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

Zinc deficiency and dipeptidyl carboxypeptidase activity. Comparative effects on epididymis and testis of rats

Dipeptidyl carboxypeptidase (DC) is highly active in the testis and epididymis of rats and increases during pubertal development. Zinc deficiency during this period depresses the activity of DC in the testis. Experiments were conducted to determine the effects of zinc deficiency on epididymal DC activity. Comparisons were made between changes seen in this organ and those observed in testis. Three dietary treatments were used; zinc-deficient, fed ad libitum; zinc-adequate, pair-fed to the deficient group; and zinc-adequate, fed ad libitum. Results confirmed that testicular DC is affected negatively by zinc deficiency. DC activity was also lower in the epididymis of zinc-deficient rats than in control rats. These effects apparently were specific relative to changes in activity of other enzymes. Alkaline phosphatase activity in the epididymis was not affected by zinc deficiency and it was depressed in the testis. Gamma-glutamyl transferase activity in the epididymis was not affected by zinc deficiency but it was elevated in the testis. The results of this study suggest that part of the effect of zinc deficiency on sexual maturity in the male rat may be caused by reduced activity of DC. This enzyme is thought to be required for maturation and development of sperm cells.

The effect of zinc oxide on Staphylococcus aureus and polymorphonuclear cells in a tissue cage model

The effect of zinc oxide on S. aureus (209 P) was studied in steel net tissue cages implanted subcutaneously in guinea pigs and rabbits. Zinc oxide installed in the tissue cages created high, sustained concentrations of zinc in the cage fluid throughout the study. In a concentration of 22 mmol/l zinc oxide reduced viable counts in tissue cage fluid inoculated with S. aureus. No deleterious effect was observed on polymorphonuclear cell function.

Zinc-containing neurons in hippocampus and related CNS structures

Recent advances in metallohistochemistry have substantiated the identification of a distinct class of neurons in the brain, the zinc-containing neurons. These neurons sequester peculiar amounts of zinc in their presynaptic boutons and show both high-affinity uptake and calcium- and impulse-dependent release of the cation. It is thought that the zinc may act to stabilize the storage of certain macromolecules in presynaptic vesicles, but there is also mounting evidence that zinc released from vesicles can produce a broad spectrum of neuromodulatory effects upon target cells. Zinc-containing neurons are found predominantly in limbic and cerebrocortical regions, and a possible role of these neurons in the modification of synaptic strength is considered.

Lipid peroxidation in mitochondria and microsomes from adult and fetal rat tissues. Effects of Zn deficiency, Fe, and salicylate

Pregnant female Wistar rats that received a control (100 ppm Zn) or a Zn-deficient diet (1.5 ppm Zn) from d 0 to 21, or nonpregnant normally fed female rats without or with five daily oral doses of 300 mg/kg salicylic acid were used for the experiments. In isolated mitochondria or microsomes from various maternal and fetal tissues, lipid peroxidation was determined as malondialdehyde formation measured by means of the thiobarbiturate method. Zn deficiency increased lipid peroxidation in mitochondria and microsomes from maternal and fetal liver, maternal kidney, maternal lung microsomes, and fetal lung mitochondria. Lipid peroxidation in fetal microsomes was very low. Zn deficiency produced a further reduction of lipid peroxidation in fetal liver microsomes. Salicylate increased lipid peroxidation in liver mitochondria and microsomes after addition in vitro and after application in vivo. The increase of lipid peroxidation by salicylate may be caused by two mechanisms: an increased cellular Fe uptake that, in turn, can increase lipid peroxidation and chelating Fe, in analogy to the effect of ADP in lipid peroxidation. The latter effect of salicylate is particularly expressed at increased Fe content.

Zinc inhibition of glucose uptake in brush border membrane vesicles from pig small intestine

The effect of zinc on sodium coupled glucose uptake was studied in pig intestinal brush border membrane vesicles. In this system zinc inhibited glucose uptake and appeared to have a Ki of 0.25 mM. When tested by spectrophotometry, electron microscopy and protein determination following centrifugation, no evidence of significant vesicle aggregation was found with 0.5 mM zinc treatment. Zinc inhibition of glucose uptake persisted when the vesicle membrane potential was clamped with identical KCl concentrations inside and outside the vesicles in the presence of valinomycin. Variation of the glucose and sodium concentrations gave results indicating that zinc reduces glucose affinity for the carrier but not sodium binding to the transporter. The glucose inhibitory effect was not due to a rapid dissipation of the sodium gradient as zinc failed to affect sodium uptake in the absence of glucose. Zinc also failed to inhibit glucose efflux from vesicles under isotopic exchange conditions, when glucose and sodium concentrations were identical inside and outside vesicles. The t1/2 of glucose inhibition by zinc was relatively long, i.e. 6 min. We conclude that zinc acts as an inhibitor of glucose transport by interacting with the sodium-glucose co-transporter. The long zinc incubation time required to achieve maximal inhibition of glucose transport suggests that this interaction takes place within vesicles.

