Involvement of autophagy upregulation in 3,4-methylenedioxymethamphetamine ('ecstasy')-induced serotonergic neurotoxicity

Preliminary Results on the Long-Term Effects of Dextromethorphan on MDMA-Mediated Serotonergic Deficiency and Volumetric Changes in Primates Based on 4-[18F]-ADAM PET/MRI

Alterations to the serotonergic system due to 3,4-methylenedioxymethamphetamine (MDMA) (ecstasy) consumption have been extensively documented. However, knowledge of the reversibility of these neurotoxic effects based on in vivo evaluations of serotonin transport (SERT) availability remains limited. This study aimed to evaluate the long-term neurotoxicity of MDMA after 66 months abstinence and explored whether Dextromethorphan, a non-competitive N-methyl-D-aspartate (NMDA) receptor, could attenuate MDMA-induced neurotoxicity using 4-[18F]-ADAM, an imaging ligand that selectively targets SERT, with positron emission tomography technology (PET). Nine monkeys (Macaca cyclopis) were used in this study: control, MDMA, and DM + MDMA. Static 4-[18F]-ADAM PET was performed at 60 and 66 months after drug treatment. Serotonin transport (SERT) availability was presented as the specific uptake ratios (SURs) of 4-[18F]-ADAM in brain regions. Voxel-based region-specific SERT availability was calculated to generate 3D PET/MR images. Structural Magnetic Resonance Imaging (MRI) volumetric analysis was also conducted at 60 months. Significantly decreased 4-[18F]-ADAM SURs were observed in the striatum and thalamus of the MDMA group at 60 and 66 months compared to controls; the midbrain and frontal cortex SURs were similar at 60 and 66 months in the MDMA and control groups. All eleven brain regions showed significantly lower (∼13%) self-recovery rates over time; the occipital cortex and cingulate recovered to baseline by 66 months. DM attenuated MDMA-induced SERT deficiency on average, by ∼8 and ∼1% at 60 and 66 months, respectively; whereas significant differences were observed between the thalamus and amygdala of the MDMA and DM + MDMA groups at 66 months. Compared to controls, the MDMA group exhibited significantly increased (∼6.6%) gray matter volumes in the frontal cortex, occipital cortex, caudate nucleus, hippocampus, midbrain, and amygdala. Moreover, the gray matter volumes of the occipital cortex, hippocampus and amygdala correlated negatively with the 4-[18F]-ADAM SURs of the same regions. DM (n = 2) did not appear to affect MDMA-induced volumetric changes. The 4-[18F]-ADAM SURs, lower self-recovery rate and increased volumetric values indicate the occipital cortex, hippocampus and amygdala still exhibit MDMA-induced neurotoxicity after 66 months’ abstinence. Moreover, DM may prevent MDMA-induced serotonergic deficiency, as indicated by increased 4-[18F]-ADAM SURs and SERT availability, but not volumetric changes.

Rapamycin Pretreatment Alleviates Cerebral Ischemia/Reperfusion Injury in Dose-Response Manner Through Inhibition of the Autophagy and NFκB Pathways in Rats

Although rapamycin can attenuate cerebral ischemia/reperfusion (I/R) injury, the potential roles of rapamycin on cerebral I/R injury remain largely controversial. The present work aims to evaluate underlying molecular mechanisms of rapamycin pretreatment on I/R injury. In total, 34 Sprague-Dawley rats were randomly grouped to 3 groups: sham group (n = 2), vehicle group (n = 16), and rapamycin-pretreatment group (n = 16). Before the focal cerebral ischemia was induced, those rats in the pretreatment group were intraperitoneally injected rapamycin (1 mg/kg body) for 20 hours, while rats in the vehicle group received same-volume saline. Then, rats in these 2 groups received focal cerebral ischemia for 3 and 6 hours, respectively (n = 8 in each group), which was followed by the application of reperfusion for 4, 24, 72 hours, and 1 week (n = 2 in each group). The results showed that the rapamycin pretreatment improved the memory functions of rats after I/R injury, which was evaluated using a Y-maze test. Rapamycin pretreatment significantly reduced the size of triphenyltetrazolium chloride infarction and decreased the expression of I/R injury markers. Moreover, the expression of LC-3 and NFκB was also significantly reduced after rapamycin pretreatment. Taken together, rapamycin pretreatment may alleviate cerebral I/R injury partly through inhibiting autophagic activities and NFκB pathways in rats.

