Low-power Laser Irradiation Research Articles

Photoactivation of Akt1/GSK3β Isoform-Specific Signaling Axis Promotes Pancreatic β-Cell Regeneration.

Promotion of insulin-secreting β-cell regeneration in patients with diabetes is a promising approach for diabetes therapy, which can contribute to rescue the uncontrolled hyperglycemia. Low-power laser irradiation (LPLI) has been demonstrated to regulate multiple physiological processes both in vitro and in vivo through activation of various signaling pathways. In the present study, we showed that LPLI promoted β-cell replication and cell cycle progression through activation of Akt1/GSK3β isoform-specific signaling axis. Inhibition of PI3-K/Akt or GSK3 with specific inhibitors dramatically reduced or increased LPLI-induced β-cell replication, revealing Akt/GSK3 signaling axis was involved in β-cell replication and survival upon LPLI treatment. Furthermore, the results of shRNA-mediated knock down of Akt/GSK3 isoforms revealed that Akt1/GSK3β isoform-specific signaling axis regulated β-cell replication and survival in response to LPLI, but not Akt2/GSK3α. The mechanism by which LPLI promoted β-cell replication through Akt1/GSK3β signaling axis involved activation of β-catenin and down-regulation of p21. Taken together, these observations suggest that Akt1/GSK3β isoform signaling axis play a key role in β-cell replication and survival induced by LPLI. Moreover, our findings suggest that activation of Akt1/GSK3β isoform signaling axis by LPLI may provide guidance in practical applications for β-cell regenerative therapies.

532 nm Low-Power Laser Irradiation Facilitates the Migration of GABAergic Neural Stem/Progenitor Cells in Mouse Neocortex.

Background and ObjectiveAccumulating evidence has shown that low-power laser irradiation (LLI) affects cell proliferation and survival, but little is known about LLI effects on neural stem/progenitor cells (NSPCs). Here we investigate whether transcranial 532 nm LLI affects NSPCs in adult murine neocortex and in neurospheres from embryonic mice.Study Design/Materials and MethodsWe applied 532 nm LLI (Nd:YVO4, CW, 60 mW) on neocortical surface via cranium in adult mice and on cultured cells from embryonic mouse brains in vitro to investigate the proliferation and migration of NSPCs and Akt expression using immunohistochemical assays and Western blotting techniques.ResultsIn vivo experiments demonstrated that 532 nm LLI significantly facilitated the migration of GABAergic NSPCs that were induced to proliferate in layer 1 by mild ischemia. In vitro experiments using GABAergic NSPCs derived from embryonic day 14 ganglionic eminence demonstrated that 532 nm LLI for 60 min promoted the migration of GAD67-immunopositive NSPCs with a significant increase of Akt expression. Meanwhile, the LLI induced proliferation, but not migration, of NSPCs that give rise to excitatory neurons.ConclusionIt is concluded that 532 nm LLI promoted the migration of GABAergic NSPCs into deeper layers of the neocortex in vivo by elevating Akt expression.

Photoactivation of Dok1/ERK/PPARγ signaling axis inhibits excessive lipolysis in insulin-resistant adipocytes

Insulin resistance is a hallmark of the metabolic syndrome and type 2 diabetes. Increased plasma FFA level is an important cause of obesity-associated insulin resistance. Over-activated ERK is closely related with FFA release from adipose tissues in patients with type 2 diabetes. Nevertheless, there are no effective strategies to lower plasma FFA level. Low-power laser irradiation (LPLI) has been reported to regulate multiple biological processes. However, whether LPLI could ameliorate metabolic disorders and the molecular mechanisms involved remain unknown. In this study, we first demonstrated that LPLI suppresses excessive lipolysis of insulin-resistant adipocytes by activating tyrosine kinases-1(Dok1)/ERK/PPARγ pathway. Our data showed that LPLI inhibits ERK phosphorylation through the activation of Dok1, resulting in decreased phospho-PPARγ level. Non-phosphorylated PPARγ maintains in nucleus to promote the expression of adipogenic genes, reversing excessive lipolysis in insulin-resistant adipocytes. In summary, the present research highlights the important roles of Dok1/ERK/PPARγ pathway in lowering FFA release from adipocytes, and our research extends the knowledge of the biological effects induced by LPLI.

