Background
Obesity is a major risk factor for dyslipidemia, type 2 diabetes, atherosclerosis, hypertension, cardiovascular disease, and certain cancers in the developed world [
1,
2]. Numerous treatments for obesity have been investigated, including the clinically available anti-obesity drug orlistat (Xenical), an intestinal lipase inhibitor [
3]. However, orlistat can cause serious side effects such as insomnia, constipation, vomiting, emesis, headache, and stomachache [
4]. Conjugated linoleic acid (CLA), which consists of a family of polyunsaturated fatty acids, is one of the most popular weight-loss supplements in the world [
5]. However, in large doses CLA can cause fat accumulation in the liver, which can lead to metabolic syndrome and diabetes [
6,
7]. Thus, there is a demand for alternative therapies, such as herbal medicines, with minimal side effects [
8]. One popular weight-loss herbal supplement is
Garcinia cambogia [
9]. This edible fruit contains large quantities of hydroxycitric acid (HCA), which has fat mass loss and lipid-lowering effects [
10].
G. cambogia protects against high-fat diet (HFD)-induced obesity by modulating adipose fatty acid synthesis and β-oxidation, but can induce hepatic fibrosis, inflammation, and oxidative stress [
11].
Allium fistulosum (Welsh onion or bunching onion) is a species of perennial onion originated in Eastern Asia [
12].
A. fistulosum is an important cooking ingredient in several Eastern countries, including China, Japan, and Korea [
13]. In Western countries,
A. fistulosum is used primarily as a scallion or salad onion, and is the species most commonly marketed for this purpose [
14]. Its leaves have nutritional value and can be used fresh all year [
15].
A. fistulosum also has traditional uses as an herbal medicine for the treatment for colds, influenza, abdominal pain, headache, constipation, dysentery, sores, ulcers, parasitic infestations, arthritis, and heart disease [
16]. In addition,
A. fistulosum has been shown to possess antifungal, antioxidative, antiplatelet, and antihypertensive properties [
16‐
18]. Our previous studies showed that oral administration of
A. fistulosum, either as a 70% ethanol extract or as a meal replacement cereal bar containing
A. fistulosum ethanol extract, inhibited increases in body weight, adipose tissue mass, fat accumulation, and serum lipid levels in HFD-induced obese mice [
19,
20]. Nutritional component analysis showed that
A. fistulosum extract powder contains low levels of total fat and is rich in vitamins (e.g., B
2, B
6, niacin, and folic acid) and iron [
20].
In the present preclinical study, the phytochemical contents of aqueous and ethanolic extracts of A. fistulosum were analyzed by high-performance liquid chromatography (HPLC). The effects of these extracts on body weight and other obesity-related parameters were explored in HFD-fed mice. The anti-obesity effects of these extracts were compared with the clinical weight-loss drug, orlistat, and the weight-loss supplements, G. cambogia extract containing HCA and CLA.
Methods
Preparation of A. fistulosum extracts
A. fistulosum was purchased as a dried herb from Omniherb Co. (Yeongcheon, Korea). A voucher specimen (No. PH-79 W and PH-79E) was deposited at the herbarium of the Department of Herbal Resources Research at the Korea Institute of Oriental Medicine. The dried bulbs and roots of A. fistulosum (100 g) were extracted twice with 10 volumes of water or 70% ethanol using a 2-h reflux extraction at 90 °C. The extract was then concentrated under reduced pressure, filtered, lyophilized, and stored at 4 °C. Yields of the aqueous and ethanolic extracts from the starting material were 11.25% and 15.91%, respectively.
HPLC determination of ferulic acid and quercetin
The sample was analyzed by reverse-phase HPLC using a Waters Alliance 2695 system (Waters Co., Milford, MA, USA) coupled with a 2998 photodiode array detector. An INNO C18 column (250 mm × 4.6 mm, particle size 5 μm; Young Jin Biochrom Co., Sungnam, Korea) was used as the stationary phase, and the mobile phase was composed of 0.1% (v/v) trifluoroacetic aqueous solution (A) and acetonitrile (B). Elution conditions were as follows. At t = 0 min the mobile phase consisted of 10% A/90% B and was held for 10 min. From 10 to 60 min, a gradient was applied to 60% A/40% B, which was followed by a wash with 100% B for 5 min and a 15-min equilibration period at 90% A/10% B. The separation temperature was kept constant at 40 °C throughout the analysis, with a flow rate of 1.0 mL/min and injection volume of 20 μL. Identification was based on retention time and UV spectra using comparison with commercial standards. The components were quantified based on peak areas at the maximal wavelength. Calibration curves of the standards, ranging from 3.125 to 100 μg/mL (six levels), showed good linearity, with R2 values exceeding 0.99 (peak areas vs. concentration). HPLC-grade reagents, acetonitrile, and water were obtained from J. T. Baker (Phillipsburg, NJ, USA). The standards of ferulic acid and quercetin (purity > 98%) were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA).
