European Journal of Pharmaceutics and Biopharmaceutics 89 (2015) 175–181
Contents lists available at ScienceDirect
European Journal of Pharmaceutics and Biopharmaceutics journal homepage: www.elsevier.com/locate/ejpb
Research paper
Phenol Esterase Activity of Porcine Skin q Joseph A. Laszlo ⇑, Leslie J. Smith, Kervin O. Evans, David L. Compton Renewable Product Technology, USDA-Agricultural Research Service, National Center for Agricultural Utilization Research, Peoria, IL, USA
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Article history: Received 30 October 2014 Accepted in revised form 3 December 2014 Available online 8 December 2014 Chemical compounds studied in this article: Tyrosol (PubChem CID 10393) Hydroxytyrosol (PubChem CID 82755) Lipoic acid (PubChem CID 864) Ferulic acid (PubChem CID 445858) Keywords: Tyrosol Hydroxytyrosol Lipoic acid Ferulic acid Antioxidant Skin penetration
a b s t r a c t The alkyl esters of plant-derived phenols may serve as slow-release sources for cutaneous delivery of antioxidants. The ability of skin esterases to hydrolyze phenolic esters was examined. Esters of tyrosol and hydroxytyrosol were prepared from decanoic and lipoic acids. Ferulic acid was esterified with octadecanol, glycerol, and dioleoylglycerol. These phenolic derivatives were treated in taurodeoxycholate microemulsion and unilamellar liposomes with ex vivo porcine skin and an aqueous extract of the skin. Extracted esterases hydrolyzed the microemulsions at rates in the order: tyrosyl lipoate > tyrosyl decanoate > hydroxytyrosyl lipoate > hydroxytyrosyl decanoate. The tyrosyl decanoate was subject to comparatively little hydrolysis (10–30% after 24 h) when incorporated into liposomes, while hydroxytyrosyl decanoate in liposomes was not hydrolyzed at all by the skin extract. Ferulate esters were not hydrolyzed by the extract in aqueous buffer, microemulsion, nor liposomes. Tyrosyl decanoate applied topically to skin explants in microemulsion were readily hydrolyzed within 4 h, while hydrolysis was minimal when applied in liposomes. These findings indicate that porcine skin displays a general esterase activity toward medium-chain esters of tyrosol and hydroxytyrosol, which can be moderated by the physiochemical properties of the lipid vehicle, but no feruloyl esterase activity. Published by Elsevier B.V.
1. Introduction Topical administration of therapeutic agents offers substantial advantages over conventional oral drug delivery methods that may suffer from low bioavailability and first pass metabolic alterations of the active agent. This is particularly true for treatments targeting epidermal and dermal tissues, although this access pathway has its challenges too. Skin penetration by a drug or neutraceutical can be limited by the stratum corneum (SC), the outermost skin layer [1]. This hydrophobic barrier limits cutaneous uptake of aqueous-soluble molecules. Molecules penetrating the SC also are potentially subject to modification by enzymes in the SC and underlying viable tissues. Prodrugs are designed to readily Abbreviations: SC, stratum corneum; p-TSA, para-toluenesulfonic acid monohydrate; hCE, human carboxylesterase; CALB, B lipase of Candida antarctica; PMSF, phenylmethylsulfonyl fluoride. q Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. ⇑ Corresponding author. USDA-ARS, NCAUR, 1815 N. University St., Peoria, IL 61604, USA. Tel.: +1 309 681 6322; fax: +1 309 681 6686. E-mail address: [email protected] (J.A. Laszlo).
http://dx.doi.org/10.1016/j.ejpb.2014.12.004 0939-6411/Published by Elsevier B.V.
permeate the SC, and then transform in vivo into their metabolically active state. Esters are a common form of prodrug. The prodrug caproyl-propranolol, for example, is fully hydrolyzed during permeation by endogenous enzymes present in the epidermis [2]. Other topically applied ingredients are similarly subject to enzymatic modification, perhaps unintentionally so. Paraben esters are common cosmetic ingredients, serving as formulation stabilizers. Methyl paraben has been shown to be hydrolyzed by skin esterases [3]. Cleaved molecules would be expected to have significantly different permeability properties compared to the parent molecule due to changes in size, hydrogen bonding, and lipophilicity. Thus, the efficiency of active agent permeation may be dynamically altered during penetration. Human skin contains serine-type esterases, associated with either cellular cytosol or microsomal fractions [4–5], that are active with a broad range of xenobiotic substrates such as the diester prednicarbate [6], ketoprofen ethyl ester [4], and 4-methyl umbelliferyl heptanoate [7]. Less clear is the extent to which carboxylesterase activity is present in the extracellular spaces of epidermal tissues, particularly the SC. The presumed major pathway for permeant molecules is through the channels formed between SC corneocytes [8,9]. It is therefore the hydrolytic capacity of the SC intercellular space that will firstly determine the fate of
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J.A. Laszlo et al. / European Journal of Pharmaceutics and Biopharmaceutics 89 (2015) 175–181
permeating esters. Molecules passing the SC may be subject to further enzymatic alterations within viable cells of the epidermis and dermis [10], such as hydroxylation and epoxidation. Apart from enzymatic influences and penetrant physiochemical properties, formulation compositions for topical and transdermal drug delivery profoundly impact delivery efficacy. The use of chemical penetration enhancers is now commonplace [9]. There is evidence that prodrug reactivity (transesterification) with alcohol-based penetration enhancers could be enzymatically catalyzed within the skin [11], potentially altering prodrug release and transport. Lipid-based colloid carriers have been promoted as effective penetration enhancers with low irritability potential [12]. Microemulsions are spontaneously formed, optically clear, aqueous dispersions (
