The effects of heat on skin barrier function and in vivo dermal absorption

Protective effect of Bifidobacterium animalis CGMCC25262 on HaCaT keratinocytes

Bifidobacteria are the most prevalent members of the intestinal microbiota in mammals and other animals, and they play a significant role in promoting gut health through their probiotic effects. Recently, the potential applications of Bifidobacteria have been extended to skin health. However, the beneficial mechanism of Bifidobacteria on the skin barrier remains unclear. In this study, keratinocyte HaCaT cells were used as models to evaluate the protective effects of the cell-free supernatant (CFS), heat-inactivated bacteria, and bacterial lysate of Bifidobacterium animalis CGMCC25262 on the skin barrier and inflammatory cytokines. The results showed that all the tested samples were able to upregulate the transcription levels of biomarker genes associated with the skin barrier, such as hyaluronic acid synthetase (HAS) and aquaporins (AQPs). Notably, the transcription of the hyaluronic acid synthetase gene-2 (HAS-2) is upregulated by 3~4 times, and AQP3 increased by 2.5 times when the keratinocyte HaCaT cells were co-incubated with 0.8 to 1% CFS. In particular, the expression level of Filaggrin (FLG) in HaCaT cells increased by 1.7 to 2.7 times when incubated with Bifidobacterial samples, reaching its peak at a concentration of 0.8% CFS. Moreover, B. animalis CGMCC25262 also decreased the expression of the proinflammatory cytokine RANTES to one-tenth compared to the levels observed in HaCaT cells induced with tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ). These results demonstrate the potential of B. animalis CGMCC25262 in protecting the skin barrier and reducing inflammatory response.

Topically applied lipid-containing emulsions based on PEGylated emulsifiers: Formulation, characterization, and evaluation of their impact on skin properties ex vivo and in vivo

PEGylated emulsifiers have been largely used in topical formulations for skin research. They have been a continuous study focus in our group as well. According to our previous studies, severe interruptions of the skin barrier were observed with certain types of emulsifiers. To restore the skin barrier function and counteract the effects of emulsifiers, we considered topically delivering lipids into the lipid matrix of the SC. Herein, PEG-20 cetyl ether (C20) -based oil-in-water (O/W) emulsions were developed owing to the stronger interactions of C20 with skin. The lipids containing ceramides (Cers), palmitic acids (PA), and cholesterol with different ratios and combinations were merged into the base emulsion. PEG-40 stearyl ether (S40)-based emulsion was used as a reference as S40 showed negligible impact on SC lipids. The evaluations were conducted ex vivo with confocal Raman spectroscopy (CRS) regarding the SC lipid, SC thickness, and skin penetration properties. In parallel, the in vivo irritation studies were also implemented including the transepidermal-water-loss (TEWL), skin hydration, and erythema index. The results indicated less SC lipid extraction of topically delivered lipids on ex vivo porcine skin with the addition and ratio of incorporated Cers influencing the extent of formulations counteracting the skin interruption by C20. The ex vivo penetration study showed a similar trend in drug penetration depths. In regards to the in vivo studies, TEWL was demonstrated to be suitable for differentiating the impact on skin barrier properties. The in vivo observations were generally correlated with the ex vivo results. The exact findings in this research can lead us to a better selection of applied lipid components and compositions. Future research will elucidate which type of Cer was predominantly extracted by C20, advancing future formulation development.

GuLF DREAM: A Model to Estimate Dermal Exposure Among Oil Spill Response and Clean-up Workers

