Cytotoxicity of propyl gallate and related compounds in rat hepatocytes

Structural Elucidation of Novel Stable and Reactive Metabolites of Green Tea Catechins and Alkyl Gallates by LC-MS/MS

Synthetic gallic acid derivatives are employed as additives in food, personal care products, and pharmaceutical formulations. Despite their widespread use, little is known about their human exposure, health effects, and metabolism. Green tea catechins are natural antioxidants, known for their health-promoting properties, and are also employed as food additives or in personal care products. The objective of this study was to establish metabolic pathways involved in the biotransformation of green tea catechins and synthetic gallate esters. Liquid chromatography coupled with high-resolution tandem mass spectrometry (LC-HRMS/MS) was used to elucidate oxidative and methylated metabolites, in addition to glutathione conjugates, formed in vitro using human liver microsomal incubations. The developed method was applied to 14 different parent compounds with a wide range of polarities, for the structural elucidation of many known and novel metabolites. These results serve to inform about the wide variety of possible metabolites formed upon exposure to these compounds.

The Anti-Apoptotic Effects of Caspase Inhibitors in Propyl Gallate-Treated Lung Cancer Cells Are Related to Changes in Reactive Oxygen Species and Glutathione Levels

Propyl gallate [3,4,5-trihydroxybenzoic acid propyl ester; PG] exhibits an anti-growth effect in various cells. In this study, the anti-apoptotic effects of various caspase inhibitors were evaluated in PG-treated Calu-6 and A549 lung cancer cells in relation to reactive oxygen species (ROS) and glutathione (GSH) levels. Treatment with 800 μM PG inhibited the proliferation and induced the cell death of both Calu-6 and A549 cells at 24 h. Each inhibitor of pan-caspase, caspase-3, caspase-8, and caspase-9 reduced the number of dead and sub-G1 cells in both PG-treated cells at 24 h. PG increased ROS levels, including O₂^∙−, in both lung cancer cell lines at 24 h. Generally, caspase inhibitors appeared to decrease ROS levels in PG-treated lung cancer cells at 24 h and somewhat reduced O₂^∙− levels. PG augmented the number of GSH-depleted Calu-6 and A549 cells at 24 h. Caspase inhibitors did not affect the level of GSH depletion in PG-treated A549 cells but differently and partially altered the depletion level in PG-treated Calu-6 cells. In conclusion, PG exhibits an anti-proliferative effect in Calu-6 and A549 lung cancer cells and induced their cell death. PG-induced lung cancer death was accompanied by increases in ROS levels and GSH depletion. Therefore, the anti-apoptotic effects of caspase inhibitors were, at least in part, related to changes in ROS and GSH levels.

Plant-inspired Pluronic-gallol micelles with low critical micelle concentration, high colloidal stability, and protein affinity

Polymeric micelles are the most common carriers used for hydrophobic drug delivery. However, they are vulnerable to physiological barriers, such as temperature changes and enzymatic degradation, and can be easily disassembled upon dilution below the critical micelle concentration (CMC) by body fluids after an intravenous injection. Here, we report that Pluronic® micelles with octyl gallate, which is a surfactant containing gallol moieties widely found in antioxidative plant polyphenols, have a low CMC, which improves their colloidal stability without the need for covalent crosslinking. Furthermore, the incorporated gallol moieties provide enzymatic degradation resistance to the micelles owing to their protein affinity, maintaining the hydrophobic cavity of unmodified Pluronic®. Thus, plant-inspired polymeric micelles with low CMC and bioavailability are promising multifunctional vehicles for drug delivery.

Propyl gallate decreases the proliferation of Calu-6 and A549 lung cancer cells via affecting reactive oxygen species and glutathione levels

Propyl gallate (3,4,5-trihydroxybenzoic acid propyl ester, PG) has an anti-proliferative effect in various cells. In this study, Calu-6 and A549 lung cancer cells were used to examine the anti-proliferative effect of PG in relation to reactive oxygen species (ROS) and glutathione (GSH) levels. PG (100-1,600 μM) dose-dependently inhibited the proliferation of Calu-6 and A549 cells at 24 h, and PG at 800-1,600 μM strongly induced cell death in both cell lines. PG (800-1,600 μM) increased cellular metabolism in Calu-6 but not A549 cells at 4 h. PG either increased or decreased ROS levels, including O₂ ˙^- and ˙OH, depending on the incubation doses and times of 1 or 24 h. Even these effects differed between Calu-6 and A549 cell types. PG reduced the activity of superoxide dismutase (SOD) in Calu-6 cells, and it augmented the activity of catalase in A549 cells. PG dose-dependently increased the number of GSH depleted cells in both Calu-6 and A549 cells at 24 h. In addition, PG decreased GSH levels in both lung cancer cells at 1 h. Furthermore, diethyldithiocarbamate (DDC; an inhibitor of SOD) and 3-amino-1,2,4-triazole (AT; an inhibitor of catalase) differently affected cellular metabolism, ROS and GSH levels in PG-treated and PG-untreated Calu-6 and A549 cells at 1 h. In conclusion, PG dose-dependently decreased the proliferation of Calu-6 and A549 lung cancer cells, which was related to changes in ROS levels and the depletion of GSH.

