Lead intoxication: its effect on the renin-aldosterone response to sodium deprivation

Effects of blood lead on coronary artery disease and its risk factors: a Mendelian Randomization study

Lead is pervasive, although lead exposure has fallen in response to public health efforts. Observationally, lead is positively associated with cardiovascular disease and hypertension. We used separate-sample instrumental variable analysis with genetic instruments (Mendelian randomization) based on 13 single nucleotide polymorphisms (SNP), from a genome wide association study, strongly (p-value < 5 × 10^-6) and independently associated with blood lead. These SNPs were applied to a large extensively genotyped coronary artery disease (CAD) study (cases = <76014, controls = <264785) largely based on CARDIoGRAPMplusC4D 1000 Genomes and the UK Biobank SOFT CAD, to the UK Biobank (n = 361,194) for blood pressure and to the DIAGRAM 1000 genomes diabetes case (n = 26,676)-control (n = 132,532) study. SNP-specific Wald estimates were combined using inverse variance weighting, MR-Egger and MR-PRESSO. Genetically instrumented blood lead was not associated with CAD (odds ratio (OR) 1.01 per effect size of log transformed blood lead, 95% confidence interval (CI) 0.97, 1.05), blood pressure (systolic -0.18 mmHg, 95% CI -0.44 to 0.08 and diastolic -0.03 mmHg, 95% CI -0.09 to 0.15) or diabetes (OR 0.98, 95% CI 0.92 to 1.03) using MR-PRESSO estimates corrected for an outlier SNP (rs550057) from the highly pleiotropic gene ABO. Exogenous lead may have different effects from endogenous lead; nevertheless, this study raises questions about the role of blood lead in CAD.

Association of low-level blood lead and blood pressure in NHANES 1999-2006

This study investigated whether low blood-lead levels (≤10 μg/dL) were associated with blood pressure (BP) outcomes. The authors analyzed data from National Health and Nutrition Examination Survey 1999-2006 and participants aged 20 years or older. Outcome variables were systolic and diastolic BP measurements, pulse pressure, and hypertension status. Multivariable linear and logistic regressions stratified by race/ethnicity and gender were performed. Blood lead levels (BLL) were significantly correlated with higher systolic BP among black men and women, but not white or Mexican-American participants. BLLs were significantly associated with higher diastolic BPs among white men and women and black men, whereas, a negative association was observed in Mexican-American men that had, also, a wider pulse pressure. Black men in the 90th percentile of blood lead distribution (BLL≥3.50 μg/dL) compared to black men in the 10th percentile of blood lead distribution (BLL≤0.7 μg/dL) had a significant increase of risk of having hypertension (adjusted POR=2.69; 95% CI: 1.08-6.72). In addition, blood cadmium was significantly associated with hypertension and systolic and diastolic blood. This study found that, despite the continuous decline in blood lead in the U.S. population, lead exposure disparities among race and gender still exist.

Lead and delta-aminolevulinic acid dehydratase polymorphism: where does it lead? A meta-analysis

BACKGROUND

Lead poisoning affects many organs in the body. Lead inhibits delta-aminolevulinic acid dehydratase (ALAD), an enzyme with two co-dominantly expressed alleles, ALAD1 and ALAD2.

OBJECTIVE

Our meta-analysis studied the effects of the ALAD polymorphism on a) blood and bone lead levels and b) indicators of target organ toxicity.

DATA SOURCE

We included studies reporting one or more of the following by individuals with genotypes ALAD1-1 and ALAD1-2/2-2: blood lead level (BLL), tibia or trabecular lead level, zinc protoporphyrin (ZPP), hemoglobin, serum creatinine, blood urea nitrogen (BUN), dimercaptosuccinic acid-chelatable lead, or blood pressure.

DATA EXTRACTION

Sample sizes, means, and standard deviations were extracted for the genotype groups.

DATA SYNTHESIS

There was a statistically significant association between ALAD2 carriers and higher BLL in lead-exposed workers (weighted mean differences of 1.93 microg/dL). There was no association with ALAD carrier status among environmentally exposed adults with BLLs < 10 microg/dL. ALAD2 carriers were potentially protected against adverse hemapoietic effects (ZPP and hemoglobin levels), perhaps because of decreased lead bioavailability to heme pathway enzymes.

CONCLUSION

Carriers of the ALAD2 allele had higher BLLs than those who were ALAD1 homozygous and higher hemoglobin and lower ZPP, and the latter seems to be inversely related to BLL. Effects on other organs were not well delineated, partly because of the small number of subjects studied and potential modifications caused by other proteins in target tissues or by other polymorphic genes.

