Ceramide 1-Phosphate Increases P-Glycoprotein Transport Activity at the Blood-Brain Barrier via Prostaglandin E2 Signaling

Bioactive sphingolipids as emerging targets for signal transduction in cancer development

Sphingolipids, crucial components of cellular membranes, play a vital role in maintaining cellular structure and signaling integrity. Disruptions in sphingolipid metabolism are increasingly implicated in cancer development. Key bioactive sphingolipids, such as ceramides, sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), and glycosphingolipids, profoundly impact tumor biology. They influence the behavior of tumor cells, stromal cells, and immune cells, affecting tumor aggressiveness, angiogenesis, immune modulation, and extracellular matrix remodeling. Furthermore, abnormal expression of sphingolipids and their metabolizing enzymes modulates the secretion of tumor-derived extracellular vesicles (TDEs), which are key players in creating an immunosuppressive tumor microenvironment, remodeling the extracellular matrix, and facilitating oncogenic signaling within in situ tumors and distant pre-metastatic niches (PMNs). Understanding the role of sphingolipids in the biogenesis of tumor-derived extracellular vesicles (TDEs) and their bioactive contents can pave the way for new biomarkers in cancer diagnosis and prognosis, ultimately enhancing comprehensive tumor treatment strategies.

ABCB1 and ABCG2 Regulation at the Blood-Brain Barrier: Potential New Targets to Improve Brain Drug Delivery

The drug efflux transporters ABCB1 and ABCG2 at the blood-brain barrier limit the delivery of drugs into the brain. Strategies to overcome ABCB1/ABCG2 have been largely unsuccessful, which poses a tremendous clinical problem to successfully treat central nervous system (CNS) diseases. Understanding basic transporter biology, including intracellular regulation mechanisms that control these transporters, is critical to solving this clinical problem.In this comprehensive review, we summarize current knowledge on signaling pathways that regulate ABCB1/ABCG2 at the blood-brain barrier. In Section I, we give a historical overview on blood-brain barrier research and introduce the role that ABCB1 and ABCG2 play in this context. In Section II, we summarize the most important strategies that have been tested to overcome the ABCB1/ABCG2 efflux system at the blood-brain barrier. In Section III, the main component of this review, we provide detailed information on the signaling pathways that have been identified to control ABCB1/ABCG2 at the blood-brain barrier and their potential clinical relevance. This is followed by Section IV, where we explain the clinical implications of ABCB1/ABCG2 regulation in the context of CNS disease. Lastly, in Section V, we conclude by highlighting examples of how transporter regulation could be targeted for therapeutic purposes in the clinic. SIGNIFICANCE STATEMENT: The ABCB1/ABCG2 drug efflux system at the blood-brain barrier poses a significant problem to successful drug delivery to the brain. The article reviews signaling pathways that regulate blood-brain barrier ABCB1/ABCG2 and could potentially be targeted for therapeutic purposes.

Dysregulated lipid metabolism in TMZ-resistant glioblastoma: pathways, proteins, metabolites and therapeutic opportunities

Glioblastoma (GBM) is a highly aggressive and lethal brain tumor with limited treatment options, such as the chemotherapeutic agent, temozolomide (TMZ). However, many GBM tumors develop resistance to TMZ, which is a major obstacle to effective therapy. Recently, dysregulated lipid metabolism has emerged as an important factor contributing to TMZ resistance in GBM. The dysregulation of lipid metabolism is a hallmark of cancer and alterations in lipid metabolism have been linked to multiple aspects of tumor biology, including proliferation, migration, and resistance to therapy. In this review, we aimed to summarize current knowledge on lipid metabolism in TMZ-resistant GBM, including key metabolites and proteins involved in lipid synthesis, uptake, and utilization, and recent advances in the application of metabolomics to study lipid metabolism in GBM. We also discussed the potential of lipid metabolism as a target for novel therapeutic interventions. Finally, we highlighted the challenges and opportunities associated with developing these interventions for clinical use, and the need for further research to fully understand the role of lipid metabolism in TMZ resistance in GBM. Our review suggests that targeting dysregulated lipid metabolism may be a promising approach to overcome TMZ resistance and improve outcomes in patients with GBM.

