Species of the family Ericaceae are a potential source of toxic diterpenes, named
grayanotoxins (GT). Grayanotoxin I (GT-1, Fig.) is one of the main compounds also
known as acetylandromedol or andromedotoxin. GT-1 causes a number of livestock poisoning
and food intoxication by toxic honey (“mad honey”) made by bees in the Black Sea region
of Turkey. The symptoms of intoxication are related to the concentration and could
cause a simple weakness up to cardiac problems.
Because of missing data about the distribution of GT in different species of the Ericaceae,
it is important to isolate pure GT as a reference standard to develop analytical methods
for detection and to study the pure toxin.
In this work we describe a way to isolate GT-1 from leaves of Rhododendron species which were deep frozen immediately after the harvest. The plant material
was extracted with hot methanol, and the dried extract was partitioned between water
and dichloromethane. Final purification was achieved by silica gel chromatography.
Afterwards, we developed a densitometric method to quantifiy the amount of GT-1 in
different Rhododendron species. Using a standard TLC plate we were able to analyse 11 samples simultaneously.
To visualize the GT-1 we used 60% sulfuric acid and heated the plate for about 3 min
at 100 °C. GT-1 was quantified by densitometry recording the remission of the TLC-spots
at 530nm. The quantification was based on an extern calibration considering the Kubelka-Munk
function.
Fig. 1
References:
[1] Humphreys DJ, Stodulski JBJ (1986) Detection of andromedotoxins for the diagnosis
of Rhododendron poisoning in animals. Journal of applied toxicology, 6(2), 121.
[2] Louis A, Petereit F, Lechtenberg M, Deters A, Hensel A (2010) Phytochemical characterization
of Rhododendron ferrugineum and in vitro assessment of an aqueous extract on cell toxicity Planta Medica 76 (14)
1550.
[3] Koca I, Koca AF (2007) Poisoning by mad honey: A brief review. Food Chem Toxicol.
45(8) 1315.
