Toshifumi Shimada

Role of host angiotensin II type 1 receptor in tumor angiogenesis and growth

Although the renin angiotensin system (RAS) is a major regulator of vascular homeostasis, the role of the RAS in tumor angiogenesis is little understood. Here we show that host angiotensin II (ATII) type 1 (AT1) receptor plays an important role in angiogenesis and growth of tumor cells engrafted in mice. Subcutaneous B16-F1 melanoma-induced angiogenesis as assessed by tissue capillary density and microangiography was prominent in WT mice but was reduced in AT1a receptor-deficient (AT1a-/-) mice. Consequently, tumor growth rate was significantly slower, and the mouse survival rate was greater, in AT1a-/- mice than in WT mice. Tumor growth was also reduced in WT mice treated with TCV-116, a selective blocker of AT1 receptor. Because the beta-galactosidase gene was inserted into the AT1a gene locus in AT1a-/- mice, the site of beta-galactosidase expression represents the AT1a receptor expression in these mutant mice. In tumor-implanted AT1a-/- mice, the major site of the beta-galactosidase expression was macrophages in tissues surrounding tumors. Moreover, the number of infiltrated macrophages was significantly lower in AT1a-/- mice than in WT mice, and double-immunofluorescence staining revealed that these macrophages expressed VEGF protein intensively. Therefore, the host ATII-AT1 receptor pathway supports tumor-associated macrophage infiltration, which results in enhanced tissue VEGF protein levels. The host ATII-AT1 receptor pathway thereby plays important roles in tumor-related angiogenesis and growth in vivo.

Angiogenesis and Vasculogenesis Are Impaired in the Precocious-Aging klotho Mouse

Background—The effects of aging on angiogenesis (vascular sprouting) and vasculogenesis (endothelial precursor cell [EPC] incorporation into vessels) are not well known. We examined whether ischemia-induced angiogenesis/vasculogenesis is altered in klotho (kl) mutant mice, an animal model of typical aging. Methods and Results—After unilateral hindlimb ischemia, laser Doppler blood-flow (LDBF) analysis revealed a decreased ischemic-normal LDBF ratio in kl mice. Tissue capillary density was also suppressed in kl mice (+/+>+/kl>kl/kl). Aortic-ring culture assay showed impaired angiogenesis in kl/kl mice, accompanied by reduced endothelium-derived nitric oxide release. Moreover, the rate of transplanted homologous bone marrow cells incorporated into capillaries in ischemic tissues (vasculogenesis) was lower in kl/kl mice than in wild-type (+/+) mice, which was associated with a decrease in the number of c-Kit+CD31+ EPC-like mononuclear cells in bone marrow and in peripheral blood. Finally, the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor cerivastatin restored the impaired neovascularization in kl/kl mice, accompanied by an increase in c-Kit+CD31+ cells in bone marrow and peripheral blood, and enhanced angiogenesis in the aortic-ring culture. Conclusions—Angiogenesis and vasculogenesis are impaired in kl mutant mice, a model of typical aging. Moreover, the age-associated impairment of neovascularization might be a new target of statin therapy.

Evidence for the importance of angiotensin II type 1 receptor in ischemia-induced angiogenesis.

The role of the renin-angiotensin system (RAS) in angiogenesis is little known. Here, we show that the angiotensin II (ATII) type 1 (AT1) receptor plays an important role in ischemia-induced angiogenesis. Well-developed collateral vessels and angiogenesis were observed in wild-type (WT) mice in response to hindlimb ischemia, whereas these responses were reduced in ATII type 1a receptor knockout (AT1a(-/-)) mice. Ischemia-induced angiogenesis was also impaired in WT mice treated with the AT1 receptor blocker TCV-116. These effects were not due to reduced systemic blood pressure (SBP), because hydralazine treatment preserved angiogenesis in WT mice although it reduced SBP to a level similar to that of AT1a(-/-) mice. Infiltration of inflammatory mononuclear cells (MNCs), including macrophages and T lymphocytes, was suppressed in the ischemic tissues of AT1a(-/-) mice compared with WT mice. Double immunofluorescence staining revealed that infiltrated macrophages and T lymphocytes expressed VEGF, and the expression of VEGF and monocyte chemoattractant protein-1 was also decreased in AT1a(-/-). Finally, the impaired angiogenesis in AT1a(-/-) mice was rescued by intramuscular transplantation of MNCs obtained from WT mice, further indicating the importance of MNC infiltration in ischemia-induced angiogenesis. Thus, the ATII--AT1 receptor pathway promotes early angiogenesis by supporting inflammatory cell infiltration and angiogenic cytokine expression.

