Stereology of myocardial hypertrophy induced by physical exercise

Heart regeneration with human pluripotent stem cells: Prospects and challenges

Cardiovascular disease, ranging from congenital heart disease to adult myocardial infarction, is the leading cause of death worldwide. In pursuit of reliable cardiovascular regenerative medicine, human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer plenty of potential cell-based applications. HPSCs are capable of proliferating indefinitely in an undifferentiated state, and are also pluripotent, being able to differentiate into virtually any somatic cell types given specific stepwise cues, thus representing an unlimited source to generate functional cardiovascular cells for heart regeneration. Here we recapitulated current advances in developing efficient protocols to generate hPSC-derived cardiovascular cell lineages, including cardiomyocytes, endothelial cells, and epicardial cells. We also discussed applications of hPSC-derived cells in combination with compatible bioactive materials, promising trials of cell transplantation in animal models of myocardial infarction, and potential hurdles to bring us closer to the ultimate goal of cell-based heart repair.

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HPSCs hold tremendous therapeutic potential for treating CVDs.

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HPSCs could differentiate into multiple cardiovascular cell lineages.

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Transplantation of hPSC-derived cardiovascular cells and biomaterials shows promising results, but challenges still remain.

3D and 4D Bioprinting of the Myocardium: Current Approaches, Challenges, and Future Prospects

3D and 4D bioprinting of the heart are exciting notions in the modern era. However, myocardial bioprinting has proven to be challenging. This review outlines the methods, materials, cell types, issues, challenges, and future prospects in myocardial bioprinting. Advances in 3D bioprinting technology have significantly improved the manufacturing process. While scaffolds have traditionally been utilized, 3D bioprinters, which do not require scaffolds, are increasingly being employed. Improved understanding of the cardiac cellular composition and multiple strategies to tackle the issues of vascularization and viability had led to progress in this field. In vivo studies utilizing small animal models have been promising. 4D bioprinting is a new concept that has potential to advance the field of 3D bioprinting further by incorporating the fourth dimension of time. Clinical translation will require multidisciplinary collaboration to tackle the pertinent issues facing this field.

A review of state-of-the-art stereology for better quantitative 3D morphology in cardiac research

The aim of stereological methods in biomedical research is to obtain quantitative information about three-dimensional (3D) features of tissues, cells, or organelles from two-dimensional physical or optical sections. With immunogold labeling, stereology can even be used for the quantitative analysis of the distribution of molecules within tissues and cells. Nowadays, a large number of design-based stereological methods offer an efficient quantitative approach to intriguing questions in cardiac research, such as "Is there a significant loss of cardiomyocytes during progression from ventricular hypertrophy to heart failure?" or "Does a specific treatment reduce the degree of fibrosis in the heart?" Nevertheless, the use of stereological methods in cardiac research is rare. The present review article demonstrates how some of the potential pitfalls in quantitative microscopy may be avoided. To this end, we outline the concepts of design-based stereology and illustrate their practical applications to a wide range of biological questions in cardiac research. We hope that the present article will stimulate researchers in cardiac research to incorporate design-based stereology into their study designs, thus promoting an unbiased quantitative 3D microscopy.

Beneficial effects of physical exercise on hypertension and cardiovascular adverse remodeling of diet-induced obese rats

BACKGROUND AND AIMS

Obesity is present among all age groups and in all socioeconomic groups. This study on obese rats aims to quantify the beneficial effects of physical exercise on blood pressure (BP), the heart, the elasticity and resistance of arteries.

METHODS AND RESULTS

Obese male Wistar rats, (obesity due to a high fat diet with 30% fat), and non-obese rats, were assigned to four groups (n=5): sedentary obese; exercise-practice obese; sedentary control; and exercise-practice control (motor treadmill for 13 weeks). Their organs were studied through light microscopy and stereology. The diet-induced obesity caused mild hypertension with adverse cardiovascular changes. Physical exercise diminished the alterations associated with BP elevation and obesity. The pressure-lowering effect observed in obese rats submitted to physical exercise improved the myocardial vascularization and the aortic and the carotid wall structure by reducing the thickness and normalizing both the elastic lamellae and the smooth muscle cells. The adaptive response of the gluteus superficialis muscle to physical exercise also improved the peripheral resistance arteries of obese rats.

