Physical and chemical stability of marine lipid-based liposomes under acid conditions

Marine phospholipid nanoliposomes: A promising therapeutic approach for inflammatory bowel disease: Preparation, safety, and efficacy evaluation

Promising findings have been emerged from studies utilizing n3 polyunsaturated fatty acids (PUFA) supplementation in animal models of inflammatory bowel disease (IBD). Introduction of marine phospholipids which combine n3 PUFA with phosphatidylcholine in a nanoliposome formulation offers enhanced pharmacological efficacy due to physical stability, improved bioavailability, and specific targeting to inflamed colitis tissues. In the present study, a marine phospholipid-based nanoliposome formulation was developed and optimized, resulting in nanovesicles of approximately 107.7 ± 1.3 nm in size, 0.18 ± 0.01 PDI, and - 32.03 ± 3.16 mV ZP. The nanoliposomes exhibited spherical vesicles with stable properties upon incubation at SGF as shown by the TEM, DLS, and turbidity measurements over 3 h. MPL nanoliposomes were cytocompatible until the concentration of 500 µg/mL as per MTT assay and taken by macrophages through macropinocytosis and caveolae pathways, and demonstrated significant inhibitory activity against reactive oxygen species (ROS) in LPS-stimulated macrophages. They were also shown to be blood-compatible and safe for administration in healthy mice. In a colitis mouse model, the nanoliposomes displayed preferential distribution in the inflamed gut, delaying the onset of colitis when administered prophylactically. These findings highlight the potential of marine phospholipid nanoliposomes as a promising therapeutic approach for managing inflammatory bowel disease.

Lipid nanovesicles for biomedical applications: 'What is in a name'?

Vesicles, generally defined as self-assembled structures formed by single or multiple concentric bilayers that surround an aqueous core, have been widely used for biomedical applications. They can either occur naturally (e.g. exosomes) or be produced artificially and range from the micrometric scale to the nanoscale. One the most well-known vesicle is the liposome, largely employed as a drug delivery nanocarrier. Liposomes have been modified along the years to improve physicochemical and biological features, resulting in long-circulating, ligand-targeted and stimuli-responsive liposomes, among others. In this process, new nomenclatures were reported in an extensive literature. In many instances, the new names suggest the emergence of a new nanocarrier, which have caused confusion as to whether the vesicles are indeed new entities or could simply be considered modified liposomes. Herein, we discussed the extensive nomenclature of vesicles based on the suffix "some" that are employed for drug delivery and composed of various types and proportions of lipids and others amphiphilic compounds. New names have most often been selected based on changes of vesicle lipid composition, but the payload, structural complexity (e.g. multicompartment) and new/improved proprieties (e.g. elasticity) have also inspired new vesicle names. Based on this discussion, we suggested a rational classification for vesicles.

Advancements in liposome technology: Preparation techniques and applications in food, functional foods, and bioactive delivery: A review

Liposomes play a significant role in encapsulation of various bioactive compounds (BACs), including functional food ingredients to improve the stability of core. This technology can be used for promoting an effective application in functional food and nutraceuticals. Incorporation of traditional and emerging methods for the developments of liposome for loading BACs resulted in viable and stable liposome formulations for industrial applications. Thus, the advance technologies such as supercritical fluidic methods, microfluidization, ultrasonication with traditional methods are revisited. Liposomes loaded with plant and animal BACs have been introduced for functional food and nutraceutical applications. In general, application of liposome systems improves stability, delivery, and bioavailability of BACs in functional food systems and nutraceuticals. This review covers the current techniques and methodologies developed and practiced in liposomal preparation and application in functional foods.

Enhanced bioactivity and efficient delivery of quercetin through nanoliposomal encapsulation using rice bran phospholipids

BACKGROUND

Quercetin is a phenolic compound occurring in many food plants and agricultural crops. It is reported to possess various health-promoting properties. However, the poor bioavailability of quercetin, due to its low aqueous solubility and its degradation during digestion, limits its nutraceutical applications. This study aimed to encapsulate quercetin in nanoliposomes using rice-bran phospholipids for its efficient delivery and controlled release, the protection of its structural stability, and enhancement of its bioactivity.