Animals and experimental diets
Male 8-week-old C57BL/6 J mice were purchased from The Jackson Laboratory (Bar Harbor, ME, USA). The mice were housed in an air-conditioned animal room with a 12-h light/12-h dark cycle at a temperature of 21 ± 2 °C and humidity of 50 ± 5%. The mice were fed a commercial diet (Ralston Purina, St. Louis, MO, USA) for 1 week, with food and water provided ad libitum.
The mice were then randomly divided into the following seven groups (
n = 6 each) according to treatment: standard chow diet (normal control), HFD alone (HFD-control), HFD plus
G. cambogia extract containing HCA (HFD-HCA), HFD plus conjugated linoleic acid (HFD-CLA), HFD plus orlistat (HFD-ORL), HFD plus
A. fistulosum aqueous extract (HFD-AFW), or HFD plus
A. fistulosum ethanolic extract (HFD-AFE). The mice receiving HCA, CLA, or ORL served as positive controls. The standard chow (Orient Bio Inc., Seongnam, Korea) provided 14% of energy as fat, 21% as protein, and 65% as carbohydrates. The HFD (Rodent Diet D12492, Research Diet, New Brunswick, NJ) provided 60% of energy as fat, 20% as protein, and 20% as carbohydrates. HCA, CLA, AFW, and AFE were dissolved in normal saline and orally administrated at a dose of 100 mg/kg/day. Orlistat (Xenical, Roche Korea Co., Seoul, Korea) was orally administered at a dose of 15.6 mg/kg, which was based on the human dosage. The normal control and HFD-control groups received vehicle (normal saline) only. Body weight and food intake were determined every week during the 6-week experimental period. The food efficiency ratio was calculated as the daily body weight gain divided by the daily food intake [
21].
This study adhered to the Guide for the Care and Use of Laboratory Animals developed by the Institute of Laboratory Animal Resources of the National Research Council and was approved by the Institutional Animal Care and Use Committee of Daejeon University in Daejeon, Korea (Permit No. DJUARB2014–042).
Serum biochemistry
At the end of the 6 weeks, the mice were anesthetized with pentobarbital (intraperitoneally, 100 mg/kg) after an overnight fasting. Blood samples were collected from the abdominal aorta into a vacuum collection tube (BD Biosciences, San Diego, CA, USA). Total cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, triacylglycerol, free fatty acids, glucose, creatinine, aspartate transaminase (AST), and alanine transaminase (ALT) concentrations were determined using an Express Plus automatic analyzer (Chiron Diagnostics, East Walpole, MA, USA). Serum leptin, adiponectin, and insulin-like growth factor I (IGF-1) levels were determined using commercially available mouse enzyme-linked immunosorbent assay kits (Diagnostic Systems Laboratories, Inc., Webster, TX, USA and Linco Research, St Charles, MO, USA) [
22].
Histologic analysis of liver and adipose tissues
After collecting the blood, white adipose tissues (subcutaneous, epididymal, and perirenal fat) [
23] and livers were removed from the mice and weighed immediately. Liver and epididymal adipose tissues were fixed in 10% neutral buffered formalin for 1 day and then embedded in paraffin. The tissues were cut (6-μm thickness) and stained with hematoxylin and eosin. Adipocyte size was determined in the stained sections using light microscopy (Olympus BX51, Olympus Optical Co., Tokyo, Japan) and an image analysis program (Image-Pro Plus 5.0, Media Cybernetics, Silver Spring, MD, USA).
