Search PubMed⌕ Search

Biomedical subjects

V Felipo

Publications and source records attributed to V Felipo.

At least 91 records · Page 5Linked to original sources
PubMed1992

Treatment of hyperammonemia with carbamylglutamate in rats.

A protein-free diet causes a paradoxical increase of blood ammonia levels that seems to be due to decreased liver content of acetylglutamate, the physiological activator of carbamylphosphate synthetase. The purpose of this study was to assess whether oral administration to rats of carbamylglutamate, a metabolically stable activator of carbamylphosphate synthetase, could decrease the blood ammonia levels increased by the protein-free diet. We show that ingestion of moderate doses of carbamylglutamate increased about sixfold the liver content of carbamylphosphate synthetase activators and restores to normal values the blood ammonia levels. Excess ammonia is eliminated in urine as urea. These results indicate that carbamylglutamate, which is not toxic, could be useful in the treatment of hyperammonemia, especially in cirrhosis.

Administration, Oral↗
PubMed1992

The susceptibility of MAP-2 to proteolytic degradation increases when bound to tubulin.

During experiments studying dietary effects on phosphorylation/dephosphorylation of MAP-2 we found that incubation of microtubules with alkaline phosphatase resulted in extensive proteolysis of MAP-2 but not of tubulin or Tau proteins. In the absence of tubulin, when microtubule-associated proteins (MAPs) were incubated with alkaline phosphatase, MAP-2 was not proteolyzed. This suggests that binding to tubulin induces a conformational change in MAP-2 which makes it more susceptible to proteolysis. The proteolysis of MAP-2 by alkaline phosphatase was prevented by inhibitors of serine proteases, suggesting that the commercial preparation of the enzyme is contaminated by a serine protease and/or that the enzyme also has a weaker proteolytic activity. In addition, selective proteolysis of MAP-2 can be obtained with the metalloprotease collagenase. Brain homogenates are shown to contain a Ca(2+)-dependent protease which selectively degrades MAP-2 bound to tubulin. These results suggest that selective proteolysis of tubulin-bound MAP-2 could play a role in the regulation of microtubule dynamics in response to extracellular signals.

Alkaline Phosphatase↗
PubMed1992

Inhibition of protein kinase C restores Na+,K(+)-ATPase activity in sciatic nerve of diabetic mice.

We have tested if inhibition of protein kinase C is able to prevent and/or to restore the decrease of Na+,K(+)-ATPase activity in the sciatic nerve of alloxan-induced diabetic mice. Mice were made diabetic by subcutaneous injection of 200 mg of alloxan/kg of body weight. The activity of Na+,K(+)-ATPase decreased rapidly (43% after 3 days) and slightly thereafter (58% at 11 days). We show that intraperitoneal injection of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), an inhibitor of protein kinase C, prevents completely the loss of Na+,K(+)-ATPase activity produced by alloxan. Also, H7 injected into diabetic mice, 4-9 days after the injection of alloxan, restores the activity of the enzyme. The amount of activity recovered depends on the dose of H7 administered; complete recovery was reached with injection of 15 mg of H7/kg of body weight. The effect of H7 is transient, with a half-life of approximately 1 h.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Ammonium ingestion prevents depletion of hepatic energy metabolites induced by acute ammonium intoxication.

Ingestion of an ammonium containing diet produces hyperammonemia and protects rats against acute ammonium intoxication. Acute ammonium toxicity has been attributed to the depletion of energy metabolite intermediates. We show here that hyperammonemia affords considerable protection against depletion of hepatic energy metabolites evoked by ammonium acetate injection. In control rats there were marked decreases in the content of acetoacetate, beta-hydroxybutyrate, ATP, 2-oxoglutarate, lactate, and pyruvate while phosphoenolpyruvate increased markedly. In hyperammonemic rats beta-hydroxybutyrate, ATP, 2-oxoglutarate, and lactate were not significantly affected while pyruvate increased markedly and phosphoenolpyruvate slightly. These results suggest that in controls the activity of pyruvate kinase is inhibited after ammonium injection while in hyperammonemic rats it is not inhibited. The content of alanine (an inhibitor of pyruvate kinase) reached 2.8 mumol/g in controls and 1.6 mumol/g in hyperammonemic rats, 15 min after ammonium injection. This could explain the different effects of ammonium injection on control and hyperammonemic rats.

Acetates↗
PubMed1991

Inhibition of protein kinase C arrests proliferation of human tumors.

We have shown that inhibition of protein kinase C by 1-5-isoquinolinylsulfonyl-2-methylpiperazine, H7, induces differentiation and inhibits proliferation of Neuro 2a cells. We have now tested if H7 is able to inhibit proliferation of: 1) human tumor cell lines from tissues other than brain; and 2) primary cultured cells from several human brain tumors. H7 inhibits, in a dose-dependent manner, proliferation of all human tumor cell lines tested and of primary cultured cells from human brain tumors. These results indicate that inhibition of protein kinase C inhibits proliferation of tumoral cells, therefore, H7, and likely other inhibitors of protein kinase C, could be useful in the clinical treatment of brain (and probably other) tumors.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1991

Control of urea synthesis and ammonia utilization in protein deprivation and refeeding.

