Effects of butylated hydroxytoluene on membrane lipid fluidity and freeze-thaw survival in mammalian cells

Ascorbate exacerbates iron toxicity on intestinal barrier function against Salmonella infection

Ascorbic acid is often used to enhance iron absorption in nutritional interventions, but it produces pro-oxidant effects in the presence of iron. This study aimed to evaluate ascorbate's role in iron toxicity on intestinal resistance against foodborne pathogens during iron supplementation/fortification. In polarized Caco-2 cell monolayers, compared to the iron-alone treatment, the iron-ascorbate co-treatment caused more than 2-fold increase in adhesion, invasion and translocation of Salmonella enterica serovar Typhimurium. According to 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, lactate dehydrogenase release and transepithelial electrical resistance, the iron-ascorbate co-treatment resulted in reduced cell viability and increased impairment of cell membrane and paracellular permeability compared to the iron-alone treatment. Butylated hydroxytoluene protected cells against these prooxidant toxicities of ascorbate. Ascorbate completely restored iron-induced intracellular oxidant burst and depletion of cytosolic antioxidant reserve, according to dichlorodihydrofluorescein fluorescence and intracellular reduced glutathione levels. In Salmonella-infected C57BL/6 mice, iron-ascorbate co-supplementation resulted in greater loss of body weight and appetite, lower survival rate, shorter colon length, heavier intestinal microvilli damage, and more intestinal pathogen colonization and translocation than the iron-alone supplementation. Overall, ascorbate would exacerbate iron toxicity on intestinal resistance against Salmonella infection through pro-oxidant impairment of intestinal epithelial barrier from extracellular side and/or by facilitating intestinal pathogen colonization.

Bisphenol AF promotes inflammation in human white adipocytes

Endocrine-disrupting chemicals interact with transcription factors essential for adipocyte differentiation. Exposure to endocrine-disrupting chemicals corresponds with elevated risks of obesity, but the effects of these compounds on human cells remain largely undefined. Widespread use of bisphenol AF (BPAF) as a bisphenol A (BPA) alternative in the plastics industry presents unknown health risks. To this end, we discovered that BPAF interferes with the metabolic function of mature human adipocytes. Although 4-day exposures to BPAF accelerated adipocyte differentiation, we observed no effect on mature fat cell marker genes. Additional gene and protein expression analysis showed that BPAF treatment during human adipocyte differentiation failed to suppress the proinflammatory transcription factor STAT1. Microscopy and respirometry experiments demonstrated that BPAF impaired mitochondrial function and structure. To test the hypothesis that BPAF fosters vulnerabilities to STAT1 activation, we treated mature adipocytes previously exposed to BPAF with interferon-γ (IFNγ). BPAF increased IFNγ activation of STAT1 and exposed mitochondrial vulnerabilities that disrupt adipocyte lipid and carbohydrate metabolism. Collectively, our data establish that BPAF activates inflammatory signaling pathways that degrade metabolic activity in human adipocytes. These findings suggest how the BPA alternative BPAF contributes to metabolic changes that correspond with obesity.

Zinc oxide as a new antimicrobial preservative of topical products: interactions with common formulation ingredients

Zinc oxide (ZnO) appears as a promising preservative for pharmaceutical or cosmetic formulations. The other ingredients of the formulations may have specific interactions with ZnO that alter its antimicrobial properties. The influence of common formulation excipients on the antimicrobial efficacy of ZnO has been investigated in simple model systems and in typical topical products containing a complex formulation. A wide variety of formulation excipients have been investigated for their interactions with ZnO: antioxidants, chelating agents, electrolytes, titanium dioxide pigment. The antimicrobial activity of ZnO against Escherichia coli was partially inhibited by NaCl and MgSO4 salts. A synergistic influence of uncoated titanium dioxide has been observed. The interference effects of antioxidants and chelating agents were quite specific. The interactions of these substances with ZnO particles and with the soluble species released by ZnO were discussed so as to reach scientific guidelines for the choice of the ingredients. The preservative efficacy of ZnO was assessed by challenge testing in three different formulations: an oil-in-water emulsion; a water-in-oil emulsion and a dry powder. The addition of ZnO in complex formulations significantly improved the microbiological quality of the products, in spite of the presence of other ingredients that modulate the antimicrobial activity.

