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    Celastrol Self-Stabilized Nanoparticles for Effective Treatment of Melanoma. Li Jinran,Jia Yuxi,Zhang Peng,Yang Huailin,Cong Xianling,An Lin,Xiao Chunsheng International journal of nanomedicine Background:Celastrol (CEL), a triterpene extracted from the Chinese herb , has been reported to have profound anticancer activities. However, poor water solubility and high side toxicities have severely restricted the clinical applications of CEL. Purpose:We proposed a facile "in situ drug conjugation-induced self-assembly" strategy to prepare CEL-loaded nanoparticles (CEL-NPs) that exhibited enhanced antitumor activity against melanoma. Methods:First, the CEL was chemically conjugated onto a methoxyl poly(ethylene glycol)--poly(L-lysine) (mPEG-PLL) backbone, resulting in the conversion of the double hydrophilic mPEG-PLL polymer into an amphiphilic polymer prodrug, mPEG-PLL/CEL. The obtained mPEG-PLL/CEL could self-assemble into stable micelles in aqueous solution due to the hydrophobic association of CEL moieties in the side chains and the possible electrostatic interaction between the carboxyl group in CEL and the residue amine group in the PLL segment. Thus, the obtained mPEG-PLL/CEL nanoparticles were named CEL self-stabilized nanoparticles (CEL-NPs), which were then characterized by dynamic light scattering and transmission electron microscopy. Furthermore, the antitumor effects of the CEL-NPs were investigated by an MTT assay in vitro and in a B16F10 tumor-bearing mice model. Results:The CEL-NPs exhibited sustained drug release behavior and were effectively endocytosed by B16F10 cells. Furthermore, the in vivo antitumor evaluation demonstrated that the CEL-NPs had remarkably higher tumor growth inhibition rates and lower systemic side effects than free CEL. Conclusion:In summary, our present work not only demonstrates the generation of stable CEL-loaded nanoparticles for the efficient treatment of melanoma but also describes a general way to prepare drug self-stabilized nanomedicine for anticancer therapy. 10.2147/IJN.S232603
    A study of inter-individual variability in the Phase II metabolism of xenobiotics in human skin. Spriggs Sandrine,Cubberley Richard,Loadman Paul,Sheffield David,Wierzbicki Antonia Toxicology letters Understanding skin metabolism is key to improve in vitro to in vivo extrapolations used to inform risk assessments of topically applied products. However, published literature is scarce and usually covers a limited and non-representative number of donors. We developed a protocol to handle and store ex vivo skin samples post-surgery and prepare skin S9 fractions to measure the metabolic activity of Phase II enzymes. Preincubation of an excess of cofactors at 37 °C for fifteen minutes in the S9 before introduction of the testing probe, greatly increased the stability of the enzymes. Using this standardised assay, the rates of sulphation (SULT) and glucuronidation (UGT) of 7-hydroxycoumarin, methylation (COMT) of dopamine and N-acetylation (NAT) of procainamide were measured in the ng/mg protein/h (converted to ng/cm/h) range in eighty-seven individuals. Glutathione conjugation (GST) of 1-chloro-2,4-dinitrobenzene was assessed in a smaller pool of fifty donors; the metabolic rate was much faster and measured over six minutes using a different methodology to express rates in μg/mg protein/min (converted to μg/cm/min). A comprehensive statistical analysis of these results was carried out, separating donors by age, gender and metabolic rate measured. 10.1016/j.toxlet.2018.04.011
    The Ussing Chamber Assay to Study Drug Metabolism and Transport in the Human Intestine. Kisser Beatrice,Mangelsen Eva,Wingolf Caroline,Partecke Lars Ivo,Heidecke Claus-Dieter,Tannergren Christer,Oswald Stefan,Keiser Markus Current protocols in pharmacology The Ussing chamber is an old but still powerful technique originally designed to study the vectorial transport of ions through frog skin. This technique is also used to investigate the transport of chemical agents through the intestinal barrier as well as drug metabolism in enterocytes, both of which are key determinants for the bioavailability of orally administered drugs. More contemporary model systems, such as Caco-2 cell monolayers or stably transfected cells, are more limited in their use compared to the Ussing chamber because of differences in expression rates of transporter proteins and/or metabolizing enzymes. While there are limitations to the Ussing chamber assay, the use of human intestinal tissue remains the best laboratory test for characterizing the transport and metabolism of compounds following oral administration. Detailed in this unit is a step-by-step protocol for preparing human intestinal tissue, for designing Ussing chamber experiments, and for analyzing and interpreting the findings. © 2017 by John Wiley & Sons, Inc. 10.1002/cpph.22
    Drug metabolism in the skin. Baron J M,Merk H F Current opinion in allergy and clinical immunology The skin performs a wide range of active metabolic functions including xenobiotic metabolism involving metabolizing enzymes specific to the skin. In this review we focus on the role of drug metabolism: (i) in allergic reactions to substances of low molecular weight; (ii) in cutaneous vitamin A and D3 metabolism and its modulation; (iii) in the interaction of transport and metabolic enzymes in skin cells; and (iv) on novel tools for the measurement of drug metabolism in various compartments of the human skin. 10.1097/01.all.0000011028.08297.b3
    [The effect of foreign-substance-metabolizing enzymes on skin diseases]. Goerz G,Merk H Der Hautarzt; Zeitschrift fur Dermatologie, Venerologie, und verwandte Gebiete Multiple drug-metabolizing enzymes are located in the skin of animals and humans: cytochrome P-450, epoxide hydrases, transferases and reductases. The distribution of cytochrome P-450 in the skin is not homogeneous; rather, it is more active in the basal epidermis, keratinocytes of the hair follicle, and sebaceous cells. The activity of drug-metabolizing enzyme can be induced, but it can also be inhibited by multiple endogenous and exogenous compounds. These enzymes detoxify many xenobiotics, but if the balance is disturbed there is the risk that xenobiotics will be activated to highly toxic compounds, which are even involved in the pathogenesis of skin cancer. Recent results indicate that cytochrome P-450 isoenzymes are also involved in the pathogenesis of psoriasis and drug-induced skin diseases.
