Bile Salt- and Lysophosphatidylcholine-induced Membrane Damage in Human Erythrocytes

Fluorescent hydrophobic ion pairs: A powerful tool to investigate cellular uptake of hydrophobic drug complexes via lipid-based nanocarriers

HYPOTHESIS

Hydrophobic ion pairs (HIPs) between two fluorescent components and incorporation into nanoemulsions (NE) allows tracking in cellular uptake studies.

EXPERIMENTS

HIPs were formed between propidium iodide and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (NBD-PE), azure A chloride and NBD-PE or coumarin 343 and 4-(4-dihexadecylaminostyryl)-N-methylpyridinium iodide) (DiA). Fluorescence spectra of the resulting complexes were recorded. HIPs were loaded into zwitterionic NE and their size, stability in different media, haemolytic properties and cytotoxicity were evaluated. Furthermore, cellular uptake at 37 °C and 4 °C was investigated via flow cytometry and confocal microscopy.

FINDINGS

HIP-formation increased lipophilicity of the hydrophilic model drugs. NE exhibited a size between 80 and 150 nm and were not toxic in concentrations up to 0.1 % but showed high haemolytic properties. Cellular uptake of propidium, azure A and coumarin 343 were 8-fold, 115-fold and 1.3-fold improved by the formation of HIPs and up to 59-fold, 120-fold and 50-fold by incorporating these HIPs in NE, respectively. Lower uptake was observed at 4 °C. In case of propidium/ NBD-PE and azure A/ NBD-PE HIPs, propidium and azure A were delivered into the cytosol, whereas NBD-PE was unable to enter cells. In case of coumarin 343/ DiA HIPs, both components accumulated in the cell membrane. Therefore, HIPs between two fluorescent compounds are a powerful tool to investigate cellular uptake of hydrophobic complexes via nanocarriers by visualization of their cellular distribution.

Biochemical and Hematological Indexes of Liver Dysfunction in Horses

In the present review, the authors, based on the multiple functions performed by the liver, analyze the multiple biochemical and hematological changes as an expression of altered liver function in the horse. The liver performs important metabolic functions related to the synthesis, degradation, and excretion of various substances. Modification of these functions can be evaluated and diagnosed by determining serum concentrations of several serum analytes, including enzymes and other endogenous substances. Hepatocellular enzymes, such as sorbitol dehydrogenase-SDH and glutamate dehydrogenase-GLDH, are released following hepatocellular necrosis. Hepatobiliary enzymes, such as γ-glutamyl transferase-GGT, increase in response to necrosis, cholestasis, and other alterations in bile conducts. Serum concentrations of mainly endogenous and exogenous substances that the liver should synthesize or eliminate, such as proteins (albumin and globulins), bile acids, urea, glucose, total and direct bilirubin, and coagulation factors, and fibrinogen should be included in the liver function test profile. The interpretation of laboratory tests of liver function will allow the diagnosis of functional loss of the organ. Some of the analytes considered provide information on the prognosis of liver disease. This review will provide an accurate and objective interpretation of the common biochemical and hematological tests in use in the diagnosis of equine hepatic disease patients, aiding still further the veterinary activity on the applied equine clinical cases.

Engineering Lipusu by lysophosphatidylcholine for improved tumor cellular uptake and anticancer efficacy

Liposomes have been developed as drug delivery carriers to enhance the antitumor efficiency of the therapeutic agents. Lipusu® (Lip), a paclitaxel (PTX) liposome, has been widely used in the treatment...

Drug Bioavailability Enhancing Agents of Natural Origin (Bioenhancers) that Modulate Drug Membrane Permeation and Pre-Systemic Metabolism

Many new chemical entities are discovered with high therapeutic potential, however, many of these compounds exhibit unfavorable pharmacokinetic properties due to poor solubility and/or poor membrane permeation characteristics. The latter is mainly due to the lipid-like barrier imposed by epithelial mucosal layers, which have to be crossed by drug molecules in order to exert a therapeutic effect. Another barrier is the pre-systemic metabolic degradation of drug molecules, mainly by cytochrome P450 enzymes located in the intestinal enterocytes and liver hepatocytes. Although the nasal, buccal and pulmonary routes of administration avoid the first-pass effect, they are still dependent on absorption of drug molecules across the mucosal surfaces to achieve systemic drug delivery. Bioenhancers (drug absorption enhancers of natural origin) have been identified that can increase the quantity of unchanged drug that appears in the systemic blood circulation by means of modulating membrane permeation and/or pre-systemic metabolism. The aim of this paper is to provide an overview of natural bioenhancers and their main mechanisms of action for the nasal, buccal, pulmonary and oral routes of drug administration. Poorly bioavailable drugs such as large, hydrophilic therapeutics are often administered by injections. Bioenhancers may potentially be used to benefit patients by making systemic delivery of these poorly bioavailable drugs possible via alternative routes of administration (i.e., oral, nasal, buccal or pulmonary routes of administration) and may also reduce dosages of small molecular drugs and thereby reduce treatment costs.

