Xenobiotic Metabolism

异生物质代谢

• 批准号: 6837337
• 负责人: Leo T Burka
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF ENVIRONMENTAL HEALTH SCIENCES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6837337
• 关键词: biotransformation; carcinogen testing; cytochrome P450; detoxification; drug metabolism; enzyme activity; genetically modified animals; glutathione; laboratory mouse; laboratory rat; lidocaine; mass spectrometry; monoterpenes; mutagen testing; naphthoquinones; nuclear magnetic resonance spectroscopy; plant extracts; toxin metabolism; urinalysis; western blottings

Pulegone is a monoterpene found in the essential oil of several mints, including Pennyroyal. These mints are used in flavoring food and beverages. Pennyroyal and Pennyroyal oil have also been used as an abortifacient. The use of Pennyroyal oil, which contains about 85% pulegone, as an abortifacient has resulted in serious toxicity and death. Pulegone has been nominated to the NTP for toxicity and carcinogenicity studies. Recent studies on pulegone have involved characterization of its metabolism in mice. Based on urinary metabolites pulegone is metabolized by rats by three major pathways: 1) hydroxylation followed by glucuronidation; 2) reduction to menthone/isomenthone followed by hydroxylation; 3) Michael addition of glutathione. Metabolism of pulegone in mice differs from rats in that several mercapturic acid and aromatic metabolites identified in rat urine are not present in mouse urine. This difference in metabolite profile could be due to the much more rapid biotransformation in mice via pathway 1. The presence of mercapturic acids implies the formation of alkylating agents. The lack of mercapturic acid metabolites correlates the observation that pulegone is less toxic to mice in the NTP studies. However, there are literature reports that high doses of pulegone deplete GSH in mice. Bile duct cannulation studies in mice revealed the presence of metabolites formed from direct addition of GSH to pulegone. Probably due to differences in transport, GSH adducts in rats are converted in liver and kidney to mercapturic acids, while in mice the adducts are excreted in bile. In both rats and mice the GSH adducts and /or the corresponding mercapturic acids are derived from direct conjugation via Michael addition with pulegone. The accepted mechanism for pulegone toxicity is metabolism first to menthofuran followed by further oxidation of the furan ring to an enonal. Interestingly none of the nearly 20 pulegone metabolites we have identified are unambiguously required to be formed via menthofuran. These observations led us to conduct metabolism studies of menthofuran to determine if there are metabolites in common and to test the hypothesis that a reactive intermediate is derived from menthofuran. In male rats 4 urinary metabolites were common to both chemicals supporting the intermediacy of menthofuran in pulegone metabolism. Other menthofuran metabolites were clearly derived from oxidation of the furan ring followed by reaction with nucleophiles such as GSH, water, sulfite, and taurine, verifying the postulated reactive intermediate. Juglone is an hydroxynaphthoquinone that has been isolated from walnut hulls. Interest in juglone arose from proposed NTP studies of black walnut extract derived from walnut hulls and sold as a dietary supplement. As a naphthoquinone juglone was expected to be reactive. In fact the reaction of juglone with GSH was almost instantaneous. Addition of GSH to the quinone gives a hydroquinone which is easily oxidized back to a quinone which in turn reacts with an additional GSH. Double reaction of quinones/hydroquinones and the related nephrotoxicity has been well explored. Thus it would expected that juglone may have a deleterious effect on the kidney. Tissue distribution studies substantiate the reactivity of juglone; there was notably more radioactivity at the site of application following dermal, iv and gavage exposures. The tissue to blood ratio was persistently high in kidney (not from contained urine), consistent with the expected nephrotoxicity. Many local anesthetics, such as lidocaine and prilocaine, contain aromatic amines (2,6-xylidene and o-toluidene in the examples cited) as part of their structure, as amides. Amides are cleaved by esterases/amidases freeing the amine. o-Toluidene and 2,6-xylidene are both positive in carcinognicity studies and are the amine component in several anesthetics. This was the basis for the nomination of this class of chemicals for NTP study. Because of the pharmacological activity of the anesthetics, a 2-year bioassay was not recommended. Instead a metabolism/mechanism study was suggested. To explore the possibility that potentially mutagenic metabolites result from biotransformation of anesthetics, the Ames mutagenicity of urine from rats treated with either 2,6-xylidine, o-toluidene, prilocaine or lidocaine was determined. The intention was to ultimately isolate and identify the mutagen/premutagen. Male rats were dosed by gavage with each of the chemicals (all doses at 100 mg/kg; n=4 rats/treatment group). Urine samples were collected for 8 hr after dosing, filter-sterilized, incubated with or without glucuronidase/sulfatase and Aroclor 1254-induced rat S9, and tested with Salmonella typhimurium strains TA98 and TA100. Results demonstrated that urine of rats receiving either of the four test chemicals (lidocaine, prilocaine, 2,6-xylidine, or o-toluidine), were neither toxic nor mutagenic to either strain TA98 or TA100. Urine from benzpyrene-treated animals (positive control) was mutagenic. No potent anesthetic-derived mutagens were detected in this study; therefore, the mutagenic potential of either lidocaine, prilocaine, 2,6-xylidine, or o-toluidine will not be further investigated. Studies of the polybrominated diphenyl ethers have only recently started. Initial results from the tetrabromodiphenyl ether indicates that the chemical is rapidly absorbed from an oral exposure. Absorption appears to be the same whether the vehicle is aqueous or corn oil. Ten daily doses of 0.1 umol/kg results in tissue concentrations almost exactly 10 times a single 0.1 umol/kg dose and approximately the same as a 1.0 umol/kg dose. This result implies nearly 100% absorption, a long half life and therefore bioaccumulation. Another interesting observation out of these preliminary studies is that thymus and thyroid have high tissue concentrations of radioactivity.