Modulating Heat Shock Proteins 70 and 90 Expression by Low Power Laser Irradiation (635nm and 780nm) in Jurkat E6.1 T-lymphocyte Leukemia Cell Line.

Heat shock proteins (HSPs) are molecular chaperones involved in protein folding, stability and turnover, and due to their role in cancer progression, the effect of low power laser irradiation (LPLI) on the expression of HSP70 and HSP90 in Jurkat E6.1 T-lymphocyte leukemia (JELT) cell line was investigated in vitro. JETL cells were irradiated with LPLI at 635nm and 780m wavelengths (energy density 9.174 J/cm(2)), and assessed for the expression of HSP70 and HSP90 by flow cytometry after 24, 48 and 72 incubation time periods (ITPs). At 24 hours ITP post-irradiation, control cultures showed that 10.7% of cells expressed HSP70, while LPLI cultures at 635nm and 780nm manifested a higher expression (32.1and 21.3%, respectively), and the difference was significant (P ≤ 0.05). However, at 48 hours ITP, the three means were decreased but approximated (5.6, 4.9 and 6.2%, respectively), while at 72 hours ITP, they were markedly increased (45.2, 76.5 and 66.7%, respectively). In contrast, HSP90 responded differently to LPLI. At 24 hours ITP, control cultures and 780nm cultures showed a similar expression (55.9 and 55.9%, respectively), but both means were significantly higher than that of 635nm cultures (24.0%). No such difference was observed at 48 hours ITP, and at 72 hours ITP, control cultures and 635nm cultures shared approximated means (31.7 and 35.6%, respectively); but both means were significantly higher than the observed mean in 780nm cultures (15.2%). The results highlighted that HSP70 and HSP90 expression responded differently to LPLI in JETL cells; an observation that may pave the way for further investigations in malignant cells.

Visible Diode Laser Enhancement of Exotic DNA Uptake by Fowl Sperm

An experiment was conducted to assess the use of low power laser irradiation and lipofectin to enhance fowl sperm uptake of exogenous DNA. Semen samples of 10 roosters were collected and pooled. The pooled sample was diluted with a semen extender and then divided into 6 aliquots for 6 different treatments. The treatments included different combinations of the inclusion of exogenous DNA (bacterial plasmid pUC18), the exposure to low power laser irradiation and the transfection with lipofectin (5%). Laser irradiation was by using visible diode laser (650 nm) at energy dose of 4 J/cm2. The recognition of the plasmid DNA in the sperm was by using two specific oligonucleotides (forward and reverse) to prime a 420-bp fragment on the pMB1 rep of the plasmid. The results indicated that low power laser irradiation enhanced the sperm uptake of the plasmid DNA. Also, lipofectin enhanced the introduction of the plasmid DNA into the sperm, whether the semen was laser irradiated or not.

Laser irradiation on growth of trichophyton rubrum: an in vitro study.

