Relationship between lead concentration in blood and biological response for porphyrin metabolism in workers occupationally exposed to lead

Summary The biological responses of the heme biosynthesis pathway in male workers moderately exposed to lead are discussed in relation to the concentration of lead in the blood. The level of erythrocyte delta-aminolevulinic acid dehydratase (ALA-D) activity in the group of lead-exposed workers was remarkably reduced while the level of erythrocyte protoporphyrin (Proto) in them was strikingly increased, compared to normal levels. On the other hand, the amounts of hemoglobin (Hb) and urinary delta-aminolevulinic acid (ALA) in the group of lead-exposed workers kept the normal levels.In the workers moderately exposed to lead, the log of erythrocyte Proto level was closely correlated to the blood lead level and the sensitivity of the Proto test was almost equal to that of erythrocyte ALA-D test. It was observed that the erythrocyte Proto was remarkably increased even in lead-exposed workers whose ALA excretion into the urine was in the range of normal level.     

Interrelationships of glutathione reductase, 5-aminolevulinic acid dehydratase, and free sulfhydryl groups in the erythrocytes of normal and lead-exposed persons

Blood lead, erythrocyte glutathione reductase (GSSG-R), 5-aminolevulinic acid dehydratase (ALA-D), and free sulfhydryl (SH) groups were measured in normal subjects and in those with occupational exposure to lead. With increasing blood lead concentration the activity of GSSG-R rises and that of ALA-D decreases. There is also a fall in the level of free SH with rising blood lead concentrations. There is a high degree of correlation between these parameters, and it is suggested that the changes represent part of a biological control mechanism to compensate for the reduction of available sulfhydryl groups by lead ions.     

Relationship between lead concentration in blood and the activities of erythrocyte pyrimidine 5′-nucleotidase and delta-aminolevulinate dehydratase in the mice exposed to lead

The relationship between the activities of both pyrimidine 5-nucleotidase (Py5N) and delta-aminolevulinate dehydratase (ALA-D) in erythrocytes and the concentration of lead in blood was investigated in the mice which were given ad libitum a drinking water containing lead of 10 to 500 ppm, for 30 days.From these results, it was demonstrated that the erythrocyte PySN activity is inhibited by lead and its activity level is negatively correlated with the concentration of lead in blood (r=–0.78). In addition, it was suggested that the erythrocyte Py5N activity is a better indicator in the exposure to relatively high lead concentration while the ALA-D is a more sensitive indicator for evaluating the lead exposure of low and moderate levels.     

Comparative study of effects of lead on the activity of erythrocyte pyrimidine 5′-nucleotidase and delta-aminolevulinate dehydratase in vivo and in vitro

The effect of lead on the activities of erythrocyte pyrimidine 5′-nucleotidase (Py5N) and delta-aminolevulinate dehydratase (ALA-D) was studied in the mice which were given ad libitum a drinking water containing lead of 10, 50 and 250 ppm, for 27 days. The erythrocyte Py5N activity was not decreased in all groups of lead-exposed mice. However, the erythrocyte ALA-D activity was markedly decreased in the groups exposed to 50 and 250 ppm lead. These data indicate that erythrocyte ALA-D is more sensitive than Py5N to lead in vivo. On the other hand, from the in vitro study, it was demonstrated that the human erythrocyte Py5N is moderately inhibited by zinc and tin, and markedly by mercury, cadmium, silver, copper, and lead, at 10⁻⁴ molar concentrations. In addition, it was observed that the erythrocyte Py5N is most remarkably inhibited by mercury while the ALA-D by lead, among metals tested.     

Interaction of lead and zinc on the prothrombin activity in rats

In 1955 Saita and coworkers reported a defect in blood coagulation in workers exposed to lead. Very little attention has been given to this observation. In our study in rats receiving 100 ppm lead (acetate) on an adequate semi-purified diet we observed a decreased prothrombin activity. This condition was more severe when dietary zinc was low (5 ppm) than when superoptimal (50 ppm). The correlation between prothrombin time and blood lead was highly significant (r = 0.842, P < 0.001). Although it has been generally accepted that altered prothrombin activity may arise from liver dysfunction, nevertheless serum glutamate-oxaloacetate transaminase (SGOT), a measure of liver function, was normal in all animals. Changes were observed, however, in serum protein pattern due to lead, the A/G ratio was lowered in lead-exposed rats receiving low zinc thus indicating a possible hepatic alteration.     

