Lipid A-activated inducible nitric oxide synthase expression via nuclear factor-κB in mouse choroid plexus cells.

Choroid plexus (CP) which is responsible for the inflammatory mediators including nitric oxide (NO) are thought to play a crucial role in the process of bacterial meningitis. The present study investigated the mechanisms regulating inducible nitric oxide synthase (iNOS) expression in the choroid plexus epithelium (CPe) in mice. Initially, the expression of iNOS in mouse CPe was strengthened by intracerebroventriclar (i.c.v.) administration of lipid A, which is part of a Gram-negative bacterial endotoxin located at one end of the lipopolysaccharide (LPS) molecule. Next, the expression of iNOS in the CP epithelial cell line ECPC-4 cells was increased from 24 to 48h after lipid A treatment, although mRNA and proteins of toll-like receptor (TLR)-2 and -4 expressed in ECPC-4 cells were not changed by lipid A. The expression of total nuclear factor κB (NFκB), an inflammatory transcriptional factor, in ECPC-4 cells was not changed for 72 h after lipid A treatment, while cytoplasmic NFκB was decreased and nuclear NFκB was increased from 1 to 2 h. In addition, the phosphorylation of inhibitor κB (IκB) was peaked at 10 min, and the level of IκB was attenuated from 10 to 45 min after lipid A treatment. Moreover, the RNA interference (RNAi) of NFκB suppressed the expression of iNOS induced by lipid A. We demonstrated that lipid A-induced iNOS expression in ECPC-4 cells was mainly regulated by the activation of NFκB-IκB intracellular signaling pathway. Thus, we propose that the CPe plays a pivotal role in innate immunity responses of the brain, that is, the signal pathway TLRs on the CPe following inflammatory stimulation such as meningitis is activated, leading to iNOS expression through NFκB.

Dietary Deficiency of Calcium and/or Iron, an Age-Related Risk Factor for Renal Accumulation of Cadmium in Mice.

The major route of cadmium (Cd) intake by non-smokers is through food ingestion. Cd is a non-essential metal absorbed through one or more transporters of essential metal ions. Expression of these transporters is affected by nutritional status. To investigate the risk factors for Cd toxicity, the effects of deficiency of essential metals on hepatic and renal accumulation of Cd were studied in mice of different ages. Mice were administered a control diet or one of the essential metal-deficient diets, administered Cd by gavage for 6 weeks, and killed; then, Cd accumulation was evaluated. Iron deficiency (FeDF) or calcium deficiency (CaDF) resulted in remarkable increases in hepatic and renal Cd accumulation compared with control-diet mice and other essential metal-deficient mice. Cd accumulation in hepatic and renal tissue was increased significantly at all ages tested in FeDF and CaDF mice. Renal Cd concentrations were higher in 4-week-old mice than in 8- and 25-week-old mice. Increase in intestinal mRNA expression of calcium transporter (CaT)1, divalent metal ion transporter-1, and metallothionein (MT)1 was also higher in 4-week-old mice than in other mice. Renal accumulation of Cd showed strong correlation with intestinal mRNA expression of CaT1 and MT1. These data suggest that CaDF and FeDF at younger ages can be a risk factor for Cd toxicity.

Effects of zinc deficiency and supplementation on leptin and leptin receptor expression in pregnant mice.

Leptin is an adipose-derived hormone that primarily regulates energy balance in response to nutrition. Human placental cells produce leptin, whereas murine placental cells produce soluble leptin receptors (Ob-R). However, the roles of these proteins during pregnancy have not been elucidated completely. As an essential metal, zinc (Zn) is central to insulin biosynthesis and energy metabolism. In the present study, the effects of Zn deficiency and supplementation on maternal plasma leptin and soluble Ob-R regulation in pregnant mice placentas were examined using enzyme-linked immunosorbent assay, reverse transcription-polymerase chain reaction, and Western blotting. Nutritional Zn deficiency significantly reduced plasma insulin concentrations and fetal and placental weights in pregnant mice. Plasma leptin concentrations in pregnant mice also increased 20- to 40-fold compared with those in non-pregnant mice. Although dietary Zn deficiency and supplementation did not affect plasma leptin concentrations in non-pregnant mice, Zn-deficient pregnant mice had significantly reduced plasma leptin concentrations and adipose leptin mRNA expression. In contrast, Zn-supplemented pregnant mice had increased plasma leptin concentrations without increased adipose leptin mRNA expression. Placental soluble Ob-R mRNA expression also decreased in Zn-deficient mice and tended to increase in Zn-supplemented mice. These results indicate that Zn influences plasma leptin concentrations by modulating mRNA expression of soluble Ob-R in the placenta, and leptin in visceral fat during pregnancy. These data suggest that both adipose and placenta-derived leptin system are involved in the regulation of energy metabolism during fetal growth.

