Effects of iron deficiency on metallothionein-I concentrations in blood and tissues of rats

Unraveling gene regulation mechanisms in fish: insights into multistress responses and mitigation through iron nanoparticles

The recent trend of global warming poses a significant threat to ecosystems worldwide. This global climate change has also impacted the pollution levels in aquatic ecosystems, subsequently affecting human health. To address these issues, an experiment was conducted to investigate the mitigating effects of iron nanoparticles (Fe-NPs) on arsenic and ammonia toxicity as well as high temperature stress (As+NH3+T). Fe-NPs were biologically synthesized using fish waste and incorporated into feed formulations at 10, 15, and 20 mg kg-1 diet. A total of 12 treatments were designed in triplicate following a completely randomized design involving 540 fish. Fe-NPs at 15 mg kg-1 diet notably reduced the cortisol levels in fish exposed to multiple stressors. The gene expressions of HSP 70, DNA damage-inducible protein (DDIP), and DNA damage were upregulated by stressors (As+NH3+T) and downregulated by Fe-NPs. Apoptotic genes (Cas 3a and 3b) and detoxifying genes (CYP 450), metallothionein (MT), and inducible nitric oxide synthase (iNOS) were downregulated by Fe-NPs at 15 mg kg-1 diet in fish subjected to As+NH3+T stress. Immune-related genes such as tumor necrosis factor (TNFα), immunoglobulin (Ig), and interleukin (IL) were upregulated by Fe-NPs, indicating enhanced immunity in fish under As+NH3+T stress. Conversely, Toll-like receptor (TLR) expression was notably downregulated by Fe-NPs at 15 mg kg-1 diet in fish under As+NH3+T stress. Immunological attributes such as nitro blue tetrazolium chloride, total protein, albumin, globulin, A:G ratio, and myeloperoxidase (MPO) were improved by dietary Fe-NPs at 15 mg kg-1 diet in fish, regardless of stressors. The antioxidant genes (CAT, SOD, and GPx) were also strengthened by Fe-NPs in fish. Genes associated with growth performance, such as growth hormone regulator (GHR1 and GHRβ), growth hormone (GH), and insulin-like growth factor (IGF 1X and IGF 2X), were upregulated, enhancing fish growth under stress, while SMT and MYST were downregulated by Fe-NPs in the diet. Various growth performance indicators were improved by dietary Fe-NPs at 15 mg kg-1 diet. Notably, Fe-NPs also enhanced arsenic detoxification and reduced the cumulative mortality after a bacterial infection. In conclusion, this study highlights that dietary Fe-NPs can effectively mitigate arsenic and ammonia toxicity as well as high temperature stress by modulating gene expression in fish.

Forgotten partners and function regulators of inducible metallothioneins

Metallothioneins are peculiar cysteine rich, heat resistant, small cellular plasma proteins expressed through almost all life forms. The currently established biological functions of metallothioneins are the homeostasis of essential metals and protection against toxic transitional metals (TM) alongside defence from oxidative stress by direct scavenging of reactive oxygen and nitrogen species (ROS and RNS). In mammals, among the four main evolutionary conserved forms, only the ubiquitously expressed metallothionein 1 and 2 (here abbreviated as MT) are inducible by TM, oxidative stress, glucocorticoids and starvation among various other stimuli. However, more than sixty years after being discovered, metallothioneins still bear unresolved issues about their possible physiological function and regulation. The biological function of MTs has still not been associated with the in vitro-demonstrated capacity of MT interaction with cellular molecules glutathione (GSH) or adenosine triphosphate (ATP), or with the possibility of direct iron-MT binding in the reducing intracellular environment of some organelles, e.g. lysosomes. Iron as the most abundant cellular TM is also one of the main physiological sources of ROS. Moreover, iron exhibits strain, sex and age differences that reflected ROS generation and MT induction in (patho)physiology and toxicology studies. A recent study showed that iron sex differences follows expression of both ferritin and MT leading to wide implications from essential TM interconnectivity to aging. This review places emphasis on biochemically proven but physiologically ignored interactions of MT with iron to stimulate advanced research for establishing a wide frame of the biological roles of MTs important for health and longevity.