Effect of lead on electrophoretic mobility of rat erythrocytes

Lead often affects the erythrocyte membrane. The relationship between the changes in erythrocyte membrane and the anemia caused by lead is still unclear. Initially, the effect of lead injected intraperitoneally on the electrophoretic mobility of rat erythrocytes was investigated in order to study the relationship between them. As indices of lead exposure, hemoglobin (Hb) levels, hematocrits (Ht), δ-aminolevulinic acid dehydratase (ALA-D) activities and blood lead (blood Pb) levels in the injected rats were also examined. Exposure to lead significantly decreased the mobility of rat erythrocytes. The changes in mobility seemed to be less sensitive than those in ALA-D activity, however, the decreases in mobility were simultaneous with or prior to those in Hb level and Ht. The decreases in mobility were evident to some extent below a blood Pb level of 100 μg/100 ml and generally present at a level of 100 μg/100 ml and over. In the rats exposed to lead a significant negative correlation was found between the mobilities and the logarithms of blood Pb level.     

Interactions of lead and glutathione with delta-aminolevulinic acid dehydratase

Because there were tendencies for normalization of lead-sensitive parameters in animals with low lead burdens, these phenomena were examined in vivo and in vitro. Lead inhibited the enzyme delta-aminolevulinic acid dehydratase (ALA-D) dose-dependently and not competitively or irreversibly competitively in vitro. The lead-blocked portion of ALA-D could be reactivated at least partially by glutathione. This part was higher in lead-contaminated animals than in the control group, though there were no significant differences in the free part of the enzyme. The free part of the enzyme was normalized by a resynthesis of the molecule. Therefore the determination of the lead-blocked part and the part reactivated by glutathione, seemed more suitable for determining the chronic lead burden than the measurement of a possible adapted total activity of ALA-D.Partly presented at the 14. Spring Meeting of the Deutsche Pharmakologische Gesellschaft, March 18 to 21, 1973, in Mainz.     

Using morphological,behavioral, and molecular biomarkers in Zebrafish to assess the toxicity of lead-contaminated sediments from a retired trapshooting range within an urban wetland

The widespread use of lead (Pb) shot in shooting activities, including at former shooting ranges, continues to pose environmental risks. The La Crosse River Marsh (located in Wisconsin, USA) is a biologically diverse urban riparian wetland with a legacy of Pb-contaminated sediment resulting from its use as a trap shooting range from 1929–1963. Within the shot fall zone, shot densities exceed 43,000 pellets/m² and surface sediments exceed 25,000 mg/kg in some areas. This study used the Zebrafish as a model to determine the acute toxicity of these contaminated sediments. Zebrafish were exposed to sediments containing approximately 13 to 13,450 mg/kg Pb for 5 days (8–120 hr post-fertilization). The toxic responses to sediments were non-monotonic. Only exposure to sediments containing “mid-range” concentrations of Pb (4580 mg/kg) induced mild skeletal malformations and a sluggish C-start response indicating that Pb was marginally bioavailable. Expression of δ-aminolevulinic acid dehydratase (ALA-D) also indicated the potential for uptake of Pb from sediments. Our findings suggest that Pb within the La Crosse River Marsh sediments is not readily bioavailable to Zebrafish, and while this metal poses a minimal acute toxicological risk, toxicity due to chronic exposure of low concentrations of Pb is possible. Further, our data demonstrated that induction of ALA-D gene expression in Zebrafish embryos shows promise as an alternative to ALA-D enzyme activity as a biomarker for acute Pb exposure under lab conditions.     

Interaction of zinc and other metal on the activity of erythrocyte delta-aminolevulinic acid dehydratase in vitro.

