Ridogrel Inhibits Systemic and Renal Formation of Thromboxane A2 and Antagonizes Platelet Thromboxane A2/Prostaglandin Endoperoxide Receptors upon Chronic Administration to Man

The effects of ridogrel, a dual thromboxane A2 (TXA2) synthase inhibitor and TXA2/prostaglandin (PG) endoperoxide receptor antagonist, on systemic and renal production of prostaglandins and on platelet TXA2/PG endoperoxide receptors was evaluated upon chronic administration (300 mg b. i. d. orally, for 8 and 29 days) to man. Such a medication with ridogrel inhibits the systemic as well as the renal production of TXA2 as measured by the urinary excretion of 2,3-dinor-TXB2 and TXB2 respectively without inducing significant changes in systemic or renal PGI2 production. Simultaneously with the latter effects, the production of TXB2 by spontaneously coagulated whole blood ex vivo is inhibited (>99%) while that of PGE2 and PGF2α is largely increased. Administration of ridogrel causes a three- to five-fold shift to the right of concentration-response curves for U46619 in eliciting platelet aggregation; no tachyphylaxis is observed after 29 days of treatment in this respect. Apart from a reduction of serum uric acid levels with a concomitant increase in urinary uric acid excretion during the first days of treatment, no clinically significant changes in hematological, biochemical, hemodynamic and coagulation parameters occur during the 8 days or 29 days study. The study demonstrates that ridogrel is a potent inhibitor of the systemic as well as renal TXA2 synthase and an antagonist of platelet TXA2/PG endoperoxide receptor in man, covering full activity during 24 h at steady-state plasma level conditions without tachyphylaxis during 29 days of medication. The compound is well tolerated, at least during 1 month of administration.

Spreading depression in human neocortical slices

Cortical spreading depression (CSD) occurrence has been suggested to be associated with seizures, migraine aura, head injury and brain ischemia-infarction. Only few studies identified CSD in human neocortical slices and no comprehensive study so far evaluated this phenomenon in human. Using the neocortical tissue excised for treatment of intractable epilepsy, we aimed to investigate CSD in human. CSD was induced by KCl injection and by modulating T-type Ca(2+) currents in incubated human neocortical tissues in an interphase mode. The DC-fluctuations were recorded by inserting microelectrodes into different cortical layers. Local injection of KCl triggered single CSD that propagated at 3.1+/-0.1 mm/min. Repetitive CSD also occurred spontaneously during long lasting application (5 h) of the T-type Ca(2+) channel blockers amiloride (50 microM) or NiCl(2) (10 microM) which was concomitant with a reversible extracellular potassium increase up to 50 mM. CSD could be blocked by the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovaleric acid in all cases. The results demonstrate that modulation of the Ca(2+) dynamics conditioned human neocortical slices and increased their susceptibility to generate CSD. Furthermore, these data indicate that glutamatergic pathway plays a role in CSD phenomenon in human.

Retinoic acid reduces apoptosis and oxidative stress by preservation of SOD protein level

Retinoic acid (RA) has already been shown to exert antiapoptotic and antioxidative activity in various cells. In this study, we determined the effect of RA on the mRNA and protein levels of the Cu-,Zn-superoxide dismutase (SOD-1) and Mn-superoxide dismutase (SOD-2) during staurosporine-induced apoptosis in primary cultures from neonatal rat hippocampus. Exposure to staurosporine (300 nM, 24 h) increased the percentage of apoptotic neurons to 62% compared with 18% in controls. We determined an increase in the reactive oxygen species (ROS) content from 4 up to 48 h after the induction of the injury. Treatment with staurosporine did not significantly change the mRNA levels of SOD-1 and SOD-2. However, the SOD-1 and SOD-2 protein levels markedly decreased 24 and 48 h after the addition of staurosporine. Compared with staurosporine-exposed controls, RA (10 nM)-treated cultures showed a significant increase in neuronal survival, a reduced neuronal ROS content, and enhanced protein levels of SOD-1 and SOD-2 24 and 48 h after the start of the exposure to staurosporine. The results suggest that RA reduced staurosporine-induced oxidative stress and apoptosis by preventing the decrease in the protein levels of SOD-1 and SOD-2, and thus supported the antioxidant defense system.

Observations on the relationship between the extracellular changes of taurine and glutamate during cortical spreading depression, during ischemia, and within the area surrounding a thrombotic infarct

Taurine and glutamate were monitored by microdialysis technique during various cerebral insults: a. Application of K+ triggered a cortical spreading depression (CSD). Taurine and glutamate increased concomitantly but recovery of glutamate was faster than that of taurine. b. Application of NMDA induced also CSD but only taurine increased. c. Induction of an infarct triggered repetitive CSDs. Taurine increased rapidly whereas glutamate rose slowly starting with some delay. d. After induction of ischemia, taurine and glutamate increased after onset of depolarisation. The increase of glutamate occurred late after a small, transient increase in parallel with the depolarisation. These data suggest a close functional relationship between the changes of both amino acids. Therefore, they should be monitored together especially in clinical settings: during excitation, only taurine will increase; during overexcitation, taurine will also increase but to a higher maximum followed by a moderate rise of glutamate; after energy failure, taurine will accumulate to its highest level followed by a continuous rise of glutamate.

NiCl2 and amiloride induce spreading depression in guinea pig hippocampal slices

Spreading depressions (SD) occur in association with ischaemia, epilepsy and migraine. Intracellular calcium oscillations have been suggested to be involved in the generation and propagation of SD. The present study was performed to study the mechanism of conditioning guinea pig hippocampal slices by the T-type calcium channel blockers NiCl2 and amiloride. SD-like fluctuations of DC potential were recorded by inserting microelectrodes into the CA1 and CA3 regions. The SD occurrence was significantly greater with 10 micromol/l NiCl2 as well as with 25 and 50 micromol/l amiloride than with other concentrations of these substances. The concentration response curve was inversely U-shaped with the maximum repetition rates of SDs being achieved at 10 micromol/l NiCl2 as well as at 25 and 50 micromol/l amiloride. SD occurrence could be completely blocked by the NMDA antagonist APV (10 micromol/l) in all cases. These data demonstrate that modulation of the Ca2+ dynamics conditioned guinea pig hippocampal slices and increased their susceptibility to generate SD.

