Fennel Oil Treatment Mimics the Anti-Depressive and Anxiolytic Effects of Fluoxetine without Altering the Serum Cholesterol Levels in Rats
Fennel Oil Treatment Mimics the Anti-Depressive and Anxiolytic Effects of Fluoxetine without Altering the Serum Cholesterol Levels in Rats
Tahira Perveen1,*, Shaista Emad1, Saara Ahmad2, Zehra Batool1, Sarwat Yousuf1, Sheeza Sheikh1, Sara Qadeer1 and Saida Haider1
1Neurochemistry and Biochemical Neuropharmacology Research Unit, Department of Biochemistry, University of Karachi, Karachi 75270, Pakistan
2Department of Biological and Biomedical Sciences, The Aga Khan University, Karachi, Pakistan
Synthetic antidepressants are effective drugs for the treatment of psychiatric disorders. Along with the effectiveness these drugs are also associated with some side effects. Since ancient times herbs are used as medicinal purposes. One such herb is Fennel (Foeniculum vulgare). Fennel has many efficacious uses. It is a common herb and spice. It is used in many culinary purposes and also it has therapeutic purposes. In the present study antidepressant effects of fennel oil was monitored by comparing it with a synthetic antidepressant drug, fluoxetine. The rats were divided into three groups as control, drug and oil which were respectively treated with water, fluoxetine (0.3 mg/kg) and fennel oil (0.5 ml/day). The treatment was continued for three weeks. Struggling time in forced swim test (FST), number of square crossed in open field test (OFT) and time spent in open arm in elevated plus maze (EPM) was monitored weekly. Repeated administration of fennel oil for 3 weeks showed significant antidepressant- and anxiolytic-like effects in FST and EPM, respectively which were comparable to fluoxetine treated group. A significant increased cholesterol levels were observed in fluoxetine treated rats which was not observed in fennel oil treated rats. Therefore, repeated administration of fennel oil may exert antidepressive- and anxiolytic-like behaviors. These effects were found to be comparable to that of the clinically used synthetic drug, fluoxetine.
Received 22 April 2017
Revised 20 June 2017
Accepted 07 July 2017
Available online 06 December 2017
TP was the Principal Investigator. SE, SA and ZB designed the experiments and wrote the manuscript. SY, SS and SQ conducted the experiments and analyzed the data. SH critically evaluated various versions of the manuscript.
Anxiety, Depression, Fennel oil, Fluoxetine.
* Corresponding author: email@example.com;
0030-9923/2017/0006-2291 $ 9.00/0
Copyright 2017 Zoological Society of Pakistan
The word depression is used in everyday language. Depression with 16% and anxiety with 10% of lifetime prevalence around the world are among the most common psychiatric disorders (). Brain is susceptible to the damaging effects of free radicals resulting in oxidative stress. Hence, oxidative stress has been implicated in the pathogenesis of psychotic illnesses (). Treatment with antioxidant compounds has shown to ameliorate deleterious pathological conditions (). It is suggested that plant-derived antioxidants may provide therapeutic protection by increasing the antioxidant levels and normalizing the damage caused by oxidative stress which further protect against neuronal damage and may result in diminution of depression and anxiety symptoms (; ).
Herbs are used as folk medicines since times. Among many herbs Foeniculum vulgare mill has enduring therapeutic antiquity. F. vulgare mill belongs to Apiaceae family, it is umbelliferous and perennial herb (). It is odoriferous and savory herb with many medical and nutritive uses (). Phytochemical studies on F. vulgare revealed the presence of essential fatty acids, phenolic components, volatile compounds, and secondary metabolites. Most of these phyto-components are present in essential oil (). Plant-derived phenolic compounds have shown multiple functions including reduction potential and act as hydrogen-donating antioxidants and free radical quenchers (, ). The major constituent of essential oil of F. vulgare is trans-anethole (60-90%). Fennel oil also contain other minor constituents such as limonene (0.1–21.5%), (E)-phytol (0.1–6.0%), neophytadiene (0–10.6%), exo-fenchyl acetate (0.3– 3.8%), estragole (0.1–2.5%), and fenchone (0.1–3.1%) (). Approximately 12% of 1,8-cineole, 5% linalool, and 4% α-terpineol have also been reported in fennel oil (). In alternative medicine it is used as a digestive, diuretic, lactagoge and carminative agent (). Pharmacological studies showed antibacterial, antioxidant, antithrombotic, antihepatotoxic, relaxant, analgesic and anti-inflammatory activities in various in vitro and in vivo paradigms (). Antifungal, antiviral, and antiprotozoal activities have also been reported previously (). Some of the publications stated that F. vulgare has chemopreventive, cytoprotective, hypoglycemic, antitumor, and oestrogenic activities (; ; ; ). The essential oil of F. vulgare has been attributed to produce these pharmacological effects (). It is suggested that the synergistic effects of major and minor compounds of essential oil have significant role in various pharmacological activity ().