The interaction of zinc and other metal such as lead, mercury (II), cadmium, silver (II) on the activity of erythrocyte delta-aminolevulinic acid dehydratase (ALA-D) was investigated in vitro. At the concentrations ranging from 0.01 to 1.0 mmol/l, lead, mercury (II), cadmium and silver (II) strikingly inhibited the erythrocyte ALA-D activity. The in vitro addition of zinc having an activating effect for the erythrocyte ALA-D, was observed to eliminate the lead-induced inhibition of the erythrocyte ALA-D activity. And the degree of the elimination seemed to depend on the molar ratio (Zn/Pb) of both metal concentrations in the ALA-D assay. However, the inhibition of erythrocyte ALA-D activity caused by mercury (II), cadmium and silver (II) was not removed by the in vitro addition of zinc.     

Decreased erythrocyte delta-aminolevulinate dehydratase activity after styrene exposure

delta-Aminolevulinate dehydratase (ALA-D:porphobilinogen synthase, 5-aminolevulinate hydro-lyase, EC 4.2.1.24) activity was depressed markedly in red cells of rats exposed to 0.21 g/m3 styrene, a chemical widely used in commercial products. The depression was not restored in vitro after treatment with dithiothreitol and zinc. Consistent with this finding, radioimmunoassay of the enzyme protein demonstrated reduction in the enzyme concentration by styrene exposure. There was a good correlation between the decrease in enzyme activity and its concentration in the styrene-treated animals, suggesting that the depression of the enzyme activity was essentially due to the reduction in the enzyme content. Decrease in the enzyme content in bone marrow cells to almost the same extent as that in erythrocytes seems to indicate the decreased synthesis of ALA-D in the bone marrow. In vitro studies showed that styrene 7,8-oxide, the major intermediate of styrene metabolism, decreased the activity of purified ALA-D but that styrene, the parent compound itself, had no inhibitory effect. The activity and concentration of erythrocyte ALA-D in workers chronically exposed to styrene were also depressed significantly. These findings indicate that the styrene exposure-mediated decrease of ALA-D activity in erythrocytes was a reflection of reduction in the enzyme protein, which may have been the result of styrene 7,8-oxide action, and they suggest that a similar process may also be involved in the reduction of erythrocyte ALA-D in styrene-exposed workers.     

Lead intoxication among demolition workers: the effect of lead on the hepatic cytochrome P-450 system in humans.

Overt clinical disease from undue lead exposure has become a relatively rare phenomenon in adult populations. However, exposure situations that may result in subclinical disease are not uncommon in various occupational settings. Five demolition workers, dismantling an old iron structure covered with lead-content paint, were studied. The use of cutting torches resulted in lead fumes, with significant exposure, albeit without gross 'lead poisoning." All five workers showed biochemical manifestations of chronic lead intoxication-that is, elevated blood lead level, inhibition of delta-aminolevulinic acid dehydratase (ALA-D), and elevated erythrocytic protoporphyrin concentration (PROTO). The effect of lead on the biosynthesis of heme was assessed by investigating the functional capacity of the cytochrome P-45O system of the liver, through drug metabolism studies. The plasma elimination rates (half-lives) of antipyrine and phenylbutazone-drugs primarily metabolized by the hemeprotein P-450 dependent hepatic microsomal enzyme system-were measured before and after chelation therapy. Prior to chelation therapy all half-lives were within the normal range. A slight decrease in the half-life of antipyrine was found after treatment. These studies show that chronic exposure to lead has only a minimal effect on hepatic cytochrome p-450 dependent enzymatic activities in adult males.     

Environmental lead exposure and activity of delta-aminolevulinic acid dehydratase (ALA-D) in maternal and cord blood.

The hypothesis that environmental lead exposure measured from blood (Pb-B) inhibits delta-aminolevulinic acid dehydratase activity (ALA-D) from whole blood was tested in 241 urban mothers and their newborns. Geometric means and (5th and 95th Percentiles) for maternal and cord Pb-B were 6.4 microg dl(-1) (3.4-11.9) and 4.6 microg dl(-1) (2.8-9.2). Spearman correlations between mother and cord Pb-B and ALA-D were all negative but statistically significant only for cord Pb-B and mother ALA-D. A potential lead threshold, was identified between 3.2 and 4.8 microg dl(-1), above which ALA-D may be inhibited by lead, and below which ALA-D may be insensitive or even activated. In conclusion, low environmental exposure to lead is responsible for a demonstrable biochemical effect. This potential ALA-D inhibition may lead to neurotoxic effects, especially in newborns who have high level of neurogenesis.     

