Z. Kállay

Effects of ionizing radiation on the blood brain barrier permeability to pharmacologically active substances

Ionizing radiation can impair the integrity of the blood brain barrier (BBB). Data on early and late damage after brain irradiation are usually reported separately, yet a gradual transition between these two types has become evident. Signs appearing within 3 weeks after irradiation are considered to be early manifestations. The mechanism of radiation-effected integrity impairment of the BBB is discussed in relation to changes in morphological structures forming the BBB, the endothelium of intracerebral vessels, and in the surrounding astrocytes. Alterations in the function of the BBB are manifested in the endothelium by changes in the ultra-structural location of the activity of phosphatases and by the activation of pinocytotic vesicular transport, and in astrocyte cytoplasm by glycogen deposition. The changes in ultrastructure were critically surveyed with regard to increasing doses of radiation to the brain in the range of 5 Gy to 960 Gy. The qualitative as well as the semiquantitative and quantitative observations on the passage of substances across the damaged BBB were treated separately. Qualitative changes are based mainly on findings of extravasation of vital stains and of labelled proteins. The quantitative studies established differences in radiation-induced changes in the permeability of the BBB depending on the structure and physico-chemical properties of the barrier penetrating tracers. Indirect evaluation of radiation-induced BBB changes is based on studies of pharmacological effects of substances acting on the CNS. In conclusion, radiation impairs significantly the integrity of the BBB following single irradiation of the brain with a dose exceeding 10-15 Gy. The response of the BBB to ionizing radiation is dependent both on the dose to which the brain is exposed and on specific properties of the tracer. Either an increase or a decrease of BBB permeability, or both, occurring in a certain time sequence, was observed. The mechanism of hyperpermeability after irradiation is not fully understood, but the activation of vesicular transport offers one possible explanation. Even less understood is the mechanism of decreased permeability. The response of the BBB to ionizing radiation is most probably nonspecific and its nature may be assumed to be similar to its responses to other physical or chemical noxious factors.

Gel permeation chromatographic characterization of sodium hyaluronate and its fractions prepared by ultrasonic degradation

SummaryHigh-molecular-weight sodium hyaluronate isolated from rooster combs was degraded by ultrasonication. The molecular weight of hyaluronate and its polydispersity was determined by gel-permeation chromatography. During 75-min treatment the molecular weight value decreased from 1.39×106 Da to 2.25×105 Da while the polydispersity of the molecular weight increased from 1.29 to 2.36. The reciprocal value of the square of the hyaluronates molecular weight was linearly proportional to the time of ultrasonication.

Determination of Ethimizol and Two of Its Metabolites in Serum by High-Pressure Liquid Chromatography

A liquid chromatographic assay has been developed for the determination of ethimizol and two of its metabolites in serum. The analysed compounds are preseparated from serum by a micro-column packed with an octadecylsilanized silica gel. Components of the micro-column eluate are analysed on a silica-gel-packed column by means of a high-performance liquid chromatograph fitted with a photometric detector. At 262 nm the detection limit of the injected amount of ethimizol is about 5 ng. The mass spectra of two ethimizol metabolites isolated from rat serum are presented. The suitability of the developed assay for pharmacokinetic studies of ethimizol is demonstrated.

Irradiation of the head by 60Co opens the blood-brain barrier for drugs in rats.

The passage of 6 model drugs; acetylsalicylic acid, chloramphenicol, ethimizol, carbisocaine, heptacaine, and diazepam, through the blood-brain barrier, was determined in unirradiated control rats and in animals 1, 3, and 7 days after irradiation of the head only with a dose of 25 Gy from a60Co source. The brain uptake index (BUI), which compares the uptake of the test substance with that of3H2O 5 s after their injection into the common carotid artery, was significantly increased in comparison with unirradiated controls 7 days after irradiation, for all substances tested except for ethimizol. For acetylsalicylic acid and chloramphenicol it was also significantly increased in the other time intervals. The less lipophilic substances showed a greater relative increase of BUI than the more lipophilic ones.

Pharmacokinetics of carbisocaine in rats and mice

Summary[14C]carbisocaine, N-(2-(2-[1-14C]-heptyloxyphenylcarbamoyloxy)-propyl)-diethylammonium chloride was administered to male Wistar rats, weighing 180–210 g IV in doses of 0.425, 1.425, 2.425 or 4.425 mg/kg or orally in a dose of 2.425 mg/kg. Extraction of carbisocaine from alkaline media into n-heptane was used for assessment of the unchanged drug in plasma, organs and excreta in predetermined time intervals. The two-way analysis of variance confirmed the insignificant effect of subject variability of experimental animals (p > 0.05) on plasma data after IV administration. Plasma data following the IV administration were approximated by a linear open two-compartment model with elimination from the central compartment. Regression analysis indicated linearity between carbisocaine plasma AUC and the IV administered dose within the range tested. The following model parameters were obtained: elimination half-life 161.2±37.5 min, total body clearance 59.5 ml/min/kg, distribution volume in steady state 5616.2 ml/kg and mean residence time 96.7 min. The systemic availability of the orally given carbisocaine was 45.2%, assessed by AUCpo/AUCiv (0–360 min). The brain uptake index of carbisocaine in relation to3H2O was 57.7±3.9%. Whole body autoradiographs of mice injected with [14C] carbisocaine documented accumulation of14C in gall and urinary bladder and in the gut contents and the effective placental barrier against carbisocaine and its metabolites.

