Solution properties of taurine and glycine conjugates of fusidic acid and its derivatives

The activation of cystacanths of Polymorphus minutus (Acanthocephala) in vitro

The factors responsible for stimulating activation of cystacanths of Polymorphus minutus in vitro have been investigated. Under the conditions used, the optimum temperature for activation was found to be 42–44 °C, at a pH of 7·0. A marked enhancement of activation rate was observed after preincubation in a 1 mM solution of sodium taurocholate and in solutions of sodium cholate, sodium glycocholate or sodium deoxycholate. This apparent effect of bile salts has been compared with that of other detergents, and a significant enhancement of activation rate above control was observed with saponin and sodium fusidate. Trypsin did not affect the rate of activation, and some inhibition occurred with lipase. The osmotic pressure of the surrounding medium has an effect on activation, the rate of which varies inversely with osmolarity. The conditions for activation in vitro are compared with those of the physicochemical environment in vivo.

In vitro evidence that phospholipid secretion into bile may be coordinated intracellularly by the combined actions of bile salts and the specific phosphatidylcholine transfer protein of liver

Using model systems, we explored a potential function of hepatic phosphatidylcholine transfer protein to extract biliary-type phosphatidylcholines from intracellular membranes (e.g., smooth endoplasmic reticulum) and deliver them to canalicular plasma membranes where biliary secretion occurs. We measured transfer rates of parinaroyl phosphatidylcholine, a naturally fluorescent phospholipid, from small unilamellar vesicles composed of sn-1 palmitoyl, sn-2 parinaroyl phosphatidylcholine, and egg yolk phosphatidylcholine (molar ratio 75:25) wherein the fluorophore is self-quenched to small unilamellar vesicles composed of phosphatidylethanolamine, sphingomyelin, phosphatidylserine, phosphatidylinositol, and cholesterol (molar ratios 22:22:10:8:38) representing model microsomal and canalicular plasma membranes, respectively. Following addition of phosphatidylcholine transfer protein (purified from bovine liver), fluorescence intensity increased exponentially indicating net phosphatidylcholine transfer from donor to acceptor vesicles. Submicellar concentrations of a wide hydrophobicity range of common and uncommon taurine and glycine conjugated bile salts species (anionic steroid detergent-like molecules), sodium taurofusidate (a conjugated fungal bile salt analog), and sodium dodecyl sulfate and octylglucoside, anionic and nonionic straight chain detergents, respectively, markedly stimulated phosphatidylcholine transfer protein activity. This 40-115-fold effect was most pronounced for the common bile salts and correlated positively with bile salt hydrophobicity. Thermodynamic analysis of net transfer revealed that the rate-limiting step was extraction of phosphatidylcholine molecules from donor vesicles and that bile salts facilitated their capture by enhancing both phosphatidylcholine transfer protein binding as well as perturbing phospholipid packing in vesicle bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Intranasal bioavailability of insulin powder formulations: effect of permeation enhancer-to-protein ratio

The intranasal administration of powder formulations containing insulin and the permeation enhancer sodium tauro-24,25-dihydrofusidate (STDHF) were investigated in the sheep model. Both the hypoglycemic response and the serum insulin levels increased as the mole ratio of STDHF to insulin was increased from 0 to 16.8. In vitro dissolution rates of the powders and the rapid tmax (approximately 5 min) observed after intranasal administration suggest that the absorption of insulin is not dissolution limited. The bioavailabilities (F) of the powder formulations ranged from 2.9 to 37.8%. In comparison, the F values for a solution formulation with a STDHF:insulin ratio of 8.4 administered as either drops or spray were 15.7 and 37.4%, respectively. The permeation enhancer STDHF increases mucosal permeability and reduces the average molecular weight of the insulin species.

