Fluid Zinc Research Articles

Decrease of non-point zinc runoff using porous concrete

The use of porous concrete columns to decrease the amount of zinc in stormwater runoff is examined. The concentration of zinc in a simulated stormwater fluid (zinc acetate solution), fed through concrete columns (∅10 × 10 cm) decreased by 50–81%, suggesting physical adsorption of zinc by the porous concrete. We propose the use of porous concrete columns (∅50 × 10 cm) as the base of sewage traps. Longer-term, high-zinc concentration monitoring revealed that porous concrete blocks adsorb 38.6 mg cm −3 of zinc. A period of no significant zinc runoff (with an acceptable concentration of zinc in runoff of 0.03 mg L −1, a zinc concentration equal to the Japanese Environmental Standard) is estimated for 41 years using a 1-ha catchment area with 20 porous concrete sewage traps. Scanning electron microscopy of the porous concrete used in this study indicates that the needle-like particles formed by hydration action significantly increase zinc adsorption. Evidence suggests that the hydrant is ettringite and has an important role in zinc adsorption, the resulting immobilization of zinc and the subsequent effects on groundwater quality.

Copper, iron, zinc and other element concentrations in cerebrospinal fluid of Parkinson’s disease patients – considerations on literature data

Copper, iron, zinc and other element concentrations in cerebrospinal fluid of Parkinson’s disease patients – considerations on literature data

Changes in Seminal Quality Following Oral Zinc Therapy

33 subfertile men with idiopathic asthenozoospermia and/or oligozoospermia were treated with oral zinc sulphate. After treatment a significant improvement in the percentage progressive and total sperm motility was noted accompanied by a significant increase in seminal fluid zinc levels.

004 Topical Zinc Oxide for Open Pilonidal Wounds

Extended healing time and lack of documented effective treatments of sacrococcygeal pilonidal disease create substantial problems. Locally applied zinc oxide has been reported to promote wound healing. We have compared topical zinc oxide (3%) with placebo meshes for pilonidal wounds healing by secondary intention in a randomized, double-blind, placebo-controlled multicenter trial. Sixty-four consecutive patients, 53 males, aged between 18 and 60 years (median 26 years) with excised pilonidal wounds were centrally randomized to local zinc oxide (30 mg/g, n = 33) or to placebo (n = 31) mesh treatment. Patients were followed with strict recording of beneficial and harmful effects. The median healing times were 54 days (42–71 days, interquartile range, n = 33) for the zinc group and 62 days (55–82 days, n = 31) for the placebo group. This difference was not statistically different (p = 0.32). Based on Cox regression analysis initial wound volume influenced healing negatively (p = 0.016) while smoking (p = 0.011) was associated with faster wound healing. Significantly (p < 0.01) more placebo (n = 12) than zinc oxide-treated patients (n = 3) needed antibiotics postoperatively. Although topical zinc oxide increased (p < 0.001) wound fluid zinc levels (1830 ± 405 μM, mean ± SEM) compared with placebo (3.1 ± 1.6 μM) serum-zinc levels did not differ significantly between the zinc (13.5 ± 0.4 μM) and placebo (12.8 ± 0.4 μm) groups on postoperative day 7. No adverse events were recorded. Topical zinc oxide treatment did not accelerate time to closure of open pilonidal wounds but was associated with reduced antibiotic usage.

Principal Cells' Apocrine Secretion of Epididymosomes and Its Function in Sperm Maturation.

