Photobiomodulation therapy mitigates cardiovascular aging and improves survival

BACKGROUND

Photobiomodulation (PBM) therapy, a form of low-dose light therapy, has been noted to be effective in several age-associated chronic diseases such as hypertension and atherosclerosis. Here, we examined the effects of PBM therapy on age-associated cardiovascular changes in a mouse model of accelerated cardiac aging.

METHODS

Fourteen months old Adenylyl cyclase type VIII (AC8) overexpressing transgenic mice (n = 8) and their wild-type (WT) littermates (n = 8) were treated with daily exposure to Near-Infrared Light (850 nm) at 25 mW/cm2 for 2 min each weekday for a total dose of 1 Einstein (4.5 p.J/cm2 or fluence 3 J/cm2 ) and compared to untreated controls over an 8-month period. PBM therapy was administered for 3.5 months (Early Treatment period), paused, due to Covid-19 restrictions for the following 3 months, and restarted again for 1.5 months. Serial echocardiography and gait analyses were performed at monthly intervals, and serum TGF-β1 levels were assessed following sacrifice.

RESULTS

During the Early Treatment period PBM treatments: reduced the age-associated increases in left ventricular (LV) mass in both genotypes (p = 0.0003), reduced the LV end-diastolic volume (EDV) in AC8 (p = 0.04); and reduced the left atrial dimension in both genotypes (p = 0.02). PBM treatments substantially increased the LV ejection fraction (p = 0.03), reduced the aortic wall stiffness (p = 0.001), and improved gait symmetry, an index of neuro-muscular coordination (p = 0.005). The effects of PBM treatments, measured following the pause, persisted. Total TGF-β1 levels were significantly increased in circulation (serum) in AC8 following PBM treatments (p = 0.01). We observed a striking increase in cumulative survival in PBM-treated AC8 mice (100%; p = 0.01) compared to untreated AC8 mice (43%).

CONCLUSION

PBM treatment mitigated age-associated cardiovascular remodeling and reduced cardiac function, improved neuromuscular coordination, and increased longevity in an experimental animal model. These responses correlate with increased TGF-β1 in circulation. Future mechanistic and dose optimization studies are necessary to assess these anti-aging effects of PBM, and validation in future controlled human studies is required for effective clinical translation.

Emergence of heartbeat frailty in advanced age I: perspectives from life-long EKG recordings in adult mice

The combined influences of sinoatrial nodal (SAN) pacemaker cell automaticity and its response to autonomic input determine the heart's beating interval variability and mean beating rate. To determine the intrinsic SAN and autonomic signatures buried within EKG RR interval time series change in advanced age, we measured RR interval variability before and during double autonomic blockade at 3-month intervals from 6 months of age until the end of life in long-lived (those that achieved the total cohort median life span of 24 months and beyond) C57/BL6 mice. Prior to 21 months of age, time-dependent changes in intrinsic RR interval variability and mean RR interval were relatively minor. Between 21 and 30 months of age, however, marked changes emerged in intrinsic SAN RR interval variability signatures, pointing to a reduction in the kinetics of pacemaker clock mechanisms, leading to reduced synchronization of molecular functions within and among SAN cells. This loss of high-frequency signal processing within intrinsic SAN signatures resulted in a marked increase in the mean intrinsic RR interval. The impact of autonomic signatures on RR interval variability were net sympathetic and partially compensated for the reduced kinetics of the intrinsic SAN RR interval variability signatures, and partially, but not completely, shifted the EKG RR time series intervals to a more youthful pattern. Cross-sectional analyses of other subsets of C57/BL6 ages indicated that at or beyond the median life span of our longitudinal cohort, noncardiac, constitutional, whole-body frailty was increased, energetic efficiency was reduced, and the respiratory exchange ratio increased. We interpret the progressive reduction in kinetics in intrinsic SAN RR interval variability signatures in this context of whole-body frailty beyond 21 months of age to be a manifestation of "heartbeat frailty."

A remarkable adaptive paradigm of heart performance and protection emerges in response to marked cardiac-specific overexpression of ADCY8

Adult (3 month) mice with cardiac-specific overexpression of adenylyl cyclase (AC) type VIII (TG^AC8) adapt to an increased cAMP-induced cardiac workload (~30% increases in heart rate, ejection fraction and cardiac output) for up to a year without signs of heart failure or excessive mortality. Here, we show classical cardiac hypertrophy markers were absent in TG^AC8, and that total left ventricular (LV) mass was not increased: a reduced LV cavity volume in TG^AC8 was encased by thicker LV walls harboring an increased number of small cardiac myocytes, and a network of small interstitial proliferative non-cardiac myocytes compared to wild type (WT) littermates; Protein synthesis, proteosome activity, and autophagy were enhanced in TG^AC8 vs WT, and Nrf-2, Hsp90α, and ACC2 protein levels were increased. Despite increased energy demands in vivo LV ATP and phosphocreatine levels in TG^AC8 did not differ from WT. Unbiased omics analyses identified more than 2,000 transcripts and proteins, comprising a broad array of biological processes across multiple cellular compartments, which differed by genotype; compared to WT, in TG^AC8 there was a shift from fatty acid oxidation to aerobic glycolysis in the context of increased utilization of the pentose phosphate shunt and nucleotide synthesis. Thus, marked overexpression of AC8 engages complex, coordinate adaptation "circuity" that has evolved in mammalian cells to defend against stress that threatens health or life (elements of which have already been shown to be central to cardiac ischemic pre-conditioning and exercise endurance cardiac conditioning) that may be of biological significance to allow for proper healing in disease states such as infarction or failure of the heart.

Age-related impairment of cerebral blood flow response to KATP channel opener in Alzheimer's disease mice with presenilin-1 mutation

Local cerebral blood flow (CBF) responses to neuronal activity are essential for cognition and impaired CBF responses occur in Alzheimer's disease (AD). In this study, regional CBF (rCBF) responses to the K_ATP channel opener diazoxide were investigated in 3xTgAD, WT and mutant Presenilin 1(PS1_M146V) mice from three age groups using Laser-Doppler flowmetry. The rCBF response was reduced early in young 3xTgAD mice and almost absent in old 3xTgAD mice, up to 30%-40% reduction with altered CBF velocity and mean arterial pressure versus WT mice. The impaired rCBF response in 3xTgAD mice was associated with progression of AD pathology, characterized by deposition of intracellular and vascular amyloid-β (Aβ) oligomers, senile plaques and tau pathology. The nitric oxide synthase (NOS) inhibitor N^ω-nitro-L-arginine abolished rCBF response to diazoxide suggesting NO was involved in the mediation of vasorelaxation. Levels of phosphor-eNOS (Ser1177) diminished in 3xTgAD brains with age, while the rCBF response to the NO donor sodium nitroprusside remained. In PS1_M146V mice, the rCBF response to dizoxide reduced and high molecular weight Abeta oligomers were increased indicating PS1_M146V contributed to the dysregulation of rCBF response in AD mice. Our study revealed an Aβ oligomer-associated compromise of cerebrovascular function in rCBF response to diazoxide in AD mice with PS1_M146V mutation.

