Liposomal Simvastatin Attenuates Neointimal Hyperplasia in Rats

Monocytes, macrophages, and inflammation play a key role in the process of neointimal proliferation and restenosis. The present study evaluated whether systemic and transient depletion of monocytes could be obtained by a single intravenous (IV) injection of simvastatin liposomes, for the inhibition of neointima formation. Balloon-injured carotid artery rats (n = 30) were randomly assigned to treatment groups of free simvastatin, simvastatin in liposomes (3 mg/kg), and saline (control). Stenosis and neointima to media ratio (N/M) were determined 14 days following single IV injection at the time of injury by morphometric analysis. Depletion of circulating monocytes was determined by flow cytometry analyzes of blood specimens. Inhibition of RAW264.7, J774, and THP-1 proliferation by simvastatin-loaded liposomes and free simvastatin was determined by the 3-(4, 5-dimethylthiazolyl-2)-2, 5- diphenyltetrazolium bromide assay. Simvastatin liposomes were successfully formulated and were found to be 1.5-2 times more potent than the free drug in suppressing the proliferation of monocytes/macrophages in cell cultures of RAW 264.7, J774, and THP-1. IV injection of liposomal simvastatin to carotid-injured rats (3 mg/kg, n = 4) resulted in a transient depletion of circulating monocytes, significantly more prolonged than that observed following treatment with free simvastatin. Administration to balloon-injured rats suppressed neointimal growth. N/M at 14 days was 1.56 ± 0.16 and 0.90 ± 0.12, control and simvastatin liposomes, respectively. One single systemic administration of liposomal simvastatin at the time of injury significantly suppresses neointimal formation in the rat model of restenosis, mediated via a partial and transient depletion of circulating monocytes.Key words: drug delivery systems, liposomes, monocytes, restenosis, statins     

Enhanced stability and in vitro bioactivity of surfactant-loaded liposomes containing Asiatic Pennywort extract

The objective of this work has been the microencapsulation of Asiatic Pennywort (AP) extract with lecithin from soybean. The effect of various quantities of non-ionic surfactant (Montanov82®) on liposomes upon physicochemical characteristics as well as their in vitro bio-activities was investigated. An addition of surfactant resulted in a decrease in particle size and an increase in percentage AP entrapment efficiency of liposomes. The surfactant-loaded liposomes demonstrated higher stability than surfactant-free liposomes where higher percentage AP remaining of liposomes can be achieved depending on surfactant concentration. No significant difference was found on AP release profiles among varied surfactant concentrations, although a presence of surfactant resulted in prolonged AP release rate. Liposomal AP with 20% w/w surfactant or higher demonstrated low cytotoxicity, a stronger anti-oxidation effect and collagen production on dermal fibroblast cells when compared with free AP and surfactant-free liposomes, possibly due to better cell internalization and less AP degradation in cells.     

Intravenous application of an anticalin dramatically lowers plasma digoxin levels and reduces its toxic effects in rats

Lipocalins tailored with high affinity for prescribed ligands, so-called anticalins, constitute promising candidates as antidotes. Here, we present an animal study to investigate both pharmacokinetic and clinical effects of an anticalin specific for the digitalis compound digoxin. Intravenous digoxin (2.5-50 μg/kg/min) was administered to rats until first changes in the ECG occurred (dose finding study) or a priori for 30 min (kinetic study). The anticalin DigA16(H86N), dubbed DigiCal, was administered intravenously at absolute doses of 1, 5, 10 and 20 mg, while the control group received isotonic saline. Hemodynamic changes, several ECG parameters and digoxin concentration in plasma were monitored at given time intervals. After DigiCal administration free digoxin concentration in plasma ultrafiltrate declined dramatically within 1 min to the presumably non-toxic range. There was also a significant and DigiCal dose-dependent effect on longer survival, less ECG alterations, arrhythmia, and improved hemodynamics. Infusion of a lower digoxin dose (2.5 μg/kg/min) resulted in a more sustained reduction of free digoxin in plasma after DigiCal administration compared to a higher digoxin dose (25 μg/kg/min), whereas ECG and hemodynamic parameters did not markedly differ, reflecting the known relative insensitivity of rats towards digoxin toxicity. Notably, we observed a re-increase of free digoxin in plasma some time after bolus administration of DigiCal, which was presumably due to toxin redistribution from tissue in combination with the relatively fast renal clearance of the rather small protein antidote. We conclude that anticalins with appropriately engineered drug-binding activities and, possibly, prolonged plasma half-life offer prospects for next-generation antidotal therapy.     

