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Biomedical subjects

Douglas L Mann

Publications and source records attributed to Douglas L Mann.

At least 19 recordsLinked to original sources
PubMed2006

Downregulation of connexin40 and increased prevalence of atrial arrhythmias in transgenic mice with cardiac-restricted overexpression of tumor necrosis factor.

Atrial arrhythmias, primarily atrial fibrillation, have been independently associated with structural remodeling and with inflammation. We hypothesized that sustained inflammatory signaling by tumor necrosis factor (TNF) would lead to alterations both in underlying atrial myocardial structure and in atrial electrical conduction. We performed ECG recording, intracardiac electrophysiology studies, epicardial mapping, and connexin immunohistochemical analyses on transgenic mice with targeted overexpression of TNF in the cardiac compartment (MHCsTNF) and on wild-type (WT) control mice (age 8-16 wk). Atrial and ventricular conduction abnormalities were always evident on ECG in MHCsTNF mice, including a shortened atrioventricular interval with a wide QRS duration secondary to junctional rhythm. Supraventricular arrhythmias were observed in five of eight MHCsTNF mice, whereas none of the mice demonstrated ventricular arrhythmias. No arrhythmias were observed in WT mice. Left ventricular conduction velocity during apical pacing was similar between the two mouse groups. Connexin40 was significantly downregulated in MHCsTNF mice. In contrast, connexin43 density was not significantly altered in MHCsTNF mice, but rather dispersed away from the intercalated disks. In conclusion, sustained inflammatory signaling contributed to atrial structural remodeling and downregulation of connexin40 that was associated with an increased prevalence of atrial arrhythmias.

Animals↗
PubMed2006

Inhibition of PPAR-alpha activity in mice with cardiac-restricted expression of tumor necrosis factor: potential role of TGF-beta/Smad3.

A shift in energy substrate utilization from fatty acids to glucose has been reported in failing hearts, resulting in improved oxygen efficiency yet perhaps also contributing to a state of energy deficiency. Peroxisome proliferator-activated receptor (PPAR)-alpha, the principal transcriptional regulator of cardiac fatty acid beta-oxidation (FAO) genes, is downregulated in heart failure, and this may contribute to reduced fatty acid utilization. Cardiomyopathic states are also accompanied by elevated levels of circulating cytokines, such as tumor necrosis factor (TNF), as well as increased local production of cytokines and profibrotic factors, such as transforming growth factor (TGF)-beta. However, whether these molecular pathways directly modulate cardiac energy metabolism and PPAR-alpha activity is not known. Therefore, FAO capacity and FAO gene expression were determined in mice with cardiac-restricted overexpression of TNF (MHCsTNF(3)). MHCsTNF(3) hearts had significantly lower FAO capacity and decreased expression of PPAR-alpha and FAO target genes compared with control hearts. Surprisingly, TNF had little effect on PPAR-alpha activity and FAO rates in cultured ventricular myocytes, suggesting that TNF acts indirectly on myocyte FAO in vivo. We found that TGF-beta expression was upregulated in MHCsTNF(3) hearts and that treatment of cultured myocytes with TGF-beta significantly suppressed FAO rates and directly impaired PPAR-alpha activity, a result reproduced by Smad3 overexpression. This work demonstrates that TGF-beta signaling pathways directly suppress PPAR-alpha activity and reduce FAO in cardiac myocytes, perhaps in response to locally elevated TNF. Although speculative, TGF-beta-driven repair mechanisms may also include the additional benefit of limiting FAO in injured myocardium.

Animals↗
PubMed2006

A pivotal role for endogenous TGF-beta-activated kinase-1 in the LKB1/AMP-activated protein kinase energy-sensor pathway.

