Transcriptional control of a nuclear gene encoding a mitochondrial fatty acid oxidation enzyme in transgenic mice: role for nuclear receptors in cardiac and brown adipose expression.

Expression of the gene encoding medium-chain acyl coenzyme A dehydrogenase (MCAD), a nuclearly encoded mitochondrial fatty acid beta-oxidation enzyme, is regulated in parallel with fatty acid oxidation rates among tissues and during development. We have shown previously that the human MCAD gene promoter contains a pleiotropic element (nuclear receptor response element [NRRE-1]) that confers transcriptional activation or repression by members of the nuclear receptor superfamily. Mice transgenic for human MCAD gene promoter fragments fused to a chloramphenicol acetyltransferase gene reporter were produced and characterized to evaluate the role of NRRE-1 and other promoter elements in the transcriptional control of the MCAD gene in vivo. Expression of the full-length MCAD promoter-chloramphenicol acetyltransferase transgene (MCADCAT.371) paralleled the known tissue-specific differences in mitochondrial beta-oxidation rates and MCAD expression. MCADCAT.371 transcripts were abundant in heart tissue and brown adipose tissue, tissues with high-level MCAD expression. During perinatal cardiac developmental stages, expression of the MCADCAT.371 transgene paralleled mouse MCAD mRNA levels. In contrast, expression of a mutant MCADCAT transgene, which lacked NRRE-1 (MCADCATdeltaNRRE-1), was not enriched in heart or brown adipose tissue and did not exhibit appropriate postnatal induction in the developing heart. Transient-transfection studies with MCAD promoter-luciferase constructs containing normal or mutant NRRE-1 sequences demonstrated that the nuclear receptor binding sequences within NRRE-1 are necessary for high-level transcriptional activity in primary rat cardiocytes. Electrophoretic mobility shift assays demonstrated that NRRE-1 was bound by several cardiac and brown adipose nuclear proteins and that these interactions required the NRRE-1 receptor binding hexamer sequences. Antibody supershift studies identified the orphan nuclear receptor COUP-TF as one of the endogenous cardiac proteins which bound NRRE-1. These results dictate an important role for nuclear receptors in the transcriptional control of a nuclear gene encoding a mitochondrial fatty acid oxidation enzyme and identify a gene regulatory pathway involved in cardiac energy metabolism.

Changes in patients undergoing coronary artery bypass grafting: 1987-1990. Northern New England Cardiovascular Disease Study Group.

A prospective study of 7,590 consecutive patients undergoing isolated coronary artery bypass grafting at five medical centers in Maine, New Hampshire, and Vermont between July 1987 and December 1990 assessed changes in patient characteristics over time. Variables included age, sex, surgical priority, ejection fraction, left ventricular end-diastolic pressure, and left main coronary artery stenosis of 90% or greater. Trends were assessed for each variable and for predicted mortality using linear regression. The mean age increased significantly, whereas ejection fraction decreased. The percentage of urgent cases increased, whereas the elective cases became less frequent. No changes were observed in the percentages of emergent cases, female patients, or patients with severe left main coronary artery disease. The predicted in-hospital mortality rose significantly from 4.2% to 5.2% (p < 0.001). The increase in urgent surgical intervention was the most substantial contributor. Subgroup analyses did not support a systematic misclassification of elective patients into the urgent group. This study demonstrates that the characteristics of the cohort of patients undergoing coronary artery bypass grafting changed substantially from 1987 to 1990. These changes should be considered when interpreting surgical outcomes.

Therapeutic strategies for atrial fibrillation. The value of decision analysis.

In the absence of randomized, controlled trials of low-dose amiodarone in atrial fibrillation or a randomized, controlled trial of ventricular rate control versus antifibrillatory therapy, a Markov decision analysis is useful in comparing different therapeutic strategies for atrial fibrillation. The decision analysis described compared warfarin, quinidine, and low-dose amiodarone in patients with asymptomatic or minimally symptomatic chronic, persistent atrial fibrillation. This model suggests that electrical cardioversion followed by low-dose amiodarone is a relatively safe, effective alternative to long-term warfarin therapy.

