Effects of HA1 (a Probucol Analogue) and ApoC3 siRNA on Lipoprotein-Amyloid Metabolism, Neurovascular Integrity and Cognitive Function in db/db Mice

Abstract

Background and aimsChronically elevated levels of circulating lipoprotein-amyloid-{beta} (A{beta}) are implicated in the disruption of the blood-brain barrier and the initiation of a neurodegenerative cascade leading to Alzheimers disease (AD). Type 2 diabetes is associated with BBB dysfunction, dyslipidaemia, and an increased risk of AD. However, alterations in triglyceride-rich lipoproteins (TRL)-A{beta} homeostasis and its downstream effects on the BBB in a diabetes context remain explored. This study aimed to 1) investigate, in a preclinical model of diabetes, the hypothesis that diabetes-induced impairments in TRL-A{beta} metabolism might compromise BBB integrity and exacerbate cognitive function and behavioural changes, and 2) assess the efficacy of interventions that improve TRL catabolism, including probucol, HA1, and ApoC3 siRNA, to prevent disease progression by lowering circulating TRL-A{beta} levels. MethodsFive-week-old db/db mice underwent a 9- or 23-weeks dietary interventions with probucol, a probucol prodrug HA1, or a standard diet with four-weekly injections of ApoC3 siRNA. Db/+ mice served as negative controls for each treatment duration. Blood levels of A{beta} and ApoB were measured using ELISA. Immunofluorescence imaging was used to quantify enterocytic levels of A{beta} and ApoB, and assess changes in neurovascular integrity (IgG, PDGFR{beta}, ZO1, occludin), neuroinflammation (GFAP, Iba1), and cerebral oxidative stress (8OHdG). ResultsOur results indicate that diabetes increased the abundance of plasma amyloid, specifically A{beta}42, which correlated with enterocytic abundance, suggesting exaggerated postprandial excretion. Disrupted plasma amyloid homeostasis was associated with BBB breakdown, including diminished barrier function, and the loss of pericytes and astrocytes. Provision of the probucol analogue, HA1, normalised plasma and enterocytic amyloidemia concomitant with the preservation of the neurovascular junction. Treatment with ApoC3 siRNA attenuated plasma A{beta}42 and modestly reduced neurovascular inflammation. ConclusionThe findings further support the hypothesis that aberrant peripheral metabolism of lipoprotein-A{beta} is associated with microvascular corruption and the development of anxiety-like behaviour. HA1 is more effective than probucol or ApoC3 siRNA in positively modulating lipoprotein-amyloid homeostasis in db/db mice and maintaining central capillary integrity. HighlightsO_LIEnterocytic and plasma lipoprotein-A{beta} levels are increased in diabetic db/db mice. C_LIO_LIElevated plasma lipoprotein-A{beta} levels correlate with BBB breakdown and anxiety-like behavior. C_LIO_LIHA1 lowers enterocytic and plasma A{beta} levels, protects BBB, alleviates oxidative stress and anxiety. C_LIO_LIApoC3 siRNA lowers plasma lipoprotein-A{beta}, mitigates neuroinflammation and anxiety. C_LI