Nitric oxide promotes survival of cerebral cortex neurons with simultaneous addition of [Fe(II)(ß-citryl-L-glutamate)] complex in primary culture.

It has been reported that the activity of mitochondrial aconitase (m-aconitase) is rapidly inhibited in a variety of cells when exposed to nitric oxide (NO). In present study, we found that NO significantly increased the number of surviving neurons via enhanced mitochondrial functions with simultaneous addition of the [Fe(II)(ß-citryl-L-glutamate; ß-CG)] complex. In vitro, a variety of aconitase-inhibitors, such as fluorocitrate, cyanide ion, ferricyanide ([Fe(CN)6]), and various oxidants including superoxide anion, inhibited the activity of m-aconitase even in the presence of Fe(II), whereas a NO-donor, nitroprusside (SNP) ([Fe(CN)5NO]), was the only agent that significantly increased activity of that enzyme. Therefore, it is reasonable to assume that NO released from SNP promotes Fe-dependent activation of aconitase. All other tested NO-donors, including 3-morpholino-sydnonimine (SIN), Deta NONOate (NOC18), and NaNO2, also promoted activation of m-aconitase in time- and dose-dependent manners in the presence of Fe(II). The promoting effects of the NO-donors on activation disappeared with the addition of NO-scavengers. In intact mitochondria, all tested NO-donors promoted reactivation of aconitase in a dose-dependent manner in the presence of Fe(II), whereas that was not seen in its absence. These findings suggest that NO released from NO-donors promotes Fe-dependent activation of aconitase. In mixed neuronal and glial cultures, NO-donors except for SNP enhanced mitochondrial activity at low concentrations. Furthermore, simultaneous addition of the [Fe(II)(ß-CG)] complex significantly enhanced those activities and greatly increased the number of surviving neurons. Thus, NO can carry Fe ions into m-aconitase via the guide of the tag of ß-CG addressed to the enzyme.

Involvement of the essential metal transporter Zip14 in hepatic Cd accumulation during inflammation.

Upregulation of Zip14 contributes to hepatic zinc (Zn) and non-transferrin-bound iron (Fe) uptake during infection and inflammation. We investigated whether this essential metal transporter is also involved in hepatic cadmium (Cd) uptake under these conditions. An injection of lipopolysaccharide (LPS), turpentine oil (Tur) and n-hexane (Hex) resulted in an decrease in plasma Zn and Fe concentrations to 25-50% and an increase in hepatic concentrations of both metals to 150-200% of control mice. LPS significantly increased plasma interleukin (IL)-6 levels more rapidly than Tur or Hex. Tur or Hex significantly increased hepatic Zip14 mRNA expression and decreased ferroportin 1 mRNA expression following continuous increase of IL-6 level. Hepatic Cd and Zn concentrations increased significantly after repeated injections of Cd in Tur- or Hex-treated mice fed a control diet. Treatment with Tur or Hex additionally increased hepatic Cd accumulation in Zn-deficient mice, unlike in Fe-deficient mice. These results suggest that Zn transporters, such as Zip14, may be involved in hepatic Cd uptake during inflammation.

Proteomic analysis of the brain tissues from a transgenic mouse model of amyloid ß oligomers.

