Reduction in cortical IMP-SPET tracer uptake with recent cigarette consumption in a young group of healthy males. San Diego HIV Neurobehavioral Research Center

Food Addiction and Tobacco Use Disorder: Common Liability and Shared Mechanisms

As food addiction is being more commonly recognized within the scientific community, parallels can be drawn between it and other addictive substance use disorders, including tobacco use disorder. Given that both unhealthy diets and smoking are leading risk factors for disability and death, a greater understanding of how food addiction and tobacco use disorder overlap with one another is necessary. This narrative review aimed to highlight literature that investigated prevalence, biology, psychology, and treatment options of food addiction and tobacco use disorder. Published studies up to August 2020 and written in English were included. Using a biopsychosocial lens, each disorder was assessed together and separately, as there is emerging evidence that the two disorders can develop concurrently or sequentially within individuals. Commonalities include but are not limited to the dopaminergic neurocircuitry, gut microbiota, childhood adversity, and attachment insecurity. In addition, the authors conducted a feasibility study with the purpose of examining the association between food addiction symptoms and tobacco use disorder among individuals seeking tobacco use disorder treatment. To inform future treatment approaches, more research is necessary to identify and understand the overlap between the two disorders.

Seeing Is Believing: Nuclear Imaging of HIV Persistence

A major obstacle to HIV eradication is the presence of infected cells that persist despite suppressive antiretroviral therapy (ART). HIV largely resides outside of the peripheral circulation, and thus, numerous anatomical and lymphoid compartments that have the capacity to harbor HIV are inaccessible to routine sampling. As a result, there is a limited understanding of the tissue burden of HIV infection or anatomical distribution of HIV transcriptional and translational activity. Novel, non-invasive, in vivo methods are urgently needed to address this fundamental gap in knowledge. In this review, we discuss past and current nuclear imaging approaches that have been applied to HIV infection with an emphasis on current strategies to implement positron emission tomography (PET)-based imaging to directly visualize and characterize whole-body HIV burden. These imaging approaches have various limitations, such as the potential for limited PET sensitivity and specificity in the setting of ART suppression or low viral burden. However, recent advances in high-sensitivity, total-body PET imaging platforms and development of new radiotracer technologies that may enhance anatomical penetration of target-specific tracer molecules are discussed. Potential strategies to image non-viral markers of HIV tissue burden or focal immune perturbation are also addressed. Overall, emerging nuclear imaging techniques and platforms may play an important role in the development of novel therapeutic and HIV reservoir eradication strategies.

Comparison of Regional Brain Perfusion Levels in Chronically Smoking and Non-Smoking Adults

Chronic cigarette smoking is associated with numerous abnormalities in brain neurobiology, but few studies specifically investigated the chronic effects of smoking (compared to the acute effects of smoking, nicotine administration, or nicotine withdrawal) on cerebral perfusion (i.e., blood flow). Predominately middle-aged male (47 ± 11 years of age) smokers (n = 34) and non-smokers (n = 27) were compared on regional cortical perfusion measured by continuous arterial spin labeling magnetic resonance studies at 4 Tesla. Smokers showed significantly lower perfusion than non-smokers in the bilateral medial and lateral orbitofrontal cortices, bilateral inferior parietal lobules, bilateral superior temporal gyri, left posterior cingulate, right isthmus of cingulate, and right supramarginal gyrus. Greater lifetime duration of smoking (adjusted for age) was related to lower perfusion in multiple brain regions. The results indicated smokers showed significant perfusion deficits in anterior cortical regions implicated in the development, progression, and maintenance of all addictive disorders. Smokers concurrently demonstrated reduced blood flow in posterior brain regions that show morphological and metabolic aberrations as well as elevated beta amyloid deposition demonstrated by those with early stage Alzheimer disease. The findings provide additional novel evidence of the adverse effects of cigarette smoking on the human brain.

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.

