Protection of DNA in HL-60 cells from damage generated by hydroxyl radicals produced by reaction of H2O2 with cell iron by zinc-metallothionein.

Scavenging of hydroxyl radicals (.OH) by the zinc form of metallothionein (ZnMT) was studied in HL-60 cells and in nuclei from such cells previously treated with ZnCl2 (ZnMT cells). Cells were grown for 48 h to label DNA for alkaline elusion experiments. During the last 24 h 0.1 mM ZnMT was included to induce ZnMT. Generation of DNA single-strand breaks (SSBs) by H2O2 in cells (5 x 10(5)/ml) treated at 4 degrees was increased by approximately 70% in Zn-treated cells by comparison with control cells. These cells had grown from an initial concentration of 5 x 10(5)/ml to a concentration at harvest of 16 x 10(5)/ml. Cells started at 6 x 10(5)/ml and growing to a final concentration of 20 x 10(5)/ml did not exhibit a similar increase in SSBs. This elevation in SSBs was traced to an increase in cell Fe content which exhibited a sharp dependence upon concentrations of cells and of ZnCl2 at the time of addition. The diffusion distance (d) from Fe to DNA of ZnMT cells treated with H2O2 was found to be 3.4 nm. This compares with a distance of 6.1 nm in control cells. SSB generation by hydroxyl radicals formed by 137Cs-gamma rays in Zn-treated cells decreased by 12%, accompanied by a decrease in d from 4.8 nm to 2.9 nm. Thus, ZnMT preferentially reacts with OH formed at some distance from DNA. In nuclei isolated from ZnMT cells started at 5 x 10(5)/ml, SSB generation by H2O2 increased by 60%. The d in these nuclei was 4.9 nm, similar to the distance in control nuclei reported previously. These data suggest that, in addition to altering the scavenging environment, treatment of cells with Zn leads to an increase in reactive Fe in cells and in isolated nuclei which can generate DNA damage through reaction with H2O2.

Cadmium decreases SGLT1 messenger RNA in mouse kidney cells.

Mouse renal cortical tubule cells in primary culture exposed to cadmium (Cd2+) develop decreased Na(+)-glucose cotransport activity as measured by uptake of the glucose analogue alpha-methyl-glucoside. RNA was isolated from kidney cell cultures, and after reversed transcription, the DNA was amplified with primers to rat SGLT1 (the high affinity isoform of the sodium glucose cotransporter) and mouse beta-actin. Only one product was identified after amplification with the rat SGLT1 primers, which on sequencing was 96% identical to rat SGLT1. Compared to beta-actin, the intensity of the SGLT1 message declined progressively as CdCl2 concentration in the medium increased from 0 to 10 microM. Similar decreases in SGLT1 mRNA were also observed as media zinc (Zn2+) concentrations rose from 0 to 75 microM or as copper (Cu) concentrations increased from 0 to 150 microM. Exposure to 8 microM Cd as Cd-metallothionein (Cd7-MT) also caused a fall in relative SGLT1 mRNA abundance, and at nearly identical internal Cd concentrations of 40-43 pmol/microgram DNA, both Cd7-MT and CdCl2 reduced SGLT1 mRNA to 33% of control. In general, the fall in SGLT1 mRNA was more rapid than the decline in Na(+)-dependent glucose uptake after cells were exposed to Cd2+. These findings suggest that the effects of Cd2+ and other metals on renal glucose transport are related to decreased expression of SGLT1 message.

Direct reaction of H2O2 with sulfhydryl groups in HL-60 cells: zinc-metallothionein and other sites.