Synthesis of new 7-amino-3,4-dihydroquinolin-2(1H)-one-peptide derivatives and their carbonic anhydrase enzyme inhibition, antioxidant, and cytotoxic activities

Six new monopeptides, seven new dipeptides, and two deprotected monopeptide dihydroquinolinone conjugates were prepared by the benzothiazole-mediated method and their structures were confirmed by nuclear magnetic resonance, mass, infrared spectroscopy, and elemental analysis methods. The human carbonic anhydrase (hCA) I and hCA II enzyme inhibition activities of the compounds were determined using the stopped-flow instrument. The synthesized peptide-dihydroquinolinone conjugates 2, 3, 6, 10, 13, and 15 showed inhibition against the hCA II enzyme in the range of 15.7-65.7 µM. However, none of the compounds showed inhibition of hCA I at a concentration of 100 µM. The antioxidant activities of the compounds were also examined using the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging method at concentrations of 12.5-125 µg/ml, but when compared with the standard antioxidant compounds α-tocopherol and butylated hydroxyanisole (BHA), weak antioxidant activities were detected. The cytotoxic effects of four compounds against the A549 and BEAS-2B cell lines were also investigated. Among the compounds studied, compound 7 was found to be most effective, with the IC₅₀ values on the A549 cells for 48 and 72 h being 26.87 and 9.979 µg/ml, respectively, and the IC₅₀ values on the BEAS-2B cells being >100 µg/ml. None of the tested compounds showed antimicrobial activity in the concentration range (800-1.56 µg/ml) studied.

Synthetic Phenolic Antioxidants: A Review of Environmental Occurrence, Fate, Human Exposure, and Toxicity

Synthetic phenolic antioxidants (SPAs) are widely used in various industrial and commercial products to retard oxidative reactions and lengthen product shelf life. In recent years, numerous studies have been conducted on the environmental occurrence, human exposure, and toxicity of SPAs. Here, we summarize the current understanding of these issues and provide recommendations for future research directions. SPAs have been detected in various environmental matrices including indoor dust, outdoor air particulates, sea sediment, and river water. Recent studies have also observed the occurrence of SPAs, such as 2,6-di-tert-butyl-4-methylphenol (BHT) and 2,4-di-tert-butyl-phenol (DBP), in humans (fat tissues, serum, urine, breast milk, and fingernails). In addition to these parent compounds, some transformation products have also been detected both in the environment and in humans. Human exposure pathways include food intake, dust ingestion, and use of personal care products. For breastfeeding infants, breast milk may be an important exposure pathway. Toxicity studies suggest some SPAs may cause hepatic toxicity, have endocrine disrupting effects, or even be carcinogenic. The toxicity effects of some transformation products are likely worse than those of the parent compound. For example, 2,6-di-tert-butyl-p-benzoquinone (BHT-Q) can cause DNA damage at low concentrations. Future studies should investigate the contamination and environmental behaviors of novel high molecular weight SPAs, toxicity effects of coexposure to several SPAs, and toxicity effects on infants. Future studies should also develop novel SPAs with low toxicity and low migration ability, decreasing the potential for environmental pollution.

Evaluation of the genotoxic, DNA-protective and antioxidant profile of synthetic alkyl gallates and gallotannins using in vitro assays

New gallotanins, methyl 2,3,4,6-tetra-O-galloyl-α-D-glucoside (G₄Glc), methyl 2,3,4,6-tetra-O-galloyl-α-D-mannoside (G₄Man), and methyl 2,3,4-tri-O-galloyl-α-L-rhamnoside (G₃Rham), have been synthesized in order to study the protective effects of synthetic polyphenols that are structurally related with natural compounds. Apart from spectral analysis, examination of antioxidant ability and protective efficiency showed the differences among newly prepared compounds and commercial antioxidants - gallic acid (GA), methyl gallate (MG), and octyl gallate (OG) applying radical scavenging 1,1-diphenyl-2-picryl-hydrazyl (DPPH), reducing power and iron-chelating assays. The genotoxicity and DNA-protective potential of tested compounds on human peripheral blood mononuclear cells (PBMCs) were evaluated using the single-cell gel electrophoresis (comet assay) and DNA-topology assay. Experimental data revealed that gallotannins G₃Rham, G₄Man, and G₄Glc possess significant radical scavenging/antioxidant activities and manifest very low genotoxic effect on human PBMCs. Moreover, tested compounds considerably reduce the level of DNA damage induced by hydrogen peroxide or Fe²⁺-ions. The results imply that new synthetic gallotannins can be considered as nontoxic agents for subsequent design of new antioxidants with potential biomedical applications.

