Sources of variability in quantifying circulating thymosin beta-4: literature review and recommendations.

INTRODUCTION: Thymosin beta-4 (TB4) is an endogenous peptide with protective and regenerative effects in models of cellular and organ injury. TB4 is increasingly measured as a potential plasma or serum biomarker in human cardiovascular, liver, infectious, and autoimmune disease. AREAS COVERED: The focus of this review is the quantification of TB4 in clinical cohort studies and whether reported TB4 concentrations differ with respect to method of sample preparation. We survey current literature for studies measuring TB4 in human serum or plasma and compare reported concentrations in healthy controls. EXPERT OPINION: We find substantial intra- and inter- study variability in healthy controls, and a lack of protocol standardization. We further highlight three factors that may confound TB4 clinical measurements and should be considered in future study design: 1) residual platelets remaining in suspension after centrifugation, 2) TB4 release following ex vivo platelet activation, and 3) specificity of assays towards posttranslational modifications. Accordingly, we put forth our recommendations to minimize residual and activated platelets during sample collection, and to cross-validate TB4 measurements using both antibody-based and mass spectrometry-based methods.

Thymosin Beta-4 Is Elevated in Women With Heart Failure With Preserved Ejection Fraction.

BACKGROUND: Thymosin beta-4 (TB4) is an X-linked gene product with cardioprotective properties. Little is known about plasma concentration of TB4 in heart failure (HF), and its relationship with other cardiovascular biomarkers. We sought to evaluate circulating TB4 in HF patients with preserved (HFpEF) or reduced (HFrEF) ejection fraction compared to non-HF controls. METHODS AND RESULTS: TB4 was measured using a liquid chromatography and mass spectrometry assay in age- and sex-matched HFpEF (n=219), HFrEF (n=219) patients, and controls (n=219) from a prospective nationwide study. Additionally, a 92-marker multiplex proximity extension assay was measured to identify biomarker covariates. Compared with controls, plasma TB4 was elevated in HFpEF (985 [421-1723] ng/mL versus 1401 [720-2379] ng/mL, P<0.001), but not in HFrEF (1106 [556-1955] ng/mL, P=0.642). Stratifying by sex, only women (1623 [1040-2625] ng/mL versus 942 [386-1891] ng/mL, P<0.001), but not men (1238.5 [586-1967] ng/mL versus 1004 [451-1538] ng/mL, P=1.0), had significantly elevated TB4 in the setting of HFpEF. Adjusted for New York Heart Association class, N-terminal pro B-type natriuretic peptide, age, and myocardial infarction, hazard ratio to all-cause mortality is significantly higher in women with elevated TB4 (1.668, P=0.036), but not in men (0.791, P=0.456) with HF. TB4 is strongly correlated with a cluster of 7 markers from the proximity extension assay panel, which are either X-linked, regulated by sex hormones, or involved with NF-κB signaling. CONCLUSIONS: We show that plasma TB4 is elevated in women with HFpEF and has prognostic information. Because TB4 can preserve EF in animal studies of cardiac injury, the relation of endogenous, circulating TB4 to X chromosome biology and differential outcomes in female heart disease warrants further study.