Hyperoxic reperfusion after global cerebral ischemia promotes inflammation and long-term hippocampal neuronal death.

In this study we tested the hypothesis that long-term neuropathological outcome is worsened by hyperoxic compared to normoxic reperfusion in a rat global cerebral ischemia model. Adult male rats were anesthetized and subjected to bilateral carotid arterial occlusion plus bleeding hypotension for 10 min. The rats were randomized to one of four protocols: ischemia/normoxia (21% oxygen for 1 h), ischemia/hyperoxia (100% oxygen for 1 h), sham/normoxia, and sham/hyperoxia.

Insulin activates the PI3K-Akt survival pathway in vulnerable neurons following global brain ischemia.

Unlabelled: Insulin is neuroprotective following transient global brain ischemia; however, the mechanisms by which insulin exerts its salutary effects remain unclear.

Objective: We assessed insulin's effect on the PI3K-Akt survival system and consequent modulation of the pro-apoptotic proteins Bim, Bad and FoxO3a.

Methods: We utilized rats subjected to 10 minutes of global brain ischemia, with or without insulin administered at the onset of reperfusion.

Insulin blocks cytochrome c release in the reperfused brain through PI3-K signaling and by promoting Bax/Bcl-XL binding.

The critical event of the intrinsic pathway of apoptosis following transient global brain ischemia is the release of cytochrome c from the mitochondria. In vitro studies have shown that insulin can signal specifically via phosphatidylinositol-3-OH-kinase (PI3-K) and Akt to prevent cytochrome c release. Therefore, insulin may exert its neuroprotective effects during brain reperfusion by blocking cytochrome c release.

Characterization of the eIF2-associated protein p67 during brain ischemia and reperfusion.

Objectives: Within the first few minutes of reperfusion after global brain ischemia, there is a severe depression of protein translation owing to phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 (eIF2). There is a 67 kDa peptide (p67) that, in its glycosylated form, binds to eIF2 and protects eIF2alpha from phosphorylation. Moreover, cells with high p67 content exhibit enhanced resistance to eIF2alpha phosphorylation.

Gene expression analysis of the development of congenital hydrocephalus in the H-Tx rat.

To discover candidate genes in the pathogenesis of congenital hydrocephalus, gene arrays were utilized to analyze transcripts from the midbrain region of 5-day-old H-Tx rats; these animals develop hydrocephalus due to closure of their cerebral aqueduct between embryonic day 18 and post-natal day 5. Of the 15,924 transcripts assayed, we detected 47 differentially expressed transcripts representing 23 genes and 24 expressed sequence tags (ESTs); 17 transcripts (7 genes and 10 ESTs) were upregulated and 30 (16 genes and 14 ESTs) were downregulated in the hydrocephalic animals relative to control non-hydrocephalic animals. Seven of these genes, Cck, Nfix, Lgals3, Gsta1, Xdh, Tnf, and Tfpi-2, can be linked to hydrocephalus.

PERK is responsible for the increased phosphorylation of eIF2alpha and the severe inhibition of protein synthesis after transient global brain ischemia.

Reperfusion after global brain ischemia results initially in a widespread suppression of protein synthesis in neurons that is due to inhibition of translation initiation as a result of the phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 (eIF2). To address the role of the eIF2alpha kinase RNA-dependent protein kinase-like endoplasmic reticulum kinase (PERK) in the reperfused brain, transgenic mice with a targeted disruption of the Perk gene were subjected to 20 min of forebrain ischemia followed by 10 min of reperfusion. In wild-type mice, phosphorylated eIF2alpha was detected in the non-ischemic brain and its levels were elevated threefold after 10 min of reperfusion.

Potential modifier role of the R618Q variant of proalpha2(I)collagen in type I collagen fibrillogenesis: in vitro assembly analysis.

An arginine to glutamine substitution in the triple helix of proalpha2(I)collagen (R618Q) was first reported in a patient with a variant of Marfan syndrome and later identified in conjunction with a second mutation in a patient with osteogenesis imperfecta (OI). The presence of the R618Q proalpha2(I)collagen allele in unaffected or mildly affected family members suggests that the R618Q allele is either a non-affecting polymorphism or a potential genetic modifier. Conservation of arginine618 across species and fibrillar collagen types suggests it is functionally significant.

Status report: Development of emergency medicine research since the Macy Report.

In Williamsburg, VA, April 17 to 20, 1994, the Josiah Macy, Jr. Foundation sponsored a conference entitled "The Role of Emergency Medicine in the Future of American Medical Care," a report on which was published in Annals in 1995. This report promulgated recommendations for the development and enhancement of academic departments of emergency medicine and a conference to develop an agenda for research in emergency medicine.

Interrelationship of homocysteine-cobalamin-folate indices in human subjects of various ages: can hyper-homocyteinemia be relieved with B-12 supplementation?

Objective: To find the effect of aging, nutrition, and gender on Homocysteine-Cobalamin-Folate (HCF) Triad and to determine if B-12 supplementation decreases high levels of homocysteine.

Methods: In 192 subjects, blood indices were determined to study the relationship of HCF triad to age and gender, 28 had low holotranscobalmin (TC II), and five had low serum cobalamin. Thirty-nine of the subjects who had hyperhomocysteinemia were daily given 100 mcg B-12 for three months.

Persistent eIF2alpha(P) is colocalized with cytoplasmic cytochrome c in vulnerable hippocampal neurons after 4 hours of reperfusion following 10-minute complete brain ischemia.

Upon brain reperfusion following ischemia, there is widespread inhibition of neuronal protein synthesis that is due to phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha), which persists in selectively vulnerable neurons (SVNs) destined to die. Other investigators have shown that expression of mutant eIF2alpha (S51D) mimicking phosphorylated eIF2alpha induces apoptosis, and expression of non-phosphorylatable eIF2alpha (S51A) blocks induction of apoptosis. An early event in initiating apoptosis is the release of cytochrome c from mitochondria, and cytochrome c release corresponds to the selective vulnerability of hippocampal CA1 neurons in rats after transient global cerebral ischemia.

Dysfunction of the unfolded protein response during global brain ischemia and reperfusion.

A variety of endoplasmic reticulum (ER) stresses trigger the unfolded protein response (UPR), a compensatory response whose most proximal sensors are the ER membrane-bound proteins ATF6, IRE1alpha, and PERK. The authors simultaneously examined the activation of ATF6, IRE1alpha, and PERK, as well as components of downstream UPR pathways, in the rat brain after reperfusion after a 10-minute cardiac arrest. Although ATF6 was not activated, PERK was maximally activated at 10-minute reperfusion, which correlated with maximal eIF2alpha phosphorylation and protein synthesis inhibition.

Molecular pathways of protein synthesis inhibition during brain reperfusion: implications for neuronal survival or death.

Protein synthesis inhibition occurs in neurons immediately on reperfusion after ischemia and involves at least alterations in eukaryotic initiation factors 2 (eIF2) and 4 (eIF4). Phosphorylation of the alpha subunit of eIF2 [eIF2(alphaP)] by the endoplasmic reticulum transmembrane eIF2alpha kinase PERK occurs immediately on reperfusion and inhibits translation initiation. PERK activation, along with depletion of endoplasmic reticulum Ca2+ and inhibition of the endoplasmic reticulum Ca2+ -ATPase, SERCA2b, indicate that an endoplasmic reticulum unfolded protein response occurs as a consequence of brain ischemia and reperfusion.