A critical physiological role of zinc in the structure and function of biomembranes

Evidence for potential application of zinc as an antidote to acetaminophen-induced hepatotoxicity

The therapeutic application of zinc sulphate as an antidote to acetaminophen overdose was examined in ICR mice. Hepatotoxicity was induced by a single oral dose of acetaminophen (750 mg/kg). Various treatments (normal saline, 15 or 30 mg/kg zinc sulphate, 150 mg/kg N-acetylcysteine, 15 mg/kg zinc sulphate + 150 mg/kg N-acetylcysteine) were given i.p. 1 h after acetaminophen overdose. Serum alanine aminotransferase, hepatic glutathione and malondialdehyde levels were measured before experiments and at various intervals after the administration of acetaminophen. Serum acetaminophen levels were also measured at different different intervals. Zinc sulphate showed protection by dose-dependently reducing alanine aminotransferase and malondialdehyde levels. The drug also partially prevented the depletion of hepatic glutathione. These effects were not as good as those of N-acetylcysteine. However, the combination of zinc sulphate with N-acetylcysteine produced even better protective effects. Furthermore, drug treatments did not affect serum acetaminophen levels. It is concluded that both drugs attenuate acetaminophen-induced hepatic toxicity, and the action is likely to be mediated through replenishment of hepatic glutathione levels. The use of zinc sulphate alone or in combination with N-acetylcysteine could be another alternative for the treatment of acetaminophen overdose in view of possible side effects produced by N-acetylcysteine.

Characterization of N-(6-methoxy-8-quinolyl)-p-toluenesulfonamide for the detection of zinc in living sperm cells

Zinc stabilizes membranes and DNA and inhibits respiration in somatic cells. It is present in high concentrations in the male reproductive tract and may stabilize spermatozoa prior to fertilization. Herein, we evaluate N-(6-methoxy-8-quinolyl)-p-toluenesulfonamide (TSQ) for analysis of Zn2+ in phosphatidylcholine (PC) vesicles and living spermatozoa using spectrofluorometry and flow cytometry. TSQ:Zn fluorescence in decanol or PC vesicles was compared to that in aqueous buffer. Evaluation of cation specificity, kinetics of TSQ:Zn binding, quenching of TSQ by dithionite and Zn2+ chelation by D-penicillamine established that TSQ is more fluorescent in decanol or PC vesicles than in aqueous buffer, has a high affinity for lipid bilayers and is specific for Zn2+ compared to Mg2+ and Ca2+. Fluorescence measurement of vesicles with and without pretreatment with Zn2+ indicated that, in the absence of Zn2+, 90% of the residual TSQ fluorescence was destroyed by dithionite but > 50% was protected by the presence of Zn2+. When D-penicillamine was added the remaining fluorescence was quenched (T1/2 = 10 s) indicating that TSQ remains in/on the membrane. These results established that TSQ can be used to effectively evaluate Zn2+ in artificial membranes and sperm cells. Additional experiments will be necessary to explain the dynamics of TSQ:Zn:membrane interactions.

Study of interaction between calcium and zinc on D-galactose intestinal transport

Zinc is an essential trace element necessary to life. This metal may exert some of its physiological effects by acting directly on cellular membranes, either by altering permeability or by modulating the activity of membrane-bound enzymes. On the other hand, calcium is an essential element in a wide variety of cellular activities. The aim of the present work was to study a possible interaction between zinc and calcium on intestinal transport of D-galactose in jejunum of rabbit in vitro. In media with Ca2+, when ZnCl2 was present at 0.5 or 1 mM, zinc was found to reduce the D-galactose absorption significantly. In Ca(2+)-free media, where CaCl2 was omitted and replaced isotonically with choline chloride, the sugar transport was not modified by zinc. Verapamil at 10(-6) M (blocking mainly Ca2+ transport) did not modify the inhibitory effect of zinc on D-galactose transport. When 10(-6) M of A 23187 (Ca(2+)-specific ionophore) was added with/without Ca2+ to the media, ZnCl2 produced no change in sugar transport. These results could suggest a possible interaction of calcium and zinc for the same chemical groups of membrane, which could affect the intestinal absorption of sugars.

Zinc supplementation in young children with acute diarrhea in India

BACKGROUND

In developing countries the duration and severity of diarrheal illnesses are greatest among infants and young children with malnutrition and impaired immune status, both factors that may be associated with zinc deficiency. In children with severe zinc deficiency, diarrhea is common and responds quickly to zinc supplementation.

METHODS

To evaluate the effects of daily supplementation with 20 mg of elemental zinc on the duration and severity of acute diarrhea, we conducted a double-blind, randomized, controlled trial involving 937 children, 6 to 35 months of age, in New Delhi, India. All the children also received oral rehydration therapy and vitamin supplements.

RESULTS

Among the children who received zinc supplementation, there was a 23 percent reduction (95 percent confidence interval, 12 percent to 32 percent) in the risk of continued diarrhea. Estimates of the likelihood of recovery according to the day of zinc supplementation revealed a reduction of 7 percent (95 percent confidence interval, -9 percent to +22 percent) in the risk of continued diarrhea during days 1 through 3 and a reduction of 38 percent (95 percent confidence interval, 27 percent to 48 percent) after day 3. When zinc supplementation was initiated within three days of the onset of diarrhea, there was a 39 percent reduction (95 percent confidence interval, 7 percent to 61 percent) in the proportion of episodes lasting more than seven days. In the zinc-supplementation group there was a decrease of 39 percent (95 percent confidence interval, 6 percent to 70 percent) in the mean number of watery stools per day (P = 0.02) and a decrease of 21 percent (95 percent confidence interval, 10 percent to 31 percent) in the number of days with watery diarrhea. The reductions in the duration and severity of diarrhea were greater in children with stunted growth than in those with normal growth.

CONCLUSION

For infants and young children with acute diarrhea, zinc supplementation results in clinically important reductions in the duration and severity of diarrhea.