Lysosomal Dysfunction and Autophagy Blockade Contribute to MDMA-Induced Neurotoxicity in SH-SY5Y Neuroblastoma Cells

Methylenedioxymethamphetamine (MDMA) is a psychostimulant with high abuse potential and severe neurotoxicity. According to our previous study, MDMA promotes autophagosome accumulation and contributes to cell death in cultured cortical and serotonergic neurons. However, the detailed mechanism underlying autophagy dysfunction remains unclear. Lysosomes play an important role in autophagic degradation. The present study aimed to examine the role of lysosomal function in autophagic flux in neuronal cultures exposed to MDMA. We showed that MDMA induced enlarged vesicles that accumulate in SH-SY5Y neuroblastoma cells. In addition, we demonstrated that MDMA stimulated dynamin-dependent but clathrin-independent endocytosis, which might contribute to vacuole expansion. Morphological and Western blot analyses revealed that MDMA induced lysosomal swelling, whereas the activity of the lysosomal hydrolytic enzymes cathepsin B and cathepsin D was decreased in SH-SY5Y and cultured cortical neurons, which might lead to autophagosome accumulation and autophagic degradation blockage. Intriguingly, inactivation of cathepsins B and D led to cell death and autophagy-lysosomal dysregulation, which mimicked MDMA-induced neurotoxicity. Consequently, impairment of lysosomal proteolysis and blockage of autophagy degradation contributed to MDMA-induced neurotoxicity in neuronal cultures.

Evaluation of brain SERT with 4-[18F]-ADAM/micro-PET and hearing protective effects of dextromethorphan in hearing loss rat model

This study investigated the protective effects of dextromethorphan (DXM) on noise-induced hearing loss (NIHL) in rats. This study aimed to improve the auditory threshold and to understand the protective effects of DXM against N-methyl-d-aspartate (NMDA)-induced neurite degeneration of serotonergic neurons. The animals were exposed to 8-kHz narrowband noise at a 118-dB sound pressure level for 3.5 h. The hearing thresholds were determined by measuring the auditory brainstem response to click stimuli. Serotonin transporter (SERT) expression was determined through micro-positron emission tomography (PET) using N,N-dimethyl-2-(2-amino-4-¹⁸F-fluorophenylthio)benzylamine (4-[¹⁸F]-ADAM). We also investigated the effects of DXM on NMDA-induced morphological changes in the primary cultures of rat serotonergic neurons. NIHL significantly improved after prophylactic treatment with DXM (p < .05). SERT density in DXM-treated rats was significantly higher than that in non-DXM-treated rats. Because prophylactic medication restored the NMDA-inhibited neurite length of serotonergic neurons and presented SERT density, DXM could be a potential agent in alleviating NIHL.

Autophagy inhibition plays a protective role against 3, 4-methylenedioxymethamphetamine (MDMA)-induced loss of serotonin transporters and depressive-like behaviors in rats

The 3,4-methylenedioxymethamphetamine (MDMA) is a popular recreational drug, which ultimately leads to serotonergic (5-HT) neurotoxicity and psychiatric disorders. Previous in vitro studies have consistently demonstrated that MDMA provokes autophagic activation, as well as damage of 5-HT axons and nerve fibers. So far, whether autophagy, a well-conserved cellular process that is critical for cell fate, also participates in MDMA-induced neurotoxicity in vivo remains elusive. Here, we first examined time-course of autophagy-related changes during repeated administration of MDMA (10 mg/kg s.c. twice daily for 4 consecutive days) using immunofluorescent staining for tryptophan hydroxylase and microtubule-associated protein 1 light chain 3 beta in rats. We also evaluated the protective effects of 3-methyadanine (3-MA, an autophagy inhibitor, 15 mg/kg i.p.) against MDMA-induced acute and long-term reductions in serotonin transporters (SERT) density in various brain regions using immunohistochemical staining and positron emission tomography (PET) imaging respectively. Plasma corticosterone measurements and forced swim tests were performed to evaluate the depressive performance. The staining results showed that repeated administration of MDMA increased expression of autophagosome and caused reduction in SERT densities of striatum and frontal cortex, which was ameliorated in the presence of 3-MA. PET imaging data also revealed that 3-MA could ameliorate MDMA-induced long-term decreased SERT availability in various brain regions of rats. Furthermore, immobility time of forced swim tests and plasma corticosterone levels were less in the group of MDMA co-injected with 3-MA compared with that of MDMA group. Together, these findings suggest that autophagy inhibition may confer protection against neurobiological and behavioral changes induced by MDMA.

