Mechanism For The Antitumor Role Of Docosahexaenoic Acid And Its Oxidation Products

?3 polyunsaturated fatty acids(PUFA)is an essential fatty acid,and its balanced intake with ?6 PUFA is the guarantee of health.However,due to the westernized diet,the national dietary intake of ?3 PUFA is significantly lower than that of ?6 PUFA.This imbalance is associated with a variety of diseases,including tumors.Among many malignant tumors,prostate cancer has the characteristics of old age,simple screening,long course of disease,good prognosis,and strong environmental involvment.Therefore,different from other cancers,nutritional support and dietary intervention have more important significance for the prevention,prognosis and prognosis of prostate cancer.This epidemiological study and that prostate specific Pten knockout mice(prostate cancer model)suggests ?3 PUFAs may play an important role in inhibiting the growth of prostate cancer,attenuate inflammation and improve the survival rate,while ?6 PUFAs has the opposite effect.Docosahexaenoic acid(DHA)has the strongest antitumor effect in ?3 PUFAs.However,in vivo,especially in tumor microenvironment,there are complex interactions between the intrinsic cells and infiltrating cells.On this level,the inhibition mechanism of ?3 PUFAs for prostate cancer is still lack of systematic research.In in vivo and in vitro studies,we found that the regulatory effect of DHA on prostate cancer depends on its oxidation process,through at least two mechanisms: 1)Resolvin(RvD)D1 and D2,the metabolites of DHA,can regulate the polarization of macrophages in tumor microenvironment and then inhibit the growth of tumor cells;2)the peroxides produced by DHA through lipoxygenase dependent or independent pathway can directly induce the ferroptosis of tumor cells.In view of these two mechanisms,this study has done the following work:(1)This study found that although dietary DHA can inhibit prostate cancer in vivo,neither DHA(10 ?M)nor RvD(100 nM)can directly inhibit the proliferation of prostate cancer cells in vitro.Unexpectedly,in the cancer macrophage co culture system,DHA and RvD significantly inhibited the proliferation of cancer cells.It was found that the antitumor effect of Rvd1 and Rvd2 was mediated by inhibiting the polarization of tumor associated macrophages(TAM or M2d)and the expression of vascular endothelial growth factor(VEGF)and epidermal growth factor(EGF)in TAM.At the same time,in human THP-1 monocytes and mouse bone marrowderived macrophages,RvD1 and RvD2 also play an anti-inflammatory role by inhibiting the M1 polarization induced by LPS-IFN ?,inhibiting the expression of M1 type cytokines such as TNF-?,promoting the M2 a polarization mediated by IL-4,and promoting the expression of M2 type cytokines such as IL-10.By screening the downstream signaling pathway of RvD receptor,we found that these differential polarization processes are at least partially mediated by protein kinase A.(2)In this study,we found that in many tumor cells,the physiological concentration of PUFA has no cytotoxicity but can greatly promote the sensitivity of tumor cells to ferroptosis inducers,and this effect is positively related to the unsaturation of PUFA,while DHA,as the most common unsaturated PUFA in vivo,has the strongest effect of promoting ferroptosis.We also used inhibitors,gene silencing and gene overexpression to confirm that the peroxidation products of DHA can be produced by both of ALOX5 dependent and independent pathways.(3)In addition to traditional antioxidants,we also found that a variety of small molecular inhibitors targeting receptor interacting serine / threonine kinase 1(RIPK1)can inhibit ferroptosis in tumor cells.The phosphorylation level of RIPK1 was also up-regulated during ferroptois.These results suggest that ripk1 may play a key role in ferroptosis.In addition,RIPK1 and sequencesome-1(SQSTM1/p62)protein had significant binding in ferroptosis.In this process,threonine 269 and serine 272 of SQSTM1/p62 were phosphorylated significantly.However,the phosphorylation and cell death of SQSTM1/p62 were significantly inhibited by using a variety of RIPK11 inhibitors or inactivating the kinase activity of RIPK1 by mutation.We further found that ripk1 and SQSTM1/p62 further regulated caspase dependent activation of gasdermin D,leading to cell death.To conclude,this study explored the mechanism of DHA antagonizing prostate cancer from many aspects,which is of great theoretical significance to understand the regulation of ?3 PUFAs on tumor and chronic inflammation,and also of great practical significance to the application of its key metabolites in the future.PUFA is a key essential fatty acid.This study also provides dietary guidance for the treatment of inflammatory and tumor related diseases.