Overexpression of a Neuronal Type Adenylyl Cyclase (Type 8) in Sinoatrial Node Markedly Impacts Heart Rate and Rhythm

Heart rate (HR) and HR variability (HRV), predictors of over-all organism health, are widely believed to be driven by autonomic input to the sinoatrial node (SAN), with sympathetic input increasing HR and reducing HRV. However, variability in spontaneous beating intervals in isolated SAN tissue and single SAN cells, devoid of autonomic neural input, suggests that clocks intrinsic to SAN cells may also contribute to HR and HRV in vivo. We assessed contributions of both intrinsic and autonomic neuronal input mechanisms of SAN cell function on HR and HRV via in vivo, telemetric EKG recordings. This was done in both wild type (WT) mice, and those in which adenylyl cyclase type 8 (ADCY8), a main driver of intrinsic cAMP-PKA-Ca²⁺ mediated pacemaker function, was overexpressed exclusively in the heart (TG^AC8). We hypothesized that TG^AC8 mice would: (1) manifest a more coherent pattern of HRV in vivo, i.e., a reduced HRV driven by mechanisms intrinsic to SAN cells, and less so to modulation by autonomic input and (2) utilize unique adaptations to limit sympathetic input to a heart with high levels of intrinsic cAMP-Ca²⁺ signaling. Increased adenylyl cyclase (AC) activity in TG^AC8 SAN tissue was accompanied by a marked increase in HR and a concurrent marked reduction in HRV, both in the absence or presence of dual autonomic blockade. The marked increase in intrinsic HR and coherence of HRV in TG^AC8 mice occurred in the context of: (1) reduced HR and HRV responses to β-adrenergic receptor (β-AR) stimulation; (2) increased transcription of genes and expression of proteins [β-Arrestin, G Protein-Coupled Receptor Kinase 5 (GRK5) and Clathrin Adaptor Protein (Dab2)] that desensitize β-AR signaling within SAN tissue, (3) reduced transcripts or protein levels of enzymes [dopamine beta-hydorxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT)] required for catecholamine production in intrinsic cardiac adrenergic cells, and (4) substantially reduced plasma catecholamine levels. Thus, mechanisms driven by cAMP-PKA-Ca²⁺ signaling intrinsic to SAN cells underlie the marked coherence of TG^AC8 mice HRV. Adaptations to limit additional activation of AC signaling, via decreased neuronal sympathetic input, are utilized to ensure the hearts survival and prevent Ca²⁺ overload.

Mammalian γ2 AMPK regulates intrinsic heart rate

AMPK is a conserved serine/threonine kinase whose activity maintains cellular energy homeostasis. Eukaryotic AMPK exists as αβγ complexes, whose regulatory γ subunit confers energy sensor function by binding adenine nucleotides. Humans bearing activating mutations in the γ2 subunit exhibit a phenotype including unexplained slowing of heart rate (bradycardia). Here, we show that γ2 AMPK activation downregulates fundamental sinoatrial cell pacemaker mechanisms to lower heart rate, including sarcolemmal hyperpolarization-activated current (I f) and ryanodine receptor-derived diastolic local subsarcolemmal Ca2+ release. In contrast, loss of γ2 AMPK induces a reciprocal phenotype of increased heart rate, and prevents the adaptive intrinsic bradycardia of endurance training. Our results reveal that in mammals, for which heart rate is a key determinant of cardiac energy demand, AMPK functions in an organ-specific manner to maintain cardiac energy homeostasis and determines cardiac physiological adaptation to exercise by modulating intrinsic sinoatrial cell behavior.

Long-term low dose dietary resveratrol supplement reduces cardiovascular structural and functional deterioration in chronic heart failure in rats

A short-term exposure to resveratrol at high dosages exerts a remarkable cardioprotective effect. Whether a long-term exposure to resveratrol at low dosages that can be obtained through consumption of a resveratrol-rich diet is beneficial to heart diseases is unknown. We tested the effects of a resveratrol-enriched diet on cardiovascular remodeling of chronic heart failure (CHF) in rats resulting from permanent ligation of left coronary artery. Two weeks after surgery, rats were started on either a resveratrol-enriched (R; 5 mg/kg per day; n = 23) or normal (Control; n = 23) diet for next 10 months. Serial echocardiography in Control showed a significant decline in LV ejection fraction, increases in LV end-systolic and end-diastolic volumes, and expansion in myocardial infarct from pre-treatment values. In R, compared with Control, there were substantial improvements in those parameters. End-point LV pressure-volume loop analysis showed a significantly improved LV systolic function and AV-coupling, an index of energy transfer efficacy between the heart and aortic tree, in R compared with Control (p < 0.05). Aortic pulse wave velocity, a measure of arterial stiffness, was significantly lower in R (389 ± 15 cm/s; p < 0.05) compared with Control (489 ± 38 cm/s). These results demonstrated that long-term dietary resveratrol supplement reduces cardiovascular structural and functional deterioration in CHF.

A Rat Carotid Balloon Injury Model to Test Anti-vascular Remodeling Therapeutics

The rat carotid balloon injury is a well-established surgical model that has been used to study arterial remodeling and vascular cell proliferation. It is also a valuable model system to test, and to evaluate therapeutics and drugs that negate maladaptive remodeling in the vessel. The injury, or barotrauma, in the vessel lumen caused by an inflated balloon via an inserted catheter induces subsequent neointimal growth, often leading to hyperplasia or thickening of the vessel wall that narrows, or obstructs the lumen. The method described here is sufficiently sensitive, and the results can be obtained in relatively short time (2 weeks after the surgery). The efficacy of the drug or therapeutic against the induced-remodeling can be evaluated either by the post-mortem pathological and histomorphological analysis, or by ultrasound sonography in live animals. In addition, this model system has also been used to determine the therapeutic window or the time course of the administered drug. These studies can leadto the development of a better administrative strategy and a better therapeutic outcome. The procedure described here provides a tool for translational studies that bring drug and therapeutic candidates from bench research to clinical applications.

