Laboratory diagnosis of zinc deficiency

Laboratory Test Ordering Patterns in Pediatrics From Naturopaths and General Practitioners

OBJECTIVES

Naturopathic medicine emphasizes prevention and the self-healing process through natural therapies. Naturopathic doctors (NDs) use clinical laboratories as frequently as traditionally trained physicians. Here we evaluated the test-ordering patterns of NDs and general practitioners (GPs).

METHODS

A retrospective analysis was performed from a tertiary pediatric hospital. We analyzed tests ordered by NDs who used laboratory services and compared the test ordering patterns with GPs from adolescent medicine, family medicine, or pediatric clinics. Requests were categorized into 10 groups. We determined the tests with the highest ordering frequencies, as well as the percentage of tests that had an abnormal result.

RESULTS

NDs ordered more tests per patient per date of specimen collection compared with GPs. The most frequently ordered tests by NDs were trace elements and toxic metals (23.2% of total), allergens (21.8%), and general chemistry (15.3%). For the same test, the percentage of tests with an abnormal result was significantly lower for NDs than GPs.

CONCLUSIONS

We observed different ordering patterns between NDs and GPs. NDs ordered more esoteric tests and had lower rates of abnormal test results compared with GPs. Understanding the patterns of testing from different providers' specialties is useful to choose effective laboratory stewardship interventions.

The role of zinc in the prevention and treatment of nonalcoholic fatty liver disease

The zinc element is an essential nutrient for human health. Zinc is involved in the glucose, lipid, and protein metabolism and antioxidant processes in biological pathways. Zinc deficiency can lead to several chronic liver diseases. Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases where zinc deficiency plays a critical role in pathogenesis. Human and animal studies showed that both NAFLD risk factors (i.e., insulin resistance, diabetes mellitus, dyslipidemia, obesity, hypertension) and NAFLD itself are associated with decreased blood levels of zinc. Additionally, endoplasmic reticulum stress and inflammation due to unfolded protein response, inadequate dietary zinc intake, and decreased zinc absorption from the gastrointestinal tract can result in zinc deficiency leading to NAFLD. Herein, we reviewed the mechanistic links between zinc deficiency and NAFLD development and the role of zinc in the prevention and treatment of NAFLD.

The Effects of Psychological and Environmental Stress on Micronutrient Concentrations in the Body: A Review of the Evidence

Stress is the nonspecific response of the body to any demand for change. Excess or chronic psychological or environmental stress is associated with an increased risk of mental and physical diseases, with several mechanisms theorized to be associated with its detrimental effects. One underappreciated potential mechanism relates to the effects of psychological and environmental stress on micronutrient concentrations. Micronutrients (vitamins and minerals) are essential for optimal physical and mental function, with deficiencies associated with an array of diseases. In this article, animal and human studies investigating the effects of various psychological and environmental stressors on micronutrient concentrations are reviewed. In particular, the effects of psychological stress, sleep deprivation, and physical exercise on micronutrient concentrations and micronutrient excretion are summarized. Micronutrients identified in this review include magnesium, zinc, calcium, iron, and niacin. Overall, the bulk of evidence suggests stress can affect micronutrient concentrations, often leading to micronutrient depletion. However, before definitive conclusions about the effects of stress can be made, the impact of different stressors, stress severity, and acute versus chronic stress on micronutrient concentrations requires investigation. Moreover, the impact of stress on micronutrients in different populations varying in age, gender, and premorbid health status and the durability of changes after a stressor is resolved require examination. The medical, physical, and psychological implications of nutrient changes caused by a stressor also remain to be determined.

Zinc Nutritional Status in Patients with Cystic Fibrosis

BACKGROUND

Zinc is an essential nutrient for all forms of life and its deficiency affects the normal growth and development of human beings.

OBJECTIVE

The main aim was to investigate zinc nutritional status by serum zinc concentration (SZC) and dietary zinc intake and their association in cystic fibrosis (CF) patients.

METHODS

A cross-sectional study was conducted in CF patients. Anthropometric measurements and respiratory and pancreatic tests were conducted. Hypozincemia was determined by SZC while using atomic absorption spectrophotometry and dietary zinc deficiency by prospective 72-h dietary surveys.

RESULTS

Mean SZC (87.2 ± 16.7 μg/dL) and dietary zinc intake (97 ± 26.9% Dietary Reference Intake) were normal. Three of 17 patients with CF (17.6%) had hypozincemia and four (23.5%) had a dietary zinc deficiency. No patient with dietary zinc deficiency had hypozincemia. A positive and significant association was observed between SZC and Z-score of BMI-for-age (p = 0.048) and weight-for-height (p = 0.012) and between dietary zinc intake and energy intake (EI, p = 0.036) and Z-score of weight-for-high (p = 0.029).

CONCLUSION

SZC was associated with the nutritional status, expressed as BMI (Body Mass Index) and weight-for-height Z score, and dietary zinc intake with EI and weight-for-height Z-score. No patient with hypozincemia had dietary zinc deficiency. This situation should alert us to a marginal zinc deficiency and it may explain why there were no overlapping cases between the two groups. We suggest that probably 41% of the cases in this study would be at elevated risk of zinc deficiency and a zinc supplementation may be considered.

