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.

[Effect of the antioxidant ionol on myocardial energy metabolism and the course of traumatic shock]

Energy metabolism was studied in experiments on rats with due regard for the individual features of the organism's reaction to trauma. The animals were divided into 2 subgroups according to the survival period during the experiment. Disorders of mitochondrial function were revealed in both subgroups, but they differed in degree according to the severity of the process. Preliminary injection of the antioxidant ionol prolonged the animals' survival and prevented disorders of mitochondrial function. The article discusses the possibility of preventing activation of free-radical oxidation of the membrane lipids and removal of their damaging effect on the mitochondria with ionol.

Glutathione and antioxidants protect microsomes against lipid peroxidation and enzyme inactivation

The study investigated the relationship between lipid peroxidation and enzyme inactivation in rat hepatic microsomes and whether prior inactivation of aldehyde dehydrogenase (ALDH) exacerbated inactivation of other enzymes. In microsomes incubated with 2.5 microM iron as ferric sulfate and 50 microM ascorbate, ALDH, glucose-6-phosphatase (G6Pase) and cytochrome P450 (Cyt-P450) levels decreased rapidly and concurrently with increased levels of thiobarbituric acid-reactive substances. Microsomal glutathione S-transferase and nicotinamide adenine dinucleotide phosphate-cytochrome c reductase were little affected during 1 hr of incubation. Addition of reduced glutathione partially protected and N,N'-diphenyl-p-phenylenediamine and butylated hydroxytoluene completely protected microsomes against inactivation of ALDH, G6Pase and Cyt-P450, as well as lipid peroxidation induced by iron and ascorbate. ALDH was more susceptible than G6Pase to inactivation by iron and ascorbate, and was thus an excellent marker for oxidative stress. Inhibition of ALDH by cyanamide injection of rats exacerbated the inactivation of G6Pase in microsomes incubated with 0.1 mM, but not 25 microM 4-hydroxynonenal (4-HN). 4-HN did not stimulate lipid peroxidation. Thus, 4-HN may play a minor role in microsomal enzyme inactivation. In contrast, lipid peroxyl radicals play an important role in microsomal enzyme inactivation, as evidenced by the prevention of both lipid peroxidation and enzyme inactivation by chain-breaking antioxidants.

The effect of butylated hydroxytoluene, with and without cortisol, on stimulated lymphocytes

In the present work we undertook to ascertain whether butylated hydroxytoluene (BHT), which is used in food as an antioxidant, is capable of either inhibiting human lymphocyte stimulation or acting synergistically with cortisol and prednisolone to the same end. BHT cytotoxicity was observed at concentrations higher than 100 micrograms/ml. In the concentration range of 0.0 to 60.0 micrograms/mL, BHT showed no effect on the uptake of 3H-thymidine by PHA stimulated lymphocytes. However, at 50 micrograms/mL BHT suppressed mixed lymphocyte reaction (MLR). A synergistic effect with regard to suppression of PHA stimulated lymphocytes was observed when the cells were incubated with BHT in the presence of either cortisol or prednisolone.

Death of serum-free mouse embryo cells caused by transforming growth factor beta 1 and effects of nutritional factors

Transforming growth factor beta 1 (1 ng/ml) caused death of serum-free mouse embryo cells cultured in a medium consisting of a 1:1 mixture of Dulbecco's Modified Eagle's medium and Ham's F12 medium supplemented with fibronectin, insulin, transferrin, epidermal growth factor, and high density lipoprotein. Cell death occurred in the presence of polyunsaturated fatty acids including linoleic acid in the absence of selenium. The death could be reversed by adding alpha-tocopherol to the culture indicating a mechanism involving fatty acid peroxidation. Butylated hydroxytoluene was a poor suppressor of cell death in contrast to alpha-tocopherol. High density lipoprotein and fatty acid-free albumin also suppressed cell death at the level of 20 micrograms/ml and 1 mg/ml, respectively. Transforming growth factor beta 1 also caused a low rate of cell growth after heat treatment of the cells at 45 degrees C.

Effect of dietary butylated hydroxytoluene on nuclear envelope cytochrome P-450 during the initiation and promotion stages of hepatocarcinogenesis

The anticarcinogenic effect of the dietary antioxidant butylated hydroxytoluene (BHT) correlates with a preservation of nuclear envelope (NE) cytochrome P-450 in rats undergoing chemically induced hepatocarcinogenesis. This effect of BHT on NE cytochrome P-450 was observed during both the initiation and the promotion stages of hepatocarcinogenesis. Complex interactions between the two different mechanisms of action of BHT (i.e., enzyme induction and antioxidant activity) may account for some of the differences between the patterns of response to BHT observed during initiation and promotion.

