Histopathological changes of the heart after neonatal dexamethasone treatment: studies in 4-, 8-, and 50-week-old rats

Prenatal glucocorticoids exposure and adverse cardiovascular effects in offspring

Glucocorticoids (GCs) are steroid hormones fundamental to the body's normal physiological functions and are pivotal in fetal growth and development. During gestation, the mother's cortisol concentration (active GCs) escalates to accommodate the requirements of fetal organ development and maturation. A natural placental GCs barrier, primarily facilitated by 11β hydroxysteroid dehydrogenase 2, exists between the mother and fetus. This enzyme transforms biologically active cortisol into biologically inactive corticosterone, thereby mitigating fetal GCs exposure. However, during pregnancy, the mother may be vulnerable to adverse factor exposures such as stress, hypoxia, caffeine, and synthetic GCs use. In these instances, maternal serum GCs levels may surge beyond the protective capacity of the placental GCs barrier. Moreover, these adverse factors could directly compromise the placental GCs barrier, resulting in excessive fetal exposure to GCs. It is well-documented that prenatal GCs exposure can detrimentally impact the offspring's cardiovascular system, particularly in relation to blood pressure, vascular function, and heart function. In this review, we succinctly delineate the alterations in GCs levels during pregnancy and the potential mechanisms driving these changes, and also analyze the possible causes of prenatal GCs exposure. Furthermore, we summarize the current advancements in understanding the adverse effects and mechanisms of prenatal GCs exposure on the offspring's cardiovascular system.

Prenatal stress induces sex- and tissue-specific alterations in insulin pathway of Wistar rats offspring

BACKGROUND AND AIMS

Prenatal stress may lead to tissue and sex-specific cardiometabolic disorders in the offspring through imbalances in the insulin signaling pathway. Therefore, we aimed to determine the sex-specific adaptations of prenatal stress on the insulin signaling pathway of cardiac and hepatic tissue of adult offspring Wistar rats.

METHODS

Wistar pregnant rats were divided into control and stress groups. Unpredictable stress protocol was performed from the 14th to the 21st day of pregnancy. After lactation, the dams were euthanized and blood was collected for corticosterone measurement and the offspring were separated into four groups according to sex and intervention (n=8/group). At 90 days old, the offspring were submitted to an oral glucose tolerance test (OGTT) and an insulin tolerance test (ITT). After euthanasia blood collection was used for biochemical analysis and the left ventricle and liver were used for protein expression and histological analysis.

RESULTS

Stress increased maternal corticosterone levels, and in the offspring, decreased glucose concentration in both OGTT and ITT, reduced insulin receptor (Irβ) and insulin receptor substrate-1 (IRS1) activation and reduced insulin receptor inhibition (PTP1B) in the liver of male offspring at 90 days old, without repercussions in cardiac tissue. Moreover, female offspring submitted to prenatal stress exhibited reduced fatty acid uptake, with lower hepatic CD36 expression, reduced high density lipoprotein (cHDL) and increased Castelli risk indexes I and II.

CONCLUSIONS

Unpredictable prenatal stress evoked reduced insulin sensitivity and liver-specific impairment in insulin signaling activation in male while increasing markers of cardiovascular risk in females.

Synergistic effects of hormones on structural and functional maturation of cardiomyocytes and implications for heart regeneration

The limited endogenous regenerative capacity of the human heart renders cardiovascular diseases a major health threat, thus motivating intense research on in vitro heart cell generation and cell replacement therapies. However, so far, in vitro-generated cardiomyocytes share a rather fetal phenotype, limiting their utility for drug testing and cell-based heart repair. Various strategies to foster cellular maturation provide some success, but fully matured cardiomyocytes are still to be achieved. Today, several hormones are recognized for their effects on cardiomyocyte proliferation, differentiation, and function. Here, we will discuss how the endocrine system impacts cardiomyocyte maturation. After detailing which features characterize a mature phenotype, we will contemplate hormones most promising to induce such a phenotype, the routes of their action, and experimental evidence for their significance in this process. Due to their pleiotropic effects, hormones might be not only valuable to improve in vitro heart cell generation but also beneficial for in vivo heart regeneration. Accordingly, we will also contemplate how the presented hormones might be exploited for hormone-based regenerative therapies.

