Increased ATP production during long-term brain ischemia in rats in the presence of propentofylline

Herba Cistanches stimulates cellular glutathione redox cycling by reactive oxygen species generated from mitochondrial respiration in H9c2 cardiomyocytes

CONTEXT

Earlier findings demonstrated that pretreatment of Herba Cistanches [the dried whole plant of Cistanche deserticola Y.C. Ma (Orobanchaceae)], a "Yang-invigorating" Chinese tonic herb, stimulated the ATP-generation capacity (ATP-GC) in mitochondria isolated from rat heart ex vivo. The enhancement of mitochondrial ATP-GC by Herba Cistanches was associated with induction of glutathione antioxidant status and protection against ischemia/reperfusion (I/R) injury in rat hearts.

OBJECTIVES

This study investigated the relationship between enhancements in mitochondrial ATP-GC and glutathione antioxidant status in H9c2 cardiomyocytes using a semipurified fraction of Herba Cistanches (HCF1).

MATERIALS AND METHODS

HCF1 (10-300 ng/mL) was tested for its effects on mitochondrial ATP generation, glutathione antioxidant status and protection against oxidant injury in H9c2 cardiomyocytes and rat hearts.

RESULTS AND DISCUSSION

HCF1 at 30 ng/mL increased mitochondrial ATP-GC and ADP-stimulated state 3 respiration (by 50 and 100%, respectively) in H9c2 cardiomyocytes. The stimulation of mitochondrial respiration was associated with the induction of mitochondrial uncoupling (27%) and enhancement of cellular glutathione redox cycling as well as protection against hypoxia/reoxygenation (hypox/reoxy)-induced apoptosis (by 60%). While HCF1 treatment increased reactive oxygen species generation from mitochondrial respiration in H9c2 cardiomyocytes, pretreatment with antioxidants (DMTU) abrogated the HCF1-induced cellular responses and the associated cytoprotective effect. HCF1 pretreatment (1.14 and 3.41 mg/kg × 14) also protected against myocardial I/R injury in rats (by 13 and 32%), presumably mediated by the induction of glutathione antioxidant response.

CONCLUSION

The long-term intake of HCF1 may offer a prospect for the prevention of ischemic heart disease.

Targeting ischemic penumbra: part I - from pathophysiology to therapeutic strategy

Penumbra is the viable tissue around the irreversibly damaged ischemic core. The purpose of acute stroke treatment is to salvage penumbral tissue and to improve brain function. However, the majority of acute stroke patients who have treatable penumbra are left untreated. Therefore, developing an effective non-recanalizational therapeutics, such as neuroprotective agents, has significant clinical applications. Part I of this serial review on "targeting penumbra" puts special emphases on penumbral pathophysiology and the development of therapeutic strategies. Bioenergetic intervention by massive metabolic suppression and direct energy delivery would be a promising future direction. An effective drug delivery system for this purpose should be able to penetrate BBB and achieve high local tissue drug levels while non-ischemic region being largely unaffected. Selective drug delivery to ischemic stroke penumbra is feasible and deserves intensive research.

Oxygen glucose deprivation model of cerebral stroke in PC-12 cells: glucose as a limiting factor

Optimum time points for oxygen-glucose deprivation (OGD) and re-oxygenation have been identified to suggest the suitability of PC-12 cells as rapid and sensitive in vitro model of cerebral stroke. Further, the precise role of glucose as one of the limiting factors was ascertained. PC-12 cells were subjected to receive OGD of 1-8 h followed by re-oxygenation for 6 to 96 h in medium having glucose 0-10 mg/ml. Loss of cell viability was assessed using trypan blue dye exclusion and MTT assays. The significant (p < 0.05) reduction in percent viable cell count was started at 2 h of OGD (80.7 +/- 2.0) and continued in further OGD periods (3, 4, 5, 6, 7, and 8 h), i.e. 65.7 +/- 3.5, 59.7 +/- 4.6, 54.3 +/- 3.2, 44.7 +/- 2.9, 20.3 +/- 4.3, 5.7 +/- 2.0 of counted cells, respectively. Cells growing in glucose-free medium have shown a gradual (p < 0.001) decrease in cell viability throughout the re-oxygenation. Re-oxygenation of 24 h was found to be first statistically significant time point for all the glucose concentrations. Glucose concentration during re-oxygenation was found to be one of the key factors involved in the growth and proliferation in PC-12 cells. The OGD of 6 h followed by a re-oxygenation period of 24 h with 4-6 mg/ml glucose concentration could be recorded as optimum conditions under our experimental conditions.