Mechanism(s) involved in meat mutagen formation and inhibition

The Maillard reaction, which involves Amadori rearrangement as a key step, also results in sugar fragmentation and free radical formation. The imidazoquinoline meat mutagens (2-amino-3-methylimidazo[4,5-f]-quinoline, or IQ, and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, or MeIQ) are formed from a reaction mixture containing alkylpyridine free radicals and creatinine. The imidazoquinoxaline meat mutagens (2-amino-3,4-dimethylimidazo[4,5-f]-quinoxaline, or MeIQx, and 2-amino-3,4,8-trimethylimidazo[4,5-f]-quinoxaline, or 4,8-DiMeIQx) may be produced by reacting a mixture containing dialkylpyrazine free radicals and creatinine. Two different pathways for free radical formation are proposed. One involves bimolecular ring formation from the enaminol form of the glycoaldehyde alkylimine and is followed by oxidative formation of the free radical. The other pathway involves formation of N,N1-dialkylpyrazinium ions from glyoxal monoalkylimine followed by reduction to produce the free radicals. The respective intermediates (glycoaldehyde alkylimine and glyoxal monoalkylamine) are formed by reacting glycoaldehyde and glyoxal with amino compounds. The glycoaldehyde system reacts faster and produces more free radicals than the glyoxal system. The reactions help to explain the formation of imidazoquinoxaline meat mutagens and their predominance in fried fish and why these mutagens are present in larger quantities in fried ground beef than the imidazoquinoline-type meat mutagens. These two pathways may not be the only mechanisms involved in formation of meat mutagens, but other free radical reactions may also contribute to meat mutagenicity and are mentioned briefly.(ABSTRACT TRUNCATED AT 250 WORDS)

[Dark and photosensitized hemolysis of erythrocytes in the presence of dithranol]

Ditranol (1,8-dihydroxy-9-antrone) induced dark lysis of erythrocytes. After irradiation of the cells with UV-light (366 nm UV-A light) in the presence of ditranol (DUVA-effect) the hemolytic effect increases. It has been found that antioxidant butylated hydroxytoluene BHT in the concentration 10(-7) M did not affect the dark lysis, while with increased BHT concentration up to 10(-5) M the hemolytic effect of ditranol was intensified. The presence of BHT in the above concentration under DUVA-effect did not change the velocity of cell lysis. Sodium aside did not affect the dark hemolysis of ditranol, but it inhibited photosensitized hemolysis.

t-butylated hydroxytoluene enhances intracellular levels of glutathione and related enzymes of rat lens in vitro organ culture

Studies were undertaken to investigate the effect of t-butylated hydroxytoluene (BHT) on reduced glutathione (GSH) levels and related enzymes in rat ocular tissues. GSH levels were significantly enhanced when 1 microM BHT was included in the medium of rat lens cultures. BHT had a dose-dependent effect on GSH levels of lenses in cultures. Inclusion of 10 microM BHT in the culture medium resulted in a twofold increase in GSH levels of the lens within 24 hr. Increased gamma-glutamylcysteine synthetase activity concomitant with the increased amount of [35S]methionine incorporation in GSH strongly suggested that BHT caused enhanced levels of GSH in lenses by increasing de novo biosynthesis. A significant increase was also observed in glutathione S-transferase (GST) levels of lenses in culture containing BHT in the medium. Present studies also demonstrated that rat lens expresses only the mu and pi class GST isoenzymes and both these classes of isoenzymes were elevated by BHT. Oral administration of BHT to rats also resulted in enhanced in vivo levels of GSH in lens, retina and cornea. In addition, a significant in vivo increase in the levels of GST, GSH-peroxidase, GSH-reductase, gamma-glutamylcysteine synthetase, and glucose 6-phosphate dehydrogenase was observed in the lens, retina, and cornea of BHT-fed rats.