Nutrition, immune function, and inflammation: an overview

The collective evidence suggests that nutritional insult to both cell-mediated and humoral immunity in the presence of protein-energy malnutrition contributes to abnormalities of inflammation. The primary goal of nutritional support in inflammatory disease is to provide adequate energy and protein to meet endogenous requirements for tissue repair, IL-1 production, and restored cellular function, thus preventing secondary infection. Substrate provision should aim at improving the acute phase of injury while avoiding immune dysfunction. This goal may be achieved by altering the eicosanoid pathway toward a more regulated inflammatory state. In the context of allograft response, macrophages are central to the initiation of allosensitization by virtue of their ability to present antigen to T-cells. Activated T-cells may further modulate macrophage function by the secretion of lymphokines. Manipulation of macrophage eicosanoid production by dietary omega-3 PUFA may reduce cellular immune response. (table; see text) Nutritional support should also focus on providing essential micronutrients, with their potentially immunomodulating role, as adjunctive therapy in order to protect the host from toxic effects of free-radicals and chemicals released during inflammatory events. (Feeding regimens currently under investigation and development are presented in Table 4.) By integrating dietary immunotherapy with the use of recombinant hormones, monoclonal antibodies, and various available monokines, an optimal outcome for each patient may be achieved. However, effective application of immunotherapy to nutritional supplementation will require accurate monitoring of immune function in individual patients in order to avoid inappropriate treatment.

Superoxide production of peritoneal macrophages in experimental gram-negative sepsis; influence of in vitro and in vivo supplements of zinc

Although zinc is essential for the optimum function of the immune system, there is some controversy regarding treatment with zinc during acute infections where low serum zinc levels are often recorded. The aim of the present study was to investigate the influence of in vitro and in vivo zinc supplementation on the potentially toxic metabolic activity of peritoneal macrophages during infection. Rats were made septic by implanting a gelatin capsule containing known amounts of E. coli, and Bacteroides fragilis into the abdomen. Peritoneal macrophages were harvested by peritoneal lavage 72 hours after the induction of sepsis. Superoxide release was measured after stimulation with phorbol myristate acetate (PMA) or serum treated zymosan (STZ). Macrophages from septic rats released significantly higher amounts of superoxide compared with macrophages from sham operated controls after stimulation with both PMA and STZ. Following in vitro supplementation, zinc inhibited the superoxide production of macrophages harvested from septic rats after stimulation with both PMA and STZ. In vivo supplementation with zinc resulted in increased superoxide production from septic macrophages when stimulated with STZ, whereas stimulation with PMA produced no significant changes. Thus, in vitro incubation inhibited the superoxide production of peritoneal macrophages in intraabdominal sepsis, whilst in vivo administration of zinc produced no such effect, and the effect seemed to vary depending on the stimuli used to initiate the respiratory burst.

Translocation of zinc may contribute to seizure-induced death of neurons

Rats were subjected to seizures induced by kainic acid, and the resulting changes in CNS zinc staining were studied with the toluene sulfonamide quinoline fluorescence method. Seizures caused a loss of zinc staining from presynaptic boutons in many limbic and cerebrocortical regions. Simultaneously, the postsynaptic neurons that were degenerating (acidophilic) in those regions as a result of the seizure developed intense fluorescence for zinc. A possible role for zinc in the death of the postsynaptic neurons is suggested.

Zinc uptake in human seminal spermatozoa: characterization and effects on cell membranes

Human ejaculated spermatozoa take up zinc in a time- and concentration-dependent manner. The kinetics of 65Zn2+ uptake is suggestive of an at least partly carrier-mediated transport. The lack of effect of the respiratory chain inhibitor antimycin A could mean that mitochondrial ATP is not required as an energy source for the uptake. The failure of nonpermeant SH reagent mersalyl to modify zinc uptake indicates that functional membrane sulfhydryl groups are not involved in the process. A dose-dependent inhibition of 65Zn2+ uptake was induced by the "anticalmodulin" drug trifluoperazine, suggesting that the calcium-binding protein calmodulin could have a role in zinc transport. In in vitro experiments this cation brought about a powerful effect in protecting the spermatozoa from being damaged by hypo-osmosis.

Selenium-induced autometallographic demonstration of endogenous zinc in organs of the rainbow trout, Salmo gairdneri

Autometallographic (AMG) silver enhancement of endogenous zinc was studied in seven organs of the rainbow trout Salmo gairdneri. Groups of trout were injected intraperitoneally with sodium selenite in doses ranging from 0.08 to 25 ppm, administered 1 h before being killed. The concentration of selenium obtained by each organ was determined by gamma-spectrometry, and compared with the autometallographic deposition of silver grains. The relative accumulation of selenium in the organs was: liver greater than spleen greater than kidney greater than intestine greater than gills greater than brain greater than muscle. In the fish labelled with 10 and 25 ppm Se, AMG-deposits were found (1) within lysosomes of liver cells, (2) within the granules and on the nuclear membrane of melanophores in the spleen, (3) on the microvilli and in the apical cytoplasm of renal proximal tubular cells, (4) within the granules and along the plasma membrane of intestinal eosinophilic granule cells, and in the apical portion of the intestinal epithelium, and (5) in the gills, within granule cells and on the surface of the ionocytes. In the trouts injected with 5 ppm Se, silver grains were still observed in the liver, the intestine, and the gills, whereas, no such grains were found in preparations from fish having received 1 ppm Se. The use of selenium for the histochemical demonstration of endogenous zinc versus exogenous metals is discussed. Also, consideration is given to the question of which part of the total tissue zinc that is histochemically reactive.

