Absolute bioavailability and pharmacokinetics of avosentan in man.

OBJECTIVE: Avosentan is a potent, selective endothelin A receptor blocker. The pharmacokinetics of avosentan were investigated in healthy male and female volunteers, following oral and i.v. administration of single doses of avosentan and its absolute bioavailability was determined. METHODS: In a randomized, balanced open-label, three-period oral crossover study, 26 healthy subjects (19 males and 7 females) received Treatments A, B and C. Treatment A consisted of a single dose of a 25 mg film-coated tablet of avosentan, Treatment B of a single dose of a 50 mg film-coated tablet of avosentan and Treatment C of 10 mg avosentan in 20 ml solution for infusion for 20 minutes (10 mg avosentan in 20 ml phosphate buffer pH 9.0 containing 1% polysorbate 20). Plasma concentrations of avosentan and its hydroxymethyl metabolite Ro 68-5925 were measured by liquid chromatography-tandem mass spectrometry. RESULTS: The absolute bioavailability values (compared with i.v. infusion) for the 25 and 50 mg film-coated tablets were 81% and 72%, respectively. The extent of absorption, as measured by partial and total AUC, increased almost proportionally with the dose. The estimated proportionality coefficient for AUC0- yen was 1.12 (90% CI 1.06, 1.18). For the rate of absorption (Cmax) strict dose-proportionality was not demonstrated (proportionality coefficient 1.13 (90% CI 1.0, 1.28)). No relevant gender differences in the pharmacokinetic characteristics were evident after a single i.v. dose and at an oral dose of 25 mg, whereas after oral administration of 50 mg of avosentan differences were seen in Cmax and t1/2. CONCLUSION: The absolute bioavailability of avosentan film-coated tablets is high, i.e. 70 - 80%.

Influence of food intake on the pharmacokinetics of avosentan in man.

OBJECTIVE: Avosentan is a potent, selective endothelin A receptor blocker. The effect of food intake on the pharmacokinetics of avosentan was investigated in healthy volunteers. METHODS: In a randomized, open-label, 2-period oral crossover study, 12 healthy subjects (8 males and 4 females) received Treatments A and B. Treatment A consisted of a single dose of avosentan 50 mg after a high-fat, high-calorie breakfast. Treatment B consisted of a single dose of avosentan 50 mg administered in the fasted state. Plasma concentrations of avosentan and its hydroxymethyl metabolite Ro 68-5925 were measured by liquid chromatography-tandem mass spectrometry. RESULTS: The overall exposure to avosentan and its metabolite, as reflected by the area under the plasma concentration-time curve from time zero to infinity (AUC0-inf), was not affected by food intake. The ratios of least square means (90% confidence interval (CI)) of AUC0-inf for avosentan and Ro 68-5925 in the fed and fasted state were 1.06 (0.96, 1.17) and 1.05 (0.96, 1.15), respectively. The maximum plasma concentration (Cmax) of avosentan and its metabolite was increased by food intake, and their apparent terminal half-life (t1/2) was shortened. The ratios of least square means (90% CI) of pharmacokinetic parameters for avosentan and its metabolite in the fed and fasted state were Cmax 1.61 (1.37, 1.90) and 1.46 (1.27, 1.67), and t1/2; 0.80 (0.69, 0.92) and 0.61 (0.51, 0.74), respectively. Single oral doses of avosentan were well tolerated under fasted and fed conditions. CONCLUSION: Food intake does not influence the pharmacokinetics of avosentan to a clinically relevant extent.

In vitro studies with purified components reveal signal recognition particle (SRP) and SecA/SecB as constituents of two independent protein-targeting pathways of Escherichia coli.

The molecular requirements for the translocation of secretory proteins across, and the integration of membrane proteins into, the plasma membrane of Escherichia coli were compared. This was achieved in a novel cell-free system from E. coli which, by extensive subfractionation, was simultaneously rendered deficient in SecA/SecB and the signal recognition particle (SRP) components, Ffh (P48), 4. 5S RNA, and FtsY. The integration of two membrane proteins into inside-out plasma membrane vesicles of E. coli required all three SRP components and could not be driven by SecA, SecB, and DeltamicroH+. In contrast, these were the only components required for the translocation of secretory proteins into membrane vesicles, a process in which the SRP components were completely inactive. Our results, while confirming previous in vivo studies, provide the first in vitro evidence for the dependence of the integration of polytopic inner membrane proteins on SRP in E. coli. Furthermore, they suggest that SRP and SecA/SecB have different substrate specificities resulting in two separate targeting mechanisms for membrane and secretory proteins in E. coli. Both targeting pathways intersect at the translocation pore because they are equally affected by a blocked translocation channel.

A simple and inexpensive high density dialysis tubing cell culture system for the in vitro production of monoclonal antibodies in high concentration.

