bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical Consequences of the Biphasic Elimination Kinetics for the Diuretic Effect of Furosemide and its Acyl Glucuronide in Humans
Authors: Vree Tom B , Van Der Ven André J A M
Published: July 2003

This review discusses the possibility of whether furosemide acyl glucuronide, a metabolite of furosemide, contributes to the clinical effect of diuresis.

First an analytical method (e.g. HPLC) must be available to measure both parent drug and furosemide acyl glucuronide. Then, with correctly treated plasma and urine samples (light protected, pH 5) from volunteers and furosemide-treated patients, the kinetic curves of both furosemide as well as its acyl glucuronide can be measured. The acyl glucuronide is formed in part by the kidney tubules and it is possible that the compound is pharmacologically active through inhibition of the Na+/2Cl-/K+ co-transport system; up to now the mechanism of action has been solely attributed to furosemide.

The total body clearance of furosemide occurs by hepatic and renal glucuronidation (50%) and by renal excretion (50%). Enterohepatic cycling of furosemide acyl glucuronide, followed by hydrolysis, results in a second and slow elimination phase with a half-life of 20-30h. This slow elimination phase coincides with a pharmacodynamic rebound phase of urine retention. After each dosage of furosemide, there is first a short stimulation of urine flow (4h), which is followed by a 3-day recovery period of the body.

The following clinical implications arise from study of the elimination kinetics of furosemide. Repetitive dosing must result in accumulation of the recovery period. Accumulation of furosemide and its acyl glucuronide in patients with end-stage renal failure results from infinite hepatic cycling. Impaired kidney function may result in impaired glucuronidation and diuresis. While kidney impairment normally requires a dose reduction for those compounds which are mainly eliminated by renal excretion, for diuretics, a dose increment is required in order to maintain a required level of diuresis.

The full clinical impact of the accumulation of furosemide and its acyl glucuronide in patients with end-stage renal failure has to be determined.
Influence of pH and Temperature on Kinetics of Ceftiofur Degradation in Aqueous Solutions
Authors: Sunkara Gangadhar , Navarre Christine B , Kompella Uday B
Published: July 2003

The objective of this study was to evaluate the stability of ceftiofur (1mgmL-1)in aqueous solutions at various pH (1, 3, 5, 7.4 and 10) and temperature (0, 8, 25, 37 and 60°C) conditions. The ionic strength of all these solutions was maintained at 0.5 M. Ceftiofur solutions at pH 5 and 7.4 and in distilled water (pH = 6.8) were tested at all the above temperatures. All other solutions were tested at 60°C. Over a period of 84 h, the stability was evaluated by quantifying ceftiofur and its degradation product, desfuroylceftiofur, in the incubation solutions. HPLC was used to analyse these compounds.

At 60°C, the rate of degradation was significantly higher at pH 7.4 compared with pH 1, 3, 5 and distilled water. At both 60°C and 25°C, degradation in pH 10 buffer was rapid, with no detectable ceftiofur levels present at the end of 10 min incubation. Degradation rate constants of ceftiofur were 0.79 ± 0.21, 0.61 ± 0.03, 0.44 ± 0.05, 1.27 ± 0.04 and 0.39 ± 0.01 day-1 at pH 1, 3, 5, 7.4 and in distilled water, respectively. Formation of desfuroylceftiofur was the highest (65%) at pH 10. The rate of degradation increased in all aqueous solutions with an increase in the incubation temperature. At pH 7.4 the degradation rate constants were 0.06 ± 0.01, 0.06 ± 0.01, 0.65 ± 0.17, and 1.27 ± 0.05 day-1 at 0, 8, 25, 37 and 67°C, respectively. The energy of activation for ceftiofur degradation was 25, 42 and 28kcalmol-1 at pH 5, 7.4 and in distilled water, respectively.

Desfurylceftiofur formation was the greatest at alkaline pH compared with acidic pH. Ceftiofur degradation accelerated the most at pH 7.4 and was most rapid at pH 10. The results of this study are consistent with rapid clearance of ceftiofur at physiological pH.
Colon-specific Delivery of Budesonide with Azopolymer-coated Pellets: Therapeutic Effects of Budesonide with a Novel Dosage Form against 2,4,6-Trinitrobenzenesulphonic Acid-induced Colitis in Rats
Authors: Tozaki Hideyuki , Fujita Takuya , Komoike Junta , Kim Sooh-Ih , Terashima Hiroshi , Muranishi Shozo , Okabe Susumu , Yamamoto Akira
Published: July 2003

The objective of this study was to achieve colon-specific delivery of budesonide using azopolymer-coated pellets and to accelerate healing of 2,4,6-trinitrobenzenesulphonic acid sodium salt (TNBS)-induced colitis in rats.

After oral administration of azopolymer-coated pellets containing budesonide, a significant increase was observed in the therapeutic effects of the drug accompanied by a decrease in its systemic adverse effects when compared with oral administration in saline or rectal administration by enema. In addition, with the use of the colon-specific oral dosage form the dose of budesonide could be reduced.

These results suggested that azopolymer-coated pellets may be a useful dosage form for the colon-specific delivery of budesonide as an anti-inflammatory steroid drug to bring about the healing of TNBS-induced colitis in rats.
Adrenal Effects and Pharmacokinetics of CFC-free Beclomethasone Dipropionate: a 14-Day Dose-Response Study
Authors: Harrison Lester I , Colice Gene L , Donnell David , Soria Inmaculada , Dockhorn Robert
Published: July 2003

Since equivalent efficacy is achieved with lower doses of the reformulated beclomethasone dipropionate in the chlorofluorocarbon (CFC)-free propellant HFA-134a (HFA) than with the original CFC-beclomethasone dipropionate formulation, it is possible the HFA-beclomethasone dipropionate may have less safety concerns than the CFC formulation. Despite its chronic use, the steady-state pharmacokinetics of beclomethasone dipropionate has never been studied before. This double-blind study examined adrenal effects and pharmacokinetics after 14 days of dosing with HFA-beclomethasone dipropionate.

