Alcohol Biomarkers: Clinical Significance and Biochemical Basis

Brief history of the alcohol biomarkers CDT, EtG, EtS, 5-HTOL, and PEth

This article traces the historical development of various biomarkers of acute and/or chronic alcohol consumption. Much of the research in this domain of clinical and laboratory medicine arose from clinics and laboratories in Sweden, as exemplified by carbohydrate deficient transferrin (CDT) and phosphatidylethanol (PEth). Extensive studies of other alcohol biomarkers, such as ethyl glucuronide (EtG), ethyl sulfate (EtS), and 5-hydroxytryptophol (5-HTOL), also derive from Sweden. The most obvious test of recent drinking is identification of ethanol in a sample of the person's blood, breath, or urine. However, because of continuous metabolism in the liver, ethanol is eliminated from the blood at a rate of 0.15 g/L/h (range 0.1-0.3 g/L/h), so obtaining positive results is not always possible. The widow of detection is increased by analysis of ethanol's non-oxidative metabolites (EtG and EtS), which are more slowly eliminated from the bloodstream. Likewise, an elevated ratio of serotonin metabolites in urine (5-HTOL/5-HIAA) can help to disclose recent drinking after ethanol is no longer measurable in body fluids. A highly specific biomarker of hazardous drinking is CDT, a serum glycoprotein (transferrin), with a deficiency in its N-linked glycosylation. Another widely acclaimed biomarker is PEth, an abnormal phospholipid synthesized in cell membranes when people drink excessively, having a long elimination half-life (median ~6 days) during abstinence. Research on the subject of alcohol biomarkers has increased appreciably and is now an important area of drug testing and analysis.

Sialometabolism in Brain Health and Alzheimer's Disease

Sialic acids refer to a unique family of acidic sugars with a 9-carbon backbone that are mostly found as terminal residues in glycan structures of glycoconjugates including both glycoproteins and glycolipids. The highest levels of sialic acids are expressed in the brain where they regulate neuronal sprouting and plasticity, axon myelination and myelin stability, as well as remodeling of mature neuronal connections. Moreover, sialic acids are the sole ligands for microglial Siglecs (sialic acid-binding immunoglobulin-type lectins), and sialic acid-Siglec interactions have been indicated to play a critical role in the regulation of microglial homeostasis in a healthy brain. The recent discovery of CD33, a microglial Siglec, as a novel genetic risk factor for late-onset Alzheimer's disease (AD), highlights the potential role of sialic acids in the development of microglial dysfunction and neuroinflammation in AD. Apart from microglia, sialic acids have been found to be involved in several other major changes associated with AD. Elevated levels of serum sialic acids have been reported in AD patients. Alterations in ganglioside (major sialic acid carrier) metabolism have been demonstrated as an aggravating factor in the formation of amyloid pathology in AD. Polysialic acids are linear homopolymers of sialic acids and have been implicated to be an important regulator of neurogenesis that contributes to neuronal repair and recovery from neurodegeneration such as in AD. In summary, this article reviews current understanding of neural functions of sialic acids and alterations of sialometabolism in aging and AD brains. Furthermore, we discuss the possibility of looking at sialic acids as a promising novel therapeutic target for AD intervention.

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.

Time course of SERCA 2b and calreticulin expression in Purkinje neurons of ethanol-fed rats with behavioral correlates

Chronic ethanol consumption for 40 weeks in adult rats results in dilation of the extensive smooth endoplasmic reticulum (SER), a major component of the calcium homeostatic system within Purkinje neuron (PN) dendrites.

AIMS

The aim of the present study was to determine whether chronic ethanol consumption results in alterations of the sarco/endoplasmic reticulum Ca(2+) ATPase pump (SERCA) on the SER membrane of PN dendrites. The density of calreticulin, a calcium chaperone, was also investigated in the PN along with balancing ability.

METHODS

Ninety 8-month-old rats were exposed to rat chow, the AIN-93 M liquid control or ethanol diets (30/diet) for a duration of 10, 20 or 40 weeks (30/duration). Age changes relative to the rat chow controls were assessed with 3-month-old control rats (n = 10). Balance was assessed prior to euthanasia. Quantitative immunocytochemistry was used to determine the density of SERCA 2b + dendrites and calreticulin + PN soma and nuclei. Molecular layer volumes were also determined.

