Background Evaluation of ethanol use before and after liver transplantation is presently hindered by the limited detection period of ethanol itself, a lack of other proven markers, and reliance on patients' verbal history. Fatty acid ethyl esters (FAEEs) are direct metabolites of ethanol that persist at least 48 hours in blood after drinking and have been used as ethanol biomarkers. Fatty acids, a substrate for FAEE synthesis, are affected by immunosuppressive medications. Low levels of ethanol, from endogenous intestinal fermentation or mouthwash, could potentially lead to spuriously increased FAEE levels in the setting of lipid-increasing immunosuppresion. Our FAEE assay detected all three predominant FAEEs (ethyl palmitate, ethyl oleate, and ethyl stearate) in all 76 samples from recently drinking individuals. We assessed whether FAEEs are detectable in plasma samples from abstinent liver transplant recipients.
Methods Thirty-five plasma samples from 30 abstinent liver transplant recipients (M:F 19:11) were analyzed; abstinence was confirmed by the Timeline Followback instrument and breath ethanol analysis. Levels of ethyl palmitate, ethyl oleate, and ethyl stearate were measured by gas chromatography-mass spectrometry after lipid extraction and solid phase extraction of the samples. Ions 88.1 and 101.1 were monitored.
Results At the time of sampling, immunosuppressive regimens included tacrolimus in 26, sirolimus in 21, prednisone in 8, cyclosporine in 8, and mycophenolate mofetil in 6 participants. Regimens included 1, 2, and 3 immunosuppressants in 6, 22, and 6 of the participants, respectively. FAEE levels above the lower limit of quantitation, 60 nM, were not found in any participant. Twenty-two samples had no measurable FAEE and 13 had trace levels, 2-38 nM, which are not distinguishable from instrument contamination due to previous FAEE-containing samples. In all the samples with trace amounts, only one of three FAEEs was present.
Conclusion There were no false-positive FAEE assays in this cohort of abstinent post liver transplant recipients, regardless of immunosuppressive treatment. FAEE monitoring in a low-dose ethanol consumption experiment is the next step in validation of this promising method of ethanol use detection in this population.
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