In vitro metabolism by human skin and fibroblasts of retinol, retinal and retinoic acid

Spectral and mass characterization of kinetic conversion from retinoids to retinoic acid in an in vitro 3-D human skin equivalent model

To investigate the effect of retinoids, such as retinol (ROL), retinal (RAL), and retinyl palmitate (RP), on epidermal integrity, skin deposition, and bioconversion to retinoic acid (RA). 3-D human skin equivalent model (EpiDermFT™) was used. Epidermal cellular integrity measured by TEER values was significantly higher for a topical treatment of ROL and RAL than RP (p < 0.05). The skin deposition (μM) of ROL and RAL was approximately 269.54 ± 73.94 and 211.35 ± 20.96, respectively, greater than that of RP (63.70 ± 37.97) over 2 h incubation. Spectral changes were revealed that the CO maximum absorbance occurred between 1600∼1800 cm-1 and was greater from ROL than that from RAL and RP, indicating conjugation of R-OH to R-CHO or R-COOH could strongly occur after ROL treatment. Subsequently, a metabolite from the bioconversion of ROL and RAL was identified as RA, which has a product ion of m/z 283.06, by using liquid a chromatography-mass spectrometry (LC-MS) - total ion chromatogram (TIC). The amount of bioconversion from ROL and RAL to RA in artificial skin was 0.68 ± 0.13 and 0.70 ± 0.10 μM at 2 h and 0.60 ± 0.04 and 0.57 ± 0.06 μM at 24 h, respectively. RA was not detected in the skin and the receiver compartment after RP treatment. ROL could be a useful dermatological ingredient to maintain epidermal integrity more effectively, more stably deposit on the skin, and more steadily metabolize to RA than other retinoids such as RAL and RP.

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.

Carotenoids in Human SkinIn Vivo: Antioxidant and Photo-Protectant Role against External and Internal Stressors

The antioxidant system of the human body plays a crucial role in maintaining redox homeostasis and has an important protective function. Carotenoids have pronounced antioxidant properties in the neutralization of free radicals. In human skin, carotenoids have a high concentration in the stratum corneum (SC)-the horny outermost layer of the epidermis, where they accumulate within lipid lamellae. Resonance Raman spectroscopy and diffuse reflectance spectroscopy are optical methods that are used to non-invasively determine the carotenoid concentration in the human SC in vivo. It was shown by electron paramagnetic resonance spectroscopy that carotenoids support the entire antioxidant status of the human SC in vivo by neutralizing free radicals and thus, counteracting the development of oxidative stress. This review is devoted to assembling the kinetics of the carotenoids in the human SC in vivo using non-invasive optical and spectroscopic methods. Factors contributing to the changes of the carotenoid concentration in the human SC and their influence on the antioxidant status of the SC in vivo are summarized. The effect of chemotherapy on the carotenoid concentration of the SC in cancer patients is presented. A potential antioxidant-based pathomechanism of chemotherapy-induced hand-foot syndrome and a method to reduce its frequency and severity are discussed.

Stability and Applicability of Retinyl Palmitate Loaded Beeswax Microcapsules for Cosmetic Use : Material properties and stability of microencapsulated actives

In our previous study, retinyl palmitate was successfully encapsulated by melt dispersion using waxes as shell materials. Herein, the objective of the present research is to evaluate the shelf life and kinetic release of the developed microcapsules. The study was conducted by measuring actual loading capacity over a period of time using spectroscopic analysis. The transfer percentage of particles from nonwoven facial wipes to skin-like surfaces was also investigated by simulating the rubbing mechanism with a robotic transfer replicator. Although particles stored as powder form under room temperature showed only eight days of shelf-life, particles stored as a dispersion in a refrigerator maintained 60% of the theoretical loading capacity after one month. The kinetic release profile of the particles in ethanol with shaking at 100 rpm and 37±2°C showed an initial burst in the first half an hour, followed by a sustained release. It also showed that 98% of the retinyl palmitate content released within 4 h. Particles incorporated into wet nonwoven wipes gave approximately 22% transfer to skin-like fabric. Thus, the study shows potentials of delivering skincare properties by means of retinyl palmitate capsule loaded textile substrates.

