Species differences in percutaneous absorption of nicorandil

The species difference in skin permeability, Kp, of nicorandil was determined by using excised skin samples from hairless mouse, hairless rat, guinea-pig, dog, pig, and human. The Kp value of nicorandil in hairless mice was the greatest among the six species, and those in pigs and humans were in good agreement. To clarify the reasons for the species difference, various skin characteristics in each species were measured. It was suggested that the difference of skin surface lipids in each species affected the partitioning of nicorandil from vehicle to stratum corneum, and that such a difference would be a main factor for the species difference in nicorandil permeability. Since pig and human skins had similar surface lipids, barrier thickness, and morphological aspects, percutaneous absorption studies using excised pig skin samples would be useful for the estimation of in vitro human skin permeation behavior.     

The selection and use of natural and synthetic membranes for in vitro diffusion experiments

The following membranes are discussed: human skin; animal models (including mouse, hairless mouse, rat, guinea pig, rabbit, monkey, pig, shed snake skin, egg-shell membrane, and synthetic stratum corneum); and synthetic membranes (including cellulose media, filter membranes, and synthetic polymers). Membrane integrity and diffusive characteristics are also considered.     

猪不同部位皮肤与人体皮肤对药物渗透性的比较

以苯甲酸、水杨酸、甲硝唑为模型药物，对猪耳和猪腹部皮肤进行体外药物渗透实验，在相同条件下与正常人体皮肤进行了渗透性差别的比较研究。结果表明：猪耳和猪腹部皮肤与人体皮肤对药物渗透性具有相似性，特别是猪耳皮肤对药物体外透皮实验是个有价值的动物模型。     

The effects of an alpha hydroxy acid (glycolic acid) on hairless guinea pig skin permeability.

The barrier integrity of hairless guinea pig skin after treatment with an alpha hydroxy acid was assessed through in vivo topical application of an oil-in-water emulsion containing 5 or 10% glycolic acid at pH 3.0. The control was a commercial moisturizing lotion, pH 7.8. A dosing regimen for the glycolic acid formulations that was tolerated by the hairless guinea pigs and significantly decreased stratum corneum turnover time was determined using the dansyl chloride staining technique. Once-daily dosing of hairless guinea pig skin for 3 weeks with the glycolic acid formulations resulted in approximately a 36-39% decrease in stratum corneum turnover time compared with the control lotion. After this treatment, hairless guinea pigs were sacrificed for the in vitro measurement of the percutaneous absorption of [14C]hydroquinone and [14C]musk xylol. No significant differences in the 24-hour absorption of either test compound were found for skin treated with the control lotion or the glycolic acid formulations. There were also no significant differences found in the absorption of [3H]water through skin from the different treatment groups. Although no increase in skin penetration occurred after treatment with the glycolic acid formulations, histology revealed approximately a twofold increase in epidermal thickness. Also the number of nucleated cell layers nearly doubled in skin treated with 5% and 10% glycolic acid compared with the control lotion and untreated skin. These studies demonstrate that substantial changes in the structure of hairless guinea pig epidermis can occur without significant effect on skin permeability of two model compounds.     

Methods for in vitro percutaneous absorption studies I. Comparison with in vivo results

The percutaneous absorption of selected radiolabeled compounds through female rat skin was determined after their application in a petrolatum vehicle. Absorption was measured during a 5-day period by in vivo and in vitro techniques. Benzoic acid, acetylsalicylic acid, urea, and caffeine were selected because of their differing skin permeability rates. Absorption was measured in vivo from urinary excretion data and in vitro with excised skin in diffusion cells. When skin absorption was expressed as the percentage of applied dose, values obtained in vitro were benzoic acid, 49.1; acetylsalicylic acid, 29.0; and urea, 7.2. Since similar values were obtained in vivo, permeability measurements of these compounds with excised skin appear reliable. With the in vitro data, the rate of skin absorption was more accurately stated in the form of a permeability constant. A method is described for the determination of a permeability constant in vivo, using measurements obtained from blood and urine samples.     

