Multicollinearity may lead to artificial interaction: an example from a cross sectional study of biomarkers.

Collinearity is the situation which arises in multiple regression when some or all of the explanatory variables are so highly correlated with one another that it becomes very difficult, if not impossible, to disentangle their influences and obtain a reasonably precise estimate of their effects. Suppressor variable is one of the extreme situations of collinearity that one variable can substantially increase the multiple correlation when combined with a variable that is only modestly correlated with the response variable. In this study, we describe the process by which we disentangled and discovered multicollinearity and its consequences, namely artificial interaction, using the data from cross-sectional quantification of several biomarkers. We showed how the collinearity between one biomarker (blood lead level) and another (urinary trans, trans-muconic acid) and their interaction (blood lead level* urinary trans, trans-muconic acid) can lead to the observed artificial interaction on the third biomarker (urinary 5-aminolevulinic acid).

Lead exposure among nursery children in Chorzów.

The main goal of this study was to determine the level of exposure to lead of selected representatives of the child population attending nursery school, aged 2 to 4 years, residing in three districts of Chorzów with different traffic intensities. The numbers of tested samples of children were 41, 43, 40. The tests were made in summer. Lead (Pb-B), zinc protoporphyrin level (ZPP), hemoglobin (Hb), erythrocyte count in blood (E), and delta-aminolevulinic acid (ALA) and creatinine concentration in urine were determined. The highest Pb-B level observed was 300 micrograms/l; the geometric means of the blood lead concentrations were 131, 132 and 119 micrograms/l and were not statistically different. Median ranges were 118, 133 and 114 micrograms/l. Ranges above the 200 micrograms/l level were found in 19.5%, 11.8% and 15% of the children. The obtained data suggest higher lead absorption in the examined child population.

Optimized fluorometric determination of urinary delta-aminolevulinic acid by using pre-column derivatization, and identification of the derivative.

We previously reported the usefulness of a fluorometric method to determine urinary delta-aminolevulinic acid (ALA) concentrations by using post-column derivatization to monitor the effect of lead exposure. We have further improved the method by introducing pre-column derivatization by using reaction of ALA with acetylacetone and formaldehyde. Response of the hematopoietic system to lead exposure can now be easily detected at blood lead concentrations as low as 162 micrograms/L. The fluorescent ALA derivative, a new aromatic product, 2-methylideneamino-3,5-diacetyl-4,6-dimethylphenylpropionic acid, is separated on octadecyl silica column by high-performance liquid chromatography and the fluorescence intensity is detected with a fluorophotometer. Sample recoveries for 12 urine samples from workers exposed to lead and unexposed controls were 91.9-110.2%. The results obtained by the pre-column derivatization method agreed with those by the post-column derivatization method. The new method increases the sensitivity to a detection limit to 10 micrograms of delta-aminolevulinic acid per milliliter of urine and is simple enough to be used for routine monitoring of the biological effect of exposure to low concentrations of lead.

Urinary excretion of porphyrins is increased in patients with HIV-1 infection.

Urine concentrations of total porphyrins and of porphyrin precursors, delta-aminolaevulinic acid and porphobilinogen, were analysed in the first-morning urine samples of 36 people with established HIV-1 infection. For comparison, we also analysed the urine samples of 26 healthy HIV-seronegative people. In patients with HIV-1 infection concentrations of total porphyrins were found to be significantly higher than in healthy controls. Furthermore, there was a close correlation between concentrations of total porphyrins and porphobilinogen and urine neopterin concentrations in patients. Our data indicate an association between chronic immune activation and altered porphyrin metabolism. The data may provide a rationale for the observation of acute porphyria in patients with HIV-1 infection.

Effects of water restriction and water loading on daily urinary excretion of heavy metals and organic substances in metal workers.

