Impact of Different Packaging Configurations on A Topical Cream Product.

PURPOSE: The objective of this study was to investigate whether different dispensing processes can alter the physicochemical and structural (Q3) attributes of a topical cream product, and potentially alter its performance. METHODS: Acyclovir cream, 5% (Zovirax®) is sold in the UK and other countries in a tube and a pump packaging configurations. The structural attributes of the cream dispensed from each packaging configuration were analyzed by optical microscopy, confocal Raman microscopy and cryo-scanning electron microscopy. Rheological behavior of the products was also evaluated. Product performance (rate and extent of skin delivery) was assessed by in vitro permeation tests (IVPT) using heat-separated human epidermis mounted in static vertical (Franz-type) diffusion cells. RESULTS: Differences in Q3 attributes and IVPT profiles were observed with creams dispensed from the two packaging configurations, even though the product inside each packaging appeared to be the same in Q3 attributes. Visible globules were recognized in the sample dispensed from the pump, identified as dimethicone globules by confocal Raman microscopy. Differences in rheological behaviour could be attributed to these globules as products not dispensed through the pump, demonstrated a similar rheological behaviour. Further, IVPT confirmed a reduced rate and extent to delivery across human epidermis from the product dispensed through a pump. CONCLUSIONS: Different methods of dispensing topical semisolid products can result in metamorphosis and Q3 changes that may have the potential to alter the bioavailability of an active ingredient. These findings have potential implications for product developers and regulators, related to the manufacturing and comparative testing of reference standard and prospective generic products dispensed from different packaging configurations.

Quantitative structure permeability relationships for phenolic compounds applied to human epidermal membranes in various solvents.

PURPOSE: This study examined how solvent-skin-solute interactions influenced the human epidermal permeation of three similar-sized phenolic compounds applied in a series of different solvents. METHODS: Human epidermal permeation fluxes and lag times of three phenolic compounds were assessed in Franz cells for a range of solvents varying in molecular size and solubility parameters. In order to develop a mechanistic understanding of the determinants of the permeation findings, the solubility of the compounds in solvents and stratum corneum, the extent of solvent uptake by the stratum corneum and the impact of the solvents on skin hydration and transepidermal water loss were also measured. RESULTS: Maximum epidermal fluxes and lag times varied greatly with the various solvent used. Markedly enhanced epidermal permeability fluxes, prolonged lag times and reduced diffusivities of the compounds were evident for many of the solvents. A solvent induced increase in stratum corneum solubility was associated with the uptake of solvent containing dissolved compound. This uptake was dependent on both the solvent molecular size and the solubility of the compounds in the solvents. The imbibed solvent acted as a reservoir in the skin, facilitating uptake and an increased thermodynamic activity that enhanced flux but, at the same time, inhibiting diffusion and prolonging lag time. CONCLUSION: The solubility, permeation and lag times of compounds in the stratum corneum can be modulated by solvent uptake. Whilst a solvent -induced stratum corneum reservoir effect for a compound may prolong its lag time for a compound before steady state permeation is reached, it does not affect its overall steady state transport defined by diffusion of its free form.

Identification and characterization of TM4SF1+ tumor self-seeded cells.

Tumor self-seeding is a process whereby circulating tumor cells (CTCs) recolonize the primary tumor, which promotes tumor growth, angiogenesis, and invasion. However, the detailed nature and functions of tumor self-seeded cells (TSCs) have not been well defined due to challenges in tracking and isolating TSCs. Here, we report an accurate animal model using photoconvertible tagging to recapitulate the spontaneous process of tumor self-seeding and identify TSCs as a subpopulation of primary tumor cells with enhanced invasiveness and survival. We demonstrate transmembrane-4-L-six-family-1 (TM4SF1) as a marker of TSCs, which promotes migration, invasion, and anchorage-independent survival in cancer cells. By analyzing single-cell RNA sequencing datasets, we identify a potential TSC population with a metastatic profile in patients with cancer, which is detectable in early-stage disease and expands during cancer progression. In summary, we establish a framework to study TSCs and identify emerging cell targets with diagnostic, prognostic, or therapeutic potential in cancers.

