Carbon dots combined with phytosphingosine inhibit acid-induced demineralization of hydroxyapatite in vitro

OBJECTIVES

To study the effects of carbon dots (CDs), in combination with phytosphingosine (PHS), against acid-induced demineralization of hydroxyapatite in vitro.

METHODS

CDs were generated from citric acid and urea by microwave heating. Transmission electron microscope (TEM), FT-IR, and fluorescence intensity were used to characterize the CDs. A hydroxyapatite (HAp) model was used to investigate the protective effects of CDs, PHS, and their combinations with and without a salivary pellicle against acid-induced demineralization in vitro. Ca2+ release as a parameter to evaluate the inhibition of demineralization was measured by capillary electrophoresis. The interactions between CDs, PHS, and HAp discs were investigated using a fluorescence detector.

RESULTS

Uniform-sized CDs were synthesized, showing typical optical characteristics. CDs exhibited no inhibition of acid-induced demineralization in vitro, in contrast to PHS. Notably, a pre-coating of CDs increased the protective effects of PHS against acid-induced demineralization, which was not disturbed by the presence of a salivary pellicle and Tween 20. Scanning electron microscope (SEM) confirmed the binding and layers formed of both CDs and PHS to the HAp surfaces. Based on fluorescence spectra CDs binding to HAp seemed to be dependent on Ca2+ and PO43- interactions.

CONCLUSIONS

CDs combined with PHS showed protective effects against acid-induced demineralization of HAp discs in vitro.

First description of adenosine production by Gnomoniopsis smithogilvyi, causal agent of chestnut brown rot

Gnomoniopsis smithogilvyi (Gnomoniaceae, Diaporthales) is the main causal agent of chestnut brown rot on sweet chestnut worldwide. The rotting of nuts leads to alterations in the organoleptic qualities and decreased fruit production, resulting in significant economic losses. In 2021, there was an important outbreak of chestnut rot in southern Galicia (Spanish northwest). The profile of secondary metabolites from G. smithogilvyi was studied, especially to determine its capability for producing mycotoxins, as happens with other rotting fungi, due to the possible consequences on the safety of chestnut consumption. Secondary metabolites produced by isolates of G. smithogilvyi growing in potato dextrose agar (PDA) medium were identified using liquid chromatography coupled with high-resolution mass spectrometry. Three metabolites with interesting pharmacological and phyto-toxicological properties were identified based on their exact mass and fragmentation patterns, namely adenosine, oxasetin, and phytosphingosine. The capacity of G. smithogilvyi to produce adenosine in PDA cultures was assessed, finding concentrations ranging from 176 to 834 µg/kg. Similarly, the production of mycotoxins was ruled out, indicating that the consumption of chestnuts with necrotic lesions does not pose a health risk to the consumer in terms of mycotoxins.

Phytosphingosine inhibits the growth of lung adenocarcinoma cells by inducing G2/M-phase arrest, apoptosis, and mitochondria-dependent pathway cell death in vitro and in vivo

In order to search for novel antitumor drugs with high efficiency and low toxicity, the anti-lung cancer activity of phytosphingosine was studied. Phytosphingosine is widely distributed in fungi, plants, animals, and has several biological activities, including anti-inflammation and anti-tumor. However, its anti-lung cancer activity needs to be further investigated. The effects and pharmacological mechanisms of phytosphingosine on lung cancer treatment were investigated both in vitro and in vivo. The results showed that phytosphingosine inhibited the growth of lung cancer cell lines. Phytosphingosine induced apoptosis through a mitochondria-mediated pathway, phytosphingosine arrested the cell cycle at the G2/M phase and induced apoptosis in a dose-dependent manner by increasing Bax/Bcl-2 ratio, which caused the decrease of mitochondrial membrane potential to promote the release of cytochrome C, caspase 9 and 3, and degrade PARP in A549 cells. The results showed that phytosphingosine could damage the mitochondrial functions, increase ROS levels, and arrest the cell cycle at the G2/M stages. Finally, phytosphingosine also inhibited the growth of tumor in mice. Taken together, phytosphingosine suppressed the growth of lung cancer cells both in vitro and in vivo and had potential application in the research and development of antitumor drugs. The aim of the present study was to explain the theoretical basis of phytosphingosine therapy for lung cancer and providing new possibilities for lung cancer treatment.

