Decrease in blood coagulation factors II (prothrombin), VII, IX and X in the rat after a single oral dose of butylated hydroxytoluene

Final report on the safety assessment of BHT(1)

BHT is the recognized name in the cosmetics industry for butylated hydroxytoluene. BHT is used in a wide range of cosmetic formulations as an antioxidant at concentrations from 0.0002% to 0.5%. BHT does penetrate the skin, but the relatively low amount absorbed remains primarily in the skin. Oral studies demonstrate that BHT is metabolized. The major metabolites appear as the carboxylic acid of BHT and its glucuronide in urine. At acute doses of 0.5 to 1.0 g/kg, some renal and hepatic damage was seen in male rats. Short-term repeated exposure to comparable doses produced hepatic toxic effects in male and female rats. Subchronic feeding and intraperitoneal studies in rats with BHT at lower doses produced increased liver weight, and decreased activity of several hepatic enzymes. In addition to liver and kidney effects, BHT applied to the skin was associated with toxic effects in lung tissue. BHT was not a reproductive or developmental toxin in animals. BHT has been found to enhance and to inhibit the humoral immune response in animals. BHT itself was not generally considered genotoxic, although it did modify the genotoxicity of other agents. BHT has been associated with hepatocellular and pulmonary adenomas in animals, but was not considered carcinogenic and actually was associated with a decreased incidence of neoplasms. BHT has been shown to have tumor promotion effects, to be anticarcinogenic, and to have no effect on other carcinogenic agents, depending on the target organ, exposure parameters, the carcinogen, and the animal tested. Various mechanism studies suggested that BHT toxicity is related to an electrophillic metabolite. In a predictive clinical test, 100% BHT was a mild irritant and a moderate sensitizer. In provocative skin tests, BHT (in the 1% to 2% concentration range) produced positive reactions in a small number of patients. Clinical testing did not find any depigmentation associated with dermal exposure to BHT, although a few case reports of depigmentation were found. The Cosmetic Ingredient Review Expert Panel recognized that oral exposure to BHT was associated with toxic effects in some studies and was negative in others. BHT applied to the skin, however, appears to remain in the skin or pass through only slowly and does not produce systemic exposures to BHT or its metabolites seen with oral exposures. Although there were only limited studies that evaluated the effect of BHT on the skin, the available studies, along with the case literature, demonstrate no significant irritation, sensitization, or photosensitization. Recognizing the low concentration at which this ingredient is currently used in cosmetic formulations, it was concluded that BHT is safe as used in cosmetic formulations.

The dose-dependent effect of BHT (butylated hydroxytoluene) on vitamin K-dependent blood coagulation in rats

Earlier studies have reported a reduction of vitamin K-dependent blood clotting factor activity and incidence of haemorrhagic death in rats fed butylated hydroxytoluene (BHT); however, the vitamin K status of the animals used in these studies was claimed to be inadequate. The aim of the study reported here was to determine the effect of BHT on vitamin K-dependent clotting factors in vitamin K-sufficient and vitamin K-supplemented rats. Rats given BHT (3000 mg/kg body weight) for up to 21 days, in a diet containing a minimum of 3 ppm vitamin K3 (six times the recommended requirement), showed decreased vitamin K-dependent blood clotting factor activities, demonstrated by increases in factor-specific clotting time assays. Clotting times were prolonged within 7 days, significantly increased within 14 days (P < 0.001) and maximally increased 5.5-fold at 21 days (P < 0.05). Supplementation with a further 250 ppm vitamin K3 reversed this effect. BHT did not increase prothrombin time (PT), the usual index of clotting. However, in a similar 14-day investigation, a small but significant increase in PT (up to 151%, P < 0.005) was seen within 7 days. Further vitamin K supplementation was incapable of reversing this effect completely. A similar trend was shown by activated partial thromboplastin time. The 1/51 dilution Thrombotest, a more sensitive indicator of vitamin K-dependent clotting factor activity in the rat, was significantly increased (more than four fold, P < 0.01) within 7 days. This increase was fully reversed by further vitamin K supplementation. Prolongation of Thrombotest time was significant at a BHT dose level of 600 mg/kg body weight per day and this could be reversed by further supplementation of only 3.0 ppm vitamin K. However, at dose levels of 125 mg BHT/kg body weight per day or less, no clotting defects were observed. These studies confirm that chronic administration of more than 600 mg BHT/kg/day to rats supplied with recommended amounts of vitamin K can depress clotting factors and precipitate haemorrhagic deaths. When further vitamin K is provided, these deaths could be prevented even though not all clotting abnormalities may be reversed. This study disapproves the proposal that BHT-related clotting factor defects are confined to rats of inadequate vitamin K status, but shows that such effects do not occur at dose levels lower than 600 mg/kg/day. The results further indicate that rats receiving a high dose of BHT have a higher vitamin K requirement than would otherwise be considered necessary. However, as BHT produces no clotting defects in these animals receiving an intake 1000 times the acceptable daily intake, such clotting effects are most unlikely to indicate a human safety problem for BHT.

