Fig. 4. Time- and concentration-dependent inhibitory effect of carnosine on GS expression in U87 and U251 cells under conditions of normoxia, hypoxia, Gln (4 mM) treatment, and Gln deprivation.

Under different conditions, cells were treated with 50 mM carnosine for different durations (24 and 48 h) (a, b) or treated with different concentrations of carnosine (25, 50, and 75 mM) for 48 h (c, d). Western blot experiments were performed to detect GS levels. The results are expressed as the mean ± SD. n ≥ 3. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 vs. control group.