Role of metallothionein in copper and zinc metabolism: special reference to inflammatory conditions

Zinc, Copper, and Metallothionein Metabolism after Jejunoileal Bypass Surgery or Small Bowel Resection in Rats

Liver dysfunction is a frequent complication of jejunoileal bypass (JIB) surgery, a procedure commonly used until recently to treat morbid obesity. It has been suggested that liver failure in JIB patients is due to bacterial overgrowth and translocation from the bypassed intestine. Because invading microorganisms cause hepatic inflammation these experiments evaluated zinc, copper, and metallothionein (MT) in two experimental rat models of intestinal surgery to determine whether their distribution in plasma and tissues was similar to the highly characteristic pattern observed during an inflammatory response. In the JIB rat model 90 per cent of the small intestine was isolated from the flow of digesta but remained viable in the abdominal cavity. In the small bowel resection (SBR) model 90 per cent of the small intestine was removed and the remaining intestine was resected. Data collected 21 days after surgery showed decreased growth rate and plasma zinc in the SBR and JIB rats that was significantly improved by supplemental zinc. All other measures of zinc, copper, and MT metabolism in the SBR rats were similar to those of controls. In JIB rats, however, liver copper, MT protein, and MT mRNA were significantly elevated, and a high proportion of the intracellular zinc and copper was associated with MT. The pattern of zinc, copper, and MT distribution in systemic circulation and liver of JIB rats suggests hepatic inflammation superimposed on low zinc and copper status. Lack of a similar response in the SBR rats confirms the involvement of the bypassed intestinal segment and supports the hypothesis that bacterial overgrowth and translocation are responsible for liver inflammation and dysfunction in JIB patients.

Zinc, T-cell pathways, aging: role of metallothioneins

Zinc is an essential trace element for many biological functions, including immune functions. Indeed zinc is required for the biological activity of a thymic hormone, called thymulin in its zinc-bound form, important for the maturation and differentiation of T-cells. With advancing age zinc, thymic functions and peripheral immune efficiency show a progressive decline. Supplementing zinc in old age restores them. Zinc is also relevant for liver extrathymic T-cell pathway, being preeminent in old age. Since zinc is also required for metallothioneins (MTs) biological functions, binding zinc with high affinity, aim of the present article is to summarize findings from our laboratory regarding the role of zinc on T-cell pathways, investigating also the possible cause of thymic involution and impaired liver extrathymic T-cell pathway in aging. Partial hepatectomy and liver regeneration are good models for this aim because of the likeness with aging for many immune functions, including thymic functions. MTs levels are increased, other than into the liver, also into the thymus during aging and in young hepatectomized (pHx) mice as compared to young sham controls. MTs may be one of the possible causes of reduced thymic efficiency and impaired liver extrathymic T-cell pathway in old age because of their higher zinc binding affinity rather than thymulin with consequent reduction of the free quota of zinc available for normal cell-mediated immunity. Following that, MTs may contribute to thymic involution and impaired peripheral immune efficiency in aging and in young pHx mice with different roles during the whole life of an organism: protective in young-adult age which may became, at least, dangerous for immune responses in aging. In order to limit or avoid this latter MTs possible role in aging, supplementing physiological zinc may be useful to improve immune responses in old age because of no interference of endogenous zinc on already high thymus MTs levels, but with caution for competition phenomena with copper, as documented in old mice and in syndrome of accelerate aging.