Toxicity studies of butylated hydroxyanisole and butylated hydroxytoluene. II. Chronic feeding studies

The antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) were fed in the diet to male F344 rats in two chronic feeding studies. In one study, feeding BHT for 76 wk at concentrations ranging from 100 to 6000 ppm produced no increase in neoplasms at any site. In a second study, feeding 12,000 ppm BHT for 110 wk had no neoplastic effect at any site, whereas feeding BHA at 12,000 ppm resulted in a small increase in squamous cell papillomas of the non-glandular squamous portion of the stomach.

Effect of route of administration on the relative efficacy and potency of 2-aminoethyl-4-(1,1-dimethylethyl)-6-iodophenol HCl (MK447) and furosemide

2-Aminoethyl-4-(1,1-dimethylethyl)-6-iodophenol hydrochloride (MK447) is a chemically novel diuretic that has oral efficacy and potency greater than furosemide (FUR). In this study, the relative efficacy and potency of MK447 and FUR were assessed following oral, i.v. bolus and i.v. infusion administration in rats and dogs. MK447 was more potent than furosemide but the two were equally efficacious when administered orally to rats and dogs. The relative potency remained unchanged when administered as an i.v. bolus to rats (1 mg/kg). However, when infused continuously there was no difference in potency or efficacy between the two compounds. These observations lead to the conclusion that pharmacokinetic differences between the two compounds play a major role in determining their relative oral potency. Comparative studies of the effects of compounds given by different routes of administration are useful in providing insight into the role of pharmacokinetics in overall response to different compounds.

Epithelial cell-fibroblast interactions in lung injury and repair

Although direct intercellular contacts between alveolar epithelial cells and fibroblasts have been described in developing and adult lung, the frequency of such contacts and their relationship to type 2 cell division and differentiation in normal and abnormal repair is not known. The authors now correlate measurements of type 2 cell basal surface, basement membrane continuity, and the incidence of epithelial-interstitial cell contacts with the proliferative index of type 2 cells and fibroblasts in normal repair (after hyperoxia) and in abnormal repair with fibrosis (after bleomycin or butylated hydroxytoluene). In each case, type 1 cell necrosis was followed by an increase in type 2 cell basal surface as the cells spread over the denuded capillary wall before dividing. After hyperoxia, a high but short-lived peak in type 2 cell division was not accompanied by fibrosis. After more severe drug-induced injury, the type 2 proliferative phase was extended and was accompanied by prolonged fibroblast growth. Type 2 cells persisted where they covered a thick interstitium of fibroblasts and fibrillar collagen. The incidence of epithelial-interstitial cell contacts decreased at the time of maximal type 2 cell division, then increased immediately after the peak. The results suggest a reciprocal epithelial-fibroblast control system whereby 1) epithelial necrosis and delayed repair promotes fibroblast growth, and 2) direct contact of epithelial cells with fibroblasts or fibrillar collagen may provide a factor important for the regulation of type 2 cell growth and differentiation.

Estimate of the maximal daily dietary intake of butylated hydroxyanisole and butylated hydroxytoluene in The Netherlands

The daily dietary intake of the phenolic antioxidants butylated hydroxyanisole (BHA) and/or butylated hydroxytoluene (BHT) was estimated using data obtained from a nationwide dietary record survey carried out in The Netherlands in 1987/1988. The estimates were based on the fat content of selected food categories and their respective maximum permitted levels of BHA and/or BHT. The results indicate that it is unlikely that the current acceptable daily intake for BHA (0-0.05 mg/kg body weight) is surpassed, even in individuals with an extremely high caloric intake, except in extreme cases in 1-6-year-olds. However, it cannot be excluded that the acceptable daily intake for BHT (FAO/WHO: 0-0.125 mg/kg; EEC: 0-0.05 mg/kg) is exceeded in all age and sex groups, but particularly in children aged 1-6 years.