Amyloid ß (Aß) oligomers are presumed to be one of the causes of Alzheimer's disease (AD). Previously, we identified the E693Δ mutation in amyloid precursor protein (APP) in patients with AD who displayed almost no signals of amyloid plaques in amyloid imaging. We generated APP-transgenic mice expressing the E693Δ mutation and found that they possessed abundant Aß oligomers from 8months of age but no amyloid plaques even at 24months of age, indicating that these mice are a good model to study pathological effects of Aß oligomers. To elucidate whether Aß oligomers affect proteome levels in the brain, we examined the proteins and phosphoproteins for which levels were altered in 12-month-old APP(E693Δ)-transgenic mice compared with age-matched non-transgenic littermates. By two-dimensional gel electrophoresis (2DE) followed by staining with SYPRO Ruby and Pro-Q Diamond and subsequent mass spectrometry techniques, we identified 17 proteins and 3 phosphoproteins to be significantly changed in the hippocampus and cerebral cortex of APP(E693Δ)-transgenic mice. Coactosin like-protein, SH3 domain-bind glutamic acid-rich-like protein 3 and astrocytic phosphoprotein PEA-15 isoform 2 were decreased to levels less than 0.6 times those of non-transgenic littermates, whereas dynamin, profilin-2, vacuolar adenosine triphosphatase and creatine kinase B were increased to levels more than 1.5 times those of non-transgenic littermates. Furthermore, 2DE Western Blotting validated the changed levels of dynamin, dihydropyrimidinase-related protein 2 (Dpysl2), and coactosin in APP(E693Δ)-transgenic mice. Glyoxalase and isocitrate dehydrogenase were increased to levels more than 1.5 times those of non-transgenic littermates. The identified proteins could be classified into several groups that are involved in regulation of different cellular functions, such as cytoskeletal and their interacting proteins, energy metabolism, synaptic component, and vesicle transport and recycling. These findings indicate that Aß oligomers altered the levels of some proteins and phosphoproteins in the hippocampus and cerebral cortex, which could illuminate novel therapeutic avenues for the treatment of AD.

Role of megalin and the soluble form of its ligand RAP in Cd-metallothionein endocytosis and Cd-metallothionein-induced nephrotoxicity in vivo.

Orally administered Cd is predominantly distributed to the intestine, and the majority of this mucosal Cd is bound to metallothionein (MT). MT attenuates heavy metal-induced cytotoxicity by sequestering these metals and lowering their intracellular concentrations. In addition, MT acts as an extracellular transporter of orally administered Cd to the kidney. Because of its low molecular weight, the Cd-MT complex is freely filtered at the glomerulus, and the filtered Cd-MT is then incorporated into renal proximal tubular cells. Megalin, a multiligand endocytic receptor (also known as low-density lipoprotein receptor-related protein 2 or Lrp2), acts as the receptor for Cd-MT in a renal proximal tubular cell model. Here, we used the soluble form of 39-kDa receptor-associated protein (sRAP; also known as Lrpap1), a ligand of megalin, to inhibit megalin function, and then analyzed the effect of megalin loss on Cd-MT distribution and Cd-MT-induced nephrotoxicity in an animal model. Administration of sRAP to mice caused acute loss of megalin function by removing megalin in the brush border membrane. The pre-injection of sRAP decreased renal Cd content and decreased Cd-MT-induced kidney damage. Our results demonstrate that sRAP reduces Cd-MT-induced kidney toxicity in vivo.

Oxidation and turnover of renal metallothioneins after an injection of ferric nitrilotriacetate.

Metallothioneins (MTs) have demonstrated strong antioxidant properties, however the biological significance of their effect against hydroxyl radical toxicity remains unclear. We investigated the oxidation and turnover of renal MTs in MT-preinduced mice after an injection of ferric nitrilotriacetate (Fe-NTA). Incubation of MTs with Fe-NTA and H(2)O(2) resulted in a loss of their metal-binding properties and a decrease in their thiol concentration independent of binding potential and isoforms. Moreover, in vitro reduction of renal oxidized MT with dithiothreitol (DTT) reversed these oxidative changes. An injection of Fe-NTA oxidized renal preinduced MT in Zn- and Cd-pretreated mice. The metal-binding properties of renal MTs were lost when the Fe-NTA dose was increased. However, analysis of renal MTs using an immunoassay showed that its protein concentration did not decrease 4h after the injection with various Fe-NTA doses. Furthermore, in vitro reduction of renal oxidized MTs with DTT resulted in an increase in the concentration of metals in the MT fraction. These data indicate that radicals produced by Fe-NTA may oxidize MTs in vitro and in vivo. When we investigated the turnover of oxidized MTs in Fe-NTA-treated mice, effects on the concentration of renal (35)S-labeled MTs were opposite to those observed in Cd-pretreated mice. The concentration of preinduced (35)S-labeled MTs in the kidneys of Cd-pretreated mice showed a significant decrease (p<0.05), whereas that of newly synthesized (35)S-labeled MTs showed a considerable increase. These data suggest that degradation of oxidized MTs may be faster than intact MTs. Therefore, the radical scavenging system of MTs may include their induction and degradation during oxidative stress conditions.

