Unfavorable effect of smoking on the elastic properties of the human aorta

BACKGROUND

Smoking is a major risk factor for cardiovascular morbidity and mortality. Because previous studies have shown that smoking affects vasomotor response, we hypothesized that smoking may also acutely alter aortic elastic properties.

METHODS AND RESULTS

We studied 40 male current and long-term smokers who underwent diagnostic cardiac catheterization for chest-pain evaluation. Twenty subjects (age, 48 +/- 2 years, mean +/- SEM) were randomly assigned to smoking and 20 (age, 47 +/- 2 years) to sham smoking studies. Aortic elastic properties were studied with the determination of the aortic pressure-diameter relation before smoking, every minute for the first 5 minutes after the initiation of smoking or sham smoking, and every 5 minutes for the following 15 minutes. Instantaneous diameter of the thoracic aorta was measured with a special ultrasonic dimension catheter developed in our laboratory and previously validated. Instantaneous aortic pressure was measured at the same site as was diameter with a Millar micromanometer. Smoking was associated with significant changes in the aortic pressure-diameter relation that denote deterioration of the elastic properties and were maintained during the whole study period: the slope of the pressure-diameter loop became steeper (baseline, 35.43 +/- 1.38; minute 1, 45.26 +/- 1.65; peak at minute 10, 46.36 +/- 1.69 mm Hg/mm; P < .001) and aortic distensibility decreased (baseline, 2.08 +/- 0.12; minute 1, 1.60 +/- 0.08; nadir at minute 5, 1.54 +/- 0.07 x 10(-6) cm2.dyne-1; P < .001). In contrast, no changes in aortic elasticity indexes were observed with sham smoking.

CONCLUSIONS

Smoking is associated with an acute deterioration of aortic elastic properties. This effect of smoking may contribute to the unfavorable consequences of smoking on the cardiovascular system.

Raman spectroscopic detection of changes in bioapatite in mouse femora as a function of age and in vitro fluoride treatment

Laser Raman microprobe spectroscopy, which characterizes the molecular structure of a mineral, was used to analyze microscopically small regions of bioapatite in mouse femora in order to study the effect of mouse age and in vitro fluoride treatment on the bone mineral (i.e., mineral identity and degree of crystallinity). Both femora that had and those that had not undergone in vitro NaF treatment underwent point analysis of 1 micron spots in the center of the compact bone's cross-section. The Raman spectra of bones treated with fluoride showed a peak up-shift of the PO4 vibration mode from 961 to 964 delta cm-1 indicating a conversion from a carbonated hydroxylapatitic to a carbonated fluorapatitic mineral phase. The spectral band width of the 961 delta cm-1 PO4 vibration in femora of 4-, 10-, and 24-week-old mice showed that aging, as well as in vitro treatment with 1.5 M NaF for 12 hours, significantly increases the degree of crystallinity of the bioapatite. In vitro fluoridation of 10-week-old mouse femora increased the bioapatite's degree of crystallinity to about the same degree as did aging to 24 weeks. Four-point bending tests indicated that the age-related increase in crystallinity of untreated bones was associated with decreased deformation to failure, i.e., increased brittleness. In contrast, the increased crystallinity following fluoridation of 10-week-old bones was associated with increased deformation, i.e., increased ductility, perhaps due to the altered mineral composition. This study shows that the laser Raman microprobe readily detects the conversion of carbonated hydroxylapatite to carbonated fluorapatite, as well as changes in crystallinity of either mineral phase, in microscopically small regions of a bone sample.

The effects of acetone, ethanol, HEMA, and air on the stiffness of human decalcified dentin matrix

During resin-bonding procedures, dentin surfaces are treated with acidic conditioners to remove the smear layer and decalcify the surface to expose the collagen fibrils of the underlying matrix. These decalcified surfaces are then either air-dried or treated with dehydrating solvents, procedures which may modify the physical properties of the dentin matrix. The purpose of this study was to evaluate the effects of dehydration on the stiffness of the decalcified dentin matrix. Small (8 x 1.7 x 0.9 mm) beams of dentin were prepared from mid-coronal dentin of extracted human molars. The ends were covered with varnish for protection, and the specimens were placed in 0.5 M EDTA for 5 days to decalcify. The stiffness was measured by both the cantilever technique and by conventional stress-strain testing. Specimens tested by the cantilever technique were sequentially exposed to water, acetone, alcohol, HEMA, and glutaraldehyde. Specimens tested by conventional stress-strain testing were exposed either to water, acetone, or HEMA, or were allowed to air-dry. The results indicate that the stiffness of decalcified human dentin matrix is very low (ca. 7 MPa), if the specimens are wet with water. As they are dehydrated, either chemically in water-miscible organic solvents or physically in air, the stiffness increases 20- to 38-fold at low strains or three- to six-fold at high strains. These increases in modulus were rapidly reversed by rehydration in water. Exposure to glutaraldehyde also produced an increase in stiffness that was not reversible when the specimens were placed back in water.

