Toxicity of oxidized β-carotene to cultured human cells

Simple Electrospinning Method for Biocompatible Polycaprolactone β-Carotene Scaffolds: Advantages and Limitations

In this study, electrospun scaffolds were fabricated using polycaprolactone (PCL) loaded with varying concentrations of β-carotene (1.2%, 2.4%, and 3.6%) via the electrospinning technique. The electrospinning process involved the melting of PCL in acetic acid, followed by the incorporation of β-carotene powder under constant stirring. Raman spectroscopy revealed a homogeneous distribution of β-carotene within the PCL matrix. However, the β-carotene appeared in particulate form, rather than being dissolved and blended with the PCL matrix, a result also confirmed by thermogravimetric analysis. Additionally, X-ray diffraction analysis indicated a decrease in crystallinity with increasing β-carotene concentration. Mechanical testing of the scaffolds demonstrated an increase in ultimate strain, accompanied by a reduction in ultimate stress, indicating a potential plasticizing effect. Moreover, antimicrobial assays revealed a marginal antibacterial effect against Escherichia coli for scaffolds with higher β-carotene concentrations. Conversely, preliminary biological assessment using KUSA-A1 mesenchymal cells indicated enhanced cellular proliferation in response to the scaffolds, suggesting the potential biocompatibility and cell-stimulating properties of β-carotene-loaded PCL scaffolds. Overall, this study provides insights into the fabrication and characterization of electrospun PCL scaffolds containing β-carotene, laying the groundwork for further exploration in tissue engineering and regenerative medicine applications.

β-Carotene oxidation products - Function and safety

β-Carotene oxidation products have newly discovered bioactivity in plants and animals. Synthetic fully oxidized β-carotene (OxBC) has application in supporting livestock health, with potential human applications. The safety of synthetic OxBC has been evaluated. An Ames test showed weak-to-moderate mutagenicity in only one cell line at high concentrations. A mouse micronucleus assay established a non-toxic dose of 1800 mg/kg body weight, and no bone marrow micronuclei were induced. Plant sources of β-carotene inevitably contain varying levels of natural OxBC. Vegetable powders and dried forages can be especially rich. Intakes of natural OxBC for humans and livestock alike have been estimated. The exposure range for humans (1-22 mg/serving) is comparable to the safe intake of β-carotene (<15 mg/d). In livestock, OxBC in alfalfa can contribute ~550-850 mg/head/d for dairy cattle but in forage-deficient poultry feed much less (~1 ppm). Livestock intake of supplemental synthetic OxBC is comparable to OxBC potentially available from traditional plant sources. Human intake of synthetic OxBC in meat from livestock fed OxBC is similar to a single serving of food made with carrot powder. It is concluded that consumption of synthetic OxBC at levels comparable to natural OxBC is safe for humans and animals.

The comparison of pegylated liposomal doxorubicin and beta-carotene effects on JAR and JEG-3 choriocarcinoma human cell culture models

Objective:

The aim was to investigate the effectiveness of pegylated liposomal doxorubicin (PLD), beta-carotene, and a combination of PLD and beta-carotene on JAR and JEG-3 human choriocarcinoma (CC) cell lines for the treatment of CC.

Material and Methods:

JAR and JEG-3 cells were cultured. PLD and beta-carotene trial groups were determined with different doses (for single drug trial; PLD 1, 2, 5 μg/mL and beta-carotene 1, 5, 10 μg/mL, and for combined drug trial; all PLD doses combined with beta-carotene 5 μg/mL). Drugs were administered to cultures simultaneously, and 72 hours later the cells were detached using trypsin-ethylenediamine tetraacetic acid solution. The percentage of apoptotic cells was determined by flow cytometry after annexin V staining. One set of the supernatant was collected before trypsin application to investigate beta-human chorionic gonadotropin (β-hCG) and hyperglycosylated hCG (H-hCG) levels. Statistical analyses of the apoptotic ratios were performed using Shapiro-Wilk, Kruskal-Wallis and Mann-Whitney U tests.

