Trimethyllysine and trimethylamine-N-oxide - pathogenic factors or surrogate markers of increased cardiovascular disease risk?

Metabolic Reprogramming, Gut Dysbiosis, and Nutrition Intervention in Canine Heart Disease

This review provides a state-of-the-art overview on recent advances in systems biology in canine cardiac disease, with a focus on our current understanding of bioenergetics and amino acid metabolism in myxomatous mitral valve disease (MMVD). Cross-species comparison is drawn to highlight the similarities between human and canine heart diseases. The adult mammalian heart exhibits a remarkable metabolic flexibility and shifts its energy substrate preference according to different physiological and pathological conditions. The failing heart suffers up to 40% ATP deficit and is compared to an engine running out of fuel. Bioenergetics and metabolic readaptations are among the major research topics in cardiac research today. Myocardial energy metabolism consists of three interconnected components: substrate utilization, oxidative phosphorylation, and ATP transport and utilization. Any disruption or uncoupling of these processes can result in deranged energy metabolism leading to heart failure (HF). The review describes the changes occurring in each of the three components of energy metabolism in MMVD and HF. It also provides an overview on the changes in circulating and myocardial glutathione, taurine, carnitines, branched-chain amino acid catabolism and tryptophan metabolic pathways. In addition, the review summarizes the potential role of the gut microbiome in MMVD and HF. As our knowledge and understanding in these molecular and metabolic processes increase, it becomes possible to use nutrition to address these changes and to slow the progression of the common heart diseases in dogs.

Metabolomics Analysis Reveals Deranged Energy Metabolism and Amino Acid Metabolic Reprogramming in Dogs With Myxomatous Mitral Valve Disease

Background

Myxomatous mitral valve disease (MMVD), a naturally occurring heart disease, affects 10% to 15% of the canine population. Canine MMVD shares many similarities with human MMVD. Untargeted metabolomics was performed to identify changes in metabolic pathways and biomarkers with potential clinical utilities.

Methods and Results

Serum samples from 27 healthy, 22 stage B1, 18 stage B2 preclinical MMVD dogs, and 17 MMVD dogs with a history of congestive heart failure (CHF) were analyzed. Linear regression analysis identified 173 known metabolites whose concentrations were different among the 4 groups (adjusted P<0.05), of which 40% belonged to amino acid super pathways, while 30% were lipids. More than 50% of significant metabolites were correlated with left atrial diameter but not left ventricular dimension. Acylcarnitines, tricarboxylic acid cycle intermediates, and creatine accumulated in proportion to MMVD severity. α‐Ketobutyrate and ketone bodies were increased as MMVD advanced. Nicotinamide, a key substrate of the main nicotinamide adenine dinucleotide (NAD⁺) salvage pathway, was decreased, while quinolinate of the de novo NAD⁺ biosynthesis was increased in CHF dogs versus healthy dogs. 3‐Methylhistidine, marker for myofibrillar protein degradation, was higher in CHF dogs than non‐CHF dogs. Trimethylamine N‐oxide (TMAO) and TMAO–producing precursors, including carnitine, phosphatidylcholine, betaine, and trimethyllysine, were increased in CHF dogs versus non‐CHF dogs. Elevated levels of uremic toxins, including guanidino compounds, TMAO, and urea, were observed in CHF dogs. Pathway analysis highlighted the importance of bioenergetics and amino acid metabolism in canine MMVD.

Conclusions

Our study revealed altered energy metabolism, amino acid metabolic programming, and reduced renal function in the development of MMVD and CHF. Complex interplays along the heart‐kidney‐gut axis were implicated.

Trimethyllysine, vascular risk factors and outcome in acute ischemic stroke (MARK-STROKE)

Trimethyllysine (TML) is involved in the generation of the pro-atherogenic metabolite trimethylamine-N-oxide (TMAO) by gut microbiota. In clinical studies, elevated TML levels predicted major adverse cardiovascular events (MACE) in patients with acute or stable coronary artery disease (CAD). In contrast to cardiovascular patients, the role of TML in patients with acute cerebral ischemia is unknown. Here, we evaluated circulating TML levels in 374 stroke patients from the prospective biomarkers in stroke (MARK-STROKE) study. Compared with 167 matched healthy controls, acute ischemic stroke patients had lower median TML plasma concentrations, i.e. 0.71 vs. 0.47 µmol/L (p < 0.001) and this difference persisted after adjusting for age and sex. TML plasma concentrations were associated with age, serum creatinine, glucose, cholesterol and lysine. Patients with prevalent arterial hypertension, atrial fibrillation or a history of myocardial infarction had increased TML levels, but this observation was not independent of age, sex and GFR. In 274 patients, follow-up data were available. During a median follow-up of 284 [25th-75th percentile: 198, 431] days, TML was not associated with incident MACE (stroke, myocardial infarction, death). In summary, our data suggests a different role of TML in acute ischemic stroke compared with CAD patients.