Effect of zinc supplementation on resistance of cultured human skin fibroblasts toward oxidant stress

Spatial expression of metallothionein, matrix metalloproteinase-1 and Ki-67 in human epidermal wounds treated with zinc and determined by quantitative immunohistochemistry: A randomised double-blind trial

Reepithelialisation is fundamental to wound healing, but our current understanding largely relies on cellular and animal studies. The aim of the present randomised double-blind three-arm controlled trial was to correlate genuine epidermal wound healing with key proteins and topical zinc treatment in humans. Sixty wounds were produced using deroofed suction blisters in 30 healthy volunteers and randomised to topical zinc sulphate (n = 20), placebo (n = 20), or control (n = 20) treatment for 4 days. All wounds with perilesional skin were processed for automatic immunostaining of paraffin tissue sections with monoclonal antibodies against Ki-67, metallothionein (MT) and matrix metalloproteinase (MMP)-1. Protein expression was quantified by automated digital image analysis. Epidermal Ki-67 and MT labelling indices were increased in keratinocytes in the neoepidermis (∼1.1 mm) and at the wound edge (0.5 mm) compared to normal skin. Increased MMP-1 immunostaining was restricted to the neoepidermis. MT was robustly upregulated in the upper dermis of the wounds. Zinc treatment enhanced MMP-1 expression beneath the neoepidermis via paracrine mechanisms and MT under the neoepidermis and in the nonepithelialised wound bed via direct actions of zinc as indicated by the induction of MT2A mRNA but not MMP-1 mRNA in cultured normal human dermal fibroblasts by zinc sulphate. The present human study demonstrates that quantitative immunohistochemistry can identify proteins involved in reepithelialisation and actions of external compounds. Increased dermal MT expression may contribute to the anti-inflammatory activities of zinc and increased MMP-1 levels to promote keratinocyte migration.

Exposure to Trace Elements and Risk of Skin Cancer: A Systematic Review of Epidemiologic Studies

Exposure to environmental trace elements has been studied in relation to many cancers. However, an association between exposure to trace elements and skin cancer remains less understood. Therefore, we conducted a systematic review of published epidemiologic literature examining the association between exposure to trace elements, and risk of melanoma and keratinocyte carcinoma in humans. We identified epidemiologic studies investigating exposure to arsenic, cadmium, chromium, copper, iron, selenium, and zinc and risk of skin cancer in humans. Among the minerals, arsenic, selenium, and zinc had more than five studies available. Exposure to arsenic was associated with increased risk of keratinocyte carcinoma, while too few studies existed on melanoma to draw conclusions. Exposure to selenium was associated with possible increased risk of keratinocyte carcinoma. Studies of zinc and skin cancer were case-control in design and were found to have inconsistent associations. The data on the association between cadmium, chromium, copper, and iron and risk of skin cancer remain too sparse to draw any conclusions. In summary, epidemiologic studies on exposure to trace elements and cutaneous malignancies are limited. Studies with larger sample sizes and prospective designs are warranted to improve our knowledge of trace elements and skin cancer.

Daily oral supplementation with collagen peptides combined with vitamins and other bioactive compounds improves skin elasticity and has a beneficial effect on joint and general wellbeing

Aging is a multifactorial and natural process that causes physiological changes in organs, tissues and cells over time. In the skin and cartilage, aging leads to a decrease in the synthesis and changes in the arrangement of proteoglycans and collagen, in addition to the loss of glycosaminoglycans, which are responsible for the integrity and health of these tissues. We hypothesized that daily oral supplementation with a liquid nutraceutical containing hydrolyzed fish collagen, vitamins, antioxidants and other active ingredients could improve skin texture and elasticity, and in addition have a protective effect on joint health. A double-blind, randomized, placebo-controlled clinical trial was conducted on 120 subjects who consumed either the test product or placebo on a daily basis for 90 days. Subjects consuming the test product had an overall significant increase in skin elasticity (+40%; P < .0001) when compared to placebo. Histological analysis of skin biopsies revealed positive changes in the skin architecture, with a reduction in solar elastosis and improvement in collagen fiber organization in the test product group. As reported in the self-perception questionnaires, these results were confirmed by the subjects' own perceptions in that participants agreed their skin was more hydrated and more elastic. In addition, the consumption of the test product reduced joint pain by -43% and improved joint mobility by +39%. Oral supplementation with collagen bioactive peptides combined with chondroitin sulphate, glucosamine, L-carnitine, vitamins, and minerals significantly improved the clinical parameters related to skin aging and joint health, and therefore, might be an effective solution to slow down the hallmarks of aging.

Tetrabromobisphenol A disturbs zinc homeostasis in cultured cerebellar granule cells: A dual role in neurotoxicity

The brominated flame retardant tetrabromobisphenol A (TBBPA) has recognized neurotoxic properties mediated by intracellular Ca²⁺ imbalance and oxidative stress. Although these factors are known to trigger the release of Zn²⁺ from intracellular stores, the effects of TBBPA on Zn²⁺ homeostasis in neurons and the role of Zn²⁺in TBBPA neurotoxicity have not yet been studied. Therefore, we investigated zinc transients in primary cultures of rat cerebellar granule cells and assessed their involvement in TBBPA neurotoxicity. The results demonstrate that TBBPA releases Zn²⁺ from the intracellular stores and increases its intracellular concentration, followed by Zn²⁺ displacement from the cells. TBBPA-evoked Zn²⁺ transients are partially mediated by Ca²⁺ and ROS. Application of TPEN, Zn²⁺ chelator, potentiates TBBPA- and glutamate-induced ⁴⁵Ca uptake, enhances TBBPA-induced ROS production and potentiates decreases in the ΔΨm in cells treated with 25 μM TBBPA, revealing the potential neuroprotective capacity of endogenous Zn²⁺. However, the administration of TPEN does not aggravate TBBPA neurotoxicity, and even slightly decreases neuronal death induced by 25 μM TBBPA. In summary, it was shown for the first time that TBBPA interferes with the cellular Zn²⁺ homeostasis in neuronal cultures, and we revealed complex roles for endogenous Zn²⁺ in cytoprotection and TBBPA toxicity in cultured neurons.

