Pharmacological Effects and Mechanisms of Sclareol

Yuqi LI, Qian CHEN, Xue SHEN, Shuang LI, Bocui SONG,2*, Chenghao JIN,3,4*

1. Molecular Mechanism of Disease & Research and Development of Bioactive Substances, College of Life Science & Technology, Heilongjiang Bayi Agricultural University, Daqing 163319, China; 2. Department of Pharmaceutical Engineering, College of Life Science & Technology, Heilongjiang Bayi Agricultural University, Daqing 163319, China; 3. College of Food Science & Technology, Heilongjiang Bayi Agricultural University, Daqing 163319, China; 4. National Coarse Cereals Engineering Research Center, Daqing 163319, China

Abstract This paper first reviewed the pharmacological effects and mechanisms of Sclareol in recent years. It discussed anti-inflammatory effects, antibacterial, and anti-photoaging effects of Sclareol. It is expected to lay a theoretical basis for its application in the pharmaceutical field.

Key words Sclareol, Anti-inflammatory, Anti-photoaging, Anti-tumor

1 Introduction

With the chemical formula of C20H34O2, Sclareol is a diterpenoid compound. It is primarily extracted from the heads of Sclareol orSalviadivinorum. Sclareol grows in the shallow mountainous areas of northern Shaanxi, China. It has aroused attention because of its high ester content and pure aroma due to the significant temperature difference between day and night in this region, thus making the temperature, humidity, and altitude suitable for the growth of this herb[1]. As a type of secondary metabolite, it generally has pharmacological activity. Fig.1 presents its chemical structure formula. It has a relative molecular weight of 308.15, and it is a white crystalline powder at ambient temperature. It is stored in a dry and cool place, with a melting point of 105 ℃, a boiling point higher than 340 ℃. Moreover, it is easily soluble in petroleum ether, ethanol, chloroform, acetone, and most other organic solvents insoluble in water. Besides, it is more stable to alkali[2]. Existing research has suggested that Sclareol has anti-inflammatory, anti-cancer, and anti-ageing effects, and it has been widely used in medicine, cosmetics, fragrances, and pesticides[3]. In this paper, we reviewed the recent research on the pharmacological effects and mechanisms of Sclareol to lay a theoretical basis for its application in the pharmaceutical field.

Fig.1 Chemical structure formula of Sclareol

2 Pharmacological effects

2.1 Anti-inflammatory effectsWu Pochangetal.[4]found that Sclareol can decrease DNCB-induced AD mice, down-regulate IgE levels, reduce the extent of mast cells infiltration, and decrease the number of leukocytes in the blood (e.g., neutrophils, eosinophils, and lymphocytes), also down-regulate the levels of pro-inflammatory cytokines (including TNF-α, IFN-γ, IL-4, IL-6, IL-1β and IL-17A) and inhibit the phosphorylation of ERK, p38, and JNK in the MAPK pathway. The results of theinvitroexperiments reveal that Sclareol inhibits the proliferation of splenocyte and significantly decreases the levels of IFN-γ, IL-4, and IL-17A. Huang Guanjhongetal.[5]suggested that Sclareol inhibits LPS-stimulated macrophage growth, reduces NO production, and down-regulates the expression of inflammation-associated proteins (INOS and COX-2) in a concentration-dependent manner. The result of theinvivoexperiments reveals that Sclareol alleviates λ-carrageenan-induced foot edema in mice, inhibits NO production, while down-regulating the expression of cytokines TNF-α. It can inhibit NO production, reduce the levels of cytokines (TNF-α and MDA), and inhibit the expression of proteins (INOS and COX-2). Theinvitroexperiments performed by Zhong Yingetal.[6]reveal that Sclareol significantly inhibits MMP-1, MMP-3, MMP-13, COX-2, and iNOS gene expression induced by IL-1β in rabbit chondrocytes, up-regulates TIMP-1 gene expression, and leads to increased TIMP-1 protein content and decreased MMP-1, iNOS, and COX-2 protein content. Since IL-1β treatment leads to increase of NO and PGE2 levels, Sclareol reverses this phenomenon.Invivostudies have suggested that Sclareol significantly inhibits the expression of MMPs, iNOS and COX-2 at the mRNA and protein levels and up-regulates the expression of TIMP-1 in a rabbit arthritis model constructed using the ACLT method; intra-articular injection of balsanol has a palliative effect on arthritis. Hsieh Yunghungetal.[7]investigated whether Sclareol can inhibit inflammation using an LPS-induced lung injury model. The result reveals that Sclareol ameliorates lung injury, decreases NO, TNF-α, IL-1β, IL-6 levels, increases IL-10 levels, and significantly inhibits iNOS, COX-2, NF-κB, protein expression and ERK, JNK, and p38 phosphorylation in mice, thus having anti-inflammatory effects. Tsai Senweietal.[8]treated collagen-induced arthritis (CIA) model in mice with Sclareol to reduce arthritis symptoms. Serum IgG, IgG1, IgG2a, IgG2b and pro-inflammatory factors (including IL-1β, TNF-α, IL-6, IL-17) are significantly reduced, and the number of Th1/Th17 cells decreases in mice.Invitro, Sclareol can down-regulate the expression of MMP-1 protein and pro-inflammatory factors TNF-α and IL-6 in IL-1β-induced SW982 cells while inhibiting NF-κB and MAPK pathways to have anti-inflammatory effects.