Previous studies have examined the effects of fennel oil on peripheral system; however, studies regarding the beneficial effects on psychological behaviors are sparse. Previously, antidepressant and anxiolytic effects of fennel oil have been reported from our lab (). This study was designed to compare the effects of repeated administration of fennel oil with conventionally used antidepressant i.e., fluoxetine on depression and anxiety-like behaviors in healthy adult rats. Prolong use of synthetic antidepressants such as specific serotonin reuptake inhibitor (SSRIs) has been associated with metabolic disturbances. Weight gain, increased serum cholesterol levels and increased body mass index have been reported previously due to the long-term use of SSRIs (). Therefore, in this comparative study serum cholesterol levels were also measured following the administration of fennel oil and fluoxetine for three weeks.
Materials and Methods
Animals were purchased from Agha Khan University animal house, Karachi, Pakistan, with an average weight of 200-250 g. To avoid the effect of social interaction, animals were housed individually with ad libitum access to cubes of standard rodent diet (4.47 kcal/g; containing 25% fat, 50% carbohydrate, and 25% protein) and tap water under a 12:12 h light/dark cycle (lights on at 7:00 AM) at controlled room temperature (22±2°C). Twenty four rats were divided into control, drug (fluoxetine) and fennel oil treated groups. Fluoxetine was purchased from Chemical Co. (St. Louis, USA) and fennel oil was purchased from local super market. 0.3 mg/kg of drug and 0.5 ml/day fennel oil () was given orally to the drug treated rats and oil treated groups respectively for three weeks, whereas, controls were treated with tap water for the same period of time. Rats were subjected to forced swim test (FST), open field test (OFT) and elevated plus maze (EPM) test on 7th, 14th and 21st day of treatment to assess the depressogenic and anxiogenic behaviors. All experiments were carried out between 10:00 AM and 5:00 PM in a balanced design to avoid influence of order and time. The experimental procedures were performed in strict accordance with National Institute of Health Guide for Care and Use of Laboratory Animals (Publication No. 85-23, revised 1985). All efforts were made to reduce animal suffering and to minimize the number of animals used in the experiments.
Forced swim test (FST)
The FST is commonly used as standard pharmacological model for evaluating depression-like symptoms in rats (). The dimensions of the apparatus and method used in the present study were same described previously (). Briefly describing when the rats are placed in an inescapable chamber which is filled with water then the development of the state of immobility reflects the cessation of persistent escape directed behavior. In this test the animal’s swimming behavior was monitored which can be defined as movement throughout the swim chamber (glass tank). In the present test immobility time was monitored. Struggling time was calculated by subtracting the immobility time from total time (300 s). The animal considered as immobile when it made no further attempts to escape and only tried to keep its head above the water.
Open field test (OFT)
The apparatus dimensions were same as mentioned by . Rats were allowed to explore an open arena for 5 min. Apparatus consisted of 25 equal squares on the floor and number of squares crossed by each animal was recorded during the allocated time to monitor the exploratory activity.
Elevated plus maze (EPM) test
The dimensions of apparatus and method were same as described previously (). Being the nocturnal animal, rat feels fear from elevated and open area therefore time spent in open arm of EPM was recorded to monitor the anxiety-like behavior. Significant increased time spent in open arm was taken as an index of anxiolytic effect of treatment.