Regulation of P-Glycoprotein in the Brain

Maintenance of the tightly regulated homeostatic environment of the brain is facilitated by the blood-brain barrier (BBB). P-glycoprotein (P-gp), an ATP-binding cassette transporter, is expressed on the luminal surface of the endothelial cells in the BBB, and actively exports a wide variety of substrates to limit exposure of the vulnerable brain environment to waste buildup and neurotoxic compounds. Downregulation of P-gp expression and activity at the BBB have been reported with ageing and in neurodegenerative diseases. Upregulation of P-gp at the BBB contributes to poor therapeutic outcomes due to altered pharmacokinetics of CNS-acting drugs. The regulation of P-gp is highly complex, but unravelling the mechanisms involved may help the development of novel and nuanced strategies to modulate P-gp expression for therapeutic benefit. This review summarises the current understanding of P-gp regulation in the brain, encompassing the transcriptional, post-transcriptional and post-translational mechanisms that have been identified to affect P-gp expression and transport activity.

Dysfunction of ABC Transporters at the Surface of BBB: Potential Implications in Intractable Epilepsy and Applications of Nanotechnology Enabled Drug Delivery

Epilepsy is a chronic neurological disorder affecting 70 million people globally. One of the fascinating attributes of brain microvasculature is the (BBB), which controls a chain of distinct features that securely regulate the molecules, ions, and cells movement between the blood and the parenchyma. The barrier's integrity is of paramount importance and essential for maintaining brain homeostasis, as it offers both physical and chemical barriers to counter pathogens and xenobiotics. Dysfunction of various transporters in the (BBB), mainly ATP binding cassette (ABC), is considered to play a vital role in hampering the availability of antiepileptic drugs into the brain. ABC (ATP-binding cassette) transporters constitute a most diverse protein superfamily, which plays an essential part in various biological processes, including cell homeostasis, cell signaling, uptake of nutrients, and drug metabolism. Moreover, it plays a crucial role in neuroprotection by out-flowing various internal and external toxic substances from the interior of a cell, thus decreasing their buildup inside the cell. In humans, forty-eight ABC transporters have been acknowledged and categorized into subfamilies A to G based on their phylogenetic analysis. ABC subfamilies B, C, and G, impart a vital role at the BBB in guarding the brain against the entrance of various xenobiotic and their buildup. The illnesses of the central nervous system have received a lot of attention lately Owing to the existence of the BBB, the penetration effectiveness of most CNS medicines into the brain parenchyma is very limited (BBB). In the development of neurological therapies, BBB crossing for medication delivery to the CNS continues to be a major barrier. Nanomaterials with BBB cross ability have indeed been extensively developed for the treatment of CNS diseases due to their advantageous properties. This review will focus on multiple possible factors like inflammation, oxidative stress, uncontrolled recurrent seizures, and genetic polymorphisms that result in the deregulation of ABC transporters in epilepsy and nanotechnology-enabled delivery across BBB in epilepsy.

A Comprehensive Analysis of Metabolomics and Transcriptomics Reveals Novel Biomarkers and Mechanistic Insights on Lorlatinib Crosses the Blood-Brain Barrier

Of late, lorlatinib has played an increasingly pivotal role in the treatment of brain metastasis from non-small cell lung cancer. However, its pharmacokinetics in the brain and the mechanism of entry are still controversial. The purpose of this study was to explore the mechanisms of brain penetration by lorlatinib and identify potential biomarkers for the prediction of lorlatinib concentration in the brain. Detection of lorlatinib in lorlatinib-administered mice and control mice was performed using liquid chromatography and mass spectrometry. Metabolomics and transcriptomics were combined to investigate the pathway and relationships between metabolites and genes. Multilayer perceptron was applied to construct an artificial neural network model for prediction of the distribution of lorlatinib in the brain. Nine biomarkers related to lorlatinib concentration in the brain were identified. A metabolite-reaction-enzyme-gene interaction network was built to reveal the mechanism of lorlatinib. A multilayer perceptron model based on the identified biomarkers provides a prediction accuracy rate of greater than 85%. The identified biomarkers and the neural network constructed with these metabolites will be valuable for predicting the concentration of drugs in the brain. The model provides a lorlatinib to treat tumor brain metastases in the clinic.