CONCLUSION

Current research supports the notion of physical exercise as a potential non-pharmacological antihypertensive treatment for diet-induced obesity hypertension.

Long-term exercise training and angiotensin-converting enzyme inhibition differentially enhance myocardial capillarization in the spontaneously hypertensive rat

OBJECTIVES

To investigate whether combined treatment with lisinopril, an angiotensin-converting enzyme (ACE) inhibitor and exercise training would have an additive effect in enhancing the capillary supply of the left ventricular (LV) myocardium in spontaneously hypertensive rats (SHR).

DESIGN

Twelve-week-old male SHR were divided into four groups (10-12 each): sedentary, sedentary treated with lisinopril (15-20 mg/kg per day by gavage), exercise trained, and exercise trained while treated with lisinopril. Exercise training consisted of 1 h a day/5 days a week of running on a treadmill.

METHODS

After 10 weeks of experimental protocols, capillary surface density and length density were sterologically determined in 1 mum thick LV tissue samples from perfuse-fixed hearts.

RESULTS

Lisinopril significantly reduced systolic blood pressure (SBP) and LV mass in the sedentary with lisinopril and exercise trained with lisinopril groups but did not affect the heart rate (HR). Exercise training did not reduce SBP or LV mass, but significantly reduced HR in the exercise trained and exercise trained with lisinopril groups. Lisinopril treatment (sedentary with lisinopril), exercise training (exercise) and their combination (exercise trained with lisinopril) significantly increased myocardial capillary surface area density by 26, 38 and 65% and length density by 38, 48 and 67%, respectively.

CONCLUSION

Lisinopril administration and exercise training independently enhanced myocardial capillarization through a reduction of myocardial mass and stimulation of angiogenesis, respectively. A combination of the two treatments enhanced myocardial capillarization more than either intervention alone. This may aid in the restoration of the normal nutritional status of cardiac myocytes compromised by the hypertrophic state of hypertension.

Spin-spin relaxation times in myocardial hypertrophy induced by endocrine agents in rat

Magnetic resonance techniques afford a significant advantage for noninvasive diagnosis of cardiovascular pathology. The purpose of our present study was to assay the proton nuclear magnetic resonance (1H-NMR) sensitivity in the differential diagnosis of certain endocrine cardiovascular complications. In this context, we investigated the water state and content in the hypertrophied myocardium. Male and female Wistar rats were treated with different hormones (hydrocortisone acetate, testosterone, estradiol, thyroid hormones) in combination with isoproterenol (a synthetic catecholamine that induces myocardial ischemia and hypertrophy). The animals were sacrificed after 20 days of treatment and samples of integral myocardium and left ventricular myocardium were analyzed on a 1H-NMR AREMI spectrometer (0.6 T; proton resonance at 25 MHz). The estimation of T2 was made by Carr Purcell-Meiboom-Gill pulse sequence. The data were fitted to a bi-exponential curve, yielding short (T21) values for bound water and long (T22) values for free water. In order to evaluate the myocardial hypertrophy, the following ratios were calculated: integral myocardium to body weight; left ventricle to body weight; left ventricle to integral myocardium. The first two ratios were also calculated for dried tissue, in order to estimate its contribution to myocardial hypertrophy. Our findings demonstrate that myocardial hypertrophy is associated with a decrease of T22, as a consequence of the increase in the dried component (i.e. proteins) of the tissue, while the total tissue water (H2Ot%), measured by gravimetry) was not significantly modified. Nevertheless, it is reasonable that the increase in the protein content would be proportional with the increase in H2Ot%. The decrease of T21 seems to be proportional with the level of left ventricle hypertrophy in female groups. The 1H-NMR measurements were much sensitive for the differential diagnosis of myocardial hypertrophy in the case of left ventricle.

