Alogliptin prevents diastolic dysfunction and preserves left ventricular mitochondrial function in diabetic rabbits

Background

There are increasing evidence that left ventricle diastolic dysfunction is the initial functional alteration in the diabetic myocardium. In this study, we hypothesized that alogliptin prevents diastolic dysfunction and preserves left ventricular mitochondrial function and structure in diabetic rabbits.

Methods

A total of 30 rabbits were randomized into control group (CON, n?=?10), alloxan-induced diabetic group (DM, n?=?10) and alogliptin-treated (12.5 mg/kd/day for 12 weeks) diabetic group (DM-A, n?=?10). Echocardiographic and hemodynamic studies were performed in vivo. Mitochondrial morphology, respiratory function, membrane potential and reactive oxygen species (ROS) generation rate of left ventricular tissue were assessed. The serum concentrations of glucagon-like peptide-1, insulin, inflammatory and oxidative stress markers were measured. Protein expression of TGF-β1, NF-κB p65 and mitochondrial biogenesis related proteins were determined by Western blotting.

Results

DM rabbits exhibited left ventricular hypertrophy, left atrial dilation, increased E/e′ ratio and normal left ventricular ejection fraction. Elevated left ventricular end diastolic pressure combined with decreased maximal decreasing rate of left intraventricular pressure (??dp/dtmax) were observed. Alogliptin alleviated ventricular hypertrophy, interstitial fibrosis and diastolic dysfunction in diabetic rabbits. These changes were associated with decreased mitochondrial ROS production rate, prevented mitochondrial membrane depolarization and improved mitochondrial swelling. It also improved mitochondrial biogenesis by PGC-1α/NRF1/Tfam signaling pathway.

Conclusions

The DPP-4 inhibitor alogliptin prevents cardiac diastolic dysfunction by inhibiting ventricular remodeling, explicable by improved mitochondrial function and increased mitochondrial biogenesis.

     

Testis glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase activities in aminoguanidine-treated diabetic rats

Severe steroidogenic and spermatogenic alterations are reported in association with diabetic manifestations in humans and experimental animals. This study was planned to determine whether oxidative stress is involved in diabetes-induced alterations in the testes. Diabetes was induced in male rats by injection of 50 mg/kg of streptozotocin (STZ). Ten weeks after injection of STZ, levels of selenium and activities of selenium dependent-glutathione peroxidase (GPx) and phospholipid hydroperoxide glutathione peroxidase (PHGPx) were measured in rat testis. Lipid and protein oxidations were evaluated as measurements of testis malondialdehyde (MDA) and protein carbonyl levels, respectively. Testis sulfydryl (SH) levels were also determined. The control levels of GPx and PHGPx activities were found to be 46.5 +/- 6.2 and 108.8 +/- 19.8 nmol GSH/mg protein/min, respectively. Diabetes caused an increase in testis GPx (65.0 +/- 21.1) and PHGPx (155.9 +/- 43.1) activities but did not affect the levels of selenium or SH. However, the testis MDA and protein carbonyl levels as markers of lipid and protein oxidation, respectively, did not increase in the diabetic group. Aminoguanidine (AG) treatment of diabetic rats returned the testis PHGPx activity (136.5 +/- 24.9) to the control level but did not change the value of GPx activity (69.2 +/- 17.4) compared with diabetic group. MDA and protein carbonyl levels in testis were not affected by AG treatment of diabetic rats, but interestingly AG caused SH levels to increase. The results indicate that reactive oxygen radicals were not involved in possible testicular complications of diabetes because diabetes-induced activations of GPx and PHGPx provided protection against oxidative stress, which was reported to be related to some diabetic complications.     

