molecules
Article
Biological Investigation of Amaryllidaceae Alkaloid Extracts
from the Bulbs of Pancratium trianthum Collected in the
Senegalese Flora
Seydou Ka 1,2 , Natacha Mérindol 1 , Insa Seck 2 , Simon Ricard 1 , Abdoulaye Diop 3 ,
Cheikh Saad Bouh Boye 3 , Karima Landelouci 4 , Benoit Daoust 1 , Lionel Berthoux 4 , Geneviève Pépin 4 ,
Matar Seck 2 and Isabel Desgagné-Penix 1,5, *
1
2
3
4
5
Citation: Ka, S.; Mérindol, N.; Seck,
I.; Ricard, S.; Diop, A.; Boye, C.S.B.;
Landelouci, K.; Daoust, B.; Berthoux,
L.; Pépin, G.; et al. Biological
Investigation of Amaryllidaceae
Alkaloid Extracts from the Bulbs of
Pancratium trianthum Collected in the
Senegalese Flora. Molecules 2021, 26,
7382. https://doi.org/10.3390/
molecules26237382
Academic Editor: Francisco Leon
Received: 3 November 2021
Accepted: 3 December 2021
Published: 5 December 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
*
Département de Chimie, Biochimie et Physique, Université du Québec à Trois-Rivières,
Trois-Rivières, QC G8Z 4M3, Canada; Seydou.Ka@uqtr.ca (S.K.); Natacha.Merindol@uqtr.ca (N.M.);
Simon.Ricard@uqtr.ca (S.R.); Benoit.Daoust@uqtr.ca (B.D.)
Laboratoire de Chimie Organique et Thérapeutique, Faculté de Médecine, de Pharmacie, et d’Odontologie de
Dakar, Dakar B.P. 5005, Senegal; insa1.seck@ucad.edu.sn (I.S.); matarsec@yahoo.fr (M.S.)
Laboratoire Bactériologie-Virologie, CHU Aristide Le Dantec, Université Cheikh Anta Diop de Dakar,
Dakar B.P. 5005, Senegal; laycoumba@yahoo.fr (A.D.); cheikh.boye@ucad.edu.sn (C.S.B.B.)
Département de Biologie Médicale, Université du Québec à Trois-Rivières,
Trois-Rivières, QC G8Z 4M3, Canada; Karima.Landelouci@uqtr.ca (K.L.); Lionel.Berthoux@uqtr.ca (L.B.);
Genevieve.Pepin3@uqtr.ca (G.P.)
Groupe de Recherche en Biologie Végétale, Université du Québec à Trois-Rivières,
Trois-Rivières, QC G8Z 4M3, Canada
Correspondence: Isabel.Desgagne-Penix@uqtr.ca; Tel.: +1-819-376-5011
Abstract: Amaryllidaceae plants are rich in alkaloids with biological properties. Pancratium trianthum
is an Amaryllidaceae species widely used in African folk medicine to treat several diseases such as
central nervous system disorders, tumors, and microbial infections, and it is used to heal wounds. The
current investigation explored the biological properties of alkaloid extracts from bulbs of P. trianthum
collected in the Senegalese flora. Alkaloid extracts were analyzed and identified by chromatography
and mass spectrometry. Alkaloid extracts from P. trianthum displayed pleiotropic biological properties.
Cytotoxic activity of the extracts was determined on hepatocarcinoma Huh7 cells and on acute
monocytic leukemia THP-1 cells, while agar diffusion and microdilution assays were used to evaluate
antibacterial activity. Antiviral activity was measured by infection of extract-treated cells with dengue
virus (DENVGFP ) and human immunodeficiency virus-1 (HIV-1GFP ) reporter vectors. Cytotoxicity
and viral inhibition were the most striking of P. trianthum’s extract activities. Importantly, noncytotoxic concentrations were highly effective in completely preventing DENVGFP replication and in
reducing pseudotyped HIV-1GFP infection levels. Our results show that P. trianthum is a rich source
of molecules for the potential discovery of new treatments against various diseases. Herein, we
provide scientific evidence to rationalize the traditional uses of P. trianthum for wound treatment as
an anti-dermatosis and antiseptic agent.
Keywords: alkaloid; Amaryllidaceae; Pancratium trianthum; antiviral; antimicrobial; dengue virus; HIV
iations.
1. Introduction
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
The Amaryllidaceae family encompasses over 1600 species scattered all around the
globe and is among the top 20 most considered medicinal plant families [1]. They are
bulbous flowering plants also exploited for ornamental purposes. Approximately one-third
of known Amaryllidaceae species grow in South Africa, and they are commonly used in folk
medicine [2,3]. Traditional usage of Amaryllidaceae ranges from simple health problems
(e.g., headache, cough, boils) to complicated diseases (e.g., cancer, tuberculosis, diabetes).
Amaryllidaceae preparations are recognized for their antimicrobial, anti-tumoral, antiacetylcholinesterase (AChE), and cytotoxic properties [4–16]. West African Amaryllidaceae
Molecules 2021, 26, 7382. https://doi.org/10.3390/molecules26237382
https://www.mdpi.com/journal/molecules
Molecules 2021, 26, 7382
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species such as Pancratium sp., collected in Senegal for traditional medicine [17], have been
scarcely studied [18]. The genus Pancratium contains approximately 20 species, extending
from the Canary Islands through the Mediterranean region to tropical Asia, and from
West Africa to Namibia [19]. P. trianthum Herb. (English name: pancratium lily; local
names: baka, ngada, tondut) [20] plant extracts are traditionally used for irritation-calming,
wound-healing, anti-oedema, anti-dermatosis, anti-septic, anti-epileptic, psychotropic, and
fungicidal properties [17,21]. P. trianthum is considered to be toxic in Senegal and Sudan
and thus is restricted to external usage only [5], while it is considered edible in Nigeria and
Western Sahara [4,22].
