Analysis of six different homologues of phosphatidylethanol from dried blood spots using liquid chromatography-tandem mass spectrometry

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.

Stability of PEth 16:0/18:1, 16:0/18:2, 16:0/20:4, 18:0/18:1, 18:0/18:2, and 18:1/18:1 in authentic whole blood samples (at room temperature)

Phosphatidylethanol (PEth) is a direct alcohol biomarker to monitor individuals' drinking behavior that has gained recognition in clinical and forensic settings. The increasing application of the marker makes investigation of the preanalytical handling necessary, and analyte stability deserves major attention. This study was conducted to investigate the change of six PEth homologues' concentration, stored in authentic samples of EDTA blood over a course of 30 days at room temperature (n = 62). The stability criterion of concentration being ±15% of the original concentration was fulfilled at mean for 10, 3, 2, 5, 2, and 7 days for PEth 16:0/18:1, 16:0/18:2, 16:0/20:4, 18:0/18:1, 18:0/18:2, and 18:1/18:1, respectively. Regarding all homologues, there were samples in which concentration had declined by >15% or by more than the critical difference on day 1. Overall, calculated concentration declines were very inhomogeneous, with inter-sample differences of 43%-73% after 30 days. PEth 16:0/18:2, 16:0/20:4, and 18:0/18:2 declined to a greater extent than PEth 16:0/18:1. Blood alcohol concentration was measured >0.1‰ in 25 samples. Three of the six samples that exceeded 115% of initial concentrations were positive for blood alcohol. The study results add to the previously reported information on PEth stability and firstly look at six homologues in comparison. Due to the high scatter of stability among the samples and the observed poor stabilities in some, it can be concluded that transportation and storage times, especially if cooling cannot be provided, must be kept short. If analyzing from dried blood, spotting should preferably be conducted at the site of sampling.

Phosphatidylethanol (B-PEth) and other direct and indirect biomarkers of alcohol consumption

When identifying, preventing and treating alcohol use disorder, a correct estimation of alcohol intake is essential. An objective marker is preferred as self-reported alcohol intake suffers from bias, and the use of alcohol biomarkers is increasing globally. An easy-to-use blood biomarker to correctly assess alcohol consumption is an invaluable asset in alcohol treatment strategies, as well as in alcohol research studies. The specific, cumulative, biomarker phosphatidylethanol, mirroring the past two weeks of consumption, has shown superiority over traditional biomarkers and is an attractive choice of proxy for alcohol intake.

Storage stability of phosphatidylethanol homologues in whole blood and dried blood spots of nonalcoholics at different temperatures over 60 days

Phosphatidylethanol (PEth) has recently become a popular direct alcohol marker for evaluating drinking behavior. This study aimed at gaining further information on the long-term stability of five PEth homologues (16:0/18:1, 16:0/18:2, 16:0/20:4, 18:0/18:1, 18:0/18:2) in whole blood (WB) and dried blood spots (DBS) stored at -80°C, 4°C, and room temperature (18°C) over a period of 60 days. Venous blood was taken from 10 volunteers (five females and five males, aged 21-40 years) with a moderate drinking behavior and a negative breath alcohol test at the time of collection. 100 μL aliquots of WB were prepared in addition to 20 μL DBS samples. The initial PEth concentrations were determined on the day of the blood collection. On days 1, 3, 5, 7, 11, 17, 40, and 60, DBS were analyzed in triplicate by means of LC-MS/MS. On these days, WB aliquots having been stored until that time were used to create further DBS in triplicate, which were subsequently stored at 18°C and analyzed in a single batch after day 60. All homologues, except PEth 16:0/20:4, were stable at -80°C in DBS and WB for 60 days. The initial PEth 16:0/18:1 concentrations remained stable in both DBS and WB in all but one volunteer's specimen at 4 and 18°C. Apart from this exception, simultaneously detected PEth homologues 16:0/18:2, 18:0/18:1, and 18:0/18:2 remained stable over at least 40 days in DBS. Nevertheless, the storage time between sample collection and analysis should be kept as short as possible if an ethanol-free sample cannot be ensured.

