Oxidative stress and redox regulation on hippocampal-dependent cognitive functions

Hippocampal-dependent cognitive functions rely on production of new neurons and maintenance of dendritic structures to provide the synaptic plasticity needed for learning and formation of new memories. Hippocampal formation is exquisitely sensitive to patho-physiological changes, and reduced antioxidant capacity and exposure to low dose irradiation can significantly impede hippocampal-dependent functions of learning and memory by reducing the production of new neurons and alter dendritic structures in the hippocampus. Although the mechanism leading to impaired cognitive functions is complex, persistent oxidative stress likely plays an important role in the SOD-deficient and radiation-exposed hippocampal environment. Aging is associated with increased production of pro-oxidants and accumulation of oxidative end products. Similar to the hippocampal defects observed in SOD-deficient mice and mice exposed to low dose irradiation, reduced capacity in learning and memory, diminishing hippocampal neurogenesis, and altered dendritic network are universal in the aging brains. Given the similarities in cellular and structural changes in the aged, SOD-deficient, and radiation-exposed hippocampal environment and the corresponding changes in cognitive decline, understanding the shared underlying mechanism will provide more flexible and efficient use of SOD deficiency or irradiation to model age-related changes in cognitive functions and identify potential therapeutic or intervention methods.

Treatment of olecranon fractures with 2.4- and 2.7-mm plating techniques

OBJECTIVES

To evaluate the outcomes of olecranon fractures treated with 2.4- and 2.7-mm plate constructs.

DESIGN

Retrospective Case Series.

SETTING

One-level 1 trauma center and 1 tertiary care hospital.

PATIENTS

Thirty-five consecutive patients meeting inclusion criteria.

INTERVENTION

A 2.7- or 2.4-mm reconstruction plate was placed on the dorsal ulnar cortex and contoured to allow passage of either a 2.7- or 3.5-mm intramedullary screw. In 9 patients, additional plates were required to control comminution. Available computed tomographic (CT) scans were evaluated for the presence of comminution.

MAIN OUTCOME MEASUREMENTS

Average Disabilities of the Arm, Shoulder, and Hand (DASH) and Mayo Elbow Performance Score (MEPS).

RESULTS

All fractures were united. Average extension deficit was 4.2 degrees, and average flexion angle was 137.4 degrees. Outcome scores were completed by 94% (33/35) of study patients. Average DASH score was 6.6, and average MEPS score was 94.5. Implants were removed in 18 patients. In the cohort of patients with CT scans, 6 of the 7 fractures thought to be simple on plain film analysis were found to have occult comminution on CT scan.

CONCLUSIONS

Comminution should be considered in all olecranon fractures, even when plain films display simple patterns; although this did not affect treatment in this series of plated patients, it may be important if selecting tension band wiring. Fixation with 2.4- and 2.7-mm plates addresses comminution in olecranon fractures, avoiding the pitfalls of tension band wiring. In patients with completed outcome scores, 97% (32/33) reported their outcomes as good or excellent according to the MEPS.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Delayed administration of alpha-difluoromethylornithine prevents hippocampus-dependent cognitive impairment after single and combined injury in mice

