Effects of Nutraceuticals on Cisplatin-Induced Cytotoxicity in HEI-OC1 Cells

Cisplatin is a chemotherapeutic drug for the treatment of several solid tumors, whose use is limited by its nephrotoxicity, neurotoxicity, ototoxicity, and development of resistance. The toxicity is caused by DNA cross-linking, increase in reactive oxygen species and/or depletion of cell antioxidant defenses. The aim of the work was to study the effect of antioxidant compounds (Lisosan G, Taurisolo®) or hydrogen sulfide (H2S)-releasing compounds (erucin) in the auditory HEI-OC1 cell line treated with cisplatin. Cell viability was determined using the MTT assay. Caspase and sphingomyelinase activities were measured by fluorometric and colorimetric methods, respectively. Expression of transcription factors, apoptosis hallmarks and genes codifying for antioxidant response proteins were measured by Western blot and/or RT-qPCR. Lisosan G, Taurisolo® and erucin did not show protective effects. Sodium hydrosulfide (NaHS), a donor of H2S, increased the viability of cisplatin-treated cells and the transcription of heme oxygenase 1, superoxide dismutase 2, NAD(P)H quinone dehydrogenase type 1 and the catalytic subunit of glutamate-cysteine ligase and decreased reactive oxygen species (ROS), the Bax/Bcl2 ratio, caspase-3, caspase-8 and acid sphingomyelinase activity. Therefore, NaHS might counteract the cytotoxic effect of cisplatin by increasing the antioxidant response and by reducing ROS levels and caspase and acid sphingomyelinase activity.

Inborn Errors of Purine Salvage and Catabolism

Cellular purine nucleotides derive mainly from de novo synthesis or nucleic acid turnover and, only marginally, from dietary intake. They are subjected to catabolism, eventually forming uric acid in humans, while bases and nucleosides may be converted back to nucleotides through the salvage pathways. Inborn errors of the purine salvage pathway and catabolism have been described by several researchers and are usually referred to as rare diseases. Since purine compounds play a fundamental role, it is not surprising that their dysmetabolism is accompanied by devastating symptoms. Nevertheless, some of these manifestations are unexpected and, so far, have no explanation or therapy. Herein, we describe several known inborn errors of purine metabolism, highlighting their unexplained pathological aspects. Our intent is to offer new points of view on this topic and suggest diagnostic tools that may possibly indicate to clinicians that the inborn errors of purine metabolism may not be very rare diseases after all.

Brain and gut microbiota disorders in the psychopathology of anorexia nervosa

Studies of pathophysiological mechanisms involved in eating disorders (EDs) have intensified over the past several years, revealing their unprecedented and unanticipated complexity. Results from many articles highlight critical aspects in each member of ED family. Notably, anorexia nervosa (AN) is a disorder due to undefined etiology, frequently associated with symptoms of depression, anxiety, obsessive-compulsiveness, accompanied by endocrine alterations, altered immune response, increased inflammation, and dysbiosis of the gut microbiota. Hence, an advanced knowledge of how and why a multisystem involvement exists is of paramount importance to understand the pathogenetic mechanisms of AN. In this review, we describe the change in the brain structure/function focusing on hypothalamic endocrine disorders and the disequilibrium of gut microbiota in AN that might be responsible for the psychopathological complication.

The Good, the Bad and the New about Uric Acid in Cancer

Simple Summary

The concentration of uric acid in blood is sex-, age- and diet-dependent and is maintained close to its maximal solubility, indicating that it plays some important role. Indeed, it has been demonstrated that, at physiological concentrations, uric acid is a powerful antioxidant and is a scavenger of singlet oxygen and radicals. At high intracellular concentration, uric acid has been demonstrated to act as a pro-oxidant molecule. Recently, uric acid has been reported to affect the properties of several proteins involved in metabolic regulation and signaling, and the relationship between uric acid and cancer has been extensively investigated. In this review, we present the most recent results on the positive and negative effects played by uric acid in cancer and some new findings and hypotheses about the implication of this metabolite in the pathogenesis of several diseases such as metabolic syndrome, diabetes, and inflammation, thus favoring the development of cancer.

Abstract

Uric acid is the final product of purine catabolism in man and apes. The serum concentration of uric acid is sex-, age- and diet-dependent and is maintained close to its maximal solubility, indicating that it plays some important role. Indeed, it has been demonstrated that, at physiological concentrations, uric acid is a powerful antioxidant, while at high intracellular concentrations, it is a pro-oxidant molecule. In this review, we describe the possible causes of uric acid accumulation or depletion and some of the metabolic and regulatory pathways it may impact. Particular attention has been given to fructose, which, because of the complex correlation between carbohydrate and nucleotide metabolism, causes uric acid accumulation. We also present recent results on the positive and negative effects played by uric acid in cancer and some new findings and hypotheses about the implication of this metabolite in a variety of signaling pathways, which can play a role in the pathogenesis of diseases such as metabolic syndrome, diabetes, and inflammation, thus favoring the development of cancer. The loss of uricase in Homo sapiens and great apes, although exposing these species to the potentially adverse effects of uric acid, appears to be associated with evolutionary advantages.

Skeletal Muscle and COVID-19: The Potential Involvement of Bioactive Sphingolipids

SARS-CoV-2 virus infection is the cause of the coronavirus disease 2019 (COVID-19), which is still spreading over the world. The manifestation of this disease can range from mild to severe and can be limited in time (weeks) or persist for months in about 30–50% of patients. COVID-19 is considered a multiple organ dysfunction syndrome and the musculoskeletal system manifestations are beginning to be considered of absolute importance in both COVID-19 patients and in patients recovering from the SARS-CoV-2 infection. Musculoskeletal manifestations of COVID-19 and other coronavirus infections include loss of muscle mass, muscle weakness, fatigue or myalgia, and muscle injury. The molecular mechanisms by which SARS-CoV-2 can cause damage to skeletal muscle (SkM) cells are not yet well understood. Sphingolipids (SLs) represent an important class of eukaryotic lipids with structural functions as well as bioactive molecules able to modulate crucial processes, including inflammation and viral infection. In the last two decades, several reports have highlighted the role of SLs in modulating SkM cell differentiation, regeneration, aging, response to insulin, and contraction. This review summarizes the consequences of SARS-CoV-2 infection on SkM and the potential involvement of SLs in the tissue responses to virus infection. In particular, we highlight the role of sphingosine 1-phosphate signaling in order to aid the prediction of novel targets for preventing and/or treating acute and long-term musculoskeletal manifestations of virus infection in COVID-19.

