Limited heme synthesis in porphobilinogen deaminase-deficient mice impairs transcriptional activation of specific cytochrome P450 genes by phenobarbital

Effects of dietary 5-aminolevulinic acid on growth performance and nonspecific immunity of Litopenaeus vannamei, as determined by transcriptomic analysis

5-aminolevulinic acid (5-ALA) is an endogenous non-protein amino acid that is frequently used in modern agriculture. This study set out to determine how dietary 5-ALA affected the nonspecific immunity and growth performance of Litopenaeus vannamei. The shrimp were supplemented with dietary 5-ALA at 0, 15, 30, 45, and 60 mg/kg for three months. Transcriptome data of the control group and the group supplemented with 45 mg/kg dietary 5-ALA were obtained using transcriptome sequencing. 592 DEGs were identified, of which 426 were up-regulated and 166 were down-regulated. The pathways and genes associated with growth performance and nonspecific immunity were confirmed using qRT-PCR. The highest survival rate, body length growth rate, and weight gain values were observed in shrimp fed diets containing 45 mg/kg 5-ALA. L. vannamei in this group had a significantly higher total hemocyte count, phagocytosis rate and respiratory burst value than those in the control group. High doses of dietary 5-ALA (45 mg/kg, 60 mg/kg) significantly increased the activities of catalase, superoxide dismutase, oxidized glutathione, glutathione-peroxidase, phenoloxidase, lysozyme, acid phosphatase, and alkaline phosphatase. At the transcriptional level, dietary 5-ALA significantly up-regulated the expression levels of antioxidant immune-related genes. The optimal concentration of 5-ALA supplementation was 39.43 mg/kg, as indicated by a broken line regression. Our study suggested that dietary 5-ALA positively impacts the growth and nonspecific immunity of L. vannamei, providing a novel theoretical basis for further research into 5-ALA as a dietary supplement.

Pathogenesis of acute encephalopathy in acute hepatic porphyria

Acute encephalopathy (AE) can be a manifestation of an acute porphyric attack. Clinical data were studied in 32 patients during AE with or without polyneuropathy (PNP) together with 12 subjects with PNP but no AE, and 17 with dysautonomia solely. Brain neuroimaging was done in 20 attacks during AE, and PEPT2 polymorphisms were studied in 56 subjects, 24 with AE. AE manifested as a triad of seizures, confusion and/or blurred vision. Symptoms lasting 1-5 days manifested 3-19 days from the onset of an attack. 55% of these patients had acute PNP independent of AE. Posterior reversible encephalopathy syndrome (PRES) was detected in 42% of the attacks. These patients were severely affected and hyponatremic (88%). Reversible segmental vasoconstriction was rare. There was no statistical difference in hypertension or urinary excretion of porphyrin precursors among the patients with or without AE. In 94% of the attacks with AE, liver transaminases were elevated significantly (1.5 to fivefold, P = 0.034) compared to a normal level in 87% of the attacks with dysautonomia, or in 25% of patients with PNP solely. PEPT2*2/2 haplotype was less common among patients with AE than without (8.3% vs. 25.8%, P = 0.159) and in patients with PNP than without (9.5% vs. 22.9%, P = 0.207), suggesting a minor role, if any, in acute neurotoxicity. In contrast, PEPT2*2/2 haplotype was commoner among patients with chronic kidney disease (P = 0.192). Acute endothelial dysfunction in porphyric encephalopathy could be explained by a combination of abrupt hypertension, SIADH, and acute metabolic and inflammatory factors of hepatic origin.

Endothelial Dysfunction in Acute Hepatic Porphyrias

Background Acute hepatic porphyrias (AHPs) are a group of rare diseases caused by dysfunctions in the pathway of heme biosynthesis. Although acute neurovisceral attacks are the most dramatic manifestations, patients are at risk of developing long-term complications, several of which are of a vascular nature. The accumulation of non-porphyrin heme precursors is deemed to cause most clinical symptoms. Aim We measured the serum levels of endothelin-1 (ET-1) and nitric oxide (NO) to assess the presence of endothelial dysfunction (ED) in patients with AHPs. Forty-six patients were classified, according to their clinical phenotype, as symptomatic (AP-SP), asymptomatic with biochemical alterations (AP-BA), and asymptomatic without biochemical alterations (AP-AC). Results Even excluding those under hemin treatment, AP-SP patients had the lowest NO and highest ET-1 levels, whereas no significant differences were found between AP-BA and AP-AC patients. AP-SP patients had significantly more often abnormal levels of ED markers. Patients with the highest heme precursor urinary levels had the greatest alterations in ED markers, although no significant correlation was detected. Conclusions ED is more closely related to the clinical phenotype of AHPs than to their classical biochemical alterations. Some still undefined disease modifiers may possibly determine the clinical picture of AHPs through an effect on endothelial functions.

Mechanisms of Neuronal Damage in Acute Hepatic Porphyrias

Porphyrias are a group of congenital and acquired diseases caused by an enzymatic impairment in the biosynthesis of heme. Depending on the specific enzyme involved, different types of porphyrias (i.e., chronic vs. acute, cutaneous vs. neurovisceral, hepatic vs. erythropoietic) are described, with different clinical presentations. Acute hepatic porphyrias (AHPs) are characterized by life-threatening acute neuro-visceral crises (acute porphyric attacks, APAs), featuring a wide range of neuropathic (central, peripheral, autonomic) manifestations. APAs are usually unleashed by external "porphyrinogenic" triggers, which are thought to cause an increased metabolic demand for heme. During APAs, the heme precursors δ-aminolevulinic acid (ALA) and porphobilinogen (PBG) accumulate in the bloodstream and urine. Even though several hypotheses have been developed to explain the protean clinical picture of APAs, the exact mechanism of neuronal damage in AHPs is still a matter of debate. In recent decades, a role has been proposed for oxidative damage caused by ALA, mitochondrial and synaptic ALA toxicity, dysfunction induced by relative heme deficiency on cytochromes and other hemeproteins (i.e., nitric oxide synthases), pyridoxal phosphate functional deficiency, derangements in the metabolic pathways of tryptophan, and other factors. Since the pathway leading to the biosynthesis of heme is inscribed into a complex network of interactions, which also includes some fundamental processes of basal metabolism, a disruption in any of the steps of this pathway is likely to have multiple pathogenic effects. Here, we aim to provide a comprehensive review of the current evidence regarding the mechanisms of neuronal damage in AHPs.