Enhancement by butylated hydroxytoluene of the in vitro activation of 3,3'-dichlorobenzidne

Mutagenicity of Salmonella TA98 and covalent binding to DNA of 3,3'-dichlorobenzidine (DCB) were used to assess the influence of di-tert.-butylated hydroxytoluene (BHT) on the in vitro activation of the arylamine by rat hepatic S9 metabolic systems. BHT at a concentration of 4 or 20 microM enhanced the mutagenicity of DCB by 32 or 21%, respectively, and the covalent binding of DCB to added DNA by 76 or 328%, respectively. The antioxidant altered the HPLC profile of isolable DCB metabolites, causing a decrease in the formation of three metabolites, an increase in the formation of one metabolite, and the formation of an entirely new metabolite. BHT inhibited the mutagenicity of the promutagen 2-acetylaminofluorene (2-AAF) but had no effect on that of the direct-acting mutagen 2,4- dinitrophenylhydrazine (DNPH). The results show that BHT enhances the mutagenicity of and DNA binding by DCB, in contrast with the predominantly inhibitory effect of the antioxidant on the mutagenicity of other chemicals that require bioactivation.

Modulation by butylated hydroxytoluene of liver and bladder carcinogenesis induced by chronic low-level exposure to 2-acetylaminofluorene

The modulating effect of five dose levels of butylated hydroxytoluene (BHT) on liver and bladder carcinogenesis induced in rats by concurrent exposure to 2-acetylaminofluorene (AAF) was investigated. AAF at a low dose of 50 ppm was fed simultaneously with concentrations of 100, 300, 1000, 3000, or 6000 ppm BHT in the diet to male F344 rats for up to 76 weeks. By 12 weeks, AAF alone induced altered hepatocellular foci, identified by iron storage deficiency and gamma-glutamyltranspeptidase activity. At subsequent time points of 24, 36, and 48 weeks, the number of foci progressively increased, and at the end of the study, the incidence of liver neoplasms was 100%, a new finding with such a low dose of AAF. Simultaneous feeding of BHT inhibited the induction of liver altered foci by AAF in a dose-related manner and reduced the incidence of hepatocellular carcinomas and the number of liver neoplasms per animal. Feeding of 6000 ppm BHT, but not of lower doses, together with AAF resulted in an increase in the incidence and multiplicity of bladder neoplasms, and 3000 ppm increased nodular hyperplasia of the bladder. These results suggest that the chemoprevention by BHT of cancer resulting from low-level long-term carcinogen exposure may be achieved at doses that do not produce adverse effects.

Mammary cancer prevention by conjugated dienoic derivative of linoleic acid

Conjugated dienoic derivative of linoleic acid (CLA) is a collective term which refers to a mixture of positional and geometric isomers of linoleic acid. It is a naturally occurring substance in food and is present at higher concentrations in products from animal sources. The present study reports that synthetically prepared CLA is an effective agent in inhibiting the development of mammary tumors induced by dimethylbenz(a)anthracene. Rats were fed either the AIN-76A basal diet or the same diet supplemented with 0.5, 1, or 1.5% CLA by weight. These diets were started 2 weeks before carcinogen administration and continued until the end of the experiment. The total number of mammary adenocarcinomas in the 0.5, 1, and 1.5% CLA groups was reduced by 32, 56, and 60%, respectively. The final tumor incidence and cumulative tumor weight were similarly diminished in rats fed the CLA-containing diets. In general, there appeared to be a dose-dependent protection at levels of 1% CLA and below, but no further beneficial effect was evident at levels above 1%. Chronic feeding of up to 1.5% CLA produced no adverse consequences in the animals. Analysis of the phospholipid fraction from liver and mammary tumor extracts showed that only the c9,t11 isomer of CLA was incorporated and that the level of incorporation increased with dietary intake. An interesting property of CLA is its ability to suppress peroxide formation from unsaturated fatty acid in a test-tube model (Cancer Res., Ha et al. 50: 1097-1101, 1990). In view of this information, the amount of thiobarbituric acid-reactive substances (lipid peroxidation products) present endogenously in liver and mammary gland was quantitated. The feeding of CLA (for either 1 or 6 months) resulted in a decrease in the extent of lipid peroxidation in the mammary gland, but such a suppressive effect was not detected in the liver. It should be noted that maximal antioxidant activity was observed with only 0.25% CLA in the diet, whereas maximal tumor inhibition was achieved at about 1% CLA. Hence there is a discrepancy between the antioxidant efficacy of CLA and its anticarcinogenic potency, suggesting that some other mechanisms might be involved in cancer protection. Unlike the stimulatory effect of linoleic acid in carcinogenesis (Cancer Res., Ip et al., 45: 1997-2001, 1985), the reaction of CLA in cancer prevention is specific, and CLA is more powerful than any other fatty acid in modulating tumor development.

