Regulation of cysteine-rich intestinal protein by dexamethasone in the neonatal rat

The cysteine-rich intestinal protein (CRIP) is an intestinal zinc-binding protein containing a single copy of a cysteine-rich domain known as the LIM motif. CRIP mRNA and protein levels increased in the rat small intestine throughout the suckling period, reaching highest levels by the late weanling stage. A similar developmental pattern of CRIP protein levels was also detected by an increase in zinc binding to CRIP-containing HPLC fractions of intestinal cytosol. Administration of the synthetic glucocorticoid hormone dexamethasone to neonates caused the precocious rise of CRIP mRNA and protein. In adult rats, CRIP mRNA levels were not significantly altered by dexamethasone. Maximal CRIP mRNA content was detected in cells from the mid-villus, as confirmed by expression of cryptdin mRNA. In this report we show the glucocorticoid regulation of the LIM motif-containing protein CRIP and suggest that glucocorticoid hormones play a role in developmental regulation of CRIP.

Cloning of rat intestinal mRNAs affected by zinc deficiency

Male rats were fed a purified diet containing 1 mg Zn/kg to induce zinc deficiency (-Zn). A second set of rats were fed a 30 mg Zn/kg diet, which supplied adequate levels of zinc (+Zn). The zinc-adequate rats were pair-fed to the rats fed the 1 mg Zn/kg diet to eliminate differences in diet intake. After 16 d, the two conditions of dietary zinc status were confirmed by assaying serum zinc concentrations and by Northern analysis for metallothionein mRNA abundance in the kidney. Messenger RNA was purified from small intestine by oligo(dT) chromatography and pooled within conditions. A cDNA plasmid library was constructed from the mRNA derived from the intestines of zinc-deficient rats. The library was then screened by the method of differential hybridization using 32P-labeled first strand cDNA probes derived from the +Zn and -Zn mRNA. After screening 10,000 independent cDNA clones, nine cDNAs were isolated and studied further, corresponding to mRNAs that are down-regulated by zinc deficiency. The ratio of the abundance between the two conditions for the nine mRNAs ranged from 1.5- to sevenfold as determined by Northern analysis of the +Zn and -Zn intestinal mRNAs. Two of these clones seemed to be specific to the intestine, and four others were abundant in the intestine and one or two other tissues. We are using these cDNAs as models to study gene regulation under various conditions of dietary zinc intake and to explore the genes most sensitive to zinc deficiency.

Erythrocyte metallothionein response to dietary zinc in humans

The response of erythrocyte metallothionein to dietary zinc in human subjects was evaluated in a controlled metabolic protocol including standard indices of zinc status. Fifteen male subjects, age 27 +/- 3.6 y, participated in a 90-d, four-phase study consisting of acclimation (7 d; 15 mg Zn/d), treatment (6 wk; either 3.2, 7.2 or 15.2 mg Zn/d), depletion (12 d; 0.55 mg Zn/d) and supplementation (30 d; self-selected diet plus 50 mg Zn/d) phases. During the treatment phase erythrocyte metallothionein decreased in the group fed 3.2 mg Zn/d. Erythrocyte metallothionein decreased during the depletion phase (46 +/- 10%) to below the normal concentration in all groups and increased in the supplementation phase. Plasma zinc concentration decreased in the group fed 3.2 mg Zn/d during the treatment phase relative to the acclimation phase. Erythrocyte zinc decreased in all groups during the depletion phase relative to the treatment phase, and then increased during the supplementation phase. These data suggest that erythrocyte metallothionein can be used as a measure of status in severe zinc depletion and that comparing the change in erythrocyte metallothionein over a 6-wk period can differentiate between low and adequate levels of dietary zinc intake.

