Proton magnetic resonance spectroscopy in alcohol use disorders: a potential new endophenotype?

Multi-modal neuroimaging reveals differences in alcohol-cue reactivity but not neurometabolite concentrations in adolescents who drink alcohol

BACKGROUND

The objective of this multi-modal neuroimaging study was to identify neuroscience-informed treatment targets for adolescent alcohol use disorder (AUD) by examining potential neural alterations associated with adolescent alcohol use.

METHODS

Adolescents (ages 17-19) who heavily used (n=49) or did not use alcohol (n=22) were recruited for a multi-modal neuroimaging protocol, including proton magnetic resonance spectroscopy within the dorsal anterior cingulate cortex (dACC) and an fMRI alcohol cue-reactivity task. The alcohol cue-reactivity task was analyzed across 11 a priori regions-of-interest (ROI), including the dACC, and in an exploratory whole-brain approach. Correlations were run between neurometabolite levels and alcohol cue-reactivity in the dACC.

RESULTS

There were no significant group differences in absolute neurometabolite concentrations. Compared to the control group, the alcohol-using group exhibited heightened alcohol cue reactivity in the left amygdala ROI (p=0.04). The whole-brain approach identified higher alcohol cue reactivity in the alcohol-using group compared to controls in the amygdala and occipital regions, and lower reactivity in the parietal lobe. Whole-brain sex effects were noted, with females displaying higher reactivity regardless of group. No significant correlations were found between neurometabolite levels and alcohol cue-reactivity in the dACC.

CONCLUSIONS

The null neurometabolic findings may be due to age, relatively low severity of alcohol use, and non-treatment-seeking status of the participants. Females showed overall higher reactivity to alcohol cues, indicating a sex effect regardless of alcohol use history. Higher amygdala reactivity in alcohol-using adolescents suggests that emotional processing related to alcohol cues may be a useful target for future adolescent AUD interventions.

Neuropharmacology of Alcohol Addiction with Special Emphasis on Proteomic Approaches for Identification of Novel Therapeutic Targets

Alcohol is a generic pharmacological agent with only a few recognized primary targets. Nmethyl- D-aspartate, gamma-aminobutyric acid, glycine, 5-hydroxytryptamine 3 (serotonin), nicotinic acetylcholine receptors, and L-type Ca2+ channels and G-protein-activated inwardly rectifying K channels are all involved. Following the first hit of alcohol on specific brain targets, the second wave of indirect effects on various neurotransmitter/neuropeptide systems begins, leading to the typical acute behavioral effects of alcohol, which range from disinhibition to sedation and even hypnosis as alcohol concentrations rise. Recent research has revealed that gene regulation is significantly more complex than previously thought and does not fully explain changes in protein levels. As a result, studying the proteome directly, which differs from the genome/transcriptome in terms of complexity and dynamicity, has provided unique insights into extraordinary advances in proteomic techniques that have changed the way we can analyze the composition, regulation, and function of protein complexes and pathways underlying altered neurobiological conditions. Neuroproteomics has the potential to revolutionize alcohol research by allowing researchers to gain a better knowledge of how alcohol impacts protein structure, function, connections, and networks on a global scale. The amount of information collected from these breakthroughs can aid in identifying valuable biomarkers for early detection and improved prognosis of an alcohol use disorder and future pharmaceutical targets for the treatment of alcoholism.

Brain metabolite alterations related to alcohol use: a meta-analysis of proton magnetic resonance spectroscopy studies

Alcohol misuse and alcohol use disorder (AlUD) have neurobiological consequences. This meta-analysis of proton magnetic resonance spectroscopy (MRS) studies aimed to assess the differences in brain metabolite levels in alcohol misuse and AUD relative to controls (PROSPERO registration: CRD42020209890). Hedge's g with random-effects modeling was used. Sub-group and meta-regression techniques explored potential sources of demographic and MRS parameter heterogeneity. A comprehensive literature review identified 43 studies, resulting in 69 models across gray and white matter (GM, WM). Lower N-acetylaspartate levels were found in frontal, anterior cingulate cortex (ACC), hippocampal, and cerebellar GM, and frontal and parietal WM, suggesting decreased neuronal and axonal viability. Lower choline-containing metabolite levels (all metabolites contributing to choline peak) were found in frontal, temporal, thalamic, and cerebellar GM, and frontal and parietal WM, suggesting membrane alterations related to alcohol misuse. Lower creatine-containing metabolite levels (Cr; all metabolites contributing to Cr peak) were found in temporal and occipital cortical GM, while higher levels were noted in midbrain/brainstem GM; this finding may have implications for using Cr as an internal reference. The lack of significant group differences in glutamate-related levels is possibly related to biological and methodological complexities. The few studies reporting on GABA found lower levels restricted to the ACC. Confounding variables were age, abstinence duration, treatment status, and MRS parameters (echo time, quantification type, data quality). This first meta-analysis of proton MRS studies consolidates the numerous individual studies to identify neurometabolite alterations within alcohol misuse and AUD. Future studies can leverage this new formalized information to investigate treatments that might effectively target the observed disturbances.

Changes in the brain directly following alcohol consumption-a study of healthy male individuals, with the use of proton magnetic resonance spectroscopy (1HMRS) and diffusion (DWI)

AIMS

To use proton magnetic resonance spectroscopy (1HMRS) and diffusion weighted imaging (DWI) to identify ethanol in the brain directly after consumption, and examine changes in brain metabolite levels and brain microstructure relative to the duration of time following exposure to alcohol.