[Studies on the teratogenic potential of 2,2'-methylenebis (4-methyl-6-tert-butylphenol) in rats]

2,2'-Methylenebis (4-methyl-6-tert-butylphenol), an antioxidant, was given orally to pregnant Wistar rats by stomach intubation at the dose levels of 93.5, 187 or 375 mg/kg body weight during days 7 to 17 of pregnancy, and the effects of the compound on dams and fetal developments were examined. In the dams at the two higher doses of 187 and 375 mg/kg, toxic signs such as hair fluffing and diarrhoea were observed, and their body weight gain and food consumption were suppressed. Two dams, which showed marked diarrhoea in the highest dose group, died. However, there was no evidence of fetal malformation attributable to treatment with the compound in any of the dose groups treated, although a slight increase in fetal death was found in the highest dose group. It is concluded that 2,2'-methylenebis (4-methyl-6-tert-butylphenol) has a weak lethal effect on fetal development but not a teratogenic effect in the rat.

Disposition of single oral doses of butylated hydroxytoluene in man and rat

The kinetics and metabolism of butylated hydroxytoluene (BHT) in man and rats have been compared. Single oral doses of 200, 63 or 20 mg BHT/kg body weight were administered to rats and a single oral dose of 0.5 mg/kg body weight was ingested by human volunteers (non-smoking males). In rats, kinetic parameters (area under the plasma concentration-time curve, plasma BHT peak levels) showed a dose-dependent increase. Plasma BHT levels after oral administration were about four times higher than those that have been reported for another synthetic food antioxidant, butylated hydroxyanisole (BHA; Verhagen et al., Fd Chem. Toxic. 27, 151-158). This may be a reflection of a smaller volume of distribution for BHT, since there were no differences in plasma elimination half-life or plasma clearance between BHT and BHA. In man, the mean plasma concentration-time profile after oral BHT intake was well below the BHT profiles observed for rats and closely followed plasma BHA kinetics in man. In rats, the simultaneous administration of BHT (200 mg/kg body weight) and BHA (200 mg/kg) significantly decreased the absorption of BHT from the gastro-intestinal tract in the first few hours after treatment; the plasma kinetics of BHA were not influenced by the simultaneous administration of BHT. In human female volunteers no alterations in plasma BHT or BHA profiles were seen after the simultaneous ingestion of BHT (0.25 mg/kg body weight) and BHA (0.25 mg/kg). Rats excrete about 10% of an oral dose of 200 mg BHT/kg as unchanged BHT in the faeces, whereas in man no BHT could be detected in the faeces. Urinary excretion of (un)conjugated 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) accounts for only a small percentage of the administered dose in both rats and humans. It is concluded that the plasma BHT concentrations reached after the administration of a single medium to high dose of BHT to rats or a single low dose to man are very different.

[Involvement of lipid peroxidation in regression of heart hypertrophy]

The regression of hypertrophied heart presupposes disassembling of all cardiomyocyte components including membrane structures. The involvement of free radical oxidation of membrane phospholipids was studied in the cardiac regression. Altitude hypertrophy was developed in barocamera (7000 m, 6 hours daily). 3 weeks of periodical hypoxia leads to 1.5-fold increase of heart weight (right ventricle weight was 2-fold increased). In 7-10 days after adaptation the heart weight reduced to normal. Both, the development and regression of myocardial hypertrophy was accompanied by changes in Mb and Hb organ concentration proportional to weight changes. In lipid extraction of maximal hypertrophied heart, the 30% decrease of lipid peroxidation product (diene conjugates) regularly occurred. The rate of regression had negative correlation with peroxidation products accumulation. Intraperitoneal injection of free radical scavenger BHT attenuate the regression rate. The results suggest that unlike the common knowledge about the membrane injury effect, lipid peroxidation can play positive role in disassembling of superfluous cell membrane structures.

[Correction of disorders of the system of blood aggregation regulation by ionol in the post-resuscitation period]

In the experiments on white rats resuscitated after a 7-minute mechanical asphyxia, phase disorders in the indices of the system of regulation of aggregate state of the blood in postresuscitation period have been revealed. They appear in the shape of a syndrome of disseminated intravascular blood coagulation with the development of hypercoagulation phase by the 3rd hour. Prophylactic introduction of ionol in a dose of 100 mg/kg in 48, 24 and 1 hour before the experiment prevents the development and progressing of the above syndrome.

