Stratum corneum absorption and retention of linalool and terpinen-4-ol applied as gel or oily solution in humans

Alpha-pinene attenuates UVA-induced photoaging through inhibition of matrix metalloproteinases expression in mouse skin

AIM

The present study was designed to examine the role of alpha-pinene (AP) against skin photoaging in UVA-irradiated mice.

MATERIALS AND METHODS

Swiss albino mice were subjected to UVA-irradiation at the rate of 10 J/cm² per day for ten days, totally mouse received 100 J/cm². One hour prior to each UVA-exposure, the mouse skin was topically treated with AP (100 mg kg/b·wt). Biochemical methods were employed to study the status of antioxidant enzymes and lipid peroxidation. Histopathological observations were performed using hematoxylin and eosin (H & E) and Verhoeff van Gieson (VVG) staining in the mouse skin. The inflammatory and apoptotic protein expression was studied by immunohistochemical and Western blot methods. The mRNA expression of matrix metalloproteinases was determined by qRT-PCR and Western blot analysis.

KEY FINDINGS

We found that AP pretreatment substantially ameliorated UVA-induced depletion of antioxidant enzymes and prevented UVA-induced lipid peroxidation in the mouse skin. Further, AP effectively inhibited UVA-induced activation of pro-angiogenic (iNOS and VEGF), inflammatory proteins (TNF-α, IL-6, and COX-2) expression and prevented the activation of NF-κB p65 in the mouse skin. Additionally, AP inhibited UVA-mediated apoptotic mediators (Bax, Bcl-2, caspase-3 and caspase 9) expression in the mouse skin. Moreover, AP inhibited mRNA expression of matrix metalloproteinases (MMP-13 and MMP-9) and tissue type IV collagenase (MMP-2) expression in the mouse skin. Histological studies showed that AP remarkably prevented the dermal tissue damage in UVA-irradiated mice.

CONCLUSION

Thus, AP treatment effectively prevented UVA-induced photoaging probably through its antioxidant property.

RIFM fragrance ingredient safety assessment, linalyl benzoate, CAS Registry Number 126-64-7

The use of this material under current conditions is supported by existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental and reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, as well as environmental safety. Data show that this material is not genotoxic. Data from the suitable read across analog linalyl phenylacetate (CAS # 7143-69-3) show that this material does not have skin sensitization potential. The repeated dose toxicity endpoint was completed using linalyl cinnamate (CAS # 78-37-5) as a suitable read across analog, which provided a MOE > 100. The developmental and reproductive toxicity endpoint was completed using linalool (CAS # 78-70-6), dehydrolinalool (CAS # 29171-20-8), benzoic acid (CAS # 65-85-0) and sodium benzoate (CAS # 532-32-1) as suitable read across analogs, which provided a MOE > 100. The local respiratory toxicity endpoint was completed using linalool (CAS # 78-70-6) and benzoic acid (CAS # 65-85-0) as suitable read across analogs, which provided a MOE > 100. The phototoxicity/photoallergenicity endpoint was completed based on suitable UV spectra. The environmental endpoint was completed as described in the RIFM Framework along with data from the suitable read across analog linalyl cinnamate (CAS # 78-375).

RIFM fragrance ingredient safety assessment, 3,7-dimethyl-1,6-nonadien-3-ol, CAS Registry Number 10339-55-6

The use of this material under current conditions is supported by existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental and reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, as well as environmental safety. Data from the suitable read across analog linalool (CAS # 78-70-6) show that this material is not genotoxic nor does it have skin sensitization potential and also provided a MOE > 100 for the local respiratory endpoint. The repeated dose, developmental and reproductive toxicity endpoints were completed using nerolidol (isomer unspecified, CAS # 7212-44-4) as a suitable read across analog, which provided a MOE > 100. The phototoxicity/photoallergenicity endpoint was completed based on suitable UV spectra. The environmental endpoint was completed as described in the RIFM Framework.

RIFM fragrance ingredient safety assessment, linalyl cinnamate, CAS Registry Number 78-37-5

The use of this material under current conditions is supported by existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental and reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, as well as environmental safety. Data show that this material is not genotoxic nor does it have skin sensitization potential. The reproductive and local respiratory toxicity endpoints were completed using the TTC (Threshold of Toxicological Concern) for a Cramer Class I material (0.03 and 1.4 mg/day, respectively). The developmental toxicity endpoint was completed using linalool (CAS # 78-70-6), dehydrolinalool (CAS # 29171-20-8) and cinnamic acid (CAS # 621-82-9) as suitable read across analogs, which provided a MOE > 100. The repeated dose toxicity endpoint was completed using data on the target material which provided a MOE > 100. The phototoxicity/photoallergenicity endpoint was completed based on suitable UV spectra. The environmental endpoint was completed as described in the RIFM Framework.

RIFM fragrance ingredient safety assessment, l-linalool, CAS Registry Number 126-91-0

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity, skin sensitization potential, as well as, environmental safety. Repeated dose toxicity was determined using a suitable read across analog to have the most conservative systemic exposure derived NO[A]EL of 36 mg/kg/day. A dermal 90-day subchronic toxicity study conducted in rats resulted in a MOE of 2250 while considering 14.4% absorption from skin contact and 100% from inhalation. A MOE of >100 is deemed acceptable.