A Review on Ethnopharmacological Applications, Pharmacological Activities, and Bioactive Compounds of Mangifera indica (Mango)

Mangifera indica (family Anacardiaceae), commonly known as mango, is a pharmacologically, ethnomedically, and phytochemically diverse plant. Various parts of M. indica tree have been used in traditional medicine for the treatment of different ailments, and a number of bioactive phytochemical constituents of M. indica have been reported, namely, polyphenols, terpenes, sterols, carotenoids, vitamins, and amino acids, and so forth. Several studies have proven the pharmacological potential of different parts of mango trees such as leaves, bark, fruit peel and flesh, roots, and flowers as anticancer, anti-inflammatory, antidiabetic, antioxidant, antibacterial, antifungal, anthelmintic, gastroprotective, hepatoprotective, immunomodulatory, antiplasmodial, and antihyperlipemic. In the present review, a comprehensive study on ethnopharmacological applications, pharmacological activities, and bioactive compounds of M. indica has been described.

Octyl gallate reduces ATP levels and Ki67 expression leading HepG2 cells to cell cycle arrest and mitochondria-mediated apoptosis

Octyl gallate (OG) is an antioxidant that has shown anti-tumor, anti-diabetic and anti-amyloidogenic activities. Mitochondria play an important role in hepatocellular carcinoma, mainly by maintaining accelerated cellular proliferation through the production of ATP. Thus, the mitochondria may be a target for antitumor therapies. Here, we investigated the effects of OG in the hepatocarcinoma cell line (HepG2) and the mechanisms involved. We report, for the first time, that treatment with OG for 24h inhibited HepG2 cell growth by decreasing mitochondrial activity and mass, which led to the reduction of ATP levels. This reduction in the energy supply triggered a decrease in Ki67 protein expression, leading cells to cycle arrest. In addition, treatment with two doses of OG for 48h induced loss of mitochondrial functionality, mitochondrial swelling and apoptosis. Finally, we report that HepG2 cells had no resistance to treatment after multiple doses. Collectively, our findings indicate that metabolic dysregulation and Ki67 protein reduction are key events in the initial anti-proliferative action of OG, whereas mitochondrial swelling and apoptosis induction are involved in the action mechanism of OG after prolonged exposure. This suggests that OG targets mitochondria, thus representing a candidate for further research on therapies for hepatocarcinoma.

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.

Therapeutic effect of umbelliferon-α-D-glucopyranosyl-(2(I)→1(II))-α-D-glucopyranoside on adjuvant-induced arthritic rats

The aim and objective of the present investigation was to evaluate the antiarthritic and antioxidant effect of umbelliferon-α-D-glucopyranosyl-(2I→1II)-α-D-glucopyranoside (UFD) in chemically induced arthritic rats. The different doses of the UFD were tested against the turpentine oil (TO), formaldehyde induced acute arthritis and complete fruend's adjuvant (CFA) induced chronic arthritis in Wistar rats. Arthritic assessment and body weight was measured at regular interval till 28 days. On day 28, all the groups animals were anaesthetized, blood were collected from the puncturing the ratro orbital and estimated the hematological parameters. The animals were sacrificed; synovial tissue was extracted and estimated the malonaldehyde (MDA), glutathione (GSH), glutathione peroxidase (GPx) and superoxide dismutase (SOD). The different doses of the UFD showed the protective effect against turpentine oil, formaldehyde induced acute arthritis and CFA induced chronic arthritis at dose dependent manner. Acute model of arthritis such as TOand formaldehyde induced inflammation due to releasing of the inflammatory mediators; significantly inhibited by the UFD at dose dependent manner. CFA induced arthritic rats treated with the different doses of the UFD showed the inhibitory effect on the delayed increase in joint diameter as seen in arthritic control group rats. UFD significantly improved the arthritic index, body weight and confirmed the antiarthritic effect. UFD showed the effect on the hematological parameter such as improved the level of the RBC, Hb and decline the level of the EBC, ESR and confirmed the immune suppressive effect. UFD significantly improved the level of the endogenous antioxidant and confirmed the antioxidant effect. This present investigation suggests that the UFD has prominent antiarthritic impact which can be endorsed to its antiarthritic and antioxidant effects.

The enhancement of propyl gallate-induced HeLa cell death by MAPK inhibitors is accompanied by increasing ROS levels

Propyl gallate (PG) as a synthetic antioxidant exerts a variety of effects on tissue and cell functions. Here, we investigated the effects of MAPK (MEK, JNK and p38) inhibitors on PG-treated HeLa cells in relation to cell death, ROS and GSH levels. PG induced cell growth inhibition and apoptosis in HeLa cells, which was accompanied by the loss of mitochondrial membrane potential (MMP; ΔΨm). ROS levels were increased or decreased in PG-treated HeLa cells depending on the incubation times. PG also increased GSH depleted cell numbers in HeLa cells. All the MAPK inhibitors slightly enhanced cell growth inhibition, death and MMP (ΔΨm) loss, and increased ROS levels in PG-treated HeLa cells. However, MAPK inhibitors did not significantly affect GSH depletion in PG-treated cells. In conclusion, the enhanced effect of MAPK inhibitors on PG-induced HeLa cell death was accompanied by increasing ROS levels but the effect was not related to changes of GSH level.

