Lecithin protects against plasma membrane disruption by bile salts

Terpinen-4-ol from tea tree oil prevents Aspergillus flavus growth in postharvest wheat grain

Plant volatile organic compounds (PVOCs) have gained increasing attention for their role in preventing fungal spoilage and insect contamination in postharvest agro-products owing to their effectiveness and sustainability. In this study, the essential oil was extracted from fresh M. alternifolia (tea tree) leaves, and the fumigation vapor of tea tree oil (TTO) completely inhibited the growth of Aspergillus flavus on agar plates at a concentration of 1.714 μL/mL. Terpinen-4-ol was identified as the major component (40.76 %) of TTO volatiles analyzed using headspace gas chromatography-mass spectrometry. Terpinen-4-ol vapor completely inhibited the A. flavus growth on agar plates and 20 % moisture wheat grain at 0.556 and 1.579 μL/mL, respectively, indicating that terpinen-4-ol serves as the main antifungal constituent in TTO volatiles. The minimum inhibitory concentration of terpinen-4-ol in liquid-contact culture was 1.6 μL/mL. Terpinen-4-ol treatment caused depressed, wrinkled, and punctured mycelial morphology and destroyed the plasma membrane integrity of A. flavus. Metabolomics analysis identified significant alterations in 93 metabolites, with 79 upregulated and 14 downregulated in A. flavus mycelia exposed to 1.6 μL/mL terpinen-4-ol for 6 h, involved in multiple cellular processes including cell membrane permeability and integrity, the ABC transport system, pentose phosphate pathway, and the tricarboxylic acid cycle. Biochemical analysis and 2,7-dichlorofluorescein diacetate staining showed that terpinen-4-ol induced oxidative stress and mitochondrial dysfunction in A. flavus mycelia. This study provides new insights into the antifungal effects of the main TTO volatile compounds terpinen-4-ol on the growth of A. flavus.

Self-Emulsifying Drug Delivery Systems (SEDDS) Containing Reverse Micelles: Advanced Oral Formulations for Therapeutic Peptides

Alternative methods to hydrophobic ion pairing for the formation of lipophilic complexes of peptide drugs to incorporate them in lipid-based nanocarriers such as self-emulsifying drug delivery systems (SEDDS) for oral administration are highly on demand. Such an alternative might be reverse micelles. Within this study, SEDDS containing dry reverse micelles (dRMsPMB ) formed with an anionic (sodium docusate; AOT), cationic (dimethyl-dioctadecyl-ammonium bromide; DODAB), amphoteric (soy lecithin; SL), or non-ionic (polysorbate 85; P85) surfactant loaded with the model peptide drug polymyxin B (PMB) are developed. They are characterized regarding size, payload, release kinetics, cellular uptake, and peptide activity. SEDDS exhibit sizes from 22.2 ± 1.7 (AOT-SEDDS-dRMsPMB ) to 61.7 ± 3.2 nm (P85-SEDDS-dRMsPMB ) with payloads up to 2% that are approximately sevenfold higher than those obtained via hydrophobic ion pairing. Within 6 h P85-SEDDS-dRMsPMB and AOT-SEDDS-dRMsPMB show no release of PMB in aqueous medium, whereas DODAB-SEDDS-dRMsPMB and SL-SEDDS-dRMsPMB show a sustained release. DODAB-SEDDS-dRMsPMB improves uptake by Caco-2 cells most efficiently reaching even ≈100% within 4 h followed by AOT-SEDDS-dRMsPMB with ≈20% and P85-/SL-SEDDS-dRMsPMB with ≈5%. The peptide drug maintains its antimicrobial activity in all SEDDS-dRMsPMB . According to these results, SEDDS containing dRMs might be a game changing strategy for oral peptide drug delivery.

PEG vs. zwitterions: How these surface decorations determine cellular uptake of lipid-based nanocarriers

AIM

To evaluate the impact of polyethylene glycol (PEG) and zwitterionic surface decoration of lipid-based nanocarriers (NC) on cellular uptake.

METHODS

Anionic, neutral and cationic zwitterionic lipid-based NCs based on lecithin were compared with conventional PEGylated lipid-based NCs regarding stability in biorelevant fluids, interaction with endosome mimicking membranes, cytocompatibility, cellular uptake and permeation across intestinal mucosa.

