Zeta-aminolevulinic acid dehydratase test for lead exposure

Effect of glycine on lead mobilization, lead-induced oxidative stress, and hepatic toxicity in rats

The effectiveness of glycine in treating experimental lead intoxication was examined in rats. Male Wistar rats were exposed to 3 g/L lead acetate in drinking water for 5 weeks and treated thereafter with glycine (100 and 500 mg/kg, orally) once daily for 5 days or glycine (1000 mg/kg, orally) once daily for 28 days. The effect of these treatments on parameters indicative of oxidative stress (glutathione and malondialdehyde levels), the activity of blood δ-aminolevulinic acid dehydratase, and lead concentration in blood, liver, kidney, brain, and bone were investigated. Liver samples were observed for histopathological changes. Glycine was found to be effective in (1) increasing glutathione levels; (2) reducing malondialdehyde levels; (3) decreasing lead levels in bone with the highest dose. However, glycine had no effect on lead mobilization when 100 and 500 mg/kg glycine were administered. In microscopic examination, glycine showed a protective effect against lead intoxication.

Possibilities of newer ALAD polymorphism influencing human susceptibility to effects of inorganic lead on the neurobehavioral functions

OBJECTIVE

A cross-sectional study was conducted to study the association between some new ALAD polymorphism and susceptibility to effects of inorganic lead on the neurobehavioral functions.

METHOD

We recruited 120 healthy male workers with lead exposure in a factory which manufacture lead stabilizer. The ALAD SNPs studied were HpyCH4, HpyIV RFLP in intron 6, Rsa and Msp RFLP in exon 4, Sau3A in intron 12 and Rsa39488 in exon 5. The World Health Organization Neurobehavioral Core Test Battery (WHO-NCTB) and a few other tests were used. General linear model (GLM) was applied to compare outcome scores between subgroups of each ALAD SNP while controlling for possible confounders.

RESULTS

The mean age of the workers was 39.7 years (S.D. 10.7), mean exposure duration of 10.2 years (S.D. 7.9) and mean blood lead of 22.1 microg/dl (S.D. 9.4). Among the 6 SNPs studied, Rsa and Rsa39488 appear to be the main candidate SNPs. Workers with Rsa and Rsa39488 ALAD 2-2 genotypes fare significantly better in the Aiming Pursue Test Correct (AC), Groove Peg Board non-preferred hand (GPNP), Groove Peg Board Mean (GPM), San Ana Preferred Hand (SAP), San Ana Both Hands (SAB) and AC, GPNH, GPM, Digit Symbol (DIS) tests; respectively compared to Rsa and Rsa39488 ALAD 1-1/1-2 genotypes adjusted for age, race, exposure duration and blood lead levels.

CONCLUSION

The presence of the homozygote Rsa and Rsa39488 ALAD 2-2 seems to offer some protection against the effect of lead on motor dexterity function. While it may appear that newer ALAD polymorphism other than the commonly reported Msp SNP might influence human susceptibility to effects of inorganic lead on the neurobehavioral functions further study involving a larger cohort of workers with Rsa and Rsa39488 ALAD2 allele would be needed to confirm this inference.

Delta-aminolevulinic acid dehydratase (ALAD) polymorphism and susceptibility of workers exposed to inorganic lead and its effects on neurobehavioral functions

We carried out a cross-sectional study on a group of male workers to determine the frequency of delta-aminolevulinic acid dehydratase (ALAD) polymorphisms among Chinese, Malays and Indians workers who were exposed to low to medium levels of inorganic lead. Also, the association between ALAD1 and ALAD2 genotypes and neurobehavioral functions among these workers were investigated. A total of 120 male workers were studied. Blood and urine were collected for each worker to determine the ALAD genotypes, blood lead levels, ALAD, and urinary delta-aminolevulinic acid (ALAU). ALAD1-1 was the predominant genotype for all three ethnic groups while ALAD2-2 was the rarest. The distribution of ALAD1-2 was higher among Malays (16.7%) and Indians (14.3%), compared to Chinese (3.6%). Selected tests from the World Health Organization Neurobehavioral Core Test Battery (WHO-NCTB) were used. Although workers in the ALAD1-1 and ALAD1-2/2-2 groups had comparable blood lead levels, the 106 workers with ALAD1-1 genotypes have significantly higher urinary ALA and significantly poorer neurobehavioral scores involving motor dexterity compared with those who have ALAD1-2/2-2 genotypes (13 workers). It is postulated that the ALAD2 allele may exert protective measures against the neurotoxic effects of lead. Further study involving a larger cohort of workers with the ALAD2 allele would be needed to confirm this hypothesis.

