Epidermal Penetration of a Therapeutic Peptide by Lipid Conjugation; Stereo-Selective Peptide Availability of a Topical Diastereomeric Lipopeptide

Characterisation of the Molecular Mechanism of Permeation of the Prodrug Me-5ALA across the Human Stratum Corneum Using Molecular Dynamics Simulations

The barrier imposed by the outer layer of the skin, the stratum corneum, creates an almost impermeable environment for exogenous substances. Few lipophilic drugs with low molecular mass can passively diffuse through this layer, highlighting the need to develop methods to enable the delivery of more drugs via the transdermal route. The prodrug approach involves modifying the structure of a drug molecule to enhance its permeability across the skin, but it is often difficult to predict how exactly changes in chemical structure affect permeation. This study uses molecular dynamics simulations to predict permeability values and adequately characterise the molecular mechanism of permeation of the prodrugs Me-5ALA and its parent compound 5ALA across a molecular model of the lipid bilayers of the human stratum corneum. The influence of increased hydrophobicity in Me-5ALA on its permeation revealed a reduction in hydrogen bonding capability that enables it to interact more favourably with the hydrophobic region of the bilayer and diffuse at a faster rate with less resistance, thus making it a better permeant compared to its more hydrophilic parent compound. This molecular simulation approach offers a promising route for the rational design of drug molecules that can permeate effectively across the stratum corneum.

Anti-ageing peptides and proteins for topical applications: a review

Skin ageing is a cumulative result of oxidative stress, predominantly caused by reactive oxygen species (ROS). Respiration, pollutants, toxins, or ultraviolet A (UVA) irradiation produce ROS with 80% of skin damage attributed to UVA irradiation. Anti-ageing peptides and proteins are considered valuable compounds for removing ROS to prevent skin ageing and maintenance of skin health. In this review, skin ageing theory has been illustrated with a focus on the mechanism and relationship with anti-ageing peptides and proteins. The effects, classification, and transport pathways of anti-ageing peptides and proteins across skin are summarized and discussed. Over the last decade, several novel formulations and advanced strategies have been developed to overcome the challenges in the dermal delivery of proteins and peptides for skin ageing. This article also provides an in-depth review of the latest advancements in the dermal delivery of anti-ageing proteins and peptides. Based on these studies, this review prospected several semi-solid dosage forms to achieve topical applicability for anti-ageing peptides and proteins.

Effects of topical application of different molecular weight marine fish skin collagen oligopeptides on UVB-induced photoaging rat skin

OBJECTIVE

The objective of this work was to develop a peptide production process of the exact molecular weight propitious to topical application for cosmetics and to investigate the effects of enzymolysis-derived peptide on UVB-induced photoaging rat skin.

METHODS

The chum salmon fish skins were hydrolyzed by alkaline protease and neutral protease and spray-dried at different conditions, and three kinds of molecular weight peptide (MFSOP) were obtained. A total of 66 ICR rats (female, 20 ± 1 g) were randomly divided into eleven groups, including the normal, model, and experimental groups. The three kinds of MFSOP were dissolved at different dosages (5‰, 2.5%, and 5%) and then applied on the ICR hairless back skins prior to exposing UVB irradiation of 3000mJ/cm² to them 4 h later. After 8 weeks, the rats were killed and the hair-shaved skins were tested for skin moisture, hyaluronic acid, hydroxyproline, antioxidant activity, and RNA expression.

RESULTS

Three kinds of MFSOP were obtained, with the average molecular weights of 495.16, 1194.00, and 2032.46 Dalton, respectively. The MFSOPs, especially the MFSOP of average molecular weight of 1194.00 Dalton, played an important role in the recovery of the UVB-injured skin tissue in lock in moisture, in antioxidant activity and in promotion in collagen and elastin protein to some extent.

CONCLUSION

MFSOPs, especially MFSOP of average molecular weight of 1194.00 Dalton, derived from enzymolysis are potential materials to apply in cosmetics for the UVB9-induced anti-photoaging activity (lock in moisture, antioxidant activity, and promotion in collagen and elastin protein).

Glycopeptide drugs: A pharmacological dimension between "Small Molecules" and "Biologics"

Peptides are an important class of molecules with diverse biological activities. Many endogenous peptides, especially neuropeptides and peptide hormones, play critical roles in development and regulating homeostasis. Furthermore, as drug candidates their high receptor selectivity and potent binding leads to reduced off-target interactions and potential negative side effects. However, the therapeutic potential of peptides is severely hampered by their poor stability in vivo and low permeability across biological membranes. Several strategies have been successfully employed over the decades to address these concerns, and one of the most promising strategies is glycosylation. It has been demonstrated in numerous cases that glycosylation is an effective synthetic approach to improve the pharmacokinetic profiles and membrane permeability of peptides. The effects of glycosylation on peptide stability and peptide-membrane interactions in the context of blood-brain barrier penetration will be explored. Numerous examples of glycosylated analogues of endogenous peptides targeting class A and B G-protein coupled receptors (GPCRs) with an emphasis on O-linked glycopeptides will be reviewed. Notable examples of N-, S-, and C-linked glycopeptides will also be discussed. A small section is devoted to synthetic methods for the preparation of glycopeptides and requisite amino acid glycoside building blocks.