The alcohol biomarker phosphatidylethanol (PEth) - test performance and experiences from routine analysis and external quality assessment

Phosphatidylethanol (PEth) are membrane molecules formed from phosphatidylcholine and ethanol through transphosphatidylation catalyzed by phospholipase D. Measurement of the main PEth form 16:0/18:1 is used as a specific and sensitive alcohol biomarker, since its formation requires ethanol, it accumulates in the blood upon repeated ethanol exposure, and it is only slowly eliminated during abstinence. PEth formation correlates with alcohol intake at the population level, albeit with considerable inter-individual variation as for the half-life during withdrawal. Over the past decade, the use of PEth has increased significantly and the applications have broadened. In Sweden, routine decision limits and the interpretation of test results for PEth were harmonized in 2013, using < 0.05 µmol/L (∼35 µg/L) as the recommended lower reporting limit and values > 0.30 µmol/L (∼210 µg/L) to indicate regular high alcohol intake. Routine test results show a large variation with about half being < 0.05 µmol/L and some even exceeding 10 µmol/L. In 2013, an external quality assessment (EQA) scheme for PEth 16:0/18:1 measurement in whole blood was also started (Equalis, Uppsala, Sweden), presently involving 56 laboratories from 13 countries. The agreement of PEth results between the laboratories has gradually improved to a CV < 15%. The current clinical and scientific information suggests that PEth values below the lower reporting limit (typically ∼0.03-0.05 µmol/L, or ∼20-35 µg/L) indicates sobriety or only low or occasional alcohol consumption, while regular high alcohol intake at levels corresponding to harmful drinking is required in most cases to reach PEth values > 0.30 µmol/L.

Development and Validation of Seven Phosphatidylethanol Homologues in Dried Blood Spots Including Preliminary Results after Excessive Use of an Ethanol-Based Hand Sanitizer

Phosphatidylethanol (PEth) has become a widespread marker offering an up to 4-week retrospective window to detect alcohol use. Due to the pandemic of coronavirus disease 2019, ethanol-based hand sanitizers are frequently used. The aim of this study was to develop and validate a method for the determination of up to seven different homologues of PEth from dried blood spots (DBSs) after use of an ethanol-based hand sanitizer. The objectives of its preliminary application were to prove whether a threshold of 20 ng/mL for PEth 16:0/18:1 is reached and whether other homologues are formed as well as if positive findings of urinary ethyl glucuronide (UEtG) can be observed with respect to assess monitoring of abstinence control programs. Ten volunteers (8 occasional and 2 regular drinkers) were recruited to excessively use an ethanol-based hand sanitizer on 5 successive days. DBSs and urine samples were collected daily. PEth and UEtG were determined by liquid chromatography--tandem mass spectrometry. In total, two volunteers with initial PEth 16:0/18:1 concentrations of 19.3 and 14.6 ng/mL exceeded the threshold of 20 ng/mL six times. Subjects drinking daily or almost daily had starting PEth 16:0/18:1 concentrations of 242 and 354 ng/mL, showing a decline of PEth concentrations in six out of the seven homologues over 5 days. In teetotalers, formation of PEth species could not be observed. Thus, not satisfying requirements in an alcohol monitoring program with initial PEth-negative blood cannot be explained by a frequent use of ethanol-based hand sanitizer only. In cases of regular alcohol consumption, PEth homologues are not likely to be further influenced. However, results indicated that individuals with a PEth concentration close to 20 ng/mL are at risk of exceeding the threshold by using ethanol-based hand sanitizer.

[Determination of phosphatidylethanol in whole-blood by liquid chromatography-tandem mass spectrometry based on intelligent scheduled time-zone acquisition technology and the application to population level survey]