A Lipolytic Lecithin:Cholesterol Acyltransferase Secreted by Toxoplasma Facilitates Parasite Replication and Egress

The protozoan parasite Toxoplasma gondii develops within a parasitophorous vacuole (PV) in mammalian cells, where it scavenges cholesterol. When cholesterol is present in excess in its environment, the parasite expulses this lipid into the PV or esterifies it for storage in lipid bodies. Here, we characterized a unique T. gondii homologue of mammalian lecithin:cholesterol acyltransferase (LCAT), a key enzyme that produces cholesteryl esters via transfer of acyl groups from phospholipids to the 3-OH of free cholesterol, leading to the removal of excess cholesterol from tissues. TgLCAT contains a motif characteristic of serine lipases "AHSLG" and the catalytic triad consisting of serine, aspartate, and histidine (SDH) from LCAT enzymes. TgLCAT is secreted by the parasite, but unlike other LCAT enzymes it is cleaved into two proteolytic fragments that share the residues of the catalytic triad and need to be reassembled to reconstitute enzymatic activity. TgLCAT uses phosphatidylcholine as substrate to form lysophosphatidylcholine that has the potential to disrupt membranes. The released fatty acid is transferred to cholesterol, but with a lower transesterification activity than mammalian LCAT. TgLCAT is stored in a subpopulation of dense granule secretory organelles, and following secretion, it localizes to the PV and parasite plasma membrane. LCAT-null parasites have impaired growth in vitro, reduced virulence in animals, and exhibit delays in egress from host cells. Parasites overexpressing LCAT show increased virulence and faster egress. These observations demonstrate that TgLCAT influences the outcome of an infection, presumably by facilitating replication and egress depending on the developmental stage of the parasite.

Bioactive lysophospholipids generated by hepatic lipase degradation of lipoproteins lead to complement activation via the classical pathway

PURPOSE

We determined bioactivity of lysophospholipids generated by degradation of the low-density (LDL), very low-density (VLDL), and high-density (HDL) lipoproteins with hepatic lipase (HL), cholesterol esterase (CE), and lipoprotein-associated phospholipase A2 (Lp-PLA2).

METHODS

The LDL, VLDL, and HDL were treated with HL, CE, and Lp-PLA2 after immobilization on plates, and complement activation studies were performed with diluted human serum. Complement component 3 (C3) fixation, a marker for complement activation, was determined with a monoclonal anti-human C3d antibody. Enzymatic properties of HL and CE were assayed with triglyceride and phosphatidylcholine substrates for triglyceride hydrolase and phospholipase A activities. The ARPE-19 cells were used for viability studies.

RESULTS

The HL degradation of human lipoproteins LDL, VLDL, or HDL results in the formation of modified lipoproteins that can activate the complement pathway. Complement activation is dose- and time-dependent upon HL and occurs via the classical pathway. Enzymatic studies suggest that the phospholipase A1 activity of HL generates complement-activating lysophospholipids. C-reactive protein (CRP), known to simultaneously interact with complement C1 and complement factor H (CFH), further enhances HL-induced complement activation. The lysophospholipids, 1-Palmitoyl-sn-glycero-3-phosphocholine and 1-Oleoyl-sn-glycero-3-phosphocholine, can be directly cytotoxic to ARPE-19 cells.

CONCLUSIONS

The HL degradation of lipoproteins, known to accumulate in the outer retina and in drusen, can lead to the formation of bioactive lysophospholipids that can trigger complement activation and induce RPE cellular dysfunction. Given the known risk associations for age-related macular degeneration (AMD) with HL, CRP, and CFH, this study elucidates a possible damage pathway for age-related macular degeneration (AMD) in genetically predisposed individuals, that HL activity may lead to accumulation of lysophospholipids to initiate complement activation, with CFH dysregulation exacerbating the effects of this process.

Expression of taurine transporter (TauT) is modulated by heat shock factor 1 (HSF1) in motor neurons of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by progressive paralysis caused by the degeneration of motor neurons throughout the central nervous system. Mutations of the free radical scavenging enzyme Cu/Zn superoxide dismutase 1 (SOD1) are a cause of familial ALS. In the present study, we demonstrated an age-dependent increase in taurine transporter (TauT) immunoreactivity in spinal cord motor neurons of ALS transgenic mice (mutant SOD1 (G93A)) and a similar increase in TauT in spinal motor neurons of patients with ALS. Chromatin immunoprecipitation analysis verified that heat shock factor 1 (HSF1) preferentially occupies the HSF1 binding element in the promoter of TauT under oxidative stress conditions. Knockdown of HSF1 by small interfering RNA reduced the transcriptional activity of TauT. Using [(3)H] taurine, we confirmed that an elevated expression of TauT directly contributes to increased taurine uptake in ALS motor neurons. In addition, we showed that taurine plays an antioxidant role and may prevent motor neuron loss due to oxidative stress in ALS. Our findings suggest that HSF1-induced TauT expression partially protects motor neurons by compensating for constitutive oxidative stress, which is thought to be a key mechanism contributing to the pathogenesis of ALS. Taken together, our results suggest that TauT is a novel pathological marker for stressed motor neurons in ALS and that modulation of TauT and taurine may slow neuronal degeneration in ALS.

