Molecular mechanisms underlying disruptions in brain glucose uptake and metabolism, linked with cognitive decline in Alzheimer’s disease (AD) patients, are only partially understood. This study investigated how soluble amyloid beta (sAβ) peptides affect glucose transport at the blood-brain barrier (BBB), the primary portal for glucose entry into the brain. We demonstrated that [ ¹⁸ F]-fluorodeoxyglucose ( ¹⁸ FDG) uptake is reduced in sAβ overproducing APP,PS1 transgenic mice compared to wild-type mice. Moreover, the influx rate of ¹⁸ FDG decreased in sAβ40 or sAβ42 pre-infused mice, highlighting the inhibitory effect of sAβ peptides on glucose transport at the BBB. Consistently, the expression of GLUT1, the primary glucose transporter at the BBB, is reduced in polarized human cerebral microvascular endothelial cell (hCMEC/D3) monolayers upon exposure to sAβ peptides and in Aβ-laden cerebral vasculature in vivo. The study further examined the influence of sAβ on the insulin-AKT pathway, known to regulate glucose uptake through modulation of thioredoxin-interacting protein (TXNIP) expression. Results showed that sAβ peptides suppress AKT phosphorylation and reduce GLUT1 expression by upregulating TXNIP levels in hCMEC/D3 monolayers. Co-incubation of resveratrol with sAβ peptides reduced TXNIP expression and rectified reductions in GLUT1 expression. In summary, toxic sAβ impairs BBB glucose transport by disrupting the insulin/AKT/TXNIP axis.

Blood-brain barrier (BBB) dysfunction is prevalent in Alzheimer’s disease and other neurological disorders. Restoring normal BBB function through RNA therapy is a potential avenue for addressing cerebrovascular changes in these disorders that may lead to cognitive decline. Although lipid nanoparticles have been traditionally used as drug carriers for RNA, bicelles have been emerging as a better alternative because of their higher cellular uptake and superior transfection capabilities. Cationic bicelles composed of DPPC/DC₇PC/DOTAP at molar ratios of 63.8/25.0/11.2 were evaluated for the delivery of RNA in polarized hCMEC/D3 monolayers, a widely used BBB cell culture model. RNA-bicelle complexes were formed at five N/P ratios (1:1 to 5:1) by a thin-film hydration method. The RNA-bicelle complexes at N/P ratios of 3:1 and 4:1 exhibited optimal particle characteristics for cellular delivery. The cellular uptake of cationic bicelles laced with 1 mol% DiI-C18 was confirmed by flow cytometry and confocal microscopy. The ability of cationic bicelles (N/P ratio 4:1) to transfect polarized hCMEC/D3 with FITC-labeled control siRNA was tested vis-a-vis commercially available Lipofectamine RNAiMAX. These studies demonstrated the higher transfection efficiency and greater potential of cationic bicelles for RNA delivery to the BBB endothelium.

Plasma pharmacokinetic (PK) data is required as an input function for graphical analysis of single positron emission computed tomography/computed tomography (SPECT/CT) and positron emission tomography/CT (PET/CT) data to evaluate tissue influx rate of radiotracers. Dynamic heart imaging data is often used as a surrogate of plasma PK. However, accumulation of radiolabel in the heart tissue may cause overprediction of plasma PK. Therefore, we developed a compartmental model, which involves forcing functions to describe intact and degraded radiolabeled proteins in plasma and their accumulation in heart tissue, to deconvolve plasma PK of ¹²⁵I-amyloid beta 40 (¹²⁵I-Aβ₄₀) and ¹²⁵I-insulin from their dynamic heart imaging data. The three-compartment model was shown to adequately describe the plasma concentration-time profile of intact/degraded proteins and the heart radioactivity time data obtained from SPECT/CT imaging for both tracers. The model was successfully applied to deconvolve the plasma PK of both tracers from their naïve datasets of dynamic heart imaging. In agreement with our previous observations made by conventional serial plasma sampling, the deconvolved plasma PK of ¹²⁵I-Aβ₄₀ and ¹²⁵I-insulin in young mice exhibited lower area under the curve than aged mice. Further, Patlak plot parameters extracted using deconvolved plasma PK as input function successfully recapitulated age-dependent blood-to-brain influx kinetics changes. Therefore, the compartment model developed in this study provides a novel approach to deconvolve plasma PK of radiotracers from their noninvasive dynamic heart imaging. This method facilitates the application of preclinical SPECT/PET imaging data to characterize distribution kinetics of tracers where simultaneous plasma sampling is not feasible. Significance Statement Knowledge of plasma pharmacokinetics (PK) of a radiotracer is necessary to accurately estimate its blood-to-brain influx. However, simultaneous plasma sampling during dynamic imaging procedures is not always feasible. In the current study, we developed approaches to deconvolve plasma PK from dynamic heart imaging data of two model radiotracers, ¹²⁵I-Aβ40 and ¹²⁵I-insulin. This novel method is expected to minimize the need for conducting additional plasma PK studies and allow for accurate estimation of the brain influx rate.

Disruptions in glucose uptake and metabolism in the brain are implicated in metabolic disorders and Alzheimer’s disease (AD). Toxic soluble amyloid-beta (sAß) peptides accumulating in the brain and plasma of AD patients were suggested to promote blood-brain barrier (BBB) dysfunction, brain hypometabolism, and cognitive decline. Exposure to sAß peptides is reported to interfere with glucose metabolism in the brain parenchyma, although their effects on the BBB have not been fully characterized. Our data showed that the brain uptake of glucose surrogate, [ ¹⁸ F]-fluorodeoxyglucose ( ¹⁸ FDG), was reduced significantly in APP/PS1 transgenic mice (overproduce Aß) compared to wild-type (WT) mice. In addition, the influx rate of ¹⁸ FDG was also decreased in both Aß40 and Aß42 pre-infused mice compared to control mice. Glucose is primarily delivered from blood into the brain via glucose transporter 1 (GLUT1). The confocal microscopy experiment showed that Aß40 and Aß42 peptides significantly decreased GLUT1 expression in polarized human cerebral microvascular endothelial cell (hCMEC/D3) monolayers. Insulin-AKT pathway has been observed to induce glucose uptake via regulating the expression of TXNIP, the only α-arrestin protein known to bind to thioredoxin. We found that Aß40 and Aß42 peptides decreased p-AKT and increased TXNIP expression in the hCMEC/D3 cell monolayers. MK2206, a kinase inhibitor of AKT, was used to confirm that inhibition of insulin/AKT pathway reduced GLUT1 expression in an insulin-independent manner in the hCMEC/D3 cell monolayers. These results suggest that inhibitory effects of sAß on GLUT1 expression are mediated by inhibition of the insulin/AKT pathway. The role of TXNIP on endothelial GLUT1 expression was investigated using resveratrol, which has been reported to downregulate TXNIP overexpression. Consistently, resveratrol treatment led to a significant increase in GLUT1 expression in the hCMEC/D3 cell monolayers. Furthermore, by co-incubation of resveratrol and sAß peptides in hCMEC/D3 cell monolayers, we found that resveratrol rectified the aberrant TXNIP expression caused by sAß peptides. Together, these findings provide novel evidence that toxic sAß peptide exposure inhibits glucose transport at the BBB by decreasing GLUT1 expression via the insulin/Akt/TXNIP axis.