Untargeted Metabolomics in Forensic Toxicology: A New Approach for the Detection of Fentanyl Intake in Urine Samples.

The misuse of fentanyl, and novel synthetic opioids (NSO) in general, has become a public health emergency, especially in the United States. The detection of NSO is often challenged by the limited diagnostic time frame allowed by urine sampling and the wide range of chemically modified analogues, continuously introduced to the recreational drug market. In this study, an untargeted metabolomics approach was developed to obtain a comprehensive "fingerprint" of any anomalous and specific metabolic pattern potentially related to fentanyl exposure. In recent years, in vitro models of drug metabolism have emerged as important tools to overcome the limited access to positive urine samples and uncertainties related to the substances actually taken, the possible combined drug intake, and the ingested dose. In this study, an in vivo experiment was designed by incubating HepG2 cell lines with either fentanyl or common drugs of abuse, creating a cohort of 96 samples. These samples, together with 81 urine samples including negative controls and positive samples obtained from recent users of either fentanyl or "traditional" drugs, were subjected to untargeted analysis using both UHPLC reverse phase and HILIC chromatography combined with QTOF mass spectrometry. Data independent acquisition was performed by SWATH in order to obtain a comprehensive profile of the urinary metabolome. After extensive processing, the resulting datasets were initially subjected to unsupervised exploration by principal component analysis (PCA), yielding clear separation of the fentanyl positive samples with respect to both controls and samples positive to other drugs. The urine datasets were then systematically investigated by supervised classification models based on soft independent modeling by class analogy (SIMCA) algorithms, with the end goal of identifying fentanyl users. A final single-class SIMCA model based on an RP dataset and five PCs yielded 96% sensitivity and 74% specificity. The distinguishable metabolic patterns produced by fentanyl in comparison to other opioids opens up new perspectives in the interpretation of the biological activity of fentanyl.

Estrogens Inhibit Amyloid-ß-Mediated Paired Helical Filament-Like Conformation of Tau Through Antioxidant Activity and miRNA 218 Regulation in hTau Mice.

BACKGROUND: The risk of developing Alzheimer's disease as well as its progression and severity are known to be different in men and women, and cognitive decline is greater in women than in men at the same stage of disease and could be correlated at least in part on estradiol levels. OBJECTIVE: In our work we found that biological sex influences the effect of amyloid-ß42 (Aß42) monomers on pathological tau conformational change. METHODS: In this study we used transgenic mice expressing the wild-type human tau (hTau) which were subjected to intraventricular (ICV) injections of Aß peptides in nanomolar concentration. RESULTS: We found that Aß42 produces pathological conformational changes and hyperphosphorylation of tau protein in male or ovariectomized female mice but not in control females. The treatment of ovariectomized females with estradiol replacement protects against the pathological conformation of tau and seems to be mediated by antioxidant activity as well as the ability to modulate the expression of miRNA 218 linked to tau phosphorylation. CONCLUSION: Our study indicates that factors as age, reproductive stage, hormone levels, and the interplay with other risk factors should be considered in women, in order to identify the best appropriate therapeutic approach in prevention of cognitive impairment.

A silver lining for 24-hydroxycholesterol in Alzheimer's disease: The involvement of the neuroprotective enzyme sirtuin 1.

It is now established that cholesterol oxidation products (oxysterols) are involved in several events underlying Alzheimer's disease (AD) pathogenesis. Of note, certain oxysterols cause neuron dysfunction and degeneration but, recently, some of them have been shown also to have neuroprotective effects. The present study, which aimed to understand the potential effects of 24-hydroxycholesterol (24-OH) against the intraneuronal accumulation of hyperphosphorylated tau protein, stressed these latter effects. A beneficial effect of 24-OH was demonstrated in SK-N-BE neuroblastoma cells, and is due to its ability to modulate the deacetylase sirtuin 1 (SIRT1), which contributes to preventing the neurotoxic accumulation of the hyperphosphorylated tau protein. Unlike 24-OH, 7-ketocholesterol (7-K) did not modulate the SIRT1-dependent neuroprotective pathway. To confirm the neuroprotective role of 24-OH, in vivo experiments were run on mice that express human tau without spontaneously developing tau pathology (hTau mice), by means of the intracerebroventricular injection of 24-OH. 24-OH, unlike 7-K, was found to completely prevent the hyperphosphorylation of tau induced by amyloid ß monomers. These data highlight the importance of preventing the loss of 24-OH in the brain, and of maintaining high levels of the enzyme SIRT1, in order to counteract neurodegeneration.

