Induction of heme oxygenase-1 by phenylarsine oxide. Studies in cultured primary liver cells.

Heme oxygenase-1, the major inducible isoform of heme oxygenase (HO), can be induced by heme and numerous other physical and chemical factors, many of which cause cellular 'stress'. This has led to the realization that HO-1 is a major highly conserved stress or heat shock protein. Recent work has implicated activation of mitogen-activated protein kinases and other kinases in the mechanism of induction of HO-1, and suggested that signal transduction pathways through tyrosine kinases are involved in induction of HO-1 gene expression by stress inducers. We hypothesized that phenylarsine oxide (PAO), an inhibitor of protein tyrosine phosphatases (PTPs), might up-regulate the HO-1 gene. Here, we show that a remarkably brief (1-15 min) exposure of normal hepatocytes to low concentrations (0.5-3 microM) of PAO produces a marked increase in mRNA and protein of HO-1. This increase is comparable to the level obtained by addition of heme (20 microM), and occurs without producing changes in cellular glutathione levels or stabilization of HO-1 message. Preincubation of cells with inhibitors of protein synthesis decreased the ability of PAO to increase levels of HO-1 mRNA, suggesting that the inductive effect requires de novo protein synthesis. Addition of thiol donors abrogated the PAO-mediated induction of HO-1 in a dose dependent fashion. Addition of genistein, a tyrosine kinase inhibitor, blunted the induction produced by both PAO and heme. After brief incubations with PAO or heme, cell extracts showed comparable increases in levels of protein tyrosine phosphorylation in general, and specifically in ZAP70 kinase. Our results are consistent with the proposition that induction of HO-1 by PAO involves inhibition of specific PTP(s), and that the mechanisms of induction of HO-1 by PAO and by heme may share some common pathways.

Effects of antidepressants and benzodiazepine-type anxiolytic agents on hepatic porphyrin accumulation in primary cultures of chick embryo liver cells.

Patients with any of the acute porphyrias may suffer from acute attacks. If these patients are treated with certain drugs, such as barbiturates, the likelihood of developing an attack is increased. Patients treated with antidepressants or benzodiazepine-type anxiolytics also could be placed at increased risk of developing porphyric attacks because little is known about the potential for some of these drugs to induce attacks. Primary cultures of chick embryo liver cells were used to study the effects of selected antidepressants and anxiolytics on porphyrin accumulation. Cells were treated with desferrioxamine (to partially block heme synthesis, simulating conditions encountered in porphyric patients) and increasing concentrations (3.16-1000 microM) of the evaluated drugs. Twenty hours later, porphyrin accumulation was measured. The drugs included four antidepressants and five benzodiazepine-type anxiolytics. The antidepressants bupropion and nefazodone significantly increased porphyrin accumulation when given with desferrioxamine, whereas neither fluoxetine nor paroxetine increased porphyrin accumulation. The benzodiazepine-type anxiolytic agents oxazepam, lorazepam, diazepam, triazolam, and midazolam all significantly increased porphyrin accumulation when given with desferrioxamine. Dose-response studies showed that diazepam, midazolam, and triazolam produced significant increases even at the lowest concentration tested (3.16 microM), whereas lorazepam and oxazepam required higher concentrations (>/=10 microM). These studies suggest that patients with acute porphyrias may be at greater risk for developing porphyric attacks when treated with bupropion or nefazodone compared with fluoxetine or paroxetine, and that the evaluated benzodiazepine derivatives should be administered with caution. Among the latter, low doses of lorazepam and oxazepam may be safer than those of diazepam, midazolam, and triazolam.

Effects of selected antihypertensives and analgesics on hepatic porphyrin accumulation: implications for clinical porphyria.