Specificity of zinc binding to myelin basic protein

Zn2+ appears to stabilize the myelin sheath but the mechanism of this effect is unknown. In a previous report we have shown that zinc binds to CNS myelin basic protein (MBP) in the presence of phosphate and this results in MBP aggregation. For this paper we used a solid phase zinc blotting assay to identify which myelin proteins bind zinc. MBP and a 58 kDa band were found to be the major targets of 65Zn binding. Moreover, using fluorescence, light scattering and electron microscopy we investigated the binding of zinc and other cations to purified MBP in solution. Among the cations tested for their ability to interfere with the binding of zinc, the most effective were cadmium, mercury and copper, but only cadmium and mercury increased the scattering intensity, whereas MBP aggregation was not inhibited by copper ions. Thus, the effect of zinc on the formation of MBP clusters seems to be specific.

Endocrine interaction between zinc and prolactin. An interpretative review

Zinc plays a very important role in animal and human metabolism. Nowadays, it is one of the most extensively studied trace element, since its sphere of action has been demonstrated to be very broad. From the biochemical standpoint, it controls more than 300 different enzymes, many of them involved with intermediary metabolism, DNA and RNA synthesis, gene expression, and immunocompetence. It also plays a significant role in hormonal homeostasis, since it can interact with almost all hormones. Zn2+ is closely related to the thyroid and steroid hormones, insulin, parathormone, and pituitary hormones, particularly prolactin (PRL). Zn2+ can inhibit PRL secretion within a range of physiologically and pharmacologically relevant concentrations. This property has raised the possibility of clinical applications of zinc. In this article, we review the literature on the subject in an attempt to provide a comprehensible general view.

Chemical modulation of metallothionein I and III mRNA in mouse brain

Metallothioneins (MTs) are sulfhydryl-rich proteins. MT-I and MT-II are found in all tissues of the body, while MT-III exists only in brain. Regulation of MT-I and MT-III mRNA was studied in brain and liver of control C57BL/6J mice and mice given chemicals known to increase MT-I, namely, lipopolysaccharide (LPS), zinc chloride (Zn), cadmium chloride (Cd), dexamethasone (Dex), ethanol, and kainic acid (KA). Northern blot analysis revealed that MT-I mRNA levels in liver were induced dramatically (12-27-fold over basal levels) by all of the chemicals, while in brain only LPS produced an increase in MT-I mRNA (2-fold). Interestingly, the MT-I inducers, Cd, Dex, ethanol, and KA, down-regulated brain MT-III mRNA levels by approx. 30%. Because brain is such a heterogenous tissue, in situ hybridization was used to localize MT-I and MT-III mRNA in control and treated mice. MT-I mRNA signal, which was most abundant in the glial cells of the Purkinje cell layer of the cerebellum in control mice, appeared to be enhanced in mice given the MT-I inducers (LPS, Zn, Cd, Dex, ethanol, and KA). MT-I mRNA hybridization signal was also enhanced in the olfactory bulbs from LPS- and Cd-treated mice, while this signal was present but weak in control brains. MT-III mRNA hybridization signals were localized in hippocampus and co-localized with MT-I message in the glial cells of the Purkinje cell layer of the cerebellum. In addition, diffuse MT-III mRNA signals were visible in areas of the cerebral cortex, and in the molecular layer of the cerebellum. Signals for MT-III in hippocampus appeared to be reduced by KA, Dex and LPS treatment, while in the cortical region, MT-III mRNA signals appeared to be enhanced by KA, Cd, and ethanol treatment. In conclusion, both MT-I and MT-III expression in brain appears to be modulated by exogenous treatment, however, the changes are small in relation to those observed in liver. Chemical-induced alterations of MT mRNA are non-uniform throughout the brain, and thus best studied in a region-specific manner.

Activities of liver microsomal fatty acid desaturases in zinc-deficient rats force-fed diets with a coconut oil/safflower oil mixture of linseed oil

The present study was conducted to investigate the effect of zinc deficiency on fatty acid desaturation in rats fed two different types of dietary fat, a mixture of coconut oil and safflower oil (7:1, w/w, "coconut oil diet") or linseed oil ("linseed oil diet"). In order to ensure an adequate food intake, all rats were force-fed by gastric tube. Zinc deficiency caused statistical significant reduction of delta 9-desaturase activity in liver microsomes of rats fed coconut oil diet and tendencial reduction (p < 0.15) in rats fed linseed oil diet compared with control rats fed diets with the same type of fat. In agreement with this effect, zinc deficiency in the rats fed both types of dietary fat increased the ratio between total saturated and total monounsaturated fatty in liver phospholipids and liver microsomes. Zinc deficient rats on the coconut oil diet had unchanged delta 6-desaturase activity with linoleic acid as substrate and lowered activity with alpha-linolenic acid as substrate. In contrast, zinc deficient rats on the linseed oil diet had increased delta 6-desaturase activity with linoleic acid as substrate and unchanged activity with alpha-linolenic acid. Because linoleic acid is the main substrate for delta 6-desaturase in the rats fed coconut oil diet, and alpha-linolenic acid is the main substrate in the rats fed linseed oil diet, it is concluded that in vivo delta 6-desaturation was not changed by zinc deficiency in the rats fed both types of dietary fat. Activity of delta 5-desaturase was also not changed by zinc deficiency in the rats fed both dietary fats. Levels of fatty acids in liver phospholipids and microsomes derived by delta 4-, delta 5-, and delta 6-desaturation were not consistently changed by zinc deficiency in the rats fed both types of dietary fat. Thus, the enzyme studies and also fatty acid composition data of liver phospholipids and microsomes indicate that zinc deficiency does not considerably disturb desaturation of linoleic and alpha-linolenic acid. Therefore, it is suggested that similarities between deficiencies of zinc and essential fatty acids described in literature are not due to disturbed desaturation of linoleic acid in zinc deficiency. The present study also indicates that zinc deficiency enhances incorporation of eicosapentaenoic acid into phosphatidylcholine of rats fed diets with large amounts of n-3 polyunsaturated fatty acids.

