HDAC inhibitor increases histone H3 acetylation and reduces microglia inflammatory response following traumatic brain injury in rats

Neutralization of interleukin-1beta modifies the inflammatory response and improves histological and cognitive outcome following traumatic brain injury in mice

Interleukin-1beta (IL-1beta) may play a central role in the inflammatory response following traumatic brain injury (TBI). We subjected 91 mice to controlled cortical impact (CCI) brain injury or sham injury. Beginning 5 min post-injury, the IL-1beta neutralizing antibody IgG2a/k (1.5 microg/mL) or control antibody was infused at a rate of 0.25 microL/h into the contralateral ventricle for up to 14 days using osmotic minipumps. Neutrophil and T-cell infiltration and microglial activation was evaluated at days 1-7 post-injury. Cognition was assessed using Morris water maze, and motor function using rotarod and cylinder tests. Lesion volume and hemispheric tissue loss were evaluated at 18 days post-injury. Using this treatment strategy, cortical and hippocampal tissue levels of IgG2a/k reached 50 ng/mL, sufficient to effectively inhibit IL-1betain vitro. IL-1beta neutralization attenuated the CCI-induced cortical and hippocampal microglial activation (P < 0.05 at post-injury days 3 and 7), and cortical infiltration of neutrophils (P < 0.05 at post-injury day 7). There was only a minimal cortical infiltration of activated T-cells, attenuated by IL-1beta neutralization (P < 0.05 at post-injury day 7). CCI induced a significant deficit in neurological motor and cognitive function, and caused a loss of hemispheric tissue (P < 0.05). In brain-injured animals, IL-1beta neutralizing treatment resulted in reduced lesion volume, hemispheric tissue loss and attenuated cognitive deficits (P < 0.05) without influencing neurological motor function. Our results indicate that IL-1beta is a central component in the post-injury inflammatory response that, in view of the observed positive neuroprotective and cognitive effects, may be a suitable pharmacological target for the treatment of TBI.

Creating zinc monkey wrenches in the treatment of epigenetic disorders

The approval of suberoylanilide hydroxamic acid by the FDA for the treatment of cutaneous T-cell lymphoma in October, 2006 sparked a dramatic increase in the development of inhibitors for the class of enzymes known as the histone deacetylases (HDACs). In recent years, a large number of combination therapies involving histone deacetylase inhibitors (HDACIs) have been developed for the treatment of a variety of malignancies and neurodegenerative disorders. Promising evidence has been reported for the treatment of pancreatic cancer, prostate cancer, and leukemia as well as a number of other previously difficult to treat cancers. Drug combination approaches have also shown promise for the treatment of mood disorders including bipolar disorder and depression. In addition to these drug combination approaches, HDACIs alone have demonstrated effectiveness in the treatment of Parkinson's disease, Alzheimer's disease, Rubinstein-Taybi syndrome, Rett syndrome, Friedreich's ataxia, Huntington's disease, multiple sclerosis, anxiety, and schizophrenia. Adverse inflammatory affects observed with traumatic brain injury and arthritis have also been alleviated by treatment with certain HDACIs. Based on the diverse utility and wide range of mechanistic actions observed with this class of drugs, the future development of better drug combination therapies and more selective HDACIs is warranted.

Histone deactylase inhibition combined with behavioral therapy enhances learning and memory following traumatic brain injury

Traumatic brain injury (TBI) induces a number of pathological events ranging from neuronal degeneration and tissue loss to impaired neuronal plasticity and neurochemical dysregulation. In rodents, exposure of brain-injured animals to environmental enrichment has been shown to be an effective means of enhancing learning and memory post-injury. Recently, it has been discovered that environmental enrichment may enhance neuronal plasticity through epigenetic changes that involve enhanced histone acetylation, a property that can be mimicked by the use of histone deactylase (HDAC) inhibitors. We therefore evaluated the consequences of the HDAC inhibitor sodium butyrate on the learning and memory of brain-injured mice. In contrast to a previous report using a mouse neurodegeneration model, sodium butyrate (1.2 g/kg daily for four weeks) did not improve learning and memory when tested after the completion of the drug treatment paradigm. In addition, sodium butyrate administration during the reported period of neurodegeneration (days 0-5) also offered no benefit. However, when administered concurrently with training in the Morris water maze task (beginning on day 14 post-injury), sodium butyrate improved learning and memory in brain-injured mice. Interestingly, when these mice were subsequently tested in an associative fear conditioning task, an improvement was observed. Taken together, our findings indicate that HDAC inhibition may mimic some of the cognitive improvements seen following enriched environment exposure, and that the improvement is observed when the treatment is carried out current with behavioral testing.

