Since cadmium (Cd) is not an essential metal, it is presumed that the entry pathways for other essential metals such as zinc (Zn) and iron (Fe) are utilized for cellular Cd incorporation. However, the precise mechanisms of cellular Cd uptake in mammalian cells still remain unclear. To solve this problem, we have established and characterized two types of Cd-resistant cells from metallothionein (MT)-null (MT-/-) and from MT-expressing (MT+/+) mouse fibroblast cells. The uptake of Cd was extremely suppressed in MT-/- Cd-resistant cells. DNA microarray and subsequent real-time PCR assays revealed that the expression of Zrt, Irt-related protein 8 (ZIP8) was markedly suppressed in MT-/- Cd-resistant cells. The introduction of shRNA of ZIP8 into parental cells resulted in a decrease in Cd accumulation. These data suggest that the down-regulation of ZIP8 plays a pivotal role in the decrease in Cd accumulation and subsequent acquisition of Cd resistance in MT-/- Cd-resistant cells. Furthermore, the uptake of manganese (Mn) was also suppressed in MT-/- Cd-resistant cells, suggesting that ZIP8 is also involved in the uptake of Mn. We also found that Cd resistance in MT+/+ Cd-resistant cells was conferred not only by enhanced expression of MT but also by a decrease in Cd accumulation. The expression of several metal transporters and channels including ZIP8, divalent metal transporter 1 (DMT1), and some voltage-dependent calcium channels were decreased in MT+/+ Cd-resistant cells. Furthermore, MT+/+ Cd-resistant cells exhibited cross-resistance to Mn due to a marked suppression of Mn incorporation. Thus, comparison of expression of metal transporters between MT-/- Cd-resistant cells (IC50 = 30 µM) and MT+/+ Cd-resistant cells (IC50 = 200 µM) suggest that ZIP8 and DMT1 may have different affinities for Cd and Mn, and therefore different roles in the uptake of Cd and Mn.
Conformational changes of Alzheimer's ß-amyloid protein (AßP) enhance its neurotoxicity, and finally lead to Alzheimer's pathogenesis. Recent studies have suggested that a common mechanism is based on the diverse diseases termed “conformational diseases”, including other neurodegenerative diseases such as prion diseases, Parkinson's disease, and triplet-repeat disease. These diseases share similarity in the formation of ß-sheet containing amyloid fibrils by disease-related proteins including prion protein, α-synuclein, polyglutamine, and the introduction of apoptotic degeneration. Trace elements can bind to these proteins and play crucial roles in their conformational changes. Aluminum is suspected to be an environmental risk factor of Alzheimer's disease. Prion protein is a copper binding protein and is believed to be implicated in copper homeostasis. We have investigated effects of aluminum, zinc, copper and other metals on the conformational changes and neurotoxicity of AßP or prion protein fragment peptide. Although the molecular mechanism of neurodegeneration induced by these conformational disease-related proteins remains elusive, these proteins have the ability to directly incorporate into membranes directly and to form calcium-permeable ion channels. Our and other numerous studies have revealed that AßP cause the abnormal elevation of intracellular calcium levels. We review here the current understanding of the pathology of the conformational diseases based on the metal-binding to disease-related proteins and on the disruption of calcium homeostasis through amyloid channels.
Organotin compounds have been widely used as antifouling biocides for ships and fishing nets, agricultural fungicides and rodent repellents. These widespread uses have resulted in the release of increasing amounts of organotins into the environment. In aquatic invertebrates, particularly marine gastropods, organotin compounds, such as tributyltin (TBT) and triphenyltin (TPT), induce irreversible sexual abnormality in females which is termed "imposex" at very low concentrations. Although it has been theorized that these compounds act as potential competitive inhibitors of aromatase, which converts androgen to estrogen, and then increase levels of unconverted androgens in gastropods, their effective concentrations for aromatase inhibition are high. In addition to wildlife, organotins may have various undesirable effects on human health. Contrary to the theory of organotin-induced aromatase inhibition in gastropods, in human choriocarcinoma cells, these compounds markedly enhance estradiol biosynthesis along with the increase of both aromatase activity and 17β-hydroxysteroid dehydrogenase type I (17β-HSD I) activity, which converts low-activity estrogen estrone to the biologically more active form estradiol, at the same low concentrations. Although there are many reports describing the potential toxicity of organotins in human and mammals, the critical target molecules for the toxicity of organotin compounds remain unclear. Recently, organotin compounds including TBT and TPT were identified as nanomolar agonists for retinoid X receptor (RXR) and peroxisome proliferator-activated receptor (PPAR) γ, which are members of the nuclear receptor superfamily. Here, we review the potential genetics action and subsequent toxicity induced by organotins via these nuclear receptors.
