Methamphetamine induces intestinal injury by altering gut microbiota and promoting inflammation in mice

Long-term exposure to advanced lipid peroxidation end products impairs cognitive function through microbiota-gut-brain axis

The frequent intake of ultra-processed, heat-processed, and fat-enriched foods rich in dietary advanced lipoxidation end-products (ALEs) has been correlated with cognitive decline; however, the underlying mechanisms of action remain unexplored. This study investigated the impact of a 12-month dietary exposure to ALEs on learning, memory, and Aβ1-42 accumulation in mice, with a focus on the AMPK/SIRT1 signaling pathway and ADAM10 expression. The gut microbiota and metabolomic profiles revealed ALEs-induced gut dysbiosis and cognitive impairment, highlighting modulation through the microbiota-gut-brain axis. Key findings include increased pathogenic bacteria and decreased beneficial bacteria, linked to metabolite profile changes that affect neurotoxic Aβ1-42 peptide accumulation. This long-term comprehensive study underscores the need for dietary guidelines to reduce ALE intake and mitigate neurodegenerative disease risk, highlighting the intricate interplay between diet, gut microbiota, and cognitive health.

Inulin alleviates GenX-induced intestinal injury in mice by modulating the MAPK pathway, cell cycle, and cell adhesion proteins

GenX, a substitute for perfluorooctanoic acid, has demonstrated potential enterotoxicity. The enterotoxic effects of GenX and effective interventions need further investigation. In the present study, the mice were administered GenX (2 mg/kg/day) with or without inulin supplementation (5 g/kg/day) for 12 weeks. Histopathological assessments revealed that GenX induced colonic gland atrophy, inflammatory cell infiltration, a reduction in goblet cell numbers, and decreased mucus secretion. Furthermore, a significant decrease in the protein levels of ZO-1, occludin, and claudin-5 indicated compromised barrier integrity. Transcriptomic analysis identified 2645 DEGs, which were mapped to 39 significant pathways. The TGF-β, BMP6, and β-catenin proteins were upregulated in the intestinal mucosa following GenX exposure, indicating activation of the TGF-β pathway. Conversely, the protein expression of PAK3, CyclinD2, contactin1, and Jam2 decreased, indicating disruptions in cell cycle progression and cell adhesion. Inulin cotreatment ameliorated these GenX-induced alterations, partially through modulating the MAPK pathway, as evidenced by the upregulation of the cell cycle and cell adhesion proteins. Collectively, these findings suggested that GenX exposure triggered intestinal injury in mice by activating the TGF-β pathway and disrupting proteins crucial for the cell cycle and cell adhesion, whereas inulin supplementation mitigated this injury by modulating the MAPK pathway.

Matrix Metalloproteinase-9 Signaling Regulates Colon Barrier Integrity in Models of HIV Infection

Infection with human immunodeficiency virus (HIV) increases risk for maladies of the gut barrier, which promotes sustained systemic inflammation even in virally controlled patients. We previously revealed morphological disorganization of colon epithelial barrier proteins in HIV-1 transgenic (Tg) rats. The current study evaluated mechanisms that may underlie gut barrier pathology induced by toxic HIV-1 proteins. Methamphetamine (meth) use is prevalent among HIV-infected individuals, and meth can exaggerate morbidity of HIV infection. Thus, we determined whether meth exposure worsened HIV-associated gut pathology using colon samples from HIV-1 Tg and non-Tg rats that self-administered meth 2 h/day for 21 days. Immunoblotting was conducted for occludin (a gut barrier protein) and matrix metalloproteinase-9 (MMP-9; a proteinase regulator of occludin). Colon levels of occludin were decreased, and MMP-9 levels and activity were increased in HIV-1 Tg rats. A Pearson correlation revealed an inverse relationship between occludin levels and MMP-9 activity. Doses of meth that were self-administered by Tg rats were lower than other rat models. Meth-induced trends in non-Tg rats were not significant, and meth did not exaggerate effects seen in Tg rats. Accordingly, only the HIV-effects on epithelial function were explored further. Transepithelial resistance (TER) across a monolayer of human colon epithelial cells (Caco-2) was used to examine treatments with the HIV-1 toxic protein, Tat, and the ability of pioglitazone, a PPARγ agonist that inhibits MMP-9, to mitigate Tat-induced changes. Exposure to Tat for 24 h decreased TER, which co-occurred with decreases in levels of barrier tight junction proteins (occludin, claudin-1, and zonula occludens-1) and with increases in the level and activity of MMP-9. Pretreatment or post-treatment with pioglitazone respectively prevented and restored Tat-induced impairments of Caco-2 barrier. Thus, while low doses of meth did not alter barrier proteins in the current study, exposure to HIV-1 proteins disrupted the gut barrier, and this action involved a dysregulation of MMP-9.

