Ceramide Accumulation Induces the Integrated Stress Response in AML.

High ceramide levels promote the apoptotic integrated stress response in acute myeloid leukemia (AML).

Ceramide from sphingomyelin hydrolysis induces neuronal differentiation, whereas de novo ceramide synthesis and sphingomyelin hydrolysis initiate apoptosis after NGF withdrawal in PC12 Cells.

BACKGROUND: Ceramide, important for both neuronal differentiation and dedifferentiation, resides in several membranes, is synthesized in the endoplasmic reticulum, mitochondrial, and nuclear membranes, and can be further processed into glycosphingolipids or sphingomyelin. Ceramide may also be generated by hydrolysis of sphingomyelin by neutral or acidic sphingomyelinases in lysosomes and other membranes. Here we asked whether the differing functions of ceramide derived from different origins. METHODS: We added NGF to PC12 cells and to TrkA cells. These latter overexpress NGF receptors and are partially activated to differentiate, whereas NGF is required for PC12 cells to differentiate. We differentiated synthesis from hydrolysis by the use of appropriate inhibitors. Ceramide and sphingomyelin were measured by radiolabeling. RESULTS: When NGF is added, the kinetics and amounts of ceramide and sphingomyelin indicate that the ceramide comes primarily from hydrolysis but, when hydrolysis is inhibited, can also come from neosynthesis. When NGF is removed, the ceramide comes from both neosynthesis and hydrolysis. CONCLUSION: We conclude that the function of ceramide depends heavily on its intracellular location, and that further understanding of its function will depend on resolving its location during changes of cell status. Video Abstract.

Ceramide and sphingomyelin reportedly are important both for differentiation of nerve cells and for their death. We studied PC12 cells, which can differentiate into neuron-like cells in the presence of nerve growth factor and cells that overexpress receptors for nerve growth factor. By combining various inhibitors, we conclude that in the presence of nerve growth factor ceramide comes from hydrolysis of sphingomyelin, but when nerve growth factor is removed and the cells atrophy and die, sphingomyelin comes from both neosynthesis and hydrolysis.

Ceramide modulates electrophysiological characteristics and oxidative stress of pulmonary vein cardiomyocytes.

BACKGROUND: Ceramide is involved in regulating metabolism and energy expenditure, and its abnormal myocardial accumulation may contribute to heart injury or lipotoxic cardiomyopathy. Whether ceramide can modulate the electrophysiology of pulmonary veins (PVs) remains unknown. MATERIALS AND METHODS: We used conventional microelectrodes to measure the electrical activity of isolated rabbit PV tissue preparations before and after treatment with various concentrations of ceramide with or without H2 O2 (2 mM), MitoQ, wortmannin or 740 YP. A whole-cell patch clamp and fluorescence imaging were used to record the ionic currents, calcium (Ca2+ ) transients, and intracellular reactive oxygen species (ROS) and sodium (Na+ ) in isolated single PV cardiomyocytes before and after ceramide (1 µM) treatment. RESULTS: Ceramide (0.1, 0.3, 1 and 3 µM) reduced the beating rate of PV tissues. Furthermore, ceramide (1 µM) suppressed the 2 mM H2 O2 -induced faster PV beating rate, triggered activities and burst firings, which were further reduced by MitoQ. In the presence of wortmannin, ceramide did not change the PV beating rate. The H2 O2 -induced faster PV beating rate could be counteracted by MitoQ or wortmannin with no additive effect from the ceramide. Ceramide inhibited pPI3K. Ceramide reduced Ca2+ transients, sarcoplasmic reticulum Ca2+ contents, L-type Ca2+ currents, Na+ currents, late Na+ currents, Na+ -hydrogen exchange currents, and intracellular ROS and Na+ in PV cardiomyocytes, but did not change Na+ -Ca2+ exchange currents. CONCLUSION: C2 ceramide may exert the distinctive electrophysiological effect of modulating PV activities, which may be affected by PI3K pathway-mediated oxidative stress, and might play a role in the pathogenesis of PV arrhythmogenesis.

Cytotoxic Impact of N-Oleoylethanolamine on Bone Cancer Cells.