RESULTS

Nanoliposomal encapsulation of quercetin by thin film-sonication method yielded spherical nanoparticles (157.33 ± 23.78 nm) with high encapsulation efficiency (84.92 ± 0.78%). Storage stability studies showed that nanoliposomal quercetin was stable at 4 °C and 27 °C for 6 and 5 months, respectively, as indicated by unchanged antioxidant activity and quercetin retention. Nanoliposomal quercetin showed a slow, limited release pattern in simulated gastric fluid (SGF), and an initial burst release followed by a slow constant releasing pattern in simulated intestinal fluid (SIF). A 1004-fold increase in 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity was observed in quercetin nanoliposomes (SC₅₀ = 4.04 ± 0.01 ppm) compared to non-encapsulated quercetin (SC₅₀ = 4053.03 ± 5.61 ppm). Similarly, the anti-angiogenic activity of quercetin, as evaluated by duck embryo chorioallantoic membrane (CAM) assay, was enhanced twofold to fivefold by nanoliposomal encapsulation.

CONCLUSION

This study showed that nanoliposomal encapsulation in rice-bran phospholipids enhanced the radical-scavenging and anti-angiogenic activities of quercetin. Furthermore, this study demonstrated that nanoliposomes can serve as efficient oral delivery system for quercetin. © 2018 Society of Chemical Industry.

Egg Yolk Extracts as Potential Liposomes Shell Material: Composition Compared with Vesicles Characteristics

Our aim was to propose simple extraction process to obtain phospholipids along with yolk-derived vitamins and fats. Five extracts marked as ethanol/acetone, methanol-chloroform/acetone, hot ethanol, hexane, and cold ethanol were developed and compared. Extracts' compositions were analyzed in terms of phospholipid, polar and nonpolar fraction, cholesterol, carotenoids, and tocopherols content. Further, liposomes prepared from extracts were characterized. The highest extraction efficiency was achieved by a one-step hexane procedure. However, that sample, in contrast to the other four extracts, revealed distinctively lower permeability when used for liposomes membrane formation. Principal component analysis proved that major components contents were decisive for liposomes membranes permeability, whereas minor constituents' content controlled zeta potential and Z-average size.

PRACTICAL APPLICATION

Liposomes are nanocarriers widely used in pharmaceutical industry. Due to intravenous route of administration, they have to be produced from phospholipids of very fine purity. On the other hand, there is increasing interest in nanoencapsulation of labile, bioactive substances for manufacturing of health promoting food. Unfortunately, high-price pure phospholipids are prohibitive for food applications. The use of raw material obtained by simple extraction procedure instead of highly purified phospholipids could be an attractive alternative for food industry.

A Review of Nanoliposomal Delivery System for Stabilization of Bioactive Omega-3 Fatty Acids

Currently, bioactive compounds are required in the design and production of functional foods, with the aim of improving the health status of consumers all around the world. Various epidemiological and clinical studies have demonstrated the salutary role of eicosapentaenoic acid (EPA, 22:6 n−3) and docosahexaenoic acid (DHA, 22:5 n−3) in preventing diseases and reducing mortality from cardiovascular diseases. The unsaturated nature of bioactive lipids leads to susceptibility to oxidation under environmental conditions. Oxidative deterioration of omega-3 fatty acids can cause the reduction in their nutritional quality and sensory properties. Encapsulation of these fatty acids could create a barrier against reaction with harmful environmental factors. Currently, fortification of foods containing bioactive omega-3 fatty acids has found great application in the food industries of different countries. Previous studies have suggested that nano-encapsulation has significant effects on the stability of physical and chemical properties of bioactive compounds. Considering the functional role of omega-3 fatty acids, this study has provided a literature review on applications of nanoliposomal delivery systems for encapsulation of these bioactive compounds.