    Drug skin metabolites and allergic drug reactions. Merk Hans F Current opinion in allergy and clinical immunology PURPOSE OF REVIEW:Presentation of recent studies about xenobiotica metabolism of the skin and its impact on drug-allergic reactions. RECENT FINDINGS:The skin possesses not only multiple cytochrome P450 isoenzymes but also influx and efflux transporter proteins. The pattern of cytochrome P450 isoenzymes in the skin differs from the pattern in the liver. Studies on the role of this metabolism in drug-induced hypersensitivity have mainly focused on sulphonamides, anticonvulsants, diclofenac and nevirapine. Studies with the contact sensitizer carvoxime provided evidence for the decisive role of xenobiotica metabolism in antigen-presenting cells. SUMMARY:The skin is a major target organ for allergic drug reactions that may be explained by its different barrier functions including immune system and the armamentarium of xenobiotica-metabolizing enzymes. 10.1097/ACI.0b013e32832dd13c
    Xenobiotic metabolism capacities of human skin in comparison with a 3D epidermis model and keratinocyte-based cell culture as in vitro alternatives for chemical testing: activating enzymes (Phase I). Götz Christine,Pfeiffer Roland,Tigges Julia,Blatz Veronika,Jäckh Christine,Freytag Eva-Maria,Fabian Eric,Landsiedel Robert,Merk Hans F,Krutmann Jean,Edwards Robert J,Pease Camilla,Goebel Carsten,Hewitt Nicola,Fritsche Ellen Experimental dermatology Skin is important for the absorption and metabolism of exposed chemicals such as cosmetics or pharmaceuticals. The Seventh Amendment to the EU Cosmetics Directive prohibits the use of animals for cosmetic testing for certain endpoints, such as genotoxicity; therefore, there is an urgent need to understand the xenobiotic metabolizing capacities of human skin and to compare these activities with reconstructed 3D skin models developed to replace animal testing. We have measured Phase I enzyme activities of cytochrome P450 (CYP) and cyclooxygenase (COX) in ex vivo human skin, the 3D skin model EpiDerm™ (EPI-200), immortalized keratinocyte-based cell lines and primary normal human epidermal keratinocytes. Our data demonstrate that basal CYP enzyme activities are very low in whole human skin and EPI-200 as well as keratinocytes. In addition, activities in monolayer cells differed from organotypic tissues after induction. COX activity was similar in skin, EPI-200 and NHEK cells, but was significantly lower in immortalized keratinocytes. Hence, the 3D model EPI-200 might represent a more suitable model for dermatotoxicological studies. Altogether, these data help to better understand skin metabolism and expand the knowledge of in vitro alternatives used for dermatotoxicity testing. 10.1111/j.1600-0625.2012.01486.x
    Regulation of cutaneous drug-metabolizing enzymes and cytoprotective gene expression by topical drugs in human skin in vivo. Smith G,Ibbotson S H,Comrie M M,Dawe R S,Bryden A,Ferguson J,Wolf C R The British journal of dermatology BACKGROUND:Individuality in the expression and regulation of hepatic drug-metabolizing enzymes (DMEs) and cytoprotective (CP) genes is an important determinant of treatment response. There is increasing evidence that many DMEs and CP genes are also expressed in human skin. Responses to topical drugs used to treat common skin diseases, such as psoriasis, are unpredictable and may potentially be rationalized, at least in part, by interindividual differences in cutaneous DME and CP gene expression. OBJECTIVES:We investigated whether three topical drugs [coal tar, all-trans retinoic acid (atRA) and clobetasol 17-propionate] used in routine clinical practice modulated the expression of a variety of DME and CP genes [cytochrome P450s, glutathione S-transferases (GSTs) and drug transporters] in healthy human skin in vivo. METHODS:Healthy adult volunteers (n = 30) were invited to participate in the study. Each subject was randomly allocated to receive two of the three study chemicals and one control site application. Crude coal tar (n = 13), atRA (n = 14) or clobetasol 17-propionate (n = 10) was applied under occlusion to photoprotected buttock skin for 96 h. A vehicle control (white soft paraffin) was also applied under the same conditions at an adjacent site in all subjects. Full-thickness punch biopsies (4-mm diameter) were then taken from treated and control sites. Total RNA was extracted and reverse transcribed into cDNA, which was used as a template in subsequent real-time polymerase chain reaction analysis, where fluorescent output was directly proportional to