Free erythrocyte protoporphyrin (FEP) and zinc protoporphyrin (ZnP) as biological parameters for lead poisoning

Lamola et al. (1974) reported that free erythrocyte protoporphyrin (FEP) is not present as free type protoporphyrin ( FPP ) but rather is chelated with zinc in lead poisoning and iron deficiency anemia. In our fluorometric study of FEP and zinc protoporphyrin ( ZnP ) in erythrocytes of lead-poisoned rabbits and lead workers, the co-existence of ZnP and FPP was observed in the severe stage of acute lead poisoning in rabbits. The ratio of ZnP to FEP in erythrocytes decreased with the progress of lead intoxication, and the amount of FPP was greater than that of ZnP in the severe stage of intoxication. This FPP accumulated in the erythrocytes was easily converted to ZnP by incubation of the hemolysate with zinc. On the other hand, increased protoporphyrin (PP) in bone marrow was present as FPP in lead intoxication. From these results, ZnP in peripheral erythrocytes is considered to be a secondary product, not a primary one. Therefore, the determination of total FEP ( FPP + ZnP ) by the acid solvent extraction method might be more reasonable than using ZnP -determination as the biological parameter of lead poisoning. We propose that erythrocyte porphyrin in lead intoxication should be expressed as FEP, not as ZnP , for the parameter. The present study also suggests that the form of erythrocyte FPP in erythropoietic protoporphyria (EPP) patients is a little different from that in lead-poisoning patients, because of its high chelation reactivity with zinc.