Mirko Rosic

ARTreat project: Three-dimensional numerical simulation of plaque formation and development in the arteries

Atherosclerosis is a progressive disease characterized by the accumulation of lipids and fibrous elements in arteries. It is characterized by dysfunction of endothelium and vasculitis, and accumulation of lipid, cholesterol, and cell elements inside blood vessel wall. In this study, a continuum-based approach for plaque formation and development in 3-D is presented. The blood flow is simulated by the 3-D Navier-Stokes equations, together with the continuity equation while low-density lipoprotein (LDL) transport in lumen of the vessel is coupled with Kedem-Katchalsky equations. The inflammatory process was solved using three additional reaction-diffusion partial differential equations. Transport of labeled LDL was fitted with our experiment on the rabbit animal model. Matching with histological data for LDL localization was achieved. Also, 3-D model of the straight artery with initial mild constriction of 30% plaque for formation and development is presented.

Histamine Blood Concentration in Ischemic Heart Disease Patients

The aim of this study was to investigate histamine blood concentration in subjects suffering from different types of ischemic heart diseases during the period of eight days. Our results showed that the histamine blood level was associated with different types of ischemic heart diseases. The blood histamine level in all investigated patients was significantly higher when compared to control subjects (44.87 ± 1.09 ng mL−1), indicating the increase of histamine release in patients suffering from coronary diseases. In patients suffering from ACS-UA and ACS-STEMI, the second day peak of histamine level occurs (90.85 ± 6.34 ng mL−1 and 121.7 ± 6.34 ng mL−1, resp.) probably as the reperfusion event. Furthermore, our data suggest that histamine can be additional parameter of myocardial ischemia along with cardiac specific enzymes and may prove to be an excellent single prognostic marker for multitude of ischemic heart diseases.

Kinetics of Thyroxine (T4) and Triiodothyronine (T3) Transport in the Isolated Rat Heart

The dynamics and kinetics of thyroid hormone transport in the isolated rat heart were examined using the modified unidirectional paired tracer dilution method. The uptake of 125I‐thyroxine (125I‐T4) and 125I‐triiodothyronine (125I‐T3) from the extracellular space into heart cells was measured relative to the extracellular space marker 3H‐mannitol. The thyroid hormone maximal uptake was 54.4% for 125I‐T4 and 52.15% for 125I‐T3. The thyroid hormone net uptake was 25.69% for 125I‐T4 and 25.49% for 125I‐T3. Backflux from the intracellular space was 53.17% for 125I‐T4 and 61.59% for 125I‐T3. In the presence of unlabelled thyroid hormones, 125I‐T4 and 125I‐T3 maximal uptakes were reduced from 10.1 to 59.74% and from 34.6 to 65.3%, respectively, depending on the concentration of the unlabelled hormone, suggesting a saturable mechanism of the thyroid hormone uptake by the heart cells, with Km(T4)= 105.46 μM and the maximal rate of 125I‐thyroid hormone flux from the extracellular space to heart cells (Vmax(T4)) = 177.84 nM min−1 for 125I‐T4 uptake, and Km(T3)= 80.0 μM and Vmax(T3)= 118.5 nM min−1 for 125I‐T3 uptake.

Glucagon Effects on Ischemic Vasodilatation in the Isolated Rat Heart

The myocardial reperfusion following ischemia leads to the ischemic vasodilation by affecting the release of various vasoactive substances, such as free radicals, NO, and histamine. In addition, some evidences suggest that glucagon itself may alter the release of those substances. In this study, we investigated the ischemic vasodilation of the isolated rat heart, as well as the concentrations of NO, TBARS, and histamine in the coronary venous effluent either in the presence or in the absence of glucagon. Our results showed that in the presence of glucagon, there was a faster restoration of coronary perfusion pressure during ischemic vasodilation compared to the absence of glucagon (124 ± 5.6 versus 81 ± 5.2 s) with no apparent changes in TBARS concentration. The glucagons administration leads to the decreased release of histamine by approximately 35%. Biphasic release of NO in the presence of glucagon initially showed augmentation by 60%, followed by the significant attenuation of 45%.

