FIGURE 6.

UDC-DHA is more stable than DHA. (A) Time course of the effect of DHA and UDC-DHA on cell viability revealed that UDC-DHA acted gradually and more persistently than DHA. (B) Pre-incubation of DHA but not UDC-DHA in culture medium greatly reduced growth inhibitory effect. DHA and UDC-DHA were incubated in culture medium at 37°C for various time periods and then added to HepG2 cells for 72 h, followed by the MTT assay. Results were obtained from at least three independent experiments and data are presented as mean ± SEM. (C) Daily change of culture medium containing DHA but not UDC-DHA significantly increased the growth inhibitory effect. HepG2 cells were treated with indicated concentrations of DHA or UDC-DHA for 72 h with or without daily change of drug containing medium and then subjected to the MTT assay. Results are presented as mean ± SEM of three independent experiments. *, p < 0.05; **, p < 0.01. (D) Stability of DHA and UDC-DHA in cell culture medium measured by HPLC-MS/MS. DHA (20 μM) or UDC-DHA (2 μM) was incubated in cell culture medium and 500 μl aliquots were extracted with ethyl acetate for HPLC-MS/MS analysis. The concentrations of DHA and UDC-DHA at 3, 6 or 24 h were calculated by comparison with that of the 0 h. The data are presented as mean ± SEM of three experiments. n.d., not detected.