Sunil K. Dhar

Improvement of Cardiac Function by a Cardiac Myosin Activator in Conscious Dogs With Systolic Heart Failure

Background—Therapy for chronic systolic heart failure (sHF) has improved over the past 2 decades, but the armamentarium of drugs is limited and consequently sHF remains a leading cause of death and disability. In this investigation, we examined the effects of a novel cardiac myosin activator, omecamtiv mecarbil (formerly CK-1827452) in 2 different models of heart failure. Methods and Results—Two different models of sHF were used: (1) pacing-induced sHF after myocardial infarction (MI-sHF) and (2) pacing-induced sHF after 1 year of chronic pressure overload left ventricular hypertrophy (LVH-sHF). Omecamtiv mecarbil increased systolic function in sHF dogs, chronically instrumented to measure LV pressure, wall thickness, and cardiac output. Omecamtiv mecarbil, infused for 24 hours, induced a sustained increase without desensitization (P<0.05) in wall thickening (25±6.2%), stroke volume (44±6.5%) and cardiac output (22±2.8%), and decreased heart rate (15±3.0%). The major differences between the effect of omecamtiv mecarbil on cardiac function and the effect induced by a catecholamine, for example, dobutamine, is that omecamtiv mecarbil did not increase LV dP/dt but rather increased LV systolic ejection time by 26±2.9% in sHF. Another key difference is that myocardial O2 consumption (MVO2), which increases with catecholamines, was not significantly affected by omecamtiv mecarbil. Conclusions—These results demonstrate that chronic infusion of the cardiac myosin activator, omecamtiv mecarbil, improves LV function in sHF without the limitations of progressive desensitization and increased MVO2. This unique profile may provide a new therapeutic approach for patients with sHF.

Proteasome inhibition decreases cardiac remodeling after initiation of pressure overload

We tested the possibility that proteasome inhibition may reverse preexisting cardiac hypertrophy and improve remodeling upon pressure overload. Mice were submitted to aortic banding and followed up for 3 wk. The proteasome inhibitor epoxomicin (0.5 mg/kg) or the vehicle was injected daily, starting 2 wk after banding. At the end of the third week, vehicle-treated banded animals showed significant (P<0.05) increase in proteasome activity (PA), left ventricle-to-tibial length ratio (LV/TL), myocyte cross-sectional area (MCA), and myocyte apoptosis compared with sham-operated animals and developed signs of heart failure, including increased lung weight-to-TL ratio and decreased ejection fraction. When compared with that group, banded mice treated with epoxomicin showed no increase in PA, a lower LV/TL and MCA, reduced apoptosis, stabilized ejection fraction, and no signs of heart failure. Because overload-mediated cardiac remodeling largely depends on the activation of the proteasome-regulated transcription factor NF-kappaB, we tested whether epoxomicin would prevent this activation. NF-kappaB activity increased significantly upon overload, which was suppressed by epoxomicin. The expression of NF-kappaB-dependent transcripts, encoding collagen types I and III and the matrix metalloprotease-2, increased (P<0.05) after banding, which was abolished by epoxomicin. The accumulation of collagen after overload, as measured by histology, was 75% lower (P<0.05) with epoxomicin compared with vehicle. Myocyte apoptosis increased by fourfold in hearts submitted to aortic banding compared with sham-operated hearts, which was reduced by half upon epoxomicin treatment. Therefore, we propose that proteasome inhibition after the onset of pressure overload rescues ventricular remodeling by stabilizing cardiac function, suppressing further progression of hypertrophy, repressing collagen accumulation, and reducing myocyte apoptosis.

