Nutritional zinc increases platelet reactivity

Injectable, Antibacterial, and Hemostatic Tissue Sealant Hydrogels

Hemorrhage and bacterial infections are major hurdles in the management of life-threatening surgical wounds. Most bioadhesives for wound closure lack sufficient hemostatic and antibacterial properties. Furthermore, they suffer from weak sealing efficacy, particularly for stretchable organs, such as the lung and bladder. Accordingly, there is an unmet need for mechanically robust hemostatic sealants with simultaneous antibacterial effects. Here, an injectable, photocrosslinkable, and stretchable hydrogel sealant based on gelatin methacryloyl (GelMA), supplemented with antibacterial zinc ferrite (ZF) nanoparticles and hemostatic silicate nanoplatelets (SNs) for rapid blood coagulation is nanoengineered. The hydrogel reduces the in vitro viability of Staphylococcus aureus by more than 90%. The addition of SNs (2% w/v) and ZF nanoparticles (1.5 mg mL-1 ) to GelMA (20% w/v) improves the burst pressure of perforated ex vivo porcine lungs by more than 40%. Such enhancement translated to ≈250% improvement in the tissue sealing capability compared with a commercial hemostatic sealant, Evicel. Furthermore, the hydrogels reduce bleeding by ≈50% in rat bleeding models. The nanoengineered hydrogel may open new translational opportunities for the effective sealing of complex wounds that require mechanical flexibility, infection management, and hemostasis.

Role of inorganic ions in wound healing: an insight into the various approaches for localized delivery

Recently, the role of inorganic ions has been explored for its wound-healing applications. Ions do play key role in the normal functioning of the skin, including the epidermal barrier property, maintaining redox balance, enzymatic activities, tissue remodeling, etc. The care of chronic wounds is a concern and new cost-effective therapeutic strategies that modulate the wound microenvironment and cell behaviour are needed. First, this review illustrates the ions that play a role in wound healing and their molecular mechanisms that are accountable for modifying the wound. Further, the emerging strategies using metal ions to modulate the healing will be discussed. In this direction, localized delivery of inorganic ions of importance using advanced wound care biomaterials for wound healing applications is discussed.

Platelet zinc status regulates prostaglandin-induced signaling, altering thrombus formation

BACKGROUND

Approximately 17.3% of the global population exhibits an element of zinc (Zn2+) deficiency. One symptom of Zn2+ deficiency is increased bleeding through impaired hemostasis. Platelets are crucial to hemostasis and are inhibited by endothelial-derived prostacyclin (prostaglandin I2 [PGI2]), which signals via adenylyl cyclase (AC) and cyclic adenosine monophosphate signaling. In other cell types, Zn2+ modulates cyclic adenosine monophosphate concentrations by changing AC and/or phosphodiesterase activity.

OBJECTIVES

To investigate if Zn2+ can modulate platelet PGI2 signaling.

METHODS

Platelet aggregation, spreading, and western blotting assays with Zn2+ chelators and cyclic nucleotide elevating agents were performed in washed platelets and platelet-rich plasma conditions. In vitro thrombus formation with various Zn2+ chelators and PGI2 was assessed in whole blood.

RESULTS

Incubation of whole blood or washed platelets with Zn2+ chelators caused either embolization of preformed thrombi or reversal of platelet spreading, respectively. To understand this effect, we analyzed resting platelets and identified that incubation with Zn2+ chelators elevated pVASPser157, a marker of PGI2 signaling. In agreement that Zn2+ affects PGI2 signaling, addition of the AC inhibitor SQ22536 blocked Zn2+ chelation-induced platelet spreading reversal, while addition of Zn2+ blocked PGI2-mediated platelet reversal. Moreover, Zn2+ specifically blocked forskolin-mediated AC reversal of platelet spreading. Finally, PGI2 inhibition of platelet aggregation and in vitro thrombus formation was potentiated in the presence of low doses of Zn2+ chelators, increasing its effectiveness in inducing platelet inhibition.

CONCLUSION

Zn2+ chelation potentiates platelet PGI2 signaling, elevating PGI2's ability to prevent effective platelet activation, aggregation, and thrombus formation.

