Activation of non-sensitizing or low-sensitizing fragrance substances into potent sensitizers - prehaptens and prohaptens

Titanium: a review on exposure, release, penetration, allergy, epidemiology, and clinical reactivity

Exposure to titanium (Ti) from implants and from personal care products as nanoparticles (NPs) is common. This article reviews exposure sources, ion release, skin penetration, allergenic effects, and diagnostic possibilities. We conclude that human exposure to Ti mainly derives from dental and medical implants, personal care products, and foods. Despite being considered to be highly biocompatible relative to other metals, Ti is released in the presence of biological fluids and tissue, especially under certain circumstances, which seem to be more likely with regard to dental implants. Although most of the studies reviewed have important limitations, Ti seems not to penetrate a competent skin barrier, either as pure Ti, alloy, or as Ti oxide NPs. However, there are some indications of Ti penetration through the oral mucosa. We conclude that patch testing with the available Ti preparations for detection of type IV hypersensitivity is currently inadequate for Ti. Although several other methods for contact allergy detection have been suggested, including lymphocyte stimulation tests, none has yet been generally accepted, and the diagnosis of Ti allergy is therefore still based primarily on clinical evaluation. Reports on clinical allergy and adverse events have rarely been published. Whether this is because of unawareness of possible adverse reactions to this specific metal, difficulties in detection methods, or the metal actually being relatively safe to use, is still unresolved.

Oxidized limonene and oxidized linalool - concomitant contact allergy to common fragrance terpenes

BACKGROUND

Limonene and linalool are common fragrance terpenes. Both oxidized R-limonene and oxidized linalool have recently been patch tested in an international setting, showing contact allergy in 5.2% and 6.9% of dermatitis patients, respectively.

OBJECTIVE

To investigate concomitant reactions between oxidized R-limonene and oxidized linalool in consecutive dermatitis patients.

METHODS

Oxidized R-limonene 3.0% (containing limonene hydroperoxides 0.33%) and oxidized linalool 6% (linalool hydroperoxides 1%) in petrolatum were tested in 2900 consecutive dermatitis patients in Australia, Denmark, Singapore, Spain, Sweden, and the United Kingdom.

RESULTS

A total of 281 patients reacted to either oxidized R-limonene or oxidized linalool. Of these, 25% had concomitant reactions to both compounds, whereas 29% reacted only to oxidized R-limonene and 46% only to oxidized linalool. Of the 152 patients reacting to oxidized R-limonene, 46% reacted to oxidized linalool, whereas 35% of the 200 patients reacting to oxidized linalool also reacted to oxidized R-limonene.

CONCLUSIONS

The majority of the patients (75%) reacted to only one of the oxidation mixtures, thus supporting the specificity of the reactions. The concomitant reactions to the two fragrance allergens suggest multiple sensitizations, which most likely reflect the exposure to the different fragrance materials in various types of consumer products. This is in accordance with what is generally seen for patch test reactions to fragrance materials.

Analysis of publically available skin sensitization data from REACH registrations 2008-2014

The public data on skin sensitization from REACH registrations already included 19,111 studies on skin sensitization in December 2014, making it the largest repository of such data so far (1,470 substances with mouse LLNA, 2,787 with GPMT, 762 with both in vivo and in vitro and 139 with only in vitro data). 21% were classified as sensitizers. The extracted skin sensitization data was analyzed to identify relationships in skin sensitization guidelines, visualize structural relationships of sensitizers, and build models to predict sensitization.

A chemical with molecular weight > 500 Da is generally considered non-sensitizing owing to low bioavailability, but 49 sensitizing chemicals with a molecular weight > 500 Da were found.

A chemical similarity map was produced using PubChem’s 2D Tanimoto similarity metric and Gephi force layout visualization. Nine clusters of chemicals were identified by Blondel’s module recognition algorithm revealing wide module-dependent variation.

Approximately 31% of mapped chemicals are Michael’s acceptors but alone this does not imply skin sensitization. A simple sensitization model using molecular weight and five ToxTree structural alerts showed a balanced accuracy of 65.8% (specificity 80.4%, sensitivity 51.4%), demonstrating that structural alerts have information value.

A simple variant of k-nearest neighbors outperformed the ToxTree approach even at 75% similarity threshold (82% balanced accuracy at 0.95 threshold). At higher thresholds, the balanced accuracy increased. Lower similarity thresholds decrease sensitivity faster than specificity.

This analysis scopes the landscape of chemical skin sensitization, demonstrating the value of large public datasets for health hazard prediction.

The formation of highly oxidized multifunctional products in the ozonolysis of cyclohexene

The prompt formation of highly oxidized organic compounds in the ozonolysis of cyclohexene (C6H10) was investigated by means of laboratory experiments together with quantum chemical calculations. The experiments were performed in borosilicate glass flow tube reactors coupled to a chemical ionization atmospheric pressure interface time-of-flight mass spectrometer with a nitrate ion (NO3(-))-based ionization scheme. Quantum chemical calculations were performed at the CCSD(T)-F12a/VDZ-F12//ωB97XD/aug-cc-pVTZ level, with kinetic modeling using multiconformer transition state theory, including Eckart tunneling corrections. The complementary investigation methods gave a consistent picture of a formation mechanism advancing by peroxy radical (RO2) isomerization through intramolecular hydrogen shift reactions, followed by sequential O2 addition steps, that is, RO2 autoxidation, on a time scale of seconds. Dimerization of the peroxy radicals by recombination and cross-combination reactions is in competition with the formation of highly oxidized monomer species and is observed to lead to peroxides, potentially diacyl peroxides. The molar yield of these highly oxidized products (having O/C > 1 in monomers and O/C > 0.55 in dimers) from cyclohexene ozonolysis was determined as (4.5 ± 3.8)%. Fully deuterated cyclohexene and cis-6-nonenal ozonolysis, as well as the influence of water addition to the system (either H2O or D2O), were also investigated in order to strengthen the arguments on the proposed mechanism. Deuterated cyclohexene ozonolysis resulted in a less oxidized product distribution with a lower yield of highly oxygenated products and cis-6-nonenal ozonolysis generated the same monomer product distribution, consistent with the proposed mechanism and in agreement with quantum chemical modeling.