Calcium enhances the hemolytic action of bile salts

Effect of Bile on Hemodynamics and Blood Micro-Rheological Parameters in Experimental Models of Bilhemia

As a rare complication of liver injury and certain interventions, bile can enter the bloodstream depending on the pressure gradient, resulting in bilhemia. Its micro-rheological and hemodynamic effects are still unclear. We aimed to study these parameters in experimental bilhemia models. Under general anesthesia, via laparotomy, bile was obtained by gallbladder puncture from pigs and by choledochal duct cannulation from rats. In vitro, 1 µL and 5 µL of bile were mixed with 500 µL of anticoagulated autologous blood. The systemic effect was also assessed (i.v. bile, 200 µL/bwkg). Hemodynamic and hematological parameters were monitored, and red blood cell (RBC) deformability and aggregation were determined. RBC deformability significantly decreased with the increasing bile concentration in vitro (1 µL: p = 0.033; 5 µL: p < 0.001) in both species. The RBC aggregation index values were concomitantly worsened (1 µL: p < 0.001; 5 µL: p < 0.001). The mean arterial pressure and heart rate decreased by 15.2 ± 6.9% and 4.6 ± 2.1% in rats (in 10.6 ± 2.6 s) and by 32.1 ± 14% and 25.2 ± 11.63% in pigs (in 48.3 ± 18.9 s). Restoration of the values was observed in 45 ± 9.5 s (rats) and 130 ± 20 s (pigs). Bilhemia directly affected the hemodynamic parameters and caused micro-rheological deterioration. The magnitude and dynamics of the changes were different for the two species.

Ileal bile acid transporter inhibition in Cyp2c70 KO mice ameliorates cholestatic liver injury

Cyp2c70 is the liver enzyme in rodents responsible for synthesis of the primary 6-hydroxylated muricholate bile acid (BA) species. Cyp2c70 KO mice are devoid of protective, hydrophilic muricholic acids, leading to a more human-like BA composition and subsequent cholestatic liver injury. Pharmacological inhibition of the ileal BA transporter (IBAT) has been shown to be therapeutic in cholestatic models. Here, we aimed to determine if IBAT inhibition with SC-435 is protective in Cyp2c70 KO mice. As compared to WT mice, we found male and female Cyp2c70 KO mice exhibited increased levels of serum liver injury markers, and our evaluation of liver histology revealed increased hepatic inflammation, macrophage infiltration, and biliary cell proliferation. We demonstrate serum and histologic markers of liver damage were markedly reduced with SC-435 treatment. Additionally, we show hepatic gene expression in pathways related to immune cell activation and inflammation were significantly upregulated in Cyp2c70 KO mice and reduced to levels indistinguishable from WT with IBAT inhibition. In Cyp2c70 KO mice, the liver BA content was significantly increased, enriched in chenodeoxycholic acid, and more hydrophobic, exhibiting a hydrophobicity index value and red blood cell lysis properties similar to human liver BAs. Furthermore, we determined IBAT inhibition reduced the total hepatic BA levels but did not affect overall hydrophobicity of the liver BAs. These findings suggest that there may be a threshold in the liver for pathological accretion of hydrophobic BAs and reducing hepatic BA accumulation can be sufficient to alleviate liver injury, independent of BA pool hydrophobicity.

Long-circulating perfluorooctyl bromide nanocapsules for tumor imaging by 19FMRI

PLGA-PEG nanocapsules containing a liquid core of perfluorooctyl bromide were synthesized by an emulsion-evaporation process and designed as contrast agents for (19)F MRI. Physico-chemical properties of plain and PEGylated nanocapsules were compared. The encapsulation efficiency of PFOB, estimated by (19)F NMR spectroscopy, is enhanced when using PLGA-PEG instead of PLGA. PLGA-PEG nanocapsule diameter, measured by Dynamic Light Scattering is around 120 nm, in agreement with Transmission Electron microscopy (TEM) observations. TEM and Scanning Electron Microscopy (SEM) reveal that spherical core-shell morphology is preserved. PEGylation is further confirmed by Zeta potential measurements and X-ray Photoelectron Spectroscopy. In vitro, stealthiness of the PEGylated nanocapsules is evidenced by weak complement activation. Accumulation kinetics in the liver and the spleen was performed by (19)F MRI in mice, during the first 90 min after intravenous injection. In the liver, plain nanocapsules accumulate faster than their PEGylated counterparts. We observe PEGylated nanocapsule accumulation in CT26 xenograft tumor 7 h after administration to mice, whereas plain nanocapsules remain undetectable, using (19)F MRI. Our results validate the use of diblock copolymers for PEGylation to increase the residence time of nanocapsules in the blood stream and to reach tumors by the Enhanced Permeation and Retention (EPR) effect.