During their transit along the epididymis, mammalian spermatozoa acquire new proteins involved in fertilization. Some of these epididymal proteins behave like integral membrane proteins when spermatozoa are submitted to different physico-chemical treatments, suggesting an unusual mechanism of secretion. In fact, Principal cells of the epididymal epithelium use an apocrine mode of secretion to deliver small membranous particles named «epididymosomes» in the epididymal intraluminal compartment. Apocrine secretion is common in reproductive organs such as the prostate and the mammary glands. It involves the formation at the apical pole of secretory epithelial cells of cytoplasmic blebs containing selected organelles. These blebs detach from the secretory cells, disintegrate releasing in the extracellular milieu its content: in the case of epididydmal principal cells, epididymosomes. These vesicles are heterogeneous with a diameter of 50-250 nm. They are characterized by a high cholesterol/phospholipids ratio and are very resistant to physico-chemical injuries such as hypertonic solution, freezing-thawing cycles and sonication. A complex electrophoretic pattern of proteins is associated with these epididymosomes. The protein composition of epididymosomes varies along the epididymis. The epididymosomes are in close relation with spermatozoa within the intraluminal epididymal compartment. Interaction between epididymosomes and spermatozoa results in the transfer of selected proteins to the maturing male gamete. The transfer of proteins from epididymosomes to spermatozoa is saturable, time and temperature dependent, and more efficient at pH 6.5. The presence of Zinc in the co-incubation increases the efficiency of protein transfer. This correlates with the relatively high concentration of Zinc in the epididymal fluid. We have characterized some proteins of epididymosomes transferred to spermatozoa. These include the enzymes of the polyol pathway, P25b proposed to be involved in zona pellucida binding and MIF (Macrophage mobility Inhibitory Factor). Whereas as P25b is GPI anchored to both epididymosomes and sperm plasma membrane, MIF is internalized and is associated to dense fibers of the flagellum. Epididymosomes contain Detergent Resistant Membrane (DRM) to which some proteins are associated while others are excluded. Once transferred, proteins associated to DRM in epididymosomes remain associated to DRM of spermatozoa. Using LC-QToF, we recently identified up to 146 different proteins associated to epididymosomes collected in the distal portion of the human excurrent duct. The function of epididymosomes is thus complex suggesting that they play a major role in sperm maturation. This work was supported by Natural Sciences and Engineering Research Council of Canada and the Canadians Institute for Health Research.

The expression of zinc transporters and metallothionein is decreased in the intestinal and alveolar epithelium of chronic alcohol‐fed rats

We have previously shown in animal models that chronic alcohol ingestion significantly alters the alveolar epithelial barrier, and renders the lung susceptible to acute inflammatory injury. Although alcoholics are known to be deficient in micronutrient zinc that protects cell membranes from oxidative damage, there are no reports on the effects of chronic alcohol ingestion on zinc bioavailability. In this study, we examined the expression of selected members of the zinc transporters ZIP (SLC39A), and ZNT (SLC30A), as well as the zinc storage protein metallothionein in the small intestinal and alveolar epithelium of alcohol‐fed and control‐fed rats. The expression of ZIP1 and ZIP4 was significantly decreased in the duodenum of alcohol‐fed rats, suggesting less zinc absorption from the diet. The expression of the ZNT4 was significantly decreased in the small intestine and alveolar epithelium, perhaps to conserve locally available zinc. In parallel, this downregulation of transporters resulted in decreased levels of zinc in the epithelial lining fluid from alcohol‐fed rats. Metallothionein expression, a good indicator of zinc status, was significantly decreased in the intestinal and alveolar epithelium of alcohol‐fed rats. These data suggest that chronic alcohol ingestion may affect zinc homeostasis in vivo through alterations in the zinc transporters and zinc storage protein.

Zinc-Amyloid β Interactions on a Millisecond Time-Scale Stabilize Non-fibrillar Alzheimer-Related Species

The role of zinc, an essential element for normal brain function, in the pathology of Alzheimer's disease (AD) is poorly understood. On one hand, physiological and genetic evidence from transgenic mouse models supports its pathogenic role in promoting the deposition of the amyloid beta-protein (Abeta) in senile plaques. On the other hand, levels of extracellular ("free") zinc in the brain, as inferred by the levels of zinc in cerebrospinal fluid, were found to be too low for inducing Abeta aggregation. Remarkably, the release of transient high local concentrations of zinc during rapid synaptic events was reported. The role of such free zinc pulses in promoting Abeta aggregation has never been established. Using a range of time-resolved structural and spectroscopic techniques, we found that zinc, when introduced in millisecond pulses of micromolar concentrations, immediately interacts with Abeta 1-40 and promotes its aggregation. These interactions specifically stabilize non-fibrillar pathogenic related aggregate forms and prevent the formation of Abeta fibrils (more benign species) presumably by interfering with the self-assembly process of Abeta. These in vitro results strongly suggest a significant role for zinc pulses in Abeta pathology. We further propose that by interfering with Abeta self-assembly, which leads to insoluble, non-pathological fibrillar forms, zinc stabilizes transient, harmful amyloid forms. This report argues that zinc represents a class of molecular pathogens that effectively perturb the self-assembly of benign Abeta fibrils, and stabilize harmful non-fibrillar forms.

