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![Spectroscopy voxel location and composition
Voxel density maps of (A) inferior frontal (MNIX,Y,Z = 40, 21, 9) and (B) occipital (MNIX,Y,Z = 17, −87, 14) voxel placement overlaid on a glass brain template. MNI coordinates refer to center of mass of the group composite voxel. Color bars indicate percentage overlap across all participants. Centroids for each participant’s ¹H-MRS voxel are shown in red. Mean spectra from all participants for (C) inferior frontal and (D) occipital voxels, showing the raw data, LCModel fit, baseline, glutamate, myo-inositol, and N-acetyl aspartate fits. NAA N-acetyl aspartate. Code for voxel density and centroid figures [77, 78] was retrieved from: https://github.com/nwd2918/MRS-voxel-plot.](publication/359246767/figure/fig1/AS:1134097791483905@1647401392126/Spectroscopy-voxel-location-and-composition-Voxel-density-maps-of-A-inferior-frontal.png)
Spectroscopy voxel location and composition Voxel density maps of (A) inferior frontal (MNIX,Y,Z = 40, 21, 9) and (B) occipital (MNIX,Y,Z = 17, −87, 14) voxel placement overlaid on a glass brain template. MNI coordinates refer to center of mass of the group composite voxel. Color bars indicate percentage overlap across all participants. Centroids for each participant’s ¹H-MRS voxel are shown in red. Mean spectra from all participants for (C) inferior frontal and (D) occipital voxels, showing the raw data, LCModel fit, baseline, glutamate, myo-inositol, and N-acetyl aspartate fits. NAA N-acetyl aspartate. Code for voxel density and centroid figures [77, 78] was retrieved from: https://github.com/nwd2918/MRS-voxel-plot.
Source publication
Anorexia nervosa (AN) and bulimia nervosa (BN) are associated with altered brain structure and function, as well as increased habitual behavior. This neurobehavioral profile may implicate neurochemical changes in the pathogenesis of these illnesses. Altered glutamate, myo-inositol and N-acetyl aspartate (NAA) concentrations are reported in restrict...
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Loneliness and, to a lesser degree, social support are considered under-researched topics in the literature on eating disorders (ED). This study attempted to expand the relevant body of research by examining loneliness in combination with social support in ED patients and in healthy controls (HC). Binge-eating problems, emotional eating, resilience...
Citations
... A sample of patients with BED was included in 3(75%) studies, a sample with AN-BP in 1(25%) study and a sample with BN in 1(25%) study. When it comes to behavior, patients with BED displayed more compulsive decision-making during the two-step task and patients with AN-BP and BN reported higher scores on the Creature Of Habit Scale (COHS) (Voon et al., 2014;Westwater et al., 2022). Furthermore, there were behavioral differences which were linked to changes in brain connectivity and metabolites. ...
... The lower resting-state connectivity between the NAc and SFG in patients with BED was correlated to more habit-directed behavior in the reversal learning task . The lower levels of NAA in the left inferior PFC in patients with AN-BP were associated with higher automaticity scores on the COHS (Westwater et al., 2022). Summarized, these studies suggest that individuals who binge eat display more habitual behavior and that this could be linked to a lower frontostriatal functional connectivity and lower levels of NAA in the frontal cortex. ...
Alcohol use disorder (AUD) and bulimia nervosa (BN) are two psychiatric disorders that are characterized by binge behavior where large quantities of alcohol (i.e., binge drinking [BD]) or food (i.e., binge eating [BE]) are consumed within a short period of time. Furthermore, both disorders are highly prevalent, impactful, and challenging to treat. Therefore, new and improved treatments are needed for both disorders, but in order to develop them, a better understanding of what triggers binge behavior is required.