Deterioration of autonomic neuronal receptor signaling and mechanisms intrinsic to heart pacemaker cells contribute to age-associated alterations in heart rate variability in vivo

We aimed to determine how age‐associated changes in mechanisms extrinsic and intrinsic to pacemaker cells relate to basal beating interval variability (BIV) reduction in vivo. Beating intervals (BIs) were measured in aged (23–25 months) and adult (3–4 months) C57BL/6 male mice (i) via ECG in vivo during light anesthesia in the basal state, or in the presence of 0.5 mg mL⁻¹ atropine + 1 mg mL⁻¹ propranolol (in vivo intrinsic conditions), and (ii) via a surface electrogram, in intact isolated pacemaker tissue. BIV was quantified in both time and frequency domains using linear and nonlinear indices. Although the average basal BI did not significantly change with age under intrinsic conditions in vivo and in the intact isolated pacemaker tissue, the average BI was prolonged in advanced age. In vivo basal BIV indices were found to be reduced with age, but this reduction diminished in the intrinsic state. However, in pacemaker tissue BIV indices increased in advanced age vs. adults. In the isolated pacemaker tissue, the sensitivity of the average BI and BIV in response to autonomic receptor stimulation or activation of mechanisms intrinsic to pacemaker cells by broad‐spectrum phosphodiesterase inhibition declined in advanced age. Thus, changes in mechanisms intrinsic to pacemaker cells increase the average BIs and BIV in the mice of advanced age. Autonomic neural input to pacemaker tissue compensates for failure of molecular intrinsic mechanisms to preserve average BI. But this compensation reduces the BIV due to both the imbalance of autonomic neural input to the pacemaker cells and altered pacemaker cell responses to neural input.

Delayed emergence of methamphetamine's enhanced cardiovascular effects in nonhuman primates during protracted methamphetamine abstinence

BACKGROUND

Methamphetamine abuse is linked with brain abnormalities, but its peripheral effects constitute an integral aspect of long-term methamphetamine use.

METHODS

Eight male rhesus monkeys with long histories of intravenous methamphetamine self-administration were evaluated 1 day, and 1, 4, 12, 26, and 52 weeks after their last methamphetamine self-administration session. On test days, isoflurane-anesthetized animals received a 0.35 mg/kg IV methamphetamine challenge. A control group consisted of 10 age and gender matched drug naïve monkeys. Cardiovascular responses to methamphetamine were followed for 2.5h. Echocardiograms were acquired at 3 and 12 months of abstinence and in the control animals.

RESULTS

No pre-methamphetamine baseline differences existed among 7 physiological measures across all conditions and controls. As expected, methamphetamine increased heart rate and blood pressure in controls. However, immediately following the self-administration period, the blood pressure response to methamphetamine challenge was reduced when compared to control monkeys. The peak and 150-min average heart rate increases, as well as peak blood pressure increases following methamphetamine were significantly elevated between weeks 12 to 26 of abstinence. These data indicate the development of tolerance followed by sensitization to methamphetamine cardiovascular effects. Echocardiography demonstrated decreased left ventricular ejection fraction and cardiac output at 3 months of abstinence. Importantly, both cardiovascular sensitization and cardiotoxicity appeared to be reversible as they returned toward control group levels after 1 year of abstinence.

CONCLUSIONS

Enhanced cardiovascular effects may occur after prolonged abstinence in addicts relapsing to methamphetamine and may underlie clinically reported acute cardiotoxic events.

Vessel ultrasound sonographic assessment of soluble receptor for advanced glycation end products efficacy in a rat balloon injury model

Objective

We aimed to assess the therapeutic efficacy of differentially modified soluble receptor for advanced glycation end products (sRAGE) in vivo using vessel ultrasound sonography and to compare the sonography data with those from postmortem histomorphologic analyses to have a practical reference for future clinical applications.

Methods

Vessel ultrasound sonography was performed in a sRAGE-treated rat carotid artery balloon injury model at different time points after the surgery, and therapeutic efficacy of different doses of sRAGE produced in Chinese hamster ovary cells and with different N-glycoform modifications were assessed.

Results

Vessel ultrasound sonography found that sRAGE produced in Chinese hamster ovary cells with complex N-glycoform modifications is highly effective, and is consistent with our recent findings in the same model assessed with histology. We also found that sonography is less sensitive than histology when a higher dose of sRAGE is administered.

Conclusions

Sonograph results are consistent with those obtained from histology; that is, sRAGE produced in Chinese hamster ovary cells has significantly higher efficacy than insect cell-originated sRAGE cells.

Synchronization of sinoatrial node pacemaker cell clocks and its autonomic modulation impart complexity to heart beating intervals

BACKGROUND

A reduction of complexity of heart beating interval variability that is associated with an increased morbidity and mortality in cardiovascular disease states is thought to derive from the balance of sympathetic and parasympathetic neural impulses to the heart. However, rhythmic clocklike behavior intrinsic to pacemaker cells in the sinoatrial node (SAN) drives their beating, even in the absence of autonomic neural input.

OBJECTIVE

To test how this rhythmic clocklike behavior intrinsic to pacemaker cells interacts with autonomic impulses to the heart beating interval variability in vivo.

METHODS

We analyzed beating interval variability in time and frequency domains and by fractal and entropy analyses: (1) in vivo, when the brain input to the SAN is intact; (2) during autonomic denervation in vivo; (3) in isolated SAN tissue (ie, in which the autonomic neural input is completely absent); (4) in single pacemaker cells isolated from the SAN; and (5) after autonomic receptor stimulation of these cells.

RESULTS

Spontaneous beating intervals of pacemaker cells residing in the isolated SAN tissue exhibit fractal-like behavior and have lower approximate entropy compared with those in the intact heart. Isolation of pacemaker cells from SAN tissue, however, leads to a loss in the beating interval order and fractal-like behavior. β-Adrenergic receptor stimulation of isolated pacemaker cells increases intrinsic clock synchronization, decreases their action potential period, and increases system complexity.

CONCLUSIONS

Both the average beating interval in vivo and beating interval complexity are conferred by the combined effects of clock periodicity intrinsic to pacemaker cells and their response to autonomic neural input.

The N-glycoform of sRAGE is the key determinant for its therapeutic efficacy to attenuate injury-elicited arterial inflammation and neointimal growth

Signaling of the receptor for advanced glycation end products (RAGE) has been implicated in the development of injury-elicited vascular complications. Soluble RAGE (sRAGE) acts as a decoy of RAGE and has been used to treat pathological vascular conditions in animal models. However, previous studies used a high dose of sRAGE produced in insect Sf9 cells (sRAGE(Sf9))and multiple injections to achieve the therapeutic outcome. Here, we explore whether modulation of sRAGE N-glycoform impacts its bioactivity and augments its therapeutic efficacy. We first profiled carbohydrate components of sRAGE produced in Chinese hamster Ovary cells (sRAGE(CHO)) to show that a majority of its N-glycans belong to sialylated complex types that are not shared by sRAGE(Sf9). In cell-based NF-κB activation and vascular smooth muscle cell (VSMC) migration assays, sRAGE(CHO) exhibited a significantly higher bioactivity relative to sRAGE(Sf9) to inhibit RAGE alarmin ligand-induced NF-κB activation and VSMC migration. We next studied whether this N-glycoform-associated bioactivity of sRAGE(CHO) is translated to higher in vivo therapeutic efficacy in a rat carotid artery balloon injury model. Consistent with the observed higher bioactivity in cell assays, sRAGE(CHO) significantly reduced injury-induced neointimal growth and the expression of inflammatory markers in injured vasculature. Specifically, a single dose of 3 ng/g of sRAGE(CHO) reduced neointimal hyperplasia by over 70%, whereas the same dose of sRAGE(Sf9) showed no effect. The administered sRAGE(CHO) is rapidly and specifically recruited to the injured arterial locus, suggesting that early intervention of arterial injury with sRAGE(CHO) may offset an inflammatory circuit and reduce the ensuing tissue remodeling. Our findings showed that the N-glycoform of sRAGE is the key determinant underlying its bioactivity and thus is an important glycobioengineering target to develop a highly potent therapeutic sRAGE for future clinical applications.

