Characterising the effects of AUD on the human brain

Alcohol use disorder (AUD) is a complex mental disorder characterised by the compulsive seeking and consumption of alcohol resulting in loss of control, as well as other adverse effects. The World Health Organisation (WHO) estimate that approximately 76.3 million people worldwide are diagnosable with AUD. AUD represents a large burden on society as it is the third leading risk factor for poor healthy globally.\ua0 There are many experimental paradigms of AUD; herein, we use brain imaging and proteomics to elucidate the cognitive and molecular effects of AUD on the human brain. In Chapter 1, we survey the literature to review the current status of brain imaging and proteomic investigations of AUD.Impaired inhibitory control is suggested to be key contributor to relapse during a period of prolonged abstinence. Changes in the µ-opioid receptor (MOR) and the D3 (DRD3) dopamine receptor pathway may negatively affect inhibitory control, making these two pathways clinically relevant in the context of addiction.\ua0 In Chapter 2, we used functional magnetic resonance imaging to measure the effects on GSK598809 and naltrexone on the DRD3 and MOR pathways on response inhibition using the go/no-go task (GNG). A semi-randomised, double-blind, placebo-controlled approach was used in groups of: abstinent alcohol-dependent (AUD), abstinent poly-substance abuse (poly-SUD) and healthy control volunteers.\ua0 For ‘stop’ trials, group effects were observed, demonstrating enhanced response in significantly identified clusters for both the GSK598809 and naltrexone. We found significant group effects in the activation of the left lingual gyrus, the right lateral occipital cortex and the right precuneous cortex for ‘stop’ trials. These results suggest that in addiction populations, enhanced activation of neural correlates indirectly associated with motor impulse control indicate a compensatory mechanism, particularly through the visual processing.Elucidating changes in the AUD brain proteome is essential to understanding the effects of alcohol consumption on the biochemical processes on the human brain. Metabolic changes in the human brain are characteristic of AUD. In Chapter 3, we used data-independent acquisition mass spectrometry proteomics to measure differences in the abundance of proteins associated with AUD in prefrontal cortex and motor cortex from autopsy brain. AUD had a substantial effect on the overall brain proteome exceeding the inherent differences between brain regions. We found changes in abundance in proteins associated with glycolysis, trafficking, the cytoskeleton, and excitotoxicity, in AUD. Furthermore, extensive changes in the abundance of key metabolic enzymes, consistent with a switch from glucose to acetate utilization in the AUD brain, were observed. We propose that metabolic adaptations allowing efficient acetate utilization contribute to ethanol dependence in AUD.Our first proteomic study used a water-soluble protein extraction method to identify changes in the AUD human brain proteome. To validate these previous findings, in Chapter 4 we used an alternative whole-protein extraction method to increase the coverage of the AUD human brain proteome. Similarly, we used data-independent acquisition mass spectrometry proteomics to measure differences in abundance in proteins extracted from the prefrontal cortex and motor cortex in AUD subjects and controls. We were able to increase the number of proteins with measurable changes in abundance with the whole-protein extraction method. Changes in key regulators of the glutamate-glutamine (GABA) cycle were observed in the AUD prefrontal cortex. STRING analysis revealed that energy consumption in the human brain is spatially differentiated. Lastly, we used immunoaffinity enrichment to enhance acetylation site identification, and identified acetylation sites on important regulatory proteins, GAPDH and histones.Ultimately, my thesis uses multidisciplinary, yet complementary approaches to investigate different facets of AUD in humans, which are integrated and discussed in Chapter 5. The results of my thesis contribute to the growing body of AUD research, which will help clinical outcomes in the future