Bentonite modified with zinc enhances aflatoxin B1 adsorption and increase survival of fibroblasts (3T3) and epithelial colorectal adenocarcinoma cells (Caco-2)

Bentonites are commonly used as feed additives to reduce the bioavailability and thus the toxicity of aflatoxins by adsorbing the toxins in the gastrointestinal tract. Aflatoxins are particular harmful mycotoxins mainly found in areas with hot and humid climates. They occur in food and feedstuff as a result of fungal contamination before and after harvest. The aim of this study was to modify Brazilian bentonite clay by incorporation of zinc (Zn) ions in order to increase the adsorption capacity and consequently reduce the toxicity of aflatoxins. The significance of Zn intercalating conditions such as concentration, temperature and reaction time were investigated. Our results showed that the Zn treatment of the bentonite increased the aflatoxin B₁ (AFB₁) adsorption and that Zn concentration had a negative effect. Indeed, temperature and time had no significant effect in the binding capacity. The modified bentonite (Zn-Bent1) was not cytotoxic to either fibroblasts (3T3) nor epithelial colorectal adenocarcinoma cells (Caco-2) cell lines. Interestingly, Zn-Bent1 has higher protective effect against AFB₁ induced cytotoxicity than the unmodified bentonite. In conclusion, the Zn modified bentonite, Zn-Bent1, represent an improved tool to prevent aflatoxicosis in animals fed on AFB₁ contaminated feed.

Relative Penetration of Zinc Oxide and Zinc Ions into Human Skin after Application of Different Zinc Oxide Formulations

Zinc oxide (ZnO) is frequently used in commercial sunscreen formulations to deliver their broad range of UV protection properties. Concern has been raised about the extent to which these ZnO particles (both micronized and nanoparticulate) penetrate the skin and their resultant toxicity. This work has explored the human epidermal skin penetration of zinc oxide and its labile zinc ion dissolution product that may potentially be formed after application of ZnO nanoparticles to human epidermis. Three ZnO nanoparticle formulations were used: a suspension in the oil, capric caprylic triglycerides (CCT), the base formulation commonly used in commercially available sunscreen products; an aqueous ZnO suspension at pH 6, similar to the natural skin surface pH; and an aqueous ZnO suspension at pH 9, a pH at which ZnO is stable and there is minimal pH-induced impairment of epidermal integrity. In each case, the ZnO in the formulations did not penetrate into the intact viable epidermis for any of the formulations but was associated with an enhanced increase in zinc ion fluorescence signal in both the stratum corneum and the viable epidermis. The highest labile zinc fluorescence was found for the ZnO suspension at pH 6. It is concluded that, while topically applied ZnO does not penetrate into the viable epidermis, these applications are associated with hydrolysis of ZnO on the skin surface, leading to an increase in zinc ion levels in the stratum corneum, thence in the viable epidermis and subsequently in the systemic circulation and the urine.

Zinc Modulates Nanosilver-Induced Toxicity in Primary Neuronal Cultures

Silver nanoparticles (NAg) have recently become one of the most commonly used nanomaterials. Since the ability of nanosilver to enter the brain has been confirmed, there has been a need to investigate mechanisms of its neurotoxicity. We previously showed that primary neuronal cultures treated with nanosilver undergo destabilization of calcium homeostasis via a mechanism involving glutamatergic NMDA receptors. Considering the fact that zinc interacts with these receptors, the aim of the present study was to examine the role of zinc in mechanisms of neuronal cell death in primary cultures. In cells treated with nanosilver, we noted an imbalance between extracellular and intracellular zinc levels. Thus, the influence of zinc deficiency and supplementation on nanosilver-evoked cytotoxicity was investigated by treatment with TPEN (a chelator of zinc ions), or ZnCl₂, respectively. Elimination of zinc leads to complete death of nanosilver-treated CGCs. In contrast, supplementation with ZnCl₂ increases viability of CGCs in a dose-dependent manner. Addition of zinc provided protection against the extra/intracellular calcium imbalance in a manner similar to MK-801, an antagonist of NMDA receptors. Zinc chelation by TPEN decreases the mitochondrial potential and dramatically increases the rate of production of reactive oxygen species. Our results indicate that zinc supplementation positively influences nanosilver-evoked changes in CGCs. This is presumed to be due to an inhibitory effect on NMDA-sensitive calcium channels.

Protein energy-malnutrition: does the in vitro zinc sulfate supplementation improve chromosomal damage repair?

Protein-energy malnutrition (PEM) is originated by a cellular imbalance between nutrient/energy supply and body's demand. Induction of genetic damage by PEM was reported. The purpose of this study was to determine the genetic effect of the in vitro zinc sulfate (ZnSO4) supplementation of cultured peripheral blood lymphocytes from children with PEM. Twenty-four samples from 12 children were analyzed. Anthropometric and biochemical diagnosis was made. For the anthropometric assessment, height-for-age index, weight-for-age index, and weight-for-height index were calculated (WHO, 2005). Micronutrient status was evaluated. A survey for assessed previous exposure to potentially genotoxic agents was applied. Results were statistically evaluated using paired sample t test and χ (2) test. Each sample was fractionated and cultured in two separate flasks to performed two treatments. One was added with 180 μg/dl of ZnSO4 (PEMs/ZnSO4) and the other remains non-supplemented (PEMs). Cytotoxic effects and chromosomal damage were assessed using the cytokinesis-block micronucleus assay (CBMN). All participants have at least one type of malnutrition and none have anemia, nor iron, folate, vitamin A, and zinc deficiency. All PEMs/ZnSO4 samples have a significant reduction in the micronucleus (MNi) frequency compared with PEMs (t = 6.25685; p < 0.001). Nuclear division index (NDI) increase in PEMs/ZnSO4 (t = -17.4226; p < 0.001). Nucleoplasmic bridge (NPBs) frequency was four times smaller in PEMs/ZnSO4 (χ (2) = 40.82; p < 0.001). No nuclear buds (NBuds) were observed. Cytotoxic effects and chromosomal damage observed in children suffering from PEM can be repaired in vitro with zinc sulfate supplementation.