H11 Kinase/Heat Shock Protein 22 Deletion Impairs Both Nuclear and Mitochondrial Functions of STAT3 and Accelerates the Transition Into Heart Failure on Cardiac Overload

Background— Cardiac overload, a major cause of heart failure, induces the expression of the heat shock protein H11 kinase/Hsp22 (Hsp22). Methods and Results— To determine the specific function of Hsp22 in that context, a knockout mouse model of Hsp22 deletion was generated. Although comparable to wild-type mice in basal conditions, knockout mice exposed to pressure overload developed less hypertrophy and showed ventricular dilation, impaired contractile function, increased myocyte length and accumulation of interstitial collagen, faster transition into heart failure, and increased mortality. Microarrays revealed that hearts from knockout mice failed to transactivate genes regulated by the transcription factor STAT3. Accordingly, nuclear STAT3 tyrosine phosphorylation was decreased in knockout mice. Silencing and overexpression experiments in isolated neonatal rat cardiomyocytes showed that Hsp22 activates STAT3 via production of interleukin-6 by the transcription factor nuclear factor-&kgr;B. In addition to its transcriptional function, STAT3 translocates to the mitochondria where it increases oxidative phosphorylation. Both mitochondrial STAT3 translocation and respiration were also significantly decreased in knockout mice. Conclusions— This study found that Hsp22 represents a previously undescribed activator of both nuclear and mitochondrial functions of STAT3, and its deletion in the context of pressure overload in vivo accelerates the transition into heart failure and increases mortality.

Longitudinal Assessment of Neuropsychological Functioning, Psychiatric Status, Functional Disability and Employment Status in Chronic Fatigue Syndrome

The longitudinal course of subjective and objective neuropsychological functioning, psychological functioning, disability level, and employment status in chronic fatigue syndrome (CFS) was examined. The relations among several key outcomes at follow-up, as well as the baseline characteristics that predict change (e.g., improvement), were also evaluated. The study sample consisted of 35 individuals who met the 1988 and 1994 CFS case definition criteria of the Centers for Disease Control (CDC) at intake. Participants were evaluated a mean of 41.9 (SEM = 1.7) months following their initial visit (range = 24-63 months). Results indicated that objective and subjective attention abilities, mood, level of fatigue, and disability improve over time in individuals with CFS. Moreover, improvements in these areas were found to be interrelated at follow-up. Finally, psychiatric status, age, and between-test duration were significant predictors of outcome. Overall, the prognosis for CFS appears to be poor, as the majority of participants remained functionally impaired over time and were unemployed at follow-up, despite the noted improvements.

Effects of cardiac overexpression of type 6 adenylyl cyclase affects on the response to chronic pressure overload

Adenylyl cyclase (AC) type 5 (AC5) and AC type 6 (AC6) are the two major AC isoforms in the heart. Cardiac overexpression of AC6 has been shown to be protective in response to several interventions. In this investigation, we examined the effects of chronic pressure overload in AC6 transgenic (TG) mice. In the absence of any stress, AC6 TG mice exhibited enhanced contractile function compared with their wild-type (WT) littermates, i.e., increased (P < 0.05) left ventricular (LV) ejection fraction (EF) (75 +/- 0.9 vs. 71 +/- 0.5%) and LV dP/dt (7,850 +/- 526 vs. 6,374 +/- 315 mmHg/s). Forskolin (25 microg x kg(-1) x min(-1) for 5 min) increased LVEF more (P < 0.05) in AC6 TG mice (14.8 +/- 1.0%) than in WT mice (7.7 +/- 1.0%). Also, isoproterenol (0.04 microg x kg(-1) x min(-1) for 5 min) increased LVEF more (P < 0.05) in AC6 TG mice (18.0 +/- 1.2%) than in WT mice (11.6 +/- 2.1%). Pressure overload, induced by 4 wk of transverse aortic constriction (TAC), increased the LV weight-to-body weight ratio and myocyte cross-sectional area similarly in both groups, but reduced LVEF more in AC6 TG mice (22%) compared with WT mice (9%), despite the higher starting level of LVEF in AC6 TG mice. LV systolic wall stress increased more in AC6 TG mice than in WT mice, which could be responsible for the reduced LVEF in AC6 TG mice with chronic pressure overload. In addition, LV dP/dt was no longer elevated in AC6 TG mice after TAC compared with WT mice. LV end-diastolic diameter was also greater (P < 0.05) in AC6 TG mice (3.8 +/- 0.07 mm) than in WT mice (3.6 +/- 0.05 mm) after TAC. Thus, in contrast to other interventions previously reported to be salutary with cardiac AC6 overpression, the response to chronic pressure overload was not; actually, AC6 TG mice fared worse than WT mice. The mechanism may be due to the increased LV systolic wall stress in AC6 TG mice with chronic pressure overload.

