Arsenic Trioxide Induces Platelet Apoptosis

Arsenic trioxide, a component of Traditional Chinese Medicine, is known as an effective anticancer drug especially in the treatment of acute promyelocytic leukaemia (APL). APL has emerged as the most curable subtype of acute myeloid leukaemia since the widely use of arsenic trioxide-based chemotherapy. However, recent researches show that thrombocytopenia occurred in 79% of the relapsed or refractory APL patients treated with arsenic trioxide, and part of the APL patients had to be stopped treatment because of catastrophic bleeding, such as intracranial and pulmonary haemorrhage. Thrombocytopenia also occurred in 43% of the myelodysplastic syndrome patients treated with arsenic trioxide. Recently, arsenic trioxide has been proved to have a pro-apoptotic effect on various kinds of nucleated tumour cells or non-tumour cells. The effect of arsenic trioxide on enucleated platelet, however, still remains unclear. The aim of current study is to investigate whether arsenic trioxide induces platelet apoptosis.

Washed platelets (3 × 10⁸/ml) were incubated with different concentrations of arsenic trioxide or vehicle at 37°C for 4 hours. Then, mitochondrial inner transmembrane potential (ΔΨm) and phosphatidylserine (PS) exposure were tested by flow cytometry. In the mean time, the treated platelets were analyzed by western blot for the expression levels of pro-apoptotic protein (Bax), and anti-apoptotic proteins (Bcl-2 and Bcl-X_L). Activation of caspase-3 was also examined by western blot using an anti-caspase-3 antibody.

ΔΨm depolarization and PS exposure were dose-dependently induced in platelets incubated with different concentrations (2 uM, 4 uM, 8 uM, 16 uM) of arsenic trioxide as detected by flow cytometry, and the lowest concentration of arsenic trioxide incurring ΔΨm depolarization and PS exposure was 4 umol/L. Simultaneously, arsenic trioxide induced up-regulation of Bax and down-regulation of Bcl-2 and Bcl-X_L in a dose-dependent manner. Furthermore, 17 kD cleaved caspase-3 fragments were dose-dependently induced in platelets treated with different concentrations of arsenic trioxide indicating that caspase-3 was activated by arsenic trioxide.

Taken together, the data indicate that arsenic trioxide induces platelet apoptosis in vitro, which might suggest a novel pathogenic mechanism of thrombocytopenia in the patients who treated with arsenic trioxide.

No relevant conflicts of interest to declare.