Heme production in animal tissues: the regulation of biogenesis of delta-aminolevulinate synthase

Porphyrias and photosensitivity: pathophysiology for the clinician

Porphyrias are disorders caused by defects in the biosynthetic pathway of heme. Their manifestations can be divided into three distinct syndromes, each attributable to the accumulation of three distinct classes of molecules. The acute neurovisceral syndrome is caused by the accumulation of the neurotoxic porphyrin precursors, delta aminolevulinic acid, and porphobilinogen; the syndrome of immediate painful photosensitivity is caused by the lipid-soluble protoporphyrin IX and, the syndrome of delayed blistering photosensitivity, caused by the water-soluble porphyrins, uroporphyrin, and coproporphyrin. Porphyrias can manifest with one, or with a combination, of these syndromes, depending on whether one or more types of molecules are being accumulated. Iron plays a significant role in some of these conditions, as evidenced by improvements in both clinical manifestations and laboratory parameters, following iron depletion in porphyria cutanea tarda, or iron administration in some cases of X-linked erythropoietic protoporphyria. While the pathophysiology of a specific type of porphyrias, the protoporphyrias, appears to favor the administration of zinc, results so far have been conflicting, necessitating further studies in order to assess its potential benefit. The pathways involved in each disease, as well as insights into their pathobiological processes are presented, with an emphasis on the development of photosensitivity reactions.

High energy shock waves and 5-aminolevulinic for sonodynamic therapy: effects in a syngeneic model of colon cancer

The cytotoxic effect of the natural porphyrin precursor 5-aminolevulinic acid (ALA) exposed to high energy shock waves (HESW) was investigated in vitro on DHD/K12/TRb rat colon cancer cells and in vivo on a syngeneic colon cancer model. In vitro, viable cell growth was determined by trypan blue exclusion assay and cell death was investigated by flow cytometry. ALA (50 µg/ml) and HESW (E1, EFD = 0.22 mJ/mm², 1000 shots or E2, EFD = 0.88 mJ/mm², 500 shots) showed a significant reduction of cancer cell proliferation at day 3 compared to cells exposed to ALA (p < 0.01) or HESW (p < 0.001) alone. An enhancement of necrotic and apoptotic cells was observed after combined treatment at day 1 with ALA and HESW E1 (a 3.1 and 6.4 fold increase vs ALA alone) or E2 (a 3.4 and 5.3 fold increase vs ALA alone). In vivo, apoptosis detection was carried out by TUNEL assay, the pro-apoptotic gene Bad and Bcl-2 mRNA expression was evaluated by quantitative SYBR Green real time RT-PCR and cleavage of poly(ADP-ribose)-polymerase (PARP) was investigated by Western Blotting. An enhancement of apoptosis was observed in tumour tissues after the combined treatment at day 1 with ALA (375 mg/kg i.v.) and HESW (E2) compared to that of ALA exposure alone with improved apoptotic index (a 2.0 fold increase), Bad enhanced mRNA expression (p < 0.01), Bcl-2 decreased mRNA expression (p < 0.05) and increased PARP cleavage. The interaction between HESW and ALA is then effective in inducing apoptosis on a syngeneic colon cancer model.

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.

Co-expression of ferrochelatase allows for complete heme incorporation into recombinant proteins produced in E. coli

Over-expression of heme binding proteins in Escherichia coli often results in sub-optimal heme incorporation and the amount of heme-bound protein produced usually varies with the protein of interest. Complete heme incorporation is important for biochemical characterization, spectroscopy, structural studies, and for the production of homogeneous commercial proteins with high activity. We have determined that recombinant proteins expressed in E. coli often contain less than a full complement of heme because they rather are partially incorporated with free-base porphyrin. Porphyrin-incorporated proteins have similar spectral characteristics as the desired heme-loaded targets, and thus are difficult to detect, even in purified samples. We present a straightforward and inexpensive solution to this problem that involves the co-expression of native ferrochelatase with the protein of interest. The method is shown to be effective for proteins that contain either Cys- or His-ligated hemes.

An integrated functional genomic study of acute phenobarbital exposure in the rat

Background

Non-genotoxic carcinogens are notoriously difficult to identify as they do not damage DNA directly and have diverse modes of action, necessitating long term in vivo studies. The early effects of the classic rodent non-genotoxic hepatocarcinogen phenobarbital have been investigated in the Fisher rat using a combination of metabolomics and transcriptomics, to investige early stage mechanistic changes that are predictive of longer term pathology.

Results

Liver and blood plasma were profiled across 14 days, and multivariate statistics used to identify perturbed pathways. Both metabolomics and transcriptomics detected changes in the liver which were dose dependent, even after one day of exposure. Integration of the two datasets associated perturbations with specific pathways. Hepatic glycogen was decreased due to a decrease in synthesis, and plasma triglycerides were decreased due to an increase in fatty acid uptake by the liver. Hepatic succinate was increased and this was associated with increased heme biosynthesis. Glutathione synthesis was also increased, presumably in response to oxidative stress. Liquid Chromatography Mass Spectrometry demonstrated a remodeling of lipid species, possibly resulting from proliferation of the smooth endoplasmic reticulum.