Propyl gallate inhibits the growth of calf pulmonary arterial endothelial cells via glutathione depletion

Propyl gallate (PG) as a synthetic antioxidant exerts a variety of effects on tissue and cell functions. Here, we evaluated the effects of PG on the growth and death of endothelial cells (ECs), especially calf pulmonary artery endothelial cells (CPAEC) in relation to reactive oxygen species (ROS) and glutathione (GSH). PG dose-dependently inhibited the growth of CPAEC and human umbilical vein endothelial cells (HUVEC) at 24h. PG induced cell death in CPAEC, which was accompanied by the loss of mitochondrial membrane potential (MMP; DeltaPsi(m)). PG generally increased ROS level in CPAEC but not in HUVEC. PG also dose-dependently increased GSH depleted cells in both ECs. The treatment with antioxidant of N-acetyl-cysteine (NAC) or ascorbate acid (AA) prevented CPAEC growth inhibition and death by PG, which was accompanied by the attenuation of GSH depletion but not by the reduction of ROS level. In conclusion, PG induced growth inhibition and death of ECs, especially CPAEC via GSH depletion.

Rubus sanctus protects against carbon tetrachloride-induced toxicity in rat isolated hepatocytes: isolation and characterization of its galloylated flavonoids

Objectives

Rubus sanctus Schreb., known from the Bible as ‘holy thorn bush’, grows wild in Egypt. Rubus sanctus aqueous alcoholic extract (RE) contains a complicated phenolic mixture (ellagitanins, flavonoids and caffeic acid derivatives). In this study, the phytochemical investigation of the plant was re-evaluated. Herein, we report on the isolation and identification of three galloylated flavonoids, namely kaempferol-3-O-(6″-O-galloyl)-4C1-β-d-galactopyranoside, quercetin-3-O-(6″-O-galloyl)-4C1-β-d-galactopyranoside and myricetin-3-O-(6″-O-galloyl)- C1-β-d-galactopyranoside for the first time from the Rubus genus. We further aimed at evaluating the potential protective effects of RE against carbon tetrachloride (CCl4)-induced toxicity in isolated rat hepatocytes.

Methods

Based on an initial concentration-response experiment, a concentration of 100 μg/ml was selected to investigate the hepatoprotective activity of RE.

Key findings

Pretreatment with RE afforded protection as indicated by counteracting CCl4-induced cell death, and reduced glutathione depletion. In addition, RE ameliorated CCl4-induced enzyme leakage by 40% for lactate dehydrogenase, 30% for alanine aminotransferase and 20% for aspartate aminotransferase as compared with CCl4-treated cells. Moreover, RE counteracted CCl4-induced lipid peroxidation and inhibited spontaneous lipid peroxidation in the control group.

Conclusions

In conclusion, RE protects against CCl4-induced toxicity in isolated rat hepatocytes.

Toxicology and safety of COMT inhibitors

The development of catechol-O-methyltransferase (COMT) inhibitors for the adjunct treatment to levodopa and aromatic L-amino acid decarboxylase (AADC) inhibitors in Parkinson's disease started in the late 1950s. The first-generation inhibitors were associated with toxic properties: they induced convulsions, or they were toxic to the liver. None of them was taken into clinical use. The second-generation inhibitors entacapone and tolcapone have now been in clinical use for over a decade, and some new inhibitors are under development. The main adverse events in the use of entacapone and tolcapone are dopaminergic and dependent of the concomitant use of levodopa, but the symptoms are generally moderate or mild. Among the non-dopaminergic adverse events, diarrhea is the most prominent one induced by both entacapone and tolcapone. In clinical use, entacapone has been safe, but tolcapone is under strict regulations on liver enzyme monitoring, since in the early years, a few hepatotoxicity cases appeared, three of them with fatal outcome. The mechanism behind tolcapone-induced liver toxicity has been evaluated both in vitro and in vivo, but no clear answer exists at the moment. In the regulatory animal studies, both inhibitors have been safe with no reported toxicity. Also nebicapone, the latest of the second-generation inhibitors in clinical trials has shown some liver enzyme elevations in human subjects. New inhibitors with a structure differing from nitrocatechols are under development. No safety concerns have been reported connected to COMT inhibiton as such. COMT knockout mice are fertile without any pathologies due to the total COMT inhibition.