Differential toxicological response to positively and negatively charged nanoparticles in the rat brain

We investigated the potential for systemic and local toxicity after administration of empty nanosized anionic and cationic PEGylated-micelles and non-PEGylated liposomes, without a ligand attached, intended for use in drug-delivery systems. The particles were administered to 5–6-week-old male rats by three intravenous (IV) administrations over a period of one week at a dose of 100 mg/kg bodyweight or after a single intracerebroventricular (ICV) injection at a dose of 50 µg. The particles were stable and well characterised with respect to size and zeta potential. ICV administration of cationic particles was associated with histological changes near the injection site (hippocampus). Here, we detected focal infiltration with phagocytic cells, loss of neurons and apoptotic cell death, which were not observed after administration of the vehicle. No significant difference was found after IV or ICV administration of the anionic micelles with regard to haematology, clinical chemistry parameters or at the pathological examinations, as compared to control animals. Our study suggests that ICV delivery of cationic particles to the brain tissue is associated with toxicity at the injection site.     

Enhanced schistosomicidal efficacy of tartar emetic encapsulated in pegylated liposomes

The aim of the present study was to evaluate the ability of liposomes to improve the efficacy of tartar emetic (TA) against established Schistosoma mansoni infection. TA was used as a schistosomicidal drug model and both conventional liposomes (CL) and long-circulating pegylated liposomes (LCL) were evaluated. In the first experiment, TA, either free or encapsulated within CL or LCL, was given intraperitoneally (i.p.) as a single dose of 11 mg Sb/kg to mice experimentally infected with S. mansoni. Only the group treated with LCL showed a significant (55%) reduction in the worm burden, compared to the control groups (untreated or treated with empty LCL). In the second experiment, the efficacy of TA-containing LCL was evaluated at a higher dose (27 mg Sb/kg) by both subcutaneous (s.c.) and i.p. routes. Reduction levels of 67 and 82% were achieved by s.c. and i.p. routes, respectively. Strikingly, all mice survived to this high dose of antimony. This is in contrast with free TA that was lethal in 100% of mice at the same dose. The present work demonstrates that LCL reduce the acute toxicity of TA and effectively deliver this drug to S. mansoni during the late stages of parasite infection.     

PHARMACOKINETIC EVALUATION OF LIPOSOMAL ENCAPSULATED AMPICILLIN IN MALE AND FEMALE RATS

The dispositions of free and liposomal entrapped ampicillin were compared in male and female rats after IV administration. Serial blood samples were collected for 2 h in the free drug study and 12 h for the liposomal formulation. Pharmacokinetic parameters obtained with free drug were not significantly different between genders. However, gender significantly influenced the disposition of liposomal encapsulated ampicillin. While no difference was observed in distribution t_1/2 between genders, female rats had a shorter MRT, smaller V_ss and V_t and faster clearance as compared to male rats. In a second study, spleen, liver, kidney, heart, and lung were harvested post-injection of free and liposomal entrapped ampicillin. Free ampicillin did not distribute extensively into the tissue compartment and no gender difference was noted. In contrast, liposomal encapsulation resulted in a substantial tissue uptake. In general, female rats had higher concentrations in the spleen and lung as compared to male rats. In vitro plasma stability was not significantly different, suggesting that destabilization of the liposomes does not play a large role in the dispositional differences observed in these studies. However, in vivo interaction of liposomes and plasma lipoproteins may influence the disposition of encapsulated drug. ©1997 by John Wiley & Sons, Ltd.     