Purification of PEGylated nanoparticles using tangential flow filtration (TFF)

A tangential flow filtration system was evaluated to purify PEGylated nanoparticles. Two widely used surfactants, PVA and sodium cholate were efficiently removed from an empty nanoparticles suspension using the proposed system. During drug loading, surfactant (PVA) was observed to be entrapped within the core of the nanoparticle to a higher extent, hence was purified at a comparatively slower rate. The presence of dextran sulfate enhanced the drug loading but also resulted in reduced purification rate; this was described by the hypothesis of PVA inclusion within the core of the nanoparticles. Practically, it was possible to correlate the slow purification rate of PVA to its reduced filtration flow during the purification of the empty and loaded nanoparticles containing dextran sulfate. Indirectly, this system was capable of revealing the influence of an excipient and drug on the nanoparticle surface.

A new method for the determination of the cytotoxicity of bile acids and aqueous phase of stool: the effect of calcium

Soluble secondary bile acids in the colon are supposed to be cytotoxic for normal colonic cells, resulting in an increased compensatory proliferation of colonic crypt cells, which is associated with an increased risk for colonic cancer. We developed a sensitive method to determine cytotoxicity of bile acids in the HT-29 colon cancer cell line, using a tetrazolium-based colorimetric assay. Only in vital cells, tetrazolium-salts are converted into formazan, which can be measured easily. Chenodeoxycholic acid and deoxycholic acid (DCA) were cytotoxic in concentrations above 100 microM, which is in the physiological range for soluble DCA in faeces. Conjugation of bile acids diminished cytotoxicity 7-10 fold. In this concentration range, no effect of calcium or calcium phosphate was demonstrated, suggesting that the effect of calcium on colonic proliferation is not mediated by a precipitation of soluble bile acids in the large bowel. Finally, we could demonstrate a significant correlation between the cytotoxicity of the aqueous phase of faeces and the soluble DCA concentration.

Taurine-conjugated bile acids act as Ca2+ ionophores

The ionophoretic properties of several taurine-conjugated bile acids have been investigated in two experimental systems: in a two-phase bulk partitioning system and in proteoliposomes. In the former, a bile acid/Ca2+ complex was extracted into the bulk organic phase and had an experimental stoichiometry of 1.75. Extraction was specific for Ca2+ over Mg2+; Na+ and K+ did not compete with the extraction of Ca2+. In the second system, bile acids at concentrations as low as 5-100 molecules/vesicle lowered the steady-state Ca2+ gradient maintained by a reconstituted sarcoplasmic reticulum Ca(2+)-ATPase. The effect was not due to nonspecific membrane perturbation. In addition to releasing intravesicular Ca2+ in a transmembraneous process, bile acids caused partition of Ca2+/bile acid complexes into the hydrophobic core of the bilayer. In both experimental systems, the Ca2+ ionophoretic activity correlated well with the concentration and the hydrophobicity of the bile acid. Taurolithocholate was most active, with a significant effect measurable at 10 microM in either system. Since bile acid concentrations equal to those used in our experiments can occur in the blood in certain liver diseases, the results support the notion that bile acids can increase the intracellular Ca2+ concentration bypassing the regulatory systems that maintain cellular Ca2+ homeostasis.