It is thought that stress and negative affect (NA) are important triggers for BD and BE. Indeed, studies in a laboratory context have shown that inducing stress and NA can lead to increased alcohol and food consumption in patients with AUD or an eating disorder respectively. Furthermore, studies conducted in daily life report that NA increases in the hours before a BE episode and that NA is higher before a BE episode than before a regular meal. However, these findings raise the question how stress and NA cause patients to experience a higher desire to binge drink or bing eat, as well as lose control, making them more likely to display binge behavior. Previous authors have hypothesized that there are several important factors such as craving, negative urgency (i.e., the tendency to act rashly under elevated stress or NA), and disturbances in reward processing including delay discounting (i.e., preferring more immediate rewards). Therefore, this thesis explores the role of these factors in how stress and NA lead to binge behavior.
First, an experience sampling method (ESM) study was performed where 76 controls, 53 patients with AUD, 51 patients with BN, and 19 patients with AUD and BN reported on their mood, behavior, and context in daily life. When it comes to BE, we found that NA was related to subsequent BE in patients with BN through rash action and craving, highlighting the importance of negative urgency and craving in the relation between NA and BE. Contrastingly, we also observed that NA was associated with subsequent not eating, indicating that NA can have competing effects on eating behaviors in patients with BN. When it comes to alcohol use, we saw that NA was non-linearly related to craving, alcohol use, and BD in patients with AUD, emphasizing that both lower and higher levels of NA can lead to alcohol consumption in patients. However, these findings raise the question whether factors such as NA, rash action, and craving can actually predict binge behavior in daily life. Therefore, we used machine learning to build person-specific and pooled prediction models for BE, alcohol use, and BD in patients with AUD and/or BN. We found that pooled models performed better at predicting BE, alcohol use, and BD, but that predictors from person-specific models might be more useful clinically. Importantly, craving and time of day were the most important predictors for all behaviors, while there were differences in how affect and social context were related to BE, alcohol use, and BD.
Second, the role of the neurobiological reward system in BE was explored by conducting a systematic review of previously published studies. We found that individuals who binge eat display a lower striatal dopamine release in rest, a change in the volume of the striatum, frontal cortex and insula as well as a lower fronto-striatal connectivity. Furthermore, there was a higher activity of the brain reward system when anticipating or receiving food, and individuals who binge eat relied more on previous experiences when making decisions and displayed more habitual behavior. These results show that individuals who binge eat display structural and functional changes in the neurobiological reward system, which could play a vital role in the onset and maintenance of BE episodes.
Third, an MRI study was performed with 50 controls, 27 patients with AUD, and 25 patients with BN. In this study, the effect of stress on alcohol and food delay discounting was investigated to see whether stress makes patients with AUD or BN prefer more immediately available alcohol or food respectively. We found that stress increased delay discounting of alcohol in patients with AUD, but not in controls, and that this was related to a lower activity of the right supplementary area. In contrast, we observed that stress increased delay discounting of food in controls, but not in patients with BN, and that this was related to a lower activity of the anterior cingulate cortex. These results suggest that acute stress could indeed make patients with AUD prefer more immediately available alcohol, while this relation might not be as straightforward in patients with BN.
Fourth, a PET/MR study was conducted in 12 controls investigating the relation between stress-induced dopamine release in the ventromedial prefrontal cortex (vmPFC), fronto-striatal functional connectivity and negative urgency in daily life. Here, stress decreased functional connectivity between the vmPFC and dorsal striatum, but increased connectivity with the contralateral ventral stiatum. However, individuals with a higher connectivity between the vmPFC and dorsal striatum showed more negative urgency in daily life. Furthermore, individuals with a higher stress-induced DA release had a higher change in fronto-striatal connectivity and displayed more daily life negative urgency. These results highlight how stress can impact dopamine signaling and fronto-striatal connectivity and how this can lead to rash action.
