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S Awazu

Publications and source records attributed to S Awazu.

At least 73 records · Page 4Linked to original sources
PubMed1988

Fluorescence study of the membrane-perturbing action of sodium caprylate as related to promotion of drug absorption.

The medium-chain fatty acid sodium caprylate released 6-carboxyfluorescein (CF), a model compound of water-soluble drugs, from the rat small intestinal brush border membrane (BBM) vesicles and liposomes containing CF. Caprylate caused a decrease in the fluorescence polarization of dansyl chloride, fluorescein isothiocyanate, and eosin maleimide covalently labeled to BBM. This indicates a perturbation of the BBM. However, no change in the fluorescence polarization of lipid-soluble fluorescent probes (2-(9-anthroyloxy) stearic acid, 12-(9-anthroyloxy) stearic acid, and 1,6-diphenyl-1,3,5-hexatriene) labeled to BBM was produced by caprylate. These findings indicate that caprylate can increase the permeability of the plasma membranes through the perturbation of the membranes. These actions of caprylate on membranes are considered one possible mechanism by which it promotes the absorption of water-soluble and poorly absorbed drugs.

Animals↗
PubMed1988

Fluorescence emitted from microsomal membranes by lipid peroxidation.

The fluorescence emitted from rat liver microsomal membranes which had undergone enzymatic and nonenzymatic lipid peroxidation was detected directly. This fluorescence produced in peroxidized membranes increased progressively with peroxidation reaction time, and the fluorescent substances produced were retained in the membranes without being released into the aqueous phase. Extracts of the peroxidized membranes with organic solvents (chloroform/methanol) emitted fluorescence which was also dependent on the peroxidation reaction time. The generation profiles of fluorescence emitted from both the peroxidized membranes and their extracted membrane lipids differed essentially from that of thiobarbituric acid-reactive substances which reached a plateau at a relatively early stage of peroxidation reaction. These results indicate that lipid peroxidation induces stepwise chemical and physical changes in membranes and that the fluorescence from peroxidized membranes will be useful in studying such changes occurring in biological membranes.

Animals↗
PubMed1988

Enhancement of colonic drug absorption by the transcellular permeation route.

The effects of sodium caprate and sodium caprylate on transcellular permeation routes were examined in rats. The release of membrane phospholipids was significantly increased only by caprate, while protein release did not change from the control in the presence of caprate or caprylate, indicating that the extent of membrane disruption was insufficient to account for enhanced permeation. Using brush border membrane (BBM) vesicles prepared from colon, with their protein and lipid component labeled by fluorescent probes, the perturbing actions of caprate and caprylate toward the membrane were examined by fluorescence polarization. Caprate interacted with membrane protein and lipids, and caprylate mainly with protein, causing perturbation to the membrane. The release of 5(6)-carboxyfluorescein previously included in BBM vesicles was increased by caprate but not by caprylate. These results suggest that caprate enhances permeability via the transcellular route through membrane perturbation.

Animals↗
PubMed1988

Enhancement of colonic drug absorption by the paracellular permeation route.

Colonic absorption of poorly absorbable cefmetazole was shown to increase considerably by the addition of 1% sodium caprate, sodium laurate, and mixed micelles composed of sodium oleate and sodium taurocholate. At 0.25%, their effects were weaker but still significant. Colonic absorption of inulin was also increased by the promoters at a concentration of 0.25%. These results suggest that there is a common route between inulin and cefmetazole absorption, i.e., the paracellular route. Sodium taurocholate, sodium caprylate, and EDTA disodium salts (EDTA-2Na) at 1% enhanced cefmetazole absorption less than caprate, laurate, or mixed micelles, but no such effect was found at 0.25%. The colonic pore radius was determined from the equivalent pore theory using an everted sac procedure. Caprate, laurate, and mixed micelles at 0.25% caused this radius to increase significantly, thus making it possible for inulin to permeate the everted sac from the mucosal to the serosal side. The effects of taurocholate, caprylate, and EDTA-2Na for increasing colonic pore sizes and the degree of inulin permeation were less than those of caprate, laurate, or mixed micelles. The change in the paracellular route is thus considered to result from the increase in pore size.

Animals↗
PubMed1988

The use of a perfluorochemical emulsion as a vascular perfusate in drug absorption.

