PHOTOSENSITIZATION BY PORPHYRINS DELIVERED TO L CELL FIBROBLASTS BY HUMAN SERUM LOW DENSITY LIPOPROTEINS. A MICROSPECTROFLUOROMETRIC STUDY

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Abstract
Human serum LDL were used as vehicles to deliver protoporphyrin and hematoporphyrin dimer to L cell mouse fibroblasts. Topographic analysis by microspectrofluorometry on single living cells shows that after digestion of LDL, protoporphyrin is localized in cytoplasmic areas. Protoporphyrin and hematoporphyrin dimer are readily bleached by 420 ± 60 nm radiations at the high fluence rate used. Complex bleaching kinetics are observed. Spectral studies using the same technique demonstrate that an intense fluorescent emission (λmax= 450 nm) is produced immediately after the onset of irradiation with 365 ± 2 nm or 420 ± 60 nm radiations using LDL loaded with protoporphyrin or Photofrin II. These fluorescent products have been previously identified as lipofuscin‐like pigments formed by reaction of lipid photoperoxides with amino groups. The permeation of lysosomal membranes is also induced after delivery of the porphyrins by LDL. This permeation can be strongly inhibited not only by the lysosomal inhibitors chloroquine and monensin but also by a‐tocopherol. On the other hand, neither α‐tocopherol nor chloroquine or monensin inhibit the lipofuscin‐like pigment formation.