Forty-three steroid-naïve asthmatic patients were randomised into 5 parallel groups and dosed every 12 h for 14 days with: HFA-placebo; 200, 400 or 800 μg day-1 HFA-beclomethasone dipropionate; or 800 μg day-1 CFC-beclomethasone dipropionate. After two weeks of dosing, the 24-h urinary free cortisol of all but one patient remained within the normal range, showing that all doses were well tolerated from a systemic safety perspective. The active HFA-beclomethasone dipropionate treatment groups showed a dose-related fall in 24-h urinary free cortisol. Total-beclomethasone (beclomethasone dipropionate and metabolites) pharmacokinetics after either the first dose of HFA-beclomethasone dipropionate or CFC-beclomethasone dipropionate were not substantially affected by subsequent doses. The extent of drug absorption from 800 μg day-1 HFA-beclomethasone dipropionate and CFC-beclomethasone dipropionate was in the ratio of 1–7: 1. A non-linear correlation between 24-h urinary free cortisol and the pharmacokinetic parameters was observed, reflecting smaller changes in 24-h urinary free cortisol than in pharmacokinetics as the dose was increased.

No clinically meaningful change in the pharmacokinetics of beclomethasone dipropionate plus metabolites was seen on multiple dosing. The greater systemic availability of HFA-beclomethasone dipropionate was still associated with adrenal effects comparable with that of the CFC formulation at the same dose.
Drug Permeation through the Three Layers of the Human Nail Plate
Authors: Kobayashi Yoichi , Miyamoto Misao , Sugibayashi Kenji , Morimoto Yasunori
Published: July 2003

The in-vitro permeation characteristics of a water soluble model drug, 5-fluorouracil, and a poorly water soluble model drug, flurbiprofen, were investigated through three layers of the human nail plate (namely, the dorsal, intermediate and ventral nail plates), using a modified side-by-side diffusion cell. The dorsal-filed nail plate, the ventral-filed nail plate and the dorsal-and-ventral-filed nail plate were prepared to known thicknesses and then used with the full-thickness nail plate to investigate the permeation characteristics of each single layer.

Most of the lipids in the human nail plate were found in the dorsal and ventral layers. The rank orders of the permeation fluxes for 5-fluorouracil and flurbiprofen were both: dorsal-and-ventral-filed nail plate > dorsal-filed nail plate > ventral-filed nail plate > full-thickness nail plate. With respect to 5-fluorouracil permeation through each single layer, the permeability coefficient of the intermediate layer was higher than those of other single layers. However in the case of flurbiprofen, the permeability coefficient of the ventral layer was higher than other single layers. The diffusion coefficients of 5-fluorouracil and flurbiprofen in the dorsal layer were the lowest of any single layer. The drug concentration in each layer was estimated using each respective permeation parameter. The drug concentration in the nail plate was observed to be dependent on the solubility and the flux of the drug.

From these findings, we suggest that the human nail plate behaves like a hydrophilic gel membrane rather than a lipophilic partition membrane and that the upper layer functions as the main nail barrier to drug permeation through its low diffusivity against the drugs.
The Presence of an Na+/Spermine Antiporter in the Rat Renal Brush-border Membrane
Authors: Kobayashi Michiya , Fujisaki Hiroko , Sugawara Mitsuru , Iseki Ken , Miyazaki Katsumi
Published: July 2003

This study was aimed at determining the driving force for spermine transport in rat renal proximal tubular brush-border membrane.

The uptake of spermine and trientine, a spermine-like drug used for treating Wilson's disease, into rat renal brush-border membrane vesicles was significantly stimulated by an outwardly directed Na+ gradient. The Na+-dependent uptake was temperature dependent and saturable. A kinetic analysis of the initial uptake of spermine with an Na+ gradient gave a Km value of 1.44μM and a Vmax value of 6.31pmol (mg protein)-1 /30 s. The Na+- dependent uptake of [3H]spermine was inhibited by spermine, trientine and tetraethylenepentamine. Substrates of the H+/organic cation transporter (cimetidine and tetraethylammonium), physiological polyamines (putrescine and spermidine) with 2 or 3 amino groups and aminoglycosides (amikacin and tobramicin) with 4 or 5 cationic amines did not affect the uptake of spermine in the presence of an outwardly directed Na+ gradient.

These results suggest that the renal tubular secretion of spermine is mediated by an Na+/spermine antiport system which is specific for a straight-chain polyamine compound with more than 4 amino groups.
Inhibition by Magnolol of Formylmethionyl-leucyl-phenyl alanine-induced Respiratory Burst in Rat Neutrophils
Authors: Wang Jih P , Hsu Ei F , Raung Shue L , Chang Ling C , Tsao Lo T , Lin Pei L , Chen Chien C
Published: July 2003

The influence of the plant product magnolol on neutrophil superoxide anion (O2-.) generation has been investigated in the rat.

