Effect of lead and genetic factors on heme biosynthesis in the human red cell

Element Concentrations in Tree Swallows (Tachycineta bicolor) from the U.S. and Binational Great Lakes Areas of Concern

Selected elements were targeted in state Remedial Action Plans as one group of chemicals affecting the Beneficial Use Impairments of Great Lakes Areas of Concern (AOCs). Livers of nestling tree swallows, Tachycineta bicolor, were harvested from 76 sites in the Great Lakes, which included multiple sites at 27 AOCs and 12 reference sites from 2010 to 2015, and were analyzed for 21 elements. Mercury concentrations were at background levels at all sites. Elevated cadmium (Cd) concentrations were associated with industry. The highest Cd values were from the Black River, OH AOC and were associated with historic coke production but were not at toxic levels. Lead (Pb) concentrations were highest on the Rouge River, MI AOC-the oldest and most heavily populated and industrialized area in southeast Michigan. Individual Pb concentrations were elevated to a level associated with delta-aminolaevulinic acid dehydratase inhibition but not to a level considered toxic. In contrast, livers harvested from sites on the southwest shore of Lake Michigan had selenium (Se) concentrations elevated to levels associated with reduced avian reproduction. One likely source of the high Se concentrations was pollution from a local coal-fired power plant. Concentrations of the remaining elements were at background levels.

Porphyria Diagnostics-Part 1: A Brief Overview of the Porphyrias

Porphyria diseases are a group of metabolic disorders caused by abnormal functioning of heme biosynthesis enzymes and characterized by excessive accumulation and excretion of porphyrins and their precursors. Precisely which of these chemicals builds up depends on the type of porphyria. Porphyria is not a single disease but a group of nine disorders: acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), variegate porphyria (VP), δ-aminolevulinic acid dehydratase deficiency porphyria (ADP), porphyria cutanea tarda (PCT), hepatoerythropoietic porphyria (HEP), congenital erythropoietic porphyria (CEP), erythropoietic protoporphyria (EPP), and X-linked protoporphyria (XLP). Each porphyria results from overproduction of heme precursors secondary to partial deficiency or, in XLP, increased activity of one of the enzymes of heme biosynthesis. Taken together, all forms of porphyria afflict fewer than 200,000 people in the United States. Based on European studies, the most common porphyria, PCT, has a prevalence of 1 in 10,000, the most common acute porphyria, AlP, has a prevalence of ∼1 in 20,000, and the most common erythropoietic porphyria, EPP, is estimated at 1 in 50,000 to 75,000. CEP is extremely rare, with prevalence estimates of 1 in 1,000,000 or less. Only six cases of ADP are documented. The current porphyria literature is very exhaustive and a brief overview of porphyria diseases is essential in order for the reader to better appreciate the relevance of this area of research prior to undertaking biochemical diagnostics procedures. This unit summarizes the current knowledge on the classification, clinical features, etiology, pathogenesis, and genetics of porphyria diseases.

Chronic exposure to lead: a cause of oxidative stress and altered liver function in plastic industry workers in kolkata, India

It is well known that chronic exposure of lead leads to adverse health effects. Workers for plastic industry are generally exposed to high concentration of lead as fume, dust, and additive that protect PVC. This study was done on them to find out the detrimental effects of chronic lead exposure on hepatic and hematological toxicity. Blood and 24 h urine sample was collected from 47 plastic industry workers and matched against 42 controls for various parameters. The study group shows significant increase in blood (p < 0.0001) and urinary level of lead (p < 0.0001). Hemoglobin levels were significantly decreased (p < 0.0001), and the liver enzymes like ALP, ALT, AST and y-GT were significantly increased (p < 0.0001) in all cases exposed for >10 years. Serum lipid peroxide by quantitative assay of thiobarbituric acid reactive substances was also found increased in the study group (p < 0.0001). The observations point towards the acute health risk faced by plastic industry workers, in whom chronic exposure to lead increases the absorption and accumulation, over a period of time, of this highly toxic element in their body. This increases oxidative stress, causes metabolic damage to RBC and cell membranes, and also suggests necrosis of liver cell, hepatocellular injury and presence of space occupying lesions. Considering the data immediate health and hygiene monitoring and proper rehabilitation for the suffering population seem to be of paramount need in plastic industry to minimize occupational hazards.