In-vitro simultaneous luminal and vascular perfusion using the perfluorochemical emulsion, FC-43 emulsion, as a vascular perfusate, was examined for drug absorption in rat jejunum. The intestinal membrane in this system was found to retain its normal barrier functions for drug transport, as evident from the following: (i) stable absorption clearance of tritiated water and salicylic acid at steady-state, (ii) agreement of this clearance with that by in-situ single-pass luminal perfusion, (iii) active transport of D-glucose and its inhibition by phloridzin and (iv) normal glutamate pyruvate transaminase activity in the intestinal mucosa. FC-43 emulsion gave a more normal absorption site blood flow than the usual vascular perfusate containing erythrocytes and albumin in Krebs-Henseleit bicarbonate buffer solution. Consequently, this emulsion was useful for examining the contribution of blood flow resistance toward drug absorption. The rate-limiting steps of absorption of tritiated water, antipyrine and salicylic acid were examined by perfusion using FC-43 emulsion. The absorption of tritiated water was almost completely blood flow-limited and its absorption clearance may possibly be an approximated absorption site blood flow. The contribution of blood flow resistance to total resistance for antipyrine absorption exceeded that for salicylic acid absorption.

Animals↗
PubMed1988

Conformational change in plasma albumin due to interaction with isolated rat hepatocyte.

The electron spin resonance spectroscopy of 4-isothiocyanato-tempo labeled to bovine serum albumin (BSA) and the absorption spectroscopy of eosin maleimide labeled to BSA in the isolated rat hepatocyte suspension indicate conformational change occurring in the albumin molecule during interaction with the hepatocellular membrane. The conformational change in the albumin molecule may possibly accelerate the dissociation of albumin-organic anion complexes at the surface of the liver cell. The conformational change in the albumin molecule may explain in part the mechanism of albumin-mediated hepatic transport.

Animals↗
PubMed1987

Influence of the N-B transition of human serum albumin on the structure of the warfarin-binding site.

The fluorescence quantum yield of warfarin increased with the viscosity of the medium and showed good correlation with it. The internal rotation of the acetonylbenzyl group of a warfarin molecule may thus possibly decrease in a viscous medium. the fluorescence quantum yield of warfarin bound to human serum albumin increased with the pH of the medium in the pH range of 6.2-9.0. Fluorescence-emission maximum wavelengths of warfarin bound to human serum albumin indicated a small blue-shift with the pH of the medium and that of free warfarin in the absence of albumin also shifted slightly to a shorter wavelength with the viscosity of the medium. Warfarin is bound more strongly to human serum albumin at basic pH than at neutral pH, and the increase in the bound fraction of warfarin correlated well with the increase in the fluorescence quantum yield of bound warfarin in the same pH range. Thus, the structure of the warfarin-binding site in the B (base) form appears more spatially confined than that in the N (neutral) form. The motion of the warfarin molecule bound to its binding site on human serum albumin in the N-B transition may thus be more restricted at basic than at neutral pH, and this may possibly be the reason for the stronger binding of warfarin to human serum albumin in the B form.

Binding Sites↗
PubMed1987

Fluorescence energy transfer study of the relationship between the lone tryptophan residue and drug binding sites in human serum albumin.

The relationship between the lone tryptophan residue at position 214 and drug binding sites (Sites I and II) in human serum albumin (HSA) was studied by fluorescence energy transfer. The distance between the lone tryptophan residue and ligands bound to HSA was estimated by Förster's equation, taking into consideration the degree of ligand binding at these sites, as determined from binding parameters (binding constant, k, and the number of binding sites, n). For all ligands investigated, the distance in each case appeared to asymptotically decrease when the occupation ratio of the binding sites increased with ligand concentration. When the primary binding site of each ligand in HSA was almost saturated, the distance attained a constant value, making possible a somewhat more exact determination of the distance. The distance ranged from approximately 22 to 23 A for ligands typical of Site I (warfarin, dansylamide, dansylglutamine), and approximately 16.1 to 17.5 A for ligands typical of Site II (dansylsarcosine, dansylproline, dansylglycine, diazepam, flufenamic acid).

Amino Acids↗
PubMed1987

Enhancement of jejunal and colonic absorption of fosfomycin by promoters in the rat.