Intraperitoneal injection of magnolol (30mgkg-1) significantly inhibited the formyl-methionyl-leucyl-phenylalanine (fMLP)-induced respiratory burst in rat whole blood ex-vivo. Magnolol also inhibited the O2-. generation with an IC50 (concentration resulting in 50% inhibition) of 15.4 ± 1.6 μM and O2 consumption in rat neutrophils in-vitro. Magnolol weakly inhibited the O2-. generation in the xanthine-xanthine oxidase system, decreased cellular cyclic AMP level and had no effect on cyclic GMP levels. It weakly inhibited neutrophil cytosolic protein kinase C activity but did not alter porcine heart protein kinase A activity. Magnolol attenuated fMLP-induced protein tyrosine phosphorylation with an IC50 of 24.0 ± 1.9 μM and the phosphorylation of mitogen-activated protein kinase p42/44 with an IC50 of 28.5 ± 4.5 μM. However, magnolol alone activated neutrophil phospholipase D activity as determined by the formation of phosphatidic acid and phosphatidylethanol in the presence of ethanol. In the presence of NADPH, the arachidonate-activated NADPH oxidase activity in a cell-free system was weakly suppressed by magnolol.

These results suggest that the inhibition of respiratory burst in fMLP-activated neutrophils by magnolol is probably attributable mainly to the attenuation of protein tyrosine phosphorylation and p42/44 mitogen-activated protein kinase activation, and partly to the suppression of protein kinase C and NADPH oxidase activities.
Ca2+/Calmodulin-dependent Protein Kinase II Inhibitors Potentiate Superoxide Production in Polymorphonuclear Leukocytes
Authors: Watanabe Manabu , Kaihatsu Takayuki , Miwa Masao , Maeda Toshio
Published: July 2003

The possible role of Ca2+/calmodulin-dependent protein kinase II (CaMK II) in superoxide anion (O2-) production induced by formyl-methionyl-leucyl-phenylalanine (FMLP) was investigated in mouse polymorphonuclear leukocytes (PMNs).

KN-93 and KN-62, specific CaMK II inhibitors, augmented FMLP-induced O2-production. KN-92, an analogue which did not inhibit CaMK II, did not affect O2-production. W-7, a calmodulin inhibitor, augmented O2- production when administered at 30 mM for 5 min. KN-93 and recombinant mouse tumour necrosis factor-α (rmTNF-α) each augmented the maximal production of O2- induced by FMLP, and an additive effect of a combination of KN-93 and rmTNF-α was observed. CaMK II activity in the PMNs was increased by FMLP, and the increase was inhibited by KN-93 but not by rmTNF-α.

These results suggest that the inhibition of CaMK II resulted in the augmentation of FMLP-induced O2- production in PMNs by a mechanism different from that of the augmentation shown by TNF-α.
Synthesis, Physicochemical Properties and Biological Evaluation of Aromatic Ester Prodrugs of 1-(2‘-Hydroxyethyl)-2-ethyl-3-hydroxypyridin-4-one (CP102): Orally Active Iron Chelators with Clinical Potential
Authors: Liu Zu Dong , Liu Ding Yong , Li Lu Shu , Hider Robert C
Published: July 2003

The synthesis of seven aromatic ester derivatives of 1-(2′-hydroxyethyl)-2-ethyl-3-hydro-xypyridin-4-one is described. These ester prodrugs have been designed to target iron chelators to the liver, the major iron storage organ. In principle this should improve chelation efficacy and minimize toxicity.

The distribution coefficients of these ester prodrugs between 1-octanol and MOPS buffer pH 7·4 were measured together with their rates of hydrolysis at pH 2 and pH 7·4, in rat blood and liver homogenate. Esters with heteroaromatic acid moieties were found to be less stable than benzoyl analogues. The in-vivo iron mobilisation efficacy of these ester prodrugs has been compared with that of the parent drug using a 59Fe-ferritin loaded rat model. Many prodrugs were found to enhance the ability of the parent hydroxypyridinone to facilitate 59Fe excretion. However, not all prodrugs provided increased efficacy, demonstrating that lipophilicity is not the only factor which influences drug efficacy. Furthermore, no clear correlation between efficacy and susceptibility to hydrolysis was detected.

The picolinic and nicotinic ester derivatives appear to offer the best potential as prodrugs as they have a relatively low LogP value and yet lead to enhanced efficacy over the parent hydroxypyridinone.
Characterization and In-vivo Ocular Absorption of Liposome-encapsulated Acyclovir
Authors: Fresta Massimo , Panico Anna Maria , Bucolo Claudio , Giannavola Claudia , Puglisi Giovanni
Published: July 2003

The potential of liposomes as an in-vivo ophthalmic drug delivery system for acyclovir was investigated.

The drug-membrane interaction was evaluated by means of differential scanning calorimetry analysis. These experiments showed that acyclovir is able to interact with both positively and negatively charged membranes via electrostatic or hydrogen bonds. No interaction was observed with neutral membranes made up of dipalmitoylphosphatidyl-choline.

Different liposome preparation procedures were carried out to encapsulate acyclovir. The drug encapsulation mainly depends on the amount of water which the liposome system is able to entrap. In the case of multilamellar vesicles, charged systems showed the highest encapsulation efficiency. No particular difference in the encapsulation efficiency was observed for oligolamellar vesicles prepared with the reverse-phase evaporation technique. Oligolamellar liposomes showed the highest acyclovir encapsulation parameters and had release profiles similar to those of multilamellar liposomes. In-vivo experiments using male New Zealand albino rabbits were carried out to evaluate the aqueous humour concentration of acyclovir bioavailability.