RESULTS

PEGylated and zwitterionic lipid-based NCs exhibited a droplet size between 100 and 125 nm with a narrow size distribution. For the PEGylated and zwitterionic lipid-based NCs only minor alterations in size and PDI in fasted state intestinal fluid and mucus containing buffer were observed, demonstrating similar bioinert properties. Erythrocytes interaction studies revealed enhanced endosomal escape properties for zwitterionic lipid-based NCs compared to PEGylated lipid-based NCs. For the zwitterionic lipid-based NCs negligible cytotoxicity on Caco-2 and HEK cells, even in the highest tested concentration of 1 % (v/v) was recorded. The PEGylated lipid-based NCs showed a cell survival of ≥75 % for concentrations ≤0.05 % on Caco-2 and HEK cells, which was considered as non-toxic. For the zwitterionic lipid-based NCs up to 60-fold higher cellular uptake on Caco-2 cells was determined compared to PEGylated lipid-based NCs. For the cationic zwitterionic lipid-based NCs the highest cellular uptake with 58.5 % and 40.0 % in Caco-2 and HEK cells, respectively, was determined. The results were confirmed visually by life cell imaging. Ex-vivo permeation experiments using rat intestinal mucosa demonstrated up to 8.6-fold enhanced permeation of the lipophilic marker coumarin-6 in zwitterionic lipid-based NCs compared to the control. Up to 6.9-fold enhanced permeation of coumarin-6 in neutral zwitterionic lipid-based NCs compared to the PEGylated counterpart was recorded.

CONCLUSION

The replacement of PEG surfactants with zwitterionic surfactants is a promising approach to overcome the drawbacks of conventional PEGylated lipid-based NCs regarding intracellular drug delivery.

Self-assembly of bile salts and their mixed aggregates as building blocks for smart aggregates

The present communication offers a comprehensive overview of the self-assembly of bile salts emphasizing their mixed smart aggregates with a variety of amphiphiles. Using an updated literature survey, we have explored the dissimilar interactions of bile salts with different types of surfactants, phospholipids, ionic liquids, drugs, and a variety of natural and synthetic polymers. While assembling this review, special attention was also provided to the potency of bile salts to alter the size/shape of aggregates formed by several amphiphiles to use these aggregates for solubility improvement of medicinally important compounds, active pharmaceutical ingredients, and also to develop their smart delivery vehicles. A fundamental understanding of bile salt mixed aggregates will enable the development of new strategies for improving the bioavailability of drugs solubilized in newly developed potential hosts and to formulate smart aggregates of desired morphology for specific targeted applications. It enriches our existing knowledge of the distinct interactions exerted in mixed systems of bile salts with variety of amphiphiles. By virtue of this, researchers can get innovative ideas to construct novel nanoaggregates from bile salts by incorporating various amphiphiles that serve as a building block for smart aggregates for their numerous industrial applications.

Self-assembled phospholipid-based mixed micelles for improving the solubility, bioavailability and anticancer activity of lenvatinib

The clinical efficacy of lenvatinib (LFT) is limited by its poor aqueous solubility and low bioavailability. In this work, LFT-loaded soy phospholipid and sodium glycocholate mixed micelles (LFT-MMs) were prepared through classical co-precipitation. And it was served as an oral administration to address these shortcomings. The preparation conditions were optimized by single-factor experiments. The mass ratio of PC, SGC and LFT, and the species of dispersing media were proved to be decisive factors in controlling the properties of LFT-MMs. The optimal LFT-MMs presented prominent enhancement (500-fold) in LFT solubility, high encapsulation efficiency (87.6 %) as well as suitable stability (>1 month at 4 °C). The biocompatibility of LFT-MMs was estimated by in vitro serum stability measurement and hemolysis test. It showed that serum proteins hardly adhered to the surface of LFT-MMs, and insignificant hemolytic rate (<0.5 %) was observed at the micelles concentration below 1 mg/mL. Cytotoxicity test (MTT assay) was carried out to judge the in vitro antitumor activity. LFT-MMs showed an enhanced inhibitory activity against two main kinds of differentiated thyroid cancer cells over LFT and LFT Mesylate. To estimate the in vivo oral bioavailability of LFT-MMs, SD rats were used as animal model. Notably, the relative bioavailability of LFT-MMs compared with the original form of LFT was 176.7 %. These superior characteristics indicated that the mixed micelles are promising water-soluble formulations suitable for LFT oral delivery.