Sexual dimorphism in cardiac triacylglyceride dynamics in mice on long term caloric restriction

Human studies indicate augmented myocardial lipid metabolism in females, and that sex and obesity interact to predict myocardial fatty acid oxidation and storage. Altered lipid dynamics precede cardiomyopathies, and many studies now address high fat diets. Conversely, caloric restriction (CR), is the most studied model for longevity and stress resistance, including protection against myocardial ischemia. However, no information exists on the effects of long-term caloric restriction (CR) on triacylglyceride (TAG) content and dynamics in the heart. This study explored the effects of CR, sex and age on TAG dynamics in mouse hearts. Male and female SVJ129 mice were fed either normal (ND) or CR diet for 3 or 10 months. In 5-month-old mice, CR similarly decreased cardiac TAG in males (ND: 25.5±4.5 nmol/mg protein; CR: 12.6±2.7, P<0.05) and females (ND: 30.1±4.4; CR: 13.7±1.2) (no significant differences in TAG content were seen between sexes). CR reduced the contribution of exogenous palmitate to oxidative metabolism in males and females, by 15% and 11% respectively, versus ND, without affecting cardiac workload. CR also induced a larger reduction in TAG turnover in male (68%) than female hearts (38%). Interestingly, in 5 month old male mice, CR reproduced the lower TAG turnover rates of middle-aged males (ND 13-month-old male=423±76 nmol/mg protein/min). Thus, long term CR reduces TAG pool dynamics. Despite reduced content, hearts of female mice subjected to CR retained a more dynamic TAG pool than males, while males respond with greater metabolic remodeling of cardiac lipid dynamics.

Cytochrome c oxidase III as a mechanism for apoptosis in heart failure following myocardial infarction.

Cytochrome c oxidase (COX) is composed of 13 subunits, of which COX I, II, and III are encoded by a mitochondrial gene. COX I and II function as the main catalytic components, but the function of COX III is unclear. Because myocardial ischemia affects mitochondrial oxidative metabolism, we hypothesized that COX activity and expression would be affected during postischemic cardiomyopathy. This hypothesis was tested in a monkey model following myocardial infarction (MI) and subsequent pacing-induced heart failure (HF). In this model, COX I protein expression was decreased threefold after MI and fourfold after HF (P < 0.05 vs. sham), whereas COX II expression remained unchanged. COX III protein expression increased 5-fold after MI and further increased 10-fold after HF compared with sham (P < 0.05 vs. sham). The physiological impact of COX III regulation was examined in vitro. Overexpression of COX III in mitochondria of HL-1 cells resulted in an 80% decrease in COX I, 60% decrease in global COX activity, 60% decrease in cell viability, and threefold increase in apoptosis (P < 0.05). Oxidative stress induced by H2O2 significantly (P < 0.05) increased COX III expression. H2O2 decreased cell viability by 47 +/- 3% upon overexpression of COX III, but only by 12 +/- 5% in control conditions (P < 0.05). We conclude that ischemic stress in vivo and oxidative stress in vitro lead to upregulation of COX III, followed by downregulation of COX I expression, impaired COX oxidative activity, and increased apoptosis. Therefore, upregulation of COX III may contribute to the increased susceptibility to apoptosis following MI and subsequent HF.