Dose dependent pharmacokinetics of a xanthine-related nootropic drug, ethimizol, in rats

Pharmacokinetics of the respiratory analeptic ethimizol, 4,5-bis(methylcarbamoyl)-1-ethylimidazole, with recently recognized nootropic properties, its metabolite 4-carbamoyl-5-methylcarbamoyl-1-ethylimidazole and of two metabolites of unknown structure was studied in plasma of rats after intravenous administration of the [2-14C]-labelled compound in 5 doses: 1.1, 3.3, 10, 20, and 30 mg/kg. The apparently monoexponential time course of dose normalized ethimizol plasma concentrations were not superimposable and the derived pharmacokinetic parameters were dose-dependent. The elimination rate constant and the initial volume of distribution decreased with increasing dose. The AUC versus dose relationship displayed disproportionate increases with increasing dose. Plasma ethimizol failed to obey the Michaelis-Menten kinetics and in an attempt to rationalize the observed nonlinearity a complete competitive product inhibition was suggested. Similar to the parent drug, the three metabolites exhibited a distinctly dose-dependent behavior as could be deduced from their dose-normalized concentration-time curves.

Uptake and Subcellular Distribution of Poly-L-Aspartic Acid, a Protectant Against Aminoglycoside-Induced Nephrotoxicity, in Rat Kidney Cortex

Williams & Hottendorf (1985), and Williams et al. (1986) have observed that the co-administration of poly-L-aspartic acid protects rats against gentamicin or amikacin-induced nephrotoxicity. Yet, they found that coadministration of polyaspartic acid increased the total amount of aminoglycoside accumulated by kidney cortex, although less drug was recovered in fractions enriched in brush-border and basolateral membranes. We showed that polyaspartic acid significantly protects against gentamicin-induced lysosomal phospholipidosis (Beauchamp et al., 1986), an early renal alteration which we previously demonstrated to be a specific and predictive index of aminoglycoside nephrotoxicity related to the accumulation of the these drugs in lysosomes (see Tulkens et al., 1985, and Tulkens, 1986, for review). Beauchamp et al. (1986), and more recently Gilbert et al. (1987) also confirmed that polyaspartic acid did not decrease, but rather increased the amount of gentamicin stored by kidney cortex. The latter results are in contradiction with the original hypothesis of Williams & Hottendorf (1985) who selected polyaspartic acid as a potential competitor for gentamicin uptake by kidney, based on the observation that it interferes with gentamicin binding to renal membrane vesicles in vitro.

Pharmacokinetic study of stobadine.

The aim of this paper is to provide a brief overview of most important results of stobadine kinetic studies in rats, dogs, and human volunteers. In these studies, stobadine dihydrochloride and stobadine dipalmitate was used for intravenous and oral administration, respectively. To evaluate kinetic properties of stobadine and its metabolites, TLC, HPLC, GLC, GC-MS, radiometric, and fluorometric methods were developed and used.

Effect of gamma-irradiation on disposition of the local anaesthetic, carbisocaine in rabbits

Abstract— 14C Labelled carbisocaine, a local anaesthetic agent, has been administered intravenously in a dose of 2 mg kg−1 to rabbits 7 days after whole‐body 60Co gamma‐irradiation with a dose of 5 Gy (1.9 Gy min−1) and to control rabbits. The plasma carbisocaine concentration‐time courses were approximated by biexponential equations. The estimated pharmacokinetic parameters obtained when the data were fitted to an open two‐compartment model were significantly different for the irradiated group relative to control animals, indicating a radiation‐induced slower elimination rate of carbisocaine: AUC: 0.37 vs 0.29% dose min mL−1, CLtot: 109.8 vs 155.4 mL min−1, Vdss: 27.6 vs 33.2 mL kg−1, kel: 0.0259 vs 0.0307 min−1, MRT: 251.7 vs 214.6 min. The total excreted amount of 14C radioactivity in the irradiated group was lower in comparison with controls: 6.5 vs 8.7% in bile and 18.3 vs 23.7% in urine. However, lower carbisocaine concentrations were recorded in the heart, lungs, liver, and kidneys of irradiated rabbits compared with controls.

Comparative Uptake and Lysosomal Phospholipidosis Induced by Gentamicin Components C1, C1a, and C2

Aminoglycosides are nephrotoxic and this adverse effect has triggered many efforts towards the design and/or the screening of less toxic derivatives (see Price, 1986 for a recent review). Yet, the first broad-spectrum and still widely used aminoglycoside, gentamicin, is not a pure substance and is actually commercialized as a mixture of three main components, C1, C1a and C2, which differ by the methylation of the N6 and C6 atoms in the 2’,6’ diaminosugar moiety. Surprisingly enough, little information is available concerning the relative nephrotoxicities of these components. Whereas some reports suggest that gentamicin C1 induces less nephrotoxicity than gentamicin complex in humans (see e.g., Mossegaard et al., 1975) , others failed to substantiate such difference (e.g., Forrey et al., 1978). Kohlepp et al. (1984) showed in a comparative study in rats that gentamicin C2 and gentamicin C1a are more nephrotoxic than gentamicin C1 at an equivalent, high dosage (40 mg/kg). The uptake of gentamicin complex by rat kidney cortex, however, is saturable, with an apparent Km in a 10–20 mg/k serum concentration range (Gauliano et al., 1986).