KEY MESSAGE

The specific N-glycoform modification is the key underlying sRAGE bioactivity Markedly reduced sRAGE dose to attenuate neointimal hyperplasia and inflammation Provide a molecular target for glycobioengineering of sRAGE as a therapeutic protein Blocking RAGE alarmin ligands during acute injury phase offsets neointimal growth.

Chronic administration of small nonerythropoietic peptide sequence of erythropoietin effectively ameliorates the progression of postmyocardial infarction-dilated cardiomyopathy

The cardioprotective properties of erythropoietin (EPO) in preclinical studies are well documented, but erythropoietic and prothrombotic properties of EPO preclude its use in chronic heart failure (CHF). We tested the effect of long-term treatment with a small peptide sequence within the EPO molecule, helix B surface peptide (HBSP), that possesses tissue-protective, but not erythropoietic properties of EPO, on mortality and cardiac remodeling in postmyocardial infarction-dilated cardiomyopathy in rats. Starting 2 weeks after permanent left coronary artery ligation, rats received i.p. injections of HBSP (60 µg/kg) or saline two times per week for 10 months. Treatment did not elicit an immune response, and did not affect the hematocrit. Compared with untreated rats, HBSP treatment reduced mortality by 50% (P < 0.05). Repeated echocardiography demonstrated remarkable attenuation of left ventricular dilatation (end-diastolic volume: 41 versus 86%; end-systolic volume: 44 versus 135%; P < 0.05), left ventricle functional deterioration (ejection fraction: -4 versus -63%; P < 0.05), and myocardial infarction (MI) expansion (3 versus 38%; P < 0.05). A hemodynamic assessment at study termination demonstrated normal preload independent stroke work (63 ± 5 versus 40 ± 4; P < 0.05) and arterioventricular coupling (1.2 ± 0.2 versus 2.7 ± 0.7; P < 0.05). Histologic analysis revealed reduced apoptosis (P < 0.05) and fibrosis (P < 0.05), increased cardiomyocyte density (P < 0.05), and increased number of cardiomyocytes in myocardium among HBSP-treated rats. The results indicate that HBSP effectively reduces mortality, ameliorates the MI expansion and CHF progression, and preserves systolic reserve in the rat post-MI model. There is also a possibility that HBSP promoted the increase of the myocytes number in the myocardial wall remote from the infarct. Thus, HBSP peptide merits consideration for clinical testing.

Acute hemodynamic effects of erythropoietin do not mediate its cardioprotective properties

Activation of nitric oxide (NO) signaling is considered, at list partially, a mechanistic basis for EPO-induced cardioprotection. Surprisingly, hemodynamic response subsequent to NO activation after EPO administration has never been reported. The objectives of this study were to evaluate the acute hemodynamic and cardiovascular responses to EPO administration, to confirm their NO genesis, and to test the hypothesis that EPO-induced cardioprotection is mediated through cardiovascular changes related to NO activation. In Experiment 1, after 3000 U/kg of rhEPO was administered intravenously to Wistar rats, arterial blood pressure, monitored via indwelling catheter, progressively declined almost immediately until it leveled off 90 minutes after injection at 20% below control level. In Experiment 2 the 25% reduction of mean blood pressure, compared to control group, was observed 2 hours after intravenous injection of either 3000 or 150 U/kg of rhEPO. Detailed pressure–volume loop analyses of cardiac performance (Experiment 3) 2 hours after intravenous injection of human or rat recombinant EPO (3000 U/kg) revealed a significant reduction of systolic function (PRSW was 33% less than control). Reduction of arterial blood pressure and systolic cardiac function in response to rhEPO were blocked in rats pretreated with a non-selective inhibitor of nitric oxide synthase (L-NAME). In Experiment 4, 24 hours after a permanent ligation of a coronary artery, myocardial infarction (MI) measured 26±3.5% of left ventricle in untreated rats. MI in rats treated with 3000 U/kg of rhEPO immediately after coronary ligation was 56% smaller. Pretreatment with L-NAME did not attenuate the beneficial effect of rhEPO on MI size, while MI size in rats treated with L-NAME alone did not differ from control. Therefore, a single injection of rhEPO resulted in a significant, NO-mediated reduction of systemic blood pressure and corresponding reduction of cardiac systolic function. However, EPO-induced protection of myocardium from ischemic damage is not associated with NO activation or NO-mediated hemodynamic responses.

Fenoterol enantiomers do not possess beneficial therapeutic properties of their racemic mixture in the rat model of post myocardial infarction dilated cardiomyopathy

PURPOSE

A salutary effect of β(2) adrenergic receptor (AR) agonist, fenoterol has been demonstrated in a rat model of post-myocardial infarction (MI) dilated cardiomyopathy (DCM). Recent reports on single cardiomyocyte experiments suggested that out of two enantiomers, RR and SS, that constitute a racemic mixture of fenoterol, only RR-enantiomer is an active component that might be a promising new drug for treatment of chronic heart failure. The objective of this study was to compare the efficacy of the RR enantiomer of fenoterol with efficacy of racemic fenoterol, and SS, an inactive enantiomer, in whole animal experimental models of DCM.

METHODS

Two weeks after induction of MI by permanent ligation of the anterior descending coronary artery early cardiac remodeling and MI size were assessed via echocardiography and rats were divided into treatment groups. Treatment (placebo, racemic fenoterol, RR- or SS-enantiomers of fenoterol) continued for 6 months while progression of DCM was followed by serial echocardiography.

RESULTS

Compared with untreated rats, rats treated with racemic fenoterol demonstrated previously described attenuation of LV remodeling, functional decline and the arrest of the MI expansion during the first 2 months of treatment. On the contrary, the treatment with either RR-, or with SS-enantiomers of fenoterol was completely ineffective.

CONCLUSION

The conclusion drawn on the basis of previous experiments with single cardiomyocytes that RR-enantiomer of fenoterol represents an active component of racemic fenoterol and can be further investigated as a new drug for treatment of chronic heart failure was not confirmed in the whole animal model of DCM.