Cerebral taurine release mechanisms in vivo: pharmacological investigations in rats using microdialysis for proof of principle

Cerebral taurine acts as neurotransmitter, as neuromodulator, or as osmoregulator. To investigate its release mechanisms in vivo, we combined the microdialysis technique with a variety of experimental paradigms. Taurine release was stimulated by either NMDA, NO or a hypotonic solution locally with or without the addition of the NMDA antagonists APV or Ketamine, or the NO synthase inhibitor L-NAME. Alternatively, the neuroprotective drug lubeluzole was applied i.v. NMDA, NO or the hypotonic solution stimulated the release of taurine. NMDA-mediated taurine release was inhibited by either APV, Ketamine or the NO synthase inhibitor L-NAME. Lubeluzole had no effect. Under the hypotonic conditions only lubeluzole was effective. These data confirm in vivo that the NMDA-induced taurine release is mediated via the NO cascade. By contrast, the release after a hypotonic stimulus is not related to the NO cascade. Instead, Na(+)- and/or Ca(2+)-mediated events might have been attenuated by lubeluzole.

Oxygen consumption and energy state in an in vitro model of rat brain perfused with artificial oxygen carrier

The present study was performed in order to determine the oxygen consumption of a rat brain perfused with an artificial oxygen carrier. Measurements were performed prior to and 2 or 30 min after an ischemic period of 5 min. In addition, the energy-related metabolites were determined. Basal oxygen consumption and energy state were comparable to in vivo conditions. The tissue concentration of the energy metabolites decreased during ischemia and completely recovered during 30 min of reperfusion. The oxygen consumption was higher in the early phase of reperfusion than under pre-ischemic conditions. However, the oxygen consumption in the later phase of reperfusion was lower than the basal consumption. The data demonstrate that the addition of an artificial oxygen carrier to the perfusate provides sufficient amounts of oxygen to the in vitro preparation and that the measurement of the oxygen consumption during the post-ischemic reperfusion is a more sensitive parameter for the detection of emerging deficits than the measurement of the tissue levels of the energy metabolites.

Extracellular changes of taurine in the peri-infarct zone: effect of lubeluzole

Lubeluzole is a neuroprotective compound that has been shown to stereoselectively rescue sensorimotor function and reduce infarct size in a photochemical stroke model in rats. Tissue swelling, which occurs in the peri-infarct zone, is accompanied by a compensatory taurine release. Therefore, using a microdialysis technique, we aimed at measuring changes of extracellular concentrations of taurine in the peri-infarct zone and the effects of lubeluzole and its R-isomer. Lubeluzole blocked the increase of taurine in tissue immediately surrounding a photochemically induced thrombotic neocortical infarct. By contrast, the R-isomer was completely inactive. We hypothesize that lubeluzole may reduce osmoregulatory stress in peri-infarct tissue.

Dose-dependent effects of tetraethylammonium on circling spreading depressions in chicken retina

The K+-channel blocker tetraethylammonium (TEA) was applied to study its effects in self-sustaining, circling spreading depression in the chicken retina (RSD). Extracellular K+ (Ke+ activities and the direct-current (DC) signal were recorded using double-barrelled microelectrodes. Superfusion of TEA-concentrations of 10 to 250 microM for 4 to 7 min reduced the RSD-associated DC amplitude (by 9 to 45%) and the maximum of the K+ concentration (by 9 to 34%) in a dose-dependent manner. Propagation velocity of the RSD was lowered by 24%. At concentrations higher than 250 microM TEA (0.5 to 10 mM), the propagation was slowed by more than 60%, after which the RSD disappeared. Recovery upon reperfusion with Ringer was immediate. These observations illustrate: 1) TEA affects the Ke+ changes during RSD at very low concentrations. 2) The reduced Ke+ transients are accompanied by a reduction of the DC shifts. 3) These changes of the electrical properties of the RSDs are paralleled by a reduction of the propagation velocity. 4) The effects of TEA are reversible. 5) The changes of these parameters occur dose-dependently. These data suggest a close relationship between the amplitudes of the ionic/electric changes during RSDs and the mechanisms of propagation.

Lubeluzole blocks increases in extracellular glutamate and taurine in the peri-infarct zone in rats

A microdialysis probe was positioned inside the peri-infarct zone of a photochemically induced neocortical infarct in rats. Extracellular glutamate rose within 20 min after the start of infarct induction and continued to increase during the 5 h observation period to 5.5-fold the pre-infarct baseline value of 0.8 +/- 0.4 micromol/l. Glutamine increased only 1.4-fold. Changes in peri-infarct glutamate were preceded by steep rises in taurine (a 3.9-fold increase from the baseline value of 2.8 +/- 0.7 micromol/l), which coincided with spreading depressions during infarct induction. Post-treatment with lubeluzole ((S)-4-(2-benzothiazolylmethylamino)-alpha-[(3,4-difluoro-phenoxy) methyl]-1-piperidineethanol, 1.25 mg/kg i.v.), a new cerebroprotective drug, blocked the peri-infarct increases of glutamate and taurine, whereas the R-enantiomer was ineffective. Since lubeluzole has previously been shown to stereospecifically decrease glutamate-activated nitric oxide (NO) toxicity in vitro, the present in vivo stereospecific effect of lubeluzole may be related to modulation of the cascade of NO toxicity, thus preventing NO toxicity-mediated increases in extracellular glutamate. Blockade of the peri-infarct taurine response suggests that lubeluzole also may have reduced cellular osmotic stress in the peri-infarct zone.

