Quantitative immunohistochemistry of metallothionein in rat placenta

Biological interactions between nanomaterials and placental development and function following oral exposure

We summarize the literature involving the deposition of nanomaterials within the placenta following oral exposure and the biological interactions between nanomaterials and placental development and function. The review focuses on the oral exposure of metal and metal oxide engineered nanomaterials (ENMs), carbon-based ENMs, and nanoplastics in animal models, with a minor discussion of intravenous injections. Although the literature suggests that the placenta is an efficient barrier in preventing nanomaterials from reaching the fetus, nanomaterials that accumulate in the placenta may interfere with its development and function. Furthermore, some studies have demonstrated a decrease in placental weight and association with adverse fetal health outcomes following oral exposure to nanomaterials. Since nanomaterials are increasingly used in food, food packaging, and have been discovered in drinking water, the risk for adverse impacts on placental development and functions, with secondary effects on embryo-fetal development, following unintentional maternal ingestion of nanomaterials requires further investigation.

Ultrastructural Demonstration of Mercury Granules in the Placenta of Metallothionein-Null Pregnant Mice after Exposure to Mercury Vapor

The placenta plays an important role in the regulation of maternal to fetal transfer of toxic substances, including nonessential metals. Metallothioneins (MTs), which are known to have protective effects against heavy metal toxicity, exist in the placenta, but the exact localization of placental MTs (both MT-I and MT-III) and their physiological role in the placenta exposed to mercury are unclear. The present study was performed to examine the localization of MTs and mercury granules in the placenta of mice exposed to mercury vapor. On gestational day 16, MT-I & II-null and wild-type mice were exposed to mercury vapor at 4.9 to 5.9 mg/m3 for 2 hours. At 24 and 48 hours after exposure, the placentas were examined for mercury distribution (autometallography), MT immunoreactivity, and MT mRNA expression (in situ hybridization). No histological changes were observed in the placentas of either MT-null or wild-type mice. Mercury deposition was demonstrated along the boundary between the junctional zone and the labyrinth zone, as well as in the yolk sac, maternal decidual cells, and labyrinth trophoblasts of both MT-null and wild-type mice. MT-I & -II immunoreactivity, which was confined to wild-type mice, was demonstrated in the yolk sac and decidual cells; mercury was also shown in both structures, suggesting that mercury granules were bound to MTs. MT-III mRNA expression was observed in the yolk sac, decidual cells, and spongiotrophoblasts in both MT-null and wild-type mice. There was, however, no evidence of MT at the boundary between the junctional and labyrinth zones, where substantial mercury deposits were demonstrated. These results suggest that placental MTs and the other unknown molecules may be related to the barrier to the placental transfer of mercury.

The influence of biological and environmental factors on metallothionein concentration in the blood

The concentration of metallothionein (MT), a low-molecular-weight protein, is regulated by many factors, primarily metals (zinc, cadmium, copper), cytokines, glucocorticoides and free radicals. These factors are determined by such aspects of human biology as gender, pregnancy and age, as well as by environmental factors including the use of oral contraceptives and cigarette smoking, all which may affect MT levels in the body. The aim of this study was to investigate the influence of these biological and environmental factors on MT concentrations in erythrocyte lysate and in plasma. MT concentrations were determined by a two-step direct enzyme-linked immunosorbent assay. Evaluation of exposure to cigarette smoking was performed by checking cotinine levels in the plasma of subjects. The studies showed higher MT concentrations in both the erythrocyte lysate and plasma of women when compared to men. Furthermore, pregnancy causes an increase of MT concentration in plasma, while oral contraceptives cause an elevated concentration of MT in erythrocyte lysate. Age impacts plasma MT concentrations in men, whereas it does not affect concentrations of MT in erythrocyte lysate.