Cytotoxicity of butylated hydroxyanisole in Vero cells

Butylated hydroxyanisole (BHA) is perhaps the most extensively used synthetic antioxidant in the food and cosmetic industry, although considerable controversy exists in the literature regarding the safety of this compound. Most in vitro studies describing the effects of BHA have been performed in cancer cells, but it is unclear whether normal cells are equally susceptible to BHA exposure. The present study investigate the toxic potential of BHA in mammalian cells, using biochemical and morphological parameters, which reveal interference with structures essential for cell survival, proliferation and/or function. Cell growth inhibition was assessed by using colorimetric assays, whereas cellular alterations after BHA exposure, were evaluated using conventional light and fluorescence microscopy. Low doses of BHA exerted a significant cytotoxic effect, associated with loss of mitochondrial function. As the concentration of BHA was increased, morphological alterations in critical subcellular targets such as lysosomes, mitochondria and actin cytoskeleton, were observed. In parallel, BHA induced an irreversible loss of cell proliferative capacity, preceding apoptosis induction. Thus, the dose-dependent activity of BHA on Vero cells appears to be cytotoxic as well as cytostatic. Our observations, although simplified with respect to the in vivo situations, allowed the assessment of the specific damage at the cellular level, and provide some clue about the effects of BHA in non-tumoral mammalian cells.

Induction of Reactive Oxygen Species by Bisphenol A and Abrogation of Bisphenol A-Induced Cell Injury by DJ-1

DJ-1 was first identified as an activated ras-dependent oncogene. DJ-1 is related to male fertility, and its expression in sperm decreases in response to exposure to a number of reproductive toxicants. DJ-1 has been associated with the onset of familial Parkinson's disease (PD) in humans, and has been found to have activity against oxidative damage by eliminating reactive oxygen species (ROS). In this study, we investigated the role of DJ-1 in oxidative stresses by administration of bisphenol A (BPA), which has been reported to induce oxidative stress in rodents, to male mice and cultured cells. In male mice, we found that BPA significantly increased the expression level of DJ-1 in the sperm and brain. In cultured Neuro2a and GC1 cells, we found that BPA induced ROS production and significantly compromised mitochondrial function concomitant with elevated expression and oxidization of DJ-1. DJ-1 was found to maintain the complex I activity against BPA-induced oxidative stress after the localization in mitochondria. The results showed that DJ-1 plays a role in the prevention of mitochondrial injury-induced cell death.

Metabolism of bisphenol A in isolated rat hepatocytes and oestrogenic activity of a hydroxylated metabolite in MCF-7 human breast cancer cells

1. The metabolites of bisphenol A (BPA; 2,2-bis(4-hydroxyphenyl)propane) in freshly isolated rat hepatocytes and the oestrogenic activities of BPA and its metabolites, particularly 3-hydroxybisphenol A (3-OH-BPA), in MCF-7 cells and competitive binding assays have been studied, respectively. 2. During a 2-h incubation, almost all of the BPA (0.25 mM) added to the hepatocyte suspensions was rapidly converted to a major conjugate, monoglucuronide (approximately 75% of total metabolites), and two minor conjugates, which were tentatively identified as monosulphates of BPA and a hydroxylated intermediate, 3-OH-BPA, as determined by mass spectroscopy coupled with HPLC or GC/MS. On the other hand, free 3-OH-BPA was identified as a trace metabolite, whose level was approximately 1 or 2 microM at 1 h in hepatocyte suspensions treated with 0.25 or 0.5 mM BPA, respectively. 3. In another experiment, 3-OH-BPA as well as BPA displaced competitively 17beta-oestradiol bound to the recombinant human oestrogen receptor alpha in a concentration dependent-manner: IC50 of diethylstilbestrol, BPA and 3-OH-BPA were approximately 2.5 x 10(-8), 10(-5) and 5 x 10(-5) M, respectively. Further, BPA and 3-OH-BPA at intermediate concentrations (10(-7) - 10(-6) M) caused proliferation of MCF-7 human breast cancer cells, whereas the effect of BPA was more potent than that of 3-OH-BPA. At higher concentrations, both BPA (> 10(-4)) and 3-OH-BPA (> 10(-5) M) were cytotoxic. 4. Based on the proliferative potency in MCF-7 cells and the IC50 for the competitive binding, the oestrogenic activity of 3-OH-BPA was less than that of BPA. These results indicate that BPA itself rather than its metabolite acts as a xeno-oestrogen and that 3-OH-BPA is cytotoxic, possibly acting via reactive semiquinone and/or quinone metabolites, rather than a xeno-oestrogenic mechanism, in MCF-7 cells.