Conclusions

The data fusion of metabolomic and transcriptomic changes proved to be a highly sensitive approach for monitoring early stage changes in altered hepatic metabolism, oxidative stress and cytochrome P450 induction simultaneously. This approach is particularly useful in interpreting changes in metabolites such as succinate which are hubs of metabolism.

Differential regulation of human ALAS1 mRNA and protein levels by heme and cobalt protoporphyrin

5-Aminolevulinic acid synthase 1 (ALAS1) is the first and rate-controlling enzyme of heme biosynthesis. This study was to determine the effects of heme and selected nonheme metalloporphyrins on human ALAS1 gene expression in hepatocytes. We found that, upon heme and cobalt protoporphyrin (CoPP) treatments, ALAS1 mRNA levels were down-regulated significantly by ca. 50% or more. Measurement of mRNA in the presence of actinomycin D showed that these down-regulations were due to the decreases in mRNA half-lives. Furthermore, the levels of mitochondrial mature ALAS1 protein were down-regulated by 60-70%, but those of the cytosolic precursor protein were up-regulated by 2-5-fold. Measurement of protein in the presence of cycloheximide (CHX) suggests that elevation of the precursor form is due to the increase in protein half-lives. These results provide novel insights into the mechanisms of heme repressional effects on ALAS1 and provide a rationale for further investigation of CoPP as a therapeutic agent for acute porphyric syndromes.

Boronated protohaemins: synthesis and in vivo antitumour efficacy

The conjugates of porphyrin macrocycles with boron-containing polyhedra are under investigation as agents for binary treatment strategies of cancer. Aiming at the design of photoactive compounds with low-to-zero dark toxicity, we synthesized a series of carboranyl and monocarbon-carboranyl derivatives of protohaemin IX using the activation of porphyrin carboxylic groups with di-tert-butyl pyrocarbonate or pivaloyl chloride. The water-soluble 1,3,5,8-tetramethyl-2,4-divinyl-6(7)-[2'-(closo-monocarbon-carborane-1''-yl)methoxycarbonylethyl]-7(6)-(2'-carboxyethyl)porphyrin Fe(III) (compound 9) exerted no discernible cytotoxicity for cultured mammalian cells, nor did it cause general toxicity in rats. Importantly, 9 demonstrated dose-dependent activity as a phototoxin in photodynamic therapy of M-1 sarcoma-bearing rats. In animals injected with 20 mg kg(-1) of 9, the tumours shrank by day 3 after one single irradiation of the tumour with red laser light. Between 7 and 14 days post-irradiation, 88.9% of rats were tumour-free; no recurrence of the disease was detectable within at least 90 days. Protohaemin IX alone was without effect, indicating that boronation is important for the phototoxic activity of 9. This is the first study that presents the synthesis and preclinical in vivo efficacy of boronated derivatives of protohaemin as phototoxins. The applicability in photodynamic treatment broadens the therapeutic potential of boronated porphyrins beyond their conventional role as radiosensitizers in boron neutron capture therapy.

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.

Photodynamic therapy causes cross-linking of signal transducer and activator of transcription proteins and attenuation of interleukin-6 cytokine responsiveness in epithelial cells

Photodynamic therapy (PDT) is a local treatment of cancers. The principle of PDT is the production of reactive oxygen species, in particular singlet oxygen, by light activation of a photosensitizer introduced into the target cells. The direct photochemical and subsequent redox reactions can lead to cell death. This study sought to identify effects occurring during PDT and some of their consequences in surviving cells. Using epithelial cells in tissue culture and in tumors, several distinct PDT-mediated reactions were found, including global dephosphorylation of proteins, induced phosphorylation of a 71-kDa protein, initiation of cellular stress responses, structural modification and loss of epidermal growth factor receptor, and cross-linking of proteins. Specific covalent cross-linking of nonactivated signal transducer and activator of transcription (STAT)-3, and to a lesser extent of STAT1 and STAT4, correlated with PDT dose. Cross-linked STAT3 was primarily localized to the cytoplasm and failed to bind to DNA. The combination of STAT cross-linking and inactivation of receptor functions rendered PDT-treated cells refractory for at least 24 hours to interleukin-6 and oncostatin M, cytokines known to be elevated at site of tissue damage and inflammation. It is suggested that the loss of responsiveness to these inflammatory cytokines in the PDT-treated field assists tumor cells in evading the growth-suppressive activity of these mediators expected to be present at tissue sites after PDT.

5-aminolevulinic acid-based photodynamic therapy in leukemia cell HL60

A study to explore the optimal experimental parameters and the photosensitization of 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) in promyelocytic leukemia cell HL60 has been conducted, in which HL60 cells and their control groups, peripheral blood mononuclear cell (PBMC), first are incubated with different concentrations of ALA in dark for different periods of time and then followed by irradiating with different wavebands for different fluences. Fluorescence microscope and spectrofluorometer have been used to detect the fluorescence of protoporphyrin IX (PpIX) endogenously produced by ALA. The response of the cells to ALA-PDT was evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2-5-diphenyl-2H-tetrazolium bromide (MTT) assay (interval between irradiation and the MTT assay is 24 h) and by flow cytometry (the length of time between irradiation and the flow assay is 30 min). MTT results will reflect the relative number of metabolically active mitochondria in the population. Propidium iodide uptake in flow cytometry will test for membrane damage. The results of parameter experiments were obtained: 1 x 10(5)/mL HL60 cell was first incubated with 1 mmol/L ALA in dark for 4 h and the maximum fluorescence of PpIX level appeared; then irradiated with 410 nm (4 mW/cm2) for 14.4 J/cm2 and maximum photodamage to membrane and mitochondrial function of HL60 cell resulted. With the normal granulocytes, such response was not detected. Therefore a hypothetical idea can be brought forward that ALA-based PDT can be used for inactivation of leukemia cell HL60 and these optimal parameters may be useful for clinical application.

