INCREASED ELASTIN-DEGRADING ACTIVITY AND NEOINTIMAL FORMATION IN PORCINE AORTIC ORGAN-CULTURE - REDUCTION OF BOTH FEATURES WITH A SERINE PROTEINASE-INHIBITOR

We investigated the association between tissue elastolytic activity an d the development of neointimal formation using a previously described porcine aortic organ culture. Neointimal formation is associated with the presence of intact endothelium (nondenuded cultures) but is marke dly reduced if endothelial cells are removed (denuded cultures). In no ndenuded organ cultures, elastolytic activity assessed by using [H-3]e lastin increased sixfold at day 3 after initiation of the culture (P<. 01), a time earlier than the previously published increase in intimal smooth muscle cells (ISMCs). Elastolytic activity did not increase fro m day 3 to day 7 despite doubling of ISMCs but did double by day 14 (P <.01) and remained elevated to day 28, correlating with increases in I SMCs. In denuded organ cultures, elastolytic activity was much lower t han in nondenuded organ cultures at day 3 (P<.05) but increased fivefo ld in the presence of nondenuded organ culture conditioned medium (P<. 01). Addition of alpha(1)-proteinase inhibitor for 14 days caused a 60 % decrease in elastolytic activity in nondenuded organ cultures and a 27% reduction in ISMCs compared with untreated controls (P<.05 for bot h). The elastolytic activity, resolved as lytic bands on an elastin su bstrate gel, reflected candidate enzymes, one at 76 kD and perhaps a d oublet at 43 and 50 kD. Our study suggests that endothelial cells rele ase a soluble agent that enhances elastin-degrading activity in the ao rta and may at least partially account for the initiation of neointima l formation.