Glucose-insulin-potassium preserves systolic and diastolic function in ischemia and reperfusion in pigs

Clinical and experimental studies have suggested benefit of treatment with intravenous glucose-insulin-potassium (GIK) in acute myocardial infarction. However, patients hospitalized with acute coronary syndromes often experience recurrent myocardial ischemia without infarction that may cause progressive left ventricular (LV) dysfunction. This study tested the hypothesis that anticipatory treatment with GIK attenuates both systolic and diastolic LV dysfunction resulting from ischemia and reperfusion without infarction in vivo. Open-chest, anesthetized pigs underwent 90 min of moderate regional ischemia (mean subendocardial blood flow 0.3 ml x g(-1) x min(-1)) and 90 min reperfusion. Eight pigs were treated with GIK (300 g/l glucose, 50 U/l insulin, and 80 meq/l KCl; infused at 2 ml x kg(-1) x h(-1)) beginning 30 min before ischemia and continuing through reperfusion. Eight untreated pigs comprised the control group. Regional LV wall area was measured with orthogonal pairs of sonomicrometry crystals. GIK significantly increased myocardial glucose uptake and lactate release during ischemia. After reperfusion, indexes of regional systolic function (external work and fractional systolic wall area reduction), regional diastolic function (maximum rate of diastolic wall area expansion), and global LV function (LV positive and negative maximum rate of change in pressure with respect to time) recovered to a significantly greater extent in GIK-treated pigs than in control pigs (all P < 0.05). The findings suggest that the clinical utility of GIK may extend beyond treatment of acute myocardial infarction to anticipatory metabolic protection of myocardium in patients at risk for recurrent episodes of ischemia.     

Tranilast attenuates diastolic dysfunction and structural injury in experimental diabetic cardiomyopathy

Diastolic dysfunction is an increasingly recognized complication of diabetes that develops in relatively young patients as a result of diabetic cardiomyopathy (DCM). With recent advances in echocardiographic technology now permitting the reliable assessment of diastolic function in the rat, we examined cardiac function and structure in diabetic rodents and assessed the effects of intervening with tranilast, an antifibrotic compound that has been shown to attenuate the actions of transforming growth factor-beta (TGF-beta) in cardiac fibroblasts. We also sought to examine the mechanism whereby tranilast inhibits the actions of TGF-beta. Six-week-old heterozygous (mRen-2)27 rats were randomized to receive either streptozotocin or citrate buffer and then further randomized to receive either tranilast (400 mg x kg(-1) x day(-1) by twice daily gavage) or vehicle for another 8 wk. Cell signaling was examined in neonatal cardiac fibroblasts. After 8 wk, diabetic rats showed evidence of impaired diastolic function with reduced early-to-late atrial wave ratio and prolonged deceleration time in association with fibrosis, apoptosis, and hypertrophy (all P < 0.05). Treatment with tranilast prevented the development of diastolic dysfunction and the histopathological features of DCM. While tranilast did not affect Smad phosphorylation, it significantly attenuated TGF-beta-induced p44/42 mitogen-activated protein kinase phosphorylation.     

Ventricular remodeling and diastolic myocardial dysfunction in rats submitted to protein-calorie malnutrition

The effects of protein-calorie malnutrition (PCM) on heart structure and function are not completely understood. We studied heart morphometric, functional, and biochemical characteristics in undernourished young Wistar rats. They were submitted to PCM from birth (undernourished group, UG). After 10 wk, left ventricle function was studied using a Langendorff preparation. The results were compared with age-matched rats fed ad libitum (control group, CG). The UG rats achieved 47% of the body weight and 44% of the left ventricular weight (LVW) of the CG. LVW-to-ventricular volume ratio was smaller and myocardial hydroxyproline concentration was higher in the UG. Left ventricular systolic function was not affected by the PCM protocol. The myocardial stiffness constant was greater in the UG, whereas the end-diastolic pressure-volume relationship was not altered. In conclusion, the heart is not spared from the adverse effects of PCM. There is a geometric alteration in the left ventricle with preserved ventricular compliance despite the increased passive myocardial stiffness. The systolic function is preserved.     

Overexpression of Kdr in adult endocardium induces endocardial neovascularization and improves heart function after myocardial infarction

Dear Editor, Coronary artery disease is a leading cause of mortality and morbidity worldwide.Blockade of effective blood flow to heart muscles results in cardi...     