Rats were fed a standard diet (20% protein) or a protein-free diet for up to 65 days. After 20 days on the protein-free diet some rats were refed the standard diet. By the 20th day the rats fed the protein-free diet showed a blood ammonia level approximately 70% higher than controls and urea excretion decreased approximately 20-fold. At this time the liver acetylglutamate decreased to approximately one-fifth of the initial and control levels, returning to normal after 3 days of refeeding the standard diet, with a concomitant increase in urea excretion. The protein-deficient diet resulted in decreased activities of liver enzymes related to ammonia metabolism. All enzyme activities assayed returned to normal values rapidly upon refeeding the standard diet, except hepatic carbamylphosphate synthetase, glutamine synthetase, and glutaminase, which took approximately 1 month to return to control values. The findings presented here are consistent with the view that urea production is controlled, at least under certain conditions, by acetylglutamate, the physiological activator of carbamylphosphate synthetase.

Ammonia↗
PubMed1990

A specific inhibitor of protein kinase C induces differentiation of neuroblastoma cells.

Recent reports suggest that protein kinase C is involved in neural differentiation. We show that 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), the more specific inhibitor of protein kinase C known, induces morphological and functional differentiation of neuro 2a cells, as indicated by the marked increase in the number of neurites/cell and in acetylcholinesterase activity. HA 1004 does not induce differentiation of neural cells. The induction of differentiation by H7 was very rapid; 3 h after addition of H7 the percentages of differentiated cells were 17, 33, 37, 55, and 75% for 17, 50, 85, 250, and 500 microM H7, respectively, while for controls it was 9%. When 500 microM H7 was added to the culture medium, protein kinase C was inhibited by 72 and 62% in cytosol and membrane, respectively. Also, acetylcholinesterase activity (a marker of functional differentiation) increased with time, reaching a 7-fold increase after 48 h.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

Hyperammonemia induces brain tubulin.

We have developed an animal model of hyperammonemia consisting of feeding rats a diet containing ammonium acetate. Using this model we have found that hyperammonemia induces tubulin synthesis in brain. Initially tubulin accumulates rapidly (28% after 2 days on diet) and continues increasing but at a slower rate, reaching a 50% increase after 100 days on the diet. The effect is reversible, rats fed the ammonium diet return to normal levels of tubulin two days after withdrawal of the ammonium diet. In contrast to the effect on brain, hyperammonemia did not increase tubulin content in liver or kidney. Moreover, the effect on brain is selective, with maximum increases of tubulin content in hippocampus, septum and reticular formation while other areas such as locus coeruleus and mammillary nucleus are not affected at all. The results presented show that the induction of tubulin is a consequence of an increased polymerization of microtubules which in turn is due to an altered phosphorylation of microtubule-associated proteins.

Ammonia↗
PubMed1990

Hyperammonemia induces polymerization of brain tubulin.

Rats were made hyperammonemic by feeding them a diet containing ammonium acetate. The tubulin content in their brain increased greater than or equal to 30% after 20 days on the diet. All the increase was found in polymerized tubulin; no increase in free tubulin was noted. When rats on the ammonium diet were then fed the standard diet, the tubulin increased slightly on the first day but decreased markedly on the second day, reaching control values on the third day. It should be noted that brain tubulin synthesis, was not reduced on the first day of feeding the standard diet but was markedly inhibited (to approximately 40% of control) on the second day, returning to control values on the third day. On the first day of refeeding there is a remarkable disassembly of microtubules with a large, proportional increase (approximately 50%) of free tubulin. Both free and polymerized tubulin levels returned to control values on the third day. These results indicate that in hyperammonemia changes in the degree of polymerization of tubulin preceded those in tubulin synthesis.

Ammonia↗
PubMed1990

Inhibition of protein kinase C induces differentiation in Neuro-2a cells.

1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine (H7), a potent inhibitor of protein kinase C, induced neuritogenesis in Neuro-2a cells, whereas N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004), which inhibits more efficiently cAMP- and cGMP-dependent protein kinases, did not. The effect, noticeable after 3 hr, was maximum (13-fold increase at 500 microM H7) between 1 and 3 days and was maintained over 2 months. In controls, 90% of the cells were undifferentiated, whereas after 3 hr with 500 microM H7 only 25% of the cells remained undifferentiated. DNA synthesis decreased as the number of differentiated cells increased. Differentiation is also functional since acetylcholinesterase activity increased approximately 7-fold after 48 hr with 500 microM H7. Phorbol 12-myristate 13-acetate, a specific activator of protein kinase C, prevented or reversed the induction of neuritogenesis and the inhibition of DNA synthesis by H7. There is a good correlation between the level of protein kinase C and the percentage of differentiated cells. The results indicate that protein kinase C may play a key role in the control of differentiation of neural cells. Some possible clinical implications are briefly discussed.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1989

Inhibition of protein kinase C induces differentiation of neuroblastoma cells.