Results:

Apoptosis increased in JAR and JEG-3 cultures after treatment with all doses of PLD (p<0.05). A single application of each beta-carotene dose increased apoptosis in JAR cells (p<0.05) but had no apoptotic effects on JEG-3 cells. In the PLD and beta-carotene combination group, apoptosis increased in both JAR and JEG-3 cells (p<0.05).

Conclusion:

To our knowledge, this is the first investigation of the effectiveness of PLD, beta-carotene, and PLD + beta-carotene combination therapy in two different CC cell lines. PLD is a promising chemotherapeutic drug, and beta-carotene can be used as a novel non-chemotherapeutic agent for treatment of CC. Based on the results of this study, vitamin A supplementation may have promise as a preventive measure. However, these data need support from animal experiments and clinical trials.

The effect of β-carotene on the mortality of male smokers is modified by smoking and by vitamins C and E: evidence against a uniform effect of nutrient

A previous analysis of the Alpha-Tocopherol Beta-Carotene (ATBC) Study on male smokers found that β-carotene supplementation increased the risk of pneumonia 4-fold in those who started smoking at the age of ≥21 years and smoked ≥21 cigarettes/d (a subgroup of 7 % of the study population). The present study hypothesised that β-carotene increases mortality in the same subgroup. The ATBC Study (1985–1993) recruited 29 133 Finnish male smokers (≥5 cigarettes/d) aged 50–69 years. Cox regression models were constructed to estimate the effect of β-carotene supplementation in subgroups. β-Carotene increased mortality (risk ratio 1·56; 95 % CI 1·06, 2·3) in those who started to smoke at ≥21 years and smoked ≥21 cigarettes/d. Within this subgroup, there was strong evidence of further heterogeneity. The effect of β-carotene supplementation was further modified by dietary vitamin C intake, fruit and vegetable intake (P = 0·0004), and by vitamin E supplementation (P = 0·011). Thus, harm from β-carotene was not uniform within the study population. Interactions between β-carotene and vitamins C and E were seen only within a subgroup of 7 % of the ATBC participants, and therefore should not be extrapolated to the general population. Heterogeneity of the β-carotene effect on mortality challenges the validity of previous meta-analyses that have pooled many diverse antioxidants for one single estimate of effect using the assumption that a single estimate equally applies to all antioxidants and all people. Trial registration: ClinicalTrials.gov NCT00342992.

Marked Inhibition of Cellular Proliferation in the Normal Human Esophageal Epithelial Cells and Human Esophageal Squamous Cancer Cells in Culture by Carotenoids: Role for Prevention and Early Treatment of Esophageal Cancer

Background:

Globally Esophageal cancer is a common cancer arising from human esophageal mucosal tissue. Epidemiological studies suggest inverse correlation between carotenoid intake and incident risk of this devastating malignancy.

Methods:

In an effort to examine the modulatory role of carotenoids in human esophageal carcinogenesis at a cellular level, we examined the effects of α-carotene and β-carotenes, on cell proliferation and DNA synthesis in human esophageal epithelial (HEE) cells and human esophageal squamous cancer (HESC) cells in in-vitro cultures. HEE and HESC cells were incubated with different concentrations of α- and β-carotenes both individually and in combination.

Results:

Both Carotenes significantly inhibited (p<0.05) cellular proliferation and decreased DNA synthesis in HEE and HESC cells. The effect of α- and β-carotene together on DNA synthesis in HEE and HESC cells was significantly greater than either carotenoid alone, suggesting a synergistic effect. Greater magnitude of cellular inhibition of DNA synthesis was observed on HEE cells than HESC cells.

Conclusion:

Our results suggest that a combination of α-and β-carotene may provide a novel strategy for prevention and treatment of esophageal and upper aero digestive tract cancer in humans.

Lutein, zeaxanthin and mammalian development: Metabolism, functions and implications for health

It is now widely accepted that nutrition during critical periods in early development, both pre- and postnatal, may have lifetime consequences in determining health or onset of major diseases in the adult life. Dietary carotenoids have shown beneficial health effects throughout the life cycle due to their potential antioxidant properties, their ability to serves as precursors of vitamin A and to the emerging signaling functions of their metabolites. The non-provitamin A carotenoids lutein and zeaxanthin are emerging as important modulators of infant and child visual and cognitive development, as well as critical effectors in the prevention and treatment of morbidity associated with premature births. This review provides a general overview of lutein and zeaxanthin metabolism in mammalian tissues and highlights the major advancements and remaining gaps in knowledge in regards to their metabolism and health effects during pre- and early post-natal development. Furthering our knowledge in this area of research will impact dietary recommendation and supplementation strategies aimed at sustaining proper fetal and infant growth.