Biphasic L‐arginine uptake by the isolated guinea‐pig heart

L‐Arginine is the physiological substrate for the formation of nitric oxide (NO) and accounts for the biological activity of endothelium‐derived relaxing factor. We have studied L‐arginine transport in the heart using a rapid dual‐isotope dilution technique. The time course of L‐[3H]arginine uptake (extraction) by the isolated perfused guinea‐pig heart was found to occur in two phases. The first phase reached a plateau in 6.6 +/− 0.6 s and lasted 8.8 +/− 0.7 s, whereas the second phase developed a plateau after 16.3 +/− 0.8 s. The first phase of maximal uptake (Umax,1) accounted for 13.4 +/− 1.4% of the total uptake and the second (Umax,2) for 32.3 +/− 1.8%. The two phases of uptake were inhibited by unlabelled L‐arginine in a dose‐dependent manner, which suggests that both phases are carrier mediated. The degree of inhibition of Umax,1 and Umax,2 by unlabelled L‐arginine was not significantly different. Studies of the kinetics of uptake of these processes revealed an apparent Km,1 of 183 +/− 10 microM with a Vmax,1 of 50 +/− 10 nmol min‐1 g‐1 for the first phase and Km,2 of 167 +/− 14 microM with a Vmax,2 of 93 +/− 13 nmol min‐1 g‐1 for the second phase of uptake. These results suggest a similar affinity for the receptors of both transport systems, but with different values for Vmax (P < 0.05). In contrast, 1 mM unlabelled D‐arginine had no effect on either the first or second phase of uptake of L‐[3H]arginine by the heart, which suggests that these processes are stereospecific. In the presence of the L‐stereoisomer of nitro‐arginine‐mono‐methyl ester (L‐NAME), a potent inhibitor of NO synthesis, the Umax,1 was inhibited by about 60% while Umax,2 was inhibited by only 20%, which suggests that there is a difference in the effect of L‐NAME on the two phases of L‐arginine uptake. The first phase most probably represents uptake into the capillary wall, i.e. endothelium and smooth muscle, while the second phase represents entry into the extra‐endothelial compartment, i.e. the cardiac myocytes and fibroblasts.

Computer simulation and experimental analysis of LDL transport in the arteries

Atherosclerosis develops from oxidized low-density lipoprotein molecules (LDL). When oxidized LDL evolves in plaque formations within an artery wall, a series of reactions occur to repair the damage to the artery wall caused by oxidized LDL. Macrophages accumulate inside arterial intima, they started to collect oxidized LDL and form foam cells. Smooth muscle cells accumulate in the atherosclerotic arterial intima, where they proliferate and secrete extracellular matrix to form a fibrous cap. In this study, experimental model of LDL transport on the isolated blood vessel from rabbit on high fat diet after 8 weeks is simulated numerically by using a specific model and histological data. The 3D blood flow is governed by the Navier-Stokes equations, together with the continuity equation. Mass transfer within the blood lumen and through the arterial wall is coupled with the blood flow by the convection-diffusion equation. LDL transport in lumen of the vessel is described by Kedem-Katchalsky equations. The inflammatory process is solved using three additional reaction-diffusion partial differential equations. Matching of histological rabbit data is performed using 3D histological image reconstruction and 3D deformation of elastic body. Computed concentrations of labeled LDL of 5.2 % and macrophages distribution of 4.2% inside the media are found to be in good agreement with experimental results. This simulation study provides a useful tool for understanding and prediction of LDL transport through the arterial wall and evolution of atherosclerotic plaques.

Glucagon Effects on 3H-Histamine Uptake by the Isolated Guinea-Pig Heart during Anaphylaxis

We estimated the influence of acute glucagon applications on 3H-histamine uptake by the isolated guinea-pig heart, during a single 3H-histamine passage through the coronary circulation, before and during anaphylaxis, and the influence of glucagon on level of histamine, NO, O2 −, and H2O2 in the venous effluent during anaphylaxis. Before anaphylaxis, glucagon pretreatment does not change 3H-histamine Umax and the level of endogenous histamine. At the same time, in the presence of glucagon, 3H-histamine Unet is increased and backflux is decreased when compared to the corresponding values in the absence of glucagon. During anaphylaxis, in the presence of glucagon, the values of 3H-histamine Umax and Unet are significantly higher and backflux is significantly lower in the presence of glucagon when compared to the corresponding values in the absence of glucagon. The level of endogenous histamine during anaphylaxis in the presence of glucagon (6.9–7.38 × 10−8  μM) is significantly lower than the histamine level in the absence of glucagon (10.35–10.45 × 10−8  μM). Glucagon pretreatment leads to a significant increase in NO release (5.69 nmol/mL) in comparison with the period before glucagon administration (2.49 nmol/mL). Then, in the presence of glucagon, O2 − level fails to increase during anaphylaxis. Also, our results show no significant differences in H2O2 levels before, during, and after anaphylaxis in the presence of glucagon, but these values are significantly lower than the corresponding values in the absence of glucagon. In conclusion, our results show that glucagon increases NO release and prevents the increased release of free radicals during anaphylaxis, and decreases histamine level in the venous effluent during cardiac anaphylaxis, which may be a consequence of decreased histamine release and/or intensified histamine capturing by the heart during anaphylaxis.