Phytosphingosine alleviates Staphylococcus aureus-induced mastitis by inhibiting inflammatory responses and improving the blood-milk barrier in mice

Mastitis is one of the common diseases in dairy cows which threatens the health of cows and impacts on economic benefits seriously. Recent studies have been showed that Subacute Ruminal Acidosis (SARA) increased the susceptibility of cow mastitis. SARA leads the disturbance of the rumen microbiota, and the rumen bacterial disordered community is an important endogenous factor of cow mastitis. That is to say, cows which suffer from SARA have a disordered rumen microbiota, a prolonged decline in ruminal PH and a high level of lipopolysaccharide (LPS) in the rumen, blood. Therefore, ruminal metabolism is closely related to the rumen microbiota. However, the specific mechanism of SARA and mastitis still not clear. We found an intestinal metabolite according to the metabonomics, which is correlated to inflammation. Phytophingosine (PS), a product from rumen fluid and milk of the cows which suffer from SARA and mastitis. It has the effect of killing bacteria and anti-inflammatory. Emerging evidences indicate that PS can alleviate inflammatory diseases. However, how PS affects mastitis is largely unknown. In this study, we explored the concrete role of PS on Staphylococcus aureus (S. aureus) -induced mastitis in mice. We found that PS obviously decreased the level of the proinflammatory cytokines. Meanwhile, PS also significantly relieved the mammary gland inflammation caused by S. aureus and restored the function of the blood-milk barrier. Here, we showed that PS increased the expression of the classic Tight-junctions (TJs) proteins including ZO-1, Occludin and Claudin-3. Moreover, PS improves S. aureus-induced mastitis by inhibiting the activation of the NF-κB and NLRP3 signaling pathways. These data indicated that PS relieved S. aureus-induced mastitis effectively. This also provides a reference for exploring the correlation between the intestinal metabolism and inflammation.

Micro-Raman spectroscopy analysis of dentin remineralization using eggshell derived nanohydroxyapatite combined with phytosphingosine

The aim of this study was to assess the remineralization efficacy of chicken eggshell-derived nano-hydroxyapatite (CEnHAp) combined with phytosphingosine (PHS) on artificially induced dentinal lesions. PHS was commercially procured whereas CEnHAp was synthesized using microwave-irradiation method and characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high-resolution scanning electron microscopy-energy-dispersive X-ray spectroscopy (HRSEM-EDX), and transmission electron microscopy (TEM). A total of 75 pre-demineralized coronal dentin specimens were randomly treated with one of the following test agents (n = 15 each): artificial saliva (AS), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), CEnHAp, PHS, and CEnHAp-PHS under pH cycling for 7, 14, and 28 days. Vickers microhardness indenter, HRSEM-EDX, and micro-Raman spectroscopy methods were used to assess the mineral changes in the treated dentin samples. Data were submitted to Kruskal-Wallis and Friedman's two-way analyses of variance (p < 0.05). HRSEM and TEM analysis depicted irregular spherical structure of the prepared CEnHAp with a particle size of 20-50 nm. The EDX analysis confirmed the presence of Ca, P, Na and Mg ions. The XRD pattern showed the characteristic crystalline peaks for hydroxyapatite and calcium carbonate that are present in the prepared CEnHAp. Dentin treated with CEnHAp-PHS revealed highest microhardness values along with complete tubular occlusion compared to other groups at all test time intervals (p < 0.05). Specimens treated with CEnHAp showed increased remineralization than those treated with CPP-ACP followed by PHS and AS groups. The intensity of mineral peaks, as observed in the EDX and micro-Raman spectra, confirmed these findings. Further, the molecular conformation of the collagen's polypeptide chains, and amide-I and CH₂ peaks attained peak intensities in dentin treated with CEnHAp-PHS and PHS whereas other groups revealed poor stability of collagen bands. Microhardness, surface topography, and micro-Raman spectroscopy analyses revealed that dentin treated with CEnHAp-PHS have an improved collagen structure and stability as well as highest mineralization and crystallinity.

