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Alpha 2-antiplasmin: functional characterization and metabolism in a heterozygote deficient patient
Abstract:
An 81-year-old male with a mild life-long bleeding history and an alpha 2-antiplasmin (alpha 2-AP) plasma level of 55% biological activity and 41% antigen activity (normal range 80-140%) was studied. The ratio of plasminogen binding (PB):non-plasminogen binding (NPB) alpha 2-AP assayed by modified crossed immunoelectrophoresis (CIE) was 7.3/2.7 (controls 6.3 +/- 0.49 SD/3.7 +/- 0.49 SD). The patient's alpha 2-AP showed decreased affinity for fibrin, i.e. 8.3% versus 32.4% of normal control alpha 2-AP associated with fibrin during clotting of plasma. A metabolic study performed with human purified 125I-alpha 2-AP (PB/NPB 7.7/2.3) showed a plasma radioactivity disappearance half-life of 72.9 h (n 60.1 +/- 5.3 h) with a normal fractional catabolic rate and a reduced absolute catabolic (synthetic) rate of 0.70 mg/kg/day (n 2.10 +/- 0.60 mg/kg/day). The exchange between the central and third compartment was increased. The increased alpha 2-AP PB form and the increased plasma radioactivity disappearance half-life are suggestive of a slower conversion of the PB form into the NPB form and/or slower degradation of the PB form. The bleeding tendency in this patient could be explained by decreased synthesis of alpha 2-AP and decreased binding to fibrin.
Insights
This study investigates alpha 2-antiplasmin (alpha 2-AP) deficiency in a patient with a bleeding history. Findings suggest reduced alpha 2-AP synthesis and fibrin binding contribute to bleeding tendencies.
Area of Science:
- Hemostasis and Thrombosis
- Protein Biochemistry
- Clinical Hematology
Background:
- Alpha 2-antiplasmin (alpha 2-AP) is a key inhibitor of fibrinolysis.
- Deficiency in alpha 2-AP can lead to bleeding disorders.
- Understanding the molecular mechanisms of alpha 2-AP dysfunction is crucial for diagnosing and managing bleeding tendencies.
Observation:
- A patient presented with a lifelong mild bleeding history and significantly reduced plasma alpha 2-antiplasmin (alpha 2-AP) levels (55% biological, 41% antigen activity).
- Analysis revealed an altered ratio of plasminogen binding (PB) to non-plasminogen binding (NPB) alpha 2-AP forms.
- The patient's alpha 2-AP exhibited markedly decreased affinity for fibrin compared to controls.
Findings:
- Metabolic studies indicated a reduced absolute catabolic (synthetic) rate of alpha 2-AP (0.70 mg/kg/day vs. normal 2.10 mg/kg/day).
- An increased plasma radioactivity disappearance half-life (72.9 h vs. normal 60.1 h) was observed, suggesting slower conversion or degradation of the PB form.
- Increased exchange between central and third compartments was noted.
Implications:
- The findings suggest that decreased synthesis of alpha 2-AP is a primary factor contributing to the patient's bleeding tendency.
- Reduced binding affinity of alpha 2-AP to fibrin further exacerbates the bleeding risk.
- This case highlights the importance of evaluating both synthesis and functional activity of alpha 2-AP in patients with unexplained bleeding disorders.