Cerebral white matter recovery in abstinent alcoholics--a multimodality magnetic resonance study

Most previous neuroimaging studies of alcohol-induced brain injury and recovery thereof during abstinence from alcohol used a single imaging modality. They have demonstrated widespread microstructural, macrostructural or metabolite abnormalities that were partially reversible with abstinence, with the cigarette smoking potentially modulating these processes. The goals of this study were to evaluate white matter injury and recovery thereof, simultaneously with diffusion tensor imaging, magnetic resonance imaging and spectroscopy in the same cohort; and to evaluate the relationships between outcome measures of similar regions. We scanned 16 non-smoking and 20 smoking alcohol-dependent individuals at 1 week of abstinence from alcohol and 22 non-smoking light drinkers using a 1.5 T magnetic resonance scanner. Ten non-smoking alcohol-dependent individuals and 11 smoking alcohol-dependent individuals were re-scanned at 1 month of abstinence. All regional diffusion tensor imaging, magnetic resonance imaging and spectroscopic outcome measures were calculated over comparable volumes of frontal, temporal, parietal and occipital white matter. At 1 week of abstinence and relative to non-smoking light drinkers, non-smoking alcohol-dependent individuals had higher mean diffusivity in frontal, temporal and parietal white matter (all P<0.008), whereas smoking alcohol-dependent individuals had elevated mean diffusivity only in frontal white matter (P=0.03). Smoking alcohol-dependent individuals demonstrated lower concentrations of N-acetyl-aspartate (a marker of neuronal viability) in frontal white matter (P=0.03), whereas non-smoking alcohol-dependent individuals had lower N-acetyl-aspartate in parietal white matter (P=0.05). These abnormalities were not accompanied by detectable white matter atrophy. However, the patterns of white matter recovery were different between non-smoking alcohol-dependent individuals and smoking alcohol-dependent individuals. In non-smoking alcohol-dependent individuals, the increase in fractional anisotropy of temporal white matter (P=0.003) was accompanied by a pattern of decreases mean diffusivity in all regions over 1 month of abstinence; no corresponding changes were observed in smoking alcohol-dependent individuals. In contrast, a pattern of white matter volume increase in frontal and temporal lobes was apparent in smoking alcohol-dependent individuals but not in non-smoking alcohol-dependent individuals. These results were not accompanied by significant changes in metabolite concentrations. Finally, there were no consistent patterns of association between measures obtained with different imaging modalities, either cross-sectionally or longitudinally. These data demonstrate significant white matter improvements with abstinence from alcohol, reflected either as microstructural recovery or volumetric increases that depend on the smoking status of the participants. We believe our results to be important, as they demonstrate that use of a single imaging modality provides an incomplete picture of neurobiological processes associated with alcohol-induced brain injury and recovery thereof that may even lead to improper interpretation of results.

In vivo brain imaging of human exposure to nicotine and tobacco

While most cigarette smokers endorse a desire to quit smoking, only 14-49% will achieve abstinence after 6 months or more of treatment. A greater understanding of the effects of smoking on brain function may result in improved pharmacological and behavioral interventions for this condition. Research groups have examined the effects of acute and chronic nicotine/cigarette exposure on brain activity using functional imaging; the purpose of this chapter is to synthesize findings from such studies and present a coherent model of brain function in smokers. Responses to acute administration of nicotine/smoking include reduced global brain activity; activation of the prefrontal cortex, thalamus, and visual system; activation of the thalamus and visual cortex during visual cognitive tasks; and increased dopamine (DA) concentration in the ventral striatum/nucleus accumbens. Responses to chronic nicotine/cigarette exposure include decreased monoamine oxidase (MAO) A and B activity in the basal ganglia and a reduction in alpha4beta2 nicotinic acetylcholine receptor (nAChR) availability in the thalamus and putamen (accompanied by an overall upregulation of these receptors). These findings indicate that smoking enhances neurotransmission through cortico-basal ganglia-thalamic circuits by direct stimulation of nAChRs, indirect stimulation via DA release or MAO inhibition, or a combination of these and possibly other factors. Activation of this circuitry may be responsible for the effects of smoking seen in tobacco-dependent smokers, such as improvements in attentional performance, mood, anxiety, and irritability.

