Emerging therapeutics for Alzheimer’s disease

Multifunctional 3-Schiff base-4-hydroxycoumarin derivatives with monoamine oxidase inhibition, anti-β-amyloid aggregation, metal chelation, antioxidant and neuroprotection properties against Alzheimer's disease

These 3-Schiff base-4-hydroxycoumarin derivatives were multifunctional agents with monoamine oxidase inhibition, anti-β-amyloid aggregation, metal chelation, antioxidant and neuroprotection properties against Alzheimer's disease.

Design, synthesis and biological evaluation of imine resveratrol derivatives as multi-targeted agents against Alzheimer's disease

A series of imine resveratrol derivatives (1-20) have been designed, synthesized, and evaluated as multi-targeted compounds for the treatment of Alzheimer's disease (AD). In vitro studies show that most of the molecules exhibit a significant ability to inhibit self-induced and Cu(2+)-induced β-amyloid (Aβ₁₋₄₂) aggregation, and to function as potential antioxidants and biometal chelators. In particular, compound 9 is a potential lead compound for AD treatment (for compound 9, IC₅₀ = 14.1 μM for the antioxidant activity using DPPH free radical method; 64.6% at 20 μM for self-induced Aβ aggregation). Moreover, it is capable of decreasing reactive oxygen species (ROS) induced by Cu-Aβ and shows good neuroprotective effects in human SH-SY5Y neuroblastoma cells. Taken together, these results suggest that 9 might be a promising lead compound for AD treatment.

Alzheimer’s disease, cerebrovascular disease, and the β-amyloid cascade

Alzheimer’s disease (AD), considered the commonest neurodegenerative cause of dementia, is associated with hallmark pathologies including extracellular amyloid-β protein (Aβ) deposition in extracellular senile plaques and vessels, and intraneuronal tau deposition as neurofibrillary tangles. Although AD is usually categorized as neurodegeneration distinct from cerebrovascular disease (CVD), studies have shown strong links between AD and CVD. There is evidence that vascular risk factors and CVD may accelerate Aβ 40-42 production/ aggregation/deposition and contribute to the pathology and symptomatology of AD. Aβ deposited along vessels also causes cerebral amyloid angiopathy. Amyloid imaging allows in vivo detection of AD pathology, opening the way for prevention and early treatment, if disease-modifying therapies in the pipeline show safety and efficacy. In this review, we review the role of vascular factors and Aβ, underlining that vascular risk factor management may be important for AD prevention and treatment.

Molecular Neurobiology of Depression: PET Findings on the Elusive Correlation with Symptom Severity

Molecular mechanisms in the brain are assumed to cause the symptoms and severity of neuropsychiatric disorders. This review concerns the elusive nature of relationships between the severity of depressive disorders and neuromolecular processes studied by positron emission tomography (PET). Recent PET studies of human depression have focused on serotonergic, dopaminergic, muscarinic, nicotinic, and GABAergic receptors, as well as central processes dependent on monoamine oxidase, phosphodiesterase type 4, amyloid plaques, neurofibrillar tangles, and P-glycoprotein. We find that reliable causal links between neuromolecular mechanisms and relief from depressive disorders have yet to be convincingly demonstrated. This situation may contribute to the currently limited use of PET for exploring the neuropathways that are currently viewed as being responsible for beneficial effects of antidepressant treatment regimes.

Memory restorative role of statins in experimental dementia: an evidence of their cholesterol dependent and independent actions