Identification of a Hemolysis Threshold That Increases Plasma and Serum Zinc Concentration

Background: Plasma or serum zinc concentration (PZC or SZC) is the primary measure of zinc status, but accurate sampling requires controlling for hemolysis to prevent leakage of zinc from erythrocytes. It is not established how much hemolysis can occur without changing PZC/SZC concentrations.Objective: This study determines a guideline for the level of hemolysis that can significantly elevate PZC/SZC.Methods: The effect of hemolysis on PZC/SZC was estimated by using standard hematologic variables and mineral content. The calculated hemolysis threshold was then compared with results from an in vitro study and a population survey. Hemolysis was assessed by hemoglobin and iron concentrations, direct spectrophotometry, and visual assessment of the plasma or serum. Zinc and iron concentrations were determined by inductively coupled plasma spectrometry.Results: A 5% increase in PZC/SZC was calculated to result from the lysis of 1.15% of the erythrocytes in whole blood, corresponding to ∼1 g hemoglobin/L added into the plasma or serum. Similarly, the addition of simulated hemolysate to control plasma in vitro caused a 5% increase in PZC when hemoglobin concentrations reached 1.18 ± 0.10 g/L. In addition, serum samples from a population nutritional survey were scored for hemolysis and analyzed for changes in SZC; samples with hemolysis in the range of 1-2.5 g hemoglobin/L showed an estimated increase in SZC of 6% compared with nonhemolyzed samples. Each approach indicated that a 5% increase in PZC/SZC occurs at ∼1 g hemoglobin/L in plasma or serum. This concentration of hemoglobin can be readily identified directly by chemical hemoglobin assays or indirectly by direct spectrophotometry or matching to a color scale.Conclusions: A threshold of 1 g hemoglobin/L is recommended for PZC/SZC measurements to avoid increases in zinc caused by hemolysis. The use of this threshold may improve zinc assessment for monitoring zinc status and nutritional interventions.

Pharmacokinetics and biodistribution of zinc-enriched yeast in rats

Zinc-enriched yeast (ZnY) and zinc sulfate (ZnSO4) are considered zinc (Zn) supplements currently available. The purpose of the investigation was to compare and evaluate pharmacokinetics and biodistribution of ZnY and ZnSO4 in rats. ZnY or ZnSO4 were orally administered to rats at a single dose of 4 mg Zn/kg and Zn levels in plasma and various tissues were determined using inductively coupled plasma-optical emission spectrometry. Maximum plasma concentration values were 3.87 and 2.81 μg/mL for ZnY and ZnSO4, respectively. Both ZnY and ZnSO4 were slowly eliminated with a half-life of over 7 h and bone had the highest Zn level in all tissues. Compared to ZnSO4, the relative bioavailability of ZnY was 138.4%, indicating that ZnY had a significantly higher bioavailability than ZnSO4.

Zinc supplementation as an adjunct to antibiotics in the treatment of pneumonia in children 2 to 59 months of age

BACKGROUND

Diarrhoeal disorders and acute respiratory infections (ARIs), especially pneumonia, are the most common causes of death in low-income countries. Studies evaluating the impact of zinc supplementation as an adjunct in the management of pneumonia are limited and have shown variable results.

OBJECTIVES

To evaluate zinc supplementation, as an adjunct to antibiotics, in the treatment (clinical recovery) of pneumonia in children aged two to 59 months.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), which contains the Cochrane Acute Respiratory Infections (ARI) Group's and the Cochrane Infectious Diseases Group's Specialised Registers, MEDLINE (1950 to March week 2, 2011), EMBASE (1974 to March 2011), CINAHL (1981 to March 2011), LILACS (1985 to March 2011), AMED (1985 to March 2011), CAB Abstracts (1910 to March 2011) and Web of Science (2000 to March 2011).

SELECTION CRITERIA

Randomised control trials (RCTs) evaluating supplementation of zinc as an adjunct to antibiotics for pneumonia in children aged two to 59 months.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility and screened all available titles and abstracts for inclusion. If the relevance could not be ascertained by screening the title and abstract, we retrieved and reviewed the full text of the article.

MAIN RESULTS

We included four trials in which 3267 children aged two to 35 months participated. Analysis showed that zinc supplementation in addition to standard antibiotic therapy in children with severe and non-severe pneumonia failed to show a statistically significant effect on clinical recovery (risk ratio (RR) 1.02; 95% confidence interval (CI) 0.93 to 1.11). Similary, zinc supplementation in children with severe pneumonia, as an adjunct to standard antibiotic therapy, did not show a statistically significant effect on clinical recovery measured as resolution of tachypnoea (respiratory rate > 50 breaths per minute) (RR 1.13; 95% CI 0.82 to 1.57) and cessation of chest indrawing (RR 1.08; 95% CI 0.88 to 1.31) as compared to the control group. Zinc supplementation in children with severe pneumonia also showed a non-significant effect on the duration of hospitalization stay as compared to the control (RR 1.04; 95% CI 0.89 to 1.22).

AUTHORS' CONCLUSIONS

Evidence provided in this review is insufficient to recommend the use of zinc as an adjunct to standard antibiotic therapy for pneumonia in children aged two to 35 months.

Serum levels of Cu, Se, and Zn in adult rural/urban residents in Ghana: paradigm shift?