Lead binding to delta-aminolevulinic acid dehydratase (ALAD) in human erythrocytes

Over 99% of the lead present in blood is usually found in erythrocytes. To investigate the nature of this selective accumulation of lead in erythrocytes, the specific binding of lead to proteins in human erythrocytes was studied using liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICP-MS). The principal lead-binding protein had a mass of approximately 240 kDa, and adsorption to specific antibodies showed that protein was delta-aminolevulinic acid dehydratase (ALAD). Thus, the previous notion that lead in erythrocytes was bound primarily to haemoglobin has to be revised. Furthermore, in lead-exposed workers, the percentage of lead bound to ALAD was influenced by a common polymorphism in the ALAD gene. Specifically, in seven carriers of the ALAD2 allele, 84% of the protein-bound lead recovered was bound to ALAD compared to 81% in seven homozygotes for the ALAD1 allele whose erythrocytes were matched for blood-lead concentration. The small difference was statistically significant in Wilcoxon matched-pairs signed-rank test (P = 0.03). No ALAD allele-specific difference in ALAD-bound lead was found among 20 unexposed controls. Perhaps the difference in ALAD-bound lead can provide an explanation for the previously reported finding of higher blood-lead levels among carriers of the ALAD2 allele than among ALAD1 homozygotes in lead-exposed populations.

The effect of aluminum chloride on some steps of heme biosynthesis in rats after oral exposure

Certain disturbances in heme biosynthesis induced by aluminum chloride were examined. The experiment was performed on female rats that received AlCl3 orally at the dose 100 mg Al/kg daily for 21 d. The effects of aluminum on the activity of delta-aminolevulinic acid synthetase (ALA-S), dehydratase (ALA-D), and heme oxygenase (O.H.) were observed on 3, 7, 14, and 21 d in liver and kidneys of rats. Also the activity of ALA-D in blood and the concentration of delta-aminolevulinic acid (ALA-U) in urine were observed. Orally administered aluminum caused increase in the activity of ALA-D in the liver and blood, and parallel decrease of ALA-U in urine (r = -0.85) of rats. Aluminum chloride also induced an increase of ALA-S and O.H. in the liver but not in the kidneys. The changes of the enzymes activity participating in heme biosynthesis after administration of aluminum may be correlated with anemia and iron metabolism in rats.

Disturbances in heme biosynthesis in rabbits after administration per os of low doses of tin or lead

The experiment was performed on female rabbits that received per os equimolar doses (17 microM Me/kg) of SnCl2 x 2 H2O or Pb (CH3 COO)2 every day for 5 d. The activity of delta-aminolevulinic acid dehydratase (ALA-D) in the whole blood, liver, kidneys, brain, spleen, and bone marrow, concentration of free erythrocyte protoporphyrins (FEP), activity of delta-aminolevulinic acid synthetase (ALA-S) in the liver and bone marrow, urine delta-aminolevulinic acid (ALA-U), and coproporphyrins (CP-U) were determined. Lead and tin concentrations in the blood were estimated. Lead caused a significant inhibition of ALA-D in the blood, increased FEP concentration, and ALA and CP excretion in urine of rabbits. Lead also decreased ALA-D activity in the bone marrow and in the liver, and did not change ALA-S activity in the liver and bone marrow. Tin did not change any of the examined indices. Tin doses applied in the present study, maintained within the limits of permissible standards of metal levels in human diet, did not affect the process of heme biosynthesis in rabbits.

