Tetramethylpyrazine Improves Monocrotaline-Induced Pulmonary Hypertension through the ROS/iNOS/PKG-1 Axis.

Background: Tetramethylpyrazine (TMP), a potent anti-free radical and anti-inflammations substance, has been demonstrated to possess a direct vessel relaxation property. This study aimed to evaluate the effect of TMP treatment in pulmonary hypertension (PH) and test the hypothesis that TMP prevents or reverses the process of PH. Methods: Rats (n = 36) injected with 50 mg/kg of monocrotaline (MCT) subcutaneously 4 weeks to develop PH were then randomized to TMP (5 mg/kg per day) for another 4 weeks. Hemodynamics was evaluated via the right ventricle. Pulmonary vessels structural remodeling and inflammation were examined by histologic and transmission electron microscopy observation. The expression of inducible nitric oxide synthase (iNOS) and cGMP-dependent protein kinases 1 (PKG-1) was detected by immunohistochemical staining and Western blot. Generation of reactive oxygen species (ROS) and antioxidation species was measured by biochemical analyses. Results: MCT increased PH and right ventricle hypertrophy. TMP alleviated pulmonary arterial pressure elevation, leukocyte infiltration, and structural remodeling of pulmonary arterials induced by MCT successfully. TMP treatment significantly increased the PKG-1 expression and suppressed the iNOS expression. The activity of superoxide dismutase (SOD), glutathione peroxidase (GSH), and catalase (CAT) was significantly higher than control group, while malondialdehyde (MDA) levels were lower compared with MCT group. Conclusion: TMP can suppress established MCT-induced PH through the ROS/iNOS/PKG axis. The underlying mechanisms may be associated with its anti-inflammatory, antioxidant, and antiproliferative properties in pulmonary arterial.

[Effects of mammalian-target-of-rapamycin pathway on lapatinib resistance in breast cancer MDA-MB-231 cells].

OBJECTIVE: To establish a lapatinib resistance cell line for elucidating the mechanisms of drug resistance of lapatinib in human breast cancer cells. METHODS: The human breast cancer MDA-MB-231 cells were exposed in an incremental dose of lapatinib to establish a lapatinib resistance rMDA-MB-231 cell line. The assay of methyl thiazolyl tetrazolium (MTT) was used to detect the cytotoxic activity of lapatinib against MDA-MB-231 and rMDA-MB-231 cells. The protein expression was detected by Western blot. Small interfering RNA was used to specifically knock down mammalian-target-of-rapamycin (mTOR) in rMDA-MB-231 cells. Apoptosis was determined by fluorescein isothiocyanate (FITC)-annexin V/PI staining and flow cytometry. RESULTS: The human breast cancer lapatinib resistance cell line rMDA-MB-231 was induced by lapatinib. The half maximal inhibitory concentration (IC50) values of lapatinib against MDA-MB-231 and rMDA-MB-231 cells were (6.1 ± 0.6) and (34.9 ± 2.7) µmol/L respectively (P < 0.01). Compared with MDA-MB-231 cells, the protein expression of mTOR in rMDA-MB-231 cells was significantly up-regulated. The protein expression of mTOR was significantly down-regulated by specific siRNA duplexes in rMDA-MB-231 cells. After siRNA interference, 20 µmol/L lapatinib was added into control, negative siRNA control and mTOR-targeted siRNA groups respectively. The percents of cell apoptosis in control, negative control and targeted siRNA groups were 13.4% ± 2.5%, 14.2% ± 2.8% and 34.6% ± 5.8% respectively, there was no significance between the first two groups (P > 0.05) , and there was significant difference between the control and targeted siRNA group (P < 0.01) . CONCLUSIONS: The up-regulation of mTOR plays an important role in the lapatinib-resistant phenotype of human breast cancer rMDA-MB-231 cells. And the down-regulation of mTOR increases the apoptotic death of lapatinib against rMDA-MB-231 cells.