Introduction

Laurus nobilis L., known as laurel (Lauraceae family) is a native plant of the Mediterranean basin and widely diffused in Northern Africa, Western Asia and Southern Europe (Parthasarathy et al. 2008). It is one of the best-known plants in the ancient Greece and Roman times where it was considered as a symbol of peace and sign of victory both in military and sport competitions. At that time, the branches were crossed to create crowns to be placed on the heads of the game winners indicating recognition and esteem and therefore the greatest honor. The poets who won and received the bay laurel wreath became "graduate poets" and people worthy of the most immense and royal esteem for this reason became “nobilis” (Parthasarathy et al. 2008). Even today we use this term when obtaining a degree and put the bay leaf crowns of the heads of the laureates.

Several myths and legends are reported on bay laurel based on its consideration as a sign of prosperity and well-being. In the language of flowers and plants, laurel is considered the symbol of power, victory and glory and being an evergreen plant, it is also a symbol of immortality (De Cleene and Lejeune 2003).

Laurel is used in the kitchen as a spicy fragrance and flavour to meat, fish, broths, and vegetables. It is a component of a typical Italian plant infusion used as digestive, named “canarino”.

The leaves are traditionally used to reduce high blood sugars, fungal and bacterial infections, and to cure gastrointestinal pains, eructation and flatulence. The Roman naturalist Pliny the Elder indicated the following series of ailments treated with bay laurel oil: paralysis, spasms, sciatica, bruises, headaches, catarrhs, ear infections, and rheumatism (Caputo et al. 2017; Chahal et al. 2017).

The plant exhibits several bioactivities including anticonvulsive, antiepileptic, anti-inflammatory, and antioxidant properties (Caputo et al. 2017; Chahal et al. 2017). This last activity was mainly studied and associated to the high content in the plant leaves of flavonoids and phenolics. In particular, apigenin, luteolin, kaempferol, myricetin and quercetin were the major flavonoid derivatives along with the related flavan-3-ols. In addition, the plant shows a rich content of free sugars, proteins, organic acids, PUFA and tocopherols (Dias et al. 2014).

This review aimed to contribute to the knowledge of laurel, L. nobilis, by providing an overview of its botany, traditional uses, phytochemistry and pharmacology.

Botanical description

L. nobilis L. is a multibranched, aromatic, broadleaf, slender, evergreen tree, or large shrub belonging to the Lauraceae family. Commonly called laurel, bay tree, Grecian laurel, bay leaf or sweetbay, it is native to the Northern Africa, Western Asia and southern Europe (Parthasarathy et al. 2008). In natural conditions it reaches up to 10 m, with thin branches forming a dense pyramidal crown. Bark is smooth, thin and pale gray. Laurel is a dioecious tree, with male and female flowers on separate plants. Leaves are alternate, short petioled, up to 10 long, lanceolate, or oblong-lanceolate, acute, coriaceous, pellucid-punctate, and with revolute, entire margins. The upper surface is glabrous and shiny glossy dark green; the lower surface is hairless, dull olive to brown with a prominent midrib and veins. Both male and female flowers are bright yellow-green, beared on short, 4–5 flowered, racemes appearing in early to mid-spring. Male flowers with 8–14 stamens 4–5 mm long, most of them with 2 basal glands. The female flowers are about 4–5 mm long, with 2–4 staminodes and contain nectaries; the ovary is superior, scarcely sunk in the receptacle, style short. Fruit is one-seeded, 1–1.5 long, ovoid, berry, with a shiny dark purple, thin pericarp, which, when broken, discloses a kernel whose seed coat adheres to the inner surface of the pericarp. The male plants produce more flowers per branch than the female plants and the mean life of male flowers is shorter than that of female (Pacini et al. 2014). The pollination is entomophilous, with honeybees as main pollinators (Brickell 2008).