Changes of gut microbiota in pregnant sows induced by 5-Aminolevulinic acid

Sow health is related to farm productivity and sustainability, but the increased resistance of bacteria to antibiotics in the pig industry has led to a decline in resistance to disease and environmental pollution. 5-Aminolevulinic acid (5-ALA) is considered a feed additive to replace antibiotics, but the effect of 5-ALA on gut microbiota has not been studied. In this study, we fed 12 healthy Landrace × Large White two-line hybrid sows with different concentrations of 5-ALA; blood and fecal samples were obtained after 110 days of pregnancy, and 16S rRNA amplicon sequencing was performed. The alpha diversity of the gut microbiota in sows was not significant among the sows fed different concentrations of 5-ALA. PCoA revealed a significant (P < 0.05) difference in the gut microbiota composition with different 5-ALA groups. LEfSe revealed that 5-ALA increased relative abundance of Streptococcus, while Myroides was enriched in CK group. Functional prediction of Tax4Fun showed that different concentrations of 5-ALA significantly (P < 0.05) increased the mean relative abundance of KEGG pathways involved in core microbiota cellular processes, environmental information processing, and genetic information processing. In summary, 5-ALA changed bacterial community composition of gut microbiota, reduced colonization of some pathogenes and increased the relative abundance of some probiotics. These results provide a theoretical basis for the healthy breeding of pigs.

Genome-wide identification, characterisation and expression analysis of the ALAS gene in the Yesso scallop (Patinopecten yessoensis) with different shell colours

Porphyrins, one of the most common shell pigments, are by-products of the haem pathway. 5-Aminolaevulinate synthase (ALAS) is the first and rate-limiting enzyme in this pathway and has been well studied in vertebrate species. However, the function of ALAS in shell colouration has been poorly studied in molluscs, which are renowned for their colourful shells. In the present study, an ALAS gene, named PyALAS, was identified through whole-genome scanning in the Yesso scallop (Patinopecten yessoensis), an economically and evolutionarily important bivalve species in which the shell colour represents polymorphism. Two conserved domains were detected in the PyALAS protein sequence, including a Preseq-ALAS domain and a 5-ALAS domain, confirming the identification of PyALAS. Phylogenetic analysis of the ALAS proteins among various invertebrate and vertebrate species revealed a high consistency between the molecular evolution of ALAS and the species taxonomy. PyALAS was ubiquitously expressed in most adult tissues of the Yesso scallop. The left mantle expressed a significantly higher level of PyALAS than the right side in brown scallops, whereas there was no significant difference in white scallops. Significantly different expression levels of PyALAS was also detected between the two different shell colour strains. These data indicate that PyALAS plays an important role in shell colouration in Yesso scallops and the present study provides new insights into the molecular mechanism of shell colouration in molluscs.

Molecular cloning, characterization and gene expression analysis of aminolevulinic acid synthase in Litopenaeus vannamei

5-Aminolevulinic acid synthase (ALAS) is the rate-limiting enzyme in the biosynthesis of heme, a prosthetic group that is found in hemoproteins, including those involved in molting. To better understand the roles of ALAS in L. vannamei (LvALAS), we analyzed its sequence and tissue distribution, the effects of age and bacterial infection on its gene expression, and the effects of LvALAS gene silencing. We also examined the expressions of three hemoproteins, the cytochrome oxidase subunit I (COX I) and subunit IV (COX IV) and catalase. Three LvALAS splicing variants were found in the hepatopancreas, with the main splicing variant having an open reading frame that encodes 532 aa. LvALAS transcripts were found in each of the eleven tissues tested in this study, with the highest gene expression in the intestine. The transcript abundances of LvALAS, COX I and COX IV in the hepatopancreas and stomach tended to decrease with age. LvALAS and catalase gene expressions significantly increased in the stomach after V. parahaemolyticus infection. LvALAS gene expression in the hepatopancreas, stomach and intestine (12- and 24-hours post-injection) was relatively lower in dsALAS-injected shrimp than in PBS-injected shrimp. All the PBS-injected shrimp molted after 8-10 days while no molting activity was observed in the dsALAS-injected shrimp group within the 14 days post-injection period. Our results provide evidence that (1) only the housekeeping form of ALAS exists in L. vannamei; LvALAS gene expression (2) decreases with age and (3) increases after bacterial infection; and (4) an ALAS-dependent pathway is necessary for proper molting in L. vannamei.

Sex differences in vascular reactivity in mesenteric arteries from a mouse model of acute intermittent porphyria

BACKGROUND AND AIMS

Acute intermittent porphyria (AIP) results from a partial deficiency of porphobilinogen deaminase (PBGD). Symptomatic AIP patients, most of whom are women, experience acute attacks characterized by severe abdominal pain and abrupt increases in blood pressure. Here, we characterized the reactivity of mesenteric arteries from male and female AIP mice with ~30% of normal PBGD activity and wild type C57BL/6 mice.

METHODS

An acute porphyric attack was induced in AIP mice by treatment with phenobarbital. Vascular responses to K⁺, phenylephrine (PE), acetylcholine (ACh), and hemin were determined (Wire Multi Myograph).

RESULTS

Maximal contraction to PE was increased in arteries from male and female AIP mice (p < .05) during an induced attack of acute porphyria. Female AIP arteries had increased sensitivity to PE (p < .05) even after nitric oxide (NO) blockade with N_ω-nitro-L-arginine methyl ester (L-NAME) (p < .05). Maximal relaxation to ACh was similar in males and females with lower sensitivity in female AIP arteries (p < .05). Hemin induced greater relaxation in AIP arteries in both males and females (p < .05).

SUMMARY/CONCLUSIONS

Sex differences in this AIP mouse model include a pro-contractile response in females. These alterations may contribute to the increased blood pressure during an acute attack and provide a novel mechanism of action whereby heme ameliorates the attacks.

Characterization of the hepatic transcriptome following phenobarbital induction in mice with AIP

Acute Intermittent Porphyria (AIP), an autosomal dominant hepatic disorder, results from hydroxymethylbilane synthase (HMBS) mutations that decrease the encoded enzymatic activity, thereby predisposing patients to life-threatening acute neurovisceral attacks. The ~1% penetrance of AIP suggests that other genetic factors modulate the onset and severity of the acute attacks. Here, we characterized the hepatic transcriptomic response to phenobarbital (PB) administration in AIP mice, which mimics the biochemical attacks of AIP. At baseline, the mRNA profiles of 14,138 hepatic genes prior to treatment were remarkably similar between AIP and the congenic wild-type (WT) mice. After PB treatment (~120 mg/kg x 3d), 1347 and 1120 genes in AIP mice and 422 and 404 genes in WT mice were uniquely up- and down-regulated, respectively, at a False Discovery Rate < 0.05. As expected, the ALAS1 expression increased 4.5-fold and 15.9-fold in the WT and AIP mice, respectively. ALA-dehydrogenase also was induced ~1.7-fold in PB-induced AIP mice, but was unchanged in PB-induced WT mice. There was no statistically significant difference in the overall expression of 155 hepatic cytochrome P450 enzymes, although Cyp2c40, Cyp2c68, Cyp2c69, Mgst3 were upregulated only in PB-induced AIP mice (>1.9-fold) and Cyp21a1 was upregulated only in PB-induced WT mice (>9-fold). Notably, the genes differentially expressed in induced AIP mice were enriched in circadian rhythm, mitochondria biogenesis and electron transport, suggesting these pathways were involved in AIP mice responding to PB treatment. These results advance our understanding of the hepatic metabolic changes in PB-induced AIP mice and have implications in the pathogenesis of AIP acute attacks.