Effects of calorie restriction on cardioprotection and cardiovascular health

Multiple health benefits of calorie restriction (CR) and alternate day fasting (ADF) regimens are widely recognized. Experimental data concerning the effects of calorie restriction on cardiac health are more controversial, ranging from evidence that ADF protects heart from ischemic damage but results in developing of diastolic dysfunction, to reports that CR ameliorates the age-associated diastolic dysfunction. Here we investigated the effects of chronic CR on morphology and function of the cardiovascular system of aged rats and cardioprotective effect of CR against ischemic damage in the experimental rat model of MI. Cardiovascular fitness of 24-month old Fisher 344 rats maintained through life on ad libitum (AL) or CR diets was extensively evaluated via echocardiography, dobutamine stress test, pressure-volume loop analyses, pulse wave velocity measurements, and histology. Groups of 2-month old AL and 29-month old CR rats were studied for comparison. Myocardial infarction (MI) was induced by a permanent ligation of the anterior descending coronary artery in 5-month old rats maintained for 3 months on CR or AL. MI size was evaluated histologically 24 hrs following coronary ligation. Cardiac remodeling was followed-up via echocardiography. Age-associated changes in 24-month old rats consisted of 33% increase of fibrosis in the myocardium and more than 2 fold increase of the collagen in the tunica media of the aorta. There was a significant decrease in the density and total number of cardiomyocytes, while their size was increased. These morphological changes were manifested in a decline of systolic and diastolic cardiac function, increase of left ventricular and aortic stiffness, and arterio-ventricular uncoupling. Tachycardic response to dobutamine challenge was absent in the old rats. Compared to AL rats, 24-month old CR rats had reduced levels of cardiac and aortic fibrosis, increased density of cardiomyocytes that were smaller in size, attenuated diastolic dysfunction, normal systolic function and arterio-ventricular coupling. Tachycardic response to dobutamine was also intact in CR 24-month old rats and aortic stiffness was reduced. Adjustment for body weight differences through ratiometric or allometric scaling did not affect the overall pattern of differences between AL and CR rats. Attenuation of morphological and functional age-associated changes in 24-month old CR rats either was not observed at all or was smaller in 29-month old CR rats. Size of MI induced by a permanent coronary ligation as well as post-MI cardiac remodeling and function were similar in CR and AL rats. CR does not increase tolerance of myocardium to ischemic damage, but attenuates the age-associated changes in the heart and major vessels. The attenuation of age-associated changes by CR cannot be explained by the effect of lower body weight but are attributable to more intimate cellular mechanisms of CR itself. Attenuation of age-associated changes by CR waned with advancing age, and is consistent with the idea that CR postponed senescence.

A small nonerythropoietic helix B surface peptide based upon erythropoietin structure is cardioprotective against ischemic myocardial damage

Strong cardioprotective properties of erythropoietin (EPO) reported over the last 10 years have been difficult to translate to clinical applications for ischemic cardioprotection owing to undesirable parallel activation of erythropoiesis and thrombogenesis. A pyroglutamate helix B surface peptide (pHBP), recently engineered to include only a part of the EPO molecule that does not bind to EPO receptor and thus, is not erythropoietic, retains tissue protective properties of EPO. Here we compared the ability of pHBP and EPO to protect cardiac myocytes from oxidative stress in vitro and cardiac tissue from ischemic damage in vivo. HBP, similar to EPO, increased the reactive oxygen species (ROS) threshold for induction of the mitochondrial permeability transition by 40%. In an experimental model of myocardial infarction induced by permanent ligation of a coronary artery in rats, a single bolus injection of 60 μg/kg of pHBP immediately after coronary ligation, similar to EPO, reduced apoptosis in the myocardial area at risk, examined 24 h later, by 80% and inflammation by 34%. Myocardial infarction (MI) measured 24 h after coronary ligation was similarly reduced by 50% in both pHBP- and EPO-treated rats. Two wks after surgery, left ventricular remodeling (ventricular dilation) and functional decline (fall in ejection fraction) assessed by echocardiography were significantly and similarly attenuated in pHBP- and EPO-treated rats, and MI size was reduced by 25%. The effect was retained during the 6-wk follow-up. A single bolus injection of pHBP immediately after coronary ligation was effective in reduction of MI size in a dose as low as 1 μg/kg, but was ineffective at a 60 μg/kg dose if administered 24 h after MI induction. We conclude that pHBP is equally cardioprotective with EPO and deserves further consideration as a safer alternative to rhEPO in the search for therapeutic options to reduce myocardial damage following blockade of the coronary circulation.

β₂ AR agonists in treatment of chronic heart failure: long path to translation

The main clinical manifestations of advanced chronic heart failure (CHF), e.g. in dilated cardiomyopathy (DCM), are reduced systolic and diastolic functions, increased arterial elastance and arterio-ventricular uncoupling, accompanied and exacerbated by an excessive sympathetic activation and extensive abnormalities in the βAR signaling. Loss of cardiomyocytes due to apoptosis is one mechanism that undoubtedly contributes to cardiac remodeling and functional deterioration associated with dilated cardiomyopathy (DCM). Research during the last decade on the single cardiomyocyte level strongly suggested that selective stimulation of β(1) AR activates the proapoptotic signaling pathways, while selective stimulation of β(2) AR is antiapoptotic, but its precise mechanisms remain to be elucidated. Extensive research in the rat model of DCM following induction of myocardial infarction (MI) showed that prolonged treatment with of β(2) AR agonist, fenoterol, in combination with a β(1) AR blocker, metoprolol, is more effective than β(1) AR blocker alone and as effective as β(1) AR blocker with ACE inhibitor with respect to survival and cardiac remodeling. This combined regimen of β(2) AR agonists and a β(1) AR blocker might be considered for clinical testing as alternative or adjunct therapy to currently acceptable CHF arsenal. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Chronic alternate-day fasting results in reduced diastolic compliance and diminished systolic reserve in rats

BACKGROUND

Based on animal experiments and limited data from the few human trials, alternate-day fasting (ADF) resulted in weight loss, prolonged life, reduced metabolic risk factors for diabetes and cardiovascular diseases, and reduced prevalence of age-related diseases. The present study is the first comprehensive examination of the long-term effects of ADF on general cardiovascular fitness in rats.

METHODS AND RESULTS

Four-month-old male Sprague-Dawley rats were started on ADF or continued on ad libitum diets and followed for 6 months with serial echocardiography. A comprehensive hemodynamic evaluation including a combined dobutamine-volume stress test was performed at the end of the study, and hearts were harvested for histological assessment. The 6-month-long ADF diet resulted in a 9% reduction (P < .01) of cardiomyocyte diameter and 3-fold increase in interstitial myocardial fibrosis. Left ventricular chamber size was not affected by ADF and ejection fraction was not reduced, but left atrial diameter was increased 16%, and the ratio of early (E) and late atrial (A) waves, in Doppler-measured mitral flow was reduced (P < .01). Pressure-volume loop analyses revealed a "stiff" heart during diastole in ADF rats, whereas combined dobutamine and volume loading showed a significant reduction in left ventricular diastolic compliance and a lack of increase in systolic pump function, indicating a diminished cardiac reserve.

