Myocardial water handling and the role of aquaporins

Cardioprotective effect of St. Thomas' Hospital No. 2 solution against age-related changes in aquaporin-7-deficient mice

OBJECTIVE

This study aimed to investigate whether St. Thomas' Hospital No. 2 solution (STH2) is equally effective in both young and aged aquaporin-7-knockout (AQP7-KO) mice and the mechanisms by which the intra-myocardial adenosine triphosphate (ATP) content is altered during ischemia without aquaporin-7.

METHODS

In study 1, isolated hearts of male wild-type (WT) and AQP7-KO mice (< 12 weeks old) were Langendorff perfused with 5-min STH2 prior to a 20-min global ischemia (GI) or 25-min GI without STH2. Similarly, in Study 2, hearts from WT and AQP7-KO mice (≥ 24 weeks old) were subjected to 2-min STH2 infusion prior to GI. In study 3, intra-myocardial ATP content was compared before (sham) and after (control or STH2) ischemia in mature WT and AQP7-KO mice.

RESULTS

In study 1, troponin T levels (ng/g wet weight) of WT and AQP7-KO hearts were significantly lower in the STH2 groups (75.6 ± 45.9 and 80.2 ± 52.2, respectively) than in the GI groups (934.0 ± 341.1 and 1089.3 ± 182.5, respectively). In Study 2, troponin T levels in aged WT and AQP7-KO mice were 566.5 ± 550.0 and 547.8 ± 594.3, respectively (p = 0.9561). In Study 3, ATP levels (μmol/g protein) in the sham, control, and STH2 AQP7-KO mice groups were 4.45, 2.57, and 3.37, respectively(p = 0.0005).

CONCLUSIONS

The present study revealed the cardio-protective efficacy of STH2 in an experimental model of isolated AQP7-KO young and aged murine hearts. Further, STH2 preserved intra-myocardial ATP during ischemia with Krebs-Henseleit buffer perfusion in the Langendorff setting.

Mechanisms of Myocardial Edema Development in CVD Pathophysiology

Myocardial edema is the excess accumulation of fluid in the myocardial interstitium or cardiac cells that develops due to changes in capillary permeability, loss of glycocalyx charge, imbalance in lymphatic drainage, or a combination of these factors. Today it is believed that this condition is not only a complication of cardiovascular diseases, but in itself causes aggravation of the disease and increases the risks of adverse outcomes. The study of molecular, genetic, and mechanical changes in the myocardium during edema may contribute to the development of new approaches to the diagnosis and treatment of this condition. This review was conducted to describe the main mechanisms of myocardial edema development at the molecular and cellular levels and to identify promising targets for the regulation of this condition based on articles cited in Pubmed up to January 2024.

Melatonin and cisplatin co-treatment against cancer: A mechanistic review of their synergistic effects and melatonin's protective actions

Combination chemotherapy appears to be a preferable option for some cancer patients, especially when the medications target multiple pathways of oncogenesis; individuals treated with combination treatments may have a better prognosis than those treated with single agent chemotherapy. However, research has revealed that this is not always the case, and that this technique may just enhance toxicity while having little effect on boosting the anticancer effects of the medications. Cisplatin (CDDP) is a chemotherapeutic medicine that is commonly used to treat many forms of cancer. However, it has major adverse effects such as cardiotoxicity, skin necrosis, testicular toxicity, and nephrotoxicity. Many research have been conducted to investigate the effectiveness of melatonin (MLT) as an anticancer medication. MLT operates in a variety of ways, including decreasing cancer cell growth, causing apoptosis, and preventing metastasis. We review the literature on the role of MLT as an adjuvant in CDDP-based chemotherapies and discuss how MLT may enhance CDDP's antitumor effects (e.g., by inducing apoptosis and suppressing metastasis) while protecting other organs from its adverse effects, such as cardio- and nephrotoxicity.

Effect of SGLT2 Inhibitor on Cardiomyopathy in a Rat Model of T2DM: Possible involvement of Cardiac Aquaporins

Diabetic cardiomyopathy (DCM) causes arrhythmia, heart failure, and sudden death. Empagliflozin, an SGLT-2 (Sodium glucose co-transporter) inhibitor, is an anti-diabetic medication that decreases blood glucose levels by stimulating urinary glucose excretion. Several aquaporins (AQPs) including AQP-1-3 and - 4 and their involvement in the pathogenesis in different cardiac diseases were detected. In the current study the effect of Empagliflozin on diabetic cardiomyopathy and the possible involvement of cardiac AQPs were investigated.

METHODS

56 adult male Sprague-Dawley rats were divided into 4 groups: Control, DCM: type 2 diabetic rats, low EMPA+DCM received empagliflozin (10 mg/kg/day) and high EMPA+DCM received empagliflozin (30 mg/kg/day) for 6 weeks.

RESULTS

Administration of both EMPA doses, especially in high dose group, led to significant improvement in ECG parameters. Also, a significant improvement in biochemical and cardiac oxidative stress markers (significant decrease in serum CK-MB, and malondialdehyde while increasing catalase) with decreased fibrosis and edema in histopathological examination and a significant attenuation in apoptosis (caspase-3) and edema (AQP-1& -4).

