Abstract
The aim of the present work is to evaluate the putative antidepressant-like effects of hydroethanolic and dichloromethanic extracts from the aerial parts of Sonchus oleraceus (Family Asteraceae) on the performance of male mice in the forced swimming test (FST) and tail suspension test (TST) models predictive of depression. The hydroethanolic and dichloromethanic extracts, both in doses of 30, 100, and 300 mg/kg, were orally administered 1 hour before carrying out the FST or the TST. The immobility time in both the FST and the TST was significantly reduced by acute oral treatment with the extracts (dose range, 100–300 mg/kg), without accompanying changes in ambulation, as assessed in an open-field test. This excluded the possibility that the effect of the extracts is due to an activation of locomotion. The efficacy of the extracts was found to be comparable to that of amitriptyline (10 mg/kg, p.o.). The present study provides evidence for an antidepressant-like effect of the active principle(s) present in the extracts of S. oleraceus in mice. Therefore, a standardized S. oleraceus extract or its purified constituents could be of potential interest for the treatment of depressive disorders.
Introduction
D
Sonchus oleraceus L. (Family Asteraceae) is edible to humans as a leaf vegetable and is frequently consumed in Mediterranean countries, 4 –8 Australia, 9 and New Zealand, particularly by the native Maori. 10 South of Minas Gerais in Brazil (southeastern Brazil), S. oleraceus, known as “serralha,” is very important in the diets of rural people, especially seasonally, and provides cash income to the harvester and relatively inexpensive vegetables to the community.
In traditional Brazilian medicine, the aerial parts of S. oleraceus are used mostly in an infusion or decoction and are administered orally for treating pain and headaches and as a general tonic. 11 –13
Based on the traditional claims surrounding S. oleraceus and the lack of scientific studies of its potential pharmacological properties, the objective of this study was to examine the antidepressant-like effect of the extract of S. oleraceus in the mouse tail suspension test (TST) and forced swimming test (FST), predictive models of antidepressant activity. 14,15
Materials and Methods
Animals
Adult male Swiss mice (weighing 22–30 g), obtained from the Central Animal Facility of the Federal University of Alfenas–MG, Alfenas, MG, Brazil, were housed under controlled light (12:12-hour light–dark cycle; lights on at 06:00 a.m.) and temperature conditions (23 ± 1°C), with access to water and food ad libitum. The animals were allowed to acclimate to the housing facilities for at least 1 week before the experiments began. Behavioral studies were carried out in a quiet room between 09:00 and 11:00 a.m. All experiments were conducted in accordance with the Declaration of Helsinki on the welfare of experimental animals and with the approval of the Ethics Committee of the Federal University of Alfenas.
Preparation of plant extracts and reference drugs
The air-dried and powdered aerial parts of S. oleraceus (150 g) was extracted by percolation with 50% ethanol (2 L) followed by dichloromethane (2 L) at room temperature to obtain the S. oleraceus hydroethanolic extract (SoHE) and dichloromethanic extract (SoDE), respectively. The SoHE was concentrated in a rotary evaporator and then dried with a spray dryer (Mini Spray Dryer B-290, BüCHI Labortechnik AG, Flawil, Switzerland). The solvent of SoDE was removed under reduced pressure. The yields of SoHE and SoDE were 8.8% and 3.6%, respectively. The residues were used for determining bioactivity.
Animals were treated with SoHE or SoDE (30, 100, and 300 mg/kg; n = 8 animals per group) or with vehicle (1% sodium carboxymethylcellulose suspension in distilled water) given by perorally 1 hour before the experiments. Amitriptyline (10 mg/kg) in vehicle was used as a reference drug. The tested drugs were administered orally.
FST
Mice were individually placed in a glass cylinder (20 cm in height, 14 cm in diameter) filled with water to a depth of 12 cm (28 ± 0.5°C). All animals were forced to swim for 6 minutes, and the duration of immobility was observed and measured during the final 4-minute interval of the test. 15 The procedure was a modification of the method described by Porsolt et al. 16 All test swim sessions were recorded by a video camera positioned directly above the cylinder. The immobility period was regarded as the time spent by the mouse floating in the water without struggling and making only those movements necessary to keep its head above the water.
TST
The total duration of immobility induced by tail suspension was measured according to a previously method described. 14 In brief, mice were suspended 50 cm above the floor by adhesive tape placed approximately 1 cm from the tip of the tail. Immobility time was recorded during a 6-minute period. 17
Locomotor activity test
To assess the possible effects of SoHE and SoDE on locomotor activity, mice were evaluated in the open-field paradigm as previously described. 18 Mice were individually placed in a box (60 × 60 × 50 cm) with the floor divided into 16 squares. The number of squares crossed with the four paws was registered during a period of 5 minutes.