RESULTS

Following 40 weeks of ethanol treatment, there were ethanol-induced decreases in SERCA 2b densities within the dendritic arbor and decreased balancing ability on the more difficult round rod balance test. There were no ethanol-induced changes in calreticulin densities.

CONCLUSION

It can be concluded that ethanol-induced decreases in the SERCA pump accompany SER dilation and contribute to previously reported ethanol-induced dendritic regression in PN. Ethanol-induced changes in balance also occurred. Chronic ethanol consumption does not alter calreticulin expression in PN.

Diagnostic values of surface-enhanced laser desorption/ionization technology for screening of habitual drinkers

BACKGROUND

The currently available biological markers are limited in sensitivity and specificity for screening of excessive alcohol drinkers. We recently purified and identified 3 potential markers for alcoholism (5.9 and 7.8 kDa peptides and 28 kDa protein) by using surface-enhanced laser desorption/ionization (SELDI-TOF MS) technology. In the present study, we determined the diagnostic values of these novel markers in screening habitual drinkers with moderate alcohol consumption (hereafter habitual drinkers) in the general population as compared with 2 conventional markers: gamma-glutamyltransferase (GGT) and carbohydrate-deficient transferrin (CDT).

METHODS

Serum samples obtained from a total of 128 Japanese who sought regular medical checkup were analyzed by SELDI-TOF MS.

RESULTS

The relative intensities of the 5.9 and the 28 kDa peak of habitual drinkers were significantly different from those in nondrinkers even in GGT nonresponders. The sensitivity and specificity were the highest in 5.9 kDa. When 5.9, 28 kDa, and GGT were combined, 96.8% of the habitual drinkers were successfully screened with a specificity of 60.9%.

CONCLUSION

The results of this study clearly indicate that the 5.9 kDa peak is a promising novel biological marker for moderate alcohol consumption.

Detection of Biomarkers for Alcoholism by Two-Dimensional Differential Gel Electrophoresis

BACKGROUND

Up to now, gamma-glutamyltransferase (gamma-GTP) and carbohydrate-deficient transferrin (CDT) have been used as markers for alcoholism most widely, but they are not satisfactory regarding sensitivity/specificity. Therefore, for novel markers need to be searched.

METHODS

To detect new biomarkers for alcoholism, albumin and immunoglobulinG were first removed from serum. Then, protein profiles of 12 serum samples before and after 3 months of abstinence treatment were examined using agarose 2-dimensional differential gel electrophoresis (agarose2-D DIGE). Two-dimensional differential gel electrophoresis images were analyzed using Shimadzu 2-D Evolution Software.

RESULTS

Eight spots whose expression were significantly altered after abstinence were detected. Of these, 2 proteins increased and 6 proteins decreased after treatment.

CONCLUSIONS

Altered expressions of several serum proteins after abstinence therapy were detected. They are promising markers for clinical application of alcoholism.

Ethanol destabilizes liver Gal beta l, 4GlcNAc alpha2,6-sialyltransferase, mRNA by depleting a 3'-untranslated region-specific binding protein

Asialoconjugates are viable biomarkers for alcohol abuse. We previously showed that chronic ethanol feeding down-regulated liver Gal beta l, 4GlcNAc alpha2,6-sialyltransferase (ST6Gal l) mRNA by destabilizing it. Since RNA-binding proteins are known to stabilize many eukaryotic mRNAs by interacting with the 3'-untranslated region (UTR), we have delineated the possible mechanism by which ethanol destabilizes ST6Gal l mRNA. Using (32)P-labeled RNA probes generated from a 2.7-kb 3'-UTR of ST6Gal l mRNA, we identified a liver cytosolic 41-kDa specific binding protein that interacts with its 3'-UTR domain and protects it from degradation in normal rat liver but disappears after chronic ethanol treatment. Mapping of the binding region revealed that four RNA probes of 80-base pair (bp) length spanning the 304 bp of the 3'-UTR of ST6Gal l mRNA showed equal binding intensity. The corresponding cDNA sequences for the four 80-bp RNA probes share the 13-bp consensus sequence. Mutagenesis analysis identified that four nucleotides, AG and TC, among the consensus sequences were critical for the RNA-protein interaction. Therefore, 5'-CAGCCTCCTCCCT-3' serves as a cis-element critically involved in this interaction. The RNA-protein complex formation progressively decreased with increasing dietary ethanol, resulting in its virtual disappearance with 36% of the dietary calories as ethanol. Concomitantly, the same ethanol diet decreased sialic acid index of plasma apolipoprotein J by 45% (p < 0.05). Thus, depletion of a binding protein that specifically interacts with its 3'-UTR region of ST6Gal l mRNA may account for its destabilization and consequent appearance of asialoconjugates as alcohol biomarkers.

