Effect of aqueous dilution on the absorption of the nerve agent VX through skin in vitro

Penetration pathways, influencing factors and predictive models for dermal absorption of exobiotic molecules: A critical review

This review provides a comprehensive summary of the skin penetration pathways of xenobiotics, including metals, organic pollutants, and nanoparticles (NPs), with a particular focus on the methodologies employed to elucidate these penetration routes. The impacts of the physicochemical properties of exogenous substances and the properties of solvent carriers on the penetration efficiencies were discussed. Furthermore, the review outlines the steady-state and transient models for predicting the skin permeability of xenobiotics, emphasizing the models which enable realistic visualization of pharmaco-kinetic phenomena via detailed geometric representations of the skin microstructure, such as stratum corneum (SC) (bricks and mortar) and skin appendages (hair follicles and sebaceous gland units). Limitations of published research, gaps in current knowledge, and recommendations for future research are highlighted, providing insight for a better understanding of the skin penetration behavior of xenobiotics and associated health risks in practical application contexts.

A method to assess dermal absorption dynamics of chemical warfare agents: Finite doses of volatile compounds

Chemical warfare agents are absorbed into the body from various entry routes and may have detrimental effects on human health. As many chemical compounds in this group are lipophilic, the outer layer of the skin is at an elevated risk. This contribution explores the dynamics of skin penetration for risk assessment. A previously validated model was applied to describe how an agent is transported across the stratum corneum following dermal exposure to a finite dose of a chemical. A mathematical construct was implemented for estimating the time constants and the cumulative amount of permeant entering the bloodstream or being released into the environment. Empirical equations were selected to determine the ratio of the steady-state evaporation rate to the steady-state dermal absorption rate and the physicochemical properties of the chemical warfare agents. Wolfram Mathematica was employed to run the simulations. The results from the newly derived expressions for the time constants matched those directly obtained from the validated model. For example, sarin gas had steady-state evaporation to an absorption rate of 991.25, and a total fractional absorption and evaporation of 5.1% and 94.9%, respectively. Combined with occupational exposure limits, the findings can help researchers assess an individual's risk level and develop protection programs.

In vitro assessment of the dermal penetration potential of sodium fluoroacetate using a formulated product

This paper presents experimental data on the skin absorption of sodium fluoroacetate from a formulated product using an in vitro approach and human skin. Sodium fluoroacetate is a pesticide, typically applied in formulation (1080) for the control of unwanted vertebrate invasive species. It has been assigned a Skin Notation by the ACGIH, and other international workplace health regulatory bodies, due to its predicted ability to permeate intact and abraded human skin. However, there is a distinct lack of experimental data on the skin absorption of sodium fluoroacetate to support this assignment. This study found that sodium fluoroacetate, as a formulated product, permeated the human epidermis when in direct contact for greater than 10 hr. A steady-state flux (J_ss) of 1.31 ± 0.043 µg/cm²/hr and a lag time of 6.1 hr was calculated from cumulative skin permeation data. This study provides important empirical evidence in support of the assignment of a Skin Notation.

The wash-in effect and its significance for mass casualty decontamination

Decontamination of skin by washing may increase dermal absorption, a phenomenon known as the wash-in effect. The wash-in effect is frequently discussed in studies investigating casualty decontamination where potentially life-saving interventions may enhance the dermal penetration of toxic chemicals, leading to an increase in incidence of morbidity and rates of mortality. However, the wash-in effect is seldom investigated within the context of mass casualty decontamination and real-life consequences are therefore poorly understood. This paper reviews the existing literature on the wash-in effect to highlight the proposed mechanisms for enhanced absorption and evaluate the wash-in effect within the context of mass casualty chemical decontamination.

Occupational exposure assessment with solid substances: choosing a vehicle for in vitro percutaneous absorption experiments

Percutaneous occupational exposure to industrial toxicants can be assessed in vitro on excised human or animal skins. Numerous factors can significantly influence skin permeation of chemicals and the flux determination. Among them, the vehicle used to solubilize the solid substances is a tricky key step. A "realistic surrogate" that closely matches the exposure scenario is recommended in first intention. When direct transposition of occupational exposure conditions to in vitro experiments is impossible, it is recommended that the vehicle used does not affect the skin barrier (in particular in terms of structural integrity, composition, or enzymatic activity). Indeed, any such effect could alter the percutaneous absorption of substances in a number of ways, as we will see. Potential effects are described for five monophasic vehicles, including the three most frequently used: water, ethanol, acetone; and two that are more rarely used, but are realistic: artificial sebum and artificial sweat. Finally, we discuss a number of criteria to be verified and the associated tests that should be performed when choosing the most appropriate vehicle, keeping in mind that, in the context of occupational exposure, the scientific quality of the percutaneous absorption data provided, and how they are interpreted, may have long-range consequences. From the narrative review presented, we also identify and discuss important factors to consider in future updates of the OECD guidelines for in vitro skin absorption experiments.

Percutaneous absorption of Carfentanil in vitro

Carfentanil is a synthetic opioid restricted to veterinary use due to its potency. Public health concerns have been raised as to the potential of carfentanil to exhibit toxicity after absorption via the percutaneous route following unintentional contamination. The current study measured the penetration of free base carfentanil through human, pig and rat skin using in vitro static diffusion cells. The human penetration rates were compared against literature toxicology values and indicated that, dependent on the contamination density, contamination area and residence time, skin decontamination and medical countermeasures may be required to ameliorate toxicity. The pig and rat skin penetration data will form the basis of future work to develop relevant in silico and in vivo models to further elucidate likely toxic effects and the medical strategies to mitigate against them.

Efficient agent degradation within skin is important for decontamination of percutaneously exposed VX

AIM OF THE STUDY

Following percutaneous exposure to the nerve agent VX, the remaining intact agent within the skin after decontamination is of great concern. Consequently, this leads to prolonged agent release to the blood circulation resulting in sustained intoxication, which may complicate the medical management. The decontamination procedure used should therefore possess the ability for agent removal both on and within the skin. The efficacy of three decontamination procedures was evaluated by measuring VX and the primary degradation product ethyl methyl phosphonic acid (EMPA) penetrated through human skin and the amount remaining within the skin.

MATERIALS AND METHODS

Decontamination was initiated 5 min post-exposure to VX on human dermatomed skin. Experiments were conducted using an in vitro skin penetration model and the amount remaining within the skin was determined by combining the tape-stripping technique and acetylcholinesterase activity measurements.

RESULTS

In control experiments without decontamination, higher amounts of VX were recovered in the deeper layers of skin compared to EMPA, which was primarily located in the stratum corneum. Both Reactive Skin Decontamination Lotion (RSDL) and the RSDL training kit (TRSDL) significantly reduced the amount of VX within the skin and decreased the penetration through the skin. However, the degradation ability of RSDL was demonstrated to be beneficial by the reduction of intact agents remaining in the skin compared to TRSDL without agent degradation capability. Soapy water decontamination caused a "wash-in" effect of VX with decreased agent amounts within stratum corneum but increased the amount VX penetrated through the skin.

CONCLUSION

Efficient skin decontamination of VX requires skin decontaminants reaching deeper layers of the skin, and that both absorption and degradation properties are important. In addition, the "wash-in" effect by using soapy water may enhance VX release to the blood circulation.