Role of macrophage lipids in regulating tumoricidal activity

The Dysregulation of Essential Fatty Acid (EFA) Metabolism May Be a Factor in the Pathogenesis of Sepsis

I propose that a deficiency of essential fatty acids (EFAs) and an alteration in their (EFAs) metabolism could be a major factor in the pathogenesis of sepsis and sepsis-related mortality. The failure of corticosteroids, anti-TNF-α, and anti-interleukin-6 monoclonal antibodies can be attributed to this altered EFA metabolism in sepsis. Vitamin C; folic acid; and vitamin B1, B6, and B12 serve as co-factors necessary for the activity of desaturase enzymes that are the rate-limiting steps in the metabolism of EFAs. The altered metabolism of EFAs results in an imbalance in the production and activities of pro- and anti-inflammatory eicosanoids and cytokines resulting in both hyperimmune and hypoimmune responses seen in sepsis. This implies that restoring the metabolism of EFAs to normal may form a newer therapeutic approach both in the prevention and management of sepsis and other critical illnesses.

Fatty acid metabolism and radiation-induced anti-tumor immunity

Fatty acid metabolic reprogramming has emerged as a major regulator of anti-tumor immune responses with large body of evidence that demonstrate its ability to impact the differentiation and function of immune cells. Therefore, depending on the metabolic cues that stem in the tumor microenvironment, the tumor fatty acid metabolism can tilt the balance of inflammatory signals to either promote or impair anti-tumor immune responses. Oxidative stressors such as reactive oxygen species generated from radiation therapy can rewire the tumor energy supply, suggesting that radiation therapy can further perturb the energy metabolism of a tumor by promoting fatty acid production. In this review, we critically discuss the network of fatty acid metabolism and how it regulates immune response especially in the context of radiation therapy.

Recent Advances on the Role of ATGL in Cancer

The hypoxic state of the tumor microenvironment leads to reprogramming lipid metabolism in tumor cells. Adipose triglyceride lipase, also known as patatin-like phospholipase= domain-containing protein 2 and Adipose triglyceride lipase (ATGL), as an essential lipid metabolism-regulating enzyme in cells, is regulated accordingly under hypoxia induction. However, studies revealed that ATGL exhibits both tumor-promoting and tumor-suppressing effects, which depend on the cancer cell type and the site of tumorigenesis. For example, elevated ATGL expression in breast cancer is accompanied by enhanced fatty acid oxidation (FAO), enhancing cancer cells’ metastatic ability. In prostate cancer, on the other hand, tumor activity tends to be negatively correlated with ATGL expression. This review outlined the regulation of ATGL-mediated lipid metabolism pathways in tumor cells, emphasizing the Hypoxia-inducible factors 1 (HIF-1)/Hypoxia-inducible lipid droplet-associated (HIG-2)/ATGL axis, peroxisome proliferator-activated receptor (PPAR)/G0/G1 switch gene 2 (G0S2)/ATGL axis, and fat-specific protein 27 (FSP-27)/Early growth response protein 1 (EGR-1)/ATGL axis. In the light of recent research on different cancer types, the role of ATGL on tumorigenesis, tumor proliferation, and tumor metastasis was systemically reviewed.

Targeting Metabolic Pathways of Myeloid Cells Improves Cancer Immunotherapy

Tumor-infiltrating myeloid cells are a prominent pro-tumorigenic immune cell population that limit host anti-tumor immunity and present a significant obstacle for many cancer immunotherapies. Targeting the mechanisms regulating myeloid cell function within the tumor microenvironment may overcome immunotherapy resistance in some cancers. Recent discoveries in the emerging field of immunometabolism reveal that the metabolic profiles of intratumoral myeloid cells are rewired to adapt to the nutrition-limited tumor microenvironment, and this shapes their pro-tumor phenotypes. Interestingly, metabolic modulation can shift these myeloid cells toward the immune-stimulating anti-tumor phenotype. In this review, we will highlight the roles of specific metabolic pathways in the activation and function of myeloid cells, and discuss the therapeutic value of metabolically reprogramming myeloid cells to augment and improve outcomes with cancer immunotherapy.

