Synthesis and characterization of O-acylated-ω-hydroxy fatty acids as skin-protecting barrier lipids

Current knowledge of the implication of lipid mediators in psoriasis

The skin is an organ involved in several biological processes essential to the proper functioning of the organism. One of these essential biological functions of the skin is its barrier function, mediated notably by the lipids of the stratum corneum, and which prevents both penetration from external aggression, and transepidermal water loss. Bioactive lipid mediators derived from polyunsaturated fatty acids (PUFAs) constitute a complex bioactive lipid network greatly involved in skin homeostasis. Bioactive lipid mediators derived from n-3 and n-6 PUFAs have well-documented anti- and pro-inflammatory properties and are recognized as playing numerous and complex roles in the behavior of diverse skin diseases, including psoriasis. Psoriasis is an inflammatory autoimmune disease with many comorbidities and is associated with enhanced levels of pro-inflammatory lipid mediators. Studies have shown that a high intake of n-3 PUFAs can influence the development and progression of psoriasis, mainly by reducing the severity and frequency of psoriatic plaques. Herein, we provide an overview of the differential effects of n-3 and n-6 PUFA lipid mediators, including prostanoids, hydroxy-fatty acids, leukotrienes, specialized pro-resolving mediators, N-acylethanolamines, monoacylglycerols and endocannabinoids. This review summarizes current findings on lipid mediators playing a role in the skin and their potential as therapeutic targets for psoriatic patients.

On the importance of chain branching in tear film lipid layer wax and cholesteryl esters

The tear film lipid layer (TFLL) is important to the maintenance of ocular surface health. Surprisingly, information on the individual roles of the myriad of unique lipids found therein is limited. The most abundant lipid species are the wax esters (WE) and cholesteryl esters (CE), and, especially their branched analogs. The isolation of these lipid species from the TFLL has proved to be tedious, and as a result, insights on their biophysical profiles and role in the TFLL is currently lacking. Herein, we circumvent these issues by a total synthesis of the most abundant iso-methyl branched WEs and CEs found in the TFLL. Through a detailed characterization of the biophysical properties, by the use of Langmuir monolayer and wide-angle X-ray scattering techniques, we demonstrate that chain branching alters the behavior of these lipid species on multiple levels. Taken together, our results fill an important knowledge gap concerning the structure and function of the TFLL on the whole.

Water-mediated catalyst-free synthesis of lysine-based ampholytic amphiphiles for multipurpose applications: Characterization and pH-responsive emulsifying properties

A novel series of lysine-based ampholytic amphiphiles, with alkylsuccinic anhydrides of varying chain lengths as hydrophobic acylating agents, were synthesized in medium to high yield (50.23-90.15%) based on a facile, catalyst-free method in water medium; and structurally confirmed by mass spectrometry (MS), Fourier transform infra-red (FTIR) spectroscopy, and ¹H/¹³C nuclear magnetic resonances (NMR) analysis. The resulting compounds were subjected to pH-dependent amphiphilic property, ferrous ion chelating, DPPH antioxidant capacity, and cytotoxicity analyses. Results showed that CMC values decrease, γ value increase, and emulsion stability increase with the increase of medium pH, suggesting that the surface activity of synthetic compounds at air/water and oil/water interface under neutral and alkaline conditions was remarkably higher than that under acidic condition. Lauryl O-acylated malic lysine (compound 4b) presented excellent foaming ability close to commercial detergent sodium dodecyl sulphate; dodecyl succinic lysine (compound 4a) afforded highly stable o/w nanoemulsion. Moreover, compound 4b displayed comparable ferrous ion chelating property to lysine and 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidative capacity similar to a commercial food ingredient, diacetyl tartaric acid esters of mono- and di-glycerides (DATEM), indicating its multi-faceted functionalities. A cytotoxicity study of compounds 3b &4b showed that they were non-toxic. Thus, these novel ampholytic amphiphiles may find multi-purpose applications in food, detergent, pharmaceutical, and cosmetic industry.

Review of Modern Techniques for the Assessment of Skin Hydration

Skin hydration is a complex process that influences the physical and mechanical properties of skin. Various technologies have emerged over the years to assess this parameter, with the current standard being electrical probe-based instruments. Nevertheless, their inability to provide detailed information has prompted the use of sophisticated spectroscopic and imaging methodologies, which are capable of in-depth skin analysis that includes structural and composition details. Modern imaging and spectroscopic techniques have transformed skin research in the dermatological and cosmetics disciplines, and are now commonly employed in conjunction with traditional methods for comprehensive assessment of both healthy and pathological skin. This article reviews current techniques employed in measuring skin hydration, and gives an account on their principle of operation and applications in skin-related research.