Aqueous suspension methods of carbon-based nanomaterials and biological effects on model aquatic organisms

The preparation of aqueous suspensions of carbon-based nanomaterials (NMs) requires the use of dispersing agents to overcome their hydrophobic character. Although studies on the toxicity of NMs have focused primarily on linking the characteristics of particles to biological responses, the role of dispersing agents has been overlooked. This study assessed the biological effects of a number of commonly used dispersing agents on Pseudokirchneriella subcapitata and Ceriodaphnia dubia as model test organisms. The results show that for a given organism, NM toxicity can be mitigated by use of nontoxic surfactants, and that a multispecies approach is necessary to account for the sensitivity of different organisms. In addition to the intrinsic physicochemical properties of NMs, exposure studies should take into account the effects of used dispersing fluids.

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.

Development of simulated intestinal fluids containing nutrients as transport media in the Caco-2 cell culture model: Assessment of cell viability, monolayer integrity and transport of a poorly aqueous soluble drug and a substrate of efflux mechanisms

The purpose of this study was to identify simulated intestinal fluids (SIFs) containing nutrients compatible with the Caco-2 cell culture model and to examine the impact of the identified medium on the transport of a poorly aqueous soluble model compound, estradiol, and a substrate of efflux mechanisms, etoposide. Monolayer integrity was evaluated by transepithelial electrical resistance and cellular viability by release of lactate dehydrogenase to the apical compartment and cellular protein content. It was shown that the viability of Caco-2 cells was enhanced by use of the CO(2) independent nutritional medium, Leibovitz's L-15 compared to Hanks' balanced salt solution. SIF containing 5mM sodium taurocholate and 1.25 mM phosphatidylcholine or lysophosphatidylcholine in Leibovitz's L-15 induced less release of lactate dehydrogenase than the traditional transport medium, HBSS. Addition of lipolysis products, 0.5mM oleic acid and 0.25 mM monoolein, did only cause increase in lactate dehydrogenase in 3 of 12 comparisons. The presence of SIFs in the apical compartment was shown to decrease flux of estradiol due to incorporation of estradiol in micelles and hence a decreased fraction of free estradiol. Further, a concentration dependent increase in the apparent permeability of etoposide was observed from apical to basolateral compartment, which indicated that components in the SIFs affects efflux mechanisms.

Enhancing effect of surfactants on fexofenadine·HCl transport across the human nasal epithelial cell monolayer

The effect of various surfactants (sodium cholate, sodium taurocholate, Tween 80 and Poloxamer F68) on enhancing the transepithelial permeability of fexofenadine.HCl was evaluated in a human nasal epithelial cell monolayer model. The cytotoxicity of the surfactants on the human nasal epithelial cells was evaluated by the MTT assay. A dose-dependent reduction of cell viability was observed at higher than critical micelle concentration (CMC) of the surfactants, and the IC50 of non-ionic surfactants (Tween 80 and Poloxamer F68) was higher than that of ionic surfactants (sodium cholate and sodium taurocholate). The TEER values significantly decreased after 2 h incubation with the ionic surfactants, but were recovered after 24 h in the fresh culture media. Ionic surfactants significantly increased the transepithelial permeability (P(app)) of fexofenadine.HCl compared to the non-ionic surfactants. The reduction of TEER values upon exposing the cell monolayer to the surfactants for 2 h correlated well with the P(app) of fexofenadine.HCl, which suggests that the permeation-enhancing mechanism of the ionic surfactants is by altering the tight junction property of the paracellular pathway. F-actin staining showed that the effect of ionic surfactants on the tight junction is temporary and reversible, which is consistent with the TEER value recovery within 24 h. These results imply that ionic surfactants are potentially useful permeation enhancers for nasal delivery of hydrophilic compounds, such as fexofenadine.HCl. This study also indicated the usefulness of the human nasal epithelial cell monolayer model not only for evaluating the in vitro nasal drug transport but also for studying the mechanism and toxicity of enhancers.

