Effects of oral administration of tin and zinc protoporphyrin on neonatal and adult rat tissue heme oxygenase activity

Gasotransmitter Heterocellular Signaling

SIGNIFICANCE

The family of gasotransmitter molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), has emerged as an important mediator of numerous cellular signal transduction and pathophysiological responses. As such, these molecules have been reported to influence a diverse array of biochemical, molecular, and cell biology events often impacting one another. Recent Advances: Discrete regulation of gasotransmitter molecule formation, movement, and reaction is critical to their biological function. Due to the chemical nature of these molecules, they can move rapidly throughout cells and tissues acting on targets through reactions with metal groups, reactive chemical species, and protein amino acids.

CRITICAL ISSUES

Given the breadth and complexity of gasotransmitter reactions, this field of research is expanding into exciting, yet sometimes confusing, areas of study with significant promise for understanding health and disease. The precise amounts of tissue and cellular gasotransmitter levels and where they are formed, as well as how they react with molecular targets or themselves, all remain poorly understood.

FUTURE DIRECTIONS

Elucidation of specific molecular targets, characteristics of gasotransmitter molecule heterotypic interactions, and spatiotemporal formation and metabolism are all important to better understand their true pathophysiological importance in various organ systems. Antioxid. Redox Signal. 26, 936-960.

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.

CONCLUSION

ZnPP-Lipid is effective and thus has potential for treating neonatal hyperbilirubinemia due to hemolysis.

Effects of light on metalloporphyrin-treated newborn mice

Zinc protoporphyrin (ZnPP) is a promising metalloporphyrin with sufficient potency, but has poor solubility and is not absorbed well orally. Intragastric administration of ZnPP microparticles (30 μmol/kg) to 3-day-old mice resulted in a twofold increase in potency and no signs of phototoxicity.

CONCLUSION

The use of polymeric particulate delivery systems can improve the stability and enhance intestinal absorption of ZnPP, while retaining HO inhibitory potency without photosensitising effects, and thus is potentially useful in treating neonatal hyperbilirubinemia.

Metalloporphyrins - an update

Metalloporphyrins are structural analogs of heme and their potential use in the management of neonatal hyperbilirubinemia has been the subject of considerable research for more than three decades. The pharmacological basis for using this class of compounds to control bilirubin levels is the targeted blockade of bilirubin production through the competitive inhibition of heme oxygenase (HO), the rate-limiting enzyme in the bilirubin production pathway. Ongoing research continues in the pursuit of identifying ideal metalloporphyrins, which are safe and effective, by defining therapeutic windows and targeted interventions for the treatment of excessive neonatal hyperbilirubinemia.

Heme in intestinal epithelial cell turnover, differentiation, detoxification, inflammation, carcinogenesis, absorption and motility

The gastrointestinal tract is lined by a simple epithelium that undergoes constant renewal involving cell division, differentiation and cell death. In addition, the epithelial lining separates the hostile processes of digestion and absorption that occur in the intestinal lumen from the aseptic environment of the internal milieu by defensive mechanisms that protect the epithelium from being breached. Central to these defensive processes is the synthesis of heme and its catabolism by heme oxygenase (HO). Dietary heme is also an important source of iron for the body which is taken up intact by the enterocyte. This review describes the recent literature on the diverse properties of heme/HO in the intestine tract. The roles of heme/HO in the regulation of the cell cycle/apoptosis, detoxification of xenobiotics, oxidative stress, inflammation, development of colon cancer, heme-iron absorption and intestinal motility are specifically examined.

Systemic effects of orally-administered zinc and tin (IV) metalloporphyrins on heme oxygenase expression in mice

Some metalloporphyrins (Mps) inhibit heme oxygenase (HO), the rate-limiting enzyme in the production of bilirubin, and are potential compounds for the treatment of neonatal jaundice. We studied the safety and efficacy of Mps following oral administration. Adult HO-1-luc reporter mice were administered 30 micromol/kg body weight of tin mesoporphyrin (SnMP), zinc bis glycol deuteroporphyrin (ZnBG), or zinc protoporphyrin (ZnPP), or vehicle by oral gavage. Bilirubin production was measured as total body carbon monoxide (CO) excretion (VeCO). HO activity was quantitated via CO measurements by gas chromatography. HO-1 protein was determined by Western blot. HO-1 transcription levels were assessed by in vivo bioluminescence imaging. A significant 28% decrease in bilirubin production occurred within 3 h of SnMP treatment and persisted beyond 48 h. Bilirubin production decreased 15% and 9% by 3 h after administration of ZnBG and ZnPP, respectively, but returned to baseline within 48 h. Maximal inhibition of liver, spleen, and intestine HO activity was seen at 3 h with inhibitory effects decreasing in the order: SnMP > or = ZnBG > or = ZnPP. After SnMP treatment, HO-1 transcription increased 5.7-fold after 24 h. Furthermore, liver and spleen HO-1 protein significantly increased 3.7- and 2.0-fold, respectively, after 24 h. HO-1 transcription and protein were not affected in ZnBG- or ZnPP-treated mice. We conclude that the three Mps are absorbed at different rates in the mouse and affect bilirubin production and HO-1 expression in a tissue- and time-dependent manner.

