title: Insulin and glucagon share the same mechanism of neuroprotection in diabetic rats: role of glutamate.
abstract: In patients with acute ischemic stroke, diabetes and hyperglycemia are associated with increased infarct size, more profound neurologic deficits and higher mortality. Notwithstanding extensive clinical and experimental data, treatment of stroke-associated hyperglycemia with insulin is controversial. In addition to hyperglycemia, diabetes and even early prediabetic insulin resistance are associated with increased levels of amino acids, including the neurotoxic glutamate, in the circulation. The pleiotropic metabolic effects of insulin include a reduction in the concentration of amino acids in the circulation. In this article, we show that in diabetic rats exposed to transient middle cerebral artery occlusion, a decrease of plasma glutamate by insulin or glucagon reduces CSF glutamate, improves brain histology, and preserves neurologic function. The neuroprotective effect of insulin and glucagon was similar, notwithstanding their opposite effects on blood glucose. The therapeutic window of both hormones overlapped with the short duration (~30 min) of elevated brain glutamate following brain trauma in rodents. Similar neuroprotective effects were found after administration of the glutamate scavenger oxaloacetate, which does not affect glucose metabolism. These data indicate that insulin and glucagon exert a neuroprotective effect within a very brief therapeutic window that correlates with their capacity to reduce glutamate, rather than by modifying glucose levels.
authors.affiliation: Department of Clinical Biochemistry, Hadassah-Hebrew University Medical Center, Jerusalem, Israel. higazi@mail.med.upenn.edu
authors.forename: Rami Abu
authors.initials: RA
authors.lastname: Fanne
authors.forename: Taher
authors.initials: T
authors.lastname: Nassar
authors.forename: Samuel N
authors.initials: SN
authors.lastname: Heyman
authors.forename: Nuha
authors.initials: N
authors.lastname: Hijazi
authors.forename: Abd Al-Roof
authors.initials: AA
authors.lastname: Higazi
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism; D001921:Brain / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000134:cerebrospinal fluid / Q000188:drug therapy*; D005934:Glucagon / Q000008:administration & dosage / Q000494:pharmacology*; D018698:Glutamic Acid / Q000097:blood / Q000134:cerebrospinal fluid / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D020244:Infarction, Middle Cerebral Artery / Q000097:blood / Q000134:cerebrospinal fluid / Q000188:drug therapy* / Q000473:pathology / Q000503:physiopathology; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D018696:Neuroprotective Agents / Q000008:administration & dosage / Q000494:pharmacology*; D062907:Oxaloacetic Acid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D018696:Neuroprotective Agents; D062907:Oxaloacetic Acid; D018698:Glutamic Acid; D005934:Glucagon