Influence of mild heat and restrictive external support on functional changes in vein grafts implanted into arterial circulation. Experimental study

Introduction. Vein grafts placed in the arterial circulation undergo a set of morphological and functional changes. The aim was to investigate the effects of external mild heat combined with internal cooling and external restrictive support on vascular reactivity of the venous grafts implanted into arterial system. Material and methods. Reversed external jugular vein interposition grafting of the carotid artery on the mongrel dogs (n = 18) was performed. The experimental animals were split into three groups: H (n = 6) - grafts were exposed to mild heat and an external sleeve was placed around, S (n = 6) - grafts only with the sleeve and C (n = 6) - control group. The grafts were explanted after 3 months. The rings from all the explanted grafts as well as from jugular veins before implantation were taken and tension study was performed. Contractions to norepinephrine (NE), phenylephrine (Phe), 5-hydroxytryptamine (5-HT) and relaxation to acetylcholine (Ach), calcium ionophore A23187 (A23187) and sodium nitroprusside (SN) were assessed. Results. After pre-treatment with mild heat reaction to the maximal concentrations of NE (37.8 &plusmn; 1.9 g/mm2 before vs. l2.0 &plusmn; 1.6 g/mm2 after), Phe (20.2 &plusmn; 1.6 g/mm2 vs. 2.0 &plusmn; 0.4 g/mm2) were markedly (p < 0.001) diminished. Vein grafts before implantation were insensitive to 5-HT. Only endothelium-independent relaxation to SN was preserved in the grafts after mild heat employment, whereas Ach, A23187 did not produce any endothelium-mediated reaction. Three months after implantation markedly lower contractile responses to maximal doses of NE (1.4 &plusmn; 0.2 g/mm2, 2.1 &plusmn; 0.3 g/mm2 and 15.4 &plusmn; 1.6 g/mm2 for H, S and C respectively), and Phe (0.4 &plusmn; 0.2 g/mm2, 1.3 &plusmn; 0.2 g/mm2 and 12.3 &plusmn; 1.2 g/mm2 for H, S and C respectively) were noted. The maximal examined dose of 5-HT provoked 66.2% of the maximal reaction to NE in group H, 66.5% in group S and 53.2% in group C. The grafts in group H and S were insensitive to endothelium-dependent relaxants, but in C the maximal responses to A23187 were significantly weaker (p < 0.05) than before implantation (40.7 &plusmn; 3.8% vs. 67.4 &plusmn; 2.3%). SN-induced endothelium-independent relaxation was observed in all groups. Conclusion. Mild heat of the venous grafts functionally destroys endothelium and significantly impairs smooth muscle cells' function. Employment of mild heat combined with external support may produce venous conduits less sensitive to vasoactive chemicals including also mitogens involved in neointima formation.Introduction. Vein grafts placed in the arterial circulation undergo a set of morphological and functional changes. The aim was to investigate the effects of external mild heat combined with internal cooling and external restrictive support on vascular reactivity of the venous grafts implanted into arterial system. Material and methods. Reversed external jugular vein interposition grafting of the carotid artery on the mongrel dogs (n = 18) was performed. The experimental animals were split into three groups: H (n = 6) - grafts were exposed to mild heat and an external sleeve was placed around, S (n = 6) - grafts only with the sleeve and C (n = 6) - control group. The grafts were explanted after 3 months. The rings from all the explanted grafts as well as from jugular veins before implantation were taken and tension study was performed. Contractions to norepinephrine (NE), phenylephrine (Phe), 5-hydroxytryptamine (5-HT) and relaxation to acetylcholine (Ach), calcium ionophore A23187 (A23187) and sodium nitroprusside (SN) were assessed. Results. After pre-treatment with mild heat reaction to the maximal concentrations of NE (37.8 &plusmn; 1.9 g/mm2 before vs. l2.0 &plusmn; 1.6 g/mm2 after), Phe (20.2 &plusmn; 1.6 g/mm2 vs. 2.0 &plusmn; 0.4 g/mm2) were markedly (p < 0.001) diminished. Vein grafts before implantation were insensitive to 5-HT. Only endothelium-independent relaxation to SN was preserved in the grafts after mild heat employment, whereas Ach, A23187 did not produce any endothelium-mediated reaction. Three months after implantation markedly lower contractile responses to maximal doses of NE (1.4 &plusmn; 0.2 g/mm2, 2.1 &plusmn; 0.3 g/mm2 and 15.4 &plusmn; 1.6 g/mm2 for H, S and C respectively), and Phe (0.4 &plusmn; 0.2 g/mm2, 1.3 &plusmn; 0.2 g/mm2 and 12.3 &plusmn; 1.2 g/mm2 for H, S and C respectively) were noted. The maximal examined dose of 5-HT provoked 66.2% of the maximal reaction to NE in group H, 66.5% in group S and 53.2% in group C. The grafts in group H and S were insensitive to endothelium-dependent relaxants, but in C the maximal responses to A23187 were significantly weaker (p < 0.05) than before implantation (40.7 &plusmn; 3.8% vs. 67.4 &plusmn; 2.3%). SN-induced endothelium-independent relaxation was observed in all groups. Conclusion. Mild heat of the venous grafts functionally destroys endothelium and significantly impairs smooth muscle cells' function. Employment of mild heat combined with external support may produce venous conduits less sensitive to vasoactive chemicals including also mitogens involved in neointima formation