Deficiencies in Cu, Se, and Zn impair one or more biochemical functions, and excess are associated with toxicity. Baseline studies on the Ghanaian population are scanty. The study was undertaken to determine whether significant rural/urban differences in the serum levels of Cu, Se, and Zn did exist. Forty males/60 females from rural and 50 males/50 females from urban Ghanaian communities were sampled. Serum Cu, Se, and Zn were determined using flame atomic absorption spectrometry. Cu level for rural and urban subjects was 997 +/- 333 and 979 +/- 290 microg/L, respectively (p = 0.68). However, Cu levels were significantly higher in the rural females (1,063 +/- 367 microg/L) than the rural males (898 +/- 249 microg/L; p = 0.0085). Se levels for rural/urban subjects were 97 +/- 36 and 87 +/- 31 microg/L, respectively (p = 0.03). Zn levels in the rural/urban subjects were 312 +/- 218 and 150 +/- 102 microg/L, respectively (p = 0.002). Additionally, Zn was significantly higher in rural females (428 +/- 204 microg/L) than the urban females (166 +/- 103 microg/L; p = 0.0002). Finally, Zn was significantly higher in rural females (428 +/- 204 microg/L) than males (172 +/- 116 microg/L; p = 0.0028). In conclusion, Cu, Se, and Zn were higher in the rural group compared to the urban group, and the generally low Zn levels were confirmed in another cohort follow-up study.

Determinants of serum zinc concentrations in a population of French middle-age subjects (SU.VI.MAX cohort)

BACKGROUND/OBJECTIVES

Few studies have been conducted on determinants of serum zinc concentration, especially in France. The aim of this study was to investigate the relationships between serum zinc concentrations, and age, education, living area and life style in a large sample cohort of French adults.

SUBJECTS/METHODS

Blood samples were collected after 12-h fasting in French adults (7448 women, 35-65 years old and 4926 men, 45-65 years old) participating to the SUpplementation in AntioXidant VItamins and Minerals cohort at enrolment. Serum zinc was determined by flame atomic absorption.

RESULTS

Serum zinc concentration was lower in women (mean: 12.9 μmol/l, 95% confidence interval: 9.2-16.6 μmol/l) compared with men (mean: 13.4 μmol/l, 95% confidence interval: 9.7-17.1 μmol/l, P<0.0001). In total, 10% of the women showed serum zinc values <10.7 μmol/l and 10% of the men showed serum zinc values <11.3 μmol/l. Age was negatively associated with serum zinc only in men (P=0.001). In women, a positive association between smoking and serum zinc concentration (P=0.0003), and a negative relationship between highest education level and serum zinc concentration (P=0.01) were observed. With regard to geographical areas, the highest serum zinc concentrations were found in the Center, and the lowest in the Southwest of France for both men and women. The association between serum zinc concentrations and food categories or macronutrient intake disappeared after stratifying by gender.

CONCLUSIONS

Age, gender and geographic area seem the main determinants of serum zinc concentrations in this study.

The effects of CCl4 on Na+/K+-ATPase and trace elements in rats

CCl4 is an industrial agent with known toxic effects on the environment. There are so many studies about hepatotoxic effects of CCl4. We herein studied the effects of CCl4 on Na+/K+-ATPase and Ca2+/Mg2+-ATPase activities on erythrocyte membranes and trace element levels of serum erythrocyte and liver tissue of rats. Study was performed on control group (group C, n=8) and a study group (group S, n=8) in which CCl4 was given. Na+/K+-ATPase and Ca2+/Mg2+-ATPase were significantly reduced in CCl4-treated group (p<0.01, p<0.001). Trace element levels also showed statistically significant differences in CCl4-treated group. Membrane Na+/K+-ATPase and Ca2+/Mg2+-ATPase activities were diminished due to CCl4-induced injury on erythrocyte membranes. CCl4 also changed the trace element levels of serum erythrocyte membrane and liver by altering the mineral substance concentrations.

A Novel Zinc Compound (Zinc Monocysteine) Enhances the Antioxidant Capacity of Human Retinal Pigment Epithelial Cells

PURPOSE

The aim of this study was to document the effect of a novel zinc amino acid combination on the concentrations of important antioxidants in cultured human retinal pigment epithelial (hRPE) cells.

METHODS

Primary confluent hRPE cells were treated with 30 microM of zinc acetate, zinc chloride, zinc cysteine, and zinc sulfate. The antioxidants catalase, glutathione, glutathione peroxidase, and metallothionein were measured. MTT assays were performed to determine the relative protection of the zinc compounds from the cytotoxic effects of H202 and t-butyl hydroperoxide.

RESULTS

Catalase and glutathione peroxidase activities were increased by the zinc formulations compared with the untreated control. Glutathione and metallothionein content were also increased. The greatest increases occurred with zinc conjugated to the amino acid cysteine. The MTT assays showed that zinc monocysteine protected cultured RPE cells from the toxicity of H2O2 and t-butyl hydroperoxide.

CONCLUSIONS

Our results demonstrate that zinc treatment of RPE cells increases antioxidants and protects cultured RPE cells from the cytotoxic effects of H2O2 and t-butyl hydroperoxide. The results show that zinc conjugated to cysteine offers greater benefits than either zinc salts or cysteine alone.

Effects of zinc deficiency on oral and periodontal diseases in rats

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate the alterations of oral and periodontal tissues in zinc-deficient rats compared with control rats.

MATERIAL AND METHODS

The study was carried out on 14 Sprague-Dawley rats, cessation of lactation on the 24th day after birth. Rats were randomly divided into two groups. Group I rats were fed with a zinc-deficient diet and group II rats were fed with a zinc-containing diet. At the end of the fourth week on experimental diets, alterations of the oral tissues in both groups were recorded. In addition, the gingival index (GI-Löe-Silness), plaque index (PI-Silness-Löe) and periodontal pocket depth scores were recorded in order to assess periodontal tissue health in the rats. Then, blood samples were taken and the serum zinc levels measured by atomic absorption spectrophotometry. At the end of the experiment, oral tissue samples were investigated by light microscopy. Finally, the results of the two groups were compared by using the Student's t-test.

