The role of lead in renal failure

Disrupted Sleep Homeostasis and Altered Expressions of Clock Genes in Rats with Chronic Lead Exposure

Sleep disturbance is one of the neurobehavioral complications of lead neurotoxicity. The present study evaluated the impacts of chronic lead exposure on alteration of the sleep–wake cycle in association with changes of clock gene expression in the hypothalamus. Sprague–Dawley rats with chronic lead exposure consumed drinking water that contained 250 ppm of lead acetate for five weeks. Electroencephalography and electromyography were recorded for scoring the architecture of the sleep–wake cycle in animals. At six Zeitgeber time (ZT) points (ZT2, ZT6, ZT10, ZT14, ZT18, and ZT22), three clock genes, including rPer1, rPer2, and rBmal1b, were analyzed. The rats with chronic lead exposure showed decreased slow wave sleep and increased wakefulness in the whole light period (ZT1 to ZT12) and the early dark period (ZT13 to ZT15) that was followed with a rebound of rapid-eye-movement sleep at the end of the dark period (ZT22 to ZT24). The disturbance of the sleep–wake cycle was associated with changes in clock gene expression that was characterized by the upregulation of rPer1 and rPer2 and the feedback repression of rBmal1b. We concluded that chronic lead exposure has a negative impact on the sleep–wake cycle in rats that predominantly disrupts sleep homeostasis. The disruption of sleep homeostasis was associated with a toxic effect of lead on the clock gene expression in the hypothalamus.

Lead nephropathy: early leads from descriptive studies

Chronic lead exposure is recognized as a potential cause of hyperuricaemia, kidney damage and hypertension. The fascinating story of lead poisoning and nephrotoxicity illustrates the utility of descriptive studies in the early elucidation of a new disease entity. The pursuit towards understanding lead nephropathy is presented as a successful illustration of human occupational and public health.

Position paper of the American Council on Science and Health: lead and human health

The potential human health risk of lead in the environment remains a topic of current debate and concern. Given sufficient exposure, lead can exert severe and chronic health effects. Today, due to successful efforts to reduce the commercial use of lead and control its release to the environment, lead "poisoning" is uncommon in our society. Blood-lead levels among the U.S. population, including those of children, have decreased dramatically over the past decade and according to current surveillance programs continue to decline. Because lead poisoning among children is no longer as prevalent as it once was, the focus has shifted to the long-term effects lead may exert on the intellectual development of children. Continued toxicological and epidemiological research will expand the understanding of this important facet of the lead issue. Trace levels of lead in consumer products remain a low health risk to humans, despite the fear and uncertainty which often accompany such concerns. Future efforts to reduce lead exposure should be aimed at high-risk groups which include the socioeconomically disadvantaged and certain minority sectors of the population. Through educational programs, improvement in personal hygiene practices, and abatement of lead-containing paint (when warranted), blood lead levels should continue to decline, reducing the health risk to lead in the environment.

Delta-aminolevulinic acid dehydratase polymorphism: influence on lead levels and kidney function in humans

Delta-aminolevulinic acid dehydratase (ALAD) polymorphism has been reported to modify lead pharmacokinetics (i.e., individuals who express the ALAD2 allele [ALAD2 subjects] have higher blood lead levels than homozygotes for the ALAD1 allele [ALAD1 subjects]). In our study of 89 lead-exposed workers (7 ALAD2 homozygotes or heterozygotes) and 34 unexposed workers (10 ALAD2 heterozygotes), concentrations of urinary calcium and creatinine were lower in ALAD2 subjects than in ALAD1 subjects (respective medians: calcium--78 mg/l versus 185 mg/l, p = .003; creatinine--11.2 mmol/l versus 14.9 mmol/l, p = .008). No association was found between ALAD genotype and blood lead levels or bone lead levels. However, expression of the ALAD2 allele occurred less frequently among lead-exposed workers than in unexposed controls. The results indicated the presence of ALAD allele-specific differences in kidney function, as well as a possible genetic healthy-worker selection.

Kidney effects in long term exposed lead smelter workers

Occupational exposure to lead may cause kidney damage. This study was carried out on a cohort of 70 active and 30 retired long term exposed lead smelter workers. Their kidney function was compared with 31 active and 10 retired truck assembly workers who had no occupational exposure to lead. The lead workers had been regularly followed up with measurements of lead concentration in blood since 1950. Previous exposure to lead was calculated as a time integrated blood lead index for each worker. Blood and urine samples were obtained from all subjects. The concentration of lead in blood (B-Pb) and urine (U-Pb) was analysed. The urinary concentrations of several sensitive indicators of early tubular (U-beta 2-microglobulin (U-beta 2-m); U-N-acetyl-beta-glucosaminidase (U-NAG)) and glomerular kidney damage (U-albumin) were determined. The B-Pb and U-Pb values were significantly higher among active and retired lead workers compared with their corresponding control groups. The highest concentrations were found among the active lead workers. The concentrations of the parameters of kidney function investigated were of the same magnitude for exposed workers and controls. No clinical signs of renal impairment were found among the workers. No correlations of clinical importance existed between concentrations of U-albumin, U-beta 2-m, and U-NAG activity on the one hand and the concentrations of B-Pb, cumulative blood lead index, U-Pb, and lead concentrations in the calcaneus and tibia on the other, among lead workers and controls. Despite many years of moderate to heavy exposure to lead, particularly for the retired lead workers, no signs of adverse effects on the kidney such as early tubular or glomerular malfunction were found. Reversible changes in kidney function during the 1950s and 1960s could not be excluded, however, due to a greater exposure to lead during that time.