Induction of morphological changes in Ustilago maydis cells by octyl gallate

The effects of octyl gallate on Ustilago maydis yeast cells were analysed in relation to its capacity to oxidize compounds (pro-oxidant actions). All phenolic compounds tested inhibited the alternative oxidase (AOX). However, only octyl gallate induced a morphological change in yeast cells and collapsed the mitochondrial membrane potential. In contrast to octyl gallate, propyl gallate and nordihydroguaiaretic acid caused only a negligible cell change and the membrane potential was not affected. Our findings show that structurally related phenolic compounds do not necessarily exert similar actions on target cells. Preincubation of U. maydis cells with trolox inhibited the change to pseudohyphal growth produced by octyl gallate. These results suggest that in addition to the inhibitory action of octyl gallate on the AOX, this compound induces a switch from yeast to a mycelium, probably through the formation of lipid peroxides.

Safety evaluation of water extracts of Toona sinensis Roemor leaf

The purposes of this study were to evaluate the safety of water extracts of Toona sinensis Roemor leaf (TSL-1). The mutagenic properties of TSL-1 was investigated using the Ames test, and no mutagenicity was found toward all tester strains (Salmonella typhimurium TA98, TA100, TA102 and TA1535). In the acute oral toxicity study, a single limit dose of 5000 mgTSL-1/kg bw was given to male and female ICR mice, then observed for a 14-day period. In the subacute study, TSL-1 was administered as oral daily dose of 1000 mg/kg bw/day for 28 days. The results showed no acute lethal effect at a maximal tested dose of 5000 mg/kg bw TSL-1 in male and female mice. The subacute toxicity showed the oral administration of 1000 mg/kg bw for consecutive 28 days was safe in male mice. TSL-1 treated female mice showed decreases of food intake and kidney relative weight in acute oral toxicity test, and decreases of body weight gain, food intake and lung relative weight in subacute toxicity trial. However, no remarked toxic effects were found in the biochemical and histopathological parameters of TSL-1 treated female mice. These effects whether related to the major components or other ingredients in TSL-1 need to elucidate in the further studies.

Comparative cytotoxicity of alkyl gallates on mouse tumor cell lines and isolated rat hepatocytes

Alkyl esters of gallic acid inhibited the respiration rate of mouse sarcoma 786A and mouse mammary adenocarcinoma TA3 cell lines and its multiresistant variant TA3-MTX-R more effectively than gallic acid, both in the absence and in the presence of the uncoupler CCCP. The order of inhibition of the respiration rate by gallates in intact cells was n-octyl- approximately iso-amyl- approximately n-amyl- approximately iso-butyl->n-butyl->iso-propyl->n-propyl-gallate>>gallic acid. Sarcoma 786A was significantly more susceptible to all seven esters than the TA3 cell line. Respiration rates of the TA3-MTX-R cell line showed almost the same sensitivity to these esters as the TA3 cell line. However, hepatocytes were significantly less sensitive than all tumor cells tested. These alkyl gallates blocked mitochondrial electron flow, mainly at the NADH-CoQ segment, preventing ATP synthesis, which would lead to cellular death. These esters also inhibited, in the same order of potencies as respiration, the growth of 786A, TA3 and TA3-MTX-R cells in culture. In mice carrying TA3 or TA3-MTX-R tumor cells, an important decrease of the tumor growth rate and an increase of survival were observed when mice were treated with iso-butyl gallate alone or in combination with doxorubicin. These results indicate that alkyl gallates are selectively cytotoxic to tumor cells, which may be due to the mitochondrial dysfunctions of these cells.

Oxidatively modified proteins and DNA in digestive gland cells of the fresh-water mussel Unio tumidus in the presence of tannic acid and its derivatives

The oxidative effect of tannic acid and its two derivatives (ellagic and gallic acid), naturally occurring plant polyphenols, has been studied on digestive gland cells of the fresh-water mussel Unio tumidus. A spectrophotometric method was used to determine the protein thiol groups after incubation of the cells with the polyphenols at concentrations of 1, 15 and 60 microM. The results showed that the oxidative modification of proteins increased in a concentration-dependent manner but no changes were observed at the concentration of 1 microM. The comet assay (single-cell gel electrophoresis assay) with the formamido-pyrimidine glycosylase (FPG) protein was used to assess oxidative DNA base damage. The cells were treated with polyphenols at the concentrations of 30 and 60 microM and post-incubated with FPG. FPG strongly enhanced DNA damage induced by the polyphenols, indicating that N-7 guanine oxidation is responsible for the observed effect. Using the comet assay in combination with proteinase K we were able to demonstrate the presence of DNA-protein cross-links as the probable cause of the decrease in DNA migration. After treatment of the cells with tannic acid and its metabolites at concentrations of 120, 180 and 240 microM, they were post-incubated with proteinase K. After this treatment an increased DNA migration was observed, indicating the presence of DNA-protein cross-links. We have also used a fluorescence method with Hoechst 33258/propidium iodide DNA-binding dyes to study the extent of DNA fragmentation after exposure of the cells to polyphenols at concentrations of 1, 5 and 60 microM. The results demonstrate that the polyphenols can induce apoptosis and necrosis at higher concentrations (5 and 60 microM). All experimental data suggest that tannic, ellagic and gallic acids at concentrations above 1 microM are able to interact with proteins and DNA, which leads to their degradation or changes in their function.