This paper describes the construction and application of a low-cost roller bottle-like culture appliance in which hybridoma cells can be cultivated in high density in dialysis tubing. The appliance facilitates the simultaneous culture of up to four cell lines yielding 50 ml culture volume of each. Samples for follow-up analysis of the cultures can easily be taken when needed through sample ports. In order to obtain high cell densities (at least 10(7) cells/ml), high cell viability (at least 50%) and high antibody yield (at least 1.0 mg/ml) the bottle is rolled at a speed of 4-6 rpm and is gassed continuously by a micropump driven by rechargeable NiCd batteries fixed to the culture flask. Depending on the individual properties of the hybridoma lines tested, the cells may be cultured for 1-2 weeks, and cell densities of up to 30 x 10(6) cells/ml with viabilities of approximately 50% and monoclonal antibodies in concentrations of up to 2.8 mg/ml may be obtained. In their properties the monoclonal antibodies produced by this in vitro procedure are indistinguishable from those prepared in the form of conventional stationary culture supernatant or of ascitic fluid. Specific antibody content is within the same range as in ascitic fluid. Consequently, the monoclonal antibodies can be purified in one step, e.g., by ion exchange chromatography from the culture supernatant. Therefore, the newly developed culture device and the culture method described is a useful alternative to ascites production in live mice.

Dose-dependent acute and sustained renal effects of the endothelin receptor antagonist avosentan in healthy subjects.

The endothelin receptor antagonist avosentan may cause fluid overload at doses of 25 and 50 mg, but the actual mechanisms of this effect are unclear. We conducted a placebo-controlled study in 23 healthy subjects to assess the renal effects of avosentan and the dose dependency of these effects. Oral avosentan was administered once daily for 8 days at doses of 0.5, 1.5, 5, and 50 mg. The drug induced a dose-dependent median increase in body weight, most pronounced at 50 mg (0.8 kg on day 8). Avosentan did not affect renal hemodynamics or plasma electrolytes. A dose-dependent median reduction in the fractional renal excretion of sodium was found (up to 8.7% at avosentan 50 mg); this reduction was paralleled by a dose-related increase in proximal sodium reabsorption. It is suggested that avosentan dose-dependently induces sodium retention by the kidney, mainly through proximal tubular effects. The potential clinical benefits of avosentan should therefore be investigated at doses of

Requirements for the translocation of elongation-arrested, ribosome-associated OmpA across the plasma membrane of Escherichia coli.

An oligodeoxynucleotide-dependent method to generate nascent polypeptide chains was adopted for use in a cell-free translation system prepared from Escherichia coli. In this way, NH2-terminal pOmpA fragments of distinct sizes were synthesized. Because most of these pOmpA fragments could be covalently linked to puromycin, precipitated with cetyltrimethylammonium bromide, and were enriched by sedimentation, they represent a population of elongation-arrested, ribosome-associated nascent chains. Translocation of these nascent pOmpA chains into inside-out membrane vesicles of E. coli required SecA and (depending on size) SecB. Whereas their translocation was strictly dependent on the H+-motive force of the vesicles, no indication for the involvement of the bacterial signal recognition particle was obtained. SecA and SecB, although required for translocation, did not mediate binding of the ribosome-associated pOmpA to membrane vesicles. However, SecA and SecB cotranslationally associated with nascent pOmpA, since they could be co-isolated with the ribosome-associated nascent chains and as such catalyzed translocation subsequent to the release of the ribosome. These results indicate that in E. coli, SecA also functionally interacts with preproteins before they are targeted to the translocase of the plasma membrane.

Comparative characterization of SecA from the alpha-subclass purple bacterium Rhodobacter capsulatus and Escherichia coli reveals differences in membrane and precursor specificity.

We have cloned the secA gene of the alpha-subclass purple bacterium Rhodobacter capsulatus, a close relative to the mitochondrial ancestor, and purified the protein after expression in Escherichia coli. R. capsulatus SecA contains 904 amino acids with 53% identity to E. coli and 54% identity to Caulobacter crescentus SecA. In contrast to the nearly equal partitioning of E. coli SecA between the cytosol and plasma membrane, R. capsulatus SecA is recovered predominantly from the membrane fraction. A SecA-deficient, cell-free synthesis-translocation system prepared from R. capsulatus is used to demonstrate translocation activity of the purified R. capsulatus SecA. This translocation activity is then compared to that of the E. coli counterpart by using various precursor proteins and inside-out membrane vesicles prepared from both bacteria. We find a preference of the R. capsulatus SecA for the homologous membrane vesicles whereas E. coli SecA is active with either type of membrane. Furthermore, the two SecA proteins clearly select between distinct precursor proteins. In addition, we show here for the first time that a bacterial c-type cytochrome utilizes the canonical, Sec-dependent export pathway.