[Fundamental and applied studies on transport and metabolism of electrolytes and glucose--aim to contact with molecular biology]

The authors' research focuses on polyuria, natriuresis, glucosuria, glycemia, and renal calcification in occupational lead poisoning and endemic fluorosis. Changes in electrolyte mobilization and in glucose metabolism and transport following the administration of lead compounds or fluoride were examined to elucidate these mechanisms. The results suggest fundamental approaches to the mechanism of aging and life style diseases. Our results show that: 1) Natriuresis and polyuria in lead poisoning and fluorosis are due to a decrease in renal Na/K-ATPase activity; 2) Renal calcification in fluorosis is due to stimulation of parathyroid function and activation of the renal phosphatidylinositol cascade; 3) Glycemia in fluorosis is due to elevation of renal and hepatic glucose-6-phosphatase activities; 4) Glusosuria in fluorosis is due to decreased renal Na/K-ATPase activity (but fluoride administered directly did not damage the renal Na/glucose cotransporter (SGLT); 5) Renal calcification in fluorosis is due to stimulation of parathyroid function; and 6) The decrease in renal Na/K-ATPase and SGLT activities with aging and hypertension is due to a decrease in phosphorylation activity by protein kinase C (PKC) etc. (decrease in PKC productivity with aging and hypertension).

An epidemiological re-appraisal of the association between blood pressure and blood lead: a meta-analysis

Studies on the possible association between blood pressure and blood lead have reached divergent conclusions. In a previous meta-analysis, a doubling of the blood lead concentration was associated with a 1.0/0.6 mm Hg increase in systolic and diastolic blood pressure (BP). This meta-analysis updates the analysis originally performed in 1994. Articles on the association between BP and blood lead were identified from computer searches from January 1980 to February 2001 using the Medical Literature Analysis and Retrieval System. Of the studies reviewed, 31 provided sufficient details to be considered. The meta-analysis included 58518 subjects recruited from the general population in 19 surveys and from occupationally exposed groups in 12 studies. In all but four studies, the results were adjusted for age, and most studies took into account additional confounding factors such as body mass index and the use of alcohol and medication. Weighted joint P-values were calculated using Stouffer's procedure. The association between BP and blood lead was similar in both men and women. In the combined studies, a two-fold increase in blood lead concentration was associated with a 1.0 mm Hg rise in the systolic pressure (95% CI +0.5 to +1.4 mm Hg; P < 0.001) and with a 0.6 mm Hg increase in the diastolic pressure (95% CI +0.4 to +0.8 mm Hg; P < 0.001). On balance, this meta-analysis suggests that there can only be a weak association between BP and blood lead.

Blood pressure elevation in young dogs during low-level lead poisoning

Clinical and experimental studies suggest an association between low-level lead exposure and hypertension. This association was investigated in six 3-month-old dogs who were randomly paired with their littermates. The daily oral dose of lead acetate was 1.0 mg Pb/kg body wt for 5 months; the controls received equimolar sodium acetate. Blood pressure was measured indirectly without anesthesia and was similar in the two groups at the start of the study. The mean blood pressure was higher in the lead-exposed group at every follow-up, from 10 days to 20 weeks. This treatment group difference in profiles was statistically significant (repeated-measures ANOVA, p = 0.0048). The final mean blood pressures were 120 +/- 6.4 (x +/- SE) vs 108 +/- 1.5 mm Hg. At 4 weeks the plasma renin activity was higher in the lead-exposed group: 3.4 +/- 0.25 vs 1.2 +/- 0.15 ng/ml/hr. The difference decreased during the study but the elevated trend persisted (repeated-measures ANOVA, p = 0.014). Lead exposure did not alter renal functions or extracellular fluid volume. This study shows that low-level lead intake in young dogs can cause an early increase in blood pressure which persists during ongoing exposure and which is associated with a small increase in the activity of the renin-angiotensin system.

Occupational lead exposure and blood pressure

Recent community studies have suggested that low level lead exposure is significantly associated with blood pressure in the general population. This finding is inconsistent with the results of recent occupational studies of lead exposed workers, although the occupational studies contained serious methodological weaknesses. The present study examined the relation between occupational lead exposure and diastolic and systolic blood pressure in randomly selected samples of 270 exposed and 158 non-exposed workers. Four exposure indicators were examined: employment at a lead battery plant nu a control plant, current blood lead value, current zinc protoporphyrin value, and time weighted average blood lead value. After controlling for other known risk factors such as age, education, income, cigarette usage, alcohol consumption, and exercise, the associations between exposure and blood pressure were small and non-significant. In the absence of a biologically feasible hypothesis regarding the mechanism by which low level lead exposure would influence blood pressure the present findings challenge the validity of the general population association.

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.

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.