TGF-beta-activated kinase-1 (TAK1), also known as MAPKK kinase-7 (MAP3K7), is a candidate effector of multiple circuits in cardiac biology and disease. Here, we show that inhibition of TAK1 in mice by a cardiac-specific dominant-negative mutation evokes electrophysiological and biochemical properties reminiscent of human Wolff-Parkinson-White syndrome, arising from mutations in AMP-activated protein kinase (AMPK), most notably, accelerated atrioventricular conduction and impaired AMPK activation. To test conclusively the biochemical connection from TAK1 to AMPK suggested by this phenotype, we disrupted TAK1 in mouse embryos and embryonic fibroblasts by Cre-mediated recombination. In TAK1-null embryos, the activating phosphorylation of AMPK at T172 was blocked, accompanied by defective AMPK activity. However, loss of endogenous TAK1 causes midgestation lethality, with defective yolk sac and intraembryonic vasculature. To preclude confounding lethal defects, we acutely ablated floxed TAK1 in culture by viral delivery of Cre. In culture, endogenous TAK1 was activated by oligomycin, the antidiabetic drug metformin, 5-aminoimidazole-4-carboxamide riboside (AICAR), and ischemia, well established triggers of AMPK activity. Loss of TAK1 in culture blocked T172 phosphorylation induced by all three agents, interfered with AMPK activation, impaired phosphorylation of the endogenous AMPK substrate acetyl CoA carboxylase, and also interfered with activation of the AMPK kinase LKB1. Thus, by disrupting the endogenous TAK1 locus, we prove a pivotal role for TAK1 in the LKB1/AMPK signaling axis, an essential governor of cell metabolism.

AMP-Activated Protein Kinases↗
PubMed2006

Toll-like receptor 2 modulates left ventricular function following ischemia-reperfusion injury.

Production of proinflammatory cytokines contributes to cardiac dysfunction during ischemia-reperfusion. The principal mechanism responsible for the induction of this innate stress response during periods of myocardial ischemia-reperfusion remains unknown. Toll-like receptor 2 (TLR2) is a highly conserved pattern recognition receptor that has been implicated in the innate immune response to a variety of pathogens. However, TLR2 may also mediate inflammation in response to noninfectious injury. We therefore hypothesized that TLR2 is essential for modulating myocardial inflammation and left ventricular (LV) function during ischemia-reperfusion injury. Susceptibility to myocardial ischemia-reperfusion injury following ischemia-reperfusion was determined in Langendorff-perfused hearts isolated from wild-type mice and mice deficient in TLR2 (TLR2D) and Toll interleukin receptor domain-containing adaptor protein. After ischemia-reperfusion, contractile performance was significantly impaired in hearts from wild-type mice as demonstrated by a lower recovery of LV developed pressure relative to TLR2D hearts. Creatinine kinase levels were similar in both groups after reperfusion. Contractile dysfunction in wild-type hearts was associated with elevated cardiac levels of TNF and IL-1beta. Ischemia-reperfusion-induced LV dysfunction was reversed by treatment with the recombinant TNF blocking protein etanercept. These studies show for the first time that TLR2 signaling importantly contributes to the LV dysfunction that occurs following ischemia-reperfusion. Thus disruption of TLR2-mediated signaling may be helpful to induce immediate or delayed myocardial protection from ischemia-reperfusion injury.

Animals↗
PubMed2006

Mitral valve surgery in heart failure: insights from the Acorn Clinical Trial.

