Tacrine is an acetylcholinesterase (AChE) inhibitor used as a cognitive enhancer 
in the treatment of Alzheimer's disease (AD). However, its low therapeutic 
efficiency and a high incidence of side effects have limited its clinical use. 
In this study, the molecular mechanisms underlying the impact on brain activity 
of tacrine and two novel tacrine analogues (T1, T2) were approached by focusing 
on three aspects: (i) their effects on brain cholinesterase activity; (ii) 
perturbations on electron transport chain enzymes activities of non-synaptic 
brain mitochondria; and (iii) the role of mitochondrial lipidome changes induced 
by these compounds on mitochondrial bioenergetics. Brain effects were evaluated 
18 h after the administration of a single dose (75.6 μmol/kg) of tacrine or 
tacrine analogues. The three compounds promoted a significant reduction in brain 
AChE and butyrylcholinesterase (BuChE) activities. Additionally, tacrine was 
shown to be more efficient in brain AChE inhibition than T2 tacrine analogue and 
less active than T1 tacrine analogue, whereas BuChE inhibition followed the 
order: T1 > T2 > tacrine. The studies using non-synaptic brain mitochondria show 
that all the compounds studied disturbed brain mitochondrial bioenergetics 
mainly via the inhibition of complex I activity. Furthermore, the activity of 
complex IV is also affected by tacrine and T1 treatments while FoF(1) -ATPase is 
only affected by tacrine. Therefore, the compounds' toxicity as regards brain 
mitochondria, which follows the order: tacrine >> T1 > T2, does not correlate 
with their ability to inhibit brain cholinesterase enzymes. Lipidomics 
approaches show that phosphatidylethanolamine (PE) is the most abundant 
phospholipids (PL) class in non-synaptic brain mitochondria and cardiolipin (CL) 
present the greatest diversity of molecular species. Tacrine induced significant 
perturbations in the mitochondrial PL profile, which were detected by means of 
changes in the relative abundance of phosphatidylcholine (PC), PE, 
phosphatidylinositol (PI) and CL and by the presence of oxidized 
phosphatidylserines. Additionally, in both the T1 and T2 groups, the lipid 
content and molecular composition of brain mitochondria PL are perturbed to a 
lesser extent than in the tacrine group. Abnormalities in CL content and the 
amount of oxidized phosphatidylserines were associated with significant 
reductions in mitochondrial enzymes activities, mainly complex I. These results 
indicate that tacrine and its analogues impair mitochondrial function and 
bioenergetics, thus compromising the activity of brain cells.