Relationship between inhibition of erythrocyte pyrimidine 5'-nucleotidase activity and biological response for porphyrin metabolism in workers occupationally exposed to lead

A rapid determination of erythrocyte pyrimidine 5'-nucleotidase (P5N) activity in lead workers was carried out using a high-performance liquid chromatograph (HPLC). The P5N activity had a good negative correlation with the concentration of lead in blood (PbB) ranging from 16 to 96 micrograms/dl (r = -0.82, n = 77). Further, the P5N was compared with other biological parameters: erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity, erythrocyte protoporphyrin (PROTO), urinary delta-aminolevulinic acid (ALA) and urinary coproporphyrin (COPRO). The correlation coefficients between P5N and ALAD, log PROTO, log ALA, and log COPRO were 0.59, -0.72, -0.65, and -0.61, respectively. On the other hand, the normal value of P5N obtained from 72 healthy subjects was 11.9 +/- 2.1 units; mumol uridine/h/g Hb (mean +/- SD), indicating that the lower limit of 95% confidence interval for normal P5N was about 8 units. When P5N was cut off at less than or equal to 8 units in 77 lead workers, the validity (sensitivity + specificity) for PbB greater than or equal to 40 micrograms/dl, PbB greater than or equal to 60 micrograms/dl, erythrocyte PROTO greater than or equal to 150 micrograms/dl RBC, urinary ALA greater than or equal to 6 mg/l, and urinary COPRO greater than or equal to 150 micrograms/l was 1.66, 1.76, 1.57, 1.68, and 1.60, respectively. From these results, it was confirmed that the erythrocyte P5N test is suitable for the biological monitoring of exposure to lead in a wide range, and its activity is useful in predicting the disturbance of porphyrin metabolism induced by lead.

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.

The chronic toxicity of aluminium, cadmium, mercury, and lead in birds: a review

The toxicity of chronic dietary metal exposure in birds is reviewed. It is concluded that significant physiological and biochemical responses to such exposure conditions occur at dietary metal concentrations insufficient to cause signs of overt toxicity. Particularly important are reproductive effects which include decreased egg production, decreased hatchability, and increased hatchling mortality. Young, growing birds are typically more sensitive to the toxic effects of chronic metal exposure than adults, and altricial species are often more sensitive than precocial species. Factors which modify the absorption and toxicity of heavy metals, such as Se for the case of Hg, and Ca for the case of Pb and Cd, are discussed. Monitoring strategies for assessing environmental metal exposure in birds are evaluated.

Evaluation of the relationship between chemical and biological monitoring of low-level lead poisoning

Blood lead levels, together with delta-aminolevulinic acid dehydratase activity determinations have been measured on rats dosed with up to 1000 ppm lead acetate in their drinking water for periods up to 5 weeks. Despite evidence of a compensation mechanism developing in the enzyme determinations, enzyme activity ratios, if properly chosen, still correlate reasonably well (r = 0.87) with blood lead levels. Activity ratios using data on the shoulders of pH-activity profiles (e.g. activity ratios of 6.4 and 7.2), however, give much less satisfactory correlations. These data provide a more stringent test of the chemical monitor-biological monitor correlation than has previously been possible.

Immunological and enzymatic studies of erythrocytic delta-aminolevulinate dehydratase. Comparison of results obtained in normal and lead-exposed subjects

The delta-aminolevulinate dehydratase (ALA.D) quantitative assay on a centrifugal fast analyser showed that subjects whose blood-lead level varies between 30 and 75 micrograms/100 ml (1.5 to 3.75 microM/l) react to blood intoxication by synthesizing de novo an amount of enzyme correlating to blood-lead levels. At higher concentrations, the reactional synthesis occurs very rarely. These results suggest that enzyme is constitutive, but also inductible as soon as its substrate accumulates; this last ability may disappear at high blood-lead levels: a hypothesis is proposed thereafter.