Mineral absorption is an enriched pathway in a brain region of restless legs syndrome patients with reduced MEIS1 expression

Restless legs syndrome is a common complex disorder with different genetic and environmental risk factors. Here we used human cell lines to conduct an RNA-Seq study and observed how the gene showing the most significant association with RLS, MEIS1, acts as a regulator of the expression of many other genes. Some of the genes affected by its expression level are linked to pathways previously reported to be associated with RLS. We found that in cells where MEIS1 expression was either increased or prevented, mineral absorption is the principal dysregulated pathway. The mineral absorption pathway genes, HMOX1 and VDR are involved in iron metabolism and response to vitamin D, respectively. This shows a strong functional link to the known RLS pathways. We observed the same enrichment of the mineral absorption pathway in postmortem brain tissues of RLS patients showing a reduced expression of MEIS1. The expression of genes encoding metallothioneins (MTs) was observed to be dysregulated across the RNA-Seq datasets generated from both human cells and tissues. MTs are highly relevant to RLS as they bind intracellular metals, protect against oxidative stress and interact with ferritins which manage iron level in the central nervous system. Overall, our study suggests that in a subset of RLS patients, the contribution of MEIS1 appears to be associated to its downstream regulation of genes that are more directly involved in pathways that are relevant to RLS. While MTs have been implicated in the pathogenesis of neurodegenerative diseases such as Parkinson’s diseases, this is a first report to propose that they have a role in RLS.

Sex-dependent expression of metallothioneins MT1 and MT2 and concentrations of trace elements in rat liver and kidney tissues: Effect of gonadectomy

Metallothioneins (MTs) exhibit binding affinity for several essential and toxic trace elements. Previous studies in rodents indicated sex differences in the hepatic and renal expression of MTs and concentrations of various elements. The mechanism responsible for these differences has not been resolved. Here, in the liver and kidney tissues of sham-operated and gonadectomized male and female rats we determined the expression of MT1 and MT2 (MT1&2) mRNA by RT-PCR, abundance of MT1&2 proteins by Western blotting and immunocytochemistry, concentrations of essential (Fe, Zn, Cu, Co) and toxic (Cd, Hg, Pb) elements by ICP-MS, and oxidative status parameters (SOD, GPx, MDA, GSH) by biochemical methods. In both organs, the expression of MT1&2 mRNA and MT1&2 proteins was female-dominant, upregulated by castration, and downregulated by ovariectomy. Concentrations of Fe in the liver and Co in the kidneys followed the same pattern. Most other elements (Zn, Cu, Cd, Hg) exhibited female- or male-dominant sex differences, affected by gonadectomy in one or both organs. Pb was sex- and gonadectomy-unaffected. GPx and MDA were elevated and associated with the highest concentrations of Fe only in the female liver. We conclude that the sex-dependent expression of MT1&2 mRNA and proteins in the rat liver and kidneys may include different mechanisms. In the liver, the female-dominant tissue concentrations of Fe may generate oxidative stress which is a potent enhancer of MTs production, whereas in kidneys, the female-dominant expression of MTs may be unrelated to Fe-mediated oxidative stress.

Metallothioneins: Emerging Modulators in Immunity and Infection

Metallothioneins (MTs) are a family of metal-binding proteins virtually expressed in all organisms including prokaryotes, lower eukaryotes, invertebrates and mammals. These proteins regulate homeostasis of zinc (Zn) and copper (Cu), mitigate heavy metal poisoning, and alleviate superoxide stress. In recent years, MTs have emerged as an important, yet largely underappreciated, component of the immune system. Innate and adaptive immune cells regulate MTs in response to stress stimuli, cytokine signals and microbial challenge. Modulation of MTs in these cells in turn regulates metal ion release, transport and distribution, cellular redox status, enzyme function and cell signaling. While it is well established that the host strictly regulates availability of metal ions during microbial pathogenesis, we are only recently beginning to unravel the interplay between metal-regulatory pathways and immunological defenses. In this perspective, investigation of mechanisms that leverage the potential of MTs to orchestrate inflammatory responses and antimicrobial defenses has gained momentum. The purpose of this review, therefore, is to illumine the role of MTs in immune regulation. We discuss the mechanisms of MT induction and signaling in immune cells and explore the therapeutic potential of the MT-Zn axis in bolstering immune defenses against pathogens.