Altered zinc metabolism occurs in murine lethal milk syndrome

The lethal milk (lm) mutation in mice causes Zn deficiency in pups nursed by lm dams. To examine tissue Zn distribution and Zn transport to milk and pups, 65Zn was administered to lactating normal and lm dams. Transport of 65Zn to milk of lm dams was approximately 50% of that transported to milk of normal dams. The lower milk 65Zn resulted in significantly less 65Zn uptake by tissues of the nursing pups. The decrease in 65Zn transport to the milk was accompanied by a significant increase in 65Zn uptake and metallothionein mRNA levels in kidney of the lm dams. The elevated Zn uptake and metallothionein expression was tissue specific and could be a reflection of altered zinc transport from mammary gland to milk. Polyacrylamide gel electrophoresis and Western transfer of mammary gland proteins from lm dams showed that a 30-kDa protein bound more 65Zn in vitro compared with proteins from normal mammary gland. Normal pups nursed by dams of the lm genotype had down-regulated metallothionein expression due to Zn deficiency. The genetic defect in lm mice decreases Zn transport to milk, thus explaining the neonatal Zn deficiency seen in normal mice fostered by lm dams. The greater metallothionein expression in dams of the lm genotype could be a secondary manifestation of altered tissue zinc distribution or a primary effect on a metallothionein regulatory mechanism.

Treatment of Wilson's disease with zinc: X. Intestinal metallothionein induction

Oral zinc therapy is effective in controlling copper balance in patients with Wilson's disease and blocks the intestinal absorption of copper, as demonstrated by uptake of copper 64 and copper balance measurements. In this study, 64Cu uptake measurements were concomitantly carried out with intestinal biopsies to investigate the relationship of reduced copper absorption to the levels of intestinal metallothionein in patients with Wilson's disease at different stages of zinc therapy. A pronounced increase in intestinal metallothionein levels and a sharp drop in 64Cu absorption were found 4 to 5 days after the initiation of zinc treatment. Conversely, metallothionein levels decreased and 64Cu uptake increased on the discontinuation of zinc therapy. The data indicate that 64Cu absorption varies as a function of intestinal metallothionein level. Intestinal metallothionein levels were found to correlate linearly with urinary zinc levels, which reflect body zinc status. These findings support our hypothesis that intestinal metallothionein induction mediates decreased copper absorption observed during zinc therapy. The suppressive effect of zinc on copper absorption appears to have a half-life of about 11 days.

Mechanisms of caeruloplasmin biosynthesis in normal and copper-deficient rats

To examine the mechanisms of holo-caeruloplasmin biosynthesis, we measured the serum caeruloplasmin concentration and oxidase activity, hepatic caeruloplasmin mRNA content and hepatocyte caeruloplasmin biosynthesis and secretion in normal and copper-deficient rats. Copper deficiency resulted in a near-complete loss of serum caeruloplasmin oxidase activity, yet only a 60% reduction in serum caeruloplasmin concentration and no change in the abundance of hepatic caeruloplasmin mRNA or the rate of caeruloplasmin biosynthesis. Both interleukin-1 alpha and lipopolysaccharide increased hepatic caeruloplasmin mRNA content and caeruloplasmin biosynthesis in normal and copper-deficient animals, but neither mediator increased caeruloplasmin oxidase activity in the copper-deficient group. Pulse-chase studies in primary hepatocytes from normal and copper-deficient rats revealed that the secretory rates for newly synthesized caeruloplasmin were identical, despite little or no holo-caeruloplasmin synthesis in hepatocytes of copper-deficient rats. We conclude that hepatocyte copper content has no effect on hepatic caeruloplasmin-gene expression or caeruloplasmin biosynthesis and that the incorporation of copper into newly synthesized caeruloplasmin is not a rate-limiting step in the biosynthesis or secretion of the apoprotein from rat hepatocytes.

Nuclear Zinc Uptake and Interactions and Metallothionein Gene Expression are Influenced by Dietary Zinc in Rats