The effects of lead on the renin-angiotensin system

Acute lead treatment of rabbits resulted in significant increases in both plasma renin activity and aldosterone concentration. No significant changes were observed in blood pressure, heart rate and plasma angiotensin-converting enzyme activity. The calcium channel-blocking drug verapamil attenuated the renin and aldosterone response in vivo. Lead increased renin release in a dose-dependent manner in a renal cortex slice preparation. Both verapamil and diltiazem attenuated the lead-induced renin release in vitro, but only with diltiazem did this attain statistical significance.

Alteration of sodium and potassium mobilization and of adrenal function by long-term ingestion of lead

Serum sodium concentration was markedly decreased by long-term (12 weeks) ingestion of lead above 5 mg Pb . kg-1 . day-1, whereas serum potassium concentration was notably decreased by the long-term (12 weeks) ingestion of lead above 2 mg Pb . kg-1. Urinary sodium and potassium in fasted rats were increased markedly 24 hr after a single lead dose (200 mg Pb/kg, o.p.) [Y. Suketa, S. Hasegawa and T. Yamamoto, Toxic. appl. Pharmac. 47, 203 (1979)]. In contrast, urinary excretion of sodium or potassium in non-fasted rats was not changed significantly by 2 weeks of lead ingestion at 200 mg Pb . kg-1 . day-1. Renal activities of Na+, K+-ATPase and K+-dependent phosphatase were decreased to 50-70% of control values by long-term (12 weeks) ingestion of lead (above 5 mg Pb . kg-1 . day-1).

The role of lead in renal failure

The CaNa2EDTA lead mobilization test permits identification of lead nephropathy in a variety of situations in which past-exposure is uncertain and acute symptoms of lead poisoning are lacking. In addition to lead workers and moonshiners, lead nephropathy has been identified in gout patients with renal failure and in hypertensives with renal failure. The presence of excessive mobilizable lead in these patients and its absence in control patients with comparable renal dysfunction suggests that unrecognized lead poisoning is sometimes responsible for renal failure in gout and hypertension. Use of the EDTA lead-mobilization test may thus permit prevention and sometimes treatment of renal failure in patients who might otherwise enter the End-Stage Renal-Disease Program. The controversies surrounding interstitial nephritis in lead poisoning, gout and hypertension may in part be explained by the surreptitious role of lead.

Lead intoxication during development: its late effects on kidney function and blood pressure

Exposure to lead in early life may result in chronic renal disease in adulthood. To test this hypothesis, we gave Sprague-Dawley rats, from 3 to 9 weeks of age, either tap water or a 1% lead acetate solution, and we studied them (in pairs) 3 and 16 weeks after exposure; that is, at 12 and 25 weeks of age. Lead-intoxicated animals failed to grow. Their GFR's were lower compared with the matched controls and fell between 12 and 25 weeks of age from 4.8 +/- 0.3 to 3.3 +/- 0.4 ml/min/g dry kidney wt (P less than 0.01). Changes in RBF and single nephron GFR were proportional to changes in total kidney GFR, indicating that superficial and deep nephrons were equally affected. The blood pressure in the lead-exposed animals studied at 25 weeks of age was 143.2 +/- 3.7 mm Hg, a value significantly higher than that of 130.4 +/- 3.3 observed in controls (P less than 0.05). These results demonstrate that limited exposure to lead during development can result in progressive renal insufficiency and hypertension.

Does exposure to elevated levels of lead enhance sodium induced hypertension?

Numerous community drinking water sources have elevated levels of both sodium and lead. Recently reported studies have indicated that elevated levels of sodium in drinking water may be a facter in the development of elevated blood pressure. The question of how elevated levels of lead may affect sodium induced elevated blood pressure is addressed. The hypothesis is developed which states that elevated levels of lead exposure will not interact with sodium to enhance the development of renin angiotensin aldosterone related hypertension but in fact may even diminish the effects of exposure to elevated amounts of sodium on blood pressure through a depression of plasma renin activity.

Pathologic hypofunction of the renin-angiotensin-aldosterone system

The literature now contains reports of many cases of aldosterone deficiency. Usually, the presenting features are persistent hyperkalemia and tendencies to serious urinary sodium loss and hypotension. A classification of defects leading to pathologic hypofunction of the renin-angiotensin-aldosterone system (RAAS hypofunction) is presented, with emphasis on idiopathic hyporeninemia (probably the most common). Criteria for diagnosis are (1) normal adrenal glucocorticoid function, (2) low aldosterone excretion under basal and stimulated conditions, and (3) renal tubular responsiveness to exogenous mineralocorticoid. The condition is effectively managed with mineralocorticoid replacement therapy and should be considered in the presence of unexplained persistent hyperkalemia, hyponatremia, or postural hypotension.