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 µmol/kg s.c.), 4-d-old mice were given 30 µmol 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 µmol/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.


CONCLUSIONS
ZnPP-Lipid is effective and thus has potential for treating neonatal hyperbilirubinemia due to hemolysis.
Department of Pediatrics, Division of Neonatal and Developmental Medicine, Stanford University School of Medicine, Stanford, California.
Kazumichi
K
Fujioka
Department of Pediatrics, Division of Neonatal and Developmental Medicine, Stanford University School of Medicine, Stanford, California.
Flora
F
Kalish
Department of Pediatrics, Division of Neonatal and Developmental Medicine, Stanford University School of Medicine, Stanford, California.
Ronald J
RJ
Wong
Department of Pediatrics, Division of Neonatal and Developmental Medicine, Stanford University School of Medicine, Stanford, California.
David K
DK
Stevenson
D000284:Administration, Oral; D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000187:drug effects* / Q000201:enzymology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004339:Drug Compounding; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D051547:Heme Oxygenase-1 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D006461:Hemolysis / Q000187:drug effects*; D051556:Hyperbilirubinemia, Neonatal / Q000097:blood / Q000201:enzymology / Q000235:genetics / Q000517:prevention & control*; D008055:Lipids / Q000737:chemistry; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D010316:Particle Size; D011524:Protoporphyrins / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D013997:Time Factors
D004791:Enzyme Inhibitors; D008055:Lipids; D008565:Membrane Proteins; D011524:Protoporphyrins; C017803:zinc protoporphyrin; D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse