Ashley J. Snider

Changes in lipid metabolism have been associated with the development of colorectal cancer (CRC), and they may serve as diagnostic markers to identify patients who have developed colorectal neoplasia. This study aimed to identify such biomarkers using untargeted lipidomics. Lipidomics were performed in serum from a racially diverse series of CRC cases and controls from Chicago and Tucson. In addition, enzymatic activity of secretory acid sphingomyelinase (aSMase; S-SMase) was measured in samples from the Tucson CRC series, and two series of adenoma patients. Untargeted lipidomics in the Chicago CRC series revealed significant alterations in sphingolipids. Targeted lipidomics revealed a robust signature of five sphingomyelins (SMs) that were significantly decreased in Chicago CRC patients compared to controls and were validated in the Tucson series. S-SMase activity, which degrades serum SMs, was elevated in CRC cases (0.13 ± 0.10 Cer/SM UACC CRC cases vs. 0.05 ± 0.04 Cer/SM controls; p<0.0001). In mostly white adenoma patients from Tucson, serum S-SMase activity could predict the presence of colorectal neoplasia (0.13 ± 0.07 Cer/SM in UACC adenoma cases vs. 0.03 ± 0.02 Cer/SM in controls; p<0.0001). However, S-SMase activity was not significantly different in Black adenoma patients from Chicago compared to controls. Together, these studies demonstrate for the first time the potential for S-SMase activity to serve as a biomarker for colorectal neoplasia in specific populations.

Background & Aims: High-fat diets (HFDs) are a major modifiable risk factor for intestinal health. Current research focuses primarily on palmitate (C16:0); however, myristate (C14:0, rich in dairy products) has been minimally investigated. HFDs increase ceramide generation which drives endoplasmic reticulum (ER) stress; with both sphingolipids and ER stress being key contributors to intestinal biology. Whether different fatty acids uniquely impact sphingolipid metabolism and ER stress in intestinal biology has not been well defined. Methods: Human colon epithelial cells were utilized to determine the role of ceramide synthases (CerS) 5 and 6 on myristate-induced ER stress using pharmacologic inhibitors and siRNA. Intestinal epithelial cell specific CerS5 and/or CerS6 knockout mice of both sexes were fed a control, high milk-fat, or high lard-fat diet for 16 weeks. Cells and colon tissues were analyzed for lipids, mRNA, and protein. Results: Myristate treatment increased C14:0-ceramide and induced IRE1α-dependent ER stress. Inhibition of CerS suppressed these effects, yet knockdown of CerS5/6, the primary enzymes generating C14:0-ceramide, unexpectedly exacerbated IRE1α activation both in vitro and in vivo, potentially due to depletion of dihydro(dh)sphingosine. Conclusions: CerS are required for myristate-induced IRE1α activation and restoration of the sphingoid base pool provides partial protection from intestinal ER stress.

Background: Metabolomic changes related to colorectal cancer (CRC) may serve as diagnostic markers to identify patients may develop or have developed CRC. Methods: Untargeted lipidomics were performed on serum from CRC cases and clean-colon controls from the Chicago Colorectal Cancer Consortium (CCCC) and the University of Arizona Cancer Center (UACC). Results: Untargeted lipidomics in the CCCC CRC series revealed significant alterations in sphingolipids. Targeted lipidomics revealed a signature of five sphingomyelins (SMs) were significantly decreased in CRC patients in CCCC and UACC CRC series. Circulating SMs are degraded primarily by S-SMase and serum S-SMase activity was significantly higher in UACC cases as compared to controls. Serum S-SMase activity was also measured in two series of adenoma patients to determine if S-SMase may serve as a biomarker for development of colorectal neoplasia. While S-SMase activity was significantly higher in adenoma patients compared to controls in the mostly white UACC series, S-SMase activity in samples from the Chicago Black series (CCCC) were indistinguishable from each other and significantly higher than UACC controls. Conclusions: Together, these studies suggest the potential for S-SMase activity to serve as a biomarker for colorectal neoplasia, with potential implications in some but perhaps not all populations.

