Evaluating the effect of low-level laser therapy on healing of tentomized Achilles tendon in streptozotocin-induced diabetic rats by light microscopical and gene expression examinations

Histological, Physiological and Biomechanical Effects of Low-Level Laser Therapy on Tendon Healing in Animals and Humans: A Systematic Review

Low-level Laser Therapy (LLLT) was widely used in clinical practice for tendon disorders. However, the underlying mechanisms and effectiveness of LLLT in treating tendon injury remain unclear. Therefore, the present study was conducted aiming to summarize the evidence regarding the histological, physiological, and biomechanical effects of LLLT on tendon healing in animal and human models. Four databases were searched for relevant literature. Four independent reviewers screened abstracts and full-text articles, extracted relevant data, evaluated the risk of bias, and quantified the quality of evidence. Database searches yielded 1400 non-duplicated citations. Fifty-five studies were included (50 animal and five human studies). Animal studies revealed that LT had stimulating effects on collagen organization, collagen I and collagen II formation, matrix metalloproteinase (MMP)-8, transforming growth factor β1, vascular endothelial growth factor, hydroxyproline, maximum load, maximum elongation before breaking, and tendon stiffness. However, LLLT had inhibitory effects on the number of inflammatory cells, histological scores, relative amount of collagen III, cyclooxygenase-2, prostaglandin E2 (PGE2), interleukin-6, tumor necrosis factor-α, MMP-1, and MMP-3. Although one human study found that LLLT reduced the concentration of PGE2 in peritendinous tissue of the Achilles tendon, other human studies revealed that the effects of LLLT on the physiology and biomechanics of human tendons remained uncertain. LLLT facilitates tendon healing through various histological, physiological, and biomechanical effects in animal models. Only post-LLLT anti-inflammatory effects were found in human studies.

Biphasic dose response in the anti-inflammation experiment of PBM

Non-invasive laser irradiation can induce photobiomodulation (PBM) effects in cells and tissues, which can help reduce inflammation and pain in several clinical scenarios. The purpose of this study is to review the current literature to verify whether PBM can produce dose effects in anti-inflammatory experiments by summarizing the clinical and experimental effects of different laser parameters of several diseases. The so-called Arndt-Schulz curve is often used to describe two-phase dose reactions, assuming small doses of therapeutic stimulation, medium doses of inhibition, and large doses of killing. In the past decade, more and more attention has been paid to the clinical application of PBM, especially in the field of anti-inflammation, because it represents a non-invasive strategy with few contraindications. Although there are different types of lasers available, their use is adjusted by different parameters. In general, the parameters involved are wavelength, energy density, power output, and radiation time. However, due to the biphasic effect, the scientific and medical communities remain puzzled by the ways in which the application of PBM must be modified depending on its clinical application. This article will discuss these parameter adjustments and will then also briefly introduce two controversial theories of the molecular and cellular mechanisms of PBM. A better understanding of the extent of dualistic dose response in low-intensity laser therapy is necessary to optimize clinical treatment. It also allows us to explore the most dependable mechanism for PBM use and, ultimately, standardize treatment for patients with various diseases.

Systematic Review of Photobiomodulation Therapy (PBMT) on the Experimental Calcaneal Tendon Injury in Rats

This systematic review analyzed the light parameters and the effects of photobiomodulation therapy (PBMT) through low-level laser therapy (LLLT) and/or LED (light-emitting diode) on tendon repair of rats submitted to calcaneal injury. This study was conducted in accordance with the guidelines of the Preferred Reporting Items for Meta-Analysis, and PubMed and MEDLINE databases were accessed to search eligible studies published in English. The search terms were as follows: "Achilles tendon" or "Calcaneal tendon" or "tendon injuries" or "soft tissue injuries" and "tendinopathy" or "tendinitis" and "low-level light therapy" or "low-level laser therapy" or "low intensity power therapy" or "light-emitting diode" or photobiomodulation." The SYRCLE (SYstematic Review Center for Laboratory animal Experimentation) risks of bias was used to assess the risk of bias for selected studies. A total of 225 studies were found based on the descriptors used, and only 33 studies were eligible. Light parameters identified per point of irradiation were approximately 60 mW (continuous mode at infrared spectra), 2 W cm^-2 , 2 J and 45 J cm^-2 . Light parameters at red spectra, continuous versus pulsed mode, and PBMT combined or compared with other therapies such as ultrasound, and studies using unhealthy rats (ovariectomized and/or diabetic models) were also identified and grouped according to these similarities. The main effects found were decreased inflammatory markers and signs of inflammatory process. PBMT (laser/LED) has positive effects in reducing the inflammatory and time for tissue repair in animal models of tendon injury and/or tendinitis using parameters identified.

