W.H. Wilson Tang

Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease

Metabolomics studies hold promise for the discovery of pathways linked to disease processes. Cardiovascular disease (CVD) represents the leading cause of death and morbidity worldwide. Here we used a metabolomics approach to generate unbiased small-molecule metabolic profiles in plasma that predict risk for CVD. Three metabolites of the dietary lipid phosphatidylcholine—choline, trimethylamine N-oxide (TMAO) and betaine—were identified and then shown to predict risk for CVD in an independent large clinical cohort. Dietary supplementation of mice with choline, TMAO or betaine promoted upregulation of multiple macrophage scavenger receptors linked to atherosclerosis, and supplementation with choline or TMAO promoted atherosclerosis. Studies using germ-free mice confirmed a critical role for dietary choline and gut flora in TMAO production, augmented macrophage cholesterol accumulation and foam cell formation. Suppression of intestinal microflora in atherosclerosis-prone mice inhibited dietary-choline-enhanced atherosclerosis. Genetic variations controlling expression of flavin monooxygenases, an enzymatic source of TMAO, segregated with atherosclerosis in hyperlipidaemic mice. Discovery of a relationship between gut-flora-dependent metabolism of dietary phosphatidylcholine and CVD pathogenesis provides opportunities for the development of new diagnostic tests and therapeutic approaches for atherosclerotic heart disease.

Intestinal microbiota metabolism of l -carnitine, a nutrient in red meat, promotes atherosclerosis

Intestinal microbiota metabolism of choline and phosphatidylcholine produces trimethylamine (TMA), which is further metabolized to a proatherogenic species, trimethylamine-N-oxide (TMAO). We demonstrate here that metabolism by intestinal microbiota of dietary l-carnitine, a trimethylamine abundant in red meat, also produces TMAO and accelerates atherosclerosis in mice. Omnivorous human subjects produced more TMAO than did vegans or vegetarians following ingestion of l-carnitine through a microbiota-dependent mechanism. The presence of specific bacterial taxa in human feces was associated with both plasma TMAO concentration and dietary status. Plasma l-carnitine levels in subjects undergoing cardiac evaluation (n = 2,595) predicted increased risks for both prevalent cardiovascular disease (CVD) and incident major adverse cardiac events (myocardial infarction, stroke or death), but only among subjects with concurrently high TMAO levels. Chronic dietary l-carnitine supplementation in mice altered cecal microbial composition, markedly enhanced synthesis of TMA and TMAO, and increased atherosclerosis, but this did not occur if intestinal microbiota was concurrently suppressed. In mice with an intact intestinal microbiota, dietary supplementation with TMAO or either carnitine or choline reduced in vivo reverse cholesterol transport. Intestinal microbiota may thus contribute to the well-established link between high levels of red meat consumption and CVD risk.

Intestinal Microbial Metabolism of Phosphatidylcholine and Cardiovascular Risk

BACKGROUND Recent studies in animals have shown a mechanistic link between intestinal microbial metabolism of the choline moiety in dietary phosphatidylcholine (lecithin) and coronary artery disease through the production of a proatherosclerotic metabolite, trimethylamine-N-oxide (TMAO). We investigated the relationship among intestinal microbiota-dependent metabolism of dietary phosphatidylcholine, TMAO levels, and adverse cardiovascular events in humans. METHODS We quantified plasma and urinary levels of TMAO and plasma choline and betaine levels by means of liquid chromatography and online tandem mass spectrometry after a phosphatidylcholine challenge (ingestion of two hard-boiled eggs and deuterium [d9]-labeled phosphatidylcholine) in healthy participants before and after the suppression of intestinal microbiota with oral broad-spectrum antibiotics. We further examined the relationship between fasting plasma levels of TMAO and incident major adverse cardiovascular events (death, myocardial infarction, or stroke) during 3 years of follow-up in 4007 patients undergoing elective coronary angiography. RESULTS Time-dependent increases in levels of both TMAO and its d9 isotopologue, as well as other choline metabolites, were detected after the phosphatidylcholine challenge. Plasma levels of TMAO were markedly suppressed after the administration of antibiotics and then reappeared after withdrawal of antibiotics. Increased plasma levels of TMAO were associated with an increased risk of a major adverse cardiovascular event (hazard ratio for highest vs. lowest TMAO quartile, 2.54; 95% confidence interval, 1.96 to 3.28; P<0.001). An elevated TMAO level predicted an increased risk of major adverse cardiovascular events after adjustment for traditional risk factors (P<0.001), as well as in lower-risk subgroups. CONCLUSIONS The production of TMAO from dietary phosphatidylcholine is dependent on metabolism by the intestinal microbiota. Increased TMAO levels are associated with an increased risk of incident major adverse cardiovascular events. (Funded by the National Institutes of Health and others.).

