In this study, most of clinical characteristics between group LaC and NC showed no significant difference. Their observable phenotype differences obviously could not be explained by the clinical findings. Lipids are essential in cellular functions as they are the vital components of the membrane structure, crucial regulators in signal transduction and energy storage. Abnormalities in lipid metabolism have been increasingly regarded as a landmark of tumor cells and are involved in many human diseases. We performed herein a comprehensive lipidome analysis of larynx tumors in patients with LaC and the controls. To the best of our knowledge, this is the first report on a systemic evaluation of tumor lipid metabolism in patients with LaC.
Our lipidomic study exhibited four primary findings. First, a lipid biomarker panel was identified to detect LaC patients from healthy individuals, with high diagnosis performance. Second, LaC caused substantial changes in lipid compositions. These changes were largely driven by accumulations in sphingolipids including Cer ad SM lipids, PLs including PC, PE and PI lipids and ether PC and PE lipids. Third, LysoPLs containg LPC and LPE were significantly reduced in LaC as compared to NC. Fourth, we found that PLs containing palmitic acid or arachidonic acid residues were significantly accumulated and lysoPLs containing palmitic acid or arachidonic acid residues were significantly decreased, in LaC as compared to NC. These findings suggest that LaC may cause the enhancement of sphingolipid and PL synthesis, and inflammatory reactions.
Currently, the identification of novel potential serum biomarkers for the detection of LaC remains a vital goal, particularly for the diagnosis of early-stage LaC. However, only a few biomarker candidates have been translated to clinical applications due to the limited study cohorts or diagnostic performance. In the present study, we employed the nontargeted lipidomics method to screen biomarkers. Some of the biomarkers may be among the unidentified lipids, but for clinical application, they should be identified. Therefore, we did our best to identify as many lipids as possible (Table S2). After systematic selection using multivariate and univariate statistical analyses, a biomarker panel consisting of LPC (16:0) and PE (18:0p_20:4) was identified. The serum biomarker panel separated LaC from the NC with very high performance. Moreover, this lipid panel effectively discriminated patients with LaCT1NOMO from the NC, highlighting the early diagnostic potential of this lipid biomarker pane.
The relative levels of most Cer and SM lipids were significantly increased in patients with LaC compared with healthy controls. Ceramide is bioactive lipids of the sphingolipid pathway and play essential roles in cell signaling. Ceramide has been shown to be involved in stress-related cellular responses and apoptosis [10, 11]. The imbalance in ceramide will greatly affect the physicochemical properties of cell, leading to cellular dysfunction. It has been demonstrated that ceramide metabolism is altered in numerous cancers characterized by an elevation of the Cer profile in tumor tissue and cancer cells [7, 12, 13]. We speculated that the significant increase in the level of the Cer lipid class in LaC could have resulted from the elevated expression of the enzymes responsible for the synthesis of ceramide. It was reported that ceramide synthase in a salvage pathway was highly activated in several different tumors, such as human colon cancer , human non-small-cell lung cancer . In vivo, Cer can be also generated by the hydrolysis of SM through the actions of sphingomyelinases. Upregulating the endogenous Cer level is regarded to be a novel therapeutic target for the anticancer intervention strategy . In all, we hypotheses that reducing Cer biosynthesis or preventing from converting SM to Cer could inhibit LaC progression.
It is well known that PL is one of the most important components of a mammalian membrane bilayer. PC is the most predominant constituent of PLs in the cellular membrane. It has been demonstrated that PC metabolism is altered in the onset and development of many cancers, characterized by an elevation of PC [17–19]. We deduced that the significant increase in PC may be due to an imbalance between PC and PE. Increased PC and an imbalance between PC and PE have been reported to be associated with obesity and NAFLD [20, 21], both of which are also associated with LaC occurance. In addition, PC and LPC mutually convert, upregulating PC level may come from LPC conversion. This point can be supported by the significantly decreased level of LPC in LaC patients. Altogether, disordered PC lipid metabolism is closely associated with the development of Lac.
PLs containing PUFA, especially arachidonic acid residues, were significantly increased in LaC in this study. Arachidonic acid is a major PUFA in mammals. Long-chain acyl-coenzyme A synthetase 4 (ACSL4), belonging to the ACSL family, shows a preferential use of arachidonic acid as its substrate and plays a role in the remodeling of AA-containing phospholipids by incorporating free AA. In consideration of the significant increase of AA-residue-enriched PLs (e.g., PC(16:0_20:4), PE(16:0_20:4), PE(16:0p_20:4), PE(18:0p_20:4), PI(16:0_20:4), etc.), and the level of AA, so-called FA (20:4) significantly decreased in LaC serum, we speculated that ACSL4 may be activated and thereby prompt PLs accumulation, which associated with a greater degree of oncocytic changes of the neoplastic cell of LaC characterized by the great abundance of mitochondria. Of course, further investigation should be performed to explore our findings.