Simultaneous determination of ethanol's four types of non-oxidative metabolites in human whole blood by liquid chromatography tandem mass spectrometry

An accurate and precise liquid chromatography-tandem mass spectrometry method for the determination of six phosphatidylethanol homologues in whole blood with phospholipid interferences minimized

Alcohol consumption is associated with a wide risk of different diseases, injury and death, and has significant social and economic consequences worldwide. Phosphatidylethanol (PEth) is a group of promising direct alcohol biomarkers, with a significantly longer half-life in blood than ethanol, which can be measured to predict different drinking patterns, such as heavy- and social drinking. This study aimed to develop and validate an accurate and precise LC-MS/MS method for the determination of six PEth homologues in whole blood with minimal interference from unwanted phospholipids. Different organic solvent mixtures for liquid-liquid extraction were investigated to obtain satisfactory recovery of PEth homologues and removal of the lyso-phospholipids and other early eluting phospholipids. The mixture of heptane/2-propanol (80:20, v:v) gave lower phospholipid background and better signal/noise values for the PEth peaks. An LC-MS/MS TQ-S system from Waters was used for the instrumental analysis. The main part of unwanted phospholipids were separated from the PEth homologues on an Acquity BEH C18 column (50 × 2.1 mm ID, 1.7 µm particles) using a buffer-free mobile phase of 0.025 % ammonia in Type 1 water, pH 10.7, as solvent A and methanol as solvent B. Validation and quantification of 22 authentic blood samples showed that the developed LC-MS/MS method is sensitive, precise and accurate for the determination of the six PEth homologues in whole blood. Lower limit of quantification was 10 nM for all compounds. No matrix effects were observed, possibly due to the successful strategies incorporated to avoid the influence of unwanted phospholipids.

Development of an LC-MS/MS assay with automated sample preparation for phosphatidylethanol (PEth)- Not your typical clinical marker

Phosphatidylethanol (PEth) is a group of phospholipids formed exclusively in the presence of ethanol on the erythrocyte membrane, making it a direct biomarker for long-term ethanol consumption for which a clinical reference interval has been established. Here, we describe an assay for quantitation for two most abundant PEth homologues, PEth 16:0/18:1 and PEth 16:0/18:2, from human whole blood, and present challenges overcome throughout the development process. Since PEth is localized within erythrocyte membranes, a reliable sample preparation technique is an important aspect of PEth analysis. Therefore, various erythrocyte lysing agents for recovery of exogenously spiked standards and controls were evaluated to identify one that performed comparably to the recovery of endogenous analytes found in authentic samples. A supported liquid extraction (SLE) technique was employed for sample cleanup and enrichment which together with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis enabled automated sample preparation, appropriate chromatographic resolution, and minimal system carryover. This resulted in a laboratory developed test with an analytical measurement range (AMR) of 10-1000 ng/mL (slope = 0.9902-1.0138, R2 = 0.9958-0.9972), that was precise (intra-day precision: 3.4-4.1%; inter-day precision: 4.4-8.2% over the AMR), accurate when compared with an available external laboratory test (slope = 0.9943-1.0206, R2 = 0.9635-0.9678, no lower decision point interpretation changes), with effective analyte recovery (77.2-83.5%), and established stability characteristics, while chromatographically separating the analytes to ensure no additive effects due to the isotopic distribution of the opposing analyte.

Development and validation of a HPLC-MS/MS method for the analysis of fatty acids - in the form of FAME ammonium adducts - in human whole blood and erythrocytes to determine omega-3 index