BACKGROUND: Cancer is a complex disease that derives from the uncontrolled proliferation of cells. Bone cancer is a type of prevalent cancer that occurs both in young and adults. Bone cancer is most common in the long bones of the pelvis, arms and legs. Statistically, more than 200 cases of osteosarcoma have been reported annually in our country. Classical treatment with chemotherapeutics remains ineffective in the cure of this cancer type. Recent studies have shown that ceramide induces apoptosis at its increased levels in the cells. Thus, many studies have been conducted to cause the accumulation of ceramide molecules in the cell by different ways to induce apoptosis. NOE (Noleoylethanolamine) is a specific inhibitor of ceramidase enzymes that hydrolyze intracellular ceramides and prevent apoptosis. OBJECTIVE: This study investigates the cytotoxic and apoptosis-inducing activities of NOE on human osteosarcoma Saos-2 cells. METHODS: Cytotoxic effects were investigated by MTT colorimetric assay. For the detection of morphological and ultrastructural indicators of apoptosis, confocal and TEM techniques were used. RESULTS: Our finding indicated that NOE is effective in the inhibition of the growth of Saos-2 cells. Confocal and TEM findings showed morphological and ultrastructural changes as chromatin condensation, fragmentation of nuclei and mitochondria as well as damaged cytoskeleton and cell shrinkage. CONCLUSION: The results revealed that NOE exerts its cytotoxicity on Saos-2 cells through changing the ultrastructure and morphology of cells with clear apoptotic sparks.

Impaired Skin Barrier Function Due to Reduced ω-O-Acylceramide Levels in a Mouse Model of Sjögren-Larsson Syndrome.

Sjögren-Larsson syndrome (SLS) is an inherited neurocutaneous disorder whose causative gene encodes the fatty aldehyde dehydrogenase ALDH3A2. To date, the detailed molecular mechanism of the skin pathology of SLS has remained largely unclear. We generated double-knockout (DKO) mice for Aldh3a2 and its homolog Aldh3b2 (a pseudogene in humans). These mice showed hyperkeratosis and reduced fatty aldehyde dehydrogenase activity and skin barrier function. The levels of ω-O-acylceramides (acylceramides), which are specialized ceramides essential for skin barrier function, in the epidermis of DKO mice were about 60% of those in wild-type mice. In the DKO mice, levels of acylceramide precursors (ω-hydroxy ceramides and triglycerides) were increased, suggesting that the final step of acylceramide production was inhibited. A decrease in acylceramide levels was also observed in human immortalized keratinocytes lacking ALDH3A2. Differentiated keratinocytes prepared from the DKO mice exhibited impaired long-chain base metabolism. Based on these results, we propose that the long-chain-base-derived fatty aldehydes that accumulate in DKO mice and SLS patients attack and inhibit the enzyme involved in the final step of acylceramide production. Our findings provide insight into the pathogenesis of the skin symptoms of SLS, i.e., decreased acylceramide production, and its molecular mechanism.

Novelty of Sphingolipids in the Central Nervous System Physiology and Disease: Focusing on the Sphingolipid Hypothesis of Neuroinflammation and Neurodegeneration.

For decades, lipids were confined to the field of structural biology and energetics as they were considered only structural constituents of cellular membranes and efficient sources of energy production. However, with advances in our understanding in lipidomics and improvements in the technological approaches, astounding discoveries have been made in exploring the role of lipids as signaling molecules, termed bioactive lipids. Among these bioactive lipids, sphingolipids have emerged as distinctive mediators of various cellular processes, ranging from cell growth and proliferation to cellular apoptosis, executing immune responses to regulating inflammation. Recent studies have made it clear that sphingolipids, their metabolic intermediates (ceramide, sphingosine-1-phosphate, and N-acetyl sphingosine), and enzyme systems (cyclooxygenases, sphingosine kinases, and sphingomyelinase) harbor diverse yet interconnected signaling pathways in the central nervous system (CNS), orchestrate CNS physiological processes, and participate in a plethora of neuroinflammatory and neurodegenerative disorders. Considering the unequivocal importance of sphingolipids in CNS, we review the recent discoveries detailing the major enzymes involved in sphingolipid metabolism (particularly sphingosine kinase 1), novel metabolic intermediates (N-acetyl sphingosine), and their complex interactions in CNS physiology, disruption of their functionality in neurodegenerative disorders, and therapeutic strategies targeting sphingolipids for improved drug approaches.

The Role of Fatty Acids in Ceramide Pathways and Their Influence on Hypothalamic Regulation of Energy Balance: A Systematic Review.

