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Biomedical subjects

Alan Daugherty

Publications and source records attributed to Alan Daugherty.

At least 19 recordsLinked to original sources
PubMed2007

Angiotensin II increases adipose angiotensinogen expression.

In addition to the well-defined contribution of the liver, adipose tissue has been recognized as an important source of angiotensinogen (AGT). The purpose of this study was to define the angiotensin II (ANG II) receptors involved in regulation of adipose AGT and the relationship of this control to systemic AGT and/or angiotensin peptide concentrations. In LDL receptor-deficient (LDLR(-/-)) male mice, adipose mRNA abundance of AGT was 68% of that in liver, and adipose mRNA abundance of the angiotensin type 1a (AT(1a)) receptor (AT(1a)R) was 38% of that in liver, whereas mRNA abundance of the angiotensin type 2 (AT(2)) receptor (AT(2)R) was 57% greater in adipose tissue than in liver. AGT and angiotensin peptide concentrations were decreased in plasma of AT(1a)R-deficient (AT(1a)R(-/-)) mice and were paralleled by reductions in AGT expression in liver. In contrast, adipose AGT mRNA abundance was unaltered in AT(1a)R(-/-) mice. AT(2)R(-/-) mice exhibited elevated plasma angiotensin peptide concentrations and marked elevations in adipose AGT and AT(1a)R mRNA abundance. Increases in adipose AGT mRNA abundance in AT(2)R(-/-) mice were abolished by losartan. In contrast, liver AGT and AT(1a)R mRNA abundance were unaltered in AT(2)R(-/-) mice. Infusion of ANG II for 28 days into LDLR(-/-) mice markedly increased adipose AGT and AT(1a)R mRNA but did not alter liver AGT and AT(1a)R mRNA. These results demonstrate that differential mRNA abundance of AT(1a)/AT(2) receptors in adipose tissue vs. liver contributes to tissue-specific ANG II-mediated regulation of AGT. Chronic infusion of ANG II robustly stimulated AT(1a)R and AGT mRNA abundance in adipose tissue, suggesting that adipose tissue serves as a primary contributor to the activated systemic renin-angiotensin system.

Adipose Tissue↗
PubMed2006

Bone marrow transplantation reveals that recipient AT1a receptors are required to initiate angiotensin II-induced atherosclerosis and aneurysms.

OBJECTIVE: Angiotensin II (AngII) infusion into hypercholesterolemic mice accelerates atherosclerosis and promotes formation of abdominal aortic aneurysms (AAAs). The purpose of this study was to define whether AngII interacts with receptors on infiltrating versus resident cells in promoting vascular pathologies. METHODS AND RESULTS: Male LDL receptor -/- mice, that were either AT1a receptor +/+ or -/-, were fed a fat enriched diet and infused with either saline or AngII. AngII-induced augmentation of atherosclerosis and formation of AAAs was ablated in AT1a receptor -/- mice. Bone marrow transplantation studies were performed to determine the role of AT1a receptors expressed on infiltrating cells. AT1a receptor +/+ and -/- mice were irradiated and repopulated with bone marrow-derived stem cells of either genotype. These 4 groups of chimeric mice were infused with either saline or AngII. Repopulation of irradiated AT1a receptor +/+ mice with -/- bone marrow-derived cells resulted in modest reductions in AngII-induced atherosclerosis. Unexpectedly, AT1a receptor-deficient recipient mice were dramatically protected from AngII-induced vascular pathologies, irrespective of donor genotype. CONCLUSIONS: AngII promotes vascular pathology via AT1a receptors. AT1a receptors expressed on infiltrating cells exert modest regulation of AngII-induced atherosclerosis. However, the presence of this receptor in resident tissue is required for the initiation of AngII-induced atherosclerosis and AAAs.

Aneurysm↗
PubMed2006

Abdominal aortic aneurysm: pathogenesis and implications for management.