Preemptive conditioning of the swine heart by H11 kinase/Hsp22 provides cardiac protection through inducible nitric oxide synthase

The second window of ischemic preconditioning (SWOP) provides maximal protection against ischemia through regulation of the inducible nitric oxide synthase (iNOS), yet its application is limited by the inconvenience of the preliminary ischemic stimulus required for prophylaxis. Overexpression of H11 kinase/Hsp22 (Hsp22) in a transgenic mouse model provides cardioprotection against ischemia that is equivalent to that conferred by SWOP. We hypothesized that short-term, prophylactic overexpression of Hsp22 would offer an alternative to SWOP in reducing ischemic damage through a nitric oxide (NO)-dependent mechanism. Adeno-mediated overexpression of Hsp22 was achieved in the area at risk of the left circumflex (Cx) coronary artery in chronically instrumented swine and compared with LacZ controls (n = 5/group). Hsp22-injected myocardium showed an average fourfold increase in Hsp22 protein expression compared with controls and a doubling in iNOS expression (both P < 0.05). Four days after ischemia-reperfusion, regional wall thickening was reduced by 58 ± 2% in the Hsp22 group vs. 82 ± 7% in the LacZ group, and Hsp22 reduced infarct size by 40% (both P < 0.05 vs. LacZ). Treatment with the NOS inhibitor N(G)-nitro-L-arginine (L-NNA) before ischemia suppressed the protection induced by Hsp22. In isolated cardiomyocytes, Hsp22 increased iNOS expression through the transcription factors NF-κB and STAT, the same effectors activated by SWOP, and reduced by 60% H(2)O(2)-mediated apoptosis, which was also abolished by NOS inhibitors. Therefore, short-term, prophylactic conditioning by Hsp22 provides NO-dependent cardioprotection that reproduces the signaling of SWOP, placing Hsp22 as a potential alternative for preemptive treatment of myocardial ischemia.

Transmission of muscle force to fascia during exercise

OBJECTIVE As the muscle contracts, fibers get thicker, forcing the fascial tubular layers surrounding the muscle (endomysium, perimysium and epimysium) to expand in diameter and hence to shorten in length. We develop a mathematical model to determine the fraction of force generated by extremity muscles during contraction that is transmitted to the surrounding tubes of fascia. METHODS Theory of elasticity is used to determine the modulus of elasticity, radial strain and the radial stress transmitted to the fascia. RESULTS Starting with published data on dimensions of muscle and muscle force, we find radial stress is 50% of longitudinal stress in the soleus, medial gastrocnemius, and elbow flexor and extensor muscles. CONCLUSION Substantial stress is transmitted to fascia during muscular exercise, which has implications for exercise therapies if they are designed for fascial as well as muscular stress. This adds additional perspective to myofascial force transmission research.

Additional hemodynamic measurements with an esophageal Doppler monitor: a preliminary report of compliance, force, kinetic energy, and afterload in the clinical setting

The esophageal Doppler monitor (EDM) is a minimally-invasive hemodynamic device which evaluates both cardiac output (CO), and fluid status, by estimating stroke volume (SV) and calculating heart rate (HR). The measurement of these parameters is based upon a continuous and accurate approximation of distal thoracic aortic blood flow. Furthermore, the peak velocity (PV) and mean acceleration (MA), of aortic blood flow at this anatomic location, are also determined by the EDM. The purpose of this preliminary report is to examine additional clinical hemodynamic calculations of: compliance (C), kinetic energy (KE), force (F), and afterload (TSVRi). These data were derived using both velocity-based measurements, provided by the EDM, as well as other contemporaneous physiologic parameters. Data were obtained from anesthetized patients undergoing surgery or who were in a critical care unit. A graphical inspection of these measurements is presented and discussed with respect to each patient’s clinical situation. When normalized to each of their initial values, F and KE both consistently demonstrated more discriminative power than either PV or MA. The EDM offers additional applications for hemodynamic monitoring. Further research regarding the accuracy, utility, and limitations of these parameters is therefore indicated.