CONCLUSION

Both doses of Empagliflozin have a cardioprotective effect and reduced myocardial tissue edema with high dose having a greater effect. This might be due to attenuation of oxidative stress, fibrosis and edema mediated through AQP-1, - 3& - 4 expression.

Utility of the burmese Python as a model for studying plasticity of extreme physiological systems

Non-traditional animal models present an opportunity to discover novel biology that has evolved to allow such animals to survive in extreme environments. One striking example is the Burmese python (Python molurus bivittatus), which exhibits extreme physiological adaptation in various metabolic organs after consuming a large meal following long periods of fasting. The response to such a large meal in pythons involves a dramatic surge in metabolic rate, lipid overload in plasma, and massive but reversible organ growth through the course of digestion. Multiple studies have reported the physiological responses in post-prandial pythons, while the specific molecular control of these processes is less well-studied. Investigating the mechanisms that coordinate organ growth and adaptive responses offers the opportunity to gain novel insight that may be able to treat various pathologies in humans. Here, we summarize past research on the post-prandial physiological changes in the Burmese python with a focus on the gastrointestinal tract, heart, and liver. Specifically, we address our recent molecular discoveries in the post-prandial python liver which demonstrate transient adaptations that may reveal new therapeutic targets. Lastly, we explore new biology of the aquaporin 7 gene that is potently upregulated in mammalian cardiac myocytes by circulating factors in post-prandial python plasma.

The role of AQP3 and AQP4 channels in cisplatin-induced cardiovascular edema and the protective effect of melatonin

BACKGROUND

The present study evaluates the development of edema, the change in the AQP3, AQP4, p53 and Bax gene expressions, and the protective effects of melatonin in rat hearts administered with cisplatin.

METHODS AND RESULTS

A total of 28 Wistar albino rats were divided into four groups. The vehicle was administered intraperitoneally (i.p.) to the rats in the control group. The melatonin group (Mel) received melatonin at a dose of 10 mg/kg for 13 days. The cisplatin group (Cis) received cisplatin on days 1, 5, 9 and 13 at a dose of 4 mg/kg. The rats in the cisplatin + melatonin (Cis+Mel) group underwent the procedures both in the Mel and Cis groups. Blood and left ventricular samples were taken and analyzed on day 14 of the study. AQP3, p53 and Bax gene expressions were found to be significantly increased following cisplatin administration compared to the control, while melatonin administration significantly decreased the expression of these genes (p < 0.05). Melatonin administration also significantly decreased the level of AQP4 gene expression compared to the cis. On histological examination, congestion, hemorrhage, extracellular and intracellular edema, and degenerative changes were significantly more common in the Cis than in the control. Melatonin administration significantly decreased intracellular edema (p = 0.010) and degenerative changes (p = 0.010), and the improvement in extracellular edema was close to statistical significance (p = 0.051) in melatonin.

CONCLUSIONS

These results indicate that melatonin had an ameliorative effect on myocardial edema and AQP channels, and that it may be used as a protective molecule against myocardial edema secondary to cisplatin administration.

Myocardial Fluid Balance and Pathophysiology of Myocardial Edema in Coronary Artery Bypass Grafting

Myocardial edema is one of the most common complications of coronary artery bypass grafting (CABG) that is linearly related to many coronary artery diseases. Myocardial edema can cause several consequences including systolic dysfunction, diastolic dysfunction, arrhythmia, and cardiac tissue fibrosis that can increase mortality in CABG. Understanding myocardial fluid balance and tissue and systemic fluid regulation is crucial in order to ultimately link how coronary artery bypass grafting can cause myocardial edema in such a setting. The identification of susceptible patients by using imaging modalities is still challenging. Future studies about the technique of imaging modalities, examination protocols, prevention, and treatment of myocardial edema should be carried out, in order to limit myocardial edema occurrence and prevent complications.

Quantification of regional myocardial mean intracellular water lifetime: A nonhuman primate study in myocardial stress

Heart failure with preserved ejection fraction (HFpEF) is typically associated with early metabolic remodeling. Noninvasive imaging biomarkers that reflect these changes will be crucial in determining responses to early drug interventions in these patients. Mean intracellular water lifetime (τ_i ) has been shown to be partially inversely related to Na, K-ATPase transporter activity and may thus provide insight into the metabolic status in HFpEF patients. Here, we aim to perform regional quantification of τ_i using dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) in the nonhuman primate (NHP) heart and evaluate its region-specific variations under conditions of myocardial stress in the context of perturbed myocardial function. Cardiac stress was induced in seven naïve cynomolgus macaques using a dobutamine stepwise infusion protocol. All animals underwent 3 T cardiac dual-bolus DCE and tagging MRI experiments. The shutter-speed model was employed to quantify regional τ_i from the DCE-MR images. Additionally, τ_i values were correlated with myocardial strains. During cardiac stress, there was a significant decrease in global τ_i (192.9 ± 76.3 ms vs 321.6 ± 70 ms at rest, P < 0.05) in the left ventricle, together with an increase in global peak circumferential strain (-15.4% ± 2.7% vs -10.1% ± 2.9% at rest, P < 0.05). Specifically, slice-level analysis further revealed that a greater significant decrease in mean τ_i was observed in the apical region (Δτ_I = 182.4 ms) compared with the basal (Δτ_i = 113.2 ms) and midventricular regions (Δτ_i = 108.4 ms). Regional analysis revealed that there was a greater significant decrease in mean τ_i in the anterior (Δτ_i = 243.9 ms) and antero-lateral (Δτ_i = 177.2 ms) regions. In the inferior and infero-septal regions, although a decrease in τ_i was observed, it was not significant. Whole heart regional quantification of τ_i is feasible using DCE-MRI. τ_i is sensitive to regional changes in metabolic state during cardiac stress, and its value correlates with strain.