Comparison of the in vivo and in vitro effects of lead on the pH-activity relationship of human erythrocytic delta-aminolaevulinic acid dehydratase

The effect of lead in vitro on the pH-activity relationship of human erythrocytic delta-aminolaevulinic acid dehydratase (delta-ALAD) and on the assessment of lead exposure with ratios of delta-ALAD activity measured at specific pH values was investigated. The addition of lead nitrate to whole blood at concentrations ranging from 0.40 to 8.1 mumole Pb2+/1, for periods of contact ranging from 16 h to 20 days at 4 degrees C, resulted in a time and dose dependent shift of the enzyme's pH optimum to a more acid value. The pH optimum shift obtained at raised lead concentrations or after long periods of contact at 4 degrees C, in both, closely approximated that observed in vivo. The loss of enzyme activity, however, was significantly less in vitro than that in vivo for similar whole blood lead concentrations. These findings indicate that the presence of trace amounts of lead in blood collection devices can seriously affect results obtained with the pH activity ratio method of assessing lead exposure.

The effects of environmental lead exposure and in vitro zinc on tissue delta-aminolevulinic acid dehydratase in urban pigeons

1. Elevated lead burdens in three urban pigeon populations caused ALAD inhibition, in blood, kidney and liver, the degree of inhibition generally corresponding to the lead content of each tissue. The values obtained are compared with those given by studies of lead exposure in mammals. 2. The usefulness of blood ALAD as an index of lead exposure is discussed. 3. The pH activity profile of ALAD in blood and kidney of urban pigeons was also changed. 4. In vitro zinc additions partially restored lead-inhibited ALAD. 5. These findings are discussed in terms of the possible manner in which lead inhibits ALAD.

Increase of delta-aminolevulinic acid dehydratase (ALAD) in rat erythrocytes in lead poisoning

The well known fact that the activity of delta-aminolevulinic acid dehydratase (ALAD: EC 4.2.1.24) is reduced in red cells of animals with lead poisoning was found to be upset, by using a modified method of Gibson's original procedure, for determination of activated ALAD activity. The modified method involves addition of 0.2 mM Zn2+ and then preheating the enzyme solution at 60 degrees C for 5 min before following Gibson's original procedure. With this methodological modification, the ALAD activity of erythrocytes of rats poisoned with lead was found increased. Furthermore, the enzyme was purified from the peripheral blood of lead-poisoned rats. ALAD protein in peripheral blood was also determined by single radial immuno diffusion using rabbit anti-serum raised against rat liver ALAD. As the result, the ALAD activity obtained from the modified method was found to be directly proportional to the absolute amount of enzyme proteins determined both by chemically and immunochemically. The modified method for measuring true ALAD content in blood cells in lead poisoning is more reliable than previous ones.

Biomonitoring lead exposure with delta-aminolevulinate dehydratase (ALA-D) activity ratios

The occupational or environmental exposure of selected populations to lead, either alone or in combination with other metals, was monitored using ratios of the activity of the erythrocytic enzyme delta-aminolevulinate dehydratase. The results obtained have reaffirmed earlier findings that this test affords several significant advantages over the use of the enzyme's activity value measured at a set pH value and other types of activity ratios to assess lead exposure. Furthermore, the activity ratios' proven sensitivity, reliability, reproducibility, specificity and stability warrant that they be considered as viable alternatives to the more widely accepted diagnostic criteria of lead intoxication namely zinc protoporphyrin and lead levels in blood.

Arginase and kallikrein activities as biochemical indices of occupational exposure to lead

In a group of 60 workers occupationally exposed to lead the blood and urine lead concentrations, haematocrit, ALA-D and arginase activities, and urinary 5-aminolaevulinic acid (ALA) and coproporphyrin concentrations, and kallikrein activity were determined. Correlation coefficients of -0.78 and 0.77 for Pb-B/ALA and Pb-B/arginase were found respectively for lead concentrations above 40 microgram/dl blood, and 0.83, 0.76, 0.74, and -0.64 for Pb-U/ALA, Pb-U/Cp-U, Pb-U/kallikrein, and Pb.U/kallikrein, respectively. It seems that the increase in serum arginase activity may be indicative of liver damage while the decrease in kallikrein activity may indicate kidney damage in workers exposed to lead.