Trichophyton rubrum is one of the most common species of dermatophytes which affects superficial keratinous tissue. It is not especially virulent but it can be responsible for considerable morbidity. Although there are different therapeutic modalities to treat fungal infections, clinicians are searching for alternative treatment because of the various side effects of the present therapeutic methods. As a new procedure, Laser therapy has brought on many advantages in clinical management of dermatophytes. Possible inhibitory potential of laser irradiation on fungal colonies was investigated invitro in this study. A total of 240 fungal plates of standard size of trichophyton rubrum colonies that had been cultured from the lesions of different patients at the mycology laboratory, were selected. Each fungal plate was assigned as control or experimental group. Experimental plates were irradiated by a laser system (low power laser or different wavelength of high power laser). The effects of different laser wavelengths and energies on isolated colonies were assessed. After laser irradiation, final size of colonies was measured on the first, the 7th and the 14th day after laser irradiation. Although low power laser irradiation did not have any inhibitory effect on fungal growth, the Q-Switched Neodymium-Doped Yttrium Aluminium Garnet (Nd:YAG) laser 532nm at 8j/cm(2), Q-Switched Nd:YAG laser 1064nm at 4j/cm(2) to 8j/cm(2) and Pulsed dye laser 595nm at 8j/cm(2) to 14j/cm(2) significantly inhibited growth of trichophyton rubrum in vitro. Q-Switched Nd:YAG 532nm at 8j/cm(2), Q-Switched Nd:YAG laser 1064nm at 4j/cm(2) to 8j/cm(2) and pulsed dye laser (PDL) 595nm at 8j/cm(2) to 14j/cm(2) can be effective to suppress trichophyton rubrum growth.

Cellular Responses by Low-power He-Ne laser Irradiation on Human Lung Cancer Cells

Helium-neon (He-Ne) laser has been used in many clinical fields, and caught our interest on cancer treatment. We conducted the study of He-Ne laser in lung cancer for the sake of the most common cause of cancer deaths worldwide, and up to 50% of the patients with advanced non-small-cell lung cancers with brain metastases. In this study, we used two human lung cancer cell lines A549, H1299, bronchial epithelial cell line BEAS-2B to detect the effects of He-Ne laser on proliferation and migration capabilities by MTT, trypan blue exclusion and wound healing analysis, followed by Western blot analysis to identify the putative signaling pathway evoked by the He-Ne laser. Low-power He-Ne laser slowed H1299 migration by inhibiting Extracellular signal-regulated protein kinases (ERK) phosphorylation, and decreased A549 cell proliferation via p38 up-regulation. However, He-Ne laser increased NT2 cell proliferation and migration activities through ERK activation. The low-power He-Ne laser had diverse effects on different cells, possibly suppressive effect on malignant cells, but growth provocation on pluripotent cells. We proposed that the low-power He-Ne laser renders a beneficial alternative for cancer treatment and for tissue repair.

Penile anesthesia in Post SSRI Sexual Dysfunction (PSSD) responds to low-power laser irradiation: A case study and hypothesis about the role of transient receptor potential (TRP) ion channels

Treatment of paroxetine-induced penile anesthesia in Post SSRI Sexual Dysfunction (PSSD) by Low-power Laser Irradiation (LPLI) is unknown in medical literature. The aim of the current article is to report partial efficacy of LPLI for paroxetine-induced persistent penile anesthesia. We report on a male patient who presented with a history of reversible loss of smell, taste and skin sensitivity occurring within a week after start of 20mg/day paroxetine-hemihydrate for a depressive period. Concurrently, patient suffered from penile anesthesia, scrotum hypesthesia, anejaculation and erectile difficulties with normal sexual desire. During 2.5 years of paroxetine treatment and throughout 2 years after paroxetine discontinuation, genital and sexual complaints persisted. Penile anesthesia was treated by LPLI with single and multi diode pulsed laser probes. After 20 LPLI-treatment sessions of 15min each, patient reported partial return of penile touch and temperature sensation. Clinical improvement of glans penis sensitivity was reported to 20% and 40%, compared to pre-paroxetine treatment penile sensitivity during erect and flaccid states, respectively. However, anejaculation and erectile difficulties remained unchanged. Briefly, in the current patient with early onset of PSSD, LPLI treatment reduced paroxetine-induced penile anesthesia. It is hypothesized that SSRI treatment induces disturbances of transient receptor potential (TRP) ion channels of mechano-, thermo- and chemosensitive nerve endings and receptors resulting in the penile anesthesia in PSSD. It is further hypothesized that there are two types of PSSD, one of which occurs soon after the start of SSRI treatment.