Abdominal aortic aneurysm (AAA) affects approximately 5% of elderly men and is responsible for a significant number of deaths in Western Countries. At present surgery by open or endovascular means is the only widely used therapy for this condition. In this review we examine the risk factors, serum, and genetic associations of AAA. Epidemiology studies suggest that smoking cessation and control of cholesterol and blood pressure should reduce the number of patients developing AAA. Natural history studies suggest that smoking cessation should reduce the rate of progression of AAA. Clear level 1 evidence for drug treatments of AAA are presently lacking; however, animal and human in vitro studies suggest that medication targeted at reducing inflammation and proteolysis are most likely to be beneficial, with limited data to support the use of statins, Angiotensin II inhibitors, and macrolides. Work has commenced in understanding which patients, identified by clinical, serum, and genotype, are more at risk of AAA progression and thus should be selected out for aggressive treatment. Well designed large multicenter randomized controlled trials are required to examine the medical treatment of AAA.

Angiotensin II Type 1 Receptor Blockers↗
PubMed2006

Deletion of p47phox attenuates angiotensin II-induced abdominal aortic aneurysm formation in apolipoprotein E-deficient mice.

BACKGROUND: Angiotensin II (Ang II) contributes to vascular pathology in part by stimulating NADPH oxidase activity, leading to increased formation of superoxide (O2-). We reported that O2- levels, NADPH oxidase activity, and expression of the p47phox subunit of NADPH oxidase are increased in human abdominal aortic aneurysms (AAAs). Here, we tested the hypothesis that deletion of p47phox will attenuate oxidative stress and AAA formation in Ang II-infused apoE-/- mice. METHODS AND RESULTS: Male apoE-/- and apoE-/-p47phox-/- mice received saline or Ang II (1000 ng x kg(-1) x min(-1)) infusion for 28 days, after which abdominal aortic weight and maximal diameter were determined. Aortic tissues and blood were examined for parameters of aneurysmal disease and oxidative stress. Ang II infusion induced AAAs in 90% of apoE-/- versus 16% of apo-/-p47phox-/- mice (P < 0.05). Abdominal aortic weight (14.1 +/- 3.2 versus 35.6 +/- 9.0 mg), maximal aortic diameter (1.5 +/- 0.2 versus 2.4 +/- 0.4 mm), aortic NADPH oxidase activity, and parameters of oxidative stress were reduced in apoE-/-p47phox-/- mice compared with apoE-/- mice (P < 0.05). In addition, aortic macrophage infiltration and matrix metalloproteinase-2 activity were reduced in apoE-/-p47phox-/- mice compared with apoE-/- mice. Deletion of p47phox attenuated the pressor response to Ang II; however, coinfusion of phenylephrine with Ang II, which restored the Ang II pressor response, did not alter the protective effects of p47phox deletion on AAA formation. CONCLUSIONS: Deletion of p47phox attenuates Ang II-induced AAA formation in apoE-/- mice, suggesting that NADPH oxidase plays a critical role in AAA formation in this model.

Adrenergic alpha-Agonists↗
PubMed2006

Reduction in ABCG1 in Type 2 diabetic mice increases macrophage foam cell formation.

Atherosclerosis development is accelerated severalfold in patients with Type 2 diabetes. In the initial stages of disease, monocytes transmigrate into the subendothelial space and differentiate into foam cells. Scavenger receptors and ATP binding cassette (ABC) Transporters play an important role in foam cell formation as they regulate the influx and efflux of oxidized lipids. Here, we show that peritoneal macrophages isolated from Type 2 diabetic db/db mice have decreased expression of the ABC transporter ABCG1 and increased expression of the scavenger receptor CD36. We found a 2-fold increase in accumulation of esterified cholesterol in diabetic db/db macrophages compared with wild-type control macrophages. Diabetic db/db macrophages also had impaired cholesterol efflux to high density lipoprotein but not to lipid-free apo A-I, suggesting that the increased esterified cholesterol in diabetic db/db macrophages was due to a selective loss of ABCG1-mediated efflux to high density lipoprotein. Additionally, we were able to confirm down-regulation of ABCG1 using C57BL/6J peritoneal macrophages cultured in elevated glucose in vitro (25 mM glucose for 7 days), suggesting that ABCG1 expression in diabetic macrophages is regulated by chronic exposure to elevated glucose. Diabetic KK(ay) mice were also studied and were found to have decreased ABCG1 expression without an increase in CD36. These observations demonstrate that ABCG1 plays a major role in macrophage cholesterol efflux and that decreased ABCG1 function can facilitate foam cell formation in Type 2 diabetic mice.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed2006