Zinc clearance correlates with clinical severity of Crohn's disease. A kinetic study

After peroral and intravenous loading of zinc in 10 patients with Crohn's disease, a kinetic analysis of serum zinc was carried out. The patients were divided into two groups depending on the clinical activity indices (group A:five with active form and group B:five with inactive form). The mean level of serum zinc was significantly reduced in group A patients, but not in group B, when compared to findings in control subjects. A significant reduction in AUCpo (area under the concentration vs time curve by peroral administration), accompanied by increased zinc clearance (ClZn) was also found in group A but not in group B. The ClZn significantly correlated with clinical activity indices. Absorption efficiency, the ratio of AUCpo/AUCiv (area under the concentration vs time curve by intravenous administration), was similar in group A, group B, and the control. Therefore, the absorption of zinc in patients with the disease seems to be intact, regardless of whether they have the active or inactive form of Crohn's disease. The hypozincemia seen in patients with Crohn's disease is presumably related to an accelerated turnover rather than to a malabsorption of zinc.

Maternal and fetal iron accumulation in Zn-deficient and salicylate-treated rats

Nonhemoglobin Fe (non Hb-Fe) content in fetal serum and liver is much higher than in maternal serum and liver. After feeding a Zn-deficient diet to pregnant rats from d 0 to 21, non Hb-Fe content in maternal and fetal serum and liver was increased. After oral application of salicylic acid (300 mg/kg) from d 16 to 20 to normally fed and Zn-deficient dams, non Hb-Fe content in maternal and particularly in fetal serum and liver was drastically increased. In the kidney, Fe was accumulated to a small amount resulting from Zn deficiency and salicylate treatment. Fe accumulation in the liver occurred in all cell fractions, particularly in microsomes. Fe accumulation was confirmed and extended histochemically by Prussian blue staining. It is assumed that salicylate increases intestinal Fe resorption and fetal transfer of Fe. It is discussed that salicylate nephrotoxicity and its enhancement by Zn deficiency is not caused by an Fe-dependent mechanism.

Hepatic zinc content in patients with various stages of alcoholic liver disease and in patients with chronic active and chronic persistent hepatitis

The hepatic zinc content was determined in liver biopsies of patients with alcoholic and nonalcoholic liver disease using proton-induced X-ray emission. The values obtained in postmortem specimens of the liver from 27 patients with no evidence of acute or chronic liver disease served as controls. The mean value and the range of the zinc content in the controls (75 +/- 24 ppm wet weight) are in good agreement with those reported in the literature. The hepatic zinc content in the control group showed no significant age or sex dependence. The mean zinc content was significantly decreased in all groups of patients with alcoholic liver disease. The decrease was comparable in biopsies from patients with alcoholic fatty liver (-56.7%, n = 12), mild alcoholic hepatitis (-50.5%, n = 6) and alcoholic cirrhosis (-45.6%, n = 10). The hepatic zinc content was also distinctly reduced in patients with chronic active hepatitis (-60.3%, n = 15) and in those with chronic persistent hepatitis (-44.9%, n = 8). The estimation of the zinc content in subcellular fractions of the liver performed in postmortem specimens from seven patients with alcoholic liver cirrhosis and in six controls revealed a significant reduction in the zinc content in the fraction containing cell nuclei and membranes and in the mitochondrial fraction. A similar decrease was seen in the 100,000 g supernatant; however, the difference did not attain statistical difference. The zinc content of the microsomal fraction in the controls was lower than in the other three cell fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of Plasmodium falciparum digestive vacuoles and partial characterization of the vacuolar membrane ATPase

Plasmodium falciparum digestive vacuoles containing ferric oxide granules were purified from parasite homogenates by centrifugation on discontinuous sucrose gradients. Digestive vacuole membranes prepared by osmotic lysis and washed with KCl showed no detectable contamination by erythrocyte membrane proteins and only minimal contamination by non-vacuolar parasite proteins. Purified vacuolar membranes were 2.6-fold enriched in total parasite membrane ATPase activity. This ATPase was optimally active at pH 7 in the presence of at least 2 mM Mg2+. Ca2+ and Mn2+ were approximately 80-90% as effective as Mg2+, and Zn2+, Co2+ and Fe2+ also exerted some stimulatory effect. The vacuolar membrane also hydrolyzed GTP, UTP, CTP and ADP, but AMP and 3',5'-cyclic AMP were hydrolyzed only one-tenth as effectively as ATP. The ATPase was unaffected by vanadate, ouabain or oligomycin but was significantly inhibited by the proton pump inhibitors NEM and NBD-Cl. Of 6 antimalarial drugs tested, quinine and quinacrine were the most effective inhibitors and mefloquine was the least effective.

