Urinary N-acetyl-beta-D-glucosaminidase activity in lead-exposed workers

Association between chronic lead exposure and markers of kidney injury: A systematic review and meta-analysis

In view of inconsistent reports on the association between chronic lead (Pb) exposure and renal injury markers (potential site of injury), the present systematic review explored their association by reviewing studies that investigated chronic Pb-exposed and those without obvious Pb exposure. Studies reporting blood Pb levels(BLL) and biomarkers of kidney injury [i.e. N-acetyl-β-D-glucosaminidase (NAG), Micro-Globulin(μG) and others] among chronic Pb-exposed and unexposed individuals were systematically searched from digital databases available until February 26, 2024. Preferred Reporting Items of Systematic Reviews and Meta-Analysis Guidelines were adhered to during the execution. Pooled effect size and heterogeneity were estimated using the random effect model and I2Studies reporting blood Pb levels(BLL) and biomarkers of kidney injury [i.e. N-acetyl-β-D-glucosaminidase (NAG), Micro-Globulin(μG) and others] among chronic Pb-exposed and unexposed individuals were systematically searched from digital databases available until February 26, 2024. Preferred Reporting Items of Systematic Reviews and Meta-Analysis Guidelines were adhered to during the execution. Pooled effect size and heterogeneity were estimated using the random effect model and I2. Pooled quantitative analysis revealed elevated BLL [25.64 (21.59-29.70) µg/dL] Pb-exposed group. The pooled analysis confirmed significantly higher urinary NAG [0.68(0.26-1.10) units], α1μG [3.82(0.96-6.68) mg/g creatinine] β2μG [1.5(0.86-2.14) units and serum creatinine [0.03(0.00-0.05) mg/dL] levels in Pb-exposed group, with high heterogeneity. Current observations indicate the proximal tubular injury as the early and potential site of Pb-induced renal injury. Pb-exposed individuals experience proximal tubular injury (KIM-1, NAG) and dysfunction (β2μG, α1μG, Cystatin-C) prior to obvious clinical renal failure. Present observations should caution the policymakers towards drafting regulations for periodic screening with markers of renal injury and / or dysfunction among those chronically exposed to lead despite the certainty of evidence is very low.

Nephrotoxic Biomarkers with Specific Indications for Metallic Pollutants: Implications for Environmental Health

Environmental and occupational exposure to heavy metals and metalloids is a major global health risk. The kidney is often a site of early damage. Nephrotoxicity is both a major consequence of heavy metal exposure and potentially an early warning of greater damage. A paradigm shift occurred at the beginning of the 21st century in the field of renal medicine. The medical model of kidney failure and treatment began to give way to a social model of risk factors and prevention with important implications for environmental health. This development threw into focus the need for better biomarkers: markers of exposure to known nephrotoxins; markers of early damage for diagnosis and prevention; markers of disease development for intervention and choice of therapy. Constituents of electronic waste, e-waste or e-pollution, such as cadmium (Cd), lead (Pb), mercury (HG), arsenic (As) and silica (SiO₂) are all potential nephrotoxins; they target the renal proximal tubules through distinct pathways. Different nephrotoxic biomarkers offer the possibility of identifying exposure to individual pollutants. In this review, a selection of prominent urinary markers of tubule damage is considered as potential tools for identifying environmental exposure to some key metallic pollutants.

