Longitudinal Trends of Salivary Oxidized Thymosin β4 and β10 in Preterm Infants with Bronchopulmonary Dysplasia

Background: Oxidative stress plays a key role in the pathogenesis of complications in preterm infants, including bronchopulmonary dysplasia (BPD). Thymosin β4 (Tβ4) and thymosin β10 (Tβ10) are proteins involved in tissue repair and responses to oxidative stress, but their role in extremely preterm neonates remains poorly understood. Methods: A total of 149 saliva samples from 18 infants with gestational age < 30 weeks were analyzed. Salivary proteins and their proteoforms were characterized using an integrated proteomic platform based on nano-HPLC-ESI-MS. Relative quantification was performed using extracted ion current (XIC) peak areas. Associations with postmenstrual age, oxygen requirement, and BPD development were assessed, including longitudinal analysis using generalized estimating equation (GEE) models. Results: Significant correlations were found between postmenstrual age and total Tβ4 (p = 0.001), oxidized Tβ4 percentage (p = 0.025), and total Tβ10 (p = 0.043). Higher oxygen requirement was associated with lower levels and percentages of oxidized Tβ10 (p = 0.005; p < 0.001). No significant differences were observed during the first week of life between neonates who later developed BPD and those who did not. However, longitudinal analysis showed that in neonates without BPD, total and oxidized Tβ10 and total Tβ4 increased over time, whereas in neonates with BPD, these biomarkers remained stable or decreased. The increase in oxidized Tβ10 percentage was slower in infants with BPD. Conclusions: Although no early differences were detected, longitudinal trajectories of Tβ4 and Tβ10 differed between infants with and without BPD. Postnatal changes in these proteins may be associated with differences in clinical course and exposure to postnatal oxidative stress.