Currently available drugs against Alzheimer's disease (AD) target cholinergic and glutamatergic neurotransmissions without affecting the underlying disease process. Putative disease-modifying drugs are in development and target β-amyloid (Aβ) peptide and tau protein, the principal neurophatological hallmarks of the disease. Areas covered: Phase III clinical studies of emerging anti-Aβ drugs for the treatment of AD were searched in US and EU clinical trial registries and in the medical literature until May 2016. Expert opinion: Drugs in Phase III clinical development for AD include one inhibitor of the β-secretase cleaving enzyme (BACE) (verubecestat), three anti-Aβ monoclonal antibodies (solanezumab, gantenerumab, and aducanumab), an inhibitor of receptor for advanced glycation end products (RAGE) (azeliragon) and the combination of cromolyn sodium and ibuprofen (ALZT-OP1). These drugs are mainly being tested in subjects during early phases of AD or in subjects at preclinical stage of familial AD or even in asymptomatic subjects at high risk of developing AD. The hope is to intervene in the disease process when it is not too late. However, previous clinical failures with anti-Aβ drugs and the lack of fully understanding of the pathophysiological role of Aβ in the development of AD, put the new drugs at substantial risk of failure.

The amyloid hypothesis (AH) is still the most accepted model to explain the pathogenesis of inherited Alzheimer's disease (IAD). However, despite the neuropathological overlapping with the non-inherited form (NIAD), AH waver in explaining NIAD. Thus, 30 years after its first statement several questions are still open, mainly regarding the role of amyloid plaques (AP) and apolipoprotein E (APOE). Accordingly, a pathogenetic model including the role of AP and APOE unifying IAD and NIAD pathogenesis is still missing. In the present understanding of the AH, we suggested that amyloid-␤ (A␤) peptides production and AP formation is a physiological aging process resulting from a systemic age-related decrease in the efficiency of the proteins catabolism/clearance machinery. In this pathogenetic model A␤ peptides act as neurotoxic molecules, but only above a critical concentration [A␤] c . A threshold mechanism triggers IAD/NIAD onset only when [A␤] ≥ [A␤] c . In this process, APOE modifies [A␤] c threshold in an isoform-specific way. Consequently, all factors influencing A␤ anabolism, such as amyloid beta precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) gene mutations, and/or A␤ catabolism/clearance could contribute to exceed the threshold [A␤] c , being characteristic of each individual. In this model, AP formation does not depend on [A␤] c . The present interpretation of the AH, unifying the pathogenetic theories for IAD and NIAD, will explain why AP and APOE4 may be observed in healthy aging and why they are not the cause of AD. It is clear that further studies are needed to confirm our pathogenetic model. Nevertheless, our suggestion may be useful to better understand the pathogenesis of AD.

The recent failure of several clinical trials on anti-β-amyloid (Aβ) drugs in Alzheimer's disease (AD) suggested earlier intervention in the disease course. Secondary prevention trials have been started in autosomal-dominant AD (ADAD) individuals without cognitive dysfunction and in cognitively healthy subjects at risk of developing sporadic AD (SAD). Areas covered: Herein, the authors discuss prevention trials in ADAD and SAD, with a focus on the anti-Aβ monoclonal antibodies solanezumab and gantenerumab presently in Phase III clinical development. These therapies are also being tested in the Dominantly Inherited Alzheimer's Network Trials Unit (DIAN-TU). Expert opinion: Anti-Aβ monoclonal antibodies are being tested in subjects at the preclinical stage of ADAD and even in symptom-free subjects at risk of developing SAD. The subsequent DIAN-TU Adaptive Prevention Trial is a 4-year study that will assess whether such biomarker effects may stop the progress of the AD process, preventing cognitive symptoms. The hope is to interfere in the disease course when it is not too late. A clinical success of these prevention trials would represent the proof of the Aβ hypothesis of AD.