Does mild heat combined with external stenting prevent from intimal hyperplasia and medial thickening in the venous grafts? Experimental study

Introduction. Intimal hyperplasia and medial thickening of the venous grafts used in coronary artery bypass grafting (CABG) often leads to wall thickening and ultimately to conduit occlusion. The purpose was to investigate the effects of mild heat (85°C) followed by utilization of restrictive sleeve on histological changes of the venous grafts implanted into an arterial system. Material and methods. Reversed external jugular vein interposition grafting of the carotid artery on the mongrel dogs (n = 18) was performed. The experimental animals were split into three groups: H (n = 6) - grafts were exposed to mild heat and an external sleeve was placed around, S (n = 6) - grafts only with the sleeve and C (n = 6) - control group. The grafts were explanted after 3 months. Prior to explantation the grafts&#8217; patency was checked using flowmeter. Afterwards harvested veins were examined in light (LM), scanning (SEM) and transmission electron microscope (TEM). Cross-sectional intima (IA), media (MA) and relative intima area (RIA) for all grafts were calculated. Tissue samples from all grafts before implantation (harvested veins and veins after exposition to mild heat) were also examined. Results. Mild heat destroyed endothelial cells (ECs) and, to a lesser degree, basement membrane but did not influence IA, MA and RIA values. Medial smooth muscle cells (SMCs) located closer to the adventitia were affected by heat pretreatment. After 3 months all grafts were patent. Intimal hyperplasia was observed in group S and C, but not in H. Intimal area was markedly higher (p < 0.05) in group S (1.97 &plusmn; 0.57 mm2) and C (1.51 &plusmn; 0.77 mm2) than in H (0.38 &plusmn; 0.08 mm2). Scanning scans 3 months after implantation showed the luminal surface of all grafts was mostly covered by ECs. Smoth muscle cells were present in the intima of all grafts in group C and S, not in H. Some of them were active synthetic type SMCs with many mitochondria and well developed Golgi apparatus (TEM). The media was atrophic in group H and S, where collagen bundles were dissociated, the collagen fibers disrupted and in random orientation in the matrix. Media area was significantly higher (p < 0.05) in group C (2.64 &plusmn; 0.32 mm2) than in S (1.71 &plusmn; 0.45 mm2) and H (1.74 &plusmn; 0.48 mm2). Conclusion. Mild heat pre-treatment and external sleeving may mitigate the formation of intimal hyperplasia and reduce medial thickening after implantation in the arterial circulation.Introduction. Intimal hyperplasia and medial thickening of the venous grafts used in coronary artery bypass grafting (CABG) often leads to wall thickening and ultimately to conduit occlusion. The purpose was to investigate the effects of mild heat (85°C) followed by utilization of restrictive sleeve on histological changes of the venous grafts implanted into an arterial system. Material and methods. Reversed external jugular vein interposition grafting of the carotid artery on the mongrel dogs (n = 18) was performed. The experimental animals were split into three groups: H (n = 6) - grafts were exposed to mild heat and an external sleeve was placed around, S (n = 6) - grafts only with the sleeve and C (n = 6) - control group. The grafts were explanted after 3 months. Prior to explantation the grafts&#8217; patency was checked using flowmeter. Afterwards harvested veins were examined in light (LM), scanning (SEM) and transmission electron microscope (TEM). Cross-sectional intima (IA), media (MA) and relative intima area (RIA) for all grafts were calculated. Tissue samples from all grafts before implantation (harvested veins and veins after exposition to mild heat) were also examined. Results. Mild heat destroyed endothelial cells (ECs) and, to a lesser degree, basement membrane but did not influence IA, MA and RIA values. Medial smooth muscle cells (SMCs) located closer to the adventitia were affected by heat pretreatment. After 3 months all grafts were patent. Intimal hyperplasia was observed in group S and C, but not in H. Intimal area was markedly higher (p < 0.05) in group S (1.97 &plusmn; 0.57 mm2) and C (1.51 &plusmn; 0.77 mm2) than in H (0.38 &plusmn; 0.08 mm2). Scanning scans 3 months after implantation showed the luminal surface of all grafts was mostly covered by ECs. Smoth muscle cells were present in the intima of all grafts in group C and S, not in H. Some of them were active synthetic type SMCs with many mitochondria and well developed Golgi apparatus (TEM). The media was atrophic in group H and S, where collagen bundles were dissociated, the collagen fibers disrupted and in random orientation in the matrix. Media area was significantly higher (p < 0.05) in group C (2.64 &plusmn; 0.32 mm2) than in S (1.71 &plusmn; 0.45 mm2) and H (1.74 &plusmn; 0.48 mm2). Conclusion. Mild heat pre-treatment and external sleeving may mitigate the formation of intimal hyperplasia and reduce medial thickening after implantation in the arterial circulation