METHODS

The study involved 44 male volunteers (18-55 years). All brain changes were assessed in the frontal lobes, occipital lobes, basal ganglia and cerebellum, however the detailed analyses focused on the frontal lobes. All participants were examined four times, i.e. before and 0.5-hour, 1 hour and 2 hours after consumption of 150 mL pure vodka (60 g of ethanol).

RESULTS

The highest ethanol levels were identified between 0.5 and 1 hour following alcohol intake. There were significant increases in the concentrations of lipids and lactates approximately one hour after alcohol consumption, and the concentration levels were found to normalise during the following two hours. Some statistically insignificant trends of changes were found for tCr, tCho, mI, GABA, Glc, Glx and tNAA. For the DWI and ADC (Apparent Diffusion Coefficient of water) values, the findings showed statistically insignificant decrease and increase, followed by a tendency towards normalisation. Similar associations in changes of metabolite concentrations and DWI and ADC values were found in the other locations investigated in the study.

CONCLUSION

A single dose of alcohol as used in this experiment produces increases in lipids and lactates in brain tissues that appear reversible.

Effect of alcohol on the central nervous system to develop neurological disorder: pathophysiological and lifestyle modulation can be potential therapeutic options for alcohol-induced neurotoxication

The central nervous system (CNS) is the major target for adverse effects of alcohol and extensively promotes the development of a significant number of neurological diseases such as stroke, brain tumor, multiple sclerosis (MS), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Excessive alcohol consumption causes severe neuro-immunological changes in the internal organs including irreversible brain injury and it also reacts with the defense mechanism of the blood-brain barrier (BBB) which in turn leads to changes in the configuration of the tight junction of endothelial cells and white matter thickness of the brain. Neuronal injury associated with malnutrition and oxidative stress-related BBB dysfunction may cause neuronal degeneration and demyelination in patients with alcohol use disorder (AUD); however, the underlying mechanism still remains unknown. To address this question, studies need to be performed on the contributing mechanisms of alcohol on pathological relationships of neurodegeneration that cause permanent neuronal damage. Moreover, alcohol-induced molecular changes of white matter with conduction disturbance in neurotransmission are a likely cause of myelin defect or axonal loss which correlates with cognitive dysfunctions in AUD. To extend our current knowledge in developing a neuroprotective environment, we need to explore the pathophysiology of ethanol (EtOH) metabolism and its effect on the CNS. Recent epidemiological studies and experimental animal research have revealed the association between excessive alcohol consumption and neurodegeneration. This review supports an interdisciplinary treatment protocol to protect the nervous system and to improve the cognitive outcomes of patients who suffer from alcohol-related neurodegeneration as well as clarify the pathological involvement of alcohol in causing other major neurological disorders.

Alterations of Metabolites in the Frontal Cortex and Amygdala Are Associated With Cognitive Impairment in Alcohol Dependent Patients With Aggressive Behavior

BACKGROUND

Alcohol dependence (AD) patients have a high prevalence of aggressive behavior (AB). The frontal cortex and amygdala contains various neurotransmitter systems and plays an important role in AB, which is also associated with cognitive deficits. However, to date, no study has addressed the association of metabolites in the frontal cortex and amygdala with cognitive deficits in Chinese aggressive behavior-alcohol dependent patients(AB-ADs).

METHODS

We recruited 80 male AD and 40 male healthy controls (HCs), who completed the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), the Modified Overt Aggression Scale (MOAS), and the proton magnetic resonance spectroscopy (¹H MRS) scan using 3.0T Siemens. The ¹H MRS data were automatically fitted with a linear combination model for quantification of metabolite levels of n-acetyl-aspartate (NAA), glutamate (Glu), Choline (Cho) and creatine (Cr). Metabolite levels were reported as ratios to Cr.

RESULTS

The AB-ADs group scored significantly lower than the non-aggression-alcohol dependent patients (NA-ADs) on these two RBANS subscales (immediate memory and attention function indices). The AB-ADs group showed a significant reduction in NAA/CR ratio in the left frontal cortex and Cho/Cr ratio in the left amygdala, and elevation in Glu/Cr ratio in the bilateral amygdala, compared with the NA-ADs group. The NAA/Cr ratio in the left frontal cortex was positively associated with immediate memory (r=0.60, P<0.05), and the Glu/Cr ratio in the right amygdala was negatively associated with delayed memory (r=-0.44,P<0.05) in AB-ADs group.

CONCLUSIONS

Metabolite alterations in the frontal cortex and amygdala may be involved in the pathophysiology of AB in AD and its associated cognitive impairment, especially immediate memory and delayed memory.

Brief Motivational Interventions Are Associated with Reductions in Alcohol-Induced Blackouts Among Heavy Drinking College Students

BACKGROUND

Alcohol-induced blackouts, a form of anterograde amnesia that restricts the encoding of short-term memories into long-term ones, are among the most severe alcohol-related consequences. College students are at high risk of experiencing alcohol-induced blackouts, and there is a need to determine whether alcohol interventions can effectively reduce blackouts in this population. The current study uses data from 3 randomized clinical trials to examine the effect of various intervention approaches on alcohol-induced blackouts.

