Pharmacologic management of Alzheimer disease, Part I: Hormonal and emerging investigational drug therapies

Selenothymidine protects against biochemical and behavioral alterations induced by ICV-STZ model of dementia in mice

The present study evaluated the neuroprotective effects of one selenium-containing AZT derivative compound (S1073) in memory and learning impairment caused by Intracerebroventricular-streptozotocin (ICV-STZ). ICV-STZ in mice causes impairment of energy metabolism with oxidative damage and cholinergic dysfunction, and provides a relevant model for sporadic dementia of Alzheimer's type (AD). Acetylcolinesterase (AChE), Catalase (CAT), dichlorofluorescein oxidation (DCFH), TBARS and thiol content were measured. Swiss adult mice were pre-treated with S1073 [1 mmol/kg] (i.p.) and after 30 min of the injection received a bilateral dose of STZ [11.3 μmol/l]. After 8 days' STZ injection, we performed the behavioral experiments (Beaker test, Open field and Morris water maze task). ICV-STZ caused significant learning and memory impairments, which were significantly improved by S1073 pre-treatment. A significant increase in cerebral DFCH, TBARS levels and AChE activity and a disturbance in the memory and learning were observed in ICV-STZ injected animals. S1073 significantly ameliorated all alterations induced by ICV-STZ in mice. All these findings support the neuroprotective role of S1073 in mice model of Alzheimer's dementia-type induced by ICV-STZ, which may be associated with its antioxidant activity and/or with its inhibitory effect in brain AChE. In fact, in silico analysis indicated that S1073 may be an inhibitor of AChE.

Agmatine improves cognitive dysfunction and prevents cell death in a streptozotocin-induced Alzheimer rat model

PURPOSE

Alzheimer's disease (AD) results in memory impairment and neuronal cell death in the brain. Previous studies demonstrated that intracerebroventricular administration of streptozotocin (STZ) induces pathological and behavioral alterations similar to those observed in AD. Agmatine (Agm) has been shown to exert neuroprotective effects in central nervous system disorders. In this study, we investigated whether Agm treatment could attenuate apoptosis and improve cognitive decline in a STZ-induced Alzheimer rat model.

MATERIALS AND METHODS

We studied the effect of Agm on AD pathology using a STZ-induced Alzheimer rat model. For each experiment, rats were given anesthesia (chloral hydrate 300 mg/kg, ip), followed by a single injection of STZ (1.5 mg/kg) bilaterally into each lateral ventricle (5 μL/ventricle). Rats were injected with Agm (100 mg/kg) daily up to two weeks from the surgery day.

RESULTS

Agm suppressed the accumulation of amyloid beta and enhanced insulin signal transduction in STZ-induced Alzheimer rats [experimetal control (EC) group]. Upon evaluation of cognitive function by Morris water maze testing, significant improvement of learning and memory dysfunction in the STZ-Agm group was observed compared with the EC group. Western blot results revealed significant attenuation of the protein expressions of cleaved caspase-3 and Bax, as well as increases in the protein expressions of Bcl2, PI3K, Nrf2, and γ-glutamyl cysteine synthetase, in the STZ-Agm group.

CONCLUSION

Our results showed that Agm is involved in the activation of antioxidant signaling pathways and activation of insulin signal transduction. Accordingly, Agm may be a promising therapeutic agent for improving cognitive decline and attenuating apoptosis in AD.

Endocrine and metabolic changes in human aging

Numerous alterations in hormonal secretion occur with aging. In general, these tend towards a disintegration of the normal cyclic secretory patterns resulting in lower total circulating levels. In addition, declines in receptors and postreceptor function further decreases the ability of the hormonal orchestra to maintain coordinated function throughout the organism. Clues to some of these age-related changes in humans may come from the study of simpler organisms where regulatory systems are known to modulate the aging process. In particular, the interactions among the environment, hormones, and insulin receptor genes have led to new insights into the genetic control of longevity and the development of syndrome X.

The n-terminal 5-MER peptide analogue P165 of amyloid precursor protein exerts protective effects on SH-SY5Y cells and rat hippocampus neuronal synapses

The disturbance of the insulin-signaling pathway plays an important role in Alzheimer's disease. Resistance to insulin signaling renders neurons energy-deficient and vulnerable to oxidization or other metabolic insults and impairs synaptic plasticity. In search of neuroprotective drugs, we synthesized a peptide analogue, P165, an active domain of the soluble amyloid precursor protein, which is resistant to degradation and is suitable for oral administration in a clinical setting. Initially, we confirmed that P165 can protect cells from streptozotocin-caused damage and stimulate cell outgrowth using cultured SH-SY5Y cell lines treated with streptozotocin. P165 significantly reduced lactate dehydrogenase leakage from damaged cells, thereby rescuing cell energy production. Insulin signaling such as insulin receptor substrate-1 (IRS-1) and phosphoinositide 3-kinase (PI3K) proteins were upregulated to stimulate cell survival and growth. We proceeded to investigate the effect of P165 on streptozotocin-treated Alzheimer's disease (AD) rats. The data showed that P165 protected synaptic loss and dysfunction by increasing synaptophysin and PSD-95 (post synaptic density-95), while simultaneously decreasing α-synuclein expression. Moreover, animal behavior testing clearly showed that P165 increased rats' learning and memory activity. Overall, these results constitute evidence that peptide analogue 165 may protect synapse and improve learning and memory ability in AD.

