Effects of all‑trans retinoic acid on VEGF and HIF‑1α expression in glioma cells under normoxia and hypoxia and its anti‑angiogenic effect in an intracerebral glioma model.

All‑trans retinoic acid (ATRA) is one of the most potent inducers of differentiation and is capable of inducing differentiation and apoptosis in glioma cells. However, the effect of ATRA on glioma angiogenesis is yet to be elucidated. The present study investigated the effects of ATRA on the expression of vascular endothelial growth factor (VEGF) and hypoxia‑inducible factor‑1α (HIF‑1α) in various glioma cell lines under normoxia and hypoxia. The effect of ATRA on angiogenesis in a rat intracerebral glioma model was also investigated, with the aim of revealing the effect of ATRA on glioma angiogenesis. In the present study, U‑87 MG and SHG44 glioma cells were treated with ATRA at various concentrations (0, 5, 10, 20 and 40 µmol/l) under normoxia or hypoxia. Quantitative polymerase chain reaction and western blot analysis were used to investigate VEGF and HIF‑1α mRNA and protein expression, respectively. An intracerebral glioma model was generated using intracerebral implantation of C6 glioma cells into rats. Tumor‑bearing rats were treated with ATRA at different doses (0, 5 and 10 mg/kg/day) for two weeks, and immunohistochemical assays were performed to detect the cluster of differentiation 34‑positive cells in order to evaluate the microvessel density (MVD) in each group. Following ATRA treatment, the expression of VEGF and HIF‑1α was found to vary among the different concentration groups. In the glioma cells in the lower concentration groups (5 and 10 µmol/l ATRA), a significant increase in VEGF and HIF‑1α expression was observed. Conversely, a significant decrease in VEGF and HIF‑1α expression was found in the glioma cells in the high ATRA concentration group (40 µmol/l), compared with that in the cells in the control group. Furthermore, in the rat intracerebral glioma model, ATRA decreased glioma MVD, particularly in the high‑dose group (10 mg/kg/day), compared with the control group. These results suggest that ATRA may exhibit a dose‑dependent effect on glioma angiogenesis and may inhibit glioma angiogenesis in vivo.