Blood Lead Level and Renal Impairment among Adults: A Meta-Analysis

Background: The adult population in lead-related occupations or environmentally exposed to lead may be at risk for renal impairment and lead nephropathy. This meta-analysis aims to determine the impact of blood lead level (BLL) on renal function among middle-aged participants. Methods: Cross-sectional, longitudinal, or cohort studies that reported BLL and renal function tests among adult participants were retrieved from PubMed, Scopus, and ISI Web of Science. Relevant studies were included and assessed for quality using the Newcastle-Ottawa Scale (NOS). The pooled mean BLL of participants with a high BLL (≥30 µg/dL), moderate BLL (20-30 µg/dL), and low BLL (<20 µg/dL) was estimated using the random effects model. The pooled mean differences in BLL, blood urea nitrogen (BUN), creatinine, uric acid, and creatinine clearance between the exposed and non-exposed participants were estimated using the random effects model. Meta-regression was performed to demonstrate the association between the effect size (ES) of the pooled mean BLL and renal function. Heterogeneity among the included studies was assessed using the Cochrane Q and I2 statistics. Cochrane Q with a p value less than 0.05 and I2 more than 50% demonstrated substantial heterogeneity among the studies included. Publication bias was assessed using the funnel plot between the effect size and standard error of the effect size. Results: Out of 1657 articles, 43 were included in the meta-analysis. The meta-analysis demonstrated that the pooled mean BLL in the participants with a high BLL, moderate BLL, and low BLL was 42.41 µg/dL (95% confidence interval (CI): 42.14-42.67, I2: 99.1%), 22.18 µg/dL (95% CI: 21.68-22.68, I2: 60.4%), and 2.9 µg/dL (95% CI: 2.9-2.9, I2: 100%), respectively. The mean BLL of the exposed participants was higher than that of the non-exposed participants (weighted mean difference (WMD): 25.5, p < 0.0001, 95% CI: 18.59-32.45, I2: 99.8%, 17 studies). The mean BUN (WMD: 1.66, p < 0.0001, 95% CI: 0.76-2.55, I2: 76%, 10 studies) and mean creatinine (WMD: 0.05, p = 0.007, 95% CI: 0.01-0.08, I2: 76.8%, 15 studies) in the exposed participants were higher than those in the non-exposed participants. The mean creatinine clearance in the exposed participants was lower than that in the non-exposed participants (standard mean difference (SMD): -0.544, p = 0.03, 95% CI: -1.035-(-0.054), I2: 96.2%). The meta-regression demonstrated a significant positive effect of BLL on BUN (p = 0.022, coefficient: 0.75, constant: -3.7, 10 studies). Conclusions: BLL was observed to be associated with abnormal renal function test parameters, including high BUN, high creatinine, and low creatinine clearance. Moreover, BUN seemed to be the most valuable prognostic marker for lead-induced renal impairment. Therefore, regular checks for renal function among lead-exposed workers should be a priority and publicly promoted.

The Effects of Lead Exposure on Serum Uric Acid and Hyperuricemia in Young Adult Workers: A Cross-sectional Controlled Study

Objectives

This study aims to evaluate the relationship between serum uric acid levels and renal functions in asymptomatic subjects who had occupational lead exposure, particularly for shorter durations whereby saturnine gout has also been discussed.

Patients and methods

In this retrospective study, files of 100 males (mean age 34.5±5.9 years; range, 21 to 47 years) with occupational risk for lead exposure and 100 healthy male controls (mean age 34.47±5.8 years; range 21 to 47 years) were reviewed. Demographic characteristics of the subjects and laboratory test results were recorded from the files. Creatinine clearance and 24-hour urinary creatinine were measured in the lead-exposed group.

Results

In the lead-exposed group, mean serum uric acid level was higher than those of the control group (p<0.001). Lead exposure time was negatively correlated with 24-hour urinary creatinine levels (r= -0.373, p<0.001). In addition, serum uric acid levels were positively correlated with serum creatinine levels (r=0.412, p<0.001) in the exposed group. Six patients had hyperuricemia (serum uric acid level >6.8 mg/dL) in the lead- exposed group; however, all subjects' serum uric acid level was lower than 6.8 mg/dL in the control group (p=0.029). Although 22 subjects had higher uric acid levels than 6.0 mg/dL in the lead-exposed group, only one control had higher uric acid level than 6.0 mg/dL (p<0.001).

Conclusion

In light of our results, we may conclude that workers with lead exposure have higher frequency of hyperuricemia and higher serum uric acid levels than those of the control group. Therefore, we may imply that higher serum uric acid levels may be associated with renal impairment in lead-exposed subjects even in the earlier stages of exposure.

Lead Nephropathy: Revisiting an Overlooked Cause of Kidney Disease

Despite the recognition of lead nephropathy as a consequence of environmental and occupational lead exposure, lead nephropathy still appears to be underrecognized by physicians as a cause and promoter of chronic kidney disease (CKD), especially in people with more apparent causative factors such as diabetes and hypertension. This review focuses on the clinical, pathophysiological and epidemiological perspectives of lead nephropathy with the objective of promoting the awareness of this important but overlooked cause of CKD among physicians. Literature was reviewed using available medical journals and online literature search through Google, Pubmed, Medline, Medscape and HINARI databases. The key words employed were: Lead Nephropathy, Environmental and Occupational lead exposure and chronic kidney disease. Lead nephropathy which is a tubulointerstitial nephritis, may present acutely or chronically in association with hypertension. The clinical diagnosis of lead nephropathy is complex, because the symptoms are varied and non-specific especially with subclinical nephrotoxicity. The recognition of lead nephropathy can be enhanced if physicians have a high index of suspicion in the assessment of patients with renal disease. It is recommended that the evaluation of environmental and occupational nephrotoxins like lead be incorporated into programs for the prevention of CKD, especially in developing countries where lead exposure and toxicity still remain largely unchecked and the prevalence and burden of CKD is increasing.