Reactive oxygen species facilitate the in vitro and in vivo lipopolysaccharide-induced release of tumor necrosis factor

Secretion of TNF from mouse peritoneal macrophages exposed to LPS in vitro was enhanced in the presence of H2O2 or sodium periodate. Neither of these agents induced release of TNF in the absence of LPS. Both iron chelators and free radical scavengers inhibited this enhanced secretion of TNF, implying the involvement of free radicals via a Fenton-type reaction. Oxidant stress, in the form of alloxan or divicine, also enhanced serum levels of TNF in mice made sensitive to LPS by low-level infection with malaria, and then given i.v. LPS. Pretreatment with the iron chelator, desferal, or the free radical scavenger, BHA, inhibited TNF release in these animals. Less TNF was also detected in mice given desferal before LPS in the absence of exogenous radical generator. These results could have implications for understanding the details of the MLR, the adherence of neutrophils to the walls of pulmonary vessels in free radical-induced lung pathology, and the side effects of bleomycin.

[Use of dibunol and delagil in the treatment of acute pancreatitis]

The effect of Dibunol and Delagil on the course of experimental pancreatitis was studied in experiments in 80 rats and 36 dogs. The intravenous injection of the drugs was shown to decrease lethality of the animals. Control of biochemical parameters has revealed decreased activity of amylase, lipase, trypsin and malonic dialdehyde, normalized level of superlight luminescence of blood plasma. A good medical effect was obtained in 15 patients with acute pancreatitis.

Photoprotective effect of vitamins A and E on polyamine and oxygenated free radical metabolism in hairless mouse epidermis

The purpose of this study was to confirm the photoprotective effect on skin of vitamins A and E, due to inhibition of polyamine synthesis and production of free radicals. These variables were measured in the lumbar epidermis of the female hairless mouse subjected to UVA + B irradiation. Polyamines were assayed in epidermal homogenate by HPLC, and production of oxygenated free radicals was determined by spectrofluorometric assay of malonyl dialdehyde. It was determined that butyl-hydroxy-toluene and vitamin E inhibited production of free radicals (56% and 60%, respectively) and caused a significant reduction in polyamine biosynthesis (P less than 0.01), whereas the inhibitory effect of malonyl dialdehyde induced by vitamin A (30%) had no associated effect on polyamine metabolism.

[Diagnosis and prevention of myocardial reperfusion injury in experimental myocardial infarction]

In an experimental study in 69 dogs with the occluded anterior descending branch of the left coronary artery, dibunol, an antioxidant, and isoptin, a Ca2+ antagonist reduced myocardial infarction area, prolonged survival time and brought down mortality rate, in spite of an increase in reperfusion-related arrhythmias. The value of various electrocardiographic parameters for the diagnosis of ischemized-myocardium reperfusion and the severity of reperfusion-related heart damage in relation to the type of preventive medication, as compared to postmortem findings, are discussed.

Tumor promotion by a hydroperoxide metabolite of butylated hydroxytoluene, 2,6-di-tert-butyl-4-hydroperoxy-4-methyl-2,5-cyclohexadienone, in mouse skin

The nature of the skin tumor promotion response to a hydroperoxide metabolite of butylated hydroxytoluene, 2,6-di-tert-butyl-4-hydroperoxyl-2,5-cyclohexadienone (BHTOOH), was examined in SENCAR mice. BHTOOH was an effective inducer of epidermal ornithine decarboxylase (ODC) activity. Maximal induction of ODC activity was observed 12 hours after a single application of BHTOOH. Dose-dependent increases were seen between 2 and 20 mumol while higher amounts were less effective. A similar dose-response relationship for papilloma and carcinoma formation was observed when BHTOOH was applied twice weekly for 50 weeks to mice previously initiated with 7,12-dimethylbenz[a]anthracene. Doses of 2, 8, and 20 mumol BHTOOH gave maximal papilloma responses of 0.1, 0.6, and 3.6 papillomas/mouse, respectively. The progression of papillomas to carcinomas was examined and at 60 weeks the incidence of carcinomas was 0, 17, and 28% for the three treatment groups. The carcinoma:papilloma ratios were 0.08 and 0.40 for the high and intermediate BHTOOH dose groups. The data suggest that BHTOOH, unlike butylated hydroxytoluene, is an effective tumor promoter in mouse skin. Additionally, BHTOOH may enhance the conversion of papillomas to carcinomas. However, BHTOOH is not a complete carcinogen in that no papillomas or carcinomas were observed in uninitiated mice treated with BHTOOH only.

