Saffron (Crocus sativus L.): As an Antidepressant

Abstract

Saffron, Crocus sativus (Iridaceae), is a perennial herb, which earned its popularity as both medicine and spice. It is an inhabitant of different mountainous regions of Asia Minor to Greece, Western Asia, Egypt, and India. The benefits of saffron as an antidepressant are well-documented. Almost 150 volatile and nonvolatile compounds are obtained from the chemical analysis of this plant. Fewer than 50 constituents elucidated and identified so far showed phytochemical characteristics. The major bioactive compounds identified are safranal, crocin, and picrocrocin, which are responsible for its aroma as well as its bitter taste. This review is an attempt to encompass the methods of analysis and pharmacodynamic and pharmacokinetic properties of saffron followed by its efficacious and safe potential.

INTRODUCTION

Crocus sativus L. belonging to Iridaceae family, commonly known as saffron, is a perennial herb widely cultivated in Iran and other countries, such as India and Greece. Commercial saffron is a spice comprises of dried red stigma with a small portion of the yellowish style attached to the flower of Crocus sativus L., in Chinese its known as Fan-Hong-Hua. From decades saffron was used in traditional Chinese medicines for its expectorant, aphrodisiac, and antispasmodic effects.[1] Saffron can be planted from an altitude of sea level to almost 2000 m, but it is more preferably adapted to hill sides and mountain valleys, ranging in altitudes between 600 and 1700 m.[2] Also, this plant can be cultivated in a dry and infertile place where there is an extreme water shortage in summer. The origin of the word saffron is the French term “Safran,” which was derived from the Latin word “safranum” and yellowish in color, phytochemical analysis have revealed that the color is mainly because of the degraded carotenoid compounds, crocin and crocetin.[3] This is one of the valuable herb in the world because it requires properly plucked stigma from the flowers. Variation and high quality of final products are due to the harvest process involved.[4]

Saffron has been famous as both medicine and spice in some cultures. The stigma of saffron has been used as a medicine over 3600 years ago.[5] Saffron was used in various opioid preparations for pain relief (sixteenth to nineteenth centuries).[6] Also, saffron has been used in coloring tunics in the region of Spain and by the Babylonian culture around 2400 BC.[7] This expensive spice can be found in different mountainous regions of Asia Minor to Greece, Western Asia, Egypt, or Kashmir.[7] Each of the flowers has three red-colored stigma, and one stigma of saffron weighs approximately 2 mg. Approximately 1 kg of this valuable spice is made from 150,000 flowers that must be carefully picked.[8]

One of the most established findings regarding the benefits of saffron is its antidepressant activity. There are clinical trials conducted, evaluating the efficacy of saffron in mild-to-moderate depression. The studies reported that saffron was more effective than placebo and at least equivalent to the therapeutic doses of imipramine and fluoxetine. One of the top five most predominant diseases worldwide is depression.[1] Depression can affect the quality of life of someone because of the facts that it can cause a headache, difficulty in thinking, and loss of interest.

Recently, approximately 150 volatile and nonvolatile compounds have been detected from the chemical analysis of C. sativus L. However, fewer than 50 constituents have been identified so far as the phytochemicals of C. sativus L. The major constituents of saffron are crocin, picrocrocin, and safranal.[9] The phytochemical agents in saffron are responsible for many pharmacological actions in the body. The phytochemical research has found that the color of saffron is mainly because of the degraded compound of carotenoids, which are crocin and crocetin.[3] Many clinical studies focused more on the antidepressant effects of saffron.

PHYTOCHEMICALS OF SAFFRON (CROCUS SATIVUS L.)