The most suitable ophthalmic drug delivery system was oligolamellar systems made up of dipalmitoylphosphatidylcholine—cholesterol—dimethyldioctadecyl glycerole bromide (7:4:1 molar ratio), which presented the highest encapsulation capacity and were able to deliver greater amounts of the drug into the aqueous humour than a saline acyclovir solution or a physical liposome/drug blend.
Control of the Dispersing Process and Pharmacokinetics in Rats for Lipid A Analogue, E5531
Authors: Asai Yasuyuki , Sano Yoshihisa , Kikuchi Kiyomi , Iwamoto Kiyoshi , Watanabe Sumio
Published: July 2003

E5531 is a synthetic disaccharide analogue of lipid A which has a low toxicity but retains the ability to reduce production of tumour necrosis factor. This analogue has potential for use in the treatment of septic shock. An injectable formulation of E5531 would be useful, but dispersion in aqueous solution is a problem. In the present study the dispersing process for E5531 was evaluated using the pH-jump method (pH 11·0·7·3). The size of the aggregates was decreased (reaching 20 nm) with increasing dispersing time in 0·003 M NaOH (pH 11·0). The membrane fluidity of the aggregates increased with increasing dispersing time. When prepared by the normal dilution method (pH 7·3·7·3), the size of the aggregates remained constant at 140 nm and the membrane fluidity was smaller than that of samples prepared by the pH-jump method. This indicates that during dispersing at basic pH, the hydration proceeded in a normal manner, but then stopped, just after adjustment of the pH to 7·3. This suggests that the degree of hydration of the membrane is dependent on the dispersing time at pH 11·0. Using samples with different degrees of hydration and different membrane fluidity prepared by the pH-jump method, the pharmacokinetics and stability of the aggregates were evaluated after intravenous injection into rats. The data thus obtained confirmed that the membrane fluidity was correlated with the pharmacokinetics and stability in rat plasma.

It was concluded that the pharmacokinetics of E5531 in rats can be controlled by changing the degree of hydration and membrane fluidity by means of using different dispersing times in alkaline solution (pH 11·0).
Effect of Pentobarbital Anaesthesia on Intestinal Absorption and Hepatic First-pass Metabolism of Oxacillin in Rats, Evaluated by Portal-Systemic Concentration Difference
Authors: Ueda Shinya , Yamaoka Kiyoshi , Nakagawa Terumichi
Published: July 2003

The effects of anaesthesia on intestinal drug absorption and hepatic first-pass metabolism in rats were investigated by observing the difference in the drug concentration between portal and systemic bloods. Oxacillin and pentobarbital were selected as a model drug and as an anaesthetic, respectively. Rats were divided into a conscious control group and an anaesthetized group. All rats were cannulated simultaneously in the portal vein and in the femoral artery, and oxacillin was orally administered after its intra-arterial injection (double dosing). For the anaesthetized group, pentobarbital was intrasubcutaneously administered twice, first before intra-arterial injection and again before oral administration of oxacillin. The arterial blood alone was sampled from the cannula in the femoral artery before oral administration, whereas the arterial and portal bloods were simultaneously sampled from both cannulated sites after oral administration. Oxacillin concentrations in plasma were assayed by HPLC.

The anaesthesia increased the absolute bioavailability (F), the mean absorption time (MAT) and the hepatic recovery ratio (FH), but caused little change in the local absorption ratio into the portal system (Fa) and the total clearance (CL). The hepatic clearance (CLH) was significantly decreased, resulting in an apparent small change in CL—CLH which is considered to be renal clearance.

By this method, it was shown directly that an increase in F due to pentobarbital anaesthesia was attributable to the significant increase in FH. It is expected that the method is useful not only to evaluate the effect of anaesthesia on the first-pass effect, but also to assess the effect of co-administration of drugs on first-pass metabolism.
Molecular Basis of Indomethacin-Human Serum Albumin Interaction
Authors: Trivedi Vishwa D , Vorum Henrik , Honoré Bent , Qasim Mohammad A
Published: July 2003

Studies on the strength and extent of binding of the non-steroidal anti-inflammatory drug indomethacin to human serum albumin (HSA) have provided conflicting results. In the present work, the serum-binding of indomethacin was studied in 55 mM sodium phosphate buffer (pH 7·0) at 28°C, by using a fluorescence quench titration technique.

The interaction of indomethacin with human serum albumin has been studied as a function of temperature, ionic strength and pH. The results suggest that electrostatic interaction plays a major role in the binding. The possible role of lysine residues in this interaction was studied by modifying exposed and buried lysine residues of HSA with potassium cyanate and studying indomethacin binding with the modified HSA. The data suggest that the interaction takes place via a salt bridge formation between the carboxylate group of indomethacin and a buried lysine residue of HSA.

A technique involving fluorescence enhancement of bilirubin upon its interaction with HSA was used to study its displacement by indomethacin. The displacement, although apparently competitive in nature, was not strong suggesting that the primary sites of interaction of bilirubin and indomethacin are different.
Pharmacokinetics of Buspirone following Oral Administration to Rhesus Monkeys
Authors: Marathe Punit H , Shen Frank , Markham Peter , Greene Douglas S
Published: July 2003

Pharmacokinetics of buspirone and its active metabolite, 1-pyrimidinyl piperazine (1-PP) following oral administration were assessed in rhesus monkeys at doses used in chronic toxicology studies. The study was conducted over four periods in three male and three female rhesus monkeys. In the first three periods, buspirone hydrochloride solution was administered in a randomized manner by oral gavage at doses (expressed as buspirone free base) of 12·5, 25 and 50 mg kg−1 once a day on days 1 and 7 and twice a day on days 2–6. In the last period, all monkeys received 25 mg kg−1 buspirone as a single daily dose for 7 days. Serial plasma samples were collected for analysis of buspirone and 1-PP on days 1 and 7 in the first three periods and on day 7 in the last period for assessment of single dose and steady-state pharmacokinetics.