Cytosolic 5'-Nucleotidase II Silencing in Lung Tumor Cells Regulates Metabolism through Activation of the p53/AMPK Signaling Pathway

Cytosolic 5′-nucleotidase II (cN-II) is an allosteric catabolic enzyme that hydrolyzes IMP, GMP, and AMP. The enzyme can assume at least two different structures, being the more active conformation stabilized by ATP and the less active by inorganic phosphate. Therefore, the variation in ATP concentration can control both structure and activity of cN-II. In this paper, using a capillary electrophoresis technique, we demonstrated that a partial silencing of cN-II in a pulmonary carcinoma cell line (NCI-H292) is accompanied by a decrease in adenylate pool, without affecting the energy charge. We also found that cN-II silencing decreased proliferation and increased oxidative metabolism, as indicated by the decreased production of lactate. These effects, as demonstrated by Western blotting, appear to be mediated by both p53 and AMP-activated protein kinase, as most of them are prevented by pifithrin-α, a known p53 inhibitor. These results are in line with our previous observations of a shift towards a more oxidative and less proliferative phenotype of tumoral cells with a low expression of cN-II, thus supporting the search for specific inhibitors of this enzyme as a therapeutic tool for the treatment of tumors.

Metabolic Aspects of Adenosine Functions in the Brain

Adenosine, acting both through G-protein coupled adenosine receptors and intracellularly, plays a complex role in multiple physiological and pathophysiological processes by modulating neuronal plasticity, astrocytic activity, learning and memory, motor function, feeding, control of sleep and aging. Adenosine is involved in stroke, epilepsy and neurodegenerative pathologies. Extracellular concentration of adenosine in the brain is tightly regulated. Adenosine may be generated intracellularly in the central nervous system from degradation of AMP or from the hydrolysis of S-adenosyl homocysteine, and then exit via bi-directional nucleoside transporters, or extracellularly by the metabolism of released nucleotides. Inactivation of extracellular adenosine occurs by transport into neurons or neighboring cells, followed by either phosphorylation to AMP by adenosine kinase or deamination to inosine by adenosine deaminase. Modulation of the nucleoside transporters or of the enzymatic activities involved in the metabolism of adenosine, by affecting the levels of this nucleoside and the activity of adenosine receptors, could have a role in the onset or the development of central nervous system disorders, and can also be target of drugs for their treatment. In this review, we focus on the contribution of 5'-nucleotidases, adenosine kinase, adenosine deaminase, AMP deaminase, AMP-activated protein kinase and nucleoside transporters in epilepsy, cognition, and neurodegenerative diseases with a particular attention on amyotrophic lateral sclerosis and Huntington's disease. We include several examples of the involvement of components of the adenosine metabolism in learning and of the possible use of modulators of enzymes involved in adenosine metabolism or nucleoside transporters in the amelioration of cognition deficits.

Protopine/Gemcitabine Combination Induces Cytotoxic or Cytoprotective Effects in Cell Type-Specific and Dose-Dependent Manner on Human Cancer and Normal Cells

The natural alkaloid protopine (PRO) exhibits pharmacological properties including anticancer activity. We investigated the effects of PRO, alone and in combination with the chemotherapeutic gemcitabine (GEM), on human tumor cell lines and non-tumor human dermal fibroblasts (HDFs). We found that treatments with different PRO/GEM combinations were cytotoxic or cytoprotective, depending on concentration and cell type. PRO/GEM decreased viability in pancreatic cancer MIA PaCa-2 and PANC-1 cells, while it rescued the GEM-induced viability decline in HDFs and in tumor MCF-7 cells. Moreover, PRO/GEM decreased G1, S and G2/M phases, concomitantly with an increase of subG1 phase in MIA PaCa-2 and PANC-1 cells. Differently, PRO/GEM restored the normal progression of the cell cycle, altered by GEM, and decreased cell death in HDFs. PRO alone increased mitochondrial reactive oxygen species (ROS) in MIA PaCa-2, PANC-1 cells and HDFs, while PRO/GEM increased both intracellular and mitochondrial ROS in the three cell lines. These results indicate that specific combinations of PRO/GEM may be used to induce cytotoxic effects in pancreatic tumor MIA PaCa-2 and PANC-1 cells, but have cytoprotective or no effects in HDFs.

SARS-CoV-2 Infection: A Role for S1P/S1P Receptor Signaling in the Nervous System?

The recent coronavirus disease (COVID-19) is still spreading worldwide. The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the virus responsible for COVID-19, binds to its receptor angiotensin-converting enzyme 2 (ACE2), and replicates within the cells of the nasal cavity, then spreads along the airway tracts, causing mild clinical manifestations, and, in a majority of patients, a persisting loss of smell. In some individuals, SARS-CoV-2 reaches and infects several organs, including the lung, leading to severe pulmonary disease. SARS-CoV-2 induces neurological symptoms, likely contributing to morbidity and mortality through unknown mechanisms. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid with pleiotropic properties and functions in many tissues, including the nervous system. S1P regulates neurogenesis and inflammation and it is implicated in multiple sclerosis (MS). Notably, Fingolimod (FTY720), a modulator of S1P receptors, has been approved for the treatment of MS and is being tested for COVID-19. Here, we discuss the putative role of S1P on viral infection and in the modulation of inflammation and survival in the stem cell niche of the olfactory epithelium. This could help to design therapeutic strategies based on S1P-mediated signaling to limit or overcome the host-virus interaction, virus propagation and the pathogenesis and complications involving the nervous system.

Purine-Metabolising Enzymes and Apoptosis in Cancer

The enzymes of both de novo and salvage pathways for purine nucleotide synthesis are regulated to meet the demand of nucleic acid precursors during proliferation. Among them, the salvage pathway enzymes seem to play the key role in replenishing the purine pool in dividing and tumour cells that require a greater amount of nucleotides. An imbalance in the purine pools is fundamental not only for preventing cell proliferation, but also, in many cases, to promote apoptosis. It is known that tumour cells harbour several mutations that might lead to defective apoptosis-inducing pathways, and this is probably at the basis of the initial expansion of the population of neoplastic cells. Therefore, knowledge of the molecular mechanisms that lead to apoptosis of tumoural cells is key to predicting the possible success of a drug treatment and planning more effective and focused therapies. In this review, we describe how the modulation of enzymes involved in purine metabolism in tumour cells may affect the apoptotic programme. The enzymes discussed are: ectosolic and cytosolic 5'-nucleotidases, purine nucleoside phosphorylase, adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase, and inosine-5'-monophosphate dehydrogenase, as well as recently described enzymes particularly expressed in tumour cells, such as deoxynucleoside triphosphate triphosphohydrolase and 7,8-dihydro-8-oxoguanine triphosphatase.