The study was aimed at investigating the effects of pitavastatin, simvastatin (lipophilic statins) and fluvastatin (hydrophilic statin) on memory deficits associated with Alzheimer's type dementia in mice. Dementia was induced with chronic administration of a high fat diet (HFD) or intracebroventricular streptozotocin (icv STZ, two doses of 3 mg/kg) in separate groups of animals. Memory of the animals was assessed by the Morris water maze (MWM) test. Brain thiobarbituric acid reactive species (TBARS) and reduced glutathione (GSH) levels were measured to assess total oxidative stress. Brain acetylcholinesterase (AChE) activity and total serum cholesterol levels were also measured. Icv STZ or HFD produced a significant impairment of learning and memory. Higher levels of brain AChE activity and TBARS and lower levels of GSH were observed in icv STZ- as well as HFD-treated animals. HFD-treated mice also showed a significant increase in total serum cholesterol levels. Pitavastatin and simvastatin each significantly attenuated STZ-induced memory deficits and biochemical changes; however, fluvastatin produced no significant effect on icv STZ-induced dementia or biochemical levels. Administration of any one of the three statins not only lowered HFD-induced rise in total serum cholesterol level but also attenuated HFD-induced memory deficits. Further pitavastatin and simvastatin administration also reversed HFD-induced changes in biochemicals level, while fluvastatin failed to produce any significant effect. This study demonstrates the potential of statins in memory dysfunctions associated with experimental dementia and provides evidence of their cholesterol-dependent and -independent actions.

Soybean supplementation helps reverse age- and scopolamine-induced memory deficits in mice

Phytoestrogens are nonsteroidal plant compounds that are able to exert estrogenic effects. Soybean is a rich source of phytoestrogens, especially isoflavones. Soy isoflavones are utilized for estrogen replacement therapy. Estrogen is reported to influence several areas of brain that are involved in cognition and behavior. Therefore, the present study was undertaken to examine whether dietary supplementation with soybean improves the cognitive function of mice. Soybean was administered in three different concentrations (2%, 5% and 10% [wt/wt]) in the normal diet to young and mature mice for 60 successive days. The passive avoidance paradigm and the elevated plus maze served as the exteroceptive behavioral models, whereas scopolamine (1.4 mg/kg, i.p.) served as the interoceptive behavioral model. The brain acetylcholinesterase activity (AChE) activity, brain thiobarbituric acid-reactive substances (TBARS), reduced glutathione (GSH), and total blood cholesterol levels were also measured in the present study. The administration of soybean for 60 consecutive days protected (P < .05) the animals from developing memory impairment. Soybean administration also resulted in diminished brain AChE activity, decrease in brain TBARS, and increase in GSH levels, thereby indicating facilitated cholinergic transmission, reduced free radical generation, and enhanced scavenging of free radicals. Thus, soybean appears to be a useful remedy for improving memory and for the management of cognitive deficits owing to its pro-estrogenic, antioxidant, procholinergic, and/or neuroprotective properties.

Mitochondria, cholesterol and amyloid beta peptide: a dangerous trio in Alzheimer disease

The molecular mechanisms of Alzheimer's disease (AD) are not fully understood. Extensive evidence from experimental models has involved the overgeneration and accumulation of toxic amyloid beta peptides (Abeta) in the onset and progression of the disease. The amyloidogenic processing of amyloid precursor protein into pathogenic Abeta fragments is thought to occur in specific domains of the plasma membrane and favored by cholesterol enrichment. Intracellular Abeta accumulation is known to induce oxidative stress, predominantly via mitochondria targeting of toxic Abeta. Recent evidence using mouse models of cholesterol loading has demonstrated that the specific mitochondrial cholesterol pool sensitizes neurons to Abeta-induced oxidant cell death and caspase-independent apoptosis due to selective mitochondrial GSH (mGSH) depletion induced by cholesterol-mediated perturbation of mitochondrial membrane dynamics. mGSH replenishment by permeable precursors such as glutathione ethyl ester protected against Abeta-mediated neurotoxicity and inflammation. Thus, these novel data expand the pathogenic role of cholesterol in AD indicating that in addition to fostering Abeta generation, mitochondrial cholesterol determines Abeta neurotoxicity via mGSH regulation.

Cerebrocortical beta activity in overweight humans responds to insulin detemir

BACKGROUND

Insulin stimulates cerebrocortical beta and theta activity in lean humans. This effect is reduced in obese individuals indicating cerebrocortical insulin resistance. In the present study we tested whether insulin detemir is a suitable tool to restore the cerebral insulin response in overweight humans. This approach is based on studies in mice where we could recently demonstrate increased brain tissue concentrations of insulin and increased insulin signaling in the hypothalamus and cerebral cortex following peripheral injection of insulin detemir.

