Abnormalities in zinc homeostasis in young infants with cystic fibrosis

A skin-interfaced, miniaturized platform for triggered induction, capture and colorimetric multicomponent analysis of microliter volumes of sweat

Eccrine sweat can serve as a source of biomarkers for assessing physiological health and nutritional balance, for tracking loss of essential species from the body and for evaluating exposure to hazardous substances. The growing interest in this relatively underexplored class of biofluid arises in part from its non-invasive ability for capture and analysis. The simplest devices, and the only ones that are commercially available, exploit soft microfluidic constructs and colorimetric assays with purely passive modes of operation. The most sophisticated platforms exploit batteries, electronic components and radio hardware for inducing sweat, for electrochemical evaluation of its content and for wireless transmission of this information. The work reported here introduces a technology that combines the advantages of these two different approaches, in the form of a cost-effective, easy-to-use device that supports on-demand evaluation of multiple biomarkers in sweat. This flexible, skin-interfaced, miniaturized system incorporates a hydrogel that contains an approved drug to activate eccrine sweat glands, electrodes and a simple circuit and battery to delivery this drug by iontophoresis through the surface of the skin, microfluidic channels and microreservoirs to capture the induced sweat, and multiple colorimetric assays to evaluate the concentrations of chloride, zinc, and iron. As demonstrated in healthy human participants monitored before and after a meal, such devices yield results that match those of traditional laboratory analysis techniques. Clinical studies that involve cystic fibrosis pediatric patients illustrate the use of this technology as a simple, painless, and reliable alternative to traditional hospital systems for measurements of sweat chloride.

CFTR is required for zinc-mediated antibacterial defense in human macrophages

Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion transporter required for epithelial homeostasis in the lung and other organs, with CFTR mutations leading to the autosomal recessive genetic disease CF. Apart from excessive mucus accumulation and dysregulated inflammation in the airways, people with CF (pwCF) exhibit defective innate immune responses and are susceptible to bacterial respiratory pathogens such as Pseudomonas aeruginosa. Here, we investigated the role of CFTR in macrophage antimicrobial responses, including the zinc toxicity response that is used by these innate immune cells against intracellular bacteria. Using both pharmacological approaches, as well as cells derived from pwCF, we show that CFTR is required for uptake and clearance of pathogenic Escherichia coli by CSF-1-derived primary human macrophages. CFTR was also required for E. coli-induced zinc accumulation and zinc vesicle formation in these cells, and E. coli residing in macrophages exhibited reduced zinc stress in the absence of CFTR function. Accordingly, CFTR was essential for reducing the intramacrophage survival of a zinc-sensitive E. coli mutant compared to wild-type E. coli. Ectopic expression of the zinc transporter SLC30A1 or treatment with exogenous zinc was sufficient to restore antimicrobial responses against E. coli in human macrophages. Zinc supplementation also restored bacterial killing in GM-CSF-derived primary human macrophages responding to P. aeruginosa, used as an in vitro macrophage model relevant to CF. Thus, restoration of the zinc toxicity response could be pursued as a therapeutic strategy to restore innate immune function and effective host defense in pwCF.

The Role of Zinc in the Pathogenesis of Lung Disease

Lung diseases, such as asthma, chronic obstructive pulmonary diseases (COPD), and cystic fibrosis (CF), are among the leading causes of mortality and morbidity globally. They contribute to substantial economic burdens on society and individuals. Currently, only a few treatments are available to slow the development and progression of these diseases. Thus, there is an urgent unmet need to develop effective therapies to improve quality of life and limit healthcare costs. An increasing body of clinical and experimental evidence suggests that altered zinc and its regulatory protein levels in the systemic circulation and in the lungs are associated with these disease’s development and progression. Zinc plays a crucial role in human enzyme activity, making it an essential trace element. As a cofactor in metalloenzymes and metalloproteins, zinc involves a wide range of biological processes, such as gene transcription, translation, phagocytosis, and immunoglobulin and cytokine production in both health and disease. Zinc has gained considerable interest in these lung diseases because of its anti-inflammatory, antioxidant, immune, and metabolic modulatory properties. Here we highlight the role and mechanisms of zinc in the pathogenesis of asthma, COPD, CF, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, and pulmonary hypertension.

Zinc status and growth in infants and young children with cystic fibrosis

BACKGROUND

Zinc deficiency is associated with poor growth in children without cystic fibrosis (CF), but its impact on growth in children with CF is unknown.

OBJECTIVE

To determine the prevalence of low serum Zn (sZn) and its relationship with growth in the first 3 years of life in children with CF.

METHODS

We utilized data from infants with CF who were enrolled in a longitudinal study of nutrition and lung health and had sZn measured as part of clinical care. Cross-sectional correlations between sZn levels and growth z scores were assessed by Pearson's correlation coefficient. To identify factors associated with sZn status and its association to longitudinal growth patterns, multiple regression analysis with repeated measures were performed using generalized estimating equations.