Traditional uses

Laurel is traditionally used as an herb (called bay leaf) to season roast meats, stews, snails, fish, sauces, soups, and boiled chestnuts, (Kermath and Bennett 2014; Alarcón et al. 2015; Motti et al. 2020). Laurel is also widely reported as a traditional herbal drug (Table 1) in many countries all around the world like Algeria, Brazil, Cyprus, Greece, Italy, Serbia, and Turkey. Leaves and fruits are used orally or topically to treat a wide range of diseases (Fig. 1). Based on the classifications of diseases and remedies in ethnomedicine and ethnopharmacology suggested by Staub et al. (2015), the major uses of L. nobilis include treatments for gastro-intestinal complaints including indigestion, constipation, flatulence also as carminative, diarrhea, hemorrhoids, and stomach aches. This species is also reported to treat kidney diseases, and for the treatment of cough, colds, influenza, and sore throat. Laurel leaves are one of the main ingredients of a preparation used for the treatment of respiratory ailments called in many cases ‘Ricotto’ or ‘Ricuotto’, still in use today and found in the traditional phytotherapy of central and southern Italian regions (Barone 1963; Scherrer et al. 2005; Motti et al. 2009; Idolo et al. 2010).

Table 1 Traditional uses of L. nobilis
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Fig. 1
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Percentages of use of laurel for different ailments categories. (Disease’s classifications according to Staub et al. (2015): CAR Cardiovascular diseases, GAS Gastrointestinal problems, GYN Gynecology, NER Nervous system, RES Respiratory complaints, SKE Skeleto-muscular system)

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L. nobilis is reported as mild sedative and against headache but also used as analgesic, antirheumatic and diaphoretic. In the gynecological field it is reported for the dysmenorrhea treatment, as galactagogue and abortifacient. Furthermore, laurel decoction is used for cardio-vascular diseases and to treat lower blood pressure. In Turkey, branches chopped up, peeled, and put into water are used against scorpion or snake bites and bee bites (Honda et al. 1996; Tuzlacı and Tolon 2000).

The essential oil was used in folk medicine to treat rheumatisms and dermatitis. However, attention needs to be given to the dosage because it can cause allergic effects (Kilik et al. 2004). Berries show ahigh fatty acids content, and thus it is used for soap production in cosmetics to treat acme and dandruff (Kilik et al. 2004).

Based on the 77 studies providing adequate and relevant data leaves (80.8%) are the most frequently used plant parts. According to the reported data, decoction (65.2%) is the most frequent preparation methods used (Fig. 2).

Fig. 2
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Plant parts used for medical applications A and main modes of preparation B, (Percentage values)

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The essential oils or leaf fumigation of laurel are also used as insect repellents and insecticides against home insects and crop pests (Baydoun et al. 2017).

Phytochemical analysis

Essential oils

Tables 2 and 3 summarize the main metabolites extracted from the different parts of the plant, their quantity, and the methods used for their analysis.

Table 2 Main organic compounds isolated by GC–MS from essential oils of L. nobilis leaves
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Table 3 Main organic compounds isolated from L. nobilis extract
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Most of the studies have focused on the analysis of essential oils extracted from laurel leaves (Table 2). The main extraction method used to separate the essential oils from leaves was hydrodistillation of powdered dried leaves for few hours, with a very variable final yield. However, other techniques can be used with similar results and here we provide a brief overview. Nafis et al. (2020) performed hydrodistillation for 4 h, obtaining 2.5% (v/w) based on dry weight. Similarly, Stefanova et al. (2020) isolated oils by 3 h-long hydrodistillation from two different varieties and obtained 1.42 ± 0.01% (v/w) yield for Greek variety, and 4.54 ± 0.04% (v/w) yield for Georgian variety. Moreover, Jemâa et al. (2012) performed hydrodistillation for 4 h on three different leaves varieties, obtaining a yield of 0.584, 0.46 and 0.655%. Ivanović et al. (2010) carried out an experiment to compare two different methods of extraction for essential oils: a 4 h-hydrodistillation, which resulted in a yield of 1.43%, and 1.4 h-long supercritical CO2 extraction, obtaining 1.37% of extract yield. Although the two yields were comparable, the compositions of the two extracts were significantly different. For example, 1,8-Cineole, the main component of the hydrodistillated fraction, was 13 times more abundant in hydrodistillated extract than in supercritical CO2 extract. Another interesting technique, solvent-free microwave extraction (SFME), was used by Bendjersi et al. (2016) and compared to hydrodistillation. The final products were different in turbidity, since SFME produced a clearer extract than the hydrodistillated one, even though the final essential oil yields of the two processes were comparable (0.61% for SFME vs 0.86% for hydrodistillation). Finally, Conforti et al. (2006) compared a wild and a cultivated varieties of L. nobilis.. They performed extraction of essential oils using n-hexane and they obtained totally different yields from them. Wild laurel yielded 0.11% of non-polar fraction, while cultivated laurel contained 1.12% of it. Probably, these large differences between the mentioned works were due to environmental and genotypic factors.

