General Introduction Chapter 1

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Chapter 1 – General introdution

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Chapter 1

General Introduction

Plants are a rich source of valuable, cost effective and easily available natural products. Phytochemicals play a central role in pharmacy and agriculture due to the big development registered to synthesise and isolate new herbal and useful drugs.

1.1 EOs – What are they?

Essential oils (EOs), commonly known as volatile oils, are a very complex mixtures of terpene derivatives, phenylpropanoids and other hydrocarbon constituents [1].

Essential oils (EOs) are extracted by steam or

hydrodistillation from various aromatic plants, generally localized in temperate to warm countries like Mediterranean and tropical countries where they represent an important part of the traditional pharmacopoeia [1]. They are liquid, volatile, soluble in lipids and organic solvents with a generally lower density than that of water. They can be synthesized by all plant organs, are stored in secretory cells, cavities, canals, epidermic cells or glandular trichomes [2], depending on the plant families.

1.2 Why EOs are so interesting?

During recent years plant EOs have an important place in herbal medicine. Their widespread use has raised the interest of scientists in basic research of essential oils [6]. EOs are known for their fragance and they are commercially important for many industrial applications, especially in pharmaceutical, agronomic, food, cosmetic and perfume industries [2].

For their antiseptic properties, EOs are used to preserve food and as antimicrobial, analgesic, sedative, anti-inflammatory, spasmolytic and locally anesthesic remedies. Their pharmaceutical and food uses are widespread as alternatives to synthetic chemical products to protect the ecological equilibrium [2] of

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2 environment and to decrease the utilization of synthetic drugs as antibiotics. Many EOs are insert in the traditional Pharmacopeia of several countries.

1.3 EOs Biological properties

Today the potential damage to human health and to the environment due to synthetic herbicides is regarded as a real problem. It has resulted in a growing interest in alternative strategies which led to the development of biodegradable and non-toxic compounds. Volatile oils and their constituents were explored for weed and pest management and are viewed as an important source of lead molecules in agriculture. Thus it is pertinent to explore and characterize the phytotoxic properties of aromatic plants and their volatile oils [3].

In nature, essential oils play an important role in protection of plants as antibacterials, antivirals, antifungals, insecticides and also against herbivores by reducing their appetite for such plants. They also may attract some insects to favour the dispersion of pollens and seeds, or repel undesirable others [2]. Bioactive terpenoids constitute an important part of the defensive mechanisms of a large number of organisms and represent a fairly untapped source of active compounds of potential use both in the agricultural and pharmaceutical fields. In general, a high presence of oxygenated monoterpenes is linked to a potent phytotoxic activity [3].

In medicine, EOs have been researched for their antibacterial, antifungal, antiviral, insecticidal, anticancer and antioxidant properties. The main advantage of these natural products is that they do not enhance antibiotic resistance as with the long-term use of synthetic antibiotics. On the other hand, the chemical composition (chemotype) of the EOs which is responsible for the antibacterial properties, is highly depended on various factors like the climatic and geographical conditions as well as harvesting, isolation techniques and storage. These factors interfere in the studies, as the results are influenced by them, thus making difficult the drawing of solid conclusions or comparisons [4].

Together with the properties listed before, EOs have more other biological effects: cytotoxicity; phototoxicity (for example, some essential oils contain photoactive molecules like furocoumarins, as Citrus bergamia. In this case, EOs penetrate the cell without damaging the membranes or proteins and DNA. Radical reactions by excitation of certain molecules and energy transfer with production of oxygen singlet occur when cells are exposed to activating light. This may cause damage to cellular macromolecules and in some cases the formation of covalent adducts to DNA, proteins and membrane lipids); carcinogenicity (most EOs are cytotoxic without being mutagenic; however, some essential oils or rather some of their constituents may be considered as secondary carcinogens after metabolic activation, as limonene of C. bergamia EO under ultraviolet A or solar light); antimutagenic properties (it may be due to inhibition of penetration of the mutagens into the cells, inactivation of the mutagens by direct scavenging, antioxidant capture of radicals produced by a mutagenor activation of cell antioxidant enzymes, inhibitionof metabolic

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3 conversion by P450 of promutagens intomutagens, or activation of enzymatic detoxification ofmutagens for instance by plant extracts [2].

