Changes in enzyme activities of glycerolipid metabolism of guinea-pig cerebral hemispheres during experimental hypoxia

Experimental selection for Drosophila survival in extremely low O(2) environment

BACKGROUND

Cellular hypoxia, if severe enough, results usually in injury or cell death. Our research in this area has focused on the molecular mechanisms underlying hypoxic tissue injury to explore strategies to prevent injury or enhance tolerance. The current experiments were designed to determine the genetic basis for adaptation to long term low O(2) environments.

METHODOLOGY/PRINCIPAL FINDINGS

With long term experimental selection over many generations, we obtained a Drosophila melanogaster strain that can live perpetually in extremely low, normally lethal, O(2) condition (as low as 4% O(2)). This strain shows a dramatic phenotypic divergence from controls, including a decreased recovery time from anoxic stupor, a higher rate of O(2 )consumption in hypoxic conditions, and a decreased body size and mass due to decreased cell number and size. Expression arrays showed that about 4% of the Drosophila genome altered in expression and about half of the alteration was down-regulation. The contribution of some altered transcripts to hypoxia tolerance was examined by testing the survival of available corresponding P-element insertions (and their excisions) under extremely low O(2) conditions. We found that down-regulation of several candidate genes including Best1, broad, CG7102, dunce, lin19-like and sec6 conferred severe hypoxia tolerance in Drosophila.

CONCLUSIONS/SIGNIFICANCE

We have identified a number of genes that play an important role in the survival of a selected Drosophila strain in extremely low O(2) conditions, selected by decreasing O(2) availability over many generations. Because of conservation of pathways, we believe that such genes are critical in hypoxia adaptation in physiological or pathological conditions not only in Drosophila but also in mammals.

Cytidine diphosphate choline administration activates brain cytidine triphosphate: phosphocholine cytidylytransferase in aged rats

Beneficial effects of cytidine (5') diphosphocholine (CDP-choline) administration on several diseases including brain aging, ischemia and stroke are based on an increase in membrane phospholipid turnover. We have studied the possible involvement of CTP:phosphocholine cytidylyltransferase (CT) in this mechanism by measuring its gene expression and enzyme activity in the brains of young and aged rats treated with 500 mg/kg per day of CDP-choline. Older animals showed higher (57%) of total CT activity in particulate (active) fraction than younger animals (46%). Treatment of aged animals for 8, 16, or 60 days had no effect on the CT gene expression but increased activation of the CT by translocation to membranes. The particulate fraction rose from 57% of total activity to more than 65% after 2 months of treatment. This may explain the long-term repairing effects of CDP-choline on damaged membranes of aged animals.

Is the Mg(2+)-ATP-dependent proton pumping activity of the synaptic vesicles a factor involved in the cerebral hypoxia?

The changes in the Mg(2+)-dependent V-type ATPase activity and the Mg(2+)-ATP-dependent H+ pumping activity of the synaptic vesicles from the cerebral cortex of rats submitted to intermittent chronic (4 weeks) mild or severe hypoxia were evaluated. The adaptation to the chronic severe hypoxia increases both the ATPase and the H+ pumping activities which are inhibited by NEM with an exponential relationship between the IC(50) values and the in vivo O2 concentration. The Mg(2+)-dependent increase in H+ pumping activity of synaptic vesicles from the rats subjected to in vivo chronic hypoxia may be antagonized by nigericin (dissipating delta pH) and by FCCP (dissipating delta pH and delta psi SV). In contrast, valinomycin (dissipating the delta psi SV) and facilitating an enhancement in delta pH) increases in vitro the H+ pumping activity that is inhibited by the addition of high concentration of K gluconate (reducing the rate of K+ efflux). The preincubation of vesicles from hypoxic rats with FCCP, but not with nigericin, inhibits the valinomycin-increased H+ pumping activity. L-glutamate increases the H+ pumping activity in synaptic vesicles from the cerebral cortex of chronic hypoxic rats, whereas other amino acids (i.e., L-aspartate and L-homocysteate) and glutamate analogs (i.e., quisqualate and ibotenate) are ineffective. The adaptation to both chronic intermittent severe hypoxia and in vivo treatment with posatireline causes a decrease in the Mg(2+)-ATPase activity consistent with the decrease in the H+ pumping one of the synaptic vesicles. The addition of nigericin into incubation medium magnifies the decrease in the H+ pumping activity, while the addition of FCCP is ineffective, suggesting that the treatment with posatireline interferes with the delta psi SV component in the delta mu H+ of the synaptic vesicles from rats submitted to chronic hypoxia. The results of the in vivo and in vitro experiments suggest that in the synaptic vesicles from hypoxic rats the delta psi SV component in delta mu H+ may be most effective in increasing the Mg(2+)-ATP-dependent H+ pumping activity.