Regulation of metallothionein gene expression by dietary zinc and the relationship of dietary zinc to nuclear zinc uptake was examined in growing rats. Zinc was fed at 5, 30 or 180 mg/kg, either in pelleted form for a 2-wk period (ad libitum) or for 2 h as a liquefied preparation (1 g in 4 mL). Two hours after the oral dose, the intestine and liver took up more zinc than other tissues. Nuclei purified from liver, kidney and spleen accumulated substantial amounts of zinc and directly reflected the dietary zinc level within the 2-h feeding period. Nuclei from kidney accumulated the largest amount of dietary zinc within 2 h, accounting for up to 6.2% of the total nuclear zinc concentration. Northern analysis demonstrated that metallothionein expression was proportional to dietary zinc intake in some tissues. It was greatest in kidney, followed in descending order by liver, intestine, spleen and heart. Thymus and lung metallothionein mRNA levels were not changed appreciably by dietary zinc intake. Chromatography of extracts from liver nuclei shows that 65Zn introduced into the portal supply is bound to discrete fractions of nuclear proteins. One of these fractions binds both 65Zn and a 32P-labeled oligonucleotide corresponding to the metal regulatory element of the metallothionein promoter. These results demonstrate that significant amounts of zinc from the diet are rapidly taken up by cell nuclei. Furthermore, they suggest that transcriptional regulation of the metallothionein gene and other genes with metal regulatory elements involves a direct interaction between the dietary supply and intranuclear factors that bind zinc.

Cysteine-rich intestinal protein and intestinal metallothionein: an inverse relationship as a conceptual model for zinc absorption in rats

Dietary zinc may regulate zinc absorption in part via the inhibitory effect of intestinal metallothionein, but the mechanism is unknown. We recently showed that cysteine-rich intestinal protein (CRIP) binds zinc during transmucosal zinc transport, and that CRIP may function as an intracellular zinc carrier. The present experiments examine the interaction of CRIP and metallothionein with zinc to evaluate their potential roles in the mechanism of zinc absorption. Intestinal metallothionein concentrations were lower and zinc absorption rates from isolated intestinal loops were higher in rats fed a low zinc diet compared with those fed a high zinc diet or given parenteral zinc to induce metallothionein synthesis. Zinc status did not affect the apparent CRIP concentration, but markedly altered the distribution of 65Zn in intestinal cytosol as determined by gel filtration HPLC. More 65Zn was associated with CRIP (40 vs. 14%) and less was bound to metallothionein (4 vs. 52-59%) in rats fed the low zinc diet compared with rats of high zinc status. Luminal zinc concentration also affected the distribution of 65Zn in the cytosol. CRIP bound progressively less (from 42 to 25%) of the 65Zn taken up from the lumen as the luminal zinc concentration was increased from 5 to 300 mumol/L. Collectively these data suggest that CRIP is a saturable, intracellular zinc transport protein, and that metallothionein inhibits zinc absorption by binding zinc in competition with CRIP. A hypothetical model for the mechanism of transcellular zinc absorption involving metallothionein and CRIP is presented and discussed.

Cysteine-rich intestinal protein binds zinc during transmucosal zinc transport

The mechanism of zinc absorption has not been delineated, but kinetic studies show that both passive and carrier-mediated processes are involved. We have identified a low molecular mass zinc-binding protein in the soluble fraction of rat intestinal mucosa that could function as an intracellular zinc carrier. The protein was not detected in liver or pancreas, suggesting a role specific to the intestine. The protein binds zinc during transmucosal zinc transport and shows signs of saturation at higher luminal zinc concentrations, characteristics consistent with a role in carrier-mediated zinc absorption. Microsequence analysis of the protein purified by gel-filtration HPLC and SDS/PAGE showed complete identity within the first 41 N-terminal amino acids with the deduced protein sequence of cysteine-rich intestinal protein [Birkenmeier, E. H. & Gordon, J. I. (1986) Proc. Natl. Acad. Sci. USA 83, 2516-2520]. These investigators showed that the gene for this protein is developmentally regulated in neonates during the suckling period, conserved in many vertebrate species, and predominantly expressed in the small intestine. Cysteine-rich intestinal protein contains a recently identified conserved sequence of histidine and cysteine residues, the LIM motif, which our results suggest confers metal-binding properties that are important for zinc transport and/or functions of this micronutrient.