An electrocardiographic,molecular and biochemical approach to explore the cardioprotective effect of vasopressin and milrinone against phosphide toxicity in rats

The present study was conducted to identify the protective effect of vasopressin (AVP) and milrinone on cardiovascular function, mitochondrial complex activities, cellular ATP reserve, oxidative stress, and apoptosis in rats poisoned by aluminum phosphide (AlP). Rats were divided into five groups (n = 12) including control, AlP (12.5 mg/kg), AlP + AVP (2.0 Units/kg), AlP + milrinone (0.25 mg/kg) and AlP + AVP + milrinone. After treatment, the animals were connected to an electronic cardiovascular monitoring device to monitor electrocardiographic (ECG) parameter. Finally, oxidative stress biomarkers, mitochondrial complex activities, ADP/ATP ratio and apoptosis were evaluated on the heart tissues. Results indicated that AlP administration induced ECG abnormalities along with a decline in blood pressure and heart rate. AVP and milrinone significantly ameliorated these changes in all treated groups. Considerable protective effects on oxidative stress biomarkers, complex IV activity, ADP/ATP ratio and caspase-3 and -9 activities in treated groups were also found. These findings were supported by flow cytometry assay of cardiomyocytes. In conclusion, administration of AVP and milrinone, not only improve cardiovascular functions in AlP poisoned rats in the short time, but after a long time can also restore mitochondrial function and ATP level and reduce the oxidative damage, which prevent cardiomyocytes from entering the apoptotic phase.     

Atrial angiotensinase activity in hypothyroid, euthyroid, and hyperthyroid rats

Thyroid dysfunction produces marked cardiovascular responses. Hypothyroidism and hyperthyroidism cause important changes in the circulating renin-angiotensin system (RAS). Modifications in cardiac RAS have also been involved in cardiovascular alterations. Studies have revealed that thyroid hormones activate some components of cardiac RAS. Angiotensin (Ang) peptides are regulated by the activity of several aminopeptidases (AP) called angiotensinases. Previous results in our laboratory have demonstrated that thyroid dysfunction altered angiotensinase activities in hypothalamus, pituitary, and kidney. In the present study, we investigated the relationship between thyroid status and local angiotensinase activities in the atrium of hypothyroid, euthyroid, and hyperthyroid adult male rats. We have determined fluorometrically soluble and membrane-bound alanyl, glutamyl, and aspartyl aminopeptidase activities using naphthylamide derivatives as substrates. These activities have been, respectively, involved in the metabolism of Ang III to Ang IV, Ang II to Ang III, and Ang I to des-Asp Ang I. Hyperthyroidism was induced with subcutaneous injections of tetraiodothyronine (300 microg/kg/day), and the hypothyroid rats were obtained with 0.03% methimazole via the drinking water. Compared with that in euthyroid rats, a highly significant increase (by 50%) of soluble aspartyl aminopeptidase activity (P < 0.001) was observed in the atrium of hyperthyroid and hypothyroid animals. In membrane fractions, T4 treatment produced an increase in alanyl aminopeptidase (37%; P < 0.05) and aspartyl aminopeptidase activities (30%; P < 0.01). These results suggest higher formation of des-Asp Ang I in both hypothyroid and hyperthyroid rats but also suggest higher metabolism of Ang III to Ang IV in hyperthyroid animals, which is in agreement with the described alterations of cardiac RAS after thyroid dysfunction.     

Intravascular and interstitial fluid dynamics in rats treated with minoxidil.