Alcohol intake is an important risk factor for cardiovascular disease， liver disease， and diabetes. The accurate and objective evaluation of alcohol intake is important for disease prevention and intervention， as well as alcohol intake monitoring. Phosphatidylethanol （PEth） is a potential clinical biomarker of alcohol consumption. Monitoring PEth levels can provide an objective and quantitative basis for alcohol intake studies. Unlike other current alcohol biomarkers， PEth can only be produced in the presence of alcohol. Therefore， PEth is highly specific for alcohol intake and not affected by confounding factors， such as age， gender， hypertension， kidney disease， liver disease， and other comorbidities. Because of its long half-life and high specificity for alcohol intake， PEth may be used as a tool for monitoring drinking behavior in the clinical， transportation， and other fields. Given rapid developments in mass spectrometry technology over the past decade， liquid chromatography-tandem mass spectrometry （LC-MS/MS） has become the preferred method for PEth detection. However， most current LC-MS/MS methods focus on the determination of one or several PEth homologs， and the number of PEth homologs that can be determined simultaneously is relatively limited. Moreover， the detection capacity of the available methods remains insufficient， and their analytical sensitivity for some PEth homologs must be further improved. In this study， a novel LC-MS/MS method based on an intelligent scheduled time-zone negative multiple reaction monitoring acquisition technology （Scheduled-MRM） was developed. The technology monitors two ion channels in each PEth to ensure reliable results and can quantify 18 PEth homologs in human whole blood simultaneously. Methanol-methyl tert-butyl ether-water was used as the extraction system. An XBridge C18 column （100 mm×2.1 mm， 3.5 μm） was selected for gradient elution with 2.5 mmol/L ammonium acetate isopropanol solution and 2.5 mmol/L ammonium acetate aqueous solution-acetonitrile （50∶50， v/v） as the mobile phases. Negative electronic spray ionization in scheduled-MRM mode was applied for MS/MS detection. The method was validated to have a linear range of 10-2500 ng/mL with correlation coefficients greater than 0.9999. The limits of detection and quantification were 0.7-2.8 and 2.2-9.4 ng/mL， respectively， and the spiked recoveries ranged from 91.0% to 102.2%. The method was confirmed to be simple， rapid， and precise， and subsequently validated for the measurement of 18 PEth homologs in human blood. Scheduled-MRM can assign a suitable scan time to each ion channel and effectively reduce the number of concurrent ion pairs monitored per unit time. This technology overcomes the problem of insufficient dwell time caused by an excessive number of ion channels， thereby avoiding the redundant monitoring of non-retention times. Scheduled-MRM significantly improved the detection sensitivity， data acquisition quality， and signal response of the proposed method. Whole blood samples from 359 volunteers with regular drinking habits were analyzed using this method. The total PEth concentrations ranged from 51.13 ng/mL to 2.89 μg/mL， with a mean of 363.16 ng/mL. PEth 16∶0/18∶1 and 16∶0/18∶2 were the two most abundant homologs， with mean concentrations of 74.21 and 48.75 ng/mL， accounting for approximately 20.43% and 13.42%， respectively， of the total PEth. Spearman correlation analyses showed that the PEth homologs correlated well with each other， γ-glutamyltransferase， a clinically available biological marker of alcohol， and other clinical biochemical parameters related to liver and kidney function. Overall， the method was demonstrated to be sensitive， precise， and accurate； thus， it may be an effective tool for monitoring alcohol intake in the clinical and other fields.

PEth 16:0/18:1 and 16:0/18:2 after consumption of low doses of alcohol-A contribution to cutoff discussion

Phosphatidylethanol in blood has gained recognition as a direct alcohol biomarker. Although different cutoffs have been suggested, there is no consensus for differentiating abstinence from alcohol consumption. In this study, 75 participants (72% female) consumed 20 g of ethanol on three consecutive evenings. Blood was sampled on each following day and PEth 16:0/18:1 and 16:0/18:2 were determined. PEth 16:0/18:1 ranged from 8.9-21.5, 8.7-19.3, and 8.8-42.3 ng/ml and PEth 16:0/18:2 from 8.7-31.7, 9.0-39.3, and 9.4-43.0 ng/ml after the respective days of ethanol consumption. PEth 16:0/18:1 yielded a sensitivity of 25%, 45%, and 49% and PEth 16:0/18:2 of 40%, 61%, and 68% for the consumption days, respectively (cutoff 10 ng/ml). PEth 16:0/18:1 reached >20 ng/ml in five samples overall. Sensitivity of PEth 16:0/18:2 > 20 ng/ml was better with 35% after the three drinking days. Overall, PEth 16:0/18:1 was >35 ng/ml in one sample and PEth 16:0/18:2 in three samples. Significantly, more women had PEth 16:0/18:1 > 10 ng/ml after the third day of consuming 20 g of alcohol (p = 0.02) and PEth 16:0/18:2 > 10 ng/ml after the second (p = 0.023) and the third (p = 0.002) consumption, which can be led back to the higher blood alcohol concentration women reach after consuming the same alcohol amount as men. Although the response rates of PEth to alcohol uptake are subject to strong interindividual differences, results suggest that PEth cutoff should be lowered for better detection of consumption of low to medium amounts of alcohol. Furthermore, it is advantageous to analyze both PEth 16:0/18:2 and 16:0/18:1.