Use of simulated intestinal fluids with Caco-2 cells and rat ileum

In most in vitro studies of oral drug permeability, little attempt is made to reproduce the gastrointestinal lumenal environment. The aim of this study was to evaluate the compatibility of simulated intestinal fluid (SIF) solutions with Caco-2 cell monolayers and Ussing chamber-mounted rat ileum under standard permeability experiment protocols. In preliminary experiments, fasted-state simulated intestinal fluid (FaSSIF) and fed-state simulated intestinal fluid (FeSSIF) solutions based on the dissolution medium formulae of Dressman and co-workers (1998) were modified for compatibility with Caco-2 cells to produce FaS-SIF and FeSSIF "transport" solutions for use with in vitro permeability models. For Caco-2 cells exposed to FaSSIF and FESSIF transport solutions, the transepithelial electrical resistance was maintained for over 4 h and mannitol permeability was equivalent to that in control (Hank's Balanced Salt Solution-treated) cell layers. Scanning electron microscopy revealed that microvilli generally maintained a normal distribution, although some shortening of microvilli and occasional small areas of denudation were observed. For rat ileum in the Ussing chambers, the potential difference (PD) collapsed to zero over 120 min when exposed to the FaSSIF transport solution and an even faster collapse of the PD was observed when the FeSSIF transport solution was used. Electron micrographs revealed erosion of the villi tips and substantial denudation of the microvilli after exposure of ileal tissue to FaSSIF and FeSSIF solutions, and permeability to mannitol was increased by almost two-fold. This study indicated that FaSSIF and FeSSIF transport solutions can be used with Caco-2 monolayers to evaluate drug permeability, but rat ileum in Ussing chambers is adversely affected by these solutions. Metoprolol permeability in Caco-2 experiments was reduced by 33% using the FaSSIF and 75% using the FeSSIF compared to permeability measured using HBSS. This illustrates that using physiological solutions can influence permeability measurements.

The Role of Phospholipid Methylation in 1-Methyl-4-Phenyl-Pyridinium Ion (MPP+)-Induced Neurotoxicity in PC12 Cells

Excessive methylation has been proposed to be involved in the pathogenesis of Parkinson's disease (PD), via mechanisms that involve phospholipid methylation. Meanwhile, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was found to stimulate phospholipid methylation via the oxidized metabolite, 1-methyl-4-phenyl-pyridinium (MPP+), in the rat brain and liver tissues. In the present study, we investigated the effect of MPP+ on phosphatidylethanolamine N-methyltransferases (PENMT) and the potential role of this pathway in MPP(+)-induced neurotoxicity using PC12 cells. The results obtained indicate that MPP+ stimulated phosphatidylethanolamine (PTE) methylation to phosphatidylcholine (PTC) and correspondingly increased the formation of lysophosphatidylcholine (lyso-PTC). Moreover, the addition of S-adenosylmethionine (SAM) to the cell culture medium increases MPP(+)-induced cytotoxicity. The incubation of 1mM MPP+ and various concentrations of SAM (0-4 mM) decreased the viability of PC12 cells from 80% with MPP+ alone to 38% viability with 4 mM SAM for 4 days incubation. The data also revealed that the addition of S-adenosylhomocysteine (SAH), a methylation inhibitor, offered significant protection against MPP(+)-induced cytotoxicity, indicating that methylation plays a role in MPP(+)-induced cytotoxicity. Interestingly, lyso-PTC showed similar actions to MPP+ in causing many cytotoxic changes with at least 10 times higher potency. Lyso-PTC induced dopamine release and inhibited dopamine uptake in PC12 cells. Lyso-PTC also caused the inhibition of mitochondrial potential and increased the formation of reactive oxygen species in PC12 cells. These results indicate that phospholipid methylation pathway might be involved in MPP+ neurotoxicity and lyso-PTC might play a role in MPP(+)-induced neurotoxicity.

Impairment of blood rheology by cholestatic jaundice in human beings

Bilirubin and bile acids may affect erythrocytes. We investigated blood viscosity and erythrocyte structure in patients with cholestatic jaundice ex vivo and studied the short-term effects of bilirubin and bile acids in vitro. Seventeen patients with cholestatic jaundice and controls were studied. Whole-blood viscosity (adjusted hematocrit 45%) at high (94.5 sec(-1)) and low (0.1 sec(-1)) shear rate and plasma viscosity were measured. Erythrocyte structure was assessed in wet preparations of fixed cells. In vitro whole blood was incubated with increasing concentrations of bilirubin (83% conjugated) and bile acids (cholic, lithocholic, deoxycholic, and chenodeoxycholic acid) and the abovementioned investigations were performed. In patients we observed increased whole-blood viscosity at high shear rate (5.82 +/- 0.69 vs 5.04+/- 0.27 mPa. sec, P =.0001), plasma viscosity (1.48 +/- 0.22 vs. 1.23 +/- 0.07 mPa. sec, P =.0004), and fibrinogen level (4.70 +/- 0.98 g/L vs 2.63 +/- 0.21 g/L, P < 0.001) were observed. The incubation of normal erythrocytes in patients' plasma confirmed an increase in blood viscosity at high shear rate. Erythrocytes from patients with jaundice demonstrated a slight degree of stomatocytic shape transformation (P <.0001). In vitro, bilirubin did not affect erythrocyte shape. Cholic and lithocholic acids caused a slight stomatocytic shape transformation, whereas deoxycholic acid and chenodeoxycholic acid influenced neither blood viscosity nor erythrocyte structure. Patients with cholestatic jaundice have increased whole-blood and plasma viscosity and slightly altered red blood cell shape, possibly the result of a combination of increased levels of bilirubin and bile acids plus an acute-phase reaction.