Intensified oxidative and nitrosative stress following combined ALA-based photodynamic therapy and local hyperthermia in rat tumors

Oxidative stress-related changes in tumors upon localized hyperthermia (HT), 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) and their combination (ALA+HT) were examined after the observation that the antitumor effects of ALA-PDT could be significantly enhanced upon simultaneous application of HT. Rats bearing s.c. DS-sarcomas (0.6-1.0 ml) on the hind foot dorsum were anesthetized and underwent one of the following treatments: (i) ALA-PDT (375 mg/kg 5-ALA i.v.); (ii) localized HT, 43 degrees C for 60 min; (iii) combined ALA-PDT and HT [=ALA+HT]. Appropriate control experiments were also performed. After treatment, tumors were excised and rapidly frozen for later analysis of nitrosative stress (protein nitration), apoptotic events (TUNEL, caspase activation, DNA and RNA fragmentation), expression of heat shock proteins (hsp70 and HO-1), glutathione (GSH) levels and glutathione peroxidase (GPx) activity. Protein nitration was found to increase upon treatment, being especially pronounced in the ALA+HT group, and could partially be related to areas surrounding microvessels. The extent of nitrosative stress also correlated well with the appearance of the markers of apoptosis and the inhibition of in vivo tumor growth as seen in a previous study. GSH levels decreased upon treatment, the reduction being most prominent in the ALA-PDT and ALA+HT groups. GPx activity, however, showed a significant decrease only in the ALA-PDT group. Whereas hsp70 expression increased upon HT, ALA-PDT caused a decrease, and these opposing effects were nullified with ALA+HT. The results obtained point to a number of cellular mechanisms-including effects on cellular defense mechanisms and an abrogation of the heat shock defense mechanism-that may interact to achieve the potentiated tumor response rate seen in vivo upon combined treatment.

Mitochondrial and endoplasmic reticulum stress-induced apoptotic pathways are activated by 5-aminolevulinic acid-based photodynamic therapy in HL60 leukemia cells

We studied the mechanism of the cytotoxic effects of 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT; induction with 1 mM ALA for 4 h followed by a blue light dose of 18 J/cm(2)) on the human promyelocytic leukemia cell line HL60 using biochemical and electron microscopy methods. The disruption of mitochondrial membrane potential, deltapsi(m), was paralleled by a decrease in ATP level, unmasking of the mitochondrial antigen 7A6, release of cytochrome c into the cytoplasm, activation of caspases 9 and 3 and cleavage of poly(ADP-ribose) polymerase (PARP). This was followed by DNA fragmentation. These data suggest that ALA-PDT activates the mitochondrial apoptotic pathway. The level of endoplasmic reticulum Ca(2+)-binding chaperones ERp57 and ERp72 and of anti-apoptotic proteins Bcl-2 and Bcl-x(L) was decreased whereas that of Ca(2+)-binding protein calmodulin and the stress protein HSP60 was elevated following ALA-PDT. Inhibition of the initiator caspase 9, execution caspase 3 and Ca(2+)-dependent protease m-calpain, did not prevent DNA fragmentation. We conclude that, in our in vitro model, ALA-based photodynamic treatment initiates several signaling processes in HL60 cells that lead to rapidly progressing apoptosis, which is followed by slow necrosis. Two apoptotic processes proceed in parallel, one representing the mitochondrial pathway, the other involving disruption of calcium homeostasis and activation of the endoplasmic reticulum stress-mediated pathway.

Role of porphyrin sequestration in the biogenesis of iron-laden astrocytic inclusions in primary culture

Astrocytes in subcortical regions of the mammalian brain progressively accumulate iron-rich, autofluorecent cytoplasmic inclusions as a function of aging. Cysteamine (CSH) accelerates the appearance of this senescent glial phenotype in situ and in primary rat astroglial cultures. Porphyrins have been implicated as the source of orange-red autofluorescence in these glial inclusions. Yet, CSH has been shown to suppress porphyrin-heme biosynthesis in cultured astroglia. To determine whether porphyrin biosynthesis or sequestration participates in the biogenesis of these glial inclusions, the porphyrin precursor, (3)H-delta-aminolevulinic acid ((3)H-ALA) was administered to CSH-exposed and control rat astroglial cultures followed by light and electron microscopic autoradiography. Control cultures exhibited faint orange-red autofluorescence, intense (3)H-ALA labeling, numerous normal mitochondria and few cytoplasmic inclusions. In these cells, (3)H-ALA labeling largely occurred over normal mitochondria. The CSH-treated astroglia exhibited diminished (3)H-ALA labeling and contained numerous orange-red autofluorescent inclusions. The latter manifested internal compartments delimited by double membranes characteristic of damaged mitochondria. The complement of normal mitochondria in the CSH-exposed cells was markedly reduced. In the CSH-treated cells, (3)H-ALA labeling predominated over the large multi-compartmental inclusions. CSH attenuates de novo porphyrin-heme biosynthesis in astroglia but may induce punctate orange-red autofluorescence in the cytoplasm of these cells by promoting large numbers of damaged, porphyrin-containing mitochondria to form tight aggregates within the nascent gliosomes.