Protective effect of tauroursodeoxycholate against chenodeoxycholate-induced damage to cultured rabbit gastric cells

Ursodeoxycholate (UDC) and tauroursodeoxycholate (TUDC) have been reported to be protective against liver injury induced by other bile salts. UDC also has been shown to be effective against refluxed bile-induced gastritis after gastric surgery. However the mechanism of the therapeutic effect of UDC on gastric mucosa has not been known. In the present study, cytoprotective actions of UDC and TUDC against chenodeoxycholate (CDC)-induced gastric injury were investigated using rabbit gastric cell cultures without systemic factors. Rabbit gastric mucosal cells were cultured after the isolation of rabbit gastric cells with collagenase and ethylenediaminetetraacetic acid. Cytotoxicity was quantified by measuring 51Cr release from prelabeled cells and MTT assay. Prostaglandin (PG) E2 was assayed by radioimmunoassay. Concentrations of CDC greater than 0.5 mM or UDC greater than 5 mM caused cellular damage and increased 51Cr release in a dose-dependent and time-dependent fashion, while TUDC up to 10 mM did not. TUDC, but not UDC, showed a significant decrease of CDC (1.5 mM)-induced 51Cr release dose dependently. The protective effect of TUDC against CDC-induced damage was confirmed by MTT assay. On phase-contrast microscopy, disruption of monolayers induced by CDC (1.5 mM) was clearly protected by TUDC (10 mM). Free radical scavengers (500 units/ml of superoxide dismutase, 300 units/ml of catalase, and 100 mM of dimethyl sulfoxide) or a calcium blocker (10(-7)-10(-5) M verapamil) did not show significant protection against CDC-induced damage. Deprivation of Ca2+ in the media did not affect CDC-induced damage. Thus free radicals or Ca2+ might not be involved in the cell toxicity of CDC.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile salt-induced intracellular Ca++ accumulation in type II pneumocytes

The pathogenesis of pneumonitis associated with meconium aspiration is poorly understood. To explore the possibility of pulmonary cytotoxicity in association with bile salt exposure and calcium accumulation, we compared cell viability, radiolabeled calcium accumulation, and intracellular [calcium] in the presence and absence of bile salts, chenodeoxycholate, and 3 beta-OH-5-cholenoate. We assessed viability of type II pneumocytes in culture by cell permeability to trypan blue dye, incorporation of leucine into cellular proteins, and cellular morphology. Intracellular calcium concentrations were monitored with fluorescent dye methodology. At micromolar concentrations, the above bile salts increased cell permeability by as much as 9-fold and decreased leucine incorporation by as much as 5-fold. Radiolabeled calcium accumulation increased by as much as 2.5-fold and intracellular [calcium] transiently increased by as much as 6-fold. Studies using bile salts extracted from meconium yielded similar results. Correlation of calcium accumulation to viability studies yielded a direct relationship with cell permeability and an inverse relationship with leucine incorporation. We speculate that bile salt-induced accumulation of intracellular calcium in lung cells may contribute to the pathogenesis of meconium aspiration pneumonitis.

Influence of individual bile acids in Escherichia coli peritonitis

Previous studies have shown that intraperitoneal bile increases bacterial growth and mortality in Escherichia coli peritonitis in the rat. The purpose of the present study was to determine a) the influence of bile acids (cholic, deoxycholic, or chenodeoxycholic) and bilirubin on survival, bacterial growth, and superoxide release by peritoneal phagocytes in this model, and b) the effect of bile acids on bacterial growth and endotoxin release when incubated with E. coli in vitro. Each of the bile acids aggravated the E. coli peritonitis, with increased bacterial counts in the peritoneal cavity and in blood and increased mortality. Deoxycholic acid was the most deleterious of the bile acids, causing suppression of superoxide release by peritoneal phagocytes, like whole bile. In vitro, bile acids did not seem to affect growth of E. coli, but cholic and deoxycholic acid seemed to enhance the release of endotoxin. It is concluded that the bile acids are responsible for the noxious effect of bile in E. coli peritonitis. It is suggested that the detergent properties of bile acids aggravate the peritonitis by solubilizing the cell membranes of both bacteria and phagocytes.