Pulegone是一种在包括Pennyroyal在内的几种薄荷的精油中发现的单二烯。这些薄荷器用于调味食品和饮料。 Pennyroyal和Pennyroyal油也已被用作流型剂。 pennyroyal油的使用含有大约85％的pulegone，作为流型牙，导致了严重的毒性和死亡。普列酮已被提名为NTP进行毒性和致癌性研究。关于pulegone的最新研究涉及其在小鼠中代谢的表征。基于泌尿代谢物，大鼠由三种主要途径代谢：1）羟基化，然后是葡萄糖醛酸化； 2）还原至薄荷/本元转基调，然后还原羟基化； 3）迈克尔添加了谷胱甘肽。小鼠中pulegone的代谢与大鼠的不同，因为在大鼠尿液中鉴定出的几种胃酸和芳族代谢产物在小鼠尿液中不存在。代谢物剖面的这种差异可能是由于小鼠通过途径1的生物转化的速度更快，硫酸的存在意味着烷基化剂的形成。缺乏苏联酸代谢物与NTP研究中pulegone对小鼠的毒性较小的观察结果相关。但是，有文献报道说，小剂量的pulegone耗尽了小鼠的GSH。小鼠的胆管管道研究揭示了从直接添加GSH形成的代谢产物。可能是由于转运的差异，大鼠的GSH加合物在肝脏和肾脏中转化为胃酸酸，而在小鼠中，加合物在胆汁中排出。在大鼠和小鼠中，GSH加合物和 /或相应的苏联酸是通过迈克尔与pulegone添加的直接结合得出的。 pulegone毒性的公认机制首先是对薄膜的代谢，然后将呋喃环进一步氧化为enonal。有趣的是，我们已经确定的近20个pulegone代谢产物都没有明确地通过薄膜形成。这些观察结果导致我们对薄膜进行代谢研究，以确定是否有共同的代谢物，并检验以下假设：反应性中间体源自薄膜。在雄性大鼠中，4尿代谢物对于两种化学物质都共同支持pulegone代谢中的薄膜中间人。其他薄膜代谢物清楚地从呋喃环的氧化中得出，然后与诸如GSH，水，亚硫酸盐和牛磺酸等亲核试剂反应，从而验证假设的反应性中间体。 Juglone是一种与核桃壳分离出来的羟基喹酮。对juglone的兴趣来自提出的对核桃壳并作为饮食补充剂出售的黑胡桃提取物的NTP研究。由于萘酮的珠宝有望具有反应性。实际上，juglone与GSH的反应几乎是瞬时的。在喹酮中添加GSH会产生一种氢醌，很容易氧化回喹酮，进而与额外的GSH反应。喹酮/氢喹酮的双重反应和相关的肾毒性已经很好地探索了。因此，它可以预期朱格隆可能会对肾脏产生有害作用。组织分布研究证实了珠宝的反应性。皮肤，IV和饲料暴露后，在应用部位的放射性明显更高。与预期的肾毒性一致的肾脏（不含尿液）的组织与血比持续高。 许多局部麻醉剂，例如利多卡因和prilocaine，都含有芳香胺（在引用的示例中，有2,6-二甲苯和O-托硅烯）作为其结构的一部分，如酰胺。酰胺被释放胺的酯酶/胺化酶裂解。 O-二甲苯和2,6-二甲基在癌性研究中都是阳性的，并且是几种麻醉药的胺成分。这是提名这类化学物质进行NTP研究的基础。由于麻醉药的药理活性，不建议使用2年的生物测定法。相反，提出了一项新陈代谢/机制研究。为了探索由麻醉药的生物转化引起的潜在诱变代谢产物的可能性，确定了用2,6-甲基二氨酸，O-甲烷，prilocaine或lidocaine治疗的大鼠尿液的尿素诱变性。目的是最终隔离并识别诱变剂/premutagen。通过饲料对每种化学物质（均以100 mg/kg的剂量; n = 4大鼠/治疗组）进行雄性大鼠。给药后，将尿液样品收集8小时，过滤过滤，用或不含葡萄糖醛酸酶/硫酸酶和Aroclor 1254诱导的大鼠S9孵育，并用Typhimurium菌株TA98和TA100进行测试。结果表明，接受四种测试化学物质（利多卡因，prilocaine，2,6-二甲苯胺或O-甲烷氨酸）中的大鼠的尿液既不是毒性也不是TA98或TA100菌株的毒性。来自苯吡啶处理的动物的尿液（阳性对照）是诱变的。在这项研究中，未检测到有效的麻醉剂。因此，不得进一步研究利多卡因，丙cain，2,6-二甲苯或O-甲烷氨酸的诱变潜力。多溴二苯基醚的研究直到最近才开始。四苯基苯基醚的初始结果表明该化学物质是从口腔暴露中迅速吸收的。无论车辆是水还是玉米油，吸收似乎都是相同的。每日10剂量为0.1 UMOL/kg会导致组织浓度几乎完全是单个0.1 Umol/kg剂量的10倍，并且与1.0 Umol/kg剂量大致相同。该结果意味着接近100％的吸收，一半寿命，因此是生物积累的。这些初步研究中的另一个有趣的观察结果是，胸腺和甲状腺具有较高的放射性浓度。