METHODS

Four interventions were compared over 3 studies: (i) a computerized feedback intervention (electronic Check-Up To Go [e-Chug]; Study 1); (ii) a single-session brief motivational intervention (BMI; Study 1); (iii) a BMI plus behavioral economic session focused on increasing substance-free activities (BMI + Substance-Free Activity Session [SFAS]; Studies 2 and 3); and (iv) a BMI plus supplemental Relaxation Training session (BMI + Relaxation Training; Studies 2 and 3). Studies 1 and 3 also included an assessment-only control condition. For each study, participants reported whether they had experienced an alcohol-induced blackout at each time point; binary logistic regressions examined differential likelihood of experiencing an alcohol-induced blackout over time.

RESULTS

Neither the single-session BMI nor e-Chug reduced alcohol-induced blackouts over assessment only; however, participants in the BMI + SFAS or BMI + Relaxation Training condition were significantly less likely to experience an alcohol-induced blackout compared to assessment only at 1-month (Wald = 4.77, odds ratio [OR] = 0.53, p = 0.03) and 6-month follow-ups (Wald = 5.72, OR = 0.52, p = 0.02). Study 2 also revealed a larger effect for the BMI + SFAS over the BMI + Relaxation Training condition at 6 months (Wald = 4.11 OR = 0.22, p = 0.043), although this was not replicated in Study 3. The effects for the 2-session BMIs lasted 6 months, at which point maturation effects diminished differences between assessment-only and intervention conditions.

CONCLUSIONS

Two sessions of BMI are a substantial enough dose to result in reductions in alcohol-induced blackouts among college student heavy drinkers.

Greater monoamine oxidase a binding in alcohol dependence

BACKGROUND

Alcohol dependence (AD) is a multiorgan disease in which excessive oxidative stress and apoptosis are implicated. Monoamine oxidase A (MAO-A) is an important enzyme on the outer mitochondrial membrane that participates in the cellular response to oxidative stress and mitochondrial toxicity. It is unknown whether MAO-A levels are abnormal in AD. We hypothesized that MAO-A VT, an index of MAO-A level, is elevated in the prefrontal cortex (PFC) during AD, because markers of greater oxidative stress and apoptosis are reported in the brain in AD and a microarray analysis reported greater MAO-A messenger RNA in the PFC of rodents exposed to alcohol vapor.

METHODS

Sixteen participants with alcohol dependence and 16 healthy control subjects underwent [(11)C]-harmine positron emission tomography. All were nonsmoking, medication- and drug-free, and had no other past or present psychiatric or medical illnesses.

RESULTS

MAO-A VT was significantly greater in the PFC (37%, independent samples t test, t₃₀ = 3.93, p < .001), and all brain regions analyzed (mean 32%, multivariate analysis of variance, F₇,₂₄ = 3.67, p = .008). Greater duration of heavy drinking correlated positively with greater MAO-A VT in the PFC (r = .67, p = .005) and all brain regions analyzed (r = .73 to .57, p = .001-.02).

CONCLUSIONS

This finding represents a new pathological marker present in AD that is therapeutically targetable through direct inhibition or by novel treatments toward oxidative/pro-apoptotic processes implicated by MAO-A overexpression.

Altered anterior cingulate neurochemistry in emerging adult binge drinkers with a history of alcohol-induced blackouts

BACKGROUND

Binge alcohol consumption is associated with multiple neurobiological consequences, including altered neurophysiology, brain structure, and functional activation. Magnetic resonance spectroscopy (MRS) studies have demonstrated neurochemical alterations in the frontal lobe of alcohol users, although most studies focused on older, alcohol-dependent subjects.

METHODS

In this study, neurochemical data were acquired using MRS at 4.0 Tesla from emerging adults (18 to 24 years old) who were binge alcohol drinkers (BD, n = 23) or light drinkers (LD, n = 31). Since binge drinking is also associated with increased prevalence of experiencing an alcohol-induced blackout, BD were stratified into alcohol-induced blackout (BDBO) and non-blackout (BDN) groups.

RESULTS

Overall, BD had significantly lower gamma amino-butyric acid (GABA) and N-acetyl-aspartate (NAA) in the anterior cingulate cortex (ACC) than LD. When stratified by blackout history, BDBO also had lower ACC glutamate (Glu) than LD. No group differences in MRS metabolites were observed in the parietal-occipital cortex. Lower ACC GABA and Glu remained significant after accounting for lower gray matter content in BD, however, NAA differences were no longer evident. In addition, low ACC GABA levels were associated with greater alcohol use consequences, and worse response inhibition and attention/mental flexibility in BD.

CONCLUSIONS

These data indicate that binge drinking affects frontal lobe neurochemistry, more so in those who had experienced an alcohol-induced blackout. Characterization of the neurochemical profiles associated with binge alcohol consumption and blackout history may help identify unique risk factors for the later manifestation of alcohol abuse and dependence, in young individuals who are heavy, frequent drinkers, but who do not meet the criteria for alcohol abuse disorders.