Tens of thousands of individuals performed oil spill response and clean-up (OSRC) activities following the 'Deepwater Horizon' oil drilling rig explosion in 2010. Many were exposed to oil residues and dispersants. The US National Institute of Environmental Health Sciences assembled a cohort of nearly 33 000 workers to investigate potential adverse health effects of oil spill exposures. Estimates of dermal and inhalation exposure are required for those individuals. Ambient breathing-zone measurements taken at the time of the spill were used to estimate inhalation exposures for participants in the GuLF STUDY (Gulf Long-term Follow-up Study), but no dermal measurements were collected. Consequently, a modelling approach was used to estimate dermal exposures. We sought to modify DREAM (DeRmal Exposure Assessment Method) to optimize the model for assessing exposure to various oil spill-related substances and to incorporate advances in dermal exposure research. Each DREAM parameter was reviewed in the context of literature published since 2000 and modified where appropriate. To reflect the environment in which the OSRC work took place, the model treatment of evaporation was expanded to include vapour pressure and wind speed, and the effect of seawater on exposure was added. The modified model is called GuLF DREAM and exposure is estimated in GuLF DREAM units (GDU). An external validation to assess the performance of the model for oils, tars, and fuels was conducted using available published dermal wipe measurements of heavy fuel oil (HFO) and dermal hand wash measurements of asphalt. Overall, measured exposures had moderate correlations with GDU estimates (r = 0.59) with specific correlations of -0.48 for HFO and 0.68 for asphalt. The GuLF DREAM model described in this article has been used to generate dermal exposure estimates for the GuLF STUDY. Many of the updates made were generic, so the updated model may be useful for other dermal exposure scenarios.

Antibacterial and safety tests of a flexible cold atmospheric plasma device for the stimulation of wound healing

Cold atmospheric plasma (CAP) devices generate an ionized gas with highly reactive species and electric fields at ambient air pressure and temperature. A flexible dielectric barrier discharge (DBD) was developed as an alternative antimicrobial treatment for chronic wounds. Treatment of Staphylococcus aureus in collagen-elastin matrices with CAP for 2 min resulted in a 4 log reduction. CAP treatment was less effective on S. aureus on dermal samples. CAP did not affect cellular activity or DNA integrity of human dermal samples when used for up to 2 min. Repeated daily CAP treatments for 2 min lowered cellular activity of dermal samples to 80% after 2 to 4 days, but this was not significant. Repeated treatment of ex vivo human burn wound models with CAP for 2 min did not affect re-epithelialization. Intact skin of 25 healthy volunteers was treated with CAP for 3× 20" to determine safety. Although participants reported moderate pain scores (numerical rating scale 3.3), all volunteers considered the procedure to be acceptable. Severe adverse events did not occur. CAP treatment resulted in a temporarily increased local skin temperature (≈3.4°C) and increased erythema. Lowering the plasma power resulted in a significantly lower erythema increase. Good log reduction (2.9) of bacterial load was reached in 14/15 volunteers artificially contaminated with Pseudomonas aeruginosa. This study demonstrated the in vitro and in vivo safety and efficacy in bacterial reduction of a flexible cold plasma device. Trial registration number NCT03007264, January 2, 2017 KEY POINTS: • CAP strongly reduced bacterial numbers both in vitro and in vivo. • Re-epithelialization of burn wound models was not affected by repeated CAP. • CAP treatment of intact skin was well tolerated in volunteers.

Vulnerability of the skin barrier to mechanical rubbing

Skin barrier function is the battlefront for preventing permeation of harmful substances and infectious diseases. However, it can be destroyed by mechanical forces, as shown in many studies. Excess rubbing may increase the permeability of the skin to aqueous material. Although the skin barrier plays an important physiological role in humans, the vulnerability of skin to mechanical rubbing is poorly understood. Therefore, we investigated the effects of rubbing on the skin in vitro; skin damage was quantified by laser-induced fluorescence. Microscopic observation showed that keratinocytes in the stratum corneum sustained traumatic damage, which reduced the barrier function in that region. The permeability of the skin to an aqueous solution increased with rubbing frequency and load, and rubbing markedly reduced the barrier function of the stratum corneum. To understand the mechanisms underlying the skin damage, we developed a simple mathematical model assuming that the skin is a viscoelastic material. We hypothesized that the increased skin permeability was caused by the damage sustained by keratinocytes in the stratum corneum, and that the permeability was proportional to the time-averaged strain. Our theoretical results showed quantitative agreement with the experimental results and illustrated that rubbing and strain relaxation play key roles in rubbing-induced permeation.

