Biomedical subjects

H Kiwada

Publications and source records attributed to H Kiwada.

At least 55 records · Page 3Linked to original sources

PubMed1994

Effects of benidipine hydrochloride (Coniel), a new calcium antagonist, on the cardiac output, regional blood flow and vascular resistance in conscious, spontaneously hypertensive rats.

Benidipine hydrochloride is a calcium antagonist with a 1,4-dihydropyridine derivative structure, and exhibits long-lasting antihypertensive effects by inhibiting the voltage-dependent Ca2+ channels. This study was undertaken to examine the effect of benidipine on central haemodynamics and regional blood flow (RBF) after intravenous administration of benidipine in conscious, spontaneously hypertensive rats. The microsphere method was used to measure cardiac output and RBF before and after the drug administration, using microspheres labelled with 57Co and 51Cr. Thirty minutes after the intravenous administration of benidipine (3 micrograms kg-1), the mean arterial pressure fell by 15% without significantly increasing the heart rate. The cardiac output increased by 41% and the systemic resistance decreased by 39%. Benidipine significantly increased RBF by 37, 35, and 22% in kidney, heart, and small intestine, respectively, and decreased vascular resistance by 38, 38, and 32%, respectively. We concluded that benidipine reduced blood pressure by increasing RBF in the kidney and heart, while keeping RBF in other organs at a normal level. These results will provide a fundamental basis in support of the clinical benefits of benidipine for hypertensive patients, particularly those with renal failure.

Animals↗

PubMed1994

Plasma factor triggering alternative complement pathway activation by liposomes.

Several plasma components, such as complement (C) components, play a role in the clearance of liposomes from the circulation. The interactions between liposomes and the C system were investigated in this study. Multilamellar vesicle (MLV) liposomes, which were damaged by activation of the complement, became susceptible depending on the density of cetylmannoside (Man) on the liposome membrane, and activation proceeded through the alternative C pathway as observed for liposomes without Man (PC-MLV) (K. Funato et al., Biochim. Biophys. Acta 1103:198-204, 1992). In addition, the capacity of Man-modified liposomes (Man-MLV) to activate the alternative C pathway was abolished by preadsorption of plasma with Man-MLV but not with PC-MLV. The results suggest that a specific plasma factor adsorbed with Man-MLV was responsible for the augmentation of the C activation and, further, that the rapid clearance of Man-MLV from the circulation is caused by both enhanced C-mediated liposome permeability and enhanced C-mediated phagocytosis of liposomes.

Animals↗

PubMed1994

Enhanced hepatic uptake of liposomes through complement activation depending on the size of liposomes.

The objective of this study was to differentiate the roles of opsonins and phagocytic cells in the size-dependent hepatic uptake of liposomes in the submicron region. The extent of opsonization decreased with the decrease in size of liposomes (from 800 to 200 nm in diameter) and no enhancement of uptake was observed at 200 nm. There was no effect of liposome size on the uptake of unopsonized liposomes. Serum was pretreated with empty liposomes of each size and its opsonic activity was measured in the perfused liver. The small liposomes could not consume the opsonic activity, while the larger ones did so substantially. These results suggest that opsonins bind to liposomes depending on the size of liposomes and phagocytic cells take up liposomes in proportion to the extent of opsonization. Size-dependent liposome degradation in serum was also found, which was consistent with the size-dependent complement activation, because liposomes with this composition have been shown to be degraded by complement. The mechanism of opsonization was examined by treating serum at 56 degrees C for 30 min or with anti-C3 antiserum. Since both treatments inhibited the opsonic activity, the hepatic uptake of liposomes is considered to occur via complement receptor. In conclusion, the size of liposomes affected complement recognition, and the liposomes were taken up by the liver depending on the extent of opsonization.

Animals↗

PubMed1994

Effects of ascorbic acid on iproniazid-induced hepatitis in phenobarbital-treated rats.

The effects of ascorbic acid (AA) on hepatic injury induced by iproniazid (IPN) in phenobarbital-treated rats were investigated by the evaluation of hepatic function using the clearance of aminopyrine (AM). Either IPN or isopropylhydrazine (IP-Hy), a potent toxic metabolite of IPN, were administered as a pretreatment to rats with or without AA. After i.v. injection of AM, the blood concentration of AM was determined by capillary gas chromatography by isotope dilution analysis using deuterium-labeled AM (AM-d9) as the internal standard. The kinetic parameters of AM, Vd, kel and total body clearance, were estimated from the time course of blood concentration. Pretreatment with IPN with AA led to a marked increase in the kel and in the clearance compared with pretreatment using IPN alone. A significant increase in the kel and the clearance was also found in the case of combined pretreatment using IP-Hy with AA. The effects of AA on the hepatic injury induced by IPN were studied according to its histological aspects. In the specimens obtained following the administration of IPN or IP-Hy with AA, the degree of cell necrosis was remarkably lowed both quantitatively and qualitatively. The present results clearly demonstrate that AA was effective in reducing IPN-induced hepatitis.