Zinc, its biological role and use in dermatology

This literature review detines the biological role ot zinc in the human body, immune homeostasis and skin physiology as well as pathophysiology ot skin diseases. It describes the current range ot systemic and topical zinc preparations and their pharmacological characteristics. The review also describes skin diseases that may be treated with the use ot zinc preparations on a grounded basis, and discloses the clinical experience ot the use ot these drugs described in the world literature. It sets out certain recommendations tor using zinc preparations in clinical practice.

Skin photoaging and the role of antioxidants in its prevention

Photoaging of the skin depends primarily on the degree of ultraviolet radiation (UVR) and on an amount of melanin in the skin (skin phototype). In addition to direct or indirect DNA damage, UVR activates cell surface receptors of keratinocytes and fibroblasts in the skin, which leads to a breakdown of collagen in the extracellular matrix and a shutdown of new collagen synthesis. It is hypothesized that dermal collagen breakdown is followed by imperfect repair that yields a deficit in the structural integrity of the skin, formation of a solar scar, and ultimately clinically visible skin atrophy and wrinkles. Many studies confirmed that acute exposure of human skin to UVR leads to oxidation of cellular biomolecules that could be prevented by prior antioxidant treatment and to depletion of endogenous antioxidants. Skin has a network of all major endogenous enzymatic and nonenzymatic protective antioxidants, but their role in protecting cells against oxidative damage generated by UV radiation has not been elucidated. It seems that skin's antioxidative defence is also influenced by vitamins and nutritive factors and that combination of different antioxidants simultaneously provides synergistic effect.

Zinc, copper, and selenium tissue levels and their relation to subcutaneous abscess, minor surgery, and wound healing in humans

Trace element involvement in wounds left to heal by secondary intention needs clarification. We have previously reported faster healing of wounds following acute surgery compared with elective excision of pilonidal sinus disease. The effect of topical zinc on the closure of the excisional wounds was mediocre compared with placebo. In contrast, parenteral zinc, copper, and selenium combined appear effective for wound healing in humans. We have investigated zinc, copper, and selenium with respect to (a) impact of acute versus chronic pilonidal sinus and (b) regional concentrations within granulating wounds treated topically with placebo or zinc in 42 (33 males) pilonidal disease patients. Baseline serum and skin concentrations of copper correlated (r S = 0.351, p = 0.033, n = 37), but not of zinc or selenium. Patients with abscesses had elevated serum C-reactive protein (CRP) and copper levels (+29 %; p < 0.001) compared with the elective patients consistent with the strong correlation between serum copper and CRP (r S = 0.715, p < 0.0005, n = 41). Seven days after elective surgery, serum CRP and copper levels were elevated (p = 0.010) versus preoperative values. The copper concentration in wound edges was higher than in periwound skin (p < 0.0005) and wound base (p = 0.010). Selenium levels were increased in wound edge compared to wound base (p = 0.003). Topical zinc oxide treatment doubled (p < 0.050) zinc concentrations in the three tissue localizations without concomitant significant changes of copper or selenium levels. In conclusion, copper and selenium are mobilized to injured sites possibly to enhance host defense and early wound healing mechanisms that are complementary to the necessity of zinc for matrix metalloproteinase activity.

Zinc in wound healing: theoretical, experimental, and clinical aspects

Zinc is an essential trace element in the human body and its importance in health and disease is appreciated. It serves as a cofactor in numerous transcription factors and enzyme systems including zinc-dependent matrix metalloproteinases that augment autodebridement and keratinocyte migration during wound repair. Zinc confers resistance to epithelial apoptosis through cytoprotection against reactive oxygen species and bacterial toxins possibly through antioxidant activity of the cysteine-rich metallothioneins. Zinc deficiency of hereditary or dietary cause can lead to pathological changes and delayed wound healing. Oral zinc supplementation may be beneficial in treating zinc-deficient leg ulcer patients, but its therapeutic place in surgical patients needs further clarification. Topical administration of zinc appears to be superior to oral therapy due to its action in reducing superinfections and necrotic material via enhanced local defense systems and collagenolytic activity, and the sustained release of zinc ions that stimulates epithelialization of wounds in normozincemic individuals. Zinc oxide in paste bandages (Unna boot) protects and soothes inflamed peri-ulcer skin. Zinc is transported through the skin from these formulations, although the systemic effects seem insignificant. We present here the first comprehensive account of zinc in wound management in relation to current concepts of wound bed preparation and the wound-healing cascade. This review article suggests that topical zinc therapy is underappreciated even though clinical evidence emphasizes its importance in autodebridement, anti-infective action, and promotion of epithelialization.

Oral zinc sulphate causes murine hair hypopigmentation and is a potent inhibitor of eumelanogenesis in vivo

BACKGROUND

C57BL/6 a/a mice have been widely used to study melanogenesis, including in electron paramagnetic resonance (EPR) studies. Zinc cations modulate melanogenesis, but the net effect of Zn2+ in vivo is unclear, as the reported effects of Zn2+ on melanogenesis are ambiguous: zinc inhibits tyrosinase and glutathione reductase in vitro, but also enhances the activity of dopachrome tautomerase (tyrosinase-related protein-2) and has agonistic effects on melanocortin receptor signalling.

OBJECTIVES

To determine in a C57BL/6 a/a murine pilot study whether excess zinc ions inhibit, enhance or in any other way alter hair follicle melanogenesis in vivo, and to test the usefulness of EPR for this study.

