Influence of gallic acid esters on drug-metabolizing enzymes of rat liver

Immunofluorescence evaluation of 4-hydroxynonenal and 8-hydroxy-2-deoxyguanosine activation in zebrafish (Daino rerio) larvae brain exposed (microinjected) to propyl gallate

Propyl gallate (PG) is a chemical compound obtained by esterification of propanol with gallic acid. Due to its antioxidative properties, it is widely used in cosmetics and pharmaceutical industries as well as to protect the oils in foods such as butter, milk-based desserts, chewing gum, mayonnaise, meat, soups, cereals, spices and seasonings from rancidity. This study has been designed to assessment 8-OHdG and 4-HNE activity, and histopathological changes in the brain tissues of zebrafish larvae, which is a lecithotrophic organism, after 96 h of PG exposure via microinjecting to yolk sac of embryo. To this end, approximately 5 nL of various concentrations of PG (1, 10, and 50 ppm) has been injected into yolk sac of fertilized embryo (final exposure concentrations are 5, 50, 250 pg/egg) with micro manipulator system. After 96 h exposure time, propyl gallate caused immunofluorescence positivity of 8-OHdG and 4-HNE in the brain tissues of zebrafish larvae. PG was not effect brain tissue histopathological in low concentrations (1 and 10 ppm) but highest concentration (50 ppm) caused degenerative changes in brain. These results suggests that PG treatment could lead oxidative DNA damage by causing an increase 8-OHdG and 4-HNE activities. This strategy will enable us to better understand the mechanisms of propyl gallate in brain tissues of zebrafish larvae.

Correlation of antimutagenic activity and suppression of CYP1A with the lipophilicity of alkyl gallates and other phenolic compounds

Alkyl gallates are widely used as food antioxidants. Methyl, ethyl, propyl, lauryl, and cetyl gallates showed antimutagenicity to activated 2-aminoanthracene (2AA)-induced SOS responses in Salmonella typhimurium TA1535/pSK1002. They also exhibited a suppressive effect on 3-methylcholanthrene (3-MC)-induced cytochrome P450 1A (CYP1A) in human hepatoma HepG2 cells, as indexed by the 7-ethoxyresorufin-O-deethylase (EROD) activity, and on CYP1A protein level. Both antimutagenicity and suppression of CYP1A appeared to be dependent on alkyl chain lengths, which suggested lipophilicity dependence. Based on those results, we investigated 26 other phenolic compounds for their lipophilicity, antimutagenicity and inhibition of EROD activity. The lipophilicity correlated well with the inhibition of EROD activity (r=0.78), and the inhibition of EROD activity correlated with the antimutagenicity of those compounds (r=0.71). The results suggest that the lipophilicity of the phenolic compounds may be an important factor in their ability to inhibit EROD activity.

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.

Generation of annexin V-positive platelets and shedding of microparticles with stimulus-dependent procoagulant activity during storage of platelets at 4 degrees C

BACKGROUND

The ability of propyl gallate to activate platelet factor 3 has been determined through the activated partial thromboplastin time, but its effect on phosphatidylserine has not been established.

STUDY DESIGN AND METHODS

A novel platelet activator, propyl gallate, was introduced to a study of platelets stored at 4 degrees C. The effects of storage on platelet coagulation activity, on phosphatidylserine, and on the shedding of activated and activable membrane particles (microparticles) were examined by activated plasma clotting time, and the effect on annexin V binding was examined by gated flow cytometry. The ratios of annexin V binding and microparticle shedding in stored platelet samples were compared with those in fresh platelets stimulated with propyl gallate.

RESULTS

Microparticle shedding by stored platelets compensated for the diminished procoagulant potential of intact platelets (shown as the total propyl gallate-dependent platelet factor 3 activity), which did not change during prolonged (20-day) storage, but levels of phosphatidylserine confined to microparticles increased dramatically as platelet counts fell. Both annexin V binding and microparticle shedding increased spontaneously with storage and artificially with propyl gallate stimulation. However, at the same level of annexin V binding, stored platelets shed more microparticles than did fresh platelets stimulated with propyl gallate.

CONCLUSION

Propyl gallate induces platelet procoagulant activity and annexin V binding. Stored platelets differ from fresh platelets in a lower reactivity to propyl gallate activation and a higher rate of microparticle shedding.

An analysis of the possibility for health implications of joint actions and interactions between food additives

The possibility that structurally unrelated food additives could show either joint actions or interactions has been assessed based on their potential to share common sites and mechanisms of action or common pathways of elimination. All food additives approved in the European Union and allocated numerical acceptable daily intake values were studied, initially based on the reports by the FAO-WHO Joint Expert Committee for Food Additives. Target organs were identified based on the effects reported at doses above the no-observed-adverse-effect level (NOAEL) in animal and human studies. The descriptions of the pathological and other changes reported were used to assess whether different additives, sharing the same target organ, would produce a common toxic effect. In all but a very few cases, the possibility of joint actions or interactions could be excluded on scientific grounds. The exceptions were on the liver (curcumin, thiabendazole, propyl gallate, and BHT), the kidney (diphenyl, o-phenylphenol, and ferrocyanide salts), the blood (azorubine and propyl gallate), and the thyroid (erythosine, thiabendazole, and nitrate). Toxicokinetic interactions were considered unlikely because of the low dosages involved, the diverse nature of the routes of metabolism and elimination, and the fact that enzyme induction or inhibition would have influenced selection of the NOAEL. Many of those additives which could not be excluded from showing joint actions or interactions would have low intakes; in some cases they were alternatives for the same application, thereby further lowering the combined intake. In consequence, joint actions or interactions between additives do not represent a significant health concern.