RESULTS

A total of 106 sZn measurements from 53 infants were identified. Seventeen infants (32%) had intermittent Zn insufficiency, defined as at least one sZn <70 mcg/dl in their first 3 years of life. There were no significant cross-sectional associations between sZn and growth z scores. However, analysis of longitudinal growth patterns revealed that weight- and length-for-age z scores in children with intermittent Zn insufficiency were lower during early infancy and their weight-for-length z scores at age 3 years were also lower compared to those who were always Zn sufficient.

CONCLUSION

Low sZn occurs in one-third of children with CF in the first 3 years of life. Cross-sectional and longitudinal analyses revealed discrepant associations between sZn and growth. Therefore, prospective studies are needed to understand the role of Zn in growth in CF.

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.

Serum zinc concentration in cystic fibrosis patients with CFTR I1234V mutation associated with pancreatic sufficiency

OBJECTIVE

To determine serum zinc (Zn) level among cystic fibrosis (CF) patients with homozygous CFTR I1234V mutation associated with pancreatic sufficiency (PS).

METHODS

A cross-sectional study was conducted including both pediatric and adult CF patients. Data on age, weight, height, body mass index (BMI), BMI Z-score, FEV1, and chronic Pseudomonas aeruginosa infection were collected. Serum Zn, albumin, and total proteins were measured and analyzed.

RESULTS

Forty-five CF patients with homozygous CFTR I1234V mutation belonging to a large Arab kindred tribe and eight CF patients with other mutations associated with pancreatic insufficiency (PI). Patient's age ranged from 2 to 49 years with a mean age of 15.1 ± 9.1 years and mean plasma Zn of 0.78 ± 0.15 mcg/mL. Seven (13.2%) patients with CFTR I1234V and PS had low Zn levels (<0.6 mcg/mL). Mean age among Zn deficient group was significantly older. The mean FEV1 in the deficient group was found to be insignificant low. Persistent P. aeruginosa colonization was more prevalent in Zn deficient group. BMI Z-scosre of CF patients were positively correlated with Zn levels. Forty-five healthy subjects belonging to the same Arab tribe were selected in order to assess their Zn levels and their mean plasma Zn of 0.84 ± 0.11 mcg/mL (range 0.65-1.1 mcg/mL) with mean age 20.4 ± 10.1 years (range 6-40 years).

CONCLUSION

These findings suggest that Zn deficiency can occur in CF patients with PS. The association of Zn levels and the frequency of P. aeruginosa isolated in CF patients need further investigation.

Nutritional status in children with Shwachman-diamond syndrome

OBJECTIVE

In Shwachman-Diamond syndrome (SDS), pancreatic insufficiency can lead to malabsorption of fat-soluble vitamins and trace elements. The aim of this study was to assess the serum concentrations of vitamins A and E, zinc, copper, and selenium and their deficiencies.

METHODS

This retrospective review was performed in 21 children (12 were male; median age, 7.8 years) with genetically confirmed SDS at a tertiary pediatric hospital. Pancreatic enzyme replacement therapy (PERT) and vitamin or trace elements supplements were documented.

RESULTS

Twenty patients (95%) had pancreatic insufficiency receiving PERT, 10 (47%) had a combined vitamin and trace element deficiency, 6 (29%) had an isolated vitamin deficiency, and 4 (19%) had an isolated trace element deficiency. Vitamins A and E deficiency occurred in 16 (76%) and 4 (19%) of 21, respectively. Low serum selenium was found in 10 (47%), zinc deficiency in 7 (33%), and copper deficiency in 5 (24%). Eleven patients (52%) were on multivitamin supplementation, and 2 (10%) on zinc and selenium supplements. No statistical differences were found between repeated measurements for all micronutrients.

CONCLUSIONS

More than 50% of the children had vitamin A and selenium deficiencies despite adequate supplementation of PERT and supplements. Micronutrients should be routinely measured in SDS patients to prevent significant complications.

Zinc deficiency in infants and children: a review of its complex and synergistic interactions

Zinc deficiency is estimated to contribute to over half a million deaths per year in infants and children under 5 years of age. This paper reviews the features of mild-to-moderate zinc deficiency, which include growth faltering, deficits in immune function and altered integrity and function of the gastro-intestinal tract. Sub-clinical features include oxidative stress and a pro-inflammatory state. The homeostatic response to low dietary zinc intake by increasing absorption is limited, especially if the source of zinc is of poor bioavailability, and conservation of endogenous intestinal losses is a critical component of adaptation. Owing to low zinc intakes, older breastfed infants, especially those of low birthweight, are predictably at risk of zinc deficiency if complementary food choices are unfortified and/or low in zinc. Host factors such as young age, poor intra-uterine zinc accretion owing to poor maternal status and/or prematurity, and gastro-intestinal dysfunction also potently predispose to zinc deficiency. Environmental enteropathy, which is prevalent in low-resource settings, may substantially impair zinc absorption and/or increase endogenous losses, and thus lead to relatively high zinc requirements. Emerging evidence highlights common features between chronic inflammation and zinc deficiency, and each may exacerbate the other. More investigations of zinc homeostasis in populations in low-resource settings are needed to better quantify absorption capacity and losses. Effective preventive strategies must address potentially higher zinc requirements as well as the underlying context that perpetuates a vicious cycle of zinc deficiency and multiple adverse outcomes.