Changes in cardiac Aquaporin expression during aortic valve replacement surgery with cardiopulmonary bypass

OBJECTIVES

Cardiopulmonary bypass (CPB) use is an essential strategy for many cardiovascular surgeries. However, its use and duration have been associated with a higher rate of postoperative complications, such as low cardiac output syndrome due to myocardial oedema and dysfunction. Though Aquaporin water channels have been implicated in myocardial water balance, their specific role in this clinical scenario has not been established.

METHODS

In a consecutive study of 17 patients with severe aortic stenosis undergoing aortic valve replacement surgery, 2 myocardial biopsies of the left ventricle were taken: 1 before and 1 after CPB use. Sociodemographic, clinical and laboratory data were collected. Western blot and immunohistochemistry studies were performed.

RESULTS

After CPB use, there was a mean increase of ∼62% in Aquaporin 1 protein levels (P = 0.001) and a mean reduction of ∼38% in Aquaporin 4 protein levels (P = 0.030). In immunohistochemistry assays, Aquaporin 1 was found lining small blood vessels, while Aquaporin 4 formed a circular label in cardiomyocytes. There were no changes in the localization of either protein following CPB use. During the observed on-pump time interval, there was a 1.7%/min mean increase in Aquaporin 1 (P = 0.021) and a 2.5%/min mean decrease in Aquaporin 4 (P = 0.018). Myocardial interstitial oedema increased by 42% (95% confidence interval 31-54%) after CPB use. Patients who developed low cardiac output syndrome were in the upper half of the median percentage change of Aquaporin expression.

CONCLUSION

Time-dependent changes in cardiac Aquaporin expression may be associated with myocardial oedema and dysfunction related to CPB use.

Aquaporin Channels in the Heart-Physiology and Pathophysiology

Mammalian aquaporins (AQPs) are transmembrane channels expressed in a large variety of cells and tissues throughout the body. They are known as water channels, but they also facilitate the transport of small solutes, gasses, and monovalent cations. To date, 13 different AQPs, encoded by the genes AQP0–AQP12, have been identified in mammals, which regulate various important biological functions in kidney, brain, lung, digestive system, eye, and skin. Consequently, dysfunction of AQPs is involved in a wide variety of disorders. AQPs are also present in the heart, even with a specific distribution pattern in cardiomyocytes, but whether their presence is essential for proper (electro)physiological cardiac function has not intensively been studied. This review summarizes recent findings and highlights the involvement of AQPs in normal and pathological cardiac function. We conclude that AQPs are at least implicated in proper cardiac water homeostasis and energy balance as well as heart failure and arsenic cardiotoxicity. However, this review also demonstrates that many effects of cardiac AQPs, especially on excitation-contraction coupling processes, are virtually unexplored.

Aquaporin-1 Deficiency Protects Against Myocardial Infarction by Reducing Both Edema and Apoptosis in Mice

Many studies have determined that AQP1 plays an important role in edema formation and resolution in various tissues via water transport across the cell membrane. The aim of this research was to determine both if and how AQP1 is associated with cardiac ischemic injury, particularly the development of edema following myocardial infarction (MI). AQP1^+/+ and AQP1^−/− mice were used to create the MI model. Under physiological conditions, AQP1^−/− mice develop normally; however, in the setting of MI, they exhibit cardioprotective properties, as shown by reduced cardiac infarct size determined via NBT staining, improved cardiac function determined via left ventricular catheter measurements, decreased AQP1-dependent myocardial edema determined via water content assays, and decreased apoptosis determined via TUNEL analysis. Cardiac ischemia caused by hypoxia secondary to AQP1 deficiency stabilized the expression of HIF-1α in endothelial cells and subsequently decreased microvascular permeability, resulting in the development of edema. The AQP1-dependent myocardial edema and apoptosis contributed to the development of MI. AQP1 deficiency protected cardiac function from ischemic injury following MI. Furthermore, AQP1 deficiency reduced microvascular permeability via the stabilization of HIF-1α levels in endothelial cells and decreased cellular apoptosis following MI.