Phytochemical studies have shown that the biological properties of Amaryllidaceae
largely originate from a specific class of specialized metabolites that they produce, called
the Amaryllidaceae alkaloids (AAs) [23–25]. AA classification describes nine different
AA-types according to their structure and their biosynthesis pathway [24]. Galanthamine,
a widely occurring AA, is currently used as an AChE inhibitor to treat Alzheimer‘s disease symptoms [26]. Several other pharmaceutically relevant AAs are under study, such
as crinamine for the treatment of Parkinson’s disease [27] or cherylline for its antiviral
properties [28,29]. Lycorine, crinine, and haemanthamine were previously described as the
most abundant types of alkaloids in the Pancratium genus [30]. A study published in 1983
identified the AAs trisphaeridine, hippeastrine, hordenine, pancratine, tazettine, lycorine,
galanthamine, and trianthine from aerial and underground plant parts of P. trianthum
collected from the Botanical Garden of Pyatigorsk State Pharmaceutical Academy in Russia [31,32]. However, no study has reported on the AA content nor the biological activities
of P. trianthum from native areas. Such study would help uncover its full therapeutic
potential and possibly lead to the development of alternative pharmaceuticals to improve
human health. Here, we continue our screening of biological activities of traditionally used
native under-studied Amaryllidaceae from Senegal [28,29]. Thus, the current investigation
explores the anti-AChE, cytotoxicity, antimicrobial, antiviral, and proinflammatory effects
of alkaloid extracts from P. trianthum collected in Senegal.
2. Results
2.1. Species Phylogenetic Analysis
To confirm the species of the bulbs collected and used in this study, we amplified
and sequenced DNA from a chloroplastic gene encoding the large chain of ribulose bisphosphate carboxylase rbcL [33]. The P. trianthum rbcL sequence obtained (Appendix AFigure A1) was blasted in the National Center for Biotechnology Information (NCBI)
database using BLASTn. Top hits were related to rbcL sequences from Pancratium species,
with over 96% sequence identity. Phylogenetic analysis was carried out using phylogeny.fr [34], with default values, including rbcL sequences from 10 Pancratium species
and 1 outgroup, from the species Lilium lancifolium Thunb., an Asparagales that belongs
to the Liliaceae instead of the Amaryllidaceae family (Figure 1). Maximum likelihood
analysis showed a monophyletic clade of the rbcL sequences from all Pancratium species,
including P. trianthum P. illyricum L. rbcL sequences clustered outside this common node,
and the outgroup L. lancifolium Thunb. was robustly separated from all Amaryllidacease
species. P. trianthum sequences grouped closely with P. canariense Ker-Gawl, P. zeylanicum
L., and P. hirtum A. Chev (Figure 1), consistently with a phylogenetic study on Pancratium
species of the Mediterranean area, which included sequences from P. trianthum collected in
Burkina Faso [33].
Molecules 2021, 26, 7382
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Figure 1. Maximum likelihood phylogenetic analysis of ribulose-bisphosphate carboxylase gene (rbcL) DNA sequences
from P. trianthum (blue) collected from Senegal. Reference sequences were identified using the GenBank accession numbers.
The rbcL sequence from Lilium lancifolum, an Asparagales belonging to Liliaceae but not Amaryllidaceae family, was used as
outgroup. The scale of branch length = 0.02 (2% of genetic variation is shown in the bottom of the tree).
2.2. Phytochemical Analysis
Next, an acid–base extraction method was performed on bulbs of P. trianthum to
isolate alkaloids from other organic compounds based on their acid–base properties. The
extraction yielded 0.06% of the initial bulb biomass extracted. Alkaloid profiles were
initially analyzed using chromatographic methods. TLC screening revealed at 254 nm,
365 nm using Dragendorff’s reagent showed the presence of different alkaloids with distinct
Rf values of 0.6, 0.4, and 0.2 (Appendix A-Figure A2).
An optimized high-performance liquid chromatography (HPLC) with photodiode
array (PDA) detector was performed to better characterize alkaloids. Three alkaloid standards (i.e., lycorine, galanthamine, and narciclasine) were used. Identification of the
alkaloids extracted from bulbs of P. trianthum was accomplished by a comparison of the retention time (RT) and absorption spectrum with those obtained for the standards. The RT of
lycorine, galanthamine, and narciclasine standards are respectively 7.19, 7.61, and 7.94 min
in the standard solution (data not shown). HPLC analysis of the P. trianthum alkaloid
extract showed peaks with RT corresponding to lycorine and narciclasine (Appendix AFigure A2B), although for the latter the absorption spectrum was different compared with
the narciclasine standard, suggesting that it was another alkaloid. No RT peak corresponding to galanthamine was detected in P. trianthum alkaloid extracts (Appendix A-Figure 2B).
Interestingly, several unidentified peaks appeared with RTs of 6.46, 7.48, 7.92, 8.40, 8.86,
and 15.40 min, suggesting potential alkaloids (Appendix A-Figure 2B).
Figure 2. Structures of identified AAs confirmed by GC-MS analysis. (1) Lycorine; (2) 11,12Dehydroanhydrolycorine; (3) Vittatine/Crinine; (4) 8-O-Demethylmaritidine; (5) Hamayne; (6)
Trisphaeridine.
Molecules 2021, 26, 7382
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P. trianthum alkaloid extracts were further investigated using GC-MS analysis, which
led to the identification of six AAs by comparing the GC-MS spectra obtained with
those available in NIST 05 database and in the literature (Table 1, Figure 2, Appendix AFigure A3). Two structures could not be attributed to any previously reported alkaloid
chemical profile. However, based on the specificity of the extraction method towards the
isolation of alkaloids with respect to their physicochemical properties, the two unknown
compounds might have been alkaloid. Furthermore, their RT and [M+ ] in the GC-MS
analysis mimicked Amaryllidaceae alkaloids (Table 1).
Table 1. Alkaloids identified by GC-MS in P. trianthum bulb extracts. Values are expressed as percentages of total ion
current (TIC).
Ring Type
Alkaloid
[M+ ]
B.P.
R.T.
(min)
TIC
(%)
Identification Source
Lycorine
Lycorine (1)
11,12-Dehydroanhydrolycorine (2)
287
249
226
248
25.902
23.811
5.9
9.1
NIST 05 Database
[13]
Crinine
Vittatine/Crinine (3a/3b)
8-O-Demethylmaritidine (4)
Hamayne (5)
271
273
287
271
273
258
21.886
22.275
25.321
3.8
15.4
39.1
NIST 05 Database
[35]
[36]
Narciclasine
Trisphaeridine (6)
223
223
19.022
5.0
[13]
unknown
unknown
Unidentified (7)
Unidentified (8)
287
279
223
278
23.547
27.682
5.2
16.4
n/a
n/a
BP, base peak; RT, retention time (in minute); TIC, total ion current; n/a, not applicable.
