Neurotoxic 1-deoxysphingolipids and paclitaxel-induced peripheral neuropathy

(1-Deoxy)ceramides in bilayers containing sphingomyelin and cholesterol

The discovery of a novel sphingolipid subclass, the (1-deoxy)sphingolipids, which lack the 1-hydroxy group, attracted considerable attention in the last decade, mainly due to their involvement in disease. They differed in their physico-chemical properties from the canonical (or 1-hydroxy) sphingolipids and they were more toxic when accumulated in cells, inducing neurodegeneration and other dysfunctions. (1-Deoxy)ceramides, (1-deoxy)dihydroceramides, and (1- deoxymethyl)dihydroceramides, the latter two containing a saturated sphingoid chain, have been studied in this work using differential scanning calorimetry, confocal fluorescence and atomic force microscopy, to evaluate their behavior in bilayers composed of mixtures of three or four lipids. When compared to canonical ceramides (Cer), a C16:0 (1-deoxy)Cer shows a lower miscibility in mixtures of the kind C16:0 sphingomyelin/cholesterol/XCer, where XCer is any (1-deoxy)ceramide, giving rise to the coexistence of a liquid-ordered phase and a gel phase. The latter resembles, in terms of thermotropic behavior and nanomechanical resistance, the gel phase of the C16:0 sphingomyelin/cholesterol/C16:0 Cer mixture [Busto et al., Biophys. J. 2014, 106, 621-630]. Differences are seen between the various C16:0 XCer under study in terms of nanomechanical resistance, bilayer thickness and bilayer topography. When examined in a more fluid environment (bilayers based on C24:1 SM), segregated gel phases are still present. Probably related to such lateral separation, XCer preserve the capacity for membrane permeation, but their effects are significantly lower than those of canonical ceramides. Moreover, C24:1 XCer show significantly lower membrane permeation capacity than their C16:0 counterparts. The above data may be relevant in the pathogenesis of certain sphingolipid-related diseases, including certain neuropathies, diabetes, and glycogen storage diseases.

Plasma Lipidomic Profiling Identifies Elevated Triglycerides as Potential Risk Factor in Chemotherapy-Induced Peripheral Neuropathy

PURPOSE

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect of cytotoxic cancer treatment, often necessitating dose reduction (DR) or chemotherapy discontinuation (CD). Studies on peripheral neuropathy related to chemotherapy, obesity, and diabetes have implicated lipid metabolism. This study examined the association between circulating lipids and CIPN.

METHODS

Lipidomic analysis was performed on plasma samples from 137 patients receiving taxane-based treatment. CIPN was graded using Total Neuropathy Score-clinical version (TNSc) and patient-reported outcome measure European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-CIPN (EORTC-QLQ-CIPN20).

RESULTS

A significant proportion of elevated baseline lipids were associated with high-grade CIPN defined by TNSc and EORTC-QLQ-CIPN20 including triacylglycerols (TGs). Multivariable Cox regression on lipid species, adjusting for BMI, age, and diabetes, showed several elevated baseline TG associated with shorter time to DR/CD. Latent class analysis identified two baseline lipid profiles with differences in risk of CIPN (hazard ratio, 2.80 [95% CI, 1.50 to 5.23]; P = .0013). The higher risk lipid profile had several elevated TG species and was independently associated with DR/CD when modeled with other clinical factors (diabetes, age, BMI, or prior numbness/tingling).

CONCLUSION

Elevated baseline plasma TG is associated with an increased risk of CIPN development and warrants further validation in other cohorts. Ultimately, this may enable therapeutic intervention.

Dysregulation of sphingolipid metabolism in pain

Pain is a clinical condition that is currently of great concern and is often caused by tissue or nerve damage or occurs as a concomitant symptom of a variety of diseases such as cancer. Severe pain seriously affects the functional status of the body. However, existing pain management programs are not fully satisfactory. Therefore, there is a need to delve deeper into the pathological mechanisms underlying pain generation and to find new targets for drug therapy. Sphingolipids (SLs), as a major component of the bilayer structure of eukaryotic cell membranes, also have powerful signal transduction functions. Sphingolipids are abundant, and their intracellular metabolism constitutes a huge network. Sphingolipids and their various metabolites play significant roles in cell proliferation, differentiation, apoptosis, etc., and have powerful biological activities. The molecules related to sphingolipid metabolism, mainly the core molecule ceramide and the downstream metabolism molecule sphingosine-1-phosphate (S1P), are involved in the specific mechanisms of neurological disorders as well as the onset and progression of various types of pain, and are closely related to a variety of pain-related diseases. Therefore, sphingolipid metabolism can be the focus of research on pain regulation and provide new drug targets and ideas for pain.

Sphingolipids in mitochondria-from function to disease

Sphingolipids are not only structural components of cellular membranes but also play vital roles in cell signaling and modulation of cellular processes. Within mitochondria, sphingolipids exert diverse effects on mitochondrial dynamics, energy metabolism, oxidative stress, and cell death pathways. In this review, we summarize literature addressing the crucial role of sphingolipids in mitochondria, highlighting their impact on mitochondrial dynamics, cellular bioenergetics, and important cell processes including apoptosis and mitophagy.

Mass Spectrometry Detects Sphingolipid Metabolites for Discovery of New Strategy for Cancer Therapy from the Aspect of Programmed Cell Death

Sphingolipids, a type of bioactive lipid, play crucial roles within cells, serving as integral components of membranes and exhibiting strong signaling properties that have potential therapeutic implications in anti-cancer treatments. However, due to the diverse group of lipids and intricate mechanisms, sphingolipids still face challenges in enhancing the efficacy of different therapy approaches. In recent decades, mass spectrometry has made significant advancements in uncovering sphingolipid biomarkers and elucidating their impact on cancer development, progression, and resistance. Primary sphingolipids, such as ceramide and sphingosine-1-phosphate, exhibit contrasting roles in regulating cancer cell death and survival. The evasion of cell death is a characteristic hallmark of cancer cells, leading to treatment failure and a poor prognosis. The escape initiates with long-established apoptosis and extends to other programmed cell death (PCD) forms when patients experience chemotherapy, radiotherapy, and/or immunotherapy. Gradually, supportive evidence has uncovered the fundamental molecular mechanisms underlying various forms of PCD leading to the development of innovative molecular, genetic, and pharmacological tools that specifically target sphingolipid signaling nodes. In this study, we provide a comprehensive overview of the sphingolipid biomarkers revealed through mass spectrometry in recent decades, as well as an in-depth analysis of the six main forms of PCD (apoptosis, autophagy, pyroptosis, necroptosis, ferroptosis, and cuproptosis) in aspects of tumorigenesis, metastasis, and tumor response to treatments. We review the corresponding small-molecule compounds associated with these processes and their potential implications in cancer therapy.

The Critical Impact of Sphingolipid Metabolism in Breast Cancer Progression and Drug Response

Breast cancer is the second leading cause of cancer-related death in women in the world, and its management includes a combination of surgery, radiation therapy, chemotherapy, and immunotherapy, whose effectiveness depends largely, but not exclusively, on the molecular subtype (Luminal A, Luminal B, HER2+ and Triple Negative). All breast cancer subtypes are accompanied by peculiar and substantial changes in sphingolipid metabolism. Alterations in sphingolipid metabolite levels, such as ceramides, dihydroceramide, sphingosine, sphingosine-1-phosphate, and sphingomyelin, as well as in their biosynthetic and catabolic enzymatic pathways, have emerged as molecular mechanisms by which breast cancer cells grow, respond to or escape therapeutic interventions and could take on diagnostic and prognostic value. In this review, we summarize the current landscape around two main themes: 1. sphingolipid metabolites, enzymes and transport proteins that have been found dysregulated in human breast cancer cells and/or tissues; 2. sphingolipid-driven mechanisms that allow breast cancer cells to respond to or evade therapies. Having a complete picture of the impact of the sphingolipid metabolism in the development and progression of breast cancer may provide an effective means to improve and personalize treatments and reduce associated drug resistance.

Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating side effect of many common anti-cancer agents that can lead to dose reduction or treatment discontinuation, which decrease chemotherapy efficacy. Long-term CIPN can interfere with activities of daily living and diminish the quality of life. The mechanism of CIPN is not yet fully understood, and biomarkers are needed to identify patients at high risk and potential treatment targets. Metabolomics can capture the complex behavioral and pathophysiological processes involved in CIPN. This chapter is to review the CIPN metabolomics studies to find metabolic pathways potentially involved in CIPN. These potential CIPN metabolites are then investigated to determine whether there is evidence from studies of other neuropathy etiologies such as diabetic neuropathy and Leber hereditary optic neuropathy to support the importance of these pathways in peripheral neuropathy. Six potential biomarkers and their putative mechanisms in peripheral neuropathy were reviewed. Among these biomarkers, histidine and phenylalanine have clear roles in neurotransmission or neuroinflammation in peripheral neuropathy. Further research is needed to discover and validate CIPN metabolomics biomarkers in large clinical studies.

Fluorescently Labeled Ceramides and 1-Deoxyceramides: Synthesis, Characterization, and Cellular Distribution Studies

Ceramides (Cer) are bioactive sphingolipids that have been proposed as potential disease biomarkers since they are involved in several cellular stress responses, including apoptosis and senescence. 1-Deoxyceramides (1-deoxyCer), a particular subtype of noncanonical sphingolipids, have been linked to the pathogenesis of type II diabetes. To investigate the metabolism of these bioactive lipids, as well as to have a better understanding of the signaling processes where they participate, it is essential to expand the toolbox of fluorescent sphingolipid probes exhibiting complementary subcellular localization. Herein, we describe a series of new sphingolipid probes tagged with two different organic fluorophores, a far-red/NIR-emitting coumarin derivative (COUPY) and a green-emitting BODIPY. The assembly of the probes involved a combination of olefin cross metathesis and click chemistry reactions as key steps, and these fluorescent ceramide analogues exhibited excellent emission quantum yields, being the Stokes' shifts of the COUPY derivatives much higher than those of the BODIPY counterparts. Confocal microscopy studies in HeLa cells confirmed an excellent cellular permeability for these sphingolipid probes and revealed that most of the vesicles stained by COUPY probes were either lysosomes or endosomes, whereas BODIPY probes accumulated either in Golgi apparatus or in nonlysosomal intracellular vesicles. The fact that the two sets of fluorescent Cer probes have such different staining patterns indicates that their subcellular distribution is not entirely defined by the sphingolipid moiety but rather influenced by the fluorophore.

Blood biomarkers of peripheral neuropathy

Traditionally, neurophysiology is the primary diagnostic and prognostic biomarker in peripheral neuropathy clinical practice; however, it may lack responsiveness in the context of slowly progressive neuropathies and where there is significant axonal damage. The development of ultrasensitive platforms for measuring serum proteins at the lower limit of detection of traditional ELISA techniques has transformed the field of blood biomarkers of peripheral neuropathy. A variety of blood biomarkers have been identified from inflammatory cytokines and apokines in diabetic neuropathy through to neuron-specific proteins such as neurofilament light chain, Schwann cell-specific proteins such as TMPRSS5 and microRNAs in other acquired and hereditary neuropathies. In this article, we review blood biomarkers of disease activity for the common subtypes of peripheral neuropathy including inflammatory demyelinating neuropathies, vasculitic neuropathy, diabetic neuropathy, chemotherapy-induced neuropathy and Charcot-Marie-Tooth disease and related disorders including TTR amyloidosis.

Emerging Roles of Ceramides in Breast Cancer Biology and Therapy

One of the classic hallmarks of cancer is the imbalance between elevated cell proliferation and reduced cell death. Ceramide, a bioactive sphingolipid that can regulate this balance, has long been implicated in cancer. While the effects of ceramide on cell death and therapeutic efficacy are well established, emerging evidence indicates that ceramide turnover to downstream sphingolipids, such as sphingomyelin, hexosylceramides, sphingosine-1-phosphate, and ceramide-1-phosphate, is equally important in driving pro-tumorigenic phenotypes, such as proliferation, survival, migration, stemness, and therapy resistance. The complex and dynamic sphingolipid network has been extensively studied in several cancers, including breast cancer, to find key sphingolipidomic alterations that can be exploited to develop new therapeutic strategies to improve patient outcomes. Here, we review how the current literature shapes our understanding of how ceramide synthesis and turnover are altered in breast cancer and how these changes offer potential strategies to improve breast cancer therapy.

Temporal Alterations of Sphingolipids in Optic Nerves Following Indirect Traumatic Optic Neuropathy

Purpose

To identify optic nerve (ON) lipid alterations associated with sonication-induced traumatic optic neuropathy (TON).

Design

Experimental study.

Subjects

A mouse model of indirect TON was generated using sound energy concentrated focally at the entrance of the optic canal using a laboratory sonifier with a microtip probe.

Methods

Analyses of datasets generated from high-performance liquid chromatography-electrospray tandem mass spectrometry of ONs dissected from the head of the ON to the optic chiasm at 1 day, 7 days, and 14 days postsonication compared with that in nonsonicated controls.

Main Outcome Measures

Lipid abundance alterations in postsonicated ONs were evaluated using 1-way analysis of variance (false discovery rate-adjusted significant P value < 0.01), lipid-related gene sets, biochemical properties, and receiver operating characteristic to identify lipids associated with optic neuropathy.

Results

There were 28 lipid species with significantly different abundances across the control and postsonication groups. The 2 most significantly upregulated lipids included a sphingomyelin (SM) species, SM(d40:7), and a hexosylceramide (CerG1) species, CerG1(d18:1/24:2). Hexosylceramide (d18:1/24:2) was noted to have a stepwise increasing trend from day 1 to day 14 after sonication-induced optic neuropathy. Investigation of biophysical properties showed notable enrichment of lipids with high and above-average transition temperatures at day 14 after sonication. Lipid-related gene set analysis revealed enrichment in sphingolipid and glycosphingolipid metabolic processes. The best classifier to differentiate day 14 postsonication from controls, based on area under the receiver operating characteristic curve, was CerG1(d18:1/24:2) (area under the receiver operating characteristic curve: 1).

Conclusions

Temporal alterations in sphingolipid metabolism and biochemical properties were observed in the ON of mice after sonication-induced optic neuropathy, with notable elevations in sphingomyelin and hexosylceramide species. Hexosylceramide (d18:1/24:2) may be associated with damage after indirect trauma, indicating that lipid membrane abnormalities may be a mediator of pathology due to trauma.

Co-occurrence and metabolic biomarkers of sensory and motor subtypes of peripheral neuropathy from paclitaxel

PURPOSE

Chemotherapy-induced peripheral neuropathy (CIPN) is the major treatment-limiting toxicity of paclitaxel, which predominantly presents as sensory symptoms, with motor symptoms in some patients. Differentiating CIPN into subtypes has been recommended to direct CIPN research. The objective of this study was to investigate whether sensory and motor CIPN are distinct subtypes with different predictive biomarkers in patients with breast cancer receiving paclitaxel.

METHODS

Data were from a prospective cohort of 60 patients with breast cancer receiving up to 12 weekly infusions of 80 mg/m2 paclitaxel (NCT02338115). European Organisation for Research and Treatment of Cancer Quality of Life questionnaire CIPN20 was used to evaluate CIPN. Clusters of the time course of sensory (CIPNS), motor (CIPNM), and the difference between sensory and motor (CIPNS-CIPNM) were identified using k-means clustering on principal component scores. Predictive metabolomic biomarkers of maximum CIPNS and CIPNM were investigated using linear regressions adjusted for baseline CIPN, paclitaxel pharmacokinetics, and body mass index.

RESULTS

More sensory than motor CIPN was found (CIPNS change: mean = 10.8, ranged [-3.3, 52.1]; CIPNM change: mean = 3.5, range: [-7.5, 35.0]). Three groups were identified with No CIPN, Mixed CIPN, and Sensory-dominant CIPN (maximum CIPNS: mean = 12.7 vs. 40.9 vs. 74.3, p < 0.001; maximum CIPNM: mean = 5.4 vs. 25.5 vs. 36.1, p < 0.001; average CIPNS-CIPNM: mean = 2.8 vs. 5.8 vs. 24.9, p < 0.001). Biomarkers of motor CIPN were similar to previously identified biomarkers of sensory CIPN, including lower serum histidine (p = 0.029).

CONCLUSION

Our findings suggest that sensory and motor CIPN co-occur and may not have differentiating metabolic biomarkers. These findings need to be validated in larger cohorts of patients treated with paclitaxel and other neurotoxic agents to determine the optimal approach to predict, prevent, and treat CIPN and improve patients' outcomes.

