Study of 99mTc-annexin V uptake in apoptotic cell models of Parkinson's disease

Objective To investigate the feasibility of radiolabelled annexin V imaging for early diagnosis of Parkinson's disease. Methods Tc-99m-HYNIC-annexin V was prepared and its binding to apoptotic cell models of Parkinson's disease was studied in vitro. Cellular models of Parkinson's disease were produced by administering different concentrations of 1-methyl-4-phenylpyridinium to PC12 and SH-SY5Y cell lines. Cell apoptosis rates were analysed by flow cytometry. Annexin V was labelled with Tc-99m by hydrazinonicotinamide (HYNIC). Cell binding studies were carried out using cellular models of Parkinson's disease. Cell uptake studies were also performed after different levels of MPP+ treatment, and the correlation between the degree of apoptosis and Tc-99m-HYNIC-annexin V uptake was analysed. Results The specific activity of (TC)-T-99m-HYNIC-annexin V was 3.7-74 x 10(5) Bq center dot mg(-1) protein. In-vitro binding of Tc-99m-HYNIC-annexin V to model cells was specific, saturable and time dependent. Scatchard analysis gave a K-d of 7.16 +/- 1.78 nmol center dot l(-1), B-max values of 179 +/- 33 fmol per 10(6) cells (PC12) and 220 +/- 26 fmol per 10(6) cells (SHSY5Y). MPP+ at different concentrations can induce cell apoptosis in a dose-dependent manner; cellular uptake of 99mTc-HYNIC-annexin V as indicated by membrane-bound radiolabelled annexin V activity was linearly correlated with total fluorescence, as observed by FITC-annexin V flow cytometry (PC12: r = 0.924; SH-SY5Y: r = 0.937, P < 0.01). Conclusions Tc-99m-HYNIC-annexin V retains its receptor-binding activity and has a high affinity to cellular models of Parkinson's disease. The uptake of radioactivity correlated well with cell apoptosis rates; thus, Tc-99m-annexin V is a potential imaging agent with which to detect early neuron damage in Parkinson's disease.