The role of mitochondria in cocaine addiction

Nicotine-induced transcriptional changes and mitochondrial dysfunction in the ventral tegmental area revealed by single-nucleus transcriptomics

Nicotine is widely recognized as the primary contributor to tobacco dependence. Previous studies have indicated that molecular and behavioral responses to nicotine are primarily mediated by ventral tegmental area (VTA) neurons, and accumulating evidence suggests that glia play prominent roles in nicotine addiction. However, VTA neurons and glia have yet to be characterized at the transcriptional level during the progression of nicotine self-administration. Here, a male mouse model of nicotine self-administration was established and the timing of three critical phases (pre-addiction, addicting, and post-addiction phase) was characterized. Single-nucleus RNA sequencing (snRNA-seq) in the VTA at each phase was performed to comprehensively classify specific cell subtypes. Adaptive changes occurred during the addicting and post-addiction phases, with the addicting phase displaying highly dynamic neuroplasticity that profoundly impacted the transcription in each cell subtype. Furthermore, significant transcriptional changes in energy metabolism-related genes were observed, accompanied by notable structural alterations in neuronal mitochondria during the progression of nicotine self-administration. The results provide insights into mechanisms underlying the progression of nicotine addiction, serving as important resource for identifying potential molecular targets for nicotine cessation.

Alcohol and e-cigarette damage alveolar-epithelial barrier by activation of P2X7r and provoke brain endothelial injury via extracellular vesicles

BACKGROUND

Use of nicotine containing products like electronic cigarettes (e-Cig) and alcohol are associated with mitochondrial membrane depolarization, resulting in the extracellular release of ATP, and mitochondrial DNA (mtDNA), mediating inflammatory responses. While nicotine effects on lungs is well-known, chronic alcohol (ETH) exposure also weakens lung immune responses and cause inflammation. Extracellular ATP (eATP) released by inflammatory/stressed cells stimulate purinergic P2X7 receptors (P2X7r) activation in adjacent cells. We hypothesized that injury caused by alcohol and e-Cig to pulmonary alveolar epithelial cells (hPAEpiC) promote the release of eATP, mtDNA and P2X7r in circulation. This induces a paracrine signaling communication either directly or via EVs to affect brain cells (human brain endothelial cells - hBMVEC).

METHODS

We used a model of primary human pulmonary alveolar epithelial cells (hPAEpiC) and exposed the cells to 100 mM ethanol (ETH), 100 µM acetaldehyde (ALD), or e-Cig (1.75 µg/mL of 1.8% or 0% nicotine) conditioned media, and measured the mitochondrial efficiency using Agilent Seahorse machine. Gene expression was measured by Taqman RT-qPCR and digital PCR. hPAEpiC-EVs were extracted from culture supernatant and characterized by flow cytometric analysis. Calcium (Ca2+) and eATP levels were quantified using commercial kits. To study intercellular communication via paracrine signaling or by EVs, we stimulated hBMVECs with hPAEpiC cell culture medium conditioned with ETH, ALD or e-cig or hPAEpiC-EVs and measured Ca2+ levels.

RESULTS

ETH, ALD, or e-Cig (1.8% nicotine) stimulation depleted the mitochondrial spare respiration capacity in hPAEpiC. We observed increased expression of P2X7r and TRPV1 genes (3-6-fold) and increased intracellular Ca2+ accumulation (20-30-fold increase) in hPAEpiC, resulting in greater expression of endoplasmic reticulum (ER) stress markers. hPAEpiC stimulated by ETH, ALD, and e-Cig conditioned media shed more EVs with larger particle sizes, carrying higher amounts of eATP and mtDNA. ETH, ALD and e-Cig (1.8% nicotine) exposure also increased the P2X7r shedding in media and via EVs. hPAEpiC-EVs carrying P2X7r and eATP cargo triggered paracrine signaling in human brain microvascular endothelial cells (BMVECs) and increased Ca2+ levels. P2X7r inhibition by A804598 compound normalized mitochondrial spare respiration, reduced ER stress and diminished EV release, thus protecting the BBB function.

CONCLUSION

Abusive drugs like ETH and e-Cig promote mitochondrial and endoplasmic reticulum stress in hPAEpiC and disrupts the cell functions via P2X7 receptor signaling. EVs released by lung epithelial cells against ETH/e-cig insults, carry a cargo of secondary messengers that stimulate brain cells via paracrine signals.