Clinical toxicology of acute glyphosate self-poisoning: impact of plasma concentrations of glyphosate, its metabolite and polyethoxylated tallow amine surfactants on the toxicity.

INTRODUCTION: Common major co-formulants in glyphosate-based herbicides, polyethoxylated tallow amine surfactants, are suspected of being more toxic than glyphosate, contributing to the toxicity in humans. However, limited information exists on using polyethoxylated tallow amine concentrations to predict clinical outcomes. We investigated if plasma concentrations of glyphosate, its metabolite and polyethoxylated tallow amines can predict acute kidney injury and case fatality in glyphosate poisoning. METHODS: We enrolled 151 patients with acute glyphosate poisoning between 2010 and 2013. Plasma concentrations of glyphosate, its metabolite, aminomethylphosphonic acid, and polyethoxylated tallow amines were determined in 2020 using liquid chromatography-tandem mass spectrometry. Associations between exposure and poisoning severity were assessed. RESULTS: Plasma concentrations of glyphosate and aminomethylphosphonic acid demonstrated good and moderate performances in predicting acute kidney injury (≥2), with an area under the receiver operating characteristic curve of 0.83 (95% CI 0.69-0.97) and 0.76 (95% CI 0.59-0.94), respectively. Polyethoxylated tallow amines were detected in one-fifth of symptomatic patients, including one of four fatalities and those with unsaturated tallow moieties being good indicators of acute kidney injury (area under the receiver operating characteristic curve ≥0.7). As the number of repeating ethoxylate units in tallow moieties decreased, the odds of acute kidney injury increased. Glyphosate and aminomethylphosphonic acid concentrations were excellent predictors of case fatality (area under the receiver operating characteristic curve >0.9). DISCUSSION: The 2.7% case fatality rate with 49% acute, albeit mild, acute kidney injury following glyphosate poisoning is consistent with previously published data. A population approach using model-based metrics might better explore the relationship of exposure to severity of poisoning. CONCLUSIONS: Plasma concentrations of glyphosate and its metabolite predicted the severity of clinical toxicity in glyphosate poisoning. The co-formulated polyethoxylated tallow amine surfactants were even more strongly predictive of acute kidney injury but were only detected in a minority of patients.

The Intermalleolar Method for Intraoperative Rotational Assessment of the Tibia-A Prospective Clinical Validation Study.

OBJECTIVES: To determine the accuracy of the intermalleolar method, an intraoperative fluoroscopic method for assessing tibial rotation in patients undergoing intramedullary nail fixation for tibial shaft fractures, by comparing it with the gold standard computed tomography (CT). DESIGN: Prospective cohort study. SETTING: Academic Level 1 trauma center. PATIENT SELECTION CRITERIA: Consecutive patients, aged 18 years and older, with unilateral tibial shaft fractures who underwent intramedullary fixation from September 2021 to January 2023. OUTCOME MEASURES AND COMPARISONS: Intraoperatively, tibial rotation measurements were obtained using the intermalleolar method on both the uninjured and injured limbs. Postoperatively, patients underwent bilateral low-dose lower extremity rotational CT scans. CT measurements were made by 4 blinded observers. Mean absolute rotational differences and standard errors were calculated to compare the injured and uninjured limbs. Subgroup analysis was performed assessing accuracy relating to injured versus uninjured limbs, body mass index, OTA/AO fracture pattern, tibial and fibular fracture location, and distal articular fracture extension requiring fixation. RESULTS: Of the 20 tibia fractures, the mean patient age was 43.4 years. The intermalleolar method had a mean absolute rotational difference of 5.1 degrees (standard error 0.6, range 0-13.7) compared with CT. Sixty percent (24/40) of the measurements were within 5 degrees, 90% (36/40) of the measurements were within 10 degrees, and 100% (40/40) were within 15 degrees of the CT. No patients were revised for malrotation postoperatively. CONCLUSIONS: The intermalleolar method is accurate and consistently provides intraoperative tibial rotation measurements within 10 degrees of the mean CT measurement for adult patients undergoing intramedullary nail fixation for unilateral tibial shaft fractures. This method may be employed in the operating room to accurately quantify tibial rotation and assist with intraoperative rotational corrections. LEVEL OF EVIDENCE: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Dynamic exposure and body burden models for per- and polyfluoroalkyl substances (PFAS) enable management of food safety risks in cattle.