Investigating the Role of Specific Tear Film Lipids Connected to Dry Eye Syndrome: A Study on O-Acyl-ω-hydroxy Fatty Acids and Diesters

Dry eye syndrome (DES) is a prevalent disease in which the tear film homeostasis is compromised. One of the main causes of DES is thought to be an alteration in the composition of the outermost layer of the tear film, the tear film lipid layer (TFLL), resulting in an increased evaporation of water from the tear film and subsequent drying of the ocular surface. Recent studies have suggested that the specific TFLL lipids, namely, O-acyl-ω-hydroxy fatty acids (OAHFAs) and diesters (DiEs), may play a role in the development of DES. However, their specific connection to DES has remained largely unknown until now because of the lack of information on their biophysical properties and their role in the TFLL. Herein, we have addressed this issue by studying the biophysical properties and evaporation resistance of a library containing 10 synthetic analogues of TFLL OAHFAs and DiEs. Our results show how the variations of chain length and polar groups affect the phase behavior of these lipids at the tear film surface. In addition, the results revealed that the OAHFAs exhibiting a liquid-expanded to solid phase transition formed films with high evaporation resistance, whereas the DiEs were found to have no evaporation resistance. Altogether, our results shed new light on the role of the OAHFAs and DiEs in the TFLL and their connection to DES, suggesting that OAHFAs are likely a key lipid class in maintaining the TFLL evaporation resistance.

Caffeoyl maleic fatty alcohol monoesters: Synthesis, characterization and antioxidant assessment

HYPOTHESIS

Caffeoyl malate anhydride, as a good nucleophilic acceptor, can react with lipophilic fatty alcohols to yield interface-confined amphiphiles. The resulting novel molecules are hypothesized to deliver combined functionalities of parent natural building blocks, as emulsifier, stabilizer, ion chelator and free radical scavenger.

EXPERIMENTS

Ring-opening reactions of caffeoyl malate anhydride with fatty alcohols of different chain lengths generated a new group of antioxidant amphiphiles. Structural verification was by MS (mass spectrometry), ¹H/¹³C NMR (nuclear magnetic resonance) and FT-IR (Fourier transform infra-red) spectroscopy. Physicochemical characterization was done by use of DSC (differential scanning calorimetry), FT-IR, determinations of critical micelle concentrations (CMC) and calculations of HLB. Antioxidant activity was assessed by DPPH (2, 2-diphenyl-1-picrylhydrazyl) and hydroxyl radical scavenging activities. Dynamic light scattering (DLS) studies demonstrated surface-activity of G8-G18. Inhibition of iron- and thermally-accelerated lipid oxidation was monitored by thiobarbituric acid reactive substances (TBARS) assay.

FINDINGS

Derivatization of caffeoyl malate anhydride with fatty alcohols maintained free radical scavenging activity, and improved hydroxyl radical scavenging activity of caffeic acid. Lipid oxidation at 22 °C was significantly inhibited (up to 3.5 times) in emulsions stabilized by G8-G18 with or without chitosan compared to emulsions stabilized by commercial emulsifiers and stabilizers. Thermal oxidation (at 80 °C) was 10 times less in emulsions facilitated by G8-G18 in combination with chitosan compared to emulsions stabilized by commercial emulsifiers and stabilizers. This study has developed a simple and straightforward approach for developing value-added compounds from underexplored fatty alcohols.

New phenophospholipids equipped with multi-functionalities: Regiospecific synthesis and characterization

HYPOTHESIS

In multi-phase systems, many complex reactions take place at the interface where a molecule equipped with manifold functionalities is demanded. By taking advantage of the surface-active property of phosphatidylcholine (PC) scaffold and antioxidant properties of phenolic acids, new multifunctional molecules are generated, which are expected to confer physical and oxidative stability to sensitive bioactive ingredients in delivery systems.

EXPERIMENTS

This work reports a successful synthesis of two new arrays of phenophospholipids sn-1-acyl(C12-C18)-sn-2-caffeoyl and sn-1-caffeoyl-sn-2-acyl phosphatidylcholines via mild scalable regiospecific pathways; as structurally verified by MS, ¹H/¹³C NMR analyses, and characterized by critical micelle concentrations (CMC), FTIR, and DSC analysis. Synthesized phenophospholipids are subjected to stabilizing o/w emulsion, and antioxidation tests as demonstrated by TBARS (Thiobarbituric Acid Reactive Substances) and DPPH (2,2-diphenyl-1-picrylhydrazyl) assays.

FINDINGS

This study has demonstrated that; (1) phenophospholipids with a broad spectrum of CMC are created, affording superior emulsion stability than soybean PC; (2) all phenophospholipids present improved oxidation inhibition and sn-2-caffeoyl phenophospholipids display superior performance to sn-1-caffeoyl phenophospholipids, soybean PC or admixture of caffeic acid and soybean PC; (3) incorporation of caffeoyl in PC scaffold does not sacrifice radical scavenging ability of caffeic acid, whilst the ion chelating capacity of sn-1-myristoyl(C14)-sn-2-caffeoyl PC enhance by 4.5 times compared to soy PC. Fluorescence Microscopy imaging verified the location of phenophospholipids in the interface as desired. Among synthetic phenophospholipids, sn-1-myristoyl(C14)-sn-2-caffeoyl PC commits the cut-off effect in most desired functionalities, which might be of great potential for multi-purpose applications.