Probable Causes of Alzheimer’s Disease

A three-part mechanism is proposed for the induction of Alzheimer’s disease: (1) decreased blood lactic acid; (2) increased blood ceramide and adipokines; (3) decreased blood folic acid. The age-related nature of these mechanisms comes from age-associated decreased muscle mass, increased visceral fat and changes in diet. This mechanism also explains why many people do not develop Alzheimer’s disease. Simple changes in lifestyle and diet can prevent Alzheimer’s disease. Alzheimer’s disease is caused by a cascade of events that culminates in damage to the blood–brain barrier and damage to neurons. The blood–brain barrier keeps toxic molecules out of the brain and retains essential molecules in the brain. Lactic acid is a nutrient to the brain and is produced by exercise. Damage to endothelial cells and pericytes by inadequate lactic acid leads to blood–brain barrier damage and brain damage. Inadequate folate intake and oxidative stress induced by activation of transient receptor potential cation channels and endothelial nitric oxide synthase damage the blood–brain barrier. NAD depletion due to inadequate intake of nicotinamide and alterations in the kynurenine pathway damages neurons. Changes in microRNA levels may be the terminal events that cause neuronal death leading to Alzheimer’s disease. A new mechanism of Alzheimer’s disease induction is presented involving lactic acid, ceramide, IL-1β, tumor necrosis factor α, folate, nicotinamide, kynurenine metabolites and microRNA.

Sphingolipids as critical players in retinal physiology and pathology

Sphingolipids have emerged as bioactive lipids involved in the regulation of many physiological and pathological processes. In the retina, they have been established to participate in numerous processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Dysregulation of sphingolipids is therefore crucial in the onset and progression of retinal diseases. This review examines the involvement of sphingolipids in retinal physiology and diseases. Ceramide (Cer) has emerged as a common mediator of inflammation and death of neuronal and retinal pigment epithelium cells in animal models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. Sphingosine-1-phosphate (S1P) has opposite roles, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1-phosphate may also contribute to uveitis. Notably, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), preserves neuronal viability and retinal function. These findings underscore the relevance of alterations in the sphingolipid metabolic network in the etiology of multiple retinopathies and highlight the potential of modulating their metabolism for the design of novel therapeutic approaches.

Distinctive sphingolipid patterns in chronic multiple sclerosis lesions

Multiple sclerosis (MS) is a CNS disease characterized by immune-mediated demyelination and progressive axonal loss. MS-related CNS damage and its clinical course have two main phases: active and inactive/progressive. Reliable biomarkers are being sought to allow identification of MS pathomechanisms and prediction of its course. The purpose of this study was to identify sphingolipid (SL) species as candidate biomarkers of inflammatory and neurodegenerative processes underlying MS pathology. We performed sphingolipidomic analysis by HPLC-tandem mass spectrometry to determine the lipid profiles in post mortem specimens from the normal-appearing white matter (NAWM) of the normal CNS (nCNS) from subjects with chronic MS (active and inactive lesions) as well as from patients with other neurological diseases. Distinctive SL modification patterns occurred in specimens from MS patients with chronic inactive plaques with respect to NAWM from the nCNS and active MS (Ac-MS) lesions. Chronic inactive MS (In-MS) lesions were characterized by decreased levels of dihydroceramide (dhCer), ceramide (Cer), and SM subspecies, whereas levels of hexosylceramide and Cer 1-phosphate (C1P) subspecies were significantly increased in comparison to NAWM of the nCNS as well as Ac-MS plaques. In contrast, Ac-MS lesions were characterized by a significant increase of major dhCer subspecies in comparison to NAWM of the nCNS. These results suggest the existence of different SL metabolic pathways in the active versus inactive phase within progressive stages of MS. Moreover, they suggest that C1P could be a new biomarker of the In-MS progressive phase, and its detection may help to develop future prognostic and therapeutic strategies for the disease.