Overexpression of glutathione peroxidase increases the resistance of neuronal cells to Abeta-mediated neurotoxicity

Senile plaques are neuropathological manifestations in Alzheimer's disease (AD) and are composed mainly of extracellular deposits of amyloid beta-peptide (Abeta). Various data suggest that the accumulation of Abeta may contribute to neuronal degeneration and that Abeta neurotoxicity could be mediated by oxygen free radicals. Removal of free radicals by antioxidant scavengers or enzymes was found to protect neuronal cells in culture from Abeta toxicity. However, the nature of the free radicals involved is still unclear. In this study, we investigated whether the neuronal overexpression of glutathione peroxidase (GPx), the major hydrogen peroxide (H2O2)-de-grading enzyme in neurons, could increase their survival in a cellular model of Abeta-induced neurotoxicity. We infected pheochromocytoma (PC12) cells and rat embryonic cultured cortical neurons with an adenoviral vector encoding GPx (Ad-GPx) prior to exposure to toxic concentrations of Abeta(25-35) or (1-40). Both PC12 and cortical Ad-GPx-infected cells were significantly more resistant to Abeta-induced injury. These data strengthen the hypothesis of a role of H2O2 in the mechanism of Abeta toxicity and highlight the potential of Ad-GPx to reduce Abeta-induced damage to neurons. These findings may have applications in gene therapy for AD.     

IGF-IR signaling attenuates the age-related decline of diastolic cardiac function

Insulin-like growth factor (IGF-I) signaling has been implicated to play an important role in regulation of cardiac growth, hypertrophy, and contractile function and has been linked to the development of age-related congestive heart failure. Here, we address the question to what extent cardiomyocyte-specific IGF-I signaling is essential for maintenance of the structural and functional integrity of the adult murine heart. To investigate the effects of IGF-I signaling in the adult heart without confounding effects due to IGF-I overexpression or adaptation during embryonic and early postnatal development, we inactivated the IGF-I receptor (IGF-IR) by a 4-hydroxytamoxifen-inducible Cre recombinase in adult cardiac myocytes. Efficient inactivation of the IGF-IR (iCMIGF-IRKO) as assessed by Western analysis and real-time PCR went along with reduced IGF-I-dependent Akt and GSK3β phosphorylation. Functional analysis by conductance manometry and MRI revealed no functional alterations in young adult iCMIGF-IRKO mice (age 3 mo). However, when induced in aging mice (11 mo) diastolic cardiac function was depressed. To address the question whether insulin signaling might compensate for the defective IGF-IR signaling, we inactivated β-cells by streptozotocin. However, the diabetes-associated functional depression was similar in control and iCMIGF-IRKO mice. Similarly, analysis of the cardiac gene expression profile on 44K microarrays did not reveal activation of overt adaptive processes. Endogenous IGF-IR signaling is required for conservation of cardiac function of the aging heart, but not for the integrity of cardiac structure and function of young hearts.     

Raloxifene attenuates oxidative stress and preserves mitochondrial function in astrocytic cells upon glucose deprivation

Oxidative stress and mitochondrial dysfunction induced by metabolic insults are both hallmarks of various neurological disorders, whereby neuronal cells are severely affected by decreased glucose supply to the brain. Likely injured, astrocytes are important for neuronal homeostasis and therapeutic strategies should be directed towards improving astrocytic functions to improve brain's outcome. In the present study, we aimed to assess the actions of raloxifene, a selective estrogen receptor modulator in astrocytic cells under glucose deprivation. Our findings indicated that pretreatment with 1 µM raloxifene results in an increase in cell viability and attenuated nuclei fragmentation. Raloxifene's actions also rely on the reduction of oxidative stress and preservation of mitochondrial function in glucose-deprived astrocytic cells, suggesting the possible direct effects of this compound on mitochondria. In conclusion, our results demonstrate that raloxifene's protective actions might be mediated in part by astrocytes in the setting of a metabolic insult.     