With increasing global focus on planetary boundaries, food safety and quality, the presence of per- and polyfluoroalkyl substances (PFAS) in the food chain presents a challenge for the sustainable production and supply of quality assured food. Consumption of food is the primary PFAS exposure route for the general population. At contaminated sites, PFAS have been reported in a range of agricultural commodities including cattle. Consumer exposure assessments are complicated by the lack of validated modelling approaches to estimate PFAS bioaccumulation in cattle. Previous studies have shown that PFAS bioaccumulation in livestock is influenced by environmental, spatial and temporal factors that necessitate a dynamic modelling approach. This work presents an integrated exposure and population toxicokinetic (PopTK) model for cattle that estimates serum and tissue concentrations of PFAS over time. Daily exposures were estimated from intakes of water, pasture, and soil, and considered animal growth, seasonal variability (pasture moisture content and temperature) and variable PFAS concentrations across paddocks. Modelled serum and tissue estimates were validated against monitoring data from Australian and Swedish cattle farms. The models were also used to develop and test practical management options for reducing PFAS exposure and to prioritise remediation for farms. Model outputs for exposure management scenarios (testing cattle rotation and targeted supplementation of feed and water) showed potential for marked reductions in consumer exposures from cattle produce.

Human Skin Drug Metabolism: Relationships between Methyl Salicylate Metabolism and Esterase Activities in IVPT Skin Membranes.

The presence of esterase enzymes in human skin and their role in drug metabolism has been reported, but their distribution in the various skin layers and the relative contributions of those layers to metabolism is poorly defined. To gain further insight into esterase distribution, we performed in vitro skin permeation of a commercial 28.3% methyl salicylate (MeSA) cream (Metsal™) in Franz diffusion cells, using a range of human skin membranes, all from the same donor. The membranes were viable epidermis separated by a dispase II enzymatic method, heat separated epidermis, dermatomed skin, and dermis separated by a dispase II enzymatic method. Methyl salicylate and its metabolite, salicylic acid (SA), were measured by high-performance liquid chromatography. Alpha naphthyl acetate and Hematoxylin and Eosin staining provided qualitative estimations of esterase distribution in these membranes. The permeation of methyl salicylate after 24 h was similar across all membranes. Salicylic acid formation and permeation were found to be similar in dermatomed skin and dermis, suggesting dermal esterase activity. These results were supported by the staining studies, which showed strong esterase activity in the dermal-epidermal junction region of the dermis. In contrast with high staining of esterase activity in the stratum corneum and viable epidermis, minimal stained and functional esterase activity was found in heat-separated and dispase II-prepared epidermal membranes. The results are consistent with dispase II digesting hemidesmosomes, penetrating the epidermis, and affecting epidermal esterases but not those in the dermis. Accordingly, whilst the resulting dispase II-generated dermal membranes may be used for in vitro permeation tests (IVPT) involving esterase-based metabolic studies, the dispase II-generated epidermal membranes are not suitable for this purpose.

Analysis of the Costs and Complications of First Metatarsophalangeal Joint Arthrodesis Comparing Locked and Non-locked Plate Fixation Constructs.