New insights into the mechanism for VACM-1/cul5 expression in vascular tissue in vivo

Vasopressin-activated calcium-mobilizing (VACM-1)/cul5 is the least conserved member of a cullin protein family involved in the formation of E3-specific ligase complexes that are responsible for delivering the ubiquitin protein to their target substrate proteins selected for ubiquitin-dependent degradation. This chapter summarizes work to date that has focused on VACM-1/cul5's tissue-specific expression in vivo and on its potential role in the control of specific cellular signaling pathways in those structures. As mammalian cells may contain hundreds of E3 ligases, identification VACM-1/cul5 as a specific subunit of the system that is expressed in the endothelium and in collecting tubules, structures known for their control of cellular permeability, may have significant implications when designing studies to elucidate the mechanism of water conservation. For example, VACM-1/cul5 expression is affected by water deprivation in some tissues and there is a potential relationship between neddylated VACM-1/cul5 and aquaporins.

Ephaptic coupling in cardiac myocytes

While it is widely believed that conduction in cardiac tissue is regulated by gap junctions, recent experimental evidence suggests that the extracellular space may play a significant role in action potential propagation. Cardiac tissue with low gap junctional coupling still exhibits conduction, with conflicting degrees of slowing that may be due to variations in the extracellular space. Inhomogeneities in the extracellular space caused by the complex cellular structure in cardiac tissue can lead to ephaptic, or field effect, coupling. Here, we present data from simulations of a cylindrical strand of cells in which we see the dramatic effect highly resistant extracellular spaces have on propagation velocity. We find that ephaptic effects occur in all areas of small extracellular spaces and are not restricted to the junctional cleft between cells. This previously unrecognized type of field coupling, which we call lateral coupling, can allow conduction in the absence of gap junctions. We compare our results with the classically used cable theory, demonstrating the quantitative difference in propagation velocity arising from the cellular geometry. Ephaptic effects are shown to be highly dependent upon parameter values, frequently enhancing, but sometimes decreasing propagation speed. Our mathematical analysis incorporates the inhomogeneities in the extracellular microdomains that cannot be directly measured by experimental techniques and will aid in optimizing cardiac treatments that require manipulation of the cellular geometry and understanding heart functionality.

Cardiac aquaporins

Aquaporins are a group of proteins with high-selective permeability for water. A subgroup called aquaglyceroporins is also permeable to glycerol, urea and a few other solutes. Aquaporin function has mainly been studied in the brain, kidney, glands and skeletal muscle, while the information about aquaporins in the heart is still scarce. The current review explores the recent advances in this field, bringing aquaporins into focus in the context of myocardial ischemia, reperfusion, and blood osmolarity disturbances. Since the amount of data on aquaporins in the heart is still limited, examples and comparisons from better-studied areas of aquaporin biology have been used. The human heart expresses aquaporin-1, -3, -4 and -7 at the protein level. The potential roles of aquaporins in the heart are discussed, and some general phenomena that the myocardial aquaporins share with aquaporins in other organs are elaborated. Cardiac aquaporin-1 is mostly distributed in the microvasculature. Its main role is transcellular water flux across the endothelial membranes. Aquaporin-4 is expressed in myocytes, both in cardiac and in skeletal muscle. In addition to water flux, its function is connected to the calcium signaling machinery. It may play a role in ischemia-reperfusion injury. Aquaglyceroporins, especially aquaporin-7, may serve as a novel pathway for nutrient delivery into the heart. They also mediate toxicity of various poisons. Aquaporins cannot influence permeability by gating, therefore, their function is regulated by changes of expression-on the levels of transcription, translation (by microRNAs), post-translational modification, membrane trafficking, ubiquitination and subsequent degradation. Studies using mice genetically deficient for aquaporins have shown rather modest changes in the heart. However, they might still prove to be attractive targets for therapy directed to reduce myocardial edema and injury caused by ischemia and reperfusion.

Human aquaporins: regulators of transcellular water flow

BACKGROUND

Emerging evidence supports the view that (AQP) aquaporin water channels are regulators of transcellular water flow. Consistent with their expression in most tissues, AQPs are associated with diverse physiological and pathophysiological processes.

SCOPE OF REVIEW

AQP knockout studies suggest that the regulatory role of AQPs, rather than their action as passive channels, is their critical function. Transport through all AQPs occurs by a common passive mechanism, but their regulation and cellular distribution varies significantly depending on cell and tissue type; the role of AQPs in cell volume regulation (CVR) is particularly notable. This review examines the regulatory role of AQPs in transcellular water flow, especially in CVR. We focus on key systems of the human body, encompassing processes as diverse as urine concentration in the kidney to clearance of brain oedema.

MAJOR CONCLUSIONS

AQPs are crucial for the regulation of water homeostasis, providing selective pores for the rapid movement of water across diverse cell membranes and playing regulatory roles in CVR. Gating mechanisms have been proposed for human AQPs, but have only been reported for plant and microbial AQPs. Consequently, it is likely that the distribution and abundance of AQPs in a particular membrane is the determinant of membrane water permeability and a regulator of transcellular water flow.

GENERAL SIGNIFICANCE

Elucidating the mechanisms that regulate transcellular water flow will improve our understanding of the human body in health and disease. The central role of specific AQPs in regulating water homeostasis will provide routes to a range of novel therapies. This article is part of a Special Issue entitled Aquaporins.

