Tissue plasminogen activator activity in human aqueous humor

Area of Science:

• Ophthalmology
• Biochemistry
• Hematology

Background:

• The aqueous humor plays a critical role in maintaining the avascular environment of the anterior eye.
• Plasminogen activators (PAs) are essential enzymes in the fibrinolytic system, regulating blood clot breakdown.
• Understanding PA activity in the aqueous humor is vital for ocular health and disease processes.

Purpose of the Study:

• To quantify plasminogen activator (PA) activity in human aqueous humor.
• To identify whether the detected PA activity is primarily tissue-type (t-PA) or urokinase-type (u-PA).

Main Methods:

• Aqueous humor samples were collected from 31 cataract surgery patients.
• Plasminogen activator activity was measured using a modified amidolytic assay.
• PA type was determined by fibrin dependence, amiloride inhibition, and specific antibody neutralization.

Main Results:

• Measurable PA activity was detected in all aqueous humor samples, with wide individual variation (0.54–26.7 mIU/ml).
• The activity was highly dependent on soluble fibrin, indicating a strong t-PA component.
• Inhibition studies and antibody blocking confirmed that the activity was almost exclusively t-PA, not u-PA.

Conclusions:

• Human aqueous humor contains significant and variable levels of plasminogen activator activity.
• The predominant form of PA activity in the aqueous humor is tissue-type plasminogen activator (t-PA).
• Similar to plasma, t-PA activity in the aqueous humor exhibits greater inter-individual variability than its antigen levels.