Plasticity of purine release during cerebral ischemia: clinical implications?

Adenosine is a powerful modulator of neuronal function in the mammalian central nervous system. During a variety of insults to the brain, adenosine is released in large quantities and exerts a neuroprotective influence largely via the A(1) receptor, which inhibits glutamate release and neuronal activity. Using novel enzyme-based adenosine sensors, which allow high spatial and temporal resolution recordings of adenosine release in real time, we have investigated the release of adenosine during hypoxia/ischemia in the in vitro hippocampus. Our data reveal that during the early stages of hypoxia adenosine is likely released per se and not as a precursor such as cAMP or an adenine nucleotide. In addition, repeated hypoxia results in reduced production of extracellular adenosine and this may underlie the increased vulnerability of the mammalian brain to repetitive or secondary hypoxia/ischemia.

Propentofylline rapidly normalizes mitochondrial respiration in a gerbil low flow unilateral forebrain ischemia

The effect of propentofylline on mitochondrial respiratory activity was assessed in gerbils after 30 min of unilateral forebrain ischemia and 5 min of incomplete reperfusion. Cerebral blood flow (CBF) measured by hydrogen clearance was reduced to 12.6+/-2.1 ml/100 g per min in the ischemic hemisphere. Propentofylline at 10 mg/kg applied intraperitoneally raised CBF to 26.7+/-3.4 ml/100 g per min (P<0.05) in ischemic areas, however, CBF remained substantially reduced in comparison to the flow in the non-ischemic hemisphere (52.9+/-4.1 ml/100 g per min). Mitochondrial ADP-stimulated as well as uncoupled respiration was significantly reduced by approximately 60% after 30 min of ischemia. Since ADP-unstimulated respiration was not reduced, the respiratory control ratio declined markedly. Five minutes after application of propentofylline all indices of the mitochondrial respiratory capacity were normalized despite persisting reduction in CBF.

Neuromodulatory effect of propentofylline on rat brain under acute and long-term hypoperfusion

1. The effects of propentofylline (PPF, 25 mg kg(-1) body weight per day) on rat cerebral energy state and cytokine expression as well as on behaviour and histopathology were studied after acute and long-term permanent bilateral common carotid artery occlusion (BCCAO). 2. In the absence of PPF, acute ischaemia led to a decrease in energy-rich phosphates in parietotemporal cortex and hippocampus which correlated with an increase in AMP and adenosine concentrations measured by high-performance liquid chromatography technique. The concentrations of cortical cytokines TNF alpha and IL1 beta were increased 12 and 19 fold, respectively. 3. PPF had a neuroprotective action after 20 min of BCCAO, reducing the deleterious effect of acute ischaemia on rat brain energy state and microglial reaction. Simultaneously, PPF treatment increased cyclic-AMP 3 fold. 4. Three weeks of permanent BCCAO did not significantly disturb brain energy metabolism, microglial reaction or histopathology. However, a significant reduction of 30 -- 50% in rat memory capacities and a locomotor hyperactivity were obtained. 5. Continuous PPF-application, however, led to a marked increase in rat working memory and to reduced locomotor activity, which were returned nearly to control levels by 1 week after permanent BCCAO. In summary, PPF showed a clear neuroprotective effect on cerebral energy state and pro-inflammatory cytokines under conditions of acute global ischaemia. Continuous administration of PPF led to memory improvement during permanent BCCAO. 6. These results underscore the benefit of treatment with PPF in clinical practice, particularly during stroke, but also in cerebrovascular and neurodegenerative disorders.