Radiation exposure due to radiological terrorism and military circumstances are a continuing threat for the civilian population. In an uncontrolled radiation event, it is likely that there will be other types of injury involved, including trauma. While radiation combined injury is recognized as an area of great significance, overall there is a paucity of information regarding the mechanisms underlying the interactions between irradiation and other forms of injury, or what countermeasures might be effective in ameliorating such changes. The objective of this study was to determine if difluoromethylornithine (DFMO) could reduce the adverse effects of single or combined injury if administered beginning 24 h after exposure. Eight-week-old C57BL/J6 young-adult male mice received whole-body cesium-137 ((137)Cs) irradiation with 4 Gy. Immediately after irradiation, unilateral traumatic brain injury was induced using a controlled cortical impact system. Forty-four days postirradiation, animals were tested for hippocampus-dependent cognitive performance in the Morris water maze. After cognitive testing, animals were euthanized and their brains snap frozen for immunohistochemical assessment of neuroinflammation (activated microglia) and neurogenesis in the hippocampal dentate gyrus. Our data show that single and combined injuries induced variable degrees of hippocampus-dependent cognitive dysfunction, and when given 24 h post trauma, DFMO treatment ameliorated those effects. Cellular changes including neurogenesis and numbers of activated microglia were generally not associated with the cognitive changes. Further analyses also revealed that DFMO increased hippocampal protein levels of the antioxidants thioredoxin 1 and peroxiredoxin 3 compared to vehicle treated animals. While the mechanisms responsible for the improvement in cognition after DFMO treatment are not yet clear, these results constitute a basis for further development of DFMO as a countermeasure for ameliorating the of risks for cognitive dysfunction in individuals subjected to trauma and radiation combined injury.

Effects of altered levels of extracellular superoxide dismutase and irradiation on hippocampal neurogenesis in female mice

PURPOSE

Altered levels of extracellular superoxide dismutase (EC-SOD) and cranial irradiation have been shown to affect hippocampal neurogenesis. However, previous studies were only conducted in male mice, and it was not clear if there was a difference between males and females. Therefore, female mice were studied and the results compared with those generated in male mice from an earlier study.

METHODS AND MATERIALS

Female wild-type, EC-SOD-null (KO), and EC-SOD bigenic mice with neuronal-specific expression of EC-SOD (OE) were subjected to a single dose of 5-Gy gamma rays to the head at 8 weeks of age. Progenitor cell proliferation, differentiation, and long-term survival of newborn neurons were determined.

RESULTS

Similar to results from male mice, EC-SOD deficiency and irradiation both resulted in significant reductions in mature newborn neurons in female mice. EC-SOD deficiency reduced long-term survival of newborn neurons whereas irradiation reduced progenitor cell proliferation. Overexpression of EC-SOD corrected the negative impacts from EC-SOD deficiency and irradiation and normalized the production of newborn neurons in OE mice. Expression of neurotrophic factors brain-derived neurotrophic factor and neurotrophin-3 were significantly reduced by irradiation in wild-type mice, but the levels were not changed in KO and OE mice even though both cohorts started out with a lower baseline level.

CONCLUSION

In terms of hippocampal neurogenesis, EC-SOD deficiency and irradiation have the same overall effects in males and females at the age the studies were conducted.

Paradoxical relationship between Mn superoxide dismutase deficiency and radiation-induced cognitive defects

Radiation therapy of the CNS, even at low doses, can lead to deficits in neurocognitive functions. Reduction in hippocampal neurogenesis is usually, but not always, associated with cognitive deficits resulting from radiation therapy. Generation of reactive oxygen species is considered the main cause of radiation-induced tissue injuries, and elevated levels of oxidative stress persist long after the initial cranial irradiation. Consequently, mutant mice with reduced levels of the mitochondrial antioxidant enzyme, Mn superoxide dismutase (MnSOD or Sod2), are expected to be more sensitive to radiation-induced changes in hippocampal neurogenesis and the related functions. In this study, we showed that MnSOD deficiency led to reduced generation of immature neurons in Sod2−/+ mice even though progenitor cell proliferation was not affected. Compared to irradiated Sod2+/+ mice, which showed cognitive defects and reduced differentiation of newborn cells towards the neuronal lineage, irradiated Sod2−/+ mice showed normal hippocampal-dependent cognitive functions and normal differentiation pattern for newborn neurons and astroglia. However, we also observed a disproportional decrease in newborn neurons in irradiated Sod2−/+ following behavioral studies, suggesting that MnSOD deficiency may render newborn neurons more sensitive to stress from behavioral trainings following cranial irradiation. A positive correlation between normal cognitive functions and normal dendritic spine densities in dentate granule cells was observed. The data suggest that maintenance of synaptic connections, via maintenance of dendritic spines, may be important for normal cognitive functions following cranial irradiation.

