Anti-obesity effects of galangin, a pancreatic lipase inhibitor in cafeteria diet fed female rats

Abstract

Context: Alpinia galanga Willd (Zingiberaceae) (AG) is a rhizomatous herb widely cultivated in shady regions of Malaysia, India, Indochina and Indonesia. It is used in southern India as a domestic remedy for the treatment of rheumatoid arthritis, cough, asthma, obesity, diabetes, etc. It was reported to have anti-obesity, hypoglycemic, hypolipidemic and antioxidant properties.

Objective: A flavonol glycoside, galangin, was isolated from AG rhizomes. Based on its in vitro pancreatic lipase inhibitory effect, the study was further aimed to clarify whether galangin prevented obesity induced in female rats by feeding cafeteria diet (CD) for 6 weeks.

Materials and methods: The in vitro pancreatic lipase inhibitory effect of galangin was determined by measuring the release of oleic acid from triolein. For in vivo experiments, female albino rats were fed CD with or without 50 mg/kg galangin for 6 weeks. Body weight and food intake was measured at weekly intervals. On day 42, serum lipids levels were estimated and then the weight of liver and parametrial adipose tissue (PAT) was determined. The liver lipid peroxidation and triglyceride (TG) content was also estimated.

Results: The IC₅₀ value of galangin for pancreatic lipase was 48.20 mg/mL. Galangin produced inhibition of increased body weight, energy intake and PAT weight induced by CD. In addition, galangin produced a significant decrease in serum lipids, liver weight, lipid peroxidation and accumulation of hepatic TGs.

Conclusion: Galangin present in AG rhizomes produces anti-obesity effects in CD-fed rats; this may be mediated through its pancreatic lipase inhibitory, hypolipidemic and antioxidant activities.

• Alpinia galanga
• antioxidant
• body weight
• hypolipidemic
• obesity

Introduction

Alpinia galanga Willd (AG), (Zingiberaceae), commonly called “greater galangal”, is a rhizomatous herb distributed in various parts of India, and throughout Southeast Asia. It is a reputed drug in the indigenous system of medicine and used in southern India as a domestic remedy for the treatment of rheumatoid arthritis, inflammation, cough, asthma, obesity, diabetes, etc. (Warrier et al., 1994). It is scientifically reported to have hypoglycemic (Akhtar et al., 2002), hypolipidemic (Achuthan & Padikkala, 1997), antioxidant (Vankar et al., 2006), antiulcer (Al-Yahya et al., 1990) and immunostimulating properties (Bendjeddou et al., 2003).

In our previous research, we have reported that AG ethanol extract produced potent inhibition of increases body weight, energy intake and parametrial adipose tissue (PAT) weight induced by cafeteria diet (CD). The extract also significantly reduced serum lipid and leptin levels, which were elevated by feeding CD (Kumar & Alagawadi, 2011).

With this previous result, the active component of AG responsible for anti-obesity activity needs to be identified in the next step. A wealth of information indicated that numerous bioactive components from nature are potentially useful in obesity treatments, particularly phenolic compounds including flavonoids and phytosterols (Yun, 2010). Hence, the phytochemical investigation was directed toward the isolation of phenolic compounds and sterols. TLC studies of the ethyl acetate fraction of the ethanol extract of AG rhizomes showed the presence of two flavonoids, namely, galangin and kaempferide.

Galangin (3-5-7-trihydroxy flavone), a member of the flavonol class of flavonoids, is present at high concentrations in propolis, a natural material produced by honeybees and in Alpinia officinarum Hance (Zingiberaceae), a common spice and herbal medicine found in Asia (Heo et al., 2001). Among several biological activities, the galangin suppresses the genotoxicity of chemicals (Heo et al., 2001), represses Cox-2 expression (O’Leary et al., 2004), inhibits viral replication (Amoros et al., 1992) and prevents oxidative damage (Sivakumar & Anuradha, 2011). However, its effect on overweight and obesity is not scientifically reported.

Hence, the present paper is aimed to report the isolation of galangin from ethanol extract of AG rhizomes and its influence on in vitro pancreatic lipase inhibitory activity and also to clarify whether galangin prevented obesity induced in female rats fed with CD for 6 weeks.