Evaluation of Heat Effects on Transdermal Nicotine Delivery In Vitro and In Silico Using Heat-Enhanced Transport Model Analysis

A combined experimental and computational model approach was developed to assess heat effects on drug delivery from transdermal delivery systems (TDSs) in vitro and nicotine was the model drug. A Franz diffusion cell system was modified to allow close control of skin temperature when heat was applied from an infrared lamp in vitro. The effects of different heat application regimens on nicotine fluxes from two commercial TDSs across human cadaver skin were determined. Results were interpreted in terms of transport parameters estimated using a computational heat and mass transport model. Steady-state skin surface temperature was obtained rapidly after heat application. Increasing skin surface temperature from 32 to 42°C resulted in an approximately 2-fold increase in average nicotine flux for both TDSs, with maximum flux observed during early heat application. ANOVA statistical analyses of the in vitro permeation data identified TDS differences, further evidenced by the need for a two-layer model to describe one of the TDSs. Activation energies associated with these data suggest similar temperature effects on nicotine transport across the skin despite TDS design differences. Model simulations based on data obtained from continuous heat application were able to predict system response to intermittent heat application, as shown by the agreement between the simulation results and experimental data of nicotine fluxes under four different heat application regimens. The combination of in vitro permeation testing and a computational model provided a parameter-based heat and mass transport approach to evaluate heat effects on nicotine TDS delivery.

Modeling Temperature-Dependent Dermal Absorption and Clearance for Transdermal and Topical Drug Applications

A computational model was developed to better understand the impact of elevated skin temperatures on transdermal drug delivery and dermal clearance. A simultaneous heat and mass transport model with emphasis on transdermal delivery system (TDS) applications was developed to address transient and steady-state temperature effects on dermal absorption. The model was tested using representative data from nicotine TDS applied to human skin either in vitro or in vivo. The approximately 2-fold increase of nicotine absorption with a 10°C increase in skin surface temperature was consistent with a 50-65 kJ/mol activation energy for diffusion in the stratum corneum, with this layer serving as the primary barrier for nicotine absorption. Incorporation of a dermal clearance component into the model revealed efficient removal of nicotine via the dermal capillaries at both normal and elevated temperatures. Two-compartment pharmacokinetic simulations yielded systemic drug concentrations consistent with the human pharmacokinetic data. Both in vitro skin permeation and in vivo pharmacokinetics of nicotine delivered from a marketed TDS under normal and elevated temperatures can be satisfactorily described by a simultaneous heat and mass transfer computational model incorporating realistic skin barrier properties and dermal clearance components.

Thermoresponsive gating membranes embedded with liquid crystal(s) for pulsatile transdermal drug delivery: An overview and perspectives

Due to the circadian rhythm regulation of almost every biological process in the human body, physiological and biochemical conditions vary considerably over the course of a 24-h period. Thus, optimal drug delivery and therapy should be effectively controlled to achieve the desired therapeutic plasma concentrations and therapeutic drug responses at the required time according to chronopharmacological concepts, rather than continuous maintenance of constant drug concentrations for an extended time period. For many drugs, it is not always necessary to constantly deliver a drug into the human body under disease conditions due to rhythmic variations. Pulsatile drug delivery systems (PDDSs) have been receiving more attention in pharmaceutical development by providing a predetermined lag period, followed by a fast or rate-controlled drug release after application. PDDSs are characterized by a programmed drug release, which may release a drug at repeatable pulses to match the biological and clinical needs of a given disease therapy. This review article focuses on thermoresponsive gating membranes embedded with liquid crystals (LCs) for transdermal drug delivery using PDDS technology. In addition, the principal rationale and the advanced approaches for the use of PDDSs, the marketed products of chronotherapeutic DDSs with pulsatile function designed by various PDDS technologies, pulsatile drug delivery designed with thermoresponsive polymers, challenges and opportunities of transdermal drug delivery, and novel approaches of LC systems for drug delivery are reviewed and discussed. A brief overview of all academic research articles concerning single LC- or binary LC-embedded thermoresponsive membranes with a switchable on-off permeation function through topical application by an external temperature control, which may modulate the dosing interval and administration time according to the therapeutic needs of the human body, is also compiled and presented. In the near future, since thermal-based approaches have become a well-accepted method to enhance transdermal delivery of different water-soluble drugs and macromolecules, a combination of the thermal-assisted approach with thermoresponsive LCs membranes will have the potential to improve PDDS applications but still poses a great challenge.