Cisplatin, clinically used anticancer Pt(II) complex, has been believed to attack DNA to form Pt-N7(Guanine) coordination, and Pt-G bond is protected from DNA repair enzyme by the aromatic ring stacking between Pt-G and Phe side chain in Pt-DNA-HMG protein adduct. The adduct mimicked 4N coordinated Pt(II) complexes M(DA)(AtCn) involving with metal coordinated aromatic diamine (DA) and anthracene ring side chain in AtCn, which could not coordinate DNA, showed not only in vitro cytotoxicity for human cancer cell lines but also strong inhibition with protein interaction such as the proteasome. The bio-activity indicated the structural dependence of both DA and AtCn. This should relate with the intramolecular aromatic ring stacking interaction which was evidenced by the X-ray structure in crystal and the H-1 NMR in H2O solution. Importantly the Pt(II) complexes showed similar bioactivity in cisplatin resistance cancer cell. These experimental results showed that the Pt complexes involving stacking structure might be new type anticancer metal compounds.
We hypothesized that macrophages have a role in the alterations in bone metabolism induced by fluoride via cytokines. In this study, interleukin-10 (IL-10) and IL-12 in addition to tumor necrosis factor α (TNFα) and IL-1β were evaluated for their mRNA expressions in J774.1 cells by quantitative real-time PCR and the protein levels in the supernatant from the cell culture by ELISA at 0, 100, 300, and 1000 µM fluoride. At 18 hours after incubation, J774.1 cells were activated by lipopolysaccharide. At 6 hours after the activation, RNAs of the cells were sampled. The mRNA expressions for TNFα, IL-1β, IL-10, and IL-12p40 were analyzed by real-time PCR. The supernatant from the cell culture were sampled at 24 hours after the activation and determined for these cytokine levels by ELISA. The cell viability in the 1000 µM group at 6 hours after the activation was significantly lower than that in the control. The mRNA expressions of TNFα, IL-1β and IL-10 in the 1000 µM group were significantly higher than those in the control. Although it did not reach the significant level, the mRNA expression of IL-12p40 in the 1000 µM group was elevated more than that in the control. The mean values of concentrations of TNFα and IL-1β in the supernatant in the 1000 µM group were significantly lower than those in the control. While, there was no significant difference for the concentration of IL-10 in the supernatant among the groups. For IL-12p40, the mean value of the concentration in the 1000 µM group was significantly higher than that in the control. The effects of fluoride on the cytokines produced by macrophages were not common for all types of cytokines. In conclusion, the effects of fluoride on the immune system may vary via alterations in cytokine productions by macrophages, resulting in the alterations in bone metabolism.
When conducting widespread medical examinations throughout our municipality, our team of clinicians discovered many subjects who exhibited symptoms of zinc deficiency despite having serum zinc levels above 65 µg/dL, the commonly accepted limit of zinc deficiency. In this paper, we propose that the range used to express zinc deficiency be adjusted upwards to a new limit of 80µg/dL. When our research team used this higher value in our diagnoses of community members involved in the study, we correctly diagnosed zinc deficiency 91% of the time, with only 9% of our diagnoses being false negatives. Using the new limit, 25% of patients may be falsely diagnosed with a zinc deficiency (false positive) if their complaints or physical signs are not appropriately considered.