Interactions in vitro and in vivo between porcine tissue kallikrein and porcine plasma proteinase inhibitors

Abstract

Bläckberg M, Ohlsson K. Interactions in vitro and in vivo between porcine tissue kallikrein and porcine plasma proteinase inhibitors. Scand J Clin Lab Invest 1994; 54: 643-51.

The elimination of radio-iodinated porcine tissue kallikrein, after intravenous injection in the pig, showed a rapid initial clearance from plasma (T_1/2 approximately 10min), followed by a phase of slower elimination (T_1/2 approximately 100min). Gel filtration of plasma samples showed complexes with alpha₁-alpha₂-macroglobulin (A₁a₂-M) and alpha₁-proteinase inhibitor (A₁PI), which decreased with time. The urinary excretion of undegraded tissue kallikrein was about 1.8%. Gel filtration of urine showed a minor peak representing free tissue kallikrein and a major peak representing degradation products. On average, 8.3% was found in the liver and 1.3% in the kidneys post mortem, indicating that these are the primary organs for the elimination of tissue kallikrein.

The in vivo findings were supported by in vitro experiments. A₁a₂-M were found to be the major inhibitors of tissue kallikrein, when a mixture of the enzyme and porcine plasma was analysed by gel filtration, Immunoelectrophoresis, crossed Immunoelectrophoresis and autoradiography. A₁PI was only a minor inhibitor of tissue kallikrein. Both the A₁a₂-M and A₁-PI complex formation was found to be time-dependent and slow; unbound glandular kallikrein was still detected after 12h, even when there was a molar surplus of A₁-M and A₁PI. The complexes with A₁a₂-M and the unbound tissue kallikrein were found to be enzymatically active against low-molecular-weight chromogenic substrate. The total tissue kallikrein-inhibiting capacity of plasma seemed to be exceeded at a concentration of 800 KU/1 when analysed using the rat uterus bioassay.

A₁a₂-M appears to be the major inhibitor of tissue kallikrein in plasma and the complexes are removed mainly by the reticulo-endothelial system, such as that in the liver.

Key Words:

• alpha-macroglobulin
• alpha₁-proteinase inhibitor
• bradykinin
• tissue kallikrein