Ginsenoside Rh2 reverses cyclophosphamide-induced immune deficiency by regulating fatty acid metabolism.

Ginsenoside Rh2 (G-Rh2) has well-established potent antitumor activity; yet, the effects of G-Rh2 on immune and metabolism regulation in cancer treatment, especially non-small cell lung cancer (NSCLC) remain unclear. We showed that G-Rh2 had a synergistic antitumor effect with cyclophosphamide (CY) on mice with NSCLC, and improved the immune deficiency caused by CY. Consistently, G-Rh2 exhibited no inhibitory effect on tumor growth of T cells-deficient nude mice. Furthermore, G-Rh2 treatment triggered the oxidative decomposition of fatty acid (FA), suppressed FA synthesis, increased ketone level, and decreased glucocorticoid (CORT) secretion. G-Rh2 significantly down-regulated the expression of fatty acid synthase (FASN). Of note, in liver-specific FASN knockout mice G-Rh2 failed to show the same immune enhancement effects. Further mechanistic exploration revealed that G-Rh2 suppressed the expression and nuclear translocation of sterol regulatory element binding protein 1 (SREBP-1), and disturbed the SREBP-1-FASN interaction in vitro.

Fatty acid metabolism complements glycolysis in the selective regulatory T cell expansion during tumor growth.

The tumor microenvironment restrains conventional T cell (Tconv) activation while facilitating the expansion of Tregs. Here we showed that Tregs' advantage in the tumor milieu relies on supplemental energetic routes involving lipid metabolism. In murine models, tumor-infiltrating Tregs displayed intracellular lipid accumulation, which was attributable to an increased rate of fatty acid (FA) synthesis. Since the relative advantage in glucose uptake may fuel FA synthesis in intratumoral Tregs, we demonstrated that both glycolytic and oxidative metabolism contribute to Tregs' expansion. We corroborated our data in human tumors showing that Tregs displayed a gene signature oriented toward glycolysis and lipid synthesis. Our data support a model in which signals from the tumor microenvironment induce a circuitry of glycolysis, FA synthesis, and oxidation that confers a preferential proliferative advantage to Tregs, whose targeting might represent a strategy for cancer treatment.

Gut Microbiota-Derived Tryptophan Metabolites Modulate Inflammatory Response in Hepatocytes and Macrophages.

The gut microbiota plays a significant role in the progression of fatty liver disease; however, the mediators and their mechanisms remain to be elucidated. Comparing metabolite profile differences between germ-free and conventionally raised mice against differences between mice fed a low- and high-fat diet (HFD), we identified tryptamine and indole-3-acetate (I3A) as metabolites that depend on the microbiota and are depleted under a HFD. Both metabolites reduced fatty-acid- and LPS-stimulated production of pro-inflammatory cytokines in macrophages and inhibited the migration of cells toward a chemokine, with I3A exhibiting greater potency. In hepatocytes, I3A attenuated inflammatory responses under lipid loading and reduced the expression of fatty acid synthase and sterol regulatory element-binding protein-1c. These effects were abrogated in the presence of an aryl-hydrocarbon receptor (AhR) antagonist, indicating that the effects are AhR dependent. Our results suggest that gut microbiota could influence inflammatory responses in the liver through metabolites engaging host receptors.

FASN-TGF-ß1-PD-L1 axis contributes to the development of resistance to NK cell cytotoxicity of cisplatin-resistant lung cancer cells.

Cisplatin remains the most effective therapy for non-small cell lung cancer (NSCLC). We previously have found cisplatin-resistant lung cancer cells (A549CisR and H157CisR) were more resistant to natural killer (NK) cell-mediated cytotoxicity than parental cells. We also discovered that fatty acid synthase (FASN) levels in cisplatin-resistant cells were significantly higher than in parental cells. To reveal whether a link exists between the up-regulated FASN levels and higher resistance to NK cell cytotoxicity, we performed inhibition studies using a FASN inhibitor and applied the FASN knockdown approach. In both approaches, we found that the FASN inhibition/knockdown significantly increased the susceptibility of cisplatin-resistant cells to NK cell cytotoxicity. We further found such decreased susceptibility was associated with an increased programmed death receptor ligand (PD-L1) level in cisplatin-resistant cells. In mechanisms studies, TGF-ß1 was found to be the FASN downstream signaling molecule that was responsible for modulating the PD-L1 levels in cisplatin-resistant cells. Accordingly, TGF-ß1 inhibition resulted in significantly increased susceptibility of cisplatin-resistant cells to NK cell cytotoxicity. We suggest that the inhibition of FASN-TGFß1-PD-L1 axis may improve the efficacy of immunotherapy in treating cisplatin-resistant lung cancer.