Brain proton magnetic resonance spectroscopy of alcohol use disorders

This chapter critically reviews brain proton magnetic resonance spectroscopy ((1)H MRS) studies performed since 1994 in individuals with alcohol use disorders (AUD). We describe the neurochemicals that can be measured in vivo at the most common magnetic field strengths, summarize our knowledge about their general brain functions, and briefly explain some basic human (1)H MRS methods. Both cross-sectional and longitudinal research of individuals in treatment and of treatment-naïve individuals with AUD are discussed and interpreted on the basis of reported neuropathology. As AUDs are highly comorbid with chronic cigarette smoking and illicit substance abuse, we also summarize reports on their respective influences on regional proton metabolite levels. After reviewing research on neurobiologic correlates of relapse and genetic influences on brain metabolite levels, we finish with suggestions on future directions for (1)H MRS studies in AUDs. The review demonstrates that brain metabolic alterations associated with AUDs as well as their cognitive correlates are not simply a consequence of chronic alcohol consumption. Future MR research of AUDs in general has to be better prepared - and supported - to study clinically complex relationships between personality characteristics, comorbidities, neurogenetics, lifestyle, and living environment, as all these factors critically affect an individual's neurometabolic profile. (1)H MRS is uniquely positioned to tackle these complexities by contributing to a comprehensive biopsychosocial profile of individuals with AUD: it can provide non-invasive biochemical information on select regions of the brain at comparatively low overall cost for the ultimate purpose of informing more efficient treatments of AUDs.

Interactive effects of chronic cigarette smoking and age on brain volumes in controls and alcohol-dependent individuals in early abstinence

Chronic alcohol-use disorders (AUDs) have been shown to interact with normal age-related volume loss to exacerbate brain atrophy with increasing age. However, chronic cigarette smoking, a highly co-morbid condition in AUD and its influence on age-related brain atrophy have not been evaluated. We performed 1.5 T quantitative magnetic resonance imaging in non-smoking controls [non-smoking light drinking controls (nsCONs); n = 54], smoking light drinking controls (sCONs, n = 34), and one-week abstinent, treatment-seeking alcohol-dependent (ALC) non-smokers (nsALCs, n = 35) and smokers (sALCs, n = 43), to evaluate the independent and interactive effects of alcohol dependence and chronic smoking on regional cortical and subcortical brain volumes, emphasizing the brain reward/executive oversight system (BREOS). The nsCONs and sALCs showed greater age-related volume losses than the nsALCs in the dorsal prefrontal cortex (DPFC), total cortical BREOS, superior parietal lobule and putamen. The nsALCs and sALCs demonstrated smaller volumes than the nsCONs in most cortical region of interests (ROIs). The sCONs had smaller volumes than the nsCONs in the DPFC, insula, inferior parietal lobule, temporal pole/parahippocampal region and all global cortical measures. The nsALCs and sALCs had smaller volumes than the sCONs in the DPFC, superior temporal gyrus, inferior and superior parietal lobules, precuneus and all global cortical measures. Volume differences between the nsALCs and sALCs were observed only in the putamen. Alcohol consumption measures were not related to volumes in any ROI for ALC; smoking severity measures were related to corpus callosum volume in the sCONs and sALCs. The findings indicate that consideration of smoking status is necessary for a better understanding of the factors contributing to regional brain atrophy in AUD.

Effects of fat on MR-measured metabolite signal strengths: implications for in vivo MRS studies of the human brain

Recent MRS studies have indicated that a higher body mass index (BMI) is associated with lower brain metabolite levels. Generally, individuals with higher BMIs have more body fat deposits than individuals with normal BMIs. This single-voxel spectroscopy (SVS) study investigated possible effects of fat on MR-measured metabolite signal areas, which may at least partly explain the observed associations of BMI with MR-measured brain metabolite levels in vivo. SVS data were acquired at 4 T from a phantom containing N-acetylaspartate, glutamate and creatine, as well as from three healthy male adults. Back fat obtained from pig was used to assess the effects of fat on metabolite signals. With the same voxel size and placement, the phantom was first scanned without fat (baseline), and then with 0.7-cm- and 1.4-cm-thick fat layers placed on it. Each participant was also scanned first without fat and then with two 0.7-cm fat layers, one placed beneath the occiput and the other on the forehead. Two spectra were acquired per participant from the anterior cingulate and the parieto-occipital cortices. The metabolite resonance and corresponding water peak areas were then fitted and metabolite to water signal ratios were used for analyses. In both phantom and in vivo experiments, the metabolite-to-water ratios decreased in the presence of fat relative to baseline metabolite-to-water ratios. The reduced metabolite signals in the presence of fat reported here are reminiscent of the negative correlations observed between BMI and MR-measured metabolite levels. These apparent physical effects of fat have potentially far-reaching consequences for the accuracy of MR measurements of brain metabolite levels and their interpretation, particularly when large fat stores exist around the skull, such as in individuals with higher BMI.

The influence of the menstrual cycle on the result of brain examination with hydrogen magnetic resonance spectroscopy - a pilot study

BACKGROUND AND PURPOSE

Hydrogen magnetic resonance spectroscopy (1HMRS) is nowadays one of the basic tools for noninvasive brain metabolism assessment. The study focuses on the important problem of the influence of hormone fluctuation during the menstrual cycle on brain metabolism, assessed by 1HMRS for clinical diagnostics.

MATERIAL AND METHODS

In 11 healthy regularly menstruating women, 1HMRS was performed at the start (phase I), in the middle (phase II) and at the end (phase III) of the menstrual cycle. The relative concentration ratios of 12 brain metabolites in every woman in all cycle phases were examined, in 6 different volumes of interest (VOIs). Finally, statistically significant differences in relative metabolite ratios between the phases examined in given locations were sought.