Altogether, we observed six alkaloids classified according to their structure into
lycorine (1 and 2), crinine (3a/b, 4, and 5), and narciclasine (6) ring types, together with two
unidentified compounds (7 and 8) (Table 1). Compounds (2) and (6) showed ions at m/z 249,
248, 190, 163, 123, and 95 and at m/z 223, 193, 164, 138, and 111, respectively, which were
not listed in NIST 05 database (Appendix A-Figure A3). However, identical fragmentations
were reported in the literature and corresponded to 11,12-dehydroanhydrolycorine (2) and
trisphaeridine (6) [13]. Hamayne (5), also not available in NIST 05 database, showed ions
at m/z 287, 258, 242, 186, and 153 and was identified by similarity with the reported AA
from Rhodophiala pratensis [36], while compound (4) displayed ions at m/z 273, 201, 175,
157, 141, and 128, identically to 8-O-demethylmaritidine from Amaryllis belladonna L. [35].
Additionally, an approximation of the relative proportion of identified AAs was estimated
as a percentage of the total ion current (TIC) chromatogram. The major compounds (i.e.,
most abundant) were hamayne (5, 39% of TIC), 8-O-demethylmaritidine (4, 15% of TIC),
and unidentified compound 8 (16% of TIC). Approximately 58% of identified alkaloids
were crinine-type, 15% of lycorine-type, and 5% of the narciclasine-type (Table 1 and
Figure 2).
2.3. In Vitro Anti-AChE Activity
P. trianthum plant preparations are used in folk medicine to treat central nervous
system disorders. Therefore, we tested the anti-AChE (human) activity of our extracts.
Galanthamine hydrobromide was used at a concentration of 3.7 µg/mL (10 µM) as a positive control, and extract dilutions matching DMSO concentrations were used as negative
controls to normalize the effect of the solvent (Figure 3A). Galanthamine blocked 59% of
acetylcholinesterase activity. P. trianthum alkaloid extracts inhibited the activity of AChE in
a dose-dependent manner at concentrations ranging from 3.9 to 500 µg/mL, with an IC50
of 94 µg/mL (Figure 3A).
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2.4
32
1.2
16
0.6
08
0.3
04
0.1
52
0.0
76
THP-1
Huh7
0.0
38
15
0
20
0
25
0
30
0
35
0
40
0
45
0
50
0
Concentration (µg/mL)
100
90
80
70
60
50
40
30
20
10
0
0.0
19
Galanthamine
P. trianthum extract
% viable cells
(normalized on DMSO)
B
100
90
80
70
60
50
40
30
20
10
0
0
50
10
0
% AChE inhibition
(normalized on DMSO)
A
Concentration (µg/mL)
Figure 3. Anti-acetylcholinesterase and cytotoxic activity of AA bulb extracts from Pancratium
trianthum (A) Anti-acetylcholinesterase (human)activity. The percentage of inhibition of acetylcholinesterase activity was calculated using DMSO as a negative control. Galanthamine hydrobromide (3.7 µg/mL or 10 µM) was used as a positive control. (B) Cellular ATP levels were measured in
Huh7 and THP-1 cells to assess viability following 72 h of incubation.
2.4. Cytotoxicity Activity
Several Pancratium species are cytotoxic plants with antiproliferative properties, and
the AA lycorine detected in P. trianthum is notoriously cytotoxic [5]. The cytotoxic activity
of P. trianthum alkaloid extracts was determined on THP-1 and Huh7 malignant cell lines,
and the cytotoxic concentration of the extract causing a 50% reduction in cell viability
(CC50 ) was calculated for each cell line (Figure 3B). Cell viability, as measured through
ATP (adenosine triphosphate) levels, was strongly affected by the alkaloid extract in a
dose-dependent manner at concentrations ranging from 0.02 to 2.5 µg/mL for both cell
lines (Figure 3B). The alkaloid extracts were found to be cytotoxic down to 0.156 µg/mL in
THP-1 and 0.313 µg/mL in Huh7, with CC50 values of 0.23 and 0.45 µg/mL, respectively
(Figure 3B).
2.5. Antibacterial Activity
P. trianthum extracts are used in folk medicine as antiseptic to treat wounds, suggesting
antimicrobial properties. Here, an agar diffusion assay was used to test the antibacterial
activities of P. trianthum alkaloid extract. MICs were determined on different bacterial
strains (Appendix A-Figure A4). The positive control cefotaxime was active at the tested
concentration against S. aureus and P. aeruginosa, with 22 mm and 24 mm diameter growth
inhibition areas, respectively. Cefotaxime MIC on S. aureus and P. aeruginosa was 2 µg/mL
(data not shown). The highest antibacterial activity of the extracts was observed against
S. aureus, with a 20 mm diameter growth inhibition area at the tested concentration of
16 mg/mL (Appendix A-Figure A4). Microdilution results confirmed that the alkaloid
extract was active against Gram-positive (S. aureus) and against Gram-negative strains
(E. coli and P. aeruginosa), though moderately, with MIC values ranging from 1 to 2 mg/mL
(Appendix A-Figure A4), respectively, suggesting that P. trianthum holds weak antibacterial properties.
2.6. Antiviral Activity
Next, the antiviral activity of alkaloid extracts from P. trianthum was measured against
lentivirus HIV-1 in THP-1 cells and dengue flavivirus in Huh7 cells (Figure 4). We used
a pseudotyped HIV-1GFP vector that infects cells, integrates into the cell genome, and
expresses viral proteins and GFP. However, they did not produce nor release infectious
viral particles. We treated THP-1 cells with 0.09 to 3.125 µg/mL of P. trianthum extract and
infected them with HIV-1GFP at an MOI = 1 (Figure 4A). GFP expression was measured
72 h post-infection. A dose-dependent inhibition of HIV-1 was observed with increasing
concentrations of AAs extract. Weakly cytotoxic (Figure 3B) concentrations of 0.09 and
0.19 µg/mL significantly reduced pseudotyped HIV-1GFP infectivity by 28% and 52%,
Molecules 2021, 26, 7382
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respectively. Interestingly, an EC50 of 0.17 µg/mL was obtained (Figure 4A), a concentration
at which viability was 65% that of the control (Figure 3B).