Fluorescence spectroscopy study of protoporphyrin IX metabolism level in cells

Fluorescence spectroscopy was used to study the protoporphyrin IX (PpIX) metabolism level in chick embryos during the cell proliferation process. The emission spectra were measured for PpIX bound to albumin from nonincubated and incubated eggs. The relative characteristic emission intensity of PpIX was used to determine the level of PpIX metabolism as a function of the embryonic development time. This technique might be used to estimate tumor development time.

Chronic activation of AMP kinase results in NRF-1 activation and mitochondrial biogenesis

The underlying mechanism by which skeletal muscle adapts to exercise training or chronic energy deprivation is largely unknown. To examine this question, rats were fed for 9 wk either with or without beta-guanadinopropionic acid (beta-GPA; 1% enriched diet), a creatine analog that is known to induce muscle adaptations similar to those induced by exercise training. Muscle phosphocreatine, ATP, and ATP/AMP ratios were all markedly decreased and led to the activation of AMP-activated protein kinase (AMPK) in the beta-GPA-fed rats compared with control rats. Under these conditions, nuclear respiratory factor-1 (NRF-1) binding activity, measured using a cDNA probe containing a sequence encoding for the promoter of delta-aminolevulinate (ALA) synthase, was increased by about eightfold in the muscle of beta-GPA-fed rats compared with the control group. Concomitantly, muscle ALA synthase mRNA and cytochrome c content were also increased. Mitochondrial density in both extensor digitorum longus and epitrochlearis from beta-GPA-fed rats was also increased by more than twofold compared with the control group. In conclusion, chronic phosphocreatine depletion during beta-GPA supplementation led to the activation of muscle AMPK that was associated with increased NRF-1 binding activity, increased cytochrome c content, and increased muscle mitochondrial density. Our data suggest that AMPK may play an important role in muscle adaptations to chronic energy stress and that it promotes mitochondrial biogenesis and expression of respiratory proteins through activation of NRF-1.

Is delta-aminolevulinic acid dehydratase rate limiting in heme biosynthesis following exposure of cells to delta-aminolevulinic acid?

Understanding the regulation and control of heme/porphyrin biosynthesis is critical for the optimization of the delta-aminolevulinic-acid (ALA)-mediated photodynamic therapy of cancer, in which endogenously produced protoporphyrin IX (PPIX) is the photosensitizer. The human breast cancer cell line MCF-7, the rat mammary adenocarcinoma cell line R3230AC, the mouse mammary tumor cell line EMT-6 and the human mesothelioma cell line H-MESO-1 were used to study ALA-induced PPIX levels and their relationship to delta-aminolevulinic acid dehydratase (ALA-D) activity in vitro. Incubation of these cell lines with 0.5 mM ALA for 3 h resulted in a significant increase in PPIX accumulation, compared with control cells, but there was no significant change in ALA-D activity. Exposure of cells incubated with ALA to 30 mJ/cm2 of fluorescent light, a dose that would cause a 50% reduction in cell proliferation, did not significantly alter the activity of ALA-D. Increasing the activity of porphobilinogen deaminase (PBGD), the enzyme immediately subsequent to ALA-D, by four- to seven-fold via transfection of cells with PBGD complementary DNA did not alter the activity of ALA-D. However, incubation of cells with various concentrations of succinyl acetone, a potent inhibitor of ALA-D, caused a concomitant decline in both PPIX accumulation and ALA-D activity. These data imply that when cells are exposed to exogenous ALA, ALA-D is an important early-control step in heme/porphyrin biosynthesis and that regulation of PPIX synthesis by this dehydratase may impact the effectiveness of ALA-mediated photosensitization.

5-Aminolaevulinate synthase gene promoter contains two cAMP-response element (CRE)-like sites that confer positive and negative responsiveness to CRE-binding protein (CREB)

