Figure 2.

Loss of TDO activity in HeLa-hTDO cells under hypoxic conditions. (a) Kynurenine detection in cell culture supernatants of tetracycline (0–160 ng/mL) stimulated HeLa-hTDO cells incubated under hypoxia (white bars) or normoxia (grey bars). (b) Kynurenine detection in cell culture supernatants in tetracycline stimulated (160 ng/mL) HeLa-hTDO cells that have been incubated under different oxygen conditions (1–20% O₂) for 72 h. (c + d) Reoxygenation study: HeLa-hTDO cells were incubated under normoxia (20% O₂) or hypoxia (1% O₂) with or without tetracycline (40 ng/mL) for 72 h. Then the kynurenine amount produced by TDO was detected in cell culture supernatants. A second experimental group was subsequently transferred to normoxia and after incubation of additional 48 h (c) or 1–5 h, 24 h, and 48 h (d) the kynurenine amount was also detected in cell culture supernatants. In all experiments a significant alteration of kynurenine production under hypoxia as compared to the normoxia control is marked with asterisks (^∗ p ≤ 0.05; ^∗∗∗ p ≤ 0.001; ^∗∗∗∗ p ≤ 0.0001, n.s. = not significant), two-tailed unpaired t-test; n = 3 independent experiments with three replicates each. The bars indicate the mean value ± SEM.