Lead poisoning. A comprehensive review and report of a case

Lead, a ubiquitous heavy metal which has realized increased use, can cause poisoning by environmental contamination in either its organic or its inorganic form. Lead poisoning can be either acute or chronic, with the latter being the more common. The clinical signs and symptoms of lead poisoning are nonspecific, resulting in a difficult diagnostic problem, especially when it is not industrially related. On occasions, the dentist or oral surgeon may be the first to see an afflicted patient because of oral manifestations.

Evaluation of methods for the estimation of 5-aminolevulinate dehydratase for a broad range of lead concentrations in the blood of exposed workers

5-aminolevulinate dehydratase activity was estimated in the blood of 30 lead-exposed workers and 15 control persons, using (I) the method of Tomokuni ((1974) Arch. Environm. Health 29, 274--281) and (II) the European standard method (Berlin & Schaller (1974) Z. Klin. Chem. Klin. Biochem. 12, 389--390). The lead level in the blood was in the range 0--11.6 mumol/l. It was found that the correlation between the activity of 5-aminolevulinate dehydratase and the lead level in blood (up to 4.35 mumol/l) are higher for method I than method II. These two methods only give similar results for the units of 5-aminolevulinate dehydratase activity when the lead concentrations in the blood are low. For higher concentrations of this metal (up to 11.6 mumol/l), a high correlation was obtained (r = -- 0.80) between the 5-aminolevulinate dehydratase activity ratio (enzyme measured at pH 6.8/enzyme measured at pH 6.0; method I) and lead concentrations in the blood.

Urinary delta-aminolevulinic acid as a biological indicator throughout penicillamine therapy in lead intoxication

A group of 121 patients with occupational lead exposure was studied. Saturnism was confirmed in 42 of them. Patients were given D-penicillamine in doses of 0.75 and 1.5 g/day. Urinary delta-aminolevulinic acid was selected as a toxicity biological indicator; its concentrations were quantified daily during therapy. Urinary delta-aminolevulinic acid is considered a good biological indicator throughout penicillamine therapy and also in the detection of lead intoxication. Likewise, the chelating test is considered an excellent method to confirm the diagnosis of lead poisoning.

Evaluation of tests for the diagnosis of lead exposure in sheep

Several laboratory tests that are currently used for the diagnosis of lead poisoning in man were evaluated for the detection of lead poisoning in sheep given 3 or 10 mg Pb/kg body weight/day for 7 weeks. Urinary porphyrins and basophilic stippling of erythrocytes were not sensitive indicators of lead poisoning in sheep, while urinary lead and urinary delta-aminolevulinic acid concentrations were too variable to have diagnostic value. However, erythrocyte delta-aminolevulinic acid dehydratase was strongly inhibited by exposure to relatively low doses of lead, while blood lead concentrations gave an indication of the level of exposure to lead poisoning.

[Biochemical methods for the detection of lead poisoning (author's transl)]

After a short description of sources of lead poisoning a review is given of toxicity, absorption, storage and excretion of lead. Afterwards its biochemical affects--especially the influence on the biosynthesis of heme--are treated. Methods for diagnosis of lead poisoning resulting from these affects--determination of coproporphyrine and delta-aminolevulinic acid excretion in urine, erythrocyte delta-aminolevulinic acid dehydratase activity and erythrocyte protoporphyrin--are discussed in detail.

Delta-aminolevulinic acid dehydratase--a sensitive indicator of lead exposure in Japanese quail

Red blood cell delta-aminolevulinic acid dehydratase (RBC-ALAD) activity has proven to be a sensitive indicator of lead exposure in humans. The depressed enzyme activity and its negative correlation to blood lead concentrations are well-known effects of lead exposure in man. The sensitivity of RBC-ALAD activity in young Japanese quail exposed to low levels of lead as lead acetate was investigated. Two groups of nine birds each were fed purified diets containing either no added lead or 25 micrograms of lead per g. of diet. After 2 weeks, blood samples for hematocrit, hemoglobin, and enzyme determinations and renal, hepatic, duodenal, and tibial tissues were collected. There were no significant differences between controls and lead-fed birds in body, kidney, duodenal, and tibial weights, or in hematocrit and hemoglobin concentrations. However, the renal, hepatic, duodenal, and tibial lead concentrations were significantly (P less than 0.001) greater in the lead-treated birds. The activity of RBC-ALAD in the group fed lead was 45% of that in the control group; these values were significantly different (P less than 0.001). RBC-ALAD activity expressed as the log. base 10 showed significant (P less than 0.02) negative correlation with both hepatic and tibial lead. The study demonstrates that the activity of RBC-ALAD in the Japanese quail is a very sensitive indicator of lead exposure.