Bioactive constituents in liposomes incorporated in orange juice as new functional food: thermal stability, rheological and organoleptic properties

Liposomes were developed with bioactive constituents (omega-3, omega-6, tocopherol) incorporated in acid food. They were made of soy phosphatidylcholine (SPC) allowing the encapsulation of antioxidant vitamin C (VC) and tocopherol. Stearic acid (SA) or calcium stearate (CaS) was added as a bilayer stabilizer. The structural and oxidative stability of the liposomes were studied considering the heat effect of pasteurization. Size was analyzed by light scattering; shape and structure were studied by optical and transmission electron microscopy, respectively. Membrane packing was studied with merocyanine 540. Surface charge and oxidative stability were analyzed by zeta potential and ORAC method, respectively. The liposomes showed significant stability in all of the parameters mentioned above and an important protective effect over thermolabile VC. To confirm their applicability in food, the rheological behavior and a sensory evaluation of liposomes with vitamin C and bioactive constituents were studied. The sensory evaluation of liposomes in orange juice was performed by the overall acceptability and triangular tests with 40 and 78 potential consumers, respectively. The incorporation of all liposomal formulation did not change the acceptability of orange juice. Noteworthy, SPC and SPC:SA systems had rheological behavior similar to a Newtonian fluid whereas that SPC:CaS presented a pseudoplastic one, both considered excellent for larger scale production. From all the obtained results, we can conclude that these liposomal formulations are suitable for food industry applications, incorporating bioactive constituents and generating functional orange juice that conserves its bioactivity after pasteurization.

Perspective and potential of oral lipid-based delivery to optimize pharmacological therapies against cardiovascular diseases

Cardiovascular diseases (CVDs) remain the major cause of morbidity and mortality globally. Despite the large number of cardiovascular drugs available for pharmacological therapies, factors limiting the efficient oral use are identified, including low water solubility, pre-systemic metabolism, food intake effects and short half-life. Numerous in vivo proof-of-concepts studies are presented to highlight the viability of lipid-based delivery to optimize the oral delivery of cardiovascular drugs. In particular, the key performance enhancement roles of oral lipid-based drug delivery systems (LBDDSs) are identified, which include i) improving the oral bioavailability, ii) sustaining/controlling drug release, iii) improving drug stability, iv) reducing food intake effect, v) targeting to injured sites, and vi) potential for combination therapy. Mechanisms involved in achieving these features, range of applicability, and limits of available systems are detailed. Future research and development efforts to address these issues are discussed, which is of significant value in directing future research work in fostering translation of lipid-based formulations into clinical applications to reduce the prevalence of CVDs.

Stability during in vitro digestion of lactoferrin-loaded liposomes prepared from milk fat globule membrane-derived phospholipids

Liposomes loaded with positively charged lactoferrin (LF) were prepared from milk fat globule membrane-derived phospholipids using a thin-layer dispersion method. The entrapment efficiency of LF in the liposomes and the stability during in vitro gastrointestinal digestion were characterized and examined using dynamic light scattering, transmission electron microscopy, and PAGE. The entrapment efficiency of LF encapsulated in the liposomes was about 46%. The entrapped LF remained unchanged as a function of time and pepsin concentration when the liposome samples were digested in a simulated gastric environment, suggesting that the liposomes prepared from milk fat globule membrane-derived phospholipids were stable and protected the entrapped LF from pepsin hydrolysis. In simulated intestinal fluid, the entrapped LF was more susceptible to hydrolysis by the protease in pancreatin, as shown by changes in the diameter and membrane structure of the liposomes. The release of free fatty acids from the liposomes during digestion in simulated intestinal fluid revealed that the phospholipids in the liposomes were partly hydrolyzed by pancreatic lipase. It was suggested that liposomes may prevent the gastric degradation of LF and reduce the rate of hydrolysis of LF in intestinal conditions.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Revisão: características de nanopartículas e potenciais aplicações em alimentos