Effects of zinc-aspartate and zinc-glycinate in healthy rats and on reserpine-induced gastric lesions

Experimental studies performed on 227 rats showed that Zn-aspartate and Zn-glycinate administered ip lowered the incidence, number, and severity of the reserpine-induced gastric lesions ensuring significant protection indices. Histochemical methods revealed increased amount of mucosal glycoproteins. The activity of dehydrogenases involved in energy metabolism that modulates acid secretion in the parietal cells was depressed. RNA content in the chief cells, as premises of pepsinogen synthesis, was decreased. ATPase reaction in the periglandular capillaries was uniform and stronger, showing an improvement of gastric mucosal microcirculation. Since these histochemical changes were also noted in healthy rats receiving Zn salts, it might be suggested that they are not the mere expression of an anti-ulcer protective effect of zinc, but rather reflect its mechanism of action, relating to the complex metabolic events induced by the trace element. Our results are in agreement with those previously reported concerning the noxious influence of Zn depletion, the accelerated healing of peptic ulcer patients after Zn treatment, and the protective effect of Zn against ulcerogenesis in several experimental models involving different pathomechanisms.

Ion modulation of membrane permeability: effect of cations on intact cells and on cells and phospholipid bilayers treated with pore-forming agents

Leakage of ions (Na+, K+) and phosphorylated metabolites (phosphorylcholine, 2-deoxyglucose 6-phosphate) through membrane lesions in intact cells or in cells modified by 'pore-forming' agent has been studied. Leakage from intact cells is induced by protons and by divalent cations such as Cu2+, Cd2+ or Zn2+. Leakage from agent-modified cells--or across phospholipid bilayers modified by agent--is prevented by low concentrations of the same cations and by higher concentrations of Ca2+, Mn2+ or Ba2+; Mg2+, dimethonium, spermine, or spermidine are virtually ineffective. The relative efficacy of a particular cation (e.g. Ca2+) depends more on cell type than on the nature of the pore-forming agent. The predominant effect is on binding of cation to specific sites, not on surface charge. Surface charge, on the other hand, does affect leakage from agent-modified cells in that suspension in nonionic media reduces leakage, which can be restored by increasing the ionic strength: univalent (Na+, K+, Rb+, NH4+) and divalent (Mg2+, dimethonium) cations are equally effective; addition of protons or divalent cations such as Zn2+ to this system inhibits leakage. From this and other evidence here presented it is concluded that leakage across membranes is modulated by the presence of endogenous anionic components: when these are in the ionized state, leakage is favored; when unionized (as a result of protonation) or chelated (by binding to divalent cation), leakage is prevented. It is suggested that such groups are exposed at the extracellular face of the plasma membrane.

Enhanced ototoxicity of gentamicin and salicylate caused by Mg deficiency and Zn deficiency

In rats, Mg deficiency caused a moderate hearing loss, measured by means of evoked potentials at 10 and 20 kHz, which was repaired after refeeding a normal diet. Application of 700 mg/kg salicylic acid or injection of 5 x 100 mg/kg gentamicin also caused a reversible hearing loss in normally fed rats. Treatment of Zn-deficient rats with salicylic acid produced a stronger although reversible hearing loss than in normally fed salicylate-treated rats. Treatment of Mg-deficient rats with gentamicin induced a strong hearing loss that was nearly complete and irreversible in 9 of 25 rats.

Zinc uptake into synaptosomes

Zinc uptake was studied in synaptosomes, isolated by the Ficoll flotation technique, using the radiotracer 65Zn. True uptake of zinc could be discriminated from binding to the outside of the synaptosomes by the absence of accumulation at 0 degree C and the dependency of the rate of uptake on the medium osmolarity. The zinc uptake, studied in the presence of various zinc-complexing agents, showed saturation kinetics when analyzed in terms of [Zn]free, yielding Km = 0.25 microM. The zinc uptake was independent of both ATP and the Na+ gradient. No efflux of zinc could be demonstrated from preloaded synaptosomes due to the formation of insoluble zinc complexes inside the synaptosomes. The results are discussed in terms of the modulation of diverse neurochemical processes by zinc.

A potential role for prolactin in zinc homeostasis

Zinc is an important trace metal co-factor for many metallo-enzymes and may have a critical role in the stabilization and function of biomembranes. Zinc-depleted animals increase their fractional absorption of zinc to restore zinc homeostasis. This increase in fractional absorption is not currently known to be hormonally-mediated. Recently, zinc has been shown to suppress the output of prolactin from dispersed pituitary cells in vitro at physiologic concentrations. Clinical states associated with a tendency to zinc deficiency are also associated with a tendency to hyperprolactinemia. These observations are consistent with the hypothesis that prolactin regulates the uptake and distribution of zinc and that zinc suppresses prolactin in closure of a negative feedback regulatory loop.