Inter-animal variability in the pharmacokinetics of buspirone was high. Examination of Cmin vs time plots revealed that the steady state was attained by day 7 except for one monkey who demonstrated much higher Cmin values. For buspirone, dose proportionality was concluded for both Cmax and AUC on day 1 but not on day 7. The accumulation factor on day 7 for buspirone was nearly 5 for Cmax and 7 for AUC when compared with day 1. For 1-PP, dose proportionality was concluded except for Cmax in male monkeys on day 7. In contrast to buspirone, 1-PP showed less than 2-fold accumulation in Cmax and AUC values on day 7 compared with those on day 1. Exposure at a dose of 25 mg kg−1 once daily was in between the 12·5 mg kg−1 and 25 mg kg−1 twice-a-day regimens.

These results document dose-dependency in the steady-state pharmacokinetics of buspirone in rhesus monkeys.
Distribution of Ciprofloxacin into the Central Nervous System in Rats with Acute Renal or Hepatic Failure
Authors: Naora Kohji , Ichikawa Nobuhiro , Hirano Hidenari , Iwamoto Kikuo
Published: July 2003

Pharmacokinetic changes of various drugs have been reported in renal or hepatic failure. The present study employed ciprofloxacin, a quinolone antibiotic having neurotoxic side effects, to assess the influence of these diseases on distribution of ciprofloxacin into the central nervous system (CNS).

After intravenous dosing of ciprofloxacin (10–30 mg kg−1), ciprofloxacin levels in plasma and brain were measured in normal rats (Wistar, male, 10-week-old) and those with acute renal and hepatic injuries which were induced by uranyl nitrate and carbon tetrachloride (CCl4), respectively. In the uranyl nitrate-treated rats, the plasma elimination half-life of ciprofloxacin was prolonged and the total body clearance was reduced when compared with those in the normal rats. Similar but smaller changes were observed in the CCl4-treated group. Brain levels of ciprofloxacin were significantly increased by both uranyl nitrate and CCl4 treatments. A proportional correlation between serum unbound levels and brain levels of ciprofloxacin was observed in the normal group. However, brainto-serum unbound concentration ratios of ciprofloxacin were reduced in the rats with renal or hepatic failure.

These results suggest that renal failure as well as hepatic failure retards elimination of ciprofloxacin from the blood, leading to elevation of the CNS level, and also that ciprofloxacin distribution in the brain is reduced in these disease states.
Effects of Mebudipine and Dibudipine, Two New Calcium-channel Blockers, on Rat Left Atrium, Rat Blood Pressure and Human Internal Mammary Artery
Authors: Mirkhani H , Omrani G R , Ghiaee S , Mahmoudian M
Published: July 2003

Mebudipine and dibudipine are two new dihydropyridine calcium-channel blockers that have been synthesized in our laboratory. In a previous study, they showed considerable relaxant effect on vascular and ileal smooth muscle. Here, the pharmacological effects of mebudipine and dibudipine on isolated rat left atrium, rat blood pressure and isolated human internal mammary artery are described. Results are compared with those obtained for nifedipine.

Mebudipine and dibudipine reduced contraction force of rat left atrium (pIC30 values: 5·37 ± 0·13 and 5·49 ± 0·15, respectively) but their negative inotropic effects were significantly weaker than that of nifedipine (pIC30 value: 6·63 ± 0·11). Mebudipine and dibudipine lowered rat blood pressure. The hypotensive effect of mebudipine was similar to that of nifedipine while dibudipine was weaker than nifedipine. It was found that the half-life of the hypotensive action of dibudipine (41·91 ± 3·77 min, 31·13 ± 2·26 min and 28·20 ± 4·37 min at 2, 4 and 8 mg kg−1 orally administered doses, respectively) was longer than that of nifedipine (11·85 ± 2·88 min, 16·65 ± 2·42 min and 14·03 ± 0·10 min at the same doses, respectively). Also, it appeared that mebudipine had a slower rate of absorption compared with nifedipine (the time to reach peak hypotensive action at 2, 4 and 8 mg kg−1 orally administered doses were, respectively, 24·00 ± 6·96 min, 23·75 ± 2·39 min and 15·00 ± 2·04 min for mebudipine and 7·80 ± 0·86 min, 13·75 ± 3·15 min and 8·33 ± 0·88 min for nifedipine). The two new compounds, as well as nifedipine, relaxed KCl-treated isolated human internal mammary artery (pEC50 values; 7·87 ± 0·12, 7·22 ± 0·24 and 7·67 ± 0·12 for mebudipine, dibudipine and nifedipine, respectively). The relaxant effects of mebudipine and dibudipine did not show any significant difference compared with that of nifedipine.

It is concluded that these new compounds are weak cardiodepressants and, with due attention to its significant vasorelaxant action, mebudipine is a vasoselective compound. In addition, these two compounds have potent blood pressure lowering effects. Also, their vasorelaxant action can be reproduced in human vascular preparations.
Paradoxical Cholinergic and Purinergic Vascular Reactivity of Rabbit Thoracic Aorta Cold-stored in University of Wisconsin Solution
Authors: Alexander B , Gryf-Lowczowski J V D , Sherlock D , Salisbury J , Benjamin I S
Published: July 2003

Endothelial dysfunction has been reported in donor blood vessels destined for organ transplantation following cold-storage preservation with University of Wisconsin solution (UW). This was investigated in the present work. Segments of rabbit thoracic aorta were mounted on isometric fine-wire myographs at 37°C and gassed with 95% O2/5% CO2. Concentration-dependent vasodilatations to acetylcholine and adenosine-5′-triphosphate (ATP) were obtained in freshly-harvested rabbit aortic rings, with and without the endothelium, and after 8 days of cold-storage, at 4°C, in either UW, Krebs-Bülbring buffer (KBB) or saline. The action of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (100 μM) was evaluated upon the concentration-response curves to determine whether nitric oxide (NO) exerted any modulatory actions.

