Absence Of Antioxidants Research Articles

Neutrophil adhesion to endothelial cells impairs the effects of catalase and glutathione in preventing endothelial injury.

We studied the effects of the CuZn superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) on endothelial permeability to 125I-albumin after activation of neutrophils (PMN) with phorbol 12-myristate-13-acetate (PMA; 10(-8) M). PMN were either in direct contact with the endothelial cell monolayer grown on a porous gelatin-coated microporous 10-microns-thick polycarbonate filter (upright system) or separated from the endothelium by a similar filter (inverted system). Transendothelial 125I-albumin clearance rates were measured as an index of endothelial permeability. In the absence of antioxidants, activation of PMN increased transendothelial 125I-albumin clearance rates in both systems from 0.041 +/- 0.006 microliters/min (baseline) to 0.262 +/- 0.18 microliters/min (upright system) and from 0.063 +/- 0.02 microliters/min to 0.244 +/- 0.06 microliters/min (inverted system). PMA induced 80-90% of PMN to adhere to either gelatin-coated filters or to endothelial cells, from the basal PMN adhesion value of 5.3 +/- 2.2% and 4.3 +/- 1.1%, respectively. SOD, which dismutases superoxide anion to hydrogen peroxide (H2O2), did not alter the transendothelial 125I-albumin clearance rates in either system at any concentration from 10-300 U/ml. CAT (100-1,000 U/ml) and GSH (0.5-10 mM), which remove the H2O2 generated during PMN activation, did not alter the increase in transendothelial 125I-clearance rates after PMN activation in the upright system, but both agents prevented the increase in transendothelial 125I-clearance rates in the inverted system. We conclude that PMN activation with PMA causes endothelial injury irrespective of PMN contact to the endothelial monolayer. Moreover, H2O2, a release product of PMN activation, is a critical mediator of PMN-dependent endothelial injury. Finally, the results indicate that CAT and GSH prevent endothelial injury only in the absence of direct PMN contact with endothelial cells, suggesting that antioxidants such as GSH and CAT are excluded from sites of PMN-endothelial contact and thus are ineffective antioxidants.

Physicochemical and biological factors influencing methylfolate stability: use of dithiothreitol for HPLC analysis with electrochemical detection

Temperature rather than light is the predominant factor influencing 5-methyltetrahydropteroylmonoglutamate loss. This loss is pH dependent. At pH 9·0 in the absence of antioxidant at 25°C it is very unstable, whilst at pH 7·3 and 3·5 the stability is much greater, with the latter two pH values producing very similar rates of loss. In the presence of dithiothreitol, at 25°C, 5-methyltetrahydropteroylmonoglutamate is stable at pH 7·3 and 9·0, although it has no protective effect at pH 3·5 (a problem which can be overcome by storage at +4°C). The relative stability of four commercially available reduced folylmonoglutamates was found to follow the order 5-formyltetrahydropteroylmonoglutamate > dihydropteroylmonoglutamate > 5-methyltetrahydropteroylmonoglutamate > tetrahydropteroylmonoglutamate. In tissue culture experiments the stability of exogenous, extracellular 5-methyltetrahydropteroylmonoglutamate was found to be greater in the presence of human peripheral blood lymphocytes than in the absence of these cells.

Isolation and characterization of oligodeoxynucleotides containing dG-N2-AAF oxidation products of dG-C8-AF

Decadeoxynucleotides containing N-(deoxyguanosine-N2-yl)-2-acetylaminofluorene (dG-N2-AAF) and three recently described products of oxidation of N-(deoxyguanosine-8-yl)-2-aminofluorene (dG-C8-AF) were isolated and characterized. dG-N2-AAF was synthesized; its structure was established by mass spectroscopic and 1H-NMR analysis. Decadeoxynucleotides containing dG-N2-AAF and dG-C8-AAF were prepared by permitting d(CACTAGTCAC) to react with N-acetoxy-AAF and separating the products by HPLC. The decamer containing dG-C8-AAF was incubated under aerobic alkaline conditions. In the presence of 2-mercaptoethanol, the adduct is deacetylated; in the absence of antioxidant, decamers bearing oxidation products are formed. Homogeneity of the modified oligomers was established by polyacrylamide gel electrophoresis. The modified oligodeoxy-nucleotides will be used to introduce dG-N2-aminofluorene adducts and oxidative lesions, site-specifically, into DNA, thereby to correlate these adducts with their mutagenic properties.