Multidirectional activity of bakuchiol against cellular mechanisms of facial aging - Experimental evidence for a holistic treatment approach

Objective

Skin ageing is a multifactorial process involving formation of reactive oxygen species, consecutive inflammation with reduced epidermal and dermal cell viability and resulting damage to the extracellular matrix. Effective dermocosmetic treatment modalities should ideally address these hallmarks in a holistic approach. Here, we determined the corresponding activity profile of bakuchiol, a plant‐derived meroterpene, in an array of in vitro, ex vivo and in vivo studies and compared it to retinol, currently considered as gold standard in topical antiageing cosmetics.

Methods

The antioxidative capacity and power of bakuchiol and retinol were analysed by measuring 2,2′‐diphenyl‐1‐picrylhydrazyl (DPPH) reduction via its absorption decay and electron spin resonance spectroscopy, respectively. Effects on prostaglandin E2 (PGE2), macrophage migration inhibitory factor (MIF), fibroblast growth factor 7 (FGF7), collagen type I and VII (COL1A1, COL7A1), fibronectin (FN) levels as well as the metabolization of water‐soluble tetrazolium 1 (WST‐1) were determined in human dermal fibroblasts. Epidermal regeneration was assessed utilizing an in vitro wound healing model. FN protein levels were analysed ex vivo after treatment with a formulation containing bakuchiol, retinol or vehicle using suction blister fluid. Skin condition improvement was determined in vivo in a split‐face comparison study after application of bakuchiol or vehicle.

Results

In contrast to retinol, bakuchiol demonstrated high antioxidative efficacy. Levels of PGE2 and MIF were significantly decreased by both bakuchiol and retinol. Bakuchiol but not retinol significantly increased FGF7 protein levels. WST‐1 metabolization levels were significantly augmented by bakuchiol and retinol. Bakuchiol and retinol application led to a significant augmentation of COL1A1, COL7A1 and FN protein levels. Wounds supplemented with bakuchiol but not retinol displayed a significant increase in epidermis regeneration. Clinically, areas treated with a bakuchiol‐containing formulation showed a statistically significant increase in FN protein values after a 4‐week application compared to untreated areas and areas treated with vehicle.

Conclusion

These data provide evidence for the multidirectional efficacy of bakuchiol against cellular hallmarks of skin ageing. Its activity profile shares some common features with retinol but demonstrates several hitherto unknown biopositive effects in our studies, namely stimulation of the critical extracellular matrix component FN, and accelerated epidermal regeneration and wound healing.

Anti-Irritant Strategy against Retinol Based on the Genetic Analysis of Korean Population: A Genetically Guided Top-Down Approach

Retinol, one of the most powerful cosmetic materials for anti-aging supported by a solid scientific background, exhibits a wide range of type and severity of irritation while showing limited user compliance. The lack of understanding of the mechanism of retinol-induced irritation has been the main hurdle in the development of anti-irritation strategies. Here, we identified 30 genetic markers related to the susceptibility to retinol-induced irritation in the Korean population. Based on the genetic analysis, a novel formula against retinol-induced irritation was developed, which mitigated the molecular pathogenesis—as indicated by the genetic markers—of the retinol-induced irritation. In human tests, this formula effectively decreased retinol-induced irritation. Furthermore, a polygenic risk score model for irritation was constructed and validated. Our comprehensive approach for the analysis of retinol-induced irritation will not only aid the development of anti-irritation strategies to ensure higher user compliance but also contribute to improving the current knowledge about the biological effects of retinoids.

Enhanced retinoid response by a combination of the vitamin A ester retinyl propionate with niacinamide and a flavonoid containing Ceratonia siliqua extract in retinoid responsive in vitro models

OBJECTIVES

Retinoids have been used for decades as efficacious topical agents to treat photoaged skin. The purpose of our present research is to evaluate whether the activity of the vitamin A ester retinyl propionate (RP) can be enhanced by niacinamide (Nam) and a flavonoid containing Ceratonia siliqua (CS) fruit extract in retinoid responsive in vitro models.

METHODS

Retinyl propionate was tested alone and in combination with Nam and CS in an RARα reporter cell line for promoter activation and compared to trans-retinoic acid (tRA) activation. These treatments were also tested in keratinocytes for gene expression profiling by qPCR using a panel of 40 retinoid responsive genes.