CONCLUSION

Chronic ADF in rats results in development of diastolic dysfunction with diminished cardiac reserve. ADF is a novel and unique experimental model of diet-induced diastolic dysfunction. The deleterious effect of ADF in rats suggests that additional studies of ADF effects on cardiovascular functions in humans are warranted.

Survival and cardioprotective benefits of long-term blueberry enriched diet in dilated cardiomyopathy following myocardial infarction in rats

Background

Despite remarkable progress in treatment of chronic heart failure (CHF) over the last two decades, mortality, personal suffering and cost remain staggering, and effective interventions are still a challenge. Previously we reported that a blueberry-enriched diet (BD) attenuated necroapoptosis and inflammation in periinfarct area in a rat model of myocardial infarction (MI).

Objectives

To test the hypothesis that BD will attenuate the course of CHF, including mortality and cardiac remodeling during the first year after induction of MI in rats.

Method and Results

Two weeks after coronary artery ligation, rats were divided into two groups of similar average MI size, measured by echocardiography, and then12-mo dietary regimens were initiated as follows: ad libitum regular diet (control, CD, n = 27) and isocaloric food with 2% blueberry supplement (BD, n = 27) also available ad libitum. These dietary groups were compared to each other and to sham group (SH). Mortality over the 12 mo was reduced by 22% in BD compared with CD (p<0.01). In the course of developing CHF, BD had no effect on the body weight, heart rate or blood pressure. Bi-monthly Echo revealed significant attenuation of the LV chamber remodeling, LV posterior wall thinning, and MI expansion in BD compared with CD. In fact, BD arrested the MI expansion.

Conclusion

This is the first experimental evidence that a blueberry-enriched diet has positive effects on the course of CHF and thus warrants consideration for clinical evaluation.

Cardioprotective effect of intermittent fasting is associated with an elevation of adiponectin levels in rats

It has been reported that dietary energy restriction, including intermittent fasting (IF), can protect heart and brain cells against injury and improve functional outcome in animal models of myocardial infarction (MI) and stroke. Here we report that IF improves glycemic control and protects the myocardium against ischemia-induced cell damage and inflammation in rats. Echocardiographic analysis of heart structural and functional variables revealed that IF attenuates the growth-related increase in posterior ventricular wall thickness, end systolic and diastolic volumes, and reduces the ejection fraction. The size of the ischemic infarct 24 h following permanent ligation of a coronary artery was significantly smaller, and markers of inflammation (infiltration of leukocytes in the area at risk and plasma IL-6 levels) were less, in IF rats compared to rats on the control diet. IF resulted in increased levels of circulating adiponectin prior to and after MI. Because recent studies have shown that adiponectin can protect the heart against ischemic injury, our findings suggest a potential role for adiponectin as a mediator of the cardioprotective effect of IF.

Therapeutic angiogenesis induced by injecting hepatocyte growth factor in ischemic canine hearts

PURPOSE

Therapeutic angiogenesis, induced by the direct injection of angiogenic growth factors or by transmyocardial laser revascularization (TMLR), has shown great potential as a new therapeutic strategy for end-stage coronary artery disease. However, no significant differences in angiogenic effects of TMLR and vascular endothelial growth factor (VEGF) have been reported. We compared the effects of the intramyocardial injection of hepatocyte growth factor (HGF), a novel angiogenic factor, with those of TMLR, by evaluating the improvement in regional blood flow and regional function in a canine heart model of chronic ischemia.

METHODS

To create a model of chronic ischemia, we ligated the left anterior descending artery (LAD) in 15 beagles. We divided the dogs into three groups according to the treatment given 1 month after ligation. Four dogs were given an intracardial injection of human recombinant HGF (H group), six dogs were given TMLR (T group), and five dogs were used as a control (C group). We compared the degree of improvement in regional blood flow and regional function 1 month after the treatment.

RESULTS

The regional myocardial blood flow and function were significantly better in the H group than in the T or C groups (P < 0.05). Histologically, there were significantly more von Willebrand factor-positive cells in the LAD region in the H group than in the T or C groups.

CONCLUSION

The intramural injection of recombinant human HGF resulted in therapeutic angiogenesis with an intrinsic contractile state, and it may have greater advantages than TMLR for the treatment of chronic ischemic heart disease.

Pharmacological Stimulation of β 2-adrenergic Receptors (β 2AR) Enhances Therapeutic Effectiveness of β 1AR Blockade in Rodent Dilated Ischemic Cardiomyopathy

BACKGROUND

We have reported that beta2 adrenoreceptor (beta2AR) stimulation is anti-apoptotic, and has strong beneficial effect on cardiac remodeling in an experimental model of post myocardial infarction chronic heart failure (CHF) in rats. Here we investigate whether the addition of chronic pharmacological beta2AR stimulation enhances the therapeutic effects of beta1AR blockade on cardiac remodeling in the same model.

METHODS AND RESULTS

Metoprolol, a beta1AR blocker, given alone (beta1) or in combination with beta2AR agonist, fenoterol (beta1beta2) were administered to rats via drinking water for 6 weeks, beginning 2 weeks following permanent coronary ligation. Progressive left ventricular (LV) remodeling of untreated animals, assessed by repeated echocardiography, occurred during the observation time, i.e., 42% and 25% increases in end-systolic and end-diastolic LV volumes respectively, 27% fall in ejection fraction, and 35% infarct expansion. Pressure-volume loop analyses at 2d and 8th post infarction weeks showed continuous deterioration of systolic and diastolic functions and arterio-ventricular mismatch. Histological evaluation at the end of 8 weeks revealed the MI expansion and hypertrophy of cardiomyocytes. beta1beta2 prevented LV remodeling, MI expansion and cardiomyocytes hypertrophy to a greater degree than beta1, due, in large part, to a vasodilatory effect of beta2AR stimulation and thus improvement of arterio-ventricular mismatch. The abnormal diastolic performance improved only in beta1beta2. beta1beta2 treatment reduced myocardial apoptosis throughout myocardium, but beta1 reduced apoptosis only in the areas remote from MI.

CONCLUSION

The therapeutic effects of chronic beta1AR blockade on cardiac remodeling of heart failure are enhanced and extended when supplemented with beta2AR stimulation.

