Effect of lidoflazine on cerebral blood flow following twelve minutes total cerebral ischemia

Neuroprotective potential for mitigating ischemia-reperfusion-induced damage

Reperfusion following cerebral ischemia causes both structural and functional damage to brain tissue and could aggravate a patient's condition; this phenomenon is known as cerebral ischemia-reperfusion injury. Current studies have elucidated the neuroprotective role of the sirtuin protein family (Sirtuins) in modulating cerebral ischemia-reperfusion injury. However, the potential of utilizing it as a novel intervention target to influence the prognosis of cerebral ischemia-reperfusion injury requires additional exploration. In this review, the origin and research progress of Sirtuins are summarized, suggesting the involvement of Sirtuins in diverse mechanisms that affect cerebral ischemia-reperfusion injury, including inflammation, oxidative stress, blood-brain barrier damage, apoptosis, pyroptosis, and autophagy. The therapeutic avenues related to Sirtuins that may improve the prognosis of cerebral ischemia-reperfusion injury were also investigated by modulating Sirtuins expression and affecting representative pathways, such as nuclear factor-kappa B signaling, oxidative stress mediated by adenosine monophosphate-activated protein kinase, and the forkhead box O. This review also summarizes the potential of endogenous substances, such as RNA and hormones, drugs, dietary supplements, and emerging therapies that regulate Sirtuins expression. This review also reveals that regulating Sirtuins mitigates cerebral ischemia-reperfusion injury when combined with other risk factors. While Sirtuins show promise as a potential target for the treatment of cerebral ischemia-reperfusion injury, most recent studies are based on rodent models with circadian rhythms that are distinct from those of humans, potentially influencing the efficacy of Sirtuins-targeting drug therapies. Overall, this review provides new insights into the role of Sirtuins in the pathology and treatment of cerebral ischemia-reperfusion injury.

Asphyxiation versus ventricular fibrillation cardiac arrest in dogs. Differences in cerebral resuscitation effects--a preliminary study

We explored the hypothesis that brain damage after cardiac arrest caused by ventricular fibrillation (VF) needs different therapies than that after asphyxiation, which has been studied less thoroughly. In 67 healthy mongrel dogs of both sexes cardiac arrest (at normothermia) by ventricular fibrillation (no blood flow lasting 10 min) or asphyxiation (no blood flow lasting 7 min) was reversed by normothermic external cardiopulmonary resuscitation, followed by intermittent positive-pressure ventilation for 20 h, and intensive care to 96 h. To ameliorate ischemic brain damage, the calcium entry blocker lidoflazine or a solution of free radical scavengers (mannitol and L-methionine in dextran 40) plus magnesium sulphate, was given intravenously immediately upon restoration of spontaneous circulation. Outcome was evaluated as functional deficit, brain creatine kinase (CK) leakage into the cerebrospinal fluid (CSF) and brain morphologic changes. Lidoflazine seemed to improve cerebral outcome after VF but not after asphyxiation. Free radical scavengers plus magnesium sulphate seemed to improve cerebral outcome after asphyxiation, but not after VF. After VF, scattered ischemic neuronal changes in multiple brain regions dominated, and total brain histopathologic damage scores correlated with final neurologic deficit scores at 96 h (r = 0.66) and with peak CK levels in CSF (r = 0.81). After asphyxiation, in addition to the same ischemic neuronal changes, microinfarcts occurred, and there was no correlation between total brain histopathologic damage scores and neurologic deficit scores or CK levels in CSF.

CONCLUSIONS

Different mechanisms of cardiac arrest, which cause different morphologic patterns of brain damage, may need different cerebral resuscitation treatments.

Failure of nimodipine to improve neurologic outcome after eighteen minutes of cardiac arrest in the cat

The calcium entry blocker nimodipine was administered to cats following resuscitation from 18 min of cardiac arrest to evaluate its effect on neurologic and neuropathologic outcome in a clinically relevant model of complete cerebral ischemia. Cardiac arrest (ventricular fibrillation) was maintained for 18 min and resuscitation was performed by a standardized protocol in 40 cats. Beginning at 5 min post-resuscitation, nimodipine, 10 micrograms/kg over 2 min followed by 1 microgram/kg per min for 10 h, or the same volume of placebo was administered in a randomized, blinded fashion. Neurologic deficits were scored at 2, 4, and 7 days post-resuscitation by observers blinded to the treatment group. Thirty cats were evaluated neurologically at 7 days post-resuscitation and were entered into data analysis (n = 15 per group). Neither neurologic deficit scores nor neuropathologic scores were significantly different between groups. The authors conclude that nimodipine administration in the manner and doses stated does not improve neurologic outcome in cats following resuscitation from cardiac arrest.