RESULTS

Statistically significant relations between menstrual cycle phases and relative ratios of 4 metabolites - Lac/Cr, NAA/Cr, Glx1/Cr and Glx2/Cr - in different brain locations were found. In all locations, mean NAA/Cr ratios were greater in phase I compared to the other phases. A similar relationship was found for Glx1/Cr ratio in one location (left occipital lobe). For Lac/Cr and Glx2/Cr ratios, a higher mean ratio value was obtained in phase II compared to phases I and III in the right occipital lobe and left basal ganglia, respectively.

CONCLUSIONS

Menstrual cycle phase should be considered in planning a date and interpretation of 1HMRS examination, performed for the verification of a disease manifesting as brain metabolite disturbances in the 1HMRS spectrum.

Polysubstance and alcohol dependence: unique abnormalities of magnetic resonance-derived brain metabolite levels

BACKGROUND

Although comorbid substance misuse is common in alcohol dependence, and polysubstance abusers (PSU) represent the largest group of individuals seeking treatment for drug abuse today, we know little about potential brain abnormalities in this population. Brain magnetic resonance spectroscopy studies of mono-substance use disorders (e.g., alcohol or cocaine) reveal abnormal levels of cortical metabolites (reflecting neuronal integrity, cell membrane turnover/synthesis, cellular bioenergetics, gliosis) and altered concentrations of glutamate and γ-aminobutyric acid (GABA). The concurrent misuse of several substances may have unique and different effects on brain biology and function compared to any mono-substance misuse.

METHODS

High field brain magnetic resonance spectroscopy at 4 T and neurocognitive testing were performed at one month of abstinence in 40 alcohol dependent individuals (ALC), 28 alcohol dependent PSU and 16 drug-free controls. Absolute metabolite concentrations were calculated in anterior cingulate (ACC), parieto-occipital (POC) and dorso-lateral prefrontal cortices (DLPFC).

RESULTS

Compared to ALC, PSU demonstrated significant metabolic abnormalities in the DLPFC and strong trends to lower GABA in the ACC. Metabolite levels in ALC and light drinking controls were statistically equivalent. Within PSU, lower DLPFC GABA levels are related to greater cocaine consumption. Several cortical metabolite concentrations were associated with cognitive performance.

CONCLUSIONS

While metabolite concentrations in ALC at one month of abstinence were largely normal, PSU showed persistent and functionally significant metabolic abnormalities, primarily in the DLPFC. Our results point to specific metabolic deficits as biomarkers in polysubstance misuse and as targets for pharmacological and behavioral PSU-specific treatment.

Chronic cigarette smoking in alcohol dependence: associations with cortical thickness and N-acetylaspartate levels in the extended brain reward system

Chronic smoking in alcohol dependence is associated with abnormalities in brain morphology and metabolite levels in large lobar regions (e.g. frontal lobe). Here, we evaluated if these abnormalities are specifically apparent in several cortical and select subcortical components of the extended brain reward system (BRS), a network that is critically involved in the development and maintenance of all forms of addictive disorders. We studied 33 non-smoking and 43 smoking alcohol-dependent individuals (ALC) with 1 week of abstinence and 42 non-smoking Controls. At 1.5 Tesla, we obtained regional measures of cortical thickness and N-acetylaspartate (NAA; a surrogate marker of neuronal integrity) concentration in major components of the BRS as well as the corresponding measures throughout the cortex. Smoking ALC and non-smoking ALC demonstrated decreased thickness compared with Controls in the dorsolateral prefrontal cortex (DLPFC), insula, orbitofrontal cortex (OFC), the total BRS, total frontal cortex and global cortex. Smoking ALC had significantly decreased thickness compared to non-smoking ALC in the ACC, insula, the total BRS and total frontal cortex. Smoking ALC had also lower NAA concentrations than both non-smoking ALC and Controls in the DLPFC, insula, superior corona radiata and the total BRS. Alcohol consumption and common medical and psychiatric co-morbidities did not mediate differences between smoking and non-smoking ALC. This dual modality magnetic resonance (MR) study indicated that chronic smoking in ALC was associated with significant cortical thinning and NAA abnormalities in anterior brain regions that are implicated in the development and maintenance of addictive disorders.

Effect of metabotropic glutamate receptor 3 genotype on N-acetylaspartate levels and neurocognition in non-smoking, active alcoholics

Background

We studied the effects of single nucleotide polymorphisms (SNPs) in the metabotropic glutamate receptor 3 (GRM3) gene on brain N-acetylaspartate (NAA) concentrations and executive function (EF) skills in non-smoking, active alcoholics, and evaluated associations between these variables.

Methods

SNPs (rs6465084, rs1468412, and rs2299225) in GRM3 were genotyped in 49 male, non-smoking, alcohol-dependent patients and 45 healthy control subjects using ligase detection reactions. NAA/creatine (Cr) ratios in left prefrontal gray matter (GM) and white matter (WM), left parietal GM, left parietal WM, and cerebellar vermis regions were measured by Proton ¹ H Magnetic resonance spectroscopy (MRS). EF was measured by the Wisconsin Card Sorting Test (WCST).

