Absorption, Distribution and Excretion
The terpenes disturb lipid arrangement in the intercellular region of the stratum corneum (SC) that leads to the increased permeability of the skin. This effect is used in technology of transdermal drug forms and depends on physicochemical properties of terpenes and their amounts penetrated to the stratum corneum; however terpenes do not need penetrate into viable skin tissue and this event is not even desired. To correlate skin absorption and elimination kinetics of four cyclic terpenes, namely alpha-pinene, beta-pinene, eucalyptol and terpinen-4-ol, applied as neat substance with their physicochemical properties. The terpenes were applied onto the human skin in vitro, and after 1-4 h their content in the separated by a tape-stripping method stratum corneum layers and in the epidermis/dermis was determined using GC. Similarly, the amounts of terpenes in the skin were analysed during 4 h following 1 h absorption. The fastest and progressive penetration into all skin layers was observed for terpinen-4-ol. All studied terpenes are absorbed in the viable epidermis/dermis, however penetration into this layers is time-dependent process, constantly increasing during 4 h. Like for stratum corneum, the largest cumulation in epidermis/dermis was observed for terpinen-4-ol. The elimination of terpenes from the stratum corneum was fast, especially in deeper layers, and much faster if the initial cumulation was small. Investigated cyclic terpenes represent different penetration and elimination characteristics and do not permeate across the skin to the acceptor medium due to large cumulation in the skin tissue. The penetration of terpenes into stratum corneum is greater if their log P-value is close to 3.
The purpose of this study was to evaluate the in vitro cutaneous penetration of five terpenes--linalool, linalyl acetate, terpinen-4-ol, citronellol and alpha-pinene--applied in pure essential oils or in dermatological formulations (o/w emulsion, oily solution or hydrogel) containing 0.75 % w/w of the essential oils. Different skin absorption was observed depending on the type of the vehicle and terpenes' log P values. Cutaneous accumulation of terpenes is several times higher when they are applied in pure essential oils than in topical vehicles. Penetration of terpinen-4-ol to the skin was better from an oily solution (approximately 90 ug/cm (2)) than from an emulsion (60 ug/cm (2)). No penetration of linalyl acetate from topical vehicles into viable skin was observed, but also for this terpene penetration to the upper layers of the stratum corneum was 2-times higher when an oily solution was used. In contrast, the cutaneous absorption of linalool was the same from both vehicles (50-60 ug/cm (2)). The skin penetration of alpha-pinene was not traceable when it was applied in an oily solution. Only a small amount (approximately 5 ug/cm (2)) of this terpene was determined in viable skin after application as a hydrogel. Citronellol applied in a hydrogel penetrated into all skin layers in a total amount of 25 ug/cm (2), while no penetration into viable skin layers after application of an oily solution was noted. Only citronellol permeated into the acceptor medium.
This work aimed to evaluate the effect induced by excipients conventionally used for topical dosage forms, namely isopropyl myristate (IPM) or oleic acid (OA) or polyethylene glycol 400 (PEG400) or Transcutol (TR), on the human skin permeability of terpinen-4-ol (T4OL) contained in the pure Tea tree oil. The effect of such excipients was determined by evaluating the absorption of T4OL using human epidermis and the perturbation of the organization of stratum corneum by ATR-FTIR. Among the tested excipients OA enhanced the absorption of T4OL by perturbing the stratum corneum lipid barrier. Other excipients caused a weak enhancement effect and their use should be carefully monitored.
The purpose of this study was to investigate dermal pharmacokinetics of terpinen-4-ol in rats following topical administration of plai oil derived from the rhizomes of Zingiber cassumunar Roxb. Unbound terpinen-4-ol concentrations in dermal tissue were measured by microdialysis. The dermal pharmacokinetic study of terpinen-4-ol was performed under non-occlusive conditions. The oil was topically applied at a dose of 2, 4, and 8 mg/square cm plai oil corresponding to the amount of 1.0, 1.9, and 3.8 mg/square cm terpinen-4-ol, respectively. Following topical application of the oil, terpinen-4-ol rapidly distributed into the dermis and demonstrated linear pharmacokinetics with no changes in the dose-normalized area under the concentration-time curves across the investigated dosage range. The mean percentages of free terpinen-4-ol distributed in the dermis per amount of administered were 0.39 +/- 0.06 %, 0.41 +/- 0.08 %, and 0.30 +/- 0.03 % for 2, 4, and 8 mg/square cm doses, respectively. The dermal pharmacokinetics of terpinen-4-ol could provide information for its further formulation development and therapy schedules.

