Kervin O. Evans

Feruloyl dioleoylglycerol antioxidant capacity in phospholipid vesicles.

Ferulic acid and its esters are known to be effective antioxidants. Feruloyl dioleoylglycerol was assessed for its ability to serve as an antioxidant in model membrane phospholipid vesicles. The molecule was incorporated into single-lamellar vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine at 1 and 5 mol fractions. Employing a lipid peroxidation inhibition assay, feruloyl dioleoylglycerol was demonstrated to express an oxidation protection ratio relative to Trolox of 0.94 and 0.74 at the 1% and 5% incorporation levels, respectively. The impact of feruloyl dioleoylglycerol incorporation on vesicle integrity was examined by determining calcein-cobalt complex leakage rates. Vesicle leakage was not influenced at 22 or 37 degrees C with 5% feruloyl dioleoylglycerol incorporation in comparison to that of vesicles lacking feruloyl dioleoylglycerol. Resonance energy transfer analysis showed that the closest approach distance between feruloyl dioleoylglycerol and 1,2-dioleoyl-sn-glycero-3-phospho-L-serine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) was approximately 31 A, which indicated that feruloyl dioleoylglycerol was thoroughly distributed throughout the bilayer plane. Conformational analysis determined that feruloyl dioleoylglycerol has a splayed conformation in which its feruloyl moiety is not closely contacted by its oleoyl groups. Feruloyl dioleoylglycerol integrates into the bilayer with its feruloyl moiety oriented close to the hydrophilic/lipophilic interface and its oleoyl groups extended deeply in the membrane. These findings indicate that feruloyl dioleoylglycerol expresses antioxidant activity by intercepting aqueous-phase free radicals as they penetrate the bilayer.

Synthesis and tribological investigation of lipoyl glycerides.

Lipoyl glycerides were synthesized by enzymatic transesterification of lipoic acid with high-oleic sunflower oil in 2-methyl-2-butanol solvent. The synthesis gave a crude product mixture comprising unreacted lipoic acid, free fatty acids, and several lipoyl glyceride structures of varying lipoic acid substitution. A more purified product mixture, devoid of unreacted lipoic acid and free fatty acids, was obtained in 61% yield. The crude and purified product mixtures were thoroughly characterized and their components positively identified. The tribological properties of the product mixtures were further investigated using a variety of methods. The product mixtures displayed significantly improved oxidation stability, cold-flow, and extreme pressure properties over those of the parent high-oleic sunflower oil. The extreme pressure results for the neat products showed a higher weld point for the crude than for the purified mixture. This was attributed to differences in the chemical properties of the components in the two product mixtures.

Carboxyl-terminated PAMAM dendrimer interaction with 1-palmitoyl-2-oleoyl phosphocholine bilayers.

Polyanionic polymers and liposomes have a great potential use as individual drug delivery systems and greater potential as a combined drug delivery system. Thus, it is important to better understand the interactions of polymers with phospholipid bilayers. A mechanistic study of the interaction between carboxyl-terminated poly(amidoamine) (PAMAM) dendrimers with 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer using fluorescence leakage and quartz crystal microbalance with dissipation monitoring (QCMD) was conducted. Fluorescence leakage experiments demonstrated that carboxyl-terminated generation 2 (G2-COOH) dendrimers caused increased liposome leakage with increasing dendrimer concentration over a 0 to 20μM range. Generation 5 (G5-COOH), on the other hand, reduced leakage over the same concentration range, presumably by increasing lipid packing. QCMD and atomic force microscopy (AFM) measurements demonstrated that G2-COOH interacting with supported bilayers resulted in small defects with some mass loss and no adsorption. In contrast, G5-COOH interaction with a bilayer resulted in adsorption and local bilayer swelling.

Octadecyl ferulate behavior in 1,2-Dioleoylphosphocholine liposomes.

Octadecyl ferulate was prepared using solid acid catalyst, monitored using Supercritical Fluid Chromatography and purified to a 42% yield. Differential scanning calorimetry measurements determined octadecyl ferulate to have melting/solidification phase transitions at 67 and 39°C, respectively. AFM imaging shows that 5-mol% present in a lipid bilayer induced domains to form. Phase behavior measurements confirmed that octadecyl ferulate increased transition temperature of phospholipids. Fluorescence measurements demonstrated that octadecyl ferulate stabilized liposomes against leakage, maintained antioxidant capacity within liposomes, and oriented such that the feruloyl moiety remained in the hydrophilic region of the bilayer. Molecular modeling calculation indicated that antioxidant activity was mostly influenced by interactions within the bilayer.

Phenol Esterase Activity of Porcine Skin

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 24h) 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 4h, 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.