Are treated alcoholics representative of the entire population with alcohol use disorders? A magnetic resonance study of brain injury

Almost all we know about neurobiological brain injury in alcohol use disorders has been derived from convenience samples of treated alcoholics. Recent research has demonstrated more comorbid conditions, poorer psychosocial functioning, and higher dependence levels in treated alcoholics than in their treatment-naive counterparts. Thus, it is not clear whether neuroimaging results from convenience samples of treated alcoholics can be generalized to the entire population with alcohol use disorders. We compared 35 treated alcoholics at 1 week of abstinence (ALC) and 32 treatment-naive heavy drinkers (HD) on regional brain volumes and metabolite concentrations obtained by in vivo magnetic resonance at 1.5 Tesla to evaluate for potential group differences. Then, we evaluated whether comorbid cigarette smoking and common demographic and clinical variables mediated any existing neurobiological group differences. ALC demonstrated smaller lobar gray matter volumes and thalami than HD, exacerbated by chronic smoking. Furthermore, concentrations of N-acetyl-aspartate (an accepted marker of neuronal viability), choline-containing metabolites (involved in membrane turnover), and myo-inositol (a putative marker of glial cells and osmolyte) were lower in multiple brain regions of ALC compared to HD. The lower N-acetyl-aspartate concentrations in white matter of ALC versus HD were explained by average number of drinks per month over the year preceding study. However, the other group differences were not explained by common drinking, demographic, and clinical variables (used as covariates at the same time) or by excluding participants with comorbid mood disorders. Taken together, this suggests that the degree of brain atrophy, as well as neuronal and membrane injury in clinical samples of alcoholics cannot be generalized to the much larger population with alcohol use disorders that does not seek treatment.

Chronic cigarette smoking modulates injury and short-term recovery of the medial temporal lobe in alcoholics

Memory function is largely mediated by the medial temporal lobe (MTL), and its compromise has been observed in alcohol dependence and chronic cigarette smoking. The effects of heavy alcohol consumption and chronic smoking on hippocampal volumes and MTL metabolites and their recovery during abstinence from alcohol have not been assessed. Male alcoholics in treatment (ALC) [13 smokers (sALC) and 11 non-smokers (nsALC)] underwent quantitative magnetic resonance imaging and short-echo proton magnetic resonance spectroscopic imaging at 1 week and 1 month of sobriety. Outcome measures were compared with 14 age-matched, non-smoking light-drinkers and were related to visuospatial learning and memory. Over 1 month of abstinence, N-acetyl-aspartate, a neuronal marker, and membrane-associated choline-containing metabolites normalized in the MTL of nsALC subjects, but remained low in the MTL of sALC subjects. Metabolite concentration changes in both groups were associated with improvements in visuospatial memory. Hippocampal volumes increased in both groups during abstinence, but increasing volumes correlated with visuospatial memory improvements only in nsALC subjects. In summary, chronic cigarette smoking in alcohol-dependent men appears to have adverse effects on MTL metabolite recovery during short-term sobriety. These data may also have implications for other conditions with established MTL involvement and significant smoking co-morbidity, such as schizophrenia-spectrum and mood disorders.

Effects of chronic alcohol dependence and chronic cigarette smoking on cerebral perfusion: a preliminary magnetic resonance study

BACKGROUND

Although approximately 80% of individuals with alcohol use disorders are chronic smokers and despite reported associations between chronic cigarette smoking and lower cerebral perfusion in nonalcoholics, previous brain perfusion studies with alcoholics did not account for the potential effects of concurrent chronic cigarette smoking.

METHODS

One-week-abstinent alcohol-dependent individuals in treatment (ALC) [19 smokers (sALC) and 10 nonsmokers (nsALC)] and 19 healthy light drinking, nonsmoking control participants (nsLD) were scanned with a pulsed arterial spin labeling method to measure cerebral perfusion without an exogenous contrast agent. Studies were performed with 2 different postlabeling delay times (time from labeling pulse to the excitation pulse; PLD=1,500 ms and PLD=1,200 ms) to assess the potential effect of arterial blood transit time on the perfusion. Average gray matter (GM) and white matter (WM) perfusion for the frontal and parietal lobes were calculated for each hemisphere from voxels containing at least 90% GM and 100% WM.