Transbuccal delivery of 2',3'-dideoxycytidine: in vitro permeation study and histological investigation

Permeation of 2',3'-dideoxycytidine (ddC), an ionic compound, through buccal mucosa was investigated in this in vitro study to identify the major permeation barrier within the epithelium of buccal mucosa and explore the feasibility of transbuccal delivery of ddC. In vitro permeation of ddC across porcine buccal mucosa was conducted in isotonic McIlvaine buffer solution (IMB) using in-line flow through diffusion cells at 37 degrees C. Sodium glycodeoxycholate (GDC) was used as the permeation enhancer in the permeation enhancement studies. Light microscopy was used in the histological studies of buccal tissue. The steady-state flux of ddC permeating through buccal mucosa increased linearly (R(2)=0.96, P<0.05) as the donor concentration of ddC was increased from 1 to 20 mg/ml. The permeabilities for the full thickness buccal mucosa, the epithelium, and the connective tissue were determined to be 1.75+/-0.74x10(-7), 2.90+/-1.86x10(-7), and 3.49+/-1.19x10(-6) cm/s, respectively. The permeability of ddC was significantly (P<0.05) enhanced by GDC at a concentration of 4 mM. The histological study revealed that the thickness of epithelium was greatly reduced after buccal tissues were immersed in IMB for 12 and 24 h but the basal lamina remained intact even after 24 h. A bilayer diffusion model was established to quantitatively describe the contributions of the epithelium and the connective tissue to the permeation barrier. In conclusion, ddC permeated through buccal mucosa by passive diffusion over the range of concentrations examined. The basal lamina layer within the epithelium of buccal mucosa acted as an important barrier to the permeation of ddC. GDC effectively enhanced the buccal permeability of ddC. The transbuccal delivery is a potential route for the administration of ddC.

Bioadhesive starch microspheres and absorption enhancing agents act synergistically to enhance the nasal absorption of polypeptides

This paper investigates the effect of starch microspheres on the absorption enhancing efficiency of various enhancer systems in formulations with insulin after application in the nasal cavity of sheep. The enhancers studied were lysophosphatidylcholine, glycodeoxycholate and sodium taurodihydroxyfusidate, a bile salt derivative. The enhancers were selected on the basis of their perceived or proven mechanism of action and worked predominantly by interacting with the lipid membrane. The bioadhesive starch microspheres were shown to increase synergistically the effect of the absorption enhancers on the transport of the insulin across the nasal membrane. Dependent on the potency of the enhancer system the increment in absorption enhancement was shown to be from 1.4 times to 5 times that obtained for the absorption enhancer in solution.

Surface active drugs: self-association and interaction with membranes and surfactants. Physicochemical and biological aspects

Many pharmacologically active compounds are of amphiphilic (or hydrophobic) nature. As a result, they tend to self-associate and to interact with biological membranes. This review focuses on the self-aggregation properties of drugs, as well as on their interaction with membranes. It is seen that drug-membrane interactions are analogous to the interactions between membranes and classical detergents. Phenomena such as shape changes, vesiculation, membrane disruption, and solubilization have been observed. At the molecular level, these events seem to be modulated by lipid flip-flop and formation of non-bilayer phases. The modulation of physicochemical properties of drugs by self-association and membrane binding is discussed. Pathological consequences of drug-membrane interaction are described. The mechanisms of drug solubilization by surfactants are reviewed from the physicochemical point of view and in relation to drug carrying and absorption by the organism.

A comparison of the permeation enhancement potential of simple bile salt and mixed bile salt:fatty acid micellar systems using the CaCo-2 cell culture model

The aim of this study was to compare the permeation enhancing potential and toxicity of simple bile salt and bile salt:fatty acid mixed micellar systems using the CaCo-2 cell culture model. The effects of micellar systems of sodium cholate, (NaC), and sodium taurocholate, (NaTC), on the permeability of the hydrophilic markers, mannitol (182) and polyethylene glycols (PEGS) 900 and 4000, were assessed. Simple micelle systems of the unconjugated bile salt, NaC, caused greater enhancement of the hydrophilic markers than the conjugated bile salt, NaTC. In the case of NaC systems the enhancement was coincident with excess membrane disruption and toxicity as indicated by altered TEERs, TEMs, MTT values, and, the lack of recovery following removal of the enhancer. In contrast, the NaTC systems were less toxic, and, in the simple micelle form the likely mechanism of enhancement of the hydrophilic markers is via a transient effect on the tight junctions. Formation of mixed micellar systems with linoleic acid (LA) accentuated the toxic effects of NaC. In comparison, NaTC:LA mixed micelles showed superior permeability enhancement versus simple micelles without increasing membrane toxicity. The mechanism of enhancement of NaTC:LA appears more complex and involves a possible combination effect on both the paracellular and transcellular routes.