Stability of a liposomal formulation containing lipoyl or dihydrolipoyl acylglycerides

Abstract Context: The acylglycerides of lipoic and dihydrolipoic acids may serve as slow-release sources for cutaneous delivery of these antioxidants when formulated in a liposomal vehicle. Objective: Testing was conducted to determine the storage stability of lipoyl glycerides in phospholipid-based liposomes. Materials and methods: Lipoyl glycerides prepared by transesterification of lipoic acid with high oleic sunflower oil were incorporated into unilamellar liposomes comprised of soy phosphatidylcholine (soyPC) or dioleoylphosphatidylcholine (DOPC). Results: Lipoyl glycerides were stable in soyPC at 4 °C (90% remaining after five weeks) and decayed with a half-life (t½) of 14 d at 40 °C. In contrast, lipoyl glycerides embedded in DOPC were completely stable for four weeks at 40 °C. Dihydrolipoyl glycerides in soyPC converted to lipoyl glycerides at 4 °C (t½ = 14 d) over four weeks, and much more rapidly so at 40 °C (t½ = 1 d). A hydroperoxide accumulation analysis indicated that lipoyl glycerides and dihydrolipoyl glycerides were modified or degraded while suppressing autoxidation of the polyunsaturated fatty acids present in soyPC. Dynamic light scattering measurements found that liposomes containing lipoyl glycerides or dihydrolipoyl glycerides did not undergo significant size changes for at least 48 d, indicating that inclusion of the lipoic acid derivatives did not induce vesicle aggregation. Discussion/Conclusion: Substitution of the soyPC with DOPC, which is not readily subject to autoxidation, provided a much more stable storage environment for lipoyl glycerides. These findings confirm the expectation that phospholipid liposomes need to be oxidatively stable vehicles for dermal delivery of lipoic acid derivatives.

Spectroscopic and time-dependent density functional investigation of the role of structure on the acid-base effects of citrinin detection

A time-dependent density functional theory (TD-DFT) study was carried out on tautomers of the mycotoxin citrinin in the neutral, anionic, and cationic forms to gain insight into the role of chemical structure on detection. Steady-state fluorescence studies of citrinin in micellar aqueous solutions produced unusual results for ionic surfactants and the neutral Triton X-100 enhanced fluorescence emission. Ground-state and time-dependent density functional studies were carried out on five tautomers of citrinin using the B3LYP density functional and the 6-311+G(2df,2p) basis set. The investigation revealed that deprotonation is a major factor governing the shifts in fluorescence excitation and emission maxima. Moreover, the position of the lowest unoccupied molecular orbitals is removed from the fluorophore moiety of citrinin in the dianionic state which is consistent with the diminished fluorescence of the toxin in basic solutions. The ionic characteristics of certain chemosensors can influence the structure and intrinsic spectroscopic properties of citrinin.

Experimental and theoretical study of the influence of water on hydrolyzed product formation during the feruloylation of vegetable oil.

BACKGROUND Feruloylated vegetable oil is a valuable green bioproduct that has several cosmeceutical applications associated with its inherent anti-oxidant and ultraviolet-absorption properties. Hydrolyzed vegetable oil by-products can influence product quality and consistency. RESULTS The formation of by-products by residual water in the enzymatic synthesis of feruloylated vegetable oil was investigated using chemical theory and experimental studies by monitoring the reaction over a 22-day period. The hydrolysis of vegetable oil is thermodynamically favored over the hydrolysis of the ethyl ferulate starting material. These results suggest that hydrolyzed vegetable oil products will be experimentally observed in greater concentrations compared to hydrolyzed ethyl ferulate products. CONCLUSION Quantum chemical studies identified several reaction mechanisms that explain the formation of side products by water, suggesting that residual water influences product quality. Efforts to reduce residual water can improve product consistency and reduce purification costs. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Phosphatidyl-hydroxytyrosol and phosphatidyl-tyrosol bilayer properties

Hydroxytyrosol and tyrosol phospholipids were enzymatically synthesized and investigated for their bilayer properties. Dynamic light scattering demonstrated that hand extrusion at 100nm consistently resulted in liposomes of nearly 85nm diameter for both phosphatidyl-hydroxytyrosol (DOPHT) and phosphatidyl-tyrosol (DOPT). Transmission electron microscopy showed DOPT and DOPHT liposomes extruded at 100-nm to be spherical and non-distinctive from one another. Zeta potential measurements resulted in surface charges<-25mV, demonstrating both DOPT and DOPHT form highly stable liposomes. Quartz crystal microbalance with dissipation monitoring measurements demonstrated that liposomal adsorption was dependent on a combination of DOPT (or DOPHT) mole-percent and calcium ions concentration. Fluorescence anisotropy measurements indicated that melting temperatures of DOPT and DOPHT were below 4°C, suggesting that adsorption behavior and liposome formation was limited by electrostatic interactions and not gel-state formation.