BACKGROUND: The ideal fixation method for the first metatarsophalangeal joint (first MTP) remains uncertain. This study compares nonunion and revision surgery rates of first MTP arthrodesis between nonlocking semitubular plates and precontoured locking plates. METHODS: Demographics, fixation technique, and complications of all patients who underwent primary first MTP arthrodesis between 2013 and 2018 were determined from radiographs and clinical records. Cost data were from a 1-year subset of isolated first MTP fusion surgeries. The primary outcome measures of this study were the nonunion and complication rates, with associated costs of patients undergoing first metatarsophalangeal arthrodesis with either a noncontoured semitubular plate or a precontoured locking plate. RESULTS: The study included 189 patients, with a mean follow-up of 18.7 months. The overall nonunion rate was 10.1%, with no difference between the locking and nonlocking plates. The prevalence of a painful implant was also similar. Surgeries using locking plates cost an average of $1,500 more than those using nonlocked plates. CONCLUSIONS: Because there was no difference in revision between locking and nonlocking plate fixation for primary first MTP arthrodesis, routine use of the more expensive locking plates may not be justified. LEVEL OF EVIDENCE: Level III (Retrospective cohort study).

Spatio-temporal trends in livestock exposure to per- and polyfluoroalkyl substances (PFAS) inform risk assessment and management measures.

The migration of per- and polyfluoroalkyl substances (PFAS) onto agricultural properties has resulted in the accumulation of PFAS in livestock. The environmental determinants of PFAS accumulation in livestock from the grazing environment are poorly understood, resulting in limited capacity to manage livestock exposure and subsequent transfer of PFAS through the food chain. Analytical- (n = 978 samples of soil, water, pasture, and serum matrices), farm management/practice- and livestock physiology data were collated and interrogated from environmental PFAS investigations across ten farms, from four agro-ecological regions of Victoria (Australia). Statistical analysis identified perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) as key analytes of concern for livestock bioaccumulation. PFOS and PFHxS concentrations in livestock drinking water were positively correlated with serum concentrations while other intake pathways (pasture and soil) had weaker correlations. Seasonal trends in PFAS body burden (serum concentrations) were identified and suggested to be linked to seasonal grazing behaviours and physiological water requirements. The data showed for the first time that livestock exposure to PFAS is dynamic and with relatively short elimination half-lives, there is opportunity for exposure management. Meat from cattle, grazed on PFAS impacted sites, may exceed health-based guideline values for PFAS, especially for markets with low limits (like the European Commission Maximum Limits or EC MLs). This study found that sites with mean livestock drinking water concentrations as low as 0.003 µg PFOS/L may exceed the EC ML for PFOS in cattle meat. Risk assessment can be used to prioritise site cleanup and development of management plans to reduce PFAS body burden by considering timing of stock rotation and/or supplementation of primary exposure sources.

Seborrheic dermatitis: topical therapeutics and formulation design.

Seborrheic dermatitis (SD) is a common dermatological disorder with symptoms that include skin flaking, erythema and pruritus. This review discusses the topical products available for treating SD, which target several aspects of disease pathobiology, including cutaneous microbial dysbiosis (driven by Malassezia yeast), inflammation, sebum production and skin barrier disruption. Among the various treatments available, zinc pyrithione (ZnPT) based products that exhibit anti-fungal action are the market leaders. A skin compartment approach is presented here for combining ZnPT exposure information with threshold levels for anti-fungal efficacy and toxicity, overall providing a comprehensive picture of ZnPT therapeutics and safety. While Malassezia yeast on the surface are effectively targeted, yeast residing beyond the superficial follicle may not receive adequate ZnPT for anti-fungal effect forming the basis for skin re-colonisation. Levels entering systemic circulation from topical delivery are well below toxic thresholds, however the elevated zinc levels within the viable epidermis warrants further investigation. Strategies to improve formulation design can be broadly classified as influencing 1) topical delivery, 2) therapeutic bioactivity, 3) skin mildness, and 4) sensory attributes. Successful SD treatment ultimately requires formulations that can balance efficacy, safety, and consumer appeal.

Nanoparticle elasticity regulates the formation of cell membrane-coated nanoparticles and their nano-bio interactions.