The first and rate-controlling step of the haem biosynthetic pathway in mammals and fungi is catalysed by the mitochondrial-matrix enzyme 5-aminolaevulinate synthase (ALAS). The purpose of this work was to explore the molecular mechanisms involved in the cAMP regulation of rat housekeeping ALAS gene expression. Thus we have examined the ALAS promoter for putative transcription-factor-binding sites that may regulate transcription in a cAMP-dependent protein kinase (PKA)-induced context. Applying both transient transfection assays with a chloramphenicol acetyltransferase reporter gene driven by progressive ALAS promoter deletions in HepG2, and electrophoresis mobility-shift assays we have identified two putative cAMP-response elements (CREs) at positions -38 and -142. Functional analysis showed that both CRE-like sites were necessary for complete PKA induction, but only one for basal expression. Co-transfection with a CRE-binding protein (CREB) expression vector increased PKA-mediated induction of ALAS promoter transcriptional activity. However, in the absence of co-transfected PKA, CREB worked as a specific repressor for ALAS promoter activity. A CREB mutant deficient in a PKA phosphorylation site was unable to induce expression of the ALAS gene but could inhibit non-stimulated promoter activity. Furthermore, a DNA-binding mutant of CREB did not interfere with ALAS promoter basal activity. Site-directed-mutagenesis studies showed that only the nearest element to the transcription start site was able to inhibit the activity of the promoter. Therefore, we conclude that CREB, through its binding to CRE-like sites, mediates the effect of cAMP on ALAS gene expression. Moreover, we propose that CREB could also act as a repressor of ALAS transcription, but is able to reverse its role after PKA activation. Dephosphorylated CREB would interfere in a spatial-disposition-dependent manner with the transcriptional machinery driving inhibition of gene expression.

Protein changes in HL60 leukemia cells associated with 5-aminolevulinic acid-based photodynamic therapy. Early effects on endoplasmic reticulum chaperones

Using two-dimensional electrophoresis we investigated the effect of 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT; induction with 1 mM ALA for 4 h followed by blue light dose of 18 J/cm2) on the protein expression in HL60 leukemia cells. ALA-PDT resulted in extensive qualitative and quantitative changes in the protein pattern of HL60 cell lysates. Of more than 1350 protein spots recognized on the protein maps of ALA-induced cells, seven proteins were enhanced and 17 suppressed following irradiation. Three of these, calreticulin precursor, p58 microsomal protein (ERp57) and protein disulfide isomerase (p55) have been identified by matrix-assisted laser desorption and ionization-mass spectrometry and the pI/molecular weight parameters of the affected proteins were estimated by computer analysis. The findings suggest participation of endoplasmic reticulum Ca(2+)-binding chaperones and/or Ca2+ signaling in ALA-PDT mediated cytotoxicity.

Transcriptional regulation of 5-aminolevulinate synthase by phenobarbital and cAMP-dependent protein kinase

5-Aminolevulinate synthase (ALA-S) is a mitochondrial matrix enzyme that catalyzes the first and rate-limiting step of the heme biosynthesis. There are two ALA-S isozymes encoded by distinct genes. One gene encodes an isozyme that is expressed exclusively in erythroid cells, and the other gene encodes a housekeeping isozyme that is apparently expressed in all tissues. In this report we examine the mechanisms by which phenobarbital and cAMP regulate housekeeping ALA-S expression. We have determined that cAMP and phenobarbital effects are additive and the combined action is necessary to observe the cAMP effect on ALA-S mRNA in rat hepatocytes. The role of the cAMP-dependent protein kinase (PKA) has been examined. A synergism effect on ALA-S mRNA induction is observed in rat hepatocytes treated with pairs of selective analogs by each PKA cAMP binding sites. A 870-bp fragment of ALA-S 5'-flanking region is able to provide cAMP and phenobarbital stimulation to chloramphenicol O-acetyltranferase fusion vectors in transiently transfected HepG2 cells. ALA-S promoter activity is induced by cotransfection with an expression vector containing the catalytic subunit of PKA. Furthermore, cotransfection with a dominant negative mutant of the PKA regulatory subunit impairs the cAMP analog-mediated increase, but the phenobarbital-mediated induction is not modified. Our data suggest that the transcription factor cAMP-response element binding protein (CREB) is probably involved in PKA induction of ALA-S gene expression. Finally, heme addition greatly decreases the basal and phenobarbital or cAMP analog-mediated induction of ALA-S promoter activity. The present work provides evidence that cAMP, through PKA-mediated CREB phosphorylation, and phenobarbital induce ALA-S expression at the transcriptional level, while heme represses it.

Effect of estrogenic perturbations on delta-aminolevulinic acid-induced porphobilinogen deaminase and protoporphyrin IX levels in rat Harderian glands, liver, and R3230AC tumors

The Harderian gland in rodents highly expresses enzymes of the heme biosynthetic pathway that are responsible for porphyrin production. Interestingly, many of the steps in Harderian gland heme biosynthesis, including protoporphyrin production, are controlled hormonally. We hypothesized that estrogenic alterations, ovariectomy or tamoxifen administration, might also alter the response of porphobilinogen deaminase activity and/or protoporphyrin IX production to delta-aminolevulinic acid administration in the hormonally responsive R3230AC rat mammary adenocarcinoma. We also determined whether the response of the R3230AC tumor, borne on ovariectomized hosts, to delta-aminolevulinic acid-based photodynamic therapy was altered compared with tumors treated on intact hosts. Ovariectomy of female Fischer rats bearing the hormonally responsive R3230AC mammary adenocarcinoma caused a significant reduction in delta-aminolevulinic acid-induced protoporphyrin IX levels and porphobilinogen deaminase activity in tumors compared with levels in tumors from intact animals treated with delta-aminolevulinic acid. In contrast, although porphobilinogen deaminase activity in the Harderian gland from ovariectomized animals was reduced significantly compared with that in glands from intact animals, protoporphyrin IX levels were unaltered. Administration of the anti-estrogen tamoxifen to tumor-bearing rats resulted in a significant increase in porphobilinogen deaminase in both tumor and Harderian gland. Although administration of delta-aminolevulinic acid increased protoporphyrin IX levels in Harderian glands in tamoxifen-treated animals, tumor levels of protoporphyrin IX remained unaltered in the tamoxifen-treated rats. Treatment of R3230AC tumors with delta-aminolevulinic acid-based photodynamic therapy in ovariectomized rats resulted in a significantly reduced response compared with the same treatment regimen in intact animals, 4.9+/-0.39 versus 10.6+/-0.6 days to reach twice the initial tumor volume, respectively. These results indicate that the hormonal status of the host should be considered when treating hormonally sensitive tumors with delta-aminolevulinic acid-based photodynamic therapy.