rhBMP-2 injected in a calcium phosphate paste (alpha-BSM) accelerates healing in the rabbit ulnar osteotomy model

This study evaluated the ability of recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in an injectable calcium phosphate carrier (alpha-BSM) to accelerate healing in a rabbit ulna osteotomy model compared to untreated surgical controls. Healing was assessed by radiography, histology and biomechanics. Bilateral mid-ulnar osteotomies were created in 16 skeletally mature rabbits. One limb in each animal was injected with either 0.1 mg rhBMP-2/alpha-BSM (BMP) (N=8) or buffer/alpha-BSM (BSM) (N=8). Contralateral osteotomies served as untreated surgical controls (SXCT). Gamma scintigraphy showed 75%, 45% and 5% of the initial 125I-rhBMP-2 dose was retained at the osteotomy site at 3 h, 1 week and 3 weeks. The biological activity of rhBMP-2 (alkaline phosphatase activity from bioassay) extracted from alpha-BSM incubated in vitro up to 30 days at 37 degrees C was unchanged. Radiographs demonstrated complete bridging of the BMP limbs at 4 weeks whereas none of the BSM or SXCT limbs were bridged. Post-mortem peripheral quantitative computed tomography determined mineralized callus area was 62% greater in BMP limbs compared to SXCT limbs. Torsional stiffness and strength were 63% and 103% greater in BMP limbs compared to SXCT limbs. There was no difference in torsional properties between BSM and SXCT limbs. Failure occurred outside the osteotomy in four out of seven of the BMP limbs. All BSM and SXCT limbs failed through the osteotomy. Histology showed bony bridging of the osteotomy and no residual carrier in the BMP limbs. BSM and SXCT groups showed less mature calluses composed of primarily fibrocartilaginous tissue and immature bone in the osteotomy gap. These data indicate rhBMP-2 delivered in alpha-BSM accelerated healing in a rabbit ulna osteotomy model compared to BSM and SXCT groups.

Altering mucus rheology to "solidify" human mucus at the nanoscale

The ability of mucus to function as a protective barrier at mucosal surfaces rests on its viscous and elastic properties, which are not well understood at length scales relevant to pathogens and ultrafine environmental particles. Here we report that fresh, undiluted human cervicovaginal mucus (CVM) transitions from an impermeable elastic barrier to non-adhesive objects sized 1 microm and larger to a highly permeable viscoelastic liquid to non-adhesive objects smaller than 500 nm in diameter. Addition of a nonionic detergent, present in vaginal gels, lubricants and condoms, caused CVM to behave as an impermeable elastic barrier to 200 and 500 nm particles, suggesting that the dissociation of hydrophobically-bundled mucin fibers created a finer elastic mucin mesh. Surprisingly, the macroscopic viscoelasticity, which is critical to proper mucus function, was unchanged. These findings provide important insight into the nanoscale structural and barrier properties of mucus, and how the penetration of foreign particles across mucus might be inhibited.

Injectable Chitin-Poly(ε-caprolactone)/Nanohydroxyapatite Composite Microgels Prepared by Simple Regeneration Technique for Bone Tissue Engineering

Injectable gel systems, for the purpose of bone defect reconstruction, have many advantages, such as controlled flowability, adaptability to the defect site, and increased handling properties when compared to the conventionally used autologous graft, scaffolds, hydroxyapatite blocks, etc. In this work, nanohydroxyapatite (nHAp) incorporated chitin-poly(ε-caprolactone) (PCL) based injectable composite microgels has been developed by a simple regeneration technique for bone defect repair. The prepared microgel systems were characterized using scanning electron microscope (SEM), Fourier transformed infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The composite microgel, with the incorporation of nHAp, showed an increased elastic modulus and thermal stability and had shear-thinning behavior proving the injectability of the system. The protein adsorption, cytocompatibility, and migration of rabbit adipose derived mesenchymal stem cells (rASCs) were also studied. Chitin-PCL-nHAp microgel elicited an early osteogenic differentiation compared to control gel. The immunofluorescence studies confirmed the elevated expression of osteogenic-specific markers such as alkaline phosphatase, osteopontin, and osteocalcin in chitin-PCL-nHAp microgels. Thus, chitin-PCL-nHAp microgel could be a promising injectable system for regeneration of bone defects which are, even in deeper planes, irregularly shaped and complex in nature.