Endothelium-dependent, NO-mediated responses to acetylcholine were unaltered after eight days of storage in UW, reduced after storage in KBB and absent after removal of the vascular endothelium, saline storage or after testing in the presence of L-NAME, suggesting improved NO-mediated endothelial function with the use of UW. Structural preservation was also confirmed using scanning electron microscopy. In contrast, endothelium-dependent responses to ATP were unchanged after eight days of storage in KBB but were reduced after storage in UW and saline, suggesting purinergic (ATP) endothelial dysfunction after storage in UW. L-NAME markedly reduced vasodilatation to ATP in freshly harvested rings and after eight days of storage in KBB. This reduction was statistically significant (P < 0·05, Student's two tailed, unpaired t-test) at —log (M) ATP concentrations of 5·5, 5·0, 4·5, 4·0 and 3·5. NO-dependent vasodilatation to ATP was not attenuated by L-NAME in UW-stored rings. Eight days' UW-storage of rabbit thoracic aortic rings appeared to have differential and paradoxical effects upon NO-dependent vasodilatation to acetylcholine and ATP.

Morphological observations using electron microscopy suggested that UW preserved the vascular endothelium and this was verified by retained vascular reactivity of endothelium-dependent vasodilatations to acetylcholine. UW-storage however, significantly reduced endothelium-dependent relaxation to ATP thereby suggesting that P2Y-purinoceptors, which are located on the vascular endothelium, may be more susceptible to biodegradation than cholinergic receptors and may be responsible for endothelial dysfunction following transplantation.
Effects of Tetraethylammonium, 4-Aminopyridine and Bretylium on Cardiovascular Tissues from Normo- and Hypertensive Rats
Authors: Nand Vinita , Doggrell Sheila A
Published: July 2003

Our objective was to test whether potassium-channel blockade is a potential positive inotropic mechanism for heart failure. Thus we studied the effects of tetraethylammonium, 4-aminopyridine and bretylium on left ventricular action potentials, left ventricular contractility in the absence and presence of hypertrophy, and on isolated blood vessels from Wistar Kyoto normotensive rats (WKY) and spontaneously hypertensive rats (SHRs).

Tetraethylammonium at 10−3-10−2M, 4-aminopyridine at 10−4-10−3M and bretylium at 10−6-10−4M prolonged the action potentials of the WKY left ventricular strip. Similar concentrations of tetraethylammonium, 4-aminopyridine and bretylium augmented the peak force, prolonged the contractions, and did not cause arrhythmias in the absence or presence of isoprenaline on left ventricular strips from 12-month-old WKY. The 12-monthold SHR has hypertrophy of the left ventricle with reduced contractility and prolongation of relaxation. The effects of tetraethylammonium and bretylium were similar on WKY and SHR, whereas the effects of 4-aminopyridine were reduced on SHR left ventricular contractility, which suggests that the function of the transient outward-blocking potassium channel may be impaired in hypertrophy. Bretylium at · 10−4M had no effect on the portal vein, intralobar or mesenteric arteries. Tetraethylammonium and 4-aminopyridine at · 10−5M increased the duration or amplitude, or both, of the portal vein contractions. Tetraethylammonium at · 10−2M and 4-aminopyridine at · 3 × 10−4M contracted the mesenteric artery, and 4-aminopyridine also contracted the intralobar pulmonary artery.

In summary, we have demonstrated that the action potential prolonging effects of potassium-channel blockade is associated with a positive inotropic effect on the rat left ventricle. The non-specific blockers, tetraethylammonium and 4-aminopyridine, do not have potential as positive inotropes in heart failure because of their widespread effects, including vasoconstriction. The potential of bretylium and some of the newer selective potassium-channel blockers as positive inotropes requires further evaluation.
The Scientific Basis for the Reputed Activity of Valerian
Authors: Houghton P J
Published: July 2003

The underground organs of members of the genus Valeriana (Valerianaceae), as well as related genera such as Nardostachys, are used in the traditional medicine of many cultures as mild sedatives and tranquillizers and to aid the induction of sleep. V. officinalis is the species most commonly used in northern Europe and still retains its official pharmaco-poeial status although it is most commonly encountered as an ingredient of herbal medicines. This plant is still the subject of considerable research aimed at establishing the chemical and pharmacological basis of the activity which has been clearly shown in a number of animal and clinical studies.

The constituents of the volatile oil are very variable due to population differences in genetics and to environmental factors. The major constituents include the monoterpene bornyl acetate and the sesquiterpene valerenic acid, which is characteristic of the species, in addition to other types of sesquiterpene. Some of these have been shown to have a direct action on the amygdaloid body of the brain and valerenic acid has been shown to inhibit enzyme-induced breakdown of GABA in the brain resulting in sedation. The non-volatile monoterpenes known as valepotriates were first isolated in 1966 and contribute to the overall activity by possessing sedative activity based on the CNS although the mode of action is not clearly known. The valepotriates themselves act as prodrugs which are transformed into homobaldrinal which has been shown to reduce the spontaneous motility of mice. More recent studies have shown that aqueous extracts of the roots contain appreciable amounts of GABA which could directly cause sedation but there is some controversy surrounding the bioavailability of this compound. Another recent finding is the presence of a lignan, hydroxypinoresinol, and its ability to bind to benzodiazepine receptors.