Interaction between calcium and zinc on L-threonine absorption in rabbit jejunum

The essential minerals calcium and zinc serve unique functions in higher organisms, and it is well recognized that homeostatic mechanisms are involved in regulating their metabolism. However, it has been reported that zinc, at higher concentrations (1 mM), inhibits intestinal absorption of sugars and amino acids. The aim of the present work was to determine whether the inhibitory effect on L-threonine absorption across the rabbit jejunum could be modified by calcium. In media with Ca2+, zinc significantly reduced L-threonine absorption. In Ca(2+)-free media, where calcium chloride was omitted and replaced isotonically with choline chloride, the amino acid transport was not modified by zinc, but when calcium chloride was replaced isotonically with magnesium chloride, the inhibition was observed. Verapamil (blocking mainly Ca2+ transport) did not modify the inhibitory effect of zinc on L-threonine transport. When A23187 (Ca(2+)-specific ionophore) was added in media with and without Ca2+, zinc produced no change in L-threonine transport. These results suggest that calcium and zinc could have an affinity with the same chemical groups of the enterocyte membrane, which would be related to the intestinal absorption of amino acids.

Antimicrobial screening of zinc in the absence or presence of oleoresins and various resin acids

Zinc and oleoresins are the main components of several wound dressings, and are also frequently used in root canal treatment. The in vitro antibacterial effects of zinc, six highly purified resin acids and two commercial oleoresins alone or combined in varying proportions were analysed. Oleoresins are composed of approximately 90% resin acids and the most common acids were included in this study. The antibacterial activity of the various chemicals was estimated using a Bioscreen robot analyser, which allowed 24 h kinetic documentation of bacterial growth. The bacteria employed were reference species commonly occurring on human skin or of oral origin. Zinc as well as the oleoresins and the pure resin acids all showed antibacterial activity when present in growth media, but the sensitivity of the bacteria varied. The presence of resin acids and oleoresins increased the antibacterial effect of zinc to varying degrees depending on the combination and the bacterial species tested. The results of the present study indicate that zinc, resin acids, or oleoresins alone, as well as combined, show antibacterial activity against selected aerobic Gram-positive and anaerobic Gram-negative bacteria.

Interleukin-1 alpha (IL-1 alpha) production by alveolar macrophages in patients with acute lung diseases: the influence of zinc supplementation

The relationship between zinc treatment and interleukin-1 alpha (IL-1 alpha) production by cultured alveolar macrophages (AM) in patients with pulmonary tuberculosis and bacterial pneumonia was investigated. AM (1 x 10(6) cells/ml) from 6 patients with pulmonary tuberculosis, 7 patients with bacterial pneumonia and 4 healthy volunteers were cultured with either two different concentrations of zinc chloride (Znl = 1 microgram/ml and Zn2 = 5 micrograms/ml) or cell culture media alone (control) for an initial period of 6 hours and then stimulated with 3 different immunomodulator agents and reincubated for a further 24 h. IL-1 alpha in culture supernatants was measured by enzyme-linked immunosorbent assay (ELISA). In the absence of Znl or Zn2 Polyinosinic:Polycytidylic acid (Poly I:C 1 microgram/ml), Lipopolysaccharide (LPS 100 ng/ml) and Tumour necrosis factor-alpha (TNF-alpha 10 ng/ml) significantly increased the production of IL-1 alpha from AM in both patients and healthy subjects (p < 0.001) compared to control (media only). Zn1 and Zn2 significantly increased the production of IL-1 alpha (p < 0.001) in culture supernatants in the absence of either Poly I:C, LPS or TNF-alpha in patients but not in healthy group. In contrast, the presence of LPS or TNF-alpha significantly reduced Zn1 or Zn2-stimulated release of IL-1 alpha from AM in patients and healthy subjects (p < 0.01). However, Poly I:C decreased only Zn1-stimulated release of IL-1 alpha. These results suggest that zinc can regulate the production of IL-1 alpha from AM in patients with pulmonary tuberculosis or bacterial pneumonia.

Permeation by zinc of bovine chromaffin cell calcium channels: relevance to secretion

Zn2+ increased the rate of spontaneous release of catecholamines from bovine adrenal glands. This effect was Ca2+ independent; in fact, in the absence of extracellular Ca2+, the secretory effects of Zn2+ were enhanced. At low concentrations (3-10 microM), Zn2+ enhanced the secretory responses to 10-s pulses of 100 microM 1,1-dimethyl-4-phenylpiperazinium (DMPP, a nicotinic receptor agonist) or 100 mM K+. In the presence of DMPP, secretion was increased 47% above controls and in high-K+ solutions, secretion increased 54% above control. These low concentrations of Zn2+ did not facilitate the whole-cell Ca2+ (ICa) or Ba2+ (IBa) currents in patch-clamped chromaffin cells. Higher Zn2+ concentrations inhibited the currents (IC50 values, 346 microM for ICa and 91 microM for IBa) and blocked DMPP- and K(+)-evoked secretion (IC50 values, 141 and 250 microM, respectively). Zn2+ permeated the Ca2+ channels of bovine chromaffin cells, although at a much slower rate than other divalent cations. Peak currents at 10 mM Ba2+, Ca2+, Sr2+ and Zn2+ were 991, 734, 330 and 7.4 pA, respectively. Zn2+ entry was also evidenced using the fluorescent Ca2+ probe fura-2. This was possible because Zn2+ causes an increase in fura-2 fluorescence at the isosbestic wave-length for Ca2+, i.e. 360 nm. There was a slow resting entry of Zn2+ which was accelerated by stimulation with DMPP or high-K+ solution. The entry of Zn2+ was concentration dependent, slightly antagonized by 1 mM Ca2+ and completely blocked by 5 mM Ni2+. The entry of Ca2+ evoked by depolarization with high-K+ solution was antagonized by Zn2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Topical zinc oxide treatment increases endogenous gene expression of insulin-like growth factor-1 in granulation tissue from porcine wounds

Application of zinc oxide has been shown to accelerate the healing of both chronic and acute wounds, but the mechanisms are unknown. We quantified the gene expression (mRNA) for one important growth factor, insulin-like growth factor-1 (IGF-1) in 12 full-thickness wounds in each of three domestic pigs treated with or without topical zinc oxide. We used a RNAase protection/solution hybridisation technique to measure IGF-1 mRNA concentrations, which were 50% higher in the granulation tissue in wounds treated with zinc oxide compared with control wounds on days 3-4 (p < 0.05), but not thereafter (up to postoperative day 11). Topical zinc oxide increased the healing rate of wounds compared to the control group (p < 0.01). The cell composition of the granulation tissue was similar in the two groups. The increased gene expression of IGF-1 may be one mechanism by which topical zinc oxide enhances wound healing.

