Carcinogenicity of tetraethyl lead

Environmental lead exposure increases micronuclei in children

The objective of this pilot study was to investigate the contribution of environmental exposures to lead in the development of cytogenetic damage detected as the frequency of micronuclei (MN) in children. The other aim was to apply the MN assay in combination with fluorescence in situ hybridization (FISH) using a pan-centromeric chromosome probe to elucidate the formation mechanism of induced MN. The examined population was composed of 9-year-old children (n = 92), living in the region where non-ferrous ores are extracted and processed. The non-exposed group consisted of 49 children of the same age from an unexposed recreational area. Exposure to lead was assessed by determination of lead concentrations in blood (PbB) by atomic absorption spectrophotometry, whereas the level of selenium (Se) in serum was detected by using graphite furnace atomic-absorption spectrometry. The frequency of MN was determined by the cytokinesis-block MN assay and fluorescence in situ hybridization performed using a specific pan-centromeric probe. Environmental exposure to lead resulted in significantly increased levels of PbB (5.29 +/- 2.09 versus 3.45 +/- 1.20 microg/dl in controls), although the average level was much below the value of the biological exposure limit = 10 microg/dl. A negative correlation between lead in blood and Se in serum concentrations (P = 0.006) was found for the pooled study population. The results showed a significant difference (P < 0.0001) in the level of MN between the exposed and control group (standard MN test: 2.96 +/- 2.36 versus 1.16 +/- 1.28; FISH technique: 3.57 +/- 3.02 versus 1.43 +/- 1.69, respectively). The frequencies of both centromere-positive (C+MN) and centromere-negative (C-MN) micronuclei were significantly increased in exposed children; however, the contribution of C+MN in the total number of MN in peripheral blood lymphocytes of exposed children was significantly higher than in the controls what may suggest a pro-aneugenic effect of the exposure to lead. The results of multiple regression analysis indicated that the exposure to lead was an important factor affecting the increase in MN frequency what was confirmed by significant correlation between the PbB and MN levels. In conclusion, our results suggest that the exposure to lead may be associated with an increased frequency of MN, especially of C+MN; however, the influence of other factors (e.g. vitamins and minerals in the diet) cannot be excluded.

Lead as a carcinogen: experimental evidence and mechanisms of action

Recent epidemiological and experimental work confirms that inorganic lead compounds are associated with increased risks of tumorigenesis. In animals, these risks can be induced at doses that are not associated with organ toxicity and in mice that do not produce alpha-2 urinary globulin in the kidney. Thus the mechanisms of lead carcinogenicity are unlikely to be fully explained as toxicity-related sequelae of high dose exposure or as a rat-specific response involving overexpression of a renal protein. Plausible mechanisms of lead carcinogenicity include direct DNA damage, clastogenicity, or inhibition of DNA synthesis or repair. Lead may also generate reactive oxygen species and cause oxidative damage to DNA. Recent data indicate that lead can substitute for zinc in several proteins that function as transcriptional regulators, including protamines. Lead further reduces the binding of these proteins to recognition elements in genomic DNA, which suggests an epigenetic involvement of lead in altered gene expression. These events may be of particular relevance in transplacental exposures and later cancer.

Perinatal growth retardation caused by triethyl lead chloride treatment of mice during late gestation

Female mice were injected intraperitoneally daily from day 18 of gestation and throughout lactation with triethyl lead chloride (TEL; 0.0, 0.5 and 1.0 mg/kg body wt). Off-spring of treated mothers displayed a slight perinatal growth retardation. Male off-spring appeared to be more sensitive to TEL, as indicated by their lower body weights. During the latter half of the lactation period the treated sucklings grew faster than controls, thereby compensating for their initially retarded growth, by the time of weaning. The hepatic cytochrome P-450 content of 9 to 10-day old sucklings of treated mothers was lower than in corresponding controls. We suggest that perinatal growth retardation is initiated by a disturbance in the uterus, e.g. reduced nutrient transport across the placenta.

