Background
Herbs have been used in traditional medicine for centuries to cure various ailments, including diabetes mellitus. Bitter gourd is a vegetable widely used in East Asian, South Asian, and Southeast Asian cuisines, and its fruit is generally consumed as a cooked food in its green or early yellowing stage". Moreover, bitter gourd has long been used as an herbal medicine in Asian and African traditional medicines [
1‐
3]. One of the most common uses of
M. charantia is as an antidiabetic agent. The application of
M. charantia to treat diabetic mellitus has been extensively studied, which is apparent by the increasing number of publications over the years. PubMed and web of science searches using the key word “
Momordica charantia” resulted in 1253 articles for the last 10 years only (2009–2018). Quite recently, several clinical trials have been conducted to examine the efficacy of
M. charantia in diabetic patients, and
M. charantia supplementation was shown to be quite successful in lowering elevated fasting plasma glucose level in prediabetes patients [
4‐
7]. The exact mechanisms of the antidiabetic and anti-obesity effects of
M. charantia are unknown; however, some of the active components isolated from
M. charantia are thought to be structurally similar to human insulin [
8]. Besides being a potent anti-diabetic supplementation, various parts of
M. charantia have also been used as a medicine to cure various conditions, such as infection [
9‐
13], wounds [
14‐
16], and osteoarthritis [
4,
17]. The plant are also used as laxative, contraceptive, abortifacient, and anthelmintic agents, and also to treat various conditions, such as scabies, jaundice, pneumonia, dysmenorrhea, eczema, gout, leprosy, piles, psoriasis, and rheumatism [
18‐
21].
M. charantia has also been shown to possess strong anticancer properties and strong cytotoxicity in various human cancer cell lines, such as lymphoid leukemia [
22], lymphoma, melanoma [
23], breast cancer [
24], prostatic cancer [
25‐
28], squamous carcinoma of the tongue and larynx. Owing to the promising biological properties and medicinal use of this plant, more than 200 compounds have been isolated and identified from the fruit, leaves, vines, seeds, and roots of
M. charantia [
29,
30].
Cardiomyopathy is one of the most common complications of diabetes mellitus which is believed to be due to the oxidative damage of the heart tissues. The antioxidant property of
M. charantia has been proven by various studies [
31‐
36]. The beneficial effect of
M. charantia against the oxidative stress complications in the heart of diabetic rats was demonstrated by [
37]. Moreover, the myocardial protective effect from polysaccharides of
M. charantia has been observed in an isoproterenol (ISP) induced myocardial infarction rat model [
38].
M. charantia fruit extract have also showed cardio-protective action in the treatment of diabetic cardiac fibrosis in streptozotocin (STZ) induced diabetes in Sprague-Dawley rats by lowing the expression of type III, type IV collagens and Hydroxyproline content which reverted morphological damages in the heart to normal [
39]. However, there is no scientific evidence so far, which can elucidate the action of
M. charantia on fetal heart development either in animal or in human. The international drug regulatory guidelines emphasize that drugs under development that will be administered to pregnant women must be tested for developmental toxicity in suitable animal models [
40,
41].
The main objective of this study was to analyze the effect of
M. charantia on embryonic heart development using zebrafish embryos. Zebrafish
(Danio rerio) belongs to the teleost family, and zebrafish embryos are routinely used in developmental toxicology testing as an excellent model organism [
42‐
48]. The main advantage of using zebrafish for such toxicological studies is that, as zebrafish embryo develops outside of mother, thus eliminating the effects of mother on the fetus development and hence toxicity of any compound can easily be assessed directly in the embryos. These mother-related effects are misleading to discover the sensitivity and mechanism of the fetus for developmental abnormalities [
49].
Methanol extracts was prepared from the fruit and seeds of M. charantia. The crude extracts were further fractionated in trichloromethane, ethyl acetate, methanol, and water. The biologically active fraction (which induced significant level of developmental toxicity in zebrafish embryos) was further fractionated by silica gel column chromatography and high-performance liquid chromatography (HPLC). Phenol and flavonoid contents of the active fraction (ethyl acetate fraction) were determined. The active constituent in seed extract were identified by gas chromatography spectroscopy (GC-MS).
