Histone Deacetylase Inhibitors Exhibit Anti-Inflammatory and Neuroprotective Effects in a Rat Permanent Ischemic Model of Stroke: Multiple Mechanisms of Action

Abstract

The pathophysiology of cerebral ischemia involves multiple mechanisms including neuroinflammation mediated by activated microglia and infiltrating macrophages/monocytes. The present study employed a rat permanent middle cerebral artery occlusion (pMCAO) model to study effects of histone deacetylase (HDAC) inhibition on ischemia-induced brain infarction, neuroinflammation, gene expression, and neurological deficits. We found that post-pMCAO injections with HDAC inhibitors, valproic acid (VPA), sodium butyrate (SB), or trichostatin A (TSA), decreased brain infarct volume. Postinsult treatment with VPA or SB also suppressed microglial activation, reduced the number of microglia, and inhibited other inflammatory markers in the ischemic brain. The reduction in levels of acetylated histone H3 in the ischemic brain was prevented by treatment with VPA, SB, or TSA. Moreover, injections with HDAC inhibitors superinduced heat-shock protein 70 and blocked pMCAO-induced down-regulation of phospho-Akt, as well as ischemia-elicited up-regulation of p53, inducible nitric oxide synthase, and cyclooxygenase-2. The motor, sensory, and reflex performance of pMCAO rats was improved by VPA, SB, or TSA treatment. The beneficial effects of SB and VPA in reducing brain infarct volume and neurological deficits occurred when either drug was administrated at least 3 h after ischemic onset, and the behavioral improvement was long-lasting. Together, our results demonstrate robust neuroprotective effects of HDAC inhibitors against cerebral ischemia-induced brain injury. The neuroprotection probably involves multiple mechanisms including suppression of ischemia-induced cerebral inflammation. Given that there is no effective treatment for stroke, HDAC inhibitors, such as VPA, SB, and TSA, should be evaluated for their potential use for clinical trials in stroke patients.Stroke, also referred to as cerebral ischemia, is a pathological condition resulting from occlusion or hemorrhage of blood vessels supplying oxygen and essential nutrients to the brain. In all cases, stroke ultimately induces death and/or dysfunction of brain cells, as well as neurological impairments that reflect the location and size of the ischemic brain area. Mechanisms leading to cell death during cerebral ischemic injury are complex, including excitotoxicity, ionic imbalance, oxidative/nitrosative stress, and inflammation (for review, see Lo et al., 2003). It is increasingly recognized that cerebral inflammation mediated by activated microglia and infiltrating leukocytes, including monocytes/macrophages, also plays a key role in focal ischemia-induced neurodegeneration. Activated microglia and invading leukocytes exert a cytotoxic function by releasing proinflammatory cytokine factors (IL-1, IL-2, and TNF-␣), nitric oxide (NO), and reactive oxygen species, which contribute to brain infarction and excitotoxicity (Gregersen et al., 2000).Valproic acid (2-propylpentanoic acid sodium salt; VPA), a drug commonly used to treat seizures and bipolar mood disorder, has been...

Epigenetic Mechanisms in Cerebral Ischemia

“…Upon HDACi, neuroprotective BCL(B cell lymphoma)-2 family members, such as BCL-2 (ref. 46,47) and BCL-XL 48 are upregulated. A coordinated response is induced, which not only includes events of gene induction but also repression.…”

“…In and around the ischemic core, a general decrease of histone H3 acetylation [46][47][48][49][50] as well as of H4 acetylation levels [51][52][53][54] was identified in multiple studies. Vast deacetylation processes occur quickly upon an ischemic insult and induce a fatal course of events.…”

“…98,99 In general, the administration of either HDACi, VPA, or SB, leads to a significant suppression of microglia activation 47,53,100 and additionally to the inhibition of further inflammatory markers like monocytes and macrophages in stroke. 47 On the gene level, HDAC inhibition impacts the expression of heat shock protein (HSP)70, a heat shock/stress protein that assists proper protein folding, and is involved in inflammatory processes. Interestingly, HSP70 can show both anti-and pro inflammatory effects depending on cell type, context, and location.…”

“…As a consequence of HDACi administration, the downregulation of pro-apoptotic players such p53 (ref. 47) with its downstream actors BCL-2-associated X protein (BAX) 104 and caspase 3 (ref. 49) can be detected.…”

Dysregulated expression of miR-101b and miR-26b lead to age-associated increase in LPS-induced COX-2 expression in murine macrophage

“…Thus, age-dependent epigenetic regulation of the miRNAs and their targets may then be the very molecular force driving the age-related immune disorders. Additionally, HDAC inhibitors have emerged as potent contenders for treatment of inflammatory diseases at present (Camelo et al 2005;Halili et al 2009;Kim et al 2007). The anti-inflammatory effect of HDAC inhibitor observed in this study is more potent in the elderly.…”