The GC–MS analysis of the essential oils of Laurel resulted in hundreds of different components, but only few dozens of molecules were repetitively found in several works. The most frequent molecules belong to the class of terpenes, unsaturated hydrocarbons mainly produced by plants. They have many biological functions, from being precursors of steroids to plant defense and pollinator attractors thanks to their pleasant and powerful odors. The main terpenes found in essential oils are monoterpenes and their derivatives, monoterpenoids, both classes formed by two isoprene units (10 carbons) with several functional groups attached to them. They were also the most abundant, and include 1,8-Cineole (or Eucalyptol), Camphene, Limonene, p-Cymene, Sabinene, Terpinen-4-ol, Linalool, α-Pinene, α-Terpinene, α-Terpineol, α-Thujene. Some of them are regularly found in many plants. Eucalyptol was the most abundant monoterpenoid, present between 25 and 60% in many studies. Moreover, other common monoterpenes were α-Pinene, which ranged between 2.5 and 32%, Sabinene (0.07–13%) and Linalool (0.1–18%) (Table 2).

Moreover, essential oils contain moderate quantities of Eugenol and Methyl eugenol. Eugenol is an allylbenzene, used in perfumes and flavoring that can be found in many plants’ essential oils. Because of the hydroxyl group and the methoxy group, Eugenol is able to scavenge free radicals and avoid reactive oxygen species formation, while Methyl eugenol is a phenylpropanoid and its main role is to attract pollinators. Both of them were moderately abundant in laurel leaves (0.1–5.1%/0.9–21.3%).

Interestingly, since these molecules represent a large portion of the essential oils, when leaves get harvested in different seasons. Shokoohinia et al. (2014) found that 1,8 cineole was the most varied molecule, with a 10% difference between June and December. The second most abundant molecule varied among the seasonal harvest, being δ-3-carene, Camphor, Camphene and Sabinene respectively in March, June, September and December, while eugenol, methyl eugenol and α-terpenyl acetate did not show variation. Furthermore, another work harvested L. nobilis leaves from October to July and found an increasing trend for α- and β-Pirene, Sabinene, δ-3-Carene, and a decreasing trend for Borneol, α-Terpinyl acetate and Eugenol (Marzouki et al. 2009).

Elemicin is a phenylpropene that can be found in essential oils from diverse plants. In the considered studies elemicin was present between 0.14 and 4.958% of the essential oils weight. Rossi et al. (2007) found that elemicin exhibited an antimicrobial activity against Campylobacter jejuni. Moreover, they disproved the theory supported by previous studies that elemicin possess genotoxic potential. The same thing was stated by De Vincenzi et al. (2004) who examined the literature and found no proves that elemicin have short-term chronic toxicity.

Among higher alkanes, n-Heneicosane, n-Heptacosane, n-Heptadecane, n-Hexacosane, n-Octacosane, n-Pentacosane, n-Tetracosane, n-Tricosane were consistently found in the essential oils from L. nobilis leaves, and their individual quantities never reached 1% of the oil mass in the studies we considered (Table 2). The composition of the essential oils at different levels of altitude was studied by Yilmaz and Deniz (2017). Their analysis showed that few compound were found to be significantly increased or decreased dependently on the increase of the altitude. α- and β-Pinene, 1,8-cineole, β-Elemene and Methyl Eugenol showed a decreasing trend in some species, whereas Linalool showed an increasing trend (Yılmaz and Deniz 2017).

