tackle important pathogens. We cover the use of methylene blue (MB) or Zn(II) porphyrins as PSs to kill bacteria, fungi, parasites, and pathogenic algae in laboratory assays. We describe the impact of MB-APDT in Dentistry and Veterinary Medicine to treat different infectious diseases. We also point out future directions combining APDT and nanotechnology. We hope this review motivates further APDT studies providing intuitive, vivid, and insightful information for the readers.

Responses of melanoma cells to photobiomodulation depend on cell pigmentation and light parameters.

Melanoma is a highly aggressive skin cancer that requires new approaches for its management. Low-level laser therapy, currently named photobiomodulation therapy (PBM), has been used to improve different conditions but its effects and safe use on melanoma remain unexplored. Herein, we investigated the PBM impact on melanoma cells differing by pigmentation using near-infrared (NIR) and red lasers in vitro. In vivo, we evaluated the effects of the red laser on melanoma-bearing mice. Amelanotic (SK-MEL-37) and melanotic (B16F10) cells were exposed in vitro to a NIR (780 nm, 40 mW) or a red laser (660 nm, 40 mW) in 3 different light doses: 30, 90, and 150 J/cm2 and responses were assessed regarding mitochondrial activity, invasiveness, migration, and VEGF production. In vivo, melanoma-bearing mice received the red laser delivering 150 J/cm2 directly to the tumor on 3 consecutive days. Mice were monitored for 15 days regarding tumor progression and mouse survival. We noticed that amelanotic cells were unresponsive to NIR light. In contrast, NIR irradiation at 30 J/cm2 promoted an increase in the invasiveness of pigmented cells, even though all light doses have inhibited cell migration. Regarding the red laser on pigmented cells, the highest light dose (150 J/cm2) decreased the VEGF production and migration. In vivo, melanoma-bearing mice treated with red laser showed smaller tumor volume and longer survival than controls. We conclude that PBM appears to be safe for amelanotic non-pigmented melanoma but triggers different responses in melanotic pigmented cells depending on light parameters. Additionally, a high dose of red laser impairs the invasive behavior of melanoma cells, probably due to the decrease in VEGF synthesis, which may have contributed to tumor arrest and increased mouse survival. These findings suggest that red laser therapy could be a new ally in the supportive care of melanoma patients.

The importance of combining methods to assess Candida albicans biofilms following photodynamic inactivation.

BACKGROUND: Methylene blue (MB)-mediated photodynamic inactivation (PDI) has shown good results in killing Candida spp. Although MB solutions are commonly used, new formulations have been designed to improve PDI. However, chemical substances in the formulation may interfere with the PDI outcome. In this sense, different methodologies should be used to evaluate PDI in vitro. Herein, we report different methodologies to evaluate the effects of PDI with an oral formulation (OF) containing 0.005% MB on Candida albicans biofilm. METHODS: Biofilms were treated using the MB-OF, with 5 min pre-irradiation time and exposure to a 640 nm LED device (4.7 J/cm2). PDI was evaluated by the XTT reduction test, counting the colony forming units (CFU), a filamentation assay, crystal violet (CV) staining, and scanning electronic microscopy (SEM). RESULTS: PDI was able to reduce around 1.5 log10 CFU/mL, even though no significant differences were noted in metabolic activity in comparison to the control immediately after PDI. A significant decrease in yeast to hyphae transition was observed after PDI, while the biofilm exhibited flattened cells and a reduced number of yeasts in SEM. The CV assay showed increased biomass. CONCLUSION: MB-OF-mediated PDI was effective in C. albicans biofilms, as it significantly reduced the CFU/mL and the virulence of surviving cells. The CV data were inconclusive, since the OF components interacted with the CV, making the data useless. Taken together, our data suggest that the association of different methods allows complementary responses to assess how PDI mediated by a formulation impacts biofilms.

Towards effective cutaneous leishmaniasis treatment with light-based technologies. A systematic review and meta-analysis of preclinical studies.

