Analysis and chemical speciation of copper and zinc in wound fluid

The Role of Copper Homeostasis in Brain Disease

In the human body, copper is an important trace element and is a cofactor for several important enzymes involved in energy production, iron metabolism, neuropeptide activation, connective tissue synthesis, and neurotransmitter synthesis. Copper is also necessary for cellular processes, such as the regulation of intracellular signal transduction, catecholamine balance, myelination of neurons, and efficient synaptic transmission in the central nervous system. Copper is naturally present in some foods and is available as a dietary supplement. Only small amounts of copper are typically stored in the body and a large amount of copper is excreted through bile and urine. Given the critical role of copper in a breadth of cellular processes, local concentrations of copper and the cellular distribution of copper transporter proteins in the brain are important to maintain the steady state of the internal environment. The dysfunction of copper metabolism or regulatory pathways results in an imbalance in copper homeostasis in the brain, which can lead to a myriad of acute and chronic pathological effects on neurological function. It suggests a unique mechanism linking copper homeostasis and neuronal activation within the central nervous system. This article explores the relationship between impaired copper homeostasis and neuropathophysiological progress in brain diseases.

Assessment of Traumatic Brain Injury by Increased 64Cu Uptake on 64CuCl2 PET/CT

Copper is a nutritional trace element required for cell proliferation and wound repair.

METHODS

To explore increased copper uptake as a biomarker for noninvasive assessment of traumatic brain injury (TBI), experimental TBI in C57BL/6 mice was induced by controlled cortical impact, and (64)Cu uptake in the injured cortex was assessed with (64)CuCl2 PET/CT.

RESULTS

At 24 h after intravenous injection of the tracer, uptake was significantly higher in the injured cortex of TBI mice (1.15 ± 0.53 percentage injected dose per gram of tissue [%ID/g]) than in the uninjured cortex of mice without TBI (0.53 ± 0.07 %ID/g, P = 0.027) or the cortex of mice that received an intracortical injection of zymosan A (0.62 ± 0.22 %ID/g, P = 0.025). Furthermore, uptake in the traumatized cortex of untreated TBI mice (1.15 ± 0.53 %ID/g) did not significantly differ from that in minocycline-treated TBI mice (0.93 ± 0.30 %ID/g, P = 0.33).

CONCLUSION

Overall, the data suggest that increased (64)Cu uptake in traumatized brain tissues holds potential as a new biomarker for noninvasive assessment of TBI with (64)CuCl2 PET/CT.

Antimicrobial clay-based materials for wound care

The historical use of clay minerals for the treatment of wounds and other skin ailments is well documented and continues within numerous human cultures the world over. However, a more scientific inquiry into the chemistry and properties of clay minerals emerged in the 19th century with work investigating their role within health gathering pace since the second half of the 20th century. This review gives an overview of clay minerals and how their properties can be manipulated to facilitate the treatment of infected wounds. Evidence of the antimicrobial and healing effects of some natural clay minerals is presented alongside a range of chemical modifications including metal-ion exchange, the formation of clay–drug composites and the development of various polymer–clay systems. While the evidence for applying these materials to infected wounds is limited, we contextualize and discuss the future of this research.

Wound Fluid in Diabetic Foot Ulceration

Valid and reproducible sampling techniques as well as processing protocols are required for the assessment of biomarkers and mediators contained in wound exudate. Moreover, the ideal technique should be easy to use even in daily clinical routine. This is challenging since wound fluid represents an inhomogeneous mixture of different exogenous and endogenous sources. Analyzing wound fluid, however, may facilitate clinical decision making. Many techniques for obtaining wound fluid have been described. There is very little validation data, and the array of different techniques appears confusing. Structuring and new standards are needed to avoid wound fluid sampling yielding an “undefined soup.” A lot of wound fluid parameters have been analyzed, although none of them have made its way into clinical practice. Nevertheless, basic principles of wound healing have been established from wound fluid analysis. With adequate techniques suitable for daily practice, basic research might foster our clinical understanding of wound healing with implications for new therapies. So far, research has mainly concentrated on analyzing available sample material with respect to either a wide variety of analytes or comparing acute with chronic wound exudate. Clinical endpoints such as healing or wound infection as well as longitudinal data may indeed be more valuable for clinical practice, enabling the discovery of meaningful biomarkers using a suitable technique.

