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 fibrobl asts by a hypoxanthine phosphoribosyl-transferase (HPRT) mutagenesis a ssay. In 18 irradiation trials, cells were exposed to eight consecutiv e 100-ps pulses of either 532 nm or 1064 nm light from a Nd:YAG laser at average irradiances of 3.0 GW/cm(2). The 532 nm irradiations produc ed 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 irradia tions produced only background (spontaneous mutation) frequencies. A H AT (hypoxanthine, aminopterin, thymidine) sensitivity test allowed us to infer that Hprt(-) clones, selected as 6-thioguanine-resistant clon es, possessed mutations at the Hprt locus after 532 nm Nd:YAG laser ir radiation. The mutagenic effects of 532 nm high-energy laser pulses an d not 1064 nm wavelengths are discussed in light of a two-photon absor ption hypothesis. These preliminary findings suggest that 460-590 nm v isible-light lasers may be mutagenic to mammalian cells either as a re sult of two-photon absorption or through some other photochemical proc ess that damages DNA. (C) 1997 by Radiation Research Society.