Sulbha K. Sharma

The Nuts and Bolts of Low-level Laser (Light) Therapy

Soon after the discovery of lasers in the 1960s it was realized that laser therapy had the potential to improve wound healing and reduce pain, inflammation and swelling. In recent years the field sometimes known as photobiomodulation has broadened to include light-emitting diodes and other light sources, and the range of wavelengths used now includes many in the red and near infrared. The term “low level laser therapy” or LLLT has become widely recognized and implies the existence of the biphasic dose response or the Arndt-Schulz curve. This review will cover the mechanisms of action of LLLT at a cellular and at a tissular level and will summarize the various light sources and principles of dosimetry that are employed in clinical practice. The range of diseases, injuries, and conditions that can be benefited by LLLT will be summarized with an emphasis on those that have reported randomized controlled clinical trials. Serious life-threatening diseases such as stroke, heart attack, spinal cord injury, and traumatic brain injury may soon be amenable to LLLT therapy.

Biphasic Dose Response in Low Level Light Therapy – An Update

Low-level laser (light) therapy (LLLT) has been known since 1967 but still remains controversial due to incomplete understanding of the basic mechanisms and the selection of inappropriate dosimetric parameters that led to negative studies. The biphasic dose-response or Arndt-Schulz curve in LLLT has been shown both in vitro studies and in animal experiments. This review will provide an update to our previous (Huang et al. 2009) coverage of this topic. In vitro mediators of LLLT such as adenosine triphosphate (ATP) and mitochondrial membrane potential show biphasic patterns, while others such as mitochondrial reactive oxygen species show a triphasic dose-response with two distinct peaks. The Janus nature of reactive oxygen species (ROS) that may act as a beneficial signaling molecule at low concentrations and a harmful cytotoxic agent at high concentrations, may partly explain the observed responses in vivo. Transcranial LLLT for traumatic brain injury (TBI) in mice shows a distinct biphasic pattern with peaks in beneficial neurological effects observed when the number of treatments is varied, and when the energy density of an individual treatment is varied. Further understanding of the extent to which biphasic dose responses apply in LLLT will be necessary to optimize clinical treatments.

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.

Photodynamic Therapy for Infections: Clinical Applications

Photodynamic therapy (PDT) was discovered over 100 years ago by its ability to kill various microorganisms when the appropriate dye and light were combined in the presence of oxygen. However it is only in relatively recent times that PDT has been studied as a treatment for various types of localized infections. This resurgence of interest has been partly motivated by the alarming increase in drug resistance amongst bacteria and other pathogens. This review will focus on the clinical applications of antimicrobial PDT.

Role of low-level laser therapy in neurorehabilitation.

This year marks the 50th anniversary of the discovery of the laser. The development of lasers for medical use, which became known as low‐level laser therapy (LLLT) or photobiomodulation, followed in 1967. In recent years, LLLT has become an increasingly mainstream modality, especially in the areas of physical medicine and rehabilitation. At first used mainly for wound healing and pain relief, the medical applications of LLLT have broadened to include diseases such as stroke, myocardial infarction, and degenerative or traumatic brain disorders. This review will cover the mechanisms of LLLT that operate both on a cellular and a tissue level. Mitochondria are thought to be the principal photoreceptors, and increased adenosine triphosphate, reactive oxygen species, intracellular calcium, and release of nitric oxide are the initial events. Activation of transcription factors then leads to expression of many protective, anti‐apoptotic, anti‐oxidant, and pro‐proliferation gene products. Animal studies and human clinical trials of LLLT for indications with relevance to neurology, such as stroke, traumatic brain injury, degenerative brain disease, spinal cord injury, and peripheral nerve regeneration, will be covered.

Effect of pulsing in low-level light therapy†

Low level light (or laser) therapy (LLLT) is a rapidly growing modality used in physical therapy, chiropractic, sports medicine and increasingly in mainstream medicine. LLLT is used to increase wound healing and tissue regeneration, to relieve pain and inflammation, to prevent tissue death, to mitigate degeneration in many neurological indications. While some agreement has emerged on the best wavelengths of light and a range of acceptable dosages to be used (irradiance and fluence), there is no agreement on whether continuous wave or pulsed light is best and on what factors govern the pulse parameters to be chosen.

Photodynamic therapy with fullerenes in vivo: reality or a dream?

Photodynamic therapy (PDT) employs the combination of nontoxic photosensitizers and visible light that is absorbed by the chromophore to produce long-lived triplet states that can carry out photochemistry in the presence of oxygen to kill cells. The closed carbon-cage structure found in fullerenes can act as a photosensitizer, especially when functionalized to impart water solubility. Although there are reports of the use of fullerenes to carry out light-mediated destruction of viruses, microorganisms and cancer cells in vitro, the use of fullerenes to mediate PDT of diseases such as cancer and infections in animal models is less well developed. It has recently been shown that fullerene PDT can be used to save the life of mice with wounds infected with pathogenic Gram-negative bacteria. Fullerene PDT has also been used to treat mouse models of various cancers including disseminated metastatic cancer in the peritoneal cavity. In vivo PDT with fullerenes represents a new application in nanomedicine.

