ABSTRACT
Stobadine is a model drug with pyridoindole structure with cardioprotective and antioxidant properties. Permeation properties of its acyl derivatives were studied to find a proper prodrug form. The experimental study of transdermal delivery of derivatives was combined with the theoretical approach in which the partition coefficients of substances were estimated by means of fragmentation or quantum chemical calculations. All modes applied showed differences in the transport properties of derivative S1 (N-acetyl stobadine). The experimental results obtained for the flux of S1 were higher by one order of magnitude than for the other derivatives and the parent drug. The results are discussed from the point of view of physicochemical properties of derivatives. We concluded that the exceptional permeation value of S1 derivative results from the concurrence of partitioning coefficient, dissociation constant, and arrangement of permeation set.
Subject(s)
Carbolines/chemical synthesis , Carbolines/pharmacokinetics , Skin Absorption/physiology , Acylation , Administration, Cutaneous , Algorithms , Animals , Chemical Phenomena , Chemistry, Physical , Chromatography, Ion Exchange , In Vitro Techniques , Permeability , RatsABSTRACT
With the use of the photoactivable dihydropyridine (DHP)-type calcium (Ca2+ channel antagonist (-)-[3H]-azidopine, a specific photoaffinity probe for Ca2+ channels, we tested the hypothesis of the existence of a separate subsite in the DHP receptor region on native polarized, stimulated depolarized and UV irradiated green monkey renal (GMR) cells preincubated with selected DHPs. Our results demonstrate that specific binding of (-)-[3H]-azidopine on GMR cells is of high affinity, stereoselective and dependent mainly on the inactivation of the membrane bound Ca2+ channel. Preincubation of the GMR cells with the DHP Ca2+ channel agonist BAY-K-8644 significantly reduced specific photolabeling. The site-directed free radicals generated after UV irradiation in DHP-preincubated renal cells inactivated Ca2+ channels and did not significantly affect the specific photoincorporation of (-)-[3H]-azidopine. (+)-Niguldipine, a DHP with the voluminous substituent on the DHP ring, significantly reduced the photolabeling. Low affinity labeling was partially prevented in (+)-nimodipine and (+)-niguldipine preincubated photoirradiated cells. The results strongly support the existence of central and peripheral subsites of the DHP region on GMR cells, with the former incorporating on photoactivation the intrinsically photoactive DHPs and with the latter labeled with a side chain bearing nitrene-generating photoreactive group, the photoaffinity probe, (-)-[3H]-azidopine.
Subject(s)
Affinity Labels/metabolism , Azides/metabolism , Dihydropyridines/metabolism , Kidney/metabolism , Muscle Proteins/metabolism , 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology , Affinity Labels/chemistry , Animals , Azides/chemistry , Binding, Competitive/drug effects , Calcium Channel Blockers/pharmacology , Calcium Channels, L-Type , Cell Line , Chlorocebus aethiops , Dihydropyridines/chemistry , Dihydropyridines/pharmacology , Free Radicals , Kidney/cytology , Kidney/drug effects , Kidney/radiation effects , Kinetics , Ligands , Membrane Potentials , Muscle Proteins/drug effects , Muscle Proteins/radiation effects , Nimodipine/pharmacology , Ultraviolet RaysABSTRACT
The interaction of propafenone enantiomers with human alpha 1-acid glycoprotein was studied using high-performance liquid chromatography. Each of the two optical antipodes interacted with one class of high-affinity binding sites characterized by Ka(R) = (6.18 +/- 0.93) x 10(5) M-1, n(R) = 1.34 +/- 0.09 for the (R)-isomer and Ka(S) = (8.93 +/- 1.82) x 10(5) M-1, n(S) = 0.99 +/- 0.08 for the (S)-isomer. Nonspecific binding to secondary low-affinity high-capacity binding site(s) was only slightly greater in the case of the (S)-enantiomer (n'k'(S) = (1.06 +/- 0.09) x 10(4) M-1) compared to the (R)-enantiomer (n'k'(R) = (6.87 +/- 0.72) x 10(3) M-1). It was concluded that both enantiomers interact with common single class of high-affinity binding sites on AAG (along with nonspecific binding) exhibiting only slight stereoselectivity for propafenone.
Subject(s)
Orosomucoid/metabolism , Propafenone/blood , Chromatography, High Pressure Liquid , Humans , Kinetics , Molecular Structure , Propafenone/chemistry , Protein Binding , StereoisomerismABSTRACT
The interaction of pirprofen enantiomers with human serum albumin (HSA) was investigated by means of high-performance liquid chromatography (HPLC), circular dichroism (CD), and 1H NMR spectroscopy. HPLC experiments indicated that both pirprofen enantiomers were bound to one class of high-affinity binding sites (n(+) = 1.91 +/- 0.13, K(+) = (4.09 +/- 0.64) x 10(5) M-1, n(-) = 2.07 +/- 0.13, K(-) = (6.56 +/- 1.35) x 10(5) M-1) together with nonspecific binding (n'K'(+) = (1.51 +/- 0.21) x 10(4) M-1, n'K'(-) = (0.88 +/- 0.13) x 10(-4) M-1). Slight stereoselectivity in specific binding was demonstrated by the difference in product n(+)K(+) = (0.77 +/- 0.08) x 10(6) M-1 vs. n(-)K(-) = (1.30 +/- 0.21) x 10(6) M-1, i.e., the ratio n(-)K(-)/n(+)K(+) = 1.7. CD measurements showed changes in the binding sites located on the aromatic amino acid side chains (a small positive band at 315 nm and a pronounced negative extrinsic Cotton effect in the region 250-280 nm). The protein remains, however, in its predominantly alpha-helical conformation. The 1H NMR difference spectra confirmed that both pirprofen enantiomers interacted with HSA specifically, most probably with site II on the albumin molecule.