It is shown that 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), a specific inhibitor of protein kinase C, induces neuritogenesis in neuro 2a cells. The percentage of differentiated cells was 9%, 20%, 59% and 85% at 0, 17, 85 and 500 microM H7, respectively. The number of neurites cell increased 2-, 8- and 14-fold over the controls for 17, 85 and 500 microM H7, respectively. These results indicate that protein kinase C plays a key role in the control of differentiation of neural cells and that its specific inhibition may be of basic as well as of practical importance.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1989

Hyperammonemia decreases body fat content in rat.

We have developed an animal model of hyperammonemia consisting of feeding rats a diet containing 20% (w/w) ammonium acetate. Ingestion of this diet markedly affects carcass composition, with a 46% reduction in lipid content. The ammonium diet alters levels of several key compounds involved in lipid metabolism. Long-chain acylcarnitine is increased in liver by approx. 60% while free carnitine and acetylcarnitine are unaffected. The hepatic content of acetyl-CoA increases by approx. 50%. The level of ketone bodies in blood increases by 32% but remains unchanged in liver. Our data indicate that hyperammonemia alters lipid metabolism and results in a significant decrease in body lipid content.

Acetates↗
PubMed1989

A simple animal model of hyperammonemia.

Rats were fed a standard diet or the standard diet supplemented with ammonium acetate (20% w/w) for up to 100 days. The effect of the ingestion of the high-ammonium diet on some aspects of nitrogen metabolism in rats was studied. Ammonia levels in blood increased approximately 3-fold; in brain, liver and muscle the increases were 36, 34 and 50%, respectively. Urea levels in blood and urea excretion increased approximately 2-fold. There was no increase of carbamyl phosphate synthase. Liver glutamine synthase activity increased by 58% and glutamate dehydrogenase by 40%, whereas glutaminase was not affected. Glutamine content in brain was twice that of controls. This new animal model to study hyperammonemia offers several advantages over others: it is simpler, is bloodless, requires no animal manipulation and permits long-term studies.

Acetates↗
PubMed1989

A protein-free diet changes synaptosomal membrane fluidity and tyrosine and glutamate transport.

Synaptosomes were isolated from cerebrums of rats fed standard (20% protein) or protein-free diets for 30 days. Arrhenius plots of their (Na+/K+)ATPase activities revealed a transition temperature of 25.5 degrees C for control rats and 23.4 degrees C for rats on protein-free diet, indicating that the latter increases synaptosomal membrane fluidity. The only change observed in the composition of the synaptosomal membranes was a 26% decrease of sialic acid. In synaptosomes from rats on protein-free diet the uptake of tyrosine was slightly reduced while that of glutamate was not affected. However, the exit of glutamate was reduced.

Animals↗
PubMed1989

Selective regional distribution of tubulin induced in cerebrum by hyperammonemia.

Ingestion of ammonium induces hyperammonemia which increases tubulin content in cerebrum but not in cerebellum. We have dissected 11 discrete areas of cerebrum and quantified the tubulin content in control and hyperammonemic rats. An heterogeneity in the induction of tubulin is shown. The areas more affected are ventral hippocampus, dorsal hippocampus, hypothalamus, septum, reticular formation and frontal cortex, in which tubulin content increased by 63%, 27%, 32%, 48%, 45%, and 25%, respectively, after two months of feeding the ammonium diet.

Ammonia↗
PubMed1989

Assembly and disassembly of brain tubulin is affected by high ammonia levels.

Rats were fed a diet containing ammonium for up to 6 months. High ammonia levels were attained in brain. The amount of polymerized tubulin in microtubules increased, while the amount of free tubulin remained unchanged. Polymerization of tubulin from brain of ammonium fed rats (30 min, 37 degrees C) was approximately 60% of control. Depolymerization of the microtubules was also affected and took approximately 3 times longer than in controls. These results indicate that both assembly and disassembly of tubulin in brain are impaired by high ammonia levels. Interestingly, the amount of microtubule-associated proteins was not affected.

Ammonia↗
PubMed1989

Effect of a prolonged protein-free diet on cell size, protein synthesis and degradation of rat liver.

Rats were fed a protein-free diet. After 9 weeks the animals' weight decreased to about 50% of the original. The liver weight was also decreased to about half, and most interestingly the average size of the liver cells was reduced about 50%. Liver protein synthesis was approximately 75% of controls tested in an "in vitro" system. Polysomes were found disaggregated in livers of rats on protein-free diet. This was not due to a reduced content or translatability of mRNA. eIF-2 partially purified from livers of rats on protein-free diet had the same activity as that from controls. The decrease of ATP, ADP and AMP in livers of rats on protein-free diet (19%, 42% and 58% respectively) may be responsible for the decreased rate of initiation of protein synthesis. Proteolysis in liver cytosol from rats on protein-free diet was 50% higher than in controls mostly due to lysosomal proteolysis.

Adenine Nucleotides↗