Interstitial Fluid Sphingosine-1-Phosphate in Murine Mammary Gland and Cancer and Human Breast Tissue and Cancer Determined by Novel Methods

Esophageal cancer risk is influenced by genetically determined blood metabolites

It remains unclear what causes esophageal cancer (EC), but blood metabolites have been connected to it. Our study performed a Mendelian randomization (MR) analysis to assess the causality from genetically proxied 1400 blood metabolites to EC level. A two-sample MR analysis was employed to evaluate the causal relationship between 1400 blood metabolites and EC. Initially, the EC genome-wide association study (GWAS) data (from Jiang L et al) were examined, leading to the identification of certain metabolites. Subsequently, another set of EC GWAS data from FINNGEN was utilized to validate the findings. Causality was primarily determined through inverse variance weighting, with additional support from the MR-Egger, weighted median, and MR-PRESSO models. Heterogeneity was assessed using the MR Cochran Q test. The MR-Egger intercept and MR-PRESSO global methods were employed to detect multicollinearity. In this study, Bonferroni corrected P value was used for significance threshold. We found 2 metabolites with overlaps, which are lipids. Docosatrienoate (22:3n3) was found to be causally associated with a decreased risk of EC, as evidenced by the EC GWAS data (from Jiang et al) (odds ratio [OR] = 0.620, 95% confidence interval [CI] = 0.390-0.986, P = .044) and the EC GWAS data (from FINNGEN) (OR = 0.77, 95% CI = 0.6-0.99, P = .042), these results were consistent across both data sets. Another overlapping metabolite, glycosyl-N-(2-hydroxyneuramoyl)-sphingosine, was associated with the risk of ES, with EC GWAS data (from Jiang L et al) (OR = 1.536, 95% CI = 1.000-2.360, P = .049), while EC GWAS data (from FINNGEN) (OR = 0.733, 95% CI = 0.574-0.937, P = .013), the 2 data had opposite conclusions. The findings of this study indicate a potential association between lipid metabolites (Docosatrienoate (22:3n3) and glycosyl-N-(2-hydroxynervonoyl)-sphingosine (d18:1/24:1 (2OH))) and the risk of esophageal carcinogenesis.

Celastrol inhibits angiogenesis and the biological processes of MDA-MB-231 cells via the DEGS1/S1P signaling pathway

Celastrol (Cel) shows potent antitumor activity in various experimental models. This study examined the relationship between Cel's antivascular and antitumor effects and sphingolipids. CCK-8 assay, transwell assay, Matrigel, PCR-array/RT-PCR/western blotting/immunohistochemistry assay, ELISA and HE staining were used to detect cell proliferation, migration and invasion, adhesion and angiogenesis, mRNA and protein expression, S1P production and tumor morphology. The results showed that Cel could inhibit proliferation, migration or invasion, adhesion and angiogenesis of human umbilical vein endothelial cells (HUVECs) and MDA-MB-231 cells by downregulating the expression of degenerative spermatocyte homolog 1 (DEGS1). Transfection experiments showed that downregulation of DEGS1 inhibited the above processes and sphingosine-1-phosphate (S1P) production of HUVECs and MDA-MB-231 cells, while upregulation of DEGS1 had the opposite effects. Coculture experiments showed that HUVECs could promote proliferation, migration and invasion of MDA-MB-231 cells through S1P/sphingosine-1-phosphate receptor (S1PR) signaling pathway, while Cel inhibited these processes in MDA-MB-231 cells induced by HUVECs. Animal experiments showed that Cel could inhibit tumor growth in nude mice. Western blotting, immunohistochemistry and ELISA assay showed that Cel downregulated the expression of DEGS1, CD146, S1PR1-3 and S1P production. These data confirm that DEGS1/S1P signaling pathway may be related to the antivascular and antitumor effects of cel.

Targeting Sphingosine-1-Phosphate Signaling in Breast Cancer

In recent years, newly emerging therapies, such as immune checkpoint inhibitors and antibody-drug conjugates, have further improved outcomes for breast cancer patients. However, recurrent and metastatic breast cancer often eventually develops resistance to these drugs, and cure is still rare. As such, the development of new therapies for refractory breast cancer that differ from conventional mechanisms of action is necessary. Sphingosine-1-phosphate (S1P) is a key molecule with a variety of bioactive activities, including involvement in cancer cell proliferation, invasion, and metastasis. S1P also contributes to the formation of the cancer microenvironment by inducing surrounding vascular- and lymph-angiogenesis and regulating the immune system. In this article, we outline the basic mechanism of action of S1P, summarize previous findings on the function of S1P in cancer cells and the cancer microenvironment, and discuss the clinical significance of S1P in breast cancer and the therapeutic potential of targeting S1P signaling.

Effects of adipocyte-conditioned cell culture media on S1P treatment of human triple-negative breast cancer cells

Sphingosine-1-phosphate (S1P) is a potent sphingolipid metabolite that regulates a wide range of biological functions such as cell proliferation, cell apoptosis and angiogenesis. Its cellular level is elevated in breast cancer, which, in turn, would promote cancer cell proliferation, survival, growth and metastasis. However, the cellular concentration of S1P is normally in the low nanomolar range, and our previous studies showed that S1P selectively induced apoptosis of breast cancer cells at high concentrations (high nanomolar to low micromolar). Thus, local administration of high-concentration S1P alone or in combination of chemotherapy agents could be used to treat breast cancer. The breast mainly consists of mammary gland and connective tissue stroma (adipose), which are dynamically interacting each other. Thus, in the current study, we evaluated how normal adipocyte-conditioned cell culture media (AD-CM) and cancer-associated adipocyte-conditioned cell culture media (CAA-CM) would affect high-concentration S1P treatment of triple-negative breast cancer (TNBC) cells. Both AD-CM and CAA-CM may suppress the anti-proliferative effect and reduce nuclear alteration/apoptosis caused by high-concentration S1P. This implicates that adipose tissue is likely to be detrimental to local high-concentration S1P treatment of TNBC. Because the interstitial concentration of S1P is about 10 times higher than its cellular level, we undertook a secretome analysis to understand how S1P would affect the secreted protein profile of differentiated SGBS adipocytes. At 100 nM S1P treatment, we identified 36 upregulated and 21 downregulated secretome genes. Most of these genes are involved in multiple biological processes. Further studies are warranted to identify the most important secretome targets of S1P in adipocytes and illustrate the mechanism on how these target proteins affect S1P treatment of TNBC.