Cystic Fibrosis Foundation evidence-based guidelines for management of infants with cystic fibrosis

Newborn screening for cystic fibrosis (CF) offers the opportunity for early medical and nutritional intervention that can lead to improved outcomes. Management of the asymptomatic infant diagnosed with CF through newborn screening, prenatal diagnosis, or sibling screening is different from treatment of the symptomatically diagnosed individual. The focus of management is on maintaining health by preventing nutritional and respiratory complications. The CF Foundation convened a committee to develop recommendations based on a systematic review of the evidence and expert opinion. These guidelines encompass monitoring and treatment recommendations for infants diagnosed with CF and are intended to help guide families, primary care providers, and specialty care centers in the care of infants with CF.

Sputum trace metals are biomarkers of inflammatory and suppurative lung disease

BACKGROUND

Induced sputum cytology and protein biomarkers can be used to assess airways inflammation. Increases in sputum iron have been described in inflammatory lung disease. We hypothesized that other sputum metals may be affected by airways inflammation and investigated their potential value as biomarkers.

METHODS

Sputum was obtained from 20 healthy control subjects and from patients with inflammatory pulmonary diseases (23 with cystic fibrosis [CF], 16 with bronchiectasis, 17 with asthma, and 23 with COPD), and iron, zinc, manganese, and copper were measured. Fourteen patients with CF were also studied through an exacerbation cycle.

RESULTS

Sputum zinc and iron were elevated in CF and non-CF bronchiectasis vs controls (P < .001, zinc; P < .01 iron). Manganese was elevated in asthma (P < .01) and bronchiectasis (P < .05) vs controls. Copper was elevated in CF vs controls (P < .05). Zinc decreased (P < .01) following treatment of CF exacerbation. In subjects with CF zinc levels correlated with other biomarkers.

CONCLUSIONS

These results suggest a relationship of high concentrations of total zinc and iron with airways inflammation in CF and non-CF bronchiectasis, with longitudinal changes being observed in CF. Further work is required to elucidate potential inflammatory mechanisms related to these observations.

Nutrition management of pediatric patients who have cystic fibrosis

Since the identification of cystic fibrosis (CF) in the 1940s, nutrition care of patients who have CF has been a challenge. Through optimal caloric intake and careful management of malabsorption, patients are expected to meet genetic potential for growth. Yet factors beyond malabsorption, including nutrient activity at the cellular level, may influence growth and health. This article reviews nutrition topics frequently discussed in relationship to CF and presents intriguing new information describing nutrients currently being studied for their impact on overall health of patients who have CF.

[Renal diseases in cystic fibrosis]

Patients with cystic fibrosis (CF) show a continuing improvement in their life expectancy thanks to advances in knowledge of this disorder, allowing better multidisciplinary routine monitoring and earlier therapeutic interventions. Likewise, more than of 40% of these patients are adults and CF is no more only a pediatric disease. Due to their higher life expectancy, CF patients present new and unusual complications that were not recorded before. Among them, some renal disorders have to be added to the CF-related renal diseases. They are due to frequent and prolonged exposure to various potentially nephrotoxic factors that need to be taken into account early enough in order to avoid renal failure : essentially risk factors for kidney stones formation, bacterial infections with their associated immune complexes diseases, nephrotoxic effects of antibiotics, diabetes mellitus. Because we observed a case of IgA glomerulonephritis in a 35-year-old patient with cystic fibrosis, we have searched about all these renal consequences due to this affection and here report them.

Newborn screening for cystic fibrosis

Newborn screening (NBS) for cystic fibrosis (CF) has evolved considerably from its beginnings. We review the early history of NBS in the USA and the evolution of CF NBS from its conception in observational studies, to the development of mass-screening methodology in the 1970s, and to its early applications in the USA and other countries. We review the development of current CF NBS algorithms, particularly the development of those used in the Wisconsin randomized controlled trial, and discuss the comparative utility of different algorithms. We also discuss the identified nutritional and respiratory benefits of CF NBS, discuss treatment strategies for newborns identified with CF, and also discuss opportunities for slowing the progression of this disease.

Zinc-mediated feedback at the synaptic terminals of vertebrate photoreceptors

There is mounting evidence that zinc release from glutamatergic nerve terminals serves as a neuromodulator at synaptic sites within the retina and CNS. However, it has not been possible to reliably measure the concentration of zinc co-released with glutamate in the confines of the synaptic cleft. Thus, much of the evidence supporting this view derives from electrophysiological studies showing the modulatory effects of exogenous zinc on the membrane currents of ligand- and voltage-gated channels. In the present study, we took advantage of the unique properties of the glutamatergic photoreceptor terminal to demonstrate a feedback signal mediated by endogenous zinc at the synaptic sites from which it is discharged. Through its ability to block voltage-gated calcium channels in the photoreceptor terminal, zinc suppresses the radial dark current of the visual cell, and reduces its release of glutamate. It follows that chelation of extracellular zinc, e.g., with histidine, will lead to an increase both in the dark current and in the release of glutamate, changes that result in an enhancement of the light-evoked a-wave of the ERG and can account for the b-wave enhancement observed previously after zinc chelation when inner retinal responses were not blocked by aspartate.

