ZIP14 zinc transporter downregulation and zinc depletion in the development and progression of hepatocellular cancer

Resveratrol-zinc combination for prostate cancer management

Zinc, an essential trace element, plays a critical role in cell signaling, and defect(s) in zinc homeostasis may contribute to adverse physiological and pathological conditions, including cancer. Zinc is present in healthy prostate at a very high concentration, where it is required for important prostatic functions. However, zinc levels are significantly diminished in cancerous tissue, and intracellular zinc level is inversely correlated with prostate cancer progression. During neoplastic transformation, zinc-accumulating, citrate-producing normal prostate cells are metabolically transformed to citrate oxidizing cells that lose the ability to accumulate zinc. Interestingly, zinc has been shown to function as chemopreventive agent against prostate cancer, albeit at high doses, which may lead to many adverse effects. Therefore, novel means to enhance bioaccumulation of sufficient zinc in prostate cells via increasing zinc transport could be useful against prostate cancer. On the basis of available evidence, we present a possibility that the grape antioxidant resveratrol, when given with zinc, may lead to retuning the zinc homeostasis in prostate, thereby abolishing or reversing malignancy. If experimentally verified in in vivo model(s) of prostate cancer, such as transgenic mouse models, this may lead to novel means toward management of prostate cancer and other conditions with compromised zinc homeostasis.

The status of zinc in the development of hepatocellular cancer: an important, but neglected, clinically established relationship

Liver cancer (hepatocellular carcinoma, HCC) is increasing worldwide. About 75% of HCC cases result in death generally within one year. The factors responsible for the initiation and progression of HCC remain largely unknown and speculative, thereby impeding advancements in the development of effective therapeutic agents and biomarkers for early detection of HCC. A consistent marked decrease in zinc in HCC tumors compared with normal liver is an established clinical relationship, which occurs in virtually all cases of HCC. However, this relationship has been largely ignored by the contemporary clinical and research community. Consequently, the factors and mechanisms involved in this relationship have not been addressed. Thus, the opportunity and potential for its employment as biomarkers for early identification of malignancy, and for development of a chemotherapeutic approach have been lacking. This presentation includes a review of the literature and the description of important recent and new data, which provide the basis for a concept of the role of zinc in the development of HCC. The basis is presented for characterizing HCC malignancy as ZIP14-deficient tumors, and its requirement to prevent zinc cytotoxic effects on the malignant cells. The potential for an efficacious zinc treatment approach for HCC is described. The involvement of zinc in the predisposition for HCC by chronic liver disease/cirrhosis is presented. Hopefully, this presentation will raise the awareness, interest, and support for the much needed research in the implications of zinc in the development and progression of HCC.

Expression analysis of zinc transporters in resting and stimulated human peripheral blood mononuclear cells

Intracellular zinc homeostasis is tightly regulated under physiological conditions; however, dysregulation of zinc levels has been reported in various chronic inflammatory and malignant diseases. In this study, we aimed to assess the expression pattern of the 24 currently known zinc transporters in resting and stimulated human peripheral blood mononuclear cells (PBMCs). The cells were isolated from healthy probands and subsequently stimulated with phytohaemagglutinin (PHA) for 3 days. The expression levels of zinc transporters [Zrt/IRT-like protein (ZIP) and cation diffusion facilitator/zinc transporter protein (CDF/ZnT) families] were analyzed by quantitative reverse transcription-polymerase chain reaction. Of the 24 genes encoding for zinc transporters, 19 were found to be ubiquitously expressed in PBMCs. ZIP5 and ZnT10 were not found in all 5 samples, whereas ZIP12, ZnT3 and ZIP2 were expressed in only 1-2 out of 5 PBMC samples. Of note, stimulation by PHA led to an overall downregulation of zinc transporters in the PBMCs of 4 out of the 5 subjects. Notably, the transcript levels of ZIP14 were consistently induced and those of ZIP3 and ZIP4 consistently downregulated in all 5 subjects, whereas the corresponding levels of the remaining 21 genes varied. Data from this study may facilitate a better understanding of the pathophysiological role of deregulated zinc transporters in chronic inflammatory diseases.

