A Basic ApoE-Based Peptide Mediator to Deliver Proteins across the Blood-Brain Barrier: Long-Term Efficacy, Toxicity, and Mechanism

Abstract

We have investigated delivery of protein therapeutics from the bloodstream into the brain using a mouse model of late-infantile neuronal ceroid lipofuscinosis (LINCL), a lysosomal disease due to deficiencies in tripeptidyl peptidase 1 (TPP1). Supraphysiological levels of TPP1 are delivered to the mouse brain by acute intravenous injection when co-administered with K16ApoE, a peptide that in trans mediates passage across the blood-brain barrier (BBB). Chronic treatment of LINCL mice with TPP1 and K16ApoE extended the lifespan from 126 to >294 days, diminished pathology, and slowed locomotor dysfunction. K16ApoE enhanced uptake of a fixable biotin tracer by brain endothelial cells in a dose-dependent manner, suggesting that its mechanism involves stimulation of endocytosis. Pharmacokinetic experiments indicated that K16ApoE functions without disrupting the BBB, with minimal effects on overall clearance or uptake by the liver and kidney. K16ApoE has a narrow therapeutic index, with toxicity manifested as lethargy and/or death in mice. To address this, we evaluated variant peptides but found that efficacy and toxicity are associated, suggesting that desired and adverse effects are mechanistically related. Toxicity currently precludes direct clinical application of peptide-mediated delivery in its present form but it remains a useful approach to proof-of-principle studies for biologic therapies to the brain in animal models.

The impact on the activity of acetylcholinesterase of a polylysine-ApoE peptide carrier targeting the blood brain barrier

“…With a demonstrated ability to transport compounds across the blood-brain barrier, this peptide has great potential (Sarkar et al, 2011(Sarkar et al, , 2014Meng et al, 2014Meng et al, , 2017 but, the toxicity of the peptide must be resolved. Although AChE is not the primary toxicity mechanism of action, it clearly plays a role.…”

“…In a mouse model of Late-infantile neuronal ceroid lipofuscinosis (LINCL) with deficiency in the lysosomal protease tripeptidyl peptidase I (TPPI) (Sleat et al, 1997(Sleat et al, , 2004, we have achieved supraphysiological levels (~800% of wild-type) of intravenously-administered recombinant TPP1 throughout the brain upon co-injection with K16ApoE. Furthermore, the mice demonstrated a significant improvement in neurological function and increased lifespan in either acute or chronic treatment with the mixture of TPP1 and K16ApoE (Meng et al, 2014(Meng et al, , 2017.…”

“…Characterization of peptide variants suggested that the toxicity and efficacy both are associated with the positive charge of K16ApoE. Eliminating the toxicity by removing the positive charges from K16ApoE resulted in diminishing the uptake of TPP1 to the brain (Meng et al, 2017).…”

Therapeutic approaches targeting Apolipoprotein E function in Alzheimer’s disease

“…Likewise, the pulsed ultrasound and AAV based approaches have unknown long-term health implications. Interestingly, a 20 amino acid stretch of the APOE protein itself has been successfully utilized for shuttling therapeutics across the BBB in a mouse model of lipofuscinosis, a pediatric neurodegenerative disorder [222,223], suggesting the possibility of using endogenous shuttling signals for efficacious delivery through the BBB. Even with these exciting breakthroughs, several challenges remain: if administered peripherally, how do we prevent the APOE therapeutic to be titered by the peripheral pools of APOE, or worse, cause systemic metabolic dysfunction and additionally, how to safely guide the therapeutic to the affected brain regions or cell types once inside the brain.…”

Reversible blood-brain barrier opening utilizing the membrane active peptide melittinin vitroandin vivo

“…Apart from hyperosmotic and vasoactive agents, little is known about other classes of molecules capable of intra-arterial BBBO. Previous studies have shown that systemic injection of membrane active peptides (MAPs) has the potential for permeabilizing biological barriers, including the BBB [21][22][23]. Importantly, MAP sequences can be engineered with customizable pharmacological properties (i.e.…”