Effects of a xanthine derivative, propentofylline, on local cerebral blood flow and glucose utilization in the rat.

The effects of the xanthine derivative propentofylline [3-methyl-1-(5'-oxohexyl)-7-propylxanthine] were measured on local cerebral blood flow and glucose utilization in the rat using quantitative autoradiographic techniques. A dose of 0.5 mg/kg/min i.v. produced increases in local cerebral blood flow and minimal effects on glucose utilization in the majority of cerebral structures measured. A higher dose of propentofylline (1.5 mg/kg/min) produced an overall increase in local cerebral blood flow and a marked reduction in glucose utilization. Furthermore, propentofylline increased the average ratio of blood flow per unit glucose utilization and thus is capable of increasing cerebral blood flow in excess of metabolic demand. While the mechanism of action of this compound has not been fully defined, it is possible that its cerebrovascular and cerebral metabolic effects can at least partially be explained by a blockade of adenosine uptake. These actions of propentofylline on cerebral blood flow and metabolism may play a role in protecting neuronal tissue under hypoxic/ischemic conditions in the brain.

Sulphoevernan, a polyanionic polysaccharide, and the narcissus lectin potently inhibit human immunodeficiency virus infection by binding to viral envelope protein.

Sulphoevernan is a sulphated alpha-1----3, 1----4 polyglucan (Mr 20,000) with a helical structure. This compound effectively inhibits both human immunodeficiency virus type 1 (HIV-1) and type 2 infection of cells in vitro at concentrations around 0.5 micrograms/ml. Moreover, the compound completely inhibits HIV-1-induced syncytium formation at a concentration of 1 microgram/ml. Competition experiments with 35S-labelled sulphoevernan revealed that the mannose-specific lectin from Narcissus pseudonarcissus prevented binding of sulphoevernan to HIV-1, whereas the antibody OKT4A did not reduce the amount of sulphoevernan bound to MT-2 cells. These data indicate that the non-cytotoxic polymer sulphoevernan binds to the virus rather than to the host cell. In vivo studies, using Rauscher leukaemia virus in NMRI mice, revealed that, at a daily dose of 20 mg/kg, the animals were protected against virus-induced increases in spleen weight. From these in vitro and in vivo data we conclude that sulphoevernan has potential in the treatment of acquired immunodeficiency syndrome.

Effect of propentofylline on the biochemical lesion of the rat brain in aluminium-induced neurotoxicity.

Acute and chronic administration of Al-gluconate (12.7% Al) at the concentration of 1 mg/kg produces edema in the rat brain, as reflected by the increase in water and Na+ content. The permeability for Evans blue is also increased, which indicates the opening of the blood-brain barrier. Higher concentrations of the Al-gluconate (10 mg/kg) change, in acute experiments, the pattern of energy metabolites in the rat brain toward a profile observed in a deep hypoxia. Chronic administration of a low concentration of Al-gluconate (1 mg/kg) increases the local utilization of glucose in 20 of 39 rat brain structures examined. This increase was particularly evident in the structures of the limbic system. Xanthine derivative propentofylline reverses the edema formation in acute and chronic experiments. Hypoxia-like changes in energy metabolism are also reversed by propentofylline. In preliminary experiments propentofylline also suppressed the increased utilization of glucose observed after administration of Al-gluconate. These results suggest that (i) the Al-gluconate model in rats can be used to study Al-neurotoxicity at a very low level of Al, and (ii) the xanthine derivative propentofylline can eventually be used to abolish the Al-neurotoxicity.

The effect of early postnatal hypoxia on the regional cerebral utilization of glucose in adult rats.

The purpose of this study was to establish if there are any later changes in the local cerebral energy metabolism after exposing 1-day-old rats for 5 days (10 hr daily) to hypobaric hypoxia (pO2 = 10.5 kPa). For this study the 2-[14C]deoxyglucose method for the determination of the regional utilization of glucose in the rat brain was employed. The results, obtained in 41 cerebral structures, show that rats subjected to an early postnatal hypoxia exhibit a significant decrease (-41%) 3 months later in the utilization of glucose in the CA, area of the hippocampus. This finding is a new one in the chain of several biochemical and behavioral changes observed in this experimental model. It is suggested that this finding could be useful in the search for a new therapeutic agent eventually able to alleviate the consequences of perinatal hypoxia.

Age-dependent stimulation of assembly and of membrane-association of polysomes in rat brain after treatment with xanthine derivatives in vivo.