Combined Statin and Glucocorticoid Therapy for the Safer Treatment of Preterm Birth

BACKGROUND

Prematurity is strongly associated with poor respiratory function in the neonate. Rescue therapies include treatment with glucocorticoids due to their anti-inflammatory and maturational effects on the developing lung. However, glucocorticoid treatment in the infant can increase the risk of long-term cardiovascular complications including hypertension, cardiac, and endothelial dysfunction. Accumulating evidence implicates a molecular link between glucocorticoid excess and depletion of nitric oxide (NO) bioavailability as a mechanism underlying the detrimental effects of postnatal steroids on the heart and circulation. Therefore, combined glucocorticoid and statin therapy, by increasing NO bioavailability, may protect the developing cardiovascular system while maintaining beneficial effects on the lung.

METHODS

We investigated combined glucocorticoid and statin therapy using an established rodent model of prematurity and combined experiments of cardiovascular function in vivo, with those in isolated organs as well as measurements at the cellular and molecular levels.

RESULTS

We show that neonatal glucocorticoid treatment increases the risk of later cardiovascular dysfunction in the offspring. Underlying mechanisms include decreased circulating NO bioavailability, sympathetic hyper-reactivity, and NO-dependent endothelial dysfunction. Combined neonatal glucocorticoid and statin therapy protects the developing cardiovascular system by normalizing NO and sympathetic signaling, without affecting pulmonary maturational or anti-inflammatory effects of glucocorticoids.

CONCLUSIONS

Therefore, combined glucocorticoid and statin therapy may be safer than glucocorticoids alone for the treatment of preterm birth.

Dose-related cardiac outcomes in response to postnatal dexamethasone treatment in premature lambs

BACKGROUND

Postnatal corticosteroids are used in the critical care of preterm infants for the prevention and treatment of bronchopulmonary dysplasia. We aimed to investigate the effects of early postnatal dexamethasone therapy and dose on cardiac maturation and morphology in preterm lambs.

METHODS

Lambs were delivered prematurely at ~128 days of gestational age and managed postnatally according to best clinical practice. Preterm lambs were administered dexamethasone daily at either a low-dose (n = 9) or a high-dose (n = 7), or were naïve to steroid treatment and administered saline (n = 9), over a 7-day time-course. Hearts were studied at postnatal Day 7 for gene expression and assessment of myocardial structure.

RESULTS

High-dose dexamethasone treatment in the early postnatal period led to marked differences in cardiac gene expression, altered cardiomyocyte maturation and reduced cardiomyocyte endowment in the right ventricle, as well as increased inflammatory infiltrates into the left ventricle. Low-dose exposure had minimal effects on the preterm heart.

CONCLUSION

Neonatal dexamethasone treatment led to adverse effects in the preterm heart in a dose-dependent manner within the first week of life. The observed cardiac changes associated with high-dose postnatal dexamethasone treatment may influence postnatal growth and remodeling of the preterm heart and subsequent long-term cardiac function.

Association between glucocorticoid use and all-cause mortality in critically ill patients with heart failure: A cohort study based on the MIMIC-III database

Background: Heart failure (HF) is the terminal stage of various heart diseases. Conventional treatments have poor efficacy, and diuretic resistance can present. Previous studies have found that the use of glucocorticoids can enhance the diuretic effect of patients with heart failure and reduce heart failure symptoms. However, the relationship between glucocorticoid use and mortality in patients with heart failure in intensive care units is unclear. Objectives: The aim of this study was to determine the association between glucocorticoid use and all-cause mortality in critically ill patients with heart failure. Methods: The information on patients with heart failure in this study was extracted from the MIMIC-III (Medical Information Mart for Intensive Care-III) database. Patients in the glucocorticoid and non-glucocorticoid groups were matched using propensity scores. The Kaplan-Meier method was used to explore the difference in survival probability between the two groups. A Cox proportional-hazards regression model was used to analyze the hazard ratios (HRs) for the two patient groups. Subgroup analyses were performed with prespecified stratification variables to demonstrate the robustness of the results. Results: The study included 9,482 patients: 2,099 in the glucocorticoid group and 7,383 in the non-glucocorticoid group. There were 2,055 patients in each group after propensity-score matching. The results indicated that the non-glucocorticoid group was not significantly associated with reduced mortality in patients with heart failure during the 14-day follow-up period [HRs = .901, 95% confidence interval (CI) = .767-1.059]. During the follow-up periods of 15-30 and 15-90 days, the mortality risk was significantly lower in the non-glucocorticoid group than in the glucocorticoid group (HRs = .497 and 95% CI = .370-.668, and HRs = .400 and 95% CI = .310-.517, respectively). Subgroup analyses indicated no interaction among each stratification variable and glucocorticoid use. Conclusion: Glucocorticoid use was associated with an increased mortality risk in critically ill patients with heart failure.

