Response: endogenous levels of D12-PGJ3 derived from eicosapentaenoic acid

In response to the comment by Tsikas and Stichtenoth,¹  we would like to provide clarification for their views and address the questions. First, while it is correct that the reactivity of the 2 electrophilic centers could make these classes of compounds less bioavailable, our data clearly demonstrates that intraperitoneal administration of D12-PGJ3 completely eradicates leukemia stem cells in the bone marrow and spleen. This suggests that the formation of Michael adducts does not affect their antileukemic activity nor systemic bioavailability. Second, it is not surprising to find that the pM concentrations of 2- and 3-series CyPGs (of the J class) in the urine. Our studies show (see Figure 1 in Hegde et al² ) that macrophages cultured with 50μM EPA for a week, produce D12-PGJ3 in the cell culture media in quantities (nM) sufficient to target leukemia stem cells. The authors show very low levels (pM) of these metabolites in urine. However they did not measure levels in the serum and it would be difficult to infer serum concentrations from these measurements. Moreover, it is not surprising that given the low rate of conversion, the level of D12-PGJ3 from ARA-derived EPA is likely to be in the pM range as described. In the future, quantitation of these metabolites in the serum will be necessary to provide a true measure of their concentration, particularly in EPA-supplemented individuals. Unpublished studies from our laboratory confirm the metabolism of dietary EPA generates D12-PGJ3 at concentrations in the serum high enough to induce apoptosis in leukemia stem cells in vitro. A manuscript with these results is being currently prepared for submission.