Are Commonly Ordered Lab Tests Useful Screens for Alcohol Disorders in Older Male Veterans Receiving Primary Care?

Although mean corpuscular volume (MCV), aspartate aminotransferase (AST), alanine aminotransferases (ALT), and the AST/ALT ratio are sometimes used as markers of alcohol disorders, their utility has not been established in older persons. We determined the tests' performance characteristics for (1) at-risk drinking, (2) CAGE positivity, (3) at-risk drinking and CAGE positivity, and (4) a clinician-recorded diagnosis of alcohol abuse/dependence in a study of older male veterans receiving primary care. Participants (n = 587) included patients who had MCV, AST, and/or ALT data collected as part of routine care no more than 12 weeks before or after enrollment. MCV, AST, and ALT test results were obtained from the VA's database. At enrollment, the Timeline Followback and Alcohol Use Disorders Identification Test (AUDIT) were used to identify at-risk drinkers (> or = 15 drinks per week or AUDIT score > or = 8), and the CAGE questionnaire was administered to identify participants with a history abuse/dependent drinking (CAGE score > or = 2). Participants' medical records were reviewed to identify subjects with a clinician-recorded diagnosis of alcohol abuse/dependence. The prevalence of abnormal test results for MCV (threshold value = > 98), AST (> 41), ALT (> 41), and the AST/ALT ratio (> 2) was 11%, 4%, 4%, and 5%, respectively. The occurrence of at-risk drinking, CAGE positivity, at-risk drinking and CAGE positivity, and a clinician-recorded diagnosis of alcohol abuse/dependence was 11%, 25%, 5%, and 9%, respectively. Test sensitivity ranged from 3.9% to 25.4% and specificity from 88.5% to 97.1%, whereas positive likelihood ratios varied from 0.72 to 4.01 and negative likelihood ratios from 0.82 to 1.04. Areas under the receiver operating characteristic curve were similar (range = 0.50-0.58) across tests. In conclusion, MCV, AST, ALT, and the AST/ALT ratio are not useful markers of alcohol disorders in older male veterans.

Alanine Aminopeptidase Activity in Urine: A New Marker of Chronic Alcohol Abuse?

BACKGROUND

The purpose of this study was to evaluate the activity of urinary alanine aminopeptidase (AAP), the enzyme released from the brush border membranes of renal proximal tubules, as a new biological marker of chronic alcohol abuse.

METHODS

The AAP activity was assayed and compared between a group of 76 alcoholics undergoing detoxification and a group of 37 alcoholics abstaining from alcohol for at least 6 weeks. In all patients, the enzyme activity was measured both in untreated urine (uAAP) and after removal of endogenous AAP inhibitors by molecular filtration on Sephadex (eAAP).

RESULTS

There was a correlation between the uAAP and eAAP activities in both groups of patients (r = 0.61 and r = 0.81 in abstinent alcoholics and in alcoholics undergoing detoxification, respectively), and both the uAAP activity and the eAAP activity were significantly and markedly higher in alcoholics being detoxified than in their abstinent counterparts. As revealed by receiver operating characteristic analysis, the discriminative power of the eAAP activity assay was higher than that of the uAAP activity assay. The area under the corresponding receiver operating characteristic curves was 0.84 +/- 0.04 and 0.78 +/- 0.05 (mean +/- SE), respectively.

CONCLUSIONS

The results of this study demonstrate that the assays of urinary AAP activity, which relate to the nephrotoxic effects of alcohol abuse, could be a valuable complement to the other presently used markers of chronic alcohol abuse that are generally based on ethanol hepatotoxicity. Compared with the uAAP activity test, the eAAP activity test is of clear diagnostic advantage.

Apo-AII is an elevated biomarker of chronic non-human primate ethanol self-administration

AIMS

Serum protein profiles were examined in naïve, ethanol self-administering and ethanol abstinent cynomolgus monkeys (Macaca fasicularis) to search for differences in protein expression which could possibly serve as biomarkers of heavy ethanol consumption.

METHODS

Surface-enhanced laser desorption ionization time-of-flight (SELDI-ToF) mass spectrometry was used for proteomic profiling of serum.