The reaction of the sulfhydryl groups in metallothionein with hydrogen peroxide was examined in HL-60 cells. Partial purification of cell cytosol using Sephadex G-75 chromatography showed that zinc-metallothionein (Zn-MT) was induced by 24-h treatment with 100 microM ZnCl2, but the cellular glutathione content and glutathione peroxidase and catalase activities were unaffected. The ratio of H202 concentrations needed to reduce cell survival 50% in Zn-induced cells compared to normal cells was 1.65 to 1. According to alkaline elution experiments, the average ratio of single-strand breaks caused by H202 at 37 degrees C in Zn-induced vs normal cells was 0.5 to 1. A similar reduction in strand breakage was seen in nuclei from Zn-treated cells exposed to H202; however, at 4 degrees C protection against DNA strand breakage by Zn pretreatment was not seen. Incubation of Zn-pretreated cells with H202 at 37 degrees C but not 4 degrees C was accompanied by loss of Zn bound to MT and a reduction in the number of MT sulfhydryl groups. In the absence or presence of Zn-MT, sulfhydryl groups from glutathione and protein fractions were also reduced by exposure of cells to H202. However, thiolate groups in the MT fraction were preferentially lost compared to the other pools of sulfhydryl residues. Zn-MT also spared glutathione sulfhydryl groups in vitro from oxidation by H202. Protection against strand breakage correlated with the ability of Zn-MT to react in vitro with H202 at 37 degrees C, but not at 4 degrees C. The reaction was slow and was not inhibited by the presence of an hydroxyl radical scavenger, dimethyl sulfoxide. Similarly, in cells dimethyl sulfoxide did not prevent the loss of sulfhydryl groups from glutathione or protein. Incubation of MT or higher molecular weight fractions from cells exposed to H202 with either 2-mercaptoethanol or dithiothreitol in the presence of Cd failed to regenerate any detectable, reduced MT, suggesting that MT sulfhydryl groups were oxidized by H202 beyond the disulfide oxidation state.

Surface chemistry and biological pathogenicity of silicates: an X-ray photoelectron spectroscopic study.

We extend our electron spectroscopy for chemical analysis studies of the chemistry of silicates to provide direct surface chemical information on the interactions involved in silicate-induced lung and tissue pathology. A total of five fibrous and non-fibrous silicate minerals, primarily amphiboles, have been studied: anthophyllite, tremolite, cummingtonite, hornblende and actinolite. We have followed the 'inlattice' surface chemistry of these materials and monitored features such as the simultaneous presence of four- and six-coordinate (with respect to oxygen) structural aluminium, and the presence of iron in the M4 octahedral positions. In vitro experiments involving contact of the silicate with cultured murine Ehrlich cells have identified modifications in the surface chemistry of Al, Mg and Fe in the silicates and changes in cellular iron content.

Comparative effects of Cd2+ and Cd-metallothionein on cultured kidney tubule cells.

The effects of Ca2(+) and Cd-metallothionein on two cultured cells with proximal tubule characteristics, mouse kidney cortical cells and pig kidney LLC-PK1 cells, have been compared. Cd2+ inhibits Na(+)-glucose cotransport in LLC-PK1 cells and in the process decreases the number of binding sites for [3H]phlorizin, a competitive inhibitor of glucose for the Na(+)-glucose cotransporter. During 24 hr incubation and over a range of concentrations in the two cell types, only Cd2+ inhibited Na(+)-glucose cotransport even when approximately equal concentrations of intracellular Cd resulted from these treatments. Indeed, at low concentrations of Cd-metallothionein in mouse cells, transporter activity was elevated. Extension of incubations to 72 hr in mouse cells led to increased Cd uptake and reduction in cell density with both sources of Cd but only a progressive decline in Na(+)-glucose cotransport activity with Cd2+. Zn-metallothionein was without effect under comparable conditions. Both forms of Cd were accumulated by these cells, with the large majority of the metal ion localizing in metallothionein as a Cd, Zn-protein in LLC-PK1 cells. Under equal exposure conditions, the net uptake of Cd from Cd-metallothionein in the two cell types. It is evident that the mechanisms of toxicity of Cd2+ and Cd-metallothionein as well as their modes of uptake differ in these two cell types.

Inhibition of Na(+)-glucose cotransport in kidney cortical cells by cadmium and copper: protection by zinc.