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Metabolism / Metabolites
(R)-Terpinen-4-ol was mixed in an artificial diet at a concentration of 1 mg/g of diet, and the diet was fed to the last instar larvae of common cutworm (Spodoptera litura). Metabolites were recovered from frass and analyzed spectroscopically. (R)-Terpinen-4-ol was transformed mainly to (R)-p-menth-1-en-4,7-diol. Similarly, (S)-terpinen-4-ol was transformed mainly to (S)-p-menth-1-en-4,7-diol. The C-7 position (allylic methyl group) of (R)- and (S)-terpinen-4-ol was preferentially oxidized.
We examined the in vitro metabolism of (+)-terpinen-4-ol by human liver microsomes and recombinant enzymes. The biotransformation of (+)-terpinen-4-ol was investigated by gas chromatography-mass spectrometry (GC-MS). (+)-Terpinen-4-ol was found to be oxidized to (+)-(1R,2S,4S)-1,2-epoxy-p-menthan-4-ol, (+)-(1S,2R,4S)-1,2-epoxy-p-menthan-4-ol, and (4S)-p-menth-1-en-4,8-diol by human liver microsomal P450 enzymes. The identities of (+)-terpinen-4-ol metabolites were determined through the relative abundance of mass fragments and retention times on GC-MS. Of 11 recombinant human P450 enzymes tested, CYP1A2, CYP2A6, and CYP3A4 were found to catalyze the oxidation of (+)-terpinen-4-ol. Based on several lines of evidence, CYP2A6 and CYP3A4 were determined to be major enzymes involved in the oxidation of (+)-terpinen-4-ol by human liver microsomes. First, of the 11 recombinant human P450 enzymes tested, CYP1A2, CYP2A6 and CYP3A4 catalyzed oxidation of (+)-terpinen-4-ol. Second, oxidation of (+)-terpinen-4-ol was inhibited by (+)-menthofuran and ketoconazole, inhibitors known to be specific for these enzymes. Finally, there was a good correlation between CYP2A6 and CYP3A4 activities and (+)-terpinen-4-ol oxidation activities in the 10 human liver microsomes.

Toxicity Summary
IDENTIFICATION AND USE: 1-Terpinen-4-ol is colorless to pale yellow liquid with pine odor. It is found in more than 200 derivatives from leaves, herbs, and flowers. It is used in artificial geranium and pepper oils and in perfumery for creating herbaceous and lavender notes. It is also used as experimental medication and topical antimicrobial. HUMAN EXPOSURE AND TOXICITY: Terpinen-4-ol can induce human leukemic MOLT-4 cell apoptosis via both intrinsic and extrinsic pathways. It suppress the production of superoxide by monocytes, but not neutrophils, suggesting the potential for selective regulation of cell types by these components during inflammation. In addition, the water-soluble components of tea tree oil can suppress pro-inflammatory mediator production by activated human monocytes. ANIMAL STUDIES: Oral LD50's range from 1.0 to 4.3 g/kg in rodents. A single study of dermal toxicity in rabbits reported a LD50 of >3 g/kg.