Phosphatidylserine (PS) and phosphatidylglycerol (PG) enriched mixed micelles (MM): A new nano-drug delivery system with anti-inflammatory potential?

Phosphatidylserine (PS) and phosphatidylglycerol (PG) are naturally occurring phospholipids (PL) with intrinsic anti-inflammatory properties. The therapeutic potential of PS and PG has not been extensively explored and the main focus had been directed towards PS- and PG-liposomes. In order to increase the formulation options, we explored whether mixed micelles (MM) could be an alternative to liposomes. Potential advantages of MM are their thermodynamic stability, small size and ease of manufacture. DOPS- and DOPG-enriched MM were obtained via a co-precipitation technique and physicochemical characterization was performed. The MM, approximately 10 nm in diameter, showed no toxicity on fibroblast cell lines in vitro and virtually no hemolytic activity. The MM suppressed the TNFα-production of mIFNγ/LPS-stimulated mouse peritoneal macrophages (MPM) in vitro similar to DOPS- and DOPG-liposomes. Therefore, DOPS- and DOPG-loaded MM are promising new options for the treatment of inflammatory diseases.

Preparation of hydroxylated lecithin complexed iodine/carboxymethyl chitosan/sodium alginate composite membrane by microwave drying and its applications in infected burn wound treatment

Improving the antibacterial properties of membrane wound dressings of natural polymers is crucial. Iodine is an important safe inorganic antibacterial agent, but was confined in the composition with polymer membranes due to the challenges of homogeneity and stability during drying. In the present work, iodine was complexed with hydroxylated lecithin (HL) to improve its stability and complexing efficiency for the composition with carboxymethly chitosan/sodium alginate. With the aid of microwave drying, hydroxylated lecithin complexed iodine/carboxymethly chitosan/sodium alginate (HLI/CMCS/SA) composite membranes with homogeneously distributions of HLI, high contents of activated iodine, good mechanical and swelling properties, proper water vapor permeability, pH controllable iodine release and excellent antibacterial properties were prepared. The composite membranes exhibited high repairing efficiencies for the infection of a rat model of the seawater immersed wound infection of deep partial-thickness burns. This novel antibacterial composite membrane can be potentially used as a high performance wound dressing for treating and repairing open trauma infections.

Preparation and toxicity evaluation of a novel nattokinase-tauroursodeoxycholate complex

Nattokinase (NK), which has been identified as a potent fibrinolytic protease, has remarkable potential in treatment of thrombolysis, and even has the ability to ameliorate chronic vein thrombosis. To reduce the hemorrhagic risk from an intravenous injection of NK, nattokinase-tauroursodeoxycholate (NK-TUDCA) complex was prepared at different pH values and with different ratios of NK and TUDCA. When assessing survival time, survival state, tail injury, and the body weight of mice, it was found that the NK-TUDCA complex (NK: 10 kIU/ml; TUDCA: 10 mg/ml; pH 5.0) had a lower toxicity when administered at an NK dosage of 130 kIU/kg in the acute toxicity test and 13 kIU/kg in the repeated low-dose challenge. From the results of the in vitro thrombolytic test and characterization of NK-TUDCA, we speculated that the delayed release of NK-TUDCA might be the main cause of toxicity reduction by the complex. This study described the preparation of an NK complex with low toxicity following intravenous administration, which could be utilized for further clinical study of NK.

Ginsenoside Rg3 bile salt-phosphatidylcholine-based mixed micelles: design, characterization, and evaluation

20(R)-Ginsenoside Rg3 (G-Rg3) has good inhibition of tumor angiogenesis and anti-tumor effect. However, its poor aqueous solubility and liposolubility are not ideal for clinical applications. In this study, a G-Rg3 bile salt-phosphatidylcholine-based mixed micelle system (BS-PC-MMS) was prepared. The optimization of G-Rg3 BS-PC-MMS was carried out using response surface methodology based on a central composite design. The encapsulation efficiency (EE) and light transmission (LT) of the optimized formulation were 90.69±2.54% and 99.10±3.12%, respectively. The average particle size of micelles was 20 nm. To increase the stability of G-Rg3 BS-PC-MMS, the lyophilized formulation of micelles was prepared. The G-Rg3 BS-PC-MMS did not produce hemolysis of erythrocytes within a certain concentration range and exhibited a good inhibition of tumor cells. The chick embryo chorioallantoic membrane assay results showed that the G-Rg3 BS-PC-MMS significantly inhibited angiogenesis. The G-Rg3 BS-PC-MMS is thus shown to be a safe, stable, and promising drug delivery system.