RESULTS

The effects of zinc deficiency were observed at 10-16 d in rats. Although body weight, body length and tail length were retarded in zinc-deficient rats, they were advanced in rats fed with a zinc-containing diet. The mean plaque index and gingival index for group II rats were significantly lower than for group I rats (p<0.001), but there was no significant difference regarding pocket depth between the two groups of rats (p>0.05). Aphthous ulcer was often seen in the study group, where it was observed on the alveolar mucosa with a high rate of 29.9%. According to histological findings, there was no difference related to the epithelial keratinization of the hard palate between the two groups. However, hyperkeratosis was found on the dorsal surface of the tongue in zinc-deficient rats.

CONCLUSION

The findings indicated that oral health was better in group II rats (those fed with a zinc-containing diet) than in group I (zinc-deficient) rats. Hyperkeratinization was more prominent in zinc-deficient rats. We suggest that zinc deficiency is a potential risk factor for oral and periodontal diseases.

Cytotoxic effects of intra and extracellular zinc chelation on human breast cancer cells

Zinc is an essential trace element with cofactor functions in a large number of proteins of intermediary metabolism, hormone secretion pathways, immune defence mechanisms, and as a cofactor of transcription factors it is also involved in the control of gene expression. Our study demonstrates that the modulation of intra and extracellular zinc alone is sufficient to induce metabolic changes or even apoptosis in two model human breast cancer cell lines MCF-7 and MDA-MB468. Treatment of breast cancer cells with different concentrations of a cell membrane permeable zinc chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and the membrane impermeable zinc chelator, diethylenetriaminepentacetic acid, (DTPA) resulted in a significant increase of cell death. Features of apoptosis, such as chromatin condensation and nuclear fragmentation accompanied the DTPA and TPEN-induced cell death. A significant increase in the activity of caspase-9 was observed in both cell lines; whereas, caspase-3 activity was only increased in MDA-MB468 cells since caspase-3 is not expressed in MCF-7 cells. Caspase-8 activation was negligible in both cell lines. Addition of Zn(2+) or Cu(2+) prevented DTPA and TPEN-induced cytotoxicity, indicating that both bivalent cations can be replaced functionally to a certain extent in our experimental system. Interestingly, addition of Ca(2+), or Mg(2+) had no effect. The antioxidant N-Acetyl-L-Cysteine inhibited the cytotoxic effect of DTPA and TPEN, indicating that oxidative stress is the likely mediator of Zn-deficiency-related cell death.

Zinc metabolism in airway epithelium and airway inflammation: basic mechanisms and clinical targets. A review

In addition to basic housekeeping roles in metalloenzymes and transcription factors, dietary zinc (Zn) is an important immunoregulatory agent, growth cofactor, and cytoprotectant with anti-oxidant, anti-apoptotic, and anti-inflammatory roles. These properties of Zn are of particular importance in maintaining homeostasis of epithelial tissues which are at the front line of defense. This review is about the role of Zn in airway epithelium (AE). The first part focuses on the cellular biology of Zn, and what is known about its distribution and function in AE. The second part of the review considers evidence for altered Zn metabolism in asthma and other chronic diseases of airway inflammation. Important issues arise from a potential therapeutic perspective as to the optimal ways to monitor circulating and epithelial Zn levels in patients and the most effective means of supplementing these levels.

Predictors of plasma zinc concentrations in children with acute diarrhea

BACKGROUND

Plasma and serum zinc concentrations are the most widely used markers of zinc status in individual persons and populations.

OBJECTIVE

The objective was to identify factors that influence plasma zinc concentrations during acute childhood diarrhea.

DESIGN

This was a cross-sectional study of 1757 cases of acute diarrhea in 6-35-mo-old Nepalese children. The association between plasma zinc concentration and several clinical, anthropometric, socioeconomic, and biochemical variables was estimated in simple and multiple linear regression analyses.

RESULTS

We observed a reduction in the mean plasma zinc concentration of 0.59 (95% CI: 0.44, 0.74) micro mol/L per degree ( degrees C) increase in axillary temperature. Having dysentery and an elevated plasma C-reactive protein concentration was also independently associated with lower plasma zinc. Children with clinical features of dehydration had higher plasma zinc concentrations than did those who were not dehydrated. Furthermore, a decrease in plasma albumin of 1 g/L was associated with a decrease in plasma zinc of 0.25 (95% CI: 0.21, 0.29) micro mol/L. The plasma albumin concentration confounded the associations between some clinical variables and plasma zinc, but the association between axillary temperature and dehydration on one hand and plasma zinc on the other was not substantially influenced by the albumin concentration. Moreover, the plasma zinc concentration increased with an increase in observed hemolysis.

CONCLUSIONS

Dehydration, clinical and biochemical indicators of inflammation and hemolysis, and, when possible, plasma albumin concentrations should be taken into account when the plasma zinc concentration is used to estimate zinc status during episodes of diarrhea in childhood.

Biomarkers of trace mineral intake and status

The emerging public health importance of zinc and selenium and the continuing public health challenges of iron and iodine draw attention to the unmet need for improved biomarkers of trace element status. Currently available biomarkers of these four trace elements are critiqued including the outstanding lack of satisfactory biomarkers for the assessment of zinc intake and status. Other trace elements are reviewed briefly including copper, for which human dietary deficiencies and excesses have been documented, and chromium, which is of possible but unconfirmed public health significance. Evolving strategies of considerable potential include molecular techniques such as the measurement of metallothionein mRNA in lymphocytes as a biomarker of zinc status, an assay that can now be performed with a dried blood spot. The judicious application of tracer techniques also has a role in advancing the quality of zinc biomarkers. Also of special current interest is full definition of the potential of plasma-soluble transferrin receptor concentrations as the biomarker of choice for the detection of early functional iron deficiency.