Tissue swelling and intracellular pH in the CA1 region of anoxic rat hippocampus

The fluorescent dye BCECF was used to simultaneously determine the intracellular pH (ratio 495 : 450 nm) and changes in relative tissue volume (fluorescence at the 450 nm isosbestic wavelength) in rat hippocampal slices. Anoxia in the presence of glucose caused tissue swelling and subsequent intracellular acidosis after a short and small transient alkaline peak. Reoxygenation reversed tissue swelling only partly and ended in persistent tissue swelling. The intracellular pH was initially further acidified before restoration to the normoxic intracellular pH occurred. Omitting glucose during anoxia caused similar but more marked changes of relative tissue volume. However, acidosis during anoxia was less marked and subsequently converted to alkalosis. Reoxygenation also caused initial acidification but the intracellular pH was not completely restored afterwards.

The measurement of extracellular inorganic phosphate gives a more reliable indication for severe impairment of cerebral cell function and cell death than the measurement of extracellular lactate

The measurement of cerebral extracellular lactate levels has been suggested to be used to monitor cerebral function in intensive care However, although an increase of extracellular lactate levels is a sensitive parameter for increased cellular activity in general, it will be shown that its prognostic value is limited in regard to the severity of the impairment of cellular function. As an alternative the measurement of the extracellular levels of inorganic phosphate (IP) or adenosine is proposed here: Whereas extracellular lactate levels increased rapidly to about the same extents during ischemia (IS) and spreading depression (SD), IP rose during IS only. Adenosine, on the other hand, increased during both events to a different degree. If, therefore, lactate was the only parameter to be monitored after a cerebral insult, the results would not allow to discriminate between a transient, spontaneously recovering event as a SD and a long lasting or an irreversible loss of cell function as in persisting ischemia/hypoxia. The measurement of IP, therefore, seems to be more suitable than that of lactate or adenosine since IP will appear within the extracellular space only after a sustained failure of membrane function. Thus, the measurement of IP changes turned out to be the more useful parameter for intensive care supervision.

Ion channel involvement in anoxic depolarization induced by cardiac arrest in rat brain

Anoxic depolarization (AD) and failure of ion homeostasis play an important role in ischemia-induced neuronal injury. In the present study, different drugs with known ion-channel-modulating properties were examined for their ability to interfere with cardiac-arrest-elicited AD and with the changes in the extracellular ion activity in rat brain. Our results indicate that only drugs primarily blocking membrane Na+ permeability (NBQX, R56865, and flunarizine) delayed the occurrence of AD, while compounds affecting cellular Ca2+ load (MK-801 and nimodipine) did not influence the latency time. The ischemia-induced [Na+]e reduction was attenuated by R56865. Blockade of the ATP-sensitive K+ channels with glibenclamide reduced the [K+]e increase upon ischemia, indicating an involvement of the KATP channels in ischemia-induced K+ efflux. The KATP channel opener cromakalim did not affect the AD or the [K+]e concentration. The ischemia-induced rapid decline of extracellular calcium was attenuated by receptor-operated Ca2+ channel blockers MK-801 and NBQX, but not by the voltage-operated Ca2+ channel blocker nimodipine, R56865, and flunarizine.

Effects of the sodium channel blocker tetrodotoxin (TTX) on cellular ion homeostasis in rat brain subjected to complete ischemia

Anoxic depolarization (AD) and failure of the cellular ion homeostasis are suggested to play a key role in ischemia-induced neuronal death. Recent studies show that the blockade of Na+ influx significantly improved the neuronal outcome. In the present study, we investigated the effects of 10 microM tetrodotoxin (TTX) on ischemia-induced disturbances of ion homeostasis in the isolated perfused rat brain. TTX inhibited the spontaneous EEG activity, delayed the ischemia-induced tissue acidification, and significantly postponed the occurrence of AD by 65%. The [Ca2+]e elevation prior to AD was attenuated from 17.8% to 6% while the increase of the [Na+]e in this period was enhanced (from 2.9% to 7.3%). These findings implied that the ischemia-induced early cellular sodium load and the corresponding shrinkage of the extracellular space was counteracted by TTX. Our results suggest that the Na+ influx via voltage-dependent channels preceding complete breakdown of ion homeostasis is one major factor leading to cell depolarization. The massive Na+ influx coinciding with AD, however, may be mainly via non-selective cation channels or/and receptor-operated channels. Persistent Na+ influx deteriorates neuronal tissue integrity by favouring Ca2+ influx and edema formation. Blockade of ischemia-induced excessive Na+ influx is, therefore, a promising pharmacological approach for stroke treatment.

Self-sustained spreading depressions in the chicken retina and short-term neuronal-glial interactions within the gray matter neuropil

The chicken retina is an accessible piece of intact gray matter in which a self-sustained form of the 'Spreading Depression' (SD) wave can be easily elicited and recorded for many hours with double barrel ion-sensitive electrodes in the extracellular space. The blockade of glial (Müller) cell potassium channels with barium chloride added to the perfusing Ringer depressed both the negative potential shift typical of SDs and the velocity of spread. Moreover, there was separation of the extracellular increase of potassium and the drop in the extracellular potential: the peak of the potassium wave was increased, as well as its duration whereas the potential wave could be depressed to zero or even inverted to positive. By contrast the transient extracellular calcium drop could not be separated from the extracellular potential wave but appeared related to it: no transient calcium drop was observed when the negative potential was completely depressed or inverted. Both, the amplitude of the extracellular potential and extracellular calcium activity appeared to be important factors controlling the velocity of spread.

