Analysis of fatty acid ethyl esters in hair as possible markers of chronically elevated alcohol consumption by headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS)

Abstract

Fatty acid ethyl esters (FAEE) are products of the nonoxidative ethanol metabolism, which are known to be detectable in blood only about 24 h after the last alcohol intake. After deposition in hair they should be suitable long-term markers of chronically elevated alcohol consumption. Therefore, a method for the analysis of ethyl myristate, ethyl palmitate, ethyl oleate and ethyl stearate from hair was developed based on the extraction of the hair sample by a dimethylsulphoxide (DMSO)/n-hexane mixture, separation and evaporation of the n-hexane phase and application of headspace solid-phase microextraction (HS-SPME) in combination with gas chromatography-mass spectrometry (GC-MS) to the extract. For use as internal standards, the corresponding D₅-ethyl esters were prepared. The HS-SPME/GC-MS measurements were automatically performed using a multi-purpose sampler. The detection limits of the FAEE were between 0.01 and 0.04 ng/mg and the reproducibility was between 3.5 and 16%. By application of the method to hair samples of 21 fatalities with known heavy alcohol abuse 0.045–2.4 ng/mg ethyl myristate, 0.35–13.5 ng/mg ethyl palmitate, 0.25–7.7 ng/mg ethyl oleate and 0.05–3.85 ng/mg ethyl stearate were measured. For social drinkers (30–60 g ethanol per week), the concentrations were about one order of magnitude smaller. For 10 teetotalers negative results or traces of ethyl palmitate were found. It was shown by supplementary investigations in single cases that FAEE are also present in sebum, that there is no strong difference in their concentrations between pubic, chest and scalp hair, and that they are detectable in hair segments after a 2 months period of abstinence. From the results follows that the measurement of FAEE concentrations in hair is a useful way for a retrospective detection of alcohol abuse.

Introduction

Hair analysis has proved to be a suitable tool for the retrospective detection of the consumption of illicit or therapeutic drugs. The physiological basis, analytical methods and practical applications were described in books [1], [2], reviews [3], [4] and special issues of journals on the occasion of hair conferences [5]. Different from these advantages up to now there is no practicable method for the detection of chronically elevated alcohol consumption by hair analysis, although ethanol is abused most frequently and has highest blood concentrations of all substances. Possible alcohol markers in hair and first investigations for their analytical measurement were reviewed in a previous paper [6]. Between them some promising results were obtained for ethyl glucuronide in first investigations by Sachs [7] and by Aderjan, Skopp et al. [8], [9], but the results of a recent closer examination of the presence of this ethanol metabolite in hair and skin horny layer of alcoholics by the same authors were rather discouraging [10]. First experiments to detect acetaldehyde modified proteins in hair of alcohol fed animals were described by Jelinkova et al. [11] and Watson et al. [12], but this method is also still far from practical application.

In orientating investigations the fatty acid ethyl esters (FAEE) ethyl palmitate, ethyl oleate and ethyl stearate were detected in methanol extracts of hair of alcoholics [6]. The enzymatic formation of FAEE after alcohol consumption was first discovered by Lange et al. in 1981 [13] and later thoroughly investigated mainly by Laposata and Laposata and coworkers [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25]. According to these results, FAEE are formed in presence of ethanol from free fatty acids, triglycerides, lipoproteins or phospholipids by action of the specific cytosolic and microsomal FAEE synthases as well as of unspecific enzymes such as carboxylesterase, lipoprotein lipase, carboxylester lipase and cholesterol esterase [18] (Fig. 1). FAEE synthase activity was detected in liver, pancreas, myocard, adipose tissue, different regions of brain or white blood cells. FAEE are regarded as a reason for the alcohol induced organ damage by different pathogenic mechanism [18], such as incorporation and disordering of organic bilayers, uncoupling of oxidative phosphorylation, increase of lysosomale fragility or decrease of protein synthesis and cell proliferation. The primary and terminal half-life in blood is about 3 and 10 h, respectively [23]. Therefore, in blood they can be used as markers of an actual or recent alcohol intake at least 24 h after completion of ethanol intake [22]. In adipose tissues of rats a half life of 16±1.6 h was determined [15].

For volunteers with a blood ethanol concentration of ≈1.0‰ the FAEE concentrations in serum were 0.4–0.75 μg/ml [24]. In other studies between 1.8 and 3.8 μg/ml in serum [20] and between 3 and 50 μg/ml in blood [16], [17], [20] were described. In alcoholics postmortem, the FAEE concentrations were 40–500 μg/g in heart tissue [26], 4–170 μg/g in brain tissue [26] and 90±14 μg/g in fat tissue [15]. In meconium of an alcohol exposed infant 13.1 μg/ml were measured [27].

The measurement of the FAEE concentrations was performed in most cases according to a method of Bernhardt et al. [25] by liquid–liquid extraction with acetone/hexane (2/5, 1/3 or 2/8, v/v), purification of the extract on aminopropyl columns and identification by gas chromatography with flame ionization detection (GC-FID) [27], [28] or with mass spectrometric detection (GC-MS) [17], [20], [24], [25] using ethyl heptadecanoate as internal standard. For separation of individual FAEE, gas chromatography was applied after purification by high-performance liquid chromatography [25]. Tissue samples were extracted with ethyl acetate and the concentrated extract suspension was directly injected into the GC-FID instrument [26]. Alternatively, thin layer chromatography on silica gel 60 plates was used for extract purification [16], [23]. In most cases, ethyl laurate, ethyl myristate, ethyl palmitate, ethyl palmitoleate, ethyl stearate, ethyl oleate, ethyl linoleate and ethyl arachidonate were analyzed. In serum, they are bound mainly to albumin or lipoproteins [17].

Like other substances, FAEE should be deposited in hair from blood. Until present experiments for detection of FAEE synthase activity in hair roots were not described in literature. However, it can be expected from the generally high enzyme activity in these cells that FAEE should be synthesized also in the basal cells of the hair roots or in the surrounding tissues. A third way of deposition could be the incorporation from sebum, although FAEE were also not yet detected in this secretion. In order to examine whether fatty acid ethyl esters are suitable hair markers of alcohol abuse an analytical method for their quantitative analysis from hair was developed and applied to hair samples of alcoholics, social drinkers and teetotalers. Headspace solid-phase microextraction (HS-SPME) in combination with capillary gas chromatography and mass spectrometry (GC-MS) was chosen as a suitable technique, which was successfully applied for the detection of volatile and semivolatile lipophilic drugs from hair in previous investigations [29], [30], [31], [32].