Glucose Tolerance and Left Ventricular Pressure-Volume Relationships in Frequently Used Mouse Strains

We investigated glucose tolerance and left ventricular contractile performance in 4 frequently used mouse strains (Swiss, C57BL/6J, DBA2, and BalbC) at 24 weeks. Glucose tolerance was tested by measuring blood glucose levels in time after intraperitoneal glucose injection (2 mg/g body weight). Left ventricular contractility was assessed by pressure-conductance analysis. Peak glucose levels and glucose area under the curve were higher (all P < .05) in C57BL/6J (418 ± 65 mg/dL and 813 ± 100 mg·h/dL) versus Swiss (237 ± 66 mg/dL and 470 ± 126 mg·h/dL), DBA2 (113 ± 20 mg/dL and 304 ± 49 mg·h/dL, P < .01), and BalbC mice (174 ± 55 mg/dL and 416 ± 70 mg·h/dL). Cardiac output was higher (all P < .05) in Swiss (14038 ± 4530 μL/min) versus C57BL/6J (10405 ± 2683 μL/min), DBA2 (10438 ± 3251 μL/min), and BalbC mice (8466 ± 3013 μL/min). Load-independent left ventricular contractility assessed as recruitable stroke work (PRSW) was comparable in all strains. In conclusion, glucose tolerance and load-dependent left ventricular performance parameters were different between 4 mice background strains, but PRSW was comparable

Diabetes mellitus and the metabolic syndrome do not abolish, but might reduce, the cardioprotective effect of ischemic postconditioning

