Increase of bone volume by a nanosecond pulsed laser irradiation is caused by a decreased osteoclast number and an activated osteoblasts.

The biostimulatory effects of laser irradiation focus not only in the field of soft tissue but also bone formation. Studies have shown that the light of a nanosecond pulsed laser which has a high peak power can produce stress waves in tissue. We have hypothesized that nanosecond pulsed laser irradiation stimulates bone formation. Our aim was to clarify the mechanism of increased bone volume by nanosecond pulsed laser irradiation. Rat femur was irradiated with a Q-switched Nd:YAG laser, which has a wavelength of 1064 nm. The quantification of trabecular architecture using three-dimensional morphometric analysis and measurement of bone mineral density (BMD) using pQCT was performed on day 1, day 3, day 5, and day 7 after laser irradiation. The laser effects on bone cells were also investigated using histological and immunohistochemical analysis. On day 1 after laser irradiation, bone volume (BV/TV), trabecular thickness (Tb.Th), and other parameters of the irradiated group did not significantly differ from the non-irradiation group (control). However, the mean BV/TV, Tb.Th, mineral apposition rate, and BMD of the laser group on day 7 after laser irradiation were significantly greater than those of the control. On histological analysis, the number of TRAP-positive osteoclasts was lower on day 3 after laser irradiation. Osteoblasts with activated clearance were seen in the laser irradiated group on day 1 and day 3. These data reveal that the increased bone volume by nanosecond pulsed laser irradiation causes an increase in osteoblast activity and a decrease in osteoclast number.

Elevation of plasma membrane permeability on laser irradiation of extracellular latex particles.

In this report, we describe a laser-latex combination system that enables membrane-impermeable molecules to penetrate cell membranes. Laser light (Q-switched Nd:YAG laser, 532.5 nm) was used to irradiate a mixture of commercial latex particles (blue dyed, 1 micro m in diameter) and mouse fibrosarcoma (Meth-A) cells. After irradiation, membrane permeability was evaluated by flow cytometric assaying using propidium iodide (PI) and fluorescein diacetate (FDA). The proportion of permeabilized-resealed cells was affected by changes in the light intensity (approximately 780 mW/cm(2)), the irradiation time (approximately 240 s), and/or the particle concentration (approximately 10(9) particles/ml). The permeability persisted up to 20 min after light irradiation. Near the sites of individual particles, the permeability of the cell membrane is modified, probably due to localized temperature changes. These results suggest that this laser-induced permeabilization strategy constitutes a new means of delivering exogenous materials into living cells.

Enhancement of cytotoxic effect of bleomycin with transient permeabilization of plasma membrane by laser-induced multiple stress waves in vitro.

We investigated the effect of multiple stress waves with peak stress of less than 3 MPa on chemosensitivity of HeLa cells adhered on plastic. HeLa cells exposed to stress waves retained more than 95% of the viability found in untreated cells. The scanning electron microscopy of cells exposed to stress waves showed ruffling microvilli, indicating a change in the cell surface morphology. The cytotoxicity of bleomycin (BLM) on HeLa cells was enhanced by the stress waves exposure. Our findings demonstrated that the low-intensity stress wave would allow to deliver the BLM molecules into cytoplasm by repetition exposure.

Detection of 1270 nm emission from singlet oxygen and photocytotoxic property of sugar-pendant 60 fullerenes.

Sugar-pendant [60] fullerene derivatives have been prepared from carbohydrate-linked azides 1a-e. Both monosugar (4a-e) and bissugar derivatives (5a-e) produce singlet oxygen ((1)O(2)) under laser irradiation (355 nm) proved by the direct observation of (1)O(2) emission at 1270 nm. Monosugar derivatives exhibit photocytotoxicity varying by the attached sugar molecule.

High-intensity pulsed laser irradiation accelerates bone formation in metaphyseal trabecular bone in rat femur.

Low-energy laser irradiation has positive effects on bone fracture healing, osteoblast proliferation, bone nodule formation, and alkaline phosphatase activity. However, the mechanism by which low-energy laser irradiation affects bone is not clearly known. It was recently found that light at a low radiation dosage is absorbed by intracellular chromophores. High-intensity pulsed laser irradiation can produce acoustic waves in the target surface by rapidly heating the tissue. We considered that the acoustic waves induced by high-intensity pulsed laser irradiation, in addition to the photochemical effects that are induced, accelerate bone formation. To clarify whether high-intensity pulsed laser irradiation accelerates bone formation, we investigated bone formation in the irradiated femur of rat, using histomorphometric analysis. Rat femurs were irradiated with a Q-switched Nd: YAG laser, which has a wavelength of 1064 nm, under two conditions: once a day, with the average fluence rate set at 100 mW/cm(2) (LA1), and twice a day, i.e., every 12 h, with the average fluence rate set at 50 mW/cm(2) (LA2). The mean bone volume and mineral apposition rate in the LA1 group were significantly higher than those in the nonirradiated group (control). These values were highest for the LA2 group, and were about 1.52 and 1.25-fold those of the control, respectively. These data demonstrated that the number of pulses, rather than the intensity of the laser irradiation, affects bone formation. Thus, this study indicated that high-intensity pulsed laser irradiation accelerates bone formation in the metaphysis. This bone formation induced by high-intensity pulsed laser irradiation might be due to laser-induced pressure waves.