Edema is a major complication of vasodilatory therapy. However, the pathophysiologic mechanisms leading to the formation of vasodilator-mediated edema are insufficiently understood. The present study therefore examined the effect of the chronic administration of the potent arteriolar vasodilator, minoxidil (Mx), on extracellular fluid dynamics in rats. Extracellular volume (ECV), plasma volume (PV), interstitial fluid volume (IV), arterial pressure (AP), and interstitial fluid pressure (IP) were measured in rats treated for 10 days with Mx (1.5 mg/kg/day) and in control animals. In addition to a decreased AP, Mx-treated animals had diminished water and sodium excretion. ECV, PV, and IV and plasma renin concentration (PRC) were also increased in the Mx-treated rats. IP, which was subatmospheric in control rats (-2.6 +/- 0.04 mm Hg), was near zero in Mx-treated animals (-0.2 +/- 0.02 mm Hg, p less than 0.05). Saline ECV expansion (20 min, Ringer infusion, 3% body weight) or rat albumin injection (300 mg/2 ml) induced similar changes in the volume of the extracellular fluid compartments in both groups. However, changes in IP were blunted in Mx-treated rats. These results, therefore, show that Mx-treated rats have changes in interstitial fluid dynamics prior to any macroscopic evidence of edema accumulation. These alterations in the extracellular compartment dynamics may be a consequence of the sustained arteriolar vasodilation induced by Mx.     

Pulmonary Targeting of Liposomal Triamcinolone Acetonide Phosphate

Purpose. To explore the use of triamcinolone acetonide phosphate liposomes as a pulmonary targeted drug delivery system. Methods. Triamcinolone acetonide phosphate liposomes composed of 1,2-distearoyl phosphatidylcholine and 1,2-distearoyl phosphatidyl glycerol and triamcinolone acetonide 21-phosphate dipotassium salt were prepared by dispersion and extruded through polycarbonate membranes. Encapsulation efficiency and in vitro stability at 37°C were assessed after size exclusion chromatography. TAP liposomes (TAP-lip) or TAP in solution (TAP-sol) were delivered to rats either by intratracheal instillation (IT) or intravenous (IV) administration. Pulmonary targeting was assessed by simultaneous monitoring of glucocorticoid receptor occupancy over time in lung (local organ) and liver (systemic organ) using an ex vivo receptor binding assay as a pharmacodynamic measure of glucocorticoid action. Results. In vitro studies in different fluids over 24 hours, showed that more than 75% of the TAP remained encapsulated in liposomes. Cumulative pulmonary effects after IT administration of TAP-lip were 1.6 times higher than liver receptor occupancy. In contrast, there was no difference in the pulmonary and hepatic receptor occupancy time profiles when TAP was administered intratracheally as a solution. No preferential lung targeting was observed when TAP-lip was administered IV. As indicated by the mean effect times, lung receptor occupancy was sustained only when TAP-lip was administered IT. Conclusions. Intratracheal administration of TAP-lip provided sustained receptor occupancy, and increased pulmonary targeting which was superior to IT administration of TAP-sol or IV administration of TAP-lip. The use of liposomes may represent a valuable approach to optimize sustained delivery of glucocorticoids to the lungs via topical administration.     

The in vivo measurement of expired 14CO2 derived from the N-demethylation of aminopyrine as a reflection of the in vitro hepatic cytochrome P-450 drug-metabolism activity in rats

