Zinc protoporphyrin
Zinc protoporphyrin refers to coordination complexes of zinc and protoporphyrin IX. It is a red-purple solid that is soluble in water. The complex and related species are found in red blood cells when heme production is inhibited by lead and/or by lack of iron.
Clinical utility
Measurement of zinc protoporphyrin in red cells has been used for screening for lead poisoning and for iron deficiency.Zinc protoporphyrin levels can be elevated as the result of a number of conditions, for instance:
- lead poisoning
- iron deficiency
- sickle cell anemia
- sideroblastic anemia
- anemia of chronic disease
- vanadium exposure
- erythropoietic protoporphyria
History
Porphyrin complexes of zinc have been known since the 1930s. In 1974 ZPP was identified as a major non-heme porphyrin formed in red cells as the result of lead poisoning or iron deficiency., It was already known at this time that non-heme protoporphyrin IX levels were elevated in these conditions, but prior investigators had used acidic extraction methods in their assays that converted ZPP to unbound Protoporphyrin IX. The early literature on quantifying zinc-PP levels may be unreliable.Early-stage cancer research
ZnPP is under in vitro research for its potential effects on cancer cells. ZnPP is a competitive inhibitor of heme oxygenase, which is a cytoprotective enzyme with higher expression in cancerous tissues. In vitro, ZnPP suppression of heme oxygenase reduces cell viability of cancer cells and increases cytotoxicity in cancer cells.In preliminary human studies conducted in 2014, ZnPP in combination with anticancer drugs increased cytotoxicity of cancer cells. Tumors from several types of cancer showed a susceptibility to ZnPP due to increased expression of heme oxygenase.
ZnPP has been encapsulated in nanoparticles with a specialized coating for drug delivery inside the body. ZnPP did not show any reduced inhibitory potential on heme oxygenase when loaded into nanoparticles.