Figure 4. Antiviral activity of P. trianthum alkaloid extracts. (A) Inhibition of HIV-1 infection. THP-1 cells were treated
with increasing concentrations of alkaloid extracts and then infected with VSV-G pseudotyped HIV-1GFP . (B) Inhibition of
DENVGFP replication. Huh7 cells treated with P. trianthum alkaloid extracts were infected with DENVGFP and measured by
flow cytometry. For (A,B), infection levels were measured at 72 h post-infection and shown are means of triplicates with
standard deviation; the x axis is in log2 scale. (C) Inhibition of DENVGFP infection in Huh7 cells treated with P. trianthum
alkaloid extracts as observed by inverted fluorescence microscopy after 72 h of infection. Representative images are
shown with cell nuclei stained with Hoechst 33342 (blue) and DENV-infected cells (green). DMSO (vehicle) was used as a
negative control.
P. trianthum alkaloid extracts were then tested for their ability to inhibit dengue flavivirus DENVGFP infection. The DENVGFP vector is replication-competent, and thus able to
propagate to neighboring cells, and produces GFP upon infection concomitant with translation of its genomic RNA. GFP expression was measured at 72 h post-infection (Figure 4B,C).
Fluorescent infected cells were visualized on an inverted microscope, and their frequency
was measured on a flow cytometer. Adenosine analog NITD008 was used as a positive
control at 5 µM, whereas matching DMSO concentrations were used as negative controls
for each dilution. DMSO treatment had no apparent effect on viral replication. Noteworthy,
all tested concentrations ranging from 0.019 to 2.5 µg/mL significantly inhibited DENVGFP
infection in a dose-dependent manner (Figure 4B, 4C). No infected cells were detected upon
treatment with alkaloid extracts at concentrations higher than 0.078 µg/mL, as monitored
either by microscopy or flow cytometry. Flow cytometry analysis showed that the lowest
Molecules 2021, 26, 7382
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tested extract concentration (0.019 µg/mL) yielded a 20% reduction in DENV infectivity
compared with controls. It also confirmed that DENV replication was nearly completely
blocked at 0.078 µg/mL, with only 3.3% of cells infected. These results demonstrate that
alkaloids extracted from P. trianthum are active against dengue virus at non-cytotoxic
concentrations, with an EC50 of 0.029 µg/mL (Figure 4B).
2.7. Pro-Inflammatory Activity
The antiviral properties of P. trianthum extracts could be associated with a proinflammatory activity. Thus, IFN-type I induction by P. trianthum extract was investigated.
IFN stimulation was measured in LL171 cell lines containing the interferon-stimulated
response element (ISRE)–luciferase reporter. DMXAA, a STING (stimulator of interferon
genes) activator, was used as positive control, whereas DMSO was used as negative control.
When cells were treated with P. trianthum extract at concentrations ranging from 0.015 to
0.5 µg/mL, there was no detectable activation of luciferase expression, and hence no IFN
production (Figure 5). However, when DMXAA was used in combination with P. trianthum
extract, luciferase expression was triggered in a reverse dose-dependent manner. ISRE
activity was increased by 2.7-fold compared with DMXAA treatment alone and by 14.4-fold
compared with DMSO at the three lowest concentrations, (0.015, 0.031, and 0.0625 µg/mL),
showing a potentiation between the extract and DMXAA. This suggests that low doses of
P. trianthum extracts have a synergistic effect when used in combination with IFN-type I
inducer DMXAA.
Figure 5. Pro-inflammatory properties of P. trianthum alkaloid extracts. Type I IFN activation
was measured through the expression of luciferase driven by the ISRE (IFN-stimulated response
element) promoter element and detected by luminescence. LL71 cells were treated with 20 µg/mL
DMXAA (a STING activator; red triangle) and P. trianthum bulb extracts at concentrations ranging
from 0.015 to 0.5 µg/mL, separately (black circles) or in combination with 20 µg/mL DMXAA
(gray circles). Matched concentrations of DMSO (black squares) were used as a negative control,
respectively. Means of triplicates with standard deviation of luminescence measured 24 h after
treatment are shown.
Molecules 2021, 26, 7382
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3. Discussion
In this study, alkaloid preparations extracted from P. trianthum bulbs collected in Senegal were investigated for their biological properties. TLC analysis of crude extracts showed
different types of AAs, while HPLC analysis revealed lycorine and narciclasine-like AAs,
along with additional peaks suggesting that other AAs were present in P. trianthum extracts. Alkaloid extracts were subjected to GC-MS analysis resulting in the identification of
lycorine (1) and vittatine (3a)/crinine (3b) by comparison with their mass spectra available
in the NIST05 database and of 11,12-dehydroanhydrolycorine (2), 8-O-demethylmaritidine
(4), hamayne (5), and trisphaeridine (6) by comparing with the mass spectra available
in the literature. As vittatine (3a) only differs from crinine (3b) in the position of the
5,10b-ethano bridge, which can only be distinguished by a circular dichroism spectrum,
(3) could be either one or the other crinine-type of AAs. Using the percentage of TIC as
approximative quantification, we observed that crinine- and lycorine-type AAs were the
most abundant AAs in P. trianthum bulb extracts. Unidentified compounds represented
approximately 16% of the crude extracts and should be isolated in future studies using
additional chromatography techniques. In contradiction to a previous report [31], but
consistent with the HPLC analysis, galanthamine, hippeastrine, hordenine, pancratine,
tazettine, and trianthine were not detected in P. trianthum extracts. This difference could
be explained by the fact that plants were not collected from the same environment as AA
production and could be affected by environmental and climatic conditions. In addition,
our study specifically targeted alkaloids extracted from bulb.
In Senegal, leaves and bulbs of P. trianthum are used to treat central nervous system
disorder, heal wounds, and soothe irritations [17], suggesting potential anti-AChE, antibacterial, and antiviral activity. The AChE inhibitory activity is generally attributed to
galanthamine and lycorine-types AAs [37,38]. Hamayne (5) detected in the extract was
also previously reported to have weak AChE inhibitory activity [39]. In our study, P. trianthum alkaloid extracts weakly inhibited AChE activity in a dose-dependent manner, with
concentrations ranging from 3.9 to 500 µg/mL. Although the observed levels of inhibition
were lower than previously observed in P. maritimum L. [40,41], they were consistent with
the lack of detection of galanthamine-type alkaloids in our extracts.
