I. Influence of sex and age on alcohol metabolism and responses Previous research indicates that alcohol metabolism differs between men and women, and may also be influenced by age. There appears to be a complex interaction between sex, age and alcohol elimination rates (AER), and differences in sex steroidal hormones, estrogen and testosterone, may underlie this interaction. Studies have also shown sex- and age-related differences in alcohol PD, although the underlying determinants of these differences are unclear. The objective of this study was to evaluate the influence of sex and age on the PK and PD of IV alcohol in social drinkers. This was a randomized, 2-session crossover study in 48 male and female - 24 young (21-25 yrs) and 24 older (55-65 yrs) - social drinkers. Subjects underwent the alcohol clamp at target BrACs of 0 and 50mg% for 3 hrs. Results showed that AERs were significantly higher in males than in females, but not influenced by age. AER per unit lean body mass (LBM) showed no difference by sex. LBM was significantly associated with AER across subjects, indicating that sex differences in AER may be due to sex differences in LBM. Alcohol had a significant effect on peak self-reports of high, intoxication and drug effects, with no sex differences in responses. Older subjects reported similar peak ratings of high and intoxicated, but significantly lower peak ratings for liking drug effects and wanting more, compared to younger subjects. The effect of alcohol on GH, IGF-1 and sex steroid levels revealed a pattern that differed by sex and age. Alcohol induced a significant decrease in free testosterone in males and a significant increase in estradiol in females. There were trends for alcohol-induced decreases in IGF-1 and GH (Vatsalya et al., 2012). There was a significant decrease in heart rate (HR) and an increase in HR variability measures during the ascending phase of the IV alcohol infusion, with no significant effects observed during the clamp phase. This suggests an initial dominant parasympathetic response, followed by a progressively increasing sympathetic response to alcohol. The change in HR was significantly associated with self-reports of alcohol effects during the ascending limb. Additional analyses, including PK-PD modeling, are being conducted to evaluate the influence of age and sex on subjective responses during the alcohol clamp. Findings from these studies will provide a better understanding of age- and sex-related differences in alcohol PK and PD, which may underlie medically important differences in alcohol effects. II. Computer-assisted self-infusion of ethanol (CASE) in humans Self-administration is a hallmark of all addictive drugs, including alcohol. Human alcohol self-administration is typically assessed by measuring the oral intake of alcoholic beverages in a laboratory bar setting. These methods tend to be imprecise and may be unreliable due to high variability in alcohol exposures resulting from high inter-individual alcohol PK variability, and differences in the definition of standardized drinks and drinking schedules, as well as non-pharmacological influences such as expectancy, beverage preference, choice and monetary value of incentives for drinking. The computer-assisted self-infusion of ethanol method (CASE), using the PBPK-model based infusion algorithm, provides subjects with the flexibility to choose when to push a button to receive alcohol, while providing the investigator with flexibility in controlling the subsequent time course of BrAC (and thus brain alcohol exposure). This method assures the same increments across all subjects and prevents BrACs from exceeding pre-set safety limits. Thus, the CASE method assesses behavior driven by the pharmacological effects of alcohol. The first phase of this project was to characterize the CASE paradigm by assessing ad-lib self-administration behavior and the resulting BrAC exposure and PD responses in social drinkers. During the session, subjects first undergo a directed priming phase, where they are prompted to push a button to receive standardized alcohol infusions, followed by an ad-lib phase, where they have free access to the same infusions. Primary measures include number of button presses, average and peak BrAC. Results from this phase (n=52) indicated high test-retest correlations between sessions, and high internal consistency among measures within sessions. There was a significant association between recent drinking history and self-administration measures, with no differences by sex. Self-report measures of liking drug effects and urges following priming predicted self-administration measures during the ad lib phase. There was a strong association between self-administration measures and peak alcohol effects of feeling drug effects, liking drug effects, intoxication and stimulation. The second phase of this project (ongoing), has focused on developing an operant CASE paradigm, using a progressive ratio (PR) schedule that requires subjects to press the button an increasing number of times for each subsequent alcohol exposure. This PR-CASE method assesses motivation for alcohol reward, and is based on the principle that people will work harder for greater rewards. Outcome measures include the breakpoint, as well as the average and peak BrAC achieved. Preliminary results from this phase (n=47) indicate that the PR-CASE method shows substantial inter-individual variability, however within-subject (test-retest) reliability between sessions is high. There was a significant association between recent drinking history and self-administration measures, with heavier drinkers showing higher BrACs and rewards earned. Subjective measures of alcohol effects and urges after priming were significantly associated with alcohol self-administration. Exposure-response analysis supports the role of the rewarding effects of alcohol driving alcohol self-administration behavior. Studies are also examining the effect of smoking history on CASE measures in non-treatment-seeking heavy drinkers (males: >20 drinks/week, females: >15 drinks/week). Initial analysis indicates that heavy drinkers (n=42) demonstrated robust IV alcohol self-administration that was associated with their Alcohol Use Disorder Identification Test (AUDIT) scores, a measure of hazardous and harmful alcohol use. There were no differences in self-administration measures between smokers and non-smokers;however, among the smokers, breath carbon monoxide levels and Fagerstrm test of nicotine dependence scores were significantly association with self-administration measures. The Section is also conducting studies using the CASE method to examine the effects of pharmacological agents on the rate, magnitude and pattern of exposure to alcohol in heavy drinkers. Such a paradigm would serve as a biomarker of clinical efficacy in the early stages of development of drugs for the treatment of alcohol-dependence. The first of these studies is ongoing and is expected to be completed in the next few months. This randomized, double-blind placebo-controlled study aims to evaluate the effect of varenicline on alcohol self-administration using the CASE method in non-treatment seeking heavy drinkers. III. Additional Studies: 1) Effect of naltrexone on the BOLD signal in the ventral striatum during the alcohol clamp in alcohol-dependent individuals (David T. George, PI). Data collection has been completed, and data analysis and manuscript development is ongoing. 2) Measuring Effects of Acute Alcohol on Human Brain Metabolites using Magnetic Resonance Spectroscopy (Reza Momenan, PI). This study was initiated in the past year and is ongoing.
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