Low power laser stimulation of the bone consolidation in tibial fractures of rats: a radiologic and histopathological analysis.

The objective of this study is to analyze the effectiveness of low power laser irradiation in the bone consolidation of tibial fractures in rats. An experimental, comparative, prospective study with control group was designed. Twenty Wistar rats were grouped into control (n = 10) and experimental groups (n = 10). A tibial fracture, with a mechanical drill, was inflicted in all rats. The experimental group received ten days of low power arsenide-gallium laser irradiation of 850 nm (KLD, Sao Paulo, Brasil)-100 mW, 8 J/cm(2), 64 s. Before and after the laser treatment, a radiologic analysis was carried out in both groups, in which the rats were graded from 0 to IV according the Montoya scale of bone consolidation. Also, we histopathologically analyzed the bone to estimate the proliferation of fibroblasts, bone matrix, and angiogénesis with a microscopy, which were graded as I (thin layer of fibroblasts and osteoid matrix), II (thick layer of fibroblasts and osteoid matrix), or III (thick layer of fibroblasts and osteoid matrix and new blood vessels). Radiologic data showed that the experimental group had a higher bone consolidation of Montoya scale after ten days of laser irradiation compared to control group (P < 0.004). Histopathologic data showed more fibroblasts and angiogenesis presence in the group receiving laser irradiation, compared to control group (P < .002). The low power laser radiation therapy may expedite the bone repair after tibial fractures in rats, according to radiologic and histopathologic analysis.

Core–shell–shell nanorods for controlled release of silver that can serve as a nanoheater for photothermal treatment on bacteria

A novel bactericidal material comprising rod-shaped core–shell–shell Au–Ag–Au nanorods is constructed as a nanoheater in the near-infrared (NIR) region. The outer Au shell melts under laser irradiation and results in exposure of the inner Ag shell, facilitating the controlled release of the antibacterial Ag shell/layer or Ag+. This results in the Au–Ag–Au nanorods having a favorable bactericidal ability as it combines the features of physical photothermal ablation sterilization of the outer Au shell and the antibacterial effect of the inner Ag shell or Ag+ to the surrounding bacteria. The sterilizing ability of Au–Ag–Au nanorods is investigated with Escherichia coli O157:H7 as a model bacterial strain. Under low-power NIR laser irradiation (785nm, 50mWcm−2), the Au–Ag–Au nanoheater exhibits a higher photothermal conversion efficiency (with a solution temperature of 44°C) with respect to that for the Au–Ag nanorods (39°C). Meanwhile, a much improved stability with respect to Au–Ag nanorods is observed, i.e., 16 successive days of monitoring reveal virtually no change in the ultraviolet–visible spectrum of Au–Ag–Au nanorods, while a significant drop in absorption along with a 92nm red shift of Localized Surface Plasmon Resonance is recorded for the Au–Ag nanorods. This brings an increasing bactericidal efficiency and long-term stability for the Au–Ag–Au nanorods. At a dosage of 10μgml−1, a killing rate of 100% is reached for the E. coli O157:H7 cells under 20min of irradiation. The use of Au–Ag–Au nanorods avoids the abuse of broad-spectrum antibiotics and reduces the damage of tissues by alleviating the toxicity of silver under controlled release and by the use of low-power laser irradiation. These features could make the bimetallic core–shell–shell nanorods a favorable nanoheater for in vivo biomedical applications.

Pre-exposure to low-power diode laser irradiation promotes cytoprotection in the rat retina.