Dual Mechanism of Toxicity for Extracellular Injection of Tau Oligomers versus Monomers in Human Tau Mice.

The mechanism of tau toxicity is still unclear. Here we report that recombinant tau oligomers and monomers, intraventricularly injected in mice with a pure human tau background, foster tau pathology through different mechanisms. Oligomeric forms of tau alter the conformation of tau in a paired helical filament-like manner. This effect occurs without tau hyperphosphorylation as well as activation of specific kinases, suggesting that oligomers of tau induce tau assembly through a nucleation effect. Monomers, in turn, induce neurodegeneration through a calpain-mediated tau cleavage that leads to accumulation of a 17 kDa neurotoxic peptide and induction of apoptotic cell death.

E2 Regulates Epigenetic Signature on Neuroglobin Enhancer-Promoter in Neuronal Cells.

Estrogens are neuroprotective factors in several neurological diseases. Neuroglobin (NGB) is one of the estrogen target genes involved in neuroprotection, but little is known about its transcriptional regulation. Estrogen genomic pathway in gene expression regulation is mediated by estrogen receptors (ERα and ERß) that bind to specific regulatory genomic regions. We focused our attention on 17ß-estradiol (E2)-induced NGB expression in human differentiated neuronal cell lines (SK-N-BE and NT-2). Previously, using bioinformatics analysis we identified a putative enhancer in the first intron of NGB locus. Therefore, we observed that E2 increased the enrichment of the H3K4me3 epigenetic marks at the promoter and of the H3K4me1 and H3K27Ac at the intron enhancer. In these NGB regulatory regions, we found estrogen receptor alpha (ERα) binding suggesting that ERα may mediate chromatin remodeling to induce NGB expression upon E2 treatment. Altogether our data show that NGB expression is regulated by ERα binding on genomic regulatory regions supporting hormone therapy applications for the neuroprotection against neurodegenerative diseases.

Aß1-42 monomers or oligomers have different effects on autophagy and apoptosis.

The role of autophagy and its relationship with apoptosis in Alzheimer disease (AD) pathogenesis is poorly understood. Disruption of autophagy leads to buildup of incompletely digested substrates, amyloid-ß (Aß) peptide accumulation in vacuoles and cell death. Aß, in turn, has been found to affect autophagy. Thus, Aß might be part of a loop in which it is both the substrate of altered autophagy and its cause. Given the relevance of different soluble forms of Aß1-42 in AD, we have investigated whether monomers and oligomers of the peptide have a differential role in causing altered autophagy and cell death. Using differentiated SK-N-BE neuroblastoma cells, we found that monomers hamper the formation of the autophagic BCL2-BECN1/Beclin 1 complex and activate the MAPK8/JNK1-MAPK9/JNK2 pathway phosphorylating BCL2. Monomers also inhibit apoptosis and allow autophagy with intracellular accumulation of autophagosomes and elevation of levels of BECN1 and LC3-II, resulting in an inhibition of substrate degradation due to an inhibitory action on lysosomal activity. Oligomers, in turn, favor the formation of the BCL2-BECN1 complex favoring apoptosis. In addition, they cause a less profound increase in BECN1 and LC3-II levels than monomers without affecting the autophagic flux. Thus, data presented in this work show a link for autophagy and apoptosis with monomers and oligomers, respectively. These studies are likely to help the design of novel disease modifying therapies.

