Paul C. Howard

Lack of Significant Dermal Penetration of Titanium Dioxide from Sunscreen Formulations Containing Nano- and Submicron-Size TiO2 Particles

Titanium dioxide (TiO(2)) is included in some sunscreen formulations to physically block ultraviolet radiation. A dermal penetration study was conducted in minipigs with three TiO(2) particles (uncoated submicron sized, uncoated nano-sized, and dimethicone/methicone copolymer-coated nanosized) applied 5% by weight in a sunscreen. These and control formulations were topically applied to minipigs at 2 mg cream/cm(2) skin (4 applications/day, 5 days/week, 4 weeks). Skin (multiple sites), lymph nodes, liver, spleen, and kidneys were removed, and the TiO(2) content was determined (as titanium) using inductively coupled plasma mass spectroscopy. Titanium levels in lymph nodes and liver from treated animals were not increased over the values in control animals. The epidermis from minipigs treated with sunscreens containing TiO(2) showed elevated titanium. Increased titanium was detected in abdominal and neck dermis of minipigs treated with uncoated and coated nanoscale TiO(2). Using electron microscopy-energy dispersive x-ray analysis, all three types of TiO(2) particles were found in the stratum corneum and upper follicular lumens in all treated skin samples (more particles visible with coated nanoscale TiO(2)). Isolated titanium particles were also present at various locations in the dermis of animals treated with all three types of TiO(2)-containing sunscreens; however, there was no pattern of distribution or pathology suggesting the particles could be the result of contamination. At most, the few isolated particles represent a tiny fraction of the total amount of applied TiO(2). These findings indicate that there is no significant penetration of TiO(2) nanoparticles through the intact normal epidermis.

Mechanistic toxicity evaluation of uncoated and PEGylated single-walled carbon nanotubes in neuronal PC12 cells.

We investigated and compared the concentration-dependent cytotoxicity of single-walled carbon nanotubes (SWCNTs) and SWCNTs functionalized with polyethylene glycol (SWCNT-PEGs) in neuronal PC12 cells at the biochemical, cellular, and gene expressional levels. SWCNTs elicited cytotoxicity in a concentration-dependent manner, and SWCNT-PEGs exhibited less cytotoxic potency than uncoated SWCNTs. Reactive oxygen species (ROS) were generated in both a concentration- and surface coating-dependent manner after exposure to these nanomaterials, indicating different oxidative stress mechanisms. More specifically, gene expression analysis showed that the genes involved in oxidoreductases and antioxidant activity, nucleic acid or lipid metabolism, and mitochondria dysfunction were highly represented. Interestingly, alteration of the genes is also surface coating-dependent with a good correlation with the biochemical data. These findings suggest that surface functionalization of SWCNTs decreases ROS-mediated toxicological response in vitro.

The Mycotoxin Fumonisin Induces Apoptosis in Cultured Human Cells and in Livers and Kidneys of Rats

Fumonisin B1 is a mycotoxin produced by Fusarium moniliforme, a fungus that infects corn and other grains in the U.S. Fumonisin ingestion causes a variety of effects including equine leukoencephalomalacia and porcine pulmonary edema, and has been associated epidemiologically with human esophageal cancer. Fumonisin B1 produces growth inhibition and increased apoptosis in primary human keratinocyte cultures and in HET-1A cells. In order to set the doses for a 2-year tumor bioassay, male and female F344 rats were fed fumonisin B1 (99, 163, 234, and 484 ppm) for 28 days and the organs examined histologically. There was a dose dependent decrease in liver and kidney weights in the rats. The liver weight loss was accompanied by the induction of apoptosis and hepatocellular and bile duct hyperplasia in both sexes, with the female rats being more responsive at lower doses. The induction of tubular epithelial cell apoptosis was the primary response of the kidneys to dietary fumonisin B1. Apoptosis was present at all doses in the kidneys of the male rats, and occurred in the females only at 163, 234, and 484 ppm fumonisin B1. These results demonstrate that fumonisin B1 treatment causes a similar increase in apoptosis both in vivo and in vitro.

Occurrence, Efficacy, Metabolism, and Toxicity of Triclosan

Triclosan has broad-spectrum anti-microbial activity against most gram-negative and gram-positive bacteria. It is widely used in personal care products, household items, medical devices, and clinical settings. Due to its extensive use, there is potential for humans in all age groups to receive life-time exposures to triclosan, and, indeed, triclosan has been detected in human tissues and the environment. Data gaps exist regarding the chronic dermal toxicity and carcinogenicity of triclosan, which is needed for the risk assessment of triclosan. The US Food and Drug Administration (FDA) nominated triclosan to the National Toxicology Program (NTP) for toxicological evaluations. Currently, the NTP is conducting several dermal toxicological studies to determine the carcinogenic potential of triclosan, evaluate its endocrine and developmental-reproductive effects, and investigate the potential UV-induced dermal formation of chlorinated phenols and dioxins of triclosan. This paper reviews data on the human exposure, environmental fate, efficacy of anti-microbial activity, absorption, distribution, metabolism and elimination, endocrine disrupting effects, and toxicity of triclosan.