Effect of zinc supplementation on respiratory tract infections in children with cystic fibrosis

Zinc (Zn) has significant anti-oxidant and anti-inflammatory activity. Zn deficiency can occur in subsets of patients with cystic fibrosis (CF) especially those with malabsorption and impaired growth. Although supplemental Zn has significantly reduced infections in various disorders, its efficacy has not been thoroughly investigated in CF. We performed a double blind placebo controlled pilot study to investigate the effect of daily 30 mg elemental Zn for 1 year on the rate of respiratory tract infections (RTIs), use of antibiotics and plasma cytokines in 26 children with CF (ages 7-18 years). Plasma Zn, Cu, inflammatory cytokines and ex vivo generation of IL-2 were measured at baseline and at the end of the study. The number of days of oral antibiotics was lower in Zn treated patients compared to placebo (P = 0.05). However, compared to placebo, the effect of Zn was greater in patients who exhibited low plasma Zn at baseline (P = 0.02) than those who had plasma Zn levels identical to normal subjects (P = 0.55). Zn supplementation was marginally effective in reducing percentage increase in plasma IL-6 and IL-8 while increasing the percentage change in ex vivo generation of IL-2 in isolated mononuclear cell. In conclusion, oral intake of 30 mg/day of Zn reduced the number of days of oral antibiotics used to treat RTIs in children with CF. A higher daily Zn dose may be needed to decrease RTIs and modify immune responses.

Serum zinc concentrations in cystic fibrosis patients aged above 4 years: a cross-sectional evaluation

AIM

Assess the risk of zinc (Zn) deficiency in the older cystic fibrosis (CF) population.

METHOD

Cross-sectional investigation of all CF patients above the age of 4 followed at the Ghent University center between 2002 and 2003. Data on age, weight, height z-score, pancreatic and pulmonary functions, chronic Pseudomonas infection, and CF transmembrane conductance regulator (CFTR) mutations were collected. Serum Zn, vitamins (vit) A and E, retinol-binding protein (RBP), albumin, sedimentation rate, total IgG, and cholesterol were determined. Serum Zn was compared with a local healthy control group (Van Biervliet et al., Biol Trace Elem Res 94:33-40, 2003) and with literature data (Hotz C, et al. Am J Clin Nutr 78:756-764, 2003).

RESULTS

101 patients (median age 16 years) were included. There was no difference in serum Zn concentration between CF patients and controls. In CF patients no difference in serum Zn concentration between pancreatic-sufficient or pancreatic-insufficient patients was seen. Serum Zn was not associated to nutritional status or height z-score. A significant association serum Zn to serum albumin (p < 0.0005) and to vit A (p < 0.01) was seen. No associations of serum Zn to serum vit E, RBP, cholesterol, or CFTR were present, but there is a significant association serum Zn to forced vital capacity (p < 0.01). Serum Zn was not associated to inflammatory parameters or chronic Pseudomonas infection.

CONCLUSION

Comparison of CF patients with local controls revealed no significant differences. However, because persisting steatorrhea increases Zn loss (Easley et al., J Pediatr Gastroenterol Nutr 26:136-139, 1998) and 12.6% of our population has a serum Zn below the p value of 2.5 of the NHANES II study (Hotz C, et al. Am J Clin Nutr 78:756-764, 2003), there could remain an increased risk of Zn deficiency in some CF patients. Furthermore, the association with pulmonary function needs more investigation.

Antioxidants in cystic fibrosis. Conclusions from the CF antioxidant workshop, Bethesda, Maryland, November 11-12, 2003

Although great strides are being made in the care of individuals with cystic fibrosis (CF), this condition remains the most common fatal hereditary disease in North America. Numerous links exist between progression of CF lung disease and oxidative stress. The defect in CF is the loss of function of the transmembrane conductance regulator (CFTR) protein; recent evidence that CFTR expression and function are modulated by oxidative stress suggests that the loss may result in a poor adaptive response to oxidants. Pancreatic insufficiency in CF also increases susceptibility to deficiencies in lipophilic antioxidants. Finally the airway infection and inflammatory processes in the CF lung are potential sources of oxidants that can affect normal airway physiology and contribute to the mechanisms causing characteristic changes associated with bronchiectasis and loss of lung function. These multiple abnormalities in the oxidant/antioxidant balance raise several possibilities for therapeutic interventions that must be carefully assessed.

Exchangeable zinc pool size at birth is smaller in small-for-gestational-age than in appropriate-for-gestational-age preterm infants

BACKGROUND

Small-for-gestational-age (SGA) infants are susceptible to postnatal zinc deficiency, but whether this susceptibility is due to intrauterine factors or to high postnatal growth requirements is unknown.

OBJECTIVE

We hypothesized that the size of the exchangeable zinc pool (EZP), which reflects metabolically available zinc, would be smaller in SGA than in appropriate-for-gestational-age (AGA) infants born prematurely.

DESIGN

Intravenous 70Zn (45 microg/kg) was administered to 10 SGA infants (8 boys) with a mean (+/-SD) gestational age of 33.3 +/- 1.8 wk and to 11 AGA infants (8 boys) with a mean (+/-SD) gestational age of 32.4 +/- 1.2 wk within 24 h of birth. The EZP was determined from isotope enrichment in spot urine collections on days 3-7.

