Faculty of Dentistry, The University of Hong Kong, Hong Kong, China.
Department of Chemistry, The University of Hong Kong, Hong Kong, China.
J Biol Inorg Chem. 2018 May;23(3):471-480. doi: 10.1007/s00775-018-1557-5. Epub 2018 Apr 5.
The presence of ionic titanium in the serum of patients with titanium implants is currently unexplained. This is presumed due to corrosion, and yet the serum titanium concentration measured in patients is far greater than that predicted by its solubility. The binding of titanium ion as Ti(IV) to human transferrin (hTF) in serum indicates that Ti(IV) ions interact with human physiology. This is an intriguing finding since there is currently no known role for titanium ions in human physiology. Thus, understanding the factors that determine in vivo titanium ion release is relevant to further understanding this metal's interactions with human biochemistry. The present study sought to determine the extent of titanium ion release of into human serum in vitro, and the role of citrate, lactate and hTF in this process. It was found that, when surgical devices of commercially pure titanium were placed into human serum, citrate and lactate concentrations were the prime determinants of titanium release. Crystallography revealed Ti(IV) bound to hTF in the presence of citrate alone, signalling that citrate can act as an independent ligand for Ti(IV) binding to hTF. Based on these findings, a two-stage process of titanium ion release into human serum that is dependent upon both citrate and hTF is proposed to explain the ongoing presence of titanium ion in human subjects with implanted titanium devices.
目前，人们尚无法解释钛植入物患者血清中存在离子态钛的原因。据推测，这是由于腐蚀所致，但患者血清中测量到的钛浓度远远高于其溶解度所预测的浓度。钛离子与血清中人转铁蛋白（hTF）结合形成 Ti(IV)表明 Ti(IV)离子与人的生理机能相互作用。这一发现很有趣，因为目前尚不知道钛离子在人体生理学中有何作用。因此，了解决定体内钛离子释放的因素对于进一步了解这种金属与人体生物化学的相互作用至关重要。本研究旨在确定钛离子在体外向人血清中释放的程度，以及柠檬酸、乳酸盐和 hTF 在这一过程中的作用。研究发现，当纯钛手术器械被置于人血清中时，柠檬酸和乳酸盐浓度是钛释放的主要决定因素。晶体学研究表明，在仅存在柠檬酸的情况下，Ti(IV)与 hTF 结合，表明柠檬酸可以作为 Ti(IV)与 hTF 结合的独立配体。基于这些发现，提出了一个两阶段的钛离子向人血清中释放的过程，该过程依赖于柠檬酸和 hTF，以解释在植入钛设备的人体中持续存在钛离子的现象。