Taken together, this thesis shows that there is a complex relation between stress and NA on the one hand and binge behavior on the other hand. Specifically, the results indicate that stress and NA might have competing effects on eating behaviors in patients with BN, while both lower and higher levels of stress and NA might be related to alcohol use in patients with AUD. Furthermore, the findings of this thesis highlight the importance of craving, negative urgency, reward processing, and delay discounting in this relation, and demonstrate the key role of dopamine transmission and fronto-striatal connectivity. Future studies should explore how stress and NA lead to binge behavior in more depth with more diverse samples, longitudinal designs, and by combining multiple modalities.
... Imaging studies probing reward learning in binge eating find different reinforcement processing in ACC, PFC, and striatum compared with control subjects, but the results vary dependent on the task and studied patient group [25,26]. Overall, more model-free learning is reported, indicating that individuals who binge eat are more likely to base their decisions on the outcomes of previous choices [27]. ...
... Second, binge eating behavior is further propelled, via repeated food reward exposure that sensitizes food cues and increases food anticipation [5,6]. In the third phase, binge behavior becomes less goal-directed but more compulsive and rigid with an overall reward hyposensitivity [8,25]. General anticipation to pursue rewards (wanting), as well as subjective pleasure (liking) to nonfood rewards may decrease in this phase [14 && ]. ...
Purpose of review
Studies increasingly show the importance of reward processing in binge eating and provide evidence of associated changes in the neurobiological reward system. This review gives an up-to-date overview of the neurobiological substrates of reward processing subconstructs in binge eating. Neural findings are linked to different behavioral theories and the clinical relevance is discussed.
Recent findings
Increased neural responses in the orbitofrontal cortex, anterior cingulate cortex as well as striatum during anticipation and receipt of food rewards are found in association to binge eating. Increased model-free learning is also found and associated with altered brain reward reactivity. Data in rest report reduced striatal dopamine release and lower frontostriatal connectivity. Mechanisms of onset of binge eating are less clear, but specific personality traits, related to frontostriatal dysconnectivity, probably increase the risk of binge eating onset.
Summary
Both structural and task-based imaging studies show differences in the neurobiological reward system in binge eating. These changes are linked to specific reward processing, such as altered reward responsiveness to food cues, reinforcement learning, and habitual behavior. Findings are lined with different behavioral theories of binge eating, and a staging model is described, from onset to full illness development. Understanding the specific underlying aberrant reward mechanism in binge eating, associated with different stages of the illness, enables caregivers to focus their treatment more precisely.
... Blasel et al. [19], who reported similar findings, argued that elevated glutamate, which may promote cell-damaging effects on neuronal tissue through excitotoxicity, may induce cell membrane degradation. However, single voxel 1 H MRS studies at 1.5 T or 3 T found no group difference between AN and HC [18,47,[49][50][51] or reduced Glx concentrations in AN [46,50]. Results from a pilot investigation at 7 T (n = 13 patients with AN) indicated a reduction of glutamate in AN but no group difference between AN and HC for glutamine [48]. ...
... Unfortunately, comparison with our results is limited, as this study included patients with AN at different stages of treatment and many were taking psychotropic medication [48], which may act on the glutamergic system [52]. Our result of reduced mIns/tCr in GM and WM in AN is in line with previous studies that reported reduced levels of mIns or ratios of mIns/tCr in AN compared to HC in WM and/or GM [20,46,50,51,53]. MIns is considered a marker of glial cell integrity as it is mainly located in astrocytes and microglia cells [54] and also has a function in axonal-glial signaling [51]. ...
... Our result of reduced mIns/tCr in GM and WM in AN is in line with previous studies that reported reduced levels of mIns or ratios of mIns/tCr in AN compared to HC in WM and/or GM [20,46,50,51,53]. MIns is considered a marker of glial cell integrity as it is mainly located in astrocytes and microglia cells [54] and also has a function in axonal-glial signaling [51]. Impaired astrocyte function has previously been shown in rodent models of AN, and a reduction in astrocytes has been associated with changes in brain volume in rodent models [55,56]. ...
