Shawn N. Whitehead

Vascular risk factors and Alzheimer’s disease

Vascular cognitive impairment risk factors include stroke, hypertension, diabetes and atherosclerosis. In the elderly, vascular risk factors occur in the presence of high levels of amyloid in the aging brain. Stroke alters the clinical expression of a given load of Alzheimer’s disease (AD) pathology. Experimentally, large vessel infarcts or small striatal infarcts are larger in the presence of amyloid. Patients with minor cerebral infarcts and moderate AD lesions will develop the clinical manifestations of dementia. Moreover, there is also an association between other vascular risk factors and the clinical expression of cognitive decline and dementia. The risk of AD is increased in subjects with adult-onset diabetes mellitus, hypertension, atherosclerotic disease and atrial fibrillation. Experimentally, small striatal infarcts in the presence of high levels of amyloid in the brain exhibit a progression in infarct size over time with enhanced degree of cognitive impairment, AD-type pathology and neuroinflammation compared with striatal infarcts or high amyloid levels alone.

Progressive Increase in Infarct Size, Neuroinflammation, and Cognitive Deficits in the Presence of High Levels of Amyloid

Background and Purpose— In the elderly, cerebral ischemia (CI) occurs in the presence of high levels of amyloid. Neuroinflammation plays a critical role in the pathophysiology of Alzheimer’s disease and CI. This study examined infarct size, neuroinflammation, and cognitive deficits over time in rat models of Alzheimer’s disease and CI. Methods— &bgr;-amyloid toxicity was modeled using bilateral intracerebroventricular injections of &bgr;-amyloid 25 to 35 peptides. CI was modeled using unilateral injections of the potent vasoconstrictor, endothelin-1, into the striatum. Results— Infarct volumes were higher in the presence of amyloid and compared with the CI model alone. In the CI model alone, the infarct volume was significantly smaller 28 days after surgery compared with 7 days after surgery. However, when Alzheimer’s disease and CI models were combined, the infarct volume was significantly larger 28 days after surgery compared with 7 days after surgery. The neuroinflammation in the region of the infarct was also significantly increased. The Barnes circular platform test showed time-dependent increases in memory and learning deficits in the &bgr;-amyloid-treated rats that were even greater when &bgr;-amyloid treatment was combined with CI. Conclusions— CI in the presence of high levels of amyloid results in progressive increases in infarct size, neuroinflammation, and cognitive deficits.

Amyloid-β42 signals tau hyperphosphorylation and compromises neuronal viability by disrupting alkylacylglycerophosphocholine metabolism

Perturbation of lipid second messenger networks is associated with the impairment of synaptic function in Alzheimer disease. Underlying molecular mechanisms are unclear. Here, we used an unbiased lipidomic approach to profile alkylacylglycerophosphocholine second messengers in diseased tissue. We found that specific isoforms defined by a palmitic acid (16:0) at the sn-1 position, namely 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16:0 PAF) and 1-O-hexadecyl-sn-glycero-3-phosphocholine (C16:0 lyso-PAF), were elevated in the temporal cortex of Alzheimer disease patients, transgenic mice expressing human familial disease-mutant amyloid precursor protein, and human neurons directly exposed to amyloid-β42 oligomers. Acute intraneuronal accumulation of C16:0 PAF but not C16:0 lyso-PAF initiated cyclin-dependent kinase 5-mediated hyperphosphorylation of tau on Alzheimer disease-specific epitopes. Chronic elevation caused a caspase 2 and 3/7-dependent cascade resulting in neuronal death. Pharmacological inhibition of C16:0 PAF signaling, or molecular strategies increasing hydrolysis of C16:0 PAF to C16:0 lyso-PAF, protected human neurons from amyloid-β42 toxicity. Together, these data provide mechanistic insight into how disruptions in lipid metabolism can determine neuronal response to accumulating oligomeric amyloid-β42.