ObjectiveIschemic preconditioning fails to protect the diabetic heart against lethal reperfusion injury. Because the pathways of ischemic pre- and postconditioning partially overlap, we evaluated the cardioprotective effect of ischemic postconditioning in mouse models of type 2 diabetes (ObOb) and the metabolic syndrome (DKO).MethodsMice (C57BL/6J, ObOb, and DKO; aged 24 weeks; n = 24, n = 28, and n = 18, respectively) underwent reperfusion after 30 minutes of coronary occlusion with or without ischemic postconditioning (3 cycles of 10 seconds reperfusion–reocclusion). Left ventricular contractility and infarct size were assessed 60 minutes later with pressure conductance analysis and 2,3,5-triphenyl-tetrazolium chloride staining, respectively. In a second cohort (C57BL/6J and DKO; aged 12 weeks; n = 31 and n = 24, respectively) cardiac cine magnetic resonance imaging was performed after 1 and 10 weeks, followed by pressure conductance analysis and Sirius red staining.ResultsIn the C57BL6/J mice, the infarct size was lower (40%, P < 10−5) and the load independent preload recruitable stroke work was greater after ischemic postconditioning (P < .05). In the ObOb and DKO mice, ischemic postconditioning reduced the infarct size by 24% (P < 10−5). In the C57BL/6J mice, the ejection fraction was greater and the myocardial mass was lower 10 weeks after ischemic postconditioning (P < .05). Tagging grid deformation was increased after ischemic postconditioning in both infarcted and remote areas. After ischemic postconditioning, the survival and ejection fraction were greater in the DKO mice (67% vs 17% and 44% ± 11% vs 59% ± 2%, P < .05 for both), and the collagen content was lower for both C57BL/6J and DKO mice (P < .05 for both).ConclusionsThe cardioprotective effect of ischemic postconditioning was sustained in C57BL/6J mice after 10 weeks and protected against adverse left ventricular remodeling. In mouse models of type 2 diabetes, protection against lethal reperfusion injury is present, leading to increased survival after ischemia and reperfusion

An electro-responsive hydrogel for intravascular applications: an in vitro and in vivo evaluation

There is a growing interest in using hydrogels for biomedical applications, because of more favourable characteristics. Some of these hydrogels can be activated by using particular stimuli, for example electrical fields. These stimuli can change the hydrogel shape in a predefined way. It could make them capable of adaptation to patient-specific anatomy even post-implantation. This is the first paper aiming to describe in vivo studies of an electro-responsive, Pluronic F127 based hydrogel, for intravascular applications. Pluronic methacrylic acid hydrogel (PF127/MANa) was in vitro tested for its haemolytic and cytotoxic effects. Minimal invasive implantation in the carotid artery of sheep was used to evaluate its medium-term biological effects, through biochemical, macroscopic, radiographic, and microscopic evaluation. Indirect and direct testing of the material gave no indication of the haemolytic effects of the material. Determination of fibroblast viability after 24 h of incubation in an extract of the hydrogel showed no cytotoxic effects. Occlusion was obtained within 1 h following in vivo implantation. Evaluation at time of autopsy showed a persistent occlusion with no systemic effects, no signs of embolization and mild effects on the arterial wall. An important proof-of-concept was obtained showing biocompatibility and effectiveness of a pluronic based electro-responsive hydrogel for obtaining an arterial occlusion with limited biological impact. So the selected pluronic-methacrylic acid based hydrogel can be used as an endovascular occlusion device. More importantly it is the first step in further development of electro-active hydrogels for a broad range of intra-vascular applications (e.g. system to prevent endoleakage in aortic aneurysm treatment, intra-vascular drug delivery)

A cardiovascular occlusion method based on the use of a smart hydrogel

Smart hydrogels for biomedical applications are highly researched materials. However, integrating them into a device for implantation is difficult. This paper investigates an integrated delivery device designed to deliver an electro-responsive hydrogel to a target location inside a blood vessel with the purpose of creating an occlusion. The paper describes the synthesis and characterization of a Pluronic/methacrylic acid sodium salt electro-responsive hydrogel. Application of an electrical bias decelerates the expansion of the hydrogel. An integrated delivery system was manufactured to deliver the hydrogel to the target location in the body. Ex vivo and in vivo experiments in the carotid artery of sheep were used to validate the concept. The hydrogel was able to completely occlude the blood vessel reducing the blood flow from 245 to 0 ml/min after implantation. Ex vivo experiments showed that the hydrogel was able to withstand physiological blood pressures of > 270 mm·Hg without dislodgement. The results showed that the electro-responsive hydrogel used in this paper can be used to create a long-term occlusion in a blood vessel without any apparent side effects. The delivery system developed is a promising device for the delivery of electro-responsive hydrogels