Cytosolic 5'-Nucleotidase II Silencing in a Human Lung Carcinoma Cell Line Opposes Cancer Phenotype with a Concomitant Increase in p53 Phosphorylation

Purine homeostasis is maintained by a purine cycle in which the regulated member is a cytosolic 5'-nucleotidase II (cN-II) hydrolyzing IMP and GMP. Its expression is particularly high in proliferating cells, indeed high cN-II activity or expression in hematological malignancy has been associated to poor prognosis and chemoresistance. Therefore, a strong interest has grown in developing cN-II inhibitors, as potential drugs alone or in combination with other compounds. As a model to study the effect of cN-II inhibition we utilized a lung carcinoma cell line (A549) in which the enzyme was partially silenced and its low activity conformation was stabilized through incubation with 2-deoxyglucose. We measured nucleotide content, reduced glutathione, activities of enzymes involved in glycolysis and Krebs cycle, protein synthesis, mitochondrial function, cellular proliferation, migration and viability. Our results demonstrate that high cN-II expression is associated with a glycolytic, highly proliferating phenotype, while silencing causes a reduction of proliferation, protein synthesis and migration ability, and an increase of oxidative performances. Similar results were obtained in a human astrocytoma cell line. Moreover, we demonstrate that cN-II silencing is concomitant with p53 phosphorylation, suggesting a possible involvement of this pathway in mediating some of cN-II roles in cancer cell biology.

Effect of Vitamin D in HN9.10e Embryonic Hippocampal Cells and in Hippocampus from MPTP-Induced Parkinson's Disease Mouse Model

It has long been proven that neurogenesis continues in the adult brains of mammals in the dentatus gyrus of the hippocampus due to the presence of neural stem cells. Although a large number of studies have been carried out to highlight the localization of vitamin D receptor in hippocampus, the expression of vitamin D receptor in neurogenic dentatus gyrus of hippocampus in Parkinson's disease (PD) and the molecular mechanisms triggered by vitamin D underlying the production of differentiated neurons from embryonic cells remain unknown. Thus, we performed a preclinical in vivo study by inducing PD in mice with MPTP and showed a reduction of glial fibrillary acidic protein (GFAP) and vitamin D receptor in the dentatus gyrus of hippocampus. Then, we performed an in vitro study by inducing embryonic hippocampal cell differentiation with vitamin D. Interestingly, vitamin D stimulates the expression of its receptor. Vitamin D receptor is a transcription factor that probably is responsible for the upregulation of microtubule associated protein 2 and neurofilament heavy polypeptide genes. The latter increases heavy neurofilament protein expression, essential for neurofilament growth. Notably N-cadherin, implicated in activity for dendritic outgrowth, is upregulated by vitamin D.

Crosstalk between sphingolipids and vitamin D3: potential role in the nervous system

Sphingolipids are both structural and bioactive compounds. In particular, ceramide and sphingosine 1-phosphate regulate cell fate, inflammation and excitability. 1-α,25-dihydroxyvitamin D3 (1,25(OH)₂ D₃ ) is known to play an important physiological role in growth and differentiation in a variety of cell types, including neural cells, through genomic actions mediated by its specific receptor, and non-genomic effects that result in the activation of specific signalling pathways. 1,25(OH)₂ D₃ and sphingolipids, in particular sphingosine 1-phosphate, share many common effectors, including calcium regulation, growth factors and inflammatory cytokines, but it is still not known whether they can act synergistically. Alterations in the signalling and concentrations of sphingolipids and 1,25(OH)₂ D₃ have been found in neurodegenerative diseases and fingolimod, a structural analogue of sphingosine, has been approved for the treatment of multiple sclerosis. This review, after a brief description of the role of sphingolipids and 1,25(OH)₂ D₃ , will focus on the potential crosstalk between sphingolipids and 1,25(OH)₂ D₃ in neural cells.

Dolichol-phosphate mannose synthase depletion in zebrafish leads to dystrophic muscle with hypoglycosylated α-dystroglycan

Defective dolichol-phosphate mannose synthase (DPMS) complex is a rare cause of congenital muscular dystrophy associated with hypoglycosylation of alpha-dystroglycan (α-DG) in skeletal muscle. We used the zebrafish (Danio rerio) to model muscle abnormalities due to defects in the subunits of DPMS. The three zebrafish ortholog subunits (encoded by the dpm1, dpm2 and dpm3 genes, respectively) showed high similarity to the human proteins, and their expression displayed localization in the midbrain/hindbrain area and somites. Antisense morpholino oligonucleotides targeting each subunit were used to transiently deplete the dpm genes. The resulting morphant embryos showed early death, muscle disorganization, low DPMS complex activity, and increased levels of apoptotic nuclei, together with hypoglycosylated α-DG in muscle fibers, thus recapitulating most of the characteristics seen in patients with mutations in DPMS. Our results in zebrafish suggest that DPMS plays a role in stabilizing muscle structures and in apoptotic cell death.

Mitochondrial Damage and Apoptosis Induced by Adenosine Deaminase Inhibition and Deoxyadenosine in Human Neuroblastoma Cell Lines

The treatment with deoxycoformycin, a strong adenosine deaminase inhibitor, in combination with deoxyadenosine, causes apoptotic cell death of two human neuroblastoma cell lines, SH-SY5Y and LAN5. Herein we demonstrate that, in SH-SY5Y cells, this combination rapidly decreases mitochondrial reactive oxygen species and, in parallel, increases mitochondrial mass, while, later, induces nuclear fragmentation, and activation of caspase-8, -9, and -3. In previous papers we have shown that a human astrocytoma cell line, subjected to the same treatment, undergoes apoptotic death as well. Therefore, both astrocytoma and neuroblastoma cell lines undergo apoptotic death following the combined treatment with deoxycoformycin and deoxyadenosine, but several differences have been found in the mode of action, possibly reflecting a different functional and metabolic profile of the two cell lines. Overall this work indicates that the neuroblastoma cell lines, like the line of astrocytic origin, are very sensitive to purine metabolism perturbation thus suggesting new therapeutic approaches to nervous system tumors. J. Cell. Biochem. 117: 1671-1679, 2016. © 2015 Wiley Periodicals, Inc.

