Clinical examination of weanling rats with early zinc deficiency

Physiological and toxicological changes in the skin resulting from the action and interaction of metal ions

The human environment contains more than 50 metal or metalloid elements. At least 15 are recognized as trace elements, with zinc, calcium, copper, magnesium, and iron having specific roles in skin morphogenesis and function. The present review focuses on the presumed role of metal ions in the skin, their competition for carrier proteins, and membrane receptors. Evidence presented shows that the balance of trace metal ions is critical for normal skin and repair mechanisms following injury. Xenobiotic ions can impair this balance, leading to pathological change. The skin acts as an organ of elimination of excess trace metals and xenobiotic ions from the body, but mechanisms of voidance vary for different metals. Metal ions are an important cause of allergies, and evidence is presented to show that the majority of metals or metal compounds can induce allergic changes. Except for chromium and nickel, which are among the most common human allergens, animal models have provided little information. At least cadmium, thorium, lead, chromium, nickel, beryllium, and arsenic and proven or putative carcinogens in animals or humans on the basis of cytological or epidemiological evidence. However, only arsenic exhibits a clear predilection for the skin. Other metals such as gold can induce subcutaneous sarcoma following injection, but the relevance of this observation in terms of human occupational risk is discounted.

Dietary subacute zinc deficiency and potassium metabolism

In a controlled animal experiment the effects of dietary subacute Zn deficiency on growth, Zn concentration, and tissue 42-K distribution were studied. Growth retardation caused lower body weight because both skeletal and heart muscle showed a reduction in cell mass. Zn concentrations were reduced in most tissues, however, they remained unaltered in heart muscle. 42-K activity increased in skeletal muscle and pancreas. We hypothesize the latter reflects the organs rate of metabolism, inducing the exocrine pancreas to increase Zn absorption; in skeletal muscle it may induce also alterations in cell potentiation, causing restless behavior. As suggested by the calculated specific K activity (Bq/mol), the K uptake was highest in liver and bone, high in pancreas and skeletal muscle and low in heart muscle. The latter suggests K retention in heart muscle. Specific activity in plasma and jejunum remained unaltered: K status and absorption seem unaffected. Zn deficiency causes different 42-K activities in the various tissues, that respond by alterations in K metabolism without the induction of K deficiency.

The uptake of zinc by erythrocytes under near-physiological conditions

The in vitro uptake of zinc by erythrocytes was measured under near-physiological conditions, using 65Zn as a radioactive tracer. Because of the presence of serum albumin--a strong zinc ligand--a low concentration of medium free zinc was maintained. Under these conditions a high-affinity carrier for zinc transport over the cell membrane was identified. With human erythrocytes, a Michaelis constant (Km) of 0.2 nM with respect to free medium zinc was measured and a Vmax of 4.5 nmoles Zn transported per h/g dry wt. The Km for medium Zn increases when the size of the internal erythrocytic Zn pool is augmented, whereas Vmax remains virtually unchanged. A model to explain this phenomenon is proposed. It is suggested that this phenomenon could underlie observations, confirmed here, that the in vitro uptake of Zn by animal erythrocytes depends on the Zn status of the animal.

Interspecies variations in response to topical application of selected zinc compounds

The dermal irritancy of six zinc compounds was examined in three animal models. In open patch tests involving five daily applications, zinc chloride (1% aqueous solution) was severely irritant in rabbit, guinea-pig and mouse tests, inducing epidermal hyperplasia and ulceration; aqueous zinc acetate (20%) was slightly less irritant. Zinc oxide (20% suspension dilute Tween 80), zinc sulphate (1% aqueous solution) and zinc pyrithione (20% suspension) were not overtly irritant, but induced a marginal epidermal hyperplasia and increased hair growth. Zinc undecylenate (20% suspension) was not irritant. Epidermal irritancy in these studies is related to the interaction of zinc ion with epidermal keratin. The compounds studied were not consistently bacteriostatic in the three species tested.