Transport of Low-Density Lipoprotein Into the Blood Vessel Wall During Atherogenic Diet in the Isolated Rabbit Carotid Artery

BACKGROUND Atherosclerosis is a chronic fibroproliferative disease that includes accumulation of cholesterol-rich lipids in the arterial wall. Though numerous studies have investigated atherosclerosis, not enough is known about the exact mechanisms of low-density lipoprotein (LDL) transport into the blood vessel wall. Therefore, we explored the (125)I-LDL transport into the arterial wall under constant perfusion flow and pressure as well as the influence of duration of atherogenic diet on (125)I-LDL transport and biomechanical properties of carotid artery. METHODS AND RESULTS The isolated segment of rabbit carotid artery was used under constant perfusion flow and pressure-induced (0 mmHg and 140 mmHg) blood vessel distension, with the possibility to change and precisely calculate shear stress during the experiment. Obtained results indicate the influence of atherogenic diet duration and consequent variation of shear stress on (125)I-LDL transport into the blood vessel wall. (125)I-LDL transport into the blood vessel wall at low pressure-induced blood vessel distension decreases by the increase of the shear stress and in relation to the atherogenic diet duration. At high pressure-induced blood vessel distension, (125)I-LDL transport increases in relation to the atherogenic diet duration and the increase of shear stress. CONCLUSIONS The influence of shear stress is a more dominant parameter on LDL uptake at low pressure-induced blood vessel distension; however, the atherogenic diet duration has more of a dominant influence on LDL uptake at high pressure-induced vessel distension.

Modeling of abdominal aortic aneurism rupture by using experimental bubble inflation test

Aneurysm rupture is a biomechanical phenomenon that occurs when the mechanical stress acting on the inner wall exceeds the failure strength of the diseased aortic tissue. Besides numerous advantages in surgical and anaesthesiological management, emergency procedure leads to fatal outcome in 20-50% of those who reach hospital. Prediction of influence of dynamic blood flow on natural history of aneurysmatic disease and outcome of therapeutic procedures could contribute to treatment strategy and results. In this study we presented experimental design for estimation of the material property of real human aorta tissue from bubble inflation test. Then we investigated fluid-structure interaction of pulsatile blood flow in the specific patient three-dimensional model of abdominal aortic aneurysms (AAAs). Numerical predictions of blood flow patterns and nonlinear wall stresses in AAAs are performed in compliant wall anisotropic model using the finite element method. These computational procedures together with experimental determination of the nonlinear material property could provide us more accurate assessment of aneurysm rupture risk.

Biphasic L-arginine uptake by isolated guinea pig heart

L-Arginine is the physiological substrate for the formation of nitric oxide (NO) and accounts for the biological activity of endothelium-derived relaxing factor. We have studied L-arginine transport in the heart using a rapid dual-isotope dilution technique. The time course of L-[3H]arginine uptake (extraction) by the isolated perfused guinea-pig heart was found to occur in two phases. The first phase reached a plateau in 6.6 +/- 0.6 s and lasted 8.8 +/- 0.7 s, whereas the second phase developed a plateau after 16.3 +/- 0.8 s. The first phase of maximal uptake (Umax,1) accounted for 13.4 +/- 1.4% of the total uptake and the second (Umax,2) for 32.3 +/- 1.8%. The two phases of uptake were inhibited by unlabelled L-arginine in a dose-dependent manner, which suggests that both phases are carrier mediated. The degree of inhibition of Umax,1 and Umax,2 by unlabelled L-arginine was not significantly different. Studies of the kinetics of uptake of these processes revealed an apparent Km,1 of 183 +/- 10 microM with a Vmax,1 of 50 +/- 10 nmol min-1 g-1 for the first phase and Km,2 of 167 +/- 14 microM with a Vmax,2 of 93 +/- 13 nmol min-1 g-1 for the second phase of uptake. These results suggest a similar affinity for the receptors of both transport systems, but with different values for Vmax (P < 0.05). In contrast, 1 mM unlabelled D-arginine had no effect on either the first or second phase of uptake of L-[3H]arginine by the heart, which suggests that these processes are stereospecific. In the presence of the L-stereoisomer of nitro-arginine-mono-methyl ester (L-NAME), a potent inhibitor of NO synthesis, the Umax,1 was inhibited by about 60% while Umax,2 was inhibited by only 20%, which suggests that there is a difference in the effect of L-NAME on the two phases of L-arginine uptake. The first phase most probably represents uptake into the capillary wall, i.e. endothelium and smooth muscle, while the second phase represents entry into the extra-endothelial compartment, i.e. the cardiac myocytes and fibroblasts.