How statins could be evaluated successfully in clinical trials for Alzheimer's disease?

Over the last decade, a large number of experimental observations have suggested a relationship between alterations in cholesterol homeostasis and Alzheimer's disease (AD). Moreover, epidemiological studies have pointed an association between statin treatment and a decrease in the risk of having AD. For these reasons, a large number of clinical trials have been carried out to determine whether the statins can prevent the progression of AD. However, these studies did not provide clear evidence for the therapeutic efficacy in AD. We consider that there are a number of explanations for this failure that may provide guidance for selecting and clinically developing statins with therapeutic efficacy in AD.