Contradictory roles of lipid metabolism in immune response within the tumor microenvironment

Complex interactions between the immune system and tumor cells exist throughout the initiation and development of cancer. Although the immune system eliminates malignantly transformed cells in the early stage, surviving tumor cells evade host immune defense through various methods and even reprogram the anti-tumor immune response to a pro-tumor phenotype to obtain unlimited growth and metastasis. The high proliferation rate of tumor cells increases the demand for local nutrients and oxygen. Poorly organized vessels can barely satisfy this requirement, which results in an acidic, hypoxic, and glucose-deficient tumor microenvironment. As a result, lipids in the tumor microenvironment are activated and utilized as a primary source of energy and critical regulators in both tumor cells and related immune cells. However, the exact role of lipid metabolism reprogramming in tumor immune response remains unclear. A comprehensive understanding of lipid metabolism dysfunction in the tumor microenvironment and its dual effects on the immune response is critical for mapping the detailed landscape of tumor immunology and developing specific treatments for cancer patients. In this review, we have focused on the dysregulation of lipid metabolism in the tumor microenvironment and have discussed its contradictory roles in the tumor immune response. In addition, we have summarized the current therapeutic strategies targeting lipid metabolism in tumor immunotherapy. This review provides a comprehensive summary of lipid metabolism in the tumor immune response.

"Cell Membrane Theory of Senescence" and the Role of Bioactive Lipids in Aging, and Aging Associated Diseases and Their Therapeutic Implications

Lipids are an essential constituent of the cell membrane of which polyunsaturated fatty acids (PUFAs) are the most important component. Activation of phospholipase A2 (PLA2) induces the release of PUFAs from the cell membrane that form precursors to both pro- and ant-inflammatory bioactive lipids that participate in several cellular processes. PUFAs GLA (gamma-linolenic acid), DGLA (dihomo-GLA), AA (arachidonic acid), EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are derived from dietary linoleic acid (LA) and alpha-linolenic acid (ALA) by the action of desaturases whose activity declines with age. Consequently, aged cells are deficient in GLA, DGLA, AA, AA, EPA and DHA and their metabolites. LA, ALA, AA, EPA and DHA can also be obtained direct from diet and their deficiency (fatty acids) may indicate malnutrition and deficiency of several minerals, trace elements and vitamins some of which are also much needed co-factors for the normal activity of desaturases. In many instances (patients) the plasma and tissue levels of GLA, DGLA, AA, EPA and DHA are low (as seen in patients with hypertension, type 2 diabetes mellitus) but they do not have deficiency of other nutrients. Hence, it is reasonable to consider that the deficiency of GLA, DGLA, AA, EPA and DHA noted in these conditions are due to the decreased activity of desaturases and elongases. PUFAs stimulate SIRT1 through protein kinase A-dependent activation of SIRT1-PGC1α complex and thus, increase rates of fatty acid oxidation and prevent lipid dysregulation associated with aging. SIRT1 activation prevents aging. Of all the SIRTs, SIRT6 is critical for intermediary metabolism and genomic stability. SIRT6-deficient mice show shortened lifespan, defects in DNA repair and have a high incidence of cancer due to oncogene activation. SIRT6 overexpression lowers LDL and triglyceride level, improves glucose tolerance, and increases lifespan of mice in addition to its anti-inflammatory effects at the transcriptional level. PUFAs and their anti-inflammatory metabolites influence the activity of SIRT6 and other SIRTs and thus, bring about their actions on metabolism, inflammation, and genome maintenance. GLA, DGLA, AA, EPA and DHA and prostaglandin E2 (PGE2), lipoxin A4 (LXA4) (pro- and anti-inflammatory metabolites of AA respectively) activate/suppress various SIRTs (SIRt1 SIRT2, SIRT3, SIRT4, SIRT5, SIRT6), PPAR-γ, PARP, p53, SREBP1, intracellular cAMP content, PKA activity and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC1-α). This implies that changes in the metabolism of bioactive lipids as a result of altered activities of desaturases, COX-2 and 5-, 12-, 15-LOX (cyclo-oxygenase and lipoxygenases respectively) may have a critical role in determining cell age and development of several aging associated diseases and genomic stability and gene and oncogene activation. Thus, methods designed to maintain homeostasis of bioactive lipids (GLA, DGLA, AA, EPA, DHA, PGE2, LXA4) may arrest aging process and associated metabolic abnormalities.

