Tài liệu Drugs and Poisons in Humans - A Handbook of Practical Analysis (Part 57) docx

In this chapter, a method for LC/MS analysis of oleandrin and its metabolite desacetylole-andrin [9] together with their related compounds, such as oleandrigenin and gitoxigenin, con-tai

© Springer-Verlag Berlin Heidelberg 2005

Introduction

Oleander ( Nerium oleander and Nerium indicum) is a relatively small evergreen tree of an

Indian origin, and growing in Honshu, Shikoku, Kyushu and Okinawa islands in Japan Th e plant contains cardiac glycosides in its leaves, stems and fl owers and is known as one of poison-ous plants; poisoning and fatal cases for domestic animals and humans due to ingestion of this plant were reported [1–6] Th e main toxin of oleander is oleandrin

Oleandrin can be measured using cross-reaction of an immunoassay kit for digoxin [1], TLC [2], HPLC [7, 8] and LC/MS [3, 6] Oleandrin is thermolabile; it is diffi cult to analyze it by

GC or GC/MS, because it gives 4 peaks due to decomposition

In this chapter, a method for LC/MS analysis of oleandrin and its metabolite desacetylole-andrin [9] together with their related compounds, such as oleandrigenin and gitoxigenin, con-tained in human specimens, is presented

Th e structures and their molecular weights of oleandrin and its related compounds are shown in > Figure 7.1.

⊡ Figure 7.1

Structures and molecular weights of oleandrin and its related compounds.

Reagents and their preparation

• A 1-mg aliquot each of oleandrin, oleandrigenin, desacetyloleandrina, gitoxigenin and digi-toxigenin (Sigma, St Louis, MO, USA) is dissolved in 10 mL acetonitrile (100 µg/mL) separately

• A 0.1-mL volume of the above digitoxigenin solution is diluted with acetonitrile to 10 mL (1 µg/mL; internal standard, IS)

HPLC conditions

Instrument: a Hitachi M-8000 type LC/3DQMS system; column: GH-C18 (III) (150 × 2.1 mm i.d., particle size 5 µm, Hitachi Ltd., Tokyo, Japan); column temperature: 40 °C; mobile phase: methanol/water (6:4, v/v); its fl ow rate: 0.2 mL/min

MS conditions

Ionization: sonic spray ionization ( SSI)b; shield temperature: 250 °C; aperture-1 temperature:

150 °C; aperture-2 temperature: 120 °C; drift voltage: 70 V; ion detection mode: positive;

microscan: 5 s; mass defect: 55/100 amu; scan range: m/z 350–650; low mass cutoff : m/z 120;

accumulation time: 500 ms

MS/MS conditionsc

Ion accumulation step: Ion accumulation mass range: m/z 350–650; low mass cutoff : m/z 120; ion accumulation time: 300 ms; ion accumulation voltage: 0 V.

Ion isolation step (MS-1): Isolation mass range: m/z 595.48–602.77; low mass cutoff : m/z 569.06; isolation time: 10 ms; isolation voltage: 0.175 V.

CID step (MS-2): CID mass range: m/z 584.15–614.64; low mass cutoff : m/z 190; CID time:

50 ms; CID voltage: 0.188 V

Procedure

i A 1-mL volume of a specimend is mixed with 4 mL distilled water and 100 µL IS solution

ii Th e above mixture is extracted with 2 mL of 1-chlorobutane by shaking for 15 min iii It is centrifuged at 2,000 g for 5 min; the organic phase is transferred to a test tube

iv Th e steps ii and iii are repeated twice

v Th e organic phases are combined and evaporated to dryness under a stream of nitrogen with warming at 40 °C

vi Th e residue is dissolved in 0.5 mL of 80 % methanol aqueous solution, and washed with

1 mL hexane twicee

vii Th e 80 % methanol layer is evaporated to dryness under a stream of nitrogen with warm-ing at 40 °C in a water bath

viii Th e residue is dissolved in 100 µL mobile phase and centrifuged at 12,000 g for 5 min; a 5-µL aliquot of the supernatant solution is injected into LC/MS

ix Each calibration curve is constructed using spiked specimens with digitoxigenin as IS

Th e concentration of an oleander toxin in a specimen is calculated using the calibration curve

Assessment of the method

Oleandrin is one of cardiac glycosides and exerts its eff ect at low concentrations To detect its therapeutic concentrations, the detection limit by an analytical method should be in the nano-grams/mL order When the present method was used in an oleander poisoning case, oleandrin could be detected from blood and cerebrospined fl uid (CSF), showing the applicability of the method

> Figure 7.2 shows a TIC and mass spectra for the authentic standards of the fi ve

com-pounds Th e spectra showed intense [M + Na]+ adduct ions at m/z 599 for oleandrin, m/z 557 for desacetyloleandrin, m/z 455 for oleandrigenin and m/z 397 for digitoxigenin used as IS; for

gitoxigenin, both [M + Na]+ and [M + Na – H2O]+ ions appeared at m/z 413 and 395,

respec-tively

⊡ Figure 7.2

TIC and mass spectra for each peak obtained by LC/MS for the authentic compounds (1 µg/mL

each) of oleandrin and its related compounds.

> Figure 7.3 shows a TIC and mass chromatograms (MCs) for the above 5 compounds,

which had been spiked into blood (0.1 µg/mL) and extracted from it Th ere were no interfering impurity peaks for each test compound in the chromatogram of blank blood

Th e recovery rates for oleandrin, desacetyloleandrin and oleandrigenin were not lower than 70 %; but that for gitoxigenin was as low as about 20 % Th ere was good linearity in the

TIC and MCs obtained by LC/MS for an extract of blood, into which oleandrin and its related compounds had been spiked (0.1 µg/mL each).