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Interactions
This study compared the antimicrobial activity of Melaleuca alternifolia (tea tree) oil with that of some of its components, both individually and in two-component combinations. Minimum inhibitory concentration and time-kill assays revealed that terpinen-4-ol, the principal active component of tea tree oil, was more active on its own than when present in tea tree oil. Combinations of terpinen-4-ol and either gamma-terpinene or p-cymene produced similar activities to tea tree oil. Concentration-dependent reductions in terpinen-4-ol activity and solubility also occurred in the presence of gamma-terpinene. Non-oxygenated terpenes in tea tree oil appear to reduce terpinen-4-ol efficacy by lowering its aqueous solubility. These findings explain why tea tree oil can be less active in vitro than terpinen-4-ol alone and further suggest that the presence of a non-aqueous phase in tea tree oil formulations may limit the microbial availability of its active components.
Terpinen-4-ol (4TRP) is a monoterpenoid alcoholic component of essential oils obtained from several aromatic plants. We investigated the psychopharmacological and electrophysiological activities of 4TRP in male Swiss mice and Wistar rats. 4TRP was administered intraperitoneally (i.p.) at doses of 25 to 200 mg/kg and intracerebroventricularly (i.c.v.) at concentrations of 10, 20, and 40 ng/2 uL. For in vitro experiments, 4TRP concentrations were 0.1mM and 1.0mM. 4TRP (i.p.) inhibited pentylenetetrazol- (PTZ-) induced seizures, indicating anticonvulsant effects. Electroencephalographic recordings showed that 4TRP (i.c.v.) protected against PTZ-induced seizures, corroborating the behavioural results. To determine whether 4TRP exerts anticonvulsant effects via regulation of GABAergic neurotransmission, we measured convulsions induced by 3-mercapto-propionic acid (3-MP). The obtained results showed involvement of the GABAergic system in the anticonvulsant action exerted by 4TRP, but flumazenil, a selective antagonist of the benzodiazepine site of the GABAA receptor, did not reverse the anticonvulsant effect, demonstrating that 4TRP does not bind to the benzodiazepine-binding site. Furthermore, 4TRP decreased the sodium current through voltage-dependent sodium channels, and thus its anticonvulsant effect may be related to changes in neuronal excitability because of modulation of these channels.
Artemisia phaeolepis, a perennial herb with a strong volatile odor, grows on the grasslands of Mediterranean region. Essential oil obtained from Artemisia phaeolepis was analyzed by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. A total of 79 components representing 98.19% of the total oil were identified, and the main compounds in the oil were found to be eucalyptol (11.30%), camphor (8.21%), terpine-4-ol (7.32%), germacrene D (6.39), caryophyllene oxide (6.34%), and caryophyllene (5.37%). The essential oil showed definite inhibitory activity against 10 strains of test microorganisms. Eucalyptol, camphor, terpine-4-ol, caryophyllene, germacrene D and caryophyllene oxide were also examined as the major components of the oil. Camphor showed the strongest antimicrobial activity; terpine-4-ol, eucalyptol, caryophyllene and germacrene D were moderately active and caryophyllene oxide was weakly active. The study revealed that the antimicrobial properties of the essential oil can be attributed to the synergistic effects of its diverse major and minor components.
The combined effect of terpinen-4-ol, the main component of tea tree oil, and capric acid against mycelial growth of Candida albicans and murine oral candidiasis was evaluated in vitro and in vivo. Mycelial growth of C. albicans was estimated by the Cristal violet method. Combination of these compounds revealed a potent synergistic inhibition of growth. Therapeutic efficacy of the combination was evaluated microbiologically in murine oral candidiasis, and its application of the compounds clearly demonstrated therapeutic activity. Based on these results, the combined agent of terpinen-4-ol and capric acid was discussed as a possible candidate for oral candidiasis therapy.
The present study investigated the hypotensive responses to intravenous (i.v.) treatment with the essential oil of Alpinia zerumbet (EOAZ) and its main constituent, terpinen-4-ol (Trp-4-ol), in the experimental model of deoxycorticosterone-acetate (DOCA)-salt hypertensive rat. In both DOCA-salt hypertensive and uninephrectomized, normotensive rats, i.v. bolus injections of EOAZ (1-20 mg/kg) or Trp-4-ol (1-10 mg/kg) decreased mean aortic pressure (MAP) in a dose-related manner. However, hypotensive responses to Trp-4-ol were significantly greater than those evoked by the same doses of EOAZ (1-10 mg/kg). Treatment with DOCA-salt significantly enhanced the maximal percentage decreases in MAP evoked by EOAZ or Trp-4-ol. Likewise, both maximal percentage and absolute decreases in MAP elicited by i.v. injection of the ganglion blocker, hexamethonium (30 mg/kg), were significantly greater in DOCA-salt hypertensive than in control rats. In DOCA-salt hypertensive rats, neither hexamethonium (30 mg/kg, i.v.) nor methylatropine (1 mg/kg, i.v.) pretreatment affected the enhancement of EOAZ-induced hypotension. These results show that i.v. treatment with either EOAZ or Trp-4-ol dose-dependently decreases blood pressure in conscious DOCA-salt hypertensive rats, and this action is enhanced when compared with uninephrectomized controls. This enhancement could be related mainly to an increase in EOAZ-induced vascular smooth muscle relaxation rather than to enhanced sympathetic nervous system activity in this hypertensive model. The data further support our previous hypothesis that hypotensive effects of EOAZ are partially attributed to the actions of Trp-4-ol.