input cDNA concentration. Triplicate measurements of skin mRNA expression were made from each sample, and the arithmetic mean values taken. After logarithmic transformation, the paired t-test was used to compare values between treated and control skin. RESULTS:Cytochrome P450s CYP1A1, CYP1A2, CYP1B1, CYP2C18, quinone reductase (NQO-1), GSTP1, gamma-glutamyl cysteine synthetase (gamma-GCS), glutathione peroxidase-1 (GPx-1), cyclooxygenase-2 (COX-2) and haem oxygenase-1 (HO-1) were induced by coal tar; CYP26, NADPH P450 reductase (CPR), GSTP1 and HO-1 by atRA; and CYP3A5 by clobetasol 17-propionate. In contrast, CYP1A1 and CYP1A2 expression was suppressed by atRA, and gamma-GCS and MRP1 by clobetasol 17-propionate. Marked interindividual variation in gene regulation by topical drugs was seen for the majority of genes examined. CONCLUSIONS:These data demonstrate that topical drugs can modulate DME gene expression in human skin in vivo and indicate that variation in the expression and regulation of these genes may be a determinant of individuality in response to topical therapies for common skin diseases. 10.1111/j.1365-2133.2006.07317.x
    Xenobiotic metabolizing enzyme activities in cells used for testing skin sensitization in vitro. Fabian E,Vogel D,Blatz V,Ramirez T,Kolle S,Eltze T,van Ravenzwaay B,Oesch F,Landsiedel R Archives of toxicology For ethical and regulatory reasons, in vitro tests for scoring potential toxicities of cosmetics are essential. A test strategy for investigating potential skin sensitization using two human keratinocytic and two human dendritic cell lines has been developed (Mehling et al. Arch Toxicol 86:1273–1295, 2012). Since prohaptens may be metabolically activated in the skin, information on xenobiotic metabolizing enzyme (XME) activities in these cell lines is of high interest. In this study, XME activity assays, monitoring metabolite or cofactor, showed the following: all three passages of keratinocytic (KeratinoSens® and LuSens) and dendritic (U937 und THP-1) cells displayed N-acetyltransferase 1 (NAT1) activities (about 6–60 nmol/min/mg S9-protein for acetylation of para-aminobenzoic acid). This is relevant since reactive species of many cosmetics are metabolically controlled by cutaneous NAT1. Esterase activities of about 1–4 nmol fluorescein diacetate/min/mg S9-protein were observed in all passages of investigated keratinocytic and about 1 nmol fluorescein diacetate/min/mg S9-protein in dendritic cell lines. This is also of practical relevance since many esters and amides are detoxified and others activated by cutaneous esterases. In both keratinocytic cell lines, activities of aldehyde dehydrogenase (ALDH) were observed (5–17 nmol product/min/mg cytosolic protein). ALDH is relevant for the detoxication of reactive aldehydes. Activities of several other XME were below detection, namely the investigated cytochrome P450-dependent alkylresorufin O-dealkylases 7-ethylresorufin O-deethylase, 7-benzylresorufin O-debenzylase and 7-pentylresorufin O-depentylase (while NADPH cytochrome c reductase activities were much above the limit of quantification), the flavin-containing monooxygenase, the alcohol dehydrogenase as well as the UDP glucuronosyl transferase activities. 10.1007/s00204-013-1090-9
    Biotransformation of drugs in human skin. Svensson Craig K Drug metabolism and disposition: the biological fate of chemicals Although it is the largest organ of the human body, skin is often not considered in discussions of drug metabolism. However, there is growing evidence that most common drug-metabolizing enzymes are expressed in the skin. Evidence for expression of cytochromes P450, flavin monooxygenases, glutathione-S-transferases, N-acetyltransferases, and sulfotransferases in human skin and skin cells are presented. Additional discussion is focused on the evidence of actual metabolism of drugs. Finally, the potential clinical implications of metabolism within the skin are discussed briefly. 10.1124/dmd.108.024794
    Highlight report: xenobiotic-metabolizing enzymes in skin models. Golka Klaus Archives of toxicology 10.1007/s00204-015-1657-8