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.

The Safety and Regulation of Natural Products Used as Foods and Food Ingredients

The use of botanicals and dietary supplements derived from natural substances as an adjunct to an improved quality of life or for their purported medical benefits has become increasingly common in the United States. This review addresses the safety assessment and regulation of food products containing these substances by the U.S. Food and Drug Administration (FDA). The issue of safety is particularly critical given how little information is available on the toxicity of some of these products. The first section uses case studies for stevia and green tea extracts as examples of how FDA evaluates the safety of botanical and herbal products submitted for consideration as Generally Recognized as Safe under the Federal Food, Drug, and Cosmetics Act. The 1994 Dietary Supplement Health Education Act (DSHEA) created a regulatory framework for dietary supplements. The article also discusses the regulation of this class of dietary supplements under DSHEA and addresses the FDA experience in analyzing the safety of natural ingredients described in pre-market safety submissions. Lastly, we discuss an ongoing interagency collaboration to conduct safety testing of nominated dietary supplements.

Carcinogenicity and mechanism of action of fumonisin B1: a mycotoxin produced by Fusarium moniliforme (= F. verticillioides).

Fumonisins are fungal metabolites and suspected human carcinogens. They inhibit ceramide synthase in vitro, enhance tumor necrosis factor alpha (TNFalpha) production, and cause apoptosis. Fumonisin B1 (FB1) was fed to rats and mice for 2 years or, in separate studies, given to rats or mice for up to 4 weeks. Kidney tubule adenomas and carcinomas were found in male rats fed > or = 50 ppm, whereas liver adenomas and carcinomas were found in female mice fed > or = 50 ppm for 2 years. In the short-term studies, increases in tissue concentration of the ceramide synthase substrate sphinganine (Sa) and the Sa to sphingosine (So) ratio were correlated with apoptosis. Further, hepatotoxicity was ameliorated in mice lacking either the TNFR1 or the TNFR2 TNFalpha receptors. Thus, FB1 was carcinogenic to rodents and thefindings support the hypothesis that disrupted sphingolipid metabolism and TNFalpha play important roles in its mode of action.

Cytotoxicity and biological effects of functional nanomaterials delivered to various cell lines.

Functional nanomaterials that included gold, silver nanoparticles and single wall carbon nanotubes were delivered to two cell lines (MLO‐Y4 osteocytic cells and HeLa cervical cancer cells) in various concentrations. The cells were found to uptake the nanomaterials in a relatively short time, a process that significantly affected the shape and the size of the cells. The percentage of cellular death, due to the delivery of these nanomaterials, was found to be the highest for carbon nanotubes and increased gradually with the concentration of these nanostructures. Moreover, when the nanomaterials were delivered to the cells combined with commonly used chemotherapeutic agents such as etoposide or dexamethasone, the number of the cells that died increased significantly (100–300%) as compared with the case when only the nanomaterials or the chemotherapeutic agents were delivered. The experimental results were confirmed by Caspase 3 studies, indicating a strong interaction between the nanomaterials used in this study and the protein structure of the cells, which allowed a more effective action of the apoptotic agents. These findings could be the foundation of a new class of cancer therapies that are composed of both chemotherapeutic agents and nanomaterials. Copyright

Xanthine oxidase catalyzed binding of 1-nitropyrene to DNA

Xanthine oxidase, a mammalian nitroreductase, catalyzed the binding of [3H]1-nitropyrene to DNA. The binding was dependent on the presence of hypoxanthine and was inhibited by allopurinol, a specific xanthine oxidase inhibitor. These data support the hypothesis that nitroreduction is a necessary step in the metabolic activation of 1-nitropyrene to a bacterial mutagen.

Renal Effects of Fumonisin Mycotoxins in Animals

Fumonisins are mycotoxins produced worldwide by Fusarium fungi, principally F. moniliforme. The fungus is present in virtually all harvested com, but the toxins produced are variable. The toxins, especially fumonisin B1, cause mild to fatal diseases in animals, with peculiar species specificity for the dominant signs of toxicity. The mechanism of toxicity is poorly understood, but it appears to be related to interference with sphingolipid biosynthesis in multiple organs. Whereas brain, lung, and liver are well-known target organs, toxic effects on the kidney are also widespread and have only recently begun to be characterized. Increased urine volume and decreased osmolality are early changes associated with the toxin, as are increased excretions of high-and low-molecular-weight proteins. Enzymuria in vivo, reduced ion transport in vitro, and elevation of free sphinganine in renal tissue and in urine are present. An increase in serum creatinine and blood urea nitrogen and histopathologic change in renal tubules occur later and at higher doses. The morphologic change principally affects the junction of cortex and medulla and includes prominent apoptosis of epithelial cells of proximal convoluted tubules. Nephrotoxicity has been reported in several species, and in rats and rabbits, the kidney appears to be the most sensitive target organ.