Benchmark dose approach for renal dysfunction in workers exposed to lead

Benchmark dose (BMD) and the lower confidence limit on the benchmark dose (BMDL) of blood lead were estimated to explore the biologic exposure limits for renal dysfunction caused by lead. One hundred thirty-five workers from one storage battery plant were selected as lead exposure group while 143 mechanics as the control. The relationship between the blood lead concentration and the urinary excretion of total protein (TP), beta2-microglobulin (beta2-MG), and N-acetyl-beta-D-glucosaminidase (NAG) was studied. The quantal linear logistic regression model (BMDS Version 1.3.1) was used to calculate BMD and BMDL of blood lead. The results showed that the levels of NAG, beta2-MG, and TP in lead-exposed workers were higher than those of control group and elevated along with rising length of employment. The levels of three indices for renal dysfunction increased with the elevated blood lead. The BMD and BMDL of blood lead for renal dysfunction were from 299.4 to 588.7 microg/L and from 253.4 to 402.3 microg/L, respectively. The BMDL of blood lead was ranged from high to low as TP, beta2-MG, and NAG. It is suggested that the urinary NAG activity could be a sensitive and early biomarker of renal tubular dysfunction induced by lead. When assessing renal function in workers occupationally exposed to lead, a blood lead level of 250 microg/L could serve as a warning signal.

Lead-related nephrotoxicity: a review of the epidemiologic evidence

Chronic kidney disease (CKD) represents a major global public health concern. Efforts to prevent and/or slow progression of CKD are essential. Lead nephropathy, characterized by chronic tubulointerstitial nephritis, is a well-known risk of chronic, high-level lead exposure. However, in recent years, lead exposure has declined sharply, particularly in developed countries. We reviewed epidemiologic research in general, occupational, and patient populations to assess whether lead, at current exposure levels, still contributes to nephrotoxicity. Other pertinent topics, such as risk in children, genetic susceptibility, and co-exposure to cadmium, are also considered. The data reviewed indicate that lead contributes to nephrotoxicity, even at blood lead levels below 5 microg/dl. This is particularly true in susceptible populations, such as those with hypertension (HTN), diabetes, and/or CKD. Low socioeconomic status is a risk factor for both lead exposure and diseases that increase susceptibility. Future public health risk for lead-related nephrotoxicity may be most significant in those rapidly developing countries where risk factors for CKD, including obesity and secondary HTN and diabetes mellitus, are increasing more rapidly than lead exposure is declining. Global efforts to reduce lead exposure remain important. Research is also needed to determine whether specific therapies, such as chelation, are beneficial in susceptible populations.

Therapeutic efficacy of lipoic acid in combination with dimercaptosuccinic acid against lead-induced renal tubular defects and on isolated brush-border enzyme activities

The combined therapeutic potentials of lipoic acid and dimercaptosuccinic acid were compared against their sole administrations in restoring the altered lead sensitive indices in urine and isolated renal brush-border preparations. Toxicity was induced in male albino rats (Wistar strain) by administering lead acetate (0.2%) in drinking water for 5 weeks, followed by therapy comprising lipoic acid (25 mg/kg body weight) and dimercaptosuccinic acid (20 mg/kg body weight) solely as well as combined during the 6th week. Changes in kidney weights encountered upon lead administration improved after therapy with lipoic acid and dimercaptosuccinic acid. Renal integrity was assessed by measuring the activities of alkaline phosphatase, acid phosphatase, lactate dehydrogenase, leucine aminopeptidase, N-acetyl-beta-D-glucosaminidase, gamma-glutamyl transferase and beta-glucuronidase in urine along with some urinary constituents (urea, uric acid, creatinine, protein and phosphorous). The effects of lead were also studied on isolated brush-border enzymes (alkaline phosphatase, acid phosphatase, gamma-glutamyl transferase and beta-glucuronidase) that showed a decline upon its administration. Increased activities of urinary enzymes were accompanied by increase in the urinary constituents. Increase in renal lead content was paralleled by a drastic fall in the renal delta-aminolevulinic acid dehydratase and a rise in urinary lead levels. Relative to the administration of lead, the combined therapy showed betterment on the renal integrity with respect to the functional parameters assessed, thereby indicating its efficacy over the monotherapies.