Materials and methods

General experimental procedures

The melting point of galangin was measured on the SI-935 digital melting point apparatus, made by Scientific International (New Delhi, India). Column chromatography was performed over silica gel (60–120 mesh; Merck, Bangalore, India). UV and IR were measured on a Shimadzu (Kyoto, Japan) UV-1700 and a Nicolet (Yokohama, Japan) iS5 FT-IR, respectively. ¹H, ¹³C NMR spectra were recorded on an Avance III 600 FT-NMR (Bruker, Bremen, Germany) at 400 MHz for ¹H and 100 MHz for ¹³C, respectively, in CH₃OD with TMS as an internal standard. The mass spectrum was recorded on a Shimadzu (Japan) LCMS-8080 mass spectrometer.

Extraction

The rhizomes of AG were collected from the agricultural fields around Belgaum in January 2012 and were positively identified by Dr S.R. Yadav, Head, Department of Botany, Shivaji University, Kolhapur, India. The rhizomes were air-dried, powdered and then extracted with 70% ethanol by the Soxhlet method. The extract was filtered with Whatman No. 1 filter paper (Sigma-Aldrich, Bangalore, India) and then the solvent was evaporated at reduced pressure by using Rotavapor apparatus (Buchi, Flawil, Switzerland) to yield a viscous mass, which was then stored at 4 °C until used. The % yield of the extract obtained was 15.8%.

Isolation of galangin

The ethanol extract of AG rhizomes was further fractionated with petroleum ether (40–60 °C), chloroform, ethyl acetate and water to isolate the bioactive flavonoids. The obtained fractions were screened for in vitro antioxidant activity by using DPPH radical scavenging assay (Gupta et al., 2004). The ethyl acetate fraction showed better free radical scavenging activity as compared to remaining fractions. Hence, the ethyl acetate fraction was further subjected to TLC studies, which showed two spots of R_f values, 0.44 and 0.66, indicating the presence of two flavonoids. For the separation and purification of these flavonoids, the ethyl acetate fraction was subjected to column chromatography.

The column was eluted successively with hexane, hexane:chloroform (1:1), chloroform, chloroform:methanol (1:1), and finally with methanol. Fractions were collected in 25 mL portions and subjected to TLC using chloroform:methanol (9:1) as a developing solvent and 5% vanillin solution as a detecting agent in order to combine the fractions with the same compounds. The fractions 31–40 obtained with chloroform:methanol (1:1) showed a single spot when exposed to vanillin reagent on TLC plate (Sigma-Aldrich, Bangalore, India). Therefore, they were combined and solvent was evaporated to dryness at room temperature. The obtained residue of light yellow powder was labeled as F1 and subjected to further characterization using spectroscopic methods.

Acute toxicity study

The acute toxicity test of isolated galangin was determined as per the Organization for European Economic Cooperation (OECD) guidelines No. 420. Female Wistar rats (150–200 g) were used for this study. The initial dose of 2000 mg/kg p.o. of galangin was administered to a group of five animals. The treated animals were monitored for 14 d, for mortality and general behavior. No toxic symptoms or mortality was observed through the end of the study. Hence, the experimental dose was selected as 50 mg/kg/d.

Measurement of pancreatic lipase activity

Lipase activity was determined by measuring the amount of the release of fatty acid from Triolein. A suspension of triolein (80 mg), phosphatidylcholine (10 mg) and taurocholic acid (5 mg) in 9 mL of 0.1 M N-Tris (hydroxymethyl) methyl-2-aminoethanesulfonic acid (TES) buffer (pH 7.0) containing 0.1 M NaCl was sonicated for 5 min. This sonicated substrate suspension (0.1 mL) was incubated with 0.05 mL (final concentration 5 units per tube) pancreatic lipase and 0.1 mL of various concentrations (100, 250, 500, 750 and 1000 mg/mL) of galangin for 30 min at 37 °C in a final volume of 0.25 mL and the released fatty acid was determined by titrating the solution against 0.02 M NaOH (standardized by 0.01 M oxalic acid) using phenolphthalein as an indicator (Han LK et al., 1999). Percent inhibition of lipase activity was calculated using the following formula: where A is the control lipase activity and B is the lipase activity in the presence of galangin. The IC₅₀ value of galangin for pancreatic lipase was then calculated graphically.