The effect of sodium tauro-24,25-dihydrofusidate on the nasal absorption of human growth hormone in three animal models

The ability of a novel permeation enhancer, sodium tauro-24,25-dihydrofusidate (STDHF), to increase the systemic delivery of human growth hormone (hGH) after intranasal administration was investigated in rat, rabbit, and sheep. Formulations of hGH with STDHF exhibited greatly enhanced nasal absorption at concentrations of STDHF above its critical micelle concentration. The increase in bioavailability was 11-fold in rats and in rabbits and 21-fold in sheep for formulations containing 0.5% STDHF as compared to those without STDHF. Glycocholate or taurocholate at 0.5% was three to five times less effective than STDHF at enhancing hGH absorption in rats. Additionally, the pulsatile absorption kinetics observed after intranasal delivery more closely resemble the endogenous secretory pattern of hGH than those obtained following subcutaneous administration.

Effects of sodium taurodihydrofusidate on nasal absorption of insulin in sheep

To investigate the utility of a novel adjuvant, sodium taurodihydrofusidate (STDHF), as an enhancer of mucosal permeation of drugs, experiments involving intranasal insulin:STDHF administration in sheep were performed. Rabbit erythrocyte lysis assays were employed to assess the relative membrane lytic activity of STDHF, as well as that of its glycine-conjugated analogue, compared with a nonionic detergent and a common bile salt. Equivalent weight concentrations of the fusidates were found to be 5- to 10-fold less lytic than the bile salt and at least 100-fold less lytic than the nonionic detergent laureth-9. Provided the concentration of STDHF was greater than its critical micellar concentration, formulations of insulin with STDHF greatly enhanced intranasal insulin absorption. Optimal nasal insulin absorption was attained at a molar ratio of STDHF to insulin of 5:1. In addition, intranasal absorption was linearly related to insulin dose. Compared with intravenous administration, the mean bioavailability of intranasal insulin was 16.4%. Interovine variability was low, with a coefficient of variation of 14% for 12 animals. It was found that intranasal absorption of sodium insulin was not significantly different from that of zinc insulin. However, formulations of both crystalline insulin preparations were absorbed more efficiently than a formulation prepared using commercially available solutions of U-500 insulin. The results taken together indicate that STDHF is an excellent enhancer of insulin absorption from the nasal mucosa.

Regulation of 3-hydroxy-3-methylglutaryl CoA reductase by analogs of cholesterol and bile acids in cultured intestinal mucosa

Sodium fusidate and its glycine conjugate, which have the same detergent properties as bile acids, significantly (p less than 0.05) stimulate HMG-CoA reductase of cultured intestine below the critical micellar concentration (CMC) without affecting brush border enzymes. Above CMC, both amphiphiles are cytotoxic. At concentrations between 1 and 5 mM, sodium fusidate decreased cholesterol contents of cultured mucosa (P less than 0.05), the increase in synthesis only partially compensating for the sterol loss. Oxygenated sterols, 7-keto- and 25-hydroxycholesterol, also depleted mucosal cholesterol at 0.5 mM, exerting their effect differently by inhibiting HMG-CoA reductase (p less than 0.01). In contrast to their marked effect on total mucosal cholesterol contents, brush border cholesterol was unaffected by both cholesterol and bile acid analogs.

Influence of taurocholate, taurochenodeoxycholate, and taurodehydrocholate on sulfobromophthalein transport into bile

To test the hypothesis that incorporation of sulfobromophthalein (BSP) into mixed micelles could account for the increase in its biliary transport maximum (Tmax) by bile salts, we have compared in hamsters the influence on BSP Tmax of taurocholate and taurochenodeoxycholate (two micelle-forming physiological bile salts) to that of taurodehydrocholate, a bile salt which, in vitro, does not form micelles. In a first series of experiments, it was observed that taurocholate and taurochenodeoxycholate increased the secretion of phospholipid (40 and 53%, respectively), and cholesterol (50 and 110%, respectively), whereas taurodehydrocholate decreased the secretion of phospholipid (-31%) and cholesterol (-43%). This result suggests that, in vivo, taurodehydrocholate or its metabolites do not form mixed micelles. In a second series of experiments, it was seen that the three bile salts induced a similar increase in BSP Tmax (63% with taurocholate, 52% with taurochenodeoxycholate, and 51% with taurodehydrocholate). These results provide circumstantial evidence for the hypothesis that mixed micelle formation is not an important determinant of maximal BSP secretion into bile.