Importance of Venous Congestion for Worsening of Renal Function in Advanced Decompensated Heart Failure

OBJECTIVES To determine whether venous congestion, rather than impairment of cardiac output, is primarily associated with the development of worsening renal function (WRF) in patients with advanced decompensated heart failure (ADHF). BACKGROUND Reduced cardiac output is traditionally believed to be the main determinant of WRF in patients with ADHF. METHODS A total of 145 consecutive patients admitted with ADHF treated with intensive medical therapy guided by pulmonary artery catheter were studied. We defined WRF as an increase of serum creatinine >/=0.3 mg/dl during hospitalization. RESULTS In the study cohort (age 57 +/- 14 years, cardiac index 1.9 +/- 0.6 l/min/m(2), left ventricular ejection fraction 20 +/- 8%, serum creatinine 1.7 +/- 0.9 mg/dl), 58 patients (40%) developed WRF. Patients who developed WRF had a greater central venous pressure (CVP) on admission (18 +/- 7 mm Hg vs. 12 +/- 6 mm Hg, p < 0.001) and after intensive medical therapy (11 +/- 8 mm Hg vs. 8 +/- 5 mm Hg, p = 0.04). The development of WRF occurred less frequently in patients who achieved a CVP <8 mm Hg (p = 0.01). Furthermore, the ability of CVP to stratify risk for development of WRF was apparent across the spectrum of systemic blood pressure, pulmonary capillary wedge pressure, cardiac index, and estimated glomerular filtration rates. CONCLUSIONS Venous congestion is the most important hemodynamic factor driving WRF in decompensated patients with advanced heart failure.

Tissue Doppler Imaging in the Estimation of Intracardiac Filling Pressure in Decompensated Patients With Advanced Systolic Heart Failure

Background— The ratio of early transmitral velocity to tissue Doppler mitral annular early diastolic velocity (E/Ea) has been correlated with pulmonary capillary wedge pressure (PCWP) in a wide variety of cardiac conditions. The objective of this study was to determine the reliability of mitral E/Ea for predicting PCWP in patients admitted for advanced decompensated heart failure. Methods and Results— Prospective consecutive patients with advanced decompensated heart failure (ejection fraction ≤30%, New York Heart Association class III to IV symptoms) underwent simultaneous echocardiographic and hemodynamic evaluation on admission and after 48 hours of intensive medical therapy. A total of 106 patients were included (mean age, 57±12 years; ejection fraction, 24±8%; PCWP, 21±7 mm Hg; mitral E/Ea ratio, 20±12). No correlation was found between mitral E/Ea ratio and PCWP, particularly in those with larger left ventricular volumes, more impaired cardiac indexes, and the presence of cardiac resynchronization therapy. Overall, the mitral E/Ea ratio was similar among patients with PCWP >18 and ≤18 mm Hg, and sensitivity and specificity for mitral E/Ea ratio >15 to identify a PCWP >18 mm Hg were 66% and 50%, respectively. Contrary to prior reports, we did not observe any direct association between changes in PCWP and changes in mitral E/Ea ratio. Conclusion— In decompensated patients with advanced systolic heart failure, tissue Doppler–derived mitral E/Ea ratio may not be as reliable in predicting intracardiac filling pressures, particularly in those with larger LV volumes, more impaired cardiac indices, and the presence of cardiac resynchronization therapy.

Cardiac troponins in renal insufficiency: review and clinical implications.

Patients with renal insufficiency may have increased serum troponins even in the absence of clinically suspected acute myocardial ischemia. While cardiovascular disease is the most common cause of death in patients with renal failure, we are just beginning to understand the clinical meaning of serum troponin elevations. Serum troponin T is increased more frequently than troponin I in patients with renal failure, leading clinicians to question its specificity for the diagnosis of myocardial infarction. Many large-scale trials demonstrating the utility of serum troponins in predicting adverse events and in guiding therapy and intervention in acute coronary syndromes have excluded patients with renal failure. Despite persistent uncertainty about the mechanism of elevated serum troponins in patients with reduced renal function, data from smaller groups of renal failure patients have suggested that troponin elevations are associated with added risk, including an increase in mortality. It is possible that increases in serum troponin from baseline in patients with renal insufficiency admitted to hospital with acute coronary syndrome may signify myocardial necrosis. Further studies are needed to clarify this hypothesis.

Diabetic Cardiomyopathy: Insights into Pathogenesis, Diagnostic Challenges, and Therapeutic Options

Diabetic cardiomyopathy is the presence of myocardial dysfunction in the absence of coronary artery disease and hypertension. Hyperglycemia seems to be central to the pathogenesis of diabetic cardiomyopathy and to trigger a series of maladaptive stimuli that result in myocardial fibrosis and collagen deposition. These processes are thought to be responsible for altered myocardial relaxation characteristics and manifest as diastolic dysfunction on imaging. Sophisticated imaging technologies also have permitted the detection of subtle systolic dysfunction in the diabetic myocardium. In the early stages, these changes appear reversible with tight metabolic control, but as the pathologic processes become organized, the changes are irreversible and contribute to an excess risk of heart failure among diabetic patients independently of common comorbidities, such as coronary artery disease and hypertension. Therapeutic agents specifically targeting processes that lead to these pathophysiologic changes are in the early stages of development. Although glycemic control and early administration of neurohormonal antagonists remain the cornerstones of therapeutic approaches, newer treatment targets are currently being explored.