Lead exposure and urinary N-acetyl beta D glucosaminidase activity in adolescent workers in auto repair workshops

PURPOSE

To investigate levels of lead (Pb) exposure and renal tubular damage among adolescent workers in auto repair workshops in Turkey.

METHODS

The study was conducted on 39 adolescent workers (mean age: 16.18 +/- 3.19 years) in auto repair workshops (8 autoelectrician, 10 motor repairman, 8 auto painter, 5 turner, 8 bonnet straighter). Thirteen adult employees of battery production in the workshops (mean age: 32.08 +/- 10.94 years) and 29 healthy rural adolescent (mean age: 14.78 +/- 2.68 years) constituted the control groups. The level of blood Pb was investigated by an atomic absorption spectrophotometer and urinary N-acetyl beta- D glucosaminidase (NAG) activity was measured by a colorimetric method. Mann-Whitney U test was performed to examine group differences.

RESULTS

All subjects and controls had normal blood urea, creatinine, uric acid, sodium, potassium levels, normal routine urine examination and tubular phosphorus reabsorption. Blood Pb levels in auto repair workers (8.13 +/- 7.41 mug/dL) were significantly higher than the rural control group (3.49 +/- 1.39 mug/dL) but lower than the battery workers (25.27 +/- 9.82 mug/dL). Urinary NAG (U/gr creatinine) (4.71 +/- 2.11) was lower than the battery workers (7.39 +/- 4.37), however significantly higher than the normal control group (3.07 +/- 1.20). In addition, auto painters had higher levels of Pb exposure and urinary NAG activity than the other workers (p <.05).

CONCLUSION

Chronic low dose Pb exposure was found to cause renal tubular injury in children workers of auto repair workshops.

Alteration of rat submandibulary gland secretion of protein, calcium and N-acetyl-beta-D-glucosaminidase activity by lead

1. Effects of various doses of long-term lead treatment (0.01%, 0.04% and 0.05%) on rat submandibular saliva were investigated in this study. 2. Both submandibular ducts were cannulated intraorally with polyethylene tubes and saliva was collected from anesthetized lead treated and control rats using pilocarpine as secretagogue. 3. Saliva protein concentration was found to be reduced in lead (0.04%)- and (0.05%)-treated groups. 4. Saliva calcium concentration had a significant reduction only in the lead (0.05%)-treated group. 5. The secretion of the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase (NAG) in saliva decreased significantly in the lead (0.04%)- and (0.05)-treated groups. Specific activity of the enzyme showed an increase in these treated groups. 6. Good correlations were found between saliva protein concentration and NAG activity, saliva protein and calcium concentrations and calcium concentration and NAG activity. 7. There was a correlation between blood and submandibular saliva lead levels, and the saliva/blood ratio was approximately constant for all treated groups. 8. With respect to the ability of lead to substitute for calcium in several intracellular regulatory events, explanation for these alterations in submandibular saliva composition can be made.

The effect of small doses of mercury on the level of selected lysosomal enzymes in the plasma and lymphocytes of sheep

1. The 12-month-old ewes, Slovak Merinos breed, were given 40 mg of mercury daily for 28 days in the form of HgCl2. 2. Administration of mercury had a significant influence on the activity of the investigated lysosomal enzymes in the plasma and lymphocytes of sheep.