Material and methods
Materials
All reagents used in this study were of HPLC-grade and purchased from Sigma Aldrich.
Methods
Collection and authentication of plant material
The fruit and the seeds of bitter gourd (M. charantia) were obtained from commercial local vegetable market and taxonomical identification was confirmed by Dr. Jacob Thomas Pandalayil, Assistant Professor/Curator, Herbarium (King Saud University) in the Department of Botany College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia. A specimen voucher sample (Acc. No. (KSU) 10626) was deposited in KSU herbarium.
Seedless, fresh fruits (200 g) of M. charantia were cut into small pieces and washed with tap water followed by distilled water. The fruits were air-dried in a ventilated area. After drying, the fruits were grounded using a commercial blender. The dried powder was extracted with methanol using a sonicator at 25 °C for 30 min and then kept in a shaking incubator for 24 h at 250 rpm and 30 °C. The extract was centrifuged at 12000 rpm for 10 min. The solvent was then evaporated using a rotary evaporator at 45 °C, and the extract was weighed and kept at − 80 °C until use. Crude seed extract was also prepared in a similar manner.
Column chromatography
M. charantia fruit extract (2 g) was subjected to column chromatography using silica gel 60 silanized (0.063–0.200 mesh; Merck, Darmstadt, Germany). The sample was prepared by adsorbing 2 g of the extract to 20 g of silica and then left to dry. The dry powder was applied on top of the column (5 × 25 cm) and then eluted using trichloromethane, ethyl acetate, and methanol-water (50:50) with pressure. Each solvent at a volume of 500 ml was collected in a beaker.
C18 cartridges were used to further fractionate the ethyl acetate active fraction isolated from M. charantia fruit. The active fraction (2 mL) was diluted with 8 mL of distilled water. The SPE cartridge used was Chromabond C18ec-cartridge (Macherey & Nagel). The cartridge was attached to a vacuum and sequentially conditioned by passing 10 mL of methanol, 10 mL of Milli-Q water, and 10 mL of methanol-water (2:8 v/v). Diluted active fraction (10 mL) was loaded onto the preconditioned cartridge and eluted at a drop-wise to ensure efficient adsorption of the compounds. Elution of C18 cartridge-bound compounds was achieved by adding 10 mL of methanol-water (2:8), followed by methanol drop-wise. Finally, two fractions were collected and concentrated using a rotary evaporator at 45 °C. The fractions were dried, reconstituted, and stored at − 80 °C until use.
Phenol estimation
Total phenolic content of the extracts was measured by the Folin-Ciocalteu method [
11]. Briefly, 12.5 μL of extract (1 mg/mL) were mixed thoroughly with 50 μL of distilled water and 12.5 μL of 25% Folin-Ciocalteu reagent for 5 min. Next, 125 μL of 7% (w/v) Na
2CO
3 (sodium carbonate) was added to the mixture, which was then allowed to stand for 1.5 h at room temperature (25 ± 2 °C) in the dark. Absorbance was measured at 760 nm using a microplate reader. Total phenol content was quantified using the standard curve of gallic acid (Joshi et al. 2013).
Flavonoid estimation
Total flavonoid content in the extracts was quantified according to a method by Ghosh et al. (2008). In brief, 100 μL of extract was mixed with 100 μL of 2% aluminum chloride. After 10 min of incubation, absorbance was measured at 368 nm. The standard curve used to estimate total flavonoids was set using quercetin standard solution (100 to 800 mg/ml).
GC/MS analysis
The gas chromatography-mass spectroscopy (GC-MS) analysis was performed in a Perkin Elmer Clarus 600 gas chromatograph inked to a mass spectrometer essentially same as described previously [
50].