Hypoxic preconditioning augments efficacy of human endothelial progenitor cells for therapeutic neovascularization.

A subset of human peripheral blood mononuclear cells (PB-MNCs) differentiate into endothelial progenitor cells (EPCs) that participate in postnatal neovascularization. Although tissue ischemia can mobilize EPCs from bone marrow, the effects of hypoxia on differentiation and angiogenic function of EPCs are little known. We examined whether hypoxic conditioning would modulate differentiation and function of human PB-MNC-derived EPCs. A subset of PB-MNCs gave rise to EPC-like attaching (AT) cells under either normoxic or hypoxic conditions. However, hypoxia much enhanced the differentiation of AT cells from PB-MNCs compared with normoxia. AT cells released vascular endothelial growth factor (VEGF) protein and expressed CD31 and kinase insert domain receptor/VEGFR-2, endothelial lineage markers, on their surface, which were also enhanced by hypoxia. Both a neutralizing anti-VEGF mAb and a KDR-specific receptor tyrosine kinase inhibitor, SU1498, suppressed PB-MNC differentiation into EPC-like AT cells in a dose-dependent manner. Migration of AT cells in response to VEGF as examined by a modified Boyden chamber apparatus was also enhanced by hypoxia. Finally, in vivo neovascularization efficacy was significantly enhanced by in vitro hypoxic conditioning of AT cells when cells were transplanted into the ischemic hindlimb of immunodeficient nude rats. In conclusion, hypoxia directly stimulated differentiation of EPC-like AT cells from human PB-MNC culture. Moreover, hypoxic preconditioning of AT cells before in vivo transplantation is a useful means to enhance therapeutic vasculogenesis.

Hyperhomocysteinemia Impairs Angiogenesis in Response to Hindlimb Ischemia

Abstract—Hyperhomocysteinemia (HH) is an independent risk factor for atherosclerosis, including peripheral arterial occlusive disease (PAOD). Because angiogenesis and collateral vessel formation are important self-salvage mechanisms for ischemic PAOD, we examined whether HH modulates angiogenesis in vivo in a rat model of hindlimb ischemia. Rats were divided into 3 groups: the control group was given tap water, the HH group was given water containing l-methionine (1 g · kg−1 · d−1), and the HH+L-arg group was given water containing methionine (1 g · kg−1 · d−1) and l-arginine (2.25 vol%). At day 14 of the dietary modifications, the left femoral artery and vein were excised, and the extent of angiogenesis and collateral vessels in the ischemic limb were examined for 4 weeks. Plasma homocysteine levels significantly increased (P <0.001), and plasma and tissue contents of nitrite+nitrate as well as tissue cGMP levels significantly decreased in the HH group compared with the control group (P <0.01). Laser Doppler blood flowmetry (LDBF) revealed a significant decrease in the ischemic/normal limb LDBF ratio in the HH group at days 7, 14, 21, and 28 (P <0.01 versus control). Angiography revealed a significant decrease in the angiographic score in the HH group at day 14 (P <0.001 versus control). Immunohistochemistry of ischemic tissue sections showed a significant reduction in the capillary density in the HH group (P <0.001 versus control). Oral l-arginine supplementation in rats with HH (HH+L-arg) restored the decreased plasma and tissue nitrite+nitrate and cGMP contents (P <0.05) as well as angiogenesis, as assessed by LDBF (P <0.05 versus HH), angiographic score (P <0.01 versus HH), and capillary density (P <0.001 versus HH). In summary, HH impaired ischemia-induced angiogenesis and collateral vessel formation in a rat model of hindlimb ischemia in vivo. The mechanism of the HH-induced impairment of angiogenesis might be mediated in part by a reduced bioactivity of endogenous NO in the HH state.

