Cellular and biochemical heterogeneity contributes to the phenotypic diversity of transfusion-dependent β-thalassemia.

Transfusion-dependent thalassemia (TDT) is a type of protein aggregation disease. Its clinical heterogeneity imposes challenges in effective management. Red blood cell (RBC) variables may be clinically relevant as mechanistic parts or tellers of TDT pathophysiology. This is a cross-sectional study of RBC and plasma physiology in adult patients with TDT vs healthy control. TDT plasma was characterized by increased protein carbonylation, antioxidants, and larger than normal extracellular vesicles. RBCs were osmotically resistant but prone to oxidative hemolysis. They overexposed phosphatidylserine and exhibited pathologically low proteasome proteolytic activity (PPA), which correlated with metabolic markers of the disease. RBC ultrastructure was distorted, with splenectomy-related membrane pits of 300 to 800 nm. Plasma metabolomics revealed differences in heme metabolism, redox potential, short-chain fatty acids, and nitric oxide bioavailability, but also in catecholamine pathways. According to coefficient of variation assessment, hemolysis, iron homeostasis, PPA, and phosphatidylserine exposure were highly variable among patients, as opposed to RBC fragility and plasma antioxidants, amino acids, and catecholamines. Sex-based differences were detected in hemolysis, redox, and energy variables, whereas splenectomy-related differences referred to thrombotic risk, RBC morphology, and plasma metabolites with neuroendocrine activity. Hepcidin varied according to oxidative hemolysis and metabolic markers of bacterial activity. Patients with higher pretransfusion hemoglobin levels (>10 g/dL) presented mildly distorted profiles and lower membrane-associated PPA, whereas classification by severity of mutations revealed different levels of hemostasis, inflammation, plasma epinephrine, hexosamines, and methyltransferase activity markers. The currently reported heterogeneity of cellular and biochemical features probably contributes to the wide phenotypic diversity of TDT at clinical level.