Effect of nicardipine on somatosensory evoked potentials in patients with acute cerebral infarction

We evaluated the effect of nicardipine, a calcium channel blocker, on somatosensory evoked potentials (SEP) in 26 patients with acute cerebral infarction. Post treatment, 58% (15/26) of the N20 and P25 latencies were prolonged in the affected hemispheres; 8% (2/26) were shortened; and 35% (9/26) did not change. The mean N20 and P25 latencies were significantly prolonged two hours post treatment in the affected hemisphere (N20, P less than 0.01, P25 P less than 0.01). Nicardipine (Ni) had no effect on SEP components in the intact hemispheres. Seventy five per cent of the 12 patients with hypertension had a decrease in blood pressure (BP) after taking nicardipine, but there were no undesirable side effects or worsening of neurological signs. Our study demonstrates that nicardipine prolongs the latencies of short-latency components of SEP in the affected hemisphere after acute ischaemic stroke and also decreases BP. These observations suggest that nicardipine therapy might impair neuronal function in the ischaemic zone.

Brain protection: physiological and pharmacological considerations. Part II: The pharmacology of brain protection

Neuroprotective agents may exert their effect by reducing cerebral oxygen demand (CMRO2), increasing cerebral oxygen delivery, or by altering ongoing pathological processes. Barbiturates provide neuroprotection by reducing the CMRO2 necessary for synaptic transmission while leaving the component necessary for cellular metabolism intact. Isoflurane may exert a neuroprotective effect by a similar mechanism but its efficacy is likely less than that of barbiturates due to adverse effects on cerebral blood flow. Lidocaine reduces CMRO2 by affecting both cellular metabolic processes and synaptic transmission and thus resembles hypothermia in its mechanism of action. Benzodiazepines reduce CMRO2 by reducing synaptic transmission and their use as neuroprotectants produces less haemodynamic compromise than barbiturates. The mechanism of protection by calcium entry blocking agents appears to be due to improved blood flow as opposed to altering abnormal Ca++ fluxes. In contrast, agents such as ketamine and MK-801 may prevent abnormal Ca++ fluxes through their competitive interaction with N-methyl-D-aspartate receptors. Phenytoin prevents K(+)-mediated ischaemic events from progressing. Agents worthy of further investigation include corticosteroids, free radical scavengers, prostaglandin inhibitors and iron chelators.

Brain protection: physiological and pharmacological considerations. Part I: The physiology of brain injury

Ischaemia, whether focal or global in nature, produces a sequence of intracellular events leading to increased cell permeability to water and ions including Ca++. There is a loss of cellular integrity and function, with increased production of prostaglandins, free radicals, and acidosis with lactate accumulation. These events may be exacerbated by glucose administration. Pharmacological agents aimed at alleviating ischaemic injury could be directed at decreasing cerebral metabolic requirements for oxygen, improving flow to ischaemic areas, preventing Ca+(+)-induced injury, inhibition of free radical formation, lactate removal, inhibition of prostaglandin synthesis, and prevention of complement-mediated leukocyte aggregation. Part I of this paper describes some of the pathophysiological events leading to ischaemic brain injury. Part 2 of this paper will consider the current agents available for brain protection.

The use of a calcium-channel blocker, nicardipine, for severely asphyxiated newborn infants

A continuous infusion of nicardipine was given to four severely asphyxiated fullterm infants who were at high risk for adverse outcome and had abnormal cerebral Doppler haemodynamic studies. The heart rate increased in all four infants and mean arterial blood pressure (MAP) fell in three. Two infants had a sudden and marked fall in MAP, together with severe impairment of skin blood-flow and a concurrent fall in cerebral blood-flow velocity. The serum level of nicardipine was less than 40ng/mL in all cases. The use of nicardipine, and possibly other calcium-channel blockers, may be associated with marked hypotension, and if there is no cerebral autoregulation, may cause further cerebral hypoperfusion, so use of these drugs in asphyxiated newborn infants should only be attempted if blood pressure is carefully monitored.