Zinc‐binding property of the major yolk protein in the sea urchin − implications of its role as a zinc transporter for gametogenesis

Major yolk protein (MYP), a transferrin superfamily protein that forms yolk granules in sea urchin eggs, is also contained in the coelomic fluid and nutritive phagocytes of the gonad in both sexes. MYP in the coelomic fluid (CFMYP; 180 kDa) has a higher molecular mass than MYP in eggs (EGMYP; 170 kDa). Here we show that MYP has a zinc-binding capacity that is diminished concomitantly with its incorporation from the coelomic fluid into the gonad in the sea urchin Pseudocentrotus depressus. Most of the zinc in the coelomic fluid was bound to CFMYP, whereas zinc in eggs was scarcely bound to EGMYP. Both CFMYP and EGMYP were present in nutritive phagocytes, where CFMYP bound more zinc than EGMYP. Saturation binding assays revealed that CFMYP has more zinc-binding sites than EGMYP. Labeled CFMYP injected into the coelom was incorporated into ovarian and testicular nutritive phagocytes and vitellogenic oocytes, and the molecular mass of part of the incorporated CFMYP shifted to 170 kDa. Considering the fact that the digestive tract is a major production site of MYP, we propose that CFMYP transports zinc, essential for gametogenesis, from the digestive tract to the ovary and testis through the coelomic fluid, after which part of the CFMYP is processed to EGMYP with loss of zinc-binding site(s).

Online in-tube solid phase extraction coupled to ICP-MS for in vivo determination of the transfer kinetics of trace elements in the brain extracellular fluid of anesthetized rats

Little is known about the in vivo kinetics of trace metal ions in the brain during various neurodegenerative events. In this paper, we describe a method for simultaneously monitoring the kinetics of several trace metal ions in vivo in brain extracellular fluid using microdialysis coupled online with in-tube solid phase extraction (SPE) and ICP-MS detection. To facilitate the online selective separation and ICP-MS detection processes, the trace metal ions in the dialysates, which contained tremendous amounts of salt matrix, were extracted online on the inner wall of a PVC tube—modified with a conditioning solution (10 mg EDTA L–1 of pH 10) in advance—and delivered to the ICP-MS using an eluent containing 20 mg L–1 of EDTA at pH 10. Coupling of the microdialysis sampling with the online in-tube SPE and ICP-MS detection allowed us to measure simultaneously the changes in the concentrations of Zn2+, Cu2+, and Mn2+ in the brain extracellular fluid over time. Using our proposed in-tube SPE process, we obtained online detection limits that were in the sub-microgram-per-litre range (based on 3σ); the temporal resolution was limited to 15 min because of the very low microdialysis perfusion rate (0.5 µL min–1). By combining with microdialysis probe, we also found the long-term stability of the continuous measurement over 5 h of each of the analyte ions was within 10% CV and there was no significant change in the recoveries of analyte ions when using the same PVC tubing with our online system to measure analyte ions at 10 µg L–1. From animal experiments we determined that the basal concentrations of Cu2+, Zn2+, and Mn2+ were 2.19 ± 0.12, 4.07 ± 1.81, and 2.74 ± 0.11 µg L–1, respectively; these values agree well with those found in the literature. Additionally, we observed apparent increases in the levels of zinc and manganese in the extracellular fluid of the brain in vivo after administering MnSO4, ZnSO4, and CuCl2 through intraperitoneal injection. We verified the reliability of this method by analyzing reference urine samples. To the best of our knowledge, our proposed online analytical system is the first example of a minimally invasive technique that is capable of simultaneously investigating the transfer kinetics of several metal ions in the brain in vivo.