Transdermal Protein Delivery Using Choline and Geranate (CAGE) Deep Eutectic Solvent

Transdermal delivery of peptides and other biological macromolecules is limited due to skin's inherent low permeability. Here, the authors report the use of a deep eutectic solvent, choline and geranate (CAGE), to enhance topical delivery of proteins such as bovine serum albumin (BSA, molecular weight: ≈66 kDa), ovalbumin (OVA, molecular weight: ≈45 kDa) and insulin (INS, molecular weight: 5.8 kDa). CAGE enhances permeation of BSA, OVA, and insulin into porcine skin ex vivo, penetrating deep into the epidermis and dermis. Studies using tritium-labeled BSA and fluorescein isothiocyanate labeled insulin show significantly enhanced delivery of proteins into and across porcine skin, penetrating the skin in a time-dependent manner. Fourier transform IR spectra of porcine stratum corneum (SC) samples before and after incubation in CAGE show a reduction in peak area attributed to SC lipid content, suggesting lipid extraction from the SC. Circular dichroism confirms that CAGE does not affect insulin's secondary conformation. In vivo studies in rats show that topical application of 10 U insulin dispersed in CAGE (25 U kg^-1 insulin dose) leads to a highly significant 40% drop in blood glucose levels in 4 h that is relatively sustained for 12 h. Taken together, these studies demonstrate that CAGE is a promising vehicle for transdermal delivery of therapeutic proteins; specifically, as a noninvasive delivery alternative to injectable insulin for the treatment of diabetes.

Phototriggered release of tetrapeptide AAPV from coumarinyl and pyrenyl cages

Ala-Ala-Pro-Val (AAPV) is a bioactive tetrapeptide that inhibits human neutrophil elastase, an enzyme involved in skin chronic inflammatory diseases like psoriasis. Caged derivatives of this peptide were prepared by proper N- and C-terminal derivatisation through a carbamate or ester linkage, respectively, with two photoactive moieties, namely 7-methoxycoumarin-2-ylmethyl and pyren-2-ylmethyl groups. These groups were chosen to assess the influence of the photosensitive group and the type of linkage in the controlled photo release of the active molecule. The caged peptides were irradiated at selected wavelengths of irradiation (254, 300, and 350 nm), and the photolytic process was monitored by HPLC-UV. The results established the applicability of the tested photoactive groups for the release of AAPV, especially for the derivative bearing the carbamate-linked pyrenylmethyl group, which displayed the shortest irradiation times for the release at the various wavelengths of irradiation (ca. 4 min at 254 nm, 8 min at 300 nm and 46 min at 350 nm).

Enhanced transdermal peptide delivery and stability by lipid conjugation: epidermal permeation, stereoselectivity and mechanistic insights

PURPOSE

Efficient delivery of therapeutic peptides to the skin will facilitate better outcomes in dermatology. The tetrapeptide AAPV, an elastase inhibitor with potential utility in the management of psoriasis was coupled to short chain lipoamino acids (Laa: C6-C10) to enhance the peptide permeation into and through human epidermis.

METHODS

AAPV was conjugated to Laas by solid phase synthesis. Peptide stability, skin distribution and permeation, elastase activity and surface activity were determined.

RESULTS

Laas increased peptide permeation into the skin. The permeation lag time and amount of peptide remaining in the skin increased with the carbon chain length of the Laa conjugate. We also demonstrated stereoselective permeation enhancement in favour of the D-diastereomer. Importantly, the elastase inhibition activity of the peptide was largely retained after coupling to the Laa conjugates, showing potential therapeutic utility. The Laa-peptide structures were shown to be surface active, suggesting that this surfactant-like activity coupled with enhanced lipophilicity may contribute to their interaction with and permeation through the lipid domains of the stratum corneum.

CONCLUSIONS

This study suggests that the Laa conjugation approach may be useful for enhancing the permeation of moderately sized peptide drugs with potential application in the treatment of skin disorders.

Transdermal delivery of proteins

Transdermal delivery of peptides and proteins avoids the disadvantages associated with the invasive parenteral route of administration and other alternative routes such as the pulmonary and nasal routes. Since proteins have a large size and are hydrophilic in nature, they cannot permeate passively across the skin due to the stratum corneum which allows the transport of only small lipophilic drug molecules. Enhancement techniques such as chemical enhancers, iontophoresis, microneedles, electroporation, sonophoresis, thermal ablation, laser ablation, radiofrequency ablation and noninvasive jet injectors aid in the delivery of proteins by overcoming the skin barrier in different ways. In this review, these enhancement techniques that can enable the transdermal delivery of proteins are discussed, including a discussion of mechanisms, sterility requirements, and commercial development of products. Combination of enhancement techniques may result in a synergistic effect allowing increased protein delivery and these are also discussed.

Synthesis and in vitro evaluation of a library of modified endomorphin 1 peptides

Endomorphin 1 (Endo-1=Tyr-Pro-Trp-Phe-NH(2)), an endogenous opioid with high affinity and selectivity for mu-opioid receptors, mediates acute and neuropathic pain in rodents. To overcome metabolic instability and poor membrane permeability, the N- and C-termini of Endo-1 were modified by lipoamino acids (Laa) and/or sugars, and 2',6'-dimethyltyrosine (Dmt) replacement of Tyr. Analogues were assessed for mu-opioid receptor affinity, inhibition of cAMP accumulation, enzymatic stability, and permeability across Caco-2 cell monolayers. C-terminus modification decreased receptor affinity, while N-terminus C8-Laa improved stability and permeability with slight change in receptor affinity. Dmt provided a promising lead compound: [C8Laa-Dmt[1]]-Endo-1 is nine times more stable (t(1/2)=43.5min), >8-fold more permeable in Caco-2 cell monolayers, and exhibits 140-fold greater mu-opioid receptor affinity (K(imu)=0.08nM).