Angiogenic bFGF expression from gas-plasma treated scaffolds

Comparison of 3 AT1 Receptor Binding Assays: Filtration Assay, ScreenReady™ Target, and WGA Flashplate®

In this article, the study of 3 different angiotensin II type 1 (AT1) receptor binding assays in terms of reproducibility, robustness, and feasibility for high-throughput screening (HTS) is described. The following methods were used: a nonhomogeneous filtration assay in a 96-well format using CHO-AT1 cell membranes and 2 homogeneous assays, which include the commercially available ScreenReady™ Target for the AT1 receptor and the wheat germ agglutinin (WGA) Flashplate®, which was coated “in-house” with the CHO-AT1 cell membranes. Receptors were labeled with [125I]-Sar1-Ile8-angiotensin II, and radioligand binding was displaced using the antagonist losartan and the natural agonist angiotensin II. Reproducible Kd, Bmax, and Ki values and good total binding/nonspecific binding (TB/NSB) ratios were obtained with both the ScreenReady™ Targets and the filtration assay, whereas the WGA Flashplates® showed unacceptably high nonspecific binding and high variation when applied as a homogeneous assay. However, when applied as a heterogeneous assay (i.e., when a wash step at the end of the assay is included), the results were significantly better. Interestingly, ligand affinities were consistently lower in Flashplate®-based assays than in the filtration assay. This may be due to the immobilization of the receptors onto the solid surface of the plate, affecting their conformation. In terms of reproducibility, robustness, and feasibility for HTS, the authors conclude that the ScreenReady™ Target plates are most suitable for AT1 receptor binding screening.

Effects of surface-modified scaffolds on the growth and differentiation of mouse adipose-derived stromal cells

PURPOSE

Adipose-derived stromal cells (ADSCs) have been shown to increase angiogenesis in ischemic tissue. Maintaining cell survival and facilitating angiogenesis in ischemic tissue, however, continues to be the major challenge of ADSCs implantation. Recently, bioengineered scaffolds were introduced to support and facilitate cell culture and differentiation. The effects of a surface modified three-dimensional (3D) scaffold on ADSC function have not been investigated. Accordingly, the objective of this study was to determine the influence of a gas-plasma treated scaffold on ADSC growth, differentiation into endothelial cell, and angiogenic gene expression.

METHODS

Freshly isolated mouse ADSCs were characterized by flow cytometry and cultured into wells containing gas-plasma treated scaffolds, non-treated scaffolds, or control wells. Either endothelial growth media or differentiation media was used to alter cell environment. After 3 and 6 days, cell proliferation was analyzed. VEGF concentration in the medium was measured by ELISA. Gene expression was quantified by real-time PCR for VEGF receptor-2 (KDR), cyclooxygenase-2 (COX-2) and matrix metalloproteinases-2 (MMP-2).

RESULTS

ADSCs expressed stem/endothelial progenitor markers CD34 and CD133 and endothelial cell marker CD31. ADSCs grew in the 3D scaffold. Cells grown on gas-plasma treated scaffolds displayed significantly increased expression of VEGF, COX-2, and MMP-2 when grown in differentiation but not growth media. When cultured in endothelial growth media, VEGF secretion and the expression of KDR, COX-2 and MMP-2 were lower in 3D scaffolds than controls.

CONCLUSIONS

This study suggests that 3D scaffolds, especially gas-plasma treated scaffolds, support ADSC growth and support differentiation into endothelial cells.

Implantation of oxygen enhanced, three-dimensional microporous L-PLA polymers: a reproducible porcine model of chronic total coronary occlusion

We have hypothesized that oxygen enhanced three-dimensional microporous poly-L-lactic acid (L-PLA) bioabsorbable polymer constructs could be implanted to produce a subacute occlusion in a porcine coronary artery, forming a thrombofibrotic occlusion containing microvascular channels. Chronic total occlusion (CTO) is increasingly prevalent in patients who present for percutaneous interventions. No reproducible animal coronary model simulating human CTOs has previously been developed. Swine coronary arteries were cannulated and a microporous L-PLA polymer pledget was advanced into a preselected segment of coronary. The coronary arteries were angiographically re-imaged at day 3, day 10, and day 28, to document the presence or absence of an occlusion. Histopathology was also performed at each time point to evaluate the lesion characteristics. A novel three-dimensional L-PLA microporous polymer construct, when implanted into porcine coronary arteries, reproducibly results in the development of a CTO at day 3. The histopathology in this porcine coronary model of CTO at day 28 closely mimics human coronary CTO, including the presence of microvascular channels and dense collagen and elastic tissue in the occlusion.

