metallothionein and Lead-Poisoning

Heavy metal exposure has long been associated with metallothionein (MT) regulation and its functions. MT is a ubiquitous, cysteine-rich protein that is involved in homeostatic metal response for the essential metals zinc and copper, as well as detoxification of heavy metals; the most commonly proposed being cadmium. MT binds in vivo to a number of metals in addition to zinc, cadmium and copper, such as bismuth. In vitro, metallation with a wide range of metals (especially mercury, arsenic, and lead) has been reported using a variety of analytical methods. To fully understand MT and its role with lead metabolism, we will describe how MT interacts with a wide variety of metals that bind in vitro. In general, affinity to the metal-binding cysteine residues of MT follows that of metal binding to thiols: Zn(II) < Pb(II) < Cd (II) < Cu(I) < Ag(I) < Hg(II) < Bi(III). To introduce the metal binding properties that we feel directly relate to the metallation of metallothionein by Pb(II), we will explore MT's interactions with metals long known as toxic, particularly, Cd(II), Hg(II), and As(III), along with xenobiotic metals, and how these metal-binding studies complement those of lead binding. Lead's effects on an organism's physiological functions are not fully understood, but it is known that chronic exposure inflicts amongst other factors pernicious anemia and developmental issues in the brain, especially in children who are more vulnerable to its toxic effects. Understanding the interaction of lead with metallothioneins throughout the biosphere, from bacteria, to algae, to fish, to humans, is important in determining pathways for lead to enter and damage physiologically significant protein function, and thereby its toxicity.

Topics: Animals; Humans; Lead; Lead Poisoning; Metallothionein; Protein Binding

Topics: Aging; Body Fluids; Cadmium; Cadmium Poisoning; Edetic Acid; Humans; Kidney Diseases; Kidney Glomerulus; Lead Poisoning; Mercury Poisoning; Metallothionein; Nephritis, Interstitial

Metallothionein (MT) is a protein with function of heavy metal detoxification. However, studies about how single nucleotide polymorphisms (SNPs) of MT genes influence lead nephropathy are relatively scarce. Therefore, our aim is to investigate the association between blood lead levels and renal biomarkers and to study whether this association is influenced by the combination of MT1A and MT2A SNPs. Blood lead, urinary uric acid (UA), and urinary N-acetyl-beta-d-glucosaminidase (NAG) levels were analyzed from 485 participants. Genotyping were performed on MT1A SNPs (rs11640851 and rs8052394) and MT2A SNPs (rs10636 and rs28366003). The combined MT1A 2A SNPs were divided into 16 groups. Among renal biomarkers, urinary UA was negatively significant associated with the time-weighted index of cumulative blood lead (TWICL), while urinary NAG was positively significant with TWICL. Furthermore, the association between urinary UA and TWICL was significantly modified by group 6 of combined SNPs (MT1A 2 A SNPs combination were AAAGGGAA, ACAGGGAA, and ACGGGGAA). In conclusion, the negative association of urinary UA and TWICL is modified by group 6, which means participants of group 6 are more susceptible to lead nephrotoxicity.

Topics: Acetylglucosaminidase; Adult; Biomarkers; Female; Humans; Kidney; Lead; Lead Poisoning; Male; Metallothionein; Middle Aged; Polymorphism, Single Nucleotide; Uric Acid

Low-level lead poisoning is an insidious disease that affects millions of children worldwide, leading to biochemical and neurological dysfunctions. Blocking lead uptake via the gastrointestinal tract is an important prevention strategy. With this in mind, we constructed the recombinant Lactococcus lactis strain pGSMT/MG1363, which constitutively expressed the fusion protein glutathione S-transferase (GST)-small molecule ubiquitin-like modifier protein (SUMO)-metallothionein-I (GST-SUMO-MT). The thermodynamic data indicated that the average number of lead bound to a GST-SUMO-MT molecule was 3.655 and this binding reaction was a spontaneous, exothermic and entropy-increasing process. The total lead-binding capacity of pGSMT/MG1363 was 4.11 ± 0.15 mg/g dry mass. Oral administration of pGSMT/MG1363 (1 × 10(10) Colony-Forming Units) to pubertal male rats that were also treated with 5 mg/kg of lead acetate daily significantly inhibited the increase of blood lead levels, the impairment of hepatic function and the decrease of testosterone concentration in the serum, which were all impaired in rats treated by lead acetate alone. Moreover, the administration of pGSMT/MG1363 for 6 weeks did not affect the serum concentration of calcium, magnesium, potassium or sodium ions. This study provides a convenient and economical biomaterial for preventing lead poisoning via the digestive tract.