The enhancement of mechanical properties and uniform degradation of electrodeposited Fe-Zn alloys by multilayered design for biodegradable stent applications

Pure Fe is a potential biodegradable stent material due to its better biocompatibility and mechanical properties, but its degradation rate needs to be improved. Alloying with Zn to form Fe-Zn alloy is anticipated to meet the degradation rate requirements while retaining the iron's inherent properties. Therefore, Fe-Zn alloys with monolayered and multilayered structures were prepared by electrodeposition. The alloys' composition, microstructure, mechanical properties, in vitro degradation and biocompatibility were assessed. Results showed that the Zn content ranged from 2.1 wt% to 11.6 wt%. After annealing at 450°C, all the alloys consisted of α(Fe) solid solution and Zn-rich B2 ordered coherent phase, except for the alloy with 11.6 wt% Zn content, in which a Fe₃Zn₁₀ phase appeared. The layered structure consisted of alternating columnar-grain and nano-grain layers, which compensated for the intrinsic brittleness of electrodeposited metals and improved the galvanic effect of the alloy, thus increasing the strength and plasticity and changing the corrosion from localized to uniform while augmenting the corrosion rate. The yield strength of the multilayered alloy exceeded 350 MPa, its elongation was more than 20%, and its corrosion rate obtained by immersion test in Hank's solution reached 0.367 mm·y^-1. Fe-Zn alloys with lower Zn content had good cytocompatibility with the human umbilical vein endothelial cells and good blood compatibility. The above results verified that the multilayered Fe-Zn alloy prepared by electrodeposition presented enhanced mechanical properties, higher degradation rate, uniform degradation mechanism and good biocompatibility. It should be qualified for the application of biodegradable stents. STATEMENT OF SIGNIFICANCE: A potential biodegradable Fe-Zn alloy, which is difficult to be obtained by the metallurgical method, was prepared by electrodeposition to solve the low degradation rate of iron-based biomaterials. A multilayered microstructure design composed of alternating columnar-grain and nano-grain layers was achieved by changing the electrical parameters. The layered design compensated for the intrinsic poor plasticity of electrodeposited metals. It increased the galvanic effect of the alloy, thus augmenting the corrosion rate and changing the corrosion mode of the alloy from localized to uniform corrosion. The yield strength of multilayered alloy exceeded 350 MPa; its elongation was more than 20%. Moreover, the layered alloy had good cytocompatibility and blood compatibility. It indicates that the alloy is qualified for biodegradable stent application.

Synergistic effect of glucagon-like peptide-1 analogue liraglutide and ZnO on the antibacterial, hemostatic, and wound healing properties of nanofibrous dressings

Bacterial infections and poor vascularization delay wound healing, thus necessitating alternative strategies for functional wound dressings. Zinc oxide (ZnO) has been shown to exert a potent antibacterial effect against bacterial species. Similarly, Glucagon-like peptide-1 (GLP-1) analogue liraglutide (LG) has been shown to promote vascularization and improve wound healing. The objective of this research was to investigate the synergistic effect of ZnO nanoparticles (ZnO-NPs) and LG to simultaneously induce antibacterial, hemostatic, and vascularization effects for infected wound healing. Electrospun poly (l-lactide-co-glycolide)/gelatin (PLGA/Gel) membranes containing ZnO-NPs and LG displayed good biocompatibility and hemostatic ability. Both, ZnO-NPs and LG exhibited synergistic antibacterial effect against Staphylococcus aureus and Escherichia coli as well as improved the migration and tubule-like network formation of human umbilical vein endothelial cells (HUVECs) in vitro. Once evaluated in a bacterial-infected wound model in rats, the membranes loaded with ZnO-NPs and LG effectively promoted wound healing causing significant reduction in wound area and scar-like tissue formation. Therefore, ZnO-NPs/LG synergism may offer an invaluable solution for the treatment of poorly healing infected wounds.

