Effect of 630-NM pulsed laser irradiation on the proliferation of HeLa cells in Photofrin(®)-mediated photodynamic therapy.

BACKGROUND AND AIMS: Red laser light of wavelength 630 nm is usually used for Photofrin(®)-mediated photodynamic therapy (PDT). The 630-nm light employed in PDT corresponds to the region of the wavelength used in low-level laser therapy (LLLT) may influence on the photodynamic effect required for killing cancer cells. The aim of this in vitro study was to investigate the changes in cell viability and degree of cell proliferation after Photofrin(®)-mediated PDT using 630-nm pulsed laser irradiation (10 Hz repetition rate and 7-9 ns pulse width), which was clinically found to induce no remarkable cell injury. MATERIALS AND METHODS: A study has been conducted in which HeLa cells are incubated with Photofrin(®) for 15 min (10 µg/ml). Irradiation was carried out at an average fluence rate of 50 mW/cm(2) with light doses of 1, 3, and 5 J/cm(2). The cytotoxic effects on the cells are evaluated by the XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide) assay. RESULTS: The results showed that the laser irradiated cells exhibited a greater clonogenic activity than normal and PDT treated cells for a short period after the laser irradiation. CONCLUSION: If the level of 630-nm pulsed laser irradiation employed in a PDT is comparatively lowered, it would have a biostimulatory effect like that of in LLLT.

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.

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.