Pharmacological Induction of Ischemic Tolerance by Glutamate Transporter-1 (EAAT2) Upregulation

Abstract

Background and Purpose-Astrocytic glutamate transporter protein, GLT-1 (EAAT2), recovers extracellular glutamate and ensures that neurons are protected from excess stimulation. Recently, ␤-lactam antibiotics, like ceftriaxone (CTX), were reported to induce the upregulation of GLT-1. Here, we investigated ischemic tolerance induction by CTX in an experimental model of focal cerebral ischemia. Methods-CTX (200 mg/kg per day, IP) was administered for 5 consecutive days before transient focal ischemia, which was induced by intraluminal thread occlusion of the middle cerebral artery for 90 minutes or permanently. Results-Repeated CTX injections enhanced GLT-1 mRNA and protein expressions after 3 and 5 days of treatment, respectively. CTX-pretreated animals showed a reduction in infarct volume by 58% (reperfusion) and 39% (permanent), compared with the vehicle-pretreated animals at 24 hours postischemia (PϽ0.01). Lower doses of CTX (20 mg/kg per day and 100 mg/kg per day) reduced infarct volumes to a lesser degree. The injection of GLT-1 inhibitor (dihydrokainate) at 30 minutes before ischemia ameliorated the effect of CTX pretreatment. However, CTX administration at 30 minutes after ischemia produced no significant reduction in infarct volume. CTX reduced the levels of proinflammatory cytokines (tumor necrosis factor-␣, FasL), matrix metalloproteinase (MMP)-9, and activated caspase-9 (PϽ0.01). In addition, CTX-pretreated animals showed better functional recovery at day 1 to week 5 after ischemia (PϽ0.05). Conclusions-This study presents evidence that CTX induces ischemic tolerance in focal cerebral ischemia and that this is mediated by GLT-1 upregulation. (Stroke. 2007;38:177-182.)

Targeting Astrocytes for Stroke Therapy

“…The CFX treatment reduced stroke volume and increased EAAT2 expression in this paradigm. 65 This CFX-mediated protection was reversed by a selective EAAT2 inhibitor, suggesting that the protection was mediated by EAAT2 function. However, because CFX induces the expression of the transcription factors NF-B and Nrf2, CFX may protect against cell death through multiple mechanisms.…”

“…66,67 In contrast to its administration before stroke, administration of CFX 30 minutes after the onset of ischemia did not significantly reduce stroke volume. 65 This lack of protection is not surprising, given that glutamate excitotoxicity is such an early event after onset of ischemia. Moreover, astrocytes experiencing severe energy failure could release more glutamate if EAAT is expressed at a higher level.…”

Pre-ischemic Treatment with Ampicillin Reduces Neuronal Damage in the Mouse Hippocampus and Neostriatum after Transient Forebrain Ischemia

“…Huber et al (1999) reported that in vitro pre-treatment with ampicillin (1 h before hypoxia) induces an increase in cellular hypoxic tolerance. It has also been reported that pre-treatment with ceftriaxone, one of the β-lactam antibiotics, exerts a neuroprotective effect in in vivo and in vitro models of brain ischemia and stroke (Chu et al, 2007;Lipski et al, 2007). Taken together, these data suggest that pre-ischemic treatment with ampicillin acts as a chemical pre- conditioning agent, resulting in the prevention of the ischemic neuronal damage induced by transient global forebrain ischemia.…”

“…Consistent with this dominant role of GLT-1, a GLT-1 knockout mouse showed increased susceptibility to acute forebrain injury (Watase et al, 1998). It has also been demonstrated that β-lactam antibiotics are potent stimulators of GLT-1 expression (Rothstein et al, 2005), and previous studies have reported that ceftriaxone, one of the β-lactam antibiotics, exerted a neuroprotective effect on ischemic injury in in vivo and in vitro experiments (Rothstein et al, 2005;Chu et al, 2007;Ouyang et al, 2007). However, whether ampicillin, another β-lactam antibiotic, protects brain tissue against ischemic damage remains to be determined.…”

“…The major forebrain astroglial glutamate transporter, GLT-1, plays an essential role in removing the glutamate that rapidly increases in the synaptic cleft within several minutes of ischemia/reperfusion (Anderson & Swanson, 2000;Rao et al, 2001;Swanson et al, 2004). It has been suggested that the neuroprotective effect of β-lactam antibiotics in vivo and in vitro is mediated by the induction of GLT-1 (Ji et al, 2005;Rothstein et al, 2005;Chu et al, 2007;Lipski et al, 2007;Lee et al, 2008). For instance, ceftriaxone, one of β-lactam antibiotics, induced upregulation of GLT-1 transduction and transcription along with the reduction of the mRNA levels of matrix metalloproteinase-9, tumor necrosis factor α and Fas ligand, thereby prevented neuronal cell death in an experimental stroke model (Chu et al, 2007).…”