Antibody-based approaches in Alzheimer's research: safety, pharmacokinetics, metabolism, and analytical tools

High morbidity, enormous socioeconomic costs, and lack of specific treatments emphasize the importance of research on protective therapies against Alzheimer's disease. The efficacy of anti-amyloid immunization strategies has been demonstrated preclinically, prompting the design of clinical studies. However, the detailed mechanisms of action of therapeutic antibodies, especially their influence on the complex amyloid beta peptide (Abeta) metabolism and various Abeta-equilibria present both within and outside the CNS, are far from being clear. Furthermore, physiological Abeta metabolism is poorly understood and the analytical tools to characterize and quantify treatment effects on Abeta metabolism are suboptimal. Thus, the design of immunization strategies with optimized benefit-to-risk ratios for patients is subjected to significant obstacles. Indeed, an active immunization trial with Abeta was discontinued because of severe adverse effects. Anti-Abeta immunization protocols designed to attain high blood levels of antibodies bear the potential to induce brain inflammation and/or hemorrhage, thus directing the biomedical research towards development of more predictable therapies for minimizing the risk of adverse effects. The focus of this review is to summarize current knowledge of Abeta metabolism under physiological and antibody-based therapeutic conditions and to introduce a promising approach, namely the passive immunization using antibody fragments, which are characterized by entirely different pharmacokinetic and pharmacodynamic properties compared with conventional monoclonal antibodies.