Obesity is a global health issue for which no major effective treatments have been well established. High-fat diet consumption is closely related to the development of obesity because it negatively modulates the hypothalamic control of food intake due to metaflammation and lipotoxicity. The use of animal models, such as rodents, in conjunction with in vitro models of hypothalamic cells, can enhance the understanding of hypothalamic functions related to the control of energy balance, thereby providing knowledge about the impact of diet on the hypothalamus, in addition to targets for the development of new drugs that can be used in humans to decrease body weight. Recently, sphingolipids were described as having a lipotoxic effect in peripheral tissues and the central nervous system. Specifically, lipid overload, mainly from long-chain saturated fatty acids, such as palmitate, leads to excessive ceramide levels that can be sensed by the hypothalamus, triggering the dysregulation of energy balance control. However, no systematic review has been undertaken regarding studies of sphingolipids, particularly ceramide and sphingosine-1-phosphate (S1P), the hypothalamus, and obesity. This review confirms that ceramides are associated with hypothalamic dysfunction in response to metaflammation, endoplasmic reticulum (ER) stress, and lipotoxicity, leading to insulin/leptin resistance. However, in contrast to ceramide, S1P appears to be a central satiety factor in the hypothalamus. Thus, our work describes current evidence related to sphingolipids and their role in hypothalamic energy balance control. Hypothetically, the manipulation of sphingolipid levels could be useful in enabling clinicians to treat obesity, particularly by decreasing ceramide levels and the inflammation/endoplasmic reticulum stress induced in response to overfeeding with saturated fatty acids.

The doxorubicin-induced cell motility network is under the control of the ceramide-activated protein phosphatase 1 alpha.

We have recently reported that a specific pool of ceramide, located in the plasma membrane, mediated the effects of sublethal doses of the chemotherapeutic compound doxorubicin on enhancing cancer cell migration. We identified neutral sphingomyelinase 2 (nSMase2) as the enzyme responsible to generate this bioactive pool of ceramide. In this work, we explored the role of members of the protein phosphatases 1 family (PP1), and we identified protein phosphatase 1 alpha isoform (PP1 alpha) as the specific PP1 isoform to mediate this phenotype. Using a bioinformatics approach, we build a functional interaction network based on phosphoproteomics data on plasma membrane ceramide. This led to the identification of several ceramide-PP1 alpha downstream substrates. Studies on phospho mutants of ezrin (T567) and Scrib (S1378/S1508) demonstrated that their dephosphorylation is sufficient to enhance cell migration. In summary, we identified a mechanism where reduced doses of doxorubicin result in the dysregulation of cytoskeletal proteins and enhanced cell migration. This mechanism could explain the reported effects of doxorubicin worsening cancer metastasis in animal models.

Burn Injury Impairs Neutrophil Chemotaxis Through Increased Ceramide.

ABSTRACT: Infection is a common and often deadly complication after burn injury. A major underlying factor is burn-induced immune dysfunction, particularly with respect to neutrophils as the primary responders to infection. Temporally after murine scald injury, we demonstrate impaired bone marrow neutrophil chemotaxis toward CXCL1 ex vivo. Additionally, we observed a reduced recruitment of neutrophils to the peritoneal after elicitation 7 days after injury. We demonstrate that neutrophil ceramide levels increase after burn injury, and this is associated with decreased expression of CXCR2 and blunted chemotaxis. A major signaling event upon CXCR2 activation is Akt phosphorylation and this was reduced when ceramide was elevated. In contrast, PTEN levels were elevated and PTEN-inhibition elevated phospho-Akt levels and mitigated the burn-induced neutrophil chemotaxis defect. Altogether, this study identifies a newly described pathway of ceramide-mediated suppression of neutrophil chemotaxis after burn injury and introduces potential targets to mitigate this defect and reduce infection-related morbidity and mortality after burn.

Dihydroceramides: their emerging physiological roles and functions in cancer and metabolic diseases.

Dihydroceramides (DhCers) are a type of sphingolipids that for a long time were regarded as biologically inactive. They are metabolic intermediates of the de novo sphingolipid synthesis pathway, and are converted into ceramides (Cers) with the addition of a double bond. Ceramides are abundant in tissues and have well-established biological functions. On the contrary, dihydroceramides are less prevalent, and despite their hitherto characterization as inert lipids, studies of the past decade began to unravel their implication in various biological processes distinct from those involving ceramides. These processes include cellular stress responses and autophagy, cell growth, pro-death or pro-survival pathways, hypoxia, and immune responses. In addition, their plasma concentration has been related to metabolic diseases and shown as a long-term predictor of type 2 diabetes onset. They are thus important players and potential biomarkers in pathologies ranging from diabetes to cancer and neurodegenerative diseases. The purpose of this mini-review is to highlight the emergence of dihydroceramides as a new class of bioactive sphingolipids by reporting recent advances on their biological characterization and pathological implications, focusing on cancer and metabolic diseases.