Lutein improves cell viability and reduces Alu RNA accumulation in hydrogen peroxide challenged retinal pigment epithelial cells

PURPOSE

Dysfunction of the microRNA (miRNA)-processing enzyme DICER1 and Alu RNA accumulation are linked to the pathogenesis of age-related macular degeneration (AMD). This study determined the optimal dose of lutein (LUT) and zeaxanthin (ZEA) to protect human retinal pigment epithelium (RPE) cells against hydrogen peroxide (H₂O₂). The effect of the optimal dose of LUT and ZEA as DICER1 and Alu RNA modulators in cultured human RPE cells challenged with H₂O₂ was investigated.

MATERIALS AND METHODS

ARPE-19 cells were pre-treated with LUT, ZEA, or both for 24 h before 200 μM H₂O₂ challenge. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. DICER1 and Alu RNA were quantified by western blotting and real-time polymerase chain reaction, respectively.

RESULTS

H₂O₂ increased cell Alu RNA expression and decreased cell viability of ARPE-19, but had no significant impact on the DICER1 protein level. LUT, alone and in combination with ZEA pre-treatment, prior to H₂O₂ challenge significantly improved cell viability of ARPE-19 and reduced the level of Alu RNA compared to the negative control.

CONCLUSIONS

These results support the use of LUT alone, and in combination with ZEA, in AMD prevention and treatment. This study is also the first to report LUT modulating effects on Alu RNA.

Biological fate of food nanoemulsions and the nutrients they carry – internalisation, transport and cytotoxicity of edible nanoemulsions in Caco-2 intestinal cells

Internalisation of edible food nanoemulsions by CaCo-2 intestinal cells. The structure of edible nanoemulsions increases five times upon incorporation of reactive/ROS producing nutrients/APIs.

Characterization of the Role of β-Carotene 9,10-Dioxygenase in Macular Pigment Metabolism

A family of enzymes collectively referred to as carotenoid cleavage oxygenases is responsible for oxidative conversion of carotenoids into apocarotenoids, including retinoids (vitamin A and its derivatives). A member of this family, the β-carotene 9,10-dioxygenase (BCO2), converts xanthophylls to rosafluene and ionones. Animals deficient in BCO2 highlight the critical role of the enzyme in carotenoid clearance as accumulation of these compounds occur in tissues. Inactivation of the enzyme by a four-amino acid-long insertion has recently been proposed to underlie xanthophyll concentration in the macula of the primate retina. Here, we focused on comparing the properties of primate and murine BCO2s. We demonstrate that the enzymes display a conserved structural fold and subcellular localization. Low temperature expression and detergent choice significantly affected binding and turnover rates of the recombinant enzymes with various xanthophyll substrates, including the unique macula pigment meso-zeaxanthin. Mice with genetically disrupted carotenoid cleavage oxygenases displayed adipose tissue rather than eye-specific accumulation of supplemented carotenoids. Studies in a human hepatic cell line revealed that BCO2 is expressed as an oxidative stress-induced gene. Our studies provide evidence that the enzymatic function of BCO2 is conserved in primates and link regulation of BCO2 gene expression with oxidative stress that can be caused by excessive carotenoid supplementation.