Tissue heterogeneity in the mouse lung: effects of elastase treatment

We developed a network model in an attempt to characterize heterogeneity of tissue elasticity of the lung. The model includes a parallel set of pathways, each consisting of an airway resistance, an airway inertance, and a tissue element connected in series. The airway resistance, airway inertance, and the hysteresivity of the tissue elements were the same in each pathway, whereas the tissue elastance (H) followed a hyperbolic distribution between a minimum and maximum. To test the model, we measured the input impedance of the respiratory system of ventilated normal and emphysematous C57BL/6 mice in closed chest condition at four levels of positive end-expiratory pressures. Mild emphysema was developed by nebulized porcine pancreatic elastase (PPE) (30 IU/day × 6 days). Respiratory mechanics were studied 3 wk following the initial treatment. The model significantly improved the fitting error compared with a single-compartment model. The PPE treatment was associated with an increase in mean alveolar diameter and a decrease in minimum, maximum, and mean H. The coefficient of variation of H was significantly larger in emphysema (40%) than that in control (32%). These results indicate that PPE treatment resulted in increased time-constant inequalities associated with a wider distribution of H. The heterogeneity of alveolar size (diameters and area) was also larger in emphysema, suggesting that the model-based tissue elastance heterogeneity may reflect the underlying heterogeneity of the alveolar structure.

Biophysical properties of normal and diseased renal glomeruli

The mechanical properties of tissues and cells including renal glomeruli are important determinants of their differentiated state, function, and responses to injury but are not well characterized or understood. Understanding glomerular mechanics is important for understanding renal diseases attributable to abnormal expression or assembly of structural proteins and abnormal hemodynamics. We use atomic force microscopy (AFM) and a new technique, capillary micromechanics, to measure the elastic properties of rat glomeruli. The Young's modulus of glomeruli was 2,500 Pa, and it was reduced to 1,100 Pa by cytochalasin and latunculin, and to 1,400 Pa by blebbistatin. Cytochalasin or latrunculin reduced the F/G actin ratios of glomeruli but did not disrupt their architecture. To assess glomerular biomechanics in disease, we measured the Young's moduli of glomeruli from two mouse models of primary glomerular disease, Col4a3(-/-) mice (Alport model) and Tg26(HIV/nl) mice (HIV-associated nephropathy model), at stages where glomerular injury was minimal by histopathology. Col4a3(-/-) mice express abnormal glomerular basement membrane proteins, and Tg26(HIV/nl) mouse podocytes have multiple abnormalities in morphology, adhesion, and cytoskeletal structure. In both models, the Young's modulus of the glomeruli was reduced by 30%. We find that glomeruli have specific and quantifiable biomechanical properties that are dependent on the state of the actin cytoskeleton and nonmuscle myosins. These properties may be altered early in disease and represent an important early component of disease. This increased deformability of glomeruli could directly contribute to disease by permitting increased distension with hemodynamic force or represent a mechanically inhospitable environment for glomerular cells.

Zoledronic acid prevents osteopenia and increases bone strength in a rabbit model of distraction osteogenesis

Prolonged healing times and stress-shielding osteopenia remain problematic in distraction osteogenesis. In this study of 30 rabbits, zoledronic acid increased regenerate volume, mineralization, and tibial strength and prevented osteopenia over a 6-week period. Translation to the clinical setting, if safe, could improve outcomes in distraction osteogenesis in children.

INTRODUCTION

Because the external fixators for limb lengthening and reconstruction are designed to control the positions of bone fragments accurately, they also produce stress-shielding effects on the forming regenerate and surrounding bone. Osteopenia, leading to refracture and limitations on rehabilitation, are common consequences, potentially increasing morbidity and detracting from final clinical outcome.

MATERIALS AND METHODS

We examined the effect of zoledronic acid on distraction osteogenesis in 42 immature male NZW rabbits. The model chosen results in reliable regenerate formation and stress-shielding osteopenia. Fourteen animals received either Saline, zoledronic acid 0.1 mg/kg at surgery (ZOL), or another dose 2 weeks postoperatively (Redosed ZOL). Rabbits underwent DXA for bone mineral content and bone mineral density in regenerate and surrounding segments of operated and contralateral tibias. After death at 6 weeks, 30 pairs of tibias underwent quantitative computerized tomography (QCT) and four-point bend testing, and 12 were examined by histomorphometry. The study was powered at 0.8 to show differences of 1.3 SDs for mineral and mechanical parameters.

RESULTS

Osteopenia observed in tibias of the Saline group was absent in ZOL and Redosed ZOL tibias, the latter exhibiting higher bone mineral density and bone mineral content over contralateral regions (p < 0.01). Regenerate bone mineral content was higher in ZOL and Redosed ZOL versus Saline groups at 4 and 6 weeks (p < 0.01). Cross-sectional area was 49% and 59% greater at 6 weeks in ZOL and Redosed ZOL regenerates compared with the Saline group (p < 0.01). ZOL and Redosed ZOL tibias were 29% and 89% stronger by four-point bending than the Saline group (p < 0.01). Histomorphometry in the regenerate of ZOL and Redosed ZOL groups revealed higher trabecular bone volume and trabecular number compared with the Saline group (p < 0.001).