The effect of phytosphingosine associated with tooth brushing on color change, surface roughness, and microhardness of dental enamel - an in vitro and in situ study

OBJECTIVE

This study evaluated the in vitro and in situ effects of phytosphingosine (PHS) associated with tooth brushing on color stability, surface roughness, and microhardness of dental enamel.

METHODS

Sixty-four specimens of bovine teeth (6 × 6 × 2 mm) were separated into 8 groups (n = 8): S + TB: PHS (spray) + tooth brushing; TB + S: tooth brushing + PHS (spray); I + TB: PHS (immersion) + tooth brushing; TB + I: tooth brushing + PHS (immersion); TB: tooth brushing; S: PHS spray; I: immersion in PHS solution, and Saliva: immersion in saliva. Tooth brushing simulation (Mavtec, Brazil) was performed (356 rpm on 3.8 cm area by the toothbrush - Soft Tek) for 1, 7, 15, and 30 days. PHS remained in contact with specimens for 15 min. The specimens were evaluated before and after tooth brushing for color alteration (Easy Shade, VITA), and surface roughness (Model SJ-201P Mitutoyo), and Knoop microhardness (HMV-2, Shimadzu Corporation). For the in situ analyses, 8 participants were recruited and received an intraoral device with 6 fragments of bovine enamel (6 × 6 × 2 mm). The properties evaluated were the same as those of the in vitro study. Participants were randomized following best results of in vitro tested protocols, for 15 days: TB, TB + S, I + TB. Data obtained by in vitro (two-way ANOVA, Tukey, p < .05) and in situ (one-way ANOVA, Tukey, p < .05) studies were analyzed.

RESULTS

The in vitro study showed that greater color change was found after 30 days. The greatest differences in surface roughness occurred between the initial value and after 1 day. Regarding microhardness, the highest values occurred after 15 and 30 days, which showed similar results. The in situ study showed greater color changes for the TB and I + TB, and greater surface roughness changes for TB as well as a similar increase in microhardness for the PHS protocols, which were higher than TB.

CONCLUSIONS

Phytosphingosine leads to an increase in performance regarding color stability, surface roughness, and microhardness when applied. In general, the application of PHS after brushing showed a positive impact on its performance.

CLINICAL RELEVANCE

Phytosphingosine proved to be interesting for compound prevention formulations in the dentistry field.

The key to the allergenicity of lipid transfer protein (LTP) ligands: A structural characterization

Plant lipid transfer proteins are a large family that can be found in all land plants. They have a hydrophobic cavity that allows them to harbor lipids and facilitates their traffic between membranes. However, in humans, this plant protein family is responsible for the main food allergies in the Mediterranean area. Nevertheless, not only the protein itself but also its ligand is relevant for allergic sensitization. The main aim of the present work is to analyse the natural ligands carried by four allergenic LTPs (Tri a 14, Art v 3, Par j 2, and Ole e 7), compared with the previously identified ligand of Pru p 3 (CPT-PHS ligand), and clarify their role within the immunological reactions. Results showed that the ligands of the LTPs studied shared a chemical identity, in which the presence of a polar head was essential to the protein-ligand binding. This ligand was transported through a skin cellular model, and phosphorylated phytosphingosine could be detected as result of cell metabolism. Since sphingosine kinase 1 was overexpressed in keratinocytes incubated with the LTP-ligand complex, this enzyme might be responsible for the phosphorylation of the phytosphingosine fraction of the CPT-PHS ligand. This way, phytosphingosine-1-phosphate could be mimicking the role of the human inflammatory mediator sphingosine-1-phosphate, explaining why LTPs are associated with more severe allergic responses. In conclusion, this work contributes to the understanding of the chemical nature and behavior of lipid ligands carried by allergens, which would help to gain insight into their role during allergic sensitization.

