Aaron Chih-Hao Chen

Biphasic Dose Response in Low Level Light Therapy

The use of low levels of visible or near infrared light for reducing pain, inflammation and edema, promoting healing of wounds, deeper tissues and nerves, and preventing cell death and tissue damage has been known for over forty years since the invention of lasers. Despite many reports of positive findings from experiments conducted in vitro, in animal models and in randomized controlled clinical trials, LLLT remains controversial in mainstream medicine. The biochemical mechanisms underlying the positive effects are incompletely understood, and the complexity of rationally choosing amongst a large number of illumination parameters such as wavelength, fluence, power density, pulse structure and treatment timing has led to the publication of a number of negative studies as well as many positive ones. A biphasic dose response has been frequently observed where low levels of light have a much better effect on stimulating and repairing tissues than higher levels of light. The so-called Arndt-Schulz curve is frequently used to describe this biphasic dose response. This review will cover the molecular and cellular mechanisms in LLLT, and describe some of our recent results in vitro and in vivo that provide scientific explanations for this biphasic dose response.

Low-Level Laser Therapy Activates NF-kB via Generation of Reactive Oxygen Species in Mouse Embryonic Fibroblasts

BACKGROUND Despite over forty years of investigation on low-level light therapy (LLLT), the fundamental mechanisms underlying photobiomodulation at a cellular level remain unclear. METHODOLOGY/PRINCIPAL FINDINGS In this study, we isolated murine embryonic fibroblasts (MEF) from transgenic NF-kB luciferase reporter mice and studied their response to 810 nm laser radiation. Significant activation of NF-kB was observed at fluences higher than 0.003 J/cm(2) and was confirmed by Western blot analysis. NF-kB was activated earlier (1 hour) by LLLT compared to conventional lipopolysaccharide treatment. We also observed that LLLT induced intracellular reactive oxygen species (ROS) production similar to mitochondrial inhibitors, such as antimycin A, rotenone and paraquat. Furthermore, we observed similar NF-kB activation with these mitochondrial inhibitors. These results, together with inhibition of laser induced NF-kB activation by antioxidants, suggests that ROS play an important role in the laser induced NF-kB signaling pathways. However, LLLT, unlike mitochondrial inhibitors, induced increased cellular ATP levels, which indicates that LLLT also upregulates mitochondrial respiration. CONCLUSION We conclude that LLLT not only enhances mitochondrial respiration, but also activates the redox-sensitive NFkB signaling via generation of ROS. Expression of anti-apoptosis and pro-survival genes responsive to NFkB could explain many clinical effects of LLLT.

Photoactivation of Endogenous Latent Transforming Growth Factor–β1 Directs Dental Stem Cell Differentiation for Regeneration

Low-power laser–activated endogenous latent transforming growth factor–β1 (LTGF-β1) directs resident dental stem cell differentiation to promote dentin regeneration. Laser Light Encourages Tooth Regeneration A small dose of light may be sufficient to promote new tooth growth, at least in animal models. Arany and colleagues shined low-power laser light on the tooth pulps of rats and saw the formation of tertiary dentin, which is a bone-like substance. Taking this as evidence of tooth regeneration, the authors investigated the mechanism by which light can cause the dental pulp to form bone. Arany et al. discovered that low-power laser activates latent transforming growth factor–β (TGF-β), leading to the generation of reactive oxygen species and the differentiation of dental stem cells into odontoblasts (dentin-forming bone cells). This mechanism was further confirmed in vivo by demonstrating that mice lacking TGF-β or treated with a TGF-β inhibitor were unable to respond to laser therapy. Because lasers are already used in dentistry, it is possible that such light-based treatment could be used in dental regeneration in people. Rapid advancements in the field of stem cell biology have led to many current efforts to exploit stem cells as therapeutic agents in regenerative medicine. However, current ex vivo cell manipulations common to most regenerative approaches create a variety of technical and regulatory hurdles to their clinical translation, and even simpler approaches that use exogenous factors to differentiate tissue-resident stem cells carry significant off-target side effects. We show that non-ionizing, low-power laser (LPL) treatment can instead be used as a minimally invasive tool to activate an endogenous latent growth factor complex, transforming growth factor–β1 (TGF-β1), that subsequently differentiates host stem cells to promote tissue regeneration. LPL treatment induced reactive oxygen species (ROS) in a dose-dependent manner, which, in turn, activated latent TGF-β1 (LTGF-β1) via a specific methionine residue (at position 253 on LAP). Laser-activated TGF-β1 was capable of differentiating human dental stem cells in vitro. Further, an in vivo pulp capping model in rat teeth demonstrated significant increase in dentin regeneration after LPL treatment. These in vivo effects were abrogated in TGF-β receptor II (TGF-βRII) conditional knockout (DSPPCreTGF-βRIIfl/fl) mice or when wild-type mice were given a TGF-βRI inhibitor. These findings indicate a pivotal role for TGF-β in mediating LPL-induced dental tissue regeneration. More broadly, this work outlines a mechanistic basis for harnessing resident stem cells with a light-activated endogenous cue for clinical regenerative applications.