Cutaneous leishmaniasis (CL) is a neglected disease that represents a serious global public health concern. We performed a systematic review with meta-analysis targeting the use of light-based therapies on CL in preclinical studies since they are essential to identify the benefits, challenges, and limitations of proposing new technologies to fight CL. We searched Pubmed and Web of Science to include original preclinical researches in English that used light-based technologies to fight CL. Inclusion criteria encompassed any animal model for CL induction, an untreated infected group as the comparator, reliable and consistent methodology to develop and treat CL, focus on an antimicrobial therapeutic approach, and data for lesion size and/or parasite load in the infection site. We identified eight eligible articles, and all of them used photodynamic therapy (PDT). For the meta-analysis, three studies were included regarding the parasite load in the infection site and four comprised the lesion size. No overall statistically significant differences were observed between untreated control and PDT groups for parasite load. Differently, PDT significantly reduced the lesion size regardless of the protocol used to treat CL (in mm, SMD: -1.90; 95% CI: -3.74 to -0.07, p = 0.04). This finding is particularly encouraging since CL promotes disfiguring lesions that profoundly affect the quality of life of patients. We conclude that PDT is a new promising technology able to be topically used against CL if applied in more than one session, making it a promising ally for the management of CL.

Photobiomodulation therapy combined with radiotherapy in the treatment of triple-negative breast cancer-bearing mice.

This work investigated the effect of photobiomodulation therapy (PBM) combined with radiotherapy (RT) on triple-negative breast cancer (TNBC)-bearing mice. Female BALB/c mice received 4 T1 cells into a mammary fat pad. Local RT was performed with a total dose of 60 Gy divided into 4 consecutive sessions of 15 Gy. For PBM, a red laser was used in three different protocols: i-) single exposure delivering 150 J.cm-2 (24 h after the last RT session), and ii-) radiant exposure of 150 J.cm-2 or iii-) fractionated radiant exposure of 37.5 J.cm-2 (after each RT session). Tumor volume, complete blood cell count, clinical condition, metastasis, and survival of animals were monitored during 3 weeks post-RT. Our results demonstrated that regardless of the protocol, PBM arrested the tumor growth, improved the clinical condition, and prevented hemolytic anemia. Besides, although PBM groups have exhibited a high neutrophil:lymphocyte ratio (NLR), they decreased the number of lung metastases and enhanced mouse survival. Worthy of note, PBM should be used along with the RT sessions in higher radiant exposures, since PBM at 150 J.cm-2 per session significantly extended the survival rate. Together, these data suggest PBM could be a potential ally to RT to fight TNBC.

Methylene blue-covered superparamagnetic iron oxide nanoparticles combined with red light as a novel platform to fight non-local bacterial infections: A proof of concept study against Escherichia coli.

Currently, antimicrobial photodynamic therapy (APDT) is limited to the local treatment of topical infections, and a platform that can deliver the photosensitizer to internal organs is highly desirable for non-local ones; SPIONs can be promising vehicles for the photosensitizer. This work reports an innovative application of methylene blue (MB)-superparamagnetic iron oxide nanoparticles (SPIONs). We report on the preparation, characterization, and application of MB-SPIONs for antimicrobial photodynamic therapy. When exposed to light, the MB photosensitizer generates reactive oxygen species (ROS), which cause irreversible damage in microbial cells. We prepare SPIONs by the co-precipitation method. We cover the nanoparticles with a double silica layer - tetraethyl orthosilicate and sodium silicate - leading to the hybrid material magnetite-silica-MB. We characterize the as-prepared SPIONs by Fourier transform infrared spectroscopy, powder X-ray diffraction, and magnetic measurements. We confirm the formation of magnetite using powder X-ray diffraction data. We use the Rietveld method to calculate the average crystallite size of magnetite as being 14 nm. Infrared spectra show characteristic bands of iron­oxygen as well as others associated with silicate groups. At room temperature, the nanocomposites present magnetic behavior due to the magnetite core. Besides, magnetite-silica-MB can promote ROS formation. Thus, we evaluate the photodynamic activity of Fe3O4-silica-MB on Escherichia coli. Our results show the bacteria are completely eradicated following photodynamic treatment depending on the MB release time from SPIONs and energy dose. These findings encourage us to explore the use of magnetite-silica-MB to fight internal infections in preclinical assays.

Global priority multidrug-resistant pathogens do not resist photodynamic therapy.