Properties of the inhibition of Na(+)-glucose cotransport by Cd2+ in mouse kidney cortical cells have been determined. In no case was any inhibition observed before 3 hr. The extent of inhibition was dependent upon both the concentration of Cd2+ and the length of exposure. Kinetic studies showed that metallothionein mRNA induction by Cd2+ was initiated within 1 hr after incubation with Cd2+ began and peaked by 3-6 hr. Metallothionein protein increased more slowly, beginning at 3 hr and continuing for at least 9 hr. The protein had both Cd2+ and Zn2+ bound to it throughout this period. Nevertheless, a pool of nonmetallothionein Cd2+ appeared after 3 hr, coinciding with the onset of inhibition of Na(+)-glucose cotransport, and increased over the next 9 hr. Pretreatment of cells with Zn2+ protected them from the effects of Cd2+ on Na(+)-glucose cotransport. It delayed the onset of inhibition of transport as well as the extent of inhibition. Detailed analysis of the distribution of Cd2+ and Zn2+ in the soluble fraction of these cells showed that the concentration of non-metallothionein bound Cd2+ was not suppressed by the presence of Zn-metallothionein after the onset of exposure to Cd2+. Incubation of cells with larger concentration of Zn2+ and Cu2+ also inhibited Na(+)-glucose cotransport.

Cadmium inhibits glucose uptake in primary cultures of mouse cortical tubule cells.

We studied the effect of cadmium (Cd2+) on transport of alpha-methylglucoside in primary cultures of mouse kidney cortical tubule cells grown in defined medium. When cultured cells were exposed to Cd2+ concentrations from 0 to 6 microM for 24 h, uptake of alpha-methylglucoside was inhibited in a dose-dependent manner by up to 50%. By contrast, acute exposure of the cells to 7 microM Cd2+ for 60 min did not inhibit alpha-methylglucoside uptake. Increasing Cd2+ concentrations progressively decreased the Vmax of Na(+)-dependent glucose cotransport but not the Km for glucose. Cell ATP/ADP ratios of unexposed monolayers and of cells exposed to 4.5 microM Cd2+ for 24 h were 5.0 and 4.9, respectively (n = 3). Intracellular volume, lactate dehydrogenase activity, and cell Na+ and K+ concentrations were unaltered even after 24 h of exposure to 7 microM Cd2+. Untreated and Cd2+-treated monolayers preloaded with alpha-methylglucoside released the sugar analogue into the medium at nearly identical rates, indicating that Cd2+ did not alter cell permeability to glucose. Uptake of the amino acid analogue alpha-(methylamino)isobutyric acid was not affected by prior Cd2+ exposure. Whereas cell DNA content declined in Cd2(+)-exposed plates, both Na(+)-glucose and Na(+)-amino acid cotransport were enhanced at lower cell densities. Protein and DNA synthesis, estimated, respectively, by incorporation of [3H]leucine and [3H]thymidine into acid-insoluble material, were not significantly affected at 6 microM Cd2+. We conclude that after a lag time Cd2+ selectively inhibits renal Na(+)-dependent glucose transport despite an unchanged gradient for Na+ across the cell membrane.

Iron deficiency in growing male rats: a cause of development of cardiomyopathy.

Weanling male rats were fed a purified iron-adequate, a purified iron-deficient or a commercial diet for 12 weeks. At that time the rats were sacrificed, their hearts and livers were excised, and blood samples were taken. Heart and liver weights were recorded; organ tissue and serum samples were analyzed for Zn, Cu and Fe. Hemoglobin and hematocrit values were also obtained. The iron-deficient rats grew much more slowly than controls on the iron-adequate or commercial diets. The iron-deficient rats were severely anemic and had enlarged hearts (cardiomegaly). A histopathologic examination of the hearts of all animals showed that each heart of the iron-deficient rats had lesions characteristic of cardiomyopathy by dilatation, whereas none of the hearts of the iron-adequate group or the chow controls showed any lesions at all. The iron-deficient animals had only about 25% of the hepatic iron found in the iron-adequate animals but about 5 times the hepatic copper of the latter group or the chow controls. Heart iron of the iron-deficient group was 27% of the concentration found in hearts of the iron-adequate rats; heart copper was similar in all groups. Animals on the commercial stock diet accumulated significantly more iron in their hearts than did those on the purified iron-adequate diet but not in the livers. There was also a direct correlation of heart iron or heart zinc with log concentrations of dietary iron and consequently a direct correlation between heart iron and zinc concentrations.

Kinetic lability of zinc bound to metallothionein in Ehrlich cells.