METHODS

ZnSO(4).7H2O was continuously administered orally to C57BL/6 a/a mice during spontaneous and depilation-induced hair follicle cycling (20 mg mL-1; in drinking water; mean+/-SD daily dose 1.2+/-0.53 mL), and hair pigmentation was examined macroscopically, by routine histology and by EPR.

RESULTS

Oral zinc cations induced a bright brown lightening of new hair shafts produced during anagen, but without inducing an EPR-detectable switch from eumelanogenesis to phaeomelanogenesis. The total content of melanin in the skin and hair shafts during the subsequent telogen phase, i.e. after completion of a full hair cycle, was significantly reduced in Zn-treated mice (P=0.0005). Compared with controls, melanin granules in precortical hair matrix keratinocytes, hair bulb melanocytes and hair shafts of zinc-treated animals were reduced and poorly pigmented. Over the course of several hair cycles, lasting hair shaft depigmentation was seen during long-term exposure to high-dose oral Zn2+.

CONCLUSIONS

High-dose oral Zn2+ is a potent downregulator of eumelanin content in murine hair shafts in vivo. The C57BL/6 mouse model offers an excellent tool for further dissecting the as yet unclear underlying molecular basis of this phenomenon, while EPR technology is well suited for the rapid, qualitative and quantitative monitoring of hair pigmentation changes.

The role of intracellular zinc in chromium(VI)-induced oxidative stress, DNA damage and apoptosis

Several studies have demonstrated that zinc is required for the optimal functioning of the skin. Changes in intracellular zinc concentrations have been associated with both improved protection of skin cells against various noxious factors as well as with increased susceptibility to external stress. Still, little is known about the role of intracellular zinc in hexavalent chromium (Cr(VI))-induced skin injury. To address this question, the effects of zinc deficiency or supplementation on Cr(VI)-induced cytotoxicity, oxidative stress, DNA injury and cell death were investigated in human diploid dermal fibroblasts during 48 h. Zinc levels in fibroblasts were manipulated by pretreatment of cells with 100 microM ZnSO4 and 4 or 25 microM zinc chelator TPEN. Cr(VI) (50, 10 and 1 microM) was found to produce time- and dose-dependent cytotoxicity resulting in oxidative stress, suppression of antioxidant systems and activation of p53-dependent apoptosis which is reported for the first time in this model in relation to environmental Cr(VI). Increased intracellular zinc partially attenuated Cr(VI)-induced cytotoxicity, oxidative stress and apoptosis by enhancing cellular antioxidant systems while inhibiting Cr(VI)-dependent apoptosis by preventing the activation of caspase-3. Decreased intracellular zinc enhanced cytotoxic effects of all the tested Cr(VI) concentrations, leading to rapid loss of cell membrane integrity and nuclear dispersion--hallmarks of necrosis. These new findings suggest that Cr(VI) as a model environmental toxin may damage in deeper regions residing skin fibroblasts whose susceptibility to such toxin depends among others on their intracellular Zn levels. Further investigation of the impact of Zn status on skin cells as well as any other cell populations exposed to Cr(VI) or other heavy metals is warranted.

Zinc and skin health: overview of physiology and pharmacology

BACKGROUND

Zinc is known to have a critical role in overall human physiology, which likely explains many of its therapeutic uses for the last several thousand years. The specific roles zinc plays in skin health and function are less widely known yet are likely just as critical based on the manifestations of dietary zinc deprivation, which include moderate to severe dermatitis.

OBJECTIVE

To provide a critical review of the scientific literature as to the physiologic importance of zinc to skin, the biochemical basis for these effects, and pharmacologic aspects of zinc therapeutics.

RESULTS AND CONCLUSIONS

Skin is in a continual state of renewal, placing a high demand on zinc-based enzymes and proteins that direct this process. The importance of zinc physiologically is especially evident in studies of wound healing and inflammation reduction. During these processes, the high needs for zinc can be supplemented externally, generally increasing the rates of the natural processes. Topical zinc delivery involves the pharmacologic optimization of zinc delivery, often mediated by the solubility of the zinc material and interactions within the product matrix.

Photoprotection

Many agents affect the transmission of ultraviolet light to human skin. These include naturally occurring photoprotective agents (ozone, pollutants, clouds, and fog), naturally occurring biologic agents (epidermal chromophores), physical photoprotective agents (clothing, hats, make-ups, sunglasses, and window glass), and ultraviolet light filters (sunscreen ingredients and sunless tanning agents). In addition, there are agents that can modulate the effects of ultraviolet light on the skin (antioxidants and others). All of the above are reviewed in this article.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to provide an overview of all aspects of photoprotection.

Zinc and Cadmium Interactions in a Renal Cell Line Derived from Rabbit Proximal Tubule

BACKGROUND

The aim of this work was to characterize the relationship between zinc (Zn(2+)) and cadmium (Cd(2+)) and the toxic effects of Cd(2+) in immortalized renal proximal tubule cells RP1.

METHODS

An RP1 cell line was developed from primary cultures of microdissected S1 and S2. Uptakes of (65)Zn and (109)Cd and competitive experiments with Cd(2+) and Zn(2+) were performed and kinetic parameters were determined. Oxygen consumption, metallothionein synthesis, and necrotic and apoptotic phenomena were studied.

RESULTS

Kinetic parameters indicate that (65)Zn (Km = 71.8 +/- 10.6 microM) and (109)Cd (Km = 23.3 +/- 2.0 microM) were both transported by a saturable carrier-mediated process. Competition between Cd(2+) and Zn(2+) uptake was reciprocal. Cd(2+) induced an increase in necrosis and apoptosis, and a decrease in oxygen consumption, depending on Cd(2+) concentrations. Concomitant addition of Zn(2+) (10 microM) reduced the number of necrotic and apoptotic cells and maintained oxygen consumption at control levels. Cd(2+) alone, or in the presence of Zn(2+), increased metallothionein levels, whereas Zn(2+) alone did not.

