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Biomedical subjects

Mehran M Sadeghi

Publications and source records attributed to Mehran M Sadeghi.

12 recordsLinked to original sources
PubMed2007

Activated alphavbeta3 integrin targeting in injury-induced vascular remodeling.

There is currently no imaging modality to track the remodeling process, a common feature of a broad spectrum of vasculopathies, in vivo. alphavbeta3 Integrin is up-regulated in proliferating vascular cells. RP748, a novel peptidomimetic tracer, binds specifically to the activated alphavbeta3 conformer and exhibits favorable binding characteristics for in vivo imaging. In a model of injury-induced vascular remodeling in apoE null mice, RP748 localization to the injured carotid arteries parallels vascular cell proliferation, providing an opportunity to image the remodeling process in vivo.

Animals↗
PubMed2006

HMG-CoA reductase inhibitor simvastatin mitigates VEGF-induced "inside-out" signaling to extracellular matrix by preventing RhoA activation.

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors exert modulatory effects on a number of cell signaling cascades by preventing the synthesis of various isoprenoids derived from the mevalonate pathway. In the present study, we describe a novel pleiotropic effect of HMG-CoA reductase inhibitors, also commonly known as statins, on vascular endothelial growth factor (VEGF)-induced type IV collagen accumulation. VEGF is an angiogenic polypeptide that is also known to play a central role in endothelial cell permeability and differentiation. Recently, VEGF has also been implicated in promoting extracellular matrix (ECM) accumulation, although the precise signaling mechanism that mediates VEGF-induced ECM expansion remains poorly characterized. Elucidation of the mechanisms through which VEGF exerts its effect on ECM is clearly a prerequisite for both understanding the complex biology of this molecule as well as targeting VEGF in several pathological processes. To this end, this study explored the underlying molecular mechanisms mediating VEGF-induced ECM expansion in mesangial cells. Our findings show that VEGF stimulation elicits a robust increase in ECM accumulation that involves RhoA activation, an intact actin cytoskeleton, and beta(1)- integrin activation. Our data also indicate that simvastatin, via mevalonate depletion, reverses VEGF-induced ECM accumulation by preventing RhoA activation.

Actin Cytoskeleton↗
PubMed2005

HMG CoA reductase inhibition modulates VEGF-induced endothelial cell hyperpermeability by preventing RhoA activation and myosin regulatory light chain phosphorylation.

The beneficial effects of statins are usually assumed to stem from their ability to reduce cholesterol biosynthesis. However, because statins are potent inhibitors of the mevalonate, which governs diverse cell signaling pathways, inhibition of 3-hydroxy-3-methylglutaryl-coenzyme-A reductase may also result in pleiotropic effects. The present study describes a novel pleiotropic effect of statins on vascular endothelial growth factor (VEGF)-induced glomerular endothelial cell (GEnC) hyperpermeability. Using live cell imaging with green fluorescent protein-tagged myosin regulatory light chain (MLC) and correlative biochemical analyses, we investigated 1) VEGF signaling pathway leading to GEnC hyperpermeability and 2) the modulatory effects of statins on VEGF signaling. Our findings indicate that VEGF stimulation elicits a robust increase in GEnC permeability. The signaling pathway that mediates VEGF-induced GEnC hyperpermeability involves RhoA activation leading to actin cytoskeletal remodeling, MLC diphosphorylation, and enhanced paracellular gap formation. Remarkably, cotreatment of endothelial cells with simvastatin, a hydrophobic statin, reversed VEGF-induced GEnC hyperpermeability by preventing MLC diphosphorylation, and cytoskeletal remodeling. In summary, this study identifies RhoA and MLC phosphorylation as key mediators of VEGF-induced endothelial cell hyperpermeability and demonstrates the modulatory effects of statins on VEGF signaling pathway.

Actins↗
PubMed2005

Alphavbeta3-targeted detection of arteriopathy in transplanted human coronary arteries: an autoradiographic study.

Graft arteriopathy (GA), characterized by diffuse concentric narrowing of coronary arteries, is the major cause of late graft failure in cardiac transplantation. alphavbeta3 Integrin is up-regulated in proliferating vascular cells and may constitute an appropriate target for imaging GA. We used a human/mouse chimeric model of GA, in which segments of human coronary artery were transplanted to severe combined immunodeficiency mice, followed by reconstitution with allogeneic human peripheral blood mononuclear cells (PBMC). This led to vascular remodeling characterized by neointima formation over a period of 4 wk. alphavbeta3 expression in the graft was minimal in animals without PBMC, considerably increased by 2 wk, and decreased toward baseline by 4 wk after PBMC reconstitution. Cell proliferation was maximal at 2 wk, correlating with peak alphavbeta3 expression. RP748, an 111In-labeled alphavbeta3 (active conformation)-targeted radiotracer was injected into groups of 5 recipients at 0, 2, and 4 wk after PBMC reconstitution. Relative uptakes, defined as autoradiographic intensity in the graft/native aortas closely tracked the proliferative process. Specificity of uptake was demonstrated using excess nonlabeled tracer. In conclusion, alphavbeta3 integrin is transiently up-regulated (and activated) in GA and may be targeted by RP748 for detection of the proliferative process in early GA.