The acute state of anorexia nervosa (AN) is associated with widespread reductions in cortical gray matter (GM) thickness and white matter (WM) volume, suspected changes in myelin content and elevated levels of the neuronal damage marker neurofilament light (NF-L), but the underlying mechanisms remain largely unclear. To gain a deeper understanding of brain changes in AN, we applied a multimodal approach combining advanced neuroimaging methods with analysis of blood-derived biomarkers. In addition to standard measures of cortical GM thickness and WM volume, we analyzed tissue-specific profiles of brain metabolites using multivoxel proton magnetic resonance spectroscopy, T1 relaxation time as a proxy of myelin content leveraging advanced quantitative MRI methods and serum NF-L concentrations in a sample of 30 female, predominately adolescent patients with AN and 30 age-matched female healthy control participants. In patients with AN, we found a reduction in GM cortical thickness and GM total N-acetyl aspartate. The latter predicted higher NF-L levels, which were elevated in AN. Furthermore, GM total choline was elevated. In WM, there were no group differences in either imaging markers, choline levels or N-acetyl aspartate levels. The current study provides evidence for neuronal damage processes as well as for increased membrane lipid catabolism and turnover in GM in acute AN but no evidence for WM pathology. Our results illustrate the potential of multimodal research including tissue-specific proton magnetic resonance spectroscopy analyses to shed light on brain changes in psychiatric and neurological conditions, which may ultimately lead to better treatments.
... (Castro-Fornieles et al., 2007). Participants were primarily diagnosed with the AN restrictive sub-type (3/7 studies; 43%), with one study including participants diagnosed with AN binge-purging sub-type only (Westwater et al., 2022) and three studies not reporting the specific diagnosis (Godlewska et al., 2017;Castro-Fornieles et al., 2010;Ohrmann et al., 2004). Of those studies that reported mental health co-morbidities (3/7), these included depression (MDD), anxiety, panic and personality disorders. ...
... The majority of studies reported measuring only one neurometabolite of interest, with one measuring two (Joos et al., 2011) and another measuring three (Godlewska et al., 2017). The measurement of GABA was reported in one study (Godlewska et al., 2017), glutamate in three (Godlewska et al., 2017;Joos et al., 2011;Westwater et al., 2022), glutamine in one (Godlewska et al., 2017), and Glx in five (Castro-Fornieles et al., 2007, 2010Ohrmann et al., 2004;Maier et al., 2020;Joos et al., 2011). Neurometabolites were measured in seven brain regions including the anterior cingulate cortex (ACC), dorsolateral PFC, inferior lateral PFC, anterior frontal cortex, insula, occipital lobe (including visual cortex), and putamen (see Table 2 and Fig. 2). ...
... not only grey matter). Only three studies (Castro-Fornieles et al., 2007;Ohrmann et al., 2004;Westwater et al., 2022) corrected for cerebral spinal fluid (CSF), white matter (WM) and grey matter (GM) volumes. The one study that measured GABA (Godlewska et al., 2017) used a 7 T scanner, and therefore, they were capable of detecting GABA using a standard STEAM sequence in contrast to the edited sequence criteria previously recommended (Peek et al., 2020). ...
The dysregulation of excitatory and inhibitory neurotransmission is considered a pathological marker of Anorexia Nervosa (AN), however, no systematic evaluation of the proton Magnetic Resonance Spectroscopy (1H-MRS) literature has been conducted to date. Accordingly, we conducted a systematic review of neurometabolite differences between individuals with AN and healthy controls (HC). A comprehensive database search (until June 2023) identified seven studies meeting inclusion criteria. Samples included adolescents and adults with similar mean age (AN: 22.20 HC: 22.60), and female percentages (AN: 98%; HC: 94%). The review found a considerable need for improving study design and the reporting of MRS sequence parameters and analysis. Reduced glutamate concentrations in the ACC and OCC, and reduced Glx concentrations in the ACC were reported by one and two studies, respectively. Lastly, only one study to date has quantified GABA concentrations, with no significant differences found. In conclusion, there is currently insufficient evidence of excitatory and inhibitory neurometabolites changes in AN. As the 1H-MRS literature in AN increases, the key questions herein proposed must be revisited.