Plasma membrane proteases as useful tool in histochemical toxicology

Compared with mitochondrial, lysosomal and endoplasmic reticulum enzymes and plasma membrane-associated hydrolases plasma membrane-linked proteases in the rat thyroid gland, liver, kidney, placenta and yolk sac were more easily affected after the administration of the drugs salicylic acid and dexamethasone. Either a decrease or an increase of protease activity was observed in the surface membrane of capillary endothelial cells, hepatocytes, fetal placental cells and visceral yolk sac epithelial cells whereby proteases being localized in the same domain of the plasma membrane showed a different response.

Zinc deficiency in the 11 day rat embryo: a scanning and transmission electron microscope study

Zinc deficient rat embryos were obtained on the 11th day of pregnancy and examined by scanning and transmission electron microscopy. Scanning electron microscopy revealed an increase in the number of deformed embryos, as well as embryonic growth retardation. In addition, the epithelium of zinc deficient embryos displayed a marked increase in surface microvilli, as well as the presence of blebbing. Transmission electron microscopy indicated extensive cell death in the neural epithelium which was apparently more severely damaged by zinc deficiency than were mesenchymal cells. Mitochondrial cristae were affected to a greater degree than any other membrane of the cell and cristael disintigration appeared to represent the principal cellular lesion preceding necrosis of neural cells and neural tube teratology.

Enhancement of maternal and fetal nephrotoxicity of salicylate by zinc deficiency. Morphological, enzyme histochemical and immunohistochemical studies

An oral dose of 700 mg/kg salicylic acid was given to normal and Zn-deficient rats at day 16 of gestation. Maternal and fetal kidneys were studied at day 19 of gestation. Zn-deficiency did not cause any lesions detectable by semi-thin section light microscopy, electron microscopy, enzyme histochemistry and immunohistochemistry. Salicylate may lead only to small morphological, enzymatic and cytoskeletal defects in the maternal and fetal kidney. However, enzyme activities decreased in plasma membranes, mitochondria, lysosomes, endoplasmic reticulum and peroxisomes in all segments of the tubular apparatus when salicylate was given to Zn-deficient rats. Cytoskeletal proteins such as keratin in the glomerular cells and epithelial lining of the collecting ducts and vimentin in vascular endothelial cells of the maternal kidney were also affected. In addition, the epithelial cells of the collecting ducts, which were comparatively less damaged, accumulated high amounts of fat. In severe cases, the enzymatic and cytoskeletal lesions were accompanied by hematuria and tubular necroses including and collecting ducts in the renal papilla. In less severe cases reduced activities of brush border hydrolases were the only sign of disturbed renal function in maternal rats indicating that membrane alteration and loss of membrane-bound enzymes are the primary defects. In the fetal kidneys, mitotic activity of the cells of the nephron anlagen and collecting ducts was reduced and enzymatic and morphological differentiation were disturbed. As a consequence less mature nephrons and collecting ducts occurred.

In vivo effects of zinc deficiency on calmodulin concentrations in selected rat tissues

Two groups of male Sprague-Dawley rats, one fed zinc-deficient diet, ad libitum, the other, pair-fed with the same diet, but given supplemental zinc in the drinking water (8 mg Zn++/ml) were studied. After ten weeks of diet, rats were exsanguinated and zinc and calmodulin concentrations in brain and testis were measured. Mean zinc concentration in testis was significantly decreased in rats fed zinc-deficient diet without supplemental Zn++, but mean zinc concentration in brain was not different. Similarly, mean calmodulin concentration in testis was decreased in rats fed zinc-deficient diet without supplemental Zn++ whereas mean calmodulin concentration in brain was not different. Distribution studies of zinc and calmodulin showed that both zinc and calmodulin were released more freely into soluble fractions of testis in rats fed zinc-deficient diet without supplemental Zn++. These results indicate, for the first time in in vivo studies, that zinc influences the calmodulin content of testis.

Zinc, ethanol, and lipid peroxidation in adult and fetal rats

Studies were performed on adult and fetal rats receiving either a zinc-deficient (<0.5 ppm) diet and/or ethanol (20%) throughout pregnancy. Liver zinc levels were depressed in fetuses exposed toin utero zinc deficiency, but brain zinc levels were unchanged. Ethanol had no effect on the concentration of zinc in the several fetal and adult tissues studies. Lipid peroxidation, as measured by endogenous levels of malondialdehyde (MDA) increased following food restriction, zinc improverishment, and alcoholism in adult and fetal livers, but not in fetal brains. Generally, levels of MDA were highest when both zinc deficiency and the ingestion of alcohol occurred concurrently. Glutathione (GSH) was depressed by zinc restriction in several adult and fetal tissues, but not in the fetal brain. Ethanol alone had no effect on GSH levels. The activity of the enzyme glutathione peroxidase (GSH-Px) was not changed in either organism by alcohol or zinc deficiency.Overall, the data point to increased lipid peroxidation in maternal and fetal rat tissues following zinc depletion and/or treatment with alcohol and draw attention to the apparent vulnerability of the fetal liver toin utero alcoholism. By contrast, the fetal brain seems to be especially resistant to alcohol and zinc-related lipoperoxidation. An association is suggested between the increased lipoperoxidation accompanying zinc deficiency and reduced levels of GSH, but this does not appear to relate to changes in the activity of GSH-Px. A similar relationship is not evident with respect to the increased levels of MDA in fetal and adult livers following chronic alcohol intoxication. A possible basis for the zinc-GSH interaction is discussed.