Effects of zinc on the reactive oxygen species generating capacity of human neutrophils and on the serum opsonic activity in vitro

To investigate the effects of zinc on non-specific immune functions, we used the chemiluminescence method to examine the capacity of human neutrophils to produce reactive oxygen species and accompanying serum opsonic activity. When neutrophils were stimulated with both opsonized zymosan and phorbol myristate acetate in the presence of 1-10(-3) mmol/L zinc lucigenin-dependent CL responses were stable or declined, whereas luminol-dependent CL responses were significantly enhanced. The results suggest that zinc activates protein kinase C and promotes MPO degranulation and ROS metabolism, especially in hypochlorous acid production, which have the direct action of causing microbial death. Further, the lucigen-dependent CL response stimulated with OZ was strongly enhanced by anti-MPO antibodies, whereas the enhancement was less in the presence of zinc, suggesting that zinc may suppress the receptor-mediated signal transduction process. Both responses were inhibited at 10 mmol/L. Serum opsonic activity was enhanced by zinc at 10(-4) and 10(-3) mmol/L but reduced at 10 mmol/L. These data indicate that addition of zinc around and above normal physiological concentrations facilitates neutrophil functional activity and serum opsonic activity, whereas these are inhibited by a lack of zinc or an excessive amount, suggesting that zinc is essential for optimal functioning of non-specific immunity.

Depletion of intracellular zinc induces macromolecule synthesis- and caspase-dependent apoptosis of cultured retinal cells

Although zinc deficiency may contribute to age-related macular degeneration (ARMD), the pathogenic mechanism is as yet uncertain. In light of evidence that cellular zinc depletion induces apoptosis in cortical neurons and thymocytes, in the present study, we examined the possibility that the same phenomenon occurs also in retinal cells. Exposure of primary retinal cell cultures to 1-3 microM of a cell membrane-permeant zinc chelator TPEN for 24 h induced concentration-dependent death of neurons, photoreceptor cells, and astrocytes. Addition of zinc or copper reversed TPEN toxicity to all cell components, indicating the particular involvement of zinc chelation in cell death. Consistent with apoptosis, oligonucleosomal DNA fragmentation and chromatin condensation accompanied, and the protein synthesis inhibitor cycloheximide blocked the TPEN-induced retinal cell death. During TPEN-induced retinal cell apoptosis, cleavage/activation of procaspase-1, but little of procaspase-3, was observed. Consistent with this finding, a broad-spectrum caspase inhibitor (zVAD-fmk) was significantly more protective than a caspase-3-selective inhibitor (DEVD-fmk). The present study has demonstrated that depletion of intracellular zinc is sufficient to induce macromolecule synthesis- and caspase-dependent apoptosis of cultured retinal cells. In light of the possibility that zinc depletion may contribute to the pathogenesis of ARMD, the current culture model may be a useful tool for the investigation of the mechanism of zinc depletion-induced retinal cell death.

[Diagnosis of zinc deficiency]

Though far more common, particularly in elderly people, than was previously assumed, marginal zinc deficiency does not lead to the classical manifestations of zinc deficiency and is therefore difficult to diagnose. There is therefore a need for sensitive parameters that can reliably demonstrate even marginal zinc deficiency, as suboptimal zinc status can seriously impair human health, performance, reproductive functions, and mental and physical development. The most important criteria for the diagnosis of zinc deficiency are critically discussed. The laboratory parameters currently considered to be the most useful indicators of marginal zinc deficiency are zinc-binding capacity and serum/plasma alkaline phosphatase activity before and after zinc supplementation (zinc tolerance test!). In order to obtain a reliable assessment of a patients zinc status, a number of different diagnostic parameters should always be measured.

The localization of endogenous zinc and the in vitro effect of exogenous zinc on the GABA immunoreactivity and formation of reactive oxygen species in the retina

1. Endogenous zinc is localized mainly in the retinal photoreceptors and retinal pigment epithelial cells in the mammalian retina. No other types of retinal neurons contain large amounts of zinc. 2. Low concentrations of exogenous zinc, like the N-methyl-D-aspartate (NMDA) antagonist MK-801, counteract the NMDA-induced changes in the gamma-aminobutyric acid (GABA) immunoreactivity in the rabbit retina. However, greater concentrations of zinc exacerbate the effects of NMDA and ischemic-like insults (lack of glucose and oxygen) on GABA immunoreactivity. The data suggest that low concentrations of zinc are neuroprotective, but higher concentrations of zinc have a negative effect. 3. When low concentrations of zinc are present during ischemic-like insults to the retina, the GABA immunoreactivity is localized to the Müller cells, suggesting that the metabolism of GABA in the Müller glial cells is prevented. 4. Ascorbate/iron-induced generation of reactive oxygen species (ROS) in the retina is prevented by deferoxamine but not by zinc. High concentrations of zinc potentiate the ascorbate/iron induced formation of ROS.