Ehrlich ascites-tumour cells normally contain a large concentration of Zn-metallothionein. When cells are placed in culture media, containing or pretreated with the metal-ion-chelating resin Chelex-100, they stop growing, remain viable and lose zinc specifically from the metallothionein (MT) pool. The kinetics of loss of zinc are first-order and are very rapid, having a rate constant of greater than or equal to 0.6 h-1. MT protein labelled with 35S is biodegraded with a rate constant of 0.07-0.014 h-1 in control cells, 0.08 h-1 in cells exposed to the zinc-deficient medium and 0.12-0.18 h-1 in cells treated directly with Chelex. Over the 6 h period in which zinc is totally lost from Zn-MT there is relatively little decrease in MT-like protein as measured by cadmium-binding to the 10,000-Mr protein fraction. Other pools of zinc and 35S-labelled protein turn over more slowly. There is no loss of zinc from rat liver Zn-MT that is dialysed against Chelex to model the possible reaction of the resin with Ehrlich-cell Zn-MT. However, Chelex does compete slowly for MT-bound zinc when resin and MT are directly mixed. Analysis of the known and possible pathways of zinc metabolism in cells in relationship to these rate constants shows that biodegradation of MT protein cannot account for the rate of loss of zinc from Zn-MT.

Cadmium-zinc interactions in the Ehrlich cell: metallothionein and other sites.

Zinc and Cadmium metabolism in cultured Ehrlich cells has been studied. Under conditions of restriction of extracellular zinc by EDTA or chelex, zinc in basal Zn-metallothionein (Mt) is transferred from metallothionein to other sites with a rate constant of 0.35 hr-1. Current studies indicate that the rate constant for biodegradation of Mt protein is 0.07-0.11 hr-1, implying that Zn leaves the protein faster than it is biodegraded. After a 30 minute exposure of cells to 17 ng atoms Cd/mg cell protein, Cd initially displaces Zn from Mt and binds to high molecular weight species. Cell proliferation is markedly slowed, although the cells remain viable. Over time Cd shifts into newly synthesized Mt. This protein is made with an apparent rate constant four times that for basal Zn-Mt. The product contains equal amounts of Cd and Zn. However, cell proliferation is not restored for many hours after Cd is sequestered in Mt.

Host zinc metabolism and the Ehrlich ascites tumour. Zinc redistribution during tumour-related stress.

Zinc redistribution between plasma and liver has been examined in mice injected with Ehrlich-ascites-tumour cells. Within 24 h of injection plasma Zn levels decrease and Zn appears in newly synthesized liver metallothionein. This response is dependent upon the number of tumour cells injected into the host. Uptake of Zn into liver and its specific accumulation in a Zn-binding protein, identified as metallothionein, continues for a number of days and reaches a plateau as tumour growth ceases. Over this time period, plasma copper rises. This redistribution also occurs in mice pretreated with cadmium in their drinking water for 1 month at levels of 20, 50, and 100 micrograms/ml. However, in each case there is a lag of 3 days before Zn increases in the livers of these animals which already contain substantial amounts of Cd/Zn-metallothionein. When Ehrlich cells are injected into mice previously placed on a Zn-deficient diet for several days, plasma Zn is already low and no net uptake of Zn into liver metallothionein is apparent. Finally, it is shown that ascites fluid can itself stimulate a transient shift of host of Zn into liver. Heat-inactivated fluid loses this property. It is suggested that, in the peritoneum, tumour cells initiate a stress response mediated by an ascites-fluid factor.

Reaction of 3-ethoxy-2-oxobutyraldehyde bis(thiosemicarbazonato) Cu(II) with Ehrlich cells. Binding of copper to metallothionein and its relationship to zinc metabolism and cell proliferation.