R56865 and flunarizine as Na(+)-channel blockers in isolated Purkinje neurons of rat cerebellum

Dose-related blocking effects of R56865, flunarizine and nimodipine on voltage-activated Na+ currents recorded in the whole-cell voltage clamp mode were studied in acutely isolated Purkinje neurons of rat cerebellum. The dose-dependences of blocking action were obtained for all drugs at a holding potential of -110 mV and rare stimulation. At stimulation frequencies 5 and 15 Hz the block produced by R56865 was increased showing a shift of dose-dependence to lower concentrations of antagonist. This shift was less pronounced for flunarizine, practically absent for nimodipine, and increased for all drugs with an increase in the amplitude of stimulating voltage pulse. With the change in holding potential to -80 mV the block produced by R56865 and flunarizine increased showing a dose-dependence shift to lower concentrations of antagonists. All the drugs tested induced parallel shifts of the steady-state voltage-dependence of inactivation of Na+ channels to more negative membrane potentials. R56865, and to a lesser extent flunarizine, slowed down the recovery of Na+ channels from steady-state inactivation increasing the relative number of channels which showed slow recovery. In the absence of Na+ current inactivation (treatment by intracellular pronase) R56865 at a concentration of 1 microM blocked modified channels preferentially in the open state, while the block produced by flunarizine showed no dependence on voltage pulse protocol. R56865 was shown to decrease the cell leakage while other drugs produced little or no effect. It is concluded that R56865 and flunarizine block Na+ currents predominantly by interacting with inactivated Na+ channels. The higher ability of R56865 to block open channels and to increase slow inactivation underlies its higher frequency-dependence. These characteristics suggest the use of R56865 and flunarizine in the treatment of cerebral ischemia.

R56865 as Ca(2+)-channel blocker in Purkinje neurons of rat: comparison with flunarizine and nimodipine

The blocking action of recently synthesized benzothiazolamine derivative R56865 was compared with that of dihydropyridine (nimodipine) and diphenylalkylamine (flunarizine) on low-voltage-activated and non-inactivating high-voltage-activated Ca2+ currents. The experiments were carried out on freshly isolated Purkinje neurons of rat cerebellum using patch-clamp technique in the whole-cell configuration. Among the substances tested R56865 was found to be the most effective blocker of the Ca2+ current. In the sequence R56865, flunarizine and nimodipine, apparent Kd values for low-voltage-activated current are 0.1, 0.9 and 3.5 microM, and for high-voltage-activated current 3.1, 9.5 and 38 microM, respectively. The current-voltage relationships for both types of currents displayed little or no shift under either flunarizine or R56865 but showed a 10-mV shift in the positive direction under the action of nimodipine. The steady-state inactivation curves for low-voltage-activated calcium currents were shifted under the action of R56865, flunarizine and nimodipine (in concentrations which blocked 50-60% of the current) to more negative membrane potentials for 20, 10 and 6 mV, respectively. In contrast to R56865, flunarizine blocked both types of Ca2+ channel in a use-dependent manner. It is concluded that the order of potency of Ca2+ antagonist for both types of channels studied is R56865 > flunarizine > nimodipine. Strong shift of steady-state inactivation relationship by R56865 can further facilitate its blocking action in in vivo conditions.

Anaerobic glycolysis and postanoxic recovery of respiration of rat cortical synaptosomes are reduced by synaptosomal sodium load

Synaptosomes of rat cerebral cortex were used to study the effect of veratridine-induced Na+ load on postanoxic recovery of respiration and on aerobic and anaerobic ATP turnover, calculated from rates of oxygen consumption and lactate production. Non-stimulated synaptosomes: after onset of anoxia lactate synthesis of synaptosomes rose immediately from 0.8 to 17.7 nmol lactate/min/mg protein indicating an anaerobic ATP turnover of 17.7 nmol ATP/min/mg protein. This value accounts for 80% of ATP synthesized during oxygenated conditions and seems to cover the energetic demand of anoxic synaptosomes. This assumption was supported by linearity of lactate production throughout anoxia (90 min), by unaffected synaptosomal integrity and by complete recovery of postanoxic respiration after 90 min of anoxia. Stimulated synaptosomes: stimulation of oxygenated synaptosomes with 10(-5) mol/l veratridine enhanced ATP turnover 5-fold, due to activation of Na+/K+ ATPase, as a result of veratridine-induced Na+ influx. Consequently, if not limited in capacity, anaerobic ATP synthesis should be enhanced after addition of veratridine during anoxia. However, the opposite effect was observed. Veratridine reduced anaerobic glycolysis in a concentration-dependent manner. This inhibitory effect could be prevented by tetrodotoxin applied 5 min prior to veratridine. Inhibition of anaerobic glycolysis was independent of extrasynaptosomal glucose (1-30 mmol/l) and Ca2+ concentration (Ca(2+)-free and 1.2 mmol/l Ca2+). Veratridine stimulation of anoxic synaptosomes reduced also the recovery of postanoxic respiration. The data indicate that Na+ load inhibits anaerobic ATP synthesis, the only energy source during anaerobic conditions. To our knowledge, inhibition of anaerobic glycolysis due to increased Na+ influx has not been shown so far.

Cryopreservation of freshly isolated synaptosomes prepared from the cerebral cortex of rats

In the present study, we established a cryopreservation method for freshly isolated synaptosomes prepared from the cerebral cortex of rats. Freshly prepared synaptosomes were either shock-frozen or frozen under temperature-controlled conditions using a programmable temperature controller. Each group was resuspended in iso-osmotic or hyperosmotic sucrose buffer prior to freezing, resulting in 4 different preservation protocols. The viability of the frozen synaptosomes was estimated by the recovery of basal and stimulated respiration after short-term storage (1 h) in liquid nitrogen. With regard to basal, FCCP- and veratridine-induced respiration, best recovery revealed controlled-frozen synaptosomes resuspended in iso-osmotic sucrose buffer (con/iso group). Basal respiration of this group recovered completely, whereas veratridine- and FCCP-induced oxygen uptake was decreased to 87.7% and 82.4% of control, respectively. Further investigations performed with the con/iso group revealed complete recovery of anaerobic and aerobic lactate synthesis, and unaffected synaptosomal integrity, as judged by the amount of released L-lactate dehydrogenase before and after the cryopreservation procedure. Long-term storage of the con/iso group in liquid nitrogen up to 88 days did not have any influence on synaptosomal viability, as evaluated by the recovery of anaerobic lactate production and synaptosomal respiration. Therefore, based on the results of respiration, synaptosomal integrity, and lactate synthesis, metabolically active synaptosomes could be obtained after cryopreservation and storage in liquid nitrogen for at least 88 days.