Topics: Administration, Oral; Animals; Brain; Calorimetry; Disease Models, Animal; Gastrointestinal Tract; Genetic Vectors; Glutathione Transferase; Humans; Intestines; Kidney; Lactococcus lactis; Lead; Lead Poisoning; Liver; Male; Metallothionein; Muscle, Skeletal; Plasmids; Rats; Recombinant Proteins; Testis; Thermodynamics; Tissue Distribution

Some dietary factors could inhibit lead toxicity. The aim of this study was to evaluate the effect of dietary compounds rich in unsaturated fatty acids (FA) on blood lead level, lipid metabolism, and vascular reactivity in rats. Serum metallothionein and organs' lead level were evaluated with the aim of assessing the possible mechanism of unsaturated FA impact on blood lead level. For three months, male Wistar rats that were receiving drinking water with (100 ppm Pb) or without lead acetate were supplemented per os daily with virgin olive oil or linseed oil (0.2 mL/kg b.w.) or egg derived lecithin fraction: "super lecithin" (50 g/kg b.w.). Mesenteric artery was stimulated ex vivo by norepinephrine (NE) administered at six different doses. Lecithin supplementation slightly reduced pressor responses of artery to NE. Lead administered to rats attenuated the beneficial effect of unsaturated FA on lipid metabolism and vascular reactivity to adrenergic stimulation. On the other hand, the super lecithin and linseed oil that were characterized by low omega-6 to omega-3 ratio (about 1) reduced the blood lead concentration. This effect was observed in lead poisoned rats (p < 0.0001) and also in rats nonpoisoned with lead (p < 0.05).

Topics: Animals; Carrier Proteins; Dietary Fats, Unsaturated; Dietary Supplements; Disease Models, Animal; Fatty Acids, Omega-3; Fatty Acids, Omega-6; Fatty Acids, Unsaturated; In Vitro Techniques; Lead; Lead Poisoning; Lecithins; Linseed Oil; Lipids; Male; Mesenteric Arteries; Metallothionein; Norepinephrine; Olive Oil; Rats; Rats, Wistar; Vasoconstrictor Agents

Lead is a renal toxin, and susceptibility to lead varies between individuals. Metallothionein (MT) is known for its metal scavenging role. The aim of the study was to investigate the association of blood lead levels, urinary uric acid (UA) and N-acetyl-beta-d-glucosaminidase (NAG) in chronic occupational lead-exposed workers, and to study whether the association was influenced by MT1A gene polymorphisms. In this cross-sectional study, 412 lead-exposed workers participated. Their annual health examination data and renal function markers were collected after the Institutional Review Broad of Kaohsiung Medical University Hospital approved the study and consent letters were obtained. From the blood samples, DNA was extracted and used for real-time PCR typing of 2 MT1A single nucleotide polymorphisms (SNPs): rs11640851 and rs8052394 on exons 2 and 3. Descriptive analysis, one-way ANOVA, and multiple linear regressions were performed. There was a significant inverted relationship of creatinine-adjusted urine UA concentrations and the time-weighted index of cumulative blood lead levels (TWICL) that may be significantly influenced by the AC genotypes of rs11640851 in exon 2 and rs8052394 in exon 3. After controlling for potential confounding factors, the creatinine-adjusted urine NAG concentrations were shown to be influenced by the GG genotype of rs8052394 in exon 3, and were weakly increased with TWICL. Therefore, we concluded that the variations of MT1A SNPs may influence urine UA and NAG excretion in chronic lead-exposed workers, and urine creatinine-adjusted urine UA as a biomarker of lead toxicity should be considered.

Topics: Acetylglucosaminidase; Adult; Alleles; Biomarkers; Cross-Sectional Studies; DNA; Female; Genotype; Humans; Lead Poisoning; Linear Models; Male; Metallothionein; Occupational Diseases; Occupational Exposure; Polymerase Chain Reaction; Polymorphism, Single Nucleotide; Prospective Studies; Retrospective Studies; Uric Acid