In vivo percutaneous penetration of some organic compounds related to anatomic site in humans: predictive assessment by the stripping method

The effect of anatomic site on the in vivo relationship between the total penetration of four compounds and the amount of the compounds present in the stratum corneum at the end of application was studied in humans. For each anatomic site, 1,000 nmol of 14C-radiolabeled benzoic acid, benzoic acid sodium salt, caffeine, or acetylsalicylic acid was applied to 1-cm2 area of skin of male Caucasian patients aged 28 +/- 2 years (groups of 6-8). For each molecule and each site, a first application on the right-hand side of the body allowed total absorption to be determined by measuring the amount excreted in the urine. A second application, performed 48 h later on the contralateral site, enabled the total amount of substance present in the stratum corneum at the end of application (30 min) to be assessed after cellophane-tape stripping of the treated area. The results showed that skin permeability varied substantially, depending both on the physicochemical nature of the molecule and on the anatomical location. In general, the rank order in skin permeability of the studied areas appears to be as follows: arm less than or equal to abdomen less than postauricular less than forehead. Whatever the compound applied, the forehead was approximately 2 times as permeable as the arm or abdomen. Independent of the origin of the differences in permeability observed among sites, there exists a linear correlation (r = 0.97, p less than 0.001) between the amounts of substance present in the stratum corneum at the end of application (30 min) and the total amounts which penetrated within a 4-d period.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Method to Predict the Percutaneous Permeability of Various Compounds: Shed Snake Skin as a Model Membrane

Penetration of various compounds through shed snake skin was measured in vitro to examine the effect of lipophilicity and molecular size of a compound on permeability through this model membrane. The permeabilities were found to be controlled by the lipophilicity and the molecular size of the permeant. The smaller and the more lipophilic the compound, the greater the permeability. Equations have been developed to predict the permeability from the molecular weight and the distribution coefficient of a compound. Further, the lipophilicity of shed snake skin is similar to that of human skin and the response of shed snake skin to the molecular size of a permeant is more similar to human skin than to hairless mouse skin. Considering the similarities between shed snake skin and human stratum coraeum in terms of structure, composition, and permeability characteristics, the same considerations may apply to permeability through human stratum corneum.     

Percutaneous Absorption of Benzoic Acid Across Human Skin. I. In Vitro Experiments and Mathematical Modeling

The percutaneous absorption of benzole acid across human skin in vitro was experimentally and mathematically modeled. Skin partition coefficients were measured over a range of benzoic acid concentrations in both saline and distilled water. The permeation of benzoic acid was measured across isolated stratum corneum, stratum corneum and epidermis, and split-thickness skin. These experiments demonstrated that the stratum corneum was the rate-limiting barrier and that the flux is proportional to the concentration of the undissociated species. The permeation data were analyzed with a comprehensive non-steady-state mathematical model of diffusion across skin. Two adjustable parameters, the effective skin thickness and diffusivity, were fit to the permeation data by nonlinear regression.     

Permeability of benzoic acid derivatives in excised guinea pig dorsal skin and effects of l-menthol

Penetration through excised guinea pig dorsal skin was examined for nine mono-substituents of benzoic acid derivatives. Permeability coefficients of the derivatives correlated well with their n-octanol/water partition coefficients. Since the regression coefficient was similar to the value obtained in human skin, it is suggested that the lipid lamellae of guinea pig skin resembled that of human skin in lipophilicity. Addition of penetration enhancer, 1% l-menthol in 15% ethanol markedly increased the flux and permeability coefficients of relatively hydrophilic derivatives and decreased the dependency of the permeability coefficients on the partition coefficients. Electron spin resonance analysis using 5-doxylstearic acid revealed the presence of a strongly immobilized component of the spin label in the skin and its disappearance in the presence of 1% l-menthol in 15% ethanol. These results suggest that the rigid lamellar structure of the stratum corneum was disrupted by l-menthol with ethanol, and caused the enhancement of penetration of relatively hydrophilic benzoic acid derivatives.     

Animal models for percutaneous absorption

Animal models are important tools to predict human in vivo percutaneous absorption/penetration. Monkey, pig, rat, rabbit, guinea pig, hairless rodents, such as hairless rat, hairless mouse, hairless guinea pig and hairless dog, are among the most used animals for this purpose. Each animal model has its own advantages and weakness or limitation. To better correlate animal data with human skin absorption, we need to be familiar with each animal model's characteristics as well as experimental method and condition. We reviewed the original papers published after 1993 that described permeability of both animal skin and human skin. It showed that monkey, pig and hairless guinea pig are more predictive of human skin absorption/penetration and common laboratory animals, such as rat, rabbit, guinea pig, generally overestimate human skin absorption/penetration. Copyright © 2014 John Wiley & Sons, Ltd.     

