Editorial Commentary: Alcohol Biomarker Papers

Confounders of Serum Phosphatidylethanol: Role of Red Blood Cell Turnover and Cirrhosis

Purpose

Ethyl glucuronide (EtG), ethyl sulfate (EtS) and phosphatidylethanol (PEth) are considered specific direct biomarkers for detecting alcohol consumption. However, PEth, which is produced in red blood cells (RBC), varies considerably between patients for unknown reasons. We here studied various confounders of PEth elimination including fibrosis after alcohol withdrawal.

Patients and Methods

EtG, EtS and PEth together with routine laboratory and clinical parameters were studied in 100 Caucasian heavy drinkers prior and after alcohol detoxification. In addition, fibrosis stage and degree of steatosis were assessed by transient elastography (Fibroscan, Echosens, Paris).

Results

All three biomarkers were highly correlated (0.61-0.72) with initial serum alcohol levels, but only PEth correlated with daily alcohol consumption. After alcohol withdrawal, PEth significantly decreased within 6.1 days from 1708 to 810 ng/mL (half-life varied from 1.6 to 15.2 days). Both levels of serum alcohol but also EtG and EtS were higher in patients with liver cirrhosis as compared to patients without fibrosis despite comparable alcohol consumption suggesting a decreased alcohol elimination in patients with cirrhosis. PEth was also elevated in cirrhosis but not significantly. In contrast, PEth elimination rate was significantly higher in patients with enhanced RBC turnover and signs of alcohol-mediated hemolytic anemia with elevated ferritin, LDH and increased mean corpuscular volume (MCV).

Conclusion

We here demonstrate that alcohol elimination is decreased in patients with liver cirrhosis. In patients with cirrhosis, PEth levels are both affected in opposite directions by enhanced red blood cell turnover and elevated alcohol levels. Our data have important implications for the use and interpretation of PEth in the clinical setting.

Ethyl glucuronide and ethyl sulfate assays in clinical trials, interpretation, and limitations: results of a dose ranging alcohol challenge study and 2 clinical trials

BACKGROUND

The ethanol metabolites, ethyl glucuronide (EtG) and ethyl sulfate (EtS), are biomarkers of recent alcohol consumption that provide objective measures of abstinence. Our goals are to better understand the impact of cutoff concentration on test interpretation, the need for measuring both metabolites, and how best to integrate test results with self-reports in clinical trials.

METHODS

Subjects (n = 18) were administered, 1 week apart, 3 alcohol doses calibrated to achieve blood concentrations of 20, 80, and 120 mg/dl, respectively. Urinary EtG/EtS was measured at timed intervals during a 24-hour hospitalization and twice daily thereafter. In addition, participants from 2 clinical trials provided samples for EtG/EtS and drinking histories. Cutoffs for EtG/EtS of 100/50, 200/100, and 500/250 ng/ml were evaluated.

RESULTS

Twelve hours following each challenge, EtG was always positive at the 100 and 200 cutoffs, but at 24 hours sensitivity was poor at all cutoffs following the low dose, and poor after 48 hours regardless of dose or cutoff. Similarly, in the clinical trials EtG sensitivity was good for detecting any drinking during the last 24 hours at the 2 lowest cutoffs, but under 40% during the last 24 to 48 hours. Sensitivity was reduced at the 500 ng/ml cutoff. Discrepancies between EtG and EtS were few. Comparison of self-reports of abstinence and EtG-confirmed abstinence indicated underreporting of drinking.

CONCLUSIONS

Any drinking the night before should be detectable the following morning with EtG cutoffs of 100 or 200 ng/ml. Twenty-four hours after drinking, sensitivity is poor for light drinking, but good for heavier consumption. At 48 hours, sensitivity is low following 6 drinks or less. Increasing the cutoff to 500 ng/ml leads to substantially reduced sensitivity. Monitoring both EtG and EtS should usually be unnecessary. We recommend EtG-confirmed self-reports of abstinence for evaluation of outcomes in clinical trials.

Ethyl glucuronide in hair and fingernails as a long-term alcohol biomarker

AIMS

This study aimed to evaluate the performance of ethyl glucuronide (EtG) in hair and fingernails as a long-term alcohol biomarker.

DESIGN

Cross-sectional survey with probability sampling.

SETTING

Midwestern United States.

PARTICIPANTS

Participants were 606 undergraduate college students between the ages of 18 and 25 years at the time of selection for potential study participation.

