Comparing structural equation models that use different measures of the level of response to alcohol

A Prospective Comparison of How the Level of Response to Alcohol and Impulsivity Relate to Future DSM-IV Alcohol Problems in the COGA Youth Panel

BACKGROUND

Alcohol problems reflect both environmental and genetic characteristics that often operate through endophenotypes like low levels of response (low LRs) to alcohol and higher impulsivity. Relationships of these preexisting characteristics to alcohol problems have been studied, but few analyses have included both low LR and impulsivity in the same model.

METHODS

We extracted prospective data from 1,028 participants in the Prospective Youth Sample of the Collaborative Study on the Genetics of Alcoholism (COGA). At Time 1 (age 18), these drinking but non-alcohol-dependent males and females completed the Barratt Impulsivity Scale and the Self-Report of the Effects of Alcohol questionnaire regarding drinks required for effects the first 5 times of drinking (SRE5-LR). Two years later, they reported perceived drinking patterns of peers (PEER), their own alcohol expectancies (EXPECT), and their drinking to cope with stress (COPE). Subsequently, at Time 3, participants reported numbers of up to 11 DSM-IV alcohol criterion items experienced in the 2 years since Time 2 (ALC PROBS). Data were analyzed using structural equation modeling (SEM).

RESULTS

In the SEM, Baseline SRE5-LR and impulsivity were weakly related and did not interact in predicting later ALC PROBS. LR was directly linked to Time 3 ALC PROBS and to PEER, but had no direct path to EXPECT, with partial mediation to ALC PROBS through PEER to EXPECT and via COPE. Impulsivity did not relate directly to ALC PROBS or PEER, but was directly related to EXPECT and COPE, with effects on ALC PROBS also operating through EXPECT and COPE.

CONCLUSIONS

Low LRs and impulsivity related to Time 3 ALC PROBS through somewhat different paths. Education- and counseling-based approaches to mitigate future alcohol problems may benefit from emphasizing different potential mediators of adverse alcohol outcomes for youth with low LRs versus those with high impulsivity or both characteristics.

The Ability of Functional Magnetic Resonance Imaging to Predict Heavy Drinking and Alcohol Problems 5 Years Later

BACKGROUND

Low levels of alcohol responses (low LRs) are genetically influenced phenotypes that are identified before alcohol dependence and predict future heavy drinking and alcohol problems. A recent paper described 13 LR-related blood oxygen level-dependent (BOLD) response contrast patterns observed during an emotional face recognition task that might reflect cognitive processes contributing to LR and that might themselves predict adverse alcohol outcomes (Paulus et al., Biol Psychiatry 2012; 72: 848). This paper evaluates the predictive implications of those functional magnetic resonance imaging (fMRI) patterns.

METHODS

Of 120 subjects from Paulus and colleagues (2012), 114 (57 low and high LRs; ~50% females) were interviewed 5 years later at age 25. Correlations between baseline fMRI patterns and alcohol-related outcomes were evaluated, and regression analyses were used to determine if BOLD response contrasts incremented over LR in predicting outcomes.

RESULTS

Baseline fMRI patterns in 5 of 13 baseline regions of interest correlated with adverse outcomes. Such patterns in insular regions, particularly the left anterior insula, and the right frontal gyrus, added to LR in predicting alcohol problems. The relationships remained robust when exact binomial procedures were used, but, reflecting the small sample size, it was not possible to adequately consider Bonferroni corrections.

CONCLUSIONS

The data suggest that fMRI BOLD response contrasts predicted heavier drinking and alcohol problems 5 years later, even after considering baseline low LRs. Future work will focus on whether fMRI results can predict outcomes in larger samples and among young nondrinkers, as well as how the imaging results increase understanding of the processes through which LR operates.