Uptake and turnover of(65)Zn in subcellular fractions of brain of rat under normal and zinc-deficient conditions

After a single injection,(65)Zn is slowly taken up by the brain of the rat to a maximum after 7 d, followed by a turnover phase, with a half-time of about 3 wk. In the brain of rats on a zinc-deficient diet, the(65)Zn content in the brain continued to increase up to 30 d after the injection.The uptake and turnover phases in six different subcellular fractions of the brain showed a pattern similar to that of the whole brain in both the control and zinc-deficient rats. There was no internal redistribution of(65)Zn in the brain under conditions of progressive zinc deficiency.The results are discussed in a model for zinc homeostasis in the brain.

Zinc status in polycythaemia

Zinc and iron status have been measured in three groups of polycythaemic patients managed by venesection: polycythaemia rubra vera, secondary polycythaemia and idiopathic erythrocytosis. Zinc status was assessed from the concentration of zinc in polymorphonuclear cells (PMN) and plasma. The mean PMN zinc value was lower than that of age-matched controls (polycythaemics 57.5 +/- 2.3 micrograms/10(10) PMN, n = 26; controls 68.9 +/- 5.2 micrograms/10(10) PMN, n = 9; means +/- SEM, p less than 0.05). The difference was most marked in polycythaemia rubra vera; the patients were iron-deficient. The reduced PMN zinc levels may indicate that polycythaemic patients managed by repeated venesection are zinc-deficient. This may contribute to some nonspecific symptoms of polycythaemia and to recurrent infections in the hypoxic patients.

Alternations in lipid membrane fluidity and the physical state of cell-surface sialic acid in zinc-deficient rat erythrocyte ghosts

Erythrocyte ghosts, prepared from the blood of rats fed zinc-deficient diets, were evaluated for membrane fluidity and surface sialic acid properties using spin-labeled probes and electron spin resonance (ESR) spectroscopy. These physical parameters of the erythrocyte ghosts from the zinc-deficient group were compared to those for erythrocyte ghosts obtained from ad libitum and pair fed controls consuming zinc-adequate diets. As the animals became progressively zinc deficient, the erythrocyte ghost membranes became more fluid than those from the control groups. In addition, the apparent rotational correlation time of Tempamine spin probes on surface sialic acid residues was smaller for the zinc deficient group, indicative of an increased rotational mobility of the spin label. These results suggest that zinc deficiency can have pronounced effects on the physical state of membrane bilayer lipids and cell surface carbohydrates and supports the view that many of the pathological signs of zinc deficiency are due to a general membrane defect.

A novel form of host defence: membrane protection by Ca2+ and Zn2+

This review focusses on two questions: (1) How can the intracellular toxicity of ions such as Ca2+ or Zn2+ be reconciled with their extracellular benefit? (2) Why is the dietary requirement for Zn2+ so high when its documented biological role is that of a tightly-bound prosthetic group of certain enzymes? An answer to both questions is provided by the observation that extracellular cations such as Ca2+ and Zn2+ protect the plasma membrane of cells against non-specific leakage, including an influx of Ca2+ or Zn2+. It is suggested that such protection, against leakage induced by microbial and other toxins, may contribute to the high dietary requirement for zinc. These arguments lead to the proposal that a previously unrecognized form of host defence is one of protection of the cell plasma membrane by divalent cations against damage induced by cytotoxic agents of environmental origin.

Xanthine oxidase-catalyzed crosslinking of cell membrane proteins

Isolated erythrocyte membranes exposed to protease-free xanthine oxidase plus xanthine and ferric iron undergo lipid peroxidation and protein crosslinking (appearance of high molecular weight aggregates on sodium dodecyl sulfate (SDS) gel electrophoresis). Spectrin is more susceptible to crosslinking than the other polypeptides. Thiol-reducible bonds (disulfides) as well as nonreducible bonds are generated, the former type relatively rapidly (detected within 10-20 min) and the latter type more slowly (usually detected after 1 h). Reducible crosslinking is inhibited by catalase, but not by superoxide dismutase, desferrioxamine, butylated hydroxyltoluene, and mannitol; whereas nonreducible crosslinking, like free radical lipid peroxidation, is inhibited by all of these agents except mannitol. Zinc(II) also inhibits lipid peroxidation, but stimulates disulfide bond formation to the virtual exclusion of all other crosslinking. Our results indicate that disulfide formation is dependent on H2O2, but not O2- or iron. However, O2-, H2O2, and iron are all required for lipid peroxidation and nondisulfide crosslinking, suggesting the intermediacy of OH generated via the iron-catalyzed Haber-Weiss reaction. The possible role of malonaldehyde (MDA, a by-product of lipid peroxidation) in the latter type of crosslinking was examined. Solubilized samples of xanthine/xanthine oxidase-treated membranes showed a strong visible fluorescence (emission maximum 450 nm; excitation 390 nm). This resembled the fluorescence of membranes treated with authentic MDA, which forms conjugated imine linkages between amino groups. Fluorescence scanning of SDS gels from MDA-treated membranes showed a strong signal coincident with crosslinked proteins and also one in the low molecular weight, nonprotein region, suggestive of aminolipid conjugates. Similar scanning on xanthine/xanthine oxidase-reacted membranes indicated that all fluorescence is associated with the lipid fraction. Thus, nonreducible protein crosslinks in this system do not appear to be of the MDA-derived, Schiff base type.