Modifications by chronic intermittent hypoxia and drug treatment on skeletal muscle metabolism

The energy metabolism was evaluated in gastrocnemius muscle from 3-month-old rats subjected to either mild or severe 4-week intermittent normobaric hypoxia. Furthermore, 4-week treatment with CNS-acting drugs, namely, alpha-adrenergic (delta-yohimbine), vasodilator (papaverine, pinacidil), or oxygen-increasing (almitrine) agents was performed. The muscular concentration of the following metabolites was evaluated: glycogen, glucose, glucose 6-phosphate, pyruvate, lactate, lactate-to-pyruvate ratio; citrate, alpha-ketoglutarate, succinate, malate; aspartate, glutamate, alanine; ammonia; ATP, ADP, AMP, creatine phosphate. Furthermore the Vmax of the following muscular enzymes was evaluated: hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase; citrate synthase, malate dehydrogenase; total NADH cytochrome c reductase; cytochrome oxidase. The adaptation to chronic intermittent normobaric mild or severe hypoxia induced alterations of the components in the anaerobic glycolytic pathway [as supported by the increased activity of lactate dehydrogenase and/or hexokinase, resulting in the decreased glycolytic substrate concentration consistent with the increased lactate production and lactate-to-pyruvate ratio] and in the mitochondrial mechanism [as supported by the decreased activity of malate dehydrogenase and/or citrate synthase resulting in the decreased concentration of some key components in the tricarboxylic acid cycle]. The effect of the concomitant pharmacological treatment suggests that the action of CNS-acting drugs could be also related to their direct influence on the muscular biochemical mechanisms linked to energy transduction.

Age-related alterations of skeletal muscle metabolism by intermittent hypoxia and TRH-analogue treatment

The characteristics of the energy metabolism were evaluated in the gastrocnemius muscle from 3- and 24-month-old rats in normoxia or subjected to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. Furthermore, 4-week treatment with saline or the TRH-analogue posatireline was performed. The muscular concentration of the following metabolites related to the energy metabolism was evaluated: glycogen, glucose, glucose 6-phosphate, pyruvate, lactate, lactate-to-pyruvate ratio; citrate, alpha-ketoglutarate, succinate, malate; aspartate, glutamate, alanine; ammonia; ATP, ADP, AMP, creatine phosphate; energy charge potential. Furthermore the maximum rate of the following muscular enzymes was evaluated: hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase; citrate synthase, malate dehydrogenase; total NADH cytochrome c reductase; cytochrome oxidase. The age-related decrease in muscular glucose 6-phosphate, pyruvate and alanine concentrations and increase in citrate concentration were consistent with the age-related decreased hexokinase and increased citrate synthase activities. Ageing was characterized by a decrease in muscular creatine phosphate concentration, while the energy mediators and the energy charge potential were unchanged. The chronic (4 weeks) intermittent normobaric mild and severe hypoxia-induced alterations of the components in the anaerobic glycolytic pathway, tricarboxylic acid cycle and energy storage, that were magnified in the skeletal muscle from the oldest animals. The effect of the chronic treatment with the TRH-analogue posatireline suggests that the action of central nervous system-acting drugs could also be related to their direct influence on the muscular biochemical mechanisms related to the energy transduction.