Blood glutathione peroxidase-1 mRNA levels can be used as molecular biomarkers to determine dietary selenium requirements in rats

Transcript (mRNA) levels are increasingly being used in medicine as molecular biomarkers for disease and disease risk, including use of whole blood as a target tissue for analysis. Development of blood molecular biomarkers for nutritional status, too, has potential application that parallels opportunities in medicine, including providing solid data for individualized nutrition. We previously reported that blood glutathione peroxidase-1 (Gpx1) mRNA was expressed at levels comparable to major tissues in rats and humans. To determine the efficacy of using blood Gpx1 mRNA to assess selenium (Se) status and requirements, we fed graded levels of Se (0-0.3 microg Se/g as selenite) to weanling male rats. Se status was determined by liver Se concentration and selenoenzyme activity, and selenoprotein mRNA abundance in liver and blood was determined by ribonuclease protection analysis. Liver Se and plasma glutathione peroxidase-3 and liver Gpx1 activities indicated that minimal Se requirements were at 0.08 microg Se/g diet. When total RNA was isolated from whole blood, Gpx1 mRNA in Se-deficient rats decreased to 10% of levels in Se-adequate (0.2 microg Se/g diet) rats. With Se supplementation, blood Gpx1 mRNA levels increased sigmoidally to a plateau with a minimum Se requirement of 0.08 microg Se/g diet, whereas glutathione peroxidase-4 mRNA levels were unaffected. Similarly, Gpx1 mRNA in RNA isolated from fractionated red blood cells decreased in Se-deficient rats to 23% of Se-adequate levels, with a minimum Se requirement of 0.09 microg Se/g diet. Additional studies showed that the preponderance of whole blood Gpx1 mRNA arises from erythroid cells, most likely reticulocytes and young erythrocytes. In summary, whole blood selenoprotein mRNA levels can be used as molecular biomarkers for assessing Se requirements, illustrating that whole blood has potential as a target tissue in development of molecular biomarkers for use in nutrition as well as in medicine.

Zinc transporters ZnT1 (Slc30a1), Zip8 (Slc39a8), and Zip10 (Slc39a10) in mouse red blood cells are differentially regulated during erythroid development and by dietary zinc deficiency

Zinc is essential for normal erythroid cell functions and therefore intracellular zinc homeostasis during erythroid differentiation is tightly regulated. However, a characterization of zinc transporters in erythrocytes has not been conducted. The membrane fraction of mature mouse RBC was screened for zinc transporter expression using western analysis as a first step in the characterization process. ZnT1, Zip8, and Zip10 were detected among the 12 transporter proteins tested. We examined expression of these zinc transporters during erythropoietin (EPO)-induced differentiation of splenic erythroid progenitor cells into reticulocytes. Both Zip8 and Zip10 mRNA increased by 2-6 h after addition of EPO to the cells. In contrast, maximal RNA levels for the zinc transporter ZnT1 and erythroid delta-aminolevulinic acid synthase were only produced by 24 h after EPO. We confirmed these changes in transcript abundance by western analysis. Dietary zinc status influences zinc-dependent functions of RBC. To determine whether the identified zinc transporters respond to dietary zinc status, mice were fed a zinc-deficient or control diet. Incorporation of (65)Zn into erythrocytes in vitro was significantly increased in cells from the zinc-deficient mice. Western analysis and densitometry revealed that erythrocyte Zip10 was upregulated and ZnT1 was downregulated in the zinc-depleted mice. Zip8 was not affected by restricted zinc intake. Collectively, these data suggest that the zinc transporters ZnT1, Zip8, and Zip10 are important for zinc homeostasis in erythrocytes and that ZnT1 and Zip10 respond to the dietary zinc supply.