A means of enhancing absorption of the antibiotic, fosfomycin, has been investigated using promoters in rat jejunum and colon. Polyoxyethylene lauryl ether (BL-9EX), saponin, the sodium salts of fatty acids and mixed micelles were effective at 1% in increasing fosfomycin absorption. Of the sodium salts of saturated medium-chain fatty acids examined, the strength of this effect was in the order caprate greater than laurate greater than caprylate. Mixed micelles, consisting of fusogenic lipids and sodium taurocholate, enhanced fosfomycin absorption independently of the degree of unsaturation of the lipids; their effectiveness far exceeded that of sodium taurocholate alone. The action of these promoters was more evident in the colon than in the jejunum, except for the sodium salts of bile acids and disodium ethylenediaminetetraacetate (EDTA-2Na). The effects of glycocholate and taurocholate were essentially the same at both absorption sites, but that of EDTA-2Na was much greater in the jejunum than the colon. Improved fosfomycin absorption was observed at more than 0.5% sodium caprate concentrations in both the jejunum and colon. BL-9EX was effective at 0.1% in the jejunum or at 0.05% in the colon. The effectiveness at these low concentrations demonstrates the practicality of promoters for improving fosfomycin absorption with only minor membrane damage, especially in the colon.

Animals↗
PubMed1987

Differences in the promotion mechanism of the colonic absorption of antipyrine, phenol red and cefmetazole.

The promotion of antipyrine, phenol red and cefmetazole absorption by sodium ethylenediaminetetraacetate (EDTA-Na) as a paracellular promoter, diethyl maleate (DEM) as a transcellular promoter, and sodium taurocholate (TC-Na), whose promotion mechanism is still unclear, has been investigated by the rat in-situ colonic loop technique. All these promoters increased AP absorption and water influx from the lumen to the blood. Ouabain treatment suppressed the increase in antipyrine absorption and water influx induced by TC-Na and EDTA-Na, but did not modify the enhancing effect of DEM. Thus, the promotion mechanism of TC-Na may be similar to that of EDTA-Na. Phenol red and cefmetazole absorption were increased by TC-Na and EDTA-Na but not by DEM. Accordingly, phenol red and cefmetazole absorption appears to be promoted via paracellular but not transcellular routes. The collection of blood for plasma samples reduced the influx of water which had been increased by TC-Na or EDTA-Na. Consequently, the enhancement in antipyrine plasma concentration by these promoters was reduced to the control level. The inhibitory mechanism for this is discussed on the basis of the blood-flow limitation of antipyrine and water absorption.

Animals↗
PubMed1987

Alteration in rat liver microsomal membranes induced by acetaminophen.

Acetaminophen caused a reversible change in the fluorescence polarization of eosin maleimide and dansyl chloride labeled to rat liver microsomes, indicating that acetaminophen acts on microsomal membrane proteins. Acetaminophen in the presence of nicotinamide adenine dinucleotide phosphate (NADPH), brought about an irreversible change in the fluorescence polarization of the probes. Acetaminophen, with or without NADPH, was also found to change the fluorescence polarization of lipid-soluble fluorescent probes, 2- and 12-(9-anthroyloxy)stearic acid labeled to microsomes, indicating its action on microsomal membrane lipids.

Acetaminophen↗
PubMed1987

Aryl sulfotransferase in rat liver: multiplicity and substrate specificity.

Rat liver aryl sulfotransferase was purified by chromatography on diethylaminoethyl-cellulose or chromatofocusing and three fractions, referred to by Sekura and Jakoby as I, II and IV, were obtained in the order of their elution, each containing sulfation activity. p-Nitrophenol (PNP) at mM order and beta-naphthol were substrates common to all three fractions, but PNP at microM order and tyramine were substrates only for IV. IV corresponded to the enzyme designated M by Rein et al. and was active with monoamine, as predicted from our previous results with rat liver cytosol. However, the effectiveness of IV in bringing about the sulfation of PNP at mM order was not evident from our previous results. The characteristics of aryl sulfotransferase multiplicity on the basis of thermostability of sulfation activity could not be determined since essentially the characteristics were the same for all three purified fractions. The multiplicity of aryl sulfotransferase purified from rat liver was different from that of human platelets, indicating possible species and/or tissue differences in this enzyme.

Animals↗
PubMed1986

Effects of salicylic acid on the permeability of the plasma membrane of the small intestine of the rat: a fluorescence spectroscopic approach to elucidate the mechanism of promoted drug absorption.