Nutraceutical properties of chestnut flours: beneficial effects on skeletal muscle atrophy

Plants contain a wide range of non-nutritive phytochemicals, many of which have protective or preventive properties for human diseases. The aim of the present work has been to investigate the nutraceutical properties of sweet chestnut flour extracts obtained from fruits collected from 7 geographic areas of Tuscany (Italy), and their ability in modulating skeletal muscle atrophy. We found that the cultivars from different geographic areas are characterized by the composition and quantity of various nutrients and specific bioactive components, such as tocopherols, polyphenols and sphingolipids. The nutraceutical properties of chestnut sweet flours have been evaluated in C2C12 myotubes induced to atrophy by serum deprivation or dexamethasone. We found that the pretreatment with both total extracts of tocopherols and sphingolipids is able to counterbalance cell atrophy, reducing the decrease in myotube size and myonuclei number, and attenuating protein degradation and the increase in expression of MAFbx/atrogin-1 (a muscle-specific atrophy marker). By contrast, polyphenol extracts were not able to prevent atrophy. Since we also found that γ-tocopherol is the major form of tocopherol in sweet flour and its content differs depending on the procedure of sweet flour preparation, the mechanisms by which γ-tocopherol as well as sphingolipids affect skeletal muscle cell atrophy have been also investigated. This is the first evidence that chestnut sweet flour is a natural source of specific bioactive components with a relevant role in the prevention of cell degeneration and maintenance of skeletal muscle mass, opening important implications in designing appropriate nutritional therapeutic approaches to skeletal muscle atrophy.

Serum deprivation alters lipid profile in HN9.10e embryonic hippocampal cells

The understanding of the mechanism of apoptosis is important to improve the use of stem cells for the treatment of neurodegenerative disorders. Sphingolipids are bioactive molecules involved in the regulation of cell fate. In HN9.10e embryonic hippocampal cells, serum deprivation induces apoptosis preceded by sphingomyelinase activation and raise of ceramide levels. Increasing evidence indicates that individual ceramide species regulated by specific pathways in distinct subcellular compartments might carry out distinct cellular functions, but the ceramides species involved in embryonic hippocampal cell death induced by growth factor deprivation are unknown. In the present paper, by using the UFLC-MS/MS methodology, we have investigated the effect of serum deprivation on the lipid profile in HN9.10e cells. At 48h of serum deprivation, we detected a decrease in cholesterol and increase in sphingosine-1-phoshate 18:1, phosphatidylcholine 18:1 18:0, sphingomyelin 18:1 16:0 and in ceramides 18:1 16:0; we also found an increase in saturated/unsaturated fatty acid ratio in sphingomyelin. We hypothesize that the rearrangement of sphingo- and glycerolipids with increase of saturated fatty acids in serum-deprivated, neural cells might represent a cellular response aimed at holding cholesterol inside the cells.

The combination of adenosine deaminase inhibition and deoxyadenosine induces apoptosis in a human astrocytoma cell line

Alterations in the functions of astrocytes contribute to the appearance of a variety of neurological pathologies. Gliomas, especially those of astrocytic origin, are particularly resistant to chemotherapy and are often characterized by a poor prognosis. Neuroblastoma is the tumour with the higher incidence in infants. Anticancer drugs can induce apoptosis and their cytotoxic effect is often mediated by this process. We have previously demonstrated that the combination of deoxycoformycin, a strong adenosine deaminase inhibitor, and deoxyadenosine is toxic for a human astrocytoma cell line. In fact, after 15 h of treatment, this combination increases both mitochondrial reactive oxygen species and mitochondrial mass, induces apoptosis as indicated by cytochrome c release from mitochondria and activation of caspase-3. These events are preceded by reduction in lactate release in the medium. In this work we demonstrate that after 8 h of incubation with deoxyadenosine and deoxycoformycin, caspase-8 is activated, mitochondrial mass increases and mitochondrial reactive oxygen species decrease. The addition of baicalein to the incubation medium reduces cell death and caspase-3 activity induced by deoxycoformycin and deoxyadenosine in combination. This protective effect is correlated to an increase of lactate released in the medium, a decrease in the intracellular levels of dATP, and an increase in ATP levels, as compared with the cells subjected to the treatment with deoxycoformycin and deoxyadenosine without any further addition. The effect of baicalein appears to be related to an inhibition of deoxyadenosine phosphorylation, rather than or in addition to the well known antioxidant activity of the compound. This work indicates that an astrocytoma cell line, reported to be resistant to mitochondria-dependent pathways of apoptosis, is indeed very sensitive to a manipulation affecting the balance of cellular purine metabolite concentrations. The same treatment is also cytotoxic on a neuroblastoma cell line, thus suggesting long term implications for cancer therapy.

Nuclear lipid microdomain as resting place of dexamethasone to impair cell proliferation

The action of dexamethasone is initiated by, and strictly dependent upon, the interaction of the drug with its receptor followed by its translocation into the nucleus where modulates gene expression. Where the drug localizes at the intranuclear level is not yet known. We aimed to study the localization of the drug in nuclear lipid microdomains rich in sphingomyelin content that anchor active chromatin and act as platform for transcription modulation. The study was performed in non-Hodgkin’s T cell human lymphoblastic lymphoma (SUP-T1 cell line). We found that when dexamethasone enters into the nucleus it localizes in nuclear lipid microdomains where influences sphingomyelin metabolism. This is followed after 24 h by a cell cycle block accompanied by the up-regulation of cyclin-dependent kinase inhibitor 1A (CDKN1A), cyclin-dependent kinase inhibitor 1B (CDKN1B), growth arrest and DNA-damage 45A (GADD45A), and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) genes and by the reduction of signal transducer and activator of transcription 3 (STAT3) and phospho signal transducer and activator of transcription 3 (phoshoSTAT3) proteins. After 48 h some cells show morphological changes characteristic of apoptosis while the number of the cells that undergo cell division and express B-cell lymphoma-2 (Bcl-2) is very low. We suggest that the integrity of nuclear lipid microdomains is important for the response to glucocorticoids of cancer cells.

The descriptive epidemiology of rheumatoid arthritis in Catalonia: a retrospective study using routinely collected data

Information on the epidemiology of rheumatoid arthritis (RA) in Southern Europe is scarce. We estimated the age- and gender-adjusted incidence and prevalence of RA in Catalonia using routinely collected primary care records. We identified incident (2009-2012) and prevalent (on 31 December 2012) cases of RA in the SIDIAP database using ICD-10 codes. SIDIAP contains anonymized data from computerized primary care records for about five million adults (>80 % of the population). We estimated age- (5-year groups) and gender-specific, and directly standardized incidence and prevalence of RA and confidence intervals (95% CIs) assuming a Poisson distribution. A total of 20,091 prevalent (among whom 5,796 incident) cases of RA were identified among 4,796,498 study participants observed for up to 4 years. Rates of RA increased with age in both genders, peaking at the age of 65-70 years. Age- and gender-standardized incidence and prevalence rates were 0.20/1,000 person-years (95% CI 0.19-0.20) and 4.17/1,000 (4.11-4.23) respectively. Rheumatoid factor was positive (≥10 IU/mL) in 1,833 (73.9 %) of 2,482 cases tested in primary care. The incidence and prevalence of RA in Catalonia are similar to those of other Southern European regions, and lower than those of northern areas. This data will inform health care planning and resource allocation.