The copper complex of 3-ethoxy-2-oxobutyraldehyde bis(thiosemicarbazone) or CuKTS is reduced and dissociated upon reaction with Ehrlich cells. Titration of the cells with the complex leads to the specific binding of copper to metallothionein with 1 to 1 displacement of its complement of zinc. Under conditions of complete titration of metallothionein, 1.25-2.5 nmol CuKTS/10(7) cells, cellular DNA synthesis is rapidly inhibited but no long term effects on cell proliferation are observed. The kinetics of redistribution of Cu and Zn in Ehrlich cells in culture and in animals were studied after pulse reaction of CuKTS with cells. After exposure of cells to the noncytotoxic concentration of 2.5 nmol of CuKTS/10(7) cells, nonmetallothionein bound copper is lost rapidly from the cells, after which copper in metallothionein decays. New zinc metallothionein is made as soon as exposed cells are placed in culture. New synthesis stops when the level of zinc in metallothionein reaches control levels. A second pulse treatment of cells with CuKTS to displace zinc from metallothionein again stimulates new synthesis of the protein to restore its normal concentration. The kinetics of metal metabolism in Ehrlich cells exposed to 5.5 nmol of CuKTS/10(7) cells, which inhibits cell proliferation, are qualitatively similar except there is a pronounced lag before new zinc metallothionein is synthesized. The Ehrlich ascites tumor in mice responds to CuKTS similarly to cells in culture. It is also shown that cultured Ehrlich cells do not make extra zinc metallothionein in the presence of high levels of ZnCl2, and fail to accumulate copper in the presence of large concentrations of CuCl2.

Binding of cis-dichlorodiammine platinum(II) to metallothionein in Ehrlich cells.

The antitumor agent, cis-dichlorodiammine Pt(II), is cytotoxic to Ehrlich cells in culture. These cells contain a substantial amount of metallothionein in the absence of inducers of the protein. At concentrations of drug which cause 60% inhibition of cell proliferation, most of the platinum is found in the cytosol. Of this about 30% is bound in the metallothionein fraction. Isolated rat liver metallothionein reacts slowly with hydrolyzed cis-dichlorodiammine Pt(II). Thus, metallothionein is a major cellular site of binding of the platinum complex at concentrations which inhibit tumor growth.

Induction of cytochrome P-450 in a selective subpopulation of hepatocytes.

The objective of this study was to determine whether the inductive effect of phenobarbital (PB) on liver cytochrome P-450 was the result of the action of this drug on all or some hepatocytes. For this purpose, a light (cell band I) and a heavy (cell band II) subpopulation of hepatocytes were separated from rat liver in a continuous density gradient. To determine the location of these hepatocytes in tissue, [14C]bromobenzene, which binds covalently to centrilobular hepatocytes, was administered. The specific activity (14C dpm/mg protein) was greater in cells of band I than in cells of band II, suggesting a predominant contribution of centrilobular hepatocytes to the lighter cell band. Microsomes were separated from each cell subpopulation after 3 days of PB administration and cytochrome P-450 was measured. Although a fivefold increment in cytochrome P-450 content of light hepatocytes was noted, the content of heavy hepatocytes was similar to that of the respective subpopulation in controls. Concomitantly, PB administered for 3 days induced the smooth endoplasmic reticulum of centrilobular hepatocytes only, as revealed by electron microscopy of whole tissue. These results indicated that PB induces cytochrome P-450 in a selective subpopulation of hepatocytes, most likely located near the terminal hepatic venule.

The uptake, excretion, and radiation hazards of tritiated thymidine in humans.

Nine patients with malignant disease were given i.v. injections of tritiated thymidine, 0.2 mCi/kg, for tumor cell kinetics studies. Serial plasma, urine, saliva, and air vapor samples were collected variously for up to 79 days, and tritium activity was measured. The initial half-life of plasma activity was rapid. After 1 day, the activity decayed with a half-life of 10.8 days, indicating equilibration of activity with the total body water. Urine activity was over 100 times the plasma activity within 1 hr, with equilibration approaching the plasma activity after 2 days, and then decayed at a similar rate. Saliva and air vapor activity increased to plasma levels and then decayed at the same rate as did plasma activity. In the first 24 hr, approximately one-third of the total injected activity was excreted in the urine. During the first 12 days there were 54.2% urinary and 10.6% insensible losses. Maximum losses determined by extrapolation of observed data were 68% urinary and 19.5% insensible losses, or a total of 87.5%. Approximately 7% of the injected activity may represent material initially incorporated into DNA but later metabolized and excreted. The radiation dose from total body water is estimated at 0.69 rad. The estimated dose absorbed by cell nuclei from incorporated material is a maximum of 20.5 rads. These radiation doses would not seem to contraindicate injection of 0.2 mCi tritiated thymidine per kg to patients in this clinical and experimental setting. Measurements of activity in personnel and room air indicate that the use of such doses is not hazardous if appropriate precautions are followed.