Mononuclear cell metallothionein mRNA levels in human subjects with poor zinc nutrition

Human zinc deficiency is thought to be prevalent worldwide, particularly in populations with diets low in zinc and animal protein and high in inhibitors of zinc absorption, such as phytic acid. Confirmation of zinc deficiency is, however, difficult in the absence of a reliable and sensitive marker of zinc status. Under controlled conditions, T-lymphocyte metallothionein-2A (MT-2A) mRNA levels change in relation to zinc status and the objective of the present study was to investigate whether these transcript levels could be related to dietary zinc intake, plasma zinc or other biochemical parameters influenced by, or influencing, zinc metabolism in human subjects likely to be zinc deficient. Rural Koreans (n 110, age 50-80 years) with a range of zinc and phytic acid dietary intake were recruited for the study and blood samples were analysed for plasma zinc, HDL, LDL, alpha-tocopherol and thiobarbituric acid reactive substances, mononuclear cell (MNC) MT-2A mRNA, serum protein and albumin, and blood haematocrit, Hb and glucose. Multiple correlation and principal component analysis showed a significant negative correlation between plasma zinc and MNC MT-2A mRNA levels. Female subjects had higher MT-2A transcript levels than males and MT-2A mRNA levels tended to increase with age. There was no significant association between dietary zinc intake or any index of zinc intake relating to dietary inhibitors of zinc absorption. It is concluded that MNC MT-2A mRNA levels cannot be used to predict poor zinc nutrition.

Metallothionein gene expression in peripheral lymphocytes and renal dysfunction in a population environmentally exposed to cadmium

In order to study the validity of metallothionein (MT) gene expression in peripheral blood lymphocytes (PBLs) as a biomarker of cadmium exposure and susceptibility to renal dysfunction, MT mRNA levels were measured using reverse transcription polymerase chain reaction (RT-PCR) in PBLs from residents living in a cadmium-contaminated area. MT mRNA levels were found to increase with the increase of blood cadmium (BCd) and urinary cadmium (UCd) levels. Basal MT mRNA levels were significantly correlated with the logarithm of BCd levels and the logarithm of UCd levels confirming that MT expression in PBLs is a biomarker of cadmium exposure and internal dose. An inverse relationship was observed between in vitro induced MT-mRNA level in PBLs and urinary N-acetyl-beta-d-glucosaminidase (UNAG) suggesting that MT gene expression in PBLs may be used as a biomarker of susceptibility to renal toxicity of cadmium.

Erythropoietin-induced metallothionein gene expression: role in proliferation of K562 cells

Recent evidence has demonstrated an appreciable expression of metallothionein (MT) in erythrocytes. However, the induction of the MT protein by hematopoietic growth factors and its subsequent functional significance on clonal expansion or differentiation of erythroid progenitor cells remain elusive. We therefore examined the effects of growth factors erythropoietin (EPO), granulocyte-monocyte colony-stimulating factor (GM-CSF), and interleukin-3 (IL-3) on MT gene expression in erythroid progenitor K562 cell line. EPO, but not IL-3 or GM-CSF, induced a 3-fold increase in MT transcripts in K562 cells. MT induction was associated with EPO-induced cellular proliferation, suggesting a specific role for MT induction by EPO in erythroid progenitor cells. However, EPO- or sodium butyrate-induced differentiation as monitored by hemoglobin formation was inhibited in K562 cells stably transfected with an expression vector containing human MT-IIA gene. This inhibition of differentiation was partially reversed in these cells by an MT antisense phosphorothioate oligonucleotide. Furthermore, the MT-induced inhibition of differentiation was associated with downregulation of EPO receptor transcripts in K562 cells. These data suggest that, among growth factors required for erythropoiesis, EPO is a potent inducer of MT, and that MT may plays a significant role in EPO-induced proliferation, but not in the erythroid-specific differentiation of the progenitor cells.

Toxicology of dietary nickel in lake whitefish (Coregonus clupeaformis)