The kinetics of 14CO2 production in rats were investigated after oral, ip, or iv administration of 14C-aminopyrine (AP) at several dose levels, and after pretreatment with phenobarbital (PB) or partial hepatectomy to produce alterations in hepatic function. Several kinetic parameters were assessed with each route of administration and at each dose level (0.1, 10, and 50 mg/kg). The parameters found most useful were: time to reach peak, peak rate, 14CO2 production per min at 20 or 30 min expressed as percentage of total administered 14C (R20 or R30), and half-life of the decline in 14CO2 production after peak. It was found that the R30 value after oral administration or R20 after the ip administration of AP (10 mg/kg) reflected alterations in hepatic function without significant overlap of values. The use of the R20 or R30 parameters determined from a single collection was further assessed in control and in PB- and CoCl2-pretreated animals and found to be capable of distinguishing between these different groups of animals. In addition, the AP breath test (ABT) kinetics were not significantly affected by 3-methylcholanthrene pretreatment. In another set of experiments, R30 values determined in controls and in PB- and CoCl2-pretreated rats demonstrated excellent correlation to changes in hepatic microsomal AP and ethylmorphine N-demethylase and aniline hydroxylase activities and cytochrome P-450 content. similar correlations were obtained with R20 after the ip administration of 10 mg of AP per kg. These findings indicate that the ABT is capable of accurately assessing AP N-demethylase activity and other parameters of hepatic mono-oxygenase activity.     

Comparison of doxorubicin- and MEN 10755-induced long-term progressive cardiotoxicity in the rat

The delayed functional cardiotoxic effects of repeated treatment with the new disaccharide anthracycline MEN 10755 and doxorubicin (1.5 mg/kg, i.v., once a week for 5 consecutive weeks) were investigated in the rat. Changes were assessed (2 days and 4 and 13 weeks after the last treatment) in ECG morphology, hemodynamics, in vivo left ventricular contractile responses to beta-adrenergic stimulation, and histopathology of both atria and ventricles. Doxorubicin induced significant and progressive prolongation of the QalphaT interval starting 2 days after suspension of treatment. At 4 and 13 weeks after the last treatment, the ECG showed a further progressive and significant impairment. MEN 10755 induced alterations similar in nature but of lesser severity compared with doxorubicin. In addition, MEN 10755-induced prolongation of the QalphaT interval was not progressive, being similar at 4 and 13 weeks after the last treatment. Although the hemodynamics were only slightly affected by both anthracyclines, a nearly complete ablation of isoprenaline-induced enhancement of ventricular function was observed 4 and 13 weeks after the last treatment with doxorubicin, whereas only mild, if any, reduction was detected in rats receiving MEN 10755. Histopathologic investigations indicated that both anthracyclines produced qualitatively similar alterations in ventricular myocytes. However, only with doxorubicin did these changes show a progression with a further significant worsening at 13 weeks as compared with 4 weeks after the last treatment. In addition, atrial lesions were evident in doxorubicin-treated rats, but not in rats receiving MEN 10755. In conclusion, an equimyelotoxic regimen of MEN 10755 produced, as compared with doxorubicin, lesser ECG alterations, smaller impairment of the ventricular response to adrenergic stimulation, and less severe myocyte lesions. Unlike doxorubicin, the histologic and functional cardiotoxic effects induced by MEN 10755 were not progressive. Further investigations are warranted to define the pharmacodynamic and/or pharmacokinetic mechanism(s) underlying the different cardiotoxic profile exhibited by the two anthracyclines.     

Chronic salt loading and cardiovascular-associated changes in experimental diabetes in rats