False Positive Results of Phosphatidylethanol (PEth) Quantitation in Dried Blood Spots (DBS): The Influence of Alcohol Vapors

The role of phosphatidylethanol (PEth) as an alcohol consumption marker is increasing in clinical and forensic medicine. During the COVID-19 pandemic, the role of hygiene increased, and it became common practice to use disinfectants almost everywhere. This paper highlights a possible source of false positive results (by the vapors of alcohols during the blood spot drying process) in dried blood spots (DBS) by LC-MS/MS quantitation of PEth. To achieve this, the PEth quantitation method was validated according to FDA guidelines. Additionally, the synthesis of phosphatidyl derivatives by phospholipase D (PLD) in the presence of methanol and 2-propanol vapors during the DBS process was determined. Each PEth-negative sample from a healthy male patient incubated in the presence of ethanol vapor becomes PEth-positive. After 4 h of DBS drying, teetotalers become “moderate drinkers”. It is necessary to avoid using alcohol-containing disinfectants in treatment rooms, where DBS is sampled.

Set-up of a population-based model to verify alcohol abstinence via monitoring of the direct alcohol marker phosphatidylethanol 16:0/18:1

BACKGROUND AND AIMS

Phosphatidylethanol 16:0/18:1 (PEth) is a biomarker for alcohol intake. It has a half-life of 7.9 days. Chronic alcohol consumption causes high PEth values. It can take weeks before PEth values fall below the decision limit for 'alcohol abstinence'. Our aim was to validate whether alcohol abstinence can be determined based on two consecutive PEth results above the decision limit.

DESIGN

Observational study.

SETTING

Belgium, February 2019. The study was linked to a social initiative in Belgium, 'Tournée Minérale'.

PARTICIPANTS

Adults (aged > 18 years, n = 796) with varying drinking habits who self-reportedly refrained from alcohol consumption during the study.

MEASUREMENTS

A validated liquid chromatography-tandem mass spectrometry method was used to quantify PEth in participants' dried blood samples, collected at three time-points via remote fingerprick-based self-sampling.

FINDINGS

A population-based algorithm to evaluate abstinence based on 95% prediction limits was developed by fitting a linear mixed-effect model to discern patterns in PEth elimination over time. It took intra- and inter-individual variability into consideration. The algorithm was included in a two-step decision tree, assessing whether (i) PEth values fell within the prediction interval and (ii) the slope between two PEth values was consistent with no alcohol consumption. Data for 74 participants reporting no alcohol intake during the study were used for validation. With a detection limit of 'four units spread over 14 days', the sensitivity and specificity of the decision tree was 89%.

CONCLUSIONS

Claims of alcohol abstinence can be verified using a two-step decision tree for phosphatidylethanol 16:0/18:1 values, even when those values are above the limit for 'alcohol abstinence'.

Phosphatidylethanol in patients with liver diseases of different etiologies: Analysis of six homologues and comparison with other alcohol markers

BACKGROUND AND AIMS

Phosphatidylethanol (PEth) is a direct alcohol biomarker. Aim of the study was to evaluate the performance of six homologues of PEth in comparison to other alcohol markers in patients with liver diseases.

METHODS

The study included 234 patients with liver disease, who gave statements about alcohol consumption during the three months prior to the doctor's appointment. Ethylglucuronide in urine (uEtG) and in hair (hEtG) and carbohydrate-deficient transferrin (CDT) were analyzed in addition to PEth.

RESULTS

Of all patients 47% stated to have drunk alcohol during the past three months. UEtG, hEtG and CDT showed a sensitivity of 29% and a specificity of 92% together for ingestion of at least two standard drinks (24 g) per week. With PEth 16:0/18:1 in addition, sensitivity increased to 59%. For consumption in the last week uEtG's sensitivity and specificity was 28% and 100%, respectively. PEth's was 75% and 93%. When looking at patients who consumed at least two standard drinks per week during the past three months and of which a hair sample could be obtained, hEtG's sensitivity was 37% and specificity 90%. PEth had a sensitivity of 53% and specificity of 100%. Quotients of PEth 16:0/18:1 with 16:0/18:2, 16:0/20:4 and 18:0/18:2 were smaller when alcohol had been consumed more recently.

