Hinokitiol
Hinokitiol (β-thujaplicin) is a naturally occurring monoterpenoid found in the wooden part of trees in the family Cupressaceae. It is a tropolone derivative and is extensively used in oral care and treatment products for its potent broad-spectrum antiviral,[1] antimicrobial[2] and anti-inflammatory [3] properties. Hinokitiol is a Zinc, and Iron Ionophore additionally approved as a food additive.[4]
It was first isolated in Taiwanese hinoki in 1936, signifying the origin of the name Hinokitiol. It is almost absent in Japanese hinoki now. At the same time, it is still contained in high concentration (about 0.04% of heartwood mass) in Juniperus Cedrus, Hiba cedarwood (Thujopsis dolabrata) and Western red cedar (Thuja plicata). It can be easily extracted from the cedarwood with solvent and ultrasonication.[5] [6]
Hinokitiol is similar to a tropolone in structure, which lacks the isopropyl substituent. Tropolones are active chelating agents.
Antimicrobial activity
Hinokitiol has a wide range of biological activities, many of which have been discovered and specified in the literature. The first, and most famous, is the potent antimicrobial activity against many bacteria and fungi, regardless of antibiotic resistance. [7][8] To be precise, Hinokitiol has shown to be effective against Streptococcus pneumonia, Streptococcus mutans, and Staphylococcus Aureus, common human pathogens. [9][10] Additionally, Hinokitiol has been demonstrated to have inhibitory effects on Chlamydia trachomatis and may be clinically beneficial as a topical drug. [11][12]
Antiviral activity
Some recent studies have shown that Hinokitiol also demonstrates antiviral action when used in combination with a zinc compound against several human viruses, including rhinovirus, coxsackievirus, and mengovirus.[13] Curing viral infections has the potential to reap the mass economic benefit and must be of dire importance to global institutions such as the World Health Organisation. By impairing viral polyprotein processing, Hinokitiol inhibits viral replication - however, this capability is dependent upon the availability of divalent metal ions, as Hinokitiol is a chelator thereof.[14] The presence of zinc, combined with Hinokitiol, supports these capabilities and is discussed further as follows.
Anti-Inflammatory
Hinokitiol revealed a modulatory effect on the production of tumor necrosis factor (TNF)-alpha, a factor that influences skin inflammation and hair follicle apoptosis. This is achieved at the transcription level by disrupting the mRNA synthesis of TNF-alpha. Additionally, it suppresses phosphorylation of PDK1, Akt/PKB, and ERK, as a result diminishing the nuclear factor (NF)-kappaB activation, hence restoring hair loss.[15] In a recent study, Hinokitiol also revealed notable protection against ocular surface inflammation in dry eye syndrome (DES by inhibiting the NF-κB pathway [16].
Other activities
In addition to antimicrobial activity, anti-inflammatory, and anti-tumor activities, characterized in several in vitro cell studies and in vivo animal studies. Hinokitiol determined to exert cytotoxicity on several prominent cancer cell lines by inducing autophagic processes.[17][18]
Anti-Cancer
This study indicates the inhibitory effect of hinokitiol on the migration of human adenocarcinoma A549 cells. The anticancer properties of hinokitiol are supported by the evaluation of results in the present study, including an increase of Bax/p53 and cytochrome c, and further activation of caspases-9/-3 and antioxidant enzymes CAT and SOD. Moreover, we discovered the inhibitory impact of hinokitiol on the A549 cell migration was accompanied through the downregulation of MMPs-9 and MMP-2. These outcomes can also illustrate a new therapeutic value of hinokitiol in anticancer therapy.
Furthermore, another research showed strong anticancer characteristics of Hinokitiol by increasing the cytotoxicity against cervical cancer cells and non-small cell lung cancer (NSCLC) cells. Most cancers cell deaths are medicated through caspase-3 in apoptosis and consequently enlarged lysosomes which are regarded as the possession of anticancer compounds and that can possibly result in lysosomal injury and increased autophagy followed by severe cell death. The choice of therapeutic to hinokitiol, a herbal product derivative, can be concluded to have a mechanism of action against NSCLC with minimum cytotoxic and maximized therapeutic effects.[19]
Further Cancer research
Hinokitiol has shown an established mechanism to antagonize epidermal growth factor receptor (EGFR) protein expression in mammosphere production breast cancer stem/progenitor cells (BCSCs) without altering the messenger RNA expression. Hinokitiol also decreased the stability of EGFR in BCSCs. The stable protein expression of EGFR and vasculogenic mimicry (VM) production capability of hinokitiol treated BCSCs were restored by combination treatment with a proteasome antagonist, MG132. It can be concluded that hinokitiol may antagonize the VM activity of BCSCs by stimulating proteasome-mediated EGFR break-down. Hinokitiol may be considered as a novel breast cancer therapeutic agent, by acting as an anti-VM. [20]
Further study demonstrated Hinokitiol regulates estrogen receptor signaling and also antagonizes the proliferation of breast cancer cells in humans. Hence, it can be considered as a promising agent against the treatment of hormone-sensitive mammary tumorigenesis.[21]
Hinokitiol with Curcumin
A potent effect was observed against NSCLC and gefitinib resistant NSCLC cells when Hinokitiol was used in combination with Curcumin. This treatment indicated minimal cytotoxicity to healthy cells. [22]
Coronavirus research
Potential antiviral effects of Hinokitiol arise from its action as a zinc ionophore. Hinokitiol enables the influx of zinc ions into cells, which inhibit the replication machinery of RNA viruses, and subsequently hindering the replication of the virus.[23] Some notable RNA viruses include the human influenza virus, SARS. Zinc ions were able to inhibit viral replication within cells significantly and proved that the action was dependent on zinc influx. This study was done with the zinc ionophore pyrithione, which functions very similarly to Hinokitiol.[24] In cell cultures, hinokitiol inhibit human rhinovirus, coxsackievirus, and mengovirus multiplication. Hinokitiol interferes with the processing of viral polyproteins, thus inhibiting picornavirus replication. Hinokitiol inhibits the replication of picornaviruses by impairing the viral polyprotein processing and that the antiviral activity of hinokitiol is dependent on the availability of zinc ions.[25]
Iron ionophore
Hinokitiol has been shown to restore hemoglobin production in rodents. Hinokitiol acts as an iron ionophore to channel iron into cells,[26][27] increasing intracellular iron levels. Approximately 70% of the iron in humans is contained within red blood cells and specifically the hemoglobin protein. Iron is essential to almost all living organisms, and it is a critical element of several anatomical functions such as the oxygen transport system, deoxyribonucleic acid (DNA) synthesis, and electron transport and an iron deficiency can lead to blood disorders such as Anemia which, can be significantly detrimental to both physical and mental performance.[28]