Previous studies showed that lycorine (1), the main phenanthridine AA in our extract, displayed a strong antitumor activity [42,43]. P. trianthum alkaloid extracts were
increasingly cytotoxic at concentrations above 0.313 µg/mL for hepatocarcinoma Huh7
cells and 0.156 µg/mL for monocytic leukemia THP-1 cells, consistent with the presence of
the cytotoxic AA lycorine. P. trianthum bulb alkaloid extracts appeared to be more cytotoxic
than reported from other Pancratium species such as P. illyricum L., but different cell lines
were used, and the contents of their alkaloids are different [44].
Crinine- and lycorine-types have also been associated with antibacterial properties [45–47]. Hence, we tested the antibacterial potency of the extract. All tested strains
were sensitive to high concentrations of the alkaloid extract. The Gram-positive species
S. aureus was more strongly inhibited than Gram-negative species (E. coli and P. aeruginosa).
This activity could be specific to limited Pancratium species, such as P. illyricum L. alkaloid
extracts that were described to be completely ineffective against both Gram-positive and
Gram-negative bacteria [42]. Thus, detected vittatine (3a)/crinine (3b) and lycorine (1)
might contribute to the antimicrobial effect of the alkaloid extract.
While the rate of new HIV-1 infection is declining and the coverage of people receiving antiretroviral therapy (ART) is growing in Senegal, prevalence remains high in
specific populations such as sex workers (4.8% infected, of which 28.3% are under ART)
and men who have sex with men (27.6%, of which 37.8% are under ART) [48]. Because
of the high prevalence and the constant threat of the virus escaping treatment due to
mutation-associated resistance, there is still a strong impetus to identify new antiviral compounds. In some studies, lycorine (1) has been shown to inhibit HIV-1 infection [49,50]. Our
results show that low concentrations of P. trianthum extracts reduce HIV-1 infectivity levels,
although full inhibition was only observed at cytotoxic concentrations. To continue our
Molecules 2021, 26, 7382
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screening of P. trianthum antiviral potential, we then measured its effect on DENV infection.
Several flaviviruses cocirculate in tropical and subtropical areas of the world and threaten
the lives of hundreds of millions of people, making the development of broad-spectrum
anti-flaviviral compounds a necessity. Previous studies showed that some Amaryllidaceae
extracts present anti-dengue potential [28,51], and the AA lycorine (1) detected in this
study potently inhibits flaviviruses in in vitro and in vivo models [52–54]. Here, we show
that non-cytotoxic concentration of P. trianthum extracts ranging from 0.019 to 0.156 µg/mL
displayed strong antiviral activity, with full inhibition at 0.156 µg/mL. When compared
with our recent study on Crinum jagus (J. Thomps.) Dandy extract, the P. trianthum antiviral activity was 8.6-fold higher (IC50 = 0.25 µg/mL vs. 0.029 µg/mL, respectively) [28].
Interestingly, low doses of P. trianthum extracts also displayed potentiation effects with
IFN-inducers. Thus, purification of alkaloids from P. trianthum could possibly lead to the
discovery of strong antiviral compounds.
4. Materials and Methods
4.1. Plant Materials, Chemicals, and Species Identification
P. trianthum bulbs were collected in Saint Louis, Senegal (16◦ 3′ 19.35′′ N, 16◦ 25′ 42.25′′ W),
in December 2018. Collected plants were taxonomically identified using the database at
the Herbarium of IFAN at the Université Cheikh Anta Diop of Dakar.
In addition, genomic DNA was extracted from dried roots of P. trianthum using the
DNeasy plant mini kit (QIAGEN) according to the manufacturer’s instructions. Yield and
purity of total extracted DNA were quantified with a Nanodrop (IMPLEN, QC, CA) and
stored at −20 ◦ C for later use. Ribulose-bisphosphate carboxylase gene (rbcL) DNA barcode
of P. trianthum was amplified by PCR using TaKaRa’s PrimeSTAR GXL Premix kit with
primers (F-5′ -GGATTACCAGCCTTGATCG-3′ and R-5′ -TTCACGAGCAAGATCACGTC3′ ) [33]. The PCR mixture (20 µL) contained 2 µL of genomic DNA, 10 µL Takara mix,
0.4 µL of each primer (10 µM, forward and reverse primers), and 7.2 µL of ultrapure-DNase
free water. The thermocycler program consisted of an initial denaturation step (98 ◦ C for
2 min), followed by 30 amplification cycles (98 ◦ C for 10 s, 55 ◦ C for 15 s, and 68 ◦ C for
75 s). After PCR, 5 µL of amplified product was loaded on a 1% agarose gel, and specific
size amplicons (1044 bp) were sequenced using both forward and reverse primers.
4.2. Crude Alkaloids Extraction and TLC Analysis
Alkaloid extraction was achieved using the method described in [55]. P. trianthum
dried bulbs (50 g) were crushed manually and macerated for 24 h with MeOH at room
temperature, and the macerate was filtered and concentrated under reduced pressure. This
crude extract was acidified with sulphuric acid (2%) at pH = 2 and extracted successively
with Et2 O (4 × 200 mL) and EtOAc (4 × 200 mL) to remove neutral material. The resulting
acidic aqueous solution was basified with concentrated ammonia (25%) up to pH = 10, then
extracted with EtOAc (4 × 200 mL) and evaporated. Alkaloid extracts were then dissolved
in EtOAc at a final concentration of 1 mg/mL and used for thin-layer chromatography
(TLC). Qualitative analysis of alkaloids was performed on TLC silica gel 60 F254 aluminum
sheets 20 × 20 cm, (Merck, Darmstadt, Germany). The TLC plate was eluted with MeOH:
EtOAc (25:75 v/v), dried at room temperature, observed under UV light at 254 nm and
365 nm, and then revealed with Dragendorff reagent [56,57].
4.3. HPLC-PDA and GC-MS Analysis of Alkaloid Extracts
For the HPLC analysis, we followed the method described by [58], with some modifications. The alkaloid extract was dissolved in MeOH at a final concentration 0.5 mg/mL.
Afterward, 10 µL of each sample and 10 µL of 100 ppm of each standard (galanthamine, narciclasine (both from Tocris Bioscience, Bristol, UK), and lycorine (Sigma-Aldrich, St. Louis,
MO, USA)) were injected and analyzed on a Shimadzu Prominence-I LC-2030C with diode
array detector (PDA). For separation, the Kinetex C18 column (150 × 4.6 mm2 , 5 µm particle
size; Phenomenex) was used. HPLC oven temperature was set at 40 ◦ C. A gradient elution
Molecules 2021, 26, 7382
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with two solvents, 1% ammonium acetate buffer (solvent A) and 100% acetonitrile (solvent
B), was used. The 90:10 B to A solvent gradient ratio was first maintained for 10 min, then
shifted to 69:31 over 1 min, 70:30 over 4 min, and finally 90:10 over 3 min. After 18 min,
A was increased to 90%, and B was reduced to 10% for 5 min, yielding a total run time of
23 min.