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.

Leaf extract from Ardisia compressa protects against 1-nitropyrene-induced cytotoxicity and its antioxidant defense disruption in cultured rat hepatocytes

Herbal tea preparations of Ardisia compressa (AC) have been used in folk medicine against liver disorders. The objective of this study was to evaluate the in vitro protective effect of an aqueous extract of dry leaves of AC on 1-nitropyrene (1-NP) induced cytotoxicity on rat hepatocytes. Lipid peroxidation (malondialdehyde), antioxidant enzyme activities (glutathione reductase, glutathione peroxidase, superoxide dismutase) and glutathione levels were studied. After 2 h of incubation, 0.25 microg/ml of 1-NP had an approximately 50% cytotoxic effect on hepatocytes. This environmental toxicant also increased malondialdehyde (77%), and glutathione peroxidase (46%), producing a significant consumption of endogenous antioxidant glutathione. (-)Epigallocatechin 3-gallato (EGCG) and AC decreased the viability of hepatocytes after 2 h of incubation at concentrations above 3 microg/ml and 2.52 microg, equivalents of (+)catechin/ml, respectively. A 100% hepatocyte protection was observed when cells were first exposed to AC (2.52 microg, equivalents of (+)catechin/ml), and then followed by 1-NP (0.25 microg/ml). Cells incubated with AC, either simultaneously or before treatment with 1-NP, were protected 75 and 84%, respectively. Cell protection of AC was superior to EGCG. Addition of AC to 1-NP (1:10) modulated superoxide dismutase and glutathione reductase activities (P<0.005), as well as the cellular level of GSH. The results indicate that AC has an antioxidant protective effect on rat hepatocytes when exposed to 1-NP.

Plasma membrane injury induced by nonyl gallate in Saccharomyces cerevisiae

AIMS

The aim was to investigate the antifungal actions of nonyl gallate against Saccharomyces cerevisiae ATCC 7754.

METHODS AND RESULTS

The maximum potency of both the growth inhibitory and the fungicidal effect against the yeast strain was found in nonyl gallate among n-alkyl gallates tested. Nonyl gallate induced ROS generation dose-dependently in growing cells. This ester rapidly killed yeast cells even when cell division was restricted by cycloheximide. This ester inhibited glucose-induced medium acidification and promoted the efflux of intracellular potassium ions in a nongrowing condition. Moreover, nonyl gallate induced a leakage of calcein from artificially prepared liposomes to a greater extent than dodecyl gallate did.

CONCLUSIONS

These results suggested nonyl gallate injured plasma membrane of S. cerevisiae, resulting in its exhibition of fungicidal effect accompanying with a leakage of intracellular materials from the cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study reveals new knowledge on the antifungal actions of nonyl gallate against S. cerevisiae. When nonyl gallate is applied as a food preservative, the level of its addition to foods may be reduced because of its potent antifungal activity compared with weak acids including sorbic acid and benzoic acid.

[Effect of gallic acid derivatives on secretion of Th1 cytokines and Th2 cytokines from anti CD3-stimulated spleen cells]

As reported previously (Kosuge et al., Yakugaku Zasshi, 120, 408 (2000)), methyl gallate, a gallic acid derivative, which has been one of compounds isolated from extracts of Psidium geneus Myrtaceae, selectively suppresses Th2 cytokine secretion. In the present study, to examine more effective compounds than methyl gallate, the effects of various gallic acid derivatives on the secretion of helper T cell subtype specific cytokines from anti CD3-stimulated spleen cells were investigated. Ten micrograms/ml of methyl gallate and ethyl gallate remarkably suppressed the secretion of IL-4 and IL-5, Th2 cytokines, but did not suppress meaningfully the secretion of IFN-gamma, a Th1 cytokine. On the other hand, the other gallic acid derivatives suppressed the secretion of both IL-4 and IFN-gamma. Ten micrograms/ml of methyl gallate suppressed the secretion of IL-2, a Th1 cytokine, but the same concentration of ethyl gallate did not suppress it. In conclusion, it seemed that ethyl gallate was the most selective inhibitor for the secretion of Th2 cytokines among gallic acid derivatives used in this study.