RESULTS

tRA or RP elicited RARα reporter activation in a dose-dependent manner. The combination of 0.5 μM or 2 μM RP with 10 mM Nam had a 56% and 95% signal increase compared to RP, respectively. The addition of 1% CS to 0.5 μM or 2 μM RP with 10 mM Nam elicited a further increase of 114% and 156%, respectively, over RP and Nam combinations. All retinoids elicited an increase in expression of 40 retinoid sensitive genes over control levels. Of the 40 genes, 27 were enhanced by either 0.1 μM RP or 0.5 μM RP with 10 mM Nam and 1% CS. Nam or CS had very modest activity in both models.

CONCLUSION

The combination of RP with Nam and CS showed a higher retinoid response than RP in two separate retinoid responsive in vitro models. We hypothesize Nam and CS enhances RP activity by modulating metabolism to tRA via increasing NAD⁺ pools and inhibiting reduction of retinal (RAL) back to retinol, respectively. The findings provide evidence that this combination may have enhanced efficacy for treating the appearance of photoaged skin.

The vitamin A ester retinyl propionate has a unique metabolic profile and higher retinoid-related bioactivity over retinol and retinyl palmitate in human skin models

Human skin is exposed daily to environmental stressors, which cause acute damage and inflammation. Over time, this leads to morphological and visual appearance changes associated with premature ageing. Topical vitamin A derivatives such as retinol (ROL), retinyl palmitate (RPalm) and retinyl propionate (RP) have been used to reverse these changes and improve the appearance of skin. This study investigated a stoichiometric comparison of these retinoids using in vitro and ex vivo skin models. Skin biopsies were treated topically to compare skin penetration and metabolism. Treated keratinocytes were evaluated for transcriptomics profiling and hyaluronic acid (HA) synthesis and treated 3D epidermal skin equivalents were stained for epidermal thickness, Ki67 and filaggrin. A retinoic acid receptor-alpha (RARα) reporter cell line was used to compare retinoid activation levels. Results from ex vivo skin found that RP and ROL have higher penetration levels compared with RPalm. RP is metabolized primarily into ROL in the viable epidermis and dermis whereas ROL is esterified into RPalm and metabolized into the inactive retinoid 14-hydroxy-4,14-retro-retinol (14-HRR). RP treatment yielded higher RARα activation and HA synthesis levels than ROL whereas RPalm had a null effect. In keratinocytes, RP and ROL stimulated similar gene expression patterns and pathway theme profiles. In conclusion, RP and ROL show a similar response directionality whereas RPalm response was inconsistent. Additionally, RP has a consistently higher magnitude of response compared with ROL or RPalm.

Enhancement of synthesis of extracellular matrix proteins on retinoic acid loaded electrospun scaffolds

Electrospinning is a renowned technique for the generation of ultrafine, micro- and nanoscale fibres due to its simplicity, versatility and tunability. Owing to its adaptability to a wide selection of materials and scaffold architectures, electrospun meshes have been developed as biocompatible scaffolds and drug delivery systems for tissue engineering. Here, we developed a drug delivery scaffold by electrospinning poly(ε-caprolactone) (PCL) directly blended with a therapeutic agent, retinoic acid (RA), at different concentrations. The release profile, DNA, and elastin analysis of direct and transwell seeded RA-loaded PCL electrospun scaffolds showed desirable controlled release at 15 kV fabrication, with 0.01% RA as the optimum concentration. The selected 0.01% (w/v) RA-loaded PCL meshes were further analysed using five different seeding cultures to investigate and extensively distinguish the effects of RA release with or without cell contact to the PCL electrospun meshes for cell morphology, proliferation and extracellular matrix (ECM) protein secretion of collagen and elastin. Upon exposure to RA-loaded PCL scaffolds, an increase of human dermal fibroblast (HDF) proliferation was observed. In contrast, human mesenchymal stromal cell (hMSC) cultures showed a decrease in cell proliferation. For both hMSC and HDF cultures, exposure to RA-loaded PCL scaffolds provided a significant increase in elastin production per cell. For collagen expression, a slight increase was measured and was outperformed by the 3D geometry stimulation from PCL scaffolds. In contrast to hMSCs, HDFs showed enhanced stress actin fibres in cultures with RA-loaded PCL scaffolds. Both cell types exhibited more vinculin expression when seeded to RA-loaded PCL scaffolds. Hence, electrospun scaffolds releasing RA in a controlled manner were able to regulate cell proliferation, morphology and ECM secretion, and present an attractive approach for optimizing tissue regeneration.