Direct assay of delta-aminolevulinic acid dehydratase in heme biosynthesis for the detection of porphyrias by tandem mass spectrometry

We report a new assay of human delta-aminolevulinic acid dehydratase (ALAD), an enzyme converting delta-aminolevulinic acid (ALA) into porphobilinogen. The assay is developed for use in the clinical diagnosis of delta-aminolevulinic acid dehydratase-deficient porphyria, a rare enzymatic deficiency of the heme biosynthetic pathway. The assay involves the incubation of erythrocyte lysate with the natural substrate, ALA, followed by quantitative in situ conversion of porphobilinogen to its butyramide, and liquid-liquid extraction into a mass spectrometer-friendly solvent. Quantitation of the butyrylated porphobilinogen is done by electrospray ionization tandem mass spectrometry, using a deuterium labeled internal standard. The assay stays well within the range wherein ALAD activity is linear with time. The K(m) of ALAD for ALA was measured as 333 microM, and the V(max) was 19.3 microM/h. Average enzyme activity among a random sample of 36 anonymous individuals was 277 micromol/L erythrocyte lysate/hour with a standard deviation of 90 micromol/L erythrocyte lysate/hour. The tandem mass spectrometric assay should easily detect the enzyme deficiency, which causes a reduction of activity by 95-99%. The assay shows good reproducibility and low background, requires a simple workup, and uses a commercially available substrate.

Highly heterogeneous nature of delta-aminolevulinate dehydratase (ALAD) deficiencies in ALAD porphyria

The properties of 9 delta-aminolevulinate dehydratase (ALAD) mutants from patients with ALAD porphyria (ADP) were examined by bacterial expression of their complementary DNAs and by enzymologic and immunologic assays. ALADs were expressed as glutathione-S-transferase (GST) fusion proteins in Escherichia coli and purified by glutathione-affinity column chromatography. The GST-ALAD fusion proteins were recognized by anti-ALAD antibodies and were enzymatically active as ALAD. The enzymatic activities of 3 ALAD mutants, K59N, A274T, and V153M, were 69.9%, 19.3%, and 41.0% of that of the wild-type ALAD, respectively, whereas 6 mutants, G133R, K59N/G133R, F12L, R240W, V275M, and delTC, showed little activity (< 8%). These variations generally reflect the phenotype of ALAD in vivo in patients with ADP and indicate that GST-ALAD fusion protein is indeed useful for predicting of the phenotype of ALAD mutants. The location of F12L mutation in the enzyme's molecular structure indicates that its disturbance of the quaternary contact of the ALAD dimer appears to have a significant influence on the enzymatic activity. Mouse monoclonal antibodies to human ALAD were developed that specifically recognized a carboxy terminal portion of ALAD, or other regions in the enzyme. This study represents the first complete analysis of 9 mutants of ALAD identified in ADP and indicates the highly heterogeneous nature of mutations in this disorder.

A novel mutation of delta-aminolaevulinate dehydratase in a healthy child with 12% erythrocyte enzyme activity

Cloning, expression and phenotype studies of the defective gene for delta-aminolaevulinate dehydratase (ALAD) in a family with an asymptomatic girl who had ALAD deficiency were carried out. The proband was identified by neonatal ALAD screening, and had erythrocyte ALAD activity at 12% of the normal control. She was heterozygous for ALAD deficiency, which was inherited from her father. Nucleotide sequence analysis of the cloned ALAD cDNA revealed C36 to G and T168 to C mutations on the same allele. The former mutation resulted in F12L substitution, whereas the latter was a silent mutation. All family members who had decreased ALAD activity had the same mutation. Expression of the mutant ALAD cDNA in Chinese hamster ovary cells produced an ALAD protein without significant enzyme activity. Additionally, the mutant ALAD cDNA which encodes F12L substitution produced an aberrant migration pattern in polyacrylamide gel electrophoresis under denaturing conditions. This finding probably reflects an abnormal folding of the F12L protein, since the mutation occurred in the alpha1 helix of the N-terminal arm of the enzyme, which is involved in the extensive quaternary interactions among the subunits. This is also the first report of ALAD gene mutation in an asymptomatic subject.

Selenium altered regulation of heme biosynthesis in chick embryos

A few selected indices of heme biosynthesis have been studied in liver and blood from chick embryos receiving different concentrations of selenium of toxicological significance 12.5, 25 and 37.5 mumoles/Kg egg.Wt.). The first rate limiting enzyme Aminolevulinic acid synthetase activity was enhanced by selenium treatment under both IN VIVO and IN VITRO conditions, while hepatic ALA dehydratase activity was unaltered. Hepatic and blood free sulfhydryl (-SH) group contents were significantly decreased by selenium. In accordance with these results, blood aminolevulinic acid dehydratase (ALA dehydratase) and hepatic ferrochelatase, both the sulfhydryl group requiring enzymes, were significantly inhibited. Further, hepatic ALA, total blood porphyrin levels were enhanced and hepatic heme levels were depleted by selenium exposure. These results suggest selenium as a novel regulator of heme biosynthesis by altering the activities of sulfhydryl group requiring enzymes of chick embryos.