Arabidopsis MHP1, a homologue of yeast Mpo1, is involved in ABA signaling

Sphingolipids and their intermediates play multiple roles in biological processes. The sphingoid long-chain base component of sphingolipids has emerged as a participant in the regulation of plant biotic and abiotic stress responses. The phytohormone abscisic acid (ABA) regulates many stress responses in plants for environmental adaptation. However, the relationship between the sphingoid bases and ABA is undetermined. In this study, mhp1-1 (the yeast Mpo1 homolog in plants) was isolated through a sodium chloride (NaCl)-sensitivity screen of Arabidopsis transfer DNA (T-DNA) insertion mutants. mhp1-1 was hypersensitivity to salt/osmotic stress and ABA. MHP1 encodes a protein with a domain of unknown function 962 (DUF962). Endoplasmic reticulum-localized MHP1 was found to interact with ABI1. MHP1, a homolog of yeast dioxygenase Mpo1, rescued the growth arrest of mpo1Δ cells caused by ER stress, suggesting functional homology of MHP1 to Mpo1. Overall, MHP1 plays important roles in response to ABA.

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.

MEDEA-interacting protein LONG-CHAIN BASE KINASE 1 promotes pattern-triggered immunity in Arabidopsis thaliana

Arabidopsis LONG-CHAIN BASE KINASE 1 (LCBK1) interacts with MEDEA, a component of PCR2 complex that negatively regulates immunity. LCBK1 phosphorylates phytosphingosine and thereby promotes stomatal immunity against bacterial pathogens. Arabidopsis polycomb-group repressor complex2 (PRC2) protein MEDEA (MEA) suppresses both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). MEA represses the expression of RPS2 and thereby attenuates AvrRpt2 effector-mediated ETI. However, the mechanism of MEA-mediated PTI diminution was not known. By screening the Arabidopsis cDNA library using yeast-2-hybrid interaction, we identified LONG-CHAIN BASE KINASE1 (LCBK1) as an MEA-interacting protein. We found that lcbk1 mutants are susceptible to virulent bacterial pathogens, such as Pseudomonas syringae pv maculicola (Psm) and P. syringae pv tomato (Pst) but not the avirulent strain of Pst that carries AvrRpt2 effector. Pathogen inoculation induces LCBK1 expression, especially in guard cells. We found that LCBK1 has a positive regulatory role in stomatal closure after pathogen inoculation. WT plants close stomata within an hour of Pst inoculation or flg22 (a 22 amino acid peptide from bacterial flagellin protein that activates PTI) treatment, but not lcbk1 mutants. LCBK1 phosphorylates phytosphingosine (PHS). Exogenous application of phosphorylated PHS (PHS-P) induces stomatal closure and rescues loss-of-PTI phenotype of lcbk1 mutant plants. MEA overexpressing (MEA-Oex) plants are defective, whereas loss-of-function mea-6 mutants are hyperactive in PTI-induced stomatal closure. Exogenous application of PHS-P rescues loss-of-PTI in MEA-Oex plants. Results altogether demonstrate that LCBK1 is an interactor of MEA that positively regulates PTI-induced stomatal closure in Arabidopsis.

Phytosphingosine Increases Biosynthesis of Phytoceramide by Uniquely Stimulating the Expression of Dihydroceramide C4-desaturase (DES2) in Cultured Human Keratinocytes

Ceramide NP is known to be the most abundant class of 12 ceramide (CER) families that form a permeability barrier in the human skin barrier. However, not many studies have been reported on the regulation of the biosynthesis of ceramide NP. Recently, it has been reported that phytosphingosine (PHS) treatment in the cultured keratinocytes (KC) notably increased the content of ceramide NP. However, the mechanism behind the PHS-induced enhancement of ceramide NP has not been elucidated. In this study, we investigated the effects of PHS on the expression of several essential genes for the biosynthesis of CER. Also, we determined the molecular mechanism behind the unique enhancement of ceramide NP upon treatment of PHS in the cultured KC. The expressions of all of the three genes (SPT, ceramide synthase 3 [CERS3], and ELOVL4) and their respective proteins were markedly increased in PHS-treated KC. In addition, the expression of the dihydroceramide C4-desaturase (DES2) responsible for conversion of dihydroceramide into ceramide NP was uniquely enhanced only by PHS treatment. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that more than 20-fold increase of ceramide NP by PHS was observed while no significant enhancement of ceramide NS and NDS was observed. This study demonstrates that PHS plays a fundamental role in strengthening the epidermal permeability barrier by stimulating the overall processes of biosynthesis of all classes of CER in epidermis. The dramatic increase of ceramide NP upon PHS treatment seemed to be the outcome of transformation of dihydroceramide and/or ceramide NS by C4-hydroxylase activity.