METHODOLOGY/PRINCIPAL FINDINGS

We studied activity of the cerebral cortex using magnetoencephalography in 12 lean and 34 overweight non-diabetic humans during a 2-step hyperinsulinemic euglycemic clamp (each step 90 min) with human insulin (HI) and saline infusion (S). In 10 overweight subjects we additionally performed the euglycemic clamp with insulin detemir (D). While human insulin administration did not change cerebrocortical activity relative to saline (p = 0.90) in overweight subjects, beta activity increased during D administration (basal 59+/-3 fT, 1(st) step 62+/-3 fT, 2(nd) step 66+/-5, p = 0.001, D vs. HI). As under this condition glucose infusion rates were lower with D than with HI (p = 0.003), it can be excluded that the cerebral effect is the consequence of a systemic effect. The total effect of insulin detemir on beta activity was not different from the human insulin effect in lean subjects (p = 0.78).

CONCLUSIONS/SIGNIFICANCE

Despite cerebrocortical resistance to human insulin, insulin detemir increased beta activity in overweight human subjects similarly as human insulin in lean subjects. These data suggest that the decreased cerebral beta activity response in overweight subjects can be restored by insulin detemir.

Role of lipid rafts in the processing of the pathogenic prion and Alzheimer's amyloid-β proteins

The conformational conversion of the cellular form of the prion protein (PrP C) into the infectious form (PrP Sc) and the proteolytic processing of the amyloid-beta (Abeta) peptide are central pathogenetic events in the prion diseases and Alzheimer's disease, respectively. Cholesterol- and sphingolipid-rich lipid rafts have emerged as important sites for the conversion of PrP C into PrP Sc, and for the proteolytic production, degradation and aggregation of Abeta. Here, we discuss these findings and their implications for our understanding of these disease processes. In addition, the potential for rafts as sites for therapeutic intervention in prion diseases and Alzheimer's disease is considered.

Stereoselective neuroimaging in vivo

Stereoselectivity is a basic property of many neuronal processes due to the spatial features of molecules involved in neurotransmission. Today, neuroimaging procedures are available for studying stereoselectivity in the living brain. Mirror-image radiotracers are the molecular tools that are used, together with single photon emission tomography (SPECT) and positron emission tomography (PET), for studying stereoselective neuronal mechanisms. This review presents the findings obtained in those studies of cholinergic, noradrenergic, dopaminergic, serotonergic, glutamatergic, opioid, cannabinoid, and second messenger neurotransmission.

Sildenafil citrate attenuates a complex maze impairment induced by intracerebroventricular infusion of the NOS inhibitor Nomega-nitro-L-arginine methyl ester

In a previous study, our laboratory reported that sildenafil citrate, a cyclic nucleotide phosphodiesterase type 5 inhibitor, reversed a learning impairment in rats induced by systemic inhibition of nitric oxide synthase (60 mg/kg, i.p., Nomega-nitro-L-arginine methyl ester; L-NAME). To limit the peripheral effects of L-NAME and further localize the site of action of sildenafil, L-NAME (48 microg, i.c.v.) was infused bilaterally into the lateral cerebral ventricles 30 min prior to maze training. Saline or sildenafil citrate (1.5 or 3.0 mg/kg, i.p.) was administered systemically 15 min before training. Drug injections occurred 24 h after pretraining rats to avoid foot shock on a one-way active avoidance straight runway. Following drug treatment, the rats received 15 training trials on a 14-unit T-maze task that requires learning a complex sequence of turns to avoid mild foot shock. This complex maze paradigm is sensitive to aging and blockade of cholinergic, N-methyl-D-aspartate and nitric oxide signaling systems. Behavioral measures of performance included deviations from the correct pathway (errors), runtime from start to goal (latency), shock frequency and shock duration. Statistical analysis revealed that central infusion of L-NAME impaired maze performance and that sildenafil (3.0 mg/kg) significantly attenuated the impairment. These results suggest that sildenafil citrate may serve as a cognitive enhancer by modulating central nitric oxide/cGMP signal transduction following N-methyl-D-aspartate receptor activation. This pathway has been implicated in age-related cognitive decline and may be a useful target for pharmacological intervention of neurodegenerative disease.