Dysfunction of ABC transporters at the blood-brain barrier: Role in neurological disorders

ABC (ATP-binding cassette) transporters represent one of the largest and most diverse superfamily of proteins in living species, playing an important role in many biological processes such as cell homeostasis, cell signaling, drug metabolism and nutrient uptake. Moreover, using the energy generated from ATP hydrolysis, they mediate the efflux of endogenous and exogenous substrates from inside the cells, thereby reducing their intracellular accumulation. At present, 48 ABC transporters have been identified in humans, which were classified into 7 different subfamilies (A to G) according to their phylogenetic analysis. Nevertheless, the most studied members with importance in drug therapeutic efficacy and toxicity include P-glycoprotein (P-gp), a member of the ABCB subfamily, the multidrug-associated proteins (MPRs), members of the ABCC subfamily, and breast cancer resistance protein (BCRP), a member of the ABCG subfamily. They exhibit ubiquitous expression throughout the human body, with a special relevance in barrier tissues like the blood-brain barrier (BBB). At this level, they play a physiological function in tissue protection by reducing or limiting the brain accumulation of neurotoxins. Furthermore, dysfunction of ABC transporters, at expression and/or activity level, has been associated with many neurological diseases, including epilepsy, multiple sclerosis, Alzheimer's disease, and amyotrophic lateral sclerosis. Additionally, these transporters are strikingly associated with the pharmacoresistance to central nervous system (CNS) acting drugs, because they contribute to the decrease in drug bioavailability. This article reviews the signaling pathways that regulate the expression and activity of P-gp, BCRP and MRPs subfamilies of transporters, with particular attention at the BBB level, and their mis-regulation in neurological disorders.

The role of the sphingolipid pathway in liver fibrosis: an emerging new potential target for novel therapies

Sphingolipids (SL) are a family of bioactive lipids and a major cellular membrane structural component. SLs include three main compounds: ceramide (Cer), sphingosine (Sp), and sphingosine-1-phosphate (S-1P), all of which have emerging roles in biological functions in cells, especially in the liver. They are under investigation in various liver diseases, including cirrhosis and end-stage liver disease. In this review, we provide an overview on the role of SLs in liver pathobiology and focus on their potential role in the development of hepatic fibrosis. We describe recent evidence and suggest SLs are a promising potential therapeutic target for the treatment of liver disease and fibrosis.

Novel signaling aspects of ceramide 1-phosphate

The bioactive sphingolipid ceramide 1-phosphate (C1P) regulates key physiologic cell functions and is implicated in a number of metabolic alterations and pathological processes. Initial studies using different types of fibroblasts and monocytes/macrophages revealed that C1P was mitogenic and that it promoted cell survival through inhibition of apoptosis. Subsequent studies implicated C1P in inflammatory responses with a specific role as pro-inflammatory agent. Specifically, C1P potently stimulated cytosolic phospholipase A₂ (cPLA₂) resulting in elevation of arachidonic acid and pro-inflammatory eicosanoid levels. However, increasing experimental evidence suggests that C1P can also exert anti-inflammatory actions in some cell types and tissues. Specifically, it has been demonstrated that C1P inhibits the release of pro-inflammatory cytokines and blocks activation of the pro-inflammatory transcription factor NF-κB in some cell types. Moreover, C1P was shown to increase the release of anti-inflammatory interleukin-10 in macrophages, and to overcome airway inflammation and reduce lung emphysema in vivo. Noteworthy, C1P stimulated cell migration, an action that is associated with diverse physiological cell functions, as well as with inflammatory responses and tumor dissemination. More recently, ceramide kinase (CerK), the enzyme that produces C1P in mammalian cells, has been shown to be upregulated during differentiation of pre-adipocytes into mature adipocytes, and that exogenous C1P, acting through a putative Gi protein-coupled receptor, negatively regulates adipogenesis. Although the latter actions seem to be contradictory, it is plausible that exogenous C1P may balance the adipogenic effects of intracellularly generated (CerK-derived) C1P in adipose tissue. The present review highlights novel signaling aspects of C1P and its impact in the regulation of cell growth and survival, inflammation and tumor dissemination.