Zinc deficiency as a possible risk factor for increased susceptibility and severe progression of Corona Virus Disease 19

The importance of Zn for human health becomes obvious during Zn deficiency. Even mild insufficiencies of Zn cause alterations in haematopoiesis and immune functions, resulting in a proinflammatory phenotype and a disturbed redox metabolism. Although immune system malfunction has the most obvious effect, the functions of several tissue cell types are disturbed if Zn supply is limiting. Adhesion molecules and tight junction proteins decrease, while cell death increases, generating barrier dysfunction and possibly organ failure. Taken together, Zn deficiency both weakens the resistance of the human body towards pathogens and at the same time increases the danger of an overactive immune response that may cause tissue damage. The case numbers of Corona Virus Disease 19 (COVID-19) are still increasing, which is causing enormous problems for health systems and economies. There is an urgent need to reduce both the number of severe cases and the resulting deaths. While therapeutic options are still under investigation, and first vaccines have been approved, cost-effective ways to reduce the likelihood of or even prevent infection, and the transition from mild symptoms to more serious detrimental disease, are highly desirable. Nutritional supplementation might be an effective option to achieve these aims. In this review, we discuss known Zn deficiency effects in the context of an infection with Severe Acute Respiratory Syndrome-Coronavirus-2 and its currently known pathogenic mechanisms and elaborate on how severe pre-existing Zn deficiency may pre-dispose patients to a severe progression of COVID-19. First published clinical data on the association of Zn homoeostasis with COVID-19 and registered studies in progress are listed.

Zinc-nutrient element based alloys for absorbable wound closure devices fabrication: Current status, challenges, and future prospects

The need for the development of load-bearing, absorbable wound closure devices is driving the research for novel materials that possess both good biodegradability and superior mechanical characteristics. Biodegradable metals (BMs), namely: magnesium (Mg), zinc (Zn) and iron (Fe), which are currently being investigated for absorbable vascular stent and orthopaedic implant applications, are slowly gaining research interest for the fabrication of wound closure devices. The current review presents an overview of the traditional and novel BM-based intracutaneous and transcutaneous wound closure devices, and identifies Zn as a promising substitute for the traditional materials used in the fabrication of absorbable load-bearing sutures, internal staples, and subcuticular staples. In order to further strengthen Zn to be used in highly stressed situations, nutrient elements (NEs), including calcium (Ca), Mg, Fe, and copper (Cu), are identified as promising alloying elements for the strengthening of Zn-based wound closure device material that simultaneously provide potential therapeutic benefit to the wound healing process during implant biodegradation process. The influence of NEs on the fundamental characteristics of biodegradable Zn are reviewed and critically assessed with regard to the mechanical properties and biodegradability requirements of different wound closure devices. The opportunities and challenges in the development of Zn-based wound closure device materials are presented to inspire future research on this rapidly growing field.

A zinc transporter, transmembrane protein 163, is critical for the biogenesis of platelet dense granules

Lysosome-related organelles (LROs) are a category of secretory organelles enriched with ions such as calcium, which are maintained by ion transporters or channels. Homeostasis of these ions is important for LRO biogenesis and secretion. Hermansky-Pudlak syndrome (HPS) is a recessive disorder with defects in multiple LROs, typically platelet dense granules (DGs) and melanosomes. However, the underlying mechanism of DG deficiency is largely unknown. Using quantitative proteomics, we identified a previously unreported platelet zinc transporter, transmembrane protein 163 (TMEM163), which was significantly reduced in BLOC-1 (Dtnbp1sdy and Pldnpa)-, BLOC-2 (Hps6ru)-, or AP-3 (Ap3b1pe)-deficient mice and HPS patients (HPS2, HPS3, HPS5, HPS6, or HPS9). We observed similar platelet DG defects and higher intracellular zinc accumulation in platelets of mice deficient in either TMEM163 or dysbindin (a BLOC-1 subunit). In addition, we discovered that BLOC-1 was required for the trafficking of TMEM163 to perinuclear DG and late endosome marker-positive compartments (likely DG precursors) in MEG-01 cells. Our results suggest that TMEM163 is critical for DG biogenesis and that BLOC-1 is required for the trafficking of TMEM163 to putative DG precursors. These new findings suggest that loss of TMEM163 function results in disruption of intracellular zinc homeostasis and provide insights into the pathogenesis of HPS or platelet storage pool deficiency.

