Diesel Particulate Matter Permeation into Normal Human Skin and Intervention Using a Topical Ceramide Formulation.

INTRODUCTION: Diesel particulate matter (DPM) emitted from diesel engines is a major source of air pollutants. DPM is composed of elemental carbon, which adsorbs organic compounds including toxic polycyclic aromatic hydrocarbons (PAHs). The skin, as well as airways, is directly exposed to DPM, and association of atopic dermatitis, psoriasis flares, and premature skin aging with air pollutant levels has been documented. In skin, the permeation of DPM and DPM-adsorbed compounds is primarily blocked by the epidermal permeability barrier deployed in the stratum corneum. Depending upon the integrity of this barrier, certain amounts of DPM and DPM-adsorbed compounds can permeate into the skin. However, this permeation into human skin has not been completely elucidated. METHODS: We assessed the permeation of PAHs (adsorbed to DPM) into skin using ex vivo normal (barrier-competent) organ-cultured human skin after application of DPM. Two major PAHs, 2-methylnaphthalene and triphenylene, and a carcinogenic PAH, benzo(a)pyrene, all found in DPM, were measured in the epidermis and dermis using liquid chromatography electrospray ionization tandem mass spectrometry. In addition, we investigated whether a topical formulation can attenuate the permeation of DPM into skin. RESULTS: 2-Methylnaphthalene, triphenylene, and benzo(a)pyrene were recovered from the epidermis. Although these PAHs were also detected in the dermis after DPM application, these PAH levels were significantly lower than those found in the epidermis. We also demonstrated that a topical formulation that has the ability to form more uniform membrane structures can significantly suppress the permeation of PAHs adsorbed to DPM into the skin. CONCLUSION: Toxic compounds adsorbed by DPM can permeate even barrier-competent skin. Hence, barrier-compromised skin, such as in atopic dermatitis, psoriasis, and xerosis, is even more vulnerable to air pollutants. A properly formulated topical mixture that forms certain membrane structures on the skin surface can effectively prevent permeation of exogenous substances, including DPM, into skin.

The absence of bumblebees on an oceanic island blurs the species boundary of two closely related orchids.

Oceanic islands offer valuable natural laboratories for studying evolution. The Izu Islands, with their recent geological origin, provide an exceptional opportunity to explore the initial evolution on oceanic islands. Another noteworthy aspect is the absence of bumblebee species on most Izu Islands. We used ecological, morphological, and molecular data to investigate the impact of bumblebee absence on the evolution of two closely related orchid species, Goodyera henryi and Goodyera similis, focusing on Kozu Island, the Izu Islands. Our investigation revealed that while G. henryi exclusively relies on a bumblebee species for pollination on the mainland, G. similis is pollinated by scoliid wasps on both the mainland and the island. Intriguingly, all specimens initially categorized as G. henryi on Kozu Island are hybrids of G. henryi and G. similis, leading to the absence of pure G. henryi distribution on the island. These hybrids are pollinated by the scoliid wasp species that also pollinates G. similis on the island. The absence of bumblebees might result in sporadic and inefficient pollination of G. henryi by scoliid wasps, consequently promoting hybrid proliferation on the island. Our findings suggest that the absence of bumblebees can blur plant species boundaries.

Exogenous Ceramide Serves as a Precursor to Endogenous Ceramide Synthesis and as a Modulator of Keratinocyte Differentiation.

Since ceramide is a key epidermal barrier constituent and its deficiency causes barrier-compromised skin, several molecular types of ceramides are formulated in commercial topical agents to improve barrier function. Topical ceramide localizes on the skin surface and in the stratum corneum, but certain amounts of ceramide penetrate the stratum granulosum, becoming precursors to endogenous ceramide synthesis following molecular modification. Moreover, exogenous ceramide as a lipid mediator could modulate keratinocyte proliferation/differentiation. We here investigated the biological roles of exogenous NP (non-hydroxy ceramide containing 4-hydroxy dihydrosphingosine) and NDS (non-hydroxy ceramide containing dihydrosphingosine), both widely used as topical ceramide agents, in differentiated-cultured human keratinocytes. NDS, but not NP, becomes a precursor for diverse ceramide species that are required for a vital permeability barrier. Loricrin (late differentiation marker) production is increased in keratinocytes treated with both NDS and NP vs. control, while bigger increases in involucrin (an early differentiation marker) synthesis were observed in keratinocytes treated with NDS vs. NP and control. NDS increases levels of a key antimicrobial peptide (an innate immune component), cathelicidin antimicrobial peptide (CAMP/LL-37), that is upregulated by a ceramide metabolite, sphingosine-1-phosphate. Our studies demonstrate that NDS could be a multi-potent ceramide species, forming heterogenous ceramide molecules and a lipid mediator to enhance differentiation and innate immunity.