Experimental animals

Albino Wistar rats (150–200 g) of female sex were selected and housed in a group of six animals for 1 week in a 12:12 h light and dark cycle at 23 ± 2 °C temperature and 55–60% relative humidity. The animals had free access to food and water. After a 1-week adaptation period, healthy animals were used for the study. The Institutional Animal Ethics Committee, KLE University, Belgaum, approved the experimental protocol.

Composition of CD

The CD consisted of three diets – (a) condensed milk (8 g) + bread (8 g); (b) chocolate (3 g) + biscuits (6 g) + dried coconut (6 g), and (c) cheese (8 g) + boiled potato (10 g). The three diets were presented to individual rats on days 1, 2 and 3, respectively, and then repeated for 42 d in the same succession (Harris, 1993). The calorie value of the CD is given in Table 1.

Table 1.  Composition and calorie value of CD.

Ingredients	Calorie value (kcal/100 g)
Condensed milk	335
Bread	230
Chocolate	550
Biscuit	360
Dried coconut	660
Cheese	320
Boiled potato	80

Treatment protocol

Animals were divided into the following four groups of six animals each:

• Group I: Normal control group fed with normal laboratory pellet chow ad libitum (calorie value = 280 kcal/100 g) and treated with 1% Tween 80 (5 mL/kg p.o.).

• Group II: CD control group received CD in addition to normal diet and received 1% Tween 80 (5 mL/kg p.o.).

• Group III: Galangin control group received CD in addition to normal diet and galangin as a suspension in 1% Tween 80 (50 mg/kg p.o.)

• Group IV: Standard control group received CD in addition to normal diet and sibutramine (2 mg/kg, i.p.).

The above treatment was continued for 6 weeks. The animals were weighed at the start of the experiment and then every week thereafter. Food intake of each group of animals was determined by measuring the difference between the preweighed chows and weight of the food that remained every 24 h initially and then every week thereafter, and the results were expressed as mean food intake in g/d for group of six rats and mean energy intake in kcal/d for a group of six rats.

Serum biochemical analysis

On day 42, blood was collected by retro-orbital puncture in ether-anaesthetized rats and subjected to centrifugation to obtain serum. The serum levels of total-cholesterol, HDL, LDL and triglycerides (TGs) were estimated using the standard biochemical kits (Beacon Diagnostics, Valsad, India). The atherogenic index of plasma (AIP) was calculated by using the formula: AIP = log (TGs/HDL).

Estimation of weight of liver and PAT, liver lipid peroxidation and liver TGs content

Animals were then killed with an overdose of diethyl ether. The liver tissue and PAT were quickly removed and weighed. The liver tissues were stored at −20 °C until the analysis was performed. The liver tissue was homogenized in 10 volume of 0.1 M phosphate buffer (pH 7.4) and the supernatant was collected and used for the assay of lipid peroxidation using the TBARS assay (Tirkey et al., 2005) and the liver TG content was determined directly using the modified method of Van Handel and Zilversmit (Butler et al., 1960), as explained below.

One milliliter of supernatant was immediately transferred to a 25 mL graduated cylinder containing about 4 g of activated zeolite moistened with 2 mL of chloroform. Chloroform (18 mL) was gradually added with intermittent shaking for 10 min (The tissue TGs are now diluted 1:200). The solution was filtered and 0.125–1 mL of filtrate (containing about 0.05 mg of TGs) was pipetted into each of three glass stoppered tubes. Standard corn oil solution (1 mL; 0.05 mg/mL) was added to each tube. The chloroform from all the tubes was evaporated by placing in a water bath maintained at 80 °C. To two out of three of each standard solution and test sample, 0.5 mL of alcoholic KOH was added (saponified sample); to the third standard and test sample, 0.5 mL of 95% alcohol was added (unsaponified sample). The tubes were maintained at 60–70 °C for 20 min and then 0.5 mL of 0.2 N H₂SO₄ was added. Alcohol was removed by placing the tubes in a boiling water bath for about 15 min. The tubes were cooled and 0.1 mL of periodate solution was added. 0.1 mL of sodium arsenite solution was added after 10 min. Chromotropic acid reagent (5 mL) was added after several minutes. The mixture was mixed well and heated for 30 min in the absence of excessive light. After cooling, the absorbance was measured at 570 nm. where A is the volume of chloroform extract taken and

Statistical analysis

The results were expressed as mean ± standard error (SEM). Data were analyzed by one-way analysis of variance (ANOVA) followed by Dunnett’s multiple comparisons test and were considered significantly different at p < 0.05 (GraphPad Prism, version 5, Graphpad, La Jolla, CA).