Cytotoxic effect of cis-parinaric acid in cultured malignant cells

Parinaric acid, a naturally occurring 18-carbon fatty acid containing 4 conjugated double bonds, is toxic to human monocytic leukemia cells at concentrations of 5 microM or less. Conditioning of the medium reduces the cytotoxic effect, suggesting that parinaric acid and not a metabolite is the active agent. The mechanism of parinaric acid toxicity appears to involve lipid peroxidation because the toxic action can be blocked by the addition of butylated hydroxytoluene. When U-937 cells are differentiated to the monocytic form, they become resistant to as much as 30 microM parinaric acid. This difference in sensitivity may be explained in part by the fact that the undifferentiated cells take up 3 to 4 times more parinaric acid. Concentrations of parinaric acid less than 5 microM are also toxic to human THP-1 monocytic leukemia, HL-60 human promyelocytic leukemia, and Y-79 human retinoblastoma cells. Measurements of protein synthesis indicate that differentiated U-937 cells, confluent cultures of human fibroblasts, bovine aortic endothelial cells, and CaCo-2 colonic mucosal cells are much less sensitive to parinaric acid than the malignant cell lines tested, suggesting that the cytotoxic action may be selective for rapidly growing malignant tumors. Thus, parinaric acid may be the prototype of a new class of lipid chemotherapeutic agents that contain a conjugated system of double bonds and act by sensitizing tumor cells to peroxidation.

Differential oxidative stress induced by two different types of skin tumor promoters, benzoyl peroxide and 12-O-tetradecanoylphorbol-13-acetate

The oxidative stress induced in vivo by benzoyl peroxide (BzPo) or 12-O-tetradecanoylphorbol-13-acetate (TPA) was evaluated in terms of chemiluminescence (CL) emitted by SENCAR mouse skin, a non-invasive method that allows an estimation of overall oxidative stress. The ability of a biomimetic superoxide dismutase, copper(II)(3,5-diisopropylsalicylate)2 (CuDIPS), to inhibit that response was also evaluated. A single application of BzPo to mouse skin resulted in a dose-dependent increase in CL up to 0.083 mumol. Sequential treatment with BzPo in a dose used for tumor promotion resulted in a fall in CL induced by the second topical application. There were no differences between initiated and non-initiated mice in their responses to BzPo-induced CL. CuDIPS, an inhibitor of tumor promotion, was an effective inhibitor of CL in all the protocols evaluated. Conversely, ZnDIPS and DIPS did not inhibit CL. Phenolic antioxidants induced partial inhibition of CL. Unlike BzPo treatment, a single application of TPA up to 105 nmol did not induce an increase in CL, but the second topical application with TPA in a dose used for tumor promotion resulted in a small but significant increase in CL. However, these values of CL were much smaller than the CL induced by BzPo. Our results show a differential response of the skin in terms of the oxidative stress induced by BzPo or TPA.

[The antiradical activity of coumarin reductones]

The antiradical activity of coumarine reductones was investigated by the method of inhibition of Fe2+ induced chemiluminescence of egg-yolk lipoproteins. All coumarines studied exhibited high antioxidant activity. The dependence of chemiluminescence intensity on the antioxidant concentration shows that coumarines reductions resemble their chemical analog--ascorbic acid rather than the lipid antioxidant butilated hydroxitoluene (ionol).

[Disordered cardiac electrical stability in beta-adrenergic damage and antioxidant protection]

The electrical threshold of ventricular fibrillation induced by premature single impulses and the ectopic activity and also an abnormal conduction during vagus inhibition of sinus node were estimated 24 hours after the administration of isoproterenol (10 mg/kg, s/c, on time) in rats. In addition the cardiac contractile function of the left ventricle was studied. The study was performed on male Wistar rats, 250-300 body weight, under nembutal anesthesia. Isoproterenol had no effect on the contractile function in the rest and during maximal isometric load, induced by coarctation of ascending aorta. But in the treated animals the threshold of fibrillation fell more than 2-fold and the vagal bradycardia was more 2-fold then in the untreated animals. The AB-block, idioventricular rhythm and extrasystoles appeared during vagal bradycardia in treated animals, while in the untreated ones there were no any disturbances. The preliminary administration of the antioxidant ionol (BMT, 30 mg/kg, per os, in sun oil) prevented the enumerated shifts.