Assessment of thyroid, testes, kidney and autonomic nervous system function in lead-exposed workers

The objective of the study was to assess whether moderate occupational exposure to lead may be associated with early changes in potential target organs (thyroid, testes, kidney, autonomic nervous system). Workers exposed to lead in a lead acid battery factory (n = 98; mean blood lead 51 micrograms/dl, range 40-75 micrograms/dl) and 85 control workers were examined. None of the indicators of kidney function (in urine: retinol-binding protein, beta 2-microglobulin, albumin, N-acetyl-beta-D-glucosaminidase; in serum: creatinine, beta 2-microglobulin), endocrine function (follicle-stimulating hormone, luteinizing hormone, thyroid-stimulating hormone, thyroxine, triiodothyronine) and autonomic nervous system (R-R interval variations on the electrocardiogram) were correlated with lead exposure (blood lead or duration of exposure) or showed significantly different mean values between the exposed group and controls. These results and an assessment of the published data suggest that compliance with the Directive of the Council of the European Communities on lead exposure (health surveillance in workers whose lead in blood exceeds 40 micrograms/dl and removal from exposure when blood lead exceeds 70-80 micrograms/dl) would prevent the occurrence of significant biological changes in the majority of lead-exposed workers.

Environmental lead exposure and the kidney

Lead and its components remain widely distributed in the environment and in some workplaces. Lead serves no useful physiological function, yet is potentially toxic to several organ systems. For many years human health effects have been recognized after heavy lead exposure. Recently more subtle human effects have been suggested invoking nervous system, reproductive and kidney function. Assessing lead body burden and dose-response relationships of this metal by blood lead determination, porphyrin assessments, chelation testing or bone lead studies may be difficult. Quantitative assessment of subtle changes in kidney function by routine BUN, creatinine, or urinalysis also poses problems. There is now mounting evidence that chronic low level environmental lead exposure may subtly effect kidney function. This paper first examines the history of lead and kidney function and then examines critically the evidence associating low-level environmental lead exposure and effects on renal function.

Chronic low-level lead exposure. Its role in the pathogenesis of hypertension

Lead is a common element in the earth's crust, serving useful purposes in industry, but serving no purpose in the human body. Increase in blood pressure is an important public health problem with numerous factors contributing to many facets of the disease. The relationship of lead exposure and increased blood pressure has long been considered, but only recently critically investigated. Reports of subtle changes in calcium metabolism and renal function, as well as in vitro studies examining end-arteriolar smooth muscle contractility, link lead exposure and increased blood pressure. This paper critically examines the evidence associating chronic low-level lead exposure and increased blood pressure. The review focuses on epidemiological, clinical, and toxicological data. The epidemiological evidence is consistent with low-level exposure to lead causing an elevation in blood pressure. The strength of that association, and the dose-response characteristics, are less certain. Individual resistance and susceptibility could affect the degree of blood pressure elevation. The results of animal and in vitro studies are consistent with the epidemiological evidence, and suggest biologically plausible mechanisms for the association. The most probable mechanisms are intracellular perturbations in calcium metabolism mediated by direct lead effects at the end-arteriole, and indirect effects via renal dysfunction. Better indices of lead exposure and lead activity are needed to quantify these effects in humans. New and safer methods of chelating lead suggest interesting approaches for studying the relationship between lead and hypertension. This link could have significant implications in determining what constitutes a 'safe' level of environmental lead exposure, and whether a proportion of essential hypertension could be 'cured' by chelation therapy.

Occupational exposure to lead and blood pressure: a study in 105 workers

A group of workers, occupationally exposed to lead and cadmium compounds (n = 53), was compared to a group of workers not exposed to these metals (n = 52). The average values of systolic, diastolic, and mean blood pressure were found to be higher in the exposed group (p less than 0.05). In contrast with the correlation between CdU and blood pressure, the correlation between PbB and systolic and mean blood pressure remained statistically significant after controlling for age and pulse rate (r = 0.22, p less than 0.05). The prevalence of potential hypertension (defined as systolic blood pressure greater than or equal to 160 mm Hg and/or diastolic blood pressure greater than or equal to 95 mm Hg and/or under treatment for hypertension) was higher in the exposed group, but the observed relative risk was not statistically significant: relative risk = 1.91 (95% confidence limits, 0.90-4.05). Furthermore, a significant correlation between PbB and Hgb (r = -0.28, p = 0.004) was observed. Differences in kidney function, as assessed in this study, were not detected.