The physiology of cardiopulmonary resuscitation

As the pathophysiology of CPR is understood, ways to alter cerebral blood flow and neurologic outcome following CPR are likely to develop. This review highlights those areas likely to be of clinical importance in the near future.

Inability of flunarizine, lidoflazine or magnesium to counteract delayed hypoperfusion after forebrain ischaemia in the rat

Local cerebral blood flow (lCBF) was measured autoradiographically 60 min after 15 min of forebrain ischaemia in rats treated with flunarizine (0.1 mg/kg b.w.), lidoflazine (1.0 mg/kg b.w.) or Mg2+ (600 mumol/kg b.w.) before or at the end of the ischaemic period. Incomplete forebrain ischaemia was produced by a combination of common carotid artery occlusion and bleeding to a mean arterial blood pressure of 50 mmHg. During ischaemia lCBFs in cortical areas were less than 1% of preischaemic values. Neither flunarizine, lidoflazine nor Mg2+ influenced lCBF during ischaemia. Sixty minutes after the start of recirculation lCBFs were decreased to between 40 and 60% of the values found in control animals. None of the instituted treatments improved postischaemic cerebral blood flow. The results do not lend support to the view that calcium plays an essential role in the pathogenesis of delayed postischaemic hypoperfusion in the brain in this model.

Brain resuscitation and protection

No drug that is used for brain protection after global brain ischaemia as a result of cardiac arrest has been shown to be of benefit. Barbiturate agents have been proved not to be beneficial whereas studies of calcium-channel blocking drugs are inconclusive. Hypothermia, haemodilution and mechanical hyperventilation are not of proven benefit. Immediate defibrillation with rapid restoration of blood pressure is the best method to improve the neurological outcome after a cardiac arrest. After severe head injury, prompt emergency care to restore ventilation, oxygenation and blood pressure improves the neurological outcome. The early evacuation of extracerebral intracranial haematomas also improves the outcome. Corticosteroid therapy does not improve the outcome. The monitoring of intracranial pressure and the control of increased intracranial pressure by hyperventilation, cerebrospinal-fluid drainage and mannitol, frusemide and barbiturate therapy appear to improve the outcome after a severe head injury, although this has not been proved by randomized controlled studies.

Cerebral ischemia and reperfusion: prevention of brain mitochondrial injury by lidoflazine

Mitochondrial degradation is implicated in the irreversible cell damage that can occur during cerebral ischemia and reperfusion. In this study, the effects of 10 min of ventricular fibrillation and 100 min of spontaneous circulation on brain mitochondrial function was studied in dogs in the absence and presence of pretreatment with the Ca2+ antagonist lidoflazine. Twenty-three beagles were separated into four experimental groups: (i) nonischemic controls (ii) those undergoing 10-min ventricular fibrillation, (iii) those undergoing 10-min ventricular fibrillation pretreated with 1 mg/kg lidoflazine i.v., and (iv) those undergoing 10-min ventricular fibrillation followed by spontaneous circulation for 100 min. Brain mitochondria were isolated and tested for their ability to respire and accumulate calcium in a physiological test medium. There was a 35% decrease in the rate of phosphorylating respiration (ATP production) following 10 min of complete cerebral ischemia. Those animals pretreated with lidoflazine showed significantly less decline in phosphorylating respiration (16%) when compared with nontreated dogs. Resting and uncoupled respiration also declined following 10 min of fibrillatory arrest. One hundred minutes of spontaneous circulation following 10 min of ventricular fibrillation and 3 min of open-chest cardiac massage provided complete recovery of normal mitochondrial respiration. Energy-dependent Ca2+ accumulation by isolated brain mitochondria was unimpaired by 10 min of complete cerebral ischemia. However, by 100 min after resuscitation, there was a small, but significant rise in the capacity for mitochondrial Ca2+ sequestration when compared to either control or fibrillated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral resuscitation: pathophysiology and therapy

The interest in the possibility of cerebral resuscitation has been growing exponentially during the last decade. It became clear that pharmacotherapeutic interaction can possibly alter the outcome of cerebral hypoxia/ischemia. The present review is an attempt to provide an organizational framework for a systematic integration of studies specifically dealing with pharmacological treatment post-insult.