Effect of Preterm Birth on Cardiac and Cardiomyocyte Growth and the Consequences of Antenatal and Postnatal Glucocorticoid Treatment

Preterm birth coincides with a key developmental window of cardiac growth and maturation, and thus has the potential to influence long-term cardiac function. Individuals born preterm have structural cardiac remodelling and altered cardiac growth and function by early adulthood. The evidence linking preterm birth and cardiovascular disease in later life is mounting. Advances in the perinatal care of preterm infants, such as glucocorticoid therapy, have improved survival rates, but at what cost? This review highlights the short-term and long-term impact of preterm birth on the structure and function of the heart and focuses on the impact of antenatal and postnatal glucocorticoid treatment on the immature preterm heart.

Glucocorticoid Maturation of Fetal Cardiovascular Function

The last decade has seen rapid advances in the understanding of the central role of glucocorticoids in preparing the fetus for life after birth. However, relative to other organ systems, maturation by glucocorticoids of the fetal cardiovascular system has been ignored. Here, we review the effects of glucocorticoids on fetal basal cardiovascular function and on the fetal cardiovascular defense responses to acute stress. This is important because glucocorticoid-driven maturational changes in fetal cardiovascular function under basal and stressful conditions are central to the successful transition from intra- to extrauterine life. The cost-benefit balance for the cardiovascular health of the preterm baby of antenatal glucocorticoid therapy administered to pregnant women threatened with preterm birth is also discussed.

Region-Specific Microstructure in the Neonatal Ventricles of a Porcine Model

The neonate transitions from placenta-derived oxygen, to supply from the pulmonary system, moments after birth. This requires a series of structural developments to divert more blood through the right heart and onto the lungs, with the tissue quickly remodelling to the changing ventricular workload. In some cases, however, the heart structure does not fully develop causing poor circulation and inefficient oxygenation, which is associated with an increase in mortality and morbidity. This study focuses on developing an enhanced knowledge of the 1-day old heart, quantifying the region-specific microstructural parameters of the tissue. This will enable more accurate mathematical and computational simulations of the young heart. Hearts were dissected from 12, 1-day-old deceased Yorkshire piglets (mass: 2.1–2.4 kg, length: 0.38–0.51 m), acquired from a breeding farm. Evans blue dye was used to label the heart equator and to demarcate the left and right ventricle free walls. Two hearts were used for three-dimensional diffusion-tensor magnetic resonance imaging, to quantify the fractional anisotropy (FA). The remaining hearts were used for two-photon excited fluorescence and second-harmonic generation microscopy, to quantify the cardiomyocyte and collagen fibril structures within the anterior and posterior aspects of the right and left ventricles. FA varied significantly across both ventricles, with the greatest in the equatorial region, followed by the base and apex. The FA in each right ventricular region was statistically greater than that in the left. Cardiomyocyte and collagen fibre rotation was greatest in the anterior wall of both ventricles, with less dispersion when compared to the posterior walls. In defining these key parameters, this study provides a valuable insight into the 1-day-old heart that will provide a valuable platform for further investigation the normal and abnormal heart using mathematical and computational models.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Prenatal Mechanistic Target of Rapamycin Complex 1 (m TORC1) Inhibition by Rapamycin Treatment of Pregnant Mice Causes Intrauterine Growth Restriction and Alters Postnatal Cardiac Growth, Morphology, and Function

Background

Fetal growth impacts cardiovascular health throughout postnatal life in humans. Various animal models of intrauterine growth restriction exhibit reduced heart size at birth, which negatively influences cardiac function in adulthood. The mechanistic target of rapamycin complex 1 (mTORC1) integrates nutrient and growth factor availability with cell growth, thereby regulating organ size. This study aimed at elucidating a possible involvement of mTORC1 in intrauterine growth restriction and prenatal heart growth.

Methods and Results

We inhibited mTORC1 in fetal mice by rapamycin treatment of pregnant dams in late gestation. Prenatal rapamycin treatment reduces mTORC1 activity in various organs at birth, which is fully restored by postnatal day 3. Rapamycin‐treated neonates exhibit a 16% reduction in body weight compared with vehicle‐treated controls. Heart weight decreases by 35%, resulting in a significantly reduced heart weight/body weight ratio, smaller left ventricular dimensions, and reduced cardiac output in rapamycin‐ versus vehicle‐treated mice at birth. Although proliferation rates in neonatal rapamycin‐treated hearts are unaffected, cardiomyocyte size is reduced, and apoptosis increased compared with vehicle‐treated neonates. Rapamycin‐treated mice exhibit postnatal catch‐up growth, but body weight and left ventricular mass remain reduced in adulthood. Prenatal mTORC1 inhibition causes a reduction in cardiomyocyte number in adult hearts compared with controls, which is partially compensated for by an increased cardiomyocyte volume, resulting in normal cardiac function without maladaptive left ventricular remodeling.

