Drug-biomolecule interactions: fluorescence studies on interaction of aminonaphthalenesulfonic acid derivatives with serum albumins.

The binding of the three aminonaphthalenesulfonic acid derivatives to human and bovine serum albumins was studied by measuring the fluorescence enhancement of the compounds. The number of binding sites of human and bovine serum albumins for these compounds appears to be one and two, respectively, under the experimental conditions. As the molar ratio of the fluorescent compounds to bovine serum albumin increased, the binding sites appeared to increase for the compounds. The quenching of the native fluorescence of albumin was examined by the successive addition of methanolic solutions of these compounds. 1-Anilinonaphthalene-8-sulfonate quenched the protein fluorescence to a greater extent than the other compounds studied, indicating that 1-anilinonaphthalene-8-sulfonate molecules are bound more closely to the tryptophan residues of albumin. The finding that the three compounds did not quench the fluorescence of tryptophan dissolved in water indicates no direct molecular interaction between tryptophan and the three fluorescent probes. The driving force for binding may be due to the structural characteristics of the amino acid sequence surrounding the tryptophan residues.

Protein binding of benz[a]anthracene and benzo[a]pyrene.

Fluorometric studies on the binding of benz[a]anthracene and benzo[a]pyrene to human serum albumin are described. The protein molecule appears to have one binding site for the hydrocarbons, but all of the sites on the protein are not fully occupied even in relatively large hydrocarbon concentrations. Equilibrium studies showed that both hydrocarbons bind to the protein to the same extent. Evidence for the energy transfer from the tryptophan residue of the protein to bound hydrocarbons is examined. By using Förster's theory, the mean distance between the tryptophan residue and bound ligand was found to be 15,2 A for benz[a]anthracene and 19.6 A for benzo[a]pyrene. It is concluded that the two hydrocarbons may bind to the same general area on the protein molecule near the tryptophan residue but at different sites. The structural differences of the hydrocarbons, which may greatly affect their orientations on the protein molecule, affect mainly the selection of the binding site rather than the binding equilibrium.

Development of a new non-surgical perfusion technique for evaluation of nasal drug delivery.

A new non-surgical perfusion technique was developed to evaluate nasal absorption using the rabbit as an animal model and insulin as a model drug. For these studies 20 ml of insulin solution (10 U/kg + 0.05% Na taurocholate) was perfused for 3.5 hours at a rate of 10 ml/hr. Spray formulations containing different levels of insulin (1.25, 2.5, 5 and 10 U/kg) and sodium taurocholate (0.05 and 1.0%) were evaluated in the same animal model. Insulin loaded polyacrylic acid microparticles were administered in 1% gel formulation to determine the comparative effect of insulin. The absorption of insulin was measured by glucose reduction. Pharmacodynamic parameters were determined relative to subcutaneously injected insulin (0.25 U/kg). The new non-surgical perfusion technique proved to be easier to control and more reproducible than the formerly used perfusion model while providing comparable results. The maximum relative absorption was observed for the 1.25 U/kg spray containing 1% NaTC. The polyacrylic acid gel formulation containing insulin loaded microparticles (10 U/kg) resulted in lower hypoglycemic effect compared to the spray formulations and subcutaneous injection.