The role of the microbiota-gut-brain axis in methamphetamine-induced neurotoxicity: Disruption of microbial composition and short-chain fatty acid metabolism

Methamphetamine (METH) abuse is associated with significant neurotoxicity, high addiction potential, and behavioral abnormalities. Recent studies have identified a connection between the gut microbiota and METH-induced neurotoxicity and behavioral disorders. However, the underlying causal mechanisms linking the gut microbiota to METH pathophysiology remain largely unexplored. In this study, we employed fecal microbiota transplantation (FMT) and antibiotic (Abx) intervention to manipulate the gut microbiota in mice administered METH. Furthermore, we supplemented METH-treated mice with short-chain fatty acids (SCFAs) and pioglitazone (Pio) to determine the protective effects on gut microbiota metabolism. Finally, we assessed the underlying mechanisms of the gut-brain neural circuit in vagotomized mice. Our data provide compelling evidence that modulation of the gut microbiome through FMT or microbiome knockdown by Abx plays a crucial role in METH-induced neurotoxicity, behavioral disorders, gut microbiota disturbances, and intestinal barrier impairment. Furthermore, our findings highlight a novel prevention strategy for mitigating the risks to both the nervous and intestinal systems caused by METH, which involves supplementation with SCFAs or Pio.

Impact of Altered Gut Microbiota on Ketamine-Induced Conditioned Place Preference in Mice

Objects

Ketamine is a drug of abuse worldwide and current treatments for ketamine abuse are inadequate. It is an urgent need to develop novel anti-addictive strategy. Since gut microbiota plays a crucial role in drug abuse, the present study investigates the impact and mechanisms of the gut microbiota in addictive behaviors induced by ketamine addiction.

Methods

Conditioned place preference (CPP) was employed to assess addiction, followed by 16S rRNA gene sequencing to elucidate alterations in the gut microbiota. Furthermore, qRT-PCR, ELISA, and immunohistochemistry were conducted to evaluate the expression levels of crucial genes and proteins associated with the gut-brain axis. Additionally, we investigated whether ketamine addiction is regulated through the gut microbiota by orally administering antibiotics to establish pseudo-germ-free mice.

Results

We found that repeated ketamine administration (20 mg/kg) induced CPP and significantly altered gut microbiota diversity and composition, as revealed by 16S rRNA gene sequencing. Compared to the control group, ketamine exposure exhibited differences in the relative abundance of 5 microbial families, with 4 (Lachnospiraceae, Ruminococcaceae, Desulfovibrionaceae and Family-XIII) showing increases, while one (Prevotellaceae) displayed a decrease. At the genus level, five genera were upregulated, while one was downregulated. Furthermore, COG analysis revealed significant differences in protein functionality between the two groups. Additionally, axis series studies showed that ketamine dependence reduced levels of tight junction proteins, GABA and GABRA1, while increasing BDNF and 5-HT. Moreover, an oral antibiotic cocktail simulating pseudo germ-free conditions in mice did not enhance the addictive behavior induced by ketamine.

Conclusion

Our study supports the hypothesis that ketamine-induced CPP is mediated through the gut microbiota. The present study provides new insights into improvement of efficient strategy for addiction treatment.