Lipid Metabolism in Tumor-Associated Macrophages

Macrophages are essential components of the immune system in tumors. It can be recruited and educated to two mainly polarized subpopulations (M1-like and M2-like) of tumor-associated macrophages (TAMs) to display anti-tumor or protumor function during the tumor occurrence and progression. Reprogramming of metabolism, especially lipid metabolism, is a typical characteristic of TAMs polarization, which was confirmed recently as a vital target for tumor therapy. However, the relationship between TAMs and lipid metabolism is still obscure in the past decade. In this review, we will first introduce the historical aspects of TAMs, and then discuss the correlation of main lipids (triglycerides, cholesterol, and phospholipids) to TAMs activation and summarize the mechanisms by which lipid metabolism mediated tumor escape the immunological surveillance as well as currently available drugs targeting these mechanisms. We hope that this chapter will give a better understanding of lipid metabolism in TAMs for those who are interested in this field, and lay a foundation to develop novel strategies for tumor therapy by targeting lipid metabolism.

Metabolism in tumour-associated macrophages: a quid pro quo with the tumour microenvironment

Lung cancer is the leading cause of death from cancer worldwide. Recent studies demonstrated that the tumour microenvironment (TME) is pivotal for tumour progression, providing multiple targeting opportunities for therapeutic strategies. As one of the most abundant stromal cell types in the TME, tumour-associated macrophages (TAMs) exhibit high plasticity. Malignant cells alter their metabolic profiles to adapt to the limited availability of oxygen and nutrients in the TME, resulting in functional alteration of TAMs. The metabolic features of TAMs are strongly associated with their functional plasticity, which further impacts metabolic profiling in the TME and contributes to tumourigenesis and progression. Here, we review the functional determination of the TME by TAM metabolic alterations, including glycolysis as well as fatty acid and amino acid metabolism, which in turn are influenced by environmental changes. Additionally, we discuss metabolic reprogramming of TAMs to a tumouricidal phenotype as a potential antitumoural therapeutic strategy.

Tumour-associated macrophages (TAMs) display a high level of functional plasticity and altered metabolism symbolised by high sensitivity to the surrounding tumour microenvironment. The metabolism of TAMs provides novel therapeutic opportunities to treat cancer.https://bit.ly/31OqHhe

Metabolism in tumor microenvironment: Implications for cancer immunotherapy

Tumor microenvironment is a special environment for tumor survival, which is characterized by hypoxia, acidity, nutrient deficiency, and immunosuppression. The environment consists of the vasculature, immune cells, extracellular matrix, and proteins or metabolic molecules. A large number of recent studies have shown that not only tumor cells but also the immune cells in the tumor microenvironment have undergone metabolic reprogramming, which is closely related to tumor drug resistance and malignant progression. Tumor immunotherapy based on T cells gives patients new hope, but faces the dilemma of low response rate. New strategies sensitizing cancer immunotherapy are urgently needed. Metabolic reprogramming can directly affect the biological activity of tumor cells and also regulate the differentiation and activation of immune cells. The authors aim to review the characteristics of tumor microenvironment, the metabolic changes of tumor‐associated immune cells, and the regulatory role of metabolic reprogramming in cancer immunotherapy.

Enhanced Lipid Accumulation and Metabolism Are Required for the Differentiation and Activation of Tumor-Associated Macrophages

Tumor-associated macrophages (TAM) are important tumor-promoting cells. However, the mechanisms underlying how the tumor and its microenvironment reprogram these cells remain elusive. Here we report that lipids play a crucial role in generating TAMs in the tumor microenvironment (TME). Macrophages from both human and murine tumor tissues were enriched with lipids due to increased lipid uptake by macrophages. TAMs expressed elevated levels of the scavenger receptor CD36, accumulated lipids, and used fatty acid oxidation (FAO) instead of glycolysis for energy. High levels of FAO promoted mitochondrial oxidative phosphorylation, production of reactive oxygen species, phosphorylation of JAK1, and dephosphorylation of SHP1, leading to STAT6 activation and transcription of genes that regulate TAM generation and function. These processes were critical for TAM polarization and activity, both in vitro and in vivo. In summary, we highlight the importance of lipid metabolism in the differentiation and function of protumor TAMs in the TME. SIGNIFICANCE: This study highlights the role of lipid metabolism in the differentiation and function of TAMs and suggests targeting TAM fatty acid oxidation as a potential therapeutic modality for human cancers.