A randomized, double‐blind, placebo‐controlled multicenter trial evaluating topical zinc oxide for acute open wounds following pilonidal disease excision

The purpose of this randomized, double-blind, placebo-controlled multicenter trial was to compare topical zinc oxide with placebo mesh on secondary healing pilonidal wounds. Sixty-four (53 men) consecutive patients, aged 17-60 years, were centrally randomized to either treatment with 3% zinc oxide (n = 33) or placebo (n = 31) by concealed allocation. Patients were followed with strict recording of beneficial and harmful effects including masked assessment of time to complete wound closure. Analysis was carried out on an intention-to-treat basis. Median healing times were 54 days (interquartile range 42-71 days) for the zinc and 62 days (55-82 days) for the placebo group (p = 0.32). Topical zinc oxide increased (p < 0.001) wound fluid zinc levels to 1,540 (1,035-2,265) microM and decreased (p < 0.05) the occurrence of Staphylococcus aureus in wounds. Fewer zinc oxide (n = 3) than placebo-treated patients (n = 12) were prescribed postoperative antibiotics (p = 0.005). Serum-zinc levels increased (p < 0.001) postoperatively in both groups but did not differ significantly between the two groups on day 7. Zinc oxide was not associated with increased pain by the visual analog scale, cellular abnormalities by histopathological examination of wound biopsies, or other harmful effects. Larger clinical trials will be required to show definitive effects of topical zinc oxide on wound healing and infection.

Use of a Zinc Fluorophore to Measure Labile Pools of Zinc in Body Fluids and Cell-Conditioned Media

Here we describe a rapid and sensitive zinquin-based fluorometric assay that enables one to monitor levels of labile Zn(II) in body fluids, buffers, and cell-conditioned culture media as well as changes in these pools in disease. Labile pools of Zn(II) are free or loosely bound pools and more tightly bound but zinquin-accessible pools in contrast to the fixed pools of Zn(II) within metalloproteins. In human plasma, mean labile Zn(II) was 8.1 microM (SEM 0.53; n = 81) and constituted about 70% of the total plasma Zn(II) and >90% of human plasma albumin Zn(II). Plasma labile Zn(II) was significantly depleted after 7 days of Zn(II) deprivation in mice, despite only small changes in body weight. Labile Zn(II) concentrations were also measured in the induced sputum plugs, saliva, and urine of normal adults and were 1.30 microM (SEM 0.27; n = 73), 0.11 microM (SEM 0.11; n = 6), and 0.23 microM (SEM 0.08; n = 8), respectively. Urinary labile Zn(II) concentration was significantly increased in some patients with type II diabetes mellitus (overall mean was 0.90 microM, SEM 0.30; n = 12). The technique may be particularly useful in assessing extracellular Zn(II) levels in diseases associated with altered Zn(II) homeostasis, identifying those subjects most in need of Zn(II) supplementation, and defining the optimum concentrations of available Zn(II) in buffers and culture media.

The effects of ultrasound on synovial fluid zinc level in patients with rheumatoid arthritis

The effects of ultrasound on synovial fluid zinc level in patients with rheumatoid arthritis

The role of iron, copper and zinc and their effects in on/off Parkinson's patients on L-dopa therapy

We have quantified levels of iron, copper and zinc in cerebrospinal fluid (CSF) and serum by atomic absorption spectrophotometer in 36 patients with Parkinson's disease (PD), all on L-dopa therapy. Out of these 36, 17 showed On or positive response to L-dopa whereas 19 patients showed On and Off response. These data were compared with 21 healthy controls. The results showed that serum levels of iron, copper as well zinc remained unchanged whereas in CSF, a significant decrease in zinc was found in both On and On/Off PD patients, indicating the deficiency of zinc which continues in the detoriating clinical condition of Off patients. The level of copper remained unchanged in both On and On/Off PD patients. Iron increases in CSF of both patients, which is clear evidence of a relationship between increased iron level in brain that could be corrolated with decrease in dopamine levels and oxidative stress in PD Patients.

Perinatal ω-3 polyunsaturated fatty acid supply modifies brain zinc homeostasis during adulthood