Short-chain fatty acids mitigate Methamphetamine-induced hepatic injuries in a Sigma-1 receptor-dependent manner

Methamphetamine (Meth) is a potent psychostimulant with well-established hepatotoxicity. Gut microbiota-derived short-chain fatty acids (SCFAs) have been reported to yield beneficial effects on the liver. In this study, we aim to further reveal the mechanisms of Meth-induced hepatic injuries and investigate the potential protective effects of SCFAs. Herein, mice were intraperitoneally injected with 15 mg/kg Meth to induce hepatic injuries. The composition of fecal microbiota and SCFAs was profiled using 16 S rRNA sequencing and Gas Chromatography/Mass Spectrometry (GC/MS) analysis, respectively. Subsequently, SCFAs supplementation was performed to evaluate the protective effects against hepatic injuries. Additionally, Sigma-1 receptor knockout (S1R-/-) mice and fluvoxamine (Flu), an agonist of S1R, were introduced to investigate the mechanisms underlying the protective effects of SCFAs. Our results showed that Meth activated S1R and induced hepatic autophagy, inflammation, and oxidative stress by stimulating the MAPK/ERK pathway. Meanwhile, Meth disrupted SCFAs product-related microbiota, leading to a reduction in fecal SCFAs (especially Acetic acid and Propanoic acid). Accompanied by the optimization of gut microbiota, SCFAs supplementation normalized S1R expression and ameliorated Meth-induced hepatic injuries by repressing the MAPK/ERK pathway. Effectively, S1R knockout repressed Meth-induced activation of the MAPK/ERK pathway and further ameliorated hepatic injuries. Finally, the overexpression of S1R stimulated the MAPK/ERK pathway and yielded comparable adverse phenotypes to Meth administration. These findings suggest that Meth-induced hepatic injuries relied on the activation of S1R, which could be alleviated by SCFAs supplementation. Our study confirms the crucial role of S1R in Meth-induced hepatic injuries for the first time and provides a potential preemptive therapy.

Characterization of Gut Microbiota in Rats and Rhesus Monkeys After Methamphetamine Self-administration

Methamphetamine (MA) is one of the most abused drugs globally, but the mechanism of its addiction remains unclear. Several animal studies have shown that the gut microbiota (GM) influences addictive behaviors, but the pattern of GM changes during addiction in animals of different species remains unclear. The aim of this study was to explore the association between dynamic changes in GM and MA self-administration acquisition among two classical mammals, rhesus monkeys (Macaca mulatta) and rats, MA self-administration models. Male Sprague-Dawley rats and male rhesus monkeys were subjected to classical MA self-administration training, and fecal samples were collected before and after MA self-administration training, respectively. 16S rRNA sequencing was used for GM analyses. We found that GM changes were more pronounced in rats than in rhesus monkeys, as evidenced by more GM taxa producing significant differences before and after MA self-administration training in rats than in monkeys. We also found that the expression of the genus Clostridia_vadinBB60_group significantly decreased after MA self-administration training in both rats and rhesus monkeys. Lactobacillus changes were significantly negatively correlated with total MA uptake in rats (Pearson R =  - 0.666, p = 0.035; Spearman R =  - 0.721, p = 0.023), whereas its change was also highly negatively correlated with total MA uptake in rhesus monkeys (Pearson R =  - 0.882, p = 0.118; Spearman R =  - 1.000, p = 0.083), although this was not significant. These findings suggest that MA causes significant alterations in GM in both rhesus monkeys and rats and that the genus Lactobacillus might be a common therapeutic target for MA uptake prevention across the species.

The gut microbiota contributes to methamphetamine-induced reproductive toxicity in male mice