Background & Aims: Patients with inflammatory bowel disease (IBD) exhibit elevated expression of acid ceramidase (AC), a sphingolipid metabolism enzyme. Recent studies have shown that myeloid cells contribute to the elevated expression of AC, such that the conditional loss of AC is protective in IBD. Methods: Bone marrow derived macrophages (BMDMs) and neutrophils (BMDNs) were utilized to assess the role of AC in immune cell mediated inflammation. We then crossed conditional ASAH1 LyzM ^CRE knockout mice with IL10 knockout mice to determine the role of AC in a model of spontaneous colitis. Colon tissues were analyzed for lipids, mRNA, and protein. We performed flow cytometry to determine the role of myeloid AC in recruiting effector T cells in disease. Results: In this study, we found that loss of AC impaired secretory and migratory functions in BMDMs, but not BMDNs. Further, the conditional loss of AC protected from spontaneous, chronic colitis. Loss of AC reduced inflammatory markers, increased colon ceramides, and reduced the inflammatory metabolite sphingosine-1-phosphate (S1P). Recruitment of immune cells into intestinal tissue was significantly impaired, namely neutrophils and effector Th1/Th17 T cells. Conclusions: Loss of AC reduced inflammation and impaired immune cell recruitment in chronic colitis. Targeting AC may serve as a promising therapeutic potential for patients with IBD by modulating immune cell sphingolipid metabolism. WHAT YOU NEED TO KNOW: BACKGROUND AND CONTEXT: Acid ceramidase expression is increased in immune cells in patients with inflammatory bowel disease, specifically in macrophages. NEW FINDINGS: We determined that loss of acid ceramidase (AC) in macrophages, but not neutrophils, impairs inflammatory functions in vitro, and that loss of AC in myeloid cells partially protects from spontaneous colitis in vivo by reducing immune cell recruitment into intestinal tissue. LIMITATIONS: The IL10 knockout model of colitis exhibits highly variable onset and severity of disease, which may be challenging to distinguish the extent of protection. CLINICAL RESEARCH RELEVENCE: This study identifies AC as a promising therapeutic target for treating inflammatory bowel disease. BASIC RESEARCH RELEVENCE: This study contributes to our understanding of the role that AC plays in inflammation within immune cells, specifically myeloid cells. Additionally, this study underscores the role of immune cell sphingolipid metabolism in inflammatory bowel disease. LAY SUMMARY: Loss of acid ceramidase in myeloid cells protects from chronic colitis by decreasing inflammation, altering immune cell function, and impairing the recruitment of effector immune cells to the colon.

The incidence of inflammatory bowel disease (IBD) has increased over the last 20 years. A variety of causes, both physiological and environmental, contribute to the initiation and progression of IBD, making disease management challenging. Current treatment options target various aspects of the immune response to dampen intestinal inflammation; however, their effectiveness at retaining remission, their side effects, and loss of response from patients over time warrant further investigation. Finding a common thread within the multitude causes of IBD is critical in developing robust treatment options. Sphingolipids are evolutionary conserved bioactive lipids universally generated in all cell types. This diverse lipid family is involved in a variety of fundamental, yet sometimes opposing, processes such as proliferation and apoptosis. Implicated as regulators in intestinal diseases, sphingolipids are a potential cornerstone in understanding IBD. Herein we will describe the role of host‐ and microbial‐derived sphingolipids as they relate to the many factors of intestinal health and IBD.

Long thought to be structural components of cell membranes, sphingolipids (SLs) have emerged as bioactive molecules whose metabolism is tightly regulated. These bioactive lipids and their metabolic enzymes have been implicated in numerous disease states, including lysosomal storage disorders, multiple sclerosis, inflammation, and cancer as well as metabolic syndrome and obesity. In addition, the indications for many of these lipids to potentially serve as biomarkers for disease continue to emerge with increasing metabolomic and lipidomic studies. The implications of these studies have, in turn, led to the examination of SL enzymes and their bioactive lipids as potential therapeutic targets and as markers for therapeutic efficacy. SIGNIFICANCE STATEMENT Many sphingolipids (SLs) and their metabolizing enzymes have been implicated in disease. This perspective highlights the potential for SLs to serve as therapeutic targets and diagnostic markers and discusses the implications for the studies and reviews highlighted in this Special Section on Therapeutic Implications for Sphingolipids in Health and Disease.

Inflammatory bowel disease (IBD), characterized by chronic inflammation in the intestinal tract, increases the risk for the development of colorectal cancer (CRC). Sphingolipids, which have been implicated in IBD and CRC, are a class of bioactive lipids that regulate cell signaling, differentiation, apoptosis, inflammation, and survival. The balance between ceramide (Cer), the central sphingolipid involved in apoptosis and differentiation, and sphingosine-1-phosphate (S1P), a potent signaling molecule involved in proliferation and inflammation, is vital for the maintenance of normal cellular function. Altered sphingolipid metabolism has been implicated in IBD and CRC, with many studies highlighting the importance of S1P in inflammatory signaling and pro-survival pathways. A myriad of sphingolipid analogues, inhibitors, and modulators have been developed to target the sphingolipid metabolic pathway. In this review, the efficacy and therapeutic potential for modulation of sphingolipid metabolism in IBD and CRC will be discussed.