CONCLUSIONS

Zoledronic acid administration led to significantly greater bone area, mineral content, strength, and trabecular number with reduced stress-shielding osteopenia in this model of distraction osteogenesis. These data suggest that intraoperative and postoperative zoledronic acid administration could improve outcomes in children undergoing limb lengthening.

Effect of dermatan sulfate glycosaminoglycans on the quasi-static material properties of the human medial collateral ligament

The glycosaminoglycan of decorin, dermatan sulfate (DS), has been suggested to contribute to the mechanical properties of soft connective tissues such as ligaments and tendons. This study investigated the mechanical function of DS in human medial collateral ligaments (MCL) using nondestructive shear and tensile material tests performed before and after targeted removal of DS with chondroitinase B (ChB). The quasi-static elastic material properties of human MCL were unchanged after DS removal. At peak deformation, tensile and shear stresses in ChB treated tissue were within 0.5% (p>0.70) and 2.0% (p>0.30) of pre-treatment values, respectively. From pre- to post-ChB treatment under tensile loading, the tensile tangent modulus went from 242+/-64 to 233+/-57 MPa (p=0.44), and tissue strain at peak deformation went from 4.3+/-0.3% to 4.4+/-0.3% (p=0.54). Tissue hysteresis was unaffected by DS removal for both tensile and shear loading. Biochemical analysis confirmed that 90% of DS was removed by ChB treatment when compared to control samples, and transmission electron microscopy (TEM) imaging further verified the degradation of DS by showing an 88% reduction (p<.001) of sulfated glycosaminoglycans in ChB treated tissue. These results demonstrate that DS in mature knee MCL tissue does not resist tensile or shear deformation under quasi-static loading conditions, challenging the theory that decorin proteoglycans contribute to the elastic material behavior of ligament.

Transient binding and dissipation in cross-linked actin networks

In contrast with entangled actin solutions, transiently cross-linked actin networks can provide highly elastic properties while still allowing for local rearrangements in the microstructure-on biological relevant time scales. Here, we show that thermal unbinding of transient cross-links entails local stress relaxation and energy dissipation in an intermediate elasticity dominated frequency regime. We quantify the viscoelastic response of an isotropically cross-linked actin network by experimentally tuning the off rate of the transiently cross-linking molecules, their density, and the solvent viscosity. We reproduce the measured frequency response by a semiphenomenological model that is predicated on microscopic unbinding events.

Higher cell stiffness indicating lower metastatic potential in B16 melanoma cell variants and in (-)-epigallocatechin gallate-treated cells

PURPOSE

To understand how nanomechanical stiffness affects metastatic potential, we studied the relationship between cell migration, a characteristic of metastasis, and cell stiffness using atomic force microscopy (AFM), which can measure stiffness (elasticity) of individual living cells.

METHODS

Migration and cell stiffness of three metastatic B16 melanoma variants (B16-F10, B16-BL6, and B16-F1 cells), and also effects of (-)-epigallocatechin gallate (EGCG), were studied using Transwell assay and AFM.

RESULTS

Migration of B16-F10 and B16-BL6 cells was 3 and 2 times higher than that of B16-F1 cells in Transwell assay, and cell stiffness determined by AFM was also different among the three variants, although they have similar morphologies and the same growth rates: Means of Young's modulus were 350.8 ± 4.8 Pa for B16-F10 cells, 661.9 ± 16.5 Pa for B16-BL6 cells, and 727.2 ± 13.0 Pa for B16-F1 cells. AFM measurements revealed that highly motile B16-F10 cells have low cell stiffness, and low motile and metastatic B16-F1 cells have high cell stiffness: Nanomechanical stiffness is inversely correlated with migration potential. Treatment of highly motile B16-F10 cells with EGCG increased cell stiffness 2-fold and inhibited migration of the cells.

CONCLUSIONS

Our study with AFM clearly demonstrates that cell stiffness is a reliable quantitative indicator of migration potential, and very likely metastatic potential, even in morphologically similar cells. And increased cell stiffness may be a key nanomechanical feature in inhibition of metastasis.