Redox regulation of Ito remodeling in diabetic rat heart

Oxidative stress and the resulting change in cell redox state are proposed to contribute to pathogenic alterations in ion channels that underlie electrical remodeling of the diseased heart. The present study examined whether K(+) channel remodeling is controlled by endogenous oxidoreductase systems that regulate redox-sensitive cell functions. Diabetes was induced in rats by streptozotocin, and experiments were conducted after 3-5 wk of hyperglycemia. Spectrophotometric assays of ventricular tissue extracts from diabetic rat hearts revealed divergent changes in two major oxidoreductase systems. The thioredoxin (TRX) system in diabetic rat heart was characterized by a 52% decrease in TRX reductase (TRXR) activity from control heart (P < 0.05), whereas TRX activity was 1.7-fold greater than control heart (P < 0.05). Diabetes elicited similar changes in the glutaredoxin (GRX) system: glutathione reductase was decreased 35% from control level (P < 0.05), and GRX activity was 2.5-fold greater than in control heart (P < 0.05). The basal activity of glucose-6-phosphate dehydrogenase, which generates NADPH required by the TRX and GRX systems, was not altered by diabetes. Voltage-clamp studies showed that the characteristically decreased density of the transient outward K(+) current (I(to)) in isolated diabetic rat myocytes was normalized by in vitro treatment with insulin (0.1 microM) or the metabolic activator dichloroacetate (1.5 mM). The effect of these agonists on I(to) was blocked by inhibitors of glucose-6-phosphate dehydrogenase. Moreover, inhibitors of TRXR, which controls the reducing activity of TRX, also blocked upregulation of I(to) by insulin and dichloroacetate. These data suggest that K(+) channels underlying I(to) are regulated in a redox-sensitive manner by the TRX system and the remodeling of I(to) that occurs in diabetes may be due to decreased TRXR activity. We propose that oxidoreductase systems are an important repair mechanism that protects ion channels and associated regulatory proteins from irreversible oxidative damage.     

Overexpression of elastin fragments in infarcted myocardium attenuates scar expansion and heart dysfunction

Ventricular dilation after myocardial infarction can cause heart failure. Increasing strength and elasticity in the infarct region might prevent ventricular dilation. Because elastin provides strength, extensibility, and resilience to tissues and maintains tissue architecture, we studied the effect of elastin expression in the infarct on scar expansion and heart function. COS-7 cells transfected with a plasmid with an elastin gene fragment or a vector were seeded into a Gelfoam mesh and cultured. Mechanical stretch test (n = 5/group) showed that the elastin mesh was more elastic (P < 0.05) and tensile (P < 0.05) than the vector mesh. In an in vivo study in rats, 6 days after left anterior descending coronary artery ligation, COS-7 cells (Cell group, n = 7) or COS-7 cells with elastin gene (Elastin group, n = 9) or vector (Vector group, n = 9) were transplanted into the infarct; infarcted rats served as controls (n = 7). Over 8 wk the Cell group did not demonstrate effects on scar expansion and deterioration of heart function vs. controls. In contrast, infarct expansion was smaller and heart function was better maintained in the Elastin group vs. the Vector group (P < 0.05). At 8 wk after cell transplantation Langendorff data showed that the Elastin group had greater (P < 0.01) developed pressure and a smaller left ventricular volume than the Vector group. Western blot and histology showed accumulated elastin in the Elastin group infarct. Changing the extracellular matrix composition of a myocardial infarct by increasing elastin fragment content attenuated scar expansion, ventricular dilation, and onset of heart dysfunction.     