Cloning and expression of the defective genes from a patient with delta-aminolevulinate dehydratase porphyria

Cloning and expression of the defective genes for delta-aminolevulinate dehydratase (ALAD) from a patient with inherited ALAD deficiency porphyria (ADP) were carried out. Cloning of cDNAs for the defective ALAD were performed from EBV-transformed lymphoblastoid cells of the proband, and nucleotide sequences were determined. Two separate point mutations resulting in a single amino acid change in each ALAD allele were identified. One, C718----T, termed 'G1', occurred in the allele within the substrate-binding site, producing an Arg240----Trp substitution; the other, G820----A, termed 'G2', occurred downstream of this site in the other allele, resulting in an Ala274----Thr substitution. Using the reverse transcription-polymerase chain reaction, the mother, the brother, and the sister were shown to have the G1 defect. Expression of the G1 cDNA in Chinese hamster ovary cells produced ALAD protein with little activity; the G2 cDNA produced the enzyme with approximately 50% normal activity. Pulse-labeling studies demonstrated that the G1 enzyme had a normal half life, while the G2 enzyme had a markedly decreased half life. These data thus define the separate point mutations in each ALAD allele, as well as the altered properties of the two enzymic proteins encoded by the mutant genes in a patient with ADP.

Evidence for pteridine regulation of lead-mediated inhibition of uroporphyrinogen and heme formation in rat bone marrow

Uroporphyrin I (URO I) accumulation has been reported in the bone marrow of rats exposed to lead, suggesting a sensitivity of uroporphyrinogen III cosynthase (COSYN) to this heavy metal. Furthermore, it has been reported that a polyglutamated folate derivative may serve as a coenzyme for the catalytic action of hepatic uroporphyrinogen III cosynthase. These findings raised the question of whether depletion of polyglutamated folate could enhance the susceptibility of bone marrow COSYN to lead and potentially interfere with the formation of heme. Nitrous oxide, an anesthetic agent capable of causing bone marrow tetrahydrofolate deficiency, depressed total bone marrow polyglutamated folate content by 42% with significant reductions in all three chain lengths (5-7) identified in the bone marrow during an exposure period of 7 days at 4 hr/day. Lead acetate (15 mg/kg) administered by ip injection at Days 0 and 2 during a 7-day exposure to nitrous oxide resulted in an 84% increase of bone marrow URO I content, which was markedly higher than the increases of 22 and 38% seen with sole administration of lead or nitrous oxide, respectively. The combination of agents also produced a 48% rise in COPRO I, a 39 and 43% decrease in COPRO III and protoporphyrin, respectively, and a 42% decline in the activity of microsomal 7-ethoxycoumarin O-deethylase, which is hemoprotein, cytochrome P-450 mediated. Heme oxygenase activity was not altered by nitrous oxide, lead, or their combination. These results suggest that bone marrow folate deficiency may render COSYN more sensitive to lead as characterized by increased uroporphyrin I and coproporphyrin I isomer content, decreased coproporphyrin III and protoporphyrin content, and depressed microsomal hemoprotein, cytochrome P-450-mediated drug-metabolizing capability.

Eclectic mechanisms of heme regulation of hematopoiesis

Regulatory features of heme (ferroprotoporphyrin IX) on hematopoietic growth/differentiation and related processes are reviewed. It is emphasized that expressions of specific erythroid and nonerythroid heme biosynthetic and degradatory enzymes are required, and the regulatory processes whereby this occurs is considered. The specificity of heme, relationship to cellular events such as differentiation, response to growth factors, oncogene and receptor expression, and how heme counteracts toxic effects such as viral growth are all discussed. The significance of heme in the hemopoietic bone marrow microenvironment and growth factor network are considered. Finally, the third pathway for arachidonic acid metabolism via the heme-cytochrome P450 monooxygenase system, in addition to cyclooxygenase and lipoxygenase, by bone marrow adherent cells and its role in cellular differentiation is briefly reviewed.

Effect of cis-platinum on heme, drug, and steroid metabolism pathways: possible involvement in nephrotoxicity and infertility

cis-Platinum, a coordination complex of platinum, is highly effective against a number of human tumors, including steroid-dependent tumors such as testicular and prostatic cancers. It is generally assumed that DNA is the cellular target responsible for the antitumor activity of the drug. Much evidence, however, has been gathered in recent years suggesting that cis-platinum has major effects on the endocrine system, particularly the hypothalamic-pituitary-testis steroidogenesis axis, and severely disrupts the normal production of testosterone. In the axis, testis is the prime target, where the LH receptor-binding capacity of Leydig cells is decreased by nearly 80%. Within the testis, the mitochondrial cytochrome P-450scc and side-chain cleavage activity are markedly depressed and the microsomal 17 alpha-hydroxylase activity and cytochrome P-450 concentration are decreased; side-chain cleavage activity is rate-limiting in testosterone production. The effects are not limited to the testis cytochrome P-450, but extend to other organs including the liver and the kidney cytochromes. In the liver, a feminization of the cytochromes P-450 profile is produced, and hence the biotransformation of endogenous steroids as well as that of exogenous chemicals is affected. In the kidney, cis-platinum appears to be the most effective inducer of cytochrome P-450, whereby the biotransformation of the prostaglandins and fatty acids could be altered. The spectrum of the effects of cis-platinum on cytochrome P-450-dependent drug metabolism and steroid hydroxylation activity mimic those produced by hypophysectomy and are for the most part reversed by the anterior pituitary hormones. These findings suggest the possibility that general feminization of steroidogenesis caused by cis-platinum may significantly contribute to the activity of cis-platinum against hormone-dependent tumors.