Inhibition of proliferation and induction of apoptosis by the combination of β-carotene and 1,25-dihydroxyvitamin D3 in human esophageal cancer EC9706 cells

Esophageal cancer is a common malignant tumor occurring in human esophageal epithelial tissue. The primary purpose of this paper was to define the effects of β-carotene and 1,25-dihydroxyvitamin D3, alone and in combination, on cell proliferation, cell cycle and apoptosis of human esophageal cancer EC9706 cells. Treatment with different concentrations of β-carotene and/or 1,25-dihydroxyvitamin D3. MTT assay showed that β-carotene and 1,25-dihydroxyvitamin D3 significantly inhibited proliferation of EC9706 cells in a dose- and time-dependent manner. Further studies also demonstrated that β-carotene alone or 1,25-dihydroxyvitamin D3 alone caused a marked increase on the induction of apoptosis in EC9706 cells. The percentage of G0/G1-phase cells significantly increased on addition of 1,25-dihydroxyvitamin D3 alone, but there were no significant changes with β-carotene alone. These two agents in combination synergistically inhibited cell growth and induced apoptosis. Therefore, our results indicate that β-carotene and 1,25-dihydroxyvitamin D3 in combination may provide a novel strategy for preventing and treating esophageal cancer.

Carotenoid oxidation products as stress signals in plants

Carotenoids are known to play important roles in plants as antioxidants, accessory light-harvesting pigments, and attractants for pollinators and seed dispersers. A new function for carotenoids has recently emerged, which relates to the response of plants to environmental stresses. Reactive oxygen species, especially singlet oxygen, produced in the chloroplasts under stress conditions, can oxidize carotenoids leading to a variety of oxidized products, including aldehydes, ketones, endoperoxides and lactones. Some of those carotenoid derivatives, such as volatile β-cyclocitral, derived from the oxidation of β-carotene, are reactive electrophile species that are bioactive and can induce changes in gene expression leading to acclimation to stress conditions. This review summarizes the current knowledge on the non-enzymatic oxidation of carotenoids, the bioactivity of the resulting cleavage compounds and their functions as stress signals in plants.

Lutein protects retinal pigment epithelium from cytotoxic oxidative stress

CONTEXT

Lutein (LUT) and zeaxanthin (ZEA) are currently under investigation in clinical trials as prophylactic nutritional agents for age-related macular degeneration (AMD). However, dose used in these trials is empirical and not been investigated in in vitro studies.

OBJECTIVE

In this study, we investigated the dose-response effect of LUT and ZEA in protecting retinal pigment epithelium (RPE) from oxidative stress, a common underlying pathology in AMD.

METHODS

Three thousand cultured human retinal pigment epithelial cells (ARPE-19) were plated in 72-well plate and after 24 h were exposed to increasing concentrations of hydrogen peroxide (H2O2). ARPE-19 cells were exposed to four different concentrations of LUT (0.5, 1, 2 and 4 µg/mL) and ZEA (0.1, 0.2, 0.4 and 0.8 µg/mL). After 24 h incubation, cells were subjected to oxidative stress induced with H2O2. Cultures containing saline solution and dichloromethane served as controls. Cell viability was assessed using the WST-1 assay. Pathophysiological pathways were evaluated by measuring caspase-3 levels as an indicator of apoptosis induction. Reactive oxygen species (ROS) levels were measured using dihydrorhodamine-123.

RESULTS

Cell viability as a percentage of control was 81.3%, 81.1%, and 88.8% at 0.5, 1, and 2 µg/ml, respectively of LUT (p < 0.001). The maximum cytoprotective effect was seen with LUT at 2 μg/mL. ZEA did not show any cytoprotective effect at all concentrations used in the study. Caspase-3 showed a corresponding decrease in levels with LUT (1 and 2 µg/ml). Significant decrease in ROS levels were measured only with LUT at 4 µg/ml (p = 0.02).

DISCUSSION AND CONCLUSIONS

Results from our study provide in vitro data to support the epidemiologic studies, which are currently underway to provide evidence that lutein may act as cofactor that modulates processes implicated in AMD pathogenesis.

Nonenzymic carotenoid oxidation and photooxidative stress signalling in plants

Carotenoids play a crucial protective role in photosynthetic organisms as quenchers of singlet oxygen ((1)O(2)). This function occurs either via a physical mechanism involving thermal energy dissipation or via a chemical mechanism involving direct oxidation of the carotenoid molecule. The latter mechanism can produce a variety of aldehydic or ketonic cleavage products containing a reactive carbonyl group. One such molecule, the volatile β-carotene derivative β-cyclocitral, triggers changes in the expression of (1)O(2)-responsive genes and leads to an enhancement of photooxidative stress tolerance. Thus, besides their well-known functions in light harvesting and photoprotection, carotenoids can also play a role through their nonenzymic oxidation in the sensing and signalling of reactive oxygen species and photooxidative stress in photosynthetic organisms. Enzymic carotenoid oxidation does not seem to play a significant role in this phenomenon. Elucidation of the carotenoid-mediated (1)O(2) signalling pathway could provide new targets for improving photooxidative stress tolerance of plants.

