The Protective Effects And Possible Mechanisms Of Phytochemicals Green Tea Polyphenols And Garlic Oil On Tributyltin-induced Toxicities

The organotin compound tributyltin (TBT), has been extensively used in boat paints because of its excellent and long-lasting antifouling properties. Since the early 1980s, the harmful effects of the TBT on marine organisms have been determined. In some selected lakes, rivers and coastal environments from China, concentrations of TBT were higher than the acute and chronic toxicity threshold of fresh water and marine organisms. The toxic effects of TBT have been observed in invertebrates, micro- and macro-algae. It was found that exposure of TBT could promote both oxidative damage and DNA damage in mammals. TBT-related toxicity, especially immunotoxicity, reproductive toxicity and neurotoxicity have been well documented.Recently, restrictions on the application of TBT compounds as vessel antifouling agents have been introduced. However, TBT pollution in fish and shellfish, marine water and sediment are still being reported. The persistent presence of TBT in coastal ecosystems poses an ecotoxicological threat to humans through the food chain because TBT could be transported to the human body by contaminated seafood. Thepossible health hazard caused by human dietary exposure to TBT through ingesting contaminated fish and shellfish is a growing concern. Currently, there is no known effective strategy to eliminate TBT's toxic effects from contaminated food.Green tea polyphenols (GTPs) have gained great interest due to their potent anti-oxidative activities combined without side effects in humans. A number of green tea polyphenolic compounds have been found to be good antioxidants against lipid peroxidation in biological systems, and they also possess anti-cancer properties. The main components of GTPs are (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) and gallic acid (GA), and EGCG is the most reported compound among these GTPs. The main biologic activities of GTPs include: (1) Affect enzyme relating with free radical generation and scavenging. (2) Act on free radical directely. (3) Combin with the metallic ion which inducing oxidation.Garlic (Allium sativum) is a widely consumed herb in foodstuffs and has been traditionally used in the treatment of fungal and bacterial infections. Numerous studies have shown that garlic exhibits diverse biological and pharmacological properties, including antitumorigenesis, antiatherosclerosis and detoxifying, and has also been shown to protect against chemical-induced toxicity in animals. The organosulfur compounds are believed to play key roles in these biological effects. Among the organosulfur compounds, diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS) are the three major constituents. These compounds vary in their efficacy depending on the number of sulphur atoms in their molecules. The detoxifying effects of organosulfur compounds were mostly thought to be related to not only their ability to prevent oxidative damage and DNA damage, but also their ability to inhibit phase I enzymes, induce phase II enzymes, or bind to exogenous toxins through sulfhydryl groups.Base on the conclusion of previous study that both green tea polyphenols (GTPs) and garlic oil (GO) are natural phytochemicals with powerful antioxidant capacity. This study was conducted to investigate the protective effect of GTPs and GO on toxicities induced by TBT in vivo as well as in vitro. The present study aimed to determine if GTPs and garlic oil, the two wildly consumed foodstuffs in the world, are able to reduce TBT-induced toxicities, and leads to find more convenient strategies to reduce the potential damage from chemical pollutants.Main results:1. GTPs and garlic oil can scavenge ROS induced by TBT effectively. The elevation of ROS production was inhibited by GTPs or garlic oil in mice liver and FL cell in a dose-depend manner in this study. It is indicated that GTPs or garlic oil can prevent ROS increasing both in vivo and in vitro.2. GTPs and garlic oil can prevent TBT-induced MDA contents increase. The mice liver MDA content increased significantly in the TBT treated group but was almost unchanged in the GTPs or garlic oil pre-treated groups compared to control.3.GTPs and garlic