One large beer, please! – Synthesis of Phosphatidylethanol 16:0/18:1 and 16:0/18:2 after consumption of low amounts of alcohol

Abstract

Phosphatidylethanol has gained recognition as a direct alcohol biomarker in the past years. It has been shown to be beneficial alone or in combination with other alcohol biomarkers in different settings and patient collectives. While different cut-offs have been suggested and applied, there is no consensus on cut-off concentrations of PEth for differentiating between abstinence and alcohol consumption. After staying abstinent for at least three weeks 75 participants consumed 20 g of ethanol (500 mL 5 Vol% beer) within 30 min on three consecutive evenings. Blood was sampled on each following day from the fingertip, using a safety lancet and a 20 μL micropipette. Dried blood spots were directly generated and later analyzed for PEth 16:0/18:1 and 16:0/18:2 via LC-MS/MS. Limit of detection for both analyzed homologues was 3.9 ng/mL. Limit of quantification (LOQ) was 8.6 ng/mL for PEth 16:0/18:1 and 6.2 ng/mL for PEth 16:0/18:2. A control group ( n = 22) consumed one liter of alcohol-free beer within one hour on three consecutive evenings. Starting concentrations for the drinking phase were < 7 ng/mL for both homologues in all participants. When applying a cut-off of 10 ng/mL it were 25% of the participants that were positive after the first consumption for PEth 16:0/18:1. After the second and third consumption it were 45% and 49%, respectively. PEth 16:0/18:2 was positive in 40%, 61% and 71% after the first, second and third consumption of alcohol, respectively. A PEth 16:0/18:1 concentration of > 20 ng/mL was only quantified in one sample after the first consumption and in five samples after the third consumption. PEth 16:0/18:2 was > 20 ng/mL in 7%, 24% and 35% on the days after the first, second and third consumption, respectively. Overall, 35 ng/mL was exceeded by PEth 16:0/18:1 in one sample and PEth 16:0/18:2 in three samples. If including the samples with concentration > 8.6 ng/mL into calculation, PEth ranged from 8.9–21.5 ng/mL [mean: 11.6 ng/mL, standard deviation (sd): 2.9] after the first consumption, 8.8–19.3 (mean 13.1 ng/mL, sd: 2.9) after the second consumption and 8.8–42.3 ng/mL (mean: 14.3 ng/mL, sd: 6.2) after the third consumption. n = 52 of the participants were female (72%). The ratio of samples > 10 ng/mL PEth 16:0/18:1 was significantly higher in women after the third consumption of alcohol than in men ( P = 0.02). For PEth 16:0/18:2 the ratio was significantly higher in women than in men after the second ( P = 0.023) and the third ( P = 0.002) consumption. Consumption of one liter of ‘alcohol-free’ beer on three consecutive days did not impact PEth concentrations in any participant on any study day ( n = 22). The high ranges of PEth concentrations among the participants highlights the interindividual dose response of PEth to ethanol, as some participants did not show any change in PEth concentrations while others reached > 20 ng/mL after initially being < LOQ. For consumption of small amounts of alcohol, the cut-off of 10 ng/mL was by far more sensitive than 20 or 35 ng/mL. It needs to be kept in mind that due to the long half-life of PEth a low concentration can also result from a consumption leading to higher PEth that lies further back. Still, in settings in which consumption of small amounts of alcohol needs to be detected it could be recommended to apply 10 ng/mL as cut-off. The quantification of the two homologues PEth 16:0/18:1 and 16:0/18:2 together increases sensitivity in opposite to only analyzing the first.