For the GC-MS analysis, 1 mg/mL of alkaloid extract in MeOH was directly injected
into the GC-MS (Agilent Technologies 6890N GC coupled with 5973N inert MSD) in EI
(Electron Ionization) mode at 70 eV. The temperature ramp used is described as follows:
temperature was set at 100 ◦ C for 2 min, followed by 100–180 ◦ C at 15 ◦ C min−1 , 180–300 ◦ C
at 5 ◦ C min−1 , and a 10 min hold at 300 ◦ C. Injector and detector temperatures were set
at 250 ◦ C and 280 ◦ C, respectively, and the flow rate of carrier gas (He) was 1 mL min−1 .
A split ratio of 1:10 was applied, and the injection volume was 1 µL [59]. Alkaloids were
identified by comparison with the 2005 National Institute of Standards database based on
matching mass spectra, GC-MS spectra of authentic compounds previously isolated and
identified by other spectroscopic methods in these species, or with data obtained from the
literature. The total ion current (TIC) percentage provided in Table 1 was connotated with
the proportion of each compound in the extract as a semi-quantitative estimate. The area of
the GC-MS peaks depends both on the concentration of the related compounds and their
relative signal intensity in MS.
4.4. In Vitro Acetylcholinesterase (AChE) Inhibition Assay
In vitro inhibition of electric eel, Electrophorus electricus, AChE by the alkaloid extract
of P. trianthum was assessed using the method described in [29].
4.5. Cell Lines
Human hepatocarcinoma cell line Huh7 (kindly provided by Professor Hugo Soudeyns,
CHU Sainte-Justine, Montréal, QC, Canada) and murine LL171 reporter cells [60] were
maintained in Dulbecco’s modified Eagle’s medium high glucose (DMEM), supplemented
with 10% fetal bovine serum (FBS) and 1% penicillin–streptomycin (PS, all from Cytiva
Hyclone) solution. Human acute monocytic leukemia cell line THP-1 was grown in Roswell
Park Memorial Institute Medium (RPMI) containing 10% FBS and 1% PS. All cells were
maintained at 37 ◦ C and 5% CO2 .
4.6. Cytotoxicity Assay
Cell viability was evaluated using the Cell-Titer GLO assay kit (Promega, Madison,
WI, USA). Briefly, 50 µL of 7.5 × 103 Huh7 cells/well or 2 × 104 THP-1 cells/well was
seeded in 96-well dark plates and cultured for 16 h. Then, they were treated with 50 µL of
alkaloid extract at concentrations (<0.5% DMSO) ranging from 0.019 to 2.5 µg/mL for 72 h.
Afterward, 100 µL of room temperature Cell-Titer GLO reagent was added in each well to
room temperature-equilibrated plates. Plates were rocked for 2 min, and the luminescence
signal was measured 10 min later using a microplate spectrophotometer (Synergy H1,
Biotek, QC, Canada). The percentage of viable cells was calculated at each concentration.
All assays were performed in triplicate.
4.7. Bacteria and Viruses
Three bacteria species including the Gram-positive strain Staphylococcus aureus ATCC
29213 and two Gram-negative strains, Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853, were obtained from the American Type Culture Collection (ATCC) and
from the Laboratory of Bacteriology-Virology at Aristide Le Dantec Hospital (Senegal).
Bacteria were cultured in Mueller Hinton (MH) agar media and incubated at 37 ◦ C for 24 h
before use.
Molecules 2021, 26, 7382
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Dengue virus vectors expressing green fluorescent protein (DENVGFP [61]) and singleround infection pseudotyped human immunodeficiency virus-1 (HIV-1GFP [62]) were
used to investigate antiviral activity. The multiplicity of infection (MOI) of HIV-1GFP was
assessed by measuring the infectivity of serially diluted vector preparation in CrandellRees Feline Kidney (CRFK) cells, while DENVGFP titer was measured by plaque assay as
described in [28].
4.8. Agar Diffusion Assay
Antimicrobial activity of the alkaloid extract was first studied using the agar diffusion
assay method. A suspension of each strain was prepared into sterile physiological water
to obtain a final inoculum, estimated at 1.5 × 108 CFU/mL according to 0.5 McFarland
turbidity. Alkaloid extracts were dissolved in DMSO at 16 mg/mL. For the assay, a sterile
cotton swab was immersed in the inoculum, then wrung on the wall of the tube. The swab
was then spread over on the agar plate to obtain uniform inoculum. Wells were made on
Mueller Hinton agar plates using a sterile cylinder of 6 mm diameter. Plates were dried
for 5 min, and 100 µL of alkaloid extract was deposited. Plates were incubated at 37 ◦ C
for 18–24 h. The antibacterial activity of the alkaloid extract was then measured as an
inhibition zone surrounding the well [63]. Cefotaxime was used as a positive control.
4.9. Broth Dilution Method for Determination of Minimal Inhibitory Concentration (MIC)
Microdilution of alkaloid extracts from P. trianthum was performed using a modification of Balouiri et al. [64]. Dilutions were started by pipetting 100 µL of alkaloid extract
into the first well of a 96-well plate containing 100 µL of MH broth. Serial dilutions were
then carried out to obtain a range of concentrations between 0.03 to 8 mg/mL. Then, 10 µL
of bacterial suspension cultures was added into each well. Plates were incubated at 37 ◦ C
for 24 h. The MIC (minimal inhibitory concentration) was determined as the lowest concentration of the alkaloid extract that completely suppressed the growth of microorganisms
(which was determined by the wells showing no turbidity). Tested bacteria were exposed
to broth without the alkaloid extract as a control.