Valerian is a good example of both the negative and positive aspects of herbal drugs. The considerable variation in its composition and content as well as the instability of some of its constituents pose serious problems for standardization but the range of components which contribute to its overall activity suggest that it may correct a variety of underlying causes of conditions which necessitate a general sedative or tranquillizing effect.
Hypericum perforatum Extracts as Potential Antidepressants
Authors: Vitiello Benedetto
Published: July 2003

Extracts of Hypericum perforatum have been used in the treatment of mild to moderate depression for many years in Europe. More recently, these extracts have become available in the USA as dietary supplements and have been popularly used to improve mood. In support of this practice, data from several controlled clinical studies suggest that Hypericum perforatum is better than placebo and as effective as established antidepressant drugs. These data have, however, several limitations that should temper our enthusiasm and argue for more research before accepting Hypericum perforatum extracts into our pharmacopoeia of established antidepressants. Extant data on the possible effects of Hypericum perforatum extracts in depression are here critically reviewed and plans for further research presented.
Flavonoids and the Central Nervous System: from Forgotten Factors to Potent Anxiolytic Compounds
Authors: Paladini A C , Marder M , Viola H , Wolfman C , Wasowski C , Medina J H
Published: July 2003

The list of activities of plant flavonoids did not include effects on the central nervous system (CNS) up to 1990, when our laboratory described the existence of natural anxiolytic flavonoids. The first of these was chrysin (5,7-dihydroxyflavone), followed by apigenin (5,7,4′-trihydroxyflavone) and flavone itself. Semisynthetic derivatives of flavone obtained by introducing halogens, nitro groups or both in its molecule, give rise to high affinity ligands for the benzodiazepine receptor, active in-vivo; 6,3′-dinitroflavone, for example, is an anxiolytic drug 30 times more potent than diazepam.

The data collected in this paper make clear that some natural flavonoids are CNS-active molecules and that the chemical modification of the flavone nucleus dramatically increases their anxiolytic potency.
Medicinal Plants and Alzheimer's Disease: from Ethnobotany to Phytotherapy
Authors: Perry Elaine K , Pickering Anne T , Wang Wei Wei , Houghton Peter J , Perry Nicolette S L
Published: July 2003

The use of complementary medicines, such as plant extracts, in dementia therapy varies according to the different cultural traditions. In orthodox Western medicine, contrasting with that in China and the Far East for example, pharmacological properties of traditional cognitive- or memory-enhancing plants have not been widely investigated in the context of current models of Alzheimer's disease. An exception is Gingko biloba in which the gingkolides have antoxidant, neuroprotective and cholinergic activities relevant to Alzheimer's disease mechanisms. The therapeutic efficacy of Ginkgo extracts in Alzheimer's disease in placebo controlled clinical trials is reportedly similar to currently prescribed drugs such as tacrine or donepezil and, importantly, undesirable side effects of Gingko are minimal. Old European reference books, such as those on medicinal herbs, document a variety of other plants such as Salvia officinalis (sage) and Melissa officinalis (balm) with memory-improving properties, and cholinergic activities have recently been identified in extracts of these plants. Precedents for modern discovery of clinically relevant pharmacological activity in plants with long-established medicinal use include, for example, the interaction of alkaloid opioids in Papaver somniferum (opium poppy) with endogenous opiate receptors in the brain. With recent major advances in understanding the neurobiology of Alzheimer's disease, and as yet limited efficacy of so-called rationally designed therapies, it may be timely to re-explore historical archives for new directions in drug development. This article considers not only the value of an integrative traditional and modern scientific approach to developing new treatments for dementia, but also in the understanding of disease mechanisms. Long before the current biologically-based hypothesis of cholinergic derangement in Alzheimer's disease emerged, plants now known to contain cholinergic antagonists were recorded for their amnesia- and dementia-inducing properties.
Therapeutic Value of Ginkgo biloba in Reducing Symptoms of Decline in Mental Function
Authors: Curtis-Prior Peter , Vere Duncan , Fray Paul
Published: July 2003

The Chinese tree Ginkgo biloba or “maiden hair tree” is extensively cultivated for the exploitation of the medicinal properties of its leaves. From these, a well-defined extract designated “EGb 761” has been developed, which was commercialized initially as Tanakan, Tebonin and Rokin; a similar product, Kaveri (LI 3170), also exists. The major therapeutic applications for these products are “cerebral insufficiency”, other cerebral disorders, neurosensory problems and peripheral circulatory disturbances. Four primary concepts of action have been proposed to explain the pharmacotherapeutic benefits of EGb761; these are: vasoregulatory, cognition-enhancing, stress-alleviating, and gene-regulatory. These actions are believed to be realized through the principal active ingredients, flavonoids and the terpenoids ginkgolides and bilobalide acting simultaneously in concert, combination and synergy, so-called polyvalent action.

It has been proposed that EGb761 may improve the memory of healthy volunteers, and in an assessment meta-analysis of forty clinical studies, it was reported that Ginkgo was able to improve the twelve different symptoms comprising ‘cerebral insufficiency’, all of which are manifest in the elderly. These were supported in a second major study, using LI1370. However, in both instances, the evidence was largely based upon the results of self-assessment questionnaires. Latterly, in a large double blind study of men and women with the diagnosis of uncomplicated dementia who were administered Ginkgo for a year, a further positive outcome was claimed. In this study, patients were tested using ADAS-cog, GERRI and CGIC.

It is suggested that whilst these different outcomes are compatible with (but do not affirm) a clinical benefit resulting from the use of Ginkgo, the application of a more objective system of assessment would be able to provide firm proof. It is proposed, therefore, that an objective, computer-based testing system for assessment of clinical improvement in volunteers and patients administered Ginkgo (such as CANTAB) would provide the convincing evidence currently being sought by patients, carers, physicians, legislators and the pharmaceutical industry.
Synthesis and Cytotoxicity Evaluation of Some 8-Hydroxyquinoline Derivatives
Authors: Shen Ai-Yu , Wu Sheng-Nan , Chiu Chih-Tsao
Published: July 2003

Interest in Mannich bases of 8-hydroxyquinoline stems from reports of their high potency against human cancer cells. In the search for potential anticancer drug candidates, Mannich bases of 8-hydroxyquinoline (7-pyrrolidinomethyl-8-hydroxyquinoline, 7-morpholinomethyl-8-hydroxyquinoline, 7-piperidinomethyl-8-hydroxyquinoline and 7-diethylamino-methyl-8-hydroxyquinoline) were synthesised by reaction with various secondary amines and formaldehyde. They were prepared as hydrochlorides.