The effects of urinary volume on daily urinary excretion of seven heavy metals and four organic substances were examined in relation to the changes in their plasma and erythrocyte concentrations and urinary creatinine excretion in 19 metal workers. The examination was conducted under the conditions of water restriction and loading for six days. The major findings were as follows: (1) urinary excretion of all heavy metals and organic substances except mercury, together with creatinine excretion, significantly decreased under the water restrictive condition whereas under the water loading condition their excretion significantly increased and (2) daily variations in urinary excretion of lead, cadmium, chromium, copper, hippuric acid, delta-aminolaevulinic acid, and coproporphyrin did not differ significantly from the variation in urinary excretion of creatinine (profile analysis, p greater than 0.05). It is suggested that glomerular filtration is the major factor determining renal excretory mechanisms of the four heavy metals and three organic substances examined.

Effects of perinatal treatment with lead and disulfiram on ALAD activity in blood, liver and kidney and urinary ALA excretion in rats.

Disulfiram, which is metabolized to diethyldithiocarbamate, is known to greatly influence the tissue distribution of lead (Pb) and potentiate the toxic effect of lead in the central nervous system. Effects on delta-aminolevulinic acid dehydratase (ALAD) activity and urinary delta-aminolevulinic acid (ALA) excretion were studied in rats pre- and postnatally exposed to lead and disulfiram, singly or in combination. Pregnant rats were treated with lead (0.25% Pb in the drinking water), with disulfiram (0.1 mmol/kg orally twice a week) or with both lead and disulfiram from day 1 of pregnancy until weaning. After parturition the disulfiram was given subcutaneously directly to the offspring. ALAD activity in blood was inhibited to a similar extent in the group treated with lead alone and in the group treated with lead and disulfiram (7 and 10% of control activity, respectively). Liver and kidney ALAD activities were not affected by the combined treatment with lead and disulfiram. However, urinary excretion of ALA was increased twice as much in the group treated with lead and disulfiram as in the group treated with only lead. The haematocrits were also significantly more depressed after combined exposure to lead and disulfiram. Two weeks after cessation of exposure ALAD activity in blood was inhibited to 47% of control activity in both the lead- and the lead plus disulfiram-treated groups. At this time there was no effect due to treatment on urinary ALA excretion of haematocrit. The results indicate that disulfiram probably influences the effects of lead on ALAD activity at the site of haem synthesis in the bone marrow.2+t is

[Excretion of porphyrin and porphyrin precursor during ethylene oxide inhalation].

The effect of chronic inhalation of ethylene oxide on urinary coproporphyrin and delta-aminolevulinic acid were studied. When Wistar male rats were exposed to 500 ppm ethylene oxide three times a week, daily urine volume was increased by 200-300% from the first week to the fifth week of the experimental period. After exposure, daily coproporphyrin excretion and urinary coproporphyrin per mg of creatinine increased by 250% and 141%, respectively. On the other hand, daily excretion of delta-aminolevulinic acid in urine tended to increase but did not increase significantly by creatinine-correction. We think this is the first report of ethylene oxide induced experimental porphyria.

Study of the lipoprotein pattern among workers exposed to lead.

Occupational exposure to lead fumes constitutes a serious problem in Egypt, since a considerable number of workers might be involved in its deleterious effect. The present study aimed to elucidate the effect of lead exposure on the lipoprotein pattern of exposed workers. The study has been carried out in a plant manufacturing lead batteries. It consists of 89 workers exposed to lead and 25 control subjects. Fasting blood samples were collected for the determination of serum lipoprotein pattern and their cholesterol and phospholipid content. Levels of lead in blood and delta amino levulinic acid in urine have been determined as biological indices of lead exposure. Lead exposure caused mainly a cumulative effect on the cholesterol and phospholipid content of lipoproteins since only workers exposed for more than 10 years showed significant changes. These changes might be referred to the effect of lead exposure on liver and/or on trace metal metabolism.

A new HPLC fluorimetric method to monitor urinary delta-aminolevulinic acid (ALA-U) levels in workers exposed to lead.