Multi-Omics Prognostic Signatures Based on Lipid Metabolism for Colorectal Cancer

Background: The potential biological processes and laws of the biological components in malignant tumors can be understood more systematically and comprehensively through multi-omics analysis. This study elaborately explored the role of lipid metabolism in the prognosis of colorectal cancer (CRC) from the metabonomics and transcriptomics.

Methods: We performed K-means unsupervised clustering algorithm and t test to identify the differential lipid metabolites determined by liquid chromatography tandem mass spectrometry (LC-MS/MS) in the serum of 236 CRC patients of the First Hospital of Jilin University (JLUFH). Cox regression analysis was used to identify prognosis-associated lipid metabolites and to construct multi-lipid-metabolite prognostic signature. The composite nomogram composed of independent prognostic factors was utilized to individually predict the outcome of CRC patients. Glycerophospholipid metabolism was the most significant enrichment pathway for lipid metabolites in CRC, whose related hub genes (GMRHGs) were distinguished by gene set variation analysis (GSVA) and weighted gene co-expression network analysis (WGCNA). Cox regression and least absolute shrinkage and selection operator (LASSO) regression analysis were utilized to develop the prognostic signature.

Results: Six-lipid-metabolite and five-GMRHG prognostic signatures were developed, indicating favorable survival stratification effects on CRC patients. Using the independent prognostic factors as variables, we established a composite nomogram to individually evaluate the prognosis of CRC patients. The AUCs of one-, three-, and five-year ROC curves were 0.815, 0.815, and 0.805, respectively, showing auspicious prognostic accuracy. Furthermore, we explored the potential relationship between tumor microenvironment (TME) and immune infiltration. Moreover, the mutational frequency of TP53 in the high-risk group was significantly higher than that in the low-risk group (p < 0.001), while in the coordinate mutational status of TP53, the overall survival of CRC patients in the high-risk group was significantly lower than that in low-risk group with statistical differences.

Conclusion: We identified the significance of lipid metabolism for the prognosis of CRC from the aspects of metabonomics and transcriptomics, which can provide a novel perspective for promoting individualized treatment and revealing the potential molecular biological characteristics of CRC. The composite nomogram including a six-lipid-metabolite prognostic signature is a promising predictor of the prognosis of CRC patients.

1-Deoxysphinganine initiates adaptive responses to serine and glycine starvation in cancer cells via proteolysis of sphingosine kinase

Cancer cells may depend on exogenous serine, depletion of which results in slower growth and activation of adaptive metabolic changes. We previously demonstrated that serine and glycine (SG) deprivation causes loss of sphingosine kinase 1 (SK1) in cancer cells, thereby increasing the levels of its lipid substrate, sphingosine (Sph), which mediates several adaptive biological responses. However, the signaling molecules regulating SK1 and Sph levels in response to SG deprivation have yet to be defined. Here, we identify 1-deoxysphinganine (dSA), a noncanonical sphingoid base generated in the absence of serine from the alternative condensation of alanine and palmitoyl CoA by serine palmitoyl transferase, as a proximal mediator of SG deprivation in SK1 loss and Sph level elevation upon SG deprivation in cancer cells. SG starvation increased dSA levels in vitro and in vivo and in turn induced SK1 degradation through a serine palmitoyl transferase-dependent mechanism, thereby increasing Sph levels. Addition of exogenous dSA caused a moderate increase in intracellular reactive oxygen species, which in turn decreased pyruvate kinase PKM2 activity while increasing phosphoglycerate dehydrogenase levels, and thereby promoted serine synthesis. We further showed that increased dSA induces the adaptive cellular and metabolic functions in the response of cells to decreased availability of serine likely by increasing Sph levels. Thus, we conclude that dSA functions as an initial sensor of serine loss, SK1 functions as its direct target, and Sph functions as a downstream effector of cellular and metabolic adaptations. These studies define a previously unrecognized "physiological" nontoxic function for dSA.

Deoxysphingolipids Upregulate MMP-1, Downregulate TIMP-1, and Induce Cytotoxicity in Human Schwann Cells

Sphingolipids are a heterogeneous class of lipids and essential components of the plasma membrane and plasma lipoproteins. Studies have shown that plasma deoxysphingolipid (DSL), a newly identified sphingolipid class, is increased in diabetic patients and associated with diabetic neuropathy. However, it remains unknown if there is a causal relationship between plasma DSL increase and diabetic neuropathy. Since matrix metalloproteinases (MMPs) play an important role in diabetic neuropathy by degrading extracellular matrix in the peripheral nervous system, we investigated the effect of DSLs on the expression of MMPs and tissue inhibitor of metalloproteinase (TIMPs), and cytotoxicity in human Schwann cells. We quantified protein secretion, gene expression, and collagenase activity, and performed cytotoxicity assays. Results showed that DSLs upregulated MMP-1, downregulated TIMP-1, and induced cytotoxicity in Schwann cells. Furthermore, we quantified DSLs in VLDL, LDL, HDL2, and HDL3 isolated from type 2 diabetes mellitus (T2DM) patients with or without neuropathy. Interestingly, lipidomic analysis showed that only HDL2 isolated from T2DM patients with neuropathy contains significantly higher level of DSLs than that isolated from T2DM patients without neuropathy. Additionally, results showed that HDL2 isolated from T2DM patients with neuropathy was more potent than that isolated from T2DM patients without neuropathy in upregulating MMP-1, downregulating TIMP-1, and stimulating collagenase activity in Schwann cell. Taken together, this study demonstrated for the first time a potential causal relationship between DSLs and diabetic neuropathy and that DSL-containing HDL2 from T2DM patients with neuropathy was more potent than that from T2DM patients without neuropathy in stimulating collagenase activity.

Metabolic Control of Sensory Neuron Survival by the p75 Neurotrophin Receptor in Schwann Cells

We report that the neurotrophin receptor p75 contributes to sensory neuron survival through the regulation of cholesterol metabolism in Schwann cells. Selective deletion of p75 in mouse Schwann cells of either sex resulted in a 30% loss of dorsal root ganglia (DRG) neurons and diminished thermal sensitivity. P75 regulates Schwann cell cholesterol biosynthesis in response to BDNF, forming a co-receptor complex with ErbB2 and activating ErbB2-mediated stimulation of sterol regulatory element binding protein 2 (SREBP2), a master regulator of cholesterol synthesis. Schwann cells lacking p75 exhibited decreased activation of SREBP2 and a reduction in 7-dehydrocholesterol (7-DHC) reductase (DHCR7) expression, resulting in accumulation of the neurotoxic intermediate, 7-dehyrocholesterol in the sciatic nerve. Restoration of DHCR7 in p75 null Schwann cells in mice significantly attenuated DRG neuron loss. Together, these results reveal a mechanism by which the disruption of lipid metabolism in glial cells negatively influences sensory neuron survival, which has implications for a wide range of peripheral neuropathies.SIGNIFICANCE STATEMENT Although expressed in Schwann cells, the role of p75 in myelination has remained unresolved in part because of its dual expression in sensory neurons that Schwann cells myelinate. When p75 was deleted selectively among Schwann cells, myelination was minimally affected, while sensory neuron survival was reduced by 30%. The phenotype is mainly due to dysregulation of cholesterol biosynthesis in p75-deficient Schwann cells, leading to an accumulation of neurotoxic cholesterol precursor, 7-dehydrocholesterol (7-DHC). Mechanism-wise, we discovered that in response to BDNF, p75 recruits and activates ErbB2 independently of ErbB3, thereby stimulating the master regulator, sterol regulatory element binding protein 2 (SREBP2). These results together highlight a novel role of p75 in Schwann cells in regulating DRG neuron survival by orchestrating proper cholesterol metabolism.

Progressive alterations in amino acid and lipid metabolism correlate with peripheral neuropathy in PolgD257A mice

Mitochondria are central to metabolic homeostasis, and progressive mitochondrial defects have diverse metabolic consequences that could drive distinct pathophysiological states. Here, we comprehensively characterized metabolic alterations in PolgD257A mice. Plasma alanine increased markedly with time, with other organic acids accumulating to a lesser extent. These changes were reflective of increased Cori and Cahill cycling in PolgD257A mice and subsequent hypoglycemia, which did not occur during normal mouse aging. Tracing with [15N]ammonium further supported this shift in amino acid metabolism with mild impairment of the urea cycle. We also measured alterations in the lipidome, observing a reduction in canonical lipids and accumulation of 1-deoxysphingolipids, which are synthesized from alanine via promiscuous serine palmitoyltransferase activity and correlate with peripheral neuropathy. Consistent with this metabolic link, PolgD257A mice exhibited thermal hypoalgesia. These results highlight the longitudinal changes that occur in intermediary metabolism upon mitochondrial impairment and identify a contributing mechanism to mitochondria-associated neuropathy.