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.

Role of biliary phosphatidylcholine in bile acid protection and NSAID injury of the ileal mucosa in rats

BACKGROUND & AIMS

We explored the role of biliary phosphatidylcholine (PC) in protection of the intestinal mucosa against bile salt (BS)-induced intestinal injury and how this property may be blocked by indomethacin (Indo), a nonsteroidal anti-inflammatory drug (NSAID) that is secreted into the bile.

METHODS

We performed in vivo studies in which bile was collected over a 2-hour period after rats were intragastrically administered Indo (25 mg/kg) or an equivalent volume of saline (controls). The bile samples (some of which were supplemented with PC) were then instilled into a loop of distal ileum of anesthetized rats. After a 30-minute exposure period, we measured the hemoglobin concentration of the ileal loop fluid, as an index of bleeding, and mucosal contact angles, as an index of surface hydrophobicity. A similar in vivo experiment was performed in which model bile containing 5 mmol/L each of the BS, sodium deoxycholate, PC, or Indo, alone and in combination, was instilled into ileal loops. In our in vitro test system, human erythrocytes were exposed to the above biliary constituents, and hemolysis was measured spectrophotometrically.

RESULTS

Bile from Indo-pretreated rats decreased the surface hydrophobicity and induced bleeding of ileal loops in comparison with control bile, and both NSAID-induced changes were reversed if PC was added to the bile. Similarly, synthetic BS caused gastrointestinal bleeding, decreased ileal contact angles, and induced erythrocyte hemolysis, all of which were reversed by addition of equimolar PC. This protective role of PC in both the in vivo and in vitro systems was partially blocked by Indo, although the NSAID had no effect on these properties on its own.

CONCLUSIONS

These findings support the hypothesis that PC protects the intestinal mucosa against injurious actions of BS, possibly by forming less toxic mixed micelles. Indo and perhaps other NSAIDs that enter the bile may damage the mucosa, not by a direct action, but by competing for the available protective PC molecules.

Identification of a taurine transport inhibitory substance in sesame seeds

An ethanol extract from sesame seeds inhibited the taurine uptake in human intestinal epithelial Caco-2 cells. The uptake of such alpha-amino acids as leucine and glutamic acid was not inhibited by the extract, indicating that this inhibition is specific to the taurine uptake. The unknown inhibitor in the sesame extract was purifled by reversed-phase HPLC by monitoring the inhibitory effect on taurine uptake. The isolated substance was identified as lysophosphatidylcholine, linoleoyl (Lyso-PC), by NMR and MS analysis. Lyso-PC inhibited the taurine uptake in a dose-dependent manner with an IC50 value of approximately 200 microM. Although Lyso-PC is known to be a surface active and cell lytic compound, neither damage nor loss of integrity of the Caco2 cell monolayer was apparent after treating with 200 microM Lyso-PC. Inhibition was observed by incubating cells with Lyso-PC for only 1 min prior to the uptake experiments. These results suggest the direct effect of Lyso-PC on the cell membrane to be the main mechanism for this inhibition. Lyso-PC may play a role in the regulation of certain intestinal transporters.

Intranasal insulin delivery and therapy

Intranasal insulin delivery has been widely investigated as an alternative to subcutaneous injection for the treatment of diabetes. The pharmacokinetic profile of intranasal insulin is similar to that obtained by intravenous injection and, in contrast to subcutaneous insulin delivery, bears close resemblance to the 'pulsatile' pattern of endogenous insulin secretion during meal-times. The literature suggests that intranasal insulin therapy has considerable potential for controlling post-prandial hyperglycaemia in the treatment of both IDDM and NIDDM. However, effective insulin absorption via the nasal route is unlikely without employing the help of absorption enhancers or promoters which are able to modulate nasal epithelial permeability to insulin and/or prolong the residence time of the drug formulation in the nasal cavity. This article discusses the structure and function of the nasal cavity, the barriers which prevent nasal insulin absorption and through the use of absorption enhancers or promoters methods by which these barriers may be overcome.