Protective effect of quercetin against intracerebral streptozotocin induced reduction in cerebral blood flow and impairment of memory in mice

The aim of the present study is to investigate the effect of quercetin, a naturally occurring flavonoid, on cerebral blood flow (CBF), brain energy metabolism, memory impairment, oxidative stress and cholinergic dysfunction in brain following intracerebral (i.c.) streptozotocin (STZ) administration in mice. STZ (0.5mg/kg, i.c.) was administered twice at an interval of 48h. We found a significant reduction in CBF as measured by Laser Doppler Flowmetry (LDF). The brain energy metabolism was also altered as evidenced by significant reduction in brain ATP content. Daily treatment with quercetin (2.5, 5 and 10mg/kg, p.o.) starting from the first dose of STZ showed a dose-dependent restoration of CBF and ATP content. Further, quercetin prevented STZ induced memory impairment as assessed by Morris water maze and passive avoidance tests. Biochemical analysis revealed that STZ significantly increased malondialdehyde (MDA), nitrite and depleted glutathione (GSH) levels in the mice brain. Quercetin decreased oxidative and nitrosative stress as evidenced by a significant decrease in MDA, nitrite and increase in GSH levels. Quercetin also attenuated elevated acetylcholinesterase activity in the STZ-treated mice. Neither STZ (i.c.) nor quercetin showed any change in locomotor activity and blood glucose level. The present study demonstrates the beneficial effects of quercetin in improving CBF along with preventing memory impairment, oxidative stress, altered brain energy metabolism and cholinergic dysfunction caused by STZ in mice. Therefore, consumption of dietary stuff rich in quercetin should be encouraged to ward off dementia associated with vascular and neurodegenerative disorders.

Candesartan improves memory decline in mice: involvement of AT1 receptors in memory deficit induced by intracerebral streptozotocin

The Renin-angiotensin system, besides blood pressure regulation, affects learning and memory as evidenced by improvement of cognition in hypertensive patients being treated with AT1 receptor blockers like candesartan. The present study examined the influence of candesartan on memory impairment induced by intracerebral streptozotocin (IC STZ 0.5 mg/kg) in mice. Candesartan (0.05 mg/kg and 0.1 mg/kg, i.p.) was given for 14 days following IC STZ administration. The dose of 0.1 mg/kg significantly improved latency period in passive avoidance test. Further, treatment with 0.1 mg/kg candesartan for 14 days significantly improved spatial memory in mice in water maze test also. In another group, after memory impairment in mice following IC STZ administration, memory improving effect of a 7 days treatment with 0.1 mg/kg candesartan lasted only for 3 subsequent days in water maze task. IC STZ increased oxidative stress but pretreatment with 0.1 mg/kg candesartan decreased oxidative stress as indicated by a decrease in MDA and increase in GSH. Further, candesartan decreased free radicals as evidenced by flow cytometry. IC STZ affected cholinergic system also by increasing acetylcholine esterase activity that was restored by pretreatment with 0.1 mg/kg candesartan. Locomotor activity and serum glucose level remained unaffected by candesartan treatment. These results suggest that AT1 receptors play a facilitatory role in STZ induced memory deficit and corroborate number of human studies that AT1 receptor blockers can be used therapeutically against cognitive decline in hypertensive patients.

The possible role of vitamin K deficiency in the pathogenesis of Alzheimer's disease and in augmenting brain damage associated with cardiovascular disease

The incidence of Alzheimer's disease (AD) increases with age and in carriers of the apolipoprotein E4 genotype. A relative deficiency of vitamin K, affecting the extrahepatic functions of the vitamin, is common in ageing men and women. The concentration of vitamin K is lower in the circulating blood of APOE4 carriers than in that of persons with other APOE genotypes. Evidence is accumulating that vitamin K has important functions in the brain, including the regulation of sulfotransferase activity and the activity of a growth factor/tyrosine kinase receptor (Gas 6/Axl). The hypothesis is now proposed that vitamin K deficiency contributes to the pathogenesis of AD and that vitamin K supplementation may have a beneficial effect in preventing or treating the disease. Vitamin K may also reduce neuronal damage associated with cardiovascular disease.