Microarray based analysis of microRNA expression in rat cerebral cortex after traumatic brain injury

MicroRNAs (miRNAs) are very important regulators of biological processes such as development, cellular differentiation, and tumor generation. MiRNA microarray has been found to be a high throughput global analysis tool for detecting miRNA expression profiling, and miRNA expression profiling will facilitate the study of the biological function of miRNAs. In this report, we describe the miRNA expression level in rat cerebral cortex after traumatic brain injury using microarray method. We choose several time points post brain injury: 6 h, 24 h, 48 h and 72 h, respectively, to reveal differential expression of miRNAs in rat brain cortex compared with control groups. Our research revealed that 136 miRNAs were expressing at 6 h post injury, in which 13 miRNAs were more than 2-fold up-regulated, and 14 miRNAs were more than 2-fold down-regulated; 118 miRNAs were expressing at 24 h post injury, in which 4 miRNAs were more than 2-fold up-regulated, and 23 miRNAs were more than 2-fold down-regulated; 149 miRNAs were expressing at 48 h post injury, in which 16 miRNAs were more than 2-fold up-regulated, and 11 miRNAs were more than 2-fold down-regulated; and 203 miRNAs were expressing at 72 h post injury, in which 19 miRNAs were more than 2-fold up-regulated, and 5 miRNAs were more than 2-fold down-regulated. Furthermore, we revealed global up-regulation of miR-21 expression within all the four time points post injury. Finally, we utilized qRT-PCR methods to verify the microarray results. The qRT-PCR results indicated good consistency with the results of the microarray method. Our microarray based analysis of microRNA expression in rat cerebral cortex after traumatic brain injury has shown that some microRNA such as miR-21 could be involved in the intricate process of TBI course.

Traumatic brain injury alters expression of hippocampal microRNAs: potential regulators of multiple pathophysiological processes

Multiple cellular, molecular, and biochemical changes contribute to outcome after traumatic brain injury (TBI). MicroRNAs (miRNAs) are known to influence many important cellular processes, including proliferation, apoptosis, neurogenesis, angiogenesis, and morphogenesis, all processes that are involved in TBI pathophysiology. However, it has not yet been determined whether miRNA expression is altered after TBI. In the present study, we used a microarray platform to examine changes in the hippocampal expression levels of 444 verified rodent miRNAs at 3 and 24 hr after controlled cortical impact injury. Our analysis found 50 miRNAs exhibited decreased expression levels and 35 miRNAs exhibited increased expression levels in the hippocampus after injury. We extended the microarray findings using quantitative polymerase chain reaction analysis for a subset of the miRNAs with altered expression levels (miR-107, -130a, -223, -292-5p, -433-3p, -451, -541, and -711). Bioinformatic analysis of the predicted targets for this panel of miRNAs revealed an overrepresentation of proteins involved in several biological processes and functions known to be initiated after injury, including signal transduction, transcriptional regulation, proliferation, and differentiation. Our results indicate that multiple protein targets and biological processes involved in TBI pathophysiology may be regulated by miRNAs.

Focal nature of neurological disorders necessitates isotype-selective histone deacetylase (HDAC) inhibitors

Histone deacetylase (HDAC) inhibitors represent a promising new avenue of therapeutic options for a range of neurological disorders. Within any particular neurological disorder, neuronal damage or death is not widespread; rather, particular brain regions are preferentially affected. Different disorders exhibit distinct focal pathologies. Hence, understanding the region-specific effects of HDAC inhibitors is essential for targeting appropriate brain areas and reducing toxicity in unaffected areas. The outcome of HDAC inhibition depends on several factors, including the diversity in the central nervous system expression of HDAC enzymes, selectivity of a given HDAC inhibitor for different HDAC enzymes, and the presence or absence of cofactors necessary for enzyme function. This review will summarize brain regions associated with various neurological disorders and factors affecting the consequences of HDAC inhibition.

The many roles of histone deacetylases in development and physiology: implications for disease and therapy

Histone deacetylases (HDACs) are part of a vast family of enzymes that have crucial roles in numerous biological processes, largely through their repressive influence on transcription. The expression of many HDAC isoforms in eukaryotic cells raises questions about their possible specificity or redundancy, and whether they control global or specific programmes of gene expression. Recent analyses of HDAC knockout mice have revealed highly specific functions of individual HDACs in development and disease. Mutant mice lacking individual HDACs are a powerful tool for defining the functions of HDACs in vivo and the molecular targets of HDAC inhibitors in disease.

Therapeutic application of histone deacetylase inhibitors for central nervous system disorders

Histone deacetylases (HDACs)--enzymes that affect the acetylation status of histones and other important cellular proteins--have been recognized as potentially useful therapeutic targets for a broad range of human disorders. Pharmacological manipulations using small-molecule HDAC inhibitors--which may restore transcriptional balance to neurons, modulate cytoskeletal function, affect immune responses and enhance protein degradation pathways--have been beneficial in various experimental models of brain diseases. Although mounting data predict a therapeutic benefit for HDAC-based therapy, drug discovery and development of clinical candidates face significant challenges. Here, we summarize the current state of development of HDAC therapeutics and their application for the treatment of human brain disorders such as Rubinstein-Taybi syndrome, Rett syndrome, Friedreich's ataxia, Huntington's disease and multiple sclerosis.