Nozomi Fukai

Adrenomedullin inhibits angiotensin II-induced oxidative stress and gene expression in rat endothelial cells.

Adrenomedullin (AM), a potent vasodilator peptide, has recently been suggested to function as an endogenous antioxidant. However, its potential site of action at the cellular level has not been clarified. The present study was undertaken to investigate whether AM directly inhibits intracellular reactive oxygen species (ROS) generation and redox-sensitive gene expression stimulated by angiotensin (Ang) II in rat aortic endothelial cells (ECs). Ang II (10-7 mol/l) significantly increased intracellular ROS levels in ECs as measured by dichlorofluorescein (DCF) fluorescence. AM inhibited Ang II-stimulated ROS generation in a dose-dependent manner and this effect was abolished by a superoxide radical scavenger, NAD(P)H oxidase inhibitor, and a protein kinase A (PKA) inhibitor, and mimicked by a cell-permeable cAMP analog. A real-time reverse transcription−polymerase chain reaction (RT-PCR) study showed that Ang II significantly upregulated a set of redox-sensitive genes (ICAM-1, VCAM-1, PAI-1, tissue factor, MCP-1, osteopontin), and these effects were blocked by an antioxidant, N-acetyl cysteine (NAC). AM similarly and dose-dependently inhibited the Ang II-induced upregulation of the entire set of these genes via a receptor-mediated and PKA-dependent pathway, and the degrees of inhibition were similar to those by NAC. In conclusion, the present study demonstrated that AM potently blocked the Ang II-stimulated intracellular ROS generation from NAD(P)H oxidase and the subsequent redox-sensitive gene expression via a cAMP-dependent mechanism in ECs, suggesting that AM has vasculoprotective effects against pro-oxidant stimuli.

Adrenomedullin is an autocrine/paracrine growth factor for rat vascular smooth muscle cells.

Adrenomedullin is a potent vasodilator peptide secreted by vascular endothelial and smooth muscle cells. Adrenomedullin stimulates the proliferation of quiescent rat vascular smooth muscle cells (VSMCs) via p42/p44 ERK/MAP kinase activation. Recently, receptor-activity-modifying proteins (RAMPs) have been shown to transport calcitonin-receptor-like-receptor (CRLR) to the cell surface to present either as CGRP receptor or adrenomedullin receptor. We investigated whether adrenomedullin acts as an autocrine/paracrine growth factor for cultured rat VSMCs and whether coexpressions of RAMP isoform and CRLR may mediate p42/p44 ERK/MAP kinase activation by adrenomedullin. Adrenomedullin dose-dependently stimulated the proliferation of quiescent rat VSMCs, and this effect was inhibited by an adrenomedullin receptor antagonist, a MAP kinase kinase inhibitor and phosphatidylinositol 3-kinase inhibitors. Addition of either CGRP(8-37) or anti-adrenomedullin antibody to exponentially growing rat VSMCs inhibited the serum-induced cell proliferation, suggesting its role as an autocrine/paracrine growth factor. Cotransfection of RAMP2 or RAMP3 with CRLR into rat VSMCs potentiated activation of cAMP activity, but not of p42/p44 ERK/MAP kinase activity in response to adrenomedullin. Our results suggest that adrenomedullin is an autocrine/paracrine growth factor for rat VSMCs via p42/p44 ERK/MAP kinase and phosphatidylinositol 3-kinase pathways and that it is not mediated by human RAMP-CRLR receptors.

Rifampicin as an oral angiogenesis inhibitor targeting hepatic cancers.

Angiogenesis is an important therapeutic target in cancer, and to fully exploit its therapeutic potential, combination chemotherapeutic/antiangiogenic regimens should be optimized and delivered earlier to more patients. Ideally, this could be done by a single potent oral agent with established safety. Rifampicin, a semisynthetic antibiotic derived from the rifamycins, is one of the most commonly used pharmaceutical compounds worldwide in the treatment of tuberculosis. Here, we present the effects of oral rifampicin on human cancer progression and its antiangiogenic properties, which were comparable to the angiogenesis inhibitor endostatin. Clinically, low-dose p.o. administration of rifampicin to six high-risk patients with hepatitis C virus-related liver cirrhosis resulted in a single occurrence of hepatocellular carcinoma during the follow-up period of 97.3 +/- 29.1 (mean +/- SD) months. Experimentally, rifampicin rapidly and markedly down-regulated the expression of a wide spectrum of angiogenesis-associated genes in growing human microvascular endothelial cells, thereby suppressing endothelial cell proliferation and migration. Rifampicin, at higher concentrations, also directly inhibited the growth of a variety of human cancer cells. P.o. administration of rifampicin significantly inhibited in vivo growth and metastases of subcutaneous human cancer xenografts. Thus, the potent antiangiogenic properties of oral rifampicin therapy were effective in suppressing cancer progression. It provides a promising new addition to antiangiogenic strategies for designing human cancer therapies. Considering the clinical pharmacokinetics of rifampicin, which enters the enterohepatic circulation and undergoes subsequent hepatic accumulation, it may be especially beneficial as an antitumor agent targeting hepatobiliary tumors.

Endothelin-1 induces cyclooxygenase-2 expression and generation of reactive oxygen species in endothelial cells.

Since both endothelin-1 (ET-1) and aldosterone have been shown to induce expression of several pro-inflammatory genes, including cyclooxygenase-2 (COX-2), in the vasculature as a cardiovascular risk hormone, the present study was undertaken to examine the effects of ET-1 and aldosterone on COX-2 gene expression as measured by a real-time reverse transcriptasepolymerase chain reaction in aortic endothelial cells. Treatment with ET-1(10-7 M) markedly upregulated COX-2 mRNA levels in rat endothelial cells, whereas aldosterone (10-7 M) did not show any effect. The ET-1-induced COX-2 upregulation was inhibited by pretreatment with a non-selective endothelin receptor antagonist (TAK044), a protein kinase C inhibitor (GF109203X), and a MEK inhibitor (PD98059). Furthermore, ET-1 increased intracellular reactive oxygen species generation as estimated by the measurement of dichlorofluorescein fluorescence, whose effect was blocked by a COX-2 inhibitor (NS398). Our data show that ET-1 induces COX-2 upregulation in rat endothelial cells via a protein kinase C-dependent and extracellular signal-regulated kinasedependent pathway, which may largely contribute to the generation of intracellular reactive oxygen species.