Results

Spectroscopic analyses

The light yellow-colored powder has a melting point at 214–215 °C. The UV spectrum showed two peaks at λ_max 267 and 370 nm. The IR absorption spectrum showed absorption bands at 3607–3084 cm⁻¹ (O–H stretch), 1659 cm⁻¹ (C=O stretch), 1190 cm⁻¹ (C–O–C stretch). The ¹H-NMR spectrum (CH₃OD) showed the signals at δ 12.43 (1H, s, 5-OH), 10.74 (1H, s, 7-OH), 9.59 (1H, s, 3-OH), 8.20 (2H, dd, Ar-H), 7.62 (2H, dd, Ar-H), 7.53 (1H, m, Ar-H), 6.43 (d, 1H, Ar-H), 6.21 (1H, d, Ar-H) ppm. The ¹³C-NMR spectrum (CH₃OD) showed 13 signals at δ 178.1 (C-4), 169.1 (C-5), 166.2 (C-7), 159.8 (C-2), 159.7 (C-9), 136.4 (C-3), 130.2 (C-1′), 128.5 (C-3′, 5′), 127.9 (C-4′), 126.1 (C-2′, 6′), 103.2 (C-10), 98.1 (C-6), 97.8 (C-8) ppm. The MS spectrum showed the [M + H⁺] and [M − H⁻] peaks at m/z = 271 and 269, respectively.

The isolated compound showed positive results for chemical tests of flavonoids. All the spectral data of the isolated compound F1 matches with that of the known compound galangin. Hence, the isolated compound F1 may be a flavonoid, i.e., galangin (3-5-7-trihydroxyflavone) with a molecular formula C₁₅H₁₀O₅ and molecular weight 270.24.

Effect of galangin on pancreatic lipase activity

Galangin showed dose-dependent inhibition of in vitro pancreatic lipase activity and the IC₅₀ of galangin for pancreatic lipase was calculated to be 48.20 mg/mL.

Effect of galangin on body weight

Feeding of CD for 6 weeks produced significant (p < 0.001) increase in the body weight compared to normal control animals fed with normal pellet chow ad libitum. The mean difference in the body weight between day 1 and day 42 observed was 159.4 ± 2.56 and 77.9 ± 2.06 g, respectively, in CD control and normal control rats. The body weight readings of different groups at weekly intervals are shown in Table 2. However, treatment with sibutramine and galangin produced highly significant (p < 0.001) inhibition of increase in the body weight of animals fed with CD, which was evident from second week onwards. The percent reduction of body weight produced by galangin and sibutramine was 40.02% and 52.58%, respectively, compared to CD control rats (Table 3).

Table 2.  Effect of galangin and sibutramine on change in body weight (g) for 6 weeks in CD-fed rats.

Weeks	Normal control	CD control	Galangin control	Sibutramine control
0	164.5 ± 4.45	166.8 ± 2.14	168.6 ± 1.04	166.6 ± 2.46
1	172.6 ± 3.18^a	202.4 ± 7.84	184.2 ± 3.44	178.6 ± 2.42^a
2	194.3 ± 2.16^b	246.6 ± 7.46	198.8 ± 2.25^b	188.4 ± 3.24^b
3	210.2 ± 4.18^b	270.4 ± 2.48	216.0 ± 3.40^b	205.2 ± 2.48^b
4	222.5 ± 4.08^b	288.2 ± 4.26	232.2 ± 2.16^b	227.8 ± 1.48^b
5	238.6 ± 2.14^b	302.8 ± 3.64	246.8 ± 2.04^b	235.6 ± 3.26^b
6	242.4 ± 4.56^b	326.2 ± 3.16	264.2 ± 2.22^b	242.2 ± 2.62^b

Values are mean ± SEM (n = 6).