Tetrabromobisphenol A (TBBPA) Alters ABC Transport at the Blood-Brain Barrier

Tetrabromobisphenol A (TBBPA, CAS No. 79-94-7) is a brominated flame retardant used in 90% of epoxy coated circuit boards. Exposures to TBBPA can induce neurotoxicity and disrupt MAPK, estrogen, thyroid, and PPAR-associated signaling pathways. Because these pathways also regulate transporters of the central nervous system barriers, we sought to determine the effect of TBBPA on the expression and activity of 3 ATP binding cassette (ABC) transporters of the blood-brain barrier (BBB). Using a confocal based assay, we measured the ex vivo and in vivo effects of TBBPA on P-glycoprotein (P-gp), breast cancer resistant protein (BCRP), and multidrug resistance-associated protein 2 (MRP2) transport activity in rat brain capillaries. Our rationale for using a rat model was based on tissue availability, ease of handling, and availability of historical TBBPA toxicokinetic data. We found that TBBPA (1-1000 nM) exposure had no significant effect on multidrug resistance-associated protein 2 transport activity in either sex, suggesting TBBPA does not compromise the physical integrity of the BBB. However, low concentrations of TBBPA (1-100 nM) significantly decreased breast cancer resistant protein transport activity in both sexes. Additionally, TBBPA exposures (1-100 nM), elicited a sex-dependent response in P-gp transport: increasing transport activity in males and decreasing transport activity in females. All TBBPA dependent changes in transport activity were dose- and time-dependent. Inhibitors of either transcription or translation abolished the TBBPA dependent increases in male P-gp transport activity. Western blot and immunofluorescent assays confirmed the TBBPA dependent P-gp increases expression in males and decreases in females. Antagonizing PPAR-γ abolished the TBBPA dependent increases in males but not the decreases in females. However, the decreases in female P-gp transport were blocked by an ER-α antagonist. This work indicates that environmentally relevant concentrations of TBBPA (1-100 nM) alter ABC transporter function at the BBB. Moreover, permeability changes in the BBB can alter brain homeostasis, hinder central nervous system drug delivery, and increase the brain's exposure to harmful xenobiotic toxicants.

Clinical application of ceramide in cancer treatment

Development of innovative strategies for cancer treatment is a pressing public health issue. Despite recent advances, the mechanisms of cancer progression and the resistance to cancer treatment have not been fully elucidated. Sphingolipids, including ceramide and sphingoshin-1-phosphate, are bioactive mediators that regulate cancer cell death and survival through the dynamic balance of what has been termed the 'sphingolipid rheostat'. Specifically, ceramide, which acts as the central hub of sphingolipid metabolism, is generated via three major pathways by many stressors, including anti-cancer treatments, environmental stresses, and cytokines. We have previously shown in breast cancer patients that elevated ceramide correlated with less aggressive cancer phenotypes, leading to a prognostic impact. Recent studies showed that ceramide have the possibility of becoming the reinforcing agent of cancer treatment as well as other roles such as nanoparticles and diagnostic biomarker. We review ceramide as one of the key molecules to investigate in overcoming resistance to current drug therapies and in becoming one of the newest cancer treatments.