Exploration of the antibacterial and wound healing potential of a PLGA/silk fibroin based electrospun membrane loaded with zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO NPs) are known for their antibacterial, antioxidant, and anti-inflammatory activities. Moreover, ZnO NPs can stimulate cell migration, re-epithelialization, and angiogenesis. All these attributes are highly relevant to wound healing. Local administration of ZnO NPs to the wound can be achieved through electrospun nanofibers. We hypothesized that the use of poly(lactide-co-glycolic acid) (PLGA)/silk fibroin (SF) nanofiber-based delivery of ZnO would maintain the bioavailability of NPs on the wound area and synchronization with the unique structural features of electrospun nanofibers, could stimulate wound closure, re-epithelialization, collagen deposition, cellular migration, and angiogenesis. In this study, we fabricated PLGA/SF (PS) nanofibrous (NF) membranes with and without ZnO NPs and extensively characterized them for various physicochemical and biological attributes. Scanning electron microscopy (SEM) revealed smooth fibers and ZnO concentration-dependent increase in the fiber diameter. Transmission electron microscopy (TEM) also confirmed the encapsulation of ZnO NPs in the polymer matrix. The successful loading of ZnO was further confirmed by X-ray diffraction. Furthermore, mechanical testing revealed a ZnO concentration-dependent increase in the tensile strength. Moreover, biocompatibility was evaluated through in vitro cell culture. A mild anti-oxidant activity was also noted mainly due to the presence of silk fibroin. In vitro antibacterial tests revealed a ZnO concentration-dependent increase in antibacterial activity and PLGA/SF/3% ZnO (PSZ3) remained completely active against E. coli and S. aureus. More importantly, NF membranes were evaluated for their in vivo wound healing potential. The PSZ3 NF membrane not only facilitated the early wound closure but also remarkably enhanced the quality of wound healing confirmed through histopathological analysis. Re-epithelialization, granulation tissue formation, collagen deposition, and angiogenesis are some of the key parameters significantly boosted by ZnO loaded composite NF membranes. Based on extensive characterization and biological evaluation, the PSZ3 NF membrane has turned out to be a potential candidate for wound healing applications.

The Effect of Mushroom Extracts on Human Platelet and Blood Coagulation: In vitro Screening of Eight Edible Species

Cardiovascular diseases remain the leading global cause of mortality indicating the need to identify all possible factors reducing primary and secondary risk. This study screened the in vitro antiplatelet and anticoagulant activities of hot water extracts of eight edible mushroom species (Agaricus bisporus, Auricularia auricularia-judae, Coprinuscomatus, Ganodermalucidum, Hericium erinaceus, Lentinulaedodes, Pleurotuseryngii, and Pleurotusostreatus) increasingly cultivated for human consumption, and compared them to those evoked by acetylsalicylic acid (ASA). The antioxidant capacity and concentration of polysaccharides, phenolic compounds, organic acids, ergosterol, macro elements, and trace elements were also characterized. The most promising antiplatelet effect was exhibited by A. auricularia-judae and P. eryngii extracts as demonstrated by the highest rate of inhibition of adenosine-5′-diphosphate (ADP)-induced and arachidonic acid (AA)-induced aggregation. The response to both extracts exceeded the one evoked by 140 µmol/L of ASA in the ADP test and was comparable to it in the case of the AA test. Such a dual effect was also observed for G. lucidum extract, even though it was proven to be cytotoxic in platelets and leukocytes. The extract of P. ostreatus revealed an additive effect on AA-induced platelet aggregation. None of the mushroom extracts altered the monitored coagulation parameters (prothrombin time, prothrombin ratio, and International Normalized Ratio). The effect of mushroom extracts on platelet function was positively related to their antioxidative properties and concentration of polysaccharides and ergosterol, and inversely related to zinc concentration. The study suggests that selected mushrooms may exert favorable antiplatelet effects, highlighting the need for further experimental and clinical research in this regard.