Alanine Transaminase↗

PubMed1994

Effects of fluidity and vesicle size on antitumor activity and myelosuppressive activity of liposomes loaded with daunorubicin.

The effects of fluidity and vesicle size on the antitumor activity and myelosuppressive activity of liposomes loaded with daunorubicin, an anthracycline antitumor drug, were investigated in Yoshida sarcoma-bearing rats. Liposomes composed of egg phosphatidylcholine (EPC) or hydrogenated egg phosphatidylcholine (HEPC), cholesterol and dicetyl phosphate in a molar ratio of 5:4:1 were injected intravenously into rats 5 d after subcutaneous inoculation of Yoshida sarcoma. At non-effect dosage in free drug, HEPC-liposomes with a diameter of 58 or 142 nm showed the greatest inhibitory effect against Yoshida sarcoma among liposomes tested, whereas larger ones (272 nm) had weaker effect. Small EPC-liposomes (57 nm) had no effect. Larger HEPC-liposomes (especially 142 nm) greatly decreased the number of peripheral white blood cell compared with free drug at the same dose, indicating relatively strong myelosuppressive toxicity. However, small EPC- and HEPC-liposomes with a diameter of 57 and 58 nm, respectively, showed toxic effects comparable to that of free drug. Examination of the dose-dependency of therapeutic effects and toxicity indicated encapsulation of daunorubicin in the small HEPC-liposomes to enhance the therapeutic index about 3 times that of free drug. These findings indicate the possibility of using small HEPC-liposome as a drug carrier for targeting solid tumors.

Animals↗

PubMed1994

Uptake of liposomes surface-modified with glycyrrhizin by primary cultured rat hepatocytes.

Previously, we synthesized 30-stearyl glycyrrhizin (GLOSt) and reported that small unilamellar liposomes containing GLOSt (GLOSt-SUV) accumulated in the liver several times more than the control liposomes (control-SUV). In the present study, to determine the interaction between GLOSt-SUV and hepatocytes, in vitro uptake experiments were achieved with primary cultured rat hepatocytes. The uptake amount of GLOSt-SUV by rat hepatocytes was considerably higher compared to the control-SUV, while GLOSt-SUV showed about a 10-fold higher uptake level than the control-SUV during 2 h of incubation. It was assumed that GLOSt-SUV not only bind to the surface of the hepatocytes but are internalized and degraded in the cells, because at 37 degrees C, GLOSt-SUV were taken up and the level of the degradable marker was lower than the inert marker, and this did not occur at 4 degrees C. Since the uptake of GLOSt-SUV was inhibited by glycyrrhizin (GL), it was suggested that a binding-site for GL is present on the surface of hepatocytes, and GLOSt-SUV are likely to be internalized via this site by the hepatocytes. Furthermore, it was confirmed that the efficacy of GLOSt on liposomes is not affected by the fluidity of the liposomal membrane.

Animals↗

PubMed1994

The complement- but not mannose receptor-mediated phagocytosis is involved in the hepatic uptake of cetylmannoside-modified liposomes in situ.

In the elimination of injected liposomes in vivo, it is considered that several serum components play an important role on hepatic uptake of them. This study was conducted to clarify the hepatic uptake mechanism of cetylmannoside (Man)-modified multilamellar vesicles (Man-MLV) using perfused rat liver. In the presence of serum, Man-MLV was taken up by the liver depending on the serum concentration, and it showed an approximately two-fold higher accumulation than MLV without any surface modifications (PC-MLV). These hepatic uptakes of liposomes were obviously inhibited by preheating the serum at 56 degrees C for thirty minutes or by the treatment with anti-rat C3 antiserum. Further, SDS-PAGE followed by immunoblot analysis showed the deposition of iC3b on the opsonized Man-MLV. These results obtained in the present study suggested that hepatic uptake of Man-MLV was mainly mediated by complement receptor rather than mannose receptor on Kupffer cells in vivo.

Animals↗

PubMed1993

Kinetic modeling of liposome degradation in blood circulation.

