Aberrant insulin signaling constitutes an early change in Alzheimer's disease (AD). Insulin receptors (IR) and low-density lipoprotein receptor-related protein-1 (LRP-1) are expressed in brain capillary endothelial cells (BCEC) forming the blood-brain barrier (BBB). There, insulin may regulate the function of LRP-1 in Aβ clearance from the brain. Changes in IR-β and LRP-1 and insulin signaling at the BBB in AD are not well understood. Herein, we identified a reduction in cerebral and cerebrovascular IR-β levels in 9-month-old male and female 3XTg-AD (PS1M146V, APPSwe, and tauP301L) as compared to NTg mice, which is important in insulin mediated signaling responses. Reduced cerebral IR-β levels corresponded to impaired insulin signaling and LRP-1 levels in brain. Reduced cerebral and cerebrovascular IR-β and LRP-1 levels in 3XTg-AD mice correlated with elevated levels of autophagy marker LC3B. In both genotypes, high-fat diet (HFD) feeding decreased cerebral and hepatic LRP-1 expression and elevated cerebral Aβ burden without affecting cerebrovascular LRP-1 and IR-β levels. In vitro studies using primary porcine (p)BCEC revealed that Aβ peptides 1-40 or 1-42 (240 nM) reduced cellular levels and interaction of LRP-1 and IR-β thereby perturbing insulin-mediated signaling. Further mechanistic investigation revealed that Aβ treatment accelerated the autophagy-lysosomal degradation of IR-β and LRP-1 in pBCEC. LRP-1 silencing in pBCEC decreased IR-β levels through post-translational pathways further deteriorating insulin-mediated responses at the BBB. Our findings indicate that LRP-1 proves important for insulin signaling at the BBB. Cerebral Aβ burden in AD may accelerate LRP-1 and IR-β degradation in BCEC thereby contributing to impaired cerebral and cerebromicrovascular insulin effects.

Background: Alzheimer is the primary cause of death in the various countries that affects wide strata of the population. The treatment of it is restricted to a few conventional oral medications that act only superficially. It is evident that the delivery of a drug to the brain across the blood-brain barrier is challenging as the BBB is armed with several efflux transporters like the P-glycoprotein as well as nasal mucociliary clearance adds up leading to decreased concentration and reduced therapeutic efficacy. Considering these, the intranasal IN route of drug administration is emerging as an alternative route for systemic delivery of a drug to the brain. The intranasal (IN) administration of lipid nanoparticles loaded with cerebroactive drugs showed promise in treating various neurodegenerative diseases, since the nasal route allows the direct nose to brain delivery by means of solid lipid nanoparticles (SLN’s). The tailoring of intranasal lipid particulate drug delivery systems is a pleasing approach to facilitate uptake of therapeutic agents at the desired site of action, particularly when a free drug has poor pharmacokinetics/ biodistribution (PK/BD) or significant off-site toxicities. Objectives: 1) In this review, key challenges and physiological mechanisms regulating intranasal brain delivery in Alzheimer’s disease, ex vivo studies, pharmacokinetics parameters including brain uptake and histopathological studies are thoroughly discussed. : 2) A thorough understanding of the in vivo behaviour of the intranasal drug carriers will be the elusive goal. : 3) The article emphasizes to drag the attention of the research community working in the intranasal field towards the challenges and hurdles of the practical applicability of intranasal delivery of cerebroactive drugs. Method: Various electronic databases, journals like nanotechnology and nanoscience, dove press are reviewed for the collection and compilation of data. Results: From in vivo biodistribution studies, pharmacokinetics parameters, and gamma scintigraphy images of various drugs, it is speculated that intranasal lipid particulates drug delivery system shows better brain targeting efficiency for various CNS disorders in comparison to other routes. Conclusion: Various routes are explored for the delivery of drugs to increase bioavailability in the brain for CNS disorders but the intranasal route shows better results that pave the way for success in the future if properly explored.

Sugar-laden foods and carbohydrate-rich diets with high glycaemic index intake are associated with weight gain, increased incidence of diabetes and is link