Effects of 810-nm Laser on Murine Bone-Marrow-Derived Dendritic Cells

OBJECTIVE The purpose of this study was to investigate the effect of 810-nm low level laser therapy (LLLT) on dendritic cells (DC) in vitro. BACKGROUND DATA LLLT can enhance wound healing and increase cell proliferation and survival, and is used to treat inflammatory conditions. However there are reports that LLLT can stimulate leukocytes and could therefore be pro-inflammatory. Recently, DC have been found to play an important role in inflammation and immune response. METHODS Murine bone-marrow-derived DC were isolated, stimulated with lipopolysaccharide (LPS) or CpG oligodeoxynucleotide and treated with 810-nm laser, using fluences of 0.3, 3, and 30  J/cm(2) delivered at irradiances of 1, 10, and 100  mW/cm(2) respectively. Confocal microscopy, flow cytometry for DC markers, viability using propidium iodide, enzyme-linked immunosorbent assays (ELISA) for secreted interleukin-12 (IL-12), and bioluminescence measurements in cells transduced with a reporter for toll-like receptor (TLR)-9/nuclear factor kappa B (NF-κB) activation, were performed. RESULTS LLLT changed the morphology of LPS-stimulated DC, increased their viability, and altered the balance of DC activation markers (major histocompatibility complex [MHC] class 2 up and CD86 down). LLLT reduced IL-12 secretion from DC stimulated by either LPS or CpG. LLLT reduced NF-κB activation in reporter cells stimulated with CpG. There was no obvious light dose response observed. CONCLUSIONS Taken together, these data suggest that 810-nm LLLT has an anti-inflammatory effect on activated DC, possibly mediated by cyclic adenosine monophosphate (cAMP) and reduced NF-κB signaling.

Low level laser therapy for traumatic brain injury

Low level laser (or light) therapy (LLLT) has been clinically applied for many indications in medicine that require the following processes: protection from cell and tissue death, stimulation of healing and repair of injuries, and reduction of pain, swelling and inflammation. One area that is attracting growing interest is the use of transcranial LLLT to treat stroke and traumatic brain injury (TBI). The fact that near-infrared light can penetrate into the brain would allow non-invasive treatment to be carried out with a low likelihood of treatment-related adverse events. LLLT may have beneficial effects in the acute treatment of brain damage injury by increasing respiration in the mitochondria, causing activation of transcription factors, reducing key inflammatory mediators, and inhibiting apoptosis. We tested LLLT in a mouse model of TBI produced by a controlled weight drop onto the skull. Mice received a single treatment with 660-nm, 810-nm or 980-nm laser (36 J/cm2) four hours post-injury and were followed up by neurological performance testing for 4 weeks. Mice with moderate to severe TBI treated with 660- nm and 810-nm laser had a significant improvement in neurological score over the course of the follow-up and histological examination of the brains at sacrifice revealed less lesion area compared to untreated controls. Further studies are underway.