Age-related changes by hypoxia and TRH analogue on synaptic ATPase activities

Some synaptosomal energy-requiring ATPases were evaluated in the cerebral cortex from 3- and 24-month-old normoxic rats and rats submitted to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. Furthermore, 4-week treatment with saline or TRH analogue posatireline was performed. The activities of Na+,K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, and Ca2+,Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to chronic intermittent mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: a) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The TRH analogue posatireline increased the high-affinity Ca(2+)-ATPase in both 3- and 24-month-old hypoxic rats, concomitant with an increase in Mg(2+)-ATPase activity in 24-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: a) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and b) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the enzymatic form located in the synaptic plasma membranes, concomitant with an increase in the form located in the synaptic vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptosomal non-mitochondrial ATPase activities: age-related alterations by chronic normobaric intermittent hypoxia

In synaptosomes and synaptosomal subfractions (namely, synaptosomal plasma membranes and synaptic vesicles) the age-related alteration in the plasticity of synaptic energy-requiring ATPases (Na+, K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase and Ca2+, Mg(2+)-ATPase) were assayed in the cerebral cortex from 3- and 24-month-old normoxic rats and rats subjected to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: (i) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats; and (ii) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: (i) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats and (ii) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the activity of the enzymatic form located in the synaptic plasma membranes (involved in ATP hydrolysis to adenosine production), concomitant with an increase in the activity of the form located in the synaptic vesicles (involved in the turnover of transmitters, e.g., glutamate).

Modifications by hypoxia and drug treatment of cerebral ATPase plasticity

The plasticity of synaptosomal non-mitochondrial ATPases was evaluated in cerebral cortex from 3-month-old normoxic rats and rats subjected to either mild or severe intermittent normobaric hypoxia [12 hr daily exposure to N2:O2 (90:10 or 91.5:8.5) for four weeks]. The activities of Na+, K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase, and Ca2+,Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely synaptosomal plasma membranes and synaptic vesicles. The evaluations were performed after a 4-week treatment with saline (controls) or alpha-adrenergic agents (delta-yohimbine, clonidine), a vasodilator compound (papaverine), and an oxygen-partial pressure increasing agent (almitrine). These treatments differently changed the adaptation to chronic intermittent hypoxia characterized by a decrease in the activity of Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase, and high-affinity Ca(2+)-ATPase, concomitant with a modification in the activity of Mg(2+)-ATPase supported in a different way by the enzymatic forms located into the synaptosomal plasma membranes and synaptic vesicles.

Age-related alterations by chronic intermittent hypoxia on cerebral synaptosomal ATPase activities

The age-related alterations in the plasticity of synaptic energy-requiring ATPases [Na+,K(+)-ATPase, low- and high-affinity Ca(2+)-ATPase, Mg(2+)-ATPase, and Ca2+,Mg(2+)-ATPase] were assayed in synaptosomes and synaptosomal subfractions [namely, synaptosomal plasma membranes and synaptic vesicles] in the cerebral cortex from 3- and 24-month-old normoxic rats and rats subjected to either mild or severe chronic (four weeks) intermittent normobaric hypoxia. With the exception of the high-affinity Ca(2+)-ATPase, aging induced a decrease in the ATPase activities from normoxic rats. The adaptation to mild hypoxia was characterized by an increase in the activity of Mg(2+)-ATPase in 3-month-old rats, concomitant with a decrease in the activities of: (i) Na+,K(+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and (ii) Ca2+,Mg(2+)-ATPase in 3-month-old ones. The adaptation to chronic intermittent severe hypoxia was characterized by a decrease in the activities of: (i) Na+,K(+)-ATPase, Ca2+,Mg(2+)-ATPase and high-affinity Ca(2+)-ATPase in both 3- and 24-month-old rats, and (ii) low-affinity Ca(2+)-ATPase only in 24-month-old ones. The effect on Mg(2+)-ATPase activity was characterized by a decrease in the activity of the enzymatic form located in the synaptic plasma membranes [involved in ATP hydrolysis to adenosine production], concomitant with an increase in the activity of the form located in the synaptic vesicles [involved in the turnover of transmitters, e.g., glutamate].