CONCLUSION

Zn(2+) and Cd(2+) probably share the same transporter in the proximal tubule. Cd(2+) caused necrotic and apoptotic cell death. Cd(2+) toxicity may occur through an effect on the mitochondrial electron transport chain and not on metallothionein synthesis. Zn(2+) protects against the renal cell toxicity of Cd(2+).

Protective effects of antioxidant micronutrients (vitamin E, zinc and selenium) in type 2 diabetes mellitus

Type 2 diabetes (T2D) is a major cause of vascular complications affecting heart, kidney, retina and peripheral nerves. Hyperglycaemia leads to oxidative stress that plays an important role in vascular degenerative lesions observed in diabetes. In this Review we consider whether vitamin E, zinc or selenium are involved in the pathogenesis of diabetes. Concerning vitamin E, major epidemiological studies do not give the expected results in preventing cardiovascular outcomes. The mechanisms of free radical overproduction in diabetes could explain these results. Superoxide anion overproduction originates from mitochondria; in these conditions antioxidant enzymes are more relevant to reduce oxygen species than vitamin E. Zinc has numerous targets to modulate insulin activity, including its antioxidant capacity. Zinc status is decreased in most T2D patients. The effect of zinc supplementation on antioxidant status is raised when complications are associated. Selenium is a major antioxidant trace element and is the co-factor of glutathione peroxidase (Se GSHpx). Low Se GSHpx activity, observed in diabetic patients, is associated with thrombosis and cardiovascular complications.

Predominant effects of Polypodium leucotomos on membrane integrity, lipid peroxidation, and expression of elastin and matrixmetalloproteinase-1 in ultraviolet radiation exposed fibroblasts, and keratinocytes

BACKGROUND

Polypodium leucotomos has been reported to have antioxidant, anti-inflammatory and photoprotective properties. Exposure of skin to ultraviolet (UV) radiation can lead to deposition of excessive elastotic material, reduction in collagen, and increased expression of matrix metalloproteinases (MMPs).

OBJECTIVE

The goal of this research was to determine the effects of P. leucotomos in the absence or presence of UVA or UVB radiation on membrane damage, lipid peroxidation, and expression of elastin and MMP-1 in fibroblasts and keratinocytes, respectively.

METHODS

Fibroblasts and keratinocytes, respectively, were irradiated by a single exposure to UVA (0.6, 1.8 or 3.6 J) or UVB radiation (0.75, 2.5 or 7.5 mJ), and then incubated with, or without, P. leucotomos (0.01, 0.1 and 1%) and examined for membrane damage, lipid peroxidation, expression of elastin (protein levels) and MMP-1 (protein levels or MMP-1 promoter activity).

RESULTS

UV radiation did not significantly alter membrane integrity, lipid peroxidation or MMP-1 expression, but increased elastin expression. P. leucotomos significantly improved membrane integrity, inhibited lipid peroxidation, increased elastin expression, and inhibited MMP-1 expression in both fibroblasts, and keratinocytes. The effects of P. leucotomos predominated in the presence of UVA or UVB in both fibroblasts and keratinocytes, respectively, with the exception of inhibition of MMP-1 protein levels in fibroblasts only in combination with UV radiation.

CONCLUSION

Lower concentration of P. leucotomos (lower than 0.1%), may be beneficial in preventing photoaging by improving membrane integrity and inhibiting MMP-1, without increasing elastin expression. Higher concentration (greater than 0.1%) of P. leucotomos may reverse the loss of normal elastic fibers associated with intrinsic aging.

Cutaneous photodamage, oxidative stress, and topical antioxidant protection

New methods to protect skin from photodamage from sun exposure are necessary if we are to conquer skin cancer and photoaging. Sunscreens are useful, but their protection is not ideal because of inadequate use, incomplete spectral protection, and toxicity. Skin naturally uses antioxidants (AOs) to protect itself from photodamage. This scientific review summarizes what is known about how photodamage occurs; why sunscreens--the current gold standard of photoprotection--are inadequate; and how topical AOs help protect against skin cancer and photoaging changes. This review is intended to be a reference source, including pertinent comprehensive reviews whenever available. Although not all AOs are included, an attempt has been made to select those AOs for which sufficient information is available to document their potential topical uses and benefits. Reviewed are the following physiologic and plant AOs: vitamin C, vitamin E, selenium, zinc, silymarin, soy isoflavones, and tea polyphenols. Their topical use may favorably supplement sunscreen protection and provide additional anticarcinogenic protection. (J Am Acad Dermatol 2003;48:1-19.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants should have an understanding of current information about how the sun damages skin to produce skin cancer and photoaging changes, how the skin naturally protects itself from the sun, the shortcomings of sunscreens, and the added advantages of topical AOs for photoprotection.

Evidence supporting zinc as an important antioxidant for skin

Antioxidants play a critical role in keeping skin healthy. The antioxidant benefits of vitamin C and E are well known, but the importance of the trace mineral, zinc, has been overlooked. This article reviews the evidence supporting zinc's antioxidant role in protecting against free radical-induced oxidative damage. Zinc protects against UV radiation, enhances wound healing, contributes to immune and neuropsychiatric functions, and decreases the relative risk of cancer and cardiovascular disease. All body tissues contain zinc; in skin, it is five to six times more concentrated in the epidermis than the dermis. Zinc is required for the normal growth, development and function of mammals. It is an essential element of more than 200 metalloenzymes, including the antioxidant enzyme, superoxide dismutase, and affects their conformity, stability, and activity. Zinc also is important for the proper functioning of the immune system, and for glandular, reproductive and cell health. Abundant evidence demonstrates the antioxidant role of zinc. Topical zinc, in the form of divalent zinc ions, has been reported to provide antioxidant photoprotection for skin. Two antioxidant mechanisms have been proposed for zinc: zinc ions may replace redox active molecules, such as iron and copper, at critical sites in cell membranes and proteins; alternatively, zinc ions may induce the synthesis of metallothionein, sulfhydryl-rich proteins that protect against free radicals. No matter how they work, topical zinc ions may provide an important and helpful antioxidant defense for skin.