Conclusions

Prenatal rapamycin treatment of pregnant dams represents a new mouse model of intrauterine growth restriction and identifies an important role of mTORC1 in perinatal cardiac growth.

Adult Consequences of Extremely Preterm Birth: Cardiovascular and Metabolic Diseases Risk Factors, Mechanisms, and Prevention Avenues

Extremely preterm babies are exposed to various sources of injury during critical stages of development. The extremely preterm infant faces premature transition to ex utero physiology and undergoes adaptive mechanisms that may be deleterious in the long term because of permanent alterations in organ structure and function. Perinatal events can also directly cause structural injury. These disturbances induce morphologic and functional changes in their organ systems that might heighten their risks for later adult chronic diseases. This review examines the pathophysiology of programming of long-term health and diseases after preterm birth and associated perinatal risk factors.

Sex-specific differences in age-dependent progression of aortic dysfunction and related cardiac remodeling in spontaneously hypertensive rats

Evidence of sex-specific differences in renin-angiotensin-system (RAS) and arterial pressure has been shown in many mammals, including spontaneously hypertensive rats (SHRs). Although SHRs have been used extensively as a leading experimental model of hypertension, the effects of sex-specific differences in RAS on aortic function and related cardiac remodeling during aging and hypertension have not been documented in detail. We examined structural and functional changes in aorta and heart of female and male SHRs at the ages of 5, 14, 29, and 36 wk. SHRs of both sexes were hypertensive from 14 wk. Aortic endothelial dysfunction and fibrosis, left ventricular (LV) hypertrophy, and cardiac fibrosis were evident at the age of 29 wk in male SHRs but first appeared only at the age of 36 wk in female SHRs. There was a pronounced delay of matrix metalloproteinase-2 activity in the aorta and heart of female SHRs, which was associated with preservation of 40% more elastin and less extensive cardiac fibrosis than in males. At 5, 29, and 36 wk of age, female SHRs showed higher levels of aortic and myocardial AT₂R and MasR mRNA and decreased ANG II-mediated aortic constriction. Although female SHRs had increased relaxation to AT₂R stimulation at 5 and 29 wk compared with males, this difference disappeared at 36 wk of age. This study documents sex-specific differences in the temporal progression of aortic dysfunction and LV hypertrophy in SHRs, which are independent of arterial pressure and are apparently mediated by higher AT₂R expression in the heart and aorta of female SHRs.

Effects of neonatal dexamethasone administration on cardiac recovery ability under ischemia-reperfusion in 24-wk-old rats

BACKGROUND

Evaluations of stress-induced cardiac functional alterations in adults after neonatal glucocorticoid (GC) treatment have been limited. In the present study, we evaluated adult cardiac functional recovery during postischemic reperfusion and measured cardiac gene expression involved energy metabolism in rats neonatally treated with dexamethasone (DEX).

METHOD

Male Wistar rats were injected DEX in first 3 d after birth and controls were received saline (SAL). At 24 wk of age, insulin tolerance tests were performed, plasma lipid levels were measured, and left ventricular function and myocardial infarct size were evaluated. Expressions of genes involved in cardiac energy metabolism were measured by quantitative real-time polymerase chain reaction (PCR) and western blot.

RESULTS

In 24-wk-old rats, neonatal DEX administration caused dyslipidemia, impaired cardiac recovery function and increased size of infarction, decreased cardiac expression of glucose transporter 4(GLUT4), peroxisome proliferative-activated receptor gamma coactivator 1α (PGC-1α) and ratios of phospho-forkhead box O1/forkhead box O1 (p-FoxO1/FoxO1) and phospho AMP-activated protein kinase/AMP-activated protein kinase (p-AMPK/AMPK) but increased pyruvate dehydrogenase kinase isoenzyme 4 (PDK4) expression compared with controls.

CONCLUSION

Neonatal DEX administration impairs cardiac functional recovery during reperfusion following ischemia in 24-wk-old rats. Reduced cardiac glucose utilization may contribute to the long-term detrimental effects caused by neonatal DEX treatment.