Quantitative immunogold study of increased expression of metallothionein-I/II in the brain perivascular areas of diabetic scrapie-infected mice

Quantitative immunogold procedure was used to study the distribution of metallothionein I/II (MT-I/II) at the ultrastructural level in the perivascular areas, including microvascular endothelial cells (ECs) and astrocytes with their perivascular end-feet, in brains of scrapie-infected hyperglycemic (diabetic) and normoglycemic (non-diabetic) mice. Samples of the fronto-parietal cortex obtained from diabetic and non-diabetic scrapie-infected, as well as from non-infected (control) SJL/J mice, were processed for immunocytochemical examination. In control mice, the labelling of the ECs was of low intensity, restricted to few immunogold particles in the cytoplasm. More intense labelling was present in the cytoplasm of astrocytic perivascular processes and perikarya, where it was associated with endoplasmic reticulum and fibrils. A few immunosignals were also present inside the nuclei of astrocytes. In diabetic mice the labelling of the EC cytoplasm was slightly increased, whereas in the cytoplasm of perivascular processes and pericarya of astrocytes, including their nuclei, there was significant enhancement of labelling. In these cells the density of immunosignals was highest in the areas of cytoplasm containing bundles of fibrils. In non-diabetic, scrapie-infected mice the intensity of immunolabelling was higher than in control mice but slightly lower than in diabetic mice. These results are similar to those in Alzheimer's disease reported by other authors, and suggest that neurodegenerative diseases as well as metabolic stress enhance the metallothionein expression in perivascular regions of brain cerebral cortex, predominantly in astrocytes.

Placental to fetal transfer of mercury and fetotoxicity

Mercury vapor is known penetrate the placental barrier more easily than inorganic mercury. A relative amount of mercury accumulates in the fetus after exposure of pregnant animals to mercury vapor. Mercury concentration in fetal organs is much lower than that in maternal organs except the liver, and fetal liver shows significantly higher mercury concentrations than maternal liver. In fetal liver, a substantial portion of mercury is bound to metallothionein (MT), which plays an important role as a reservoir of mercury during the prenatal period. The mercury retained in fetal liver is redistributed to other organs, such as the brain and kidney, with diminishing MT levels during postnatal development. Consequently, an increase in mercury concentration in the brain and kidney of the neonate is observed. In studies on animal offspring in utero exposed to mercury vapor, behavioral changes, such as radial arm maze, morris maze and lever-press durations, are observed when the levels of mercury vapor exceed the threshold limit value (TLV).

Immunohistochemical demonstration of metallothionein in eyes with choroidal melanomas

PURPOSE

The since immunohistochemically detectable metallothionein (MT) overexpression has been described in a variety of human tumours, including skin melanomas, in relation to different stages of tumour development and progression.

MATERIALS AND METHODS

We used a monoclonal antibody to investigate the distribution of MT in 18 formalin-fixed, paraffin-embedded, surgically enucleated eyes with choroidal melanomas, from 18 patients (8 male, 10 female; age range 30-83 years, mean 58.7). Clinico-pathological details and follow-up data (2-124 months, mean 36.1) were also available. MT immunoreactivity was recorded and the percentage of stained cells was graded for semiquantitative purposes. Correlations between immunohistochemical data and morphological characteristics of melanomas were investigated using non-parametric methods; survival analysis was done by the Kaplan-Meier method and the survival curves were compared by the Mantel-Cox log-rank test.

RESULTS

MT immunoexpression was found in 15/18 cases (83.3%) with staining scores from 1 to 3; MT staining varied in intensity and was mainly localized in the cytoplasm, although a combined nuclear/cytoplasmic reactive pattern was seen in neoplastic elements. No differences in MT immunostaining were seen in relation to age or sex, tumour size, histotype and amount of pigment; univariate analysis of survival data showed no prognostic significance regarding MT expression.

CONCLUSIONS

The immunohistochemical evidence of MT in neoplastic elements could be related to the production of this scavenging protein in the tumour for cell defense mechanisms against hydroxyl free radicals, and to act as a Zn donor, since Zn is required for the synthesis of DNA and DNA-repair enzymes.