Interaction Between a Rat Model of Cerebral Ischemia and β-Amyloid Toxicity Inflammatory Responses

Background and Purpose— Clinical data suggest that Alzheimer disease (AD) and stroke together potentiate cognitive impairment. Inflammatory mechanisms are involved in AD pathology and stroke and may be the mediator between AD and stroke toxicity. Methods— AD was modeled by cerebroventricular injections of &bgr;-amyloid (A&bgr;[25–35]) and subcortical lacunar infarcts by striatal endothelin injections. Inflammatory mechanisms were examined using immunohistochemical analysis. Memory and motor tasks were assessed using the Montoya staircase test. Results— A&bgr; injections elicited increases in pathological and inflammatory correlates of AD in multiple forebrain sites. Increases in astrocytosis and reactive microglia in the hippocampus were enhanced with the combination of endothelin and A&bgr;(25–35). A&bgr;(25–35) treatment decreased performance in the Montoya staircase behavioral test. Conclusions— The enhanced inflammatory response with A&bgr; toxicity and ischemia may mediate the inability to improve behavioral performance caused by the stroke. Anti-inflammatory treatment may ameliorate the pathological and behavioral deficits associated with the combination of AD and stroke.

Antihypertensive treatment can prevent stroke and cognitive decline

Hypertension is a highly prevalent risk factor for stroke and dementia, and is the greatest risk factor for small-vessel disease—a frequent cause of lacunar infarction and intracerebral haemorrhage. Lacunar and cortical strokes contribute to the development of dementia in patients with, and in those without, Alzheimer disease pathology; this relationship between stroke and dementia is probably mediated by ischaemia-induced neuroinflammation. Antihypertensive treatment can reduce the risk of stroke and dementia, but requires optimal blood pressure targets to be established for individual patients. Although the rate of treatment and control of hypertension has improved markedly over the past two decades, many physicians remain reluctant to prescribe antihypertensive medication to elderly patients owing to potential adverse events such as cardiovascular morbidity and postural hypotension. In this article we argue that, in patients of all ages, not treating hypertension is a missed opportunity to prevent some of the most prevalent brain diseases.

HIV protease inhibitors modulate apoptosis signaling in vitro and in vivo

HIV protease inhibitors are an integral part of effective anti-HIV therapy. The drugs block HIV protease, prevent proper packaging of HIV virions, and decrease the HIV viral burden in the peripheral blood of infected individuals. In addition to direct anti-viral effects, the HIV protease inhibitors also modulate apoptosis. A growing body of work demonstrates the anti-apoptotic effects of HIV protease inhibitors on CD4+ and CD8+ T cells during HIV infection. The mechanism of this apoptosis inhibition is supported by several proposed hypotheses for how they alter the fate of the cell, including preventing adenine nucleotide translocator pore function, which consequently prevents loss of mitochondrial transmembrane potential. More recently, the anti-apoptotic effects of the HIV protease inhibitors have been tested in non-HIV, non-immune cell, whereby protease inhibitors prevent apoptosis, and disease in animal models of sepsis, hepatitis, pancreatitis and stroke. Interestingly, when HIV protease inhibitors are used at supra-therapeutic concentrations, they exert pro-apoptotic effects. This has been demonstrated in a number of tumor models. Although it is unclear how HIV protease inhibitors can induce apoptosis at increased concentrations, future research will define the targets of the immunomodulation and reveal the full clinical potential of this intriguing class of drugs.

Interaction Between a Rat Model of Cerebral Ischemia and β-Amyloid Toxicity II. Effects of Triflusal

Background and Purpose— Clinical data suggest that Alzheimer disease (AD) and stroke together potentiate cognitive impairment. Our rat model demonstrates that this interaction may be mediated through inflammatory cells and pathways. Thus, anti-inflammatory agents such as Triflusal, a nonsteroidal anti-inflammatory agent (NSAID), may provide neuroprotection for susceptible neurons in AD and cerebral ischemia. Methods— AD was modeled by cerebroventricular injections of &bgr;-amyloid (A&bgr;25–35) and subcortical lacunar infarcts by striatal endothelin injections. Inflammatory mechanisms were examined by immunohistochemical analysis. Behavioral tasks were assessed with the Montoya staircase test. Results— Triflusal reduced pathologic and inflammatory markers and functional deficits in rats receiving A&bgr; or endothelin alone but was less effective in the more severe pathology of the combined A&bgr;/endothelin model. Conclusions— Higher doses or more prolonged treatment with NSAIDs may be required for more effective neuroprotection in combined AD and stroke conditions.