Saturated Fatty Acids, MUFAs and PUFAs Regulate Ferroptosis

Apoptosis, necroptosis, autophagy, and ferroptosis are distinct mechanisms of cell death. In this issue of Cell Chemical Biology, Magtanong et al. (2019) demonstrated that exogenous monounsaturated fatty acids (MUFAs) induce a ferroptosis-resistant cell state by suppressing the accumulation of lipid peroxides and decreasing levels of oxidizable polyunsaturated fatty acids (PUFAs).

Bioactive lipids as modulators of immune check point inhibitors

It is proposed that arachidonic acid (AA, 20:4 n-6) and other polyunsaturated fatty acids (PUFAs) in combination with immune check point inhibitors and tumor infiltrating lymphocytes (TILs) enhances the activity of T and NK cells and macrophages and thus, aids in the elimination of tumor cells and suppresses inflammatory side effects due to immune check point inhibitors.

Arachidonic acid and other unsaturated fatty acids and some of their metabolites function as endogenous antimicrobial molecules: A review

Our body is endowed with several endogenous anti-microbial compounds such as interferon, cytokines, free radicals, etc. However, little attention has been paid to the possibility that lipids could function as antimicrobial compounds. In this short review, the antimicrobial actions of various polyunsaturated fatty acids (PUFAs, mainly free acids) and their putative mechanisms of action are described. In general, PUFAs kill microbes by their direct action on microbial cell membranes, enhancing generation of free radicals, augmenting the formation of lipid peroxides that are cytotoxic, and by increasing the formation of their bioactive metabolites, such as prostaglandins, lipoxins, resolvins, protectins and maresins that enhance the phagocytic action of leukocytes and macrophages. Higher intakes of α-linolenic and cis-linoleic acids (ALA and LA respectively) and fish (a rich source of eicosapentaenoic acid and docosahexaenoic acid) might reduce the risk pneumonia. Previously, it was suggested that polyunsaturated fatty acids (PUFAs): linoleic, α-linolenic, γ-linolenic (GLA), dihomo-GLA (DGLA), arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic acids (DHA) function as endogenous anti-bacterial, anti-fungal, anti-viral, anti-parasitic, and immunomodulating agents. A variety of bacteria are sensitive to the growth inhibitory actions of LA and ALA in vitro. Hydrolyzed linseed oil can kill methicillin-resistant Staphylococcus aureus. Both LA and AA have the ability to inactivate herpes, influenza, Sendai, and Sindbis virus within minutes of contact. AA, EPA, and DHA induce death of Plasmodium falciparum both in vitro and in vivo. Prostaglandin E1 (PGE1) and prostaglandin A (PGA), derived from DGLA, AA, and EPA inhibit viral replication and show anti-viral activity. Oral mucosa, epidermal cells, lymphocytes and macrophages contain and release significant amounts of PUFAs on stimulation. PUFAs stimulate NADPH-dependent superoxide production by macrophages, neutrophils and lymphocytes to kill the invading microorganisms. Cytokines induce the release of PUFAs from cell membrane lipid pool, a potential mechanism for their antimicrobial action. AA, EPA, and DHA give rise to lipoxins (LXs), resolvins, protectins, and maresins that limit and resolve inflammation and have antimicrobial actions. Thus, PUFAs and their metabolites have broad antimicrobial actions.

Cellular metabolism of tumor-associated macrophages - functional impact and consequences

Macrophages are innate immune cells that play a role not only in host defense against infections, but also in the pathophysiology of autoimmune and autoinflammatory disorders, as well as cancer. An important feature of macrophages is their high plasticity, with high ability to adapt to environmental changes by adjusting their cellular metabolism and immunological phenotype. Macrophages are one of the most abundant innate immune cells within the tumor microenvironment that have been associated with tumor growth, metastasis, angiogenesis and poor prognosis. In the context of cancer, however, so far little is known about metabolic changes in macrophages, which have been shown to determine functional fate of the cells in other diseases. Here, we review the current knowledge regarding the cellular metabolism of tumor-associated macrophages (TAMs) and discuss its implications for cell function. Understanding the regulation of the cellular metabolism of TAMs may reveal novel therapeutic targets for treatment of malignancies.