Metallothionein in carcinogenesis and cancer chemotherapy

1. Despite considerable progress, cancer continues to remain the number one health threat to human beings. Currently, the targeted antineoplastic therapy is based on an understanding of the molecular mechanisms that govern the normal proliferation and functioning of the cellular elements. Furthermore, the gene-directed therapies and antibody-based approaches are also based on modulating specific signalling processes influencing growth factors and oncogenes that alter cellular proliferation. 2. The intracellular level of metallothionein, a low molecular weight metal binding protein consisting of 25-30% cysteine, containing no aromatic amino acids or disulfide bonds and binding between 5 and 7 g atoms of group II B heavy metals per mole protein, may play an important role in regulating cellular responsiveness to DNA interactive antineoplastic agents. For example, cells with acquired resistance to cisplatin or chlorambucil overexpress metallothionein, which tends to bind these alkylating agents to a higher extent than the non-resistant cells. Since humans synthesize several isoforms of metallothionein. It is not certain which isoforms are increased in cells with acquired resistance to anti-cancer drugs. In addition to sequestering electrophilic anti-cancer drugs, metallothionein, by regulating the activities of zinc-requiring metalloenzymes or scavenging radical species, may alter the therapeutic efficacy of antineoplastic agents.

Measurement of zinc in hepatocytes by using a fluorescent probe, zinquin: relationship to metallothionein and intracellular zinc

Zinquin [ethyl (2-methyl-8-p-toluenesulphonamido-6-quinolyloxy)acetate], a new intracellular zinc fluorophore, was used to reveal and to measure Zn in cultured rat hepatocytes before and after metallothionein (MT) induction. Hepatocytes labelled with an intense extranuclear fluorescence. Culture with combinations of Zn, dexamethasone and interleukin-6, increased intracellular MT by 24-fold, Zn 3-fold, and Zinquin fluorescence by approx. 2-fold above control values. Zinquin fluorescence correlated in descending order with the total cellular Zn (r = 0.747), exchangeable Zn (r = 0.735), soluble cytosolic Zn (r = 0.669) and MT (r = 0.666). When Zinquin was incubated with a cytosolic fraction of liver proteins before Sephadex G-75 column chromatography, it fluoresced with free, MT-incorporated and protein-bound Zn. Although only a slight attenuation of fluorescence was seen with high-molecular-mass protein-bound Zn, MT was degraded by 60% in the presence of Zinquin. The undegraded Zn-MT fluoresced at about 20% of the expected intensity. Although Zinquin fluoresces with all cytosolic Zn, caution is required when comparisons are made between samples with different concentrations of MT. This limitation was demonstrated by staining liver slices from adjuvant-treated rats where MT was increased 24-fold, intracellular Zn by 77%, but Zinquin fluorescence by only 19% above controls. Nevertheless, Zinquin should prove to be a useful tool for studying the distribution of Zn in living cells.

Flux of intracellular labile zinc during apoptosis (gene-directed cell death) revealed by a specific chemical probe, Zinquin

BACKGROUND

The transition metal Zn(II) is thought to regulate cell and tissue growth by enhancing mitosis (cell proliferation) and suppressing the counterbalancing process of apoptosis (gene-directed cell death). To investigate the role of Zn(II) further, we have used a UV-excitable Zn(II)-specific fluorophore, Zinquin. The ester group of Zinquin is hydrolyzed by living cells, ensuring its intracellular retention; this allows the visualization and measurement of free or loosely-bound (labile) intracellular Zn(II) by fluorescence video image analysis or fluorimetric spectroscopy.

RESULTS

Here we show that in cells undergoing early events of apoptosis, induced spontaneously or by diverse agents, there is a substantial increase in their Zinquin-detectable Zn(II). This increase occurred in the absence of exogenous Zn(II) and before changes in membrane permeability, consistent with a release of Zn(II) from intracellular stores or metalloproteins rather than enhanced uptake from the medium. We propose that there is a major redistribution of Zn(II) during the induction of apoptosis, which may influence or precipitate some of the later biochemical and morphological changes.

CONCLUSIONS

The phenomenon of Zn(II) mobilization, revealed by Zinquin, presents a new element in the process of apoptosis for investigation and may permit rapid and sensitive identification of apoptotic cells, particularly in those tissues where their frequency is low.

Induction of metallothionein and stomatin by interleukin-6 and glucocorticoids in a human amniotic cell line

Interleukin 6 (IL-6) is an important mediator of various kinds of inflammatory and immune responses. The human amniotic cell line UAC has an increased number of IL-6 receptors after treatment by glucocorticoids. To find a possible activity of IL-6 on these cells, a cDNA library of IL-6- and dexamethasone-treated cells was screened with cDNA probes from both induced and non-induced cells. Two cDNAs showed a differential hybridization signal. The first one corresponds to metallothionein, a group of small cysteine-rich proteins thought to participate in the metabolism and storage of zinc and to protect cells against oxidative damage. A second cDNA corresponds to the recently cloned cDNA of band 7 integral membrane protein also called stomatin. In hereditary stomatocytosis, absence of this protein in erythrocyte membranes is associated with high Na+ and low K+ intracellular concentrations [Stewart, G. W., Hepworth-Jones, B. E., Keen, J. N., Dash, B. C. J., Argent, A. C. & Casimir, C. M. (1992) Blood 79, 1593-1601]. In UAC cells both metallothionein and stomatin are induced by dexamethasone and IL-6 in a more than additive manner. Western blot analysis shows that stomatin protein is induced in a similar way as its mRNA. IL-6 and dexamethasone induce a state of resistance against hydrogen peroxide toxicity in UAC cells. Metallothionein induction might be partly responsible for this cytoprotection against oxidative stress.

