Photodynamic Toxicity of Polycyclic Aromatic Hydrocarbons in Tissue Culture.

SUMMARY Cells grown in culture were exposed to benzo[a}pyrene and related polycyclic aro matic hydrocarbons dissolved in serum, following which procedure they were irradi ated with long-wave ultraviolet light. The sequence of biological responses resulting from this photodynamic effect on the cells was dependent upon the total energy ab sorbed by the hydrocarbons incorporated in the cells. The most sensitive response was that of temporary interference with mitotic proc eases in cells in mitosis or in interphase at the time of irradiation. Cells in the resting stage were not adversely affected. A moderate grade of the response produced gradual cell damage characterized by membrane retraction, blebbing and vacuoiiza tion of the cytoplasm, pyknosis of the nucleus, and ultimate cell death within a day or two. An extreme degree of the response resulted in an instant death of the cell with a swelling and reticulation of the cytoplasm. Irradiation with conventional light and fluorescent lamps for a short time was also capable of inducing responses, provided sufficient benzo[a]pyrene was incorporated into the cells. Continuous exposure in the dark of FL and HeLa cells containing benzo[a]pyrene and other related hydrocarbons did not result in a significant adverse effect even after a week's exposure at the highest concentrations. In contrast, M-5' cells, after exposure to 5 ,@g/m1of benzola]pyrene, showed no effect for 3 days, follow ing which there was disarrangement of the growth pattern. No significant quantitative or qualitative difference in the photodynamic activities of several carcinogenic and noncarcinogenic polycyclic hydrocarbons could be observed when the effect was compared on the basis of assumed energy absorption. The marked photosensitizing effect of carcinogenic hydrocarbons on living cells was first reported by Lewis (25) in his study of chick embryo cells. This observation was confirmed by many investigators using various bio logical systems including infusorian Coleps (30), Para mecium caudatum (13), Paramecium bursaria (8), Dro sophilia mdanogaster (27), and yeast (23). This property was studied in nonliving systems as well, when it was shown that hemolysis of red blood cells (4), depolymeriza tion of macromolecules (2), and denaturation of serum (32) could be induced. These as well as other findings led to a postulated as sociation between photosensitizing reaction and the car cinogenic effect exerted by polycyclic aromatic hydro carbons (31). Though this parallelism has had limited acceptance, several studies have been undertaken in this area during the intervening years. 1 Human embryonic skin, diploid …