Increasing drug solubility by means of bile salt-phosphatidylcholine-based mixed micelles

Study of the solubilization of commercial grades of soya phosphatidylcholine (SPC) with different purities by bile salts (BS) indicated that only highly pure grades of SPC are suitable for the preparation of clear solutions of BS/SPC-mixed micelles (BS/SPC-MM). The solubilizing capacity of different BS towards SPC increased in the following order; Sodium cholate (SC) < sodium deoxycholate (SDC) < sodium glycocholate (SGC). Moreover, egg phosphatidylcholine (EPC) was solubilized to a higher extent than SPC. Furthermore, the solubility study of different drugs in the prepared MM showed substantial enhancement of solubility, the extent of which is essentially affected by the chemical nature of the drug and the composition of MM. Benzodiazepine drugs such as clonazepam, tetrazepam, diazepam, and lorazepam displayed higher affinity for MM compared with BS alone, whereas steroidal drugs, such as estradiol, prednisolone and progesterone, compared with benzodiazepines, displayed relatively higher affinity for BS alone. The solubilizing capacity of MM for the different drugs was increased to different degrees by the addition of benzyl alcohol which was comparable to the solubility of the drug in pure benzyl alcohol. The interaction between benzyl alcohol and the drug in MM could be proved by NMR.

Effect of polysorbates on drug release from wax matrices

The purpose of this study was to investigate the effect of various types and amounts of polysorbates on potassium chloride release. Potassium chloride, which is a highly water-soluble model drug, was embedded into wax (containing surfactants) to produce a sustained-release dosage form. Various kinds of polysorbates were chosen as surfactants to control the dissolution profile. The release of the model drug was tested by rotating paddle method of USP 23 and the dissolution process was characterized by the Weibull distribution. The surface tension of the aqueous solutions of polysorbates was determined by a computer-controlled Sigma 70 tensiometer. The application of polysorbates in more than 2% concentration did not alter either the release rate of the embedded potassium chloride, or the surface tension values of the aqueous solutions. The results of this study allow the determination of the optimal concentration of polysorbates in the case of the potassium chloride release.

Effects of the bile salt sodium deoxycholate, protamine, and inflammatory mediators on the potassium permeability of the frog nerve perineurium

An electrophysiological method was used to measure the potassium permeability (PK) of the perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens. Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (delta DC) in response to challenge with 100 mM [K+] Ringer was used to assess the K+ permeability of the perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the perineurium was calculated from the published calibration curve relating delta DC to bathing [K+] in desheathed nerves of Abbott et al. (1997). In the control condition, PK was < 1.1 x 10(-6) cm.s-1. The bile salt sodium deoxycholate (DOC, 1-4 mM) caused a dose-dependent increase in PK, which reached a maximum of 1.7 x 10(-5) cm.s-1 after 2-min exposure to 4 mM DOC, but access of K+ to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1-5 mg/ml equals 0.125-6.25 mM) had no effect on PK. Neither histamine (0.4-40 mg/ml), bradykinin (0.1-5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1-5 mg/ml) affected PK. The frog nerve perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood-nerve barrier and the blood-brain barrier.

Carrier effects on biological activity of amphotericin B

Amphotericin B (AmB), the drug of choice for the treatment of most systemic fungal infections, is marketed under the trademark Fungizone, as an AmB-deoxycholate complex suitable for intravenous administration. The association between AmB and deoxycholate is relatively weak; therefore, dissociation occurs in the blood. The drug itself interacts with both mammalian and fungal cell membranes to damage cells, but the greater susceptibility of fungal cells to its effects forms the basis for its clinical usefulness. The ability of the drug to form stable complexes with lipids has allowed the development of new formulations of AmB based on this property. Several lipid-based formulations of the drug which are more selective in damaging fungal or parasitic cells than mammalian cells and some of which also have a better therapeutic index than Fungizone have been developed. In vitro investigations have led to the conclusion that the increase in selectivity observed is due to the selective transfer of AmB from lipid complexes to fungal cells or to the higher thermodynamic stability of lipid formulations. Association with lipids modulates AmB binding to lipoproteins in vivo, thus influencing tissue distribution and toxicity. For example, lipid complexes of AmB can be internalized by macrophages, and the macrophages then serve as a reservoir for the drug. Furthermore, stable AmB-lipid complexes are much less toxic to the host than Fungizone and can therefore be administered in higher doses. Experimentally, the efficacy of AmB-lipid formulations compared with Fungizone depends on the animal model used. Improved therapeutic indices for AmB-lipid formations have been demonstrated in clinical trials, but the definitive trials leading to the selection of an optimal formulation and therapeutic regimen have not been done.