Fluid Biomarkers for Monitoring Structural Changes in Polyneuropathies: Their Use in Clinical Practice and Trials

Reliable and responsive tools for monitoring disease activity and treatment outcomes in patients with neuropathies are lacking. With the emergence of ultrasensitive blood bioassays, proteins released with nerve damage are potentially useful response biomarkers for many neurological disorders, including polyneuropathies. In this review, we provide an overview of the existing literature focusing on potential applications in polyneuropathy clinical care and trials. Whilst several promising candidates have been identified, no studies have investigated if any of these proteins can serve as response biomarkers of longitudinal disease activity, except for neurofilament light (NfL). For NfL, limited evidence exists supporting a role as a response biomarker in Guillain-Barré syndrome, vasculitic neuropathy, and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Most evidence exists for NfL as a response biomarker in hereditary transthyretin-related amyloidosis (hATTR). At the present time, the role of NfL is therefore limited to a supporting clinical tool or exploratory endpoint in trials. Future developments will need to focus on the discovery of additional biomarkers for anatomically specific and other forms of nerve damage using high-throughput technologies and highly sensitive analytical platforms in adequality powered studies of appropriate design. For NfL, a better understanding of cut-off values, the relation to clinical symptoms and long-term disability as well as dynamics in serum on and off treatment is needed to further expand and proceed towards implementation.

Vincristine in Combination Therapy of Cancer: Emerging Trends in Clinics

Treatment of blood malignancies and other cancer diseases has been mostly unfeasible, so far. Therefore, novel treatment regimens should be developed and the currently used ones should be further elaborated. A stable component in various cancer treatment regimens consists of vincristine, an antimitotic compound of natural origin. Despite its strong anticancer activity, mostly, it cannot be administered as monotherapy due to its unspecific action and severe side effects. However, vincristine is suitable for combination therapy. Multidrug treatment regimens including vincristine are standardly applied in the therapy of non-Hodgkin lymphoma and other malignancies, in which it is combined with drugs of different mechanisms of action, mainly with DNA-interacting compounds (for example cyclophosphamide), or drugs interfering with DNA synthesis (for example methotrexate). Besides, co-administration of vincristine with monoclonal antibodies has also emerged, the typical example of which is the anti-CD20 antibody rituximab. Although in some combination anticancer therapies, vincristine has been replaced with other drugs exhibiting lesser side effects, though, in most cases, it is still irreplaceable. This is strongly evidenced by the number of active clinical trials evaluating vincristine in combination cancer therapy. Therefore, in this article, we have reviewed the most common cancer treatment regimens employing vincristine and bring an overview of current trends in the clinical development of this compound.

1-Deoxysphingolipids cause autophagosome and lysosome accumulation and trigger NLRP3 inflammasome activation

1-Deoxysphingolipids (deoxySLs) are atypical sphingolipids of clinical relevance as they are elevated in plasma of patients suffering from hereditary sensory and autonomic neuropathy (HSAN1) or type 2 diabetes. Their neurotoxicity is described best but they inflict damage to various cell types by an uncertain pathomechanism. Using mouse embryonic fibroblasts and an alkyne analog of 1-deoxysphinganine (doxSA), the metabolic precursor of all deoxySLs, we here study the impact of deoxySLs on macroautophagy/autophagy, the regulated degradation of dysfunctional or expendable cellular components. We find that deoxySLs induce autophagosome and lysosome accumulation indicative of an increase in autophagic flux. The autophagosomal machinery targets damaged mitochondria that have accumulated N-acylated doxSA metabolites, presumably deoxyceramide and deoxydihydroceramide, and show aberrant swelling and tubule formation. Autophagosomes and lysosomes also interact with cellular lipid aggregates and crystals that occur upon cellular uptake and N-acylation of monomeric doxSA. As crystals entering the lysophagosomal apparatus in phagocytes are known to trigger the NLRP3 inflammasome, we also treated macrophages with doxSA. We demonstrate the activation of the NLRP3 inflammasome by doxSLs, prompting the release of IL1B from primary macrophages. Taken together, our data establish an impact of doxSLs on autophagy and link doxSL pathophysiology to inflammation and the innate immune system.Abbreviations: alkyne-doxSA: (2S,3R)-2-aminooctadec-17yn-3-ol; alkyne-SA: (2S,3R)-2- aminooctadec-17yn-1,3-diol; aSA: alkyne-sphinganine; ASTM-BODIPY: azido-sulfo-tetramethyl-BODIPY; CerS: ceramide synthase; CMR: clonal macrophage reporter; deoxySLs: 1-deoxysphingolipids; dox(DH)Cer: 1-deoxydihydroceramide; doxCer: 1-deoxyceramide; doxSA: 1-deoxysphinganine; FB1: fumonisin B1; HSAN1: hereditary sensory and autonomic neuropathy type 1; LC3: MAP1LC3A and MAP1LC3B; LPS: lipopolysaccharide; MEF: mouse embryonal fibroblasts; MS: mass spectrometry; N3635P: azido-STAR635P; N3Cy3: azido-cyanine 3; N3picCy3: azido-picolylcyanine 3; NLRP3: NOD-like receptor pyrin domain containing protein 3; P4HB: prolyl 4-hydroxylase subunit beta; PINK1: PTEN induced putative kinase 1; PYCARD/ASC: PYD and CARD domain containing; SPTLC1: serine palmitoyltransferase long chain base subunit 1; SQSTM1: sequestosome 1; TLC: thin layer chromatography.

Altered plasma serine and 1-deoxydihydroceramide profiles are associated with diabetic neuropathy in type 2 diabetes and obesity

Recent studies suggest that the accumulation of atypical, 1-deoxysphingolipids that lack the C1 hydroxyl group may be associated with diabetic neuropathy (DN). We hypothesized that specific plasma 1-deoxysphingolipids associate with DN severity, and that alterations in plasma serine and alanine associate with 1-deoxysphingolipid elevation in patients with type 2 diabetes (T2D). We examined individual 1-deoxysphingolipid species using LC/MS/MS in plasma samples from 75 individuals including lean controls (LC, n = 19), those with obesity (n = 19), obesity with T2D without DN (ob/T2D, n = 18), and obesity with T2D with DN (Ob/T2D/DN, n = 19). We observed a step wise increase in 1-deoxydihydroceramides across these four groups (spearman correlation coefficient r = 0.41, p = 0.0002). Mean total concentrations of 1-deoxydihydroceramides, and most individual 1-deoxydihydroceramide species, were higher in ob/T2D/DN versus LC group (8.939 vs. 5.195 pmol/100 μL for total 1-deoxydihydroceramides p = 0.005). No significant differences in 1-deoxydihydroceramides were observed between the ob/T2D and ob/T2D/DN groups. l-alanine was higher and l-serine lower in ob/T2D/DN versus LC groups (326.2 vs. 248.0 μM, p = 0.0086 and 70.2 vs. 89.8 μM, p = 0.0110), consistent with a potential contribution of these changes to the observed 1-deoxysphingolipids profiles. 1-deoxydihydroceramides correlated inversely with leg intraepidermal nerve fiber density (CC -0.40, p = 0.003). These findings indicate that 1-deoxydihydroceramides may be important biomarkers and/or mediators of DN.

The Complex Clinical and Genetic Landscape of Hereditary Peripheral Neuropathy

Hereditary peripheral neuropathy (HPN) is a complex group of neurological disorders caused by mutations in genes expressed by neurons and Schwann cells. The inheritance of a single mutation or multiple mutations in several genes leads to disease phenotype. Patients exhibit symptoms during development, at an early age or later in adulthood. Most of the mechanistic understanding about these neuropathies comes from animal models and histopathological analyses of postmortem human tissues. Diagnosis is often very complex due to the heterogeneity and overlap in symptoms and the frequent overlap between various genes and different mutations they possess. Some symptoms in HPN are common through different subtypes such as axonal degeneration, demyelination, and loss of motor and sensory neurons, leading to similar physiologic abnormalities. Recent advances in gene-targeted therapies, genetic engineering, and next-generation sequencing have augmented our understanding of the underlying pathogenetic mechanisms of HPN.

