Jacobus P. Van Wouwe

CLINICAL AND LABORATORY ASSESSMENT OF ZINC DEFICIENCY IN DUTCH CHILDREN : A REVIEW

The clinical spectrum of acrodermatitis enteropathica (n=226) is compared with symptoms reported in other Zn deficiencies: total parenteral nutrition without Zn (n=21), protein energy malnutrition (n=24), gastrointestinal disease (n=79), geophagia (n=227), and dietary, low intake (n=23). Common features of deficiency are diarrhea, recurrent infection, and growth retardation. Dermatitis is less common in other types of deficiency than in acrodermatitis enteropathica (9 vs 88% of cases). Anorexia and/or hypogeusia is reported more frequently in the other types of deficiency (30 vs 16%). The main symptoms in acrodermatitis enteropathica vary with age. These differences in the clinical picture of Zn deficiency are discussed in relation to the degree of the deficiency (acute, subacute, or chronic; severe, mild, or subclinical).The results of the conventional laboratory tests to diagnose Zn deficiency (Zn levels in serum, urine or hair) are reviewed. In healthy Dutch infants and children, the mean values of these levels vary by a factor of 1.6–3.0. Also, the clinical interpretation of their results is prone to errors. Therefore, we advocate the erythrocytic65Zn uptake test. Its mean varies by 1.3. However, its reference values for different age intervals need to be established.From the comparison of the results of three conventional tests of samples taken concurrently (serum, urine, and hair) in groups of Dutch children with symptoms common in Zn deficiency (diarrhea, recurrent infection, or growth retardation) it is estimated that ±1% of Dutch children with minor complaints suffer from either acute or subacute Zn deficiency. Other deficiencies occur occasionally.In order to detect the individual patient with deficiency, the erythrocytic65Zn uptake test is promising and needs to be evaluated. Therefore, we review a set of reference laboratory tests with results that alter during sequential stages of overload and deficiency. Such a scheme is advocated as a guidance for future clinical research on deficiency, and solves the problem of differentiating those conditions that identify the individual patients who need treatment by supplementation.

The role of the pancreas in the regulation of zinc status

A low Zn diet resulted in subacute Zn deficiency in young rats. Thirty minutes after the intubation of a trace 65-Zn we determined the total tissue Zn activity in plasma, erythrocytes, liver, pancreas, bone, muscle, and proximal jejunum. Assuming the body behaved like a closed multicompartmental system in steady state, we estimated the initial Zn exchange between plasma, and the erythrocytes or these tissues. In comparison with control animals the exchanges between plasma and erythrocytes or pancreas increased threefold during subacufe Zn deficiency. In the pancreas the ratio also reversed from <1.0 to>1.0. This confirmed earlier, observations that the specific activity (kBq 65-Zn/mol Zn) increased mostly in the pancreas. By increased net Zn uptake during subacute deficiency, the pancreas Zn content remained constant in chronic Zn deficiency.We discussed the regulation of the Zn status by the pancreas. We hypothesize that the exocrine pancreas modulates Zn absorption by an exocrine ligand that enhances absorption in the jejunum during subacute deficiency: Unsaturated with Zn it binds dietary intraluminal Zn and increases the Zn absorption. The literature provides evidence in confirmation. This hypothesis explains also conflicting data on the inherited Zn malabsorption syndrome Acrodermatitis Enteropathica.

In Vitro Exchangeable Erythrocytic Zinc

Exchangeable erythrocytic zinc is measured by65Zn uptake in and release from erythrocytes under standarized and near, physiological conditions: 7.6 μM zinc and 580 μM albumin in the medium. The intracellular exchangeable erythrocytic zinc pool in healthy volunteers amounts to 5 μmol zinc/L packed cells. The half-time of the exchange is 7 h, its activation energy 84 kJ/mol. The effects of the variation in temperature and the concentrations of albumin, as well as the effects of some zinc carriers, cell transport inhibitors, and stress hormones on the65Zn uptake are measured.

Laboratory Assessment of Early Dietary, Subclinical Zinc Deficiency: A Model Study on Weaning Rats

ABSTRACT: Male weaning rats were pair-fed a low-zinc diet or a controt diet. After 10 d, the animals fed the low-zinc diet showed physiologic signs of deficiency; however, they showed no clinical symptoms. Their estimated whole body zinc was 25 μtmol versus 39 μmol for the controls. The 65Zn absorption increased 2-fold and the tissue distribution altered: muscle and erythrocytes contained more, small intestine and liver less activity at 0.5 h postdose. in vitro, the erythrocyte 65Zn uptake rate increased also. The 65Zn uptake experiments required small quantities of erythrocytes. The difference observed between the deficient and control cells was significant and showed little overlap. The increase of the 65Zn uptake from a medium was not affected when the animals underwent endotoxn exposure 24 h before, as was reported to occur in whole blood 65Zn uptake. Therefore, we suggest the in vitro erythrocyte 65Zn uptake, performed in a standardized, near physiologic medium, to detect early, subclinical zinc deficiency.

