William J. Bettger

The physiological role of zinc as an antioxidant

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

Fatty acid analysis of blood plasma of patients with Alzheimer's disease, other types of dementia, and cognitive impairment.

Fatty acid differences, including docosahexaenoic acid (DHA; 22:6n-3) have been shown in the brains of Alzheimers patients (AD) as compared with normal age-matched individuals. Furthermore, low serum DHA is a significant risk factor for the development of AD. The relative concentration of DHA and other fatty acids, however, in the plasma of AD patients compared with patients with other kinds of dementias (other dementias; OD), patients who are cognitively impaired but nondemented (CIND), or normal patients is not known. In this study we analyzed the total phospholipid, phosphatidylcholine (PC), phosphatidylethanolamine (PE), and lysophosphatidylcholine (lysoPC) fractions of plasma from patients diagnosed with AD, OD, or CIND and compared them with a group of elderly control subjects with normal cognitive functioning. Plasma phospholipid and PC levels of 20:5n-3, DHA, total n-3 fatty acids, and the n-3/n-6 ratio were lower in the AD, OD, and CIND groups. Plasma phospholipid 24:0 was lower in the AD, OD, and CIND groups as compared with the group of control patients, and total n-6 fatty acid levels were higher in the AD and CIND groups only. In the plasma PE fraction, levels of 20:5n-3, DHA, and the total n-3 fatty acid levels were significantly lower in the AD, OD, and CIND groups. DHA levels were lower in the lysoPC fraction of CIND individuals only. There were no other differences in the fatty acid compositions of the different phospholipid fractions. Therefore, in AD, OD, and CIND individuals, low levels of n-3 fatty acids in the plasma may be a risk factor for cognitive impairment and/or dementia. Interestingly, a decreased level of plasma DHA was not limited to the AD patients but appears to be common in cognitive impairment with aging.

Erythrocytes, erythrocyte membranes, neutrophils and platelets as biopsy materials for the assessment of zinc status in humans.

During a controlled zinc depletion-repletion study, fifteen men aged 25.3 (SD 3.3) years were fed on a low-Zn diet with high phytate:Zn and phytate x calcium:Zn molar ratios for 7 weeks, followed by a 2 week repletion period when 30 mg supplemental Zn/d was given. Changes in plasma, urine, and hair Zn concentrations, taste acuity, and cellular immune response confirmed the development of mild Zn deficiency. Zn concentrations in neutrophils, platelets, erythrocytes and erythrocyte membranes, mean platelet volume, and activities of alkaline phosphatase (EC 3.1.3.1) and alpha-D-mannosidase (EC 3.2.1.24) in neutrophils did not respond to changes in Zn status. In contrast, alkaline phosphatase activity in erythrocyte membranes showed a significant decline which was consistent in all subjects (nmol product formed/min per mg protein; baseline v. 7-week Zn depletion, 0.656 (SD 0.279) v. 0.506 (SD 0.230), at 7 weeks; P < 0.05); neutral phosphatase activity remained unchanged. Alkaline phosphatase activity in erythrocyte membranes may be a potential index of Zn status in humans.

Effects of copper and zinc status of rats on the concentration of copper and zinc in the erythrocyte membrane

Abstract Short term, severe dietary zinc and copper deficiencies have been produced in young rats. Copper deficiency significantly depresses erythrocyte copper, 1.4 vs 3.4 μg/g protein, but does not affect erythrocyte membrane copper concentration. However, copper deficiency causes a significant increase in erythrocyte membrane zinc, 78 vs 60 μg/g protein. Dietary zinc deficiency causes a depression in erythrocyte membrane zinc, 41 vs 61 μg/g protein.

Chronic toxicity of dietary disodium arsenate heptahydrate to juvenile rainbow trout (Oncorhynchus mykiss).

Juvenile rainbow trout were fed semi-purified diets containing graded levels of disodium arsenate heptahydrate (DSA) for 12–24 weeks under standard laboratory conditions to define the maximum acceptable toxicant concentration (MATC) and to correlate signs of toxicity with diet and tissue arsenic concentrations. The MATC for DSA was between 13 and 33 μg As/g diet or 0.281–0.525 mg As/kg body weight/day. The most sensitive and reliable indicator of chronic dietary DSA toxicity in rainbow trout was chronic inflammation of the gallbladder wall. Chronic inflammatory changes in the sub-epithelial tissues of the gallbladder wall were evident in 71% of rainbow trout exposed to 33 μg As/g diet for 24 weeks, and 100% of rainbow trout exposed to 65 μg As/g diet for 24 weeks or 49 μg As/g diet for 12 weeks. No fish exposed to 13 μg As/g diet or less for up to 24 weeks showed any demonstrable gallbladder lesions or any other ill effect of arsenic exposure. Other signs of chronic dietary DSA toxicity to rainbow trout included decreased growth rate, mild to moderate anemia, and, at higher levels of exposure, active feed refusal leading to decreased feed consumption. Mild nephrocalcinosis was noted in one experiment where kidney arsenic residues exceeded 14 μg As/g tissue dry weight.