Intestinal metallothionein gene expression and zinc absorption in rats are zinc-responsive but refractory to dexamethasone and interleukin 1 alpha

The effects of dexamethasone and interleukin 1 alpha on intestinal metallothionein gene expression and zinc absorption were studied. Rats given parenteral zinc served as positive controls. A single intraperitoneal or intravenous dose of dexamethasone, interleukin 1 alpha or zinc markedly increased liver metallothionein synthesis 3-9 h after injection. Intestinal metallothionein mRNA and metallothionein protein were not affected by dexamethasone or interleukin 1 alpha, but were markedly increased by parenteral zinc. Absorption of 65Zn from isolated duodenal segments was inversely related to intestinal metallothionein concentration in rats given zinc, but was not affected by dexamethasone or interleukin 1 alpha. Plasma zinc concentrations decreased in rats given dexamethasone or interleukin 1 alpha and increased in those given zinc, but they were not related to 65Zn absorption. Similarly, multiple intraperitoneal administration of either dexamethasone or interleukin 1 alpha, or oral administration of dexamethasone, for 7 d markedly increased liver metallothionein synthesis but did not affect intestinal metallothionein concentration or 65Zn absorption. These results suggest that intestinal metallothionein gene expression and 65Zn absorption are refractory to glucocorticoid hormone and interleukin 1 alpha.

Maintenance of zinc-dependent hepatic functions in rat hepatocytes cultured in medium without added zinc

Hepatocytes were cultured with Waymouth's media containing zinc at concentrations of 1 (the endogenous zinc concentration of basal medium), 16 and 48 mumols Zn/L to examine the effects of extracellular zinc on a variety of zinc-related functions. The zinc concentrations were chosen with the intention of simulating zinc-deficient, adequate and excess extracellular conditions. Basal medium had no effect on cell zinc, metallothionein (MT) or MTmRNA for up to 48 h but reduced delta-aminolevulinic acid dehydratase (delta-ALA-D) activity to 75% of the initial level by 3 h. The addition of zinc at 16 or 48 mumols Zn/L during the initial 3 h of culture did not prevent the decrease in delta-ALA-D activity. Reintroducing zinc at concentrations of 16 or 48 mumols Zn/L to hepatocytes after the initial 3 h of culture in basal medium significantly increased cell zinc, MT and MTmRNA levels and fully restored delta-ALA-D activity by 24 h. Medium zinc had no apparent effect on membrane integrity assessed as leakage of lactate dehydrogenase activity into culture media or de novo protein synthesis as examined by two-dimensional gel electrophoresis of 35S-labeled proteins. Hepatocytes cultured in basal medium resisted losses in cell zinc concentration even when EDTA and bovine serum albumin were present in culture medium. Kinetic experiments using 65Zn suggest hepatocytes maintain zinc concentrations by reducing zinc efflux. The ability of hepatocytes cultured in basal (1 mumol Zn/L) medium to maintain cell zinc content and some zinc-dependent functions underscores the difficulty of producing zinc deficiency in primary hepatocyte culture.

Interleukin 6 regulates metallothionein gene expression and zinc metabolism in hepatocyte monolayer cultures

Attention has focused on the cytokine interleukin 6 (IL-6) as a major mediator of acute-phase protein synthesis in hepatocytes in response to infection and tissue injury. We have evaluated the effects of IL-6 and IL-1 alpha as well as extracellular zinc and glucocorticoid hormone on metallothionein gene expression and cellular zinc accumulation in rat hepatocyte monolayer cultures. Further, we have evaluated the teleological basis for cytokine mediation by examining cytoprotection from CCl4-induced damage. Incubation of hepatocytes with IL-6 led to concentration-dependent and time-dependent increases in metallothionein-1 and -2 mRNA and metallothionein protein. The level of each was increased within 3 hr after the addition of IL-6 at 10 ng/ml (10 hepatocyte-stimulating factor units/ml). Maximal increases in metallothionein mRNA and metallothionein protein were achieved after 12 hr and 36 hr, respectively. In contrast, IL-1 alpha concentrations as high as 20 ng/ml (1000 lymphocyte-activating factor units/ml) had no effect. Concomitant with the up-regulation of metallothionein gene expression, IL-6 also increased cellular zinc. Responses to IL-6 required the synthetic glucocorticoid hormone dexamethasone and were optimized by increased extracellular zinc. In addition, IL-6 with dexamethasone, dexamethasone alone, and increased extracellular zinc each reversed, in decreasing potency, the deleterious effects of CCl4 on hepatocyte viability as measured by cell protein and lactate dehydrogenase activity of the medium. Thus, IL-6 is a major cytokine mediator of metallothionein gene expression and zinc metabolism in hepatocytes and provides cytoprotection from CCl4-induced hepatotoxicity via a mode consistent with dependence upon increased cellular metallothionein synthesis and zinc accumulation.