Interaction of fusidates with bile acid uptake by isolated rat hepatocytes

The interaction of fisidic acid and two of its conjugates with carrier-mediated uptake of bile acids was investigated in isolated rat hepatocytes. All three fusidates inhibited the uptake of both cholate and taurocholate competitively suggesting a direct interaction of fusidates with bile acid carrier. The inhibition constants for all three fusidates for the inhibition of cholate uptake were significantly different from the respective inhibition constants for the inhibition of taurocholate uptake. This would indicate that both cholate and taurocholate are transported by more than one carrier into hepatocytes. The results may also indicate that taurine conjugated bile acids may be transported preferentially by one transport system while unconjugated bile acids may be preferentially transported by another transport system.

The specificity of bile salts in the intestinal absorption of micellar cholesterol in the rat

1. Two aspects of cholesterol absorption; (a) the importance of solubilization and (b) the effects of different bile salts on the mucosal metabolism and lymphatic output of cholesterol, have been investigated using two different in vivo techniques. 2. Bile diverted lymph fistula rats were infused intraduodenally at a steady rate with a constant lipid mixture containing labelled cholesterol, labelled oleic acid and mono-olein. The lipids were completely solubilized in either bile salts or a non-toxic non-ionic detergent, Pluronic F68. Labelled fatty acid was efficiently absorbed from either micellar infusate but virtually no labelled cholesterol appeared in the lymph in the absence of bile salts. 3. Short-term perfusions of the intestine of anaesthetized rats with the same micellar perfusates as above showed approximately 20% of the labelled cholesterol in the mucosa after 30 min perfusion with the bile salt micellar solutions. When the non-ionic micelles were used virtually no isotopic cholesterol left the lumen. 4. Mucosal uptake of labelled cholesterol was linearly dependent on the concentration of solubilized cholesterol in the perfusate and was not dependent on the bile salt concentration. 5. After 30 min the total amount of perfused isotopic cholesterol was recovered from either the lumen or the mucosa, but some fatty acid appeared to have been transported away from the mucosa by this time. 6. The initial rate of mucosal uptake of labelled cholesterol was similar from micellar perfusates using either taurocholate, taurodeoxycholate or taurofusidate. In contrast, after 8 h of infusion, lymphatic output of labelled cholesterol was markedly greater with taurocholate. 7. The increased lymph output with taurocholate was associated with an increase in the esterified fraction of both labelled and unlabelled cholesterol. Fatty acid was absorbed and esterified equally from all three types of perfusate. 8. These results suggested that for the first step in cholesterol absorption, viz. uptake from the lumen, solubilization by a planar detergent was essential. After uptake, the more rapid transfer of cholesterol to lymph in the presence of trihydroxybile acids appeared to be related to a more efficient esterification of cholesterol, but not to a more efficient resynthesis of triglyceride, the other major component of lymph chylomicrons.

Glycodihydrofusidate: biliary excretion and its effect on biliary secretion of the rat

Glycodihydrofusidate, which has the same detergent properties a bile salts, is excreted almost exclusively by the bile duct after intravenous injection in the rat. As with bile salts, it leads to a significant (P less tthan or equal to 0.05) increase in excretion of lecithins and cholesterol (0.15 mumol lecithin and 0.026 mumol cholesterol per 1 mumol of glycodihydrofusidate excreted). In addition, this drug simulataneously inhibits excretion of both endogenous bile salts and bile pigments.