Dyrk1a regulates the cardiomyocyte cell cycle via D-cyclin-dependent Rb/E2f-signalling

AIMS

Down syndrome-associated dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A (DYRK1A) is a ubiquitously expressed protein kinase. Up to date a variety of targets have been identified, establishing a key role for Dyrk1a in selected signalling pathways. In cardiomyocytes, Dyrk1a acts as a negative regulator of hypertrophy by phosphorylating transcription factors of the NFAT family, but its mechanistic function in the heart remains poorly understood. This study was designed to investigate a potential protective role of Dyrk1a in cardiac hypertrophy in vivo.

METHODS AND RESULTS

We generated transgenic mice with cardiac-specific overexpression of Dyrk1a. Counterintuitively, these mice developed severe dilated cardiomyopathy associated with congestive heart failure and premature death. In search for the cause of this unexpected phenotype, we found that Dyrk1a interacts with all members of the D-cyclin family and represses their protein levels in vitro and in vivo. Particularly, forced expression of Dyrk1a leads to increased phosphorylation of Ccnd2 on Thr280 and promotes its subsequent proteasomal degradation. Accordingly, cardiomyocytes overexpressing Dyrk1a display hypo-phosphorylated Rb1, suppression of Rb/E2f-signalling, and reduced expression of E2f-target genes, which ultimately results in impaired cell cycle progression.

CONCLUSIONS

We identified Dyrk1a as a novel negative regulator of D-cyclin-mediated Rb/E2f-signalling. As dysregulation of this pathway with impaired cardiomyocyte proliferation leads to cardiomyopathy, dose-specific Dyrk1a expression and activity appears to be critical for the hyperplastic and hypertrophic growth of the developing heart.

Dexamethasone Treatment of Newborn Rats Decreases Cardiomyocyte Endowment in the Developing Heart through Epigenetic Modifications

The potential adverse effect of synthetic glucocorticoid, dexamethasone therapy on the developing heart remains unknown. The present study investigated the effects of dexamethasone on cardiomyocyte proliferation and binucleation in the developing heart of newborn rats and evaluated DNA methylation as a potential mechanism. Dexamethasone was administered intraperitoneally in a three day tapered dose on postnatal day 1 (P1), 2 and 3 to rat pups in the absence or presence of a glucocorticoid receptor antagonist Ru486, given 30 minutes prior to dexamethasone. Cardiomyocytes from P4, P7 or P14 animals were analyzed for proliferation, binucleation and cell number. Dexamethasone treatment significantly increased the percentage of binucleated cardiomyocytes in the hearts of P4 pups, decreased myocyte proliferation in P4 and P7 pups, reduced cardiomyocyte number and increased the heart to body weight ratio in P14 pups. Ru486 abrogated the effects of dexamethasone. In addition, 5-aza-2'-deoxycytidine (5-AZA) blocked the effects of dexamethasone on binucleation in P4 animals and proliferation at P7, leading to recovered cardiomyocyte number in P14 hearts. 5-AZA alone promoted cardiomyocyte proliferation at P7 and resulted in a higher number of cardiomyocytes in P14 hearts. Dexamethasone significantly decreased cyclin D2, but not p27 expression in P4 hearts. 5-AZA inhibited global DNA methylation and blocked dexamethasone-mediated down-regulation of cyclin D2 in the heart of P4 pups. The findings suggest that dexamethasone acting on glucocorticoid receptors inhibits proliferation and stimulates premature terminal differentiation of cardiomyocytes in the developing heart via increased DNA methylation in a gene specific manner.

Melatonin prevents neonatal dexamethasone induced programmed hypertension: histone deacetylase inhibition

Adulthood hypertension can be programmed by corticosteroid exposure in early life. Oxidative stress, epigenetic regulation by histone deacetylases (HDACs), and alterations of renin-angiotensin system (RAS) are involved in the developmental programming of hypertension. We examined whether melatonin prevented neonatal dexamethasone (DEX)-induced programmed hypertension and how melatonin prevented these processes. We also examined whether HDAC inhibition by trichostatin A (TSA, a HDAC inhibitor) had similar effects. Male offspring were assigned to 5 groups (n=6/group): control, DEX, melatonin, DEX+melatonin, and DEX+TSA. Male rat pups were injected i.p. with DEX on day 1 (0.5mg/kg BW), day 2 (0.3mg/kg BW), and day 3 (0.1mg/kg BW) after birth. Melatonin was administered in drinking water at the dose of 0.01% during the lactation period. The DEX+TSA group received DEX and 0.5mg/kg TSA subcutaneous injection once daily for 1 week. All rats were killed at 16 weeks of age. Neonatal DEX exposure induced hypertension in male offspring at 16 weeks of age, which melatonin prevented. Neonatal DEX exposure decreased gene expression related to apoptosis, nephrogenesis, RAS, and sodium transporters. Yet DEX treatment increased protein levels of HDAC-1, -2, and -3 in the kidney. Melatonin therapy preserved the decreases of gene expression and decreased HDACs. Similarly, HDAC inhibition prevented DEX-induced programmed hypertension. In conclusion, melatonin therapy exerts a long-term protection against neonatal DEX-induced programmed hypertension. Its beneficial effects include alterations of RAS components and inhibition of class I HDACs. Given that the similar protective effects of melatonin and TSA, melatonin might inhibit HDACs to epigenetic regulation of hypertension-related genes to prevent programmed hypertension.