[Toxicology of the synthetic antioxidants BHA and BHT in comparison with the natural antioxidant vitamin E]

The toxicology of the food preservatives butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT) as well as the naturally occurring vitamin E (alpha-tocopherol) is described. In high dosages all three compounds induce in animals impairment of blood clotting, which can be explained by an antagonism with vitamin K. Specific toxic effects to the lung have only been observed with BHT. The other described toxic effects of BHA and BHT are less characteristic and often occur only after high dosage and long-term treatment. However, BHA induces in animals tumours of the forestomach, which are dose dependent, whereas BHT induces liver tumours in long-term experiments. Because there is no indication of genotoxicity of BHA and BHT, all published findings agree with the fact that BHA and BHT are tumour promoters. In contrast to BHA and BHT, vitamin E is not carcinogenic. On the other hand, all three antioxidants have also anticarcinogenic properties. The intake of the necessary high doses as for these effects are, however, contraindicated with BHA and BHT because of their carcinogenic effects. The present overview concludes that the concentrations of BHA and BHT nowadays used in food, drugs and cosmetics are probably harmless. In addition, vitamin E can also be used in higher doses without the occurrence of adverse effects.

Biological and toxicological consequences of quinone methide formation

Quinone methides are a class of reactive, electrophilic compounds which are capable of alkylating cellular macromolecules. They are formed during xenobiotic biotransformation reactions and are hypothesized to mediate the toxicity of a large number of quinone antitumor drugs as well as several alkylphenols. In addition, oxidation of specific endogenous alkylphenols (e.g. coniferyl alcohol) and alkylcatechols (e.g. N-acetyldopamine, dopa) to quinone methides plays an important role in the synthesis of several complex plant and animal polymers, including lignin, cuticle and melanin. The role of quinone methides in these various processes is reviewed.

Some properties of rat platelet aggregation and effects of butylated hydroxytoluene, warfarin and aspirin

The platelet aggregation characteristics of male Sprague-Dawley (Jcl:SD) rats were investigated. Epinephrine, ristocetin, serotonin and platelet-activating factor were ineffective in rat platelets. Heparinized platelet-rich plasma (PRP) was more sensitive than citrated PRP to three aggregating agents, ADP, collagen and arachidonic acid. Butylated hydroxytoluene (BHT) and BHT quinone methide (2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone) inhibited ADP- and collagen-induced aggregation at concentrations over 10(-3) M in vitro. The ADP-, collagen- and arachidonic acid (0.5-2.0 mM)-induced aggregations of PRP obtained from rats given 1.20% BHT in the diet for 7 days were normal, while arachidonic acid (3.9 mM)-induced aggregation of PRP from BHT-fed rats was significantly lower than control. PRP from rats given aspirin and warfarin also aggregated normally with ADP or collagen addition. These results suggest that heparinized PRP may be preferable in platelet aggregation analyses in rats and reaffirmed that effects on platelet aggregation may not play a key role in BHT-induced bleeding. Platelet aggregation capacity also does not necessarily reduce in haemorrhages induced by aspirin or warfarin.