The cytotoxic activity of 7-pyrrolidinomethyl-8-hydroxyquinoline, 7-morpholinomethyl-8-hydroxyquinoline and 7-diethylaminomethyl-8-hydroxyquinoline compounds in the National Cancer Institute in-vitro cancer cell line panel was determined. It was found that they exhibited substantial cytotoxic activity against leukaemia. The log concentration of 7-pyrrolidinomethyl-8-hydroxyquinoline, 7-morpholinomethyl-8-hydroxyquinoline and 7-diethylaminomethyl-8-hydroxyquinoline that inhibited 50% of 60 cell lines' growth were —4·81M, —5·09M and —5·35M, respectively. Compound 7-pyrrolidinomethyl-8-hydroxyquinoline was selected for further in-vivo testing. The electrophysiological effect of 7-pyrrolidinomethyl-8-hydroxyquinoline also was tested in human myeloma cells (RPMI 8226). The outward current was voltage dependent, activating at —40 mV and believed to be the voltage-activated K+ current IK(V). 7-Pyrrolidinomethyl-8-hydroxy-quinoline (1–30 μM) caused the inhibition of IK(V) in a concentration-dependent manner. The IC50 value of 7-pyrrolidinomethyl-8-hydroxyquinoline-induced inhibition of IK(V) is 23 μM. The GI50 value of 7-pyrrolidinomethyl-8-hydroxyquinoline-induced inhibition of cell growth is 14 μM.

The results suggest that at least part of the cytotoxicity effect of 7-pyrrolidinomethyl-8-hydroxyquinoline on myeloma cells could be related to blockade of voltage-activated K+ channels.
Synthesis and Anticonvulsant Activity of N-Benzyloxycarbonyl-Amino Acid Prodrugs of Phenytoin
Authors: Scriba Gerhard K E , Lambert Didier M
Published: July 2003

Glycine, which has weak anticonvulsant properties, has been shown to potentiate the activity of several antiepileptic drugs but not phenytoin. Recently, studies have shown that N-(benzyloxycarbonyl)glycine (Z-glycine) antagonized seizures more than glycine in addition to possessing activity in the maximal electroshock test, a convulsive model in which glycine is inactive. In the present study esters of 3-hydroxymethylphenytoin, a phenytoin prodrug, and Z-glycine as well as the homologous N-(benzyloxycarbonyl)-ω-amino acids, Z-β-alanine and Z-σ-aminobutyric acid (Z-GABA), were prepared and tested for their anticonvulsant and acute neurotoxic activities.

The phenytoin prodrugs were obtained by esterification of bis(2-oxo-3-oxazolidinyl)-phosphinic acid chloride-mediated esterification of 3-hydroxymethylphenytoin with the respective N-benzyloxycarbonyl-protected amino acid. The Z-glycine-phenytoin ester was the most active anticonvulsant derivative. Compared with phenytoin the compound exhibited a decreased median effective dose (ED50) in the MES test and an increased median toxic dose (TD50), resulting in an significantly improved protective index expressed as the ratio between TD50 and ED50.

The present data suggest that covalent binding of phenytoin to Z-glycine results in an improved pharmacological profile of the drug.
Vascular-selective Effect of Lercanidipine and other 1,4-Dihydropyridines in Isolated Rabbit Tissues
Authors: Angelico P , Guarneri L , Leonardi A , Testa R
Published: July 2003

The aim of this study was to characterize the in-vitro vasoselectivity of lercanidipine (in comparison with lacidipine, amlodipine, nitrendipine and felodipine) by evaluating its functional calcium antagonistic activity on rabbit vascular (aorta) and cardiac tissues (heart ventricle).

Although incubation with all the compounds tested elicited a concentration-dependent relaxant effect on vascular tissue precontracted with KCl (80 mM), 50% relaxation was reached at different times for each concentration and drug tested. At 10 nM concentration 50% relaxation was reached after 210 min with lercanidipine, 278 min with amlodipine, 135 min with lacidipine, 75 min with nitrendipine and 70 min with felodipine. The onset of the effect was, therefore, similar for lercanidipine, amlodipine and lacidipine, but faster for nitrendipine and felodipine. Similarly, all the compounds tested concentration-dependently reduced the force of cardiac contraction (negative inotropic activity). In this model, the time needed to reach 50% reduction in contractile force was also concentration-dependent, and the ranking order of the speed of onset of the effect (evaluated as the ratio of the IC50 values (the concentrations inhibiting contraction by 50%) calculated after 1 and 4h incubation) was lacidipine (3.8) > amlodipine (9.6) > felodipine (39) > lercanidipine (68) = nitrendipine (89). The vasoselectivity, expressed as the ratio of the IC50 values obtained on cardiac and vascular tissue, were (for 4 h incubation) 730, 193, 95, 6 and 3 for lercanidipine, lacidipine, amlodipine, felodipine and nitrendipine, respectively, showing that lercanidipine is the most vasoselective of the calcium-antagonists tested.

The results show that lercanidipine reduces the inotropic force of the rabbit heart to a lesser extent than do other calcium antagonists, and that this drug had the best heart/vessel selectivity index among the compounds tested at all the times tested.