Carcinogenesis Bioassay of Propyl Gallate in F344 Rats and B6C3FJ Mice

Safety and efficacy of propyl gallate for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of propyl gallate as feed additive for all animal species. Propyl gallate is neither genotoxic nor carcinogenic. Propyl gallate a is safe for veal calves, cattle for fattening, dairy cows, sheep, goats, sows, horses and salmonids at the proposed maximum use level of 40 mg/kg and for ornamental fish at the proposed maximum use level of 100 mg/kg. The following concentrations (mg/kg complete feed) are considered safe for the other target species: 15 for chickens for fattening; 20 for turkeys for fattening, laying hens and rabbits; 27 for piglets and pigs for fattening and 71 for dogs. The Panel cannot conclude on a safe level for cats. The exposure of the consumer to propyl gallate and its metabolites cannot be estimated owing to the absence of reliable data on residues of propyl gallate and its metabolites in edible tissues and products. Therefore, the FEEDAP Panel is not in the position to conclude on the safety for the consumer of propyl gallate, when used as a feed additive for all food-producing animal species. Propyl gallate is irritant to skin and eyes and a dermal sensitiser. Exposure via inhalation is possible and it is considered a hazard. The use of the additive in animal nutrition does not pose a risk for the environment. The FEEDAP Panel concludes that propyl gallate has the potential to act as an antioxidant in feedingstuffs. The Panel did not see a reason for the use of propyl gallate as an antioxidant in water for drinking.

Monoclonal antibody-directed analysis of benzo[a]pyrene metabolism in rat liver and extrahepatic tissues: effect of propyl and octyl gallate

Monoclonal antibody (MAb) 1-7-1 against 3-methylcholanthrene (MC)-induced forms of cytochrome P-450 (CYP) was used to characterize benzo[a]pyrene (B[a]P) metabolism in rat liver and extrahepatic tissues and its modulation by phenolic antioxidants, propyl and octyl gallates. Male Wistar rats were treated with these food additives (50 mg/kg body wt i.p.) twice weekly for 14 days alone or in combination with MC. Immunochemical inhibition of aryl hydrocarbon hydroxylase (AHH) and [14C]B[a]P metabolism (analyzed by high-performance liquid chromatography) were measured in liver, kidney, and lung microsomes. Organ-specific changes in levels of MAb-mediated inhibition of microsomal metabolism of B[a]P were observed. In liver microsomes from untreated rats, AHH was not affected by MAb, but in kidney and lung, there was 70% and 50% inhibition, respectively. In MC-treated rats, MAb reduced AHH activity by 43% in liver. Kidney and lung AHH was inhibited up to 80% by this MAb. Formation of B[a]P metabolites in MC-induced microsomes from liver and kidney was affected by MAb in a similar way. In lung, the total metabolism was inhibited by 50% by MAb treatment, but significant differences in inhibition of individual metabolites were observed. Treatment with propyl or octyl gallate alone had no effect on MAb inhibition of AHH activity in liver and lung but decreased the level of inhibition in kidney. Combined treatment with MC and propyl or octyl gallate slightly reduced the effect of MAb on AHH activity in liver and significantly reduced the level of inhibition in kidney but did not affect AHH activity in lung. The same treatment regimen dramatically reduced MAb inhibition of B[a]P metabolism in kidney but had no effect on B[a]P metabolite formation in liver. Inhibition by MAb of renal 3-hydroxy-B[a]P, 7,8-B[a]P-dihydrodiol, and 1,6-quinone-B[a]P was the most affected. In lung, treatment with gallates affected only formation of 7,8-B[a]P-dihydrodiol. These results suggest that treatment with gallates affects the CYP 1A and may change the CYP isozyme composition and, thus, alter the tissues' susceptibility to tumor induction by B[a]P.