Alcohol and e-cigarette damage alveolar-epithelial barrier by activation of P2X7r and provoke brain endothelial injury via extracellular vesicles

Background

Use of nicotine containing products like electronic cigarettes (e-Cig) and alcohol are associated with mitochondrial membrane depolarization, resulting in the extracellular release of ATP, and mitochondrial DNA (mtDNA), mediating inflammatory responses. While nicotine effects on lungs is well-known, chronic alcohol (ETH) exposure also weakens lung immune responses and cause inflammation. Extracellular ATP (eATP) released by inflammatory/stressed cells stimulate purinergic P2X7 receptors (P2X7r) activation in adjacent cells. We hypothesized that injury caused by alcohol and e-Cig to pulmonary alveolar epithelial cells (hPAEpiC) promote the release of eATP, mtDNA and P2X7r in circulation. This induces a paracrine signaling communication either directly or via EVs to affect brain cells (human brain endothelial cells - hBMVEC).

Methods

We used a model of primary human pulmonary alveolar epithelial cells (hPAEpiC) and exposed the cells to 100 mM ethanol (ETH), 100 μM acetaldehyde (ALD), or e-Cig (1.75μg/mL of 1.8% or 0% nicotine) conditioned media, and measured the mitochondrial efficiency using Agilent Seahorse machine. Gene expression was measured by Taqman RT-qPCR and digital PCR. hPAEpiC-EVs were extracted from culture supernatant and characterized by flow cytometric analysis. Calcium (Ca2+) and eATP levels were quantified using commercial kits. To study intercellular communication via paracrine signaling or by EVs, we stimulated hBMVECs with hPAEpiC cell culture medium conditioned with ETH, ALD or e-cig or hPAEpiC-EVs and measured Ca2+ levels.

Results

ETH, ALD, or e-Cig (1.8% nicotine) stimulation depleted the mitochondrial spare respiration capacity in hPAEpiC. We observed increased expression of P2X7r and TRPV1 genes (3-6-fold) and increased intracellular Ca2+ accumulation (20-30-fold increase) in hPAEpiC, resulting in greater expression of endoplasmic reticulum (ER) stress markers. hPAEpiC stimulated by ETH, ALD, and e-Cig conditioned media shed more EVs with larger particle sizes, carrying higher amounts of eATP and mtDNA. ETH, ALD and e-Cig (1.8% nicotine) exposure also increased the P2X7r shedding in media and via EVs. hPAEpiC-EVs carrying P2X7r and eATP cargo triggered paracrine signaling in human brain microvascular endothelial cells (BMVECs) and increased Ca2+ levels. P2X7r inhibition by A804598 compound normalized mitochondrial spare respiration, reduced ER stress and diminished EV release, thus protecting the BBB function.

Conclusion

Abusive drugs like ETH and e-Cig promote mitochondrial and endoplasmic reticulum stress in hPAEpiC and disrupts the cell functions via P2X7 receptor signaling. EVs released by lung epithelial cells against ETH/e-cig insults, carry a cargo of secondary messengers that stimulate brain cells via paracrine signals.

Ketogenic diet: a potential adjunctive treatment for substance use disorders

Substance use disorders (SUD) can lead to serious health problems, and there is a great interest in developing new treatment methods to alleviate the impact of substance abuse. In recent years, the ketogenic diet (KD) has shown therapeutic benefits as a dietary therapy in a variety of neurological disorders. Recent studies suggest that KD can compensate for the glucose metabolism disorders caused by alcohol use disorder by increasing ketone metabolism, thereby reducing withdrawal symptoms and indicating the therapeutic potential of KD in SUD. Additionally, SUD often accompanies increased sugar intake, involving neural circuits and altered neuroplasticity similar to substance addiction, which may induce cross-sensitization and increased use of other abused substances. Reducing carbohydrate intake through KD may have a positive effect on this. Finally, SUD is often associated with mitochondrial damage, oxidative stress, inflammation, glia dysfunction, and gut microbial disorders, while KD may potentially reverse these abnormalities and serve a therapeutic role. Although there is much indirect evidence that KD has a positive effect on SUD, the small number of relevant studies and the fact that KD leads to side effects such as metabolic abnormalities, increased risk of malnutrition and gastrointestinal symptoms have led to the limitation of KD in the treatment of SUD. Here, we described the organismal disorders caused by SUD and the possible positive effects of KD, aiming to provide potential therapeutic directions for SUD.

Cardiolipin and OPA1 Team up for Methamphetamine-Induced Locomotor Activity by Promoting Neuronal Mitochondrial Fusion in the Nucleus Accumbens of Mice