Effects of glucocorticoid exposure on growth and structural maturation of the heart of the preterm piglet

Inadequate maintenance of systemic blood flow in neonates following preterm birth is associated with increased morbidity and mortality, and may be due in part to structural immaturity of the myocardium. Maternal glucocorticoid administration is associated with improved cardiovascular function, and possibly promotes structural maturation of the myocardium. This study assessed the structural maturity of the myocardium in male and female preterm and term piglets, and preterm piglets exposed to a regimen of maternal glucocorticoids as used clinically. In preterm, term and glucocorticoid exposed preterm piglets cardiomyocyte maturity was examined by measuring the proportion of binucleated myocytes and the volumes of single living ventricular cardiomyocytes with fluorescence microscopy. Ventricular apoptosis and proliferation were measured by immunohistochemistry. Preterm piglet hearts had fewer binucleated myocytes, smaller myocytes, and more proliferative and fewer apoptotic nuclei than term hearts. Maternal glucocorticoid treatment resulted in increased binucleation with no increase in myocyte volume, and levels of proliferation and apoptosis that were more similar to the term heart. Atrial weights were increased and in female piglets there was an increase in the ratio of left to right ventricular weight. The observed changes in atrial mass and myocyte structural maturation correlated with changes in cardiac function of isolated hearts of littermates. In conclusion, the association between increased myocardial maturation following glucocorticoid exposure, improved cardiac function in littermates, and clinical improvement in human neonatal cardiac function exposed to antenatal glucocorticoids, suggests that glucocorticoid exposure contributes to improved cardiovascular function in preterm infants by promoting myocardial structural maturity.

Morphological and functional effects on cardiac tissue induced by moderate zinc deficiency during prenatal and postnatal life in male and female rats

The aim of this study was to evaluate whether moderate zinc restriction in rats throughout fetal life, lactation, and/or postweaning growth results in early changes in cardiac morphology predisposing the onset of cardiac dysfunction in adult life as well as sex-related differences in the adaptation to this nutritional injury. Female Wistar rats received low or control zinc diets from the beginning of pregnancy up to offspring weaning. After being weaned, offspring were fed either a low or control zinc diet until 81 days. Systolic blood pressure was measured. Echocardiographic and electrocardiographic examinations, morphological experiments, and apoptosis by TUNEL assay were performed in the left ventricle. In the early stages, zinc-deficient male and female offspring showed an increase in cardiomyocyte diameter, probably associated with an increase in cardiac apoptotic cells, but smaller myocyte diameters in adulthood. In adult males, this nutritional injury induced decreased contractility and dilatation of the left ventricle, not allowing the heart to compensate the higher levels of blood pressure, and hypertrophic remodeling of coronary arteries associated with increased blood pressure. Adequate zinc intake during postweaning life did not overcome blood pressure levels but reversed some of the detrimental effects of earlier zinc deficiency in cardiac morphology and function. Females were less sensitive to this deficiency, exhibiting normal levels of blood pressure and no structural or functional heart alterations in adult life. The present study demonstrates that the effects of zinc deficiency on blood pressure, cardiac morphology, and function differ between sexes, with males more predisposed to develop cardiovascular diseases in adulthood.

Age- and gender-dependent changes of bovine myocardium architecture

Growth, gravidity and lactation put high demands on the performance of the myocardium. The aim of this study, which was performed in 40 female and 20 male bovines ranging from 1 to 4.5 years old, was to determine gross and microscopic morphometric data of bovine myocardium to establish a comparative measure of myocardial growth during juvenile development. During the developmental stage of young adulthood, age-related increases in female myocardial characteristics included cardiac mass, left and right ventricular mass and the ratio of cardiac mass to loose connective tissue. Age-related decreases were observed in the number of myocyte nuclei per mm(2) and the thickness of the right ventricular wall. Sex differences in these parameters were found between 2-year-old bulls (N = 20) and 2-year-old heifers (N = 10), with males having heavier hearts, thicker ventricular walls, less myocytes in the left ventricle and less connective tissue in both ventricles. Age and sex had no influence on the ratio of capillaries to myocytes, estimated at 0.98 in the adult bovine. Capillary density does not change during juvenile development, but cross-sectional capillary area does adapt to myocyte cross-sectional area, accounting for this relatively constant ratio.