Interaction of drugs with extranuclear genetic elements and its consequences

Bacterial ancestry of mitochondria and plastids is now generally accepted. Both organelles contain their own DNA and transcription-translation apparatus of a prokaryotic type. Due to this fact these systems carry bacteria-like properties. Thus organellar DNA and ribosomes are essentially different from nuclear DNA and cytoplasmic ribosomes in physical as well as in functional respects. Due to the bacterial character of both types of organelles they are susceptible to various antibacterial chemicals. Inhibitors of bacterial protein synthesis inhibit mitochondrial (plastidial) biogenesis. Therefore the cellular content of mitochondria (plastids)-made proteins decreases during cytoplasmic turnover or cell division in the presence of these drugs. Such drug activity consequently leads to a reduced capacity for oxidative phosphorylation or photosynthesis. Organellar genomes are less stable and more sensitive to mutagenesis as compared to nuclear genome. It means also that genotoxic agents induce various disorders of mitochondrial (plastidial) functions. Impairments in the respiratory chain are associated with structural as well as functional abnormalities of mitochondria. These are clinically expressed mostly in tissues with a high demand for ATP: brain, heart, skeletal muscle, and retina. On the other hand, some antibacterial inhibitors of mitochondrial biogenesis (e.g., tetracyclines) inhibit selectively tumor cell proliferation. Therefore they may be considered for use in anticancer therapy. The article summarizes the response of mitochondria and plastids in various organisms to drugs and environmental xenobiotics. Various model organisms suitable for detection of xenobiotic effect on mitochondria (plastids) are presented as well as the possible consequences of such interaction.

Depletion of liver regulatory heme in benzene exposed rats

The effect of a single dose of benzene (0.5 ml/kg body wt i.p.) on the heme saturation of tryptophan pyrrolase activity in liver was examined. There was a significant decrease in the heme saturation of hepatic tryptophan pyrrolase, suggesting depletion of "regulatory heme". After benzene administration there was significant increase in delta-aminolevulinate (ALA) synthetase activity (approx. 2-fold) while delta-aminolevulinate dehydratase activity was significantly decreased, however, ferrochelatase and heme oxygenase activities were unaltered. Administration of tryptophan to benzene pretreated rats showed a reversal of benzene effects on heme synthesizing enzymes: there is an increase in the heme saturation of tryptophan pyrrolase and decrease in delta-aminolevulinate synthetase. However, there was no significant alteration in the activity of delta-aminolevulinate dehydratase.

Erythrocyte delta-aminolevulinic acid dehydratase in birds. I. The effects of lead and other metals in vitro

The effects of buffering ions, pH, temperature, and various metal cations on the activity of avian red blood cell aminolevulinic acid dehydratase (RBC-ALA-d) in blood hemolysates was studied. The pH optimum of the enzyme was approximately 6.6 in both citrate and morpholinethanesulfonic acid (MES) buffers, and maximal activity was comparable in both buffer systems. Enzyme activity was increased by about 20% at 42 degrees C (avian body temp.) relative to that at 37 degrees C. Pb2+ was 10-100-fold more potent than Cu2+, Cd2+, Hg2+ or CH3Hg+ as an inhibitor of RBC-ALA-d activity. The IC50 for Pb2+ was 0.03-0.04 mumol/ml blood. Zn2+ added to Pb-pretreated hemolysates was able to induce up to 65% recovery of enzyme activity. Pb2+ was a more effective inhibitor of delta-aminolevulinic acid dehydratase (ALA-d) activity in MES buffer than in citrate buffer, possibly because of chelation of Pb2+ by citrate.

Aminolaevulinate dehydratase porphyria in infancy. A clinical and biochemical study

Homozygous deficiency of aminolaevulinate dehydratase (porphobilinogen synthase, EC 4.2.1.24) was diagnosed in a small child. The clinical presentation was unique since severe symptoms were already present in the neonatal period. The patient, a boy, now three-years old, had recurrent attacks of pain, vomiting, hyponatraemia and symptoms of polyneuropathy engaging motor functions including respiration. The clinical course of the disease from birth on is related, as are the results of various attempts at therapy. The patient excreted large amounts of 5-aminolaevulinic acid and coproporphyrin and minor amounts of porphobilinogen in the urine. Faecal excretion of coproporphyrin and harderoporphyrin was increased as was erythrocyte porphyrin concentration. Diagnosis was established by the finding that erythrocyte aminolaevulinate dehydratase activity was less than 5 per cent of normal in the patient and between 26 and 51 per cent of normal in both the parents, the grandfathers and a sibling. The activity of the enzyme could not be restored by the addition of dithiothreitol (10(-3) mol/l) alone, or in combination with zinc or manganese in varying concentrations. The enzyme Km did not differ between affected and nonaffected members of the family.