Effect of photobiomodulation and exercise on early remodeling of the Achilles tendon in streptozotocin-induced diabetic rats

The aim of this study was to compare the treatment effects of laser photobiomodulation (LPBM) therapy and aerobic exercise on the biomechanical properties, tissue morphology and the expression of tendon matrix molecules during early remodeling of Achilles tendon (AT) injury in diabetic rats. Animals were randomly assigned to five groups: injured non diabetic (I, n = 15), injured diabetic (ID, n = 15), injured diabetic plus LPBM (IDL, n = 16), injured diabetic plus aerobic exercise (IDE, n = 16) and injured diabetic plus aerobic exercise and LPBM (IDEAL, n = 17). Type 1 diabetes was induced via a single intravenous injection of Streptozotocin at a dose of 40 mg/kg. A partial tenotomy was performed in the right AT. LPBM was performed with an indium-gallium-aluminum-phosphide 660 nm 10 mW laser device (spot size 0.04 cm2, power density 250 mW/cm2, irradiation duration 16 s, energy 0.16 J, energy density 4 J/cm2) on alternate days for a total of 9 sessions over 3 weeks (total energy 1.44 J), using a stationary contact technique to a single point over the dorsal aspect of the AT. Moderate aerobic exercise was performed on a motorized treadmill (velocity 9 m/min for 60 minutes). At 3 weeks post-injury, biomechanical analyzes as well as assessment of fibroblast number and orientation were performed. Collagen 1 (Col1) and 3 (Col3) and matrix metalloproteinases (MMPs) -3 and 13 protein distributions were studied by immunohistochemistry; while Col1 and Col3 and MMP-2 and 9 gene expression were assessed by quantitative RT-PCR (qRT-PCR). IDEAL exhibited significant increases in several biomechanical parameters in comparison to the other groups. Moreover, IDEAL presented stronger Col1 immunoreactivity when compared to ID, and weaker Col3 immunoreactivity than IDE. Both IDL and IDEAL demonstrated weaker expression of MMP-3 in comparison to I, while IDL presented no expression of MMP-13 when compared to ID. ID, IDL and IDE showed an increased number of fibroblasts in comparison to I, while IDEAL decreased the number of these cells in comparison to ID and IDE. IDL and IDEAL groups exhibited decreased angular dispersion among the fibroblasts when compared to I. The gene expression results showed that IDE demonstrated a downregulation in Col1 mRNA expression in comparison to I and ID. IDEAL demonstrated upregulation of Col1 mRNA expression when compared to IDL or IDE alone and increased MMP-2 expression when compared to IDL and IDE. MMP-9 expression was upregulated in IDEAL when compared to I, IDL and IDE. Our results suggest a beneficial interaction of combining both treatment strategies i.e., aerobic exercise and LPBM, on the biomechanical properties, tissue morphology and the expression of matrix molecules in diabetic tendons.

Role of photobiomodulation on the activation of the Smad pathway via TGF-β in wound healing

Wound healing is an essential process in which the separated or destroyed tissue attempts to restore itself into its normal state. In some instances, healing is prolonged and remains stagnant in the inflammatory phase, and is referred to as a chronic wound. At a cellular and molecular level, many factors are required during the process of successful wound healing, such as cytokines, polypeptide growth factors and components of the extracellular matrix (ECM). Transforming growth factor-beta (TGF-β) is considered as one of the essential growth factors in wound healing. Working through the Smad pathway, it is the main inducer of fibroblast differentiation which is essential for wound healing. Photobiomodulation (PBM) shows significant advantages in wound healing, and may stimulate cellular processes and tissue regeneration that results in an increase in growth factors and a decrease in inflammatory cytokines. Moreover, it leads to enhanced cell proliferation, migration, angiogenesis, and increased adenosine triphosphate (ATP) and cytochrome C oxidase (CCO) activity. In this review paper, we discuss the effects of PBM and its role on the activation of the TGF-β/Smad pathway in the process of wound healing.

Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy

Photobiomodulation (PBM) also known as low-level laser (or light) therapy (LLLT), has been known for almost 50 years but still has not gained widespread acceptance, largely due to uncertainty about the molecular, cellular, and tissular mechanisms of action. However, in recent years, much knowledge has been gained in this area, which will be summarized in this review. One of the most important chromophores is cytochrome c oxidase (unit IV in the mitochondrial respiratory chain), which contains both heme and copper centers and absorbs light into the near-infra-red region. The leading hypothesis is that the photons dissociate inhibitory nitric oxide from the enzyme, leading to an increase in electron transport, mitochondrial membrane potential and ATP production. Another hypothesis concerns light-sensitive ion channels that can be activated allowing calcium to enter the cell. After the initial photon absorption events, numerous signaling pathways are activated via reactive oxygen species, cyclic AMP, NO and Ca2+, leading to activation of transcription factors. These transcription factors can lead to increased expression of genes related to protein synthesis, cell migration and proliferation, anti-inflammatory signaling, anti-apoptotic proteins, antioxidant enzymes. Stem cells and progenitor cells appear to be particularly susceptible to LLLT.

