Beneficial Effects Of Tri-lithium Pyrroloquinoline Quinonein On Behaviors And Pathology In A Mouse Model Of Alzheimer’s Disease

Alzheimer’s disease (AD) is a devastating disease characterized by pathological alterations in the brain:amyloid plaques, neurofibrillary tangles, as well as synapse-and neuron-loss. Unfortunately, efficient disease-modifying therapies are unavailable. Because the β-amyloid (Aβ) hypothesis is supported by numerous experimental and clinical studies, current treatment strategies for AD have focused on the clearance of amyloid plaques. However, almost all the clinical trials targeted at eliminating Aβ deposit have done little to improve cognitive function. This frustrating situation has promoted us to reconsider therapeutic strategies.In this study, we synthesized a new organic lithium salt, tri-lithium pyrroloquinoline quinonein (Li3PQQ). Lithium is the first discovered and the most extensively tested the inhibitor of glycogen synthase kinase-3(GSK-3) in multiple animal models. GSK-3has been demonstrated to be involved in AD pathogenesis by modulating tau phosphorylation and Aβ production. Pyrroloquinoline quinone (PQQ) is a newly identified redox-cofactor vitamin for mammals, which not only serves to mediate redox reactions in the mitochondrial respiratory chain, but also plays a potential role in scavenging reactive oxygen species and attenuating oxidative stress in mitochondria. As a cofactor of Aβ-binding alcohol dehydrogenase (ABAD), PQQ might protect mitochondria from oxidative damage in AD. Therefore, this novel chemical Li3PQQ could exhibit powerful beneficial effects in halting AD neurodegenerative progression by targeting multiple AD-causing mechanisms.In the first part, we conducted a safety evaluation in Kuming mice by determining the acute toxicity of Li3PQQ. The median lethal doses (LD50) were shown to be5.0g/kg body weight for females and over5.0g/kg for males, which are significantly higher than those of lithium chloride (LiCl,2.5g/kg body weight).Secondly, we tested the effect of chronic treatment of Li3PQQ on learning and memory. The drug (1.5,3,6and12mg/kg body weight) was gastrically gavaged daily for8weeks to the APP/PS1mice (20-28weeks), a mouse model of AD and12mg/kg body weight was gastrically gavaged daily for8weeks to the APP/PS1mice (40-48weeks).In the Morris water maze test, mice were trained four trials per day for5days and then tested on the sixth day. We showed that mice administered with Li3PQQ (3,6and12mg/kg body weight) performed significantly better than transgenic (TG) vehicle controls in the Morris water maze learning and memory test.To further study the synaptic mechanisms underlying the enhanced learning and memory in the APP/PSl transgenic mice, we recorded field excitatory postsynaptic potentials (fEPSPs) from the CA1area of hippocampal slices. Both LiCl (100mg/kg bodyweight) and Li3PQQ (12mg/kg bodyweight) significantly increased the magnitude of TBS-induced LTP, indicating that both drugs facilitate the hippocampal synaptic plasticity of APP/PS1transgenic mice.By immunochemical staining in cortical slices, we analyzed the numbers and area of amyloid plaques in APP/PS1transgenic mice after the drug treatment. We found that chronic treatment of Li3PQQ significantly reduced both the number of amyloid plaques and area of amyloid plaques. By enzyme-linked immunosorbent assay (ELSIA) in cortex, we tested the concentration of Aβ1-42, which is known as the most harmful amyloid protein. Li3PQQ significantly reduced the concentration of Aβ1-42. Furthermore, Li3PQQ (6,12mg/kg) significantly reduced the number of the phosphorylated tau-positive cells, as shown by immunochemical staining in cortical slices. By western blotting, we found that the phosphorylation of tau in serine396was significantly reduced in the group of LiCl and Li3PQQ but not in the group of donepezil.To confirm that Li3PQQ indeed targets at ABAD and GSK-3, we tested the expression and activities of these enzymes in the cortex of the APP/PSl mice after the chronic drug treatment. We showed that Li3PQQ was effective in modulating the activities of GSK-3and ABAD in vivo. Li3PQQ at6mg/kg and12mg/kg did not affect the level of ABAD, but it dose-dependently increased the enzymatic activity of ABAD. By contrast, while Li3PQQ did not change the expression of GSK-3in the cortex of the APP/PS1mice, it dose-dependently increased the ratio of phospho-GSK-3α (Ser21)/GSK-3α and phospho-GSK-3β (Ser9)/GSK-3β. Increased phosphorylation levels of GSK-3α (Ser21) and GSK-3α (Ser9) indicate decreased activities for both enzymes. Consistently. Li3PQQ at6and12mg/kg significantly decreased the enzyme activity of total GSK-3. as well as that of GSK-3α and GSK-3β. Given that drugs against single targets are insufficient to prevent AD progression, the development of new drugs against multiple targets involved in AD pathogenesis or cocktail therapies represent an attractive approach for AD treatment. Our study showed that Li3PQQ exhibited significantly beneficial effects on behaviors and pathology through modulating multiple pathophysiological processes in a mouse model of Alzheimer’s disease.