Despite the high doses of radiation delivered in the treatment of patients with glioblastoma multiforme (GBM), the tumors invariably recur within the irradiation field, resulting in a low cure rate. Understanding the mechanism of such recurrence is therefore important. Here we have shown in an intracranial GBM xenograft model that irradiation induces recruitment of bone marrow-derived cells (BMDCs) into the tumors, restoring the radiation-damaged vasculature by vasculogenesis and thereby allowing the growth of surviving tumor cells. BMDC influx was initiated by induction of HIF-1 in the irradiated tumors, and blocking this influx prevented tumor recurrence. Previous studies have indicated that BMDCs are recruited to tumors in part through the interaction between the HIF-1-dependent stromal cell-derived factor-1 (SDF-1) and its receptor, CXCR4. Pharmacologic inhibition of HIF-1 or of the SDF-1/CXCR4 interaction prevented the influx of BMDCs, primarily CD11b + myelomonocytes, and the postirradiation development of functional tumor vasculature, resulting in abrogation of tumor regrowth. Similar results were found using neutralizing antibodies against CXCR4. Our data therefore suggest a novel approach for the treatment of GBM: in addition to radiotherapy, the vasculogenesis pathway needs to be blocked, and this can be accomplished using the clinically approved drug AMD3100, a small molecule inhibitor of SDF-1/CXCR4 interactions.

Apelin is a potent inodilator with recently described antiatherogenic properties. We hypothesized that apelin might also attenuate abdominal aortic aneurysm (AAA) formation by limiting disease-related vascular wall inflammation. C57BL/6 mice implanted with osmotic pumps filled with apelin or saline were treated with pancreatic elastase to create infrarenal AAAs. Mice were euthanized for aortic PCR analysis or followed ultrasonographically and then euthanized for histological analysis. The cellular expression of inflammatory cytokines and chemokines in response to apelin was also assessed in cultured macrophages, smooth muscle cells, and fibroblasts. Apelin treatment resulted in diminished AAA formation, with a 47% reduction in maximal cross-sectional area (0.74 vs. 1.39 mm(2), P < 0.03) and a 57% reduction in macrophage infiltrate (113 vs. 261.3 cells/high-power field, P < 0.0001) relative to the saline-treated group. Apelin infusion was also associated with significantly reduced aortic macrophage colony-stimulating factor expression and decreased monocyte chemattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1alpha, interleukin (IL)-6, and tumor necrosis factor (TNF)-alpha mean mRNA levels. Apelin stimulation of cultured macrophages significantly reduced MCP-1 and TNF-alpha mRNA levels relative to baseline (2.03- and 1.89-fold reduction, P < 0.03, respectively) but did not affect intimal adhesion molecule expression or medial or adventitial cell cytokine production. Apelin significantly reduces aneurysm formation in the elastase model of human AAA disease. The mechanism appears to be decreased macrophage burden, perhaps related to an apelin-mediated decrease in proinflammatory cytokine and chemokine activation.

