Growth-modulating effects of dichloro myristic and dichloro stearic acid in cell cultures

Chloro-containing fatty acids are a major fraction of extractable, organically bound chlorine in fish. It has been suggested that dichloro stearic acid (9,10-dichlorooctadecanoic acid) (C18) is metabolized to dichloro myristic acid (5,6-dichlorotetradecanoic acid) (C14) which accumulates in tissues. Hence, the biological effects of the C18 dichloro fatty acid could be due to formation of the C14 dichloro fatty acid. In this study we have compared the effects of dichloro stearic and dichloro myristic acid on growth of three widely differing cell lines. Both fatty acids inhibited cell growth; however, dichloro myristic acid had a weaker growth inhibitory effect than dichloro stearic acid. Dichloro myristic acid had a biphasic effect (i.e. growth was stimulated at low concentrations, followed by inhibition at higher concentrations) on the growth of human hepatoma cells and immortalized human kidney epithelial cells, but no such effect on human microvascular endothelial cells. The order of potency for growth inhibition by dichloro myristic acid was consistently human hepatoma cells>immortalized human kidney epithelial cells >human microvascular endothelial cells, whereas the relative potency of dichloro stearic acid was variable. Albumin alone stimulated cell growth and had a stronger protective effect against growth inhibition by dichloro myristic acid than against that of dichloro stearic acid. It seems unlikely that a major part of the effect of dichloro stearic acid on cell growth is caused by conversion to dichloro myristic acid.