Buccal adhesive films with moisturizer- the next level for dry mouth syndrome?

This study was undertaken to prepare films by solvent evaporation method comprising well-known polymers in order to investigate their potential for buccal suitability. Mucoadhesive films were manufactured using different polymers such as ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose as well as carboxymethyl cellulose. Buccal films were evaluated in regards of mucoadhesiveness, swelling and physico-chemical properties. Furthermore rheological measurement and adhesion study were carried out on the buccal porcine mucosa. Moreover, allantoin as humectant was incorporated and trans-mucosal water loss was determined. The results showed that physico-chemical, buccal adhesive and swelling properties varied depending on the composition of the polymers. The findings indicated films containing allantoin to be suitable for buccal application. In completion, adhesive films are appropriate and promising formulations in the treatment of various disease in the intraoral cavity.

Malathion dermal permeability in relation to dermal load: Assessment by physiologically based pharmacokinetic modeling of in vivo human data

Estimates of dermal permeability (K_p), obtained by fitting an updated human PBPK model for malathion to previously reported data on excreted urinary metabolites after 29 volunteers were dermally exposed to measured values of [¹⁴C]malathion dermal load (L), were used to examine the empirical relationship between K_p and L. The PBPK model was adapted from previously reported human biokinetic and PBPK models for malathion, fit to previously reported urinary excretion data after oral [¹⁴C]malathion intake by volunteers, and then augmented to incorporate a standard K_p approach to modeling dermal-uptake kinetics. Good to excellent PBPK-model fits were obtained to all of 29 sets of cumulative urinary metabolite-excretion data (ave. [±1 SD] R² = 0.953 [±0.064]). Contrary to the assumption that K_p and L are independent typically applied for dermally administered liquids or solutions, the 29 PBPK-based estimates of K_p obtained for malathion exhibit a strong positive association with the 2/3rds power of L (log-log Pearson correlation = 0.925, p = ∼0). Possible explanations of this observation involving physico-chemical characteristics and/or in vivo cutaneous effects of malathion are discussed. The PBPK model presented, and our observation that K_p estimates obtained by fitting this model to human experimental urinary-excretion data correlate well with L^2/3, allow more realistic assessments of absorbed and metabolized dose during or after a variety of scenarios involving actual or potential dermal or multi-route malathion exposures, including for pesticide workers or farmers who apply malathion to crops.

Advances in the bioanalytical study of drug delivery across the skin

The study of a drug's dermal penetration profile provides important pharmaceutical data for the rational development of topical and transdermal delivery systems because the skin is a broadly used delivery route for local and systemic drugs and a potential route for gene therapy and vaccines. Monitoring drug penetration across the skin and quantifying its levels in different skin layers have been constant challenges due to the detection limitations of the available techniques, as well as the inherent interference in this tissue. This review explores and discusses several bionalytical methods that are indispensable tools to study drugs across the skin. In addressing the main topic, we structure the review highlighting the skin as an important route of drug administration and its structure, skin membrane models most used and its properties, in vitro and in vivo assays most used in the study of drug delivery to the skin, the techniques for processing the skin for subsequent analysis by bioanalytical methods that have a theoretical and practical approach showing its applicability, limitations and also including examples of its use. This review has a comprehensive approach in order to help researchers design their experiments and update the applicability and advances in this area of expertise.