Effects of 5-Aminolevulinic Acid on Gene Expression, Immunity, and ATP Levels in Pacific White Shrimp, Litopenaeus vannamei

With the emergence of several infectious diseases in shrimp aquaculture, there is a growing interest in the use of feed additives to enhance shrimp immunity. Recently, the use of 5-aminolevulinic acid (5-ALA), a non-protein amino acid that plays a rate-limiting role in heme biosynthesis, has received attention for its positive effect on immunity in livestock animals. To evaluate the effect of 5-ALA in the Pacific white shrimp, Litopenaeus vannamei, we conducted microarray analysis, a Vibrio parahaemolyticus immersion challenge test, an ATP level assay, and gene expression analysis of some hemoproteins and genes associated with heme synthesis and degradation. Out of 15,745 L. vannamei putative genes on the microarray, 101 genes were differentially expressed by more than fourfold (p < 0.05) between 5-ALA-supplemented and control shrimp hepatopancreas. 5-ALA upregulated 99 of the 101 genes, 41 of which were immune- and defense-related genes based on sequence homology. Compared to the control, the 5-ALA-supplemented group had a higher survival rate in the challenge test, higher transcript levels of porphobilinogen synthase, ferrochelatase, catalase, nuclear receptor E75, and heme oxygenase-1 and higher levels of ATP. These findings suggest that dietary 5-ALA enhanced the immune response of L. vannamei to V. parahaemolyticus, upregulated immune- and defense-related genes, and enhanced aerobic energy metabolism, respectively. Further studies are needed to elucidate the extent of 5-ALA use in shrimp culture.

Effects of volatile anaesthetics on heme metabolism in a murine genetic model of Acute Intermittent Porphyria. A comparative study with other porphyrinogenic drugs

BACKGROUND

Acute Intermittent Porphyria (AIP) is an inherited disease produced by a deficiency of Porphobilinogen deaminase (PBG-D). The aim of this work was to evaluate the effects of Isoflurane and Sevoflurane on heme metabolism in a mouse genetic model of AIP to further support our previous proposal for avoiding their use in porphyric patients. A comparative study was performed administering the porphyrinogenic drugs allylisopropylacetamide (AIA), barbital and ethanol, and also between sex and mutation using AIP (PBG-D activity 70% reduced) and T1 (PBG-D activity 50% diminished) mice.

METHODS

The activities of 5-Aminolevulinic synthetase (ALA-S), PBG-D, Heme oxygenase (HO) and CYP2E1; the expression of ALA-S and the levels of 5-aminolevulinic acid (ALA) were measured in different tissues of mice treated with the drugs mentioned.

RESULTS

Isoflurane increased liver, kidney and brain ALA-S activity of AIP females but only affected kidney AIP males. Sevoflurane induced ALA-S activity in kidney and brain of female AIP group. PBG-D activity was further reduced by Isoflurane in liver male T1; in AIP male mice activity remained in its low basal levels. Ethanol and barbital also caused biochemical alterations. Only AIA triggered neurological signs similar to those observed during human acute attacks in male AIP being the symptoms less pronounced in females although ALA-S induction was greater. Heme degradation was affected.

DISCUSSION

Biochemical alterations caused by the porphyrinogenic drugs assayed were different in male and female mice and also between T1 and AIP being more affected the females of AIP group.

GENERAL SIGNIFICANCE

This is the first study using volatile anaesthetics in an AIP genetic model confirming Isoflurane and Sevoflurane porphyrinogenicity.

Transcriptional analysis of the conidiation pattern shift of the entomopathogenic fungus Metarhizium acridum in response to different nutrients

Background

Most fungi, including entomopathogenic fungi, have two different conidiation patterns, normal and microcycle conidiation, under different culture conditions, eg, in media containing different nutrients. However, the mechanisms underlying the conidiation pattern shift are poorly understood.

Results

In this study, Metarhizium acridum undergoing microcycle conidiation on sucrose yeast extract agar (SYA) medium shifted to normal conidiation when the medium was supplemented with sucrose, nitrate, or phosphate. By linking changes in nutrients with the conidiation pattern shift and transcriptional changes, we obtained conidiation pattern shift libraries by Solexa/Illumina deep-sequencing technology. A comparative analysis demonstrated that the expression of 137 genes was up-regulated during the shift to normal conidiation, while the expression of 436 genes was up-regulated at the microcycle conidiation stage. A comparison of subtractive libraries revealed that 83, 216, and 168 genes were related to sucrose-induced, nitrate-induced, and phosphate-induced conidiation pattern shifts, respectively. The expression of 217 genes whose expression was specific to microcycle conidiation was further analyzed by the gene expression profiling via multigene concatemers method using mRNA isolated from M. acridum grown on SYA and the four normal conidiation media. The expression of 142 genes was confirmed to be up-regulated on standard SYA medium. Of these 142 genes, 101 encode hypothetical proteins or proteins of unknown function, and only 41 genes encode proteins with putative functions. Of these 41 genes, 18 are related to cell growth, 10 are related to cell proliferation, three are related to the cell cycle, three are related to cell differentiation, two are related to cell wall synthesis, two are related to cell division, and seven have other functions. These results indicate that the conidiation pattern shift in M. acridum mainly results from changes in cell growth and proliferation.

Conclusions

The results indicate that M. acridum shifts conidiation pattern from microcycle conidiation to normal conidiation when there is increased sucrose, nitrate, or phosphate in the medium during microcycle conidiation. The regulation of conidiation patterning is a complex process involving the cell cycle and metabolism of M. acridum. This study provides essential information about the molecular mechanism of the induction of the conidiation pattern shift by single nutrients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2971-0) contains supplementary material, which is available to authorized users.

Functional coupling of ATP-binding cassette transporter Abcb6 to cytochrome P450 expression and activity in liver

Although endogenous mechanisms that negatively regulate cytochrome P450 (P450) monooxygenases in response to physiological and pathophysiological signals are not well understood, they are thought to result from alterations in the level of endogenous metabolites, involved in maintaining homeostasis. Here we show that homeostatic changes in hepatic metabolite profile in Abcb6 (mitochondrial ATP-binding cassette transporter B6) deficiency results in suppression of a specific subset of hepatic P450 activity. Abcb6 null mice are more susceptible to pentobarbital-induced sleep and zoxazolamine-induced paralysis, secondary to decreased expression and activity of Cyp3a11 and Cyp2b10. The knock-out mice also show decrease in both basal and xeno-inducible expression and activity of a subset of hepatic P450s that appear to be related to changes in hepatic metabolite profile. These data, together with the observation that liver extracts from Abcb6-deficient mice suppress P450 expression in human primary hepatocytes, suggest that this mouse model may provide an opportunity to understand the physiological signals and the mechanisms involved in negative regulation of P450s.