Microbial drug-resistance demands immediate implementation of novel therapeutic strategies. Antimicrobial photodynamic therapy (aPDT) combines the administration of a photosensitizer (PS) compound with low-irradiance light to induce photochemical reactions that yield reactive oxygen species (ROS). Since ROS react with nearly all biomolecules, aPDT offers a powerful multitarget method to avoid selection of drug-resistant strains. In this study, we assayed photodynamic inactivation under a standardized method, combining methylene blue (MB) as PS and red light, against global priority pathogens. The species tested include Acinetobacter baumannii, Klebsiella aerogenes, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecium, Enterococcus faecalis, Staphylococcus aureus, Candida albicans and Cryptococcus neoformans. Our strain collection presents resistance to all tested antimicrobials (>50). All drug-resistant strains were compared to their drug-sensitive counterparts. Regardless of resistance phenotype, MB-aPDT presented species-specific dose-response kinetics. More than 5log10 reduction was observed within less than 75 s of illumination for A. baumannii, E. coli, E. faecium, E. faecalis and S. aureus and within less than 7 min for K. aerogenes, K. pneumoniae, P. aeruginosa, C. albicans and C. neoformans. No signs of correlations in between drug-resistance profiles and aPDT sensitivity were observed. Therefore, MB-aPDT can provide effective therapeutic protocols for a very broad spectrum of pathogens. Hence, we believe that this study represents a very important step to bring aPDT closer to implementation into mainstream medical practices.

Photodynamic Activity on Biofilm in Endotracheal Tubes of Patients Admitted to an Intensive Care Unit.

Ventilator-associated pneumonia (VAP) is an infection that arises after endotracheal intubation affecting patients under intensive care. The presence of the endotracheal tube (ETT) is a risk factor since it is colonized by multispecies biofilm. Antimicrobial photodynamic therapy (aPDT) could be a strategy to decontaminate ETTs. We verify if methylene blue (MB) associated with external illumination of the ETT could be an alternative to destroy biofilm. We performed an in vitro and ex vivo study. In vitro study was performed with P. aeruginosa biofilm grew over ETT for 7 days. After treatment, the surviving cells were cultured for 3 days and the biofilm was analyzed by crystal violet absorbance. Ex vivo study employed ETT obtained from extubated patients. aPDT was performed with MB (100 µm) and red LED (λ = 640±20 nm). We quantified the biofilm thickness and used scanning electron microscopy and fluorescence technique to verify morphological and functional changes after aPDT. Our results showed that bacteria remain susceptible to aPDT after sequential treatments. We also attested that aPDT can reduce biofilm thickness, disrupt biofilm attachment from ETT surface and kill microbial cells. These data suggest that aPDT should be investigated to decrease VAP incidence via ETT decontamination.

Cell death mechanisms in Leishmania amazonensis triggered by methylene blue-mediated antiparasitic photodynamic therapy.

Antiparasitic photodynamic therapy (ApPDT) is an emerging approach to manage cutaneous leishmaniasis (CL) since no side effects, contraindications and parasite resistance have been reported. In addition, methylene blue (MB) is a suitable photosensitizer to mediate ApPDT on CL. In this study we aimed to look for the best parameters to eradicate Leishmania amazonensis and investigated the cell death pathways involved in MB-mediated ApPDT. MB uptake by parasites was determined using different MB concentrations (50, 100, 250 and 500 µM) and incubation times (10, 30 and 60 min). L. amazonensis promastigotes were cultured and submitted to ApPDT using different concentrations of MB (50, 100 and 250 µM) combined to a red LED emitting at 645 ±â€¯10 nm. The pre-irradiation time was 10 min. Two optical powers (100 mW and 250 mW) were tested and cells were exposed to 60 and 300 s of MB-mediated ApPDT delivering energies of 6, 15, 30 and 75 J and fluences of 21.2, 53.1, 106.2 and 265.4 J/cm2, respectively. Following ApPDT, cells were prepared for flow cytometry and transmission electron microscopy to unravel the mechanisms of cell death. Our results showed the lowest MB concentration (50 µM) and the lowest optical power (100 mW) promoted the highest percentage of cell decrease. ApPDT caused alterations on cell membrane permeability as well depolarization of mitochondrial membrane potential. We also observed ultrastructural changes of the parasites such as cell shrinkage, intense vacuolization of the cytoplasm, enlargement of mitochondrion-kinetoplast complex, and small blebs on parasite flagella and cell membrane after MB-mediated ApPDT. Taken together, our findings ratify that ApPDT parameters play a pivotal role in cell susceptibility and suggest that apoptosis is involved in parasite death regardless MB-mediated ApPDT protocol.