Polar components

Less commonly, L. nobilis leaves were subjected to the extraction of molecules with different procedures to retain the polar fraction, using mixtures of ethanol, methanol, ethyl acetate and water.

We listed some relevant examples as follows. Yoshikawa et al. (2000) used methanol to extract polar molecules and then ethyl acetate:water to partition them. Hibasami et al. (2003) focused on sesquiterpenes isolation, soaking the leaves in hexane for one week and then partitioned with hexane, dichloromethane, ethyl acetate and methanol. Duc Dat et al. (2019) separated megastigmanes by extracting with 95% methanol and then partitioning with dichloromethane, and ethyl acetate, and each fraction was further separated using different solvent combinations. Finally, De Marino et al. (2004, 2005) identified many compounds among sesquiterpenes and megastigmanes which they extracted using methanol, and then partitioned using n-hexane, tetrachloromethane, chloroform, and n-butanol. Then, the polar extracts were usually analyzed by NMR or HPLC-MS (Table 3).

Most abundant metabolites belong to the classes of hydroxycinnamic acids, flavonoids, sesquiterpenes and megastigmanes.

Hydroxycinnamic acids are molecules formed by C6 and C3 structures linked together, usually creating a structure with a benzene and a three-carbon side chain. Their importance is related to the ability to help plants in several developmental processes and, moreover, they are used by plants to withstand plant stresses thanks to their antioxidant properties. Concerning human nutrition, they are important in cardiovascular diseases, diabetes, and cancer prevention. In L. nobilis leaves, the most abundant hydroxycinnamic acids are Caffeic Acid, Chlorogenic Acid, p-Coumaric Acid, Cinnamic acid, Sinapic acid and Ferulic acid. They were found to range between 22.7 and 607 µg/g of dried leaves, with Sinapic acid showing the highest registered quantity, as observed in the study by Stefanova et al. (2020) (Table 3).

Sesquiterpenes have been isolated from the leaves extracts by many research groups (Matsuda et al. 2000; Yoshikawa et al. 2000; Hibasami et al. 2003; De Marino et al. 2004; Komiya et al. 2004; Fang et al. 2005; Chen et al. 2014). The most found sesquiterpenes in non-polar fraction were Costunolide, β-Caryophyllene (0.09–2.1%), Caryophyllene oxide (0.1–1.8%), and β-Elemene (0.1–7.45%) (Table 2). Sesquiterpene lactones are a class of sesquiterpenoids known for their pharmacological properties due to their structure. Many studies demonstrated that the α-methylene-γ-lactone group is the one linked to the biological activities of these molecules (Barla et al. 2007; Ghantous et al. 2010; Lin et al. 2015). Costunolide and dehydrocostuslactone, are two common sesquiterpene lactones with demonstrated beneficial activities including inhibition of cancer cells proliferation, anti-angiogenic activity, induction of cancer cell differentiation, anti-tumor activity (Lin et al. 2015). Luna-Herrera et al. (2007) identified and purified the same two sesquiterpene lactones, costunolide and dehydrocostuslactone, to test them individually, and found out that their antimicrobial synergistic effect was stronger than the single effects exerted by each molecule. Turk et al. (2019) isolated 21 different molecules belonging to sesquiterpene lactones class, including reynosin, santamarine, costunolide, dehydrocostus lactone, zaluzanin C and D, and other minor ones. They also found that sesquiterpene lactones from the leaves of L. nobilis exert their anti-inflammatory activity by inhibiting Nuclear Factor-κB (NF-κB), highlighting their importance in development of anti-inflammatory products.

Many other works have isolated well-known and unknown sesquiterpene lactones to enrich scientific literature, such as Barla et al. (2007) and Dall’Acqua et al. (2006), who demonstrated a cytotoxic activity against cancer cells, Petkova et al. (2019), who investigated the antimicrobial activity of laurel fruits.

Sesquiterpene lactones commonly found in L. nobilis leaves extracts were Costunolide, Santamarine, Zaluzanin D. Contrarily to essential oils, which contained non-polar sesquiterpenes, leaves extracts contained sesquiterpenes lactones, which contain several oxygen atoms. To give some examples, De Marino et al. (2004, 2005) extracted 1.17 g of Costunolide and 1 mg of Santamarine out of 404 g of dried leaves, while Hibasami et al. (2003) obtained 12 mg of Costunolide and 5.4 mg of Zaluzanin D. starting from 21 g of dried leaves (Table 3).