Relationship of delta-aminolevulinic acid-induced protoporphyrin IX levels to mitochondrial content in neoplastic cells in vitro

Protoporphyrin IX, induced by the exogenous addition of delta-aminolevulinic acid, reaches different levels in different tumor cells. Because many of the steps in heme biosynthesis, of which protoporphyrin IX is penultimate, are located in the mitochondria, we surmised that the mitochondrial content of cells may relate to the amount of protoporphyrin IX synthesized in response to excess delta-aminolevulinic acid. We observed that accumulation of MitoTracker, a fluorescent mitochondrial probe, delta-aminolevulinic acid-induced protoporphyrin IX levels, and porphobilinogen deaminase activity all presented with the same cell-line-dependent rank order among the four different neoplastic cells. This rank order, however, differed for cytochrome c oxidase activity, the final enzyme in mitochondrial electron transport, and for accumulation of radioactive label from [(14)C]delta-aminolevulinic acid. The data demonstrate that enzymes involved in heme biosynthesis, in general, display a rank order associated with mitochondrial content. These data imply that such parameters may have value as prognosticators of cells to produce delta-aminolevulinic acid-induced protoporphyrin IX, a photosensitizer for photodynamic therapy of cancer.

A missing metabolic pathway in the cattle tick Boophilus microplus

Heme proteins are involved in a wide variety of biological reactions, including respiration, oxygen transport and oxygen metabolism [1]. The heme prosthetic group is synthesized in almost all living organisms except for a few pathogenic bacteria and trypanosomatids that use blood as food [2] [3]. There is a general belief that all nucleated animal cells synthesize heme [1] [4]. However, blood-feeding arthropods ingest enormous amounts of vertebrate blood in a single meal and the heme pathway has not been studied in these animals. We have examined heme synthesis in two hematophagous arthropods - the blood-sucking bug Rhodnius prolixus and the cattle tick Boophilus microplus. We show that R. prolixus makes heme and has a fully operative heme biosynthetic pathway, while B. microplus does not. To our knowledge, this is the first report of an animal that does not synthesize its own heme and relies solely on the recovery of heme present in the diet. Because of the inability of Boophilus to synthesize heme and its ability to deal efficiently with large amounts of free heme, we propose this organism as a good model for studying heme transport and reutilization in animal cells.

Delta-aminolaevulinic acid-induced photodynamic therapy inhibits protoporphyrin IX biosynthesis and reduces subsequent treatment efficacy in vitro

Recently, considerable interest has been given to photodynamic therapy of cancer using delta-aminolaevulinic acid to induce protoporphyrin IX as the cell photosensitizer. One advantage of this modality is that protoporphyrin IX is cleared from tissue within 24 h after delta-aminolaevulinic acid administration. This could allow for multiple treatment regimens because of little concern regarding the accumulation of the photosensitizer in normal tissues. However, the haem biosynthetic pathway would have to be fully functional after the first course of therapy to allow for subsequent treatments. Photosensitization of cultured R3230AC rat mammary adenocarcinoma cells with delta-aminolaevulinic acid-induced protoporphyrin IX resulted in the inhibition of porphobilinogen deaminase, an enzyme in the haem biosynthetic pathway, and a concomitant decrease in protoporphyrin IX levels. Cultured R3230AC cells exposed to 0.5 mM delta-aminolaevulinic acid for 27 h accumulated 6.07 x 10(-16) mol of protoporphyrin IX per cell and had a porphobilinogen deaminase activity of 0.046 fmol uroporphyrin per 30 min per cell. Cells cultured under the same incubation conditions but exposed to 30 mJ cm(-2) irradiation after a 3-h incubation with delta-aminolaevulinic acid showed a significant reduction in protoporphyrin IX, 2.28 x 10(-16) mol per cell, and an 80% reduction in porphobilinogen deaminase activity to 0.0088 fmol uroporphyrin per 30 min per cell. Similar effects were evident in irradiated cells incubated with delta-aminolaevulinic acid immediately after, or following a 24 h interval, post-irradiation. There was little gain in efficacy from a second treatment regimen applied within 24 h of the initial treatment, probably a result of initial metabolic damage leading to reduced levels of protoporphyrin IX. These findings suggest that a correlation may exist between the delta-aminolaevulinic acid induction of porphobilinogen deaminase activity and the increase in intracellular protoporphyrin IX accumulation.