Effect of erythropoietin on hepatic cytochrome P450 expression and function in an adenine-fed rat model of chronic kidney disease

BACKGROUND AND PURPOSE

Erythropoietin (EPO) is used to treat anaemia associated with chronic kidney disease (CKD). Hypoxia is associated with anaemia and is known to cause a decrease in cytochrome P450 (P450) expression. As EPO production is regulated by hypoxia, we investigated the role of EPO on P450 expression and function.

EXPERIMENTAL APPROACH

Male Wistar rats were subjected to a 0.7% adenine diet for 4 weeks to induce CKD. The diet continued for an additional 2 weeks while rats received EPO by i.p. injection every other day. Following euthanasia, hepatic P450 mRNA and protein expression were determined. Hepatic enzyme activity of selected P450s was determined and chromatin immunoprecipitation was used to characterize binding of nuclear receptors involved in the transcriptional regulation of CYP2C and CYP3A.

KEY RESULTS

EPO administration decreased hepatic mRNA and protein expression of CYP3A2 (P < 0.05), but not CYP2C11. Similarly, EPO administration decreased CYP3A2 protein expression by 81% (P < 0.001). A 32% decrease (P < 0.05) in hepatic CYP3A enzymatic activity (Vmax ) was observed for the formation of 6βOH-testosterone in the EPO-treated group. Decreases in RNA pol II recruitment (P < 0.01), hepatocyte nuclear factor 4α binding (P < 0.05) and pregnane X receptor binding (P < 0.01) to the promoter region of CYP3A were also observed in EPO-treated rats.

CONCLUSIONS AND IMPLICATIONS

Our data show that EPO decreases the expression and function of CYP3A, but not CYP2C in rat liver.

Hepatocyte Transplantation Ameliorates the Metabolic Abnormality in a Mouse Model of Acute Intermittent Porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant disorder characterized by insufficient porphobilinogen deaminase (PBGD) activity. When hepatic heme synthesis is induced, porphobilinogen (PBG) and 5-aminolevulinic acid (ALA) accumulate, which causes clinical symptoms such as abdominal pain, neuropathy, and psychiatric disturbances. Our aim was to investigate if hepatocyte transplantation can prevent or minimize the metabolic alterations in an AIP mouse model. We transplanted wild-type hepatocytes into PBGD-deficient mice and induced heme synthesis with phenobarbital. ALA and PBG concentrations in plasma were monitored, and the gene transcriptions of hepatic enzymes ALAS1, PBGD, and CYP2A5 were analyzed. Results were compared with controls and correlated to the percentage of engrafted hepatocytes. The accumulation of ALA and PBG was reduced by approximately 50% after the second hepatocyte transplantation. We detected no difference in mRNA levels of PBGD, ALAS1, or CYP2A5. Engraftment corresponding to 2.7% of the total hepatocyte mass was achieved following two hepatocyte transplantations. A lack of precursor production in less than 3% of the hepatocytes resulted in a 50% reduction in plasma precursor concentrations. This disproportional finding suggests that ALA and PBG produced in PBGD-deficient hepatocytes crossed cellular membranes and was metabolized by transplanted cells. The lack of effect on enzyme mRNA levels suggests that no significant efflux of heme from normal to PBGD-deficient hepatocytes takes place. Further studies are needed to establish the minimal number of engrafted hepatocytes needed to completely correct the metabolic abnormality in AIP and whether amelioration of the metabolic defect by partial restoration of PBGD enzyme activity translates into a clinical effect in human AIP.

Heme and heme biosynthesis intermediates induce heme oxygenase-1 and cytochrome P450 2A5, enzymes with putative sequential roles in heme and bilirubin metabolism: different requirement for transcription factor nuclear factor erythroid- derived 2-like 2

Cytochrome P450 2A5 (CYP2A5) oxidizes bilirubin to biliverdin and represents a putative candidate for maintaining bilirubin at safe but adequate antioxidant levels. Curiously, CYP2A5 is induced by both excessive heme and chemicals that inhibit heme synthesis. We hypothesized that heme homeostasis is a key modifier of Cyp2a5 expression via transcription factor nuclear factor erythroid-derived 2-like 2 (Nrf2) and characterized the coordination of CYP2A5 and heme oxygenase-1 (HMOX1) responses using wild-type and Nrf2(-/-) primary mouse hepatocytes. HMOX1 was rapidly elevated by exogenous hemin, thereby limiting the transactivation of Cyp2a5 until high heme (> 5µM) exposure. Nrf2 was mandatory for CYP2A5 but not for HMOX1 induction by heme. CYP2A5 was intensively and HMOX1 moderately elevated in heme synthesis blockades by succinylacetone and N-methyl protoporphyrin IX, and Nrf2 partially mediated the induction of CYP2A5. Immunoelectron microscopy revealed that CYP2A5 is targeted Nrf2 dependently both to the endoplasmic reticulum (ER) and mitochondria. However, excessive heme increased CYP2A5 predominantly in the ER. Phenobarbital, dibutyryl-cAMP, and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) overexpression stimulate heme biosynthesis and induce CYP2A5. Acute but not chronic CYP2A5 induction by phenobarbital required Nrf2, whereas CYP2A5 induction by dibutyryl-cAMP and PGC-1α was potentiated by Nrf2 knockout. Collectively, heme homeostasis is established as a crucial regulator of hepatic Cyp2a5 expression mediated via Nrf2 activation, whereas Nrf2 is redundant for Hmox1 induction by heme. Similar subcellular targeting and coordination of CYP2A5 and HMOX1 responses suggest favorable conditions for enhanced CYP2A5-mediated bilirubin maintenance in altered heme homeostasis that predisposes to oxidative stress.

Early failure of N-methyl-D-aspartate receptors and deficient spine formation induced by reduction of regulatory heme in neurons

An initial stage of many neurodegenerative processes is associated with compromised synaptic function and precedes synapse loss, neurite fragmentation, and neuronal death. We showed previously that deficiency of heme, regulating many proteins of pharmacological importance, causes neurodegeneration of primary cortical neurons via N-methyl-d-aspartate receptor (NMDAR)-dependent suppression of the extracellular signal-regulated kinase 1/2 pathway. Here, we asked whether the reduction of heme causes synaptic perturbation before neurite fragmentation in neuronal cultures and investigated molecular mechanisms of synaptic dysfunction in these cells. We showed the change in the NR2B subunit phosphorylation that correlates with compromised NMDAR function after the reduction of regulatory heme and a rapid rescue of NR2B phosphorylation and NMDAR function by exogenous heme. Electrophysiological recordings demonstrated diminished NMDAR currents and NMDAR-mediated calcium influx after 24 h of inhibition of heme synthesis. These effects were reversed by treatment with heme; however, inhibition of the Src family kinases abolished the rescue effect of heme on NMDA-evoked currents. Diminished NMDAR current and Ca(2+) influx resulted in suppressed cGMP production and impairment of spine formation. Exogenous heme exerted rescue effects on NR2B tyrosine phosphorylation and NMDA-evoked currents within minutes, suggesting direct interactions within the NMDAR complex. These synaptic changes after inhibition of heme synthesis occurred at this stage without apparent dysfunction of major hemoproteins. We conclude that regulatory heme is necessary in maintaining NR2B phosphorylation and NMDAR function. NMDAR failure occurs before neurite fragmentation and may be a causal factor in neurodegeneration; this could suggest a route for an early pharmacological intervention.