One of the most important secondary metabolite classes is flavonoids class, a subclass of polyphenols whose general molecular structure consists of two benzene rings and a heterocyclic ring containing one oxygen atom. They are responsible of several roles in plants such as pigmentation, signaling and regulation processes. The most efficient method to extract phenolic compounds, according to Muñiz-Márquez et al. (2013) is an extraction with a solid/liquid ratio of 1:12 (g/mL), and using sonication for 40 (min) with an ethanol concentration of 35%. However, few works among the ones we considered used an ultrasound-assisted method.

Apigenin, Hesperetin, Luteolin, Myricetin, Quercetin are the principal flavonoids found in Laurus nobilis leaves which were present in an order of magnitude of dozens or hundreds of micrograms every gram of dried weight. Stefanova et al. (2020) performed an extraction from laurel leaves and obtained 268.6 µg/g of Apigenin, 116.4 µg/g Hesperetin, 4.8 (Greece) and 59 (Georgia) µg/g of Luteolin, 124.5 (Greece) e 75 (Georgia) µg/g of Myricetin, 48.9 (Greece) and 65.3 (Georgia) µg/g of Quercetin (Table 3). Dall’Acqua et al. (2009) isolated ten glycosides of kaempferol and quercetin listed in Table 2 and performed in-vitro experiments to highlight the antioxidant properties of the extracts containing these compounds.

Megastigmanes are also important because of their aromatic properties. They are a class of molecules with 6 carbon-ring substituted on carbon 1 and 5, and with a four-carbon sidechain attached on carbon 6. The megastigmanes found in L. nobilis leaves extracts are different types of Laurusides (A, B, C, D, E, F, G), which consist of the general megastigmanes structure substituted with several hydroxyl groups and a glucopyranose group. These molecules are contained in few milligrams per hundreds of dried laurel leaves (De Marino et al. 2004; Panza et al. 2011; Duc Dat et al. 2019), with Lauroside A being the most abundant (2.5 mg/404 g dw).

Concerning carbohydrates, the major component in the extract was D-Gluco-L-glycero-3-octulose (37.29 ± 1.19%). The compound has been determined by classical approach by 1H and 13C NMR spectroscopy Sakata et al. (1989) and by metabolomics GC–MS and 1H and 2D NMR methods (de Falco et al. 2018) (Table 3).

Pharmacological activity

Table 4 lists the biological activity of laurel extracts that have been studied in published articles. Several activities have been reported on essential oils and plant extracts including antibacterial, antimicrobial, antifungal, antioxidant, cytotoxic, insecticidal, nematicidal, inhibiting nitric oxide (NO) production and inhibiting microglial activation. Studies were performed on the essential oils and on the organic and aqueous extracts of the plant. Leaves were the part of the plant mostly studied and tested with different solvents used for the extraction of metabolites. In general, a certain variation of the biological activity was observed due to the geographical origin of the plant, the growing conditions, the seasonal variation, and the solvent used for metabolite extraction.

Table 4 Biological activity of L. nobilis based on plant material and solvent extract
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Essential oils

Bay leaf essential oils find applications for several pharmacological activities. A complete review of the observed biological activity was reported by Chahal et al. (2017) with particular interest to antibacterial, antifungal, antioxidant, insecticidal and nematicidal effects.

Antibacterial and antifungal activities were shown in several studies on a variety of bacteria and fungi (Table 4). Very recently, Nafis et al. (2020) evaluated antibacterial and antifungal effects in vitro of laurel essential oils in combination with the conventional antimicrobial drugs, fluconazole, ciprofloxacin, and vancomycin. The essential oil alone showed high activity with minimal inhibitory concentrations (MICs) ranging from 1.39 to 22.2 mg/mL for bacteria and between 2.77 and 5.55 mg/mL for yeasts. A synergistic effect was observed when essential oil was tested in combination with antibiotics with fractional inhibitory concentration (FIC) index values in the range of 0.266 to 0.75 for bacteria, and between 0.258 and 0.266 for yeast. Thus, this evidence could constitute the basis for further studies to treat antibiotic-resistant pathogens.

