Identifi cation of Melatonin Poisoning Markers in Biological Samples by Liquid Chromatography–tandem Mass Spectrometry: Case Report and Analysis

ZHANG Leiping, HAN Xu, DU Hongyan, LIU Yongtao, XU Duoqi, REN Xinxin, SONG Ge

(1. Institute of Forensic Science, Ministry of Public Security, Beijing 100038, China; 2.Institute of Forensic Science, Tianjin Public Security Bureau, Tianjin 300384, China; 3.Beijing Center of Forensic Science for Public Security and Justice, Beijing 100192, China; 4. People`s Public Security University of China, Beijing 100038, China)

Identifi cation of Melatonin Poisoning Markers in Biological Samples by Liquid Chromatography–tandem Mass Spectrometry: Case Report and Analysis

ZHANG Leiping1, HAN Xu2, DU Hongyan1, LIU Yongtao3, XU Duoqi4, REN Xinxin1, SONG Ge1

(1. Institute of Forensic Science, Ministry of Public Security, Beijing 100038, China; 2.Institute of Forensic Science, Tianjin Public Security Bureau, Tianjin 300384, China; 3.Beijing Center of Forensic Science for Public Security and Justice, Beijing 100192, China; 4. People`s Public Security University of China, Beijing 100038, China)

Melatonin is one of the hypnotics commonly used by the current elderly and people of insomnia. In recent years, melatonin has begun to emerge in drug-facilitated criminal cases since the offenders take it as an auxiliary crimecommitting tool. A homicide case involving melatonin has been reported in this paper. The protomer of melatonin and its metabolite 6-hydroxy-melatonin, served as the poisoning markers, were analyzed by ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), together with the deep mining of the revealed information. The established method is simple, fast and effective in practice. This study should be of great signifi cance in getting more information or details in related cases.

forensic toxicology; melatonin; 6-hydroxy melatonin; poisoning markers; UPLC-MS/MS

Melatonin is one of the most common hypnotics in hospital and pharmacy. It can effectively supplement the gradual reducing of endogenous melatonin in human body due to senility or some reasons so as to achieve the hypnotic effect, which is especially welcome among the elderly and insomnia sufferers. Recently, melatonin has been used as an auxiliary tool by some drug-facilitated offenders. This paper reports a case involving melatonin poisoning. An ultra high performance liquid chromatography-tandem mass spectrometry was established for sensitively detecting melatonin and its metabolite 6-hydroxy melatonin, two biomarkers of melatonin-poisoning in biological samples. This article also mines the deep information associated with this chemical and the case, with purpose to provide a reference for the identifi cation and determination of future melatonin-related cases.

1 Case Information

1.1 Simple Introduction of the Case

A case, where the victim was strangled during sleep after drinking with the suspected culprit on one day of 2015, was submitted for us to discover the truth. The death cause was mechanical asphyxia. Frozen gastric contents and blood of the victim were extracted, ready for toxicological analysis.

1.2 Materials and Methods

1.2.1 Instruments and Setting-up

A Shimadzu 30A-LC (Shimadzu Corporation, Japan) system, equipped with a reversed phase C18 analytical column (100 mm×2.1 mm and 1.8 μm) (Zorbax Eclipse XDB-C18), was used for LC analysis. The injection was 2 μL. The mobile phases were consisted of two eluents: 0.1% formic acid in water as eluent A and the absolute acetonitrile as eluent B. The gradient elution was performed at a fl ow rate of 0.5 mL/min, starting from 90% A and being kept for 0.6 min, then decreased to 50% A within 0.4 min and maintained for 1.0 min until returning to initial condition in 0.1 min. An equilibration time of 1.9 min was allowed prior to the next injection.

MS analysis was conducted on an API5500 QTRAP (Applied Biosystems Inc., USA) system with an electrospray ionization source (ESI) operated in positive ionization mode. The following parameters were selected for all of the experiments: ion source temperature, 600℃; capillary voltage, 5500 V; desolvation gas, 70 psi; cone gas, 8 psi. The scan mode was multiple reaction monitoring (MRM). The MS/MS parameters targeting at each compound, including retention time (Rt), ion pairs for qualitative and quantitative test, declustering potential and collision energy, were summarized in Table 1.

Table 1 The MS/MS parameters for determination of melatonin and 6-hydroxy melatonin

1.2.2 Chemicals and Reagents

Acetonitrile and formic acid, both HPLC grade, were obtained from Merk (Darmstadt, Germany). Melatonin and 6-hydroxy melatonin standards were purchased from TRC Chemical Reagent Limited Corporation (Canada).

1.2.3 Sample Preparationn

Stock standard solutions were prepared in acetonitrile at concentration of 1 mg/mL, stored at -20℃. Working solutions were products from the standard stock solutions by appropriate sequential dilutions with distilled water, stored at 4 ℃.

For protein precipitation, 1 mL of blood sample was mixed with 2 mL of acetonitrile, then subjected to vortex for 30 s, sonicated for 10 min and fi nally centrifuged at 8000 rpm for 20 min. The supernatant of either blood sample or the gastric contents was diluted up to 100 times with distilled water, and followed to undergo LCMS/MS analysis after fi ltration through a membrane of pores about 0.22 μm.

1.3 Results

For this case, an LC-MS/MS was decided to detect the drug (poison). Both melatonin and its metabolite 6-hydroxy melatonin were found in blood sample while only the melatonin protomer being left in the stomach contents. The negative and positive control tests confirmed the effectiveness of the method by the blank blood, and further so did it by the spiked blood sample. Extract ion chromatograms were respectively shown for the case blood, blank blood and spiked blood samples in Fig. 1～3.