Mitochondria are highly dynamic organelles with coordinated cycles of fission and fusion occurring continuously to satisfy the energy demands in the complex architecture of neurons. How mitochondria contribute to addicted drug-induced adaptable mitochondrial networks and neuroplasticity remains largely unknown. Through liquid chromatography-mass spectrometry-based lipidomics, we first analyzed the alteration of the mitochondrial lipidome of three mouse brain areas in methamphetamine (METH)-induced locomotor activity and conditioned place preference. The results showed that METH remodeled the mitochondrial lipidome of the hippocampus, nucleus accumbens (NAc), and striatum in both models. Notably, mitochondrial hallmark lipid cardiolipin (CL) was specifically increased in the NAc in METH-induced hyperlocomotor activity, which was accompanied by an elongated giant mitochondrial morphology. Moreover, METH significantly boosted mitochondrial respiration and ATP generation as well as the copy number of mitochondrial genome DNA in the NAc. By screening the expressions of mitochondrial dynamin-related proteins, we found that repeated METH significantly upregulated the expression of long-form optic atrophy type 1 (L-OPA1) and enhanced the interaction of L-OPA1 with CL, which may promote mitochondrial fusion in the NAc. On the contrary, neuronal OPA1 depletion in the NAc not only recovered the dysregulated mitochondrial morphology and synaptic vesicle distribution induced by METH but also attenuated the psychomotor effect of METH. Collectively, upregulated CL and OPA1 cooperate to mediate METH-induced adaptation of neuronal mitochondrial dynamics in the NAc, which correlates with the psychomotor effect of METH. These findings propose a potential therapeutic approach for METH addiction by inhibiting neuronal mitochondrial fusion.

Cocaine perturbs mitovesicle biology in the brain

Cocaine, an addictive psychostimulant, has a broad mechanism of action, including the induction of a wide range of alterations in brain metabolism and mitochondrial homeostasis. Our group recently identified a subpopulation of non-microvesicular, non-exosomal extracellular vesicles of mitochondrial origin (mitovesicles) and developed a method to isolate mitovesicles from brain parenchyma. We hypothesised that the generation and secretion of mitovesicles is affected by mitochondrial abnormalities induced by chronic cocaine exposure. Mitovesicles from the brain extracellular space of cocaine-administered mice were enlarged and more numerous when compared to controls, supporting a model in which mitovesicle biogenesis is enhanced in the presence of mitochondrial alterations. This interrelationship was confirmed in vitro. Moreover, cocaine affected mitovesicle protein composition, causing a functional alteration in mitovesicle ATP production capacity. These data suggest that mitovesicles are previously unidentified players in the biology of cocaine addiction and that target therapies to fine-tune brain mitovesicle functionality may be beneficial to mitigate the effects of chronic cocaine exposure.

Thymic involution caused by repeated cocaine administration includes apoptotic cell loss followed by ectopic adipogenesis

Cocaine abuse has a negative impact on the immune system. To investigate the adverse effects of binge cocaine administration on lymphoid organs such as thymus and spleen, we examined the effects of repeated intravenous (i.v.) administration of cocaine on rats. Sprague Dawley rats (male, 8 weeks old) received 20 mg/kg body weight of cocaine hydrochloride per day for 7 or 14 days. In addition to a significant loss in the weight of the spleen, consistent with our previous intraperitoneal (i.p.) injection model of binge cocaine abuse (50 mg/kg cocaine for 7 days), we also found a significant loss of weight as well as apparent shrinkage of the thymus in the cocaine group. Transcriptome analysis of the thymus revealed increased expressions of genes involved in apoptosis, such as Ifi27 and Traf2, as well as decreased expressions of several genes related to lipid metabolism, such as Cd36, Adipoq, Scd1, and Fabp4, in the thymus of the cocaine group (7 days), suggesting an apoptotic loss of thymic cells as well as alterations in lipid metabolism. Paradoxically, cocaine activates PPARγ, a key transcriptional factor activating lipid metabolism, although ectopic adipogenesis was scarcely observed in the thymus. Further analysis of rats administered 20 mg/kg cocaine for 14 days revealed ectopic adipogenesis, which was accompanied with the activation of PPARγ as well as increased expression of Adipoq and Fabp4, in the thymus. Taken together, these results indicate that repeated cocaine administration induces thymic involution, which is initiated by the loss of thymic cells through apoptosis and subsequent ectopic adipocyte development.

The fluorescent aptasensor based on CRISPR-Cas12a combined with TdT for highly sensitive detection of cocaine

Ultrasensitive and specific detection of cocaine is of great significance for monitoring cocaine abuse. Herein, a fluorescent aptasensor via coupling CRISPR-Cas12a, with magnetic nanoparticles (MNPs), split-aptamer, and terminal deoxynucleotidyl transferase (TdT), was developed for the detection of cocaine. In short, the complete cocaine aptamer is split into two parts, one is modified on magnetic nanoparticles (MNPs) and the other is free. The presence of cocaine will mediate the binding of these two segments. Then TdT will mediate the extension to form an ultra-long sequence that can bind with multiple CRISPR-Cas12a resulting in the trans-cleavage activity of CRISPR-Cas12a being triggered. Thence, the DNA reporter which is bi-labeled with fluorophore and quencher is cleaved resulting in the generation of a fluorescence signal. The developed fluorescent aptasensor realizes the detection of cocaine with excellent sensitivity and specificity. The detection limit is low down to 33 pM, and the linear range is from 330 to 1.65 × 10⁵ pM. Most importantly, this fluorescent aptasensor can be successfully applied to the determination of cocaine in human plasma samples.

