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Biomedical subjects

S Awazu

Publications and source records attributed to S Awazu.

At least 37 records · Page 2Linked to original sources
PubMed1998

Intestinal absorption and analgesic activity of aminopeptidase-resistant cellobiose-coupled leucine enkephalinamide.

Leucine enkephalinamide (LEamide), aminopeptidase-degradable opioid peptide, was coupled with cellobiose (cellobiose-coupled LEamide, CcpLEamide). CcpLEamide was absorbed from the rat small intestine in vitro, whereas LEamide was not. CcpLEamide on the mucosal side was more stable than aminopeptidase-resistant cellobiose-coupled leucine enkephalin (CcpLE) in the presence of inhibitors of enkephalinase and angiotensin converting enzyme, and much more stable than LEamide. The absorption rate (clearance) of CcpLEamide was comparable with that of CcpLE in the presence of these peptidase inhibitors. Analgesic activities of these enkephalins were tested by the acetic acid writhing assay and hot-plate assay after subcutaneous administration to mice. Both assays indicated CcpLEamide-induced analgesia. On the other hand, the analgesic activity of LEamide was not observed, but pretreatment with amastatin (a peptidase inhibitor) produced LEamide-induced analgesia. These results indicate that CcpLEamide is stable in the body and has analgesic effects without pretreatment with peptidase inhibitors, and was stable enough to be absorbed from the small intestine. We propose CcpLEamide as an orally active analgesic peptide candidate.

Aminopeptidases↗
PubMed1998

Evaluation of damaged small intestine of mouse following methotrexate administration.

PURPOSE: Methotrexate (MTX) treatment causes damage to the small intestine, resulting in malabsorption and diarrhea. The active and passive transport capacities of the small intestine are decreased by the treatment. The purpose of this study was to evaluate the damage to the small intestine of mice caused by MTX administration by examining the permeability of the paracellular pathway of the small intestinal epithelium. METHODS: MTX was administered orally to male ddY mice once daily for 1-6 days. The permeability of the small intestine to the nonabsorbable markers phenol red (PR) and fluorescein isothiocyanate (FITC) dextrans was examined using everted segments of the intestine. RESULTS: PR and FITC dextran permeation through the small intestine increased significantly in parallel with changes in body weight of the mice, wet weight of the small intestine and chemical composition of the small intestinal epithelium. CONCLUSIONS: In addition to changes in permeation through the transcellular pathway reported previously, this study revealed that MTX treatment disorders the paracellular barrier function of the small intestinal epithelium, resulting in increased permeation of nonabsorbable markers via the paracellular pathway of the small intestinal mucosa. The present approach to the examination of the barrier function of the intestinal epithelium could be of great use in evaluating the damage to the small intestine and malabsorption.

Administration, Oral↗
PubMed1998

Spontaneous chemiluminescence production, lipid peroxidation, and covalent binding in rat hepatocytes exposed to acetaminophen.

Spontaneous chemiluminescence associated with the cell injury was observed in the isolated rat hepatocyte suspension during acetaminophen (APAP) metabolism, indicating the occurrence of oxidative stress. APAP apparently affected the hepatocytes in various manners. APAP, at low concentrations (1-2 mM), damaged the hepatocytes due to lipid peroxidation provoked during APAP metabolism, while at high concentrations (5-50 mM), APAP protected the hepatocytes due to a chemical antioxidant effect of the unmetabolized APAP that remained in the medium because of the saturation of APAP metabolism. The covalent binding of APAP to the hepatocytes increased with APAP concentration up to 50 mM without loss of cell viability. When an overdose of APAP was administered to rats, the APAP plasma concentration was around 1-3 mM, which corresponded to the concentration range where lipid peroxidation occurred in the isolated hepatocytes. Thus, it seems likely that lipid peroxidation contributes to the APAP-induced hepatotoxicity in the early stage of the toxic process.

Acetaminophen↗
PubMed1998

Absorption-enhancing effects of sodium caprate and palmitoyl carnitine in rat and human colons.