Rapid dilation of the abdominal aorta during infusion of angiotensin II detected by noninvasive high-frequency ultrasonography.

BACKGROUND: Infusion of angiotensin II (AngII) via subcutaneous osmotic pumps into mice promotes the development of abdominal aortic aneurysms (AAAs). These AngII-induced AAAs develop via a complex process in which there is a transmedial break, lumen dilation, thrombus formation, inflammation involving cells of both the innate and acquired immune systems, and remodeling. The recent development of a high-frequency ultrasound machine has permitted the noninvasive detection of murine abdominal aortas. We assessed the ability of a Visualsonics Vevo 660 high-resolution imaging system to detect AAAs and sequentially quantify the aortic luminal diameter. This system had 100% accuracy in detecting AngII-induced AAAs in vivo, with intrauser and interuser variation coefficients of less than 10% for quantification of the aortic lumen diameter. METHODS: Male apolipoprotein E (apoE)(-/-) mice were infused subcutaneously with either saline or AngII and were monitored with this ultrasonic system to define the temporal changes in aortic lumen diameter. Aortic luminal diameters were measured in the aneurysm-susceptible region of the suprarenal aorta. For internal controls, abdominal aortic diameters were measured at the level of the left renal branch, because this landmark region did not dilate during AngII infusion. RESULTS: Luminal diameters of the suprarenal aorta did not change significantly in saline-infused mice over 28 days of measurement (P = .71). In contrast, AngII infusion led to rapid dilation of suprarenal aortas during the initial 7 days of infusion (0.071 mm/d; P = .0037 for the change in the initial expansion rate). Further luminal diameter expansions occurred for the remaining 21 days of observation at a more modest rate (0.023 mm/d; P = .0001 for continued expansion after day 7). Within the initial 14 days of AngII infusion, some apoE(-/-) mice died as a result of rupture of the aorta in the suprarenal region. We had previously assumed that aortic dilation and rupture occurred simultaneously. However, in the AngII-infused mice that succumbed to aortic rupture, luminal diameters increased several days before death. CONCLUSIONS: High-frequency ultrasonography demonstrated that suprarenal aortic expansion occurs rapidly after the initiation of AngII infusion into apoE(-/-) mice.

Angiotensin II↗
PubMed2006

Role of the renin-angiotensin system in the development of abdominal aortic aneurysms in animals and humans.

The mediators for the initiation, progression, and rupture of abdominal aortic aneurysms (AAAs) have not been defined. Recent evidence has demonstrated that chronic infusion of angiotensin II via subcutaneously placed osmotic pumps can reproducibly form AAAs in mice. The evolution of AngII-induced AAAs in these mice is complex. Rapid medial macrophage accumulation precedes transmedial breaks and large lumen expansion, which are restricted to the suprarenal aorta. After this initial phase, there is a more gradual rate of lumen expansion that is progressive with continued AngII exposure. There is extensive aortic remodeling during this gradual expansion phase. An initial prominent thrombus gradually resolves and is replaced by fibrous tissue containing several types of inflammatory cells. At prolonged intervals of AngII infusion, internal aortic diameters of the suprarenal aorta can increase up to fourfold compared to the same region in saline-infused mice. The extrapolation of these data in mice to the development of human AAAs remains to be determined. However, there are a considerable number of drugs available to potentially test the efficacy of inhibiting the renin-angiotensin system on the progression of the human disease.

Angiotensin II↗
PubMed2005

Angiotensin II infusion induces site-specific intra-laminar hemorrhage in macrophage colony-stimulating factor-deficient mice.