The heavy metal lead-induced oxidative stress on Caenorhabditis elegans was examined at the level of catalase activity and on innate immunity. Stress-induced C. elegans was exposed to Pseudomonas aeruginosa PA14::GFP for monitoring the impact at the physiological level. Role of catalase on the innate-immune responses of C. elegans was examined. PA14::GFP did not colonize lead pretreated C. elegans intestinal cells significantly compared to untreated controls, indicating stress-mediated upregulation of host-immunity. Semiquantitative PCR analyses of lead-exposed and PA14-infected C. elegans mRNA showed significant upregulation of candidate antimicrobial enzyme gene lys-7 after 24 h of exposures. Upregulation of metallothionein(mtl-1) when compared to mtl-2 in response to the lead suggesting active detoxification of metal by mtl-1. Exogenously provided Catalase (0.4-3.2 U) induced significant upregulation of lys-7 compared to controls. lys-7 upregulation during lead exposure was reconfirmed by real-time PCR. Confocal microscopy and fluorescence spectrophotometer analyses indicated that the lead pretreated C. elegans was significantly less colonized by PA14::GFP when compared to controls. Relative expression of ctl-1 and ctl-2 mRNA was measured using real time PCR and found to be regulated during lead exposures. Over all, the upregulation of antimicrobial gene expression appears to be correlated with the level of catalase during stress emphasizing their key roles in defensive mechanism(s). These results provide a link between the stress and related immune responses which can be explored in higher systems.

Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Catalase; Gene Expression; Green Fluorescent Proteins; Immunity, Innate; Lead; Lead Poisoning; Metallothionein; Oxidation-Reduction; Oxidative Stress; Pseudomonas aeruginosa; Real-Time Polymerase Chain Reaction; Up-Regulation

In gunshot wounds to the head, the bullet containing neurotoxic lead may remain in the brain after trauma, and brain damage is therefore anticipated. We developed an animal model incorporating a lead ball implanted in the brain, or a glass ball as a control, and analyzed histological and biochemical changes in the brain for 28 days after surgery. The concentration of lead in the brain increased with time after implantation of the lead ball, while lead was not detected in brains implanted with a glass ball. A number of changes were noted following implantation of the lead ball. The number of neutrophils increased significantly at 7-28 days, while the number of macrophages also increased significantly with time. The number of neurons was significantly decreased by 28 days, and apoptotic cells were identified at 14-28 days. Expression of genes encoding N-methyl-d-aspartate receptors, which are related to cognitive function and help regulate apoptosis, was significantly suppressed at 7-21 days after implantation. Expression of metallothionein protein increased significantly with time. Metallothionein detoxifies lead and its overexpression is a known method of protection against lead neurotoxicity. These findings indicate that intracerebral lead induces neuronal degeneration that is attributable in part to the inflammation and apoptosis caused by leached lead. Although the severity of the brain damage primarily depends on the destructive effect of the moving bullet, the results of this study indicate that lead leaching from the residual bullet also damages the brain.

Topics: Animals; Apoptosis; Brain; Brain Chemistry; Cell Count; Immunohistochemistry; Lead; Lead Poisoning; Macrophages; Male; Metallothionein; Nerve Degeneration; Neurons; Neutrophils; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction

Metallothioneins belong to the group of intracellular, high molecular and cysteine-rich proteins whose content increase with increasing concentration of a heavy metal. Here we applied the adsorptive transfer stripping differential pulse voltammetry Brdicka reaction for the determination of metallothionein in human blood serum of patient poisoned by lead and/or treated by platinum. The increased metallothionein concentrations in both cases were observed.

Topics: Child; Electrochemistry; Female; Humans; Lead Poisoning; Metallothionein; Platinum Compounds

Susceptibility to lead toxicity in MT-null mice and cells, lacking the major forms of the metallothionein (MT) gene, was compared to wild-type (WT) mice or cells. Male MT-null and WT mice received lead in the drinking water (0 to 4000 ppm) for 10 to 20 weeks. Lead did not alter body weight in any group. Unlike WT mice, lead-treated MT-null mice showed dose-related nephromegaly. In addition, after lead exposure renal function was significantly diminished in MT-null mice in comparison to WT mice. MT-null mice accumulated less renal lead than WT mice and did not form lead inclusion bodies, which were present in the kidneys of WT mice. In gene array analysis, renal glutathione S-transferases were up-regulated after lead in MT-null mice only. In vitro studies on fibroblast cell lines derived from MT-null and WT mice showed that MT-null cells were much more sensitive to lead cytotoxicity. MT-null cells accumulated less lead and formed no inclusion bodies. The MT-null phenotype seems to preclude lead-induced inclusion body formation and increases lead toxicity at the organ and cellular level despite reducing lead accumulation. This study reveals important roles for MT in chronic lead toxicity, lead accumulation, and inclusion body formation.