Effect of ageing and malnutrition on rat myocardium. II. The microvasculature

The modulating effects of ageing and malnutrition on rat myocardium were studied morphometrically with respect to the microvasculature. An increase in capillary density together with a decrease in capillary lumen cross-sectional area was noted during starvation. The important changes seen in the myocyte T-system were paralleled by a decreased diffusion distance for oxygen from the capillary lumen to the mitochondrion. The changes described in the aged rat heart point to an altered inter-relationship between parenchyma and vascularization with a lower capillary volume fraction and a greater diffusion distance from the capillary lumen to the mitochondrion; this is caused by hypertrophy of the aged myocyte. This reduction in capacity to exchange substrates is further reduced by the less developed T-system in the older myocyte.

Capillary growth in the heart

Experiments were performed to test the hypothesis that increased stretch and/or tension of myocytes in the absence of changes in blood flow could induce capillary growth in the heart. Chronic treatment with either dobutamine (rabbits) or alinidine (rats) which increased force of contraction and/or stroke volume respectively without increases in coronary blood flow led to enlargement of the anatomical size of the capillary bed, with no change in cardiac weight, thus supporting the role of external mechanical factors in angiogenesis.

Capillary neoformation in the rat heart--stereological studies on papillary muscles in hypertrophy and physiologic growth

Stereological investigations on myocardial capillaries provided evidence that the common estimator of capillarity, the capillary density (i.e., number of capillary profiles per unit transverse sectional area), underestimates the true capillary supply since the capillary axes are not oriented perfectly in parallel to the myofiber axes. Recently, we studied the "true" capillarity, i.e., the length density of capillaries (LV = capillary length per capillary volume), in some experimental models of cardiac hypertrophy which have been published elsewhere. It has been shown that LV decreases in renovascular hypertension, but is maintained in physical exercise and after chronic thyroxin application. However, the growth pattern of capillaries in hypertrophic hearts has not yet been analyzed. In the present paper it is demonstrated that important information on the capillary network can be derived from the two-dimensional capillary-to-fiber ratios (2D CFR: capillary profiles per myofiber profiles in transverse sections) and from the three-dimensional capillary-to-fiber ratios (3D CFR: capillary length per unit myofiber length). Increase in both suggests neoformation of additional capillary branches in parallel connection. Retrospective analysis of the quantitative data indicates that in hypertrophy induced by physical exercise or by chronic thyroxin application capillary neoformation in parallel connection counterbalances increase of oxygen diffusion distance due to myofiber enlargement. In renovascular hypertension, capillary neoformation in parallel connection does not occur. Studies on normal growth indicated both a slight decrease of LV of capillaries, as well as a continuous neoformation of additional capillary branches.

Pathologic changes in the long-term transplanted heart: a morphometric study of myocardial hypertrophy, vascularity, and fibrosis

Myocyte hypertrophy and myocardial fibrosis have been observed in transplanted human hearts, and both could potentially have an adverse effect on long-term cardiac function. There has been some concern that distant donor heart procurement and cyclosporine treatment increase the risk of these changes, but their incidence and severity have not been documented quantitatively in large numbers of cardiac transplant recipients. We used light microscopic morphometric methods to estimate myocardial collagen volume fraction and myocyte width in right ventricular endomyocardial biopsies from 95 recipients at 3 years posttransplantation, and electron microscopic stereology to estimate myocardial vascularity and myocyte myofibril content in 40 recipients, also at 3 years posttransplantation. We compared those with locally and distantly procured donor hearts (mean ischemic time 160 minutes) and cyclosporine versus noncyclosporine immunosuppression. Controls were pretransplant right ventricular biopsies from 20 donor hearts which were free of heart disease. We found no significant differences in myocardial collagen volume fractions. Myocyte hypertrophy was typical of all the transplant biopsies (mean myocyte width 20.2 microns, SD 3.0 in all transplants versus 11.8 microns, SD 2.2 in controls, P less than 0.001), but distant donor procurement and cyclosporine had no significant effect. There were significant reductions of myofibril volume fraction in the transplants, which raises the possibility of gradual decompensation in some patients. There were no significant differences in myocardial vascularity, although a few patients were well below the control range. We conclude that distant donor heart procurement, with ischemic times averaging less than 3 hours, and cyclosporine treatment are not responsible for significant hypertrophy or fibrosis in most transplants. Hypertrophy is typical of the transplanted heart, and it is possible that associated abnormalities might have an effect on cardiac function in some long-term survivors.