Subcutaneously injected ivermectin-loaded mixed micelles: formulation, pharmacokinetics and local irritation study

Clinical application of ivermectin (IVM) is limited by several unfavorable properties, induced by its insolubility in water. Slight differences in formulation may change the plasma pharmacokinetics and efficacy. In this study, an IVM-loaded Soy phosphatidylcholine-sodium deoxycholate mixed micelles (IVM-SPC-SDC-MMs) were developed to improve its aqueous solubility, aiming to make it more applicable for clinical use. First, IVM-SPC-SDC-MMs were prepared using the co-precipitation method. After formulation optimization, the particle size was 9.46 ± 0.16 nm according to dynamic light scattering. The water solubility of IVM in SPC-SDC-MMs (4.79 ± 0.02 mg/mL) was improved by 1200-fold, comparing with free IVM (0.004 mg/mL). After subcutaneous administration, the pharmacokinetic study showed that IVM-SPC-SDC-MMs and commercially available IVM injection were bioequivalent. Also, the local irritation study confirmed that IVM-SPC-SDC-MMs reduced side reactions of the commercially available IVM injection. These results indicated that IVM-SPC-SDC-MMs represented a promising new drug formulation suitable for subcutaneous delivery of IVM.

Effects of phosphatidylethanolamine N-methyltransferase on phospholipid composition, microvillus formation and bile salt resistance in LLC-PK1 cells

Bile salts are potent detergents and can disrupt cellular membranes, which causes cholestasis and hepatocellular injury. However, the mechanism for the resistance of the canalicular membrane against bile salts is not clear. Phosphatidylethanolamine (PE) is converted to phosphatidylcholine (PC) in the liver by phosphatidylethanolamine N-methyltransferase (PEMT). In this study, to investigate the effect of PEMT expression on the resistance to bile salts, we established an LLC-PK1 cell line stably expressing PEMT. By using enzymatic assays, we showed that the expression of PEMT increased the cellular PC content, lowered the PE content, but had no effect on the sphingomyelin content. Consequently, PEMT expression led to reductions in PE/PC and sphingomyelin/PC ratios. Mass spectrometry demonstrated that PEMT expression increased the levels of PC species containing longer acyl chains and almost all ether-linked PC species. PEMT expression enhanced the resistance to duramycin and lysenin, suggesting decreased ratios of PE and sphingomyelin in the apical membrane, respectively. In addition, SEM revealed that PEMT expression increased the diameter of microvilli. The expression of PEMT resulted in reduced resistance to unconjugated bile salts, but surprisingly in increased resistance to conjugated bile salts, which might be attributable to modifications of the phospholipid composition and/or structure in the apical membrane. Because most bile salts exist as conjugated forms in the bile canaliculi, PEMT may be important in the protection of hepatocytes from bile salts and in cholestatic liver injury.

Effect of carrot (Daucus carota) microstructure on carotene bioaccessibilty in the upper gastrointestinal tract. 1. In vitro simulations of carrot digestion

Studies investigating carotene bioaccessibility (release from the food matrix to a solubilized form) directly from plant material during the process of digestion are scarce, mainly due to the difficulties associated with obtaining such material. Therefore, this paper examines the relationship between tissue microstructure and carotene bioaccessibility using an in vitro digestion model. Dietary oil provides a pool for the initial solubilization. Therefore, carotene partitioning into an emulsified oil phase was assessed using raw carrot tissue and carrot tissue subjected to various degrees of heating and particle size reduction and, in all cases, was found to be greatly reduced compared with juiced carrot. Carotene bioaccessibility was found to be greater from raw tissues than heated tissues of the same size. This is because heating increases the propensity for intact cells to separate, effectively encapsulating the carotene. Although the gross structure of the tissues was found to be relatively unaffected by in vitro digestion, at the cellular level some cell-wall swelling and cell death were observed, particularly close to the surfaces of the tissue. This study suggests that cell-wall rupture prior to digestion is an absolute requirement for carotene bioaccessibility in the upper intestine and that heating does not enhance carotene release from intact cells.