Angiotensin II (AngII) infusion promotes macrophage infiltration into the aortic wall resulting in several forms of vascular pathology. To determine the causal role of macrophages in these vascular diseases, we used osteopetrotic (op) male mice in which a natural mutation ablates production of M-CSF and results in severe depletion of monocytes. AngII infusion into apoE-/- mice resulted in increased atherosclerosis that was attenuated in op mice. AngII infusion in op mice unexpectedly produced grossly discernable thickening of the proximal thoracic aorta characterized by intra-mural hematoma. This pathology was also observed in apoE+/+ x op male mice, and therefore, independent of hyper-lipidemia. No perceptible structural properties of aortas from op mice could be discerned prior to AngII infusion. Regional effects in the contractile response to phenylephrine were noted in aortic rings with enhanced responsivity in the upper thoracic aortas of op mice compared to those from +/+ mice. No differences in contractile response were noted in aortic rings from the lower thorax. In conclusion, deficiency of M-CSF attenuated AngII-induced atherosclerosis but led to an unanticipated pathology of intra-laminar hemorrhage in the upper aortic regions.

Angiotensin II↗
PubMed2005

COX-2 up-regulation and vascular smooth muscle contractile hyperreactivity in spontaneous diabetic db/db mice.

OBJECTIVE: Abnormalities in vascular constriction and dilatation are associated with early diabetes and contribute to diabetic vascular complications. However, mechanisms underlying such vascular dysfunction remain to be fully elucidated. The current study tests the role of cyclooxygenase-2 (COX-2) in diabetic vascular smooth muscle dysfunction. METHODS: Small mesenteric artery and aorta are isolated from type 2 diabetic db/db and control mice. Isometric contractions in response to serotonin, angiotensin II, phenylephrine and high potassium are determined in small spiral mesenteric arterial or aortic strips. COX-2 mRNA and protein levels are analyzed by using DNA microarray, real-time PCR and immunoblot. RESULTS: Contractions induced by serotonin, angiotensin II, phenylephrine and high potassium are significantly higher in endothelium-denuded smooth muscle strips isolated from db/db mice than in those isolated from control mice. The contractile hyperreactivity is observed in aortic and third-order branch small mesenteric arterial smooth muscle strips. DNA microarray, real-time PCR and immunoblot analysis show that compared with control mice, COX-2 mRNA and protein are significantly increased in db/db mice aortic smooth muscle. The COX-2 up-regulation is temporally associated with the development of diabetes mellitus and vascular smooth muscle contractile hyperreactivity. Inhibition of COX-2 with NS-398 or SC-58125 partially--but significantly--alleviates agonist-induced but not potassium-induced contractile hyperreactivity. In addition, serum isolated from db/db mice induces COX-2 expression and increases thromboxane A2 production in primary cultured vascular smooth muscle cells (VSMC). SQ-29548, a TP receptor antagonist, diminished the db/db mice vascular smooth muscle contractile hyperreactivity. CONCLUSIONS: COX-2 is up-regulated and contributes at least in part to the vascular smooth muscle contractile hyperreactivity in db/db mice.

Animals↗
PubMed2005

Thematic review series: The immune system and atherogenesis. Cytokine regulation of macrophage functions in atherogenesis.

This review will focus on the role of cytokines in the behavior of macrophages, a prominent cell type of atherosclerotic lesions. Once these macrophages have immigrated into the vessel wall, they propagate the development of atherosclerosis by modifying lipoproteins, accumulating intracellular lipids, remodeling the extracellular environment, and promoting local coagulation. The numerous cytokines that have been detected in atherosclerosis, combined with the expression of large numbers of cytokine receptors on macrophages, are consistent with this axis being an important contributor to lesion development. Given the vast literature on cytokine-macrophage interactions, this review will be selective, with an emphasis on the major cytokines that have been detected in atherosclerotic lesions and their effects on properties that are relevant to lesion formation and maturation. There will be an emphasis on the role of cytokines in regulating lipid metabolism by macrophages. We will provide an overview of the major findings in cell culture and then put these in the context of in vivo studies.

