1. This study used 1H-NMR spectroscopy to investigate the transportation of monocrotaline (MCT), a toxic pyrrolizidine alkaloid, and its metabolites dehydromonocrotaline (DHM) and dehydroretronecine (DHR) in human blood plasma and red blood cells (RBCs). 2. The study found that MCT and its precursor retronecine (RET) remained intact in plasma and could enter RBCs. DHM rapidly hydrolyzed in plasma but bound to RBC contents. DHR disappeared immediately in plasma. 3. The results confirm that both plasma and RBCs can transport MCT

1. 1H-NMR Study of monocrotaline and its metabolites
in human blood
Yi-Cheng Yanga, John Crowdera, Nick J. Wardlea, Li Yangb, Kenneth N. Whitea, Zheng-Tao Wanga,b, S. W. Annie Bligha*
aInstitute for Health Research and Policy, London Metropolitan University, 166 - 220 Holloway Road, London N7 8DB, UK
bKey Laboratory of Standardization of Chinese Medicines of Ministry of Education, Shanghai University of Traditional Chinese Medicine, 1200 Cai Lun
Road, Zhangjiang Hi-Tech Park, Shanghai 201203, PR ChinaRoad, Zhangjiang Hi-Tech Park, Shanghai 201203, PR China
Overview
Monocrotaline (MCT) is a phytotoxin and belongs to a class of pyrrolizidine alkaloids
obtained from Crotalaria spectabilis and Crotalaria retusa (Figure 1). Metabolites of
MCT, dehydromonocrotaline (DHM) and dehydroretronecine (DHR), are reported to
produce pathological injury not only to liver, but also to other organs, such as lung,
kidney and heart, and the question arises how toxic metabolites being transported
from the liver to other organs. This study is aimed at further understanding the
Figure 1. Plants of Crotalaria spectabilis
and Crotalaria retusa
from the liver to other organs. This study is aimed at further understanding the
transportation of MCT, DHM and DHR in blood in mediating its toxicity.
For the first time, It is confirmed that both human plasma and Red Blood Cells (RBCs)
can be the carriers for the transportation of MCT and its metabolites, DHM and DHR,
from the liver to other organs by using 1H nuclear magnetic resonance spectroscopy
(1H-NMR). It is found that the transport of MCT and RET by RBCs provides them a
chance to develop toxic metabolites in other organs; and DHM and DHR are stabilized
by interacting with plasma and RBCs during the transport and exert toxicities in the
Aims and Objectives
MCT and RET were found
to enter RBCs and stable in
the cell, while DHM could be
hydrolyzed to give
hydrolyzed necic acid and
To investigate the state of MCT and its metabolites DHM, RET and
DHR (Figure 2) in blood plasma and red blood cells by using 1H-NMR.
To semi-quantified the uptake of MCT and DHM by RBCs.
by interacting with plasma and RBCs during the transport and exert toxicities in the
destined organs.
lactone acid (H-17”, H-18”
and H-19”) and DHR bind to
the cell contents once being
mixed with RBCs (Figure 4). Figure 4. NMR spectra of MCT and its metabolites in RBCs
being recorded after 30 min incubation.
Table 1. The uptake of MCT by RBCs after 0.5, 1, 1.5 and 2h
incubation at 37°°°°C.
MCT DHM RET DHR
Figure 2 Chemical structures of MCT and its metabolites.
The uptake of MCT and
DHM was performed by
measuring the amount of Incubation time (h) 0.5 1.0 1.5 2.0
Concentration of MCT in the 1st washing (mM) 0.7902 0.7327 0.7071 0.7104
MCT outside RBCs (%) 53.9 50.1 48.3 48.5
MCT entered RBCs (%) 46.1 49.9 51.7 51.5
Materials and Methods
NMR study of plasma with MCT, DHM, RET and DHR MCT, DHM,
RET and DHR were added into plasma and recorded by 1H-NMR
immediately as well as after being incubated at 37°C overnight .
NMR study of RBCs with MCT, DHM, RET and DHR RBCs were
incubated with MCT, DHM, RET and DHR at 37°C for 30 min and
then washed five times with PBS. The first, fifth washings and cells
measuring the amount of
MCT and DHM outside RBCs,
which was mainly in the 1st
washing. The uptake of
MCT was summarized in
Table 1.
As the uptake of DHM could be contributed by its hydrolyzed ester
products from outside cells, the RBCs enter rate of those products
was obtained. The actual uptake of DHM by RBCs were showed in
Table 2.
Incubation time (h) 0.5 1.0 1.5 2.0
DHM hydrolyzed ester products in the buffer without the presence of RBCs (%) 71.2 71.3 72.9 74.4
DHM hydrolyzed ester products in the buffer with the presence of RBCs (%) 65.5 62.9 64.5 64.2
DHM hydrolyzed ester products entered RBCs (%) 5.7 8.4 8.4 10.2
Actual uptake of DHM by RBCs (%) 48.9 49.7 50.5 52.1
then washed five times with PBS. The first, fifth washings and cells
contents were taken for 1H-NMR analysis.
Time study of the uptake of MCT and DHM by RBCs Time studies of
MCT and DHM internalised by RBCs were carried out at timed
intervals of 0.5 h, 1 h, 1.5 h and 2 h.
Results
Discussion
MCT and RET remained intact and weakly associated with
plasma proteins; and DHM was rapidly hydrolysed releasing the
Table 2. The uptake of DHM by RBCs after 0.5, 1, 1.5 and 2h incubation at 37°°°°C.
Table 2.
In this study we have demonstrated that by using 1H-NMR
Discussion
Conclusion
Our findings confirm that MCT, a hepatotoxic retronecine
pyrrolizidine alkaloid, is stable in blood plasma and can enter human
red blood cells and stay intact. Reactions of DHM and DHR in both
plasma and RBCs can prevent them from losing their alkylating
abilities in other organs, such as lungs, to cause further damage.
plasma proteins; and DHM was rapidly hydrolysed releasing the
hydrolyzed necic acid (H-17’, H-18’ and H-19’). All proton signals of
DHR disappeared immediately after mixing with plasma (Figure 3).
Acknowledgements
Yicheng acknowledges the financial support of Institute for Health Research and Policy at London Metropolitan University.
The authors are grateful to Prof. Zheng Tao Wang (SUTCM) for his kind donation of PAs reference standards used in this study.
In this study we have demonstrated that by using 1H-NMR
spectroscopy, MCT and metabolites can be monitored for reaction in
human blood. It confirmed that both human plasma and RBCs can
be the carriers for the transportation of MCT and its metabolites,
DHM and DHR, from the liver to other organs.
Figure 3. NMR spectra of MCT and its metabolites in plasma being recorded immediately after mixing.