Physiologic consequences of local heart irradiation in rats

Noninvasive methods have been used to study the long-term cardiovascular and pulmonary functional changes at rest and after exercise in adult rats following local heart irradiation with single x-ray doses of 15, 17.5 or 20 Gy, and in non-irradiated control animals. Rats that had undergone a chronic exercise program were compared with untrained cohorts. The earliest dysfunction detected was an increased respiratory rate (f) at 10 weeks after irradiation in the highest dose group. In contrast, both telemetric heart-rate (HR) and rhythm and indirect systolic blood pressure measurements performed at rest only revealed changes starting at 43 weeks after irradiation with 20 Gy, up to which point the rats showed no clinical signs of heart failure. However, the number of minutes required for the recovery of the HR to pre-exercise levels following the implementation of a standardized exercise challenge was elevated in untrained rats compared with their trained cohorts at 18 weeks after irradiation with 20 Gy. Increases in recovery times were required in the two lowest dose groups, starting at 26 weeks after irradiation. It was concluded that the reserve capacity of the cardiopulmonary system masks functional decrements at rest for many months following local heart irradiation, necessitating the use of techniques which reveal reductions in reserve capacities. Further, the influence of local irradiation to the heart and lungs deserves closer scrutiny due to mutual interactions.

Fine structure of capillary proliferation in myocardium of volume overloaded rats

We studied the fine structure of capillary endothelial cells of volume over-loaded cardiac hypertrophy in rats using A-V shunt between the left common carotid artery and the left external jugular vein. The duration of experiment was 1, 2 and 4 weeks. Volume overload of the heart was constantly induced, because blood flow index (ml/min/kg) of both carotid arteries was increased throughout the experiment and the volume and the weight of the left ventricle were significantly increased in 2 and 4 weeks. After the making of the large panorama photograph composed of 24 TEM photographs, the number of the endothelial cells of each capillary was directly counted under TEM. In 2-week shunted animals, incidences of over 3 endothelial cells per capillary were definitely increased. Also bulging of the endothelial cells, overlapping of two endothelial cells and increasing of microvilli on the luminal surface were mostly prominent in 2 weeks. Endothelial cells of intramyocardial capillaries are considered to be activated as early as 1 week and proliferated in around 2 weeks after volume-overload. An increase of coronary blood flow might be one of the most important causes of the endothelial proliferation and regulated by dilatation of the capillary lumen.

New perspectives on left ventricular hypertrophy: anatomy, physiology, and significance

The advent of echocardiography has added an important and sensitive tool for assessment of left ventricular hypertrophy (increased left ventricular mass). Recent echocardiographic studies in large population-based samples suggest an epidemic of left ventricular hypertrophy. Preliminary data suggesting important prognostic importance for such left ventricular hypertrophy (independent of standard risk factors) has fueled interest in the development, determinants, and other features of the hypertrophy. Hemodynamic and neurohumoral factors are the most prominent stimuli to adaptive (physiologic) myocardial hypertrophy, which can progress to maladaptive (pathologic) hypertrophy. The overall blood pressure experience, overweight, the cardiovascular response to recurrent psychosocial stress and physical activity level are four important correlates and potential determinants of left ventricular mass in various urban-suburban populations. Determination of the relative contributions and interrelations of these and other factors (such as heredity) to various forms of left ventricular hypertrophy found in various demographic groups warrants intensive investigation.

Beneficial effect of chronic bradycardial pacing on capillary growth and heart performance in volume overload heart hypertrophy