Caputo et al. (2017) studied the bioactivities of the essential oils. Antimicrobial and antifungal activities were demonstrated for essential oil and for 1,8-cineole in vitro. In addition, the cytotoxicity of the essential oil was tested against SH-SY5Y cell line, as well as the influence of the essential oil on the expression of adenylate cyclase 1 (ADCY1), suggesting possible oil effects on the Central Nervous System.

Insecticidal activity of the essential oil from Tunisia, Algeria and Morocco was reported against Tribolium castaneum and Rhyzopertha dominica Jemâa et al. (2012). Results showed that all tested oils were repellent and toxic to adult insects, being the activity dependent upon insect species and oil origin. Both in filter paper tests and in fumigant activity test, L. nobilis essential oil from Morocco showed high insecticidal activity compared to the oils from Tunisia and Algeria. Their work indicated the efficacy of laurel essential oil as insecticide and repellent against stored product pests. Nematicidal activity of bay leaf essential oil, its fractions, isolated and derivatized compounds was testes against the root-knot nematodes, Meloidogyne spp. (Chahal et al. 2017). Bay leaf essential oil and its fractions and derivatized compounds were effective to inhibit egg hatch and to increase the juvenile mortality at all concentrations tested and durations of the exposed trial. In particular, the bay leaf essential oil showed the highest egg hatch inhibition and mortality. The study revealed indicated the potential use of bay leaf essential oil against M. incognita and the needing of further studies to evaluate the nematicidal properties and understand the mechanism of action.

Several studied also reported antioxidant activity of essential oil tested by DPPH assay and as total reduction capacity Riabov et al. (2020), DPPH free radical scavenging and β-carotene/linoleic acid test systems (Chahal et al. 2017) DPPH and ABTS assay (Cherrat et al. 2014; Ovidi et al. 2021) and stimulated mice peritoneal neutrophils (Bendjersi et al. 2016).

Leaves extracts

The leaves of the plant were also subjected to a pharmacological screening. Antimicrobial activity and antifungal activity have been recently demonstrated by different research groups (Rizwana et al. 2019; Jamzad and Kamari Bidkorpeh 2020). Rizwana et al. (2019) evaluated the antibacterial and antifungal activity by extracting L nobilis leaves with solvents of increasing polarites. The acetone extract had the largest inhibition against Streptococcus pneumoniae (37.16 ± 0.23 mm) while ethanol and methanol extracts exhibited high inhibition against Alternaria alternata (91.33 ± 0.47; 90.66 ± 0.94). Jamzad and Kamari Bidkorpeh (2020) reported an approach by green nanotechnology based on the application of biomaterials in the synthesis of nanoparticles. Thus, iron oxide nanoparticles were synthesized in the phase of hematite (α-Fe2O3) by the aqueous extract of L. nobilis leaves in a simple and eco-friendly method. The obtained nanoparticles were tested against three bacteria and two fungi. The results showed that the nanoparticles were moderately effective on the Gram-positive bacterium of Listeria monocytogenes and the fungi Aspergillus flavus and Penicillium spinulosum and therefore could be of potential use as antibacterial and antifungal agents.

Rizwana et al. (2019) and Kazeem et al. (2015) also reported cytotoxic activity of the plant extracts, the last activity reported by Brahmi et al. (2015) on HepG2 hepatic cell lines.

However, many studies were related to the antioxidant activity of the organic and aqueous leaf extracts (Conforti et al. 2006; Elmastaş et al. 2006; Ouchikh et al. 2011; Vardapetyan et al. 2013; Brahmi et al. 2015; Kazeem et al. 2015; Casamassima et al. 2017; Oudjedi et al. 2019; Brinza et al. 2021; deFalco et al. 2018).