Up-regulation of ß-amyloidogenesis in neuron-like human cells by both 24- and 27-hydroxycholesterol: protective effect of N-acetyl-cysteine.

An abnormal accumulation of cholesterol oxidation products in the brain of patients with Alzheimer's disease (AD) would further link an impaired cholesterol metabolism in the pathogenesis of the disease. The first evidence stemming from the content of oxysterols in autopsy samples from AD and normal brains points to an increase in both 27-hydroxycholesterol (27-OH) and 24-hydroxycholesterol (24-OH) in the frontal cortex of AD brains, with a trend that appears related to the disease severity. The challenge of differentiated SK-N-BE human neuroblastoma cells with patho-physiologically relevant amounts of 27-OH and 24-OH showed that both oxysterols induce a net synthesis of Aß1-42 by up-regulating expression levels of amyloid precursor protein and ß-secretase, as well as the ß-secretase activity. Interestingly, cell pretreatment with N-acetyl-cysteine (NAC) fully prevented the enhancement of ß-amyloidogenesis induced by the two oxysterols. The reported findings link an impaired cholesterol oxidative metabolism to an excessive ß-amyloidogenesis and point to NAC as an efficient inhibitor of oxysterols-induced Aß toxic peptide accumulation in the brain.

ß-amyloid 1-42 induces physiological transcriptional regulation of BACE1.

The pathogenesis of Alzheimer's disease (AD) is only partially understood. ß-amyloid (Aß) is physiologically generated by sequential cleavage of its precursor protein by the ß- and the γ-secretase and it is normally disposed of. In Alzheimer's disease, Aß is excessively produced or less dismissed, but the hypothesis on its physiological and pathological role are heterogeneous and often discordant. It has been described a positive feedback loop from the γ- to the ß-secretase cleavages of Aß precursor protein, which is activated by mutations of Presenilin 1 (PS1), the catalytic core of the γ-secretase. These findings show that Aß precursor protein as well the activity of the γ-secretase are required to obtain the up-regulation of ß-secretase which is induced by Presenilin 1 mutations. Then, Aß 1-42 is the Aß precursor protein derivative that up-regulates the expression of ß-secretase, and c-jun N-terminal kinase (JNK)/c-Jun and ERK1/2 are involved. Here, we describe the activation of ß-secretase and c-jun N-terminal kinase related proteins by monomeric Aß 1-42, defining the conditions that most efficiently strike the described signaling without producing toxicity. Taken together these data imply that monomeric Aß 1-42, at non-toxic concentrations and time frames, are able to induce a signaling pathway that leads to transcriptional activation of ß-secretase.

Aß1-42-mediated down-regulation of Uch-L1 is dependent on NF-κB activation and impaired BACE1 lysosomal degradation.

Amyloid-ß 1-42 accumulation is the major pathogenetic event in Alzheimer's disease (AD), believed to be responsible for synaptic dysfunction and neuronal cell death. However, the physiologic activity of Aß peptides remains elusive: Aß might not only play a toxic role, but also act as a functional signaling intermediate. We recently reported that Aß1-42 promotes BACE1 transcription through the activation of the JNK-c-jun pathway. Here, we show that the Aß1-42-mediated increase in BACE1 expression is accompanied by a decrease in ubiquitin C-terminal hydrolase L1 (Uch-L1) expression and activity in different cellular models such as neuroblastoma SH-SY5Y as well as NT(2) neuronal cells. We also found that the increase in BACE1 and the decrease in Uch-L1 are related events and depend on NF-κB pathway; thus, Aß1-42 is able to activate NF-κB pathway and the pretreatment with a pharmacological inhibitor, able to block the nuclear translocation of the transactivating unit p65, almost completely prevents both the decrease in Uch-L1 and the increase in BACE1 expression. In addition, the decrease in Uch-L1 activity interferes with the lysosomal degradation of BACE1, as demonstrated by the decrease in Cathepsin D activity and the partial accumulation of BACE1 in lysosomes after Aß1-42 treatment as well after Uch-L1 inhibition. In support of the in vitro data, we observed low protein levels of Uch-L1 associated with high protein levels of BACE1 in sporadic AD brains. Our data suggest that Uch-L1 could be an attractive target for the development of new therapeutic approaches for AD.