⊡ Figure 7.3

range of 5–100 ng/mL for oleandrin, desacetyloleandrin and oleandrigenin Th e detection limits from blood were 3 ng/mL for oleandrin, 2 ng/mL for desacetyloleandrin and oleandri-genin, and 30 ng/mL for gitoxigenin

Poisoning case, and toxic and fatal concentrations

A 49-year-old female boiled an oleander branch with leaves in water, and took a large amount

of the extract solution; she underwent therapy, but died one day later Th e blood and CSF specimens obtained at the postmortem inspection of the above victim were analyzed by the present method Th e TIC and MCs obtained for the victim by LC/MS are shown in > Fig-ure 7.4 Oleandrin could be detected; but desacetyloleandrin, oleandrigenin and gitoxigenin

could not Th e peak at m/z 599 observed in the MC was confi rmed to be due to oleandrin by

MS/MS analysis as shown in > Figure 7.5 Th e concentration of oleandrin was 10 ng/mL for both blood and CSF

Th e blood or plasma concentrations in cases of poisoning by oleandrin, digoxin and digi-toxin are shown in > Table 7.1 Th ere is another report dealing with LC/MS detection of oleandrin in an oleander poisoning case [6] except our case; there are also 2 reports dealing with the immunoassay detection of oleandrin using its cross-reaction [1, 4]; the immunoassay kit had been developed for measurements of digoxin, and thus the values of oleandrin in blood were expressed as the concentrations of digoxin (5.8 and 4.2 ng/mL) However, the digoxin immunoassay method does not give quantitative results for oleandrin; it seems useful only for tentative qualitative analysis, but is not reliable for its quantitation

⊡ Table 7.1

Concentrations of oleandrin, digoxin and digitoxin in blood or plasma of cardiac glycoside

poisoning cases

(ng/mL)

oleandrin 1.1

10

blood blood

survived dead

[6]

the present case digoxin 7–24

22 30

plasma blood blood

dead dead dead

[10]

[10]

[10]

digitoxin 260

320

plasma plasma

survived dead

[10]

[10]

TIC and MCs obtained by LC/MS for an extract of blood in a case of oleander poisoning.

⊡ Figure 7.4

Authentic oleandrin

blood extract

MS/MS mass spectra of an extract of blood in a case of oleander poisoning and of the authentic

oleandrin Product ions were obtained from peaks detected by mass chromatography at m/z 599.

⊡ Figure 7.5

Notes

a) Desacetyloleandrin was synthesized by deacetylation in anhydrous methanol with sodium methoxide as catalyst

b) Sonic spray ionization ( SSI) is relatively similar to atmospheric pressure chemical ionization ( APCI) Th e mobile phase is electrically neutral; but in a small region, especially around the surface layer of the solution, charge separation can occur In SSI, nebulization is done

so that the surface layer of the solution, in the region of charge separation, is stripped by fast nitrogen gas fl ow and electrically charged airborne droplets are created Th e diameters

of these electrically charged droplets shrinks by vaporization of solvent molecules from the surface, and protonated molecular ions are formed in the gas phase Th e interface does not require heating upon nebulizing; thus it is suitable for sensitive analysis of thermolabile compounds

c) Th e MS/MS conditions with 3-dimensional QMS for oleandrin are described here; the con-ditions are highly dependent on a compound to be analyzed It is essential to optimize conditions for each compound

d) As specimens, blood, plasma and urine can be used

e) Such washing to remove compounds of low polarity is useful, especially when repeated analyses are required

References

1) Osterloh J, Herold S, Pond S (1982) Oleander interference in the digoxin radioimmunoassay in a fatal ingestion JAMA 247:1596–1597

2) Blum LM, Rieders F (1987) Oleandrin distribution in a fatality from rectal and oral Nerium oleander extract administration J Anal Toxicol 11:219–221

3) Rule G, McLaughlin LG, Henion J (1993) A quest for oleandrin in decayed human tissue Anal Chem 65:857–863 4) Nakata M, Miyata S, Endo K et al (1995) A fatal case of oleander poisoning J Okinawa Med Assoc 34:97 (in

5) Gupta A, Joshi P, Jortani SA et al (1997) A case of nondigitalis cardiac glycoside toxicity Ther Drug Monit 19:711–714

6) Tracqui A, Kintz P, Branche F et al (1998) Confirmation of oleander poisoning by HPLC/ MS Int J Legal Med 111:32–34

7) Tor ER, Holstege DM, Galey FD (1996) Determination of oleander glycosides in biological matrices by high-per-formance liquid chromatography J Agric Food Chem 44:2716–2719

8) Namera A, Yashiki M, Okada K et al (1997) Rapid quantitative analysis of oleandrin in human blood by high-performance liquid chromatography Jpn J Legal Med 51:315–318

9) Takaesu H, Fuke C, Arao T et al (1998) A study on the methods of verifying oleander poisoning through the analysis of biological materials Jpn J Forensic Toxicol 16:136–137 (in Japanese with an English abstract) 10) Moffat AC, Jackson JV, Moss MS et al (eds) (1986) Clarke’s Isolation and Identification of Drugs, 2nd edn The pharmaceutical Press, London, pp 541–544