Two alternative approaches to conventional person-mean imputation scoring of the Self-Rating of the Effects of Alcohol Scale (SRE)

A low level of response to alcohol is considered a significant risk factor for alcohol use disorder. Survey measures of this construct assess the number of drinks required to experience various alcohol effects, so data will be missing for effects participants have not experienced. Furthermore, missingness will likely be more common for items with higher means, as more severe effects are likely experienced both less commonly and at higher consumption levels. We explored whether these atypical characteristics of response-to-alcohol survey data cause problems when using conventional person-mean imputation scoring. This scoring approach involves averaging across nonmissing items for each participant, implicitly assuming that missing items have similar distributional properties (e.g., means) as nonmissing items. Analyses used data from the most commonly utilized response-to-alcohol survey measure: The Self-Rating of the Effects of Alcohol Scale (SRE). Results (a) revealed a strong relationship between higher item means and greater item missingness, (b) established that this relation causes person-mean imputation to produce more downwardly biased response-to-alcohol summary scores for participants with more missing data, (c) established that this induced a spurious relationship between higher response-to-alcohol summary scores and higher alcohol-effect endorsement (i.e., the number of SRE alcohol effects experienced), and (d) found that these biases can be reduced with 2 alternative scoring approaches. We discuss these and other potential problems with person-mean imputation, and common and unique advantages of the 2 alternative approaches. We consider generalizability, including how the problems shown here may vary in practical significance across different populations and measures. (PsycINFO Database Record

Type 2 ryanodine receptors are highly sensitive to alcohol

Exposure to ethanol levels reached in circulation during alcohol intoxication (>10mM) constricts cerebral arteries in rats and humans. Remarkably, targets and mechanisms underlying this action remain largely unidentified. Artery diameter is regulated by myocyte Ca(2+) sparks, a vasodilatory signal contributed to by type 2 ryanodine receptors (RyR2). Using laser confocal microscopy in rat cerebral arteries and bilayer electrophysiology we unveil that ethanol inhibits both Ca(2+) spark and RyR2 activity with IC50<20 mM, placing RyR2 among the ion channels that are most sensitive to ethanol. Alcohol directly targets RyR2 and its lipid microenvironment, leading to stabilization of RyR2 closed states.

Stability of scores and correlations with drinking behaviors over 15 years for the Self-Report of the Effects of Alcohol Questionnaire

BACKGROUND

The low level of response (LR) to alcohol is an endophenotype that predicts future heavy drinking and alcohol use disorders (AUDs). LR can be measured by laboratory-based alcohol challenges or by the retrospective Self-Report of the Effects of Alcohol (SRE) questionnaire. This paper reports the relationships among these two measures and how each related to both recent and future drinking quantities and problems across 15 years in 235 men.

METHODS

Probands from the San Diego Prospective Study (SDPS) participated in alcohol challenges to determine their LR at age 20, and subsequently at ages 35, 40, 45 and 50 filled out an SRE regarding the number of standard drinks needed for up to four effects early in life (SRE5) and across early, recent, and heaviest drinking life epochs (SRET). Changes in SRE scores across time were evaluated with ANOVAs and Pearson correlations were used to evaluate how SRE5, SRET and earlier alcohol challenge-based LRs related to prior five-year drinking histories and future alcohol involvement.

RESULTS

While SRE scores decreased 9% over the 15 years, the relationships between SRE values with prior five-year drinking parameters and with future alcohol intake and problems remained robust, and even improved with advancing age. A similar pattern was seen for correlations between SRE and alcohol challenge-based LRs 15-30 years previously.

CONCLUSIONS

Alcohol challenge and SRE-based LRs related to each other, to alcohol use patterns, and to future alcohol problems across age 35-50 in the men studied here.

Early subjective response and acquired tolerance as predictors of alcohol use and related problems in a clinical sample

BACKGROUND

Previous studies have demonstrated that a low subjective response (SR) to alcohol is a risk factor for alcohol use disorders (AUDs), and a recent study suggests that acquired tolerance can be differentiated from initial SR and is also significantly associated with drinking problems. Because the prior study of SR and tolerance focused on a sample of moderate drinkers, the goal of the current study was to examine relations between early SR, acquired tolerance, alcohol use, and alcohol-related problems in a sample of young adults with clinically significant alcohol problems.

METHODS

The current study examined associations between early SR and acquired tolerance and both drinking behavior and alcohol-related problems within a sample of 113 heavy drinking young adults (66.1% male) volunteering for a clinical trial of naltrexone in combination with brief motivational counseling.