Screening of various Swertia species extracts in primary monolayer cultures of rat hepatocytes against carbon tetrachloride- and paracetamol-induced toxicity

Swertia chirata Buch-Ham. (Gentianaceae), one of the oldest medicinal herbs of India, is a source of the Indian ayurvedic drug 'chirata' used for the treatment of liver disorders and malarial fevers. In this study, eight species of Swertia were collected. Each of the dry whole plant was extracted into methanol, the aqueous extract of which was sequentially extracted into hexane, chloroform and butanol extracts. The extracts were screened for their anti-hepatotoxic activity against carbon tetrachloride (CCl4) and paracetamol (acetaminophen (AAP)) toxicity in primary monolayer cultures of rat hepatocytes. The primary cultures, 2.5 x 10(6) cells /3 ml medium/60 mm collagen-coated plates, were exposed to 2.5 mM CCl4 or 12 mM AAP in the presence or absence of plant extracts (100 microg/ml culture medium). Cells and medium were harvested after 22 h of treatment for the assay of cellular reduced gluthathione (GSH) content and leakage of lactate dehydrogenase as biological end-points of toxicity. Both CCl4 and AAP at the indicated concentrations reduced GSH by almost 50 and 80%, respectively, while the enzyme leakage was almost 15% above the untreated control. Hexane and methanol extracts of most of the species in general offered relatively good protection. The anti-hepatotoxic activity, nevertheless, was evident in all Swertia species against both the toxicants. However, Swertia purpurascens, Swertia chirata, Swertia paniculata and Swertia cordata exhibited better activity compared with other species investigated. In addition, influence of various extracts (10-100 microg/ml medium) was examined on cellular growth of rat Reuber hepatoma cell line H4IIEC3/G-. Except for the butanol extract of S. chirata, no other extracts exerted toxicity in terms of neutral red uptake by the cells.

Effect of dietary treatment with n-propyl gallate or vitamin E on the survival of mice exposed to phosgene

Phosgene, widely used in industrial processes, can cause life-threatening pulmonary edema and acute lung injury. One mechanism of protection against phosgene-induced lung injury may involve the use of antioxidants. The present study focused on dietary supplementation in mice using n-propyl gallate (nPG)--a gallate acid ester compound used in food preservation--and vitamin E. Five groups of male mice were studied: group 1, control-fed with Purina rodent chow 5002; group 2, fed 0.75% nPG (w/w) in 5002; group 3, fed 1.5% nPG (w/w) in 5002; group 4 fed 1% (w/w) vitamin E in 5002; and group 5, fed 2% (w/w) vitamin E also in 5002. Mice were fed for 23 days. On day 23 mice were exposed to 32 mg m-3 (8 ppm) phosgene for 20 min (640 mg. min m-3) in a whole-body exposure chamber. Survival rates were determined at 12 and 24 h. In mice that died within 12 h, the lungs were removed and lung wet weights, dry weights, wet/dry weight ratios, lipid peroxidation (thiobarbituric acid reactive substances, TBARS) and glutathione (GSH) were assessed. Vitamin E had no positive effect on any outcome measured. There was no significant difference between 1.5% nPG and any parameter measured or survival rate compared with 5002 + phosgene. However, dietary treatment with 0.75% nPG significantly increased survival rate (P </= 0.002) and lowered TBARS (P </= 0.05) compared with 5002 + phosgene at 12 h after exposure. Mice fed 0.75% nPG had a lower wet/dry wt ratio compared with those fed 1.5% nPG and a significantly increased lung tissue GSH 36%, compared with the 5002 + phosgene group. In conclusion, dietary treatment with a low level of the antioxidant nPG protected mice by decreasing lipid peroxidation and increasing lung tissue GSH. The higher level of nPG and both levels of vitamin E diets were ineffective, suggesting that a ceiling threshold level of antioxidants in lung tissue is required for survival against phosgene-induced lung injury. Published in 2001 by John Wiley & Sons, Ltd.

Mechanism of mitochondrial dysfunction and cytotoxicity induced by tropolones in isolated rat hepatocytes

The mechanism of mitochondrial dysfunction and toxicity induced by the tropolones, beta-thujaplicin (4-isopropyl tropolone), tropolone and tropone, has been studied in freshly isolated rat hepatocytes. Incubation of hepatocytes with beta-thujaplicin (1-4 mM) elicited a concentration and time-dependent cell killing. The toxicity was accompanied by losses of cellular ATP, total adenine nucleotides and glutathione, independently of lipid peroxidation and protein thiol oxidation. The beta-thujaplicin-induced cytotoxicity was enhanced by the pretreatment of hepatocyte suspensions with EDTA (4 mM), a hydrophilic chelator, or by incubation in Ca2+ and Mg2+-deficient Krebs-Henseleit buffer. The partition coefficient of beta-thujaplicin, which formed complex with the divalent cations in Krebs-Henseleit buffer, in n-octanol/buffer was increased either in the presence of EDTA or absence of divalent cations. Comparison of toxic effects based on cell viability and adenine nucleotide levels showed that beta-thujaplicin was more toxic than tropolone or tropone in Krebs-Henseleit buffer containing EDTA (4 mM). The addition of beta-thujaplicin to isolated hepatic mitochondria reduced state 3 respiration with NAD+-linked substrate (pyruvate plus malate) and/or with an FAD-linked substrate (succinate plus rotenone), whereas state 3 respiration of ascorbate plus tetramethyl-p-phenylenediamine (cytochrome oxidase-linked respiration) was not significantly affected by beta-thujaplicin. Further, the addition of these tropolones caused a concentration-dependent increase in the rate of state 4 oxygen consumption, indicating an uncoupling effect. These results indicate that beta-thujaplicin- and tropolone-induced cytotoxicity are associated with an acute ATP depletion via mitochondrial dysfunction related to oxidative phosphorylation and that the induction of cytotoxicity is affected by EDTA or divalent cations.

