Tissue zinc and copper levels in diabetic C57BL/KsJ (db/db) mice fed a zinc-deficient diet: lack of evidence for specific depletion of tissue zinc stores

Zinc and diabetes--clinical links and molecular mechanisms

Zinc is an essential trace element crucial for the function of more than 300 enzymes and it is important for cellular processes like cell division and apoptosis. Hence, the concentration of zinc in the human body is tightly regulated and disturbances of zinc homeostasis have been associated with several diseases including diabetes mellitus, a disease characterized by high blood glucose concentrations as a consequence of decreased secretion or action of insulin. Zinc supplementation of animals and humans has been shown to ameliorate glycemic control in type 1 and 2 diabetes, the two major forms of diabetes mellitus, but the underlying molecular mechanisms have only slowly been elucidated. Zinc seems to exert insulin-like effects by supporting the signal transduction of insulin and by reducing the production of cytokines, which lead to beta-cell death during the inflammatory process in the pancreas in the course of the disease. Furthermore, zinc might play a role in the development of diabetes, since genetic polymorphisms in the gene of zinc transporter 8 and in metallothionein (MT)-encoding genes could be demonstrated to be associated with type 2 diabetes mellitus. The fact that antibodies against this zinc transporter have been detected in type 1 diabetic patients offers new diagnostic possibilities. This article reviews the influence of zinc on the diabetic state including the molecular mechanisms, the role of the zinc transporter 8 and MT for diabetes development and the resulting diagnostic and therapeutic options.

Enhancing insulin action: from chemical elements to thiazolidinediones

Type 2 diabetes is characterized by two fundamental biological defects: a reduced glucose-dependent insulin secretion and an increased resistance to the action of insulin at the level of various target tissues. While the use of agents to improve the insulin secretory activity of the islets of Langerhans has witnessed the flourishing of several new drugs over the years, a much greater difficulty has been experienced in the search for insulin-sensitizing drugs. The aim of this article is to critically review this topic, and to emphasize the importance of providing alternative strategies for the management of Type 2 diabetes.

Dietary zinc deficiency enhances esophageal cell proliferation and N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumor incidence in C57BL/6 mouse

The effect of zinc deficiency on N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumor formation in rats has been well documented. Our previous work showed that zinc deficiency and its associated increased esophageal cell proliferation were of paramount importance in esophageal tumor development in the NMBA-rat model. However, there has been no report concerning zinc deficiency and NMBA-induced esophageal tumor formation in mice. In this study, weanling C57BL/6 mice were fed ad libitum with either a zinc-sufficient or a zinc-deficient diet containing 3-4 ppm of zinc, and received six intragastric doses of NMBA (2 mg/kg; twice weekly for 3 weeks). The animals were sacrificed 46 weeks later after in vivo bromodeoxyuridine (BrDU) labeling followed by immunohistochemical detection of cells in S-phase. At 46 weeks, the tumor incidences in zinc-deficient mice were 57, 100, and 100% respectively, in the esophagus, forestomach and squamocolumnar junction with the glandular stomach (SCJ), as compared to 17, 39, and 67% in the corresponding tissue of zinc-sufficient mice. The difference between the two dietary groups was significant at P < 0.02 for the esophagus, and P < 0.001 for the forestomach and the SCJ. BrDU labeling revealed that the esophageal labeling index and the number of labeled cells were increased by zinc deficiency. These results support a role of increased cell proliferation in esophageal carcinogenesis in the mouse.

Effect of clopamide, a thiazide diuretic, on copper and zinc levels in hypertensive patients

Thiazide diuretics, which are often prescribed to treat mild to moderate hypertension, commonly cause an increase in urinary zinc (Zn) excretion. Metabolic interrelationships between Zn and copper (Cu) are known to exist; consequently, Zn might influence Cu levels. This study aims to determine whether or not Cu and Zn levels in hypertensive patients were influenced by treatment with clopamide, a thiazide diuretic. Eight male patients, aged 36-59 and with an average supine diastolic pressure of 95-115 mm Hg, were treated with single daily doses of clopamide 5 mg as monotherapy for 16 weeks. Plasma, erythrocyte (RBC), and mononuclear leukocyte (WBC) levels of Cu and Zn were determined immediately before therapy (week 0) and again at weeks 8 and 16. There was a significant fall in Cu in mononuclear WBCs from 13.25 (SEM = 0.86) to 1.9 fg/cell (SEM = 0.56) (p less than 0.001) and an increase in Zn from 33.87 (SEM = 3.7) to 70.8 fg/cell (SEM = 11.7) (p less than 0.001), with no change in either cell count or measurable cell volume. Plasma Cu levels increased significantly (p less than 0.001), but the Zn levels decreased only slightly (p less than 0.03). Changes in RBC Cu levels during the treatment period were not significantly altered (p less than 0.1). Zn levels in RBCs were significantly (p less than 0.04) lower. It is concluded that treatment with clopamide may induce some changes in Cu and Zn levels in normal hypertensives, particularly in WBCs. Further investigation is needed to determine the extent of this influence.