RESUMEN
Tolevamer, (GT160-246), is a sodium salt of styrene sulfonate polymer that is under development for the treatment of diarrhea caused by infection with Clostridium difficile. Pulsed ultrafiltration binding experiments in phosphate buffer containing 0.15 M Na(+) provide per polymer chain dissociation constants of 133 nM and 8.7 microM for the binding of tolevamer to C. difficile toxins A and B, respectively. At 0.05 M Na(+), the binding of toxin A to tolevamer is irreversible, whereas the dissociation constant to toxin B under these conditions is 120 nM. Binding constants obtained from fluorescence polarization data for toxin A binding to tolevamer at 0.15 M Na(+) agree substantially with those obtained by pulsed ultrafiltration. The binding activity of tolevamer reported here correlates well with previously reported results for the inhibition of the biological activity of C. difficile toxins A and B. From the fluorescence polarization data, it is estimated that one toxin A molecule interacts with between 600 to 1000 monomer units on tolevamer at 0.15 M Na(+). Thus, the data suggest a very large interaction surface between polymer and toxin A.
Asunto(s)
Toxinas Bacterianas/química , Clostridioides difficile/química , Polarización de Fluorescencia/métodos , Iones/química , Polímeros/química , Interacciones Farmacológicas , Ácidos Sulfónicos , Ultrafiltración/métodosRESUMEN
BACKGROUND: Clinical studies have shown sevelamer HCl (Renagel) to be effective for the reduction of serum phosphate in hemodialysis patients. These studies also consistently have demonstrated a significant reduction of low-density lipoprotein (LDL) cholesterol following treatment with sevelamer. METHODS: Equilibrium binding of bile acids and oleic acid was determined by incubating sevelamer with ligand containing buffer. Aliquots of the solution were filtered and the free ligand concentrations quantitated by high-pressure liquid chromatography (HPLC). Flow kinetics were determined using a cylindrical flow cell containing trapped sevelamer. Bile acid and oleic acid were pumped through the stirred cell in a manner designed to mimic the in vivo situation. Binding was monitored by HPLC. RESULTS: Sevelamer binds bile acids cooperatively and with high capacity. At low binding densities, the presence of the more hydrophobic bile acids enhances the binding of the less hydrophobic bile acids, and the presence of oleic acid enhances the binding of all bile acids. At saturating oleic acid concentrations, the bile acid binding capacity of sevelamer is reduced by only a factor of two. Moreover, the presence of oleic acid dramatically diminishes the release rate of bile acids from sevelamer. CONCLUSIONS: The favorable bile acid binding characteristics of sevelamer provide a compelling explanation for its ability to lower LDL cholesterol in hemodialysis patients and in healthy volunteers.