Interleukin-2 enhances angiogenesis and preserves cardiac function following myocardial infarction

We previously demonstrated that injection of IL-2-activated natural killer (NK) cells contribute to vascular remodeling via a4b7 integrin and killer cell lectin-like receptor (KLRG) 1 and promote cardiac repair following myocardial infarction (MI). The aim of the present study is to test the hypothesis that injection of recombinant human interleukin (rhIL)-2 improves angiogenesis and preserves heart function after MI. A single IV injection of rhIL-2 two days following MI improved by 27.7% the left ventricular (LV) fractional shortening of immune competent (C57Bl6) mice, but had no effect on cardiac function of immune-deficient (NOD-SCID IL2Rγnull) mice. Immunohistochemical analysis of C57Bl6 cross sections of heart revealed that collagen deposition was reduced by 23.1% and that capillary density was enhanced in the scar area and the border zone of the infarct respectively by 22.4% and 33.6% following rhIL-2 injection. In addition, rhIL-2 enhanced 1.6-fold the in vivo endothelial cell proliferation index and 1.8-fold the number of NK cell infiltrating the infarcted heart, but had no effect on the number of cardiac CD4 and CD8 cells. In vitro, rhIL-2 activated NK cells enhanced cardiac endothelial cell proliferation by 17.2%. Here we show that a single IV injection of rhIL-2 positively impacted cardiac function by improving angiogenesis through a process involving NK cells.     

Hypothermia preserves myocardial function and mitochondrial protein gene expression during hypoxia

Hypothermia before and/or during no-flow ischemia promotes cardiac functional recovery and maintains mRNA expression for stress proteins and mitochondrial membrane proteins (MMP) during reperfusion. Adaptation and protection may occur through cold-induced change in anaerobic metabolism. Accordingly, the principal objective of this study was to test the hypothesis that hypothermia preserves myocardial function during hypoxia and reoxygenation. Hypoxic conditions in these experiments were created by reducing O2 concentration in perfusate, thereby maintaining or elevating coronary flow (CF). Isolated Langendorff-perfused rabbit hearts were subjected to perfusate (Po2 = 38 mmHg) with glucose (11.5 mM) and perfusion pressure (90 mmHg). The control (C) group was at 37 degrees C for 30 min before and 45 min during hypoxia, whereas the hypothermia (H) group was at 29.5 degrees C for 30 min before and 45 min during hypoxia. Reoxygenation occurred at 37 degrees C for 45 min for both groups. CF increased during hypoxia. The H group markedly improved functional recovery during reoxygenation, including left ventricular developed pressure (DP), the product of DP and heart rate, dP/dtmax, and O2 consumption (MVo2) (P < 0.05 vs. control). MVo2 decreased during hypothermia. Lactate and CO2 gradients across the coronary bed were the same in C and H groups during hypoxia, implying similar anaerobic metabolic rates. Hypothermia preserved MMP betaF1-ATPase mRNA levels but did not alter adenine nucleotide translocator-1 or heat shock protein-70 mRNA levels. In conclusion, hypothermia preserves cardiac function after hypoxia in the hypoxic high-CF model. Thus hypothermic protection does not occur exclusively through cold-induced alterations in anaerobic metabolism.     

Colchicine attenuates left ventricular hypertrophy but preserves cardiac function of aortic-constricted rats.

To investigate the effects of colchicine on left ventricular (LV) function and hypertrophy (LVH) of rats subjected to constriction of transverse aorta (TAoC), we evaluated SO (sham operated, vehicle; n = 25), SO-T (sham operated, colchicine 0.4 mg/kg body wt ip daily; n = 38), TAoC (vehicle; n = 37), and TAoC-T (TAoC, colchicine; n = 34) on the 2nd, 6th, and 15th day after surgery. Colchicine attenuated LVH of TAoC-T compared with TAoC rats, as evaluated by ratio between LV mass (LV(M)) and right ventricular mass, LV wall thickness, and average diameter of cardiac myocytes. Systolic gradient across TAoC ( approximately 45 mmHg), LV systolic pressure, LV end-diastolic pressure, and rate of LV pressure increase (+dP/dt) were comparable in TAoC-T and TAoC rats. However, the baseline and increases of LV systolic pressure-to-LV(M) and +dP/dt-to-LV(M) ratios induced by phenylephrine infusion were greater in TAoC-T and SO-T compared with SO rats. Baseline and increases of +dP/dt-to-LV(M) ratio were reduced in TAoC compared with SO rats. TAoC rats increased polymerized fraction of tubulin compared with SO, SO-T, and TAoC-T rats. Our results indicate that colchicine treatment reduced LVH to pressure overload but preserved LV function.     