RESULTS

At PLD=1,500 ms, multivariate analyses compared ALC (combined sALC and nsALC) with nsLD (p=0.04) and contrasted sALC, nsALC, and nsLD (p=0.006). ALC, as a group, showed 13% lower frontal GM perfusion (p=0.005) and 8% lower parietal GM perfusion than nsLD (p=0.03). With ALC separated into smokers and nonsmokers, sALC showed 19% lower frontal GM perfusion (p=0.001) and 12% lower parietal GM perfusion than nsLD (p=0.004). In sALC, a higher number of cigarettes smoked per day was associated with lower perfusion. Overall, regional perfusion did not differ significantly between nsALC and nsLD. Results obtained with PLD=1,200 ms generally confirmed the 1,500 ms findings.

CONCLUSIONS

This study provides preliminary evidence that chronic cigarette smoking adversely affects cerebral perfusion in frontal and parietal GM of 1-week-abstinent alcohol-dependent individuals. These results are in line with our spectroscopic and structural magnetic resonance studies that suggest chronic cigarette smoking compounds the detrimental effects of alcohol dependence on brain neurobiology.

Functional brain imaging of tobacco use and dependence

While most cigarette smokers endorse a desire to quit smoking, only about 14% to 49% will achieve abstinence after 6 months or more of treatment. A greater understanding of the effects of smoking on brain function may (in conjunction with other lines of research) result in improved pharmacological (and behavioral) interventions. Many research groups have examined the effects of acute and chronic nicotine/cigarette exposure on brain activity using functional imaging; the purpose of this paper is to synthesize findings from such studies and present a coherent model of brain function in smokers. Responses to acute administration of nicotine/smoking include: a reduction in global brain activity; activation of the prefrontal cortex, thalamus, and visual system; activation of the thalamus and visual cortex during visual cognitive tasks; and increased dopamine (DA) concentration in the ventral striatum/nucleus accumbens. Responses to chronic nicotine/cigarette exposure include decreased monoamine oxidase (MAO) A and B activity in the basal ganglia and a reduction in alpha4beta2 nicotinic acetylcholine receptor (nAChR) availability in the thalamus and putamen. Taken together, these findings indicate that smoking enhances neurotransmission through cortico-basal ganglia-thalamic circuits either by direct stimulation of nAChRs, indirect stimulation via DA release or MAO inhibition, or a combination of these factors. Activation of this circuitry may be responsible for the effects of smoking seen in tobacco dependent subjects, such as improvements in attentional performance, mood, anxiety, and irritability.

Imaging the neurochemistry of nicotine actions: studies with positron emission tomography

Although the effects of nicotine in the brains of laboratory animals have been investigated extensively, very little is known about its effects in the human brain. With positron emission tomography (PET), a non-invasive imaging technology that allows measurement of the concentration of positron-labeled compounds that are of physiological and pharmacological relevance, it has become possible to investigate the effects of nicotine in the human brain. These imaging studies have shown that nicotine has very fast pharmacokinetics in the human brain, that it changes cerebral blood flow (CBF) and brain metabolism, and that at least some of these effects show acute tolerance. PET studies have also shown that, in addition to nicotine, cigarettes possess other pharmacological actions that may contribute to their reinforcing effects, that cigarettes inhibit monoamine oxidase (MAO) A and B in the brain, and that this inhibition recovers with cigarette discontinuation. Although the nicotine receptors have not yet been imaged in the living human brain, PET studies in the primate brain have shown very high concentration of receptors in the thalamus and a high rate of blockade by doses of nicotine that approximate plasma levels achieved by humans when smoking cigarettes. However, further studies are required to determine the levels of nicotine receptor occupancies achieved when smoking a cigarette and those required for the nicotine patch to be therapeutically effective, to measure the half-life for MAO inhibition by cigarettes and the mechanisms underlying this inhibition, and to evaluate the effects of smoking on nicotine receptors and on other neurotransmitter systems in the human brain.