When patients with acute porphyrias are treated with antihypertensives and analgesics, they could be placed at increased risk of developing porphyric attacks, since little is known about the potential for many of these drugs to induce these attacks. We used primary chick embryo liver cells, which maintain intact heme synthesis and regulation, to study the effects of antihypertensives and analgesics on porphyrin accumulation. Cells were treated with desferrioxamine to block heme synthesis partially, simulating conditions encountered in porphyric patients. Typically, cells were treated for 20 hr with the test drugs (3.16 to 1000 microM), along with desferrioxamine. Porphyrins were measured spectrofluorometrically, as uro-, copro,- and protoporphyrin. The evaluated drugs included six antihypertensives (two calcium channel blockers, an angiotensin receptor antagonist, and three inhibitors of angiotensin converting enzyme) and eight analgesics. Of the calcium channel blockers tested, nifedipine greatly increased porphyrin accumulation, whereas diltiazem caused only a slight increase. Losartan (an angiotensin receptor antagonist), captopril, or lisinopril (two angiotensin converting enzyme inhibitors) produced only small increases in porphyrin accumulation. In contrast, enalapril (another angiotensin converting enzyme inhibitor) substantially increased porphyrin accumulation when given in high concentrations. Among the analgesics tested, fentanyl and tramadol produced the highest porphyrin accumulations. Nalbuphine, hydrocodone, oxycodone, and dezocine were moderately or weakly porphyrogenic, whereas buprenorphine and morphine did not increase porphyrin accumulation. These studies suggest that patients with acute porphyrias may be at greater risk for developing porphyric attacks when treated with nifedipine (compared with diltiazem), enalapril (compared with captopril or lisinopril), and tramadol (compared with the other analgesics).

Effects of new anticonvulsant medications on porphyrin synthesis in cultured liver cells: potential implications for patients with acute porphyria.

Some patients with acute hereditary porphyrias have seizures and require anticonvulsant therapy, but many anticonvulsants induce exacerbations of the hepatic porphyrias. Recently, several new anticonvulsants have become available. Among these are gabapentin, vigabatrin, felbamate, lamotrigine, and tiagabine. Little is known about their potential for induction of porphyric attacks. We used a cell culture model of primary chicken embryo liver cells, which maintain intact heme synthesis and regulation, to study the effects of these new anticonvulsants on porphyrin accumulation. Treatment of the cells with deferoxamine (250 microM) led to a partial block in heme synthesis, simulating the conditions encountered in human beings with porphyria. Concomitant exposure of these cells to phenobarbital (2 mM) strongly induced accumulation of porphyrins, serving as a positive control in this model. Cells were treated for 20 hours with increasing doses (3.2 to 1,000 microM) of the newer anticonvulsants, with or without deferoxamine. For most of these anticonvulsants 5 to 100 microM is representative of the concentrations achieved in humans with therapeutic doses. Porphyrins were measured spectrofluorometrically as uro-, copro-, and protoporphyrins. Results were confirmed by high-pressure liquid chromatography. Neither vigabatrin nor gabapentin treatment, with or without deferoxamine, led to any increase in porphyrin accumulation. Similar doses of felbamate (with deferoxamine) led to a marked increase in (mainly proto-) porphyrin levels, qualitatively and quantitatively almost identical to the accumulation produced by phenobarbital. Lamotrigine or tiagabine (with deferoxamine) caused similar porphyrin accumulation. Tiagabine treatment up to 100 microM (with deferoxamine) also resulted in very high levels of predominantly proto-porphyrin. In contrast to the other anticonvulsants tested, tiagabine without deferoxamine led to mild porphyrin accumulation. In the presence of deferoxamine, phenobarbital, felbamate, lamotrigine, or tiagabine, but not gabapentin or vigabatrin, increased levels of the mRNA of ALA synthase, the first and rate-controlling enzyme of porphyrin synthesis. Such enzyme induction is a sine qua non for acute porphyric attacks. We conclude that neither vigabatrin nor gabapentin is porphyrogenic, whereas felbamate, lamotrigine, and, especially, tiagabine lead to much accumulation of porphyrins. The latter three anticonvulsants, therefore, may precipitate or exacerbate acute porphyric attacks in humans. We recommend use of vigabatrin or gabapentin, but not felbamate, lamotrigine, or tiagabine, in patients with acute porphyria and seizures.

Regulation of expression of the human heme oxygenase-1 gene in transfected chick embryo liver cell cultures.