A new sensitive HPLC method for the determination of urinary delta-aminolevulinic acid (ALA-U) was used to evaluate the relationship between blood-lead (Pb-B) and ALA-U levels in male workers exposed to lead. The differences between the ALA-U levels determined by this method (ALA-U-HP) and by a colorimetric method (ALA-U-CL) are discussed. The HPLC method gave values similar to the ALA-U-CL values at high ALA-U level. However, at low blood-lead levels (58 +/- 22 micrograms/l, n = 23), the mean ALA-U-HP level corrected by urinary creatinine level was one-third of the corrected ALA-U-CL level (0.83 +/- 0.14 and 2.4 +/- 0.5 mg/g creatinine, respectively). A significant increase of the mean corrected ALA-U-HP level was observed at 162 +/- 22 micrograms/l Pb-B (P less than 0.05, n = 26), while that of ALA-U-CL was observed at 245 +/- 30 micrograms/l Pb-B (P less than 0.01, n = 37). The regression equation based on the logistic model fitted well to the relationship data between the Pb-B level and the percentage of the subjects with corrected ALA-U-HP above the cut-off point (1.12 mg/g creatinine) and the expected Pb-B level for 50% response was 270 micrograms/l Pb-B, while it did not fit well to the relationship data between Pb-B level and the percentage of the subjects with corrected ALA-U-CL above the cut-off point (3.5 mg/g creatinine).(ABSTRACT TRUNCATED AT 250 WORDS)

[The value of determining delta-aminolevulinic acid in urine (method II, East German occupational monitoring) as a screening procedure for the assessment of internal residues in occupational exposure to lead]. / Der Wert der Bestimmung von Delta-Aminolävulinsäure im Urin (Methode II, AB-DDR) als Screeningverfahren zur Einschätzung der inneren Belastung bei beruflicher Exposition gegenüber Blei.

For the purpose of supervising workers exposed to lead the ratio of blood lead is determined several times per year. The withdrawal of blood samples from the vein necessary for this purpose as well as the comparatively high analytic expense make it essential to revise, whether it is possible to give up the analysis of blood lead at least partially in favour of other diagnostic measures less affecting the worker. Our investigation gave evidence of the fact, that the validity of a screening test for evaluating the blood lead concentration on the basis of the determination of delta-aminolaevulinic acid in urine (method II, AB-DDR; 2 nd morning urine) is insufficient.

Blood lead and maximal urinary excretion of delta-aminolevulinic acid.

Reliability and ease of use are certainly the two major qualities of a screening test or medical surveillance in the workplace. The advantages of using a reliable urinary test thus are evident: the sampling is easy, rapid, noninvasive and, therefore, well accepted. Screening tests or medical surveillance can measure the toxic chemical itself, its metabolites or its consequences on metabolism. In this study the relation between blood lead levels--the most commonly used test for screening and surveillance of saturnism--and urinary excretion of delta-aminolevulinic acid (ALA-U) was measured. The original part of this study is that it takes into account the chronobiology of ALA-U excretion. The samples are collected in the afternoon when ALA urinary excretion is at its highest level. Using a 5 mg/g of creatinine level as a threshold to detect blood lead levels equal to or higher than 60 micrograms/dL the test has an 88% sensitivity, a 91% specificity and a 37% positive predictive value. No worker whose blood lead level is equal to or higher than 65 micrograms/dL has been missed. It is suggested that using 5 mg of ALA-U/g of creatinine as a threshold to prescreen workers who should have their blood lead level measured could be useful in workplaces where lead exposure is moderate or low.

Species difference of urinary excretion of delta-aminolevulinic acid and coproporphyrin in mice and rats exposed to lead.