Methamphetamine (METH) is a psychostimulant drug belonging to the amphetamine-type stimulant class, known to exert male reproductive toxicity. Recent studies suggest that METH can disrupt the gut microbiota. Furthermore, the gut-testis axis concept has gained attention due to the potential link between gut microbiome dysfunction and reproductive health. Nonetheless, the role of the gut microbiota in mediating the impact of METH on male reproductive toxicity remains unclear. In this study, we employed a mouse model exposed to escalating doses of METH to assess sperm quality, testicular pathology, and reproductive hormone levels. The fecal microbiota transplantation method was employed to investigate the effect of gut microbiota on male reproductive toxicity. Transcriptomic, metabolomic, and microbiological analyses were conducted to explore the damage mechanism to the male reproductive system caused by METH. We found that METH exposure led to hormonal disorders, decreased sperm quality, and changes in the gut microbiota and testicular metabolome in mice. Testicular RNA sequencing revealed enrichment of several Gene Ontology terms associated with reproductive processes, as well as PI3K-Akt signaling pathways. FMT conveyed similar reproductive damage from METH-treated mice to healthy recipient mice. The aforementioned findings suggest that the gut microbiota plays a substantial role in facilitating the reproductive toxicity caused by METH, thereby highlighting a prospective avenue for therapeutic intervention in the context of METH-induced infertility.

A gut (microbiome) feeling about addiction: Interactions with stress and social systems

In recent years, an increasing attention has given to the intricate and diverse connection of microorganisms residing in our gut and their impact on brain health and central nervous system disease. There has been a shift in mindset to understand that drug addiction is not merely a condition that affects the brain, it is now being recognized as a disorder that also involves external factors such as the intestinal microbiota, which could influence vulnerability and the development of addictive behaviors. Furthermore, stress and social interactions, which are closely linked to the intestinal microbiota, are powerful modulators of addiction. This review delves into the mechanisms through which the microbiota-stress-immune axis may shape drug addiction and social behaviors. This work integrates preclinical and clinical evidence that demonstrate the bidirectional communication between stress, social behaviors, substance use disorders and the gut microbiota, suggesting that gut microbes might modulate social stress having a significance in drug addiction.

Associations between impulsivity and fecal microbiota in individuals abstaining from methamphetamine

INTRODUCTION

Methamphetamine (MA) abuse is a major public problem, and impulsivity is both a prominent risk factor and a consequence of addiction. Hence, clarifying the biological mechanism of impulsivity may facilitate the understanding of addiction to MA. The microbiota-gut-brain axis was suggested to underlie a biological mechanism of impulsivity induced by MA.

METHODS

We therefore recruited 62 MA addicts and 50 healthy controls (HCs) to investigate the alterations in impulsivity and fecal microbiota and the associations between them in the MA group. Thereafter, 25 MA abusers who abstained from MA for less than 3 months were followed up for 2 months to investigate the relationship between impulsivity and microbiota as abstinence became longer. 16S rRNA sequencing was conducted for microbiota identification.

RESULTS

Elevated impulsivity and dysbiosis characterized by an increase in opportunistic pathogens and a decrease in probiotics were identified in MA abusers, and both the increased impulsivity and disrupted microbiota tended to recover after longer abstinence from MA. Impulsivity was related to microbiota, and the effect of MA abuse on impulsivity was mediated by microbiota.

CONCLUSION

Our findings potentially highlighted the importance of abstention and implicated the significant role of the microbiota-gut-brain axis in the interrelationship between microbiota and behaviors, as well as the potential of microbiota as a target for intervention of impulsivity.

Effects of Multiple High-Dose Methamphetamine Administration on Enteric Dopaminergic Neurons and Intestinal Motility in the Rat Model

Several studies have identified the effects of methamphetamine (MA) on central dopaminergic neurons, but its effects on enteric dopaminergic neurons (EDNs) are unclear. The aim of this study was to investigate the effects of MA on EDNs and intestinal motility. Male Sprague-Dawley rats were randomly divided into MA group and saline group. The MA group received the multiple high-dose MA treatment paradigm, while the controls received the same saline treatment. After enteric motility was assessed, different intestinal segments (i.e., duodenum, jejunum, ileum, and colon) were taken for histopathological, molecular biological, and immunological analysis. The EDNs were assessed by measuring the expression of two dopaminergic neuronal markers, dopamine transporter (DAT) and tyrosine hydroxylase (TH), at the transcriptional and protein levels. We also used c-Fos protein, a marker of neural activity, to detect the activation of EDNs. MA resulted in a significant reduction in TH and DAT mRNA expression as well as in the number of EDNs in the duodenum and jejunum (p < 0.05). MA caused a dramatic increase in c-Fos expression of EDNs in the ileum (p < 0.001). The positional variability of MA effects on EDNs paralleled the positional variability of its effect on intestinal motility, as evidenced by the marked inhibitory effect of MA on small intestinal motility (p < 0.0001). This study found significant effects of MA on EDNs with locational variability, which might be relevant to locational variability in the potential effects of MA on intestinal functions, such as motility.