Induction of heme oxygenase (HO) has been proposed as a protective cellular mechanism against oxidative damage. In previous work (Tyrrell et al., Carcinogenesis [1993] 14, 761-765), portions of the 5' promoter region of the human HO-1 gene linked to the reporter gene chloramphenicol acetyl transferase (CAT), had been transiently expressed in HeLa cells. To extend the study of human HO gene expression into primary liver cells, these reporter gene fusion constructs, containing 121 or 1416 base pairs of the untranscribed 5'-upstream sequences of the human HO-1 gene, were used along with pSV beta-Gal plasmid to dually transfect primary cultures of chick embryo liver cells (CELC). The transfected cells were treated with selected metals, heme, phorbol ester, and chemical agents that produce oxidative stress (H2O2 or sodium arsenite). Reporter gene activities were measured 18-20 h later. Our major findings are: (1) these HO-CAT constructs were expressed in CELC; (2) unlike HeLa cells, the expression of CAT was detected in CELC without the need for the SV40 enhancer; (3) sodium arsenite and cobalt chloride induced the expression of the HO-CAT constructs whereas heme had no effect on or decreased CAT expression for all of the transfected constructs; (4) study of endogenous chick HO-1 gene expression in CELC showed that HO-1 responded to sodium arsenite treatment in a dose-dependent fashion, and the response was rapid and transient. We conclude that, in chick liver cell cultures, induction of the HO-1 gene by heme is fundamentally different from that produced by transition metals or sodium arsenite. Furthermore, the results suggest that expression of the HO-1 gene is highly conserved across species.

Mechanism of induction of heme oxygenase by metalloporphyrins in primary chick embryo liver cells: evidence against a stress-mediated response.

Heme oxygenase catalyzes the first and rate-controlling step in heme catabolism. One of the two forms of heme oxygenase (heme oxygenase-1) has been shown to be increased by heme, metals, and in some systems, by certain environmental stresses. However, it remains uncertain whether heme induces hepatic heme oxygenase-1 by a general stress response, or a specific heme-dependent cellular response. The work communicated here explores this issue by examining possible mechanisms whereby heme and other metalloporphyrins induce heme oxygenase-1 in normal liver cells. Primary cultures of chick embryo liver cells were tested for their ability to increase heme oxygenase mRNA after exposure to selected metalloporphyrins (heme, chromium mesoporphyrin, cobalt protoporphyrin and manganese protoporphyrin). The ability of antioxidants to decrease metalloporphyrin-mediated induction of heme oxygenase-1 mRNA was also tested. Our results indicate that: 1) the increase in heme oxygenase-1 mRNA mediated by heme or other metalloporphyrins may involve a short-lived protein(s) since the increase was prevented by several inhibitors of protein synthesis; and 2) in normal liver cells, heme-dependent oxidative stress does not play a key role in the heme-mediated induction of heme oxygenase-1. We conclude that heme and other non-heme metalloporphyrins induce heme oxygenase-1 through a mechanism requiring protein synthesis, not because metalloporphyrins increase cellular oxidative or other stress.

Hepatic 5-aminolevulinic acid synthase mRNA stability is modulated by inhibitors of heme biosynthesis and by metalloporphyrins.

Hepatic 5-aminolevulinic acid synthase, the first and normally rate-controlling enzyme of heme biosynthesis, is regulated by heme. One of the known mechanisms whereby increased cellular heme regulates 5-aminolevulinic acid synthase is by decreasing the stability of its mRNA. In primary cultures of chick embryo liver cells, we tested whether a decrease in cellular heme might increase 5-aminolevulinic acid synthase mRNA stability and whether heme or other metalloporphyrins could reverse this stabilization. We found that: (a) The stability of 5-aminolevulinic acid synthase mRNA was markedly increased by inhibitors of heme biosynthesis, namely, 4,6-dioxoheptanoic acid or deferoxamine; (b) This increased stability of 5-aminolevulinic acid synthase mRNA was reversed by the addition of heme (10 microM) or by the combination of zinc mesoporphyrin (50 nM), an inhibitor of heme oxygenase, and heme (200 nM); (c) Repression of 5-aminolevulinic acid synthase mRNA levels by zinc mesoporphyrin (10 microM) was due to inhibition of heme oxygenase, rather than a direct, heme-like, effect of zinc mesoporphyrin on 5-aminolevulinic acid synthase mRNA; (d) Among the several non-heme metalloporphyrins tested, only zinc mesoporphyrin and chromium mesoporphyrin significantly decreased 5-aminolevulinic acid synthase mRNA without increasing heme oxygenase mRNA.