SARS-CoV-2 induced HDL dysfunction may affect the host's response to and recovery from COVID-19

INTRODUCTION

Covid-19 is linked with the development of cardio-metabolic disorders, including dyslipidemia, dysregulation of high-density lipoprotein (HDL), and low-density lipoprotein (LDL). Furthermore, SARS-Co-2 infection is associated with noteworthy changes in lipid profile, which is suggested as a possible biomarker to support the diagnosis and management of Covid-19.

METHODS

This paper adopts the literature review method to obtain information about how Covid-19 affects high-risk group patients and may cause severe and critical effects due to the development of acute lung injury and acute respiratory distress syndrome. A narrative and comprehensive review is presented.

RESULTS

Reducing HDL in Covid-19 is connected to the disease severity and poor clinical outcomes, suggesting that high HDL serum levels could benefit Covid-19. SARS-CoV-2 binds HDL, and this complex is attached to the co-localized receptors, facilitating viral entry. Therefore, SARS-CoV-2 infection may induce the development of dysfunctional HDL through different mechanisms, including induction of inflammatory and oxidative stress with activation of inflammatory signaling pathways. In turn, the induction of dysfunctional HDL induces the activation of inflammatory signaling pathways and oxidative stress, increasing Covid-19 severity.

CONCLUSIONS

Covid-19 is linked with the development of cardio-metabolic disorders, including dyslipidemia in general and dysregulation of high-density lipoprotein and low-density lipoprotein. Therefore, the present study aimed to overview the causal relationship between dysfunctional high-density lipoprotein and Covid-19.

Triptolide Inhibits the Biological Processes of HUVECs and HepG2 Cells via the Serine Palmitoyltransferase Long Chain Base Subunit 2/Sphingosine-1-Phosphate Signaling Pathway

Triptolide (TP) has demonstrated innumerous biological effects and pharmacological potential against different cancer types. Hepatocellular carcinoma has a high incidence in men, and its incidence is increasing year by year. Studies have shown that angiogenesis plays an important role in the formation of tumors and that angiogenesis is closely related to tumor growth and metastasis. Deregulation of sphingolipids signaling has been associated with several pathological conditions, including cancer. In the present study, we aimed at exploring the potential molecular mechanism of TP's antivascular and antitumor effects in vitro from the perspective of sphinolipids. Human umbilical vein endothelial cells (HUVECs) and HepG2 cells were, respectively, treated with different concentrations of TP and transfected. Then, the effect of HUVECs on HepG2 cells was investigated using a three-dimensional coculture model system. CCK-8 assay was performed for cell proliferation. Cell migration and invasion abilities were assessed using the transwell assay. Cell adhesion and tube formation were detected by Matrigel. RT-PCR and western blotting were used to detect the mRNA and protein expression. The S1P production was measured via ELISA assay. Our results showed that TP inhibited HUVECs and HepG2 cells proliferation, migration, invasion, adhesion, angiogenesis, and serine palmitoyltransferase long chain base subunit 2 (SPTLC2) expression; upregulating SPTLC2 facilitated the proliferation, migration, invasion, adhesion, angiogenesis, and sphingosine-1-phosphate (S1P) production of HUVECs and HepG2 cells, while interfering with SPTLC2 expression inhibited them; HUVECs facilitated the proliferation, migration, invasion, S1P production, S1PR1, and S1PR2 expression of HepG2 cells, while S1PR3 expression was decreased. In conclusion, SPTLC2 may be associated with the antivascular and antitumor effects of TP, and SPTLC2 is expected to become a new marker for tumor therapy. HUVECs can promote the proliferation, migration, and invasion of HepG2 cells, which may be related to the S1P/sphingosine-1-phosphate receptor (S1PR) signaling pathway.

The key role of sphingolipid metabolism in cancer: New therapeutic targets, diagnostic and prognostic values, and anti-tumor immunotherapy resistance

Biologically active sphingolipids are closely related to the growth, differentiation, aging, and apoptosis of cancer cells. Some sphingolipids, such as ceramides, are favorable metabolites in the sphingolipid metabolic pathway, usually mediating antiproliferative responses, through inhibiting cancer cell growth and migration, as well as inducing autophagy and apoptosis. However, other sphingolipids, such as S1P, play the opposite role, which induces cancer cell transformation, migration and growth and promotes drug resistance. There are also other sphingolipids, as well as enzymes, played potentially critical roles in cancer physiology and therapeutics. This review aimed to explore the important roles of sphingolipid metabolism in cancer. In this article, we summarized the role and value of sphingolipid metabolism in cancer, including the distribution of sphingolipids, the functions, and their relevance to cancer diagnosis and prognosis. We also summarized the known and potential antitumor targets present in sphingolipid metabolism, analyzed the correlation between sphingolipid metabolism and tumor immunity, and summarize the antitumor effects of natural compounds based on sphingolipids. Through the analysis and summary of sphingolipid antitumor therapeutic targets and immune correlation, we aim to provide ideas for the development of new antitumor drugs, exploration of new therapeutic means for tumors, and study of immunotherapy resistance mechanisms.

Plasma Sphingosine-1-Phosphate Levels Are Associated with Progression of Estrogen Receptor-Positive Breast Cancer

Although numerous experiments revealed an essential role of a lipid mediator, sphingosine-1-phosphate (S1P), in breast cancer (BC) progression, the clinical significance of S1P remains unclear due to the difficulty of measuring lipids in patients. The aim of this study was to determine the plasma concentration of S1P in estrogen receptor (ER)-positive BC patients, as well as to investigate its clinical significance. We further explored the possibility of a treatment strategy targeting S1P in ER-positive BC patients by examining the effect of FTY720, a functional antagonist of S1P receptors, on hormone therapy-resistant cells. Plasma S1P levels were significantly higher in patients negative for progesterone receptor (PgR) expression than in those positive for expression (p = 0.003). Plasma S1P levels were also significantly higher in patients with larger tumor size (p = 0.012), lymph node metastasis (p = 0.014), and advanced cancer stage (p = 0.003), suggesting that higher levels of plasma S1P are associated with cancer progression. FTY720 suppressed the viability of not only wildtype MCF-7 cells, but also hormone therapy-resistant MCF-7 cells. Targeting S1P signaling in ER-positive BC appears to be a possible new treatment strategy, even for hormone therapy-resistant patients.