Objective Diabetes mellitus (DM) is associated with reduced progression of abdominal aortic aneurysm (AAA) disease. Mechanisms responsible for this negative association remain unknown. We created AAAs in hyperglycemic mice to examine the influence of serum glucose concentration on experimental aneurysm progression. Methods Aortic aneurysms were induced in hyperglycemic (DM) and normoglycemic models by using intra-aortic porcine pancreatic elastase (PPE) infusion in C57BL/6 mice or by systemic infusion of angiotensin II (ANG) in apolipoprotein E-deficient (ApoE−/−) mice, respectively. In an additional DM cohort, insulin therapy was initiated after aneurysm induction. Aneurysmal aortic enlargement progression was monitored with serial transabdominal ultrasound measurements. At sacrifice, AAA cellularity and proteolytic activity were evaluated by immunohistochemistry and substrate zymography, respectively. Influences of serum glucose levels on macrophage migration were examined in separate models of thioglycollate-induced murine peritonitis. Results At 14 days after PPE infusion, AAA enlargement in hyperglycemic mice (serum glucose ≥ 300 mg/dL) was less than that in euglycemic mice (PPE-DM: 54% ± 19% vs PPE: 84% ± 24%, P < .0001). PPE-DM mice also demonstrated reduced aortic mural macrophage infiltration (145 ± 87 vs 253 ±119 cells/cross-sectional area, P = .0325), elastolysis (% residual elastin: 20% ± 7% vs 12% ± 6%, P = .0209), and neovascularization (12 ± 8 vs 20 ± 6 vessels/high powered field, P = .0229) compared with PPE mice. Hyperglycemia limited AAA enlargement after ANG infusion in ApoE−/− mice (ANG-DM: 38% ± 12% vs ANG: 61% ± 37% at day 28). Peritoneal macrophage production was reduced in response to thioglycollate stimulation in hyperglycemic mice, with limited augmentation noted in response to vascular endothelial growth factor administration. Insulin therapy reduced serum glucose levels and was associated with AAA enlargement rates intermediate between euglycemic and hyperglycemic mice (PPE: 1.21 ± 0.14 mm vs PPE-DM: 1.00 ± 0.04 mm vs PPE-DM + insulin: 1.14 ± 0.05 mm). Conclusions Hyperglycemia reduces progression of experimental AAA disease; lowering of serum glucose levels with insulin treatment diminishes this protective effect. Identifying mechanisms of hyperglycemic aneurysm inhibition may accelerate development of novel clinical therapies for AAA disease. Clinical Relevance This report provides mechanistic insight into prior population-based clinical studies identifying a negative association between diabetes mellitus and abdominal aortic aneurysm (AAA). The inhibitory effects of hyperglycemia on aneurysm development are examined independent of other AAA risk factors. Further investigations into these or related mechanisms may accelerate the development of effective medical strategies to suppress progression of AAA disease.

BackgroundDespite the importance of the renin-angiotensin (Ang) system in abdominal aortic aneurysm (AAA) pathogenesis, strategies targeting this system to prevent clinical aneurysm progression remain controversial and unproven. We compared the relative efficacy of two Ang II type 1 receptor blockers, telmisartan and irbesartan, in limiting experimental AAAs in distinct mouse models of aneurysm disease.Methodology/Principal FindingsAAAs were induced using either 1) Ang II subcutaneous infusion (1000 ng/kg/min) for 28 days in male ApoE−/− mice, or 2) transient intra-aortic porcine pancreatic elastase infusion in male C57BL/6 mice. One week prior to AAA creation, mice started to daily receive irbesartan (50 mg/kg), telmisartan (10 mg/kg), fluvastatin (40 mg/kg), bosentan (100 mg/kg), doxycycline (100 mg/kg) or vehicle alone. Efficacy was determined via serial in vivo aortic diameter measurements, histopathology and gene expression analysis at sacrifice. Aortic aneurysms developed in 67% of Ang II-infused ApoE−/− mice fed with standard chow and water alone (n = 15), and 40% died of rupture. Strikingly, no telmisartan-treated mouse developed an AAA (n = 14). Both telmisartan and irbesartan limited aneurysm enlargement, medial elastolysis, smooth muscle attenuation, macrophage infiltration, adventitial neocapillary formation, and the expression of proteinases and proinflammatory mediators. Doxycycline, fluvastatin and bosentan did not influence aneurysm progression. Telmisartan was also highly effective in intra-aortic porcine pancreatic elastase infusion-induced AAAs, a second AAA model that did not require exogenous Ang II infusion.Conclusion/SignificanceTelmisartan suppresses experimental aneurysms in a model-independent manner and may prove valuable in limiting clinical disease progression.

Background-Extracellular matrix degradation is a sentinel pathologic feature of abdominal aortic aneurysm (AAA) disease. Diabetes mellitus, a negative risk factor for AAA, may impair aneurysm progression through its influence on the fibrinolytic system. We hypothesize that hyperglycemia limits AAA progression through effects on endogenous plasminogen activator inhibitor-1 (PAI-1) levels and subsequent reductions in plasmin generation.