Knockdown of cytosolic 5'-nucleotidase II (cN-II) reveals that its activity is essential for survival in astrocytoma cells

IMP preferring cytosolic 5'-nucleotidase (cN-II) is an ubiquitous nucleotide hydrolysing enzyme. The enzyme is widely distributed and its amino acid sequence is highly conserved among vertebrates. Fluctuations of cN-II activity have been associated with the pathogenesis of neurological disorders. The enzyme appears to be involved in the regulation of the intracellular availability of the purine precursor IMP and also of GMP and AMP, but the contribution of this activity and of its regulation to cell metabolism and to CNS cell functions remains uncertain. To address this issue, we used a vector based short hairpin RNA (shRNA) strategy to knockdown cN-II activity in human astrocytoma cells. Our results demonstrated that 53 h after transduction, cN-II mRNA was reduced to 17.9+/-0.03% of control cells. 19 h later enzyme activity was decreased from 0.7+/-0.026 mU/mg in control ADF cells to 0.45+/-0.046 mU/mg, while cell viability (evaluated by the MTT reduction assay) decreased up to 0.59+/-0.01 (fold vs control) and caspase 3 activity increased from 136+/-5.8 pmol min(-1) mg(-1) in control cells to 639+/-37.5 pmol min(-1) mg(-1) in silenced cells, thus demonstrating that cN-II is essential for cell survival. The decrease of enzyme activity causes apoptosis of the cultured cells without altering intracellular nucleotide and nucleoside concentration or energy charge. Since cN-II is highly expressed in tumour cells, our finding offers a new possible therapeutical approach especially against primary brain tumours such as glioblastoma, and to ameliorate chemotherapy against leukemia.

Molecular mechanisms of euplotin C-induced apoptosis: involvement of mitochondrial dysfunction, oxidative stress and proteases

The metabolite euplotin C (EC), isolated from the marine ciliate Euplotes crassus, is a powerful cytotoxic and pro-apoptotic agent in tumour cell lines. For instance, EC induces the rapid depletion of ryanodine Ca(2+) stores, the release of cytochrome c from the mitochondria, and the activation of caspase-3, leading to apoptosis. The purpose of this study was to gain further insight into the mechanisms of EC-induced apoptosis in rat pheochromocytoma PC12 cells. We found that EC increases Bax/Bcl-2 ratio and that Bax is responsible of the EC-induced dissipation of the mitochondrial membrane potential (Deltapsi(m)). In addition, EC induces the generation of reactive oxygene species (ROS) without involvement of p53. The inhibition of ROS generation prevents, at least in part, the pro-apoptotic effects of EC as well as the effects of EC on Bax, Deltapsi(m) and intracellular free Ca(2+), indicating a cross-talk between different pathways. However, definition of the effector cascade turns out to be more complex than expected and caspase-independent mechanisms, acting in parallel with caspases, should also be considered. Among them, EC increases the expression/activity of calpains downstream of ROS generation, although calpains seem to exert protective effects.

Serum-withdrawal-dependent apoptosis of hippocampal neuroblasts involves Ca++ release by endoplasmic reticulum and caspase-12 activation

Apoptotic death caused by diseases or toxic insults is preceded and determined by endoplasmic reticulum dysfunction and altered intraluminar calcium homeostasis in many different cell types. With the present study we have explored the possibility that the ER stress could be involved also in apoptotic death induced by serum deprivation in neuronal cells. We have chosen as a model of study the cell line HN9.10e, constituted by immortalized hippocampal neuroblasts. The Ca(++) concentration in the lumen of the ER has been evaluated by using the low affinity Ca(++) probe Mag-fluo-4. We show that serum deprivation lowers the ER Ca(++) concentration with a time course closely related to the increase of apoptosis incidence. Serum deprivation also enhances the expression of a well-known marker of ER stress, the glucose-regulated protein-78 (GRP-78), a member of the heat shock/stress response protein family. Moreover, in serum-deprived neuroblasts, following GRP-78 up-regulation, the ER-associated procaspase-12 is cleaved with a time course which parallels the ER calcium loss while activation of caspase-3 is a later event. Depletion of ER Ca(++) by thapsigargin, a specific inhibitor of the ER-associated Ca(++) ATPase, also produces caspase-12 processing and apoptotic cell death, whereas agents capable of reducing the ER calcium loss protect the cells from serum-deprivation-induced apoptosis. These findings indicate that, in hippocampal neuroblasts, Ca(++) mobilization from ER and caspase-12 activation are components of the molecular pathway that leads to apoptosis triggered by serum deprivation and may constitute an amplifying loop of the mitochondrial pathway.

5 '-Amino-4-imidazolecarboxamide riboside induces apoptosis in human neuroblastoma cells via the mitochondrial pathway

5'-Amino-4-imidazolecarboxamide (AICA) riboside induces apoptosis in neuronal cell models. In order to exert its effect, AICA riboside must enter the cell and be phosphorylated to the ribotide. In the present work, we have further studied the mechanism of apoptosis induced by AICA riboside. The results demonstrate that AICA riboside activates AMP-dependent protein kinase (AMPK), induces release of cytochrome c from mitochondria and activation of caspase 9. The role of AMPK in determining cell fate is controversial. In fact, AICA riboside has been reported to be neuroprotective or to induce apoptosis depending on its concentration, cell type or apoptotic stimuli used. In order to clarify whether the activation of AMPK is related to apoptosis in our model, we have used another AMPK stimulator, metformin, and we have analysed its effects on cell viability, nuclear morphology and AMPK activity. Five mM metformin increased AMPK activity, inhibited viability, and increased the number of apoptotic nuclei. AICA riboside, which can be generated from the ribotide (an intermediate of the purine de novo synthesis) by the action of the ubiquitous cytosolic 5'-nucleotidase (cN-II), may accumulate in those individuals in which an inborn error of purine metabolism causes both a building up of intermediates and/or an increase of the rate of de novo synthesis, and/or an overexpression of cN-II. Therefore, our results suggest that the toxic effect of AICA riboside on some types of neurons may participate in the neurological manifestations of syndromes related to purine dismetabolisms.