Gastric retention and delayed absorption of a large dose of butylated hydroxytoluene in the rat

1. After a single oral dose of 800 mg/kg of butylated hydroxytoluene to rats, the plasma concentration of 2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone (BHT quinone methide), an active metabolite of BHT, reached a maximum 18 h after dosing. 2. The gastrointestinal content of BHT remained constant from 0.5 to 12 h, and began to decline 18 h after dosing. 3. BHT concentrations in epididymal and subcutaneous adipose tissues also attained maxima 18 h after dosing. 4. Volumes and weights of stomachs and contents, and volumes of gastric contents of rats given 800 mg/kg BHT, were 2-3 times larger than those of controls 4-7 h after dosing while there were no significant differences at 24-27 h after dosing. 5. Retention of ingested material in the stomachs was also observed when 18-h starved rats were given 800 mg/kg BHT. 6. Thirty minutes after intraduodenal administration of 800 mg/kg BHT to anaesthetized rats. BHT, but not BHT quinone methide, was 0.4-1.4 micrograms/ml in portal vein plasma. No BHT was detected in plasma from the aorta descendens. BHT and/or BHT radical, and BHT alone, were also found in liver and epididymal adipose tissue at 7-20 and 25-40 micrograms/g wet weight, respectively. 7. These results indicate that delay in attainment of maximum concentration of BHT or its metabolites in internal organs may be due to the long retention in the stomach, caused by high dosage and the inhibitory effect of BHT on gastric function. Moreover, most BHT may not enter lymphatic fluid but it can be absorbed into portal blood.

Retinoid-induced hemorrhaging and bone toxicity in rats fed diets deficient in vitamin K

The recent increase in the clinical use of synthetic vitamin A compounds has led to concern of possible side effects. Some of these effects are known to be influenced by dietary levels of vitamin K. We therefore compared the toxic effects of 13-cis-retinoic acid (13cisRA), retinyl acetate (ROAc), and N-(4-hydroxyphenyl)retinamide (4HPR) in male Sprague-Dawley rats maintained on diets containing different levels of vitamin K. Animals were fed either an NIH-07 diet supplemented with menadione (3.1 ppm vitamin K3), an NIH-07 diet not supplemented with menadione, or an AIN-076 purified diet devoid of vitamin K. The retinoids had no effect on prothrombin times of animals fed the supplemented diet. When menadione was omitted from the diet, however, 4HPR-dosed animals had elevated prothrombin times. This effect was observed as early as Day 7 and was accompanied by one confirmed hemorrhagic death. 13cisRA-dosed animals showed no change in prothrombin times. In the high-dose ROAc group, there was a twofold increase in prothrombin times but only after prolonged dosing. In animals fed the NIH-07 diets, 13cisRA and ROAc induced multiple bone fractures at all dose levels. In contrast, 4HPR administered at the highest dose induced only one fracture in one animal. Animals fed the purified diet lost weight faster and diet sooner than those maintained on the other diets. Bone fractures were not observed in these animals because of early deaths resulting from hemorrhaging. For all retinoid-dosed groups maintained on the purified diet, changes in prothrombin times occured as early as 1 week. The order of effect was 4HPR greater than ROAc greater than 13cisRA, with increases in prothrombin times correlating with increases in hemorrhagic deaths. Hence, the degree of retinoid-induced hemorrhage, but not the incidence of bone fractures, was inversely related to vitamin K levels in the diet. 13cisRA and ROAc, but not 4HPR, caused a dose-dependent reduction in plasma osteocalcin, an effect that correlated with retinoid-induced bone effects. In contrast, serum alkaline phosphatase was elevated in animals dosed with 13cisRA or 4HPR but not in those dose with ROAc. For this enzyme, the electrophoretic pattern on agarose gel showed a decrease, compared to controls, in the major isozyme in serum of ROAc-dosed animals. Hence, plasma osteocalcin is a better predictor of retinoid-induced bone effects than serum alkaline phosphatase.

2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone (BHT quinone methide): an active metabolite of BHT causing haemorrhages in rats

Male Sprague-Dawley rats and male ICR mice, species respectively susceptible and resistant to the haemorrhagic effect of butylated hydroxytoluene (BHT), were administered BHT quinone methide (2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone) orally; 24 or 48 h later the plasma concentrations of blood coagulation factors II (prothrombin), VII, IX and X were determined. BHT quinone methide caused a decrease in factors II, VII, IX and X in a dose-dependent manner after 48 h, while a similar dose of BHT did not. Haemorrhages in epididymis or thymus were found in BHT quinone methide-treated rats. These findings may support the belief that BHT quinone methide is an active metabolite which disturbs the vitamin K redox cycle in BHT-induced haemorrhage.