Evidence of differential hematopoietic compensation to lead intoxication in blood, liver and kidney

The dependence of fluorescent porphyrin levels on the concentration of lead in blood, liver and kidney has been examined as functions of both the level and duration of dosing. Individually housed male Wistar COBS rats of 200 g were randomly selected for 3, 7, 21 and 35 day dosing periods in groups of: control, 50, 100 and 1000 ppm dosing in drinking water. The plot of all data points for porphyrin concentration against measured lead burden covers the same range of levels and closely resembles the scatter of data observed in humans. However, subsets of this plot defined by individual dose levels and durations yield well-defined linear relationships. At all dose levels at 7 days the correlation of porphyrin concentration to lead tissue burden is negative in all tissues, showing a direct inhibition of hemopoiesis with lead burden. Depending on the tissue the slope becomes less negative, or, as in blood, positive at 21 and 35 days at all doses. This compensation is most rapid in blood, then liver and is least evident in kidney. The time at which compensation is observed is the same for all doses in each tissue and seems therefore, to depend on the rate of protein turnover in different tissue types. These results suggest that a direct correlation of porphyrin concentration to lead burden is not valid without knowledge of the dosing history. As well, evidence of compensation in one tissue does not imply successful compensation in other affected tissues where regeneration rates are slower.(ABSTRACT TRUNCATED AT 250 WORDS)

delta-Aminolevulinic acid dehydrase (porphobilinogen synthase) in two families with inherited enzyme deficiency

The inheritance of a deficient delta-aminolevulinic acid dehydrase (ALA-D; synonym: porphobilinogen synthase; EC 4.2.1.24) was studied in blood samples of two families over three generations. The propositus in each family was a young male acute hepatic porphyria patient with an almost complete ALA-D deficiency in the homozygous state (ALA-D activity less than 2% of controls). Heterozygotes are clinically non-affected (mean ALA-D 36% of controls). The mode of transmission could be traced by enzyme activity and electrophoretic polymorphism studies. Heterozygotes are detected by the demonstration of enzyme activity in the gel. The notation D was used for the gene expressing the defective enzyme. The "phenotype" D-1 was observed in six, the "phenotype" D-2 in three of all heterozygotes studied. These results are compatible with a single normal allele in heterozygotes responsible for enzyme activity. Quantitative assays and the segregation pattern in both families suggest a 3-allele-system for the inheritance of ALA-D deficiency.

Lead poisoning as a toxogenetic disease

In two non-related patients suffering from acute lead intoxication a persistent decrease in red cell delta-aminolevulinic acid dehydratase (synonym: porphobilinogen synthase) activity of 30%-60% of controls was noted after treatment and normalisation of lead levels and heme precursors in urine and blood. An inherited enzyme deficiency was suggested and confirmed by a subnormal activity in the mothers of both patients. These four persons are considered as heterozygotes with an increased sensitivity to lead exposure.

Lead poisoning in inherited delta-aminolevulinic acid dehydratase deficiency

delta-Aminolevulinic acid dehydratase (ALA-D), respectively porphobilinogen synthase, EC 4.2.1.24) activity can be lowered by toxic, metabolic and hereditary factors. A 30-year-old painter was suffering from lead poisoning with an acute abdominal-neurologic syndrome and anemia. Blood lead was measured at 414 micrograms/l. Urinary ALA and coproporphyrin excretion as well as erythrocyte protoporphyrin had increased extremely, whereas ALA-D activity in erythrocytes had decreased extremely to 8% of controls. Excretion parameters, protoporphyrin, hemoglobin and lead returned to normal after treatment, but four years later ALA-D activity still remained diminished (30% of controls). An inherited enzyme deficiency was assumed and found in the mother, analogous to the subnormal ALA-D activity in heterozygotes of four other families. The inherited enzyme deficiency sensitized the patient to lead exposure and intoxication, which is a toxogenetic disease in this case.

New developments in the regulation of heme metabolism and their implications

Various endogenous and exogenous chemicals, such as hormones, drugs, and carcinogens and other environmental pollutants are enzymatically converted to polar metabolites as a result of their oxidative metabolism by the mixed-function oxidase system. This enzyme complex constitutes the major detoxifying system of man and utilizes the hemoprotein--cytochrome P-450--as the terminal oxidase. Recent studies with trace metals have revealed the potent ability of these elements to alter the synthesis and to enhance the degradation of heme moiety of cytochrome P-450. An important consequence of these metal actions is to greatly impair the ability of cells to oxidatively metabolize chemicals because of the heme dependence of this metabolic process. In this report the effects of exposure to trace metals on drug oxidations is reviewed within the framework of metal alterations of heme metabolism, including both its synthesis and degradation, since these newly discovered properties of metals have made it possible to define a major dimension of metal toxicity in terms of a unified cellular mechanism of action.