Cytotoxic effects and apoptotic signalling mechanisms of the sesquiterpenoid euplotin C, a secondary metabolite of the marine ciliate Euplotes crassus, in tumour cells

Most antitumour agents with cytotoxic properties induce apoptosis. The lipophilic compound euplotin C, isolated from the ciliate Euplotes crassus, is toxic to a number of different opportunistic or pathogenic microorganisms, although its mechanism of action is currently unknown. We report here that euplotin C is a powerful cytotoxic and pro-apoptotic agent in mouse AtT-20 and rat PC12 tumour-derived cell lines. In addition, we provide evidence that euplotin C treatment results in rapid activation of ryanodine receptors, depletion of Ca2+ stores in the endoplasmic reticulum (ER), the release of cytochrome c from the mitochondria, activation of caspase-12, and activation of caspase-3, leading to apoptosis. Intracellular Ca2+ overload is an early event which induces apoptosis and is parallelled by ER stress and the release of cytochrome c, whereas caspase-12 may be activated by euplotin C at a later stage in the apoptosis pathway. These events, either independently or concomitantly, lead to the activation of the caspase-3 and its downstream effectors, triggering the cell to undergo apoptosis. These results demonstrate that euplotin C may be considered for the design of cytotoxic and pro-apoptotic new drugs.

Nuclear sphingomyelin pathway in serum deprivation-induced apoptosis of embryonic hippocampal cells

Sphingomyelin (SM) cycle has been involved in the regulation of proliferation, differentiation, and apoptosis. Increases in ceramide have been found after a larger number of apoptotic stimuli including cytokines, cytotoxic drugs, and environmental stresses. Accumulating evidence suggest that the subcellular localization of ceramide generation is a critical factor in determining the cellular behavior. Since recently enzymes involved in ceramide metabolism such as sphingomyelinase, SM synthase, sphingosine kinase and ceramidase have been found in the nucleus of hepatocyte cells, we have studied first the presence and the physicochemical characteristics of SM metabolism enzymes in nuclei isolated from embryonic hippocampal cells (cell line HN9.10e). The activities of sphingomyelinase and SM-synthase have been assayed and the ceramide production evaluated at different times after serum deprivation in these neurones cultivated in serum-deficient medium. We report that both enzymes are present in the nucleus of embryonic hippocampal cells and differ from those present in the homogenate in optimum pH. After serum deprivation, that induces a time-dependent decrease in cell viability and increase of the cell percentage in G1 phase of the cell cycle, a nuclear sphingomyelinase activation together with SM-synthase inhibition and a consequent increase of nuclear ceramide pool have been demonstrated. No similar enzyme activity modifications in homogenate have been identified. The possible role of nuclear sphingomyelinase/sphingomyelin-synthase balance in serum deprivation-induced apoptosis in the embryonic hippocampal cell is discussed.

Sphingolipid metabolites in neural signalling and function

Sphingolipid metabolites, such as ceramide, sphingosine, sphingosine-1-phosphate (S1P) and complex sphingolipids (gangliosides), are recognized as molecules capable of regulating a variety of cellular processes. The role of sphingolipid metabolites has been studied mainly in non-neuronal tissues. These studies have underscored their importance as signals transducers, involved in control of proliferation, survival, differentiation and apoptosis. In this review, we will focus on studies performed over the last years in the nervous system, discussing the recent developments and the current perspectives in sphingolipid metabolism and functions.

5'-aminoimidazole-4-carboxamide riboside induces apoptosis in human neuroblastoma cells

5'-Aminoimidazole-4-carboxamide riboside (AICA riboside) has been previously shown to be toxic to two neuronal cell models [Neuroreport 11 (2000) 1827]. In this paper we demonstrate that AICA riboside promotes apoptosis in undifferentiated human neuroblastoma cells (SH-SY5Y), inducing a raise in caspase-3 activity. In order to exert its effect on viability, AICA riboside must enter the cells and be phosphorylated to the ribotide, since both a nucleoside transport inhibitor, and an inhibitor of adenosine kinase produce an enhancement of the viability of AICA riboside-treated cells. Short-term incubations (2 h) with AICA riboside result in five-fold increase in the activity of AMP-dependent protein kinase (AMPK). However, the activity of AMPK is not significantly affected at prolonged incubations (48 h), when the apoptotic effect of AICA riboside is evident. The results demonstrate that when the cell line is induced to differentiate both toward a cholinergic phenotype (with retinoic acid) or a noradrenergic phenotype (with phorbol esters), the toxic effect is significantly reduced, and in the case of the noradrenergic phenotype differentiation, the riboside is completely ineffective in promoting apoptosis. This reduction of effect correlates with an overexpression of Bcl-2 during differentiation. AICA riboside, derived from the hydrolysis of the ribotide, an intermediate of purine de novo synthesis, is absent in normal healthy cells; however it may accumulate in those individuals in which an inborn error of purine metabolism causes an increase in the rate of de novo synthesis and/or an overexpression of cytosolic 5'-nucleotidase, that appears to be the enzyme responsible for AICA ribotide hydrolysis. In fact, 5'-nucleotidase activity has been shown to increase in patients affected by Lesch-Nyhan syndrome in which both acceleration of de novo synthesis and accumulation of AICA ribotide has been described, and also in other neurological disorders of unknown etiology. Our results raise the intriguing clue that the neurotoxic effect of AICA riboside on the developing brain might contribute to the neurological manifestations of syndromes related to purine dismetabolisms.

Serum deprivation increases ceramide levels and induces apoptosis in undifferentiated HN9.10e cells

Sphingolipid metabolites have been involved in the regulation of proliferation, differentiation and apoptosis. While cellular mechanisms of these processes have been extensively analysed in the post-mitotic neurons, little is known about proliferating neuronal precursors. We have taken as a model of neuroblasts the embryonic hippocampal cell line HN9.10e. Apoptosis was induced by serum deprivation and by treatment with N-acetylsphingosine (C2-Cer), a membrane-permeant analogue of the second messenger ceramide. Following C2-Cer addition, cytochrome c was released from mitochondria, [Ca(2+)](i) and caspase-3-like activity increased. Both cytochrome c release and rise of [Ca(2+)](i) occurred before caspase-3 activation and nuclear condensation. The intracellular levels of ceramide peaked at 1h following the serum deprivation. These results indicate that the serum deprivation induces a rise in the intracellular ceramide level, and that increased ceramide concentration leads to calcium dysregulation and release of cytochrome c followed by caspase-3 activation. We show that cytochrome c is released without a loss of mitochondrial transmembrane potential.