Collagen-based Tissue Engineering as Applied to Heart Valves

Using the method of directed collagen gel shrinkage, we have been fabricating heart valves and mitral valve chordae [1,2,3]. The principle involves mixing solubilized collagen with the appropriate cells. When the collagen-cell mixture is neutralized, soluble collagen reassembles into fibrils and a gel is created. When the gel is mechanically constrained, the collagen fibrils align in the direction of constraint. The generation of tensile force during contraction is crucial for the formation of highly aligned, compacted collagenous constructs. So far, inappropriate mechanical properties have been one of the main limitations of most collagen-based tissue equivalents. In this study, we focused on providing both biomechanical and biochemical stimuli to increase cellular proliferation, matrix synthesis, and hence improve the mechanical properties of the collagen constructs. We explored a number of holder materials and configurations, with an objective to maximize the lateral compaction of our constructs. We designed a bioreactor that can provide controlled static tension to our collagen constructs. We also developed a nutrition-fortified medium that includes trace elements (Zn2+, Cu2+, Fe2+ and Mn2+), various amino acids, and vitamins (A, B complex, and C). Our ultimate goal was to combine biomechanical and biochemical stimuli, and enhance the mechanical strength of our collagen constructs.

Dioxygen oxidation Cu(II) → Cu(III) in the copper complex of cyclo(Lys-dHis-βAla-His): a case study by EXAFS and XANES approach

A former spectroscopic study of Cu(II) coordination by the 13-membered ring cyclic tetrapeptide c(Lys-dHis-βAla-His) (DK13), revealed the presence, at alkaline pH, of a stable peptide/Cu(III) complex formed in solution by atmospheric dioxygen oxidation. To understand the nature of this coordination compound and to investigate the role of the His residues in the Cu(III) species formation, Cu K-edge XANES, and EXAFS spectra have been collected for DK13 and two other 13-membered cyclo-peptides: the diastereoisomer c(Lys-His-βAla-His) (LK13), and c(Gly-βAla-Gly-Lys) (GK13), devoid of His residues. Comparison of pre-edge peak features with those of Cu model compounds, allowed us to get information on copper oxidation state in two of the three peptides, DK13 and GK13: DK13 contains only Cu(III) ions in the experimental conditions, while GK13 binds only with Cu(II). For LK13/Cu complex, EXAFS spectrum suggested and UV-vis analysis confirmed the presence of a mixture of Cu(II) and Cu(III) coordinated species. Theoretical XANES spectra have been calculated by means of the MXAN code. The good agreement between theoretical and experimental XANES data collected for DK13, suggests that the refined structure, at least in the first coordination shell around Cu, is a good approximation of the DK13/Cu(III) coordination species present at strongly alkaline pH. All the data are consistent with a slightly distorted pyramidal CuN(4) unit, coming from the peptide bonds. Surprisingly, the His side-chains seemed not involved in the final, stable, Cu(III) scaffold.

Short-chain oligopeptides with copper(II) binding properties: The impact of specific structural modifications on the copper(II) coordination abilities

A series of linear tetrapeptides containing two histidyl residues in position 2 and 4, namely DHGH, DHGdH, KHGH, KHGdH, Ac-DHGH-NH(2), Ac-DHGdH-NH(2), Ac-KHGH-NH(2), and Ac-KHGdH-NH(2), were synthesized and characterised. Their copper(II) binding properties were investigated in depth through a variety of physicochemical methods. Potentiometric titrations were first carried out to establish the stoichiometry and the stability of the resulting copper(II)-peptide complexes. The copper(II) chromophores that are formed in the various cases in dependence of pH were subsequently characterised by extensive spectroscopic analysis (UV-Vis, EPR, CD) in strict correlation with potentiometric data. The effects of the nature of the first amino acid (Lys versus Asp) and of N-terminal amino group protection on copper(II) binding were specifically addressed. On turn, the careful comparison of the copper(II) coordination abilities of the linear peptides with those of their cyclic analogs provided insight into the effects of cyclization on the overall metal binding properties.