The aim of this study is to develop a kinetic model for the quantitative evaluation of, and to examine dose dependency in liposome degradation in blood circulation in vivo. Multilamellar liposomes labeled with 3H-inulin were administered intravenously into rats and the time courses of blood concentration and urinary excretion of 3H-inulin were measured. The dosages of liposomes were fixed at 1, 5, and 100 mumolPCkg-1. Remarkable saturation was found in the time courses of both blood concentration and urinary excretion. Then a kinetic model for the degradation of liposomes in blood was developed, assuming that the degradation follows the first order rate process for each dose. The model fitted the observed time courses of excreted 3H-inulin well, and dose dependency could be observed in the rate constants for liposome degradation, which are more sensitive than urinary excretion of 3H-inulin. The degradation rate constant correlated well with the uptake rate constant, which suggests the same underlying mechanism for both uptake and degradation. These results indicate the usefulness of kinetic modeling in the quantitative evaluation of liposome degradation in blood circulation in vivo.

Animals↗

PubMed1993

Kinetic analysis of tissue distribution of doxorubicin incorporated in liposomes in rats (II).

The objective of this study is to perform kinetic modelling of the tissue distribution of doxorubicin encapsulated into liposomes (L-DXR), especially to the heart and liver. The release process of doxorubicin (DXR) from liposomes in blood was quantified by a release clearance. This parameter defines a release rate of DXR based on the concentration of L-DXR in blood and was estimated from kinetic modelling of DXR distribution to the heart after L-DXR administration. The distribution of free DXR to the heart was modelled separately. The experimental data for this modelling were reported previously (Harashima et al., Biopharm. Drug. Disposit., 13, 155-170 (1992)). This analysis provided a free DXR concentration profile as well as a release clearance of DXR after L-DXR administration. There was a remarkable difference in the free DXR concentration in blood between free and liposomal administration. The area under the DXR curve in the heart was reduced by approximately one third from that for the first two hours after DXR administration by liposomal encapsulation, which could be the reason for reduced cardiac toxicity. In our previous report, the distribution of L-DXR to the liver was shown to be explained by a sequentially linked two-compartment model with efflux process. The validity of this efflux model was examined in this study by a repeated dose study. The apparent uptake clearance decreased with time and showed a second peak after the repeated dose, which justified the efflux model. These kinetic analyses give quantitative understanding of the effect of liposomal encapsulation on the tissue distribution of DXR.

Animals↗

PubMed1993

Kinetic analysis of AUC-dependent saturable clearance of liposomes: mathematical description of AUC dependency.

The objective of this study was to examine the AUC dependency of saturable hepatic clearance (CLh) of liposomes and to postulate a mathematical model to describe the characteristics. The AUC dependency of saturable CLh was examined under intravenous rapid administration at various doses. The CLh increased with increasing blood concentration but decreased with the increase of AUC at each dose. In addition, the relationship between AUC and CLh was consistent with that observed in previously reported infusion studies. These experimental data confirm the AUC dependency of saturable CLh of liposomes. A mathematical model was developed for this AUC dependency. The decrease of CLh was described by the uptake amount (X) as follows: CLh = CLm(1-X/Xm), where CLm and Xm represent the maximum uptake clearance and the maximum uptake amount, respectively. The rate equation for uptake was analytically solved as CLh = X/AUC = Xm/AUC(1-exp(CLm/XmAUC)). Uptake clearance can be described by CLm, Xm, and AUC, and so uptake clearance is constant if AUC is constant. These experimental analyses and theoretical considerations show the validity of the AUC-dependent saturable CLh of liposomes.

Animals↗

PubMed1993

Distinction between the depletion of opsonins and the saturation of uptake in the dose-dependent hepatic uptake of liposomes.

Opsonins play a role in the hepatic uptake of particles such as bacteria, lipid emulsion, and liposomes. The objective of this study was to distinguish between opsonin depletion and uptake saturation in the dose-dependent hepatic uptake of liposomes. The uptake of opsonized and unopsonized liposomes was determined in the isolated perfused liver. Serum (2.9 mL) was required to opsonize 1 mumol liposomes fully, indicating that a rat (250 g with 10 mL of serum) can opsonize 3.5 mumol liposomes. Next the dose effect on hepatic uptake of opsonized and unopsonized liposomes was examined. Saturation of uptake was found only for the opsonized liposomes. On the other hand, the hepatic uptake clearance decreased dose dependently from 4.31 to 0.79 (mL/min), with increasing doses from 0.075 to 17 mumol/250 g, respectively, after i.v. administration. Thus, the decrease in the hepatic uptake clearance at the medium dose was due to the saturation of uptake alone, and at the high dose it was due to opsonin depletion as well. These results show that the saturation of liposomal uptake in the liver and the depletion of opsonins occurred at different liposome dosage levels.