Zinc Homeostasis in Platelet-Related Diseases

Zn²⁺ deficiency in the human population is frequent in underdeveloped countries. Worldwide, approximatively 2 billion people consume Zn²⁺-deficient diets, accounting for 1-4% of deaths each year, mainly in infants with a compromised immune system. Depending on the severity of Zn²⁺ deficiency, clinical symptoms are associated with impaired wound healing, alopecia, diarrhea, poor growth, dysfunction of the immune and nervous system with congenital abnormalities and bleeding disorders. Poor nutritional Zn²⁺ status in patients with metastatic squamous cell carcinoma or with advanced non-Hodgkin lymphoma, was accompanied by cutaneous bleeding and platelet dysfunction. Forcing Zn²⁺ uptake in the gut using different nutritional supplementation of Zn²⁺ could ameliorate many of these pathological symptoms in humans. Feeding adult rodents with a low Zn²⁺ diet caused poor platelet aggregation and increased bleeding tendency, thereby attracting great scientific interest in investigating the role of Zn²⁺ in hemostasis. Storage protein metallothionein maintains or releases Zn²⁺ in the cytoplasm, and the dynamic change of this cytoplasmic Zn²⁺ pool is regulated by the redox status of the cell. An increase of labile Zn²⁺ pool can be toxic for the cells, and therefore cytoplasmic Zn²⁺ levels are tightly regulated by several Zn²⁺ transporters located on the cell surface and also on the intracellular membrane of Zn²⁺ storage organelles, such as secretory vesicles, endoplasmic reticulum or Golgi apparatus. Although Zn²⁺ is a critical cofactor for more than 2000 transcription factors and 300 enzymes, regulating cell differentiation, proliferation, and basic metabolic functions of the cells, the molecular mechanisms of Zn²⁺ transport and the physiological role of Zn²⁺ store in megakaryocyte and platelet function remain elusive. In this review, we summarize the contribution of extracellular or intracellular Zn²⁺ to megakaryocyte and platelet function and discuss the consequences of dysregulated Zn²⁺ homeostasis in platelet-related diseases by focusing on thrombosis, ischemic stroke and storage pool diseases.

Bioinorganics and Wound Healing

Wound dressings and the healing enhancement (increasing healing speed and quality) are two components of wound care that lead to a proper healing. Wound care today consists mostly of providing an optimal environment by removing waste and necrotic tissues from a wound, preventing infections, and keeping the wounds adequately moist. This is however often not enough to re-establish the healing process in chronic wounds; with the local disruption of vascularization, the local environment is lacking oxygen, nutrients, and has a modified ionic and molecular concentration which limits the healing process. This disruption may affect cellular ionic pumps, energy production, chemotaxis, etc., and will affect the healing process. Biomaterials for wound healing range from simple absorbents to sophisticated bioactive delivery vehicles. Often placing a material in or on a wound can change multiple parameters such as pH, ionic concentration, and osmolarity, and it can be challenging to pinpoint key mechanism of action. This article reviews the literature of several inorganic ions and molecules and their potential effects on the different wound healing phases and their use in new wound dressings.

Zinc in Wound Healing Modulation

Wound care is a major healthcare expenditure. Treatment of burns, surgical and trauma wounds, diabetic lower limb ulcers and skin wounds is a major medical challenge with current therapies largely focused on supportive care measures. Successful wound repair requires a series of tightly coordinated steps including coagulation, inflammation, angiogenesis, new tissue formation and extracellular matrix remodelling. Zinc is an essential trace element (micronutrient) which plays important roles in human physiology. Zinc is a cofactor for many metalloenzymes required for cell membrane repair, cell proliferation, growth and immune system function. The pathological effects of zinc deficiency include the occurrence of skin lesions, growth retardation, impaired immune function and compromised would healing. Here, we discuss investigations on the cellular and molecular mechanisms of zinc in modulating the wound healing process. Knowledge gained from this body of research will help to translate these findings into future clinical management of wound healing.

The contribution of zinc to platelet behaviour during haemostasis and thrombosis

Platelets are the primary cellular determinants of haemostasis and pathological thrombus formation leading to myocardial infarction and stroke. Following vascular injury or atherosclerotic plaque rupture, platelets are recruited to sites of damage and undergo activation induced by a variety of soluble and/or insoluble agonists. Platelet activation is a multi-step process culminating in the formation of thrombi, which contribute to the haemostatic process. Zinc (Zn(2+)) is acknowledged as an important signalling molecule in a diverse range of cellular systems, however there is limited understanding of the influence of Zn(2+) on platelet behaviour during thrombus formation. This review evaluates the contributions of exogenous and intracellular Zn(2+) to platelet function and assesses the potential pathophysiological implications of Zn(2+) signalling. We also provide a speculative assessment of the mechanisms by which platelets could respond to changes in extracellular and intracellular Zn(2+) concentration.