The impact of psychostimulants on central and peripheral neuro-immune regulation: a scoping review of cytokine profiles and their implications for addiction

It is now well-accepted that psychostimulants act on glial cells causing neuroinflammation and adding to the neurotoxic effects of such substances. Neuroinflammation can be described as an inflammatory response, within the CNS, mediated through several cytokines, reactive oxygen species, chemokines and other inflammatory markers. These inflammatory players, in particular cytokines, play important roles. Several studies have demonstrated that psychostimulants impact on cytokine production and release, both centrally and at the peripheral level. Nevertheless, the available data is often contradictory. Because understanding how cytokines are modulated by psychoactive substances seems crucial to perspective successful therapeutic interventions, here, we conducted a scoping review of the available literature. We have focused on how different psychostimulants impact on the cytokine profile. Publications were grouped according to the substance addressed (methamphetamine, cocaine, methylphenidate, MDMA or other amphetamines), the type of exposure and period of evaluation (acute, short- or long-term exposure, withdrawal, and reinstatement). Studies were further divided in those addressing central cytokines, circulating (peripheral) levels, or both. Our analysis showed that the classical pro-inflammatory cytokines TNF-α, IL-6, and IL-1β were those more investigated. The majority of studies have reported increased levels of these cytokines in the central nervous system after acute or repeated drug. However, studies investigating cytokine levels during withdrawal or reinstatement have shown higher variability in their findings. Although we have identified fewer studies addressing circulating cytokines in humans, the available data suggest that the results may be more robust in animal models than in patients with problematic drug use. As a major conclusion, an extensive use of arrays for relevant cytokines should be considered to better determine which cytokines, upon the classical ones, may be involved in the progression from episodic use to the development of addiction. A concerted effort is still necessary to address the link between peripheral and central immune players, including from a longitudinal perspective. Until there, the identification of new biomarkers and therapeutic targets to envision personalized immune-based therapeutics will continue to be unlikely.

Gut microbiota contribute to Methamphetamine-induced cardiotoxicity in mouse model

Methamphetamine (METH) is a psychotropic drug known to cause cardiotoxicity. The gut-heart axis is emerging as an important pathway linking gut microbiota to cardiovascular disease, but the precise association between METH-induced cardiotoxicity and gut microbiota has yet to be elucidated. In this study, we established an escalating dose-multiple METH administration model in male BALB/c mice, examined cardiac injury and gut microbiota, and investigated the contribution of gut microbiota to cardiotoxicity induced by METH. Additionally, we treated mice with antibiotics and fecal microbiota transplantation (FMT) to assess the impact of gut microbiota on cardiotoxicity. Our results showed that METH exposure altered the p53 and PI3K/Akt signaling pathways and modulated the apoptosis pathway in heart tissue, accompanied by elevated levels of Bax/BCL-2 expression and cleaved caspase-3 proteins. METH exposure increased the diversity and richness of gut microbiota, and significantly changed the microbial community composition, accompanied by elevated abundance of Lactobacillus, Bifidobacterium, and decreased abundance of Bacteroides, norank_f_Muribaculaceae and Alistipes. Eliminating gut microbiota by antibiotics treatment alleviated METH-induced cardiotoxicity, while FMT treatment transferred similar cardiac injury manifestations from METH-exposed mice to healthy recipient mice. Our study unveils the crucial involvement of gut microbiota in the development of cardiotoxicity induced by METH and provides potential strategies for treating cardiac complications caused by METH.

Microbial community succession in the intestine of mice with deep partial-thickness burns

Introduction

Burn injury has been shown to lead to changes in the composition of the gut microbiome and cause other damage in patients. However, little is known about how the gut microbial community evolves in individuals who have recovered from burn injury.