Isolation and identification of metallothionein isoforms (MT-1 and MT-2) in the rat testis

It has been a long-lasting controversial issue as to whether or not the male genital organs, such as the testis and prostate, contain metallothioneins (MTs), a group of cysteine-rich heavy-metal-binding proteins that play a role in detoxifying heavy metals such as cadmium (Cd). Earlier studies reported that the rodent testis lacks MTs and concluded that this is why the testis is very susceptible to Cd, although other indirect experimental evidence suggests that MTs are present in this organ. A deficiency of MTs in the testis was originally suspected on the basis of amino acid composition analysis, since MT-like proteins isolated as Cd-binding proteins did not have a characteristic MT structure. In the present study, we demonstrate that the rat testis indeed expresses Cd-binding proteins with sequences identical to those previously described for MT-1 and MT-2, the major isoforms. To confirm that MT-1 and MT-2 are present in the rat testis, we purified and isolated Cd-binding proteins by homogenization using Cd-containing buffer, followed by sequential purification using Sephadex G-75 gel filtration chromatography and anion HPLC column chromatography, which yielded Cd-binding protein-1 (Cd-BP-1) and -2 (Cd-BP-2). After pyridylethylation, Cd-BP-1 and Cd-BP-2 were subjected to specific protein fragmentation by acids and endopeptidases, which revealed that these Cd-binding proteins have the same primary structures as MT-1 and MT-2 respectively. Thus we believe that the present results clearly resolve the long-standing debate about the presence of MTs in the testis, at least in the rodent.

Immunohistochemical expression of metallothionein in normal human colorectal mucosa, in adenomas and in adenocarcinomas and their associated metastases

The immunohistochemical distribution pattern of metallothionein, a low molecular weight protein with strong affinity for divalent heavy metal ions, has been investigated in normal and neoplastic conditions of the large bowel. Utilizing a monoclonal mouse antibody the following formalin-fixed paraffin-embedded surgical or biopsy samples were studied: tubulo-villous adenomas (8 cases); adenocarcinomas with various degree of differentiation (85), nine of which were mucinous-type; synchronous tubular or tubulo-villous adenomas separate from carcinomas (30); transitional mucosa (45); metastases in lymph nodes (43); and distant metastases (45). Twenty biopsies from the right and left colon of 10 patients affected by irritable bowel syndrome were also analyzed. Normal colonic mucosa as well as transitional mucosa showed metallothionein immunopositivity in enterocytes at the luminal surface and crypts. Evident nuclear and cytoplasmic staining was encountered in tubulo-villous adenomas; the same reactivity was noted in the basal glandular component of colorectal carcinomas-synchronous adenomas, while less intense staining was noted in the apical villous portions. A variable metallothionein immunostaining was observed in adenocarcinomas (62.3%), in lymph node (55.8%) and distant hepatic (17.2%) and omental (43.8%) metastases, although it was not always concordant with that reported in the corresponding primary tumour. Whether the metallothionein positivity observed in normal and neoplastic cells is the result of expression of a stable form of the protein or an accumulation in the nucleus and cytoplasm remains to be clarified.

Metallothionein in the ovaries of laying hens exposed to cadmium

The presence of metallothionein (MT) and its mRNA in the ovaries of laying hens is reported. In laying hens injected with cadmium (Cd), Cd accumulated in the follicle walls of the ovaries not in the follicle yolks. In the follicle walls, (Cd, Zn)-MT and its mRNA were found. This indicates that MT bound to Cd is biosynthesized in the follicle walls. We suggest that MT might play a role in sequestering Cd. On the other hand, zinc (Zn) was found in the follicle walls and yolks in the Cd-treated laying hens. The relationship between Zn and (Cd, Zn)-MT is also discussed.

The localization of mercury and metallothionein in the cerebellum of rats experimentally exposed to methylmercury

Rats were dosed with methylmercuric chloride, either by gastric gavage (5 x 10 mg kg-1 body weight over a 15-day period), or in their drinking water (20 mg methylmercuric chloride l-1 for 14 or 42 days). Localization of mercury within the cerebellum was performed with a silver physical development technique, and metallothionein with dinitrophenyl hapten-sandwich immunohistochemistry. Mercury was detected in structurally undamaged Purkinje neurones and adjacent Bergmann glial cells; no mercury was detected in granule cells even though these small cells nearest the Purkinje layer had a high incidence of pyknotic nuclei. In general, metallothionein was detected mainly in Bergmann glial cells, Purkinje cells, astrocytes and glial cells of white matter; no metallothionein was detected in granule cells. We hypothesized that the resistance of Purkinje cells to methylmercuric chloride reflects their ability to transform organic mercurials to inorganic mercury that, in turn, induces the synthesis of radical-scavenging metallothionein molecules.