Serum cholesterol estimation
Results are represented as Mean+SD. Data of behavioral testing were analyzed by two-way ANOVA with repeated measure design with Bonferroni test to compare the different groups. One-way ANOVA was used to analyze serum cholesterol levels followed by Tukey’s post-hoc test. p>0.05 was considered to be non-significant.
The comparative effects of standard antidepressant drug and fennel oil administration in FST, OFT and EPM test are shown in . Data for FST, which was analyzed by two-way ANOVA with repeated measure design, revealed significant effect of treatment [F(2,21)=23.3, p<0.01], weeks [F(2,42)=7.58, p<0.01] and significant interactions between treatment × weeks [F(4,42)=878.39, p<0.01]. In the present study rats were subjected to FST weekly during the treatment. It was observed that the rats treated with water showed gradual decrease in struggling time which was significantly reduced on third week as compared to that of first week (p<0.01). This pattern of struggling time was not observed in drug treated rats (p>0.05) because of its anti-depressant effects. The same pattern of drug was also observed in fennel oil treated rats. When the fennel oil treated rats were compared with controls, a significant increase in struggling time was observed indicating the potential anti-depressant like effects of fennel oil.
Data for OFT was also monitored by two-way ANOVA with repeated measure design. There was significant effect of treatment [F(2,21)=21.67, p<0.01], weeks [F(2,42)=59.75, p<0.01] and significant interaction between treatment × weeks [F(4,42)=6.33, p<0.01]. Post-hoc analysis by Bonferroni test revealed a significant decrease in exploratory activity in water treated rats with weekly exposure to OFT. Second and third week activity in these rats were significantly lower as compared to that of first week activity (p<0.01). Drug treated animals showed significantly increased activity as compared to that of controls (p<0.01) in all three weeks. But the gradual decrease in exploratory activity on second and third week was also observed in standard drug treated animals as compared to that of first week activity (p<0.01). Rats treated with fennel oil also showed significantly increased OFT activity during second and third week as compared to that of controls (p<0.01). Whereas in contrast to controls and drug treated animals, the fennel oil treated rats showed persistent exploratory activity in all three weeks showing the anti-depressant potential of fennel oil.
Analysis of data for EPM by two-way ANOVA with repeated measure design revealed significant effect of treatment [F(2,21)=111.4, p<0.01], weeks [F(2,42)=6.99, p<0.01] and significant interactions between treatment × weeks [F(4,42)=8.53, p<0.01]. Rats were exposed to the EPM weekly during the treatment in this study. The rats treated with water showed gradual decrease in time spent in open arm which was significantly reduced on second and third week as compared to the activity observed in first week (p<0.01). Standard drug treated (p>0.05) and fennel oil (p>0.05) treated rats did not exhibit reduced time spent in open on repeated exposure. Moreover, standard drug as well as fennel oil administration showed significant increased time spent in open arm as compared to that of controls on weekly exposure demonstrating the anti-anxiety potential of fennel oil administration.
The serum cholesterol levels were also measured following the administration of synthetic drug and fennel oil. One-way ANOVA revealed significant effects of treatment [F(2,21)=7.164, p<0.01]. Three weeks administration of drug significantly increased cholesterol level as compared to controls (p<0.01) whereas, this increase in cholesterol levels were not observed in fennel oil treated rats ().
Depression is the most common widespread forms of psychopathology, characterized by variety of symptoms like hopelessness, relationship problems, fatigue, lack of energy, inability to experience happiness in life and many other dramatic changes are observed in depressed individual that vary with the severity as well. In medicinal science the role of certain food and food components have found to have beneficial physiological and psychological effects ().