MEASUREMENTS

EtG concentrations in hair and fingernails were measured by liquid chromatography-tandem mass spectrometry at three thresholds [30 picograms (pg) per milligram (mg); 20 pg/mg; and 8 pg/mg]. Any weekly alcohol use, increasing-risk drinking and high-risk drinking on average during the past 12 weeks was assessed by participant interview using the time-line follow-back method.

FINDINGS

In both hair and fingernails at all three EtG thresholds, sensitivity was greatest for the high-risk drinking group [hair: 0.43, confidence interval (CI)=0.17, 0.69 at 30 pg/mg, 0.71, CI=0.47, 0.95 at 20 pg/mg; 0.93, CI=0.79, 1.00 at 8 pg/mg; fingernails: 1.00, CI=1.00-1.00 at 30, 20 and 8 pg/mg] and specificity was greatest for any alcohol use (hair: 1.00, CI=1.00, 1.00 at 30 and 20 pg/mg; 0.97, CI=0.92-0.99 at 8 pg/mg; fingernails: 1.00, CI=1.00-1.00 at 30, 20 and 8 pg/mg). Areas under the receiver operating characteristic curves were significantly higher for EtG concentration in fingernails than hair for any weekly alcohol use (P = 0.02, DeLong test, two-tailed) and increasing-risk drinking (P = 0.02, DeLong test, two-tailed).

CONCLUSIONS

Ethyl glucuronide, especially in fingernails, may have potential as a quantitative indicator of alcohol use.

Proteomic approaches and identification of novel therapeutic targets for alcoholism

Recent studies have shown that gene regulation is far more complex than previously believed and does not completely explain changes at the protein level. Therefore, the direct study of the proteome, considerably different in both complexity and dynamicity to the genome/transcriptome, has provided unique insights to an increasing number of researchers. During the past decade, extraordinary advances in proteomic techniques have changed the way we can analyze the composition, regulation, and function of protein complexes and pathways underlying altered neurobiological conditions. When combined with complementary approaches, these advances provide the contextual information for decoding large data sets into meaningful biologically adaptive processes. Neuroproteomics offers potential breakthroughs in the field of alcohol research by leading to a deeper understanding of how alcohol globally affects protein structure, function, interactions, and networks. The wealth of information gained from these advances can help pinpoint relevant biomarkers for early diagnosis and improved prognosis of alcoholism and identify future pharmacological targets for the treatment of this addiction.

Protein biomarkers of alcohol abuse

Alcohol abuse can lead to a number of health and social issues. Our current inability to accurately assess long-term drinking behaviors is an important obstacle to its diagnosis and treatment. Biomarkers for chronic alcohol consumption have made a number of important advances but have yet to become highly accurate and as accepted as objective tests for other diseases. Thus, there is a crucial need for the development of more sensitive and specific markers of alcohol abuse. Recent advancements in proteomic technologies have greatly increased the potential for alcohol abuse biomarker discovery. Here, the authors review established and novel protein biomarkers for long-term alcohol consumption and the proteomic technologies that have been used in their study.

Phosphatidylethanol (PEth) as a biomarker of alcohol consumption in HIV-positive patients in sub-Saharan Africa

BACKGROUND

Alcohol is heavily consumed in sub-Saharan Africa and affects HIV transmission and treatment and is difficult to measure. Our goal was to examine the test characteristics of a direct metabolite of alcohol consumption, phosphatidylethanol (PEth).

METHODS

Persons infected with HIV were recruited from a large HIV clinic in southwestern Uganda. We conducted surveys and breath alcohol concentration (BRAC) testing at 21 daily home or drinking establishment visits, and blood was collected on day 21 (n = 77). PEth in whole blood was compared with prior 7-, 14-, and 21-day alcohol consumption.

RESULTS

(i) The receiver operator characteristic area under the curve (ROC-AUC) was highest for PEth versus any consumption over the prior 21 days (0.92; 95% confidence interval [CI]: 0.86 to 0.97). The sensitivity for any detectable PEth was 88.0% (95% CI: 76.0 to 95.6) and the specificity was 88.5% (95% CI: 69.8 to 97.6). (ii) The ROC-AUC of PEth versus any 21-day alcohol consumption did not vary with age, body mass index, CD4 cell count, hepatitis B virus infection, and antiretroviral therapy status, but was higher for men compared with women (p = 0.03). (iii) PEth measurements were correlated with several measures of alcohol consumption, including number of drinking days in the prior 21 days (Spearman r = 0.74, p < 0.001) and BRAC (r = 0.75, p < 0.001).