RESULTS

The mean birth weight of the SGA infants was 1.30 +/- 0.2 kg and of the AGA infants was 1.84 +/- 0.3 kg (P = 0.0001). The EZP size was significantly smaller in the SGA than in the AGA infants on an absolute basis (13.3 +/- 2.8 and 25.2 +/- 8.1 mg; P = 0.0002) and relative to body weight (10.3 +/- 2.5 and 13.9 +/- 4.5 mg/kg; P = 0.02). The difference remained significant after adjustment for gestational age and birth weight.

CONCLUSION

These data provide evidence for differential zinc status at birth between SGA and AGA infants born prematurely at similar stages of gestation and offer at least a partial explanation for the reported benefits of postnatal zinc supplementation.

Anti-inflammatory effects of zinc and alterations in zinc transporter mRNA in mouse models of allergic inflammation

There is clinical evidence linking asthma with the trace element, zinc (Zn). Using a mouse model of allergic inflammation, we have previously shown that labile Zn decreases in inflamed airway epithelium (Truong-Tran AQ, Ruffin RE, Foster PS, Koskinen AM, Coyle P, Philcox JC, Rofe AM, Zalewski PD. Am J Respir Cell Mol Biol 27: 286-296, 2002). Moreover, mild nutritional Zn deficiency worsens lung function. Recently, a number of proteins belonging to the Solute Carrier Family 39 (ZIP) and Solute Carrier Family 30 (ZnT) have been identified that bind Zn and regulate Zn homeostasis. Mice were sensitized, and subsequently aerochallenged, with ovalbumin to induce acute and chronic airway inflammation. Mice received 0, 54, or 100 microg of Zn intraperitoneally. Tissues were analyzed for Zn content and histopathology. Inflammatory cells were counted in bronchoalveolar lavage fluid. Cytokine and Zn transporter mRNA levels were determined by cDNA gene array and/or real-time PCR. Zn supplementation decreased bronchoalveolar lavage fluid eosinophils by 40 and 80%, and lymphocytes by 55 and 66%, in the acute and chronic models, respectively. Alterations in Zn transporter expression were observed during acute inflammation, including increases in ZIP1 and ZIP14 and decreases in ZIP4 and ZnT4. Zn supplementation normalized ZIP1 and ZIP14, but it did not affect mRNA levels of cytokines or their receptors. Our results indicate that inflammation-induced alterations in Zn transporter gene expression are directed toward increasing Zn uptake. Increases in Zn uptake may be needed to counteract the local loss of Zn in the airway and to meet an increased demand for Zn-dependent proteins. The reduction of inflammatory cells by Zn in the airways provides support for Zn supplementation trials in human asthmatic individuals.

Plasma zinc and growth status in preadolescent children with cystic fibrosis

OBJECTIVE

To investigate plasma zinc status in relation to dietary and supplemental zinc intake, growth and pulmonary status in preadolescent children with cystic fibrosis (CF) and pancreatic insufficiency (PI).

METHODS

Fasting plasma zinc was assessed in children (age, 8-11 years) with CF and PI. Food (7-day weighed records) and supplemental zinc intake, serum alkaline phosphatase and albumin, pulmonary function (spirometry), coefficient of fat absorption (%COA, 72-hour fecal fat) and growth status [height adjusted for genetic potential (AHAZ), weight (WAZ) and BMI Z scores (BMIZ)] were assessed.

RESULTS

For the 62 children (32 males), mean plasma zinc (+/-SD) was 16.8 +/- 3.1 micromol/L (110 +/- 20 ug/dL). Sixty-five percent of the subjects had levels above the study reference range of 9.2 to 15.3 micromol/L (60-100 ug/dL); no subjects had low zinc levels. Median (range) total daily zinc intake was 279% (83-988%) recommended dietary allowance, growth status was suboptimal (mean +/- SD: AHAZ, -0.8 +/- 1.0; WAZ, -0.5 +/- 1.2; BMIZ, -0.2 +/- 1.1), and forced expiratory volume at 1 second (FEV1) was 92 +/- 13% predicted. Plasma zinc was not correlated with growth, pulmonary or alkaline phosphatase status. Plasma zinc was correlated with serum albumin (r = 0.25, P < 0.05) and was inversely correlated with coefficient of fat absorption (as %; r = -0.30, P = 0.02).

CONCLUSIONS

Under current patterns of care in CF Centers, total zinc intake and plasma zinc status were adequate. These findings suggest that zinc was not a limiting micronutrient for preadolescent children with CF and PI and mild-to-moderate lung disease, and not likely contributing to their suboptimal growth status.