AGEs/RAGE complex upregulates BACE1 via NF-κB pathway activation.

Although the pathogenesis of sporadic Alzheimer disease (AD) is not clearly understood, it is likely dependent on several age-related factors. Diabetes is a risk factor for AD, and multiple mechanisms connecting the 2 diseases have been proposed. Hyperglycemia enhances the formation of advanced glycation end products (AGEs) that result from the auto-oxidation of glucose and fructose. The interaction of AGEs with their receptor, named RAGE, elicits the formation of reactive oxygen species that are also believed to be an early event in AD pathology. To investigate a functional link between the disorders diabetes and AD, the effect of 2 AGEs, pentosidine and glyceraldehydes-derived pyridinium (GLAP), was studied on BACE1 expression both in vivo, in streptozotocin treated rats, and in vitro in differentiated neuroblastoma cells. We showed that pentosidine and GLAP were able to upregulate BACE1 expression through their binding with RAGE and the consequent activation of NF-κB. In addition, both pentosidine and GLAP were found to be increased in the brain in sporadic AD patients. Our findings demonstrate that activation of the AGEs/RAGE axis, by upregulating the key enzyme for amyloid-ß production, provides a pathologic link between diabetes mellitus and AD.

Amyloid-ß42 activates the expression of BACE1 through the JNK pathway.

The sequential endoproteolytic cleavages operated by the γ-secretase and the ß-secretase (BACE1) on the amyloid-ß protein precursor (AßPP) result in the production of the amyloid-ß (Aß) species, with two C-terminal variants, at residue 40 or at residue 42. Accumulation in brain tissue of small, soluble aggregates of Aß42 is the major pathogenic event of Alzheimer's disease (AD). However, the physiologic activity of Aß peptides is still elusive. Here, we show that expression of BACE1 is regulated by Aß42, which augments BACE1 gene transcription through the JNK/c-jun signaling pathway. Of note, Aß40 has much less effect on BACE1 expression. These findings unveil a positive feedback loop in which γ-secretase cleavage of AßPP releases a functionally-active peptide, Aß42, that promotes BACE1 transcription. Thus, gene expression induced by Aß42 may have implications in the neuronal dysfunction and degeneration that occurs in AD.

Dysregulation of SREBP2 induces BACE1 expression.

ß-Amyloid hyperproduction has been observed in response to alterations in neuronal intracellular cholesterol storage, efflux, and synthesis, induced in rats by a high-fat diet. It has been suggested that cholesterol homeostasis is altered in Alzheimer's disease resulting in higher ß- and γ-secretase activity. In the current study the neuronal activation status of sterol regulatory element binding protein 2 (SREBP2) as well as its involvement in ß-secretase BACE1 activity was investigated in high-fat fed rats (26% fat and 4% cholesterol for 20 weeks), and in SK-N-BE neuroblastoma cells exposed to 20 µM cholesterol. This work demonstrates that in the brain a hyperlipidic diet is able to induce a hyper-expression of BACE1 and determine an unbalance in cerebral cholesterol homeostasis so that SREBP2 is activated. In addition, we show for the first time the involvement of SREBP2 on expression of BACE1 in SK-N-BE cells exposed to high cholesterol. Although the enhanced risk of Alzheimer's disease in metabolic syndrome is related to several factors, our results suggest that SREBP2, which can be modulated by the impairment of cerebral cholesterol homeostasis, has a direct role on BACE1 expression and may be involved in Alzheimer's disease progression.

Interaction between 24-hydroxycholesterol, oxidative stress, and amyloid-ß in amplifying neuronal damage in Alzheimer's disease: three partners in crime.