Binucleation of cardiomyocytes: the transition from a proliferative to a terminally differentiated state

Cardiomyocytes possess a unique ability to transition from mononucleate to the mature binucleate phenotype in late fetal development and around birth. Mononucleate cells are proliferative, whereas binucleate cells exit the cell cycle and no longer proliferate. This crucial period of terminal differentiation dictates cardiomyocyte endowment for life. Adverse early life events can influence development of the heart, affecting cardiomyocyte number and contributing to heart disease late in life. Although much is still unknown about the mechanisms underlying the binucleation process, many studies are focused on molecules involved in cell cycle regulation and cytokinesis as well as epigenetic modifications that can occur during this transition. Better understanding of these mechanisms could provide a basis for recovering the proliferative capacity of cardiomyocytes.

Antioxidant treatment improves neonatal survival and prevents impaired cardiac function at adulthood following neonatal glucocorticoid therapy

Glucocorticoids are widely used to treat chronic lung disease in premature infants but their longer-term adverse effects on the cardiovascular system raise concerns. We reported that neonatal dexamethasone treatment in rats induced in the short term molecular indices of cardiac oxidative stress and cardiovascular tissue remodelling at weaning, and that neonatal combined antioxidant and dexamethasone treatment was protective at this time. In this study, we investigated whether such effects of neonatal dexamethasone have adverse consequences for NO bioavailability and cardiovascular function at adulthood, and whether neonatal combined antioxidant and dexamethasone treatment is protective in the adult. Newborn rat pups received daily i.p. injections of a human-relevant tapering dose of dexamethasone (D; n = 8; 0.5, 0.3, 0.1 μg g(-1)) or D with vitamins C and E (DCE; n = 8; 200 and 100 mg kg(-1), respectively) on postnatal days 1-3 (P1-3); vitamins were continued from P4 to P6. Controls received equal volumes of vehicle from P1 to P6 (C; n = 8). A fourth group received vitamins alone (CCE; n = 8). At P100, plasma NO metabolites (NOx) was measured and isolated hearts were assessed under both Working and Langendorff preparations. Relative to controls, neonatal dexamethasone therapy increased mortality by 18% (P < 0.05). Surviving D pups at adulthood had lower plasma NOx concentrations (10.6 ± 0.8 vs. 28.0 ± 1.5 μM), an increased relative left ventricular (LV) mass (70 ± 2 vs. 63 ± 1%), enhanced LV end-diastolic pressure (14 ± 2 vs. 8 ± 1 mmHg) and these hearts failed to adapt output with increased preload (cardiac output: 2.9 ± 2.0 vs. 10.6 ± 1.2 ml min(-1)) or afterload (cardiac output: -5.3 ± 2.0 vs.1.4 ± 1.2 ml min(-1)); all P < 0.05. Combined neonatal dexamethasone with antioxidant vitamins improved postnatal survival, restored plasma NOx and protected against cardiac dysfunction at adulthood. In conclusion, neonatal dexamethasone therapy promotes cardiac dysfunction at adulthood. Combined neonatal treatment with antioxidant vitamins is an effective intervention.

From a regional cohort of extremely low birth weight infants: cardiac function at the age of 7 years

BACKGROUND

The long-term impact of prematurity on cardiac structure and function has not yet been fully discovered.

OBJECTIVES

To assess long-term cardiac complications in the regional cohort of extremely low birth weight (ELBW) children born in 2002-2004.

MATERIAL AND METHODS

Eighty-one children born as ELBW infants (91% of the available cohort) with a median birth weight of 890 g (25-75th percentile: 760-950) were evaluated at the mean age of 6.7 years. The control group included 40 children born full-term, selected from one general practice in the district. Echocardiography and 24-hour ambulatory blood pressure measurements (ABPM) were performed. The primary outcome variable was the presence of cardiac complications such as left ventricular hypertrophy (LVH), diastolic dysfunction or systolic dysfunction.