O objetivo desta revisão é abordar as aplicações de nanotecnologia em alimentos, enfatizando o uso de nanopartículas lipídicas sólidas, nanoemulsões, nanocápsulas e de nanocompósitos para embalagens de alimentos, bem como os métodos de obtenção, a funcionalidade e as suas características. A aplicação da nanotecnologia em alimentos é nova em comparação com a área biomédica e as indústrias de tecnologia de informação, nas quais a nanotecnologia já é utilizada na fabricação de materiais. No entanto, já existem inúmeras oportunidades que podem ser exploradas, como a elaboração de produtos com características funcionais e nutracêuticas, o desenvolvimento de processos e as embalagens inteligentes. Esta revisão aborda os seguintes itens: nanopartículas lipídicas sólidas, nanoemulsões, nanocápsulas, nanocompósitos em embalagem e os riscos e a legislação para a nanotecnologia. Nanopartículas lipídicas sólidas são sistemas de transporte coloidal empregados para encapsular, proteger e entregar componentes funcionais. Nanoemulsão consiste em uma dispersão muito fina composta por uma fase de óleo e uma fase aquosa, com tamanho de gota, em escala nanométrica; em função do seu tamanho característico, as nanoemulsões são transparentes ou translúcidas, e possuem estabilidade contra a sedimentação. Nanocápsulas são compostas por um invólucro polimérico disposto ao redor de um núcleo, no qual se encontra o composto ativo, conferindo proteção contra o oxigênio, a água e/ou a luz; permitem, dessa forma, uma liberação controlada da substância e/ou previnem o contato com outros componentes em uma mistura. Em nanotecnologia de embalagens, aborda-se a utilização de nanopartículas, tais como nanofibras de celulose e nanoargila, bem como a aplicação de nanomateriais com propriedades nutricionais e/ou antimicrobianas, e nanosensores. Serão abordados também aspectos relacionados aos riscos e à legislação em nanotecnologia de alimentos.

Perspectives on the use of marine and freshwater hydrobiont oils for development of drug delivery systems

Marine foods represent a unique source of poly-unsaturated fatty acids (PUFA) of the omega-3 (n-3) family. Today it is generally accepted that fish oil is important in a healthy and balanced omnivorous human diet. This favorable health perception of fish oil is however troubled by the high level of PUFA oxidation and low absorption in the gastro-intestinal tract. In this work we present and described various types of delivery systems which are used to improve PUFA and fish oil availability and oxidative stability.

Oxidative stability of marine phospholipids in the liposomal form and their applications

Marine phospholipids (MPL) have attracted a great deal of attention recently as they are considered to have a better bioavailability, a better resistance towards oxidation and a higher content of eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) than oily triglycerides (fish oil) from the same source. Due to their tight intermolecular packing conformation at the sn-2 position and their synergism with α-tocopherol present in MPL extracts, they can form stable liposomes which are attractive ingredients for food or feed applications. However, MPL are still susceptible to oxidation as they contain large amounts polyunsaturated fatty acids and application of MPL in food and aquaculture industries is therefore a great challenge for researchers. Hence, knowledge on the oxidative stability of MPL and the behavior of MPL in food and feed systems is an important issue. For this reason, this review was undertaken to provide the industry and academia with an overview of (1) the stability of MPL in different forms and their potential as liposomal material, and (2) the current applications and future prospects of MPL in both food and aquaculture industries with special emphasis on MPL in the liposomal form.

Early dissimilar fates of liver eicosapentaenoic acid in rats fed liposomes or fish oil and gene expression related to lipid metabolism

The study was undertaken to determine whether eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3), esterified in phospholipids (PL) as liposomes or in triglycerides (TG) as oil, exhibited comparable fates in liver lipids and whether these fates were associated with gene expressions related to fatty acid (FA) metabolism. PL and TG mixtures with close contents in EPA and DHA were administered to rats over 2 weeks. Most relevant events occurred after 3 days for both treatments. At that time, liposomes, compared with oil, increased the liver content in PL with a FA composition enriched in n-6 FA, comparable in DHA and much lower in EPA. Moreover, liposomes increased the activity and mRNA levels of carnitine palmitoyltransferase (CPT) I. In contrast, fish oil exerted opposite effects on CPT I and increased the genic expression of lipogenic enzymes. Liposomes, unlike fish oil, apparently increased the mRNA levels of acyl-CoA oxidase and the activity of the peroxisomal FA-oxidising system. Concomitantly, mRNA levels of hepatic lipoprotein receptors were increased with both diets, but intracellular proteins involved in free FA uptake and lipid synthesis were up-regulated only with liposome-treated rats. The quasi absence of EPA in hepatic PL of liposome-treated rats on the short term could result from increased beta-oxidation activities through metabolic regulations induced by more available free EPA and other PUFA.