[Ceramides, crucial actors in the development of insulin resistance and type 2 diabetes]. / Céramides, acteurs cruciaux dans le développement de l'insulino-résistance et du diabète de type 2.

In healthy subjects, the balance between glucose production and its usage is precisely controlled. When circulating glucose reaches a critical threshold, pancreatic ß-cells secrete insulin, which has two major actions: lowering circulating glucose concentrations by facilitating its uptake mainly in skeletal muscles and the liver, and inhibiting glucose production. Triglycerides are the main source of fatty acids to meet the energy needs of oxidative tissues and any excess is stored in adipocytes. Thus, adipose tissue acts as a trap for excess fatty acids released from plasma triglycerides. When the buffering action of adipose tissue to store fatty acids is impaired, they accumulate in other tissues where they are metabolized in several lipid species, including sphingolipid derivatives such as ceramides. Numerous studies have shown that ceramides are among the most active lipid second messengers to inhibit insulin signalling. This review describes the major role played by ceramides in the development of insulin resistance in peripheral tissues.

TITLE: Céramides, acteurs cruciaux dans le développement de l'insulino-résistance et du diabète de type 2. ABSTRACT: L'insulino-résistance, qui caractérise le diabète de type 2 et l'obésité, est due à une diminution de l'action de l'insuline sur ses tissus cibles (foie, tissu adipeux, muscles squelettiques). Il est maintenant bien documenté qu'au niveau de ces tissus, l'accumulation ectopique d'acides gras, et en particulier de métabolites dérivés de ces acides gras, comme les céramides, joue un rôle crucial dans l'altération du message insulinique. Cette revue décrit le rôle majeur joué par les céramides dans le développement de l'insulino-résistance des tissus périphériques.

[Ceramids and their role in the development of cardiovascular diseases (review of literature).]

Almost all known stress stimuli, including inflammatory agonists, chemotherapeutic agents and saturated fatty acids, cause the synthesis of ceramide and its metabolites. In recent studies, it has been shown that excessive synthesis of ceramides causes the development of various metabolic diseases, such as obesity, diabetes and cardiovascular diseases. Currently, the role of cеramids in the development of obesity and diabetes has been studied quite well. At the same time, studies devoted to the study of lipid data in the development of cardiovascular disease are not large. In this review, we generalize the data on this new class of bioactive lipids for understanding their role in the development of cardiovascular diseases.

Endothelial Sphingolipid De Novo Synthesis Controls Blood Pressure by Regulating Signal Transduction and NO via Ceramide.

Ceramides are sphingolipids that modulate a variety of cellular processes via 2 major mechanisms: functioning as second messengers and regulating membrane biophysical properties, particularly lipid rafts, important signaling platforms. Altered sphingolipid levels have been implicated in many cardiovascular diseases, including hypertension, atherosclerosis, and diabetes mellitus-related conditions; however, molecular mechanisms by which ceramides impact endothelial functions remain poorly understood. In this regard, we generated mice defective of endothelial sphingolipid de novo biosynthesis by deleting the Sptlc2 (long chain subunit 2 of serine palmitoyltransferase)-the first enzyme of the pathway. Our study demonstrated that endothelial sphingolipid de novo production is necessary to regulate (1) signal transduction in response to NO agonists and, mainly via ceramides, (2) resting eNOS (endothelial NO synthase) phosphorylation, and (3) blood pressure homeostasis. Specifically, our findings suggest a prevailing role of C16:0-Cer in preserving vasodilation induced by tyrosine kinase and GPCRs (G-protein coupled receptors), except for Gq-coupled receptors, while C24:0- and C24:1-Cer control flow-induced vasodilation. Replenishing C16:0-Cer in vitro and in vivo reinstates endothelial cell signaling and vascular tone regulation. This study reveals an important role of locally produced ceramides, particularly C16:0-, C24:0-, and C24:1-Cer in vascular and blood pressure homeostasis, and establishes the endothelium as a key source of plasma ceramides. Clinically, specific plasma ceramides ratios are independent predictors of major cardiovascular events. Our data also suggest that plasma ceramides might be indicative of the diseased state of the endothelium.