The effect of zinc in the form of erythromycin-zinc complex (Zineryt lotion) and zinc acetate on metallothionein expression and distribution in hamster skin

The occurrence of zinc-induced synthesis of metallothionein in skin after topical application of the anti-acne drug Zineryt lotion was investigated in hamster ears. The dinitrophenyl hapten-sandwich immunohistochemical method involving a monoclonal anti-metallothionein (MT) antibody (E9) was used to detect and localize zinc-binding MT in the 'treated' and untreated hamster skin. Atomic absorption spectrophotometry and dithizone histochemistry indicated that zinc penetrated the skin more readily, and accumulated more efficiently within the sebaceous glands, when applied to the skin surface as the organo-zinc complex, rather than as the inorganic zinc salt. MT and zinc had similar distributions in hamster skin exposed to the metal. Thus, MT immunoreactivity was especially intense in the sebaceous glands of Zineryt lotion-treated skin, with evidence of nuclear distribution in some cells. Zinc delivered to the sebaceous glands, and released from the organo-complex under the prevailing aqueous conditions, certainly induced MT synthesis; the cysteine-rich protein may protect the pilosebaceous units during the inflammatory phase of acne by scavenging generated oxyradical species.

Immunohistochemical localization of metallothionein in the eye of rats

In order to elucidate possible physiological roles of metallothionein (MT), we have studied immunohistological localization of MT in the eye of the rat, using an avidin-biotin peroxidase complex method. As a result, strong MT immunostaining was observed in the epithelium of the lens and cornea. In the retina, considerably strong MT immunostaining was observed in the pigment cell layer while the nerve fiber layer and inner plexiform layer showed weak MT staining. Glial cells in the optic nerve were found to have marked MT staining. The present result is consistent with the hypothesis that MT may be involved not only in activation of zinc enzymes and cell proliferation through supply of zinc ions, but also in a protective mechanism in the blood-retina barrier.

Effects of cadmium exposure during pregnancy on cadmium and zinc concentrations in neonatal liver and consequences for the offspring

The effects of cadmium exposure during pregnancy (by means of daily subcutaneous injections of 4.4 mumol/kg to the mother) on the neonates were investigated. No effect was observed on fetal or neonatal body weights, nor on neonatal liver weights. These parameters were examined up to 5 weeks after birth. The weight of neonatal thymuses was decreased 7 and 14 days after birth due to cadmium exposure of the mothers as compared with controls. This may be caused by zinc deficiency, because zinc concentrations in fetal and neonatal livers after cadmium exposure were found to be very low 20 days after conception and 5 h after birth. Cadmium concentration in neonatal liver decreased; however, cadmium in malignant liver increased as age increased. In the mother, cadmium was transferred to the milk, as it was demonstrated in the stomach contents of the pups. Simultaneous administration of zinc in amounts equimolar to cadmium did not have any noticeable effect on the amount of cadmium transferred to the fetus or on cadmium concentrations in any of the organs investigated. It could not prevent zinc deficiency in fetal and neonatal liver. In addition, growth retardation of the thymus from exposed pups could not be prevented by zinc administration.

Cadmium and zinc concentrations in fetal and maternal rat tissue after parenteral administration of cadmium during pregnancy

Cadmium (Cd) and zinc (Zn) concentrations were determined by solid sampling atomic absorption spectrometry (AAS) in rat maternal and fetal tissues after exposure to cadmium. Cadmium was administered subcutaneously as CdCl2 in saline daily during pregnancy. Two experiments were performed. In expt. I we investigated the tissue concentration at day 19 (gestational age) after administration of several doses: 0, 1.1, 2.2, 4.4, and 8.8 mumol Cd/kg/day. In expt. II the course of the Cd and Zn concentrations during pregnancy was investigated by collecting samples at days 14, 16, 18 and 20, after daily injections of 4.4 mumol Cd/kg. Cadmium concentrations in blood, maternal liver, placenta and fetal liver increased with dose and duration of exposure. Cadmium was heavily accumulated in the liver and transferred to the fetus only in small amounts. The zinc concentration in the maternal liver was positively correlated with the cadmium concentration. In the placenta the zinc concentration was not affected. Zinc in fetal liver was decreased from day 18 onward. Despite relatively high cadmium levels and decreased zinc levels in the fetus, we observed no adverse effects on various reproduction parameters, such as birth weights and obvious malformations.