Bromocriptine Induces Autophagy-Dependent Cell Death in Pituitary Adenomas.

BACKGROUND: Bromocriptine (BRC) is effective in patients with prolactinoma. However, the cytotoxic mechanism of BRC remains unknown.

METHODS: Slices for immunohistochemical pathology were randomly selected from 37 paraffin-embedded prolactinoma tissue sections. LC3 was detected by immunohistochemistry. GH3 and MMQ cells were treated by BRC and/or rapamycin (RAPA). Cell viability and the cell cycle were measured by CCK-8 and flow cytometry, respectively. Enzyme-linked immunosorbent assay measured prolactin secretion. Protein expression was detected by Western blot or immunofluorescence.

RESULTS: LC3 was significantly expressed in prolactinoma in which patients were treated exclusively with BRC. LC3 expression was negative in normal tissues and prolactinoma in which patients were not treated with BRC. Treatment with 60 μM BRC for 24 hours induced cell death in MMQ cells by up to 50%. However, 110 μM BRC was required to produce a similar effect in GH3 cells. The cell cycle was arrested at the G0-G1 phase and S phase. As the concentration and time increased, the conversion ratio of LC3-I to LC3-II increased and prolactin secretion decreased. In addition, Bcl-2 and BAX expression was decreased. The cell viability, prolactin level, and G0-G1 cells are similar in MMQ cells treated with RAPA and a low concentration of BRC and MMQ cells treated with a high concentration of BRC. Compared with the effects of a high concentration of BRC, treatment with RAPA and a low concentration of BRC effectively increase the conversion rate of LC3-I to LC3-II.

CONCLUSION: BRC-treated pituitary adenoma cells mainly underwent autophagic cell death rather than apoptosis.