Chemical and biological monitoring of chronic lead poisoning in the rat. Implications to the assessment of hazard of low-level lead

A study on rats of the effects of lead on delta-aminolevulinate dehydratase (ALA-D) activity, and its pH-dependent maximal enzyme activity is reported. Over a 5-week period, the lead burden and ALA-D activity in kidney, liver and brain are documented. Lead concentrations in the organs, expressed as micrograms/g protein are in the sequence kidney greater than liver greater than brain and reach essentially a constant level after 3 days of exposure. This is consistent with the existence of an efficient mechanism removing lead from these organs. Lead affects the ALA-D in all three organs by reducing the activity and shifting the pH of maximum enzyme activity to more acidic values. In common with the lead levels, the ALA-D activity does not deteriorate beyond the levels reached after 3 days of exposure. The existence of a mechanism removing lead from the organs is further supported in a recovery study on blood and kidney, in which both lead level and ALA-D activity return essentially to normal values after 7 days of no exposure to lead.     

Correlation between clinical indicators of lead poisoning and oxidative stress parameters in controls and lead-exposed workers

The present study was undertaken to investigate the involvement of oxidative damage in lead-induced toxicity in humans and to enlighten whether oxidative stress indicators are correlated with the known indices of lead toxicity. For these purposes, selected oxidative stress parameters along with some clinical indices of lead poisoning were determined in blood of battery plant workers and control subjects. Workers had significantly increased erythrocyte malondialdehyde (MDA) levels, catalase and glucose-6-phosphate dehydrogenase (G6PD) activities, and decreased blood glutathione:glutathione disulfide ratio compared to the controls. Increased blood lead concentrations and zinc protoporphyrin (ZPP) levels, and decreased delta-aminolevulinic acid dehydratase (ALAD) activity were used as clinical indices of lead toxicity. Statistically significant correlation between oxidative stress parameters and clinical indices implies that disrupted prooxidant/antioxidant balance might contribute to lead-induced toxicity in erythrocytes. A significant correlation was found between ALAD activity and blood lead levels in human subjects. Similarly significant correlation between ALAD activity and erythrocyte MDA concentrations was shown. Present data indicates that ALAD can serve as a valuable biomarker of oxidative stress in lead-exposed hematological system as well as being a biochemical indicator of lead exposure.     

Effect of lead on the activity of erythrocyte porphobilinogen deaminase in vivo and in vitro

The effect of lead on the activity of erythrocyte porphobilinogen deaminase (PBGD) in vivo and in vitro was investigated using blood specimens obtained from controls and lead-exposed workers. When lead nitrate was added to the incubation mixture at a final concentration of 10⁻⁴ M, 83% inhibition of erythrocyte PBGD activity was found. However, in workers occupationally exposed to lead, no inhibition of erythrocyte PBGD activity was detected. This finding indicates that the erythrocyte PBGD test is not useful for evaluating exposure to lead in workers. In addition, the in vitro study confirmed that mercuric chloride strongly inhibits erythrocyte PBGD activity.     

Effect of aluminum on delta-aminolevulinic acid dehydratase from mouse blood

The objective of this study was to investigate aluminum deposition in whole blood and plasma of mice and the activity of blood delta-aminolevulinic acid dehydratase (ALA-D) after in vitro and in vivo exposure to this element. In vitro experiments showed activation and inhibition of the enzyme activity when 0.01-5.0 mM of aluminum sulphate were used (IC(50): 1.31 mM). Treatment with citrate and aluminum plus citrate increased ALA-D activity in vivo and the increase in enzyme activity was parallel to the increase in aluminum content in blood and plasma. These results show that aluminum has a distinct effect on ALA-D activity: first, at relatively lower concentrations it activated, and at high concentration it inhibited, blood ALA-D in vitro; second, it activated the enzyme when administered to drinking water. One important toxicological finding of the present report is that the apparent irrelevant addition of citrate to the drinking water significantly increased the level of aluminum in blood and plasma. Thus, in order to predict more accurately the extent of human exposure to aluminum it would be advantageous to consider the level of citrate ingestion and not exclusively the aluminum level in water or food.     