Cell membrane-coated nanoparticles are emerging as a new type of promising nanomaterials for immune evasion and targeted delivery. An underlying premise is that the unique biological functions of natural cell membranes can be conferred on the inherent physiochemical properties of nanoparticles by coating them with a cell membrane. However, the extent to which the membrane protein properties are preserved on these nanoparticles and the consequent bio-nano interactions are largely unexplored. Here, we synthesized two mesenchymal stem cell (MSC) membrane-coated silica nanoparticles (MCSNs), which have similar sizes but distinctly different stiffness values (MPa and GPa). Unexpectedly, a much lower macrophage uptake, but much higher cancer cell uptake, was found with the soft MCSNs compared with the stiff MCSNs. Intriguingly, we discovered that the soft MCSNs enabled the forming of a more protein-rich membrane coating and that coating had a high content of the MSC chemokine CXCR4 and MSC surface marker CD90. This led to the soft MCSNs enhancing cancer cell uptake mediated by the CD90/integrin receptor-mediated pathway and CXCR4/SDF-1 pathways. These findings provide a major step forward in our fundamental understanding of how the combination of nanoparticle elasticity and membrane coating may be used to facilitate bio-nano interactions and pave the way forward in the development of more effective cancer nanomedicines.

A thermodynamic and kinetic analysis of human epidermal penetration of phenolic compounds: II. Maximum flux and solute diffusion through stratum corneum lipids.

Warming the skin is a key means of promoting solute permeation through the skin. Changes in solute permeation associated with variations in skin temperature also assist in understanding the mechanism by which solutes permeate the skin. However, few studies have considered the relative impact of temperature on the main determinants of the maximum flux for a solute across the skin, the solubility of a solute and its diffusivity in the stratum corneum. In this study, we quantified for the first time the thermodynamics associated with the maximum skin fluxes for a series of phenolic compounds of similar size but with varying lipophilicity (defined by the logarithms of their octanol/water partition coefficient, logP). These studies were undertaken using aqueous donor solutions (along with testosterone as a reference solute) across human epidermal membranes in vertical Franz diffusion cells at 4 °C, 24 °C and 37 °C with intermittent receptor sampling and volume replacement over 24 h. Kinetic and thermodynamic analyses included the estimation of the stratum corneum (SC) apparent SC diffusivity from the SC maximum fluxes and SC solubilities and the associated activation energies, enthalpies and entropies for diffusion. The key findings were that the differences in the maximum flux of phenolic compounds varying in lipophilicity mainly arose from differences in SC solubility at the various temperatures and that, at the highest temperature, SC permeability and SC diffusion were affected by SC lipid fluidisation and that variations in SC - water partitioning enthalpies explain some of the previously low activation energies for permeation of the more lipophilic phenols. Higher enthalpies for diffusion were seen for solutes with addition hydrogen bonding capacity and the highest negative entropy was observed with the more compact solutes. Various relationships between the derived thermodynamic parameters were explored and interpreted in a proposed model for solute partitioning into and permeation through the SC intercellular lipid lamellae.

Thermodynamic and kinetic analysis of human epidermal penetration of phenolic compounds: I. Stratum corneum solubility and partitioning.

Warming of the skin is now an accepted means of promoting skin permeation. Accordingly, the usually quite onerous thermodynamic studies on solute transport through the skin have practical applications. Phenolic compounds permeate through the skin by partitioning into and diffusing through the stratum corneum (SC) intercellular lipids, with their size being the main determinant of their maximal solute flux through skin. This paper sought to characterise the enthalpic and entropic changes associated with the solubility and equilibrium partitioning into the human SC of a series of phenols similar in size but with differing log P from aqueous vehicles. The solubilities of 9 phenolic compounds, covering a range of polarities, were determined in water and SC following 72 h at 4, 24, 32 and 37 °C which allowed the estimation of the SC-water partition coefficients. Van't Hoff plots were then used to estimate the enthalpies and entropies for the SC solubility, water solubility and SC partitioning of phenols. In addition, partition coefficients of 3 of the 9 phenols from mineral oil into hydrated and dehydrated SC were measured at the same temperatures. Van't Hoff plots were then used to estimate the enthalpies and entropies for the SC solubility, water solubility and SC partitioning of phenols from the oil. The SC solubility for the polar phenols increased more with temperature than the non-polar phenols, with the SC-water partition coefficients increasing with temperature for the polar phenols but decreasing with temperature for the non-polar phenols. Thermodynamic analyses suggest that, while enthalpy and entropy effects are involved in the SC partitioning of the non-polar solutes, the SC partitioning of the polar phenols were almost entirely entropy driven. The resultant thermodynamic parameters are consistent with the polar phenols being mainly associated with the SC polar head groups whereas the nonpolar phenols were more likely to be located in the interior interface SC lipid region adjacent to the polar head groups. Further, hydrating the SC led to an increase in the enthalpy of partitioning for both the polar and non-polar phenols studied. The estimated entropy of the partitioning for solutes from dehydrated SC suggests this is not only a hydrophobic effect in water but that the partitioning arises from the nature of phenolic compound - SC intercellular lipid interactions and SC intercellular lipid entropy. This partitioning process is dominated more by the extent of interaction between the SC and solute than the hydrophobic effect in water and is likely to be even greater above the SC lipid phase transition at around 36 °C for hydrated epidermal membranes.