The effect of inorganic lead and/or a polychlorinated biphenyl on the developing immune system of mice

Approximately 200 female Swiss-Webster mice, six to eight weeks of age, were divided into eight groups. Three of these groups were fed 10, 100, or 250 ppm Aroclor 1254. One group was treated with 1000 ppm lead. Three groups were exposed simultaneously to lead and Aroclor 1254 at concentrations of 10 ppm PCB + 1000 ppm Pb, 100 ppm PCB + 1000 ppm Pb, and 250 ppm PCB + 1000 ppm Pb. Control mice received deionized water and rat food only. All groups were exposed for a period of 12 wk, then bred, with exposure continued throughout gestation and lactation. Offspring were weaned onto the control diet at 3 wk of age. Results from this study indicate a varied effect of lead and/or PCBs on body and organ weights of both dams and their pups, no noticeable detrimental effect on reproduction, and very little effect on the pups' ability to mount an immune response upon challenge with foreign antigens.

Porphobilinogen-synthase (delta-aminolevulinic acid dehydratase) deficiency in bone marrow cells of two patients with porphobilinogen-synthase defect acute porphyria

Two male patients aged 23 and 25 years with intermittent acute, frequently repeated porphyria syndromes presented an almost total deficiency of porphobilinogen-synthase [(PBG-S); synonym: delta-aminolevulinic acid dehydratase] in peripheral erythrocytes. PBG-S was investigated in bone marrow cells obtained by sternal puncture. A minimal enzyme activity of less than 3% of controls was established. Specific activity and protoporphyrin concentration decreased considerably during the course of erythropoiesis. Both patients are homozygous gene carriers; their parents (father and mother) as well as most of their brothers and sisters are heterozygotes with a PBG-S deficiency of approximately 50% of controls. All people with PBG-S deficiency are especially endangered by alcohol intake and lead exposure, because alcohol and lead toxically inhibit PBG-S.

The effect of low lead doses in vitro and in vivo on the d-ala-d activity of erythrocytes, bone marrow cells, liver and brain of the mouse

The d-ala-d activity in erythrocytes (RBC), femur bone marrow, liver and brain of mice was determined using a modification of the method of Berlin and Schaller (1974). In vitro incubation of lead acetate (PbAc) with these tissues resulted in a dose-dependent inhibition of the d-ala-d activity. The lead concentration which caused a 50% inhibition of the d-ala-d activity after 10 min incubation [ED-50(10 min)] was 0.78 mg PbAc/femur bone marrow, 3.72 micrograms PbAc/ml RBC, 15.85 micrograms PbAc/g brain and 43.05 micrograms PbAc/g liver. An increase in the incubation time to 60 min reduced these ED-50 values between 44% for the erythrocytic enzyme and 67% for the brain enzyme. In vivo treatment of mice with oral lead administration (absorbed dose range: 1-100 micrograms PbAc/kg b.w.) for 1 or 3 months led to a dose-dependent and organ-specific inhibition of the d-ala-d activity. After 3 months of oral lead supply the maximum enzyme inhibition (54%) was found in the bone marrow. At the same time the lowest enzyme inhibition could be seen in the brain which retained 73% of its activity. The erythrocytic and liver enzyme activity was 71% and 72% resp. of the appropriate control. Within 3 weeks after completing the oral lead administration the brain enzyme activity was completely restored. The erythrocytic and liver enzyme activities were still significantly, but not very markedly inhibited, whereas the bone marrow d-ala-d remained seriously depressed. According to these experiments, the lead dose which causes a long term inhibition of the bone marrow and erythrocytic d-ala-d activities is assumed to range between 50 and 100 micrograms PbAc/kg b.w. and day, as an absorbed dose.

Acute lead poisoning in inherited porphobilinogen synthase (delta-aminolevulinic acid dehydrase) deficiency

The second enzyme of the porphyrin and heme synthesis pathway, porphobilinogen synthase (EC 4.2.1.24), can be lowered due to a hereditary defect or toxic damage. Lead is the most common cause for a toxically lowered activity. We report on a 48-year-old patient with an acute abdominal syndrome, anemia and a grave toxic disorder of porphyrin metabolism which was diagnosed as acute lead intoxication. Although the hematologic findings and porphyrins in the blood, as well as porphyrin precursors and porphyrin excretion in the urine, returned to normal within five months after exacerbation of the acute symptoms the activity of porphobilinogen synthase showed only 50% physiologic activity of healthy subjects six years after the acute syndrome with complete normalization of prophyrin metabolites and lead levels in blood and urine. The influence of alcohol was excluded. Enzyme activation by zinc and reactivation by dithiothreitol lies within the normal range and thus contradicts an increased body burden of lead. In connection with findings of a familiar porphobilinogen synthase defect we are most likely dealing with a hereditarily determined enzyme deficiency in this patient which sensitizes him to a lead intoxication.