A new pharmacological approach is described to change the structural state of polyribosomes in old rats. It is shown that the ratio of free to membrane-bound polysomes in rat brain increases significantly depending on age (immature animals, 1.40; mature and old rats, 1.48 and 1.67, respectively). Moreover, the portion of heavy polysomes (number of ribosomes: five and greater) decreases age-dependently with respect to light polysomes (number of ribosomes: four and smaller). The values for the fraction of free polysomes are as follows: immature animals; 4.0; mature and old animals; 4.3 and 2.9, respectively; and for membrane-bound polysomes: immature, 4.9; mature, 4.7; and old 3.3. It is shown that after in vivo application (80 mumol/kg p.o. daily for 14 days) the xanthine derivative propentofylline reverted the structural state of the polyribosomal translation system in old brain to those values which are characteristic for polysomes in immature and mature brains. The xanthine derivatives theophylline, theobromine and caffeine were without effect under otherwise identical conditions. It is suggested that propentofylline has an activating influence on polysomal function in old rat brain.

Differential effects of methylxanthines on local cerebral blood flow and glucose utilization in the conscious rat.

The aim of this study was to test the effects of the three "classical" methylxanthines, theophylline, caffeine and theobromine, on local cerebral blood flow and glucose utilization. Equimolar doses (1.6 mumol/kg/min i.v.) of theophylline and caffeine produced increases in local cerebral glucose utilization and decreases in local cerebral blood flow. These compounds, therefore, re-set the ratio of cerebral blood flow per unit of glucose utilization at a lower level. These results are interpreted with respect to the known adenosine antagonist properties of caffeine and theophylline. Theobromine, a substance with less significant adenosine antagonist properties, had minimal effects on local cerebral blood flow and glucose utilization at a dose of 1.6 mumol/kg/min i.v. These data may provide supportive evidence for the hypothesis that adenosine plays an important role in cerebral blood flow-metabolism coupling.

[Energy metabolism in the brain]. / Energiestoffwechsel im Gehirn.

In this review of brain energy metabolism, the utilization of glucose as the sole energy source in the normal brain is described and presented in a schematic form. Important reactions concerned with the synthesis and degradation of the energy carrier in the cell, ATP, are also noted. Changes in energy metabolism with acute oxygen deficiency are shown in the example of rat brain energy metabolism during 30 seconds of nitrogen breathing (significant decrease of phosphocreatine, ATP, total adenine nucleotides and adenylate energy charge). Several important metabolic changes, particularly in ion and lipid metabolism during the decrease in the cerebral blood flow (ischemia), are described in some detail and presented in schematic form. A short description of the [14C]-2-deoxyglucose method developed by L. Sokoloff for the determination of local cerebral utilization of glucose is followed by a description of the application of this method in the study of aging in rats.

Uptake of adenosine by isolated bovine cortex microvessels.

The uptake of adenosine is studied in microvessels isolated from a bovine cortex. The KM value for adenosine uptake is 1.92 microM and the Vmax is 1.93 picomole/mg protein/10 min. This high affinity uptake system is very sensitive to inhibition by dipyridamole and papaverine. The uptake of adenosine by microvessels is also inhibited by CuCl2 and by high concentration (2 mM) of adenine nucleotides. Using a series of four xanthines is observed that the adenosine uptake system is most inhibited by 3-methyl-l-(5'-oxohexyl)-7-propylxanthine and the least by caffeine. Theophylline causes a stimulation of adenosine uptake by microvessels. The results obtained agree with the existence of the nucleoside transport system associated with the blood-brain barrier, as previously observed by in vivo studies and experiments with rat brain capillaries.

Effect of theophylline administration on ketone bodies level in rat plasma and brain.

Administration of theophylline (100 mg/kg b.w. p.o.) produces increases in 3-hydroxybutyrate and acetoacetate levels in plasma and brain of rats.

The effect of 1-(5'-oxohexyl)-3-methyl-7-propyl-xanthine on the respiratory activity of the rat brain mitochondria.

The effect of 1-(5'-oxohexyl)-3-methyl-7-propyl-xanthine (HWA 285) on the respiration and oxidative phosphorylation in mitochondria isolated from normal (CM), ischemic (IsM) and postischemic (PIsM) rat brain was investigated. After the administration of 10 mg/kg HWA 285 p.o. daily for 14 days the mitochondrial ATPase activity was significantly increased, whereas O2-consumption and the respiratory control rate (RCR) were decreased. In IsM the RCR was increased, if they consumed glutamate and malate as substrates (from 3.7 +/- 0.8 to 5.0 +/- 0.75) as consequence of increased oxygen consumption in status 3. The pretreatment of the rats with 10 mg/kg HWA 285 p.o. induced a normalization of RCR in mitochondria from ischemic brains. The RCR in PIsM was apparently not influenced by HWA 285 but the oxidative phosphorylation was slightly increased. These results are consistent with the assumption that HWA 285 exerts a modulative effect on the rat brain mitochondria dependent on their functional status.