Action of zinc on enzymatic digestion and intestinal transport of sugar in the rabbit

The aim of the present work was to study whether zinc chloride added to the drinking water of rabbits affected the intestinal absorption of D-galactose and the activity of sucrase in the jejunum. The results showed that zinc decreased D-galactose absorption in the jejunal tissue. The effect appeared to be due mainly to an action on the active transport of the sugar by the mucosal border of the intestinal epithelium, because the zinc seemed not to affect its diffusion across the intestinal epithelium. Zinc was also shown to inhibit the (Na(+)-Ka+)-ATPase activity of the enterocyte, which might explain the inhibition of the Na(+)-dependent transport of D-galactose. Nevertheless, a possible direct action of the zinc ion on the Na(+)-dependent carrier cannot be discounted. Zinc did not alter the activity of sucrase in the jejunum of the rabbit.

Factors affecting the thiobarbituric acid test as index of red blood cell susceptibility to lipid peroxidation: a multivariate analysis

The relationship between formation of thiobarbituric acid reactive substances (TBARS) in red blood cells (RBC) after exposure to H2O2 and factors potentially able to modulate it was investigated by a multivariate analysis in 92 healthy volunteers. The independent covariates considered were: RBC membrane fatty acids and cholesterol, RBC antioxidant enzymes and zinc, plasma vitamins A and E and serum selenium, zinc and copper. The stepwise multiple-linear-regression analysis revealed RBC membrane fatty acids and cholesterol as predictors of a consistent proportion of the RBC-TBARS variability whereas none of the antioxidants entered the equation. The unsaturation index was the most important individual predictor; RBC-TBARS increased with increasing concentrations of total omega-3 polyunsaturated fatty acids, C 20:5 omega-3 and cholesterol, whereas they decreased with increasing concentrations of total monounsaturated fatty acids, saturated fatty acids, C 16:0 and C 18:0. It is suggested that formation of TBARS, at least in currently used conditions, reflects mainly the lipid composition of the tissue under investigation, without giving sufficient information about the status of the antioxidant defences.

Influence of nutrients and cytokines on endothelial cell metabolism

The vascular endothelium plays an active role in physiological processes such as hemostasis, regulation of vessel tone and vascular permeability. Cell injury, or any event which disrupts endothelial integrity and thus endothelial permeability properties, may be involved in the early events leading to atherosclerotic lesion formation. Because of its constant exposure to blood components, including prooxidants, diet-derived fats and their derivatives, the endothelium is susceptible to oxidative stress and to injury mediated by blood lipid components. It is likely that these events potentiate the overall inflammatory response to injury by increasing cytokine release in proximity to the endothelium, which then could further disrupt endothelial barrier function. Even though mechanisms associated with lipid/cytokine-mediated endothelial cell dysfunction are unclear, our data suggest that they may be both oxidative and non-oxidative in nature. We suggest that dietary fats, rich in certain unsaturated fatty acids are atherogenic by enhancing the formation of reactive oxygen intermediates. These intermediates can activate oxidative stress-responsive transcription factors, such as NF-kappa B, which in turn may promote cytokine production, adhesion molecule expression and ultimately endothelial barrier dysfunction. The resulting disturbances in endothelial integrity possibly allow increased penetration of cholesterol-rich lipoprotein remnants into the arterial wall, a critical event in the etiology of atherosclerosis. Data suggest that certain nutrients, which have antioxidant and/or membrane stabilizing properties, protect endothelial cells by interfering with the above proposed mechanisms of endothelial cell dysfunction.

Effects of chronic caffeine feeding on the activities of oxygen free radical defense enzymes in the growing rat heart and liver

The purpose of the present study was to determine the relationship between concentration of Zn, Cu and Fe, and the catalase, glutathione peroxidase and superoxide dismutase activities in the heart and liver of newborn rats whose dams were fed a diet supplemented with caffeine. Heart Zn levels of the 22- and 30-day-old rats of the caffeine group showed a decrease, whereas liver Zn levels showed an increase compared to the control. Cu levels in the liver at day 22 in the caffeine group were less than in the control. Cu- and Zn-containing superoxide dismutase activities showed an increase in the hearts of the caffeine group compared to the control. The activity of catalase and glutathione peroxidase showed no difference in the heart and liver between the groups. The present study suggests the possible involvement of superoxide dismutase enzyme in the impairment of heart formation as a result of chronic caffeine intake in the early growing period.

Zinc hydroxide induced respiratory burst in rat neutrophils

The effects of zinc hydroxide on the respiratory burst and phagocytosis by rat neutrophils were examined. Zinc hydroxide induced an increase in oxygen consumption and O2- production. Electronmicroscopy showed that neutrophils engulfed zinc hydroxide particles by phagocytosis. Pertussis toxin (0.25, 0.5, 1.0 micrograms/ml) and EGTA (1, 2, 5 mM) inhibited zinc hydroxide-induced O2- production in a dose-dependent manner. The inhibitors of protein kinase C, 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine and N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide inhibited zinc hydroxide-induced O2- production with IC50 values ranging between 10 microM and 25 microM. The inhibitory study using an inhibitor of myosin light chain kinase, 1-(5-iodo-naphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine, showed IC50 values ranging from 5 microM to 10 microM. These findings indicate that zinc hydroxide induces respiratory burst and phagocytosis by rat neutrophils.