A role for Sp and nuclear receptor transcription factors in a cardiac hypertrophic growth program.

During cardiac hypertrophy, the chief myocardial energy source switches from fatty acid beta-oxidation (FAO) to glycolysis-a reversion to fetal metabolism. The expression of genes encoding myocardial FAO enzymes was delineated in a murine ventricular pressure overload preparation to characterize the molecular regulatory events involved in the alteration of energy substrate utilization during cardiac hypertrophy. Expression of genes involved in the thioesterification, mitochondrial import, and beta-oxidation of fatty acids was coordinately down-regulated after 7 days of right ventricular (RV) pressure overload. Results of RV pressure overload studies in mice transgenic for the promoter region of the gene encoding human medium-chain acyl-CoA dehydrogenase (MCAD, which catalyzes a rate-limiting step in the FAO cycle) fused to a chloramphenicol acetyltransferase reporter confirmed that repression of MCAD gene expression in the hypertrophied ventricle occurred at the transcriptional level. Electrophoretic mobility-shift assays performed with MCAD promoter fragments and nuclear protein extracts prepared from hypertrophied and control RV identified pressure overload-induced protein/DNA interactions at a regulatory unit shown previously to confer control of MCAD gene transcription during cardiac development. Antibody "supershift" studies demonstrated that members of the Sp (Sp1, Sp3) and nuclear hormone receptor [chicken ovalbumin upstream promoter transcription factor (COUP-TF)/erbA-related protein 3] families interact with the pressure overload-responsive unit. Cardiomyocyte transfection studies confirmed that COUP-TF repressed the transcriptional activity of the MCAD promoter. The DNA binding activities and nuclear expression of Sp1/3 and COUP-TF in normal fetal mouse heart were similar to those in the hypertrophied adult heart. These results identify a transcriptional regulatory mechanism involved in the reinduction of a fetal metabolic program during pressure overload-induced cardiac hypertrophy.

Managing chronic atrial fibrillation: a Markov decision analysis comparing warfarin, quinidine, and low-dose amiodarone.

OBJECTIVE: To compare the relative risks and benefits of several clinical strategies for managing patients with chronic atrial fibrillation. DESIGN: Five recent randomized controlled trials of warfarin in atrial fibrillation, 6 randomized controlled trials of quinidine, and 13 longitudinal studies of low-dose amiodarone were used. A MEDLINE search was also done (1966 to present). MEASUREMENTS: A Markov decision analysis model was used to assess outcomes in large, hypothetical cohorts of patients with atrial fibrillation followed from 65 to 70 years of age within four clinical strategies: 1) no treatment; 2) warfarin; 3) electrical cardioversion followed by quinidine to maintain normal sinus rhythm; and 4) electrical cardioversion followed by low-dose amiodarone. RESULTS: IN this hypothetical cohort, fewer patients had disabling events with amiodarone (1.4%) than with quinidine (1.8%), warfarin (2.6%), or no treatment (7.4%). Amiodarone appeared to be associated with the lowest 5-year mortality (13.6%) when compared with warfarin (14.4%), quinidine (15.2%), and no treatment (18.2%). In terms of quality-adjusted life-years, amiodarone had the highest expected value (4.75 years), followed by warfarin (4.72 years), quinidine (4.68 years), and no treatment (4.55 years). Amiodarone remained the preferred strategy using the most plausible scenarios of risks associated with atrial fibrillation. Choices among warfarin, quinidine, and no treatment depended on estimates of bleeding rates with warfarin, stroke rates after discontinuing warfarin, quinidine-related mortality, and the quality of life with warfarin. CONCLUSION: Cardioversion followed by low-dose amiodarone to maintain normal sinus rhythm appears to be a relatively safe and effective treatment for patients with chronic atrial fibrillation.