Lead intoxication in paint removal workers on the Sydney Harbour Bridge

Lead intoxication is far more prevalent than is recognized by those persons who are exposed to lead fumes and dust in industry, as the early symptoms of intoxication are subtle and non-specific. The levels of lead in blood are a poor reflection of lead stores in the body and their potential toxicity, but are used frequently as the only test for screening of lead intoxication. Chelation of lead with calcium-EDTA is a more sensitive test to detect those persons who are at risk of toxicity. Industrial workers who are exposed regularly to lead must be screened on a periodic basis and a diagnosis of lead poisoning must be considered if substantial morbidity is to be avoided. We report six cases of men with significant lead intoxication who were employed on the Sydney Harbour Bridge, all of whom have benefited symptomatically from calcium-EDTA chelation therapy.

Lead intoxication

Lead intoxication was recognised as early as 2000 BC and the widespread use of lead has been a cause of endemic chronic plumbism in several societies throughout history. In the twentieth century, lead intoxication is still a common problem. In children it is largely due to ingestion of pica and environmental exposure, whereas adult groups at greatest risk are the industrially exposed: thus, screening of these workers should be undertaken at regular intervals. The clinical features of lead intoxication are nonspecific and often go unrecognised. The early manifestations are largely neuropsychiatric, followed by more significant disturbances of the central and peripheral nervous systems, symptomatic gastrointestinal, musculoskeletal, haematological and endocrine abnormalities. The association of lead poisoning with renal disease is well documented and must be considered, particularly if there is associated hypertension and/or gout. Blood lead concentrations are an unreliable predictor of body lead stores as they are indicative only of recent exposure. Haematological parameters have been used to assess those at risk of toxicity, but although more reliable than blood concentrations, they also fail to predict those patients at risk of toxicity. The recommended assessment for patients with suspected lead intoxication is a calcium disodium edetate chelation test, which is a sensitive marker for assessing body stores and subsequent intoxication. In children the dosage should be 50 mg/kg up to 1000 mg, and in adults 1000 mg administered intravenously or 2000 mg intramuscularly in divided doses 12 hours apart with subsequent 72 hour urinary lead estimations. Lead excretion levels greater than 350 micrograms/72 hours should be considered as suggestive of intoxication, particularly if supported by historical, clinical or biochemical evidence of lead exposure. Treatment of patients with positive chelation tests involves symptomatic treatment and a course of chelation therapy utilising calcium disodium edetate in doses similar to those used for testing, and in the more severely intoxicated patient, the addition of dimercaprol in doses of 75 mg/m2 every 4 hours to a total of 300 mg/m2/day. The safety of these treatment regimens is well documented.

Increased urinary enzyme excretion in workers exposed to nephrotoxic chemicals

Nephrotoxic chemicals are commonly present in the environment, particularly in the workplace. The level of occupational exposure to these chemicals has been so reduced that exposure to these agents now rarely causes clinically evident acute renal disease. A sensitive indicator of renal injury, urinary excretion of N-acetyl-beta-glucosaminidase, was utilized to evaluate persons exposed in the workplace to lead, mercury, or organic solvents, for evidence of renal effects from this exposure. None of the persons had clinically evident renal disease by history, none had hypertension, and all had normal findings on urinalysis. When compared with appropriate control populations, workers exposed to lead, workers exposed to mercury, and two of three groups of workers exposed to organic solvents had significant increases in urinary acetyl glucosaminidase activity. The third group of laboratory workers with low exposure to organic solvents had no increase in urinary acetyl glucosaminidase activity. It is concluded that exposure to environmental nephrotoxins at levels currently considered safe can produce renal effects as manifested by elevations of urinary acetyl glucosaminidase excretion. It is speculated that these renal effects are not always innocuous.

Contribution of lead to hypertension with renal impairment

Hypertension of unknown cause is generally termed "essential." Because hypertension has long been considered a possible complication of lead poisoning and the EDTA lead-mobilization test has proved to be a sensitive indicator of excessive body stores of lead, we used this test to evaluate cumulative past lead absorption in 48 men diagnosed as having essential hypertension. Patients who had hypertension with reduced renal function (i.e., serum creatinine level greater than 1.5 mg per deciliter [133 mumols per liter]) had significantly larger amounts of mobilizable lead than did patients who had hypertension without renal impairment. The increase in mobilizable lead was not due to the renal disease itself, since 22 control patients without a history of essential hypertension but with comparable renal impairment from known causes excreted significantly less lead chelate during the three-day test. These data suggest that lead may have an etiologic role in the renal disease of some patients usually designated as having "essential" hypertension.