Promotive effects of hyperthermia on the inhibition of DNA synthesis in ehrlich ascites tumor cells by eicosapentaenoic and docosahexaenoic acids.

OBJECTIVE

To evaluate inhibitory effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on DNA synthesis in combination with hyperthermia in vitro.

METHODS

A suspension of Ehrlich ascites tumor cells (EAT) was mixed with DHA or EPA in a glass tube, heated at 37 degrees C, 40 degrees C, or 42 degrees C for 1 h in a water bath, and cultured at 37 degrees C for 19 or 96 h. DNA synthesis was assayed by monitoring of the incorporation of [3H]-thymidine into the acid-insoluble fraction. DHA or EPA incorporated into EAT cells was extracted and measured by thin-layer chromatography and gas-liquid chromatography.

RESULTS

The inhibition of DNA synthesis by EPA or DHA increased markedly upon the treatment at 42 degrees C and 40 degrees C compared to that at 37 degrees C. At 37 degrees C, inhibitory action of EPA was more potent than that of DHA at low concentrations (at 50 microM -- DNA synthesis level: EPA, 63.1%; DHA, 87.9%), whereas inhibitory action of DHA was higher at 150 muM (16.7%, 4.4%, ibid.). The effect of DHA compared to EPA was more marked at 40 degrees C (29.0%, 19.2% at 100 microM) or 42 degrees C (19.7%, 10.6% at 100 microM). Evaluation of DNA synthesis rate in the cells treated for 1 h by EPA or DHA with the next culturing of EAT cells for 19 h resulted in the enhanced inhibitory activity of EPA even at concentrations as low as 50 microM at either 37 degrees C (0.5%, 11.3%) or 42 degrees C (0.6%, 4.5%), which in these conditions was higher than that of DHA. At the same time the rate of incorporation of EPA in EAT cells at 37 degrees C or 42 degrees C was lower than that of DHA.

CONCLUSIONS

Administration of DHA or EPA in vitro significantly inhibit DNA synthesis, and such effect is enhanced by combination of PUFAs with hyperthermia.