RESULTS

Consistent with the 1 prior study examining simultaneous effects of early SR and tolerance, both early SR and acquired tolerance were positively associated with typical drinking behavior, although tolerance was a much stronger predictor within this clinical sample. In contrast to the prior study, early SR was inversely associated with risk for alcohol-related problems, and tolerance was not a significant predictor of problems.

CONCLUSIONS

The results suggested that, controlling for weekly drinking, a low early SR protected against acute negative consequences within a sample of heavy drinkers who had acquired significant tolerance to alcohol effects. It is possible that this protective effect may eventually shift to a risk factor by allowing individuals with a low SR to persist in a pattern of hazardous drinking.

Sex differences in how a low sensitivity to alcohol relates to later heavy drinking

INTRODUCTION AND AIMS

A low level of response (LR), or low sensitivity, to alcohol is a genetically influenced characteristic that predicts future heavy drinking and alcohol problems. While previous analyses of how LR relates to heavier drinking reported the process is similar in males and females, some potential sex differences have been identified. This difference is further explored in these analyses.

DESIGN AND METHODS

Prospective structural equation models (SEMs) were evaluated for 183 young adult females and 162 males, none of Asian background, from the Collaborative Study on the Genetics of Alcoholism. Invariance analyses and SEM evaluations by sex were used to compare across females and males for these primarily Caucasian (75%), non-Asian young (mean age 19) subjects.

RESULTS

The prospective SEM for the full set of 345 subjects had good fit characteristics and explained 37% of the variance. While the initial invariance analyses identified few sex differences, comparisons of correlations and direct evaluations of path coefficients across males and females indicated that only females showed a link between a low LR and future alcohol problems that was partially mediated by more positive alcohol expectancies and drinking to cope. These sex differences were reflected in the different structures of the SEM results for female versus male subjects.

DISCUSSION AND CONCLUSIONS

These prospective results indicate that there might be some important sex differences regarding how a lower LR relates to alcohol outcomes that should be considered in protocols focusing on preventing the impact of LR on future drinking problems.

Comparison across two generations of prospective models of how the low level of response to alcohol affects alcohol outcomes

OBJECTIVE

This article presents the first direct comparison of level of response (LR)-based prospective models in two generations of the same families. To accomplish this, we describe results from the first prospective evaluation of potential mediators of how an earlier low LR to alcohol relates to adverse alcohol outcomes in offspring from the San Diego Prospective Study (SDPS).

METHOD

To compare with data from probands in the SDPS, new data were gathered from 86 drinking offspring (age ~20 years) during the 25-year follow-up of these families. Consistent with the usual effect of a low LR, outcomes 5 years later for both generations focused on drinking quantities as well as alcohol problems during the follow-up. A structural equation model (SEM) was used to analyze the relationships among variables, and the models in proband and offspring generations were compared using direct observations of the model results and through invariance procedures.

RESULTS

In these drinking offspring, LR correlated with 5-year outcomes (r = .48, p < .001) and the SEM R² was .48, with good fit statistics. As predicted, the LR relationship to alcohol-related outcomes was both direct and partially mediated by heavier peer drinking, positive alcohol expectancies, and using alcohol to cope with stress. These results were similar to a previously published prospective model in SDPS probands, although path coefficients were generally higher in the younger group.

CONCLUSIONS

The LR-based model of heavier drinking operated similarly across generations, with some modest differences. These results indicate that the model may be meaningful in both younger and middle-age groups.

Structuring a college alcohol prevention program on the low level of response to alcohol model: a pilot study

BACKGROUND

New approaches are needed to bolster the modest effects of campus drinking prevention programs. However, more definitive research on new paradigms is very expensive, and in the current economic climate, progress can be made by evaluating smaller pilot studies. This study describes one such approach.