oil can prevent TBT induced DNA damage. Both tail length and tail moment data (comet assay) demonstrated that the number of cells with damaged DNA in un-protected mice was found to be significantly higher compared to GTPs or garlic oil protected mice.4. GTPs and garlic oil can prevent thymocytes from TBT-induced damage. Damage to the nuclei and mitochondria in un-protected group was apparent under electron microscope observation, while in GTPs, EGCG or garlic oil protected group, the damage of thymocytes induced by TBT observably alleviated.5. TBT-induced reduction of cell viability was prevented by GTPs and garlic oil in human FL cells. Mice in GTPs or garlic oil protected group exhibited similar cell viability to control. The cell viability decreased in a dose-dependent in TBT treated cells, and exhibited almost no change in GTPs or garlic oil protected cells.6.Increased apoptosis ratio induced by TBT was inhibited by GTPs or garlic oil in mice liver. As detected by TUNEL assay in mice liver, both high and low concentrations of GTPs or garlic oil exhibite obvious protective effects on the increasing of apoptosis ratio induce by TBT.7. EGCG and garlic oil can affect the change of apoptosis related protein (Bax and Bcl-2) level induced by TBT. The data indicated that both EGCG and garlic oil can affect the increasing of Bax and the decreasing of Bcl-2 protein level induced by TBT. The antagonizing effects of EGCG or garlic oil on TBT-induced apoptosis protein change were obvious.8.EGCG can protect FL cells cytoskeleton (F-actin) from TBT induced alteration. Data from FL cells cytoskeleton (F-actin) observation showed that EGCG could avoid TBT induced cells cytoskeleton (F-actin) change in a dose-depend manner. The variety of cytoskeleton (F-actin) induced by TBT was alleviated after FL cells pretreated with EGCG.Main conclusion:1.GTPs and garlic oil can prevent TBT-induced oxidative damage. Data of ROS level and MDA contents in this study indicated that ROS induced by TBT can be efficiently scavenged by GTPs and garlic oil, and TBT-induced lipid peroxidation in mice was also prevented. Therefore it can be concluded that GTPs and garlic oil can prevent oxidative damage induced by TBT.2. GTPs and garlic oil can prevent TBT-induced DNA damage and thymocytes damage. The number of cells with damaged DNA in the lymphocyte of peripheral blood of the un-protected group differed significantly from both GTPs and garlic oil protected group. The damage of nucleolus and mitochondria in thymus, the main target orgain of TBT, was prevented by GTPs, EGCG and garlic oil. It is confirmed that GTPs, EGCG and garlic oil can prevent TBT-induce DNA breakage and thymocytes damage. Taking together the data of GTPs and garlic oilpreventing oxidative damage and DNA damge, it could be speculated that GTPs and garlic oil prevent TBT-induced thymocytes damage by inhibiting oxidative damage.3. GTPs and garlic oil can antagonize TBT-induced apoptosis. Aapoptosis ratios (TUNEL assay) confirm the fact that EGCG and garlic oil can reduce TBT-induced apoptotic rate. Data from western-blot indicated that both EGCG and garlic oil can affect Bax and Bcl-2, the two apoptosis related protein level. And data of F-actin showed that EGCG could prevent TBT induced cytoskeleton (F-actin)alteration, which is related to apoptosis.4. The preventive effects of GTPs and garlic oil on TBT-induced oxidative damage, DNA damage, nucleus damage and apoptosis are close related. Data obtained from this study implied that TBT-induced toxicities initiated at oxidative damage, and the preventing of oxidative damage may be the key step due to the powerful ability of GTPs and garlic oil to scavenge ROS and prevent DNA breaks. So it could be speculated that the the preventive effects of GTPs and garlic oil on TBT-induced toxicities are compositive and extensive.5. Daily taking in green tea polyphenols or garlic oil can reduce the harm from TBT- contaminated sea food. This study suggested that GTPs and garlic oil can be applied as chemopreventive agents against TBT-induced toxicity. The exact mechanism of how green tea polyphenols and garlic oil reducing the toxicity of TBT, or if the protective effects also work in preventing the toxicities of other chemical pollutants needs further investigation.