Lidoflazine does not improve neurologic outcome when administered after complete cerebral ischemia in primates

In order to investigate the effects of the calcium entry blocker lidoflazine on neurologic outcome in primates following an episode of global brain ischemia, 12 pigtail monkeys (Macaca nemestrina) were subjected to 17 min of complete cerebral ischemia, followed by 48 h of intensive care treatment and daily neurologic evaluations for 96 h. The monkeys were randomly assigned to receive, in a blind fashion, either lidoflazine 1.0 mg/kg (n = 6) or inactive lidoflazine solvent (n = 6) at 5 min, 8 h, and 16 h postischemia. One monkey in the lidoflazine group did not meet preestablished protocol criteria and was excluded from data analysis. The remaining monkeys were well matched for age, sex, and other physiologic variables. Neurologic outcome was not significantly different between the lidoflazine- and placebo-treated groups (p greater than 0.5). No monkey in either group achieved a normal neurologic exam by 96 h postischemia. Three lidoflazine-treated monkeys and two placebo-treated monkeys died prior to the 96-h neurologic evaluation. These deaths were judged to be neurologic in origin. The authors concluded that lidoflazine does not improve neurologic outcome in primates when administered after 17 min of complete cerebral ischemia.

Prevention of gastric mucosal lesions following aortic cross-clamping

Stress ulceration is frequently encountered after cardiovascular surgery. In this study of 32 male baboons, severe gastric ischaemia was used to produce gastric stress lesions. The occurrence of these lesions was reduced by allopurinol (P = 0.03) and completely prevented by the combination of allopurinol with superoxide dismutase (P = 0.004). A shorter ischaemic period also reduced the number of lesions (P = 0.02). Concurrent with the stress lesion formation, there was a fall in mucosal glutathione and oxidized glutathione levels (P less than 0.05).

Cross-clamping of the thoracic aorta. Influence of aortic shunts, laminectomy, papaverine, calcium channel blocker, allopurinol, and superoxide dismutase on spinal cord blood flow and paraplegia in baboons

There is a high incidence of paraplegia associated with thoracic aortic cross-clamping, even when cardiopulmonary bypass or shunts are used. In 56 adult baboons, spinal cord blood flow (SCBF), vascular anatomy, and paraplegia rates were evaluated. Tissue blood flow was measured by radioactive microspheres. Various procedures were used to increase SCBF and to prevent ischemia-reperfusion injury. It was found that the rate of paraplegia was inversely correlated with neural tissue ischemia (SCBF) and directly correlated with reperfusion hyperemia. Two methods completely prevented paraplegia. These two methods were a thoracic shunt with occlusion of the infrarenal aorta or cerebrospinal fluid drainage plus intrathecal papaverine injection, both of which were associated with an increased SCBF. Furthermore, papaverine dilated the anterior spinal artery (ASA) (p = 0.007) and increased the blood flow through the lower ASA. Whereas procedures utilizing a calcium channel blocker (flunarizine), allopurinol, superoxide dismutase (SOD), laminectomy alone, and a thoracoabdominal shunt not perfusing the arteria radicularis magna (ARM) all failed to prevent paraplegia, allopurinol (p = 0.026) and SOD (p = 0.004) did prevent gastric stress lesions, indicating that their failure to prevent paraplegia was not due to a lack of activity. Of great clinical interest is that, if a shunt is used and the ARM is perfused, infrarenal aortic cross-clamping increases SCBF, thus preventing paraplegia. Intrathecal application of papaverine proved to be even more effective in increasing SCBF and also completely prevented paraplegia. As this is a safer procedure than the insertion of shunts, this is the method of choice for the prevention of paraplegia associated with thoracic aortic cross-clamping. The preliminary trial using intrathecal papaverine in human beings has thus far shown no adverse side effects from the drug, and no paraplegia has occurred.

Recovery of monkey brain after prolonged ischemia. I. Electrophysiology and brain electrolytes

Adult normothermic monkeys were submitted to 1 h of total cerebral ischemia, followed by blood recirculation for 1.5-24 h. During ischemia EEG and evoked potentials were suppressed within 12 s and 3 min, respectively. Upon recirculation, high-voltage EEG bursts began to reappear after 82-125 min, followed by gradual return of continuous background activity and near normalization of EEG frequency pattern within 24 h. Somatically evoked potentials, in contrast, exhibited only partial recovery, and consciousness did not return during the observation period. At the end of the experiments, tissue contents of sodium, potassium, calcium, and magnesium were measured in the gray and white matter of parietal lobe by atomic absorption spectroscopy. Gray matter sodium content gradually increased by approximately 50% from 41.0 to 59.8 mumol/g wet wt during 24 h of recirculation. The other electrolytes including calcium did not change during the observation period. Postischemic recovery reported in this and the accompanying article is attributed to careful control of postischemic general physiological state and prevention or treatment of postischemic complicating side effects such as postischemic brain edema, hypotension, acidosis, pulmonary distress, and anuria. No specific drug treatment such as application of calcium antagonists or metabolic inhibitors was necessary to achieve this effect.