A study of the physicochemical interactions between biliary lipids and chlorpromazine hydrochloride. Bile-salt precipitation as a mechanism of phenothiazine-induced bile secretory failure

Since chlorpromazine hydrochloride [2-chloro-10-(3-dimethylaminopropyl)-phenothiazine hydrochloride] is commonly implicated in causing bile-secretory failure in man and is secreted into bile, we have studied the physicochemical interactions of the drug with the major components of bile in vitro. Chlorpromazine hydrochloride molecules are amphiphilic by virtue of possessing a polar tertiary amine group linked by a short paraffin chain to a tricyclic hydrophobic part. At pH values below the apparent pK (pK'a 7.4) the molecules are water-soluble cationic detergents. We show that bile salts in concentrations above their critical micellar concentrations are precipitated from solution by chlorpromazine hydrochloride as insoluble 1:1 salt complexes. In the case of mixed bile-salt/phosphatidylcholine micellar solutions, however, the degree of precipitation is inhibited by the phospholipid in proportion to its mole fraction. With increases in the concentration of chlorpromazine hydrochloride or bile salt, micellar solubilization of the precipitated complexes results. Sonicated dispersions of the negatively charged phospholipid phosphatidylserine were also precipitated, but dispersions of the zwitterionic phospholipid phosphatidylcholine were not. Chlorpromazine hydrochloride efficiently solubilized these membrane phospholipids as mixed micellar solutions when the drug:phospholipid molar ratio reached 4:1. Polarizing-microscopy and X-ray-diffraction studies revealed that the precipitated complexes were amorphous and potentiometric studies confirmed the presence of a salt bond. Some dissociation of the complex occurred in the case of the most polar bile salt (Ks 0.365). As canalicular bile-salt secretion determines much of bile-water flow, we propose that complexing and precipitation of bile salts by chlorpromazine hydrochloride and its metabolites may be physicochemically related to the reversible bile-secretory failure produced by this drug.

Effects of taurodihydrofusidate, a bile salt analogue, on bile formation and biliary lipid secretion in the rhesus monkey

Bile salts play a major role in bile formation and biliary lipid secretion. Sodium taurodihydrofusidate (TDHF), a derivative of the antibiotic fusidic acid, closely resembles bile salts in terms of structure, micellar characteristics, and capacity ot solubilize otherwise insolbule lipids. We have therefore studied the biliary secretion of this bile salt analogue and its influence on bile formation and biliary lipid secretion in primates. Alert, unanesthetized female rhesus monkeys prepared with a total biliary fistula were allowed to reach a steady bile salt secretion rate before each study. In three animals (group I),[14C]TDHF was infused intravenously. Most of the compound was secreted rapidly in bile chemically unchanged. The biliary secretion of this drug produced a twofold increase in bile flow; however, the bile salt output was markedly reduced during the infusion. In spite of this reduction, the phospholipid output remained essentially unchanged whereas the cholesterol output increased almost twofold. In five other animals (group II), the effect of TDHF on the bile salt secretion was further investigated by an intravenous infusion of [14C]taurocholate followed by a combined infusion of [14C]taurocholate and TDHF. When TDHF was added to the infusate, a reduction in the [14C]taurocholate output and a progressive rise in the plasma [14C]taurocholate concentration were observed in each animal. An analysis of the data in both groups indicates that (a) the most likely explanation to account for the decreased bile salt output is that the bile salt analogue, TDHF, interfered with bile salt secretion into the biliary canaliculi; (b) TDHF induces a greater secretion of biliary water than was observed with bile salts, an effect consistent with a stimulation of the bile salt-independent canalicular flow; (c) at similar 3alpha-hydroxysteroid secretion rates TDHF caused a significant increase in cholesterol secretion compared to that induced by bile salt. This finding suggests that TDHF affects cholesterol metabolism or secretion in a way distinct from bile salts. Thus, the solubilization of biliary lipids in mixed micelles, although essential, is only one of the factors which determine their secretion into bile.