In addition, (Brinza et al. 2021) investigated the ability of bay leaf incense (BL) to elicit the memory formation via the action on the cholinergic system using a scopolamine (Sco)-induced rat model. Thus, rats were exposed to BL over 5 min once daily for 22 days, whereas memory impairment was induced by Sco (0.7 mg/kg), a muscarinic receptor antagonist. The data obtained indicated that the exposure to BL significantly ameliorated Sco-induced cognitive impairment and oxidative stress in the rat hippocampus thus suggesting that BL-induced ameliorative cognitive effects are mediated by enhancement of the cholinergic system and antioxidant activities.

Antiviral activity of the L. nobilis leaf ethanolic extract has been reported by Aurori et al. (2016) on virus targeting bee. The authors performed the antiviral tests on forager honeybees naturally infected with BQCV (Black queen cell virus). Higher extract concentration (≥ 5 mg/ml) significantly reduced virus replication although the activity was observed also at low concentrations. The evaluation of vitellogenin gene expression as an indicator of transcript homeostasis indicated constant RNA levels both before and after treatment. This data suggests that its expression was not impacted by the plant treatment.

Inhibition of nitrogen oxide (NO) production has been reported for the methanolic extract of the plant leaf on lipopolysaccharide-LPS activated mouse macrophages (Matsuda et al. 2000; De Marino et al. 2005). The methanol extract of laurel was shown to inhibit the nitric oxide production in mouse peritoneal macrophages activated with lipopolysaccharide (LPS). The activity was ascribable to sesquiterpene compounds that were further isolated and tested following a bioassay-guided separation. Among the isolated compounds, the sesquiterpene lactone showed the highest activity thus pointing to the importance of the α-methylene-γ-butyrolactone moiety as key structural element for the activity. Study of the mechanism further indicated inhibition of inducible nitric oxide synthase (iNOS) induction in accordance with induction of heat shock protein 72 (HSP 72). Therefore, they suggested that sesquiterpene lactones induce HSP 72 thereby preventing nuclear factor-κB activation followed by iNOS induction.

De Marino et al. (2004) further reported megastigmane and phenolic glucosides from leaves extract along with their effect on nitric oxide production in lipopolysaccharide-activated murine macrophages. Further studies indicated for the megastigmane glycoside, lauroside B, antiproliferative activity against three human melanoma cell lines, A375, WM115, and SK-Mel-28. The inhibition was due to the induction of apoptosis, as showed by FACS analysis with annexin V/PI staining, and confirmed by the activation of caspase-3 and by the cleavage of poly(ADP-ribose) polymerase (PARP). In addition, the exposure of human melanoma cells to lauroside B inhibited IκB-α degradation and constitutive NF-κB DNA-binding activity as well as the expression, regulated by NF-κB, of two antiapoptotic genes, XIAP and c-FLIP. Thus, lauroside B could be a promising drug candidate in human aggressive melanoma cell lines Panza et al. (2011).

Sesquiterpenes compounds from the leaves of laurel showed to inhibit microglial activation as reported by Chen et al. (2014). This activity could be of potential use for the treatment of neurodegenerative diseases. In effect, the leaves extract showed moderate inhibition on microglial activation while the test on the purified sesquiterpenes revealed these compounds as responsible of the observed inhibitory activities on LPS-induced microglial activation and therefore improving the human cognitive heath.

Conclusion

Laurel is an aromatic broadleaf evergreen tree or large shrub belonging to the Lauraceae family. It is a common plant originating and diffused in the Mediterranean basin. The plant has been used since ancient times as a food ingredient and traditional remedy mainly to help sleeping, as laxative, to reduce chest pains and inflammation of throat and tongue. Additionally, antipyretic, lowering fever and refreshing liver properties were also reported. Due to its wide use, the chemical composition and the biological activity of the plant have been largely studied. The essential oils and the plant leaf extracts were studied in detail with different methods. A rich content of metabolites including proteins, free sugars, organic acids, PUFA and tocopherols has been reported. In addition, several pharmacological studied scientifically demonstrated some of the activity known from traditional medicine including overall antimicrobial and antioxidant properties. Thus, this review, reporting the existing studies on L. nobilis botany, traditional uses, chemistry, and pharmacology, may be exploited as scientific basis for further research.