1. High-sodium intake may increase blood pressure and diabetes is a salt-sensitive condition. In the present study, we evaluated cardiovascular changes and their neurohumoral mechanisms in streptozotocin (STZ)-diabetic rats that underwent chronic salt loading. 2. We studied male Wistar rats (150-280 g) 14 days after the injection of either STZ (50 mg/kg, i.v.; D; n = 18) or citrate buffer (C; n = 16). After the induction of diabetes, animals were maintained for 14 days with free access to standard rat chow and tap water (C and D groups) or 1% NaCl solution (C-S and D-S groups). We conducted two experiments. Experiment 1 consisted of basal arterial pressure (AP) measurement (30 min) followed by the evaluation of AP responsiveness to phenylephrine and sodium nitroprusside. One day later, with the rats anaesthetized, a blood sample was collected to test for glycaemia, plasma angiotensin-converting enzyme (ACE) activity and renin. Kidneys were removed for the determination of tissue ACE activity. Experiment 2 comprised 24 h urine collection followed by 3 days of cardiovascular records, which consisted of a 30 min basal AP measurement, followed by injection of blockers of the vasopressin system, the renin-angiotensin system (RAS) and the sympathetic system. Basal haemodynamic data, baroreflex evaluation and AP responses to blockade of the vasopressin system with vasopressin V(1) receptor antagonist (aAVP; 10 mg/kg, i.v.), the RAS by losartan (10 mg/kg, i.v.) and the sympathetic system by hexamethonium (20 mg/kg, i.v.) were determined. 3. Glycaemia was similar between C and C-S (P = 0.612) and between D and D-S (P = 0.552), but higher in diabetic compared with non-diabetic rats (P < 0.0001). The D-S rats had an increment of 24% in mean AP compared with D (120 +/- 4 vs 97 +/- 2 mmHg, respectively; P = 0.0001), which was not seen in C-S compared with C rats. A positive association was noted between urinary sodium and mean AP (r = 0.37; P = 0.04). Plasma renin was undetectable in D-S rats. The response to acute drug blockade of vasopressin and the RAS was similar among groups, but hexamethonium elicited a more pronounced decrease in AP in D-S compared with D rats (P = 0.001). 4. The main neurohumoral mechanisms of salt-induced cardiovascular changes in STZ-diabetes are increased sodium and vascular sensitivity to adrenergic stimuli, which act in combination to produce a final result of higher AP levels, a finding not observed in control rats. Baroreflex derangements induced by diabetes were not affected by salt overload.     

Assessment of Glucocorticoid Lung Targeting by ex-Vivo Receptor Binding Studies in Rats

Triamcinolone acetonide (TA, 22 µg) was given to rats by intravenous (IV) injection or intratracheal (IT) instillation. Free glucocorticoid receptors were monitored over time in liver and lung using an ex-vivo receptor binding technique. After IV administration of a TA solution, the reduction of free receptors over time was very similar in lung and liver (AUC_Lung = 280 ± 47 %*h; AUC_Liver = 320 ± 76 %*h). Intratracheal instillation of the same solution produced time profiles which mirrored those of IV injection (AUC_Lung = 260 ± 41 %*h; AUC_Liver = 330 ± 50 %*h). The lack of lung targeting was also reflected in the failure to show any significant difference in the pulmonary targeting factor T (AUC_Lung/AUC_Liver) between IV (T = 0.84 ± 0.18) and IT (T = 0.78 ± 0.03) administration. In contrast, a certain degree of lung specificity was observed after IT instillation of a glucocorticoid suspension (22 µg; AUC_Lung = 160 ± 135 %*h; AUC_Liver = 65 ± 91 %*h, T = 2.3 ± 0.5) as indicated by significant differences in T between IV injection and IT instillation (p = 0.038). The method presented provides a means of simultaneously assessing pulmonary and systemic effects after different forms and routes of administration and might be of value in further studying multiple aspects of inhalation glucocorticoid therapy.     

Protective effect of a specific platelet-activating factor antagonist, BN 52021, on bupivacaine-induced cardiovascular impairments in rats

Administration of the local anaesthetic bupivacaine (1.5 or 2 mg/kg, i.v.) to rats elicited a marked decrease of mean arterial blood pressure (MBP) and heart rate (HR) leading to death (in 67% or 90% of animals respectively). Intravenous injection of the specific platelet-activating factor (PAF) antagonist BN 52021 (10 mg/kg), 30 min before bupivacaine administration (2 mg/kg i.v.) suppressed both the decrease of MBP and HR. In contrast, doses of 1 mg/kg BN 52021 given 30 min before or 10 mg/kg administered 5 min before i.v. injection of bupivacaine were ineffective. When BN 52021 (20 mg/kg i.v.) was injected immediately after bupivacaine (2 mg/kg), a partial reversion of the decrease of MBP and HR was observed, whereas the dose of 10 mg/kg was ineffective. A partial recovery of bupivacaine-induced ECG alterations was observed after pretreatment of the rats with BN 52021. Since the administration of BN 52021, at all doses studied, did not alter MBP and HR at the doses used, the bulk of these results clearly demonstrate a protective action of BN 52021, a specific antagonist of PAF, against bupivacaine-induced cardiovascular toxicity. Thus, consistent with its direct effect on heart, PAF appears to be implicated in bupivacaine-induced cardiovascular alterations.     

