Hemin uptake and release by neurons and glia

Hemin accumulates in intracerebral hematomas and may contribute to cell injury in adjacent tissue. Despite its relevance to hemorrhagic CNS insults, very little is known about hemin trafficking by neural cells. In the present study, hemin uptake and release were quantified in primary murine cortical cultures, and the eff ect of the hemin-binding compound deferoxamine (DFO) was assessed. Net uptake of 55 Fe-hemin was similar in mixed neuron-glia, neuron, and glia cultures, but was 2.6-3.6-fold greater in microglia cultures. After washout, 40-60% of the isotope signal was released by mixed neuron-glia cultures into albumin-containing medium within 24 h. Inhibiting hemin breakdown with tin protoporphyrin IX (SnPPIX) had minimal eff ect, while release of the fl uorescent hemin analog zinc mesoporphyrin was quantitatively similar to that of Fe-55-hemin. Isotope was released most rapidly by neurons (52.2 + 7.2% at 2 h), compared with glia (15.6 +/- 1.3%) and microglia (17.6 +/- 0.54%). DFO did not alter Fe-55-hemin uptake, but signifi cantly increased its release. Mixed cultures treated with 10 mu M hemin for 24 h sustained widespread neuronal loss that was attenuated by DFO. Concomitant treatment with SnPPIX had no eff ect on either enhancement of isotope release by DFO or neuroprotection. These results suggest that in the presence of a physiologic albumin concentration, hemin uptake by neural cells is followed by considerable extracellular release. Enhancement of this release by DFO may contribute to its protective effect against hemin toxicity.