Oxidized low density lipoprotein can reduce the pinocytic activity in cultured human endothelial cells as measured by cellular uptake of [ 14C]sucrose

The effect of low density lipoprotein (LDL) on the pinocytic activity in human endothelial cells in culture, as measured by the uptake of [ 14C]sucrose, was studied. The cells were preincubated for 48 h with a low concentration of LDL (25 μg protein/ml) or a high concentration of LDL (150 μg protein/ml) in the presence of lipoprotein deficient serum. Then the pinocytic activity of the cells was measured in a subsequent incubation by measuring the uptake of [ 14C]sucrose. The higher LDL concentration resulted in a reduced cellular uptake of [ 14C]sucrose compared to the lower concentration of LDL When the additional LDL (the lower concentration subtracted from the higher) was replaced by high density lipoprotein, albumin or gamma globulin, no reduction of the uptake of [ 14C]sucrose was observed. The inhibitory effect of LDL on the uptake of [ 14C]sucrose was seen in endothelial cell cultures of different age and cell density. When the endothelial cell proliferation was arrested by gamma irradiation, the reducing effect of LDL on the pinocytic activity was unchanged as compared to nonirradiated controls. LDL prepared in the presence of EDTA and glutathione did not have the same reducing effect on the uptake of [ 14C]sucrose as control LDL prepared in the absence of antioxidants. Thus, oxidized LDL reduced the pinocytic activity in cultured endothelial cells. The inhibitory effect of LDL on the rate of pinocytosis was present before endothelial cell injury could be observed.

Effects of Antioxidants on Rancidity Development and Palatability of Frozen Bacon

The efficacy of four antioxidants for retarding rancidity development and maintaining the palatability of frozen bacon slices were examined. The antioxidants (ascorbic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and propyl gallate) were incorporated into a dry sugar bacon cure alone or in combination. Results indicated that the incorporation of these antioxidants alone or in combination generally reduced rancidity develoment in bacon slices during prolonged frozen storage. However, the combination of BHA, BHT and propyl gallate was the only antioxidant treatment which was effective for extending the frozen storability of bacon slices from the standpoint of flavor desirability and overall palatability. Bacon slices cured in the presence of this antioxidant combination remained acceptable for ca. 84 d longer during frozen storage than bacon cured in the absence of antioxidants.

Study of the fate of Bronopol and the effects of antioxidants on N‐nitrosamine formation in shampoos and skin creams

Synopsis The role of antioxidants in preventing nitrosamine (N-nitroso diethanolamine) formation in shampoos and skin creams and the levels of Bronopol (2-bromo, 2-nitropropane-1, 3-diol) addition in relation to the resultant levels of N-nitroso compounds have been studied. The addition of 0.05% BHT, alpha-tocopherol or ascorbate was effective in preventing nitrosamine formation (limit of determination: 2.5 mug kg(-1)) in products preserved with 0.01% Bronopol. At 0.05% Bronopol, 0.2% of all three antioxidants was effective in preventing nitrosamine formation but at 0.1% Bronopol only alpha-tocopherol was effective. Levels of Bronopol found in shampoo formulations stored for 2 weeks at 37 degrees C with initial concentrations of 0.005-0.1% were reduced by 64-86%, independent of the initial concentration. The levels in skin creams stored for extended periods at ambient temperature with 0.01% Bronopol initially were reduced by, on average, 60%. High nitrite levels (NO(2) (-)) were found in formulations containing 0.01% Bronopol but no antioxidants (200-250 mg kg(-1)). Detected levels of nitrite in skin cream formulations were greater than could be formed by stoichiometric decomposition of Bronopol. In formulations with both Bronopol and antioxidants the levels of nitrite were considerably reduced. When alpha-tocopherol rather than BHT or ascorbate was the antioxidant then the nitrite levels were appreciably higher but formation of N-nitroso diethanolamine was no greater. High nitrite levels correlated with the formation of detectable levels of N-nitroso compounds in the absence of antioxidants.

Photo-oxidation of commercial polyethylene containing titanium dioxide (rutile)/ antioxidant systems

The weathering performance of various grades of untreated (or uncoated) and treated (or coated) rutile pigments in commercial polyethylene in the absence and presence of primary and secondary antioxidants is examined. Using carbonyl index as a monitor of the rate of photo-oxidation, untreated rutile sensitizes the photo-oxidation of polyethylene, whereas the treated grades act as photostabilisers. The photosensitizing effect of untreated rutile is markedly inhibited by a synergistic combination of a hindered phenol (Topanol CA) and a sulphur containing antioxidant (DLTDP). Further, the order of weathering stability of the treated rutile pigments in the absence of any antioxidant in the polymer is altered significantly when an antioxidant system is present. The imporance of pigment/antioxidant interactions is discussed. The photo-oxidation of polyethylene containing the treated rutile pigments is also significantly improved by the presence of a primary antioxidant or a primary/secondary antioxidant system compared with a secondary antioxidant alone. These results indicate that peroxides play only a minor role in the photo-oxidation of TiO2 (rutile) pigmented polyethylene.

Spectrophotometric characteristics of bilirubin.