Saffron has intensive fragrant with slightly bitter taste and produces a bright yellow-orange solution when soaked in warm water.[10] Its stigma was shown to contain carbohydrates, minerals, mucilage, vitamins B1 and B2, and pigments. Crocin, crocetin, carotene, lycopene, and gigantic[11] anthocyanin, alpha-carotene, beta-carotene, and zeaxanthin are the oil-soluble pigments that can be found in the stigma.[12] The color of saffron is the result of degradation of carotenoid compounds named crocin. According to Wallis,[13] crocin constituent of saffron, which highly related to its intense color, is the natural water-soluble carotenoid. Crocetin in C. sativus L. is a water-insoluble conjugated polyene with two carboxylic acid residues.[14] Crocetin esters or also known as crocin, which is hydrophilic and water soluble, are usually found in the saffron extract in which α-crocin, the glycosyl ester of crocetin, is the main contributor for the significant bright yellow-orange color of saffron.[15] Saffron has a unique flavor that is related mainly to the glycoside picrocrocin.[16] Picrocrocin is responsible for the unique flavor of C. sativus L., which is found to be stable in fresh raw saffron and broken down when heated to release.[17] Specific essential oils of the flower contribute to the sweet fragrance of saffron. The principal constituent of total essential oil of C. sativus L., safranal is a carboxaldehyde volatile compound formed by deglucosylation of picrocrocin.[16] Saffron is widely used in food processing industry as colorant and flavoring agents. The essential oils also comprised several terpene aldehydes, ketones, and terpene derivatives (pinene and cineol).[10] The secondary metabolites present in the petals of C. sativus L. are tannins, anthocyanins, and flavonoids, which include rutin, quercetin, luteolin, hesperidin, and bioflavonoids. Those compounds have been reported to have many pharmacological activities, including anti-inflammatory,[18] antinociceptive,[19] and blood pressure lowering effects.[20]

All trans and cis isomers of crocin reflect the characteristics of carotenoids by having ultraviolet (UV)-Vis spectra highlighting double peaks between 400 and 500 nm in the visible region.[21] Safranal is responsible for aroma, whereas its precursor picrocrocin, which is a monoterpene glycoside, is accountable for the bitter taste of saffron.[21] The pattern of UV absorption of picrocrocin can be seen with a broad band at 250 nm with the maximum absorption of 254 nm, reflecting the presence of an α,β-unsaturated cycloaldehyde functional group in its molecular structure.[22] Picrocrocin underwent enzymatic or chemical hydrolysis to produce glucose and aglycone and then yielded safranal via dehydration during drying process.[22] Active components that indicate the quality and pharmacological studies of saffron are the enzymatic oxidative metabolites of glucoside derivative of zeaxanthin, which include cis- and trans-crocin, crocetin, picrocrocin, and safranal.[23] The main phytochemicals that may contribute to the biological activities of C. sativus L. are crocin, picrocrocin, and safranal.

Crocin and saffron extract had been revealed to prevent memory and spatial learning impairment because of chronic-induced stress.[24] Prophylactic property of saffron against memory deficiency had been proposed to occur as the result of the correlation between the antioxidant activity of saffron and the impairment because of oxidative stress.[21] Akhondzadeh et al.,[25] in 2004, had shown saffron extract to be equally efficient to imipramine during double-blind and randomized trial conducted over 6 weeks. The dried saffron petal also had been revealed to be effective in mild-to-moderate depression based on 6 weeks of double-blind randomized clinical trials.[26] Crocin (30 mg/day), the main antioxidant constituent of saffron stigmas, was shown to amplify the effects of selective serotonin reuptake inhibitors in treating patients with mild-to-moderate depression with the absence of substantial side effects based on the observation of 4 weeks of randomized, double-blind, prospective, placebo-controlled pilot clinical trial with 40 patients of major depressive disorder.[27] Scientifically proven traditional uses of saffron as antidepressant suggested that crocin exerts its antidepressant effect by increasing cAMP response element binding protein, brain-derived neurotrophic factor and nerve growth factor inducible levels in rat hippocampus.[28] Subacute administration of crocin was indicated to cause antidepressant effects in the rat. When saffron capsules administered to patients with a prior history of percutaneous coronary intervention who had depression, it was found to be equally effective as fluoxetine.[29] In one of the 6-week pilot double-blind, randomized trial, the petal of the C. sativus L. was found to be equally valid with the stigma in the treatment of depressed outpatients.[30] The petal constituent of C. sativus L., kaempferol, was revealed to have antidepressant effect when evaluated using forced swimming test in mice and rats.[31] It has been perceived that current findings of biological activities of C. sativus L., particularly its main constituent crocin, supported its medicinal used in traditional practices.

