Transient generation of hydrogen peroxide is responsible for carcinostatic effects of hydrogen combined with platinum nanocolloid,together with increases intracellular ROS,DNA cleavages,and proportion of G2/M-phase

In our previous study, we demonstrated that combined treatment with hydrogen (H₂) and platinum nanocolloid (Pt-nc) exerted markedly antiproliferative effects on cancer cells compared with each treatment alone. However, because the related mechanisms remain unclear, we investigated carcinostatic mechanisms of the combined treatment with H₂ + Pt-nc. Significant suppression of cell proliferation was confirmed at 52?h following combined treatment, and the similar effect was also observed by the 30- or 40-min transient treatment with H₂?+?Pt-nc. The transient treatments led to changes in cell size and morphology, loss of microvilli, and apoptosis-like cell death at 120 h after treatment. Moreover, transient combined treatment with H₂?+?Pt-nc induced cell-cycle arrest, as reflected by decreased proportions of G1-phase cells and accumulation of G2/M-phase cells. In contrast, intracellular peroxide levels were temporarily and significantly increased immediately after H₂?+?Pt-nc treatment but not after treatment with H₂ or Pt-nc alone. Additionally, combined treatment-induced carcinostatic effects were significantly diminished in the presence of catalase, and marked hydrogen peroxide (H₂O₂) generation was confirmed after mixing Pt-nc into cell culture media containing a high concentration of H₂. These changes are in agreement with the results that carcinostatic effects were induced after only 40 min of treatment with H₂?+?Pt-nc. Thus, transient and marked generation of H₂O₂ is responsible for the carcinostatic effects of combined treatment with H₂?+?Pt-nc.