Zinc resistance impairs sensitivity to oxidative stress in HeLa cells: protection through metallothioneins expression

To analyze the effects of high concentrations of zinc ions on oxidative stress protection, we developed an original model of zinc-resistant HeLa cells (HZR), by using a 200 microM zinc sulfate-supplemented medium. Resistant cells specifically accumulate high zinc levels in intracellular vesicles. These resistant cells also exhibit high expression of metallothioneins (MT), mainly located in the cytoplasm. Exposure of HZR to Zn-depleted medium for 3 or 7 d decreases the intracellular zinc content, but only slightly reduces MT levels of resistant cells. No changes of the intracellular redox status were detected, but zinc resistance enhanced H2O2-mediated cytotoxicity. Conversely, zinc-depleted resistant cells were protected against H2O2-induced cell death. Basal- and oxidant-induced DNA damage was increased in zinc resistant cells. Moreover, measurement of DNA damage on zinc-depleted resistant cells suggests that cytoplasmic metal-free MT ensures an efficient protection against oxidative DNA damage, while Zn-MT does not. This newly developed Zn-resistant HeLa model demonstrates that high intracellular concentrations of zinc enhance oxidative DNA damage and subsequent cell death. Effective protection against oxidative damage is provided by metallothionein under nonsaturating zinc conditions. Thus, induction of MT by zinc may mediate the main cellular protective effect of zinc against oxidative injury.

The relationship between UVB screening and cytoprotection by microcorpuscular ZnO or ascorbate against DNA photodamage and membrane injuries in keratinocytes by oxidative stress

Decreased cell viability and increased formation of cyclobutane-type pyrimidine dimers (CPDs) in DNA of UVB-irradiated keratinocytes were shown to be appreciably restored by the addition of w/o emulsion of microcorpuscular zinc oxide (mcZnO) with a corpuscle diameter of 0.15 microm. The cytoprotection was exerted only by 20 wt/wt% mcZnO at levels equivalent to 40- to 100-microm-thick emulsion layers, which screened 90-92% of the incident UVB. However, protection was not seen by mcZnO below 20-microm thickness, which, unexpectedly, screened 79% of the incident radiation. This suggests that thorough UVB screening is necessary for cytoprotection. This may be attributable to involvement of intracellular reactive oxygen species (ROS) secondarily generated from UVB-irradiated mcZnO. Intracellular ROS was increased in mcZnO-added cells in a time-dependent manner even after UVB irradiation, contrasting with reduction of intracellular ROS in ascorbic acid-added cells. UVB-induced disruption of cell membrane integrity was reduced by mcZnO at 100-microm thickness, equivalent to the addition of ascorbic acid of 50 microM. Thus, mcZnO was thought to be cytoprotective through reductions of intracellular ROS generation, CPD formation and cell membrane disintegration when added so abundantly so as to achieve UVB-screening more than 90%.

Zinc in the retina

Experimental evidence exists to suggest that zinc can have positive and negative effects on the physiology of cells depending on the "local" concentration, localisation (extracellular vs. intracellular) and/or state (bound vs. free). The retina contains particularly high amounts of zinc suggesting a pivotal role in the tissue. There is also suggestive evidence that zinc deficiency in humans may result in abnormal dark adaptation and/or age-related macular degeneration. The purpose of this article is to provide an overview of various proposed functions for zinc, particularly in the retina. Endogenous chelatable zinc in the retina is localised mainly to the photoreceptors and retinal pigment epithelial cells. Moreover, the zinc localisation in the photoreceptors varies in dark and light, suggesting a role for zinc in a light-regulated process. Some zinc is also located to other areas of the retina but clearly defined zinc-enriched neurones could not be identified as has been shown to occur in certain areas of the brain. Neurones post-synaptic to zinc-enriched neurones in the brain have been suggested to be particularly vulnerable in ischaemia. The role of zinc in retinal ischaemia has been investigated to determine how it is involved in the process. It would appear that when zinc is administered in low concentrations it generally has a positive effect on an insulted retina as in ischaemia. However, higher concentrations of zinc exacerbates the influence of the insult and also acts as a toxin. Use of zinc supplements in diet must, therefore, be taken with caution.

Modern approaches to photoprotection

UV light reacts with skin to produce undesirable changes, including photoaging and skin cancer. Sunscreen strategies are useful for protection against UV-B and short-wave UV-A, but complete protection against long-wave UV-A has not been achieved. Because UV-A is especially efficient at generating reactive oxygen species, it is being recognized increasingly as an important cause of photoaging and skin cancer.

The inhibitory effect of zinc on cadmium-induced cell apoptosis and reactive oxygen species (ROS) production in cell cultures

The prevention of apoptosis by Zn(2+) is a well-known phenomenon. Both in in vitro and in vivo Zn(2+) supplementation prevents apoptosis induced by a variety of agents, among them by cadmium ions. The target for protective action of Zn ions on cell apoptosis is still unknown. In this paper we have evaluated the effect of in vitro ZnCl(2) supplementation at a concentration corresponding to the physiological level (10 microM) and higher (50 microM), on apoptosis induced with different Cd concentrations in two cell types: HeLa human tumor cell line and bovine aorta endothelial cells (BAECs). We demonstrated that Zn supplementation, especially at 10 microM concentration, significantly inhibited apoptosis in both types of cells. To assess the mechanism involved in the Zn effect we examined the influence of Zn supplementation on Cd accumulation in cells, Cd-induced superoxide anion (O(2)(-)) and hydrogen peroxide (H(2)O(2)) production. Zn caused 1.2-2.0-fold inhibition of Cd accumulation, 1.2-2.0-fold inhibition of Cd-induced apoptotic cell death, 1.1-2.0-fold decrease in reactive oxygen species (ROS) production in HeLa cells and in BAECs. These results indicate that inhibition of Cd-induced apoptosis in cells by Zn might be due, not only by inhibition of Cd accumulation in cells but, at least in part, to inhibition of Cd-induced production of ROS, which in turn are known as strong inducers of apoptosis.