Effect of pharmacologic doses of zinc on the therapeutic index of brain tumor chemotherapy with carmustine

To evaluate the potential differential effect of pretreatment with pharmacologic doses of the trace element zinc on the chemosensitivity of glioma cells and bone marrow cells for carmustine (BCNU), we performed in vitro and in vivo studies of zinc toxicity as well as of the combined treatment with zinc and the anticancer drug. We studied the in vitro effects on established human and rat glioma cell lines using a microcolorimetric growth assay and on murine bone marrow using a clonogenic assay for committed progenitor cells of the granulocyte-monocyte lineage. Zinc exposures of up to 100 microM for 120 h did not influence the growth of six of seven human glioma cell lines. Only U87MG demonstrated statistically significant toxicity during high zinc exposure (100 microM over 120 h). Dose-response growth curves generated for BCNU did not show protection against the anticancer agents by a 48-h pretreatment with different zinc concentrations. The clonogenic capacity of bone marrow cells was slightly reduced by in vitro culture for 24 and 48 h. Although this effect appeared to be more prominent in the presence of zinc supplementation, overall a statistically significant inhibition was seen only after exposure to a concentration of 100 microM zinc over 48 h. As compared with chemotherapy alone, in vitro pretreatment with 50 microM zinc over 48 h followed by chemotherapy resulted in an increased number of colony-forming unit-granulocyte monocyte (CFU-GM): CFU-GM increased by a factor of 2 for BCNU (60 microM x 2 h). This statistically significant in vitro chemoprotection would translate into a dose-protection factor of 1.5, i.e., for the same level of myelosuppression, zinc pretreatment would allow administration of a 50% increased dose of BCNU. The in vivo studies were performed in an s.c. xenograft model of the human glioma cell line U87MG in athymic mice. The maximal tolerable pretreatment with zinc was determined to be a 10-day course of daily i.p. injections of 10 mg/kg ZnCl2. The subsequent i.p. administration of the dose lethal to 10% of the mice (LD10) and of a 1.5 x LD10 dose of BCNU resulted in less bone marrow toxicity in pretreated animals than in non-zinc-pretreated mice as determined in a CFU-GM assay. Glioma colony-forming efficiency (CFE) assays, on the other hand, did not show any zinc-related difference in the BCNU sensitivity of U87MG.(ABSTRACT TRUNCATED AT 400 WORDS)

Nutrition, endothelial cell metabolism, and atherosclerosis

The vascular endothelium that forms an interface between the blood and the surrounding tissues is continuously exposed to both physiologic and pathophysiologic stimuli. These stimuli are often mediated by nutrients that can contribute to the overall function of the endothelial cell in the regulation of vascular tone, coagulation and fibrinolysis, cellular growth and differentiation, and immune and inflammatory responses. Therefore, nutrient-mediated functional changes of the endothelium and the underlying tissues may be significantly involved in the atherosclerotic disease process. There is evidence that individual nutrients or nutrient derivatives may either provoke or prevent metabolic and physiologic perturbations of the vascular endothelium. Preservation of nutrients that exhibit antiatherogenic properties may, therefore, be a critical issue in the preparation and processing of foods. This review focuses on selected nutrients as they affect endothelial cell metabolism and their possible implications in atherosclerosis.

Characteristics of zinc binding to human red blood cell membranes

The objective of the present study was to standardize the analysis of zinc binding on human red blood cell (RBC) membranes in 20 normal adults. The displacement studies revealed that at the maximal stable zinc concentration tested (600 microM), 57% (mean) of the bound 65Zn was displaced and to displace half maximal 65Zn, the stable zinc concentration was 300 microM. Scatchard plots revealed two classes of binding sites for zinc on RBC membranes: one with higher affinity, Kd = 1.20 x 10(-5) M (site I), and the other with lower affinity, Kd = 2.77 x 10(-4) M (site II). Binding sites occupancy was 97% means and 58.5% means for sites I and II, respectively. The displacement was affected by temperature, membrane protein concentration, freezing, thawing, and dialysis. Other metal cations, including Co++, Fe++, and Mn++, had very little effect on 65Zn displacement, in contrast copper displaced 65Zn from its binding sites on RBC membranes. Zinc binding to RBC membranes was rapid and readily reversible in a dynamic equilibrium with its binding sites. It is anticipated that this method will be applicable to studies of a wide variety of diseases specifically related to zinc metabolism in humans as well as in animals.

Correlation of apoptosis with change in intracellular labile Zn(II) using zinquin [(2-methyl-8-p-toluenesulphonamido-6-quinolyloxy)acetic acid], a new specific fluorescent probe for Zn(II)

Zinquin [(2-methyl-8-p-toluenesulphonamido-6-quinolyloxy)-acetic acid], a membrane-permeant fluorophore specific for Zn(II), was used with spectrofluorimetry and video image analysis to reveal and quantify labile intracellular Zn. Zinquin labelled human chronic-lymphocytic-leukaemia lymphocytes, rat splenocytes and thymocytes with a weak diffuse fluorescence that was quenched when intracellular Zn was chelated with NNN'N'-tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN) and was greatly intensified by pretreatment of cells with the Zn ionophore pyrithione and exogenous Zn. There was substantial heterogeneity of labile Zn among ionophore-treated cells, and fluorescence was largely extranuclear. The average contents of labile Zn in human leukaemic lymphocytes, rat splenocytes and rat thymocytes were approx. 20, 31 and 14 pmol/10(6) cells respectively. Morphological changes and internucleosomal DNA fragmentation indicated substantial apoptosis in these cells when the level of intracellular labile Zn was decreased by treatment with TPEN. Conversely, increasing labile Zn by pretreatment with Zn plus pyrithione suppressed both spontaneous DNA fragmentation and that induced by the potent apoptosis-induced agents colchicine and dexamethasone. These results suggest that prevention of apoptosis is a function of labile Zn, and that a reduction below a threshold concentration in this Zn pool induces apoptosis.