The aim of this study was to investigate whether pre-exposure to low-power laser irradiation can provoke an effect on cellular protection in the rat retina. The right eyes of 40 rats were exposed to a 3-mm diode laser beam for 1 min in different light intensities and different experimental sets: group A low power of 60 mW (34.27 J/cm(2) on the retina in consideration of the energy losses along the optical pathway) prior to high power of 80 mW (44.88 J/cm(2) on the retina in consideration of the energy losses along the optical pathway), group B high power, group C low power, group D (the left eyes from the counterpart of group A) and group E (untreated rat eyes) as controls. Morphological retinal change retinas were assessed using light microscopy and/or transmission electron microscopy. Heat shock protein (Hsp) 70 and cleaved caspase 3 protein expression were analyzed by immunohistochemical staining and Western blot. Cellular injury was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay. Hsp 70 expression in the inner plexiform layer and the outer plexiform layer in group A were 73.09 ± 6.49 and 78.03 ± 3.05%, respectively, which was significantly higher (P < 0.05) than those observed in group B (59.07 ± 1.40 and 32.25 ± 4.26%, respectively). The Hsp70/β-actin ratio was 0.49 ± 0.06 in group C, which was significantly higher (P < 0.05) than that of group B (0.27 ± 0.04). Cleaved caspase 3 expression in group C both was significantly lower than that observed in group B. TUNEL staining showed that positive cells in the outer nuclear layer and inner nuclear layer in group A were significantly lower than those of group B. Pre-exposure to a 60-mW (34.27 J/cm(2) on the retina) power laser irradiation stimulates a hyperexpression of Hsp70 together with a hypoexpression of cleaved caspase 3 in rat retina, which may suggest a cellular protective effect.

Low-power laser irradiation fails to improve liver regeneration in elderly rats at 48 h after 70 % resection.

The liver regeneration is an important clinical issue after major hepatectomies. Unfortunately, many organs (including the liver) exhibit age-related impairments regarding their regenerative capacity. Recent studies found that low-power laser irradiation (LPLI) has a stimulatory effect on the liver regeneration process. However, its effects in elderly remain unknown. Thus, this study aimed to investigate the main molecular mechanisms involved in liver regeneration of partially hepatectomized elderly rats exposed to LPLI. The effects of 15 min of LPLI (wavelength of 632.8 nm; fluence of 0.97 J/cm(2); total energy delivered of 3.6 J) were evaluated in hepatectomized elderly Wistar male rats. Afterwards, through immunoblotting approaches, the protein expression and phosphorylation levels of hepatocyte growth factor (HGF), Met, Akt and Erk 1/2 signaling pathways as well as the proliferating cell nuclear antigen (PCNA) were investigated. It was observed that LPLI was not able to improve liver regeneration in elderly rats as evidenced by the lack of improvement of HGF and PCNA protein expression or phosphorylation levels of Met, Akt and Erk 1/2 in the remnant livers. In sum, this study demonstrated that the main molecular pathway, i.e. HGF/Met → Akt and Erk 1/2 → PCNA, involved in the hepatic regeneration process was not improved by LPLI in elderly hepatectomized rats, which in turn rules out LPLI as an adjuvant therapy, as observed in this protocol of liver regeneration evaluation (i.e. at 48 h after 70 % resection), in elderly.

Photoactivation of GLUT4 translocation promotes glucose uptake via PI3-K/Akt2 signaling in 3T3-L1 adipocytes