Reduction of 2-acetylaminofluorene-induced unscheduled DNA synthesis in human and rat hepatocytes by butylated hydroxytoluene

Butylated hydroxytoluene (BHT) protected against DNA damage induced in rat hepatocytes by 2-acetylaminofluorene (2AAF) or N-hydroxy 2AAF as shown by a marked reduction of unscheduled DNA synthesis. BHT also inhibited 2AAF-induced DNA damage (as shown by reduced repair) in human hepatocytes. In addition, rats pre-treated with BHT in the diet (0.5% w/w for 10 days) provided hepatocytes which exhibited less unscheduled DNA synthesis than did hepatocytes from control rats when these cells were exposed to either 2AAF or N-hydroxy 2AAF. The results indicate both direct (in vitro) and indirect (by pre-treatment in vivo) inhibitory effects of BHT on the genotoxicity of 2AAF in liver cells, in accord with the reported anti-tumorigenicity in the liver. This effect contracts with a BHT-mediated increase in the efflux of 2AAF-derived mutagens from liver cells which may contribute to enhanced extrahepatic carcinogenesis.

Interactions of aflatoxin and the antioxidant butylated hydroxytoluene in two-week-old chicks

Two-week dietary administration of 2500 ppb aflatoxin was sufficient to cause a decrease in bursal weights and a reduction in the number of splenic leukocytes in chicks. No significant effects on weight gain or feed efficiency were evident. The chicks also had elevated heterophil-to-lymphocyte ratios, suggesting a heightened reaction to stress. This effect could be blocked by dietary administration of the antioxidant butylated hydroxytoluene (BHT) at a concentration eight-fold over that normally present to preserve control feed. The BHT treatment increased the activities of the enzymes glutathione-S-transferase, aniline hydroxylase and O-demethylase, which metabolize aflatoxins in the liver.

[Effect of subchronic administration of phenazepam and synthetic antioxidants on the functional status of synaptic membranes in the cerebral cortex of rats subjected to prolonged stress]

Monoamine oxidase activity, lipid peroxidation and membrane structure were tested after chronic stress and 7-day treatment with drugs in the brain cortex synaptosomal membranes of rats. The most potent corrector of stress-induced changes, as compared to hydrophobic antioxidant dibunol and tranquilizer phenazepam, was compound 3-OP, a hydrophilic antioxidant.

[Prevention of myocardial damage during reperfusion of the coronary artery in dogs using dibunol combined with verapamil]

An experimental study in 69 dogs examined the effect of isolated and combined use of dibunol and verapamil (isoptin) on the course of reperfusion of ischemized myocardium after 180 minutes' coronary occlusion. Verapamil alone had no protective effect on reperfused myocardium, whereas dibunol, and particularly its combination with verapamil, essentially limited the size of necrosis, reduced plasma CPK activity and animal mortality rate and maintained ultrastructural integrity of cardiomyocytes, which was accompanied by a decrease of plasma lipid peroxidation products and a stabilization of cardiomyocyte sarcolemma. The significance of membrane damage and uncontrolled calcium entrance into cardiomyocytes for the mechanism of myocardial damage at the recovery of coronary circulation is discussed.

