From worst-case to reality - Case studies illustrating tiered refinement of consumer exposure to cosmetic ingredients.

Consumer exposure to cosmetic ingredients is estimated in a tiered manner. Simple Tier1 deterministic aggregate exposure modelling generates a worst case estimate of exposure. Tier1 assumes that a consumer uses all cosmetic products concomitantly daily, at maximum frequency, and products always contain the ingredient at the maximum allowed % w/w concentration. Refining exposure assessment from worst case to more realistic estimates uses evidence from surveys of actual use levels of ingredients and Tier2 probabilistic models, where distributions of consumer use data can be applied. In Tier2+ modelling, occurrence data provides evidence of products on the market actually containing the ingredient. Three case studies are presented using this tiered approach to illustrate progressive refinement. The scale of refinements from Tier1 to Tier2+ modelling for the ingredients, propyl paraben, benzoic acid and DMDM hydantoin were: 0.492 to 0.026; 1.93 to 0.042 and 1.61 to 0.027 mg/kg/day exposure dose. For propyl paraben, moving from Tier1 to Tier2+ represents a refinement from 49-fold to 3-fold overestimate of exposure when compared to a maximum estimate of 0.01 mg/kg/day exposure seen in human studies. Such refinements from worst case to realistic levels of exposure estimation can be critical in the demonstration of consumer safety.

Safety evaluation for ingredients used in baby care products: Consideration of diaper rash.

Diaper rash can adversely impact the barrier properties of skin, with potential implications for increased absorption of chemicals through the skin, and this should be accounted for in any exposure assessment used in the safety evaluation of consumer products used in the diaper ("nappy") area. In the absence of a quantitative evaluation of the potential impact of diaper rash, a default assumption of 100% dermal penetration is often made for substances applied in the diaper area. We consider here the extent, duration and severity of diaper rash and make a recommendation for conservative assumptions to incorporate into exposure assessments. Using a time-weighted average, the potential impact of diaper rash is illustrated for substances that have varying degrees of absorption through healthy skin. Results confirm that for assessments that already assume dermal absorption of 50% or higher, there is no impact on the overall exposure assessment. For substances that have a very low degree of dermal penetration (1%) through healthy skin, the impact of rash is expected to be less-than four-fold. This can be refined with additional data as there are many examples of poorly absorbed compounds for which dermal penetration is still low even for compromised skin.

Exposure Factor considerations for safety evaluation of modern disposable diapers.

Modern disposable diapers are complex products and ubiquitous globally. A robust safety assessment for disposable diapers include two important exposure parameters, i) frequency of diaper use & ii) constituent transfer from diaper to skin from direct and indirect skin contact materials. This article uses published information and original studies to quantify the exposure parameters for diapers. Using growth tables for the first three years of diapered life, an average body weight of 10-11 kg can be calculated, with a 10th percentile for females (8.5-8.8 kg). Data from surveys and diary studies were conducted to determine the frequency of use of diapers. The overall mean in the US is 4.7 diapers per day with a 75th, 90th, and 95th percentile of 5.0, 6.0, and 7.0 respectively. Using diaper topsheet-lotion transfer as a model, direct transfer to skin from the topsheet was 3.0-4.3% of the starting amount of lotion. Indirect transfer of diaper core materials as a measure of re-wetting of the skin via urine resurfacing back to the topsheet under pressure was estimated at a range of 0.32-0.66% averaging 0.46%. As described, a thorough data-based understanding of exposure is critical for a robust exposure based safety assessment of disposable diapers.

Colors in Disposable Diapers: Addressing Myths.

Colors are frequently added to disposable diapers to enhance the diapering experience. The colors in the interior of diapers are composed of nonsensitizing pigments that are bound during the fiber-making process into the fibers of the nonwoven that covers the absorbent core materials. In the past, the use of color in diapers has been called into question based on the presumed use of disperse dyes, known sensitizers in the textile industry, and erroneous reports in literature. In fact, disperse dyes are not used in leading disposable diapers; the colors used in these disposable diapers are nonsensitizing pigments with favorable safety profiles. Numerous safety tests, such as skin patch tests with pigments used on diaper backsheets, have found no evidence of skin irritation or sensitization.

Spectral characteristics of the photocycle of channelrhodopsin-2 and its implication for channel function.

In 2003, channelrhodopsin-2 (ChR2) from Chlamydomonas reinhardtii was discovered to be a light-gated cation channel, and since that time the channel became an excellent tool to control by light neuronal cells in culture as well as in living animals with high temporal and spatial resolution in a noninvasive manner. However, little is known about the spectral properties and their relation to the channel function. We have expressed ChR2 in the yeast Pichia pastoris and purified the protein. Flash-photolysis data were combined with patch-clamp studies to elucidate the photocycle. The protein absorbs maximally at approximately 480 nm before light excitation and shows flash-induced absorbance changes with at least two different photointermediates. Four relaxation processes can be extracted from the time course that we have analysed in a linear model for the photocycle leading to the kinetic intermediates P(1) to P(4). A short-lived photointermediate at 400 nm, suggesting a deprotonation of the retinal Schiff base, is followed by a red-shifted (520 nm) species with a millisecond lifetime. The first three kinetic intermediates in the photocycle, P(1) to P(3), are described mainly by the red-shifted 520-nm species. The 400-nm species contributes to a smaller extent to P(1) and P(2). The fourth one, P(4), is spectroscopically almost identical with the ground state and lasts into the seconds time region. We compared the spectroscopic data to current measurements under whole-cell patch-clamp conditions on HEK 293 cells. The lifetimes of the spectroscopically and electrophysiologically determined intermediates are in excellent agreement. The intermediates P(2) and P(3) (absorbing at 520 nm) are identified as the cation permeating states of the channel. Under stationary light, a modulation of the photocurrent by green light (540 nm) was observed. We conclude that the red-shifted spectral species represents the open channel state, and the thermal relaxation of this intermediate, the transition from P(3) to P(4), is coupled to channel closing.

Deletion of connexin45 in mouse retinal neurons disrupts the rod/cone signaling pathway between AII amacrine and ON cone bipolar cells and leads to impaired visual transmission.

Connexin45 (Cx45) is known to be expressed in the retina, but its functional analysis was problematic because general deletion of Cx45 coding DNA resulted in cardiovascular defects and embryonic lethality at embryonic day 10.5. We generated mice with neuron-directed deletion of Cx45 and concomitant activation of the enhanced green fluorescent protein (EGFP). EGFP labeling was observed in bipolar, amacrine, and ganglion cell populations. Intracellular microinjection of fluorescent dyes in EGFP-labeled somata combined with immunohistological markers revealed Cx45 expression in both ON and OFF cone bipolar cells. The scotopic electroretinogram of mutant mice revealed a normal a-wave but a 40% reduction in the b-wave amplitude, similar to that found in Cx36-deficient animals, suggesting a possible defect in the rod pathway of visual transmission. Indeed, neurotransmitter coupling between AII amacrine cells and Cx45-expressing cone bipolar cells was disrupted in Cx45-deficient mice. These data suggest that both Cx45 and Cx36 participate in the formation of functional heterotypic electrical synapses between these two types of retinal neurons that make up the major rod pathway.