Study of the Relationship Between Endogenous Protoporphyrin IX Concentration in Human Lymphoblastoid Cells and Inactivation by UVA Radiation

Intracellular content of the endogenous chromophore protoporphyrin IX (PPIX) can be modulated by administration of the haem precursor d-aminolevulinic acid (ALA). Exogenous addition of ALA effectively bypasses the rate limiting ALA synthesis step in the haem biosynthetic pathway leading to the accumulation of PPIX. The purpose of this study was to examine the relationship between PPIX concentration and the level of inactivation of cultured human lymphoblastoid cells in order to determine if the basal PPIX content of these cells determines the level of inactivation by UVA. >From the relationship between inactivation rate constants at each PPIX concentration an estimate was made of the basal level of PPIX that would be necessary to mediate significant cell death by UVA radiation. It is concluded that the basal content of PPIX is insufficient to make a major contribution to the UVA inactivation of these lymphoblastoid cells. (author)