Lactate and postischemic recovery of energy metabolism and electrical activity in the isolated perfused rat brain

The aim of the present study was to evaluate whether lactate can maintain the energy metabolism and electrical activity of isolated perfused rat brain in the absence of glucose. To exhaust cerebral glucose stores and simultaneously raise endogenous lactate, complete ischemia was induced. After ischemia, when a glucose-free perfusate was supplied, restoration of interstitial potassium (Ke+), cortical discontinuous current (DC) potential, electroencephalogram (EEG) activity, and ATP and phosphocreatine (PCr) was not significantly different from postischemic recovery findings when a glucose-containing perfusate was used. In the group receiving glucose-free perfusate, postischemic application of 1 mM iodoacetic acid did not inhibit the recovery of electrical activity, Ke+, or DC potential. After recovery of Ke+ in glucose-free reperfusion, a 20-30-Hz EEG pattern appeared and was maintained for about 20 min followed by disappearance of spontaneous electrical activity. An abrupt increase of Ke+, a steep negative DC shift, and a substantial decrease of ATP and PCr occurred after about 22 min of reperfusion. During the first 5 min of glucose-free reperfusion, consumption of lactate was significantly higher (0.89 mumol/g wet weight/min) than during reperfusion with medium containing glucose (0.41 mumol/g ww/min). Increasing amounts of tissue lactate prolonged maintenance of electrical function in glucose-free reperfusion. This correlation could not be found for free fatty acids. In conclusion, after a few minutes of ischemia, the brain is able to recover cellular ion transport and electrical activity without a supply of glucose, preferentially by combustion of lactate accumulated in brain tissue. This mechanism is only useful during a limited time period until the lactate accumulated during ischemia is combusted.

Effects of R 56865 and phenytoin on mechanical, biochemical, and morphologic changes during ouabain intoxication in isolated perfused rabbit heart

The Na+/Ca2+ overload inhibitor R 56865 (N-[1-[4-(4-fluorophenoxy)-butyl]-4-piperidinyl)-N-methyl-2- benzothiazolamine) has been reported to prevent or attenuate ischemia- as well as ouabain-induced cellular sodium and calcium load. We investigated the potency of this compound in preventing mechanical, biochemical, and ultrastructural consequences of ouabain (OUA) intoxication in isolated rabbit heart. The protective effect of the digitalis antidote phenytoin (PHT) on the consequences of ouabain intoxication was examined for comparison. In isolated perfused rabbit heart, OUA (0.4 microM) caused an increase in left ventricular end-diastolic pressure (LVEDP) that was accompanied by depletion of high-energy phosphates (80% less than in control), accumulation of tissue lactate (12-fold) and damage of contractile elements and mitochondria. Accumulation of lactate was associated with a decrease in oxygen consumption by the isolated perfused heart. R 56865 (1.0 microM) and phenytoin (60 microM) prevented increase in LVEDP, breakdown of the energy-rich phosphates creatine phosphate (CrP) and ATP, accumulation of lactate, and morphologic changes induced by OUA. The above-mentioned toxic effects of OUA are interpreted as consequences of mitochondrial failure finally leading to breakdown of the oxidative phosphorylation. Thus, we conclude that the protective action of both compounds, R56865 and PHT, may be attributed to prevention or attenuation of mitochondrial failure due to OUA-induced disturbance of ion homeostasis.

Ridogrel inhibits systemic and renal formation of thromboxane A2 and antagonizes platelet thromboxane A2/prostaglandin endoperoxide receptors upon chronic administration to man

The effects of ridogrel, a dual thromboxane A2 (TXA2) synthase inhibitor and TXA2/prostaglandin (PG) endoperoxide receptor antagonist, on systemic and renal production of prostaglandins and on platelet TXA2/PG endoperoxide receptors was evaluated upon chronic administration (300 mg b.i.d. orally, for 8 and 29 days) to man. Such a medication with ridogrel inhibits the systemic as well as the renal production of TXA2 as measured by the urinary excretion of 2,3-dinor-TXB2 and TXB2 respectively without inducing significant changes in systemic or renal PGI2 production. Simultaneously with the latter effects, the production of TXB2 by spontaneously coagulated whole blood ex vivo is inhibited (greater than 99%) while that of PGE2 and PGF2 alpha is largely increased. Administration of ridogrel causes a three- to five-fold shift to the right of concentration-response curves for U46619 in eliciting platelet aggregation; no tachyphylaxis is observed after 29 days of treatment in this respect. Apart from a reduction of serum uric acid levels with a concomitant increase in urinary uric acid excretion during the first days of treatment, no clinically significant changes in hematological, biochemical, hemodynamic and coagulation parameters occur during the 8 days or 29 days study. The study demonstrates that ridogrel is a potent inhibitor of the systemic as well as renal TXA2 synthase and an antagonist of platelet TXA2/PG endoperoxide receptor in man, covering full activity during 24 h at steady-state plasma level conditions without tachyphylaxis during 29 days of medication. The compound is well tolerated, at least during 1 month of administration.

Extracellular changes of inorganic phosphate are different during spreading depression and global cerebral ischemia of rats

Tissue levels of inorganic phosphate (iP-) and lactate (lac) increase during cerebral ischemia and cortical spreading depression (SD). Since cell membranes become leaky during these insults, iP- and lac were expected to leak into the extracellular space (ECS). In order to find out whether this occurs or does not, a microdialysis (MD) fiber was implanted into the cortex of anesthetized rats and extracellular lactate (lac(e)) and extracellular iP- (iPe-) were determined during various insults. Extracellular lactate increased to about the same extent during ischemia and SD. In contrast, iPe- increased during ischemia but not during SD. Instead, iPe- started to rise after SD and reached its maximum about 45 min later. The distinct pattern of iPe- in comparison to lac(e) during the above mentioned insults points to a qualitative difference of the underlying mechanisms: whereas lac appears within the ECS at any stressful situation, elevation of iP- within the ECS indicates depletion of energy stores in parallel to the lack of control of ion homeostasis.