Evaluation of red light scattering in gingival tissue - in vivo study.

Antimicrobial photodynamic therapy (aPDT) has been used to treat periodontal disease, thus the aim of this study was to investigate red light (ʎ = 660 nm) attenuation in gingival tissue. This clinical trial included 30 patients with chronic periodontitis; three incisors from each patient were selected for the experimental procedures. A laser source with a radiant power output of 100 mW was used. Two digital photographs were taken of each selected incisor (in frontal and occlusal position). The images were analyzed in the ImageJ program. The results demonstrated that at a 3 mm distance from the laser probe, there is an attenuation of light intensity of 50%, along frontal and occlusal views. Light attenuation in gingival tissue should be considered when setting optimal parameters for antimicrobial photodynamic therapy or photobiomodulation.

Effects of corticopuncture (CP) and low-level laser therapy (LLLT) on the rate of tooth movement and root resorption in rats using micro-CT evaluation.

The aim of this study was to compare the rate of tooth displacement, quantity of root resorption, and alveolar bone changes in five groups: corticopuncture (CP), low-level laser therapy (LLLT), CP combined with LLLT (CP + LLLT), control (C), and negative control (NC). A total of 60 half-maxilla from 30 male Wistar rats (10 weeks old) were divided randomly into five groups: three (CP, LLLT, and CP + LLLT) test groups with different stimulation for accelerated-tooth-movement (ATM), one control (C) group, and one negative control (NC) group with no tooth movement. Nickel-titanium coil springs with 50 g of force were tied from the upper left and right first molars to micro-implants placed behind the maxillary incisors. For the CP and CP + LLLT groups, two perforations in the palate and one mesially to the molars were performed. For the LLLT and CP + LLLT groups, GaAlAs diode laser was applied every other day for 14 days (810 nm, 100 mW, 15 s). The tooth displacements were measured directly from the rat's mouth and indirectly from microcomputer (micro-CT) tomographic images. Bone responses at the tension and compression sites and root resorption were analyzed from micro-CT images. The resulting alveolar bone responses were evaluated by measuring bone mineral density (BMD), bone volume fraction (BV/TV), and trabecular thickness (TbTh). Root resorption crater volumes were measured on both compression and tension sides of mesial and distal buccal roots. The tooth displacement in the CP + LLLT group was the greatest when measured clinically, followed by the CP, LLLT, and control groups (C and NC), respectively (p <0.05). The tooth movements measured from micro-CT images showed statistically higher displacement in the CP and CP + LLLT groups compared to the LLLT and control groups. The BMD, BV/TV, and TbTh values were lower at the compression side and higher at the tension side for all three test groups compared to the control group. The root resorption crater volume of the distal buccal root was higher in the control group, followed by CP, LLLT, and CP + LLLT, mostly at the compression site. Combining corticopuncture and low-level laser therapy (CP + LLLT) produced more tooth displacement and less root resorption at the compression side. The combined technique also promoted higher alveolar bone formation at the tension side.

Antimicrobial photodynamic therapy for infectious stomatitis in snakes: Clinical views and microbiological findings.

BACKGROUND: Antimicrobial photodynamic therapy (APDT) has been broadly investigated as an alternative to treat localized infections, without leading to the selection of resistant microorganisms. Infectious stomatitis is a multifactorial disease frequently reported in captive snakes characterized by infection of the oral mucosa and surrounding tissues. In this study, we investigated methylene blue (MB)-mediated APDT to treat infectious stomatitis in snakes and verified the resistance phenotype and genotype before and after APDT. METHODS: Three Boid snakes presented petechiae, edema and caseous material in their oral cavities. MB (0.01%) was applied on the lesions and after 5min they were irradiated using a red laser (λ=660nm), fluence of 280J/cm2, 8J and 80s per point, 100mW, spot size 0.028cm2 and fluence rate of 3.5W/cm2. APDT was repeated once a week during 3 months. Samples of the lesions were collected to identify bacteria and antibiotic resistance profiles. To analyze the clonality of bacterial isolates before and after APDT, isolates were subjected to ERIC PCR analysis. RESULTS: Snakes presented clinical improvement such as reduction of inflammatory signs and caseous material. Pseudomonas aeruginosa and Escherichia coli were present in all snakes; Klebsiella pneumoniae and Morganella morganii were also identified in some animals. We also observed that the oral microbiota was completely replaced following APDT. However, K. pneumoniae isolates before and after APDT were a single clone with 100% of genetic similarity that lost resistance phenotype for seven antibiotics of four classes. CONCLUSIONS: These results show that APDT can be used to treat infectious stomatitis in snakes.