The interaction of antioxidants and structurally related compounds with mitochondrial oxidative phosphorylation

The antioxidants, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), interact with mitochondrial oxidative phosphorylation in two ways. They uncouple phosphorylation from oxidation by making the mitochondrial inner membrane more permeable to protons. They also inhibit respiration by a direct interaction with the electron transport chain. Here we separated out these two properties of BHA and BHT by determining their effects on respiration in coupled and uncoupled mitochondria. Similar experiments were carried out with compounds structurally related to BHA and BHT. Most of these compounds had uncoupling and inhibitory properties essentially similar to BHA and BHT. In contrast, the dimer of BHA had no inhibitory effects on uncoupled respiration and little uncoupling activity. The implications of these results for the interactions of BHA and BHT with mitochondrial oxidative phosphorylation and the design of antioxidants are discussed.

Selective in vivo inhibition of rat mammary 7,12-dimethylbenz[a]anthracene-DNA adduct formation by dietary butylated hydroxytoluene

The in vivo formation of specific 7,12-dimethylbenz[a]-anthracene (DMBA)-DNA adducts in the mammary gland of the female Sprague-Dawley rat was studied in response to dietary butylated hydroxytoluene (BHT). Dietary BHT concentrations of 0.4 and 0.8% significantly inhibited total DMBA-DNA binding by 41.5 and 35.6% respectively, as compared to controls. However, the decrease in total binding associated with intake of BHT was not due to a uniform inhibition in the formation of all individual adducts. The formation of two adducts resulting from the binding of the anti-dihydrodiolepoxide of DMBA to deoxyguanosine (anti-dGuo) was significantly decreased by a combined average of 51.5% for rats fed BHT-supplemented diets as compared to controls. However, syn-derived DMBA-DNA adducts were not consistently inhibited by dietary BHT. Adduct formation resulting from the binding of the syn-dihydrodiolepoxide of DMBA to deoxyadenosine (syn-dAdo) was significantly inhibited only for rats fed a diet supplemented with 0.4% BHT. The formation of the syn-dGuo adduct was not affected by the feeding of BHT-supplemented diets. These results suggest that in vivo inhibition by BHT of mammary DNA adducts formed from the anti-diastereomer of DMBA may be an important contribution to the inhibitory effect of BHT on the initiation stage of DMBA-induced mammary carcinogenesis.

[Antiradical activity of 3-substituted coumarins and their effect on iron-dependent chemiluminescence]

The antioxidant capacity of 3-aminocoumarin, 3-oxycoumarin, 3-acetylaminocoumarin, and 3-coumarin carbonic acid has been investigated with chemiluminescence measurement and by the accumulation of TBA-active products. All coumarins were found to be antioxidants, with 3-oxy-, 3-amino- and 3-acetylamino coumarins being capable of amplifying chemiluminescence at early stages of the process.

Quinolone antibacterial-agent-induced cutaneous phototoxicity: ear swelling reactions in Balb/c mice

The phototoxic potentials of quinolone derivatives and the possibility of free radical contribution to their phototoxicity were investigated by measuring increments in ear thickness. Balb/c mice, fasted overnight, were orally administered ofloxacin (OFLX), lomefloxacin (LMFX), enoxacin (ENX), ciprofloxacin (CPFX) and DR-3355 (the s-isomer of OFLX), and immediately exposed to ultraviolet-A light (UVA: 320-400 nm) for 4 h (21.6 joules/cm2). Measurement of ear thickness was carried out 0, 24 and 48 h after the end of irradiation. The time-course profiles of ear thickness varied with both the doses and the quinolone used, but linear dose-response curves were obtained from the data 24 h after irradiation ended. The 50% ear thickness increment-inducing doses of LMFX, ENX, OFLX, CPFX and DR-3355 were calculated as 24.8, 81.9, 428.0, 457.9 and 526.6 mg/kg, respectively. The phototoxic potential of these quinolones coincided with the data obtained previously by measuring the incidence of erythema on the ears. Pretreatment with butylated hydroxtoluene, a free radical scavenger, almost completely prevented all swelling reactions induced by the quinolones. These results suggest that the degree of phototoxicity induced by the quinolones used could depend on the balance between the generation of free radicals and the effectiveness of the defense systems against toxic radicals.

Enhancement of endogenous prostaglandin I2 (prostacyclin) generation in vivo by a phenolic anti-inflammatory agent in the rabbit

Angiotensin II (i.v.) increased the plasma level of 6-keto-PGF1 alpha from 241 +/- 60 pg/ml (n = 8) to 612 +/- 108 pg/ml (n = 8) in anesthetized rabbits, which was further significantly increased by pretreatment with a phenolic anti-inflammatory agent, MK-447, to 1007 +/- 218 pg/ml (n = 8). MK-447 alone did not affect the level. The level of thromboxane B2 was not affected by these treatments. These results suggest that MK-447 may selectively enhance the PGI2 level by acting as a tryptophan-like cofactor of PG endoperoxide synthase.