Extracellular zinc and ATP-gated P2X receptor calcium entry channels: New zinc receptors as physiological sensors and therapeutic targets

In this review, we focus on two attributes of P2X receptor channel function, one essential and one novel. First, we propose that P2X receptors are extracellular sensors as well as receptors and ion channels. In particular, the large extracellular domain (that comprises 70% of the molecular mass of the receptor channel protein) lends itself to be a cellular sensor. Moreover, its exquisite sensitivity to extracellular pH, ionic strength, and multiple ligands evokes the function of a sensor. Second, we propose that P2X receptors are extracellular zinc receptors as well as receptors for nucleotides. We provide novel data in multiple publications and illustrative data in this invited review to suggest that zinc triggers ATP-independent activation of P2X receptor channel function. In this light, P2X receptors are the cellular site of integration between autocrine and paracrine zinc signaling and autocrine and paracrine purinergic signaling. P2X receptors may sense changes in these ligands as well as in extracellular pH and ionic strength and transduce these sensations via calcium and/or sodium entry and changes in membrane potential.

Acrodermatitis enteropathica-like eruption and food allergy

BACKGROUND

Acrodermatitis enteropathica-like eruption (AE) is a distinct rash associated with profound zinc deficiency. It is seen in a variety of conditions but has not been reported as a presentation of food allergy.

OBJECTIVE

To report AE as an unusual presentation of food allergy in infants.

METHODS

Acrodermatitis enteropathica-like eruption was diagnosed by a characteristic rash and a low serum zinc level. The diagnosis of food allergy was made by history, serum total IgE and food specific IgE levels, or oral challenge with suspected foods.

RESULTS

Two infants with AE, diarrhea, and low serum zinc levels were evaluated. Food allergy was found in both infants. The first infant had a serum IgE level of 4642 IU/mL. Specific IgE levels to milk, soybean, wheat, and peanut were 39.04, 10.14, 5.65, and 102.61 kU/L, respectively. Oral challenges to milk and peanut were positive and to soybean were negative. The second infant had a serum IgE level of 991 IU/mL; specific IgE levels to soybean and milk were 36.9 and 0.53 kU/L, respectively. Evaluation for other possible causes of diarrhea revealed homozygous delta F508 in the first infant, confirming the coexistence of cystic fibrosis; findings in the second infant were negative.

CONCLUSIONS

Undiagnosed food allergy can lead to profound zinc deficiency. Food allergy should be suspected in a child with acquired AE.

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.

Zinc homeostasis in premature infants does not differ between those fed preterm formula or fortified human milk

The objectives of this study were to compare zinc homeostasis in premature infants enterally fed with either preterm infant formula or fortified human milk; to examine interrelationships of variables of zinc homeostasis; and to examine the findings in relation to estimated zinc requirements of preterm infants. Zinc homeostasis was studied in 14 infants (8 male), with mean gestational age of 31 wk and birth weight appropriate for gestational age, who were exclusively fed either preterm formula (n = 9) or own mother's milk with human milk fortifier (n = 5). Zinc stable isotopes were administered intravenously ((70)Zn) and orally as an extrinsic label ((67)Zn) over multiple feeds for determination of fractional absorption by dual isotope tracer ratio in urine; endogenous fecal zinc was determined by isotope dilution; and exchangeable zinc pool (EZP) size was estimated from linear regression of log-transformed urine (70)Zn enrichment data. Results indicated no significant differences in the variables of zinc homeostasis between the feeding groups; data for all subjects were thus combined. Mean (+/- SD) fractional absorption was 0.26 +/- 0.07; net absorbed zinc 0.43 +/- 0.25 mg/d (0.31 +/- 0.19 mg/kg/d). Mean EZP was 20 +/- 10 mg/kg, and was positively correlated with total absorbed zinc and with net absorbed zinc. Feeding type and total absorbed zinc were significantly related to daily weight gain (p = 0.003). Current zinc intakes from fortified human milk or formula are associated with acceptable weight gain, but whether the observed net zinc absorption was optimal in the human milk group cannot be definitively determined from these data.

Extracellular Zinc and ATP Restore Chloride Secretion across Cystic Fibrosis Airway Epithelia by Triggering Calcium Entry

Cystic fibrosis (CF) is caused by defective cyclic AMP-dependent cystic fibrosis transmembrane conductance regulator Cl(-) channels. Thus, CF epithelia fail to transport Cl(-) and water. A postulated therapeutic avenue in CF is activation of alternative Ca(2+)-dependent Cl(-) channels. We hypothesized that stimulation of Ca(2+) entry from the extracellular space could trigger a sustained Ca(2+) signal to activate Ca(2+)-dependent Cl(-) channels. Cytosolic [Ca(2+)](i) was measured in non-polarized human CF (IB3-1) and non-CF (16HBE14o(-)) airway epithelial cells. Primary human CF and non-CF airway epithelial monolayers as well as Calu-3 monolayers were used to assess anion secretion. In vivo nasal potential difference measurements were performed in non-CF and two different CF mouse (DeltaF508 homozygous and bitransgenic gut-corrected but lung-null) models. Zinc and ATP induced a sustained, reversible, and reproducible increase in cytosolic Ca(2+) in CF and non-CF cells with chemistry and pharmacology most consistent with activation of P2X purinergic receptor channels. P2X purinergic receptor channel-mediated Ca(2+) entry stimulated sustained Cl(-) and HCO(3)(-) secretion in CF and non-CF epithelial monolayers. In non-CF mice, zinc and ATP induced a significant Cl(-) secretory response similar to the effects of agonists that increase intracellular cAMP levels. More importantly, in both CF mouse models, Cl(-) permeability of nasal epithelia was restored in a sustained manner by zinc and ATP. These effects were reversible and reacquirable upon removal and readdition of agonists. Our data suggest that activation of P2X calcium entry channels may have profound therapeutic benefit for CF that is independent of cystic fibrosis transmembrane conductance regulator genotype.