Study of plasma and red cell phospholipid fatty acids in extrahepatic cholestatic jaundice

The poor outcome in patients with extrahepatic cholestatic jaundice seems in some way related to reticuloendothelial dysfunction. Similar dysfunction can be caused by abnormal tissue phospholipid fatty acid patterns. Little is, however, known about such patterns in extrahepatic cholestatic jaundice. The phospholipid fatty acid patterns in 42 controls were compared with 42 patients with extrahepatic cholestatic jaundice. Many abnormalities were found. The general pattern was of a fall in polyunsaturated fatty acids and a rise in monounsaturated fatty acids, with a consequent fall in the double bond index (mean number of double bonds per fatty acid) showing an overall rise in saturation. All three major substrates for eicosanoid production were reduced in the jaundiced group. The changes seemed to be associated with jaundice itself, rather than the cause of the jaundice. The central roles of fatty acids in the determination of membrane function and in the provision of substrates of eicosanoid production, mean that these changes may explain some of the reticuloendothelial dysfunction found in extrahepatic cholestatic jaundice.

Phagocytic functions of pulmonary alveolar macrophages in genetically selected lean and obese swine and the effects of exogenous linolenic acid upon cell function

Alveolar macrophages from genetically selected obese and lean swine were compared for in vitro phagocytic capabilities, using Fc (gamma)- and C3-mediated phagocytosis. Cells from obese pigs were significantly more effective at Fc (gamma)-mediated phagocytosis than those from lean pigs, both for percentage of total cells phagocytosing (P less than 0.044) and for the average number of opsonized sheep erythrocytes (SRBC) ingested per phagocyte (P less than 0.045). A seasonal interaction was noted for average number of SRBC ingested per phagocyte: the relative difference in macrophage responses between obese and lean groups became significantly more pronounced during winter and spring months (P less than 0.080). Macrophages from obese pigs also exhibited higher phagocytic activities at C3-mediated phagocytosis than did cells from lean pigs, but these differences were significant only for average number of SRBC ingested per phagocyte (P less than 0.080). Exogenous linolenic acid was added to selected cultures undergoing Fc (gamma)-mediated phagocytosis. Addition of the fatty acid frequently caused enhanced phagocytosis. Macrophages from obese pigs were stimulated by fatty acid treatment more frequently than cells from lean pigs (P less than 0.05). Relatively greater enhancement was also seen in cells from obese pigs, when compared with those from lean swine (P less than 0.025). These results suggest that genetically transferred factors are of primary importance in alveolar macrophage phagocytic responses and that linolenic acid can induce increased phagocytic activity by porcine alveolar macrophages in vitro.

Effects of polyunsaturated fatty acids and of their oxidation products on cell survival

The stimulatory, cytostatic and cytotoxic effects of polyunsaturated fatty acids, prostaglandins, thromboxanes, hydroperoxy fatty acids, hydroxy fatty acids and leukotrienes on normal and tumor cells are described. Their effects are related to the ability of the cells to undergo lipid peroxidation. The significance of controlled peroxidation of selected polyunsaturated fatty acids in the control of tumor development is examined. It is suggested that selected polyunsaturated fatty acids if used at appropriate concentrations may have a protective role against cancer development by inducing and/or mediating cytotoxic reactions in malignant cells directly or indirectly through the intermediacy of immune cells.

Effect of cellular fatty acid composition on the phospholipase A2 activity of bone marrow-derived macrophages, and their ability to induce lucigenin-dependent chemiluminescence

Mouse bone marrow macrophages were obtained by cultivation in serum-free medium. Addition of specific fatty acids to the medium leads to macrophage populations which differ in their fatty acid composition. The fatty acid composition of the cellular membranes directly modulates functional abilities of the macrophages such as the generation of superoxide anion and phospholipase A2 activity in response to phorbol ester and zymosan. Both capacities were lowest in macrophages cultured serum-free without lipids. Incorporation of unsaturated fatty acids into macrophage phospholipids leads to an increase of O2- production as measured by lucigenin-dependent chemiluminescence and to an increased phospholipase A2 activity after challenge with phorbol ester or zymosan.