Post-translational protein modification by carotenoid cleavage products

Carotenoids are known to generate various aldehydes, known as carotenoid-derived aldehydes (CDAs), which could efficiently react with protein or DNA. In this in vitro model study, interaction between CDA and protein has been studied. Various proteins were incubated with CDA, and protein modification and adduct formation were confirmed by using matrix-assisted laser desorption and ionization time-of-flight, amino acid analysis, and measuring enzyme activity on modification with CDA. Using radiolabeled NaB((3) H)H(4) and Raney nickel as well as sulfhydryl assay (Ellman's reagent), we confirmed that CDA could conjugate with cysteine through a thioether linkage. The carbonyl assay using 2,4-dinitrophenylhydrazine revealed the possible involvement of Schiff's base reaction between CDA and lysine. The adducts formed between β-apo-8-carotenal (BA8C) and N-acetylcysteine and BA8C and N-acetyllysine were confirmed by HPLC and ESI-MS. Our results suggest that CDA could alter protein function by post-translational interaction with cysteine and lysine by thioether linkage and by schiff's based bonds, respectively. Thus, the formation of CDA adducts with proteins could alter functional properties of proteins responsible for maintaining cell homeostasis and thereby cause cellular toxicity. In view of these observations, further studies are required to understand the delicate balance between beneficial and/or harmful effects of carotenoids as a dietary supplement to slow age-related macular degeneration progression.

Lycopene epoxides and apo-lycopenals formed by chemical reactions and autoxidation in model systems and processed foods

To gain a better understanding of the reactions and the underlying mechanisms of the oxidative degradation of lycopene, the products formed by epoxidation with m-chloroperbenzoic acid (MCPBA), oxidative cleavage with KMnO(4), and autoxidation in low-moisture and aqueous model systems, under light exposure, at ambient temperature were identified. The presence of oxidation products was also verified in processed products (tomato juice, tomato paste, tomato puree, guava juice, "goiabada"). A total of 8 lycopene epoxides and a cyclolycopene diol were formed by the reaction of lycopene with MCPBA and 6 apo-lycopenals were produced with KMnO(4). Some of these oxidation products were not detected in the model systems and in the foods analyzed, but the acid-catalyzed rearrangement product 2,6-cyclolycopene-1,5-diol and apo-12'-lycopenal were found in all model and food systems and lycopene-1,2-epoxide and 2,6-cyclolycopene-1,5-epoxide were found in the model systems and in all but 1 ("goiabada") of the 5 foods analyzed. Other epoxides and apo-lycopenals were found in some systems. The inability to detect an intermediate product could be due to a fast turn over. Increased Z-isomerization was also observed and Z-isomers of the oxidation products were detected.

Biocompatibility and modification of the protein-based adhesive secreted by the Australian frog Notaden bennetti

When provoked, Notaden bennetti frogs secrete a proteinaceous exudate, which rapidly forms a tacky and elastic glue. This material has potential in biomedical applications. Cultured cells attached and proliferated well on glue-coated tissue culture polystyrene, but migrated somewhat slower than on uncoated surfaces. In organ culture, dissolved glue successfully adhered collagen-coated perfluoropolyether lenses to debrided bovine corneas and supported epithelial regrowth. Small pellets of glue implanted subcutaneously into mice were resorbed by surrounding tissues, and all of the animals made a full recovery. An initial but transient skin necrosis at the implant site was probably caused by some of the potentially toxic metabolites present in the frog secretion; these include sterols and carotenoids, as well as fatty alcohols, aldehydes, ketones, acids, and aromatic compounds. Removal of the carotenoid pigments did not significantly alter the glue's material properties. In contrast, peroxidase treatment of dissolved glue introduced unnatural crosslinks between molecules of the major protein (Nb-1R) and resulted in the formation of a soft hydrogel, which was very different to the original material.

