XIAP is a potent suppressor of apoptosis that directly inhibits specific members of the caspase family of cysteine proteases. Here we demonstrate a novel role for XIAP in the control of intracellular copper levels. XIAP was found to interact with MURR1, a factor recently implicated in copper homeostasis. XIAP binds to MURR1 in a manner that is distinct from that utilized by XIAP to bind caspases, and consistent with this, MURR1 did not affect the antiapoptotic properties of XIAP. However, cells and tissues derived from Xiap-deficient mice were found to contain reduced copper levels, while suppression of MURR1 resulted in increased intracellular copper in cultured cells. Consistent with these opposing effects, XIAP was observed to negatively regulate MURR1 protein levels by the formation of K48 polyubiquitin chains on MURR1 that promote its degradation. These findings represent the first described phenotypic alteration in Xiap-deficient mice and demonstrate that XIAP can function through MURR1 to regulate copper homeostasis.

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We have utilized an experimental model of human zinc deficiency for study of cytokines production by TH1 and TH2 cells. Additionally, we determined ratios of CD4+ to CD8+ and CD4+ CD45RA+ to CD4+CD45RO+ cells and percentages of CD73+ T cytolytic cells in the CD8+ subset. The data were collected during baseline, at the end of the zinc-restricted period, and following zinc repletion. Our results showed that functions of TH1 cells, as evidenced by production of interferon-gamma, interleukin-2 (IL-2), and tumor necrosis factor-alpha, were decreased, whereas functions of TH2 cells (production of IL-4, IL-6, and IL-10) were unaffected by zinc deficiency. Thus an imbalance between TH1 and TH2 cells resulted because of zinc deficiency in humans. Our studies also showed that zinc may be required for regeneration of new CD4+ T lymphocytes and maintenance of T cytolytic cells. We conclude that an imbalance between TH1 and TH2 cells, decreased recruitment of T naive cells, and decreased percentage of T cytolytic cells may account for decreased cell-mediated immune functions in zinc-deficient subjects.

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The activity of thymulin (a thymic hormone) is dependent on the presence of zinc in the molecule. We assayed serum thymulin activity in three models of mildly zinc-deficient (ZD) human subjects before and after zinc supplementation: (a) two human volunteers in whom a specific and mild zinc deficiency was induced by dietary means; (b) six mildly ZD adult sickle cell anemia (SCA) subjects; and (c) six mildly ZD adult non-SCA subjects. Their plasma zinc levels were normal and they showed no overt clinical manifestations of zinc deficiency. The diagnosis of mild zinc deficiency was based on the assay of zinc in lymphocytes, granulocytes, and platelets. Serum thymulin activity was decreased as a result of mild zinc deficiency and was corrected by in vivo and in vitro zinc supplementation, suggesting that this parameter was a sensitive indicator of zinc deficiency in humans. An increase in T101-, sIg-cells, decrease in T4+/T8+ ratio, and decreased IL 2 activity were observed in the experimental human model during the zinc depletion phase, all of which were corrected after repletion with zinc. Similar changes in lymphocyte subpopulation, correctable with zinc supplementation, were also observed in mildly ZD SCA subjects. Inasmuch as thymulin is known to induce intra-and extrathymic T cell differentiation, our studies provide a possible mechanism for the role of zinc on T cell functions.

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Copper and iron are essential but also toxic metals. Their essentiality is known, but their toxicity, except for the genetic overload diseases, Wilson's disease and hemochromatosis, is not so well known. Yet, their toxicities are so general in the population that they are a looming public health problem in diseases of aging and in the aging process itself. Both metals are transition elements, and their resulting redox properties have been used during evolution in the development of oxidative energy generation. But both contribute to the production of excess damaging oxidant radicals. Evolution has kept stores of copper and iron in excess during the reproductive years because they are so vital to life. But the oxidant damage from these excess stores of metals builds up as we age, and natural selection ceases to act after about age 50 since diseases after that do not contribute to reproductive fitness. Diseases of aging such as Alzheimer's disease, other neurodegenerative diseases, arteriosclerosis, diabetes mellitus, and others may all be contributed to by excess copper and iron. A very disturbing study has found that in the general population those in the highest fifth of copper intake, if they are also eating a relatively high fat diet, lose cognition at over three times the normal rate. Inorganic copper in drinking water and in supplements is handled differently than food copper and is therefore more toxic. Trace amounts of copper in drinking water, less than one-tenth of that allowed in human drinking water by the Environmental Protection Agency, greatly enhanced an Alzheimer's-like disease in an animal model. In the last part of this review, I will provide advice on how to lower risks from copper and iron toxicity.

Copper is a tightly regulated trace element. Disruptions of copper homeostasis are rare and they cause serious disorders such as Wilson's disease and Menkes disease. Copper also plays an important role in promoting physiological and malignant angiogenesis. Formation of new blood vessels by a tumor enables tumor growth, invasion and metastasis. The copper chelator tetrathiomolybdate (TM), which quickly and effectively depletes copper stores, is under investigation as an anti-angiogenic agent. Promising results in vitro, in pre-clinical animal models and in an early (phase I) clinical trial have led to ongoing phase II evaluation of TM in patients with advanced cancers.