The pH dependence of the hemolytic potency of bile salts

The membrane damaging potential of dilute solutions of bile salts was evaluated by monitoring continuously the hemolysis of a small sample of red blood cells (RBC) introduced into a defined media containing the bile salts at various pH values. The strength of the hemolytic bile salt was characterized by the rate of the induced hemolysis and by the time that elapsed between the introduction of the RBC sample into the bile salt containing solution and the onset of hemolysis. The potency of the unconjugated bile acids was extremely sensitive to pH, e.g. the rate of hemolysis caused by a 7.5 mM cholate was 1.5%, 20% and 64% per min when the pH of the solution was 7.65, 7.3 and 6.85, respectively. At low pH values the membrane damaging effects of deoxycholate was clearly discerned at micromolar concentration range. The hemolytic potency of glycodeoxycholate was also enhanced significantly by lowering the pH. The taurine-conjugated cholate and deoxycholate were only slightly sensitive to variations in pH. Taurocholate at concentrations that were not hemolytic greatly enhanced the injurious potency of deoxycholate. These results imply that in acidic solutions the presence of bile acids can cause damage to cell membranes. It is suggested that the acidic environment in the proximal duodenum and acidosis developed during hypoxia in the liver are two situations in which the bile salts may constitute a pathogenic factor.

The order of hepatic cytotoxicity of bile salts in vitro does not agree with that examined in vivo in rats

Using an enzyme release from isolated rat hepatocytes incubated with a bile salt as a marker, the cytotoxic order of bile salts was found to be taurochenodeoxycholate, glycochenodeoxycholate greater than tauroursodeoxycholate, glycoursodeoxycholate, cholate greater than taurocholate, glycocholate. Thus, the cytotoxicity of conjugates of ursodeoxycholate was greater than that of conjugates of cholate. However, these data do not agree with the order of cytotoxicity of these bile salts previously studied in vivo by the authors which demonstrated the least cytotoxic nature of conjugates of ursodeoxycholate.

Taurocholate increases the biliary output of bilirubin pigments in the rat, due to haemolysis

In order to investigate the effect of bile salts on the biliary transport of bilirubin, we infused rats with taurocholate at 1-3 mumol/min/kg body weight. When administered in saline, taurocholate induced haemolysis, and a dose-dependent increase in biliary excretion and serum concentration of all bilirubin pigments. The addition of human or rat serum albumin to the infusate, at an albumin:taurocholate molar ratio equal to or above 200, completely prevented haemolysis and the above-mentioned alterations in bilirubin transport, without any change in the bile acid output. In order to mimic a haemolytic condition, an erythrocyte haemolysate was further added to the taurocholate-albumin solution. This again resulted in an increased bilirubin output. We suggest that taurocholate treatment increases bilirubin output due to the increased load of the pigment on the liver, as a result of the bile acid-induced haemolysis.

Bile salt-induced calcium fluxes in artificial phospholipid vesicles

The ionic permeability of selected biological membranes is increased by bile salts. To examine changes in calcium permeability during the exposure of artificial membranes to bile salts, we investigated calcium uptake by unilamellar and multilamellar phospholipid vesicles. In the presence of 750 microM taurodeoxycholate, uptake of radiolabelled calcium by unilamellar vesicles increased 2.5-fold over control values. Calcium uptake by multilamellar vesicles as measured with a free calcium indicator, arsenazo III, increased 2.2- or 21-fold in the presence of 60 microM lithocholate or 3 beta-hydroxy-5-cholenoate, respectively. Results were directly influenced by experimental variables such as bile salt hydrophobicity, external calcium concentration, and the bile salt/lipid molar ratio. Observed membrane solubilization was minimal despite increased calcium permeability. Comparison of radiolabelled calcium uptake with radiolabelled sodium or radiolabelled rubidium uptake indicated that bile salt-dependent calcium uptake was 60-140-times greater than bile salt-dependent uptake of either monovalent cation. In an effort to delineate forces affecting calcium translocation, vesicles were exposed either to valinomycin, which induced an electrochemical gradient across the membrane, or to nigericin, which induced a proton gradient. Exposure to valinomycin minimally influenced bile salt-induced calcium uptake while exposure to nigericin significantly promoted uptake by 40-70%. The results suggest that bile salts promote calcium uptake by a mechanism which may be similar to those of other carboxylic ionophores.