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Non-Human Toxicity Values
LD50 Rabbit Dermal >3 g/kg
LD50 Rat Oral 4.3 g/kg
LD50 rat oral 1300 mg/kg
LD50 Mice oral 1016 mg/kg

[1]. Terpinen-4-ol, the main component of the essential oil of Melaleuca alternifolia (tea tree oil), suppresses inflammatory mediator production by activated human monocytes. Inflamm Res. 2000 Nov;49(11):619-26.

[2]. Terpinen-4-ol: A Novel and Promising Therapeutic Agent for Human Gastrointestinal Cancers. PLoS One. 2016 Jun 8;11(6):e0156540.

4-terpineol is a terpineol that is 1-menthene carrying a hydroxy substituent at position 4. It has a role as a plant metabolite, an antibacterial agent, an antioxidant, an anti-inflammatory agent, an antiparasitic agent, an antineoplastic agent, an apoptosis inducer and a volatile oil component. It is a terpineol and a tertiary alcohol.
Terpinen-4-ol is under investigation in clinical trial NCT01647217 (Demodex Blepharitis Treatment Study).
4-Carvomenthenol has been reported in Anthriscus nitida, Tetradenia riparia, and other organisms with data available.
Terpinen-4-ol is a metabolite found in or produced by Saccharomyces cerevisiae.
See also: Lavender Oil (part of); Juniper Berry Oil (part of); Peumus boldus leaf (part of).