Conflicting roles of EGFR expression by subtypes in breast cancer

Epidermal growth factor receptor (EGFR) is one of the receptors that belong to the epidermal growth factor family of receptor tyrosine kinases (ErbBs). Several malignancies including breast cancer that express EGFR have poor prognosis. Our study examined the EGFR expression among 5176 breast cancer patients from GSE96058 and METABRIC cohorts and the contribution of tumor immune microenvironment in different subtypes. We found that among different breast cancer subtypes, EGFR expression in TNBC was the highest compared to other subtypes. EGFR high ER-positive/HER2-negative breast cancer had significantly higher survival compared to EGFR low ER-positive/HER2-negative breast cancer. It was also associated with high level of intratumor heterogeneity and homologous recombination defects (HRD). This group was also enriched in immune-related gene sets. On the other hand, low EGFR tumor was enriched in cell proliferation-related gene sets. However, these findings were not observed in TNBC. Interestingly, there was a greater infiltration of anti-cancer immune cells in high EGFR ER-positive/HER2-negative breast cancers, while, TNBC with higher EGFR expression had lower fraction of immune cells along with low level of cytolytic activity. Tumor cells have significantly higher EGFR expression compared to immune cells in single cell sequencing data. There was higher expression of immune checkpoint molecules in high EGFR ER-positive/HER2-negative breast cancer but lower expression in TNBC. High EGFR metastatic tumor was significantly associated with worse survival, but no association with infiltrating immune cells was observed. Our study shows that higher EGFR expression in ER-positive/HER2-negative breast cancer is associated with improved outcomes and an anti-cancer immune microenvironment.

Sphingosine-1-Phosphate Catabolizing Enzymes Predict Better Prognosis in Triple-Negative Breast Cancer Patients and Correlates With Tumor-Infiltrating Immune Cells

Background: Triple-negative breast cancer (TNBC) is associated with a poor prognosis. Sphingosine-1-phosphate (S1P), a potent sphingolipid metabolite, has been implicated in many processes that are important for breast cancer (BC). S1P signaling regulates tumorigenesis, and response to chemotherapy and immunotherapy by affecting the trafficking, differentiation or effector function of tumor-infiltrating immune cells (TIICs). Objective: In this study, using bioinformatics tools and publicly available databases, we have analyzed the prognostic value of S1P metabolizing genes and their correlation with TIICs in BC patients. Methods: The expression of S1P metabolizing genes and receptors was evaluated by the UALCAN cancer database. The correlation between mRNA expression of S1P metabolizing genes and receptors and survival outcome of breast cancer patients was analyzed by the Kaplan-Meier plotter database. The association between the gene expression and infiltration of immune cells in the tumors was analyzed by "Tumor-Infiltrating Immune Estimation Resource (TIMER). In silico protein expression analysis was done using the Human Protein Atlas" database. Results: TNBC patients with lower expression of S1P phosphatase 1 (SGPP1) or lipid phosphate phosphatase 3 (PLPP3) have much shorter relapse-free survival than the patients with a higher expression of these genes. SGPP1 and PLPP3 expression show a strong positive correlation with tumor-infiltrating dendritic cells (DCs), CD4+ and CD8+ T cells, neutrophils, and macrophages in the TNBC subtypes. In addition, S1P receptor 4 (S1PR4), an S1P receptor exhibit a strong positive correlation with DCs, CD4+ and CD8+ T cells and neutrophils in TNBC. We, therefore, conclude that low expression of SGPP1 and PLPP3 may hinder the recruitment of immune cells to the tumor environment, resulting in the blockage of cancer cell clearance and a subsequent poor prognosis.

Lipid metabolism in cancer progression and therapeutic strategies

Dysregulated lipid metabolism represents an important metabolic alteration in cancer. Fatty acids, cholesterol, and phospholipid are the three most prevalent lipids that act as energy producers, signaling molecules, and source material for the biogenesis of cell membranes. The enhanced synthesis, storage, and uptake of lipids contribute to cancer progression. The rewiring of lipid metabolism in cancer has been linked to the activation of oncogenic signaling pathways and cross talk with the tumor microenvironment. The resulting activity favors the survival and proliferation of tumor cells in the harsh conditions within the tumor. Lipid metabolism also plays a vital role in tumor immunogenicity via effects on the function of the noncancer cells within the tumor microenvironment, especially immune-associated cells. Targeting altered lipid metabolism pathways has shown potential as a promising anticancer therapy. Here, we review recent evidence implicating the contribution of lipid metabolic reprogramming in cancer to cancer progression, and discuss the molecular mechanisms underlying lipid metabolism rewiring in cancer, and potential therapeutic strategies directed toward lipid metabolism in cancer. This review sheds new light to fully understanding of the role of lipid metabolic reprogramming in the context of cancer and provides valuable clues on therapeutic strategies targeting lipid metabolism in cancer.

In Vivo Evidence for Serine Biosynthesis-Defined Sensitivity of Lung Metastasis, but Not of Primary Breast Tumors, to mTORC1 Inhibition

In tumors, nutrient availability and metabolism are known to be important modulators of growth signaling. However, it remains elusive whether cancer cells that are growing out in the metastatic niche rely on the same nutrients and metabolic pathways to activate growth signaling as cancer cells within the primary tumor. We discovered that breast-cancer-derived lung metastases, but not the corresponding primary breast tumors, use the serine biosynthesis pathway to support mTORC1 growth signaling. Mechanistically, pyruvate uptake through Mct2 supported mTORC1 signaling by fueling serine biosynthesis-derived α-ketoglutarate production in breast-cancer-derived lung metastases. Consequently, expression of the serine biosynthesis enzyme PHGDH was required for sensitivity to the mTORC1 inhibitor rapamycin in breast-cancer-derived lung tumors, but not in primary breast tumors. In summary, we provide in vivo evidence that the metabolic and nutrient requirements to activate growth signaling differ between the lung metastatic niche and the primary breast cancer site.