2.2 Antibacterial effectsLeonora Mendozaetal.[9]found that Sclareol can more significantly inhibit the growth of gray mold than the commercial fungicide Iprodione. It can also reach the mitochondria without changing the plasma membrane, which leads to uncoupling of oxidative phosphorylation and has an antibacterial effect. Staphylococcus aureus is a common gram-positive bacterium, which follows a food-borne pathogenic microorganism. Ouyang Pingetal.[10]suggested that Sclareol significantly inhibits the secretion of α-hemolysin (Hla), an exotoxin of Staphylococcus aureus, down-regulates the transcript levels of Hla and RNAIII, and protects against Staphylococcus aureus-induced alveolar epithelial cell injury, thus having an antibacterial effect.

2.3 Anti-photoaging effectsAs people’s standard of living has been improving, the awareness of skin protection has been increasing, UV rays can lead to the occurrence of photoaging of the skin. However, Sclareol has been less studied in anti-photoaging. In a study by Park[11], the anti-photoaging ability of Sclareol was evaluated using uvb-induced skin photoaging. A human skin fibroblast cell line was used for UVB irradiation and treatment with aromatic Sclareol restores cell viability. MMP is significantly related to the regulation of skin photoaging AP-1 transcription factor that stimulates the production of MMP. The results of this paper reveal that Sclareol inhibits skin photoaging by regulating AP-1 and thus down-regulating the expression of MMP-1, MMP-3, and MMP-9. The result of the RHE model experiments reveal that Sclareol restores the UVB-induced skin thickness thinning and thins the stratum corneum. In clinical trials, the use of a cream containing 0.2% Sclareol is effective in reducing crow’s feet after 12 weeks. We are also intended to lay a theoretical basis for the development of Sclareol in the field of cosmetics.

2.4 Anti-tumor effectsIt is generally known that nowadays cancer is still a leading cause of death in the world according to the2020GlobalCancerStatisticsReport, suggesting that the number of new cancer cases was expected to be 19 292 789, and the number of new deaths was expected to be 9 958 133 in 2020 worldwide[12]. Cancer treatment can be classified into three types, including chemotherapy, surgery, and radiation therapy. Cancer is difficult to cure, the patient treatment process is painful, and the age of cancer patients has been younger in recent years. Attacking cancer is an urgent task for researchers, and a highly effective chemotherapeutic drug with low toxic side effects is urgently required.