Methods

In this study, we established a model of deep partial-thickness burn in mice and collected fecal samples at eight time points (pre-burn, 1, 3, 5, 7, 14, 21, and 28 days post-burn) for 16S rRNA amplification and high-throughput sequencing.

Results

The results of the sequencing were analyzed using measures of alpha diversity, and beta diversity and taxonomy. We observed that the richness of the gut microbiome declined from day 7 post-burn and that the principal component and microbial community structure varied over time. On day 28 after the burn, the microbiome composition largely returned to the pre-burn level, although day 5 was a turning point for change. Some probiotics, such as the Lachnospiraceae_NK4A136_group, decreased in composition after the burn but were restored in the later recovery period. In contrast, Proteobacteria showed an opposite trend, which is known to include potential pathogenic bacteria.

Conclusion

These findings demonstrate gut microbial dysbiosis after burn injury and provide new insights into the burn-related dysbiosis of the gut microbiome and strategies for improving the treatment of burn injury from the perspective of the microbiota.

Obeticholic acid protects against methamphetamine-induced anxiety-like behavior by ameliorating microbiota-mediated intestinal barrier impairment

Methamphetamine (Meth) abuse can cause severe anxiety disorder and interfere with gut homeostasis. Obeticholic acid (OCA) has emerged as a protective agent against diet-related anxiety that improves gut homeostasis. The potential for OCA to ameliorate Meth-induced anxiety, and the microbial mechanisms involved, remain obscure. Here, C57/BL6 mice were intraperitoneally injected with Meth (15 mg/kg) to induce anxiety-like behavior. 16 S rRNA sequence analysis and fecal microbiome transplantation (FMT) were used to profile the gut microbiome and evaluate its effects, respectively. Orally administered OCA was investigated for protection against Meth-induced anxiety. Results indicated that Meth mediated anxiety-like behavior, aroused hippocampal neuroinflammation through activation of the TLR4/MyD88/NF-κB pathway, weakened intestinal barrier and disturbed the gut microbiome. Specifically, abundance of anxiety-related Rikenella was increased. FMT from Meth-administrated mice also weakened intestinal barrier and elevated serum LPS, inducing hippocampal neuroinflammation and anxiety-like behavior in recipient mice. Finally, OCA pretreatment ameliorated Meth-induced impairment of gut homeostasis by reshaping the microbial composition and improving the intestinal barrier. Meth-induced anxiety-like behavior and hippocampal neuroinflammation were also ameliorated by OCA pretreatment. These preliminary findings reveal the crucial role of gut microbiota in Meth-induced anxiety-like behavior and neuroinflammation, highlighting OCA as a potential candidate for the prevention of Meth-induced anxiety.

Differences in clinical features and gut microbiota between individuals with methamphetamine casual use and methamphetamine use disorder

Background

The transition from methamphetamine (MA) casual use (MCU) to compulsive use is enigmatic as some MA users can remain in casual use, but some cannot. There is a knowledge gap if gut microbiota (GM) play a role in differing MCU from MA use disorder (MUD). We aimed to investigate the clinical features and GM differences between individuals with MCU and MUD.

Method

We recruited two groups of MA users -MCU and MUD - and matched them according to age and body mass index (n=21 in each group). Participants were accessed using the Semi-Structured Assessment for Drug Dependence and Alcoholism, and their fecal samples were undergone 16S ribosomal DNA sequencing. We compared the hosts' clinical features and GM diversity, composition, and structure (represented by enterotypes) between the two groups. We have identified differential microbes between the two groups and performed network analyses connecting GM and the clinical traits.