Effects of Sphingosine-1-Phosphate on Cell Viability, Differentiation, and Gene Expression of Adipocytes

Sphingosine-1-phosphate (S1P) is a highly potent sphingolipid metabolite, which controls numerous physiological and pathological process via its extracellular and intracellular functions. The breast is mainly composed of epithelial cells (mammary gland) and adipocytes (stroma). Adipocytes play an important role in regulating the normal functions of the breast. Compared to the vast amount studies on breast epithelial cells, the functions of S1P in breast adipocytes are much less known. Thus, in the current study, we used human preadipocyte cell lines SGBS and mouse preadipocyte cell line 3T3-L1 as in vitro models to evaluate the effects of S1P on cell viability, differentiation, and gene expression in adipocytes. Our results showed that S1P increased cell viability in SGBS and 3T3-L1 preadipocytes but moderately reduced cell viability in differentiated SGBS and 3T3-L1 adipocytes. S1P was also shown to inhibit adipogenic differentiation of SGBS and 3T3-L1 at concentration higher than 1000 nM. Transcriptome analyses showed that S1P was more influential on gene expression in differentiated adipocytes. Furthermore, our network analysis in mature adipocytes showed that the upregulated DEGs (differentially expressed genes) were related to regulation of lipolysis, PPAR (peroxisome proliferator-activated receptor) signaling, alcoholism, and toll-like receptor signaling, whereas the downregulated DEGs were overrepresented in cytokine-cytokine receptor interaction, focal adhesion, starch and sucrose metabolism, and nuclear receptors pathways. Together previous studies on the functions of S1P in breast epithelial cells, the current study implicated that S1P may play a critical role in modulating the bidirectional regulation of adipocyte-extracellular matrix-epithelial cell axis and maintaining the normal physiological functions of the breast.

Sphingosine Kinase 1 is Associated With Immune Cell-Related Gene Expressions in Human Breast Cancer

BACKGROUND

Although previous experiments have implicated sphingosine-1-phosphate (S1P) as a links between immune reactions and cancer progression, the exact mechanism of this interaction has not comprehensively studied in clinical human samples. This study sought to evaluate the S1P regulation by sphingosine kinase 1 (SPHK1), an S1P-producing enzyme, in the immunity/immuno-reactivity of clinical human breast cancer surgical specimens.

METHODS

S1P levels were examined in tumor, peritumoral, and normal human breast samples using mass spectrometry. Genomics Data Commons data portal of The Cancer Genome Atlas cohort was used to assess the expression of S1P-related and immune-related genes.

RESULTS

S1P levels were significantly higher in tumor samples compared to peritumoral (P < 0.05) or normal human breast samples (P < 0.001). SPHK1 gene expression was elevated in tumoral samples compared to normal breast samples (P < 0.01). Furthermore, the elevated expression of SPHK1 in breast cancer tissue was associated with an increased expression of the different kinds of immune-related genes, such as CD68, CD163, CD4, and FOXP3 (forkhead box P3), in HER2-negative breast cancer. Network analysis showed the central role of SPHK1 in the interaction of S1P signaling and expression of immune cell-related proteins.

CONCLUSIONS

We demonstrated that S1P is mainly produced by tumor tissue, rather than peritumoral tissue, in breast cancer patients. Our data revealed the involvement of S1P signaling in the regulation of immune-related genes, suggesting the links between S1P and complicated immune-cancer interactions in breast cancer patients.

Detrimental role of sphingosine kinase 1 in kidney damage in DOCA-salt hypertensive model: evidence from knockout mice

Background

Sphingosine-1-phosphate (S1P) is a bioactive metabolite of sphingolipids and produced by sphingosine kinases (SphK1 and SphK2). SphK1/S1P pathway is implicated in the progression of chronic kidney disease. However, the role of SphK1/S1P pathway in renal injury in hypertension has not been reported. This study tested the hypothesis that SphK1/S1P pathway mediates the kidney damage in DOCA-salt hypertensive mice.

Methods

Male wild type (WT) C57BL6 and SphK1 knockout (KO) mice were subjected to unilateral nephrectomy, subcutaneous implant containing 50 mg of deoxycorticosterone acetate (DOCA) and 1% NaCl drinking water for 7 weeks. At the end of experiments, blood pressure data, 24 h urine and kidney samples were collected. Renal mRNA levels of SphK1 were measured by real-time RT-PCR. Markers for fibrogenesis and immune cell infiltration in kidneys were detected using Western blot and immunohistochemistray analysis, respectively. The glomerular morphological changes were examined in kidney tissue slides stained with Periodic-Acid Schiff. Four groups were studied: wild type control (WT-C), WT-DOCA, KO-C and KO-DOCA.

Results

The renal SphK1 mRNA expression was significantly upregulated in WT-DOCA mice, whereas this upregulation of renal SphK1 mRNA was blocked in KO-DOCA mice. There was no difference in DOCA-salt-induced hypertension between WT and KO mice. The urinary albumin was increased in both DOCA-salt groups. However, the albuminuria was significantly lower in KO-DOCA than in WT-DOCA group. There were increases in glomerulosclerosis indices in both DOCA-salt groups, whereas the increases were also significantly lower in KO-DOCA than in WT-DOCA mice. Renal protein levels of α-smooth muscle actin were upregulated in both DOCA-salt groups, but the increase was significant lower in KO-DOCA than in WT-DOCA group. The increased staining areas of collagen detected by Sirius Red-staining in kidney tissue sections were also attenuated in KO-DOCA compared with WT-DOCA mice. In contrast, the increased infiltration of CD43+ (a T cell marker) or CD68+ (a macrophage marker) cells in DOCA-salt kidneys showed no significant difference between WT-DOCA and KO-DOCA mice.

Conclusions

SphK1/S1P signaling pathway mediates kidney damage in DOCA-salt hypertensive mice independent of blood pressure and immune modulation.

T cells are the main population in mouse breast milk and express similar profiles of tight junction proteins as those in mammary alveolar epithelial cells

Immune cells are present in the breast milk of several mammalian species; however, their immunological function and transmigration mechanisms to milk remain unknown. Some researchers hypothesize that milk leukocytes have a mammary gland (MG) origin and transmigrate thorough the paracellular pathway, but mammary alveolar epithelial cells strictly regulate the paracellular movement of milk components during lactation via barrier structures, such as tight junctions (TJs). To investigate this discrepancy, we compared leukocyte populations in mouse MG and milk and explored TJ protein expression profiles in MG leukocytes. The main subsets of milk leukocytes were CD8⁺ and CD4⁺ T cells displaying the memory phenotype. The proportions of myeloid, B, and dendritic cells were significantly lower in milk than in the MG. CD8⁺ T cells expressed genes encoding the TJ proteins claudin-3, -7, -12, and ZO-1 at higher levels when compared with myeloid and B cells in the MG among lactating mice. Alveolar epithelial cells in the MG expressed claudin-3, -4, and -7. Administration of FTY720, an inhibitory agonist of sphingosine 1-phosphate receptor 1 that stabilizes TJ permeability, increased the myeloid cell proportion in milk. Different leukocyte populations in the MG and milk suggest active and selective mechanisms of cell transmigration to milk. Both TJ-forming components in alveolar epithelial cells from the MG and TJ protein expression profiles in leukocytes from the MG appear to regulate milk leukocyte populations. T cells are the main population in mouse breast milk and express similar profiles of TJ proteins as those in mammary alveolar epithelial cells.