Topical Products for the Aging Face

This article focuses on nonprescription home-use topical treatment technologies for the aging face and is intended to serve as a guide for the core cosmeceutical technologies currently used and to help educate and assist the selection of topical antiaging products by the professional staff and their patients. Antiaging topical treatments for patient home use should be nonirritating, compatible with the patient skin type, effective, and complementary to surgical and minimally invasive office procedures, and aesthetically elegant. New topical antiaging technologies, formulated as monotherapy or as combinations with well-known cosmeceuticals, should present adequate clinical studies to support their selection for use.

Do tetracyclines and erythromycin exert anti-acne effects by inhibition of P450-mediated degradation of retinoic acid?

For decades, retinoic acid (RA) is known as the most potent therapeutic option in the therapy of acne and altered homeostasis of endogenous retinoids has been discussed in the context of acne pathogenesis. Besides retinoids, antibiotics such as tetracyclines or erythromycin are well established in acne pharmacotherapy. Accumulating evidence points towards common molecular pathways being targeted by both RA and anti-acne antibiotics; however, a precise 'common denominator' connecting these chemically diverse anti-acne agents has not yet been identified. Interestingly, tetracyclines are associated with the occurrence of pseudotumor cerebri, a rare neurological side effect otherwise associated with retinoid intoxication or RA exposure. This association at the clinical level suggests an interaction between tetracyclines and endogenous RA signalling. As erythromycin does not cross the blood brain barrier, CNS side effects are not to be expected, yet not precluding a possible local interaction of erythromycin with endogenous RA metabolism in the skin. We hypothesize tetracyclines and erythromycin to locally inhibit endogenous RA metabolism in the skin and thus mimic therapeutic action of RA. This readily testable hypothesis suggests inhibition of endogenous RA metabolism and amplification of endogenous RA signalling as a mechanism underlying the biochemical actions of antibiotics in acne therapy. Elucidation of such interactions may ultimately enhance our understanding of acne therapy and pathogenesis and may yield a sound, scientific basis for hypothesis-driven development of novel therapeutic compounds.

Cosmeceuticals for children: should you care?

PURPOSE OF REVIEW

Cosmeceuticals are substances that exert physiologic changes to the skin for aesthetic purposes and are popular alternatives to invasive cosmetic procedures for antiaging. Cosmeceuticals are being used on children; yet studies of cosmeceuticals in the pediatric population are limited.

RECENT FINDINGS

Cosmeceuticals remain an unrecognized category by the US Food and Drug Administration, and therefore stringent regulatory pathways do not exist to guide research and marketing. To date, no safety and efficacy study exists on cosmeceutical use in pediatric patients. Increasing knowledge of the mechanisms underlying intrinsic and extrinsic skin aging, including reactive oxygen species formation, effects of declining hormones, and ultraviolet radiation, forms the scientific basis for common cosmeceuticals such as retinoids, botanicals such as soy isoflavones, and even moisturizers and sunscreen. Virtually all studies on cosmeceuticals have been performed in women with varying degrees of skin aging. The cosmeceuticals most likely to be used by younger children are moisturizers and sunscreens. As the popularity and availability of other antiaging cosmeceuticals grow, practitioners will encounter more and more beauty-conscious teenagers using these products for preventive rather than restorative purposes.

SUMMARY

Pediatricians should be familiar with the use of common cosmeceuticals used in children, especially the use of broad-spectrum sunscreen. In the future, more children will be exposed to cosmeceuticals and may experience side effects such as contact dermatitis and skin irritation.

