Apoptosis and delayed luminescence of human leukemia jurkat T-cells after proton-irradiation and treatments with oxidant agents and flavonoids

We investigated apoptosis and delayed luminescence (DL) of human leukemia Jurkat cells under oxidative stress and irradiation conditions. Irradiation with 2 Gy but not 10 Gy of protons produced a significant increase in the apoptotic rate at 48 h after irradiation. Both doses consistently blocked the cell cycle at the G2/M phase within 24 h after irradiation, and there was a consistent decrease in the G2/M cell fraction 48 h after irradiation with 2 Gy but not 10 Gy. DL spectroscopy indicated that irradiation with 10 Gy of protons had rather modest effect on mitochondrial respiration and production of reactive oxygen species in Jurkat cells. The oxidant agents menadione (MD), hydrogen peroxide and the flavonoid quercetin (QC) potently induced apoptosis and G2/M arrest in Jurkat cells and decreased DL considerably. A significant enhancement of apoptosis induced by MD was obtained by pre-incubating Jurkat cells with 5uM QC or 0.5 uM epigallocatechin gallate (EHCG) for 24 h, as well as with 10 uM QC for 1 h, but not with 0.5uM QC for 24 h. Moreover, in the EGCG-MD combination the G2/M blockage persisted for at least 48 h, whereas a short incubation with 10 UM QC for 1 h exerted protective effects against H2O2. QC and MD at thigh doses exhibited virtually identical effects on DL over a wide time- interval (100 us – 10 ms), whereas EGCG exhibited a fairly uniform reduction of DL on the entire DL time-scale (11 us – 10 ms)