Overexpression of CuZnSOD in coronary vascular cells attenuates myocardial ischemia/reperfusion injury

Superoxide dismutase scavenges oxygen radicals, which have been implicated in ischemia/reperfusion (I/R) injury in the heart. Our experiments were designed to study the effect of a moderate increase of copper/zinc superoxide dismutase (CuZnSOD) on myocardial I/R injury in TgN(SOD1)3Cje transgenic mice. A species of 0.8 kb human CuZnSOD mRNA was expressed, and a 273% increase in CuZnSOD activity was detected in the hearts of transgenic mice with no changes in the activities of other antioxidant enzymes. Furthermore, immunoblot analysis revealed no changes in the levels of HSP-70 or HSP-25 levels. Immunocytochemical study indicated that there was increased labeling of CuZnSOD in the cytosolic fractions of both endothelial cells and smooth muscle cells, but not in the myocytes of the hearts from transgenic mice. When these hearts were perfused as Langendorff preparations for 45 min after 35 min of global ischemia, the functional recovery of the hearts, expressed as heart rate x LVDP, was 48 +/- 3% in the transgenic hearts as compared to 30 +/- 5% in the nontransgenic hearts (p <.05). The improved cardiac function was accompanied by a significant reduction in lactate dehydrogenase release from the transgenic hearts. Our results demonstrate that overexpression of CuZnSOD in coronary vascular cells renders the heart more resistant to I/R injury.     

Regulation of cardiomyocyte apoptosis in ischemic reperfused mouse heart by glutathione peroxidase

Apoptosis, a genetically controlled programmed cell death, has been found to play a role in ischemic reperfusion injury in several animal species including rats and rabbits. To examine whether this is also true for other animals, an isolated perfused mouse heart was subjected to 30 min of ischemia followed by 2 h of reperfusion. Experiments were terminated before ischemia (baseline), after ischemia, and at 30, 60, 90 and 120 min of reperfusion. At the end of each experiment, hearts were processed for the evaluation of apoptosis and DNA laddering. The in situ end labeling (ISEL) technique was used to detect apoptotic cardiomyocyte nuclei while DNA laddering was evaluated by subjecting the DNA obtained from the cardiomyocytes to 1.8% agarose gel electrophoresis followed by photographing under UV illumination. The results of our study revealed that apoptotic cells appear only after 60 min of reperfusion as demonstrated by the intense fluorescence of the immunostained genomic DNA when observed under fluorescence microscopy. None of the ischemic hearts showed any evidence of apoptosis. These results were corroborated with the findings of DNA fragmentation showing increased ladders of DNA bands in the same reperfused hearts representing integer multiples of the internucleosomal DNA length (about 180 bp). Since our previous studies showed a role of glutathione peroxidase (GSHPx) in apoptotic cell death, we performed identical experiments using isolated hearts from GSHPx-l knockout mice and transgenic mice overexpressing GSHPx-l. GSHPx-l knockout mice showed evidence of apoptotic cell death even after 30 min of reperfusion. Significant number of apoptotic cells were found in the cardiomyocytes as compared to non-transgenic control animals. To the contrary, very few apoptotic cells were found in the hearts of the transgenic mice overexpressing GSHPx-l. Hearts of GSHPx-l knockout mice were more susceptible to ischemia/reperfusion injury while transgenic mice overexpressing GSHPx- 1 were less susceptible to ischemia reperfusion injury compared to non-transgenic control animals. The results of this study clearly demonstrate a role of GSHPx in ischemia/reperfusion-induced apoptosis in mouse heart.