The application of in vitro data in the derivation of the acceptable daily intake of food additives

The acceptable daily intake (ADI) for food additives is commonly derived from the NOAEL (no-observed-adverse-effect level) in long-term animal in vivo studies. To derive an ADI a safety or uncertainty factor (commonly 100) is applied to the NOAEL in the most sensitive test species. The 100-fold safety factor is considered to be the product of both species and inter-individual differences in toxicokinetics and toxicodynamics. Although in vitro data have previously been considered during the risk assessment of food additives, they have generally had no direct influence on the calculation of ADI values. In this review 18 food additives are evaluated for the availability of in vitro toxicity data which might be used for the derivation of a specific data-derived uncertainty factor. For the majority of the food additives reviewed, additional in vitro tests have been conducted which supplement and support the short- and long-term in vivo toxicity studies. However, it was recognized that these in vitro studies could not be used in isolation to derive an ADI; only when sufficient in vivo mechanistic data are available can such information be used in a regulatory context. Additional short-term studies are proposed for the food additives which, if conducted, would provide data that could then be used for the calculation of data-derived uncertainty factors.

Effect of tannic acid on benzo[a]pyrene-DNA adduct formation in mouse epidermis: comparison with synthetic gallic acid esters

Tannic acid, a naturally occurring plant phenol, was shown to inhibit the mutagenicity and/or tumorigenicity of several polycyclic aromatic hydrocarbons in mouse skin. In this study the effect of topical application of tannic acid on epidermal aryl hydrocarbon hydroxylase, glutathione S-transferase, and binding of benzo[a]pyrene (B[a]P) to epidermal DNA was compared with the activity of synthetic gallic acid esters. Single topical application of 8 mumol octyl and dodecyl gallate had no effect on the induction of aryl hydrocarbon hydroxylase, whereas propyl gallate and tannic acid increased the enzyme activity by nearly 200%. Application of the phenolics one hour before 0.2 mumol of B[a]P enhanced the enzyme activity, but the observed differences were not significant in comparison with a B[a]P-treated group of mice. Application of dodecyl and octyl gallates to mouse skin resulted in three- and twofold increases, respectively, in the activity of glutathione S-transferase. Combined treatment with dodecyl gallate and B[a]P also resulted in significant enhancement of this enzyme activity. Application of the same dose of tannic acid to mouse skin one hour before the application of 0.2 or 1 mumol of B[a]P afforded 60% inhibition of covalent benzo[a]pyrene-diol-epoxide binding to epidermal DNA. Gallic acid esters with the exception of dodecyl gallate were less effective inhibitors of benzo[a]pyrene-diol-epoxide binding, especially when the higher dose of B[a]P was used. These results indicate that the antitumorigenic activity of tannic acid involves the interaction of the ultimate carcinogen with DNA rather than an altered metabolism. The linkage between gallic acid and glucose in natural plant phenols is also more effective at inhibiting B[a]P binding to epidermal DNA than the linkage with the alkyl group in synthetic gallates.

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.

Enhancement and inhibition of benzo[a]pyrene-induced SOS function in E. coli by synthetic antioxidants

8 antioxidants were tested in the SOS chromotest for induction of SOS function and for modulation of benzo[a]pyrene-induced SOS function. None of the antioxidants leads to increased beta-galactosidase activity by itself. Butylated hydroxytoluene at concentrations between 10(-5) M and 3 X 10(-4) M enhances benzo[a]pyrene-induced SOS function at benzo[a]pyrene concentrations between 10(-6) M and 3 X 10(-5) M. Butylated hydroxyanisole, ethoxyquin, propyl gallate and octyl gallate also slightly enhance benzo[a]pyrene-induced SOS function at concentrations up to 3 X 10(-4) M though to a lesser degree than butylated hydroxytoluene. Dodecyl gallate, vitamin C and alpha-tocopherol do not increase benzo[a]pyrene action. In concentrations exceeding 3 X 10(-4) M all synthetic antioxidants tested but not vitamin C and alpha-tocopherol decrease beta-galactosidase activity both in the absence and, more extensively, in the presence of benzo[a]pyrene. Preliminary data suggest that the apparent suppression of benzo[a]pyrene-induced SOS function is not due to an effect on the formation of benzo[a]pyrene metabolites by the metabolizing system used.

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.

Interaction of Clostridium difficile toxins and mouse hepatic microsomes

Intraperitoneal administration of toxins of Clostridium difficile to mice resulted in loss of hepatic cytochrome P450 and peroxidation of microsomal lipids. Pretreatment with the microsomal enzyme inducer beta-naphthoflavone partially alleviated these effects and increased survival time of intoxicated animals.