The effects of sodium salicylate on the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), 2-hydroxyoctadecanoic acid, 9-anthroate (2-AS), 12-hydroxyoctadecanoic acid, 9-anthroate (12-AS), 8-anilino-1-naphthalenesulfonic acid (ANS) and 2',4',5',7'-tetrabromo-5-maleimidofluorescein, disodium salt (EM), with which rat small intestinal brush border membrane vesicles were labeled, were examined. Salicylate ion decreased the fluorescence polarization of ANS and EM in these vesicles, however, it had no influence on the fluorescence polarization of DPH, 2-AS and 12-AS-labeled vesicles. It also released trapped 6-carboxyfluorescein (3',6'-dihydroxy-3-oxospiro-[phthalan-1,9'-xanthene]-6-carbo xylic acid) (CF) from the vesicles, but caused no leakage of trapped CF from liposomes. These results indicate that salicylate ion increases the plasma membrane permeability by effecting the plasma membrane proteins rather than directly interacting with the membrane lipids. The action of salicylate ion on these vesicles could possibly promote nonabsorbable drug absorption in vivo.

Animals↗
PubMed1986

Factors influencing the tissue distribution of coenzyme Q10 intravenously administered in an emulsion to rats: emulsifying agents and lipoprotein lipase activity.

The tissue distribution of coenzyme Q10 (CoQ10) administered intravenously in an emulsion prepared with egg yolk phosphatidylcholine (PC), egg yolk sphingomyelin (SPM) or a combination of PC and a polyoxyethylene derivative of hydrogenated castor oil (HCO-60) (PC + HCO-60) was investigated. The disappearance from the plasma of CoQ10 administered in three different emulsions of lipid particle size less than 0.5 micron varied with the particular emulsifier. Its disappearance occurred most rapidly from the PC emulsion; with the addition of HCO-60, its disappearance was much slower. In the reticuloendothelial system, the concentration of CoQ10 was higher in the spleen, for both the SPM and PC + HCO-60 emulsions than for the PC emulsion. HCO-60 reduced the CoQ10 distribution in the liver from the PC emulsion. Differences in disappearance rates from the plasma are thus considered to be due to the extent of CoQ10 distribution in the liver. CoQ10 concentration in the heart, a target organ, was greatest with the PC emulsion. Its distribution was related to lipoprotein lipase (LPL) activity in this organ. The effects caused by HCO-60, however, could not be explained by LPL activity alone. CoQ10 distribution in the adrenal gland and kidney can be explained partly by LPL activity but in the presence of HCO-60, the distribution mechanism apparently involves other factors.

Animals↗
PubMed1986

Heterogeneous distribution of the conjugation activity of acetaminophen and p-nitrophenol in isolated rat liver cells.

The uneven distribution of the glucuronidation and sulfation activity of acetaminophen (APAP) and p-nitrophenol (PNP) in liver was studied using centrilobular and periportal regions of isolated rat hepatocytes obtained by Percoll density gradient centrifugation, in a manner similar to that for harmol reported previously. The glucuronidation of APAP and PNP occurred predominantly in the periportal region. Glucuronidation activity of APAP in the centrilobular region was not detected. This finding may reflect the existence of different forms of uridine diphosphate-glucuronyltransferase (UDPGT) for APAP and PNP. The regional difference in Km values was observed for PNP, but not for harmol as reported in the previous paper. This suggests the existence of multiple forms of UDPGT for PNP as well as the heterogeneous distribution of this enzyme in liver lobules. The sulfation rates of APAP and PNP in the centrilobular region were smaller than those in the periportal region. The regional difference of APAP sulfation was due to different Vmax values. As shown in the harmol experiment, the predominant distribution of sulfation activity of APAP and PNP in the periportal region agreed with the results in the perfused liver previously reported by other investigators but that of glucuronidation activity was at variance with them.

Acetaminophen↗
PubMed1986

Characterization of the interaction of albumin with isolated rat liver cells to reveal the mechanism of albumin-mediated hepatic transport.

The binding of bovine serum albumin (BSA), containing 125I-BSA, to isolated rat hepatocytes was studied over a 300-fold concentration range of BSA to characterize the interaction between albumin and the liver cells in albumin-mediated hepatic transport. The binding of BSA with a high affinity to the cell surface of hepatocytes was not found in the binding behavior. The bound fraction of BSA with hepatocytes was about 1% over those concentration range of BSA.

Animals↗