Lactate dehydrogenase leakage as a marker for apoptotic cell degradation induced by influenza virus infection in human fetal membrane cells.

OBJECTIVE In order to elucidate the implication of apoptosis in lactate dehydrogenase (LDH) leakage from influenza virus-infected cells, the effects of a general caspase inhibitor, N-t-Boc-Asp(OMe)-fluoromethylketone (Boc-D-fmk), on LDH leakage, apoptosis induction and virus proliferation were examined. METHODS Cultured human fetal membrane chorion and amnion cells were incubated with or without Boc-D-fmk after influenza virus infection. LDH leakage was estimated by measuring LDH activities in the culture supernatants and cell lysates. The extent of apoptosis was determined by caspase-3 protein cleavage and DNA fragmentation. Virus proliferation was determined by a plaque-forming assay. RESULTS While virus proliferation was observed in both chorion and amnion cells, the virus infection resulted in LDH leakage, caspase-3 protein cleavage, and oligonucleosomal DNA fragmentation, all of which were observed only in the chorion cells and inhibited by the presence of Boc-D-fmk except for the virus proliferation. CONCLUSION LDH level in amniotic fluid is known to be one of markers for predicting fetal membrane damage. Therefore, this study provides a possible diagnostic application of LDH level to predict the extent of tissue damage of fetal membranes via apoptosis induced by influenza virus infection.