Elevated Levels of Phosphorylated Sphingobases Do Not Antagonize Sphingobase- or Fumonisin B1-Induced Plant Cell Death

Long-chain bases (LCBs), also termed sphingobases, are building blocks of sphingolipids, which make up a significant proportion of the cellular membrane system. They are also bioactive molecules regulating intracellular processes. Elevated levels of LCBs like phytosphingosine and dihydrosphingosine can induce cell death in plants and correlate with programmed cell death (PCD) reactions after pathogen recognition. We investigated the previously hypothesized antagonism between phosphorylated and nonphosphorylated LCBs with respect to cell death in Arabidopsis thaliana. Using HPLC-MS/MS, we determined levels of phosphorylated and nonphosphorylated LCBs after cell death induction by LCB application or by Fumonisin B1 (FB1) treatment. We show that previously reported antagonistic effects of phosphorylated LCBs after simultaneous application with nonphosphorylated LCBs are linked to reduced uptake of nonphosphorylated LCBs into the tissue. Furthermore, phosphorylated LCBs did not antagonize PCD induced by avirulence protein recognition. In a functional approach, we used Arabidopsis lines with perturbed levels of phosphorylated LCBs. In these plants, the degree of FB1-induced cell death did not consistently correlate negatively with levels of phosphorylated LCBs, but positively with levels of major nonphosphorylated LCBs phytosphingosine and dihydrosphingosine. As treatment with phosphorylated LCBs did not antagonize cell death, and elevated in vivo levels of these LCB species did not reduce FB1-induced cell death, we conclude that the hypothesized general cell death-antagonizing effect of phosphorylated LCBs in plant cell death reactions should be rejected. Instead, our time-course analysis of LCB levels during cell death reactions showed a positive correlation between levels of nonphosphorylated LCBs and cell death.

A rapid synthesis of sphingosine from phytosphingosine

A simple and efficient protocol for the synthesis of a sphingosine starting from cost-effective phytosphingosine has been described. Two alternative synthetic pathway have been disclosed based on the use of two different kinds of protective groups for the protection of the amino group in the phytosphingosine. The protected phytosphingosine was subsequently transformed into sphingosine in 5 steps i.e. protection of the amine group, protection of 1,3-diol, leaving group insertion, elimination, and one-pot deprotection.

Facile determination of sphingolipids under alkali condition using metal-free column by LC-MS/MS

Extraction and analysis of sphingolipids from biological samples is a critical step in lipidomics, especially for minor species such as sphingoid bases and sphingosine-1-phosphate. Although several liquid chromatography-mass spectrometry methods enabling the determination of sphingolipid molecular species have been reported, they were limited in analytical sensitivity and reproducibility by causing significant peak tailing, especially by the presence of phosphate groups, and most of the extraction techniques are laborious and do not cover a broad range of sphingolipid metabolites. In this study, we developed a rapid single-phase extraction and highly sensitive analytical method for the detection and quantification of sphingolipids (including phosphates) comprehensively using liquid chromatography-triple quadruple mass spectrometry. After validating the reliability of the method, we analyzed the intestinal tissue sphingolipids of germ-free (GF) and specific pathogen-free (SPF) mice and found significantly higher levels of free sphingoid bases and sphingosine-1-phosphate in the GF condition as compared to the SPF condition. This method enables a rapid extraction and highly sensitive determination of sphingolipids comprehensively at low femtomolar ranges. Graphical abstract Diagrammatic comparision of sphingolipid (phosphates) analysis between conventional and this method.

Anti-melanogenic activity of phytosphingosine via the modulation of the microphthalmia-associated transcription factor signaling pathway

BACKGROUND

Microphthalmia-associated transcription factor (MITF) suppresses the expression of enzymes controlling the production of melanin. Phytosphingosine is a well-known cosmetic agent, but its anti-melanogenic activity and mechanism of action remain unclear.

