Takuma Arai

Shinshu University, Shonai, Nagano, Japan

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Publications (7)32.3 Total impact

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    ABSTRACT: Adrenomedullin (AM) is a vasoactive peptide that possesses various bioactivities. AM receptors are dimers consisting of CLR with one of two accessory proteins, RAMP2 or RAMP3. The functional difference between CLR/RAMP2 and CLR/RAMP3 and the relationship between the two receptors remain unclear. To address these issues, we generated RAMP2 and RAMP3 knockout (-/-) mice and have been studying their physiological activities in the vascular system. AM-/- and RAMP2-/- mice die in utero due to blood vessel abnormalities, which is indicative of their essential roles in vascular development. In contrast, RAMP3-/- mice were born normally without any major abnormalities. In adult RAMP3-/- mice, postnatal angiogenesis was normal, but lymphangiography using indocyanine green (ICG) showed delayed drainage of subcutaneous lymphatic vessels. Moreover, chyle transport by intestinal lymphatics was delayed in RAMP3-/- mice, which also showed more severe interstitial edema than wild-type mice in a tail lymphedema model, with characteristic dilatation of lymphatic capillaries and accumulation of inflammatory cells. In scratch-wound assays, migration of isolated RAMP3-/- lymphatic endothelial cells was delayed as compared to wild-type cells, and AM administration failed to enhance the re-endothelialization. The delay in re-endothelialization was due to a primary migration defect rather than a decrease in proliferation. These results suggest that RAMP3 regulates drainage through lymphatic vessels, and that the AM-RAMP3 system could be a novel therapeutic target for controlling postoperative lymphedema.
    Journal of Molecular and Cellular Cardiology 09/2014; 77. DOI:10.1016/j.yjmcc.2014.09.017 · 5.22 Impact Factor
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    ABSTRACT: Background The purpose of this study was to analyze the influence of age on both the risk of hepatectomy and the prognosis in patients with hepatocellular carcinoma (HCC). Methods Patients undergoing an initial hepatectomy for HCC were classified into two age groups: ≥ 75 years (n = 113) and < 75 years (n = 499). Results A zero 90-day mortality was achieved in the elderly. Although the recurrence rate and recurrence sites were almost similar between the two groups, the 5-year survival rate in the elderly patients was significantly lower than that in the younger patients (46.0% vs. 57.6%; P = .018), possibly because of the higher incidence of deaths from other causes (26.8% vs. 10.4%; P = .011) in the elderly. Conclusions Selected elderly HCC patients can undergo a hepatectomy safely and can benefit from long-term HCC control comparable to that of their younger counterparts.
    The American Journal of Surgery 08/2014; DOI:10.1016/j.amjsurg.2014.05.026 · 2.41 Impact Factor
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    ABSTRACT: The aim of the present study was to evaluate whether serum alpha-fetoprotein (AFP) and des-gamma-carboxy prothrombin (DCP) trends might be correlated with overall survival rates in patients with recurrent hepatocellular carcinoma (HCC) undergoing trans-catheter arterial chemo-embolization (TACE). We performed a retrospective cohort study of 142 patients with recurrent HCC who were treated by TACE at our hospital from April 1990 to December 2011. Patients were divided into three groups, as follows, according to the trends of the two tumor markers AFP and DCP: the low group, comprising patients with tumor marker levels below the cutoff values (AFP 100 ng/mL and DCP 100 mAU/mL) both pre- and post-TACE; the decreased group, comprising patients with elevated tumor marker levels pre-TACE in whom the levels decreased post-TACE; and the elevated group, comprising patients with elevated tumor marker levels post-TACE. Analysis using a Cox proportional hazards model identified the DCP trend (elevated group vs. low group, hazard ratio 8.47, 95 % confidence interval 4.53-15.84, p < 0.0001), but not the AFP trend, as an independent prognostic factor for survival. While the AFP trend was correlated only with the overall response rate assessed using the modified Response Evaluation Criteria in Solid Tumors (mRECIST; p = 0.041), the DCP trend was strongly associated with both the overall response rate (p = 0.009) and the disease control rate (p = 0.004). The DCP trend might be useful for assessing treatment outcomes after TACE in patients with recurrent HCC.
    International Journal of Clinical Oncology 11/2013; 19(5). DOI:10.1007/s10147-013-0634-6 · 2.17 Impact Factor
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    ABSTRACT: Adrenomedullin (ADM), originally identified as a vasodilating peptide, is now recognized to be a pleiotropic molecule involved in both the pathogenesis of cardiovascular diseases and circulatory homeostasis. Homozygotes of ADM knockout mice (ADM-/-) were lethal at mid-gestation with abnormalities of vascular development and this finding clarified the angiogenic potency of ADM. Calcitonin gene-related peptide (CGRP), which has a structure and function similar to that of ADM, has been identified as a family peptide of ADM. Unlike ADM-/-, CGRP-/- were apparently normal. Therefore, the study of knockout mice first clarified the distinctly different physiological roles between ADM and CGRP. In contrast, heterozygotes of ADM knockout mice (ADM+/-) were alive but showed blood pressure elevation, reduced neovascularization, and enhanced neointimal formation by arterial injury. Based on these observations, there was hope ADM would have a therapeutic use. However, ADM has a short half-life in the blood stream and its application in chronic disease has limitations. Therefore, we focused on the ADM receptor system. The calcitonin-receptor-like receptor (CLR), which is the ADM receptor, associates with one of the accessory proteins, called receptor activity-modifying proteins (RAMPs). By interacting with RAMP1, CLR exhibits a high affinity for CGRP, whereas by interacting with either RAMP2 or -3, CLR exhibits a high affinity for ADM. We generated RAMP knockout mice and found that vascular phenotypes similar to ADM-/- were reproduced only in RAMP2-/-. This shows that RAMP2 is the key determinant of the vascular functions of ADM. RAMP2 could be an attractive therapeutic target in cardiovascular diseases.