Genetic deletion of aquaporin-1 results in microcardia and low blood pressure in mouse with intact nitric oxide-dependent relaxation, but enhanced prostanoids-dependent relaxation

The water channels, aquaporins (AQPs) are key mediators of transcellular fluid transport. However, their expression and role in cardiac tissue is poorly characterized. Particularly, AQP1 was suggested to transport other molecules (nitric oxide (NO), hydrogen peroxide (H2O2)) with potential major bearing on cardiovascular physiology. We therefore examined the expression of all AQPs and the phenotype of AQP1 knockout mice (vs. wild-type littermates) under implanted telemetry in vivo, as well as endothelium-dependent relaxation in isolated aortas and resistance vessels ex vivo. Four aquaporins were expressed in wild-type heart tissue (AQP1, AQP7, AQP4, AQP8) and two aquaporins in aortic and mesenteric vessels (AQP1-AQP7). AQP1 was expressed in endothelial as well as cardiac and vascular muscle cells and co-segregated with caveolin-1. AQP1 knockout (KO) mice exhibited a prominent microcardia and decreased myocyte transverse dimensions despite no change in capillary density. Both male and female AQP1 KO mice had lower mean BP, which was not attributable to altered water balance or autonomic dysfunction (from baroreflex and frequency analysis of BP and HR variability). NO-dependent BP variability was unperturbed. Accordingly, endothelium-derived hyperpolarizing factor (EDH(F)) or NO-dependent relaxation were unchanged in aorta or resistance vessels ex vivo. However, AQP1 KO mesenteric vessels exhibited an increase in endothelial prostanoids-dependent relaxation, together with increased expression of COX-2. This enhanced relaxation was abrogated by COX inhibition. We conclude that AQP1 does not regulate the endothelial EDH or NO-dependent relaxation ex vivo or in vivo, but its deletion decreases baseline BP together with increased prostanoids-dependent relaxation in resistance vessels. Strikingly, this was associated with microcardia, unrelated to perturbed angiogenesis. This may raise interest for new inhibitors of AQP1 and their use to treat hypertrophic cardiac remodeling.

Attenuated expression of gelsolin in association with induction of aquaporin-1 and nitric oxide synthase in dysfunctional hearts of aging mice exposed to endotoxin

Sepsis triggered by endotoxinemia may impair cardiac function. A decline in tolerance to septic shock occurs with aging. This study addressed the hypothesis that aging negatively impairs expression of gelsolin, and axerts the regulatory effects on the water channel protein aquaporin-1 (AQP-1) and endotoxin-inducible nitric oxide synthase (iNOS). We explored whether the age-related gene changes are associated with the cardiac dysfunction induced by endotoxic stress exposure. Male mice at young (3-month) and old (12-month) ages received intraperitoneal injections of saline or lipopolysaccharide (LPS, 30mg/Kg). Cardiac performance and morphology were analyzed by echocardiography at baseline and 2 and 24 h after injection. At the end of treatment, the animals were sacrificed, and cardiac tissues were collected for assessing expression of gelsolin, AQP-1, iNOS, and transcription-3 (STAT3). LPS administration led to a decreased contractility while increasing cardiac dimensions in both young and old mice. LPS also markedly induced expression of gelsolin in both animal groups. However, compared to young mice, old mice showed compromised induction of gelsolin and cardiac performance in response to endotoxin. Meanwhile, the LPS-exposed old animals exhibited higher levels of AQP-1, iNOS, and phosphorylated STAT3. Gelsolin-null mice had increased expression of glycosylated AQP-1 and STAT3 phosphorylation as well as cardiac dysfunction. Thus, endotoxin administration induces expression of gelsolin, AQP-1 and pro-inflammatory genes, such as iNOS. Our data suggest that changed expression of gelsolin, AQP-1 and iNOS may contribute to dysfunction of hearts in aged subjects with septic endotoxinemia.

Time-dependent expression patterns of cardiac aquaporins following myocardial infarction

Aquaporins (AQPs) are expressed in myocardium and the implication of AQPs in myocardial water balance has been suggested. We investigated the expression patterns of AQP subtypes in normal myocardium and their changes in the process of edema formation and cardiac dysfunction following myocardial infarction (MI). Immunostaining demonstrated abundant expression of AQP1, AQP4, and AQP6 in normal mouse heart; AQP1 in blood vessels and cardiac myocytes, AQP4 exclusively on the intercalated discs between cardiac myocytes and AQP6 inside the myocytes. However, neither AQP7 nor AQP9 proteins were expressed in CD1 mouse myocardium. Echocardiography revealed that cardiac function was reduced at 1 week and recovered at 4 weeks after MI, whereas myocardial water content determined by wet-to-dry weight ratio increased at 1 week and rather reduced below the normal at 4 weeks. The expression of cardiac AQPs was up-regulated in MI-induced groups compared with sham-operated control group, but their time-dependent patterns were different. The time course of AQP4 expression coincided with that of myocardial edema and cardiac dysfunction following MI. However, expression of both AQP1 and AQP6 increased persistently up to 4 weeks. Our findings suggest a different role for cardiac AQPs in the formation and reabsorption of myocardial edema after MI.