Biphasic adaptative responses in VLDL metabolism and lipoprotein homeostasis during Gram-negative endotoxemia

Dyslipidemia and hepatic overproduction of very low density lipoprotein (VLDL) are hallmarks of the septic response, yet the underlying mechanisms are not fully defined. We evaluated the lipoprotein subclasses profile and hepatic VLDL assembly machinery over 24 h in fasted LPS-treated rats. The response of serum non-esterified fatty acids (NEFA) and glucose to endotoxin was biphasic, with increased levels of NEFA and hypoglycemia in the first 12 h-phase, and low NEFA and high glucose in the second 12 h-phase. Hypertriglyceridemia was more marked in the first 12 h (6.8-fold), when triglyceride abundance increased in all lipoprotein subclasses, and preferentially in large VLDL. The abundance of medium-sized VLDL and the increase in the number of VLDL particles was higher in the second phase (10-fold vs 5-fold in the first phase); however, apoB gene transcript abundance increased only in the second phase. Analysis of putative pre-translational mechanisms revealed that neither increased Apob transcription rate nor increased transcript binding to mRNA stabilizing HuR (Hu antigen R) protein paralleled the increase in apoB transcripts. In conclusion, endotoxin challenge induces increases in plasma NEFA and large, triglyceride-rich VLDL. After approximately 12 h, the triglyceride-rich VLDLs are replaced by medium-sized, triglyceride-poor VLDL particles. Hepatic apoB mRNA abundance also increases during the second period, suggesting a role for apoB protein expression in the acute reaction against sepsis.

Zonation of heme synthesis enzymes in mouse liver and their regulation by β-catenin and Ha-ras

Cytochrome P450 (CYP) hemoproteins play an important role in hepatic biotransformation. Recently, β-catenin and Ha-ras signaling have been identified as players controlling transcription of various CYP genes in mouse liver. The aim of the present study was to analyze the role of β-catenin and Ha-ras in the regulation of heme synthesis. Heme synthesis-related gene expression was analyzed in normal liver, in transgenic mice expressing activated β-catenin or Ha-ras, and in hepatomas. Regulation of the aminolevulinate dehydratase promoter was studied in vitro. Elevated expression of mRNAs and proteins involved in heme biosynthesis was linked to β-catenin activation in perivenous hepatocytes, in transgenic hepatocytes, and in hepatocellular tumors. Stimulation of the aminolevulinate dehydratase promoter by β-catenin was independent of the β-catenin/T-cell-specific transcription factor dimer. By contrast, activation of Ha-ras repressed heme synthesis-related gene expression. The present data suggest that β-catenin enhances the expression of both CYPs and heme synthesis-related genes, thus coordinating the availability of CYP apoprotein and its prosthetic group heme. The reciprocal regulation of heme synthesis by β-catenin and Ha-ras-dependent signaling supports our previous hypothesis that antagonistic action of these pathways plays a major role in the control of zonal gene expression in healthy mouse liver and aberrant expression patterns in hepatocellular tumors.

Cytochrome P450 regulation: the interplay between its heme and apoprotein moieties in synthesis, assembly, repair, and disposal

Heme is vital to our aerobic universe. Heme cellular content is finely tuned through an exquisite control of synthesis and degradation. Heme deficiency is deleterious to cells, whereas excess heme is toxic. Most of the cellular heme serves as the prosthetic moiety of functionally diverse hemoproteins, including cytochromes P450 (P450s). In the liver, P450s are its major consumers, with >50% of hepatic heme committed to their synthesis. Prosthetic heme is the sine qua non of P450 catalytic biotransformation of both endo- and xenobiotics. This well-recognized functional role notwithstanding, heme also regulates P450 protein synthesis, assembly, repair, and disposal. These less well-appreciated aspects are reviewed herein.

Hepatic heme-regulated inhibitor (HRI) eukaryotic initiation factor 2alpha kinase: a protagonist of heme-mediated translational control of CYP2B enzymes and a modulator of basal endoplasmic reticulum stress tone

We have reported previously that the hepatic heme-regulated inhibitor (HRI)-eukaryotic initiation factor 2 alpha (eIF2 alpha) kinase is activated in acute heme-deficient states, resulting in translational shut-off of global hepatic protein synthesis, including phenobarbital (PB)-mediated induction of CYP2B enzymes in rats. These findings revealed that heme regulates hepatic CYP2B synthesis at the translational level via HRI. As a proof of concept, we have now employed a genetic HRI-knockout (KO) mouse hepatocyte model. In HRI-KO hepatocytes, PB-mediated CYP2B protein induction is no longer regulated by hepatic heme availability and proceeds undeterred even after acute hepatic heme depletion. It is noteworthy that genetic ablation of HRI led to a small albeit significant elevation of basal hepatic endoplasmic reticulum (ER) stress as revealed by the activation of ER stress-inducible RNA-dependent protein kinase-like ER-integral (PERK) eIF2 alpha-kinase, and induction of hepatic protein ubiquitination and ER chaperones Grp78 and Grp94. Such ER stress was further augmented after PB-mediated hepatic protein induction. These findings suggest that HRI normally modulates the basal hepatic ER stress tone. Furthermore, because HRI exists in both human and rat liver in its heme-sensitive form and is inducible by cytochrome P450 inducers such as PB, these findings are clinically relevant to acute heme-deficient states, such as the acute hepatic porphyrias. Activation of this exquisitely sensitive heme sensor would normally protect cells by safeguarding cellular energy and nutrients during acute heme deficiency. However, similar HRI activation in genetically predisposed persons could lead to global translational arrest of physiologically relevant enzymes and proteins, resulting in the severe and often fatal clinical symptoms of the acute hepatic porphyrias.

Impaired dexamethasone-mediated induction of tryptophan 2,3-dioxygenase in heme-deficient rat hepatocytes: translational control by a hepatic eIF2alpha kinase, the heme-regulated inhibitor

Tryptophan 2,3-dioxygenase (TDO), a liver-specific cytosolic hemoprotein, is the rate-limiting enzyme in L-tryptophan catabolism and thus a key serotonergic determinant. Glucocorticoids transcriptionally activate the TDO gene with marked enzyme induction. TDO is also regulated by heme, its prosthetic moiety, as its expression and function are significantly reduced after acute hepatic heme depletion. Here we show in primary rat hepatocytes that this impairment is not due to faulty transcriptional activation of the TDO gene but rather due to its posttranscriptional regulation by heme. Accordingly, in acutely heme-depleted hepatocytes, the de novo synthesis of TDO protein is markedly decreased (>90%) along with that of other hepatic proteins. This global suppression of de novo hepatic protein syntheses in these heme-depleted cells is associated with a significantly enhanced phosphorylation of the alpha-subunit of the eukaryotic initiation factor eIF2 (eIF2alpha), as monitored by the phosphorylated eIF2alpha/total eIF2alpha ratio. Heme supplementation reversed these effects, indicating that heme regulates TDO induction by functional control of an eIF2alpha kinase. A cDNA was cloned from heme-depleted rat hepatocytes, and DNA sequencing verified its identity to the previously cloned rat brain heme-regulated inhibitor (HRI). Proteomic, biochemical, and/or immunoblotting analyses of the purified recombinant protein and the immunoaffinity-captured hepatic protein confirmed its identity as a rat heme-sensitive eIF2alpha kinase. These findings not only document that a hepatic HRI exists and is physiologically relevant but also implicate its translational shut-off of key proteins in the pathogenesis and symptomatology of the acute hepatic heme-deficient conditions clinically known as the hepatic porphyrias.