Contributions of molecular binding events and cellular compliance to the modulation of leukocyte adhesion

The interaction of leukocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) is central to the regulation of adhesion in leukocytes. In this report, we investigated the mechanisms by which phorbol myristate acetate (PMA) promotes LFA-1-dependent cell adhesion. The adhesion of PMA-stimulated cells to immobilized ICAM-1 was quantified in direct force measurements acquired by atomic force microscopy (AFM). Enhanced adhesion of PMA-stimulated cells to immobilized ICAM-1 stemmed from an increase in the number of LFA-1-ICAM-1 complexes formed between the two apposing surfaces on contact, rather than by affinity modulation of LFA-1. Single molecule force measurements revealed that the force spectrum of the LFA-1-ICAM-1 complex formed by PMA-stimulated cells is identical to the force spectrum of the complex formed by resting cells. Thus, PMA stimulation does not modify the mechanical strength of the individual LFA-1-ICAM-1 interaction. Instead, the enhanced cell adhesion of PMA-stimulated cells appears to be a complex process that correlates with changes in the mechanical properties of the cell. We estimate that changes in the elasticity of the cell gave rise to a more than 10-fold increase in cell adhesion.

Effects of locally applied vascular endothelial growth factor (VEGF) and VEGF-inhibitor to the rabbit tibia during distraction osteogenesis

INTRODUCTION

Therapeutic angiogenesis, a novel concept in tissue engineering, is neo-formation of blood vessels in a tissue upon delivery of an angiogenic growth factor to the tissue. We hypothesised that therapeutic angiogenesis could enhance bone formation and challenged the hypothesis in an experimental model of distraction osteogenesis.

METHODS

Rabbits, divided into three equal groups of 12, had their right tibia lengthened by distraction osteogenesis. A mini-osmotic pump delivered to the osteotomy gap either recombinant human vascular endothelial growth factor (VEGF), VEGF-inhibitor, or vehicle alone during the latency and distraction phase. After consolidation, we assessed bone blood flow by radioactive microsphere entrapment, measured torsional stiffness and bone mineral content, and did histomorphometry.

RESULTS

VEGF and VEGF-inhibitor treatment failed to influence bone blood flow, torsional stiffness, bone mineral content and histomorphometric indices of the bone regenerate. However, VEGF treatment increased the blood flow in bone of the distracted limb and VEGF-inhibitor treatment decreased bone blood flow.

CONCLUSION

The regenerate was unresponsive to VEGF and VEGF-inhibitor treatment in contrast to the neighbouring bone, which implies different biological properties of the vasculature in native and regenerating bone. VEGF is not recommended for enhancement of bone formation in this setting.

Effect of clarithromycin on nasal mucus properties in healthy subjects and in patients with purulent rhinitis

Erythromycin inhibits mucus glycoconjugate secretion from airway cells in vitro and may increase mucus clearance in patients with asthma or diffuse panbronchiolitis. Because mucus hypersecretion is common in purulent rhinitis, we questioned whether clarithromycin would change the properties of nasal mucus from subjects without sinus disease and from patients with acute purulent rhinitis. Nasal secretions were collected before and after nasal methacholine challenge from 10 adults without nasal symptoms and without methacholine from 10 patients with purulent rhinitis. After 2 wk of oral clarithromycin (500 mg twice daily), secretions were again collected from both groups. Secretions were analyzed for viscoelasticity, cohesion, hydration, and ciliary and airflow (sneeze) transportability. Compared with secretions from healthy subjects, rhinitis secretions had decreased wettability (contact angle on Teflon 100 degrees versus 84.67 degrees; p = 0.001), increased cohesion (36.8 versus 24.3 mm; p = 0.003), decreased sneeze clearability (20.6 versus 32 mm; p = 0.04), and increased percent solids (4.61 versus 2.82%; p = 0.04). After clarithromycin, the rheology, hydration, cohesion, and transportability of the rhinitis secretions were similar to those of the postclarithromycin secretions from the healthy subjects. Secretion volume also decreased (500.1 versus 28.3 mg; p = 0.01), and mucociliary transportability increased by 30% (0.76 versus 0.99; p = 0.005). Although clarithromycin reduced mucus secretion in both rhinitis patients and normal subjects, it did not alter the secretory response to methacholine.

Disaggregation of in vitro preformed platelet-rich clots by abciximab increases fibrin exposure and promotes fibrinolysis

