Submicroscopic histochemical demonstration of intracellular reactive zinc in beta cells of pancreatic islets

Histochemical Investigation of Influence of Diabetogenic Zinc Binding Chemicals In Vitro on Human Pancreatic Β-Cells and its Prevention

BACKGROUND: Amount of zinc-ions is correspond to insulin content in cytoplasm of β-cells. Diabetogenic zinc binding chemicals (DZC) formed with zinc in β-cells chelat complex that result destruction and death of β-cells within 10–15 min in animals. AIM: The aim of the study was to investigate using of specific histochemical methods the content of zinc and insulin in β-cells of pancreatic islets of human intact fetal pancreas tissue and under action of diabetogenic and non-diabetogenic zinc-binding substances diabetogenic zinc diethyldithiocarbamate (DZ and DDC). METHODS: Pancreas from 8-week-old human embryos and adult rabbits were used. Fixed or frozen islets were used in vitro effect. Histochemical methods for insulin and zinc in β-cells were used. RESULTS: Results showed that zinc in human β-cells is clearly revealed using of histochemical methods. In embryo pancreas, not integral islets were found as clusters of cells or even individual β-cells. Insulin content in ß-cells is for 7–20% lower and Zn2+ by 16–18% in compared with rabbits; Zinc in human ß-cells formed chelat complexes with 8PTSQ and DZ as Zn2+ –8PTSQ and Zn2+–DZ. Sodium DDC, a non-diabetogenic Zn2+ chelator, formed not toxic complexes with Zn2+ in fetal β-cells that protect cells of destruction caused by DZC as in animal’s pancreas. CONCLUSION: (1) Intracellular reactive zinc contained in human fetal pancreatic ß-cells clearly revealed using of histochemical methods and also (2) demonstrated that DZC in human ß-cells result formation with zinc of chelat complexes. (3) As in animals, non-toxic chemical as DDC is able to block zinc in ß-cells that result prevention of its destruction caused by DZC.

A recessive X-linked mutation causes a threefold reduction of total body zinc accumulation in Drosophila melanogaster laboratory strains

A newly identified human locus on chromosome 15 was recently associated with zinc accumulation. Based on a prior report of a threefold difference in zinc accumulation between fumble¹ heterozygous mutants and control fly strains, it was suggested that phosphopantothenoylcysteine decarboxylase might affect zinc status through its effects on vitamin B5 (pantothenate) metabolism. We report here that outcrossed fumble¹ heterozygous mutant flies with low zinc content have been recovered, suggesting that pantothenate metabolism did not alter zinc homeostasis in fumble¹ heterozygous flies. We show instead that the Drosophila condition of low body zinc accumulation is an X-chromosome-linked recessive trait.

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Flies with a threefold reduction in zinc accumulation remain viable and fertile.

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There is no causal association between zinc accumulation and fly pantothenate kinase mutants.

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A widespread X-linked mutation causes a threefold reduction in zinc accumulation in Drosophila.

Immunohistochemical localization of metallothionein in chronic pancreatitis

Metallothionein (MT) is a low-molecular weight intracellular protein, rich in sulfhydryl residues, and able to bind bivalent metals. MT, like Zn, is a component of the diversified elements of antioxidant system. Recent studies have shown that reactive oxygen species play a role in the pathogenesis and development of chronic pancreatitis. The aim of the study was to identify immunohistochemically (LSAB2-HRP; DAKOCytomation) the localization of metallothionein and to determine MT expression in 9 patients with chronic pancreatitis. Our studies confirm that MT is present in exocrine and endocrine cells of patients with chronic pancreatitis and chronic pancreatitis with concomitant diabetes. They also indicate increased expression of MT, particularly in acinar cells of the pancreas. This suggests that MT is greatly involved in homeostasis of the pancreas and synthesis of pancreatic hormones.

New markers for pancreatic islets and islet cell tumors

Islets of Langerhans account for 2 g of endocrine tissue in the pancreas, comprising approximately one million islets, with each containing 1000 endocrine cells. The major hormone secreted from the islets is insulin, which regulates blood glucose, the main fuel of the body. Islets also secrete glucagon, somatostatin and pancreatic polypeptide and all are involved in the paracrine mechanism. Islet cells can be stained immunohistochemically for the general endocrine markers, chromogranin A, synaptophysin, neuron-specific enolase and Leu7. Beta islet cells are well equipped with glucose transporter 2, which binds to glucose and regulates diffusion of glucose through the beta cell membrane. As all four islet hormones are initially synthesized as prohormones, all islet cells are equipped with prohormone convertase 1/3 and 2. In addition, islet cells also contain zinc-containing matrix metalloproteinases and their inhibitors, metallothionein, cyclin-dependent kinases and insulin-like growth factors, and many more hormones, peptides and enzymes. Thus, islets not only secrete insulin and other pancreatic hormones but are a complex organ whose major function is glucose homeostasis.