TiF4 gel effects on tubular occlusion of eroded/abraded human dentin.

This in situ study evaluated the tubular occlusion caused by 4% TiF4 gel on the surface of eroded/abraded dentin. Sixty human dentin samples were eroded in vitro and assigned into six groups (n = 10) according to the in situ surface treatment and number of cycling days: 4% TiF4 gel applied once (TiF4 1), twice (TiF4 2), or three times (TiF4 3) followed by 2, 4, and 6 days of erosive/abrasive in situ cycling, respectively. Control groups (no treatment) were subjected to 2 (C1), 4 (C2), and 6 (C3) days of erosive/abrasive in situ cycling only. A seventh group (n = 10) was comprised by in vitro uneroded samples (UN), subjected to 6 days of in situ erosive/abrasive cycling. Each cycling day consisted on six erosive (0.5% citric acid, pH 2.6) and one abrasive events. Environmental scanning electron microscopy micrographs were taken. For all groups, blinded examiners assessed dentin tubules occlusion using visual scores (0-unoccluded, 1-partially occluded by granular deposits, 2-partially occluded by reduction in tubular lumen into diamond shape, 3-completely occluded) on images captured prior and after the in situ phase. Scheirer-Ray-Hare test demonstrated that treatments significantly affected tubule occlusion (p < .001). Dunn's test showed that tubule occlusion in TiF4 3 was significantly higher than in C1. Tubule occlusion in remaining groups did not differ from that observed in groups TiF4 3 and C1. Tubule occlusion was significantly higher after in situ phase. It may be suggested that TiF4 , when applied three times, was able to positively change tubule occlusion of dentin samples.

Type I and Type II Photosensitized Oxidation Reactions: Guidelines and Mechanistic Pathways.

Here, 10 guidelines are presented for a standardized definition of type I and type II photosensitized oxidation reactions. Because of varied notions of reactions mediated by photosensitizers, a checklist of recommendations is provided for their definitions. Type I and type II photoreactions are oxygen-dependent and involve unstable species such as the initial formation of radical cation or neutral radicals from the substrates and/or singlet oxygen (1 O21 ∆g ) by energy transfer to molecular oxygen. In addition, superoxide anion radical (O2·-) can be generated by a charge-transfer reaction involving O2 or more likely indirectly as the result of O2 -mediated oxidation of the radical anion of type I photosensitizers. In subsequent reactions, O2·- may add and/or reduce a few highly oxidizing radicals that arise from the deprotonation of the radical cations of key biological targets. O2·- can also undergo dismutation into H2 O2 , the precursor of the highly reactive hydroxyl radical (·OH) that may induce delayed oxidation reactions in cells. In the second part, several examples of type I and type II photosensitized oxidation reactions are provided to illustrate the complexity and the diversity of the degradation pathways of mostly relevant biomolecules upon one-electron oxidation and singlet oxygen reactions.

Glucose modulates antimicrobial photodynamic inactivation of Candida albicans in biofilms.

Candida albicans biofilm is a main cause of infections associated with medical devices such as catheters, contact lens and artificial joint prosthesis. The current treatment comprises antifungal chemotherapy that presents low success rates. Photodynamic inactivation (PDI) involves the combination of a photosensitizing compound (PS) and light to generate oxidative stress that has demonstrated effective antimicrobial activity against a broad-spectrum of pathogens, including C. albicans. This fungus senses glucose inducing an upregulation of membrane transporters that can facilitate PS uptake into the cell. The aim of this study was to evaluate the effects of glucose on methylene blue (MB) uptake and its influence on PDI efficiency when combined to a red LED with central wavelength at λ=660nm. C. albicans biofilms were grown on hydrogel disks. Prior to PDI assays, MB uptake tests were performed with and without glucose-sensitization. In this system, the optimum PS administration was determined as 500µM of MB in contact with the biofilm during 30min before irradiation. Irradiation was performed during 3, 6, 9, 12, 15 and 18min with irradiance of 127.3mW/cm2. Our results showed that glucose was able to increase MB uptake in C. albicans cells. In addition, PDI without glucose showed a higher viability reduction until 6min; after 9min, glucose group demonstrated a significant decrease in cell viability when compared to glucose-free group. Taken together, our data suggest that glucose is capable to enhance MB uptake and modulate photodynamic inactivation of C. albicans biofilm.