Basic aspects of frozen storage of semen

Basic concepts of cryopreservation and the causes of cryoinjury are reviewed. The possible roles of cryoprotectants and additives are considered in the context of their putative interactions with the sperm plasma membrane. Modern approaches to the laboratory assessment of spermatozoa after freeze-thawing are also briefly discussed.

Maternal antioxidant treatments prevent diabetes-induced alterations of mitochondrial morphology in rat embryos

Previous studies have suggested that production of reactive oxygen species by embryonic mitochondria may have a role in the induction of both high-amplitude mitochondrial swelling and embryonic dysmorphogenesis in diabetic pregnancy. The present study analyzed the relationships between a putative metabolite-induced production of free oxygen radicals, mitochondrial lipid peroxidation, and high-amplitude mitochondrial swelling in embryos during organogenesis. For studies in vitro, day 9 embryos of normal rats were cultured for 48 h with a high concentration of glucose in the absence or presence of alpha-cyano-4-hydroxycinnamic acid (CHC), a mitochondrial pyruvate transport inhibitor. The morphology of mitochondria in the neuroepithelium of the embryos was studied with the aid of transmission electron microscopy. For studies in vivo, normal and diabetic pregnant rats were fed a diet supplemented with the antioxidants alpha-tocopherol (vitamin E) or 2,6-di-tert-butyl-4-methylphenol (BHT), and the ultrastructure of mitochondria in the embryonic neuroepithelium and in the visceral yolk sac was investigated on gestational day 11. Exposure to a high concentration of glucose in vitro or to maternal diabetes in vivo induced high-amplitude swelling of mitochondria in the neuroepithelium of the embryos. The swelling of mitochondria was prevented by addition of CHC to the culture media or by maternal ingestion of antioxidant-supplemented food. In diabetic pregnancy, embryonic mitochondria during organogenesis produce free oxygen radicals that cause mitochondrial lipid peroxidation and swelling and furthermore embryonic dysmorphogenesis. Dietary supplementation with antioxidants to the mother may prevent embryonic malformations in diabetic pregnancy by inhibition of mitochondrial dysfunction.

Cytotoxicity of propyl gallate and related compounds in rat hepatocytes

The cytotoxic effects of propyl gallate (PG), its related gallates and gallic acid have been studied in freshly isolated rat hepatocytes. Addition of PG (0.5-2.0 mM) to hepatocyte suspension elicited concentration-dependent cell death accompanied by losses of intracellular ATP, adenine nucleotide pools, glutathione (GSH) and protein thiols. The rapid loss of intracellular ATP preceded the onset of cell death caused by PG. In the comparative toxic effects of PG and related gallates at concentration of 1 mM, octyl gallate (OG), dodecyl gallate (DG) and butyl gallate (BG) elicited an abrupt depletion of ATP, followed by an acute cell death. These gallates were more toxic than PG; the toxic effects of PG were similar to those of methyl gallate (MG) and ethyl gallate (EG). In mitochondria isolated from rat liver, PG caused a concentration-dependent increase in the rate of state 4 oxygen consumption, indicating an uncoupling effect. The rate of state 3 oxygen consumption was inhibited by OG and DG. According to the respiratory control index, the order of impairment potency to mitochondria was OG > BG, DG > PG > EG, MG > gallic acid. These results indicate that PG and related gallates are toxic to hepatocytes and that the acute cytotoxicity may be due to mitochondrial dysfunction.