The dark art of light measurement: accurate radiometry for low-level light therapy

Lasers and light-emitting diodes are used for a range of biomedical applications with many studies reporting their beneficial effects. However, three main concerns exist regarding much of the low-level light therapy (LLLT) or photobiomodulation literature; (1) incomplete, inaccurate and unverified irradiation parameters, (2) miscalculation of ‘dose,’ and (3) the misuse of appropriate light property terminology. The aim of this systematic review was to assess where, and to what extent, these inadequacies exist and to provide an overview of ‘best practice’ in light measurement methods and importance of correct light measurement. A review of recent relevant literature was performed in PubMed using the terms LLLT and photobiomodulation (March 2014–March 2015) to investigate the contemporary information available in LLLT and photobiomodulation literature in terms of reporting light properties and irradiation parameters. A total of 74 articles formed the basis of this systematic review. Although most articles reported beneficial effects following LLLT, the majority contained no information in terms of how light was measured (73 %) and relied on manufacturer-stated values. For all papers reviewed, missing information for specific light parameters included wavelength (3 %), light source type (8 %), power (41 %), pulse frequency (52 %), beam area (40 %), irradiance (43 %), exposure time (16 %), radiant energy (74 %) and fluence (16 %). Frequent use of incorrect terminology was also observed within the reviewed literature. A poor understanding of photophysics is evident as a significant number of papers neglected to report or misreported important radiometric data. These errors affect repeatability and reliability of studies shared between scientists, manufacturers and clinicians and could degrade efficacy of patient treatments. Researchers need a physicist or appropriately skilled engineer on the team, and manuscript reviewers should reject papers that do not report beam measurement methods and all ten key parameters: wavelength, power, irradiation time, beam area (at the skin or culture surface; this is not necessarily the same size as the aperture), radiant energy, radiant exposure, pulse parameters, number of treatments, interval between treatments and anatomical location. Inclusion of these parameters will improve the information available to compare and contrast study outcomes and improve repeatability, reliability of studies.

Hormones and tendinopathies: the current evidence

BACKGROUND

Tendinopathies negatively affect the quality of life of millions of people, but we still do not know the factors involved in the development of tendon conditions.

SOURCES OF DATA

Published articles in English in PubMed and Google Scholar up to June 2015 about hormonal influence on tendinopathies onset. One hundred and two papers were included following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

AREAS OF AGREEMENT

In vitro and in vivo, tenocytes showed changes in their morphology and in their functional properties according to hormonal imbalances.

AREAS OF CONTROVERSY

Genetic pattern, sex, age and comorbidities can influence the hormonal effect on tendons.

GROWING POINTS

The increasing prevalence of metabolic disorders prompts to investigate the possible connection between metabolic problems and musculoskeletal diseases.

AREAS TIMELY FOR DEVELOPING RESEARCH

The influence of hormones on tendon structure and metabolism needs to be further investigated. If found to be significant, multidisciplinary preventive and therapeutic strategies should then be developed.

Photobiomodulation in promoting wound healing: a review

Despite diverse methods being applied to induce wound healing, many wounds remain recalcitrant to all treatments. Photobiomodulation involves inducing wound healing by illuminating wounds with light emitting diodes or lasers. While used on different animal models, in vitro, and clinically, wound healing is induced by many different wavelengths and powers with no optimal set of parameters yet being identified. While data suggest that simultaneous multiple wavelength illumination is more efficacious than single wavelengths, the optimal single and multiple wavelengths must be better defined to induce more reliable and extensive healing of different wound types. This review focuses on studies in which specific wavelengths induce wound healing and on their mechanisms of action.

Second messengers mediating the proliferation and collagen synthesis of tenocytes induced by low-level laser irradiation

For decades, low-level laser therapy (LLLT) has widespread applications in tendon-related injuries. Although the therapeutic effect of LLLT could be explained by photostimulation of target tissue and cells, how tenocytes sense photonic energy and convert them into cascades of cellular and molecular events is still not well understood. This study was designed to elucidate the effects of LLLT on cell proliferation and collagen synthesis by examining the associated second messengers including ATP, Ca(2+), and nitric oxide using rat Achilles tenocytes. Moreover, proliferating cell nuclear antigen (PCNA) and transforming growth factor-β1 (TGF-β1) related to cell proliferation and matrix metabolism were also studied. The results showed that 904 nm GaAs laser of 1 J/cm(2) could significantly increase the MTT activity and collagen synthesis of tenocytes. Second messengers including ATP and intracellular Ca2+ were increased after laser treatment. Quantitative PCR analysis of tenocytes treated with laser revealed up-regulated expression of PCNA, type I collagen, and TGF-β1. Besides, laser-induced TGF-β1 expression was significantly inhibited by extracellular signal-regulated kinase (ERK) specific inhibitor (PD98059). The findings suggested that LLLT stimulated ATP production and increased intracellular calcium concentration. Directly or indirectly via production of TGF-β1, these second messengers mediated the proliferation of tenocytes and synthesis of collagen.