The distribution of zinc and copper in plasma, erythrocytes and erythrocyte membranes of rainbow trout (Salmo Gairdneri)

1. The zinc and copper concentration of plasma was determined in rainbow trout, lake trout, walleye and whitefish. 2. These fish had mean plasma zinc concentrations ranging from 9.3 to 15.1 ppm and copper concentrations from 0.6 to 1.3 ppm. 3. In rainbow trout, the concentration of zinc and copper is greater in the erythrocyte membrane than in the total erythrocyte. 4. Ultrafilterable plasma zinc and copper concentration in rainbow trout was determined to be 0.03 and 0.019 ppm, respectively. 5. Dialysis of rainbow trout plasma against 20 mM EDTA results in removal of 99% of the zinc and 88% of the copper from plasma proteins.

Calcium competes with zinc for a channel mechanism on the brush border membrane of piglet intestine.

Interactions between Ca(+2) and Zn(+2) at the intestinal brush border membrane occur via unclear mechanisms. We hypothesized that Zn(+2) and Ca(+2) are transported across the brush border membrane via a multidivalent metal channel. Using brush border membrane vesicles (BBMV) prepared from intestines of 8 sow-fed piglets, we sought to determine whether Ca(+2) competes with Zn(+2) for uptake. Extravesicular Zn(+2) was removed with ethylenediamine-tetraacetic acid. Time curves of Zn(+2) and Ca(+2) uptake by BBMV were conducted with increasing concentrations of Ca(+2) and Zn(+2), respectively. Saturation curves compared kinetic parameters of Zn(+2) uptake with and without Ca(+2). In addition, Zn(+2) uptake was measured in the presence of various classical Ca(+2) channel modulators. Over 20 min, a 0.4x concentration of Zn(+2) lowered Ca(+2) uptake by vesicles, whereas a 30x concentration of Ca(+2) was necessary to lower Zn(+2) uptake. These data suggest that Ca(+2) has lower affinity than Zn(+2) for a brush border membrane transport protein. Kinetic parameters showed higher K(m) values with 4 or 15 mM Ca(+2) but unchanged J(max), suggesting competitive inhibition. The Ca(+2) channel blocking agents, La(+3), Ba(+2), verapamil, and diltiazem, inhibited Zn(+2) uptake, whereas calcitriol, trans 1,2 cyclohexanediol, cis/trans 1,3 cyclohexanediol, and the L-type Ca(+2) channel agonist, Bay K8644, induced Zn(+2) uptake. These data were consistent with competition for a common transport mechanism on the brush border membrane, possibly a novel multimetal channel. Copyright 2001 Elsevier Science Inc.

Indices of iron and copper status during experimentally induced, marginal zinc deficiency in humans

This study examined the effect of diet-induced, marginal zinc deficiency for 7 wks in 15 men (aged 25.3±3.3 yrs; mean±SD) on selected indices of iron and copper status. The regimen involved lowzinc diets based on egg albumin and soy protein with added phytate and calcium such that mean [phytate]/[Zn] and [phytate]×[Ca]/[Zn] molar ratios were 209 and 4116, respectively, for 1 wk, followed by 70 and 2000, respectively, for 6 wks. Subjects were then repleted with 30 mg Zn/d for 2 wks. Plasma copper, Cu,Zn-superoxide dismutase (Cu, Zn-SOD) activity in plasma and red blood cells (RBC), hemoglobin, hematocrit, and serum ferritin were determined weekly on fasting blood samples. Significant reductions (p<0.05) after 7 wks in RBC Cu, Zn-superoxide dismutase (49.5±7.2 vs 33.6±6.3 U/mg Hb) and serum ferritin (69.2±38.7 vs 53.8±33.7 μg/L) occurred; no comparable decline was noted for plasma Cu, hemoglobin, or hematocrit. Significant (p<0.05) but less consistent changes were also observed in plasma superoxide dismutase activity. None of the changes were associated with the decreases in plasma, urinary and hair zinc concentrations, and alkaline phosphatase activity in RBC membranes. Results indicate that the biochemical iron and copper status of the subjects was marginally impaired, probably from the dietary regimen that induced marginal zinc deficiency.

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.

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 dietad libitum. Control rats were either pair-fed orad 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 pairfed 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.