Recent scientific studies in the field of health and nutrition have unanimously affirmed the importance of consuming the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), because of their cardioprotective properties. Fatty acid profiling in erythrocyte membranes allows the omega-3 index, which is a recognized indicator of the risk of developing cardiovascular disease, to be calculated. One consequence of the upward trend in healthy lifestyles and longevity is an increase in the number of studies into the omega-3 index, which requires a reliable method for the quantitative analysis of fatty acids. This article describes the development and validation of a sensitive and reproducible liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method for the quantitative analysis of 23 fatty acids (in the form of fatty acid methyl esters, FAMEs) in 40 µl of whole blood and erythrocytes. The list of acids includes saturated, omega-9 unsaturated, omega-6 unsaturated and omega-3 unsaturated fatty acids as well as their trans-isomers. The limit of quantitation was 250 ng ml-1 for C12:0, C16:0 and C18:0; and 62.5 ng ml-1 for other FAMEs, including EPA, DHA and trans-isomers of FAME C16:1, C18:1 and C18:2 n-6. Sample preparation for fatty acid (FA) esterification/methylation with boron trifluoride-methanol (BF3) has been optimized. Chromatographic separation has been carried out on a C8 column in gradient mode using a mixture of acetonitrile, isopropanol and water with the addition of 0.1% formic acid and 5 mM ammonium formate. As a result, the problem of separating the cis- and trans-isomers of FAME C16:1, C18:1 and C18:2 n-6 has been solved. The electrospray ionization mass spectrometry (ESI-MS) detection of FAMEs, in the form of ammonium adducts, has been optimized for the first time, which has made the method more sensitive that when the protonated species are used. This method has been applied to 12 samples from healthy subjects that consumed omega-3 supplements and has proven to be a reliable tool for determining the omega-3 index.

Quantitative Determination of Ethyl Glucuronide and Ethyl Sulfate in Postmortem and Antemortem Whole Blood Using Phospholipid Removal 96-Well Plate and UHPLC-MS-MS

Postmortem ethanol formation is a well-known problem in forensic toxicology. Ethyl glucuronide (EtG) and ethyl sulfate (EtS) are ethanol metabolites that can be used to distinguish antemortem alcohol intake from postmortem formation of ethanol and in addition can be a helpful tool in assessment of the hip-flask defense. To an aliquot of 100 µL whole blood, internal standard (IS) and water was added before protein precipitation treatment (PPT) with ice-cold acetonitrile (ACN). The supernatants were filtered through a 96-well phospholipid removal plate, evaporated to dryness and reconstituted in 150 µL water/ACN/formic acid (FA). Identification of compounds was performed using multiple reaction monitoring (MRM) in negative mode. Gradient elution was performed on a C18 column with methanol (MeOH) and 0.1% FA. The run time was 4.5 min, and 0.5 µL was injected on an ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS-MS) instrument. Linearity was achieved (coefficient of determination (R²) ≥ 0.999) for EtG in the range of 0.089 to 22 mg/L (0.40–100 µM) and EtS 0.025 to 6.3 mg/L (0.20–50 µM). The limit of quantification (LOQ) was 0.067 mg/L (0.30 µM) for EtG and 0.019 mg/L (0.15 µM) for EtS. Between assay accuracy was –15% to 8% and precision reported as relative standard deviation (RSD) was ≤ 4.5%. Precision, estimated as the RSD of the concentration difference between results from two independent analyses of authentic whole blood samples, was ≤ 6.7%. Recovery was ≥ 61% for EtG and ≥ 77% for EtS and matrix effects (ME) were 99% to 103%. Method comparison was carried out with a previously used UHPLC–MS-MS method, and satisfactory agreement was achieved, and external proficiency testing control samples had z-score < ± 1. The method has been used in routine work for more than 4 years analyzing about 6,000 antemortem and postmortem whole blood samples and has proven to be robust and reliable.