Amino acid levels determine metabolism and CYP450 function of hepatocytes and hepatoma cell lines

Predicting drug-induced liver injury in a preclinical setting remains challenging, as cultured primary human hepatocytes (PHHs), pluripotent stem cell-derived hepatocyte-like cells (HLCs), and hepatoma cells exhibit poor drug biotransformation capacity. We here demonstrate that hepatic functionality depends more on cellular metabolism and extracellular nutrients than on developmental regulators. Specifically, we demonstrate that increasing extracellular amino acids beyond the nutritional need of HLCs and HepG2 cells induces glucose independence, mitochondrial function, and the acquisition of a transcriptional profile that is closer to PHHs. Moreover, we show that these high levels of amino acids are sufficient to drive HLC and HepG2 drug biotransformation and liver-toxin sensitivity to levels similar to those in PHHs. In conclusion, we provide data indicating that extracellular nutrient levels represent a major determinant of cellular maturity and can be utilized to guide stem cell differentiation to the hepatic lineage.

Orthotopic Implantation Achieves Better Engraftment and Faster Growth Than Subcutaneous Implantation in Breast Cancer Patient-Derived Xenografts

Patient-Derived Xenograft (PDX) is now accepted as a murine model that better mimics human cancer when compared to a conventional cancer cell-line inoculation model. Some claim the advantage of orthotopic site implantation of patient tumor (OS) over ectopic implantation into the subcutaneous space (SQ); however, there has been no study that describes a head-to-head comparison of oncological differences between these two models to date. We hypothesize that OS tumors re-transplant and grow better than SQ tumors and are therefore a better model to evaluate tumor aggressiveness. Breast cancer PDXs were generated using the tumors derived from 11 patients into NOD scid gamma (NSG) mice. We used six ER(+)HER2(-) tumors and five triple negative (TN) tumors for a total of 11 tumors. Five PDX lines grew for an overall engraftment rate of 45%. We present our OS implantation method in detail. The re-transplantation rate of TN tumors in each transplant site was significantly higher in OS when compared to SQ tumors (70.1% vs. 32.1%, p < 0.01). OS tumors grow significantly faster than SQ tumors. Similarly, OS tumors demonstrated significantly more mitotic figures and Ki-67 positive cells than SQ tumors. The tumor re-transplantation rate significantly increased by the second and third generations with the OS method. The time from implantation to development of a palpable tumor dramatically decreased after the first passage. PDX of ER(+) tumors demonstrated significantly lower engraftment rates and slower tumor growth than TN tumors, which remarkably improved by the first passage. Orthotopically implanted PDX tumors showed better re-transplantation rates, greater tumor size, and more significant growth compared to the subcutaneously implanted model.

S1P Signaling in the Tumor Microenvironment

Sphingosine-1-phosphate (S1P), together with other phosphosphingolipids, has been found to regulate complex cellular function in the tumor microenvironment (TME) where it acts as a signaling molecule that participates in cell-cell communication. S1P, through intracellular and extracellular signaling, was found to promote tumor growth, angiogenesis, chemoresistance, and metastasis; it also regulates anticancer immune response, modulates inflammation, and promotes angiogenesis. Interestingly, cancer cells are capable of releasing S1P and thus modifying the behavior of the TME components in a way that contributes to tumor growth and progression. Therefore, S1P is considered an important therapeutic target, and several anticancer therapies targeting S1P signaling are being developed and tested in clinics.

Sphingosine-1-phosphate signaling: A novel target for simultaneous adjuvant treatment of triple negative breast cancer and chemotherapy-induced neuropathic pain

Triple-negative breast cancer (TNBC) is very aggressive with high metastatic and mortality rates and unfortunately, except for chemotherapy, there are few therapeutic options. The bioactive sphingolipid metabolite sphingosine-1-phosphate (S1P) regulates numerous processes important for cancer progression, metastasis, and neuropathic pain. The pro-drug FTY720 (fingolimod, Gilenya) used to treat multiple sclerosis is phosphorylated in the body to a S1P mimic that binds to S1PRs, except S1PR2, and also acts as a functional antagonist of S1PR1. This review highlights current findings showing that FTY720 has multiple anti-cancer activities and simultaneously prevents formation and actions of S1P. Moreover, in mouse breast cancer models, treatment with FTY720 reduces tumor growth, metastasis, and enhances sensitivity of advanced and hormonal refractory breast cancer and TNBC to conventional therapies. We discuss recent studies demonstrating that neuropathic pain induced by the chemotherapeutic bortezomib is also greatly reduced by administration of clinically relevant doses of FTY720, likely by targeting S1PR1 on astrocytes. FTY720 also shows promising anticancer potential in pre-clinical studies and is FDA approved, thus we suggest in this review that further studies are needed to pave the way for fast-tracking approval of FTY720/fingolimod for enhancing chemotherapy effectiveness and reduction of painful neuropathies.

Fatty acids: Adiposity and breast cancer chemotherapy, a bad synergy?

Globally, breast cancer continues to be a major concern in women's health. Lifestyle related risk factors, specifically excess adipose tissue (adiposity) has reached epidemic proportions and has been identified as a major risk factor in the development of breast cancer. Dysfunctional adipose tissue has evoked research focusing on its association with metabolic-related conditions, breast cancer risk and progression. Adipose dysfunction in coordination with immune cells and inflammation, are responsible for accelerated cell growth and survival of cancer cells. Recently, evidence also implicates adiposity as a potential risk factor for chemotherapy resistance. Chemotherapeutic agents have been shown to negatively impact adipose tissue. Since adipose tissue is a major storage site for fatty acids, it is not unlikely that these negative effects may disrupt adipose tissue homeostasis. It is therefore argued that fatty acid composition may be altered due to the chemotherapeutic pharmacokinetics, which in turn could have severe health related outcomes. The underlying molecular mechanisms elucidating the effects of fatty acid composition in adiposity-linked drug resistance are still unclear and under explored. This review focuses on the potential role of adiposity in breast cancer and specifically emphasizes the role of fatty acids in cancer progression and treatment resistance.