Sphingolipids as Regulators of Neuro-Inflammation and NADPH Oxidase 2

Neuro-inflammation accompanies numerous neurological disorders and conditions where it can be associated with a progressive neurodegenerative pathology. In a similar manner, alterations in sphingolipid metabolism often accompany or are causative features in degenerative neurological conditions. These include dementias, motor disorders, autoimmune conditions, inherited metabolic disorders, viral infection, traumatic brain and spinal cord injury, psychiatric conditions, and more. Sphingolipids are major regulators of cellular fate and function in addition to being important structural components of membranes. Their metabolism and signaling pathways can also be regulated by inflammatory mediators. Therefore, as certain sphingolipids exert distinct and opposing cellular roles, alterations in their metabolism can have major consequences. Recently, regulation of bioactive sphingolipids by neuro-inflammatory mediators has been shown to activate a neuronal NADPH oxidase 2 (NOX2) that can provoke damaging oxidation. Therefore, the sphingolipid-regulated neuronal NOX2 serves as a mechanistic link between neuro-inflammation and neurodegeneration. Moreover, therapeutics directed at sphingolipid metabolism or the sphingolipid-regulated NOX2 have the potential to alleviate neurodegeneration arising out of neuro-inflammation.

Clinical and biochemical markers in CIPN: A reappraisal

The increased survival of cancer patients has raised growing public health concern on associated long-term consequences of antineoplastic treatment. Chemotherapy-induced peripheral neuropathy (CIPN) is a primarily sensory polyneuropathy, which may be accompanied by pain, autonomic disturbances, and motor deficit. About 70% of treated cancer patients might develop CIPN during or after the completion of chemotherapy, and in most of them such complication persists after six months from the treatment. The definition of the potential risk of development and resolution of CIPN according to a clinical and biochemical profile would be certainly fundamental to tailor chemotherapy regimen and dosage on individual susceptibility. In recent years, patient-reported and clinician-related tools along with quality of life instruments have been featured as primary outcomes in clinical setting and randomized trials. New studies on metabolomics markers are further pursuing accurate and easily accessible indicators of peripheral nerve damage. The aim of this review is to outline the strengths and pitfalls of current knowledge on CIPN, and to provide a framework for future potential developments of standardized protocols involving clinical and biochemical markers for CIPN assessment and monitoring.

Blood molecular biomarkers for chemotherapy-induced peripheral neuropathy: From preclinical models to clinical practice

Chemotherapy-induced peripheral neuropathy (CIPN) has long been recognized as a clinically significant issue in patients treated with antineoplastic drugs. This common long-term toxic side-effect which negatively impacts the outcome of the disease can lead to disability and have detrimental effects on patients' quality of life. Since axonal injury is a prominent feature of CIPN, responsible for several sensory symptoms, including pain, sensory loss and hypersensitivity to mechanical and/or cold stimuli in the hands and feet, neurophysiological assessments remain the gold standard for clinical diagnosis of CIPN. Given the large impact of CIPN on cancer patients, there is increasing emphasis on biomarkers of adverse outcomes in safety assessment and translational research, to prevent permanent neuroaxonal damage. Since the results on reliable blood molecular markers for axonal degeneration are still controversial, here we provide a brief overview of blood molecular biomarkers used for assessing and/or predicting CIPN in preclinical and clinical settings.

Neuroinflammatory Process Involved in Different Preclinical Models of Chemotherapy-Induced Peripheral Neuropathy

Peripheral neuropathies are characterized by nerves damage and axonal loss, and they could be classified in hereditary or acquired forms. Acquired peripheral neuropathies are associated with several causes, including toxic agent exposure, among which the antineoplastic compounds are responsible for the so called Chemotherapy-Induced Peripheral Neuropathy (CIPN). Several clinical features are related to the use of anticancer drugs which exert their action by affecting different mechanisms and structures of the peripheral nervous system: the axons (axonopathy) or the dorsal root ganglia (DRG) neurons cell body (neuronopathy/ganglionopathy). In addition, antineoplastic treatments may affect the blood brain barrier integrity, leading to cognitive impairment that may be severe and long-lasting. CIPN may affect patient quality of life leading to modification or discontinuation of the anticancer therapy. Although the mechanisms of the damage are not completely understood, several hypotheses have been proposed, among which neuroinflammation is now emerging to be relevant in CIPN pathophysiology. In this review, we consider different aspects of neuro-immune interactions in several CIPN preclinical studies which suggest a critical connection between chemotherapeutic agents and neurotoxicity. The features of the neuroinflammatory processes may be different depending on the type of drug (platinum derivatives, taxanes, vinca alkaloids and proteasome inhibitors). In particular, recent studies have demonstrated an involvement of the immune response (both innate and adaptive) and the stimulation and secretion of mediators (cytokines and chemokines) that may be responsible for the painful symptoms, whereas glial cells such as satellite and Schwann cells might contribute to the maintenance of the neuroinflammatory process in DRG and axons respectively. Moreover, neuroinflammatory components have also been shown in the spinal cord with microglia and astrocytes playing an important role in CIPN development. Taking together, better understanding of these aspects would permit the development of possible strategies in order to improve the management of CIPN.

1-Deoxysphingolipids, Early Predictors of Type 2 Diabetes, Compromise the Functionality of Skeletal Myoblasts

Metabolic dysfunction, dysregulated differentiation, and atrophy of skeletal muscle occur as part of a cluster of abnormalities associated with the development of Type 2 diabetes mellitus (T2DM). Recent interest has turned to the attention of the role of 1-deoxysphingolipids (1-DSL), atypical class of sphingolipids which are found significantly elevated in patients diagnosed with T2DM but also in the asymptomatic population who later develop T2DM. In vitro studies demonstrated that 1-DSL have cytotoxic properties and compromise the secretion of insulin from pancreatic beta cells. However, the role of 1-DSL on the functionality of skeletal muscle cells in the pathophysiology of T2DM still remains unclear. This study aimed to investigate whether 1-DSL are cytotoxic and disrupt the cellular processes of skeletal muscle precursors (myoblasts) and differentiated cells (myotubes) by performing a battery of in vitro assays including cell viability adenosine triphosphate assay, migration assay, myoblast fusion assay, glucose uptake assay, and immunocytochemistry. Our results demonstrated that 1-DSL significantly reduced the viability of myoblasts in a concentration and time-dependent manner, and induced apoptosis as well as cellular necrosis. Importantly, myoblasts were more sensitive to the cytotoxic effects induced by 1-DSL rather than by saturated fatty acids, such as palmitate, which are critical mediators of skeletal muscle dysfunction in T2DM. Additionally, 1-DSL significantly reduced the migration ability of myoblasts and the differentiation process of myoblasts into myotubes. 1-DSL also triggered autophagy in myoblasts and significantly reduced insulin-stimulated glucose uptake in myotubes. These findings demonstrate that 1-DSL directly compromise the functionality of skeletal muscle cells and suggest that increased levels of 1-DSL observed during the development of T2DM are likely to contribute to the pathophysiology of muscle dysfunction detected in this disease.

The noncanonical chronicles: Emerging roles of sphingolipid structural variants

Sphingolipids (SPs) are structurally diverse and represent one of the most quantitatively abundant classes of lipids in mammalian cells. In addition to their structural roles, many SP species are known to be bioactive mediators of essential cellular processes. Historically, studies have focused on SP species that contain the canonical 18‑carbon, mono-unsaturated sphingoid backbone. However, increasingly sensitive analytical technologies, driven by advances in mass spectrometry, have facilitated the identification of previously under-appreciated, molecularly distinct SP species. Many of these less abundant species contain noncanonical backbones. Interestingly, a growing number of studies have identified clinical associations between these noncanonical SPs and disease, suggesting that there is functional significance to the alteration of SP backbone structure. For example, associations have been found between SP chain length and cardiovascular disease, pain, diabetes, and dementia. This review will provide an overview of the processes that are known to regulate noncanonical SP accumulation, describe the clinical correlations reported for these molecules, and review the experimental evidence for the potential functional implications of their dysregulation. It is likely that further scrutiny of noncanonical SPs may provide new insight into pathophysiological processes, serve as useful biomarkers for disease, and lead to the design of novel therapeutic strategies.