CONCLUSION

Despite the rather poor overall sensitivity of alcohol biomarkers in this study, PEth showed best sensitivity for all time periods of alcohol consumption.

Investigating the use of PEth, CDT and MCV to evaluate alcohol consumption in a cohort of homeless individuals- A comparison of different alcohol biomarkers

In a cohort including individuals with suspected high alcohol consumption, the concentrations of the indirect alcohol biomarkers carbohydrate-deficient transferrin (CDT) and mean corpuscular volume (MCV) and the direct alcohol biomarker phosphatidylethanol (PEth) were investigated. Blood alcohol concentration (BAC) was analysed as a marker for acute alcohol ingestion. In addition to questions about subjective alcohol consumption behaviour, 147 homeless persons underwent a physical examination with blood sampling. BAC, PEth, CDT and MCV were determined in the blood samples. Special focus was on the comparison of PEth and CDT for indicating excessive alcohol consumption. BAC was measured above 0.1‰ in 39 blood samples (0.1-2.5‰, median 0.75‰). PEth was detected in all of them. Overall, PEth was positive (≥10 ng/ml) in 104 samples (71%) (11-5687 ng/ml, median 650 ng/ml) with 68 (46%) being above the cut-off for excessive alcohol consumption (210 ng/ml). In 26 subjects PEth was the only positive alcohol biomarker. CDT was ≥ 1.7% in 66 cases (47%) (1.8-22.2%, median 4.4%) and ≥ 2.5% in 52 (35%) cases. MCV was elevated (≥95 fl) in 58 subjects (39%). CDT and PEth concentrations showed a significant positive correlation (spearman's correlation coefficient ρ = 0.77, p < 0.001). PEth concentrations were significantly higher in samples that were also CDT positive than solely PEth positive (p = 0.004). PEth did not indicate excessive alcohol consumption (< 210 ng/ml) in eight and two cases in which CDT was ≥ 1.7% and ≥ 2.5%, respectively. On the other hand, CDT was< 1.7% and< 2.5% in ten and 18 cases, respectively, in which PEth was above cut-off for excessive alcohol consumption. Taking the self-reports of the participants into consideration, PEth's sensitivity for detecting excessive alcohol consumption was 100% (10 ng/ml) and 94% (210 ng/ml) and CDT's was 88% (1.7%) and 75% (2.5%). In individuals of the investigated cohort unusually high concentrations of the alcohol consumption markers PEth and CDT were quantified, which proves the assumption of chronic excessive alcohol consumption in parts of the cohort. PEth was the marker that was positive most often and was more sensitive for excessive alcohol consumption than CDT.

Fully automated correction for the hematocrit bias of non-volumetric dried blood spot phosphatidylethanol analysis

The quantitative analysis of substances in dried blood spots (DBS) has gained vast popularity in the past decade. The World Anti-Doping Agency (WADA) also recently committed to implementing DBS. Currently, DBS sampling mainly has focused on various volumetric sampling devices such as Hemaxis, Capitainer, and Mitra. These devices are designed to collect a specific sample volume, independent of the hematocrit (HCT), to enable quantitative DBS analysis. Here, we present an automated solution that makes the necessity of volumetric sampling for quantitative DBS analysis obsolete. Combining automated reflectance-based HCT correction in combination with fully automated DBS LC-MS/MS analysis, the novel strategy permits high-throughput analysis in combination with HCT independence. Studying the model compound phosphatidylethanol 16:0/18:1, which is HCT-dependent due to incorporation into red blood cells, an implementation of DBS HCT normalization is presented. First, the performance of the automated HCT module with DBS is demonstrated compared to standardized HCT analysis from whole blood using a centrifuge. Second, the HCT dependency of fully automated PEth analysis from DBS is evaluated. Third, a solution to correct for the HCT dependency of PEth using the HCT scanner is presented. The study demonstrates that as soon as the HCT dependence of an analyte is known, a correction factor can be applied for the normalization of HCT levels. In the context of PEth, a linear increase in PEth concentration was observed, as the analyte is primarily located within the cellular fraction. Based on the obtained results, the use of a common correction factor for PEth DBS is possible.