Spectrophotometric characteristics of bilirubin at low concentrations (0.005-2.500 mg/100 ml) have been studied under various physical conditions in order to gain a better understanding of the state of bilirubin when preparing "solutions" for laboratory use. Standing, minimal shaking, or stirring of the bilirubin preparations at pH 7.4 progressively reduced and altered the maximal spectral absorption of bilirubin (440 nm) in aqueous buffered media. The shift to 415-420 nm is attributed to oxidation of the pigment whereas shoulder formation is attributed to the formation of large size particles (flocculants). In the presence of antixidants (L-ascorbic acid and nitrogen gas) and EDTA the maximal absorption peak remained at 440 nm but decreased in magnitude concomitant with development of progressively increasing shoulder at 480-560 nm. In the absence of antioxidants and EDTA maximal absorption shifted to 415-420 nm and the magnitude of 480-560 nm shoulder formation was less. At the higher concentrations of bilirubin and with reduction in pH of the buffer in the absence of antioxidants, the shift to lower wave lengths was reduced and 450-560 nm shoulder formation was increased. In the absence of antioxidants and EDTA at the lower concentrations of bilirubin and in more alkaline media, the reduction at 440 nm and the shift of maximal absorption to the shorter wave lengths was enhanced. At pH 12, stirring of antioxidant-EDTA-containing solutions of bilirubin resulted in neither a shift of maximal absorption to the shorter wave lengths nor the formation of 480-560 nm shoulder. The formation of 480-560 nm shoulder was accompanied by the visual appearance of turbidity. The formation of flocculants when a "solution" is agitated indicates that significant portions of the pigment were in fact, not in solution and must have existed previously as a finely dispersed colloidal sol or supersaturated solution which progressed to a colloidal sol. Spectral curves of bilirubin, therefore, may represent a composite resulting from four physical states of bilirubin: (1) bilirubin truly in solution with the spectral peak at 440 nm; (2) bilirubin in the fine colloidal dispersion with spectral characteristics similar to those of bilirubin in solution; (3) bilirubin flocculant giving 480-560 nm shoulder; and (4) oxidation products of bilirubin with the spectral peaks lower than 440 nm. Increasing the pH of the aqueous media containing bilirubin (0.05 mg/100 ml) from 7.4 to 12.0 increased the molar extinction coefficient of bilirubin, E1M/440 1cm, progressively to a maximum at pH 12 of 6.35 X 10(4). Very dilute bilirubin preparations (0.005-0.050 mg/100 ml) in aqueous media, pH 7.4, exhibited spectral evidence of rapid oxidation (more so at higher pH), but spectral shoulder formation was still observed after mechanical agitation. Thus, the solubility of bilirubin in 0.1 M phosphate buffer at pH 7.4 appears to be less than 0.005 mg/100 ml.

Reaction of fuming nitric acid with polyethylenes

The oxidative effect of fuming nitric acid upon finely ground polyethylenes is observed by plotting changes in specific solution viscosity values against duration of reaction. The similarity in relationship between this reaction and that of polyethylenes with oxygen is set forth. It is shown that this reaction, like that between polyethylenes and oxygen gas, produces hydroperoxide and carbonyl structures, and results largely in scission of the polymeric chains. The effect of these oxidative alterations in decreasing the electrical resistivity and in increasing the flow properties of the subject resins is illustrated. The identical influence of methyl branching in favoring the reaction of polyethylenes with both oxygen and with fuming nitric acid is demonstrated. Nitration is seen to be a consequence of extent of reaction rather than of reaction temperature itself. The utility of this reaction in differentiating among polyethylenes is indicated. In this regard it is seen that the linear polymers are more severely affected by fuming nitric acid than are conventional polyethylenes. Finally, the usefulness of this reaction in assessing the inherent oxidizability of polyethylene resins, independent of the presence or absence of antioxidants, is proposed.

Oxidative Stress Relaxation Studies of Radiation Cured Vulcanizates, with and without Antioxidant

Abstract Turner has shown that irradiation of natural rubber results in the formation of carbon to carbon crosslinks by combination of allylic radicals; the same type of crosslinks are formed by heating rubber in presence of organic peroxides2. Since peroxide vulcanizates may be freed from excess vulcanizing ingredients and by products by extraction while radiation crosslinking may be effected without additive, it is expected that the two types of vulcanizate should age in an analogous manner. The present study was undertaken in order to see whether radiation vulcanizates did show the same aging behavior as peroxide vulcanizates according to measurements of oxidative stress relaxation, and, if so, to ascertain whether the efficiency of antioxidants of the dithiocarbamate type was affected by the irradiation and whether such materials had an adverse effect upon cure. It has been stated that radiation vulcanizates are resistant to aging even in the absence of antioxidant and their stability has been attributed to the presence of purely carbon-carbon crosslinks. However, it has recently been demonstrated that a carbon-carbon crosslink is not a sufficient condition for vulcanizate stability in the absence of antioxidant. Previous studies concerning the aging of radiation cures appear to have been made using materials containing carbon black, which is now known to act as an antioxidant; it is necessary, for work of fundamental significance, to use gum stocks based on very pure rubber.