Differential regulation of wild-type and mutant alpha-synuclein binding to synaptic membranes by cytosolic factors

BackgroundAlpha-Synuclein (α-syn), a 140 amino acid protein associated with presynaptic membranes in brain, is a major constituent of Lewy bodies in Parkinsons disease (PD). Three missense mutations (A30P, A53T and E46K) in the α-syn gene are associated with rare autosomal dominant forms of familial PD. However, the regulation of α-syns cellular localization in neurons and the effects of the PD-linked mutations are poorly understood.ResultsIn the present study, we analysed the ability of cytosolic factors to regulate α-syn binding to synaptic membranes. We show that co-incubation with brain cytosol significantly increases the membrane binding of normal and PD-linked mutant α-syn. To characterize cytosolic factor(s) that modulate α-syn binding properties, we investigated the ability of proteins, lipids, ATP and calcium to modulate α-syn membrane interactions. We report that lipids and ATP are two of the principal cytosolic components that modulate Wt and A53T α-syn binding to the synaptic membrane. We further show that 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16:0 PAF) is one of the principal lipids found in complex with cytosolic proteins and is required to enhance α-syn interaction with synaptic membrane. In addition, the impaired membrane binding observed for A30P α-syn was significantly mitigated by the presence of protease-sensitive factors in brain cytosol.ConclusionThese findings suggest that endogenous brain cytosolic factors regulate Wt and mutant α-syn membrane binding, and could represent potential targets to influence α-syn solubility in brain.

Comorbid Rat Model of Ischemia and β-Amyloid Toxicity: Striatal and Cortical Degeneration

Levels of cerebral amyloid, presumably β‐amyloid (Abeta), toxicity and the incidence of cortical and subcortical ischemia increases with age. However, little is known about the severe pathological condition and dementia that occur as a result of the comorbid occurrence of this vascular risk factor and Abeta toxicity. Clinical studies have indicated that small ischemic lesions in the striatum are particularly important in generating dementia in combination with minor amyloid lesions. These cognitive deficits are highly likely to be caused by changes in the cortex. In this study, we examined the viability and morphological changes in microglial and neuronal cells, gap junction proteins (connexin43) and neuritic/axonal retraction (Fer Kinase) in the striatum and cerebral cortex using a comorbid rat model of striatal injections of endothelin‐1 (ET1) and Abeta toxicity. The results demonstrated ventricular enlargement, striatal atrophy, substantial increases in β‐amyloid, ramified microglia and increases in neuritic retraction in the combined models of stroke and Abeta toxicity. Changes in connexin43 occurred equally in both groups of Abeta‐treated rats, with and without focal ischemia. Although previous behavioral tests demonstrated impairment in memory and learning, the visual discrimination radial maze task did not show significant difference, suggesting the cognitive impairment in these models is not related to damage to the dorsolateral striatum. These results suggest an insight into the relationship between cortical/striatal atrophy, pathology and functional impairment.

Triflusal reduces cerebral ischemia induced inflammation in a combined mouse model of Alzheimer's disease and stroke.

Clinical data has shown that stroke exacerbates dementia in Alzheimers disease (AD) patients. Previous work, combining rat models of AD and stroke have shown that neuroinflammation may be the common mediator between AD and stroke toxicity. This study examined the effects of triflusal (2-acetoxy-4-trifluoromethylbenzoic acid) in APP(23) transgenic mice receiving strokes. Six month-old APP(23) mice over-expressing mutant human amyloid precursor protein (APP) were used to model AD in this study. Unilateral injections of a potent vasoconstrictor, endothelin-1, into the striatum were used to mimic small lacunar infarcts. Immunohistochemical analysis was performed to examine AD-like pathology and inflammatory correlates of stroke and AD. APP(23) mice showed increases in AD-like pathology and inflammatory markers of AD in the cortex and hippocampus. Endothelin-induced ischemia triggered an inflammatory response along with increases in AD pathological markers in the region of the infarct. Triflusal reduced inflammation surrounding the endothelin-induced infarct only. At the dose used, anti-inflammatory treatment may be beneficial in reducing the AD and inflammatory correlates of stroke in a combined AD-stroke mouse model.