A novel anti-ageing mechanism for retinol: induction of dermal elastin synthesis and elastin fibre formation

Dermal elastic fibres are extracellular matrix protein complexes produced by fibroblasts and involved in skin elasticity. Elastin fibres decrease with age as a result of reduced synthesis and increased degradation, resulting in skin sagging and reduced skin elasticity. In this study, we show that retinol (ROL), known to enhance dermal collagen production, is also enhancing elastin fibre formation. ROL induced elastin gene expression and elastin fibre formation in cultured human dermal fibroblasts. Topical treatment of cultured human skin explants with a low dose (0.04%) of ROL increased mRNA and protein levels of tropoelastin and of fibrillin-1, an elastin accessory protein, as documented by QPCR and immunohistochemistry staining. Luna staining confirmed the increased elastin fibre network in the ROL-treated skin explants, as compared with untreated controls. These data demonstrate that ROL exerts its anti-ageing benefits not only via enhanced epidermal proliferation and increased collagen production, but also through an increase in elastin production and assembly.

Physiological Role of Retinyl Palmitate in the Skin

The skin is similar to other organs in how it absorbs, stores, and metabolizes vitamin A. However, because of the anatomical location of skin and the specialized physiological roles it plays, there are ways in which the skin is rather unique. The stratified structure of the epidermis results from the orchestration of retinoid-influenced cellular division and differentiation. Similarly, many of the physiological responses of the skin, such as dermal aging, immune defense, and wound healing, are significantly affected by retinoids. While much is known about the molecular events through which retinoids affect the skin's responses, more remains to be learned. Interest in the effects of retinol, retinyl palmitate, and other retinoids on the skin, fueled in part by the promise of improved dermatologic and cosmetic products, will undoubtedly make the effects of retinoids on skin a subject for continued intense investigation.

Enhanced Delivery of Retinoic Acid to Skin by Cationic Liposomes

We studied the delivery of retinoic acid to skin by using cationic liposomes consisting of double-chained cationic surfactant, phosphatidylcholine (PC) and retinoic acid in excised guinea pig dorsal skin. Egg yolk PC liposomes contaning retinoic acid at a molar ratio of 4 : 1 increased the delivery of retinoic acid about two-fold, compared with its addition as an isopropyl myristate solution. Cationic liposomes containing 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) further enhanced the incorporation dependent on the DOTAP content. Liposomes consisting of DOTAP, egg yolk PC, and retinoic acid at a molar ratio of 2 : 2 : 1 induced a 3.7-fold increase in the skin incorporation compared with the egg yolk PC liposomes without DOTAP. Significant difference was not observed when either dimyristoylphosphatidylcholine (DMPC) or dipalmitoylphosphatidylcholine (DPPC) was used instead of egg yolk PC as well as when dimethyldipalmitylammonium was used instead of DOTAP. These results suggest the potential of the use of the cationic liposomes for the intradermal delivery of lipophilic drugs like retinoic acid.

Ultraviolet light-enhanced visualization of cutaneous signs of carotene and vitamin A dietary deficiency

Dietary deficiencies are multiple and some of them may induce specific changes in the skin biology and structure. Vitamin A deficiency is well identified as a cause of xerosis and follicular keratosis. Skin of the forehead and balding scalp was examined in 3 homeless alcoholic men who suffered from altered liver functions and denutrition including carotene and vitamin A deficiencies. The ultraviolet light-enhanced visualization (ULEV) method was used with a computer-assisted video camera equipped with an internal ultraviolet-emitting unit. Twenty healthy age- and phototype-matched men served as controls. Subclinical alterations of the stratum corneum and tiny follicular horny spikes at the skin surface were disclosed by ULEV. They were consistent with discrete flakiness on the forearms. By contrast, skin of the face and scalp showed follicular horny impactions corresponding to kerosis without any evidence for interfollicular xerosis. The skin condition was markedly improved after a 10-week dietary normalization. It is concluded that the ULEV method reveals some of the mildest and subclinical skin changes secondary to carotene and vitamin A deficiency. It could tentatively be used as a cheap and non-invasive aid in clinical screening programs among populations at risk.