Treatment of zebrafish embryos
The embryos were obtained by natural pairwise breeding. The breeding pairs were set at evening after sunset in 3-l breeding tanks purchased from Pentair (Pentair Aquatic Eco-Systems, Inc., Apopka, FL, USA). The embryos were collected the following morning by siphoning after the zebrafish spawned at first sunlight. The eggs were washed with distilled water and transferred to embryo water [NaCl 5.03 mM, KCl 0.17 mM, CaCl2•2H2O 0.33 mM, MgSO4•7H2O 0.33 mM, and methylene blue 0.1% (w/v)]. Synchronized stage embryos at 8 cell stage were exposed to serial dilutions of the extracts in sterile 35-mm glass dishes. Untreated or mock 0.5% (v/v) methanol-treated embryos served as controls. The embryos were treated for up to 6 days (5 dpf). The experiment was repeated at least three times by using different batches of embryos each time. The criteria to confirm the teratogenic effect of M. charantia in zebrafish embryonic development was when more than 60% of treated embryos had same effect and also show same p in all three biological replicates.
After the end of experiment the embryos were euthanized by 0.03% Tricaine mesylate (Tricaine methanesulfonate, TMS, MS-222, Cat # E10521,Sigma Aldrich), freeze and discarded as safe biological waste.
Statistics
Origin (version 6.1052; Origin Lab Corp Northampton, MA, U.S.A.) was used for statistical analysis to calculate the standard deviation between three biological replicates.
Discussion
The most common medicinal use of
M. charantia is as an effective treatment of diabetes. Number of studies have been conducted to determine the safety profile of
M. charantia in experimental animals; and all have found that
M. charantia did not show any kind of toxicity when tested in non-pregnant animals [
8,
51‐
56].
The safety profile of
M. charantia is largely unknown in pregnant women so far, and consumption of
M. charantia as an antidiabetic remedy by pregnant women cannot be overruled. Moreover,
M. charantia has never been extensively studied in pregnant animals to elucidate the potential risk of
M. charantia on fetus development. We have found only one report in the literature describing the teratological profile of
M. charantia in pregnant experimental animals. Multiple congenital litter malformations were observed following exposure of pregnant Sprague Dawley rats to a water extract of fruit of
M. charantia [
57]. Guidelines by the Food and Drug Administration (FDA) clearly indicate that new developing drug that are intended for use in pregnant women must first be tested in suitable pregnant animal models [
58].
The fruit and seeds of
M. charantia, both are being used in anti-diabetic remedies [
59,
60], however, the toxicity profile of fruit part in animal models systems has been investigated in previous reports but we did not find any published literature prior to this study, describing any toxicity profile of seeds of
M. charantia. Various mammalian systems are traditionally used to examine the developmental toxicity of chemicals. The traditional methods are lengthy, costly, and often require a large number of animals, which raises ethical concerns. Moreover, testing any compound isolated from natural sources would be impractical owing to the limitation of quantity, because a large quantity of test material is normally needed for such screening methods. Zebrafish has emerged as a cost-effective and useful model for in vivo toxicity testing, and it is being routinely used for assessing the developmental toxicity of drugs or chemicals [
43,
61]. Zebrafish embryos are very small in size; thus, by using this animal, it is possible to conduct a high-throughput screening in 90-well cell culture plates using very small quantity of test materials. Furthermore, a large number of embryos can be used for statistical application without ethical concerns because zebrafish embryo and larvae up to 5 dpf are exempted from requirement of approval by an ethical committee for animal use and care (Bartlett & Silk, 2016; Strahle et al., 2012).
The development process of zebrafish is largely comparable to that of mammalians [
47,
62,
63], and this model is even used as a model for studying type 2 diabetes mellitus [
64].
Treatment with crude seed extract of M. charantia to zebrafish embryos resulted in severely malformed embryos. The treated embryos were severely developmentally delayed than their non-treated counterparts, thus the seed extract or any supplementation prepared from the seed of M. charantia must be used with utmost care in pregnant women owing to the possible risk of fetus malformation, based on the result of this study.