We have previously reported that chronic bradycardial pacing increases both capillary density/mm2 (CD) and maximal work output in normal rabbit hearts. This technique has now been applied to rabbits with volume-overload hypertrophy due to lesion of the aortic valve. Four groups of animals were studied: controls (C), paced (P), valve-lesioned (VL), and paced valve-lesioned (PVL). The aortic valve was lesioned 8 weeks before the acute experiments; pacing was started 4 weeks before the acute experiments, and thus, the PVL group had developed hypertrophy before pacing was started. The degree of hypertrophy was similar in VL hearts whether paced or not: heart wt/body wt ratio increased by 33.5 +/- 8.9% (mean +/- SEM) in VL and 25.2 +/- 8.2% in PVL versus control animals of similar body weight (p less than 0.001). The hearts of the PVL animals showed a higher CD (2,277 +/- 107) than VL hearts (1,383 +/- 43), CD in C hearts of similar weights being 1,595 +/- 103, and in P hearts 2,350 +/- 194. Thus, CD was lower by 14% in VL and higher by 43% in PVL than in C hearts. Valve-lesioning had a significant effect in reducing maximal cardiac minute work (p less than 0.001), whereas pacing significantly improved maximal cardiac minute work (p less than 0.001) to 2.467 +/- 0.206 J/g x 10(-4) in the P group versus 1.609 +/- 0.105 in the C group.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of swimming exercise to improve capillarization in cardiac hypertrophy of renal hypertensive rats

Female Sprague-Dawley rats were made hypertensive by the two kidney/one clip Goldblatt procedure, while control animals were sham-operated. One week later, half of the animals were subjected to a moderate swimming exercise and the other half remained sedentary. Thus, four experimental groups, each consisting of 14 rats, were formed: control animals that were exercised or kept sedentary and corresponding renal hypertensive animals either exercised or sedentary. In hypertensive rats, a significantly increased left ventricular weight and reduced coronary reserve were found. Cardiac hypertrophy in hypertensive rats was characterized by a lower number of capillaries on a tissue cross-section, larger heterogeneity of the capillary net, and a less uniform orientation of capillaries in space. Total length of capillaries in the hypertrophic hearts increased significantly, but less than the increase in cardiac weight, resulting in reduced capillary length density. Chronic swimming for 2 hr/day for a period of 6 weeks, subsequent to a 4-week acclimation period, did not significantly influence any of the investigated indexes of capillaries from hypertrophic hearts. In the normotensive rats, chronic swimming resulted only in a moderate increase in total capillary length associated with a small increase in the left ventricular weight of similar degree. Thus, chronic exercise in normotensive rats induced a moderate increase in total capillary length per left ventricle, while it did not alleviate impaired capillarization of hypertrophic hearts from hypertensive rats.

Synergistic effects of diabetes mellitus and renovascular hypertension on the rat heart--stereological investigations on papillary muscles

The effects of combined renovascular hypertension and diabetes mellitus on the rat heart were investigated in order to detect possible synergistic effects of the two conditions. Hypertensive diabetic and hypertensive nondiabetic young male Wistar rats were compared with diabetic and non-diabetic controls. Since the normal body weight increase of the diabetic animals was markedly suppressed a weight-matched nondiabetic control group was introduced in addition. Hypertension was established for eight weeks by a surgical stenosis of the left renal artery, diabetes mellitus was maintained for four weeks after a single intraperitoneal injection of 75 mg/kg streptozotocin. Light and electron microscopic stereological parameters were obtained for the left ventricular papillary muscles. The whole hearts were also investigated histologically. Qualitative morphology failed to substantiate synergistic effects in the hypertensive diabetic rats. Vascular abnormalities were not observed. The stereological parameters, however, revealed microstructural reactions which were observed exclusively in the hypertensive diabetic group: the volume ratio of mitochondria-to-myofibrils was decreased, the surface-to-volume ratio of mitochondria was increased (reduction of mitochondrial size) and the mean cross sectional area of capillaries was decreased. Similar quantitative mitochondrial changes have been frequently described in long-standing hypertension, but in the present investigation, they were not found in the nondiabetic hypertensive group. It is therefore concluded that diabetes mellitus potentiates the effects of chronic pressure overload on myocardial cells. However, the myocardial fibrosis which has been found by other groups at later stages of hypertension and/or diabetes mellitus was not detected in the present study. The reduced mean cross sectional area of capillaries in hypertensive-diabetic rats may be correlated with early molecular changes of the myocardial interstitium or with early abnormalities of small arteries. Thus our stereological results support the hypothesis that a non-coronary hypertensive diabetic cardiomyopathy occurs in mammalian hearts.