Importance of biliary excretion of indomethacin in gastrointestinal and hepatic injury

BACKGROUND AND AIMS

A mechanism for protection of gastrointestinal (GI) and hepatic cells from damaging detergent actions of bile acids appears to involve the bile component, phosphatidylcholine (PC). Non-steroidal anti-inflammatory drugs (NSAIDs) induce intestinal injury in direct proportion to their ability to be excreted into bile, and are known to chemically associate with PC. We investigated the role of bile acids and PC in the mechanism of indomethacin-induced epithelial injury.

METHODS

Rats were injected orally or intravenously with radiolabeled indomethacin and their bile was collected over time for determination of NSAID secretion. Bile from rats treated with or without indomethacin was used in studies of red blood cell (RBC) hemolysis as a measure of membrane cytotoxicity. The bile salt, sodium deoxycholate (SDC), and indomethacin were tested alone and in combination with PC on RBC and on hepatic HepG2 cells.

RESULTS

Intravenously or orally given indomethacin was quantitatively excreted (approximately 50%) into bile over a 2-h study period. Bile from a rat treated with indomethacin or bile with exogenous indomethacin was cytotoxic to RBC, and the injury was prevented by the addition of PC. Hepatocytes exposed to SDC showed injury that could be dose-dependently prevented by PC, and reversed by indomethacin.

CONCLUSIONS

Biliary PC plays an important physiological role in protecting GI and hepatic epithelia from the cytotoxic actions of bile salts. The ability of NSAIDs excreted into the bile to associate with mixed bile salt micelles and reduce the protective action of the PC may be a critical component in the drugs' pathogenic mechanism.

Role of phosphatidylcholine saturation in preventing bile salt toxicity to gastrointestinal epithelia and membranes

BACKGROUND AND AIM

The mechanism which protects the biliary and intestinal mucosa from the detergent properties of bile acids is not fully understood. We employed three contrasting in vitro model systems (human red blood cells, polarized intestinal [Caco-2] cells, and synthetic liposomes), to compare the efficacy of saturated and unsaturated phosphatidylcholine (PC) to protect cells and membranes from bile salt injury.

METHODS

Hemolysis of red blood cells, electrical resistance across confluent monolayers of Caco-2 cells, and disruption of synthetic PC liposomes were assessed after incubation with varying concentrations of bile salt (sodium deoxycholate) alone or in the presence of saturated or unsaturated PC.

RESULTS

The hemolytic activity of deoxycholate on red blood cells was observed at > or =2 mM, and could be blocked by equimolar concentration or greater of both saturated or unsaturated PC. In contrast, exposure of Caco-2 cells to deoxycholate at > or =0.8 mM induced a maximal decrease in resistance, which was reversed by > or =0.8 mM unsaturated PC or 5 mM saturated PC. Similarly, synthetic liposomes were permeabilized by 0.8 mM deoxycholate and were protected by a lower concentration of unsaturated PC (2 mM) than saturated (5 mM).

CONCLUSIONS

Cells can show variable resistance to bile salt toxicity. Extracellular PC, especially in the unsaturated state, can directly protect cell and artificial membranes from bile salt injury. These findings support a role for biliary PC in the formation of mixed micelles that have low cytotoxic properties.

Indomethacin enhances bile salt detergent activity: relevance for NSAIDs-induced gastrointestinal mucosal injury