Effect of zinc ions on the cytotoxicity induced by the amyloid beta-peptide

Insoluble aggregates of the amyloid beta-peptide (A beta) are a major constituent of senile plaques found in brains of Alzheimer's disease patients. The beta-amyloid fragment A beta(1-40) is toxic to rat pheochromocytoma PC12 cells, leading to a concentration-dependent decrease in the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The detrimental effects of A beta(1-40) are enhanced in the presence of 1 mM zinc, whereas 50 microM zinc exerts a protective effect against A beta(1-40)-induced toxicity. Exposure of PC12 cells to low zinc concentrations (50 microM) affords a decrease (1.4-fold) in the extent of lipid peroxidation, a decrement in protein oxidation (1.1-fold), and an increase in ATP levels (1.2-fold), although the differences were not statistically significant. However, treatment of cells with high concentrations of zinc (1 mM) led to significant increases in lipid peroxidation (3.7-fold) and protein oxidation (1.5-fold) and to depletion of the ATP pool (21-fold). These data suggest that zinc has a concentration-dependent dual effect, protective and toxic, thus playing an important role in the pathogenesis of Alzheimer's disease.

Zinc protects against ultraviolet A1-induced DNA damage and apoptosis in cultured human fibroblasts

Ultraviolet A1 (UVA1) radiation generates reactive oxygen species and the oxidative stress is known as a mediator of DNA damage and of apoptosis. We exposed cultured human cutaneous fibroblasts to UVA1 radiation (wavelengths in the 340-450-nm range with emission peak at 365 nm) and, using the alkaline unwinding method, we showed an immediate significant increase of DNA strand breaks in exposed cells. Apoptosis was determined by detecting cytoplasmic nucleosomes (enzyme-linked immunosorbent assay method) at different time points in fibroblasts exposed to different irradiation doses. In our conditions, UVA1 radiation induced an early (8 h) and a delayed (18 h) apoptosis. Delayed apoptosis increased in a UVA dose-dependent manner. Zinc is an important metal for DNA protection and has been shown to have inhibitory effects on apoptosis. The addition of zinc (6.5 mg/L) as zinc chloride to the culture medium significantly decreased immediate DNA strand breaks in human skin fibroblasts. Moreover, zinc chloride significantly decreased UVA1-induced early and delayed apoptosis. Thus, these data show for the first time in normal cutaneous cultured cells that UVA1 radiation induces apoptosis. This apoptosis is biphasic and appears higher 18 h after the stress. Zinc supplementation can prevent both immediate DNA strand breakage and early and delayed apoptosis, suggesting that this metal could be of interest for skin cell protection against UVA1 irradiation.

Zinc protects against oxidative damage in cultured human retinal pigment epithelial cells

This study was undertaken to determine whether bioavailable zinc can influence the effects of oxidative stress on cultured human retinal pigment epithelial (RPE) cells. RPE cells were maintained for 7 d in culture medium containing 14 microM total zinc, or in medium containing 0.55 microM total zinc. After 1 week, MTT assays were performed to determine the relative cytotoxicity of H2O2 or paraquat on RPE cells. Conjugated dienes and thiobarbituric acid reactive substances (TBARS) were measured in RPE cells treated with 0, 0.5 mM H2O2, 10 microM FeSO4 + 0.5 mM H2O2 or 10 microM FeSO4 + xanthine/xanthine oxidase for 24 h or paraquat for 7 d. Oxidized proteins were determined by the formation of carbonyl residues. The antioxidants metallothionein, catalase, superoxide dismutase, and glutathione peroxidase were also measured. The MTT assays showed that zinc protected cultured RPE from the toxicity of H2O2 and paraquat. RPE cells in 0.55 microM zinc medium contained higher levels of TBARS, conjugated dienes and protein carbonyls due to the oxidative stresses, compared to cells in 14 microM zinc. Catalase and MT content were reduced in cells cultured in 0.55 microM zinc medium and were reduced additionally when treated with above stresses. Superoxide dismutase activity increased in 0.55 microM zinc medium in response to these stresses. Our results show RPE cells cultured in zinc-reduced medium are more susceptible to oxidative insult.

Involvement of zinc in intracellular oxidant/antioxidant balance

The effect of zinc (Zn) on cellular oxidative metabolism is complex and could be explained by multiple complementary interactions. In this study, we evaluated the impact of Zn on the pro-oxidant/antioxidant balance of HaCaT keratinocytes. Cells were submitted to a diffusible metal chelator able to induce intracellular Zn deprivation, TPEN, in combination or not with Zn chloride (ZnCl2), in the culture medium. The intracellular amount of Zn, copper (Cu), and iron (Fe) was determined, as well as CuZnSOD and MnSOD activities and glutathione reserves. The consequence of the modulation of Zn concentration on lipid peroxidation was also evaluated. TPEN induced a significant dose-dependent decrease in intracellular Zn and Cu (from 394-181 and 43-21 microg/g protein, respectively, after 6 h of TPEN 50 microM). No significant change in intracellular Fe concentration was found following TPEN exposure. The SOD activities were unchanged after 6 h of TPEN 50 microM application, either CuZnSOD or MnSOD. Cells exposure to TPEN induced a deep time- and dose-dependent decrease in their glutathione content (from 65-8 microM/g protein after 6 h of TPEN 50 microM), and a concomitant increase in glutathione in the cell-culture supernatants. No significant change in lipid peroxidation products was detected.