Different effects of l- and d-menthol on the microstructure of ceramide 5/cholesterol/palmitic acid bilayers.

The optical activity of transdermal permeation enhancers is one of the crucial factors for the enhancement of drug permeation via the skin. We investigated the effects of optically active menthols on a lipid bilayer model composed of ceramide 5, cholesterol, and palmitic acid. We first examined the fluidizing effects of l- and d-menthols on the lipid bilayers. The fluorescence anisotropy and thermodynamic parameters, such as the transition temperature and transition enthalpy, were significantly reduced by treatment with the optically active menthols. The effects of d-menthol were stronger than those of l-menthol. To discuss further, we also performed a detergent insolubility study and measured wide angle X-ray scattering. The amount of liquid-ordered phase membranes in the bilayers was significantly reduced by treatment with d-menthol. Whereas, l-menthol did not affected to the liquid-ordered phase membranes. The apparent ratio of orthorhombic hydrocarbon chain packing was substantially reduced by treatment with l-menthol. Thus, the distinct effects of optically active menthols on lipid bilayers were clarified: l-menthol acts on orthorhombic hydrocarbon chain packing with high selectivity, whereas d-menthol has no such specific effect. These findings extend our understanding of the mechanisms by which menthols affect the intercellular lipids in the stratum corneum.

Novel preparation of intercellular lipid models of the stratum corneum containing stereoactive ceramide.

The microstructure formed by intercellular lipids in the stratum corneum is important for the barrier function of the skin. However, the correlation between lipid composition and microstructure has not yet been clarified. To elucidate the microstructure of intercellular lipids in the stratum corneum, an intercellular lipid model was prepared from ceramide 5 (CER5), cholesterol (CHOL), and palmitic acid (PA), considering the nonuniformity of the lipid components of the stratum corneum. A response surface method incorporating thin-plate spline interpolation (RSM-S) was employed to prepare the CER5/CHOL/PA lipid bilayers. Fluorescence anisotropy of the CER5/CHOL/PA bilayers showed four distinct clusters based on Kohonen's self-organizing maps (SOM). At the centroid formulation of those clusters, the microstructures of CER5/CHOL/PA bilayers were determined using synchrotron X-ray scattering. Three kinds of lamellar structures and two kinds of lateral packing-namely, hexagonal and orthorhombic-were formed. The microstructure of the CER5/CHOL/PA bilayers was likely to be intrinsic to the intercellular lipids in the stratum corneum. In conclusion, the CER5/CHOL/PA bilayers prepared based on RSM-S and SOM were useful as models of the intercellular lipids in the stratum corneum.

Effect of l-menthol on the thermotropic behavior of ceramide 2/cholesterol mixtures as a model for the intercellular lipids in stratum corneum.

The major components of the intercellular lipids in the stratum corneum are ceramides (CERs), cholesterol (CHOL) and free fatty acids. To estimate the effects of l-menthol on the intercellular lipids, we elucidated the thermotropic behavior and lateral structure of a CER2/CHOL mixture. This formed a eutectic mixture at molar fraction of CHOL (Xch) = 0.6, as a lamellar structure with a repeat distance of 3.99 nm, and it showed a hexagonal hydrocarbon chain packing conformation at ambient temperature. In thermograms of the CER2/CHOL mixtures, the addition of l-menthol broadened the transition peaks and reduced the enthalpy of transition. The effect of l-menthol on the change in transition temperature of the eutectic mixture at Xch = 0.6 was weaker than for other molar fractions of CHOL. This suggested that the structure of the eutectic mixture was stable to the effects of l-menthol. Furthermore, l-menthol increased the repeat distance of the lamellar structure and inhibited the formation of hexagonal hydrocarbon chain packing. Therefore, l-menthol induced a disturbance of the lateral structure of the eutectic mixture of CER2/CHOL and the phase transition became unclear. These effects of l-menthol could enhance transdermal drug delivery.

Synthesis of l-muscone by asymmetric methylation via enol esters.

An effective synthetic route of l-muscone (1) by asymmetric methylation, followed by enolate-trapping to generate enol esters as intermediates, was described. Interestingly, the enol esters can be used as substrates for enzymatic optical resolution to improve optical purity. Additionally, several excellent new chiral ligands were discovered for asymmetric methylation of (E)-cyclopentadec-2-enone to produce l-muscone with high optical purity.