Gastroduodenal toxicity of nonsteroidal anti-inflammatory drugs (NSAIDs) is partly independent from cyclooxygenase inhibition, possibly related to increased intermixed micellar-vesicular (nonphospholipid-associated) bile salt concentrations thought to be responsible for bile salt cytotoxicity. We evaluated the effects of indomethacin on bile salt cytotoxicity with complementary in vitro and ex vivo systems. In the erythrocyte model, indomethacin alone did not induce hemolysis. In contrast, indomethacin enhanced and phospholipids decreased hemolysis induced by hydrophobic taurodeoxycholate (TDC). Hydrophilic tauroursodeoxycholate (TUDC) enhanced rather than decreased TDC-induced hemolysis in the presence of indomethacin. Indomethacin did not affect intermixed micellar-vesicular bile salt concentrations or compositions. Indomethacin also increased TDC-induced lactate dehydrogenase release in CaCo-2 cells and bile salt-induced rat colonic mucosal injury, and prevented potential protective effects of TUDC in these systems. Our data show that indomethacin enhances bile salt-induced cytotoxicity without affecting intermixed micellar-vesicular bile salt concentrations or compositions. These findings may be relevant for gastroduodenal injury during NSAID therapy.

Solubilization of carotenoids from carrot juice and spinach in lipid phases: II. Modeling the duodenal environment

We have been investigating the factors determining the bioavailability of carotenoids from vegetables. The previous paper [Rich, G.T., Bailey, A.L., Faulks, R.M., Parker, M.L., Wickham, M.S.J., and Fillery-Travis, A. (2003) Solubilization of Carotenoids from Carrot Juice and Spinach in Lipid Phases: I. Modeling the Gastric Lumen, Lipids 38, 933-945] modeled the gastric lumen and studied the solubilization pathway of carotenes and lutein from carrot juice and homogenized spinach to oil. Using the same vegetable preparations, we have extended our investigations to solubilization pathways potentially available in the duodenum and looked at the ease of solubilization of carotenes and lutein within simplified lipid micellar and oil phases present within the duodenum during digestion. Micellar solubility of raw spinach carotenoids was low and was enhanced by freezing, which involved a blanching step. The efficiency of solubilization of carotenoids in glycodeoxycholate micelles decreased in the order lutein(carrot) > lutein(blanched-frozen spinach) > carotene(blanched-frozen spinach) > carotene(carrot). Frozen spinach carotenoids were less soluble in simple micelles of taurocholate than of glycodeoxycholate. The results comparing the solubility of the carotenoids in mixed micelles (bile salt with lecithin) with simple bile salt micelles are explained by the relative stability of the carotenoid in the organelle compared to that in the micelle. The latter is largely determined by the polarity of the micelle. Below their critical micelle concentration (CMC), bile salts inhibit transfer of carotenoids from tissue to a lipid oil phase. Above their CMC, the bile salts that solubilize a carotenoid can provide an additional route to the oil from the tissue for that carotenoid by virtue of the equilibrium between micellar phases and the interfacial pathway. Mixed micellar phases inhibit transfer of both carotenoids from the tissue to the oil phase, thereby minimizing this futile pathway.

Appearance of atypical 3 alpha,6 beta,7 beta,12 alpha-tetrahydroxy-5 beta-cholan-24-oic acid in spgp knockout mice

Bile formation and its canalicular secretion are essential functions of the mammalian liver. The sister-of-p-glycoprotein (spgp) gene was shown to encode the canalicular bile salt export protein, and mutations in spgp gene were identified as the cause of progressive familial intrahepatic cholestasis type 2. However, target inactivation of spgp gene in mice results in nonprogressive but persistent cholestasis and causes the secretion of unexpectedly large amounts of unknown tetrahydroxylated bile acid in the bile. The present study confirms the identity of this tetrahydroxylated bile acid as 3 alpha,6 beta,7 beta,12 alpha-tetrahydroxy-5 beta-cholan-24-oic acid. The data further show that in serum, liver, and urine of the spgp knockout mice, there is a significant increase in the concentration of total bile salts containing a large amount of tetrahydroxy-5 beta-cholan-24-oic acid. The increase in total bile acids was associated with up-regulation of the mRNA of cholesterol 7 alpha-hydroxylase in male mice only. It is suggested that the lower severity of the cholestasis in the spgp knockout mice may be due to the synthesis of 3 alpha,6 beta,7 beta,12 alpha-tetrahydroxy-5 beta-cholan-24-oic acid, which neutralizes in part the toxic effect of bile acids accumulated in the liver.

