title: Differential regulation of heme oxygenase isozymes by Sn- and Zn-protoporphyrins: possible relevance to suppression of hyperbilirubinemia.
abstract: Synthetic metalloporphyrins decrease heme oxygenase (HO)-dependent bilirubin formation. Presently, the effects in vivo and in vitro of Sn- and Zn-protoporphyrins on HO-1 (HSP-32) and HO-2 at the protein and transcript levels were examined. Western blot analysis of HO-2 in testes microsomes of Sn-protoporphyrin-treated rats revealed a dramatic disruption of the integrity of the HO-2 protein. Similar observations were made with the liver and adrenal HO-2 and the NADPH-cytochrome P-450 reductase of treated rats. Northern blot analysis, however, suggested unaltered tissue levels of HO-2 transcripts (approximately 1.9 and approximately 1.3 kb). The HO-1 protein integrity in organs of treated rats was less dramatically affected by the metalloporphyrin and an increase in its 1.8 kb mRNA level in the testes was detected. Zn-protoporphyrin also increased HO-1 mRNA level in the testes, but did not affect HO-2 protein integrity. In in vitro studies with purified HO-1 and HO-2, both Sn- and Zn-protoporphyrins were equally inhibitory to HO-1 activity; Sn-protoporphyrin, however, was by far more inhibitory to HO-2-dependent activity than to that of HO-1. Together, these findings and the fact that HO-2 under normal conditions is the predominant form of the enzyme in most organs suggest that loss of HO-2 protein integrity may to a significant degree account for suppression of bilirubin formation by Sn-protoporphyrin. These in turn may reflect differences between HO-1 and HO-2, both at the transcriptional level with HO-2 being noninducible, and in structure/composition of the isozymes, with HO-2 being more labile.
authors.affiliation: University of Rochester School of Medicine, Department of Biophysics, NY 14642.
authors.forename: M D
authors.initials: MD
authors.lastname: Maines
authors.forename: G M
authors.initials: GM
authors.lastname: Trakshel
mesh_terms: D000311:Adrenal Glands / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001663:Bilirubin / Q000378:metabolism; D015152:Blotting, Northern; D015153:Blotting, Western; D004247:DNA; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D006932:Hyperbilirubinemia / Q000201:enzymology*; D007527:Isoenzymes / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D008297:Male; D008665:Metalloporphyrins / Q000502:physiology*; D008969:Molecular Sequence Data; D011524:Protoporphyrins / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013737:Testis / Q000201:enzymology
chemical_list: D007527:Isoenzymes; D008665:Metalloporphyrins; D011524:Protoporphyrins; C017803:zinc protoporphyrin; D004247:DNA; C032628:tin protoporphyrin IX; D006419:Heme Oxygenase (Decyclizing); D001663:Bilirubin