A Simple Method for Mass-Production of Liposomes, in Particular Large Liposomes, Suitable for Delivery of Free Amino Acids to Filter Feeding Zooplankton

In marine fish larviculture the live feed organisms are often enriched in order to enhance their nutritional value. One of the challenges is to enhance the phospholipids (PL) content, and another is to enhance the content of specific water soluble nutrients, like free amino acids (FAA). There are a few studies where this has been achieved by the use of liposomes. The aim of this study was to develop a simple method for mass-production of liposomes within a size range of 1-5 mum a size range suitable to feed live food organisms. Furthermore, the liposomes should have a high FAA concentration and be stable under conditions typical for short-time enrichment of live feed organisms. The method used in the present study is based on a combination of a reverse-phase evaporation method for preparing liposomes and re-hydration of freeze-dried, empty liposomes. The liposomal membrane was made of soy phosphatydilcholine and was loaded with a highly concentrated free amino acids solution. Most of the liposomes produced were 2-8 mum in diameter and the FAA encapsulation efficiency was 42.6%. Two experiments simulating 2 hr of live food enrichment were used to evaluate the liposomes. The results showed the liposome did not disintegrate or aggregate when suspended in seawater and that only 9% of the FAA content of the liposomes was lost after 2 hr suspension. The developed method was easy and reliable, producing tens of grams of liposomes per batch.

Physical stability of liposomes prepared from milk fat globule membrane and soya phospholipids

Previous research has shown that liposomes prepared from a milk fat globule membrane (MFGM) phospholipid fraction had a significantly higher phase transition temperature, thicker membrane, and lower membrane permeability than liposomes prepared from soya phospholipid material. Subsequent investigations into the relative stability of the two liposome dispersions have found that the MFGM phospholipid liposomes are more stable than their soya counterparts in a range of pH conditions, at a variety of storage and processing temperatures, and in the presence of mono- and divalent cations. These results illustrate some potential advantages in the use of MFGM phospholipids for the manufacture of liposomes for use in food systems.

Influence of pH on the Micelle-to-Vesicle Transition in Aqueous Mixtures of Sodium Dodecyl Benzenesulfonate with Histidine

Small unilamellar vesicles (approximately 100 nm in diameter) form spontaneously in aqueous mixtures of histidine and sodium dodecyl benzenesulfonate. By manipulating pH, a gradual transition from micelles to vesicles to bilayers to precipitate is observed. The self-assembly of vesicles occurs over a wide range of compositions when the solution pH is lower than 6.0, the pKa of the imidazole moiety on the histidine molecule. This phenomenon is likely the result of attractive interactions between the negatively charged benzenesulfonate headgroups and the positively charged imidazole group in the amino acid. Similar results are obtained when imidazole salt itself is used.

Archaeosomes based on novel synthetic tetraether-type lipids for the development of oral delivery systems

The in vitro stability of archaeosomes made from novel synthetic membrane-spanning tetraether lipids was evaluated in conditions mimicking those of oral route application in terms of bile salts, serum and low pH..

Marine lipid-based liposomes increase in vivo FA bioavailability

Liposomes made from an extract of natural marine lipids and containing a high n-3 PUFA lipid ratio were envisaged as oral route vectors for FA supplements in order to increase PUFA bioavailability. The absorption of FA in thoracic lymph duct-cannulated rats, after intragastric feeding of dietary fats in the form of liposomes or fish oil, was compared. Lipid and FA analyses were also performed on feces. Five mole percent alpha-tocopherol was added to fish oil and incorporated into the liposome membrane. The influence of alpha-tocopherol on FA lymph recovery was also investigated. In vivo, FA absorption in rats was favored by liposomes (98 +/- 1%) compared to fish oil (73 +/- 6%). In the same way, the DHA proportion in lymph was higher after liposome ingestion (78%) than after fish oil ingestion (47%). However, phospholipid (PL) concentration in lymph was not affected by the kind of dietary fat ingested, suggesting a PL regulation due to de novo TAG synthesis. The influence of the intramolecular distribution of n-3 PUFA in dietary lipids (TAG and PL) on the intramolecular FA distribution in TAG of chylomicrons was also investigated. The results obtained showed that the distribution of n-3 PUFA esterified on the sn-2 position of chylomicron TAG depended on the lipid source administered. All these results correlated, at least partly, with in vitro liposome behavior under conditions that mimic those of the gastrointestinal tract. As a whole, this study pointed out that marine PL may constitute an attractive material for the development of liposomes as oral PUFA supplements.