Animals↗

PubMed1992

Contribution of complement system on destabilization of liposomes composed of hydrogenated egg phosphatidylcholine in rat fresh plasma.

Large multilamellar vesicles (MLV) composed of hydrogenated egg phosphatidylcholine (HEPC), cholesterol (CH), and dicetyl phosphate (DCP) rapidly release part of an entrapped aqueous marker when incubated with fresh rat plasma and thus have severely limited usefulness as drug carriers. The mechanisms causing the instability of liposomes in plasma were investigated in this study. The leakage of liposomal constituents was completely inhibited by pre-heating at 56 degrees C for 30 min with plasma or by treating with EDTA, K-76COOH, or anti-C3 antiserum but was not inhibited with EGTA/MgCl2. These results indicated that the destabilization of liposomes in fresh rat plasma was induced by activation of the alternative complement pathway (ACP). Furthermore, the complement third component (C3) was detected from the liposomes incubated with fresh plasma by SDS-PAGE followed by Western blotting and immune detection. The C3b deposited on the liposomal surface via ACP was rapidly cleaved to iC3b. The results obtained in the present study suggest a possibility that the liposomes composed of HEPC (without any surface modification) may be effective carriers for macrophages because C3b and its degradative products, iC3b are related to the opsonic function on phagocytosis of foreign particles by macrophages.

Animals↗

PubMed1992

Kinetic analysis of tissue distribution of doxorubicin incorporated in liposomes in rats: I.

The purpose of this study was to perform a kinetic analysis of the tissue distribution of doxorubicin (DXR) and liposomes separately after intravenous administration of DXR entrapped in liposomes in rats. Liposomes were double labeled with 14C-DXR (L-DXR) and 3H-inulin (L-INU). Blood and tissues were sampled at specified times until 120 min. Blood clearance of L-DXR was similar to that of L-INU. Distribution of both L-DXR and L-INU into the liver was parallel and extensive, while in the heart, the pattern of distribution differed between L-DXR and L-INU after peak concentration. Time courses of tissue concentration were explained well by dividing tissue into a shallow compartment with efflux and a deep compartment without efflux. In the liver, pharmacokinetic parameters of L-DXR and L-INU were similar, and the two kinetically different compartments may correspond to different uptake processes in hepatic endocytosis. In the heart, the shallow compartment was considered to correspond to the cardiac vascular space, and the intercompartmental rate constant (k3) for L-DXR was much larger than that for L-INU. The estimated half-life for this process was 20 min. The half-life for the degradation of liposomes in blood circulation was also estimated at 20 min from data on the urinary excretion of released 3H-inulin. These results suggest that the release of DXR from liposomes may be the rate-limiting process in the tissue distribution of DXR to the heart.

Animals↗

PubMed1992

In vivo evaluation of the effect of the size and opsonization on the hepatic extraction of liposomes in rats: an application of Oldendorf method.

In the hepatic uptake of large particles such as liposomes, a serum component called opsonin plays an important role. In this study, the 'Oldendorf method' is introduced to evaluate the hepatic extraction under the condition of single passage, which enabled examination of the effect of opsonization on liposome uptake by the intact liver. 14C-labelled liposomes and, an internal reference, 3H-H2O were injected as a bolus into portal vein. Liver uptake index (LUI) was calculated from the ratio of the extraction of 14C to that of 3H. The effect of liposome size (mean diameter of 0.8, 0.4, 0.2, and 0.05 micron) and opsonization (preincubation with fresh blood for 5 min) on liposomal hepatic uptake were investigated using this method. LUI increased with size significantly (p < 0.001), and opsonization enhanced LUI only for the large liposomes (0.8 micron). This result suggests that the critical diameter of opsonization for these liposomes lies between 0.4 and 0.8 micron.

Animals↗

PubMed1992

Non-Michaelis-Menten type hepatic uptake of liposomes in the rat.