A deficiency in dietary gamma-linolenic and/or eicosapentaenoic acids may determine individual susceptibility to AIDS

We hypothesize that a relative deficiency in gamma-linolenic and eicosapentaenoic acids and in their derivatives may contribute to the development of AIDS. These polyunsaturated fatty acids (PUFAs) may be the source of natural endogenous agents against AIDS by preventing the spread of viral infection due to their ability to destroy enveloped viruses, by controlling cancer development either directly due to their cytostatic and cytotoxic effects on cancer cells or indirectly by modulating the immune response and by protecting from genetic damage. Supplementation of these dietary PUFAs in the prevention, and possibly in the treatment of AIDS, is considered.

Free radicals as possible mediators of the actions of interferon

Interferons (IFNs), in addition to their antiviral action, have been shown to inhibit cell proliferation, induce differentiation of some tumor cells, activate NK cells and macrophages, and modulate phagocytosis. The exact mechanism(s) by which IFN can bring about these pleiotropic actions is not known. Recent studies, including our own (presented here), showed that IFN can augment free radical generation in the cells. Free radicals can stimulate lymphocytes mitogenically and activate macrophages and NK cells. It is also known that activated machophages and polymorphs produce oxidative metabolites, such as hydrogen peroxide, which is responsible for sterilizing action against microorganisms and cytotoxic activity against tumor cells. Free radicals are also known to inhibit cell division. Since IFN can augment free radical generation, it is suggested that free radicals mediate some of the actions of IFN.

In vitro effect of levan-activated macrophages on Lewis lung carcinoma cells

The polysaccharide levan (polyfructose) has previously been shown to exert an inhibitory effect on the growth of several murine tumors. This activity is mediated by a host reaction, involving mainly macrophages but also other elements of the immune system. It was not clear, however, whether levan-activated macrophages act by a direct cytocidal effect on the tumor cells or via the activation of a specific immune response to the tumor. In the present study, the possibility of a direct cytotoxicity of levan-activated macrophages against Lewis lung carcinoma cells was tested by coculture in vitro. It was found that levan-induced (as well as paraffin oil induced) macrophages actually exert a direct cytotoxic effect on Lewis lung carcinoma cells. The tumor cell killing is mediated by cell to cell contact. A cytoplasmic bridge was often seen between the macrophage and the tumor cell. The remaining tumor cells in the lysed area appear slender, shrunken and non-dividing.

Role of macrophage lipids in regulating tumoricidal activity. II. Internal genetic and external physiologic regulatory factors controlling macrophage tumor cytotoxicity also control characteristic lipid changes associated with tumoricidal cells

Peritoneal macrophages (M phi) from C3H/HeN mice became cytotoxic for 1023 tumor cells after incubation with lymphokine (LK) for 8-12 hr and lost tumoricidal activity by 22 hr in the continued presence of LK; bacterial endotoxin (LPS) was ineffective in inducing tumoricidal activity. M phi from C3H/HeJ mice were not activated for tumor cytotoxicity after treatment with LK or LPS. C3H/HeN M phi acquisition of tumoricidal activity was accompanied by unique changes in M phi lipid composition: cellular content of cholesterol (CHOL) and polyunsaturated fatty acids (UFA) increased two- to threefold when the cells showed maximal tumoricidal activity and returned to control levels when the M phi lost tumoricidal activity. LPS treatment of C3H/HeN M phi and LK or LPS treatment of C3H/HeJ M phi did not cause characteristic M phi lipid alterations. To determine at what stage during M phi activation the correlative CHOL and UFA compositional changes were occurring, C3H/HeN M phi were primed with LPS or low concentrations of LK and triggered with LPS or Lk; M phi lipid and fatty acid composition was monitored at each stage. LK was shown to be able to prime and trigger whereas LPS could only trigger LK-primed M phi for tumor cytotoxicity. In all cases, the increase in M phi CHOL and UFA content occurred at the triggering step for tumor cytotoxicity rather than at the priming step. These data suggest that there is a correlation between the effects of endogenous and exogenous factors that control expression of M phi tumoricidal activity and their effects on M phi CHOL and UFA content; the establishment of these changes in M phi lipid composition occurs at a time when the cells are triggered for tumor cytotoxicity.