Isoflurane prevents delayed cell death in an organotypic slice culture model of cerebral ischemia

BACKGROUND

General anesthetics reduce neuronal death caused by focal cerebral ischemia in rodents and by in vitro ischemia in cultured neurons and brain slices. However, in intact animals, the protective effect may enhance neuronal survival for only several days after an ischemic injury, possibly because anesthetics prevent acute but not delayed cell death. To further understand the mechanisms and limitations of volatile anesthetic neuroprotection, the authors developed a rat hippocampal slice culture model of cerebral ischemia that permits assessment of death and survival of neurons for at least 2 weeks after simulated ischemia.

METHODS

Survival of CA1, CA3, and dentate gyrus neurons in cultured hippocampal slices (organotypic slice culture) was examined 2-14 days after 45 min of combined oxygen-glucose deprivation at 37 degrees C (OGD). Delayed cell death was serially measured in each slice by quantifying the binding of propidium iodide to DNA with fluorescence microscopy.

RESULTS

Neuronal death was greatest in the CA1 region, with maximal death occurring 3-5 days after OGD. In CA1, cell death was 80 +/- 18% (mean +/- SD) 3 days after OGD and was 80-100% after 1 week. Death of 70 +/- 16% of CA3 neurons and 48 +/- 28% of dentate gyrus neurons occurred by the third day after OGD. Both isoflurane (1%) and the N-methyl-D-aspartate antagonist MK-801 (10 microm) reduced cell death to levels similar to controls (no OGD) for 14 days after the injury. Isoflurane also reduced cell death in CA1 and CA3 caused by application of 100 but not 500 microm glutamate. Cellular viability (calcein fluorescence) and morphology were preserved in isoflurane-protected neurons.

CONCLUSIONS

In an in vitro model of simulated ischemia, 1% isoflurane is of similar potency to 10 microm MK-801 in preventing delayed cell death. Modulation of glutamate excitotoxicity may contribute to the protective mechanism.

[Refractures following metal removal. A follow up of surgically treated tibial shaft fractures]

This study presents the follow-up of 187 patients with 194 diaphyseal fractures of the tibia (20% open), which were operated upon between 1980 and 1984 at our institution. We were mainly interested in the question of refractures after implant removal. The majority of fractures (98.79%) had no complications after removal of the implants, but 2 patients (1.03%) sustained another fracture of the same leg between 4 and 19 months after plate removal. Both are considered to be "true" refractures, as the new fracture occurred at the original fracture site. In one case the plate was removed far too early (9 months after the initial ORIF) and no warning or additional cast was given. Two other patients sustained a new fracture at different sites 4 and 7 years after the original surgery, respectively. The possible reasons for refractures as well as the best way to prevent them are discussed.

Distribution and elimination of coated polymethyl [2-14C]methacrylate nanoparticles after intravenous injection in rats

Surfactant-coated polymethyl [2-14C]methacrylate nanoparticles had significantly different time-course distribution patterns in rats than noncoated and albumin-coated particles. Blood concentrations of poloxamer 188-coated particles were 70-fold higher after 30 min, and the particles persisted at higher levels in the circulation for up to 2 h. The initial and final liver levels were significantly lower (38% after 30 min, 51% after 7 d) and spleen levels were significantly higher (21% after 30 min, 23% after 7 d) than non-coated particles (74% in the liver and 5% in the spleen after 7 d) and the albumin-coated particles (84% in the liver and 5% in the spleen after 7 d). Specific activity was somewhat higher for the surfactant-coated particles in other organs such as the lungs, kidneys, testicles, ovaries, and lymph nodes. The bovine serum albumin sorption behavior of polymethyl methacrylate nanoparticles was followed under various conditions, and adsorption was found to increase with increasing protein concentration and increasing temperature, reaching a maximum at the isoelectric point of pH 4.9 after approximately 12 h of incubation. The zeta potential of the particles decreased with increasing pH, and the change was more pronounced with the albumin-coated particles.