    Xenobiotic metabolizing enzymes in human skin and SkinEthic reconstructed human skin models. Eilstein Joan,Léreaux Guillaume,Arbey Eric,Daronnat Edwige,Wilkinson Simon,Duché Daniel Experimental dermatology Skin metabolism is becoming a major consideration in the development of new cosmetic ingredients, skin being the first organ exposed to them. In order to replace limited samples of Excised human skin (EHS), in vitro engineered human skins have been developed. 3D models are daily used to develop and evaluate new cosmetic ingredients and have to be characterized and compared with EHS in terms of metabolic capabilities. This work presents the determination of apparent catalytic parameters (apparent Vmax, Km and the ratio Vmax/Km) in 3D models compared with EHS for cytochrome P450 dependent monooxygenase isoforms involved in drug metabolism, esterases, alcohol dehydrogenases, aldehyde dehydrogenases, peroxidases, glutathione S-transferases, N-acetyl transferases, uridinyl diphosphate glucuronyl transferases and sulfotransferases. Results show that all these enzymes involved in the metabolism of xenobiotics are expressed and functional in the EHS and 3D models. Also, the Vmax/Km ratios (estimating the intrinsic metabolic clearances) show that the metabolic abilities are the most often comparable between the skin models and EHS. These results indicate that the 3D models can substitute themselves for EHS to select cosmetic ingredients on the basis of their metabolism, efficacy or/and safety. 10.1111/exd.12694
    Xenobiotic-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models. Oesch F,Fabian E,Guth K,Landsiedel R Archives of toxicology The exposure of the skin to medical drugs, skin care products, cosmetics, and other chemicals renders information on xenobiotic-metabolizing enzymes (XME) in the skin highly interesting. Since the use of freshly excised human skin for experimental investigations meets with ethical and practical limitations, information on XME in models comes in the focus including non-human mammalian species and in vitro skin models. This review attempts to summarize the information available in the open scientific literature on XME in the skin of human, rat, mouse, guinea pig, and pig as well as human primary skin cells, human cell lines, and reconstructed human skin models. The most salient outcome is that much more research on cutaneous XME is needed for solid metabolism-dependent efficacy and safety predictions, and the cutaneous metabolism comparisons have to be viewed with caution. Keeping this fully in mind at least with respect to some cutaneous XME, some models may tentatively be considered to approximate reasonable closeness to human skin. For dermal absorption and for skin irritation among many contributing XME, esterase activity is of special importance, which in pig skin, some human cell lines, and reconstructed skin models appears reasonably close to human skin. With respect to genotoxicity and sensitization, activating XME are not yet judgeable, but reactive metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the "Overview and Conclusions" section in the end of this review. 10.1007/s00204-014-1382-8
    Characterization of xenobiotic metabolizing enzymes of a reconstructed human epidermal model from adult hair follicles. Bacqueville Daniel,Jacques Carine,Duprat Laure,Jamin Emilien L,Guiraud Beatrice,Perdu Elisabeth,Bessou-Touya Sandrine,Zalko Daniel,Duplan Hélène Toxicology and applied pharmacology In this study, a comprehensive characterization of xenobiotic metabolizing enzymes (XMEs) based on gene expression and enzyme functionality was made in a reconstructed skin epidermal model derived from the outer root sheath (ORS) of hair follicles (ORS-RHE). The ORS-RHE model XME gene profile was consistent with native human skin. Cytochromes P450 (CYPs) consistently reported to be detected in native human skin were also present at the gene level in the ORS-RHE model. The highest Phase I XME gene expression levels were observed for alcohol/aldehyde dehydrogenases and (carboxyl) esterases. The model was responsive to the CYP inducers, 3-methylcholanthrene (3-MC) and β-naphthoflavone (βNF) after topical and systemic applications, evident at the gene and enzyme activity level. Phase II XME levels were generally higher than those of Phase I XMEs, the highest levels were GSTs and transferases, including NAT1. The presence of functional CYPs, UGTs and SULTs was confirmed by incubating the models with 7-ethoxycoumarin, testosterone, benzo(a)pyrene and 3-MC, all of which were rapidly metabolized within 24h after topical application. The extent of metabolism was dependent on saturable and non-saturable metabolism by the XMEs and on the residence time within the model. In conclusion, the ORS-RHE model expresses a number of Phase I and II XMEs, some of which may be induced by AhR ligands. Functional XME activities were also demonstrated using systemic or topical application routes, supporting their use in cutaneous metabolism studies. Such a reproducible model will be of interest when evaluating the cutaneous metabolism and potential toxicity of innovative dermo-cosmetic ingredients. 10.1016/j.taap.2017.05.040
