biomolecules Review Bioactivities and Medicinal Value of Solanesol and Its Accumulation, Extraction Technology, and Determination Methods Ning Yan *, Yanhua Liu, Linqing Liu, Yongmei Du, Xinmin Liu, Hongbo Zhang and Zhongfeng Zhang Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao 266101, China * Correspondence: [email protected]; Tel.: +86-532-8870-1035 Received: 24 June 2019; Accepted: 1 August 2019; Published: 2 August 2019 Abstract: Solanesol, an aliphatic terpene alcohol composed of nine isoprene units, is mainly found in solanaceous plants. Particularly, tobacco (Nicotiana tabacum), belonging to the Solanaceae family, is the richest plant source of solanesol, and its leaves have been regarded as the ideal material for solanesol extraction. Since the discovery of solanesol in tobacco, significant progress has been achieved in research on solanesol’s bioactivities, medicinal value, accumulation, extraction technology, and determination methods. Solanesol possesses strong free radical absorption ability and antioxidant activity owing to the presence of several non-conjugated double bonds. Notably, solanesol’s anti-inflammatory, neuroprotective, and antimicrobial activities have been previously demonstrated. Solanesol is a key intermediate in the synthesis of coenzyme Q10, vitamin K2, and the anticancer agent synergiser N-solanesyl-N,N0-bis(3,4-dimethoxybenzyl) ethylenediamine. Other applications of solanesol include solanesol derivative micelles for hydrophobic drug delivery, solanesol-derived scaffolds for bioactive peptide multimerization, and solanesol-anchored DNA for mediating vesicle fusion. Solanesol accumulation in plants is influenced by genetic and environmental factors, including biotic stresses caused by pathogen infections, temperature, illumination, and agronomic measures. Seven extraction technologies and seven determination methods of solanesol are also systematically summarized in the present review. This review can serve as a reference for solanesol’s comprehensive application. Keywords: solanesol; bioactivity; medicinal value; accumulation; extraction technology; determination methods 1. Introduction Solanesol, an aliphatic terpene alcohol composed of nine isoprene units, is mainly found in Solanaceae plants such as tobacco (Nicotiana tabacum), tomato (Solanum lycopersicum), and potato (Solanum tuberosum)[1–5]. As the chemical synthesis of solanesol is difficult due to its long carbon chains [6], solanesol is mainly obtained through extraction from solanaceous plants [1–4,7]. To the best of our knowledge, tobacco is the richest plant source of solanesol; among the various organs of tobacco plants, leaves possess the highest content of solanesol, followed by stems and roots [1,2,8]. Therefore, tobacco leaves have been regarded as the ideal material for solanesol extraction. Solanesol accumulation in the leaves of plants is affected by genetic and environmental factors [1,9,10]. The solanesol content of tobacco leaves are jointly determined by the major genes and polygenes, with the major genes being dominant, and is also influenced by environmental factors [10]. Pathogen infections, temperature, illumination, and agronomic measures influence solanesol accumulation in tobacco plants [1–4]. Notably, solanesol content in tobacco leaves is the main limiting factor for its extraction. Biomolecules 2019, 9, 334; doi:10.3390/biom9080334 www.mdpi.com/journal/biomolecules Biomolecules 2019, 9, x FOR PEER REVIEW 2 of 17 Biomolecules 2019, 9, 334 2 of 17 tobacco plants [1–4]. Notably, solanesol content in tobacco leaves is the main limiting factor for its extraction. Since the the discovery discovery of of solanesol solanesol in intobacco tobacco by byRowland Rowland et al. et [11] al.,[ significant11], significant progress progress has been has achievedbeen achieved in research in research on its on bioactivities, its bioactivities, medicinal medicinal value, value, biosynthesis, biosynthesis, extraction extraction technology technology and determinationand determination methods methods [1–3] [1. –In3]. aIn previous a previous review, review, we we provided provided a adetailed detailed summary summary of of the physiological functions of solaneso solanesoll in plants as well as the biosynthetic pathway and key enzymes of solanesol biosynthesis [3] [3].. Other Other studies studies have have proven proven that that solanesol solanesol possesses possesses antioxidant antioxidant [12,13], [12,13], antianti-inflammatory-inflammatory [14], [14], neuroprotective neuroprotective [15], [15], and and antimicrobial antimicrobial [16] [16] activities (Figure 11).). Notably,Notably, solanesol serves serves as as an anintermediate intermediate in the in synthesis the synthesis of coenzyme of coenzyme