Retinol, at concentrations greater than the physiological limit, induces oxidative stress and apoptosis in human dermal fibroblasts

We have investigated the dose (in the range of microM) and time-dependent effects of four different retinoids (retinol, retinal, retinoic acid and retinol palmitate) on human dermal fibroblasts cultivated in vitro. Retinol and retinal, at a concentration of 20 microM, caused cell damage as evaluated by lactate dehydrogenase activity released into the culture medium. The oxidised glutathione (GSSG)/reduced glutathione (GSH) ratio and malondialdehyde production indicated that 20 microM of retinol provoked oxidative stress in the cultivated human fibroblasts. In the first 8 h after retinol treatment the levels of p53 and Bax proteins as well as caspase 3 activity increased, suggesting apoptotic cell death during the first hours of treatment. If the retinol treatment exceeded 18-24 h we observed necrotic cell death. Vitamin E and coenzyme Q(10) had a protective effect against oxidative stress generated by retinol. Both antioxidant molecules reduced retinol uptake, and in the case of vitamin E the expression of CRABP-II mRNA was induced, providing a plausible explanation for its protective effect.

Clinical trial of bleaching treatment with 10% all-trans retinol gel

BACKGROUND

Although an aggressive use of tretinoin along with hydroquinone enables an efficient treatment of hyperpigmented skin lesions, irritant dermatitis remains to be solved.

OBJECTIVE

To evaluate the efficiency and adverse effects of 10% all-trans retinol (ROL) gel for improvement of skin hyperpigmentation.

METHODS

Ten-percent ROL gel was used instead of 0.1% tretinoin gel in our two-phased bleaching protocol (bleaching and healing phases); 5% hydroquinone and 7% lactic acid ointment were used along with ROL gel in the bleaching phase (2 to 6 weeks). Five-percent hydroquinone and 7% ascorbic acid ointment were used alone during the healing phase (4 to 6 weeks). Twenty-one Japanese patients with hyperpigmented lesions on the face were enrolled in this study, and 18 patients who were followed for more than 10 weeks were analyzed.

RESULTS

Improvement of pigmentation was seen in 16 of 18 patients after an average treatment period of 11.3 weeks, and in 6 patients, pigmentation was almost eliminated after treatment. Erythema and scaling were seen, however, during the bleaching phase as well as the bleaching treatment with tretinoin gel.

CONCLUSION

ROL can improve skin hyperpigmentation to a similar extent to tretinoin when used at high concentration, whereas it induces irritant dermatitis as well.

Influence of ion pairing on topical delivery of retinoic acid from microemulsions

The purpose of the present study was to determinate the significance of ion pairing on the topical permeation of retinoic acid (R.A) using microemulsions as delivery vehicles. Phenylalanine methyl ester, phenylalanine ethylester, histidine methyl ester, tryptophan methyl ester and valine methyl ester were used as counter ions. Results of diffusion studies through polydimethylsiloxane membrane (PDMS) indicate that retinoic acid permeation from ethanol-pH 6.4 buffer mixture significantly increased in the presence of counter ions. A linear relationship was found between apparent partition coefficients and permeation coefficients. The highest values were with valine methyl ester and phenylalanine ethyl ester. In order to develop alternative formulations for topical administration of R.A, microemulsions were evaluated as delivery vehicles. Oil-in-water (O/W) and water-in-oil (W/O) microemulsion formulations were prepared using water, isopropyl myristate, lecithin, caprylyl-capryl glucoside and ethanol or 1,2 hexanediol. Experiments with PDMS membranes showed decreasing permeabilities of R.A from microemulsions in the presence of counter ions. This was related to the increased lipophilicity and different vehicle membrane affinity of the ion pairs The ability of the systems to deliver R.A through the skin was evaluated in vitro using pig-skin. R.A permeabilities were much lower with microemulsions than with solution, while a large increase in R.A skin deposition was observed only from O/W microemulsions in the presence of counter ions. The depth of skin accumulation was below 100 microm after 24 h application. The results suggest that O/W microemulsions containing a counter ion can be used to optimise drug targeting without a concomitant increase in systemic absorption.

A randomized, placebo-controlled trial of topical retinol in the treatment of cellulite

BACKGROUND

Cellulite occurs to varying degrees on the thighs and buttocks of many otherwise healthy women. Among the many purported treatments for cellulite, only a handful have been tested in clinical trials.

OBJECTIVE

The aim of this study was to critically explore the reputed effect of topical retinol in the treatment of cellulite.

MATERIALS AND METHODS

The study compared the effect of topical retinol to a placebo formulation in a left-right randomized trial in order to eliminate the massage-effect. The study was conducted in 15 women aged from 26 to 44 years who had requested liposuction to improve mild to moderate cellulite.

