Cyclooxygenase-2 activity following traumatic brain injury in the developing rat.

Cyclooxygenase (COX) is the rate-limiting enzyme in the production of prostaglandins. COX-2, the predominant COX isoform in brain, is induced by synaptic activity. COX-2-generated prostaglandins are important regulators for a range of activities under physiologic conditions. However, under pathologic conditions, COX-2 activity can produce reactive oxygen species and toxic prostaglandin metabolites that can exacerbate brain injury. In this study, we examine the developmental production of COX-2 and test the ability of a COX-2 inhibitor, SC58125, to attenuate traumatic brain injury in developing rats. We show that constitutive COX-2 concentration is low (0.5-fold adult concentration) during the first postnatal week and then increases to 3-fold of adult levels between days 14-60. Controlled cortical impact (CCI) at postnatal day (PND) 17, but not PND 7, caused an additional 3-fold increase in COX-2 content and was associated with an increase in the COX-2 product PGE2. Treatment with the COX-2 inhibitor SC58125 in PND17 rats exposed to CCI attenuated the rise in PGE2 but did not attenuate lesion volume or improve performance in the Morris water maze.

Preconditioning suppresses inflammation in neonatal hypoxic ischemia via Akt activation.

BACKGROUND AND PURPOSE: Hypoxic preconditioning (PC) confers robust neuroprotection against neonatal hypoxic-ischemic brain injury (H-I), yet the underlying mechanism is poorly understood. In the adult brain, neuronal survival after ischemia is associated with the activation of the phosphatidylinositol 3-kinase (PI3-K)/Akt signaling pathway. Suppression of inflammation is a newly identified direct consequence of PI3-K/Akt signaling. We therefore investigated whether PI3-K/Akt suppresses inflammation and contributes to PC-induced neuroprotection. METHODS: Postnatal day 7 rats were exposed for 3 hours to either ambient air or 8% oxygen, which induces hypoxic PC. H-I was produced 24 hours later by unilateral carotid artery ligation followed by 2.5 hours of hypoxia. Animals were euthanized 0 to 24 hours later for detecting Akt and glycogen synthetase kinase-3beta phosphorylation (p-Akt, p-GSK-3beta), 24 hours later for assessing cytokine expression and inflammatory markers, and 7 days later for measuring brain tissue loss. In addition, LY294002 was injected intracerebroventricularly to inhibit PI3-K/Akt. RESULTS: Brains with H-I without PC showed delayed but sustained reduction in p-Akt. PC restored the levels of p-Akt and the Akt substrate GSK-3beta, reduced proinflammatory markers (NF-kappaB, COX-2, CD68, myeloperoxidase, and microglial activation), and markedly ameliorated H-I-induced brain tissue loss. Inhibition of PI3-K/Akt using LY294002 attenuated PC neuroprotection and promoted the expression of NF-kappaB, COX-2, and CD68. Proteomic microarray analysis revealed that PC inhibited expression of proinflammatory cytokines induced by H-I or a dose of lipopolysaccharide that resulted in minimal tissue damage. CONCLUSIONS: Suppression of inflammatory responses may contribute to PC neuroprotection against neonatal H-I brain injury. This effect is mediated in part via upregulating PI3-K/Akt activity.

Preterminal gasping during hypoxic cardiac arrest increases cardiac function in immature rats.

Newborn animals are more resistant to anoxia than older animals, partly due to an increased tolerance of the immature heart to anoxia. Newborn animals also have a more robust preterminal gasp. We investigated the relationship between gasping and cardiac function in immature and maturing rats exposed to anoxia. Immature postnatal day 7 (PND7) rats (n = 13) and maturing PND17 rats (n = 13) were exposed to 100% nitrogen (anoxia) for 10 min. Echocardiography was used to calculate cardiac contractility (CC) by left ventricular shortening fraction and cardiac output (CO) from Doppler velocity recordings of pulmonary artery blood flow. In a separate group of PND7 rats, CC and CO were recorded after the paralytic agent pancuronium was used to prevent gasping. Anoxia decreased CC and CO in PND7 and PND17 rats, followed by a partial and transient recovery. Gasping preceded recovery of CO and was required to sustain CO. Gasping in PND7 rats lasted longer (541 s versus 351 s, p < 0.01) and resulted in a greater recovery of CC and CO. Anoxia-induced gasping and the associated recovery of cardiac function were abolished by paralysis. Thus, anoxia-induced gasping transiently improves cardiac function, and more robust gasping in immature rats is associated with increased cardiac anoxic tolerance.

TAT-mediated delivery of Bcl-xL protein is neuroprotective against neonatal hypoxic-ischemic brain injury via inhibition of caspases and AIF.

Systemic delivery of recombinant Bcl-xL fusion protein containing the TAT protein transduction domain attenuated neonatal brain damage following hypoxic ischemia (H-I). Within 30 min after intraperitoneal injection of TAT-Bcl-xL protein into 7-day-old rats, substantially enhanced levels of Bcl-xL were found in several brain regions. Administration of TAT-Bcl-xL at the conclusion of the H-I insult decreased cerebral tissue loss in a dose-dependent manner measured 1 and 8 weeks later. Neuroprotection provided by TAT-Bcl-xL was significantly greater than that of the pan-caspase inhibitor BAF, suggesting that protection is only partially attributable to caspase inhibition by TAT-Bcl-xL. TAT-Bcl-xL not only inhibited caspases-3 and -9 activities after H-I but also prevented nuclear translocation of AIF. Taken together, these results substantiate the feasibility of peripheral delivery of an anti-apoptotic factor into the brain of neonatal animals to reduce H-I-induced brain injury.