Ceramides and diabetes mellitus: an update on the potential molecular relationships.

Recent evidence suggests that ceramides can play an important pathophysiological role in the development of diabetes. Ceramides are primarily recognized as lipid bilayer building blocks, but recent work has shown that these endogenous molecules are important intracellular signalling mediators and may exert some diabetogenic effects via molecular pathways involved in insulin resistance, ß-cell apoptosis and inflammation. In the present review, we consider the available evidence on the possible roles of ceramides in diabetes mellitus and introduce eight different molecular mechanisms mediating the diabetogenic action of ceramides, categorized into those predominantly related to insulin resistance vs those mainly implicated in ß-cell dysfunction. Specifically, the mechanistic evidence involves ß-cell apoptosis, pancreatic inflammation, mitochondrial stress, endoplasmic reticulum stress, adipokine release, insulin receptor substrate 1 phosphorylation, oxidative stress and insulin synthesis. Collectively, the evidence suggests that therapeutic agents aimed at reducing ceramide synthesis and lowering circulating levels may be beneficial in the prevention and/or treatment of diabetes and its related complications.

The Role of Sphingolipids and Specialized Pro-Resolving Mediators in Alzheimer's Disease.

Alzheimer's disease (AD) is the leading cause of dementia worldwide giving rise to devastating forms of cognitive decline, which impacts patients' lives and that of their proxies. Pathologically, AD is characterized by extracellular amyloid deposition, neurofibrillary tangles and chronic neuroinflammation. To date, there is no cure that prevents progression of AD. In this review, we elaborate on how bioactive lipids, including sphingolipids (SL) and specialized pro-resolving lipid mediators (SPM), affect ongoing neuroinflammatory processes during AD and how we may exploit them for the development of new biomarker panels and/or therapies. In particular, we here describe how SPM and SL metabolism, ranging from ω-3/6 polyunsaturated fatty acids and their metabolites to ceramides and sphingosine-1-phosphate, initiates pro- and anti-inflammatory signaling cascades in the central nervous system (CNS) and what changes occur therein during AD pathology. Finally, we discuss novel therapeutic approaches to resolve chronic neuroinflammation in AD by modulating the SPM and SL pathways.

The Role of Ceramide 1-Phosphate in Inflammation, Cellular Proliferation, and Wound Healing.

The phospho-sphingolipid, ceramide 1-phosphate (C1P), has long been implicated as a dynamic bioactive agent. Over two decades of research has begun to characterize various regulatory roles for C1P from mammalian inflammatory response and wound healing to cellular proliferation and survival. As a metabolite of the intricately balanced "sphingolipid rheostat", C1P stands as a crucial physiological regulator of both upstream and downstream mechanisms. This chapter serves as an overview of established and implicated roles for C1P in cellular processes vital to diseases and mammalian physiology. Additionally, we discuss potential clinical roles for C1P in cancer treatment, wound therapy, and pre-disease diagnosis. While many questions remain regarding C1P metabolism and the extent of signaling factors targeted by this bioactive lipid, new technologies and methodologies show great promise to discern key targets, signaling pathways, and physiologies regulated by C1P.

Ceramide Domains in Health and Disease: A Biophysical Perspective.

Ceramides are the central molecules in sphingolipid metabolism. In addition, they are recognized as important modulators of cell function, playing key roles in several cellular processes that range from cell proliferation to cell death. Moreover, ceramides were implicated in multiple diseases, including cancer, neurodegenerative and metabolic diseases, and also in infection by different pathogens. The mechanisms underlying the diverse biological and pathological actions of ceramides are yet to be fully elucidated. Several lines of evidence suggest that the structural features of ceramides, namely their high hydrophobicity and ability to establish strong H-bond network, are responsible for changes in the biophysical properties of biological membranes that can affect the activity of proteins and activate signaling pathways. Ceramide-induced alterations in membrane biophysical properties might also influence the internalization, trafficking and sorting of lipids, proteins, drugs and even pathogens contributing to cell pathophysiology. In this chapter, we critically discuss the ability of ceramides to form lipid domains with atypical biophysical properties and how these domains can be involved in those processes.

Invited review: Sphingolipid biology in the dairy cow: The emerging role of ceramide.