4.10. In Vitro DENVGFP Infectivity Assay
Briefly, Huh7 cells were seeded at 1.5 × 104 cells per well in 48-well plates, cultured
for 16 h, and then pretreated with concentrations of P. trianthum alkaloid extract ranging
from 0.02 to 2.5 µg/mL, infected with DENVGFP 2 h later at a multiplicity of infection (MOI)
of 0.1 PFU/cell and incubated at 37 ◦ C for 72 h. Green fluorescence signal of infected cells
was visualized and pictured on a Axio Observer microscope (Carl Zeiss, Inc., Toronto, ON,
Canada). Cells were trypsinized and fixed in 4% aqueous formaldehyde, then processed
for flow cytometry analysis of GFP expression using a FC500 MPL cytometer (Beckman
Coulter, Inc., CA) coupled with the FCS Express 6 software (De Novo Software, Pasadena,
CA, USA). The adenosine analogue NITD008 (10 µM) was used as a positive control for
inhibition of DENV infection. Extract-matched concentrations of DMSO were used as a
negative control. All assays were performed in triplicate at least twice.
4.11. In Vitro Pseudotyped HIV-1GFP Infectivity Assay
The antiretroviral activity of P. trianthum Herb.’s crude extract was evaluated using
pseudotyped HIV-1GFP in THP-1 cells. THP-1 cells were seeded at 2.0 × 104 cells per well
in 96-well plates and incubated overnight. Cells were treated with 5 concentrations of
extract (from 0.1 to 1.56 µg/mL) and then infected with HIVGFP at a MOI at 1. After 72 h,
the percentage of infected cells was measured using a FC500 MPL cytometer (Beckman
Coulter, Inc., Brea, CA, USA) and analyzed using FlowJo software (FlowJo LLC, Ashland,
OR, USA). Matched concentrations of DMSO were used as a negative control. All assays
were performed in triplicate.
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4.12. In Vitro Proinflammatory Assay
In vitro proinflammatory assay was performed using the Luciferase Assay Systems kit
(Promega). Briefly, 200 µL LL171 cells was seeded at 1.5 × 104 cells/well in 96-well plates
and cultured for 16 h. Then, the medium was replaced with medium containing alkaloid
extract at a concentration ranging from 0.015 to 0.5 µg/mL for 24 h. The supernatant
was removed, and cells were rinsed with PBS. Then, 30 µL of lysis buffer was added and
homogenized. Afterward, 20 µL of each lysate was transferred into 96-well opaque plates,
100 µL of Luciferase Assay Reagent (Promega) was added, and luminescence was measured
at 480 nm using a microplate spectrophotometer (Synergy H1, Biotek, Quebec, Canada).
5,6-Dimethylxanthenone-4-acetic acid (DMXAA, 20 µg/mL) was used as a positive control.
All assays were performed in triplicate.
5. Conclusions
In conclusion, this study led to the detection of eight AAs, six of which were identified
by GC-MS, in the alkaloid extract of P. trianthum Herb.’s bulb collected in Senegalese
flora. Based on the traditional use of the Pancratium genus for wound-healing, central
nervous system disorder, and antiproliferative and antiviral purposes, the alkaloid extracts
prepared were screened for antibacterial, anti-AChE, cytotoxic, and antiviral properties.
Alkaloid extracts displayed antibacterial effect, with MIC values of 1 mg/mL for S. aureus
and 2 mg/mL for E. coli and P. aeruginosa but weak anti-AChE property (IC50 = 94 µg/mL).
Interestingly, the P. trianthum extracts displayed strong and moderate antiviral activity
against DENVGFP and pseudotyped HIV-1GFP , with EC50 of 0.029 and 0.17 µg/mL, respectively. We conclude that the medicinal properties of P. trianthum may be attributed to
its alkaloid components and provide the scientific basis for its traditional use to prevent
infections. Finally, this study supports the role of Amaryllidaceae species as a source of
compounds with potential therapeutical applications.
Author Contributions: S.K. designed and executed experiments, analyzed data, and prepared the
manuscript. N.M. designed and executed experiments, analyzed data, revised the manuscript,
and supervised the work. A.D., I.S. and C.S.B.B. helped S.K. to conduct antibacterial activity. L.B.
provided viruses and cells and revised the manuscript. K.L. and G.P. provided the materials and
helped design and execute experiments related to pro-inflammatory properties with S.K., B.D. and
S.R. conducted and analyzed the GC-MS study with S.K., M.S. helped design the experiments,
analyzed data, revised the manuscript, and co-supervised S.K., I.D.-P. secured fund acquisition,
designed experiments, analyzed data, revised the manuscript, and supervised the entire research
work. All authors have read and agreed to the published version of the manuscript.
Funding: This work was funded by the Canada Research Chair on plant specialized metabolism
Award No 950-232164 to Isabel Desgagné-Penix. Many thanks are extended to the Canadian taxpayers
and to the Canadian government for supporting the Canada Research Chairs Program.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: The authors would like to thank Fatma Meddeb, Manel Ghribi, and all the lab
members for their technical support and useful advice. Warm thanks to Professors Hugo Germain,
Céline Van Themsche, and Carlos Reyes-Moreno for kindly providing cells and cell culture equipment.
The authors also wish to acknowledge Sebastien Santini (CNRS/AMU IGS UMR7256, France) and the
PACA Bioinfo platform (supported by IBISA) for the availability and management of the phylogeny.fr
website used to confirm plant species.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the dried bulbs are limited but available from the authors.
Molecules 2021, 26, 7382
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Appendix A
>Pt_rbcL
CATTGAGGCCGTTGTTGGGGAAGGAAATCAATATATTGCTTATGTAGCTTATCCTT
TAGACCTTTTTGAAGAAGGTTCTGTTACTAACATGTTTACTTCCATTGTGGGTAAT
GTATTTGGTTTCAAAGCCCTACGAGCTCTACGTCTGGAGGATCTGCGAATTCCCC
CTGCTTATTCCAAAACTTTCCAAGGCCCGCCCCATGGCATCCAATCTGAAAGAGA
TAAATTGAACAAGTATGGTCGTCCCCTATTGGGATGTACTATTAAACCAAAATTG
GGATTATCCGCAAAAAACTACGGTAGAGCGGTTTATGAATGTCTACGCGGTGGG
CTTGATTTTACCAAGGATGACGAAAACGTGAACTCCCAACCTTTTATGCGTTGGA
GAGACCGTTTCTTATTTTGTGCTGAAGCAATTTATAAAGCGCAAGCCGAAACAGG
TGAAATCAAAGGACATTACTTGAATGCAACTGCGGGTACATGTGAAGAAATGAT
CAAAAGGGCCGTATTTGCCAGAGAATTGGGAGTTCCTATCGTAATGCATGACTAC
TTAACTGGGGGATTCACTGCAAATACTAGTTTGGCTTTTTATTGCCGCGACAACG
GTCTACTTCTTCACATCCACCGCGCAATGCATGCAGTTATTGATAGACAGAAAAA
TCATGGTATGCATTTTCGTGTACTAGCTAAAGCATTACGTATGTCTGGTGGAGATC
ATATTCACGCTGGTACAGTGTAAGGTAAACTGGAAGGGGAACGCGAGATGACTT
TAGGTTTTGTTGATTTATTACGTGATGATTATATTGAAAAAGACCGAAGTCGTGGT
ATTTTTTTCACTCAAGATTGGGTTTCTATGCCAGGTGATCTGCGTATTGCCTATGG
GGGTATTCATGTTTGGCATATGCCGCCCTACGGAATCTTTGGGATGATTCCGTACT
ACAGTTCGGTGGAGGAACTTTAGGACACCCTTGGGGAAATGCACCTGGTGCGTA
GCTAATCGGGTAGCTTTAGAAGCGATATAGA
Figure A1. P. trianthum rbcL sequence amplified from bulbs and obtained from Sanger sequencing.
