Involvement of cysteine proteinases in excystment of
Paragonimus ohirai metacercariae induced by sodium cholate and A23187.
Ikeda T.
Department of Medical Zoology, Kanazawa Medical University, Uchinada, Ishikawa,
920-0293.
The involvement of intrinsic proteinases in the excystment of Paragonimus ohirai
metacercariae was studied in in vitro excystment induced by sodium (Na) cholate,
a bile salt and A23187, a Ca2+ ionophore. The effects of various proteinase
inhibitors on the in vitro excystment were examined and similar inhibitory
profiles were obtained. Benzyloxycarbonyl-L-leucyl-L-leucinal (Z-Leu-Leu-H), a
cysteine proteinase inhibitor and 4-(2-aminoethyl)-benzenesulfonyl fluoride (Pefabloc
SC), a serine proteinase inhibitor completely inhibited excystment, while
L-3-carboxy-2,3-trans-epoxypropionyl-leucylamido (4-guanidino)-butane (E-64), a
cysteine proteinase inhibitor and leupeptin, a cysteine/serine proteinase
inhibitor permitted partial excystment at a lower rate, but inhibited it from
proceeding from the partial excystment stage. In secretions released from
metacercariae during excystment, proteinase activities detected towards various
fluorogenic peptidyl substrates were almost completely inhibited by Z-Leu-Leu-H
and E-64, but not by Pefabloc SC. Sodium cholate induced a higher secretion of
cysteine proteinases and a higher rate of excystment than A23187. Profiles of
cysteine proteinase activities towards five peptidyl substrates detected were
markedly different among the two secretions and the lysate of newly excysted
juveniles. Newly excysted juveniles released cysteine proteinases with similar
activity profiles and levels to metacercariae induced by Na cholate-incubation,
whereas the release of cysteine proteinases was reduced compared with
metacercariae induced by A23187-incubation. These results provide valuable
information about the involvement of intrinsic proteinases in metacercarial
excystment.