Results

Compared to controls, alcoholics had lower NAA/Cr ratios in prefrontal GM and WM regions and performed more poorly on all EF tests (P < 0.001). Alcoholics with the A/A genotype for SNP rs6465084 had lower NAA/Cr ratios in prefrontal GM and WM regions and had poorer EF skills than alcoholics who were G-carriers for this SNP (P < 0.01). Non-alcoholics with the A/A genotype for rs6465084 also had lower NAA/Cr levels in prefrontal GM and made more random errors in the WCST than G-carriers (P < 0.01). The A/A genotype group for SNP rs6465084 was significantly different from the G carriers for the variables of NAA/Cr ratios and WCST scores in both alcoholics and controls (P < 0.05). Alcoholics who were T-carriers for rs1468412 had lower NAA/Cr ratios in prefrontal GM and showed poorer EF skills (P < 0.05). No effects of rs2299225 genotype on NAA/Cr or executive skills were observed. NAA/Cr in left prefrontal regions correlated with certain parameters of EF testing in both alcoholics and controls (P < 0.05), but the significance of this correlation among alcoholics disappeared after adjustment for the effects of genotype.

Conclusions

Our results provide evidence that glutamate system dysfunction may play a role in the prefrontal functional abnormalities seen in alcohol dependence. It is possible that certain GRM3 SNP genotypes (the A/A genotype of rs6465084 and the T allele of rs1468412) may further lower NAA/Cr levels and EF skills in addition to the effect of alcohol.

Ethanol withdrawal-induced brain metabolites and the pharmacological effects of acamprosate in mice lacking ENT1

Acamprosate is clinically used to treat alcohol-dependent patients. While the molecular and pharmacological mechanisms of acamprosate remain unclear, it has been shown to regulate γ-aminobutyric acid (GABA) or glutamate levels in the cortex and striatum. To investigate the effect of acamprosate on brain metabolites in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc), we employed in vivo 16.4 T proton magnetic resonance spectroscopy. We utilized type 1 equilibrative nucleoside transporter (ENT1) null mice since acamprosate attenuates ethanol drinking in these mice. Our findings demonstrated that ethanol withdrawal reduced GABA levels and increased phosphorylated choline compounds in the mPFC of both wild-type and ENT1 null mice. Notably, acamprosate normalized these withdrawal-induced changes only in ENT1 null mice. In the NAc, ethanol withdrawal increased glutamate and glutamine (Glx) levels only in wild-type mice. Interestingly, acamprosate reduced Glx levels in the NAc compared to the withdrawal state in both genotypes. These results provide a molecular basis for the pharmacological effect of acamprosate in the cortical-striatal circuit.

Loss in connectivity among regions of the brain reward system in alcohol dependence

A recently developed measure of structural brain connectivity disruption, the loss in connectivity (LoCo), is adapted for studies in alcohol dependence. LoCo uses independent tractography information from young healthy controls to project the location of white matter (WM) microstructure abnormalities in alcohol-dependent versus nondependent individuals onto connected gray matter (GM) regions. LoCo scores are computed from WM abnormality masks derived at two levels: (1) groupwise differences of alcohol-dependent individuals (ALC) versus light-drinking (LD) controls and (2) differences of each ALC individual versus the LD control group. LoCo scores based on groupwise WM differences show that GM regions belonging to the extended brain reward system (BRS) network have significantly higher LoCo (i.e., disconnectivity) than those not in this network (t = 2.18, P = 0.016). LoCo scores based on individuals' WM differences are also higher in BRS versus non-BRS (t = 5.26, P = 3.92 × 10(-6) ) of ALC. These results suggest that WM alterations in alcohol dependence, although subtle and spatially heterogeneous across the population, are nonetheless preferentially localized to the BRS. LoCo is shown to provide a more sensitive estimate of GM involvement than conventional volumetric GM measures by better differentiating between brains of ALC and LD controls (rates of 89.3% vs. 69.6%). However, just as volumetric measures, LoCo is not significantly correlated with standard metrics of drinking severity. LoCo is a sensitive WM measure of regional cortical disconnectivity that uniquely characterizes anatomical network disruptions in alcohol dependence.

Subjective responses to alcohol: a paradigm shift may be brewing

BACKGROUND

The meta-analysis by Quinn and Fromme (2011) is reviewed and integrated into the larger field. Guidelines for future research are presented.

RESULTS

With results of the meta-analysis along with those of a recent comprehensive prospective study by our group (King et al., 2011), there is a call to the field to specify terms and integrate theoretical frameworks to advance our knowledge and improve comparisons across trials.

CONCLUSIONS

The meta-analysis is both timely and thorough and will provide clinical researchers with important information to move the field forward.

Alcohol and the human brain: a systematic review of different neuroimaging methods

BACKGROUND

Imaging techniques have been in widespread use in the scientific community for more than 3 decades. They facilitate noninvasive, in vivo studies of the human brain in both healthy and diseased persons. These brain-imaging techniques have contributed significantly to our understanding of the effects of alcohol abuse and dependence on structural and functional changes in the human brain. A systematic review summarizing these contributions has not previously been conducted, and this is the goal of the current paper.

METHODS

The databases PubMed, PsycINFO, and PSYNDEX were searched using central key words. Fulfilling the inclusion criteria were 140 functional and structural imaging studies, together comprising data from more than 7,000 patients and controls. The structural imaging techniques we considered were cranial computerized tomography and various magnetic resonance imaging-based techniques, including voxel-based morphometry, deformation-based morphometry, diffusion tensor magnetic resonance imaging, and diffusion-weighted magnetic resonance imaging. The functional methods considered were magnetic resonance spectroscopy, positron emission tomography, single photon emission computed tomography, and functional magnetic resonance imaging.

