シンクロトロン放射光を用いた微量元素分析とその医学応用

筋萎縮性側索硬化症（ALS）の神経変性における 遷移金属の酸化ストレスについて

抄録

Synchrotron radiation (SR) is an ideal x-ray source, which provides an extremely high brilliance (high intense photon) and tunibility (energy variability) to investigate trace metallic elements contained in biological specimens at the cellular level.

Firstly, x-ray fluorescence (XRF) with a SR micro beam (about 10 μm in diameter) are a highly sensitive technique to determine existence and distribution of ultra-trace elements within a single cell. The detection limits of the techniques are extremely low (< 0.01ppm) and the isolating and purifying procedures are basically unnecessary. An x-ray beam of SR does not destroy biological samples due to its small heat load under normal conditions and it is comparatively easy to perform the spectroscopy using x-ray in a low vacuum or in air. Even after the x-ray analysis, therefore, the same specimens allow histochemical observation to compare with the pathological conditions.

Secondly, x-ray absorption fine structure (XAFS) analysis is a useful technique to investigate chemical state and fine structure of metals contained in the active site of metallic proteins. XAFS has two techniques, such as extended X-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) spectroscopies. They provide information about electronic structure and binding configuration of probing element.

Using both XRF and XANES spectroscopies with a SR micro beam, we have non-destructively examined the distributions and chemical states of transition metals within a neuron of neurodegenerative diseases, such as Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Alzheimer diseases (AD). It is postulated that the oxidative stress caused by transition metals, such as iron (Fe), copper (Cu) and Zinc (Zn), might play an important role in the neurodegeneration of these diseases, developing the specific intracytoplasmic inclusions, composed of α-synuclein, TDP-43 and Tau proteins. We have applied these techniques at cellular level, to investigate the role of oxidative stress induced by these transition metals in this degenerative process.

Previously, we reported the results of XRF/XANES study of the two familial ALS (fALS) cases (one of which with SOD1 mutation), showing the disturbance of Cu/Zn metabolism detrimental to neuronal death. In this paper, we reported the additional results of XRF/XANES study of the two sporadic ALS (sALS), focused on the disturbance of Fe metabolism and its chemical state within a spinal motor neuron.