PHARMACOLOGICAL ACTION OF SAFFRON (CROCUS SATIVUS L.)

According to Murray and Lopez,[32] depressive disorder is one of the most prevalent psychiatric diseases and has been estimated to affect up to 21% of the world’s population. Majority of patients are often reluctant to take synthetic antidepressant drugs in their appropriate doses because of the anticipated side effects such as the inability to drive a car, dry mouth, constipation, and libido.[32] Hence, plant extracts are some of the most attractive sources of new drugs and have been shown to produce a better result with low side effects in the treatment of depression.[1]

C. sativus L. or commonly known as saffron is an expensive traditional spice. Its active components have shown several useful pharmacological effects such as anticonvulsant, antidepressant, anti-inflammatory, antitumor, radical scavenger effects, and learning and memory-improving effects.[33] Akhondzadeh et al.[30] stated that saffron had been widely used to relieve stomachaches, ease the pain of kidney stones, and treat depression in Persian traditional medicine.

According to Srivastava et al.,[34] two active ingredients of C. sativus L., which are crocin and safranal, have shown antidepressant effects. This is in accordance to the study carried out by Hosseinzadeh et al.,[35] regarding the effects of aqueous and ethanolic extracts of C. sativus L. stigma and their constituents, safranal and crocin, for the antidepressant activity by using forced swimming test in mice. The result obtained shows that the aqueous and ethanolic extracts of stigma (0.2–0.8 g/kg), safranal (0.15–0.5 mL/kg), and crocin (50–600 mg/kg) could reduce the immobility time of the mice and the swimming time increased greatly. It is suggested that the inhabitation of dopamine, norepinephrine, and serotonin reuptake by crocin and safranal might be the possible mechanism of antidepressive effect of saffron.[30] Akhondzadeh et al.[25] also conducted a randomized trial to compare the efficacy of saffron with imipramine in the treatment of mild-to-moderate depression. In another study, patients were assigned to receive capsule saffron (30 mg/day) three times a day (tds) or capsule imipramine (100 mg/day tds) for a 6-week research.[25] The result showed that saffron at this dose was found to be effective comparable to imipramine in the treatment of mild-to-moderate depression.

Because the stigma of C. sativus L. (saffron) is very expensive, the researchers use the leaves of this plant as it is cheaper and possesses antidepressant effect. In a double-blind, placebo-controlled, and randomized trial performed by Srivastava et al.,[34] 40 patients were randomly assigned to receive a capsule of the petal of C. sativus L. at dose of (30 mg/day) twice daily (bd) and capsule of placebo twice daily (bd) for a 6-week study. At 6 weeks, the petal of C. sativus L. produced a significantly better outcome on Hamilton Depression Rating Scale than placebo. Hence, it is proven that the petal of C. sativus L. does give antidepressant effect. Karimi et al.[36] also conducted a study regarding the effects of aqueous and ethanolic extracts of the stigma and petal of C. sativus L. for the antidepressant activity according to the forced swimming test in mice. It was shown that both stigma and petal reduced immobility time of the mice. In a double-blind and randomized trial performed by Akhondzadeh Basti et al.,[26] patients were randomly assigned to receive a capsule of petal of C. sativus L. (15 mg bid) (Group 1) and fluoxetine (10 mg bid) (Group 2) for an 8-week study. At the end of the trial, the petal of C. sativus L. was found to be effective as similar to fluoxetine in the treatment of mild-to-moderate depression. In study by Melnyk et al. (2010), kaempferol (the active constituent in saffron petals) at doses of 100 and 200 mg/kg in mice and 50 mg/kg in rat reduces depressive symptoms similar to fluoxetine.[37] Wang et al.[1] also conducted research regarding the antidepressant properties of stigmas and corms of C. sativus L. The corms of C. sativus L. were fractionated based on polarity and yielded petroleum ether fraction and dichloromethane fraction. At doses of 150, 300, and 600 mg/kg, it showed significant antidepressant-like activities as the immobility time in the forced swimming test and tail suspending test was significantly reduced by these two fractions.