Percutaneous absorption of corticosteroids: age, site, and skin-sectioning influences on rates of permeation of hairless mouse skin by hydrocortisone

As part of a long-range plan to decipher the mechanism of mass transfer of corticosteroids across skin, the permeation of [3H]hydrocortisone through hairless mouse skin was characterized by in vitro diffusion cell techniques. Age and anatomical site-related behaviors were explored mainly with whole skin but also with skin stripped of its horny layer. Permeability of the mouse skin was low shortly after birth and increased during the singular normal hair cycle exhibited by the SKH-hr-1 mouse strain. The return to a hairless state over a period of 20-35 d was accompanied by decreased permeability of hydrocortisone. A permeability coefficient of approximately 2 X 10(-4) cm/h was found for the mature mouse. For whole skin, there was no difference in the permeabilities of dorsal and abdominal skin sections, but for stratum corneum-free membranes and dermal membranes, the abdominal site appeared to be more permeable, which is consistent with its thinner dimensions. Totally stripped skin and isolated dermis are approximately 500 and approximately 1000 times more permeable than intact skin, respectively; the unaltered stratum corneum of the hairless mouse is thus shown to be the major barrier to the mass transfer of hydrocortisone.     

Effect of barrier disruption by acetone treatment on the permeability of compounds with various lipophilicities: implications for the permeability of compromised skin.

The permeability of compromised skin barrier was investigated in vitro using acetone-disrupted hairless mouse skin as a model membrane. The effect of compound lipophilicity was studied using sucrose, caffeine, hydrocortisone, estradiol, and progesterone as model compounds. The results demonstrated that permeability barrier disruption by acetone treatment significantly enhanced the permeability of the skin to both hydrophilic and amphipathic compounds, including sucrose, caffeine and hydrocortisone. This effect was more prominent with caffeine and hydrocortisone at different transepidermal water loss (TEWL) levels. Acetone treatment, however, didn't appear to alter the percutaneous penetration of highly lipophilic compounds, such as estradiol and progesterone. The characteristics of skin permeability were described by parabolic relationships between log P(WS) (permeability coefficient of whole skin) and log K(O/W) (octanol/water partition coefficient) at different degrees of permeability barrier disruption. The optimal log K(O/W) of compounds for skin penetration appeared to decrease with an increase in TEWL levels. The maximal permeability achieved was similar through skin displaying different TEWL levels. In an attempt to explore the underlying mechanisms for the changes in skin permeability, the stratum corneum/normal saline partition coefficients of water, caffeine, and hydrocortisone either decreased or remained unaffected with an increase in TEWL. Electron microscopic examinations have revealed reductions in stratum corneum lipid content and alterations in intercellular membrane structures as a result of acetone treatment, whereas negligible changes in the number of horny layers were observed by safranin staining of the stratum corneum. We have concluded that the enhancement in skin permeability to both hydrophilic and amphipathic compounds by acetone treatment arose mainly because of the increase in stratum corneum diffusivity at higher TEWL levels. The results imply the possibility of using both TEWL and drug lipophilicity to predict alterations in skin permeability and hence the dose adjustment of topically applied medication for patients with impaired skin barrier function.     

Mechanism of urea effect on percutaneous absorption of clonidine

The urea effect on skin permeation of clonidine was investigated to reduce a log time and to increase a permeability. ICR mouse skin and human skin were used and were assumed to be a two-layer membrane consisted of stratum corneum and viable epidermis. The urea acted as a skin denaturant and humectant in the whole epidermis. Also it enhanced the skin permeability of clonidine about 3.5 times. On the other hand, it enhanced the skin permeability by acting as a humectant in the viable epidermis. But the urea effect on the whole epidermis was shown to be greater than that on the viable epidermis. Therefore, it was found that the effect of urea was greater on the stratum corneum than the viable epidermis. Variation of enhancing effect according to the concentration of urea was not found in the range of 1% to 20%.     

Dermal penetration enhancement profile of hexamethylenelauramide and its homologues: in vitro versus in vivo behavior of enhancers in the penetration of hydrocortisone

Several amides of cyclic amines were prepared and tested as penetration enhancers in the diffusion of various drugs through hairless mouse skin in vitro. Hexamethylenelauramide (hexahydro-1-lauroyl-1H-azepine) was selected as a broad spectrum penetration enhancer worthy of further study. Later, the duration of the effect of various enhancers on the penetration barrier in vivo was determined by evaluating the in vitro diffusion of hydrocortisone through skins that had been pretreated in vivo. We found that the longer the pretreatment, the smaller the amount of penetrated hydrocortisone. Furthermore, our results suggested that differences exist in the retention of various enhancers in living mouse skin. The in vitro pretreatment experiments revealed that the penetration through dead skin is slow compared with the penetration through living skin. Neither the nature of the receptor phase, nor the increased temperature of the in vitro experiments, explain the striking differences between the in vivo and the in vitro experiments. Finally, the penetration of hydrocortisone through the stratum corneum in the presence of enhancers, as well as the penetration of 1-dodecylhexahydro-2H-azepin-2-one (laurocapram), hexamethylenelauramide, and oleic acid, were determined using a stratum corneum stripping technique. More hydrocortisone penetrated through the stratum corneum during the first 3 h in the presence of hexamethylenelauramide than in the presence of laurocapram or oleic acid.     