Animals↗
PubMed2005

Vitamin E inhibits abdominal aortic aneurysm formation in angiotensin II-infused apolipoprotein E-deficient mice.

BACKGROUND: Abdominal aortic aneurysms (AAAs) in humans are associated with locally increased oxidative stress and activity of NADPH oxidase. We investigated the hypothesis that vitamin E, an antioxidant with documented efficacy in mice, can attenuate AAA formation during angiotensin II (Ang II) infusion in apolipoprotein E-deficient mice. METHODS AND RESULTS: Six-month-old male apolipoprotein E-deficient mice were infused with Ang II at 1000 ng/kg per minute for 4 weeks via osmotic minipumps while consuming either a regular diet or a diet enriched with vitamin E (2 IU/g of diet). After 4 weeks, abdominal aortic weight and maximal diameter were determined, and aortic tissues were sectioned and examined using biochemical and histological techniques. Vitamin E attenuated formation of AAA, decreasing maximal aortic diameter by 24% and abdominal aortic weight by 34% (P<0.05, respectively). Importantly, animals treated with vitamin E showed a 44% reduction in the combined end point of fatal+nonfatal aortic rupture (P<0.05). Vitamin E also decreased aortic 8-isoprostane content (a marker of oxidative stress) and reduced both aortic macrophage infiltration and osteopontin expression (P<0.05, respectively). Vitamin E treatment had no significant effect on the extent of aortic root atherosclerosis, activation of matrix metalloproteinases 2 or 9, serum lipid profile, or systolic blood pressure. CONCLUSIONS: Vitamin E ameliorates AAAs and reduces the combined end point of fatal+nonfatal aortic rupture in this animal model. These findings are consistent with the concept that oxidative stress plays a pivotal role in Ang II-driven AAA formation in hyperlipidemic mice.

Angiotensin II↗
PubMed2005

Nobiletin, a citrus flavonoid isolated from tangerines, selectively inhibits class A scavenger receptor-mediated metabolism of acetylated LDL by mouse macrophages.

Flavonoids are a class of chemically related polyphenols that are nearly ubiquitous in nature. Of the more-than 4000 flavonoids thus identified, citrus fruit-derived flavonoids are suggested to have an inverse association with the occurrence of coronary heart disease via their ability to reduce plasma cholesterol concentrations. Our current studies examined whether citrus flavonoids possess an additional antiatherogenic effect by modulating macrophage metabolism of the specific class A scavenger receptor (SR-A) ligand, acetylated LDL (acLDL). In this study, both acLDL-metabolism and SR-A expression by cultured murine J774A.1 macrophages was examined following 24 h pretreatment (100 microM) with the flavonoids: naringenin (from grapefruit), hesperetin (from oranges), and tangeretin and nobiletin (from tangerines). Of these flavonoids, only nobiletin inhibited (50-72%) acLDL metabolism as measured by both cellular cholesterol ester mass and [3H]oleate incorporation into cholesterol esters. This nobiletin-mediated effect was specific for SR-A and not a global effect on lipoprotein metabolism by the macrophage, as all four citrus flavonoids significantly reduce the metabolism of beta-VLDL, which is primarily taken up by macrophages via the LDL receptor. Nevertheless, nobiletin did not affect SR-A protein expression, as measured by Western blot analysis, nor was cell surface expression of SR-A affected as measured by 4 degrees C binding studies using [125I]acLDL. In conclusion, our findings suggest that in addition to reducing plasma cholesterol concentrations, nobiletin may prevent atherosclerosis at the level of the vascular wall by inhibiting macrophage foam-cell formation.

Animals↗
PubMed2005

Development of experimental designs for atherosclerosis studies in mice.