Implantation of an Elastic Ring at Equator of the Left Ventricle Influences Cardiac Mechanics in Experimental Acute Ventricular Dysfunction

ObjectivesWe hypothesize that the implantation of an endoventricular elastic ring at the left ventricle (LV) equatorial site will positively affect the cardiac mechanics in an experimental model of acute LV dysfunction.BackgroundChanges in the elastic properties of LV occur in the dilated and failing heart, contributing to overall cardiac mechanical dysfunction. No interventions are as yet specifically designed to improve LV elasticity in failing hearts.MethodsAcute LV enlargement and dysfunction was induced in 13 healthy sheep via the insertion of a large Dacron patch into the lateral wall. In 6 of these sheep, a customized elastic ring was implanted at the inner surface of the LV equator (ring group), and the remaining 7 served as control subjects (dysfunction group). Systolic and diastolic function was evaluated using echocardiography and pressure–volume (P–V) analysis.ResultsIn the ring group, both the maximum rate of pressure increase and the slope of end-systolic P–V relationship were significantly different from those without ring (1,718 ± 726 vs. 1,049 ± 269 and 1.25 ± 0.30 vs. 0.88 ± 0.19; both p < 0.05). Preload recruitable stroke work changed even more prominently (33 ± 11 vs. 17 ± 5; p = 0.005), along with stroke volume, ejection fraction, and stroke work. Although ring implantation had no effect on end-diastolic P–V relationship, it positively affected the active component of diastole: the maximum rate of pressure decrease declined significantly (p = 0.037). The time constant of relaxation tended to decrease (37 ± 8 vs. 44 ± 6; p = 0.088).ConclusionsImproving the elastic component of the LV at its equatorial site substantially augments contractility and early relaxation in acute systodiastolic LV dysfunction

Increased Cardiac Myocyte PDE5 Levels in Human and Murine Pressure Overload Hypertrophy Contribute to Adverse LV Remodeling

Background: The intracellular second messenger cGMP protects the heart under pathological conditions. We examined expression of phosphodiesterase 5 (PDE5), an enzyme that hydrolyzes cGMP, in human and mouse hearts subjected to sustained left ventricular (LV) pressure overload. We also determined the role of cardiac myocyte-specific PDE5 expression in adverse LV remodeling in mice after transverse aortic constriction (TAC). Methodology/Principal Findings: In patients with severe aortic stenosis (AS) undergoing valve replacement, we detected greater myocardial PDE5 expression than in control hearts. We observed robust expression in scattered cardiac myocytes of those AS patients with higher LV filling pressures and BNP serum levels. Following TAC, we detected similar, focal PDE5 expression in cardiac myocytes of C57BL/6NTac mice exhibiting the most pronounced LV remodeling. To examine the effect of cell-specific PDE5 expression, we subjected transgenic mice with cardiac myocyte-specific PDE5 overexpression (PDE5-TG) to TAC. LV hypertrophy and fibrosis were similar as in WT, but PDE5-TG had increased cardiac dimensions, and decreased dP/dtmax and dP/dtmin with prolonged tau (P<0.05 for all). Greater cardiac dysfunction in PDE5-TG was associated with reduced myocardial cGMP and SERCA2 levels, and higher passive force in cardiac myocytes in vitro. Conclusions/Significance: Myocardial PDE5 expression is increased in the hearts of humans and mice with chronic pressure overload. Increased cardiac myocyte-specific PDE5 expression is a molecular hallmark in hypertrophic hearts with contractile failure, and represents an important therapeutic target