Hausenblas et al.[38] stated that, similar to antidepressants, saffron may exert its antidepressant effect by modulating the levels of certain chemicals in the brain, including serotonin (a mood-elevating neurotransmitter). Although it has been proposed that saffron increases serotonin levels in the brain, the exact mechanism of action for this is unknown. More specifically, a saffron extract might inhibit serotonin reuptake in synapses. Inhibiting synaptic serotonin reuptake keeps serotonin in the brain longer, thereby enhancing its positive effects while combating depression.

METHOD OF ANALYSIS OF SAFFRON (CROCUS SATIVUS L.)

Several analytical methods have been developed for the systematic separation and quantification of saffron (C. sativus L.) metabolites.[39] Several methodologies have been reported using different analytical tools to analyze the bioactive constituents of saffron, that is, picrocrocin, safranal, and crocin.[39,40,41,42,43] UV-vis spectrometry method is recommended by the International Standardization Organization to characterize the quality of saffron. The technique has been used for quality and stability studies of saffron, whereby the process is considered to be appropriate for recognizing the taste, color, and flavor of the spice (ISO/TS 3632, 2003). However, this method is not suitable for the identification and quantification of each component of saffron extract. This is because the technique is not specific and cannot adequately separate. Hence, because of mentioned reasons, the advanced stationary phases of analytical and preparative methods have been developed such as high-performance liquid chromatography (HPLC), gel column chromatography, thin-layer chromatography, multilayer coil counter current chromatography with silica gel, aluminum oxide, and Sephadex LH-20.[41,42,44,45]

Tarantilis et al.[39] and Tarantilis and Polissiou[43] in their studies reported other analytical methods such as reverse-phase high-performance liquid chromatography (RP-HPLC) coupled together with mass spectrometry and photodiode array detector, and for the detection of volatile compounds, gas chromatography with mass spectrometer (MS).

Most of the studies conducted have been focused on the analytical determination of the structure of crocin. However, the methods to isolate high-purity crocin have not been established.[45,46] To obtain adequately pure crocin, the compound is first separated by chromatography on Sephadex LH-20 and then by preparative HPLC.[42] Through this method, crocin can only maximally be separated to seven fractions. The method also implies repeated procedures, which are time-consuming, before purified crocin can be isolated. A simple two-step method in which 20 fractions of crocin are separated simultaneously in the first step, and then high-purity pigment is obtained in a subsequent step has been reported by Zhang et al.[46] The purity of the crocin compound was reported to be above 95%, whereby the methods used two-step, low-pressure liquid chromatography without preparative HPLC. Tarantilis and Polissiou[43] reported that isolation method namely micro-simultaneous steam distillation-solvent extraction and vacuum head space were more suitable to isolate the aroma components of saffron as compared to standard distillation method. Another method for the separation of crocin reported was crystallization, whereby the amount of obtained crocin from the first crystallization step was 17% of the stigma powder, but its purity was approximately 85%. The purity increased to more than 97% after a second crystallization step was performed. Therefore, the total amount of crocin obtained is 10% from the initial stigma powder of saffron.[45]

PHARMACOKINETIC ASPECTS OF CROCIN AND CROCETIN

Other than the investigation of the biological activities of crocetin and crocin, it is also important to determine the pharmacokinetic aspects of the compounds such as its absorption, distribution, metabolism, and excretion in the body. Until now, most of the studies were carried out using in vitro and in vivo animal model, which mainly focuses on the absorption and metabolism parameters. Also, the review of the pharmacokinetic profile of those compounds in human body remains inadequate. A study was conducted by Umigai et al.[47] on 10 healthy human volunteers with a single dose of crocetin orally administered at three doses (7.5, 15, and 22.5 mg) in the 1-week interval to investigate the pharmacokinetic profile of plasma crocetin by using RP-HPLC. They reported that crocetin was rapidly absorbed and detected in the plasma within 1h and reached a peak of mean maximum plasma concentration, C_max (100.9–279.7 ng/ml) around 4–4.8 h. The C_max value was also reported to be increasing in a dose-dependent manner. Besides, the mean elimination half-life of crocetin, T_1/2, in human plasma was also ranging from 6.1 to 7.5 h.[47]