Mitigation of surfactant erythrocyte toxicity by egg phosphatidylcholine

Polyoxyethylene alkyl ether surfactants have been shown to have excellent penetration enhancing abilities although they are associated with a high level of local toxicity. We have compared the toxicity of a range of polyoxyethylene alkyl ethers (Brij 96, Brij 76, Brij 56, 10 lauryl ether and 9 lauryl ether) to an anionic surfactant (sodium dodecyl sulphate (SDS)), an ampholytic surfactant (lysophosphatidylcholine) and a cationic surfactant (tetradecyltrimethylammonium bromide (TTAB)), in the presence and absence of egg phosphatidylcholine. The toxicity of the surfactants or phospholipid/surfactant mixtures was assessed by measuring haemolytic activity. The test samples were incubated with a suspension of red blood cells for 30 min and Drabkin's reagent was used to indicate the amount of haemoglobin released. All of the polyoxyethylene alkyl ethers, SDS, TTAB and lysophosphatidylcholine exhibited haemolytic activity at concentrations between 0.10 and 0.25 mM. The addition of egg phosphatidylcholine reduced the toxicity for all of the surfactants, with the toxicity of Brij 96 being mitigated to a greater extent than the toxicity of the other polyoxyethylene surfactants examined. The rate of haemolysis induced by Brij 96 or 10 lauryl ether was also reduced by increasing concentrations of phosphatidylcholine. As the phosphatidylcholine content of a mixed surfactant system comprising egg phosphatidylcholine: Brij 96 was replaced by lysophosphatidylcholine and fatty acid, the haemolytic action of the mixture increased markedly. The results from this study show that the toxicity of surfactants to erythrocytes can be mitigated by the addition of egg phosphatidylcholine. Synthetic surfactants combined with phosphatidylcholine may generate drug delivery systems worthy of more extensive investigation.

Cholesterol enhances membrane-damaging properties of model bile by increasing the intervesicular-intermixed micellar concentration of hydrophobic bile salts

Bile salts are potent detergents that, at concentrations attained in bile and intestine, can disrupt cell membranes. Hepatic secretion of vesicles containing lecithin and cholesterol appears to be critical in preventing bile salt damage to hepatobiliary epithelia. We hypothesize that the protective effect of biliary lipids results from lowering of the bile salt intervesicular intermixed micellar bile salt concentration (IMMC) to which epithelial membranes are exposed. We further hypothesize that increases in biliary cholesterol, by reducing association of bile salts with vesicles and mixed micelles, may increase bile toxicity by raising the bile salt IMMC.

METHOD

Large unilamellar lecithin vesicles (100 nm) with varying cholesterol:lecithin molar ratios (C:L) of 0, 0.5, and 1 were added to taurochenodeoxycholate (TCDCA), taurocholate (TCA), or taurodeoxycholate (TDCA) in Tris-buffered saline, pH 7.4. Human erythrocyte ghosts (model target membrane), prepared by osmotic hemolysis and resealed with [14C]inulin trapped inside, were added and incubated at 37 degrees C for 30 min and 4 h. Plasma membrane disruption was quantified by [14C]inulin release and bile salt IMMC was determined by ultrafiltration.

RESULTS

Membrane disruption started at a concentration of 0.5 mM for TDCA, 1 mM for TCDCA, and 2 mM for TCA and was complete within 4 h at concentrations of 1, 2, and 4 mM, respectively. Addition of 2 mM lecithin to 2 mM TDCA, 4 mM TCDCA, or 5 mM TCA reduced or eliminated membrane leakage and lowered the IMMC. For TDCA and TCDCA, the protective effect of vesicles was entirely attributable to reduction in IMMC; in contrast for TCA, the protective effect exceeded that which would have been expected based solely on reduction of the IMMC. Inclusion of cholesterol attenuated the binding of bile salts to vesicles and raised the IMMC, thereby reducing the protective effect of lecithin over the time course of these studies. Although there was loss of phospholipid and cholesterol from the erythrocyte membranes on addition of bile acids even in the presence of vesicles, the ratio of cholesterol to phospholipid in the erythrocyte membrane did not change.

CONCLUSION

Lecithin protects against membrane disruption by hydrophobic bile salts by lowering the IMMC. Cholesterol added to lecithin raises the bile salt IMMC and reduces or eliminates this protective effect. This mechanism of potentiation of bile salt toxicity by cholesterol may be an important contributor to the pathogenesis of gallbladder disease in cholesterol cholelithiasis.