Zinc metabolism in alcoholic liver disease

Alterations in zinc metabolism or zinc deficiency frequently occur in patients with alcoholic liver disease. Potential manifestations of zinc deficiency include skin lesions, hypogonadism, impaired night vision, impaired immune function, anorexia, altered protein metabolism, diarrhea, and depressed mental function. Because of the variety of ways in which zinc deficiency may present in alcoholic liver disease, clinicians must maintain a high index of suspicion for this nutrient deficiency when caring for these patients. Not only may zinc deficiency occur with alcoholic liver disease, but there also may be altered zinc metabolism. Recent data from alcoholic hepatitis patients demonstrate increased serum levels of the monokine interleukin 1, which is known to cause hypozincemia and an internal redistribution of zinc. This monokine has a host of metabolic functions other than its effect on mineral metabolism that have relevance for alcoholic liver disease such as fever production, neutrophilia, and muscle catabolism. We suggest that the patient with alcoholic liver disease frequently has problems with either zinc deficiency or altered zinc metabolism and the potential implications of this are discussed.

Kindled seizure induction alters and is altered by zinc absorption

Amygdala kindling stimulation produced significant changes in plasma zinc levels in cats otherwise unaffected by zinc loading or deprivation. While a normal diet had no effect, moderate zinc loading was accompanied by a marked increase in plasma zinc during kindling. Conversely, plasma zinc sharply declined in animals fed a zinc-deficient diet. Corresponding differences were obtained in the development of generalized seizures with kindling such that loading delayed and deprivation accelerated this process.

Effect of pure zinc deficiency on glucose tolerance and insulin and glucagon levels

The effect of zinc deficiency on glucose tolerance was investigated using intragastric force feeding to obviate decreased food intake and altered eating patterns. Three groups of weanling male Sprague-Dawley rats were fed a purified zinc-deficient diet: zinc-deficient, ad libitum-fed animals (ZDA) were offered powdered zinc-deficient diet; zinc-replete, force-fed controls (ZRF) were tube fed a diet blended with water containing 25 ppm of zinc; zinc-deficient, force-fed animals (ZDF) were similarly tube fed the zinc-deficient diet. The ZRF and ZDF groups received a diet of identical amount based on the intake of ad libitum-fed, zinc-replete rats. After 8 days of feeding, the ZDF group had impaired glucose tolerance curves, yet blood insulin and glucagon levels were normal. The ZDA group had normal glucose tolerance with low insulin levels compared with the ZRF group. The islet cell morphology among the three dietary groups were similar. These results suggest that the glucose intolerance observed in ZDF rats is not due to altered blood insulin and glucagon levels but rather to peripheral resistance to insulin action.

Synergistic effects of micromolar concentrations of Zn2+ and Ca2+ on membrane fusion

Resonance Energy Transfer between N-(7-nitro-2,1,3 benzoxadiazol -4 yl) phosphatidyl ethanolamine and N-Lissamine-Rhodamine B sulfonyl) phosphatidyl ethanolamine embedded in two different populations of small unilamellar vesicles made of phosphatidyl serine has been used to study the fusion process induced by Zn2+ and Ca2+. Lipid intermixing demonstrating fusion of liposome membranes can already be observed at 125 and 250 mumol/l of Zn2+. After short time pre-incubations with micromolar concentrations of Zn2+ as low as 150 mumol/l, Ca2+ induces an instantaneous increase of vesicle fusion. The lipid intermixing induced by micromolar concentrations of Ca2+ (250-500 mumol/l) could be increased up to 4 times when pre-incubated with 150 or 200 mumol/l of Zn2+. The effect of 1 mM of Ca2+ alone on lipid intermixing can be mimicked by 150 mumol/l of Zn2+ followed by 500 mumol/l of Ca2+. Our data demonstrate that Zn2+ and Ca2+ act synergistically to affect cation-induced membrane fusion. We suggest that Zn2+ specifically alters the physical state of phospholipid membranes making them more prone to calcium-triggered fusion.