METHODS

A sample of 18-year-old or older, healthy, drinking freshmen at our university was assigned to 2 groups stratified to be similar on demography, drinking histories, and their level of response (LR) to alcohol. In the spring quarter of the school year, the 32 subjects in each of 2 groups viewed four 45-minute Internet-based videotapes as part of 4 prevention sessions. All 8 modules were based on the same techniques and general content, but the 4 videos for the first group were structured around the validated model of how a low LR affects heavy drinking (the low level of response-based [LRB] Group), with partial mediation by heavier drinking peers, positive alcohol expectancies, and drinking to cope with stress. Videos for the state-of-the-art (SOTA) comparison group did not place the similar prevention messages into the low LR framework. Changes in drinking were evaluated at 3 times: before Module 1, before Module 4, and 1 month after Module 4.

RESULTS

Usual and maximum drinks per occasion decreased over time for both high and low LR subjects in both LRB and SOTA groups. As predicted, the low LR students showed greater decreases in the LRB Group, while high LR students showed greater decreases in the more generic SOTA Group.

CONCLUSIONS

The results support the hypothesis that tailoring prevention efforts to address specific predisposing factors, such as a low LR, may be associated with beneficial effects on drinking quantity. We hope that these data will encourage additional efforts to validate the low LR-based prevention paradigm and test other interventions that are targeted toward predisposing phenotypes such as impulsivity and negative affect.

fMRI differences between subjects with low and high responses to alcohol during a stop signal task

BACKGROUND

A low level of response (i.e., a low LR) to alcohol is a genetically influenced phenotype that predicts later alcoholism. While the low LR reflects, at least in part, a low brain response to alcohol, the physiological underpinnings of the low LR have only recently been addressed.

METHODS

Forty-nine drinking but not yet alcoholic matched pairs of 18- to 25-year-old subjects (N = 98; 53% women) with low and high LRs as established in separate alcohol challenges were evaluated in 2 event-related functional magnetic resonance imaging (fMRI) sessions (placebo and approximately 0.7 ml/kg of alcohol) while performing a validated stop signal task. The high and low LR groups had identical blood alcohol levels during the alcohol session.

RESULTS

Significant high versus low LR group and LR group × condition effects were observed in blood oxygen level-dependent (BOLD) signal during error and inhibitory processing, despite similar LR group performance on the task. In most clusters with significant (corrected p < 0.05, clusters > 1,344 μl) LR group × alcohol/placebo condition interactions, the low LR group demonstrated relatively less, whereas the high LR group demonstrated more, error and inhibition-related activation after alcohol compared with placebo.

CONCLUSIONS

This is one of the first fMRI studies to demonstrate significant differences between healthy groups with different risks of a future life-threatening disorder. The results may suggest a brain mechanism that contributes to how a low LR might enhance the risk of future heavy drinking and alcohol dependence.

Testing a level of response to alcohol-based model of heavy drinking and alcohol problems in 1,905 17-year-olds

BACKGROUND

The low level of response (LR) to alcohol is one of several genetically influenced characteristics that increase the risk for heavy drinking and alcohol problems. Efforts to understand how LR operates through additional life influences have been carried out primarily in modest-sized U.S.-based samples with limited statistical power, raising questions about generalizability and about the importance of components with smaller effects. This study evaluates a full LR-based model of risk in a large sample of adolescents from the United Kingdom.

METHODS

Cross-sectional structural equation models were used for the approximate first half of the age 17 subjects assessed by the Avon Longitudinal Study of Parents and Children, generating data on 1,905 adolescents (mean age 17.8 years, 44.2% boys). LR was measured with the Self-Rating of the Effects of Alcohol Questionnaire, outcomes were based on drinking quantities and problems, and standardized questionnaires were used to evaluate peer substance use, alcohol expectancies, and using alcohol to cope with stress.

RESULTS

In this young and large U.K. sample, a low LR related to more adverse alcohol outcomes both directly and through partial mediation by all 3 additional key variables (peer substance use, expectancies, and coping). The models were similar in boys and girls.

CONCLUSIONS

These results confirm key elements of the hypothesized LR-based model in a large U.K. sample, supporting some generalizability beyond U.S. groups. They also indicate that with enough statistical power, multiple elements contribute to how LR relates to alcohol outcomes and reinforce the applicability of the model to both genders.