Relationship between mitochondrial dysfunction and toxicity of propyl gallate in isolated rat hepatocytes

The relationship between cytotoxicity and mitochondrial dysfunction caused by propyl gallate (PG) has been studied in hepatocytes freshly prepared from fasted rats. Hepatocytes isolated from fasted (18 h) rats were significantly more susceptible to the toxicity of PG than hepatocytes from fed rats. The addition of fructose (15 mM), an alternative carbohydrate source, to hepatocyte suspensions resulted in the prevention of PG (1 mM)-induced cell killing accompanied by decrease in intracellular ATP loss during a 3 h-incubation period. Despite this, fructose did not completely prevent an abrupt loss of intracellular glutathione caused by PG, but effectively inhibited the loss of protein thiol levels. Fructose elicited a concentration (0.5-20mM)-dependent protection against the cytotoxicity of 1.5 mM PG. The incubation of hepatocytes with sodium azide (4 mM), an inhibitor of oxidative phosphorylation, enhanced the toxicity induced by PG (1 mM), but coincubation with fructose delayed the onset of toxicity. Neither azide alone nor fructose plus azide did affect the cell viability during the incubation period. Furthermore, the addition of 2 mM salicylamide, nontoxic to hepatocytes during the incubation period, enhanced PG (1 mM)-induced cytotoxicity and decreased the loss of free PG. These results indicate that the onset of cytotoxicity caused by PG may depend on the intracellular energy status and that mitochondria are critical target for the compound. In addition, the toxicity caused by the inhibition of mitochondrial ATP synthesis is related to the concentration of PG remaining in cell suspensions.

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.

Antioxidants--carcinogenic and chemopreventive properties

Synthetic and naturally occurring antioxidants have a wide variety of biological actions in rodents in addition to their primary antioxidant activity. Some of the included biological effects are of direct interest in relation to studies of carcinogenicity and/or modulation of carcinogenesis. Since the synthetic antioxidant BHA was first found to exert carcinogenic potential in rat and hamster forestomach epithelium, many other synthetic and naturally occurring antioxidants have been examined for their ability to induce proliferative activity in the alimentary canal. These studies have revealed that caffeic acid and sesamol are also tumorigenic for rat forestomach epithelium, whereas catechol and p-methylcatechol induce neoplasia in rat glandular stomach epithelium. Although the proliferative response is very rapid, with inflammation and ulceration, it takes a very long time before carcinomas develop. The proliferative lesions in the forestomach induced by BHA or caffeic acid are largely reversible, in contrast to those induced by genotoxic carcinogens, which generally persist and develop into cancer. Therefore, chronic irritation is considered to be responsible for the induction of stomach cancer by antioxidants. Butylated hydroxyanisole can undergo oxidative metabolism in vitro, and some of the metabolites formed have the potential for binding to proteins. Neither BHA nor its metabolites binds to DNA in vivo, but protein binding in the forestomach was greater than 10 times higher than that in the glandular stomach. It is thus conceivable that BHA is oxidatively metabolized in the forestomach epithelium (possibly entering into redox cycling), and reactive metabolites including semiquinone radicals or active oxygen species are responsible for the carcinogenesis by a mechanism involving binding to macromolecules. Many antioxidants have been shown to modify carcinogenesis, and as a rule, they inhibit the initiation stage by reducing the interaction between carcinogen and DNA. However, both promotion and inhibition have been reported for second-stage carcinogenesis, depending on the organ site, species of animal, or initiating carcinogen. They can also block reaction of amine and nitrite to form nitrosamines or reduce TPA promotion of skin carcinogenesis. Generally high doses of antioxidants are required for carcinoma induction or modification of chemical carcinogenesis. The significance of the reported tumorigenicity and strong promoting activity of antioxidants for forestomach epithelium of animals to the development of human cancer appears limited mainly because humans do not have a forestomach. The carcinogenic and strong promoting activities of catechol and its structurally related compounds on rat glandular stomach epithelium are of greater concern because this tissue is directly analogous to human gastric epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicology of gallates: a review and evaluation

