These plant metabolites have been shown to ameliorate AD by increasing the expression of insulin degrading enzyme (IDE), neprilysin (NEP), PPAR-γ, and α-secretase, and decreasing the expression of β-secretase (BACE-1) to reduce the levels of Aβ oligomers (Aβ<sub>O</sub>) deposition in brain neurons.
These results are discussed in terms of the relevance of Aβ<sub>4-9</sub>, a major Cu(II) binding Aβ fragment generated by neprilysin, as a possible Cu(II) carrier in the brain.
Moreover, SRE feeding prevented elevation of the amyloid-β42 level while improving the gene expression of neprilysin and decreasing beta-site APP-cleaving enzyme 1 in the brain.
Membrane metalloendopeptidase (MME) and insulin-degrading enzyme (IDE) are two types of proteases that could cleave beta-amyloid (Aβ) peptides generated by neuron cells of AD patients.
The data obtained allowed us to conclude that the decrease in the activity of the amyloid-degrading enzyme NEP, as well as a reduction in the number of labile interneuronal contacts in the hippocampus, contribute to early cognitive deficits caused by prenatal hypoxia and that there are therapeutic avenues to restore these deficits via NEP activation which could also be used for designing preventive strategies in AD.
Overall, our results suggest sustained reduction of NEP and IDE expression in response to Pb sensitizes recovery SH-SY5Y cells to Aβ accumulation; however, administration of VPA is demonstrated to be beneficial in modulating Aβ clearance.
In the triple transgenic AD mouse model (3xTg-AD), repeated administration of 3 and 10 mg/kg of RGFP-966 reverses pathological tau phosphorylation at Thr<sup>181</sup>, Ser<sup>202</sup>, and Ser<sup>396</sup>, increases levels of the Aβ degrading enzyme Neprilysin in plasma, decreases Aβ<sub>1-42</sub> protein levels in the brain and periphery, and improves spatial learning and memory.
In the present study, we measured plasma levels of amyloid-β1-42(0.142±0.029μg/L)and furin(2.292±1.54μg/L), together with those of the metalloproteinases, insulin-degrading enzyme(1.459±1.14μg/L) and neprilysin(0.073±0.015μg/L), in order to develop biomarkers for AD.
N-terminally truncated amyloid-β42 accumulation showed significant regional association with BACE1 and neprilysin, but not PSD95 that regionally associated with full-length amyloid-β42 accumulation.
We have now extended our work and shown that, unlike NEP, another amyloid-degrading enzyme, IDE, is not related to over-expression of APP695 in neuroblastoma SH-SY5Y cells but is up-regulated by APP751 and APP770 isoforms independently of AICD but correlating with reduced HDAC1 binding to its promoter.
Previously, we have documented that prenatal hypoxia can aggravate the cognitive impairment and Alzheimer's disease (AD) neuropathology in APP(Swe) /PS1(A246E) (APP/PS1) transgenic mice, and valproic acid (VPA) can prevent hypoxia-induced down-regulation of β-amyloid (Aβ) degradation enzyme neprilysin (NEP) in primary neurons.
Presently, co-culture of human umbilical cord blood mesenchymal stem cells (hUCB-MSCs) with BV2 microglia under amyloid-β42 (Aβ42) exposure induced a reduction of Aβ42 in the medium as well as an overexpression of the Aβ-degrading enzyme neprilysin (NEP) in microglia.
An alternative model of amyloidosis utilizes intracerebroventricular infusion of thiorphan or phosphoramidon to block the activity of key Aβ degrading enzymes (NEP, NEP2) resulting in accumulation of Aβ.
Correlation analyses suggested that NEP expression was correlated with Aβ accumulation and clinical diagnosis, being lower in AD than in no cognitive impairment.
Neprilysin (NEP) is one of the rate-limiting Abeta-degrading enzymes, and its enhancement ameliorates extracellular amyloid pathology, synaptic dysfunction, and memory defects in mouse models of Abeta amyloidosis.
In vivo, DSP4-treatment decreased expression and activity of the Abeta degrading enzyme neprilysin, while in vitro NA increased phagocytosis of Abeta1-42 by microglia.
These data further support a role for neprilysin in regulating cerebral amyloid deposition and suggest that gene transfer approaches might have potential for the development of alternative therapies for Alzheimer's disease.