Insulin resistance is a hallmark of the metabolic syndrome and type 2 diabetes. Dysfunction of PI-3K/Akt signaling was involved in insulin resistance. Glucose transporter 4 (GLUT4) is a key factor for glucose uptake in muscle and adipose tissues, which is closely regulated by PI-3K/Akt signaling in response to insulin treatment. Low-power laser irradiation (LPLI) has been shown to regulate various physiological processes and induce the synthesis or release of multiple molecules such as growth factors, which (especially red and near infrared light) is mainly through the activation of mitochondrial respiratory chain and the initiation of intracellular signaling pathways. Nevertheless, it is unclear whether LPLI could promote glucose uptake through activation of PI-3K/Akt/GLUT4 signaling in 3T3L-1 adipocytes. In this study, we investigated how LPLI promoted glucose uptake through activation of PI-3K/Akt/GLUT4 signaling pathway. Here, we showed that GLUT4 was localized to the Golgi apparatus and translocated from cytoplasm to cytomembrane upon LPLI treatment in 3T3L-1 adipocytes, which enhanced glucose uptake. Moreover, we found that glucose uptake was mediated by the PI3-K/Akt2 signaling, but not Akt1 upon LPLI treatment with Akt isoforms gene silence and PI3-K/Akt inhibitors. Collectively, our results indicate that PI3-K/Akt2/GLUT4 signaling act as the key regulators for improvement of glucose uptake under LPLI treatment in 3T3L-1 adipocytes. More importantly, our findings suggest that activation of PI3-K/Akt2/GLUT4 signaling by LPLI may provide guidance in practical applications for promotion of glucose uptake in insulin-resistant adipose tissue.

Effects of LPLI on microglial phagocytosis in LPS-induced neuroinflammation model

Microglial activation plays an important role in neurodegenerative diseases. Once activated, they have macrophage-like capabilities, which can be beneficial by phagocytosis and harmful by secretion of neurotoxins. However, the resident microglia always fail to trigger an effective phagocytic response to clear dead cells or Aβ deposits during the progression of neurodegeneration. Therefore, the regulation of microglial phagocytosis is considered a useful strategy in searching for neuroprotective treatments. In this study, our results showed that low-power laser irradiation (LPLI) (20 J/cm2) could enhance microglial phagocytic function in LPS-activated microglia. We found that LPLI-mediated microglial phagocytosis is a Rac-1-dependent actin-based process, that a constitutively activated form of Rac1 (Rac1Q61L) induced a higher level of actin polymerization than cells transfected with wild-type Rac1, whereas a dominant negative form of Rac1 (Rac1T17N) markedly suppressed actin polymerization. In addition, the involvement of Rac1 activation after LPLI treatment was also observed by using a Raichu fluorescence resonance energy transfer (FRET)-based biosensor. We also found that PI3K/Akt pathway was required in the LPLI-induced Rac1 activation. Our research may provide a feasible therapeutic approach to control the progression of neurodegenerative diseases.

Photo-Thermal Conversion and Stability of Gold and Silver Nanostructures

Gold and silver nanostructures (such as Au nanorods and Ag nanoplates) exhibit strong and tunable surface plasmon resonance in the near-infrared region (NIR). Under a certain NIR laser irradiation, noble metal nanostructrues achieve a high photo-thermal effect, which would be useful in the therapy. In this work, Au nanorods with longitude surface plasmon resonance (SPRL) shifting in the region of 650 ~1100 nm were synthesized by a seed method. Ag nanoplates and nanocubes with SPR located in the region of 650~850 nm were produced by a hydrothermal method. Through adjusting laser power and irradiating time, the photo-thermal conversions of these nanostructures were studied under NIR laser irradiation. Under low power laser (808 nm, &lt;1W) irradiation, the shape of the Au nanorods are stable and the temperature of colloid increase from room temperature to ~57°C. However, Au nanorods undergo deformation from rod to spherical particle under irradiation of high power (808 nm laser; 6W; 1064nm laser, 7W), resulting in the disappearance of SPRL. Morphology evolutions and photo-thermal conversion of Ag nanostructures were also studied. Ag nanostructures have a lower photo-thermal conversion compared with that of Au nanorods colloid. Snipping and dendrite can be observed for Ag nanoplates after irradiating, while Ag nanocubes have no obvious shape change.