^ap < 0.05, ^bp < 0.001 significant as compared to the respective CD control value.

Table 3.  Percent reduction in body weight produced by galangin and sibutramine in CD-fed rats.

	Mean difference in body weight in g between days 1 and 42	% Reduction in body weight compared to CD control group
Normal control	77.9	–
CD control	159.4 (104.62%)	–
Galangin control	95.6 (22.72%)	40.02%
Sibutramine control	75.6 (−2.95%)	52.58%

Values in parenthesis indicate % change in body weight as compared to the normal control group.

Effect of galangin on food intake

There was no significant change in the amount of food intake between normal and CD control rats. However, there was significant increase (p < 0.001) in calorie intake in CD control rats as compared to normal control rats. The mean energy intake observed for 6 week intervals was 386.10 ± 2.31 and 474.00 ± 3.28 kcal/d for normal control and CD control group of rats, respectively. However, treatment with sibutramine and galangin produced significant (p < 0.001) decrease in the amount of food intake as well as energy intake of animals fed with CD. The mean food/energy intake values observed with various treatments are depicted in Table 4.

Table 4.  Effect of galangin and sibutramine on food/energy intake in CD-fed rats.

	Food intake in g/d	Energy intake in kcal/d
Normal control	137.89 ± 2.22	386.10 ± 2.31^a
CD control	143.63 ± 2.45	474.00 ± 3.28
Galangin control	115.26 ± 2.48^a	380.36 ± 3.08^a
Sibutramine control	105.18 ± 1.84^a	347.10 ± 4.00^a

Values are mean ± SEM (n = 6).

^ap < 0.001 significant as compared to the CD control value.

Effect on galangin on serum lipids level

There was significant increase (p < 0.001) in the serum concentration of total-cholesterol, LDL-cholesterol and TGs in CD control rats in comparison to normal diet fed rats. However, there was no significant difference in serum HDL-cholesterol levels among CD control and normal control group of rats. Sibutramine and galangin produced a significant decrease in serum concentrations of total-cholesterol, LDL-cholesterol and TGs. The galangin and sibutramine also produced an increase in serum HDL-cholesterol levels compared to CD control rats. These results produced a significant decrease in AIP values with galangin or sibutramine treated rats in comparison with CD control rats. The serum lipid levels and AIP values of different groups of animals are tabulated in Table 5.

Table 5.  Effect of galangin and sibutramine on serum biochemical parameters in CD-fed rats.

	Normal control	CD control	Galangin control	Sibutramine control
Glucose	141.00 ± 2.96^a	153.28 ± 2.56	140.46 ± 3.20^b	134.24 ± 2.76^c
Total cholesterol	96.83 ± 3.01^c	125.20 ± 2.83	111.24 ± 2.12^b	103.92 ± 2.69^c
HDL	23.50 ± 1.17	25.50 ± 1.17	35.32 ± 1.56^c	35.83 ± 1.24^c
LDL	50.67 ± 1.54^c	100.20 ± 1.40	66.20 ± 2.32^c	69.67 ± 1.43^c
TGs	64.17 ± 3.37^c	100.3 ± 2.84	75.64 ± 2.52^c	76.50 ± 3.48^c
AIP value	0.076	0.235	−0.087	−0.031

Values are mean ± SEM (n = 6) expressed as mg/dL, except for the AIP value.

^ap < 0.05, ^bp < 0.01, ^cp < 0.001 significant as compared to the CD control value.

Effect of galangin on liver weight, PAT weight and liver lipid peroxidation and TGs content

The rats fed with CD for 6 weeks resulted in a highly significant (p < 0.001) increase in the weight of liver tissue and PAT. Treatment with galangin or sibutramine a produced significant (p < 0.001) decrease in the liver and PAT weight as compared to that observed in CD control rats. The concentration of liver tissue malondialdehyde (MDA), produced due to the peroxidation of cellular lipids by reactive oxygen species, was significantly (p < 0.001) larger (1.66 ± 0.09 µM/mg of protein) in CD control rats as compared to that in normal diet-fed rats (0.84 ± 0.01 µM/mg of protein). The galangin and sibutramine produced a significant (p < 0.001) decrease in the concentration of MDA in the liver tissue. The liver TG concentration was significantly (p < 0.001) increased in CD control rats (12.45 ± 0.44 mg/g) as compared to the normal control group of rats (5.71 ± 0.25 mg/g). However, the rats treated with sibutramine or galangin showed a significant (p < 0.001) decrease in liver TG concentrations as compared to CD control rats (Table 6).