Mini review: Lipids in Peripheral Nerve Disorders

Neurons are polarized cells whose fundamental functions are to receive, conduct and transmit signals. In bilateral animals, the nervous system is divided into the central (CNS) and peripheral (PNS) nervous system. The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Sensory axons can be up to 3 feet in length. Because of its long-reaching and complex structure, the peripheral nervous system (PNS) is exposed and vulnerable to many genetic, metabolic and environmental predispositions. Lipids and lipid intermediates are essential components of nerves. About 50 % of the brain dry weight consist of lipids, which makes it the second highest lipid rich tissue after adipose tissue. However, the role of lipids in neurological disorders in particular of the peripheral nerves is not well understood. This review aims to provide an overview about the role of lipids in the disorders of the PNS.

Targeting the Sphingosine-1-Phosphate Axis for Developing Non-narcotic Pain Therapeutics

Chronic pain is a life-altering condition affecting millions of people. Current treatments are inadequate and prolonged therapies come with severe side effects, especially dependence and addiction to opiates. Identification of non-narcotic analgesics is of paramount importance. Preclinical and clinical studies suggest that sphingolipid metabolism alterations contribute to neuropathic pain development. Functional sphingosine-1-phosphate (S1P) receptor 1 (S1PR1) antagonists, such as FTY720/fingolimod, used clinically for non-pain conditions, are emerging as non-narcotic analgesics, supporting the repurposing of fingolimod for chronic pain treatment and energizing drug discovery focused on S1P signaling. Here, we summarize the role of S1P in pain to highlight the potential of targeting the S1P axis towards development of non-narcotic therapeutics, which, in turn, will hopefully help lessen misuse of opioid pain medications and address the ongoing opioid epidemic.

Role of 1-Deoxysphingolipids in docetaxel neurotoxicity

A major dose-limiting side effect of docetaxel chemotherapy is peripheral neuropathy. Patients' symptoms include pain, numbness, tingling and burning sensations, and motor weakness in the extremities. The molecular mechanism is currently not understood, and there are no treatments available. Previously, we have shown an association between neuropathy symptoms of patients treated with paclitaxel and the plasma levels of neurotoxic sphingolipids, the 1-deoxysphingolipids (1-deoxySL) (Kramer et al, FASEB J, 2015). 1-DeoxySL are produced when the first enzyme of the sphingolipid biosynthetic pathway, serine palmitoyltransferase (SPT), uses L-alanine as a substrate instead of its canonical amino acid substrate, L-serine. In the current investigation, we tested whether 1-deoxySL accumulate in the nervous system following systemic docetaxel treatment in mice. In dorsal root ganglia (DRG), we observed that docetaxel (45 mg/kg cumulative dose) significantly elevated the levels of 1-deoxySL and L-serine-derived ceramides, but not sphingosine-1-phosphate (S1P). S1P is a bioactive sphingolipid and a ligand for specific G-protein-coupled receptors. In the sciatic nerve, docetaxel decreased 1-deoxySL and ceramides. Moreover, we show that in primary DRG cultures, 1-deoxysphingosine produced neurite swellings that could be reversed with S1P. Our results demonstrate that docetaxel chemotherapy up-regulates sphingolipid metabolism in sensory neurons, leading to the accumulation of neurotoxic 1-deoxySL. We suggest that the neurotoxic effects of 1-deoxySL on axons can be reversed with S1P.

Demyelination in hereditary sensory neuropathy type-1C

OBJECTIVE

Sphingolipids are enriched in the nerves. Serine-palmitoyltransferase (SPT) catalyzes the key step of sphingolipids biosynthesis. Mutations in SPT subunits (SPTLC) lead to the excessive production of neurotoxic deoxysphingolipids (DoxSLs) in patients with Hereditary Sensory Neuropathy Type-1C (HSN1C). HSN1C is an autosomal dominant peripheral neuropathy characterized by sensory loss and distal muscle weakness. In this study, by leveraging a HSN1C family with a previously reported N177D mutation in SPTLC2, we aim to further define the spectrum of DoxSL species and the peripheral neve pathology of the disease.

METHODS

Next-generation sequencing along with Sanger confirmation was performed for family members and healthy controls. LC-MS was used for lipidomic analysis in participants' plasma. Quantitative magnetic resonance imaging (qMRI) was performed to study sciatic nerve pathologies.

RESULTS

A heterozygous N177D mutation in SPTLC2 was co-segregated in individuals with sensory-motor deficits in the limbs. Nerve conduction studies (NCS) revealed nonuniform slowing of conduction velocities. In line with the NCS, qMRI detected a pattern of nerve changes similar to those in acquired demyelinating polyneuropathies. Additionally, we detected a significant increase in multiple species of deoxysphingoid bases and deoxyceramides in patients' plasma.

INTERPRETATION

Mutations in the SPTLC2 cause a demyelinating phenotype resembling those in acquired demyelinating polyneuropathy. The species of increased DoxSLs in HSN1C may be more diverse than originally thought.

Combination treatment with artemisinin and oxaliplatin inhibits tumorigenesis in esophageal cancer EC109 cell through Wnt/β-catenin signaling pathway

Background

Esophageal cancer (EC) is a prevalent malignant cancer worldwide. Interestingly, the antimalaria compound artemisinin (ART) is also reported to have anticancer potential, although its underlying mechanism in EC is unclear. In this study, we explored the anticancer role of ART in EC109 and further explored the combination of ART and oxaliplatin (OXA) for their synergetic anticancer functions.

Methods

Human EC cell line EC109 was used. After ART or oxaliplatin (OXA) treatment, cell proliferation, migration, and invasion were measured by MTT, transwell, and scratch wound assays, respectively. Flow cytometry was performed to examine the cell cycle and apoptosis. The mRNA and protein levels were determined using qRT‐PCR and western blotting.

Results

The migration and invasion abilities of EC109 were suppressed by ART. This was due to the inhibitory effect of ART on the Wnt/β‐catenin signaling pathway. The levels of β‐catenin, c‐myc, and survivin were also downregulated by ART. ART inhibits the proliferation of EC109 cells by arresting the cells in the G1‐phase of cell cycle. By using LiCl, an activator of the Wnt/β‐catenin pathway, we further verified that the inhibition of the Wnt/β‐catenin pathway was indeed due to ART. Remarkably, ART enhanced the anticancer effects of OXA in EC109 cells. OXA combined with ART was found to be more efficient in decreasing tumor growth compared to the individual drugs.

Conclusions

ART could suppress tumor progression by inhibiting Wnt/β‐catenin signaling pathway, and it may also enhance the antitumor effect of OXA in EC. Thus, ART could be a novel anticancer drug for EC treatment.

Key points

Significant findings of the study

ART could be a novel anticancer drug for esophageal cancer (EC) treatment.

What this study adds

Combination treatment with artemisinin and oxaliplatin inhibits tumorigenesis in esophageal cancer EC109 cells through the Wnt/β‐catenin signaling pathway.

A Metabolomics Approach for Early Prediction of Vincristine-Induced Peripheral Neuropathy

Vincristine is a core chemotherapeutic drug administered to pediatric acute lymphoblastic leukemia patients. Despite its efficacy in treating leukemia, it can lead to severe peripheral neuropathy in a subgroup of the patients. Peripheral neuropathy is a debilitating and painful side-effect that can severely impact an individual’s quality of life. Currently, there are no established predictors of peripheral neuropathy incidence during the early stage of chemotherapeutic treatment. As a result, patients who are not susceptible to peripheral neuropathy may receive sub-therapeutic treatment due to an empirical upper cap on the dose, while others may experience severe neuropathy at the same dose. Contrary to previous genomics based approaches, we employed a metabolomics approach to identify small sets of metabolites that can be used to predict a patient’s susceptibility to peripheral neuropathy at different time points during the treatment. Using those identified metabolites, we developed a novel strategy to predict peripheral neuropathy and subsequently adjust the vincristine dose accordingly. In accordance with this novel strategy, we created a free user-friendly tool, VIPNp, for physicians to easily implement our prediction strategy. Our results showed that focusing on metabolites, which encompasses both genotypic and phenotypic variations, can enable early prediction of peripheral neuropathy in pediatric leukemia patients.

Diabetic neuropathy: what does the future hold?