The objective of this study was to verify the methodology for measuring uptake clearance of liposomes and to characterize kinetically the saturable hepatic uptake of liposomes-through phagocytosis. The correction of vascular space was important in the evaluation of hepatic uptake. The efflux of liposomes from liver was shown to be negligible, by a repeated dose study, and thus, hepatic clearance can be obtained by the hepatic uptake divided by the area under the blood concentration-time curve (AUC). The determinant parameter which describes the saturability of uptake clearance of liposomes, independent of infusion rate, was investigated, using the data of an in-vivo constant infusion study, where infusion rate-dependent saturable hepatic clearance was observed. The mean blood concentration failed to obtain an infusion rate-independent function. On the other hand, the AUC could explain the saturability of hepatic clearance for every infusion rate by a unique relationship. The hepatic uptake amount could also explain this saturability, independent of infusion rate. These kinetic characteristics are inconsistent with Michaelis-Menten type kinetics, therefore a new model is required to describe the saturable hepatic clearance in the disposition of liposomes.

Animals↗

PubMed1992

[Effects of ascorbic acid on the metabolic fate and the free radical formation of iproniazid].

The effects of ascorbic acid (AA) on the metabolic fate of iproniazid (IPN) and on the free radical intermediates derived from IPN were investigated in rats. After oral administration of IPN with or without AA, the plasma concentration and the urinary excretion of IPN and its metabolites were determined by gas chromatography-mass spectrometry using stable isotope labeled compounds as internal standards. In the excretion of IPN and its metabolites except hydrazine (Hy), the differences between co-administration and single administration were not observed. The excretion of Hy, which is a known hepatotoxic metabolite, decreased clearly in the co-administration of IPN and AA. When IPN and AA were co-administered orally, the profiles of plasma levels of IPN and its metabolites were almost similar after the administration of IPN alone. Furthermore, no differences between i.v. co-administration and i.v. administration alone were observed. These results indicated that AA did not affect both absorption and metabolism of IPN. By the electron spin resonance (ESR) spectroscopy and spin-trapping technique, the ESR signals due to the alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) adducts induced by isopropylhydrazine (IP-Hy) were two-fold higher than those by IPN in microsomal systems. The free radical formations of IPN and IP-Hy were significantly inhibited by AA in a dose dependent manner. The 4-POBN-trapped radical species generated from IPN and IP-Hy were presumed to be an isopropyl radical by the results of mass spectrometry.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Potential value of cetylmannoside-modified liposomes as carriers of macrophage activators to human blood monocytes.

The present study was undertaken to examine the potential value of cetylmannoside-modified multilamellar liposomes (Man-MLV) as carriers for transfer of macrophage activators to blood monocytes. Highly purified blood monocytes were isolated by centrifugal elutriation from healthy donors under endotoxin-free conditions. Freshly prepared monocytes phagocytosed Man-MLV to a lesser extent than monocyte-derived macrophages, but they took up Man-MLV much more effectively than control liposomes without cetylmannoside (control MLV). Phagocytosis of Man-MLV, but not control MLV by monocytes was inhibited by addition of D-mannose, but not of D-galactose. Desmethyl-muramyl dipeptide (norMDP) entrapped in Man-MLV was far more effective than norMDP entrapped in MLV in activating monocytes to the tumoricidal state. The effect of encapsulation of recombinant human macrophage colony-stimulating factor (M-CSF) in Man-MLV on prolongation of survival of monocytes was examined. Blood monocytes that had been incubated for up to 21 days with Man-MLV containing 5-20 U of M-CSF per ml were effective in prolonging monocyte survival, but monocytes that had been incubated in medium with less than 50 U/ml of M-CSF or with control MLV containing 5-10 U of M-CSF showed no increase of monocyte survival over that in medium alone. Addition of rabbit anti-M-CSF antiserum did not affect survival prolongation of monocytes by M-CSF encapsulated in Man-MLV. We conclude that liposomes modified with cetylmannoside are far more effective than unmodified liposomes as a carrier to deliver biological response modifiers to human blood monocytes.

Cell Survival↗

PubMed1991

Saturable, non-Michaelis-Menten uptake of liposomes by the reticuloendothelial system.

Multilamellar vesicles (300-350 nm) were infused into the rat femoral vein at the rate of 4, 40 and 400 nmol phosphatidycholine min-1 for 6 h using [3H]inulin as an aqueous marker. The time courses of blood concentration of vesicles, normalized for infusion rate, were not superimposable, showing the non-linearity of liposome disposition in the blood circulation. These time courses of blood concentration were well fitted by a single Michaelis-Menten equation. On the other hand, the time courses of tissue content could not be so accommodated. Additionally, the observed relationship between the uptake of liposomes by the liver and their clearance from it and other organs differed essentially from a simulation based on Michaelis-Menten type saturable kinetics. Therefore, it is suggested that there is a time-dependent non-Michaelis-Menten type process in the phagocytosis of macrophages in the reticuloendothelial system.

Animals↗