OBJECTIVE

This study was designed to investigate the effects of phytosphingosine on melanin synthesis and elucidate the plausible mechanism of actions in vitro and ex vivo systems.

METHODS

Melanin content, cell viability, tyrosinase activity, p-CREB DNA binding activity, and the protein gene expression levels of the enzymes and proteins involved in melanogenesis were measured with the treatment of phytosphingosine.

RESULTS

Phytosphingosine inhibits melanin synthesis in cultured melan-a cells and a reconstructed human skin model. One possible mechanism of the anti-melanogenic activity of phytosphingosine appears to be associated with the modulation of MITF, which suppresses the expression of tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2. Further analysis revealed that phytosphingosine suppressed paired box 3 and SRY-related HMG-box 10, critical transcription factors of MITF. Phytosphingosine also effectively downregulated the protein levels of β-catenin and the phospho-cAMP response element binding protein, an upstream regulatory factor of MITF. These results are closely related to the suppression of MITF gene expression. In addition, treatment with phytosphingosine for over 12h, which is a relatively long period of time, did not directly suppress these MITF transcriptional factors. Instead, phytosphingosine induced ERK activation, which led to MITF phosphorylation, followed by its degradation. Therefore, the downregulation of MITF protein levels by phytosphingosine with a long time exposure is in part associated with MITF protein degradation through the MAPK kinase activation pathway.

CONCLUSION

The modulation of MITF by phytosphingosine is closely related with the signaling pathways, such as the suppression of the MITF gene expression and the degradation of the MITF protein, depending on the duration of treatment time. These results suggest that phytosphingosine might serve as an effective melanogenesis inhibitor in melanocytes via the regulation of the MITF signaling pathways.

Toxin distribution and sphingoid base imbalances in Fusarium verticillioides-infected and fumonisin B1-watered maize seedlings

Fusarium verticillioides is a major maize pathogen and there are susceptible and resistant cultivars to this fungal infection. Recent studies suggest that its main mycotoxin fumonisin B1 (FB1) may be involved in phytopathogenicity, but the underlying mechanisms are mostly still unknown. This work was aimed at assessing whether FB1 disseminates inside the plants, as well as identifying possible correlations between the maize resistant/susceptible phenotype and the unbalances of the FB1-structurally-related sphingoid base sphinganine (Sa) and phytosphingosine (Pso) due to toxin accumulation. Resistant (RH) and susceptible hybrid (SH) maize seedlings grown from seeds inoculated with a FB1-producer F. verticillioides and from uninoculated ones irrigated with FB1 (20 ppm), were harvested at 7, 14 and 21 days after planting (dap), and the FB1, Sa and Pso levels were quantified in roots and aerial parts. The toxin was detected in roots and aerial parts for inoculated and FB1-irrigated plants of both hybrids. However, FB1 levels were overall higher in SH seedlings regardless of the treatment (infection or watering). Sa levels increased substantially in RH lines, peaking at 54-fold in infected roots at 14 dap. In contrast, the main change observed in SH seedlings was an increase of Pso in infected roots at 7 dap. Here, it was found that FB1 disseminates inside seedlings in the absence of FB1-producer fungal infections, perhaps indicating this might condition the fungus-plant interaction before the first contact. Furthermore, the results strongly suggest the existence of at least two ceramide synthase isoforms in maize with different substrate specificities, whose differential expression after FB1 exposure could be closely related to the susceptibility/resistance to F. verticillioides.

Differential cytotoxicity of long-chain bases for human oral gingival epithelial keratinocytes, oral fibroblasts, and dendritic cells