Frustratingly, disease-modifying treatments for diabetic neuropathy remain elusive. Glycaemic control has a robust effect on preventing neuropathy in individuals with type 1 but not in those with type 2 diabetes, which constitute the vast majority of patients. Encouragingly, recent evidence points to new metabolic risk factors and mechanisms, and thus also at novel disease-modifying strategies, which are desperately needed. Obesity has emerged as the second most important metabolic risk factor for neuropathy (diabetes being the first) from consensus findings of seven observational studies in populations across the world. Moreover, dyslipidaemia and altered sphingolipid metabolism are emergent novel mechanisms of nerve injury that may lead to new targeted therapies. Clinical history and examination remain critical components of an accurate diagnosis of neuropathy. However, skin biopsies and corneal confocal microscopy are promising newer tests that have been used as outcome measures in research studies but have not yet demonstrated clear clinical utility. Given the emergence of obesity as a neuropathy risk factor, exercise and weight loss are potential interventions to treat and/or prevent neuropathy, although evidence supporting exercise currently outweighs data supporting weight loss. Furthermore, a consensus has emerged advocating tricyclic antidepressants, serotonin-noradrenaline (norepinephrine) reuptake inhibitors and gabapentinoids for treating neuropathic pain. Out-of-pocket costs should be considered when prescribing these medications since their efficacy and tolerability are similar. Finally, the downsides of opioid treatment for chronic, non-cancer pain are becoming increasingly evident. Despite these data, current clinical practice frequently initiates and continues opioid prescriptions for patients with neuropathic pain before prescribing guideline-recommended treatments.

The combination of artesunate and carboplatin exerts a synergistic anti-tumour effect on non-small cell lung cancer

Carboplatin (CBP) is a widely used targeted anticancer therapeutic drug; however, multi-drug resistance induced by the accumulation of CBP eventually causes diseases progression. The anti-malarial drug artesunate (ART) also exerts anticancer effects in various cancers; however, the combined effect of ART and CBP on non-small cell lung cancer (NSCLC) remains unclear. In the present study, the NSCLC cell line A549 was pretreated with various concentrations of CBP, ART and gemcitabine (GEM). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were conducted to detect cell viability. Cell apoptosis was evaluated by both flow cytometry and TUNEL apoptotic assay. The expression profiles of cell cycle-related proteins and apoptotic proteins were determined by western blot. Cell clone numbers were visualized using crystal violet staining. Here, we found that both CBP and ART suppressed cell viability, and promoted cell apoptosis, and the combined application of ART and CBP at a lower concentration exhibited synergistic effects. Specifically, the combination of ART and CBP at a lower concentration suppressed cell clone numbers, promoted cell cycle arrest at the G₂ /M phase, and induced the expression of the cell cycle and apoptosis-related proteins BAX, p21, p53, and Caspase-3, while decreasing Bcl-2 and Cyclin B1 expression. Based on these results, we concluded that combined application of ART and CBP exerts synergistic anti-tumour effects on NSCLC by enhancing cell apoptosis in a mitochondria-dependent manner.

Mechanisms of Ceramide-Dependent Cancer Cell Death

Mechanistic details for the roles of sphingolipids and their downstream targets in the regulation of tumor growth, response to chemo/radiotherapy, and metastasis have been investigated in recent studies using innovative molecular, genetic and pharmacologic tools in various cancer models. Induction of ceramide generation in response to cellular stress by chemotherapy, radiation, or exogenous ceramide analog drugs mediates cell death via apoptosis, necroptosis, or mitophagy. In this chapter, distinct functions and mechanisms of action of endogenous ceramides with different fatty acyl chain lengths in the regulation of cancer cell death versus survival will be discussed. In addition, importance of ceramide subcellular localization, trafficking, and lipid-protein binding between ceramide and various target proteins in cancer cells will be reviewed. Moreover, clinical trials from structure-function-based studies to restore antiproliferative ceramide signaling by activating ceramide synthesis will also be analyzed. Future studies are important to understand the mechanistic involvement of ceramide-mediated cell death in anticancer therapy, including immunotherapy.

Cytotoxicity of 1-deoxysphingolipid unraveled by genome-wide genetic screens and lipidomics in Saccharomyces cerevisiae

Hereditary sensory and autonomic neuropathy (HSAN) types IA and IC (IA/C) are caused by elevated levels of an atypical class of lipid named 1-deoxysphingolipid (DoxSL). How elevated levels of DoxSL perturb the physiology of the cell and how the perturbations lead to HSAN IA/C are largely unknown. In this study, we show that C₂₆-1-deoxydihydroceramide (C₂₆-DoxDHCer) is highly toxic to the cell, while C₁₆- and C₁₈-DoxDHCer are less toxic. Genome-wide genetic screens and lipidomics revealed the dynamics of DoxSL accumulation and DoxSL species responsible for the toxicity over the course of DoxSL accumulation. Moreover, we show that disruption of F-actin organization, alteration of mitochondrial shape, and accumulation of hydrophobic bodies by DoxSL are not sufficient to cause complete cellular failure. We found that cell death coincides with collapsed ER membrane, although we cannot rule out other possible causes of cell death. Thus, we have unraveled key principles of DoxSL cytotoxicity that may help to explain the clinical features of HSAN IA/C.

Deoxysphingolipids and ether-linked diacylglycerols accumulate in the tissues of aged mice

Background

Senescence is a well-known risk factor for several diseases, such as neurodegenerative disorders. Therefore, studies exploring the mechanisms underlying aging are expected to guide the discovery of novel drug targets and biomarkers for these diseases. However, a comprehensive overview of the metabolic and lipidomic changes in healthy aging mammals is lacking. To understand the changes of metabolism with aging, especially lipid metabolism, we analyzed the metabolomes and lipidomes of the cerebral cortex, liver, femoral muscle, and epididymal fat in young and aged mice.

Results

Two-dimensional cluster analysis revealed clear separation between the metabolite profiles of the aged and young groups. Deoxydihydroceramide (doxDHCer), deoxyceramide (doxCer), and ether-linked diacylglycerol (DAG) levels were elevated during aging.

Conclusion

This is the first report of age-related variations in deoxysphingolipid and ether-linked DAG levels in mice. DoxCer, doxDHCer, and ether-linked DAGs may be associated with senescence in mammalian tissues.

Electronic supplementary material

The online version of this article (10.1186/s13578-019-0324-9) contains supplementary material, which is available to authorized users.

Does nab-paclitaxel have a higher incidence of peripheral neuropathy than solvent-based paclitaxel? Evidence from a systematic review and meta-analysis

Paclitaxel-induced peripheral neuropathy is a common reason for dose reduction or early cessation of therapy. Nab-paclitaxel was developed to provide additional clinical benefits and overcome the safety drawbacks of solvent-based paclitaxel. However, the incidence of peripheral neuropathy induced by nab-paclitaxel was reported higher than solvent-based paclitaxel but evidence remains inconsistent. Therefore, we conducted a meta-analysis to compare the incidence and severity of peripheral neuropathy between nab-paclitaxel and solvent-based paclitaxel mono-chemotherapy. In total, 24 articles were included in this meta-analysis. Results revealed the incidence of peripheral neuropathy induced by nab-paclitaxel was higher than solvent-based paclitaxel. The dosage and assessment method could influence the comparison of the incidence and severity of peripheral neuropathy between nab-paclitaxel and solvent-based paclitaxel. Current evidence suggests the incidence of peripheral neuropathy induced by nab-paclitaxel was higher than solvent-based paclitaxel among cancer patients received mono-chemotherapy. When received nab-paclitaxel, more attention should be paid to peripheral neuropathy.

Quantifying 1-deoxydihydroceramides and 1-deoxyceramides in mouse nervous system tissue

Accumulation of deoxysphingolipids (deoxySLs) has been implicated in many neural diseases, although mechanisms remain unclear. A major obstacle limiting understanding of deoxySLs has been the lack of a method easily defining measurement of deoxydihydroceramide (deoxydhCer) and deoxyceramide (deoxyCer) in neural tissues. Furthermore, it is poorly understood if deoxySLs accumulate in the nervous system with aging. To facilitate investigation of deoxydhCer and deoxyCer in nervous system tissue, we developed a method to evaluate levels of these lipids in mouse brain, spinal cord, and sciatic nerve. Many deoxydhCers and brain C24-deoxyCer were present at 1, 3, and 6 months of age. Furthermore, while ceramide levels decreased with age, deoxydhCers increased in sciatic nerve and spinal cord, suggesting they may accumulate in peripheral nerves. C22-deoxydhCer was the highest deoxydhCer species in all tissues, suggesting it may be important physiologically. The development of this method will facilitate straightforward profiling of deoxydhCers and deoxyCers and the study of their metabolism and function. These results also reveal that deoxydhCers accumulate in peripheral nerves with normal aging.