ß-Citryl-L-glutamate acts as an iron carrier to activate aconitase activity.

The compound ß-citryl-L-glutamate (ß-CG) was initially isolated from developing brains, though its functional roles remain unclear. In in vitro experiments, the [Fe(II)(ß-CG)] complex activated aconitase in the presence of reducing reagents, whereas no Fe complex with citrate, glutamate, or deferoxamine displayed such an effect. ß-CG and [Fe(II)(ß-CG)] both bound to the fourth labile Fe atom (Fe(a)) in the [4Fe-4S] cluster of aconitase. Furthermore, [Fe(II)(ß-CG)] reactivated aconitase damaged by ammonium peroxodisulfate (APS), while ß-CG and citrate had no effect. These findings suggest that [Fe(II)(ß-CG)] can transfer Fe to aconitase disassembled by APS. In intact mitochondria, both ß-CG and [Fe(II)(ß-CG)] bound to Fe(a) of aconitase, whereas only [Fe(II)(ß-CG)] reactivated the enzyme disassembled by APS. In cultured neuronal cells, ß-CG significantly enhanced cell viability by accelerating mitochondrial activity in primary cultures of neurons from newborn mouse cerebrum tissues. Thus, the ß-CG plays a role as an Fe-carrier for mitochondrial aconitase, and then activates it. Taken together, these findings suggest that ß-CG is an endogenous low molecular weight Fe chaperone for aconitase.

Increased hepatic accumulation of ingested Cd is associated with upregulation of several intestinal transporters in mice fed diets deficient in essential metals.

Essential metals (EMs) can affect the metabolism of nonessential metals. It has been suggested that Fe deficiency increases intestinal absorption of Cd via divalent metal transporter 1 (DMT1). To investigate whether EM nutritional status is a host risk factor for Cd accumulation, we studied the effect of nutritional status of Ca, Cu, Mg, Zn, and Fe that most often ingested by humans at levels below recommended dietary allowances on tissue accumulation of orally administered Cd. Mice were divided into groups and given different EM-deficient (EMDF) diets (CaDF, CuDF, MgDF, ZnDF, or FeDF) for 4 weeks. EMDF mice had significantly (p < 0.05) lower plasma or hepatic concentrations of the deficient EM than did mice receiving control diets. Hepatic Cd accumulation was significantly (p < 0.05) increased after oral Cd administration in all EMDF mice, but not in any EM-supplemented mice. Intestinal expression of mRNAs for the Fe-transporters DMT1 and ferroportin was increased in FeDF mice, but not in other EMDF mice, causing an increase in hepatic Fe concentration. Similarly, intestinal expression of mRNA for calcium transporter 1 was significantly increased in CaDF mice, but not in other EMDF mice. These results suggest that DMT1 is not the sole transporter of Cd, and that Cd is absorbed and accumulated through multiple pathways that maintain EM homeostasis in EMDF condition. Therefore, EM nutritional status is a risk factor for increasing hepatic accumulation of ingested Cd.

Effect of hemolytic and iron-deficiency anemia on intestinal absorption and tissue accumulation of cadmium.

Abnormal iron (Fe) metabolism induces iron-deficiency anemia (FeDA) and also affects body cadmium (Cd) accumulation. However, whether hemolytic anemia also affects Cd metabolism is not known. We compared the intestinal absorption and tissue accumulation of Cd after oral administration of Cd to mice with hemolytic anemia induced by treatment with phenylhydrazine (PHA mice) to that in mice with FeDA. Although the hematocrit decreased significantly in mice with either type of anemia, the Fe concentration decreased in the livers and kidneys of FeDA mice, but increased in those of PHA mice. After an oral administration with various amounts of Cd, hepatic and renal Cd concentrations significantly increased in both FeDA and PHA mice. An intraduodenal injection of Fe raised the hepatic Fe content in FeDA mice to the control level and raised the hepatic Fe content in PHA mice to 2.4 times that in control mice. Intestinal divalent metal transporter 1 (DMT1) expression increased significantly in mice with both types of anemia. These data indicate that, despite the accumulation of hepatic Fe associated with PHA, PHA also significantly increases hepatic and renal Cd accumulation according to an stimulation of intestinal DMT1 expression, as occurs in FeDA mice. This suggests that anemia may be a risk factor for Cd accumulation.