Rescue of hypercholesterolemia-related impairment of angiogenesis by oral folate supplementation

OBJECTIVES We examined whether oral folate supplementation would rescue a hypercholesterolemia (HC)-related impairment of ischemia-induced angiogenesis. BACKGROUND Folate protects against endothelial dysfunction, but the effect of folate supplementation on angiogenesis is little known. METHODS Sprague-Dawley rats were divided into four groups. Control rats were fed a normal diet (n = 18); HC rats (n = 18) were fed 2% cholesterol diet; and HC + folate (HC+F) rats were fed an HC diet with oral folate (0.003% in water). The left femoral artery and vein were surgically excised, and angiogenesis in the ischemic limb was evaluated. We also examined the effects of Nomega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, on angiogenesis in the HC+F state. RESULTS Laser Doppler blood flow (LDBF) analysis showed lower ischemic/normal LDBF ratio in the HC group than in the control group. Angiographic and histologic analyses on day 14 revealed a smaller angiographic score (p < 0.001) and capillary density (p < 0.001) in the HC group than in controls, which were associated with reduced tissue NOx and cyclic guanosine monophosphate (cGMP) levels. The LDBF ratio, angiographic score, and capillary density were significantly restored in the HC+F group (p < 0.01 vs. HC), which were associated with increased serum folate and tissue NOx and cGMP levels. Finally, L-NAME treatment abolished the beneficial action of folate on angiogenesis in the HC state. CONCLUSIONS Ischemia-induced angiogenesis was inhibited by HC, which was rescued by oral folate supplementation, at least in part, via an NO-dependent manner.

Recurrent embolic stroke originating from an internal carotid aneurysm in a young adult.

An unruptured intracranial aneurysm is an uncommon but possible embolic source to the brain. We report a young patient who developed recurrent ischemic strokes occurring mainly in the left internal carotid arterial territory within a short interval; the first stroke occurred midway through a long-distance race, and the second stroke occurred immediately following a bowel movement. The angiographical contrast deficit indicated a thrombus in the left anterior cerebral artery as a result of the embolism. A saccular aneurysm of the left distal internal carotid artery was the only detectable potential embolic source. Initially anticoagulant therapy was given, and then surgical clipping of the aneurysm was performed. The patient has been free from stroke recurrence. As a cause of ischemic stroke in young adults, a carotid saccular aneurysm should be considered. Hard exercise and a Valsalva maneuver may be important triggers of thrombus detachment from the aneurysm.

Acute Pulmonary Embolism due to Paget-Schroetter Syndrome.

A 17-year-old Japanese male athlete presented to the emergency department at our hospital with a chief complaint of exertional dyspnea. Although there were no significant findings in the right and left upper extremities on a physical examination, a chest computed tomography scan showed bilateral multiple thrombosis in the pulmonary arteries, indicating pulmonary thromboembolism, and deep vein thrombosis in the left subclavian vein. Upper limb venography showed interruption of the left subclavian vein (so-called Paget-Schroetter syndrome; PSS). We herein report this rare case of PSS that led to pulmonary thromboembolism in a young, male field athlete.

Coronary artery stent dislodgement and aortic dissection in a patient with a severely calcified lesion in the proximal right coronary artery

In atherosclerosis progression, calcium deposition may have an impact on the natural history of coronary atherosclerosis, and the amount of calcium may affect the success rate of percutaneous coronary intervention (PCI). Coronary stent dislodgement does not commonly occur in the modern PCI era; however, it may lead to fatal death. If it occurs, retrieval of a dislodged stent can be performed either surgically or percutaneously using a variety of retrieval techniques, including inflating a catheter balloon distal to the undeployed stent, twirling 2 wires around the stent, a loop snare, or forceps. Here, we report a rare case that coronary artery stent dislodgement and aortic dissection simultaneously occurred during PCI for a severely calcified lesion in the proximal right coronary artery with shepherds crook morphology. The situation was successfully rectified by using balloons to deploy the stent, as well as by applying an additional stent and minimizing the contrast used to treat aortic dissection. Learning objective: During percutaneous coronary intervention (PCI), stent dislodgement and aortic dissection are extremely rare, but life-threatening complications. In this rare case of simultaneous stent dislodgement in the coronary artery and aortic dissection during PCI for a severely calcified lesion in the right coronary artery with shepherds crook morphology, the situation was successfully rectified by using balloons to retrieve and deploy the stent, as well as by applying an additional stent and minimizing the contrast used to treat aortic dissection.