Neurite degeneration induced by heme deficiency mediated via inhibition of NMDA receptor-dependent extracellular signal-regulated kinase 1/2 activation

The early stages of many neurodegenerative diseases and age-related degeneration are characterized by neurite damage and compromised synaptic function that precede neuronal cell death. We investigated the signaling mechanisms underlying neurite degeneration using cortical neuron cultures. Inhibition of heme synthesis caused neurite damage, without neuronal death, and was mediated by reduced NMDA receptor (NMDAR) expression and phosphorylation. The signaling toward the degenerative phenotype involved suppression of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, and electrophysiological recording showed that the neurodegeneration is accompanied by reduced NMDAR current and Ca2+ influx, as well as reduced voltage-gated sodium currents, consistent with compromised neurite integrity. Rescue from the degenerative phenotype by heme replacement was dependent on restoration of NR2B subunit phosphorylation and expression of NMDAR currents with higher Ca2+ permeability, consistent with triggering prosurvival ERK1/2 signaling to maintain and extend neurites. This study demonstrated a new mechanism of neurodegeneration in which impaired heme synthesis led to NMDAR signaling dysfunction, suppression of the prosurvival ERK1/2 pathway, and progressive fragmentation of neuronal projections.

Haem repression of the housekeeping 5-aminolaevulinic acid synthase gene in the hepatoma cell line LMH

Haem is essential for the health and function of nearly all cells. 5-Aminolaevulinic acid synthase-1 (ALAS-1) catalyses the first and rate-controlling step of haem biosynthesis. ALAS-1 is repressed by haem and is induced strongly by lipophilic drugs that also induce CYP (cytochrome P450) proteins. We investigated the effects on the avian ALAS-1 gene promoter of a phenobarbital-like chemical, Glut (glutethimide), and a haem synthesis inhibitor, DHA (4,6-dioxoheptanoic acid), using a reporter gene assay in transiently transfected LMH (Leghorn male hepatoma) hepatoma cells. A 9.1 kb cALAS-1 (chicken ALAS-1) promoter-luciferase-reporter construct, was poorly induced by Glut and not by DHA alone, but was synergistically induced by the combination. In contrast, a 3.5 kb promoter ALAS-1 construct was induced by Glut alone, without any further effect of DHA. In addition, exogenous haem (20 microM) repressed the basal and Glut- and DHA-induced activity of luciferase reporter constructs containing 9.1 and 6.3 kb of ALAS-1 5'-flanking region but not the construct containing the first 3.5 kb of promoter sequence. This effect of haem was subsequently shown to be dependent on the -6.3 to -3.5 kb region of the 5'-flanking region of cALAS-1 and requires the native orientation of the region. Two deletion constructs of this approx. 2.8 kb haem-repressive region (1.7 and 1.1 kb constructs) retained haem-dependent repression of basal and drug inductions, suggesting that more than one cis-acting elements are responsible for this haem-dependent repression of ALAS-1. These results demonstrate that there are regulatory regions in the 5'-flanking region of the cALAS-1 gene that respond to haem and provide a basis for further investigations of the molecular mechanisms by which haem down-regulates expression of the ALAS-1 gene.

Heme-reversible impairment of CYP2B1/2 induction in heme-depleted rat hepatocytes in primary culture: translational control by a hepatic alpha-subunit of the eukaryotic initiation factor kinase?

The role of heme in the phenobarbital-mediated induction of CYP2B1/2 was reexamined in rat hepatocytes in monolayer culture, acutely depleted of heme by treatment with either 3,5-dicarbethoxy-2,6-dimethyl-4-ethyl-1,4-dihydropyridine (DDEP) or N-methylprotoporphyrins (NMPP). The findings revealed that such acute hepatic heme depletion markedly impaired CYP2B1/2 protein induction, an effect that was reversible by heme resupplementation. However, TaqMan analyses of hepatic mRNA isolated from these heme-depleted cells revealed that this impairment was not due to faulty transcriptional activation of either CYP2B1 or CYP2B2 gene expression as previously proposed, thereby confirming literature reports that heme is not a transcriptional regulator of the CYP2B1/2 gene. In contrast, the rate of de novo CYP2B1/2 protein synthesis was found to be dramatically inhibited in both DDEP- and NMPP-treated hepatocytes. Concurrently, a marked (>80%) suppression of de novo hepatocellular protein synthesis was also observed, along with a significantly enhanced phosphorylation of the alpha-subunit of the eukaryotic initiation factor eIF2 (eIF2alpha), as monitored by the phosphorylated eIF2alpha/total eIF2alpha ratio in these heme-depleted cells. Indeed, the parallel reversal of all these three effects by heme supplementation suggests that this impaired CYP2B1 induction most likely stems from blocked translational initiation resulting from the activation of a heme-sensitive eIF2alpha kinase. Such global suppression of hepatic protein synthesis may disrupt a myriad of vital cellular functions, thereby contributing to the clinical symptoms of acute hepatic heme-deficient states such as the hepatic porphyrias.

Hepatic gene expression in protoporphyic Fech mice is associated with cholestatic injury but not a marked depletion of the heme regulatory pool

BALB/c Fech(m1Pas) mice have a mutated ferrochelatase gene resulting in protoporphyria that models the hepatic injury occurring sporadically in human erythropoietic protoporphyria. We used this mouse model to study the development of the injury and to compare the dysfunction of heme synthesis with hepatic gene expression of liver metabolism, oxidative stress, and cellular injury/inflammation. From an early age expression of total cytochrome P450 and many of its isoforms was significantly lower than in wild-type mice. However, despite massive accumulation of protoporphyrin in the liver, expression of the main genes controlling heme synthesis and catabolism (Alas1 and Hmox1, respectively) were only modestly affected even in the presence of the cytochrome P450-inducing CAR agonist 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene. In contrast, in BALB/c mice exhibiting griseofulvin-induced hepatic protoporphyria with induction and destruction of cytochrome P450, both Alas1 and Hmox1 genes were markedly up-regulated. Other expression profiles in BALB/c Fech(m1Pas) mice identified roles for oxidative mechanisms in liver injury while modulated gene expression of hepatocyte transport proteins and cholesterol and bile acid synthesis illustrated the development of cholestasis. Subsequent inflammation and cirrhosis were also shown by the up-regulation of cytokine, cell cycling, and procollagen genes. Thus, gene expression profiles studied in Fech(m1Pas) mice may provide candidates for human polymorphisms that explain the sporadic hepatic consequences of erythropoietic protoporphyria.

