ATP-binding cassette transporter A1 mediates the beneficial effects of the liver X receptor agonist GW3965 on object recognition memory and amyloid burden in amyloid precursor protein/presenilin 1 mice.

The cholesterol transporter ATP-binding cassette transporter A1 (ABCA1) moves lipids onto apolipoproteins including apolipoprotein E (apoE), which is the major cholesterol carrier in the brain and an established genetic risk factor for late-onset Alzheimer disease (AD). In amyloid mouse models of AD, ABCA1 deficiency exacerbates amyloidogenesis, whereas ABCA1 overexpression ameliorates amyloid load, suggesting a role for ABCA1 in Aß metabolism. Agonists of liver X receptors (LXR), including GW3965, induce transcription of several genes including ABCA1 and apoE, and reduce Aß levels and improve cognition in AD mice. However, the specific role of ABCA1 in mediating beneficial responses to LXR agonists in AD mice is unknown. We evaluated behavioral and neuropathogical outcomes in GW3965-treated female APP/PS1 mice with and without ABCA1. Treatment of APP/PS1 mice with GW3965 increased ABCA1 and apoE protein levels. ABCA1 was required to observe significantly elevated apoE levels in brain tissue and cerebrospinal fluid upon therapeutic (33 mg/kg/day) GW3965 treatment. At 33 mg/kg/day, GW3965 was also associated with a trend toward redistribution of Aß to the carbonate-soluble pool independent of ABCA1. APP/PS1 mice treated with either 2.5 or 33 mg/kg/day of GW3965 showed a clear trend toward reduced amyloid burden in hippocampus and whole brain, whereas APP/PS1-treated mice lacking ABCA1 failed to display reduced amyloid load in the whole brain and showed trends toward increased hippocampal amyloid. Treatment of APP/PS1 mice with either dose of GW3965 completely restored novel object recognition memory to wild-type levels, which required ABCA1. These results suggest that ABCA1 contributes to several beneficial effects of the LXR agonist GW3965 in APP/PS1 mice.

Mechanisms of cerebral edema in traumatic brain injury: therapeutic developments.

PURPOSE OF REVIEW: Although a number of factors contribute to the high mortality and morbidity associated with traumatic brain injury (TBI), the development of cerebral edema with brain swelling remains the most significant predictor of outcome. The present review summarizes the most recent advances in the understanding of mechanisms associated with development of posttraumatic cerebral edema, and highlights areas of therapeutic promise. RECENT FINDINGS: Despite the predominance of cytotoxic (or cellular) edema in the first week after traumatic brain injury, brain swelling can only occur with addition of water to the cranial vault from the vasculature. As such, regulation of blood-brain barrier permeability has become a focus of recent research seeking to manage brain edema. Aquaporins, matrix metalloproteinases and vasoactive inflammatory agents have emerged as potential mediators of cerebral edema following traumatic brain injury. In particular, kinins (bradykinins) and tachykinins (substance P) seem to play an active physiological role in modulating blood-brain barrier permeability after trauma. Substance P neurokinin-1 receptor antagonists show particular promise as novel therapeutic agents. SUMMARY: Attenuating blood-brain barrier permeability has become a promising approach to managing brain edema and associated swelling given that increases in cranial water content can only be derived from the vasculature. Inflammation, both classical and neurogenic, offers a number of attractive targets.

Validation of reference genes for normalization of real-time quantitative RT-PCR data in traumatic brain injury.

Careful validation of reference genes used for the normalization of real-time RT-PCR data is required to obtain accurate results regarding gene expression. We evaluated the stability of seven commonly used reference genes in the cerebral cortex and hippocampus of rats 3 days following traumatic brain injury (TBI). HPRT, SDHA, and GUSB were found to be the most stable reference genes in the cerebral cortex, whereas B2MG, TBP, and GAPDH were the most stable in the hippocampus. The use of three reference genes was determined to be the optimal number for accurate normalization of data. To illustrate this point, when our gene of interest, substance P (SP), was normalized against the three most stable reference genes in both brain areas, we found no significant difference between injured and uninjured rats at the 3-day time point. However, when our SP data were normalized to each reference gene individually, SP mRNA level was highly variable depending on the reference gene chosen. The results of the present study highlight the importance of validating reference genes to be used for real-time RT-PCR analysis. The use of the most stable reference genes presented here will allow more accurate normalization of gene expression data in TBI.

Substance P in traumatic brain injury.