Endogenous fecal losses of calcium compromise calcium balance in pancreatic-insufficient girls with cystic fibrosis

OBJECTIVE

Bone mineral density is compromised in individuals with cystic fibrosis (CF); calcium is the major bone mineral. This study examined the impact of endogenous fecal calcium (V(endo)) losses on calcium balance in girls with CF. Study design V(endo) was measured in 12 girls with CF (aged 7-18 years): 7 younger, premenarcheal girls with compromised nutritional status; and 5 older, postmenarcheal girls with adequate nutritional status. V(endo) was measured as the amount of intravenously administered (42)Ca, a calcium stable isotope, in stool relative to urine over 6 days. V(endo) was compared between pre- and postmenarcheal girls by Student's t test. Actual calcium balance [absorbed calcium-(urinary calcium (V(u))+V(endo))] was compared with estimated balance (assuming V(endo)=1.6 mg/kg/day calcium) by paired t test.

RESULTS

V(endo) was 99.3+/-42.3 mg/day. By body weight, V(endo) was highest among premenarcheal girls (3.37+/-1.09 mg/kg/day), resulting in excess losses (>1.6 mg/kg/day) of 55.0+/-45.7 mg/day. Over 1 year, this represents 20.1+/-16.7 g of unattained bone calcium or 6.7+/-4.2% of the bone calcium content of these girls.

CONCLUSIONS

V(endo) is a significant source of calcium loss in individuals with CF and may limit calcium availability for bone mineral deposition.

Elemental and ion composition of exhaled AIR condensate in cystic fibrosis

BACKGROUND

In cystic fibrosis (CF) the exact ion composition of the airway surface fluid is still debated and it is not clear if it differs from healthy subjects. The air that we exhale contains small droplets, which are generated by shear forces from the airway surface fluid and very likely mirror its ion composition. We hypothesized that differences between CF-patients and healthy controls would be reflected by differences in their exhaled air.

METHODS

In nasally collected exhaled breath condensate from 20 children and young adults with cystic fibrosis and 20 healthy subjects, the elements and anions were determined by optical emission spectroscopy and ion-exchange chromatography.

RESULTS

The concentrations of the major components Na and Cl- did not differ, Zn was higher and NO3- was lower in CF-patients. During a given time period, CF-patients produced a slightly larger volume of breath condensate and they exhaled more Na, K and Zn. Fluoride was detected in half of all samples, whereas copper, iron, magnesium, phosphorus and sulfur were present only sporadically, with no differences.

CONCLUSIONS

These data detail the composition of exhaled breath condensate and suggest a similar Na and Cl- concentration in CF-airway surface fluid as in healthy subjects.

The association of nephrolithiasis with cystic fibrosis

BACKGROUND

There is a growing body of evidence regarding the association between cystic fibrosis (CF) and nephrolithiasis and the role that Oxalobacter formigenes may have in that association.

METHODS

We performed a MEDLINE search of "cystic fibrosis and nephrolithiasis" and "Oxalobacter formigenes." Epidemiological and experimental evidence and possible mechanisms explaining the association were critically reviewed.

RESULTS

Of patients with CF, 3.0% to 6.3% are affected with nephrolithiasis, a percentage greater than that of age-matched controls without CF, in whom the rate is 1% to 2%. Studies have suggested possible mechanisms for the association, including hyperuricosuria, hyperoxaluria, primary defects in calcium handling caused by mutation of the CF transmembrane regulator (CFTR), hypocitraturia, and lack of colonization with O formigenes, an enteric oxalate-degrading bacterium. The absence of colonization could be related to frequent courses of antibiotics.

CONCLUSION

Although the incidence of stones in patients with CF may be increased compared with controls without CF, many possible mechanisms are implicated. The relative contributions of these mechanisms remain uncertain. Future directions may include specific identification of lithogenic risks and therapy aimed at stone prevention in this population.

Newborn screening for cystic fibrosis

Early diagnosis of cystic fibrosis (CF) provides an opportunity to improve disease control and prevent early complications. Of patients with CF in the United States, 10% are identified early through newborn screening (including infants born in Colorado, Massachusetts, New Jersey, New York, Wisconsin, Wyoming, and parts of California, Connecticut, Pennsylvania, and Montana). Successful screening programs in these states have stimulated other states to consider adding CF screening to their newborn programs. Additionally, new technology permits expanded screening for numerous genetic conditions. Genetic screening, such as that used most frequently for CF, creates new challenges for the clinician, including atypical disease presentations and carrier detection. In this review, we examine the many advances in CF newborn screening and early care that were reported during the last few years.