Effects of triethyllead chloride on hepatic microsomal N- and C-oxygenation of N,N-dimethylaniline in rats

Triethyllead chloride was added directly to male rat liver microsomes (0.0, 0.05, 0.25, 0.5, 1.0, and 3.0 mM), or the rats were pretreated with ip injections, once a day for 2 days (0.0, 1.5, and 3.0 mg triethyllead chloride/kg body wt), and microsomes prepared without any further treatment on Day 3. The effects of these treatments on microsomal N-oxygenation and C-oxygenation in vitro were studied by using N-oxide formation and N-demethylation of N,N-dimethylaniline (DMA) as test reactions. Increased microsomal N-oxygenation was obtained by in vivo treatment and decreased microsomal C-oxygenation by in vitro treatment. As a result, either treatment thus gave rise to an increase in the N-oxygenation/C-oxygenation ratio. Conditions favoring accumulation of the N-oxide product may potentiate the tumor-inducing characteristics of carcinogenic aromatic amines.

Role of cobalt, iron, lead, manganese, mercury, platinum, selenium, and titanium in carcinogenesis

The possible carcinogenicity of cobalt, iron, lead, manganese, mercury, platinum, selenium, and titanium is reviewed, taking into account epidemiological data, the results of animal experimental studies, data on mutagenic effects and on other in vitro test systems. Of the great variety of occupations where exposure to one of these metals may occur, only haematite mining has been clearly shown to involve an increased human cancer risk. While the possibility that haematite might in some way act as a carcinogen has to be taken into consideration it is more likely that other carcinogens are responsible. Certain platinum coordination complexes are used in cancer chemotherapy, are mutagenic, and likely to be carcinogenic. Cobalt, its oxide and sulfide, certain lead salts, one organomanganese, and one organotitanium compound have been shown to have a limited carcinogenic effect in experimental animal studies, and except for titanium appear to be mutagenic. Certain mercury compounds are mutagenic but none have been shown to be carcinogenic. The presently available data are inadequate to assess the possible carcinogenicity of selenium compounds, but a few observations suggest that selenium may suppress the effect of other carcinogens administered to experimental animals and may even be associated with lower cancer mortality rates in man. Epidemiological observations are essential for the assessment of a human cancer risk, but the difficulty in collecting past exposure data in occupational groups and the complexity of multiple occupational exposures with changes over time, limits the usefulness of retrospective epidemiological studies.

Exposure of motor vehicle examiners to carbon monoxide: a historical prospective mortality study

The National Institute for Occupational Safety and Health (NIOSH) investigated the health effects of chronic exposure to low concentrations of carbon monoxide by conducting a historical prospective cohort study of mortality patterns among 1,558 white male motor vehicle examiners who were employed in New Jersey for a minimum of 6 months between 1944 and 1973. Industrial hygiene surveys indicated that the examiners were exposed to carbon monoxide at a time-weighted average (TWA) of 10-24 ppm; the exposure level recommended by NIOSH is 35 ppm TWA. A modified life table technique was used to calculate cause-specific expected deaths for the cohort adjusted for age and calendar time periods. The expected deaths were compared to the number of observed deaths through August 1973. The cohort demonstrated a slight overall increase in cardiovascular disease deaths (124 observed vs. 118.4 expected), but a more pronounced excess was observed within the first 10 yr. following employment (28 observed vs. 20.9 expected). A statistically significant excess of cancer mortality was found for motor vehicle examiners after 30 yr latency (13 observed vs. 6.9 expected, P < 0.5); this excess, however, was not confined to any particular organ site. The number of deaths due to accidents was significantly lower than expected (8 observed vs. 19.6 expected, P < .01).

Long-term occupational lead exposure, chronic nephropathy, and renal cancer: a case report

The case of a 61-year-old male with repeated episodes of overt clinical lead poisoning and courses of chelation therapy during his 34 years of employment in a secondary lead smelter is presented. Renal function impairment with elevated serum creatinine and blood urea nitrogen and with markedly reduced glomerular filtration rate was detected several years before the discovery of a clear cell adenocarcinoma of the right kidney. After successful surgical removal of the tumor, the patient's renal function continued its previous trend of slow deterioration.