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 delta-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.

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

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.

Sublethal effects of chronic lead ingestion in mallard ducks

Mallard drakes (Anas platyrhynchos) fed 1, 5, or 25 ppm lead nitrate were bled and sacrificed at 3-wk intervals. No mortality occurred, and the pathologic lesions usually associated with lead poisoning were not found. Changes in hematocrit and hemoglobin concentration did not occur. After 3-wk ducks fed 25 ppm lead exhibited a 40% inhibition of blood delta-aminolevulinic acid dehydratase activity that persisted through 12 wk exposure. After 12 wk treatment similar enzyme inhibition was present in the ducks fed 5 ppm lead. At 3 wk there was a small accumulation of lead (less than 1 ppm) in the liver and kidneys of ducks fed 25ppm lead; no further increases occurred throughout the exposure. No significant accumulation of lead occurred the the tibiae or wing bones. Groups of ducks fed 5 and 25 ppm diets for 12 wk were placed on clean feed and examined through a 12 wk posttreatment period. After 3 wk on clean diet delta-aminolevulinic acid dehydratase activity and lead concentrations in the blood had returned to pretreatment levels. Even though lead concentrations in the blood, soft organs and bone were low, a highly significant negative correlation between blood lead and blood enzyme activity was obtained. This enzyme bioassay should provide a sensitive and precise estimate for monitoring lead in the blood for waterflow.

Erythrocyte protoporphyrin test for occupational lead exposure

Determination of erythrocyte protoporphyrin levels was performed in workers who are occupationally exposed to lead. The level of erythrocyte protoporphyrin was easily measured with microsamples of blood by utilizing a fluorescent assay. The log of erythrocyte protoporphyrin level was closely correlated to blood lead level (r = .72) in lead-exposed workers. The erythrocyte protoporphyrin test is especially useful in the detection of mild increases in blood lead concentration under conditions of occupational exposure.

Relationship between activation of delta-aminolevulinic acid dehydratase by heating and blood lead level

Both blood lead and erythrocyte delta-aminolevulinic acid dehydratase (ALA-D) activity were determined for workers with and without an occupational lead exposure. In workers occupationally exposed to lead, it was demonstrated that the erythrocyte ALA-D is markedly activated by heating the hemolysate at 60 degrees C for 5 min and there is a good positive correlation between the ratio of heated to nonheated ALA-D activity and the blood lead level (r=0.799). In addition, by heating the hemolsyate, the ALA-D activity of the lead-exposed workers appears to be returned into the normal range regardless of the extent of lead absorption. However, in normal workers without the occupational lead exposure, no significant correlation was found between the ratio of heated to nonheated ALA-D activity and the blood head level, although the normal ALA-D also can be slightly activated by heating the hemolysate at 60 degrees C for 5 min.

Different behaviors of erythrocyte delta-aminolevulinic acid dehydratase. A comparison study between lead workers and normals

Different characteristics of erythrocyte delta-aminolevulinic acid dehydratase (ALA-D1) between the workers with the history of occupational lead exposure and normals are described. In the blood of lead workers, when the hemolysates are heated at 60 C for five minutes, the activity of the erythrocytes ALA-D increases up to about 3.6-fold of an initial level, and as a result of heating the optimum in pH-activity curvee changes from pH 6.0 to pH 6.6, which is similar to the optimum pH of normal ALA-D. On the contrary, in normal blood, the optimum in the pH-activity curve is but little changed, even though the erythrocyte ALA-D activity is increased up to about 1.3-fold of the initial level by heating the hemolysates at 60 C for five minutes.