Renal toxicity after oral administration of lead acetate during pre- and post-implantation periods: effects on trace metal composition, metallo-enzymes and glutathione

The present study was undertaken to compare the effects of 10-50 mg/kg b.wt. of Pb acetate after chronic treatment through oral gavage on: (a) the distribution of trace elements such as Fe, Cu, Zn, and Mn, (b) enzyme activity of delta-amino levulinic acid dehydratase (delta-ALAD) and alkaline phosphatase, and (c) glutathione (GSH) in kidney and (d) delta-ALAD in blood of pregnant and non-pregnant mice. Treatment with Pb acetate was given on every alternate day for 4 weeks prior to mating and for 3-4 weeks until pregnancy became apparent and confirmed by laporatomy. Lead administration reduced the rate of reproduction as assessed by number of living viable embryos. During normal pregnancy renal Cu, Fe and GSH tended to decline although non-significantly and continued to do so after lead administration. Mn was considerably and significantly elevated, whereas activity of delta-ALAD (non-activated) was quite low in pregnant mice. Following administration of Pb acetate, kidneys of pregnant and non-pregnant dams accumulated Pb in a dose-dependent manner, but as compared to non-pregnant mice, Pb increase in pregnant dams was significantly lower. Pb toxicity was associated with the loss of delta-ALAD in blood and kidney, but unlike the non-activated form of delta-ALAD, the dithiothreitol-activated form of delta-ALAD declined in a significant amount. The residual activity showed a high degree of negative correlation with endogenous Pb as well as with Zn/Pb ratio. Pb toxicity did not modify renal Fe, Cu, and Zn in the pregnant state, but reduced renal Fe during pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of occupational lead nephropathy using early renal markers

Automotive use of leaded gasoline continues to be an important source of occupational exposure to lead in India and other countries. The present study assessed the renal function and markers of early renal damage of 22 mechanics at three automobile garages. Urinary N-acetyl-3-D-glucosaminidase activity and beta-2-microglobulin levels were significantly increased in auto garage mechanics with blood leads of 30-69 micrograms/dL. A significant correlation was observed between blood lead levels and urinary N-acetyl-3-D-glucosaminidase activity but not with urine beta-2-microglobulin levels. A marginal impairment in creatinine clearance was not statistically significant. Urinary N-acetyl-3-D-glucosaminidase activity offers a sensitive monitor of blood lead and renal tubular injury.

Trichloroethylene exposure in vapour degreasing and the urinary excretion of N-acetyl-beta-D-glucosaminidase

In order to elucidate the potential nephrotoxicity of low level occupational exposure to trichloroethylene (TRI), urine analysis of the tubular enzyme N-acetyl-beta-D-glucosaminidase (U-NAG) was included in a cross-sectional study of metal degreasers in central Sweden. Eighty-six percent of 8-h TRI in air measurements were well below 50 mg/m3. Normal levels of NAG were found in morning urine samples from 29 workers compared to a historical reference group. A weak positive correlation (r = 0.48; P < 0.01) was observed between U-NAG activity and the concentration of the TRI metabolite trichloroacetic acid in urine but not with other estimates of recent or long-term exposure. In conclusion, TRI does not seem to be nephrotoxic at low exposure levels.

Urinary N-acetyl-beta-D-glucosaminidase and beta-aminoisobutyric acid in workers occupationally exposed to metals such as chromium, nickel, and iron

To examine the relationships between the urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) and beta-aminoisobutyric acid (AIBA) as a metabolite of thymine, and exposure to chromium, nickel, and iron, we determined these parameters in 58 workers engaged in the cutting and grinding of stainless steel or iron-steel plates. A significant increase in urinary NAG activity or urinary AIBA excretion was found in some of these workers. However, we could not find a significant positive correlation between the urinary excretion of NAG or AIBA and the urinary concentration of chromium, nickel, or iron as an indicator of internal dose.

Lead nephrotoxicity and associated disorders: biochemical mechanisms

Lead may exert toxic effects on several organ systems, but those in the kidney are the most insidious. Acute lead nephropathy is characterized by proximal tubular dysfunction with the development of a Fanconi-type syndrome, alterations in mitochondrial structure and the development of cytosolic and nuclear inclusion bodies. Intracellular lead is associated with specific high affinity proteins and can also bind to metallothionein. Chronic lead nephropathy is irreversible and is typically accompanied by interstitial fibrosis, both hyperplasia and atrophy of the tubules, glomerulonephritis and, ultimately, renal failure. In addition, lead produces renal neoplasms in experimental animals. Chronic lead exposure is also implicated in the development of saturnine gout and hypertension. The metal interacts with renal membranes and enzymes and disrupts energy production, calcium metabolism, glucose homeostasis, ion transport processes and the renin-angiotensin system. This review summarizes the biochemical effects of lead on the kidney to understand the mechanisms of lead-induced nephropathy and other associated disorders.