GPCR Modulation in Breast Cancer

Breast cancer is the most prevalent cancer found in women living in developed countries. Endocrine therapy is the mainstay of treatment for hormone-responsive breast tumors (about 70% of all breast cancers) and implies the use of selective estrogen receptor modulators and aromatase inhibitors. In contrast, triple-negative breast cancer (TNBC), a highly heterogeneous disease that may account for up to 24% of all newly diagnosed cases, is hormone-independent and characterized by a poor prognosis. As drug resistance is common in all breast cancer subtypes despite the different treatment modalities, novel therapies targeting signaling transduction pathways involved in the processes of breast carcinogenesis, tumor promotion and metastasis have been subject to accurate consideration. G protein-coupled receptors (GPCRs) are the largest family of cell-surface receptors involved in the development and progression of many tumors including breast cancer. Here we discuss data regarding GPCR-mediated signaling, pharmacological properties and biological outputs toward breast cancer tumorigenesis and metastasis. Furthermore, we address several drugs that have shown an unexpected opportunity to interfere with GPCR-based breast tumorigenic signals.

Different Roles of Sphingosine Kinase 1 and 2 in Pancreatic Cancer Progression

BACKGROUND

Pancreatic cancer is a disease with poor prognosis, and development of new treatments is necessary. Sphingosine-1-phosphate (S1P), a bioactive lipid mediator produced by sphingosine kinases (SphK1 and SphK2), plays a critical role in progression of many types of cancer. However, little is known about the role of sphingosine kinases in pancreatic cancer. This study investigated the roles of sphingosine kinases in pancreatic cancer progression.

MATERIALS AND METHODS

S1P levels in pancreatic cancer and noncancerous pancreatic tissue were measured in 10 patients. We generated PAN02 murine pancreatic cancer cell lines with a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated system genes 9 (Cas9)-mediated deletion of SphK1 or SphK2 and assessed cell growth and migration. In an animal model, we assessed the survival of mice injected with PAN02 cells intraperitoneally.

RESULTS

S1P levels in the pancreatic cancer tissue were significantly higher than those in noncancerous tissue. SphK1 knockout (KO) cells showed greater proliferation and migration than wild type (WT) cells, and SphK2 KO cells showed less proliferation and migration than WT cells. Animal experiments showed that the survival of mice injected with SphK1 KO cells was significantly shorter than those injected with WT cells, and the survival of mice injected with SphK2 KO cells was longer than those injected with WT cells. Surprisingly, cytotoxic assay using gemcitabine showed that SphK1 KO cells survived less than WT cells, and SphK2 KO cells survived more than WT cells.

CONCLUSIONS

S1P produced by SphK1 and SphK2 may have different functions in pancreatic cancer cells. Targeting both SphK1 and SphK2 may be a potential strategy for pancreatic cancer treatment.

The role of sphingosine-1-phosphate in inflammation and cancer progression

Many inflammatory mediators are involved in the process of carcinogenesis and cancer progression. In addition to cytokines and chemokines, lipid mediators have recently attracted attention as signaling molecules associated with inflammatory diseases. Sphingosine-1-phosphate (S1P) is a pleiotropic lipid mediator that regulates cell survival and migration, immune cell recruitment, angiogenesis and lymphangiogenesis. S1P also plays a significant role in inflammation and cancer. The gradation of S1P concentration in the blood, lymph and tissue regulates lymphocyte trafficking, an important component of inflammation. Furthermore, cancer cells produce elevated levels of S1P, contributing to the tumor microenvironment and linking cancer and inflammation. Future technological advances may reveal greater detail about the mechanisms of S1P regulation in the tumor microenvironment and the contribution of S1P to cancer progression. Considering the critical role of S1P in linking inflammation and cancer, it is possible that the S1P signaling pathway could be a novel therapeutic target for cancers with chronic inflammation.

The signalling roles of sphingosine-1-phosphate derived from red blood cells and platelets

Sphingosine-1-phosphate (S1P) is an essential, bioactive lysophospholipid mediator that regulates various physiological functions such as lymphocyte trafficking, inflammation and behavioural characteristics of the vascular system. S1P signalling is mediated via a family of five GPCRs, which are expressed in various cell types and tissues. S1P concentration is maintained in a gradient through the activity of S1P degrading enzymes, and this gradient is critical for lymphocyte egress. To exert its extracellular signalling roles, S1P must be secreted out of the cells by protein transporters. The recent discovery of S1P transporters has shed light on the sources of S1P. However, these transporters still need to be clarified as they are important in defining the S1P gradient for lymphocyte recirculation and the source of S1P for maintenance of blood vessels. Here, we review the current understanding of S1P sources, highlighting the roles of S1P transporters with an emphasis on haematopoietic cells as a major source of circulatory S1P.

Neutral Sphingomyelinases in Cancer: Friend or Foe?

For many years, neutral sphingomyelinases (N-SMases) were long thought to be anticancer enzymes owing to their roles as key producers of ceramide linked to apoptosis, growth arrest, and the chemotherapeutic response. However, in recent years, with the cloning of multiple isoforms and with new information on their cellular roles, particularly for nSMase2, a more complex picture is emerging suggesting that N-SMases have both pro- and anticancer roles. In this chapter, we will summarize current knowledge on N-SMase expression in cancer and the roles of N-SMase activity and specific isoforms in cancer-relevant biologies. We will also discuss what we see as the major challenges ahead for research into N-SMases in cancer.

Ceramide species are elevated in human breast cancer and are associated with less aggressiveness

Sphingolipids have emerged as key regulatory molecules in cancer cell survival and death. Although important roles of sphingolipids in breast cancer progression have been reported in experimental models, their roles in human patients are yet to be revealed. The aim of this study was to investigate the ceramide levels and its biosynthesis pathways in human breast cancer patients. Breast cancer, peri-tumor and normal breast tissue samples were collected from surgical specimens from a series of 44 patients with breast cancer. The amount of sphingolipid metabolites in the tissue were determined by mass spectrometry. The Cancer Genome Atlas was used to analyze gene expression related to the sphingolipid metabolism. Ceramide levels were higher in breast cancer tissue compared to both normal and peri-tumor breast tissue. Substrates and enzymes that generate ceramide were significantly increased in all three ceramide biosynthesis pathways in cancer. Further, higher levels of ceramide in breast cancer were associated with less aggressive cancer biology presented by Ki-67 index and nuclear grade of the cancer. Interestingly, patients with higher gene expressions of enzymes in the three major ceramide synthesis pathways showed significantly worse prognosis. This is the first study to reveal the clinical relevance of ceramide metabolism in breast cancer patients. We demonstrated that ceramide levels in breast cancer tissue were significantly higher than those in normal tissue, with activation of the three ceramide biosynthesis pathways. We also identified that ceramide levels have a significant association with aggressive phenotype and its enzymes have prognostic impact on breast cancer patients.

