Pulmonary hypertension (PH), classified into five categories according to different etiology, is a kind of progressive cardiovascular disease (CVD) that results in heart failure and death eventually (1). Although the knowledge on PH pathogenesis and treatment has improved in the past decade, it is still regarded as an extremely complex disease that required comprehensive and time-consuming inspections and evaluations, and the survival of the patient is still worrying. Nowadays, how to better manage patients to improve their prognosis is a tremendous challenge.

Facing this plateau, the exploration of serological biomarkers in PH is a promising way for effective disease management (1). However, the well-recognized serological biomarker is lacking except for brain natriuretic peptide (BNP) and N-terminal pro-BNP (NT-proBNP) up to date. A growing body of literature recently implicates metabolites that include betaine, choline, and trimethylamine N-oxide in CVD risk (2–6). Betaine was obtained from food sources, such as grain products, vegetables, red meat, eggs, and fish (7), or synthesized de novo from the irreversible oxidation of choline via betaine aldehyde dehydrogenase and choline dehydrogenase predominantly in the liver, a process under homeostatic control in healthy humans (8). It has been suggested that high betaine levels may exert the prognostic value of major adverse cardiovascular event risk in table cardiac subjects who underwent elective diagnostic coronary angiography (9) and high dietary betaine intake was associated with an increased risk of incident coronary heart disease (10). Similar results were also reported in patients with diabetes mellitus (11).

To our best knowledge, the role of betaine in PH has never been investigated. Here, we aimed to investigate the association of plasma betaine concentration and disease severity of patients with PH and to examine whether betaine could be served as a biomarker in clinical outcomes. Moreover, we also preliminarily explored the value of dynamic changes of betaine (Δbetaine) in PH.

This is a clinical study designed to evaluate the association between betaine levels and PH. The study was approved by the Ethics Committees of Fuwai Hospital and adhered to the Declaration of Helsinki. All patients were provided written informed consent.

Pulmonary hypertension is an under-recognized global health concern, and the general treatment of PH predominantly depends on the type and severity and the patient’s symptoms (14). Metabolomics provides the measurement of various metabolites in human samples, which holds great promise for the discovery of pathways linked to disease processes in clinical research (15). Researchers had observed associations between betaine with the prevalence of type 2 diabetes mellitus (16). Additionally, systemic levels of choline and betaine, two closely connected metabolites in the dietary lipid phosphatidylcholine, were also reported to be independently associated with the prevalence of CVDs (15). Moreover, a number of studies have reported increased concentration of betaine associated with the increased incidence of acute coronary syndromes and increased blood lipid concentrations (9, 17, 18). These studies suggest a potential link between betaine with type 2 diabetes mellitus and CVDs. However, less is known about the role of betaine in PH. In this study, we conducted a clinical study to assess the associations between plasma betaine concentration with severity and prognosis of patients with PH.

The current study’s 50th percentile of plasma betaine concentration was 49.8 mmol/L (interquartile range, 39.0–68.3), which was comparable with two cohorts of patients with CVDs (9, 19). Based on this baseline, we divided the study cohort into low and high betaine groups. Several key findings were noted in the baseline and correlation analysis. First, plasma betaine level was higher in older patients, and patients with high betaine were characterized by poor WHO-FC classification, higher NT-proBNP levels, larger RVD, and lower TAPSE and cardiac output index compared to those with low levels. Second, plasma betaine level was correlated positively with age, NT-proBNP, creatinine, and WHO-FC, and negatively with TAPSE, peak VO₂, VO₂%, and cardiac output index, of which WHO-FC, NT-proBNP, TAPSE, and cardiac output index remained statistically significant after adjusting for confounding factors. These correlating variables from the laboratory tests, echocardiography, and hemodynamics were all consensus-based criteria that have been identified to evaluate the severity and the risk stratification of patients with PH (1, 20). The worsening WHO-FC is not only a strong predictor of follow-up survival but also an alarming indicator of disease progression. NT-proBNP is not specific for PH but remains the biomarker in the routine practice to provide information of myocardial stress at the time of diagnosis and follow-up assessments, which is also regarded as a strong prognostic predictor in PH (21, 22). The cardiac output index assessed by RHC and the TAPSE measured by non-invasive echocardiogram are both robust reflections of heart function and are commonly used as indicators for severity assessment (1). Moreover, high levels of betaine remained robust to predict increased adverse prognosis regardless of potential confounders. Together, these results indicated that the plasma betaine level might have a positive correlation with PH severity in our study cohort. We had noticed no statistical differences in 6MWD and peakVO₂ between groups were explored. This might attribute to the fact that severe patients with PH did not receive 6MWD and cardiopulmonary exercise tests, which narrowed the actual gap between the two groups.