Pancreatic tissue protective nature of D-Pinitol studied in streptozotocin-mediated oxidative stress in experimental diabetic rats

The present study was aimed to investigate the possible pancreatic tissue protective nature of D-Pinitol, a cyclitol present in soybean, against free radical-mediated oxidative stress in streptozotocin-induced diabetic rats by assaying the activity of pancreatic enzymatic antioxidants such as superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and glutathione-S-transferase (GST) and the levels of plasma non-enzymatic antioxidants such as vitamin E, vitamin C, ceruloplasmin and reduced glutathione (GSH). To assess the extent of oxidative stress, the levels of lipid peroxidation (LPO) and hydroperoxides in both plasma and pancreatic tissues were also measured. A significant increase in the levels of both lipid peroxides and hydroperoxides with a concomitant decrease in antioxidant status was observed in the diabetic rats when compared to control rats. Oral administration of D-Pinitol (50 mg/kg b.w./day for 30 days), a major cyclitol present in soybean, ameliorates the free radical-mediated alterations to near normalcy. The pancreatic tissue protective nature of D-Pinitol was further evidenced by histological observations. The results were statistically comparable with glyclazide, a standard hypoglycemic drug. Thus, the results of the present study suggest that D-Pinitol protects the pancreatic tissue from free radical-mediated oxidative stress in addition to its antidiabetic property.     

Use of polyglycerol (PG), instead of polyethylene glycol (PEG), prevents induction of the accelerated blood clearance phenomenon against long-circulating liposomes upon repeated administration

The accelerated blood clearance (ABC) phenomenon accounts for the rapid systemic clearance of PEGylated nanocarriers upon repeated administrations. IgM production against the polyethylene glycol (PEG) coating in PEGylated liposomes is now known to be responsible for such unexpected pharmacokinetical alterations. The ABC phenomenon poses a remarkable clinical challenge by reducing the therapeutic efficacy of encapsulated drugs and causing harmful effects due to the altered tissue distribution pattern of the drugs. In this study, we investigated the in vivo performance of liposomes modified with polyglycerol (PG) upon repeated injection, and the in vivo therapeutic efficacy of such liposomes when they encapsulated a cytotoxic agent, doxorubicin (DXR). Repeated injection of PEG-coated liposomes in rats induced the ABC phenomenon, while repeated injection of PG-coated liposomes did not. In addition, DXR-containing PG-coated liposomes showed antitumor activity that was superior to that of free DXR and similar to that of DXR-containing PEG-coated liposomes upon repeated administration. These results indicate that polyglycerol (PG) might represent a promising alternative to PEG via enhancing the in vivo performance of liposomes by not eliciting the ABC phenomenon upon repeated administration.     