Influence of zinc on selected cellular functions of cultured human retinal pigment epithelium

Zinc is a necessary micronutrient, usually abundant in human RPE. Our study was undertaken to determine the effects of short-term, zinc deficiency on human retinal pigment epithelium (RPE) using a culture model of fetal human RPE cells. Human fetal RPE cells were isolated and cultured in Coon's modified Ham's F-12 medium. For zinc depletion studies, cells were cultured for 1 week in Chelex-treated Dulbecco's modified Eagle's medium containing low (0.25 microM) or physiologic (11 microM) total zinc concentrations as determined by flame atomic absorption spectroscopy. Protein synthesis was determined by incorporation of 35S-cysteine/methionine and labeled proteins analysed by polyacrylamide gel electrophoresis. Several cell parameters and enzymes were significantly reduced below control when cultured in low zinc: zinc content (40%), proliferation (63%), protein/well (50%), catalase activity (68%), alkaline phosphatase activity (61%), alpha-mannosidase activity (68%), and metallothionein (82%). No statistically significant decline was seen in acid phosphatase activity, superoxide dismutase activity, glutathione peroxidase activity and dexamethasone induction of metallothionein. Zinc repletion (100 microM, 1 h) increased catalase and alpha-mannosidase activities from 32% and 33% of control to 75% and 73%, respectively. Cycloheximide did not inhibit this short-term zinc-induced repletion of catalase or alpha-mannosidase. Protein synthesis in low zinc medium was depressed, but not significantly, as shown by incorporation of radiolabeled 35S-cysteine/methionine into newly synthesized proteins. The effects of zinc deficiency in cultured human RPE are selective. Adequate intracellular zinc was required for maximal activity of some enzymes. The dependence of catalase activity on zinc was not predicted and may help explain the observed decline in catalase activity seen with age in RPE. Our model of zinc deficiency should prove useful in elucidating the complex effects of zinc deficiency and repletion in human RPE.

Zinc, human diseases and aging

Zinc is one of the most important trace elements in the body for many biological functions; it is required as a catalytic component for more than 200 enzymes, and as a structural constituent of many proteins, hormones, neuropeptides, hormone receptors, and probably polynucleotides. Due to its role in cell division and differentiation, programmed cell death, gene transcription, biomembrane functioning and obviously many enzymatic activities, zinc is considered a major element in assuring the correct functioning of an organism, from the very first embryonic stages to the last periods of life. This biological role together with the many factors that modulate zinc turnover explains on one hand, the variety of clinical and laboratory signs resulting from its reduced bioavailability, and on the other, the high number of human pathologies characterized by alterations in the zinc pool. As zinc supplementation is efficacious in most of these conditions, it is regarded more as an oriented therapeutical support, than a simple dietary integrator. Furthermore, the relevance of zinc status to many age-associated diseases and, according to experimental studies, the aging itself of the major homeostatic mechanisms of the body, i.e., the nervous, neuroendocrine and immune systems, places zinc in a pivotal position in the economy of the aging organism.

Marginal zinc deficiency in older adults: responsiveness of zinc status indicators

OBJECTIVE

Suspicions that mild zinc deficiency is common among the elderly cannot be confirmed or refuted because definitive indicators of zinc status are lacking. The goal of this study was to document the clinical responsiveness of parameters of zinc status in a group of older adults consuming a carefully controlled diet: first moderately low in zinc (3.97 mg/day for 15 days) and then high in zinc (28.19 mg/day for 6 days).

METHODS

Fifteen older adults (mean age = 66.6 yrs) volunteered to consume a marginally zinc-deficient diet for 15 days followed by 6 days of zinc repletion. Plasma concentrations of erythrocyte metallothionein and the enzyme 5'-nucleotidase, as well as levels of zinc, alkaline phosphatase, copper and ceruloplasmin were measured before and after zinc depletion and repletion.

RESULTS

Plasma zinc levels were not altered during the study. Alkaline phosphatase (AP) values did not change in the expected direction, although a small decrease in AP following zinc repletion was statistically significant. Erythrocyte metallothionein results followed a pattern similar to that of alkaline phosphatase, little change, but a small, statistically significant drop after zinc repletion. As expected, there were no diet-associated changes in plasma copper and ceruloplasmin levels. In contrast, plasma concentrations of the enzyme 5'-nucleotidase decreased (p < 0.01) from 2.7 +/- 0.5 to 1.1 +/- 0.5 U during zinc depletion and increased (p < 0.05) to 2.2 +/- 0.4 U after 6 days of repletion.

CONCLUSIONS

Mild zinc deficiency is difficult to detect. In this study, traditional indicators such as plasma zinc and alkaline phosphatase did not change as would be expected in response to alterations in zinc intake. Likewise, erythrocyte metallothionein did not respond to altered zinc intakes as expected but this factor may reflect long-standing or more severe zinc depletion and thus requires additional study. Activity of the enzyme 5'-nucleotidase appears responsive to acute changes in zinc intake; however, more work is needed to define how well these activities will reflect zinc intake in other types of subjects.

Comparison between total and ultrafiltrable serum zinc as test to diagnose zinc deficiency in infants and children

Total Serum Zinc (TSZn) and albumin were determined, and low molecular weight serum Zn measured by radiochemical UltraFiltration (UFSZn) in healthy Dutch infants and children, and in samples obtained from those with diseases that are expected to alter TSZn. Our control TSZn values, 10.2 +/- 3.5 mumol/L, were low compared to those reported in the literature. Variation in serum albumin could not explain this: No correlation of TSZn with serum albumin was found (p > 0.5). Likely explanations are the nonfasting state and the stress owing to hospital surroundings at the time of sampling. A range of other influences not registered may be active and are discussed. No significant age-dependence was found (p < 0.8). Boys over 9 yr of age showed higher TSZn compared with girls of the same age (p < 0.08). In a separate experiment a 17% decrease in TSZn was demonstrated by food intake (eggs). These results support the opinion that TSZn is of little value to measure Zn status. There was no discrimination in TSZn between healthy subjects and patients. Our UFSZn values, 0.28 +/- 0.13 mumol/L in the controls as well as in the patients, were correlated with TSZn and therefore not a suitable alternative for the measurement of TSZn as parameter to determine the Zn status. The UFSZn was not correlated with serum albumin (p < 0.7). UFSZn values were higher in infants (p < 0.01), no sex dependence was found. We conclude that TSZn as well as UFSZn are of limited clinical relevance.