Result

Compared with the casual users, individuals with MUD had higher incidences of MA-induced neuropsychiatric symptoms (e.g., paranoia, depression) and withdrawal symptoms (e.g., fatigue, drowsiness, and increased appetite), as well as stronger cravings for and intentions to use MA, and increased MA tolerance. The GM diversity showed no significant differences between the two groups, but four genera (Halomonas, Clostridium, Devosia, and Dorea) were enriched in the individuals with MUD (p<0.05). Three distinct enterotypes were identified in all MA users, and Ruminococcus-driven enterotype 2 was dominant in individuals with MUD compared to the MCU (61.90% vs. 28.60%, p=0.03). Network analysis shows that Devosia is the hub genus (hub index = 0.75), which is not only related to the counts of the MUD diagnostic criteria (ρ=0.40; p=0.01) but also to the clinical features of MA users such as reduced social activities (ρ=0.54; p<0.01). Devosia is also associated with the increased intention to use MA (ρ=0.48; p<0.01), increased MA tolerance (ρ=0.38; p=0.01), craving for MA (ρ=0.37; p=0.01), and MA-induced withdrawal symptoms (p<0.05).

Conclusion

Our findings suggest that Ruminococcus-driven enterotype 2 and the genera Devosia might be two influential factors that differentiate MA casual use from MUD, but further studies are warranted.

Exploring the role and mechanism of gut microbiota in methamphetamine addiction using antibiotic treatment followed by fecal microbiota transplantation

Recently, the role of the gut microbiota in the context of drug addiction has attracted the attention of researchers; however, the specific effects and underlying mechanisms require further exploration. To accomplish this, C57BL/6 mice were firstly treated with methamphetamine (MA). Conditioned place preference (CPP) behavior changes, gut permeability and function, microglial activation, and inflammatory cytokine expression were systematically analyzed in antibiotics-treated mice with microbiota depletion and in fecal microbiota transplantation mice with microbiota reconstitution. MA treatment altered microbiota composition and caused gut dysbiosis. Depletion of gut microbiota with antibiotics inhibited MA-induced CPP formation, and fecal microbiota transplantation reversed this inhibition. Mechanistic analyses indicated that antibiotic treatment decreased gut permeability and neuroinflammation, while fecal microbiota transplantation offset the impact of antibiotic treatment. Additionally, MA-induced microglial activation was suppressed by antibiotics but restored by microbiota transplantation, and this correlated well with the CPP score. Compared to antibiotic treatment, microbiota transplantation significantly increased 5-HT4 receptor expression in both the nucleus accumbens and the hippocampus. Furthermore, when fecal microbiota from healthy mice was transplanted into MA-treated mice, the CPP scores decreased. Our results provide a novel avenue for understanding MA addiction and suggest a potential future intervention strategy.

Silencing the Tlr4 Gene Alleviates Methamphetamine-Induced Hepatotoxicity by Inhibiting Lipopolysaccharide-Mediated Inflammation in Mice

Methamphetamine (METH) is a stimulant drug. METH abuse induces hepatotoxicity, although the mechanisms are not well understood. METH-induced hepatotoxicity was regulated by TLR4-mediated inflammation in BALB/c mice in our previous study. To further investigate the underlying mechanisms, the wild-type (C57BL/6) and Tlr4^−/− mice were treated with METH. Transcriptomics of the mouse liver was performed via RNA-sequencing. Histopathological changes, serum levels of metabolic enzymes and lipopolysaccharide (LPS), and expression of TLR4-mediated proinflammatory cytokines were assessed. Compared to the control, METH treatment induced obvious histopathological changes and significantly increased the levels of metabolic enzymes in wild-type mice. Furthermore, inflammatory pathways were enriched in the liver of METH-treated mice, as demonstrated by expression analysis of RNA-sequencing data. Consistently, the expression of TLR4 pathway members was significantly increased by METH treatment. In addition, increased serum LPS levels in METH-treated mice indicated overproduction of LPS and gut microbiota dysbiosis. However, antibiotic pretreatment or silencing Tlr4 significantly decreased METH-induced hepatic injury, serum LPS levels, and inflammation. In addition, the dampening effects of silencing Tlr4 on inflammatory pathways were verified by the enrichment analysis of RNA-sequencing data in METH-treated Tlr4^−/− mice compared to METH-treated wild-type mice. Taken together, these findings implied that Tlr4 silencing, comparable to antibiotic pretreatment, effectively alleviated METH-induced hepatotoxicity by inhibiting LPS-TLR4-mediated inflammation in the liver.