Plasma and red blood cell zinc in cystic fibrosis

The objectives of this study were to measure plasma and red blood cell (RBC) zinc concentrations in patients with cystic fibrosis (CF), and examine their relationship to nutritional status and pulmonary function. Plasma and RBC zinc levels were compared in 53 CF patients ranging in age from 0.5-46 years. Their relationships to weight (% ideal weight) and forced expired volume in 1 sec (FEV(1)) (% predicted value) were examined. After excluding improperly handled specimens, RBC zinc levels in 51 patients and plasma zinc concentrations in 40 patients were included for analysis. Sixteen of 51 (31%) patients had low RBC zinc levels compared to 4 of 40 (10%) with low plasma zinc concentrations (P < 0.01). Thirteen of 38 patients (34%) in whom both values were obtained had low RBC zinc concentrations compared to 4 of 38 (11%) with low plasma zinc levels (P < 0.022). Neither low RBC nor plasma zinc levels correlated with nutritional status or lung function. In conclusion, about one third of patients with CF had low RBC zinc levels. Plasma zinc concentrations may not adequately reflect overall zinc status. This deficiency did not appear to be related to either nutritional status or lung function. The significance of low RBC zinc in CF is unknown.

Zinc homeostasis in Malawian children consuming a high-phytate, maize-based diet

BACKGROUND

Zinc deficiency in children is an important public health concern in the developing world, and the consumption of predominantly cereal-based diets with a high phytate content may contribute to the risk. The gastrointestinal tract plays a central role in absorbing and conserving zinc, yet it has not been carefully studied in such children.

OBJECTIVE

This study investigated zinc homeostasis in healthy, free-living Malawian children with habitually high-phytate diets to better understand the role of the gastrointestinal tract.

DESIGN

We evaluated zinc homeostasis in 10 children aged 2-5 y who were consuming a maize-based diet (phytate:zinc molar ratio of 23:1). Zinc stable isotopes were administered orally and intravenously. The tracer and tracee were measured in urine and feces.

RESULTS

Endogenous fecal zinc was high in comparison with results for this measure in previous studies. Typical correlations seen in subjects consuming a low-phytate diet between total absorbed zinc, the size of the exchangeable zinc pool, and endogenous fecal zinc were not observed. Fractional absorption of zinc was 0.24.

CONCLUSIONS

Zinc homeostasis was perturbed, particularly by large, endogenous fecal zinc losses, in this vulnerable population. The effects of interventions to improve zinc status, including dietary phytate reduction, on zinc homeostasis merit further study.

Zinc deficiency in nursing infants

Zinc deficiency during nursing can occur even in breast-fed infants. Zinc reserves accumulated during fetal development modulate the infant's susceptibility to zinc deficiency. Improvement of maternal zinc nutrition during pregnancy is the key for infant's zinc nutritional support and prevention of low-for-lactation-age zinc concentrations of breast-milk.

Fatty acids, alpha-fetoprotein, and cystic fibrosis

Docosahexaenoic acid, found lacking in animal models of cystic fibrosis, has been proposed as a dietary supplement therapy for this genetic disorder. Alpha-fetoprotein, which binds and transports docosahexaenoic acid, may be a useful marker to improve the management and follow-up in newborn screening programs for cystic fibrosis, because only 20% of such infants are diagnosed at birth.

Cystic fibrosis screening in newborns: results from existing programs

Newborn screening for cystic fibrosis (CF) provides early identification and initiation of treatment to infants with this fatal and often misdiagnosed genetic disease. Although reports of health benefits continue to mount from decade-old screening programs in Wisconsin, France, and Australia, newborn screening for CF is still a highly debated topic in genetic policy development. This article summarizes the literature published between May 2000 and April 2001 regarding the health benefits, risks, cost-effectiveness, and programmatic issues of newborn screening for CF. The literature consistently shows evidence of benefits and lack of harm from newborn screening for CF.

Overview of zinc absorption and excretion in the human gastrointestinal tract

Zinc homeostasis is primarily maintained via the gastrointestinal system by the processes of absorption of exogenous zinc and gastrointestinal secretion and excretion of endogenous zinc. Although these processes modulate net absorption and the size of the readily exchangeable zinc pools, there are limits to the effectiveness of the homeostatic mechanisms of these and other systems. As a result of the interplay of the subcellular regulation of these mechanisms and host, dietary and environmental factors, zinc deficiency is not uncommon, especially on a global basis. This overview briefly reviews current understanding about the subcellular mechanisms of zinc absorption and transport. Factors recognized to affect zinc absorption at the whole body level are reviewed and include the amount and form of zinc consumed; dietary promoters, such as animal protein and low-molecular-weight organic compounds; dietary inhibitors, such as phytate and possibly iron and calcium when consumed as supplements; and physiologic states, such as pregnancy, lactation and early infancy, all of which increase the demand for absorbed zinc. The control of endogenously secreted zinc is less well understood. Available data suggest that the quantity of secreted zinc with each meal may be considerable and that efficient reabsorption is critical to the maintenance of normal zinc balance. Factors that have been proposed to interfere with the normal reabsorption of endogenous zinc include phytate and unabsorbed fat. Understanding of the dietary, physiologic, pathologic and environmental factors that may adversely affect these processes, and therefore zinc homeostasis, will be critical to preventing and treating zinc deficiency in human populations.