Increased plasma pyridoxal-5'-phosphate when alkaline phosphatase activity is reduced in moderately zinc-deficient rats

It is generally believed that the zinc metalloenzyme alkaline phosphatase is required to hydrolyze phosphorylated forms of vitamin B-6 prior to their use. To test this hypothesis, rats were fed a liquid diet containing either adequate or moderately low zinc during gestation and lactation. Zinc deficiency was produced in dams evidenced by significant reductions in zinc concentration of plasma (49%), liver (25%), and femur (24%), and plasma alkaline phosphatase activity (48%). Plasma pyridoxal-5'-phosphate (PLP), which significantly increased (61%) in these same rats, was negatively correlated (r = -0.74, P < 0.02) with plasma alkaline phosphatase activity. Maternal liver PLP concentration was unaffected by zinc status. The zinc and vitamin B-6 relationship seen in dams was less observable in offspring. Stimulation of erythrocyte alanine aminotransferase activity by exogenously added PLP in vitro tended to be higher in both moderately zinc-deficient mothers and their offspring, but the difference was not significant. Our results support the hypothesis that alkaline phosphatase activity is required for the hydrolysis of plasma PLP. Our results also suggest that zinc status as alkaline phosphatase activity should be defined in an individual if plasma PLP is to be used as an indicator of vitamin B-6 status.

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.

Recurrent aphthous ulceration with zinc deficiency and cellular immune deficiency

Zinc deficiency (serum zinc level 65 micrograms/dl) and cellular immune deficiency (confirmed by lymphoblastic transformation assay) were found in a 15-year-old boy who had had recurrent aphthous ulceration for 6 years. Despite the previous therapy (orally administered steroid, isoprinosine, interferon, lysozyme, and local treatment), the ulcers recurred monthly. After 3 months of zinc therapy (50 mg zinc sulfate orally three times daily) the aphthae disappeared and did not reappear for 1 year. The lymphoblastic transformation activity and serum zinc levels were also normalized with this treatment.

Overt hepatic encephalopathy precipitated by zinc deficiency

Encephalopathy in liver disease may be unresponsive to protein restriction, lactulose, and neomycin. Zinc supplements have been reported to improve psychometric performance in liver cirrhosis, but the importance of zinc deficiency in overt hepatic encephalopathy has not yet been clearly established. A patient with severe recurrent hepatic encephalopathy was studied to determine the relation between her signs of encephalopathy and zinc deficiency. The study included a period in which zinc deficiency was artificially induced by oral histidine. An episode of overt encephalopathy occurred that was identical to earlier episodes and responded to oral zinc. The study showed an association between encephalopathy and zinc deficiency by successive zinc depletion and supplementation regimens. Long-term zinc supplementation improved severe recurrent hepatic encephalopathy and therefore the quality of life.

Clinical and laboratory diagnosis of acrodermatitis enteropathica

Acrodermatitis enteropathica is an inborn error of metabolism resulting in zinc malabsorption and severe zinc deficiency. From personal experience and a literature review the following conclusions were drawn: 1. Symptoms other than dermatitis, vary with age. Diarrhoea, mood changes, anorexia, and neurological disturbance were reported most frequently in infancy. Growth retardation, alopecia, weight loss and recurrent infections were prevalent in toddlers and schoolchildren. Spontaneous remission may occur at adolescence. 2. The severity of symptoms also varies. Intermittent or mild cases of the disease and those presenting with uncommon features such as ophthalmic, cerebral or hepatic involvement, are easily overlooked. In the severe cases this may result in a fatal outcome. If untreated, the overall mortality rate is 20%, being higher in males. 3. The laboratory diagnosis is hazardous. In patients, mean zinc values in serum, urine and hair were ca. 50% of normal levels. There is a 15% overlap with healthy controls; moreover, low zinc levels in serum, urine or hair are also found in other diseases. A more specific test is required. 4. In cases of doubt, in vitro or in vivo zinc absorption tests using radioisotopes (65Zn or 69mZn) may be performed. These appear not to be influenced by other conditions and show less overlap with controls. If such tests are unavailable, the clinical response to 3-30 mumol zinc/kg per day for 5 days may be awaited. This is recommended in infants or children with one or more symptoms of acrodermatitis enteropathica.

Concentration of zinc and zinc-copper superoxide dismutase activity in red blood cells in normals and children with cancer

Zinc concentrations and Cu, Zn superoxide dismutase activity in erythrocytes were investigated in 138 healthy children and in 35 children with cancer. The mean zinc concentration in the erythrocytes of healthy children was found to be age-dependent. In the youngest group (children up to 1 year of age) the zinc concentration in erythrocytes is 18.8 +/- 3.4 micrograms/g Hb (5.89 +/- 1.23 mg/l packed cells), which is significantly lower than in other age groups. A strong logarithmic correlation (r = 0.327, p less than 0.0001 and r = 0.436, p less than 0.00001) was found between age and zinc concentration in erythrocytes, expressed as microgram/g Hb and as mg/l packed red cells, respectively. Cancer children were divided into two groups (neuro- and nephroblastoma). In the group of children with neuroblastoma no statistical differences in zinc concentration or enzyme activity were observed. In the patients with nephroblastoma, significantly higher zinc concentrations (p less than 0.05) were observed in erythrocytes. The changes of zinc concentration are accompanied by significant (p less than 0.02) decreases of enzyme activity. In this group of cancer children, statistically significant differences were observed in the zinc concentrations in erythrocytes (microgram/g Hb) between the second and the third stages of the disease. No correlation was observed between the concentration of zinc and enzyme activity in healthy children or in cancer children.

