Purple versus yellow: preventing neonatal jaundice with tin-porphyrins

Metalloporphyrin phototoxicity

The phototoxicities of six metalloporphyrin dimethylesters (i.e. cobalt (Co), copper (Cu), manganese (Mn), nickel (Ni), tin (Sn) and zinc (Zn) were investigated. Hemolysis of human erythrocytes and inactivation of two enzymes (acetylcholinesterase and beta-galactosidase) were used to assess the phototoxic efficacy of these metal chelates. Tin protoporphyrin (SnPP), the only porphyrin found to hemolyze erythrocytes at a concentration of 40 microM (radiation dose, 230 kJ m-2), was much less efficient than either free protoporphyrin IX or hematoporphyrin. SnPP completely inactivated beta-galactosidase at concentrations above 15 microM (radiation dose, 75 kJ m-2) and drastically interfered with acetylcholinesterase activity at a concentration of 150 microM (radiation dose, 75 kJ m-2). CoPP, CuPP, MnPP, NiPP and ZnPP were ineffective photohemolytic agents at 40 microM (radiation dose, 230 kJ m-2), but inactivated acetylcholinesterase and beta-galactosidase activity to varying degrees. These results suggest that (i) metal ions reduce the phototoxicity of protoporphyrin IX, (ii) different metal ions reduce the phototoxic activity of protoporphyrin IX to different degrees and (iii) the biological activities of the various metal complexes vary in different assay systems.

Dangerous effects of tin-protoporphyrin plus photoirradiation on neonatal rats

In vivo and in vitro effects of porphyrins (tin-protoporphyrin [SnPP], cobalt-mesoporphyrin, haemin and protoporphyrin) on neonatal rats were investigated. Under photoirradiation a high mortality rate was recognized in SnPP injected rats. None died from the application of SnPP without photoirradiation. In photoirradiated rats the median lethal dose (LD50) value of SnPP was calculated to be about 7.4 mumol/kg body weight. Haemolysis and malonaldehyde formation of red blood cells were induced by SnPP together with photoirradiation. SnPP may be useful in reducing bilirubin levels in severely jaundiced infants under non-photoirradiated conditions or dim light, but prophylactic administration of SnPP to the majority of infants is not recommended.