Differential effects of butylated hydroxytoluene analogs on bull sperm subjected to cold-induced membrane stress

Previous reports established that butylated hydroxy toluene (BHT) minimized cold-induced membrane rupture in sperm from several species. No data regarding the specificity of its effect is available. In this study 25 BHT analogs were tested for their effect on bovine sperm membrane stability. Fourteen were membrane lytic at 25 degrees C and 6 were neither membrane lytic nor membrane stabilizing. The remaining 5 compounds, a family of 2,6-tert-butyl phenols with substitutions at position 4 of hydrogen, methyl (BHT), ethyl, butyl, hexyl, or octyl, afforded effective membrane protection to cold shock. Since membrane protection is a function of both the ability of a compound to partition into the membrane and a molecule's effectiveness once there, an analysis of each analog's membrane partitioning, assessed by measuring the cellular analog/cholesterol ratio, showed the following extents of transfer for the analogs: ethyl = butyl greater than methyl = hydrogen greater than hexyl greater than octyl. Thus, an optimum chain length exists for partitioning from micellar donors into cells. A separate experiment established that all analogs, when incorporated in equivalent amounts, protect equally plasma and mitochondrial membranes from cold shock. No effect on acrosomal membrane stability was noted. BHT, but not the other analogs, reduced sperm motility. Addition of egg yolk to extender containing BHT analog protected sperm motility from cold shock but had little effect on membrane stabilization. Analysis of sperm membrane compartments revealed that little to no analog was partitioned into the outer acrosomal membrane or the plasma membrane overlying the acrosome, but rather was localized in other portions of the sperm. We conclude that (a) the effective BHT analogs, if partitioned into the membrane, are indistinguishable with regard to their capacity to eliminate cold-induced membrane lysis; (b) membrane-linked events (e.g., motility) are uniquely disrupted by a subset of this analog family; and (c) when concentrations of egg yolk and BHT analogs are carefully controlled, unique synergistic effects are noted.

Relationship of membrane fluidity, chemoprotection, and the intrinsic toxicity of butylated hydroxytoluene

In isolated rat hepatocytes, many chemicals elicit toxicity which is inhibitable by antioxidants such as butylated hydroxytoluene (BHT). Although BHT protection is evident at concentrations of less than about 50 nmol/mg protein, higher concentrations exhibit intrinsic concentration-dependent toxicity, which involves mitochondrial dysfunction. We evaluated the possibility that both chemoprotection and intrinsic toxicity could be explained by a common mechanism involving alterations in the physical properties of cellular membranes. In the red blood cell (RBC) osmotic fragility assay, BHT at less than 60 nmol/mg protein protected against osmotic fragility; however, BHT at higher concentrations enhanced osmotic fragility such that total osmolysis occurred at 135 nmol/mg. The BHT-mediated alterations in osmotic fragility correlated with changes in membrane fluidity, determined by fluorescence polarization of the hydrophobic probe 1,6-diphenyl-1,3,5-hexatriene. Protection from osmolysis correlated with decreased fluidity, while enhanced RBC fragility correlated with increased fluidity. In rat hepatocyte suspensions, high BHT concentrations also permeabilized the plasma and mitochondrial membranes to enzyme leakage, and these effects were accompanied by enhanced membrane fluidity. Although other mechanisms may be operative, alterations in membrane fluidity appear to be, in part, responsible for the observed chemoprotective effects at low concentrations, and intrinsic toxicity at higher concentrations of BHT.

Mechanism accounting for the induction of nonspecific permeability of the inner mitochondrial membrane by hydroperoxides

The effect of antioxidants on the nonspecific permeability of the inner mitochondrial membrane induced by cumene hydroperoxide or Ca(2+) has been studied. Butylated hydroxytoluene, butylated hydroxyanisole and 2,2,5,7,8-pentamethyl-6-chromanol, taken at a concentration up to 50 microM, suppress the cumene hydroperoxide-induced accumulation of lipid peroxidation products. In the same range of concentrations, these antioxidants inhibit the activation of nonspecific permeability by cumene hydroperoxide or Ca(2+). Propyl gallate, being less effective under such conditions, fails to affect the induction of nonspecific permeability. Additionally, 2,2,5,7,8-pentamethyl-6-chromanol at a concentration decreasing the accumulation of lipid peroxidation products by 70% has been shown not to increase the lag period of nonspecific permeability induction. Higher antioxidant concentrations, while leading to an increase in the lag period of nonspecific permeability induction, cause but minor suppression of lipid peroxidation. From the results obtained we can assume that free radicals formed in the course of hydroperoxide decomposition or on mitochondrial redox complex interact directly with a system responsible for nonspecific permeability or with regulating components of this system.