Statistical analysis
The data obtained were analyzed using the GraphPad Prism software program version 4.0 (GraphPad Software, San Diego, CA, USA) and expressed as mean ± SEM values. Statistically significant differences between groups were calculated by the application of an analysis of variance followed by the Newman-Keuls test. Values of P < .05 were considered significant.
Results and Discussion
In the present study, SoHE and SoDE produced a significant antidepressant-like effect in mice as assessed by both the FST and the TST. Furthermore, the effect of the extracts of S. oleraceus in the FST and TST was similar to the effect produced by the oral administration of amitriptyline, used as a positive control. Both the FST and TST are used routinely to characterize antidepressant activity of a wide variety of test compounds. 14 –21
In the FST, mice are forced to swim in a restricted space from which they cannot escape and are induced to assume a characteristic behavior of immobility. This behavior reflects a state of helplessness or despair, which can serve as a valuable test for screening antidepressant drugs. The immobility in this test reflected either a failure of persistence in escape-directed behavior (i.e., behavioral despair) or the development of passive behavior that disengages the animal from active forms of coping with stressful stimuli, and this behavior is sensitive for antidepressants. 15,16 The TST also induces a state of immobility in animals, in a fashion similar to that of the FST. 14 Similar to behavioral despair in FST, when the animal is suspended from the tail it immediately engages in several “agitation- or escape-like” behaviors, followed by increasing bouts of immobility that are reversed by antidepressant drugs. TST is a relatively rapid and sensitive test to detect the short-term antidepressant effects. 14,22 The administration of SoHE or SoDE significantly reduces the time of immobility in both FST (Fig. 1; F 7,63 = 9.502; P < .001) and TST (Fig. 1; F 7,63 = 10.16; P < .001). The results from the FST and the TST indicate that at doses 100 and 300 mg/kg, SoHE and SoDE significantly reduced the duration of immobility compared with vehicle control. In this regard, the effect of the two doses was indistinguishable as they produced a comparable reduction of immobility time.
Effect of treatment with SoHE or standard drug (amitriptylin), given orally, on the immobility of mice in the (
The antidepressant-like effect of S. oleraceus extracts seems not to be associated with any motor effects (F 7,63 = 1.621; P = .148) because they had no effect on locomotor activity of mice compared with the control (Fig. 2). This indicates that increased motor activity was not involved in the antidepressant-like action of the extracts in either the FST or the TST and confirms that the antidepressant-like effect is specific.
Effect of treatment with SoHE or SoDE or standard drug (amitriptylin), given orally, on locomotor activity evaluated in the open field test. Data are mean ± SE values of the number of squares crossed in 5 minutes of locomotor activity test (n = 8 animals per group).
In summary, our data indicate an antidepressant-like effect of SoHE and SoDE because the reduction of immobility time elicited by its administration cannot be attributable to any psychostimulant effect.
Previous phytochemical investigation of S. oleraceus resulted in the isolation of flavonoids (luteolin, apigenin, kaempferol, quercetin, and luteolin 7-glucoside) 23 and terpenes, such as sonchucides A–D, glucozaluzamin, macroliniside, crepidiaside, and picriside. 24 However, none of these chemical components present in S. oleraceus had its potential behavioral effect evaluated, excepting quercetin. It has been demonstrated that quercetin decrease the immobility time in diabetic mice subjected to the FST. 21 In addition, quercetin inhibits monoamine oxidase and catechol-O-methytransferase enzymes, which are the key enzymes responsible for metabolism of catecholamines in the brain. 25 The rationale to evaluate the antidepressant effect of the extracts was supported by popular description of S. oleraceus use as a general tonic, 13 suggesting a central effect. Furthermore, chemical analysis of the extract will be conducted to isolate and characterize the active principles responsible for the observed effects.
Use of S. oleraceus is prevalent, especially in rural areas. 11 –13 In order to support appropriate and safe use of such medicines, it is essential to collect pharmacological evidence for the action and the underlying mechanisms of these extracts. Although the precise mechanisms by which S. oleraceus extracts produced antidepressant-like activity are not completely understood, they may have potential therapeutic value for the management of depressive disorders.
Footnotes
Acknowledgments
This work was supported by FAPEMIG, CNPq, and CAPES. AG.-P. received a research fellowship from CNPq; F.C.V. received postgraduate scholarships from CAPES.
Author Disclosure Statement
No competing financial interests exist.