It is previously reported that depression slow downs the normal activities of individuals (). For this purpose we used forced swim test to measure the antidepressant activity following fennel oil administration on animal behavior. The results of our present study showed that the drug (fluoxetine) increased the struggling time of animal in all 3 weeks and this increase in struggling time was also observed in rats administrated with fennel oil as compared to that of controls. This antidepressant effects following the administration of standard antidepressant and fennel oil were also observed in OFT paradigm. Another parameter i.e., EPM test was used to measure the anxiety levels in rats. Results of our present study showed that the time spent in open arm was significantly increased by drug (fluoxetine) as well as by fennel oil in rats suggested the anxiolytic effects of drug and fennel oil. However, the observed effects of antidepressant and anxiolytics were more prominent in fennel oil treated rats. These results are consistent with previously suggested effects of fennel oil from our lab (). Extensive studies carried out to understand the relationship of oxidative stress and psychiatric disorders pave the way to suggest the role of free radicals in the pathogenesis of depression and anxiety (). The current studies suggest that the interrelationship between oxidative stress and psychiatric disorders may be due to oxidative stress-induced neuroinflammation, dysfunction of mitochondria, impaired neuroplasticity and deficits of signal transduction (; ). The antioxidant effects of antidepressant and anxiolytics have demonstrated in various clinical and preclinical trials. The compelling evidence suggests that these drugs decrease oxidative stress by scavenging free radicals and inhibiting the oxidative pathway which may lead to the attenuation of depressive or anxiogenic symptoms (; ). The major constituents of essential oil of F. vulgare include anethole, fenchone, estragole and limonene. Anethole has shown anticarcinogenic and anti-inflammatory effects (). Other pharmacological activities of anethole include oestrogenic action, insecticide, anesthetic and antithrombotic activities (; ). Studies have shown antioxidant property of anethole and its derivatives by inhibiting the lipid peroxidation. investigated the antioxidant and antimicrobial activity of fennel oil and they found significant free radical scavenging and appreciable antioxidant activities.
To treat the depression, increased availability of serotonin (5-hydroxytryptamine; 5-HT) at the post-synaptic receptors is the main pharmacological target of antidepressants (). Inhibition of 5-HT reuptake or decreasing the activity of catabolic enzyme is involved in reducing the symptoms of depression. In a study conducted by , anethole was reported to particularly inhibit the activity of monoamine oxidase B (MAO-B) enzyme. The increased catabolism of monoamines by MAO is involved in increased generation of free radicals leading to increase in oxidative stress which may further worsen the psychiatric illnesses. Increased oxidative stress has been shown previously due to increased catabolism of 5-HT by MAO-B (). Inhibition of MAO-B by anethole may also account for its antioxidative effects which may have the potential to alleviate the psychiatric disorders. Therefore, being the antioxidant and MAO-B inhibitor, anethole (main component of fennel oil) may be involved in decreasing the depressogenic and anxiogenic behaviors by increasing the availability of 5-HT towards its receptors in the synapse.
Although SSRIs are the most widely prescribed drug for the treatment of depression but these medications are reported to be associated with many side effects. Such side effects include weight gain, drugs interaction and sexual dysfunction. Increased serum cholesterol levels have been observed in patients using SSRIs for a longer period of time (). Use of SSRIs upregulated the genes involve in the biosynthesis of cholesterol and fatty acids (). It has been reported that elevated cholesterol levels results in reduced response to fluoxetine treatment (). In the present study, three weeks of fluoxetine administration induced increase in serum cholesterol level which was not observed in fennel oil treated rats. It is reported previously that fennel oil decreases cholesterol along with decrease in peroxidative damage (), suppresses blood lipid level () inhibits fat absorption () and enhances beta oxidation (). Thus, it can be suggested that the potential antidepressant and anxiolytic effects of fennel oil observed in this study may be attributed to its antioxidant property ().
In the present study, at the first time, we suggest that depressive- and anxiogenic-behaviors can be reversed by the repeated administration of fennel oil which showed efficacy comparable to that of the clinically used synthetic drug, fluoxetine. Moreover, repeated administration of fennel oil is not associated with the metabolic disturbance as evident by normal serum cholesterol levels. Further investigations are needed to explore these anti-psychiatric effects and the possible underlying biochemical mechanism in animal model of depression and anxiety before recommending the use of fennel oil for the treatment of psychiatric disorders.
The authors wish to acknowledge the University of Karachi, Karachi, Pakistan for providing the funds for this study.
Statement of conflict of interest
Authors declare no conflict of interest
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