Recent evidence has suggested that neuropeptides, and in particular substance P (SP), may play a critical role in the development of morphological injury and functional deficits following acute insults to the brain. Few studies, however, have examined the role of SP, and more generally, neurogenic inflammation, in the pathophysiology of traumatic brain injury and stroke. Those studies that have been reported suggest that SP is released following injury to the CNS and facilitates the increased permeability of the blood brain barrier, the development of vasogenic edema and the subsequent cell death and functional deficits that are associated with these events. Inhibition of the SP activity, either through inhibition of the neuropeptide release or the use of SP receptor antagonists, have consistently resulted in profound decreases in edema formation and marked improvements in functional outcome. The current review summarizes the role of SP in acute brain injury, focussing on its properties as a neurotransmitter and the potential for SP to adversely affect outcome.

Downregulation of amyloid precursor protein (APP) expression following post-traumatic cyclosporin-A administration.

The aim of these studies was to assess and quantitate the effects of cyclosporin-A (CyA) on brain APP messenger RNA and neuronal perikaryal APP antigen expression following controlled focal head impact in sheep. Impact results in a significant increase in both APP mRNA and neuronal perikaryal APP antigen expression. Post-traumatic administration of CyA (intrathecal 10 mg/kg) resulted in a reduction in APP mRNA and neuronal perikaryal antigen expression. At 2 h postinjury, CyA treatment caused a statistically significant (p < 0.05) 1.3 +/- 0.1-fold decrease in APP mRNA in the central gray matter of impacted sheep compared to untreated impacted sheep. A more profound reduction in APP mRNA synthesis (1.6 +/- 0.2 fold) was evident at 6 h (p < 0.05). The mean percentage brain area with APP immunoreactive neuronal perikarya at 6 h post-injury was 94.5% in untreated impacted animals, 10.0% in CyA-treated impacted animals, 5.5% in untreated nonimpacted animals, and 6% in CyA-treated non-impacted controls. These results demonstrate that CyA has a downregulatory effect on increased APP expression caused by TBI.

A substance P antagonist reduces axonal injury and improves neurologic outcome when administered up to 12 hours after traumatic brain injury.

Previous studies have demonstrated that the compound N-acetyl-L-tryptophan (NAT) reduces brain edema and improves functional outcome following traumatic brain injury (TBI). In this study we examined whether this effect was mediated via the neurokinin-1 receptor, and whether there was an effect on axonal injury. We also explored whether the compound was effective, even when administered at delayed time points. Male Sprague-Dawley rats were subject to acceleration-induced, diffuse TBI and administered NAT, its inactive D-enantiomer, or saline vehicle. In contrast to NAT (2.5 mg/kg), the inactive D-enantiomer was ineffective at improving rotarod motor performance after TBI. NAT also improved cognitive outcome as assessed by the Morris water maze and novel object recognition tests, and reduced axonal injury at 5 and 24 h after TBI as assessed by amyloid precursor protein immunohistochemistry. However, efficacy of the membrane-impermeable NAT was limited to administration within 5 h, whereas administration of a form of NAT, L-732,138 (47 mg/kg), in which a trifluoromethyl benzyl ester group has been added, making it highly lipid soluble and able to cross the intact blood-brain barrier, significantly improved motor outcome, even when administration was delayed by as much as 12 h. We conclude that the neuroprotective effects of NAT are receptor-mediated, and that administration of the membrane-permeable form of the compound can be effective even up to 12 h after TBI.

Substance P is associated with the development of brain edema and functional deficits after traumatic brain injury.

Brain edema and swelling is a critical factor in the high mortality and morbidity associated with traumatic brain injury (TBI). Despite this, the mechanisms associated with its development are poorly understood and interventions have not changed in over 30 years. Although neuropeptides and neurogenic inflammation have been implicated in peripheral edema formation, their role in the development of central nervous system edema after brain trauma has not been investigated. This study examines the role of the neuropeptide, substance P (SP), in the development of edema and functional deficits after brain trauma in rats. After severe diffuse TBI in adult male rats, neuronal and perivascular SP immunoreactivity were increased markedly. Perivascular SP colocalized with exogenously administered Evans blue, supporting a role for SP in vascular permeability. Inhibition of SP action by administration of the neurokinin-1 (NK1) antagonist, N-acetyl-L-tryptophan, at 30 mins after trauma attenuated vascular permeability and edema formation. Administration of the NK1 antagonist also improved both motor and cognitive neurologic outcomes. These findings suggest that SP release is integrally linked to the increased vascular permeability and edema formation after brain trauma, and that treatment with an NK1 receptor antagonist reduces edema and improves neurologic outcome.