OBJECTIVE: The study objective was to evaluate in a prospective, randomized, multicenter trial the safety and efficacy of mitral valve surgery with and without the CorCap cardiac support device (Acorn Cardiovascular, St Paul, Minn) in patients with New York Heart Association Class II to IV heart failure. BACKGROUND: Although mitral valve surgery has been performed successfully in patients with heart failure, the safety and long-term efficacy have not been established in a multicenter prospective trial. Cardiac support devices that reduce ventricular wall stress and promote beneficial reverse remodeling have been proposed as a new treatment option as a stand-alone procedure and as an adjunct to mitral valve surgery. METHODS: A subgroup of 193 patients were enrolled in the mitral valve repair or replacement stratum of the Acorn Clinical Trial; 102 patients were randomized to the mitral valve surgery alone group (control) and 91 patients were randomized to mitral valve surgery with implantation of the CorCap cardiac support device. Patients were followed for a median duration of 22.9 months. RESULTS: For the entire mitral valve surgery group, the 30-day operative mortality rate was only 1.6% at 30 days. Mitral surgery was associated with progressive reductions in left ventricle end-diastolic volume, left ventricle end-systolic volume, and left ventricular mass, and increases in left ventricle ejection fraction and sphericity index, all consistent with reverse remodeling. Recurrence of clinically significant mitral regurgitation was uncommon. Quality of life, exercise performance, and New York Heart Association functional class were all improved. Finally, the addition of the CorCap cardiac support device led to greater decreases in left ventricular end-diastolic volume and left ventricular end-systolic volume, a more elliptical shape, and a trend for a reduction in major cardiac procedures and improvement in quality of life compared with mitral surgery alone. CONCLUSIONS: These findings suggest that there is clear benefit to the surgical elimination of mitral regurgitation and that there is additional benefit with the CorCap cardiac support device. Given the improvement in left ventricle structure and function, along with a low mortality rate, physicians should strongly consider offering mitral valve surgery in combination with the CorCap cardiac support device to patients with heart failure who are on an optimal medical regimen.

Cardiac Surgical Procedures↗
PubMed2006

The Seattle Heart Failure Model: prediction of survival in heart failure.

BACKGROUND: Heart failure has an annual mortality rate ranging from 5% to 75%. The purpose of the study was to develop and validate a multivariate risk model to predict 1-, 2-, and 3-year survival in heart failure patients with the use of easily obtainable characteristics relating to clinical status, therapy (pharmacological as well as devices), and laboratory parameters. METHODS AND RESULTS: The Seattle Heart Failure Model was derived in a cohort of 1125 heart failure patients with the use of a multivariate Cox model. For medications and devices not available in the derivation database, hazard ratios were estimated from published literature. The model was prospectively validated in 5 additional cohorts totaling 9942 heart failure patients and 17,307 person-years of follow-up. The accuracy of the model was excellent, with predicted versus actual 1-year survival rates of 73.4% versus 74.3% in the derivation cohort and 90.5% versus 88.5%, 86.5% versus 86.5%, 83.8% versus 83.3%, 90.9% versus 91.0%, and 89.6% versus 86.7% in the 5 validation cohorts. For the lowest score, the 2-year survival was 92.8% compared with 88.7%, 77.8%, 58.1%, 29.5%, and 10.8% for scores of 0, 1, 2, 3, and 4, respectively. The overall receiver operating characteristic area under the curve was 0.729 (95% CI, 0.714 to 0.744). The model also allowed estimation of the benefit of adding medications or devices to an individual patient's therapeutic regimen. CONCLUSIONS: The Seattle Heart Failure Model provides an accurate estimate of 1-, 2-, and 3-year survival with the use of easily obtained clinical, pharmacological, device, and laboratory characteristics.

Adult↗
PubMed2005

Targeted anticytokine therapy and the failing heart.

Recent studies have identified the importance of proinflammatory mediators in the development and progression of chronic heart failure (CHF). The growing appreciation of the pathophysiologic consequences of sustained expression of proinflammatory mediators in preclinical and clinical CHF models culminated in a series of multicenter clinical trials that used targeted approaches to neutralize tumor necrosis factor in patients with moderate-to-advanced CHF. However, these targeted approaches have resulted in worsening CHF, thereby raising a number of important questions about what role, if any, proinflammatory cytokines play in the pathogenesis of CHF. This review summarizes what has been learned from the negative clinical trials, as well as the potential direction of future research in this area.

Clinical Trials as Topic↗
PubMed2005

Proapoptotic effects of caspase-1/interleukin-converting enzyme dominate in myocardial ischemia.