CONCLUSIONS

The data add support to the body of evidence for PEth as a useful marker of alcohol consumption with high ROC-AUC, sensitivity, and specificity. Future studies should further address the period and level of alcohol consumption for which PEth is detectable.

Serotonin transporter genomic biomarker for quantitative assessment of ondansetron treatment response in alcoholics

Paucity of sensitive biomarkers to quantify transient changes in alcohol consumption level remains a critical barrier for the development of efficacious therapeutic agents to treat alcoholism. Recently, in an 11-week, randomized, placebo-controlled, double-blind trial of 283 alcohol-dependent individuals, we demonstrated that ondansetron was efficacious at reducing the severity of drinking (measured as drinks per drinking day; DDD) in alcoholics carrying the LL compared with the LS/SS genotype of the serotonin transporter gene, 5'-HTTLPR. Using peripheral blood samples from a cohort of 41 of these subjects, we determined whether there was a relationship between mRNA expression level of the 5'-HTTLPR genotypes (measured at weeks 0, 4, and 11) and self-reported alcohol consumption following treatment with either ondansetron (4 μg/kg twice daily; N = 19) or placebo (N = 22). Using a mixed-effects linear regression model, we analyzed the effects of DDD and 5'-HTTLPR genotypes on mRNA expression levels within and between the ondansetron and placebo groups. We found a significant three-way interaction effect of DDD, 5'-HTTLPR genotypes, and treatment on mRNA expression levels (p = 0.0396). Among ondansetron but not placebo recipients, there was a significant interaction between DDD and 5'-HTTLPR genotype (p = 0.0385 and p = 0.7938, respectively). In the ondansetron group, DDD was associated positively with mRNA levels at a greater rate of expression alteration per standard drink in those with the LL genotype (slope = +1.1698 in ln scale). We suggest that the combination of the LL genotype and 5'-HTTLPR mRNA expression levels might be a promising and novel biomarker to quantify drinking severity in alcoholics treated with ondansetron.

Past and current alcohol consumption patterns and elevations in serum hepatic enzymes among US adults

OBJECTIVE

The aim of this study was to examine the association between patterns of past and current alcohol consumption and elevations in serum hepatic enzymes among a nationally representative sample of adults in the United States.

METHODS

We estimated the age-adjusted prevalence of elevated serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyltransferase (GGT) among 8993 adults aged 20 years or older who participated in the 2005-2008 National Health and Nutrition Examination Survey (NHANES). We produced prevalence ratios by using patterns of alcohol consumption as a predictor; elevations in serum ALT, AST, and GGT were used as an outcome variable while adjusting for covariates in multivariate regression models.

RESULTS

The age-adjusted prevalence of elevated serum ALT, AST, and GGT in adults was 9.7%, 16.0%, and 8.6%, respectively. Male excessive current drinkers had 50%-71% and 75%-314% increased likelihoods of having elevated serum AST and GGT, respectively; female excessive drinkers with a history of consuming 5 or more drinks almost daily had a 226% increased likelihood of having elevated serum GGT, when compared to their respective counterparts who were lifetime abstainers.

CONCLUSIONS

The results of this study indicate that elevations in serum hepatic enzymes, especially AST and GGT, are common in adults who are excessive current drinkers. There is evidence to suggest that excessive current drinkers with a history of protracted drinking are especially vulnerable to potential liver injury. These findings lend further support to the early identification of excessive drinkers who may have an increased risk for alcohol-related morbidity and mortality in health care settings.

Molecular targets of alcohol action: Translational research for pharmacotherapy development and screening

Alcohol abuse and dependence are multifaceted disorders with neurobiological, psychological, and environmental components. Research on other complex neuropsychiatric diseases suggests that genetically influenced intermediate characteristics affect the risk for heavy alcohol consumption and its consequences. Diverse therapeutic interventions can be developed through identification of reliable biomarkers for this disorder and new pharmacological targets for its treatment. Advances in the fields of genomics and proteomics offer a number of possible targets for the development of new therapeutic approaches. This brain-focused review highlights studies identifying neurobiological systems associated with these targets and possible pharmacotherapies, summarizing evidence from clinically relevant animal and human studies, as well as sketching improvements and challenges facing the fields of proteomics and genomics. Concluding thoughts on using results from these profiling technologies for medication development are also presented.