Trace mineral balance during acute diarrhea in infants

To evaluate the magnitude of copper and zinc losses during acute diarrhea requiring hospitalization, we studied 14 infants, 3 to 14 months of age, and compared them with a control group of 15 infants of similar age, birth weight, and nutritional status. Metabolic balance studies were conducted in the study group during an initial 48 hours (period 1) and on days 6 and 7 after admission (period 2). The control group was studied after recovery from respiratory disease. Copper and zinc content of feces, urine, and food samples was measured by atomic absorption spectrophotometry. Mean (+/- SD) fecal losses were higher for period 1 in the diarrhea group than in control subjects: Cu 55.7 +/- 21.2 versus 28.8 +/- 6.7 micrograms/kg/body weight/day (p less than 0.01); Zn 159.4 +/- 59.9 versus 47.4 +/- 6.4 micrograms/kg/day (p less than 0.0001). For period 2, Zn losses were similar in both groups, but Cu balance remained negative only in the study group. Retention of Zn for the study group went from -21.2 +/- 46.7 in period 1 to 204.5 +/- 103.0 micrograms/kg/day in period 2 (p less than 0.0001), and fecal weight decreased from 70.5 +/- 20.6 in period 1 to 36.8 +/- 20.0 gm/kg/day in period 2. Fecal weight and fecal losses were correlated: r = 0.71 (p less than 0.01) for Cu and r = 0.81 (p less than 0.001) for Zn. Plasma mean Cu and Zn levels were low in period 1 but rose in period 2, especially for Zn. A negative correlation was found between fecal Zn losses and plasma Zn: r = 0.74 (p less than 0.001). We conclude that acute diarrhea leads to Cu and Zn depletion and that plasma levels and Cu balance remain abnormal a week after admission.

The effect of maternal smoking on the relationship between maternal and fetal zinc status and infant birth weight

We have previously reported a trapping of zinc in the placenta directly related to circulating cadmium that comes from cigarette smoke. The purpose of this study was to examine in detail the effect of smoking on (a) the relationship between maternal and fetal zinc status and (b) the relationship between zinc status and birth weight. One hundred and eighteen smokers and 172 nonsmokers without any medical complications during pregnancy were studied. Atomic absorption spectroscopy was used to assess zinc status in maternal and cord vein plasma and red blood cells. Plasma alkaline phosphatase was also determined as an index of zinc status. Thiocyanate was used as an index of smoking status. The data were analyzed using univariate correlations and repeated measures analysis of variance. Infants of smokers had a statistically significant decrease in plasma zinc (5%), alkaline phosphatase (13%), and in cord vein RBC zinc (12%). Furthermore, the results showed an altered relationship between maternal and fetal indices of zinc status and zinc status and birth weight due to maternal smoking. The infant of the nonsmoking mother appears to be able to maintain adequate zinc status due to depletion of maternal zinc. However, it appears that the infant of the smoking mother may be marginally zinc deficient. These findings support studies of zinc supplementation in the pregnancy complicated by smoking.

Determination of zinc in blood serum by electrothermal atomic absorption spectrometry with matrix modification

Zinc determination in serum microsamples can be treated by graphite furnace atomic absorption spectrometry. To reduce the contamination risks and to obtain results as right as possible, the serum has been twenty fold diluted instead of 100-fold diluted (rate frequently obtained). In these conditions, the use as diluent of a 1% Triton X 100 solution or of a 33.7 mmol/l magnesium nitrate did not allow to obtain exact results. Yet, with an 37.8 mmol/l ammonium phosphate solution, the results given by the direct calibration on an aqueous calibration curve were in good accordance with those found with a recommended flame atomic absorption spectrometry method. The within-run RSD of our method was 2.6%.

Esophageal zinc content in human squamous esophageal cancer

Zinc and vitamin A are known to interact, and deficiencies have been associated with carcinogenesis in experimental animals and humans. Since we previously have demonstrated decreased plasma zinc and vitamin A levels in patients with esophageal cancer, we wished to examine endoscopically obtained epithelial tissue for vitamin A and zinc content. This was not feasible for vitamin A, but using newly developed techniques for zinc analysis of small tissue samples, we measured esophageal epithelial zinc as well as plasma zinc and plasma vitamin A in 21 patients with esophageal cancer, 17 patients with esophagitis, and 12 normals. Mean plasma zinc in the esophageal cancer group (56 +/- 3 micrograms/dl) (mean +/- SEM) was significantly less than in the esophagitis group (72 +/- 5 micrograms/dl) and the normals (78 +/- 5 micrograms/dl). Mean plasma vitamin A in the esophageal cancer group (32 +/- 3 micrograms/dl) was significantly less than the esophagitis group (57 +/- 4 micrograms/dl) or the normals (58 +/- 5 micrograms/dl). There was no significant difference in tissue zinc content (measured as micrograms zinc/g wet weight of tissue, mean +/- SEM) among cancerous tissue (57 +/- 5 micrograms/g) and adjacent normal tissue (61 +/- 4 micrograms/g), esophagitis tissue (66 +/- 6 micrograms/g) and adjacent normal tissue (61 +/- 6 micrograms/g), or normal esophageal tissue (59 +/- 6 micrograms/g). We conclude that deficiencies of zinc or vitamin A may be cofactors in the induction of human esophageal cancer, but a mechanism cannot be accounted for by differences in epithelial zinc content.