We examined the enhancing action of sodium caprate and palmitoylcarnitine on the permeability of fluorescein isothiocyanate dextran 4000 as a paracellular permeant compound in isolated rat and human colon samples using the Ussing-type chamber method. In the absence of an enhancer, the permeation clearance of fluorescein isothiocyanate dextran 4000 was not significantly different in the rat and human colons, but the electric membrane resistance was smaller in the rat colon than in the human colon. Sodium caprate and palmitoylcarnitine increased permeation clearance and decreased electric membrane resistance in both types of colonic membrane, showing that the rat colon can be used as a model of the human colon for studies of enhancer effects. A calmodulin antagonist significantly inhibited the action of sodium caprate in both colonic membranes. However, it tended to promote the effects of palmitoylcarnitine on permeation clearance and electric membrane resistance. These results suggest that sodium caprate induces the contraction of the perijunctional actomyosin ring to widen the tight junction and that the mechanism of palmitoylcarnitine is different from that of sodium caprate in the human colon, as reported previously for Caco-2 cell monolayers.

Aged↗
PubMed1998

Intestinal absorption of stable cyclic dipeptides by the oligopeptide transporter in rat.

Intestinal absorption of four cyclic dipeptides was studied in the everted small intestine of the rat. Cyclic seryltyrosine (cyclo(Ser-Tyr)) was stable enough to be transported whereas linear seryltyrosine was not. The absorption clearance of cyclo(Ser-Tyr) was concentration-dependent, and for cyclo(Ser-Tyr) at 125 microM decreased in the presence of glycylsarcosine (10 mM) or cephalexin (10 mM), which were reported to be absorbed by oligopeptide transporter. The absorption clearance was also reduced at 4 degrees C and in the presence of 1 mM dinitrophenol. Kinetic analysis of cyclo(Ser-Tyr) absorption showed that Km and Vmax were 19.8 microM and 0.295 nmol min(-1) cm(-1), respectively. It was also suggested that cyclic aspartylphenylalanine and cyclic histidylphenylalanine were absorbed by oligopeptide transporters, but cyclic histidylproline was not. The absorption clearance of cyclo(Ser-Tyr) in the control was much higher than the value of the correlation line representing a plot of passive transport (which was obtained from the absorption clearance of cyclic peptides in the presence of glycylsarcosine (10 mM)) against hydrophobicity (oil-water partition coefficient). These results indicate that cyclo(Ser-Tyr) is absorbed by the oligopeptide transporter.

Animals↗
PubMed1998

Retention mechanism of imidazoles in connective tissue. IV. Identification of a nucleophilic imidazolone metabolite in rats.

Formation of a nucleophilic 4(5H)(or 5(4H))-imidazolone structure has been postulated from in vitro studies to be one of the causative elements involved in the retention of drugs with imidazole moiety in connective tissue. To confirm this, we searched for the imidazolone-related metabolite in rats after intravenous dosing of 2-methylimidazole (2MI; 14C-labeled and unlabeled form, 3 and 300 micromol/kg body weight) as a model compound. The excreted urine, the major route of elimination of the compound, was collected and analyzed using the HPLC/MS system with a counterion effect for metabolite separation. 2-Methyl-4(5H)(or 5(4H))-imidazolone (2MIone) was identified as a urinary metabolite by chromatographic and mass-spectral inspection with the corresponding authentic standard. Pretreatment of rats with either SKF-525A (50 mg/kg, i.p.) or cimetidine (200 mg/kg, i.p.) significantly increased the excreted amount of 2MIone in urine and the irreversible binding of 2MI equivalents in the aortic tissue, whereas both factors were reduced by pretreatment with triethylenetetramine dihydrochloride (150 mg/kg/d for 5 d, s.c.). These results support the aforementioned deduction, and also raise the possibility that a cytochrome P450-independent, copper-related metabolic reaction might be involved in the imidazolone formation in vivo.

Animals↗
PubMed1998

Retention mechanism of imidazoles in connective tissue. II. Activation of imidazoles in cupro-ascorbate system for irreversible binding formation with aortic tissue in vitro.

In order to obtain an insight into the retention mechanism of drugs with imidazole moiety in the connective tissue, the in vitro characteristics of the interaction between 14C-labeled imidazoles (imidazole and its 2-methyl derivative) and slices of dog aorta were studied. We found that cupro-ascorbate-catalyzed oxidative reactions for the imidazoles led to their irreversible binding with connective tissue, and that, from a study using protein modifiers, the aldehydic function intrinsic to the tissue protein was involved in the binding formation. This characteristic in vitro was observed under physiological conditions, hence it can be extrapolated to the in vivo situation and could also give a clue to the nature of the retention of imidazole-containing drugs in connective tissue.

