Delivery of an anti‐transthyretin Nanobody to the brain through intranasal administration reveals transthyretin expression and secretion by motor neurons

Abstract

Transthyretin (TTR) is a transport protein of retinol and thyroxine in serum and CSF, which is mainly secreted by liver and choroid plexus, and in smaller amounts in other cells throughout the body. The exact role of TTR and its specific expression in Central Nervous System (CNS) remains understudied. We investigated TTR expression and metabolism in CNS, through the intranasal and intracerebroventricular delivery of a specific anti‐TTR Nanobody to the brain, unveiling Nanobody pharmacokinetics to the CNS. In TTR deficient mice, we observed that anti‐TTR Nanobody was successfully distributed throughout all brain areas, and also reaching the spinal cord. In wild‐type mice, a similar distribution pattern was observed. However, in areas known to be rich in TTR, reduced levels of Nanobody were found, suggesting potential target‐mediated effects. Indeed, in wild‐type mice, the anti‐TTR Nanobody was specifically internalized in a receptor‐mediated process, by neuronal‐like cells, which were identified as motor neurons. Whereas in KO TTR mice Nanobody was internalized by all cells, for late lysosomal degradation. Moreover, we demonstrate that in vivo motor neurons also actively synthesize TTR. Finally, in vitro cultured primary motor neurons were also found to synthesize and secrete TTR into culture media. Thus, through a novel intranasal CNS distribution study with an anti‐TTR Nanobody, we disclose a new cell type capable of synthesizing TTR, which might be important for the understanding of the physiological role of TTR, as well as in pathological conditions where TTR levels are altered in CSF, such as amyotrophic lateral sclerosis.

Neuronal megalin mediates synaptic plasticity—a novel mechanism underlying intellectual disabilities in megalin gene pathologies

“…2C and D ). In addition, we observed that a specific-TTR nanobody (Nb) ( Gomes et al , 2018 )—169F7 [described to bind/block the epitope responsible for TTR-megalin interaction ( Gomes et al , 2019 )], was able to block TTR-induced megalin upregulation ( Fig. 2C ).…”

“…The fact that TTR is affecting/regulating megalin levels mainly in the hippocampus and spinal cord, and not in other CNS areas, such as the cerebral cortex or the cerebellum ( Fig. 1F–I ), is probably related to the fact that TTR has been described to be either synthesized by hippocampal/motor neurons or uptaken from the CSF TTR pool, making these regions more prone to the effects of TTR over megalin ( Stein and Johnson, 2002 ; Sousa et al , 2007 a ; Buxbaum et al , 2008 ; Li et al , 2011 ; Gomes et al , 2018 ). TTR does not seem to affect megalin mRNA expression levels in vivo , although it affects megalin protein levels ( Fig.…”

Brain Delivery of Single-Domain Antibodies: A Focus on VHH and VNAR

“…Ablynx has patented intranasal delivery of therapeutic polypeptides and proteins including VHHs [ 75 ]. This strategy has been applied to a VHH against transthyretin protein, used as a research tool, allowing a positive brain distribution into several areas [ 76 ].…”

Brain-targeted intranasal delivery of dopamine with borneol and lactoferrin co-modified nanoparticles for treating Parkinson’s disease

“…Intranasal delivery systems are more efficient in noninvasively delivering drugs to the brain via the olfactory and trigeminal nerves from the nasal olfactory epithelium by circumventing the blood–brain barrier (Haque et al., 2014 ; Akilo et al., 2016 ; Mittal et al., 2016 ; Chu et al., 2018 ; Md et al., 2013 ). Direct and brain-targeted drug delivery may allow enhanced therapeutic effects even at a lower drug dose, allow rapid drug absorption at the target site, avoid first-pass elimination, and reduce toxicity (Lalani et al., 2014 ; Gomes et al., 2018 ). Several studies on piperine (Elnaggar et al., 2015 ), tarenflurbil (Muntimadugu et al., 2016 ), risperidone (Narayan et al., 2016 ), glycyrrhizic acid (Ahmad et al., 2019 ) and alginate (Haque et al., 2014 ) have substantiated the theory of nose-to-brain delivery systems.…”