Gas chromatographic-mass spectrometric determination of 11-dehydrothromboxane B2 in human urine

The extension of a method for the determination of thromboxane B2 (TxB2), 2,3-dinor-TxB2, 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and 2,3-dinor-6-keto-PGF1 alpha to quantify 11-dehydro-TxB2 in the same urinary sample is described. After phenylboronic acid and C18 column chromatography, 11-dehydro-TxB2, which is present in urine as the lactone and its corresponding hydroxy acid, was quantitatively converted into its lactone form for a thin-layer purification step and pentafluorobenzyl esterification. Quantification of eicosanoids was achieved by analysing their trimethylsilyl ethers with gas chromatography and negative-ion chemical ionization mass spectrometry. The overall recovery from urine for tritiated 11-dehydro-TxB2 was 80%. The detection limit was 10 pg/ml. The method was applied to the determination of these eicosanoids in volunteers and in patients suffering from acute myocardial infarction.

Ouabain-induced changes of calcium and potassium in slices of hippocampus of the rat: comparison to hypoxia and effect of R 56865

Simple and reliable in vitro models of cerebral ischaemia are important for the identification of antiischaemic/antihypoxic compounds. Alterations of the concentrations of potassium and calcium were recorded in slices of hippocampus of the rat. The slices were subjected to hypoxia in the presence and absence of intoxication with glucose or ouabain (1 mmol/l). Normoxic slices of hippocampus showed an extracellular space of 57% and a tissue concentration of potassium of 45 mmol/kg wet wt. A cellular concentration of potassium of 92 mmol/kg was calculated. Hypoxia, in the presence of glucose, only slightly reduced tissue concentrations of potassium and did not influence concentrations of calcium. Omission of glucose during hypoxia led to tissue concentrations of potassium below 10 mmol/kg, within 10-30 min of hypoxia. Concentrations of calcium only increased from 3.3 to 3.5 mmol/kg after 30 min of hypoxia, without glucose. Intoxication with ouabain is proposed as alternative experimental model of ionic movements, associated with cerebral ischaemia/hypoxia. Tissue concentrations of potassium fell rapidly to values below 10 mmol/kg, within 5 min and concentrations of calcium rose to 5.2 mmol/kg, within 30 min of intoxication with ouabain. In quantitative terms, the model for cerebral ischaemia with intoxication with ouabain is suggested to be superior to the model based on hypoxia without glucose. To verify intoxication with ouabain as an experimental model for ischaemic/hypoxic insults, the effect of an investigational drug with antiischaemic/hypoxic properties (R 56865) was evaluated in the model. The drug R 56865 produced dose-dependent attenuation of the fall in tissue concentrations of potassium, between 3 x 10(-7) and 5 x 10(-6) mol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Flunarizine and R 56865 suppress veratridine-induced increase in oxygen consumption and uptake of 45Ca2+ in rat cortical synaptosomes

The effect of the anti-ischemic compounds flunarizine and R 56865 on the veratridine-induced uptake of Ca2+ and Na+ was observed in cortical synaptosomes in the rat. The veratridine-induced uptake of Na+ and Ca2+ was determined by means of a measurement of synaptosomal oxygen consumption and a method for the uptake of 45Ca2+, respectively. Veratridine (10(-5) M) was found to induce a 3-fold increase in synaptosomal oxygen consumption (uptake of Na+) and uptake of 45Ca2+, both of which were inhibited by tetrodotoxin (10(-5) M). Nitrendipine (10(-5) M) and omega-conotoxin (5 x 10(-7) M) were ineffective on the veratridine-induced response. Nimodipine (10(-5) M) suppressed the veratridine-induced uptake of 45Ca2+ but also diminished the unstimulated uptake of 45Ca2+. The veratridine-induced uptake of Na+ was not influenced by nimodipine. Flunarizine (3 x 10(-6)-10(-5) M), as well as R 56865 (10(-6)-10(-5) M), attenuated the veratridine-induced uptake of both Na+ and 45Ca2+. In conclusion, the veratridine-induced uptake of Na+ and 45Ca2+ was shown to be closely correlated to the activity of Na+ channels but not to voltage-operated Ca2+ channels. Secondly, flunarizine and R 56865 seemed to evoke their effects by interfering with the permeability of Na+ channels. Since veratridine-induced uptake of Na+ and Ca2+ shares some similarities with ischaemia-induced uptake of Na+ and Ca2+, it is proposed, that flunarizine and R 56865 exert their anti-ischaemic effects by reducing ischaemia-induced Na+ and Ca2+ load, probably by inhibiting a TTX-sensitive Na+ channel.

Lactate and pH change in close correlation in the extracellular space of the rat brain during cortical spreading depression

pH sensitive microcelectrodes were used in combination with microdialysis (MD) technique to measure extracellular pH (pHe) and extracellular lactate (lace) within the cortex of rat brains during cortical spreading depression (SD). SD was induced by local K(+)-application and identified by DC recordings. It was accompanied by an extracellular acidification of 0.34 +/- 0.06 pH units and by a 2.8 +/- 0.80 fold increase of lace; the recovery of pHe took place within three phases, that of lace within 2 phases. The recovery of both parameters was complete about 45 min after the onset of SD. We conclude that the changes of lace and pHe are closely related. This indicates both lactate and protons to be transported in parallel.