Liquid chromatography determination of liposome components using a light-scattering evaporative detector

Analysis of liposomal components is important in stability testing of formulations. An LC method for the analysis of liposomal components cholesterol, phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine and their lyso-forms was developed. The method uses a light-scattering evaporative detector and isocratic mobile phase. In addition, components of pH-sensitive liposomes, cholesterylhemisuccinate and cationic lipid dimethyldioctadecylammonium bromide used in transfections were determined by the method. The separations were carried out on a Spherisorb S5 NH2 cartridge column or Zorbax NH2 column (25 cm x 4.6 mm, 5 microns particle size). The mobile phase consisted of acetonitrile-methanol-ammonium acetate solution (pH 4.8, 0.1 M) (52:32:16, v/v/v) at a flow rate of 2 ml min-1. Detection limits were 1.3-8.0 micrograms ml-1 depending on the lipid. The precision (RSD) of the method was 1.5-3.3% for lipid standard solutions at 50 micrograms ml-1 concentration and 2.0-11.8% for lipids analyzed from liposome suspensions.

Effect of formulation additives upon the intranasal bioavailability of a peptide drug: tetracosactide (ACTH1-24)

Nasal absorption of tetracosactide (ACTH1-24; Synacthen) was evaluated in anesthetized rats and compared to intravenous and intramuscular (i.m.) administration. The effect of formulation additives on tetracosactide bioavailability was studied following modification of nasal saline solution. Poloxamer 407 (Pluronic F-127) was used as a vehicle for drug sustained release, whereas sodium glycocholate and bacitracin were used as enhancers. Tetracosactide plasma levels were monitored with radioimmunoassay. Nasal bioavailability was low (4.4%) compared to i.m. (24%). Poloxamer 407 addition did not improve drug kinetics profiles and showed a non-significant decrease in bioavailability (4%). On the other hand, both enhancers effectively increased tetracosactide nasal absorption. The sodium glycocholate effect was very fast (Tmax = 5 min), but did not last long. Moreover, absorption was increased threefold compared to the simple formulation. On the other hand, maximum tetracosactide levels in plasma were reached after 15 min for the formulation containing bacitracin as enhancer, and tetracosactide bioavailability was strongly increased, to 24%, i.e., as much as after an i.m. injection.

Treatment of murine candidiasis and cryptococcosis with amphotericin B incorporated into egg lecithin-bile salt mixed micelles

Amphotericin B (AmB) with deoxycholate (Fungizone) and AmB incorporated into mixed micelles (AmB-mixMs) composed of egg lecithin with glycocholate, deoxycholate, or taurocholate were compared as treatments for murine infections. For mice infected with Candida albicans, treatment consisted of a single intravenous injection; for mice infected with Cryptococcus neoformans, treatment consisted of two intravenous injections. The maximal tolerated doses of AmB as Fungizone were 1.25 mg/kg of body weight in mice with candidiasis and 2.5 mg/kg of body weight in mice with cryptococcosis. The AmB-mixMs were nontoxic to mice at doses of 80 and 100 mg/kg of body weight and were therapeutically more active than the maximal tolerated dose of Fungizone in both models of infection. However, when Fungizone or AmB-mixMs were administered at equivalent doses of AmB, AmB-mixMs were more active in treating murine candidiasis, whereas Fungizone was more active in treating murine cryptococcosis.

The mitigating effects of phosphatidylcholines on bile salt- and lysophosphatidylcholine-induced membrane damage

The effects, at pH 7.0, of a series of 0.2 mM phosphatidylcholines (PC), namely dicaproyl-PC (DCPC), didecanoyl-PC (DDPC), dilauroyl-PC (DLaPC), dimyristoyl-PC (DMPC), dipalmitoyl-PC (DPPC), dioleoyl-PC (DOPC) and dilinoleoyl-PC (DLPC) and a series of 0.2 mM fatty acid salts (namely sodium myristate, palmitate, stearate, oleate and linoleate) upon the erythrocyte haemolysis induced by 2 mM sodium taurodeoxycholate (STDC) were determined. The influence of egg PC and dihexadecyl phosphate (DHDP) concentration upon the haemolysis induced by 1.4 mM sodium deoxycholate (SDC), 2 mM STDC and 0.1 mM lysophosphatidylcholine (LPC) were also established. A bile salt:egg PC mole ratio of 0.5 virtually abolished the haemolysis induced by SDC and STDC, whereas the same ratio of LPC:egg PC only reduced haemolysis from 65 to 40% (maximum haemolysis). DHDP had no effect on the haemolytic action of SDC or STDC. The salts of the fatty acids were non-haemolytic, and when mixed with STDC did not affect the level of haemolysis induced by the bile salt. In contrast, DDPC and DLaPC enhanced the haemolysis of STDC and DCPC had no effect, whereas DMPC, DPPC, DSPC, DOPC, DLPC and egg PC all reduced haemolysis. Maximum reduction was determined for DMPC and egg PC. The mixed micelle preparation temperature (either room or 60 degrees C) and temperature of incubation (either 20 degrees C for 30 min or 37 degrees C for 5 min) had only minor effects on the net haemolysis induced by STDC. These findings may be of significance in understanding the aetiology of certain gastrointestinal diseases and in determining whether mixed bile salt micelles have a role as drug penetration enhancers.