Cytotoxicity tests on eye drop preparations by LDH release assay in human cultured cell lines

Using a simple protocol developed for sensitive assays of lactate dehydrogenase (LDH) release by cultured human cell lines, cytotoxicity was observed in seven of nine commercially available eye drop preparations tested using a human lung carcinoma cell line, SQ-5, and in eight of nine preparations using a human leukaemia cell line, HL60. However, six of nine preparations were found to be cytotoxic to SQ-5 using the neutral red uptake assay. One of these eye drop preparations induced release of LDH within 1 min from SQ-5 cells and within 5 min from HL60 cells. This preparation also induced a three-fold increase in LDH activity in tears, 10 sec after its application to human eyes, suggesting that cells in contact with the tears were injured by the eye drops in vivo. An eye drop preparation that had no detectable cytotoxicity in vitro caused no change of LDH activity in human tears. LDH release assay has therefore been shown to be a useful method for detecting a direct relationship between in vitro cytotoxicity and weak in situ cytotoxicity to human eyes.