Changes of the Cu and Zn contents in lung and liver in intestinal ischemic reperfusion and general ischemic reperfusion in rabbits

The changes of pulmonary and liver Cu-Zn contents were determined and evaluated in intestinal ischemic reperfusion (IIR) and general ischemic reperfusion (GIR) of rabbits. The contents of pulmonary Zn and liver Cu were found to be lower, and Cu/Zn ratio increased in lung tissue and decreased in liver tissue in IIR. The contents of pulmonary Zn were increased, and the contents of liver Cu were decreased; Cu/Zn ratio also decreased in both tissues in GIR. Pulmonary Cu and liver Zn contents were not changed in IIR and GIR. These results showed that lower or higher Zn in lung tissue and lower Cu in liver tissue were related to the acute tissue injury during IIR and GIR, suggesting that regulating the state of pulmonary Zn and liver Cu should be attempted during the prevention and treatment of both ischemic reperfusions.

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.

Effect of zinc deficiency on lipid peroxidation status and infarct size in rat hearts

The objective of this study was to investigate the effect of dietary zinc on endogenous production of lipid peroxides, and on myocardial infarct size in rats. Male rats were fed a zinc-deficient diet containing 4 ppm zinc, or a standard diet containing 60 ppm zinc. After 3 weeks of diet, half of the animals underwent occlusion of the left coronary artery. The remaining animals underwent sham operation without occlusion. Forty-eight hours later, the hearts were sampled and lipid peroxide levels and infarct size were evaluated. Coronary occlusion was associated with an increase in cardiac lipid peroxide levels which were more pronounced in the zinc deficient group. However, infarct size appeared to be independent from zinc deficiency, despite the free radical-mediated lipid peroxide augmentation reported here. The pharmacological limitation of infarct size in rats with permanent coronary occlusion is discussed.

Effect of zinc supplementation on resistance of cultured human skin fibroblasts toward oxidant stress

In purified system zinc has been shown to have an antioxidant role. Its effects on the resistance of cultured cells towards oxidative stress in vitro were examined. Diploid human skin fibroblasts were grown for 21 d in culture media (RPMI 1640 containing 15% fetal calf serum) added with different zinc (Zn) concentrations (100, 125, and 150 microM as Zinc chlorur ZnCl2). In comparison, cell controls were grown in standard culture media (6.5 microM Zn). The intracellular zinc levels of treated fibroblasts increased from 3- to 7-fold (2330 +/- 120 ng/mg protein in 150-microM Zn-treated cells versus 331 +/- 21 ng/mg protein in control cells). The intracellular copper increased 3- fold whereas the iron content slightly but not significantly decreased. The index of basal lipid peroxidation measured as thiobarbituric acid reactants (TBARs) of zinc-supplemented cells was lower than that of non zinc supplemented controls (0.89 mumol/g protein in 150 microM Zn-treated cells versus 1.59 mumol/g protein in controls). At these high doses of zinc, fibroblasts expressed lower antioxidant metalloenzymes activities. Diminished TBARs in Zn treated cells tends to support that Zn acts protectively against free radical mediated damage. However when the cells were challenged with extracellular oxidant stresses mediated by hypoxanthine/xanthine oxidase or hydrogen peroxide (H2O2), an increased toxicity in Zn-supplemented cells was observed. When we applied an intracellular oxidative stress as UV-B or UV-A radiation, Zn-treated fibroblasts were more resistant than cells grown in normal medium. If Zn has shown antioxidant effect in some in vitro or in vivo systems our observations clearly demonstrate that this role is not mediated by antioxidant metalloenzymes.

Copper and zinc toxicity in two rat hepatoma cell lines varying in differentiation

1. The differentiation status of cells is considered to represent an important factor in determining the effects of toxic components. 2. Two rat hepatoma cell lines, MH1C1 and HTC, were used to study differences in the sensitivity to two toxic metals: copper and zinc. 3. The differentiation of the cell lines was characterized using light microscopy, growth pattern, gamma glutamyltransferase (GGT) activity and albumin production as parameters. 4. The MH1C1 cell line was described to be more differentiated. 5. Albumin production in the MH1C1 cells was significantly higher than in the HTC cells whereas the GGT activity was only slightly different. 6. Toxicity of Cu and Zn was compared. Zn appeared to be more toxic to the cells than Cu, when leakage of lactate dehydrogenase and potassium were measured, whereas both metals were equally toxic when expressed as DNA remaining after 24 hr. 7. The MH1C1 cell line appeared to be more sensitive to Cu and Zn than the HTC. 8. The two metals appeared to have different targets in the cell; Cu may affect the nucleus and Zn the cell membrane.

Influence of periconceptional zinc deficiency on embryonic plasma membrane function in mice

Periconceptional Zn deprivation can affect development of 2- and 4-cell mouse embryos in vitro as evidenced by fewer cells per embryo and delayed blastocyst development after 72 h in culture. One mechanism by which this could be occurring is through changes in oocyte and embryonic membrane structure/function. To test this idea, 3H-glycine uptake was measured in unfertilized oocytes and preimplantation embryos recovered from mice fed control (+Zn; 50 micrograms Zn/g diet) or low Zn (-Zn; < or = 0.4 micrograms Zn/g diet) diets for 6 days. In a second experiment, we assessed the in vitro development of preimplantation embryos in medium designed to inhibit cavitation through changes in membrane-associated sodium flux. Preimplantation embryos from -Zn and +Zn mice recovered on day 1 of gestation were cultured in medium containing 147.2 mM sodium (normal) or 123 mM sodium (low sodium) for 48 h. In experiment 1, glycine uptake was similar in embryos from +Zn and -Zn mice, suggesting that the impaired in vitro development of embryos from -Zn mice is not due to gross changes in sodium-dependent cell membrane function. In experiment 2, embryos recovered from -Zn mice and cultured in normal sodium medium contained fewer cells than controls. Embryos from both groups cultured in low sodium medium contained fewer cells than their normal sodium controls; the percent difference in cell number was 50 +/- 8% and 56 +/- 11% for embryos from +Zn and -Zn mice, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Improvement of yellow nail syndrome with oral zinc supplementation

An unusual case of yellow nail syndrome (YNS) is reported. Total resolution of yellow nails and lymphoedema was observed following oral zinc supplementation for 2 years. A few years later, the patient developed a classical seropositive rheumatoid arthritis (RA). YNS, alone or associated with RA remains a rare clinical condition. The reported beneficial effects of zinc supplementation in YNS, as well as in several other pathological conditions, raise interest about the role of this trace element and its potential therapeutic implications and suggest further investigations are necessary.