Chen Hsianglaietal.[13]suggested that Sclareol induces a G1 phase block in small cell lung cancer H1688 cells, which induces apoptosis in a concentration-dependent manner. Sclareol inhibits the expression of cell cycle regulators cyclin E, cyclin D, CDK4, pRb (ser 780), and up-regulates the expression of E2F1. It induces G1 phase block and apoptosis via the ATR pathway in response to DNA damage. The result of theinvivoexperiments reveals that Sclareol inhibits tumor growth in xenograft animal models with no significant toxic effects. Among the therapeutic agents for non-small cell lung cancer, cisplatin remains the drug of choice, whereas the problem of drug resistance is still challenging. Pan Chunhsuetal.[14]confirmed that the combination of Sclareol and cisplatin significantly inhibits the survival and migration of non-small cell lung cancer A549 cells, down-regulates ERCC1 and upstream regulatory factor expression in A549 cells, and reduces cisplatin resistance in A549 cells. The result of theinvivoexperiments reveals that Sclareol in combination with cisplatin significantly reduces tumor volume with no significant toxic side effects. Hamed Hamishehkaretal.[15]prepared solid lipid nanoparticles containing Sclareol, which decreases the survival of lung cancer A549 cells by fragmenting chromatin DNA and blocking the cell cycle to induce apoptosis in A549 cells. Kostas Dimasetal.[16]found that Sclareol at a concentration of 20 mg /mL inhibits DNA synthesis and cell growth in leukemia cells. It alters cell morphology and induces apoptosis in a concentration-dependent manner. Sclareol leads to the accumulation of two human leukemia cell lines, including H33AJ-JA13 and MOLT3, in the G0/1 phase and induces apoptosis. Shokoofe Noorietal.[17]evaluated the immunotherapeutic effect of direct intra-tumor injection of Sclareol. The results reveal that intra-tumor injection of Sclareol reduces tumor size, significantly increases the number of lymphocytes, and up-regulates IFN-γ levels, decreases IL-4 levels; the numbers of CD4+, CD25+, Foxp3+, and Treg cells decrease over time. Thus, the role played by Sclareol in tumor immunotherapy was evaluated. Havva Afsharietal.[18]found that Sclareol reduces cell viability and induces apoptosis in breast cancer cells MCF-7. Sclareol combined with cyclophosphamide, a commonly used breast cancer treatment drug, significantly reduces MCF-7 cell viability and increases the number of apoptotic cells. Sclareol also up-regulates apoptosis-associated gene p53 and Bax expression, down-regulates Bcl-2 expression, inhibits STAT3 phosphorylation, and activates caspase-8 and caspase-9. The effect is more significant when Sclareol is combined with cyclophosphamide. In a study by Zhang Tingetal.[19], Sclareol was used to treat cervical cancer Hela cells. The result reveals that Sclareol inhibits HeLa cell proliferation and induces apoptosis in HeLa cells. The expression of the tumor suppressor geneCav1is up-regulated, the expression ofSOD1gene is down-regulated, and the expression of both genes is negatively correlated. Sclareol, combined with the anticancer drug bortezomib to treat HeLa cells, has a more significant inhibitory effect on cancer cell proliferation than Sclareol or bortezomib alone and significantly increases Cav1 protein levels. Konstantinos Dimasetal.[20]suggested that Sclareol treatment of colon cancer cells HCT116 results in cell cycle arrest in the G1 phase, induces cell apoptosis by inducing DNA damage, inhibits HCT116 cell proliferation, and down-regulates caspase-8 and caspase-9 expression. The result of theinvivoexperiments reveals that Sclareol bound to liposomes significantly reduces tumor size and inhibits tumor cell proliferation. Sophia Hatziantoniouetal.[21]found that growth inhibition of colon cancer HCT116 cells is time- and dose-dependent when Sclareol is combined with liposomes. The result of theinvivoexperiments suggests that Sclareol binding to liposomes reduces tumor size with low toxic side effects. Duan Guoqingetal.[22]found that Sclareol inhibits the proliferation of osteosarcoma MG63 cells, induces apoptosis, up-regulates Cyt-c and Bax expression, down-regulates anti-apoptotic gene Bcl-2 expression, and significantly decreases mitochondrial membrane potential.

2.5 Improving metabolic disordersThe global incidence of obesity in children and adolescents is on a continuous rise, and obesity has become a major global public health problem that threatens health and cause metabolic disorders[23]. However, Sclareol has been less studied in improving metabolic disorders. In the study of Cerri Gabriela Cavazza[24], it was found that lipid nanoparticles containing Sclareol effectively reduced blood glucose levels, decreased the number of adipocytes, inhibited mRNA expression of pro-inflammatory cytokines and lipogenesis-associated markers. Significantly increased serum levels of high-density lipoprotein (HDL) in obese mice. The results reveal that lipid nanoparticles containing Sclareol have therapeutic effects on metabolic disorders caused by obesity.

2.6 Analgesic effectDysmenorrhea is the most common gynecological condition affecting fertile women worldwide, with a prevalence of 16%-91%[25-26]. There have been rare reports of Sclareol exerting analgesic effect. Wong Jenniferetal.[27]found that Sclareol significantly inhibits uterine contractions and reduces the expression of uterine contraction-associated proteins COX-2, MLCK, p-ERK, p-p38 and p-MLC20 proteins in uterine tissues induced using PGF2α. Treatment of the acetic acid-induced writhing model with Sclareol significantly reduces the writhing times. Sclareol increases the number of writhing. Decreases in uterine contraction-associated proteins were detected in an oxytocin-induced motility model, thus having analgesic effects.

3 Conclusions

Sclareol, a diterpenoid natural product extracted from the inflorescence and stems and leaves of Sclareol in the Labiatae family, shows the advantages of low price, low toxicity, and easy availability. According to current literature studies, Sclareol has been found to possess various biological activities (e.g., anti-inflammatory, antibacterial, anti-photoaging, obesity improvement, and anti-tumor). Existing research on Sclareol is still at an early stage. For subsequent studies, the molecular mechanisms andinvivostudies of its therapeutic diseases can be expanded, or Sclareol can be combined with different nanomaterials to increase the pharmacological activity of Sclareol in terms of pharmacokinetics and pharmacotoxicology, and its absorption, distribution, metabolism, and excretion processes in the body can be improved. There have been rare reports on Sclareol derivatives. In future studies, if the multiple pharmacological activities of Sclareol are investigated thoroughly and extensively, the focus can be shifted to Sclareol derivatives. The comprehensive and in-depth development of Sclareol will lay a theoretical basis to promote the early market entry of Sclareol as a clinical drug.