Rapid determination of polyethoxylated tallow amine surfactants in human plasma by LC-MSMS.

The potential exposure to the widely used glyphosate-based herbicides, including attempted suicide by ingestion, is of world-wide concern. Whilst the major focus to date has been on managing exposure to the active ingredient glyphosate, it is now recognised that a common major 'inert' surfactant ingredient, polyethoxylated tallow amine (POEA) and related compounds, may be more toxic. However, the information on the toxicokinetics of POEA surfactants after exposure is limited, in part, due to the lack of suitable methods for their analysis in biological matrices. We therefore developed and validated a robust LC-MSMS method that allowed, for the first time, a rapid analysis of 11 POEA homologues in human plasma. Chromatographic separation was achieved on a Kinetex EVO C18 column under a 5 min gradient elution with mobile phase A containing water/acetonitrile/formic acid (95:5:0.1, v/v/v) and mobile phase B containing acetonitrile/water/formic acid (95:5:0.1, v/v/v). Amlodipine was chosen as the internal standard (IS) for this assay. Amlodipine-d4 would be an ideal alternative IS to expand the applicability of the established method especially in antihypertensive patients. Multiple reaction monitoring (MRM) methods were optimized for 11 POEA homologues and the IS. Sample pre-treatment was performed using simple protein precipitation with methanol at a ratio of 4:1, requiring only 20 µL plasma. The validated method showed good specificity, accuracy and precision with lower limits of quantification (LLOQ) ranging from 0.35 to 10.8 ng mL-1 for all selected POEA homologues. The method was then used to measure concentrations of the various POEA surfactants in more than 600 human plasma samples from 151 patients admitted to hospital with acute glyphosate intoxication. The highest concentrations ranged from 1.07 ng mL-1 for C18u(EO)4-362.70 ng mL-1 for C16s(EO)2. The analysis of POEA surfactants plasma concentrations as described here underpins the assessment of POEA internal exposure and the relationships between POEA related glyphosate toxicity and the extent of poisoning.

In vitro screening of topical formulation excipients for epithelial toxicity in cancerous and non-cancerous cell lines.

Chemical excipients used in topical formulations may be toxic to living skin cells. Here, we compared the in vitro toxicity of some common solubilizing excipients against human melanoma cells, human keratinocytes (HaCaT) and primary skin fibroblasts (FB) as examples of cancerous, immortalized and primary human skin cells, often used as experimental models representative of in vivo conditions. Two distinct endpoint assays (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and crystal violet (CV)) were used. The mechanism of cell death after excipient exposure was assessed through Reactive Oxygen Species (ROS) production, cell membrane integrity and cell cycle progression. Results showed that the surfactants, Labrasol®, Labrafil® and Transcutol®, were less toxic than Triton X-100 (a model irritant) in all cell types whereas the oil, Labrafac®, was non-toxic. The human melanoma WM164 cell line showed the greatest sensitivity toward cytotoxicity after chemical exposure, while the other cell lines were more resistant. The relative excipient cytotoxicity responses observed in the MTT and CV assays were comparable and similar trends were seen in their estimated 50 % inhibitory concentration (IC50) values. DNA fragmentation by flow cytometry after exposing the cells to IC50 concentrations of the excipients showed negligible apoptotic populations. ROS production was increased in all cell types after toxic exposure; however, ROS elevation did not lead to apoptosis. The toxicity profiles of each excipient are not only relevant to their use in formulating safe topical products but also in the potential synergistic efficacy in the topical treatment of melanoma.