The glycoprotein IIb/IIIa receptor inhibitor abciximab has been shown to facilitate the rate and the extent of pharmacological thrombolysis with recombinant tissue plasminogen activator (rtPA) in patients with acute myocardial infarction. However, the underlying mechanisms remain not fully determined. We sought to demonstrate that this facilitating effect of abciximab could be related to its potential to modify the clot architecture and the clot physical properties. Compared with fibrin-rich clots, platelets dramatically modified the in vitro properties of the fibrin network, leading to a significant increase of the permeability (K(s)) and the viscoelasticity (G') indexes but also leading to the appearance of platelet aggregates (surface area [S.ag]). These modifications resulted in a 2.6-fold decrease of the fibrinolysis rate when rtPA (1 nmol/L) was added before the initiation of clotting. Adding aspirin (100 microgram/mL) or abciximab (0.068 micromol/L) before the clotting of platelet-rich clots (PRCs) lowered K(s) by 50% and 70%, respectively (P<0.01), G' by 41% and 66%, respectively (P<0.01), and S.ag by 32% and 61%, respectively (P<0.01). As a consequence, the lysis speed was increased by 21% with aspirin (P<0.01) and 45% with abciximab (P<0.01). However, unlike aspirin, permeation of preformed PRCs with abciximab (0.068 micromol/L) decreased G' (37%, P<0.01), K(s) (35%, P<0.001) and S.ag (25%, P=NS) and resulted in a 27% (P<0.01) increase of the lysis speed when abciximab and rtPA (0.2 micromol/L) were simultaneously permeated. This effect was found to be time dependent and was observed only with early permeation, starting within the first 10 minutes of clotting. These changes in the physical properties of the PRC architecture suggest that fibrin is removed from the platelet-fibrin aggregates and reexposed into the surrounding fibrin network, increasing rtPA access to fibrin and therefore the fibrinolysis rate. The superiority of abciximab over aspirin in accelerating fibrinolysis of forming and preformed PRCs is related to its ability to modulate the interactions of fibrinogen and fibrin with platelets. These findings provide new mechanistic information on reperfusion therapy.

Controlled dual delivery of fibroblast growth factor-2 and Interleukin-10 by heparin-based coacervate synergistically enhances ischemic heart repair

Myocardial infarction (MI) causes myocardial necrosis, triggers chronic inflammatory responses, and leads to pathological remodeling. Controlled delivery of a combination of angiogenic and immunoregulatory proteins may be a promising therapeutic approach for MI. We investigated the bioactivity and therapeutic potential of an injectable, heparin-based coacervate co-delivering an angiogenic factor, fibroblast growth factor-2 (FGF2), and an anti-inflammatory cytokine, Interleukin-10 (IL-10) in a spatially and temporally controlled manner. Coacervate delivery of FGF2 and IL-10 preserved their bioactivities on cardiac stromal cell proliferation in vitro. Upon intramyocardial injection into a mouse MI model, echocardiography revealed that FGF2/IL-10 coacervate treated groups showed significantly improved long-term LV contractile function and ameliorated LV dilatation. FGF2/IL-10 coacervate substantially augmented LV myocardial elasticity. Additionally, FGF2/IL-10 coacervate notably enhanced long-term revascularization, especially at the infarct area. In addition, coacervate loaded with 500 ng FGF2 and 500 ng IL-10 significantly reduced LV fibrosis, considerably preserved infarct wall thickness, and markedly inhibited chronic inflammation at the infarct area. These results indicate that FGF2/IL-10 coacervate has notably greater therapeutic potential than coacervate containing only FGF2. Overall, our data suggest therapeutically synergistic effects of FGF-2/IL-10 coacervate, particularly coacervate with FGF2 and 500 ng IL-10, for the treatment of ischemic heart disease.

Effects of water and water-free polar solvents on the tensile properties of demineralized dentin

OBJECTIVES

The aim of this study was to test the null hypothesis that the tensile properties of demineralized dentin are not influenced by the hydrogen bonding ability of anhydrous polar solvents.

METHODS

Dentin disks 0.5mm thick were prepared from mid-coronal dentin of extracted, unerupted, human third molars. 'I' beam and hour-glass shaped specimens were prepared from the disks, the ends protected with nail varnish and the central regions completely demineralized in 0.5M EDTA for 5 days. Ultimate tensile stress (UTS) and low-strain apparent modulus of elasticity (E) were determined with the specimens immersed for 60 min in water, methanol, HEMA, acetone or air prior to testing in those same media. Apparent moduli of elasticity were measured on the same specimens in a repeated measures experimental design. The results were analyzed with a one-way ANOVA on ranks, followed by Dunn's test at alpha=0.05. Regression analysis examined the relationship between UTS or E and Hansen's solubility parameter for hydrogen bonding (delta(h)) of each solvent.

RESULTS

The UTS of demineralized dentin in water, methanol, HEMA, acetone and air was 18(7), 29(7), 31(6), 41(13) and 146(27)MPa, x(SD), n=10. Low-strain E for the same media were 11(7), 43(12), 79(21), 132(31) and 253(115)MPa. Regression analysis of UTS vs delta(h) revealed a significant (p<0.0005, r=-0.69, R(2)=0.48) inverse, exponential relationship. A similar inverse relationship was obtained between low-strain E vs delta(h) (p<0.0001, r=-0.93, R(2)=0.86).

SIGNIFICANCE

The tensile properties of demineralized dentin are dependent on the hydrogen bonding ability of polar solvents (delta(h)). Solvents with low delta(h) values may permit new interpeptide H-bonding in collagen that increases its tensile properties. Solvents with high delta(h) values prevent the development of these new interpeptide H-bonds.