Neurobiological Mechanisms Modulating Emotionality, Cognition and Reward-Related Behaviour in High-Fat Diet-Fed Rodents

Affective and substance-use disorders are associated with overweight and obesity-related complications, which are often due to the overconsumption of palatable food. Both high-fat diets (HFDs) and psychostimulant drugs modulate the neuro-circuitry regulating emotional processing and metabolic functions. However, it is not known how they interact at the behavioural level, and whether they lead to overlapping changes in neurobiological endpoints. In this literature review, we describe the impact of HFDs on emotionality, cognition, and reward-related behaviour in rodents. We also outline the effects of HFD on brain metabolism and plasticity involving mitochondria. Moreover, the possible overlap of the neurobiological mechanisms produced by HFDs and psychostimulants is discussed. Our in-depth analysis of published results revealed that HFDs have a clear impact on behaviour and underlying brain processes, which are largely dependent on the developmental period. However, apart from the studies investigating maternal exposure to HFDs, most of the published results involve only male rodents. Future research should also examine the biological impact of HFDs in female rodents. Further knowledge about the molecular mechanisms linking stress and obesity is a crucial requirement of translational research and using rodent models can significantly advance the important search for risk-related biomarkers and the development of clinical intervention strategies.

A Scientometric Visualization Analysis for Molecular Mechanisms of Substance Abuse and Its Neurotoxicity From 1997 to 2021

Substance abuse has become a global problem due to drug-induced addiction and neurotoxicity, which causes a huge physical, social, and financial burden. Various kinds of drugs can hijack the users’/abusers’ behavior and associated neurocircuitry. To summarize recent scientific advances on drug abuse, we reviewed relevant publications to analyze research progress and such trends through bibliometric ways. Based on retrieval strategies, a total of 681 scientific records published from 1997 to 2021 were screened and included in the Web of Science (WoS) database. Further scientometric analysis revealed that annual publication output increased across this period, with the United States of America (USA) contributing a significant number of reasons. Research has focused on neurotransmitter, oxidative stress, mitochondrial system injury, and other neurotoxic mechanisms. Neuroimmune, neurotoxic targets, and new psychoactive substances have been hot topics in recent years, which deserve continued research in the future. Specific research on molecular mechanisms has progressed across this period, with an emphasis on the root cause of toxicity and molecular targets for therapy. Moreover, collaborations of international multi-disciplinary research teams have been efficient and need to be encouraged for addiction research and the development of appropriate therapeutic processes.

Role of Mitochondrial Dynamics in Cocaine's Neurotoxicity

The dynamic balance of mitochondrial fission and fusion maintains mitochondrial homeostasis and optimal function. It is indispensable for cells such as neurons, which rely on the finely tuned mitochondria to carry out their normal physiological activities. The potent psychostimulant cocaine impairs mitochondria as one way it exerts its neurotoxicity, wherein the disturbances in mitochondrial dynamics have been suggested to play an essential role. In this review, we summarize the neurotoxicity of cocaine and the role of mitochondrial dynamics in cellular physiology. Subsequently, we introduce current findings that link disturbed neuronal mitochondrial dynamics with cocaine exposure. Finally, the possible role and potential therapeutic value of mitochondrial dynamics in cocaine neurotoxicity are discussed.

ΔFOSB: A Potentially Druggable Master Orchestrator of Activity-Dependent Gene Expression

ΔFOSB is a uniquely stable member of the FOS family of immediate early gene AP1 transcription factors. Its accumulation in specific cell types and tissues in response to a range of chronic stimuli is associated with biological phenomena as diverse as memory formation, drug addiction, stress resilience, and immune cell activity. Causal connections between ΔFOSB expression and the physiological and behavioral sequelae of chronic stimuli have been established in rodent and, in some cases, primate models for numerous healthy and pathological states with such preclinical observations often supported by human data demonstrating tissue-specific ΔFOSB expression associated with several specific syndromes. However, the viability of ΔFOSB as a target for therapeutic intervention might be questioned over presumptive concerns of side effects given its expression in such a wide range of cell types and circumstances. Here, we summarize numerous insights from the past three decades of research into ΔFOSB structure, function, mechanisms of induction, and regulation of target genes that support its potential as a druggable target. We pay particular attention to the potential for targeting distinct ΔFOSB isoforms or distinct ΔFOSB-containing multiprotein complexes to achieve cell type or tissue specificity to overcome off-target concerns. We also cover critical gaps in knowledge that currently limit the exploitation of ΔFOSB's therapeutic possibilities and how they may be addressed. Finally, we summarize both current and potential future strategies for generating small molecules or genetic tools for the manipulation of ΔFOSB in the clinic.