Table 6.  Effect of galangin and sibutramine on weight of liver and PAT, liver MDA content and liver TGs content in CD-fed rats.

	Normal control	CD control	Galangin control	Sibutramine control
PAT weight (g)	4.02 ± 0.23^a	10.65 ± 0.48	6.88 ± 0.42^a	6.56 ± 0.16^a
Liver weight (g)	5.99 ± 0.18^a	12.46 ± 0.41	7.52 ± 0.36^a	5.92 ± 0.19^a
MDA (µM/mg of protein)	0.84 ± 0.01^a	1.66 ± 0.09	0.96 ± 0.02^a	0.95 ± 0.02^a
Liver TGs (mg/g)	5.71 ± 0.25^a	12.45 ± 0.44	8.24 ± 0.24^a	7.14 ± 0.27^a

Values are mean ± SEM (n = 6).

^ap < 0.01 significant as compared to the CD control value.

Discussion

It has been reported that natural products can produce anti-obesity effects based on their distinct mechanisms. They may produce decreased lipid absorption, decreased energy intake, increased energy expenditure, decreased pre-adipocyte differentiation and proliferation or decreased lipogenesis and increased lipolysis (Yun, 2010).

Among treatments for obesity, one of the most promising strategies in the effort to reduce energy intake through gastrointestinal mechanisms, without altering the central mechanisms, is the development of nutrient digestion and absorption inhibitors. Since dietary lipids represent the major source of unwanted calories, specifically inhibiting TG digestion forms a new approach for the reduction of fat absorption.

It is well known that, dietary lipid is not directly absorbed from the intestine unless it has been subjected to the action of pancreatic lipase enzyme. The two products formed by the hydrolysis of fat in the presence of pancreatic lipase enzyme are fatty acids and 2-monoacylglycerol, which are absorbed (Verger, 1984). Thus, the inhibition of this enzyme is beneficial in the treatment of obesity. Orlistat, an approved anti-obese drug, is clinically reported to prevent obesity and hyperlipidemia through the increment of fat excretion into feces and the inhibition of pancreatic lipase enzyme (Drent et al., 1995). Inhibition of pancreatic lipase is an attractive targeted approach for the discovery of potent anti-obesity agents for obesity treatment (Thomson et al., 1997). In the present study, in vitro pancreatic lipase activity was markedly inhibited in the presence of galangin, signifying its lipid digestion and absorption inhibitory effect.

Various animal models of obesity have been used to emulate obesity like condition in humans in order to develop effective anti-obesity treatments. Among the animal models of obesity, rats that are fed a high-fat diet are considered useful; a high percent of fat in their diet is considered to be an important factor in the development of obesity, leading to accumulation of body fat even in the absence of an increase in calorie intake (Kusunoki et al., 2000). The in vivo anti-obesity effect of galangin isolated from the ethanol extract of AG rhizomes was investigated in rats fed with high-fat CD for 6 weeks by analyzing the effects on body weight, food intake, serum lipids, liver and PAT weight, liver lipid peroxidation and liver TG content.

The present study showed that, the administration of CD for 6 weeks caused obesity like conditions with an increase in body weight, PAT weight and serum lipid levels. Furthermore, it also induced fatty liver with the accumulation of hepatic TGs. Treatment with galangin at the dose of 50 mg/kg/d significantly reduced the increase in body weight induced by CD, a clear sign of an anti-obesity effect.