Involvement of intestinal calcium transporter 1 and metallothionein in cadmium accumulation in the liver and kidney of mice fed a low-calcium diet.

Essential metals can affect the metabolism of nonessential metals. Calcium (Ca) is an essential mineral that is commonly lacking in the diet. When we fed 5-week-old male mice for 4 weeks on a purified diet containing 0.005% Ca (CaDF mice), the Ca concentration in the plasma, liver and kidneys did not decreased. Cd accumulation increased in the liver and kidneys of CaDF mice given 1mg/kg Cd orally each day for 5 days, but not in those given intraperitoneal injections of Cd or Cd-metallothionein (Cd-MT). The zinc (Zn) concentration increased significantly in the intestinal cytosol and plasma during the time the mice were fed the low-Ca diet, and expression of both MT-1 and ZnT-1 sharply increased with a similar time course. Intestinal mRNA expression of CaT1, a Ca transporter, was more than 10 times higher in CaDF mice than in controls, although expression of other transporters, including DMT1, decreased in CaDF mice. These results suggest that CaT1 may stimulate the intestinal absorption of Cd and Zn, and some Cd may be distributed to the kidneys along with MT induced by Zn.

[Physiological significance of metallothionein in oxidative stress].

Metallothionein (MT), a ubiquitous family of low-molecular weight metal-binding proteins, comprises 30% cysteine residues. Although all of the thiol residues in MT are bound to metals, it still remains active to reactive oxygen species. Each cysteine residue in MT is more effective at protecting DNA from hydroxyl radical attack than the glutathione cysteine in vitro. Prooxidative agents such as paraquat and carbon tetrachloride induce MT synthesis mediated by some responsive elements. MT demonstrates strong antioxidant properties, yet the physiological relevance of its antioxidant action is not clear. An injection of ferric nitrilotriacetate (Fe-NTA), which produces reactive oxygen species, caused transcriptional induction of MT synthesis in the liver and kidney. Pretreatment of mice with Zn attenuated nephrotoxicity induced by Fe-NTA. After a Fe-NTA injection, a loss of Cd-binding properties of preinduced MT was observed only in kidneys of Zn-pretreated mice but not in liver. MT-enriched hepatocytes are resistant to Fe-NTA toxicity, oxidative DNA, and cell damage during conditions of glutathione depletion. In glutathione-depleted cells, but not in non-treated cells, Cd-binding properties of cellular MT decreased with increasing concentration of Fe-NTA. Moreover, Cd released from MT after an injection of Fe-NTA induced new MT protein again. Thus MT may act as a secondary antioxidant in cellular protection system against oxidative stress.

Metallothionein-enriched hepatocytes are resistant to ferric nitriloacetate toxicity during conditions of glutathione depletion.

Metallothionein (MT) is involved not only in heavy metal homeostasis/detoxification but also in radical scavenging, yet the relevance to other antioxidant systems and physiological significance under oxidative stress has not been clarified. We studied that ability of MT, induced by zinc and cadmium, to protect against oxidative damage induced by ferric nitrilotriacetate (Fe-NTA) in glutathione depleted primary cell cultures. Treatment with Fe-NTA resulted in significant decreases in cell survival and increases in medium LDH activity in control cells following depletion of glutathione. The toxic effects of Fe-NTA were modulated in Zn-MT-enriched cells. In glutathione-depleted cells, but not in non-treated cells, Cd-binding properties of cellular Zn-MT decreased with increasing concentration of Fe-NTA. Both Zn-MT and Cd-MT-enriched cells were resistant to higher doses of Fe-NTA. These results indicate that MT may act a cellular radical scavenger in the absence of GSH. Thus, MT may function as a secondary antioxidant in a cellular protection system.

Induction of hepatic and renal metallothionein synthesis by ferric nitrilotriacetate in mice: the role of MT as an antioxidant.