Induction of heme oxygenase-1 in LMH cells. Comparison of LMH cells to primary cultures of chick embryo liver cells.

Heme oxygenase catalyzes the degradation of heme into biliverdin, carbon monoxide, and iron. Two forms of this enzyme, heme oxygenase-1 and -2, have been identified; only heme oxygenase-1 is subject to induction by heme, metal ions, and other chemical and physical perturbations (e.g. drugs, oxidants, and heat shock). Primary chick embryo liver cells are widely used for the study of heme metabolism because of their ease of preparation, low cost, and high degree of similarity to human heme metabolism. Nonetheless, this system has some limitations: new cultures must be prepared every week; the resulting cell populations are non-homogeneous; and cells are short-lived, limiting the feasible duration of time course and transfection studies. LMH cells are the first chicken hepatoma cell line to be established. The aim of this study was to characterize the regulation of heme oxygenase-1 in LMH cells, and to compare this regulation to that previously described in primary chick embryo liver cells. The induction of heme oxygenase-1 was assessed by measuring changes in mRNA levels or enzyme activities in response to several treatments, including heme, heavy metals, sodium arsenite, and heat shock, which have been shown to increase the expression of heme oxygenase. Similarities were observed with respect to regulation of heme oxygenase-1 expression in primary hepatocytes and LMH cells. We report the first measurable heat shock response of heme oxygenase-1 in CELC or LMH cells; and show that LMH cells are a useful model for the study of heme oxygenase-1 regulation.

Chitovibrin: a chitin-binding lectin from Vibrio parahemolyticus.

A novel 134 kDa, calcium-independent chitin-binding lectin, 'chitovibrin', is secreted by the marine bacterium Vibrio parahemolyticus, inducible with chitin or chitin-oligomers. Chitovibrin shows no apparent enzymatic activity but exhibits a strong affinity for chitin and chito-oligomers > dp9. The protein has an isoelectric pH of 3.6, shows thermal tolerance, binds chitin with an optimum at pH 6 and is active in 0-4 M NaCl. Chitovibrin appears to be completely different from other reported Vibrio lectins and may function to bind V. parahemolyticus to chitin substrates, or to capture or sequester chito-oligomers. It may be a member of a large group of recently described proteins in Vibrios related to a complex chitinoclastic (chitinivorous) system.

Thermostable, salt tolerant, wide pH range novel chitobiase from Vibrio parahemolyticus: isolation, characterization, molecular cloning, and expression.

A chitobiase gene from Vibrio parahemolyticus was cloned into plasmid pUC18 in Escherichia coli strain DH5 alpha. The plasmid construct, pC120, contained a 6.4 kb Vibrio DNA insert. The recombinant gene expressed chitobiase [EC 3.2.1.30] activity similar to that found in the native Vibrio. The enzyme was purified by ion exchange, hydroxylapatite and gel permeation chromatographies, and exhibited an apparent molecular weight of 80 kDa on SDS-polyacrylamide gel electrophoresis. Chitobiose and 6 more substrates, including beta-N-acetyl galactosamine glycosides, were hydrolyzed by the recombinant chitobiase, indicating its putative classification as an hexosaminidase [EC 3.2.1.52]. The enzyme was resistant to denaturation by 2 M NaCl, thermostable at 45 degrees C and active over a very unusual (for glycosyl hydrolases) pH range, from 4 to 10. The purified cloned chitobiase gave 4 closely focussed bands on an isoelectric focusing gel, at pH 4 to 6.5. The N-terminal 43 amino acid sequence shows no homology with other proteins in commercial databanks or in the literature, and from its N-terminal sequence, appears to be a novel protein, unrelated in sequence to chitobiases from other Vibrios reported and unrelated to hexosaminidases from other organisms.