Knockdown of POLDIP2 suppresses tumor growth and invasion capacity and is linked to unfavorable transformation ability and metastatic feature in non-small cell lung cancer

The main problem in the treatment of non-small cell lung cancer (NSCLC) is metastasis. Epithelial-mesenchymal transition (EMT) is known as the critical signaling in tumor progression, metastasis, and also the drug resistance. In this study, we reported a novel gene Polymerase delta-interacting protein 2 (POLDIP2) was downregulated in NSCLC tissues and first demonstrated that overexpression of POLDIP2 increased the anchorage-independent growth (AIG) and invasiveness of H1299 cells. In addition, we examined that knockdown of POLDIP2 in H1299 and A549 cells reduced tumorigenicity and metastatic capacity in vitro and also in vivo. Moreover, downregulation of the cell proliferation marker cyclin D1 and EMT markers CDH2, Slug, and Twist was showed in H1299 cells by POLDIP2 knockdown, suggesting that the inhibition of malignancy was affected by modulating key genes for tumor growth and invasiveness. Taken together, our study is the first study that demonstrated that POLDIP2 gene was function as an oncogene in NSCLC and implied the oncogenic ability might be through promoting cell proliferation or EMT.

The Designer Drug 3-Fluoromethcathinone Induces Oxidative Stress and Activates Autophagy in HT22 Neuronal Cells

Synthetic cathinones are psychoactive substances, derivatives of a natural psychostimulant cathinone. Although many synthetic cathinones have lost their legal status in many countries, their abuse still continues worldwide. Recently, they have been reported to exert neurotoxic effects in vitro and in vivo. The molecular mechanisms of their action have not been fully elucidated. Recently, they have been linked to the induction of oxidative stress, autophagy, and apoptosis. The aim of this study was to investigate whether 3-fluoromethcathinone (3-FMC), a synthetic cathinone, is able to induce oxidative stress, autophagy, and apoptosis in HT22 immortalized mouse hippocampal cells. We found that treatment of HT22 cells with this compound results in a concentration-dependent increase in the intracellular production of reactive oxygen species. Moreover, 3-FMC induced concentration-dependent conversion of cytosolic LC3-I to membrane-bound LC3-II and formation of autophagic vacuoles. Additionally, the level of p62/SQSTM1 protein decreased after 3-FMC treatment, suggesting that accumulation of autophagic vacuoles resulted from activation rather than inhibition of autophagy. Our results also showed that 3-FMC at millimolar concentration is able to induce caspase-dependent apoptotic cell death in HT22 cells. Our findings suggest that abuse of 3-FMC may disturb neuronal homeostasis and impair functioning of the central nervous system.

Methylone and MDPV activate autophagy in human dopaminergic SH-SY5Y cells: a new insight into the context of β-keto amphetamines-related neurotoxicity

Autophagy has an essential role in neuronal homeostasis and its dysregulation has been recently linked to neurotoxic effects of a growing list of psychoactive drugs, including amphetamines. However, the role of autophagy in β-keto amphetamine (β-KA) designer drugs-induced neurotoxicity has hitherto not been investigated. In the present study, we show that two commonly abused cathinone derivatives, 3,4-methylenedioxymethcathinone (methylone) and 3,4-methylenedioxypyrovalerone (MDPV), elicit morphological changes consistent with autophagy and neurodegeneration, including formation of autophagic vacuoles and neurite retraction in dopaminergic SH-SY5Y cells. Methylone and MDPV prompted the formation of acidic vesicular organelles (AVOs) and lead to increased expression of the autophagy-associated protein LC3-II in a concentration- and time-dependent manner. Electron microscopy confirmed the presence of autophagosomes with typical double membranes and autolysosomes in cells exposed to both β-KA. The autophagic flux was further confirmed using bafilomycin A1, a known inhibitor of the late phase of autophagy. Moreover, we showed that autophagy markers were activated before the triggering of cell death and caspase 3 activation, suggesting that β-KA-induced autophagy precedes apoptotic cell death. To address the role of oxidative stress in autophagy induction, we also investigated the effects of antioxidant treatment with N-acetyl-L-cysteine (NAC) on autophagy and apoptotic markers altered by these drugs. NAC significantly attenuated methylone- and MDPV-induced cell death by completely inhibiting the generation of reactive oxygen and nitrogen species, and hampering both apoptotic and autophagic activity, suggesting that oxidative stress plays an important role in mediating autophagy and apoptosis elicited by these drugs.

