Vitamin B12 (VitB12) is an essential micronutrient needed for life. It is synthesized exclusively by certain bacteria and archaea and, thanks to their interaction with animals and plants, VitB12 can enter the food chain of human beings. Deficiency of VitB12 or in-born defects related to VitB12 metabolism determine several impairments including neurological disorders. This project aims to characterize the role of VitB12 in neurological homeostasis evaluating neurotrophic action, neuroprotection and soluble- and extracellular vesicles (EVs) -mediated inflammation following deficiency of VitB12 or alteration of VitB12 metabolism in motoneurons and oligodendrocytes in vitro cell models. Furthermore, the myelination process will be studying using a 3D co-culture method (Brain MicroPhysiological System, BMPS). VitB12-loaded EVs and VitB12-loaded nanoparticles (lipid- and mesoporous-silica-based) will be produced and rescue of a neurodegenerative state determined by deficiency of VitB12 or VitB12 metabolism defect (induced by silencing of MMACHC gene) will be evaluated using mentioned complexes.
The pivotal role of VitB12 both in the development and the homeostasis maintenance of the CNS is well known, however, the precise mechanisms have not been fully described, yet. VitB12 deficit can decrease the S-adenosylmethionine pool and in turn determine hypomethylation and demyelination of CNS and a reduction in the synthesis of phospholipids (Gröber et al., 2013). Indeed, Schwann cells and oligodendrocytes (cells producing myelin) in case of VitB12 depletion show defects in myelin formation and remyelination and regeneration of nerves after peripheral injury (Nielsen et al., 2012; Ducan et al., 2018; Nishimoto et al., 2015). Irreversible demyelinating and following neurologic disease is also a hallmark of aciduria methylmalonic with homocysteinemia, which is due to an inborn metabolic defect of vitamin B12 metabolism (Motte et al., 2019). Other defects can be found after VitB12 deficiency or VitB12 metabolism defects including the incorporation of abnormal fatty acids into neuronal cells and modification of the level of some neurotransmitters (Nielsen et al., 2012; Ducan et al., 2018; Nishimoto et al., 2015) and accumulation of homocysteine which can affect the oxidative stress and modify calcium influx besides to be toxic when accumulated in the organism (Gröber et al., 2013; Nielsen et al., 2012; Ducan et al., 2018).
Although the mechanism of intestinal uptake of the VitB12 has been well characterized, how it overcomes the BBB and reaches the CNS remains unknown (Nielsen et al., 2012). The latter makes a limit for specifically target CNS that could lead to high benefit respect the usual administration (that includes intramuscular injection in the more severe cases). Between noninvasive medical formulation, the use of nanoparticles is a promising strategy. Thanks to the very small size of nanoparticles, they are a good candidate to cross the BBB (Bors et al., 2019). Furthermore, a very recent and innovative approach uses naturally-occurring cell-derived membrane vesicles (CMV) that include exosomes, i.e., nanosized vesicles deriving from endocytotic compartments (Bors et al., 2019; Doeppner et al., 2015). CMV can be engineered and loaded with exogenous molecules and can act as carriers. In zebrafish and mouse models, exosomes isolated from brain endothelial cells have shown the ability to overcome the BBB and deliver their content to CNS thus making exosomes a new cutting-edge in the field of nanocarriers (Boers et al., 2019) and their application in VitB12, in our opinion, could represent a very promising treatment in the case of neuropathologies, albeit no data are currently available.
Altogether, this project aims, on one hand, to study the role of VitB12 deficiency on the brain to fill the current data gap, and, on the other hand, to establish innovative VitB12 nano-delivery to target specific organs and possible improve brain homeostasis.
References
Bors, L.A. et al., Sci. Pharm. 2019, 87, 6.
Doeppner, T.R.H.J. et al., Stem Cells Transl. Med. 2015, 2, 1131:1143.
Duncan, I.D. et al., Proc. Natl. Acad. Sci. USA 2018, 115, E11807:E11816.
Gröber, U. et al., Nutrients 2013, 5, 5031¿5045.
Motte J et al., Ther Adv Neurol Disord. 2019 24;12:1756286419872115.
Nielsen, M.J. et al., Nat. Rev. Gastroenterol. Hepatol. 2012, 9, 345:354.
Nishimoto, S. et al., Front. Cell. Neurosci. 2015, 9, 1:13.