ABCC1-Exported Sphingosine-1-phosphate, Produced by Sphingosine Kinase 1, Shortens Survival of Mice and Patients with Breast Cancer

Sphingosine-1-phosphate (S1P), a bioactive sphingolipid mediator, has been implicated in regulation of many processes important for breast cancer progression. Previously, we observed that S1P is exported out of human breast cancer cells by ATP-binding cassette (ABC) transporter ABCC1, but not by ABCB1, both known multidrug resistance proteins that efflux chemotherapeutic agents. However, the pathologic consequences of these events to breast cancer progression and metastasis have not been elucidated. Here, it is demonstrated that high expression of ABCC1, but not ABCB1, is associated with poor prognosis in breast cancer patients. Overexpression of ABCC1, but not ABCB1, in human MCF7 and murine 4T1 breast cancer cells enhanced S1P secretion, proliferation, and migration of breast cancer cells. Implantation of breast cancer cells overexpressing ABCC1, but not ABCB1, into the mammary fat pad markedly enhanced tumor growth, angiogenesis, and lymphangiogenesis with a concomitant increase in lymph node and lung metastases as well as shorter survival of mice. Interestingly, S1P exported via ABCC1 from breast cancer cells upregulated transcription of sphingosine kinase 1 (SPHK1), thus promoting more S1P formation. Finally, patients with breast cancers that express both activated SPHK1 and ABCC1 have significantly shorter disease-free survival. These findings suggest that export of S1P via ABCC1 functions in a malicious feed-forward manner to amplify the S1P axis involved in breast cancer progression and metastasis, which has important implications for prognosis of breast cancer patients and for potential therapeutic targets.Implication: Multidrug resistant transporter ABCC1 and activation of SPHK1 in breast cancer worsen patient's survival by export of S1P to the tumor microenvironment to enhance key processes involved in cancer progression. Mol Cancer Res; 16(6); 1059-70. ©2018 AACR.

Targeting the SphK1/S1P/S1PR1 Axis That Links Obesity, Chronic Inflammation, and Breast Cancer Metastasis

Although obesity with associated inflammation is now recognized as a risk factor for breast cancer and distant metastases, the functional basis for these connections remain poorly understood. Here, we show that in breast cancer patients and in animal breast cancer models, obesity is a sufficient cause for increased expression of the bioactive sphingolipid mediator sphingosine-1-phosphate (S1P), which mediates cancer pathogenesis. A high-fat diet was sufficient to upregulate expression of sphingosine kinase 1 (SphK1), the enzyme that produces S1P, along with its receptor S1PR1 in syngeneic and spontaneous breast tumors. Targeting the SphK1/S1P/S1PR1 axis with FTY720/fingolimod attenuated key proinflammatory cytokines, macrophage infiltration, and tumor progression induced by obesity. S1P produced in the lung premetastatic niche by tumor-induced SphK1 increased macrophage recruitment into the lung and induced IL6 and signaling pathways important for lung metastatic colonization. Conversely, FTY720 suppressed IL6, macrophage infiltration, and S1P-mediated signaling pathways in the lung induced by a high-fat diet, and it dramatically reduced formation of metastatic foci. In tumor-bearing mice, FTY720 similarly reduced obesity-related inflammation, S1P signaling, and pulmonary metastasis, thereby prolonging survival. Taken together, our results establish a critical role for circulating S1P produced by tumors and the SphK1/S1P/S1PR1 axis in obesity-related inflammation, formation of lung metastatic niches, and breast cancer metastasis, with potential implications for prevention and treatment.Significance: These findings offer a preclinical proof of concept that signaling by a sphingolipid may be an effective target to prevent obesity-related breast cancer metastasis. Cancer Res; 78(7); 1713-25. ©2018 AACR.

Sphingosine kinase 1 in breast cancer

Breast cancer affects 1 out of 8 women in the US and is the second highest cause of death from cancer for women, leading to considerable research examining the causes, progression, and treatment of breast cancer. Over the last two decades, sphingosine-1-phosphate (S1P), a potent sphingolipid metabolite, has been implicated in many processes important for breast cancer including growth, progression, transformation and metastasis, and is the focus of this review. In particular, one of the kinases that produces S1P, sphingosine kinase 1 (SphK1), has come under increasing scrutiny as it is commonly upregulated in breast cancer cells and has been linked with poorer prognosis and progression, possibly leading to resistance to certain anti-cancer therapies. In this review, we will also discuss preclinical studies of both estrogen receptor (ER) positive as well as triple-negative breast cancer mouse models with inhibitors of SphK1 and other compounds that target the S1P axis and have shown good promise in reducing tumor growth and metastasis. It is hoped that in the future this will lead to development of novel combination approaches for effective treatment of both conventional hormonal therapy-resistant breast cancer and triple-negative breast cancer.

Paradoxical Association of Postoperative Plasma Sphingosine-1-Phosphate with Breast Cancer Aggressiveness and Chemotherapy

Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator that has been shown to serve an important regulatory function in breast cancer progression. This study analyzes plasma S1P levels in breast cancer patients undergoing adjuvant therapy as compared to healthy control volunteers. 452 plasma S1P samples among 158 breast cancer patients, along with 20 healthy control volunteers, were analyzed. Mean S1P levels did not significantly differ between cancer patients and controls. Smoking was associated with higher S1P levels in cancer patients. Baseline S1P levels had weak inverse correlation with levels of the inflammatory mediator interleukin- (IL-) 17 and CCL-2 and positive correlation with tumor necrosis factor alpha (TNF-α). Midpoint S1P levels during adjuvant therapy were lower than baseline, with near return to baseline after completion, indicating a relationship between chemotherapy and circulating S1P. While stage of disease did not correlate with plasma S1P levels, they were lower among patients with Her2-enriched and triple-negative breast cancer as compared to luminal-type breast cancer. Plasma S1P levels are paradoxically suppressed in aggressive breast cancer and during adjuvant chemotherapy, which raises the possibility that postoperative plasma S1P levels do not reflect S1P secretion from resected breast cancer.

