Reverting Metabolic Dysfunction in Cortex and Cerebellum of APP/PS1 Mice, a Model for Alzheimer's Disease by Pioglitazone, a Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) Agonist.

Identification of molecular mechanisms underlying early-stage Alzheimer's disease (AD) is important for the development of new therapies against and diagnosis of AD. In this study, gas chromatography time-of-flight mass spectrometry (GC-TOF-MS)-based metabolomics approach was employed to investigate the metabolic profiles in plasma and brain tissues harvested from 5-month-old APP/PS1 transgenic mice and their wildtype counterparts. Since different brain regions were expected to have their own distinct metabolic signals, four different brain regions, namely cortex, hippocampus, midbrain and cerebellum tissues, were dissected and had their metabolic profiles studied separately. Biochemical assays were also performed on plasma and brain cortex tissue of transgenic mice and wildtype mice, with a focus on mitochondrial health. Amyloid precursor protein and amyloid-ß levels in plasma, brain cortex tissue and mitochondria fractions isolated from brain cortex were measured to assess the amyloid pathology. Our findings include the observation of extensive metabolic alterations in cortex and cerebellum of APP/PS1 mice, but not in their hippocampus, midbrain and plasma. The major pathways affected in cortex and cerebellum of APP/PS1 mice were closely related to impaired energy metabolism and perturbation of amino acid metabolism in these mice. APP/PS1 mice also exhibited higher amyloid-ß40 and amyloid-ß42 in their cortex, accumulation of mitochondria APP in their cortex, and presented an altered oxidative state in their brain. Treatment with the peroxisome proliferator-activated receptor gamma (PPARγ) agonist pioglitazone (PIO) successfully restored the energy metabolism, lowered amyloid-ß levels and afforded the APP/PS1 mice a better antioxidative capacity in their cortex.

Influence of drug transporters and stereoselectivity on the brain penetration of pioglitazone as a potential medicine against Alzheimer's disease.

Pioglitazone is currently undergoing clinical trials for treatment of Alzheimer's disease (AD). However, poor brain penetration remains an obstacle to development of the drug for such intended clinical uses. In this study, we demonstrate that the inhibition of P-glycoprotein (P-gp) significantly increases brain penetration of pioglitazone, whereas inhibition of breast cancer resistance protein (BCRP) has little effect. We also investigate the stereoselectivity of pioglitazone uptake in the brain. When mice were dosed with racemic pioglitazone, the concentration of (+)-pioglitazone was 46.6% higher than that of (-)-pioglitazone in brain tissue and 67.7% lower than that of (-)-pioglitazone in plasma. Dosing mice with pure (+)-pioglitazone led to a 76% increase in brain exposure levels compared to those from an equivalent dose of racemic pioglitazone. Pure (+)-pioglitazone was also shown to have comparable amyloid-lowering capabilities to the racemic pioglitazone in an in vitro AD model. These results suggest that P-gp may act as a stereoselective barrier to prevent pioglitazone entry into the brain. Dosing with (+)-pioglitazone instead of the racemic mixture may result in higher levels of brain exposure to pioglitazone, thus potentially improving the development of pioglitazone treatment of AD.

Metabolic profiling of CHO-AßPP695 cells revealed mitochondrial dysfunction prior to amyloid-ß pathology and potential therapeutic effects of both PPARγ and PPARα Agonisms for Alzheimer's disease.

In this study, we performed gas chromatography time-of-flight mass spectrometry (GC-TOFMS)-based extracellular metabolic profiling on AßPP-transfected CHO cells (CHO-AßPP695) and its wildtype. Orthogonal partial least squares discriminant analysis (OPLS-DA) was then used to identify discriminant metabolites, which gave clues on the effects of AßPP transgene on cellular processes. To confirm the hypotheses generated based on the metabolic data, we performed biochemical assays to gather further evidence to support our findings. The OPLS-DA showed a robust differentiation following 24 h of incubation (Q2(cum) = 0.884) and 15 discriminant metabolites were identified. In contrast, extracellular Aß42 was identified to increase significantly in CHO-AßPP695 only after incubation for 48 h. The observed 24-h metabolic fluxes were associated with increased mitochondrial AßPP and reduced mitochondrial viabilities, which occurred before extracellular Aß accumulation. We also investigated the therapeutic potential of peroxisome proliferator-activated receptor gamma (PPARγ) agonists, namely rosiglitazone (RSG) and pioglitazone (PIO), by employing the same approach to characterize the metabolic profiles of CHO-AßPP695 treated with RSG and PIO, with or without their respective receptor blockers. Treatment with PIO was found to reduce the perturbation of the discriminant metabolites in CHO-AßPP695 to a larger extent than treatment with RSG. We also attributed the PIO effects on the lowering of Aß42, and restoration of mitochondrial activity to PPARγ and PPARα agonism, respectively. Taken together, PIO was demonstrated to be therapeutically superior to RSG. Our findings provide further insights into early disease stages in this AßPP model, and support the advancement of PIO in AD therapy.