Natural Ceramides and Lysophospholipids Cosegregate in Fluid Phosphatidylcholine Bilayers

The mode of interactions between palmitoyl lysophosphatidylcholine (palmitoyl lyso-PC) or other lysophospholipids (lyso-PLs) and palmitoyl ceramide (PCer) or other ceramide analogs in dioleoylphosphatidylcholine (DOPC) bilayers has been examined. PCer is known to segregate laterally into a ceramide-rich phase at concentrations that depend on the nature of the ceramides and the co-phospholipids. In DOPC bilayers, PCer forms a ceramide-rich phase at concentrations above 10 mol%. In the presence of 20 mol% palmitoyl lyso-PC in the DOPC bilayer, the lateral segregation of PCer was markedly facilitated (segregation at lower PCer concentrations). The thermostability of the PCer-rich phase in the presence of palmitoyl lyso-PC was also increased compared to that in the absence of palmitoyl lyso-PC. Other saturated lyso-PLs (e.g., palmitoyl lyso-phosphatidylethanolamine and lyso-sphingomyelin) also facilitated the lateral segregation of PCer in a similar manner as palmitoyl lyso-PC. When examined in the DOPC bilayer, it appeared that the association between palmitoyl lyso-PC and PCer was equimolar in nature. It is proposed that the interaction of PCer with lyso-PLs was driven by the need of ceramide to obtain a large-headgroup co-lipid, and saturated lyso-PLs were preferred co-lipids over DOPC because of the nature of their acyl chain. Structural analogs of PCer (1- or 3-deoxy-PCer) were also associated with palmitoyl lyso-PC, similarly to PCer, suggesting that the ceramide/lyso-PL interaction was not sensitive to structural alterations in the ceramide molecule. Binary complexes containing palmitoyl lyso-PC and ceramide were prepared, and these had a bilayer structure as ascertained by transmission electron microscopy. It is concluded that ceramides and lyso-PLs associated with each other both in binary bilayers and in ternary systems based on the DOPC bilayers. This association may have biological relevance under conditions in which both sphingomyelinases and phospholipase A₂ enzymes are activated, such as during inflammatory processes.

Randomized trial of l-serine in patients with hereditary sensory and autonomic neuropathy type 1

Objective

To evaluate the safety and efficacy of l-serine in humans with hereditary sensory autonomic neuropathy type I (HSAN1).

Methods

In this randomized, placebo-controlled, parallel-group trial with open-label extension, patients aged 18–70 years with symptomatic HSAN1 were randomized to l-serine (400 mg/kg/day) or placebo for 1 year. All participants received l-serine during the second year. The primary outcome measure was the Charcot-Marie-Tooth Neuropathy Score version 2 (CMTNS). Secondary outcomes included plasma sphingolipid levels, epidermal nerve fiber density, electrophysiologic measurements, patient-reported measures, and adverse events.

Results

Between August 2013 and April 2014, we enrolled and randomized 18 participants, 16 of whom completed the study. After 1 year, the l-serine group experienced improvement in CMTNS relative to the placebo group (−1.5 units, 95% CI −2.8 to −0.1, p = 0.03), with evidence of continued improvement in the second year of treatment (−0.77, 95% CI −1.67 to 0.13, p = 0.09). Concomitantly, deoxysphinganine levels dropped in l-serine-treated but not placebo-treated participants (59% decrease vs 11% increase; p < 0.001). There were no serious adverse effects related to l-serine.

Conclusion

High-dose oral l-serine supplementation appears safe in patients with HSAN1 and is potentially effective at slowing disease progression.

Clinicaltrials.gov identifier

NCT01733407.

Classification of evidence

This study provides Class I evidence that high-dose oral l-serine supplementation significantly slows disease progression in patients with HSAN1.

1-Deoxysphingolipids

Sphingolipids (SLs) are fundamental components of eukaryotic cells. 1-Deoxysphingolipids differ structurally from canonical SLs as they lack the essential C1-OH group. Consequently, 1-deoxysphingolipids cannot be converted to complex sphingolipids and are not degraded over the canonical catabolic pathways. Pathologically elevated 1-deoxySLs are involved in several disease conditions. Within this review, we will provide an up-to-date overview on the metabolic, physiological and pathophysiological aspects of this enigmatic class of "headless" sphingolipids.

On the Importance of the C(1)-OH and C(3)-OH Functional Groups of the Long-Chain Base of Ceramide for Interlipid Interaction and Lateral Segregation into Ceramide-Rich Domains

Ceramides are important intermediates in sphingolipid biosynthesis (and degradation) and are normally present in only small amounts in unstressed cells. However, following the receptor-mediated activation of neutral sphingomyelinase, sphingomyelin can acutely give rise to substantial amounts of ceramides, which dramatically alter membrane properties. In this study, we have examined the role of the 1-OH and 3-OH functional groups of ceramide for its membrane properties. We have specifically examined how the oxidation of the primary alcohol to COOH or COOMe in palmitoyl ceramide (PCer) or the removal of either the primary alcohol or C(3)-OH (deoxy analogs) affected ceramides' interlipid interactions in fluid phosphatidylcholine bilayers. Measuring the time-resolved fluorescence emission of trans-parinaric acid, or its steady-state anisotropy, we have obtained information about the propensity of the ceramide analogs to form ceramide-rich domains and the thermostability of the formed domains. We observed that the oxidation of the primary alcohol to COOH shifted the ceramide's gel-phase onset concentration to slightly higher values in 1-palmitoyl-2-oleoyl- sn-3- glycero-3-phosphocholine (POPC) bilayers. Methylation of the COOH function of the ceramide did not change the segregation tendency further. The complete removal of the primary alcohol dramatically reduced the ability of 1-deoxy-PCer to form ceramide-rich ordered domains. However, the removal 3-OH (in 3-deoxy-PCer) had only small effects on the lateral segregation of the ceramide analog. The thermostability of the ceramide-rich domains in the POPC bilayers decreased in the following order: 1-OH > COOH > COOMe = 3-deoxy > 1-deoxy. We conclude that ceramide needs a hydrogen-bonding-competent functional group in the C(1) position to be able to form laterally segregated ceramide-rich domains of high packing density in POPC bilayers. The presence or absence of 3-OH was not functionally critical for ceramide's lateral segregation properties.

Sphingoid bases and their involvement in neurodegenerative diseases

Sphingoid bases (also known as long-chain bases) form the backbone of sphingolipids. Sphingolipids comprise a large group of lipid molecules, which function as the building blocks of biological membranes and play important signaling and regulatory roles within cells. The roles of sphingoid bases in neurotoxicity and neurodegeneration have yet to be fully elucidated, as they are complex and multi-faceted. This comprises a new frontier of research that may provide us with important clues regarding their involvement in neurological health and disease. This paper explores various neurological diseases and conditions which result when the metabolism of sphingoid bases and some of their derivatives, such as sphingosine-1-phosphate and psychosine, becomes compromised due to the inhibition or mutation of key enzymes. Dysregulation of sphingoid base metabolism very often manifests with neurological symptoms, as sphingolipids are highly enriched in the nervous system, where they play important signaling and regulatory roles.

Side Effects in Cancer Therapy: Are Sphingolipids to Blame?

Cancer patients' quality of life is greatly dependent on the efficacy of treatments and their associated side effects, which can significantly reduce the overall quality of life. Although the effectiveness of cancer treatments has improved over time, adverse effects persist with each treatment. Some side effects, such as paclitaxel-induced peripheral neuropathy, can be dose limiting, thus further reducing the potential of paclitaxel chemotherapy treatment. Premature ovarian failure in young female patients due to radiation and chemotherapy therapy can have devastating infertility consequences. In recent years, a class of lipids known as sphingolipids has been identified as playing a role in the side effects of cancer therapies. Advanced analytical technologies, such as mass spectrometry, have provided great aid in detecting and distinguishing individual sphingolipids at low concentrations. Sphingolipids play an important role in cell proliferation and apoptosis and, importantly, sphingolipid metabolism has been shown to be dysregulated in cancer. The goal of this review is to summarize the latest findings of the role of sphingolipids in the injurious side effects in various cancer treatments. A better understanding of the molecular mechanisms driving these sphingolipid-induced side effects can help develop new drugs and treatments for cancer that have fewer side effects, thus improving treatment efficacy and quality of life.