MDMA-induced neurotoxicity of serotonin neurons involves autophagy and rilmenidine is protective against its pathobiology

Toxicity of 3,4-methylenedioxymethamphetamine (MDMA) towards biogenic amine neurons is well documented and in primate brain predominantly affects serotonin (5-HT) neurons. MDMA induces damage of 5-HT axons and nerve fibres and intracytoplasmic inclusions. Whilst its pathobiology involves mitochondrially-mediated oxidative stress, we hypothesised MDMA possessed the capacity to activate autophagy, a proteostatic mechanism for degradation of cellular debris. We established a culture of ventral pons from embryonic murine brain enriched in 5-HT neurons to explore mechanisms of MDMA neurotoxicity and recruitment of autophagy, and evaluated possible neuroprotective actions of the clinically approved agent rilmenidine. MDMA (100 μM-1 mM) reduced cell viability, like rapamycin (RM) and hydrogen peroxide (H₂O₂), in a concentration- and time-dependent manner. Immunocytochemistry revealed dieback of 5-HT arbour: MDMA-induced injury was slower than for RM and H₂O₂, neuritic blebbing occurred at 48 and 72 h and Hoechst labelling revealed nuclear fragmentation with 100 μM MDMA. MDMA effected concentration-dependent inhibition of [³H]5-HT uptake with 500 μM MDMA totally blocking transport. Western immunoblotting for microtubule associated protein light chain 3 (LC3) revealed autophagosome formation after treatment with MDMA. Confocal analyses and immunocytochemistry for 5-HT, Hoechst and LC3 confirmed MDMA induced autophagy with abundant LC3-positive puncta within 5-HT neurons. Rilmenidine (1 μM) protected against MDMA-induced injury and image analysis showed full preservation of 5-HT arbours. MDMA had no effect on GABA neurons, indicating specificity of action at 5-HT neurons. MDMA-induced neurotoxicity involves autophagy induction in 5-HT neurons, and rilmenidine via beneficial actions against toxic intracellular events represents a potential treatment for its pathobiology in sustained usage.

Effects of dextromethorphan on MDMA-induced serotonergic aberration in the brains of non-human primates using [123I]-ADAM/SPECT

3,4-Methylenedioxymethamphetamine (MDMA), a common recreational drug, is known to cause serotonergic neurotoxicity in the brain. Dextromethorphan (DM) is a widely used antitussive reported to exert anti-inflammatory effect in vivo. In this study, we examined the long-term effect of MDMA on the primate serotonergic system and the protective property of DM against MDMA-induced serotonergic abnormality using single photon emission computed tomography (SPECT). Nine monkeys (Macaca cyclopis) were divided into three groups, namely control, MDMA and co-treatment (MDMA/DM). [¹²³I]-ADAM was used as the radioligand for serotonin transporters (SERT) in SPECT scans. SERT levels of the brain were evaluated and presented as the uptake ratios (URs) of [¹²³I]-ADAM in several regions of interest of the brain including midbrain, thalamus and striatum. We found that the URs of [¹²³I]-ADAM were significantly lower in the brains of MDMA than control group, indicating lower brain SERT levels in the MDMA-treated monkeys. This MDMA-induced decrease in brain SERT levels could persist for over four years. However, the loss of brain SERT levels was not observed in co-treatment group. These results suggest that DM may exert a protective effect against MDMA-induced serotonergic toxicity in the brains of the non-human primate.