Zn(2+) release behavior and surface characteristics of Zn/LDPE nanocomposites and ZnO/LDPE nanocomposites in simulated uterine solution

To decrease the side effects of the existing copper-bearing intrauterine devices, the zinc/low-density polyethylene (Zn/LDPE) nanocomposite and zinc-oxide/low-density polyethylene (ZnO/LDPE) nanocomposite have been developed in our research for intrauterine devices (IUDs). In this study, the influences of preparation methods of nanocomposites and particle sizes of zinc and zinc oxide on Zn(2+) release from composites incubated in simulated uterine solution were investigated. All release profiles are biphasic: an initial rapid release phase is followed by a near zero-order release period. Zn(2+) release rates of nanocomposites prepared by compressing moulding are higher than those of the nanocomposites prepared by hot-melt extrusing. Compared with Zn(2+) release from the microcomposites, the release profiles of the nanocomposites exhibit a sharp decrease in Zn(2+) release rate in the first 18 days, an early onset of the zero-order release period and a high release rate of Zn(2+) at the later stage. The microstructure of the Zn/LDPE sample and the ZnO/LDPE sample after being incubated for 200 days was characterized by SEM, XRD and EDX techniques. The results show that the dissolution depth of ZnO/LDPE nanocomposite is about 60 mum. Lots of pores were formed on the surface of the Zn/LDPE sample and ZnO/LDPE sample, indicating that these pores can provide channels for the dissolution of nanoparticles in the matrix. The undesirable deposits that are composed of ZnO are only detected on the surface of Zn/LDPE nanocomposite, which may increase the risk of side effects associated with IUDs. It can be expected that ZnO/LDPE nanocomposite is more suitable for IUDs than Zn/LDPE nanocomposite.

The copper(II) coordination abilities of three novel cyclic tetrapeptides with -His-Xaa-His- motif

Three novel cyclic tetrapeptides, containing either l- or d-histidine residues and either Lys or Asp side chains, namely c(HGd-HK) (1), cHGHD (2) and c(HGd-HD) (3), were designed, synthesized, characterized and tested as potential copper(II) ligands. Their pH dependent copper(II) binding properties were analysed in depth by a number of potentiometric and spectroscopic determinations. A rather exhaustive description of the species existing in solution has emerged for each copper(II)/oligopeptide system; solution structures for the individual species are proposed. The specific role of the various side chains in the overall metal coordination process is discussed in comparison with the case of Cu(II)-c(HGHK), previously reported. Data obtained in this study highlight the strong impact of the d-His residue on the metal binding abilities of these cyclic peptides. Remarkably, the cyclic tetrapeptides containing two l-His residues are able to form, at physiologically relevant pH values, a characteristic chromophore where the mononuclear copper(II) centre is simultaneously coordinated by two imidazole nitrogens and two amidic nitrogens of the tetrazadodecane ring. This latter type of copper(II) chromophore has been carefully modelled by computational methods. The potentialities of the applied experimental strategy are stressed.

Zn2+ release from zinc and zinc oxide particles in simulated uterine solution

Zn(2+) release from Zn and ZnO particles with different sizes in simulated uterine solution were investigated by absorbance measurements. The effects of pH and human serum albumin (HSA) on Zn(2+) release were also studied. The morphology of Zn and ZnO particles was observed by scanning electron microscopy, and the corrosion products of zinc nanoparticles were analyzed by XRD. The results indicate that the maximum release ratios of Zn(2+) from Zn and ZnO nanoparticles are higher than those from Zn and ZnO microparticles. Zn(2+) release ratio depends not only on the pH of the simulated uterine solution but also the presence of human serum albumin. It decreases as the pH of the uterine solution increases. The trends of Zn(2+) release ratios are almost the opposite for solutions with and without HSA. XRD analysis results indicate that zinc oxide is the main corrosion product of zinc particles.

Therapeutic action of citrate in urolithiasis explained by chemical speciation: increase in pH is the determinant factor

BACKGROUND

The therapeutic action of citrate in the management of calcium oxalate urolithiasis has been attributed to the depletion of free calcium ions by complexation of the latter by citrate itself. However, little attention has been given to the nature of such complexes and the chemical conditions which control their formation because it is very difficult to measure them in solution. We therefore modelled the theoretical formation of these complexes in urine following administration of a citrate-containing preparation, using a powerful speciation program, JESS (Joint Expert Speciation System), which has been widely used to model metal-ligand equilibria in biological systems but which has hitherto not been applied in urolithiasis research. This program has an extensive database of thermodynamic constants and is able to calculate mixed ligand speciation.