Zinc is a transmembrane agonist that induces platelet activation in a tyrosine phosphorylation-dependent manner

Following platelet adhesion and primary activation at sites of vascular injury, secondary platelet activation is induced by soluble platelet agonists, such as ADP, ATP, thrombin and thromboxane. Zinc ions are also released from platelets and damaged cells and have been shown to act as a platelet agonist. However, the mechanism of zinc-induced platelet activation is not well understood. Here we show that exogenous zinc gains access to the platelet cytosol and induces full platelet aggregation that is dependent on platelet protein tyrosine phosphorylation, PKC and integrin αIIbβ3 activity and is mediated by granule release and secondary signalling. ZnSO4 increased the binding affinity of GpVI, but not integrin α2β1. Low concentrations of ZnSO4 potentiated platelet aggregation by collagen-related peptide (CRP-XL), thrombin and adrenaline. Chelation of intracellular zinc reduced platelet aggregation induced by a number of different agonists, inhibited zinc-induced tyrosine phosphorylation and inhibited platelet activation in whole blood under physiologically relevant flow conditions. Our data are consistent with a transmembrane signalling role for zinc in platelet activation during thrombus formation.

Accelerating degradation rate of pure iron by zinc ion implantation

Pure iron has been considered as a promising candidate for biodegradable implant applications. However, a faster degradation rate of pure iron is needed to meet the clinical requirement. In this work, metal vapor vacuum arc technology was adopted to implant zinc ions into the surface of pure iron. Results showed that the implantation depth of zinc ions was about 60 nm. The degradation rate of pure iron was found to be accelerated after zinc ion implantation. The cytotoxicity tests revealed that the implanted zinc ions brought a slight increase on cytotoxicity of the tested cells. In terms of hemocompatibility, the hemolysis of zinc ion implanted pure iron was lower than 2%. However, zinc ions might induce more adhered and activated platelets on the surface of pure iron. Overall, zinc ion implantation can be a feasible way to accelerate the degradation rate of pure iron for biodegradable applications.

The molecular basis of memory. Part 2: chemistry of the tripartite mechanism

We propose a tripartite mechanism to describe the processing of cognitive information (cog-info), comprising the (1) neuron, (2) surrounding neural extracellular matrix (nECM), and (3) numerous "trace" metals distributed therein. The neuron is encased in a polyanionic nECM lattice doped with metals (>10), wherein it processes (computes) and stores cog-info. Each [nECM:metal] complex is the molecular correlate of a cognitive unit of information (cuinfo), similar to a computer "bit". These are induced/sensed by the neuron via surface iontophoretic and electroelastic (piezoelectric) sensors. The generic cuinfo are used by neurons to biochemically encode and store cog-info in a rapid, energy efficient, but computationally expansive manner. Here, we describe chemical reactions involved in various processes that underline the tripartite mechanism. In addition, we present novel iconographic representations of various types of cuinfo resulting from"tagging" and cross-linking reactions, essential for the indexing cuinfo for organized retrieval and storage of memory.

Zinc and redox signaling: perturbations associated with cardiovascular disease and diabetes mellitus

Cellular signal transduction pathways are influenced by the zinc and redox status of the cell. Numerous chronic diseases, including cardiovascular disease (CVD) and diabetes mellitus (DM), have been associated with impaired zinc utilization and increased oxidative stress. In humans, mutations in the MT-1A and ZnT8 genes, both of which are involved in the maintenance of zinc homeostasis, have been linked with DM development. Changes in levels of intracellular free zinc may exacerbate oxidative stress in CVD and DM by impacting glutathione homeostasis, nitric oxide signaling, and nuclear factor-kappa B-dependent cellular processes. Zinc ions have been shown to influence insulin and leptin signaling via the phosphoinositide 3′-kinase/Akt pathway, potentially linking an imbalance of zinc at the cellular level to insulin resistance and dyslipidemia. The oxidative modification of cysteine residues in zinc coordination sites in proteins has been implicated in cellular signaling and regulatory pathways. Despite the many interactions between zinc and cellular stress responses, studies investigating the potential therapeutic benefit of zinc supplementation in the prevention and treatment of oxidative stress-related chronic disease in humans are few and inconsistent. Further well-designed randomized controlled trials are needed to determine the effects of zinc supplementation in populations at various stages of CVD and DM progression.