The neuroprotective effect of cerebral poly(ADP-ribose)polymerase inhibition in a rat model of global ischemia

In the present study, the effect of poly(ADP-ribose) polymerase (PARP) inhibition on rat cortical energy state was investigated at 24 h after global cerebral ischemia induced by permanent bilateral common carotid artery ligation plus transient hypotension. The specific PARP inhibitor 3-aminobenzamide was injected 10 min before induction of ischemia at a dosage of 5, 10, and 20 mg/kg intracerebroventricularly. Twenty-four hours after ischemia cortical PARP enzyme activity increased from 0.425+/-0.144 to 0.794+/-0.193 units/mg protein. Cerebral ischemia was associated by a decrease in adenosine triphosphate (ATP) and phosphocreatine concentrations to 72.5 and 76.8% of controls, respectively. In addition, an 1.9- and 2. 2-fold increase in adenosine monophosphate and adenosine was observed. Specific PARP inhibition with 10 mg/kg 3-aminobenzamide protected the rat energy state by preserving cortical phosphocreatine and NAD(+). Cortical ATP was not changed significantly after PARP inhibition. In conclusion, activation of the nuclear enzyme PARP plays an important role in cerebral energy metabolism during rat global ischemia. Therefore, specific PARP inhibition may offer new strategies in the therapy of vascular diseases such as stroke.

Linear relation between cerebral phosphocreatine concentration and memory capacities during permanent brain vessel occlusions in rats

The present study investigates the interrelation between cerebral energy state and memory capacities in a rat model of stepwise cerebral vessel occlusions. After acute and subchronic permanent vessel occlusions, cortical energy metabolites (ATP, phosphocreatine, ADP, AMP) were detected by high-pressure liquid chromatography (HPLC) analysis, and the effects on learning, memory, and cognitive behavior were evaluated using a hole-board test. The results of the study demonstrated a drastic decrease in energy-rich phosphates by 33% for phosphocreatine and by 44% for ATP after acute vessel occlusions. In addition, rat working and reference memories were strikingly decreased to about 5% of controls. In contrast, two weeks after four-vessel occlusion, the energy state was almost completely restored to control levels. However, a significant decrease in memory capacities was observed in subchronic state. In summary, this study has demonstrated a close linear relationship (p < 0.001) between an impaired cerebral energy state and brain memory dysfunction after acute and permanent cerebral four-vessel occlusion. Thus, this animal model of stepwise reduction of the cerebral blood supply may reflect some clinically relevant processes occurring during cerebrovascular and neurodegenerative diseases.

Interrelation between cerebral energy metabolism and behaviour in a rat model of permanent brain vessel occlusion

The present study investigates the interrelation between cerebral energy metabolism and memory capacities after acute and permanent occlusions of carotid and vertebral arteries in adult Wistar rats (n=60). Tissue ATP, phosphocreatine, ADP, AMP and adenosine concentrations were determined in rat brain by high-pressure liquid chromatography (HPLC) analysis. Lactate and pyruvate were measured spectrophotometrically. Rats underwent psychometric testing by means of a holeboard test, closed field activity, and passive avoidance behaviour. Acute cerebral ischaemia was associated with a substantial deficit in energy load (-50%). Cortical adenosine and lactate exhibited a 7- and a 10-fold increase, respectively, in concentration. After 2 weeks of four-vessel occlusion, cortical ATP and phosphocreatine showed a partial enhancement in their concentrations if compared with acute ischaemia. Consequently, energy load (micromol/g) increased from 0.59 to 1.42 in cerebral cortex and from 0.58 to 1.14 in hippocampus under conditions of acute and permanent ischaemia, respectively. While lactate was normalized, adenosine showed a 2-fold increase in its cortical concentration. All animals improved their abilities in learning, memory and cognition after a 7-day training period. Acute vessel occlusion severely decreased working memory (WM), reference memory (RM) and locomotor activity. Simultaneously, the passive avoidance test showed a significant reduction in latency time from 247+/-85 s (sham) to 145+/-132 s. The partial improvement in brain energy state was accompanied by a relative improvement in WM and RM, although both memory capacities remained significantly lower than in controls. The data of the present study demonstrate a linear relationship between cerebral energy metabolism and brain memory capacities after acute and permanent vessel occlusions in rats.