RESULTS

Two proteins were identified by SELDI-ToF to be increased in ethanol self-administering compared with abstinent animals. These proteins were identified to be apolipoprotein AI (Apo-AI) and apolipoprotein AII (Apo-AII) by peptide mass fingerprinting and comparison with spectra of purified human Apo-AI and AII proteins. Immunoblot analysis of Apo-AI and Apo-AII was performed on a separate group of animals (within-animal ethanol-naïve and self-administering) and confirmed a statistically significant increase in Apo-AII, while Apo-AI was unchanged.

CONCLUSIONS

An open proteomic screen of serum and confirmation in a separate set of animals found Apo-AII to be increased in the serum of ethanol self-administering monkeys. These results are consistent with previous clinical studies of human ethanol consumption and serum apolipoprotein expression. Moreover, these results validate the use of non-human primates as a model organism for proteomic analysis of ethanol self-administration biomarkers.

The future of proteomics in the study of alcoholism

This article represents the proceedings of a workshop at the 2003 annual meeting of the Research Society on Alcoholism in Fort Lauderdale, FL. The workshop organizers/chairpersons were Chinnaswamy Kasinathan and Paul Manowitz. The presentations were (1) Introduction to the field of proteomics, by Kent Vrana; (2) Use of proteomics in the identification of urinary biomarkers for alcohol intake, by Chinnaswamy Kasinathan, Paul Thomas, and Paul Manowitz; (3) Proteomics screening illuminates ethanol-mediated induction of HDL proteins in macaques, by Kent Vrana, Randy Gooch, Travis Worst, Stephen Walker, Aaron Xu, Peter Pierre, Heather Green, and Kathleen Grant; and (4) Proteomics applied to the study of the liver, by Laura Beretta.

Use of biomarkers for alcohol use disorders in clinical practice

BACKGROUND

Biomedical markers may provide additive objective information in screening and confirmation of acute or recent consumption, intoxication, relapse, heavy drinking, hazardous/harmful use/abuse and dependence and alcohol use related organ dysfunction (alcohol use-related disorders: AUDs).

AIMS

To review the use of biomarkers in clinical practice to detect AUDs.

FINDINGS

About one-fifth of the patients seen in clinical practice have AUDs, which offer a variety of treatment options if diagnosed. The diagnosis of AUDs relies on clinical and alcohol-related history, physical examination, questionnaires and laboratory values. No clinical available laboratory test [e.g. for acute abuse: alcohol in blood or breath; for chronic alcohol abuse: gamma-glutamyl transferase (GGT), mean corpuscular volume (MCV), carbohydrate-deficient transferrin (CDT)] is reliable enough on its own to support a diagnosis of alcohol dependence, harmful use or abuse. Sensitivities, specificities and the predictive values may vary considerably according to patient and control group characteristics (e.g. gender, age or related comorbidity). In patient groups with limited cooperation markers may be helpful when considering treatment options.

CONCLUSIONS

More research is needed to determine the value of markers (single or combined, with questionnaires) in the context of clinical decision-making algorithms in defined settings and with defined dichotomous outcome variables.

A comparison of five questionnaires to assess alcohol consumption in a Mediterranean population

OBJECTIVE

To evaluate the reliability of alcohol consumption measured by five different dietary methods in the Catalan Nutrition Survey (1992-1993).

DESIGN

The different questionnaires used were: (1) two 7-day food records, (2) five items addressing alcoholic beverages in a 76-item food-frequency questionnaire, (3) a 1-week recall of 13 alcoholic beverages, (4) a 13-item alcoholic beverages frequency questionnaire and (5) two 24-hour recalls.

SUBJECTS

Ninety-three of the 120 adults (aged 20 to 70 years) initially recruited completed the questionnaires and provided a peripheral blood sample.

RESULTS

Mean daily alcohol intakes as assessed by the questionnaires were very similar. Beer was the alcoholic beverage most frequently consumed, followed by wine and liquor. Eighty-two per cent of the study population consumed less than 20 g of alcohol per day. No biochemical parameters were significantly correlated with alcohol intake estimated from the questionnaires.

CONCLUSIONS

We found a satisfactory level of reproducibility and validity in the pattern of alcohol consumption across different levels and types of alcoholic beverage intake. We also found that the self-administered 13-item questionnaire and the 1-week recall were the best techniques to measure moderate or low alcohol consumption, suggesting that the two methods are the most suitable to assess overall alcohol intake in the general population.