Rapid stiffening of integrin receptor-actin linkages in endothelial cells stimulated with thrombin: a magnetic bead microrheology study

By using magnetic bead microrheology we study the effect of inflammatory agents and toxins on the viscoelastic moduli of endothelial cell plasma membranes in real time. Viscoelastic response curves were acquired by applying short force pulses of ~500 pN to fibronectin-coated magnetic beads attached to the surface membrane of endothelial cells. Upon addition of thrombin, a rapid stiffening of the membrane was observed within 5 s, followed by recovery of the initial deformability within 2 min. By using specific inhibitors, two known pathways by which thrombin induces actin reorganization in endothelial cells, namely activation of Ca2+-calmodulin-dependent myosin light chain kinase and stimulation of Rho/Rho-kinase, were excluded as possible causes of the stiffening effect. Interestingly, the cytotoxic necrotizing factor of Escherichia coli, a toxin which, in addition to Rho, activates the GTPases Rac and CDC42Hs, also induced a dramatic stiffening effect, suggesting that the stiffening may be mediated through a Rac- or Cdc42Hs-dependent pathway. This work demonstrates that magnetic bead microrheometry is not only a powerful tool to determine the absolute viscoelastic moduli of the composite cell plasma membrane, but also a valuable tool to study in real time the effect of drugs or toxins on the viscoelastic parameters of the plasma membrane.

Effect of glycosaminoglycan degradation on lung tissue viscoelasticity

We tested the hypothesis that matrix glycosaminoglycans contribute to lung tissue viscoelasticity. We exposed lung parenchymal strips to specific degradative enzymes (chondroitinase ABC, heparitinase I, and hyaluronidase) and determined whether the mechanical properties of the tissue were affected. Subpleural parenchymal strips were obtained from Sprague-Dawley rats and suspended in a Krebs-filled organ bath. One end of the strip was attached to a force transducer and the other to a servo-controlled lever arm that effected sinusoidal oscillations. Recordings of tension and length at different amplitudes and frequencies of oscillation were recorded before and after enzyme exposure. Resistance, dynamic elastance, and hysteresivity were estimated by fitting the equation of motion to changes in tension and length. Quasi-static stress-strain curves were also obtained. Exposure to chondroitinase and heparitinase I caused significant increases in hysteresivity, no decrement in resistance, and similar decreases in dynamic elastance relative to control strips exposed to Krebs solution only. Conversely, measures of static elastance were different in treated versus control strips. Hyaluronidase treatment did not alter any of the mechanical measures. These data demonstrate that digestion of chondroitin sulfate and heparan sulfate alters the mechanical behavior of lung parenchymal tissues.

Recovery of elasticity of aged human epithelial cells in vitro

We recently found a considerable increase in rigidity of human epithelial cells during aging in vitro. This is important because the loss in elasticity of epithelial tissues with aging contributes to many human diseases. We also found that cultured cells had three distinct regions of rigidity and that the increase in rigidity correlated with an increase in density of cytoskeletal fibers. However, it was not clear which type of fiber was important. Atomic force microscopy and immunofluorescence microscopy were used in this study to characterize aging human epithelial cells in vitro, both before and after treatment with cytochalasin B. We found that the fibers associated with increased rigidity were mostly F-actin microfilaments. Furthermore, using cytochalasin B, a chemical that inhibits polymerization of F-actin, we restored the rigidity of old cells to the young level in all three areas of rigidity simultaneously. These results clarify how the cell mechanics changes during aging in vitro, and they may be relevant for treatment of age-related loss of elasticity in epithelial tissues.

The biomechanical response to doses of TGF-beta 2 in the healing rabbit medial collateral ligament

Ligament injuries result in significant disability in over 100,000 patients each year. Despite current methods of treatment, 13% of patients with medial collateral ligament (MCL) injury develop early signs of arthritis, suggesting an incomplete return of knee stability. The principal hypothesis of this work was that the addition of TGF-beta 2 to the healing MCL would accelerate the development of scar strength and stiffness. Forty-four rabbits were divided evenly into four groups, with each group receiving either 0.1, 1 or 5 microg of TGF-beta 2 and the fourth group receiving 1 microg TGF-beta 2 and 1 microg of PDGF. Each rabbit underwent bilateral transection of the MCL, with one side having treatment with one of four doses of growth factor and the other side left untreated. All animals were sacrificed at 6 weeks and the structural properties of maximum load at failure, stiffness, and energy absorbed at failure measured. All treatment groups demonstrated an increase in scar mass, but no group had a significant increase in scar load at failure at 6 weeks. The addition of 0.1 microg TGF-beta 2 led to a significant increase in scar stiffness. The addition of PDGF had no significant effect on any of the parameters studied. This study suggests the mechanical stiffness, but not the load at failure, of ligament scar can be significantly altered by the administration of TGF-beta 2.