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.

Effect of EDTA and zinc-methionine complex on zinc absorption by rat intestine

The effects of zinc chelators on 65Zn uptake, absorption and tissue distribution were determined in rats using ligated duodenal loops. 65Zn was supplied as Zn-methionine complex, ZnCl2, ZnCl2 + L-methionine or ZnCl2 + EDTA. The effect of EDTA was also determined in the presence of phytic acid. Absorption of 65Zn was markedly reduced in rats given Zn-methionine complex or ZnCl2 + EDTA. The 65Zn level in tissues (liver, bone, muscle, skin, kidney, and thymus) of rats given ZnCl2 + EDTA was also significantly reduced compared to that of rats given ZnCl2. Reduced absorption due to phytic acid was not improved by EDTA, although EDTA increased mucosal 65Zn retention. High performance gel filtration chromatography showed six 65Zn-binding peaks in the mucosal cytosol of rats given ZnCl2. A seventh peak attributable to Zn-EDTA was observed in cytosol from rats given ZnCl2 + EDTA. A comparable peak in plasma was not observed. Both EDTA and Zn-methionine complex reduced 65Zn-binding to a low-molecular-weight component of mucosal cytosol that was not metallothionein. The results suggest that Zn-EDTA is transported intact from the lumen into mucosal cells but not across the basolateral membrane. The adverse effects of EDTA and Zn-methionine complex on zinc absorption were associated with reduced 65Zn-binding to a component of mucosal cytosol that may be involved in zinc absorption.

Zinc uptake by basolateral membrane vesicles from rat small intestine

Zinc uptake (transport and binding) by basolateral membrane vesicles was investigated using membranes derived from small intestines of rats fed zinc-adequate and zinc-deficient diets. Uptake was separated into saturable and nonsaturable (diffusion) components. Kinetic analysis of initial rates of the saturable component of uptake (at 1 min) indicates half maximal uptake (Km) by vesicles from zinc-adequate rats was observed at a medium Zn2+ concentration of 24 microM. The maximum Zn2+ uptake rate (Jmax) of the saturable component was 17 nmol/(mg protein.min). Dietary zinc intake did not affect these parameters. Zn2+ transport by the basolateral membrane may involve an ATP-driven mechanism.

Kinetics of zinc metabolism in the rat: effect of dibutyryl cAMP

N6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (Bt2cAMP) administration to rats is shown to reduce serum zinc levels and increase liver zinc and metallothionein significantly. Such redistribution is similar to that seen in the acute phase response to stress. To determine the sites of regulation of zinc metabolism involved in zinc redistribution, we compared the kinetics of intravenously administered 65Zn between control and Bt2cAMP-treated rats. 65Zn disappeared more rapidly from the plasma of Bt2cAMP rats, whereas 65Zn content of liver and liver metallothionein was increased. 65Zn in spleen and bone marrow also increased. No change was seen in muscle or kidney, and 65Zn content decreased in skin, bone, small intestine, and feces. These kinetic data were integrated into two compartmental models describing zinc metabolism in control and Bt2cAMP-treated states. Models were constructed using the SAAM and CONSAM modeling programs. Comparison of models suggest several sites of regulation due to Bt2cAMP. Zinc uptake into liver metallothionein from both plasma and other zinc pools within the liver was increased, whereas the release of metallothionein-bound zinc to plasma decreased. These changes increased liver zinc at the expense of plasma zinc, tissue zinc (principally skin, bone, and small intestine), and fecal zinc excretion. Bone marrow, spleen, and muscle were protected against zinc loss due primarily to decreased rates of tissue zinc loss. It was also postulated that Bt2cAMP increased the transfer of liver zinc to secreted alpha 2-macroglobulin. These results demonstrate that Bt2cAMP-induced zinc redistribution is tissue specific and related in part to metallothionein synthesis.