Human epidermal in vitro permeation test (IVPT) analyses of alcohols and steroids.

This study examined a number of factors that can impact the outcomes of in vitro human epidermal permeation coefficients for aliphatic alcohols and steroids, including receptor phase composition and study conditions. We determined experimentally the solubilities and IVPT permeation of a homologous series of 14C labeled aliphatic alcohols (ethanol, propanol, pentanol, heptanol, octanol and decanol) in different receptor fluids as recommended by Organisation Economic Co-operation and Development (OECD). We used human epidermal membranes at 25 °C and phosphate-buffered saline (PBS), 2 %w/v bovine serum albumin (2 %w/v BSA), 50 %w/v ethanol and 0.1, 2 and 6 %w/v Oleth-20 receptor phases. We also explored and confirmed the discrepancies between in vitro human epidermal permeability coefficients (kp) and diffusion lag times for steroids from Scheuplein's group with our own work and that of others. The main reason for the observed differences is not clear but is likely to be multifactorial, including the effects of diffusion cell design, receptor phase solubility, unstirred receptor phase effects, epidermal membrane hydration, diffusion cell configuration, transport through appendageal pathways and steroid lipophilicity. We conclude with a summary of experimental conditions that should be considered in undertaking IVPT studies.

Mechanistic Modeling of In Vitro Skin Permeation and Extrapolation to In Vivo for Topically Applied Metronidazole Drug Products Using a Physiologically Based Pharmacokinetic Model.

Physiologically based pharmacokinetic (PBPK) modeling has increasingly been employed in dermal drug development and regulatory assessment, providing a framework to integrate relevant information including drug and drug product attributes, skin physiology parameters, and population variability. The current study aimed to develop a stepwise modeling workflow with knowledge gained from modeling in vitro skin permeation testing (IVPT) to describe in vivo exposure of metronidazole locally in the stratum corneum following topical application of complex semisolid drug products. The initial PBPK model of metronidazole in vitro skin permeation was developed using infinite and finite dose aqueous metronidazole solution. Parameters such as stratum corneum lipid-water partition coefficient (Ksclip/water) and stratum corneum lipid diffusion coefficient (Dsclip) of metronidazole were optimized using IVPT data from simple aqueous solutions (infinite) and MetroGel (10 mg/cm2 dose application), respectively. The optimized model, when parameterized with physical and structural characteristics of the drug products, was able to accurately predict the mean cumulative amount permeated (cm2/h) and flux (µg/cm2/h) profiles of metronidazole following application of different doses of MetroGel and MetroCream. Thus, the model was able to capture the impact of differences in drug product microstructure and metamorphosis of the dosage form on in vitro metronidazole permeation. The PBPK model informed by IVPT study data was able to predict the metronidazole amount in the stratum corneum as reported in clinical studies. In summary, the proposed model provides an enhanced understanding of the potential impact of drug product attributes in influencing in vitro skin permeation of metronidazole. Key kinetic parameters derived from modeling the metronidazole IVPT data improved the predictions of the developed PBPK model of in vivo local metronidazole concentrations in the stratum corneum. Overall, this work improves our confidence in the proposed workflow that accounts for drug product attributes and utilizes IVPT data toward improving predictions from advanced modeling and simulation tools.

Percutaneous absorption of steroids from finite doses: Predicting urinary excretion from in vitro skin permeation testing.