Cardioprotection by intermittent fasting in rats

BACKGROUND

Intermittent fasting (IF), a dietary regimen in which food is available only every other day, increases the life span and reduces the incidence of age-associated diseases in rodents. We have reported neuroprotective effects of IF against ischemic injury of the brain. In this study, we examined the effects of IF on ischemic injury of the heart in rats.

METHODS AND RESULTS

After 3 months of IF or regular every-day feeding (control) diets started in 2-month-old rats, myocardial infarction (MI) was induced by coronary artery ligation. Twenty-four hours after MI, its size in the IF group was 2-fold smaller, the number of apoptotic myocytes in the area at risk was 4-fold less, and the inflammatory response was significantly reduced compared with the control diet group. Serial echocardiography revealed that during 10 weeks after MI (with continuation of the IF regimen), the left ventricular (LV) remodeling and MI expansion that were observed in the control diet group were absent in the IF group. In a subgroup of animals with similar MI size at 1 week after MI, further observation revealed less remodeling, better LV function, and no MI expansion in the IF group compared with the control group.

CONCLUSIONS

IF protects the heart from ischemic injury and attenuates post-MI cardiac remodeling, likely via antiapoptotic and antiinflammatory mechanisms.

Beneficial Effects of Chronic Pharmacological Manipulation of β-Adrenoreceptor Subtype Signaling in Rodent Dilated Ischemic Cardiomyopathy

Background— Studies in isolated cardiac myocytes have demonstrated that signaling via specific β 1 -adrenergic receptor subtypes (β 1 ARs) promotes but that signaling via β 2 ARs protects from cell death. We hypothesized that prolonged β 2 AR stimulation or β 1 AR blockade would each protect myocytes from death and thereby ameliorate cardiac remodeling in chronic heart failure.

Methods and Results— A large myocardial infarction (MI) induced in rats by coronary artery ligation resulted in a dilated cardiomyopathy (DCM) characterized by infarct expansion and a progressive increase in left ventricular (LV) end-diastolic volume, accompanied by a reduction in ejection fraction (EF), as assessed by repeated echocardiography. Pressure-volume analysis at 8 weeks after ligation showed that diastolic stiffness (Eed) and arterial elastance (Ea) were increased, end-systolic elastance (Ees) was decreased, and arterioventricular (AV) coupling (Ea/Ees) had deteriorated. Apoptosis was present in both peri-infarct and remote myocardium. Chronic (6-week) administration of the β 2 AR agonists fenoterol or zinterol, starting at 2 weeks after MI, reduced the extent of LV dilation, infarct expansion, and EF decline. The β 1 AR blocker metoprolol did not affect the former and preserved EF to a lesser extent than did the β 2 AR agonists. At 8 weeks after ligation, apoptosis was reduced by all drugs but to a greater extent by β 2 AR agonists than by the β 1 AR blocker. Both β 2 AR agonists and the β 1 AR blocker improved AV coupling, the former mainly by reducing Ea and the latter mainly by increasing Ees. Only the β 2 AR agonists reduced the Eed and the MI size by reducing infarct expansion.

Conclusions— These results provide proof of concept for the efficacy of chronic β 2 AR stimulation in this DCM model.

Erythropoietin reduces myocardial infarction and left ventricular functional decline after coronary artery ligation in rats

Erythropoietin (EPO), well known for its role in stimulation of erythropoiesis, has recently been shown to have a dramatic neuroprotective effect in animal models of cerebral ischemia, mechanical trauma of the nervous system, and excitotoxins, mainly by reducing apoptosis. We studied the effect of single systemic administration of recombinant human EPO (rhEPO) on left ventricular (LV) size and function in rats during 8 weeks after the induction of a myocardial infarction (MI) by permanent ligation of the left descending coronary artery. We found that an i.p. injection of 3,000 units/kg of rhEPO immediately after the coronary artery ligation resulted, 24 h later, in a 50% reduction of apoptosis in the myocardial area at risk. Eight weeks after the induction of MI, rats treated with rhEPO had an infarct size 15-25% of the size of that in untreated animals. The reduction in myocardial damage was accompanied by reductions in LV size and functional decline as measured by repeated echocardiography. Thus, a single dose of rhEPO administered around the time of acute, sustained coronary insufficiency merits consideration with respect to its therapeutic potential to limit the extent of resultant MI and contractile dysfunction.

Gene transfer of hepatocyte growth factor improves angiogenesis and function of chronic ischemic myocardium in canine heart

BACKGROUND

Hepatocyte growth factor (HGF) induces angiogenesis in myocardium. In the present study, its effects in chronic ischemic myocardium were tested.

METHODS

Four weeks after left anterior descending coronary artery ligation in canine hearts, HVJ-liposome containing either human HGF gene (160 microg; HGF group, n = 7) or nothing (control group, n = 6) was directly injected into ischemic myocardium. Four weeks after gene transfection, the thickness fraction (TF), an index of regional myocardial contractility (assessed by epicardial pulse-Doppler crystals), the myocardial perfusion flow (assessed by color microspheres), and the capillary density (assessed by immunostaining of vessels) were evaluated in ischemic myocardium.

RESULTS

Thickness fraction (percent of nonischemic myocardium) was significantly improved in the HGF group (80 +/- 15 from 52 +/- 16 of pregene; p < 0.05) whereas it was not changed in the control group (52 +/- 10 from 50 +/- 8 of pregene). The perfusion flow (% of nonischemic myocardium) was significantly improved in the HGF group (98 +/- 17 from 51 +/- 14 of pregene; p < 0.05) while it was not changed in the Control group (58 +/- 13 from 62 +/- 18 of pregene). The capillary density was significantly higher in the HGF group (894 +/- 211/mm2; p < 0.05) than that in the control group (511 +/- 127/mm2).

CONCLUSIONS

Gene transfection of HGF improved angiogenesis, thereby improved regional myocardial function and perfusion in chronic ischemic myocardium. It indicates a potent therapeutic value of HGF gene transfection for chronic ischemic heart diseases such as myocardial infarction.

Gene transfection of hepatocyte growth factor attenuates cardiac remodeling in the canine heart: A novel gene therapy for cardiomyopathy

OBJECTIVE

Hepatocyte growth factor, a potent angiogenic agent, is unique in having the effects of antiapoptosis and antifibrosis. In the present study we used the rapid pacing-induced heart failure canine model to investigate the effect of gene transfection of hepatocyte growth factor on the failing heart.

METHODS

Four weeks after onset of rapid pacing, either the human hepatocyte growth factor gene (160 microg; hepatocyte growth factor group, n = 7) or empty vector (control group, n = 7) was directly injected into the left ventricular myocardium by means of the hemagglutinating virus of Japan liposome method.