A new group of synthetic phenolic-containing amphiphilic molecules for multipurpose applications: Physico-chemical characterization and cell-toxicity study

Nine synthetic amphiphilic phenolic lipids, varied in phenolic moiety (caffeoyl/dimethylcaffeoyl) and fatty acid chain lengths (8-18) were characterized by differential scanning calorimetry (DSC), temperature-ramp Fourier transform infra-red spectroscopy (FT-IR) and atomic force microscopy (AFM). FT-IR and DSC results revealed that the physical state and lateral packing of synthetic molecules were largely governed by fatty acyls. The critical micelle concentrations (CMC) of synthetic lipids was in the range of 0.1 mM to 2.5 mM, affording generation of stable oil-in-water emulsions; as evidenced by the creaming index (<5%) of emulsions stabilized by compounds C12‒C16, and C12a‒C16a after 7 days' storage. AFM analysis revealed that compound C14 formed stable double-layers films of 5.2 nm and 6.7 nm. Application studies showed that formulations stabilized by synthesized compounds containing 30% fish oil had superior physical and oxidative stability compared to formulations containing commercial emulsifiers or their mixtures with phenolic acids. Moreover, the synthetic compounds were non-toxic against in vitro transformed keratinocytes from histologically normal skin and Caco-2 cell lines. This study demonstrates the relevance of using a natural hydroxycarboxylic acid as a flexible linker between natural antioxidants, glycerol and fatty acids to generate multifunctional amphiphiles with potential applications in food, pharmaceutical and cosmetic industry.

Enzymatic alkylsuccinylation of tyrosol: Synthesis, characterization and property evaluation as a dual-functional antioxidant

This work reports a novel approach to generate a new group of tyrosol-based amphiphilic lipid alkylsuccinylated tyrosol by lipase-catalyzed succinylation of tyrosol with alkylsuccinic anhydrides of varying alkyl chain lengths, in high yields (80-95%). The structures of the compounds were confirmed by MS, FTIR &¹H NMR; and their properties were characterized by Temperature-Ramp FTIR, DSC & CMC measurements. The synthesized compounds integrate water-soluble phenylethanoid and hydrophobic alkyl into one molecule thus are endowed with dual functions: retaining the antioxidant property of tyrosol and entailing tyrosol with new surface-active property. The DPPH activity of tyrosol (13.77%) was significantly enhanced by 2-dodecen-1-ylsuccinylated tyrosol (16.01%). Compared to tyrosol-based emulsions (76.63%), the lipid oxidation is reduced to 21.57% and 42.32% in 2-octen-1-ylsuccinylated/2-dodecen-1-ylsuccinylated tyrosol emulsions, respectively. This work brings new members to the library of functional lipid excipients and open a novel and effective synthetic pathway for derivation of phenyl alcohols.

Fractionated aliphatic alcohols as synthetic precursors of ultra long-chain monoacylglycerols for cosmetic applications

BACKGROUND

Xerosis is an abnormally dry and flaky skin condition that is associated with a change in the packing behaviour of the lipid matrix in the stratum corneum (SC), the outermost layer of the skin. This skin condition can lead to an increase in transepidermal water loss (TEWL). As ultralong-chain fatty acids have a positive effect on maintaining the packing behaviour of the SC lipid matrix, a moisturizer which contains glycerides of ultralong-chain fatty acids could act as a semi-occlusive layer on the surface of the skin. This will lower the rate of water evaporation through the epidermis and consequently help prevent or improve skin xerosis.

OBJECTIVE

To identify a novel source of ultralong-chain lipids and develop monoacylglycerols with mixed fatty acyl chain lengths that have occlusive properties superior to petrolatum.

METHODS

Initially, Performacol 425, a mixture of very long-chain fatty alcohols, was fractionated using short path distillation to yield a fraction enriched with C22:0-C26:0 fatty alcohols. The fatty alcohol fraction was then oxidized using Jones reagent, and the resulting fatty acids were esterified with glycerol to yield the corresponding monoglycerides using Novozym 435. These were then evaluated using Fourier transform infrared spectroscopy, differential scanning calorimetry and water vapour transmission rate measurements.

RESULTS

The monoacylglycerols enriched with C22:0-C26:0 displayed a melting point of 80°C and orthorhombic packing; packing behaviour mainly present in healthy SC. In addition, a phospholipid-structured emulsion containing 3% of the monoglycerides displayed occlusive properties superior to the vehicle containing 3% petrolatum jelly.

CONCLUSIONS

Performacol 425 can be a potential source of fatty alcohols to synthesize monoacylglycerols that can improve the occlusive behaviour of phospholipid-structured emulsions.