Mitochondrial damage during cerebral ischemia

Cerebral ischemia causes a rapid decline in the ability of brain mitochondria to synthesize adenosine triphosphate when they are exposed to oxygen and oxidizable substrates. Ischemia also results in a decreased capacity for energized mitochondria to sequester the abnormally high levels of calcium that are present within ischemic tissue. The degree to which these processes are affected is likely to influence the maintenance of cell viability during cerebral resuscitation. Factors that have been proposed to account for mitochondrial damage during ischemia and reperfusion include intracellular acidosis, Ca2+-induced membrane damage, and free-radical-dependent membrane lipid peroxidation. Ongoing research indicates that measures can be taken to manipulate these factors so that mitochondrial damage may be minimized and cell viability optimized during resuscitation.

Ischemic brain protection

Despite advances in the understanding of the pathophysiology of cerebral ischemia, no single brain resuscitation therapy has yet been shown to be clinically superior to brain-oriented intensive care. Basic concepts in cardiopulmonary-cerebral resuscitation (CPCR) are discussed, as are two specific phases of CPCR, cerebral preservation and cerebral resuscitation. Cerebral preservation is initiated during cardiac arrest (ie, prior to restoration of spontaneous circulation [ROSC]) and includes use of artificial perfusion techniques and drugs to produce cerebral perfusion during this phase. Cerebral resuscitation is brain-oriented therapy initiated after ROSC. Pharmacologic agents currently under study for cerebral resuscitation include the barbiturates, calcium antagonists, and iron chelators. With respect to defining efficacy of the pharmacologic agents, the concept of therapeutic window is important. Although no agent has been proven clinically, several appear to be promising.

The effects of lidoflazine and flunarizine on cerebral reactive hyperemia

Cerebral blood flow in the rat was monitored by a venous outflow technique with an extracorporeal circulation, which allows for the continuous recording of flow over periods of several hours. The bi-fluorophenyl-piperazine derivatives, lidoflazine and flunarizine, enhanced the reactive hyperemia elicited by a brief (30 s) anoxic challenge. They did not alter resting cerebral blood flow rates. Verapamil, a potent calcium slow channel blocker, decreased resting flow rates but did not alter the duration of the reactive hyperemia. As lidoflazine and flunarizine are potent inhibitors of adenosine uptake, whereas verapamil is not, the results are consistent with the hypothesis that adenosine plays a significant role in cerebral vascular autoregulation.

Mitochondrial calcium sequestration in cortical and hippocampal neurons after prolonged ischemia of the cat brain

Adult normothermic cats were submitted to 1- h complete cerebrocirculatory arrest, followed by blood recirculation for 6-8 h. Two groups of animals could be distinguished: In one group electrocorticogram and somatically evoked primary cortical potentials steadily recovered after ischemia, and in another electrophysiologic recovery was absent. At the end of the recirculation period, calcium content was measured in tissue samples taken from cerebral cortex and hippocampus, and compared with mitochondrial calcium sequestration as assessed by electron-microscopic cytochemistry. Protein content of cortex and hippocampus was also determined for evaluation of tissue swelling. The two regions were selected because previous experiments had revealed that in animals with electrophysiologic recovery cerebral cortex remains intact although hippocampus is selectively injured, whereas in animals without electrophysiologic recovery both cerebral cortex and hippocampus are damaged. In animals with functional recovery, neither calcium content nor mitochondrial calcium sequestration were significantly increased in either cerebral cortex or hippocampal subfield CA1. Only in dentate gyrus a minor degree of mitochondrial calcium sequestration was present. Calculation of tissue swelling revealed no change in cerebral cortex, but a volume increase by 18% in hippocampus, indicating development of brain edema in this region. In animals without functional recovery tissue calcium significantly increased both in cortex and hippocampus (by 49% and 73% of control, respectively), and there was significant mitochondrial calcium accumulation in both regions. Calculated brain swelling in these animals amounted to 16% and 26% in cortex and hippocampus, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)