All three cholesterol oxidation products implicated thus far in the pathogenesis of Alzheimer's disease, 7ß-hydroxycholesterol, 24-hydroxycholesterol, and 27-hydroxycholesterol, markedly enhance the binding of amyloid-beta (Aß) to human differentiated neuronal cell lines (SK-N-BE and NT-2) by up-regulating net expression and synthesis of CD36 and ß1-integrin receptors. However, only 24-hydroxycholesterol markedly potentiates the pro-apoptotic and pro-necrogenic effects of Aß(1-42) peptide on these cells: 7ß-hydroxycholesterol and 27-hydroxycholesterol, like unoxidized cholesterol, show no potentiating effect. This peculiar behavior of 24-hydroxycholesterol at physiologic concentrations (1 µm) depends on its strong enhancement of the intracellular generation of NADPH oxidase-dependent reactive oxygen species (ROS), mainly H(2) O(2) , and the consequent impairment of neuronal cell redox equilibrium, measured in terms of the GSSG/GSH ratio. Cell incubation with antioxidants quercetin or genistein prevents 24-hydroxycholesterol's pro-oxidant effect and potentiation of Aß-induced necrosis and apoptosis. Thus, the presence of 24-hydroxycholesterol in the close vicinity of amyloid plaques appears to enhance the adhesion of large amounts of Aß to the plasma membrane of neurons and then to amplify the neurotoxic action of Aß by locally increasing ROS steady-state levels. This report further supports a primary involvement of altered brain cholesterol metabolism in the complex pathogenesis of Alzheimer's disease.

Intracellular reactive oxygen species are required for directional migration of resident and bone marrow-derived hepatic pro-fibrogenic cells.

BACKGROUND & AIMS: Liver fibrogenesis is sustained by myofibroblast-like cells originating from hepatic stellate cells (HSC/MFs), portal fibroblasts or bone marrow-derived cells, including mesenchymal stem cells (MSCs). Herein, we investigated the mechanistic role of intracellular generation of reactive oxygen species (ROS) and redox-sensitive signal transduction pathways in mediating chemotaxis, a critical profibrogenic response for human HSC/MFs and for MSC potentially engrafting chronically injured liver. METHODS: Intracellular generation of ROS and signal transduction pathways were evaluated by integrating morphological and molecular biology techniques. Chemokinesis and chemotaxis were evaluated by wound healing assay and modified Boyden's chamber assay, respectively. Additional in vivo evidence was obtained in human specimens from HCV-related cirrhosis. RESULTS: Human MSCs and HSC/MFs migrate in response to a panel of polypeptide chemoattractants and extracellularly generated superoxide anion. All polypeptides induced a NADPH-oxidase-dependent intracellular rise in ROS, resulting in activation of ERK1/2 and JNK1/2. Moreover, menadione or 2,3-dimethoxy-1,4-naphthoquinone, which generate intracellular superoxide anion or hydrogen peroxide, respectively, induced ERK1/2 and JNK1/2 activation and migration. JNK1 activation was predominant for migration as shown by specific silencing. Finally, activation of ERK1/2 and JNK1/2 was found in extracts obtained from HSC/MFs during the course of an oxidative stress-mediated model of liver injury and phosphorylated JNK1/2 isoforms were detected in α-smooth muscle actin-positive myofibroblasts lining fibrotic septa in human cirrhotic livers. CONCLUSIONS: Intracellular generation of ROS, through activation of specific signaling pathways, is a critical event for directional migration of HSC/MFs and MSCs.

The up-regulation of BACE1 mediated by hypoxia and ischemic injury: role of oxidative stress and HIF1alpha.