A prospective evaluation of how a low level of response to alcohol predicts later heavy drinking and alcohol problems

BACKGROUND AND OBJECTIVES

Evaluations of how a genetically influenced characteristic, such as the low level of response (a low LR) to alcohol, relates to later heavy drinking and alcohol problems usually include environmental contributors. The best way to understand how LR works in the context of these additional characteristics is to study the process prospectively, but such analyses tend to be complex and the papers are sometimes cluttered with jargon. This report attempts to offer a more straightforward description of the results from such a prospective model of how a lower LR at age 20 relates to alcohol outcomes at age 40.

METHODS

A structural equation model of LR at age ∼20, outcomes of heavy drinking and problems at age ∼40, and additional characteristics at age ∼35 were tested in 378 men from the San Diego Prospective Study.

RESULTS

The results support both direct effects of age-20 LR on age-40 heavy drinking and alcohol problems, as well as indirect effects of LR through characteristics of these men at age 35. The latter include using alcohol to cope with stress and heavier drinking among peers.

CONCLUSIONS

A low LR to alcohol is an example of how both genes and environment can contribute to the risk for adverse alcohol outcomes. The identification of mechanisms through which LR impacts on later heavy drinking and problems can be approached in cross-sectional studies, but those may not be as sensitive as longitudinal models for identifying additional potential mediators of the LR-to-outcome relationship.

Comment on the paper by Quinn and Fromme entitled subjective response to alcohol challenge: a quantitative review

BACKGROUND

This commentary discusses the recent paper by Quinn and Fromme (2011), placing their results into perspective.

RESULTS

Quinn and Fromme's meta-analysis is an important and useful synthesis of a complex literature. It is clear, well written, and well reasoned, with conclusions that are relevant to both the Low Level of Response Model and the Differentiator Model.

CONCLUSIONS

Drs. Quinn and Fromme use a thorough and thoughtful approach, and I encourage researchers to address the important questions raised by their meta-analysis.

Binge eating and binge drinking: an integrative review

The primary goal of this review is to provide a framework for understanding two highly overlapping behaviors: binge eating and binge drinking. Research is presented that suggests binge eating and drinking behaviors may share several important features, including personality correlates such as neuroticism and urgency, as well as affective characteristics, such as elevated levels of negative affect. Additionally, the review describes common explanatory models, which are helpful in terms of their potential to link these common features to the functions of, or reasons why individuals engage in, binge eating and drinking behaviors. Implications for understanding potentially common etiological pathways and development of interventions designed to target multiple behaviors are discussed.

Alcohol effects on cerebral blood flow in subjects with low and high responses to alcohol

BACKGROUND

Although there are multiple indications that alcohol can alter many physiological brain functions, including cerebral blood flow (CBF), studies of the latter have generally used small- or modest-sized samples. Few investigations have yet evaluated how CBF changes after alcohol relate to subsets of subjects with elevated alcoholism risks, such as those with lower levels of response (LR) to alcohol. This study used arterial spin labeling (ASL) after alcohol administration to evaluate a large sample of healthy young men and women with low and high alcohol responses, and, thus, varying risks for alcohol use disorders (AUD).

METHODS

Healthy young adult social drinkers with low and high LR (N=88, 50% women) matched on demography and drinking histories were imaged with whole-brain resting ASL ~1 hour after ingesting ~3 drinks of ethanol and after a placebo beverage (i.e., 178 ASL sessions). The relationships of CBF changes from placebo to alcohol for subjects with low and high LR were evaluated.

RESULTS

CBF increased after alcohol when compared to placebo in 5 frontal brain regions. Despite identical blood alcohol concentrations, these increases with alcohol were less prominent in individuals who required more drinks to experience alcohol-related effects (i.e., had a lower LR to alcohol). The LR group differences remained significant after covarying for recent drinking quantities.

CONCLUSIONS

The results confirm that alcohol intake is associated with acute increases in CBF, particularly in frontal regions. Less intense CBF changes were seen in subjects with a genetically influenced characteristic, a low LR to alcohol, that relates to the future risk of heavy drinking and alcohol problems.