Physicochemical study of percutaneous absorption enhancement by dimethyl sulfoxide: kinetic and thermodynamic determinants of dimethyl sulfoxide mediated mass transfer of alkanols

By first determining the thermodynamic activities and activity coefficients of methanol, 1-butanol and 1-octanol in binary dimethyl sulfoxide:water media, it has been possible to separate solubilizing (thermodynamic) effects of dimethyl sulfoxide from its kinetic (diffusive) influence as they relate to the skin permeation of these small, nonelectrolyte alkanols. This was done by normalizing the experimental permeability coefficients found with full-thickness hairless mouse skin membranes to unit activity in the vehicle. When the dimethyl sulfoxide media were placed on both sides of the skin sections in a two compartment diffusion cell, activity-adjusted permeability coefficients of the permeants were invariant to dimethyl sulfoxide concentrations of 50% strength. Thus, up to this concentration and in the absence of net solvent crosscurrents, the permeabilities of methanol, 1-butanol, and 1-octanol appear to be strictly determined by partitioning into the stratum corneum. However, when the dimethyl sulfoxide percentage strength was raised to greater than or equal to 75%, activity-adjusted permeability increased systematically and profoundly, indicating severe barrier impairment with increased diffusion across the horny layer (kinetic effect). When neat dimethyl sulfoxide was placed on both sides of the skin, the experimental permeability coefficients of the three alcohols were maximal and equal in magnitude, suggesting total functional impairment of the stratum corneum. When the dimethyl sulfoxide media were placed in contact with the stratum corneum surface of the skin membranes only, accelerating effects were noted at dimethyl sulfoxide concentrations less than 50%, further supporting the idea that solvent cross flows themselves disrupt the horny structure. The degree of impairment was quantified under all experimental circumstances.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prediction of skin permeability of drugs: comparison of human and hairless rat skin.

Relationships between skin permeability and physicochemical properties of drugs were examined to establish a predictive method for the steady-state permeation rate of drugs through human skin. Human skin permeation properties fell into two categories: one in which the permeability coefficient is correlated to the partition coefficient, revealed with lipophilic drugs; and the other in which the permeability coefficients are almost constant, shown with hydrophilic drugs. The stratum corneum, the main barrier in skin, could be considered as a membrane with two parallel permeation pathways: lipid and pore pathways, and an equation for predicting the steady-state permeation rate of drugs was derived. The skin permeabilities of drugs for man were compared with those for hairless rat. The species difference in skin permeability found was suggested to be due to the difference in skin permeation pathways, since lipid content and water uptake of the stratum corneum varied between human and hairless rat skin.     

Enhancement of percutaneous absorption by laurocapram.

The in vitro treatment of shed snake skin and hairless rat skin with laurocapram resulted in dramatic decreases in the amounts of cholesterol, phospholipids, and ceramides but not triglycerides in the skins. Scanning electron microscopic observations of hairless rat skin treated with laurocapram indicated looseness and cell separation of the stratum corneum probably caused by the extensive extraction of the intercellular lipids. An ESR study demonstrated the increased fluidity of the corneum lipids after laurocapram treatment. The apparent rotational correlation time of 16-doxyl-stearic acid was decreased by 1.6-2 times after treatment with laurocapram. No penetration of laurocapram itself through shed snake skin and hairless rat skin was detected in vitro, except when the reservoir solvent was 60% ethanol or propylene glycol. The enhancer was hardly metabolized during a 48-h incubation with skin homogenate. Pretreatment of shed snake skin with laurocapram increased significantly the penetration of sulfanilamide and indomethacin through the skin. These results indicate that laurocapram penetrating into the stratum corneum interacts with structured lipids in the intercellular channels and releases them, thereby enhancing the penetration of hydrophilic drugs through the channels. Additionally, laurocapram penetrating into the intracellular matrix of the corneum fluidizes the intracellular lipids and causes the reduction of diffusional resistance.     

Effects of cinnamene enhancers on transdermal delivery of ligustrazine hydrochloride.