Low-level laser therapy stimulates bone metabolism and inhibits root resorption during tooth movement in a rodent model.

This study evaluated the biological effects of low-level laser therapy (LLLT) on bone remodeling, tooth displacement and root resorption, occurred during the orthodontic tooth movement. Upper first molars of a total of sixty-eight male rats were subjected to orthodontic tooth movement and euthanized on days 3, 6, 9, 14 and 21 days and divided as negative control, control and LLLT group. Tooth displacement and histomorphometric analysis were performed in all animals; scanning electron microscopy analysis was done on days 3, 6 and 9, as well as the immunohistochemistry analysis of RANKL/OPG and TRAP markers. Volumetric changes in alveolar bone were analyzed using MicroCT images on days 14 and 21. LLLT influenced bone resorption by increasing the number of TRAP-positive osteoclasts and the RANKL expression at the compression side. This resulted in less alveolar bone and hyalinization areas on days 6, 9 and 14. LLLT also induced less bone volume and density, facilitating significant acceleration of tooth movement and potential reduction in root resorption besides stimulating bone formation at the tension side by enhancing OPG expression, increasing trabecular thickness and bone volume on day 21. Taken together, our results indicate that LLLT can stimulate bone remodeling reducing root resorption in a rat model. LLLT improves tooth movement via bone formation and bone resorption in a rat model.

Photobiomodulation reduces abdominal adipose tissue inflammatory infiltrate of diet-induced obese and hyperglycemic mice.

Systemic inflammation is closely related to the development of insulin resistance and type-2 diabetes, since the activation of pro-inflammatory pathways leads to inhibition of insulin signaling. Although photobiomodulation (PBM) has proven beneficial effects on the treatment of inflammatory disorders, the phototherapeutic approach to manage the chronic inflammatory component of obesity and hyperglycemia had never been explored. In this work, obese and hyperglycemic mice are treated with PBM, and their body mass, glycemia and inflammatory infiltrate of abdominal adipose tissue are evaluated. During four weeks, irradiated animals are exposed to six irradiation sessions using an 843 nm LED (5.7 J cm-2 at 19 mW cm-2 per session). Non-irradiated control animals display inflammatory areas almost five times greater than the treated group (p < 0.001). This result on inflammatory infiltrate may have caused impacts on the significant lower blood glucose level from irradiated animals (p = 0.04), twenty-four hours after the last irradiation session. PBM on obese and hyperglycemic mice reduced five times the areas of inflammatory infiltrate within abdominal adipose tissue (a, b), whereas dense inflammatory regions were a common finding amidst non-irradiated animals (c). The asterisks on (c) correspond to the inflammatory infiltrate permeating adipocytes.

Optical coherence tomography for blood glucose monitoring in vitro through spatial and temporal approaches.

As diabetes causes millions of deaths worldwide every year, new methods for blood glucose monitoring are in demand. Noninvasive approaches may increase patient adherence to treatment while reducing costs, and optical coherence tomography (OCT) may be a feasible alternative to current invasive diagnostics. This study presents two methods for blood sugar monitoring with OCT in vitro. The first, based on spatial statistics, exploits changes in the light total attenuation coefficient caused by different concentrations of glucose in the sample using a 930-nm commercial OCT system. The second, based on temporal analysis, calculates differences in the decorrelation time of the speckle pattern in the OCT signal due to blood viscosity variations with the addition of glucose with data acquired by a custom built Swept Source 1325-nm OCT system. Samples consisted of heparinized mouse blood, phosphate buffer saline, and glucose. Additionally, further samples were prepared by diluting mouse blood with isotonic saline solution to verify the effect of higher multiple scattering components on the ability of the methods to differentiate glucose levels. Our results suggest a direct relationship between glucose concentration and both decorrelation rate and attenuation coefficient, with our systems being able to detect changes of 65 mg/dL in glucose concentration.