Locomotor damage and brain oxidative stress induced by lead exposure are attenuated by gallic acid treatment

We investigated the antioxidant potential of gallic acid (GA), a natural compound found in vegetal sources, on the motor and oxidative damages induced by lead. Rats exposed to lead (50 mg/kg, i.p., once a day, 5 days) were treated with GA (13.5 mg/kg, p.o.) or EDTA (110 mg/kg, i.p.) daily, for 3 days. Lead exposure decreased the locomotor and exploratory activities, reduced blood ALA-D activity, and increased brain catalase (CAT) activity without altering other antioxidant defenses. Brain oxidative stress (OS) estimated by lipid peroxidation (TBARS) and protein carbonyl were increased by lead. GA reversed the motor behavior parameters, the ALA-D activity, as well as the markers of OS changed by lead exposure. CAT activity remained high, possibly as a compensatory mechanism to eliminate hydroperoxides during lead poisoning. EDTA, a conventional chelating agent, was not beneficial on the lead-induced motor behavior and oxidative damages. Both GA (less) and EDTA (more) reduced the lead accumulation in brain tissue. Negative correlations were observed between the behavioral parameters and lipid peroxidation and the lead levels in brain tissue. In conclusion, GA may be an adjuvant in lead exposure, mainly by its antioxidant properties against the motor and oxidative damages resulting from such poisoning.     

Selenium and lead: Mutual detoxifying effects

Antagonistic toxic effects of selenium and lead were studied in growing rats. Chronic lead intoxication was produced by cutaneous application of lead naphthenate solution (80–200 mg Pb/kg body weight) for a period of 8 weeks and chronic selenium intoxication was induced by giving 5 ppm, 10 ppm and 15 ppm selenium in drinking water. The growth rate and food consumption of rats receiving selenium in addition to lead approached normal rate while animals treated with only one of them showed hampered growth rate and lower food consumption. The enzymatic activity of δ-aminolevulinic acid dehydrase (ALA-D) in whole blood, liver and kidney and liver P-450 enzyme activity were normal in rats receiving both selenium and lead. The enzymic activities assayed were, however, depressed in the animals receiving either lead or selenium.Assay of lead and selenium in liver, brain, kidney and blood was carried out. Rats receiving both metals and higher concentrations of these metals in the organs studied, as compared to those only receiving one component. The data seem to indicate that the effect of selenium on the toxic effects of lead is similar to its protective role against methylmercury intoxication.     

The in Vitro and in Vivo Effects of Lead on δ-Aminolevulinic Acid Dehydratase and Pyrimidine 5′-Nucleotidase

The in vitro and in vivo effects of lead on the activity of pyrimidine-5′-nucleotidase (P5N, E. C. 3.1.3.5) and δ-aminolevulinic acid dehydratase (ALA-D, E.C. 4.2.1.24) were studied. Incubation of blood with lead at concentrations of up to 3 μmol/1 (about 60 μg/dl) did not appear to affect the activity of P5N, while the activity of ALA-D decreased dose-dependently with lead. Administration of lead caused a marked and rapid suppression of ALA-D in rats. The suppression of lead on P5N appeared to be a rather slow process. The decrease of its activity only came into effect 20 days after administration with lead. These findings suggest that lead induced P5N inhibition is a slow process while the suppression of ALA-D activity occurs much earlier.     

Heat stable protein with anticoagulant and smooth muscle contractile actions isolated from Habu (Trimeresurus flavoviridis) venom

The biological activity of a Habu (Trimeresurus flavoiridis) venom fraction with drug-metabolizing enzyme inhibitory action was studied. The venom fraction, which was isolated through Sephadex G-100 gel filtration and cation exchange chromatography on Amberlite CG50, caused an increase of vascular permeability and hemorrhage, but these actions were lost after heating at 70 degrees C for 5 min. The fraction showed anticoagulant activity on citrated blood, and this activity remained after heating of the venom. Guinea pig ileum was contracted by treatment with nonheated or heated venom fraction, and these contractions were inhibited with atropine and potentiated with physostigmine. These results suggest that the drug-metabolizing enzyme inhibitor isolated from Habu venom involves the heat stable component with anticoagulant activity and smooth muscle contractile action.