... In this paper, the authors managed to improve self-control of food intake and weight alterations by NAc deep-brain stimulation during food craving in two patients with obesity and BED. Binge episodes are also associated with altered habitual behavior, and more compulsive decision making [76,77]. Data from human studies reveal that BED is characterized by altered DA function, with increased food-reward sensitivity and impulsivity/compulsivity (for a recent review, see [78]). ...
Eating disorders are multifactorial disorders that involve maladaptive feeding behaviors. Binge eating disorder (BED), the most prevalent of these in both men and women, is characterized by recurrent episodes of eating large amounts of food in a short period of time, with a subjective loss of control over eating behavior. BED modulates the brain reward circuit in humans and animal models, which involves the dynamic regulation of the dopamine circuitry. The endocannabinoid system plays a major role in the regulation of food intake, both centrally and in the periphery. Pharmacological approaches together with research using genetically modified animals have strongly highlighted a predominant role of the endocannabinoid system in feeding behaviors, with the specific modulation of addictive-like eating behaviors. The purpose of the present review is to summarize our current knowledge on the neurobiology of BED in humans and animal models and to highlight the specific role of the endocannabinoid system in the development and maintenance of BED. A proposed model for a better understanding of the underlying mechanisms involving the endocannabinoid system is discussed. Future research will be necessary to develop more specific treatment strategies to reduce BED symptoms.
... experimental task, with patients with anorexia showing reduced levels of prefrontal glutamate and N-acetyl aspartate (NAA) during increased automatic task performance [33]. Maladaptive habit formation was recently investigated as treatment target in a proof-of-concept study probing a psychotherapeutic intervention aimed at breaking habits [34]. ...
Introduction:
Anorexia nervosa is a frequent eating disorder that affects predominantly young women and may take a severe and chronically worsening course of disease contributing to its high mortality rate. Although a multitude of treatment options exist, this disease still bears a high relapse rate. In light of these facts, an improvement of existing and development of new treatment targets and options is warranted.
Areas covered:
The present review article covers recent developments in psychotherapy associated with the respective neuropsychological and brain alterations as well as highlights current and future pharmacotherapeutic options.
Expert opinion:
Several encouraging developments in the field of psychotherapy such as interventions targeting neurocognitive profiles or addressing reward processing, brain stimulation as well as pharmacological modulation of hormones, namely leptin, oxytocin, ghrelin and nesfatin-1 signaling might be - most likely as part of a multimodal treatment approach - efficacious in order to improve treatment of patients with anorexia nervosa, especially those with a severe course of disease as well as comorbidities. As anorexia nervosa represents a complex and severe mental disorder, it seems most likely that a combination and integration of different evidence-based treatment approaches and settings will contribute to an improved prognosis of this eating disorder. This should be further explored in future studies.
... The clinical literature has provided some insight into the involvement of the glutamatergic system in these aspects of AN. Three 1 H-MRS studies have investigated the association between excitatory and inhibitory neurometabolites and AN symptoms [24,81,127]. The earliest of these studies by Ohrmann et al. [81] reported decreased levels of the composite neurometabolite measure Glx (glutamate, GABA and glutamine) in the rostral ACC of participants with AN were correlated with increased levels of depression. ...
... Notably, N-acetyl-aspartate (NAA) levels in the insula were also negatively associated with shape concerns, suggesting dysfunctional processing in the insula may be due to neuronal loss. In a recent study, Westwater et al. [127] found reduced glutamate and NAA levels in the right inferior lateral PFC were associated with a higher propensity for automatic routine-like behaviours. ...