    Xenobiotica-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models. Oesch F,Fabian E,Landsiedel Robert Archives of toxicology Studies on the metabolic fate of medical drugs, skin care products, cosmetics and other chemicals intentionally or accidently applied to the human skin have become increasingly important in order to ascertain pharmacological effectiveness and to avoid toxicities. The use of freshly excised human skin for experimental investigations meets with ethical and practical limitations. Hence information on xenobiotic-metabolizing enzymes (XME) in the experimental systems available for pertinent studies compared with native human skin has become crucial. This review collects available information of which-taken with great caution because of the still very limited data-the most salient points are: in the skin of all animal species and skin-derived in vitro systems considered in this review cytochrome P450 (CYP)-dependent monooxygenase activities (largely responsible for initiating xenobiotica metabolism in the organ which provides most of the xenobiotica metabolism of the mammalian organism, the liver) are very low to undetectable. Quite likely other oxidative enzymes [e.g. flavin monooxygenase, COX (cooxidation by prostaglandin synthase)] will turn out to be much more important for the oxidative xenobiotic metabolism in the skin. Moreover, conjugating enzyme activities such as glutathione transferases and glucuronosyltransferases are much higher than the oxidative CYP activities. Since these conjugating enzymes are predominantly detoxifying, the skin appears to be predominantly protected against CYP-generated reactive metabolites. The following recommendations for the use of experimental animal species or human skin in vitro models may tentatively be derived from the information available to date: for dermal absorption and for skin irritation esterase activity is of special importance which in pig skin, some human cell lines and reconstructed skin models appears reasonably close to native human skin. With respect to genotoxicity and sensitization reactive-metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the Conclusions section in the end of this review. 10.1007/s00204-018-2232-x
    Nitric Oxide-Releasing Biomaterials for Biomedical Applications. Zhou Xin,Zhang Jimin,Feng Guowei,Shen Jie,Kong Deling,Zhao Qiang Current medicinal chemistry Nitric oxide (NO), as an essential signaling molecule, participates in various physiological processes such as cardiovascular homeostasis, neuronal transmission, immunomodulation, and tumor growth. The multiple role of NO in physiology and pathophysiology has triggered a massive interest in the strategies of delivering exogenous NO for biomedical applications. Hence, different kinds of NO prodrugs have been developed up to date, including diazeniumdiolates, S-nitrosothiol, metal-nitrosyl, nitrobenzene, and so on. However, the clinical application of these low molecular weight NO donors has been restricted due to the problems of burst release, low payloads, and untargeted delivery. The delivery of NO by biomaterialbased carrier offers a beneficial strategy to realize the controlled and sustained delivery of NO to the targeted tissues or organs. In detail, NO-donor prodrugs have been attached and loaded to diverse biomaterials to fabricate nanoparticles, hydrogels, and coating platforms by means of physical, chemical, or supramolecular techniques. These NO-releasing biomaterials hold promise for a number of biomedical applications ranging from therapy of the ischemic disease and several types of cancer to cardiovascular devices and wound dressing. First, surface coating with NO-releasing biomaterials could mimic the physiological function of vascular endothelium, therefore promoting vascularization and improving the patency of cardiovascular implants. Next, because NO also mediates many important processes that take place after cutaneous injury, NO-releasing biomaterials could serve as ideal wound dressing to accelerate tissue regeneration. Finally, biomaterials enable localized delivery of high dose of NO to tumors in a sustained manner, thus generating potent tumoricidal effect. In this review, we will summarize the progress of different NO-releasing biomaterials, and highlight their biomedical applications with a hope to inspire new perspectives in the area of biomaterial-based NO-delivery systems.