METHODS

Urine data obtained before and after citrate administration in four groups of subjects (male and female normals and stone formers) were used as input for JESS to calculate the speciation of calcium, citrate and oxalate. The program was also used to examine the effects of varying different urinary components on the nature and concentration of the various species.

RESULTS

The speciation predicted the formation of a key calcium-citrate-phosphate species (previously unreported in urolithiasis research), which accounts for a significant percentage of the complexation of the free calcium. Moreover, the formation of this complex was found to be dependent on an increase in urinary pH rather than on an increase in urinary citrate concentration per se.

CONCLUSION

The therapeutic action of citrate in the management of calcium oxalate urolithiasis is due to the formation of a pH dependent calcium-citrate-phosphate complex which reduces the concentration of the free calcium ion species, thereby reducing the risk of stone formation.

Biotinylated GHK peptide incorporated collagenous matrix: A novel biomaterial for dermal wound healing in rats

Matrikines are small peptide fragments of extracellular matrix proteins that display potent tissue repair activities. Difficulties in achieving sustained delivery of bioactive concentration of matrikines in the affected area limits their therapeutic use. The present study evaluates the effects biotinylated matrikine peptide (bio-glycyl-histidyl-lysine) incorporated collagen membrane for dermal wound healing processes in rats. Biotinylated peptide incorporated collagen matrix (PIC) showed better healing when compared to wounds treated with collagen matrix [CF (collagen film)] and without collagen [CR (control)]. Binding studies indicate that biotinylated GHK (Bio-GHK) binds effectively to the collagen matrix and red blood cell (RBC) membrane when compared with t-butyloxycarbonyl substituted GHK (Boc-GHK). Wound contraction, increased cell proliferation, and high expression of antioxidant enzymes in PIC treated group indicate enhanced wound healing activity when compared to CF and CR groups. Interestingly Bio-GHK incorporated collagen increases the copper concentration by ninefold at the wound site indicating the wound healing property of Bio-GHK can also be linked with both copper localization and matrikine activities. These results demonstrate the possibility of using Bio-GHK incorporated collagen film as a therapeutic agent in the wound healing process.

Calcium: a potential central regulator in wound healing in the skin

Calcium has an established role in the normal homeostasis of mammalian skin and serves as a modulator in keratinocyte proliferation and differentiation. Gradients of calcium concentration increasing from 0.5 mM in the basal layer to > 1.4 mM in the stratum granulosum are consistent with migration patterns in response to minor abrasion (normal wear). Dermal fibroblasts require calcium but are approximately 100 times less sensitive than keratinocytes. Normal calcium metabolism in the skin is dependent on cell membrane and cytosolic calcium binding proteins (calmodulin, cadherins, etc.), but their modulation through parathyroid hormone, vitamin D or growth factors in normal or damaged tissue is not well documented. In wound repair, calcium is predominantly involved as Factor IV in the hemostatic phase, but it is expected to be required in epidermal cell migration and regeneration patterns in later stages of healing. Calcium alginate dressings are designed to liberate calcium early in the acute phase to promote hemostasis, but it is presently unclear whether the supplementary calcium influences the intracellular environment at later stages of wound repair, notably during the remodeling phase. Although experimental studies suggest that control of calcium is obligatory in wound management, we know very little as to how calcium in the wound bed is modulated through hormones, vitamin D, or various growth factors. Also, there is limited information as to how calcium released either from dressings, platelets, or from the circulation through the action of parathyroid hormone, growth factors or other modulators influences cell migration and remodeling in skin wounds, although experimental models suggest that management of calcium is essential in wound management.

Using wound fluid analyses to identify trace element requirements for efficient healing

A series of wound fluid and blood plasma samples from 20 patients with breast cancer were analysed by Potentiometric Stripping Analysis and computer-aided chemical speciation to quantify the concentrations of the trace elements of copper and zinc in the samples and to investigate the individual species of copper and zinc present. Comparisons were made between total concentrations of copper and zinc in wound fluid, pre-operative blood plasma levels and reference values. A wound fluid model constructed using JESS identified the main copper and zinc species present. It was also used to investigate the effects of a change in pH and changes in the total concentrations of certain components on their predominance. The clinical significance of the research is discussed, together with suggestions for a continuation in the research.