... Within the literature, most studies investigated markers of neuronal integrity (e.g. NAA) [158][159][160][161]. Regarding the studies that measured brain neurometabolites involved in excitatory and inhibitory neurotransmission, five investigated glutamate independent of Glx [25,127,[162][163][164], six quantified the composite Glx [24,80,81,163,165,166] and only one study measured GABA [25]. Compared with healthy controls, significantly decreased levels of glutamate in participants with AN were only reported in one study [25]. ...
Anorexia nervosa is a disorder associated with serious adverse health outcomes, for which there is currently considerable treatment ineffectiveness. Characterised by restrictive eating behaviours, distorted body image perceptions and excessive physical activity, there is growing recognition anorexia nervosa is associated with underlying dysfunction in excitatory and inhibitory neurometabolite metabolism and signalling. This narrative review critically explores the role of N-methyl-d-aspartate receptor-mediated excitatory and inhibitory neurometabolite dysfunction in anorexia nervosa and its associated biomarkers. The existing magnetic resonance spectroscopy literature in anorexia nervosa is reviewed and we outline the brain region-specific neurometabolite changes that have been reported and their connection to anorexia nervosa psychopathology. Considering the proposed role of dysfunctional neurotransmission in anorexia nervosa, the potential utility of zinc supplementation and sub-anaesthetic doses of ketamine in normalising this is discussed with reference to previous research in anorexia nervosa and other neuropsychiatric conditions. The rationale for future research to investigate the combined use of low-dose ketamine and zinc supplementation to potentially extend the therapeutic benefits in anorexia nervosa is subsequently explored and promising biological markers for assessing and potentially predicting treatment response are outlined.
... Only one study investigated metabolite concentrations in the brain with magnetic resonance spectroscopy (MRS). In this study, patients with AN-BP had lower levels of myo-inositol and N-acetylaspartate (NAA) in the inferior left PFC, but this was not the case in patients with BN (Westwater et al., 2022). These lower levels of myo-inositol and NAA were associated with eating disorder and depressive symptoms in the BN group, but not in patients with AN-BP. ...
... A sample of patients with BED were included in three (75%) studies, a sample with AN-BP in one (25%) study, and a sample with BN in one (25%) study. When it comes to behavior, patients with BED displayed more compulsive decisionmaking during the two-step task and patients with AN-BP and BN reported higher scores on the Creature of Habit Scale (COHS) (Voon et al., 2015;Westwater et al., 2022). Furthermore, there were behavioral differences that were linked to changes in brain connectivity and metabolites. ...
... The lower resting-state connectivity between the NAc and SFG in patients with BED was correlated with more habit-directed behavior in the reversal learning task (Haynos et al., 2021). The lower levels of NAA in the left inferior PFC in patients with AN-BP were associated with higher automaticity scores on the COHS (Westwater et al., 2022). Summarized, these studies suggest that individuals who binge eat display more habitual behavior and that this could be linked to a lower frontostriatal functional connectivity and lower levels of NAA in the frontal cortex. ...
Objective:
Changes in reward processing are hypothesized to play a role in the onset and maintenance of binge eating (BE). However, despite an increasing number of studies investigating the neurobiological reward system in individuals who binge eat, no comprehensive systematic review exists on this topic. Therefore, this review has the following objectives: (1) identify structural and functional changes in the brain reward system, either during rest or while performing a task; and (2) formulate directions for future research.
Methods:
A search was conducted of articles published until March 31, 2022. Neuroimaging studies were eligible if they wanted to study the reward system and included a group of individuals who binge eat together with a comparator group. Their results were summarized in a narrative synthesis.
Results:
A total of 58 articles were included. At rest, individuals who binge eat displayed a lower striatal dopamine release, a change in the volume of the striatum, frontal cortex, and insula, as well as a lower frontostriatal connectivity. While performing a task, there was a higher activity of the brain reward system when anticipating or receiving food, more model-free reinforcement learning, and more habitual behavior. Most studies only included one patient group, used general reward-related measures, and did not evaluate the impact of comorbidities, illness duration, race, or sex.