Role of mitochondria in serum withdrawal-induced apoptosis of immortalized neuronal precursors

The intracellular mechanisms controlling apoptosis in immature neurons are still largely unknown. Taking immortalized hippocampal neuronal precursors (mouse cell line HN9.10e) as a model, we have analyzed the cellular events associated to apoptosis induced by serum deprivation. We observed translocation of Bax from cytosol to mitochondria after 1 h of serum withdrawal followed, 2 h later, by cytochrome c release from mitochondria. These events occurred without mitochondrial membrane potential loss nor mitochondrial calcium raise. As calcium is implicated in several cell death pathways, we analyzed intracellular calcium levels after longer periods of serum deprivation. After 6 h, an increase of cytosolic Ca2+ was detected in HN9.10e cells loaded with the Ca2+ indicator Fluo3-AM. This increase of calcium preceded morphological signs of apoptosis such as cell shrinkage and nuclear fragmentation, and was followed by a more pronounced raise that persisted until the terminal phases of the apoptotic process. Cells serum-deprived for 4 h and then grown in complete medium for 20 h fully recovered viability. Summarizing, in HN9.10e cells, calcium deregulation occurs in the late phases of apoptosis; earlier events involve translocation of Bax, release of cytochrome c, and maintenance of mitochondrial functionality. This allows an enlargement of the temporal window in which commitment to death is reversible.

Neurotoxic effects of caulerpenyne

1. In this paper the authors tested the effect of caulerpenyne (CYN), a sesquiterpene synthesized by the green alga Caulerpa taxifolia onto the central nervous system of the leech Hirudo medicinalis. Investigations have been performed with three different approaches: neuroethological, electrophysiological and neurochemical techniques. 2. CYN application mimics the effect of a nociceptive stimulation (brushing), eliciting a clear-cut potentiation of the animal swim response to the test stimulus (non associative learning process such as sensitization). This effect is similar to that one induced by the endogenous neurotransmitter serotonin (5HT). 3. CYN strongly reduces the after-hyperpolarization (AHP) recorded from T sensory neurons. This effect overlaps that one produced by 5HT, but it is not affected by the serotonergic antagonist methysergide. 4. The decrease of AHP amplitude due to CYN application is observed also in presence of apamin, a blocking agent of Ca++-dependent K+ channels, suggesting that CYN is acting through the inhibition of the Na+/K+ electrogenic pump. 5. The depression of the AHP driven by CYN is not prevented by application of MDL 12330A, an adenylate cyclase inhibitor. On the other hand MDL 12330A counteracts the reduction of AHP due to 5HT application. 6. Incubation of the leech central nervous system with CYN induces the phosphorylation of proteins of 29, 50, 66 and 100 kDa. This pattern of phosphorylation is similar to that one elicited by 5HT treatment. 7. The data demonstrate that CYN exerts remarkable effects on leech neurons by acting onto specific molecular targets such as the Na+/K+ ATPase. This effect may influence important neural integrative functions and may explain the sensitizing action produced by the toxin on swim induction. Finally, caulerpenyne does not act through the pathways involved in the 5HT action, and its effect is not mediated by the second messenger cyclic AMP. The mechanism of action of CYN are still under investigations.

Cytosolic 5'-nucleotidase hyperactivity in erythrocytes of Lesch-Nyhan syndrome patients

Lesch-Nyhan syndrome is a metabolic-neurological syndrome caused by the X-linked deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Metabolic consequences of HGPRT deficiency have been clarified, but the connection with the neurological manifestations is still unknown. Much effort has been directed to finding other alterations in purine nucleotides in different cells of Lesch-Nyhan patients. A peculiar finding was the measure of appreciable amount of Z-nucleotides in red cells. We found significantly higher IMP-GMP-specific 5'-nucleotidase activity in the erythrocytes of seven patients with Lesch-Nyhan syndrome than in healthy controls. The same alteration was found in one individual with partial HGPRT deficiency displaying a severe neurological syndrome, and in two slightly hyperuricemic patients with a psychomotor delay. Since ZMP was a good substrate of 5'-nucleotidase producing Z-riboside, we incubated murine and human cultured neuronal cells with this nucleoside and found that it is toxic for our models, promoting apoptosis. This finding suggests an involvement of the toxicity of the Z-riboside in the pathogenesis of neurological disorders in Lesch-Nyhan syndrome and possibly in other pediatric neurological syndromes of uncertain origin.

Sphingomyelinase metabolites control survival and apoptotic death in SH-SY5Y neuroblastoma cells

There is increasing evidence that sphingolipids are involved in cell survival, differentiation or commitment to death. The effect of different sphingolipids and inhibitors of mitogen-activated protein kinase (MAPK) cascade on SH-SY5Y neuroblastoma cell death has been studied. Permeant ceramide analogues C2-Cer, C8-Cer, and C8-Cer-1-phosphate, but not dihydro C2-Cer induce apoptosis, as shown by Hoechst staining. Inhibition of ceramidase and sphingosine kinase, as well as incubation with sphingosine, decreases cell viability, measured as 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide reduction, whereas addition of sphingosine-1-phosphate increases proliferation. Both PD98059 (MAPKK inhibitor) and SB202190 (p38 MAPK inhibitor) decreased viability, but only SB202190 abolished the effect of ceramide. These results suggest that in SH-SY5Y neuroblastoma cells, death is signalled by increases in ceramide, ceramide-phosphate or sphingosine content through p38 MAPK pathway while survival requires MAPK and high sphingosine-1-phosphate/ceramide ratio.

Neurobiological principles of learning and memory

An increasing flow of evidences collected on elementary forms of learning processes in selected animal models evidentiates some mechanisms which can represent the basic cellular principles underlying plastic changes: 1. 5HT and second messengers of nucleotide type (like cAMP) have a pivotal role in the learning process. 2. In almost all short-term learning processes the modifications are subserved by a mechanism of protein phosphorylation. 3. In various animal models the modulation of K+ and Ca2+ channels is the molecular mechanism for learning. Experiments performed in sensory T neuron of the leech indicate that the modulation of Na+/K+ electrogenic pump is one of the fundamental mechanism for learning. 4. In long-term plastic changes, the most important finding is that newly synthesized proteins are formed. 5. In addition to what has been observed in the Aplysia model, where changes in synaptic efficacy represent the basic principles of memory storage, in the leech it has been demonstrated that a molecular machinery present in a single neuron can adapt the activity of the cell to environmental stimuli.