While it is well established that stroke and cerebral hypoperfusion are both significant risk factors for Alzheimer's disease, the molecular link between ischemia and amyloid precursor protein processing has only been recently established. Specifically, hypoxia significantly increases beta-site APP cleaving enzyme (BACE1) gene transcription through the over-expression of hypoxia inducible factor 1alpha, resulting in increased BACE1 secretase activity and amyloid-beta production. In this study, we significantly extend these findings both in vitro, in differentiated SK-N-BE neuroblastoma cells, and in vivo, in rats subjected to cerebral ischemia, showing that hypoxia up-regulates BACE1 expression through a biphasic mechanism. The early post-hypoxic up-regulation of BACE1 depends on the production of reactive oxygen species mediated by the sudden interruption of the mitochondrial electron transport chain, while the later expression of BACE1 is caused by hypoxia inducible factor 1alpha activation. The involvement of reactive oxygen species released by mitochondria in the BACE1 up-regulation was confirmed by the complete protection exerted by complex I inhibitors such as rotenone and diphenyl-phenylen iodonium. Moreover, the oxidative stress-mediated up-regulation of BACE1 is mediated by c-jun N terminal kinase pathway as demonstrated by the protection exerted by the silencing of c-jun N-terminal kinase isoforms 1 and 2. Our study strengthens the hypothesis that oxidative stress is a basic common mechanism of amyloid-beta accumulation.

JNK and ERK1/2 pathways have a dual opposite effect on the expression of BACE1.

The activity of beta-secretase (BACE1), the endo-protease essential for the production of amyloid beta (Abeta) peptides, is increased in brain of late-onset sporadic Alzheimer's disease (AD), and oxidative stress is the potential cause of this event. Oxidative stress up-regulates the expression and the activity of BACE1 in cellular and animal models, through a mechanism that involves the increase of gamma-secretase cleavage on APP and the activation of c-jun N-terminal kinase/activator protein 1 (JNK/AP1) pathway. We further characterized the cellular pathways that control BACE1 expression under oxidative stress. We investigated the involvement of extracellular signal regulated MAP kinase (ERK1/2) pathway in the regulation of BACE1 expression, since it has been recently shown that ERK1/2 is an endogenous regulator of the gamma-secretase activity. We found that ERK1/2 pathway negatively modulates BACE1 expression and activity. Moreover, we observed that conditions that abrogate the gamma-secretase activity favor the activation of signalling pathways that promote cell survival, such as ERK1/2 and the serine/threonine kinase Akt/protein kinase B (Akt). These data suggest that the positive or negative cellular responses to oxidative stress parallel the activities of the beta- and the gamma-secretase. ERK1/2 and JNK pathways are involved in this bipartite response, which can lead to neurodegeneration or neuroprotection depending on the cellular and environmental conditions or cooperation with other signalling pathways such as Akt cascade.

Clusterin up-regulation following sub-lethal oxidative stress and lipid peroxidation in human neuroblastoma cells.

Clusterin/apolipoprotein J is a multifunctional protein up-regulated during various pathophysiological states. Since oxidative stress plays an important role in brain aging, and in many neurodegenerative disorders, to further understand the mechanistic underpinnings of clusterin expression, in this study, we examined clusterin expression in human neuroblastoma cells under conditions of increased production of reactive oxygen species and lipid peroxidation. Specifically, we analyzed clusterin mRNA and protein levels in human neuroblastoma IMR-32 and SH-SY5Y cells following exposure to sub-lethal amounts of iron-ascorbate to induce an increase in reactive oxygen species generation and lipid peroxidation. Under such conditions, we observed a time-dependent up-regulation of clusterin protein and mRNA levels, detected by immunoblot analysis and RT-PCR, respectively. Given the known roles of clusterin, the results of the present study support the notion that an increase in clusterin expression may be a physiological defence mounted to reduce cell damage and maintain cell viability during periods of increased oxidative stress.

Beta-site APP cleaving enzyme up-regulation induced by 4-hydroxynonenal is mediated by stress-activated protein kinases pathways.