Effect of intermittent mild hypoxia and drug treatment on synaptosomal nonmitochondrial ATPase activities

Synaptosomal nonmitochondrial ATPases linked to the energy-utilizing systems were evaluated in cerebral cortex from normoxic rats and rats submitted to mild intermittent normobaric hypoxia [12 hr daily exposure to N2:O2 (90:10) mixture for 4 weeks]. The activities of Na+,K(+)-ATPase; high- and low-affinity Ca(2+)-ATPase; basal Mg(2+)-ATPase; and Ca2+, Mg(2+)-ATPase were assayed in synaptosomes and synaptosomal subfractions, namely, synaptosomal plasma membranes and synaptic vesicles. The evaluations were performed either in normoxic rats or in hypoxic rats submitted to 4-week treatment with saline (controls) or a vasodilator agent (papaverine), an energy-metabolism interfering agent (theniloxazine), a calcium blocker (nicardipine), and a lipid-metabolism interfering agent (phosphatidylcholine) in order to define the plasticity and the selective changes in individual ATPases. In synaptosomes from rat cerebral cortex, the enzyme adaptation to the daily mild intermittent hypoxia for 4 weeks was characterized by an increase in the activity of Mg(2+)-ATPase, concomitant with a decrease in the activities of Na+,K(+)-ATPase, high-affinity Ca(2+)-ATPase, and Ca2+, Mg(2+)-ATPase. In hypoxic rats the enzyme adaptation to the 4-week treatment with phosphatidylcholine was characterized by an increase in Ca2+, Mg(2+)-ATPase activity and a decrease in Mg(2+)-ATPase activity. The action involves the enzymatic form located in the synaptic plasma membranes. In hypoxic rats the adaptation to the 4 week treatment with nicardipine was characterized by an increase in high-affinity Ca(2+)-ATPase activity, while the 4-week-treatment with theniloxazine induced an increase in Na+,K(+)-ATPase activity. The actions of both nicardipine and theniloxazine were related to the enzymatic forms located in the synaptic plasma membranes. The effects on the biophase induced by the sequential cycles of hypoxia/normoxia and the treatment with the various agents tested should also be related to the changes induced in the activity of some synaptosomal ATPases.

Effects of CDP-choline on phospholipase A2 and cholinephosphotransferase activities following a cryogenic brain injury in the rabbit

Within the tissue surrounding the necrotic lesion, following a cryogenic injury of the brain, there is a definite activation of phospholipase A2 (at 2 and 4 hr post lesion) that accounts, at least in part, for the phospholipid breakdown. There is also an activation of cholinephosphotransferase (at 2 hr post lesion) that may correspond to an early process of phospholipid resynthesis. Oral CDP-choline in this model is able to completely inhibit the activation of phospholipase A2, but has no detectable effect on cholinephosphotransferase activity. The beneficial effect of CDP-choline might be explained by a prevention of destruction rather than by an enhancement of reconstruction of phospholipids.

Brain enzyme adaptation to mild normobaric intermittent hypoxia

The adaptation to repeated periods of intermittent normobaric hypoxia (oxygen:nitrogen = 10:90, 12 hr daily for 5 days) of some specific enzymatic activities related to energy metabolism has been observed in different rat brain areas (cerebral cortex, hippocampus, corpus striatum, hypothalamus, cerebellum, and medulla oblongata). The evaluation of the maximum rate (Vmax) of the enzymes was carried out on: the homogenate "in toto," the nonsynaptic mitochondrial fraction, and the crude synaptosomal fraction. The adaptation to intermittent normobaric hypoxic exposure was characterized by significant modifications of some enzyme activities in the homogenate "in toto" (decrease of hexokinase activity in cerebellum), in the nonsynaptic mitochondrial fraction (increase of succinate dehydrogenase activity in corpus striatum and decrease of cytochrome oxidase activity in cerebral cortex), and, particularly, in the synaptosomal fraction (decrease of cytochrome oxidase activity in cerebral cortex, hippocampus, corpus striatum, and cerebellum, and decrease of malate dehydrogenase and lactate dehydrogenase activity in cerebellum). The adaptation to normobaric intermittent hypoxia differs according to the brain area, subcellular fraction, and enzyme activity tested.