The sublethal toxicity associated with exposure of adult lake whitefish (Coregonus clupeaformis) to diets containing 0, 10, 100, and 1000 microg Ni per g for 10, 31, and 104 days was assessed through the measurement of responses, through a range of levels of biological organization. The accumulation and distribution of Ni in these fish are described in the previous manuscript (Ptashynski and Klaverkamp, 2001. Aquat. Toxicol. in press). Hematological parameters, including concentrations of glucose and hemoglobin and hematocrit, were not different between control and treated fish. Organ and whole organism parameters, including LSI, growth, and condition factor, were also unaffected. Histopathological lesions in kidney and liver proved to be the most sensitive and reliable indicators of Ni exposure. In livers of treated fish, areas of focal necrosis and altered bile ducts were observed. Histological alterations were observed throughout the posterior kidneys, in glomeruli, tubules, collecting ducts, and hematopoietic tissue, in fish fed medium and high dose diets. In whitefish kidneys, the frequency (%) of altered distal tubules and fields of views with alterations increased with the dose and duration of exposure. Significant increases in metallothionein concentrations were observed in intestine of whitefish fed the high dose diet on day 10, but these increases were not sustained. Significant increases in lipid peroxide concentrations were also observed in plasma of whitefish fed the high dose diet on day 31, but were not observed on day 104. These biochemical responses to dietary Ni require further evaluation. To evaluate exposure of natural populations of fish to Ni, analysis of Ni in kidney and liver and assessment of renal and hepatic histopathology are recommended for use in field bio-monitoring programs.

A role of zinc in the regulation of gene expression

Zn, without question, has important functions related to gene expression. Newer technologies applied to address these functions are providing answers relating to the importance of this micronutrient in human and animal health.

Metallothionein expression is increased in monocytes and erythrocytes of young men during zinc supplementation

The metallothionein gene is transcriptionally regulated by zinc. Consequently, metallothionein has potential for serving as an index of dietary zinc status in humans. To examine this possibility, an enzyme-linked immunoassay (ELISA) based on a sandwich approach that utilizes monoclonal and chicken egg yolk antibodies was used to compare the response of erythrocyte metallothionein protein levels with the response of monocyte metallothionein mRNA levels as measured by competitive reverse transcriptase-polymerase chain reaction (CRT-PCR) during zinc supplementation. Young male subjects participated in an 18-d supplementation study in which zinc was provided at 50 mg/d. Control subjects received a placebo. The zinc supplement resulted in significantly greater erythrocyte metallothionein levels by d 8 of supplementation compared with controls. Monocyte metallothionein mRNA levels were significantly greater than those of controls by d 2 of supplementation. Both remained elevated through d 18. They returned to base line by 8 and 4 d after supplementation, respectively. The plasma zinc concentration was significantly greater than in controls by d 6 and had returned to control levels by d 22 of supplementation. The results presented here show that both monocyte metallothionein mRNA and erythrocyte metallothionein protein concentrations change in human subjects in response to elevated dietary zinc intake and that monocyte metallothionein mRNA responds more rapidly to elevation of dietary zinc status than erythrocyte metallothionein protein. Consequently, both erythrocyte metallothionein and monocyte metallothionein mRNA may prove to be measures useful for assessment of either zinc depletion or the bioavailability of zinc supplements.

Competitive reverse transcriptase-polymerase chain reaction shows that dietary zinc supplementation in humans increases monocyte metallothionein mRNA levels

Zinc status is difficult to evaluate in humans. Metallothionein gene expression is transcriptionally regulated by dietary zinc and thus could serve as an assessment parameter based on zinc-dependent function. We used semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to establish that MT mRNA is increased in a human monocytic cell line by addition of zinc to the medium. To examine this response in human subjects, a dietary supplement of 50 mg zinc gluconate/d was given for 15 d. Monocytes were purified from venous blood using NycoPrep 1.068. Monocyte purity was determined by flow cytometry using fluorescent anti-human monocyte CD14 antibodies. Total monocyte RNA was extracted and converted to cDNA by reverse transcription. Competitive RT-PCR was used to analyze differences between cDNA levels that are proportional to MT mRNA levels in monocytes from zinc-supplemented and control subjects. RT-PCR oligonucleotide primers were designed to amplify both a 201 bp segment of the human MT cDNA and a 180 bp competitor cDNA template. The 180 bp competitor cDNA template was used for MT cDNA quantitation. The RT-PCR data show that there was a significant increase in monocyte MT mRNA in subjects within 6 d of zinc supplementation, which remained elevated at d 15 of supplementation. In contrast, plasma zinc was greater at d 6 of zinc supplementation, but by d 15 of supplementation, while still elevated, was close to control levels. These data suggest that monocyte MT mRNA levels respond to zinc supplementation and that the response could serve as a more useful assessment variable than plasma zinc for the measurement of zinc status in humans.