The physiological control of lactation through coordinated adaptations is of fundamental importance for mammalian neonatal life. The putative actions of reduced insulin sensitivity and responsiveness and enhanced adipose tissue lipolysis spare glucose for the mammary synthesis of milk. However, severe insulin antagonism and body fat mobilization may jeopardize hepatic health and lactation in dairy cattle. Interestingly, lipolysis- and dietary-derived fatty acids may impair insulin sensitivity in cows. The mechanisms are undefined yet have major implications for the development of postpartum fatty liver disease. In nonruminants, the sphingolipid ceramide is a potent mediator of saturated fat-induced insulin resistance that defines in part the mechanisms of type 2 diabetes mellitus and nonalcoholic fatty liver disease. In ruminants including the lactating dairy cow, the functions of ceramide had remained virtually undescribed. Through a series of hypothesis-centered studies, ceramide has emerged as a potential antagonist of insulin-stimulated glucose utilization by adipose and skeletal muscle tissues in dairy cattle. Importantly, bovine data suggest that the ability of ceramide to inhibit insulin action likely depends on the lipolysis-dependent hepatic synthesis and secretion of ceramide during early lactation. Although these mechanisms appear to fade as lactation advances beyond peak milk production, early evidence suggests that palmitic acid feeding is a means to augment ceramide supply. Herein, we review a body of work that focuses on sphingolipid biology and the role of ceramide in the dairy cow within the framework of hepatic and fatty acid metabolism, insulin function, and lactation. The potential involvement of ceramide within the endocrine control of lactation is also considered.

Lipid-gene regulatory network reveals coregulations of triacylglycerol with phosphatidylinositol/lysophosphatidylinositol and with hexosyl-ceramide.

Lipid homeostasis is important for executing normal cellular functions and maintaining physiological conditions. The biophysical properties and intricate metabolic network of lipids underlie the coordinated regulation of different lipid species in lipid homeostasis. To reveal the homeostatic response among different lipids, we systematically knocked down 40 lipid metabolism genes in Drosophila S2 cells by RNAi and profiled the lipidomic changes. Clustering analyses of lipids reveal that many pairs of genes acting in a sequential fashion or sharing the same substrate are tightly clustered. Through a lipid-gene regulatory network analysis, we further found that a reduction of triacylglycerol (TAG) is associated with an increase of phosphatidylinositol (PI) and lysophosphatidylinositol (LPI) or a reduction of hexosyl-ceramide (HexCer) and hydroxylated hexosyl-ceramide (OH-HexCer). Importantly, negative coregulation between TAG and LPI/PI, and positive coregulation between TAG and HexCer, were also found in human Hela cells. Together, our results reveal coregulations of TAG with PI/LPI and with HexCer in lipid homeostasis.

Are Sphingolipids and Serine Dipeptide Lipids Underestimated Virulence Factors of Porphyromonas gingivalis?

The keystone periodontal pathogen Porphyromonas gingivalis produces phosphorylated dihydroceramide lipids (sphingolipids) such as phosphoethanolamine dihydroceramide (PE DHC) and phosphoglycerol dihydroceramide (PG DHC) lipids. Phosphorylated DHCs (PDHCs) from P. gingivalis can affect a number of mammalian cellular functions, such as potentiation of prostaglandin secretion from gingival fibroblasts, promotion of RANKL-induced osteoclastogenesis, promotion of apoptosis, and enhancement of autoimmunity. In P. gingivalis, these lipids affect anchoring of surface polysaccharides, resistance to oxidative stress, and presentation of surface polysaccharides (anionic polysaccharides and K-antigen capsule). In addition to phosphorylated dihydroceramide lipids, serine dipeptide lipids of P. gingivalis are implicated in alveolar bone loss in chronic periodontitis through interference with osteoblast differentiation and function and promotion of osteoclast activity. As a prerequisite for designation as bacterial virulence factors, bacterial sphingolipids and serine dipeptide lipids are recovered in gingival/periodontal tissues, tooth calculus, human blood, vascular tissues, and brain. In addition to P. gingivalis, other bacteria of the genera Bacteroides, Parabacteroides, Porphyromonas, Tannerella, and Prevotella produce sphingolipids and serine dipeptide lipids. The contribution of PDHCs and serine dipeptide lipids to the pathogenesis of periodontal and extraoral diseases may be an underappreciated area in microbe-host interaction and should be more intensively investigated.