In vivo uptake of [3H]nimodipine in focal cerebral ischemia: modulation by hyperglycemia

Diabetic Goto-Kakizaki rats display pronounced hyperglycemia and longer-lasting cognitive impairments following ischemia induced by cortical compression

Hyperglycemia has been shown to worsen the outcome of brain ischemia in several animal models but few experimental studies have investigated impairments in cognition induced by ischemic brain lesions in hyperglycemic animals. The Goto-Kakizaki (GK) rat naturally develops type 2 diabetes characterized by mild hyperglycemia and insulin resistance. We hypothesized that GK rats would display more severe cerebral damage due to hyperglycemia-aggravated brain injury and, accordingly, more severe cognitive impairments. In this study, recovery of motor and cognitive functions of GK and healthy Wistar rats was examined following extradural compression (EC) of the sensorimotor cortex. For this purpose, tests of vestibulomotor function (beam-walking) and combined tests of motor function and learning (locomotor activity from day (D) 1 to D5, operant lever-pressing from D14 to D25) were used. EC consistently reduced cerebral blood flow in both strains. Anesthesia-challenge and EC resulted in pronounced hyperglycemia in GK but not in Wistar rats. Lower beam-walking scores, increased locomotor activity, impairments in long-term habituation and learning of operant lever-pressing were more pronounced and observed at later time-points in GK rats. Fluoro-Jade, a marker of irreversible neuronal degeneration, revealed consistent degeneration in the ipsilateral cortex, hippocampus and thalamus at 2, 7 and 14 days post-compression. The amount of degeneration in these structures was considerably higher in GK rats. Thus, GK rats exhibited marked hyperglycemia during EC, as well as longer-lasting behavioral deficits and increased neurodegeneration during recovery. The GK rat is thus an attractive model for neuropathologic and cognitive studies after ischemic brain injury in hyperglycemic rats.

How Important is Hyperglycemia During Acute Brain Infarction?

BACKGROUND

Although well supported by animal studies, it remains unproven whether lowering hyperglycemia during acute cerebral infarction will improve outcomes. Further support for this therapeutic approach comes from clinical studies in acute myocardial infarction and in ventilated postsurgical patients, where lowering hyperglycemia improved outcomes.

REVIEW SUMMARY

Animal studies support the hypothesis that hyperglycemia during acute brain ischemia augments the brain injury, but only in models with reperfusion. The available human studies to date are all observational and they usually find an association between hyperglycemia during acute cerebral infarction and worse outcome. Also, there is evidence that hyperglycemia during acute cerebral infarction is detrimental only with reperfusion. This association appears to be linear in the glucose ranges tested (normal to high). In addition, there is an association between admission hyperglycemia and hemorrhagic conversion of an acute cerebral infarct when thrombolytics are used.

CONCLUSION

Sufficient evidence has accumulated to proceed to clinical efficacy trials to see if tight glycemic control compared with persistent hyperglycemia during acute cerebral infarction will improve outcomes. If such therapy proves beneficial, the increased cost, effort, and risk associated with tight glycemic control during acute cerebral infarction could be justified. Randomized clinical trials to test this hypothesis are currently in progress.

Effects of admission hyperglycemia on stroke outcome in reperfused tissue plasminogen activator--treated patients

BACKGROUND AND PURPOSE

We sought to investigate the impact of hyperglycemia before reperfusion on long-term outcome in patients treated with intravenous tissue plasminogen activator (tPA).

METHODS

Of 268 consecutive patients with a nonlacunar middle cerebral artery (MCA) stroke evaluated at <3 hours after onset, 73 (27.2%) received intravenous tPA. Serum glucose was determined at baseline before tPA administration. Hyperglycemia was defined as a glucose level >140 mg/dL. National Institutes of Health Stroke Scale (NIHSS) scores were obtained at baseline and 24 hours. Transcranial Doppler monitoring of recanalization and reocclusion was conducted during the first 24 hours. Total infarct volume was measured on CT at day 5 to 7. Modified Rankin Scale was used to assess outcome at 3 months.

RESULTS

Median NIHSS score was 17. At baseline, 31 patients (42.5%) were hyperglycemic and 42 (57.5%) normoglycemic. Early reperfusion (<6 hours) occurred in 43 patients (58.9%). Admission blood glucose correlated negatively with the degree of neurological improvement at 24 hours in reperfused (r=-0.43; P=0.019) but not in nonreperfused (r=-0.20; P=0.21) tPA-treated patients. Increased age (P=0.014), history of diabetes mellitus (P=0.043), admission glucose >140 mg/dL (P=0.002), and early reocclusion (P=0.004) were factors associated with poor outcome among reperfused patients. A logistic regression modeling revealed that only admission glucose value >140 mg/dL (odds ratio, 8.4; 95% CI, 1.76 to 40.02; P=0.005) emerged as an independent predictor of poor outcome despite tPA-induced recanalization. In patients with 6-hour persistent MCA occlusion, baseline NIHSS score >15 points (P=0.011) and proximal MCA occlusion (P=0.039) were variables associated with poor outcome on univariate analysis. In a logistic regression model, only NIHSS score >15 points (odds ratio, 11.9; 95% CI, 1.48 to 97.1; P=0.032) remained as an independent predictor of poor outcome and functional dependence at 3 months in nonreperfused tPA-treated patients.

CONCLUSIONS

Hyperglycemia before reperfusion may in part counterbalance the beneficial effect of early restoration of blood flow, which translates into a worse outcome in hyperglycemic patients despite tPA-induced recanalization.

Nimodipine improves the disruption of spatial cognition induced by cerebral ischemia

The direct neuroprotective effect of nimodipine, a central Ca antagonist, was investigated in in vitro experiments. Also, in in vivo experiments, the effects of nimodipine and amlodipine, a noncentral Ca antagonist, on rat cerebral ischemia models developing by different mechanisms were compared. In an in vitro ischemic model using acidotic and hypoglycemic rat cerebellar granule cells, nimodipine directly protects against brain neuronal cell damage. In in vivo models of single (one 10-min, four-vessel occlusion) and repeated rat cerebral ischemia (two 10-min, four-vessel occlusions; a 50-min interval), the impairment observed 24 h after the single ischemic procedure was likely to be prevented by nimodipine (0. 1-5mg/kg, i.p.). At 7 days after the repeated cerebral ischemia, the disruption of spatial cognition was significantly prevented by nimodipine (5 mg/kg, i.p.) but not amlodipine (5 mg/kg, i.p.), which was given after each ischemia. These results indicated that nimodipine may protect neuronal cells by a more persistent mode of action, that is, nimodipine may enter into the cell and control the intracellular Ca ion cascade by inhibiting excessive Ca(2)+ influx into the mitochondria.