Fig.1 Extract ion chromatograms of both melatonin and 6-hydroxy-melanin obtained from the case-submitted blood sample

Fig.2 Extract ion chromatograms from the blank blood sample

Fig.3 Extract ion chromatograms of both melatonin and 6-hydroxy-melanin harvested from the spiked blood sample.

2 Discussion

Melatonin, usually an endogenous hormone-category hypnotic, shows no obvious side effects in normal dose when being replenished as a medicament. Its pharmacological effect plays an auxiliary role in the cases of abnormal death from the other direct factors, for example, mechanical asphyxia in the case reported here.

Melatonin has a short elimination half-life of 0.3 ～ 0.5 h[1]. Due to this property, the elimination may result in false negative results. To avoid such mistakes happening and improve the detection efficiency for related cases, many experts suggest the analysis of melatonin protomer together with its metabolite. Melatonin and 6-hydroxymelatonin were used as markers of intoxication in this test because melatonin turns into 6-hydroxy-melatonin after being undergone the metabolism in human liver[2]. In this measurement, the concentrations of melatonin were 49.2 ng/mL and 605 ng/mL in the blood and stomach contents samples, respectively, yet 6-hydroxy-melatonin was only 19 ng/mL detected in the blood sample. The results showed that the blood concentration of melatonin was higher than that of 6-hydroxy melatonin when melatonin was orally taken, indicating the occurring process of melatonin absorption (absorbed into the blood from stomach digesting) and metabolism. Very likely, the victim died shortly after taking melatonin. In physiological course, the normal secretion of melatonin displays a distinct circadian rhythm, keeping the melatonin serum concentration at 30-120 pg/mL during night while only 10 pg/mL in daytime. The general hypnotic-curing oral dose of melatonin is 1 to 3 mg so that the blood drug concentration achieves more than 1.9 ng/mL after 1 hour of melatonin administration. Therefore, the victim's blood concentration of melatonin is beyond 25 times of the acting hypnotic dose, causing a strong hypnotic effect that made the victim lose consciousness.

According to the investigation by the police and the confession from the suspect that the victim was cheated to take seven pieces of melatonin after drinking and was strangled 1 hour from then on. The test results of the samples were consistent with the case fact, providing an objective evidence for the court judgment with confi rmation of the suspect's statements. There are many methods available for melatonin analysis in biological samples, such as SPE-GC/MS[3], LC/MS[4]and HPLC[5], but rare reports have been found about the detection of 6-hydroxy melatonin. This article presents an approach for detecting melatonin and its metabolite 6-hydroxy melatonin. With the simplicity, rapidity and effectiveness, this method is capable of meeting the detection of melatonin-related cases and helping to deep mine case information for better results to achieve.

[1] 张蕾萍, 于忠山, 何毅, 等. 法庭科学中的新型催眠药[J]. 刑事技术, 2008, 5: 37-40.

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[3] 张蕾萍, 杜鸿雁, 栾玉静, 等. 固相萃取－气相色谱法提取全血中的外源性褪黑素[J]. 中国法医学杂志, 2010, 25(2): 84-86.

[4] 文冰亭, 熊歆, 刘娜, 等. 液相色谱-质谱法测定唾液内的褪黑素浓度[J]. 中国临床药理学杂志, 2010, 26(4):299-301.

[5] 张林, 钟历勇, 孙子林,等. 高效液相色谱电化学法测定血清褪黑激素水平[J]. 东南大学学报, 2005, 24(2): 105-108.

血液中褪黑素中毒标记物鉴定

张蕾萍1，韩 旭2，杜鸿雁1，刘永涛3，徐多麒4，任昕昕1，宋 歌1

（1.公安部物证鉴定中心，北京 100038；2.天津市公安局物证鉴定中心，天津300384；
3.北京市公安司法鉴定中心，北京 100192；4.中国人民公安大学，北京100038）

褪黑素是失眠及老年人常用的催眠药之一。近年来，一些犯罪分子利用其为作案工具，从而使之也出现在物证鉴定的检验项目中。本文报道一起涉及褪黑素的麻醉凶杀案的检验鉴定，以原体及代谢物作为中毒标记物，对褪黑素及其代谢物6-羟基褪黑素进行分析检验，并对案件信息作深度挖掘。使用日本岛津30A-LC液相色谱仪串联美国AB SCIEX公司API5500 QTRAP质谱仪，对送检样品进行测定化验，发现受害人血液褪黑素浓度超过正常起催眠作用的浓度达25倍以上。本文建立的液相色谱/串联质谱检验分析，方法简单、快速、有效，效果良好。

法医毒物分析；褪黑素；6-羟基褪黑素；中毒标记物；液相色谱-质谱

DF795.1

A

1008-3650(2016)05-0402-03

2016-04-19

格式：ZHANG Leiping, HAN Xu, DU Hongyan, et al. Identification of Melatonin Poisoning Markers in Biological Samples by Liquid Chromatography-tandem Mass Spectrometry: Case Report and Analysis[J].刑事技术，2016,41(5):402-404.

DF795.1 Document Code: A Article ID: 1008-3650(2016)05-0402-03

10.16467/j.1008-3650.2016.05.014

Fund: Projects of Key Research (No. 201302ZDYJ002) and Technical Exchange & Skill Training (B2013001A)

Author: Zhang leiping(1980—), female, master, associate researcher, engaged in toxicological identification and research. Email: zlpbjft@sohu.com