Aquaporin 1 plays an important role in myocardial edema caused by cardiopulmonary bypass surgery in goat

Myocardial stunning, which is closely related to myocardial edema, is a severe complication that may occur following cardiac surgery. In this study, we examined the expression of aquaporin 1 (AQP1) and Connexin 43 (Cx43) following cardiopulmonary bypass (CPB) surgery in goats. We assessed myocardial muscle tissue water content according to changes in dry-wet weight. Our results showed that AQP1 expression and myocardial muscle tissue water content increased significantly 6 h after CPB surgery, reaching peak levels 48 h after surgery; additionally, the protein expression of Cx43 was inversely correlated with AQP1 expression. Overexpression of AQP1 during CPB surgery enhanced the degree of myocardial edema, whereas the addition of water channel protein inhibitor Hg2+ in cold crystalloid cardioplegia and knockdown of AQP1 during surgery weakened the degree of myocardial edema. These findings revealed that the severity of myocardial edema after CPB surgery is correlated with AQP1 protein expression levels, suggesting the important role played by AQP1 protein in the regulation of Cx43 in the pathological progression of myocardial edema.

Cardiovascular-metabolic impact of adiponectin and aquaporin

Visceral fat accumulation is located upstream of metabolic syndrome. Recent progress in adipocyte biology has clarified the molecular mechanism for pathophysiology of metabolic syndrome and its related disorders. In this review we summarize adiponectin and aquaporin 7 (AQP7) in the role of metabolic syndrome and cardiovascular diseases.

The cardioprotection of simvastatin in reperfused swine hearts relates to the inhibition of myocardial edema by modulating aquaporins via the PKA pathway

BACKGROUND AND OBJECTIVE

Myocardial edema plays a role in myocardial no-reflow and infarction during ischemia and reperfusion. The effects of statins against no-reflow and infarction may relate to the inhibition of myocardial edema. The current study investigated the role of protein kinase A (PKA) in statin-reduced myocardial edema in reperfused swine hearts.

METHODS AND RESULTS

Minipigs were treated with simvastatin (SIM, 2mg/kg), SIM+H-89 (a PKA inhibitor, 1.0 μg/kg/min), or H-89 alone 1h before 90-min ischemia and 3-h reperfusion or sham operation. Ischemia or ischemia-reperfusion induced severe myocardial edema, PKA activation, and up-regulation of aquaporin-1, -4, -8, and -9 in the reflow and no-reflow myocardium. SIM pretreatment reduced the sizes of no-reflow and infarct areas by 18.5% and 11.1% (P<0.01), decreased water content in the left ventricle, reflow and no-reflow myocardium by 1.4%, 5.3%, and 4.3% (P<0.05), inhibited cardiomyocytes swelling in the reflow and no-reflow areas by 19.8% and 13.1% (P<0.01), suppressed mitochondrial water accumulation in the reflow and no-reflow areas by 49.0% and 35.9% (P<0.01), increased PKA activity (P<0.01), and blocked the up-regulation of aquaporin-1, -4, -8, and -9 in the reflow and no-reflow myocardium. However, these beneficial effects of SIM were partially abolished by inhibiting PKA with H-89.

CONCLUSIONS

The cardioprotective effects of acute SIM therapy against myocardial no-reflow and infarction relate to the reduction of myocardial edema by suppressing the expression of aquaporin-1, -4, -8, and -9 in a partially PKA-dependent manner.

VACM-1/cul5 expression in vascular tissue in vivo is induced by water deprivation and its expression in vitro regulates aquaporin-1 concentrations

VACM-1, a cul5 gene product, when overexpressed in vitro, has an antiproliferative effect. In vivo, VACM-1/cul5 is present in tissues involved in the regulation of water balance. Neither proteins targeted for VACM-1/cul5-specific degradation nor factors that may regulate its expression in those tissues have been studied. To identify genes that may be misregulated by VACM-1 cDNA, we performed microarray analysis. Our results indicate that in cos-1 cells transfected with VACM-1 cDNA, mRNA levels for several genes, including AQP1, were decreased when compared to the control group. Our results also indicate that in cos-1 cells transfected with VACM-1 cDNA, endogenous AQP1 protein was decreased about 6-fold when compared to the controls. To test the hypothesis that VACM-1/cul5 may be regulated by conditions that compromise water homeostasis in vivo, we determined if 24 h of water deprivation affects VACM-1/cul5 levels or the effect of VACM-1/cul5 on AQP1. VACM-1 mRNA and protein levels were significantly higher in rat mesenteric arteries, skeletal muscle and the heart ventricle but not in the heart atrium from 24-h water-deprived rats when compared to the controls. Interestingly, 24 h of water deprivation increased modification of VACM-1 by an ubiquitin-like protein, Nedd8, essential for cullin-dependent E3 ligase activity. Although water deprivation did not significantly change AQP1 levels in the mesenteric arteries, AQP1 protein concentrations were inversely correlated with the ratio of the VACM-1 to Nedd8-modified VACM-1. These results suggest that VACM-1/cul5 may regulate endothelial AQP1 concentration both in vivo and in vitro.