The mouse has become the de facto model for the majority of atherosclerosis studies. Studies involving the quantification of lesions in mouse models of the disease represent the basis of our evolving concepts on the biochemical and cellular mechanisms underlying the atherogenic process. Many issues of experimental design, including specific model, strain, gender, atherogenic stimulus, duration of study, group size, and statistical analysis may influence the outcome and interpretation of atherosclerosis studies. The selection of vascular bed in which to quantify atherosclerotic lesion size could also impact the interpretation of results. Early studies quantified atherosclerotic lesion size in either specific regions or all of the aortic sinus. Measurement of atherosclerosis throughout the aortic intimal surface has become a common mode for defining lesion size. It is likely that other vascular regions will be increasingly used. In addition to size, there is an increased emphasis on identifying and quantifying the cellular and chemical composition of atherosclerotic lesions.

Animals↗
PubMed2005

Aldosterone does not mediate angiotensin II-induced atherosclerosis and abdominal aortic aneurysms.

We have demonstrated previously that infusion of angiotensin II (AngII) into hyperlipidemic mice augments atherosclerosis and results in the formation of abdominal aortic aneurysms (AAA). The purpose of this study was to determine the role of aldosterone in these AngII-induced vascular pathologies. Male apolipoprotein E-/- (apoE) mice were infused with either vehicle or aldosterone (50 or 200 ng kg(-1) min(-1)). Arterial blood pressure was determined throughout the study and serum lipid concentrations and vascular pathology were quantified after 28 days of infusion. Infusion of aldosterone did not influence body weight or serum cholesterol concentrations. Kidney weight was increased dose-dependently by aldosterone infusion. Systolic blood pressure was not significantly altered by aldosterone. Plasma aldosterone concentrations were increased dose-dependently by infusion of aldosterone. However, there was no effect of aldosterone on the extent of atherosclerosis and AAAs were not formed. Implantation of pellets containing spironolactone (16 mg kg(-1) day(-1)) in AngII-infused apoE-/- mice (1000 ng kg(-1) min(-1)) had no effect on AngII-induced elevations in blood pressure. Plasma aldosterone concentration was not influenced by coadministration of spironolactone with AngII. Spironolactone administration did not influence the extent of atherosclerosis. Moreover, spironolactone had no significant effect on AngII-induced AAA (incidence of AAA formation: 80 versus 70% for vehicle versus spironolactone, respectively; not significant). These studies demonstrate that the AngII-induced vascular pathologies of atherosclerosis and AAA formation are not mediated through aldosterone.

Aldosterone↗
PubMed2005

Zinc deficiency increases plasma lipids and atherosclerotic markers in LDL-receptor-deficient mice.

Low zinc concentration can be associated with an increased risk of cardiovascular diseases. In the current study, we hypothesize that zinc deficiency can increase and zinc supplementation can decrease proatherosclerotic events in LDL receptor knock-out (LDL-R-/-) mice fed a moderate-fat diet. Mice were fed either a zinc-deficient (0 micromol Zn/g), a control (0.45 micromol Zn/g), or a zinc-supplemented (1.529 micromol Zn/g) diet for 4 wk. Mice fed the zinc-deficient diet had significantly increased concentrations of cholesterol and triacylglycerides in the VLDL and HDL fractions. Zinc supplementation decreased these lipid variables compared with control mice. We detected significantly higher concentrations of glutathione reductase mRNA in the thoracic aortae of zinc-deficient mice. Furthermore, inflammatory markers, such as nuclear factor-kappaB and vascular cell adhesion molecule-1, were significantly increased in zinc-deficient mice compared with mice of the control or supplemented groups. In addition, zinc deficiency significantly reduced the DNA binding activity of peroxisome proliferator activate receptors (PPARs) in liver extracts. Interestingly, mRNA expression levels of PPARgamma were significantly increased in thoracic aortae of zinc-deficient mice, indicating an adaptation process to decreased PPAR signaling. These data provide in vivo evidence of zinc deficiency inducing proinflammatory events in an atherogenic mouse model. These data also suggest that adequate zinc may be a critical component in protective PPAR signaling during atherosclerosis.

Animals↗