The influence of temperature on 5-aminolevulinic acid-based photodynamic reaction in keratinocytes in vitro

Background/purpose: Based on the observation that increasing skin temperature could improve 5‐aminolevulinic acid (ALA) penetration and accumulation of protoporphyrin IX (PpIX) in the ALA‐based photodynamic therapy (PDT), this study was designed to investigate how temperature change varied the therapeutic effect of ALA‐based PDT in vitro.

Photodynamic Therapy as Consolidation Treatment for Primary Cutaneous Adenoid Cystic Carcinoma: A Case Report

OBJECTIVE The purpose of this case report was to evaluate the efficacy of photodynamic therapy (PDT) for a patient with primary cutaneous adenoid cystic carcinoma (PCACC). MATERIALS AND METHODS A 53-year-old female patient presented with a lesion at the pre-auricular area. After performing a local resection along a margin of 0.5 cm beyond the surrounding tissue, PCACC was clearly revealed based on the histological features and the exclusion of differentiation of other metastasis in the skin. The patient was then treated repetitively with 5-aminolevulinic acid (ALA)-PDT. After the final PDT treatment, the control pathological biopsy at the same location demonstrated no tumor cell in the specimen. RESULTS The 40-month follow-up diagnosis showed no evidence of recurrence or metastasis observed on the treated area. CONCLUSION ALA-PDT was a safe and effective therapy for obtaining good cosmetic results and reducing recurrence in this case report.

Can dendritic cells see light

There are many reports showing that low-level light/laser therapy (LLLT) can enhance wound healing, upregulate cell proliferation and has anti-apoptotic effects by activating intracellular protective genes. In the field of immune response study, it is not known with any certainty whether light/laser is proinflammatory or anti-inflammatory. Increasingly in recent times dendritic cells have been found to play an important role in inflammation and the immunological response. In this study, we try to look at the impact of low level near infrared light (810-nm) on murine bone-marrow derived dendritic cells. Changes in surface markers, including MHC II, CD80 and CD11c and the secretion of interleukins induced by light may provide additional evidence to reveal the mystery of how light affects the maturation of dendritic cells as well how these light-induced mature dendritic cells would affect the activation of adaptive immune response.

Role of ROS-mediated TGF beta activation in laser photobiomodulation

The ability of laser light to modulate specific biological processes has been well documented but the precise mechanism mediating these photobiological interactions remains an area of intense investigation. We recently published the results of our clinical trial with 30 patients in an oral tooth-extraction wound healing model using a 904nm GaAs laser (Oralaser 1010, Oralia, Konstnaz, Germany), assessing healing parameters using routine histopathology and immunostaining (Arany et al Wound Rep Regen 2007, 15, 866). We observed a better organized healing response in laser irradiated oral tissues that correlated with an increased expression of TGF-beta1 immediately post laser irradiation. Our data suggested the source of latent TGF-beta1 might be from the degranulating platelets in the serum, an abundant source of in vivo latent TGF-beta, in the freshly wounded tissues. Further, we also demonstrated the ability of the low power near-infrared laser irradiation to activate the latent TGF-beta complexes in vitro at varying fluences from 10sec (0.1 J/cm2) to 600secs (6 J/cm2). Using serum we observed two isoforms, namely TGF-beta1 and TGF-beta3, were capable of being activated by laser irradiation using an isoform-specific ELISA and a reporter based (p3TP) assay system. We are presently pursuing the precise photomolecular mechanisms focusing on potential chromophores, wavelength and fluence parameters affecting the Latent TGF-beta activation process in serum. As ROS mediated TGF-beta activation has been previously demonstrated and we are also exploring the role of Laser generated-ROS in this activation process. In summary, we present evidence of a potential molecular mechanism for laser photobiomodulation in its ability to activate latent TGF-beta complexes.