N-3 PUFA dietary supplementation inhibits proliferation and store-operated calcium influx in thymoma cells growing in Balb/c mice

The antitumor effect of daily individual administration of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (2 g/kg body weight) in Balb/c mice bearing a transplantable thymoma was investigated. Mice received oleic acid (control group), EPA and DHA ethyl esters starting 10 days before tumor inoculation. Analysis of phospholipid composition of neoplastic cell revealed that EPA and DHA levels were significantly increased (63 and 22% increase) after EPA and DHA treatments, respectively. Conversely, decreased levels of arachidonic acid were found in both cases (19 and 24% decrease in EPA and DHA groups, respectively). EPA and DHA delayed the appearance of macroscopic ascites (100% of animal, from 7 to 28 days), prolonged animal survival (100% of animal, from 22 to 32 and 33 days, respectively) and reduced the percentage of proliferating tumor cells detected by immunostaining of proliferation cell nuclear antigen (PCNA) (80 and 85% decrease, respectively). Moreover, the regulatory effects of these dietary n;-3 fatty acids on the influx of Ca(2+), activated by depletion of intracellular stores with thapsigargin (Tg), were investigated. By using a Ca(2+)-free/Ca(2+)-reintroduction protocol and Fura-2 as fluorescent indicator of intracellular free Ca(2+)([Ca(2+)](i)), we observed that EPA and DHA treatments markedly decreased Tg-induced rise in [Ca(2+)](i) (49 and 37% decrease, respectively). This effect was related to the inhibition of the store-operated Ca(2+) influx, as confirmed also by Mn(2+) influx experiments. The inhibitory action of EPA and DHA on the store-operated Ca(2+) influx could explain, at least in part, their antitumoral activity, as this Ca(2+) mobilization pathway appears to be involved in the cell signaling occurring in non-excitable cells to evoke many cellular processes, including cell proliferation.