RESULTS

Results from studies using structural imaging techniques have revealed that chronic alcohol use is accompanied by volume reductions of gray and white matter, as well as microstructural disruption of various white matter tracts. These changes are partially reversible following abstinence. Results from functional imaging methods have revealed metabolic changes in the brain, lower glucose metabolism, and disruptions of the balance of neurotransmitter systems. Additionally, functional imaging methods have revealed increased brain activity in the mesocorticolimbic system in response to alcohol-themed pictures relative to nondrug-associated stimuli, which might be of predictive value with regard to relapse.

CONCLUSIONS

There has been tremendous progress in the development of imaging technologies. Use of these technologies has clearly demonstrated the structural and functional brain abnormalities that can occur with chronic alcohol use. The study of the alcoholic brain provides an heuristic model which furthers our understanding of neurodegenerative changes in general, as well as their partial reversibility with sustained abstinence. Additionally, functional imaging is poised to become an important tool for generating predictions about individual brain functioning, which can then be used as a basis for personalized medicine.

Perturbation of the glutamate-glutamine system in alcohol dependence and remission

As acute ethanol exposure inhibits N-methyl-D-aspartate glutamate (Glu) receptors, sudden withdrawal from chronic alcohol use may lead to an increased activation of these receptors with excitotoxic effects. In the longer term, brain levels of Glu and its metabolites, such as glutamine (Gln), are likely to be chronically altered by alcohol, possibly providing a measure of overall abnormal Glu-Gln cycling. However, few studies have assessed concentrations of these metabolites in clinical populations of individuals with alcohol use disorders. Glu and Gln levels were compared in groups of 17 healthy controls and in 13 participants with alcohol dependence. Within the alcohol-dependent group, seven participants had current alcohol use disorder (AUD), and six had AUD in remission for at least 1 year (AUD-R). Neurometabolite concentrations were measured with proton magnetic resonance spectroscopy ((1)H-MRS) in a predominantly gray matter voxel that included the bilateral anterior cingulate gyri. Tissue segmentation provided an assessment of the proportion of gray matter in the (1)H-MRS voxel. The Drinker Inventory of Consequences (DrInC) and Form-90 were administered to all participants to quantify alcohol consequences and use. Glu level was lower and Gln level was higher in the AUD and AUD-R groups relative to the control group; creatine, choline, myo-inositol, and total N-acetyl groups, primarily N-acetylaspartate did not differ across groups. These results were not confounded by age, sex, or proportion of gray matter in the (1)H-MRS voxel. Neurometabolite concentrations did not differ between AUD and AUD-R groups. Subsequent regressions in the combined clinical group, treating voxel gray matter proportion as a covariate, revealed that total score on the DrInC was positively correlated with Gln but negatively correlated with both Glu and gray matter proportion. Regression analyses, including DrInC scores and smoking variables, identified a marginal independent effect of smoking on Gln. The current findings of higher Gln and lower Glu in the combined AUD and AUD-R groups might indicate a perturbation of the Glu-Gln cycle in alcohol use disorders. The absence of differences in mean Glu and Gln between the AUD and AUD-R groups suggests that altered Glu-Gln metabolism may either predate the onset of abuse or persist during prolonged abstinence.

Chronic cigarette smoking: implications for neurocognition and brain neurobiology

Compared to the substantial volume of research on the general health consequences associated with chronic smoking, little research has been specifically devoted to the investigation of its effects on human neurobiology and neurocognition. This review summarizes the peer-reviewed literature on the neurocognitive and neurobiological implications of chronic cigarette smoking in cohorts that were not seeking treatment for substance use or psychiatric disorders. Studies that specifically assessed the neurocognitive or neurobiological (with emphasis on computed tomography and magnetic resonance-based neuroimaging studies) consequences of chronic smoking are highlighted. Chronic cigarette smoking appears to be associated with deficiencies in executive functions, cognitive flexibility, general intellectual abilities, learning and/or memory processing speed, and working memory. Chronic smoking is related to global brain atrophy and to structural and biochemical abnormalities in anterior frontal regions, subcortical nuclei and commissural white matter. Chronic smoking may also be associated with an increased risk for various forms of neurodegenerative diseases. The existing literature is limited by inconsistent accounting for potentially confounding biomedical and psychiatric conditions, focus on cross-sectional studies with middle aged and older adults and the absence of studies concurrently assessing neurocognitive, neurobiological and genetic factors in the same cohort. Consequently, the mechanisms promoting the neurocognitive and neurobiological abnormalities reported in chronic smokers are unclear. Longitudinal studies are needed to determine if the smoking-related neurobiological and neurocognitive abnormalities increase over time and/or show recovery with sustained smoking cessation.

Body mass index is associated with brain metabolite levels in alcohol dependence--a multimodal magnetic resonance study

BACKGROUND

Recent studies demonstrated that alcohol dependence and excessive alcohol consumption are associated with increased rates of obesity. In healthy light-drinkers, we and others have observed associations between elevated body mass index (BMI) and reductions in brain volumes, lower concentrations of N-acetyl-aspartate (NAA, marker of neuronal viability) and choline-containing compounds (Cho, involved in membrane turnover), and lower glucose utilization, particularly in frontal lobe-a brain region that is particularly vulnerable to the effects of alcohol dependence. Here, we evaluated whether BMI in alcohol-dependent individuals was independently associated with regional measures of brain structure, metabolite concentrations, and neocortical blood flow.

METHODS

As part of a study on the effects of alcohol dependence on neurobiology, we analyzed retrospectively data from 54 alcohol-dependent males, abstinent from alcohol for about 1 month and with BMI between 20 and 37 kg/m(2) by structural MRI, perfusion MRI (blood flow), and proton magnetic resonance spectroscopic imaging.

