Protective effect of zinc against ethanol toxicity in mice

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.

[Zinc--update of an essential trace element]

Since the recognition of zinc as an essential trace element in man and animals there has been a remarkable progress in our knowledge of the role of zinc in nutritional physiology, biology and medicine during the last few decades. Highlights in zinc research, mechanisms and homeostatic regulation of zinc absorption, sources of zinc intake, dietary factors and mineral interactions affecting zinc bioavailability are reviewed in the present paper. This is followed by an overview of the biochemical functions of zinc in enzymes, gene expression, endocrinology, immunology and oxidative stress. General signs and metabolic consequences of zinc deficiency as well as excessive intake and toxicity of zinc are summarized. Furthermore, national and international dietary zinc recommendations and different methods to determine the zinc status are discussed.

Augmentation of endotoxin hepatotoxicity by zinc

The present study was undertaken in rats to determine whether zinc protects against endotoxin hepatotoxicity and mortality. Treatment with zinc (50-200 mumol/kg body weight) alone or endotoxin (lipopolysaccharide B, Escherichia coli 026:B6, Difco, 2 mg/kg body weight) alone did not induce significant morphological changes in the liver parenchyma or any abnormalities in liver function tests. The mortality rate was 0%. In the rats pretreated with 100 mumol of zinc and then injected with endotoxin, the mortality rate, the incidence of focal hepatocellular coagulative necrosis and serum transaminase activity increased markedly. Eleven of the 12 rats pretreated with 200 mumol of zinc died within 4 h after endotoxin injection. In the rats pretreated with 50 mumol of zinc and then injected with endotoxin, there was no conspicuous change, in the mortality rate, liver function tests or morphology of the liver. These experimental data indicate that zinc increases the mortality rate in endotoxemic rats and augments biochemical and morphological evidence of endotoxin hepatotoxicity.

Combined effect of vanadium and zinc on certain selected haematological indices in rats

1. Two-month-old Wistar rats of both sexes received, as sole drinking liquid, an aqueous solution of ammonium metavanadate (AMV) and zinc chloride (ZC) at concentrations of 0.30 mg V/cm3 and 0.12 mg Zn/cm3 respectively, for a period of 4 weeks. 2. The reference groups received for drinking at this time: water, AMV or ZC solutions at the same concentration. 3. In all groups of animals there was a statistically significant decrease in the uptake of food, AMV or ZC, as well AMV-ZC solutions, as compared with the food and water taken up by the control group. 4. In the group of animals receiving AMV or AMV-ZC solution for drinking the body weight increment diminished significantly. 5. In the animals drinking the AMV-ZC solution a statistically significant decrease in the erythrocyte count and haemoglobin level in the peripheral blood were recorded, similar to the groups drinking AMV or ZC solution. 6. In rats drinking aqueous AMV or ZC solutions and in females receiving AMV-ZC solution the percentage of reticulocytes and polychromatophilic erythrocytes increased, moreover, in the peripheral blood. It was not, however, associated with marked percentage changes in the composition of the bone marrow cells.

Protective effects of zinc on cultured rat primary hepatocytes to metals with low affinity for metallothionein

The purpose of this study was to determine if Zn pretreatment could protect rat primary hepatocyte cultures from the cytotoxicity of five metals that have little or no affinity for metallothionein (MT). Hepatocytes were grown in monolayer cultures for 22 h and subsequently treated with ZnCl2 (100 microM) for 24 h; which increased the MT concentration 15-fold. Following Zn pretreatment, hepatocytes were exposed to various concentrations of Mn, V, Cr, Se, or Fe for an additional 24 h. Cytotoxicity was assessed by enzyme leakage and loss of intracellular K+. The toxicity of all five metals was significantly reduced in the Zn-pretreated cells. Zn pretreatment had no appreciable effect on the hepatocellular uptake (1-24 h) of Mn or Se. Zn pretreatment also did not increase the distribution of Mn or Se to the cytosol and neither metal was bound to MT, suggesting the protection was not due to their binding to MT. However, Zn pretreatment significantly decreased Mn-, Cr-, and V-induced cellular glutathione depletion. In summary, Zn pretreatment of rat primary hepatocyte cultures protects against Cr-, Mn-, Fe-, Se-, or V-induced hepatotoxicity. This protection does not appear to be related to MT induction but may be due to Zn-induced thiol or membrane stabilization and/or other biological changes produced by Zn.

Protection against salicylate-induced hepatic injury by zinc. A histochemical and biochemical study

Female Wistar rats received an oral dose of 700 mg salicylic acid/kg body wt., given as sodium salicylate. Some of the salicylate-treated rats received two subcutaneous injections of 100 mumol kg-1 ZnCl2 (24 h before and simultaneously with the salicylate administration). Other animals were given one subcutaneous injection of 100 mumol kg-1 ZnCl2 simultaneously with the salicylate treatment. Control rats were similarly injected with ZnCl2. Twenty four hours after salicylate treatment, serum and livers were taken for histochemical and biochemical analysis. The most remarkable effects of the treatment were enrichment of lipid droplets and iron and a reduction of glycogen, particularly in the periportal hepatocytes. The effects of salicylate were partially prevented by two ZnCl2 injections. The protective effects of ZnCl2 may be due to lower iron uptake into hepatocytes and by the induction of zinc metallothionein, which can serve as a scavenger for oxygen radicals.

The physiological role of zinc as an antioxidant

The purpose of this review is to consider whether an essential biochemical function of zinc (Zn) is to serve as an antioxidant. Zn has been shown to have an antioxidant role(s) in defined chemical systems. Two mechanisms have been elucidated; the protection of sulfhydryl groups against oxidation and the inhibition of the production of reactive oxygens by transition metals. Supraphysiological concentrations of Zn have antioxidant-like effects in organelle-based systems and isolated cell-based systems in vitro. Administration of pharmacological doses of Zn in vivo has a protective effect against general and liver-specific prooxidants. Dietary Zn deficiency causes increased susceptibility to oxidative damage in membrane fractions from some tissues suggesting that increased oxidative stress may be a small but significant component of the pathology observed in dietary Zn deficiency. However, the biochemical basis for Zn deficiency pathology remains unelucidated; critical antioxidant functions for Zn may still be uncovered.