Effect of prolonged and intermittent hypoxia on some cerebral enzymatic activities related to energy transduction

The adaptation to repeated, alternate normobaric hypoxic and normoxic exposures (12 h/day, for 5 days) and to pharmacological treatment was evaluated by studying the specific activities of some enzymes related to cerebral energy metabolism. Measurements were carried out on (a) the homogenate in toto, (b) the purified mitochondrial fraction, and (c) the crude synaptosomal fraction in different areas of rat brain--cerebral cortex, hippocampus, corpus striatum, hypothalamus, cerebellum, and medulla oblongata. The adaptation to intermittent normobaric hypoxic-normoxic exposures was characterized by significant modifications of some enzyme activities in synaptosomes (decrease of cytochrome oxidase activity in the hippocampus, corpus striatum, and cerebellum; decrease of malate dehydrogenase activity in the cerebellum) and in the purified mitochondrial fraction (increase of succinate dehydrogenase activity in the corpus striatum). Daily treatment with three doses of naftidrofuryl (10, 15, and 22.5 mg/kg i.m.) modified some enzyme activities affected or unaffected by intermittent hypoxia and, particularly, decreased acetylcholinesterase activity.

Soman toxication in hypoxia acclimated rats: alterations in brain neuronal RNA and survival

Effects of prior hypoxia acclimation (14-day at 380 mm Hg) on soman (pinacolyl methylphosphonofluoridate) induced brain neuronal RNA and acetylcholinesterase (AChE) depletion and lethality were monitored in rats following their return to ambient oxygenation. Quantitative cytochemical techniques were used to measure RNA and AChE changes in individual cerebrocortical (Layer III) and striatal (caudate plus putamen) neurons. In ambient Po2 controls, soman eventuated in a moderate diminution of neuronal RNA in both brain regions and severe, dose-dependent suppression of AChE activity. Hypoxia acclimation per se induced RNA alterations as manifested in cortical RNA depletion and increased variability of striatal neuron RNA contents. In hypoxia acclimated rats, the extent of neuronal RNA depletion following soman injection was attenuated in both brain regions, yet there were no discernible differences in saline control AChE levels or in the extent of soman-induced AChE inhibition in ambient control versus hypoxia acclimated treatment groups. Hypoxia acclimated rats, however, were found to be even more susceptible to lethal actions of soman as assessed using 24- and 48-hour survival following a three-point treatment regimen. These data indicate that while compensatory systemic and central metabolic adjustments associated with 14d acclimation to reduced oxygen availability may retard soman-induced neuronal RNA depletion, resistance to lethal or near-lethal soman exposure is not enhanced. It is postulated that hypoxia acclimation is associated with complex adaptive and maladaptive neurophysiological alterations influencing CNS responsiveness to soman toxication, and that detrimental consequences exceed protection afforded by metabolic adaptation.

Influence of intermittent hypoxia and pyrimidinic nucleosides on cerebral enzymatic activities related to energy transduction

The effect of intermittent normobaric hypoxia and of biological pyrimidines (uridine and cytidine) on the specific activities of some enzymes related to cerebral energy metabolism were studied. Measurement were carried out on the following: homogenate in toto; purified mitochondrial fraction; crude synaptosomal fraction, in different areas of rat brain: cerebral cortex, hippocampus, corpus striatum, hypothalamus, cerebellum, and medulla oblongata. Intermittent normobaric hypoxia (12 hours daily for 5 days) caused modifications of the enzyme activities in the homogenate in toto (decrease of hexokinase in cerebellum; increase of pyruvate kinase in medulla oblongata), in the purified mitochondrial fraction (increase of succinate dehydrogenase in the corpus striatum) and in the crude synaptosomal fraction (decrease of cytochrome oxidase activity in cerebral cortex, hippocampus, and cerebellum; decrease of malate dehydrogenase in hippocampus and cerebellum; decrease of lactate dehydrogenase in cerebellum). Daily treatment with cytidine or uridine altered some enzyme activities either affected or unaffected by intermittent hypoxia.