Persistent protoporphyrinemia in hereditary porphobilinogen synthase (delta-aminolevulinic acid dehydrase) deficiency under low lead exposure. A new molecular basis for the pathogenesis of lead intoxication

For several years, a 4-12-fold increase of the upper normal limit in erythrocyte protoporphyrin concentrations persisted in two men 34 and 39 years of age who were chronically exposed to lead. We are dealing with a zinc protoporphyrinemia in both cases, without lead intoxication or anemia. The 34-year-old had been a regular blood donor for 10 years and had already been treated for iron deficiency several times. Hemoglobin, red cell counts, hematocrit, and iron were at the lower normal limit. The activity of porphobilinogen synthase (PBG-S), uroporphyrinogen-synthase and -decarboxylase as well as urinary porphyrin precursors and porphyrin excretion were normal. Protoporphyrinemia was said to be due to a prelatent/latent iron deficiency. In the 39-year-old, the activity of PBG-S was lowered to 388 mumol/1 . h, as compared to the mean of controls (1,190 +/- 210, x +/- SD, n = 50), in connection with a slightly elevated excretion of delta-aminolevulinic acid and coproporphyrin in the urine and a high-normal blood lead level. In his family there was no history of either a protoporphyrinemia or a hematological disturbance. Six of eight family members in three generations showed a diminished activity of PBG-S: 600 +/- 160, P less than 0.001 compared to controls. These family members are heterozygous with regard to the PBG-S deficiency; they are clinically unobtrusive in comparison to homozygotes with an acute prophyria syndrome. Activation by zinc and reactivation by dithiothreitol were normal in contrast to PBG-S from patients with lead intoxication. The cause of biochemical symptoms of subclinical lead intoxication developed by the propositus is probably due to the hereditary PBG-S deficiency which sensitizes him to low-level lead exposure. The determination of red cell PBG-S activity can be recommended as a test detecting heterozygotes. The hereditary PBG-S deficiency is recognized as a new molecular basis for the pathogenesis of lead intoxication.

Bone marrow cells of mice under the influence of low lead doses

The influence of lead on the number of nucleated bone marrow cells and pluripotent stem cells in femur bone marrow was investigated in mice. It was found that neither a single nor 10 days' oral administration of lead at doses of 10-1,000 micrograms PbAc/kg b.w. led to any change in the bone marrow cellularity. After 1 month's oral administration of 1,000 micrograms PbAc/kg b.w., on the other hand, there was a significant reduction of nucleated bone marrow cells and pluripotent stem cells in the femur bone marrow of up to 20% in comparison with controls. Within 14 days after completing the lead administration, however, normal values in the bone marrow cellularity were found again. Three months' oral administration of lead at doses of 100 and 1,000 micrograms PbAc/kg b.w. led to a significant reduction in nucleated bone marrow cells and pluripotent stem cells in the femur bone marrow of up to 28% compared with the controls. In contrast to the experiments with 1 month's oral administration of lead the regeneration of the bone marrow was not completed 14 days after completing the administration of the lead. These results show that lead at doses above 100 micrograms PbAc/kg b.w. causes on long-term administration a clear reduction of the nucleated bone marrow cells combined with a depressed regeneration ability of the pluripotent stem cells.

New type of acute porphyria with porphobilinogen synthase (delta-aminolevulinic acid dehydratase) defect in the homozygous state

In two male patients with acute hepatic porphyria and persisting paralysis which increased in intensity intermittently, the activity of porphobilinogen synthase (PBG-S; delta-aminolevulinic acid dehydr(at)ase) was diminished in peripheral erythrocytes and bone marrow cells below 3% of normal controls. In contrast, the activities of uroporphyrinogen synthase and decarboxylase were normal. Both patients have been excreting high quantities of delta-aminolevulinic acid and porphyrins in urine for years. Lead intoxication and tyrosinemia could definitely be excluded. There was no experimental evidence for the existence of an inhibitor to PBG-S in urine, serum and erythrocytes from these two patients. The PBG-S deficiency was confirmed after DEAE cellulose chromatography: the concordance of relative and specific activity before and after chromatography of PBG-S from patients and controls differs from the findings in lead poisoning. A mutation of PBG-S probably at the level of the structural gene is concluded as the molecular basis of the inherited PBG-S defect porphyria. Since the relatives also show lower activities of PBG-S (approximately 50% of controls), the disease of these two patients represents a new enzymatic type of inherited acute hepatic porphyria, the excretion profile of which is qualitatively completely different from those of the known acute porphyrias. The discovery of this porphyria confirms the theory of overlapping transition in the biochemical signs and clinical symptoms as well as analogies among the acute hepatic porphyrias and lead poisoning.

Hereditary prophobilinogen synthase deficiency in human associated with acute hepatic porphyria

Deficient porphobilinogen-synthase (PBG-S) of a previously reported patient with PBG-S defect porphyria (red cell PBG-S activity approximately 2% of the physiological level) has been characterized in erythrocytes after DEAE cellulose chromatography, ultrafiltration and polyacrylamide gel electrophoresis: Residual specific activity of 2.5%, increase of Km, but identical fractionation, concentration and electrophoretic mobility of the enzyme protein compared to controls. These results provide evidence for a structural mutation of the gene specifying the enzyme PBG-S connected with a homozygous state of this new enzymatic type of hereditary acute porphyria.