Dietary omega-3 polyunsaturated fatty acid (PUFA) influences the expression of a number of genes in the brain. Zinc transporter (ZnT) 3 has been identified as a putative transporter of zinc into synaptic vesicles of neurons and is found in brain areas such as hippocampus and cortex. Neuronal zinc is involved in the formation of amyloid plaques, a major characteristic of Alzheimer's disease. The present study evaluated the influence of dietary omega-3 PUFA on the expression of the ZnT3 gene in the brains of adult male Sprague-Dawley rats. The rats were raised and/or maintained on a control (CON) diet that contained omega-3 PUFA or a diet deficient (DEF) in omega-3 PUFA. ZnT3 gene expression was analyzed by using real-time PCR, free zinc in brain tissue was determined by zinquin staining, and total zinc concentrations in plasma and cerebrospinal fluid were determined by atomic absorption spectrophotometry. Compared with CON-raised animals, DEF-raised animals had increased expression of ZnT3 in the brain that was associated with an increased level of free zinc in the hippocampus. In addition, compared with CON-raised animals, DEF-raised animals had decreased plasma zinc level. No difference in cerebrospinal fluid zinc level was observed. The results suggest that overexpression of ZnT3 due to a perinatal omega-3 PUFA deficiency caused abnormal zinc metabolism in the brain. Conceivably, the influence of dietary omega-3 PUFA on brain zinc metabolism could explain the observation made in population studies that the consumption of fish is associated with a reduced risk of dementia and Alzheimer's disease.

Occupational exposure to welding fume among welders: alterations of manganese, iron, zinc, copper, and lead in body fluids and the oxidative stress status.

Welders in this study were selected from a vehicle manufacturer; control subjects were from a nearby food factory. Airborne manganese levels in the breathing zones of welders and controls were 1.45 +/- SD1.08 mg/m and 0.11 +/- 0.07 microg/m, respectively. Serum levels of manganese and iron in welders were 4.3-fold and 1.9-fold, respectively, higher than those of controls. Blood lead concentrations in welders increased 2.5-fold, whereas serum zinc levels decreased 1.2-fold, in comparison with controls. Linear regression revealed the lack of associations between blood levels of five metals and welder's age. Furthermore, welders had erythrocytic superoxide dismutase activity and serum malondialdehyde levels 24% less and 78% higher, respectively, than those of controls. These findings suggest that occupational exposure to welding fumes among welders disturbs the homeostasis of trace elements in systemic circulation and induces oxidative stress.

Susceptibility to kainate-induced seizures under dietary zinc deficiency.

Zinc homeostasis in the brain is altered by dietary zinc deficiency, and its alteration may be associated with the etiology and manifestation of epileptic seizures. In the present study, susceptibility to kainate-induced seizures was enhanced in mice fed a zinc-deficient diet for 4 weeks. When Timm's stain was performed to estimate zinc concentrations in synaptic vesicles, Timm's stain in the brain was attenuated in the zinc-deficient mice. In rats fed the zinc-deficient diet for 4 weeks, susceptibility to kainate-induced seizures was also enhanced. When the release of zinc and neurotransmitters in the hippocampal extracellular fluid of the zinc-deficient rats was studied using in vivo microdialysis, the zinc concentration in the perfusate was less than 50% of that of the control rats and the increased levels of zinc by treatment with kainate were lower than the basal level in control rats, suggesting that vesicular zinc is responsive to dietary zinc deficiency. The levels of glutamate in the perfusate of the zinc-deficient rats were more increased than in the control rats, whereas the levels of GABA in the perfusate were not at all increased in the zinc-deficient rats, unlike in the control rats. The present results demonstrate an enhanced release of glutamate associated with a decrease in GABA concentrations as a possible mechanism for the increased seizure susceptibility under zinc deficiency.

Manganese, copper, and zinc in cerebrospinal fluid from patients with multiple sclerosis.

The concentrations of manganese, copper, and zinc in cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS) and patients with no known neurological disease (control group) were measured. Manganese and copper levels were determined by two different analytical methods: atomic absorption spectrometry (AAS) and high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS), whereas zinc levels were determined by HR-ICP-MS only. Manganese levels (mean+/-SEM) were significantly decreased in the CSF of MS patients (1.07+/-0.13 microg/L, ICP-MS; 1.08+/-0.11 microg/L, AAS) compared to the levels in the control group (1.78+/-0.26 microg/L, ICP-MS; 1.51+/-0.17 microg/L, AAS). Copper levels were significantly elevated in the CSF of MS patients (10.90+/-1.11 microg/L; ICP-MS, 11.53+/-0.83 microg/L, AAS) compared to the levels in the control group (8.67+/-0.49 microg/L, ICP-MS; 9.10+/-0.62 microg/L, AAS). There were no significant differences between the CSF zinc levels of MS and control patients. The physiological basis for the differences in manganese and copper concentrations between MS patients and controls is unknown, but could be related to alterations in the manganese- containing enzyme glutamine synthetase and the copper-containing enzyme cytochrome oxidase.