Marinosomes, marine lipid-based liposomes: physical characterization and potential application in cosmetics

Marinosomes are liposomes based on a natural marine lipid extract containing a high polyunsaturated fatty acid (PUFA) ratio. They were prepared and characterized in conditions that mimic that of topical application in terms of pH, temperature and calcium. Marinosomes were stable in storage conditions for 1 month. At low pH (pH 4) or in presence of high calcium concentrations (9 mM), complex structural rearrangements, such as aggregation and size reduction, occurred which were kinetically dependant.

Incorporation of alpha-tocopherol in marine lipid-based liposomes: in vitro and in vivo studies

Liposomes made from a natural marine lipid extract and containing a high polyunsaturated n-3 fatty lipid ratio were envisaged as oral route vectors and a potential alpha-tocopherol supplement. The behavior of vesicles obtained by simple filtration and of giant vesicles prepared by electroformation was investigated in gastrointestinal-like conditions. The influence of alpha-tocopherol incorporation into liposomes was studied on both physical and chemical membrane stability. Propanal, as an oxidation product of n-3 polyunsaturated fatty acids, was quantified by static headspace gas chromatography when alpha-tocopherol incorporation into liposome ratios ranged from 0.01 to 12 mol%. Best oxidative stability was obtained for liposomes that contained 5 mol% alpha-tocopherol. Compared to the other formulas, propanal formation was reduced, and time of the oxidation induction phase was longer. Moreover, alpha-tocopherol induced both liposome structural modifications, evidenced by turbidity, and phospholipid chemical hydrolysis, quantified as the amount of lysophospholipids. This physicochemical liposome instability was even more pronounced in acid storage conditions, i.e., alpha-tocopherol incorporation into liposome membranes accelerated the structural rearrangements and increased the rate of phospholipid hydrolysis. In particular, giant vesicles incubated at pH 1.5 underwent complex irreversible shape transformations including invaginations. In parallel, the absorption rate of alpha-tocopherol was measured in lymph-cannulated rats when alpha-tocopherol was administrated, as liposome suspension or added to sardine oil, through a gastrostomy tube. Alpha-tocopherol recovery in lymph was increased by almost threefold, following liposome administration. This may be related to phospholipids that should favor alpha-tocopherol solubilization and to liposome instability in the case of a high amount of alpha-tocopherol in the membranes. A need to correlate results obtained from in vitro liposome behavior with in vivo lipid absorption was demonstrated by this study.

In vitro behavior of marine lipid-based liposomes. Influence of pH, temperature, bile salts, and phospholipase A2

To deliver polyunsaturated fatty acids (PUFA) by the oral route, liposomes based on a natural mixture of marine lipids were prepared by filtration and characterized in media that mimic gastrointestinal fluids. First the influence of large pH variations from 1.5-2.5 (stomach) to 7.4 (intestine) at the physiological temperature (37 degrees C) was investigated. Acidification of liposome suspensions induced instantaneous vesicle aggregation, which was partially reversible when the external medium was further neutralized. Simultaneously, complex morphological bilayer rearrangements occurred, leading to the formation of small aggregates. These pH- and temperature-dependent structural changes were interpreted in terms of osmotic shock and lipid chemical alterations, i.e., oxidation and hydrolysis, especially in the first hours of storage. Besides, oxidative stability was closely related to the state of liposome aggregation and the supramolecular organization (vesicles or mixed micelles). The effects of bile salts and phospholipase A2 (PLA2) on the liposome structures were also studied. Membrane solubilization by bile salts was favored by preliminary liposome incubation in acid conditions. PLA2 showed a better activity on liposome structures than on the corresponding mixed lipid-bile salt micelles. As a whole, in spite of slight morphological modifications, vesicle structures were preserved after an acid stress and no lipid oxidation products were detected during the first 5 h of incubation. Thus, marine lipids constituted an attractive material for the development of liposomes as potential oral PUFA supplements.