Structure-odor relationships of linalool, linalyl acetate and their corresponding oxygenated derivatives

Linalool 1 is an odorant that is commonly perceived as having a pleasant odor, but is also known to elicit physiological effects such as inducing calmness and enhancing sleep. However, no comprehensive studies are at hand to show which structural features are responsible for these prominent effects. Therefore, a total of six oxygenated derivatives were synthesized from both 1 and linalyl acetate 2, and were tested for their odor qualities and relative odor thresholds (OTs) in air. Linalool was found to be the most potent odorant among the investigated compounds, with an average OT of 3.2 ng/L, while the 8-hydroxylinalool derivative was the least odorous compound with an OT of 160 ng/L; 8-carboxylinalool was found to be odorless. The odorant 8-oxolinalyl acetate, which has very similar odor properties to linalool, was the most potent odorant besides linalool, exhibiting an OT of 5.9 ng/L. By comparison, 8-carboxylinalyl acetate had a similar OT (6.1 ng/L) as its corresponding 8-oxo derivative but exhibited divergent odor properties (fatty, greasy, musty). Overall, oxygenation on carbon 8 had a substantial effect on the aroma profiles of structural derivatives of linalool and linalyl acetate.

RIFM fragrance ingredient safety assessment, linalyl isobutyrate, CAS registry number 78-35-3

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity, skin sensitization potential, as well as, environmental safety. Reproductive toxicity was based on the Threshold of Toxicological Concern (TTC) of 0.03 mg/kg/day for a Cramer Class I material. The estimated systemic exposure is determined to be below this value while assuming 80% absorption from skin contact and 100% from inhalation. A systemic exposure below the TTC value is acceptable.

RIFM fragrance ingredient safety assessment, Linalyl isovalerate, CAS Registry Number 1118-27-0

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity, skin sensitization potential, as well as, environmental safety. Reproductive toxicity was based on the Threshold of Toxicological Concern (TTC) of 0.03 mg/kg/day for a Cramer Class I material. The estimated systemic exposure is determined to be equal to this value while assuming 100% absorption from skin contact and inhalation. A systemic exposure at or below the TTC value is acceptable.

RIFM fragrance ingredient safety assessment, 2-methyl-3-buten-2-ol, CAS Registry Number 115-18-4

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity, skin sensitization potential as well as environmental safety. Repeated dose, developmental, and reproductive toxicities were determined to have the most conservative systemic exposure derived NO[A]EL of 50 mg/kg/day, based on OECD gavage toxicity studies in rats, that resulted in a MOE of 4545455 after considering 100% absorption from skin contact and inhalation. A MOE of >100 is deemed acceptable.

Inhibitory effect of terpinen-4-ol on voltage-dependent potassium currents in rat small sensory neurons

The biological and pharmacological activities of the terpenoid terpinen-4-ol (1), which include depressant effects in the central nervous system, are of potential therapeutic interest. In the present study, the effects of 1 on neuronal excitability and voltage-dependent K(+) currents in the somatic sensory system were investigated. Intact and dissociated neurons of rat dorsal root ganglia (DRG) were used for intracellular and patch-clamp recordings, respectively. In neurons of intact DRG, 1 caused concentration-dependent depolarization of the resting membrane potential and increased input resistance. 1 also inhibited action potentials (AP) and decreased AP parameters, with the exception of AP duration, which was increased. In dissociated DRG neurons, 1 partially blocked the total K(+) current in a concentration-dependent manner. 1 inhibited I(A), I(D), and I(K) with IC50 values of 3.2 ± 03, 0.7 ± 0.1, and 1.6 ± 0.7 mM, respectively. 1 did not shift either the steady-state activation or inactivation curves of I(A), I(D), and I(K) but reduced the decay time course of I(A). The alterations in DRG reported here are consistent with the inhibition of K(+) currents and might partially explain the effect of 1 on excitable tissues.

The effects of excipients for topical preparations on the human skin permeability of terpinen-4-ol contained in Tea tree oil: infrared spectroscopic investigations

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.

Semisolid formulations containing dimethyl sulfoxide and α-tocopherol for the treatment of extravasation of antiblastic agents

The topical treatment with dimethyl sulfoxide (DMSO) and/or alpha-tocopherol (alpha-T) is widely used in order to prevent the local complications of extravasation of cytostatic drugs and protect patients against skin ulceration. Till now, DMSO and alpha-T have been mainly used in solution. The goal of this study was to formulate semisolid preparations for cutaneous application differing in the hydrophilic and lipophilic properties and containing DMSO and alpha-T in combination. With respect to solutions, the use of semisolid preparations containing DMSO and alpha-T could be advantageous in patients having extravasation as DMSO and alpha-T can remain in contact with the skin over an extended period of time. As a consequence, the action of the active principles can be limited specifically on the injured skin area, reducing the cutaneous irritative effects of DMSO. The following types of semisolid formulations containing 50% m/m DMSO and 2.5% m/m alpha-T were prepared: hydrophilic ointment, o/w emulsion, hydrophilic gel and lipophilic gel. The ex vivo skin permeation of DMSO and alpha-T was evaluated by using modified Franz's diffusion cells and human stratum corneum and epidermis (SCE) as a membrane. The permeated and retained amounts of DMSO and alpha-T were determined. The oleogel preparation, the hydrophilic gel and the o/w emulsion were uniform in colour and aspect, without any evidences of phase separation over the period of the study. Hydrophilic ointments were discarded as they showed phase separation after 12 h. All formulations had a different behaviour in terms of skin permeability. In particular, hydrogel and o/w emulsion showed the best control on the drug release considering the interactions of the vehicle components with the SCE and the drugs partition between the vehicle and the SCE. The DMSO permeated amount after 24 h was 4.1 mg/cm(2) for hydrogel and 2.5 mg/cm(2) for emulsion while the permeated amount of pure DMSO after 24 h was 47.5 mg/cm(2). Therefore, aiming to reduce side effects after the topical application of the antidotes DMSO and alpha-T, these results suggested that hydrogel and o/w emulsion could be considered the most promising formulations for further clinical evaluations in managing of extravasation of anthracyclines.