Transport of 2-deoxy-D-[3H]glucose in microvessels isolated from bovine cerebral cortex.

Microvessels were isolated from a bovine cortex and the transport of glucose was investigated by using 2-deoxy-D-[3H]glucose (2-DG). The apparent Km for 2-DG transport was 118 microM and therefore indicates a significant high affinity for the substrate. The inhibition of 2-DG uptake by D-glucose showed an apparent Ki of 222 microM. Other sugars, e.g., 3-methyl-D glucose and D-fructose, also inhibited the 2-DG uptake by 60.6 and 36.0%, respectively. Phloretin (1 X 10(-3) M) inhibited the 2-DG transport more than phlorizin (83.7 vs. 53.8%). Ouabain (1 and 5 X 10(-4) M) did not inhibit the uptake of 2-DG but 2,4-dinitrophenol (1 X 10(-4) M) did (78.0%). The uptake of 2-DG could not be demonstrated in homogenized microvessels. Adenine nucleotides (conc. 2 mM) had various effects on the 2-DG uptake by microvessels. ATP inhibited the uptake by 20.7%, ADP was virtually without effect, and AMP stimulated the uptake of 2-DG by 8.5%. It was also found that the decrease of adenylate energy charge favors the uptake of 2-DG. All these findings suggest that, in cerebral microvessels of a bovine cortex, 2-DG is apparently transported by a specific, carrier-mediated transport system.

[The effect of pentoxifylline on the Ca2+-induced potassium efflux and on the ATPase-activity of erythrocytes (author's transl)]. / Die Wirkung von Pentoxifyllin auf den Ca++-induzierten Kalium-Ausstrom und auf die ATPase-Aktivität von Erythrozyten.

The efflux of K+ from aged human erythrocytes is regulated by Ca2+: 5--100 mumol/l Ca2+ stimulate and 1--5 mmol/l Ca2+ inhibit K+-efflux. In fresh erythrocytes Ca2+ is virtually without effect on transport of K+. 3,7-Dimethyl-1-(5-oxohexyl)-xanthine (pentoxifylline) (5.5 mmol/l) decreases the K+-efflux from fresh erythrocytes by 10%. Similar effect of pentoxifylline is observed on the Ca2+-induced K+-efflux from aged erythrocytes. The ATPase-activity of a human erythrocyte membrane is stimulated in in vitro experiments by 1--100 mumol/l Ca2+. Increased concentration of Ca2+ (1--5 mmol/l), inhibits ATPase-activity. Pentoxifylline (0.5 mmol/l) modulates the effect of Ca2+ (conc. 1 mmol/l) on ATPase. It can be suggested that the rheological effect of pentoxifylline (possibly chelated with Ca2+) is caused by the decrease of Ca2+-caused K+-efflux and by the regulation of ATPase-activity of erythrocyte membrane.

Cyclic nucleotide phosphodiesterases in normal and malignant human tissues.

Biopsy samples were obtained from tumor tissue and surrounding normal tissue from the same organs of the same patients in 25 patients. Adequate studies could be performed on all parameters in 18 tissue pairs: 12 malignant melanomas, 4 sarcomas, and 2 others. Significantly higher levels of cAMP low affinity phosphodiesterases were found in the tumors as compared to the controls. Similar differences were seen in the high affinity cAMP phosphodiesterases, but these were of borderline significance. High affinity cGMP phosphodiesterase levels did not differ significantly between normal and neoplastic tissue samples. Low affinity cGMP phosphodiesterases were not detectable in either tissues. These studies together with earlier experimental findings suggest possible auxiliary therapeutic trials with phosphodiesterase inhibitors.

The role of biochemistry in drug research.

The present and the future role of biochemistry in the search for a new therapeutic agent is reviewed. It is stated that the great importance of the various disciplines of biochemistry, including pathobiochemistry and pharmacological biochemistry, is presently recognized, and the involvement of biochemistry in drug research is increasing. Biochemistry at the present time and in the future will utilize the already known basic biological principles for the new development of new and more useful medicines. It is emphasized that the limiting factor in new drug discovery today, however, is the lack of new basic discoveries in biology.

Cyclic 3',5'-adenosine monophosphate phosphodiesterase (cAMP PDE) and cyclic 3',5'-guanosine monophosphate phosphodiesterase (cGMP PDE) in microvessels isolated from bovine cortex.