Efficacy of Angiotensin Receptor Blockers in Cardiovascular Disease

The cardiovascular continuum describes the progression of pathophysiologic events from cardiovascular risk factors to symptomatic cardiovascular disease (CVD) and life-threatening events. Pharmacologic intervention early in the continuum may prevent or slow CVD development and improve quality of life. The renin-angiotensin-aldosterone system (RAAS) is central to the pathophysiology of CVD at many stages of the continuum. Numerous clinical trials of angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) have shown that RAAS blockade provides benefits to patients across the continuum. ARBs are as effective as ACE inhibitors in the treatment of hypertension; however tolerability and adherence to therapy appear to be improved with ARBs. Large clinical trials have shown that ARBs may provide therapeutic benefits beyond blood pressure control in patients with diabetes, heart failure or at risk of heart failure following a myocardial infarction. In addition, ARBs have been shown to provide protective effects in patients with impaired renal function or left ventricular hypertrophy. Additional clinical trials are ongoing to further characterize the role of ARBs in CVD management.

Effect of the renin--angiotensin system on the vessel wall: using ACE inhibition to improve endothelial function

Plasma renin activity and cardiovascular disease (CVD) incidence correlate closely in people with hypertension. The effects of angiotensin II (Ang II) on blood pressure (BP) are important in hypertensive patients; accumulating data suggest that the growth effects of Ang II in the cardiovascular system play a critical role in the development of atherosclerosis. Atherosclerosis development in hypertensive patients requires fundamental changes in endothelial structure and function. Key among the factors that may affect the endothelium is the renin--angiotensin--bradykinin system. Ang II, independent of other environmental and neurohormonal factors, mediates the vessel wall changes critical for the development of atherosclerotic disease. A strong correlation appears to exist between Ang II and CVD. Blockade of the renin-angiotensin system has a major impact on arterial structure and function independent of BP. Certain angiotensin-converting enzyme (ACE) inhibitors produce significant improvements in arterial compliance, which may yield a reduction in cardiovascular events. Blockade of the neurohormonal system may be a critical first-line approach to management of hypertension in an effort to prevent or reverse endothelial dysfunction. Moreover, the effects of ACE inhibition, in addition to its effect on BP, suggest that this therapeutic approach may be appropriate for managing patients at risk of CVD who do not yet have hypertension. The ideal antihypertensive agent should yield smooth, consistent BP control over the entire 24-hour period, both to avoid BP variability that places patients at increased risk of cardiovascular events and to offer protection during the vulnerable early morning hours when patients are well known to be at high risk.

Practical nerve morphometry

Histopathological examination of peripheral nerves is often complemented by morphometric analysis in both clinical and research settings. However, existing manual or semi-automated methods are highly tedious, labour intensive and time-consuming, whereas fully automated morphometry is prone to error from the conversion of maldetected particles to spurious data. Both fully and interactive-automated morphometry have significant hardware requirements and may be difficult to implement. A new method for nerve morphometry is described aiming to combine the speed of automated morphometry with the accuracy of manual or semi-automated methods, and requiring only a digital image of the nerve section and two widely available software packages. Comparison with a standard digitizer pen method of nerve morphometry without sampling yielded statistically similar axon counts, mean area assessments and axonal area frequency distribution histograms, with assessment times of the new method between 35% and 45% of those of the standard method. This has widespread potential experimental and clinical applications and offers a means of relieving much of the tedium currently associated with nerve morphometry.

RAS inhibition in hypertension

Drugs that inhibit the renin-angiotensin system (RAS), namely angiotensin-converting enzyme inhibitors (ACE-I) and angiotensin receptor antagonists (ARA) are gaining increasing popularity as initial medications for the management of hypertensive patients. In the year 2002, ACE-I were the most commonly prescribed drugs for the treatment of hypertension in USA. Although their antihypertensive efficacy as monotherapy is similar to other antihypertensive agents, they have the advantage of better tolerability, limited side effects and a favorable metabolic profile. When compared to other antihypertensive agents (diuretics, beta-adrenergic blockers and calcium antagonists) in large clinical trials, ACE-I and ARA provided no additional advantages regarding improvement in cardiovascular and total mortality. With the exception of the superiority of ARA in prevention of stroke, RAS inhibitors have no advantage over other agents in prevention of other cardiovascular morbid events, namely, heart failure (though ACE-I are superior to calcium antagonists), coronary heart disease and total cardiovascular events. However, there is the possibility that these agents have other benefits beyond blood pressure lowering. At equal degrees of blood pressure reduction, RAS inhibitors prevent or delay the development of diabetes mellitus and provide better end-organ protection, kidneys, blood vessels and the heart when compared with other antihypertensive agents. The combined use of ACE-I and ARA is particularly useful in organ protection. RAS inhibitors are specifically indicated in the treatment of hypertension in patients with impaired left ventricular systolic function, diabetes, proteinuria, impaired kidney function, myocardial infarction, multiple cardiovascular risk factors and possibly elderly patients. The main limitation of the ACE-I is cough and rarely angioedema. Elderly patients or those who are volume depleted or receiving large doses of diuretics or in heart failure are liable to develop hypotensive reaction and/or deterioration in kidney function.