Family evaluations in acute intermittent porphyria using red cell uroporphyrinogen I synthetase

Acute intermittent porphyria (AIP) is a primary disorder of haem biosynthesis that is chemically characterised by raised urinary porphobilinogen (PBG). A defect in the biochemical pathway at the step of PBG conversion to uroporphyrinogen has been shown to be a result of a partial deficiency of the enzyme uroporphyrinogen I synthetase (uro I syn). The ascertainment rate of latent AIP (that is, chemically manifest but clinically asymptomatic) was examined in 185 individuals from 12 AIP kindreds using three parameters: red cell uro I syn, quantitative urinary PBG, and pedigree analysis with respect to uro I syn. Approximately 80% of individuals could be assigned as normal or latent AIP on the basis of the uro I syn assay alone. The remaining 20% could not be assigned because of an intermediate range of activity for the red cell assay in which the diagnosis cannot be certain. When the pedigree was used in the evaluation of the uro I syn data, the number of uncertain individuals, with respect to AIP, decreased to 10%. The enzyme method detected latent AIP in 37.5% of blood relatives, whereas quantitative urinary PBG alone detected only 15.2%. The pattern of inheritance for the uro I syn deficiency is consistent with Mendelian dominant inheritance, and it is likely that it is the basic inherited defect in AIP.

Occupational lead exposure in Denmark: screening with the haematofluorometer

The zinc protoporphyrin/haemoglobin (ZPP/Hb) ratio was measured in the field with a haematofluorometer. A significant increase in ZPP/Hb ratio with advancing age was found in 1295 men who denied any excess exposure to lead. Ninety-seven per cent of the results were below 110 mumol ZPP/mol Hb(Fe) (4.4 microgram ZPP/g Hb). The ZPP/Hb ratio was determined in a lead-exposed population of 2275 men, and in 305 a blood lead analysis was also performed. A blood lead limit of 2.9 mumol/l (60 microgram/100 ml) corresponds to about 500 mumol ZPP/mol Hb(Fe) (20 microgram/g). This limit was exceeded in workers engaged in secondary lead smelting, storage battery manufacture, car radiator repair, crystal glass manufacture, storage battery repair, ship breaking, metal foundries, the ceramic industry, scrap metal handling, and PVC plastic manufacture. Other occupations caused lower lead exposures with ZPP/Hb ratios between 110 and 500 mumol ZPP/mol Hb(Fe): such ratios were found in men from shooting ranges, in leaded pane manufacturers, gunsmiths, car paint sprayers, type setters, steel rolling mill workers, shipbuilders and welders, car mechanics, lead pigment handlers, and solderers. Increased ZPP/Hb ratios and blood lead levels in 210 workers were associated with a decrease in haemoglobin concentration in the blood. Thus, the haematofluorometer has proved to be very useful for screening purposes. A blood lead determination should be performed if the ZPP/Hb ratio exceeds 300 microgram ZPP/mol Hb(Fe) (12 microgram/g).

Studies in porphyria. IV. Expression of the gene defect of acute intermittent porphyria in cultured human skin fibroblasts and amniotic cells: prenatal diagnosis of the porphyric trait

The gene lesion of the porphyrin-heme synthetic pathway in acute intermittent porphyria (AIP) is reflected in a deficient level of activity of the cytosol enzyme uroporphyrinogen I synthetase (URO-S). A marked URO-S deficiency has been demonstrated in the liver and in circulating erythrocytes of individuals with both active and latent AIP. This enzymic abnormality accounts for the excessive production and excretion into urine of the porphyrin precursors, lamda-aminolevulinic acid (ALA) and porphobilinogen (PBG) in AIP subjects. In this study, utilizing cell culture techniques, a marked URO-S deficiency has also been demonstrated in skin fibroblasts from AIP patients and in cells derived through aminocentesis from an approximately 17-wk old fetus. The prenatal diagnosis of the AIP trait in this fetus was confirmed postnatally by the demonstration in the child of a deficient level of erythrocyte URO-S activity which was comparable to those found in her AIP mother and affected sibling and which was approximately one-half the levels characterizing her normal father and aunt and a second unaffected sibling. The identification of the URO-S deficiency in cultured human fibroblasts from AIP patients was facilitated by a newly developed, sensitive assay for the enzyme activity. In this assay, the ability of such cells to convert ALA to protoporphyrin was quantitated; in the sequence of reactions involved in this transformation, URO-S is limiting so that the gene defect of AIP could be simply and precisely determined by appropriate spectrofluorometry of cell extracts. The technique described has distinct advantages over the direct enzymatic assay for URO-S activity in cultured human skin fibroblasts and permits clear differentiation of AIP carrier from normal individuals.