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 Ultra-Filtration (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 μmol/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 μmol/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.

Histidine supplement and Zn status in Swiss random mice.

The influence of either histidine supplement or nutritional Zn deficiency on growth and the organ and tissue Zn content of mice during a 21-d period was compared with a control group. When the histidine intake was increased from 5 to 9 μmol/g body wt/d we noted increased body weight and higher Zn concentrations in liver, pancreas, spleen, and muscle. As a result, the estimated whole body Zn mass increased. This was explained by enhanced utilization of dietary Zn. These results differed from those seen in Zn deficient animals (fed 5 nmol Zn/g body wt/d instead of 29).Dietary Zn deficiency was characterized by anorexia and growth retardation, lower Zn concentrations in pancreas, muscle, bone, tail, and plasma, plus higher Zn concentrations in spleen and fur. As a result, the estimated total body Zn mass was 20% lower than in the control animals, despite a two-to threefold increase in utilization of dietary Zn.These results are discussed in view of the available literature. It is concluded that in humans and in animals both the absorption and the excretion of Zn may be increased by histidine. Below a certain dose the former will prevail, viz., a situation of increased utilization exists, preventing the development of Zn deficiency.

Dietary subacute zinc deficiency and potassium metabolism

In a controlled animal experiment the effects of dietary subacute Zn deficiency on growth, Zn concentration, and tissue 42-K distribution were studied. Growth retardation caused lower body weight because both skeletal and heart muscle showed a reduction in cell mass. Zn concentrations were reduced in most tissues, however, they remained unaltered in heart muscle. 42-K activity increased in skeletal muscle and pancreas. We hypothesize the latter reflects the organs rate of metabolism, inducing the exocrine pancreas to increase Zn absorption; in skeletal muscle it may induce also alterations in cell potentiation, causing restless behavior. As suggested by the calculated specific K activity (Bq/mol), the K uptake was highest in liver and bone, high in pancreas and skeletal muscle and low in heart muscle. The latter suggests K retention in heart muscle. Specific activity in plasma and jejunum remained unaltered: K status and absorption seem unaffected. Zn deficiency causes different 42-K activities in the various tissues, that respond by alterations in K metabolism without the induction of K deficiency.

Zinc and copper of fetal organs during the second trimester of pregnancy

In fetus with a mean gestational age of 18 weeks (range 15–25,n=14), zinc and copper concentrations in liver, femur, rib, and skeletal muscle were measured. Zinc and copper concentrations are highest in liver. A trend of decreasing liver zinc concentrations during gestational age is suggested. Zinc concentrations are significantly correlated with copper concentrations in liver and in femur, suggesting steady growth in both organs. Femur zinc values rank ca. 30% of those in liver, femur copper, ca. 2%. Zinc or copper concentrations in rib are of the same levels as in skeletal muscle. Their concentration for zinc ranks ca. 20%, for copper, ca. 5% of the values in liver. All zinc and copper values are lower than reported in third trimester fetal organs.Calculated zinc/copper molar ratios are distinctive for the various organs: in liver, 6±1, in femur, 73±8, and in soft tissues, 26±3. Calculated ratios from published values obtained from the third tri|mester of pregnancy show that the ratios in liver and skeletal muscle maintain these levels. The zinc/copper molar ratio can serve as an internal reference in zinc and/or copper measurements.

Changes of Zinc Values in Children During Malignant Disease

In 47 children with malignancy, zinc status, growth, and performance during standard treatment were compared with those in controls. At diagnosis, growth was retarded and hair zinc values were high, 2.4±0.7 μmol/g, as in chronic deficiency. During induction therapy, serum declined to 10.4±2.3 μmol/L and urinary excretion increased to 5.3±2.8 μmol/mol creatinine, as in acute exacerbation of deficiency. Control CSF values in children in remission, 0.04±0.01 μmol/L, were lower than reference values in adults. No difference in mean CSF zinc was observed during therapy, or in those with acute lymphoblastic leukemia (1) at high risk, (2) with central nervous system involvement, (3) with low performance, or (4) resistant to therapy. In six children unexplained values, up to 0.28 μmol/L during induction, were measured. No correlations between the various zinc parameters were found.

A histidine supplement and regulation of the zinc status in Swiss random mice

The effects of histidine on the zinc status are controversial. In mice, we studied the effects of a moderate histidine supplement on the regulation of the zinc status using subcutaneously administered65Zn. In animals fed a zinc-adequate diet, histidine supplement did not cause changes in the zinc status (zinc concentrations,65Zn tissue distribution, and tissue specific activities). Neither effects on the regulation of the zinc status (65Zn retention, excretion and biological half-life) could be demonstrated. However, the combination of a low zinc diet and moderate histidine supplementation caused changes in the regulation of the zinc status (lower65Zn retention, associated with increased fecal excretion and a shorter biological half-life), aggravating the dietary deficiency (lower bone zinc, a shift in the65Zn tissue distribution). Reviewing the literature, it seems that only a molar histidine/zinc ration of 2,000 or higher will cause zinc deficiency.