The essential oil compositions of three Sicilian accessions of Viscum album L. growing on three different host trees

Abstract Viscum album L., (Common Mistletoe), is a hemiparasitic shrub that lives on a wide range of woody plant species, known since Neolithic period for its ritual and for pharmacological properties. Up to now, no investigation has been reported on the chemical composition of the essential oils of V. album aerial parts in relation with the diverse host trees. Consequently, the essential oils compositions of three Sicilian accession of V. album, growing on Quercus suber L., Crataegus monogyna Jacq. and Olea europaea L. var. europaea cv. 'Santagatese', respectively, were evaluated by GC-MS. The three populations showed quite different profiles indicating that the nature of the host considerably influences the chemical composition of the guest plant, V. album. Graphical Abstract


Introduction
Viscum album L., known as European or Common Mistletoe, is an evergreen, perennial, epiphytic, hemiparasitic shrub that lives on a wide range of woody plant species CONTACT PRODUCT RESEARCH 2023, VOL. 37, NO. 15, 2623-2627 https://doi.org/10.1080/14786419.2022.2058940 (Zuber 2004 Phytochemical investigations carried out on the non-volatile metabolites of the plant revealed some important therapeutic agents such as, viscin, viscotoxin, saponins, flavonoids, acetylcholine, lectins, mucilage ascorbate, and tocopherol (Bujor 2003;Zuber 2004;Vicas et al. 2009). Some of the medicinal effects of V. album have also been related to the presence of triterpene acids such as oleanolic acid, betulinic acid and ursolic acid (Mulsow et al. 2016). These compounds proved to be effective in the treatment of acute lymphoblastic leukemia, myeloid leukemia (Delebinski et al. 2015) and to exert apoptosis-inducing activity against different malignant cells (Urech et al. 2005).
Some years ago, a complete review on the phytochemical composition and the therapeutic properties of V. album has been published (Nazaruk and Orlikowski 2016).
Although some studies done on the non-volatile solvent extracts of V. album plants growing on different hosts showed a noteworthy variation of the metabolic composition in relation with the host tree (Orhan et al. 2014;Soursouri et al. 2019;Majeed et al. 2021), none of investigation has been reported on the chemical variation of the essential oil of plants growing on different host tree.
Consequently, in the frame of our ongoing researches on Sicilian plants (Schicchi et al. 2017(Schicchi et al. , 2020Giardinieri et al. 2019;Loizzo et al. 2021), it was decided to determinate the chemical composition of the essential oils from aerial parts of three Sicilian accessions of V. album, growing on Quercus suber L. (Fagaceae), Crataegus monogyna Jacq. (Rosaceae) and Olea europaea L. var. europaea cv. 'Santagatese' (Oleaceae), respectively.

Results and discussion
Hydrodistillation of the aerial parts (leaves and fruits) of the three populations of V. album gave three pale-yellow oils, VA1 (samples collected on Q. suber), VA2 (samples collected on C. monogyna) and VA3 (samples collected on O. europaea) (yield: 0.03% (v/w) for VA1, 0.04% (v/w) for VA2 and 0.03% (v/w) for VA3, respectively). Overall, 105 compounds were identified, representing 94.38%, 97.84% and 91.62% of the total compositions, respectively. The chromatograms of the three essential oils are reported in Supplementary material (Figures S1-S3) The components are listed in Table S1 (Supplementary material) according to their retention indices on a DB-Wax column and are classified based on their chemical structures into seven classes. Table 1 reports the main compounds (> 3%) and the total amount of each classes of the three oils. VA1 was characterized by similar amounts of aldehydes (38.69%) and alkanes (34.98%), with nonanal (21.15%), tricosane (15.57%) and pentacosane (10.85%) as main components, whereas carboxylic acids (1.63%), esters (3.78%) and alcohols (2.39%) were present in quite low amounts. Terpenoids were well represented (11.56%), with (E)-nerolidol (2.58%) as main metabolites of the class. A similar quantity of terpenoids (8.72%) was present also in VA2 that, on the other hand, was characterized by a dominant presence of alkanes (72.87%), being tricosane (31.95%) and pentacosane (20.26%), the main constituents of the oil. Among the aldehydes, the second class of the oil (12.37%), it is noteworthy the occurrence of tetradecanal (5.78%), and nonanal (3.35%). A completely different composition profile was observed for VA3. In fact, it was very rich in carboxylic acid (53.11%) [main compounds linoleic acid (15.48%), hexadecanoic acid (13.50%) and nonanoic acid (10.76%)], practically absent in VA1 and VA2. With respect to the other two oils the content of alkanes in VA3 was lower (20.24%), with tricosane (7.87%) and pentacosane (7.00%) as principal products of the class. Furthermore, this oil showed to be devoid of terpenoids.
Comparison of our results with the few data present in literature allowed us to point out some interesting ideas. In fact, Turkish accession of V. album subsp. album, growing on Prunus armeniaca L (syn. Arımeniaca vulgaris Lam., apricot) (K€ urkç€ uoǧlu et al. 2002), showed the occurrence of large amount of terpenoids (52.7%), with cedrol (8.9%) and thymol (8.3%) as the most abundant ones. Main metabolite of the oil was (E)-2-hexenal (10.2%) belonging to the aldehydes class (24.5%). It is noteworthy, a total absence of alkanes and carboxylic acids in this oil. The other report on the essential oil of V. album subsp. album concerns commercial samples, bought in Germany, and whose host tree was not indicated (Hayashi et al. 1996). In this case, as for VA3, carboxylic acids were the main class (64.05%) being hexanoic acid (25.88%), octanoic acid (10.30%) and nonanoic acid (9.81%) the principal metabolites. Among the aldehydes (7.25%), the second class of this oil, hexanal (2.93%) represented the most abundant constituent.

Conclusion
This investigation conducted on V. album growing on three species from three different families clearly showed that hosts significantly influence the composition of essential oils. Alkanes, which protect plants from pests and predators, are usually present in very small amounts; the oil extracted from the Viscum population growing on C. monogyna (VA2) was found to be very rich in tricosane and pentacosane, which are also the main constituents of all samples of the essential oils from the inflorescences and unripe fruits of Crategus azarolus L. and Crategus pallasii Grisb. analyzed by Agiel et al. (2019). In addition, the oil extracted from the Viscum population on O. europaea (VA3) revealed a high amount of carboxylic acids including oleic and linoleic acids, which are the main fatty acids contained in the olive fruit.
In conclusion, the results of our investigation make a contribution to the understanding the influence of the host on the composition of V. album essential oil. Further studies would be required in order to evaluate the effect of the host on the non-volatile metabolites providing an opportunity to test the products obtained for therapeutic purposes.

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
This work was supported by grants from MIUR-ITALY PRIN 2017 (Project N. 2017A95NCJ).