Pneumotoxicity of butylated hydroxytoluene applied dermally to CD-1 mice

Pneumotoxicity of butylated hydroxytoluene (BHT) applied to the skin of CD-1 mice was investigated and compared with that of butylated hydroxyanisole (BHA). To 6 groups of 10 male mice and 10 female mice 0.1 ml of dimethylsulfoxide (DMSO) solutions containing 0, 5, 10, 20, or 30 mg of BHT or 30 mg of BHA were topically applied 3 times weekly for 4 weeks. Between the 4th and 8th day BHT-treated mice exhibited respiratory distress with subsequent dose-dependent mortality. At autopsy dead animals were found to have congestion and enlargement of the lung with oozing of froth from the trachea. Histologically, collapse of the alveoli and dilatation of the alveolar ducts associated with degeneration or necrosis of type I alveolar epithelial cells were evident. The lethal effect of BHT was more manifest in female than in male mice. In contrast, none of the BHA-treated or control mice showed lung abnormalities. In another series of experiments to study the species difference of BHT pneumotoxicity, F-344 rats of both sexes and male Syrian golden hamsters were exposed to BHT by dermal application 3 times weekly for 4 weeks at a dose of 240 mg in rats or 480 mg in hamsters. However, no pulmonary alterations were observed in either species.

Anticarcinogenic and hepatotoxic interactions between retinyl acetate and butylated hydroxytoluene in rats

The natural retinoid, retinyl acetate (RA), and the phenolic antioxidant, butylated hydroxytoluene (BHT), are both effective inhibitors of mammary carcinogenesis in rats. The present study was designed to determine if an increased inhibition of mammary carcinogenesis is obtained when RA and BHT are administered in combination. At age 50 days (time 0), virgin, female Sprague-Dawley rats received a single intragastric instillation of 16 mg of 7,12-dimethylbenz(a)anthracene dissolved in 1 ml sesame oil. Groups of 30 carcinogen-treated rats received Wayne Lab Chow supplemented with (per kg diet) 250 mg RA, 5000 mg BHT, or 250 mg RA plus 5000 mg BHT by the following schedule: -2 to +1 week; +1 week until the end of the experiment; -2 weeks to end; or none. Combined administration of RA plus BHT by the -2 weeks to end schedule was more effective in mammary cancer chemoprevention than was RA alone or BHT alone; the interaction of RA and BHT was additive. Similarly, administration of RA plus BHT by the -2 weeks to end protocol was more active in chemoprevention than was RA plus BHT administered either from weeks -2 to +1 or +1 week to end. Chronic exposure to RA plus BHT induced a high incidence of hepatic fibrosis and bile duct hyperplasia; these changes were not observed in controls and were seen in low incidence in animals exposed to RA only or BHT only. These data indicate that enhanced anticarcinogenic activity can be obtained through the use of "combination chemoprevention" regimens; however, chemopreventive compounds may interact not only to inhibit carcinogenesis but also to induce toxicity.

Combination chemoprevention of rat mammary carcinogenesis by indomethacin and butylated hydroxytoluene

Indomethacin, a nonsteroidal antiinflammatory agent which inhibits prostaglandin biosynthesis, is an effective inhibitor of mammary carcinogenesis in rats. However, the activity of indomethacin as a chemopreventive agent is limited by toxicity. The present studies were conducted to determine if the toxic and anticarcinogenic effects of indomethacin can be modified by the phenolic antioxidant, butylated hydroxytoluene (BHT). Simultaneous administration of BHT resulted in a dose-related inhibition of indomethacin toxicity in female Sprague-Dawley rats, and increased the tolerable indomethacin dose from 50 to 150 mg/kg diet. When BHT (5000 mg/kg diet) and indomethacin (50 mg/kg diet) were administered in combination, no increased inhibition of 7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis was observed above that attained by administration of BHT alone or indomethacin alone at those doses. However, when the indomethacin dose was increased to 100 mg/kg diet, an enhanced inhibition of carcinogenesis was attained when BHT and indomethacin were administered from 2 weeks prior to until 1 week after 7,12-dimethylbenz(a)anthracene administration. These data indicate that "combination chemoprevention" regimens can be utilized to reduce the toxicity of anticarcinogenic drugs. However, the BHT-indomethacin interaction appears to involve a functional or dispositional antagonism which limits the anticarcinogenic efficacy of increasing indomethacin dose level.