Animals↗
PubMed1998

Retention mechanism of imidazoles in connective tissue. III. Aldehyde adduct formation of a 4(5H)(or5(4H))-imidazolone product in vitro.

2-Methylimidazole (2MI), as well as imidazole, has been thought to undergo cupro-ascorbate (Cu-VC)-catalyzed oxidative transformation in vitro to become a reactive species capable of combining with aldehydes intrinsic to connective-tissue proteins. We attempted to seize the essence of the above reaction through obtaining the structural information of an aldehyde-bonding species. As major products from 2MI in the in vitro Cu-VC system, 2-hydroxymethylimidazole (2(OH)MI) and 2-methyl-4(5H)(or 5(4H))-imidazolone (2MIone) were identified by mass-spectral and chromatographic comparison with the corresponding authentic standards synthesized. The in situ addition of acetaldehyde or propionaldehyde as a simple protein-aldehyde model to the system resulted in the deducible formation of an aldol condensate, 2-methyl-4(or 5)-ethylidene-4(5H)(or 5(4H))-imidazolone (2MEIone) or its possible analogue with a propylidene moiety, respectively. The authentic compound of 2MIone directly reacted with acetaldehyde and easily afforded the products assignable to the isomers of 2MEIone through the ethylidene moiety at physiological pH and temperature, whereas neither 2MI or 2(OH)MI reacted at all. These results suggest that a 4(5H)(or 5(4H))-imidazolone product, although simply a monooxygenated form, is sufficiently reactive to give aldol condensation-typed covalent adducts with aldehydes, even under physiological conditions, probably having an activated methylene moiety in the ring structure. Based on the present results, we discussed the mechanism of the retention of imidazole-containing drugs in connective tissue.

Acetaldehyde↗
PubMed1998

Glutathione disulfide formation during naproxen metabolism in the isolated rat hepatocytes.

As naproxen was found to induce lipid peroxidation in liver microsomes and isolated hepatocytes of rats during its oxidative metabolism, we studied changes of glutathione on its metabolism. Intracellular oxidized glutathione (GSSG) content increased in isolated rat hepatocytes during naproxen metabolism. The intracellular GSSG increased preceding the production of thiobarbituric acid reactive substances (TBARS) and the release of lactate dehydrogenase (LDH). The glutathione-depleted hepatocytes treated with diethymaleate (DEM) enhanced TBARS production and LDH release, compared to the untreated hepatocytes. The production of GSSG may possibly be an early stage of the naproxen-induced oxidative stress which leads to lipid peroxidation and lethal cell injury.

Animals↗
PubMed1998

Intestinal metabolism and transport of alpha-disaccharide conjugates: the role of disaccharidase in the Na+/glucose cotransporter-mediated transport.

Intestinal transport and metabolism of p-nitrophenyl alpha-disaccharides were studied. In the absorption of p-nitrophenyl alpha-melibioside, no compounds other than p-nitrophenyl alpha-melibioside were detected on either the mucosal or the serosal side. In the absorption of p-nitrophenyl alpha-maltoside, on the other hand, p-nitrophenyl alpha-glucoside was formed on the mucosal side to appear on the serosal side. p-Nitrophenol and p-nitrophenyl beta-glucuronide also appeared on the serosal side in the absorption of p-nitrophenyl alpha-maltoside, and the total amount transported to the serosal side was significantly decreased in the absence of Na+ (a cosubstrate of Na+/glucose cotransporter (SGLT1)). Furthermore, the total transport clearance of p-nitrophenyl alpha-glucoside formed from p-nitrophenyl alpha-maltoside on the mucosal side in the p-nitrophenyl alpha-maltoside absorption, was similar to that of the absorption of p-nitrophenyl alpha-glucoside itself. These results led to the conclusion that the intestinal absorption of disaccharide conjugate depended on disaccharidase, and the absorption of the alpha-maltose conjugate occurred sequentially by the maltase-catalyzed hydrolysis of the disaccharide conjugate and SGLT1-mediated transport of the glucose conjugate.

Animals↗
PubMed1997

Intravenous administration of irinotecan elevates the blood beta-glucuronidase activity in rats.