Enzyme-linked immunosorbent assay for human metallothionein: correlation of induction with infection

Very little information is available concerning the relationship between metallothionein and disease in humans. Recently, investigators have used the Cd-heme method to measure metallothionein levels in human liver samples obtained from autopsy. This assay, however, is not sensitive enough to measure metallothionein in small tissue biopsy specimens. As an alternative, we report the development of a human metallothionein enzyme-linked immunosorbent assay (ELISA). This assay used high-performance liquid chromatography-purified human metallothionein-1 and purified sheep anti-human metallothionein-1 IgG. A limiting antigen coating concentration of 100 ng/ml and a minimal antibody dilution of 1:4000 were chosen. The sensitivity of the ELISA extended to 300 ng/ml (15 ng). The coefficients of interassay and intraassay variation were 15.4% and 4.2%, respectively. Human livers obtained from autopsy were assayed by this method and the values compared with values obtained by the Cd-heme method. The livers were separated by their autopsy reports into four groups: normal, immunosuppression, cancer, and infection. Livers from the infection group (ELISA 2979 micrograms/gm, Cd-heme 1201 micrograms/gm) contained significantly more metallothionein than those from the normal (ELISA, 1035 micrograms/gm, Cd-heme 245 micrograms/gm) and the immunosuppression (ELISA 1272 micrograms/gm, Cd-heme 221 micrograms/gm) groups (p less than 0.05). The cancer group (ELISA 2415 micrograms/gm) also had significantly elevated liver metallothionein levels. We conclude that this ELISA is sensitive enough for the measurement of tissue samples. Furthermore this assay is comparable to the Cd-heme assay in its ability to reflect metallothionein values among various treatment groups. We postulate that hepatic metallothionein induction is mediated by disease-related mechanisms such as interleukin-1, glucocorticoid secretion, or both.

Theoretical and practical aspects of zinc uptake and absorption

The purpose of this review is to describe our present understanding of the theoretical aspects of zinc uptake and absorption. An attempt has been made to include a selected amount of older literature to illustrate specific points. The zinc acquisition system appears to respond to the dietary zinc supply and the extent of digestive capacity. Up regulation of the uptake process with limited zinc intake seems to increase the pool of zinc that is subsequently exported from mucosal cells to the vascular compartment. Intracellular factors such as metallothionein influence the rate and/or extent of zinc acquisition and are regulated by dietary zinc availability and physiological factors.

Maternal zinc deprivation and interleukin-1 influence metallothionein gene expression and zinc metabolism of rats

The influence of maternal dietary zinc intake and recombinant human interleukin-1 alpha (rhIL-1 alpha) administration on metallothionein gene expression and the distribution of 65Zn were investigated. Pregnant rats were fed diets containing 1, 5, 30 or 180 mg Zn/kg diet in an equalized regime from d 13-20 of gestation. Metallothionein gene expression was examined by Northern blot and dot blot hybridization using combined 60-mer oligonucleotides specific for rat metallothionein-1 and -2 genes. Expression was progressively depressed in the fetal livers and livers and kidneys of dams fed diets marginal (5 mg/kg) and deficient (1 mg/kg) in zinc content. Administration of rhIL-1 alpha increased expression in maternal liver, placenta and in fetal liver of dams fed adequate or deficient diets. Kinetics of intravenously administered 65Zn showed that in response to rhIL-1 alpha, there was a higher uptake by the maternal liver and bone marrow with less 65Zn uptake by bone, intestine and plasma activity compared to controls. No change was observed in 65Zn taken up by the placenta or transferred to the fetus. Alteration of metallothionein gene expression could represent, in part, the mechanism whereby altered effects of zinc metabolism and function are mediated during fetal development.

