In vitro studies of effects of light and riboflavin on DNA and HeLa cells.

The widespread use of phototherapy for neonatal hyperbilirubinemia has caused some concern since substances other than bilirubin may be photoactivated. The toxic properties of these photoactivated substances might prove to be more harmful to the neonatal infant than bilirubin. The purpose of the present study was to investigate the effect of photoactivated riboflavin in low concentration, on purified DNA. The results demonstrate extensive changes in the structure of DNA (see Table 1) manifested by (1) a change in the peak absorbance in the ultraviolet, (2) a decrease in the temperature of the thermal helix-coil transition, (3) a slight decrease in the sedimentation coefficient, and (4) an increase in the buoyant density values (1.704-1.709). These observations are consistent with the interpretation that there has been an alteration of one of the base moieties with minimal cleavage of the phosphodiester linkages. Results with human cells in tissue culture indicate that a similar photodynamic effect of riboflavin on the DNA occurs in living cells.