Mutagenic activity of high-energy 532 nm ultra-short laser pulses

The mutagenic activity of green (532 nm) and infrared (1064 nm) ultra-short laser light pulses was tested in cultured Syrian hamster fibroblasts by a hypoxanthine phosphoribosyl-transferase (HPRT) mutagenesis assay. In 18 irradiation trials, cells were exposed to eight consecutive 100-ps pulses of either 532 nm or 1064 nm light from a Nd:YAG laser at average irradiances of 3.0 GW/cm2. The 532 nm irradiations produced Hprt mutations at an average observed frequency of 5.3-5.6 x 10(-6), 10-fold higher than control trials (P < 0.01), while 1064 nm irradiations produced only background (spontaneous mutation) frequencies. A HAT (hypoxanthine, aminopterin, thymidine) sensitivity test allowed us to infer that Hprt- clones, selected as 6-thioguanine-resistant clones, possessed mutations at the Hprt locus after 532 nm Nd:YAG laser irradiation. The mutagenic effects of 532 nm high-energy laser pulses and not 1064 nm wavelengths are discussed in light of a two-photon absorption hypothesis. These preliminary findings suggest that 460-590 nm visible-light lasers may be mutagenic to mammalian cells either as a result of two-photon absorption or through some other photochemical process that damages DNA.