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

The elimination of radio-iodinated porcine tissue kallikrein, after intravenous injection in the pig, showed a rapid initial clearance from plasma (T1/2 approximately 10min), followed by a phase of slower elimination (T1/2 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.