Beta-secretase as a target for the treatment of Alzheimer's disease

Inhibition of tumor necrosis factor-alpha-converting enzyme by a selective antagonist protects brain from focal ischemic injury in rats

Tumor necrosis factor alpha (TNFalpha) is an immunomodulatory and proinflammatory cytokine implicated in neuroinflammation and neuronal damage in response to cerebral ischemia. Tumor necrosis factor-alpha converting enzyme (TACE or ADAM17) is a key sheddase that releases TNFalpha from its inactive cell-bound precursor. Using a selective small molecule inhibitor of TACE, DPH-067517, we tested the hypothesis that inhibition of TNFalpha formation might have a salutary effect in ischemic stroke induced by embolic occlusion of the middle cerebral artery (MCAO). DPH-067517 selectively inhibited TACE enzyme activity in vitro (K(i) = 2.8 nM), and effectively suppressed ischemia-induced increase in soluble TNFalpha in brain tissue after systemic administration. DPH-067517 (3 and 30 mg/kg, i.p. administered 15 min before MCAO) produced 43% (n = 8, p = 0.16) and 58% (n = 8, p < 0.05) reduction in infarct size and 36% (p < 0.05) and 23% (p < 0.05) reduction in neurological deficits, respectively. The salutary effect of DPH-067517 in ischemic brain injury was also observed when the first dose was administrated 60 min after the onset of ischemia. Inhibition of TACE had no effect on apoptosis measured by levels of active caspase-3 expression and DNA fragmentation. Our data suggest that inhibition of TACE might be a potential therapeutic strategy for neuroprotection after focal ischemic stroke.

Efficient inhibition of β-secretase gene expression in HEK293 cells by tRNAVal-driven and CTE-helicase associated hammerhead ribozymes

The beta-amyloid peptide (Abeta) is a major component of toxic amyloid plaques found in the brains of patients with Alzheimer's disease. Abeta is liberated by sequential cleavage of amyloid precursor protein (APP) by beta- and gamma-secretases. The level of Abeta depends directly on the hydrolytic activity of beta-secretase. Therefore, beta-secretase is an excellent target for drug design. An approach based on RNA-cleaving ribozymes was developed to control expression of beta-secretase. Two sites of mRNA coding beta-site APP cleaving enzyme were chosen as target sequences for endogenously delivered ribozymes. The ribozyme cassette was designed to constitute a catalytic hammerhead core and substrate recognition arms, flanked at the 5'-terminus by tRNAVal and at the 3'-terminus by constitutive transport element sequences. Ribozyme cassettes were cloned into a pUC19 plasmid and used for transient transfection of HEK293 cells. We demonstrate that such ribozymes efficiently inhibit beta-secretase gene expression at both the mRNA (up to 95%) and the protein (up to 90%) levels. Inhibition of beta-site APP cleaving enzyme activity directly influences the intra- and extracellular population of Abeta peptide. Therefore, such ribozymes may be considered as molecular tools for silencing the beta-secretase activity, and further, as therapeutic agents for anti-amyloid treatment.