Discussion:
Confirming previous hypotheses, this review finds structural and functional changes in the neurobiological reward system in BE. Future studies should compare disorders, use measures that are specific to BE, and investigate the impact of confounding factors.
Public significance statement:
This systematic review finds that individuals who binge eat display structural and functional changes in the brain reward system. These changes could be related to a higher sensitivity to food, relying more on previous experiences when making decisions, and more habitual behavior. Future studies should use a task that is specific to binge eating, look across different patient groups, and investigate the impact of comorbidities, illness duration, race, and sex.
Objective
Individuals with eating disorders transdiagnostically engage in binge eating (BE) and/or purging, despite life‐threatening consequences. Little is known about factors that contribute to the persistence of these behaviors. This study explored whether habitual control over binge/purge (B/P) spectrum behaviors contributes to symptom persistence and whether negative reinforcement via reductions in negative affect is less influential in maintaining B/P behaviors that are under habitual control and are persistent.
Method
Women with BE and/or purging ( N = 81) completed self‐report measures assessing habit strength of BE and purging. Then, they completed a 14‐day ecological momentary assessment (EMA) protocol during which they completed measures of negative affect, BE, and purging multiple times per day.
Results
Habitual control over purging was associated with a greater frequency of purging during the EMA period. However, habitual control over BE was not associated with the severity of loss of control eating or the frequency of BE episodes. Habitual control did not moderate temporal relations between negative affect and B/P behaviors during the EMA period. However, exploratory analyses revealed that individuals with a longer duration of BE and greater habitual control over BE showed a less pronounced reduction in negative affect following BE.
Discussion
Overall, these findings suggest that purging may be maintained by habitual stimulus–response learning. In addition, they support the possibility that reduction in negative affect may play a less prominent role in maintaining BE that is habitual and persistent.
Public significance
This study investigated whether habit contributes to the persistence of symptoms in women with binge/purge spectrum behaviors and whether negative reinforcement via reductions in negative affect is less influential in maintaining binge/purge behaviors that are under habitual control. The findings suggest that purging may be maintained through habit. This supports the potential utility of habit reversal interventions to decrease habitual purging.
The existing data regarding the effects of polyethylene (PE) microplastics (MPs) smaller than 5 mm in size on earthworms are insufficient to fully comprehend their toxicity. In this study, earthworms Eisenia fetida were exposed to artificially added PE at a concentration ranging from 0.05 to 20 g/kg soil (0.005%-2%) for 60 days to determine the concentration range causing negative effects on earthworms and to uncover the potential toxic mechanisms. The individual growth, reproduction, and metabolic enzyme activities, including phase I enzymes (cytochrome P450 [CYP] 1A2, 2B6, 2C9, and 3A4), and phase II metabolic enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione sulfotransferase (GST)), and metabolomics were measured. The observed variations in responses of multiple cross-scale endpoints indicated that individual indices are less responsive to PE MPs than metabolic enzymes or metabolomics. Despite the absence of significant alterations in growth inhibition based on body weight, PE MPs at concentrations equal to or exceeding 2.5 g/kg were found to exert a toxic effect on earthworms, which was evidenced by significant changes in metabolic enzyme activities (CYP1A2, 2B6, 2C9, and 3A4, SOD, CAT, and GST) and important small molecule metabolites screened based on metabolomics, likely due to the bioaccumulation of PE. The toxicity of PE MPs to earthworms is inferred to be associated with neurotoxicity, oxidative damage, decreased detoxification capacity, energy metabolism imbalance, and impaired amino acid and purine metabolism due to bioaccumulation. The findings of this study will enhance our understanding of the molecular toxicity mechanisms of PE MPs and contribute to a more accurate assessment of the ecological risks posed by PE MPs in soil.