RESULTS

LVH was diagnosed in 4/81 ELBW children and 2/40 control children (p = 1.0). Concentric remodeling was detected in 8 (10%) subjects from the ELBW group and in 2 (5%) from the control group (p = 0.49). There were no patients with diastolic or systolic dysfunction in either group. After having expressed the results of M-mode echocardiography as z-scores for body surface area (BSA), statistically significant differences were observed for right-ventricle dimension in diastole (-1.49 ± 1.25 vs. -0.31 ± 0.91; p < 0.001), LV inner dimension in diastole (-0.53 ± 1.26 vs. 0.13 ± 0.94; p = 0.01) and left atrium (-0.93 ± 1.07 vs. -0.15 ± 1.02; p < 0.01). Heart rate (HR) was significantly faster in ELBW children (92.9 ± 8.4 vs. 86.7 ± 7.4 bpm; p = 0.01 adjusted for BSA) and they also had significantly higher night-time blood pressure [mean (z-score): 1.15 vs. 0.2; p = 0.02] without nocturnal dipping (night-time dipping <10%: 13 (16.7%) vs. 2 (5.2%), p = 0.13).

CONCLUSIONS

No differences were found between the groups in the occurrence of cardiac complications. Ex-preterm ELBW children at age 6 may have a faster HR, smaller cardiac dimensions on echocardiography and higher nocturnal blood pressure. The clinical relevance of these findings is unknown.

Prematurity and low weight at birth as new conditions predisposing to an increased cardiovascular risk

Although the survival rate for preterm subjects has improved considerably, due to the progress in the field of perinatal medicine, preterm birth is frequently the cause underlying a series of notorious complications: morphological, neurological, ophthalmological, and renal alterations. In addition, it has recently been demonstrated how low gestational age and reduced foetal growth contribute towards an increased cardiovascular risk in preterm neonates. In fact, cardiovascular mortality is higher among former preterm adults than those born at term. This condition is referred to as cardiovascular perinatal programming. In the light of the above, an early, constant, and prolonged cardiological followup programme should be implemented in former preterm individuals. The aim of this paper was to perform a comprehensive literature review about two new emerging conditions predisposing to an increased cardiovascular risk: prematurity and low weight at birth.

Cardiac remodelling as a result of pre-term birth: implications for future cardiovascular disease

AIMS

Pre-term birth affects 10-12% of live births and occurs when the myocardium is still developing; therefore, the final structure of the myocardium could be altered. We hypothesized that, in response to pre-term birth, structural remodelling occurs within the myocardium which enables the immature heart muscle to adapt to the haemodynamic transition at birth but results in persistent alterations in its structure. Our objective was to determine how pre-term birth alters the final structure of the myocardium.

METHODS AND RESULTS

Using sheep, pre-term birth was induced at 0.9 of term; hearts were examined at 9 weeks after term-equivalent age, when cardiomyocyte proliferation and maturation have ceased. In pre-term lambs, we found that cardiomyocytes of both ventricles and the interventricular septum were hypertrophied. Cardiomyocyte maturation in pre-term lambs was altered in that there was a greater proportion of mononucleated, polyploid (4n) cardiomyocytes in both ventricles compared with controls; importantly, induction of polyploidy is associated with irreversible stress-related changes in DNA. We also found a six- to seven-fold increase in collagen deposition, usually accompanied by lymphocytic infiltration.

CONCLUSION

We conclude that pre-term birth leads to remodelling of the myocardium that alters its final structure. This may programme for long-term cardiac vulnerability.

Neonatal dexamethasone treatment in the rat leads to kidney damage in adulthood

Recently, concern has been raised that corticosteroid treatment of preterm neonates might be associated with adverse effects later in life, including early development of hypertension. Here, we investigate the impact of neonatal dexamethasone (Dex) treatment on early renal cell proliferation and nephron number. We analyzed mitotic activity in renal cortex of rat pups neonatally treated with Dex. Nephron number was measured and possible renal damage was quantified by counting inflammatory foci, ED-1 positive cells (macrophages), and the desmin score (activated podocytes). Mitotic activity was 34 and 29% lower on d 2 and 4 in Dex-treated rats compared with saline-treated controls. The number of glomeruli was lower at 4 wk, but nephron size was unchanged after Dex treatment, as calculated from glomerular density and (lower) body- and kidney weight. At wk 50, the glomerular number was significantly lower in Dex-treated rats, whereas body and kidney weight were the same as in Sal controls. Dex rats also showed more kidney damage, manifested by a approximately 3.5-fold increase in inflammation foci/mm and in ED-1 positive cells/mm and a approximately 4.3-fold increased desmin score. Temporary suppression of mitotic activity during neonatal Dex treatment leads to reduction of nephron number and more kidney damage later in life.