7-Ethyl-10-hydroxycamptothecin (SN-38) is the active metabolite of an anticancer drug, irinotecan (CPT-11). Severe late diarrhea is the dose-limiting toxic effect of CPT-11. This diarrhea has been examined regarding biliary excretion and deconjugation of SN-38 glucuronide by the enzyme beta-glucuronidase (beta-GL) in intestinal microflora. Prompted by the enzymological and structural similarity of CPT-11 to organophosphorus and carbamate insecticides, we studied the effect of CPT-11 on blood beta-GL activity in rats. The i.v. injection of CPT-11 in rats significantly elevated their plasma beta-GL activity (with phenolphthalein glucuronide as a substrate) at doses of 10 and 40 mg/kg, with peak activity observed 2-3 h after administration. SN-38 lactone and carboxylate had no effect on the plasma beta-GL level. The enhancement of the activity was also observed in serum using SN-38 glucuronide as a substrate. The serum beta-GL levels showed a close correlation between these substrates. The enhancement of plasma (serum) beta-GL activity is suggested to be a result of the release of beta-GL from liver microsomes. Serum and microsomal carboxylesterase were not significantly affected by CPT-11 administration.

Animals↗
PubMed1997

Intestinal transport and metabolism of analgesic dipeptide, kyotorphin: rate-limiting factor in intestinal absorption of peptide as drug.

Intestinal transport and metabolism of kyotorphin (KTP) were studied in rat everted small intestine. KTP on the mucosal side was metabolized completely within 60 min, and any amounts of KTP were not detected on the serosal side. On the other hand, [D-Arg2]-KTP (D-KTP) was stable on the mucosal side to appear on the serosal side. However, N-t-butoxycarbonyl-KTP (Boc-KTP), which was metabolized on the mucosal side faster than KTP, appeared on the serosal side. In intestinal homogenate, KTP was metabolized, and the metabolic clearance (CL(met)) was decreased by peptidase inhibitors, bestatin, o-phenanthrolin and tryptophan hydroxamate. In the presence of these peptidase inhibitors, the absorption clearance (CL(abs)) of KTP was increased. The less the CL(met) of KTP was, the more the CL(abs) of KTP was. Meanwhile, Boc-KTP in intestinal homogenate was stable even in the absence of peptidase inhibitors. The CL(abs) of Boc-KTP was constant irrespective of the stability on the mucosal side. Kinetic analysis by the metabolic inhibition model indicated that the stabilization of KTP in the intestinal tissue could increase the CL(abs) up to 0.247 microl/min per cm, which was as much as the CL(abs) of stable D-KTP. These results led to the conclusion that rate-limiting process in intestinal absorption of KTP is metabolic degradation in intestinal tissue during the absorption.

Analgesics↗
PubMed1997

Amelioration of methotrexate-induced malabsorption by vitamin A.

Methotrexate (MTX) induces damage to the small intestine, resulting in malabsorption and diarrhea. We found that the coadministration of vitamin A (VA) with MTX protected the small intestine from MTX-induced damage. In this study, the permeability of D-glucose, D-xylose and L-leucine through the small intestine of rats treated with MTX and/or VA was studied using everted segments of small intestine. MTX treatment decreased permeability and VA coadministration prevented the decrease. The transport of D-glucose in the small intestine of MTX plus VA- and VA-treated rats and of control rats followed Michaelis-Menten kinetics, in contrast to the transport kinetics in MTX-treated rats. The pharmacokinetics of orally administered [14C]-D-glucose in control rats and MTX- and/or VA-treated rats was also studied. The bioavailability of D-glucose in MTX-treated rats was lower than in the other three groups. VA coadministration improved the bioavailability of D-glucose. Thus, it seems likely that VA ameliorates MTX-induced malabsorption.

Administration, Oral↗
PubMed1997

Intestinal absorption of stable cyclic glycylphenylalanine: comparison with the linear form.

The absorption, especially the stability and transportability, of the cyclic peptide cyclic glycylphenylalanine (cyclo(Gly-Phe)) and the linear peptides glycylphenylalanine, glycyl-D-phenylalanine and phenylalanylglycine have been studied in rat small intestine. Linear peptides were degraded on the mucosal side and only glycyl-D-phenylalanine appeared on the serosal side. However, cyclo(Gly-Phe) was stable on the mucosal side and appeared on the serosal side. Furthermore, the absorption clearance of cyclo(Gly-Phe) was higher than that of glycyl-D-phenylalanine. In the presence of the peptidase inhibitor bestatin, the degradation of linear peptides was reduced and linear peptides appeared on the serosal side, but only phenylalanylglycine, which is transported by the oligopeptide transporter, was absorbed faster than cyclo(Gly-Phe). The absorption clearance of cyclo(Gly-Phe) was reduced as its concentration was increased from 125 microM to 500 microM. Furthermore, the absorption clearance of cyclo(Gly-Phe) at 125 microM was reduced at 4 degrees C or in the presence of glycylsarcosine and cephalexin, which are transported by the oligopeptide transporter. These results indicated that cyclo(Gly-Phe) was stable enough to be absorbed and was transported in part by the oligopeptide transporter rather than completely by passive diffusion.