Determination of 6-keto-PGF1 alpha, 2,3-dinor-6-keto-PGF1 alpha, thromboxane B2, 2,3-dinor-thromboxane B2, PGE2, PGD2 and PGF2 alpha in human urine by gas chromatography-negative ion chemical ionization mass spectrometry

A method for quantification of 6-keto-PGF1 alpha, 2,3-dinor-6-keto-PGF1 alpha TXB2, 2,3-dinor TXB2, PGE2, PGD2 and PGF2 alpha in human urine samples, using gas chromatography-negative ion chemical ionization mass spectrometry, is described. Deuterated analogues were used as internal standards. Methoximation was carried out in urine samples which were subsequently applied to phenylboronic acid cartridges, reversed-phase cartridges and thin-layer chromatography. The eluents were further derivatized to pentafluorobenzyl ester trimethylsilyl ethers for final quantification by gas chromatography-mass spectrometry. The overall recovery was 77% for tritiated 6-keto-PGF1 alpha and 55% for tritiated TXB2. Urinary levels of prostanoids were determined in a group of six volunteers before and after intake of the thromboxane synthase inhibitor Ridogrel, and related to creatinine clearance.

Synaptosomal respiration: a potent indicator of veratridine-induced Na influx

Inhibition of the voltage-dependent Na channel by tetrodotoxin (5 mumol/l) decreased by about 86% the stimulation of the respiration of rat brain synaptosomes induced by veratridine (10 mumol/l). A similar effect was achieved by blocking Na(+)-K(+)-ATPase with ouabain (1 mmol/l). Pharmacological manipulations of Ca homeostasis suggested that the veratridine-induced stimulation of respiration did not depend upon Ca entry. These data suggest that the veratridine-induced stimulation of synaptosomal respiration may result primarily from an increase in intracellular Na+. They provide the basis for an indirect method, which only requires recording of synaptosomal respiration, to test drugs for their possible interaction with excessive Na influxes.

A rapid redistribution of hydrogen ions is associated with depolarization and repolarization subsequent to cerebral ischemia reperfusion

1. The aim of this study was to examine the rapid changes in extracellular hydrogen ion activity [( H+]o or pHo) which are associated with depolarization and repolarization subsequent to cerebral ischemia reperfusion. Two parallel studies were performed with different rat models of ischemia: repetitive severe ischemia produced in anesthetized animals by occlusion of the vertebral and carotid arteries and temporary interruption of blood flow in isolated brain. [H+]o and direct current potential (DC potential) were recorded simultaneously in all experiments. Examination of these two parameters was supplemented by recording tissue concentration of carbon dioxide (PtCO2) in the four-vessel occlusion model and assaying major metabolites involved in energy production in experiments with isolated brains. 2. Measurements of [H+]o during ischemia consistently revealed a steady increase of [H+]o on which was superimposed an abrupt and transient fall in [H+]o closely related to the occurrence of the fast negative shift of DC potential characterizing brain-cell depolarization. Analysis of the relationship between the magnitude of the transient fall in H+ and the level of [H+]o at which this occurred showed that the amplitude of the transient fall in H+ increased with tissue acidosis. 3. We propose that this phenomenon is indirect evidence that rapid transfer of acid equivalents occurs across the plasmalemma, concomitantly to its depolarization. Both events probably result from a common cause, i.e., nonspecific increase of the cell-membrane permeability to ions subsequent to opening of membrane channels. 4. Early on during recirculation, an acidotic [H+]o shift associated with membrane repolarization was clearly visible whenever the ionic gradients recovered rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosanoids in rat brain during ischemia and reperfusion--correlation to DC depolarization

The effects of complete ischemia on cerebral arachidonic acid (AA) metabolism were investigated in the isolated perfused rat brain. During 12.5 min of ischemia, AA, 5-hydroxy-6,8,11,14-eicosatetraenoic acid, and 15-hydroxy-5,8,11,13-eicosatetraenoic acid increased 129-, 4-, and 10-fold, respectively, while subsequent reperfusion for 30 min resulted in normalized levels independently of the duration of preceding ischemia. Prostaglandin (PG) F2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and thromboxane (Tx) B2 remained at preischemic levels during 12.5 min of complete ischemia. However, at the end of subsequent reperfusion for 30 min, the levels of the prostanoids PGF2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and TxB2 increased according to the preceding ischemic time. The levels reached a maximum after 7.5 min of ischemia and were elevated by 7-, 14-, 48-, 3-, and 30-fold, respectively. A prolongation of ischemia of up to 12.5 min was not associated with further increases of prostanoids at the end of reperfusion. The mechanisms underlying the metabolism of eicosanoids are discussed in relation to the changes of cortical direct current potential.

Enzymatic synthesis and chromatographic purification of lignan glucuronides

Enterolactone, enterodiol and secoisolariciresinol were conjugated with glucuronic acid by solubilized rabbit liver microsomal UDP-glucuronyltrasnferase. The monoglucuronide conjugate of all three substrates was formed and its identity confirmed by nuclear magnetic resonance (NMR) spectroscopy. Analytical high pressure liquid chromatography (HPLC) and NMR spectroscopy indicated conjugation with glucuronic acid to occur at several positions in the molecule. The enzymatic conjugation was monitored by analytical capillary isotachophoresis (ITP). The Km-values for enterlactone, enterodiol, and secoisolariciresinol were calculated to be 0.30, 0.23, and 0.22 mmol/l respectively.

Adsorption and desorption characteristics of nucleotide based coenzymes on agarose encapsulated resins for long term cofactor supply of enzymatic reactions

In order to find optimal long term cofactor supply for continuous enzymatic detoxification processes, different resins of varying surface, dipole moment, pore size, and chemical structure were investigated for their adsorptive capacity as well as their desorption behaviour towards various nucleotide based coenzymes. UDPGA, NADPGH, NADH, and SAM were gently shaken with agarose coated resins XAD-12, XAD-8, XAD-7, XAD-4, XAD-2, Dowex 1 X 2 (50-100; 200-400), Dowex 1 X 4 (20-50; 200-400), Dowex 2 X 8, and charcoal until all nucleotide was adsorbed or a saturation of the resins was achieved. High adsorption capacity was not always found to correlate with a steady release of cofactor in desorption experiments. Under this premise the optimal resin-cofactor combinations for long term cofactor supply were found to be XAD-12 for UDPGA, Dowex 2 X 8 for NADPH, Dowex 1 X 4 (20-50) for NADH, and XAD-7 for SAM.