Animals↗
PubMed2005

Noninvasive imaging of angiogenesis with a 99mTc-labeled peptide targeted at alphavbeta3 integrin after murine hindlimb ischemia.

BACKGROUND: Noninvasive imaging strategies play a critical role in assessment of the efficacy of angiogenesis therapies. The alpha(v)beta3 integrin is activated in angiogenic vessels and represents a potential target for noninvasive imaging of angiogenesis. METHODS AND RESULTS: We evaluated a 99mTc-labeled peptide (NC100692) targeted at alpha(v)beta3 integrin for imaging in an established murine model of angiogenesis induced by hindlimb ischemia. Control mice (n=9) or mice with surgical right femoral artery occlusion (n=29) were injected with NC100692 (1.5+/-0.2 mCi IV) at different times after femoral occlusion (1, 3, 7, and 14 days) for in vivo pinhole planar gamma camera imaging. Tissue from hindlimb proximal and distal to occlusion was excised for gamma well counting and for immunostaining. On in vivo pinhole images, increased focal NC100692 activity was seen distal to the occlusion at days 3 and 7. This increase in relative NC100692 activity was confirmed by gamma well counting. Lectin staining confirmed increased angiogenesis in the ischemic hindlimb at these time points. A fluorescent analogue of NC100692 was used to confirm specificity and localization of the targeted tracer in cultured endothelial cells. In addition, endothelial cell specificity was confirmed on tissue sections with the use of dual immunofluorescent staining of endothelium and the fluorescent analogue targeted at the alpha(v)beta3 integrin. CONCLUSIONS: A 99mTc-labeled peptide (NC100692) targeted at alpha(v)beta3 integrin selectively localized to endothelial cells in regions of increased angiogenesis and could be used for noninvasive serial "hot spot" imaging of angiogenesis. This targeted radiotracer imaging approach is a major advance in tracking therapeutic myocardial angiogenesis and has an important clinical potential.

Animals↗
PubMed2004

Detection of injury-induced vascular remodeling by targeting activated alphavbeta3 integrin in vivo.

BACKGROUND: The alpha(v)beta3 integrin plays a critical role in cell proliferation and migration. We hypothesized that vascular cell proliferation, a hallmark of injury-induced remodeling, can be tracked by targeting alpha(v)beta3 integrin expression in vivo. METHODS AND RESULTS: RP748, a novel 111In-labeled alpha(v)beta3-specific radiotracer, was evaluated for its cell-binding characteristics and ability to track injury-induced vascular proliferation in vivo. Three groups of experiments were performed. In cultured endothelial cells (ECs), TA145, a cy3-labeled homologue of RP748, localized to alpha(v)beta3 at focal contacts. Activation of alpha(v)beta3 by Mn2+ led to increased EC binding of TA145. Left common carotid artery wire injury in apolipoprotein E-/- mice led to vascular wall expansion over a period of 4 weeks. RP748 (7.4 MBq) was injected into groups of 9 mice at 1, 3, or 4 weeks after left carotid injury, and carotids were harvested for autoradiography. Relative autographic intensity, defined as counts/pixel of the injured left carotid area divided by counts/pixel of the uninjured right carotid area, was higher at 1 and 3 weeks (1.8+/-0.1 and 1.9+/-0.2, respectively) and decreased significantly by 4 weeks after injury (1.4+/-0.1, P<0.05). Carotid alpha(v) and beta3 integrin expression was maximal at 1 week and decreased by 4 weeks after injury. The proliferation index, as determined by Ki67 staining, followed a temporal pattern similar to that of RP748 uptake. Dynamic gamma imaging demonstrated rapid renal clearance of RP748. CONCLUSIONS: RP748 has preferential binding to activated alpha(v)beta3 integrin and can track the injury-induced vascular proliferative process in vivo.

Animals↗
PubMed2004

Simvastatin modulates angiotensin II signaling pathway by preventing Rac1-mediated upregulation of p27.

Recent experimental observations have suggested that statins may exert modulatory effects on a number of pathobiological processes beyond their cholesterol-lowering properties. Some of the pleiotropic effects of statins seem to be mediated by their ability to block the synthesis of isoprenoid intermediates, which serve as important lipid attachments required for the proper function and activation of the small GTP-binding proteins. The current study explored the modulatory effects of simvastatin (SMV) on the angiotensin II (Ang II)-induced Rac1-mediated, upregulation of cyclin-dependent kinase inhibitor p27. Ang II (100 nM) stimulation of rat mesangial cells induced a significant increase in p27 protein expression. Co-treatment of cells with SMV (1 microM) inhibited Ang II-induced upregulation of p27 protein. Addition of mevalonate (200 microM) or geranylgeranyl pyrophosphate (5 microM) reversed the inhibitory effect of SMV on p27 protein expression, suggesting that the effect of SMV is geranylgeranyl dependent. This study also provides evidence for a sequential link between Ang II stimulation and downstream activation of Rac1, intracellular H2O2 production, and Akt kinase leading to upregulation of p27 protein in mesangial cells. It was also shown that SMV, by inhibiting Rac1 activity, reversed Ang II-induced increase in intracellular H2O2 production, Akt activation, and p27 protein expression. The data presented in this study not only elucidate Ang II-mediated signaling cascade in mesangial cells but also demonstrate for the first time the modulatory effects of SMV on Ang II-induced signaling pathway at the cell cycle level.