Caspase-1/interleukin-converting enzyme (ICE) is a cysteine protease traditionally considered to have importance as an inflammatory mediator, but not as an apoptotic effector. Because of the dual functions of this caspase, the pathophysiological impact of its reported upregulation in hypertrophy and heart failure is not known. Here, the consequences of increased myocardial expression of procaspase-1 were examined on the normal and ischemically injured heart. In unstressed mouse hearts with a 30-fold increase in procaspase-1 content, unprocessed procaspase-1 was well tolerated, without detectable pathology. Cardiomyocyte processing and activation of caspase-1 and caspase-3 occurred after administration of endotoxin or with transient myocardial ischemia. In post-ischemic hearts, procaspase-1 overexpression was associated with strikingly increased cardiac myocyte apoptosis in the peri- and noninfarct regions and with 50% larger myocardial infarctions. Tissue culture studies revealed that procaspase-1 processing/activation is stimulated by hypoxia, and that caspase-1 acts in synergy with hypoxia to stimulate caspase-3 mediated apoptosis without activating upstream caspases. These data demonstrate that the proapoptotic effects of caspase-1 can significantly impact the myocardial response to ischemia and suggest that conditions in which procaspase-1 in the heart is increased may predispose to apoptotic myocardial injury under conditions of physiological stress.

Animals↗
PubMed2005

Left ventricular size and shape: determinants of mechanical signal transduction pathways.

Heart failure may be viewed as a progressive disorder that is impelled, at least in part, by progressive left ventricular (LV) remodeling. In the present discussion we will review the role of LV remodeling in the pathogenesis of heart failure, with a focus on the contribution that changes in LV size and shape play in the development and progression of the progression of heart failure. The clinical implication of this review is that existing neurohormonal strategies may not completely prevent disease progression in the failing heart, and that adjunctive strategies that are designed to specifically prevent and/or attenuate LV remodeling may play an important role in the clinical treatment of heart failure.

Heart Failure↗
PubMed2005

Treatment of the metabolic syndrome: the impact of lifestyle modification.

Along with the increasing prevalence of obesity comes a constellation of metabolic derangements: dyslipidemias, hypertension, insulin resistance, and glucose intolerance, as well as increased prothrombotic and inflammatory markers. The association of these factors has been termed the "metabolic syndrome" and increases the risk of developing cardiovascular disease. Aside from pharmaceutical therapy, lifestyle modification is necessary to aggressively treat this syndrome in its entirety. This involves a holistic approach of behavioral counseling, education, increased physical activity, and dietary modification. Even modest weight loss (7% to 10% of body weight) results in decreased fat mass, blood pressure, glucose, low-density lipoprotein, and triglyceride levels. These benefits can also translate into improved long-term outcome, especially if weight loss and lifestyle alterations are maintained. However, the remaining challenge is how to promote long-term adherence to a healthier, more active lifestyle and avoid reversion to old habits.

Body Composition↗
PubMed2005

TNF-alpha acts via p38 MAPK to stimulate expression of the ubiquitin ligase atrogin1/MAFbx in skeletal muscle.

Atrogin1/MAFbx is an ubiquitin ligase that mediates muscle atrophy in a variety of catabolic states. We recently found that H2O2 stimulates atrogin1/MAFbx gene expression. Since the cytokine tumor necrosis factor-alpha (TNF-alpha) stimulates both reactive oxygen production and general activity of the ubiquitin conjugating pathway, we hypothesized that TNF-alpha would also increase atrogin1/MAFbx gene expression. As with H2O2, we found that TNF-alpha exposure up-regulates atrogin1/MAFbx mRNA within 2 h in C2C12 myotubes. Intraperitoneal injection of TNF-alpha increased atrogin1/MAFbx mRNA in skeletal muscle of adult mice within 4 h. Exposing myotubes to either TNF-alpha or H2O2 also produced general activation of the mitogen-activated protein kinases (MAPKs): p38, ERK1/2, and JNK. The increase in atrogin1/MAFbx gene expression induced by TNF-alpha was not altered significantly by ERK inhibitor PD98059 or the JNK inhibitor SP600125. In contrast, atrogin1/MAFbx up-regulation and the associated increase in ubiquitin conjugating activity were both blunted by p38 inhibitors, either SB203580 or curcumin. These data suggest that TNF-alpha acts via p38 to increase atrogin1/MAFbx gene expression in skeletal muscle.

Animals↗