Antioxidant activity of gallates: an electrochemical study in aqueous media

The electron-donating ability of gallates, which are food and pharmaceutical antioxidants, is quantitatively assessed on the basis of their electrochemical characteristics. Gallic acid and the propyl, i-propyl, butyl, i-butyl, pentyl and i-pentyl gallate derivatives were electrochemically oxidized on the glassy carbon electrode by using differential pulse voltammetry, cyclic voltammetry and hydrodynamic voltammetry on the rotating disk electrode. All the compounds under study were easily oxidized in acidic and neutral solutions. Electrochemical oxidation occurs via two electron-transfer steps; however good resolution for the second wave was obtained only by using hydrodynamic conditions. The oxidation process results to be irreversible, diffusion controlled and pH-dependent. The introduction of the alkyl groups seems to affect the intensities of the semiquinone gallate radicals as can be ascribed from the observed differences in i(II)d/i(I)d ratio obtained from hydrodynamic voltammetric experiments for the different derivatives. We have found that the intensity of the gallate radicals follows the sequence GA > or = i-PG > PG > i-BG > BG > i-PeG > PeG. From the pH-dependence of the peak current it is possible to affirm that pH 2 is the better condition for the oxidative activity showing that the antioxidant behaviour of these compounds are important in the stomach acid.

Motility of ram spermatozoa during storage in a chemically-defined diluent containing antioxidants

The effects of five antioxidants--Vitamin E (VE), butylated hydroxyanisole (BHA), n-propyl gallate (n-PG), deferoxamine mesylate (Desferal) and catalase (EC 1 . 11 . 1 . 6)--on the maintenance of motility of ram spermatozoa in a chemically-defined ram semen diluent (RSD-1) have been evaluated. VE, n-PG and Desferal inhibited spermatozoal motility. The relative inhibition (i.e., ratio of change in % motility over 24 h between the treatment group and the corresponding control) at equimolar concentrations (100 microM) of Desferal, VE and n-PG were 1.6, 1.8 and 3.6 respectively. BHA had no effect at 10 microM but at lower concentrations, gave a slight improvement in motility in freshly diluted spermatozoal samples and in those stored for 1 day at 15 degrees C. The addition of catalase to RSD-1 was also ineffective in improving the motility of spermatozoa. The lack of beneficial effects of the tested antioxidants suggests that RSD-1 itself may destroy reactive oxygen species and the antioxidant activity of RSD-1 components requires further study.

Furan-mediated uncoupling of hepatic oxidative phosphorylation in Fischer-344 rats: an early event in cell death

Furan is a potent rodent hepatotoxicant and carcinogen. The present study was done to examine the effects of furan on hepatic energy metabolism both in vivo and in vitro in male F-344 rats. Furan produced concentration- and incubation time-dependent irreversible reductions in ATP in freshly isolated F-344 rat hepatocytes. Furan-mediated depletion of ATP occurred prior to cell death and was prevented by including 1-phenylimidazole, a cytochrome P450 inhibitor, in the suspensions. Male F-344 rats were treated with furan (0-30 mg/kg, po) and killed 24 hr later to prepare hepatic mitochondria. Furan produced dose-dependent increases in state 4 respiration and ATPase activity. Both of these changes were prevented by 1-phenylimidazole cotreatment. In a separate series of experiments, mitochondria were prepared from isolated rat hepatocytes following incubation with furan (2-100 microM) for 1-4 hr. Furan produced incubation time- and concentration-dependent increases in state 4 respiration and ATPase activity. Furan-mediated mitochondrial changes were prevented by adding 1-phenylimidazole to the hepatocyte suspensions. These results indicate that the ene-dialdehyde metabolite of furan uncouples hepatic oxidative phosphorylation in vivo and in vitro. In vitro studies using an isolated hepatocyte suspension/culture system demonstrated that the concentration response for furan-mediated mitochondrial changes in suspension corresponded with the concentration responses for cell death after 24 hr. Including 1-phenylimidazole or oligomycin plus fructose in hepatocyte suspensions prevented furan-induced cell death after 24 hr in culture. The results of this study indicate that furan-induced uncoupling of oxidative phosphorylation is an early, critical event in cytolethality both in vivo and in vitro.

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.