Abstract-Oxidized low-density lipoproteins increase arginase activity and reciprocally decrease endothelial NO in human aortic endothelial cells. Here, we demonstrate that vascular endothelial arginase activity is increased in atherogenicprone apolipoprotein E-null (ApoE Ϫ/Ϫ ) and wild-type mice fed a high cholesterol diet. In ApoE Ϫ/Ϫ mice, selective arginase II inhibition or deletion of the arginase II gene (Arg II Ϫ/Ϫ mice) prevents high-cholesterol diet-dependent decreases in vascular NO production, decreases endothelial reactive oxygen species production, restores endothelial function, and prevents oxidized low-density lipoprotein-dependent increases in vascular stiffness. Furthermore, arginase inhibition significantly decreases plaque burden. These data indicate that arginase II plays a critical role in the pathophysiology of cholesterol-mediated endothelial dysfunction and represents a novel target for therapy in atherosclerosis. (Circ Res. 2008;102:923-932.) Key Words: vascular stiffness Ⅲ eNOS uncoupling Ⅲ pulse wave velocity Ⅲ nitric oxide Ⅲ L-arginine I n atherosclerosis, 1 oxidized low-density lipoprotein (OxLDL) is known to impair endothelial NO production by mechanisms that involve altered endothelial NO synthase (eNOS) expression, increased reactive oxygen species (ROS) production, 2 and alterations in proteins that regulate eNOS function (eg, caveolin and heat shock protein-90). 3 The concept has emerged that arginase, which shares the substrate L-arginine with NO synthase (NOS), reciprocally regulates NOS activity by competing for arginine and can inhibit NO-dependent processes by depleting the substrate pool for NO biosynthesis. This is dependent on L-arginine concentrations in microdomains in which NOS isoforms and/or arginase are located. 4 Reciprocal regulation of NOS by arginase has been demonstrated in cells/organs in which NO is an important signaling molecule including the endothelium, 5 cardiac myocyte, 6 penis, 7,8 airway, 9 skin, 10 and inflammatory cells. 11 Upregulation of arginase activity contributes to vasoregulatory dysfunction in systemic [12][13][14] and pulmonary hypertension, 15,16 aging, 5,17,18 diabetes, 19 and erectile dysfunction 20 and to bronchodilatory dysfunction in asthma. 21 In cultured endothelial cells, we have demonstrated that OxLDL-dependent activation and upregulation of arginase impairs NO production and endothelial function. 22 This novel mechanism may be pivotal in the pathogenesis of atherosclerosis. 23 We have demonstrated that OxLDL facilitates arginase II (ArgII) release from the endothelial microtubular structure, 22 and the resulting increased arginase activity contributes to impaired endothelial cell NO production. Finally, L-arginine depletion secondary to arginase activation and upregulation may result in eNOS uncoupling, 24,25 with increased endothelial ROS production and nitroso-redox imbalance.Our objectives were to determine: (1) whether OxLDLdependent activation of arginase causes impaired vascular NO production, increased ROS production,...

Brain metastasis, the most lethal form of melanoma and carcinoma, is the consequence of favorable interactions between the invading cancer cells and the brain cells. Peroxisome proliferator-activated receptor γ (PPARγ) has ambiguous functions in cancer development, and its relevance in advanced brain metastasis remains unclear. Here, we demonstrate that astrocytes, the unique brain glial cells, activate PPARγ in brain metastatic cancer cells. PPARγ activation enhances cell proliferation and metastatic outgrowth in the brain. Mechanistically, astrocytes have a high content of polyunsaturated fatty acids that act as "donors" of PPARγ activators to the invading cancer cells. In clinical samples, PPARγ signaling is signifi cantly higher in brain metastatic lesions. Notably, systemic administration of PPARγ antagonists signifi cantly reduces brain metastatic burden in vivo. Our study clarifi es a prometastatic role for PPARγ signaling in cancer metastasis in the lipid-rich brain microenvironment and argues for the use of PPARγ blockade to treat brain metastasis. SIGNIFICANCE: Brain-tropic cancer cells take advantage of the lipid-rich brain microenvironment to facilitate their proliferation by activating PPARγ signaling. This protumor effect of PPARγ in advanced brain metastases is in contrast to its antitumor function in carcinogenesis and early metastatic steps, indicating that PPARγ has diverse functions at different stages of cancer development.