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Therapeutic Uses
EXPL THER To evaluate potential antiinflammatory properties of tea tree oil, the essential oil steam distilled from the Australian native plant, Melaleuca alternifolia. The ability of tea tree oil to reduce the production in vitro of tumour necrosis factor-alpha (TNFalpha), interleukin (IL)-1beta, IL-8, IL-10 and prostaglandin E2 (PGE2) by lipopolysaccharide (LPS)-activated human peripheral blood monocytes was examined. Tea tree oil emulsified by sonication in a glass tube into culture medium containing 10% fetal calf serum (FCS) was toxic for monocytes at a concentration of 0.016% v/v. However, the water soluble components of tea tree oil at concentrations equivalent to 0.125% significantly suppressed LPS-induced production of TNFalpha, IL-1beta and IL-10 (by approximately 50%) and PGE2 (by approximately 30%) after 40 h. Gas chromatography/mass spectrometry identified terpinen-4-ol (42 %), a-terpineol (3 %) and 1,8-cineole (2%, respectively, of tea tree oil) as the water soluble components of tea tree oil. When these components were examined individually, only terpinen-4-ol suppressed the production after 40 h of TNFalpha, IL-1beta, IL-8, IL-10 and PGE2 by LPS-activated monocytes. The water-soluble components of tea tree oil can suppress pro-inflammatory mediator production by activated human monocytes.
EXPL THER To evaluate the regulatory properties of the essential oil of Melaleuca alternifolia (tea tree oil) on the production of oxygen derived reactive species by human peripheral blood leukocytes activated in vitro. The ability of tea tree oil to reduce superoxide production by neutrophils and monocytes stimulated with N-formyl-methionyl-leucyl-phenylalanine (fMLP), lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA) was examined. The water-soluble fraction of tea tree oil had no significant effect on agonist-stimulated superoxide production by neutrophils, but significantly and dose-dependently suppressed agonist-stimulated superoxide production by monocytes. This suppression was not due to cell death. Chemical analysis identified the water-soluble components to be terpinen-4-ol, alpha-terpineol and 1,8-cineole. When examined individually, terpinen-4-ol significantly suppressed fMLP- and LPS- but not PMA-stimulated superoxide production; alpha-terpineol significantly suppressed fMLP-, LPS- and PMA-stimulated superoxide production; 1,8-cineole was without effect. Tea tree oil components suppress the production of superoxide by monocytes, but not neutrophils, suggesting the potential for selective regulation of cell types by these components during inflammation.
EXPL THER The aim of this study was to compare both the antimicrobial activity of terpinen-4-ol and tea tree oil (TTO) against clinical skin isolates of meticillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative staphylococci (CoNS) and their toxicity against human fibroblast cells. Antimicrobial activity was compared by using broth microdilution and quantitative in vitro time-kill test methods. Terpinen-4-ol exhibited significantly greater bacteriostatic and bactericidal activity, as measured by minimum inhibitory and bactericidal concentrations, respectively, than TTO against both MRSA and CoNS isolates. Although not statistically significant, time-kill studies also clearly showed that terpinen-4-ol exhibited greater antimicrobial activity than TTO. Comparison of the toxicity of terpinen-4-ol and TTO against human fibroblasts revealed that neither agent, at the concentrations tested, were toxic over the 24-hr test period. Terpinen-4-ol is a more potent antibacterial agent against MRSA and CoNS isolates than TTO with neither agent exhibiting toxicity to fibroblast cells at the concentrations tested. Terpinen-4-ol should be considered for inclusion as a single agent in products formulated for topical treatment of MRSA infection.
EXPL THER To examine the in vitro anticancer activity of Melaleuca alternifolia (tea tree) oil (TTO), and its major active terpene component, terpinen-4-ol, against two aggressive murine tumour cell lines, AE17 mesothelioma and B16 melanoma. Effects of TTO and terpinen-4-ol on the cellular viability of two tumour cell lines and fibroblast cells were assessed by MTT assay. Induction of apoptotic and necrotic cell death was visualised by fluorescent microscopy and quantified by flow cytometry. Tumour cell ultrastructural changes were examined by transmission electron microscopy and changes in cell cycle distribution were assessed by flow cytometry, with changes in cellular morphology monitored by video time lapse microscopy. TTO and terpinen-4-ol significantly inhibited the growth of two murine tumour cell lines in a dose- and time-dependent manner. Interestingly, cytotoxic doses of TTO and terpinen-4-ol were significantly less efficacious against non-tumour fibroblast cells. TTO and terpinen-4-ol induced necrotic cell death coupled with low level apoptotic cell death in both tumour cell lines. This primary necrosis was clarified by video time lapse microscopy and also by transmission electron microscopy which revealed ultrastructural features including cell and organelle swelling following treatment with TTO. In addition, both TTO and terpinen-4-ol induced their inhibitory effect by eliciting G1 cell cycle arrest. TTO and terpinen-4-ol had significant anti-proliferative activity against two tumour cell lines. Moreover, the identification of primary necrotic cell death and cell cycle arrest of the aggressive tumour cells highlights the potential anticancer activity of TTO and terpinen-4-ol.
For more Therapeutic Uses (Complete) data for 4-Terpineol (6 total), please visit the HSDB record page.

C₁₀H₁₈O

154.25

154.135

562-74-3

11230

Colorless to light yellow liquid

0.9±0.1 g/cm3

209.0±0.0 °C at 760 mmHg

79.4±0.0 °C

0.0±0.9 mmHg at 25°C

1.485

2.99

1

1

1

11

170

0

O([H])C1(C([H])([H])C([H])=C(C([H])([H])[H])C([H])([H])C1([H])[H])C([H])(C([H])([H])[H])C([H])([H])[H]

WRYLYDPHFGVWKC-UHFFFAOYSA-N

InChI=1S/C10H18O/c1-8(2)10(11)6-4-9(3)5-7-10/h4,8,11H,5-7H2,1-3H3

4-methyl-1-propan-2-ylcyclohex-3-en-1-ol

Terpinen4ol; Terpinen 4 ol

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: This product requires protection from light (avoid light exposure) during transportation and storage.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~100 mg/mL (~648.30 mM)
H2O : ≥ 25 mg/mL (~162.07 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (16.21 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (16.21 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (16.21 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 100 mg/mL (648.30 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)