    Skin Metabolism: Relevance of Skin Enzymes for Rational Drug Design. Pyo Sung Min,Maibach Howard I Skin pharmacology and physiology Transdermal therapeutic systems (TTS) have numerous pharmacological benefits. Drug release, for example, is independent of whether a patient is in a fed or a fasted state, and lower doses can be given as gastrointestinal and hepatic first-pass metabolism is avoided. In addition, inter- and intrapatient variability is minimized as the release of the drug is mainly controlled by the system. This makes TTS interesting as alternative systems to the most common dosage form of oral tablets. The difficulty with the dermal administration route is transporting the drug through the skin, since the skin is an efficient barrier against foreign bodies. Various strategies have been reported in the literature of how drug penetration can be improved. Most of them, however, focus on overcoming the stratum corneum as the first (mechanical) skin barrier. However, penetration is much more complex, and the skin's barrier function does not only depend on the stratum corneum; what has been underestimated is the second (biological) skin barrier formed of enzymes. Compared to the stratum corneum, very little is known about these enzymes, e.g., which enzymes are present in the skin and where exactly they are localized. Hence, very few strategies can be found for how to bypass or even use the skin enzyme barrier for TTS development. This review article provides an overview of the skin enzymes considered to be relevant for the biotransformation of dermally applied drugs. Also, we discuss the use of dermal prodrugs and soft drugs and give the stereoselectivity of skin metabolism careful consideration. Finally, we provide suggestions on how to make use of the current knowledge about skin enzymes for rational TTS design. 10.1159/000501732
    Site-specific drug delivery in the skin for the localized treatment of skin diseases. Chen Yang,Feng Xun,Meng Shengnan Expert opinion on drug delivery : Due to the well-organized structure and barrier function of the skin, it is generally difficult for drugs applied directly on the surface of skin to reach their expected site of action. Accordingly, site-specific drug delivery in the skin has been increasingly explored to facilitate the treatment of skin diseases and reduce the systemic toxicity. : An overview of the generally used sites for drug delivery in the skin is herein presented. Different strategies including particle-based carriers, physical technologies, and chemical approaches are discussed with regards to their potential application in site-specific drug delivery in the skin. : Particle-based carriers are of particular significance for the enhancement of drug delivery in the skin. Although no recommendation can be made regarding which type of carriers can provide better skin penetration, the lipid-based colloidal systems appear to be favored due to their compatibility. In addition, the physical technologies provide unique advantages in delivering hydrophilic macromolecules for the skin immunization. As a new class of permeation enhancers, skin penetrating peptides are gaining more attention in drug delivery to skin cells. For the design of robust site-specific drug delivery systems, the impacts of diseased state and drug properties should not be disregarded. 10.1080/17425247.2019.1645119
    Prodrug strategy for enhancing drug delivery via skin. Fang Jia-You,Leu Yann-Lii Current drug discovery technologies Skin as a route for drug delivery has been extensively investigated. However, because of the predominant barrier function of stratum corneum in skin, the clinical application is limited. One strategy to solve this problem of drug permeation via skin is the use of prodrugs. Prodrugs are inactive compounds which are metabolized either chemically or enzymatically in a controlled or predictable manner to its parent active drug. Prodrugs can enhance dermal/transdermal drug delivery via different mechanisms, including increased skin partitioning, increased aqueous solubility, and reduced crystallization, etc. Besides the prodrug itself, the optimization of vehicle is important as well. The prodrug partitioning between skin and vehicle as well as prodrug-vehicle interaction may influence the enhancing efficacy on skin permeation. This review explores the synthesis and enhancing mechanisms of prodrugs for topical drug delivery. The prodrugs categorized by the therapeutic use of the parent drugs, including anticancer drugs, analgesics, anti-inflammatory drugs and vitamins, are systemically introduced in this review. 10.2174/157016306780136772
    Innovations in transdermal drug delivery: formulations and techniques. Tiwary Ashok K,Sapra Bharti,Jain Subheet Recent patents on drug delivery & formulation The transdermal route of drug delivery has attracted researchers due to many biomedical advantages associated with it. However, excellent impervious nature of skin is the greatest challenge that has to be overcome for successfully delivering drug molecules to the systemic circulation by this route. Various formulation approaches used to systemically deliver drug molecules include use of prodrugs/lipophilic analogs, permeation enhancers, sub saturated systems and entrapment into vesicular systems. Further, the adhesive mixture, physical system of the delivery system and release liner influence drug release and its permeation across the skin. In addition, great strides in designing delivery systems for maximizing percutaneous drug permeation without comprising with ease of therapy cannot be neglected in improving functionality of transdermal drug delivery systems. This article deals with the innovations pertaining to formulation and techniques as described in recent patents. 10.2174/187221107779814087
    [Skin permeation and transdermal delivery systems of drugs: history to overcome barrier function in the stratum corneum]. Sugino Masahiro,Todo Hiroaki,Sugibayashi Kenji Yakugaku zasshi : Journal of the Pharmaceutical Society of Japan Transdermal Drug Delivery Systems (TDDS), where active drugs must be absorbed into the systemic circulation after penetrating the skin barrier, were first launched in 1979, and about 10 TDDS containing different kinds of drugs were developed during the initial decade. Interestingly, a developmental rush has come again in the present century. Various penetration-enhancing approaches to improve drug permeation of the skin (stratum corneum) have been attempted. These approaches are of two types: chemical and physical. Examples of the chemical approach are enhancers such as alcohol, monoterpenes and fatty acid esters, as well as chemical modification of prodrugs. In contrast, physical approaches include the use of electrical-, thermal- and mechanical-energy, as well as microneedles, needle-free injectors or electroporation to completely or partially evade the barrier function in the stratum corneum. The chemical approaches are mainly effective in increasing the skin permeation of low-molecular chemicals, whereas physical means are effective for these chemicals but also high-molecules like peptides, proteins and nucleotides (DNA or RNA). Marked development has been observed in these physical means in the past decade. In addition, recent developments in tissue engineering technologies enables the use of cultured skin containing keratinocytes and fibroblasts as a TDDS. An effective "cell delivery system" may be a reality in the near future. This paper will look back on the 30-year history of TDDS and evaluate the feasibility of a new generation of these systems.