Clinical Impact of Sphingosine-1-Phosphate in Breast Cancer

Breast cancer metastasizes to lymph nodes or other organs, which determine the prognosis of patients. It is difficult to cure the breast cancer patients with distant metastasis due to resistance to drug therapies. Elucidating the underlying mechanisms of breast cancer metastasis and drug resistance is expected to provide new therapeutic targets. Sphingosine-1-phosphate (S1P) is a pleiotropic, bioactive lipid mediator that regulates many cellular functions, including proliferation, migration, survival, angiogenesis/lymphangiogenesis, and immune responses. S1P is formed in cells by sphingosine kinases and released from them, which acts in an autocrine, paracrine, and/or endocrine manner. S1P in extracellular space, such as interstitial fluid, interacts with components in the tumor microenvironment, which may be important for metastasis. Importantly, recent translational research has demonstrated an association between S1P levels in breast cancer patients and clinical outcomes, highlighting the clinical importance of S1P in breast cancer. We suggest that S1P is one of the key molecules to overcome the resistance to the drug therapies, such as hormonal therapy, anti-HER2 therapy, or chemotherapy, all of which are crucial aspects of a breast cancer treatment.

Doxorubicin effect is enhanced by sphingosine-1-phosphate signaling antagonist in breast cancer

BACKGROUND

Doxorubicin is one of the most commonly used chemotherapeutic drugs for breast cancer; however, its use is limited by drug resistance and side effects. We hypothesized that adding FTY720, a sphingosine-1-phosphate (S1P) receptor functional antagonist, to doxorubicin would potentiate its effects by suppression of drug-induced inflammation.

MATERIALS AND METHODS

The Cancer Genome Atlas, Gene Expression Omnibus data sets, and National Cancer Institute-60 panel were used for gene expressions and gene set enrichment analysis. E0771 syngeneic mammary tumor cells were used. OB/OB mice fed with western high-fat diet were used as an obesity model.

RESULTS

STAT3 expression was significantly increased after doxorubicin treatment in human breast cancer that implicates that doxorubicin evokes inflammation. Expression of sphingosine kinase 1, the enzyme that produces S1P and links inflammation and cancer, tended to be higher in doxorubicin-resistant human cancer and cell lines. In a murine breast cancer model, sphingosine kinase 1, S1P receptor 1, interleukin 6, and STAT3 were overexpressed in the doxorubicin-treated group, whereas all of them were significantly suppressed with addition of FTY720. Combination therapy synergistically suppressed cancer growth both in vitro and in vivo. Furthermore, combination therapy showed higher efficacy in an obesity breast cancer model, where high body mass index demonstrated trends toward worse disease-free and overall survival, and high-serum S1P levels in human patients and volunteers.

CONCLUSIONS

We found that FTY720 enhanced the efficacy of doxorubicin by suppression of drug-induced inflammation, and combination therapy showed stronger effect in obesity-related breast cancer.

The role of sphingosine-1-phosphate in the tumor microenvironment and its clinical implications

Elucidating the interaction between cancer and non-cancer cells, such as blood vessels, immune cells, and other stromal cells, in the tumor microenvironment is imperative in understanding the mechanisms underlying cancer progression and metastasis, which is expected to lead to the development of new therapeutics. Sphingosine-1-phosphate is a bioactive lipid mediator that promotes cell survival, proliferation, migration, angiogenesis/lymphangiogenesis, and immune responsiveness, which are all factors involved in cancer progression. Sphingosine-1-phosphate is generated inside cancer cells by sphingosine kinases and then exported into the tumor microenvironment. Although sphingosine-1-phosphate is anticipated to play an important role in the tumor microenvironment and cancer progression, determining sphingosine-1-phosphate levels in the tumor microenvironment has been difficult due to a lack of established methods. We have recently developed a method to measure sphingosine-1-phosphate levels in the interstitial fluid that bathes cancer cells in the tumor microenvironment, and reported that high levels of sphingosine-1-phosphate exist in the tumor interstitial fluid. Importantly, sphingosine-1-phosphate can be secreted from cancer cells and non-cancer components such as immune cells and vascular/lymphatic endothelial cells in the tumor microenvironment. Furthermore, sphingosine-1-phosphate affects both cancer and non-cancer cells in the tumor microenvironment promoting cancer progression. Here, we review the roles of sphingosine-1-phosphate in the interaction between cancer and non-cancer cells in tumor microenvironment, and discuss future possibilities for targeted therapies against sphingosine-1-phosphate signaling for cancer patients.

Measurement of Lysophosphatidic Acid and Sphingosine-1-Phosphate by Liquid Chromatography-Coupled Electrospray Ionization Tandem Mass Spectrometry

Lysophosphatidic acids and sphingosine-1-phosphate are bioactive lipids that regulate diverse cellular and physiological processes through actions that are largely mediated by cell surface receptors. The roles played by these lipids in multiple disease processes make the enzymes and receptors involved in their synthesis, inactivation, and signaling attractive targets for pharmacological therapies. In this chapter we describe methods for sensitive accurate quantitation of LPA and S1P levels in biological fluids using liquid chromatography-coupled electrospray ionization tandem mass spectrometry.

Sphingosine-1-phosphate in the lymphatic fluid determined by novel methods

Background

Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid mediator that regulates many physiological and pathological processes. It has been suggested that S1P gradient with high concentrations in the blood and lymphatic fluid and low concentrations in the peripheral tissue plays important roles in immune cell trafficking and potentially cancer progression. However, only a few reports have assessed S1P levels in the lymphatic fluid due to lack of an established easy-to-use method. Here, we report a simple technique for collection of lymphatic fluid to determine S1P.

Materials and methods

Lymphatic fluid was collected directly with a catheter needle (classical method) or was absorbed onto filter paper after incision of cisterna chyli (new method) in murine models. Blood, lymphatic fluid and mesenteric lymph nodes were corrected from wild type and sphingosine kinase 2 (SphK2) knockout mice to determine S1P levels by mass spectrometry.

Results

The volume of lymphatic fluid collected by the new method was at least three times greater than those collected by the classical method. S1P concentrations in lymphatic fluid are lower than in blood and higher than in lymph nodes. Interestingly, S1P levels in lymphatic fluid from SphK2 knockout mice were significantly higher than those in wild type, suggesting an important role of SphK2 and/or SphK1 to regulate S1P levels in lymphatic fluid.

Conclusions

In agreement with the previous theory, our results confirm “S1P gradient” among blood, lymphatic fluid and peripheral lymphatic tissues. Convenient methods for collection and measurement of sphingolipids in lymphatic fluid are expected to provide new insights on functions of sphingolipids.