Real-time reverse-transcription polymerase chain reaction
Total RNA from liver and epididymal adipose tissue was isolated with TRI Reagent (Sigma-Aldrich) and then digested with DNase I (Life Technologies, Grand Island, NY, USA) to remove chromosomal DNA (cDNA). Total RNA (μg) was reverse transcribed into cDNA with the First Strand cDNA Synthesis Kit (Amersham Pharmacia, Piscataway, NJ, USA). Real-time reverse-transcription polymerase chain reaction (RT-PCR) was performed using the Applied Biosystems 7500 Real-Time PCR system (Applied Biosystems). The primer and probe sequences are shown in Table
1. The probes were labeled with 6-carboxyfluorescein, a fluorescent reporter dye. PCR reactions were carried out with TaqMan Universal PCR Master Mix containing DNA polymerase (Applied Biosystems) according to the manufacturer’s instructions, using the following PCR conditions: 2 min at 50 °C, 10 min at 95 °C, followed by 40 cycles of 15 s at 95 °C and 1 min at 60 °C. Relative target gene expression was determined using the comparative Ct (threshold cycle number at the cross-point between the amplification plot and threshold) method with glyceraldehyde 3-phosphate dehydrogenase as an internal control. The expression levels of mRNA were normalized to those of GAPDH and calculated using the 2
-△△Ct method according to the manufacturer’s instructions.
Table 1
The primer and probe sequences used in the real-time RT-PCR analysis
Leptin | sense | 5’-AACCCTTACTGAACTCAGATTGTTAG-3’ |
| antisense | 5’-TAAGTCAGTTTAAATGCTTAGGG-3’ |
UCP-2 | sense | 5’-TTCAAATGAGATTGTGGGAAAAT-3’ |
| antisense | 5’-ACCGATACAGTACAGTACAGTA-3’ |
Adiponectin | sense | 5’-CCCAAGGGAACTTGTGCAGGTTGGATG-3’ |
| antisense | 5’-GTTGGTATCATGGTAGAGAAGAAAGCC-3’ |
AMPKα2 | sense | 5′-GATGATGAGGTGGTGGA-3’ |
| antisense | 5’-GCCGAGGACAAAGTGC-3’ |
AMPKα1 | sense | 5’-AAGCCGACCCAATGACATCA-3’ |
| antisense | 5’-CTTCCTTCGTACACGCAAAT-3’ |
PPAR-γ | FAM | 5’-TCGGAATCAGCTCTGTGGACCTCTCC-3’ |
GAPDH | VIC | 5’-TGCATCCTGCACCACCAACTGCTTAG-3’ |
Statistical analysis
Groups were compared by one-way analysis of variance followed by Duncan’s multiple range post hoc test. Results are expressed as the mean ± standard error of the mean (SEM); p < 0.05 was considered significant.
Discussion
In the present study, oral administration of AFW and AFE attenuated the HFD-induced increase in serum levels of triacylglycerol, free fatty acids, and leptin; lipid accumulation in the liver; liver and adipose tissue weight; adipocyte size; and body weight in mice. In addition, AFE attenuated the HFD-induced increase in total cholesterol and LDL-cholesterol. We found that serum HDL-cholesterol and adiponectin levels were higher in HFD-fed mice treated with AFW and AFE than in normal controls and mice receiving the HFD only.
The insulin/IGF-1 axis plays an important role in the association between obesity and risk of breast cancer [
24]. Some studies have demonstrated that obese children exhibit the highest levels of serum IGF-1 and also exhibit a positive relationship between IGF-1 and adiposity, which perhaps contributes to their increased risk of obesity-related cancers [
25]. In this study, the HFD-induced increase in serum IGF-1 levels was significantly attenuated in mice treated with AFW and AFE. Expression of AMPK, which is a cellular energy sensor involved in energy homeostasis, was evaluated in adipose tissue and liver. AMPK triggers catabolic pathways, such as glucose transport and fatty acid β-oxidation, and inhibits anabolic pathways such as fatty acid, cholesterol, and protein synthesis [
26]. Because of its critical role in metabolism, AMPK is a target for drugs used to treat cancer, diabetes, and metabolic syndrome [
27]. Our results show that treating HFD-fed mice with AFW or AFE increased mRNA levels of AMPKα in the liver, suggesting that AFW and AFE may lower lipid accumulation and serum lipid levels through the regulation of lipid metabolism in the liver. In adipose tissue, AFW and AFE increased UCP2 and adiponectin expression. In addition, AFE decreased the expression of PPAR-γ, which is a ligand-activated transcription factor that plays an important role in adipocyte differentiation and lipid storage [
28] and regulates the expression of adiponectin through a PPAR-responsive element in its promoter [
29]. UCP2, a mitochondria inner membrane transporter, promotes fatty acid oxidation in adipose tissue and lowers body weight [
30].