Contents lists available at ScienceDirect
European Journal of Pharmaceutics and Biopharmaceutics journal homepage: www.elsevier.com/locate/ejpb
Research paper
Phenol Esterase Activity of Porcine Skin q Joseph A. Laszlo ⇑, Leslie J. Smith, Kervin O. Evans, David L. Compton Renewable Product Technology, USDA-Agricultural Research Service, National Center for Agricultural Utilization Research, Peoria, IL, USA
a r t i c l e
i n f o
Article history: Received 30 October 2014 Accepted in revised form 3 December 2014 Available online 8 December 2014 Chemical compounds studied in this article: Tyrosol (PubChem CID 10393) Hydroxytyrosol (PubChem CID 82755) Lipoic acid (PubChem CID 864) Ferulic acid (PubChem CID 445858) Keywords: Tyrosol Hydroxytyrosol Lipoic acid Ferulic acid Antioxidant Skin penetration
a b s t r a c t The alkyl esters of plant-derived phenols may serve as slow-release sources for cutaneous delivery of antioxidants. The ability of skin esterases to hydrolyze phenolic esters was examined. Esters of tyrosol and hydroxytyrosol were prepared from decanoic and lipoic acids. Ferulic acid was esterified with octadecanol, glycerol, and dioleoylglycerol. These phenolic derivatives were treated in taurodeoxycholate microemulsion and unilamellar liposomes with ex vivo porcine skin and an aqueous extract of the skin. Extracted esterases hydrolyzed the microemulsions at rates in the order: tyrosyl lipoate > tyrosyl decanoate > hydroxytyrosyl lipoate > hydroxytyrosyl decanoate. The tyrosyl decanoate was subject to comparatively little hydrolysis (10–30% after 24 h) when incorporated into liposomes, while hydroxytyrosyl decanoate in liposomes was not hydrolyzed at all by the skin extract. Ferulate esters were not hydrolyzed by the extract in aqueous buffer, microemulsion, nor liposomes. Tyrosyl decanoate applied topically to skin explants in microemulsion were readily hydrolyzed within 4 h, while hydrolysis was minimal when applied in liposomes. These findings indicate that porcine skin displays a general esterase activity toward medium-chain esters of tyrosol and hydroxytyrosol, which can be moderated by the physiochemical properties of the lipid vehicle, but no feruloyl esterase activity. Published by Elsevier B.V.
1. Introduction Topical administration of therapeutic agents offers substantial advantages over conventional oral drug delivery methods that may suffer from low bioavailability and first pass metabolic alterations of the active agent. This is particularly true for treatments targeting epidermal and dermal tissues, although this access pathway has its challenges too. Skin penetration by a drug or neutraceutical can be limited by the stratum corneum (SC), the outermost skin layer [1]. This hydrophobic barrier limits cutaneous uptake of aqueous-soluble molecules. Molecules penetrating the SC also are potentially subject to modification by enzymes in the SC and underlying viable tissues. Prodrugs are designed to readily Abbreviations: SC, stratum corneum; p-TSA, para-toluenesulfonic acid monohydrate; hCE, human carboxylesterase; CALB, B lipase of Candida antarctica; PMSF, phenylmethylsulfonyl fluoride. q Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. ⇑ Corresponding author. USDA-ARS, NCAUR, 1815 N. University St., Peoria, IL 61604, USA. Tel.: +1 309 681 6322; fax: +1 309 681 6686. E-mail address: [email protected] (J.A. Laszlo).
http://dx.doi.org/10.1016/j.ejpb.2014.12.004 0939-6411/Published by Elsevier B.V.
permeate the SC, and then transform in vivo into their metabolically active state. Esters are a common form of prodrug. The prodrug caproyl-propranolol, for example, is fully hydrolyzed during permeation by endogenous enzymes present in the epidermis [2]. Other topically applied ingredients are similarly subject to enzymatic modification, perhaps unintentionally so. Paraben esters are common cosmetic ingredients, serving as formulation stabilizers. Methyl paraben has been shown to be hydrolyzed by skin esterases [3]. Cleaved molecules would be expected to have significantly different permeability properties compared to the parent molecule due to changes in size, hydrogen bonding, and lipophilicity. Thus, the efficiency of active agent permeation may be dynamically altered during penetration. Human skin contains serine-type esterases, associated with either cellular cytosol or microsomal fractions [4–5], that are active with a broad range of xenobiotic substrates such as the diester prednicarbate [6], ketoprofen ethyl ester [4], and 4-methyl umbelliferyl heptanoate [7]. Less clear is the extent to which carboxylesterase activity is present in the extracellular spaces of epidermal tissues, particularly the SC. The presumed major pathway for permeant molecules is through the channels formed between SC corneocytes [8,9]. It is therefore the hydrolytic capacity of the SC intercellular space that will firstly determine the fate of
176
J.A. Laszlo et al. / European Journal of Pharmaceutics and Biopharmaceutics 89 (2015) 175–181
permeating esters. Molecules passing the SC may be subject to further enzymatic alterations within viable cells of the epidermis and dermis [10], such as hydroxylation and epoxidation. Apart from enzymatic influences and penetrant physiochemical properties, formulation compositions for topical and transdermal drug delivery profoundly impact delivery efficacy. The use of chemical penetration enhancers is now commonplace [9]. There is evidence that prodrug reactivity (transesterification) with alcohol-based penetration enhancers could be enzymatically catalyzed within the skin [11], potentially altering prodrug release and transport. Lipid-based colloid carriers have been promoted as effective penetration enhancers with low irritability potential [12]. Microemulsions are spontaneously formed, optically clear, aqueous dispersions (