Erythrocyte metallothionein in relation to other biochemical zinc indices in pregnant and nonpregnant women

Erythrocyte metallothionein (E-MT) is considered a promising index of zinc status in humans, since it may be more sensitive than other biochemical indices to changes in dietary zinc. However, conditions of high zinc demand with substantial redistribution of tissue zinc and specific changes in hormone profile, such as pregnancy, may have an influence on E-MT levels in addition to dietary zinc. In this study, we compared E-MT concentrations in relation to other biochemical zinc indices in healthy pregnant women at delivery (n = 40) and non-pregnant women (n = 22) with similar habitual dietary zinc intakes (average 13.3 mg/d). Pregnant women had lower serum zinc and albumin-bound serum zinc, but higher levels of alpha 2-macroglobulin-bound serum zinc than the nonpregnant women. Erythrocyte zinc (E-Zn) was similar in both groups, but E-MT (mean +/- SE) was slightly but significantly (p < 0.05) higher in the pregnant women (2.9 +/- 0.09 nmol/g protein) compared to nonpregnant women (2.6 +/- 0.06 nmol/g protein). A significant correlation was observed between E-MT and E-Zn in the nonpregnant women (r = 0.70; p < 0.001), consistent with the role of intracellular zinc in the regulation of metallothionein synthesis. However, such correlation was not observed in the pregnant women, suggesting that E-MT levels in pregnancy may be influenced by factors related to the pregnant state.

Influence of dietary iron deficiency on nickel, lead and cadmium intoxication

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 young rats to ascertain whether the toxic effects of these metals modify under anemic conditions. The administration of Cd induced hepatic, renal and intestinal MT while that of Ni or Pb induced hepatic MT only. While dietary Fe deficiency did not affect MT induction by Cd, it enhanced the synthesis of renal and intestinal MT by Ni and Pb. The accumulation of Pb in liver and kidney and that of Cd in liver only, were enhanced by Fe deficiency; the tissue deposition of Ni remained unaffected by Fe deficiency. The induction of hepatic MT by Ni, Pb or Cd appears to be related to the concomitant rise in the hepatic Zn, Ca and Fe levels in normal rats. However, dietary Fe deficiency increased the hepatic Zn in response to Ni or Cd and the hepatic Ca in response to Pb administration.

Interactions of mercury in rat brain

In order to study the metabolism of mercury (Hg), its affinity to metallothionein (MT), and its influence on levels of the essential metals copper and zinc in the brain tissue of rats exposed to elemental mercury (HgO) vapor was investigated. The major findings were: 1. After long-term exposure, about 40% of mercury was found in the brain water-soluble phase (supernatant); 2. In brain supernatant, about 80% of Hg was found in the range of low-molecular-weight proteins; the MT-like protein Hg-Cu-Zn-thionein was isolated and partially characterized; 3. HgO vapor exposure resulted in increased tissue levels of essential Cu and Zn in addition to exogenous Hg; and 4. Experiments showed that HgO vapor exposure can induce the stimulation of rat brain MT synthesis.

Effects of marginal and severe iron deficiency on hepatic proteins in developing rats are reversible with dietary iron repletion

Transferrin, metallothionein, cytochrome P-450, and the in vitro formation of DNA-benzo[a]pyrene adducts were studied in the offspring of dams that were fed diets moderately or severely deficient in iron (Fe). The study was designed to determine whether Fe deficiency-induced alterations were reversible or if they persisted with post-weaning iron repletion. Throughout gestation and lactation the dams were fed a Control diet = 120 micrograms Fe/g diet, a Marginal Iron diet = 11 micrograms Fe/g diet, or a Low Iron diet = 7 micrograms Fe/g diet. On day 14 of lactation, 4 pups per litter were killed. On day 21, the dams were killed. Half of the remaining pups in each litter were fed their respective diets until they were killed on day 42 (Marginal Iron-Marginal Iron and Low Iron-Low Iron groups). The other half were fed the Control diet (Marginal Iron-Control and Low Iron-Control groups). The dietary intake of the Restricted Fed offspring was matched to rats in the Low Iron-Low Iron group. Offspring in the iron-deficient groups had hematocrits, hemoglobin concentrations, and liver iron levels that were lower than Controls. Day 42 offspring in the iron-deficiency groups had a lower food intake and higher liver zinc and copper levels than Controls. Day 14 Marginal and Low Iron pups had liver metallothionein levels that were lower than Controls. Day 42 Restricted Fed offspring had liver metallothionein levels that were higher than all other groups. Cytochrome P-450 levels and the in vitro formation of benzo[a]pyrene-DNA adducts were higher in Low Iron-Low Iron males than in Control males. Ethoxycoumarin O-deethylase activity was higher in day 42 Low Iron-Low Iron offspring than in Controls. These results show that the iron deficiency-induced alterations were transient, reversible with iron repletion, and in the case of cytochrome P-450 and ethoxycoumarin O-deethylase activity, dependent on the age and sex of the animal.