Active Transport, Cell Nucleus↗
PubMed2004

Noninvasive imaging of myocardial angiogenesis following experimental myocardial infarction.

Noninvasive imaging strategies will be critical for defining the temporal characteristics of angiogenesis and assessing efficacy of angiogenic therapies. The alphavbeta3 integrin is expressed in angiogenic vessels and represents a potential novel target for imaging myocardial angiogenesis. We demonstrated the localization of an indium-111-labeled ((111)In-labeled) alphavbeta3-targeted agent in the region of injury-induced angiogenesis in a chronic rat model of infarction. The specificity of the targeted alphavbeta3-imaging agent for angiogenesis was established using a nonspecific control agent. The potential of this radiolabeled alphavbeta3-targeted agent for in vivo imaging was then confirmed in a canine model of postinfarction angiogenesis. Serial in vivo dual-isotope single-photon emission-computed tomographic (SPECT) imaging with the (111)In-labeled alphavbeta3-targeted agent demonstrated focal radiotracer uptake in hypoperfused regions where angiogenesis was stimulated. There was a fourfold increase in myocardial radiotracer uptake in the infarct region associated with histological evidence of angiogenesis and increased expression of the alphavbeta3 integrin. Thus, angiogenesis in the heart can be imaged noninvasively with an (111)In-labeled alphavbeta3-targeted agent. The noninvasive evaluation of angiogenesis may have important implications for risk stratification of patients following myocardial infarction. This approach may also have significant clinical utility for noninvasively tracking therapeutic myocardial angiogenesis.

Animals↗
PubMed2003

Simultaneous optical coherence tomography imaging and beta particle detection.

A prototype hybrid catheter device designed for imaging and detection of vascular diseases is introduced. The prototype device integrates a high-resolution optical coherent tomography probe and a high-sensitivity beta detector into a single unit. With this prototype device we demonstrate the feasibility of simultaneous optical coherence tomography imaging and detection of beta particles.

Beta Particles↗
PubMed2002

3-Hydroxy-3-methylglutaryl CoA reductase inhibitors prevent high glucose-induced proliferation of mesangial cells via modulation of Rho GTPase/ p21 signaling pathway: Implications for diabetic nephropathy.

Inhibitors of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, also known as statins, are lipid-lowering agents widely used in the prevention of coronary heart disease. Recent experimental and clinical data, however, indicate that the overall benefits of statin therapy may exceed its cholesterol-lowering properties. We postulate that statins may ameliorate the detrimental effects of high glucose (HG)-induced proliferation of mesangial cells (MCs), a feature of early stages of diabetic nephropathy, by preventing Rho isoprenylation. Rat MCs cultured in HG milieu were treated with and without simvastatin, an HMG-CoA reductase inhibitor. Simvastatin inhibited HG-induced MC proliferation as measured by [(3)H]thymidine incorporation. This inhibitory effect was reversed with geranylgeranyl pyrophosphate, an isoprenoid intermediate of the cholesterol biosynthetic pathway. At the cell-cycle level, the HG-induced proliferation of MCs was associated with a decrease in cyclin dependent kinase (CDK) inhibitor p21 protein expression accompanied by an increase in CDK4 and CDK2 kinase activities. Simvastatin reversed the down-regulation of p21 protein expression and decreased CDK4 and CDK2 kinase activities. Exposure of MCs to HG was associated with an increase in membrane-associated Ras and Rho GTPase protein expression. Cotreatment of MCs with simvastatin reversed HG-induced Ras and Rho membrane translocation. Immunofluorescence microscopy revealed that the overexpression of the dominant-negative RhoA led to a significant increase in p21 expression. Our data suggest that simvastatin represses the HG-induced Rho GTPase/p21 signaling in glomerular MCs. Thus, this study provides a molecular basis for the use of statins, independently of their cholesterol-lowering effect, in early stages of diabetic nephropathy.

Animals↗
PubMedDate not supplied

Hybrid positron detection and optical coherence tomography system: design, calibration, and experimental validation with rabbit atherosclerotic models.

We evaluate the performance of our novel hybrid optical coherence tomography (OCT) and scintillating probe, demonstrate simultaneous OCT imaging and scintillating detection, and validate the system using an atherosclerotic rabbit model. Preliminary data obtained from the rabbit model suggest that our prototype positron probe detects local uptake of fluorodeoxyglucose (FDG) labeled with 18F positron (beta) radionuclide emitter, and the high-uptake regions correlate with sites of injury and extensive atherosclerosis areas. Preliminary data also suggest that coregistered high-resolution OCT images provide imaging of detailed plaque microstructures, which cannot be resolved by positron detection.

Animals↗