Q10, vitamin Q10, K2, vitamin and the K2, anticancer and the agentanticancer synergiser agent synergiser N-solanesylN-solanesyl--N,N′-bis(3,4N,N-dimethoxybenzyl)0-bis(3,4-dimethoxybenzyl) ethylenediamine ethylenediamine (SDB) (SDB)[1,8], [and1,8], solanesoland solanesol derivative derivative micelles micelles have havebeen beenused usedin the in delivery the delivery of hydrophobic of hydrophobic drugs drugs [17,18] [17. ,18An]. economicAn economic crop crop widely widely planted planted in the in world, the world, tobacco tobacco has marked has marked medical medical value value because because of its of rich its contentrich content of solanesol of solanesol and other and beneficial other beneficial active ingredients active ingredients [1–5]. Moreove [1–5].r, Moreover,the extraction the technology extraction andtechnology determination and determination methods of methods solanesol of solanesolare the basis are the for basis further for further research, research, development development,, and applicationand application [5,11] [5., 11Therefore,]. Therefore, this this review review provides provides a detailed a detailed summary summary of of solanesol’s solanesol’s bioactivities, bioactivities, medicinal value, accumulation, ext extractionraction technology, technology, and and determination determination methods methods to to serve serve as as a reference for its comprehensive application. Figure 1. BioactivitiesBioactivities ( (AA)) and and medicinal medicinal value ( B) of solanesol solanesol.. 2. Bioactivities Bioactivities of of S Solanesololanesol 2.1. Antioxidant Antioxidant Activity Activity Solanesol possesses possesses strong strong free free radical radical absorption absorption ability ability due due to the to presence the presence of several of several non- conjugatednon-conjugated double double bonds bonds [1]. In[ 1addition,]. In addition, this compound this compound has excellent has excellent antioxidant antioxidant activity, with activity, its scavengingwith its scavenging activities activities for superoxide for superoxide anion and anion hydroxyl and hydroxyl radicals being radicals comparable being comparable to those of to Trolox those of Trolox [19]. Huang et al. [12] performed ethanol-modified supercritical CO extraction of crude [19]. Huang et al. [12] performed ethanol-modified supercritical CO2 extraction2 of crude solanesol fromsolanesol tobacco from leaves tobacco and leaves observed and observed that crude that solanesol crude solanesol exhibited exhibited good anti good-free anti-free radical radical activity activity (2,2 diphenyl(2,2 diphenyl-1-picrylhydrazyl-1-picrylhydrazyl radical radical-scavenging-scavenging activity). activity). Meanwhile, Meanwhile, it itwas was found found that that the the extract’s extract’s antianti-free-free radical activity correlatedcorrelated veryvery wellwellwith with the the crude crude solanesol solanesol yield, yield, resulting resulting in in a a model model with with a 2 ahigh high coe coefficientfficient of determination of determination (R = (R0.946).2 = 0.946). Furthermore, Furthermore, solanesol solanesol can effectively can effectively absorb ultraviolet absorb ultravioletradiation and radiation inhibit and tyrosinase, inhibit tyrosinase, which is a which key enzyme is a key in enzyme melanin in synthesis melanin synthesis and closely and linked closely to linkedhuman to pigmentation human pigmentation disorders [disorders20]. Therefore, [20]. solanesolTherefore, may solanesol potentially may bepotentially used in the be inhibitionused in the of Biomolecules 2019, 9, 334 3 of 17 skin ageing and age spots formation. In a study by Yao et al. [13], it was found that solanesol protected human hepatic L02 cells from ethanol-induced oxidative injury via upregulation of haem oxygenase-1 (HO-1), an inducible enzyme with major antioxidant and anti-inflammatory functions [21], and heat shock protein 70, which plays a key cytoprotective role in protein homeostasis and participates in multiple cellular signaling events [22]. A recent study by Banoži´cet al. [23] showed that solanesol and phenolics are the main bioactive compounds in the extracts of different types of tobacco industry wastes (scrap, dust, and midrib). Furthermore, noticeable differences in bioactive compound content and antioxidant activity are found in extracts related to ultrasound-assisted extraction conditions and type of tobacco waste. 2.2. Anti-Inflammatory Activity Solanesol has been extracted from tobacco scrap and tested for its topical anti-inflammatory activity against carrageenan-induced hind paw oedema [24]; the results revealed that the developed solanesol herbal gel formulation demonstrated comparable topical anti-inflammatory properties. Yao et al. [14] examined the