Tissue-specific regulation of zinc metabolism and metallothionein genes by interleukin 1

Interleukin 1 (IL 1) production is stimulated by infection, cellular injury, and inflammation. This cytokine directs a wide spectrum of host responses. Human interleukin 1 alpha (IL 1 alpha) was used to examine the time course of effects on zinc metabolism as part of the acute phase response. IL 1 produced a transient depression in the serum zinc concentration and increased serum ceruloplasmin. Metallothionein levels were increased in liver 14-fold after IL 1. Increased expression of metallothionein-1 and -2 genes following IL 1 were observed in liver, bone marrow, and thymus. Pulse-labeling experiments with i.v.-administered 65Zn showed that IL 1 drastically altered zinc distribution kinetics among tissues. More 65Zn was taken up (and/or retained) by the liver, bone marrow, and thymus 6 h after IL 1, whereas correspondingly less 65Zn was found in bone, skin, and intestine. Uptake by other tissues was not affected by IL 1. Chromatography of cytosol from tissues with increased 65Zn uptake suggests the IL 1-induced redistribution may be driven by enhanced metallothionein synthesis. Collectively, the results show that IL 1 regulates zinc metabolism and may direct its preferential, tissue-specific distribution via elevated metallothionein-1 and -2 gene expression.

Zinc suppression of free radicals induced in cultures of rat hepatocytes by iron, t-butyl hydroperoxide, and 3-methylindole

The effect of zinc on lipid peroxidation initiated by either ferric-nitrilotriacetate, t-butyl hydroperoxide, or 3-methylindole was studied using primary monolayer cultures of rat liver parenchymal cells. The malondialdehyde content of the cells and culture medium was used to estimate the extent of lipid peroxidation. As the zinc concentration of the culture medium was increased from 1 to 48 microM, peroxidation was diminished. Cellular zinc and metallothionein levels were proportionally increased by supplemental zinc. Zinc supplementation of the medium inhibited NADPH-cytochrome c reductase activity and stimulated glutathione peroxidase activity. The uptake of iron into the hepatocytes was significantly reduced as the level of zinc was raised, suggesting that zinc antagonizes uptake of chelated iron into isolated hepatocytes and in this way blocks iron-induced peroxidation. Furthermore, induction of metallothionein synthesis by zinc may contribute to the reduction in free radicals. Spectra from electron spin resonance studies, using phenylbutylnitrone as a spin-trapping reagent, demonstrated that free radical production was inversely related to the zinc concentration of the culture medium. Spin trap data suggest that metallothionein added to lysed cells in vitro decreases free radical production. Studies using the spin trap, 3,3,5,5-tetramethylpyrroline-N-oxide indicated that cumulatively the predominant radical present in the cultures was a phenyl radical with hydroperoxide or methylindole. Collectively, our data demonstrate that zinc inhibits free radical production and lipid peroxidation in cultured hepatocytes. The mode of action of zinc could occur via free radical scavenging by zinc-induced metallothionein and/or by processes related to cytochrome P-450 and glutathione peroxidase, since these were also found to be sensitive to zinc supplementation levels of the culture medium.

An enzyme-linked immunoadsorbent assay for rat ceruloplasmin

A noncompetitive, colorimetric enzyme-linked immunoadsorbent assay (ELISA)+ was developed for measuring rat ceruloplasmin in serum and in medium from culture hepatocytes. The assay utilized polystyrene immobilized antibody which bound ceruloplasmin which then bound biotinylated antibody. The biotinylated antibody-antigen complex was detected with strepavidin-alkaline phosphatase conjugate. Standard curves for rat ceruloplasmin were constructed in the range between 10 and 50 ng/mL. Increases of 10 ng produced an increase in A403 of more than 0.2. With this immunoassay, serum ceruloplasmin levels were found to average 35 mg Cp/dL in control rats and 87 mg/dL in rats with experimental inflammation. Liver parenchymal cells secreted 1.6 micrograms Cp/5 x 10(5) cells/24 h. This ELISA assay for ceruloplasmin will facilitate studies on the regulation of ceruloplasmin synthesis and secretion in both intact rats and isolated hepatocytes.