Cytosolic persistence of mouse brain CYP1A1 in chronic heme deficiency

Previous work has demonstrated that the function of extrahepatic cytochrome P450 CYP1A1 is dependent on the availability of heme. CYP1A1 is involved in the activation of polyaromatic hydrocarbons. In the present study we used a transgenic mouse model with chronic impairment of heme synthesis - female porphobilinogen deaminase-deficient (PBGD-/-) mice - to investigate the effects of limited heme in untreated and beta-naphthoflavone (beta-NF)-treated animals on the function of CYP1A1 in brain. The heme content of PBGD-/- mice was diminished in the liver and brain compared to wild types. In the liver, partial heme deficiency led to less potent induction of CYP1A1 mRNA after beta-NF treatment. In the brain, CYP1A1 protein was detected not only at the endoplasmic reticulum (ER), but also in the cytosol of PBGD-/- mice. Furthermore, 7-deethylation of ethoxyresorufin, an indicator of CYP1A1 metabolic activity, could be restored by heme in cytosol of PBGD-/- mouse brain. Independent of the genotype, we found only one cyp1a1 gene product, indicating that the cytosolic appearance of CYP1A1 most likely did not originate from mutant alleles. We conclude that heme deficiency in the brain leads to incomplete heme saturation of CYP1A1, which causes its improper incorporation into the ER membrane and persistence in the cytosol. It is suggested that diseases caused by relative heme deficiency, such as hepatic porphyrias, may lead to impaired hemoprotein function in brain.

Adenoviral-mediated expression of porphobilinogen deaminase in liver restores the metabolic defect in a mouse model of acute intermittent porphyria

The aim of this study was to investigate the potential of gene therapy in the treatment of acute intermittent porphyria (AIP), a disorder caused by a partial deficiency of porphobilinogen deaminase (PBGD), the third enzyme in heme synthesis. The condition is biochemically characterized by accumulation of the porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG). Here we present the first experiments in vivo using adenoviral vectors to replace the deficient enzyme in the liver of an AIP mouse model. The use of adenoviral vector carrying the cDNA of luciferase in wild-type mice confirmed that transgene expression after intravenous administration was found mainly in liver. When PBGD-deficient mice were administered with adenoviral vector carrying the cDNA of mouse PBGD, the hepatic PBGD activity increased in a dose- and time-dependent manner. The highest activity was found 7 days after injection and remained high after 29 days. The expressed enzyme was shown to correct the metabolic defect in the PBGD-deficient mice as no accumulation of ALA or PBG occurred in plasma, liver, or kidney after induction of heme synthesis by phenobarbital. The study demonstrates that hepatic PBGD expression prevents the accumulation of porphyrin precursors, suggesting a future potential for gene therapy in AIP.

Hepatic expression of cytochrome P450s in hepatocyte nuclear factor 1-alpha (HNF1alpha)-deficient mice

Hepatocyte nuclear factor 1 alpha (HNF1alpha) is a liver enriched homeodomain-containing transcription factor that has been shown to transactivate the promoters of several cytochrome P450 (CYP) genes, including CYP2E1, CYP1A2, CYP7A1, and CYP27, in vitro. In humans, mutations in HNF1alpha are linked to the occurrence of maturity onset diabetes of the young type 3, an autosomal dominant form of non-insulin-dependent diabetes mellitus in which afflicted subjects generally develop hyperglycemia before 25 years of age. Mice lacking HNF1alpha also develop similar phenotypes reminiscent of non-insulin-dependent diabetes mellitus. To investigate a potential role for HNF1alpha in the regulation of CYPs in vivo, the expression of major CYP genes from each family was examined in the livers of mice lacking HNF1alpha. Analysis of CYP gene expression revealed marked reductions in expression of Cyp1a2, Cyp2c29 and Cyp2e1, and a moderate reduction of Cyp3a11. In contrast Cyp2a5, Cyp2b10 and Cyp2d9 expression were elevated. There are also significant changes in the expression of genes encoding CYPs involved in fatty acid and bile acid metabolism characterized by a reduction in the expression of Cyp7b1, and Cyp27 as well as elevations in Cyp4a1/3, Cyp7a1, Cyp8b1, and Cyp39a1 expression. These results point to a critical role for HNF1alpha in the regulation of CYPs in vivo and suggest that this transcription factor may have an important influence on drug metabolism as well as lipid and bile acid homeostasis in maturity onset diabetes of the young type 3 diabetics.

Biochemical characterization of porphobilinogen deaminase-deficient mice during phenobarbital induction of heme synthesis and the effect of enzyme replacement

Acute intermittent porphyria (AIP) is a genetic disorder caused by a deficiency of porphobilinogen deaminase (PBGD), the 3rd enzyme in heme synthesis. It is clinically characterized by acute attacks of neuropsychiatric symptoms and biochemically by increased urinary excretion of the porphyrin precursors porphobilinogen (PBG) and 5-aminolevulinic acid (ALA). A mouse model that is partially deficient in PBGD and biochemically mimics AIP after induction of the hepatic ALA synthase by phenobarbital was used in this study to identify the site of formation of the presumably toxic porphyrin precursors and study the effect of enzyme-replacement therapy by using recombinant human PBGD (rhPBGD). After 4 d of phenobarbital administration, high levels of PBG and ALA were found in liver, kidney, plasma, and urine of the PBGD-deficient mice. The administration of rhPBGD intravenously or subcutaneously after a 4-d phenobarbital induction was shown to lower the PBG level in plasma in a dose-dependent manner with maximal effect seen after 30 min and 2 h, respectively. Injection of rhPBGD subcutaneously twice daily during a 4-d phenobarbital induction reduced urinary PBG excretion to 25% of the levels found in PBGD-deficient mice administered with only phenobarbital. This study points to the liver as the main producer of PBG and ALA in the phenobarbital-induced PBGD-deficient mice and demonstrates efficient removal of accumulated PBG in plasma and urine by enzyme-replacement therapy.

Regulation of nitric oxide-sensitive guanylyl cyclase

In this review, we outline the current knowledge on the regulation of nitric oxide (NO)-sensitive guanylyl cyclase (GC). Besides NO, the physiological activator that binds to the prosthetic heme group of the enzyme, two novel classes of GC activators have been identified that may have broad pharmacological implications. YC-1 and YC-1-like substances act as NO sensitizers, whereas the substance BAY 58-2667 stimulates NO-sensitive GC NO-independently and preferentially activates the heme-free form of the enzyme. Sensitization and desensitization of NO/cGMP signaling have been reported to occur on the level of NO-sensitive GC; in the present study, an alternative mechanism is introduced explaining the adaptation of the NO-induced cGMP response by a long-term activation of the cGMP-degrading phosphodiesterase 5 (PDE5). Finally, regulation of GC expression and a possible modulation of GC activity by other factors are discussed.