Long-chain bases, found in the oral cavity, have potent antimicrobial activity against oral pathogens. In an article associated with this dataset, Poulson and colleagues determined the cytotoxicities of long-chain bases (sphingosine, dihydrosphingosine, and phytosphingosine) for human oral gingival epithelial (GE) keratinocytes, oral gingival fibroblasts (GF), dendritic cells (DC), and squamous cell carcinoma (SCC) cell lines [1]. Poulson and colleagues found that GE keratinocytes were more resistant to long-chain bases as compared to GF, DC, and SCC cell lines [1]. In this study, we assess the susceptibility of DC to lower concentrations of long chain bases. 0.2–10.0 µM long-chain bases and GML were not cytotoxic to DC; 40.0–80.0 µM long-chain bases, but not GML, were cytotoxic for DC; and 80.0 µM long-chain bases were cytotoxic to DC and induced cellular damage and death in less than 20 mins. Overall, the LD₅₀ of long-chain bases for GE keratinocytes, GF, and DC were considerably higher than their minimal inhibitory concentrations for oral pathogens, a finding important to pursuing their future potential in treating periodontal and oral infections.

Hypoxia remodels the composition of the constituent ceramide species of HexCer and Hex2Cer with phytosphingosine and hydroxy fatty acids in human colon cancer LS174T cells

Oxygen-requiring enzymes, such as Δ4-desaturase (dihydroceramide desaturase), sphingolipid Δ4-desaturase/C-4-hydroxylase, and fatty acid 2-hydroxylase are involved in ceramide synthesis. We prepared free ceramides, sphingomyelins and glycosphingolipids (GSLs) from cancer cells cultivated under conditions of normoxia and hypoxia, and analyzed these compounds using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Human colon cancer LS174T cells were employed because these cells highly express hydroxyl fatty acids and phytosphingosine (t18:0) which are expected to be greatly influenced by changes in oxygen levels. As expected, the populations of dihydro-species of free ceramide and sphingomyelin with C16:0 non-hydroxy fatty acid were elevated, and the populations of HexCers and Hex2Cers, composed of C16:0 or C16:0 hydroxy fatty acid (C16:0h), and sphingosine (d18:1) or t18:0, were decreased under hypoxia. However, appreciable populations of HexCer and Hex2Cer species of C24:0 or C24:0h and t18:0 remained. These results suggest that the individual species of GSLs with fatty acids possessing different alkyl chain lengths, either non-hydroxy fatty acids or hydroxyl fatty acids, may be metabolized individually.

Differential cytotoxicity of long-chain bases for human oral gingival epithelial keratinocytes, oral fibroblasts, and dendritic cells

Long-chain bases are present in the oral cavity. Previously we determined that sphingosine, dihydrosphingosine, and phytosphingosine have potent antimicrobial activity against oral pathogens. Here, we determined the cytotoxicities of long-chain bases for oral cells, an important step in considering their potential as antimicrobial agents for oral infections. This information would clearly help in establishing prophylactic or therapeutic doses. To assess this, human oral gingival epithelial (GE) keratinocytes, oral gingival fibroblasts (GF), and dendritic cells (DC) were exposed to 10.0-640.0 μM long-chain bases and glycerol monolaurate (GML). The effects of long-chain bases on cell metabolism (conversion of resazurin to resorufin), membrane permeability (uptake of propidium iodide or SYTOX-Green), release of cellular contents (LDH), and cell morphology (confocal microscopy) were all determined. GE keratinocytes were more resistant to long-chain bases as compared to GF and DC, which were more susceptible. For DC, 0.2-10.0 μM long-chain bases and GML were not cytotoxic; 40.0-80.0 μM long-chain bases, but not GML, were cytotoxic; and 80.0 μM long-chain bases induced cellular damage and death in less than 20 min. The LD50 of long-chain bases for GE keratinocytes, GF, and DC were considerably higher than their minimal inhibitory concentrations for oral pathogens, a finding important to pursuing their future potential in treating periodontal and oral infections.

The roles of cutaneous lipids in host defense

Lauric acid (C12:0) and sapienic acid (C16:1Δ6) derived from human sebaceous triglycerides are potent antimicrobials found at the human skin surface. Long-chain bases (sphingosine, dihydrosphingosine and 6-hydroxysphingosine) are also potent and broad-acting antimicrobials normally present at the skin surface. These antimicrobials are generated through the action of ceramidases on ceramides from the stratum corneum. These natural antimicrobials are thought to be part of the innate immune system of the skin. Exogenously providing these lipids to the skin may provide a new therapeutic option, or could potentially provide prophylaxis in people at risk of infection. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.