The role of ethanol in fatalities in Jeddah, Saudi Arabia

In Saudi Arabia, alcohol consumption is prohibited by law, but interpreting postmortem ethanol can be complicated by its postmortem production. This study developed and validated a method using headspace gas chromatography with flame ionization detection and liquid chromatography tandem mass spectroscopy to detect ethanol and its polar metabolites (ethyl glucuronide [EtG] and ethyl sulfate [EtS]) in postmortem blood and urine specimens, respectively. All calibration curves were linear with coefficients of determination greater than 0.999. The limits of detection ranged 4.5-5.0mg/dL for ethanol and 0.05-0.06mg/L for EtG and EtS. The limits of quantification were 10.0mg/dL for ethanol and 0.075mg/L for EtG and EtS. Within-run precision was less than 11% for all analytes of interest. Matrix effects for EtG and EtS ranged 3-47%. After excluding matrix effects, analytical recoveries ranged 72-100%. This validated method was then used for routine postmortem forensic toxicology analyses in 592 routine postmortem cases to distinguish between antemortem ethanol consumption and its postmortem microbial formation. Among them, 98 blood samples (17%) were positive for ethanol or its polar metabolites. Thirty-two of these cases (33%) were positive for EtG and EtS and therefore due to antemortem ethanol consumption. The remaining 66 (67%) cases were negative for both EtG and EtS and therefore due to postmortem ethanol synthesis. Because this is the first study to report the problem of alcohol consumption in Saudi Arabia, further studies are essential for validating these findings.

Stability of Ethyl Glucuronide, Ethyl Sulfate, Phosphatidylethanols and Fatty Acid Ethyl Esters in Postmortem Human Blood

The lack of systematic studies on the stability of ethanol's non-oxidative metabolites in postmortem specimens restricts their use in forensic cases. This study aimed to compare the stability of ethyl glucuronide (EtG), ethyl sulfate (EtS), phosphatidylethanols (PEths) and fatty acid ethyl esters (FAEEs) in postmortem human blood. Three groups were established based on the level and source of ethanol: the blank group, the ethanol-spiked group and the ethanol-positive group. Each group contained six blood samples from different corpses. The samples in each group were placed at 37, 25, 4 and -20°C. Every 24 h for 7 days, 50 μL was collected from each sample. The levels of EtG, EtS, PEths and FAEEs were determined by liquid chromatography-mass spectrometry, and their stability was evaluated. EtG was not detected in the blank group, but it was found in samples in the ethanol-spiked group placed at 37°C, and it was degraded in the ethanol-positive group at 37 and 25°C. EtS showed no change in any of the groups. PEths were not detected in the blank group, but formation was found in the ethanol-spiked group at all temperatures. In the ethanol-positive group, PEth levels fluctuated at 37°C, decreased at 25°C and increased at -20°C. FAEEs were generated in the blank group and in the ethanol-spiked group at all temperatures. In the ethanol-positive group, FAEEs were degraded at 37 and 25°C but were generated at 4 and -20°C. EtS is a reliable biomarker of ethanol consumption, and EtG could be used as a biomarker at low temperatures (4 and -20°C), but PEths and FAEEs are not appropriate biomarkers of ethanol consumption.

Determination of phosphatidylethanol 16:0/18:1 in whole blood by 96-well supported liquid extraction and UHPLC-MS/MS

BACKGROUND

Phosphatidylethanols (PEths) are specific, direct alcohol biomarkers that can be determined in human blood to distinguish between heavy and social drinking. PEth 16:0/18:1 is among the most predominant PEth homologues in human blood. The aim of the study was to develop a high throughput and sensitive UHPLC-MS/MS method for the determination of PEth 16:0/18:1 in whole blood.

METHODS

Whole blood samples were prepared by 96-well supported liquid extraction (SLE). Extracted samples were analyzed for PEth 16:0/18:1 by reversed phase UHPLC-MS/MS.

RESULTS

The developed UHPLC-MS/MS method was fully validated in whole blood with PEth 16:0/18:1-D₅ as internal standard. Intermediate precision and intermediate accuracy were within ≤± 12% and ≤± 17%, respectively, at PEth 16:0/18:1 concentrations of 1.4-2112 ng/mL (2.0-3004 nmol/L). Limit of quantification (LOQ) was 1.7 ng/mL (2.4 nmol/L).

CONCLUSION

For the first time, 96-well SLE was used for preparation of a PEth homologue in biological samples. A mixture of tert-butyl methyl ether and 2-propanol (5:1, v:v) was chosen as organic eluent based on an evaluation of extraction recovery, purity of extracts, and evaporation time. The developed UHPLC-MS/MS method can be used for high throughput analyses and sensitive determinations of PEth 16:0/18:1 in whole blood.