Trace elements analysis of ascitic fluid in benign and malignant diseases

Objectives: To evaluate differences in ascitic fluid trace element concentrations which might be useful in discrimination between benign and malignant ascites. Design and Methods: The concentrations of copper, zinc, magnesium and iron in ascitic fluid and venous blood in 17 patients were investigated. The relationship between these trace elements and type of disease were examined. Investigations were carried out in a group of 5 males and 5 females aged 54 to 77 yr who had cirrhosis ascites and in a group of 7 females aged 41 to 76 yr with ascites due to gynecologic neoplasms. Results: The mean ascitic fluid and serum concentrations of copper were significantly higher in neoplastic diseases compared to benign disease states (118,43 vs. 97,50, 91,14 vs. 26.90) ( p < 0,05 and p < 0,01 respectively). The zinc levels in ascitic fluid and serum were significantly different between the groups ( p < 0,01). Neoplastic patients had significantly higher ascitic fluid magnesium levels than the benign disease group (2,17 vs. 1,55, p < 0,001). The serum levels of iron were significantly lower in the neoplastic diseases group (92, 28 vs. 255, p < 0, 01). In benign diseases the concentration of zinc in ascitic fluid correlated positively with ascitic fluid copper concentrations. The concentrations of zinc and iron in malignant ascites correlate positively with the magnesium concentrations. Statistically significant negative correlations were found between ascites zinc and magnesium and magnesium and copper in cirrhotic patients and magnesium and copper in malignant diseases. Conclusions: The results showed that zinc, magnesium and iron levels were significantly different between cirrhotic and neoplastic illness. Analysis of serum and ascitic fluid trace element composition may be helpful in identifying and distinguishing the malignant and nonmalignant ascites and provides useful information on processes regulating passage of blood components into the peritoneal cavity.

Proinflammatory cytokines, prostaglandins and zinc in febrile convulsions.

Some changes in the levels of proinflammatory cytokines, prostaglandins and zinc (Zn) in peripheral blood and cerebrospinal fluid (CSF) have been suggested to occur for the pathogenesis of febrile convulsions (FC). In order to test this hypothesis, the levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 alpha, IL-1 beta and prostaglandins (PGE(2), PGF(2 alpha), PGD(2)) in the CSF and plasma and the levels of Zn in serum and CSF were investigated in children during the acute and late phases of FC. Results were compared with control subjects with meningismus. During the acute phase of FC, children had significantly elevated plasma levels of IL-1 beta, CSF levels of TNF-alpha, plasma levels of PGE(2), PGF(2 alpha) and PGD(2) and CSF levels of PGD(2) (P<0.05). A positive correlation between the degree of fever and plasma IL-1 beta levels was observed in both patients and controls. Three months after the acute phase of FC, plasma levels of IL-1 beta had returned to levels seen in controls. Children with FC also had significantly decreased serum Zn levels during the acute phase (P<0.05). However, there was no significant difference between the groups with respect to CSF Zn levels (P>0.05). During the acute phase of FC, patients had significantly increased plasma IL-1 beta and prostaglandin levels and decreased serum Zn levels. These changes may be responsible for FC pathogenesis.

Analysis and chemical speciation of copper and zinc in wound fluid

A novel method for the analysis of trace element chemical speciation at parts per billion (ppb) levels in wound fluid samples both contributes to the fundamental inorganic biochemistry of the healing process and permits improved treatments. Potentiometric Stripping Analysis in combination with acid digestion has been used to quantify the total copper and zinc levels in a series of 0.5 ml samples of fluid obtained from surgical wounds. Further, the degree of blood contamination has been investigated using visible spectroscopy. The prevailing chemical speciation (chemical forms) of these total concentrations of copper and zinc amongst low molecular mass ligands in wound fluid has been investigated by computer modelling using JESS, the Joint Expert Speciation System. The model, involving 38 components, generates in the region of 3500 individual low molecular mass complexes including copper, zinc, iron, calcium and manganese species, and predicts that the majority of low molecular mass ( lmm) copper complexes are electrically net-neutral, whilst those of zinc are predominantly charged. Further studies indicate that supplementing the concentrations of histidine and tryptophan may increase the net-neutral zinc fraction, the optimum effect being achieved at pH=7.4. This may be important in transporting zinc into healing cells.