Combined blockade of AT1-receptors and ACE synergistically potentiates antihypertensive effects in SHR

OBJECTIVES AND DESIGN

To check whether antihypertensive effects are additive or synergistic upon blockade of both angiotensin (AT1)-receptors and angiotensin-converting enzyme (ACE), spontaneously hypertensive rats (SHR) were treated with candesartan-cilexetil (0.1-30 mg/kg per day), ramipril (0.03-10 mg/kg per day), the calcium-antagonist mibefradil (1-150 mg/kg per day) or combinations thereof. Systolic blood pressure (SBP), left ventricular weight (LVW) and the cardiac activity/mRNA levels of ACE were determined.

RESULTS

SBP was decreased by candesartan-cilexetil [inhibitory concentration (IC50) (mg/kg): 2.47], ramipril (1.97), mibefradil (4.41), candesartan-cilexetil/ramipril (0.68), and candesartan-cilexetil/mibefradil (5.68). Combining candesartan-cilexetil with ramipril increased SBP reduction synergistically rather than additively, since the dose-response curve was shifted 6.6-fold leftwards compared to a hypothetically generated additive curve, calculated by summing up the doses and corresponding effects of the ramipril and candesartan-cilexetil monotreatment regimes. A total threshold dose < 5.14 mg/kg (derived from dose-response curves) was found to exert synergistic effects when candesartan-cilexetil was combined with ramipril. Antihypertensive effects of mibefradil can not be increased when combined with candesartan-cilexetil. When LVW was correlated with SBP reduction, regression lines of candesartan-cilexetil, ramipril and their combination were congruent, while that for mibefradil was significantly flatter and became steeper under candesartan-cilexetil co-administration. Cardiac ACE activity was greatly reduced by ramipril independently of SBP reduction and dosage. With SBP-ineffective doses of ramipril, cardiac ACE mRNA levels were doubled, indicating a positive feedback mechanism. The increase in ACE mRNA was renormalized when SPB-effective ramipril doses were applied, suggesting a blood pressure-dependent regulation of cardiac ACE expression.

CONCLUSIONS

Since synergy was observed only after combining low doses of ramipril and candesartan-cilexetil, prospective clinical trials should be performed on a low-dose combination, revealing the antihypertensive/antiproliferative benefits.

Proliferation and β-tubulin for human aortic endothelial cells within gas-plasma scaffolds

PURPOSE

We determined if human aortic endothelial cells (HAEC) enhanced proliferative and angiogenic phenotypes within gas-plasma treated bioresorbable D,L-polylactic acid (D,L-PLA) three-dimensional scaffolds.

METHOD

6 x 10(3) HAEC (N=120) were incubated for 6, 12 or 18 days within either non-treated control or treated scaffolds. Before removing media, unstained wells were observed for apparent cell densities. Quantitative colorimetric WST-1 mitochondrial assays were determined for pooled conditioned media from both HAEC attached to wells and their respective HAEC-containing scaffolds. Fixed HAEC in scaffolds were examined using non-quantitative laser confocal microcopy with FITC-conjugated consensus, Types-I/II or Type-III beta-tubulin.

RESULTS

WST-1 indicated that significantly (p<0.05) less mitochondria were on cell culture plates than inside scaffolds but for different reasons. For example, a 12-18 days comparison between WST-1 and beta-tubulin indicated that wells decreased because of overgrowth apotosis; whereas, mitochondrial activity inside treated scaffolds decreased with increased tubulogenesis. Observed with consensus and Type-I/II beta-tubulin, HAEC-treated scaffolds exhibited increased cell-cell interconnections and angiogenic cords undergoing tubulogenesis to form vessels with central lumens as well as increased Type-III beta-tubulin, predominantly in cells of smaller surface areas. Moreover, beta-tubulin inside HAEC-treated scaffolds appeared in discrete cytoskeletal and podial regions; yet, beta-tubulin for HAEC-control scaffolds was located in more diffuse cytoplasmic regions especially at 18 days.

CONCLUSIONS

HAEC-treated scaffolds undergo increased migration, proliferation, beta-tubulin expression and quiescent cord formation. HAEC in scaffolds represent a potential model to study mechanisms for vascular cord progression into tubes. WST-1 does not represent accurate cell densities in three-dimensional scaffold matrices.