Benefits of laser phototherapy on nerve repair

Post-traumatic nerve repair represents a major challenge to health sciences. Although there have been great advances in the last few years, it is still necessary to find methods that can effectively enhance nerve regeneration. Laser therapy has been widely investigated as a potential method for nerve repair. Therefore, in this article, a review of the existing literature was undertaken with regard to the effects of low-power laser irradiation on the regeneration of traumatically/surgically injured nerves. The articles were selected using either electronic search engines or manual tracing of the references cited in key papers. In electronic searches, we used the key words as "paresthesia", "laser therapy", "low-power laser and nerve repair", and "laser therapy and nerve repair", considering case reports and clinical studies. According to the findings of the literature, laser therapy accelerates and improves the regeneration of the affected nerve tissues, but there are many conflicting results about laser therapy. This can be attributed to several variables such as wavelength, radiation dose, and type of radiation. All the early in vivo studies assessed in this research were effective in restoring sensitivity. Although these results indicate a potential benefit of the use of lasers on nerve repair, further double-blind controlled clinical trials should be conducted in order to standardize protocols for clinical application.

Effect of Low Power Laser Irradiation on the Ability of Cell Growth and Myogenic Differentiation of Myoblasts CulturedIn Vitro

As a therapeutic modality, low power laser irradiation (LPLI) has been used clinically in the treatment of skeletal muscle injuries and other myopathic conditions, but the cellular and molecular mechanisms attributed to this therapy were still unclear. Myoblasts are a type of myogenic stem cells quiescence in mature skeletal muscle fibers and are considered as the source cells during the regenerating process. The purpose of this paper was to investigate the effects of LPLI on the proliferation and myogenic differentiation of the cultured myoblasts and to find out the major candidates responsible for LPLI-induced muscle regenerationin vivo. In this study, primary rat myoblasts were exposed to helium-neon (He-Ne) laser. Cell proliferation, differentiation, and the cellular responses to LPLI were monitored by using morphological observation and molecular biological methods. It was found that LPLI at a certain fluence could increase the cell growth potential for myoblasts and further induce more cells entering into S phase of the mitotic cycle as indicated by high levels of bromodeoxyuridine (BrdU) incorporation, while at the same time inhibiting theirin vitrodifferentiation and decreasing the expression of myogenic regulatory genes to a certain extent. Taken together, these results provide experimental evidence for the clinical applications of LPLI in regenerating skeletal muscle.

低强度激光照射对视网膜谷氨酸受体表达的影响

低强度激光照射对视网膜谷氨酸受体表达的影响

低强度激光照射对视网膜谷氨酸受体表达的影响

低强度激光照射对视网膜谷氨酸受体表达的影响

Cancer PhototherapyviaSelective Photoinactivation of Respiratory Chain Oxidase to Trigger a Fatal Superoxide Anion Burst

Here, we develop a novel cancer treatment modality using mitochondria-targeting, high-fluence, low-power laser irradiation (HF-LPLI) in mouse tumor models and explore the mechanism of mitochondrial injury by HF-LPLI. We demonstrated that the initial reaction after photon absorption was photosensitization of cytochrome c oxidase (COX), to inhibit enzymatic activity of COX in situ and cause respiratory chain superoxide anion (O2(-•)) burst. We also found that HF-LPLI exerted its main tumor killing effect through mitochondrial O2(-•) burst via electron transport chain (ETC). These phenomena were completely absent in the respiration-deficient cells and COX knockdown cells. With a carefully selected irradiation protocol, HF-LPLI could efficaciously destroy tumors. The inhibition of enzymatic activity of COX and generation of O2(-•) by HF-LPLI in vivo were also detected. It is the first time that the mechanism involved in the interaction between light and its photoacceptor under HF-LPLI treatment is clarified. Our results clearly indicate that HF-LPLI initiates its effects via targeted COX photoinactivation and that the tumor-killing efficacy is dependent of the subsequent mitochondrial O2(-•) burst via ETC. Based on both in vitro and in vivo results, we conclude that HF-LPLI can selectively photoinactivate respiratory chain oxidase to trigger a fatal mitochondrial O2(-•) burst, producing oxidative damage on cancer cells. This study opens up the possibilities of applications of HF-LPLI as a mitochondria-targeting cancer phototherapy.