Inhibition of heme oxygenase activity using a microparticle formulation of zinc protoporphyrin in an acute hemolytic newborn mouse model
Background:Increased bilirubin production due to hemolysis can lead to neonatal hyperbilirubinemia. Inhibition of heme oxygenase (HO) the rate limiting enzyme in heme catabolism, by metalloporphyrins (Mps) may be an ideal preventive strategy for neonatal hemolytic disease. Zinc protoporphyrin (ZnPP) is a naturally occurring Mp, potent, not phototoxic, with minimal HO 1 upregulation, but is not orally absorbed. Recently, we designed a lipid based ZnPP formulation (ZnPP Lipid) which is orally absorbed by newborn mice. Here, we evaluated the efficacy of ZnPP Lipid in heme loaded newborn mice, a model analogous to hemolytic infants.Methods:After 24 h of heme administration (30 umol/kg s.c. 4 d old mice were given 30 umol ZnPP Lipid/kg via intragastric injections. After 3 h, liver and brain HO activity were measured. HO 1 upregulation was assessed by determinations of HO 1 protein, promoter activity, and mRNA by Western blot, in vivo bioluminescence imaging, and RT PCR, respectively.Results:After heme loading, liver HO activity significantly increased ~1.6 fold, which was inhibited in a dose dependent manner by ZnPP Lipid. A dose of 30 umol/kg returned activity to control levels. Brain HO activity was not inhibited. No significant increases in liver and brain HO 1 protein, promoter activity, and mRNA were observed.Conclusion:ZnPP Lipid is effective and thus has potential for treating neonatal hyperbilirubinemia due to hemolysis.
Pediatric Research