Clinical response of alopecia, trichorrhexis nodosa, and dry, scaly skin to zinc supplementation

Two unrelated patients had dry brittle hair, alopecia, trichorrhexis nodosa, dry scaly skin, pigment dyschromia, short stature, and neurosecretory growth hormone deficiency. By means of the zinc tolerance test, patient 1 was shown to have zinc deficiency, whereas no clear zinc deficiency could be demonstrated in patient 2. In both patients, hair and the skin abnormalities responded to oral zinc therapy.

Zinc deficiency in the rat alters the lipid composition of the erythrocyte membrane Triton shell

The effect of dietary zinc deficiency on the lipid composition of the erythrocyte membrane Triton shell was determined. Weanling male Wistar rats were fed an egg white-based diet containing < 1.0 mg Zn/kg diet ad libitum. Control rats were either pair-fed or ad libitum-fed the basal diet supplemented with 100 mg Zn/kg diet. A Zn refed group was fed the -Zn diet until day 18 and then pair-fed the +Zn diet until day 21. Dietary Zn deficiency caused an increased cholesterol/phospholipid ratio in Triton shells compared to those from pair-fed controls. Zn deficiency caused a decreased double bond index of fatty acids in phosphatidylinositol (PI) and phosphatidylcholine (PC); there was a decreased proportion of 18:2n-6 and 22:4n-6 in PC and 20:4n-6 in PI as compared to that found in pair-fed controls. All glycerophospholipids that were retained in the shell had a lower double bond index and increased content of 16:0 and/or 18:0 relative to the phospholipid in the intact membrane.

Applications of molecular physics ‘biotechnology’ to the rational design of an improved phenytoin analogue

This study exploits molecular physics, in conjunction with a large scale computing environment, as a tool for understanding the clinical phenomenology of phenytoin (PHT) toxicology at a molecular level and for employing this understanding in an attempt to design improved drugs. The application of molecular physics techniques, such as quantum mechanics and molecular force field calculations, to the process of rational anticonvulsant drug design remains virtually unexplored. A 3-step strategy for applying these techniques to the design of an improved PHT molecule is presented. Step 1 employs quantitative structure-activity relationship calculations on 80 PHT analogues to ascertain the portion of the PHT molecule necessary for bioactivity (i.e. the 'bioactive face' of PHT); the N3-C4(O)-C5-R fragment of PHT was identified as the bioactive face. Step 2 employs molecular modelling studies to determine the portion of the PHT molecule necessary for the teratogenic, mutagenic and connective tissue toxicities of PHT (i.e. the 'biotoxic face'); the C2(O)-N3 fragment of PHT was identified as the biotoxic face. Step 3 experiments design an 'improved' PHT analogue, which maintains the bioactive face while eliminating the integrity of the biotoxic face; 2-deoxy-5,5-diphenylhydantoin was designed and synthesized as the improved PHT analogue. This compound had biological activity equivalent to PHT, but was unable to bind to nucleic acids or to chelate metals involved in connective tissue metabolism.

Competition of Mn2+ and Zn2+ with 59Fe2+ and 59Fe3+ for the plasma membrane receptors from lactating mouse mammary gland

Nonlabeled MnCl2 and ZnSO4 compete with 59Fe(2+)-ascorbate and 59Fe2(3+)O3 for transport binding sites situated on the plasma membranes of lactating mouse mammary gland cells. The binding was found to be a process reaching saturation. The heterologous competition used here ruled out the participation of transferrin and to propose that Fe, Mn, and Zn are transported from blood to milk by a mechanism involving one receptor during lactation. Further experiments are necessary to establish the details of the transport mechanism.

Inhibition of D-galactose transport across the small intestine of rabbit by zinc

Zinc is an essential trace element necessary to life. Many metallo-enzymes involved in the metabolism of carbohydrates, lipids, proteins, and nucleic acids require zinc for their functions. The aim of this study was to characterize how zinc acts on the intestinal sugar absorption in rabbit. Results obtained show that zinc decreases both D-galactose accumulation in the jejunum tissue, and mucosal to serosal transepithelial flux of this sugar, in a dose-dependent way. Furthermore, zinc seems not to modify sugar diffusion across the intestinal epithelium. The inhibition of intestinal sugar transport by zinc seems to be of a competitive type and it is reversed in high proportion with dithioerythritol (thiol groups protector). The results suggest that zinc decreases carrier-mediated intestinal sugar absorption.

Heary metals and lipofuscinogenesis. A study on myocardial cells cultured under varying oxidative stress

The aim of this study was to examine the influence on lipofuscinogenesis of a number of transition and non-transition heavy metals in cultured post-mitotic cells (neonatal rat myocytes) at varying oxidative stress. The effects of Al, Cd, Cr, Cu, Hg, Pb and Zn, added to the medium as chlorides, were examined after 14 days in culture under 5, 20 and 40% ambient oxygen. Lipofuscin was quantified by microspectrofluorometry of individual cells. The addition of Al (40 microM), Cd (40 nM), Hg (30 microM) and Pb (40 microM) to the culture growth medium markedly increased the amount of intracellular lipofuscin, whereas Cr (40 microM), Cu (40 microM) and Zn (40 microM) had the opposite effect. Transmission electron microscopic examination of the myocytes showed greatly increased numbers of autophagic vacuoles in cells exposed to those heavy metals that increased lipofuscin formation. This effect was most pronounced when cells were grown at high (40%) oxygen tension. Possible explanations for the metal augmented pigment formation may be (i) inhibition of lysosomal enzymes, (ii) catalytic interference with peroxidative reactions, or (iii) general toxicity with unspecifically increased autophagocytosis. The decreased pigment accumulation after the addition of Zn, Cr and Cu may, at least partly, be related to the replacement of iron, which has catalytic activity in Fenton reactions.