To better understand the prognostic role of betaine in PH treatment, we conducted an analysis with follow-up ascertainment of primary endpoints in patients who received recommended therapies. Here, we found that both low plasma betaine and dynamic decreased levels were associated with a preferable prognosis in patients with PH. The results remind us of the role of NT-proBNP in PH and we reasonably postulate plasma betaine probably plays a similar role as a biomarker. Betaine changes could provide more information about the patient, and the lifestyle and diet of the patients included in the analysis are relatively consistent, which could largely reduce the effect of diet on betaine biosynthesis. In addition, Δbetaine was positively correlated with ΔNT-proBNP, indicating the dynamic change of betaine might reflect the disease condition and help for the management of PH.

The evidence showed that betaine enabled to protect internal organs, improve vascular risk factors, and enhance performance (8). The positive effects of betaine supplementation in treating hyper-homocystinurics (23, 24) and alcohol-induced hepatic steatosis (25) have also been elucidated. As a multifunctional agent, betaine possesses various physiological activities that include anti-oxidation, anti-inflammation, and anti-fibrosis (26–28). Notably, one study found that betaine exerted an anti-angiogenic activity in vivo and in vitro through the suppression of nuclear factor-κ B (NF-κ B) and Akt activation (29), another study showed betaine attenuated isoproterenol-induced acute myocardial ischemia via the regulation of signal transducer and activator of transcription 3 and apoptotic pathways (30). However, our study pointed out that high betaine levels were associated with poor clinical outcomes in patients with PH. Similarly, a meta-analysis also revealed that increased concentrations of betaine were correlated with the risk of major adverse cardiovascular events (31). We postulated that the increase of betaine in plasma might be a consequence due to disease progression rather than a cause. Lever et al. (19) speculated that betaine might be leaking from tissues where it was accumulated as an osmolyte. The leakage was a part of pathology in disease indicating the metabolic failure in patients. More severe patients probably have more leakage resulting in higher metabolite concentrations in plasma. However, further studies are needed to dissect the underlying mechanisms involved in this association.

Our study is by far the largest of its kind to examine the relationship of plasma betaine with PH development and prognosis. The cohort included PH patients without connective tissue disease, immune disease, acute coronary syndromes, active infection, malignancy, congestive heart failure, or diabetes. As such, our findings are less likely confounded by other pre-existing disease conditions and medication usage. However, several potential concerns or limitations are worth mentioning. Firstly, we do not have information regarding the dietary patterns, which are significantly related to the betaine concentration detected in the blood (32). Similarly, no information was available regarding non-prescriptive dietary supplements that may have been utilized by patients at the time of the study. Moreover, as a single-center cohort, this research was conducted on Chinese populations, where dietary habits differ dramatically from that of western countries. As such, the prospective association between plasma betaine and PH remains uncertain in western populations. Regardless, we would like to emphasize that our study findings are preliminary and were just hypothesize generating. Since this work was designed as an observational study, the associations in the current study cannot be considered causal, all findings need to be further investigated by large-scale randomized trials. Our findings, if further confirmed, call for collaborative research effort in the next decade could lead to significant further progress and perhaps even a cure of PH.

The increase in plasma betaine was associated with PH severity and heralded a poor prognosis of patients with PH. Moreover, the dynamic rise of betaine level was also associated with adverse prognosis. Our study revealed the promising biomarker role of betaine and further explorations are calling for.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Ethics Committees of Fuwai Hospital (Approval No: 2018-1063). The patients/participants provided their written informed consent to participate in this study.

YY, JXu, JXue, and JZ contributed to the study design and interpretation of the results. YY, JXu, JXue, JZ, XL, BS, and BY contributed to the collection, analysis, or interpretation of data. YY and JXu prepared the manuscript. ZL, ZZ, QL, QZ, LZ, and CX critically revised the manuscript. All authors read and approved the final submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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