    Current Protein and Peptide Science 06/2013; DOI:10.2174/13892037113149990052 · 2.33 Impact Factor
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    ABSTRACT: BACKGROUND: Revealing the mechanisms underlying the functional integrity of the vascular system could make available novel therapeutic approaches. We previously showed that knocking out the widely expressed peptide adrenomedullin (AM) or receptor activity-modifying protein 2 (RAMP2), an AM-receptor accessory protein, causes vascular abnormalities and is embryonically lethal. Our aim was to investigate the function of the vascular AM-RAMP2 system directly. METHODS AND RESULTS: We generated endothelial cell-specific RAMP2 and AM knockout mice (E-RAMP2-/-, E-AM-/-). Most E-RAMP2-/- mice died perinatally. In surviving adults vasculitis occurred spontaneously. With aging, E-RAMP2-/- mice showed severe organ fibrosis with marked oxidative stress and accelerated vascular senescence. Later, liver cirrhosis, cardiac fibrosis and hydronephrosis developed. We next used a line of drug-inducible E-RAMP2-/- mice (DI-E-RAMP2-/-) to induce RAMP2-deletion in adults, which enabled us to analyze the initial causes of the aforementioned vascular and organ damage. Early after the induction, pronounced edema with enhanced vascular leakage occurred. In vitro analysis revealed the vascular leakage to be caused by actin disarrangement and detachment of endothelial cells. We found that the AM-RAMP2 system regulates the Rac1-GTP/RhoA-GTP ratio and cortical actin formation, and that a defect in this system causes the disruption of actin formation, leading to vascular and organ damage at the chronic stage after the gene deletion. CONCLUSIONS: Our findings show that the AM-RAMP2 system is a key determinant of vascular integrity and homeostasis from prenatal stages through adulthood. Furthermore, our models demonstrate how endothelial cells regulate vascular integrity and how their dysregulation leads to organ damage.
    Circulation 01/2013; 127(7). DOI:10.1161/CIRCULATIONAHA.112.000756 · 14.95 Impact Factor
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    ABSTRACT: Embryonic stem cells (ESCs) are a useful source for various cell lineages. So far, however, progress toward reconstitution of mature liver morphology and function has been limited. We have shown that knockout mice deficient in adrenomedullin (AM), a multifunctional endogenous peptide, or its receptor-activity modifying protein (RAMP2) die in utero due to poor vascular development and hemorrhage within the liver. In this study, using embryoid bodies (EBs)-culture system, we successfully induced liver sinusoidal endothelial-like cells by modulation of AM-RAMP2. In an EB differentiation system, we found that co-administration of AM and SB431542, an inhibitor of transforming growth factor β (TGFβ) receptor type 1, markedly enhanced differentiation of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1)/stabilin-2-positive endothelial cells. These cells showed robust endocytosis of acetylated low-density lipoprotein (Ac-LDL) and upregulated expression of liver sinusoidal endothelial cells (LSECs)-specific markers, including factor 8 (F8), Fc-γ receptor 2b (Fcgr2b), and mannose receptor C type 1 (Mrc1), and also possessed fenestrae-like structure, a key morphological feature of LSECs. In RAMP2-null liver, by contrast, LYVE-1 was downregulated in LSECs, and the sinusoidal structure was disrupted. Our findings highlight the importance of AM-RAMP2 signaling for development of LSECs.
    Peptides 07/2011; 32(9):1855-65. DOI:10.1016/j.peptides.2011.07.005 · 2.61 Impact Factor
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    ABSTRACT: Donor organ damage caused by cold preservation is a major problem affecting liver transplantation. Cold preservation most easily damages liver sinusoidal endothelial cells (LSECs), and information about the molecules modulating LSECs function can provide the basis for new therapeutic strategies. Adrenomedullin (AM) is a peptide known to possess anti-apoptotic and anti-inflammatory properties. AM is abundant in vascular endothelial cells, but levels are comparatively low in liver, and little is known about its function there. In this study, we demonstrated both AM and its receptors are expressed in LSECs. AM treatment reduced LSECs loss and apoptosis under cold treatment. AM also downregulated cold-induced expression of TNFalpha, IL1beta, IL6, ICAM1 and VCAM1. AM reduced apoptosis and expression of ICAM1 and VCAM1 in an in vivo liver model subjected to cold storage. Conversely, apoptosis was exacerbated in livers from AM and RAMP2 (AM receptor activity-modifying protein) knockout mice. These results suggest that AM expressed in LSECs exerts a protective effect against cold-organ damage through modulation of apoptosis and inflammation.
    Peptides 05/2010; 31(5):865-71. DOI:10.1016/j.peptides.2010.01.011 · 2.61 Impact Factor