Topics: Animals; Cells, Cultured; Genetic Predisposition to Disease; Inclusion Bodies; Kidney; Lead; Lead Poisoning; Male; Metallothionein; Mice; Mice, Knockout

The influence of dietary iron deficiency on acute nickel, lead or cadmium toxicity as reflected by the induction of hepatic, renal and intestinal metallothionein (MT), disposition of the metals, and alterations in hematological parameters was investigated in rats. The administration of cadmium induced the hepatic, renal and intestinal MT while that of nickel or lead induced hepatic MT only. However, dietary iron deficiency did not influence the cadmium induced tissue MT but enhanced the ability of nickel or lead to restore the normal synthesis of renal and intestinal MT lowered under the influence of reduced body iron status. The accumulation of lead in liver and kidney and that of cadmium enhanced in liver only, while tissue deposition of nickel remained unaffected by iron deficiency. The induction of hepatic MT by three metals appears related to the concomitant rise in the hepatic zinc, calcium and iron levels in normal rats. However, dietary iron deficiency increased the hepatic zinc in response to nickel or cadmium and that of heptic calcium in response to lead.

Topics: Animals; Cadmium; Cadmium Poisoning; Diet; Intestinal Mucosa; Intestines; Iron Deficiencies; Kidney; Lead; Lead Poisoning; Liver; Male; Metallothionein; Nickel; Rats; Rats, Inbred Strains; Trace Elements

We have studied the erythrocytes from 24 workers occupationally exposed to inorganic lead, one asymptomatic lead worker showing exceptionally high exposure, and eight control subjects (blood lead 300-750, 1800, and < 100 micrograms/L, respectively). High performance protein chromatography, electrophoresis, and trace metal analysis have identified a low M.Wt., copper, and zinc-containing protein in all cases. This protein (designated protein M) bound lead on in vitro incubation with buffered lead nitrate. Purified samples of protein M were found to show characteristics consistent with metallothionein (M.Wt. approximately 6500, low pI, and greater UV absorbance at 254 nm). Amino acid analysis found a composition of 33% cysteine but no aromatic amino acids. The highly exposed subject showed endogenous lead binding to protein M, which on further purification by ion exchange was found to be associated with one particular constituent (protein M5). Protein M5 was present in much lower quantities in control subjects. These findings suggest the existence of a metallothionein-like protein in erythrocytes which binds lead, sequestering it into a nonbioavailable form and hence protects against lead toxicity.

Topics: Adult; Carrier Proteins; Erythrocytes; Humans; In Vitro Techniques; Isoelectric Point; Lead; Lead Poisoning; Male; Metallothionein; Molecular Weight; Occupational Diseases; Occupational Exposure; Protein Binding

Studies of protein excretion were undertaken in seven males, aged 35-42 years, who had more than 5 years exposure to industrial lead and had clinically established Pb intoxication. Heavy metal intoxication with Cd and Hg causes proximal tubular abnormalities, i.e., aminoaciduria, glycosuria, phosphaturia. Similar abnormalities occur in Pb intoxication except that the nature of the proteinuria remains controversial. Studies of urinary proteins included 24-hr urine protein excretion, dextran gel separations, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and beta 2 microglobulin (B2M) measurements. Creatinine clearances, and serum B2M concentrations were normal. Urine total protein distribution by SDS-PAGE and the B2M excretion rate were also normal. These data imply that the nephrotoxicity of Cd and Hg are different than that of Pb. We speculate on what might account for this difference. This study suggests that when examining a population exposed to Pb, the finding of tubular proteinuria should alert investigators to search for the presence of other toxic agents.

Topics: Adult; Cadmium; Humans; Kidney; Lead; Lead Poisoning; Male; Metallothionein; Molecular Weight; Proteinuria

In summary, this brief overview of the cellular localization of toxic metals in renal tubular cells demonstrates a spectrum of mechanisms for the sequestration of the metals. Common features are affinity for a metal-binding protein, such as insoluble acidic nuclear proteins or the soluble, low-molecular weight metallothionein. Accumulation in lysosomes follows assimilation of metal containing protein by lysosomes or autophagocytosis of degenerating metal containing mitochondria. Currently available methods have not demonstrated the presence of metals in immune complex deposits in glomerular basement membrane and epithelial cells. The principal methods employed for the localization of metals within cells have been X-ray microanalysis of thin preparation of tissue, or direct analysis of subcellular fractions by atomic absorption spectroscopy or detection of radioactive metal.

Topics: Cadmium; Cell Nucleus; Chelating Agents; Gold; Humans; Inclusion Bodies; Lead; Lead Poisoning; Metallothionein; Metals; Methylmercury Compounds; Subcellular Fractions