Location of two antioxidants in oriented model membranes. Small-angle x-ray diffraction study

Small-angle x-ray diffraction has been applied in locating either butylated hydroxytoluene (BHT) or delta-tocopherol and their brominated analogues at a concentration of 40 mol% in oriented bilayers of dipalmitoylphosphatidylcholine (DPPC) or DPPC + 15 mol% cholesterol at 20 degrees C. Phases were determined using swelling experiments with structure factors plotted in reciprocal space, creating a relatively smooth curve as the amount of water between the bilayers was changed. Continuous Fourier transforms were also calculated using sampling theory (Shannon, C. E. 1949. Proc. Inst. Radio Engrs. NY. 37:10-21) to further test the consistency of the phase assignments. Fourier synthesis of structure factors resulted in absolute electron density profiles for different bilayers to a resolution of 5-6 A. In addition, difference Patterson maps were constructed to confirm the positions of the bromine atoms in the unit cell. Analysis of the data indicates the following: (a) The BHT molecules are dispersed throughout the alkyl-chain region in DPPC samples with and without cholesterol. (b) The chromanol ring of delta-tocopherol is in the vicinity of the glycerol backbone-headgroup region in samples of DPPC or DPPC + 15 mol% cholesterol. (c) Difference Patterson maps confirm the localization of bromine atoms in the various delta-tocopherol samples and lack of bromine localization in the various BHT samples.

Effect of butylated hydroxytoluene on bilineage differentiation of the human HL-60 myeloblastic leukemia cell

Butylated hydroxytoluene (BHT), which has both antioxidant and membrane active properties, has been reported to affect cellular differentiation. We studied its effect on the bipotent lineage differentiation of the important HL-60 human myeloblastic leukemia cell line using reduction of nitroblue tetrazolium, cell cycle analysis, population growth rate, monoclonal antibodies, and morphology. BHT markedly accelerated retinoic acid-induced myelocytic differentiation and dihydroxyvitamin D3-induced monocytic differentiation in a concentration and time-dependent manner. Butylated hydroxyanisole (BHA) had a comparable effect. Preincubation with the compounds was not necessary to evoke the acceleration Other antioxidants and inhibitors of eicosanoid synthesis were inactive. We conclude that the important food preservatives BHT and BHA accelerate the kinetics of terminal differentiation of human leukemia and that this effect is likely due at least in part to their membrane active properties.

Cytotoxicity of butylated hydroxyanisole and butylated hydroxytoluene in isolated rat hepatocytes

The effects of the antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on isolated rat hepatocytes were investigated. Both antioxidants were observed to be cytotoxic in a concentration-dependent manner at concentrations ranging from 100 to 750 microM. At equimolar concentrations BHT was more cytotoxic than BHA. Their toxicity appeared to be independent of their metabolism to reactive intermediates since inhibitors of cytochrome P-450 (metyrapone, SKF 525-A and piperonyl butoxide) had no effect on the cytotoxicity and N-acetylcysteine was also without protective effect. In addition, deuterated BHT was equitoxic with BHT. Only low temperature incubation (4 degrees), which has previously been shown to inhibit the insertion of these compounds into biomembranes, was effective in inhibiting the cytotoxic effects. Using isolated rat liver mitochondria we observed that both BHA and BHT inhibited respiratory control primarily by stimulating state 4 respiration and thus acting as membrane uncouplers. BHA and BHT also effectively dissipated membrane potential across the mitochondrial membrane and caused the release of calcium and mitochondrial swelling. These mitochondrial effects were reflected by a rapid decrease in ATP levels in intact hepatocytes which preceded cell death. These results suggest that the observed cytotoxicity of BHA and BHT to hepatocytes is related to their effects on biomembranes and mitochondrial bioenergetics.