Fatty acid synthase regulates the pathogenicity of Th17 cells.

T cell activation and effector function is characterized by changes in metabolism. Altered metabolism is common to almost all types of activated T cells, but fatty acid synthesis seems to especially drive the formation of Th17 cells. Indeed, research has demonstrated that inhibition of early fatty acid synthesis through targeting of acetyl-CoA carboxylase (ACC1) can inhibit Th17 cell formation and instead promote the generation of regulatory T cells. Fatty acid synthase (FASN) is downstream of ACC, and previous studies have shown that FASN activity influences both cancer and inflammation. However, it remains to be determined whether FASN is a viable target for inhibiting Th17 cell function. Here, we demonstrate that FASN is a critical metabolic control for the generation of inflammatory subsets of Th17 cells. Conversely, inhibiting FASN function promotes IFN-γ production by Th1 and Th1-like Th17 cells. In vivo, inhibition of FASN, specifically in Th17 cells, leads to reduction of experimental autoimmune encephalomyelitis disease. These studies demonstrate the necessity of FASN in the autoimmune inflammatory function of Th17 cells.

Usefulness of immunohistochemical expression analysis of metabolic-related molecules in differentiating between intracranial neoplastic and non-neoplastic lesions.

As the histologic features of reactive glial proliferation seen in many non-neoplastic lesions and of diffusely infiltrating gliomas overlap, tumor-specific diagnostic markers are needed. A mutation in isocitrate dehydrogenase 1 (IDH1), the enzyme involved in lipid metabolism and glucose sensing, has been identified in a variety of diffuse gliomas. The expression of fatty acid synthase (FAS), the enzyme responsible for the de novo synthesis of fatty acids, has been examined in several types of tumors including high-grade meningiomas, but not or less examined in normal tissues and benign tumors. We analyzed the expression of mutant IDH1 and FAS proteins in 10 non-neoplastic and 52 neoplastic lesions. Paraffin-embedded samples were immunostained with anti-IDH1R132H and -FAS antibodies. Staining of mutant IDH1 was positive in nine neoplastic lesions (3 diffuse astrocytomas, 2 anaplastic astrocytomas, and 1 oligodendroglioma, oligoastrocytoma, anaplastic oligodendroglioma, and glioblastoma); it was negative in all ten non-neoplastic lesions. Moreover, FAS expression was increased in glioblastomas (83.3%), anaplastic oligodendrogliomas and oligoastrocytomas (80%), and anaplastic astrocytomas (78.9%) compared with non-neoplastic lesions (20%). Immunostaining with mutant IDH1R132H-specific and FAS antibodies may be helpful to differentiate reactive from neoplastic cells in diffuse infiltrative or highly proliferative gliomas.

AMPK-sensed cellular energy state regulates the release of extracellular Fatty Acid Synthase.

Fatty Acid Synthase (FASN), a 250-kDa cytosolic multi-enzyme catalyzing eukaryotic de novo FA biogenesis, unexpectedly localizes in cancer cell culture supernatants and in the blood of cancer patients. High levels of "extracellular FASN" have recently been found in supernatants from Hepatitis C Virus-infected liver cells. The ultimate mechanism regulating FASN release, however, remained completely undefined. When the AMPK-activating drug AICAR was used to simulate an elevated AMP/ATP ratio in breast cancer cells, ELISA-based analyses revealed that extracellular FASN dramatically augmented in a dose- and time-dependent manner. Immunoblotting procedures using a battery of anti-FASN antibodies further confirmed that, in response to AMPK activation, FASN protein is depleted from the cytosol to accumulate as different FASN isoforms in the extracellular milieu. siRNA-induced blockade of AMPK expression largely attenuated AICAR-promoted FASN release. FASN release might represent a previously unrecognized mechanism through which AMPK monitor and restores cellular energy state in response to increasing AMP/ATP ratios.