Pharmacokinetic (PK) models are widely used to describe drug permeation across the epidermal membrane barrier, the stratum corneum (SC). Here, we extend our previously reported diffusion and compartment-in-series models to describe plasma concentrations, urinary excretion-time profiles and exposure estimates after topically applied finite doses of solvent deposited solids. In vivo models were derived by convolution of a skin absorption input function for finite dosing with that for in vivo disposition PK. In vitro skin permeation test (IVPT) and in vivo urinary excretion data for cortisone, desoxycorticosterone, and testosterone were extracted from literature for model validation and establishment of in vitro - in vivo relationships (IVIVR). Both SC diffusion and SC 3-compartment-in-series PK models adequately described experimental in vitro and in vivo permeation data, with similar model parameter estimates for SC diffusion time and bioavailability. A satisfactory IVIVR was generated for cortisone, whereas testosterone and desoxycorticosterone showed higher bioavailability in vitro compared to in vivo. In recognising that future prospective studies need to both have an adequate sampling schedule and be harmonized for robust IVIVRs, we developed expressions for predicting extent of absorption and time for peak absorption for both in vitro and in vivo studies. Other study parameters, such as application site, applied dose, and application techniques, can also affect drug permeability through skin during dosage form metamorphosis after finite dose application, and a lack of correlation may result if these are poorly matched.

An updated database of human maximum skin fluxes and epidermal permeability coefficients for drugs, xenobiotics, and other solutes applied as aqueous solutions.

The dataset represented in this article is referred to by the review article entitled "Topical drug delivery: history, percutaneous absorption, and product development" (MS Roberts et al., 2021) [1]. The dataset contains maximal flux (Jmax ), and permeability coefficient (kp ) values collated from In Vitro human skin Permeation Test (IVPT) reports published to date for various drugs, xenobiotics, and other solutes applied to human epidermis from aqueous solutions. Also included are each solute's physicochemical properties and the experimental conditions, such as temperature, skin thickness, and skin integrity, under which the data was generated. This database is limited to diluted or saturated aqueous solutions of solutes applied on human epidermal membranes or isolated stratum corneum in large volumes so that there was minimal change in the donor phase concentration. Included in this paper are univariate Quantitative Structure-epidermal Permeability Relationships (QSPR) in which the solute epidermal permeation parameters (kp , and Jmax ) are related to potential individual solute physicochemical properties, such as molecular weight (MW), log octanol-water partition coefficient (log P), melting point (MP), hydrogen bonding (acceptor - Ha , donor - Hd ), by scatter plots. This data was used in the associated review article to externally validate existing QSPR regression equations used to forecast the kp and Jmax for new therapeutic agents and chemicals. The data may also be useful in developing new QSPRs that may aid in: (1) drug choice and (2) product design for both topical and transdermal delivery, as well as (3) characterizing the potential skin exposure of hazardous substances.

Multi-Modal Imaging to Assess the Follicular Delivery of Zinc Pyrithione.

Zinc pyrithione (ZnPT) is a widely used antifungal, usually applied as a microparticle suspension to facilitate delivery into the hair follicles, where it then dissociates into a soluble monomeric form that is bioactive against yeast and other microorganisms. In this study, we use multiphoton microscopy (MPM) and fluorescence lifetime imaging microscopy (FLIM) to characterise ZnPT formulations and map the delivery of particles into follicles within human skin. To simulate real-world conditions, it was applied using a massage or no-massage technique, while simultaneously assessing the dissolution using Zinpyr-1, a zinc labile fluorescent probe. ZnPT particles can be detected in a range of shampoo formulations using both MPM and FLIM, though FLIM is optimal for detection as it allows spectral and lifetime discrimination leading to increased selectivity and sensitivity. In aqueous suspensions, the ZnPT 7.2 µm particles could be detected up to 500 µm in the follicle. The ZnPT particles in formulations were finer (1.0-3.3 µm), resulting in rapid dissolution on the skin surface and within follicles, evidenced by a reduced particle signal at 24 h but enhanced Zinpyr-1 intensity in the follicular and surface epithelium. This study shows how MPM-FLIM multimodal imaging can be used as a useful tool to assess ZnPT delivery to skin and its subsequent dissolution.