RESULTS

At 4 weeks after gene transfection, the left ventricular global function, assessed by means of pressure-volume loop analysis, was improved in the hepatocyte growth factor group as preload-recruitable stroke work (percentage of baseline: 80% +/- 20% from 38% +/- 15% before gene transfection, P =.005), whereas it was not changed in the control group (50% +/- 18% from 50% +/- 18%). Weekly echocardiography showed that this improvement began in the week after gene transfer. The hearts in the hepatocyte growth factor group had a large wall thickness, large myocyte diameter, high capillary density, low fibrotic area fraction, and low density of apoptotic nuclei revealed by means of histologic analysis compared with that in the control group. Myocardial perfusion flow, assessed with color microspheres, was increased in the hepatocyte growth factor group (percentage of baseline: 79% +/- 16% from 48% +/- 14%, P =.010), whereas it was reduced in the control group (30% +/- 12% from 45% +/- 17%).

CONCLUSIONS

Gene transfection of hepatocyte growth factor promoted angiogenesis, improved perfusion, decreased fibrosis and apoptosis, promoted recovery from myocyte atrophy, and thereby attenuated cardiac remodeling and improved myocardial function in the failing heart. It is a novel gene therapy for human heart failure.

Cardioprotective effect of diadenosine tetraphosphate (AP4A) cardioplegia in isolated rat hearts

Preischemic administration of diadenosine tetraphosphate (AP4A) has been shown to be cardioprotective. We evaluated the protective effect of AP4A when used as a cardioplegic adjuvant and tested contributions of the ATP-sensitive potassium channel (K ATP channel), adenosine receptor (AR), and purine 2y receptor (P2yR) to the effect of AP4A. Isolated buffer-perfused rat hearts were subjected to 23 min of ischemia (37 degrees C) followed by 20 min of reperfusion. Cardioplegia solution (St. Thomas Hospital solution) was infused during the first 3 min of ischemia. AP4A (10 microM) or AP4A with glibenclamide (K ATP channel blocker, 100 microM), 8-SPT (AR antagonist, 300 microM) or reactive blue (P2yR antagonist, 13 nM) were added to the cardioplegia solution. Compared with the cardioplegia solution alone, administration of AP4A with the solution significantly increased the recovery of rate-pressure production (75% +/- 11% vs 58% +/- 10%; P < 0.05) and dp/dt at the end of reperfusion, and reduced the leakage of creatine kinase (3.2 +/- 3.7 vs 13.2 +/- 10.1 IU/g; P < 0.05) during reperfusion. This effect was reversed by coadministration of glibenclamide or reactive blue but not 8-SPT. The addition of AP4A into the cardioplegia solution led to an added cardioprotective effect, either by opening the K ATP channel or by activating P2yR.

Myocardial protection using diadenosine tetraphosphate with pharmacological preconditioning

BACKGROUND

We have reported a similar cardioprotective effect and mechanism of diadenosine tetraphosphate (AP4A) and ischemic preconditioning in rat hearts. In this study, the applicability of AP4A administration to cardiac surgery was tested by using a canine cardiopulmonary bypass model.

METHODS

Hearts underwent 60 minutes of cardioplegic arrest (34 degrees C) by a single dose of cardioplegia. Cardioplegia contained either AP4A (40 micromol/L; n = 6) or saline (n = 6). Beagles were weaned from cardiopulmonary bypass 30 minutes after reperfusion, and left ventricular function was evaluated after another 30 minutes by using the cardiac loop analysis system.

RESULTS

Administration of AP4A significantly improved the postischemic recovery of cardiac function and reduced the leakage of serum creatine kinase compared with saline. Systemic vascular resistance, mean aortic blood pressure, and the electrocardiographic indices were not significantly altered by AP4A administration.

CONCLUSIONS

Administration of AP4A was cardioprotective without apparent adverse effects. Because the cardioprotective mechanism may be similar to that of ischemic preconditioning, the addition of AP4A into cardioplegia may be a novel safe method for clinical application of preconditioning cardioprotection.

Diadenosine tetraphosphate (AP4A) mimics cardioprotective effect of ischemic preconditioning in the rat heart: contribution of KATP channel and PKC

Diadenosine tetraphosphate (AP4A) administration is reported to mimic the effect of ischemic preconditioning (PC) via purine 2y receptors (P2yR) and adenosine receptors. This study was designed to test the contributions of the ATP-sensitive potassium channel (KATP channel) and protein kinase C (PKC), two of the main regulator in PC, to the effect of AP4A. Isolated buffer-perfused rat hearts were subjected to 20 min of global ischemia (37 degrees C) and 20 min of reperfusion. Three cycles of 1-min ischemia and 3-min reperfusion induced PC. Chemicals were administrated for 2 min before 20 min of ischemia. AP4A (10 microM) administration was as effective as PC in improving the recovery of post-ischemic contractile function and reducing creatine kinase leakage after reperfusion, whereas adenosine (10 and 100 microM) have not effect. AP4A had not effect on reperfusion-induced arrhythmia, whereas PC significantly prevented it. These effects of AP4A and PC were reversed by co-administration of glibenclimade (KATP channel blocker, 100 microM) and GF109203X (PKC inhibitor, 10 microM); the effects of AP4A but not PC were reversed by co-administration of reactive blue (P2yR antagonist, 13 nM). AP4A appears to activate the KATP channel and PKC via P2yR mimic the effects of PC in part. The role of P2yR indicated that trigger mechanism of the effect of PC and AP4A administration might differ in rat hearts.

Cardioprotective effect of diadenosine tetraphosphate (AP4A) preservation in hypothermic storage and its relation with mitochondrial ATP-sensitive potassium channels

BACKGROUND

The preconditioning effect of diadenosine tetraphosphate (AP4A) was reported in ischemia/reperfused hearts, but its effect in heart preservation was unknown. According to the possible role of mitochondrial ATP-sensitive potassium channel (mK(ATP) channel) in the effect of ischemic preconditioning, the contribution of mK(ATP) channel to the effect of AP4A was tested.

METHODS

Isolated rat hearts were arrested and preserved by Eurocollin's (EC) solution at 4 degrees C for 8 hr. AP4A (80 microM) or AP4A with the 5-hydroxydecanoic acid (100 microM), a selective inhibitor of the mK(ATP) channel, was added into the EC solution. The preischemic and postischemic cardiac functions were evaluated on a buffer-perfused Langendorff apparatus before storage and after 20 min of reperfusion.

RESULTS

AP4A administration improved the recovery of poststorage cardiac functions (the rate-pressure production, left ventricular systolic pressure, heart rate, coronary flow rate, and derivative of left ventricular systolic pressure; P<0.05) and reduced the leakage of lactate dehydrate and creatine kinase during reperfusion, compared with EC alone. Those effects of AP4A were completely reversed by 5-hydroxydecanoic acid administration in combination subjects.

CONCLUSION

AP4A administration protects the heart through opening of the mK(ATP) channel during hypothermic preservation. Thus, addition of AP4A into cardioplegia may be a novel method of ischemic preconditioning in the transplantation context.