Effect of zinc on lipid peroxidation and antioxidant enzymes in hepatic and brain tissues of chick embryos

Chick embryos were treated with different concentrations (25 and 75 mumoles/kg egg wt.) of zinc on the 14th day of embryonic development. The levels of thiobarbuturic acid reacting substances (TBARS), glutathione (GSH) and activity levels of antioxidant enzymes such as glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST), superoxide dismutase (SOD) and catalase were measured in both hepatic and brain tissues after different time intervals (24 h, 72 h and 120 h) of zinc exposure. Increased levels of TBARS were observed after 24 h of zinc treatment and thereafter (72 h and 120 h) the levels were decreased in both the tissues. Significant induction was observed in antioxidant enzyme activities in both the tissues after 24 h and 72 h when compared to 120 h. However, the GSH levels were increased at 24 h and 72 h and thereafter decreased in both the tissues at 120 h. The elevated levels of antioxidant enzymes at 24 h and 72 h may be responsible for the reduction of TBARS at 72 h and 120 h in developing chick embryos.

Adding Zn2+ induces DNA fragmentation and cell condensation in cultured human Chang liver cells

Zinc (Zn) is a trace element in human cells and regarded as an essential nutrient with established deficiency states affecting multiple organs in the body. However, it has been reported that Zn uptake is associated with some serious harmful effects, such as inhibition of DNA synthesis and enhanced toxicity from reactive oxygen species. We have previously shown that in vivo administration of Zn2+ in C57/6J mice induces weight loss and massive hair loss where the normal course hair becomes replaced by fine vello hair, simulating the side effects from cancer chemotherapy where oxidative free radical damage is implicated in association with DNA fragmentation and programmed cell death (PCD). Here, in vitro flow cytometric studies on human Chang liver showed Zn2+ causing cell condensation with DNA fragmentation that occurred in a dose-dependent manner, an effect replicated by micrococcal nuclease digestion. Specific terminal deoxynucleotidyl transferase-(TdT) mediated labeling of 3'-OH ends of DNA nicks corroborated the flow cytometric profiles of propidium iodide-DNA binding where degradation of both 2 and 4 N genomic DNA resulted in a solitary 1N peak presentation. DNA degradation concomitant with cell condensation is seen as an established hallmark of PCD. We further showed that Zn2+ could enhance the generation of hydroxyl free radicals (OH.) by the transition metal vanadium. Glutathione, the cell's main reducing agent, underwent corresponding reduction. The results suggested that Zn supplementation could induce features resembling PCD.

Zinc and DNA fragmentation in keratinocyte apoptosis: its inhibitory effect in UVB irradiated cells

Zinc has been shown to have antioxidant properties and to exhibit inhibitory effects on apoptosis. In this work we investigated the effect of zinc on DNA integrity and on apoptosis of HaCaT keratinocytes. Cells were submitted to zinc deprivation by a diffusible zinc chelator, (N,N,N',N'-tetrakis (2-pyridylmethyl)ethylenediamine) (TPEN) or supplied with zinc chloride and submitted to UVB radiation. After cell exposure to TPEN for 2 h, strand breaks significantly impaired DNA resistance to alkaline denaturation. DNA strand breaks induced by a 6 h TPEN application were significantly prevented if zinc chloride was supplied together with the chelator. TPEN also generated, after 4-6 h of application, cytoplasmic histone-associated DNA fragments (mononucleosomes and oligonucleosomes), features of cell death by apoptosis. Moreover, UVB irradiation led to early DNA strand breaks and to an increase in cytoplasmic nucleosomes which was maximum 10 h after irradiation. These effects were prevented by the supply of zinc chloride (0.1 mM) in the culture medium. These results suggest that zinc ions interfere with the apoptosis process at an early stage, by decreasing DNA damage able to trigger apoptosis.

Protection by zinc against UVA- and UVB-induced cellular and genomic damage in vivo and in vitro

For many years, zinc salts have been used both topically and orally to treat minor burns and abrasions as well as to enhance wound repair in man and animals. In this study we describe the protective effects of zinc against UV-induced genotoxicity in vitro and against sunburn cell formation in mouse skin in vivo. Cultured skin cells from neonatal mice showed a dramatic increase in the number of micronuclei as a result of UVA and UVB irradiation. Inclusion of zinc at 5 micrograms/mL in the medium significantly reduced the frequency of micronuclei and of micronucleated cells. In hairless mice, topical application of zinc chloride for 5 consecutive days or a single application 2 h prior to UV exposure reduced the number of sunburn cells in the epidermis as did application of zinc 1 h after exposure. Application 2 h after irradiation also tended to have a protective effect, although there was a large variation between animals. It is proposed that an influx of zinc can protect epidermal cells against some of the more delayed effects of UV-induced damage.

The effect of zinc supplementation on plasma lipids and low-density lipoprotein oxidation in males

Recent studies in animals and in vitro support the hypothesis that zinc, an essential micronutrient, possesses antioxidant properties. The aims of this study were to determine whether zinc provides antioxidant protection in humans by decreasing low-density lipoprotein (LDL) oxidizability and to determine the effect of zinc supplementation on plasma lipid and its distribution among lipoproteins. Ten healthy male volunteers were recruited to participate in a randomized crossover trial. Subjects were asked to consume 50 mg zinc as 220 mg zinc sulphate (equivalent to 4 x recommended dietary intake, or RDI) daily for 4 weeks, followed by placebo, and vice versa. Venous blood samples were collected at 2-week intervals for the determination of plasma lipids and the in vitro oxidizability of LDL in the presence of copper ions. No changes in the oxidizability of LDL or the plasma concentrations of total cholesterol, high-density lipoprotein (HDL) cholesterol and its subfractions, LDL cholesterol, or triacylglycerol were observed following zinc supplementation compared to placebo. Plasma zinc concentrations were increased significantly, indicating that the lack of effect was not due to poor compliance. The antioxidant effect of zinc in relation to LDL was not demonstrated in humans at this dose, and higher doses are unlikely to be effective given the adverse interaction with copper metabolism and the potential decrease in the activity of superoxide dismutase, a free radical quenching enzyme. The findings of this study suggest that zinc provides little, if any, antioxidant protection against LDL oxidation in humans.