Ca2+ dynamics in the mitochondria - state of the art

The importance of [Ca2+] in the mitochondrial matrix, [Ca2+]mito, had been proposed by early work of Carafoli and others [1 ], [2 ] and [3 ]. The key suggestion in the 1970s [4 ] was that regulatory [Ca2+]mito played a role in controlling the rate of activation of tricarboxylic acid cycle dehydrogenases, important in the regulation of ATP production by the electron transport chain (ETC) during oxidative phosphorylation. This view is now established [5 ] and [6 ] and the key questions currently debated are to what extent do the mitochondria acquire and release Ca2+, and what impact do mitochondria have on the dynamic Ca2+ signal in the cardiac ventricular myocyte [7 ]. Although investigations of Ca2+ dynamics in mitochondria have been problematic, disparate and inconclusive, they have also been both provocative and exciting. A recent special issue of this journal presented contrasting perspectives on the speed, extent and mechanisms of changes in [Ca2+]mito, and how these changes may influence cellular spatio-temporal [Ca2+]i dynamics [8 ]. An audio discussion is also available online [9 ]. The uncertain nature of the signaling pathways is noted in Table 1 (see below) which shows mitochondrial proteins and processes that are of current focus and which remain contentious. Each of the “items” listed is largely unsettled, or is a “work in progress”. There may be advocates for opposing positions noted or recent discoveries that must still be tested at multiple levels by diverse laboratories. Currently, the first item, the mitochondrial sodium/calcium exchanger (NCLX) [10 ], appears the most solid with respect to the molecular identification and physiological function, whereas, the recently described candidates of the mitochondrial Ca2+ uniporter (MCU) [11 ] and [12 ] still need to be verified and broadly examined by the scientific community.

Evaluation of right ventricle function in children with primary nephrotic syndrome

BACKGROUND

We aimed to evaluate right ventricle (RV) function in children with primary nephrotic syndrome (PNS).

METHODS

RV hemodynamics were evaluated by Doppler echocardiography in 50 children with PNS (aged 2.5-12 years), either at PNS onset (n = 37) or relapse (n = 13), and in 50 normal controls. Heart rate, stroke volume, cardiac output, RV enddiastolic and end-systolic volume, RV ejection fraction, RV end-diastolic pressure, RV peak systolic and end-systolic pressure were determined from pressure-volume loops. The maximal rates of RV pressure upstroke and fall (dP/d t(max) and dP/d t(min), respectively) were calculated. Effective pulmonary arterial elastance was calculated as end-systolic pressure divided by stroke volume. Plasma tumor necrosis factor-alpha (TNF-alpha) and insulin-like growth factor 1 (IGF-1) were also measured.

RESULTS

RV end-diastolic pressure was increased by an average of 20% in 39 of the patients with PNS, whereas RV ejection fraction was reduced by an average of 15% compared with controls (p < 0.05 for both). Cardiac output and stroke volume were maintained, indicating compensation at the expense of increased RV end-diastolic and end-systolic volumes and increased RV filling pressure (p < 0.05). Plasma TNF-alpha was elevated in patients with PNS (326 +/- 117 kU/L vs. 75 +/- 23 kU/L, p < 0.05); IGF-1 was similar in PNS patients and controls.

CONCLUSION

Right ventricle function was impaired in children with PNS. The characteristics were unrelated to blood pressure and IGF-1, but may be correlated with TNF-alpha and disease duration. Further studies are needed to evaluate the etiology and clinical implications of this abnormality.

Cardiac dysfunction in HgCl2-induced nephrotic syndrome

The experimental model of HgCl2 injection is characterized by a systemic autoimmune disease which leads to the development of nephrotic syndrome (NS). NS seems to be accompanied by cardiovascular alterations, since patients with NS present an increased incidence in cardiac disease. The aim of our work was to study the effects of HgCl2-induced NS on myocardial function and morphometry. Normotensive Brown–Norway rats were injected with HgCl2 (1 mg/kg, HgCl2 group; n = 6, subcutaneous) or the vehicle (control group; n = 6, subcutaneous) on days 0, 2, 4, 7, 9 and 11. The animals were placed in metabolic cages for evaluation of urinary excretion of noradrenaline, sodium, total proteins, albumin and creatinine. Fourteen and 21 days after the first HgCl2 injection, left ventricle (LV) hemodynamics was evaluated through pressure micromanometers in basal and isovolumetric heartbeats. The heart and gastrocnemius muscle weights and tibial length were also examined. In an additional group of animals cardiac dimensions and ejection fraction were assessed by echocardiography and LV apoptosis and fibrosis were studied. HgCl2-injected rats presented proteinuria, albuminuria, hyperlipidemia, anemia, sodium retention and ascites at day 14. These alterations were accompanied by LV hemodynamic changes only in isovolumetric heartbeats. Similarly, on day 21, HgCl2-injected rats presented proteinuria, albuminuria, hyperlipidemia, anemia, but no sodium retention or ascites. These animals presented LV systolic and diastolic dysfunction in both basal and isovolumetric heartbeats, as well as cardiac atrophy, LV fibrosis and an increase in myocyte apoptosis. In conclusion, HgCl2-induced NS is accompanied by LV dysfunction and can be a promising model for studying the link between NS and cardiac disease.