In pharmacokinetic study, one of the factors affecting the bioavailability of a compound is its solubility and absorption through the gastrointestinal tract. The research carried out by Xi et al.[48] using HPLC observed that crocin remained undetected in the serum of tested rats, regardless of gender, following single or repeated doses of oral administration. However, its hydrolysis product, crocetin, was found in low concentration in the serum. Crocin also was excreted mainly in feces. Besides, following repeated oral doses of crocin, no accumulation of crocetin was found in the serum.[48] This suggests that crocin is hydrolyzed in the intestine into crocetin before being absorbed into the bloodstream following oral administration. In detail, on the basis of in vitro study, crocin was reported to get hydrolyzed into deglycosylated trans-crocetin and subsequently, absorbed by passive transcellular diffusion to a high extent within short time interval through intestinal cells.[49]

However, a recent study by Zhang et al.[50] showed that orally administered crocin could be absorbed through gastrointestinal tract with poorer bioavailability as compared to its metabolite, crocetin, using ultra-performance liquid chromatography and mass spectroscopy. Interestingly, orally administered crocin showed higher bioavailability of crocetin in rat plasma as compared to orally administered crocetin itself in equivalent molar dose. This may be due to high lipophilicity, which renders lower aqueous solubility of crocetin in the gastrointestinal tract.[50] This means less amount of crocetin compound can penetrate through the intestinal tract because of aqueous surroundings in the intestinal lumen. Moreover, as suggested from the same study, the absorption of crocetin was saturated following an increased dose of oral administration.[50] Besides, crocetin was also suggested to be serving as a substrate for efflux pumps, P-glycoprotein, when studied using CaCO₂ cell.[49] These may support the reasons that repeated oral doses of crocin do not tend to accumulate the plasma crocetin concentration.

Also, to exert its pharmacological activity as an antidepressant, the compound should be able to cross the blood–brain barrier (BBB). In the study by Lautenschläger et al.[49] using in vitro models of porcine brain capillary endothelial cells and blood–cerebrospinal fluid barrier, it was observed that the penetration across BBB occurs at a quite slow rate with a constant velocity.

The exact mechanism for distribution of crocetin in blood remains unknown, yet it was thought that crocetin distributed in blood by strongly binding to the plasma albumin through mainly occupying the free fatty acid binding site. While another proposed possibility of crocetin distribution in blood is through plasma lipoprotein transport method.[51] However, a more recent study by Kanakis et al.[52] stated that the interaction of crocetin with human serum albumin showed a weak ligand–protein interaction. So, the less bound ligand to the plasma protein tends to get easily distributed, suggesting that crocetin is well distributed into the body tissues.[47] The latter concept is accepted because strongly bound ligand to the plasma protein will cause the compound to have less tendency to dissociate and distribute into the target body tissues to show its pharmacological activities.

In the aspect of metabolism, crocetin was reported to be in intact (free) as well as conjugated forms in the plasma of the tested rat. The reported conjugated forms, crocetin diglucuronide and crocetin monoglucuronide, were formed by undergoing glucuronidation process. This was due to the partial metabolism of orally administered crocetin, which occurred in the intestinal mucosa before or during absorption or both and also in the liver of the tested mice.[53] As stated before, crocin was found to be excreted largely through feces. However, to the best of our knowledge, no literature was found to investigate the major route of excretion for crocetin.

SAFETY AND TOXICITY OF SAFFRON (CROCUS SATIVUS L.)

According to Bostan et al.,[54] generally, the therapeutic doses of saffron exhibited no significant toxicity in both clinical and experimental investigations. In double-blind, placebo-controlled study by Ayatollahi et al.,[55] the result showed that on saffron tablet (200 and 400 mg/day) treatment for 1 week, no adverse effect as coagulation was reported. The safety of saffron and crocin in patients with schizophrenia was investigated as well by Mousavi et al. (2015) in a clinical trial.[56] The dosage of 15 mg twice daily (bd) of saffron and crocin reported no toxic effects on kidney, liver, thyroid, and hematologic system.[56]

As a herb supplement, it is also important to know whether it can be used safely in pregnancy. Teratogenicity test has been conducted on more than 4000 chemical substances, and results revealed that 65% were nonteratogenic.[57] Also, the results showed that approximately 7% in more than one species and 18% in most species were a teratogen.