Animals↗
PubMed1997

Inhibition of the hepatic uptake of paracetamol sulphate by anionic compounds.

The effect of anionic compounds on the hepatic uptake of paracetamol sulphate, a conjugative metabolite of paracetamol, has been studied. Hepatic uptake of paracetamol sulphate by isolated hepatocytes was inhibited by bromosulphophthalein, dibromosulphophthalein and p-nitrophenyl sulphate, but not by probenecid or cholic acid. Bromosulphophthalein and dibromosulphophthalein also inhibited the uptake of paracetamol sulphate in the rat isolated perfused liver. Saturable uptake of paracetamol sulphate was also observed in the absence of inorganic sulphate. The uptake of paracetamol sulphate was reduced by 1 and 10 mM inorganic sulphate. Bromosulphophthalein and p-nitrophenyl sulphate inhibited the uptake of paracetamol sulphate in the absence of inorganic sulphate. These results indicate that paracetamol sulphate shares a transporter with bromosulphophthalein, dibromosulphophthalein and p-nitrophenyl sulphate, all of which contain the sulphate or sulphonate group. Therefore, the sulphate or sulphonate moiety might be crucial for interaction with the transporter, and mutual inhibition of hepatic uptake among these compounds is likely.

Acetaminophen↗
PubMed1997

Preference of Peyer's patches to jejunal epithelium for intestinal absorption of oligopeptides, tyrosylglycylglycine and D-kyotorphin.

The intestinal absorption of oligopeptides, peptidase-degradable tyrosylglycylglycine (TGG) and peptidase-resistant L-tyrosyl-D-arginine (D-kyotorphin, D-KTP) across Peyer's patches (PP) in rabbit intestine were studied using an Ussing-type chamber and in situ closed perfusion methods. The clearance for the serosal appearance of intact TGG across PP by the Ussing-type chamber method was a little higher than that across the jejunal epithelium (JE). Meanwhile, the in situ closed perfusion experiment showed that the clearance for the plasma appearance of intact TGG across PP was about 10 times that of JE. Furthermore, it was shown that the clearance for the plasma appearance of D-KTP in PP was about twice that in JE by the in situ closed perfusion method, indicating that the membrane permeability of PP was higher than that of JE. Therefore, these results indicate that PP had less metabolic peptidase activity than JE, and that the PP was a suitable site for the intestinal absorption of oligopeptides, especially peptidase-degradable peptides.

Animals↗
PubMed1997

Plasma pharmacokinetics of 7-ethyl-10-hydroxycamptothecin (SN-38) after intravenous administration of SN-38 and irinotecan (CPT-11) to rats.

We studied the plasma pharmacokinetics of the lactone form and the carboxylate form of 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan (CPT-11), after intravenous bolus administrations of each form of SN-38 and of CPT-11 to rats. After the SN-38 lactone injection, SN-38 lactone was predominant at first, and then the lactone to the carboxylate concentration ratio (LC ratio) was maintained from 30 to 90 min after the injection. The carboxylate was predominant throughout the period after the carboxylate dosing. Model-dependent analyses showed that the SN-38 lactone had greater plasma clearance and a greater distribution volume than the carboxylate. The CPT-11 administration resulted in a predominant plasma SN-38 lactone concentration. The contribution of the SN-38 lactone AUC to the total SN-38 AUC (57%) was independent of the dose of CPT-11. These results suggest that it is possible to estimate the SN-38 lactone concentration and AUC from the total SN-38 concentration without separate determination of the lactone and carboxylate. Our results showed that both SN-38 lactone and CPT-11 administration gave the predominant SN-38 lactone in plasma; however, only CPT-11 could sustain the lactone concentration at a high level, which is necessary for antitumor activity.

1-Octanol↗