Physiological and pathological factors of human breast disease that can influence optical diagnosis

The 'normal' human female breast is a very complex organ that changes considerably during development, pregnancy and menopause. In addition, it is an excretory organ that, during lactation, discharges various metabolites and certain drugs that can be optically active. Optical diagnosis of breast cancers requires detection of differential concentrations of 1) various absorbers and scatterers or 2) native or exogenous fluorophores to distinguish cancers from surrounding 'normal' and benign breast tissues. The differential concentrations are due to the biology of the cancer cells and the host responses to the cancer growth. For most patients, the cancer will be intermixed with a complex 3-dimensional array of 'normal' breast tissue and benign breast lesions. This complexity will challenge the optical biopsy investigator but, with the recent advances in our understanding of light transport, optical diagnostic techniques and devices can be developed to complement and supplement current breast cancer screening techniques.

A regulatory role for porphobilinogen deaminase (PBGD) in delta-aminolaevulinic acid (delta-ALA)-induced photosensitization?

As an initial approach to optimize delta-aminolaevulinic acid (delta-ALA)-induced photosensitization of tumours, we examined the response of three enzymes of the haem biosynthetic pathway: delta-ALA dehydratase, porphobilinogen deaminase (PBGD) and ferrochelatase. Only PBGD activity displayed a time- and dose-related increase in tumours after intravenous administration of 300 mg kg(-1) delta-ALA. The time course for porphyrin fluorescence changes, reflecting increased production of the penultimate porphyrin, protoporphyrin IX (PPIX), showed a similar pattern to PBGD. This apparent correlation between PBGD activity and porphyrin fluorescence was also observed in four cultured tumour cell lines exposed to 0.1-2.0 mM delta-ALA in vitro. The increase in PBGD activity and PPIX fluorescence was prevented by the protein synthesis inhibitor cycloheximide. As the apparent Km for PBGD was similar before and after delta-ALA, the increase in PBGD activity was attributed to induction of enzyme de novo. These observations of an associated response of PBGD and PPIX imply that PBGD may be a rate-limiting determinant for the efficacy of delta-ALA-induced photosensitization when used in photodynamic therapy.

Evidence that protein kinase C is involved in delta-aminolevulinate synthase expression in rat hepatocytes

There are many factors that regulate the rate of synthesis of delta-aminolevulinate synthase (ALA-S), the enzyme which governs the rate-limiting step in heme biosynthesis. In rat hepatocytes, phenobarbital increases ALA-S gene transcription and dibutyryl cAMP potentiates this induction, whereas insulin and glucose have the opposite effect. The present report provides evidence that protein kinase C (PKC) activation negatively influences ALA-S mRNA levels, as measured by Northern and slot-blot analysis. The addition of 1,2-dioctanoyl-sn-glycerol (DOG) or 12-O-tetradecanoylphorbol 13-acetate (TPA), a PKC activator that mimics diacylglycerol function, to cultures led to a significant decrease of both basal and phenobarbital-induced ALA-S mRNA levels in a dose-dependent manner. This TPA effect depends on the specific activation of PKC because the analog 4 alpha-phorbol 12,13-diacetate, a nonstimulatory PKC phorbol ester, is unable to inhibit ALA-S mRNA. Furthermore, the effect of TPA is blocked by the PKC inhibitors staurosporine and calphostin C. Desensitization of the PKC pathway by prolonged exposure to TPA abolished the subsequent action of the phorbol ester. On the other hand, neither TPA nor DOG modified the half-life of ALA-S mRNA. The study of the combinatorial action of TPA and cAMP revealed that the inhibitory effect of TPA overcomes dibutyryl cAMP induction. Thus, these results indicate that PKC plays an essential role in regulating ALA-S expression, probably at a transcriptional level.

Glucose inhibits phenobarbital-induced delta-aminolevulinate synthase expression in normal but not in diabetic rat hepatocytes

In the present work, we demonstrate the presence of a glucose inhibitory effect on the phenobarbital-mediated induction of the delta-aminolevulinate synthase mRNA in normal rat hepatocytes, consistent with the results obtained with the delta-aminolevulinate synthase activity previously reported. This "glucose effect" can be prevented by adding cAMP, adenylate cyclase activators, or a phosphodiesterase inhibitor. Delta-Aminolevulinate synthase mRNA half-life is not modified in the presence of phenobarbital or glucose. When the same experiments are performed using diabetic cells, no glucose effect is observed, even when the endogenous cAMP content is lowered to normal levels. The results obtained in this study suggest that glucose decreases delta-aminolevulinate synthase biosynthesis by acting at a pretranslational step. Assuming that the glucose effect operates by a repression mechanism exerted by metabolites derived from or related to glucose, the present results may reflect a derangement in the formation of these metabolites as a result of the abnormal metabolism operating in the diabetic state.