Topical Antimicrobials for Burn Wound Infections

Throughout most of history, serious burns occupying a large percentage of body surface area were an almost certain death sentence because of subsequent infection. A number of factors such as disruption of the skin barrier, ready availability of bacterial nutrients in the burn milieu, destruction of the vascular supply to the burned skin, and systemic disturbances lead to immunosuppression combined together to make burns particularly susceptible to infection. In the 20th century the introduction of antibiotic and antifungal drugs, the use of topical antimicrobials that could be applied to burns, and widespread adoption of early excision and grafting all helped to dramatically increase survival. However the relentless increase in microbial resistance to antibiotics and other antimicrobials has led to a renewed search for alternative approaches to prevent and combat burn infections. This review will cover patented strategies that have been issued or filed with regard to new topical agents, preparations, and methods of combating burn infections. Animal models that are used in preclinical studies are discussed. Various silver preparations (nanocrystalline and slow release) are the mainstay of many approaches but antimicrobial peptides, topical photodynamic therapy, chitosan preparations, new iodine delivery formulations, phage therapy and natural products such as honey and essential oils have all been tested. This active area of research will continue to provide new topical antimicrobials for burns that will battle against growing multidrug resistance.

Stable Synthetic Cationic Bacteriochlorins as Selective Antimicrobial Photosensitizers

ABSTRACT Photodynamic inactivation is a rapidly developing antimicrobial treatment that employs a nontoxic photoactivatable dye or photosensitizer in combination with harmless visible light to generate reactive oxygen species that are toxic to cells. Tetrapyrroles (e.g., porphyrins, chlorins, bacteriochlorins) are a class of photosensitizers that exhibit promising characteristics to serve as broad-spectrum antimicrobials. In order to bind to and efficiently penetrate into all classes of microbial cells, tetrapyrroles should have structures that contain (i) one or more cationic charge(s) or (ii) a basic group. In this report, we investigate the use of new stable synthetic bacteriochlorins that have a strong absorption band in the range 720 to 740 nm, which is in the near-infrared spectral region. Four bacteriochlorins with 2, 4, or 6 quaternized ammonium groups or 2 basic amine groups were compared for light-mediated killing against a Gram-positive bacterium (Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli), and a dimorphic fungal yeast (Candida albicans). Selectivity was assessed by determining phototoxicity against human HeLa cancer cells under the same conditions. All four compounds were highly active (6 logs of killing at 1 μM or less) against S. aureus and showed selectivity for bacteria over human cells. Increasing the cationic charge increased activity against E. coli. Only the compound with basic groups was highly active against C. albicans. Supporting photochemical and theoretical characterization studies indicate that (i) the four bacteriochlorins have comparable photophysical features in homogeneous solution and (ii) the anticipated redox characteristics do not correlate with cell-killing ability. These results support the interpretation that the disparate biological activities observed stem from cellular binding and localization effects rather than intrinsic electronic properties. These findings further establish cationic bacteriochlorins as extremely active and selective near-infrared activated antimicrobial photosensitizers, and the results provide fundamental information on structure-activity relationships for antimicrobial photosensitizers.

Comparison of therapeutic effects between pulsed and continuous wave 810-nm wavelength laser irradiation for traumatic brain injury in mice.

Background and Objective Transcranial low-level laser therapy (LLLT) using near-infrared light can efficiently penetrate through the scalp and skull and could allow non-invasive treatment for traumatic brain injury (TBI). In the present study, we compared the therapeutic effect using 810-nm wavelength laser light in continuous and pulsed wave modes in a mouse model of TBI. Study Design/Materials and Methods TBI was induced by a controlled cortical-impact device and 4-hours post-TBI 1-group received a sham treatment and 3-groups received a single exposure to transcranial LLLT, either continuous wave or pulsed at 10-Hz or 100-Hz with a 50% duty cycle. An 810-nm Ga-Al-As diode laser delivered a spot with diameter of 1-cm onto the injured head with a power density of 50-mW/cm2 for 12-minutes giving a fluence of 36-J/cm2. Neurological severity score (NSS) and body weight were measured up to 4 weeks. Mice were sacrificed at 2, 15 and 28 days post-TBI and the lesion size was histologically analyzed. The quantity of ATP production in the brain tissue was determined immediately after laser irradiation. We examined the role of LLLT on the psychological state of the mice at 1 day and 4 weeks after TBI using tail suspension test and forced swim test. Results The 810-nm laser pulsed at 10-Hz was the most effective judged by improvement in NSS and body weight although the other laser regimens were also effective. The brain lesion volume of mice treated with 10-Hz pulsed-laser irradiation was significantly lower than control group at 15-days and 4-weeks post-TBI. Moreover, we found an antidepressant effect of LLLT at 4-weeks as shown by forced swim and tail suspension tests. Conclusion The therapeutic effect of LLLT for TBI with an 810-nm laser was more effective at 10-Hz pulse frequency than at CW and 100-Hz. This finding may provide a new insight into biological mechanisms of LLLT.