Genotoxic effects of carotenoid breakdown products in human retinal pigment epithelial cells

PURPOSE

To investigate the genotoxic effects of lutein (LBP) and beta -carotene breakdown products (beta -apo-8-carotenal, BA8C) and the preventive role of GSH in human retinal pigment epithelial cells (ARPE-19).

METHODS

LBP- and BA8C-induced DNA damage in human retinal pigment epithelial cells (ARPE-19) was determined by comet assay. The DNA damage was quantified by the image analysis system using Comet Score software. ARPE-19 cell viability was determined by CellTiter 96 AQ(ueous) one-solution cell proliferation assay kit. Intracellular GSH levels were measured by Ellman's reagent.

RESULTS

Incubation of serum-starved ARPE-19 cells with LBP and BA8C caused significant DNA damage in a dose- and time-dependent manner. The DNA damage and cell death incurred by LBP and BA8C were significantly prevented by N-acetylcysteine (NAC) but not by alpha -tocopherol + ascorbic acid (T + AA). Furthermore, BSO-induced GSH depletion in ARPE-19 cells caused a significant elevation in LBP- and BA8C-induced DNA damage, whereas increased GSH levels in ARPE-19 cells prevented it.

CONCLUSIONS

Our results suggest that breakdown products of dietary carotenoids could be genotoxic in ARPE-19 cells. LBP-induced genotoxic effects could worsen oxidative stress. The intracellular GSH pool in ARPE-19 cells might play a critical role in carotenoid breakdown products-induced genotoxicity.

Carotenoid maintenance handicap and the physiology of carotenoid-based signalisation of health

Despite a reasonable scientific interest in sexual selection, the general principles of health signalisation via ornamental traits remain still unresolved in many aspects. This is also true for the mechanism preserving honesty of carotenoid-based signals. Although it is widely accepted that this type of ornamentation reflects an allocation trade-off between the physiological utilisation of carotenoids (mainly in antioxidative processes) and their deposition in ornaments, some recent evidence suggests more complex interactions. Here, we further develop the models currently proposed to explain the honesty of carotenoid-based signalisation of heath status by adding the handicap principle concept regulated by testosterone. We propose that under certain circumstances carotenoids may be dangerous for the organism because they easily transform into toxic cleavage products. When reserves of other protective antioxidants are insufficient, physiological trade-offs may exist between maintenance of carotenoids for ornament expression and their removal from the body. Furthermore, we suggest that testosterone which enhances ornamentation by increasing carotenoid bioavailability may also promote oxidative stress and hence lower antioxidant reserves. The presence of high levels of carotenoids required for high-quality ornament expression may therefore represent a handicap and only individuals in prime health could afford to produce elaborate colourful ornaments. Although further testing is needed, this 'carotenoid maintenance handicap' hypothesis may offer a new insight into the physiological aspects of the relationship between carotenoid function, immunity and ornamentation.

Carotenoid derived aldehydes-induced oxidative stress causes apoptotic cell death in human retinal pigment epithelial cells

Carotenoids have been advocated as potential therapeutic agents in treating age-related macular degeneration (AMD). In ocular tissues carotenoids may undergo oxidation and form carotenoid-derived aldehydes (CDA), which would be toxic to tissues. We have investigated the cytotoxic effects of CDA from beta-carotene, Lutein and Zeaxanthin on human retinal pigment epithelial cells (ARPE-19). The serum-starved ARPE-19 cells were treated with CDA without or with antioxidant, N-acetylcysteine (NAC) and cell viability, apoptosis, reactive oxygen species (ROS) levels, nuclear chromatin condensation as well as fragmentation, change in mitochondrial membrane potential (MMP) and activation of transcription factors NF-kappaB and AP-1 were determined. We observed a dose and time-dependent decline in cell viability upon incubation of ARPE-19 cells with CDA. The CDA treatment also led to elevation in ROS levels in a dose-dependent manner. Upon CDA treatment a significant number of apoptotic cells were observed. Also early apoptotic changes in ARPE-19 cells induced by CDA were associated with change in MMP. Increased nuclear chromatin condensation and fragmentation were also observed in cells treated with CDA. The cytotoxicity of CDA in ARPE-19 cells was significantly ameliorated by the antioxidant, NAC. Furthermore, CDA induced the activation of NF-kappaB and AP-1 which was significantly inhibited by NAC. Thus our results demonstrate that CDA could increase the oxidative stress in ARPE-19 cells by elevating ROS levels that would cause imbalance in cellular redox status, which could lead to cell death. This would suggest that high carotenoid supplementation for treatment of AMD should be used cautiously.