Modulation of low-density lipoprotein-induced inhibition of intercellular communication by antioxidants and high-density lipoproteins

In order to study the capacity of antioxidants and high-density lipoproteins (HDL) to modulate the effects of low-density lipoprotein (LDL) on intercellular communication, arterial smooth muscle cells and a dye transfer method were used. LDL, in contrast to HDL, inhibited the communication between arterial smooth muscle cells from human umbilical cord and thoracic aorta in a dose-dependent manner. LDL, which can be oxidized, as detected by the lipid-peroxidation assay and gel electrophoresis, did not influence cell-cell communication in the presence of the antioxidants butylated hydroxytoluene (BHT), alpha-tocopherol and glutathione. The results suggest that LDL must undergo oxidative modification before it can influence intercellular communication. Like antioxidants, HDL diminished the LDL-induced inhibition of cell-cell communication. This study suggests that the modulation of gap-junctional communication by the balance of HDL and LDL in plasma may influence atherogenesis.

5-Lipoxygenase is not essential in macrophage-mediated oxidation of low-density lipoprotein

The concentration-dependent effects of a series of lipoxygenase inhibitors and antioxidants on the macrophage-mediated oxidative modification of low-density lipoprotein (LDL) were measured. Their influence on macrophage 5-lipoxygenase pathway activity was also studied over the same concentration range. No correlation between inhibition of 5-lipoxygenase and of macrophage-mediated oxidation of LDL was observed. The capacity of the compounds to prevent cell-mediated modification of LDL could be explained in terms of their activity as either aqueous- or lipid-peroxyl radical scavengers. Two potent 5-lipoxygenase inhibitors (MK 886 and Revlon 5901), which had no radical-scavenging properties, were unable to block LDL modification. It is concluded that 5-lipoxygenase is not essential for LDL oxidation by macrophages.

The antioxidant butylated hydroxytoluene stimulates platelet protein kinase C and inhibits subsequent protein phosphorylation induced by thrombin

The phenolic antioxidant 2,6-bis(1,1-dimethyl ethyl)-4-methylphenol (BHT) evokes a transient phosphorylation of two platelet proteins of Mr 20,000 and 47,000 that are well-known substrates of protein kinase C (PKC) and, similarly to phorbol esters, a slight but persistent phosphorylation of a protein of Mr 26,000. These effects are observed both in the presence and in the absence of extracellular calcium, but are abolished in the presence of the protein kinase C inhibitor staurosporine. The phosphorylation of the 47 kDa protein takes place mostly at the serine and, to a lesser extent, at threonine residues. BHT induces an increased binding of tritiated phorbol dibutyrate to platelets indicating a PKC translocation from cytosol to plasma membrane. Addition of BHT (20 microM) a few min prior to thrombin causes inhibition of both agonist-evoked protein phosphorylation and increase in the Ca2+ concentration, the latter inhibition being counteracted by staurosporine. The inhibitory effect lasts for several minutes even after removal of BHT from the cellular suspending medium. Similar results are obtained with nordihydroguaiaretic acid, whereas 2- and 3-tert-butyl-4-methoxyphenol (BHA) produce only slight effects. BHT activates the protein kinase C purified from pig brain in a concentration-dependent manner (up to 200 microM), whereas it does not affect the activity of other purified protein kinases such as type 1 and 2 casein kinases, type II A, II B and III tyrosine protein kinases from rat spleen and the catalytic subunit of cyclic AMP-dependent protein kinase. It is concluded that, similarly to diacylglycerols and phorbol esters, these phenolic antioxidants activate the protein kinase C, which in turn desensitizes platelets towards subsequent phospholipase C activation.

Phenylarsine oxide induces the cyclosporin A-sensitive membrane permeability transition in rat liver mitochondria

This paper reports an investigation on the effects of the hydrophobic, bifunctional SH group reagent phenylarsine oxide (PhAsO) on mitochondrial membrane permeability. We show that PhAsO is a potent inducer of the mitochondrial permeability transition in a process which is sensitive to both the oxygen radical scavanger BHT and to cyclosporin A. The PhAsO-induced permeability transition is stimulated by Ca2+ but takes place also in the presence of EGTA in a process that maintains its sensitivity to BHT and cyclosporin A. Our findings suggest that, at variance from other known inducers of the permeability transition, PhAsO reacts directly with functional SH groups that are inaccessible to hydrophilic reagents in the absence of Ca2+.