甲基汞与含硒生物分子在体内的结合与转化及其在甲基汞代谢中的作用

Methylmercury (MeHg), as a highly neurotoxic pollutant, can be bioaccumulated through the food chain and cause human exposure and health risks through food consumption. Current studies on MeHg metabolism and toxicity mostly focus on the interaction of MeHg with sulfur compounds in biological bodies, due to the high affinity between Hg and sulfur. However, selenium (Se), as an analogue to sulfur, has a higher affinity towards Hg binding in comparison to sulfur, and it is likely that Se-containing biomolecules may form complexes with MeHg and subsequently affect MeHg metabolism and toxicity. A few previous studies on MeHg and Se, including the protective effect of Se against MeHg toxicity, dysfunction of selenoenzyme caused by MeHg and formation of mercury selenide nanoparticles (HgSe NPs) in marine mammals and human brains, may be indicative of the occurrence of MeHg complexes with Se-containing biomolecules. Much remains unclear yet on the formation and transformation of MeHg complexes with Se-containing biomolecules (MeHg-SeR), probably because of the limitations of current analytical methods. The project is aimed at developing new methods for MeHg-SeR analysis and further studying the role of Se on MeHg metabolism through the formation and transformation of MeHg-SeR. This research will develop and improve techniques for analysis of MeHg-SeR and HgSe NPs, based on the hyphenated platform of continuous-flow gel electrophoresis (GE)/liquid chromatograph (LC)/single particle (SP) - inductively coupled plasma mass spectrometry (ICP-MS). Simulated experiments using tris buffer will be conducted to investigate the interactions of MeHg with selenoamino acids/selenoproteins and factors influencing the formation of MeHg-SeR. Lastly, the speciation, distribution and transformation of MeHg-SeR in mice will be investigated after exposure of MeHg and selenium in order to provide molecular-level insights on the effects of Se on MeHg metabolism and toxicological effects.

甲基汞具有生物累积和生物放大的特性，可沿食物链进入人体并产生严重的神经毒性。甲基汞与硫的结合是目前研究甲基汞代谢和毒性的主要切入点，但与硫性质相似的硒和汞具有更强的亲和作用，可能与甲基汞形成结合态，进而影响其代谢和毒性。硒对甲基汞毒性的拮抗效应、甲基汞引发硒酶功能受损、硒化汞纳米颗粒在生物体内的检出均提示存在甲基汞-硒结合态。可能受分析方法所限，目前对甲基汞-硒结合态在生物体内的形成及转化过程缺乏理解。本项目拟基于柱凝胶电泳/液相色谱/单颗粒-电感耦合等离子质谱联用技术，建立和完善甲基汞-硒结合态及硒化汞纳米颗粒的有效分析方法；通过在溶液中模拟甲基汞与硒代氨基酸/硒蛋白的体内反应，研究甲基汞-硒结合态的生成、转化及影响因素；进一步开展甲基汞和硒共暴露实验，研究小鼠体内甲基汞-硒结合态在各组织器官中的分布情况与转化规律，从分子水平上阐明硒在甲基汞体内代谢和致毒机制中的作用。

汞的毒性效应与其在生物体内的吸收、分布及形态转化等过程密切相关。硒具有减轻和抑制无机汞和甲基汞毒性的作用，目前推测的几种可能机制均与汞-硒之间的结合与转化密切相关，在海洋哺乳动物体内发现的硒化汞颗粒是其最直接的证据。作为一种惰性汞形态并且极有可能来自于甲基汞，硒化汞颗粒被认为是汞代谢和解毒的最终产物。尽管如此，目前尚未有甲基汞在体内转化为硒化汞颗粒的直接证据，对其生成机制及去向等过程更是知之甚少。.本项目利用单颗粒（single particle, SP）-电感耦合等离子体质谱（Inductively Coupled Plasma Mass Spectrometry, ICP-MS）、高效液相色谱（High Performance Liquid Chromatography, HPLC）-ICP-MS联用等技术手段研究硒化汞颗粒的生成过程，在分子水平上探讨生物体内HgSe颗粒的生成机制，探索硒对汞的体内代谢及转化的影响机制。具体研究内容如下：.首先，利用大鼠实验研究了硒对无机汞和甲基汞体内代谢和形态转化的影响。首次证实了在大鼠体内存在硒促进甲基汞转化为含汞颗粒的过程，揭示了生物体内甲基汞去甲基化的一条新途径和新机制；发现了无机汞在体内转化为含汞颗粒的现象，并且当硒存在时血浆中生成的含汞颗粒物占据血浆总汞的比例高达70-80%，表明含汞颗粒可能是硒汞共暴露时生物体内的重要汞形态，对汞的体内代谢转化具有重要意义。.其次，为了探索硒化汞颗粒生成的分子机制，利用体外实验研究了汞与含硒生物分子结合与转化的化学过程，揭示了由无机汞(inorganic mercury, iHg) /甲基汞(methylmercury, MeHg)生成HgSe颗粒的两种可能机制。结果表明，还原型的含硒生物分子（R-SeH和HSe-）是该过程中的关键分子，而iHg在该反应中的活性比MeHg更强。.本工作通过体内/体外实验研究了HgSe颗粒体内生成过程及其对汞代谢的影响。首次证实了甲基汞与硒共暴露时在大鼠体内生成HgSe颗粒的过程，发现硒对iHg/MeHg向含Hg颗粒转化具有显著促进作用，并且含Hg颗粒态占总Hg比例高达8-80%，提示其在Hg的体内代谢和解毒机制中十分重要。