Cytochemical techniques for zinc and heavy metals localization in nerve cells

Zinc is one of the most abundant oligoelements in the living cell. It appears tightly bound to metallothioneins, loosely bound to some metalloproteins and nucleic acids, or even as free ion. Small amounts of zinc ions (in the nanomolar range) regulate a plentitude of enzymatic proteins, receptors, and transcription factors; thus, cells need accurate homeostasis of zinc ions. Some neurons have developed mechanisms to accumulate zinc in specific membrane compartments ("vesicular zinc") which can be revealed using histochemical techniques. This article is a short report on the different direct-indirect experimental approaches for zinc and heavy metal detection in neurons. Substances giving a bright color or emitting fluorescence when in contact with divalent metal ions are currently used to detect them inside cells; their use leads to the so called "direct" methods. The fixation and precipitation of metal ions as insoluble salt precipitates, their maintenance along the histological process, and their demonstration after autometallographic development are essential steps for other methods, the so-called "indirect methods" (Timm and Danscher Neo-Timm methods).

Metallothionein in pancreatic endocrine neoplasms

Metallothioneins (MTs) are intracellular proteins that bind to metal ions and are involved in heavy metal homeostasis and detoxification. Pancreatic islets were shown to be positive for zinc-containing matrix metalloproteinase-2 and -9 by immunocytochemical staining. The immunolocalization of matrix metalloproteinases in pancreatic islets prompted us to study further the link between zinc and MT in 34 cases of pancreatic endocrine neoplasms, including insulinomas, glucagonomas, gastrinomas, pancreatic polypeptide-omas, and non-functioning endocrine neoplasms. Four types of islet cells were found to be positive for MT, whereas pancreatic endocrine neoplasms mostly were either weakly positive or negative for MT. The presence of MT in normal islet cells and pancreatic endocrine neoplasms is consistent with the notion that MTs modulate zinc homeostasis and metabolism in pancreatic islet cells and pancreatic endocrine neoplasms as those tissues contain zinc-containing matrix metalloproteinases.

Immunocytochemical localization of metallothionein in human pancreatic islets

Metallothioneins (MTs) are small intracellular proteins that bind to metal ions and are involved in heavy-metal homeostasis and detoxication. Pancreatic islets were previously reported to contain zinc-containing matrix metalloproteinases (MMPs) and inhibitors of metalloproteinases (TIMPs) by immunocytochemical staining. The immunolocalization of MMPs and TIMPs in pancreatic islets prompted us to investigate further the link between zinc and MTs. Both beta and nonbeta islet cells were found to contain MTs by this immunocytochemical staining, suggesting that MTs may be involved in pancreatic hormone synthesis and secretion, in addition to their roles in zinc homeostasis and detoxification.

Evidence from dithizone and selenium zinc histochemistry that perivascular mossy fiber boutons stain preferentially "in vivo"

This paper describes a perivascular staining pattern that is obtained when dithizone or sodium selenite are used to label zinc intravitally. Our observations indicate that the perivascular staining is a result of zinc labeling in mossy fiber boutons adjacent to capillaries and suggest that there might be a special blood brain barrier in the mossy fiber regions.

Cellular and subcellular demonstration of mercury in situ by modified sulfide-silver technique and photoemulsion histochemistry

Young adult C57BL/6J mice were injected with 4.0 mg/kg body wt of methylmercuric chloride (MMC) for 3 consecutive days for a total of 12.0 mg/kg. Control animals received physiological saline in place of MMC. One week following the last injection, the animals were sacrificed. Representative tissue blocks and sections from the brain, kidney, and liver were subjected to a modified sulfide-silver technique (SST) and the photoemulsion histochemical method. The results show that both of these techniques demonstrate consistent and distinct localization of mercury (Hg) gains in cells and subcellular organelles. These methods are based on the principle that Hg compounds react strongly with sulfhydryl groups in tissues and cells to form Hg-sulfides and also on the affinity of Hg and silver to form an amalgam when placed in a physical developer or photographic emulsion. Thus Hg in cells is demonstrable without prior treatment of sulfide solution. The methods are simple and reliable when used with proper controls. Specific localization of Hg in cells in situ without the use of radioactive material and without disruption of anatomical relationships provided by these methods offers distinct advantages over other methods of Hg determination. Thus it would be possible to conduct a retrospective or prospective study of human autopsy materials and also would allow direct correlation of Hg deposition with pathological changes in cells and subcellular organelles.