Repetitive treatment with serotonin modifies protein synthesis and protein phosphorylation in the central nervous system of Hirudo medicinalis

Serotonin (5HT) is the neurotransmitter involved in some forms of short-term memory in the leech. Behavioral experiments have demonstrated that long-term memory requires new protein synthesis. With the aim of studying the molecular mechanism underlying memory processes in the leech, we have analyzed the effect of 5HT on protein synthesis and protein phosphorylation. Segmental ganglia of the leech central nervous system have been labeled, proteins have been separated by two-dimensional-electrophoresis and labeled proteins detected by autoradiography. Our findings indicate that repetitive treatment with 5HT produces either the persistence of phosphorylation or changes in protein synthesis in several proteins.

Interleukin-1 and interleukin-6 modify protein phosphorylation in the central nervous system of Hirudo medicinalis

Recent data suggest that IL-1-like molecules have been conserved during evolution. The signal transduction mechanism of IL-1 is not known, but kinase activation has been reported. With the aim of studying if human IL-1 has any effect on the leech nervous system, we have added this cytokine to segmental ganglia labeled with [32P]ortophosphoric acid; proteins have been separated by electrophoresis and phosphoproteins detected by autoradiography. In the present paper we show that human IL-1 and IL-6 are able to induce changes on protein phosphorylation in the leech central nervous system and that these changes are similar to those ones induced by the neurotransmitter serotonin.

Effect of serotonin on protein phosphorylation in the central nervous system of the leech Hirudo medicinalis

1. Phosphoproteins of different regions of the Hirudo medicinalis central nervous system have been analysed by means of two-dimensional electrophoresis. 2. Serotonin, 8-Br-cAMP and phorbol 12,13-dibutyrate stimulate phosphorylation of a number of proteins whose isoelectric points and molecular weights are presented. 3. A group of proteins of 78 kDa and pI = 6-6.5, whose level of phosphorylation increases in the presence of serotonin, 8-Br-cAMP and phorbol ester, is observed only in segmental but not in cephalic or caudal ganglia. 4. The putative roles of these phosphoproteins are discussed.

Effect of phorbol ester on protein phosphorylation in the central nervous system of the leech Hirudo medicinalis: a two-dimensional electrophoretical analysis

1. Proteins of different regions of the Hirudo medicinalis central nervous system have been analyzed by means of two-dimensional electrophoresis. 2. Subcellular distribution of phosphoproteins has been studied in leech segmental ganglia. 3. Phorbol 12,13-dibutyrate, a protein kinase C activator, stimulates the phosphorylation of a number of proteins whose isoelectric points and mol. wts are presented. 4. Putative roles for these phosphoproteins are discussed.

Seasonal variation of serotonin content and nonassociative learning of swim induction in the leech Hirudo medicinalis

It is possible to obtain habituation of swim induction by stimulating the leech with repetitive light electrical trains. After obtaining this simple form of non-associative learning, it is also possible to potentiate its response by a series of nociceptive skin brushings (dishabituation). Serotonin applied to the animal is the only neurotransmitter found to mimick dishabituation. We have observed that in the period April-June most animals did not exhibit potentiation of the swimming response after nociceptive stimulation while injection of serotonin mimicked dishabituation as in the animals treated in the period October-March. We have seen correlation between the changes in nonassociative learning and the seasonal variation of serotonin levels in segmental ganglia. This finding strengthens the hypothesis of serotonin as the neurotransmitter mediating dishabituation in swim induction of the leech.

Effects of cyclic nucleotides and calcium/calmodulin on protein phosphorylation in the CNS of Hirudo medicinalis

Protein phosphorylation plays an important role in the regulation of neural functions. We have studied the phosphorylation of proteins in homogenates of segmental ganglia of the leech Hirudo medicinalis. We describe a number of proteins whose phosphorylation is dependent on calcium/calmodulin or cyclic nucleotides. Most of the proteins whose phosphorylation is increased in the presence of calcium seem to be substrates for cyclic nucleotide-dependent protein kinases. Only two of the phosphoproteins described appear to be specific substrates for calcium/calmodulin protein kinase(s), and at least six phosphoproteins appear to be specific substrates for cyclic nucleotide-dependent kinase(s). The leech nervous system, with large and identifiable neurons, provides a good tool for studies of neural functions, such as learning. The results are discussed in the context of the role of protein phosphorylation on learning processes.

Dexamethasone inhibits receptor-activated phosphoinositide breakdown in rat basophilic leukemia (RBL-2H3) cells

The activation of rat basophilic leukemia cells for histamine release is accompanied by Ca2+ influx and arachidonic acid release. IgE receptor but not A23187 ionophore stimulation of these cells also resulted in phosphoinositide breakdown. In these experiments, the culture of these cells with dexamethasone inhibited IgE- and ionophore-mediated histamine release. The concentration for 50% of maximal inhibition was 12 nM, and prolonged exposure to the drug was required, with maximal effect observed in 8 to 15 hr. The inhibitory effect of dexamethasone was reversible (t1/2 for recovery was 16 hr). Dexamethasone blocked the IgE-mediated 45Ca2+ influx and the release of [14C]-arachidonic acid (IC50 of 1 nM and 10 nM respectively). Dexamethasone inhibited the IgE receptor-mediated phosphoinositide breakdown (IC50 of 5 nM). It also decreased arachidonic acid release after A23187 stimulation demonstrating an effect on phospholipase A2. Therefore, exposure of the cells to dexamethasone results in the inhibition of both phospholipase A2 and phospholipase C pathways of arachidonic acid generation.

Dexamethasone inhibits receptor-activated phosphoinositide breakdown in rat basophilic leukemia (RBL-2H3) cells

The activation of rat basophilic leukemia cells for histamine release is accompanied by Ca2+ influx and arachidonic acid release. IgE receptor but not A23187 ionophore stimulation of these cells also resulted in phosphoinositide breakdown. In these experiments, the culture of these cells with dexamethasone inhibited IgE- and ionophore-mediated histamine release. The concentration for 50% of maximal inhibition was 12 nM, and prolonged exposure to the drug was required, with maximal effect observed in 8 to 15 hr. The inhibitory effect of dexamethasone was reversible (t1/2 for recovery was 16 hr). Dexamethasone blocked the IgE-mediated 45Ca2+ influx and the release of [14C]-arachidonic acid (IC50 of 1 nM and 10 nM respectively). Dexamethasone inhibited the IgE receptor-mediated phosphoinositide breakdown (IC50 of 5 nM). It also decreased arachidonic acid release after A23187 stimulation demonstrating an effect on phospholipase A2. Therefore, exposure of the cells to dexamethasone results in the inhibition of both phospholipase A2 and phospholipase C pathways of arachidonic acid generation.