    Prodrug strategies for enhancing the percutaneous absorption of drugs. N'Da David D Molecules (Basel, Switzerland) The transdermal application of drugs has attracted increasing interest over the last decade or so, due to the advantages it offers, compared to other delivery methods. The development of an efficient means of transdermal delivery can increase drug concentrations, while reducing their systemic distribution, thereby avoiding certain limitations of oral administration. The efficient barrier function of the skin, however, limits the use of most drugs as transdermal agents. This limitation has led to the development of various strategies to enhance drug-skin permeation, including the use of penetration enhancers. This method unfortunately has certain proven disadvantages, such as the increased absorption of unwanted components, besides the drug, which may induce skin damage and irritancy. The prodrug approach to increase the skin's permeability to drugs represents a very promising alternative to penetration enhancers. The concept involves the chemical modification of a drug into a bioreversible entity that changes both its pharmaceutical and pharmacokinetic characteristics to enhance its delivery through the skin. In this review; we report on the in vitro attempts and successes over the last decade by using the prodrug strategy for the percutaneous delivery of pharmacological molecules. 10.3390/molecules191220780
    Percutaneous penetration of anticancer agents: Past, present and future. Ita Kevin Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie Cancer occurs as a result of alterations in oncogenes, tumor-suppressor genes, and microRNA genes. Over the past few decades, efforts have been made to understand the dominant oncogenes and tumor suppressor genes whose respective activation/upregulation or loss of function serve to impart aberrant properties on normal cells. Cancer continues to be a source of public health concern due to widespread prevalence, morbidity and mortality. The most common types include but are not limited to lung, prostate, colorectal, breast, ovarian and skin cancers. In 2012, there were more than 8 million deaths worldwide related to cancer from 14 million new cases. Cancer chemotherapy frequently requires long periods of multiple intravenous infusions which may compel patients to abandon treatment. One approach to overcome this challenge is through the use of transdermal drug delivery systems. The major obstacle with transdermal drug delivery is that the stratum corneum, which is the outermost layer of the skin, hinders the penetration of therapeutic agents. An avalanche of techniques is available to enhance the penetration of anticancer agents across the skin including iontophoresis, sonophoresis, microneedles, prodrugs, microemulsions and elastic liposomes. In this review, attention is focused on the numerous techniques used to overcome the skin barrier and enhance the percutaneous penetration of anticancer agents. 10.1016/j.biopha.2016.09.098
    Dermal and transdermal delivery: prodrugs. Sloan Kenneth B,Devarajan-Ketha Hemamalini,Wasdo Scott C Therapeutic delivery Attempts to deliver drugs into and through the skin (dermal and transdermal delivery) have not been very successful because the physicochemical properties of drugs are often not optimal. Prodrugs can be used to optimize those physicochemical properties of drugs and optimize their delivery by transiently masking their polar functional groups. For a drug to cross the rate-limiting barrier to delivery (the stratum corneum) it must dissolve in and cross multiple lipid and aqueous phases within the stratum corneum. Prodrugs can be designed to exhibit increased lipid and aqueous solubilities resulting in increased delivery. In order to identify the optimal prodrugs, they must be evaluated as saturated solutions where their thermodynamic activities are maximal in the solution and in the skin. If prodrugs are evaluated at concentrations less than at saturation, inaccurate conclusions about the optimal physicochemical properties may result. Prodrugs must be designed to optimize both their lipid and aqueous solubilities to optimize their delivery into and through the skin. 10.4155/tde.10.83
    The application of skin metabolomics in the context of transdermal drug delivery. Li Jinling,Xu Weitong,Liang Yibiao,Wang Hui Pharmacological reports : PR Metabolomics is a powerful emerging tool for the identification of biomarkers and the exploration of metabolic pathways in a high-throughput manner. As an administration site for percutaneous absorption, the skin has a variety of metabolic enzymes, except other than hepar. However, technologies to fully detect dermal metabolites remain lacking. Skin metabolomics studies have mainly focused on the regulation of dermal metabolites by drugs or on the metabolism of drugs themselves. Skin metabolomics techniques include collection and preparation of skin samples, data collection, data processing and analysis. Furthermore, studying dermal metabolic effects via metabolomics can provide novel explanations for the pathogenesis of some dermatoses and unique insights for designing targeted prodrugs, promoting drug absorption and controlling drug concentration. This paper reviews current progress in the field of skin metabolomics, with a specific focus on dermal drug delivery systems and dermatosis. 10.1016/j.pharep.2016.10.011