Zinc Protoporphyrin: A Metabolite with a Mission

Zinc protoporphyrin (ZnPP) is a normal metabolite that is formed in trace amounts during heme biosynthesis. The final reaction in the biosynthetic pathway of heme is the chelation of iron with protoporphyrin. During periods of iron insufficiency or impaired iron utilization, zinc becomes an alternative metal substrate for ferrochelatase, leading to increased ZnPP formation. Evidence suggests that this metal substitution is one of the first biochemical responses to iron depletion, causing increased ZnPP to appear in circulating erythrocytes. Because this zinc-for-iron substitution occurs predominantly within the bone marrow, the ZnPP/heme ratio in erythrocytes reflects iron status in the bone marrow. In addition, ZnPP may regulate heme catabolism through competitive inhibition of heme oxygenase, the rate-limiting enzyme in the heme degradation pathway that produces bilirubin and carbon monoxide. Physiological roles, especially relating to carbon monoxide and possibly nitric oxide production, have been suggested for ZnPP. Clinically, ZnPP quantification is valuable as a sensitive and specific tool for evaluating iron nutrition and metabolism. Diagnostic determinations are applicable in a variety of clinical settings, including pediatrics, obstetrics, and blood banking. ZnPP analytical methodologies for clinical studies are discussed. In addition to diagnostic tests and metabolic studies, ZnPP has a potential therapeutic application in controlling bilirubin formation in neonates as a preventive measure for hyperbilirubinemia. Biochemical research techniques, both in vivo and in vitro, are described for further studies into the role of ZnPP in metabolism and physiology.

Differential effects of metalloporphyrins on messenger RNA levels of delta-aminolevulinate synthase and heme oxygenase. Studies in cultured chick embryo liver cells

The acute porphyrias in relapse are commonly treated with intravenous heme infusion to decrease the activity of delta-aminolevulinic acid synthase, normally the rate-controlling enzyme in heme biosynthesis. The biochemical effects of heme treatment are short-lived, probably due in part to heme-mediated induction of heme oxygenase, the rate-controlling enzyme for heme degradation. In this work, selected nonheme metalloporphyrins were screened for their ability to reduce delta-aminolevulinic acid synthase mRNA and induce heme oxygenase mRNA in chick embryo liver cell cultures. Of the metalloporphyrins tested, only zinc-mesoporphyrin reduced delta-aminolevulinic acid synthase mRNA without increasing heme oxygenase mRNA. The combination of zinc-mesoporphyrin and heme, at nanomolar concentrations, decreased delta-aminolevulinic acid synthase mRNA in a dose-dependent manner. The combination of zinc-mesoporphyrin (50 nM) and heme (200 nM) decreased the half-life of the mRNA for delta-aminolevulinic acid synthase from 5.2 to 2.5 h, while a similar decrease was produced by heme (10 microM) alone (2.2 h). The ability of zinc-mesoporphyrin to supplement the reduction of delta-aminolevulinic acid synthase mRNA by heme, in a process similar to that observed with heme alone, provides a rationale for further investigation of this compound for eventual use as a supplement to heme therapy of the acute porphyrias and perhaps other conditions in which heme may be of benefit.

Induction of heme oxygenase in intestinal epithelial cells: studies in Caco-2 cell cultures

Enterally administered, heme is a good source of iron in humans and other animals, but the metabolism of heme by enterocytes has not been fully characterized. Caco-2 cells in culture provide a useful model for studying cells that resemble small intestinal epithelium, both morphologically and functionally. In this paper we show that heme oxygenase, the rate-controlling enzyme of heme catabolism, is present in abundance in Caco-2 cells, and that levels of its mRNA and activity can be increased by exposure of the cells to heme or metal ions (cadmium, cobalt). Caco-2 cells also contain biliverdin reductase activity which, in the basal state, is similar to that of heme oxygenase (approximately 40 pmole of product per mg protein per minute); however, when heme oxygenase is induced, biliverdin reductase may become rate-limiting for bilirubin production.

Inhibition of heme oxygenase after oral vs intraperitoneal administration of chromium porphyrins

The effects of chromium porphyrins on suckling rat heme oxygenase activity were compared following oral vs intraperitoneal dosing. Chromium protoporphyrin (CrPP), chromium mesoporphyrin (CrMP), or chromium deuteroporphyrin 2,4 bis glycol (CrBG) were administered at 40 mumol/kg to 2-week old suckling rats either orally or intraperitoneally. Six hours after intraperitoneal dosing, CrPP and CrMP had significantly reduced hepatic and splenic heme oxygenase activity by more than 55%. CrBG effectively reduced hepatic heme oxygenase activity by 42%. More importantly, only CrMP was an effective inhibitor of hepatic heme oxygenase activity 6 hr after oral administration. In the first reported comparison of chromium porphyrin efficacy in vivo, our data suggest that chromium porphyrins, and particularly CrMP, may be effective in chemopreventive strategies for the treatment of neonatal jaundice.