Mechanism of an inhibitory effect of nipradilol on rat vascular smooth muscle cell growth

Complete estrogen receptor blocker ICI182,780 promotes the proliferation of vascular smooth muscle cells

ICI182,780 is used in adjuvant therapies of breast cancer. As a complete estrogen receptor (ER) blocker, ICI182,780 may antagonize the effects of estrogen on the cardiovascular system. Estrogen inhibits the proliferation of vascular smooth muscle cells (VSMCs), which is one of the mechanisms that estrogen can exert cardioprotective effects. In the present study, to assess the effects of ICI182,780 on the proliferation of VSMCs, we cultured VSMCs isolated from rat aorta with or without the ER antagonist ICI182,780. The results of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, bromodeoxyuridine incorporation assay, viable cell count, immunochemical staining for proliferating cell nuclear antigen (PCNA), and S-phase ratio determined by flow cytometry revealed a remarkable proliferation of VSMCs after ICI182,780 treatment. ICI182,780 significantly enhanced cell growth in a dose-dependent manner (10(-8)-10(-5) M). Furthermore, the number of PCNA-positive cells and the S-phase progression of VSMCs increased after treatment with ICI182,780. Reverse transcriptase-polymerase chain reaction (RT-PCR) and western blot analysis showed that the mRNA and protein level of cyclin D1 in VSMCs increased under the treatment of ICI182,780. These data suggested that ICI182,780 can promote the growth of VSMCs, which might produce some adverse effects on the cardiovascular system.

Characterization of activation of MAP kinase superfamily in vasculature from diabetic rats

AIM

This study was investigated to characterize the activation mechanism of a mitogen-activated protein (MAP) kinase superfamily in diabetes in aortae and cultured vascular smooth muscle cells (VSMCs) from rats.

METHODS

Male Sprague-Dawley rats were used for this procedure, and diabetes was induced by streptozotocin injection at 50 mg/kg. After 6 weeks, the thoracic aortae from normal and diabetic rats were removed for detection of the MAP kinase superfamily by immunoblot analysis.

RESULTS

In aortae, the protein levels of extracellular signal-regulated protein kinase (ERK)-1, c-jun NH2-terminal protein kinase (JNK)-1 and -2, and p38 increased significantly more in diabetic rats than in normal rats. In contrast, phosphorylated protein levels of ERK-1 and -2, JNK-1, and p38 were significantly more elevated in diabetic rats than in normal rats. In VSMCs from normal rats, a high concentration of glucose cultured for three days significantly increased the phosphorylated protein levels of ERKs and p38, but not JNKs, without any change of these protein levels. Serum interleukin (IL)-1beta was significantly higher in diabetic rats than in normal rats. Several types of proinflammatory cytokine dose-dependently phosphorylated the levels of ERKs, JNK-1, and p38, but not JNK-2, in VSMCs from normal rats. In cells from diabetic rats, phosphorylated protein levels of ERKs and p38 were significantly elevated by IL-1beta. In addition, interferon-gamma phosphorylated the levels of ERKs in diabetic cells more than in normal cells.

CONCLUSION

Our results suggest that, under diabetic conditions, the MAP kinase superfamily was activated by different pathways in the vasculature; i.e., ERKs and p38 might be mainly phosphorylated by a complex of high concentrations of glucose and of several types of proinflammatory cytokines, but the phosphorylation of JNK-1 might depend on the concentration of proinflammatory cytokines such as IL-1beta, and/or additional unknown factors, except glucose.