Exome sequencing identifies rare LDLR and APOA5 alleles conferring risk for myocardial infarction

Summary Myocardial infarction (MI), a leading cause of death around the world, displays a complex pattern of inheritance1,2. When MI occurs early in life, the role of inheritance is substantially greater1. Previously, rare mutations in low-density lipoprotein (LDL) genes have been shown to contribute to MI risk in individual families3–8 whereas common variants at more than 45 loci have been associated with MI risk in the population9–15. Here, we evaluate the contribution of rare mutations to MI risk in the population. We sequenced the protein-coding regions of 9,793 genomes from patients with MI at an early age (≤50 years in males and ≤60 years in females) along with MI-free controls. We identified two genes where rare coding-sequence mutations were more frequent in cases versus controls at exome-wide significance. At low-density lipoprotein receptor (LDLR), carriers of rare, damaging mutations (3.1% of cases versus 1.3% of controls) were at 2.4-fold increased risk for MI; carriers of null alleles at LDLR were at even higher risk (13-fold difference). This sequence-based estimate of the proportion of early MI cases due to LDLR mutations is remarkably similar to an estimate made more than 40 years ago using total cholesterol16. At apolipoprotein A-V (APOA5), carriers of rare nonsynonymous mutations (1.4% of cases versus 0.6% of controls) were at 2.2-fold increased risk for MI. When compared with non-carriers, LDLR mutation carriers had higher plasma LDL cholesterol whereas APOA5 mutation carriers had higher plasma triglycerides. Recent evidence has connected MI risk with coding sequence mutations at two genes functionally related to APOA5, namely lipoprotein lipase15,17 and apolipoprotein C318,19. When combined, these observations suggest that, beyond LDL cholesterol, disordered metabolism of triglyceride-rich lipoproteins contributes to MI risk.

Insights From a Cardiac Resynchronization Optimization Clinic as Part of a Heart Failure Disease Management Program

OBJECTIVES Our aim was to determine the feasibility and value of a protocol-driven approach to patients with cardiac resynchronization therapy (CRT) who did not exhibit a positive response long after implant. BACKGROUND Up to one-third of patients with advanced heart failure do not exhibit a positive response to CRT. METHODS A total of 75 consecutive ambulatory patients with persistent advanced heart failure symptoms and/or adverse reverse remodeling and CRT implanted >6 months underwent a comprehensive protocol-driven evaluation to determine the potential reasons for a suboptimal response. Recommendations were made to maximize the potential of CRT, and adverse events were documented. RESULTS All patients (mean left ventricular [LV] ejection fraction 23 +/- 9%, LV end-diastolic volume 275 +/- 127 ml) underwent evaluation. Eighty-eight percent of patients had significantly better echocardiographic indexes of LV filling and LV ejection with optimal setting of their CRT compared with a temporary VVI back-up setting. Most patients had identifiable reasons for suboptimal response, including inadequate device settings (47%), suboptimal medical treatment (32%), arrhythmias (32%), inappropriate lead position (21%), or lack of baseline dyssynchrony (9%). Multidisciplinary recommendations led to changes in device settings and/or other therapy modifications in 74% of patients and were associated with fewer adverse events (13% vs. 50%, odds ratio: 0.2 [95% confidence interval: 0.07 to 0.56], p = 0.002) compared with those in which no recommendation could be made. CONCLUSIONS Routine protocol-driven approach to evaluate ambulatory CRT patients who did not exhibit a positive response is feasible, and changes in device settings and/or other therapies after multidisciplinary evaluation may be associated with fewer adverse events.

National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: Clinical Utilization of Cardiac Biomarker Testing in Heart Failure

### A. Context of Biochemical Marker Testing in Heart Failure Biochemical marker testing has revolutionized the approach to diagnosis and management of heart failure over the past decade. There is an unsurpassed excitement in the heart failure community that significant advances in our understanding of currently available and future cardiac biomarkers will facilitate improved characterization of heart failure disease states and promote individualized therapy in heart failure and beyond. However, like most novel diagnostic tests, the promising findings from pivotal trials have met with ongoing challenges when applied in the clinical setting. The material discussed in this guidelines document addresses clinical use of BNP/NT-proBNP and cardiac troponin testing in the context of heart failure diagnosis, risk stratification and management, including therapeutic guidance in adult (>18 year-old) patients. Together with the associated document titled “ National Academy of Clinical Biochemistry and IFCC Committee for Standardization of Markers of Cardiac Damage Laboratory Medicine Practice Guidelines: Analytical Issues for Biomarkers of Heart Failure ”, …