Acute pain alters P-glycoprotein-containing protein complexes in rat cerebral microvessels: Implications for P-glycoprotein trafficking

P-glycoprotein (PgP) is the major drug efflux pump in human cerebral microvessels. PgP prevents pathogens, toxins and therapeutic drugs from entering the CNS. Understanding the molecular regulation of PgP activity will suggest novel mechanisms to improve CNS drug delivery. Previously, we found that during peripheral inflammatory pain (PIP) (3 h after λ carrageenan injection in the rat paw), PgP traffics to the cortical microvessel endothelial cell plasma membrane concomitant with increased PgP activity. In the current study, we measured the changes in composition of PgP-containing protein complexes after PIP in rat microvessel isolates. We found that a portion of the PgP is contained in a multi-protein complex that also contains the caveolar proteins CAV1, SDPR, PTRF and PRKCDBP. With PIP, total CAV1 bound to PgP was unchanged; however, phosphorylated CAV1 (Y14P-CAV1) in the complex increased. There were few PgP/CAV1 complexes relative to total PgP and CAV1 in the microvessels suggesting CAV1 bound to PgP is unlikely to affect total PgP activity. However, both PgP and CAV1 trafficked away from the nucleus in response to PIP. These data suggest that P-CAV1 bound to PgP potentially regulates PgP trafficking and contributes to the acute PgP activity increase after a PIP stimulus.

Isolation of Cerebral Capillaries from Fresh Human Brain Tissue

Understanding blood-brain barrier function under physiological and pathophysiological conditions is critical for the development of new therapeutic strategies that hold the promise to enhance brain drug delivery, improve brain protection, and treat brain disorders. However, studying the human blood-brain barrier function is challenging. Thus, there is a critical need for appropriate models. In this regard, brain capillaries isolated from human brain tissue represent a unique tool to study barrier function as close to the human in vivo situation as possible. Here, we describe an optimized protocol to isolate capillaries from human brain tissue at a high yield and with consistent quality and purity. Capillaries are isolated from fresh human brain tissue using mechanical homogenization, density-gradient centrifugation, and filtration. After the isolation, the human brain capillaries can be used for various applications including leakage assays, live cell imaging, and immune-based assays to study protein expression and function, enzyme activity, or intracellular signaling. Isolated human brain capillaries are a unique model to elucidate the regulation of the human blood-brain barrier function. This model can provide insights into central nervous system (CNS) pathogenesis, which will help the development of therapeutic strategies for treating CNS disorders.

A Simple and Reproducible Method to Prepare Membrane Samples from Freshly Isolated Rat Brain Microvessels

The blood-brain barrier (BBB) is a dynamic barrier tissue that responds to various pathophysiological and pharmacological stimuli. Such changes resulting from these stimuli can greatly modulate drug delivery to the brain and, by extension, cause considerable challenges in the treatment of central nervous system (CNS) diseases. Many BBB changes that affect pharmacotherapy, involve proteins that are localized and expressed at the level of endothelial cells. Indeed, such knowledge on BBB physiology in health and disease has sparked considerable interest in the study of these membrane proteins. From a basic science research standpoint, this implies a requirement for a simple but robust and reproducible method for isolation of microvessels from brain tissue harvested from experimental animals. In order to prepare membrane samples from freshly isolated microvessels, it is essential that sample preparations be enriched in endothelial cells but limited in the presence of other cell types of the neurovascular unit (i.e., astrocytes, microglia, neurons, pericytes). An added benefit is the ability to prepare samples from individual animals in order to capture the true variability of protein expression in an experimental population. In this manuscript, details regarding a method that is utilized for isolation of rat brain microvessels and preparation of membrane samples are provided. Microvessel enrichment, from samples derived, is achieved by using four centrifugation steps where dextran is included in the sample buffer. This protocol can easily be adapted by other laboratories for their own specific applications. Samples generated from this protocol have been shown to yield robust experimental data from protein analysis experiments that can greatly aid the understanding of BBB responses to physiological, pathophysiological, and pharmacological stimuli.