The propyl, octyl and dodecyl esters of gallic acid have been studied extensively in a large number of animal experiments involving oral dosing. Experimental data on general toxicity and studies on reproduction, teratogenicity and mutagenicity are also available. Most of the key toxicity studies, however, date back to the 1950s, do not meet current standards of toxicity testing and do not provide evidence for carcinogenic or mutagenic action of the gallates. Mutagenicity studies with octyl gallate and dodecyl gallate are lacking. The biokinetics of propyl gallate apparently differ from those of octyl and dodecyl gallate, the octyl and dodecyl esters being absorbed and hydrolysed to a lesser degree than the propyl ester. In toxicity studies with propyl gallate, growth retardation, anaemia, kidney and liver changes and hyperplasia of the forestomach were the most prominent effects at dose levels above 10,000 mg/kg feed. At 5000 mg/kg feed, liver enzyme induction was seen. In the available studies with octyl gallate or dodecyl gallate as the test compound, effects were found at 3000 mg/kg feed or higher levels. In studies performed with the various gallates, no effects were observed at a dose level of 1000 mg/kg feed, a level that was adopted as the no-effect level by the FAO/WHO Joint Expert Committee on Food Additives (JECFA) in 1976. This committee established an acceptable daily intake (ADI) for man of 0.2 mg/kg body weight (as a sum of propyl, octyl and dodecyl gallates). A re-evaluation of the toxicity of gallates indicates that a 'classic' long-term toxicity study of propyl gallate meeting current standards is required. As yet, the available toxicological evidence indicates that gallates may be used safely as antioxidants.

No evidence of carcinogenicity of D-mannitol and propyl gallate in F344 rats or B6C3F1 mice

Chronic toxicity and carcinogenicity studies were conducted on D-mannitol and propyl gallate in F344 rats and B6C3F1 mice. Groups of 50 rats and 50 mice of each sex were maintained on diets containing either 0, 2.5 or 5.0% D-mannitol or 0, 0.6 or 1.2% propyl gallate for 103 wk. D-Mannitol had no effect on survival or mean body weight of rats and mice, and feed consumption was approximately the same in control and treated groups in each species. Gastric fundal gland dilation occurred at a higher incidence in treated female rats than in controls. A mild nephrosis characterized by focal vacuolization of the renal tubular epithelium was observed in an increased incidence in treated mice. No significant increase in tumour incidence was observed in any of the treated groups in comparison with the corresponding controls. Survival of rats and mice given propyl gallate was similar to that of the controls. Mean body weights were lower in chemically exposed animals, and more so for females. Male rats exposed to propyl gallate showed an increased incidence of hepatic cytoplasmic vacuolization and suppurative inflammation of the prostate gland. Tumours of the preputial gland, islet-cell tumours of the pancreas, and phaeochromocytoma of the adrenal gland occurred at a significantly (P less than 0.05) higher incidence in the low-dose male rats. Malignant lymphoma occurred with a positive trend in male mice (control 1/50, low dose 3/49 and high dose 8/50), and the incidence in the high-dose group was significantly (P less than 0.05) higher than in the control group. However, since the incidence in the control group was much less than the historical control rate (36/398 or 9%) in this laboratory, this apparent increase was not considered to be related to propyl gallate administration. Under the conditions of these studies, neither D-mannitol nor propyl gallate was considered to be carcinogenic to F344 rats or B6C3F1 mice of either sex.

Synthetic antioxidants: biochemical actions and interference with radiation, toxic compounds, chemical mutagens and chemical carcinogens

Biological actions of 4 commonly used synthetic antioxidants--butylated hydroxyanisole, butylated hydroxytoluene, ethoxyquin and propyl gallate--on the molecular, cellular and organ level are complied. Such actions may be divided into modulation of growth, macromolecule synthesis and differentiation, modulation of immune response, interference with oxygen activation and miscellaneous. Moreover, an overview of beneficial and adverse interactions of these antioxidants with exogenous noxae is given. Beneficial interactions include radioprotection, protection against acute toxicity of chemicals, antimutagenic activity and antitumorigenic action. Possible mechanisms of the antitumorigenic action of antioxidants are discussed. This discussion is centered around antioxidant properties which may contribute to a modulation of initiation-related events, especially their ability to interfere with carcinogen metabolism. The beneficial interactions of antioxidants with physical and chemical noxae are contrasted to those leading to unfavorable effects. These include radiosensitization, increased toxicity of other chemicals, increased mutagen activity and increased tumor yield from chemical carcinogens. At present, the latter one can most adequately be characterized as tumor promotion at least in the case of butylated hydroxytoluene. It is concluded that current information is insufficient to promote expectations as to the use of antioxidants in the prevention of human cancer.