Though there was a significant difference in body weight between the CD control and normal control group, no significant difference in the quantity of food intake between them was observed. This shows that differences of the diet content do not affect to the amount of food consumed by the animals. The CD group of rats continuously consumed similar quantities of food regardless of the calorie content in the diet. As a result, the calorie intake was significantly higher in the CD group than the normal group of rats. The high-calorie intake was proportional to the increment of body weight, hence resulting in an obese state. There was a significant decrease in calorie intake of the galangin treated group of animals as compared to CD control rats, implicating for the hypophagic property of the galangin.

Significant increase in serum lipids, such as total-cholesterol, LDL and TGs, is typically observed in obese animals and people. In addition, a decrease in the HDL/LDL ratio is also detected in obese human and animal subjects. Thus, alteration of these lipid profiles can be used as an index of obesity. Treatment with galangin caused significant changes in serum biochemical parameters, including a decreased level of total cholesterol, LDL and TGs, but an increased level of HDL-cholesterol. AIP correlates with the size of pro- and anti-atherogenic lipoprotein particles and is known to predict cardiovascular risk. An AIP value of <0.10, 0.11 to 0.20 and >0.21 predicts low, intermediate and high cardiovascular risk (Frohlich & Dobiasova, 2003). There was marked increase in the AIP value of the CD control group of rats compared to normal control rats, accounting for increased cardiovascular risk associated with high-fat diet. Galangin-treated rats showed significant improvement in the AIP value and resulted in low cardiovascular risk. Thus, galangin-produced suppression of high-fat diet induced obesity by modulating lipid metabolism and could also reduce the risk of cardiovascular diseases.

It has been previously reported that weights of epididymal and retroperitoneal adipose tissue deposits were significantly higher in the high-fat diet rats than in the low-fat diet rats. This could be due to an increase in the number and size of adipocytes coupled with increased accumulation of fats in them (Hill et al., 1992). Liver is the central organ for cholesterol, phospholipids and lipoprotein metabolism. In obesity, liver is the receiver of large amounts of fatty acids, which increases its weight and there is a possibility of impairment of normal catabolism of liver lipids leading to consequent accumulation of lipids in the liver (Festi et al., 2004). Consumption of high-fat CD for 6 weeks produced significant increases in liver and PAT weight compared with the consumption of normal diet. Furthermore, the high-fat diet also induced fatty liver with an accumulation of TGs compared with the normal control group. However, CD-fed rats treated with galangin showed significant reduction in the weight of liver, PAT and liver TG contents. The rate of reduction in body weight corresponded to that of the reduction in PAT weight. Thus, anti-obesity effects of the galangin could be linked to its anti-adiposity and anti-fatty liver effects.

Obesity is a principle causative factor for the coexistence of metabolic syndromes in the same individual. It has been reported that obesity may induce systemic oxidative stress and that increased oxidative stress in accumulated fat is associated with dysregulation of adipocytokines and the development of metabolic syndrome (Furukawa et al., 2004). It has been reported that diet-induced obesity in rat models results in increased level of oxidative stress in the liver due to excessive production of reactive oxygen species and/or decreased antioxidant potential (Fardet et al., 2008). A number of studies have also demonstrated that antioxidants may act as a regulator of obesity in mice or rats with high-fat diets (Han et al., 2003). In order to investigate whether oxidative stress was increased in CD-fed rats, we measured lipid peroxidation in liver tissue by estimating the MDA content using the TBARS assay. The high concentration of liver tissue MDA observed in CD control rats was an indication of increased oxidative stress in them. However, the galangin-supplemented animals showed a significant decrease in MDA concentration, thus reducing lipid peroxidation. The ability of the galangin to significantly suppress lipid peroxidation could be due to its previously reported free radical scavenging activity and its ability to enhance antioxidant defensive mechanisms of the body (Russo et al., 2002; Sivakumar et al., 2010).

Conclusions

Thus, we can conclude that galangin present in the ethanol extract of AG rhizomes could be responsible for modulating overweight and obesity by reducing the excess accumulation of body fat due to inhibition of pancreatic lipase activity, alteration of lipid profiles and antioxidant activity. Therefore, galangin can be considered for further development as a therapeutic agent for the treatment of excess weight and obesity.

Declaration of interest

The authors report no declarations of interest.

Acknowledgements

The authors are thankful to the Principal, KLEU’s College of Pharmacy, Belgaum, India, for providing all the necessary facilities to carry out the research work.