Sphingolipid Metabolism: A New Therapeutic Opportunity for Brain Degenerative Disorders

Neurodegenerative diseases represent a class of fatal brain disorders for which the number of effective therapeutic options remains limited with only symptomatic treatment accessible. Multiple studies show that defects in sphingolipid pathways are shared among different brain disorders including neurodegenerative diseases and may contribute to their complex pathogenesis. In this mini review, we discuss the hypothesis that modulation of sphingolipid metabolism and their related signaling pathways may represent a potential therapeutic approach for those devastating conditions. The plausible “druggability” of sphingolipid pathways is greatly promising and represent a relevant feature that brings real advantage to the development of new therapeutic options for these conditions. Indeed, several molecules that selectively target sphingolipds are already available and many of them currently in clinical trial for human diseases. A deeper understanding of the “sphingolipid scenario” in neurodegenerative disorders would certainly enhance therapeutic perspectives for these conditions, by taking advantage from the already available molecules and by promoting the development of new ones.

mPEG-PLA/TPGS mixed micelles via intranasal administration improved the bioavailability of lamotrigine in the hippocampus

Purpose

This study aimed to develop a novel methoxy poly(ethylene glycol)-poly(lactide) (mPEG-PLA)/D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) mixed micelle drug delivery system to improve lamotrigine (LTG) distribution in the hippocampus.

Methods

LTG-loaded mPEG-PLA/TPGS mixed micelles and LTG-loaded mPEG-PLA micelles were formulated, and their characteristics, particle size, surface morphology, and release behavior in vitro were researched. Then, a microdialysis sampling technique coupled with two validated chromatographic systems was developed for the continuous measurement of the protein-unbound form of LTG in the rat plasma and hippocampus after administering two kinds of micelles and LTG solution intranasally.

Results

The drug loading and mean size of LTG-loaded micelles and LTG-loaded mixed micelles prepared with optimal formulation were 36.44%±0.14%, 39.28%±0.26%, 122.9, and 183.5 nm, respectively, with a core–shell structure. The cumulative release rate in vivo of LTG-loaded mixed micelles was 84.21% at 24 hours and showed more sustained release while that of LTG-loaded micelles was 80.61% at 6 hours. The T_max and area under concentration-time curve from zero to time of last quantifiable concentration of LTG solution, LTG-loaded micelles, and LTG-loaded mixed micelles were 55, 35, and 15 minutes and about 5,384, 16,500, and 25,245 (min⋅μg)/L in the hippocampus, respectively.

Conclusion

The results revealed that LTG-loaded mPEG-PLA/TPGS mixed micelles enhanced the absorption of LTG at the nasal cavity and reduced the efflux of LTG in the brain, suggesting that the function of TPGS inhibited P-glycoprotein and LTG-loaded mPEG-PLA/TPGS mixed micelles had the potential to overcome refractory epilepsy.

The Role of Sphingosine-1-Phosphate and Ceramide-1-Phosphate in Inflammation and Cancer

Inflammation is part of our body's response to tissue injury and pathogens. It helps to recruit various immune cells to the site of inflammation and activates the production of mediators to mobilize systemic protective processes. However, chronic inflammation can increase the risk of diseases like cancer. Apart from cytokines and chemokines, lipid mediators, particularly sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P), contribute to inflammation and cancer. S1P is an important player in inflammation-associated colon cancer progression. On the other hand, C1P has been recognized to be involved in cancer cell growth, migration, survival, and inflammation. However, whether C1P is involved in inflammation-associated cancer is not yet established. In contrast, few studies have also suggested that S1P and C1P are involved in anti-inflammatory pathways regulated in certain cell types. Ceramide is the substrate for ceramide kinase (CERK) to yield C1P, and sphingosine is phosphorylated to S1P by sphingosine kinases (SphKs). Biological functions of sphingolipid metabolites have been studied extensively. Ceramide is associated with cell growth inhibition and enhancement of apoptosis while S1P and C1P are associated with enhancement of cell growth and survival. Altogether, S1P and C1P are important regulators of ceramide level and cell fate. This review focuses on S1P and C1P involvement in inflammation and cancer with emphasis on recent progress in the field.