血栓靶向尿激酶脂质体的制备及其体内溶栓效果

目的制备血栓靶向的尿激酶脂质体,并在大鼠颈总动脉血栓模型上考察其溶栓情况。方法通过液相合成法合成出靶向于血栓的特异性配体H-Arg-Gly-Asp-Ser-OH (RGDS),并将其与monocarboxyl poly (ethylene glycol) 3 500 distearoyl phosphatidylethalnolamine (DSPE-PEG_{3 500}-COOH)偶联后插入到脂质体双层膜中得到血栓靶向尿激酶脂质体;通过制备方法的改进,以氢化豆磷脂在室温下制备尿激酶脂质体;在大鼠颈总动脉血栓模型上,考察了血栓靶向脂质体的体内溶栓效果。 结果所得的尿激酶脂质体包封率高、粒径小,稳定性好;与空白对照组的栓重相比,在相同剂量(60 kU·kg^-1,小剂量)下,游离尿激酶组几乎无任何改变,尿激酶脂质体组血栓重量稍有减轻但无显著性差异,血栓靶向尿激酶脂质体组血栓重量明显减轻(P<0.001);干重时的情况略有不同。与同剂量的普通脂质体相比,血栓靶向尿激酶脂质体溶栓效果显著改善(湿重时P<0.01,干重时P<0.05),表现出明显的靶向溶栓能力。 结论所制备的血栓靶向尿激酶脂质体具有靶向溶栓的效果。     

Protective effect of taurine against acute paraquat intoxication in rats

The effect of taurine (TA) on acute paraquat (PQ) intoxication was investigated in rats. Treatment with TA was begun 10 min after rats received a s. c. injection of PQ 40 mg/kg. Saline (0.9%) or 5% TA solution were infused i.v. for 5-6 min (short-interval infusion study). One hour after TA infusion, PQ concentration in the blood was increased and that in the urine was lowered, as compared with those in the saline-infused group. Significant increases of the PQ concentration was observed in kidney at 3 hours after TA administration. Excreted urine volume was significantly higher in the TA group during the time-period of 0-1 and 0-5 hours after the 5% TA administration compared with that of the saline group. However, there were no significant differences in total urinary PQ excretion between the two groups. Saline or 2.5% and 5% TA was infused continuously during the time-period of 0-1, 0-3 or 0-5 hours (long-interval infusion study). A marked increase in PQ concentration in blood and a reduction of PQ concentration in kidney were noticed during the time-period of 1-5 hours after the 5%TA infusion. Urinary excretion was remarkably accelerated by 5% TA infusion and the total urine volume increased to 20 times during the time-period 0-1 hour and 1.7 times during the time-period of 3-5 hours as compared with the saline control. In addition, urinary volume during the time-period of 0-5 hours almost reached that of 5% TA volume which infused to animals. The mortality rate of the groups that received either single or double short-time infusion of 5% TA was 100%. Thus, these results suggest that a long continuous infusion of 5% TA increased urine output and inhibits of PQ accumulation in renal tissue despite a rise in blood PQ concentration.     

Effect of domperidone on renal response to certain atrial natriuretic substances in rats

Anesthetized rats, maintained on an intravenous (1 ml/h) infusion of saline, were injected with either atrial extract from normal rats (AE), atriopeptin III (APIII, 24 amino acids) or atrial peptide (AP, 28 amino acids) as either a bolus injection (1 atrial equivalent of AE, 1 microgram APIII, or 1 microgram AP) or by constant infusion (1.7 ng APIII or AP/min for 30 min) in isotonic saline. Diuretic, natriuretic, and kaliuretic responses were determined by subtraction of baseline values from the renal response during the first 15 min after administration of the atrial natriuretic factor (ANF). The change in renal response observed in rats receiving saline and a bolus injection of an ANF was compared to the change in response observed in the same rats that received the dopaminergic antagonist, domperidone (0.2 microgram/kg, i.v.), and the same ANF. In the case of the renal response following infusion of an ANF, a paired comparison was made between domperidone-treated and untreated rats. Domperidone attenuated the renal response to AP, administered either as a bolus injection or a constant infusion, whereas domperidone significantly reduced renal response to APIII only following constant infusion. The renal response to a bolus injection of AE was not affected by the administration of domperidone. These findings suggest that the renal action of the putative circulating form of ANF, i.e. AP, is mediated via dopaminergic receptors, and that the route of administration may affect the mechanism of action of an ANF.