Metallothionein (MT) demonstrates strong antioxidant properties, yet the physiological relevance of its antioxidant action is not clear. Injection of mice with ferric nitrilotriacetate (Fe-NTA) caused a dose-dependent increase in hepatic and renal MT. Fe-NTA caused a greater increase in hepatic and renal MT concentration (2.5- and 4-fold) compared with FeCl(3) at the same dose of ferric ion. MT mRNA levels were markedly elevated in both of tissues. Thiobarbituric acid (TBA) values in both tissues reached a maximum after 2-4 h. The MT concentrations were significantly increased after 2-4 h in liver and after 8-16 h in kidneys. Plasma concentrations of cytokines such as IL-6 and TNFalpha were elevated by 4 h; IL-6 levels were 24 times higher after Fe-NTA than that after injection of FeCl(3). Pretreatment of mice with ZnSO(4) attenuated nephrotoxicity induced by Fe-NTA after 2 h, but was not effective 4 h after injection. After a Fe-NTA injection, a loss of Cd-binding properties of preinduced MT was observed only in kidneys of Zn-pretreated mice but not in liver. Treatment with BSO, glutathione (GSH) depletor, intensified a loss of its Cd-binding properties after a Fe-NTA injection. These results indicate that induction of MT synthesis may result from reactive oxygen species (ROS) generated by Fe-NTA, and MT may act in vivo as a complementary antioxidant.

Deciphering the molecular basis of the broad substrate specificity of alpha-glucosidase from Bacillus sp. SAM1606.

The alpha-glucosidase of Bacillus sp. strain SAM1606 is a member of glycosyl hydrolase family 13, and shows an extraordinarily broad substrate specificity and is one of very few alpha-glucosidases that can efficiently hydrolyze the alpha-1,1-glucosidic linkage of alpha,alpha'-trehalose (trehalose). Phylogenetic analysis of family-13 enzymes suggests that SAM1606 alpha-glucosidase may be evolutionally derived from an alpha-1,6-specific ancestor, oligo-1,6-glucosidase (O16G). Indeed, replacement of Pro(273*) and Thr(342*) of B. cereus O16G by glycine and asparagine (the corresponding residues in the SAM1606 enzyme), respectively, was found to cause 192-fold enhancement of the relative catalytic efficiency for trehalose, suggesting that O16G may easily "evolved" into an enzyme with an extended substrate specificity by substitution of a limited number of amino acids, including that at position 273* (an asterisk indicates the amino-acid numbering of the SAM1606 sequence). To probe the role of the amino acid at position 273* of alpha-glucosidase in determination of the substrate specificity, the amino acid at position 273 of SAM1606 alpha-glucosidase was replaced by all other naturally occurring amino acids, and the resultant mutants were kinetically characterized. The results showed that substitution of bulky residues (e.g., isoleucine and methionine) for glycine at this position resulted in large increases in the K(m) values for trehalose and maltose, whereas the affinity to isomaltose was only minimally affected by such an amino-acid substitution at this position. Three-dimensional structural models of the enzyme-substrate complexes of the wild-type and mutant SAM1606 alpha-glucosidases were built to explore the mechanism responsible for these observations. It is proposed that substitution by glycine at position 273* could eliminate steric hindrance around subsite +1 that originally occurred in parental O16G and is, at least in part, responsible for the acquired broad substrate specificity of SAM1606 alpha-glucosidase.

Glucocorticoids suppress the inflammation-mediated tolerance to acute toxicity of cadmium in mice.

Several compounds have been shown to cause acute toxicity to cadmium (Cd). The mechanism of tolerance to Cd toxicity induced by glucocorticoids or by inflammation involves induction of metallothionein (MT) synthesis via glucocorticoid response elements or by inflammatory cytokines. We have demonstrated previously that the synthetic glucocorticoid dexamethasone suppresses inflammation-mediated induction of hepatic MT synthesis. Here we investigated the effect of glucocorticoid on tolerance to Cd induced by inflammation in mice. The LD50 of Cd for mice with induced inflammation by injection with turpentine oil (Tur-mice) was higher than the LD50 in control mice. Pretreatment of Tur-mice with dexamethasone to the Tur-mice (Dex+Tur-mice) resulted in a decrease in LD50 after Cd treatment. A significant increase in plasma alanine aminotransferase and aspartate aminotransferase levels in the Dex+Tur-mice was observed at lower doses of Cd than in the Tur-mice and at higher doses of Cd than in control mice. Dexamethasone did not suppress tolerance to cadmium toxicity in the testes of the Tur-mice. Pretreatment of Tur-mice with dexamethasone resulted in suppression of both plasma interleukin (IL)-6 elevation and in suppression of hepatic MT levels when induced by inflammation but not when induced by Cd. These data suggest that suppression of tolerance to Cd toxicity induced by glucocorticoid may involve hepatic MT synthesis mediated by inflammatory cytokines, such as IL-6. We suggest that the inflammatory response can modulate Cd toxicity by induction of MT by inflammatory cytokines.