    Cutaneous metabolism in transdermal drug delivery. Zhang Qian,Grice Jeffrey E,Wang Guangji,Roberts Michael S Current drug metabolism The skin is the major interface between the body and the environment. The cutaneous metabolic activity has been identified and widely studied in recent years. It is clear that active enzymes in viable skin tissues have a capacity for bio-transforming topically applied compounds, with a consequence of an altered pharmacological effect. Although the extent of cutaneous metabolism is modest compared to major metabolism in liver, it is important to consider the effect of inherent metabolic function on both local and systematic transdermal delivery. In this review, recent literatures concerning in vitro & in vivo models and techniques used in the study of skin metabolic processes were summarized. The potential influence from skin transporters, diseased conditions, and the chemicals used in skin absorption studies on cutaneous metabolic function, was then discussed. We also reviewed the prodrug design strategy and its applications in transdermal drug delivery. 10.2174/138920009787846350
    Polymer conjugated retinoids for controlled transdermal delivery. Castleberry Steven A,Quadir Mohiuddin A,Sharkh Malak Abu,Shopsowitz Kevin E,Hammond Paula T Journal of controlled release : official journal of the Controlled Release Society All-trans retinoic acid (ATRA), a derivative of vitamin A, is a common component in cosmetics and commercial acne creams as well as being a first-line chemotherapeutic agent. Today, formulations for the topical application of ATRA rely on creams and emulsions to incorporate the highly hydrophobic ATRA drug. These strategies, when applied to the skin, deliver ATRA as a single bolus, which is immediately taken up into the skin and contributes to many of the known adverse side effects of ATRA treatment, including skin irritation and hair loss. Herein we present a new concept in topical delivery of retinoids by covalently bonding the drug through a hydrolytically degradable ester linkage to a common hydrophilic polymer, polyvinyl alcohol (PVA), creating an amphiphilic nanomaterial that is water-soluble. This PVA bound ATRA can then act as a pro-drug and accumulate within the skin to allow for the sustained controlled delivery of active ATRA. This approach was demonstrated to release active ATRA out to 10days in vitro while significantly enhancing dermal accumulation of the ATRA in explant pig skin. In vivo we demonstrate that the pro-drug formulation reduces application site inflammation compared to free ATRA and retains the drug at the application site at measurable quantities for up to six days. 10.1016/j.jconrel.2017.07.003
    Evaluation of diclofenac prodrugs for enhancing transdermal delivery. Lobo Shabbir,Li Henan,Farhan Nashid,Yan Guang Drug development and industrial pharmacy UNLABELLED:Abstract Objective: The purpose of this study was to evaluate the approach of using diclofenac acid (DA) prodrugs for enhancing transdermal delivery. METHODS:Methanol diclofenac ester (MD), ethylene glycol diclofenac ester (ED), glycerol diclofenac ester (GD) and 1,3-propylene glycol diclofenac ester (PD) were synthesized and evaluated for their physicochemical properties such as solubilities, octanol/water partition coefficients, stratum corneum/water partition coefficients, hydrolysis rates and bioconversion rates. In vitro fluxes across human epidermal membrane (HEM) in the Franz diffusion cell were determined on DA-, MD-, ED-, GD- and PD-saturated aqueous solutions. RESULTS:The formation of GD and ED led to the prodrugs with higher aqueous solubilities and lower partition coefficients than those of the parent drug. Prodrugs with improved aqueous solubility showed better fluxes across HEM in aqueous solution than that of the parent drug, with GD showing the highest aqueous solubility and also the highest flux. There is a linear relationship between the aqueous solubility and flux for DA, ED and PD, but GD and MD deviated from the linear line. CONCLUSION:Diclofenac prodrugs with improved hydrophilicity than the parent drug could be utilized for enhancing transdermal diclofenac delivery. 10.3109/03639045.2013.767828
    Synthesis and in vitro stability of amino acid prodrugs of 6-β-naltrexol for microneedle-enhanced transdermal delivery. Eldridge Joshua A,Milewski Mikolaj,Stinchcomb Audra L,Crooks Peter A Bioorganic & medicinal chemistry letters A small library of amino acid ester prodrugs of 6-β-naltrexol (NTXOL, 1) was prepared in order to investigate the candidacy of these prodrugs for microneedle-enhanced transdermal delivery. Six amino acid ester prodrugs were synthesized (6a-f). 6b, 6d, and 6 e were stable enough at skin pH (pH 5.0) to move forward to studies in 50% human plasma. The lead compound (6 e) exhibited the most rapid bioconversion to NTXOL in human plasma (t1/2 = 2.2 ± 0.1h). 10.1016/j.bmcl.2014.09.072
    Prodrugs for transdermal drug delivery - trends and challenges. Ita Kevin B Journal of drug targeting Prodrugs continue to attract significant interest in the transdermal drug delivery field. These moieties can confer favorable physicochemical properties on transdermal drug delivery candidates. Alkyl chain lengthening, pegylation are some of the strategies used for prodrug synthesis. It is usually important to optimize partition coefficient, water and oil solubilities of drugs. In this review, progress made in the field of prodrugs for percutaneous penetration is highlighted and the challenges discussed. 10.3109/1061186X.2016.1154562