Enzymatic detoxification using lipophilic hollow-fiber membranes: II. Sulfation reactions

A lipophilic hollow-fiber technique was used in the enzymatic sulfation of lipophilic toxins. Endogenous and exogenous toxins, for which glucuronidation reactions already were demonstrated with this technique, were submitted to sulfate transferase reaction as an alternative phase-II detoxification route. Native enzyme was circulated on the external side of a lipophilic hollow-fiber membrane while the toxin-containing media (serum or aqueous solution) were circulated inside the hollow fiber. Sulfation reactions were catalyzed by rabbit liver cytosol, with a specific sulfate transferase activity of 626 nmol/min-mg protein. Clearance of the hollow-fiber module for phenol, p-cresol, paracetamol, 2-aminophenol, and 5-hydroxyindol were determined to be 38.1, 47.2, 2.7, 5.3, and 3.2 pmol/mg protein/h/cm2 hollow-fiber surface, respectively. This technique allows sulfation reactions with crude enzyme preparations over long periods without loss of activity from covalent immobilization and without immunological hazards.

Enzymatic detoxification using lipophilic hollow-fiber membranes: I. Glucuronidation reactions

A lipophilic hollow-fiber membrane preparation was used in the enzymatic detoxification of lipophilic toxins. Native enzymes were circulated on one side of the lipophilic membrane, while the toxin-containing media (blood, serum, waste fluids, etc.) were circulated inside the hollow fiber. Lipophilic substances that accumulate in and penetrate the lipophilic membrane were converted by the corresponding enzymes. Phase II detoxifying enzymes converted the lipophilic toxins to hydrophylic compounds that made a rediffusion of these molecules back to the blood impossible. Glucuronidation reactions were catalyzed by a crude preparation of solubilized uridine-5'-diphosphate-glucuronyltransferase (EC 2.1.1.9) with a specific activity of 10.0 nmol/min/mg protein in the presence of uridine-5'- diphosphoglucuronic acid (acceptor: phenol as reference substrate). Clearance rates of phenol, 1- naphthol , 2- naphthol , and p-cresol were measured, respectively, to be 141, 195, 300, and 251 pmol/h/mg protein/cm2 hollow fiber. The advantage of this technique lies in the possibility of using highly active, soluble enzyme preparations and a fully utilizable cofactor supply. The lipid membrane ensures the absence of immunological hazards, while mass transfer of the toxin is not impaired.

Solubilization characteristics of pig liver S-methyltransferase

S-methyltransferase was solubilized from pig liver microsomes by five different types of detergents: Triton X-100, zetyltrimethyl-ammonium bromide, sodium cholate, Zwittergent, and sodium dodecylsulfate. As regards enzyme activity, stability, and critical detergent concentration, Zwittergent proved superior to the four other detergents utilized. A striking difference was found in the catalytic activity relative to the chain length of homologous substrates between the microsomal and the solubilized enzyme. The microsomal enzyme preparation showed highest activity towards C1 substrate (methane thiol) while the solubilized enzyme had its maximal activity for C7 substrate. This observation accorded with the active site affinity for the corresponding substrates. From the reaction of the enzyme to the different detergents and the distribution coefficient of substrates in membranes and cytosol, it can be deduced that the enzyme is located on the surface of microsomal membranes with the active site directed towards the cytoplasm.

Immobilization of S-methyltransferase

S-methyltransferase was solubilized from pig liver microsomes by treatment with N-dodecyl-N,N-dimethyl-3-ammonio-1-sulfonate (Zwittergent). The soluble enzyme was immobilized by covalent binding to agarose and by copolymerization with acrylamide. The specific activity for the agarose-bound enzyme towards the substrate ethane thiol was 0.87 nmol/min/mg and for the acrylamide-bound enzyme 0.55 nmol/min/mg. The specific activity of the soluble enzyme was found to vary with increasing chain length of the substrate molecules from 0.5 nmol/min/mg for methane thiol (C1) to 6.3 nmol/min/mg for n-heptane thiol (C7). After binding of the enzyme to agarose beads, the increase in specific activity towards substrates with increasing chain length was no longer detectable. Instead, a relatively constant specific activity of 1.1 nmol/min/mg was observed for the whole range of substrates tested from C1 to C7. The stability of the agarose immobilized enzyme at -20 degrees C is twice as good as the soluble enzyme. The acrylamide immobilized enzyme is less stable than the soluble enzyme.

Gas chromatographic method for the quantitative assay of alkane thiol S-methyltransferase

A method is described for the quantitative assay of the methylation of alkane-thiols from the methyl-donor S-adenosylmethionine, catalysed by the microsomal enzyme S-adenosyl-L-methionine:thiol S-methyltransferase (E.C. 2.1.1.9). The reaction is carried out in sealed vials, one fifth of whose volume is taken up by an aqueous phase containing the enzyme and reactants. The volatile substrates and products of the reaction, thiols and thioethers, respectively, are present in equilibrium both in the liquid and gas phases in the reaction vessels. Aliquots of the gas phase are removed at intervals in gas-tight syringes, and analysis is performed directly on a gas chromatograph fitted with a flame-ionization detector. The amounts of thiol and thioether detected are then related to the total amounts of substance in the reaction vessels from calibration measurements, so that the kinetics of the enzymatic process can be evaluated. This technique offers distinct advantages over previously reported methods, in that no radioactively labelled compounds are required. Furthermore, decreases in substrate and increases in product can be assayed simultaneously, and the methylation of a mixture of thiols can be monitored in a single set of analyses.