The urinary excretion of delta-aminolevulinic acid (ALA) was first investigated in mice exposed to lead in the drinking water (500 ppm) for 30 days, and the results were compared with those obtained from rats exposed to lead under the same exposure condition. The result indicated that the level of urinary ALA excretion in lead-exposed mice was much higher than that in lead-exposed rats. This finding suggests a species difference between mice and rats with regard to sensitivity to lead. On the other hand, urinary coproporphyrin (CP) was also determined in rats and mice exposed to lead. The result obtained indicated that the increasing level of urinary CP excretion was higher in rats than in mice, contrary to expectation. The reason for the discrepancy between urinary excretion of ALA and that of CP in rats and mice exposed to lead is, however, unknown.

Effect of intratracheal gallium arsenide administration on delta-aminolevulinic acid dehydratase in rats: relationship to urinary excretion of aminolevulinic acid.

Exposure to gallium arsenide (GaAs) is a potential hazard in the semiconductor industry and there is a need for specific biological indicators of exposure/toxicity for this compound. These studies examined effects of GaAs exposure on the heme biosynthetic pathway enzyme delta-aminolevulinic acid dehydratase (ALAD). Male CD rats received GaAs suspensions at doses of 50, 100, or 200 mg/kg via a single intratracheal instillation. Six days after treatment a dose-dependent inhibition of blood ALAD was observed with activity decreasing to 5% of controls at the highest dose, with a concomitant marked increase in the urinary excretion of aminolevulinic acid (ALA). Inhibition of blood ALAD following administration of GaAs was maximal (30% of control) 3 to 6 days postexposure and returned to approximately control values on day 18. Urinary excretion of ALA was maximal 3 to 6 days postexposure and recovered toward control values at 18 days. Inhibition of kidney and liver ALAD following GaAs exposure was also evident. Intratracheal instillation of silica did not alter the activity of ALAD in blood, liver, or kidney. Marked increases in lung wet weight/body weight ratios were evident in lungs of silica- and GaAs-treated rats. Histopathological changes in the lungs were characterized by multifocal granulomas following silica treatment and Type II pneumocyte hyperplasia following GaAs treatment; mild necrosis was evident in both groups. Rats treated with 100 mg/kg GaAs exhibited swelling of kidney proximal tubule mitochondria 6 days following exposure. Silica and GaAs exposure produced marked decreases in cumulative weight gain. The concentration of gallium required to achieve half-maximal inhibition of ALAD in vitro was 200-fold less in blood and 40-fold less in kidney and liver than that required for arsenite and the inhibition was partially prevented by excess zinc. These data suggest that gallium is the primary inhibitor of ALAD following dissolution of GaAs in vivo and that competition for or displacement of zinc from the enzyme active site may be involved in the mechanism of inhibition. The data also demonstrated the utility of including a particulate control group when assessing the chemical-induced toxicity of compounds administered intratracheally as particulate suspensions. Finally, measurement of heme precursors, e.g., ALA, in urine coupled with assay of red blood cell ALAD activity may be of value as an early biological indicator of GaAs exposure and/or toxicity.

Comparison between the fluorometric HPLC method and the conventional method for determining urinary delta-aminolevulinic acid and coproporphyrin as indices of lead exposure.

Fluorometric methods for determining delta-aminolevulinic acid (ALA) and coproporphyrin (CP) in urine have been recently developed by using high-performance liquid chromatography (HPLC). In the present study, urinary ALA and CP in lead-exposed workers were determined with these fluorometric HPLC methods and the conventional methods, and the results obtained were compared. In lead workers with a urinary ALA greater than or equal to 5 mg/l, the values obtained with the fluorometric HPLC method corresponded well with those measured with the conventional colorimetric method. In contrast, in lead workers with ALA less than 5 mg/l, ALA values obtained with the fluorometric HPLC method were lower than those measured with the conventional method, suggesting the possibility of matrix interference in urine. The urinary CP values obtained with the conventional method of Rimington (1971) were higher than those measured with the fluorometric HPLC method, though the correlation was good.