Liquid chromatography-electrospray ionization mass spectrometry (LC-MS) is an effective and popular technique used in lipid metabolomic studies. Although many LC-MS methods enabling the determination of sphingolipid molecular species have been reported, they do not cover a broad range of sphingolipid metabolites with expanding glycerophospholipids (GPLs) and diacylglycerol (DAG). In this study, we developed an approach for the comprehensive analysis of sphingolipids, GPLs and DAG molecular species in a biological sample, without alkaline hydrolysis. After validating the reliability of this approach, we analyzed tissue lipids of sphingomyelin synthase 2-knockout mice and found that changes in sphingolipid metabolism in the liver affect the level of docosahexaenoic acid-containing GPLs. Our method analyzes GPLs and DAG, as well as sphingolipids within biological samples and, thus, will facilitate more comprehensive studies of sphingolipid metabolism in pathology and diagnostics.

No abstract

The tumor microenvironment (TME) formation involving host cells and cancer cells through cell adhesion molecules (CAMs) is essential for the multiple steps of cancer metastasis and growth. Sphingomyelin synthase 2 (SMS2) is involved in inflammatory diseases such as obesity and diabetes mellitus by regulation of the SM/ceramide balance. However, the involvement of SMS2 in TME formation and metastasis is largely unknown. Here, we report that SMS2‐deficient (SMS2‐KO) mice show suppressed the EL4 cell infiltration to liver and prolonged survival time. ICAM‐1 was identified as a candidate for the inhibition of TME formation in immortalized mouse embryonic fibroblasts (tMEFs) from mRNA array analysis for CAMs. Reduced SM/ceramide balance in SMS2‐KO tMEFs suppressed the attachment of EL4 cells through transcriptional reduction of ICAM‐1 by the inhibition of NF‐κB activation. TNF‐α‐induced NF‐κB activation and subsequent induction of ICAM‐1 were suppressed in SMS2‐KO tMEFs but restored by SMS2 re‐introduction. In the EL4 cell infiltration mouse model, EL4 injection increased ICAM‐1 expression in WT liver but not in SMS2‐KO mouse liver. Therefore, inhibition of SMS2 may be a therapeutic target to suppress the infiltration of malignant lymphoma.

Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine skin cancer, with approximately 80% of cases related to Merkel cell polyomavirus (MCPyV). Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2) are the key rate-limiting enzymes of the tryptophan to kynurenine (KYN) metabolic pathway. With aryl hydrocarbon receptor (AhR), an intracellular transcription factor, they play a role in escaping the immunosurveillance process in several cancers. IDO1/TDO2/AhR expression associated with the MCPyV status and prognosis in MCC was investigated. Samples included 24 MCPyV-positive MCCs, 12 MCPyV-negative MCCs with squamous cell carcinoma, and seven MCPyV-negative pure MCCs. They were stained immunohistochemically with IDO1, TDO2, and AhR antibodies and analyzed. Higher IDO1 expression in MCC tumor cells was found in MCPyV-negative than in MCPyV-positive MCC (P < .001). The tumor microenvironment (TME) in MCPyV-negative MCC expressed higher TDO2 than MCPyV-positive MCC (P < .001). Kaplan-Meier and log-rank tests showed that MCC with lower IDO1 expression in tumor cells and with lower TDO2 and AhR expressions in TME had better overall survival than otherwise (P = .043, .008, and .035, respectively); lower TDO2 expression in TME was also associated with longer disease-specific survival (P = .016). This suggests that IDO1, TDO2, and AhR express differentially in tumor cells or TME and play different roles in tumorigenesis between MCPyV-positive and -negative MCC that may affect the MCC biology. Evaluating IDO1/TDO2/AhR expression is important for selecting the most likely patients with MCC for immunotherapies targeting the IDO1/TDO2-AhR pathway.