Hosseini et al.[58] tested teratogenicity of aqueous extract of saffron with different doses of 0.8%, 0.4%, and 0.2% in laboratory bred strain of albino mice. The study reported morphological abnormalities such as reduction of tail length, biparietal diameter, mean fetal weight, and placental weight and diameter in gestational period. In addition, increasing mortality rate was reported as well. Saffron extracts elevated the number of a resorbed fetuses of the tested group relative to control group in dose-dependent pattern.

To support the fact that saffron may have teratogenic effect, phytochemicals in saffron, which are crocin given intraperitoneal (IP) at dose of (200 mg/kg and 600 mg/kg) and safranal (0.075 mL/kg and 0.225 mL/kg, IP), disrupted skeleton formation in mice. Other than that, crocetin, another phytochemical of saffron was demonstrated in frog (Xenopus) embryos by American researchers, and it was found that the extract of 10, 25, 50, 100, and 200 µM decreased its head-to-tail length and eye diameters.

According to Ajam et al.,[59] the abortion rate was significantly higher among pregnant females who were exposed to high level of saffron in comparison to control. The possible mechanism may be through the uterine contraction and bleeding, which were induced by saffron.[59]

Drugs.com does not recommend the utilization of saffron as a health supplement in pregnancy due to the toxic effects which have been reported in 5 g, which lead to uterine stimulant, thrombocytopenia, serious bleeding, and abortifacient results. The same study also reported that 10 g is enough to cause abortion and 20 g is fatal. However, if consumed in culinary amounts, saffron is not associated with toxicity.[6] According to Gainer and Chisolm,[60] a study on the animal study found that the median lethal dose has been determined at 20.7 g/kg as a decoction for crocetin and saffron extract of 600 mg/kg body weight for mice.[6] However, for human, acute nausea, vomiting, diarrhea, and bleeding are the results observed on saffron ingestion (1200–2000 mg).[6] A study in 1994 revealed prolonged intake (26 weeks) of saffron (60 mg daily) leads to reduction in red and white blood cell counts as well as platelets, along with a drop in systolic and diastolic blood pressure levels of 10.8–11.7%.[61] Moreover, the same study reported associated complaints of sedation, hypomania, and changes in appetite on exposure for 8 weeks.

CONCLUSION

In summary further research required to get a good quality data regarding saffron mechanism of action, effectiveness, and safety. As well, more data will facilitate a better comprehensive understanding of publication bias and potential moderator variables. Most emphasis, part of trials screening was the effects of imipramine and fluoxetine on symptoms of depression, no vital differences were noticed between saffron and the antidepressant drugs in terms of improvements in depressive symptoms. Despite the fact that studies have revealed more sound scientific evidence for saffron as a potential depression management, the limited period of its usage and inadequacy of precise data on saffron mechanism of action, and small sample sizes prevent us from drawing solid conclusions about the consequences on saffron on depression. While results of increased mental wellness coupled with good short-term basic safety profile recommend saffron may be an exceedingly efficient alternative approach for the treating depression. It is at present unidentified that the positive results of saffron obtained during preliminary trials will proceeds in long-term health benefits until well-controlled and longer-term research are achieved. Large-level, multi-site trials must be conducted to clarify saffron potential function, basic safety profile, and mechanisms of actions for the treating depression. Furthermore, Research conducted up to now provides initial support for the use of saffron for the treatment of mild-to-moderate depression. Further research is recommended to increase our understanding about the role and actions of saffron in major depression.

Financial support and sponsorship

This study has been funded by the endowment grant (EDW14B-094-0979) approved by the Research Management Centre, International Islamic University Malaysia, Kuantan, Pahang, Malaysia.

Conflicts of interest

There are no conflicts of interest.