Liver-specific deletion of the NADPH-cytochrome P450 reductase gene: impact on plasma cholesterol homeostasis and the function and regulation of microsomal cytochrome P450 and heme oxygenase

A mouse model with liver-specific deletion of the NADPH-cytochrome P450 reductase (Cpr) gene (designated Alb-Cre/Cprlox mice) was generated and characterized in this study. Hepatic microsomal CPR expression was significantly reduced at 3 weeks and was barely detectable at 2 months of age in the Alb-Cre+/-/Cprlox+/+ (homozygous) mice, with corresponding decreases in liver microsomal cytochrome P450 (CYP) and heme oxygenase (HO) activities, in pentobarbital clearance, and in total plasma cholesterol level. Nevertheless, the homozygous mice are fertile and are normal in gross appearance and growth rate. However, at 2 months, although not at 3 weeks, the homozygotes had significant increases in liver weight, accompanied by hepatic lipidosis and other pathologic changes. Intriguingly, total microsomal CYP content was increased in the homozygotes about 2-fold at 3 weeks and about 3-fold at 2 months of age; at 2 months, there were varying degrees of induction in protein (1-5-fold) and mRNA expression (0-67-fold) for all CYPs examined. There was also an induction of HO-1 protein (nearly 9-fold) but no induction of HO-2. These data indicate the absence of significant alternative redox partners for liver microsomal CYP and HO, provide in vivo evidence for the significance of hepatic CPR-dependent enzymes in cholesterol homeostasis and systemic drug clearance, and reveal novel regulatory pathways of CYP expression associated with altered cellular homeostasis. The Alb-Cre/Cprlox mouse represents a unique model for studying the in vivo function of hepatic HO and microsomal CYP-dependent pathways in the biotransformation of endogenous and xenobiotic compounds.

Microsomal enzyme induction and clinical aggravation of porphyria: the evaluation of human urinary 6beta-hydroxycortisol/cortisol ratio as the index of hepatic CYP3A4 activity

The clinical aspect of porphyria has been investigated, and it is well known that porphyrinogens such as estrogens and alcohol or other inducers of P450 isoenzymes exacerbate the porphyric state. However, there can be a delay in diagnosing porphyria and a difficulty in selecting safe medicine for it even today. A 21-year-old woman developed epilepsy, disturbance of mental state, and spastic tetraparesis during the convalescent period after acute viral encephalitis. She was diagnosed with porphyria after the fifth hospitalization. In the course of modifying her anticonvulsant regimen, the authors examined the 6beta-hydroxycortisol/cortisol ratio (6beta-OHF/F) in her urine, which can be the index of hepatic CYP3A4 activity, with electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS). Generalized and partial complex seizures, other neurological signs and symptoms, and laboratory data were improved after modification of her anticonvulsant regimen. This is the first report of evaluating the urinary 6beta-hydroxycortisol/cortisol ratio in a case of porphyria.

Drugs mediate the transcriptional activation of the 5-aminolevulinic acid synthase (ALAS1) gene via the chicken xenobiotic-sensing nuclear receptor (CXR)

Heme is an essential component in oxygen transport and metabolism in living systems. In non-erythropoietic cells, 5-aminolevulinate synthase (ALAS1) is the first and rate-limiting enzyme in the heme biosynthesis pathway. ALAS1 expression and heme levels are increased in vivo by drugs and other chemical inducers of cytochrome P450 hemoproteins through mechanisms that are poorly understood. In the present studies, a chicken genomic cosmid library was employed to isolate a major portion of the ALAS1 gene. Two drug-responsive enhancer sequences, 176 and 167 base pairs in length, were identified in the 5'-flanking region of the gene in reporter gene assays in the hepatoma cell line LMH. The relative potency of inducers to activate these enhancers corresponds to induction of ALAS1 mRNA levels in LMH cells. Analysis of putative transcription factor binding sites within the enhancers revealed DR5 and DR4 type recognition sequences for nuclear receptors. Drug activation of the enhancer elements was reduced at least 60% after mutagenesis of individual nuclear receptor binding sites and was virtually eliminated following alteration of both recognition sites within the respective elements. Electrophoretic mobility shift assays and transactivation studies demonstrate direct interactions between the nuclear receptor binding sites and the recently described chicken xenobiotic-sensing receptor, (CXR) implicating drug activation mechanisms for ALAS1 similar to those found in inducible cytochrome(s) P450. This is the first report describing direct transcriptional activation of ALAS1 by drugs via drug-responsive enhancer sequences.

Growth characteristics, angiotensin II generation, and microarray-determined gene expression in vascular smooth muscle cells from young spontaneously hypertensive rats

BACKGROUND

We have demonstrated that vascular smooth muscle cells (VSMCs) derived from spontaneously hypertensive rats (SHR) show exaggerated growth and produce angiotensin (Ang) II and growth factors. These may reflect intrinsic abnormalities in SHR that are not caused by excessive blood pressure, and are associated with genetic abnormalities.

OBJECTIVE

To evaluate whether these characteristics of VSMCs from SHR are associated with hypertension or genetic factors.

DESIGN AND METHODS

VSMCs were obtained by an explant method from aortas of 4-week-old male SHR/Izumo and Wistar-Kyoto (WKY)/Izumo rats. We evaluated growth characteristics by [3H]thymidine incorporation and cell number increases, immunofluorescence of alpha-smooth muscle (alpha-SM) actin, mRNA expressions of phenotype markers, Ang II-generating system components, and growth factors by reverse transcription and polymerase chain reaction analysis, and Ang II levels by radioimmunoassay in VSMCs. Expression of 850 genes in VSMCs was evaluated by microarray.

RESULTS

VSMCs from young SHR showed increased basal DNA synthesis and higher responses of DNA synthesis and cell numbers in response to calf serum. Ang II was significantly increased in conditioned medium and cell extracts from SHR-derived VSMCs than in those from WKY rat-derived VSMCs. mRNA expression of Ang II-generating proteinases, such as cathepsin D and angiotensin-converting enzyme, was greater in VSMCs from SHRs than in cells from WKY rats. Expression of transforming growth factor-beta1, platelet-derived growth factor A-chain and basic fibroblast growth factor mRNAs was greater in VSMCs from SHRs than in cells from WKY rats. Expression of mRNAs of phenotype markers, such as matrix gamma-carboxyglutamic acid (Gla) and osteopontin, was also greater in VSMCs from SHR than in cells from WYK rats. Microarray study showed that VSMCs derived from young SHR increasingly express genes for many enzymes, adhesion molecules and cytokines.

CONCLUSION

This study determined that VSMCs derived from young SHR show exaggerated growth, produce Ang II and increasingly express several enzymes, adhesion molecules and cytokines, which are independent of hypertension and possibly associated with genetic abnormalities.