The heart requires glycerol as an energy substrate through aquaporin 7, a glycerol facilitator

AIMS

Cardiomyocytes require fatty acids and glucose for energy production. However, other nutrients and substrates that may serve as possible candidates for a cardiac energy source have not been fully studied. Several reports showed that a moderate expression of aquaporin 7 (AQP7), a member of the aquaglyceroporin family that is permeated by glycerol and water, is observed in heart tissue. However, the functional role of cardiac AQP7 is not clear. The aim of this study was to investigate the significance of glycerol as a cardiac energy substrate and to clarify the role of cardiac AQP7.

METHODS AND RESULTS

Heart function and morphology were examined in AQP7-knockout (KO) mice under basal conditions and during pressure overload [isoproterenol infusion and transverse aortic constriction (TAC)]. Glycerol uptake and glycerol-dependent ATP production were measured in AQP7-knockdown cardiac cells. Cardiac glycerol consumption was analysed in ex vivo beating hearts. Cardiac morphology and function in KO mice were similar to those of wild-type (WT) mice under basal conditions, although low glycerol and ATP content were noted in hearts of KO mice. In H9c2 cardiomyotubes, knockdown of AQP7 was associated with a significant reduction of glycerol uptake. The ex vivo heart study demonstrated that cardiac glycerol consumption levels in KO mice were significantly lower than those of WT mice. Furthermore, isoproterenol challenge induced severe left ventricular hypertrophy in KO mice, and TAC resulted in a higher mortality rate in KO mice than in WT mice.

CONCLUSION

The results indicate that AQP7 acts as a glycerol facilitator in cardiomyocytes and that glycerol is a substrate for cardiac energy production.

Peri-operative management of paediatric patients undergoing cardiac surgery--focus on respiratory aspects of care

Children requiring cardiac surgery present particular challenges in peri-operative respiratory management. The wide variety of conditions and operations and their varied impact on respiratory function makes dialogue with related medical staff essential. In most circumstances, cardiac performance is the main determinant of respiratory outcomes. Changing cardiologic and surgical approaches have combined to diminish the severity and frequency of pulmonary hypertensive issues and new treatment modalities are simplifying the intensive care approach. Patients with Down's syndrome and 22q11 deletion syndrome present particular issues related to anatomy, physiology and respiratory function. Certain conditions, including tetralogy of Fallot and cavopulmonary connections, present unique circumstances where respiratory management, sometimes including extubation, may assist in optimisation of cardiac performance. These and other conditions highlight the complexities of cardiopulmonary interactions. Cardiac performance remains the principal determinant of outcome after paediatric cardiac surgery and has the biggest impact on respiratory function.

Cardiac remodeling and dysfunction in nephrotic syndrome

There is an increased incidence of heart disease in patients with chronic nephrotic syndrome (NS), which may be attributable to the malnutrition and activated inflammatory state accompanying the sustained proteinuria. In this study, we evaluated renal function, cardiac morphometry, contractile function, and myocardial gene expression in the established puromycin aminonucleoside nephrosis rat model of NS. Two weeks after aminonucleoside injection, there was massive proteinuria, decreased creatinine clearance, and a negative sodium balance. Skeletal and cardiac muscle atrophy was present and was accompanied by impaired left ventricular (LV) hemodynamic function along with decreased contractile properties of isolated LV muscle strips. The expression of selected cytokines and proteins involved in calcium handling in myocardial tissue was evaluated by real time polymerase chain reaction. This revealed that the expression of interleukin-1beta, tumor necrosis factor-alpha, and phospholamban were elevated, whereas that of cardiac sarco(endo)plasmic reticulum calcium pump protein was decreased. We suggest that protein wasting and systemic inflammatory activation during NS contribute to cardiac remodeling and dysfunction.

Cardiac aquaporin expression in humans, rats, and mice

Water accumulation in the heart is important in ischemia-reperfusion injury and operations performed by using cardiopulmonary bypass, with cardiac dysfunction associated with myocardial edema being the principal determinant of clinical outcome. As an initial step in determining the role of aquaporin (AQP) water channels in myocardial edema, we have assessed the myocardial expression of AQPs in humans, rats, and mice. RT-PCR revealed expression of AQP-1, -4, -6, -7, -8, and -11 transcripts in the mouse heart. AQP-1, -6, -7, and -11 mRNAs were found in the rat heart as well as low levels of AQP-4 and -9. Human hearts contained AQP-1, -3, -4, -5, -7, -9, -10, and -11 mRNAs. AQP-1 protein expression was confirmed by Western blot analysis in all three species. AQP-4 protein was detected in the mouse heart but not in the rat or human heart. To determine the potential functional consequences of myocardial AQP expression, water permeability was measured in plasma membrane vesicles from myocardial cells of wild-type versus various AQP knockout mice. Water permeability was reduced by AQP-1 knockout but not by AQP-4 or AQP-8 knockout. With the use of a model of isolated rat heart perfusion, it was found that osmotic and ischemic stresses are not associated with changes in AQP-1 or AQP-4 expression. These studies support a possible functional role of AQP-1 in myocardium but indicate that early adaptations to osmotic and ischemic stress do not involve transcriptional or posttranslational AQP-1 regulation.