Figure A2. Phytochemical analysis of P. trianthum alkaloid extracts. (A) TLC revealed by UV at 254 nm and 365 nm, using
Dragendorff’s reagent. (B) HPLC-DAD chromatogram of P. trianthum alkaloid extract at 280 nm. The peak corresponding to
lycorine is indicated with an arrow.
Molecules 2021, 26, 7382
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Lycorine (1)
Abundance
Scan 3814 (
25.
871 m i
n)
:SKCG 30sept
2020.
D\
dat
a.
ms
226
19000
18000
17000
16000
15000
14000
13000
12000
11000
10000
9000
8000
7000
6000
287
5000
268
250
4000
3000
207
147
2000
0
40
60
119
91
65
1000
191
167
80
100
120
140
160
355
315
180
200
220
240
260
280
300
320
340
417
360
380
400
420
m/
z>
11,12-Dehydroanhydrolycorine (2)
Abundance
Scan 3417 (
23.
811 m i
n)
:SKPT30sept
2020.
D\
dat
a.
ms
248
90000
80000
70000
60000
50000
40000
30000
190
20000
223
95
10000
123
81
0
40
50
63
60
110
80
100
120
163
138
207
177
140
160
180
200
265
220
240
260
281
280
341 355
300
320
340
m/
z>
Vittatine/crinine (3)
Abundance
Scan 3043 (
21.
871 m i
n)
:SKCG 30sept
2020.
D\
dat
a.
ms
271
36000
34000
32000
30000
28000
199
26000
24000
22000
187
20000
18000
16000
252
14000
12000
115
10000
128
8000
6000
157
77
4000
228
173
56
91
2000
214
141
102
240
283
0
60
80
100
120
140
160
m/
z>
Figure A3. Cont.
180
200
220
240
260
280
Molecules 2021, 26, 7382
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8-O-Demethylmaritidine (4)
Abundance
Scan 3121 (22.275 m in):SK-PT-30sept2020.D \data.m s
273
25000
20000
201
15000
10000
223
175
5000
115 128
56
0
40
77
60
141
91
80
254
157
188
239
100
120
140
160
180
200
220
355
240
260
280
300
320
340
m /z-->
Hamayne (5)
Abundance
Scan 3708 (
25.
321 m i
n)
:SKPT30sept
2020.
D\
dat
a.
ms
258
55000
50000
45000
40000
35000
30000
25000
20000
15000
223
10000
5000
77
56
0
40
95
80
242
153
100
120
207
169
135
60
287
186
115
140
160
343
315
180
200
220
240
260
280
300
320
417
340
360
380
400
420
m/
z>
Triphaeridine (6)
Abundance
Scan 2494 (
19.
022 m i
n)
:SKPT30sept
2020.
D\
dat
a.
ms
223
34000
32000
30000
28000
26000
24000
22000
20000
18000
16000
14000
12000
10000
8000
138
6000
164
111
4000
2000
0
87
69
51
60
80
99
100
151
126
120
140
177
160
m/
z>
Figure A3. Cont.
180
193
207
200
281
220
240
260
280
Molecules 2021, 26, 7382
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Abundance
Scan 3366 (
23.
547 m i
n)
:SKPT30sept
2020.
D\
dat
a.
ms
223
11000
Unidentified (7)
Abundance
10000
Scan 3366 (
23.
547 m i
n)
:SKPT30sept
2020.
D\
dat
a.
ms
223
9000
11000
8000
174
10000
7000
9000
6000
8000
5000
174
7000
4000
287
148
6000
188
3000
161
5000
2000
1000
m/
z>
188
65
51
161
60
80
89
239
203
100
270
341
120
140
160
180
200
65
51
254
131
111
0
287
148
89
1
000
300
0
203
131
111
2
000
400
0
220
240
254
239
260
280
300
320
340
270
341
0
60
Abundance
80
100
120
140
160
180
200
220
240
260
280
300
320
340
m/
z>
Unidentified
(8)
160000
Scan 4163 (
27.
682 m i
n)
:SKPT30sept
2020.
D\
dat
a.
ms
278
Abundance
Scan 4163 (
27.
682 m i
n)
:SKPT30sept
2020.
D\
dat
a.
ms
278
140000
160000
120000
140000
120000
100000
100000
80000
80000
60000
60000
40000
40000
235
20000
20000
0
0
m/
z>
51
51
75
75
60
60
80
178
89
89
110
110
80
100
125
100
120
125
140
140
163
120
140
140
160
178
163
191
191
160
180
235
207
180
200
220
207
200
220
263
248
220 263
248
220
240
240
260
280
260
300
315
280
320
315
342 355
300
320
342 355
340
340
m/
z>
Figure A3. Mass spectra of alkaloids extracted from P. trianthum obtained by GC-MS analysis.
Figure A4. Antibacterial activity of P. trianthum alkaloid extracts. The effects of alkaloid extracts were measured on the
growth of Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. (A) Agar diffusion assay. Growth inhibition
areas surrounding wells containing 16 mg/mL of extracts observed after 18–24 h incubation at 37 ◦ C. (B) Quantification of
the antibacterial activity as measured in the agar diffusion assay as well as using the minimum inhibitory concentration
(MIC) approach (see Materials and Methods).
Molecules 2021, 26, 7382
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