4-Hydroxynonenal (HNE), an aldehydic product of lipid peroxidation, up-regulates expression of the beta-site APP cleaving enzyme (BACE-1), an aspartyl protease responsible for the beta-secretase cleavage of amyloid precursor protein (AbetaPP), and results in increased levels of amyloid beta (Abeta) peptide. The mechanisms underlying this remain unclear but are of fundamental importance because prevention of BACE-1 up-regulation is viewed as an important therapeutic strategy. In this study, we exposed NT(2) neurons to a range of HNE concentrations (0.5-5 microm) that elicited an up-regulation of BACE-1 expression, a significant increase in intracellular and secreted levels of Abeta peptides as well as apoptosis involving poly-ADP ribose polymerase cleavage and activation of caspase 3. To delineate the molecular events involved in HNE-mediated BACE-1 activation, we investigated the involvement of stress-activated protein kinases (SAPK), signal transducers and activators of transcription (STAT) and serine-threonine kinase B/phosphatidylinositol phosphate 3 kinase (Akt/PtdIns3K). Using specific pharmacological inhibitors, our results show that activation of c-Jun N-terminal kinases and p38(MAPK.), but not STAT or Akt/PtdIns3K, pathways mediate the HNE-dependent up-regulation of BACE-1 expression. Therefore, HNE, an oxidative stress mediator detected in vivo in the brains of Alzheimer's disease patients, may play a pathogenetic role in Alzheimer's disease by selectively activating SAPK pathways and BACE-1 that regulate the proteolytic processing of AbetaPP.

4-Hydroxynonenal modulation of p53 family gene expression in the SK-N-BE neuroblastoma cell line.

4-Hydroxynonenal (HNE), a product of lipid peroxidation, inhibits proliferation of several tumor cells. The p53 tumor suppressor protein plays a critical role in cell cycle control, by inducing p21 expression, and in apoptosis, by inducing bax expression. Recently, two other proteins with many p53-like properties, TAp73 (p73) and TAp63 (p63), have been discovered. SK-N-BE human neuroblastoma cells express the three p53 family proteins and can be used for the study of their induction. We investigated HNE action in the control of proliferation, differentiation, and apoptosis in SK-N-BE cells and the HNE effect on the expression of p53, p63, p73, p21, bax, and G1 cyclins. Retinoic acid (RA) was used as a positive control. HNE inhibited cell proliferation without inducing differentiation; it decreased S-phase cells and increased the number of apoptotic cells. RA reduced the proportion of S-phase cells and did not induce apoptosis. HNE increased p53, p73, p63, p21, and bax expression at different time points. HNE reduced cyclin D2 expression and the phosphorylation of pRb protein. Our results demonstrated that HNE inhibits SK-N-BE cell proliferation by increasing the expression of p53 family proteins and p53 target proteins which modulate cell cycle progression and apoptosis.

Multiple signaling events in amyloid beta-induced, oxidative stress-dependent neuronal apoptosis.

Current evidence suggests that amyloid beta peptides (Abeta) may play a major role in the pathogenesis of Alzheimer's disease by eliciting oxidative stress and neuronal apoptosis. In this study we have used differentiated SK-N-BE neurons to investigate molecular mechanisms and regulatory pathways underlying apoptotic neuronal cell death elicited by Abeta(1-40) and Abeta(1-42) peptides as well as the relationships between apoptosis and oxidative stress. Abeta peptides, used at concentrations able to induce oxidative stress, elicit a classic type of neuronal apoptosis involving mitochondrial regulatory proteins and pathways (i.e. affecting Bax and Bcl-2 protein levels as well as release of cytochrome c in the cytosol), poly-ADP rybose polymerase cleavage and activation of caspase 3. This pattern of neuronal apoptosis, that is significantly prevented by alpha-tocopherol and N-acetylcysteine and completely abolished by specific inhibitors of stress-activated protein kinases (SAPK) such as JNKs and p38(MAPK), involved early elevation of p53 protein levels. Pretreatment of neurons with alpha-pifithrin, a specific p53 inhibitor, resulted in a 50-60% prevention of Abeta induced apoptosis. These results suggest that oxidative stress - mediated neuronal apoptosis induced by amyloid beta operates by eliciting a SAPK-dependent multiple regulation of pro-apoptotic mitochondrial pathways involving both p53 and bcl-2.