The contribution of DNA repair and antioxidants in determining cell type-specific resistance to oxidative stress

The aims of this study were; (i) to elucidate the mechanisms involved in determining cell type-specific responses to oxidative stress and (ii) to test the hypothesis that cell types which are subjected to high oxidative burdens in vivo, have greater oxidative stress resistance. Cultures of the retinal pigment epithelium (RPE), corneal fibroblasts, alveolar type II epithelium and skin epidermal cells were studied. Cellular sensitivity to H2O2 was determined by the MTT assay. Cellular antioxidant status (CuZnSOD, MnSOD, GPX, CAT) was analyzed with enzymatic assays and the susceptibility and repair capacities of nuclear and mitochondrial genomes were assessed by QPCR. Cell type-specific responses to H2O2 were observed. The RPE had the greatest resistance to oxidative stress (P>0.05; compared to all other cell types) followed by the corneal fibroblasts (P < 0.05; compared to skin and lung cells). The oxidative tolerance of the RPE coincided with greater CuZnSOD, GPX and CAT enzymatic activity (P < 0.05; compared to other cells). The RPE and corneal fibroblasts both had up-regulated nDNA repair post-treatment (P < 0.05; compared to all other cells). In summary, variations in the synergistic interplay between enzymatic antioxidants and nDNA repair have important roles in influencing cell type-specific vulnerability to oxidative stress. Furthermore, cells located in highly oxidizing microenvironments appear to have more efficient oxidative defence and repair mechanisms.

Lack of antioxidative properties of vitamin C and pyruvate in cultured retinal pigment epithelial cells

BACKGROUND

Oxidative damage to the retinal pigment epithelium might be involved in the pathogenesis of age related macular degeneration. Thus antioxidative protection represents a rationale for a causative therapy or prophylaxis. The aim of the present study is to evaluate antioxidative properties of vitamin C and pyruvate at retinal pigment epithelial (RPE) cells exposed to oxidative stress.

METHODS

The ability of vitamin C and pyruvate to quench hydroxyl radicals was tested using the di-hydro-rhodamine (DHR) assay. Cells of the human RPE cell line ARPE-19 were exposed for 8 min to hydroxyl radicals generated by the Fenton reaction from 2.25 mM H2O2 and 30 microM Fe3+ -nitrilo-tri-acetate. This was done in the absence and presence of 0.3-3.0 mM pyruvate and vitamin C, respectively. Cell survival was analysed by vitality staining (life-dead-assay) and expressed as cell survival ratio. A survival ratio <1.0 indicates cell loss.

RESULTS

At concentrations from 0.1 to 1.0 mM vitamin C and pyruvate quench hydroxyl radicals in the DHR assay in absence of living matter. In the presence of 0.1- 0.3 mM vitamin C and pyruvate, ARPE-19 showed a reduced survival ratio (0.87 +/- 0.01 to 0.89 +/- 0.02 after 6 h) which was not the case at the higher concentrations between 1 and 3 mM. The exposure of ARPE-19 cells to hydroxyl radicals reduced the survival ratio to 0.92 +/- 0.02. At concentrations at which vitamin C and pyruvate exert toxic effects, a potentiation of radical induced cell death can be observed (survival ratio 0.79 +/- 0.02 and 0.82 +/- 0.03, respectively). Higher concentrations of vitamin C or pyruvate had no explicit protective effect to the hydroxyl radical induced damage.

DISCUSSION

Although vitamin C and pyruvate are potent hydroxyl radical quenchers in vitro they failed to protect cultured ARPE-19 cells from oxidative stress induced cell death. In contrast, when applying the scavengers at low concentrations a potentiation of cell damage was observed.