Quantitative determination of skin penetration of PEG-coated CdSe quantum dots in dermabraded but not intact SKH-1 hairless mouse skin.

Many cosmetics, sunscreens, and other consumer products are reported to contain nanoscale materials. The possible transdermal absorption of nanoscale materials and the long-term consequences of the absorption have not been determined. We used polyethylene glycol coated cadmium selenide (CdSe) core quantum dots (QD; 37 nm diameter) to evaluate the penetration of nanoscale material into intact, tape stripped, acetone treated, or dermabraded mouse skin. QD were suspended in an oil-in-water emulsion (approximately 9 microM) and the emulsion was applied at 2 mg/cm(2) to mouse dorsal skin pretreated as follows: intact; tape stripped to remove the stratum corneum; acetone pretreated; dermabraded to remove stratum corneum and epidermis. QD penetration into the skin was monitored in sentinel organs (liver and regional draining lymph nodes) using inductively coupled plasma mass spectrometry analysis of cadmium (from the CdSe QD). No consistent cadmium elevation was detected in the sentinel organs of mice with intact, acetone pretreated, or tape-stripped skin at 24- and 48-h post-QD application; however, in dermabraded mice, cadmium elevations were detected in the lymph nodes and liver. QD accumulation (as cadmium) in the liver was approximately 2.0% of the applied dose. The passing of QD through the dermabraded skin was confirmed using confocal fluorescence microscopy. These results suggest that transdermal absorption of nanoscale materials depends on skin barrier quality, and that the lack of an epidermis provided access to QD penetration. Future dermal risk assessments of nanoscale materials should consider key barrier aspects of skin and its overall physiologic integrity.

Simulated solar light-induced p53 mutagenesis in SKH-1 mouse skin: a dose-response assessment.

Sunlight and ultraviolet-induced mutation of the p53 gene is a frequent, possibly obligate step in skin cancer development, making quantitative measurement of p53 mutation an ideal biomarker for sunlight-induced skin carcinogenesis. To understand how the appearance of p53 mutation relates to skin tumor development, SKH-1 hairless mice were exposed 5 d per week to one of four different doses of simulated solar light (SSL; 0, 6.85, 13.70, 20.55 mJ x CIE/cm(2)) previously characterized for their tumorigenic potential. Allele-specific competitive blocker-PCR (ACB-PCR) was used to measure levels of p53 codon 270 CGT to TGT mutation within DNA isolated from dorsal skin of exposed mice. For each dose, p53 mutant fraction (MF) was measured after 4, 16, and 28 wk of exposure. Significant dose- and time-dependent increases in p53 MF were identified. All p53 MF measurements were integrated by relating the observed p53 MF to the cumulative dose of SSL. The increase in the logarithm of p53 MF was described by the linear function: log(10) MF = alpha + 0.0016 x d, where alpha is the spontaneous log(10) MF after a particular time point and d is the dose of SSL in mJ x CIE/cm(2). The p53 MF induced in nontumor bearing skin by 28 wk of exposure at the high dose of SSL was significantly lower than that found in skin tumors induced by approximately 32 wk of exposure to the same dose of SSL. p53 MF showed a strong negative correlation with tumor latency, suggesting this quantitative biomarker has the potential to predict tumorigenicity.

Migration of intradermally injected quantum dots to sentinel organs in mice.

Topical exposure to nanoscale materials is likely from a variety of sources including sunscreens and cosmetics. Because the in vivo disposition of nanoscale materials is not well understood, we have evaluated the distribution of quantum dots (QDs) following intradermal injection into female SKH-1 hairless mice as a model system for determining tissue localization following intradermal infiltration. The QD (CdSe core, CdS capped, poly[ethylene glycol] coated, 37 nm diameter, 621 nm fluorescence emission) were injected intradermally (ID) on the right dorsal flank. Within minutes following intradermal injection, the highly UV fluorescent QD could be observed moving from the injection sites apparently through the lymphatic duct system to regional lymph nodes. Residual fluorescent QD remained at the site of injection until necropsy at 24 h. Quantification of cadmium and selenium levels after 0, 4, 8, 12, or 24 h in multiple tissues, using inductively coupled plasma mass spectrometry (ICP-MS), showed a time-dependent loss of cadmium from the injection site, and accumulation in the liver, regional draining lymph nodes, kidney, spleen, and hepatic lymph node. Fluorescence microscopy corroborated the ICP-MS results regarding the tissue distribution of QD. The results indicated that (1) ID injected nanoscale QD remained as a deposit in skin and penetrated the surrounding viable subcutis, (2) QD were distributed to draining lymph nodes through the sc lymphatics and to the liver and other organs, and (3) sentinel organs are effective locations for monitoring transdermal penetration of nanoscale materials into animals.

Levels of retinyl palmitate and retinol in stratum corneum, epidermis and dermis of SKH-1 mice.

Vitamin A (retinol) regulates many biological functions, including epidermal cell growth. Retinyl palmitate (RP) is the major esterified form of retinol and the predominant component of retinoids in the skin; however, how endogenous levels of RP and retinol in the skin are affected by the age of the animal remains unknown. Furthermore, the levels of retinol and RP in the various skin layers - the stratum corneum, epidermis and dermis of skin - have not been reported. In this paper, we report the development of a convenient method for separation of the skin from SKH-1 female mice into the stratum corneum, epidermis, and dermis and the determination of the levels of RP and retinol in the three fractions by HPLC analysis. The total quantities of RP and retinol from the stratum corneum, epidermis, and dermis are comparable to those extracted from the same amount of intact skin from the same mouse. There was an age-related effect on the levels of RP and retinol in the skin and liver of female mice. An age-related effect was also observed in the stratum corneum, epidermis, and dermis. The levels of RP and retinol were highest in the epidermis of 20-week-old mice, and decreased when the age increased to 60- and 68-weeks. The total amount of RP at 20 weeks of age was found to be 1.52 ng/mg skin, and decreased about 4-fold at 60- and 68-weeks of age. A similar trend was found for the effects of age on the levels of retinol.

Genotoxicity of malachite green and leucomalachite green in female Big Blue B6C3F1 mice.

Malachite green, a triphenylmethane dye used in aquaculture as an antifungal agent, is rapidly reduced in vivo to leucomalachite green. Previous studies in which female B6C3F1 mice were fed malachite green produced relatively high levels of liver DNA adducts after 28 days, but no significant induction of liver tumors was detected in a 2-year feeding study. Comparable experiments conducted with leucomalachite green resulted in relatively low levels of liver DNA adducts but a dose-responsive induction of liver tumors. In the present study, we fed transgenic female Big Blue B6C3F1 mice with 450 ppm malachite green and 204 and 408 ppm leucomalachite green (the high doses used in the tumor bioassays) and evaluated genotoxicity after 4 and 16 weeks of treatment. Neither malachite green nor leucomalachite green increased the peripheral blood micronucleus frequency or Hprt lymphocyte mutant frequency at either time point; however, the 16-week treatment with 408 ppm leucomalachite green did increase the liver cII mutant frequency. Similar increases in liver cII mutant frequency were not seen in the mice treated for 16 weeks with malachite green or in female Big Blue rats treated with a comparable dose of leucomalachite green for 16 weeks in a previous study [Mutat. Res. 547 (2004) 5]. These results indicate that leucomalachite green is an in vivo mutagen in transgenic female mouse liver and that the mutagenicities of malachite green and leucomalachite green correlate with their tumorigenicities in mice and rats. The lack of increased micronucleus frequencies and lymphocyte Hprt mutants in female mice treated with leucomalachite green suggests that its genotoxicity is targeted to the tissue at risk for tumor induction.