Adiponectin is a hormone secreted by adipose tissue that modulates glucose and lipid metabolism by stimulating fatty acid oxidation in almost all its major target tissues, including skeletal muscle, liver, and adipocytes [
31]. The beneficial effects of adiponectin in these target tissues are dramatically attenuated in UCP2-deficient mice and by expression of dominant negative AMPK [
32]. In patients with obesity and diabetes, plasma adiponectin levels are inversely correlated with body fat content, suggesting that adiponectin is an important factor for the treatment of obesity [
33,
34]. In the present study, it was found that serum adiponectin levels and adiponectin mRNA levels in adipose tissue were higher in AFE-treated mice compared with mice receiving the HFD only. Conversely, the HFD-induced increase in serum leptin levels was significantly attenuated in mice treated with AFW and AFE, although leptin mRNA levels in adipose tissue were not significantly decreased in the treatment groups. Blood levels of leptin are positively associated with adiposity and increased body weight in humans and rodents [
35]. These results suggest that the regulation of adiponectin and lipid metabolism-related genes expression by AFW and AFE may be responsible for the decrease in serum lipid levels and the attenuation of adiposity in HFD mice.
HPLC analysis identified ferulic acid and quercetin in AFE and AFW. Ethanol and water are the most common solvent to extract the bioactive compounds of herbal medicine for HPLC analysis and traditional decoction, respectively. Our HPLC analysis identified ferulic acid and quercetin in AFE and AFW. The ferulic acid concentration in AFW was 2 times that of AFE and the quercetin concentration in AFE was 5.2 times that of AFW. The HPLC analysis was performed using commercial standards and compound libraries. Other compounds containing vanillic acid, tyrosol, 4-hydroxybenzaldehyde, and koumine were detected in the small peaks, but the content of these compounds in AFE and AFW was extremely low. Quercetin and ferulic acid, which are naturally occurring polyphenolic flavonoid compounds in fruits and vegetables, have been reported to suppress body weight, fat accumulation and hyperlipidemia in obese mice by enhancing antioxidant activities [
36,
37]. The anti-obesity effect of quercetin is mediated by the AMPK signaling pathway in 3 T3-L1 adipocytes [
38]. Structurally, hydroxyl groups of these flavonoids participate in radical stabilization via electron delocalization, thus contributing to the strong antioxidant and anti-obesity activities [
39‐
41]. These phenolic compounds therefore may be partly responsible for the anti-obesity effects of AFW and AFE. In this study, especially, the quercetin concentration in AFE was high. Among the flavonoids, quercetin is an effective protector against lipid oxidation due to the presence and location of five hydroxyl groups on the aromatic ring [
42]. Additionally, AFE exerted the stronger anti-obesity effects than AFW by enhancing adiponectin levels and reducing serum cholesterol levels in obese mice. Thus, this difference in anti-obesity action might be attributed to their chemical difference of quercetin.
However, it cannot be excluded that other components of these extracts may contribute to their anti-obesity activities. It has been reported that
A. fistulosum contains
p-coumaric acid, isoquercitrin, quercitrin, stigmasterol, β-sitosterol, campesterol, and allicin [
15,
43]
. Thus, further study is needed to determine the anti-obesity components of
A. fistulosum, including the development of optimized methods of chemical analysis to identify the bioactive compounds in the AFE and AFW extracts.
Conclusions
This study showed that the oral administration of AFW and AFE significantly reduced body weight, adipose tissue and liver weights, and fat accumulation in a mouse model of obesity. In addition, AFW and AFE improved the serum levels of triacylglycerol, total cholesterol, LDL-cholesterol, free fatty acids, and HDL-cholesterol. These findings indicate that A. fistulosum may be useful as a functional food material or therapeutic agent for the treatment of obesity and obesity-associated metabolic syndrome.