It was established that microvessels of a bovine cortex exhibit significant cyclic 3',5'-adenosine monophosphate phosphodiesterase (cAMP PDE) and cyclic 3',5'-guanosine monophosphate phosphodiesterase (cGMP PDE) activities. These activities are dependent on the presence of Mg2+. Absence of Ca2+ was virtually without effect. When both Mg2+ and Ca2+ were absent, PDE activities increased compared with activities observed in the absence of Mg2+. Xanthines (caffeine, theobromine, and theophylline) were better inhibitors of cAMP PDE than of cGMP PDE. Imidazole, in very high concentration (1 X 10(-2) M) only, exhibited PDE stimulatory activity at high concentrations of both substrates. Otherwise, it exhibited PDE-inhibitory properties.

Influence of theophylline on concentrations of cyclic 3',5'-adenosine monophosphate and cyclic 3',5'-guanosine monophosphate of rat brain.

The influence of theophylline (2.5--100 mg/kg p.o.) on cyclic 3',5'-adenosine monophosphate (cAMP) and cyclic 3',5'-guanosine monophosphate (cGMP) in brain of Sprague-Dawley rats (0.5--3.0 hr after administration of theophylline) was investigated. It was found that theophylline increases cAMP and cGMP levels when administered in a dose of 25 mg/kg or higher. A significant decrease of cGMP level was observed after administration of 10 mg/kg. The results of this study suggest that the influence of theophylline on cyclic nucleotide levels of rat brain is the result of two factors: (a) inhibitory properties of theophylline on cAMP and cGMP phosphodiesterases and (b) competition of theophylline with adenosine.

[The influence of pentifylline and theophylline on reaction kinetics on rat brain ATPase stimulatable by catecholamines (author's transl)]. / Der Einfluss von Pentifyllin und Theophyllin auf die Reaktionskinetik von Katecholamin-stimulierbarer ATPase aus Rattenhirn.

The effects of 1-hexyl-3,7-dimethyl-xanthine (pentifylline, Cosaldon) and theophylline on rat brain Na+-, K+-, Mg2+ ATPase activities were investigated in in vitro experiments. It was established that pentifylline inhibits catecholamine sensitive ATPase in a dose dependent manner. Theophylline was without effect. Pentifylline also inhibited the Mg2+-dependent portion of Na+, K+-, Mg2+-ATPase. The effect of pentifylline on the kinetic parameters of Na+-, K+-, Mg2+-ATPase of synaptosomes was studied in detail. It was shown by a Lineweaver-Burk plot under the influence of pentifylline that the Michaelis constant (Km) increases from 1.0 x 10(-4) mol/l to 6.7 x 10(-4) mol/l. Km by norepinephrine stimulated ATPase decreases from 3.7 x 10(-4) mol/l to 2.9 x 10(-4) mol/l. In both experimental situations a decrease of maximal reaction velocity (Vmax) was observed. At high concentration of potassium in incubation medium the ATPase of synaptosomes was significantly more sensitive to pentifylline than at low concentration of potassium. The inhibition of ATPase by pentifylline was not influenced by the change in Na+/K+ ratio in the incubation medium. In all these experiments, theophylline used as a standard xanthine, was virtually without effect on the reaction kinetic of Na+-, K+-ATPase.

On the biochemical mechanism of action of 1-propyl-3-methyl-7-(5-hydroxy-hexyl)-xanthine (HWA 153), a new bronchospasmolytically active methyl xanthine derivative.

1-Propyl-3-methyl-7-(5-hydroxy-hexyl)-xanthine (HWA 153) is a new bronchospasmolytic agent with a significant influence on the cAMP system of lungs and bronchi. In in vitro experiments HWA 153 inhibits cAMP phosphodiesterase (PDE) isolated from bovine bronchi more than does theophylline. HWA 153 is (in conc. 5 x 10(-4) mol/l) 1.8 and 4.3 times more active as a PDE inhibitor of guinea pig lungs and bronchi, respectively, than theophylline-ethylenediamine. HWA 153 also stabilizes rat erythrocyte membrane against hypoosmotic shock. In isolated guinea pig bronchi HWA 153 (in conc. 5 x 10(-4) mol/l) decreases by 77% bronchial spasm induced by the addition of histamine (5 x 10(-5) mol/l). A significant increase in cAMP level of bronchi was simultaneously observed. In in vivo experiments HWA 153 (25 mg/kg p.o.) inhibits PDE of lungs and bronchi of guinea pigs. Simultaneously, a significant increase in cAMP level in these organs was observed. In in vivo experiments with hypoxic rats, HWA 153 (25 mg/kg p.o.) increases ATP, ATP/ADP ratio and adenylate energy charge (AEC) in hypoxic rats, 1 h after administration. This indicates a positive influence of HWA 153 on the energy metabolism of red blood cells.