The Effect of Zinc Supplementation in Humans on Plasma Lipids, Antioxidant Status and Thrombogenesis

The potential exists for zinc to influence numerous metabolic functions and to impact a range of diseases. In the present review we examine the reported relationships between zinc and plasma lipids, haemostasis and other factors postulated to play a role in atherogenesis. Ecological studies that investigated zinc intake or status, and incidence of coronary heart disease (CHD) reveal no consistent pattern. The conflicting observations may be explained by differences in the extent of CHD, site of atherosclerosis, or confounding factors. In most studies the diurnal variation in serum zinc concentrations, and the lifestyle factors that affect cholesterol metabolism were not explicitly considered. Results of randomised controlled trials show that low-density lipoprotein (LDL) oxidation and the concentrations of LDL-cholesterol (c), total cholesterol and triglycerides in plasma are unaffected by supplementation with up to 150 mg Zn/d. In contrast, plasma high-density lipoprotein (HDL)-c concentrations decline when zinc supplements provide a dose >50 mg/d. Limited data suggest that sustained hyperzincaemia predisposes individuals to thrombogenesis, whereas acute zinc depletion impairs platelet aggregation and prolongs bleeding time. In addition, Zinc supplements have been shown in some studies to decrease Cu/Zn-superoxide dismutase activity, primarily due to the antagonistic relationship between high zinc intakes and copper absorption. Besides the demonstrated adverse effect of zinc supplementation on plasma HDL-c concentrations in apparently healthy men, there is insufficient evidence to determine the role of zinc supplementation in influencing other risk factors for CHD such as antioxidant status and thrombogenesis.

Packaging zinc, fibrinogen, and factor XIII in platelet alpha-granules

Zinc(II) accumulated by platelets has profound effects on platelet activity. This study is focused on the distribution of Zn(II) between human platelet subcellular compartments. After incubation with 86Rb+ and platelet lysis, the organelles were separated by sucrose density gradient centrifugation. Fibrinogen served as a marker for alpha-granules. 86Rb+ and factor XIII served as markers for the cytoplasmic fractions. Zn(II) was found to be distributed between the cytoplasm and the alpha-granules, with variations between different individual units. The total platelet Zn concentration and its relative subcellular distribution were dependent on its extracellular level. Incubation of platelets with 100 microM Zn(II) resulted in a twofold increase of its level in the cytoplasm and by one order of magnitude in the alpha-granules. In addition to the anticipated factor XIII activity in the cytoplasmic pool fraction, we found thrombin-inducible factor XIII activity within the alpha-granules. Immunoblotting confirmed the presence of both the a and b subunits of plasma factor XIII (a2b2 form) in the alpha-granules. As fibrinogen is not synthesized in the platelet, we propose that by virtue of their mutual binding, fibrinogen, Zn(II) and plasma factor XIII-a2b2 are simultaneously taken up into the alpha-granules by endocytosis, presumably through the vehicle of the GPIIb/IIIa fibrinogen receptor. A rationale for co-packaging these components within the alpha-granules is that Zn(II) inhibits factor XIII activity and thereby prevents the premature cross-linking of the concentrated fibrinogen prior to platelet activation and secretion. By contrast, cytoplasmic Zn(II) may increase platelet responsiveness to agonists due to its interaction with cytoplasmic modulators of platelet activity.

Platelet multielemental composition, lability, and subcellular localization

Diagnostic X-ray spectrometry (DXS), based on X-ray fluorescence, was used to quantitate directly the multiple elemental composition of washed, intact human platelets (n = 16), with the following results: K = 3.08 +/- 1.00 mg/g, Ca = 1.18 +/- 0.29 mg/g, Zn = 35 +/- 9 micrograms/g. These values show that washed platelets contain significant pools of K, Ca, and Zn, the latter some 30-60-fold higher than plasma levels. Dialysis of whole platelets against cation exchange resin (Chelex-100) did not extract Ca(II) and Zn(II) sequestered within whole cells. To identify the subcellular locale of the elements, platelet lysate was subjected to 30-70% sucrose gradient ultracentrifugation and subcellular enriched fractions were obtained. Fractions were analyzed by DXS (for elements), electron microscopy (for dense granules), and subcellular markers fibrinogen and von Willebrand factor. In contrast to Ca and K, which accumulate in the dense granules and the cytoplasm, respectively, Zn appears to be distributed in the alpha-granules (40%) and the cytoplasm (60%). The subcellular distribution of Zn(II) is discussed within the context of the sensitivity of platelet response to the availability of Zn(II) and the platelet release reactions following stimulation.