L-alanine: 4,5-dioxovalerate transaminase in Leishmania donovani that differs from mammalian enzyme

Leishmania protozoans are the causative agents of leishmaniasis, a major parasitic disease in humans. The parasites manifest a nutritional requirement for heme compounds since they are deficient in heme biosynthesis. In this study we have demonstrated for the first time the presence of the enzyme L-alanine: 4,5-dioxovalerate transaminase in Leishmania donovani. This enzyme catalyzes the synthesis of 5-aminolevulinic acid (ALA), the first committed step in heme synthesis. Thus the defect in heme biosynthesis pathway in Leishmania must lie at some enzymatic level subsequent to synthesis of ALA. The enzyme was found to be present in both virulent and avirulent strains of L. donovani. The virulent promastigotes showed a 41% higher specific activity as compared to the avirulent strain. The enzyme activity was found to be inhibited in the presence of heme and methylglyoxal. Immunoblot analysis revealed that L-alanine: 4,5-dioxovalerate transaminase in L. donovani was immunologically different from that in mammals.

Repression of ALA synthase by heme and zinc-mesoporphyrin in a chick embryo liver cell culture model of acute porphyria

We characterize a liver cell culture model for acute hepatic porphyrias that recapitulates the biochemical features of the human syndrome. In chick embryo liver cells in primary culture exposed to glutethimide and 4,6-dioxoheptanoic acid, heme alone produced a transient dose-dependent decrease in delta-aminolevulinate synthase and a concomitant increase in heme oxygenase. The addition of low concentrations of zinc-mesoporphyrin (50-200 nM), an inhibitor of heme oxygenase, led to more prolonged decreases in activity of the synthase and to an additive effect with heme. These effects of zinc-mesoporphyrin were associated with prolonged inhibition of heme oxygenase. These results suggest that the treatment of choice of acute porphyric syndromes may be the combination of low doses of heme and zinc-mesoporphyrin or another similarly non-toxic inhibitor of heme oxygenase.

5'-Aminolevulinate synthase activity is decreased in skeletal muscle of anemic rats

Expression of the rate-limiting heme biosynthetic enzyme 5'-aminolevulinate synthase (ALAS) was investigated in skeletal muscle of 3-wk-old rats fed an iron-deficient diet. After 14 days, ALAS activity had declined 70% relative to control (2.1 +/- 0.2 vs. 0.6 +/- 0.1 nmol.h-1.g-1; P less than 0.005). Similar decreases were observed for blood hemoglobin (11.4 +/- 0.2 vs. 3.9 +/- 0.3 g/dl; P less than 0.005) and muscle cytochrome c (14.5 +/- 1.3 vs. 7.1 +/- 0.6 nmol/g; P less than 0.005). An iron-deficient diet decreased body and skeletal muscle growth by 15 (P less than 0.005) and 10% (P less than 0.05), respectively, whereas concentrations of protein, RNA, ALAS mRNA, and citrate synthase activity in muscle were not different from control. One mechanism by which heme biosynthesis may be slowed in muscle of young anemic rats is a decrease in ALAS activity. At a time when enzyme activity was decreased, ALAS mRNA expression was not affected by an iron-deficient diet, suggesting that steps after transcription of the ALAS gene may regulate the decrease in activity.

Phenobarbital induction of cytochrome P-450 gene expression

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Heme regulates hepatic 5-aminolevulinate synthase mRNA expression by decreasing mRNA half-life and not by altering its rate of transcription

Hepatic 5-aminolevulinate (ALA) synthase, the first and rate-limiting enzyme in the heme biosynthetic pathway, is known to be feedback repressed by the end product of the pathway, heme. We investigated whether heme regulates ALA synthase mRNA expression transcriptionally or post-transcriptionally in primary cultures of chick embryo hepatocytes. 2-Propyl-2-isopropylacetamide increased the rate of transcription of the ALA synthase gene, whereas heme or an inhibitor of heme biosynthesis, desferrioximine, had no effect on the drug-induced transcription rate. Heme decreased the half-life of ALA synthase mRNA from approximately 3.5 h to 1.2 as recently reported by Drew and Ades (1989, Biochem. Biophys. Res. Commun. 162, 102-107). We also found that the heme-mediated decrease in mRNA stability was prevented by cycloheximide treatment, suggesting that the heme effect was mediated by a labile protein. These results support a model for hepatic ALA synthase regulation in which inducing drugs directly stimulate ALA synthase gene transcription, whereas heme regulates ALA synthase expression post-transcriptionally by modulating mRNA stability as well as by blocking translocation of ALA synthase enzyme into the mitochondrion.

Production of delta-aminolevulinic acid: characterization of murine liver 4,5-dioxovaleric acid: L-alanine aminotransferase

1. We report on the kinetic properties of murine liver 4,5-dioxovaleric acid:L-alanine aminotransferase (DOVA transaminase). 2. The transamination of 4,5-dioxovaleric acid (DOVA) led to the production of delta-aminolevulinic acid. 3. L-Alanine was the preferred amino group donor among the common 20 amino acids. 4. The optimum pH of the reaction was 7-8. 5. A Km of 220 microM for DOVA and a Km of 970 microM for L-alanine were obtained. 6. The reaction was inhibited by each of the following: glyoxylate, beta-chloroalanine, methylglyoxal, delta-aminolevulinate, pyruvate, heme, and gabaculine. 7. None of several xenobiotic inducers of microsomal mixed function oxidases tested had a significant effect on DOVA transaminase activity in studies performed with murine primary hepatocyte cultures.