On metallothionein, cadmium, copper and zinc relationships in the liver and kidney of adult rats

1. A short-term exposure of adult Wistar rats to Cu (50 micrograms/ml) and Cd (10.0 micrograms/ml drinking water) caused significant changes in the subcellular concentrations of Cd, Cu, Zn and metallothionein (MT) in the liver and kidney; the concentrations were close to the physiological values, however. 2. To establish a relationship between these changes in the subcellular concentrations of Cd, Cu, Zn and the level of MT in the post-mitochondrial fraction of the liver and kidney, the analytical data (N = 42) were subjected to the multiple regression analysis. 3. The analysis showed that MT synthesis in the liver was principally induced by small amounts of Cd (0.32-1.4 micrograms/g wet wt) whereas in the kidney a level of MT in the post-mitochondrial fraction correlated positively with the renal Cd and Cu, as well as with the level of this protein in the liver. 4. The above results together with the positive correlation between the level of MT in the post-mitochondrial fraction and the concentration of Cu in this fraction, as well as the fact that under normal physiological conditions the capacity of MT (beta-domain) in the liver and kidney was sufficient to bind 50-100% of the total post-mitochondrial Cu suggest that MT, first induced by small amounts of Cd, may be involved in the metabolism of Cu.

Determination of nonheme iron using inductively coupled plasma-atomic emission spectrometry

A technique for the rapid and accurate estimation of nonheme iron using inductively coupled plasma-atomic emission spectrometry is described. Yttrium was used as an internal standard. An external calibration method was used. The standards were prepared in a matrix composed of 2.5N HCl in 10% (w/v) trichloroacetic acid. The supernatant and coagulum fractions of liver nonheme iron were separated by the method of Drysdale and Ramsay with minor modification. The data determined by this procedure was compared and found to be agreement with data determined by the method of Hallgren. To evaluate the iron status of rats, hemoglobin and liver nonheme iron were determined. Hemoglobin and all of the nonheme iron fractions of the rats fed an iron-deficient diet were significantly lower than those of the rats fed an iron-sufficient diet. The blood content in the liver was estimated to be 80 microL/g from the blood iron concentration, and the difference between total and nonheme iron concentration in liver.

Erythrocyte metallothionein as an index of zinc status in humans

Metallothionein concentrations in erythrocyte lysates derived from human subjects were measured by an ELISA procedure. IgG obtained from serum of sheep injected with human metallothionein 1 was used in this competitive assay. Subjects were fed a semipurified zinc-deficient diet (0.7 mg of zinc per kg of diet) for an 8-day depletion period after 3 days of acclimation. Fasting plasma zinc concentrations were reduced approximately 7%. Metallothionein in the erythrocyte lysates was significantly decreased to 59% of the initial level by the end of the depletion period. Supplementation of these depleted subjects with zinc (50 mg) did not increase erythrocyte metallothionein levels within 24 hr. Daily supplementation of control subjects with zinc (50 mg/day) increased erythrocyte metallothionein to a 7-fold maximum within 7 days. These levels were reduced by 61% within 14 days after zinc supplementation was terminated. Incubation of rat [35S]metallothionein with human erythrocyte lysate showed a time-dependent increase in 35S soluble in 20% trichloroacetic acid, indicating degradation of the labeled protein, presumably via protease activity in the lysate. It is proposed that zinc supplementation induces erythrocyte metallothionein during erythropoiesis and that low zinc intake decreases synthesis and/or accelerates degradation of the protein in reticulocytes/erythrocytes. Metallothionein levels in erythrocytes may provide a useful index upon which to assess zinc status in humans.