The Protection of Transparent Vulcanizates against Aging in Sunlight

Abstract Care has to he taken in choosing antioxidants for use in transparent natural rubber vulcanizates since some amines commonly employed as protective agents against thermal degradation photosensitize aging in ultraviolet (uv) light. Further studies using the technique of stress relaxation, undertaken in order to find the most satisfactory type of antioxidant for protection against sunlight aging, have shown that, with additives introduced into extracted samples of peroxide vulcanizate by swelling from ethyl acetate solution, the best results were obtained using a mixture of a substituted bis-phenol and an absorber of uv light. Hitherto, nickel isopropylxanthate (NPX) has been regarded as the most potent protective agent against light; however, the rate of degradation in the presence of NPX was unchanged by the addition of uv absorber and the mixture of bis-phenol and absorber was markedly more effective. Furthermore, the nickel salt is green, whereas the bis-phenols are relatively nonstaining. The work described here is an evaluation of vulcanizates in which the phenol and absorber have been incorporated before cure. The phenol employed was 2,2′-methylene-bis(4-methyl-6-tert-butyl phenol) (Antioxidant 2246 of the American Cyanamid Co.) and the absorber was Tinuvin P (a product of undisclosed formula marketed by Geigy Ltd.), chosen since it protected better in the absence of antioxidant than two other commercial absorbers. Two types of transparent vulcanizate were examined, one being an accelerated sulfur cure and the other a dicumyl peroxide cure. The recipes were as follows:

Studies on Abrasion and Wear of Rubber. I. The Chemistry of Carbon Black and Its Effect on Abrasion as Determined by the National Bureau of Standards Method

Abstract A series of carbon blacks of approximately constant surface area were prepared by heating a strongly acidic carbon black in N2 in the range of 200–1000° C. Their adsorption capacity for alkali and acid, catalytic behavior in H2O2 decomposition, and magnetic susceptibility have been studied and related to their effect on abrasion resistance when incorporated into a standard tire tread stock in the absence of antioxidants. It is suggested that there are, at least, two distinct chemical mechanisms by which carbon blacks can produce reinforcement, that is, by their (irreversible) action as polyphenol type antioxidants (acidic = low-temperature blacks), or in a catalytic (reversible) fashion through temporary stabilization of broken rubber chains on their surface (neutral = medium-temperature blacks).

油脂の酸化防止に關する研究

To examine the relation between the structure of o-dihydroxyphenyi-alkanoic acid and their antioxygenic property, caffeic and dihydrocaffeic esters were synthesized and their effectiveness for stabilizing vitamin A in cod-liver oil was determined using the Beckman spectrophotometer. As the standard antioxidant ethyl gallate was added to liver oil in concentration of 0.05% and other compounds to be tested were incorporated with it on an equivalent molecular basis. The liver oil was shaken on a rotary shaker (190_??_200 r. /min) at 24° The stability value of the control (i, e., the time in days for 500 loss of vitamin A in the absence of antioxidants) was 11 days. The stability value of ethyl protocatechuate was 13 days, but introduction of C=C dcuble bond between phenyl and carbonyl groups as in caffeic esters led to marked enhancement in effectiveness to 32 days. Moreover, hyurogenation of the double bond as in dihydrocaffeic esters increased activity to 35 days but activity of these compounds was inferior to that of ethyl gallate (stability value, 46 days).

Absorption of Oxygen by Rubbers

Abstract Constant-pressure oxidation experiments on natural rubber in the absence of antioxidant confirm that the reaction is autocatalytic and essentially similar to that for the oxidation of simple, unconjugated olefins. The results are in accord with a free-radical chain reaction mechanism. In the presence of antioxidant at constant pressure, rubbers reach a dynamic equilibrium state of oxidation at a constant rate. This rate is greater, the greater the pressure, but increases less rapidly than pressure. Several graphs are given to show the relation between equilibrium oxidation rate and oxygen pressure for several rubbers. If the pressure is reduced and again maintained constant after the attainment of the equilibrium oxidation rate at one pressure, the rate at the new pressure falls slowly over several hours from an initial high value to that consistent with the new pressure. This effect is more marked the less susceptible the rubber to oxidation. Methods of investigating the rubber-oxygen reaction in which pressure is allowed to fall spontaneously as oxidation proceeds are experimentally shown to lead to erroneous conclusions. The reasons suggested for this are the auto-catalytic nature of the reaction in the absence of antioxidants and the persistence of a high oxidation rate after a pressure reduction in the presence of anti-oxidant. An approximate relation is deduced between uniformity of oxidation, oxidizability, and specimen dimension for rubbers containing antioxidant.