The status of zinc in malaria (Plasmodium falciparum) infected human red blood cells: stage dependent accumulation, compartmentation and effect of dipicolinate

The inhibitory effect of metal chelators on intraerythrocytic malarial parasites imply that trace metal have a vital role in the biology of these organisms. In the present work X-ray fluorometry was used to study the status of zinc and iron in human red blood cells infected with Plasmodium falciparum in culture conditions. It was found that while the iron level remains constant throughout the parasite cell cycle, that of zinc increases in parallel with parasite maturation to reach a 2.3-fold higher level than that of uninfected red blood cells. Compartment analysis of infected red blood cells indicated that most of this gain was associated with the parasite and some with the host-cell membrane. Analysis of the malarial pigment showed that the zinc/iron ratio was similar to that of red blood cells, implying the this compound, which results from the digestion of host-cell cytosol, sequesters the zinc of host metalloenzymes. Dipicolinic acid (DPA), like other chelators, was found to inhibit the intracellular development of the parasite with an ED50 of 1 mM. DPA does not penetrate into normal red blood cells but readily permeates into infected cells, although it does not leach out their zinc. It is uncertain whether the inhibitory effect of DPA is exerted through alterations of host cell metabolism or by directly affecting that of the parasite. The putative receptors of zinc in the infected red blood cell are discussed.

Trace elements in nutrition of the elderly. 1. Established RDAs for iron, zinc, and iodine

Trace elements play a poorly understood role in human metabolism and nutrition. In the elderly, the normal effects of aging further complicate an understanding of trace element nutriture. The RDA standards established to date for the elderly have important limitations in that "healthy" persons 51 years of age and older constitute a single, regrettably imprecise category. Although any minor elemental constituent of the body is considered to be a trace element, only 16 are currently believed to be of biologic importance to humans. A recommended dietary allowance (RDA) has been established for only three of these--iron, zinc, and iodine.

Micromolar concentrations of Zn2+ potentiates Ca2+-induced phase separation of phosphatidyl serine containing liposomes

Fluorescence quenching of 1-acyl-2-[6[(7 nitro-2,1,3-benzoxadiazol-4yl) amino]caproyl] phosphatidyl choline in small unilamellar vesicles consisting of phosphatidyl serine has been used to monitor the lipid phase separation induced by Zn2+ and Ca2+. Phase separation of vesicle membranes was observed with Zn2+ at concentrations as low as 125 microM. Low concentrations of Zn2+ required long incubation times to reach maximal quenching (120 minutes at 375 microM). When low concentrations of Ca2+ were added to the preparation during the developing phase of Zn2+-induced quenching, an explosive increase in fluorescence quenching was instantenously observed. Phase separation induced by sub-millimolar concentrations of Ca2+ could be increased at least 4 times when vesicles were pre-incubated with 250 microM of Zn2+.

Pancreatic acinar cell function and morphology in rats fed zinc-deficient and marginal zinc-deficient diets

The prevalence of marginal zinc nutriture in several populations of people in this country and the lack of reports on the effect of marginal zinc nutriture in experimental animals prompted us to look at pancreatic acinar cell function and morphology in rats fed a zinc-deficient diet ad libitum: 4 and 50 ppm zinc-supplemented diets in amounts isocaloric to a zinc-deficient diet and Rodent-Blox fed ad libitum for a period of 49 +/- 1 (SEM) days. Because of a diminished rate of energy expenditure in zinc-deficient rats, animals receiving 50 ppm zinc-supplemented diets were offered less food, resulting in decreased body weight and pancreas weight, DNA, RNA, total protein, lipase, amylase, and secretion of protein. Specific changes due to zinc deficiency included (a) further decrease in body weight and (b) increase in content, specific activity, and secretion of lipase. Both the size and volume fraction of zymogen granules were reduced in zinc deficiency. The lumina of acinar and small ducts were collapsed with paucity of secretion products. Zinc deficiency may therefore lead to a defect in discharge mechanism. A further reduction in volume fraction of zymogen granules in the 4 ppm zinc-supplemented group was associated with increased secretion of serine proteases (trypsinogen and chymotrypsinogen), which constitute approximately 46% of total secretory protein in the pancreas under normal dietary conditions. This indicated an accelerated discharge due to an unknown mechanism. Changes in the secretion of digestive enzymes in the present study simulated ethanol-induced secretory alterations that were previously observed. Because abnormal zinc nutriture and chronic alcoholism are commonly associated, it is speculated that zinc deficiency may play a role in the ethanol-induced secretory alterations.

Effect of dietary zinc intake on the hematological profile of the rat

The effect of dietary zinc deficiency (imposed at weaning) on the hematological profile of the male rat was studied. Lack of dietary zinc resulted in elevated numbers of erythrocytes and segmented neutrophils and decreased reticulocyte number. The hematocrit of zinc-deficient rats was significantly elevated after the first week. The mean lifespan of erythrocytes from zinc-deficient rats (tested in adult control rats) was not significantly altered from that of controls. The lack of dietary zinc did not cause a major change in the erythrocyte density (age) distribution.