Metformin suppresses growth and adrenocorticotrophic hormone secretion in mouse pituitary corticotroph tumor AtT20 cells.

Pituitary corticotroph tumors lead to excess adrenocorticotrophic hormone (ACTH) secretion, resulting in Cushing's disease (CD), which is associated with significant mortality. Standard treatments include neurosurgery, radiotherapy and medical therapy. Both surgery and radiotherapy have undesirable complications and high recurrence rates. At present, there is only one medical option available that targets pituitary adenoma and ACTH secretion, the drug pasireotide. However, hyperglycemia is common during pasireotide treatment. In addition, some patients have discontinued pasireotide treatment because of hyperglycemia-related adverse events or uncontrolled diabetes. New medical treatments directly targeting the corticotroph cells and suppressing ACTH secretion are urgently required. Metformin is a commonly used antidiabetic drug that has been widely used to control the hyperglycemia that occurs in patients with CD, which is secondary to both cortisol excess and pasireotide treatment. Recent studies suggest that metformin has direct anticancer activities against many tumor cell lines. In the present study, we investigated whether metformin exerts an anti-tumor effect by directly targeting pituitary corticotroph tumors and exploring the underlying mechanisms. Using the mouse corticotroph tumor cells, AtT20 cells, we report that metformin inhibited cell proliferation, promoted cell apoptosis and decreased ACTH secretion but did not block the cell cycle in cells. The apoptosis induced by metformin was accompanied by increased caspase-3 activity. Meanwhile, metformin down-regulated the anti-apoptotic protein B cell lymphoma 2 (Bcl-2) but up-regulated the pro-apoptotic protein Bcl2-associated X (BAX), which suggests the involvement of the mitochondrial-mediated apoptosis pathway. Furthermore, metformin promoted AMP-activated protein kinase (AMPK) phosphorylation but inhibited insulin-like growth factor-1 receptor (IGF-1R) expression, protein kinase B (PKB/AKT) phosphorylation and mammalian target of rapamycin (mTOR) phosphorylation. Finally, the IGF-1R inhibitor picropodophyllin (PPP) significantly inhibited the cell proliferation of AtT20 cells. We conclude that metformin inhibits cell proliferation and induces apoptosis in AtT20 cells by activating AMPK/mTOR and inhibiting IGF-1R/AKT/mTOR signaling pathways. Metformin may have direct antitumor activity against pituitary corticotroph tumors.

[Effect of metformin on proliferation and apoptosis of rat prolactinoma MMQ cells and related mechanisms].

Objective To investigate the effect of metformin on the cell proliferation, cell cycle and apoptosis of rat prolactinoma MMQ cells in vitro and related molecular mechanisms. Methods The MMQ cells were treated with 1.25, 2.5, 5, 10, 20 mmol/L metformin for 48 hours. CCK-8 assay was used to assess the cell proliferation ability; flow cytometry was used to analyze the cell cycle distribution and apoptosis; Western blotting was performed to detect the expressions of AMPKα1/2, p-AMPKα, mTOR, p-mTOR, insulin like growth factor 1 receptor (IGF-1R), ERK1/2, p-ERK1/2, AKT, p-AKT, P21, CDK4, cyclin D1, caspase-3, cleaved caspase-3(c-caspase-3), Bcl-2 and BAX. Results Compared with the control group, metformin inhibited cell proliferation, induced cell cycle arrest in the G0/G1 phase and promoted cell apoptosis in MMQ cells. The expressions of P21 and c-caspase-3 increased, meanwhile, the expressions of CDK4, cyclin D1, caspase-3 and Bcl-2 decreased by metformin. Besides, the expression of p-AMPKα was elevated, but p-mTOR was reduced. Furthermore, the expressions of IGF-1R, p-AKT and p-ERK descended after metformin treatment. Conclusion Metformin could inhibit cell proliferation, induce cell cycle arrest and apoptosis in MMQ cells by activating AMPK/mTOR signaling pathway and inhibiting IGF-1R signaling pathway.

Isolated double adrenocorticotropic hormone-secreting pituitary adenomas: A case report and review of the literature.

Only a few cases of double or multiple pituitary adenomas have previously been reported in the literature; however, isolated double adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas are even more rare. The present study reports a rare case of a 50-year-old female patient who presented with typical clinical features of Cushing's disease and was diagnosed with isolated double ACTH-secreting pituitary adenomas. Endocrinological examination revealed an ACTH-producing pituitary adenoma, and preoperative magnetic resonance imaging (MRI) demonstrated a microadenoma with a lower intensity on the right side of the pituitary gland. The patient underwent endoscopic endonasal transsphenoidal surgery, which revealed another pituitary tumor in the left side of the pituitary gland. The two, clearly separated, pituitary adenomas identified in the same gland were completely resected. Immunohistochemistry and pathology revealed that the clearly separated double pituitary adenomas were positive for ACTH, thyroid-stimulating, growth and prolactin hormones. Postoperatively, the levels of ACTH and cortisol hormone decreased rapidly. The case reported in the present study is considerably rare, due to the presence of a second pituitary adenoma in the same gland, which was not detected by preoperative MRI scan, but was noticed during surgery. Intraoperative evaluation may be important in the identification of double or multiple pituitary adenomas.

[Role of TRPV4 channels in regulation of eNOS expression in brain microvascular endothelial cells under the condition of mechanical stretch].

OBJECTIVE: To identify the subtype of transient receptor potential (TRPs) channel involved in stretch-induced injury of human brain microvascular endothelial cells (HBMEC) and to explore the mechanism responsible for eNOS expression.
 METHODS: TRPs expression was examined by Western blot and immunocytofluoresence in the cultured HBMEC. Mechanical stretch was performed by mini-type multi-functional bio-impact machine. The levels of free calcium ion in cells were examined by the flow cytometry. The eNOS expression was detected by Western blot.
 RESULTS: The mRNA and protein expression of TRPV4 was detected in HBMEC by qRT-PCR, Western blot and immunocytofluoresence. The levels of free calcium ion in the stretch-treated HBMEC was significantly decreased in the presence of TRPV4 specific inhibitor (P<0.001), but there was no difference in calcium levels between the stretch and the control or unspecific inhibitor group (P=0.072 or 0.308). The levels of eNOS protein in the stretch-treated HBMEC were reduced in the presence of TRPV4 specific inhibitor or NOS inhibitor (P<0.05), but it was not changed compared with that in the control group (P>0.05).
 CONCLUSION: The eNOS expression is up-regulated under the condition of mechanic stretch, which is related to the activation of TRPV4, resulting in the influx of calcium.