A Review of the Current Status and Concept of the Emerging Implications of Zinc and Zinc Transporters in the Development of Pancreatic Cancer

Pancreatic cancer (adenocarcinoma) remains a deadly untreatable cancer with no effective early detection procedure. Little is known concerning the factors involved in the development of pancreatic malignancy, which impedes advancements in its treatment and detection. Altered cellular zinc has been implicated in several cancers. Recent studies provide evidence that zinc and zinc transporters are important factors in pancreatic cancer. This review discusses the current information relating to the status of zinc and zinc transporters in human pancreatic adenocarcinoma. Relationships of the physiology and biochemistry of zinc in mammalian cells are presented, which should be applied to the conduct, interpretation, and translational application of human studies and experimental models. Evidence from human pancreatic tissue studies supports a new concept of the role of zinc in the development of pancreatic adenocarcinoma. The zinc level of the normal ductal and acinar epithelium is markedly decreased in the development of the malignant cells and the premalignant PanIN cells. ZIP3 is identified as the likely zinc uptake transporter, which is down regulated concurrently with the loss of zinc. Ras responsive binding protein (RREB1) is identified as the possible transcription factor involved in the silencing of ZIP3 expression. The evidence supports the current views of transdifferentiation of PanIN epithelium to ductal adenocarcinoma, and the possibility that acinar epithelial dedifferentiation might be a source of premalignant cells. These zinc-associated events occur early in oncogenesis to protect the malignant cells from the cytotoxic effects of zinc levels that exist in the normal cells. Hopefully, this presentation will stimulate interest in and support for much needed research into the implications of zinc and zinc transporters as important events in pancreatic carcinogenesis. The potential exists for the RREB1-ZIP3-zinc concept and/or other implications of zinc as new approaches for the development of effective treatment and for diagnostic biomarkers for pancreatic cancer.

Cytotoxic/tumor suppressor role of zinc for the treatment of cancer: an enigma and an opportunity

A major issue relating to many cancers is the absence of effective chemotherapeutic agents; so that most often untreatable morbidity and death are prevalent once the cancer has been detected and has advanced. The search for efficacious anticancer agents is imperative. One potential agent is zinc, which is decreased in the development of some cancers in order to avoid its cytotoxic/tumor suppressor effects on the malignant cells. This provides the basis and opportunity to employ a treatment regimen that restores elevated zinc levels in the malignant cells and elicits the cytotoxic/tumor suppressor effects of zinc. The enigma is that this approach and expectation has not reached fruition. The question is "why?". This article provides a discussion of relevant zinc issues that need to be considered and resolved. Important areas of research are identified as being essential for the successful application of zinc cytotoxicity/tumor suppression actions for the treatment of specific cancers.

Physiologic implications of metal-ion transport by ZIP14 and ZIP8

Zinc, iron, and manganese are essential trace elements that serve as catalytic or structural components of larger molecules that are indispensable for life. The three metal ions possess similar chemical properties and have been shown to compete for uptake in a variety of tissues, suggesting that they share common transport proteins. Two likely candidates are the recently identified transmembrane proteins ZIP14 and ZIP8, which have been shown to mediate the cellular uptake of a number of divalent metal ions including zinc, iron, manganese, and cadmium. Although knockout and transgenic mouse models are beginning to define the physiologic roles of ZIP14 and ZIP8 in the handling of zinc and cadmium, their roles in the metabolism of iron and manganese remain to be defined. Here we review similarities and differences in ZIP14 and ZIP8 in terms of structure, metal transport, tissue distribution, subcellular localization, and regulation. We also discuss potential roles of these proteins in the metabolism of zinc, iron, manganese, and cadmium as well as recent associations with human diseases.

Zinc and liver disease

Zinc is an essential trace element required for normal cell growth, development, and differentiation. It is involved in DNA synthesis, RNA transcription, and cell division and activation. It is a critical component in many zinc protein/enzymes, including critical zinc transcription factors. Zinc deficiency/altered metabolism is observed in many types of liver disease, including alcoholic liver disease (ALD) and viral liver disease. Some of the mechanisms for zinc deficiency/altered metabolism include decreased dietary intake, increased urinary excretion, activation of certain zinc transporters, and induction of hepatic metallothionein. Zinc deficiency may manifest itself in many ways in liver disease, including skin lesions, poor wound healing/liver regeneration, altered mental status, or altered immune function. Zinc supplementation has been documented to block/attenuate experimental ALD through multiple processes, including stabilization of gut-barrier function, decreasing endotoxemia, decreasing proinflammatory cytokine production, decreasing oxidative stress, and attenuating apoptotic hepatocyte death. Clinical trials in human liver disease are limited in size and quality, but it is clear that zinc supplementation reverses clinical signs of zinc deficiency in patients with liver disease. Some studies suggest improvement in liver function in both ALD and hepatitis C following zinc supplementation, and 1 study suggested improved fibrosis markers in hepatitis C patients. The dose of zinc used for treatment of liver disease is usually 50 mg of elemental zinc taken with a meal to decrease the potential side effect of nausea.