Emerging evidence supports the idea that arginase, expressed in the vascular endothelial cells of humans and other species, modulates endothelial nitric oxide (NO) synthase-3 (NOS-3) activity by regulating intracellular L-arginine bioavailability. Arginase II is thought to be expressed in the mitochondria of a variety of nonendothelial cells, whereas arginase I is known to be confined to the cytosol of hepatic and other cells. The isoforms that regulate NOS-3 and their subcellular distribution, however, remain incompletely characterized. We therefore tested the hypothesis that arginase II is confined to the mitochondria and that mitochondrial arginase II reciprocally regulates vascular endothelial NO production. Western blot analysis, immunocytochemistry with MitoTracker, and immunoelectron microscopy confirmed that arginase II is confined predominantly but not exclusively to the mitochondria. Arginase activity was significantly decreased, whereas NO production was significantly increased in the aorta and isolated endothelial cells from arginase II knockout (ArgII(-/-)) mice compared with wild-type (WT) mice. The vasorelaxation response to acetylcholine (ACh) was markedly enhanced and the vasoconstrictor response to phenylephrine (PE) attenuated in ArgII(-/-) in pressurized mouse carotid arteries. Furthermore, inhibition of NOS-3 by N(G)-nitro-L-arginine methyl ester (L-NAME) impaired ACh response and restored the PE response to that observed in WT vessels. Vascular stiffness, as assessed by pulse wave velocity (PWV), was significantly decreased in ArgII(-/-) compared with WT mice. On the other hand, 14 days of oral L-NAME treatment significantly increased PWV in both WT and ArgII(-/-) mice, such that they were not significantly different from one another. These data suggest that arginase II is predominantly confined to the mitochondria and that this mitochondrial arginase II regulates NO production, vascular endothelial function, and vascular stiffness by modulating NOS-3 activity.

Purpose The Pheochromocytoma of the Adrenal Gland Scaled Score (PASS) and the Grading System for Adrenal Pheochromocytoma and Paraganglioma (GAPP) are scoring systems to predict metastatic potential in pheochromocytoma and paragangliomas (PCC/PGL). The goal of this study is to assess PASS and GAPP as metastatic predictors and to correlate with survival outcomes. Methods The cohort included PCC/PGL with ≥5 years of follow-up or known metastases. Surgical pathology slides were re-reviewed. PASS and GAPP scores were assigned. Univariable and multivariable logistic regression, Kaplan-Meier survival analysis, and Cox proportional hazards were performed to assess recurrence free survival (RFS) and disease specific survival (DSS). Results From 143 subjects, 106 tumors were PCC, and 37 were PGL. Metastases developed in 24%. The median PASS score was 6.5 (IQR:4.0-8.0) and median GAPP score was 3.0 (IQR:2.0-4.0). Interrater reliability was low-moderate for PASS (ICC:0.6082) and good for GAPP (ICC:0.7921). Older age (OR:0.969, p=0.0170) was associated with longer RFS. SDHB germline pathogenic variant (OR:8.205, p=0.0049), extra-adrenal tumor (OR:6.357, p&0.0001), Ki-67 index 1-3% (OR:4.810, p=0.0477), and higher GAPP score (OR:1.537, p=0.0047) were associated with shorter RFS. PASS score was not associated with RFS (p=0.1779). On Cox regression, a GAPP score in the moderately-differentiated range was significantly associated with disease recurrence (HR:3.367, p=0.0184) compared to well-differentiated score. Conclusion Higher GAPP scores were associated with aggressive PCC/PGL. PASS score was not associated with metastases and demonstrated significant inter-observer variability. Scoring systems for predicting metastatic PCC/PGL may be improved by incorporation of histopathology, clinical data, and germline and somatic tumor markers.