RESULTS

After 6-months of treatment, skin elasticity was increased by 10.7% while viscosity was decreased by 15.8% at the retinol-treated site. Such an effect on the tensile properties of skin was more prominent where the mattress phenomenon was the only evidence of cellulite. The lumpy-bumpy appearance of the skin showed either little response or was not responsive to the treatment. Although gross microanatomical differences were not disclosed between the comparative sites at completion of the study, evidence for a shift in the phenotype of connective tissue cells was obtained. The main retinol-related change consisted of a 2- to 5-fold increase in the number of factor XIIIa+ dendrocytes both in the dermis and fibrous strands of the hypodermis.

CONCLUSIONS

We hypothesize that the functional and phenotypic changes seen in this study were linked and represent the result of a direct or indirect modulating effect of retinol on cellulite. Such features ultimately improve the resting tensions inside the skin which should in turn smooth the skin surface.

High-performance liquid chromatography of non-polar retinoid isomers

Normal-phase high-performance liquid chromatograms of retinal, retinol and retinyl palmitate isomers using n-heptane-tert.-butyl methyl ether as mobile phase are presented. Methods for the synthesis of various isomers of these retinoids are described. This enables one to produce standard chromatograms and to select various isomers for cochromatography and the identification of the various peaks under study. Assignment of the peaks is based on chromatograms published previously in this journal. For the main isomers it is possible to get baseline separation of the commonly occurring isomeric forms in a reasonably short analysis time.

Expression and localization of human alcohol and aldehyde dehydrogenase enzymes in skin

Alcohol dehydrogenase (ADH; EC 1.1.1.1) and aldehyde dehydrogenase (ALDH; EC 1.2.1.3.) are important enzymes involved in the biotransformation of both alcohols and aldehydes. Today, six classes of ADH and twelve classes of ALDH have been defined in mammals. Here we report the detection and localisation of three classes of ADH and two classes of ALDH in human skin, using Western blot analysis and immunohistochemistry with class-specific antisera. Western blot analysis of human skin cytosol revealed that class I-III ADH and class 1 and class 3 ALDH enzymes are expressed, constitutively, in three different anatomical regions of human skin (foreskin, breast, abdomen). Densitometric analysis of the immunoreactive bands revealed differential constitutive expression of these enzymes in foreskin, breast, and abdomen skin. Immunohistochemistry showed the presence of class I ADH and class III ADH enzymes, predominantly in the epidermis with some localised expression in the dermal appendages of human skin. In comparison, staining for class II ADH was more faint in the epidermis with very little dermal expression. Class 1 ALDH and class 3 ALDH were predominantly localised to the epidermis with minimal, highly localised dermal appendageal expression. These cutaneous ADH and ALDH enzymes may play significant roles in the metabolism of endogenous or xenobiotic alcohols and aldehydes.

Dermal fibroblasts actively metabolize retinoic acid but not retinol

The accessibility of plasma retinol and retinoic acid to the epidermis may be influenced by the number and metabolic capacity of fibroblasts in papillary dermis. The metabolism of retinol-binding protein-bound all-trans-retinol, and albumin-bound all-trans-retinoic acid, by fibroblasts cultured on plastic dishes or in type I collagen gels, was examined. There were no significant differences in the metabolism of either retinoid by fibroblasts as a function of culture condition. There were large differences between retinoids, however. Retinoic acid was rapidly taken up and metabolized to unidentified polar metabolites that were released to the medium. Metabolic capacity was not saturated up to a medium retinoic acid concentration of 1 microM, and was induced further by prior exposure to retinoic acid. In contrast, retinol, although readily taken up, was not metabolized, i.e., neither retinoic acid nor retinyl ester was formed. By immunohistochemistry, the average number of fibroblasts in a 100 microm thickness of papillary dermis was estimated to be 1 x 10(6) cells per cm2. Utilizing this value, the capacity of dermal fibroblasts to metabolize retinoic acid based on fibroblast abundance in the dermis was calculated. The results suggest that fibroblasts could limit delivery of plasma retinoic acid but not retinol to the epidermis on the basis of their metabolic capacity and abundance in the dermis.