Photodynamic effects on human cells exposed to light in the presence of hematoporphyrin. pH effects.

Human cells derived from a carcinoma in situ (NHIK 3025) were exposed in vitro to visible light and hematoporphyrin at different pH levels. The cells were inactivated more efficiently at pH 6.7 and 7.2 than at pH 7.8 The treatment with light and hematoporphyrin also induced DNA damage more efficiently at the former pH values than at the latter one. The variation in the efficiency of the photodynamic effect with the pH is mainly due to the fact that the cellular uptake of hematoporphyrin increases with decreasing pH.