Low-level laser therapy (810 nm) protects primary cortical neurons against excitotoxicity in vitro

Review of light parameters and photobiomodulation efficacy: dive into complexity

Photobiomodulation (PBM) therapy, previously known as low-level laser therapy, was discovered more than 50 years ago, yet there is still no agreement on the parameters and protocols for its clinical application. Some groups have recommended the use of a power density less than 100  mW/cm2 and an energy density of 4 to 10  J/cm2 at the level of the target tissue. Others recommend as much as 50  J/cm2 at the tissue surface. The wide range of parameters that can be applied (wavelength, energy, fluence, power, irradiance, pulse mode, treatment duration, and repetition) in some cases has led to contradictory results. In our review, we attempt to evaluate the range of effective and ineffective parameters in PBM. Studies in vitro with cultured cells or in vivo with different tissues were divided into those with higher numbers of mitochondria (muscle, brain, heart, nerve) or lower numbers of mitochondria (skin, tendon, cartilage). Graphs were plotted of energy density against power density. Although the results showed a high degree of variability, cells/tissues with high numbers of mitochondria tended to respond to lower doses of light than those with lower number of mitochondria. Ineffective studies in cells with high mitochondrial activity appeared to be more often due to over-dosing than to under-dosing.

Flexible nine-channel photodetector probe facilitated intraspinal multisite transcutaneous photobiomodulation therapy dosimetry in cadaver dogs

Noninvasive photobiomodulation therapy (PBMT) of spinal cord disease remains speculative due to the lack of evidence for whether photobiomodulatory irradiances can be transcutaneously delivered to the spinal cord under a clinically acceptable PBMT surface irradiation protocol. We developed a flexible nine-channel photodetection probe for deployment within the spinal canal of a cadaver dog after hemilaminectomy to measure transcutaneously transmitted PBMT irradiance at nine sites over an eight-cm spinal canal length. The probe was built upon a 6.325-mm tubular stem, to the surface of which nine photodiodes were epoxied at approximately 1 cm apart. The photodiode has a form factor of 4.80  mm×2.10  mm×1.15  mm (length×width×height). Each photodiode was individually calibrated to deliver 1 V per 7.58  μW/cm2 continuous irradiance at 850 nm. The outputs of eight photodiodes were logged concurrently using a data acquisition module interfacing eight channels of differential analog signals, while the output of the ninth photodiode was measured by a precision multimeter. This flexible probe rendered simultaneous intraspinal (nine-site) measurements of transcutaneous PBMT irradiations at 980 nm in a pilot cadaver dog model. At a surface continuous irradiance of 3.14  W/cm2 applied off-contact between L1 and L2, intraspinal irradiances picked up by nine photodiodes had a maximum of 327.48  μW/cm2 without the skin and 5.68  μW/cm2 with the skin.

Multicolor two-photon imaging of endogenous fluorophores in living tissues by wavelength mixing

Two-photon imaging of endogenous fluorescence can provide physiological and metabolic information from intact tissues. However, simultaneous imaging of multiple intrinsic fluorophores, such as nicotinamide adenine dinucleotide(phosphate) (NAD(P)H), flavin adenine dinucleotide (FAD) and retinoids in living systems is generally hampered by sequential multi-wavelength excitation resulting in motion artifacts. Here, we report on efficient and simultaneous multicolor two-photon excitation of endogenous fluorophores with absorption spectra spanning the 750-1040 nm range, using wavelength mixing. By using two synchronized pulse trains at 760 and 1041 nm, an additional equivalent two-photon excitation wavelength at 879 nm is generated, and achieves simultaneous excitation of blue, green and red intrinsic fluorophores. This method permits an efficient simultaneous imaging of the metabolic coenzymes NADH and FAD to be implemented with perfect image co-registration, overcoming the difficulties associated with differences in absorption spectra and disparity in concentration. We demonstrate ratiometric redox imaging free of motion artifacts and simultaneous two-photon fluorescence lifetime imaging (FLIM) of NADH and FAD in living tissues. The lifetime gradients of NADH and FAD associated with different cellular metabolic and differentiation states in reconstructed human skin and in the germline of live C. Elegans are thus simultaneously measured. Finally, we present multicolor imaging of endogenous fluorophores and second harmonic generation (SHG) signals during the early stages of Zebrafish embryo development, evidencing fluorescence spectral changes associated with development.

Two-photon autofluorescence lifetime imaging of human skin papillary dermis in vivo: assessment of blood capillaries and structural proteins localization

The papillary dermis of human skin is responsible for its biomechanical properties and for supply of epidermis with chemicals. Dermis is mainly composed of structural protein molecules, including collagen and elastin, and contains blood capillaries. Connective tissue diseases, as well as cardiovascular complications have manifestations on the molecular level in the papillary dermis (e.g. alteration of collagen I and III content) and in the capillary structure. In this paper we assessed the molecular structure of internal and external regions of skin capillaries using two-photon fluorescence lifetime imaging (FLIM) of endogenous compounds. It was shown that the capillaries are characterized by a fast fluorescence decay, which is originated from red blood cells and blood plasma. Using the second harmonic generation signal, FLIM segmentation was performed, which provided for spatial localization and fluorescence decay parameters distribution of collagen I and elastin in the dermal papillae. It was demonstrated that the lifetime distribution was different for the inner area of dermal papillae around the capillary loop that was suggested to be due to collagen III. Hence, we propose a generalized approach to two-photon imaging of the papillary dermis components, which extends the capabilities of this technique in skin diagnosis.

Quantifying collagen fiber orientation in breast cancer using quantitative phase imaging

Tumor progression in breast cancer is significantly influenced by its interaction with the surrounding stromal tissue. Specifically, the composition, orientation, and alignment of collagen fibers in tumor-adjacent stroma affect tumor growth and metastasis. Most of the work done on measuring this prognostic marker has involved imaging of collagen fibers using second-harmonic generation microscopy (SHGM), which provides label-free specificity. Here, we show that spatial light interference microscopy (SLIM), a label-free quantitative phase imaging technique, is able to provide information on collagen-fiber orientation that is comparable to that provided by SHGM. Due to its wide-field geometry, the throughput of the SLIM system is much higher than that of SHGM and, because of the linear imaging, the equipment is simpler and significantly less expensive. Our results indicate that SLIM images can be used to extract important prognostic information from collagen fibers in breast tissue, potentially providing a convenient high throughput clinical tool for assessing patient prognosis.

Optical clearing of skin enhanced with hyaluronic acid for increased contrast of optoacoustic imaging

Enhanced delivery of optical clearing agents (OCA) through skin may improve sensitivity of optical and optoacoustic (OA) methods of imaging, sensing, and monitoring. This report describes a two-step method for enhancement of light penetration through skin. Here, we demonstrate that topical application of hyaluronic acid (HA) improves skin penetration of hydrophilic and lipophilic OCA and thus enhances their performance. We examined the OC effect of 100% polyethylene and polypropylene glycols (PPGs) and their mixture after pretreatment by HA, and demonstrated significant increase in efficiency of light penetration through skin. Increased light transmission resulted in a significant increase of OA image contrast in vitro. Topical pretreatment of skin for about 30 min with 0.5% HA in aqueous solution offers effective delivery of low molecular weight OCA such as a mixture of PPG-425 and polyethylene glycol (PEG)-400. The developed approach of pretreatment by HA prior to application of clearing agents (PEG and PPG) resulted in a ∼ 47-fold increase in transmission of red and near-infrared light and significantly enhanced contrast of OA images.