RESULTS

After correction for age, smoking status, and various measures of alcohol consumption, higher BMI was associated with lower concentrations of NAA, Cho, creatine and phosphocreatine (Cr, involved in high energy metabolism), and myo-inositol (m-Ino, a putative marker of astrocytes) primarily in the frontal lobe, in subcortical nuclei, and cerebellar vermis (p < 0.004). Regional brain volumes and perfusion were not significantly related to BMI. Furthermore, comorbid conditions, clinical laboratory measures, and nutritional assessments were not significant predictors of these MR-based measures.

CONCLUSIONS

The results suggest that BMI, independent of age, alcohol consumption, and common comorbidities, is related to regional NAA, Cho, Cr, and m-Ino concentrations in this cohort of alcohol-dependent individuals. Additionally, as some common comorbid conditions in alcohol dependence such as cigarette smoking are associated with BMI, their associations with regional brain metabolite levels in alcohol-dependent individuals may also be influenced by BMI.

Neurochemistry of drug action: insights from proton magnetic resonance spectroscopic imaging and their relevance to addiction

Proton magnetic resonance spectroscopy ((1)H MRS) is a noninvasive imaging technique that permits measurement of particular compounds or metabolites within the tissue of interest. In the brain, (1)H MRS provides a snapshot of the neurochemical environment within a defined volume of interest. A search of the literature demonstrates the widespread utility of this technique for characterizing tumors, tracking the progress of neurodegenerative disease, and for understanding the neurobiological basis of psychiatric disorders. As of relatively recently, (1)H MRS has found its way into substance abuse research, and it is beginning to become recognized as a valuable complement in the brain imaging toolbox that also contains positron emission tomography, single-photon-emission computed tomography, and functional magnetic resonance imaging. Drug abuse studies using (1)H MRS have identified several biochemical changes in the brain. The most consistent alterations across drug class were reductions in N-acetylaspartate and elevations in myo-inositol, whereas changes in choline, creatine, and amino acid transmitters also were abundant. Together, the studies discussed herein provide evidence that drugs of abuse may have a profound effect on neuronal health, energy metabolism and maintenance, inflammatory processes, cell membrane turnover, and neurotransmission, and these biochemical changes may underlie the neuropathology within brain tissue that subsequently gives rise to the cognitive and behavioral impairments associated with drug addiction.

Pontocerebellar volume deficits and ataxia in alcoholic men and women: no evidence for "telescoping"

INTRODUCTION

Brain volume shrinkage is common in treatment-seeking patients with alcohol use disorders. Whether women are more vulnerable to brain dysmorphology than men despite lower alcohol consumption levels or shorter dependency ("telescoping effect") remains controversial and has not been considered with respect to infratentorial structures or their potential contribution to ataxia.

METHODS

The 200 participants included 64 men and 31 women with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition alcohol dependence and 105 controls. An infratentorial region (pons, cerebellar hemispheres, vermis (anterior, posterior, and inferior sectors), fissures, cisterns, fourth ventricle) was quantified with atlas-based parcellation. To enable comparison of men and women, regional tissue volumes were expressed as ratios of tissue in the volume. Participants also completed quantitative ataxia testing.

RESULTS

Total infratentorial and vermian tissue ratios were significantly smaller in alcoholics than controls; alcoholic women did not show disproportionately greater volume deficits than alcoholic men. A re-analysis including alcoholic men and women matched in alcohol consumption, onset age, abstinence duration, and age revealed again that alcoholic women did not have disproportionately greater regional vermian volume deficits than alcoholic men. Alcoholic men and women were impaired in all measures of ataxia, which correlated with low infratentorial tissue ratios in men.

DISCUSSION

Alcoholic men showed deficits of pontocerebellar volume ratios, yet alcoholic women did not display signs of "telescoping". Further, alcoholic men and women both showed signs of ataxia of gait and balance, related to affected pontocerebellar systems in the men but not the women, suggesting the need to consider other neural substrates for ataxia in women.

Associations between anterior cingulate cortex glutamate and gamma-aminobutyric acid concentrations and the harm avoidance temperament

Converging lines of evidence have suggested that the personality traits might have neurobiological underpinnings. The anterior cingulate cortex (ACC) has been implicated to play an important role in the human fear and anxiety. Functional and structural characteristics of ACC have been suggested to be associated with the harm avoidance (HA) temperament, one of the important temperament dimensions. Therefore, we aimed to investigate correlations between neurometabolite concentrations in ACC, specifically glutamate and gamma-aminobutyric acid (GABA), which are major excitatory and inhibitory neurotransmitters, respectively, and HA scores. Neurometabolite concentrations were measured using high resolution single voxel proton magnetic resonance spectroscopy ((1)H-MRS), and the HA temperament was evaluated using the Temperament and Character Inventory (TCI). Correlations between HA scores from 37 participants (21 men/16 women, age of 30.3+/-7.0) and glutamate and GABA concentrations in the mid-ACC region were evaluated. HA scores correlated negatively with glutamate concentrations in ACC (partial correlation, R=-0.54, df=33, P=0.001) and positively with GABA concentrations in ACC (partial correlation, R=0.48, df=30, P=0.005). These findings suggest that glutamate and GABA concentrations in ACC are closely related to levels of the HA temperament in healthy subjects.