Temporal analysis of vascular smooth muscle cell elasticity and adhesion reveals oscillation waveforms that differ with aging

A spectral analysis approach was developed for detailed study of time-resolved, dynamic changes in vascular smooth muscle cell (VSMC) elasticity and adhesion to identify differences in VSMC from young and aged monkeys. Atomic force microscopy (AFM) was used to measure Young's modulus of elasticity and adhesion as assessed by fibronectin (FN) or anti-beta 1 integrin interaction with the VSMC surface. Measurements demonstrated that VSMC cells from old vs. young monkeys had increased elasticity (21.6 kPa vs. 3.5 kPa or a 612% increase in elastic modulus) and adhesion (86 pN vs. 43 pN or a 200% increase in unbinding force). Spectral analysis identified three major frequency components in the temporal oscillation patterns for elasticity (ranging from 1.7 × 10(-3) to 1.9 × 10(-2) Hz in old and 8.4 × 10(-4) to 1.5 × 10(-2) Hz in young) and showed that the amplitude of oscillation was larger (P < 0.05) in old than in young at all frequencies. It was also observed that patterns of oscillation in the adhesion data were similar to the elasticity waveforms. Cell stiffness was reduced and the oscillations were inhibited by treatment with cytochalasin D, ML7 or blebbistatin indicating the involvement of actin-myosin-driven processes. In conclusion, these data demonstrate the efficacy of time-resolved analysis of AFM cell elasticity and adhesion measurements and that it provides a uniquely sensitive method to detect real-time functional differences in biomechanical and adhesive properties of cells. The oscillatory behavior suggests that mechanisms governing elasticity and adhesion are coupled and affected differentially during aging, which may link these events to changes in vascular stiffness.

The mechanical properties of individual, electrospun fibrinogen fibers

We used a combined atomic force microscopic (AFM)/fluorescence microscopic technique to study the mechanical properties of individual, electrospun fibrinogen fibers in aqueous buffer. Fibers (average diameter 208 nm) were suspended over 12 microm-wide grooves in a striated, transparent substrate. The AFM, situated above the sample, was used to laterally stretch the fibers and to measure the applied force. The fluorescence microscope, situated below the sample, was used to visualize the stretching process. The fibers could be stretched to 2.3 times their original length before breaking; the breaking stress was 22 x 10 (6)Pa. We collected incremental stress-strain curves to determine the viscoelastic behavior of these fibers. The total stretch modulus was 17.5 x 10 (6)Pa and the relaxed elastic modulus was 7.2 x 10 (6)Pa. When held at constant strain, electrospun fibrinogen fibers showed a fast and slow stress relaxation time of 3 and 55 s. Our fibers were spun from the typically used 90% 1,1,1,3,3,3-hexafluoro-2-propanol (90-HFP) electrospinning solution and re-suspended in aqueous buffer. Circular dichroism spectra indicate that alpha-helical content of fibrinogen is approximately 70% higher in 90-HFP than in aqueous solution. These data are needed to understand the mechanical behavior of electrospun fibrinogen structures. Our technique is also applicable to study other nanoscopic fibers.

Ascorbic acid selectively improves large elastic artery compliance in postmenopausal women

The compliance of large elastic arteries in the cardiothoracic region decreases with advancing age/menopause and plays an important role in the increased prevalence of cardiovascular diseases in postmenopausal women. We determined whether oxidative stress contributes to the reduced large elastic artery compliance of postmenopausal women. Carotid artery compliance was measured during acute intravenous infusions of saline (baseline control) and supraphysiological doses of the potent antioxidant ascorbic acid in premenopausal (n=10; 23+/-1; mean+/-SE) and estrogen-deficient postmenopausal (n=21; 55+/-1 years) healthy sedentary women. Carotid artery compliance was 56% lower in postmenopausal compared with premenopausal women during baseline control (P<0.0001). Ascorbic acid infusion increased carotid artery compliance by 26% in postmenopausal women (1.11+/-0.07 to 1.38+/-0.08 mm2/mm Hgx10(-1); P<0.001) but had no effect in premenopausal women (2.50+/-0.25 versus 2.43+/-0.20 mm2/mm Hgx10(-1)). Carotid artery diameter, blood pressure, and heart rate were unaffected by ascorbic acid. In the pooled population, the change in arterial compliance with ascorbic acid correlated with baseline waist-to-hip ratio (r=0.56; P=0.001), plasma norepinephrine (r=0.58; P=0.001), and LDL cholesterol (r=0.54; P=0.001). These results suggest that oxidative stress may be an important mechanism contributing to the reduced large elastic artery compliance of sedentary, estrogen-deficient postmenopausal women. Increased abdominal fat storage, sympathetic nervous system activity, and LDL cholesterol may be mechanistically involved in oxidative stress-associated suppression of arterial compliance in postmenopausal women.