The autoradiographic localization of zinc within the pancreatic islets of the rainbow trout, Salmo gairdneri

This experiment reports on the localization of zinc within the pancreatic islets of Salmo gairdneri. Individual fish were injected with 65Zn and the distribution of the isotope within the islets was determined by autoradiography. Insulin cells were found to accumulate approximately twice as much zinc per unit area as the rest of the islet tissue. It is presumed that this zinc is involved with the crystallization and storage of insulin within the insulin cells. Various histological methods were investigated to ascertain the procedure which best precipitated zinc and at the same time avoided excess leaching.

Secretion in the B-cells of islets of Langerhans as demonstrated by zinc staining

Intact islets of Langerhans were isolated from Wistar rats by means of vital fixation, microdissection and development of the metal sulfides formed with Timms reagent. In such intact islets, the beta-granules and the cell organelles can be shown up well electron microscopically. The endocrine pancreas tissue of normal rats contains a relatively constant average of 715 densely structured granules per 100 microns2. After administration of sulfonylurea, the number of (less dense) granules is reduced to 125 (in adipose animals 115) granules per 100 microns2. Besides empty 'sacs', large-vesicle Golgi apparatus and ballooned forms of the endoplasmic reticulum occur.

Calcium, zinc and other elements in islet and exocrine tissue of the rat pancreas as measured by histochemical methods and electron-probe micro-analysis, Effects of fasting and tolbutamide

Fasting for 24 or 72 h causes a strong decrease of pancreatic islet calcium content as detected by glyoxal-bis-(2-hydroxyanil), (GBHA). There is strong evidence that GBHA only detects ionized calcium and not total calcium (Wolters et al., 1979). Fasting does not influence the zinc content as detected by dithizone (DZN), and aldehyde-fuchsin (AF) staining intensity is only slightly decreased. After degranulation of islets by tolbutamide (which reduced the insulin content of the pancreas to 10% of the control value) the staining intensities of GBHA, DZN and AF were strongly depressed. Calcium (as well as other elements) were also measured by electron-probe micro-analysis (EPMA). It appeared that 24 or 72 h of fasting did neither affect the total content of Ca nor of Na, P, S, and K of the islets significantly. In exocrine tissue the Ca content increased gradually as a result of fasting. Thus, after 72 h of fasting the Ca content was 25% higher than in fed controls. On the other hand after 72 h of fasting the K content appeared to be decreased. EPMA revealed that after degranulation of islets the Ca content decreased markedly (35%). S appeared to be decreased by only 14%, whereas the content of the other elements was not changed. The results show that GBHA-detectable Ca is only a part of EPMA-detectable Ca. The GBHA-Ca "pool" which contains ionized Ca, is subjected to changes when the animals are fasted, the total Ca content as measured by EPMA does not change. Thus, at least two distinguishable pools of Ca exist within the islets (GBHA-detectable and not-GBHA-detectable). It is suggested that as a result of fasting Ca passes from one pool to another.

The ultrastructural localisation of cadmium

A modified technique for the ultrastructural localisation of heavy metals is described in this paper. The method involves precipitation of heavy metals as sulphides in the tissue by using (NH4)2 S after brief fixation in glutaraldehyde. The sulphides are, in the presence of a physical developer, then used to catalyse the reduction of silver ions into visible molecular silver. This latter step of physical development has been normally carried out after embedding and sectioning. However, when we followed this method we found that the dark metal sulphide was lost from the tissue during the embedding in epoxy resin. Hence the method was unsuitable for our proposed experiment on the ultrastructural localisation of cadmium. We subsequently modified the technique primarily by treating very thin tissue slices with the developer before dehydration and embedding, thus eliminating any problem from sulphide loss. This modified technique was used to investigate the ultrastructural localisation of cadmium in the kidneys of mice which had been exposed to 50 ppm cadmium in their drinking water for up to eight months. The molecular silver was found to be located mainly in the proximal tubule cells, either as dense clumps in apical vesicles and lysosomes or diffuse grains throughout the cytoplasm of the cells particularly in the basal region. We interpret these results as indicating that cadmium is found in the apical vesicles, lysosomes and cytoplasm of proximal tubule cells.