The fruit part of
M.charantia has been extensively studied and also lot of phytochemical has been identified from fruit part. The chemical constituents which have been identified from the fruit part of
M. charantia has been best reviewed by [
18]. The phytochemical from the seeds of
M. charantia is largely unknown, hence only seeds extract was subjected to GC-MS analysis in this study. The GC-MS analysis helped to identify six new phytochemicals from the seeds of
M. charantia. 1,2-CYCLOPENTANEDIONE has been identified with major peak which covered almost 60% of the areas. The molecular weight of,2-CYCLOPENTANEDIONE estimated to be 98.11. The biological activity of 1,2-CYCLOPENTANEDIONE is largely unknown but a similar compound 3-methyl-1,2-cyclopentanedione has been shown to be peroxisome proliferator-activated receptor γ (PPARγ) agonist [
65]. Interestingly peroxisome proliferator-activated receptor γ (PPARγ) agonist are insulin sensitizers and widely used in the treatment of type 2 diabetes and cardiac hypertrophy has been reported in few preclinical studies using such agonists [
66]. Whether 1,2-CYCLOPENTANEDIONE is PPARγ agonist or not need to be investigated experimentally, however, the cardiac hypertrophy in zebrafish embryos by seeds extract of
M. charantia mimics the PPARγ agonist phenotype, which means 1,2-CYCLOPENTANEDIONE could be PPARγ agonist as well and hence 1,2-CYCLOPENTANEDIONE which has been identified as a major compound in seeds extract could be causing agent for cardiac hypertrophy in zebrafish embryos.
Treatment with the crude extract of unripe fruits of
M. charantia did not induce sever level of malformation in zebrafish embryos in this study. The treated embryos were synchronous in development, as compared to the untreated control embryos. However, 100% of the treated zebrafish embryos developed cardiac hypertrophy, which was evident from 24 hpf onward. Severity of cardiac hypertrophy was directly correlated to the concentration of extract. The treated embryos developed cardiac hypertrophy after treatment with ≤25 μg/ml of fruit crude extract, whereas heart malformation was only evident in the zebrafish embryos treated with ≥30 μg/ml of fruit extract. The heart is the first organ to form and function during embryonic development in zebrafish, as in other vertebrates as well. Cardiac development in vertebrates usually begins with the specification of myocardial and endocardial progenitor cells, and cell-labeling techniques have helped visualizing the first myocardial progenitor cells in developing zebrafish embryos at approximately 5 hpf (before gastrulation starts) [
67,
68]. The cardiovascular system of zebrafish is a closed system, as in other vertebrates, and the physiology of its cardiac cycle is highly representative of that of humans [
69].
A specific time window treatment was planned to treat the embryos at different stages of cardiac development in order to elucidate either cardiac development or cardiac growth has been compromised by
M. charantia.. Cardiac development monitoring during zebrafish embryonic development by various labeling and imaging techniques has revealed that the first myocardial progenitor cells undergo specification at approximately 5 hpf (before gastrulation starts) in developing zebrafish embryos. Myocardial cells start differentiation at the 12-somite stage (15 hpf). Cardiac looping takes place between 36 and 48 hpf, and functional heart, which has completed the cardiac development process, occurs at approximately 48 hpf [
67,
68]. The cardiac hypertrophy was only apparent in treated zebrafish embryos when they were exposed to the crude extract of
M. charantia, between one-cell and 5 hpf, that is before the onset of cardiac cell specification, and cardiac toxicity was not observed in those embryos which were treated with the same extract at same concentration at or after 48 hpf (after the cardiac development process had completed) and also did not show any obvious embryonic malformations. The exact mechanism and underlying molecular pathway which have been affected by
M. charantia resulting the cardiac toxicity in zebrafish embryos is not known but the result from this study clearly indicates that the crude fruit extract of
M. charantia affected the specification of myocardial cells and possibly by blocking those biological process and transcription factors which are normally required for the specification of myoblast. The cardiac toxicity of bitter gourd has also been reported in at least one another study. [
58] Observed a significant increase in the cardiac weights of newly born litters of pregnant Sprague Dawley females rats which were treated with water fruit extract of
M. charantia as compared to non-treated control group. The cardiac hypertrophy as observed in treated zebrafish embryos in this study confirmed the findings of [
58] and hence the use of bitter gourd supplementation as anti-diabetic remedy in pregnant women must be use with extreme cautions to avoid any possible toxicity to developing fetus. The cardiac toxicity of
M. charantia in adult animals or human is unknown; however, a clinical case of mild atrial fibrillation has been reported in one patient who consumed large amount of
M. charantia juice [
70].
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