Cinnamene compounds, cinnamic acid, cinnamaldehyde and cinnamic alcohol, were employed as enhancers. The effects and mechanisms of penetration promoters on the in vitro percutaneous absorption of ligustrazine hydrochloride across hairless porcine dorsal skin were investigated. Transdermal fluxes of ligustrazine hydrochloride through porcine skin were determined in vitro by Franz-type diffusion cells. The results indicated that the penetration flux of ligustrazine hydrochloride by cinnamic acid was the greatest. Significant statistical differences (P<0.05) were found between cinnamic acid and other promoters. Fourier transform-infrared (FT-IR) were carried out to analyze the effects of enhancers on the biophysical properties of the stratum corneum and the permeation enhancement mechanisms. FT-IR results revealed that the changes of peak shift and peak area due to C-H stretching vibrations in the stratum corneum lipids were associated with the selected enhancers. All of them could perturb and extract the stratum corneum lipids to different extent. Morphological changes of the skin treated with enhancers were monitored by a scanning electron microscope. It was demonstrated that the extraction of the stratum corneum lipids by the enhancers led to the disruption of stratum corneum and the desquamation of stratum corneum flake. Apparent density was newly proposed to estimate the desquamated extent of stratum corneum flake. Correlation analysis revealed that there was a linear relationship between apparent density and decrease in peak area. The results showed that the permeation enhancement mechanisms of cinnamene were pleiotropic ones, including disordering the lipids, extracting the lipids and competitive hydrogen bonding between cinnamene enhancers and amides of ceramide head groups in stratum corneum.     

Transdermal oxymorphone formulation development and methods for evaluating flux and lag times for two skin permeation-enhancing vehicles

Oxymorphone is a candidate for transdermal delivery since it is a very potent analgesic, is not very effective orally, and has a short duration of action. In developing a transdermal delivery system, two criteria that were considered important were achieving adequate flux and minimizing the lag time. Oxymorphone skin permeation rates in vitro were very low unless skin permeation enhancers were included in the vehicle. After an initial screen of 17 formulations, two skin permeation-enhancing formulations were selected for further study. These were myristic acid:propylene glycol:oxymorphone base (A), and decylmethylsulfoxide:ethanol:water:oxymorphone.HCl (B). With either formulation and either human or hairless guinea pig skin, there was little dependence of either in vitro flux or lag time on the section of skin used (stratum corneum, epidermis, epidermis/dermis). There were significant differences between human skin and hairless guinea pig skin when comparing in vitro fluxes with the two formulations. With formulation A, fluxes through hairless guinea pig skin were three-to fivefold greater than through human skin. With B, however, fluxes through human skin were up to fivefold greater than through hairless guinea pig skin. In vitro lag times with A were generally long (approximately 24 h), whereas those with B were much lower (approximately 1 to 10 h). The species dependence of permeation enhancement and the differences in lag time between formulations could be related to differences in the mechanisms of permeation enhancement. In vivo lag times with the fatty acid:propylene glycol vehicle were estimated in hairless guinea pigs based on plasma oxymorphone concentrations. These were much lower than in vitro lag times.     

Characterization of Esterase and Alcohol Dehydrogenase Activity in Skin. Metabolism of Retinyl Palmitate to Retinol (Vitamin A) During Percutaneous Absorption

Retinyl palmitate, a widely used ingredient in cosmetic products, is promoted for its beneficial effects on the appearance of skin. Previous studies suggest that enzymes are available in skin to metabolize this ingredient during skin absorption. Esterase activity hydrolyzes retinyl palmitate to retinol (vitamin A), which is oxidized in many tissues to retinoic acid primarily by alcohol dehydrogenase. The activities of esterase and alcohol dehydrogenase were characterized in hairless guinea pig skin by using flow-through diffusion cells and radiolabeled model compounds (methyl salicylate and benzyl alcohol) previously shown to be metabolized by these enzymes. Methyl salicylate was hydrolyzed by esterase to a greater extent in viable skin than in nonviable skin. Glycine conjugation of salicylic acid and benzoic acid occurred only in viable skin. The metabolism of methyl salicylate and benzyl alcohol occurred to a greater extent in male guinea pig skin than in female guinea pig skin. The percutaneous absorption of both radiolabeled compounds was similar in viable and nonviable skin. About 30 and 18% of topically applied retinyl palmitate were absorbed from an acetone vehicle by hairless guinea pig skin and human skin, respectively. Less than 1% of the applied dose of this lipophilic compound diffused from skin into the receptor fluid. Retinol was the only detectable metabolite of retinyl palmitate in both hairless guinea pig and human skin. In human skin, 44% of the absorbed retinyl palmitate was hydrolyzed to retinol. The use of retinyl palmitate in cosmetic formulations may result in significant delivery of retinol into the skin.James Boehnlein: Results submitted as partial fulfillment of requirements for the M.S. in Pharmaceutical Science degree (Cosmetic Science),