Others specific activities of EOs are: molluscicidal; insecticidal; effects on skeletal muscle (EOs relax the smooth muscles); neurological effects of EO constituents (linalool and linalyl acetate are able to cause central nervous system depression, and further investigations demonstrated that L. angustifolia oil, as well as linalyl acetate and linalool, possess local anaesthetic activity both in vitro and in vivo); effect on Blood Pressure Action (decreasing of blood pressure); gastro-protection effect (1,8-cineole); sedative properties and antisposmolytic actions (for example linalool, a monoterpene compound prevalent in EO of plant species traditionally used as sedatives, has been characterized as anticonvulsant in several experimental models) [5].

1.4 EOs Compositions

EOs are still used as raw materials in many fields, including perfumes, cosmetics, aromatherapy and phytotherapy, spices, and nutrition. Therefore, an intimate knowledge of essential oil composition allows for a better and specially directed application. Their composition is dependent on such characteristics as the geographic character of the location from which the plant is obtained, seasonal variations and climate, production technique and purity. The effect of plant maturity at the time of oil production and the existence of chemotypic differences can also drastically affect the composition suggesting that ecological condition and/or physiological states could interfere with the presence of biologically active compounds in the plant. These variations are of di stinct importance for the study of biological and pharmacological activities of these natural products, because the value of an essential oil in aromatherapy has to be related to its chemical composition. [5] The existence of infraspecific chemical differences in the essential oils of some aromatic plants (or chemovarieties) means that morphologically identical plants can possess different secondary metabolites. It is believed that the existence of these chemotypes has evolved over time as a response to environmental and living conditions experienced by the plant. Thus, infraspecific differences can be defined as being chemotypes or chemically distinct species. Furthermore, chemotypes are manifestations of the differences that exist in the genome of the plant. In addition, the existence of chemotypes and their subgroups is proposed are recognition of qualitative and quantitative differences that are biosynthetically related. [5]

Does synergism between the components of essential oils? Regarding their biological properties, it has to remeber that EOs are complex mixtures of numerous molecules.In the literature in most cases, only the main constituents of certain essential oils were analyzed. Generally, the major components are found to reflect quite well the biophysical and biological features of the essential oils from which they were isolated, the amplitude of their effects being just dependent on their concentration when they were tested alone or comprised in essential oils. Thus, synergistic functions of the various molecules contained in an essential

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4 oil, in comparison to the action of one or two main components of the oil, seems questionable. However, it is possible that the activity of the main components is modulated by other minor molecules. Moreover, it is likely that several components of the essential oils play a role in defining the fragrance, the density, the texture, the colour and above all, cell penetration, lipophilic or hydrophilic attraction and fixation on cell walls and membranes, and cellular distribution [2].

1.5 Aim of the PhD project

The object of this PhD project was the extraction and evaluation of many Essential Oils (EOs) and volatile compounds extracted from various Mediterranean plant species, with the aim to contribute to their chemical characterization especially for plants never studied before, or to exploit their industrial and biological use. The volatile sampling and the hydrodistillations were performed in the lab of Departement of Pharmacy in Pisa and here analysed and evaluated, with the supervision of Prof. Luisa Pistelli. The biological activity was performed in Department of Veterinary Sciences of Pisa, in collaboration with Prof. Francesca Mancianti and Dr. Valentina V. Ebani. The statistical analysis were performed thanks to the botanist dr. Daniela Ciccarelli of the Department of Biology of the University of Pisa.

References

[1] G. Flamini, B. Melai, L. Pistelli and C. Chiappe, How to make a green product greener: use of ionic liquids as additives during essential oil hydrodistillation, RSC Adv., 2015, 5, 69894–69898.

[2] F. Bakkali, S. Averbeck, D. Averbeck, M. Idaomar, Biological effects of essential oils – A review, Food and Chemical Toxicology, 2008, 46, 446–475.

[3] Luiz Fernando Rolim de Almeida, Fernando Frei, Emilia Mancini, Laura De Martino and Vincenzo De Feo, Molecules 2010, 15, 4309-4323

[6] Yuangang Zu, Huimin Yu, Lu Liang, Yujie Fu, Thomas Effert, Xia Liu and Nan Wu. Molecules, 2010, 15, 3200-

[4] A. Alexopoulos, A.C. Kimbaris, S. Plessas, I. Mantzourani, I. Theodoridou, E. Stavropoulou, M.G. Polissiou, E. Bezirtzoglou, Anaerobe 17 (2011) 399-402