Nanotechnology, cosmetics and the skin: is there a health risk?

Cosmetic formulations may contain nano-emulsions and microscopic vesicles consisting of traditional cosmetic materials, although it is uncertain whether they should be qualified as actual nanomaterials. Vesicle materials do not penetrate into living human skin. Vesicle formulations may enhance or reduce skin absorption of ingredients, albeit at a limited scale. Sunscreens contain TiO2 or ZnO nanoparticles (NP), which are efficient UV filters. A number of studies suggest that insoluble NP do not penetrate into or through human skin. The results of in vivo toxicity tests showed that TiO2 and ZnO NP are non-toxic. In vitro and in vivo cytotoxicity, genotoxicity, photogenotoxicity, acute toxicity, sensitisation and ecotoxicology studies on TiO2 NP found no difference in the safety profile of micro- or nano-sized materials, all of which were non-toxic. Although some in vitro investigations on TiO2 particles reported cell uptake, oxidative cell damage or genotoxicity, these results may be secondary to phagocytosis of cells exposed to excessive particle concentrations. Studies on wear debris nano- and microparticles support the traditional view that toxicity of small particles is related to their chemistry, rather than their particle size. There is little evidence supporting a general rule that adverse effects of particles on the skin or other tissues increase with smaller particle size, or produce novel toxicities relative to those of larger particles. Overall, the current evidence suggests that nano-sized cosmetic or sunscreen ingredients pose no potential risk to human health, whereas their use in sunscreens has large benefits, such as the protection of human skin against skin cancer.

Human percutaneous absorption of a direct hair dye comparing in vitro and in vivo results: implications for safety assessment and animal testing.

Although in vitro skin absorption studies often detect small residues of applied test material in the epidermis/dermis, it is uncertain whether the residue is within the living skin. We studied the dermal absorption of a hair dye hydroxyanthraquinone-aminopropyl methyl morpholinium methosulphate (HAM) in human skin in vivo and in vitro. In vivo, skin (back and scalp) received 0.5% HAM in a commercial formulation at 20microg/cm2 After 0.5 or 48h, skin was tape stripped, followed by cyanoacrylate biopsies (CAB). Sebum from scalp sites was collected for 48h. In vitro, skin was treated with 20mg/cm2 dye for 0.5h, penetration determined after 24h. In vivo, at 0.5h, total recovery (back) was 0.67microg/cm2 (tape strips+CAB). Fluorescence microscopy showed HAM in the hair follicle openings (HFO). At 0.5h, scalp tape strips contained 1.80microg/cm2, HFO 0.82microg/cm2. At 48h, HFO contained 0.21microg/cm2, sebum 0.80microg/cm2. In vivo, skin residues were in the non-living skin and eliminated via desquamation and sebum secretion. In vitro, the SC contained 1.50microg/cm2, epidermis/dermis 0.86microg/cm2, receptor fluid<0.04microg/cm2, a total of 0.90microg/cm2 was considered to be bioavailable. In vitro epidermis/dermis residues were nearly identical to those located in non-living skin in vivo. In conclusion, in vitro percutaneous penetration studies may produce seemingly bioavailable material , which raises the need for a Threshold of Skin Absorption (TSA) addressing a negligible dermal absorption in order to avoid unnecessary in vivo toxicity studies on substances that produce no significant human systemic exposure.

The contribution of arginine residues within the P6-P1 region of alpha 1-antitrypsin to its reaction with furin.

A series of mutants incorporating furin recognition sequences within the P6-P1 region of the reactive site loop of alpha(1)-antitrypsin were constructed. Variants containing different combinations of basic residues in the P1, P2, P4, and P6 positions replacing the wild type (P6)LEAIPM(P1) sequence were evaluated for their capacity to establish SDS-resistant complexes with furin, to affect association rate constants (k(ass) and k'(ass)), or to inhibit furin-dependent proteolysis of a model precursor in vivo. Each variant abolished processing of pro-von Willebrand factor in transfected hEK293 cells. The k(ass) of all variants were found to be similar (1.1-1.7 x 10(6) m(-1) s(-1)) except for one mutant, RERIRR, which had a k(ass) of 3.3 x 10(5) m(-1) s(-1). However, the stoichiometry of inhibition varied with values ranging from 2.9 to >24, indicating rapid formation of the acyl-enzyme intermediate (high k'(ass)). Moreover, those variants having high stoichiometry of inhibition values were accompanied by the rapid formation of cleaved forms of the inhibitors. The data suggest that the rate of conversion of the acyl-enzyme (EI') into the highly stable complex (EI*) was affected by replacement of specific residues within the reactive site loop. Taken together, the results reveal how furin recognition sequences within the context of the biochemical properties of serpins will play a role in the capacity of the protein to follow either the inhibitory or the substrate pathway.

Characterization of METH-1/ADAMTS1 processing reveals two distinct active forms.

METH-1/ADAMTS1 is a member of a newly described family of genes that contain metalloprotease, disintegrin, and thrombospondin-like motifs. We have recently shown that METH-1 protein is a potent inhibitor of angiogenesis. Here, we demonstrate that secreted human pro-METH-1 is processed in two consecutive steps to release both p87 and p65 active forms. The p87 form lacks the N-terminal prodomain and p65 results from an additional processing event in the C-terminal end. Generation of p87 was blocked with specific inhibitors of furin, and incubation of pro-METH-1 with purified furin released the p87 fragment but not p65. Generation of p65 required preformation of p87 and was suppressed by inhibitors of matrix metalloproteases. We demonstrate that matrix metalloproteases 2, 8, and 15 were able to release p65 when p87 was used as substrate. This second processing step removes two thrombospondin repeats from the carboxyl-terminal end of p87-METH-1 and alters the affinity of the protein to heparin and endothelial cultures. Furthermore, this deletion was associated with a reduced activity upon suppression of endothelial cell proliferation. We hypothesize that METH-1 processing is relevant for the modulation of the anti-angiogenic properties displayed by the protein.

Serpin-like properties of alpha1-antitrypsin Portland towards furin convertase.

Recent studies have demonstrated that a serpin variant, alpha1-antitrypsin Portland (AT-PDX), can inhibit the mammalian convertase furin. Here, we examine the mechanism by which this inhibition takes place. We find that furin, which does not belong to the trypsin-like serine protease family, the usual targets of serpins, forms an SDS-heat denaturation-resistant complex with AT-PDX both in vitro and in vivo. AT-PDX inhibited furin with an association rate constant (k(ass)) of 1.5 x 10(6) M(-1) s(-1) which is similar to k(ass) values reported for serpins with trypsin-like enzymes. These results illustrate that AT can be modified to act essentially as a suicide inhibitor of furin, an enzyme of the subtilase superfamily of serine proteases.